Light-shielding adhesive resin composition, multilayer film, uses of the multilayer film, and laminate film

Abstract

To provide a light-shielding adhesive resin composition for bonding a barrier resin layer and a heat-sealable resin layer which exhibits extremely high light-shielding properties, and prevents degradation of heat-sealability of the multilayer film when used as one layer of the multilayer film.SOLUTION: A multilayer film is composed of an acid-modified polyethylene-based resin having an interlayer adhesive strength of 6.0 N / 15 mm or more, a black pigment, and a polyethylene-based resin blended as needed, in which a blending ratio of an acid-modified polyethylene-based resin: black pigment: polyethylene-based resin=50-97 mass%: 3-30 wt.%: 0-40 wt.%. A multilayer film has at least a barrier resin layer 11, light-shielding adhesive resin layers 12 and 12' composed of the light-shielding adhesive resin composition, and a heat-sealable resin layer 13 in this order and has a thickness of 200 μm or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a light-shielding adhesive resin composition. It also relates to a multilayer film having excellent barrier properties using the resin composition. Specifically, it relates to a resin composition exhibiting excellent light-shielding properties and a multilayer film having excellent heat-sealing properties using the resin composition.

Background Art

[0002] As packaging materials for foods such as retort foods, oils and fats, frozen foods, and snack foods, and industrial products such as photosensitive resins, films that block light rays from the ultraviolet region to the visible light region and further have excellent gas barrier properties are required. As materials having excellent light-shielding properties and gas barrier properties, films such as aluminum foil and films with metal vapor deposition are known, and laminated films in which a base film / aluminum foil / sealant film are laminated in order are widely adopted as packaging materials for snack foods and the like. However, laminated films using metal foils such as aluminum foil or metal vapor deposition films react with metal detectors, so it was difficult to detect foreign substances (metal pieces) using a metal detector in packages using such laminated films. In addition, laminated films using aluminum foil sometimes generate sparks when heated in a microwave oven and could not be used for applications where the temperature is raised in the oven. Furthermore, films containing metal also had the problem of generating a large amount of residue when incinerated after use.

[0003] Patent Document 1 is an invention related to a co-extruded laminated film including a light-shielding resin layer and a barrier resin layer. Since the light-shielding resin layer of Document 1 is composed of a resin composition containing a polyolefin-based resin as a main component and a black pigment and a white pigment, the problems of the above-mentioned metal detector and the problem due to microwave heating do not occur. However, the multilayer film disclosed in the examples of Patent Document 1 has insufficient total light transmittance (0.2 to 0.3%) despite a film thickness of 70 μm and is not suitable for applications requiring high light-shielding properties.

[0004] Patent Document 2 also relates to an invention concerning a laminated film that does not contain aluminum and has excellent light-shielding and gas barrier properties, disclosing a co-extruded laminated film in which a white resin layer, a first light-shielding adhesive resin layer, a barrier resin layer, a second light-shielding adhesive resin layer, and a heat-sealable resin layer are sequentially laminated. However, looking at the examples, even though the film of Patent Document 2 has a film thickness of 70 μm, the total light transmittance is not sufficient (0.2-0.5%), and it is not suitable for applications that require high light-shielding properties. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2005-231041 [Patent Document 2] Japanese Patent Publication No. 2008-080506 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] The inventors investigated a multilayer film that can exhibit gas barrier properties without using metal foil or metal vapor-deposited film, and which has an extremely low total light transmittance, specifically below 0.1%. First, they investigated increasing the amount of black pigment added to the light-shielding resin layer in a co-extruded film disclosed in Patent Document 2, in which a white resin layer, a first light-shielding adhesive resin layer, a barrier resin layer, a second light-shielding adhesive resin layer, and a heat-sealable resin layer are sequentially laminated. However, increasing the amount of black pigment in the light-shielding resin layer resulted in a decrease in the seal strength when the multilayer films were stacked and heat-sealed.

