Biaxially oriented polypropylene resin film and packaging using the same

Abstract

The present invention provides a biaxially oriented polypropylene resin film that is suitable for automated packaging systems, satisfies both the heat seal strength after automated packaging and the heat seal strength in the heat-sealing method, and exhibits superior anti-fogging, anti-drip, slipperiness, and anti-blocking properties. [Solution] A biaxially oriented polypropylene resin film having a base layer (A) made of a resin composition containing a polypropylene resin and a polyethylene resin, a seal layer (B) made of a polypropylene resin composition mainly composed of a propylene-butene-1 copolymer on one side of the base layer (A), and a surface layer (C) on the side of the base layer (A) opposite to the seal layer (B), and satisfying the following conditions a) to d). a) The melt flow rate of the polyethylene resin constituting the base layer (A) is 1.5 g / 10 min or more and 10 g / 10 min or less at 190°C, and its density is 0.910 g / cm³. 3 More than 0.930g / cm 3 The following is true, and it is contained in an amount of 1% to 20% by weight relative to the total of 100% of the polypropylene resin and polyethylene resin that constitute the base layer (A). b) The thickness of the sealing layer (B) is 1 μm or less. c) The polypropylene composition constituting the sealing layer (B) contains an anti-fogging agent in an amount of 0.1% to 1.0% by weight. d) The thickness of the surface layer (C) is 1 μm or less.

Description

[Technical Field]

[0001] The present invention relates to a biaxially oriented polypropylene resin film and packaging using the same, and more particularly to fresh produce consisting of plants such as vegetables, fruits, and flowers that require high freshness, which have heat sealability and anti-fogging effect (hereinafter referred to in this specification) This invention relates to a biaxially oriented polypropylene resin film suitable for packaging fruits and vegetables (which are referred to as fresh produce) and a packaging body using the same. [Background technology]

[0002] Conventionally, biaxially oriented polypropylene resin films have been widely used in packaging fields such as food packaging and textile packaging due to their excellent optical properties, mechanical properties, and packaging suitability. In particular, anti-fog films are widely used for packaging fresh produce such as vegetables.

[0003] In particular, in the packaging of fresh produce, the recent decline in the agricultural population has led to a demand for labor-saving solutions in farming, and automated packaging methods are becoming increasingly popular. The so-called pillow packaging method is used for automated packaging of fresh produce, and it allows for the simultaneous execution of the heat-sealing bag-making process and the filling of contents.

[0004] For applications in automated packaging systems, a propylene-ethylene-butene copolymer with a melting point 10-90°C lower than that of the outer layer is melted onto an outer layer consisting of a biaxially oriented film made primarily of crystalline polypropylene resin. Laminated films are disclosed (see, for example, Patent Document 1).

[0005] A packaging film has been disclosed that is suitable for automated packaging systems and has excellent heat seal strength, comprising a laminate of two or more layers having a base layer mainly composed of a polypropylene resin and a heat seal layer mainly composed of a polyolefin resin using propylene-butene-1 copolymer and propylene-ethylene-butene-1 copolymer (see, for example, Patent Document 2).

[0006] Furthermore, a packaging film that can be used for both automated packaging methods such as pillow packaging and heat-sealed packaging has been disclosed (see, for example, Patent Document 3). However, even with these conventional heat-sealable polypropylene laminated films, there was a need for further improvements in anti-fogging properties, particularly in anti-drip properties, slipperiness, and anti-blocking properties.

[0007] A heat-sealable biaxially oriented polypropylene film containing plant-derived polyethylene has also been disclosed (see, for example, Patent Document 4). [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Patent No. 3104166 [Patent Document 2] Patent No. 4385443 [Patent Document 3] Japanese Patent Publication No. 2019-166830 [Patent Document 4] Japanese Patent Publication No. 2019-6461 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] This invention was made against the backdrop of the problems of the prior art. Specifically, the object of this invention is to provide a biaxially oriented polypropylene resin film that is suitable for automated packaging systems, satisfies both the heat seal strength after automated packaging and the heat seal strength in the heat-sealing method, and has superior drip resistance, slipperiness, and blocking resistance. [Means for solving the problem]

[0010] In view of the above problems, the present invention has been diligently studied and found that by specifying the properties of the polypropylene resin and polyethylene resin constituting the base layer (A), their respective ratios, and the properties of the seal layer (B) and surface layer (C) within a specific range, and by specifying the properties of the seal layer (B) and surface layer (C), the present invention has been able to obtain a polypropylene laminated film that is particularly excellent in drip resistance, slipperiness, and blocking resistance, and also possesses both smear sealing and heat sealing properties. In other words, the present invention has the following configuration.

[0011] 1. A biaxially oriented polypropylene resin film having a base layer (A) made of a resin composition containing a polypropylene resin and a polyethylene resin, a seal layer (B) made of a polypropylene resin composition mainly composed of a propylene-butene-1 copolymer on one side of the base layer (A), and a surface layer (C) on the side of the base layer (A) opposite to the seal layer (B), and satisfying the following conditions a) to d). a) The melt flow rate of the polyethylene resin constituting the base layer (A) is 1.5 g / 10 min or more and 10 g / 10 min or less at 190°C, and its density is 0.910 g / cm³. 3 More than 0.930g / cm 3 The following is true, and it is contained in an amount of 1% to 20% by weight relative to the total weight of the polypropylene resin and polyethylene resin constituting the base layer (A) (100% by weight). b) The thickness of the sealing layer (B) is 1 μm or less. c) The polypropylene composition constituting the sealing layer (B) contains an anti-fogging agent in an amount of 0.1% to 1.0% by weight. d) The surface roughness SRa (arithmetic mean roughness) of the surface layer (C) is 0.018 μm or greater.

[0012] 2. The biaxially oriented polypropylene resin film according to 1, wherein the melting point of the propylene-butene-1 copolymer, or a plurality of propylene-butene-1 copolymers, is in the range of 120 to 130°C.

[0013] 3. The biaxially oriented polypropylene-based resin film according to 1. or 2., wherein the content of the propylene-butene-1 copolymer or a plurality of propylene-butene-1 copolymers is in the range of 50% by weight or more.

[0014] 4. The biaxially oriented polypropylene-based resin film according to any one of 1. to 3., wherein the thickness of the seal layer (B) is 1.5% or more and 4% or less with respect to the total thickness of the film.

[0015] 5. The biaxially oriented polypropylene-based resin film according to any one of 1. to 4., wherein the base material layer (A) is made of a polypropylene-based resin composition mainly composed of at least one polypropylene-based resin selected from the group consisting of an isotactic propylene homopolymer, a propylene-ethylene copolymer, a propylene-butene-1 copolymer, a propylene-ethylene-butene-1 copolymer, or a propylene-pentene copolymer.

