Biaxially oriented polypropylene resin film and packaging material using the same

Abstract

To provide a biaxially oriented polypropylene-based resin film suitable for an automatic packaging system, and capable of satisfying both of a heat seal strength after automatic packaging and a heat seal strength in a fusion seal system.SOLUTION: A biaxially oriented polypropylene-based resin film includes: a substrate (A) comprising a resin composition containing 80 wt.% or more of at least one polypropylene-based resin selected from the group consisting of an isotactic propylene homopolymer, a propylene ethylene copolymer, and a propylene ethylene butene-1 copolymer or a propylene pentene copolymer; and a seal layer (B) comprising a resin composition containing 90 wt.% or more of a propylene butene-1 copolymer having a melting point of 120-130°C on only one side of the substrate (A), and satisfies the following conditions a), b), c), and d). a) A thickness of the seal layer (B) is 1 μm or less. b) The seal layer (B) contains an antifogging agent. c) The thickness of the seal layer (B) is 1.5% or more and 4% or less to total layers of the film. d) A dew-attached area on a film surface after the following operations is 1 / 4 or less. 1) 300 cc of warm water of 50°C is charged in an upper part-opened container of 500 cc. 2) An opened part of the container is sealed by the film with an antifogging property-measuring surface of the film inside. 3) The sealed container is left for 20 sec. at 20°C.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a biaxially oriented polypropylene-based resin film and a package using the same, and in particular to a biaxially oriented polypropylene-based resin film having heat sealability and anti-fogging effects, and therefore suitable for packaging fresh produce consisting of plants such as vegetables, fruits, and flowers that require high freshness (hereinafter, these will be referred to as "fruit and vegetables" in this specification), and a package using the same. [Background technology]

[0002] Biaxially oriented polypropylene resin films have been widely used in the field of packaging, such as food packaging and textile packaging, because of their excellent optical properties, mechanical properties, packaging suitability, etc. In particular, anti-fog films are widely used for packaging fruits and vegetables.

[0003] In particular, in the packaging of fruits and vegetables, there is a demand for labor saving in farm work due to the recent decline in the agricultural population, and automatic packaging methods are becoming more widespread. The so-called pillow packaging method is used as an automatic packaging method for fruits and vegetables, and it is possible to carry out the process of making bags by heat sealing and the process of filling the contents simultaneously.

[0004] As an example that can be applied to an automatic packaging system, a laminated film has been disclosed in which a propylene-ethylene-butene copolymer having a melting point 10 to 90°C lower than the melting point of the outer layer is melt-extruded onto an outer layer made of a biaxially oriented film-like material whose main component is crystalline polypropylene resin (see, for example, Patent Document 1).

[0005] A packaging film consisting of a laminate of two or more layers, which has a base layer mainly made of polypropylene resin and a heat seal layer mainly made of polyolefin resin using propylene-butene-1 copolymer and propylene-ethylene-butene-1 copolymer, has been disclosed as being suitable for automatic packaging systems and having excellent heat seal strength (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 3104166 [Patent Document 2] Patent No. 4385443 Summary of the Invention [Problem to be solved by the invention]

[0007] Currently, the packaging film of the above-mentioned patent document is used in an automatic packaging system. However, there are still many fruits and vegetables that are not automatically packaged and for which bag making and filling are carried out separately, and in such cases, bag making is often carried out by a heat-cutting and sealing method. However, although the packaging film of the above-mentioned patent document is suitable for an automatic packaging system, it is not satisfactory in terms of both the heat-sealing strength after automatic packaging and the heat-sealing strength in the heat-cutting and sealing method.

[0008] However, if fruit and vegetable packaging film could be used for both automatic packaging methods such as pillow packaging and heat-cut seal packaging, it would be of great benefit to consumers such as farmers and converters in terms of inventory management, as they would no longer need to purchase different types of packaging film for each method.

