WO2018142983A1 - Biaxially oriented polypropylene-based film - Google Patents

Abstract

Provided is a biaxially oriented polypropylene-based film that exhibits high laminate strength with respect to another film member and achieves excellent adhesion of print ink and excellent print ink transferability from a print roll to a film without compromising the excellent transparency and mechanical properties inherent to a biaxially oriented polypropylene-base film. This biaxially oriented polypropylene-based film is characterized by having a base material layer (A) which consists chiefly of a polypropylene-based resin and a surface layer (B) which consists chiefly of a polypropylene-base resin and which is disposed at least on one surface of the base material layer (A), wherein: the surface of the surface layer (B) on the side opposite to the base material layer (A) has a surface roughness of 0.027-0.040 μm, has a specific surface resistance of at least 15 Log Ω, and has a wet tensile strength of at least 38 mN/m; and the film has a film thickness of 9-200μm and a haze (transparence) value of at most 5%.

Description

Biaxially oriented polypropylene film

The present invention relates to a biaxially oriented polypropylene film. Specifically, the present invention relates to a biaxially stretched polypropylene film having excellent adhesion to printing ink and adhesion to an adhesive used for laminating with other member films.

Conventionally, biaxially oriented polypropylene-based films are widely used as packaging materials for various articles such as foods and textile products because of their excellent transparency and mechanical properties. However, as a problem of polypropylene film, for example, since polypropylene resin is nonpolar, the surface energy is small, and therefore, the adhesiveness with printing ink or other materials is not sufficient in processing of printing ink or laminate, etc. It has been pointed out that there is no.

In particular, when a biaxially oriented polypropylene film is used as a packaging material, it is generally performed to laminate with another member film using an adhesive, but the laminate strength between these films is weak. In some cases, the strength of the packaging material is weakened and it breaks and the contents protrude, and oxygen and water vapor enter and exit through the torn part of the bag, so that it does not serve as a food packaging material. As mentioned.

In addition, biaxially oriented polypropylene film is generally printed, but from the viewpoint of color development and color fading, printing from the ink printing roll to the surface of the biaxially oriented polypropylene film. Improvements in ink transferability and adhesion of printing ink to the film surface are more demanded.

Various methods have been proposed as countermeasures against such problems. For example, a skin layer composed of a composition in which organic polymer fine particles are blended with a propylene-ethylene random copolymer is formed on the surface of a biaxially oriented polypropylene film. Although a laminated film is disclosed (for example, see Patent Document 1), not only the adhesion of the printing ink is insufficient, but also a process of separately providing a skin layer is required, resulting in poor productivity.

JP 2000-127310 A

The present invention does not impair the excellent transparency and mechanical properties inherent in the biaxially oriented polypropylene film, has a high lamination strength with other member films, and transfers printing ink from the printing roll to the film. It is an object to provide a biaxially oriented polypropylene film having excellent properties and adhesion of printing ink.

The present invention that has solved the above problems is a surface layer (B) having a polypropylene resin as a main component on at least one surface of a base material layer (A) having a polypropylene resin as a main component and a substrate layer (A). The surface roughness of the surface of the surface layer (B) opposite to the substrate layer (A) is 0.027 μm or more and 0.040 μm or less, and the substrate layer of the surface layer (B) The surface resistivity of the surface opposite to (A) is 15 LogΩ or more, the wetting tension of the surface of the surface layer (B) opposite to the base material layer (A) is 38 mN / m or more, and the film The biaxially oriented polypropylene film is characterized in that the thickness is 20 μm or more and 50 μm or less, and the haze (transparency) value of the film is 5% or less.

It is preferable that the center surface peak height SRp + center surface valley depth of the surface of the surface layer (B) opposite to the base material layer (A) is 1.0 μm or more and 2.0 μm or less.

It is preferable that the heat shrinkage rate at 150 ° C. in the longitudinal direction and the transverse direction of the biaxially oriented polypropylene film is 11% or less.

A laminate having a printing layer on the side opposite to the substrate layer of the surface layer (B) of the biaxially oriented polypropylene film described in any one of the above is preferable.

The biaxially oriented polypropylene film of the present invention has a large laminate strength with other member films without impairing the excellent transparency and mechanical properties inherent to the biaxially oriented polypropylene film, and a printing roll The film is excellent in transferability of printing ink from film to film and adhesion of printing ink, and can be produced efficiently.

The biaxially oriented polypropylene film of the present invention has a surface layer (B) containing a polypropylene resin as a main component on at least one surface of a base material layer (A) and a base material layer (A) containing a polypropylene resin as a main component. The arithmetic average roughness of the surface of the surface layer (B) opposite to the substrate layer (A) is 0.027 μm or more and 0.040 μm or less, and the substrate of the surface layer (B) The surface resistivity of the surface opposite to the layer (A) is 15 LogΩ or more, and the wetting tension of the surface of the surface layer (B) opposite to the base material layer (A) is 38 mN / m or more, The film thickness is 20 μm or more and 50 μm or less, and the haze value of the film is 5% or less.
Here, the arithmetic surface roughness SRa of the surface layer (B) opposite to the base material layer (A) is measured in the X direction using a three-dimensional roughness meter at a stylus pressure of 20 mg. The length of 1 mm, the feed pitch in the Y direction is 2 μm, the number of recorded lines is 99, the height direction magnification is 20000 times, and the cutoff is 80 μm. According to the definition of arithmetic mean roughness described in JISB 0601 (1994), It is.

