Double-structured container

Abstract

To provide a double structured container that exhibits excellent oxygen barrier property by utilizing the passive barrier performance of a water soluble resin.SOLUTION: A double structured container 100 including an outer container 101 and an inner container 103 stored in the outer container 101 is characterized in that a water soluble barrier coating α is provided on the outer surface of the inner container 103.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a double-structure container, and more particularly to a double-structure container excellent in recyclability and oxygen barrier properties. [Background technology]

[0002] In recent years, plastics have been used for various purposes because they can be easily molded into various shapes. However, plastic products have inferior gas barrier properties compared to metal products and glass products. For this reason, in plastic products used in applications requiring barrier properties against oxygen, such as packaging materials such as containers and films, multi-layer structures using layers of passive barrier materials such as ethylene-vinyl alcohol copolymer resins are being introduced. Meanwhile, active barrier materials for oxidizable organic compounds have been developed recently (see, for example, Patent Document 1), and have come to be used in the field of packaging materials and the like. In addition, a colored resin layer may be provided for the purpose of providing a light barrier (light blocking) property.

[0003] However, packaging materials and colored resins whose gas barrier properties have been improved by the above-mentioned barrier materials have the drawback that they are difficult to recycle and are difficult to reuse. That is, in a multi-layered container having a barrier layer using the above-mentioned barrier material, the barrier material cannot be separated from other container material resins (e.g., PET or polyolefin), and similarly, the colorant cannot be separated from the container material resin, making it difficult to reuse these material resins. Barrier technology that takes into account the reusability of material resins has hardly been studied.

[0004] For example, recently, a double-structure container having a double structure consisting of an inner container and an outer container has been put into practical use as an airless container for storing seasoning liquid such as soy sauce. Such a double-structure container is used in combination with a cap with a check valve, and the contents filled in the inner container are discharged from the pouring passage formed in the cap by squeezing and concaving the body wall of the bottle, which is the outer container, from the outside, and when the discharge of the contents is terminated by stopping the pressing of the body wall of the bottle, air is not introduced into the inner container due to the action of the check valve, but is introduced into the space between the inner container and the outer container through a flow path different from the pouring passage of the cap. As a result, the inner container shrinks by the amount of the contents discharged, and the inner container shrinks every time the contents are discharged. In a double-structure container in which the contents are discharged in this way, the contents can be dispensed in small amounts, and the intrusion of air into the inner container filled with the contents is effectively prevented, so that the oxidation deterioration of the contents can be effectively avoided and the freshness of the contents can be maintained for a long period of time.

[0005] However, even in the above-mentioned double-structure container, it is necessary to introduce air between the inner container and the outer container to discharge the contents, so it is desirable to impart oxygen barrier properties to the inner container.For example, Patent Document 2 proposes a technique in which, when a preform for the inner container and a preform for the outer container are stacked and stretch-molded to produce a container having a double structure, an agent that does not decompose at the stretching temperature, such as an organic oxygen absorber or deodorizer, is applied between the preform for the inner container and the preform for the outer container. However, in this technology, the powdered medicine is merely filled into the space between the inner container and the outer container, so the adhesion between the medicine and the inner container or the outer container is insufficient. Moreover, such powdered medicine hinders the reusability of the container material resin, so this technology has not yet been put to practical use. In addition, if recyclability is not a consideration for double-walled containers, a barrier material may be blended into the inner container to improve the oxygen barrier properties. However, the inner container of a double-walled container is in the form of a bag and is very thin. For this reason, in the case of active barrier materials, when hygiene and other factors are taken into consideration, the amount that can be blended into the inner container is very small, and satisfactory barrier properties cannot be achieved. Similarly, passive barrier materials such as ethylene-vinyl alcohol copolymers must be made into a very thin layer, and sufficient barrier properties cannot be achieved.

[0006] Incidentally, the present applicant previously proposed a double structure, particularly a double structure container, with improved recyclability and oxygen barrier properties (Patent Application No. 2019-198393). In this double structure container, a barrier coating that can be removed by washing with water is formed on the outer surface of the inner container, and in some cases, the barrier coating uses a water-soluble resin as a binder (matrix) and a barrier material is further dispersed in this binder. In such a double structure container, the barrier coating formed on the outer surface of the inner container can be removed by washing with water, so that it is possible to achieve excellent barrier properties while ensuring recyclability.

[0007] As the inventors further developed the technology of the above-mentioned prior application (Patent Application No. 2019-198393), they discovered the novel finding that the passive barrier performance of the water-soluble resin is highly dependent on the relative humidity, and that when the relative humidity of the coating layer of the water-soluble resin is high, the resin exhibits almost no oxygen barrier performance, but when this relative humidity decreases, the oxygen barrier performance is expressed. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2018-21128 A [Patent Document 2] Japanese Patent Application Publication No. 5-228988 Summary of the Invention [Problem to be solved by the invention]

[0009] Therefore, an object of the present invention is to provide a double-structure container that utilizes the passive barrier properties of a water-soluble resin to exhibit excellent oxygen barrier properties. Another object of the present invention is to provide a double-walled container which is excellent not only in oxygen barrier properties but also in recyclability. It is still another object of the present invention to provide a stack preform for producing the above-mentioned double-structure container. [Means for solving the problem]

[0010] According to the present invention, in a double-structure container comprising an outer container and an inner container housed in the outer container, The outer container and the inner container have a single-layer structure, The outer surface of the inner container is provided with a water-soluble barrier coating. only is established. 、 The water-soluble barrier coating is formed from a water-soluble resin with an oxygen permeability coefficient of 0.222cc·20μm / m2·day·atm (@22℃, 60%RH) or less. The present invention provides a double-walled container characterized in that

[0011] In the double-structure container of the present invention, the following aspects are preferably adopted. (1) The inner container comprises a neck and a bag-shaped portion connected to the neck, and the water-soluble barrier coating is provided on the outer surface of the bag-shaped portion. 。 ( 2 2.) The water-soluble barrier coating is formed from a vinyl alcohol polymer containing 70 mol % or more of vinyl alcohol units. ( 3 ) An air layer is formed between the outer surface of the water-soluble barrier coating and the inner surface of the outer container. ( 4 1.) A water-containing substance is contained inside the inner container.

[0012] According to the present invention, there is also provided a stack preform for a double-structure container, which comprises an outer container preform and an inner container preform held in the outer container preform, and which is used to mold a double-structure container by blow molding, comprising: the outer container preform and the inner container preform have a single-layer structure, The outer surface of the inner container preform is coated with a water-soluble barrier material to form a water-soluble layer. only is formed 、 The water-soluble barrier material is a water-soluble resin with an oxygen permeability coefficient of 0.222cc·20μm / m2·day·atm (@22℃, 60%RH) or less. A stack preform for a double-structure container is provided.

