Polyethylene-based film and laminate

Abstract

To provide a polyethylene-based film and a laminate, allowing odor reduction attributable to recycled raw materials in films produced using the recycled raw materials.SOLUTION: A laminated film composed mainly of a polyethylene-based resin, the laminated film including at least three layers of a first surface layer, an intermediate layer, and a second surface layer, the intermediate layer containing 5 to 95 wt.% of a recycled polyolefin-based resin and 5 to 95 wt.% of either a petroleum-derived polyethylene-based resin or a plant-derived polyethylene-based resin, or a mixture thereof, the first surface layer and the second surface layer being composed of either a petroleum-derived polyolefin-based resin or a plant-derived polyolefin-based resin, or a mixture thereof, and the laminated film containing 3 wt.% or more of the recycled polyolefin-based resin.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polyethylene film and a laminate, and more particularly to a polyethylene film and a laminate made from recycled materials. [Background technology]

[0002] In recent years, efforts have been made to reduce greenhouse gas emissions as a measure to prevent global warming. For example, since carbon dioxide generated when waste plastic materials are incinerated is a greenhouse gas that is believed to cause global warming, efforts have been made to regenerate and recycle plastics from waste plastic materials as a measure to prevent global warming.

[0003] As a recycled thermoplastic resin composition using such recycled resin, a recycled thermoplastic resin composition consisting of 10 to 90% by weight of a high-molecular-weight polyolefin resin having a weight-average molecular weight of 500,000 or more and 90 to 10% by weight of a recycled polyolefin resin has been proposed (see Patent Document 1). The recycled thermoplastic resin composition of Patent Document 1 has mechanical properties equal to or better than those of ordinary virgin thermoplastic resin, and is particularly excellent in long life (creep resistance), and is therefore used for civil engineering and construction components such as structural materials, construction members, and water storage tanks.

[0004] In the future, due to growing awareness of environmental issues such as global warming, it is expected that the use of recycled materials will also increase in the field of packaging films. Therefore, the use of plastics recycled from waste plastic materials in packaging films has been considered. However, since waste plastic materials contain foreign matter such as colorants and solvents, there is concern that plastics recycled from such waste plastic materials may emit odors due to the foreign matter. In particular, in packaging films for food, etc., it is necessary to reduce odors in order to maintain the original taste of the food. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-119697 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been proposed in view of the above points, and provides a polyethylene film and laminate that make it possible to reduce odors caused by recycled materials in films made from recycled materials. [Means for solving the problem]

[0007] That is, the first invention relates to a laminated film mainly made of polyethylene-based resin, consisting of at least three layers: a first surface layer, an intermediate layer, and a second surface layer, wherein the intermediate layer is made of 5 to 95 wt% recycled polyolefin-based resin and 5 to 95 wt% of either a petroleum-derived polyethylene-based resin or a plant-derived polyethylene-based resin, or a mixture thereof; the first surface layer and the second surface layer are made of either a petroleum-derived polyolefin-based resin or a plant-derived polyolefin-based resin, or a mixture thereof; and the content of the recycled polyolefin-based resin in the laminated film is 3 wt% or more.

[0008] A second invention relates to the polyethylene film of the first invention, wherein 0.1 to 10 wt % of a crystal nucleating agent is added to at least one of the first surface layer, the intermediate layer, and the second surface layer.

[0009] A third invention relates to the polyethylene film of the first invention, wherein a cyclic olefin resin or an alicyclic resin is added to at least one of the first surface layer, the intermediate layer, and the second surface layer.

[0010] A fourth invention relates to the polyethylene film according to any one of the first to third inventions, wherein an odor adsorbent is added to at least one of the first surface layer, the intermediate layer, and the second surface layer.

[0011] A fifth invention relates to the polyethylene film according to any one of the first to third inventions, wherein 1 to 30 wt % of a polyethylene elastomer is added to the intermediate layer as a compatibilizer.

[0012] A sixth invention relates to the polyethylene film according to any one of the first to third inventions, wherein a phenol-based antioxidant or a phosphorus-based antioxidant is added to the intermediate layer.

[0013] The seventh invention relates to a laminate using the polyethylene film of the first to third inventions, which is a laminate consisting of a plurality of resin layers including the polyethylene film. [Effects of the Invention]

[0014] The polyethylene film according to the first aspect of the present invention is a laminated film primarily made of polyethylene resin, consisting of at least three layers: a first surface layer, an intermediate layer, and a second surface layer. The intermediate layer is made of 5 to 95 wt% recycled polyolefin resin and 5 to 95 wt% of either a petroleum-derived polyethylene resin or a plant-derived polyethylene resin, or a mixture thereof. The first surface layer and the second surface layer are made of either a petroleum-derived polyolefin resin or a plant-derived polyolefin resin, or a mixture thereof. Since the recycled polyolefin resin content in the laminated film is 3 wt% or more, the first and second surface layers function as barrier layers that prevent the migration of odorous components generated from the intermediate layer due to the recycled polyolefin resin, thereby making it possible to reduce odors caused by the recycled polyolefin resin (recycled raw materials).

