Biaxially oriented polyolefin film

Abstract

To provide a biaxially drawn polyolefin film which has excellent transparency and see-through feeling, and elasticity, is also excellent in productivity, and is reduced in load to environment.SOLUTION: A biaxially drawn polyolefin film for packaging that is composed of at least two or more layers of a plurality of layers includes a propylene-based polymer layer composed of a resin composition mainly containing a propylene homopolymer, and a polyethylene resin layer mainly containing a biomass-derived polyethylene resin having a density of 0.900-0.950 g / cm3 on at least one surface of the propylene-based polymer layer.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a biaxially oriented polyolefin film. [Background technology]

[0002] In recent years, there has been a strong demand for efforts to create a recycling-oriented society that reduces the burden on the environment by increasing the use of renewable resources. Renewable resources are mainly resources made from processed plants or plant-derived raw materials, and are also called biomass resources. In the case of biomass resources, carbon dioxide in 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 widely adopted in the future from the perspective of carbon neutrality.

[0003] In the field of plastics, biomass-derived plastics such as polylactic acid and biodegradable polymers are being produced as biomass-derived plastics, but production volumes are limited and they cannot be said to be in widespread use. On the other hand, for polyethylene, the most widely used material among general-purpose plastics, a method of obtaining polyethylene from plant-derived sugar via ethanol has been commercialized and is in widespread use.

[0004] As a resin film using biomass-derived polyethylene, a film using only ethylene-based resin has been proposed (see, for example, Patent Document 1). However, this film is poor in heat resistance because it is composed only of ethylene-based resin. Also, a film has been proposed in which biomass-derived polyethylene is added to a polypropylene-based resin (see, for example, Patent Documents 2 and 3). However, these films tend to be poor in transparency and see-through quality.

[0005] Therefore, the inventors conducted extensive research and developed a biaxially oriented polyolefin film that is widely used in the packaging field, and that has excellent transparency, see-through quality, and stiffness, and that contains a large amount of resin derived from biomass resources, thereby reducing the environmental impact and allowing for excellent productivity. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 5862055 [Patent Document 2] JP 2018-65267 A [Patent Document 3] JP 2019-6461 A Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been proposed in view of the above circumstances, and provides a biaxially oriented polyolefin film that has excellent transparency, see-through feeling, and stiffness, as well as excellent productivity and reduced environmental impact. [Means for solving the problem]

[0008] That is, the first invention is a biaxially oriented polyolefin film for packaging, which is composed of at least two layers, Consists of A propylene-based polymer layer made of a resin composition and a propylene-based polymer layer having a density of 0.900 to 0.950 g / cm on at least one surface of the propylene-based polymer layer. 3 and a polyethylene resin layer mainly composed of the biomass-derived polyethylene resin. The polyethylene resin layer has a biomass content of 84% or more, The biaxially oriented polyolefin film is characterized in that the tensile modulus of elasticity in the winding direction of the biaxially oriented polyolefin film measured in accordance with JIS K 7127 (1999) is 1.0 GPa or more.

[0009] A second invention relates to the biaxially oriented polyolefin film according to the first invention, which is composed of a laminate of 3 to 5 layers in which the propylene-based polymer layers and the polyethylene resin layers are alternately laminated.

[0010] The third invention relates to the biaxially oriented polyolefin film according to the first or second invention, wherein one of the layers constituting the biaxially oriented polyolefin film is a base layer, and the layer thickness of the base layer is greater than the layer thickness of the polyethylene resin layer.

[0011] The fourth invention relates to a biaxially stretched polyolefin film according to any one of the first to third inventions, wherein the haze of the biaxially stretched polyolefin film measured in accordance with JIS K 7136 (2000) is 9% or less, and the narrow-angle diffuse transmittance is 15% or less.

[0012] The fifth invention relates to the biaxially oriented polyolefin film according to any one of the first to fourth inventions, in which the propylene-based polymer layer and the polyethylene resin layer are integrated without an adhesive layer.

