CN1620533A - Perforated sheet and method of manufacturing the sheet - Google Patents

Abstract

The present invention relates to a punched sheet (1); the thermal contracted nonwoven fabric (10) having a plurality of slits (11) is contracted such that each of these slits (11) can be expanded to form a plurality of holes (2) remain opened on the thermal contracted nonwoven fabric (10) even when no tension was exerted on it. The method of manufacturing the punched sheet according to the present invention is characterized in that the thermal contracted nonwoven fabric (10) having a plurality of slits (11) is treated with heat yet the contraction by width and length of the thermal contracted nonwoven fabric is restricted such that each of these slits (11) can be expanded and then a punched sheet (1) having a plurality of holes (2) can be obtained.

Description

Apertured sheet and its manufacturing method

technical field

The present invention relates to a perforated sheet material and a manufacturing method thereof, in detail it relates to a perforated sheet material with a large perforated area (diameter) and a perforated ratio, a low weight per unit area and high strength, and an avoidable material. A method for producing an apertured sheet that is wasteful and economically efficient for manufacturing the above apertured sheet.

Moreover, the present invention relates to a surface sheet for absorbent articles and a method for producing the same, on the surface of which liquid excreted on the surface, particularly highly viscous liquid, is less likely to remain, and eczema (ムレ) or macule (カブレ) is less likely to occur. )wait.

Background technique

As constituent sheets of disposable bodily fluid absorbent articles such as sanitary napkins and disposable diapers, nonwoven fabrics that are stable in quality and can be produced at low cost are widely used, and the use of nonwoven fabrics with holes formed therein has been proposed. A solution to improve the function of non-woven fabrics or add new functions.

Conventional techniques for opening holes in nonwoven fabrics include: (a) the method of piercing nonwoven fabrics with heated or unheated needles to open holes; (b) the use of heated or unheated embossing rolls; A method of crushing fibers under high pressure to open and form holes, (c) a method of cutting by laser light or flame burning or melting a nonwoven fabric with a heating pin (cooking pin) to make holes, etc.

However, it is difficult to manufacture an apertured sheet having a large aperture area (pore diameter) and aperture ratio by these methods. Furthermore, the above-mentioned method (c) has disadvantages that the periphery of the opening becomes hard, and scorching and polymer balls occur.

As a method of obtaining an apertured sheet with a large aperture area (aperture diameter) and aperture ratio, there is a method of punching a part of the nonwoven fabric into a predetermined shape to form apertures (punching), but in this case Under this condition, not only the strength of the sheet material is greatly reduced, but also the punched part is wasted, and a process and equipment for removing the punched part must also be provided.

In addition, as another technique for opening holes in nonwoven fabrics, there is a method of forming slits in the nonwoven fabric and then stretching the nonwoven fabric to form holes. However, in this case, if it is not an elastic nonwoven fabric, It is very easy to twist or break the sheet due to the extension, and it cannot maintain the open state without using other parts to fix it in the extended state.

In addition, Japanese Patent Application Laid-Open No. 62-250257 describes a mesh member formed by expanding the slit cut into a sheet material, but the opening is also formed by stretching the sheet material. Generated.

The surface sheet for absorbent articles such as sanitary napkins needs to have the following performance and characteristics, that is, the absorption performance that can quickly transfer liquids such as menstrual blood or urine discharged to the absorbent body, and the ability to communicate with the user. The skin-contacting surface is soft, and the surface characteristics are less irritating to the skin.

In the past, as surface sheets for absorbent articles, non-woven fabrics made by various methods, materials subjected to perforation as reprocessing, or synthetic resins made of polyethylene or the like have been used. Porous films and the like have not yet been able to provide a material that can sufficiently satisfy both of the above-mentioned absorbing performance and surface characteristics at the same time.

Japanese Patent Laying-Open No. 9-111631 (Patent No. 3131557) describes the use of wrinkled non-woven fabrics as non-woven fabrics suitable for disposable diapers and sanitary napkins for menstrual periods. The layer of adhesive fibers and the layer containing non-heat-shrinkable fibers are laminated, and after the two layers are partially joined and integrated in the thickness direction, the layer containing heat-shrinkable fibers is thermally shrunk, thereby forming a layer on the surface. Striped (stringy) folds made of another layer.

However, even such a wrinkled nonwoven fabric has a disadvantage that eczema, rash, and the like are likely to occur, although liquids excreted on the surface, especially high-viscosity liquids, do not easily remain on the surface.

In addition, the non-woven fabric described in Japanese Patent Laid-Open No. 9-3755 is a non-woven fabric used as a female part of a surface fastener (face faasuna) used for disposable diapers, etc. When one of the first and second fiber layers is thermally shrunk, the other protrudes to one side, thereby forming regular protrusions. However, this nonwoven fabric tends to be a relatively hard material, and it is not sufficiently designed to prevent discomfort and skin problems caused by eczema, so it is not suitable for use as a top sheet for absorbent articles.

In addition, Japanese Patent Laid-Open No. 11-253490 discloses a disposable diaper in which a plurality of slits are formed on a top sheet, and the top sheet is stretched in a direction perpendicular to the slits. , forming openings. The apertures of the diaper are also created by stretching the sheet material. Also, the top sheet forming the openings does not have a multilayer structure, and the openings are not three-dimensional.

Contents of the invention

The object of the present invention is to provide a kind of perforated sheet material and the manufacturing method of perforated sheet material, this perforated sheet material is made of non-woven fabric, perforated area (aperture diameter) and perforated rate are extremely large, and the surface is smooth without concavo-convex, And the weight per unit area is low, and the strength is high; the manufacturing method of the above-mentioned perforated sheet can eliminate the waste of materials, thereby economically and effectively manufacturing the above-mentioned perforated sheet.

Another object of the present invention is to provide a surface sheet for an absorbent article, and a method for producing the same. The surface sheet for an absorbent article is less likely to leave liquid excreted on the surface, especially menstrual blood or loose stools. Highly viscous liquid, and not easy to produce eczema or rash.

In order to achieve the above object, the present invention provides a perforated sheet, which shrinks a heat-shrinkable nonwoven fabric with a plurality of slits so that the above-mentioned slits are expanded, and on the heat-shrinkable nonwoven fabric, multiple Even in the state where no tension is applied, the opening state is maintained (hereinafter referred to as the first invention when referring to this invention).

