Biaxially oriented polypropylene film for packaging

Abstract

To provide a biaxially oriented polypropylene film for packaging provided with excellent transparency and sense of perspective, glossy feeling and fusion cutting strength, in addition, for reduction of a load on an environment.SOLUTION: A biaxially oriented polypropylene film used for packaging and composed of a plurality of layers of at least three or more layers of an outer surface layer, an intermediate layer, and an inner surface layer, and the outer surface layer and the inner surface layer are composed of a resin composition mainly composed of the same or different propylene polymers, and the intermediate layer is composed of a propylene polymer of 85-98 wt.% and an ethylene polymer (E) of 2-15 wt.%, the ethylene-based polymer has density of 0.904-0.945 g / cm3, a melt flow rate (190°C., 2.16 kg load) of 1.0-8.0 g / 10 min, and a narrow angle diffusion transmittance (LSI) of 50% or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a biaxially oriented polypropylene film for packaging applications. [Background technology]

[0002] Biaxially oriented polypropylene film is widely used as a packaging material because of its excellent transparency and gloss. Among them, it is often used in the form of a bag, which is sometimes processed by welding and sealing.

[0003] As a polypropylene film to be melt-cut and sealed to form a bag, a film stretched at a low ratio in the MD (machine direction) has been proposed (see, for example, Patent Document 1). However, because the stretching is done at a low ratio, there is a risk of uneven stretching. In addition, because the stretching is done at a high temperature, there is a concern that the sheet will adhere to the roll, resulting in deterioration of film formability and appearance.

[0004] Other films have been proposed that improve sealability by laminating a low-melting-point resin, such as an olefin copolymer or a polyethylene resin, on the surface (see, for example, Patent Documents 2 to 4). However, the use of a low-melting-point resin on the inner surface tends to make the film sticky, raising concerns about reduced slipperiness and blocking resistance. Furthermore, the reduced slipperiness and blocking resistance may worsen processability and ease of opening.

[0005] In recent years, there has been a strong demand for initiatives to create a recycling-oriented society that reduces the burden on the environment by increasing the use of renewable resources. Renewable resources are primarily resources made from processed plants or plant-derived materials, and are also called biomass resources. In the case of biomass resources, carbon dioxide from the atmosphere is absorbed as the plant grows. When used as a biomass resource for fuel, etc., it is decomposed again into water and carbon dioxide. Therefore, the amount of carbon dioxide does not increase. In other words, biomass resources are a resource that will need to be incorporated on a large scale in the future from the perspective of carbon neutrality.

[0006] In the field of plastics, biomass-derived plastics such as polylactic acid and biodegradable polymers are being produced, but production volumes are limited and they cannot be said to be widely used.On the other hand, with regard to polyethylene, the most commonly used material among general-purpose plastics, a method of obtaining polyethylene from plant-derived sugars via ethanol has been commercialized and is becoming widespread.

[0007] As a resin film using biomass-derived polyethylene, a film using only an ethylene-based resin has been proposed (see, for example, Patent Document 5). However, since this film is composed only of an ethylene-based resin, it has poor heat resistance. Also, a film has been proposed in which biomass-derived polyethylene is added to a polypropylene-based resin (see, for example, Patent Document 6). However, these films tend to be poor in transparency and see-through ability.

[0008] Therefore, the inventors conducted extensive research and developed a biaxially oriented polypropylene film that is widely used in the packaging field, particularly when formed into bags by welding and sealing, and that has excellent transparency, gloss, and welding and sealing strength.Furthermore, by containing a large amount of resin derived from biomass resources, it is possible to reduce the environmental burden. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 9-169050 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-90543 [Patent Document 3] Japanese Patent Application Laid-Open No. 2007-253349 [Patent Document 4] Japanese Patent Application Laid-Open No. 2013-27977 [Patent Document 5] Patent No. 5862055 [Patent Document 6] Japanese Patent Application Publication No. 2018-65267 Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention has been proposed in view of the above circumstances, and provides a biaxially oriented polypropylene film for packaging that has excellent transparency, see-through quality, glossiness, and welding seal strength, and furthermore, that can reduce the burden on the environment. [Means for solving the problem]

