plastic containers

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 a plastic container.

Background Art

[0002] Patent Document 1 discloses a plastic container capable of accommodating contents such as mayonnaise.

Prior Art Document

Patent Document

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Plastic containers such as those in Patent Document 1 are often discarded after the contents are used up. However, considering the environmental impact, it is desirable to recycle the plastic containers to obtain recycled resin.

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

[0006] The present invention has been made in view of such circumstances, and provides a plastic container capable of obtaining high-quality recycled resin by recycling.

Means for Solving the Problems

[0007] According to the present invention, a plastic container for containing contents is provided, comprising, in order from the inner surface of the container, an inner layer, an intermediate layer, and an outer layer, wherein 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.

[0008] In the present invention, during recycling, the dissolution of the intermediate layer containing water-soluble resin is promoted by the foaming of the adjacent layer. This allows for the separation of the inner and outer layers, and then sorting of the inner and outer layers based on their specific gravity. Therefore, it is easy to obtain high-quality recycled resin by extracting only the outer layer.

[0009] The following are examples of various embodiments of the present invention. The embodiments shown below can be combined with each other. Preferably, the foamed layer is a plastic container containing an acid-modified polyolefin resin. Preferably, the plastic container described above is a plastic container in which one or both of the inner layer and the outer layer are such that the layer adjacent to the intermediate layer does not contain adhesive resin. Preferably, the plastic container is as described above, wherein the inner layer and the outer layer have different tensile moduli. [Brief explanation of the drawing]

[0010] [Figure 1] This is a front view showing the plastic container 1 and cap 13. [Figure 2] Figure 2A is a diagram of the layer structure of the plastic container 1 according to the first embodiment of the present invention, Figure 2B shows the crushed pieces 1p obtained by crushing the plastic container 1, and Figure 2C shows the state after the intermediate layer 3p in the crushed pieces 1p is dissolved and the inner layer 2p and outer layer 4p are separated. [Figure 3]Figure 3A is a diagram of the layer structure of the plastic container 1 according to the second embodiment of the present invention, Figure 3B shows the crushed pieces 1p obtained by crushing the plastic container 1, and Figure 3C shows the state after the intermediate layer 3p in the crushed pieces 1p is dissolved and the inner layer 2p and outer layer 4p are separated. [Modes for carrying out the invention]

[0011] Embodiments of the present invention will be described below. The various features shown in the embodiments below can be combined with each other. Furthermore, each feature can stand alone as an independent invention.

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

[0013] Figure 1 shows a schematic diagram of a plastic container 1 according to one embodiment of the present invention. As shown in Figure 1, container 1 is a container for holding contents. The contents are not particularly limited, but examples include those containing oil (e.g., cooking oil or mayonnaise) or those with strong spices (e.g., sauces). Contents containing oil are difficult to remove by washing during recycling, and those with strong spices retain their odor even after washing. Therefore, with conventional containers, it is difficult to obtain high-quality recycled resin when the contents contain oil or strong spices. On the other hand, with container 1 of this embodiment, high-quality recycled resin can be obtained even when such contents are held inside.

[0014] Container 1 dispenses its contents by constricting the body 14, etc., through a spout 12 with a screw thread 11. Normally, the spout 12 is sealed with a cap 13. Container 1 is a blow-molded body formed by blow molding. Details of blow molding will be described later.

[0015] Container 1 has a multilayer structure. Figure 2A shows an example of the layer structure of container 1, which comprises, in order from the inner surface of 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 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 a concentration of 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 water-soluble resins include saponified polyvinyl acetate, polyvinylpyrrolidone, polyethylene glycol, polyacrylamide, polymethacrylamide, polyhydroxyethyl methacrylate, polypentaerythritol triacrylate, polypentaerythritol tetraacrylate, polydiethylene glycol diacrylate, copolymers of monomers comprising these, and copolymers of 2-methacryloyloxyethyl phosphorylcholine with other monomers (e.g., butyl methacrylate). Among these, a structure consisting of one or more selected from saponified polyvinyl acetate, polyvinylpyrrolidone, and polyethylene glycol, and a functional group described later, is preferred.