[0013] In such a stack preform, the following aspects are preferably adopted. (a) The inner container preform includes a neck portion which is a non-stretch molded portion and a stretch molded portion which is continuous with the neck portion, and the water-soluble layer is provided on the outer surface of the stretch molded portion. 。 ( b 2.) The water-soluble barrier material is a vinyl alcohol polymer containing 70 mol % or more of vinyl alcohol units. Effect of the Invention

[0014] A notable feature of the double-structure container of the present invention is that a water-soluble barrier coating is provided on the outer surface of the inner container. As can be understood from the fact that this barrier coating is water-soluble, it has a water-soluble resin as a membrane component, and this water-soluble resin exhibits oxygen barrier properties as a passive barrier material, but since it is water-soluble, after use when the contents are discharged, this barrier coating can be easily removed by washing with water in the recycling process. In other words, according to the present invention, it is possible to ensure barrier properties against oxygen and the like while ensuring recyclability, and to maintain the quality of the contents.

[0015] The double-structure container of the present invention exhibits particularly excellent effects when the content contained in the inner container is a water-containing substance such as soy sauce, and is therefore suitably used as a container for such water-containing substances. [Brief description of the drawings]

[0016] [Figure 1] A conceptual diagram to explain the function of a double-structure container. [Diagram 2] 2 is a diagram showing the relationship between the storage period and the oxygen concentration inside the inner container in the double-structure container of FIG. 1 when the contents are not discharged (37°C, 30% RH). [Diagram 3] This is a diagram showing the relationship between the storage period and the oxygen concentration inside the inner container of the double-structure container of Figure 1 when some of the contents have been expelled and the inner container has shrunk under storage conditions (37°C, 30% RH). [Figure 4] 1 is a schematic cross-sectional side view showing an example of a double-structure container of the present invention. [Diagram 5] 3 is a schematic cross-sectional side view showing the formation of a first preform (preform for molding an outer container) and a second preform (preform for molding an inner container) used in manufacturing the double-structure container of FIG. 2. [Figure 6] FIG. 2 is a schematic cross-sectional side view showing a stacked preform in which a second preform is received and held within a first preform. [Figure 7] FIG. 4 is a schematic cross-sectional side view showing another example of a double-structure container of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] <Principle of the present invention> In FIG. 1, the double-structure container is generally indicated by 100, with a bag-shaped inner container 103 housed within an outer container 101, and the opening at the upper end of the inner container 103 being closed by a cap 105 equipped with a check valve.

[0018] In the double-structure container 100, in a normal state in which the contents are filled in the inner container 103 after molding and the cap 105 is closed and stored, the outer surface of the inner container 103 is in close contact with the inner surface of the outer container 101, as shown in FIG. 1(a). In this state, when the cap 105 is opened, the double-structure container 100 is tilted, and the body of the outer container 101 is pressed (squeezed), the body of the outer container 101 is depressed, and the contents are discharged from the bag-shaped inner container 103, and the bag-shaped inner container 103 contracts by the amount of the contents discharged. On the other hand, when a predetermined amount of contents is discharged and the pressure is stopped, the body of the outer container 101 returns to its original shape due to elasticity. As a result, a negative pressure is created between the outer container 101 and the inner container 103, and air is introduced between them from the outside, forming an air layer 107, as shown in FIG. 1(b). Therefore, if the double-structure container 100 is then tilted and the body of the outer container 101 is pressed, the inner container 103 is pressed via the air layer 107, the contents in the inner container 103 are quickly discharged and further contract, but the outer container 101 returns to its original shape, and the air layer 107 is similarly formed between the inner container 103 and the outer container 101. In other words, if the air layer 107 is not formed between the inner container 103 and the outer container 101, the inner container 103 will contract significantly as the contents are discharged, and the outer container will need to be significantly dented in order to discharge the contents, but by forming the air layer 107, the contents can always be discharged by applying an appropriate amount of pressure.

[0019] In the double-structure container 100 of the present invention, a water-soluble barrier coating α is formed on the outer surface of the inner container 103 (see the partially enlarged side cross-sections in Fig. 1(a) and Fig. 1(b)). This barrier coating α is made of a water-soluble resin, typically a vinyl alcohol polymer such as polyvinyl alcohol, and can be easily removed by washing with water. In the present invention, the passive barrier performance of this barrier coating α is maximized.

[0020] For example, Fig. 2 shows a diagram illustrating the relationship between the storage period and the oxygen concentration in the inner container 103 when the double-structure container 100 in Fig. 1 is in a normal state with the contents not being discharged and is stored at 37°C and 30% RH (for detailed conditions, see Experimental Example 1 described later). That is, in such a double-structure container 100, as shown in the partially enlarged side cross-sectional view of Fig. 1, the barrier coating α adheres closely to the inner surface of the outer container 101, and no air layer is formed between them.

[0021] In this state, when the inside of the inner container 103 is kept dry (0% RH), the oxygen concentration inside the bag-shaped inner container 103 is maintained at 0% even after four weeks, as shown by curve A. In this case, both the outer container 101 and the barrier coating α function as barrier materials to prevent oxygen from entering the inner container 103.

[0022] However, when a water-containing substance is contained in the inner container 103 and the relative humidity is maintained at 100%, as in commonly used double-walled containers, if the barrier coating α is not formed, the oxygen concentration increases to approximately 0.25% after four weeks, as shown by curve B. On the other hand, when a water-soluble barrier coating α is formed on the outer surface of the inner container 103 in accordance with the present invention, the oxygen concentration after four weeks is exactly the same as when the barrier coating α is not formed. That is, when a water-containing substance is contained in the inner container 103 and the relative humidity is 100% (RH=100%), the passive barrier performance of the barrier coating α is not exhibited, and even when the barrier coating α is provided, oxygen still permeates in the same way as when the barrier coating α is not provided.

[0023] In contrast, Fig. 3 shows a diagram illustrating the relationship between the storage period and the oxygen concentration inside the inner container 103 when the double-structure container 100 in Fig. 1 is stored at 37°C and 30% RH with the contents partly discharged and the bag-like inner container 103 in a shrunk state. That is, in such a double-structure container 100, as shown in the partially enlarged side cross-sectional view, an air layer 107 is formed, and the barrier coating α is exposed to an atmosphere of 30% RH.