[0016] 6. The biaxially oriented polypropylene-based resin film according to any one of 1. to 5., wherein the surface layer (C) is made of a resin composition mainly composed of at least one polypropylene-based resin selected from the group consisting of a propylene-ethylene-butene-1 copolymer, a propylene-butene-1 copolymer, or a propylene-ethylene copolymer.

[0017] 7. The biaxially oriented polypropylene-based resin film according to any one of 1. to 6., wherein the melting point of the polypropylene-based resin constituting the surface layer (C) is in the range of 130 to 140°C.

[0018] 8. The biaxially oriented polypropylene-based resin film according to any one of 1. to 7., wherein the thickness of the surface layer (C) is 1.5% or more and 4% or less with respect to the total thickness of the film.

[0019] 9. The polypropylene-based laminated film according to any one of 1. to 8., wherein the heat seal strength when the seal layers (B) of the biaxially oriented polypropylene-based resin film are heat-sealed at 120°C is 3.5 N / 15 mm or more.

[0020] 10. A polypropylene laminated film according to any one of 1 to 9, wherein the blocking value measured by combining the sealing layer (B) and the surface layer (C) of the biaxially oriented polypropylene resin film is 110 mN / 200 mm or less.

[0021] 11. A polypropylene laminated film according to any one of 1. to 10., wherein the coefficient of friction between the surface layers (C) of the biaxially oriented polypropylene resin film is 0.35 or less.

[0022] A packaging material using a biaxially oriented polypropylene resin film as described in any of sections 12.1 to 12.11. [Effects of the Invention]

[0023] The biaxially oriented polypropylene resin film of the present invention exhibits excellent slipperiness and blocking resistance, satisfies both the heat seal strength after automatic packaging and the heat seal strength in the heat-sealing method, and reduces fogging due to water droplets after vegetable packaging, making it suitable for preserving the freshness of vegetables. Modes for carrying out the invention

[0024] The biaxially oriented polypropylene resin film of the present invention comprises a base layer (A) made of a resin composition containing a polypropylene resin and a polyethylene resin, a seal layer (B) made of a resin composition mainly composed of a propylene-butene-1 copolymer on one side of the base layer (A), and a surface layer (C) on the side of the base layer (A) opposite to the seal layer (B).

[0025] (Base material layer (A)) [Polypropylene resin] In the present invention, the resin composition constituting the base layer (A) includes a polypropylene resin. The polypropylene resin preferably consists of at least one resin selected from the group consisting of n-heptane-insoluble isotactic propylene homopolymers and copolymers of propylene and other α-olefins containing 70 mol% or more of propylene. n-heptane insolubility is an indicator of the crystallinity of polypropylene and also indicates its safety when used for food packaging. In this invention, it is preferable to use polypropylene that conforms to the n-heptane insolubility specified in Ministry of Health and Welfare Notification No. 20 of February 1982 (eluted content of 150 ppm or less when extracted at 25°C for 60 minutes [30 ppm or less for usage temperatures exceeding 100°C]).

[0026] When using a mixture of an isotactic propylene homopolymer and a copolymer of propylene containing 70 mol% or more of propylene and other α-olefins, it is desirable that the content of the copolymer of propylene containing 70 mol% or more of propylene and other α-olefins relative to the entire resin composition used in the substrate layer (A) be 50% by weight or more. More preferably, it is 70% by weight or more, and even more preferably 90% by weight or more.

[0027] The α-olefin copolymer component of the copolymer of propylene and other α-olefins is preferably an α-olefin having 2 to 8 carbon atoms, such as ethylene, butene-1, pentene-1, hexene-1, or 4-methyl-1-pentene. Here, the copolymer is preferably a random or block copolymer obtained by polymerizing propylene with one or more of the α-olefins exemplified above, and is preferably a propylene-ethylene copolymer, propylene-butene-1 copolymer, propylene-ethylene-butene-1 copolymer, or propylene-pentene copolymer. The ratio of the α-olefin monomer-derived component to the total of the propylene monomer-derived component and the α-olefin monomer-derived component of the polypropylene resin used in the base layer (A) is preferably 0.3 mol% or more from the viewpoint of anti-fogging, and especially anti-drip properties. This makes it possible to achieve a high level of both rigidity and heat-sealing properties. It is more preferably 0.4 mol% or more, and even more preferably 0.5 mol% or more. The melting point of the polypropylene resin used in the base layer (A) is preferably 156°C or higher. The melting point is measured by the method described in the examples below. A melting point of 156°C or higher makes it easier to transport the film more smoothly during automated packaging and reduces the likelihood of wrinkles in the resulting bags. In the polypropylene resin used in the base layer (A), the proportion of the α-olefin monomer-derived component to the total of the propylene monomer-derived component and the α-olefin monomer-derived component is preferably 1.0 mol% or less from the viewpoint of melting point. This makes it easier to obtain melt-seal properties. It is more preferably 0.9 mol% or less, and even more preferably 0.8 mol% or more. Furthermore, the melt flow rate (MFR) can be exemplified in the range of 0.1 to 100 g / 10 min, preferably 0.5 to 20 g / 10 min, and more preferably 1.0 to 10 g / 10 min.

[0028] [Polyethylene resin] In the present invention, the resin composition constituting the base layer (A) includes a polyethylene-based resin. The polyethylene-based resin is a resin mainly composed of ethylene, and in addition to being able to use any of the ethylene homopolymers such as high-pressure low-density polyethylene, linear low-density polyethylene, medium-density polyethylene and high-density polyethylene, it is also possible to use crystalline, low-crystalline or amorphous random or block copolymers with monomers such as propylene, butene-1, pentene-1, hexene-1, 3-methylbutene-1, 4-methylpentene-1, octene-1, vinyl acetate, (meth)acrylic acid, and (meth)acrylic acid esters, or mixtures thereof.

[0029] The polyethylene resin is preferably contained in an amount of 1% by weight or more and 20% by weight or less, based on 100% by weight in total of the polypropylene resin and the polyethylene resin that constitute the base material layer (A). When it is 1% by weight or more, the heat seal strength, slipperiness, blocking resistance, and drip-proof property are improved. More preferably, it is 5% by weight or more, and still more preferably, it is 8% by weight. When it is 20% by weight or less, it is easy to maintain rigidity. More preferably, it is 18% by weight or less, and still more preferably, it is 15% by weight or less as follows.

[0030] Regarding the melting point of the polyethylene resin, from the viewpoints of heat resistance, transparency, mechanical properties, and film-forming property, it is preferably in the range of 100°C or more and 135°C or less, more preferably in the range of 105°C or more and 130°C or less. Also, regarding the density, it is measured according to JIS K7112, and it is preferably 0.90 g / cm 3 or more and 0.94 g / cm 3 or less, more preferably 0.91 g / cm 3 or more and 0.94 g / cm 3 or less.