[0009] An object of the present invention is to provide a biaxially oriented polypropylene resin film which is suitable for automatic packaging systems and is satisfactory in terms of both heat seal strength after automatic packaging and heat seal strength in a melt-cutting sealing system. [Means for solving the problem]

[0010] That is, the present invention has the following configuration. 1. A biaxially oriented polypropylene resin film having a base layer (A) made of a resin composition mainly containing a polypropylene resin and a seal layer (B) made of a resin composition mainly containing a propylene-butene-1 copolymer on only one side of the base layer (A), and satisfying the following conditions a) and b): a) The thickness of the sealing layer (B) is 1 μm or less. b) The sealing layer (B) contains an anti-fogging agent in an amount of 0.3% by weight or more and 1.0% by weight or less. 2. 2. The biaxially oriented polypropylene resin film according to 1 above, wherein the propylene-butene-1 copolymer has a melting point in the range of 120 to 130°C. 3. 3. The biaxially oriented polypropylene resin film according to 1 or 2 above, wherein the content of the propylene-butene-1 copolymer or the plurality of propylene-butene-1 copolymers is in the range of 50% by weight or more. 4. 4. The biaxially oriented polypropylene resin film according to any one of 1. to 3. above, wherein the thickness of the sealing layer (B) is 1.5% or more and 4% or less of the total thickness of the film. 5. 5. The biaxially oriented polypropylene resin film according to any one of 1. to 4. above, wherein the base layer (A) is mainly composed 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, and propylene-pentene copolymer. 6. The biaxially oriented polypropylene resin film according to any one of 1. to 5., which has a surface layer (C) on the side of the base layer (A) opposite the seal layer (B), the surface layer (C) being made of a resin composition mainly composed of at least one resin selected from the group consisting of propylene-ethylene-butene-1 copolymer, propylene-butene-1 copolymer, and propylene-ethylene copolymer. 7. 7. The biaxially oriented polypropylene resin film according to 6., wherein the melting point of at least one resin selected from the group consisting of propylene-ethylene-butene-1 copolymer, propylene-butene-1 copolymer, and propylene-ethylene copolymer is in the range of 130 to 140°C. 8. 8. The biaxially oriented polypropylene resin film according to any one of 1. to 7. above, wherein the thickness of the surface layer (C) is 1.5% or more and 4% or less of the total thickness of the film. 9. A packaging material comprising the biaxially oriented polypropylene resin film according to any one of 1. to 8. above. Effect of the Invention

[0011] The biaxially oriented polypropylene resin film of the present invention is suitable for automatic packaging systems, and is capable of providing satisfactory heat seal strength after automatic packaging and heat seal strength in a melt-cutting seal system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The biaxially oriented polypropylene resin film of the present invention has a base layer (A) made of a resin composition mainly composed of a polypropylene resin, and 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).

[0013] (Base layer (A)) In the present invention, the base layer (A) is made of a resin composition mainly composed of a polypropylene-based resin. The polypropylene-based resin referred to here is preferably made 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 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 Notification No. 20 of the Ministry of Health and Welfare of February 1982 (the eluted amount when extracted at 25°C for 60 minutes is 150 ppm or less [30 ppm or less for those used at temperatures exceeding 100°C]). Such a polypropylene resin is contained in an amount of preferably 80% by weight or more, and more preferably 90% by weight or more, based on the resin composition constituting the substrate layer (A).

[0014] When an isotactic propylene homopolymer and a copolymer of propylene and other α-olefins containing 70 mol % or more of propylene are mixed and used, the content of the copolymer of propylene and other α-olefins containing 70 mol % or more of propylene is desirably 20 wt % or less, more preferably 10 wt % or less, based on the entire resin composition used in the base layer (A). The content of the isotactic propylene homopolymer in the entire resin composition used in the substrate layer (A) is desirably 80% by weight or more, and more preferably 90% by weight or more.

[0015] The α-olefin copolymerization component of the copolymer of propylene and another α-olefin is preferably an α-olefin 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 copolymer. 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. If the melting point is less than 156° C., the film cannot be conveyed more smoothly in an automatic packaging process, and the resulting bag product is more likely to wrinkle. The melt flow rate (MFR) is, for example, 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.

