Biaxially oriented polypropylene resin film and packaging using the same

Abstract

To provide a biaxially oriented polypropylene-based resin film which has high rigidity and is excellent in both fusion sealability and heat sealability.SOLUTION: A film has a base layer (A) composed of a polypropylene-based resin composition, and surface layers (B) composed of a polypropylene-based resin composition on both surfaces thereof, and satisfies the following conditions. a) The polypropylene-based resin composition constituting the base layer (A) contains a plurality of polypropylene homopolymers, a highest mesopentad fraction is 97.5% or more, and a lowest mesopentad fraction is 96.5% or less. b) an α-olefin monomer-derived component in the polypropylene-based resin composition of the base layer (A) is 0.2 mol% or less. c) A butene-1 monomer-derived component in the polypropylene-based resin composition in the surface layer (B) is 5 mol% or more and 10 mol% or less. d) Thickness of a biaxially oriented polypropylene-based resin film is 60 μm or less, and thickness of the surface layer (B) to the thickness of the whole film layer is 3% or more and 10% or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polypropylene-based laminate film that is suitable for packaging sandwiches and the like by easily maintaining the shape of the packaged contents and making the contents easy to see, and more particularly to a polypropylene-based laminate film that has high rigidity and is capable of being melt-cut and heat-sealed. [Background technology]

[0002] Conventionally, polypropylene films have been used for packaging food and various other products. The polypropylene film used preferably has low water vapor and oxygen permeability, and is preferably capable of undergoing both fusion sealing and heat sealing as heat sealing methods for bag production, so that it can be used by a wide variety of users. Furthermore, films used to package foods such as sandwiches are required to be able to be made into bags that fit the shape of the food, to have heat-sealing properties and airtightness for making bags, to have visibility of the contents, to be printable, and to be resistant to deformation of the package. However, conventional polypropylene films that can be melt-cut or heat-sealed have room for improvement in mechanical properties (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] WO2017 / 170330 publication Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention has been made in view of the problems of the prior art. That is, an object of the present invention is to provide a biaxially oriented polypropylene resin film having high rigidity and excellent both in melt-cutting sealability and heat-sealability. [Means for solving the problem]

[0005] That is, the present invention has the following configuration. [1] A biaxially oriented polypropylene resin film having a base layer (A) made of a polypropylene resin composition and surface layers (B) made of polypropylene resin compositions on both sides thereof, and satisfying the following conditions a) to d): a) The polypropylene resin composition constituting the base layer (A) has a mesopentad fraction of 95.0% or more and 99.5% or less. b) The proportion of the α-olefin monomer-derived component relative to the total of the propylene monomer-derived component and the α-olefin monomer-derived component in the entire polypropylene-based resin composition constituting the base layer (A) is 0.2 mol % or less. c) The proportion of the butene-1 monomer derived component relative to the total of the propylene monomer derived component and the α-olefin monomer derived component in the polypropylene resin composition constituting the surface layer (B) is 5 mol % or more and 10 mol % or less. d) The thickness of the biaxially oriented polypropylene resin film is 60 μm or less, and the ratio of the thickness of the surface layer (B) to the total thickness of the biaxially oriented polypropylene resin film is 3% or more and 10% or less.

[0006] [2] A biaxially oriented polypropylene resin film having a base layer (A) made of a polypropylene resin composition and surface layers (B) made of polypropylene resin compositions on both sides thereof, and satisfying the following conditions A) to D): A) The polypropylene resin having the lowest DSC melting point in the polypropylene resin composition constituting the base layer (A) has a melting point peak temperature of 160°C or higher. B) The proportion of the α-olefin monomer-derived component relative to the total of the propylene monomer-derived component and the α-olefin monomer-derived component in the entire polypropylene-based resin composition constituting the base layer (A) is 0.2 mol % or less. C) The proportion of the butene-1 monomer derived component relative to the total of the propylene monomer derived component and the α-olefin monomer derived component in the polypropylene resin composition constituting the surface layer (B) is 5 mol % or more and 10 mol % or less. D) The thickness of the biaxially oriented polypropylene resin film is 60 μm or less, and the ratio of the thickness of the surface layer (B) to the total thickness of the biaxially oriented polypropylene resin film is 3% or more and 10% or less.

[0007] [3] The biaxially oriented polypropylene resin film according to [1] or [2], wherein the melt flow rate (MFR) of the entire polypropylene resin composition constituting the base layer (A) is 2.0 g / 10 min or more and 4.5 g / 10 min or less.

[0008] [4] The biaxially oriented polypropylene resin film according to any one of [1] to [3], wherein the polypropylene resin composition constituting the base layer (A) contains a plurality of polypropylene homopolymers, and the polypropylene homopolymer having the highest mesopentad fraction has a mesopentad fraction of 97.5% or more, and the polypropylene homopolymer having the lowest mesopentad fraction has a mesopentad fraction of 96.5% or less.

[0009] [5] The biaxially oriented polypropylene resin film according to any one of [1] to [4], wherein the polypropylene resin composition constituting the base layer (A) contains at least one polymer selected from the group consisting of propylene homopolymer, propylene-ethylene copolymer, propylene-butene-1 copolymer, propylene-ethylene-butene-1 copolymer, and propylene-pentene-1 copolymer.

[0010] [6] The biaxially oriented polypropylene resin film according to any one of [1] to [5], wherein the Young's modulus of the biaxially oriented polypropylene resin film in the longitudinal direction is 2.0 GPa or more and the Young's modulus in the width direction is 4.0 GPa or more.

[0011] [7] The biaxially oriented polypropylene resin film according to any one of [1] to [6], wherein the biaxially oriented polypropylene resin film has a welding seal strength of 18 N / 15 mm or more.

[0012] [8] The biaxially oriented polypropylene resin film according to any one of [1] to [7], wherein the biaxially oriented polypropylene resin film has a heat seal strength of 3 N / 15 mm or more.

[0013] [9] A package using the biaxially oriented polypropylene resin film according to any one of [1] to [8]. [Effects of the Invention]

[0014] The biaxially oriented polypropylene resin film of the present invention has high rigidity and excellent both in weld-cutting sealability and heat sealability, and provides visibility for packaging products such as sandwiches, prevents the shape of the package from collapsing, and improves the appearance of the contents. It also contributes to environmental friendliness by reducing the thickness of the film. DETAILED DESCRIPTION OF THE INVENTION

[0015] The biaxially oriented polypropylene resin film of the present invention has a base layer (A) made of a polypropylene resin composition and surface layers (B) made of a polypropylene resin composition on both sides of the base layer (A).

[0016] (Base layer (A) In the present invention, the base layer (A) is made of a polypropylene-based resin composition, and preferably contains at least one polymer selected from the group consisting of propylene homopolymers and copolymers of propylene and other α-olefins containing 90 mol% or more of propylene as a main component. The content of the at least one polymer selected from the group consisting of propylene homopolymers and copolymers of propylene and other α-olefins containing 90 mol% or more of propylene is preferably 95% by weight or more, more preferably 97% by weight or more, even more preferably 98% by weight or more, and particularly preferably 99% by weight or more.