In order to achieve the above object, the present invention provides a method for manufacturing a perforated sheet. On a heat-shrinkable nonwoven fabric having a plurality of slits, in a state where the shrinkage of the width and length of the heat-shrinkable nonwoven fabric is restricted, By performing heat treatment, each of the above-mentioned slits is expanded to produce a perforated sheet having a plurality of perforations (hereinafter referred to as the second invention, this invention).

In order to achieve the above object, the present invention provides a topsheet for absorbent articles in which a first layer provided on the skin side and a second layer provided on the absorber side are laminated, and the two layers are partially bonded together. , to form a joint portion of a predetermined pattern, the portion of the first layer other than the above-mentioned joint portion is protruding, and has a slit on the first layer and/or the second layer (hereinafter referred to as the third invention).

Description of drawings

Fig. 1 is a schematic plan view showing an embodiment of the apertured sheet of the present invention.

FIG. 2 is a schematic diagram showing an outline of the manufacturing apparatus of the perforated sheet shown in FIG. 1 .

3 is a schematic view showing a slit forming step and an expanding step in the manufacturing process of the perforated sheet shown in FIG. 1 (partial perspective view of a part of the manufacturing apparatus in FIG. 2 seen from above).

Fig. 4 is a schematic perspective view showing an embodiment of the top sheet for absorbent articles of the present invention.

Fig. 5 is a schematic sectional view taken along line X-X of Fig. 4 .

Fig. 6 is a drawing showing the slits formed in the second layer and the openings formed by expanding the slits, and Fig. 6(a) is a view of part of the surface sheet shown in Fig. 4 from the second layer side In the accompanying drawings, FIG. 6(b) is a diagram showing a pattern of slits cut into the first layer in order to form the opening shown in FIG. 3(a).

FIGS. 7( a ) to 7 ( c ) are diagrams showing examples of formation patterns of bonding portions, respectively.

8( a ) to 8( c ) are drawings showing preferred embodiments of the method for producing the top sheet for absorbent articles of the present invention, respectively.

Fig. 9 is a schematic perspective view showing another embodiment of the topsheet for absorbent articles of the present invention.

Detailed ways

Hereinafter, it will be described according to preferred embodiments of the present invention.

The perforated sheet 1 which is an embodiment of the perforated sheet of the present invention (the first invention) is, as shown in FIGS. A plurality of openings 2 are formed in the heat-shrinkable nonwoven fabric 10 by expanding each slit 11, and the openings 2 can maintain an open state even in a state where tension is not applied.

The perforated sheet 1 of this embodiment will be described in detail below.

The perforated sheet 1 has a longitudinal direction (vertical direction in FIG. 1 ) corresponding to the flow direction (left-right direction in FIGS. 2 and 3 ) of the heat-shrinkable nonwoven fabric during manufacture, and a width direction (vertical direction) perpendicular thereto. 1, the direction indicated by symbol W in FIG. 1), a plurality of openings 2 are formed in a row in the longitudinal direction and width direction of the perforated sheet 1, respectively. Furthermore, each opening 2 is formed in a substantially elliptical shape having a major axis in the longitudinal direction of the perforated sheet 1 and a minor axis in the width direction.

The apertured sheet 1 is composed of a single-layer nonwoven fabric containing heat-shrinkable fibers that can shrink (including crimp) due to heat. Depending on the heat-shrinkable non-woven fabric used as the raw material, the heat-shrinkable fiber may be curled or the outer diameter of the fiber may become thicker.

The perforated sheet 1 can maintain the perforated state of each perforated hole 2 even in a state where tension is not applied. That is, what is shown in FIG. 1 is the apertured sheet 1 in a state where no tension is applied (natural state).

Next, one embodiment of the method for producing the perforated sheet of the present invention will be described by taking the case of producing the above perforated sheet 1 as an example.

The heat-shrinkable nonwoven fabric 10' is pulled out from the raw material roll (former roll) 10A, and while the heat-shrinkable nonwoven fabric 10' is conveyed continuously, the heat-shrinkable nonwoven fabric is cut by the rotary cutter 3. A plurality of slits 11 are formed in the woven fabric 10'. The rotary cutter 3 is equipped with: a cutting roller 32, which has a plurality of blades 31 formed along the circumferential direction; The flow direction is parallel.

Next, the heat-shrinkable nonwoven fabric 10 cut with the slit 11 is continuously introduced into the pin tenter heating device 4, and in the pin tenter heating device 4, the heat-shrinkable nonwoven fabric 10 passes The needle 41 that flows and moves (synchronously) fixes both ends of the heat-shrinkable non-woven fabric 10 in a state where the width of the heat-shrinkable non-woven fabric 10 does not shrink, and simultaneously the heat-shrinkable non-woven fabric 10 Carry out heat treatment, the method of heat treatment can also use far-infrared treatment etc. besides blowing hot air.

Since the above-mentioned heat treatment applies tension in the flow direction of the heat-shrinkable nonwoven fabric 10 by continuous conveyance, the heat treatment is performed in a state in which the length shrinkage of the heat-shrinkable nonwoven fabric 10 is restricted.

Here, the state where the shrinkage of the width and length of the heat-shrinkable nonwoven fabric is restricted refers to a state where the heat-shrinkable nonwoven fabric is allowed to shrink partially but does not cause shrinkage in width and length of the entire heat-shrinkable nonwoven fabric. This state is not limited to the case where the width (the length in the direction perpendicular to the flow direction) and the length (the length in the same direction as the flow direction) of the nonwoven fabric do not change at all before and after the heat treatment, but also includes width and/or Or the case where the length has a certain degree of reduction. However, from the standpoint of forming pores with large pore area and pore ratio, it is preferable that the change rates of the width and length of the nonwoven fabric before and after the heat treatment be within 10%. The rate of change of the width and length of the nonwoven fabric is obtained by measuring the width and length of the nonwoven fabric before and after heat treatment in a natural state.

By shrinking the heat-shrinkable nonwoven fabric 10 through the heat treatment, the slits 11 are expanded to form a plurality of openings 2 .

The shrinkage (partial shrinkage) of the heat-shrinkable nonwoven fabric 10 is different from the shrinkage of the width and length of the heat-shrinkable nonwoven fabric 10, and it means that the heat-shrinkable nonwoven fabric 10 shrinks except for the slit. .

In this way, the perforated sheet 1 having a large perforated area and perforated ratio can be continuously obtained as a belt-shaped sheet.