[0011] That is, the first invention is a biaxially oriented polypropylene film used for packaging, which comprises at least three or more layers, namely an outer surface layer, an intermediate layer, and an inner surface layer, wherein the outer surface layer and the inner surface layer are each made of a resin composition mainly containing the same or different propylene-based polymers, and the thickness of the outer surface layer and the inner surface layer is configured to be greater than 0.8 μm, and the intermediate layer has a composition containing 85 to 98 wt % of a propylene-based polymer and 2 to 15 wt % of an ethylene-based polymer (E), and the ethylene-based polymer (E) has a density of (e1) 0.916 g / cm 3 (e2) Melt flow rate (190°C, 2.16 kg load) 1.0 The present invention relates to a biaxially oriented polypropylene film for packaging, characterized in that the narrow angle diffuse transmittance (LSI) is 50% or less, and the surface gloss of the biaxially oriented polypropylene film measured in accordance with JIS Z 8741 (1997) is 100% or more.

[0012] A second invention relates to the biaxially oriented polypropylene film for packaging according to the first invention, characterized in that the ethylene polymer (E) is a linear low-density polyethylene.

[0013] The third invention relates to the biaxially oriented polypropylene film for packaging according to the first or second invention, characterized in that the ethylene polymer (E) is produced using a Ziegler-Natta catalyst.

[0014] The fourth invention relates to a biaxially oriented polypropylene film for packaging according to any one of the first to third inventions, characterized in that the haze value of the biaxially oriented polypropylene film measured in accordance with JIS K 7136 (2000) is 6% or less.

[0016] No. 5 The inventions are the first to 4 The present invention relates to a biaxially stretched polypropylene film for packaging, characterized in that the ethylene polymer (E) is a biomass-derived ethylene polymer.

[0017] No. 6 The inventions are the first to 5 The present invention relates to a packaging bag made of any one of the biaxially oriented polypropylene films for packaging. [Effects of the Invention]

[0018] According to the first aspect of the present invention, there is provided a biaxially oriented polypropylene film for packaging, which is used for packaging and comprises at least three or more layers, namely an outer surface layer, an intermediate layer, and an inner surface layer, wherein the outer surface layer and the inner surface layer are each made of the same or different resin compositions mainly containing a propylene-based polymer, and the thickness of the outer surface layer and the inner surface layer is configured to be greater than 0.8 μm, and the intermediate layer has a composition containing 85 to 98 wt % of a propylene-based polymer and 2 to 15 wt % of an ethylene-based polymer (E), and the ethylene-based polymer (E) has a density of (e1) 0.916 g / cm 3 (e2) Melt flow rate (190°C, 2.16 kg load) 1.0The biaxially oriented polypropylene film has a narrow angle diffuse transmittance (LSI) of 50% or less, and a surface gloss of 100% or more as measured in accordance with JIS Z 8741 (1997). This means that the biaxially oriented polypropylene film has excellent transparency, visibility, gloss, and weld seal strength, as well as excellent gloss and a luxurious appearance.

[0019] According to the biaxially oriented polypropylene film for packaging of the second invention, since the ethylene polymer (E) in the first invention is a linear low-density polyethylene, it has better transparency and gloss.

[0020] According to the biaxially oriented polypropylene film for packaging of the third invention, in the first or second invention, the ethylene polymer (E) is produced from a Ziegler-Natta catalyst, and therefore has better melt-cutting and sealing properties.

[0021] According to the biaxially oriented polypropylene film for packaging of the fourth invention, in any of the first to third inventions, the haze value of the biaxially oriented polypropylene film measured in accordance with JIS K 7136 (2000) is 6% or less, and therefore the film has excellent transparency and see-through properties.

[0023] No. 5 According to the biaxially oriented polypropylene film for packaging of the present invention, 4 In any one of the above aspects, the ethylene polymer (E) is a biomass-derived ethylene polymer, thereby reducing the environmental load.

[0024] No. 6 According to the packaging bag of the present invention, the first to third 5 Since the biaxially oriented polypropylene film for packaging according to any one of the above aspects is made of a film having excellent transparency, see-through, glossiness and welding seal strength, the packaging bag can be made to have a luxurious feel, be strong, and be resistant to tearing. [Brief explanation of the drawings]

[0025] [Figure 1] 1 is a schematic cross-sectional view of a three-layer biaxially oriented polypropylene film according to one embodiment of the present invention. [Figure 2] 1 is a schematic diagram showing positions at which test pieces of a bag-shaped biaxially oriented polypropylene film of the present invention are cut out to be used for measuring the welding seal strength. DETAILED DESCRIPTION OF THE INVENTION

[0026] The film of the present invention is used for bag production by welding and sealing. A heated rod-shaped heater (a welding blade) is pressed against a film folded in half in a direction perpendicular to the folded part that will become the bottom, cutting the film, thereby bonding and sealing the film with heat and forming it into a bag. The method for producing bags by welding and sealing can be appropriately selected from known methods.