[0017] The propylene homopolymer is preferably an n-heptane insoluble isotactic propylene homopolymer. N-heptane insolubility is an index of the crystallinity of polypropylene and also indicates its safety when used for food packaging. In the present invention, it is preferable to use polypropylene that satisfies the n-heptane insolubility criteria specified in Ministry of Health and Welfare Notification No. 20 of February 1982 (the elution content after extraction at 25°C for 60 minutes is 150 ppm or less [30 ppm or less for use at temperatures exceeding 100°C]).

[0018] The other α-olefins are preferably α-olefins having 2 to 8 carbon atoms, such as ethylene, butene-1, pentene-1, hexene-1, 4-methyl-1-pentene, etc. Here, the copolymer is preferably a random or block copolymer obtained by polymerizing one or more of the above-listed α-olefins with propylene, and is preferably a propylene-ethylene copolymer, a propylene-butene-1 copolymer, a propylene-ethylene-butene-1 copolymer, or a propylene-pentene-1 copolymer.

[0019] The polypropylene homopolymer preferably accounts for 97% by weight or more of the polypropylene resin composition constituting the base layer (A), more preferably 98% by weight or more, even more preferably 99% by weight or more, and particularly preferably 100% by weight.

[0020] When a propylene-α-olefin copolymer containing 90 mol % or more of propylene is used in combination, the content of the propylene-α-olefin copolymer containing 90 mol % or more of propylene is preferably 3 wt % or less, more preferably 2 wt % or less, even more preferably 1 wt % or less, and particularly preferably 0 wt %, based on the total polypropylene resin composition used in the base layer (A).

[0021] The polypropylene resin having the lowest DSC melting point in the polypropylene resin composition constituting the base layer (A) preferably has a melting point peak temperature of 160°C or higher. The melting point is measured by the method described in the Examples below. When the peak melting point temperature of the polypropylene resin with the lowest DSC melting point is 160°C or higher, the shape of the package is less likely to be distorted, the film can be conveyed more smoothly during high-speed packaging processing, and the resulting bag is less likely to wrinkle.

[0022] Alternatively, from the viewpoint of weld-cutting sealability, the proportion of the α-olefin monomer-derived component relative to the total of the propylene monomer-derived component and the α-olefin monomer-derived component in the entire polypropylene-based resin composition used in the base layer (A) is preferably 0.2 mol% or less. This allows for a high level of both rigidity and weld-cutting sealability. It is more preferably 0.1 mol% or less, even more preferably 0.05 mol% or less, and particularly preferably 0 mol%.

[0023] The isotactic mesopentad fraction of the entire polypropylene resin composition constituting the base layer (A) is preferably 95% or more from the viewpoint of rigidity. This allows for a high level of both rigidity and weld-sealability. It is more preferably 97.0% or more. Furthermore, from the viewpoint of film formability, it is preferably 99.5% or less.

[0024] The melt flow rate (MFR) of the polypropylene resin composition used in the base layer (A) is preferably 2.0 g / 10 min or more from the viewpoint of weld-cutting sealability. This allows for a higher level of both rigidity and weld-cutting sealability. From the viewpoint of film elongation, the MFR is preferably 6.0 g / 10 min or less.

[0025] In this case, the polypropylene resin composition constituting the base layer (A) may contain a plurality of polypropylene homopolymers. In this case, the polypropylene homopolymer having the highest mesopentad fraction preferably has a mesopentad fraction of 97.5% or more, more preferably 98.0% or more, and particularly preferably 98.5% or more. The polypropylene homopolymer having a mesopentad fraction of 97.5% or more preferably has a mesopentad fraction of 30% to 70% by weight, more preferably 40% to 60% by weight. In this case, the mesopentad fraction of the polypropylene homopolymer having the lowest mesopentad fraction is preferably 96.5% or less, more preferably 95.5% or less, and particularly preferably 95.0% or less. The polypropylene homopolymer having a mesopentad fraction of 96.5% or less is preferably 30% by weight or more and 70% by weight or less, and more preferably 40% by weight or more and 60% by weight or less.

[0026] The thickness of the base layer (A) varies depending on the application and method of use, but from the viewpoints of film rigidity and water vapor barrier property, it is preferably 10 μm or more, more preferably 15 μm or more, and even more preferably 20 μm or more. From the viewpoints of transparency and environmental impact, it is preferably 50 μm or less, more preferably 45 μm or less, even more preferably 40 μm or less, and particularly preferably 37 μm or less.

[0027] An anti-fogging agent can be added to the polypropylene resin composition constituting the base layer (A) and / or surface layer (B). Typical examples of the anti-fogging agent added to the polypropylene resin composition constituting the base layer (A) of the biaxially oriented polypropylene resin film of the present invention include fatty acid esters of polyhydric alcohols, amines of higher fatty acids, amides of higher fatty acids, and ethylene oxide adducts of amines or amides of higher fatty acids. The amount of such an anti-fogging agent present in the film is preferably 0.1 to 10% by weight, particularly 0.2 to 5% by weight, calculated as the total weight of the film.

[0028] The mechanism by which the biaxially oriented polypropylene resin film of the present invention exhibits anti-fogging properties is that by adding an anti-fogging agent to the resin forming the base layer (A), the anti-fogging agent gradually migrates to the surface layer (B) during film production and storage after film formation, and the film surface becomes anti-fogging. This effect can be exerted when the film is used to package fresh produce, which is characterized by maintaining its physiological activity even after harvest. In order to maintain excellent anti-fogging properties over the long term during distribution, it is desirable to store the package at room temperature rather than in a frozen state. Therefore, it is preferable to select an anti-fogging agent that will continue to exhibit anti-fogging properties over a period of repeated temperature changes between 5 and 30°C, taking into consideration temperature changes during storage and distribution.

[0029] Furthermore, the polypropylene resin composition constituting the base layer (A) may contain various additives for improving qualities such as slipperiness and antistatic properties, for example, lubricants such as wax and metal soaps for improving productivity, plasticizers, processing aids, and known heat stabilizers, antioxidants, antistatic agents, and ultraviolet absorbers that are commonly added to polypropylene films, as long as the effects of the present invention are not impaired.

[0030] (Surface layer (B)) The polypropylene resin used in the polypropylene resin composition constituting the surface layer (B) preferably contains a propylene-α-olefin copolymer containing at least butene-1. By using a propylene-α-olefin copolymer containing at least butene-1, the melting point of the propylene-α-olefin copolymer can be lowered even with a relatively low proportion of copolymerization components, and the surface layers (B) can be more easily mixed, resulting in a high heat seal strength. Furthermore, sufficient heat seal strength can be achieved even if the thickness of the surface layer (B) is reduced.

[0031] The α-olefin other than butene-1 is preferably an α-olefin having 2 to 8 carbon atoms, such as ethylene, pentene-1, hexene-1, 4-methyl-1-pentene, etc. The propylene-α-olefin copolymer containing at least butene-1 is preferably a random or block copolymer obtained by polymerizing propylene with one or more α-olefins containing at least butene-1, and is preferably at least one copolymer selected from the group consisting of propylene-butene-1 copolymer and propylene-ethylene-butene-1 copolymer.