[0015] According to the polyethylene film of the second invention, in the first invention, a nucleating agent is added in an amount of 0.1 to 10 wt % to at least one of the first surface layer, the intermediate layer, and the second surface layer, thereby increasing the crystallinity of at least one layer, further hindering the migration of odorous components from the intermediate layer, and suppressing the release of odor from the film.

[0016] According to the polyethylene film of the third invention, in the first invention, a cyclic olefin resin or an alicyclic resin is added to at least one of the first surface layer, the intermediate layer, and the second surface layer, thereby further suppressing odor emission from the film.

[0017] According to the polyethylene film of the fourth invention, in the first to third inventions, an odor adsorbent is added to at least one of the first surface layer, the intermediate layer, and the second surface layer, thereby adsorbing odor components generated from the intermediate layer and further suppressing odor emission from the film.

[0018] According to the polyethylene-based film of the fifth invention, in the first to third inventions, 1 to 30 wt % of a polyethylene-based elastomer is added to the intermediate layer as a compatibilizer, thereby reducing the occurrence of fisheyes due to incompatible resins and suppressing the occurrence of poor appearance.

[0019] According to the polyethylene film of the sixth invention, in the first to third inventions, a phenolic antioxidant or a phosphorus-based antioxidant is added to the intermediate layer, thereby reducing the deterioration of the recycled polyolefin resin due to thermal oxidation.

[0020] The laminate of the seventh invention is composed of multiple resin layers including the polyethylene-based films of the first to third inventions, and by laminating resin layers with physical properties according to the application, it is possible to utilize recycled polyolefin-based resins (recycled raw materials) while maintaining the performance required of a film. DETAILED DESCRIPTION OF THE INVENTION

[0021] A polyethylene-based film according to one embodiment of the present invention is a laminate film mainly made of a polyethylene-based resin and consisting of at least three layers: a first surface layer, an intermediate layer, and a second surface layer. The polyethylene-based film of the present invention can be used as a base film or a laminate film for a laminate consisting of multiple resin layers. This laminate film is suitable for use as a packaging material for various items such as food, daily necessities, and parts.

[0022] The intermediate layer is a layer containing recycled polyolefin resin in order to promote the use of recycled materials. It is composed of a recycled polyolefin resin and either a petroleum-derived polyethylene resin or a plant-derived polyethylene resin, or a mixture thereof. Examples of recycled polyolefin resins that can be used include polyolefins recycled from products and waste materials. Examples of such waste materials include plastic materials such as container packaging materials, building materials, and fibers. Note that waste plastic materials contain foreign matter such as colorants and solvents, which can cause odors, as described below.

[0023] Recycled polyolefin resins are regenerated by methods such as material recycling and chemical recycling. Examples of recycled polyolefin resins include polyethylene resins, polypropylene resins, polystyrene, etc. As the recycled polyolefin resin, polyethylene resins are preferred from the viewpoint of compatibility with petroleum-derived polyethylene resins or plant-derived polyethylene resins.

[0024] Petroleum-derived polyethylene resins are polyethylenes produced from ethylene obtained from fossil fuels such as petroleum. Examples of petroleum-derived polyethylene resins include linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), and low-density polyethylene (LDPE).

[0025] Plant-derived polyethylene resins are polyethylenes produced by processing plant raw materials. Specifically, polyethylene is produced by a method in which ethanol is produced by alcoholic fermentation using yeast from sugar liquid extracted from plant raw materials such as sugarcane, and then ethylene is converted into ethanol, followed by a known resinification process. Alternatively, all or part of bio-naphtha produced by decomposing non-edible oils such as tall oil and waste cooking oil is mixed with petroleum-derived naphtha to produce polyethylene by a conventional method. Plant-derived polyethylene resins are produced in whole or in part using bioethylene produced from these plant-derived raw materials, and contribute to reducing the use of petroleum-derived raw materials.

[0026] Petroleum-derived polyethylene resins are widely available and are available in a wide variety of types, making them advantageous in terms of price. On the other hand, plant-derived polyethylene resins are advantageous in that, although they generate greenhouse gases (carbon dioxide) when incinerated, this greenhouse gas is balanced with the carbon dioxide absorbed during the growth of the plants that served as the raw materials for the plant-derived polyethylene resin, thereby virtually eliminating greenhouse gas emissions. Therefore, using a plant-derived polyethylene resin in the intermediate layer can conserve fossil fuels such as petroleum and reduce the environmental impact. The petroleum-derived polyethylene resin or plant-derived polyethylene resin may be appropriately selected and incorporated into the intermediate layer depending on the application and purpose, or a mixture of petroleum-derived and plant-derived polyethylene resins may be incorporated into the intermediate layer.