[0031] Also, regarding the density, it is measured according to JIS K7112, and it is preferably 0.90 g / cm 3 or more and 0.94 g / cm 3 or less, more preferably 0.91 g / cm 3 or more and 0.94 g / cm 3 or less. The melt flow rate (MFR) of the polyethylene resin measured under the conditions of 190°C and a load of 2.16 kg in accordance with ASTM D1238 is preferably 0.5 g / 10 min or more, more preferably 1 g / 10 min or more, still more preferably 2 g / 10 min or more, and from the viewpoint of further stabilizing the moldability, it is preferably 20 g / 10 min or less, more preferably 15 g / 10 min or less, still more preferably 10 g / 10 min or less.

[0032] For polyethylene resins, it is preferable to use polyethylene resins made from plant-derived ethylene. The bio-based content of the polyethylene resin, as measured in accordance with ISO 16620, is preferably 50% to 100%, preferably 70% to 100%, and more preferably 80% to 100%.

[0033] According to the inventors' research, when the polypropylene resin composition constituting the base layer (A) contains a polypropylene resin and a specific polyethylene resin, fine surface irregularities are formed on the surface of the seal layer (B) and the surface layer (C), resulting in improved slipperiness and resistance to blocking. Furthermore, polyethylene resins have a lower melting point than polypropylene resins, resulting in higher heat seal strength. For example, using a polyethylene resin with a melting point of around 120°C will result in higher heat seal strength when heat-sealed at 120°C. Furthermore, it was discovered that when the polypropylene resin composition constituting the base layer (A) includes both a polypropylene resin and a specific polyethylene resin, the film becomes less prone to fogging, even when the amount of water droplets adhering to the film surface is small in low-temperature environments. This is thought to be because the crystallinity of the polypropylene resin composition constituting the base layer (A) decreases, which further promotes and sustains the migration (bleed-out) of the anti-fogging agent to the seal layer (B) and surface layer (C).

[0034] [Anti-fogging agent] It is preferable that the resin composition constituting the base layer (A) contains an antifogging agent. By including an antifogging agent in the resin composition constituting the base layer (A), the antifogging agent in the base layer (A) sequentially migrates to the seal layer (B) and the surface layer (C), making it easier to maintain the antifogging properties of the film surface. Typical antifogging agents include, for example, fatty acid esters of polyhydric alcohols, amines of higher fatty acids, amides of higher fatty acids, and ethylene oxide adducts of amines and amides of higher fatty acids. The amount of such antifogging agent in the substrate layer (A) is preferably 0.1 to 1.0% by weight, more preferably 0.2 to 0.8% by weight, even more preferably 0.3 to 0.8% by weight, and particularly preferably 0.4 to 0.8% by weight, on a total layer basis.

[0035] [Thickness of base layer (A)] The thickness of the substrate layer (A) is preferably 10 μm or more and 100 μm or less, more preferably 15 μm or more and 50 μm or less, and even more preferably 15 μm or more and 25 μm or less.

[0036] (Seal layer (B)) [Polypropylene resin] The polypropylene resin composition constituting the seal layer (B) is mainly composed of propylene-butene-1 copolymer. Because the main component is propylene-butene-1 copolymer, mixing between the seal layer (B) layers is facilitated, reducing the formation of interfaces and enabling the achievement of heat seal strength. Furthermore, propylene-butene-1 copolymer has a low copolymer content, making delamination at the interface with the substrate layer (A) less likely. Therefore, sufficient heat seal strength can be obtained even with a thin seal layer (B). Multiple propylene-butene-1 copolymers can be used as the propylene-butene-1 copolymer, but a single type of propylene-butene-1 copolymer is preferred. The melting point of these propylene-butene-1 copolymers is preferably in the range of 120 to 130°C. If the melting point is 130°C or lower, the heat seal rises well even when an anti-fogging agent is included, and the temperature does not easily become too high. If the melting point is 120°C or higher, the heat seal rises well, and the temperature does not easily become too low. The content of propylene-butene-1 copolymer in the polypropylene resin composition constituting the seal layer is preferably 90% by weight or more, and more preferably 95% by weight or more, in order to improve the heat seal strength.

[0037] From the viewpoint of achieving heat seal strength, a polypropylene resin composition mainly composed of propylene-butene-1 copolymer is used for the seal layer. However, in order to achieve a heat seal rise temperature of 115 to 125°C, it is important to ensure that the amount of antifogging agent in the seal layer (B) is 0.3% by weight or more to prevent the heat seal rise temperature from becoming too low. If the amount of antifogging agent is less than 0.3% by weight, the heat seal rise temperature will decrease. Preferably, it is 0.3 to 0.8% by weight, and more preferably 0.45 to 0.7% by weight. In this case, when packaging fruits and vegetables and displaying or distributing them in supermarkets, it is possible to prevent the inside from becoming cloudy due to the physiological effects of the contents.

[0038] [Anti-fogging agent] The polypropylene resin composition constituting the sealing layer (B) contains an anti-fogging agent. This effect is particularly effective when packaging fruits and vegetables that retain their physiological functions even after harvesting. Even if the antifogging agent is added only to the base layer (A) during the manufacturing of the biaxially oriented polypropylene resin film of the present invention, the antifogging agent will sequentially migrate to the seal layer (B) (bleed out) during film manufacturing and storage after film formation, resulting in the film surface having antifogging properties. Alternatively, the antifogging agent may be added to all three layers (A, B, and C) during film manufacturing.

[0039] Furthermore, in order to maintain excellent anti-fogging properties over the long term during the distribution process, it is preferable to store the packaging at room temperature rather than frozen. Therefore, considering the temperature fluctuations during storage and distribution, it is preferable to select an anti-fogging agent that exhibits continuous anti-fogging properties while repeatedly undergoing temperature changes between 5 and 30°C. Typical antifogging agents include, for example, fatty acid esters of polyhydric alcohols, amines of higher fatty acids, amides of higher fatty acids, and ethylene oxide adducts of amines and amides of higher fatty acids. The amount of such antifogging agent in the seal layer (B) is preferably 0.1 to 1.0% by weight, more preferably 0.2 to 0.8% by weight, even more preferably 0.3 to 0.8% by weight, and particularly preferably 0.4 to 0.8% by weight on a total layer basis.

[0040] [Additives] Furthermore, within limits that do not impair the effects of the present invention, various additives for improving quality such as slipperiness and antistatic properties may be incorporated, such as lubricants like waxes 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. Furthermore, it is preferable to incorporate inorganic or organic fine particles to ensure the film's resistance to blocking and its slipperiness.

[0041] Examples of inorganic fine particles include silicon dioxide, calcium carbonate, titanium dioxide, talc, kaolin, mica, and zeolite. These particles can be spherical, elliptical, conical, or amorphous, and their particle size can be customized to suit the film's intended use and application. Furthermore, as organic fine particles, cross-linked particles such as acrylic, methyl acrylate, and styrene-butadiene can be used, and in terms of shape and size, a wide variety of options are available, similar to inorganic fine particles. In addition, various surface treatments can be applied to the surface of these inorganic or organic fine particles, and these can be used individually or in combination of two or more types.