[0013] A sixth invention relates to the biaxially stretched polyolefin film according to any one of the first to fifth inventions, wherein the biaxially stretched polyolefin film has a thickness in the range of 1 μm to 100 μm.

[0014] A seventh invention relates to the biaxially oriented polyolefin film according to any one of the first to sixth inventions, wherein the biaxially oriented polyolefin film is formed by biaxially stretching through coextrusion. Effect of the Invention

[0015] According to the first aspect of the present invention, there is provided a biaxially oriented polyolefin film for packaging, which comprises at least two or more layers, and is made of a propylene homopolymer. Consists of A propylene-based polymer layer made of a resin composition and a propylene-based polymer layer having a density of 0.900 to 0.950 g / cm on at least one surface of the propylene-based polymer layer.3 and a polyethylene resin layer mainly composed of a biomass-derived polyethylene resin. The polyethylene resin layer has a biomass content of 84% or more; Since the tensile modulus of the biaxially stretched polyolefin film in the winding direction measured in accordance with JIS K 7127 (1999) is 1.0 GPa or more, the biaxially stretched polyolefin film has excellent transparency, see-through feeling, and stiffness, and is excellent in productivity and processability for film printing, packaging, etc., and has a reduced burden on the environment.

[0016] According to the biaxially oriented polyolefin film of the second invention, in the first invention, the propylene-based polymer layers and the polyethylene resin layers are alternately laminated to form a laminate of 3 to 5 layers, so that an appropriate layer can be used as a surface layer depending on the application of the film while further reducing the environmental load.

[0017] According to the biaxially oriented polyolefin film of the third invention, in the first or second invention, among the layers constituting the biaxially oriented polyolefin film, one of the propylene-based polymer layers is a base layer, and the layer thickness of the base layer is configured to be thicker than the layer thickness of the polyethylene resin layer, thereby resulting in excellent film productivity.

[0018] According to the biaxially oriented polyolefin film of the fourth invention, in any of the first to third inventions, the haze of the biaxially oriented polyolefin film measured in accordance with JIS K 7136 (2000) is 9% or less, and the narrow-angle diffuse transmittance is 15% or less, so that the film has excellent transparency and see-through feeling and a luxurious appearance.

[0019] According to the biaxially oriented polyolefin film of the fifth invention, in any one of the first to fourth inventions, the propylene-based polymer layer and the polyethylene resin layer are integrated without an adhesive layer, eliminating the need for a processing step using an adhesive and resulting in excellent productivity, and also contributing to reducing the environmental load since no solvent is used.

[0020] According to the biaxially oriented polyolefin film of the sixth invention, in any of the first to fifth inventions, the biaxially oriented polyolefin film has a thickness in the range of 1 μm to 100 μm, so that the film can be used as a packaging film with excellent suitability for printing and processing into bags.

[0021] The seventh invention, in any one of the first to sixth inventions, is such that the biaxially oriented polyolefin film is produced by co-extrusion biaxially oriented film formation, thereby making it possible to increase the strength of the film while facilitating production and improving productivity. [Brief description of the drawings]

[0022] [Figure 1] FIG. 1 is a schematic cross-sectional view of a two-layer biaxially oriented polyolefin film according to one embodiment of the present invention. [Diagram 2] FIG. 1 is a schematic cross-sectional view of a three-layer biaxially oriented polyolefin film according to one embodiment of the present invention. [Diagram 3] FIG. 1 is a schematic cross-sectional view of a four-layer biaxially oriented polyolefin film according to one embodiment of the present invention. [Figure 4] FIG. 1 is a schematic cross-sectional view of a five-layer biaxially oriented polyolefin film according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] FIG. 1 is a schematic cross-sectional view of a biaxially oriented polyolefin film 10 according to an embodiment of the present invention. This film 10 is a laminated film consisting of a propylene-based polymer layer 11 mainly made of a propylene homopolymer and a polyethylene resin layer 12 mainly made of a biomass-derived polyethylene resin. This film 10 is produced by a known production method such as a T-die method in which the raw material resins of each layer are melted and extruded at a predetermined thickness from a T-die or the like and co-extruded. By producing the film by co-extrusion, the layers are integrated without an adhesive layer between them, so that it is possible to reduce the environmental load while improving productivity, and it is also excellent in transparency and see-through feeling. Note that the biaxially oriented polyolefin film 10 is preferably in the range of 1 to 100 μm in thickness from the viewpoint of printability and processability as a packaging film.