[0027] Fig. 1 is a schematic cross-sectional view of a biaxially oriented polypropylene film 10 according to one embodiment of the present invention. The film 10 is a laminated film 20 composed of at least three layers: an outer surface layer 11, an intermediate layer 12, and an inner surface layer 13. The film 10 is produced by biaxially stretching a sheet obtained by co-extruding a melted raw resin of each layer, extruding the melted raw resin from a T-die or the like to a predetermined thickness, and then stretching the resulting sheet by a known stretching method. From the viewpoints of ease of handling and strength, the thickness of the biaxially oriented polypropylene film 10 is preferably in the range of 1 to 100 µm.

[0028] The outer surface layer 11 and the inner surface layer 13 of the film 10 are composed of a resin composition mainly containing a propylene-based polymer, and an appropriate resin such as a propylene homopolymer (homopolypropylene) or a propylene-ethylene random copolymer is selected. Polypropylene-based polymers have excellent heat resistance, chemical resistance, and strength. The outer surface layer 11 and the inner surface layer 13 may be made of the same resin or different resins, which can be selected appropriately depending on the application of the film. Additives such as antiblocking agents, antistatic agents, antioxidants, neutralizing agents, and colorants may be added to the outer surface layer 11 and the inner surface layer 13 as needed.

[0029] As described in the examples below, the outer surface layer 11 and the inner surface layer 13 are configured to have a thickness of more than 0.8 μm because if the thickness of the surface layer is 0.8 μm or less, transparency and glossiness are impaired.

[0030] The intermediate layer is composed of a propylene polymer and an ethylene polymer (E), and the composition is 85 to 98% by weight of the propylene polymer and 2 to 15% by weight of the ethylene polymer. Preferably, the propylene polymer is 92 to 98% by weight and the ethylene polymer is 2 to 8% by weight. If the amount of the ethylene polymer added is less than 2% by weight, the film's welding seal strength may decrease, and the desired strength may not be achieved. If the amount of the ethylene polymer added is more than 15% by weight, the transparency and gloss of the film may be impaired.

[0031] The propylene-based polymer used in the intermediate layer may be the same as or different from the propylene-based polymer used in the outer surface layer and the inner surface layer, and can be appropriately selected depending on the desired film performance.

[0032] The ethylene polymer (E) used in the intermediate layer has a density of 0.904 to 0.945 g / cm 3 (e1), and preferably 0.916 to 0.938 g / cm 3 The melt flow rate (MFR) (190°C, 2.16 kg load) is 1.0 to 8.0 g / 10 min (e2), preferably 1.0 to 5.0 g / 10 min. The density is 0.904 g / cm. 3 If the density is less than 0.945 g / cm, the transparency and gloss of the film may be impaired. 3 Similarly, if the melt flow rate is lower or higher than the above range, the transparency and gloss of the film may be impaired, and the melt-cutting and sealing strength may also be reduced.

[0033] Furthermore, the ethylene polymer (E) is preferably a linear low-density polyethylene, which has excellent transparency and gloss when made into a film. Furthermore, the ethylene polymer (E) is preferably produced by a polymerization method using a Ziegler-Natta catalyst, because this tends to provide higher weld-seal strength when made into a film than ethylene polymers produced by a polymerization method using a metallocene catalyst.

[0034] The ethylene polymer (E) is preferably a biomass-derived polyethylene resin. The biomass-derived polyethylene resin is a polyethylene resin obtained by processing plant raw materials. Specifically, ethanol is produced from a sugar solution extracted from a plant raw material such as sugarcane through alcoholic fermentation using yeast, and then ethylene is produced from the ethanol through a known resinification process to produce polyethylene. This biomass-derived polyethylene resin contributes to reducing the environmental impact of the final product.

[0035] The haze of a biaxially oriented polypropylene film should be 6% or less. A film with a haze of less than 6% has excellent transparency. Haze is measured in accordance with JIS K 7136 (2000), as described in the examples below. Furthermore, the narrow-angle diffuse transmittance (LSI) of a biaxially oriented polypropylene film should be 50% or less. If the narrow-angle diffuse transmittance (LSI) exceeds 50%, the film may have poor transparency and may be less suitable for use as a packaging film.