[0027] The content of the recycled polyolefin resin and either or a mixture of petroleum-derived polyethylene resin or plant-derived polyethylene resin in the intermediate layer is preferably 5 to 95 wt% recycled polyolefin resin and 5 to 95 wt% petroleum-derived polyethylene resin or plant-derived polyethylene resin or a mixture thereof. The content of the recycled polyolefin resin is 5 wt% or more from the viewpoint of promoting the use of recycled raw materials, with the upper limit being 95 wt% from the viewpoint of ensuring film formability and quality equivalent to films that do not contain recycled raw materials. A more preferable content is 10 to 70 wt%. The content of either or a mixture of petroleum-derived polyethylene resin or plant-derived polyethylene resin is 5 to 95 wt%, preferably 30 to 90 wt%, from the viewpoint of ensuring properties such as mechanical strength and heat resistance. In particular, the use of plant-derived polyethylene resin can contribute to reducing environmental impact.

[0028] If the recycled polyolefin resin content is too low or the petroleum-derived polyethylene resin or plant-derived polyethylene resin content is too high, the recycled raw materials will not be fully utilized. If the recycled polyolefin resin content is too high or the petroleum-derived polyethylene resin or plant-derived polyethylene resin content is too low, the quality of the polyethylene film may be reduced due to foreign matter or odors originating from the recycled raw materials (recycled polyolefin resin).

[0029] The first and second surface layers sandwiching the intermediate layer are made of either a petroleum-derived polyolefin resin or a plant-derived polyolefin resin, or a mixture thereof. Examples of the petroleum-derived polyolefin resin or plant-derived polyolefin resin include polyethylene, polypropylene, and polystyrene. As the petroleum-derived polyolefin resin or plant-derived polyolefin resin, a petroleum-derived polyethylene resin or a plant-derived polyethylene resin is preferred from the viewpoint of compatibility with the petroleum-derived polyethylene resin or plant-derived polyethylene resin of the intermediate layer.

[0030] Using a petroleum-derived polyolefin resin for the first and second surface layers can reduce odors caused by the recycled polyolefin resin contained in the intermediate layer and poor appearance due to foreign matter contained in the recycled polyolefin resin. Furthermore, using a plant-derived polyolefin resin for the first and second surface layers not only achieves the same effects as using a petroleum-derived polyolefin resin for the first and second surface layers (reducing odors and poor appearance), but also conserves fossil fuels such as petroleum and reduces environmental impact. The petroleum-derived polyolefin resin or plant-derived polyolefin resin can be selected appropriately depending on the application and purpose. For example, the first and second surface layers can be made of the same polyolefin resin, or the first surface layer can be made of a petroleum-derived polyolefin resin and the second surface layer can be made of a plant-derived polyolefin resin, with different polyolefin resins used for each surface layer. Alternatively, a mixture of a petroleum-derived polyolefin resin and a plant-derived polyolefin resin can be used for the first and second layers. This mixture can also be the same as the mixture contained in the intermediate layer.

[0031] In order to effectively utilize recycled raw materials, the laminate film should contain 3 wt% or more of recycled polyolefin resin, preferably 6 wt%. If the recycled polyolefin resin content is too low, the recycled raw materials in the laminate film will not be fully utilized. On the other hand, there is no particular upper limit to the recycled polyolefin resin content. The recycled polyolefin resin content in the laminate film depends on the resin content of the first and second surface layers of the laminate film, but can be appropriately increased by increasing the recycled polyolefin resin content of the intermediate layer. For example, the recycled polyolefin resin content in the laminate film can be increased to a high concentration of 70 wt% or more, more preferably 80 wt% or more. The higher the recycled polyolefin resin content in the laminate film, the greater the contribution to reducing environmental impact, making it preferable.

[0032] In the present invention, in order to promote the use of recycled raw materials in the field of packaging films, the intermediate layer contains a recycled polyolefin resin. This recycled polyolefin resin is obtained by recycling waste plastic materials containing foreign matter such as colorants and solvents through material recycling, chemical recycling, etc. Therefore, in promoting the use of recycled raw materials, there has been concern that the recycled polyolefin resin may emit an odor caused by the foreign matter.

[0033] Therefore, the inventors discovered that by using recycled polyolefin resin as a constituent material for an intermediate layer in a polyethylene film made from recycled polyolefin resin, and by forming a laminate film in which a first surface layer and a second surface layer are laminated with the intermediate layer sandwiched between them, the first surface layer and the second surface layer function as barrier layers that prevent the migration of odorous components that are generated from the intermediate layer due to the recycled polyolefin resin, and thus it is possible to effectively suppress the release of odors from the film.