The perforated sheet 1 of the present embodiment has the perforations 2 formed by expanding the slits 11. When the perforations are formed, the movement of the fibers does not occur and the number of fibers is reduced. Therefore, even when the perforated area is formed, And when the opening ratio is relatively large, the decrease in the strength of the sheet can be greatly suppressed, so that the strength of the sheet is higher than that of a perforated sheet in which the openings are formed by punching (punching), for example. Sheet.

The perforated sheet of the present invention may have an average perforated area of, for example, 2 to 350 mm ² , preferably 10 to 100 mm ² .

Furthermore, the porosity of the perforated sheet may be, for example, 5 to 90%, preferably 10 to 80%.

The measurement of the above average pore area and the above pore ratio is as follows.

〔Measurement method of average opening area and opening ratio〕

The light source [Sunlight SL-230K2; manufactured by LPL Co., Ltd.], the bracket [コピースタンド CS-5; manufactured by LPL Corporation], the lens [24mm/F2.8D Nikon lens], and the CCD camera [by (HV- 37; Hitachi Electronics Co., Ltd.) F-MOUNT connected to the lens] and a video capture card (Spectra 3200; Canopus Co., Ltd.) to obtain an image of the surface side or the back side of the surface sheet 1. Will The obtained image uses the image analysis software (version 4.20) made by NEXUS Corporation to carry out binarization processing to its opening part. Obtain the opening area of each opening from the image after the binarization processing, and take these The average of the average to obtain the average aperture area. Then, divide the sum of the aperture area after binarization by the area of the whole image to obtain the aperture ratio (%). In the aperture area of each aperture In the case where the measurement is difficult, auxiliary processing such as painting the entire surface of the hole on the image can be performed.

In addition, the apertured sheet 1 of this embodiment, even when using a heat-shrinkable nonwoven fabric with a low basis weight (per unit weight) (for example, less than 30 g/m ² , especially less than 20 g/m ² ), , can also form obvious openings.

In addition, the perforated sheet 1 of the present embodiment has no distortion or breakage and no unevenness on the surface compared to the perforated sheet 1 in which the nonwoven fabric with the slits is stretched to form the pores. Smooth and bright open cell sheet.

In addition, in the manufacturing method of the perforated sheet according to the present embodiment, the slit 11 is expanded to form the perforation 2. When forming the perforation, the number of fibers will not be reduced due to fiber migration. Even in the case of forming holes with a large hole area (diameter) and hole ratio, the reduction in sheet strength can be significantly suppressed compared with the method of forming holes by punching (punching). Therefore, it is possible to manufacture a high-strength porous sheet 1 having an extremely large opening area (pore diameter) and opening ratio.

Moreover, unlike the case of forming the opening by punching (punching), when the opening is formed, since the punched sheet is not used, the process and equipment required for the process are not required, so it can be suppressed. Waste of material, thereby producing economical open-celled sheets.

The heat-shrinkable non-woven fabric used in the present invention is not particularly limited if it is a non-woven fabric that shrinks after heat treatment in a non-stressed state, but it can be obtained from the large opening area (aperture diameter) and opening ratio. From the point of view, it is best to shrink the width and length by more than 30% respectively by heat treatment at 80 to 250 degrees Celsius in the natural state (non-stressed state).

As the heat-shrinkable nonwoven fabric, for example, a nonwoven fabric containing fibers prone to crimping (latent crimping fibers) can be used. The crimp-prone fiber is a fiber that has the following shrinkage properties, that is, before being heated, it can be treated in the same way as the conventional fiber for nonwoven fabrics, and by heating at a predetermined temperature, it can exhibit a spiral shape. curled up. The crimp-prone fiber is an eccentric core-sheath type composite fiber (eccentric core-sheath type composite fiber) or side-by-side composite fiber (Said·Bai·Said type composite fiber) composed of two thermoplastic polymer materials having, for example, different shrinkage rates. )composition. For example, it is described in Japanese Patent Application Laid-Open No. 9-296325 and Japanese Patent No. 2759331.

When a nonwoven fabric containing fibers prone to curling is used, a shrinkable and relatively soft open-cell sheet can be obtained. Furthermore, as the heat-shrinkable nonwoven fabric, a nonwoven fabric containing other fibers such as fibers such as rayon, cotton, and hydrophilic acrylic fibers can be used together with curl-prone fibers. The heat-shrinkable fiber content in the heat-shrinkable nonwoven fabric is at least 30% by weight, particularly preferably 50-100%.

As a method for producing a nonwoven fabric containing fibers with a tendency to crimp, it is possible to use air through, heating rolls, ultrasonic waves, spinning machines, etc. to process cotton webs (card webs). The method of the nonwoven fabric, or the spunbond method, the airlaid method, the meltblown method, the wet method, and the like.

The apertured sheet of the present invention can be used in various applications, and its application is not particularly limited. For example, it can be used as a constituent material (surface) of bodily fluid absorbent articles such as sanitary napkins, incontinence pads, and disposable diapers. Sheets, sheets placed between the surface sheet and the absorbent body to increase liquid diffusivity and permeability or strength, etc.), cleaning sheets installed on cleaning tools, sheets for cooking, etc. materials etc.

For the perforated sheet of the present invention, the maximum point load in the MD direction is preferably in the range of greater than or equal to 10N, especially preferably greater than or equal to 15N, and the maximum point load in the CD direction is the lowest in terms of handling during manufacture and strength in use. Fortunately, the range is greater than or equal to 0.5N, especially preferably greater than or equal to 1N. The method of measuring the maximum point load is as described in the examples below.

As mentioned above, although each embodiment of the perforated sheet of this invention and its manufacturing method was demonstrated, this invention (1st, 2nd invention) is not limited to the said embodiment.

For example, the heat treatment of the heat-shrinkable nonwoven fabric 10 can also be performed by using other devices instead of the pin tenter heat treatment device. In the state (the state of restricting the shrinkage of the length and width), it is heat-treated; when using the heating roller heating device, the sheet is rolled up while the tension is applied by the heating roller, so that the length and width can be limited. Heat treatment is performed in a state where the width is shrunk, and these devices may be used alone or in combination of two or more.

