Plastic container

Abstract

To provide a plastic container from which high-quality recycled resin can be obtained through recycling.SOLUTION: According to the present invention, a plastic container for accommodating a content is provided, which comprises, in order from the inner surface side of the container, an inner layer, an intermediate layer, and an outer layer. The intermediate layer is water-soluble, the inner layer and the outer layer have different specific gravities, and one or both of the inner layer and the outer layer have a foamed layer adjacent to the intermediate layer (except for those in which the foamed layer is a urethane foam layer).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to plastic containers. [Background technology]

[0002] Patent Document 1 discloses a plastic container capable of storing contents such as mayonnaise. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2016-190654 A Summary of the Invention [Problem to be solved by the invention]

[0004] Plastic containers such as those described in Patent Document 1 are often discarded after the contents have been used up, but in consideration of the impact on the environment, it is desirable to recycle plastic containers to obtain recycled resin.

[0005] However, in plastic containers such as those described in Patent Document 1, the contents adhere to the inner surface and may not be easily removed even by washing, and the recycled resin obtained by recycling such plastic containers is unlikely to be of high quality.

[0006] The present invention has been made in view of the above circumstances, and aims to provide a plastic container which can be recycled to obtain high-quality regenerated resin. [Means for solving the problem]

[0007] According to the present invention, there is provided a plastic container for accommodating contents, comprising, in order from the inner surface side of the container, an inner layer, an intermediate layer, and an outer layer, the intermediate layer being water-soluble, the inner layer and the outer layer having different specific gravities, and one or both of the inner layer and the outer layer having a foamed layer adjacent to the intermediate layer.

[0008] In the case of the plastic container of the present invention, when recycling, the dissolution of the intermediate layer containing the water-soluble resin is promoted by the foaming of the layer adjacent thereto. This allows the inner layer and the outer layer to be separated and then sorted based on their specific gravity. Therefore, it is easy to obtain high-quality recycled resin by extracting only the outer layer.

[0009] Various embodiments of the present invention will be described below. The embodiments described below can be combined with each other. Preferably, the foamed layer is a plastic container comprising an acid-modified polyolefin resin. Preferably, in the plastic container described above, one or both of the inner layer and the outer layer adjacent to the intermediate layer does not contain an adhesive resin. Preferably, in the plastic container described above, the inner layer and the outer layer have different tensile moduli. [Brief description of the drawings]

[0010] [Figure 1] FIG. 2 is a front view showing the plastic container 1 and the cap 13. [Diagram 2] FIG. 2A is a layer structure diagram of a plastic container 1 according to a first embodiment of the present invention, FIG. 2B shows pulverized pieces 1p obtained by crushing the plastic container 1, and FIG. 2C shows the state after the middle layer 3p in the pulverized pieces 1p has been dissolved to separate the inner layer 2p and the outer layer 4p. [Diagram 3]FIG. 3A is a layer structure diagram of a plastic container 1 according to a second embodiment of the present invention, FIG. 3B shows pulverized pieces 1p obtained by crushing the plastic container 1, and FIG. 3C shows the state after the middle layer 3p in the pulverized pieces 1p has been dissolved to separate the inner layer 2p and outer layer 4p. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, embodiments of the present invention will be described. Various features shown in the following embodiments can be combined with each other. Also, each feature can be an invention independently.

[0012] 1. First embodiment 1-1. Composition of plastic containers

[0013] FIG. 1 shows a schematic diagram of a plastic container 1 according to one embodiment of the present invention. As shown in FIG. 1, the container 1 is a container that contains contents. The contents are not particularly limited, but include oily contents (e.g., edible oil and mayonnaise) and spicy contents (e.g., sauce). Oily contents are difficult to remove by washing during recycling, and spicy contents leave an odor even after washing. Therefore, with conventional containers, it is difficult to obtain high-quality recycled resin when the contents are oily or spicy. On the other hand, with the container 1 of this embodiment, high-quality recycled resin can be obtained even when such contents are stored.