[0034] In the present invention, as a means for further suppressing the migration of odorous components generated from the intermediate layer due to the recycled polyolefin resin, it is preferable to add a nucleating agent to at least one of the first surface layer, intermediate layer, and second surface layer. The nucleating agent is an additive that promotes crystallization of the resin constituting the layer to which it is added. By increasing the degree of crystallinity of the resin, odorous components are less likely to migrate from the intermediate layer, thereby suppressing the release of odor outside the film. The amount of nucleating agent added is preferably 0.1 to 10 wt%, more preferably 0.1 to 3 wt%, of the layer to which it is added. If the amount of nucleating agent added is too small, the degree of crystallinity of the layer to which the nucleating agent is added cannot be increased, allowing the migration of odorous components, which may result in insufficient reduction of odor emitted from the film.

[0035] The nucleating agent is not particularly limited as long as it is a substance that promotes the crystallization of the resin, and may be either an organic nucleating agent or an inorganic nucleating agent. Examples of the organic nucleating agent include a metal carboxylate nucleating agent, a sorbitol nucleating agent, and a metal phosphate nucleating agent, while examples of the inorganic nucleating agent include talc.

[0036] In the present invention, as another means for further suppressing the migration of odorous components generated from the intermediate layer, a cyclic olefin resin or an alicyclic resin may be added to at least one of the first surface layer, intermediate layer, and second surface layer. Cyclic olefin resins and alicyclic resins have the property of suppressing the migration of odorous components. Examples of cyclic olefin resins include polymers of cyclic olefin monomers and copolymers of cyclic olefin monomers with other monomers such as ethylene. Examples of alicyclic resins include those obtained by hydrogenating aromatic resins. Examples of alicyclic resins include polymerized resins and terpene resins made from aliphatic, aromatic, or dicyclopentadiene (DCPD) monomers. The properties of the cyclic olefin resin or alicyclic resin added to at least one of the above-mentioned layers suppress the migration of odorous components from the intermediate layer, thereby suppressing odor emission from the film.

[0037] In the present invention, as a means for suppressing odor emission from the film, an odor adsorbent may be added to at least one of the first surface layer, the intermediate layer, and the second surface layer. The odor adsorbent has the function of absorbing odorous components. Examples of odor adsorbents include activated carbon, zeolite, silicon dioxide, alumina, aluminum hydroxide, and mixtures thereof. The odor adsorbent added to at least one of the layers can adsorb odorous components generated from the intermediate layer due to the recycled polyolefin resin. This further suppresses odor emission from the film. The odor adsorbent can also be used in combination with a crystal nucleating agent, a cyclic olefin resin, or an alicyclic resin. Note that it is preferable to add the odor adsorbent to the intermediate layer to more effectively adsorb odorous components.

[0038] In the present invention, in order to reduce the appearance defects caused by the inclusion of resins with low compatibility in the film, it is preferable to add a polyethylene-based elastomer as a compatibilizer to the intermediate layer. Examples of polyethylene-based elastomers include copolymers of ethylene and α-olefins other than ethylene, and resins graft-polymerized with maleic anhydride.

[0039] Because the recycled polyolefin resin contained in the intermediate layer contains a large amount of resins that are incompatible with polyethylene, fish eyes due to the incompatible resins may occur in the film. The occurrence of fish eyes in the film may result in poor appearance and a decrease in the commercial value of the film. The compatibilizer is used to improve the compatibility between resins. The amount of compatibilizer added is 1 to 30 wt%, preferably approximately 10 wt%, from the viewpoint of improving the compatibility between the recycled polyolefin resin and either the petroleum-derived polyethylene resin or the plant-derived polyethylene resin, or a mixture thereof, in the intermediate layer. If the amount of compatibilizer added is too small, the compatibility between the recycled polyolefin resin and either the petroleum-derived polyethylene resin or the plant-derived polyethylene resin, or a mixture thereof, may be insufficient. If the amount of compatibilizer added is too large, the rigidity and breaking strength of the film may decrease, resulting in insufficient mechanical properties. By improving compatibility with an appropriate amount of compatibilizer, the occurrence of fish eyes due to incompatible resins can be reduced, thereby suppressing the occurrence of poor appearance of the film.

[0040] If the number of fisheyes on a film increases, the film surface will become rough and other appearance defects will occur. Therefore, regarding appearance defects caused by fisheyes, the ten-point average roughness (R Z ) and the quality can be evaluated based on the ten-point mean roughness (R Z If the ten-point average roughness (R Z ) exceeds 2 μm, a good appearance can be obtained.

[0041] In the present invention, a phenolic antioxidant or a phosphorus-based antioxidant may be added to the intermediate layer. For example, when a resin product is heated during the molding process, the resin that constitutes the product is thermally damaged. When such a resin product is used as a recycled raw material, the recycled raw material is heated again during the film molding process, which may cause further thermal damage and make the resin more susceptible to degradation. Therefore, by adding a phenolic antioxidant or a phosphorus-based antioxidant to the intermediate layer containing a recycled polyolefin resin (recycled raw material), it is possible to reduce the degradation of the recycled polyolefin resin due to thermal oxidation.