[0036] The surface gloss of biaxially oriented polypropylene film should be 100% or higher. A surface gloss of more than 100% gives the film a luxurious appearance. The surface gloss is measured in accordance with JIS Z 8741 (1997), as described in the examples below. [Example]

[0037] [Film molding] The films of Prototype Examples 1 to 16 and Comparative Examples 1 and 2 were molded as follows. The materials described below were kneaded and melted, and the layers were laminated in the order of inner surface layer, intermediate layer, and outer surface layer. The materials were coextruded from a three-layer coextrusion T-die film molding machine set at 240°C, cooled on a 50°C cooling roll, and solidified to obtain a sheet-like material. The sheet-like material was then preheated at a set temperature of 100-115°C, stretched 4.8 times in the longitudinal direction (MD), and annealed at a set temperature of 135°C. The sheet was preheated in a tenter at a set temperature of 180°C, stretched 8.0 times in the transverse direction (TD) at a set temperature of 155°C, and annealed at a set temperature of 160°C. After exiting the tenter, the film was subjected to corona discharge treatment and wound on a winder to obtain a biaxially oriented polypropylene film. The biaxially oriented polypropylene film was produced to a thickness of 30 μm. The melt flow rate (MFR) is measured in accordance with JIS K 7210 (2014), at 190°C for polyethylene resins and 230°C for polypropylene resins.

[0038] [Materials used as propylene polymers in each layer] The following resins PP1 and PP2 were used as the polypropylene resins constituting the resin compositions of the outer and inner surface layers and the intermediate layer. Powdered synthetic silica (manufactured by Fuji Silysia Ltd., product name "Sylisia 730") was added appropriately to the outer and inner surface layers as an anti-blocking agent. Resin PP1: Homopolypropylene (Japan Polypropylene Corporation, product name "FL203D", density 0.90 g / cm 3 , MFR: 3.0g / 10min) Resin PP2: Random polypropylene (Japan Polypropylene Corporation, product name "FX4G", density 0.90 g / cm 3 , MFR: 5.0g / 10min)

[0039] [Materials used as ethylene polymers in the intermediate layer] For the intermediate layer, the following resins PE1 to PE3 were used as biomass-derived polyethylene resins, and the following resins PE4 to PE10 were used as non-biomass-derived polyethylene resins. Resin PE1: Biomass-derived linear low-density polyethylene polymerized using a Ziegler-Natta catalyst (manufactured by Braskem, product name "SLH118", density: 0.916 g / cm 3 , MFR: 1.0g / 10min) Resin PE2: Biomass-derived linear low-density polyethylene polymerized using a Ziegler-Natta catalyst (manufactured by Braskem, product name "SLH218", density: 0.916 g / cm 3 , MFR: 2.3g / 10min) Resin PE3: Biomass-derived high-density polyethylene polymerized using a Ziegler-Natta catalyst (manufactured by Braskem, product name "SGF4960", density: 0.961 g / cm 3 , MFR: 0.34g / 10min) Resin PE4: Linear low-density polyethylene polymerized using a metallocene catalyst (manufactured by Ube Maruzen Polyethylene Co., Ltd., product name "4040FC", density: 0.938 g / cm 3 , MFR: 3.5g / 10min) Resin PE5: Linear low-density polyethylene polymerized using a metallocene catalyst (manufactured by Ube Maruzen Polyethylene Co., Ltd., product name "4540F", density: 0.944 g / cm 3 , MFR: 4.0g / 10min) Resin PE6: Linear low-density polyethylene polymerized using a metallocene catalyst (manufactured by Ube Maruzen Polyethylene Co., Ltd., product name "2040FC", density: 0.919 g / cm 3 , MFR: 5.0g / 10min) Resin PE7: Linear low-density polyethylene polymerized using a metallocene catalyst (manufactured by Ube Maruzen Polyethylene Co., Ltd., product name "022GS", density: 0.904 g / cm 3 , MFR: 8.0g / 10min) Resin PE8: Linear low-density polyethylene polymerized using a metallocene catalyst (Prime Polymer Co., Ltd., product name "SP2020", density: 0.916 g / cm 3 , MFR: 2.3g / 10min) Resin PE9: Linear low-density polyethylene polymerized using a metallocene catalyst (Prime Polymer Co., Ltd., product name "SP3010", density: 0.926 g / cm 3 , MFR: 0.8g / 10min) Resin PE10: Linear low-density polyethylene polymerized using a metallocene catalyst (manufactured by Ube Maruzen Polyethylene Co., Ltd., product name "015AN", density: 0.911 g / cm 3 , MFR: 14.0g / 10min)