[0024] The main resin of the propylene-based polymer layer 11 is a propylene homopolymer (homopolypropylene), which has high crystallinity and excellent heat resistance, chemical resistance, and strength. For this reason, the propylene-based polymer layer 11 serves as a substrate layer. By using a layer with high heat resistance as the substrate during biaxial stretching, productivity can be improved. Additives such as antiblocking agents, antistatic agents, antioxidants, neutralizing agents, and colorants are added to the propylene-based polymer layer 11 serving as the substrate layer as necessary.

[0025] The polyethylene resin layer 12 is a layer laminated on the propylene-based polymer layer 11, and is made of a biomass-derived polyethylene resin alone or a polyethylene resin mainly composed of a biomass-derived polyethylene resin. Since the propylene-based polymer layer 11 serves as a base layer, the layer thickness of the propylene-based polymer layer 11 is configured to be thicker than the layer thickness of the polyethylene resin layer 12. Additives such as an antiblocking agent, an antistatic agent, an antioxidant, a neutralizing agent, and a colorant are appropriately added to the polyethylene resin layer 12 as necessary.

[0026] As shown in Figs. 2 to 4, the propylene-based polymer layer 11 and the polyethylene resin layer 12 can be alternately laminated to form a multilayer film consisting of 3 to 5 layers or more. The propylene-based polymer layer 11 is excellent in printability since it is mainly composed of a propylene homopolymer. The polyethylene resin layer 12 is excellent in heat sealability, so that it is possible to appropriately select which layer will be the front or back depending on the application. Furthermore, by forming the film into a multilayer, it is possible to form a film containing a large amount of biomass-derived polyethylene resin, which can further reduce the environmental load.

[0027] Biomass-derived polyethylene resins are polyethylene resins obtained by processing plant raw materials. Specifically, ethanol is produced from sugar liquid extracted from plant raw materials such as sugar cane through alcohol fermentation by yeast, and then ethylene is produced, followed by a known resinification process to produce polyethylene. This biomass-derived polyethylene resin contributes to reducing the environmental impact of the final product.

[0028] Biomass-derived polyethylene resin is a linear low-density polyethylene resin with a density of 0.900 to 0.950 g / cm 3 If a resin exceeding this range is used, sheet molding and stretching at the die outlet becomes difficult, and productivity tends to decrease.

[0029] The tensile modulus of the biaxially oriented polyolefin film in the winding direction is preferably 1.0 GPa or more. If the tensile modulus is less than 1.0 GPa, the film will have poor processing suitability and will be prone to deformation, which may lead to reduced productivity in printing and packaging. The tensile modulus is measured in accordance with JIS K 7127 (1999) as described in the following examples.