[0032] The polypropylene-based resin composition constituting the surface layer (B) may contain a propylene homopolymer or a copolymer of propylene and an α-olefin other than butene-1 containing 90 mol% or more of propylene, but the content of these in the polypropylene-based resin composition constituting the surface layer (B) is preferably 10 wt% or less, more preferably 5 wt% or less, even more preferably 3 wt% or less, and particularly preferably 0 wt%. The content of the propylene-butene-1 copolymer in the polypropylene resin composition constituting the surface layer (B) is preferably 20 to 50% by weight, more preferably 25 to 50% by weight. The other propylene-α-olefin copolymer preferably includes a propylene-ethylene-butene-1 copolymer, and the content of the other propylene-α-olefin copolymer in the polypropylene resin composition constituting the surface layer (B) is preferably 50 to 80% by weight or more, more preferably 50 to 75% by weight or more.

[0033] In order to achieve high welding seal strength, the butene-1 monomer-derived component is preferably 5 mol% or more, more preferably 5.5 mol% or more, and even more preferably 5.7 mol% or more, of the total of the propylene monomer-derived component and the α-olefin monomer-derived component of the polypropylene-based resin composition constituting the surface layer (B). When the butene-1 monomer-derived component is 5 mol % or more relative to the total of the propylene monomer-derived component and the α-olefin monomer-derived component in the polypropylene-based resin composition constituting the surface layer (B), the growth of spherulites can be suppressed. This is because, when stretching a base layer (A) made of a polypropylene-based resin composition with a high melting point, the stretching temperature must be raised. However, raising the stretching temperature makes it easier for spherulites to grow in the polypropylene-based resin composition making up the surface layer (B) when the stretched film is cooled slowly (for example, when it leaves the tenter stretching machine), and large spherulites are likely to form. If spherulites are present in the molten area after welding and sealing, an interface is formed, which tends to reduce the strength of the welding and sealing. This tendency is more pronounced when the melting point of the polypropylene-based resin composition making up the base layer (A) is higher, as the film is stretched at a higher temperature. However, if the content of the butene-1 monomer-derived component is too high, the shape of the sealed portion is likely to become non-uniform. Therefore, the content of the butene-1 monomer-derived component relative to the total of the propylene monomer-derived component, the ethylene monomer-derived component, and the butene-1 monomer-derived component in the polypropylene resin composition constituting the surface layer (B) is preferably 10 mol % or less, more preferably 9.5 mol % or less, even more preferably 9 mol % or less, particularly preferably 8 mol % or less, and most preferably 6.5 mol % or less. When the polypropylene resin composition constituting the surface layer (B) is at least one copolymer selected from the group consisting of propylene-butene-1 copolymer and propylene-ethylene-butene-1 copolymer, the content of the butene-1 monomer-derived component relative to the total of the propylene monomer-derived component, the ethylene monomer-derived component and the butene-1 monomer-derived component is preferably 5 mol % or more, more preferably 5.5 mol % or more, and even more preferably 5.7 mol % or more, in order to achieve high weld seal strength. However, if the content of the butene-1 monomer-derived component is too high, the shape of the sealed portion is likely to become non-uniform. Therefore, the content of the butene-1 monomer-derived component relative to the total of the propylene monomer-derived component, the ethylene monomer-derived component, and the butene-1 monomer-derived component in the polypropylene resin composition constituting the surface layer (B) is preferably 10 mol % or less, more preferably 9.5 mol % or less, even more preferably 9 mol % or less, particularly preferably 8 mol % or less, and most preferably 6.5 mol % or less.

[0034] Furthermore, if the proportion of the α-olefin monomer-derived components relative to the total of the propylene monomer-derived components and α-olefin monomer-derived components in the entire polypropylene-based resin composition constituting the surface layer (B) is high, peeling is likely to occur at the interface between the base layer (A) and the surface layer (B). Therefore, the proportion of the component derived from an α-olefin monomer in the polypropylene resin used in the polypropylene resin composition constituting the surface layer (B) is preferably 20 mol % or less.

[0035] The polypropylene resin composition constituting the surface layer (B) can be made of a single propylene-α-olefin copolymer or multiple propylene-α-olefin copolymers, but the propylene-α-olefin copolymer with the lowest DSC melting point in the polypropylene resin composition preferably has a melting point peak temperature of 100°C or higher. In this case, spherulites are less likely to be present in the molten part after welding and sealing, and the welding seal strength is less likely to decrease.

[0036] From the viewpoint of weld-seal strength, the ratio of the thickness of the surface layer (B) to the total thickness of the biaxially oriented polypropylene resin film is preferably 10% or less, more preferably 9.5% or less, even more preferably 8% or less, and particularly preferably 6% or less. When the ratio of the thickness of the surface layer (B) is 10% or less, spherulites in the fused portion called poly pools in the weld-sealed portion are reduced, and the ratio of low-melting-point resin is reduced, so that the weld-seal strength is less likely to decrease. From the viewpoint of heat sealing, the thickness ratio of the surface layer (B) is preferably 3% or more, more preferably 4% or more, even more preferably 4.5% or more, and particularly preferably 5% or more.

[0037] Furthermore, as long as the effects of the present invention are not impaired, the surface layer (B) can also be blended with various additives for improving qualities such as slipperiness and antistatic properties, for example, lubricants such as wax and metal soap for improving productivity, plasticizers, processing aids, and known heat stabilizers, antioxidants, antistatic agents, ultraviolet absorbers, etc. that are commonly added to polypropylene films. Inorganic or organic fine particles can also be blended to ensure the film's anti-blocking properties and slipperiness.

[0038] Examples of inorganic fine particles include silicon dioxide, calcium carbonate, titanium dioxide, talc, kaolin, mica, and zeolite, and the shape of these particles may be any type, such as spherical, elliptical, conical, or irregular, and the particle diameter may be selected according to the intended use and method of use of the film. As organic fine particles, crosslinked particles such as acrylic, methyl acrylate, and styrene-butadiene can be used, and as with inorganic fine particles, various shapes and sizes can be used. Various surface treatments can also be applied to the surfaces of these inorganic or organic fine particles, and these can be used alone or in combination of two or more. The above also applies to the surface layer (B) described below.

[0039] (Total film thickness) The total thickness of the biaxially oriented polypropylene resin film of the present invention varies depending on its application and usage, but from the viewpoint of film strength, sealability, or water vapor barrier property, it is preferably 10 μm or more, more preferably 15 μm or more, and even more preferably 20 μm or more. In terms of high-speed packaging processability or visibility, the thickness is preferably 60 μm or less, more preferably 50 μm or less, particularly preferably 45 μm or less, and most preferably 40 μm or less.

[0040] (Method for producing biaxially oriented polypropylene resin film) The biaxially oriented polypropylene resin film of the present invention can be produced under film-forming conditions that are no different from those for general polyolefins. For example, the film can be melt-laminated by a T-die method, inflation method, or the like using an extruder suitable for the number of layers, and then cooled by a cooling roll method, water cooling method, or air cooling method to form a laminated film, which can then be stretched by a sequential biaxial stretching method, a simultaneous biaxial stretching method, a tube stretching method, or the like. Here, as an example of the conditions for manufacturing by the sequential biaxial stretching method, the resin melt-extruded through a T-shaped die is cooled and solidified in a casting machine to produce a raw sheet. In this case, the roll temperature for melt casting is preferably set between 15°C and 40°C in order to suppress crystallization of the resin and improve transparency.

