WO2015159978A1 - Composite short fibers for absorbent article, process for producing same, thermally bonded nonwoven fabric for absorbent article, surface sheet for absorbent article, and absorbent article - Google Patents

Abstract

The present invention provides: composite short fibers for absorbent articles, the short fibers having the property of satisfactorily passing through carding machines and being suitable for obtaining thermally bonded nonwoven fabric for absorbent articles which feels smooth to the touch and has high opacifying properties; a process for producing the short fibers; thermally bonded nonwoven fabric for absorbent articles which includes the short fibers; a surface sheet for absorbent articles; and an absorbent article. The composite short fibers for absorbent articles are core-sheath composite short fibers of a concentric circle structure which comprise a core component and a sheath component, wherein the core component comprises 50 mass% or more polypropylene which, after spinning, has a ratio of mass-average molecular weight (Mw) to number-average molecular weight (Mn), Mw/Mn, of 3.0-8.0 and the sheath component comprises 60 mass% or more high-density polyethylene which has a melting point lower by at least 5°C than that of the polypropylene. The core component and the sheath component have been composited in a ratio of 52/48 to 73/27 in terms of the volume ratio of core component/sheath component. The composite short fibers contain an inorganic filler in an amount of 0.5-10 mass% relative to 100 mass% the composite short fibers, and have a fineness of 1.1-2.0 dtex.

Description

Composite staple fiber for absorbent articles, method for producing the same, heat-bonding nonwoven fabric for absorbent articles, surface sheet for absorbent articles, and absorbent article

The present invention relates to absorbent articles such as sanitary napkins and paper diapers, composite staple fibers for absorbent articles used in absorbent articles, heat-bonding nonwoven fabrics for absorbent articles and surface sheets for absorbent articles, and composites for absorbent articles The present invention relates to a method for producing short fibers. Specifically, composite staple fibers for absorbent articles whose core component and sheath component are mainly composed of a polyolefin resin, heat-bonding nonwoven fabrics for absorbent articles containing the same, surface sheets and absorbent articles for absorbent articles, and absorption The present invention relates to a method for producing composite short fibers for functional articles.

In absorbent articles such as sanitary napkins and paper diapers, the feel of the surface sheet that directly contacts the wearer's skin and the feel of the back sheet that forms the outer part of the absorbent article such as paper diapers are smoother and softer. It is requested to do.

For the surface sheet of the absorbent article, a heat-bonded nonwoven fabric is used in which a fiber web containing heat-bonding fibers is manufactured using a card machine, and a high-temperature air stream is blown onto the fiber web to thermally bond the constituent fibers. . In order to soften the tactile sensation of the heat-bonding nonwoven fabric, it is considered effective to reduce the fineness of the fiber and to make the resin constituting the fiber a softer resin. As a heat-bonding fiber used for the heat-bonding nonwoven fabric, a polyester-based composite fiber containing a polyester resin and a polyolefin-based composite fiber containing a polyolefin resin are known. When comparing polyester-based composite fibers containing polyester resin with polyolefin-based composite fibers containing polyolefin resin, polyolefin resin is softer than polyester resin, so if the fibers are the same thickness, non-woven fabric using polyolefin-based composite fibers It is considered that the touch is softer than the non-woven fabric using the polyester composite fiber. Therefore, by making a heat-bonded nonwoven fabric using polyolefin composite fibers with fineness and using it for the surface sheet and back sheet of the absorbent article, the comfort and tactile sensation when the absorbent article is mounted are further improved. Improvements are being made.

However, as the fineness of the polyolefin-based composite fiber is reduced, the card passing property of the fiber is lowered, and the productivity of the nonwoven fabric is likely to be lowered. The cause is that the polyolefin resin is soft, so the elasticity of the fiber is lost by making it finer, and when the fiber web is opened and made into a fiber web, the fibers get entangled inside the card machine. It is easy to generate a granular fiber lump called. Also, since the polyolefin resin is soft, the crimped shape cannot be maintained, and when the card web is opened and made into a card web, it tends to be in a so-called "fly" state that does not get entangled with the card wire. Is one of the causes. In particular, since the polyolefin composite short fibers having a fineness are low in strength and elasticity of the fibers, there is a possibility that when the fiber web is produced at high speed, nep and fly occur frequently and the fiber web cannot be produced.

Moreover, the nonwoven fabric used for the absorbent article is required to have a white appearance, that is, a high whiteness. In particular, the surface sheet used on the surface of the non-woven fabric used for absorbent articles that comes in contact with the skin of the wearer is not only white in appearance, but also blood discharged from the body (menstrual blood), urine and fluidity In addition to rapidly absorbing excrement such as stool, so-called concealment is required to make the absorbed blood and excrement difficult to see from the surface. Synthetic fibers used in absorbent articles for the purpose of increasing the apparent whiteness (whiteness) of nonwoven fabrics or improving the concealability of nonwoven fabrics include titanium dioxide (also simply referred to as titanium oxide) and zinc oxide. Inorganic filler is mixed with synthetic resin. Synthetic fibers containing an inorganic filler not only have a low spinnability because the inorganic filler works as a foreign substance, but also have a low single fiber strength and fiber elasticity. Flying easily occurs. In this way, from the decrease in card passage due to the fineness and the decrease in card passage due to the addition of the inorganic filler, the composite short fiber for absorbent articles contains an inorganic filler and has a fineness polyolefin-based It was difficult to obtain composite short fibers.

Furthermore, when trying to obtain a surface sheet for absorbent articles using a polyolefin composite short fiber having a fineness, the bulkiness and liquid permeability of the nonwoven fabric can be a problem. Since the polyolefin-based composite short fibers are soft thermoplastic resins, there is a tendency to be inferior in the bulk (specific volume) of the nonwoven fabric obtained as compared with the composite short fibers containing a polyester resin. When the bulk of the heat-bonding nonwoven fabric is small, there is a possibility that a desired tactile sensation cannot be obtained as the surface sheet for absorbent articles. In addition, there is a possibility that a nonwoven fabric containing a polyolefin fine composite fiber having a fineness is not sufficient in bulk, and since the fiber is thin and bulky, it is difficult to increase the bulk. There is a possibility that the fiber layer is too dense with few voids between the layer fibers. In the surface sheet for absorbent articles, if the surface touching the skin becomes too dense, it may take time when a liquid such as blood or urine passes through the fiber layer, and the liquid permeability may be deteriorated.

As a polyolefin-based composite fiber that can be used for a heat-bonding nonwoven fabric such as a sanitary material surface material such as a sanitary napkin, for example, Patent Document 1 discloses a composite fiber composed of polypropylene and polyethylene, and the fiber cross section is an eccentric core-sheath type or a parallel type. A polyolefin composite fiber having a single yarn fineness of 1 to 2d and a fiber length of 20 to 40 mm is described. Moreover, as a surface sheet used for an absorbent article, Patent Document 2 includes a non-woven fabric having an upper layer facing the skin and a lower layer positioned below the upper layer, and at least the fibers constituting the upper layer contain titanium oxide. However, surface materials have been proposed in which the elongation rate of the fibers constituting the lower layer is lower than that of the fibers constituting the upper layer and the tensile strength is increased. Patent Document 3 discloses a first layer having a fiber diameter of 11 to 18 μm as a constituent fiber and a second layer disposed adjacent to the first layer and having a fiber diameter of a constituent fiber of 19 to 31 μm. A top sheet used for an absorbent article made of a non-woven fabric has been proposed.

JP-A-8-60441 JP 2001-61891 A JP 2004-166831 A

The composite fiber described in Patent Document 1 has an eccentric core-sheath type or a parallel type fiber cross section. In these cross-sectional structures, since there is a thin portion of the sheath component, that is, the heat-bonding component, the strength of the heat-bonded bonding point is insufficient, and the strength of the heat-bonded nonwoven fabric itself may be insufficient, or due to friction during use, the nonwoven fabric The surface may become fuzzy and the surface feel may be deteriorated. In addition, the reduction in card passage due to the inclusion of the inorganic filler is not taken into consideration, and there is a possibility that measures against the reduction in the card passage when the inorganic filler is contained are insufficient.

In Patent Document 2 and Patent Document 3, a surface sheet having a high concealability, a smooth texture, and hardly causing rewet (also referred to as liquid return) is obtained. The surface sheet for absorbent articles using sapphire has not been sufficiently studied, especially the improvement of the liquid absorption characteristics such as run-off and liquid absorption speed, and the improvement of the initial bulk of heat-bonded nonwoven fabrics containing polyolefin composite short fibers. Not.

The present invention has been made in view of such a situation, and is suitable for obtaining a heat-bonding nonwoven fabric for absorbent articles having good card passing properties, smooth tactile sensation, and high concealability. Provided are composite short fibers for absorbent articles and a method for producing the same. Further, it contains a polyolefin-based composite short fiber of fineness, has a smooth feel, is bulky, and has good liquid absorption characteristics such as run-off and liquid absorption speed. , And absorbent articles containing them.

The present invention is a composite short fiber for absorbent articles comprising a core component and a sheath component, wherein the core component has a ratio Mw / Mn of the weight average molecular weight Mw and the number average molecular weight Mn after spinning of 3.0 or more and 8 0.0 or less of polypropylene is contained in an amount of 50% by mass or more, and the sheath component contains 60% by mass or more of high-density polyethylene whose melting point is 5 ° C. or more lower than that of the polypropylene. Is a core-sheath type composite short fiber in which the composite ratio of the core component and the sheath component is 52/48 to 73/27 in terms of the volume ratio of the core component / sheath component. The short fiber contains an inorganic filler in an amount of 0.5 to 10% by mass with respect to 100% by mass of the composite short fiber, and the fineness of the composite short fiber is 1.1 to 2.0 dtex. Concerning composite short fibers for absorbent articles .

The present invention also relates to a method for producing the above-described composite short fiber for absorbent articles, wherein the mass ratio of Mw / Mn between the weight average molecular weight Mw and the number average molecular weight Mn is 3.0 to 10.0. A core component containing at least 5% and a sheath component containing at least 60% by mass of a high-density polyethylene having a melting point of 5 ° C. or more lower than that of the polypropylene, the sheath component covering the surface of the composite short fiber in the fiber cross section, Is supplied to a composite type nozzle arranged so as to have a concentric circular structure in which the center of gravity of the composite short fiber coincides with the position of the center of gravity of the composite short fiber, and the core component is spun at a temperature of 250 ° C. The present invention relates to a method for producing a composite staple fiber for absorbent articles, which includes a step of melt spinning at a temperature of 0 ° C. or lower.

The present invention also relates to a heat-bonding nonwoven fabric for absorbent articles that contains 20% by mass or more of the composite short fibers for absorbent articles, and at least a part of the composite short fibers for absorbent articles is bonded by a sheath component.

The present invention is also an absorbent article surface sheet comprising a first fiber layer in contact with the skin and a second fiber layer adjacent to the first fiber layer, the first fiber layer, The core component contains 50% by mass or more of first core-sheath type composite short fiber containing 50% by mass or more of high density polyethylene having a melting point of 5 ° C. or more lower than the melting point of the polypropylene. The second fiber layer includes a polyester resin as a core component, a sheath component as a thermoplastic resin having a melting point lower by 50 ° C. or more than a melting point of the polyester resin, and the center of gravity of the core component is A fiber layer containing 50% by mass or more of the second core-sheath type composite short fiber shifted from the center of gravity of the fiber, wherein the first core-sheath type composite short fiber has a fineness of 1.1 dtex or more and 2.0 dtex or less; 2-core sheath type composite short fiber has fineness The first core-sheath type composite short fiber is 2.2 dtex or more and 5.2 dtex or less, and the core component and the sheath component are arranged substantially concentrically, and the composite ratio of the core component and the sheath component is a core component. / Polypropylene having a volume ratio of 52/48 to 73/27 in the sheath component and 50% by mass or more in the core component has a ratio Mw / Mn of the weight average molecular weight Mw and the number average molecular weight Mn after spinning. 3.0 to 8.0, and the first core-sheath-type composite short fiber contains 0.5% by mass or more and 10% by mass or less of an inorganic filler with respect to 100% by mass of the composite short fiber. It is a composite short fiber, and at least a part of the first core-sheath type composite short fiber and the second core-sheath type composite short fiber is composed of the first core-sheath type composite short fiber and the second core-sheath type composite short fiber. It is related with the surface sheet for absorbent articles heat-bonded by the sheath component.

The present invention also relates to an absorptive article including the heat-adhesive nonwoven fabric for absorptive articles or the top sheet for absorptive articles.

The composite short fiber for absorbent articles according to the present invention includes 50% by mass or more of polypropylene whose core component has a ratio Mw / Mn of the weight average molecular weight Mw to the number average molecular weight Mn of 3.0 or more and 8.0 or less after spinning. The sheath component contains 60% by mass or more of high-density polyethylene whose melting point is 5 ° C. or lower than the polypropylene contained in the core component, and the core component and the sheath component are arranged substantially concentrically. When the composite ratio is 52/48 to 73/27 in terms of the volume ratio of the core component / sheath component, the card passing property is good, and a card web having an excellent formation can be obtained. Further, in the composite short fiber for absorbent articles of the present invention, since the core component and the sheath component are arranged concentrically, the sheath component having a low melting point is uniformly present on the surface of the composite short fiber, which is easy. The fibers can be thermally bonded to each other to provide a heat-bonded nonwoven fabric having high adhesive strength. In addition, the composite short fiber for absorbent articles of the present invention contains an inorganic filler of 0.5% by mass or more and 10% by mass or less, and has good card passing properties even when the fineness is 1.1 dtex or more and 2.0 dtex or less. The heat-bonding nonwoven fabric for absorbent articles and the absorbent article containing the composite short fibers for absorbent articles have a smooth and soft touch. In addition to the fact that the composite short fiber for absorbent articles of the present invention contains an inorganic filler, the fineness is 2.0 dtex or less, so that the thermal bonding for absorbent articles containing the composite short fiber for absorbent articles The nonwoven fabric and the absorbent article have excellent concealability when absorbing blood and excreta.

FIG. 1 is a schematic cross-sectional view showing a fiber cross section of a composite short fiber according to an embodiment of the present invention. 2A to 2D are schematic views showing crimped forms of composite short fibers. FIG. 3 is a schematic cross-sectional view of a top sheet for absorbent articles according to an embodiment of the present invention. FIG. 4 is a schematic cross-sectional view showing a fiber cross section of an eccentric core-sheath composite short fiber used in the top sheet for absorbent articles of the present invention.

First, the composite short fiber for absorbent articles of the present invention will be described in detail. As a result of intensive studies on the polyolefin-based composite short fibers for absorbent articles, the inventors of the present invention have found that the polyolefin-based composite short fibers include polypropylene contained in the core component in an amount of 50% by mass or more (hereinafter referred to as “main component polypropylene”). As a ratio of the weight average molecular weight Mw and the number average molecular weight Mn after spinning Mw / Mn (hereinafter also referred to as “Q value”) of 3.0 or more and 8.0 or less (hereinafter referred to as PP). In addition, the sheath component contains 60% by mass or more of high-density polyethylene having a melting point of 5 ° C. or more lower than that of the main component polypropylene, and the composite ratio of the core component to the sheath component in the composite short fiber is defined as the core component / sheath. The volume ratio of the components is 52/48 to 73/27 to increase the ratio of the core component, and the cross-sectional structure in which the core component and the sheath component are arranged substantially concentrically. By making it, the rigidity of the composite short fiber as a whole becomes high, the fineness is 2.0 dtex or less, and even if the composite short fiber contains a specific amount of inorganic filler, the card passing property is good and thermal bonding The present inventors have found that it is excellent in tactile sensation and adhesive strength when made into a non-woven fabric, and reached the present invention.

The composite short fiber for absorbent articles of the present invention is a core-sheath type composite short fiber having a concentric structure in which a core component and a sheath component are arranged substantially concentrically.