[0024] In this state, when the inside of the inner container 103 is dry (0% RH), the oxygen concentration inside the inner container 103 after 4 weeks increases slightly, as shown by curve A. That is, in this case, since the air layer 107 is formed, the outer container 101 does not function at all as a barrier material, but since the barrier coating α functions sufficiently as a passive barrier material, oxygen permeation from the air layer 107 into the inner container 103 is effectively suppressed.

[0025] However, when a water-containing substance is contained in the inner container 103 and the relative humidity is maintained at 100%, if the barrier coating α is not formed and the bag-shaped inner container 103 has a single-layer structure, the oxygen concentration increases significantly over time, reaching about 2% after four weeks, as shown by curve B. In other words, an air layer 107 is formed inside the bag-shaped inner container 103, and a large amount of oxygen permeates from this air layer 107 into the inner container 103.

[0026] However, when a barrier coating α made of a water-soluble resin is formed on the outer surface of the inner container 103 according to the present invention, the passive barrier performance of the barrier coating α is effectively exhibited, as shown by curve C, and oxygen permeation from the air layer 107 into the inner container 103 is effectively suppressed. In other words, curve C extends in a state close to curve A.

[0027] To summarise the experimental results shown in Figures 2 and 3, the passive barrier performance of the barrier coating α formed from a water-soluble resin is greatly dependent on the relative humidity RH of the surface of the barrier coating α; the lower the relative humidity RH, the better the oxygen barrier property is, and the higher the relative humidity, the worse the oxygen barrier property is. For example, in the double-structure container 100 used in the above experiment, the thickness of the outer container 101 is about four times (4t) the thickness t of the bag-shaped inner container 103. Therefore, when a water-containing substance is contained in the inner container 103 and the relative humidity RH inside the inner container 103 is 100% and the outside is 30%, the calculated relative humidity on the barrier coating α surface is about 86% under normal conditions, as shown in the partially enlarged cross-sectional side view of FIG. 1(a). On the other hand, when a part of the water-containing substance, which is the content, is discharged and the inner container 103 is in a contracted state, the relative humidity on the barrier coating α surface is 30%, as shown in the partially enlarged cross-sectional side view of FIG. 1(b). Therefore, when the relative humidity on the barrier coating α surface is maintained at about 86%, the barrier coating α does not function as a barrier material, but when the relative humidity on the surface is about 30% (for example, the relative humidity in a storage environment such as a refrigerator), it functions sufficiently as a passive barrier material to block the transmission of oxygen.

[0028] Thus, when the double-structure container of the present invention is used to store water-containing substances such as soy sauce, and the contents have not been discharged and the container is unused (the state of FIG. 1(a)), the outer container 101 functions as a passive barrier to suppress the permeation of oxygen into the inner container 103. When part of the contents has been discharged, the inner container 103 has shrunk, and an air layer 107 has formed between the inner container 103 and the outer container 101 (the state of FIG. 1(b)), the barrier coating α fully functions as a passive barrier to suppress the permeation of oxygen into the inner container 103. Moreover, since the barrier coating α is formed from a water-soluble resin, after use, the barrier coating α can be removed by removing the inner container 103 and washing it with water, thereby ensuring sufficient recyclability.

[0029] <Water-soluble barrier coating α> In the present invention, the water-soluble barrier coating α is formed from a water-soluble resin and is formed by application such as spraying, dipping, roll coating, or the like. That is, wastes of various plastic products are collected for each plastic that constitutes the product, and are mechanically separated from other parts that are used together with the plastics and collected, which allows the reuse of various plastics or other parts, etc. However, if the plastic product has a multi-layer structure including a barrier material, this barrier material cannot be removed, making it difficult to reuse the plastics. However, in the present invention, since the barrier coating α can be removed by washing with water, it can be easily removed, for example, by immersing the outer container 101 and inner container 103 in a 1.5% alkaline aqueous solution heated to 90°C for 15 minutes as indicated in the voluntary design guidelines for designated PET bottles published by the PET Bottle Recycling Promotion Council. Therefore, by making the outer container 101 and inner container 103 into a single-layer structure, recyclability can be ensured, and the plastic materials that constitute them can be reused.

[0030] In the present invention, various water-soluble materials can be used as the water-soluble resin that forms the water-soluble barrier coating α as described above, so long as they have the film-forming ability to form a film and have water solubility that allows them to be removed by washing with water. Specific examples include, but are not limited to, polymers such as vinyl alcohol polymers (vinyl alcohol polymers), polycarboxylic acid polymers, polyallylamine, polyethyleneimine, etc., and polysaccharides such as starch, carboxymethylcellulose, sodium alginate, etc., or derivatives thereof.

[0031] In the present invention, among the above-mentioned water-soluble resins, those having high passive barrier performance, for example, an oxygen permeability coefficient of 40 cc· at 22°C and 60% RH, are used. 20 μm / m 2Water-soluble resins with a viscosity of 100 / day atm or less are preferably used because they exhibit high oxygen barrier properties. Among the above, vinyl alcohol polymers and polycarboxylic acid polymers are representative water-soluble resins with high passive barrier properties.

[0032] The vinyl alcohol polymer is obtained by polymerizing a vinyl ester compound and then completely or partially saponifying it, and is not limited to the so-called highly saponified polyvinyl alcohol, but may be an ethylene-vinyl alcohol copolymer or a butenediol-vinyl alcohol copolymer, so long as it contains 70 mol % or more of vinyl alcohol units. This is because a certain level of water solubility is ensured if the polymer contains a large amount of vinyl alcohol units. Furthermore, as the polycarboxylic acid polymer, a homopolymer or copolymer of a monomer having a carboxyl group, such as polyacrylic acid, polymethacrylic acid, polymaleic acid, polyitaconic acid, or an acrylic acid-methacrylic acid copolymer, or a partially neutralized product thereof, can be used, and it is preferable to use polyacrylic acid or polymethacrylic acid. In the present invention, among the above-mentioned water-soluble resins, vinyl alcohol polymers are most suitable from the viewpoints of availability, film-forming properties, and the like.

[0033] In the present invention, in order to reinforce the oxygen barrier property, a functional material for enhancing the oxygen blocking property can be dispersed in the water-soluble resin and used as the water-soluble barrier coating α.

[0034] functional materials; Functional materials for improving oxygen barrier properties include so-called passive barrier materials and active barrier materials.

[0035] As the passive barrier material, for example, layered clay minerals such as montmorillonite and so-called gas barrier resins can be used, but layered clay minerals are particularly preferred in the present invention because they can be uniformly dispersed in the water-soluble barrier coating α and exhibit high oxygen barrier properties. However, the amount of layered clay minerals should be limited to a small amount in terms of specific gravity, and it is particularly preferred to limit the amount to 20 parts by mass or less per 100 parts by mass of the water-soluble resin.