[0014] The container 1 is configured so that the contents are expelled from a spout 12 having a screw thread 11 by squeezing a body 14, etc., and the spout 12 is usually sealed with a cap 13. The container 1 is a blow molded body formed by blow molding. The details of blow molding will be described later.

[0015] The container 1 has a multi-layer structure. Fig. 2A shows an example of the layer structure of the container 1, which comprises, from the inside surface side of the container 1, an inner layer 2, an intermediate layer 3, and an outer layer 4. The intermediate layer 3 is water-soluble, and the inner layer 2 and the outer layer 4 have different specific gravities.

[0016] The intermediate layer 3 is preferably composed of a resin composition containing a water-soluble resin. The water-soluble resin is a resin that can be dissolved to 1% by mass (preferably 2, 3, 4, or 5% by mass) or more by immersion and stirring in water at 100°C (preferably 20, 30, 40, 50, 60, 70, 80, or 90°C).

[0017] Examples of the water-soluble resin include saponified polyvinyl acetate, polyvinylpyrrolidone, polyethylene glycol, polyacrylamide, polymethacrylamide, polyhydroxyethyl methacrylate, polypentaerythritol triacrylate, polypentaerythritol tetraacrylate, polydiethylene glycol diacrylate, copolymers of monomers constituting these, copolymers of 2-methacryloyloxyethyl phosphorylcholine and other monomers (e.g., butyl methacrylate, etc.), etc. Among these, a structure consisting of one or more selected from saponified polyvinyl acetate, polyvinylpyrrolidone, and polyethylene glycol and a functional group described below is preferred.

[0018] Examples of the saponified polyvinyl acetate include polyvinyl alcohol or a copolymer of vinyl alcohol and other compounds, and saponified vinyl acetate modified with a hydrophilic group, a hydrophobic group, an anion, a cation, an amide group, or a reactive group such as an acetoacetyl group, and vinyl alcohol. The degree of saponification of the saponified polyvinyl acetate is not particularly limited, but is preferably 20 to 100 mol %, more preferably 50 to 95 mol %, of the entire polyvinyl acetate.

[0019] The water-soluble resin is preferably butenediol vinyl alcohol copolymer (BVOH), because BVOH has excellent gas barrier properties and water solubility. Commercially available BVOH products include Nichigo G-Polymer (manufactured by Mitsubishi Chemical Corporation).

[0020] The resin composition constituting the intermediate layer 3 may contain additives and resins other than the water-soluble resin, as long as the water-solubility of the intermediate layer 3 is not impaired.

[0021] The inner layer 2 is a layer closer to the inner surface of the container 1 than the intermediate layer 3, and may have a single layer structure or a multilayer structure. In this embodiment, the inner layer 2 includes, in order from the inner surface side of the container 1, an innermost layer 2a and an adhesive resin layer 2b. The outer layer 4 is a layer closer to the outer surface of the container 1 than the intermediate layer 3, and may have a single layer structure or a multilayer structure. In this embodiment, the outer layer 4 includes, in order from the inner surface side of the container 1, an adhesive resin layer 4a, a repro layer 4b, and an outermost layer 4c. The inner layer 2 and the outer layer 4 may include layers other than those shown here, and may not include some of the layers shown here. For example, when the adhesion between the inner layer 2 or the outer layer 4 and the intermediate layer 3 is high, the adhesive resin layers 2b and 4a can be omitted.

[0022] The innermost layer 2a and the outermost layer 4c can be composed of a resin composition containing a resin (preferably a thermoplastic resin). Examples of the resin include polyolefin (e.g., polyethylene, polypropylene), polyester (e.g., PET), EVOH, nylon, etc. The resin composition may contain only a resin, or may contain a resin and an additive. Examples of the additive include a lubricant and a filler.