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

[0019] The water-soluble resin is preferably butenediol vinyl alcohol copolymer (BVOH). This is because BVOH has excellent gas barrier properties and water solubility. A commercially available example of BVOH is Nichigo G Polymer (manufactured by Mitsubishi Chemical Corporation).

[0020] The resin composition constituting the intermediate layer 3 may contain additives or resins other than water-soluble resins, as long as they do not hinder the water-soluble nature of the intermediate layer 3.

[0021] The inner layer 2 is a layer closer to the inner surface of the container 1 than the intermediate layer 3, and may be a single-layer structure or a multi-layer structure. In the present embodiment, the inner layer 2 includes, in order from the inner surface side of the container 1, the innermost layer 2a and the 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 be a single-layer structure or a multi-layer structure. In the present embodiment, the outer layer 4 includes, in order from the inner surface side of the container 1, the adhesive resin layer 4a, the repro layer 4b, and the outermost layer 4c. The inner layer 2 and the outer layer 4 may include layers other than the layers shown here, or may not include some of the layers shown here. For example, when the adhesiveness between the inner layer 2 or the outer layer 4 and the intermediate layer 3 is high, the adhesive resin layers 2b, 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 polyolefins (e.g., polyethylene, polypropylene), polyesters (e.g., PET), EVOH, nylon, etc. The resin composition may contain only the resin or may contain the resin and additives. Examples of the additives include lubricants and fillers.

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

[0024] Preferably, one or both of the inner layer 2 and the outer layer 4 have foamed layers adjacent to the intermediate layer 3 (hereinafter referred to as "adjacent layers"). 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 layers are foamed, water can easily penetrate to the intermediate layer 3 through the adjacent layers in the dissolution process described later, thereby promoting the dissolution of the intermediate layer 3. The adjacent layers (adhesive resin layers 2b, 4a) can be foamed by mixing a foaming agent with the resin (adhesive resin). A commercially available foaming agent is PEX-CF40E-J (manufactured by Tokyo Ink Co., Ltd.). The above effect is achieved even if only the adjacent layer of one 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 repro layer 4b is composed of a resin composition containing repro material obtained by recycling scrap generated during the molding of the container 1. Since the scrap contains all the layers of the container 1, the repro material is a mixture of the resin compositions that make up each of the layers of the container 1.

[0026] The specific gravity of the inner layer 2 may be greater or less than that of the outer layer 4. The difference in specific gravity between the inner layer 2 and the outer layer 4 can be achieved by using different specific gravity resins or by using different types or amounts of additives. It is preferable that the specific gravity of one of the inner layer 2 or 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 or outer layer 4 will float on the water surface and the other will sink in the water, making specific gravity sorting easy. 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, this difference in specific gravity may be, 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, 1.2, and may be within the range of any two of the 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 the range of any two of the 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 the range of any two of the values ​​exemplified here.

[0028] To make the specific gravity of the inner layer 2 greater than that of the outer layer 4, a resin with a higher specific gravity than the resin of the outer layer 4 can be used for the inner layer 2. Since EVOH and nylon generally have a higher specific gravity than polyolefins (e.g., polyethylene, polypropylene), if the outer layer 4 contains 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 gravity of the resin in the inner layer 2 and the resin in the 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 amount of additives with a higher specific gravity than the resin (e.g., talc, calcium carbonate) in the inner layer 2 compared to the amount in the outer layer 4.

[0030] Furthermore, it is preferable to use a resin composition that includes a biodegradable resin, a material mainly composed of cellulose nanofibers (e.g., "MAPKA" (manufactured by Environmental Management Research Institute Co., Ltd.), treated as paper), or a material mainly composed of calcium carbonate (e.g., "LIMEX" (manufactured by TBM Co., Ltd.), treated as limestone paper) as the resin composition constituting the inner layer 2. Biodegradable resins have a low environmental impact because they can be processed in compost, and materials mainly composed of cellulose nanofibers or calcium carbonates have a low environmental impact because they are treated as non-plastics and are easy to dispose of.