(Core component)
The core component of the composite short fiber for absorbent articles of the present invention contains 50% by mass or more of polypropylene having a Q value after spinning of 3.0 or more and 8.0 or less. Polypropylene resins having a large Q value have a large molecular weight distribution because many high molecular weight polypropylene molecules are present inside the resin. On the other hand, a polypropylene resin having a small Q value cuts a high molecular weight molecular chain generated by polymerization and aligns the length of the molecular chain, so that the remaining amount of the high molecular weight polypropylene molecule is reduced and the width of the molecular weight distribution is reduced. Is getting smaller. In addition, by using a polypropylene having a Q value before spinning of 3.0 or more and 10.0 or less, the Q value of polypropylene after spinning can be made 3.0 or more and 8.0 or less.

When polypropylene is melt-spun, if a polypropylene having a small molecular weight distribution, that is, a small Q value is used, there are many amorphous regions (tie molecules) in unstretched fibers. Tend to remain. In the amorphous region, the polypropylene molecules are often not oriented, or the orientation of the polypropylene molecules is often not uniform, and the more the amorphous region of the polypropylene in the drawn fiber, the lower the strength of the fiber and the card passing property. It is likely to be low. On the other hand, when a polypropylene having a large molecular weight distribution and a large molecular weight distribution, that is, a polypropylene having a large Q value is used, the high molecular weight polypropylene molecule tends to be crystallized, and the stretching treatment is performed. Thus, a fiber with a small amorphous region can be obtained. Since the ratio of the amorphous region is small and the fiber has a high degree of crystallinity, it is presumed that the fiber containing polypropylene having a large Q value has a high fiber strength and a high card passing property.

The Q value after spinning of the main component polypropylene is 3.0 or more and 8.0 or less, preferably 3.0 or more and 6.5 or less, and more preferably 3.2 or more and 6.0 or less. Preferably, it is 3.4 or more and 5.5 or less, more preferably 3.6 or more and 5.2 or less. When the Q value after spinning of the polypropylene is 3.0 or more and 8.0 or less, the composite staple fiber for absorbent articles has excellent card passing properties, and the composite staple fiber for absorbent articles is manufactured. The productivity is also good.

The Q value before spinning of the main component polypropylene is 3.0 or more and 10.0 or less, preferably 3.0 or more and 8.5 or less, more preferably 3.2 or more and 7.0 or less. Preferably, it is 3.4 or more and 6.5 or less. When the Q value before spinning of the polypropylene is 3.0 or more and 10.0 or less, the composite staple fiber for absorbent articles has excellent card passing properties, and the composite staple fiber for absorbent articles is manufactured. The productivity is also good.

The Q value of the main component polypropylene may be different before and after spinning. Particularly, a polypropylene having a Q value after spinning of 3.0 or more and 8.0 or less may have a Q value before spinning of more than 8. This is because the bonds between the molecules constituting the relatively high molecular weight polypropylene molecule are broken by the heat during spinning, or a part of the relatively high molecular weight polypropylene molecule is chain-transferred to the low molecular weight polypropylene molecule. It is guessed that. In the present invention, the value of the Q value is a value after spinning unless otherwise stated as a value before spinning.

The core component of the composite short fiber for absorbent articles contains 50% by mass or more of the main component polypropylene. In the core component of the composite short fiber for absorbent articles, the content of the main component polypropylene is preferably 80% by mass or more, more preferably 90% by mass or more, further preferably 95% by mass or more, Particularly preferably, in the core component, the resin component excluding the inorganic filler described later is all polypropylene. The main component polypropylene is not particularly limited, and for example, a homopolymer, a random copolymer, a block copolymer, or a mixture thereof can be used. Examples of the random copolymer and block copolymer include a copolymer of propylene and at least one α-olefin selected from the group consisting of ethylene and an α-olefin having 4 or more carbon atoms. The α-olefin having 4 or more carbon atoms is not particularly limited, but examples thereof include 1-butene, 1-pentene, 3,3-dimethyl-1-butene, 4-methyl-1-pentene, and 4,4-dimethyl. -1-pentene, 1-decene, 1-dodecene, 1-tetradecene, 1-octadecene and the like. The propylene content in the copolymer is preferably 50% by mass or more. Among these, from the viewpoint of bulk recovery of nonwoven fabrics containing composite short fibers for absorbent articles, the polymer is selected from the group consisting of propylene homopolymers, ethylene-propylene copolymers, and ethylene-butene-1-propylene terpolymers. In consideration of the productivity, card passability and economy (manufacturing cost) of the resulting composite short fiber for absorbent articles, the propylene homopolymer is particularly preferable as the polypropylene in the core component.

In the composite short fiber for absorbent articles, the core component may contain a resin other than the main component polypropylene in addition to the main component polypropylene as long as the effects of the present invention are not impaired. The resin other than the main component polypropylene is not particularly limited, and examples thereof include polyolefin resin, polyester resin, polyamide resin, polycarbonate, polystyrene and the like. The polyolefin resin is not particularly limited, and examples thereof include high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, polymethylpentene, polybutene-1, and acrylic acid, methacrylic acid, and maleic acid. Unsaturated carboxylic acid such as acid, unsaturated carboxylic acid such as acrylic acid ester, methacrylic acid ester and maleic acid ester, unsaturated carboxylic acid such as acrylic acid anhydride, methacrylic acid anhydride and maleic acid anhydride Examples thereof include those obtained by copolymerizing at least one selected from the group consisting of products, those obtained by graft polymerization, and elastomers thereof. The polyester resin is not particularly limited, and examples thereof include polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polylactic acid, and acid components such as isophthalic acid, succinic acid, and adipic acid, and 1 Glycol components such as 1,4-butanediol and 1,6-hexanediol, copolymers with polytetramethylene glycol and polyoxymethylene glycol, and elastomers thereof. Although it does not specifically limit as said polyamide resin, For example, nylon 6, nylon 66, nylon 11, nylon 12, etc. are mentioned. In addition, various known additives may be added to the core component as long as the effects of the present invention are not hindered and do not affect fiber productivity, nonwoven fabric productivity, thermal adhesiveness, and touch. . Additives that can be added to the core component include known crystal nucleating agents, antistatic agents, pigments, matting agents, heat stabilizers, light stabilizers, flame retardants, antibacterial agents, lubricants, plasticizers, softeners, oxidation agents. Examples thereof include an inhibitor and an ultraviolet absorber.

In the core component of the composite short fiber for absorbent articles, the melt flow rate of the main component polypropylene is not particularly limited, but the melt flow rate (MFR) measured according to JIS-K-7210 (measurement temperature 230 ° C., load 2) .16 kgf (21.18 N), hereinafter referred to as MFR230) is preferably 10 g / 10 min or more and 50 g / 10 min or less. More preferable MFR230 is 20 g / 10 min or more and 40 g / 10 min or less, and particularly preferable MFR230 is 25 g / 10 min or more and 35 g / 10 min or less. When MFR230 of the main component polypropylene is within the above range, not only the take-up property and stretchability are improved, but also the core component has sufficient elasticity to pass through the card machine, and the absorption The card passing property of the composite short fiber for a functional article is improved.

In the core component of the composite short fiber for absorbent articles, the melting point of the main component polypropylene is not particularly limited, but is preferably 150 ° C or higher, more preferably 152 ° C or higher, and 155 ° C or higher. Is particularly preferred. When the melting point of the main component polypropylene is 150 ° C. or more, the bulk of the fibrous web of the nonwoven fabric is difficult to decrease, and a bulky and soft touch-bonded nonwoven fabric is easily obtained. The upper limit of the melting point of the main component polypropylene is not particularly limited, but may be 170 ° C. or lower and may be 168 ° C. or lower. In the present invention, the melting point refers to a melting peak temperature obtained from a DSC curve measured according to JIS-K-7121.

(Sheath component)
In the composite short fiber for absorbent articles, the sheath component contains 60% by mass or more of high-density polyethylene having a melting point of 5 ° C. or lower than the main component polypropylene in the core component. Since high density polyethylene has a higher density than other polyethylenes, the resulting composite short fiber is likely to have high rigidity, and the card passing property and crimp expression of the composite short fiber are improved and obtained. A bulky thermal bonding nonwoven fabric can be easily obtained. The content of the high-density polyethylene contained in the sheath component is preferably 80% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, and particularly preferably in the sheath component, The resin component excluding the inorganic filler described later is a high-density polyethylene.

In the composite short fiber for absorbent articles, the melt flow rate of the high-density polyethylene contained in the sheath component is not particularly limited, but the melt flow rate (MFR) measured according to JIS-K-7210 (measurement temperature 190 ° C., It is preferable that the load is 2.16 kgf (21.18 N), and hereinafter referred to as MFR190) is 5 g / 10 min or more and 30 g / 10 min or less. More preferred MFR 190 is 8 g / 10 min or more and 23 g / 10 min or less, and particularly preferred MFR 190 is 10 g / 10 min or more and 18 g / 10 min or less. When the MFR 190 of the high-density polyethylene is within the above range, not only the take-up property and stretchability are improved, but also the sheath component of the resulting composite short fiber is elastic enough to pass through the card machine. Thus, the card passing property of the composite short fiber is improved.

Since the surface of the composite short fiber for absorbent articles is substantially composed of a sheath component containing 60% by mass or more of the high-density polyethylene, the high-density polyethylene mainly melts due to the thermal adhesiveness of the composite short fiber. Depends on the liquidity at the time. In addition, the strength of the heat-bonded nonwoven fabric using the composite short fiber for absorbent articles depends mainly on the strength of the heat-bonding points between the constituent fibers generated by melting and heat-bonding the sheath component during heat treatment. ing. When the MFR 190 of the high-density polyethylene satisfies the above-described range, the fluidity at the time of melting of the sheath component can be moderately suppressed. As a result, when the fiber web containing the composite short fibers for absorbent articles is heat-treated near the melting point of the high-density polyethylene, the entire sheath component of the composite short fibers melts, but the flowability is suppressed, so that it is difficult to flow. As a result, the thickness of the sheath component is uniform, and thermal bonding points with uniform bonding strength are formed between constituent fibers at any bonding point, and the strength of the obtained thermal bonding nonwoven fabric is sufficient. Presumed to be expensive. If the MFR190 of high-density polyethylene exceeds 30 g / 10 min, the sheath component tends to flow during heat treatment, resulting in unevenness in the thickness of the sheath component in the composite short fiber, and the adhesive strength in which the sheath component is thermally bonded to the thin portion There is a possibility that a low thermal bonding point may be formed inside the nonwoven fabric. As a result, if the nonwoven fabric is pulled longitudinally and / or laterally, or if friction is applied by rubbing the surface of the nonwoven fabric, the adhesive point with weak adhesive strength is likely to come off, resulting in insufficient strength of the nonwoven fabric or causing the nonwoven fabric to fluff. There is a fear. On the other hand, if the MFR 190 of the high-density polyethylene is less than 5 g / 10 minutes, the fluidity of the sheath component is too low, and there is a possibility that the spinning take-up property and stretchability may be lowered.

In the sheath component of the composite short fiber for absorbent articles, the melting point of the high-density polyethylene is not particularly limited as long as it is lower by 5 ° C. or more than the melting point of the main component polypropylene contained in the core component. Considering the passability and the productivity, strength and heat resistance of the heat-bonded nonwoven fabric, the melting point of the high-density polyethylene is preferably 125 ° C. or higher and 140 ° C. or lower, and more preferably 128 ° C. or higher and 138 ° C. or lower. preferable.

In the composite short fiber for absorbent articles of the present invention, the sheath component may contain a resin other than the high-density polyethylene as long as the effect of the present invention is not impaired. The resin other than the high-density polyethylene is not particularly limited, and examples thereof include polyolefin resins other than the high-density polyethylene, polyester resins, polyamide resins, polycarbonates, polystyrenes, and the like. The polyolefin resin other than the high-density polyethylene is not particularly limited. For example, polypropylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, polymethylpentene, polybutene-1, and acrylic acid, methacrylic acid, and these. Unsaturated carboxylic acid such as acid, maleic acid, unsaturated carboxylic acid ester such as acrylic acid ester, methacrylic acid ester, maleic acid ester, unsaturated carboxylic acid such as acrylic acid anhydride, methacrylic acid anhydride, maleic acid anhydride Examples include those obtained by copolymerizing at least one selected from the group consisting of acid anhydrides, those obtained by graft polymerization, and elastomers thereof. The polyester resin is not particularly limited, and examples thereof include polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polylactic acid, and acid components such as isophthalic acid, succinic acid, and adipic acid, and 1 Glycol components such as 1,4-butanediol and 1,6-hexanediol, copolymers with polytetramethylene glycol and polyoxymethylene glycol, and elastomers thereof. Although it does not specifically limit as said polyamide resin, For example, nylon 6, nylon 66, nylon 11, nylon 12, etc. are mentioned. In addition, various known additives can be added to the sheath component as long as the effects of the present invention are not hindered and the fiber productivity, the nonwoven fabric productivity, the thermal adhesiveness, and the touch are not affected. is there. Additives that can be added to the sheath component include known crystal nucleating agents, antistatic agents, pigments, matting agents, heat stabilizers, light stabilizers, flame retardants, antibacterial agents, lubricants, plasticizers, softeners, oxidation agents. An inhibitor, an ultraviolet absorber, etc. can be contained.

The composite short fiber for absorbent articles contains 0.5% by mass or more and 10% by mass or less of an inorganic filler with respect to 100% by mass of the composite short fiber. By including the inorganic filler in the above-described range, the apparent whiteness, that is, the whiteness of the heat-bonding nonwoven fabric including the composite short fiber for absorbent articles is increased. In addition, since the fineness of the composite short fiber for absorbent articles is 2.0 dtex or less, if the nonwoven fabric has the same basis weight, the number of fibers constituting the nonwoven fabric increases. It tends to be expensive. When the heat-bonded nonwoven fabric containing the composite short fiber for absorbent articles is used for the top sheet of the absorbent article, menstrual blood, urine, etc. absorbed by the absorber located under the top sheet due to high whiteness The so-called concealing property that makes the color of the excrement difficult to see from the surface becomes high. From the viewpoint of further improving the concealability, the inorganic filler is preferably an inorganic powder having a high whiteness. Specifically, white inorganic powders such as titanium dioxide, zinc oxide, barium sulfate, calcium carbonate, magnesium oxide, silica (silicon dioxide), mica, zeolite, and talc are contained in the composite short fiber as an inorganic filler. The inorganic filler preferably contains at least one selected from the group consisting of titanium dioxide, zinc oxide, calcium carbonate, barium sulfate, silica and talc, more preferably contains at least titanium oxide, substantially. It is particularly preferable that only titanium oxide is contained as an inorganic filler.

In the composite short fiber for absorbent articles, the content of the inorganic filler may be 0.5% by mass or more and 10% by mass or less with respect to 100% by mass of the composite short fiber, but with respect to 100% by mass of the composite short fiber. It is preferably 0.8% by mass or more and 8% by mass or less, more preferably 1.0% by mass or more and 6.0% by mass or less, and 1.2% by mass or more and 5.0% by mass or less. Is more preferably 1.3% by mass or more and 3.5% by mass or less. When the heat-bonded nonwoven fabric containing the composite short fiber is used for the absorbent article, the composite short fiber for absorbent articles contains an inorganic filler. The tactile sensation of the short fiber itself and the heat-bonded nonwoven fabric containing the short fiber also tends to be soft. In addition, the inclusion of the inorganic filler reduces the occurrence of neps during the production of the card web and improves the card passing property. The inorganic filler may be contained in one or both of the sheath component and the core component constituting the composite short fiber. However, it is preferable that at least the core component contains an inorganic filler from the viewpoints of productivity of the composite short fiber for absorbent articles and concealment of the nonwoven fabric produced using the composite short fiber for absorbent articles. Further, in the composite short fiber for absorbent articles, when the content of the inorganic filler with respect to 100% by mass of the composite short fiber exceeds 4% by mass or 5% by mass, the inorganic filler is only one resin component of the sheath component or the core component. When it is contained, the spinnability of the resin component containing the inorganic filler is extremely lowered. Therefore, it is preferable to contain the inorganic filler in both the sheath component and the core component.