[0036] In addition, the active barrier material is easily oxidized by reacting with oxygen, and various organic and inorganic materials are known. However, organic oxidizable materials are preferably used, from the viewpoint of being able to be uniformly dispersed in the water-soluble resin described above and ensuring transparency.

[0037] Representative examples of organic oxidizable materials include compounds known as oxygen absorbents or antioxidants, such as ascorbic acid (vitamin C), tocopherol (vitamin E), dibutylhydroxytoluene, butylhydroxyanisole, sodium erythorbate, and propyl gallate, polyene polymers having aliphatic unsaturated bonds, such as polybutadiene and polyisoprene, and compounds having an unsaturated alicyclic structure. Among these, compounds having an unsaturated alicyclic structure are preferably used. Such organic oxidizable materials not only have high oxygen barrier properties, but also have no coloring problems and can be preferably used in applications requiring transparency. In addition, when a compound having an unsaturated alicyclic structure comes into contact with oxygen, the unsaturated bond in the ring is easily oxidized, thereby absorbing oxygen and exhibiting oxygen absorbing properties, but an unsaturated bond present in an aromatic ring does not exhibit such oxidizability.

[0038] In the present invention, examples of the compound having an unsaturated alicyclic structure (unsaturated alicyclic structure compound) include methyltetrahydroindene, 5-ethylidene-2-norbornene, 5-methylene-2-norbornene, 5-isopropylidene-2-norbornene, 5-vinylidene-2-norbornene, 6-chloromethyl-5-isopropenyl-2-norbornene, dicyclopentadiene, and the like. In the present invention, the compound having an unsaturated alicyclic structure is particularly preferably a compound represented by the following formula (1): [ka] In the formula, ring X is an aliphatic ring having one unsaturated bond. Y is an alkyl group. At least one selected from the group consisting of acid anhydrides represented by the formula (I) and (II), esters, amides, imides or dicarboxylic acids derived from the acid anhydrides, and polymers having structural units derived from the acid anhydrides, is most preferably used.

[0039] In the above formula (1), the aliphatic ring X is a 6-membered ring having one unsaturated bond, i.e., a cyclohexene ring, and the position of the unsaturated bond may be either the 3rd or 4th position, but is particularly preferred from the viewpoint of oxidizability. The alkyl group is not particularly limited, but generally, from the viewpoint of synthesis and oxidizability, a lower alkyl group having 3 or less carbon atoms, particularly a methyl group, is preferred, and the bonding position may generally be either the 3rd or 4th position. Such an acid anhydride is an alkyltetrahydrophthalic anhydride, which is obtained by the Diels-Alder reaction of maleic anhydride and a diene, and is obtained in the form of a mixture of isomers, and the mixture can be used as it is as a functional material. In the present invention, the most suitable example of the acid anhydride is 3-methyl-Δ 4 -tetrahydrophthalic anhydride, and 4-methyl-Δ 3 -tetrahydrophthalic anhydride.

[0040] [ka]

[0041] [ka]

[0042] The above acid anhydrides can form derivatives by known methods, and as long as the unsaturated alicyclic structure is maintained, such derivatives can be used as the oxygen-absorbing component (B). That is, esters, amides, imides, or dicarboxylic acids derived from the above acid anhydrides can be used as oxidizable functional materials.

[0043] The above esters are esters obtained by reacting an acid anhydride such as alkyltetrahydrophthalic anhydride with various alcohols. The alcohol used for esterification is not particularly limited, and any of aliphatic alcohols such as methyl alcohol, ethyl alcohol, and propyl alcohol, and aromatic alcohols such as phenol and benzyl alcohol can be used. Furthermore, polyhydric alcohols such as glycol can also be used. In this case, the number of unsaturated alicyclic structures corresponding to the number of alcohols in one molecule can be introduced. Such esters may also be partial esters of the above acid anhydrides. That is, such an ester is, for example, represented by the following formula: RO-OC-Z-CO-OR HOOC-Z-CO-OR or HOOC-Z-CO-ORO-CO-Z-COOH In the formula, Z is an unsaturated alicyclic ring contained in the acid anhydride. R is an organic group derived from the alcohol used in the reaction.

[0044] The above amides can be obtained by reacting an acid anhydride such as alkyltetrahydrophthalic anhydride with various amine compounds. The amine to be used is not particularly limited, and any of aliphatic amines such as methylamine, ethylamine, propylamine, etc., and aromatic amines such as phenylamine, etc., can be used, and one of the two carbonyl groups forming the acid anhydride group may be amidated, or both may be amidated.Furthermore, it is not limited to monoamines, and polyamines such as diamines and triamines can also be used, and in this case, the number of unsaturated alicyclic structures corresponding to the number of amines in one molecule can be introduced.

[0045] The imide is obtained by subjecting the above amide to a heat treatment to convert it into an imidized form, and is, for example, a compound represented by the following formula: HOOC-Z-CONH-R or HOOC-Z-CONH-R-CONH-Z-COOH In the formula, Z is an unsaturated alicyclic ring contained in the acid anhydride. R is an organic group derived from the amine used in the reaction. and the amide represented by the following formula: Z-(CO) 2 -NR or Z-(CO) 2 -NRN-(CO) 2 -Z In the formula, Z and R are the same as above. It is expressed as:

[0046] Furthermore, a dicarboxylic acid is formed by hydrolysis of an acid anhydride to cleave the acid anhydride group, and is represented by the following formula: HOOC-Z-COOH In the formula, Z is the same as above.

[0047] Furthermore, polymers having structural units derived from the above-mentioned acid anhydrides also exhibit oxygen absorption properties and can therefore be used as functional materials to be incorporated into the water-soluble barrier coating α. That is, the acid anhydrides represented by the above-mentioned formula (1) can be used as dibasic acid components forming polyesters. Such copolymerized polyesters have unsaturated alicyclic structures in their molecular chains and therefore exhibit a certain degree of oxygen absorption (oxidizability), making them usable as functional materials that impart oxygen blocking properties.

[0048] In the present invention, among the acid anhydrides represented by the above general formula or compounds derived from the acid anhydrides, non-polymeric compounds (i.e., compounds that do not have repeating units in the molecule) having a molecular weight of 2000 or less, more preferably 1000 or less, are particularly preferred. This is because such low molecular weight non-polymeric compounds have high molecular mobility, and therefore are particularly reactive with oxygen and exhibit high oxygen absorption. Among such low molecular weight non-polymeric compounds, imide compounds obtained by heat treatment of amide, which is a reaction product of the acid anhydride of the general formula (1) and an amine, are particularly preferred because they exhibit high oxygen absorption ability.