[0042] Examples of phenolic antioxidants include tetrakis[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane, 2,6-di-t-butyl-4-methylphenol, n-octadecyl-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate, tris(3,5-di-t-butyl-4-hydroxybenzyl)isocyanurate, etc. Examples of phosphorus-based antioxidants include tris(2,4-di-t-butylphenyl)phosphite, tris(nonylphenyl)phosphite, distearyl pentaerythritol diphosphite, tetrakis(2,4-di-t-butylphenyl)-4,4'-biphenylene diphosphonite, etc.

[0043] Furthermore, the polyethylene film of the present invention may have a laminate structure including layers other than the first surface layer, intermediate layer, and second surface layer, as needed. For example, as a laminated polyethylene film, any layer may be laminated between the first surface layer and the intermediate layer or between the second surface layer and the intermediate layer, as needed. The polyethylene film of the present invention preferably has a laminate structure of 3 to 5 layers.

[0044] The thickness of the polyethylene film of the present invention is not particularly limited and can be appropriately determined depending on the demand, application, etc., and is, for example, 5 to 150 μm, preferably 10 to 100 μm. Of these, the thickness of the first and second surface layers of the polyethylene film is 0.3 to 50 μm, preferably 0.5 to 35 μm, and more preferably 0.6 to 20 μm. The thickness of the intermediate layer is 2 to 135 μm, preferably 3 to 90 μm, and more preferably 4 to 54 μm. If the surface layer is too thin, it may not function adequately as a barrier layer that prevents the migration of odorous components. If the surface layer is too thick, the intermediate layer will be relatively thin, reducing the amount of recycled polyolefin resin added to the intermediate layer, which is unsuitable from the perspective of promoting the use of recycled raw materials.

[0045] The polyethylene film of the present invention can be obtained by a known film molding method, whether stretched or unstretched. Unstretched films can be obtained by extruding a molten resin to a predetermined thickness from a T-die, a circular die, or the like, and then cooling and solidifying the extruded molten resin using a cooling roll or air. Stretched films can be obtained by uniaxially or biaxially stretching using a known method such as a tenter method, a tubular method, or roll stretching.

[0046] In the present invention, the polyethylene film is used as a substrate film, and a laminate consisting of multiple resin layers including the polyethylene film can be provided. When a multilayer body is formed, the resin constituting each layer of the multilayer body and the resin constituting the polyethylene film can be co-extruded together, or the films constituting each layer can be attached to form a laminate having any layer structure. For such a laminate, by laminating resin layers having physical properties according to the application, recycled polyolefin resin (recycled raw material) can be used while maintaining the performance required as a film.

[0047] The present invention can also provide a laminated film in which a polyethylene film used as a substrate film is printed and a gas barrier layer or the like is appropriately laminated thereon. The printing is performed on the surface of the polyethylene film, and known methods such as screen printing, flexographic printing, offset printing, and gravure printing are used. Furthermore, when printing is performed on the polyethylene film of the present invention, the film surface is subjected to the above-mentioned surface treatment such as corona discharge treatment prior to printing, thereby improving ink compatibility and adhesion.

[0048] The gas barrier layer is disposed on the surface layer directly or via an anchor coat layer for the purpose of imparting barrier properties to water vapor, oxygen, etc. The gas barrier layer can be formed by a known deposition method such as vacuum deposition, sputtering, or ion plating. When a gas barrier layer is disposed on the polyethylene film of the present invention, the film surface is previously subjected to a surface treatment such as corona discharge treatment, thereby improving the wettability and adhesion of the anchor coat layer and gas barrier layer.

[0049] The anchor coat layer is not particularly limited, and examples thereof include polyurethane-based resins and polyester-based resins. The gas barrier layer is also not particularly limited, and examples thereof include metal thin film layers and inorganic oxide layers. The metal thin film layer is a thin film layer made of known metals such as aluminum, gold, silver, copper, and chromium, and may be a thin film layer of oxides, sulfides, or nitrides of these metals. The metal thin film layer may be a single layer or a plurality of layers made of two or more different or identical types. The inorganic oxide layer is made of known inorganic oxides such as aluminum oxide, silicon oxide, magnesium fluoride, and magnesium oxide, and may be a thin film layer using one or more inorganic oxides.

[0050] Furthermore, when another resin film is laminated on the polyethylene-based film of the present invention in a laminate film, the other resin film may be made of the same or substantially the same resin material as the polyethylene-based film, thereby making it possible to realize a mono-material laminate, and packaging materials, packaging bags, etc. using the laminate. [Example]

[0051] [Preparation of unstretched polyethylene film] The materials described below were blended, melted, and kneaded, and the resulting extruded film was laminated in this order using a T-die method, followed by cooling with a cooling roll, to produce the unstretched films of Prototype Examples 1 to 9. In each prototype, the blending ratio of each material was 100 wt% for each of the first surface layer, intermediate layer, and second surface layer. The materials used for each layer of Prototype Examples 1 to 9 are shown in Tables 1 and 2 below. The unstretched films of Prototype Examples 1 to 9 were produced to a thickness of 60 μm, with the first surface layer and second surface layer each having a thickness of 12 μm, and the intermediate layer having a thickness of 36 μm.

