JPH01192549A - Multilayer structure for packing - Google Patents

Abstract

PURPOSE:To obtain a multilayer structure for packing capable of highly keeping an oxygen barrier property even under a high humidity and high temp. condition, by containing a water-soluble polymer having an ionizable group in at least one of layers surrounding an oxygen barrier resin layer. CONSTITUTION:The layer surrounding an oxygen barrier resin layer 3 is constituted of a protective layer consisting of an inner layer 5 and an outer layer 1 and the adhesive resin layer 2 achieving function for bonding the oxygen barrier resin layer 3 to other layers or the interposing layer present between the protective layer and the adhesive resin layer 2. The mixing ratio of the water-soluble polymer having an ionizable group contained in the protective layer, the adhesive resin layer and the interposing layer is set to 99.5:0.5-60:40. By this method, moisture transmits through the outer and inner layers 1, 5 composed of a humidity resistant resin from the inner and outer surfaces of this multilayer structure under a high humidity and high temp. condition to be transferred to the adhesive resin layers 2, 4 and is brought into contact with the water-soluble polymer 6 having the ionizable group dispersed in the adhesive resin to dissolve said polymer to be absorbed thereby. Therefore, said moisture does not reach the oxygen barrier resin layer 3.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a multilayer structure for packaging, and more specifically,
It can maintain good oxygen barrier properties over time and has excellent preservation of contents such as food and medical products, and is suitable for various packaging such as bottles, tubes, cups, pouches, bags, wraps and other packaging containers, and films. The present invention relates to a packaging structure useful for various applications.

[Conventional technology]

Oxygen barrier resins such as saponified ethylene-vinyl acetate copolymers have low oxygen permeability but are highly dependent on humidity, so oxygen permeation tends to increase significantly in high humidity regions. Therefore, packaging structures are generally made by covering and laminating a moisture-dependent oxygen barrier resin layer with a protective layer such as polyethylene with low water absorption.
The oxygen barrier resin layer is devised to avoid direct contact with water or humidity, thereby maintaining the oxygen barrier properties of the packaging structure (for example, Japanese Utility Model Application Publication No. 47-23
Publication No. 353). However, under high humidity and high temperature conditions such as during retort processing for sterilization, the water absorption rate of the polyethylene itself that protects the oxygen barrier resin layer increases, and its moisture permeability increases significantly. As a result, moisture that has passed through the protective layer migrates to the oxygen barrier resin layer, resulting in a disadvantage that the oxygen barrier properties of the packaging structure are significantly impaired.

In order to improve these drawbacks, a water-absorbing substance is blended into the protective layer or the adhesive intermediate layer, and this water-absorbing substance-containing layer absorbs water, and the permeated water is transferred to the oxygen barrier resin layer. It has been proposed to reduce the For example, JP-A-57-170748 discloses a laminated structure having a layer of a water-sensitive polymer such as a saponified ethylene-vinyl acetate copolymer, which is composed of an inorganic compound such as calcium chloride or a saccharide such as sucrose. It has been shown that oxygen barrier properties can be maintained by providing a layer containing a desiccant agent to protect the moisture sensitive polymer layer.

Also, JP-A-58-98251 and JP-A-61-11
Publication No. 339 discloses an intervening material in which highly water-absorbent synthetic resin-based water-absorbing polymer particles are dispersed in a thermoformable resin that can be formed into a layer between the gas barrier resin layer and the moisture-resistant resin inner and outer surface layers. It is disclosed that a layer is provided.

[Problem to be solved by the invention]

In the case of a multilayer structure made by blending a desiccant as shown in JP-A-57-170748, even if it is blended with the resin constituting the inner and outer layers or the adhesive layer, the water absorption of the desiccant is Therefore, it is actually difficult to create a multilayer structure that maintains the expected oxygen barrier properties unless a large amount is added. On the other hand, if an excessive amount of desiccant is added to the resins that make up the layers in order to improve the water absorption effect, the properties of the resins that make up each layer, such as transparency and physical strength, will be impaired. .