[0041] Next, the raw sheet is heated to a temperature suitable for stretching, and then stretched in the sheet flow direction by utilizing the speed difference between the stretching rolls. In this case, the stretching ratio is preferably set between 3 and 6 times in order to ensure stable production without uneven stretching. Next, both edges of the longitudinally stretched sheet are gripped with tenter clips, and the sheet is stretched while being successively expanded in the direction perpendicular to the sheet flow while being heated with hot air to a temperature suitable for stretching. The transverse stretching ratio at this time is preferably set between 7 and 10 times, taking into consideration thickness fluctuations and productivity.

[0042] Next, while both edge portions of the transversely stretched film are held with tenter clips, the film is preferably heat-treated at a temperature in the range of 160°C to 170°C. The heat treatment time is preferably set to 2 to 10 seconds. Furthermore, while both edge portions are held with tenter clips, the film is preferably relaxed within a range of 1 to 10% of the width. Next, it is preferable to subject the surface of the surface layer (B) to a corona discharge treatment using a corona discharge treatment machine to increase the surface tension of the surface layer (B), thereby improving the anti-fogging properties.

[0043] The biaxially oriented polypropylene resin film of the present invention is preferably subjected to a surface treatment of the substrate layer (A) in order to improve printability, lamination properties, etc. Examples of surface treatment methods include corona discharge treatment, plasma treatment, flame treatment, acid treatment, etc. Corona discharge treatment, plasma treatment, and flame treatment are preferred because they allow continuous treatment and can be easily carried out before the winding step in the production process of this film.

[0044] (Film characteristics) The biaxially oriented polypropylene resin film of the present invention preferably has the following properties. Here, the longitudinal direction means the direction in which the film flows from the step of casting the raw resin composition to the step of winding the stretched film, and the width direction means the direction perpendicular to the flow direction. The same applies to the following properties.

[0045] (Young's modulus) The biaxially oriented polypropylene resin film of the present invention preferably has an initial Young's modulus in the longitudinal direction measured by the measurement method described below of 2.0 MPa or more, more preferably 2.2 MPa or more. The biaxially oriented polypropylene resin film of the present invention preferably has an initial Young's modulus in the width direction measured by the method described below of 4.0 MPa or more, more preferably 4.5 MPa or more.

[0046] (5% elongation stress) The biaxially oriented polypropylene resin film of the present invention preferably has a 5% elongation stress in the longitudinal direction measured by the measurement method described below of 40 MPa or more, more preferably 42 MPa or more. The biaxially oriented polypropylene resin film of the present invention preferably has a 5% elongation stress in the width direction measured by the below-mentioned method of 110 MPa or more, more preferably 110 MPa or more.

[0047] (breaking strength) The biaxially oriented polypropylene resin film of the present invention preferably has a longitudinal breaking strength measured by the below-mentioned method of 125 MPa or more, more preferably 130 MPa or more, and even more preferably 140 MPa or more. The biaxially oriented polypropylene resin film of the present invention preferably has a widthwise breaking strength of 330 MPa or more, more preferably 350 MPa or more, even more preferably 360 MPa or more, and particularly preferably 370 MPa or more, as measured by the method described below.

[0048] (breaking elongation) The biaxially oriented polypropylene resin film of the present invention preferably has a longitudinal breaking elongation measured by the method described below of 200% or more, more preferably 220% or more, and even more preferably 240% or more. The biaxially oriented polypropylene resin film of the present invention preferably has a breaking elongation in the width direction measured by the below-mentioned method of 40% or more, more preferably 45% or more.

[0049] (Thermal shrinkage rate) The biaxially oriented polypropylene resin film of the present invention preferably has a heat shrinkage rate in the longitudinal direction measured by the method described below of 3% or less, more preferably 2.5% or less. The biaxially oriented polypropylene resin film of the present invention preferably has a heat shrinkage rate in the width direction measured by the method described below of 2.5% or less, more preferably 2.0% or less, even more preferably 1.5% or less, and particularly preferably 1.0% or less.

[0050] (Hayes) The biaxially oriented polypropylene resin film of the present invention preferably has a haze of 10% or less, more preferably 7% or less, as measured by the method described below.

[0051] (glossiness) The biaxially oriented polypropylene resin film of the present invention preferably has a glossiness of 150° or less in both the longitudinal direction and the width direction, as measured by the method described below, and more preferably 140° or less.

[0052] (dynamic friction coefficient) The biaxially oriented polypropylene resin film of the present invention preferably has a dynamic friction coefficient of 0.4 or less, more preferably 0.3 or less, in both the longitudinal and transverse directions, as measured by the method described below.

[0053] (wetting tension) The biaxially oriented polypropylene resin film of the present invention preferably has a wet tension of 30 mN / m or more, more preferably 35 mN / m or more, as measured by the method described below.

[0054] (Surface resistivity) The biaxially oriented polypropylene resin film of the present invention preferably has a surface resistance in the longitudinal direction measured by the measurement method described below of 15 Log Ω or less, more preferably 13 Log Ω or less. The biaxially oriented polypropylene resin film of the present invention preferably has a surface resistance in the width direction measured by the measurement method described below of 15 Log Ω or less, more preferably 13 Log Ω or less.

[0055] (Water vapor permeability) The biaxially oriented polypropylene resin film of the present invention has a water vapor permeability of 7.0 (g / (m)) as measured by the method described below. 2 d)) or less, and more preferably 6.0 (g / (m 2 ·d)) or less, and more preferably 4.5 (g / (m2 ·d)) is below.

[0056] (Heat seal start temperature) The heat seal rise temperature of the surface layer (B) of the biaxially oriented polypropylene resin film of the present invention is preferably 125°C or lower. If it is 125°C or lower, heat sealing can be performed while maintaining sufficient heat seal strength even at a low heat seal temperature, allowing for high-speed operation during automatic packaging. In addition, the sealed portion has excellent sealing properties, and since heat sealing can be performed at a low temperature, the entire film is less likely to shrink and wrinkles are less likely to form in the heat seal portion, further improving the sealing properties of the heat seal portion. However, from the viewpoint of heat-cutting seal strength, it is preferable that the heat seal rise temperature of the surface layer (B) is 115°C or higher.

[0057] (130℃ heat seal strength) In order to prevent the contents from dropping out, the biaxially oriented polypropylene resin film of the present invention preferably has a heat seal strength of 3.5 N / 15 mm or more in the longitudinal direction and width direction at 130°C measured by the method described below, more preferably 4.0 N / 15 mm or more, and even more preferably 4.5 N / 15 mm or more.

[0058] (140℃ heat seal strength) In order to prevent the contents from dropping out, the biaxially oriented polypropylene resin film of the present invention preferably has a heat seal strength of 4.0 N / 15 mm or more in the longitudinal direction and width direction at 140°C measured by the measurement method described below, and more preferably 4.5 N / 15 mm or more.

[0059] (Ring Crush) The biaxially oriented polypropylene resin film of the present invention preferably has a ring crush strength in the longitudinal direction of 0.40 kg or more, as measured by the method described below. The biaxially oriented polypropylene resin film of the present invention preferably has a ring crush strength in the width direction of 0.50 kg or more, as measured by the method described below.