[0040] [Prototype 1] In prototype 1, the inner surface layer was made of resin PP1 with a thickness of 1.0 μm, the middle layer was made of 98% by weight of resin PP1 and 2% by weight of resin PE1, and the outer surface layer was made of resin PP2 with a thickness of 1.2 μm. Corona treatment was performed on the surface of the outer surface layer.

[0041] [Prototype 2] Prototype 2 is a film formed in the same manner as Prototype 1, except that the composition of the intermediate layer was changed to 96% by weight of resin PP1 and 4% by weight of resin PE1.

[0042] [Prototype 3] Prototype 3 is a film formed in the same manner as Prototype 1, except that the composition of the intermediate layer was changed to 92% by weight of resin PP1 and 8% by weight of resin PE1.

[0043] [Prototype 4] Prototype 4 is a film formed in the same manner as Prototype 1, except that the composition of the intermediate layer was 85% by weight of resin PP1 and 15% by weight of resin PE1.

[0044] [Prototype 5] Prototype 5 is a film formed in the same manner as Prototype 4, except that the thickness of the inner surface layer was 0.8 μm and the thickness of the outer surface layer was 0.8 μm.

[0045] [Prototype 6] Prototype 6 is a film formed in the same manner as Prototype 5, except that the composition of the intermediate layer was changed to 75% by weight of resin PP1 and 25% by weight of resin PE1.

[0046] [Prototype 7] Prototype 7 is a film formed in the same manner as Prototype 5, except that the resin PE1 in the intermediate layer was changed to resin PE2.

[0047] [Prototype 8] Prototype 8 is a film formed in the same manner as Prototype 4, except that the resin PE1 in the intermediate layer was changed to resin PE4.

[0048] [Prototype 9] Prototype 9 is a film formed in the same manner as Prototype 4, except that the resin PE1 in the intermediate layer was changed to resin PE5.

[0049] [Prototype 10] Prototype 10 is a film formed in the same manner as Prototype 4, except that the resin PE1 in the intermediate layer was changed to resin PE6.

[0050] [Prototype 11] Prototype 11 is a film formed in the same manner as Prototype 4, except that the resin PE1 in the intermediate layer was changed to resin PE7.

[0051] [Prototype 12] Prototype 12 is a film formed in the same manner as Prototype 1, except that resin PP2 was used for the inner surface layer, the composition of the middle layer was 85% by weight of resin PP1 and 15% by weight of resin PE2, and resin PP1 was used for the outer surface layer. Corona treatment was performed on the surface on the inner surface layer side.

[0052] [Prototype 13] Prototype 13 is a film formed in the same manner as Prototype 12, except that the resin PE2 in the intermediate layer was changed to resin PE8.

[0053] [Prototype 14] Prototype 14 is a film formed in the same manner as Prototype 4, except that the resin PE1 in the intermediate layer was changed to resin PE9.

[0054] [Prototype 15] Prototype 15 is a film formed in the same manner as Prototype 4, except that the resin PE1 in the intermediate layer was changed to resin PE10.

[0055] [Prototype 16] Prototype 16 is a film formed in the same manner as Prototype 1, except that the composition of the intermediate layer was 95.2% by weight of resin PP1 and 4.8% by weight of resin PE3.

[0056] [Comparative Example 1] Comparative Example 1 is a film formed in the same manner as in Prototype Example 1, except that the composition of the intermediate layer was 100% by weight of resin PP1.

[0057] Comparative Example 2 Comparative Example 2 is a film formed in the same manner as Comparative Example 1, except that the resins of the inner surface layer and the outer surface layer were interchanged. Corona treatment was performed on the surface on the inner surface layer side.

[0058] For the films of Prototype Examples 1 to 16 and Comparative Examples 1 and 2, the resin composition of each layer, the layer subjected to corona treatment, and the thickness of the inner surface layer and outer surface layer are shown in Tables 1 to 4.

[0059] [Table 1]

[0060] [Table 2]

[0061] [Table 3]

[0062] [Table 4]

[0063] [Film performance evaluation] The films of Prototype Examples 1 to 16 and Comparative Examples 1 and 2 were measured for haze, narrow-angle diffuse transmittance, surface gloss (inner surface layer, outer surface layer), and welding seal strength.