[0016] It is preferable to add an anti-fog agent to the resin composition mainly composed of polypropylene resin constituting the base layer (A). The mechanism of anti-fog properties of the biaxially oriented polypropylene resin film of the present invention is that, by adding an anti-fog agent to the resin composition forming the base layer (A), the anti-fog agent is transferred to the sealing layer (B) during film production and storage after film formation, and the anti-fog agent is present on the surface of the sealing layer (B), so that the film surface has anti-fog properties. This effect can be exhibited when packaging fruits and vegetables, which are characterized by maintaining their physiological activity even after harvest. In order to maintain excellent anti-fogging properties over the long term during distribution, it is preferable 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 the course of repeated temperature changes between 5 and 30°C, taking into consideration changes in temperature during storage and distribution.

[0017] Typical examples of the antifogging agent added to the resin composition mainly composed of polypropylene resin 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, ethylene oxide adducts of amines or amides of higher fatty acids, etc. The amount of such antifogging agent in the film including the base layer (A) and the seal layer (B) is preferably 0.1 to 10% by weight, particularly preferably 0.2 to 5% by weight, calculated on the basis of the total layers.

[0018] In addition, as long as the effect of the present invention is not impaired, the quality of the product may be improved, such as smoothness and antistatic properties. It is also possible to compound various additives for improving productivity, such as lubricants such as wax and metal soap, plasticizers, processing aids, and known heat stabilizers, antioxidants, antistatic agents, and ultraviolet absorbers that are usually added to polypropylene-based films.

[0019] (Sealing layer (B)) The resin composition that constitutes the seal layer (B) is mainly made of propylene-butene-1 copolymer. By using propylene-butene-1 copolymer as the main component, the seal layers are easily mixed together, which makes it difficult for interfaces to form and allows the heat seal strength to be achieved. In addition, propylene-butene-1 copolymer has a small amount of copolymerization components, so peeling at the interface with the base layer (A) is unlikely to occur. Therefore, even if the thickness of the seal layer is thin, sufficient heat seal strength can be obtained. As the propylene-butene-1 copolymer, a plurality of propylene-butene-1 copolymers can be used, but it is preferable to use a single type of propylene-butene-1 copolymer. 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 rise temperature is unlikely to become too high even if an anti-fogging agent is included, and if the melting point is 120° C. or higher, the heat seal rise temperature is unlikely to become too low. The content of propylene-butene-1 copolymer in the resin composition constituting the seal layer is preferably 90% by weight or more in order to improve the heat seal strength, and more preferably 95% by weight or more.

[0020] From the viewpoint of seal strength, a resin composition mainly made of propylene-butene-1 copolymer is used for the seal layer (B), but in order to achieve a heat seal rise temperature of 115 to 125°C, it is important to make the anti-fog agent in the seal layer 0.3% by weight or more so that the heat seal rise temperature does not become too low. If the amount of anti-fog agent is less than 0.3% by weight, the heat seal rise temperature will decrease. It is preferably 0.3 to 0.8% by weight, more preferably 0.45 to 0.7% by weight. In this case, when the fruits and vegetables are packaged and displayed in supermarkets or distributed, it is possible to prevent the inside from becoming cloudy due to physiological actions of the contents.

[0021] (Seal layer thickness) The thickness of the sealing layer (B) must be 1 μm or less. If it exceeds 1 μm, the strength of the heat seal when the bag is made by the heat seal method will be insufficient. In addition, it is preferable that the thickness of the sealing layer (B) is 1.5% or more of the total film thickness in terms of heat seal strength after automatic packaging, and 4% or less in terms of heat seal strength. The size of the fused resin part called the poly pool during heat seal also has a large effect on the heat seal strength. The sealing layer (B) needs to 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 will stick to the sealing bar during the automatic packaging process, which can easily result in packaging defects.

[0022] (film thickness) The film thickness of the biaxially oriented polypropylene-based resin film of the present invention varies depending on the application and method of use, but a polypropylene-based film used as a packaging film is generally about 10 to 100 μm, and from the standpoint of mechanical strength and transparency, it is more preferably about 15 to 50 μm, and particularly preferably about 15 to 40 μm.