[0042] The average particle size of the inorganic or organic fine particles is preferably 1 μm or larger, more preferably 2 μm or larger, and even more preferably 3 μm or larger. Furthermore, the average particle size is preferably 5 μm or smaller, and more preferably 4 μm or smaller. The average particle size of the fine particles was measured as follows. Particles were dispersed in ion-exchanged water stirred at a predetermined rotational speed (approximately 5000 rpm) using a high-speed agitator. This dispersion was then added to Isoton (physiological saline) and further dispersed using an ultrasonic disperser. Finally, the particle size distribution was determined by the Cole counter method and the average particle size was calculated. The content of fine particles is preferably 0.3% by weight or more, more preferably 0.5% by weight or more, even more preferably 0.7% by weight or more, even more preferably 1.0% by weight or more, and also preferably 3.0% by weight or less, more preferably 2.0% by weight or less, and even more preferably 1.7% by weight or less, relative to the polypropylene resin composition constituting the seal layer (B).

[0043] [Thickness of the sealing layer (B)] The presence of the sealing layer (B) and surface layer (C) promotes the migration of the anti-fogging agent to the film surface (bleed-out). A thicker layer provides a greater effect on water-repellent properties, but the thickness of the sealing layer (B) must be 1 μm or less. If it exceeds 1 μm, the heat-seal strength when the bag is made using the heat-seal method becomes insufficient, and fine surface irregularities are formed on the surface of the sealing layer (B), resulting in improved slipperiness and blocking resistance. Furthermore, it is preferable that the thickness of the sealing layer (B) be 1.5% or more of the total film layer in terms of heat seal strength after automatic packaging, and 4% or less in terms of heat-seal strength. The strength of the heat-sealed seal is greatly influenced by the size of the fused resin portion, known as the poly-retention area, during the heat-sealing process. The thickness of the seal layer (B) is preferably 0.1 μm or more. The sealing layer (B) must be provided on only one side of the base layer (A). If it is provided on both sides of the base layer (A), the film is likely to stick to the sealing bar during the automated packaging process, leading to packaging defects.

[0044] (Surface layer (C)) [Polypropylene resin] The surface layer (C) can be mainly composed of at least one polypropylene resin selected from the group consisting of propylene-ethylene-butene-1 copolymer, propylene-butene-1 copolymer, and propylene-ethylene copolymer. Using one of these resins facilitates mixing between the seal layers, reduces the formation of interfaces, and facilitates the achievement of heat seal strength. The melting point of the polypropylene resin is preferably in the range of 130 to 140°C. If the melting point is 140°C or lower, the heat seal rises well even when an anti-fogging agent is included, and the temperature does not easily become too high. If the melting point is 130°C or higher, the heat seal rises well, and the temperature does not easily become too low. The content of at least one polypropylene resin selected from the group consisting of propylene-ethylene-butene-1 copolymer, propylene-butene-1 copolymer, and propylene-ethylene copolymer in the polypropylene resin composition constituting the surface layer (C) is preferably 90% by weight or more, and more preferably 95% by weight or more, in order to improve the heat seal strength.

[0045] It is preferable that the heat seal rise temperature of the surface layer (C) is 130°C or higher and 140°C or lower. The heat seal rise temperature of the surface layer (C) is defined as the heat seal pressure of 1 kg / cm when the surfaces of the surface layer (C) of the film of the present invention are facing each other. 2 The time is 1 second, and the temperature is such that the heat seal strength is 1 N / 15 mm when heat-sealed. When the heat seal rise temperature of the surface layer (C) is 130°C or higher, the surface layer (C) is less likely to fuse to the seal bar during heat sealing of pillow packaging, making it easier to manufacture the bags. When it is 140°C or lower, the back seal portion fuses easily with the outer packaging of the pillow packaging, resulting in a better appearance, and the back seal portion does not catch when the packages are stacked, preventing problems such as the seal peeling off.

[0046] [Anti-fogging agent] The surface of the surface layer (C) preferably has anti-fogging properties. This is because when fruits and vegetables are packaged and displayed in supermarkets, condensation can cause the surface to fog up, which improves its appearance. Typical antifogging agents include, for example, fatty acid esters of polyhydric alcohols, amines of higher fatty acids, amides of higher fatty acids, and ethylene oxide adducts of amines and amides of higher fatty acids. The amount of such antifogging agent in the surface layer (C) is preferably 0.1 to 1.0% by weight, more preferably 0.2 to 0.8% by weight, even more preferably 0.3 to 0.8% by weight, and particularly preferably 0.4 to 0.8% by weight, on a total layer basis.

[0047] [Additives] Furthermore, within limits that do not impair the effects of the present invention, various additives for improving quality such as slipperiness and antistatic properties may be incorporated, such as lubricants like waxes 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. Furthermore, it is preferable to incorporate inorganic or organic fine particles to ensure the film's resistance to blocking and its slipperiness.

[0048] Examples of inorganic fine particles include silicon dioxide, calcium carbonate, titanium dioxide, talc, kaolin, mica, and zeolite. These particles can be spherical, elliptical, conical, or amorphous, and their particle size can be customized to suit the film's intended use and application. Furthermore, as organic fine particles, cross-linked particles such as acrylic, methyl acrylate, and styrene-butadiene can be used, and in terms of shape and size, a wide variety of types can be used, similar to inorganic fine particles. Furthermore, various surface treatments can be applied to the surfaces of these inorganic or organic fine particles, and these can be used individually or in combination of two or more.

[0049] The average particle size of the inorganic or organic fine particles is preferably 1 μm or larger, more preferably 2 μm or larger, and even more preferably 3 μm or larger. Furthermore, the average particle size is preferably 5 μm or smaller, and more preferably 4 μm or smaller. The average particle size of the fine particles was measured as follows. Particles were dispersed in ion-exchanged water stirred at a predetermined rotational speed (approximately 5000 rpm) using a high-speed agitator. This dispersion was then added to Isoton (physiological saline) and further dispersed using an ultrasonic disperser. Finally, the particle size distribution was determined by the Cole counter method and the average particle size was calculated. The content of fine particles is preferably 0.3% by weight or more, more preferably 0.5% by weight or more, even more preferably 0.7% by weight or more, even more preferably 1.0% by weight or more, and also preferably 3.0% by weight or less, more preferably 2.0% by weight or less, and even more preferably 1.7% by weight or less, relative to the polypropylene resin composition constituting the surface layer (C).