[0064] [Haze measurement] Haze (%) is an index of transparency and was measured in accordance with JIS K 7136 (2000) using a haze meter (NDH-5000, manufactured by Nippon Denshoku Industries Co., Ltd.) For the films of Prototype Examples 1 to 16 and Comparative Examples 1 and 2, a measurement result of 4.0% or less was evaluated as an excellent product with a double circle, 4.1 to 6.0% was evaluated as a fair product with a circle, and 6.1% or more was evaluated as an x.

[0065] [Measurement of narrow-angle diffuse transmittance] The narrow angle diffuse transmittance (LSI) (%) is an index of see-through feeling, and indicates the ratio of the amount of scattered light at a scattering angle of 0.4° to 1.2° to the amount of total light transmitted. LSI is a measure of see-through feeling to the naked eye, and the lower the value, the better the see-through feeling. LSI was measured using a visual transparency tester (manufactured by Toyo Seiki Seisaku-sho, Ltd.). For the films of Prototype Examples 1 to 16 and Comparative Examples 1 and 2, measurement results of 35.0% or less were evaluated as excellent products with a "◎", 35.1 to 50.0% were evaluated as fair products with a "◯", and 50.1% or more were evaluated as "X".

[0066] [Surface gloss measurement] The surface gloss (%) is an index showing the glossiness of the film surface, and was measured in accordance with JIS Z 8741 (1997) using a digital gloss meter (VG-7000, manufactured by Nippon Denshoku Kogyo Co., Ltd.) For the films of Prototype Examples 1 to 16 and Comparative Examples 1 and 2, a measurement result of 121% or more was evaluated as an excellent product with a "◎", a measurement result of 100 to 120% was evaluated as a fair product with a "◯", and a measurement result of 99% or less was evaluated as an "×".

[0067] [Measurement of welding seal strength] Using the films of Prototype Examples 1 to 16 and Comparative Examples 1 and 2, bags were made by welding sealing, with the inner surface layer facing the inside of the bag. The film flowing in the MD direction was folded in half, and a welding sealing machine (Totani Giken Kogyo Co., Ltd., "HK-40V") was used to press a welding blade arranged perpendicular to the flow direction against the film to perform welding sealing to form a bag-like product. As shown in the schematic diagram of Figure 2, a bag-like product 30 was obtained, with the bottom edge 31 being a folded portion 41 and both side edges 32, 33 being welding-sealed portions 42, 43. The welding sealing conditions were as follows. The reference numeral 34 in the figure denotes an opening. Sealing temperature: 300℃, 350℃, 400℃ Heating blade tip angle: 120 degrees Fusing interval: 200mm Shot rate: 72 shots / minute

[0068] Twenty bags were selected from each bag-shaped product obtained at each sealing temperature and subjected to the following measurements. As shown in FIG. 2, a 15 mm wide, 100 mm long test piece 50 was cut from each of the weld-sealed portions 42 and 43 on both sides of the bag-shaped product (1) so that the weld-sealed portion was located in the center. The dashed-dotted line in the figure indicates the cut line 51. The test piece was fixed in the chuck of a tensile tester (Shimadzu Corporation, "AUTOGRAPH AGS-X 50N") and the chuck distance of the test piece was adjusted to 50 mm. The test piece was pulled at 200 mm / min, and the strength at which the weld-sealed portion broke was measured. The average value of all measurement results for the weld-sealed portions of the bags produced at each sealing temperature (300°C, 350°C, and 400°C) was used as the weld-seal strength (N / 15 mm).

[0069] [comprehensive evaluation] In the overall evaluation, if a result of "◎" was obtained for all of the evaluation items described below, it was given an "A," if at least one item was given a "〇," it was given a "B," and if at least one item was given an "×," it was given a "C." The results are shown in Tables 5 to 8 below.