[0060] (suitable for automatic packaging) The biaxially oriented polypropylene resin film of the present invention is preferably evaluated as ◯ or Δ for automatic packaging suitability as determined by the measurement method described below, more preferably ◯.

[0061] (Fusing seal strength) The biaxially oriented polypropylene resin film of the present invention preferably has a welding seal strength measured by the below-mentioned method of 19 N / 15 mm or more, more preferably 20 N / 15 mm or more. [Example]

[0062] The present invention will be further described below by way of examples, but the present invention is not limited to the following examples as long as it does not deviate from the gist of the invention. The properties in this specification were evaluated by the following methods.

[0063] (1) DSC melting point The melting point was determined as the temperature of the maximum melting peak in the DSC curve of the polyolefin resin film obtained using a Shimadzu DSC-60 differential scanning calorimeter manufactured by Shimadzu Corporation. The starting temperature was 30°C, the heating rate was 5°C / min, and the end temperature was 180°C. Five samples were measured, and the average value was calculated.

[0064] (2) Mesopentad fraction The mesopentad fraction ([mmmm]%) of polypropylene resin is measured as follows: 13 The mesopentad fraction was calculated according to the method described in Zambelli et al., Macromolecules, Vol. 6, p. 925 (1973). 13 C-NMR measurements were performed using a BRUKER AVANCE500 by dissolving 200 mg of sample in an 8:2 mixture of o-dichlorobenzene-d4 and benzene-d6 at 135°C and then at 110°C. Five samples were measured and the average value was calculated. The mesopentad fraction of a polypropylene resin made of a mixture of a plurality of polypropylene resins is a value measured by the above method for the mixture.

[0065] (3) Melt flow rate (MFR) The melt flow rate (MFR) was measured in accordance with JIS K7210 at a temperature of 230°C and a load of 2.16 kgf. The isotactic mesopentad fraction of a polypropylene resin made of a mixture of a plurality of polypropylene resins is a value measured by the above method for the mixture.

[0066] (4) Proportion of α-olefin monomer-derived components (mol%) The contents of propylene, butene-1, and ethylene in propylene-ethylene copolymer, propylene-butene-1 copolymer, and propylene-ethylene-butene-1 copolymer were determined by the method described on pages 615-617 of the Polymer Analysis Handbook (published by Kinokuniya Shoten in 1995). 13 It can also be determined by IR spectroscopy using the method described in the section "(i) Random Copolymer" on page 256 of the same book. The value measured by the above method for the proportion of α-olefin monomer-derived components in a polypropylene-based resin consisting of a mixture of multiple polypropylene resins is used.

[0067] (5) Total film thickness The biaxially oriented polypropylene resin film was cut into 1cm x 1cm pieces, and cross-sectional samples were prepared using a microtome. These were then observed using a differential interference microscope, and the thicknesses of the base layer (A), surface layer (B), and total film layer were measured. Five points on the sample were measured, and the average value was calculated.

[0068] (6) Young's modulus, F5, tensile strength at break, tensile elongation at break A biaxially oriented polypropylene resin film was cut into a size of 200 mm in the longitudinal direction and 15 mm in the width direction, and the chuck width was set to 100 mm and set in a tensile tester (Instron 5965, dual column tabletop tester, manufactured by Instron Japan Co., Ltd.). A tensile test was carried out in an atmosphere of 23°C at a tensile speed of 200 mm / min in accordance with JIS K7127. From the obtained strain-stress curve, the Young's modulus was calculated from the slope of the linear portion from the start of elongation to 0.6% elongation. The stress at 5% elongation was taken as F5. The tensile strength at break and the tensile elongation at break were respectively the strength and elongation at the time the sample broke. Five samples were measured and the average value was calculated. A sample was cut to a size of 200 mm in the width direction and 15 mm in the longitudinal direction, and the same measurement was performed. The longitudinal direction here means the direction in which the film flows from the process of casting the raw material resin composition to the process of winding up the stretched film, and the width direction means the direction perpendicular to the flow direction. The same applies to the following measurements.

[0069] (7) Heat shrinkage rate The biaxially oriented polypropylene resin film was cut into a size of 200 mm in the longitudinal direction and 20 mm in the transverse direction, and was hung in a hot air oven at 120°C for 5 minutes, and the length after heating was measured in accordance with JIS Z1712. The difference between the length after heating and the original length before heating was measured as a percentage of the original length before heating, and the heat shrinkage rate was calculated. Five samples were measured and the average value was calculated. The biaxially oriented polypropylene resin film was cut into a size of 200 mm in the width direction and 20 mm in the length direction, and the same procedure was carried out.

[0070] (8) Hayes One side and the other side of the biaxially oriented polypropylene resin film were measured using a haze meter (NDH5000 manufactured by Nippon Denshoku Industries Co., Ltd.) at 23° C. in accordance with JIS K7105, and the average value of these values was calculated.

[0071] (9) Glossiness The 60-degree specular gloss in the longitudinal direction of the film was measured on one side and the other side of the biaxially oriented polypropylene resin film using a glossmeter (VG-1D manufactured by Nippon Denshoku Kogyo Co., Ltd.) in accordance with JIS K7105 5.2 Gloss: 2004. The average value of these values was calculated.

[0072] (10) Coefficient of dynamic friction Two biaxially oriented polypropylene resin films were placed with the surface layer (B) side facing each other, and the measurement was performed in accordance with JIS K7125 at 23° C. Five sets of samples were measured, and the average value was calculated.

[0073] (11) Wetting tension (mN / m) A biaxially oriented polypropylene resin film was cut into a size of 297 mm in the longitudinal direction and 210 mm in the transverse direction, and after aging for 24 hours at a temperature of 23°C and a relative humidity of 50%, the corona-treated surface was measured in a laboratory atmosphere at a temperature of 23°C and a relative humidity of 50% according to the following procedure in accordance with JIS K7100. Place the test specimen on the hand coater substrate, drop a few drops of the test mixture onto the specimen, and immediately spread it by pulling the wire bar. If using a cotton swab or brush to spread the test mixture, the liquid should be at least 6 cm 2 Spread the liquid quickly over the above area. The amount of liquid should be enough to form a thin layer without creating any puddles. The wetting tension is determined by observing the liquid film of the test mixture in a bright place and checking the state of the liquid film after 3 seconds. If the liquid film remains in the same state as when it was applied for 3 seconds or more without breaking, it is considered to be wet. If the wetting persists for more than 3 seconds, proceed to the mixture with the next highest surface tension. Conversely, if the liquid film breaks in 3 seconds or less, proceed to the next mixed liquid with a lower surface tension. Repeat this process to select a mixed liquid that can accurately wet the surface of the test piece in 3 seconds. Use a new cotton swab for each test. Brushes or wire burrs should be cleaned with methanol and dried after each use, as residual liquid will change composition and surface tension upon evaporation. The procedure is repeated at least three times to select a mixture that can wet the corona-treated surface in 3 seconds, and the surface tension of the mixture thus selected is reported as the wetting tension of the film.