[0049] As the amine used in the production of such an imide compound, either an aliphatic amine or an aromatic amine can be used.

[0050] Examples of the above aliphatic amines and aromatic amines include methylamine, methylenediamine, propylamine, propylenediamine, butylamine, butylenediamine, pentylamine, pentamethylenediamine, hexylamine, hexamethylenediamine, heptylamine, heptamethylenediamine, octylamine, octamethylenediamine, nonylamine, nonamethylenediamine, decylamine, decamethylenediamine, undecylamine, undecamethylenediamine, dodecylamine, dodecamethylenediamine, tridecylamine, tridecamethylenediamine, tetradecylamine, tetradecamethylenediamine, pentadecylamine, tetra ... Examples of the amines that can be used include dimethylamine, pentadecamethylendiamine, hexadecylamine, hexadecamethylendiamine, heptadecylamine, heptadecamethylendiamine, octadecylamine, octadecamethylendiamine, nonadecylamine, nonadecamethylendiamine, eicosylamine, 1,3-bis(aminomethyl)cyclohexane, tris(2-aminoethyl)amine, m-xylylenediamine, p-xylylenediamine, p-phenylenediamine, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl ether, 2,4,6-triamino-1,3,5-triazine, and 2,4,6-triaminopyrimidine.

[0051] In the present invention, among the various functional materials described above, compounds having an aliphatic unsaturated bond or an unsaturated alicyclic structure are preferably used from the viewpoint of exhibiting particularly high oxygen barrier properties, and in particular, compounds having an unsaturated alicyclic structure are most preferably used.

[0052] When a compound having an aliphatic unsaturated bond or an unsaturated alicyclic structure is used as the functional material, a known transition metal catalyst may be dispersed in the barrier coating α in order to promote the reaction between the unsaturated bond and oxygen (oxygen absorption). Such transition metal catalysts can be used in a so-called catalytic amount, and are usually used in an amount of 1000 ppm or less in terms of transition metal per compound, as appropriate, in the form of a low-valent inorganic salt, organic salt or complex salt of the transition metal.

[0053] In such transition metal catalysts, the transition metal is preferably a metal of Group VIII of the periodic table such as iron, cobalt, nickel, etc., but may also be a metal of Group I such as copper, silver, etc., a metal of Group IV such as tin, titanium, zirconium, etc., a metal of Group V such as vanadium, a metal of Group VI such as chromium, a metal of Group VII such as manganese, etc. Among these, cobalt is particularly preferred because it significantly promotes oxygen absorption (oxidation of oxidizable organic components).

[0054] Examples of the inorganic salts of the transition metals include halides such as chlorides, sulfur oxysalts such as sulfates, nitrogen oxysalts such as nitrates, phosphorus oxysalts such as phosphates, and silicates.

[0055] Examples of organic salts of transition metals include carboxylates, sulfonates, and phosphonates, and in the present invention, carboxylates are preferred.Specific examples of the organic salts of transition metals include acetic acid, propionic acid, isopropionic acid, butanoic acid, isobutanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, isoheptanoic acid, octanoic acid, 2-ethylhexanoic acid, nonanoic acid, 3,5,5-trimethylhexanoic acid, decanoic acid, neodecanoic acid, undecanoic acid, lauric acid, myristic acid, palmitic acid, margaric acid, stearic acid, arachidic acid, Linderic acid, tsuzuic acid, petroselinic acid, oleic acid, linoleic acid, linolenic acid, arachidonic acid, formic acid, oxalic acid, sulfamic acid, and naphthenic acid.

[0056] Complexes of transition metals include those with β-diketones or β-keto acid esters.

[0057] In the present invention, the above-mentioned functional material may be blended in an amount that provides sufficient oxygen absorption, i.e., oxygen blocking, depending on the type of the material, and does not impair the properties of the water-soluble resin (e.g., removability by water washing and passive barrier properties under low humidity). In particular, the use of the above-mentioned functional material is suitable for improving the oxygen barrier properties in the state shown in FIG. 1(a) (a state in which the air layer 107 is not formed).

[0058] The water-soluble barrier coating α can also contain colorants and ultraviolet absorbing agents within the range that does not impair its water solubility (removability by washing with water), thereby imparting light blocking properties in addition to oxygen barrier properties. Known pigments and dyes can be used as colorants. Furthermore, in addition to the colorant and the UV absorber, the barrier coating α may contain known compounding agents such as a viscosity modifier, an antifoaming agent, a filler, a heat stabilizer, a weathering stabilizer, an antioxidant, an antiaging agent, a light stabilizer, an antistatic agent, a metal soap, a wax, a modifying resin or rubber, etc., according to a formulation known per se, within a range that does not impair the properties of the barrier coating α.

[0059] The thickness of the water-soluble barrier coating α as described above is set to a thickness (for example, 0.1 to 100 μm) that ensures the required oxygen barrier properties without impairing the shrinkage properties of the inner container described below.

[0060] The water-soluble barrier coating α can be easily formed, for example, by putting the above-mentioned water-soluble resin and any appropriate functional materials and transition metal catalysts into a volatile solvent such as water or ethanol, mixing them, applying the obtained coating liquid to the surface of an inner container preform (described later) that has been subjected to a surface treatment or anchor coat to improve coatability as necessary, and drying it.

[0061] <Specific form of double-walled container> The double-structure container of the present invention, in which a water-soluble barrier coating α formed from the above-mentioned water-soluble resin is provided on the outer surface of the inner container, is molded by blowing and stretching a stack preform in which an outer container preform and an inner container preform are stacked (this is called a stack preform method), and a specific form thereof is shown, for example, in FIG. 4.

[0062] In Figure 4, this double-structure container is generally indicated by 10 and is composed of an outer container 1 and an inner container 3 (3a to 3d) contained inside the outer container 1, and the outer surface of the inner container 3 is provided with the water-soluble barrier coating α described above.

[0063] In Fig. 4, the outer container 1 is formed of a neck 1a, a body 1b connected to the neck 1a, and a bottom 1c closing the lower end of the body 1b, the body 1b and the bottom 1c being blow-stretched parts, and the neck 1a being a fixed part that is not blow-stretched and is not thinned by blow-stretching. An air inlet 7 is formed in the neck 1a, and a recessed squeeze area is formed in the center of the body 1b to make it easier to squeeze.

[0064] In the example of FIG. 4, a support ring 1d is formed on the outer surface of the neck portion 1a of the outer container 1.