Moreover, as a slit forming device for forming a slit on a heat-shrinkable nonwoven fabric, in addition to a rotary punching knife (Rotary Daikatsuta), an equalizer cutter (Siera Kattor), a laser, etc. can also be used. cutter, ultrasonic cutter, etc. Moreover, the slits are not limited to being formed in a direction parallel to the flow direction of the heat-shrinkable nonwoven fabric, for example, openings extending in a direction perpendicular to the flow direction, or in a direction inclined to the flow direction may also be formed. (For example, a 45-degree direction) extending openings can also form cross-shaped slits. The opening of the desired shape can be obtained by changing the shape and direction of the slit.

As a surface sheet 110A for an absorbent article according to one embodiment (first embodiment) of the present invention (third invention), as shown in FIGS. The second layer 102 is provided on the side close to the absorber, and the two layers 101, 102 are partially bonded to form a bonded part 103 in a rhombus grid pattern (predetermined pattern) [see FIG. 7(a)].

Each joint portion 103 in this embodiment is circular in plan view and formed discontinuously. The joining portion 103 is compacted, and has a smaller thickness and a higher density than other portions of the surface sheet 110A.

The junction part 103 is formed by various joining methods, such as thermal embossing, ultrasonic embossing, bonding with an adhesive, etc., for example. Although the junction part 103 of this embodiment is circular, the shape of each junction part 103 may be an ellipse, a triangle, a rectangle, or combinations thereof other than a circle. Furthermore, the joining portion 103 may be formed in a continuous shape, for example, a linear shape such as a straight line or a curved line, a grid shape, or the like. Another example of the pattern of the bonding portion 103 is shown in FIG. 7( b ) and FIG. 7( c ).

The area ratio of the joint portion 103 corresponding to the area of the top sheet [the ratio of the total area of the joint portion 103 included in the unit area of the top sheet to the unit area of the top sheet, a value expressed as a percentage , before making the second layer shrinkage], starting from the following points, it is preferably 3 to 50%, most preferably 5 to 35%. A sufficiently high dot and a dot that can exhibit a large volume (high height) can be formed by sufficiently forming a protrusion-like three-dimensional shape from the first layer.

The first layer 101 is composed of fiber aggregates, and the portion other than the joining portion 103 with the second layer 102 is formed into a protrusion toward the skin side. That is to say, the surface sheet 110A has a plurality of closed regions, which are formed by being surrounded by the bonding portion 103 composed of the above-mentioned pattern, and in the closed regions, the first layer 101 is formed into a dome-shaped protrusion (refer to Figure 4 and Figure 5). The inside of the protruding portion (convex portion) 104 of the first layer 101 is filled with fibers constituting the first layer, and the interface between the first layer 101 and the second layer 102 in the portion other than the joint portion 103 is not It is not bonded but is in a state of close contact across the entire area. The shape of the protrusions formed in the first layer is mainly determined by the shape of the fiber aggregates constituting the first layer 101 and the pattern of the bonding portion 103 .

The first layer 101 is composed of aggregates of fibers of different types and/or arrangements from the fibers constituting the second layer 102 .

The height T (refer to FIG. 5 ) of the protrusions (protrusions) 104 formed by the first layer 101 of the surface sheet is from the viewpoint of giving the surface sheet sufficient compression deformability and bulkiness (high volume). 0.3 to 5 mm, particularly preferably 0.5 to 3 mm. By making the protrusion height T greater than or equal to 0.3mm, the contact area with the skin can be reduced, and itching (mure) and rash (cabre) etc. caused by skin clogging during use can be prevented. Furthermore, by setting the height T of the convex portion to 5 mm or less, the distance for the absorbed liquid to reach the second layer 102 can be reduced, and the liquid can be absorbed smoothly even under a low load.

Here, the height of the convex portion 104 was tested in the following manner.

First, a test piece having a vertical and horizontal length of 30 mm×30 mm was cut out from the surface sheet. Furthermore, a cut surface is made on a line substantially parallel to the longitudinal direction [the fiber orientation direction of the fiber aggregate constituting the first layer (the flow direction of the fiber aggregate during production)] and passing through the junction 3. An enlarged photograph of the cross-section was obtained with a high power lens (Hyskopp) (manufactured by Olympus, SZH10).

Based on the scale of the enlarged photograph, the height from the top to the bottom of the convex portion 104 (the upper surface of the adjacent joint portion 103 ) was measured.

The second layer 102 is composed of heat-shrinkable fiber aggregates, and as shown in FIGS. 5 and 6( a ), openings 105 penetrating the second layer are regularly formed in a predetermined pattern. The openings 105 are formed by expanding the slits 105' [refer to FIG. A vertically long shape formed by joining two circular arcs. The openings 105 are arranged in a zigzag pattern as a whole. The shape of the opening 105 can also be oval, circular, gourd-shaped, egg-shaped, etc. Furthermore, a plurality of openings 105 may be arranged side by side in both directions of MD and CD. Furthermore, the apertures 105 are preferably uniformly dispersed throughout the entire facesheet area.

Except for the case where the slit is formed as a pattern surrounded by the pattern of the laminated and integrated part of the first layer and the second layer, or the same integrated pattern as the staggered pattern of the slit, the first layer In the case of any combination of the laminated integrated pattern and the slit pattern of the second layer, since the integrally fixed part increases or decreases the shortening or contraction range of the slit length, the shape of the opening varies depending on each part. And form a random hole shape and hole area.

The average opening area of each opening 105 should be 3 to 320 mm ² , particularly preferably 7 to 120 mm ^{2 ,} from the viewpoint of passage of the high-viscosity liquid. Furthermore, the opening ratio of the second layer [a value expressed as a percentage of the ratio of the total opening area of the openings 105 contained in the unit area (100 cm ² ) of the surface sheet to the unit area (100 cm 2 ) ], from the standpoint of passage of highly viscous liquids, it should be 5 to 70%, particularly preferably 7 to 50%.

The above average pore area and the above pore ratio are measured as follows.

〔Measurement method of average open area and opening ratio〕

Light source [Sunlight SL-230K2; manufactured by LPL Co., Ltd.], stand [Corpi Stand CS-5; manufactured by LPL Corporation], lens [24mm/F2.8D Nikon lens], CCD camera [by (HV-37 ; Hitachi Electronics Co., Ltd.) F-MOUNT connected to the lens] and a video capture card [Spectra 3200; Kanopus Co., Ltd.] to obtain the surface sheet 1 with the image of the side of the hole. The obtained image was binarized using image analysis software (version 4.20) manufactured by NEXUS Corporation. The opening area of each opening was calculated|required from the binarized image, and these were averaged to obtain the average opening area. Then, the opening ratio (%) can be obtained by dividing the sum of the areas of the openings subjected to the binarization process by the total image area. When it is difficult to measure the opening area of each opening, it is possible to perform auxiliary processing such as full painting on the opening portion on the image.