[0030] The haze of the biaxially oriented polyolefin film is preferably 9% or less. A film with a haze of more than 9% is poor in transparency and is not suitable for handling as a transparent film. The haze is measured in accordance with JIS K 7136 (2000) as described in the following examples. The narrow angle diffuse transmittance (LSI) of the biaxially oriented polyolefin film is preferably 15% or less. When the narrow angle diffuse transmittance (LSI) is less than 15%, the sense of see-through is significantly improved and there is almost no distortion when viewed through the film, improving suitability as a packaging film and giving a luxurious feel as a packaging material. EXAMPLES

[0031] [Film Creation] For the films of Prototype Examples 1 to 9 and Comparative Examples 1 and 2, the materials described below were mixed and melted, and films were produced using a two-layer co-extrusion T-die film molding machine followed by a biaxial stretching machine. The stretching ratio was 5 times in the vertical direction (winding direction) and 8 times in the horizontal direction (width direction), and the films were produced by sequential biaxial stretching. The MFR is the melt flow rate measured at 190°C for polyethylene resins and 230°C for polypropylene resins in accordance with JIS K 7210 (2014).

[0032] [Materials used in the propylene polymer layer] In the propylene-based polymer layer, the following resin PP1 was used as the polypropylene-based resin. An appropriate amount of an antistatic agent used in general films was also added. Resin PP1: Propylene homopolymer (Japan Polypropylene Corporation, product name "FL100A", MFR: 3.0g / 10min)

[0033] [Materials used for the polyethylene resin layer] For the polyethylene resin layer, the following resins PE1 to PE4 were used as biomass-derived polyethylene resins, and the following resin PP2 was used as a non-biomass-derived polyethylene resin for comparison. An appropriate amount of an anti-blocking agent used in general films was added. Resin PE1: Linear low-density polyethylene (manufactured by Braskem, product name "SLH218", density: 0.916g / cm 3 , MFR: 2.3g / 10min) Resin PE2: High density polyethylene (manufactured by Braskem, product name "SGF4960", density: 0.961g / cm 3 , MFR: 0.3g / 10min) Resin PE3: Low-density polyethylene (manufactured by Braskem, product name "SEB853", density: 0.923g / cm 3 , MFR: 2.7g / 10min) Resin PE4: High density polyethylene (manufactured by Braskem, product name "SHE150", density: 0.948g / cm 3 , MFR: 1.0g / 10min) Resin PP2: Ethylene-propylene-butene copolymer (Japan Polypropylene Corporation, product name "FX4G", MFR: 5.0g / 10min)

[0034] [Prototype 1] Prototype example 1 is a film in which the propylene polymer layer, which is the base layer, is composed of 100% by weight of propylene homopolymer (resin PP1) and the polyethylene resin layer is composed of 100% by weight of linear low-density polyethylene (resin PE1), with the propylene polymer layer being 19 μm thick and the polyethylene resin layer being 1 μm thick.

[0035] [Prototype 2] Prototype 2 is a film formed in the same manner as Prototype 1, except that the thickness of the propylene-based polymer layer was 17 μm and the thickness of the polyethylene resin layer was 3 μm.

[0036] [Prototype 3] Prototype 3 is a film formed in the same manner as Prototype 1, except that the thickness of the propylene-based polymer layer was 11 μm and the thickness of the polyethylene resin layer was 9 μm.

[0037] [Prototype 4] Prototype 4 is a film formed in the same manner as Prototype 2, except that the polyethylene resin layer was made of 100% by weight of low-density polyethylene (resin PE3).

[0038] [Prototype 5] Prototype 5 is a film formed in the same manner as Prototype 4, except that the polyethylene resin layer was made of 50% by weight of high density polyethylene (resin PE3) and 50% by weight of high density polyethylene (resin PE4).

[0039] [Prototype 6] Sample 6 is a film formed in the same manner as Sample 4, except that the polyethylene resin layer was made of 20% by weight of high density polyethylene (resin PE3) and 80% by weight of high density polyethylene (resin PE4).

[0040] [Prototype 7] Prototype 7 is a film formed in the same manner as Prototype 4, except that the polyethylene resin layer was made of 100% by weight of high density polyethylene (resin PE4).

[0041] [Prototype 8] Sample 8 is a film formed in the same manner as Sample 1, except that high density polyethylene (resin PE2) was used for the polyethylene resin layer.