In the composite short fiber for absorbent articles, the cross-sectional structure has a concentric structure in which the center of gravity of the core component substantially coincides with the center of gravity of the composite short fiber. That is, in the fiber cross section, the center of gravity of the core component is not substantially deviated from the center of gravity of the composite short fiber. FIG. 1 is a schematic diagram of a fiber cross section of a composite short fiber for absorbent articles having a concentric structure. The sheath component 11 is disposed around the core component 12, and the sheath component 11 surrounds the periphery of the core component 12, so that the fiber surface other than the cut surface is covered with the sheath component 11 in the composite short fiber 10. Thereby, the surface of the sheath component 11 is melted and the fibers are thermally bonded to each other when the fiber web composed of the composite short fibers is thermally bonded. In the composite short fiber 10, the core component 12 is not decentered, that is, has a concentric circular structure. Therefore, the thickness of the sheath component 11 in the fiber cross section is almost constant in any part of the fiber cross section. As a result, when heat-treating a fiber web composed of composite short fibers, even if any other fiber comes into contact with any portion of the composite short fibers in which the sheath component on the fiber surface is softened and melted, it is uniform. Since a strong heat-bonding point is formed, the heat-bonded nonwoven fabric using the composite short fiber for absorbent articles has a high bond strength, is resistant to friction and is difficult to fluff. The gravity center position 13 of the core component 12 is not substantially deviated from the gravity center position 14 of the composite short fiber 10. The fact that the center of gravity of the core component does not substantially deviate from the position of the center of gravity of the composite short fiber means that the ratio of deviation obtained by the following method (hereinafter also referred to as eccentricity) is 10% or less, preferably 7% or less. , Particularly preferably 5% or less, most preferably 3% or less.

<Eccentricity>
The cross section of the composite short fiber 10 is magnified by a scanning electron microscope or the like, the center of gravity position 13 of the core component 12 is C1, the center of gravity 14 of the composite short fiber 10 is Cf, and the radius 15 of the composite short fiber 10 is rf. Is calculated by the following mathematical formula 1.

[Equation 1]
Eccentricity (%) = [(Cf−C1) / rf] × 100

In the composite short fiber for absorbent articles, the composite ratio of the core component and the sheath component is 52/48 to 73/27, preferably 55/45 to 70/30, as the volume ratio of the core component / sheath component. More preferably, it is 60/40 to 70/30, and still more preferably 62/38 to 68/32. The core component mainly affects the elasticity of the entire composite short fiber, and the sheath component mainly affects the adhesive strength, tactile sensation, and hardness of the heat-bonded nonwoven fabric containing the composite short fiber. When the composite ratio of the core component and the sheath component in the composite short fiber for absorbent articles is 52/48 to 73/27, the card passing property of the composite short fiber and the adhesive strength of the heat-bonding nonwoven fabric containing the composite short fiber Both tactile sensations can be achieved. When the sheath component is too large, for example, when the composite ratio of the core component and the sheath component is 50/50, the strength of the nonwoven fabric increases, but the touch of the nonwoven fabric may be hardened. In addition, since the ratio of the core component is small, the fiber has no elasticity, the card passing property is likely to be lowered, and the crimp developing property is also likely to be lowered. On the other hand, when the core component becomes too large, for example, when the composite ratio of the core component and the sheath component is 80/20, the ratio of the sheath component contributing to the thermal bonding between the constituent fibers is small, and the sheath component is a composite short fiber. Because it exists as a thin layer covering the side surface of the fabric, the thermal bond point is small even when heat-treated to form a thermal bond point between the constituent fibers, and it is easy to come off by external force, so the nonwoven fabric strength is small There is a risk that fluffing may occur easily when friction is applied to the nonwoven fabric.

In the composite short fiber for absorbent articles, the shape of the core component in the fiber cross section may be elliptical, Y-shaped, X-shaped, polygonal, star-shaped, etc. The shape in the fiber cross section may be elliptical, Y-shaped, X-shaped, polygonal, star-shaped, or other hollow shapes, or a hollow shape in addition to the circular shape.

The composite short fiber for absorbent articles has a fineness of 1.1 dtex or more and 2.0 dtex or less. When the fineness is 2.0 dtex or less, the heat-bonded nonwoven fabric including the composite short fibers for absorbent articles has a smooth feel and becomes a soft nonwoven fabric. In addition, in the case of non-woven fabric with the same basis weight due to the small fineness, since the number of fibers constituting the non-woven fabric is larger than the non-woven fabric composed of fibers with a high fineness, the texture and appearance of the non-woven fabric is fine and high concealment Easy to become non-woven fabric. When the fineness of the composite short fiber for absorbent articles exceeds 2.0 dtex, a non-woven fabric having a soft and smooth feel and high concealability cannot be obtained. The fineness of the composite short fiber for absorbent articles is preferably 1.8 dtex or less, and more preferably 1.7 dtex or less. In the composite short fiber for absorbent articles, when the fineness is 1.1 dtex or more, the card passing property of the composite short fiber is improved, and the productivity is improved. The fineness of the composite short fiber for absorbent articles is more preferably 1.2 dtex or more. The fineness of the composite short fiber for absorbent articles can be adjusted as desired by adjusting the fineness and draw ratio of the spinning filament described later.

The composite staple fiber for absorbent articles mainly has at least one kind of crimp selected from the group consisting of sawtooth crimps (also referred to as mechanical crimps) shown in FIG. 2A and corrugated crimps shown in FIG. 2B. The number of crimps is preferably 5/25 mm or more and 25/25 mm or less. A more preferable number of crimps is 8 pieces / 25 mm or more and 22 pieces / 25 mm or less, and a more preferred number of crimps is 10 pieces / 25 mm or more and 20 pieces / 25 mm or less. In addition, the composite staple fiber for absorbent articles is crimped from the viewpoint of the card passing property of the composite staple fiber for absorbent articles and the tactile sensation and bulk recovery of the heat-bonded nonwoven fabric containing the composite staple fiber for absorbent articles. The rate is preferably 5% or more and 20% or less, more preferably 6% or more and 18% or less, and further preferably 6.5% or more and 16% or less.

The fiber length of the composite short fiber for absorbent articles is not particularly limited, but is preferably 25 mm or more and less than 65 mm. This is because, when the fiber length satisfies this range, the composite staple fiber for absorbent articles is excellent in card passing property even if it has a fineness, and can produce a fiber web (card web) with good formation. If the fiber length is less than 25 mm, the fiber length is too short and does not catch on the card, so that a so-called fly state is likely to occur, and the card web may not be manufactured. When the fiber length is 65 mm or more, the so-called nep frequently occurs in which the composite short fibers are caught on the wire of the card machine or the composite short fibers are easily entangled with each other. There is a risk that it will not be possible. The fiber length of the composite short fiber for absorbent articles is more preferably 28 mm or more and 55 mm or less, further preferably 30 mm or more and 48 mm or less, and particularly preferably 34 mm or more and 45 mm or less.

Although the single fiber strength of the composite short fiber for absorbent articles is not particularly limited, it is preferably 2.4 cN / dtex or more and 6.0 cN / dtex or less, more preferably 2.6 cN / dtex or more and 5.6 cN / dtex. Or less, more preferably 2.8 cN / dtex or more and 5.4 cN / dtex or less. Further, the elongation of the composite short fiber for absorbent articles is not particularly limited, but from the viewpoint of card passing properties of the composite short fiber for absorbent articles, the breaking elongation is preferably 20% or more and 120% or less, More preferably, they are 25% or more and 100% or less, More preferably, they are 28% or more and 90% or less, Especially preferably, they are 30% or more and 80% or less.

The Young's modulus of the absorbent article for composite short fibers is not particularly limited, in view of the card passing property, it is preferable that the apparent Young's modulus is 1500 N / mm ² or more 3200N / mm ² or less, more preferably 1600 N / mm ² or more 3000N / mm ² or less, further preferably 1800 N / mm ² or more 2800N / mm ² or less.

Hereinafter, a method for producing the composite short fiber for absorbent articles of the present invention will be described. Although the said composite short fiber for absorbent articles is not specifically limited, For example, it can manufacture as follows.

First, a sheath component containing 60% by mass or more of high-density polyethylene and a core component containing 50% by mass or more of polypropylene having a melting point higher by 5 ° C. than the melting point of the high-density polyethylene are prepared. Next, in the fiber cross section, a composite type nozzle, for example, a concentric circular core, is arranged so that the sheath component covers the surface of the composite short fiber and the center of gravity of the core component is concentric with the center of gravity of the composite short fiber. The sheath component and the core component are supplied to the sheath type composite nozzle, the core component is melt-spun at a spinning temperature of 250 ° C. to 350 ° C., the sheath component is melt-spun at a spinning temperature of 230 ° C. to 330 ° C., and the take-up speed is 500 m / min to 2500 m / Take up in less than a minute to obtain a spun filament. By using polypropylene having a Q value before spinning of 3.0 or more and 10.0 or less as the main component polypropylene contained in the core component, the Q value of the main component polypropylene in the core component after spinning is 3.0 or more and 8.0. Adjust to:

Next, the obtained spinning filament is stretched at a stretching ratio of not less than 3.0 times and not more than 8.5 times at a stretching temperature of 40 ° C. or higher and lower than the melting point of the sheath component. A more preferable lower limit of the stretching temperature is 60 ° C. or higher. A more preferable upper limit of the stretching temperature is a temperature 5 ° C. lower than the melting point of the sheath component, and a particularly preferable upper limit of the stretching temperature is a temperature 10 ° C. lower than the melting point of the sheath component. When the stretching temperature is less than 40 ° C., the crystallization of the sheath component is difficult to proceed, so that the thermal shrinkage tends to increase and the bulk recovery property tends to decrease. If the stretching temperature is equal to or higher than the melting point of the sheath component, the fibers tend to be fused. A more preferable lower limit of the draw ratio is 3.3 times or more. A more preferable upper limit of the draw ratio is 8.0 times or less. When the draw ratio is 3.0 times or more, crystallization of the sheath component and the core component proceeds, and a fiber having good card passability is obtained. The stretching method is not particularly limited, and wet stretching is performed while being heated with a high-temperature liquid such as high-temperature hot water, dry stretching is performed while being heated in a high-temperature gas or a high-temperature metal roll, and 100 ° C. or higher. A known stretching process such as steam stretching, in which stretching is performed while heating the fiber under normal pressure or pressurized state, can be performed. Among these, wet stretching using warm water or dry stretching using a high-temperature gas or a high-temperature metal roll is preferable. The stretching process may be so-called one-stage stretching in which the stretching process is only one stage, may be two-stage stretching in which the stretching process has two stages, or may be multi-stage stretching in which the stretching process exceeds two stages. Since the composite short fiber for absorbent articles of the present invention has a fineness of as small as 2.0 dtex or less, it is often drawn at a high magnification. Therefore, the stretching step is preferably multistage stretching performed in a plurality of times. In addition, before and after the stretching process, an annealing process may be performed as necessary.

Then, if necessary, crimps of 5 crimps / 25 mm or more and 25/25 mm or less are provided using a known crimping machine such as a stuffing box type crimper. The crimped shape after passing through the crimper may be a serrated crimp and / or a corrugated crimp. When the number of crimps is less than 5 pieces / 25 mm, the card passing property tends to deteriorate, and the initial bulk and bulk recoverability of the nonwoven fabric tend to deteriorate. On the other hand, when the number of crimps exceeds 25 pieces / 25 mm, the number of crimps is too large, so that the card passing property is lowered, and the formation of the nonwoven fabric is deteriorated. Moreover, you may process with a fiber processing agent as needed before or after providing a crimp.

Furthermore, it is preferable that after the crimping is performed by the crimping machine, an annealing treatment is performed. The annealing treatment is preferably performed in an atmosphere such as dry heat, moist heat, and steam within a temperature range of 80 ° C. to 120 ° C., and more preferably 90 ° C. to 120 ° C. Specifically, after applying the fiber treatment agent to the fiber bundle, crimping is performed with a crimping machine, and the drying process is performed simultaneously with the annealing process in a dry heat atmosphere of 90 ° C. or more and 120 ° C. or less. Can be simplified. When the annealing treatment is performed at a temperature of 90 ° C. or higher, the dry heat shrinkage of the obtained composite short fiber does not increase, and the composite short fiber expresses a clear crimped shape. Become.

The composite short fiber obtained by the above method mainly has at least one kind of crimp selected from the group consisting of sawtooth crimps (also referred to as mechanical crimps) shown in FIG. 2A and corrugated crimps shown in FIG. 2B. In addition, since the number of crimps is 5/25 mm or more and 25/25 mm or less, a nonwoven fabric having a soft and smooth texture can be obtained without deteriorating the card passing property, which is preferable. And it cut | disconnects to desired fiber length, and an actual crimpable composite staple fiber is obtained.

The fineness of the composite short fiber for absorbent articles can be adjusted as desired by adjusting the fineness of the spinning filament and the draw ratio. After the above-described annealing treatment, the composite short fiber for absorbent articles having a predetermined length is obtained by cutting the fiber.

When the composite short fiber for absorbent articles is contained in the nonwoven fabric in an amount of 20% by mass or more, a nonwoven fabric having excellent surface tactile sensation, excellent bulkiness, flexibility in the thickness direction, and bulk recoverability is formed. As an example of the nonwoven fabric containing the composite short fiber for absorbent articles of the present invention, a thermally bonded nonwoven fabric will be described together with its production method. The heat-bonding nonwoven fabric for absorbent articles of the present invention contains 20% by mass or more of the composite short fibers for absorbent articles, and at least a part of the composite short fibers for absorbent articles is bonded by a sheath component. The heat-bonding nonwoven fabric for absorbent articles is obtained by producing a fiber web containing 20% by mass or more of the composite short fibers for absorbent articles, thermally bonding the obtained fiber web, and integrating the fibers. be able to. When other fibers are used, examples of the other fibers include natural fibers such as cotton, silk, wool, hemp, and pulp, regenerated fibers such as rayon and cupra, purified cellulose fibers such as tencel and lyocell, acetate, Examples include semi-synthetic fibers such as triacetate, synthetic fibers such as acrylic fibers, polyester fibers, polyamide fibers, polyolefin fibers, and polyurethane fibers. As the other fibers, one or more kinds of fibers can be appropriately selected from the above-described fibers according to the use. Other fibers may be used by mixing with the composite short fiber for absorbent articles of the present invention, or a fiber web composed of the composite short fiber for absorbent articles of the present invention and a fiber web composed of other fibers are laminated. May be used.

Examples of the fiber web used when producing the heat-bonding nonwoven fabric for absorbent articles include card webs such as parallel web, semi-random web, random web, cross web, and Chris cross web, airlaid web, and the like. Since the nonwoven fabric used for the absorbent article, particularly the surface sheet of the absorbent article, is required to have bulkiness, flexibility, and a certain amount of voids between the fibers, the fiber web is preferably a card web. As the thermobonding nonwoven fabric, two or more types of different types of fiber webs may be laminated and used.

It is preferable to obtain a non-woven fabric in the form of a heat-bonded non-woven fabric obtained by heat-treating the fiber web and thermally bonding the fibers with a sheath component. This is because the heat-bonded nonwoven fabric remarkably exhibits the effects brought about by the composite short fiber of the present invention, such as flexibility in the thickness direction, bulk recoverability, and smooth texture of the nonwoven fabric surface. In order to entangle the fibers, the fiber web may be subjected to an entanglement process such as a needle punch process or a hydroentanglement process before and / or after the heat treatment, if necessary.

In order to obtain a heat-bonding nonwoven fabric, the fiber web is subjected to heat treatment by a known heat treatment means. As the heat treatment means, a heat treatment machine in which pressure such as wind pressure is not so much applied to the fiber web, such as a hot air penetration type heat treatment machine, a hot air blowing type heat treatment machine and an infrared heat treatment machine, is preferably used. The heat treatment conditions such as the heat treatment temperature are selected, for example, such that the sheath component is sufficiently melted and / or softened so that the fibers are joined at the contact or intersection and the crimp is not collapsed. For example, the heat treatment temperature is the melting point of the high-density polyethylene contained in the sheath component before spinning (if a plurality of high-density polyethylenes are contained in the sheath component, the melting point of the high-density polyethylene having the highest melting point) is Tm. In this case, it is preferable that the temperature be in the range of Tm or more and (Tm + 40 ° C.) or less.