[0023] (Surface layer (C)) In the present invention, the surface layer (C) made of a resin composition mainly containing a polypropylene-based resin may be provided on the surface of the base layer (A) opposite the sealing layer (B). The surface layer (C) can be mainly composed of at least one 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 makes it easier for the seal layers to mix together, makes it difficult for an interface to form, and makes it easier to achieve heat seal strength. The heat seal rise temperature of the surface layer (C) is preferably 130° C. or more and 140° C. or less. The heat seal rise temperature of the surface layer (C) is the temperature at which the surfaces of the surface layers (C) of the film of the present invention are placed face to face with each other and a heat seal pressure of 1 kg / cm is applied. 2This is the temperature at which the heat seal strength is 1N / 15mm when heat sealing is performed for 1 second. If the heat seal start temperature of the surface layer (C) is 130°C or higher, the surface layer (C) is less likely to fuse to the seal bar when heat sealing pillow packaging, making it easier to make bags. Also, if it is 140°C or lower, the back adhesive part is more likely to fuse to the exterior part of the package when it is pillow packaging, resulting in a good appearance, and the back adhesive part does not get caught when the packages are stacked, preventing problems with the seal peeling off.

[0024] When a surface layer (C) is provided, the thickness of the surface layer (C) is preferably 1 μm or less. If it exceeds 1 μm, the heat seal strength becomes insufficient. In addition, the thickness of the surface layer (C) is preferably 1.5% or more of the total film thickness in terms of heat seal strength after automatic packaging, and 4% or less in terms of heat seal strength when the film is made into a bag by a heat seal method.

[0025] It is preferable that the surface of the surface layer (C) has anti-fogging properties, which improves the appearance of the packaged fruits and vegetables when they become cloudy due to condensation when they are displayed in a supermarket or the like.

[0026] In addition, it is also possible to add 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, ultraviolet absorbers, etc. that are usually added to polypropylene-based films, so long as the effects of the present invention are not impaired. It is also possible to add inorganic or organic fine particles for ensuring the blocking resistance and slipperiness of the film.

[0027] 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 amorphous, and the particle size thereof may be selected according to the application and method of use of the film. As the organic fine particles, crosslinked particles such as acrylic, methyl acrylate, and styrene-butadiene can be used, and as with the inorganic fine particles, various shapes and sizes can be used. In addition, the surfaces of these inorganic or organic fine particles can be subjected to various surface treatments, and these can be used alone or in combination of two or more types. The above also applies to the sealing layer (B) described below.

[0028] (Method for producing biaxially oriented polypropylene resin film) The biaxially oriented polypropylene resin film of the present invention can be prepared, for example, by melt laminating the films by a T-die method, an inflation method, or the like using an extruder suitable for the number of layers, followed by cooling by a cooling roll method, a water cooling method, or an 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 from 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. Next, the raw sheet is heated to a temperature suitable for stretching, and then stretched by using the speed difference between the stretching rolls. The sheet is stretched in the machine direction, and 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 machine-stretched sheet are held by tenter clips, and the sheet is stretched while being successively expanded in the direction perpendicular to the machine direction while being heated to a temperature suitable for stretching with hot air. The transverse stretching ratio is preferably set between 7 and 10 times in consideration of thickness variation and productivity.

[0029] The biaxially oriented polypropylene resin film of the present invention can be surface-treated to improve printability, lamination, etc. Examples of the surface treatment method include corona discharge treatment, plasma treatment, flame treatment, acid treatment, etc., and are not particularly limited. It is preferable to carry out corona discharge treatment, plasma treatment, or flame treatment, which can be performed continuously and can be easily carried out before the winding step in the production process of this film.

[0030] (Film characteristics) The biaxially oriented polypropylene resin film of the present invention preferably has the following properties.