[0031] To make the specific gravity of the inner layer 2 less than that of the outer layer 4, a resin with a lower specific gravity than the resin of the outer layer 4 can be used for the inner layer 2. Polyesters such as PET usually have a higher specific gravity than polyolefins (e.g., polyethylene, polypropylene), so if the outer layer 4 contains polyester and the inner layer 2 contains polyolefin, 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 polyolefin, and the resin of the outermost layer 4c can be polyester.

[0032] 1-2. Manufacturing method of plastic container 1 Container 1 can be formed by blow molding 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 molds, and air is blown into the parison to manufacture container 1. In injection blow molding, a test tube-shaped bottomed parison called a preform is formed by injection molding, and blow molding is performed using this parison.

[0033] In any blow molding process, the layer structure of the parison is the same as that of container 1. Multilayer parisons can be formed by co-extrusion molding, multilayer injection molding, or other methods.

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

[0035] 1-3. Recycling methods for plastic containers 1 A method for recycling a plastic container 1 according to one embodiment of the present invention comprises a crushing step, a dissolution step, and a specific gravity separation step.

[0036] In the grinding process, as shown in Figure 2B, the container 1 is ground to form multiple ground pieces 1p. Each ground piece 1p comprises an inner layer 2p, an intermediate layer 3p, and an outer layer 4p. The inner layer 2p, intermediate layer 3p, and outer layer 4p correspond to the inner layer 2, intermediate layer 3, and outer layer 4 of the container 1. The size of the ground pieces 1p is not particularly specified, but it is preferable that they are small enough to allow the intermediate layer 3 to dissolve in the dissolution process.

[0037] In the initial stages of grinding, the container 1 is ground while the inner layer 2 and outer layer 4 are adhered together, forming a fragment 1p. Subsequently, due to shear force, a portion of the fragment 1p is detached, separating it into the inner layer 2p and the outer layer 4p. At this time, the intermediate layer 3p usually adheres to either the inner layer 2p or the outer layer 4p.

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

[0039] Of these, for (e), it is essential to separate the inner layer 2p and the outer layer 4p in the dissolution process, and for (a) and (c), it is desirable to dissolve the intermediate layer 3p in the dissolution process, but the dissolution process is not essential. On the other hand, the dissolution process is a time-consuming process, and it is desirable to minimize the amount of crushed material 1p that is fed into the dissolution process. For this reason, it is desirable to perform preliminary separation on the crushed material 1p discharged from the crusher and to feed only a portion of the crushed material 1p into the dissolution process. The proportion of crushed material 1p that is fed into the dissolution process is, for example, 5 to 95% by mass, and preferably 30 to 90% by mass. Specifically, this proportion is, for example, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95% by mass, and may be within the range of any two of the values ​​exemplified here.

[0040] Preliminary separation can be performed, for example, based on how easily each layer is crushed. Generally, the lower the tensile modulus of the material to be crushed, the easier it is to stretch and the harder it is to cut. Therefore, the time it takes for the material to be crushed and pass through the mesh provided at the exit of the crusher is longer the lower the tensile modulus of the material. Accordingly, by making the tensile moduli 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, if the tensile modulus of the outer layer is lower than that of the inner layer, the timing of discharge from the crusher will generally be in the order of (d), (e), and (b) above. The timing of discharge for (a) and (c) will vary depending on the tensile modulus of the intermediate layer. For example, if the tensile modulus of the intermediate layer is between that of the inner and outer layers, the timing of discharge from the crusher will generally be in the order of (d), (c), (e), (a), and (b). As mentioned above, (d) and (b) do not need to be sent to the dissolution process, and (c) and (a) do not necessarily need to be sent to the dissolution process. Therefore, by measuring the elapsed time from a predetermined starting point (e.g., the start of crushing, the time when the first crushed piece 1p passes through the mesh, etc.) and feeding only the crushed piece 1p that has passed through the mesh during the time between the first threshold and the second threshold (second threshold > first threshold) into the dissolution process, the amount of crushed piece 1p fed into the dissolution process can be reduced. The first and second thresholds can be appropriately selected according to the physical properties required of the recycled material. For example, if a slightly lower purity of the recycled material is acceptable, the time between the first and second thresholds can be shortened to reduce the amount of crushed material 1p fed into the dissolution process. Similarly, even if the relationship between the tensile moduli of each layer differs from the example above, the amount of crushed material 1p fed into the dissolution process can be reduced by feeding only the crushed material 1p that has passed through the mesh during a specific time period into the dissolution process.