The heat-bonding nonwoven fabric for absorbent articles is a nonwoven fabric having a good surface feel. The surface tactile sensation of the heat-bonded nonwoven fabric can be sensory evaluated. Moreover, the surface tactile sensation of the heat-bonded nonwoven fabric can be measured and evaluated based on the KES (Kawabata Evaluation System) method, which is one of methods for objectively evaluating the texture of the fabric. Specifically, as a characteristic value of the surface friction, an average friction coefficient (hereinafter also referred to as MIU) and a variation of the average friction coefficient (sometimes referred to as an average deviation of the friction coefficient μ, hereinafter also referred to as MMD). Measured. MIU represents the difficulty (or ease of slipping) of slipping on the surface, and the larger the value, the more difficult it is to slip. MMD shows the dispersion | variation in friction, and it shows that the surface is so rough that this is large. The surface of the heat-bonded nonwoven fabric of the present invention tends to have a relatively small MIU, and MMD tends to be particularly small compared to conventional nonwoven fabrics. Such a non-woven fabric not only has a small feeling of friction when touching the hand or skin, but also has a small coefficient of friction variation, that is, any part of the non-woven fabric surface has a low coefficient of friction, and feels like it gets caught on fingers or skin. Because it does not give, it gives a light touch that is slippery even when it comes into contact with the skin. The equipment for measuring the characteristic value of the surface friction is not particularly limited as long as the equipment can measure the surface friction based on the KES method. For the characteristic value of surface friction, for example, a friction tester (“KES-SE”, manufactured by Kato Tech Co., Ltd.), an automated surface tester (“KES-FB4-AUTO-A”, manufactured by Kato Tech Co., Ltd.), etc. are used. Can be measured.

The surface characteristics of the heat-bonded nonwoven fabric, that is, the surface friction of the heat-bonded nonwoven fabric is determined by applying heat treatment with hot air to the surface opposite to the surface on which the hot air is blown when manufacturing the heat-bonded nonwoven fabric. When making the nonwoven fabric, the fiber web was placed and was in contact with the conveyance support used to convey the inside of the heat treatment machine (for example, a conveyor net that introduces and conveys the fiber web into the hot air through heat treatment machine). Measure on the surface. The surface that was in contact with the transport support is more likely to be smoother than the surface to which hot air is blown, and a smooth tactile sensation is easily obtained. This is because, when used on a contact surface (skin contact surface), the tactile sensation becomes smoother than when a surface blown by hot air is applied to the skin, and the usability of the absorbent article is improved. When measuring the surface friction of the heat-bonded nonwoven fabric, if it is not clear which surface is the surface to which hot air was blown during heat treatment or the surface that was placed on the transport support during heat treatment, the surface friction The surface where the MMD is a smaller value is taken as the measurement surface.

The heat-bonding nonwoven fabric for absorbent articles of the present invention is smooth and soft to the touch. Among the characteristic values of surface friction based on the KES method described above, MMD affects the smoothness when the nonwoven fabric is touched. Since the nonwoven fabric containing the composite short fiber for absorbent articles of the present invention not only has a small MMD, but also has a relatively small average coefficient of friction (MIU), the surface of the nonwoven fabric is in contact with the skin as described above. Gives a slippery and light touch.

Some composite short fibers have a large MIU and a small MMD when the surface of the nonwoven fabric containing the composite short fibers is evaluated based on the KES method. Since such a non-woven fabric is transmitted to the fingers and skin without a relatively large friction, it gives a “moist touch” and “smoothness” to feel the friction in a smooth touch. Since such a non-woven fabric is also preferable as a non-woven fabric used in the absorbent article, it is considered that the non-woven fabric used in the absorbent article is required to have as small an average friction coefficient variation (MMD) as possible.

The heat-bonding nonwoven fabric using the composite short fiber for absorbent articles of the present invention preferably has an average coefficient of friction fluctuation (MMD) of less than 0.01, more preferably 0.0095 or less. Preferably, it is 0.009 or less. The lower limit of the average friction coefficient variation (MMD) is not particularly limited and is preferably closer to 0, but may be 0.0005 or more, or 0.001 or more.

The heat-bonding nonwoven fabric for absorbent articles of the present invention is soft as a whole and gives a smooth feel when touching the nonwoven fabric surface. The heat-bonding nonwoven fabric for absorbent articles is preferably used as a top sheet for various absorbent articles such as sanitary napkins, infant paper diapers, adult paper diapers, animal diapers such as mammals, panty liners, and incontinence liners. It can be used for applications such as infant paper diapers and adult paper diaper backsheets that can be touched from the outside. When used as a surface sheet of an absorbent article, it is preferable that the composite short fiber for absorbent articles of the present invention is contained in an amount of 20% by mass or more on the skin contact surface. Further, in order to make use of the flexibility of the entire nonwoven fabric and the concealing property of the nonwoven fabric, in the absorbent article, the absorption is also applied to the so-called second sheet located on the absorber side, for example, directly below the surface sheet, with respect to the surface sheet that directly touches the skin. A heat-bonding nonwoven fabric for adhesive articles can be preferably used.

The basis weight of the heat-bonding nonwoven fabric for absorbent articles of the present invention is not particularly limited, but is preferably 5 g / m ² or more and 70 g / m ² or less, more preferably 8 g / m ² or more and 60 g / m ² or less. More preferably, it is 10 g / m ² or more and 55 g / m ² or less, and particularly preferably 15 g / m ² or more and 50 g / m ² or less. The basis weight of the heat-bonding nonwoven fabric for absorbent articles of the present invention may be outside these ranges depending on the type of absorbent article. Further, the heat-bonding nonwoven fabric for absorbent articles is used for various applications, for example, various paper diapers and sanitary napkin surface sheets, various paper diaper back sheets, and second sheets disposed directly under the absorbent article surface sheet. In this case, the basis weight is appropriately selected according to the application.

The heat-bonding nonwoven fabric for absorbent articles is required from the viewpoints of strength required when used as a nonwoven fabric constituting the absorbent article, prevention of surface fluff due to friction during use, and soft touch when touched. The longitudinal breaking strength measured according to JIS L 1096 8.14.1 A method (strip method) is preferably 15 N / 5 cm or more, more preferably 20 N / 5 cm or more, and 25 N / 5 cm. More preferably, it is the above.

Next, the surface sheet for absorbent articles of the present invention will be described in detail. As a result of intensive studies on improving the tactile sensation, bulkiness and liquid absorption characteristics of the surface sheet for absorbent articles, the present inventors are adjacent to the first fiber layer that contacts the skin and the first fiber layer. In the absorbent article topsheet including the second fiber layer, the core component includes 50 mass% or more of the core component of the first fiber layer, and the sheath component has a melting point lower by 5 ° C or more than the melting point of the polypropylene. A fiber layer containing 50% by mass or more of a first core-sheath type composite short fiber containing 60% by mass or more of high-density polyethylene is used, and the second fiber layer has a core component containing a polyester resin, and the sheath component is a melting point of the polyester resin. Including a thermoplastic resin having a melting point lower by 50 ° C. or more, and a fiber layer containing 50% by mass or more of second core-sheath type composite short fibers in which the center of gravity of the core component is shifted from the center of gravity of the fiber, The fineness of the core-sheath type composite short fiber is 1.1 dtex or more and 2.0 dtex or less, and the fineness of the second core-sheath type composite short fiber is 2.2 dtex or more and 5.2 dtex or less, and the first core-sheath type composite short fiber Wherein the core component and the sheath component are arranged substantially concentrically, and the composite ratio of the core component and the sheath component is 52/48 to 73/27 in the volume ratio of the core component / sheath component Polypropylene that is a type composite short fiber and is contained in the core component in an amount of 50% by mass or more, the ratio Mw / Mn of the mass average molecular weight Mw and the number average molecular weight Mn after spinning is 3.0 or more and 8.0 or less. The first core-sheath type composite short fiber contains 0.5% by mass or more and 10% by mass or less of an inorganic filler with respect to 100% by mass of the composite short fiber. At least part of the two-core-sheath-type composite short fiber is mixed with the first core-sheath-type composite short fiber and the first By heat-bonding with the sheath component of the two-core-sheath type composite short fiber, the surface sheet for absorbent articles has a smooth tactile sensation and liquid absorption characteristics such as run-off and liquid absorption speed are improved. Invented.

That is, in the absorbent article topsheet including the first fiber layer that contacts the skin and the second fiber layer adjacent to the first fiber layer, the first fiber layer that configures the first fiber layer that contacts the skin. The fineness of the core-sheath type composite short fiber and the fineness of the second core-sheath type composite short fiber constituting the second fiber layer adjacent to the first fiber layer are set within a specific range, and The fineness is made smaller than that of the second core-sheath composite short fiber. In addition, the core component of the first core-sheath-type composite short fiber is a resin component containing 50% by mass or more of polypropylene in which the ratio (Mw / Mn) of the weight average molecular weight Mw to the number average molecular weight Mn after spinning satisfies a specific range. The core component of the second core-sheath type composite short fiber includes a polyester resin, and the second core-sheath type composite short fiber has an eccentric cross section. As a result, it was found that the surface sheet for absorbent articles has a smooth tactile sensation and good liquid absorption characteristics such as run-off and liquid absorption speed.

The top sheet for absorbent articles of the present invention includes a first fiber layer in contact with the skin and a second fiber layer adjacent to the first fiber layer. FIG. 3 is a schematic cross-sectional view of a top sheet for absorbent articles according to an embodiment of the present invention. As shown in FIG. 3, the absorbent article topsheet 30 is composed of a first fiber layer 31 and a second fiber layer 32 adjacent to the first fiber layer 31.

(First fiber layer)
The first fiber layer includes 50% by mass or more of polypropylene in which the core component satisfies a specific range in the ratio (Mw / Mn) of the weight average molecular weight Mw and the number average molecular weight Mn after spinning, and the sheath component has a melting point of the polypropylene. 50% of a first core-sheath type composite short fiber containing 60% by mass or more of high-density polyethylene having a melting point lower by 5 ° C. or more, containing a certain proportion of inorganic filler, and having a fineness of 1.1 dtex or more and 2.0 dtex or less. A fiber layer containing at least mass%. The first fiber layer preferably contains 60% by mass or more of the first core-sheath type composite short fiber, more preferably 70% by mass of the first core-sheath type composite short fiber, from the viewpoint of excellent tactile sensation and liquid absorption characteristics. More preferably, the first core-sheath type composite short fiber is contained in an amount of 80% by mass or more, and particularly preferably the first core-sheath type composite short fiber is contained in an amount of 90% by mass or more. When the first fiber layer includes other fibers in addition to the first core-sheath composite short fibers, for example, natural fibers, regenerated fibers, and synthetic fibers can be used as the other fibers. Examples of the natural fiber include cotton, silk, wool, hemp, and pulp. Examples of the regenerated fiber include rayon and cupra. Examples of the synthetic fiber include acrylic fiber, polyester fiber, polyamide fiber, polyolefin fiber, and polyurethane fiber. As the other fibers, one or more kinds of fibers can be appropriately selected from the above-described fibers depending on the application.

<Core component>
The content of polypropylene in the core component of the first core-sheath composite short fiber is 50% by mass or more, preferably 60% by mass or more, more preferably 80% by mass or more, and particularly preferably 90% by mass or more. Most preferably, in the core component, all the resin components excluding the inorganic filler described later are made of polypropylene. As said polypropylene, a homopolymer, a random copolymer, a block copolymer, or mixtures thereof can be used, for example. It is particularly preferable that the preferred polypropylene is a propylene homopolymer as well as the polypropylene contained in the core component of the composite staple fiber for absorbent articles of the present invention. The aspect of polypropylene contained in the core component of the first core-sheath type composite short fiber is as described in the aspect of polypropylene contained in the core component of the composite short fiber for absorbent articles of the present invention. Description is omitted. In the following description of the first core-sheath type composite short fiber, unless otherwise specified, “polypropylene contained in the core component of the first core-sheath type composite short fiber” means “the first core-sheath type composite short fiber”. It means polypropylene contained in the core component by 50% by mass or more.

The polypropylene contained in the core component of the first core-sheath composite short fiber has a ratio Mw / Mn (hereinafter also referred to as “Q value”) of the weight average molecular weight Mw and the number average molecular weight Mn after spinning of 3. It is preferably 0 or more and 8.0 or less, more preferably 3.0 or more and 6.5 or less, further preferably 3.2 or more and 6.0 or less, and 3.4 or more and 5.5 or less. Particularly preferred is 3.6 or more and 5.2 or less. The first core-sheath-type composite short fiber has excellent card-passability and has a first core-sheath-type composite short fiber produced by having a Q value after spinning of the polypropylene of 3.0 or more and 8.0 or less. Productivity is also improved.

The Q value of polypropylene contained in the core component of the first core-sheath composite short fiber may be different before and after spinning. Particularly, a polypropylene having a Q value after spinning of 3.0 or more and 8.0 or less may have a Q value before spinning of more than 8. This is because the bonds between the molecules constituting the relatively high molecular weight polypropylene molecule are broken by the heat during spinning, or a part of the relatively high molecular weight polypropylene molecule is chain-transferred to the low molecular weight polypropylene molecule. It is guessed that. In the present invention, the value of the Q value is a value after spinning unless otherwise stated as a value before spinning.

In the first core-sheath type composite short fiber, the core component may contain other resin in addition to the polypropylene. The types and contents of resins other than polypropylene contained in the core component of the first core-sheath composite short fiber are the types and contents of resins other than polypropylene contained in the core component of the composite short fiber for absorbent articles of the present invention. Since this is the same as described above, the description thereof is omitted here. Various known additives for the core component of the first core-sheath type composite short fiber as long as the effects of the present invention are not hindered and do not affect the fiber productivity, the nonwoven fabric productivity, the thermal adhesiveness, and the touch. May be added. Additives that can be added to the core component of the first core-sheath composite short fiber include known crystal nucleating agents, antistatic agents, pigments, matting agents, heat stabilizers, light stabilizers, flame retardants, antibacterial agents, and lubricants. , Plasticizers, softeners, antioxidants, ultraviolet absorbers and the like.

The polypropylene contained in the core component of the first core-sheath-type composite short fiber has the same melt flow rate (MFR230) and preferable melting point as the polypropylene contained in the core component of the composite short fiber for absorbent articles of the present invention. is there. That is, the melt flow rate (MFR230) of polypropylene contained in the core component of the first core-sheath composite short fiber is preferably 10 g / 10 min or more and 50 g / 10 min or less, and 20 g / 10 min or more and 40 g / 10 min. More preferably, it is more preferably 25 g / 10 min or more and 35 g / 10 min or less. Further, the melting point of the polypropylene is preferably 150 ° C. or higher, more preferably 152 ° C. or higher, and particularly preferably 155 ° C. or higher. The preferable reason for the range of the melt flow rate and the melting point is the same as that of the main component polypropylene of the core component of the composite staple fiber for absorbent articles of the present invention, and is the same as described above. .

<Sheath component>
In the first core-sheath-type composite short fiber, the sheath component contains 60% by mass or more of high-density polyethylene having a melting point of 5 ° C. or more lower than that of the polypropylene in the core component. When the sheath component of the first core-sheath-type composite short fiber contains high-density polyethylene, the first core-sheath-type composite short fiber is likely to be highly rigid and combined with polypropylene that satisfies the above-mentioned specific Q value range. By configuring the composite short fiber, the elasticity of the entire fiber becomes high, and the card passing property and crimp expression of the first core-sheath type composite short fiber are likely to be good. Moreover, the 1st fiber layer containing a 1st core-sheath-type composite short fiber and the surface sheet for absorbent articles containing a 1st fiber layer are easy to become bulky. The content of the high-density polyethylene contained in the sheath component of the first core-sheath composite short fiber is preferably 80% by mass or more, more preferably 90% by mass or more, and further preferably 95% by mass or more. Particularly preferably, in the sheath component, all the resin components excluding the inorganic filler described later are high-density polyethylene.