Arithmetic average roughness SRa is not easily affected by one protruding large peak or valley, and is relatively small formed on a surface other than a relatively large peak or valley formed locally by an antiblocking agent or lubricant. It becomes an index that represents uneven undulations. Since most of the printing ink adheres to the surface other than the relatively large peaks and valleys formed by the antiblocking agent or lubricant, it has a great relationship with the adhesion of the printing ink. This is different from the center plane mountain height SRp and the center plane valley depth SRv described later.
Further, the surface specific resistance value of the surface layer (B) opposite to the base material layer (A) is different from the amount of the antistatic agent present on the surface, and the antistatic material existing on the surface. The surface resistance value increases as the amount of the agent decreases.
Further, the wetting tension of the surface layer (B) represents the numerical value of the surface tension (μN / cm) of the mixed solution reagent determined to wet the film surface, and is related to the wettability of the printing ink and the adhesive. .
Further details will be described below.

(1) Base material layer (A)
The polypropylene resin used for the base layer (A) of the biaxially oriented polypropylene film of the present invention is a propylene polymer or propylene and ethylene and / or an α-olefin having 4 or more carbon atoms of 0.5 mol% or less. Refers to a polymer copolymerized with The copolymer component in the copolymer is preferably 0.3 mol% or less, more preferably 0.1 mol% or less, and most preferably complete homopolypropylene containing no copolymer component.
When ethylene and / or an α-olefin having 4 or more carbon atoms is copolymerized in excess of 0.5 mol%, the crystallinity and rigidity may be excessively lowered, and the thermal shrinkage at high temperatures may increase. You may blend and use such resin.

The mesopentad fraction ([mmmm]%) measured by 13C-NMR, which is an index of stereoregularity of the polypropylene resin constituting the base material layer (A) of the biaxially oriented polypropylene film of the present invention, is 98 to It is preferable that it is 99.5%. More preferably, it is 98.1% or more, More preferably, it is 98.2% or more. When the mesopentad ratio of the polypropylene resin is small, the elastic modulus is low and the heat resistance may be insufficient. 99.5% is a realistic upper limit.

The mass average molecular weight (Mw) of the polypropylene resin constituting the substrate layer (A) of the biaxially oriented polypropylene film of the present invention is preferably 180,000 to 500,000.
If it is less than 180,000, the melt viscosity is low, so that it is not stable at the time of casting, and the film-forming property may deteriorate. When Mw exceeds 500,000, the amount of the component having a molecular weight of 100,000 or less becomes 35% by mass, and the heat shrinkage rate at high temperature is reduced.
The lower limit of Mw is more preferably 190,000, still more preferably 200,000, and the upper limit of more preferable Mw is 320,000, more preferably 300,000, particularly preferably 250,000.

The number average molecular weight (Mn) of the polypropylene resin constituting the base layer (A) of the biaxially oriented polypropylene film of the present invention is preferably 20,000 to 200,000.
If it is less than 20,000, the melt viscosity is low, so that it is not stable at the time of casting, and the film-forming property may deteriorate. When it exceeds 200,000, the thermal shrinkage rate at a high temperature is reduced.
The lower limit of Mn is more preferably 30,000, more preferably 40,000, particularly preferably 50,000, and the upper limit of Mn is more preferably 80,000, still more preferably 70,000, particularly preferably 60,000. is there.
In addition, when a high molecular weight component is added to the polypropylene, the high molecular weight component promotes crystallization of a low molecular weight component, but the entanglement between molecules becomes strong, and the thermal shrinkage rate increases even if the crystallinity is high. There is also a trend. is there. If Mw / Mn is too large, the high molecular weight component increases and the thermal shrinkage rate may increase, which is not preferable. Even if a high molecular weight component is added, Mw / Mn is preferably in the range of 5.5 to 20 or less.

In addition, Mw / Mn, which is an index of molecular weight distribution, is preferably 2.8 to 8 in the polypropylene resin of the base material layer (A). More preferably, it is 2.8 to 7, more preferably 2.8 to 6, and particularly preferably 2.8 to 5.4. Further, the lower limit is preferably 3 or more, and more preferably 3.3 or more.
The molecular weight distribution of polypropylene resin is determined by polymerizing different molecular weight components in a series of plants in multiple stages, blending different molecular weight components offline in a kneader, or blending catalysts with different performance. It can be adjusted by polymerizing or using a catalyst capable of realizing a desired molecular weight distribution.

When the Mw / Mn is in the range of 2.8 to 5.4, the polypropylene resin of the base layer (A) of the biaxially oriented polypropylene film of the present invention has a melt flow rate (MFR: 230 ° C., 2. 16 kgf) is preferably from 4 g / 10 min to 20 g / 10 min.
The lower limit of the MFR of the polypropylene resin of the base material layer (A) is more preferably 5 g / 10 minutes, further preferably 6 g / 10 minutes, and particularly preferably 7 g / 10 minutes. The upper limit of the MFR of the polypropylene resin of the base material layer (A) is more preferably 15 g / 10 minutes, and further preferably 12 g / 10 minutes.
When the Mw / Mn and MFR of the polypropylene resin of the base material layer (A) are within this range, the heat shrinkage rate at high temperatures can be kept small, and the film has good adhesion to the cooling roll. Excellent in properties.