[0007] The problem that the present invention aims to solve is to provide a light-shielding adhesive resin composition for bonding a barrier resin layer and a heat-sealable resin layer, which exhibits extremely high light-shielding properties, and furthermore, does not reduce the heat-sealability of a multilayer film when used as one layer of the multilayer film. Furthermore, the objective is to provide a multilayer film that exhibits high light-shielding properties without reducing heat-seal strength, using the resin composition. The present invention aims to provide a multilayer film that does not use metal foil or metal vapor-deposited film, exhibits gas barrier properties and heat sealability, and further demonstrates unprecedentedly high light-shielding properties. [Means for solving the problem]

[0008] The inventors investigated the reason why the heat seal strength of a multilayer film decreases when the amount of black pigment in the light-shielding adhesive resin layer of a co-extruded film, in which a white resin layer, a first light-shielding adhesive resin layer, a barrier resin layer, a second light-shielding adhesive resin layer, and a heat-sealable resin layer are sequentially laminated. They hypothesized that the heat seal strength is related not only to the resin composition and thickness of the heat-sealable resin layer, but also to the adhesive strength between each layer. Specifically, they hypothesized that even if the heat-sealable resin layer exhibits sufficient seal strength, the heat seal strength will be low if the interlayer adhesive strength is low. Furthermore, they hypothesized that increasing the amount of black pigment reduces the proportion of acid-modified resin in the light-shielding adhesive resin layer, which lowers the interlayer adhesive strength and reduces the seal strength when the multilayer film is heat-sealed. Therefore, by adopting an acid-modified polyethylene resin with high interlayer adhesive strength as the adhesive resin used in the light-shielding adhesive resin layer, the above problems were solved.

[0009] In other words, according to the present invention, the following [1] to [8] are provided as means for solving the above problems. [1] A light-shielding adhesive resin composition characterized by comprising an acid-modified polyethylene resin having an interlayer adhesive strength of 6.0 N / 15 mm or more as measured by the following method, a black pigment, and polyethylene resin added as needed, wherein the mixing ratio is acid-modified polyethylene resin:black pigment:polyethylene resin = 50-97% by weight:3-30% by weight:0-40% by weight. <Method for measuring interlaminar adhesion strength> Acid-modified polyethylene resin is co-extruded together with linear low-density polyethylene and ethylene-vinyl alcohol copolymer using a T-die co-extrusion method to produce a three-layer film consisting of a 40 μm linear low-density polyethylene layer, a 10 μm acid-modified polyethylene resin layer, and a 20 μm ethylene-vinyl alcohol copolymer layer. This film is then cut into a 15 mm wide rectangle to create a test specimen. The test specimen is peeled in a T-shape between the acid-modified polyethylene resin layer and the ethylene-vinyl alcohol copolymer layer at a peeling speed of 300 mm / min in accordance with JIS K 6854-3:1999, and the force required for peeling is measured.

[0010] [2] A multilayer film having a thickness of 200 μm or less, comprising in order at least a barrier resin layer, a light-shielding adhesive resin layer, and a heat-sealable resin layer, wherein the light-shielding adhesive resin layer is made of the light-shielding adhesive resin composition of [1]. [3] A multilayer film having a thickness of 200 μm or less, comprising in order a white resin layer / a first light-shielding adhesive resin layer / a barrier resin layer / a second light-shielding adhesive resin layer / a heat-sealable resin layer, wherein the first light-shielding adhesive resin layer and / or the second light-shielding adhesive resin layer are made of the light-shielding adhesive resin composition of [1]. [4] A multilayer film having a thickness of 200 μm or less, comprising in order at least a barrier resin layer, a light-shielding adhesive resin layer, and a heat-sealable resin layer, wherein the total light transmittance measured in accordance with JIS K 7361-1:1997 is 0.1% or less, and the heat seal strength of the portion heat-sealed under the conditions of upper and lower heating plate temperature of 110°C, heating plate width of 10 mm, sealing pressure of 1 MPa, and sealing time of 0.7 seconds is 6.0 N / 15 mm or more, measured in accordance with JIS Z 0238:1998. [5] A multilayer film according to any one of [2] to [4], characterized in that the barrier resin layer is a layer made of an ethylene-vinyl alcohol copolymer. [6] The multilayer film according to any one of [2] to [5], characterized in that the heat-sealable resin layer contains a white pigment.