[0050] (Thickness of the surface layer (C)) When the polypropylene resin composition constituting the base layer (A) contains both a polypropylene resin and a specific polyethylene resin, fine surface irregularities are formed on the surface of the surface layer (C). Therefore, a smaller thickness of the surface layer (C) results in larger surface irregularities, but this makes it more difficult to achieve anti-fogging properties, making the surface layer (C) essential. However, if the thickness of the surface layer (C) is too large, the size of the surface irregularities decreases, so it is also necessary to control the thickness. The thickness of the surface layer (C) is preferably 1 μm or less. A thickness of 1 μm or less makes it easier to obtain thermal seal strength, and also creates fine surface irregularities on the surface of the surface layer (C), resulting in improved slipperiness and blocking resistance. Furthermore, it is preferable that the thickness of the surface layer (C) be 1.5% or more of the total film layer in terms of heat seal strength after automatic packaging, and 4% or less in terms of heat seal strength when the bag is made by heat sealing. It is preferable that the thickness of the surface layer (C) be 0.1 μm or more.

[0051] (Film thickness) The thickness of the biaxially oriented polypropylene resin film of the present invention varies depending on its application and method of use, but polypropylene films used as packaging films are generally about 10 to 100 μm thick, more preferably about 15 to 50 μm thick, even more preferably about 15 to 40 μm thick, and particularly preferably about 15 to 25 μm thick, in terms of mechanical strength and transparency.

[0052] (Method for manufacturing biaxially oriented polypropylene resin films) The biaxially oriented polypropylene resin film of the present invention is produced under conditions no different from those for general polyolefins. For example, one method involves melt lamination using an extruder appropriate to the number of layers, employing a T-die method or inflation method, followed by cooling using a cooling roll method, water cooling method, or air cooling method to form a laminated film, and then stretching it using 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 using the sequential biaxial stretching method, the resin is melt-extruded from a T-shaped die and then cooled and solidified in a casting machine to create a raw material sheet. In this case, the roll temperature for melt casting is preferably set between 15°C and 40°C in order to suppress resin crystallization and improve transparency. Next, the raw sheet is heated to a temperature suitable for stretching, and then stretched in the direction of the sheet's flow using the speed difference between the stretching rolls. The stretching ratio at this stage is preferably set between 3 and 6 times to ensure even and stable production. Next, both edges of the longitudinally stretched sheet are gripped with tenter clips, and the sheet is stretched by sequentially spreading it in a direction perpendicular to the sheet's flow while heating it with hot air to a temperature suitable for stretching. The transverse stretching ratio at this stage is preferably set between 7 and 10 times, taking into consideration thickness variations and productivity.

[0053] The biaxially oriented polypropylene resin film of the present invention can be surface-treated to improve printability, lamination, and other properties. Examples of surface treatment methods include corona discharge treatment, plasma treatment, flame treatment, and acid treatment, and are not particularly limited. Corona discharge treatment, plasma treatment, and flame treatment are preferred because they allow for continuous processing and can be easily performed before the winding process in the manufacturing process of this film.

[0054] (Film characteristics) The biaxially oriented polypropylene resin film of the present invention preferably has the following properties.

[0055] (Heat seal rise temperature) In the present invention, it is preferable that the heat seal rise temperature of the seal layer (B) is 115°C or higher and 125°C or lower. The heat seal rise temperature of the seal layer (B) is the temperature at which the heat seal strength is 1 N / 15 mm when the surfaces of the seal layer (B) of the film of the present invention are facing each other and heat-sealed at a heat seal pressure of 1 kg / cm2 and for a time of 1 second.

[0056] If the heat-seal rise temperature of the sealing layer (B) is 125°C or lower, it is possible to heat-seal the product while maintaining sufficient strength even at low heat-seal temperatures, making it easier to operate at high speeds during automated packaging. Furthermore, the seal area has excellent airtightness, and this, combined with its anti-fogging properties, helps maintain the freshness of perishable goods, improves the appearance of the contents, and makes the package easy to handle. If the heat seal rise temperature of the seal layer (B) is 125°C or lower, the melting point difference with the base layer (A), which is mainly made of polypropylene resin, becomes large. This makes it easier to sufficiently increase the operating speed of the automatic packaging without raising the temperature of the seal bar. Also, since it is not necessary to raise the set temperature to increase the heat seal strength, the entire laminated film is less likely to shrink during heat sealing, wrinkles are less likely to occur in the heat-sealed area, and it is less likely to cause sealing failure in the heat-sealed area. If the heat seal rise temperature of the seal layer (B) is less than 115°C, the heat seal strength when making bags using the heat-sealing method decreases, making it difficult to use both the automatic packaging method and the heat-sealing method.

[0057] (Heat seal strength achieved at 120℃) In order to prevent the contents from falling out, the biaxially oriented polypropylene resin film of the present invention preferably has a heat seal strength of 3.5 N / 15 mm or higher in the longitudinal and transverse directions at 120°C, as obtained by the measurement method described later. Here, the longitudinal direction refers to the direction in which the film flows from the process of casting the raw resin composition to the process of winding the stretched film, and the transverse direction refers to the direction perpendicular to the flow direction. The same applies to the following distance characteristics.

[0058] (Anti-fog properties) The biaxially oriented polypropylene resin film of the present invention preferably has an anti-fogging performance evaluation of rank 3 or higher, obtained by the measurement method described later. More preferably, it has a rank of rank 2 or higher, and even more preferably, a rank of rank 1.

[0059] (Uneven anti-fogging properties) The biaxially oriented polypropylene resin film of the present invention preferably has an anti-fogging unevenness evaluation of rank 2 or lower, obtained by the measurement method described later. More preferably, it has a rank of rank 1.

[0060] (Water-resistant) The biaxially oriented polypropylene resin film of the present invention preferably has a drip-proof performance evaluation of rank 3 or lower, obtained by the measurement method described later. More preferably, it is rank 2 or lower, and even more preferably rank 1.

[0061] (Suitable for automated packaging) The biaxially oriented polypropylene resin film of the present invention preferably has an automatic packaging suitability evaluation of ○ or △ obtained by the measurement method described later. More preferably it is ○.

[0062] (Seal strength) The biaxially oriented polypropylene resin film of the present invention preferably has a heat-seal strength of 25 N / 15 mm or more, obtained by the measurement method described later. More preferably, it is 28 N / 15 mm or more, and even more preferably 29 N / 15 mm or more.

[0063] (Heat shrinkage rate at 120°C) The biaxially oriented polypropylene resin film of the present invention preferably has a thermal shrinkage rate of 3.7% or less in the longitudinal direction at 120°C, as obtained by the measurement method described later. More preferably, it is 3.5% or less, even more preferably 3.0% or less, and particularly preferably 2.5% or less. Preferably, the thermal shrinkage rate at 120°C obtained by the measurement method described later is 3.5% or less in the width direction. More preferably, it is 3.0% or less, even more preferably 2.0% or less, even more preferably 1.6% or less, and particularly preferably 1.3% or less.