(2) Surface layer (B)
It is preferable that the surface roughness of the surface layer (B) of the surface layer (B) of the biaxially oriented polypropylene film of the present invention is 0.027 μm or more and 0.040 μm or less. If it is less than 0.027 μm, the adhesion to the printing ink and the laminate strength with other member films are not sufficient, and if it exceeds 0.040 μm, the haze increases or the color developability of printing deteriorates. Occurs.
The surface roughness of the surface layer (B) opposite to the base material layer (A) is more preferably 0.028 μm or more, further preferably 0.029 μm or more, particularly preferably 0.030 μm or more.
In order for the surface roughness of the surface of the surface layer (B) opposite to the base material layer (A) to be 0.027 μm or more and 0.040 μm or less, the polypropylene resin composition for forming the surface layer (B) As a product, it is preferable to use a mixture of two or more polypropylene resins having different melt flow rates (MFR). In this case, the MFR difference is preferably 3 g / 10 min or more, and more preferably 3.5 g / 10 min or more.
As described above, if the difference in the melt flow rate (MFR) of two or more kinds of polypropylene resins in the mixture of polypropylene resins is different, the crystallization speed and the degree of crystallization of each polypropylene are different. It is presumed that the arithmetic average roughness of the surface on the side opposite to the base material layer (A) of B) is 0.028 μm or more. Moreover, the arithmetic mean roughness of the surface of the surface layer (B) opposite to the base material layer (A) is unlikely to exceed 0.040 μm.
As the polypropylene resin having a smaller MFR, a polymer obtained by copolymerizing propylene and ethylene and / or an α-olefin having 4 or more carbon atoms can also be used. Examples of the α-olefin having 4 or more carbon atoms include 1-butene, 1-hexene, 4-methyl / 1-pentene, 1-octene and the like. Moreover, you may use the maleic acid etc. which have polarity as another copolymerization component.
The total amount of ethylene and / or α-olefin having 4 or more carbon atoms and other copolymer components is preferably 8.0 mol% or less. When the copolymerization exceeds 8.0 mol%, the film may be whitened to have a poor appearance, or may become sticky and film formation may be difficult.
These resins may be used in a blend of two or more. When blending, individual resins may be copolymerized in excess of 8.0 mol%, but the blend is preferably monomer units and monomers other than propylene at 8.0 mol% or less. .
Further, as the polypropylene resin having a larger MFR, a polymer obtained by copolymerizing the above propylene and ethylene and / or an α-olefin having 4 or more carbon atoms can be used, or a propylene homopolymer can be used. I can do it. It is preferable to use a propylene homopolymer.

In addition, the polypropylene resin composition of the surface layer (B) of the biaxially oriented polypropylene film of the present invention preferably has an MFR of 1.0 g / 10 min to 8 g / 10 min. The lower limit of the MFR of the polypropylene resin composition of the surface layer (B) is more preferably 2 g / 10 minutes, and further preferably 3 g / 10 minutes. The upper limit of the MFR of the polypropylene resin composition of the surface layer (B) is more preferably 7 g / 10 minutes, and further preferably 6.0 g / 10 minutes. Within this range, the film-forming property is good and the appearance is also excellent.
When the MFR of the polypropylene resin composition of the surface layer (B) is smaller than 1.0 g / 10 min, the base layer (A) and the surface layer ( Since the viscosity difference of B) becomes large, unevenness (raw fabric unevenness) is likely to occur during film formation. If the MFR of the polypropylene resin composition of the surface layer (B) exceeds 8 g / 10 minutes, the adhesion to the cooling roll will be poor, air will be involved, the smoothness will be poor, and there will be many drawbacks starting from it. Therefore, it may be difficult to obtain an appropriate surface roughness.

It is preferable that the surface specific resistance value of the surface of the surface layer (B) of the biaxially oriented polypropylene film of the present invention on the side opposite to the base material layer (A) is 15 LogΩ or more. When the surface specific resistance value is 15 LogΩ or more, the adhesion to the printing ink and the adhesive is improved. The surface specific resistance value is more preferably 16 LogΩ or more. In order to make the surface specific resistance value 15 LogΩ or more, it is mentioned that an additive of a low molecular weight compound such as an antistatic agent or an antifogging agent is not used as much as possible. If it is used, the additive contained in the base material layer (A) may bleed to the surface of the surface layer (B) on the opposite side of the base material layer (A). Care must be taken because it is difficult to decrease.
In order to make the surface specific resistance value 15 LogΩ or more, it is preferable to perform physicochemical surface treatment such as corona treatment and flame treatment.
For example, in the corona treatment, it is preferable to discharge in the air using a preheating roll and a treatment roll.

It is preferable that the wetting tension of the surface opposite to the base material layer (A) of the surface layer (B) of the biaxially oriented polypropylene film of the present invention is 38 mN / m or more. When the wetting tension is 38 mN / m or more, the adhesiveness with the adhesive used for laminating with the printing ink or other member film is improved.
In order to increase the wetting tension to 38 mN / m or more, additives such as antistatic agents and surfactants are usually used. However, these methods have an effect of reducing the surface resistivity. It is preferable to perform physicochemical surface treatment such as corona treatment and flame treatment.
For example, in the corona treatment, it is preferable to discharge in the air using a preheating roll and a treatment roll.
Here, the surface specific resistance value is mainly related to the strength of the corona treatment, but the wetting tension is also related to the bleed-out amount of the antistatic agent, so it is effective to set each in a suitable range.

In the biaxially oriented polypropylene-based film of the present invention, the surface layer (B) has a center surface peak height SR) on the side opposite to the base material layer (A) and a center surface valley depth SRv of 1.0 μm or more and 2.0 μm. The following is preferable.
Here, the surface roughness of the surface layer (B) opposite to the base material layer (A) is the surface roughness center plane height SRp and the center plane valley depth SRv using a three-dimensional roughness meter. At a stylus pressure of 20 mg, a measurement length of 1 mm in the X direction, a feed pitch of 2 μm in the Y direction, 99 recording lines, a magnification in the height direction of 20000 times, and a cut-off of 80 μm were measured, as described in JISB 0601 (1994) According to the definition of arithmetic mean roughness,

The center plane peak height SRp + center plane valley depth SRv of the surface opposite to the base layer (A) of the surface layer (B) of the biaxially oriented polypropylene film of the present invention is locally increased by an antiblocking agent or the like. It is an indicator of the state of the relatively large irregularities formed, for example, the biaxial orientation of the present invention having a surface layer (B) on at least one surface of the substrate layer (A) and the substrate layer (A) This is largely related to the slipperiness between the surface layer (B) and the base material layer (A) when the polypropylene film is rolled up.
When the surface layer (B) of the biaxially oriented polypropylene film of the present invention has a center surface peak height SRp + center surface valley depth SRv of the surface opposite to the base layer (A) of 1.0 μm or more, a roll The unwinding property from a film improves and transparency is maintained as it is 2.0 micrometers or less.
The center plane peak height SRp + center plane valley depth SRv of the surface layer (B) opposite to the base material layer (A) is preferably 1.1 μm or more, more preferably 1.2 μm or more, and 1.3 μm or more. Is particularly preferred.