[0074] (12) Surface resistivity (LogΩ) The biaxially oriented polypropylene resin film was cut into a size of 100 mm in the longitudinal direction and 100 mm in the transverse direction, and the film was aged at 23°C for 24 hours, after which the corona-treated surface of the film was measured in accordance with JIS K6911.

[0075] (13) Water vapor permeability The biaxially oriented polypropylene resin film was cut into a length of 100 mm and a width of 100 mm, and the water vapor transmission rate was measured using a water vapor transmission rate measuring device (PERMATRAN-W3 / 33 manufactured by MOCON) with the corona-treated side of the film facing the high humidity side at a temperature of 37.8°C and a humidity of 90%. Three samples were measured, and the average value was calculated.

[0076] (14) Heat seal rise temperature A biaxially oriented polypropylene resin film was cut into a length of 20 cm in the longitudinal direction and 5 cm in the width direction. The two cut-out films were stacked with the corona-treated surface layers (B) facing each other, and five heat seal bars with a sealing surface of 3 cm in the longitudinal direction and 1 cm in the transverse direction were heat-sealed simultaneously using a thermal gradient tester (manufactured by Toyo Seiki Co., Ltd.), with a longitudinal spacing of 1 cm between each seal bar. The temperatures of the five heat seal bars were set at 5°C intervals from 80°C. The heat sealing pressure was 1 kg / cm. 2 The time was 1 second. The long axis of the heat seal bar was parallel to the longitudinal direction of the film and positioned at the center of the film in the width direction. The distance between the end of the short axis of the sample and the seal bar was 0.5 cm. Similarly, heat sealing was carried out with five heat seal bars, with the temperature set at 5°C intervals from 105°C. A 15 mm section was cut from the center of each seal area (3 cm x 1 cm) in the longitudinal direction across the width, attached to the upper and lower chucks of a tensile testing machine (Instron 5965 dual column benchtop testing machine), and the heat seal strength of each was measured when pulled at a pulling speed of 200 mm / min (unit: N / 15 mm). A linear graph was drawn with the temperature on the horizontal axis and the heat seal strength on the vertical axis, and the temperature at which the heat seal strength reached 1 N / 15 mm was taken as the heat seal start temperature. This was repeated three times and the average value was calculated.

[0077] (15) Heat seal strength A biaxially oriented polypropylene resin film was cut into a length of 297 mm in the longitudinal direction and 210 mm in the transverse direction. The two cut-out films were stacked with the corona-treated surface layers (B) facing each other, and heat-sealed using a heat-sealing bar with a sealing surface of 15 mm in the longitudinal direction and 30 mm in the transverse direction using a thermal gradient tester (manufactured by Toyo Seiki Co., Ltd.). The temperature of the heat-sealing bar was set to 130°C. The heat-sealing pressure was 1 kg / cm. 2 The time was 1 second. The long axis direction of the heat seal bar was parallel to the longitudinal direction of the film and positioned at the center of the film in the width direction. Three samples were measured and the average value was calculated. The same procedure was carried out at 140°C.

[0078] (16) Welding seal strength Using a welding sealer (Kyoei Printing Machinery Materials Co., Ltd.: PP500 type), welding seal pouches were made from biaxially oriented polypropylene resin film with the corona treatment on the inside. conditions: Cutting edge: 60° cutting edge angle Sealing temperature: 370℃ Shot rate: 120 bags / min Bag shape: 20 cm vertically, 20 cm horizontally, with the film's horizontal direction as the vertical direction. The weld-sealed portion at the bottom of the above weld-sealed bag was cut out lengthwise in a width of 15 mm horizontally, and with slack removed, both ends were held in the gripping parts of a tensile tester (Instron 5965 dual column benchtop tester) with a gripping distance of 200 mm and pulled at a pulling rate of 200 mm / min. The strength at which the seal broke was taken as the weld-seal strength (N / 15 mm). Five samples were measured and the average value was calculated.

[0079] (17) Ring Crush A biaxially oriented polypropylene resin film was cut into a length of 152 mm in the longitudinal direction and 12.7 mm in the transverse direction. An attachment spacer was set on the sample table of a digital ring crush tester (manufactured by Tester Sangyo Co., Ltd.) according to the thickness of the film sample, and inserted along the circumference so that the long axis was in the circumferential direction. The maximum load when compressing the compression plate at 23°C at a descending speed of 12 mm / min. was taken as the ring crush measurement value. Three samples were measured, and the average value was calculated. A biaxially oriented polypropylene resin film was cut into a piece 152 mm in the width direction and 12.7 mm in the length direction, and the same procedure was carried out.

[0080] (18) Automatic packaging suitability Using a horizontal pillow bag making machine (Kyoei Printing Machinery Materials Co., Ltd.: PP500 type), pillow packages were made from biaxially oriented polypropylene resin film with the corona treatment facing inward. conditions: Cutting edge: 60° cutting edge angle Sealing temperature: 370℃ Shot rate: 120 bags / min Bag shape: 20 cm vertically, 20 cm horizontally, with the width of the film as the vertical direction. The suitability for automatic packaging was evaluated on the following three-point scale based on the smoothness of the film during transport and the degree of wrinkles in the bagged products. ○: Good film transportability, no wrinkles in the bag △: Either film transportability or wrinkles in the bag were poor ×: Poor film transportability and wrinkles in the bag

[0081] The polypropylene resins constituting the layers used in the following Examples and Comparative Examples are as follows: [PP-1]: Propylene homopolymer: "FL203D" manufactured by Japan Polypropylene Corporation, MFR: 3 g / 10 min, melting point: 160.6 °C, mesopentad fraction: 94.8% [PP-2]: Propylene homopolymer: "FY6H" manufactured by Japan Polypropylene Corporation, MFR: 1.9 g / 10 min, melting point: 163°C, mesopentad fraction: 98.9% [PP-3]: Propylene homopolymer: "FS2012" manufactured by Sumitomo Chemical Co., Ltd., MFR: 2.5 g / 10 min, melting point: 163°C, mesopentad fraction: 98.7% [PP-4]: Propylene-ethylene random copolymer: "FS2011DG3" manufactured by Sumitomo Chemical Co., Ltd., ethylene content: 0.6 mol%, MFR: 2.7 g / 10 min, melting point: 158°C, mesopentad fraction: 97.0% [PP-5]: Propylene-ethylene-butene random copolymer: "FSX66E8" manufactured by Sumitomo Chemical Co., Ltd., ethylene content: 2.5 mol%, butene content: 7 mol%, MFR: 3.1 g / 10 min, melting point: 133°C [PP-6]: Propylene-butene-1 copolymer: "SP3731" manufactured by Sumitomo Chemical Co., Ltd., butene content: 12 mol%, MFR: 8.5 g / 10 min, melting point: 130°C [PP-7]: Propylene-butene-1 copolymer: "SPX38F4" manufactured by Sumitomo Chemical Co., Ltd., butene content: 25 mol%, MFR: 8.5 g / 10 min, melting point: 128 °C