On the other hand, JP-A-58-98251 and JP-A-81-11
Highly water-absorbent synthetic resin-based water-absorbing polymer particles as shown in Publication No. 339 are made by crosslinking water-soluble synthetic resin to make them water-insoluble and swellable, and have a higher water absorption rate than the desiccant mentioned above. However, when these water-insoluble synthetic resin-based water-absorbing polymer particles are mixed and dispersed in the polyolefin resin used for the intervening layer, the polyolefin resin at the interface of the dispersed particles, that is, the surrounding polyolefin resin, absorbs water. Almost no decrease in hardness is observed, that is, the water absorption and swelling properties are low and it is difficult to swell, so it suppresses the swelling caused by water absorption of the mixed and dispersed water-insoluble synthetic resin-based water-absorbing polymer particles. It has the disadvantage of suppressing its water absorption capacity. Furthermore, the above-mentioned water-insoluble synthetic resin-based water-absorbing polymer has unreacted substances remaining due to the cross-linking reaction, which poses a hygiene problem if they are separated and precipitated from the multilayer structure. ,
In particular, when mixed and dispersed in a layer near the surface, it is not suitable for medical or food use.

Therefore, the purpose of the present invention is to solve the above problems and
It is an object of the present invention to provide a multilayer structure for packaging that can maintain oxygen barrier properties over time, has excellent preservability of contents, and has excellent hygiene.

Another object of the present invention is to maintain high oxygen barrier properties not only during storage but also under high humidity and high temperature conditions such as heat sterilization and hot filling, without deteriorating the various properties of each constituent layer. It is an object of the present invention to provide a multilayer structure for packaging at a relatively low cost.

[Means to solve the problem]

In order to achieve the above object, the multilayer structure for packaging of the present invention is a multilayer structure having an oxygen barrier resin layer, in which at least one layer surrounding the oxygen barrier resin layer has a water-soluble It is characterized by containing a polymer.

Here, the layer surrounding the oxygen barrier resin layer containing a water-soluble polymer having an ionizable group refers to the inner and outer protective layers, and the layer that is located close to the oxygen barrier resin layer and contains the oxygen barrier resin layer. It refers to an adhesive resin layer that serves to bond one layer to another layer, or an intervening layer made of recycled resin or the like between a protective layer and an adhesive resin layer.

Each component of the present invention will be explained in detail below.

Oxygen barrier resin layer: Oxygen permeability coefficient is I x 10-” cc-cm/cd・
A layer made of a resin having a temperature of sec-crnHg (37°C, R, H, 0%) or less, for example, a layer made of saponified ethylene-vinyl acetate copolymer, polyamide, polyvinyl alcohol, and modified products or mixtures thereof. .

Among these, saponified ethylene-vinyl acetate copolymers having an ethylene content of 25 to 50 mol% and a saponification degree of 96% or more are particularly preferred. By setting the ethylene content to 25 mol% or more, extrusion moldability and blow moldability become good, while by suppressing it to 50 mol% or less, good oxygen barrier properties are exhibited, and the degree of saponification is made to be 96% or more. This improves oxygen barrier properties.

Protective layer (inner layer/outer layer): Crystalline thermoplastic resin with a melting point of 100°C or higher measured with a differential scanning calorimeter, or flow start temperature measured with a Koka type flow tester (load 100, die lllllIφ
A layer made of an amorphous thermoplastic resin with a temperature of 100°C or higher (temperature when the flow becomes 2 rraA/see), such as polypropylene, polystyrene, high-density polyethylene, low-density polyethylene, polyethylene terephthalate, This layer is made of polycarbonate, acrylonitrile-styrene-butadiene copolymer, and modified products or mixtures thereof.

Adhesive resin layer: polyethylene, graft-modified with unsaturated carboxylic acid, unsaturated polycarboxylic acid, or their acid anhydrides;
Modified polyolefins containing polar groups such as polypropylene and ethylene-vinyl acetate copolymers, ethylene-vinyl acetate copolymers and their saponified products, ethylene-ethyl acrylate copolymers, ethylene-acrylic acid copolymers, ethylene-methacrylic acid This layer is made of a copolymer and an ionomer crosslinked with metal ions thereof, or a block copolymer of styrene and butadiene.