The center plane peak height SRp + center plane valley depth SRv of the surface opposite to the base layer (A) of the surface layer (B) of the biaxially oriented polypropylene film of the present invention is 1.0 μm or more and 2.0 μm or less. For this purpose, an antiblocking agent is preferably added to the polypropylene resin composition forming the surface layer (B).
As the anti-blocking agent, it can be appropriately selected from inorganic particles such as silica, calcium carbonate, kaolin and zeolite, and organic particles such as acrylic, polymethacrylic and polystyrene. . Among these, it is particularly preferable to use polymethacrylic particles. The average particle size of the antiblocking agent is preferably 1.0 to 2.5 μm, more preferably 1.0 to 2.0 μm. The measurement method of the average particle diameter here is a method in which a photograph is taken with a scanning electron microscope, the ferret diameter in the horizontal direction is measured using an image analyzer, and the average value is displayed.
The antiblocking agent is preferably 0.15% by mass relative to the entire polypropylene resin or mixture thereof.

The polypropylene resin used in the present invention is a polymer of propylene as a raw material alone or a copolymer of propylene and ethylene and / or α-olefin using a known catalyst such as a Ziegler-Natta catalyst or a metallocene catalyst. Is obtained. Among these, in order to eliminate the heterogeneous bond, it is preferable to use a Ziegler-Natta catalyst and a catalyst capable of polymerization with high stereoregularity.
As a polymerization method, a known method may be employed, for example, a method of polymerizing in an inert solvent such as hexane, heptane, toluene, xylene, a method of polymerizing in a liquid monomer, or adding a catalyst to a gaseous monomer. And the method of superposing | polymerizing in a gaseous-phase state, the method of superposing | polymerizing combining these, etc. are mentioned.

The base layer (A) of the biaxially oriented polypropylene film of the present invention of the present invention may contain additives and other resins. Examples of the additive include an antioxidant, an ultraviolet absorber, a nucleating agent, an adhesive, an antifogging agent, a flame retardant, and an inorganic or organic filler.
Examples of the other resin include polypropylene resins other than the polypropylene resin used in the present invention, random copolymers that are copolymers of propylene and ethylene and / or α-olefins having 4 or more carbon atoms, and various elastomers. These are sequentially polymerized using a multistage reactor, blended with a polypropylene resin and a Henschel mixer, or master pellets prepared in advance using a melt kneader are diluted with polypropylene to a predetermined concentration. Alternatively, the whole amount may be melt kneaded in advance.
The base material layer (B) may contain additives and other resins. Examples of the additive include an antioxidant, an ultraviolet absorber, a nucleating agent, an adhesive, an antifogging agent, a flame retardant, and an inorganic or organic filler.

(3) Biaxially oriented polypropylene film The biaxially oriented polypropylene film of the present invention may be a film having a two-layer structure having a base layer (A) and a surface layer (B) one by one. It is good also as a structure more than a layer. Preferred is a two-layer structure of substrate layer (A) / surface layer (B), but surface layer (B) / A layer / surface layer (B), / substrate layer (A) / intermediate layer (C). ) / Surface layer (B) three-layer structure or more than that.
In addition, when there are a plurality of substrate layers (A) and surface layers (B), the compositions may be different as long as each layer satisfies the characteristics.
The total thickness of the biaxially oriented polypropylene film of the present invention is preferably 9 to 200 m, more preferably 10 to 150 μm, still more preferably 12 to 100 μm, and particularly preferably 12 to 80 μm.

As the ratio of the thickness of the entire surface layer (B) and the thickness of the base material layer (A) in the biaxially oriented polypropylene film of the present invention, the thickness of the entire surface layer (B) / the thickness of the base material layer (A) is It is preferably from 0.01 to 0.5, more preferably from 0.02 to 0.4, and even more preferably from 0.03 to 0.3. When the total surface layer (B) / total base material layer (A) exceeds 0.5, the shrinkage rate tends to increase. The total thickness of the base layer (A) is preferably 50 to 99%, more preferably 60 to 97%, and particularly preferably 70 to 95% with respect to the total thickness of the film. The remainder becomes the surface layer (B) or the surface layer (B) and the intermediate layer (C). The substantial thickness of the entire surface layer (B) is preferably 0.5 to 4 μm, more preferably 1 to 3.5 μm, and even more preferably 1.5 to 3 μm.

The evaluation of the ink adhesion of the biaxially oriented polypropylene film of the present invention was carried out by performing a peel test of gravure-printed printing ink and performing the number of peeled portions out of the total 25 locations. The number of peeled portions is preferably 5 or less, more preferably 3 or less, and most preferably 0. If the number exceeds 5, the degree to which the printing ink peels becomes large, which is a problem. A method for evaluating ink adhesion will be described later.

The lamination strength in the longitudinal direction after lamination to the biaxially oriented polypropylene film of the present invention is preferably 1.2 to 2.5 N / 15 mm, more preferably 1.3 to 2.5 N / mm, and 1.4 to 2.5 N / mm is more preferable. A method for measuring the laminate strength will be described later.

The dynamic friction coefficient of the biaxially oriented polypropylene film of the present invention is preferably 0.5 or less, more preferably 0.48 or less, and particularly preferably 0.45 or less. When the dynamic friction coefficient is 0.5 or less, the film can be smoothly unwound from the roll film, and printing is easy. A method for measuring the dynamic friction coefficient will be described later.