[0052] [Preparation of stretched polyethylene film] The materials described below were blended, melted, and kneaded, and the resulting extrusion was performed using a T-die method to laminate the first surface layer, intermediate layer, and second surface layer in this order. The extrusion was cooled using a cooling roll to produce a 1.6 mm sheet, which was then stretched 5 times in the longitudinal direction and then 8 times in the transverse direction using a batch-type stretching machine in an atmosphere of 120°C to produce the stretched film of Prototype Example 10. The materials used for each layer of Prototype Example 10 are shown in Table 2 below. The stretched film of Prototype Example 10 was produced to a thickness of 40 μm, with the first surface layer and second surface layer each having a thickness of 2 μm, and the intermediate layer having a thickness of 36 μm.

[0053] The materials used for each layer were petroleum-derived polyolefin resin (petroleum-derived polyethylene resin), recycled polyolefin resin, nucleating agent, alicyclic resin, odor absorbent, and compatibilizer. The melt flow rates (MFR) of the petroleum-derived polyolefin resin (petroleum-derived polyethylene resin) and recycled polyolefin resin were measured at a test temperature of 190°C in accordance with JIS K 7210 (2014) unless otherwise specified. The weight-average molecular weights (Mw) of the petroleum-derived polyolefin resin (petroleum-derived polyethylene resin) and recycled polyolefin resin were measured using a high-temperature GPC system (manufactured by Tosoh Corporation) equipped with the following equipment under the following measurement conditions: High temperature GPC equipment HLC-8321GPC / HT Dissolution and filtration equipment DF-8321 Column: TSKgel guard column HHR(S)HT + TSKgel GMHHR-H(S)HT x 3 Eluent ODCB Melting / measurement temperature 145℃ Sample concentration: 0.1 wt / vol% Injection volume 0.3ml Flow rate 1.0ml / min Detector: Differential refractometer

[0054] [Petroleum-derived polyolefin resin (petroleum-derived polyethylene resin)] PE1: Petroleum-derived polyethylene (Ube Maruzen Polyethylene Co., Ltd.; 2040F), MFR: 4g / 10min, Mw: 160000 PE2: Petroleum-derived polyethylene (Dow Chemical Company; TF80), MFR: 1.7 g / 10 min, Mw: 180,000

[0055] [Recycled polyolefin resin] R-PE1: Material recycled polyethylene (soft PE manufactured by Toyama Environmental Protection Co., Ltd.), MFR: 0.91 g / 10 min, Mw: 310,000 R-PE2: Recycled polyethylene (MarLENE (registered trademark) manufactured by Martogg LCM), MFR: 0.6 g / 10 min, Mw: 410,000 R-PE3: Chemically recycled polyethylene (UT404 manufactured by Lotte Chemical), MFR: 2.8g / 10min, Mw: 180000

[0056] [Nucleating agent] CN: Crystal nucleating agent masterbatch for polyethylene (Rikemaster (registered trademark) CN001, manufactured by Riken Vitamin Co., Ltd.)

[0057] [Alicyclic resin] PR: Alicyclic hydrocarbon petroleum resin (ENEOS Corporation; PR801)

[0058] [Odor absorbent] OR: Activated carbon (Futamura Chemical Co., Ltd.; SA1000)

[0059] [Compatibilizer] CP: Polyethylene elastomer (manufactured by Mitsui Chemicals, Inc.; Toughmer (registered trademark) P0280)

[0060] [Prototype 1] Prototype 1 is a non-oriented polyethylene film in which the first surface layer is made of 100 wt% PE1, the middle layer is made of 90 wt% PE1 and 10 wt% R-PE1, and the second surface layer is made of 100 wt% PE1.

[0061] [Prototype 2] Prototype 2 is an unstretched polyethylene film that uses 100 wt% PE1 for the first surface layer, 87.5 wt% PE1, 10 wt% R-PE1, and 2.5 wt% CN for the middle layer, and 100 wt% PE1 for the second surface layer.

[0062] [Prototype 3] Prototype 3 is an unstretched polyethylene film that uses 100 wt% PE1 for the first surface layer, 80 wt% PE1, 10 wt% R-PE1, and 10 wt% PR for the middle layer, and 100 wt% PE1 for the second surface layer.

[0063] [Prototype 4] Prototype 4 is an unstretched polyethylene film that uses 100 wt% PE1 for the first surface layer, 85 wt% PE1, 10 wt% R-PE1, and 5 wt% OR for the middle layer, and 100 wt% PE1 for the second surface layer.