Intervening layer: A layer (recycled layer) made of synthetic resins or grinds (scrap crushed products) of synthetic resins constituting the protective layer, oxygen barrier resin layer, and adhesive resin layer, or polyolefins such as low-density polyethylene, high-density polyethylene, and polypropylene. It is a layer consisting of

Water-soluble polymer having an ionizable group: A water-soluble polymer exhibiting an equilibrium moisture content of 20% or more based on absolute dry weight at a temperature of 20°C and a relative humidity of 65% in an isothermal hygroscopic curve. , and an ionizable group, that is, a carboxyl group (-COO-), a sulfonic acid group (-8
Sodium carboxylate group that produces ions such as 03-) (
-COONa), potassium carboxylate group (-COOK
), carboxylic acid ammonium group (-COONH4)
It is a polymer electrolyte having a sodium sulfonate group (-3O3Na), etc.

The water-soluble polymers mentioned above include synthetic polymers, semi-synthetic polymers, and natural polymers.

Synthetic polymer systems include polyacrylates and acrylates with ionizable groups such as carboxylates and sulfonates.
Water-soluble polymers such as acrylamide copolymers, vinyl alcohol-unsaturated carboxylic acid salt copolymers, isobutylene-maleic anhydride copolymers, and polymethallyl sulfonates can be used. In addition, acrylates, methacrylates, etc. obtained by graft polymerizing acrylonitrile, methyl acrylate, methyl methacrylate, acrylamide, etc. to polyvinyl alcohol or ethylene-vinyl alcohol copolymer, and further hydrolyzing with an alkali, etc. A water-soluble polymer obtained by graft polymerization can also be used. Specifically, for example, "Banakayaku B" manufactured by Nippon Kayaku ■,
Examples include sodium polyacrylate such as Panakayaku Bulk NPJ, sodium poly-L-glutamate, etc. In semi-synthetic polymer systems, carboxymethyl cellulose (CMC), which is made by converting cellulose to sodium carboxymethyl, is available.
)and so on. In addition, in the case of natural polymers, sodium alginate (for example, ``Kimitsu Algin'' manufactured by Kimitsu Chemical Industry Co., Ltd.)
)and so on.

Multilayer structure: A structure consisting of two or more layers by coextrusion, etc. Typical examples of the layer structure are shown below.

2 layers・(A:X)/B 3 layers・(A:X)/B/(A:X) (A+X)/B/A 4 layers・A/(D:X)/B/A (A: X )/D/B/A (A:X)/D/B/(A;X) (A;X)/(D:X)/B/A (A:X)/(D:X)/ B/(A:X) 5 layers・(A:
X)/C/B/C/A (A;X)/C/B/C/(A:X) A/(C:X)/B/C/A A/(C:X)/B/ (C:X)/A (A:X)/(C:X)/B/C/(A:X) (A:X
)/(C:X)/B/(C:X)/(A:X) 6 layers・(
A:X)/D/C/B/C/A(A:X)/D/
C/B/C/(A:X)AICD:X)/C/B/CI
A A/D/(C:X)/B/C/A A/D/(C:X)/B/(C:X)/AA/(I):
X)/(C:X)/B/C/AA/(D:X)/(C;
X)/B/(C:X)/A(A:X)/(D:X)/C
/B/C/A(A:X)/(D:X)/C/B/C/(
A:X) (A:X)/D/(niX)/B/C/A(A:
X)/D/(C;X)/B/C/(A:X)(A:X)
/(D:X)/(C;X)/B/C/A(A:X)/(
D:X)/(C:X)/B/C/(A:X)(A:X)
/(D:X)/(C;X)/B/(C:X)/A(A:
X)/(D:X)/(C:X)/B/(C:X)/(A
:X) [However, A is a protective layer, B is an oxygen barrier resin layer,
C is an adhesive resin layer, D is an intervening layer, X is a water-soluble polymer having an ionizable group, and 0 indicates that the above materials are mixed. The mixing ratio of the water-soluble polymer X having an ionizable group contained in the protective layer A and the intervening adhesive resin layer C1 (
Weight ratio) is (A, C, D:X) -99,5:0.
5-60:40, preferably 99:1-75:25
It is desirable to set the ratio within the range of . If the ratio of water-soluble polymer The dispersibility of the mixed resin into the resin becomes poor, and the water-soluble polymer may be present in continuous clumps in the mixed resin, or the water-soluble polymer may be exposed at the interface between the layers, which may actually impair the oxygen barrier properties. It is undesirable because it gets stored away.