The haze of the biaxially oriented polypropylene film of the present invention is preferably 5% or less, more preferably 0.2 to 5%, further preferably 0.3 to 4.5%, and particularly preferably 0.4 to 4%. . If it exceeds 5%, the transparency is inferior and the printed display may be difficult to see. For example, when the stretching temperature and heat setting temperature are too high, the haze tends to be worse when the cooling roll temperature is high, the cooling rate of the unstretched (raw material) sheet is slow, or when there are too many low molecular weight components. By doing so, it can be within the above range. A method for measuring haze will be described later.

The biaxially oriented biaxially oriented polypropylene film of the present invention preferably has a heat shrinkage rate of 150% at 150 ° C. in the machine direction and the transverse direction, preferably 10% or less, more preferably 8% or less. It is particularly preferred. By setting the thermal shrinkage rate to 11% or less, it is possible to reduce the pitch deviation during printing. A method for measuring thermal shrinkage will be described later.

In the biaxially oriented polypropylene film of the present invention, the thermal shrinkage in the longitudinal direction at 150 ° C. is preferably 0.2 to 8%, more preferably 0.3 to 7%, and more preferably 0.5 to 6 % Is particularly preferred. If the heat shrinkage rate is in the above range, it can be said that the film has excellent heat resistance, and can be used in applications that may be exposed to high temperatures. If the thermal shrinkage at 150 ° C. is up to about 1.5%, for example, it is possible to increase the low molecular weight component, adjust the stretching conditions and the heat setting conditions, but in order to lower it below, anneal offline. It is preferable to perform the treatment.

The tensile modulus in the machine direction of the biaxially oriented polypropylene film of the present invention is preferably 1.8 to 4 GPa, more preferably 2.1 to 3.7 GPa, and 2.2 to 3.5 GPa. Is more preferable, and 2.3 to 3.4 GPa is particularly preferable. The tensile modulus in the transverse direction is preferably 3.8 to 8 GPa, more preferably 4 to 7.5 GPa, still more preferably 4.1 to 7 GPa, and 4.2 to 6.5 GPa. Is particularly preferred. If the tensile elastic modulus is in the above range, the elasticity becomes strong and the film can be used even if the film thickness is small, so the amount of film used can be reduced. A method for measuring the tensile modulus will be described later.

The lower limit of the plane orientation coefficient of the biaxially oriented polypropylene film of the present invention is preferably 0.011, more preferably 0.012, and even more preferably 0.013. Within the above range, the heat resistance and rigidity of the film tend to increase.
The stretched laminated polypropylene film generally has a crystal orientation, and its direction and degree greatly affect the film properties. The degree of crystal orientation tends to change depending on the molecular structure of the polypropylene resin used and the process and conditions in film production, and can be adjusted to the above range by adjusting these. A method for measuring the plane orientation coefficient will be described later.

(4) Film-forming method The biaxially oriented polypropylene film of the present invention is obtained by melt-extruding the polypropylene resin composition for the base layer (A) and the polypropylene resin composition for the surface layer (B) by separate extruders. It is obtained by co-extrusion from a die, cooling with a cooling roll to form an unstretched sheet, stretching the unstretched sheet in the machine direction (MD) and the width direction (TD), and then heat setting. be able to.
The melt extrusion temperature is preferably about 200 to 280 ° C. In order to obtain a laminated film having a good appearance without disturbing the layer within this temperature range, the polypropylene raw material for the base layer (A) and the polypropylene for the surface layer (B) The viscosity difference (MFR difference) of the raw materials is preferably 6 g / 10 minutes or less. When the viscosity difference is larger than 6 g / 10 min, the layer is disturbed and the appearance is liable to be poor. More preferably, it is 5.5 g / 10 minutes or less, More preferably, it is 5 g / 10 minutes or less.

The surface temperature of the cooling roll is preferably 25 to 35 ° C, more preferably 27 to 33 ° C. When the temperature exceeds 35 ° C., the film surface tends to be rough.

The lower limit of the draw ratio in the machine direction (MD) is preferably 3 times, more preferably 3.5 times. If it is less than the above, film thickness unevenness may occur. The upper limit of the MD draw ratio is preferably 8 times, more preferably 7 times. When the above is exceeded, it may be difficult to carry out TD stretching continuously. The lower limit of the MD stretching temperature is preferably 120 ° C, more preferably 125 ° C, and even more preferably 130 ° C. If it is less than the above, the mechanical load may increase, the thickness unevenness may increase, or the film surface may be roughened. The upper limit of the MD stretching temperature is preferably 150 ° C, more preferably 145 ° C, and further preferably 140 ° C. A higher temperature is preferable for lowering the thermal shrinkage, but it may adhere to the roll and cannot be stretched, or surface roughness may occur.

The lower limit of the draw ratio in the width direction (TD) is preferably 4 times, more preferably 5 times, and even more preferably 6 times. If it is less than the above, thickness unevenness may occur. The upper limit of the TD stretch ratio is preferably 20 times, more preferably 17 times, still more preferably 15 times, and particularly preferably 12 times. If the above is exceeded, the thermal shrinkage rate may be increased or the film may be broken during stretching. The preheating temperature in TD stretching is preferably set to 5 to 15 ° C. higher than the stretching temperature in order to quickly raise the film temperature in the vicinity of the stretching temperature. The TD stretching is performed at a higher temperature than the conventional stretched polypropylene film. The lower limit of the TD stretching temperature is preferably 155 ° C, more preferably 157 ° C, still more preferably 158 ° C, and particularly preferably 160 ° C. If it is less than the above, it may break without being sufficiently softened, or the thermal shrinkage rate may be increased. The upper limit of the TD stretching temperature is preferably 170 ° C, more preferably 168 ° C, and further preferably 163 ° C. In order to lower the thermal shrinkage rate, it is preferable that the temperature is higher. However, if the temperature is higher than the above, the low molecular component is melted and recrystallized to lower the orientation, and the surface may be roughened or the film may be whitened.