[0031] (Heat seal start temperature) In the present invention, the seal layer (B) is mainly made of a polypropylene-based resin consisting of a propylene-butene-1 copolymer, and the heat seal initiation temperature of the seal layer (B) is preferably 115° C. or higher and 125° C. or lower. The heat seal initiation temperature of the surface layer (B) is determined by placing the surfaces of the surface layers (B) of the film of the present invention face each other and applying a heat seal pressure of 1 kg / cm. 2 The temperature is the temperature at which the heat seal strength is 1N / 15mm when heat sealing is performed for 1 second. When the heat seal start temperature of the sealing layer (B) is 125°C or less, sufficient strength is maintained even at a low heat seal temperature, making it easy to heat seal, and making it easy to operate at high speeds when automatically packaging.In addition, the sealing part has excellent sealing properties, and this, combined with the anti-fogging properties, maintains the freshness of fresh produce, the appearance of the contents is also good, and the package is easy to handle. Furthermore, when the heat seal start temperature of the sealing layer (B) is 125°C or lower, the difference in melting point with the base layer (A) mainly made of polypropylene resin becomes large, making it easy to sufficiently increase the operating speed of automatic packaging without raising the temperature of the heat seal bar, and since there is no need to set a high 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 sealing defects in the heat sealed area are less likely to occur. When the heat seal start temperature of the sealing layer (B) is 115°C or higher, the heat seal strength is less likely to decrease when bags are made using the heat seal method, making it easy to use both the automatic packaging method and the heat seal method.

[0032] (Heat seal strength) In the present invention, the heat seal strength of the seal layer (B) is preferably 3.5 N / 15 mm or more, which is sufficient for use as an automatic package to prevent the contents from falling out.

[0033] (Anti-fogging) The polypropylene resin film of the present invention is preferably rated as rank 3 or higher in anti-fogging property by the measurement method described below, more preferably rank 2 or higher, and even more preferably rank 1.

[0034] (Anti-fog unevenness) The polypropylene resin film of the present invention is preferably rated as rank 3 or higher, more preferably rank 2 or higher, and even more preferably rank 1, in terms of anti-fog unevenness measured by the measurement method described below.

[0035] (Suitable for automatic packaging) The biaxially oriented polypropylene resin film of the present invention is preferably evaluated as ◯ or Δ in terms of suitability for automatic packaging as measured by the measurement method described below, and more preferably ◯.

[0036] (Fusing seal strength) The biaxially oriented polypropylene resin film of the present invention preferably has a heat-cutting seal strength measured by the measurement method described below of 25 N / 15 mm or more, more preferably 27 N / 15 mm or more. EXAMPLES

[0037] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples without departing from the gist of the present invention. The characteristics in this specification were evaluated by the following methods.

[0038] (1) Melting point of resin Using a differential scanning calorimeter (Perkin-Elmer, "DSC-8500"), 5 mg of the sample was heated to 230°C at 10°C / min under a nitrogen atmosphere, held for 5 minutes, cooled to 30°C at -10°C / min, held for 5 minutes, and then heated to 230°C at 10°C / min. The melting point was determined from the peak top of the peak observed on the highest temperature side of the melting endothermic curve obtained by heating 5 mg of the sample at 230°C at 10°C / min under a nitrogen atmosphere. (2) Layer thickness A biaxially oriented polypropylene resin film that can be automatically packaged was cut into a size of 1 cm x 1 cm, embedded in a UV-curable resin, and hardened by irradiating UV for 5 minutes. After that, a cross-sectional sample was prepared using a microtome and observed using a differential interference microscope, and the thickness of the entire film layer, the seal layer (B), and the surface layer (C) were measured. Five points were measured on the sample, and the average value was calculated.

[0039] (3) Heat seal start temperature The sealing layers (B) of biaxially oriented polypropylene resin films that can be automatically packaged were placed face to face, and the heat seal pressure was 1 kg / cm using a thermal gradient tester (manufactured by Toyo Seiki Co., Ltd.). 2The heat seal strength is the temperature at which the heat seal strength reaches 1N / 15mm when heat-sealed at temperatures starting from 80℃, increasing by 5℃ in increments, for 1 second. The heat seal layer surfaces of a 5cm x 20cm film were placed face to face, and heat-sealed simultaneously with five heat seal bars (seal surface 1cm x 3cm) set at temperatures in 5℃ increments. The center of each piece was cut to a width of 15mm, attached to the upper and lower chucks of a tensile tester, and stretched at a tensile speed of 200mm / min. The strength of each piece was measured, and the heat seal strength was calculated (units: N / 15mm). 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 1N / 15mm was taken as the heat seal rise temperature.