Multilayer structure for packaging: In the present invention, the multilayer structure for packaging refers to foods such as mayonnaise, ketchup, edible oils, fruits, vegetables, cooked foods, soups, jams, fruit drinks, or blood, plasma substitutes, and infusions. Bottles, tubes, and bags containing pharmaceuticals, other liquids, viscous materials, and powder materials, and film-like, sheet-like packing materials and sealing materials that are their constituent parts.

[Action of the invention]

The effect of the multilayer structure of the present invention will be explained with reference to FIG. FIG. 1 is for schematically showing the effect of the multilayer structure of the present invention, and the layer structure is: outer layer 1/adhesive resin layer 2 containing a water-soluble polymer having an ionizable group/oxygen barrier layer 2. The adhesive resin layer 3/adhesive resin layer 4 containing a water-soluble polymer having an ionizable group/inner layer 5. The effect is similar for other layer configurations.

As mentioned above, under high-humidity, high-temperature conditions such as in retort processing, the relative humidity inside and outside the container is generally 100%, so the moisture absorption rate of the moisture-resistant resin itself, such as polyethylene, increases, and the first As shown by the dashed arrows in the figure, moisture is absorbed from the inner and outer surfaces of the multilayer structure through the outer layer 1 made of moisture-resistant resin.
It then passes through the inner layer 5 and transfers to the adhesive resin layers 2 and 4. This water contacts the water-soluble polymer 6 having ionizable groups dispersed in the adhesive resin, and dissolves the water-soluble polymer 6 in water. At this time, the water-soluble polymer 6 can absorb water by simply dissolving in water without swelling, so the adhesive resin layers 2 and 4 do not inhibit the absorption. Moreover, the water-soluble polymer 6 having this ionizable group has a hydronium ion (for example, -COO-) as a polymer electrolyte.
Due to the form of the counter ion of H3"O) and its string-like structure, it has excellent water retention properties, and the absorbed water is transferred to the adhesive resin layer 2.
and 4 to reach the oxygen barrier resin layer 3, so the oxygen barrier properties are not impaired.

〔Example〕

Hereinafter, the present invention will be specifically explained by showing Examples and Comparative Examples.

Examples 1 and 2 Adhesive resin C was prepared using the materials shown in Table 1 and the composition shown in Table 2.
After mixing water-soluble polymer X or Xl having an ionizable group with 1, the materials are melt-kneaded in an extruder, and when fed from the extruder to an extrusion die, A1 and C1: Xl, C
The material of 1;
(Ct: X + )/A1 or AI/C+:
Five layers of X2/BT/(C1:

Then, the extruded parisne in a plastic state is placed between split-type molds that have a container-forming cavity inside, and the molds are closed, so that the bottom end of the bottomless parisne is compressed between the molds. After joining and forming the parison into a bottomed shape, pressurized air was introduced into the parison and blow molding was carried out. After the mold was cooled, the molded product was taken out to obtain a multilayer bottle with a capacity of 500 cc as shown in FIG.

The multilayer bottle 7 obtained by the above molding method has a mouth part 8 at the top and a pinch-off part 9 formed by pressure-bonding the parison at the bottom, and is made of material A1 as shown in FIG. Inner layer 5 and outer layer 1, intermediate layer (oxygen barrier resin layer) 3 made of the material of B1, (C1:Xl) or (C1:Xl)
) Adhesive layer (adhesive resin layer) 4 and 2-5 made of the material
It is structured in layers.

Example 3 Using the materials shown in Table 1 in the composition shown in Table 2, adhesive resin C2 was mixed into oxygen barrier resin B, and A
After mixing water-soluble polymer X having an ionizable group into 1, (A1:X,)/(B:C2)/(A1
:Xl) were joined in three layers, and a multilayer bottle with a three-layer structure was obtained using the same method and mold as in Example 1.

Comparative Example 1 A multilayer bottle with a five-layer structure was obtained by molding using the same method and mold as in Example 1 except that a water-soluble polymer having an ionizable group was not mixed.

Comparative Example 2 A multilayer bottle with a five-layer structure was obtained by molding using the same method and mold as in Example 1, except that calcium chloride Y was used instead of the water-soluble polymer having an ionizable group.

Comparative Example 3 The same method as in Example 1 was carried out, except that instead of the water-soluble polymer having an ionizable group, cross-linked polyacrylic acid Z made water-insoluble by cross-linking a water-soluble synthetic resin was used. A multilayer bottle with a five-layer structure was obtained by molding with a metal mold.