[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 for the inner layer to have a higher modulus. This is because the contents adhere to the inner layer, so it is desirable to have more outer layer material than inner layer material. However, materials with high specific gravity are generally expensive, and increasing the specific gravity of the outer layer increases the amount of expensive material used.

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

[0044] In the dissolution process, as shown in Figures 2B to 2C, the intermediate layer 3p contained in the crushed piece 1p is dissolved to separate the inner layer 2p and the outer layer 4p. The dissolution process can be carried out, for example, by adding the crushed piece 1p to water and stirring. The dissolution process can be carried out simultaneously with the washing of the crushed piece 1p.

[0045] In the specific gravity separation process, the inner layer 2p and the outer layer 4p are separated based on their specific gravity. In specific gravity separation, when the inner layer 2p and the outer layer 4p are placed in a liquid having a specific gravity between that of the inner layer 2p and the outer layer 4p, one of the inner layer 2p and the outer layer 4p will float on the surface of the liquid, while the other will sink, thus allowing the inner layer 2p and the outer layer 4p to be separated and recovered. If 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 made of a single material and is free from contamination and 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, and other processes are used to reprocess them into raw materials, and then they are remade into new plastic products.

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

[0048] 2. Second Embodiment Using Figure 3, we will describe the plastic container 1 of the second embodiment of the present invention. The plastic container 1 of this embodiment has a different layer structure from that of the first embodiment. The differences will be explained below.

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

[0050] If the adjacent layer in either or both of the inner layer 2 and the outer layer 4 does not contain adhesive resin, water can easily penetrate between the adjacent layer and the intermediate layer 3 during the dissolution process, thereby promoting the dissolution of the intermediate layer 3. The above effect is also achieved when the adjacent layer in only one of the inner layer 2 and the outer layer 4 does not contain adhesive resin, but the effect is more pronounced when the adjacent layer in both the inner layer 2 and the outer layer 4 does not contain adhesive resin. Furthermore, 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 further 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: Reproductive layer 4c: Outermost layer 4p: outer layer 11: Screw thread 12: Outlet 13: Cap 14: Torso

Claims

1. A plastic container for holding contents, The container comprises, in order from the inner surface, an inner layer, an intermediate layer, and an outer layer. The aforementioned intermediate layer is water-soluble, The inner layer and the outer layer have different specific gravities. In the inner layer and the outer layer, or both, the layer adjacent to the intermediate layer is foamed. The foamed layer is a plastic container containing an acid-modified polyolefin resin.

2. A plastic container for holding contents, The container comprises, in order from the inner surface, an inner layer, an intermediate layer, and an outer layer. The aforementioned intermediate layer is water-soluble, The inner layer and the outer layer have different specific gravities. In the inner layer and the outer layer, or both, the layer adjacent to the intermediate layer is foamed. The foamed layer is an adhesive resin layer composed of an adhesive resin, The adhesive resin is an acid-modified polyolefin resin, used in plastic containers.

3. A plastic container according to claim 1 or claim 2, A plastic container in which the inner layer and the outer layer have different tensile moduli.

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