[0040] (4) Heat seal strength The sealing layers (B) of biaxially oriented polypropylene resin films that can be automatically packaged were placed face to face, and the heat seal pressure was 1 kg / cm using a thermal gradient tester (manufactured by Toyo Seiki Co., Ltd.). 2 The sample was heat-sealed at 135°C for 1 second, the centre of which was cut to a width of 15 mm, attached to the upper and lower chucks of a tensile testing machine, and pulled at a speed of 200 mm / min. The heat seal strength was calculated (units: N / 15 mm).

[0041] (5) Anti-fogging properties 1) Pour 300cc of 50°C warm water into a 500cc open-top container. 2) The opening of the container is sealed with the film, with the anti-fogging property measurement surface of the film facing inward. 3) Leave in a cold room at 5°C. 4) After the warm water in the container had completely cooled to the ambient temperature, the degree of condensation on the film surface was evaluated on a 5-point scale. Grade 1: No dew on the entire surface (0 surface area) Grade 2: Some dew adhesion (up to 1 / 4 of surface area) Grade 3: Dew adhesion to about 1 / 2 (up to 2 / 4 of the adhesion area) Grade 4: Almost all dew is attached (up to 3 / 4 of the surface area) Grade 5: Dew on the entire surface (3 / 4 or more of the surface area)

[0042] (6) Anti-fog unevenness 1) Pour 300cc of 50°C warm water into a 500cc open-top container. 2) The opening of the container is sealed with the film, with the anti-fogging property measurement surface of the film facing inward. 3) Leave at 20°C for 20 seconds. 4) The degree of dew adhesion on the film surface was evaluated on a 5-point scale. Grade 1: No dew on the entire surface (0 surface area) Grade 2: Some dew adhesion (up to 1 / 4 of surface area) Grade 3: Dew adhesion to about 1 / 2 (up to 2 / 4 of the adhesion area) Grade 4: Almost all dew is attached (up to 3 / 4 of the surface area) Grade 5: Dew on the entire surface (3 / 4 or more of the surface area)

[0043] (7) Suitability for automatic packaging Heat-sealable layers of biaxially oriented polypropylene resin films that can be automatically packaged were placed face to face and tested at a heat-sealing pressure of 1 kg / cm using a thermal gradient tester (manufactured by Toyo Seiki Co., Ltd.). 2 The heat sealing time was 1 second. At that time, the presence or absence of fusion of the surface layer (C) to the seal bar and the heat seal start temperature were evaluated according to the following criteria. ○: No adhesion to the seal bar; start-up temperature: 115℃ to 125℃ △: No adhesion to the seal bar; start-up temperature is less than 115℃ or more than 125℃ ×: Welded to the seal bar

[0044] (8) Strength of melt-cut seal Using a welding seal machine (Kyoei Printing Machinery Materials Co., Ltd.: PP500 type), we created welding seal bags of polypropylene-based resin multilayer film that can be automatically packaged. Conditions: Cutting blade; cutting edge angle 60° Sealing temperature: 370℃ Shot rate: 120 bags / min The weld-sealed portion of the above weld-sealed bag was cut to a width of 15 mm, and both ends were held in the grip of a tensile tester (grip interval: 200 mm) with no slack, and pulled at a tensile speed of 200 mm / min. The weld-seal strength (N / 15 mm) was calculated from the strength at which the sealed portion broke. Measurements were taken five times and averaged. A value of 20 N / 15 mm or more was deemed to be suitable for weld-sealing.