[0065] On the other hand, the inner container 3 has a neck portion 3a, which is a non-stretched portion, and a body portion 3b that has been blown and stretched to have a thin, bag-like shape. Immediately after molding, the outer surface of the body portion 3b is in close contact with the inner surfaces of the body portion 1b and bottom portion 1c of the outer container 1, as shown in the partially enlarged side cross-sectional view of Figure 1(a). In such an inner container 3, the neck 3a is fitted into the neck 1a of the outer container 1. In the example of FIG. 1, the upper part of the neck 3a protrudes from the neck 1a of the outer container 1, and a screw 3c for screwing and fixing the cap is formed in this protruding part. Furthermore, a protrusion 3d that acts as a stopper is formed below the screw 3c to prevent the inner container 3 from penetrating too deeply into the outer container 1. Of course, the shape of the double-structure container 10 to which the present invention is applicable is not limited to the shape shown in Figure 4. For example, only a protrusion 3d serving as a stopper can be provided at the upper end of the neck 3a of the inner container 3, and a screw for attaching a cap can be provided on the outer surface of the neck 1a of the outer container 1 (above the support ring 1d).

[0066] The outer container 1 is made of a blow moldable thermoplastic resin. Examples of such a thermoplastic resin include the following. Olefin resins, such as low-density polyethylene (LDPE), medium-density polyethylene (MDPE), high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE), polypropylene (PP), poly-1-butene, poly-4-methyl-1-pentene, or random or block copolymers of α-olefins such as ethylene, propylene, 1-butene, and 4-methyl-1-pentene, cyclic olefin copolymers, etc.; Ethylene-vinyl copolymers, such as ethylene-vinyl acetate copolymers, ethylene-vinyl alcohol copolymers, ethylene-vinyl chloride copolymers, ionically cross-linked olefin copolymers (ionomers), etc.; Styrene-based resins, such as polystyrene, acrylonitrile-styrene copolymers, ABS, α-methylstyrene-styrene copolymers, etc.; Vinyl resins, such as polyvinyl chloride, polyvinylidene chloride, vinyl chloride-vinylidene chloride copolymers, polymethyl acrylate, polymethyl methacrylate, etc.; Polyamide resins, such as nylon 6, nylon 6-6, nylon 6-10, nylon 11, nylon 12, etc.; Polyester resins, for example, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polyethylene furanoate (PEF), polytrimethylene furanoate (PTF), and copolymer polyesters thereof; Polycarbonate resin; Polyphenylene oxide resin; Biodegradable resins, such as polylactic acid (PLA), polybutylene succinate (PBS), polyhydroxyalkanoate (PHA) and copolymers thereof; Of course, blends of these thermoplastic resins can also be used as long as the moldability is not impaired.

[0067] In the present invention, in principle, the outer container 1 can be formed by blow molding using any of the thermoplastic resins listed above. However, taking into consideration the properties required of the outer container 1, such as container strength, flexibility (squeezability), etc., polyesters such as polyethylene terephthalate (PET) and olefin-based resins such as polyethylene and polypropylene are generally preferred, and taking transparency into consideration, polyesters, and most preferably PET, are used.

[0068] It is also possible to improve the oxygen barrier property of the outer container 1 by forming a multi-layer structure with an intermediate layer of a gas barrier resin such as ethylene-vinyl alcohol or a layer containing the above-mentioned oxygen-absorbing functional material, but in this case, recyclability is impaired, and in a state in which the inner container 3 has shrunk and an air layer is formed, the oxygen barrier property is not required for the outer container 1. Therefore, it is preferable that the outer container 1 has a single-layer structure using the above-mentioned thermoplastic resin.

[0069] Furthermore, like the outer container 1, the inner container 3 is also formed from a blow-moldable thermoplastic resin, and since it is easy to set molding conditions, particularly when performing blow stretching using the stack preform method, it is preferable that the thermoplastic resin used to form the inner container 3 and the thermoplastic resin used to form the outer container 1 are of the same type.

[0070] In the double-structure container 10 to which the present invention is applied, as shown in FIG. 4, the above-mentioned water-soluble barrier coating α is present between the outer surface of the inner container 3 and the double-structure container 10 . That is, as described above, this barrier coating α effectively prevents oxygen from passing into the inner container 3, effectively avoids oxidative deterioration of the contents contained in the inner container 3, and enables the freshness of the contents to be maintained for a long period of time. Moreover, since this barrier coating α can be easily removed by washing with water, the double-structure container 10 discarded after use can be quickly removed by washing with a dilute alkaline aqueous solution or the like in the recycling process, facilitating reuse of the resin such as PET that forms the inner container 3. Furthermore, if the outer container 1 has a single-layer structure, the resin that forms the outer container 1 can also be reused.

[0071] The body 1b (particularly the squeezed region) of the outer container 3 is required to be easily depressed by pressure and to return to its original shape when pressure is released, so the thickness of this portion is relatively thick, for example, about 200 to 600 μm. On the other hand, the bag-shaped body 3b of the inner container 3 shrinks as the contents are discharged, so its thickness is extremely thin, usually about 20 to 150 μm.

[0072] In the present invention, the above-mentioned double-structure container 10 is provided with the barrier coating α as described above, and is therefore manufactured by the so-called stack preform method. That is, a first preform (preform for molding the outer container) obtained by injection molding using a resin for the outer container 1 and a second preform (preform for molding the inner container) obtained by injection molding using a resin for the inner container 3 are used, the second preform is inserted into the first preform to form a stack preform with a multi-layer structure, and this stack preform is then subjected to biaxial stretch blow molding to produce the product. That is, according to this method, the barrier coating α can be easily formed on the outer surface of the second preform.

[0073] Please refer to Figures 5 and 6 for explaining the stack preform method. First, a stack preform for molding the double-structured container 10 of Figure 4 is generally indicated by 20 in Figure 6, and is formed from a first preform 11 (see Figure 5(a)) and a second preform 13 (see Figure 5(b)), both of which have a test tube shape as shown in Figure 5. That is, the first preform 11 is a preform for molding an outer container, and the second preform 13 is a preform for molding an inner container, and the second preform 13 is inserted into the first preform and held in place to form a stack preform 20 that is to be subjected to the blow-stretching process.

[0074] 5, both the first preform 11 and the second preform 13 have portions corresponding to the neck 1a of the outer container 1 and the neck 3a of the inner container 3. In other words, neither of these portions is stretch molded, and the first preform 11 has a support ring 1d and an air inlet 7 formed by post-processing after injection molding, while the second preform 13 has a screw 3c and a protrusion 3d. The first preform 11 has a cylindrical portion 11b below the neck portion 1a, the lower end of which is closed, which is the portion to be stretch molded, and is shaped into the body portion 1b and bottom portion 1c of the outer container 1 by blow stretching. Furthermore, the cylindrical portion 13b, the lower end of which is closed below the neck portion 3a of the second preform 13, is the portion to be stretch-molded, and is shaped by blow-stretching into the shape of the body portion 3b of the inner container 3. That is, the water-soluble barrier coating α is formed by applying the above-mentioned water-soluble resin to the outer surface of the portion that will become the body portion 3b by stretch molding.