Next, a preferable manufacturing method of the surface sheet 110A of the first embodiment will be described with reference to FIG. 8( a ).

In this manufacturing method, as the second layer 102, a heat-shrinkable fiber aggregate is used, and as the first layer 101, a fiber aggregate constituting the second layer that does not undergo heat shrinkage below the shrinkage start temperature is used. Shrunken fiber aggregates.

First, the second layer 102 made of heat-shrinkable fiber aggregates is pulled out from the raw material roll 120 and conveyed continuously, and a plurality of slits 105' are formed in a predetermined pattern by the rotary cutter 6 on the second layer 102 [refer to Figure 6(b)]. The rotary cutter 6 is provided with: a cutting roller 61 having a plurality of blades formed in the circumferential direction; machine direction, MD direction) parallel to each other.

The length in the longitudinal direction of each slit (in the present embodiment, the length in the MD direction of the surface sheet) is preferably 5 to 50 mm. This is from the viewpoint of transverse strength and opening area. In addition, the slit The maximum width (the width in the direction perpendicular to the longitudinal direction) is preferably 1 to 20 mm, which is from the viewpoint of high-viscosity liquid passage and strength.

Next, the second layer 102 cut into the slit 105' is laminated with the first layer 101, and the laminated two layers 101, 102 are passed through the heat embossing roll device 7 to partially join them in a predetermined pattern. The heat embossing roller device 7 is between the concave-convex roller 71 and the smooth roller 72 with a predetermined pattern formed on the peripheral surface, or between the concave-convex rollers, and partially heats and presses the two layers, so that the two layers have a thickness direction integration.

Then, the laminated sheet 110' in which the first and second layers are laminated and integrated is continuously introduced into the pin tenter heating device 8. In the pin tenter heating device 8 , the needles that move in conjunction with the flow of the laminated sheet 110 ′ fix both sides of the laminated sheet 110 ′, and the degree of shrinkage of the width of the second layer 102 The laminated sheet 110' is heat-treated to a temperature equal to or higher than the shrinkage start temperature of the fiber aggregates constituting the second layer 102 while controlling the condition that it does not shrink below a predetermined width. As the heat treatment method, a method of passing hot air through the laminated sheet, a method of blowing hot air from the second layer side, a heating roller method, and far-infrared treatment can be used.

Through this heat treatment, the second layer 102 shrinks, and the slits 105' expand to form the openings 105. Furthermore, as the second layer 102 shrinks, the portion other than the joint portion of the first layer 101 deforms into a protrusion, or the height of the portion formed into the protrusion becomes higher, and at the same time, the fiber density of this portion decreases.

Thus, 110 A of surface sheets for absorbent articles which concerns on 1st Embodiment are obtained.

In the above-mentioned heat treatment, since the laminated sheet 110' being continuously conveyed is heat-treated under a state where tension is applied in the flow direction, it is possible to control the shrinkage of the second layer 102 in the width direction and the longitudinal direction. Under heat treatment.

In this way, by performing heat treatment in the state of controlling the shrinkage of the second layer in the width direction and/or in the longitudinal direction, preferably in a state of controlling the shrinkage of the second layer in both width and length directions, it is possible to produce The openings formed by heat shrinkage, and the control of the resulting opening area becomes easy.

Here, the state of controlling the shrinkage of the second layer in the width direction and/or the longitudinal direction means that although the fiber aggregates constituting the second layer are allowed to shrink locally, the shrinkage of the width and length of the second layer as a whole is controlled. Completely inhibited or inhibited below a predetermined ratio. This state is not limited to the case where the width (the length perpendicular to the flow direction) and the length (the length in the same direction as the flow direction) of the second layer are completely unchanged before and after the heat treatment, but also includes a certain difference in the width and/or length. a degree of shrinkage. However, from the standpoint of obtaining a clear range of openings and managing the increase in weight per unit area, the areal shrinkage rate before and after shrinkage of the second layer is 0 to 60%, particularly preferably 5 to 50%. The areal shrinkage rate of the second layer can be obtained from the reference area S ₀ before shrinkage and the area S ₁ after shrinkage of the reference area by the following formula (1).

Shrinkage rate (%) = (S ₀ -S ₁ )/S ₀ ×100 (1)

In the case of the surface sheet 110A for absorbent articles according to the first embodiment, since the first layer bulges into protrusions, the fibers expand to reduce the density, while the second layer has a high density due to heat shrinkage. area and open area. Since the fiber densities of the first layer and the second layer are different, in the case of hydrophilic fibers, there is a difference in the state of penetration of liquid due to capillary phenomenon. Since the first layer is low density (thick), highly viscous liquids pass through easily. Since the second layer has sufficient openings for passing the highly viscous liquid, the highly viscous liquid can smoothly flow to the absorber through the openings. Furthermore, the low-viscosity liquid remaining in the first layer transfers from the first layer to the second layer by utilizing the difference in capillary phenomena between the first layer and the second layer. Therefore, high-viscosity liquid can be smoothly permeated, and no liquid remains on the surface, so that hot flashes are not easy to obtain a dry (dry) feeling.

Furthermore, according to the above-mentioned method for producing a surface sheet, since the fibers around the slit are thermally shrunk, a large-volume (high-volume) sheet having relatively large openings can be produced at high speed.

When explaining the fibers constituting the first layer and the second layer, as the fibers constituting the first layer, it is preferable to use heat-melt-adhesive fibers, in particular, fibers composed of thermoplastic polymer materials are suitably used. Examples of thermoplastic polymer materials include polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate, and polyamides. Furthermore, core-sheath type composite fibers or side-by-side type composite fibers composed of combinations of these thermoplastic polymer materials may also be used.

As the form of the fiber aggregates constituting the first layer, for example, fiber webs formed by carding (card method), non-woven fabrics formed by thermal fusion bonding, hydroentangling (water flow entangling) method), nonwoven fabric formed by needle punching method, nonwoven fabric formed by solvent bonding method, nonwoven fabric formed by spunbond method, nonwoven fabric formed by meltblown method , or knitted fabrics, etc.

The first layer 101 of the first embodiment may also be composed of a fiber web obtained by carding. If the first layer 101 is composed of a fiber web formed by a carding method, it is less likely to be deformed or twisted due to heat shrinkage than a nonwoven fabric, so it is easy to obtain a uniform protrusion shape matching an integrated pattern.