The stretched film is heat-set. The heat setting can be performed at a higher temperature than a conventional stretched polypropylene film. The lower limit of the heat setting temperature is preferably 165 ° C, more preferably 166 ° C. If it is less than the above, the thermal shrinkage rate may increase. In addition, a long time treatment is required to lower the heat shrinkage rate, and productivity may be inferior. The upper limit of the heat setting temperature is preferably 176 ° C, more preferably 175 ° C. When the above is exceeded, the low molecular component may melt and recrystallize, and the surface roughness or the film may be whitened.

It is preferable to relax (relax) during heat setting. The lower limit of relaxation (relaxation) is preferably 2%, more preferably 3%. If it is less than the above, the thermal shrinkage rate may increase. The upper limit of relaxation (relaxation) is preferably 10%, more preferably 8%. When the above is exceeded, the thickness unevenness may increase.

Furthermore, in order to reduce the thermal shrinkage rate, the film produced in the above process can be once wound into a roll and then annealed offline. The lower limit of the offline annealing temperature is preferably 160 ° C, more preferably 162 ° C, and even more preferably 163 ° C. If it is less than the above, the effect of annealing may not be obtained. The upper limit of the offline annealing temperature is preferably 175 ° C., more preferably 174 ° C., and further preferably 173 ° C. When the above is exceeded, the transparency may decrease, or the thickness unevenness may increase.

The lower limit of the offline annealing time is preferably 0.1 minutes, more preferably 0.5 minutes, and even more preferably 1 minute. If it is less than the above, the effect of annealing may not be obtained. The upper limit of the offline annealing time is preferably 30 minutes, more preferably 25 minutes, and further preferably 20 minutes. When the above is exceeded, productivity may be reduced.

The biaxially oriented polypropylene film thus obtained can be subjected to corona discharge, plasma treatment, flame treatment, etc., if necessary, and then wound with a winder to obtain the biaxially oriented polypropylene film roll of the present invention. it can.

The biaxially oriented polypropylene film of the present invention can be widely used, for example, for applications in which processing such as printing ink or lamination is performed.

Hereinafter, the present invention will be described in more detail by way of examples. However, the following examples are not intended to limit the present invention, and modifications and implementations without departing from the spirit of the present invention are included in the present invention.

(Measuring method)
The measuring method of the film physical property obtained by the Example and the comparative example is as follows.

1) Stereoregularity The mesopentad fraction ([mmmm]%) was measured using 13C-NMR. The mesopentad fraction was calculated according to the method described in “Zambelli et al., Macromolecules, Vol. 6, 925 (1973)”. The 13C-NMR measurement was performed at 110 ° C. by using “AVANCE 500” manufactured by BRUKER, and dissolving 200 mg of a sample in an 8: 2 (volume ratio) mixture of o-dichlorobenzene and heavy benzene at 135 ° C.

2) Melt flow rate (MFR; g / 10 min)
According to JIS K7210, the temperature was 230 ° C. and the load was 2.16 kgf.
In the case of a raw material resin, pellets (powder) were used as they were by weighing out the required amount. In the case of a film, after cutting out a necessary amount, a sample cut into about 5 mm square was used.

3) Molecular weight and molecular weight distribution The molecular weight and molecular weight distribution of the raw resin and film were determined on the basis of monodisperse polystyrene using gel permeation chromatography (GPC). The measurement conditions such as the column used and the solvent in GPC measurement are as follows.
Solvent: 1,2,4-trichlorobenzene Column: TSKgel GMHHR-H (20) HT × 3
Flow rate: 1.0 ml / min
Detector: RI
Measurement temperature: 140 ° C

The number average molecular weight (Mn), the mass average molecular weight (Mw), and the molecular weight distribution are respectively represented by the molecular number (N _i ) of the molecular weight (M _i ) at each elution position of the GPC curve obtained through the molecular weight calibration curve. It is defined by an expression.
Number average molecular weight: Mn = Σ (N _i · M _i ) / ΣN _i
Mass average molecular weight: Mw = Σ (N _i · M _i ² ) / Σ (N _i · M _i )
Molecular weight distribution: Mw / Mn
When the baseline was not clear, the baseline was set in the range from the elution peak closest to the elution peak of the standard substance to the lowest position of the bottom of the high molecular weight side.

4) Thickness The thickness of each of the base layer (A) and the surface layer (B) is measured by cutting a cross section of a biaxially stretched laminated polypropylene film hardened with a modified urethane resin with a microtome and observing with a differential interference microscope. did.

5) Thermal shrinkage (%)
Based on JIS Z1712, it measured by the following method. The film was cut into a width of 20 mm and a length of 200 mm in each of the MD direction and the TD direction, suspended in a hot air oven at 150 ° C. and heated for 5 minutes. The length before and after heating was measured, the ratio (%) of the length obtained by subtracting the length after heating from the length before heating to the length before heating was determined, and the thermal shrinkage rate was determined.

6) Tensile modulus (GPa)
Based on JIS K7127, the tensile elastic modulus in the MD direction and TD direction of the film was measured at 23 ° C. under the following conditions.
Measuring equipment: Shimadzu Corporation, Autograph ASS-100NJ
Sample size: width 15mm x length 200mm
Crosshead speed: 200mm / min
Distance between chucks: 100mm
Elasticity measurement strain range: 0.1-0.6%

7) Haze (Unit:%)
It measured according to JIS K7105.

8) Coefficient of dynamic friction According to JIS K7125, the surface layer (B) surfaces of two films were superposed and measured at 23 ° C.

9) Refractive index, plane orientation coefficient Measured using an Atago Abbe refractometer according to JIS K7142-1996 5.1 (Method A). The refractive indexes along the MD and TD directions were Nx and Ny, respectively, and the refractive index in the thickness direction was Nz. The plane orientation coefficient (ΔP) was determined by (Nx + Ny) / 2−Nz.