[0064] (Hayes) The biaxially oriented polypropylene resin film of the present invention preferably has a haze of 8% or less, obtained by the measurement method described later. More preferably, it is 7% or less, even more preferably 6% or less, and even more preferably 5% or less.

[0065] (Coefficient of kinetic friction) The biaxially oriented polypropylene resin film of the present invention preferably has a dynamic friction coefficient of 0.38 or less in both the longitudinal and width directions, as obtained by the measurement method described later. More preferably it is 0.35 or less, even more preferably 0.32 or less, even more preferably 0.30 or less, and particularly preferably 0.28 or less.

[0066] (Blocking resistance) The biaxially oriented polypropylene resin film of the present invention preferably has a blocking value of 110 mN / 200 mm or less, and more preferably 100 mN / 200 mm or less, obtained by the measurement method described later.

[0067] (Surface roughness SRa) The biaxially oriented polypropylene resin film of the present invention preferably has a surface roughness SRa of 0.018 μm or more, and more preferably 0.019 μm or more, obtained by the measurement method described later. [Examples]

[0068] The present invention will be further described below with reference to specific examples, but the present invention does not deviate from its gist. Unless otherwise specified, the following examples are not limited to those described below. The characteristics described herein were evaluated using the following methods.

[0069] (1) Layer thickness A biaxially oriented polypropylene resin film was cut to a size of 1 cm x 1 cm, embedded in UV-curable resin, and solidified by UV irradiation for 5 minutes. Cross-sectional samples were then prepared using a microtome and observed with a differential interference microscope. The thickness of the entire film, the sealing layer (B), and the surface layer (C) was measured. Five samples were measured, and the average value was calculated.

[0070] (2) Heat seal rise temperature The heat seal strength is defined as the temperature at which the heat seal strength is 1 N / 15 mm when two biaxially oriented polypropylene resin films are stacked facing each other and heat-sealed using a thermal gradient tester (manufactured by Toyo Seiki Co., Ltd.) at a heat seal pressure of 1 kg / cm2 and a time of 1 second, increasing in 5°C increments from 80°C. The heat seal layer surfaces of 5 cm x 20 cm films were placed facing each other and simultaneously heat-sealed using five heat seal bars (seal surface 1 cm x 3 cm) with temperatures set at 5°C intervals. The center of each section was cut to a width of 15 mm, attached to the upper and lower chucks of a tensile testing machine, and the strength of each section was measured when pulled at a tensile speed of 200 mm / min, and the heat seal strength was calculated (unit: N / 15 mm). A linear graph was drawn with temperature on the horizontal axis and heat seal strength on the vertical axis, and the temperature at which the heat seal strength exceeded 1 N / 15 mm was defined as the heat seal start-up temperature.

[0071] (3) Heat seal strength at 120℃ Two sealing layers (B) of biaxially oriented polypropylene resin films were stacked facing each other and heat-sealed at 120°C using a thermal gradient tester (manufactured by Toyo Seiki Co., Ltd.) at a heat sealing pressure of 1 kg / cm² and a time of 1 second. The central part was then cut to a width of 15 mm, attached to the upper and lower chucks of a tensile testing machine, and the heat sealing strength was calculated from the strength when pulled at a tensile speed of 200 mm / min (unit: N / 15 mm).

[0072] (4) Anti-fogging properties 1) Pour 300cc of 50°C warm water into a 500cc container with an open top. 2) Place the anti-fog measuring surface of the film inward and seal the container opening with the film. 3) Leave it in a cool room at 5°C. 4) With the hot water inside the container completely cooled to ambient temperature, the degree of dew adhesion on the film surface was evaluated on a 5-point scale. • Rating Grade 1: No dew on any surface (adhesion area 0) • Grade 2: Slight dew adhesion (up to 1 / 4 of the surface area) • Rating Grade 3: Dew adhesion on approximately 1 / 2 of the surface area (up to 2 / 4 of the surface area). • Rating 4: Almost no dew adhesion (adhesion up to 3 / 4 of the surface area) • Rating Grade 5: Dew covering the entire surface (more than 3 / 4 of the surface area is covered)

[0073] (5) Anti-fogging unevenness 1) Pour 300cc of 50°C warm water into a 500cc container with an open top. 2) Place the anti-fog measuring surface of the film inward and seal the container opening with the film. 3) Leave at 20°C for 20 seconds. 4) The degree of dew adhesion to the film surface was evaluated on a 5-point scale. • Rating Grade 1: No dew on any surface (adhesion area 0) • Grade 2: Slight dew adhesion (up to 1 / 4 of the surface area) • Rating Grade 3: Dew adhesion on approximately 1 / 2 of the surface area (up to 2 / 4 of the surface area). • Rating 4: Almost no dew adhesion (adhesion up to 3 / 4 of the surface area) • Rating Grade 5: Dew covering the entire surface (more than 3 / 4 of the surface area is covered)

[0074] (6) Water-resistant 1) Pour 300cc of 30°C warm water into a 500cc container with an open top. 2) Place the anti-fog measuring surface of the film inward and seal the container opening with the film. 3) Leave it in a cool room at 5°C. 4) With the hot water inside the container completely cooled to ambient temperature, the degree of dew adhesion on the film surface was evaluated on a 5-point scale. • Rating Grade 1: No dew on any surface (adhesion area 0) • Grade 2: Slight dew adhesion (up to 1 / 4 of the surface area) • Rating Grade 3: Dew adhesion on approximately 1 / 2 of the surface area (up to 2 / 4 of the surface area). • Rating 4: Almost no dew adhesion (adhesion up to 3 / 4 of the surface area) • Rating Grade 5: Dew covering the entire surface (more than 3 / 4 of the surface area is covered) The evaluation of water resistance uses 30°C hot water, which results in a smaller amount of water droplets adhering to the film surface compared to using 50°C hot water, thus requiring a stricter evaluation.

[0075] (7) Suitability for automated packaging Two heat-sealed layers of biaxially oriented polypropylene resin films were stacked facing each other and heat-sealed using a thermal gradient tester (manufactured by Toyo Seiki Co., Ltd.) at a heat-sealing pressure of 1 kg / cm² and a time of 1 second. The presence or absence of fusion of the surface layer (C) to the seal bar and the heat seal rise temperature were evaluated according to the following criteria. ○: No fusion to the seal bar; rise temperature 115°C to 125°C. △: No fusion to the seal bar; rise temperature below 115°C or above 125°C. ×: Fusion to the seal bar

[0076] (8) Heat-seal strength We created heat-sealed bags using biaxially oriented polypropylene resin film with a heat-sealing machine (Kyoei Printing Machinery & Materials Co., Ltd.: PP500 model). Conditions: Cutting blade; cutting edge angle 60° Sealing temperature: 370℃ Shot rate: 120 bags / minute The heat-sealed portion of the above heat-sealed bag is cut to a width of 15 mm, and with the slack removed, both ends are gripped into the gripping section of a tensile testing machine (grip spacing: 200 mm). The sealing strength (N / 15mm) was calculated from the strength at which the seal broke when it was pulled at a tensile speed of 200 mm / min. Five measurements were taken, and the average was calculated. A rating of 20N / 15mm or higher was determined to indicate good suitability for heat sealing.