The fiber web formed by the carding method is a fiber aggregate in a state before being nonwoven. That is to say, it is in the state where the post-processing applied to the cotton web used in the manufacture of the nonwoven fabric is not carried out, for example, the state in which the heat fusion bonding treatment by the air-through method or the calendering method is not carried out A fiber aggregate in a state where the fibers are extremely loosely entangled with each other.

When using a fiber web formed by a carding method for the first fiber layer, the fibers in the first layer 101 are passed together while the first layer 101 and the second layer 102 are joined or after they are joined. Hot melt bonding or solvent bonding or mechanically interwoven.

As the fibers constituting the second fiber layer, it is preferable to use heat-shrinkable fibers, especially those made of a thermoplastic polymer material and having heat-shrinkability. It is preferable to use fibers with a tendency to curl from the point of maintaining stretchability even after thermal shrinkage and being soft as a surface sheet.

The crimp-prone fiber is a fiber that has shrinkage properties such that it can be treated in the same way as conventional fibers for nonwoven fabrics before being heated, and can take on a helical shape by heating at a predetermined temperature. curled up (curl).

The crimp-prone fiber is composed of, for example, an eccentric core-sheath type composite fiber or a side-by-side type composite fiber composed of two types of thermoplastic polymer materials having different shrinkage rates. For example, the contents described in JP-A-9-296325 and JP-A-2759331.

As the form of the fiber aggregates constituting the second fiber layer, it may be (1) a fiber web formed by carding that contains fibers prone to crimping, or (2) a heat-shrinkable nonwoven fabric. Examples of the cloth include nonwoven fabrics formed by heating rolls, nonwoven fabrics formed by thermal fusion bonding, nonwoven fabrics formed by hydroentangling, nonwoven fabrics formed by needle punching, and nonwoven fabrics formed by solvent bonding. Formed non-woven fabric. Nonwoven fabrics formed by the spunbond method, nonwoven fabrics formed by the meltblown method, and the like. Here, the heat-shrinkable nonwoven fabric refers to a nonwoven fabric having a property of shrinking when heated at a predetermined temperature. The second layer 102 of the first embodiment is formed of a heat-shrinkable nonwoven fabric made of heat-shrinkable fibers.

The first layer 101 and the second layer 102 may be mixed with fibers other than the above, for example, water-absorbent fibers such as rayon, cotton, and hydrophilic acrylic fibers.

Next, the surface sheet 110B for absorbent articles which is 2nd Embodiment is demonstrated.

About the surface sheet 110B of 2nd Embodiment, the difference from 110 A of surface sheets of 1st Embodiment is mainly demonstrated, and description of the same structure is abbreviate|omitted. In particular, the same as the first embodiment, the above-mentioned description related to the first embodiment can be used as appropriate for the parts that are not described.

The first layer 101 and the second layer 102 in the surface sheet 110B are formed of any nonwoven fabric. The pattern in which the first layer 101 and the second layer 102 are bonded is the pattern shown in FIG. 7( b ).

In the second embodiment, as shown in FIG. 9 , a slit 105B is cut in a protruding portion 104 of the first layer 101 (a portion other than the joining portion of the first layer 101 ). The slit 105B is formed as a protrusion by the first layer 101, and the slit is expanded to form a step difference on the sheet on the left and right of the slit, thereby forming an opening.

The surface sheet 110B of the second embodiment is produced by the method shown in FIG. 8( b ).

That is to say, the first layer 101 made of fiber aggregates that do not thermally shrink below the thermal shrinkage start temperature of the fiber aggregates used as the second layer 102 is pulled out from the raw material roll and transported, and passed through a rotary cutter. 6. Slits are cut into the first layer 101. Next, the second layer 102 made of heat-shrinkable fiber aggregates (nonwoven fabric) is laminated on the first layer, and the two layers 101, 102 are partially bonded by the heat embossing roll device 7, so that It is integrally formed in the thickness direction. The laminated sheet 110' in which the first and second layers are laminated as a whole is introduced into the pin tenter heating device 8, and heat-treated at a temperature equal to or higher than the shrinkage start temperature of the fiber aggregates constituting the second layer 102. , so that the second layer 102 heat shrinks.

Through this heat treatment, while the second layer 102 shrinks, the portion other than the joint portion 103 of the first layer 101 is deformed into a protruding shape, and at the same time, the slit of the protruding portion is bent to form an arch. Unlike the curvature, the slit expands and creates a step difference between the left and right sides of the slit and the arch, thereby forming an opening.

Thus, the surface sheet 110B for absorbent articles which concerns on 2nd Embodiment is obtained. The formation of the slits, the bonding of the first and second layers, the conditions of the heat treatment, etc. can all be performed in the same manner as the method shown in FIG. 8(a) above.

In the case of the surface sheet 110B for absorbent articles according to the second embodiment, gaps are generated due to the steps between the arches, so the highly viscous liquid can smoothly pass through the first layer through the gaps, thereby achieving high viscosity. It is difficult for liquid to remain on the surface.

Furthermore, according to the method for producing the topsheet shown in Fig. 8(b) above, a bulky topsheet having high viscosity liquid permeability can be rapidly produced.

Next, a top sheet for absorbent articles as a third embodiment will be described.

As the surface sheet of the third embodiment, differences from the surface sheet 110A of the first embodiment will be mainly described, and the description of the same configuration will be omitted. In particular, the same as the first embodiment, the above-mentioned description related to the first embodiment can be used as appropriate for the parts that are not described.

The surface sheet 110C of the third embodiment has openings produced by expanding the slits penetrating the first and second layers.

The surface sheet of the third embodiment is produced by the method shown in FIG. 8( c ).

That is to say, the second layer 102 made of heat-shrinkable fiber aggregates, and the first layer 101 made of fiber aggregates that do not heat shrink below the heat shrinkage start temperature of the fiber aggregates constituting the second layer, For lamination, the two layers 101 and 102 are passed through the heat embossing roll device 7 to be partially bonded in a predetermined pattern. Then, for the laminated sheet 110' in which the first and second layers are integrally laminated, slit formation by the rotary cutter 6 and heat treatment by the pin tenter heating device 8 are sequentially performed.