[0064] [Prototype 5] Prototype 5 is an unstretched polyethylene film in which the first surface layer is 100 wt% PE1, the middle layer is 80 wt% PE1, 10 wt% R-PE1, and 10 wt% CP, and the second surface layer is 100 wt% PE1.

[0065] [Prototype 6] Prototype 6 is a non-oriented polyethylene film in which the first surface layer is made of 100 wt% PE1, the middle layer is made of 90 wt% PE1 and 10 wt% R-PE2, and the second surface layer is made of 100 wt% PE1.

[0066] [Prototype 7] Prototype 7 is a non-oriented polyethylene film in which the first surface layer is made of 100 wt% PE1, the middle layer is made of 30 wt% PE1 and 70 wt% R-PE3, and the second surface layer is made of 100 wt% PE1.

[0067] [Prototype 8] Prototype 8 is a non-stretched polyethylene film in which the first surface layer is made of 100 wt% PE1, the middle layer is made of 100 wt% PE1, and the second surface layer is made of 100 wt% PE1.

[0068] [Prototype 9] Prototype example 9 is an unstretched polyethylene film in which the first surface layer is made of 100 wt% PE1, the middle layer is made of 90 wt% PE1 and 10 wt% R-PE1, and the second surface layer is made of 90 wt% PE1 and 10 wt% R-PE1.

[0069] [Prototype 10] Prototype 10 is a biaxially oriented polyethylene film in which the first surface layer is made of 100 wt% PE1, the middle layer is made of 90 wt% PE2 and 10 wt% R-PE2, and the second surface layer is made of 100 wt% PE1.

[0070] The environmental performance, odor, and film appearance of prototypes 1 to 10 were evaluated. The evaluation results are shown in Tables 1 and 2 below.

[0071] [Environmental performance evaluation] Environmental performance is an index used to determine whether a film is recyclable or not by using recycled polyolefin resin (recycled material). The environmental performance was evaluated based on the following criteria. Good: The content of recycled polyolefin resin (recycled material) in the film is 3 wt% or more, and the recyclability is good. ×: The content of recycled polyolefin resin (recycled material) in the film is less than 3 wt %, and the recyclability is not good.

[0072] [Odor evaluation] Odor refers to unpleasant odors such as fishy or putrid odors that humans find unpleasant. To evaluate odor, 5 cm x 10 cm samples were cut from the films of Samples 1 to 10, sealed in 300 ml flasks, and stored in an oven at 40°C for 72 hours. After storage, the samples were left at room temperature for 24 hours. Sensory evaluation of the samples after storage was performed. The sensory evaluation was based on the average score of five panelists based on the six-point odor intensity rating system shown below. The odor evaluation was considered good if the average odor intensity score did not exceed 4. Odor intensity 0: Odorless Odor intensity 1: barely detectable odor Odor intensity 2: A weak odor that is easy to identify Odor intensity 3: Easily detectable odor Odor intensity 4: Strong odor Odor intensity 5: Strong odor

[0073] [Film appearance evaluation] The appearance of the film is an index for judging the quality of the film surface (commercial value of the film) based on the presence or absence of fisheyes. Since the roughness of the film surface increases as the number of fisheyes increases, the appearance of the film is evaluated using a laser microscope (Keyence Corporation: VK-X3000) to measure the ten-point average roughness (R Z In this appearance evaluation, the surface of the second surface layer was measured using a laser microscope and the ten-point average roughness (R Z The film appearance was evaluated by the ten-point average roughness (R Z ) was rated as good when it did not exceed 2 μm.

[0074] [Table 1]

[0075] [Table 2]

[0076] [Results and Discussion] Prototype 8 is a film that does not contain recycled materials. As shown in Table 2, Prototype 8 has extremely good film performance in terms of odor and appearance. However, because it does not contain recycled materials, it is not suitable as a film that meets recent societal demands for environmental consideration. Therefore, the films of prototypes 1 to 7, 9, and 10, which contain recycled materials and meet environmental performance requirements, will be examined based on the film performance in terms of odor and appearance. Note that the recycled polyolefin resin (R-PE1) used as the recycled material emits a strong odor, while the other recycled polyolefin resins (R-PE2, R-PE3) emit a weak odor.

[0077] Prototype Examples 1 to 7 and 10 all had the desired film properties (odor, film appearance), whereas Prototype Example 9 did not have the desired properties in terms of odor and film appearance.

[0078] Prototype 1 is a film in which the middle layer contains a recycled material (R-PE1) with a strong odor, and neither the first nor second surface layer contains recycled material. In contrast, Prototype 9 is a film similar to Prototype 1 except that the second surface layer is made of a resin containing the same recycled material (R-PE1) as the middle layer.