[0077] (9) Thermal contraction The following measurements were taken in accordance with JIS Z1712: A biaxially oriented polypropylene resin film was cut to a width of 20 mm and a length of 200 mm in both the MD and TD directions, and then suspended in a 120°C hot air oven and heated for 5 minutes. The length after heating was measured, and the thermal shrinkage rate was determined as the ratio of the length shrunk to the original length.

[0078] (10) Hayes Measurements were taken in accordance with JIS K7105.

[0079] (11) Coefficient of kinetic friction Two biaxially oriented polypropylene resin films were placed side-by-side (C) and measured at 23°C in accordance with JIS K7125. Five sample sets were measured, and the average value was calculated.

[0080] (12) Blocking value A biaxially oriented polypropylene resin film was cut to a length of 150 mm and a width of 200 mm. The sealing layer (B) and surface layer (C) were placed together, sandwiched between the two layers, and a 20 kg weight was placed in the center. The film was then placed in a 60°C oven. After 24 hours, it was removed and seasoned at 23°C and 65% humidity for 1 hour. A 6.35Φ test rod was then fixed to the bonded area. Using a tensile testing machine (Instron 5965 dual-column benchtop testing machine), the film was gripped with a 200mm gap between the film and the fixing jig, and pulled at a tensile speed of 100mm / min. The strength at which the films separated was defined as the blocking value (mN / 200mm). Three samples were measured, and the average value was calculated.

[0081] (12) Surface roughness SRa The surface roughness of the obtained biaxially oriented polypropylene resin film was evaluated using a three-dimensional roughness meter (Kosaka Laboratory Co., Ltd., model ET-30HK). Measurements were taken with a needle pressure of 20 mg, a measurement length of 1 mm in the X direction, a feed rate of 100 μm / sec, a feed pitch of 2 μm in the Y direction, 99 recorded lines, a height magnification of 20,000 times, and a cutoff of 80 μm. The arithmetic mean roughness was calculated according to the definition of arithmetic mean roughness described in JIS B 0601 (1994). Each surface roughness SRa was evaluated using the average value of three trials.

[0082] (Example 1) (1)Resin used The polypropylene resin, polyethylene resin, and additives used as raw materials for each layer in the manufacturing example below are as follows: (1) Base material layer (A) [PP-1]: Propylene-ethylene random copolymer: Sumitomo Chemical Co., Ltd. "FS2011DG3", Ethylene content: 0.6 mol%, MFR: 2.7 g / 10 min, Melting point: 158℃, Mesopentad fraction: 97.0% [Anti-fogging agent-1]: Glycerin monostearate (Matsumoto Oil & Fat Pharmaceutical Co., Ltd., TB-123) [Anti-fogging agent-2]: Polyoxyethylene(2) stearylamine (Matsumoto Oil & Fat Pharmaceutical Co., Ltd., TB-12) [Anti-fogging agent-3]: Polyoxyethylene (2) stearylamine monostearate (Matsumoto Oil & Fat Pharmaceutical Co., Ltd., Elex 334) [PE-1]: Ethylene homopolymer: Braskem's "SLH218", MFR: 2.3g / 10min, Melting point: 126℃, Bio-based: 84%

[0083] (2) sealing layer (B) [PP-2]: Propylene-butene-1 copolymer: Sumitomo Chemical Co., Ltd. "SPX78J1", Butene content: 25 mol, MFR: 8.5 g / 10 min, Melting point: 128℃ [Anti-fogging agent-1]: Glycerin monostearate (Matsumoto Oil & Fat Pharmaceutical Co., Ltd., TB-123)

[0084] (4) Surface layer (C) resin composition [PP-3]: Propylene-ethylene-butene random copolymer: Sumitomo Chemical Co., Ltd. "FSX66E8", Ethylene content: 2.5 mol, Butene content: 7 mol, MFR: 3.1 g / 10 min, Melting point: 133℃ [Anti-fogging agent-1]: Glycerin monostearate (Matsumoto Oil & Fat Pharmaceutical Co., Ltd., TB-123) [Organic polymer microparticles]: Cross-linked acrylic particles: CS30: Sumitomo Chemical Co., Ltd., particle size: 3.5 μm

[0085] The raw materials used for the base layer (A), seal layer (B), and surface layer (C) were mixed in the proportions shown in Table 1. Using three melt extruders, the mixed raw materials for the base layer (A) were melt-extruded from the first extruder at a resin temperature of 280°C, the mixed raw materials for the surface layer (C) were melt-extruded from the second extruder at a resin temperature of 250°C, and the mixed raw materials for the seal layer (B) were melt-extruded from the third extruder at a resin temperature of 250°C. The layers were then stacked in the order of surface layer (C) / base layer (A) / seal layer (B) from the chill roll contact surface in the T-die so that the thickness ratio was surface layer (C) / base layer (A) / seal layer (B) = 0.6 / 18.7 / 0.7, and then extruded. The sheets were cooled and solidified on a cooling roll at 30°C to obtain an unstretched sheet. Next, the material was stretched 4.5 times in the longitudinal direction using the difference in peripheral speed between metal rolls heated to 130°C, and then introduced into a tenter stretcher for further stretching 9.5 times in the transverse direction. The preheating temperature of the tenter stretcher was 168°C, and the stretching temperature was 155°C for stretching, after which heat setting was performed at 163°C.

[0086] The surface of the surface layer (C) was subjected to corona discharge treatment using a corona discharge treatment machine manufactured by Kasuga Electric Co., Ltd., and then the sealing layer (B) was subjected to the same corona discharge treatment to obtain a biaxially oriented polypropylene resin film that could be wound up with a film winder and automatically packaged. The final film thickness was 20 μm, and the thickness ratio of the sealing layer (B) to the total film was 3.5%. The resulting multilayer film satisfies the requirements of the present invention, and its suitability for automatic packaging, heat sealing, anti-fogging, and anti-drip properties is at a level that poses no problems for packaging fresh produce. The film composition and physical properties are shown in Table 1.

[0087] (Example 2) A laminated film was obtained in the same manner as in Example 1, except that the [PE-1] content of the base layer (A) was set to 10% by weight. The obtained multilayer film satisfied the requirements of the present invention, and its suitability for automatic packaging, heat sealing, anti-fogging, and anti-drip properties was at a level that posed no problems for packaging fresh produce. The film composition and physical properties are shown in Table 1.