By this heat treatment, as the second layer 102 shrinks, the first layer 101 bonded to the second layer 102 also shrinks, and the slits are opened to form holes in both parts of the first and second layers. Further, as the second layer 102 shrinks, the portion other than the junction portion of the first layer 101 is deformed into a protrusion, or the height of the portion formed into the protrusion becomes higher, and the thickness of the portion increases.

Thus, 110 C of surface sheets for absorbent articles which concerns on 3rd Embodiment are obtained. Formation of the slit, bonding of the first and second layers, conditions of heat treatment, etc. can be performed by the same method as shown in FIG.

In the case of the top sheet 110C for absorbent articles according to the third embodiment, since the slits penetrating the first and second layers are formed and holes are formed, a top sheet with a large opening area can be obtained, It can also increase the suction speed and suction volume of highly viscous liquids, and has good permeability to the absorbent body.

Moreover, according to the method of manufacturing the surface sheet shown in FIG. 8( c ), since a slit penetrating both layers is formed, it is easy to form the slit and high-speed production is possible.

Moreover, in the method shown in FIG. 8(c), although the slits are formed after the first layer and the second layer are bonded together, it is also possible to form the slit in the reverse order, that is, after the laminated layer After the slits are formed in the first and second layers, the two are partially joined to form a whole. Even in this case, the same effect can be obtained.

The surface sheet for absorbent articles of the 3rd invention and its manufacturing method are not limited to each embodiment mentioned above.

For example, the slits are not limited to local slits such as a predetermined pattern as in the above-described embodiments, and may be continuous slits. In addition, the direction of the slit is not limited to the MD direction, and a CD direction or an oblique slit may be used.

In the case where the slits are provided on the first layer and the second layer, it is also possible to form the slits on each layer and then join them to form a whole (the slits at the same position are not penetrated). Can).

Furthermore, for example, the first layer of the first embodiment may be formed of a nonwoven fabric, and the first layer of the second embodiment may be formed of a fiber web formed by a carding method.

Examples of the absorbent article of the present invention include sanitary napkins, disposable diapers, incontinence pads, panty liners, and the like. Furthermore, as other constituent members of the absorbent article, for example, the absorber and the back sheet, members conventionally used in absorbent articles such as sanitary napkins and disposable diapers can be used without particular limitation. For example, the absorber may be formed by covering a fiber aggregate, or a fiber aggregate and a superabsorbent polymer, with a covering sheet made of water-permeable paper or nonwoven fabric.

The parts omitted from the description in the above-mentioned one embodiment and the requirements of only one embodiment can be appropriately applied to other embodiments, and the requirements of the respective embodiments can be appropriately replaced between the embodiments.

Embodiments of the first and second inventions

Example 1

1) Manufacture of non-woven fabrics without openings

A cotton web of 100% latent helically crimped (crimped) fiber [CPP fiber (trade name), 2.2 dtex x 51 mm] manufactured by Yamato Bosho Co., Ltd. was nonwoven by a heated roll. The processing conditions of the heating roll were embossing roll 140°C, flat roll 130°C, embossing rate 28% (dots), and speed 80m/min.

2) Formation of slits

On the 200 mm wide area in the center of the width direction of the obtained non-perforated nonwoven fabric, a plurality of rows of slits with a length [length in the flow direction (MD direction)] of 9 mm are formed so that they are respectively parallel to the MD direction, and such that The interval between adjacent slits in the MD direction is 3 mm. The interval between the slits in adjacent rows (the interval in the CD direction) was 5 mm, and the positional relationship between the slits in adjacent rows was different from each other (staggered arrangement).

3) Perforation processing (manufacture of perforated sheet)

From the area where the slits of the nonwoven fabric with slits are formed, take a test piece with a MD direction of 1000 mm and a CD direction of 210 mm, leave a part of the width direction center of the test piece that is 120 mm wide, Both sides are pressed with weights (重り) with a width of 35 mm and a length of 1000 mm. Like this, just can limit the width direction of test piece and the shrinkage of lengthwise direction, thereby carry out heat treatment [heating condition: 142 degrees centigrade, wind speed 2m/second, heating time 25 seconds (speed 4.5m/min)].

Example 2

In the 201 mm wide area in the center of the width direction of the non-perforated nonwoven fabric obtained in the same manner as in Example 1, a plurality of rows of 18 mm long slits are formed, and the distance between adjacent slits in the MD direction is A perforated sheet was obtained in the same manner as in Example 1, except that the interval between slits in adjacent rows (interval in the CD direction) was 6 mm.

comparative example

In the 162 mm wide region in the center of the width direction of the non-perforated nonwoven fabric obtained in the same manner as in Example 1, circular holes with a diameter of 18 mm are formed in rows in two directions of the MD direction and the CD direction, thereby obtaining an aperture. perforated sheet. The round holes were formed by punching (punching), and the intervals between the round holes were 6 mm in both the MD direction and the CD direction.

The weight per unit area and the like were measured for the perforated sheets of Examples and Comparative Examples, and the results are collectively shown in Table 1. The non-woven fabric without pores in Table 1 is the non-woven fabric without pores in Example 1 before the slits are formed.

[Measuring method of maximum point load and maximum point elongation]

The measurement was performed in a tension mode using a tensile compression testing machine "RTM-100 (trade name)" manufactured by Toyo Polydowin Co., Ltd. First, the sheet was cut to a size of 150 mm×50 mm when measuring the sheet in the MD direction and 100 mm×50 mm when measuring the sheet in the CD direction, and this was used as the measuring sheet. Put the measuring piece between air chucks (Ea-Chick) installed on the tensile and compression testing machine, set the initial sample length (distance between the chucks) to 100 mm for the measuring piece in the MD direction, and 50 mm for the measuring piece in the CD direction, so that The chuck attached to the load cell (rated output: 5 kg) of the tension-compression testing machine was raised at a speed of 300 mm/min, thereby stretching the measurement piece. By this measurement, the maximum point load can be measured, and the elongation at the time of the maximum point load is taken as the maximum point elasticity. In addition, the so-called MD direction measuring piece is the measuring piece whose tensile direction of the tensile compression testing machine is the same as the MD direction of the measuring piece; and the CD direction measuring piece is the tensile direction of the tensile compression testing machine and the CD direction of the measuring piece. Same measuring sheet.

〔How to measure the thickness〕

The measurement was performed using a laser displacement meter of Keyence Co., Ltd.