[0075] By inserting the second preform 13 into the first preform 11, a stack preform 20 in the form shown in Fig. 6 is assembled, placed in a blow mold, and the part including the neck parts 1a, 3a is fixed with a predetermined jig (the region indicated by X in Fig. 6), and the stack preform 20 is heated to a temperature at which it can be stretched (above the glass transition temperature and below the melting point of the resin forming the preforms 11, 13) by high-frequency heating or the like, and a stretch rod (not shown) is inserted into the stack preform 20 (second preform 13) to stretch it in one axial direction, and further, a blowing fluid such as air is supplied to expand it in the circumferential direction, thereby obtaining a double-structured container 10 in the form shown in Fig. 4. That is, the region indicated by Y in Fig. 6 of the stack preform 20 is the part to be stretched.

[0076] In the present invention, by forming the double-structure container 10 by the method described above, a water-soluble barrier coating α can be easily formed on the outer surface of the inner container 3 contained within the outer container 1. For example, in a method in which a preform is molded by co-injection molding and then biaxially stretched and blow molded, a thermoplastic barrier resin or a thermoplastic resin with a barrier material dispersed therein must be used to form a barrier layer between the outer container 1 and the inner container 3. As already mentioned, when imparting oxygen barrier properties using such a method, the barrier material cannot be removed from the bottle that is discarded after use, which impairs recyclability. However, when the above-mentioned stack method is adopted, the preform for the outer container 1 (first preform 11) and the preform for the inner container 3 (second preform 13) are molded separately, so that the water-soluble barrier coating α can be easily formed on the outer surface of the second preform 13, and furthermore, such barrier coating α can be easily removed by washing with water, so that recyclability is not impaired.

[0077] Furthermore, during blow stretch molding, the water-soluble resin (and also the functional material) in the barrier coating α is in a fluid state, so it is stretched together with the second preform 13 without causing film breakage, etc., and the barrier coating α can be provided in a specified area.

[0078] The double-structure container 10 manufactured as described above can also be used as an airless container by providing a path for introducing air between the inner surface of the outer container 1 and the outer surface of the inner container 3, either in advance or after processing, and then fitting a cap with a known check valve to the neck 1a of the outer container 1 after the contents have been placed in the body 3b of the inner container 3.

[0079] In addition, in the above-mentioned double-structure container 10, an air inlet 7 is provided in the neck portion 1a of the outer container 1, but the present invention can also be applied to a double-structure container that does not have such an air inlet 7. In this type of double-structure container, a gap is formed between the neck 1a of the outer container 1 and the neck 3a of the inner container 3, and air is allowed to flow in and out of the gap via the upper ends of the necks 1a and 3a. An example of such a double-structure container is shown in FIG.

[0080] In FIG. 7, this double-structure container is generally designated by 30, and is composed of an outer container 1 and an inner container 3, similar to the double-structure container 10 described above, except for the shape of the neck.

[0081] The outer container 1 is composed of a neck 1a, a body 1b, and a bottom 1c, with a support ring 1d formed on the outer surface of the neck 1a, and a head 1e with an outwardly enlarged diameter formed on the neck 1a, which is used for fitting and fixing a cap.

[0082] Meanwhile, the inner container 3 is formed of a neck 3a and a bag-shaped body 3b, like the double-structure container 10 described above, but the upper end of the neck 3a is set at approximately the same height as the neck 1a of the outer container 1, and a gap is formed between the neck 1a and the upper end of the neck 3a, so that an air passage X leading to the inside is formed. Also, a fitting ring 3e is formed on the outer surface of the neck 3a of the inner container 3, and the inner container 3 is stably held by fitting this ring 3e into the neck 1a of the outer container 1. Furthermore, a part of this ring 3e is cut out (or a groove extending in the axial direction is formed on the inner surface of the neck 3a of the inner container 3), so that the above-mentioned air passage X is connected between the body 1b and 3b. That is, in this type of double-structure container 30, when the cap is fitted and fixed, a check valve is positioned in the cap to regulate the flow of air in and out of the air passage X leading to the interior from the gap between the upper ends of the neck portions 1a and 3a, and the air inlet 7 described above is not necessary. Such a double-structure container 30 is manufactured by stretch blow molding using a stack preform whose neck portion has the above-mentioned configuration.

[0083] In the double-structure containers 10, 30 to which the present invention is applied, the contents filled in the inner container 3 are discharged, for example, by squeezing (pressing) the recessed portion (squeezed area) of the body 1b of the outer container 1, and the body 3b of the inner container 3 is reduced in volume as the contents are discharged. However, air is introduced from the air inlet 7 (or air path X) between the body 3b and the body 1b of the outer container 1 to form an air layer, and the contents are then effectively discharged.

[0084] In the present invention, the barrier coating α effectively suppresses and prevents oxygen from entering the interior of the inner container 3 through the body 3b, effectively preventing oxidative deterioration of the contents. Furthermore, the barrier coating α can be easily removed from containers discarded after use by rinsing with water, ensuring excellent recyclability.

[0085] The present invention is suitably applied to the storage of various water-containing foods which contain a lot of water and require quality maintenance by preventing oxidation, in particular, seasoning liquids such as soy sauce. EXAMPLES

[0086] The present invention will be further illustrated by the following examples, but the present invention is not limited to these examples. The materials and test methods used in the examples and comparative examples are shown below.

[0087] <Preparation of coating solution> (Coating solution A) Polyvinyl alcohol (manufactured by Fujifilm Wako Pure Chemical Industries: polyvinyl alcohol 1,000 fully saponified type, containing 96 mol% vinyl alcohol units) was prepared as a water-soluble barrier coating. Coating solution A was prepared by adding 10 g of this polyvinyl alcohol to 100 g of distilled water, heating to 95° C., and stirring until completely dissolved.

[0088] (Coating liquid B) A butenediol-vinyl alcohol copolymer (Mitsubishi Chemical: G Polymer BVE8049Q, containing 94.8 mol% vinyl alcohol units) was prepared as a water-soluble barrier coating. Coating solution B was prepared by adding 20 g of this butenediol-vinyl alcohol copolymer to 100 g of distilled water, heating to 95° C., and stirring until completely dissolved.