In the first core-sheath type composite short fiber, the preferred range of the melt flow rate (MFR190) and the melting point of the high-density polyethylene contained in the sheath component is high in the sheath component of the composite short fiber for absorbent articles of the present invention. Same as density polyethylene. That is, the melt flow rate (MFR190) of the high-density polyethylene contained in the sheath component of the first core-sheath composite short fiber is preferably 5 g / 10 min or more and 30 g / 10 min or less, and 8 g / 10 min or more and 23 g / min. It is more preferably 10 minutes or less, and particularly preferably 10 g / 10 minutes or more and 18 g / 10 minutes or less. The melting point of the high-density polyethylene is preferably 125 ° C. or higher and 140 ° C. or lower, and more preferably 128 ° C. or higher and 138 ° C. or lower. The preferred reason for the melt flow rate and the melting point range of the high-density polyethylene is the same as that of the high-density polyethylene resin contained in the core component of the composite staple fiber for absorbent articles of the present invention, and is as described above. The description is omitted here.

In the first core-sheath composite short fiber, the sheath component may contain other resin in addition to the high-density polyethylene. Although it does not specifically limit as said other resin, For example, what was enumerated as another resin added to the core component of a 1st core-sheath-type composite short fiber can be used. Further, the sheath component of the first core-sheath type composite short fiber is also known as long as the effect of the present invention is not hindered and does not affect fiber productivity, nonwoven fabric productivity, thermal adhesiveness, and touch. Various additives can be added.

The first core-sheath type composite short fiber includes 0.5% by mass or more and 10% by mass or less of an inorganic filler with respect to 100% by mass of the composite short fiber. In the first core-sheath type composite short fiber, the content of the inorganic filler is 0.8% by mass or more and 8% by mass or less, and more preferably 1.0% by mass or more and 6.% by mass with respect to 100% by mass of the composite short fiber. It is 0 mass% or less, More preferably, it is 1.2 mass% or more and 5.0 mass% or less, Most preferably, it is 1.3 mass% or more and 3.5 mass% or less. The reason for the preferred range of the inorganic filler content contained in the first core-sheath-type composite short fiber, and the usable inorganic filler and the preferred inorganic filler are the same as those of the composite short fiber for absorbent articles of the present invention. Therefore, the description thereof is omitted here. The inorganic filler may be contained in one or both of the sheath component and the core component constituting the first core-sheath type composite short fiber. From the viewpoint of concealing the surface sheet for absorbent articles, it is preferable to contain an inorganic filler in at least the core component of the first core-sheath composite short fiber. In addition, when the content of the inorganic filler with respect to 100% by mass of the first core-sheath type composite short fiber exceeds 4% by mass or 5% by mass, the inorganic filler is contained only in one resin component of the sheath component or the core component. Since the spinnability of the resin component including the inorganic filler is extremely lowered, it is preferable to include the inorganic filler in both the sheath component and the core component.

The first core-sheath type composite short fiber is a core-sheath type composite short fiber having a concentric structure in which the core component and the sheath component are arranged substantially concentrically. The structure of the first core-sheath-type composite short fiber is the same as that of the composite short fiber for absorbent articles of the present invention in which the core component and the sheath component are arranged substantially concentrically, as described above. The description is omitted here. When the first core-sheath type composite short fiber is the core-sheath type composite short fiber having the concentric structure shown in FIG. 1, the sheath component 11 is disposed around the core component 12, and the sheath component 11 surrounds the core component 12. Thus, in the core-sheath type composite short fiber 10 having the concentric circular structure, the fiber surface other than the cut surface is covered with the sheath component 11. Thus, when the fiber web composed of the first core-sheath type composite short fibers having the concentric circular structure is thermally bonded, the sheath component constituting the surface of the first core-sheath type composite short fibers is melted, and the fibers are thermally bonded. To do. Since the first core-sheath type composite short fiber has a concentric circular structure, the thickness of the sheath component in the fiber cross section is substantially constant at any location in the fiber cross section. As a result, when the fiber web containing the first core-sheath composite short fiber is heat-treated, the other component contacts the first core-sheath composite short fiber in which the sheath component is softened and melted. However, since a heat bond point having a uniform strength is formed, the first fiber layer using the first core-sheath composite short fiber has a high adhesive strength, is resistant to friction and is difficult to fluff. The fact that the center of gravity of the core component is not substantially deviated from the center of gravity of the composite short fiber means that the eccentricity obtained by the above method is 10% or less, preferably 7% or less, particularly preferably 5% or less, most preferably. Indicates 3% or less.

In the first core-sheath composite short fiber, the composite ratio of the core component to the sheath component is 52/48 to 73/27, preferably 55/45 to 70/30, as the volume ratio of the core component / sheath component, More preferably, it is 60/40 to 70/30, and particularly preferably 62/38 to 68/32. When the composite ratio of the core component to the sheath component in the first core-sheath-type composite short fiber is in the above-described range, the card-passability of the first core-sheath-type composite short fiber and the first core-sheath-type composite short fiber are included. The tactile sensation of the surface sheet for absorbent articles is improved.

In the first core-sheath type composite short fiber, the shape of the core component in the fiber cross section may be elliptical, Y-shaped, X-shaped, polygonal, star-shaped, etc. The form in the fiber cross section may be elliptical, Y-shaped, X-shaped, polygonal, star-shaped or other irregular shape, or hollow shape other than circular.

The first core-sheath type composite short fiber has a fineness of 1.1 dtex or more and 2.0 dtex or less. When the fineness of the first core-sheath type composite short fiber is 2.0 dtex or less, the tactile sensation of the surface sheet for absorbent articles tends to be smooth and the concealability tends to be high. From the viewpoint of improving the tactile sensation and concealing property of the top sheet for absorbent articles, the fineness of the first core-sheath composite short fiber is preferably 1.8 dtex or less, and more preferably 1.7 dtex or less. When the fineness is 1.1 dtex or more, the liquid absorption properties such as the run-off of the top sheet for absorbent articles is shortened and the liquid absorption speed is increased. From the viewpoint of shortening the run-off of the top sheet for absorbent articles and improving the liquid absorption characteristics, the fineness of the first core-sheath composite short fiber is preferably 1.2 dtex or more, and 1.3 dtex or more. Is more preferable.

The first core-sheath type composite short fiber mainly has at least one kind of crimp selected from the group consisting of a saw-tooth crimp (also referred to as a mechanical crimp) shown in FIG. 2A and a corrugated crimp shown in FIG. 2B. The number of crimps is preferably 5/25 mm or more and 25/25 mm or less. A more preferable number of crimps is 8 pieces / 25 mm or more and 20 pieces / 25 mm or less, and a more preferred number of crimps is 10 pieces / 25 mm or more and 20 pieces / 25 mm or less. The first core-sheath type composite short fiber preferably has a crimp rate of 5% or more and 20% or less, more preferably 6% or more and 18% or less, and 6.5% or more and 16% or less. More preferably it is. Further, the first core-sheath type composite short fiber preferably has a fiber length of 25 mm or more and less than 65 mm, more preferably 28 mm or more and 55 mm or less, further preferably 30 mm or more and 48 mm or less, and 34 mm or more and 45 mm. It is particularly preferred that The reason for the preferred range of the number of crimps, the crimp rate, and the fiber length of the first core-sheath composite short fiber is the same as that of the composite short fiber for absorbent articles of the present invention, and is as described above. Then, the explanation is omitted. As the first core-sheath type composite short fiber, the above-described composite short fiber for absorbent articles of the present invention can be suitably used.

(Second fiber layer)
In the second fiber layer, the core component includes a polyester resin, the sheath component includes a thermoplastic resin having a melting point that is lower by 50 ° C. than the melting point of the polyester resin, and the center of gravity of the core component deviates from the center of gravity of the fiber. It is a fiber layer containing 50 mass% or more of the second core-sheath type composite short fiber. The second fiber layer preferably includes 60% by mass or more of the second core-sheath type composite short fiber, more preferably 70% by mass or more, and further preferably 80% by mass or more from the viewpoint of excellent liquid absorption characteristics. Especially preferably, it contains 90 mass% or more. When the second fiber layer includes other fibers in addition to the second core-sheath type composite short fibers, the first fiber layer includes other fibers in addition to the first core-sheath type composite fibers. The fibers exemplified in (2) can also be included in the second fiber layer. As the other fibers, one or more kinds of fibers can be appropriately selected from known fibers including the above-described fibers according to the use.

The second core-sheath type composite short fiber is an eccentric core-sheath type composite short fiber in which the position of the center of gravity of the core component is shifted from the position of the center of gravity of the fiber. FIG. 4 is a schematic cross-sectional view showing a fiber cross section of an eccentric core-sheath type composite short fiber. As shown in FIG. 4, the gravity center position 43 of the core component 42 is shifted from the gravity center position 44 of the core-sheath type composite short fiber 40. The crimped shape of the eccentric core-sheath type composite short fiber is generally a corrugated crimp shown in FIG. 2B or a helical crimp shown in FIG. 2C (also called a coiled crimp) rather than the sawtooth crimp shown in FIG. 2A. ). Further, the crimped shape of the eccentric core-sheath type composite short fiber may be a crimped shape in which a wave-shaped crimp and / or a spiral crimp are mixed in a sawtooth-shaped crimp. FIG. 2D is a schematic view of a crimped shape in which serrated crimps and corrugated crimps are mixed. And compared with the composite short fiber which has a serrated crimp, the composite short fiber in which a wave shape crimp, a spiral crimp, a serrated crimp, a wave shape crimp, and / or a spiral crimp are mixed. The heat-bonded nonwoven fabric using is likely to be a bulky, non-woven fabric having a sparse internal structure in which many voids are present inside the nonwoven fabric. Therefore, by including the second core-sheath type composite short fiber, which is an eccentric core-sheath type composite short fiber, in the second fiber layer, the second fiber layer becomes a fiber layer having a sparse structure with many voids. It is easy to draw liquid absorbed by one fiber layer (for example, blood such as menstrual blood and excrement such as urine) into the second fiber layer, and a core-sheath type composite short having a concentric structure as a fiber constituting the second fiber layer. As compared with the case where fibers are used, the liquid absorption characteristics such as the run-off becomes shorter and the liquid absorption speed becomes faster. The second core-sheath type composite short fiber preferably has an eccentricity of more than 10% and 50% or less, more preferably 15% or more and 30% or less. The eccentricity ratio of the second core-sheath type composite short fiber is obtained by magnifying a cross section of the core-sheath type composite short fiber with a scanning electron microscope or the like, the center of gravity position 43 of the core component 42 is C1, and the core-sheath type composite short fiber. When the center of gravity position 44 of 40 is Cf and the radius 45 of the composite short fiber is rf, it can be calculated by Equation 1 described above.

The second core-sheath type composite short fiber has a fineness of 2.2 dtex or more and 5.2 dtex or less. By making the fineness of the second core-sheath type composite short fiber constituting the second fiber layer larger than the fineness of the first core-sheath type composite short fiber constituting the first fiber layer, the surface sheet for absorbent articles is appropriate. It has excellent cushioning properties, and the tactile sensation is smooth, and the liquid absorption property is also good. When the fineness of the second core-sheath type composite short fiber is less than 2.2 dtex, the second fiber layer is small because the fineness is small even if the second core-sheath type composite short fiber is an eccentric core-sheath type composite short fiber. As a result, the second fiber layer has a dense structure and does not absorb excreta such as menstrual blood or urine. Further, when the fineness of the second core-sheath type composite short fiber exceeds 5.2 dtex, the fineness of the second core-sheath type composite short fiber is large, so that the number of constituents of the second fiber layer is relatively reduced. The second fiber layer becomes too sparse and does not absorb excreta such as menstrual blood or urine. The fineness of the second core-sheath type composite short fiber is more preferably 2.6 dtex or more and 4.8 dtex or less, and further preferably 2.8 dtex or more and 4.6 dtex or less.

In the second core-sheath type composite short fiber, the core component preferably contains 50% by mass or more of the polyester resin, more preferably 60% by mass or more, further preferably 70% by mass or more, and particularly preferably 80% by mass or more. Including. When the core component contains 50% by mass or more of the polyester resin, the card passing property of the second core-sheath composite short fiber becomes good. The polyester resin is not particularly limited, and examples thereof include polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polylactic acid, and acid components such as isophthalic acid, succinic acid, and adipic acid, and 1 , 4-butanediol, 1,6 hexanediol and other glycol components, polytetramethylene glycol, polyoxymethylene glycol and other copolymers, and elastomers thereof. The polyester resin is preferably polyethylene terephthalate (hereinafter also referred to as PET) from the viewpoints of bulkiness, cushioning properties, and liquid absorption speed of the surface sheet for absorbent articles.

In the second core-sheath composite short fiber, the thermoplastic resin having a melting point of 50 ° C. or more lower than that of the polyester resin contained in the core component is not particularly limited, but high-density polyethylene is preferably used. When the sheath component of the second core-sheath-type composite short fiber contains high-density polyethylene, the second core-sheath-type composite short fiber tends to have high rigidity, and the card-passing property of the second core-sheath-type composite short fiber can be improved. Shrinkage tends to be good. The content of the high-density polyethylene contained in the sheath component of the second core-sheath type composite short fiber is preferably 80% by mass or more, more preferably 90% by mass or more, and further preferably 95% by mass or more. Especially preferably, it is 100 mass%. As said high density polyethylene, the high density polyethylene which can be used for the sheath component of the 1st core sheath type composite short fiber mentioned above can be used. It is preferable that the high-density polyethylene contained in the sheath component of the first core-sheath composite short fiber and the high-density polyethylene contained in the sheath component of the second core-sheath composite short fiber have substantially the same melting point. It becomes easy to thermally bond the first core-sheath type composite short fiber and the second core-sheath type composite short fiber by the sheath component of the first core-sheath type composite short fiber and the second core-sheath type composite short fiber.

In the second core-sheath type composite short fiber, the shape of the core component in the fiber cross section may be elliptical, Y-shaped, X-shaped, polygonal, star-shaped, etc. The form in the fiber cross section may be elliptical, Y-shaped, X-shaped, polygonal, star-shaped or other irregular shape, or hollow shape other than circular.

The fiber length of the second core-sheath type composite short fiber is not particularly limited, and may be, for example, 76 mm or less. From the viewpoint of processability when producing a surface sheet for absorbent articles, the fiber length is preferably 35 mm or more and 65 mm or less, more preferably 40 mm or more and 60 mm or less, and still more preferably 44 mm or more and 55 mm or less.

In the top sheet for absorbent articles of the present invention, at least a part of the first core-sheath composite short fiber and the second core-sheath composite short fiber is composed of the first core-sheath composite short fiber and the second core-sheath composite short fiber. It is thermally bonded by the sheath component of the fiber. A first fiber web containing 50 mass% or more of the first core-sheath type composite short fiber and a second fiber web containing 50 mass% or more of the second core-sheath type composite short fiber are laminated, and a fiber web having a laminated structure is obtained. Heat treatment is performed to thermally bond at least a part of the first core-sheath type composite short fiber and the second core-sheath type composite short fiber with the sheath component.

Examples of the fiber web include a parallel web, a semi-random web, a random web, a cross web, a card web such as a Chris cross web, an airlaid web, and the like. Since the surface sheet for absorbent articles is required to have bulkiness, flexibility, and a certain amount of voids between the fibers, the fiber web is preferably a card web. The first fiber layer and the second fiber layer may be different types of fiber webs.

The fiber web having the laminated structure is subjected to heat treatment, and the first core-sheath composite short fiber and the second core-sheath composite short fiber are formed by the sheath component of the first core-sheath composite short fiber and the second core-sheath composite short fiber. The surface sheet for absorbent articles of the present invention can be obtained in the form of a heat-bonded nonwoven fabric including a first fiber layer (first fiber web) and a second fiber layer (second fiber web). it can. This is because, in the form of a heat-bonded nonwoven fabric, effects such as flexibility in the thickness direction, bulk recoverability, and a smooth texture on the nonwoven fabric surface are remarkably exhibited. In order to entangle the fibers, the fiber web may be subjected to an entanglement process such as a needle punch process or a hydroentanglement process before and / or after the heat treatment, if necessary. The first fiber web and the second fiber web may be entangled with each other near the boundary.