[0070] [Table 5]

[0071] [Table 6]

[0072] [Table 7]

[0073] [Table 8]

[0074] [Results and Discussion] As shown in Tables 5 to 8, the overall evaluation was "C" for Prototypes 5 to 7, 14 to 16, and Comparative Examples 1 and 2. Prototypes 5 and 7 are prototypes in which the thicknesses of the outer surface layer and inner surface layer of Prototypes 4 and 12, respectively, were reduced. It was found that when the thicknesses of the outer surface layer and inner surface layer are each thinner than 0.8 μm, the transparency and glossiness decrease, making it impossible to obtain a film with the desired functions. Furthermore, Prototype 6 is a prototype in which the proportion of ethylene-based polymer in the intermediate layer composition of Prototype 5 is increased, and it is even inferior in transparency and glossiness compared to Prototype 5, so it was understood that the upper limit of the proportion of ethylene-based polymer in the intermediate layer is 15 wt%.

[0075] Prototype 14 is a prototype example in which the composition of the intermediate layer of Prototype 4 was changed to a resin with a smaller MFR value of the ethylene polymer. Prototype 15 is a prototype example in which the composition of the intermediate layer of Prototype 4 was changed to a resin with a larger MFR value of the ethylene polymer. Both were found to have inferior see-through properties compared to Prototype 4, demonstrating that the MFR value of the resin used in the intermediate layer must be within a specified range. Furthermore, Prototype 16 also revealed that see-through properties and glossiness were impaired when the density of the ethylene polymer constituting the intermediate layer exceeded a certain level.

[0076] Generally, the corona-treated surface tends to be less susceptible to heat fusion, but it was shown that the weld-cutting seal strength can be improved by including a specified amount of a specified ethylene polymer in the composition of the intermediate layer. In particular, Comparative Examples 1 and 2 tend to have poorer weld-cutting seal strength than the other prototypes.

[0077] In contrast, the prototypes containing a specified amount of a specified ethylene polymer in the intermediate layer were all evaluated as excellent or good, demonstrating that a film having the desired functions can be provided, and that a film can be provided that has sufficient strength when made into a bag by welding sealing, and that can be used to obtain a bag-like product having excellent functionality such as transparency, see-through feeling, and gloss, as well as a luxurious feel.

[0078] Furthermore, Prototypes 1 to 4 and 12, which used biomass-derived ethylene polymers, were also well-reviewed and excellent films were produced. This means that films can be produced that have excellent transparency, see-through quality, glossiness, and excellent welding seal strength while reducing the environmental impact. [Industrial Applicability]

[0079] The biaxially oriented polyolefin film for packaging of the present invention has excellent transparency, see-through quality, and glossiness, as well as excellent weld-seal strength, and is therefore suitable for a wide range of applications, such as packaging bags for foods and miscellaneous goods. Furthermore, the film contains a large amount of resin derived from biomass resources, which helps reduce the environmental impact. [Explanation of symbols]

[0080] 10 Biaxially oriented polypropylene film 11 Outer surface layer 12 Middle Class 13 Inner surface layer 20 Laminated Film 30 Bags 31 Bottom 32,33 Side part 34 Opening 41 Turning section 42,43 Welding seal part

Claims

1. A biaxially oriented polypropylene film used for packaging, which is composed of at least three layers, an outer surface layer, an intermediate layer, and an inner surface layer, the outer surface layer and the inner surface layer are each made of the same or different resin compositions mainly containing a propylene-based polymer, The outer surface layer and the inner surface layer each have a thickness greater than 0.8 μm, the intermediate layer has a composition containing 85 to 98% by weight of a propylene-based polymer and 2 to 15% by weight of an ethylene-based polymer (E), The ethylene polymer is (e1) Density 0.916 g / cm ３ year, (e2) Melt flow rate (190 ° C, 2.16 kg load) is 1.0 g / 10 min, The narrow angle diffuse transmittance (LSI) is 50% or less, The surface gloss of the biaxially oriented polypropylene film measured in accordance with JIS Z 8741 (1997) is 100% or more. A biaxially oriented polypropylene film for packaging.

2. 2. The biaxially oriented polypropylene film for packaging according to claim 1, wherein the ethylene polymer (E) is a linear low-density polyethylene.

3. 3. The biaxially oriented polypropylene film for packaging according to claim 1, wherein the ethylene polymer (E) is produced using a Ziegler-Natta catalyst.

4. 4. The biaxially oriented polypropylene film for packaging according to claim 1, wherein the haze value of the biaxially oriented polypropylene film measured in accordance with JIS K 7136 (2000) is 6% or less.

5. 5. The biaxially oriented polypropylene film for packaging according to claim 1, wherein the ethylene polymer (E) is a biomass-derived ethylene polymer.

6. A packaging bag made of the biaxially oriented polypropylene film for packaging according to any one of claims 1 to 5.

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