[0011] Uses of multilayer films as sealant films as described in any of [7] [2] to [6]. A laminate film obtained by laminating a multilayer film described in any of [8] [2] to [6] with a base film. [Effects of the Invention]

[0012] Because the multilayer film of the present invention does not use metal foils such as aluminum foil or metal-deposited films, packages wrapped in this film can be detected for foreign objects using a metal detector. Furthermore, food wrapped in this film can be heated in a microwave oven without transferring it to a plate or other container. In addition, there is less residue when incinerated after use. Furthermore, because it exhibits higher light-blocking properties than conventional films, it is suitable for packaging items that are easily damaged by light. When this film is used for food packaging, it can suppress food deterioration and contribute to extending food shelf life, thus improving the problem of food waste. It is also suitable for packaging pharmaceuticals, such as eye drops, whose quality deteriorates due to light and oxygen. Furthermore, adding a white pigment to the heat-sealable resin layer can lower the lower limit of the heat-sealable temperature range. This reduces the amount of energy required for heat sealing. Furthermore, conventional laminate films using metal foil required two lamination steps (a step of bonding the metal foil to the base film and a step of bonding the metal foil to the sealant film). However, by using the multilayer film of the present invention, since the film combines the functions of aluminum foil and sealant film, a laminate film with excellent properties such as barrier properties, light shielding properties, and heat sealability can be obtained in a single lamination step. [Brief explanation of the drawing]

[0013] [Figure 1] This is a schematic cross-sectional view showing one embodiment of the multilayer film of the present invention. [Figure 2] This is a schematic cross-sectional view showing one embodiment of the laminate film of the present invention.

Mode for Carrying Out the Invention

[0014] Hereinafter, the present invention will be described in detail, but the present invention is not limited to the following forms, and various embodiments can be taken within the scope where the same effects can be obtained.

[0015] [Light-Shielding Adhesive Resin Composition] The light-shielding adhesive resin composition of the present invention is composed of an acid-modified polyethylene-based resin which is an adhesive resin, a black pigment, and a polyethylene-based resin blended as required. The acid-modified polyethylene-based resin is a resin obtained by modifying polyethylene or a polyethylene-based resin with acrylic acid, methacrylic acid, oleic acid, linoleic acid, maleic acid, fumaric acid, other unsaturated carboxylic acids, or their anhydrides. In the present invention, one of these acid-modified polyethylene-based resins can be used alone, or two or more of them can be blended and used. In consideration of interlayer adhesion strength and economy, as the acid-modified polyethylene-based resin, a maleic acid-modified polyethylene-based resin obtained by modifying polyethylene or a polyethylene-based resin with maleic acid or its anhydride is particularly preferable.

[0016] In the present invention, among the acid-modified polyethylene-based resins, an acid-modified polyethylene-based resin having a particularly large interlayer adhesion strength is used. Specifically, those having an interlayer adhesion strength measured by the following method for measuring interlayer adhesion strength exceeding 6.0 N / 15 mm are used. The interlayer adhesion strength is preferably 8.0 N / 15 mm or more, and particularly preferably 8.5 N / 15 mm or more. In order to increase the interlayer adhesion strength of the acid-modified polyethylene-based resin, measures such as increasing the degree of acid modification may be taken. There is no particular upper limit to the interlayer adhesion strength, but those exceeding 12.0 N / 15 mm, particularly those exceeding 15.0 N / 15 mm, are difficult to obtain.

[0017] <Method for Measuring Interlayer Adhesion Strength> The interlayer adhesion strength of the acid-modified polyethylene-based resin is obtained by first (1) forming a test film, (2) cutting it into a predetermined width to prepare a test piece, and (3) measuring the peel strength of the test piece. (1) Formation of test film The test film is a three-layer film consisting of a linear low-density polyethylene layer, an acid-modified polyethylene resin layer, and an ethylene-vinyl alcohol copolymer layer, which are produced by T-die co-extrusion along with linear low-density polyethylene and ethylene-vinyl alcohol copolymer. The thickness of each layer is 40 μm for the linear low-density polyethylene layer, 10 μm for the acid-modified polyethylene resin layer, and 20 μm for the ethylene-vinyl alcohol copolymer layer. (2) Preparation of test specimens (1) Cut the test film prepared in (1) into a rectangle with a width of 15 mm, and use this as the test specimen. The length of the test specimen is not particularly limited, but it is desirable that it be greater than 200 mm. (3) Measurement of peel strength The peel strength will be measured in accordance with JIS K 6854-3:1999. The peeling speed will be 300 mm / min, and the force required to peel in a T-shape will be measured using a tensile testing machine. It is recommended to pre-peel one end of the test specimen by approximately 50 mm between the acid-modified polyethylene resin layer and the ethylene-vinyl alcohol copolymer layer, and then attach this peeled section to the chuck of the tensile testing machine.