[0089] (Coating solution C) An ethylene-vinyl alcohol copolymer (Kuraray: Exeval RS-4104, vinyl alcohol unit ratio 92 mol%) was prepared as a water-soluble barrier coating. Coating solution C was prepared by adding 20 g of this ethylene-vinyl alcohol copolymer to 100 g of distilled water, heating to 95° C., and stirring until completely dissolved.

[0090] (Coating solution D) Polyvinyl alcohol (Gohsenol NL05, manufactured by Mitsubishi Chemical, vinyl alcohol unit ratio 98.5 mol%) was prepared as a water-soluble barrier coating. 20 g of this polyvinyl alcohol was added to 100 g of distilled water, heated to 95° C., and stirred until completely dissolved, to prepare coating solution D.

[0091] <Example 1> Preforms for the inner container (8 g) and the outer container (21 g) were obtained by injection molding from copolymerized polyethylene terephthalate resin (5015W: manufactured by Shinkogosen, IV=0.83) with isophthalic acid (copolymerization ratio=1.8 mol%). After surface treatment with oxygen plasma was performed on the preforms for the inner container using a microwave plasma surface treatment device (Micro Labo-PS2: manufactured by Nissin Co., Ltd.), coating liquid A was applied to the outer surface by dipping and dried with a dryer (the dry coating amount of coating liquid A was 0.2 g). The preforms for the outer container were stacked and biaxially stretched and blow molded into a 450 mL bottle. The thickness of the inner container at the bottle body was about 80 μm, and the thickness of the outer container was about 320 μm. Furthermore, the pressure inside the bottle was reduced to shrink only the inner container, and an air layer was provided between the inner container and the outer container. The capacity of the inner container at this time was about 300 mL.

[0092] <Example 2> A biaxially stretched blown bottle having an air layer between the inner container and the outer container was obtained in the same manner as in Example 1, except that the coating solution A was changed to the coating solution B and the dry coating amount was set to the amount shown in Table 1.

[0093] <Example 3> A biaxially stretched blown bottle having an air layer between the inner container and the outer container was obtained in the same manner as in Example 1, except that the coating solution A was changed to the coating solution C and the dry coating amount was set to the amount shown in Table 1.

[0094] <Example 4> A biaxially stretched blown bottle having an air layer between the inner container and the outer container was obtained in the same manner as in Example 1, except that the coating solution A was changed to the coating solution D and the dry coating amount was set to the amount shown in Table 1.

[0095] <Comparative Example 1> A biaxially stretched blow-molded bottle having an air layer between the inner and outer containers was obtained in the same manner as in Example 1, except that no coating was applied.

[0096] The oxygen permeability coefficient of the above barrier coating, and the barrier properties and recyclability of the biaxially stretched blown bottles produced in the Examples and Comparative Examples were evaluated by the following methods, and the results are shown in Table 1 together with the type of coating solution used and the amount applied.

[0097] (Oxygen permeability measurement of barrier coating) The oxygen permeability of the barrier coating was evaluated using an oxygen permeability measuring device (MODERN CONTROL OX-TRAN2 / 22). The PET films coated with the above coating solutions (A) and (B) were biaxially stretched, and the oxygen permeability was measured at 22°C and 60% RH.

[0098] (Barrier performance evaluation of biaxially stretched blown bottles) The molded bottles were sealed with aluminum foil laminated film or transparent vapor-deposited PET sealant in a nitrogen-substituted glove box. At this time, 5 mL of water was added to adjust the humidity inside the bottle to 100% RH. After storing in a 37°C, 30% RH environment for 28 days, the oxygen concentration inside the bottle was measured using a non-destructive high-sensitivity oxygen concentration meter (Oxy-4 Trace v3: manufactured by Presens). The smaller the oxygen concentration, the more excellent the oxygen barrier performance.

[0099] (Recyclability evaluation) The body of the molded bottle was cut into 1 cm squares and immersed in a 1.5% aqueous solution of sodium hydroxide heated to 90° C. After 15 minutes, it was removed and washed with tap water, and then visually observed, the surface was measured by the ATR method using a Fourier transform infrared spectrophotometer (FTS7000 SIRIES: manufactured by VARIAN), and the transmittance was measured using an integrating sphere device attached to a spectrophotometer (UV-3100: manufactured by Shimadzu Corporation) to evaluate recyclability based on the presence or absence of a barrier component. Good: Excellent recyclability. (Barrier components have been removed.) ×: Poor recyclability (barrier components remain)

[0100] [Table 1] [Explanation of symbols]

[0101] 100:Double structure container 101: Outer container 103: Inner container 105: Cap 107: Air layer α: Barrier coating 1: Outer container 3: Inner container 7: Air inlet 10:Double structure container 11: First preform 13: Second preform

Claims

1. A double-structure container comprising an outer container and an inner container housed within the outer container, The outer container and the inner container have a single-layer structure, the outer surface of the inner container is provided with only a water-soluble barrier coating; The double-structure container is characterized in that the water-soluble barrier coating is formed from a water-soluble resin having an oxygen permeability coefficient of 0.222 cc·20 μm / m 2 ·day·atm (@22° C., 60% RH) or less.

2. 2. The double-walled container according to claim 1, wherein the inner container comprises a neck and a bag-shaped portion connected to the neck, and the water-soluble barrier coating is provided on an outer surface of the bag-shaped portion.

3. 3. The double-walled container according to claim 1, wherein the water-soluble barrier coating is formed from a vinyl alcohol polymer containing 70 mol % or more of vinyl alcohol units.

4. 4. The double-structure container according to claim 1, wherein an air layer is formed between the outer surface of the water-soluble barrier coating and the inner surface of the outer container.

5. 5. The double-structure container according to claim 1, wherein a water-containing substance is accommodated inside the inner container.

6. A stack preform for a double-structure container, which comprises an outer container preform and an inner container preform held in the outer container preform, and is used to form a double-structure container by blow molding, the outer container preform and the inner container preform have a single-layer structure, On the outer surface of the inner container preform, only a water-soluble layer is formed by coating with a water-soluble barrier material; The stack preform for a double structure container, wherein the water-soluble barrier material is a water-soluble resin having an oxygen permeability coefficient of 0.222 cc·20 μm / m 2 ·day·atm (@22° C., 60% RH) or less.

7. The stack preform for a double-structure container as described in claim 6, wherein the preform for the inner container includes a neck portion which is a non-stretch molded portion and a stretch molded portion connected to the neck portion, and the water-soluble layer is provided on the outer surface of the stretch molded portion.

8. 8. The stack preform for a double-structure container according to claim 6 or 7, wherein the water-soluble barrier material is a vinyl alcohol polymer containing 70 mol % or more of vinyl alcohol units.

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