The pressure plate was placed on the fixed plate without placing the test piece (nonwoven fabric) in between, and the thickness at this time was indicated as 0.000 mm. Next, the test piece was placed on the fixed plate, and the pressure plate was placed on it, and the thickness was read in a state where the numerical value stabilized after about 5 seconds. Let the average value of the thickness of 5 test pieces be the thickness of a sample.

The above-mentioned pressurized plate is an aluminum circular plate with a diameter of 56 mm, and the thickness of each sample is the thickness in a pressurized state of 0.5 gf/cm ² (49 Pa). And the third decimal place of the thickness was rounded off to calculate to the second decimal place. Other conditions and the like are as described below.

Sensor head: LK-080, amplification component: LK-2100, image simulation controller: RJ-800, measuring piece: 100mm×150mm

Table 1 non-woven fabric comparative example Example 1 Example 2 Stretch in MD direction Weight per unit area (g/m ² ) 16.8 9.6 22.5 20.0 Maximum point load (N) 9.79 2.04 30.5 17.1 Maximum point elongation (%) 5.8 5.3 13.3 25.7 Stretch in CD direction Weight per unit area (g/m ² ) 16.4 9.8 21.8 18.8 Maximum point load (N) 1.29 0.27 1.97 2.09 Maximum point elongation (%) 17.6 15.2 63.6 179.0 Thickness (mm) 0.30 0.28 0.51 0.61 F(%) - 44.2 28.2 60.1 Average opening area(mm ² ) - 254.0 12.7 33.7 Equivalent circle diameter (φ) - 18.0 4.0 6.5

As shown in Table 1, the perforated sheets of Examples not only have extremely large perforated area (aperture diameter) and perforated ratio, but also have low weight per unit area and high strength. In addition, when the appearance of the perforated sheets of Examples was observed with the naked eye, the surface was found to be a smooth surface with almost no irregularities.

Industrial availability

According to the perforated sheet of the present invention, it is possible to provide a perforated sheet with extremely large perforated area (aperture diameter) and perforated ratio, low weight per unit area, and high strength.

According to the method of manufacturing an apertured sheet of the present invention, it is possible to provide an apertured sheet manufacturing method that can economically and efficiently manufacture an apertured sheet having the above-mentioned characteristics and eliminate waste of materials.

The surface sheet for absorbent articles of the present invention can prevent liquid excreted on the surface, especially highly viscous liquid, from remaining on the surface, so that eczema, rash, etc. are less likely to occur.

According to the manufacturing method of the topsheet for absorbent articles of this invention, the said topsheet which has excellent characteristics can be manufactured efficiently and economically.

Claims (10)

1. Open hole sheet, it is characterized in that, make the heat-shrinkable non-woven fabric that has a plurality of slits shrink, make above-mentioned each slit expand, on this heat-shrinkable non-woven fabric, form a plurality of even Open cells are maintained even when tension is not applied. 2 . The perforated sheet according to claim 1 , wherein the average perforation area of the perforations is 2 to 350 mm ² . 3. The manufacturing method of the perforated sheet is characterized in that, on the heat-shrinkable nonwoven fabric with a plurality of slits, in the state of limiting the shrinkage of the width and length of the heat-shrinkable nonwoven fabric, by implementing Heat treatment expands each of the slits to produce an apertured sheet having a plurality of apertures. 4. A surface sheet for absorbent articles, characterized in that a first layer provided on the skin side and a second layer provided on the absorber side are laminated, and the two layers are partially bonded together to obtain The junction part of the predetermined pattern is formed, the part other than the said junction part of the 1st layer becomes a protrusion shape, and slits are provided in the 1st layer and/or the 2nd layer. 5. The top sheet for absorbent articles according to claim 4, which has openings formed by expanding the slits. 6. The surface sheet for absorbent articles according to claim 4, wherein the first and second layers have openings formed by widening the slit penetrating both layers. 7. The surface sheet for absorbent articles according to claim 4, wherein the second layer is composed of heat-shrinkable fiber aggregates, and the first layer is formed by the heat shrinkability of the second layer. The aforementioned protruding part is formed. 8. A method for producing a top sheet for an absorbent article, comprising laminating a first layer provided on the skin side and a second layer provided on the absorber side, and locally bonding the two layers, Thereby forming the joint part of predetermined pattern, the part other than the above-mentioned joint part of the first layer becomes protruding shape, has the opening that the slit expands and generates on the second layer, it is characterized in that, heat-shrinkable fiber aggregate is used as While using as the second layer, use a fiber aggregate that does not heat shrink below the shrinkage start temperature of the fiber aggregate as the first layer, cut the slit into the second layer, and laminate the first layer and the second layer , and locally bonded in a predetermined pattern, and then heat-treated at a temperature above the shrinkage start temperature of the fiber aggregate constituting the second layer to expand the above-mentioned slit while shrinking the second layer. 9. A method for producing a topsheet for an absorbent article, comprising laminating a first layer provided on the skin side and a second layer provided on the absorber side, and locally bonding the two layers, Thereby forming the joint part of predetermined pattern, the part other than the above-mentioned joint part of the first layer becomes protruding shape, and cuts slit in the part that becomes protruding shape, it is characterized in that, use heat-shrinkable fiber aggregate as the second At the same time, use a fiber aggregate that does not thermally shrink below the shrinkage start temperature of the fiber aggregate as the first layer, cut a slit in the first layer, and layer the first layer with the slit into the second layer. Then, heat treatment is performed at a temperature higher than the thermal shrinkage temperature of the fiber aggregate of the second layer, thereby causing the second layer to shrink. 10. A method for producing a topsheet for an absorbent article, comprising laminating a first layer provided on the skin side and a second layer provided on the absorber side, and locally bonding the two layers, Thereby forming a joint part of a predetermined pattern, the part other than the above-mentioned joint part of the first layer becomes a protrusion, and the surface sheet for absorbent articles has an opening formed by widening the slit penetrating the first and second layers, It is characterized in that, while using a shrinkable fiber aggregate as the second layer, a fiber aggregate that does not thermally shrink below the shrinkage start temperature of the fiber aggregate is used as the first layer, and the first layer and the second layer After lamination and local bonding in a predetermined pattern, slits are cut into the two layers, or the first layer and the second layer are laminated, and after the two layers are cut into slits, the two layers are cut in a predetermined pattern Partial bonding is performed, and then heat treatment is performed at a temperature equal to or higher than the heat shrinkage temperature of the fiber aggregate of the second layer to expand the above-mentioned slit while shrinking the second layer.

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