[0018] The black pigment employs one or more conventionally known colorants, such as iron black, graphite, or carbon black, as coloring agents. Among these, carbon black is readily available and has excellent functionality, making it a suitable choice. The amount of black pigment incorporated into the light-shielding adhesive resin composition is preferably about 3 to 30% by weight, and particularly preferably 10 to 20% by weight. If the amount of black pigment is less than 3% by weight, the total light transmittance may exceed 0.1%, and if it exceeds 30% by weight, the adhesive strength between layers of the multilayer film may decrease.

[0019] When adding pigments to resin, direct addition can lead to uneven coloring. Therefore, most pigments are sold in the form of masterbatches (hereinafter abbreviated as MB as needed), in which pigments are dispersed at high concentrations in the resin. Commercially available grades of carbon black MB use polyethylene-based resins, while carbon black MB using acid-modified polyethylene-based resins is more expensive. Conventional light-shielding layers were forced to use carbon black MB with an acid-modified polyethylene resin as the base resin in order to maintain the interlayer adhesive strength. However, because the present invention has high interlayer adhesive strength with an acid-modified polyethylene resin, it is also possible to use general-purpose carbon black MB with a polyethylene resin as the base resin. The light-shielding adhesive resin composition can contain 0 to 40% by weight, preferably 1 to 30% by weight of polyethylene resin. Therefore, it is best to use carbon black MB with a polyethylene resin as the base resin so that the amount of polyethylene resin contained falls within this range.

[0020] In the light-shielding adhesive resin composition, the blending ratio of acid-modified polyethylene resin, black pigment, and polyethylene resin is preferably acid-modified polyethylene resin:black pigment:polyethylene resin = 50-97% by weight:3-30% by weight:0-40% by weight, and particularly preferably 70-90% by weight:10-20% by weight:1-30% by weight.

[0021] [Multilayer film] The multilayer film of the present invention comprises, in order, at least a barrier resin layer, a light-shielding adhesive resin layer, and a heat-sealable resin layer. Preferably, as shown in Figure 1, it comprises, in order, a white resin layer 14 / a first light-shielding adhesive resin layer 12' / a barrier resin layer 11 / a second light-shielding adhesive resin layer 12 / a heat-sealable resin layer 13. Generally, as the thickness of a multilayer film increases, the light-shielding adhesive resin layer also increases, reducing the total light transmittance. However, the multilayer film of the present invention can achieve a total light transmittance of 0.1% or less even with a film thickness of 200 μm or less. From an economic standpoint, the film thickness of the multilayer film is preferably 150 μm or less, particularly 100 μm or less, even more preferably 70 μm or less, particularly 65 μm or less, and even more preferably 50 μm or less. From a functional standpoint, it is preferably 15 μm or more, particularly 20 μm or more, and even more preferably 30 μm or more. While the thickness of each layer is not particularly limited, it is desirable that the white resin layer / light-shielding adhesive resin layer / barrier resin layer / light-shielding adhesive resin layer / heat-sealable resin layer be 3-50 μm / 2-30 μm / 3-40 μm / 2-30 μm / 3-50 μm, in particular 5-40 μm / 2-20 μm / 3-30 μm / 2-20 μm / 5-40 μm, and even 10-30 μm / 2-10 μm / 3-15 μm / 2-10 μm / 10-30 μm. If each layer is too thin, it will not be able to perform the desired function, and if it is too thick, it will lead to an increase in the cost of the multilayer film.

[0022] <White resin layer> The white resin layer is a layer located on the surface of the multilayer film. When using this film as a sealant film, it is preferable to laminate it to the base film so that the white resin layer is located on the base film side. The white resin layer consists of a thermoplastic resin such as a polyolefin resin and a white pigment. As the polyolefin resin, one or more types can be used, including low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, polypropylene, ethylene-vinyl acetate copolymer, ionomer resin, ethylene-ethyl acrylate copolymer, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, ethylene-propylene copolymer, methylpentene polymer, and acid-modified polyolefin resins obtained by modifying polyethylene, polyethylene-based resins, or polypropylene-based resins with acrylic acid, methacrylic acid, maleic anhydride, fumaric acid, or other unsaturated carboxylic acids. Among these, considering the interlayer adhesion strength with the adjacent first light-shielding adhesive resin layer 12', low-density polyethylene, medium-density polyethylene, high-density polyethylene, and linear low-density polyethylene are preferred, with low-density polyethylene and / or linear low-density polyethylene being particularly preferred. Since the white resin layer does not significantly affect the heat seal strength, an inexpensive resin may be used to prioritize economic efficiency.