[0023] The adhesive resin layers 2b and 4a are made of adhesive resin. Examples of adhesive resins include acid-modified polyolefin resins (e.g., maleic anhydride-modified polyethylene and maleic anhydride-modified polypropylene). By providing the adhesive resin layers 2b and 4a, the adhesion between the layers adjacent to the adhesive resin layers 2b and 4a is improved.

[0024] In one or both of the inner layer 2 and the outer layer 4, the layer adjacent to the intermediate layer 3 (hereinafter, "adjacent layer") is preferably foamed. In this embodiment, the adjacent layer of the inner layer 2 is the adhesive resin layer 2b, and the adjacent layer of the outer layer 4 is the adhesive resin layer 4a. When the adjacent layer is foamed, water is easily permeated into the intermediate layer 3 through the adjacent layer in the dissolution process described below, and dissolution of the intermediate layer 3 is promoted. The adjacent layer (adhesive resin layer 2b, 4a) can be foamed by mixing a foaming agent with the resin (adhesive resin). An example of a commercially available foaming agent is PEX-CF40E-J (manufactured by Tokyo Ink Co., Ltd.). The above effect is achieved even when only one of the adjacent layers of the inner layer 2 and the outer layer 4 is foamed, but the above effect is more pronounced if both the adjacent layers of the inner layer 2 and the outer layer 4 are foamed.

[0025] The reproductive layer 4b is made of a resin composition containing a reproductive material obtained by recycling scrap generated during the molding of the container 1. The scrap contains all layers of the container 1, so the reproductive material is a mixture of the resin compositions constituting each of the layers of the container 1.

[0026] The specific gravity of the inner layer 2 may be larger or smaller than that of the outer layer 4. The difference in specific gravity between the inner layer 2 and the outer layer 4 can be realized by changing the specific gravity of the resin used or by changing the type or amount of additives. It is preferable that the specific gravity of one of the inner layer 2 and the outer layer 4 is less than 1, and the specific gravity of the other is greater than 1. In this case, one of the inner layer 2 and the outer layer 4 floats on the water surface and the other sinks in the water, making it easy to select by specific gravity. The difference in specific gravity between the inner layer 2 and the outer layer 4 is, for example, 0.05 to 1.2, and preferably 0.1 to 0.4. Specifically, the difference in specific gravity is, for example, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, or 1.2, and may be within a range between any two of the numerical values ​​exemplified here.

[0027] The specific gravity of one of the inner layer 2 and the outer layer 4 is, for example, 0.8 to 0.99, specifically, for example, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, and may be within a range between any two of the numerical values ​​exemplified here. The specific gravity of the other of the inner layer 2 and the outer layer 4 is, for example, 1.01 to 2, specifically, for example, 1.01, 1.05, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, and may be within a range between any two of the numerical values ​​exemplified here.

[0028] In order to make the specific gravity of the inner layer 2 greater than that of the outer layer 4, a resin having a greater specific gravity than that of the outer layer 4 can be used for the inner layer 2. EVOH and nylon usually have a greater specific gravity than polyolefins (e.g., polyethylene and polypropylene). Therefore, when the outer layer 4 contains a polyolefin and the inner layer 2 contains EVOH or nylon, the specific gravity of the inner layer 2 can be made greater than that of the outer layer 4. For example, the resin of the innermost layer 2a can be EVOH or nylon, and the resin of the outermost layer 4c can be polyolefin.

[0029] Furthermore, even if the specific gravities of the resins of the inner layer 2 and outer layer 4 are the same, the specific gravity of the inner layer 2 can be made greater than that of the outer layer 4 by increasing the content of additives (e.g., talc, calcium carbonate) which have a larger specific gravity than the resin in the inner layer 2 than in the outer layer 4.

[0030] Furthermore, it is preferable to use a resin composition that contains a biodegradable resin, a material mainly made of cellulose nanofiber (e.g., "Mapuka" (manufactured by Environmental Management Research Institute Co., Ltd.), treated as paper), or a material mainly made of calcium carbonate (e.g., "LIMEX" (manufactured by TBM Co., Ltd.), treated as limestone paper) as the resin composition that constitutes the inner layer 2. Biodegradable resins have a small environmental impact because they can be composted, and materials mainly made of cellulose nanofiber or calcium carbonate are treated as non-plastic, making them easy to dispose of and therefore less of a burden on the environment.