[0079] As can be seen from the odor tests in Tables 1 and 2, Prototype 9, which contained recycled resin in the second surface layer, did not produce good results in the odor test, whereas Prototype 1, which had surface layers (first and second surface layers) that did not contain recycled materials on either side of the intermediate layer that contained recycled resin, produced good results in the odor test. By sandwiching the intermediate layer containing recycled materials between surface layers that did not contain recycled materials, both surface layers (first and second surface layers) functioned as barrier layers that prevented the migration of odorous components originating from the recycled materials, and it is thought that this suppressed the release of odor from the film.

[0080] As can be seen from the appearance tests in Tables 1 and 2, Prototype 1 and Prototype 9 showed poor results in the appearance test for Prototype 9, while Prototype 1 showed good results in the appearance test. This suggests that films containing recycled material (R-PE1) are more likely to develop appearance defects such as fisheyes. This is thought to be because the recycled material (R-PE1) contains a large amount of foreign matter, which adversely affects the appearance of the film.

[0081] In prototypes 2 to 4, a crystal nucleating agent (prototype 2), an alicyclic resin (prototype 3), and an odor absorbent (prototype 4) were added as additives to the intermediate layer. In prototypes 2 to 4, the results of the odor test were all improved compared to prototype 1. Therefore, it is believed that adding these additives can more effectively reduce odors.

[0082] Prototype 5 is an example in which a compatibilizer was added to the intermediate layer. Prototype 5 showed improved results in the appearance test compared to Prototype 1. Therefore, it is believed that adding a compatibilizer can more effectively reduce appearance defects.

[0083] Prototypes 6 and 7 are examples in which recycled materials (R-PE2 and R-PE3) different from those used in Prototype 1 were used. In Prototypes 6 and 7, the intermediate layer was sandwiched between the first and second surface layers, just like in Prototype 1, and good results were obtained in terms of both odor and appearance.

[0084] Prototype 10 is an example of a stretched film (biaxially stretched) with a laminated structure in which the intermediate layer contains recycled material (R-PE2) and the first and second surface layers do not contain recycled material. In Prototype 10, good results were obtained in both odor and appearance because the intermediate layer was sandwiched between the first and second surface layers, demonstrating that problems with odor and appearance can be improved with stretched films as well as with unstretched films.

[0085] As described above, the polyethylene film of the present invention is a laminate film primarily made of polyethylene resin, consisting of at least three layers: a first surface layer, an intermediate layer, and a second surface layer. The intermediate layer is made of a recycled polyolefin resin and either a petroleum-derived polyethylene resin or a plant-derived polyethylene resin, or a mixture thereof. The first and second surface layers are made of either a petroleum-derived polyolefin resin or a plant-derived polyolefin resin, or a mixture thereof. The first and second surface layers function as barrier layers that prevent the migration of odorous components originating from the intermediate layer due to the recycled polyolefin resin, thereby suppressing odor emission from the film. This allows for a reduction in odors originating from recycled polyolefin resins (recycled raw materials). [Industrial Applicability]

[0086] The polyethylene film of the present invention is a film made from recycled materials, and has a laminate structure in which an intermediate layer containing recycled materials is sandwiched between first and second surface layers that do not contain recycled materials, thereby making it possible to reduce odors caused by recycled materials. Furthermore, for a laminate consisting of multiple resin layers including the polyethylene film of the present invention, by laminating resin layers with physical properties appropriate for the application, recycled materials can be used while maintaining the performance required of a film. Furthermore, the laminate can also be made into packaging. This makes it a promising substitute for existing laminates and packaging as a film or packaging made from recycled materials.

Claims

1. A laminated film mainly made of a polyethylene resin, which comprises at least three layers: a first surface layer, an intermediate layer, and a second surface layer, the intermediate layer is composed of 5 to 95 wt % recycled polyolefin resin and 5 to 95 wt % of either a petroleum-derived polyethylene resin or a plant-derived polyethylene resin, or a mixture thereof; the first surface layer and the second surface layer are made of either a petroleum-derived polyolefin resin or a plant-derived polyolefin resin, or a mixture thereof; The content of the recycled polyolefin resin in the laminated film is 3 wt % or more. A polyethylene film characterized by:

2. 2. The polyethylene film according to claim 1, wherein a crystal nucleating agent is added to at least one of the first surface layer, the intermediate layer, and the second surface layer in an amount of 0.1 to 10 wt %.

3. The polyethylene film according to claim 1, wherein a cyclic olefin resin or an alicyclic resin is added to at least one of the first surface layer, the intermediate layer, and the second surface layer.

4. 4. The polyethylene film according to claim 1, wherein an odor adsorbent is added to at least one of the first surface layer, the intermediate layer, and the second surface layer.

5. 4. The polyethylene film according to claim 1, wherein the intermediate layer contains 1 to 30 wt % of a polyethylene elastomer as a compatibilizer.

6. 4. The polyethylene film according to claim 1, wherein the intermediate layer contains a phenol-based antioxidant or a phosphorus-based antioxidant.

7. A laminate comprising a plurality of resin layers containing the polyethylene film according to claim 1 .

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