The heat treatment can be performed by a known heat treatment machine. For example, a heat treatment machine in which pressure such as wind pressure is not so much applied to the fiber web, such as a hot air through heat treatment machine, a hot air blowing type heat treatment machine, and an infrared heat treatment machine, is preferably used for the heat treatment. The heat treatment conditions such as the heat treatment temperature are selected, for example, such that the sheath component is sufficiently melted and / or softened so that the fibers are joined at the contact points or intersections and the crimps are not collapsed. For example, the heat treatment temperature is the melting point of the high-density polyethylene contained in the sheath component before spinning (if a plurality of high-density polyethylenes are contained in the sheath component, the melting point of the high-density polyethylene having the highest melting point) is Tm. In this case, it is preferable that the temperature be in the range of Tm or more and (Tm + 40 ° C.) or less. A more preferable heat treatment temperature range is (Tm + 5 ° C.) or more and (Tm + 30 ° C.) or less.

The surface sheet for absorbent articles has good tactile sensation. The tactile sensation of the surface sheet for absorbent articles can be measured and evaluated based on the KES (Kawabata Evaluation System) method, which is one of methods for objectively evaluating the texture of the fabric. Specifically, in the surface sheet for absorbent articles, the surface of the first fiber layer as the measurement surface, the variation of the average friction coefficient based on the KES method (sometimes referred to as the average deviation of the friction coefficient μ, It is also referred to as MMD.) And the tactile sensation is evaluated. MMD shows the dispersion | variation in friction, and it shows that the surface is so rough that this is large. The instrument for measuring the variation of the average friction coefficient is not particularly limited as long as it is an instrument capable of measuring the surface friction based on the KES method. For example, a friction tester (“KES-SE”, manufactured by Kato Tech Co., Ltd.), an automated surface tester (“KES-FB4-AUTO-A”, manufactured by Kato Tech Co., Ltd.), or the like can be used.

From the viewpoint of having a smooth tactile sensation and excellent texture, the top sheet for absorbent articles has a surface of the first fiber layer as a measurement surface, and the variation in average friction coefficient measured based on the KES method is 0.0092. Or less, more preferably 0.009 or less, and even more preferably 0.0088 or less. The lower limit of the average friction coefficient variation (MMD) is not particularly limited and is preferably closer to 0, but may be 0.0005 or more, or 0.001 or more.

From the viewpoint that the top sheet for absorbent articles has no liquid leakage of excrement such as menstrual blood and urine and is excellent in liquid absorption characteristics, the run-off measured as described later is preferably 45 mm or less, and 40 mm or less. More preferably, it is 35 mm or less. In addition, the top sheet for absorbent articles is preferably 40 seconds or less, more preferably 35 seconds or less, as measured from the third time, as described later, from the viewpoint of excellent liquid absorption characteristics. Yes, more preferably 30 seconds or less.

In the surface sheet for absorbent articles, the basis weight of the first fiber layer is preferably lower than the basis weight of the second fiber layer from the viewpoint of liquid absorption characteristics. From the viewpoint of low liquid return and excellent wet back resistance, the basis weight of the first fiber layer is preferably 4 g / m ² or more and 18 g / m ² or less, and preferably 5 g / m ² or more and 18 g / m ² or less. Is more preferably 7 g / m ² or more and 15 g / m ² or less, and particularly preferably 8 g / m ² or more and 14 g / m ² or less. Further, from the viewpoint of low liquid return and excellent wet-back resistance, the basis weight of the second fiber layer is preferably 10 g / m ² or more and 30 g / m ² or less, and 12 g / m ² or more and 28 g / m ² or less. More preferably, it is 12 g / m ² or more and 25 g / m ² or less.

In the top sheet for absorbent articles, the first fiber layer contacts the skin of the wearer wearing the absorbent article. When the first fiber layer including the first core-sheath type composite short fiber hits the skin, a comfortable feeling of use can be given to the user of the absorbent article. The top sheet for absorbent articles is preferably used as a top sheet for various absorbent articles such as sanitary napkins, infant paper diapers, adult paper diapers, paper diapers for animals including mammals, panty liners, incontinence liners, etc. it can.

The absorbent article of the present invention is not particularly limited as long as the absorbent article includes the surface sheet for absorbent articles. Examples include sanitary napkins, infant paper diapers, adult paper diapers, paper diapers for animals such as mammals, panty liners, incontinence liners, and the like.

Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples.

The measurement method and evaluation method used in this example are as follows.

(Number average molecular weight Mn, mass average molecular weight Mw, and Q value)
Number average molecular weight Mn, mass from gel permeation chromatography (GPC) using ortho-dichlorobenzene (ODCB) as measurement solvent using cross fractionator (CFC) and Fourier transform infrared absorption spectrum analysis (FT-IR) The ratio of average molecular weight Mw and mass average molecular weight / number average molecular weight (Mw / Mn: Q value) was measured.

The Q value of PP before spinning was measured using the used PP resin pellets as it was, and the Q value of PP after spinning was measured using the obtained composite short fiber. The PP Q value after spinning is determined by melting and extruding the PP resin from the extruder with the spinning nozzle set at 290 ° C. and without attaching the spinning nozzle when performing melt spinning. Measurement may be performed by preparing a rod-shaped resin strand having a diameter of 5 to 8 mm and cutting the rod-shaped resin strand into a length of about 3 mm.

(Spinnability during melt spinning)
The spinnability of the composite short fiber for absorbent articles was evaluated based on the following criteria based on the occurrence state and frequency of yarn breakage when melt spinning for 30 minutes continuously.
A: The number of yarn breaks is 0 to 2 in 30 minutes of continuous melt spinning, and the spinnability is good.
B: The number of yarn breaks is 3-5 times in 30 minutes of continuous melt spinning, but there is no problem in the process.
C: The number of yarn breakage is 6 times or more in 30 minutes of continuous melt spinning, or yarn breakage occurs frequently and spinning is impossible.

(Extensible)
The drawability of the composite short fibers for absorbent articles was evaluated based on the following criteria based on the occurrence of yarn breakage during the drawing process and the passability of the stuffing box type crimper used for crimping.
A: Yarn breakage hardly occurs in the drawing process, and the stuffing box type crimper passes easily, so there is no problem in production.
B: In the drawing process, thread breakage or clogging in the stuffing box type crimper occurs, but there is no problem in production.
C: Productivity is very poor because yarn breakage frequently occurs and winding around the drawing tank and drawing roll occurs, or clogging frequently occurs in the stuffing box type crimper or in the discharge port.

(Card passability)
Evaluate the card passability of composite short fibers for absorbent articles based on the following conditions, based on the state of occurrence of nep and fly when a fiber web is produced using a card machine, and the texture of the obtained fiber web did.
A: Since the fiber easily passes through the card machine, and almost no nep or fly occurs, a fiber web having a good texture can be obtained.
B: Nep is slightly generated but does not significantly affect the formation of the fiber web.
C: The fiber web cannot be obtained because the card passing property is poor or a large amount of neps are generated.

(Number of crimps and crimp rate)
It measured according to JIS L 1015 (2010).

(Single fiber strength, elongation at break and apparent Young's modulus)
The single fiber strength and elongation at break of the fiber were measured according to JIS L 1015 (2010). The apparent Young's modulus was obtained from the single fiber strength.

(Breaking strength of nonwoven fabric)
In accordance with JIS L 1096 8.14.1 A method (strip method), using a constant-speed tension type tensile tester, the specimens were tensioned with a width of 5 cm, a grip interval of 10 cm, and a tensile speed of 30 ± 2 cm / min. It applied to the test and the load value (tensile strength) at the time of cutting was measured, and it was set as the breaking strength. The tensile test was carried out with the longitudinal direction (MD direction) of the nonwoven fabric as the tensile direction. All the evaluation results are shown as an average of values measured for three samples.

(Surface feel)
The surface of the nonwoven fabric was touched and evaluated according to the following evaluation criteria.
A: Very smooth.
B: I feel a little rough.
C: It is rough.

(Bulky)
The bulkiness of the nonwoven fabric was evaluated by measuring the thickness at a load of 3 g / cm ² . The thickness was measured according to JIS-L-1096 using a thickness measuring machine (trade name “THICKNESS GAUGE”, model “CR-60A”, manufactured by Daiei Kagaku Seiki Seisakusho Co., Ltd.).

Polypropylene (PP), high density polyethylene (HDPE), and titanium oxide-containing polypropylene (titanium oxide-containing PP) used in Examples and Comparative Examples are as follows.
(1) PP-A (melting point: 160 ° C., MFR230: 30 g / 10 min, Q value (before spinning): 4.6)
(2) PP-B (melting point: 160 ° C., MFR230: 20 g / 10 min, Q value (before spinning): 5.6)
(3) PP-C (melting point: 161 ° C., MFR230: 13.5 g / 10 min, Q value (before spinning): 2.8)
(4) HDPE-A (melting point: 130 ° C., MFR190: 12 g / 10 min)
(5) HDPE-B (melting point: 130 ° C., MFR190: 22 g / 10 min)
(6) Titanium oxide-containing PP (hereinafter also referred to as master batch, MB): 60 parts by mass of titanium oxide powder and 40 parts by mass of PP are kneaded by a twin screw extruder, and the obtained kneaded product is about 5 mm square. To obtain PP containing 60% by mass of titanium oxide.

(Examples 1 to 10, Comparative Examples 1 to 4)
The above-described high-density polyethylene was used as the sheath component, and the above-described polypropylene was used as the core component. Further, in the core component polypropylene, a master batch was mixed so that the content of titanium oxide in the entire composite short fiber was in the proportions shown in Tables 1 and 2. Each of the prepared sheath component and core component was adjusted so that the composite ratio (volume ratio) of the sheath component to the core component was the composite ratio described in Table 1 and Table 2, using a concentric core-sheath composite nozzle (600 holes). Melt spinning was performed by adjusting the discharge amount of the components. The spinning temperature of the sheath component was 270 ° C., the spinning temperature of the core component was 290 ° C., and the extruded molten filament was taken up at the take-up speed shown in Tables 1 and 2, and the spinning filaments having the finenesses shown in Tables 1 and 2 were used. Got.

The obtained spinning filament was wet-drawn in hot water at 90 ° C. at the draw ratios shown in Tables 1 and 2, and further drawn to a draw ratio of 1.1 times in hot water at 95 ° C. Drawn filaments having the same fineness (fineness described in Tables 1 and 2). Next, 0.3% by mass of an oil agent obtained by blending 35 parts by mass of C8 alkyl phosphate potassium salt and 65 parts by mass of C12 alkyl phosphate potassium salt was added as a fiber treatment agent, and then the stuffing box type was applied to the drawn filament. Mechanical crimp was applied with a crimper. And the annealing process and the drying process were simultaneously performed in the relaxed state for 15 minutes with the hot air spraying apparatus set to 110 degreeC. Thereafter, the filament was cut into predetermined lengths as shown in Tables 1 and 2 to obtain composite short fibers for absorbent articles.

In any of Examples and Comparative Examples, the spinnability and stretchability were good.

(Measurement of thermal bonding nonwoven fabric manufacturing method and number of neps)
Using the fibers obtained in Examples and Comparative Examples, a fiber web having a basis weight of about 25 g / m ² was produced by a roller type card machine. Under the present circumstances, the card | curd permeability of the composite short fiber was evaluated by the said evaluation criteria. The obtained fiber web was subjected to heat treatment for 10 seconds using a hot air spraying device set at 135 ° C., and the sheath component was melted to obtain a heat-bonded nonwoven fabric. The obtained heat-bonded nonwoven fabric was cut into a size of 60 cm × 25 cm, and the number of neps generated in the nonwoven fabric was visually confirmed and measured. And the mass of the nonwoven fabric cut | judged to the said predetermined | prescribed magnitude | size was measured, and the number of neps (pieces / g) per nonwoven fabric mass was computed from the measured number of neps and the mass of a nonwoven fabric. These results are shown in Tables 1 and 2 below.

The performances of the fibers and nonwoven fabrics obtained in each Example and each Comparative Example are shown in Table 1 and Table 2 below. In Table 1, the Q value is the Q value of PP after spinning.

As can be seen from the data in Tables 1 and 2, the core-sheath type composite short fibers of Examples 1 to 10 had a number of neps per 1 g of fibers of 20 or less, and the card passing property was good. From the results of Examples 8 to 10, it was found that as the content of titanium oxide in the composite short fiber for absorbent articles increases, the generation of neps decreases. In addition, the heat-bonded nonwoven fabric containing the composite short fibers for absorbent articles of Examples 1 to 10 was bulky, had a smooth feel, and was excellent in texture. In addition, the heat-bonded nonwoven fabric containing the composite short fibers for absorbent articles of Examples 1 to 10 was excellent in breaking strength.

On the other hand, the heat-bonding nonwoven fabric containing the eccentric core-sheath composite short fiber of Comparative Example 1 in which the center of gravity of the core component deviates from the position of the center of gravity of the fiber had a low breaking strength. Due to the low breaking strength, when the heat-bonded nonwoven fabric is used as a surface sheet for absorbent articles, the surface of the nonwoven fabric becomes fuzzy due to friction during use, and it tends to have a rough feel. The heat-bonded nonwoven fabric containing the core-sheath composite short fiber of Comparative Example 2 having a core-sheath ratio of 50/50 and a large amount of sheath components had poor touch feeling. The core-sheath type composite short fiber of Comparative Example 4 having a fineness of less than 1.1 dtex had a number of neps per gram of more than 20, and the card passing property was poor. The core-sheath type composite short fiber of Comparative Example 3 in which the Q value after spinning of the polypropylene constituting the core component is less than 3.0 has more than 20 neps per 1 g of fiber, and the card passing property is poor. It was.

(Examples 11 to 12, Comparative Examples 5 to 6)
A heat-bonded nonwoven fabric was produced using the core-sheath type composite short fibers obtained in Examples 6 and 7 and the following fibers 1 to 3. First, as the first fiber layer, predetermined fibers were put into a roller card machine so as to have a basis weight described in Table 3, and a fiber web (first fiber layer) was produced. Next, as the second fiber layer, predetermined fibers were put into a roller-type card machine so as to have a basis weight described in Table 3, and a fiber web (second fiber layer) was produced. A fiber web to be the second fiber layer was placed on the fiber web to be the first fiber layer to obtain a laminated fiber web. The laminated fiber web was subjected to hot air treatment for 15 seconds using a hot air spraying device set at 135 ° C., and the sheath component was melted to bond the core-sheath composite short fibers to obtain a heat-bonded nonwoven fabric. At this time, the hot air was blown against the fiber web from the second fiber layer side, and the first fiber layer side was in contact with the conveyor net of the hot air blowing device.

(1) Fiber 1: Core component is PET (melting point 256 ° C.), sheath component is HPDE (melting point: 130 ° C., MFR 190: 12 g / 10 min), and volume ratio of core component / sheath component (core-sheath ratio) ) Was 64/36, and an eccentric core-sheath type composite short fiber (fineness: 2.6 dtex, fiber length: 51 mm) having an eccentricity of 25% was used.
(2) Fiber 2: Core component is PET (melting point 256 ° C.), sheath component is HPDE (melting point: 130 ° C., MFR 190: g / 10 min), and volume ratio of core component / sheath component (core-sheath ratio) ) Was 64/36, and a core-sheath type composite short fiber (fineness: 2.2 dtex, fiber length: 51 mm) having a concentric structure in which a core component and a sheath component were arranged concentrically was used.
(3) Fiber 3: The core component is PET (melting point 256 ° C.), the sheath component is HPDE (melting point: 130 ° C., MFR 190: 12 g / 10 min), and the volume ratio of the core component / sheath component (core-sheath ratio) ) Was 64/36, and an eccentric core-sheath type composite short fiber (fineness: 3.3 dtex, fiber length: 51 mm) having an eccentricity of 25% was used.

About each obtained heat bonding nonwoven fabric, the measurement and evaluation of the surface characteristic based on KES (Kawabata Evaluation System) method were performed.