[0031] In order to make the specific gravity of the inner layer 2 smaller than that of the outer layer 4, the resin for the inner layer 2 can have a smaller specific gravity than that of the outer layer 4. Since polyesters such as PET usually have a larger specific gravity than polyolefins (e.g., polyethylene and polypropylene), when the outer layer 4 contains polyester and the inner layer 2 contains polyolefin, the specific gravity of the inner layer 2 can be made larger than that of the outer layer 4. For example, the resin for the innermost layer 2a can be polyolefin, and the resin for the outermost layer 4c can be polyester.

[0032] 1-2. Manufacturing method of plastic container 1 The container 1 can be formed by blow molding of a parison. The blow molding may be direct blow molding or injection blow molding. In direct blow molding, a molten cylindrical parison extruded from an extruder is sandwiched between a pair of split dies and air is blown into the parison to manufacture the container 1. In injection blow molding, a test tube-shaped parison with a bottom called a preform is formed by injection molding, and blow molding is performed using this parison.

[0033] In any blow molding, the layer structure of the parison is the same as the layer structure of the container 1. A multi-layer parison can be formed by co-extrusion molding, multi-layer injection molding, or the like.

[0034] When forming a container 1 by direct blow molding, the portion of the cylindrical parison inside the cavity formed by a pair of split molds becomes the container 1, and the portion other than the container 1 becomes scrap. This scrap contains the constituent materials of all the layers that make up the container 1. Reproduction materials can be obtained by subjecting this scrap to recycling processes such as crushing.

[0035] 1-3. How to recycle plastic containers 1 The method for recycling plastic containers 1 according to one embodiment of the present invention includes a crushing step, a dissolving step, and a gravity separation step.

[0036] In the crushing step, the container 1 is crushed to form a plurality of crushed pieces 1p, as shown in Fig. 2B. Each crushed piece 1p has an inner layer 2p, an intermediate layer 3p, and an outer layer 4p. The inner layer 2p, the intermediate layer 3p, and the outer layer 4p correspond to the inner layer 2, the intermediate layer 3, and the outer layer 4 of the container 1. The size of the crushed pieces 1p is not particularly limited, and is preferably small enough to dissolve the intermediate layer 3 in the dissolving step.

[0037] In the initial stage of crushing, the container 1 is crushed to form crushed pieces 1p while the inner layer 2 and the outer layer 4 are adhered to each other. Then, due to shear force, a part of the crushed pieces 1p is peeled off and separated into the inner layer 2p and the outer layer 4p. At this time, the intermediate layer 3p usually adheres to the inner layer 2p or the outer layer 4p.

[0038] The crushed pieces 1p are discharged from the crusher through a mesh. The discharged crushed pieces 1p can be classified into the following five types. (a) Outer layer + middle layer (b) Outer layer (c) Inner layer + middle layer (d) Inner layer (e) Inner layer + outer layer + middle layer

[0039] Of these, for (e), it is essential to separate the inner layer 2p and the outer layer 4p in the dissolving step, and for (a) and (c), it is desirable to dissolve the intermediate layer 3p in the dissolving step, but the dissolving step is not essential. On the other hand, the dissolving step is a time-consuming step, and it is desirable to reduce the amount of pulverized pieces 1p to be input to the dissolving step as much as possible. For this reason, it is desirable to perform preliminary separation on the pulverized pieces 1p discharged from the pulverizer and input only a part of the pulverized pieces 1p to the dissolving step. The ratio of the pulverized pieces 1p to be input to the dissolving step is, for example, 5 to 95 mass%, and preferably 30 to 90 mass%. This ratio is specifically, for example, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, and 95 mass%, and may be within a range between any two of the numerical values ​​exemplified here.