[0023] The white pigment incorporated into the white resin layer can be any conventionally known pigment without particular limitations. For example, titanium dioxide, zinc oxide, zinc sulfide, barium sulfate, lead white, basic carbonate, basic silicate, lithopone, antimony trioxide, and calcium carbonate can be used. Among these, titanium dioxide (TiO2) is suitable for this application due to its color, cost-effectiveness, and availability. If the amount of white pigment is too small, the appearance of the multilayer film will be close to the color (black) of the light-shielding adhesive resin layer, which may degrade the appearance of the print applied to the base film when used as a sealant film. On the other hand, if the amount of white pigment is too large, there will be insufficient resin, making it difficult to form the white resin layer. Considering these factors, the mixing ratio of polyolefin resin and white pigment in the white resin layer is polyolefin resin:white pigment = 50-95% by weight:5-50% by weight, preferably 70-90% by weight:10-30% by weight, and particularly preferably 75-90% by weight:10-25% by weight.

[0024] <Light-shielding adhesive resin layer> The light-shielding adhesive resin layers 12 and 12' are layers that bond the barrier resin layer 11 to the heat-sealable resin layer 13, or the barrier resin layer 11 to the white resin layer 14, and further impart light-shielding properties to the multilayer film. In the multilayer film 1 of the present invention, at least one, preferably both, of the first light-shielding adhesive resin layer 12' and the second light-shielding adhesive resin layer 12 are made of the light-shielding adhesive resin composition described above.

[0025] <Barrier resin layer> The barrier resin layer 11 of the present invention is made of a resin with high oxygen gas barrier properties, such as polyvinylidene chloride resin, polyvinyl alcohol resin, ethylene-vinyl alcohol copolymer, or nylon MXD6 resin. In the present invention, among the above resins, it is preferable to use a resin that melts with heat and can be co-extruded together with the aforementioned polyolefin resin, specifically, an ethylene-vinyl alcohol copolymer or nylon MXD6 resin, with ethylene-vinyl alcohol copolymer being particularly preferred. It is also possible to use a blend of multiple ethylene-vinyl alcohol copolymers with different ethylene contents as the barrier resin layer 11.

[0026] <Heat-sealable resin layer> The heat-sealable resin layer 13, like the white resin layer, mainly consists of one or more thermoplastic resins such as polyolefin resins. As the polyolefin resin, one or more types of low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, polypropylene, ethylene-vinyl acetate copolymer, ionomer resin, ethylene-ethyl acrylate copolymer, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, ethylene-propylene copolymer, methylpentene polymer, acid-modified polyolefin resins obtained by modifying polyethylene, polyethylene resins, or polypropylene resins with acrylic acid, methacrylic acid, maleic anhydride, fumaric acid, or other unsaturated carboxylic acids, and other heat-sealable polyolefin resins can be used. Among these, considering the interlayer adhesion strength with the adjacent second light-shielding adhesive resin layer 12 and the heat-sealability of the multilayer film 1, low-density polyethylene, medium-density polyethylene, high-density polyethylene, and linear low-density polyethylene are preferred, and low-density polyethylene and / or linear low-density polyethylene are particularly preferred.

[0027] Furthermore, it is preferable that a white pigment be incorporated into the heat-sealable resin layer 13. The white pigment lowers the temperature range in which heat sealing is possible, thereby reducing the amount of energy required for heat sealing. The white pigment incorporated into the heat-sealable resin layer 13 can be any conventionally known pigment without particular limitation, similar to the white resin layer 14. For example, titanium dioxide, zinc oxide, zinc sulfide, barium sulfate, lead white, basic carbonate, basic silicate, lithopone, antimony trioxide, and calcium carbonate can be used. Among these, titanium dioxide (TiO2) is suitable for this application because it has excellent thermal conductivity and is readily available. The mixing ratio of polyolefin resin and white pigment in the heat-sealable resin layer is polyolefin resin:white pigment = 50~95% by weight:5~50% by weight, preferably 70~90% by weight:10~30% by weight, and particularly preferably 75~90% by weight:10~25% by weight. If the amount of white pigment is too small, it will be difficult to lower the heat-sealable temperature range, and the film's appearance will become closer to black or gray, which is undesirable for food applications. If the amount of white pigment is too large, the heat seal strength may decrease.