[0082] Example 1 The resin used for the base layer (A) was a mixture of 57% by weight of [PP-1] and 43% by weight of [PP-2]. The resin used for the surface layer (B) was a mixture of 70% by weight of [PP-5] and 30% by weight of [PP-6]. Using two melt extruders, the base layer (A) was melt-extruded from the first extruder at a resin temperature of 280 ° C., and the surface layer (B)-forming resin was melt-extruded from the second extruder at a resin temperature of 250 ° C. The layers were laminated and extruded in a T-die in the order of surface layer (B) / base layer (A) / surface layer (B) from the chill roll contact surface, and then cooled and solidified with a cooling roll at 30 ° C. to obtain an unstretched sheet. Subsequently, the sheet was stretched 4.5 times in the machine direction using the difference in peripheral speed between metal rolls heated to 130 ° C., and then introduced into a tenter stretching machine and stretched 9.5 times in the width direction. The preheating section temperature of the tenter stretching machine was 175 ° C., and the stretching section temperature was 165 ° C. After further stretching in the width direction, heat setting was performed at 165°C. Next, the surface of the surface layer (B) (the surface not in contact with the chill roll) was subjected to corona discharge treatment using a corona discharge treatment machine manufactured by Kasuga Electric Co., Ltd., and then wound up with a film winder to obtain a biaxially oriented polypropylene resin film. The final film thickness was 35 μm. The thickness ratio of each layer was surface layer (B) / base layer (A) / surface layer (B) = 0.8 μm / 33.4 μm / 0.8 μm. The biaxially oriented polypropylene resin film obtained satisfied the requirements of the present invention, exhibiting sufficient heat-seal strength and ultimate strength at low temperatures, and exhibiting both suitability for automatic packaging and weld-cutting and sealing. The film composition and physical properties are shown in Table 1.

[0083] Example 2 A biaxially oriented polypropylene resin film was obtained in the same manner as in Example 1, except that the thickness ratio of each layer was surface layer (B) / base layer (A) / surface layer (B) = 1.5 μm / 32.0 μm / 1.5 μm. The obtained biaxially oriented polypropylene resin film had sufficient heat seal strength and ultimate strength at low temperatures, as in Example 1, and was suitable for both automatic packaging and welding sealing. The film composition and physical properties are shown in Table 1.

[0084] Example 3 A biaxially oriented polypropylene resin film was obtained in the same manner as in Example 1, except that the resin composition of the base layer (A) was 47% by weight of [PP-1] and 53% by weight of [PP-2]. The obtained biaxially oriented polypropylene resin film had sufficient heat seal strength and ultimate strength at low temperatures, as in Example 1, and was suitable for both automatic packaging and heat-cutting and sealing. The film composition and physical properties are shown in Table 1.

[0085] Example 4 A biaxially oriented polypropylene resin film was obtained in the same manner as in Example 1, except that the resin composition of the base layer (A) was 67% by weight of [PP-1] and 33% by weight of [PP-2]. The obtained biaxially oriented polypropylene resin film had sufficient heat seal strength and ultimate strength at low temperatures, as in Example 1, and was suitable for both automatic packaging and welding sealing. The film composition and physical properties are shown in Table 1.

[0086] Example 5 A biaxially oriented polypropylene resin film was obtained in the same manner as in Example 1, except that the resin composition of the base layer (A) was 100% by weight of [PP-3]. The obtained biaxially oriented polypropylene resin film had sufficient heat seal strength and ultimate strength at low temperatures, as in Example 1, and was suitable for both automatic packaging and welding sealing. The film composition and physical properties are shown in Table 1.

[0087] Example 6 The resin used for the base layer (A) was a mixture of [PP-1] with 0.16 wt% glycerin monostearate (TB-123, Matsumoto Yushi Pharmaceutical Co., Ltd.), 0.2 wt% polyoxyethylene (2) stearylamine (TB-12, Matsumoto Yushi Pharmaceutical Co., Ltd.), and 0.6 wt% polyoxyethylene (2) stearylamine monostearate (Elex 334, Matsumoto Yushi Pharmaceutical Co., Ltd.) ([PP-8]) in a ratio of 57 wt% and 43 wt% [PP-2]. A biaxially oriented polypropylene resin film was obtained in the same manner as in Example 1, except that the resin for the sealing layer (B) was a mixture of 70 wt% [PP-9] (PP-5) to which 0.50 wt% of glycerin monostearate (TB-123, Matsumoto Yushi Pharmaceutical Co., Ltd.) had been added and 25 wt% [PP-6]. The obtained biaxially oriented polypropylene resin film satisfied the requirements of the present invention, having sufficient heat-seal strength and ultimate strength at low temperatures, and was suitable for both automatic packaging and heat-cutting and sealing. The film composition and physical properties are shown in Table 1.

[0088] (Comparative Example 1) The resin used for the base layer (A) was 100% by weight of [PP-4], and the resin used for the surface layer (B) was a mixture of 82% by weight of [PP-5] and 18% by weight of [PP-6]. Using two melt extruders, the base layer (A) was melt-extruded from the first extruder at a resin temperature of 280 ° C., and the surface layer (B)-forming resin was melt-extruded from the second extruder at a resin temperature of 250 ° C. The layers were laminated and extruded in a T-die in the order of surface layer (B) / base layer (A) / surface layer (B) from the chill roll contact surface, and then cooled and solidified with a cooling roll at 30 ° C. to obtain an unstretched sheet. Subsequently, the sheet was stretched 4.5 times in the machine direction using the peripheral speed difference between metal rolls heated to 130 ° C., and then introduced into a tenter stretching machine and stretched 9.5 times in the width direction. The preheating section temperature of the tenter stretching machine was 168 ° C., and the stretching section temperature was 158 ° C. Furthermore, in the latter half of the tenter stretching machine, heat setting was performed at 165°C, and then the surface of the surface layer (B) was subjected to corona discharge treatment using a corona discharge treatment machine manufactured by Kasuga Electric Co., Ltd., and the film was wound up using a film winder to obtain a biaxially oriented polypropylene resin film that could be automatically packaged. The final film thickness was 35 μm. The thickness ratio of each layer was surface layer (B) / base layer (A) / surface layer (B) = 1.1 μm / 32.8 μm / 1.1 μm. The biaxially oriented polypropylene resin film obtained had a low initial Young's modulus and poor stiffness. The film composition and physical properties are shown in Table 2.

[0089] (Comparative Example 2) A laminated film was obtained in the same manner as in Comparative Example 1, except that a mixture of 70% by weight of [PP-5] and 30% by weight of [PP-6] was used as the resin for the surface layer (B). The obtained biaxially oriented polypropylene resin film had poor weld-sealability. The film composition and physical properties are shown in Table 2.