[0042] [Prototype 9] Sample 9 is a film formed in the same manner as Sample 2, except that high density polyethylene (resin PE2) was used for the polyethylene resin layer.

[0043] [Comparative Example 1] Comparative Example 1 is a film formed in the same manner as Prototype Example 1, except that an ethylene-propylene-butene copolymer (resin PP2) was used for the polyethylene resin layer.

[0044] [Comparative Example 2] Comparative Example 2 is a film formed in the same manner as Prototype Example 1, except that the propylene polymer layer is a resin made by kneading 85% by weight of propylene homopolymer (resin PP1) and 15% by weight of linear low-density polyethylene (resin PE1), and an ethylene-propylene-butene copolymer (resin PP2) is used for the polyethylene resin layer.

[0045] [Film performance evaluation] The films of Prototype Examples 1 to 9 and Comparative Examples 1 and 2 were measured for tensile modulus, haze, narrow angle diffuse transmittance, and productivity. In the overall evaluation, a "good" (○) was given when good results were obtained in all of the evaluations of the items described below, and a "bad" (×) was given when one or more unfavorable results were obtained or when the biomass-derived resin layer was not included. The results are shown in Tables 1 and 2 below.

[0046] [Measurement of tensile modulus] The tensile modulus (GPa) is an index of processability and was measured in accordance with JIS K 7127 (1999) using a tensile tester (V1-D, manufactured by Toyo Seiki Seisakusho Co., Ltd.) For the films of Prototype Examples 1 to 9 and Comparative Examples 1 and 2, films with a measurement result of 1.0 GPa or more were considered to be good products.

[0047] [Haze measurement] The 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 9 and Comparative Examples 1 and 2, a measurement result of 9% or less was determined to be a pass.

[0048] [Measurement of narrow angle diffuse transmittance] Narrow angle diffuse transmittance (LSI) (%) is an index of see-through feeling, and LSI indicates the ratio of the amount of scattered light with a scattering angle of 0.4° or more and 1.2° or less to the total amount of transmitted light. LSI is a measure of see-through feeling to the naked eye, and the lower the value, the better the transmittance. LSI was measured using a visual transparency tester (manufactured by Toyo Seiki Seisakusho Co., Ltd.). For the films of prototypes 1 to 9 and comparative examples 1 and 2, a measurement result of 15% or less was considered to be a pass.

[0049] [Physical property evaluation] In the evaluation of the physical properties, a product that was good in all of the above-mentioned evaluations of tensile modulus, haze, and narrow-angle diffuse transmittance was given a "good" mark, and a product that was bad in any one of these evaluations was given a "bad" mark.

[0050] [Productivity evaluation] The productivity was evaluated as follows: those that could not be biaxially stretched or could not be formed into a sheet were marked "X", those that were difficult to biaxially stretch were marked "A", and those that could be easily biaxially stretched were marked "O".

[0051] [comprehensive evaluation] In the overall evaluation, those with a physical property evaluation of "◯" and a productivity evaluation of "◯" were rated as "good", and those with even one "×" were rated as "not good". In addition, Comparative Example 1, which does not contain a biomass-derived polyethylene resin, was also rated as "not good" from the perspective of reducing the environmental load.

[0052] [Table 1]

[0053] [Table 2]

[0054] [Table 3]

[0055] [Results and Discussion] As shown in Tables 1 to 3, the overall evaluation of the physical properties and productivity was "Fail" for Prototypes 8 and 9 and Comparative Example 2. Prototypes 8 and 9 are examples using a high-density biomass-derived polyethylene resin. In general, films using high-density polyethylene are inferior in tearability compared to films using low-density polyethylene. As a result, for Prototype 8, although tears occurred during biaxial stretching, film molding was possible, so the productivity evaluation was "△ (Fail)", and the haze was higher than the standard, so the overall evaluation was "Fail (X)". For Prototype 9, it was not possible to mold it into a sheet, so the productivity evaluation was "X (Fail)" and physical properties could not be evaluated.