[0040] The preliminary separation can be performed, for example, based on the ease of crushing of each layer. In general, the lower the tensile modulus of the object to be crushed, the easier it is to stretch the object to be crushed when it is cut, and the harder it is to cut. Therefore, the lower the tensile modulus of the object to be crushed, the longer the time it takes for the object to be crushed to pass through the mesh provided at the outlet of the crusher. Therefore, by making the tensile modulus of the inner layer 2 and the outer layer 4 different from each other, it becomes possible to perform preliminary separation depending on the timing of discharge from the crusher.

[0041] For example, when the tensile modulus of the outer layer is lower than that of the inner layer, the timing of discharge from the pulverizer is generally in the order of (d), (e), and (b). The timing of discharge of (a) and (c) varies depending on the tensile modulus of the intermediate layer. For example, when the tensile modulus of the intermediate layer is a value between that of the inner layer and that of the outer layer, the timing of discharge from the pulverizer is generally in the order of (d), (c), (e), (a), and (b). As described above, (d) and (b) do not need to be sent to the dissolving process, and (c) and (a) do not necessarily need to be sent to the dissolving process. For this reason, the amount of pulverized pieces 1p input to the dissolving process can be reduced by measuring the elapsed time from a predetermined start point (e.g., the start point of pulverization, the point at which the first pulverized pieces 1p pass through the mesh, etc.) and inputting only the pulverized pieces 1p that pass through the mesh between the first threshold value and the second threshold value (the second threshold value>the first threshold value) into the dissolving process. The first threshold value and the second threshold value can be appropriately selected according to the physical properties required for the recycled material. For example, if the purity of the recycled material is acceptable even if it is somewhat low, the time between the first threshold and the second threshold can be shortened to reduce the amount of pulverized pieces 1p input to the melting process. Even if the relationship between the tensile modulus of each layer is different from the above example, the amount of pulverized pieces 1p input to the melting process can be reduced by inputting only the pulverized pieces 1p that have passed through the mesh during a specific time.

[0042] The tensile modulus can be measured in accordance with JIS K 7139 1A. The tensile modulus may be higher for either the inner layer 2 or the outer layer 4, but it is preferable that the inner layer has a higher modulus. This is because it is desirable to have more outer layers than inner layers since the contents adhere to the inner layers, but materials with high specific gravity are generally expensive, and increasing the specific gravity of the outer layer increases the amount of expensive materials used.

[0043] The difference in tensile modulus is, for example, 700 MPa or more, preferably 700 to 3000 MPa. This difference is, specifically, for example, 700, 800, 900, 1000, 1500, 2000, 2500, 3000 MPa, and may be within the range between any two of the numerical values ​​exemplified here or any more. The tensile modulus of the lower one of the inner layer 2 and the outer layer 4 is, for example, 300 MPa or less, preferably 50 to 300 MPa. This bending modulus is, specifically, for example, 50, 100, 150, 200, 250, 300 MPa, and may be within the range between any two of the numerical values ​​exemplified here or any more. The tensile modulus of the higher one of the inner layer 2 and the outer layer 4 is, for example, 1000 MPa or more, preferably 1000 to 3300 MPa. Specifically, the tensile modulus is, for example, 1000, 1500, 2000, 2500, 3000, or 3300 MPa, and may be within a range between any two of the numerical values ​​exemplified here or equal to or greater than any one of them.

[0044] In the dissolving step, as shown in Figures 2B to 2C, the middle layer 3p contained in the pulverized pieces 1p is dissolved to separate the inner layer 2p and the outer layer 4p. The dissolving step can be performed, for example, by putting the pulverized pieces 1p into water and stirring the water. The dissolving step can be performed simultaneously with washing the pulverized pieces 1p.