10) Surface roughness The surface roughness of the obtained film was evaluated using a three-dimensional roughness meter (manufactured by Kosaka Laboratories, model number ET-30HK) at a stylus pressure of 20 mg and measured length in the X direction. 1 mm, feed speed 100 μm / second, Y-direction feed pitch 2 μm, 99 recording lines, height direction magnification 20000 times, cut-off 80 μm were measured, and the arithmetic average roughness described in JISB 0601 (1994) was measured. Calculated according to the definition.
Arithmetic average roughness (SRa), center plane mountain height (SRp), and center plane valley depth (SRv) were each evaluated three times and evaluated by their average values.

11) Surface resistivity (LogΩ)
In accordance with JIS K6911, the surface layer (B) surface of the film was measured after aging the film at 23 ° C. for 24 hours.

12) Wetting tension (mN / m)
In accordance with K6768: 1999, the film was aged for 24 hours at 23 ° C. and 50% relative humidity, and then the corona-treated surface of the film was measured by the following procedure.
Procedure 1)
The measurement is performed in a standard laboratory atmosphere (see JIS K 7100) at a temperature of 23 ° C and a relative humidity of 50%.
Step 2)
Place the test piece on the substrate of the hand coater (4.1), drop a few drops of the test mixture on the test piece and immediately pull the wire bar to spread.
When using a cotton swab or brush to spread the test mixture, the liquid is quickly spread over an area of at least 6 cm2. The amount of liquid is such that a thin layer is formed without creating a pool.
The wet tension is determined by observing the liquid film of the test liquid mixture in a bright place and in the liquid film state after 3 seconds. It is wet to maintain the state when applied for 3 seconds or more without causing the liquid film to break. When the wetting is maintained for 3 seconds or more, the process proceeds to a liquid mixture having the next highest surface tension. Conversely, when the liquid film is broken within 3 seconds or less, the process proceeds to the next liquid mixture having a low surface tension.
This operation is repeated, and a liquid mixture that can accurately wet the surface of the test piece in 3 seconds is selected.
Step 3)
Use a new swab for each test. The brush or wire bar is washed with methanol and dried after each use because the remaining liquid changes its composition and surface tension by evaporation.
Step 4)
The operation of selecting a mixed solution that can wet the surface of the test piece in 3 seconds is performed at least three times. The surface tension of the mixture thus selected is reported as the wetting tension of the film.

13) Ink adhesion On the surface layer (B) of the film, gravure printing (printing ink amount 2 g / m ² ) was performed at a speed of 50 m / min using a gravure printing machine (manufactured by Mitani Iron Works Co., Ltd.). The ink at this time is a water-based ink (manufactured by Dainippon Ink & Chemicals, Inc .: trade name Eco Fine 709 White).
(Registered trademark) Using this print sample, it was evaluated by grid peeling (2 mm square x 25 pieces, 90 ° peeling method using cello tape (registered trademark) 18 mm width manufactured by Nichiban Co., Ltd.). Judgment was made and the next ranking was performed.

Cross-section peeling part: 0 ·····: Excellent in printing ink adhesion.
〃 1 to 5 ... ○: Good adhesion of printing ink.
６ 6 to 15 ・ ・ ・ Δ: Poor adhesion to printing ink.
〃 1 or more ········ ×: No printing ink adhesion.

14) Laminate strength The laminate strength was measured by the following procedure.
Procedure 1) Preparation of a laminate film with a sealant film A continuous dry laminating machine was used as follows.
The surface layer (B) surface of the biaxially oriented polypropylene film obtained in Examples and Comparative Examples was gravure-coated so that the coating amount when dried was 3.0 g / m ^2, and then led to the drying zone. Dried at 80 ° C. for 5 seconds. Subsequently, it was bonded to a sealant film between rolls provided on the downstream side (roll pressure 0.2 MP, roll temperature: 60 ° C.). The obtained laminate film was subjected to an aging treatment at 40 ° C. for 3 days while being wound up.
The adhesive was obtained by mixing 17.9% by mass of a main agent (manufactured by Toyo Morton, TM329), 17.9% by mass of a curing agent (CAT8B, manufactured by Toyo Morton) and 64.2% by mass of ethyl acetate. An ether adhesive was used, and a non-stretched polypropylene film (Pyrene (registered trademark) CTP1128, thickness 30 μm) manufactured by Toyobo Co., Ltd. was used as the sealant film.
Procedure 2) Measurement of laminate strength The laminate film obtained above was cut into a strip shape (length: 200 mm, width: 15 mm) having a long side in the longitudinal direction of a biaxially oriented polypropylene film, and a tensile tester (Tensilon, Orientec) Was used, and the peel strength (N / 15 mm) at the time of T-peeling at a tensile rate of 200 mm / min in an environment of 23 ° C. was measured. The measurement was performed three times, and the average value was taken as the laminate strength.

(Raw resin)
The details of the polypropylene resin materials used in the following examples and comparative examples are shown in Table 1.

Example 1
Polypropylene homopolymer PP-1 shown in Table 1 was used for the base material layer (A).
In the surface layer (B), 49% by weight of the polypropylene homopolymer PP-1 shown in Table 1 and 51 parts by weight of the ethylene copolymer polypropylene polymer PP-3 shown in Table 1 were mixed. What mixed the quantity corresponding to 0.15 mass% of the said mixture was used for the thing by using commercially available polymethylmethacrylate (PMMA) particle | grains (average particle diameter: 1.4 micrometers) as an antiblocking agent. At this time, the melt flow rate (g / 10 min) of a mixture of 49% by weight of the polypropylene homopolymer PP-1 and 51% by weight of the ethylene copolymer polypropylene polymer PP-3 was 5.3.
The base material layer (A) was melted at 250 ° C. using a 60 mm extruder and the surface layer (B) was a 65 mm extruder, respectively, and coextruded into two layers in a sheet form from a T die. After the (A) side was in contact with the cooling roll and cooled and solidified with a 30 ° C. cooling roll, it was stretched 4.5 times in the longitudinal direction (MD) of 125 ° C. Next, in the tenter, the film width direction both ends are clipped, preheated at 170 ° C., stretched 8.2 times in the width direction (TD) at 158 ° C., and relaxed by 6.7% in the width direction (TD). And heat-fixed at 165 ° C.
The film forming condition at this time was defined as film forming condition a.
Thus, a biaxially oriented polypropylene film in which the base material layer (A) and the surface layer (B) were laminated one by one was obtained.
After the corona treatment was performed on the surface layer (B) side of the biaxially oriented polypropylene film using a corona treatment machine manufactured by Sophtal Corona & Plasma GmbH under the condition of applied current value: 0.75A, I wound it up with a winder. The thickness of the obtained film was 20 μm.