[0028] Furthermore, in each layer constituting the multilayer film of the present invention, additives such as lubricants, crosslinking agents, antioxidants, ultraviolet absorbers, light stabilizers, fillers, reinforcing agents, antistatic agents, flame retardants, fire retardants, foaming agents, antifungal agents, other pigments, dyes, dispersants, surfactants, antiblocking agents, and modifying resins may be used, to the extent that they do not hinder the effects of the present invention.

[0029] [Manufacturing method for multilayer films] The multilayer film of the present invention can be manufactured by conventionally known manufacturing methods. For example, resin compositions forming each layer can be prepared and then co-extruded using a T-die co-extruder, an inflation co-extruder, or the like. This is merely one example of a manufacturing method for the multilayer film of the present invention, and the present invention is not limited thereto.

[0030] [Laminating film] The multilayer film of the present invention may be used as is as a packaging film, but because it has excellent heat-sealing properties, it can also be used as a sealant film. Figure 2 is a schematic cross-sectional view showing one embodiment of the laminate film 2 of the present invention. The laminate film 2 in Figure 2 consists of a multilayer film 10 of the present invention used as a sealant film, a base film 20, and a lamination layer 30. This film can be suitably used in applications requiring strength, such as standing pouches. The method for laminating the base film 20 and the sealant film (the multilayer film 10 of the present invention) is not particularly limited, and conventionally known lamination methods such as dry lamination or extrusion lamination can be used. Furthermore, any printing can be applied to the surface, back surface, or both sides of the base film 20.

[0031] As the base film 20 used in the laminate film 2, films or sheets of various resins such as polyester resin, polyamide resin, polyaramid resin, polyethylene resin, polypropylene resin, polycarbonate resin, polyacetal resin, fluororesin, and others can be used. Furthermore, as the above-mentioned resin films or sheets, either unstretched films or stretched films stretched in one or two axes can be used. Furthermore, considering strength, puncture resistance, rigidity, cost, etc., a biaxially oriented film with a thickness of 12 to 50 μm is preferred as the base film, and in particular, it is preferable to use a biaxially oriented polyester resin, biaxially oriented polyamide resin, or biaxially oriented polypropylene resin film with a thickness of 9 μm to 30 μm. The base film may be a single-layer film, or it may be a composite film made by laminating two or more base films. [Examples]

[0032] [Example Test] Prior to the examples, we confirmed the change in the heat-sealable temperature range due to the application of a white pigment.

[0033] In the test examples of the present invention, the heat seal strength is measured by the following method. <Heat seal strength> Two layers of film are stacked and heat-sealed using a 10mm wide heating plate with a sealing time of 0.7 seconds and a sealing pressure of 0.1 MPa. During this process, the temperature of the lower heating plate is fixed at 110°C, while the temperature of the upper heating plate is varied from 110°C to 180°C. Next, a test piece measuring 15 mm in width and 100 mm in unfolded length is prepared from the sealed film, and the heat seal strength is measured in accordance with the heat seal strength test for bags specified in JIS Z 0238:1998. The distance between the chucks is 40 mm, and the tensile speed is 500 mm / min.

[0034] [Test Example 1] Linear low-density polyethylene (density = 926 kg / m³) 3 (MI = 0.85 g / 10 min) 71.2% by weight, high-pressure method low-density polyethylene (density = 924 kg / m³) 3 A resin composition was prepared by mixing 25.1% by weight of (MI=1.9g / 10min) and 3.7% by weight of titanium dioxide. A 60 μm single-layer film was fabricated by inflation extrusion. The heat seal strength of the obtained film was measured. The results are shown in Table 1. [Test Example 2] Linear low-density polyethylene (density = 926 kg / m³) 3 A resin composition consisting of 78.5% by weight of (MI=0.85g / 10min) and 21.5% by weight of high-pressure low-density polyethylene (density=924kg / m3, MI=1.9g / 10min) was used to produce a 60μm single-layer film by inflation extrusion. The heat seal strength of the obtained film was measured. The results are shown in Table 1.