Specifically, in order to evaluate the surface characteristics, a surface friction test of the heat-bonded nonwoven fabric was performed, and the average friction coefficient (MIU) and the average friction coefficient fluctuation (MMD) were measured as the surface characteristic values. A “KES-SE” friction tester manufactured by Kato Tech Co., Ltd. was used for the test and measurement of surface friction on the heat-bonded nonwoven fabric. At the time of measurement, the measurement surface is opposite to the surface on which the hot-bonded nonwoven fabric was blown with hot air during manufacture (that is, the surface placed on the conveyor net surface of the hot air blowing device), and the static load on the friction element is 25 gf ( 245N), the friction element was moved in a direction parallel to the vertical direction of the nonwoven fabric at a moving speed of 1 mm / second, and the average friction coefficient (MIU) and the variation of the average friction coefficient (MMD) of the heat-bonded nonwoven fabric were measured. The measurement results are shown in Table 3.

As can be seen from the data in Table 3, the nonwoven fabrics of Examples 11 and 12 using the composite short fibers for absorbent articles of the present invention have an average coefficient of friction variation (MMD) that affects the smoothness when touching the skin. Was particularly small. This is because the fineness is reduced, the core component and the sheath component constituting the composite short fiber are mainly composed of polyolefin resin, and the number of fibers contained in the nonwoven fabric with the same basis weight because the fineness of the fiber itself is small. This is thought to be due to the finer texture on the nonwoven fabric surface. Further, when the nonwoven fabric of Example 11 and the nonwoven fabric of Example 12 are compared, since the value of MMD is smaller in Example 11 in which the composite short fibers having a finer fineness are used, the smaller the fineness, the present invention. It is considered that the texture of the heat-bonded nonwoven fabric is improved.

On the other hand, the nonwoven fabrics of Comparative Examples 5 to 6 each using a polyester composite short fiber having a fineness of 2.2 dtex and a polyester composite short fiber having a fineness of 2.6 dtex had an average friction coefficient (MIU) of the nonwoven fabric surface of Example 11, Although it is about the same as 12 nonwoven fabrics, the average coefficient of friction variation (MMD) value is not as small as the nonwoven fabrics of the examples. From these results, the composite staple fiber for absorbent articles of the present invention is a composite staple fiber having a fineness mainly composed of polyolefin resin, and compared with conventional composite staple fibers, particularly polyester composite staple fibers. And it can be said that it becomes a heat-bonding nonwoven fabric with a smoother tactile sensation when touching the skin.

(Examples 13 to 20, Comparative Examples 7 to 10)
A laminated nonwoven fabric was produced using the fibers shown below. In order to measure the thickness of the obtained nonwoven fabric and evaluate its adaptability to the surface sheet for absorbent articles, the run-off, liquid absorption rate, liquid return test, surface characteristics based on the KES method Measurement and evaluation were performed.

(1) Polyolefin-based core composite short fiber 1: The core component is the PP-A, the sheath component is the HDPE-A, and the core-sheath ratio (the volume ratio of the core component / sheath component is the same hereinafter) is 65/35. A core-sheath composite short fiber (fineness: 1.4 dtex, fiber length: 38 mm) in which a core component and a sheath component are arranged concentrically.
(2) Polyolefin-based composite short fiber 2: The core component is the PP-A, the sheath component is the HDPE-A, the core-sheath ratio is 65/35, and the core component and the sheath component are arranged concentrically. Concentric circular core-sheath type composite short fibers (fineness: 1.6 dtex, fiber length: 38 mm).
(3) Polyolefin-based composite short fiber 3: The core component is the PP-B, the sheath component is the HDPE-B, the core-sheath ratio is 65/35, and the core component and the sheath component are arranged concentrically. Concentric circular core-sheath type composite short fiber (fineness: 1.1 dtex, fiber length: 38 mm).
(4) Polyester-based composite short fibers 1: The core component is PET (melting point: 256 ° C.), the sheath component is the HDPE-A, the core-sheath ratio is 45/55, and the eccentricity is 25%. Core-sheath type composite short fiber (fineness: 2.6 dtex, fiber length: 51 mm).
(5) Polyester-based composite short fiber 2: the core component is PET (melting point: 256 ° C.), the sheath component is the HDPE-A, the core-sheath ratio is 45/55, and the eccentricity is 25%. Core-sheath type composite short fiber (fineness: 3.3 dtex, fiber length: 51 mm).
(6) Polyester-based composite short fiber 3: The core component is PET (melting point: 256 ° C.), the sheath component is the HDPE-A, the core-sheath ratio is 45/55, and the eccentricity is 25%. Core-sheath type composite short fiber (fineness: 4.4 dtex, fiber length: 51 mm).
(7) Polyester-based composite short fiber 4: The core component is PET (melting point: 256 ° C.), the sheath component is the HDPE-A, the core-sheath ratio is 45/55, and the eccentricity is 25%. Core-sheath type composite short fiber (fineness: 5.6 dtex, fiber length: 51 mm).
(8) Polyester-based composite short fiber 5: The core component is PET (melting point: 256 ° C.), the sheath component is the HDPE-A, the core-sheath ratio is 37/63, and the core component and the sheath component are concentric. Core-sheath type composite short fibers (concentration: 2.2 dtex, fiber length: 51 mm) arranged concentrically.
(9) Polyester-based composite short fiber 6: The core component is PET (melting point: 256 ° C.), the sheath component is the HDPE-A, the core-sheath ratio is 40/60, and the core component and the sheath component are concentric. Core-sheath type composite short fibers (concentration: 3.3 dtex, fiber length: 51 mm) arranged concentrically.
(10) Polyester-based composite short fiber 7: The core component is PET (melting point: 256 ° C.), the sheath component is HDPE-A, the core-sheath ratio is 40/60, and the core component and the sheath component are concentric. A core-sheath type composite short fiber (fineness: 4.4 dtex, fiber length: 51 mm) arranged in a concentric circle.
The polyolefin composite short fibers 1 to 3 and the polyester composite short fibers 1 to 4 were added with titanium dioxide to the core component. In the polyolefin composite short fiber, the content of titanium dioxide was 1.95% by mass with respect to 100% by mass of the fiber. In the polyester composite short fibers 1 to 4, the content of titanium dioxide was 1.67% by mass with respect to 100% by mass of the fiber.

In the above fiber, the Q value of the polymer is a value measured by the above method.

(Example 13)
First, a first fiber web having a basis weight of 10 g / m ² was produced using a polyolefin-based composite short fiber 1 by a roller type card machine. Next, a second fiber web having a basis weight of 15 g / m ² was produced by using a polyester-based composite short fiber 1 with a roller type card machine. Next, after laminating the second fiber web on the first fiber web, the obtained laminated fiber web was heat-treated for 15 seconds using a hot air through heat treatment machine set at 135 ° C. And a sheath component in the polyester-based composite short fiber is melted to thermally bond the polyolefin-based composite short fiber 1 and the polyester-based composite short fiber 1 to form a heat-bonded nonwoven fabric including a first fiber layer and a second fiber layer (weight per unit 26. 0 g / m ² ) was obtained. At this time, the laminated fiber web is heat-treated in a state in which the first fiber web to be the first fiber layer is in contact with the conveyor net surface of the hot air penetration type heat treatment machine, and the hot air is applied to the laminated fiber web from the second fiber layer side. I sprayed.

(Example 14)
A heat-bonded nonwoven fabric containing a first fiber layer and a second fiber layer (weight per unit: 24.0 g / m) in the same manner as in Example 13 except that the polyester-based composite short fiber 2 was used instead of the polyester-based composite short fiber 1. ² ) got.

(Example 15)
The first fiber was the same as in Example 13 except that the polyolefin composite short fiber 2 was used in place of the polyolefin composite short fiber 1 and the polyester composite short fiber 3 was used in place of the polyester composite short fiber 1. A heat-bonded nonwoven fabric (weight per unit area 25.7 g / m ² ) including the layer and the second fiber layer was obtained.

(Example 16)
The polyolefin composite short fiber 1 is used instead of the polyolefin composite short fiber 1, the polyester composite short fiber 1 is used instead of the polyester composite short fiber 1, the basis weight of the first fiber web is 7 g / m ² , A heat-bonded nonwoven fabric (weight per unit area: 24.7 g / m ² ) including the first fiber layer and the second fiber layer was obtained in the same manner as in Example 13 except that the basis weight of the two-fiber web was changed to 18 g / m ² .

(Example 17)
The first fiber was the same as in Example 13 except that the polyolefin composite short fiber 3 was used instead of the polyolefin composite short fiber 1 and the polyester composite short fiber 2 was used instead of the polyester composite short fiber 1. A heat-bonding nonwoven fabric (weight per unit area: 25.0 g / m ² ) including a layer and a second fiber layer was obtained.

(Example 18)
First, a first fiber web was prepared using a polyolefin-based composite short fiber 2 and having a basis weight of about 7 g / m ² using a parallel card machine. Next, a second fiber web was prepared using polyester-based composite short fibers 2 so that the basis weight was 18 g / m ² using a parallel card machine. After laminating the second fiber web on the first fiber web, the obtained laminated fiber web was heat-treated using a hot-air through heat treatment machine set at 135 ° C., and the polyolefin composite short fiber 2 and the polyester composite The sheath component in the short fiber 2 is melted to thermally bond the polyolefin-based composite short fiber 2 and the polyester-based composite short fiber 2 so that the heat-bonded nonwoven fabric including the first fiber layer and the second fiber layer (weight per unit: 25.0 g / m) ² ) got. At this time, it heat-processed in the state which the 1st fiber web used as a 1st fiber layer contacted the conveyor net | network surface of a hot air penetration type heat processing machine, and the hot air was sprayed with respect to the laminated fiber web from the 2nd fiber layer side.

(Example 19)
The polyolefin composite short fiber 2 is used in place of the polyolefin composite short fiber 1, the polyester composite short fiber 2 is used in place of the polyester composite short fiber 1, and the basis weight of the first fiber web is 20 g / m ² . Except that the basis weight of the two-fiber web was changed to 18 g / m ² , a heat-bonded nonwoven fabric (weight per unit area 38.0 g / m ² ) including the first fiber layer and the second fiber layer was obtained in the same manner as in Example 13.

(Example 20)
The polyolefin composite short fiber 1 is used instead of the polyolefin composite short fiber 1, the polyester composite short fiber 1 is used instead of the polyester composite short fiber 1, the basis weight of the first fiber web is 7 g / m ² , Except that the basis weight of the two-fiber web was 35 g / m ² , a heat-bonding nonwoven fabric (weight per unit area: 45.0 g / m ² ) including the first fiber layer and the second fiber layer was obtained in the same manner as in Example 13.

(Comparative Example 7)
A heat-bonded non-woven fabric containing a first fiber layer and a second fiber layer (weight per unit: 26.3 g / m) in the same manner as in Example 14 except that the polyester-based composite short fiber 6 was used instead of the polyester-based composite short fiber 2. ² ) got.

(Comparative Example 8)
A heat-bonded nonwoven fabric including a first fiber layer and a second fiber layer (weight per unit: 24.7 g / m) is the same as in Example 15 except that the polyester-based composite short fibers 7 are used instead of the polyester-based composite short fibers 3. ² ) got.

(Comparative Example 9)
A heat-bonded non-woven fabric containing a first fiber layer and a second fiber layer (weight per unit: 26.7 g / m) in the same manner as in Example 15 except that the polyester composite short fiber 4 was used instead of the polyester composite short fiber 3. ² ) got.

(Comparative Example 10)
A heat-bonded nonwoven fabric containing a first fiber layer and a second fiber layer (weight per unit: 26.0 g / m) in the same manner as in Example 16 except that the polyester-based composite short fiber 5 was used instead of the polyolefin-based composite short fiber 2. ² ) got.

The thickness, run-off, liquid absorption speed, and liquid return amount of the heat-bonded nonwoven fabrics (surface sheets for absorbent articles) of Examples 13 to 20 and Comparative Examples 7 to 10 were evaluated as follows. Further, the variation (MMD) in the average friction coefficient of the heat-bonded nonwoven fabrics (surface sheets for absorbent articles) of Examples 13 to 20 and Comparative Examples 7 to 10 was evaluated as follows. The results are shown in Tables 4 and 5 below. In Tables 4 and 5 below, “−” means not measured.

(Thickness)
The thickness of the non-woven fabric was measured using a thickness measuring machine (trade name “THICKNESS GAUGE”, model “CR-60A”, manufactured by Daiei Kagaku Seisakusho Co., Ltd.) and a load of 3 g per 1 cm ^{2 of} sample according to JIS-L-1096. It measured in the state which added.

(Runoff)
(1) A sheet of four “Kim Towel (registered trademark)” made by Nippon Paper Crecia Co., Ltd. is laid on a support base having a substantially vertical isosceles triangle cross section having a 45 ° angle with the horizontal plane. The nonwoven fabric (longitudinal direction (machine direction) 18 cm, lateral direction 7 cm) was placed thereon and fixed so that the longitudinal direction of the nonwoven fabric forms an angle of 45 degrees with the horizontal plane.
(2) From the position of the upper end of the nonwoven fabric surface, 6 g of physiological saline is dropped at a rate of 1 g / 10 seconds with a microtube pump, and all of the poured physiological saline is absorbed by the nonwoven fabric, and the physiological saline The position at which the water droplet disappeared from the surface of the nonwoven fabric was measured, and the distance between the position and the position at which the physiological saline was dropped on the nonwoven fabric surface where the saline water droplet flowed on the nonwoven fabric surface was determined. In the above, physiological saline may be dropped using a burette instead of the microtube pump.

(Liquid absorption speed, liquid return amount)
(1) In order to measure the liquid absorption speed and the liquid return amount, the following articles were prepared.
Absorber: MEZGER inc. A laminate of three manufactured Lister Papers (Grade 989, 10 cm × 10 cm) was used as an absorber.
Saline filter paper: ADVANTEC (registered trademark) No. 2, 10cm x 10cm
Weight: 4kg
Plate: Acrylic resin, 125mm x 125mm, thickness 5mm
Measuring instrument: “Lister” manufactured by Lenzing Instruments (hereinafter also simply referred to as “Lister tester”)
(2) Method The liquid absorption speed and the liquid return amount were measured according to the following procedures.
(I) A nonwoven fabric ((longitudinal direction (machine direction) 10 cm, lateral direction 10 cm)) is placed on the absorbent body (three layers of Lister Paper (Grade 989, 10 cm × 10 cm) made by MEZGER Inc.), and this state To set the measuring instrument.
(Ii) 5 ml of physiological saline was dropped onto the set nonwoven fabric using a Lister tester. At this time, the physiological saline is not visible from the nonwoven fabric surface (the physiological saline is transferred from the nonwoven fabric to the absorbent body located under the nonwoven fabric, and no physiological saline is confirmed as a liquid on the nonwoven fabric surface). Liquid time) was measured and used as the first liquid absorption rate.
(Iii) The physiological saline is left for 30 seconds after it disappears from the nonwoven fabric surface, and after 30 seconds, the same part as the part where the physiological saline was dropped in the first liquid absorption test is the same as the procedure (ii). 5 ml of physiological saline was dropped again by the method, and the time until the physiological saline disappeared from the nonwoven fabric surface (liquid absorption time) was measured to obtain the second liquid absorption speed.
(Iv) After measuring the second liquid absorption rate, the procedure (iii) was repeated, and the time until the physiological saline disappeared from the nonwoven fabric surface (liquid absorption time) was measured to obtain the third liquid absorption rate. .
(V) After the measurement of the third absorption rate was completed, the strike through plate of the Lister tester was removed, an acrylic resin plate was placed on the surface of the nonwoven fabric, and a 4 kg weight was placed thereon for 3 minutes.
(Vi) After 3 minutes, the weight and the acrylic resin plate were removed, and the filter paper (ADVANTEC (registered trademark) No. 2 manufactured by Toyo Roshi Kaisha, Ltd.) whose mass was measured in advance on the nonwoven fabric was placed. A 4 kg weight was placed on the filter paper for 2 minutes. Two minutes later, the filter paper was taken out, the mass of the filter paper that absorbed physiological saline was measured, the mass of the filter paper before being placed on the nonwoven fabric was subtracted, and the liquid return amount was calculated.