[0045] Example 1 (1)Resin used The resins constituting the respective layers used in the following production examples are as follows. [PP-1]: Propylene homopolymer: "FS2011DG3" manufactured by Sumitomo Chemical Co., Ltd., MFR: 2.5g / 10min, melting point: 158℃, [PP-2]: 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-3]: Propylene-butene-1 copolymer: "SPX78J1" manufactured by Sumitomo Chemical Co., Ltd., butene content: 25 mol%, MFR: 8.5 g / 10 min, melting point: 128°C

[0046] (2) Base layer (A) resin composition [PP-1] was mixed with 0.16 wt% glycerin monostearate (Matsumoto Yushi Pharmaceutical Co., Ltd., TB-123), 0.2 wt% polyoxyethylene (2) stearylamine (Matsumoto Yushi Pharmaceutical Co., Ltd., TB-12), and 0.6 wt% polyoxyethylene (2) stearylamine monostearate (Matsumoto Yushi Pharmaceutical Co., Ltd., Elex 334) as anti-fogging agents to produce [PP-4], which was used at 100 wt% as the resin forming the base layer (A).

[0047] (4) Sealing layer (B) resin composition [PP-6] was prepared by adding 0.50% by weight of glycerin monostearate (Matsumoto Yushi Seiyaku Co., Ltd., TB-123) as an anti-fogging agent to [PP-3], and this was used as the resin for forming the sealing layer (B).

[0048] (3) Surface layer (C) resin composition [PP-2] was mixed with 1.5% by weight of organic polymer particles (CS30: Sumitomo Chemical Co., Ltd.: particle size 3.5 μm) and 0.45% by weight of glycerin monostearate (Matsumoto Yushi Seiyaku Co., Ltd., TB-123) as an anti-fogging agent, and melted and mixed to a resin temperature of 240°C to form pellets. This raw material was designated [PP-5] and used at 100% by weight as the resin for forming the surface layer (C).

[0049] Using three melt extruders, the base layer (A) was melt extruded from the first extruder at a resin temperature of 280 ° C., the surface layer (C) forming resin was melt extruded from the second extruder at a resin temperature of 250 ° C., and the seal layer (B) forming resin was melt extruded from the third extruder at a resin temperature of 250 ° C., and the layers were laminated and extruded in the order of surface layer (C) / base layer (A) / seal layer (B) from the chill roll contact surface so that the thickness ratio of surface layer (C) / base layer (A) / seal layer (B) = 0.6 / 18.7 / 0.7 in the T-die, and cooled and solidified with a cooling roll of 30 ° C. to obtain an unstretched sheet. Subsequently, between metal rolls heated to 130 ° C., the sheet was stretched 4.5 times in the longitudinal direction using the peripheral speed difference, and further introduced into a tenter stretching machine and stretched 9.5 times in the transverse direction. The preheating zone temperature of the tenter stretching machine was 168°C, and the stretching zone temperature was 155°C.

[0050] Furthermore, in the latter half of the tenter stretching machine, heat setting was performed at 163°C, and then the surface of the surface layer (C) was subjected to a corona discharge treatment using a corona discharge treatment machine manufactured by Kasuga Electric Co., Ltd., and then the seal layer (B) was similarly subjected to a corona discharge treatment, and a biaxially oriented polypropylene-based resin film that could be wound up by a film winder and automatically packaged was obtained. The final film thickness was 20 μm, and the thickness ratio of the seal layer (B) to the entire film was 3.5%. The obtained multilayer film satisfied the requirements of the present invention, and had sufficient heat seal strength and ultimate strength at low temperatures, and was suitable for automatic packaging and heat-cutting and sealing. The anti-fogging properties were also at a level that did not pose a problem when packaging fruits and vegetables. The film composition and physical properties are shown in Table 1.

[0051] Example 2 A laminated film was obtained in the same manner as in Example 1, except that the thickness of the base layer (A) was increased to make the film thickness 25 μm and the thickness ratio of the seal layer (B) 2.8%. The obtained laminated film had both automatic packaging suitability and melt-cutting and sealing suitability, as in Example 1. The anti-fogging properties were also at a level that did not pose a problem when packaging fruits and vegetables. The film composition and physical properties are shown in Table 1.

[0052] 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 increased to make the film thickness 30 μm and the thickness ratio of the seal layer (B) 2.3%. The obtained laminated film had both automatic packaging suitability and melt-cutting and sealing suitability, as in Example 1. The anti-fogging properties were also at a level that did not pose a problem when packaging fresh produce. The film composition and physical property results are shown in Table 1.