[0035] [Table 1] *All units are in N / 15mm

[0036] JIS Z 0238:1998 specifies a guideline of 6 N / 15 mm for typical heat seal strength. The film in Test Example 1 can achieve this strength at an upper heating plate temperature of 150-160°C, while the film in Test Example 2 requires an upper heating plate temperature of 160-170°C. This test confirmed that adding a white pigment reduces the amount of energy required for heat sealing.

[0037] Next, we will present the examples. In the examples, the multilayer film will be evaluated by the following method. <Heat seal strength> Two multilayer films are stacked so that the heat-sealable resin layers are in contact, and measurements are taken in the same manner as in the test example.

[0038] <Total light transmittance> The total light transmittance of the multilayer film of the present invention is measured in accordance with JIS K 7361-1:1997. A haze meter NDH4000 manufactured by Nippon Denshoku Industries Co., Ltd. is used for the measurement. <Oxygen permeability> The oxygen permeability of the multilayer film of the present invention will be measured in accordance with JIS K7126-2:2006. The measurement will be performed using a MOCON oxygen permeability measuring device OX-TRAN 2 / 21H manufactured by Hitachi High-Tech Science Corporation, under conditions of room temperature of 23°C and humidity of 60%. <Water vapor transmission rate> The water vapor transmission rate of the multilayer film of the present invention will be measured in accordance with JIS K 7129:2008. The measurement will be performed using a MOCON water vapor transmission rate measuring device PERMATRAN-W 3 / 34G manufactured by Hitachi High-Tech Science Corporation, under conditions of room temperature of 40°C and humidity of 90%.

[0039] [Example 1] As the white resin layer, a resin composition is used which is a mixture of 54.3% by weight of linear low-density polyethylene (LL), 13.9% by weight of low-density polyethylene (LD), and 31.8% by weight of titanium dioxide MB, which is obtained by kneading low-density polyethylene (LD) with titanium dioxide (TiO2) in a weight ratio of 3:7. As the first light-shielding adhesive resin layer, a resin composition is used which is a mixture of 58.8% by weight of an acid-modified polyolefin resin (PE-a1) with an interlayer adhesive strength of 6.2 N / 15 mm, 3.0% by weight of linear low-density polyethylene, and 38.2% by weight of carbon black MB, which is a mixture of low-density polyethylene (LD) and carbon black (CB) in a weight ratio of 6:4. Ethylene vinyl alcohol (EVOH) is used as the gas barrier resin. The same resin composition as the first light-shielding adhesive resin layer is used for the second light-shielding adhesive resin layer. As the heat-sealable resin layer, a resin composition is used which is a mixture of 39.9% by weight of linear low-density polyethylene (LL), 13.9% by weight of low-density polyethylene (LD), 14.4% by weight of a modifier (low-crystallinity α-olefin copolymer), and 31.8% by weight of titanium dioxide MB, which is obtained by kneading titanium dioxide (TiO2) with low-density polyethylene (LD) in a weight ratio of 3:7. Each resin was extruded into an annular die, and a multilayer film consisting of a white resin layer, a first light-shielding adhesive resin layer, a barrier resin layer, a second light-shielding adhesive resin layer, and a heat-sealable resin layer was fabricated by inflation co-extrusion. The thicknesses of each layer were 22.0 μm, 4.8 μm, 4.9 μm, 3.7 μm, and 19.6 μm, respectively, for the white resin layer, the first light-shielding adhesive resin layer, the barrier resin layer, the second light-shielding adhesive resin layer, and the heat-sealable resin layer. The physical properties of the obtained film are shown in Table 2.

[0040] [Example 2] A multilayer film was obtained in the same manner as in Example 1, except that the resin composition of each layer was changed as shown in Table 2. The physical properties of the obtained film are also shown in Table 2.

[0041] [Comparative Example 1] To evaluate the performance of the multilayer film of the present invention, the light-shielding laminated sealant film of Example 1 in Patent Document 2 is used as Comparative Example 1, and its physical properties are described in Table 2. The interlayer adhesive strength of the acid-modified polyethylene (PE-a3: manufactured by Mitsui Chemicals, Inc., Admer® NF528) used in Comparative Example 1 is 5.9 N / 15 mm.