[0045] In the gravity sorting step, the inner layer 2p and the outer layer 4p are sorted based on their specific gravities. In gravity sorting, when the inner layer 2p and the outer layer 4p are put into a liquid having a specific gravity between the inner layer 2p and the outer layer 4p, one of the inner layer 2p and the outer layer 4p floats on the liquid surface and the other sinks in the liquid, so that the inner layer 2p and the outer layer 4p can be sorted and recovered. When the specific gravity of one of the inner layer 2p and the outer layer 4p is less than 1 and the specific gravity of the other is greater than 1, water can be used as the liquid, which is preferable.

[0046] The outer layer 4p is a mono-material and has no dirt or odor from the contents, making it a high-quality recycled material suitable for bottle-to-bottle material recycling. Material recycling is a recycling method in which used plastic products are collected, crushed, washed, etc., and re-used as raw materials, and then remade into plastic products.

[0047] On the other hand, the inner layer 2p can be used for heat recovery (thermal recycling) or cascade recycling (recycling into products with reduced quality). If the inner layer 2p is made of biodegradable resin, it can be composted. Furthermore, if the inner layer 2p is made of a material mainly made of cellulose nanofiber or calcium carbonate, it can be disposed of as a non-plastic.

[0048] 2. Second embodiment A plastic container 1 according to a second embodiment of the present invention will be described with reference to Fig. 3. The plastic container 1 according to this embodiment has a layer structure different from that of the first embodiment. The following description will focus on the differences.

[0049] This embodiment is characterized in that one or both of the inner layer 2 and the outer layer 4, the layer adjacent to the intermediate layer 3 (hereinafter, "adjacent layer"), does not contain an adhesive resin. In this embodiment, the inner layer 2 does not include an adhesive resin layer 2b, and the inner layer 2 that does not contain an adhesive resin is in contact with the intermediate layer 3 as an adjacent layer. The inner layer 2 can be composed of the same resin composition as the innermost layer 2a of the first embodiment. The outer layer 4 does not include an adhesive resin layer 4a, and the reprint layer 4b that does not contain an adhesive resin is in contact with the intermediate layer 3 as an adjacent layer. The explanation of the reprint layer 4b is the same as in the first embodiment.

[0050] When the adjacent layer in either or both of the inner layer 2 and the outer layer 4 does not contain an adhesive resin, water easily penetrates between the adjacent layer and the intermediate layer 3 in the dissolution step, accelerating the dissolution of the intermediate layer 3. The above effect is achieved even when the adjacent layer in only one of the inner layer 2 and the outer layer 4 does not contain an adhesive resin, but the above effect is more pronounced when the adjacent layer in both of the inner layer 2 and the outer layer 4 does not contain an adhesive resin. In addition, the adjacent layer in either or both of the inner layer 2 and the outer layer 4 may be foamed as in the first embodiment. In this case, the dissolution of the intermediate layer 3 is more significantly promoted. [Explanation of symbols]

[0051] 1: Plastic container 1p: crushed pieces 2: Inner layer 2a: Innermost layer 2b: Adhesive resin layer 2p: Inner layer 3: Middle class 3p: middle class 4: Outer layer 4a: Adhesive resin layer 4b: Reproduction layer 4c: Outermost layer 4p: outer layer 11: Thread 12: Outlet 13: Cap 14: Torso

Claims

1. A plastic container for containing contents, The container includes, in order from the inner surface side, an inner layer, an intermediate layer, and an outer layer, The intermediate layer is water-soluble, The inner layer and the outer layer have different specific gravities, A plastic container in which one or both of the inner layer and the outer layer adjacent to the intermediate layer is foamed (excluding those in which the foamed layer is a urethane foam layer).

2. 2. The plastic container of claim 1, The foamed layer comprises an acid-modified polyolefin resin.

3. 2. The plastic container of claim 1, A plastic container, wherein one or both of the inner layer and the outer layer adjacent to the intermediate layer does not contain an adhesive resin.

4. The plastic container according to any one of claims 1 to 3, A plastic container, wherein the inner layer and the outer layer have different tensile moduli.

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