[0053] 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 increased to make the film thickness 40 μm and the thickness ratio of the seal layer (B) 1.8%. The obtained laminated film had both automatic packaging suitability and melt-cutting seal suitability, as in Example 1. The anti-fogging properties were also at a level that did not pose a problem when packaging fresh produce. The film composition and physical property results are shown in Table 1.

[0054] Example 5 A laminated film was obtained in the same manner as in Example 1, except that the surface layer (C) was not provided, and the thickness of the base layer (A) was increased to make the film thickness 40 μm and the thickness ratio of the seal layer (B) 1.8%. The obtained laminated film had both automatic packaging suitability and melt-cutting seal suitability, as in Example 1. The anti-fogging properties were also at a level that did not pose a problem when packaging fresh produce. The film composition and physical property results are shown in Table 1.

[0055] Comparative Example 1 A laminated film was obtained in the same manner as in Example 1, except that the amount of [PP-6] added to the seal layer (B) was 40% by weight and the amount of [PP-3] added was 60% by weight. The obtained laminated film had anti-fogging unevenness and was inferior in anti-fogging properties. The film composition and physical properties are shown in Table 1.

[0056] Comparative Example 2 A laminated film was obtained in the same manner as in Example 4, except that the thickness of the base layer was 38.2 μm and the thickness of the seal layer (B) was 1.2 μm. The obtained laminated film had anti-fogging unevenness, was inferior in anti-fogging properties, and was also inferior in melt-cutting seal strength. The film composition and physical property results are shown in Table 1.

[0057] Comparative Example 3 A laminated film was obtained in the same manner as in Example 1, except that the amount of [PP-6] added to the seal layer (B) was 10% by weight, the amount of [PP-3] added was 70% by weight, and the amount of [PP-2] added was 20% by weight. The obtained laminated film had anti-fogging unevenness and was inferior in anti-fogging properties. The film composition and physical properties are shown in Table 1.

[0058] Comparative Example 4 A laminated film was obtained in the same manner as in Example 2, except that the thickness of the base layer was 28.7 μm, the amount of [PP-6] added to the seal layer (B) was 10% by weight, the amount of [PP-3] added was 70% by weight, and the amount of [PP-2] added was 20% by weight. The obtained laminated film had anti-fogging unevenness and was inferior in anti-fogging properties. The film composition and physical properties are shown in Table 1.

[0059] Comparative Example 5 A laminated film was obtained in the same manner as in Example 4, except that the amount of [PP-6] added to the seal layer (B) was 10% by weight, the amount of [PP-3] added was 70% by weight, and the amount of [PP-2] added was 20% by weight. The obtained laminated film had anti-fogging unevenness and was inferior in anti-fogging properties. The film composition and physical properties are shown in Table 1.

[0060] [Table 1] [Industrial Applicability]

[0061] The biaxially oriented polypropylene resin film of the present invention, which can be used for automatic packaging, can be provided with good pillow packaging suitability at a lower cost than conventional films by optimizing the seal thickness and composition, and since it also has anti-fogging properties, it is particularly suitable for packaging fruits and vegetables.

Claims

1. The laminated ... A biaxially oriented polypropylene resin film that satisfies the following conditions a), b), c), and d). a) The thickness of the sealing layer (B) is 1 μm or less. b) The sealing layer (B) contains an anti-fogging agent. c) The thickness of the sealing layer (B) is 1.5% or more and 4% or less of the total thickness of the film. d) After the following operations, the dew area of ​​the film surface is 1 / 4 or less. 1) Pour 300cc of 50°C hot water into a 500cc open-top container. 2) The opening of the container is sealed with the film, with the surface of the film to be measured for anti-fogging property facing inward. 3) Leave at 20°C for 20 seconds.

2. The biaxially oriented polypropylene resin film according to claim 1, further comprising a surface layer (C) on the opposite side of the base layer (A) to the seal layer (B), the surface layer (C) being made of a resin composition mainly composed of at least one resin selected from the group consisting of propylene-ethylene-butene-1 copolymer and propylene-ethylene copolymer.

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

4. A packaging material comprising the biaxially oriented polypropylene resin film according to any one of claims 1 to 3.

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