In the above examples, the method for incorporating a water-soluble polymer having an ionizable group into the inner layer, outer layer, and adhesive layer is to add the water-soluble polymer to a part of the resin constituting the layer in advance using a mixing roll machine. was melted and kneaded to form a pellet-like masterbatch, and then the oxygen barrier resin and masterbatch were blended, mixed and melted, and uniformly dispersed.

The oxygen permeability (cc/ryf・24 hr) of the multilayer bottles obtained in Examples 1 to 3 and Comparative Examples 1 to 3 above, and the rear opening of the multilayer bottles filled with 80°C hot water are made of aluminum. Table 2 shows the measurement results of oxygen permeability after sealing with a film and retorting at 120° C. for 30 minutes.

Table 2 also shows the measurement results of the transparency (%) of the multilayer bottles obtained in Examples 1 to 3 and Comparative Examples 1 to 3. The transparency was measured using Elma Photoelectric Colorimeter AE-22 manufactured by Elma Optical.
According to J I 5K-6714, the total light transmittance (filter 570 u) was measured using a test piece obtained by cutting out the body wall of a multilayer bottle.

As shown in Table 1 and Table 2, the multilayer bottles obtained in Examples 1 to 3, like the multilayer bottles obtained in Comparative Examples 1 to 3, showed a significant change in oxygen permeability after retorting. Unable to do so.
Furthermore, it had higher transparency than Comparative Example 2 in which calcium chloride was mixed in the adhesive layer. Furthermore, as is clear from the results of Comparative Example 3, when the water-insoluble synthetic resin-based water-absorbing polymer is mixed into the adhesive layer, the effect of the present invention of suppressing the decrease in oxygen barrier properties after retorting cannot be obtained. It turns out that there isn't.

In addition, the layer in which the water-soluble polymer having an ionizable group is mixed is an adhesive resin layer and a protective layer in the above example, but
Considering the decrease in barrier properties due to the elution of water-soluble polymers with ionizable groups and the increase in the absolute amount of water-soluble polymers with ionizable groups to be mixed due to the thickness of the protective layer, the layer to be mixed should be smaller than the protective layer. An adhesive resin layer or an intervening layer is also suitable.

〔Effect of the invention〕

As described above, since the multilayer structure for packaging of the present invention contains a water-soluble polymer having an ionizable group in at least one layer surrounding the oxygen barrier resin layer, oxygen is absorbed over time. In addition to maintaining barrier properties, unlike conventional water-insoluble synthetic resin-based water-absorbing polymers,
The water-soluble polymer having an ionizable group used in the present invention can absorb water simply by dissolving in water without swelling, and moreover, because of the formation of counter ions by the ionizable group and its thread-like structure, It also has excellent water retention and does not release the water that has been absorbed, so it can maintain a high level of oxygen barrier properties even after retorting, and the contents have excellent storage stability. Moreover, there is no problem of separation and precipitation of unreacted substances remaining during the crosslinking reaction when conventional water-insoluble synthetic resin-based water-absorbing polymers are used, so it is highly hygienic and suitable for food or medical use. It can be suitably used for packaging containers.

Further, as described in claim 2, by setting the mixing ratio of the water-soluble polymer having an ionizable group to the synthetic resin constituting the layer to be added at a specific ratio, the dispersibility thereof is improved, and the above-mentioned The effects of the present invention can be further exhibited.

[Brief explanation of the drawing]

FIG. 1 is a partial cross-sectional view of a five-layer structure schematically showing the action of the multi-layer structure of the present invention, and FIG. 2 is a partially broken pressure surface view showing an embodiment of the multi-layer bottle according to the present invention. 1: outer layer, 2: adhesive resin layer, 3: oxygen barrier resin layer, 4: adhesive resin layer, 5: inner layer, 6: water-soluble polymer. Applicant Kyora Ri Co., Ltd. Agent Patent Attorney Masaaki Yonehara

Claims (2)

[Claims] (1) A multilayer structure for packaging having an oxygen barrier resin layer, wherein at least one layer surrounding the oxygen barrier resin layer contains a water-soluble polymer having an ionizable group. Structure. (2) Mixing ratio (weight ratio) of water-soluble polymer X having ionizable groups to synthetic resin A constituting the layer to be added
The multilayer structure for packaging according to claim 1, wherein A:X=99.5:0.5 to 60:40.