[0088] (Example 3) A laminated film was obtained in the same manner as in Example 1, except that the [PE-1] content of the base layer (A) was set to 20% by weight. The obtained multilayer film satisfied the requirements of the present invention, and its suitability for automatic packaging, heat sealing, anti-fogging, and anti-drip properties was at a level that posed no problems for packaging fresh produce. The film composition and physical properties are shown in Table 1.

[0089] (Example 4) A laminated film was obtained in the same manner as in Example 1, except that the mixed raw materials for the sealing layer (B) consisted of 80% by weight of [PP-2] and 20% by weight of [PP-3]. The resulting multilayer film satisfies the requirements of the present invention, and its suitability for automatic packaging, heat sealing, anti-fogging, and anti-drip properties is at a level that poses no problems for packaging fresh produce. The film composition and physical properties are shown in Table 1.

[0090] (Example 5) A laminated film was obtained in the same manner as in Example 1, except that the thickness of the base layer (A) was 38.7 μm, the film thickness was 40 μm, and the thickness ratio of the seal layer (B) was 1.8%. The obtained multilayer film satisfied the requirements of the present invention, and its suitability for automatic packaging, heat sealing, anti-fogging, and anti-drip properties was at a level that posed no problems for packaging fresh produce. The film composition and physical properties are shown in Table 1.

[0091] (Example 6) A laminated film was obtained in the same manner as in Example 2, except that the thickness of the base layer (A) was increased to 38.7 μm, the film thickness was set to 40 μm, and the thickness ratio of the seal layer (B) was set to 1.8%. The obtained multilayer film satisfied the requirements of the present invention, and its suitability for automatic packaging, heat sealing, anti-fogging, and anti-drip properties was at a level that posed no problems for packaging fresh produce. The film composition and physical properties are shown in Table 1.

[0092] (Example 7) A laminated film was obtained in the same manner as in Example 3, except that the thickness of the base layer (A) was 38.7 μm, the film thickness was 40 μm, and the thickness ratio of the seal layer (B) was 1.8%. The obtained multilayer film satisfied the requirements of the present invention, and its suitability for automatic packaging, heat sealing, anti-fogging, and anti-drip properties was at a level that posed no problems for packaging fresh produce. The film composition and physical properties are shown in Table 1.

[0093] (Comparative Example 1) A laminated film was obtained in the same manner as in Example 1, except that the amount of [PE-1] added to the base layer (A) was set to 0% by weight. The obtained laminated film exhibited poor water-repellent properties, slipperiness, and blocking resistance. The film composition and physical properties are shown in Table 1.

[0094] (Comparative Example 2) A laminated film was obtained in the same manner as in Example 5, except that the amount of [PE-1] added to the base layer (A) was set to 0% by weight. The obtained laminated film also showed similar deterioration in drip resistance, slipperiness, and blocking resistance. The film composition and physical properties are shown in Table 1.

[0095] (Comparative Example 3) A laminated film was obtained in the same manner as in Example 1, except that the thickness of the base layer (A) was 19.3 μm and the thickness of the surface layer (C) was 0.0 μm. The obtained laminated film exhibited significantly worse anti-fogging properties. The film composition and physical properties are shown in Table 1.

[0096] (Comparative Example 4) A laminated film was obtained in the same manner as in Example 1, except that the thickness of the base layer (A) was 18.1 μm and the thickness of the surface layer (C) was 1.2 μm. The obtained laminated film exhibited poor thermal seal strength, slipperiness, and blocking resistance. The film composition and physical properties are shown in Table 1.

[0097] (Comparative Example 5) A laminated film was obtained in the same manner as in Example 5, except that the thickness of the base layer (A) was 39.3 μm and the thickness of the surface layer (C) was 0.0 μm. The obtained laminated film exhibited significantly worse anti-fogging properties. The film composition and physical properties are shown in Table 1.

[0098] (Comparative Example 6) A laminated film was obtained in the same manner as in Example 5, except that the thickness of the base layer (A) was 38.1 μm and the thickness of the surface layer (C) was 1.2 μm. The obtained laminated film exhibited poor thermal seal strength, slipperiness, and blocking resistance. The film composition and physical properties are shown in Table 1.

[0099] [Table 1] [Industrial applicability]

[0100] The automatically packageable biaxially oriented polypropylene resin film of the present invention is a film with excellent anti-fogging and anti-drip properties, excellent slipperiness and blocking resistance, and high heat seal strength at 120°C, making it suitable for food packaging, especially for vegetable packaging.

Claims

1. A biaxially oriented polypropylene resin film having a base layer (A) made of a resin composition containing a polypropylene resin and a polyethylene resin, a seal layer (B) made of a polypropylene resin composition mainly composed of a propylene-butene-1 copolymer on one side of the base layer (A), and a surface layer (C) on the side of the base layer (A) opposite to the seal layer (B), and satisfying the following conditions a) to e). a) The melt flow rate of the polyethylene resin constituting the base layer (A) is 1.5 g / 10 min or more and 10 g / 10 min or less at 190°C, and its density is 0.910 g / cm³. ３ 0.930g / cm or more ３ The following is true, and it is contained in an amount of 1% to 20% by weight relative to the total weight of 100% by weight of the polypropylene resin and polyethylene resin that constitute the base layer (A). b) The thickness of the sealing layer (B) is 1.5% or more and 1 μm or less of the total film thickness. c) The polypropylene composition constituting the sealing layer (B) contains 0.1% to 1.0% by weight of an anti-fogging agent. d) The thickness of the surface layer (C) is 1.5% or more and 1 μm or less of the total film thickness. e) The surface layer (C) is mainly composed of at least one polypropylene resin selected from the group consisting of propylene-ethylene-butene-1 copolymer, propylene-butene-1 copolymer, and propylene-ethylene copolymer.

2. The biaxially oriented polypropylene resin film according to claim 1, wherein the melting point of the propylene-butene-1 copolymer in the sealing layer (B) is in the range of 120 to 130°C.

3. The biaxially oriented polypropylene resin film according to claim 1 or 2, wherein the thickness of the sealing layer (B) is 1.5% or more and 4% or less of the total film layer.

4. The biaxially oriented polypropylene resin film according to claim 1 or 2, wherein the base layer (A) is made of a resin composition mainly consisting of at least one polypropylene resin selected from the group consisting of isotactic propylene homopolymer, propylene-ethylene copolymer, propylene-butene-1 copolymer, propylene-ethylene-butene-1 copolymer, or propylene-pentene copolymer.

5. The biaxially oriented polypropylene resin film according to claim 1 or 2, wherein the melting point of the polypropylene resin constituting the surface layer (C) is in the range of 130 to 140°C.

6. The biaxially oriented polypropylene resin film according to claim 1 or 2, wherein the thickness of the surface layer (C) is 1.5% or more and 4% or less of the total film layer.

7. A packaging body using a biaxially oriented polypropylene resin film according to claim 1 or 2.

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