[0090] (Comparative Example 3) The resin used for the base layer (A) was a mixture of 57% by weight of [PP-1] and 43% by weight of [PP-2]. The resin used for the surface layer (B) was a mixture of 70% by weight of [PP-5] and 30% by weight of [PP-6]. Using two melt extruders, the base layer (A) was melt-extruded from the first extruder at a resin temperature of 280 ° C., and the surface layer (B)-forming resin was melt-extruded from the second extruder at a resin temperature of 250 ° C. The layers were laminated and extruded in a T-die in the order of surface layer (B) / base layer (A) / surface layer (B) from the chill roll contact surface, and then cooled and solidified with a cooling roll at 30 ° C. to obtain an unstretched sheet. Subsequently, the sheet was stretched 4.5 times in the machine direction using the difference in peripheral speed between metal rolls heated to 120 ° C., and then introduced into a tenter stretching machine and stretched 9.5 times in the width direction. The preheating zone temperature of the tenter stretching machine was 172 ° C., and the stretching zone temperature was 159 ° C. Furthermore, in the latter half of the tenter stretching machine, heat setting was performed at 165°C, and then the surface of the surface layer (B) was subjected to corona discharge treatment using a corona discharge treatment machine manufactured by Kasuga Electric Co., Ltd., and the film was wound up using a film winder to obtain a biaxially oriented polypropylene resin film that could be automatically packaged. The final film thickness was 35 μm. The thickness ratio of each layer was surface layer (B) / base layer (A) / surface layer (B) = 2.0 μm / 31.0 μm / 2.0 μm. The biaxially oriented polypropylene resin film obtained was inferior in low-temperature heat sealing suitability. The film composition and physical properties are shown in Table 2.

[0091] Comparative Example 4 The resin used for the base layer (A) was 100% by weight of [PP-4], and the resin used for the surface layer (B) was a mixture of 20% by weight of [PP-5] and 80% by weight of [PP-7]. Using two melt extruders, the base layer (A) was melt-extruded from the first extruder at a resin temperature of 280 ° C., and the surface layer (B)-forming resin was melt-extruded from the second extruder at a resin temperature of 250 ° C. The layers were laminated and extruded in a T-die in the order of surface layer (B) / base layer (A) / surface layer (B) from the chill roll contact surface, and then cooled and solidified with a cooling roll at 30 ° C. to obtain an unstretched sheet. Subsequently, the sheet was stretched 4.5 times in the machine direction using the difference in peripheral speed between metal rolls heated to 120 ° C., and then introduced into a tenter stretching machine and stretched 9.5 times in the width direction. The preheating zone temperature of the tenter stretching machine was 172 ° C., and the stretching zone temperature was 159 ° C. Furthermore, in the latter half of the tenter stretching machine, heat setting was performed at 165°C, and then the surface of the surface layer (B) was subjected to corona discharge treatment using a corona discharge treatment machine manufactured by Kasuga Electric Co., Ltd., and the film was wound up using a film winder to obtain a biaxially oriented polypropylene resin film that could be automatically packaged. The final film thickness was 35 μm. The thickness ratio of each layer was surface layer (B) / base layer (A) / surface layer (B) = 1.1 μm / 32.8 μm / 1.1 μm. The biaxially oriented polypropylene resin film obtained was inferior in low-temperature heat sealing and heat-cutting sealing properties. The film composition and physical properties are shown in Table 2.

[0092] (Comparative Example 5) A laminated film was obtained in the same manner as in Example 1, except that 100% by weight of [PP-1] was used. The obtained biaxially oriented polypropylene resin film had poor weld-sealing suitability. The film composition and physical properties are shown in Table 2.

[0093] [Table 1]

[0094] [Table 2] [Industrial Applicability]

[0095] The highly rigid polypropylene laminate film of the present invention is suitable for packaging fruits and vegetables, contributes to the appearance of the fruit and vegetables when they are packaged and displayed, contributes to environmental conservation by reducing the thickness of the film, and is therefore a major contributor to the industry.

Claims

1. A biaxially oriented polypropylene resin film having a base layer (A) made of a polypropylene resin composition and surface layers (B) made of polypropylene resin compositions on both sides of the base layer (A), and satisfying the following conditions a) to d): a) The polypropylene resin composition constituting the base layer (A) has an overall mesopentad fraction of 95.0% or more and 99.5% or less, contains a plurality of polypropylene homopolymers, and the polypropylene homopolymer having the highest mesopentad fraction has a mesopentad fraction of 97.5% or more, and the polypropylene homopolymer having the lowest mesopentad fraction has a mesopentad fraction of 96.5% or less. b) The proportion of the α-olefin monomer-derived component relative to the total of the propylene monomer-derived component and the α-olefin monomer-derived component in the entire polypropylene-based resin composition constituting the base layer (A) is 0.2 mol % or less. c) The proportion of the butene-1 monomer-derived component relative to the total of the propylene monomer-derived component and the α-olefin monomer-derived component in the polypropylene-based resin composition constituting the surface layer (B) is 5 mol % or more and 10 mol % or less. d) The thickness of the biaxially oriented polypropylene resin film is 60 μm or less, and the ratio of the thickness of the surface layer (B) to the total thickness of the biaxially oriented polypropylene resin film is 3% or more and 10% or less.

2. A biaxially oriented polypropylene resin film having a base layer (A) made of a polypropylene resin composition and surface layers (B) made of polypropylene resin compositions on both sides of the base layer (A), and satisfying the following conditions A) to D): A) The polypropylene resin composition constituting the base layer (A) has a polypropylene resin with the lowest DSC melting point that has a melting point peak temperature of 160°C or higher, contains a plurality of polypropylene homopolymers, and the polypropylene homopolymer with the highest mesopentad fraction has a mesopentad fraction of 97.5% or higher, and the polypropylene homopolymer with the lowest mesopentad fraction has a mesopentad fraction of 96.5% or lower. B) The proportion of the α-olefin monomer-derived component relative to the total of the propylene monomer-derived component and the α-olefin monomer-derived component in the entire polypropylene-based resin composition constituting the base layer (A) is 0.2 mol % or less. C) The proportion of the butene-1 monomer-derived component relative to the total of the propylene monomer-derived component and the α-olefin monomer-derived component in the polypropylene-based resin composition constituting the surface layer (B) is 5 mol % or more and 10 mol % or less. D) The thickness of the biaxially oriented polypropylene resin film is 60 μm or less, and the ratio of the thickness of the surface layer (B) to the total thickness of the biaxially oriented polypropylene resin film is 3% or more and 10% or less.

3. 3. The biaxially oriented polypropylene resin film according to claim 1, wherein the melt flow rate (MFR) of the entire polypropylene resin composition constituting the base layer (A) is 2.0 g / 10 min or more and 4.5 g / 10 min or less.

4. The biaxially oriented polypropylene resin film according to any one of claims 1 to 3, wherein the polypropylene resin composition constituting the base layer (A) contains at least one polymer selected from the group consisting of propylene homopolymer, propylene-ethylene copolymer, propylene-butene-1 copolymer, propylene-ethylene-butene-1 copolymer, and propylene-pentene-1 copolymer.

5. The biaxially oriented polypropylene resin film according to any one of claims 1 to 4, wherein the Young's modulus in the longitudinal direction of the biaxially oriented polypropylene resin film is 2.0 GPa or more and the Young's modulus in the width direction is 4.0 GPa or more.

6. The biaxially oriented polypropylene resin film according to any one of claims 1 to 5, wherein the biaxially oriented polypropylene resin film has a welding seal strength of 18 N / 15 mm or more.

7. The biaxially oriented polypropylene resin film according to any one of claims 1 to 6, wherein the heat seal ultimate strength of the biaxially oriented polypropylene resin film is 3 N / 15 mm or more.

8. A packaging product using the biaxially oriented polypropylene resin film according to any one of claims 1 to 7.

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