[0056] Comparative Example 1 showed good results in terms of film performance, but since it did not contain biomass-derived resin, it did not meet the objective of the present invention from the perspective of reducing environmental impact, and was overall rated as "unacceptable." Comparative Example 2 is an example in which a biomass-derived resin was mixed into the base layer. Polyethylene and polypropylene are not completely compatible, and as a result of mixing, a phase separation structure is formed within the layer, which tends to be higher than the LSI standard. Comparative Example 2 was inferior in see-through feeling, and was overall rated as "unacceptable."

[0057] In contrast, the overall evaluation was "good" for prototypes 1 to 7. These prototypes were composed of a propylene-based polymer layer made of a propylene homopolymer and a polyethylene resin layer made of a biomass-derived polyethylene resin, and it was found that the thicker the propylene-based polymer layer, the more excellent the tensile modulus.

[0058] The polyethylene resin that is the main component of the polyethylene resin layer is 0.900 to 0.950 g / cm 3 It was found that by using a biomass-derived polyethylene resin with a density in this range, even a film using a biomass-derived resin to reduce the environmental impact can have good haze and narrow-angle diffuse transmittance, and a film with excellent transparency and see-through properties can be obtained.

[0059] As described above, the biaxially stretched polyolefin film of the present invention comprises a propylene-based polymer layer made of a resin composition mainly composed of a propylene homopolymer, and a polyethylene resin layer mainly composed of a biomass-derived polyethylene resin. In particular, since the film has a layer mainly composed of a biomass-derived polyethylene resin, it can be made into a film having excellent transparency, see-through feeling, and stiffness while reducing the environmental load. [Industrial Applicability]

[0060] The biaxially oriented polyolefin film of the present invention has a layer mainly made of a biomass-derived polyethylene resin, and thus has excellent transparency and visibility while reducing the environmental impact. Therefore, it is expected to be used for new packaging films and the like, and is advantageous in utilizing biomass resources. [Explanation of symbols]

[0061] 10 Biaxially oriented polyolefin film 11 Propylene-based polymer layer 12 Polyethylene resin layer

Claims

1. A biaxially oriented polyolefin film for packaging, comprising at least two or more layers, a propylene-based polymer layer made of a resin composition made of a propylene homopolymer; At least one surface of the propylene-based polymer layer has a density of 0.900 to 0.950 g / cm ３ and a polyethylene resin layer mainly composed of the biomass-derived polyethylene resin. The polyethylene resin layer has a biomass ratio of 84% or more, The tensile modulus of the biaxially oriented polyolefin film in the winding direction measured in accordance with JIS K 7127 (1999) is 1.0 GPa or more. A biaxially oriented polyolefin film.

2. 2. The biaxially oriented polyolefin film according to claim 1, which comprises a laminate of 3 to 5 layers in which the propylene-based polymer layers and the polyethylene resin layers are alternately laminated.

3. 3. The biaxially oriented polyolefin film according to claim 1 or 2, wherein one of the propylene-based polymer layers is a base layer, and the layer thickness of the base layer is greater than the layer thickness of the polyethylene resin layer.

4. 4. The biaxially oriented polyolefin film according to claim 1, wherein the haze of the biaxially oriented polyolefin film measured in accordance with JIS K 7136 (2000) is 9% or less, and the narrow angle diffuse transmittance is 15% or less.

5. 5. The biaxially oriented polyolefin film according to claim 1, wherein the propylene-based polymer layer and the polyethylene resin layer are integrated without an adhesive layer.

6. The biaxially oriented polyolefin film according to any one of claims 1 to 5, wherein the biaxially oriented polyolefin film has a thickness in the range of 1 µm to 100 µm.

7. 7. The biaxially oriented polyolefin film according to claim 1, which is obtained by biaxially oriented coextrusion film formation.

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