(Change in average friction coefficient)
The variation of the average friction coefficient was measured based on the KES method. Specifically, “KES-SE” friction tester manufactured by Kato Tech Co., Ltd. was used. The measurement surface is the surface of the first fiber layer, a static load is applied to the friction element of 25 gf (245 N), and the friction element is moved in the direction parallel to the longitudinal direction of the nonwoven fabric at a moving speed of 1 mm / second to average the nonwoven fabric. Friction coefficient variation (MMD) was measured.

As can be seen from the data in Tables 4 and 5, the top sheets for absorbent articles of Examples 13 to 20 have a short distance of run-off of 45 mm or less, and the third liquid absorption speed is a fast speed of 40 seconds or less. Yes, and had excellent liquid absorption characteristics. Moreover, the surface sheets for absorbent articles of Examples 14, 16, and 18 had a small variation of the average friction coefficient of 0.0092 or less, smooth tactile sensation, and excellent texture. From the comparison of Examples 13 to 18 and Examples 19 to 20, the basis weight of the first fiber layer is 18 g / m ² or less, the basis weight of the second fiber layer is 30 g / m ² or less, It can be seen that when the basis weight of the second fiber layer is larger than the basis weight, the liquid return is less and the liquid absorption property is more excellent.

On the other hand, the surface sheet for absorbent articles of Comparative Example 7 had a run-off exceeding 45 mm and had poor liquid absorption characteristics. The top sheet for absorbent articles of Comparative Example 8 had a third liquid absorption speed exceeding 40 seconds, and the liquid absorption characteristics were poor. In the top sheet for absorbent articles of Comparative Example 7 and Comparative Example 8, the second fiber layer is composed of concentric core-sheath composite short fibers and has a dense structure, so that the liquid is the second fiber layer. It was difficult to move to. The surface sheet for absorbent articles of Comparative Example 9 had a run-off exceeding 45 mm, and the liquid absorption characteristics were poor. In the top sheet for absorbent articles of Comparative Example 9, the second fiber layer is composed of an eccentric core-sheath type composite short fiber having a fineness exceeding 5.2 dtex, and the second fiber layer is too sparse to cause capillary action. It was difficult to do. In the surface sheet for absorbent articles of Comparative Example 10, the variation in average friction coefficient exceeded 0.0092, and the texture was poor. This is because, in the top sheet for absorbent articles of Comparative Example 10, the fineness of the first core-sheath type composite short fiber constituting the first fiber layer exceeded 2.0 dtex, and therefore the surface was not rough. Conceivable. Moreover, the surface sheet for absorbent articles of Comparative Example 10 had a third liquid absorption speed exceeding 40 seconds, and the liquid absorption characteristics were poor. This is because the fineness of the core-sheath composite short fiber constituting the first fiber layer exceeds 2.1 dtex in the top sheet for absorbent articles of Comparative Example 10, and the first fiber layer is too sparse and liquid. It is thought that this is because it was difficult to transfer to the second fiber layer.

The composite short fiber for absorbent articles of the present embodiment, a method for producing the same, a heat-bonding nonwoven fabric for absorbent articles including the same, a surface sheet for absorbent articles, and an absorbent article including these include the following aspects.
(Aspect 1)
A composite short fiber for absorbent articles comprising a core component and a sheath component,
In the composite short fiber, the core component and the sheath component are arranged substantially concentrically, and the composite ratio of the core component and the sheath component is 52/48 to 73/27 in volume ratio of the core component / sheath component. Is a core-sheath type composite short fiber,
The core component includes 50% by mass or more of polypropylene having a ratio Mw / Mn of 3.0 or more and 8.0 or less of the weight average molecular weight Mw and the number average molecular weight Mn after spinning,
The sheath component contains 60% by mass or more of high-density polyethylene having a melting point lower than that of the polypropylene by 5 ° C. or more,
The composite short fiber contains 0.5% by mass to 10% by mass of an inorganic filler with respect to 100% by mass of the composite short fiber,
A composite staple fiber for absorbent articles, wherein the composite staple fiber has a fineness of 1.1 dtex to 2.0 dtex.
(Aspect 2)
The absorption according to aspect 1, wherein the melt flow rate of the high-density polyethylene measured under the conditions of a measurement temperature of 190 ° C. and a load of 21.18 N according to JIS-K-7210 is 5 g / 10 min or more and 30 g / 10 min or less. Composite short fiber for functional articles.
(Aspect 3)
The composite short fiber for absorbent articles according to aspect 1 or 2, wherein the fiber length is 25 mm or more and less than 65 mm.
(Aspect 4)
Any one of embodiments 1 to 3, wherein the inorganic filler is at least one inorganic filler selected from the group consisting of titanium dioxide, zinc oxide, calcium carbonate, and talc, and the core component contains the inorganic filler. The composite staple fiber for absorbent articles described in 1.
(Aspect 5)
Any one of Embodiments 1 to 4, wherein the single fiber strength is 2.4 cN / dtex or more and 6.0 cN / dtex or less, the elongation at break is 20% or more and 120% or less, and the apparent Young's modulus is 1200 N / mm ² or more. The composite short fiber for absorbent articles according to item 1.
(Aspect 6)
The composite short fiber for absorbent articles according to any one of embodiments 1 to 5, wherein the number of crimps is 5/25 mm or more and 25/25 mm or less, and the crimp rate is 5% or more and 20% or less.
(Aspect 7)
A method for producing a composite staple fiber for absorbent articles according to any one of aspects 1 to 6,
A core component containing 50% by mass or more of a polypropylene having a ratio Mw / Mn of 3.0 or more and 10.0 or less and a mass average molecular weight Mw to a number average molecular weight Mn of 60, and a high-density polyethylene having a melting point of 5 ° C. or more lower than the polypropylene. The sheath component containing mass% or more is arranged in a fiber cross section so that the sheath component covers the surface of the composite short fiber, and the center of gravity of the core component coincides with the center of gravity of the composite short fiber. A method for producing composite short fibers for absorbent articles, comprising a step of supplying the composite nozzle to melt spinning the core component at a spinning temperature of 250 ° C. to 350 ° C. and the sheath component at a spinning temperature of 230 ° C. to 330 ° C.
(Aspect 8)
For absorbent articles, comprising 20% by mass or more of the composite short fibers for absorbent articles according to any one of aspects 1 to 6, wherein at least a part of the composite short fibers for absorbent articles is bonded by a sheath component Thermal bonding nonwoven fabric.
(Aspect 9)
A top sheet for absorbent articles comprising a first fiber layer in contact with the skin and a second fiber layer adjacent to the first fiber layer,
The first fiber layer includes a first core-sheath composite short in which the core component includes 50% by mass or more of polypropylene, and the sheath component includes 60% by mass or more of high-density polyethylene having a melting point that is 5 ° C. lower than the melting point of the polypropylene. A fiber layer containing 50 mass% or more of fibers,
In the second fiber layer, the core component includes a polyester resin, the sheath component includes a thermoplastic resin having a melting point that is lower by 50 ° C. than the melting point of the polyester resin, and the center of gravity of the core component is from the center of gravity of the fiber. It is a fiber layer containing 50 mass% or more of the second core-sheath type composite short fiber that is displaced,
The first core-sheath composite short fiber has a fineness of 1.1 dtex or more and 2.0 dtex or less,
The second core-sheath type composite short fiber has a fineness of 2.2 dtex or more and 5.2 dtex or less,
In the first core-sheath-type composite short fiber, the core component and the sheath component are disposed substantially concentrically, and the composite ratio of the core component and the sheath component is 52 / 48-73 / 27,
Polypropylene contained in the core component in an amount of 50% by mass or more has a ratio Mw / Mn of the weight average molecular weight Mw and the number average molecular weight Mn after spinning of 3.0 to 8.0,
The first core-sheath type composite short fiber is a core-sheath type composite short fiber containing 0.5% by mass to 10% by mass of an inorganic filler with respect to 100% by mass of the composite short fiber,
At least a part of the first core-sheath type composite short fiber and the second core-sheath type composite short fiber are thermally bonded by a sheath component of the first core-sheath type composite short fiber and the second core-sheath type composite short fiber. A surface sheet for absorbent articles.
(Aspect 10)
Absorption according to aspect 9, wherein the melt flow rate of the high density polyethylene measured under the conditions of a measurement temperature of 190 ° C. and a load of 21.18 N according to JIS-K-7210 is 5 g / 10 min or more and 30 g / 10 min or less. Surface sheet for functional articles.
(Aspect 11)
The top sheet for absorbent articles according to the aspect 9 or 10, wherein a fiber length of the first core-sheath composite short fiber is 25 mm or more and less than 65 mm.
(Aspect 12)
The basis weight of the first fiber layer is 4 g / m ² or more and 18 g / m ² or less, the basis weight of the second fiber layer is 10 g / m ² or more and 30 g / m ² or less, and the basis weight of the second fiber layer is The top sheet for absorbent articles according to any one of embodiments 9 to 11, wherein the basis weight of the first fiber layer is larger.
(Aspect 13)
Any one of Aspects 9 to 12, wherein in the top sheet for absorbent articles, the average friction coefficient variation (MMD) measured based on the KES method with the surface of the first fiber layer as the measurement surface is 0.0092 or less. The surface sheet for absorbent articles as described in the item.
(Aspect 14)
An absorbent article comprising the heat-bonding nonwoven fabric for absorbent articles according to aspect 8, or the surface sheet for absorbent articles according to any one of aspects 9 to 13.

The composite staple fiber for absorbent articles of the present invention can be contained in a heat-bonded nonwoven fabric, and the heat-bonded nonwoven fabric is a paper diaper for animals including sanitary napkins, infant paper diapers, adult paper diapers, and mammals. In addition, it can be preferably used for the surface sheet of various absorbent articles such as panty liners, incontinence liners, etc. In applications such as infant paper diapers and adult paper diaper back sheets, in absorbent articles, the absorbent side, for example, the surface It can also be preferably used for a second sheet located directly under the sheet. In particular, the surface sheet for absorbent articles of the present invention using polyolefin fine composite fibers having a fineness is excellent in the texture of the skin contact surface and also has a good liquid absorbency. Therefore, sanitary napkins and infant paper diapers It can be preferably used as a surface sheet for various absorbent articles such as adult paper diapers, paper diapers for animals such as mammals, panty liners, incontinence liners and the like.

10, 40 Composite short fiber 11, 41 Sheath component 12, 42 Core component 13, 43 Center of gravity position in fiber cross section of core component 14, 44 Center of gravity position in fiber cross section of composite short fiber 15, 45 Radius in fiber cross section of composite short fiber 30 Top sheet for absorbent articles 31 First fiber layer 32 Second fiber layer

Claims (14)

A composite short fiber for absorbent articles comprising a core component and a sheath component,
In the composite short fiber, the core component and the sheath component are arranged substantially concentrically, and the composite ratio of the core component and the sheath component is 52/48 to 73/27 in volume ratio of the core component / sheath component. Is a core-sheath type composite short fiber,
The core component includes 50% by mass or more of polypropylene having a ratio Mw / Mn of 3.0 or more and 8.0 or less of the weight average molecular weight Mw and the number average molecular weight Mn after spinning,
The sheath component contains 60% by mass or more of high-density polyethylene having a melting point lower than that of the polypropylene by 5 ° C. or more,
The composite short fiber contains 0.5% by mass to 10% by mass of an inorganic filler with respect to 100% by mass of the composite short fiber,
A composite staple fiber for absorbent articles, wherein the composite staple fiber has a fineness of 1.1 dtex to 2.0 dtex. The melt flow rate of the high-density polyethylene measured under conditions of a measurement temperature of 190 ° C and a load of 21.18 N according to JIS-K-7210 is 5 g / 10 min to 30 g / 10 min. Composite short fiber for absorbent articles. The composite short fiber for absorbent articles according to claim 1 or 2, wherein the fiber length is 25 mm or more and less than 65 mm. 4. The inorganic filler according to claim 1, wherein the inorganic filler is at least one inorganic filler selected from the group consisting of titanium dioxide, zinc oxide, calcium carbonate, and talc, and the core component contains the inorganic filler. The composite short fiber for absorbent articles as described in the item. The single fiber strength is 2.4 cN / dtex or more and 6.0 cN / dtex or less, the elongation at break is 20% or more and 120% or less, and the apparent Young's modulus is 1200 N / mm ² or more. The composite short fiber for absorbent articles according to claim 1. The composite short fiber for absorbent articles according to any one of claims 1 to 5, wherein the number of crimps is 5/25 mm or more and 25/25 mm or less, and the crimp rate is 5% or more and 20% or less. A method for producing a composite short fiber for absorbent articles according to any one of claims 1 to 6,
A core component containing 50% by mass or more of a polypropylene having a ratio Mw / Mn of 3.0 or more and 10.0 or less and a mass average molecular weight Mw to a number average molecular weight Mn of 60, and a high-density polyethylene having a melting point of 5 ° C. or more lower than the polypropylene. The sheath component containing mass% or more is arranged in a fiber cross section so that the sheath component covers the surface of the composite short fiber, and the center of gravity of the core component coincides with the center of gravity of the composite short fiber. A method for producing composite short fibers for absorbent articles, comprising a step of supplying the composite nozzle to melt spinning the core component at a spinning temperature of 250 ° C. to 350 ° C. and the sheath component at a spinning temperature of 230 ° C. to 330 ° C. An absorbent article comprising 20% by mass or more of the composite short fiber for absorbent article according to any one of claims 1 to 6, wherein at least a part of the composite short fiber for absorbent article is adhered by a sheath component. Thermal bonding nonwoven fabric. A top sheet for absorbent articles comprising a first fiber layer in contact with the skin and a second fiber layer adjacent to the first fiber layer,
The first fiber layer includes a first core-sheath composite short in which the core component includes 50% by mass or more of polypropylene, and the sheath component includes 60% by mass or more of high-density polyethylene having a melting point that is 5 ° C. lower than the melting point of the polypropylene. A fiber layer containing 50 mass% or more of fibers,
In the second fiber layer, the core component includes a polyester resin, the sheath component includes a thermoplastic resin having a melting point that is lower by 50 ° C. than the melting point of the polyester resin, and the center of gravity of the core component is from the center of gravity of the fiber. It is a fiber layer containing 50 mass% or more of the second core-sheath type composite short fiber that is displaced,
The first core-sheath composite short fiber has a fineness of 1.1 dtex or more and 2.0 dtex or less,
The second core-sheath type composite short fiber has a fineness of 2.2 dtex or more and 5.2 dtex or less,
In the first core-sheath-type composite short fiber, the core component and the sheath component are disposed substantially concentrically, and the composite ratio of the core component and the sheath component is 52 / 48-73 / 27,
Polypropylene contained in the core component in an amount of 50% by mass or more has a ratio Mw / Mn of the weight average molecular weight Mw and the number average molecular weight Mn after spinning of 3.0 to 8.0,
The first core-sheath type composite short fiber is a core-sheath type composite short fiber containing 0.5% by mass to 10% by mass of an inorganic filler with respect to 100% by mass of the composite short fiber,
At least a part of the first core-sheath type composite short fiber and the second core-sheath type composite short fiber are thermally bonded by a sheath component of the first core-sheath type composite short fiber and the second core-sheath type composite short fiber. A surface sheet for absorbent articles. The melt flow rate measured under the conditions of a measurement temperature of 190 ° C and a load of 21.18 N according to JIS-K-7210 of the high-density polyethylene is 5 g / 10 min to 30 g / 10 min. Absorbent article surface sheet. The top sheet for absorbent articles according to claim 9 or 10, wherein a fiber length of the first core-sheath composite short fiber is 25 mm or more and less than 65 mm. The basis weight of the first fiber layer is 4 g / m ² or more and 18 g / m ² or less, the basis weight of the second fiber layer is 10 g / m ² or more and 30 g / m ² or less, and the basis weight of the second fiber layer is The top sheet for absorbent articles according to any one of claims 9 to 11, wherein the surface sheet is larger than the basis weight of the first fiber layer. The average surface friction coefficient (MMD) measured based on the KES method using the surface of the first fiber layer as a measurement surface in the top sheet for absorbent articles is 0.0092 or less. The top sheet for absorbent articles according to item 1. An absorbent article comprising the heat-bonding nonwoven fabric for absorbent articles according to claim 8 or the top sheet for absorbent articles according to any one of claims 9 to 13.

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