(Example 2)
The resin used for the base material layer (A) is changed to polypropylene resin PP-2, the base material layer (A) is a 60 mm extruder and the surface layer (B) is a 65 mm extruder, and the raw material resin is 250 ° C. respectively. And then coextruded into a sheet form from a T-die, cooled and solidified with a 30 ° C. cooling roll, and then stretched 4.5 times in the 135 ° C. longitudinal direction (MD). Next, in the tenter, both ends in the film width direction are sandwiched between clips, preheated at 175 ° C., stretched 8.2 times in the width direction (TD) at 160 ° C., and relaxed by 6.7% in the width direction (TD). And heat-fixed at 170 ° C. The film forming conditions at this time were set as film forming conditions b.
Thus, a biaxially oriented polypropylene film in which the base material layer (A) and the surface layer (B) were laminated one by one was obtained.

(Example 3)
A biaxially stretched laminated polypropylene film was obtained in the same manner as in Example 1 except that the thickness of the base material layer (A) was changed to 38 μm.

Example 4
A biaxially stretched laminated polypropylene film was obtained in the same manner as in Example 1 except that the thickness of the base material layer (A) was changed to 18 μm.

(Comparative Example 1)
In the surface layer (B), 0.15% by mass of polymethyl methacrylate (PMMA) particles (average particle size: 1.4 μm) as an antiblocking agent is blended with the polypropylene homopolymer PP-1. A biaxially stretched laminated polypropylene film was obtained in the same manner as in Example 1 except that it was used.

(Comparative Example 2)
A biaxially stretched laminated polypropylene film was obtained in the same manner as in Example 1 except that polypropylene homopolymers PP-1 and PP-4 were used for the surface layer (B).

(Comparative Example 3)
For the surface layer (B), a biaxially stretched laminated polypropylene film was obtained in the same manner as in Example 1 except that no antiblocking agent was used.

(Comparative Example 4)
For the base material layer (A), polypropylene homopolymer PP-1 and stearyl diethanolamine stearate (MATMOTO KYM-4K) as an antistatic agent were added to the polypropylene homopolymer PP-1. A biaxially stretched laminated polypropylene film was obtained in the same manner as in Example 1 except that 0% by mass was used. Table 3 shows the physical properties of the obtained film.

(Comparative Example 5)
A biaxially stretched laminated polypropylene film was obtained in the same manner as in Example 1 except that the surface layer (B) side of the biaxially oriented polypropylene film was not subjected to corona treatment.

(Comparative Example 6)
After cooling and solidifying with a 40 ° C. cooling roll, the film was stretched 4.5 times in the longitudinal direction (MD) at 135 ° C., and then sandwiched with clips at both ends in the film width direction in a tenter, preheated at 175 ° C. and then at 163 ° C. Except that the film was stretched 8.2 times in the width direction (TD) and relaxed by 6.7% in the width direction (TD), heat fixed at 1772 ° C., and subjected to the same corona treatment, but the same as in Example 1. It was.
The film forming condition at this time was defined as film forming condition c.

Table 2, Table 3, and Table 4 show the raw materials used in the above Examples and Comparative Examples, the film forming conditions, and the physical properties of the obtained films, respectively.

The biaxially stretched laminated polypropylene films obtained in Examples 1 to 4 had high laminate strength and excellent printing ink adhesion. Furthermore, the thermal shrinkage rate was low and the Young's modulus was high.
On the other hand, the films of Comparative Examples 1 to 5 were all poor in printing ink adhesion.
Moreover, all the films of Comparative Example 6 had high haze and were inferior in transparency.

Since the biaxially stretched laminated polypropylene film of the present invention has good printing ink adhesion, it can be used not only for food packaging used for confectionery, but also for labels, etc. Since it can be manufactured, it is industrially useful.

Claims (4)

A surface layer (B) having a base material layer (A) mainly composed of a polypropylene resin and a surface layer (B) mainly composed of a polypropylene resin on at least one surface of the base material layer (A). The arithmetic average roughness of the surface opposite to the base material layer (A) is 0.027 μm or more and 0.040 μm or less, and the surface layer (B) has a surface opposite to the base material layer (A). The surface specific resistance value is 15 LogΩ or more, the wetting tension of the surface layer (B) opposite to the base material layer (A) is 38 mN / m or more, the film thickness is 9 μm or more, 200 μm or less, And the haze value of a film is 5% or less, The biaxially oriented polypropylene film characterized by the above-mentioned. 2. The biaxial orientation according to claim 1, wherein the surface layer (B) has a center surface peak height SRp + center surface valley depth SRv on the side opposite to the base material layer (A) of 1.0 μm or more and 2.0 μm or less. Polypropylene film. The biaxially oriented polypropylene film according to claim 1 or 2, wherein a heat shrinkage rate at 150 ° C in the machine direction and the transverse direction of the film is 11% or less. A laminate having a printing layer on the surface opposite to the base material layer (A) of the surface layer (B) of the biaxially oriented polypropylene film according to any one of claims 1 to 3.