[0042] [Table 2]

[0043] The multilayer film of the present invention was found to exhibit high light-shielding properties (film thickness 55 μm, total light transmittance 0.00%) despite being thinner than the film disclosed in the examples of Patent Document 2 (film thickness 70 μm, total light transmittance 0.2-0.5%). Furthermore, it was confirmed that it exhibited a heat seal strength exceeding 6 N / 15 mm despite a high amount of carbon black content. This is because a resin exhibiting excellent interlayer adhesion strength was adopted as the acid-modified resin in the resin composition portion containing carbon black, allowing a large amount of carbon black to be incorporated into the layer without reducing the heat seal strength. In addition, the heat seal strength at 100°C significantly exceeded 6.0 N / 15 mm, which is thought to be the effect of the modifier (low-crystallinity α-olefin copolymer). In addition, both the films of Examples 1 and 2 exhibited excellent oxygen barrier and water vapor barrier properties.

[0044] [Examples 3-5] A multilayer film was obtained in the same manner as in Example 1, except that the resin composition of each layer was changed as shown in Table 3. The physical properties of the obtained film are described in accordance with Table 3. In Example 5, an acid-modified polyolefin resin (PE-a2) with an interlayer adhesion strength of 9.0 N / 15 mm was used as the acid-modified resin.

[0045] [Table 3]

[0046] By comparing Example 3 and Example 4, it was confirmed that even when using the same PE-a1, increasing the thickness of the heat-sealable resin layer improved the heat seal strength. Furthermore, by comparing the differences between Example 3 and Example 4, and between Example 3 and Example 5, it was confirmed that the interlayer adhesion strength of the acid-modified polyethylene resin used in the light-shielding adhesive resin layer had a greater influence on the heat seal strength than the thickness of the heat-sealable resin layer. [Explanation of Symbols]

[0047] 1. 10-layer film 11 Barrier resin layer 12 (Second) light-shielding adhesive resin layer 13 Heat-sealable resin layer 12' (First) Light-Blocking Adhesive Resin Layer 14 White resin layer 2. Laminating film 20 Base film 30 Layers for bonding

Claims

1. A co-extruded multilayer film having a thickness of 200 μm or less, comprising, in order, a barrier resin layer, a light-shielding adhesive resin layer, and a heat-sealable resin layer, The barrier resin layer is a layer made of an ethylene-vinyl alcohol copolymer. The light-shielding adhesive resin layer comprises a maleic acid-modified polyethylene resin having an interlayer adhesive strength of 6.0 N / 15 mm or more as measured by the following method, a black pigment, and a polyethylene resin (excluding the maleic acid-modified polyethylene resin), and the blending ratio is maleic acid-modified polyethylene resin: black pigment: polyethylene resin = 50-97% by weight: 3-30% by weight: 1-30% by weight. <Method for measuring interlaminar adhesion strength> A maleic acid-modified polyethylene resin is co-extruded together with linear low-density polyethylene and ethylene-vinyl alcohol copolymer using a T-die co-extrusion method to produce a three-layer film consisting of a 40 μm linear low-density polyethylene layer, a 10 μm maleic acid-modified polyethylene resin layer, and a 20 μm ethylene-vinyl alcohol copolymer layer. This film is then cut into a 15 mm wide rectangle to create a test specimen. The test specimen is peeled in a T-shape between the maleic acid-modified polyethylene resin layer and the ethylene-vinyl alcohol copolymer layer at a peeling speed of 300 mm / min, in accordance with JIS K 6854-3:1999, and the force required for peeling is measured.

2. A co-extruded multilayer film having a thickness of 200 μm or less, comprising in order a white resin layer / a first light-shielding adhesive resin layer / a barrier resin layer / a second light-shielding adhesive resin layer, A co-extruded multilayer film characterized in that the first light-shielding adhesive resin layer and / or the second light-shielding adhesive resin layer consists of the light-shielding adhesive resin layer described in claim 1.

3. The total light transmittance measured in accordance with JIS K 7361-1:1997 is 0.1% or less. The co-extruded multilayer film according to claim 1 or 2, characterized in that the heat seal strength of the portion heat-sealed under the conditions of upper and lower heating plate temperature of 110°C, heating plate width of 10 mm, sealing pressure of 1 MPa, and sealing time of 0.7 seconds is 6.0 N / 15 mm or more, as measured in accordance with JIS Z 0238:1998.

4. The co-extruded multilayer film according to any one of claims 1 to 3, characterized in that the heat-sealable resin layer contains a white pigment.

5. Use of the co-extruded multilayer film according to any one of claims 1 to 4 as a sealant film.

6. A laminate film obtained by laminating a co-extruded multilayer film according to any one of claims 1 to 4 with a base film.

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