JPH0429845A - Plastic container - Google Patents

Abstract

PURPOSE:To make gas barrier characteristics excellent when retort treatment is not performed and to get rid of putrefaction, detrioration and discoloration of a content just after retort heating and sterilization treatment and after storage for a long time by providing steam diffusion-preventing layers with a specified steam permeability in such a way that they sandwiches a gas barrier layer so as to bringing them into contact with the gas barrier layer and providing an amorphous polyamide layer with a specified quantity of heat of fusion of crystallite and a specified glass transition temp. between the steam diffusion-preventing layer and an inner surface layer and an outer surface layer. CONSTITUTION:Steam diffusion-preventing layers 7 and 8 each with a steam permeabil ity measured at 40 deg.C of smaller than 60g/m<2>.24 hr are placed in such a way that they sandwiches a gas barrier layer 3 consistion of an ethylene-vinyl alcohol copolymer so as to bring them into contact with the gas barrier layer and substantially amorphous polyamide layers 4 and 5 each with a quantity of heat of fusion of crystallity measured by means of a differential scanning calorimeter of smaller than 2.0cal/g and a glass transition temp. measured by means of a calorimeter of 80-180 deg.C are provided between the steam diffusion-preventing layers and an inner surface layer 1 and an outer surface layer 2 wherein each a propylene polymer is a main ingredient.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a plastic container useful for food. More specifically, as the intermediate layer, substantially ethylene-
The present invention relates to a plastic container provided with a gas barrier layer made of a vinyl alcohol copolymer, and the object is to obtain a plastic container with excellent gas barrier properties.

[Conventional technology]

In recent years, olefin polymers (for example,
Plastic molded containers using a saponified ethylene-vinyl acetate copolymer as a gas barrier layer are suitable for food preservation due to their extremely excellent gas barrier properties. Currently expanding.

[Problem to be solved by the invention]

However, when the conventionally started molded container body is filled with contents (e.g., soup) and sealed, and then subjected to retort heat sterilization treatment (e.g., at a temperature of 125°C for 30 minutes), the heat sterilization process The saponified product of the ethylene-vinyl acetate copolymer in the intermediate layer absorbs moisture, resulting in a significant decrease in gas barrier properties and problems such as spoilage, deterioration, and discoloration of the contents.

From the above, the present invention does not have these drawbacks (problems), that is, it not only has excellent gas barrier properties when not retorted, but also retains the contents even after retort heat sterilization treatment and even after long-term storage. To obtain a thermoplastic resin container that is free from rot, deterioration, and discoloration.

[Means and effects for solving the problems] According to the present invention, these problems can be solved by providing a gas barrier layer substantially made of an ethylene-vinyl alcohol copolymer and a gas barrier layer sandwiched therebetween. This is a multilayer plastic container formed by a laminate of inner and outer surface layers of a thermoplastic resin mainly composed of a propylene-based polymer, and is sandwiched in contact with the gas barrier layer. Measured water vapor permeability is 60g/m
There is a water vapor diffusion prevention layer having a heat of fusion of less than 2.24 hr, and between the water vapor diffusion prevention layer and the inner surface layer and the outer surface layer, the heat of crystal fusion measured by a differential scanning calorimeter is 2.24 hr.
and a substantially amorphous polyamide layer having a glass transition temperature of less than 0 cal/g and a glass transition temperature of 80°C to 180°C as measured by the calorimeter. I can do it. The present invention will be explained in detail below.

(A) Propylene polymer In the present invention, the propylene polymer constituting the inner surface layer and the outer surface layer is a propylene homopolymer or a random polymer containing ethylene or other α-olefin containing at least 70% by weight of propylene. Alternatively, a block copolymer may be used, and when a container is obtained by thermoforming, such as vacuum forming, a good product can be obtained by mixing 1.0 to 50% by weight of an ethylene polymer with a propylene polymer. The melt index (measured according to JIS K-7210 under conditions 14, hereinafter referred to as rMI (1) J) of these propylene polymers is 0.005 to 8.
0g/10min, 0. O1 to 60 g/10 min is desirable, and propylene polymers of 0.01 to 40 g/10 min are particularly preferred. M I (1) is 0.0
When using a propylene-based polymer of less than 0.05 g/10 min,
The molding processability to obtain the container is poor, making it impossible to obtain a good container.
Furthermore, if a propylene-based polymer exceeding 80 g/lO is used, the impact resistance of the container will be weak and the container will not be suitable for practical use.

As the propylene polymer in the present invention, one to which an inorganic filler described later may be added may be used.

In this case, when forming a container and filling the container with food, from the viewpoint of food hygiene, a propylene polymer that does not contain an inorganic filler is added inside the inner layer of the propylene polymer that contains an inorganic filler. It is preferable to provide a layer of.

The inorganic filler is generally one widely used in the fields of synthetic resins and rubber.

These inorganic fillers are preferably inorganic compounds that do not react with oxygen and water, and that do not decompose during crosstalk or molding.

Examples of the inorganic filler include oxides of metals such as aluminum, copper, iron, lead, nickel, magnesium, calcium, barium, zinc, zirconium, molybdenum, silicon, antimony, and titanium, and hydrates (hydroxides) thereof; It is broadly classified into compounds such as sulfates, carbonates, and silicates, their double salts, and mixtures thereof. Representative examples of the inorganic filler are described in Japanese Patent Application No. 124481/1981.

Among these inorganic fillers, those in powder form have a diameter of 3
It is preferably 0 ρ or less (preferably 10 − or less). In addition, for fibrous materials, the diameter is 1 to 500 mm (preferably 1 to 500 mm).
800 μs), and the length is 0.1 to [i, 0+on+
(preferably 0.1 to 5 mm) is desirable.

Further, it is preferable that the plate-shaped one is 30 tlrr1 or less (preferably 10 mound or less). Among these inorganic fillers, those in the form of flat plates (flake) and those in the form of powder are particularly suitable.

The composition ratio (content ratio) of the inorganic filler in the inorganic filler-containing propylene polymer is at most 70% by weight, preferably 5 to 65% by weight, and particularly preferably 5 to 60% by weight. .

If the composition ratio of the inorganic filler in the inorganic filler-containing propylene polymer exceeds 70% by weight, the impact resistance of the resulting container will be significantly reduced, resulting in a container that is not suitable for practical use.

(B) Ethylene-ruvinyl alcohol copolymer Furthermore, in the present invention, ethylene-acetic acid is a starting material for the ethylene-vinyl alcohol copolymer constituting the intermediate layer interposed between the inner surface layer and the outer surface layer. The copolymerization ratio of ethylene in the vinyl copolymer is 15 to 60 mol%, and 1
5 to 55 mol% is preferred. In particular, the degree of saponification is 80
% or more, preferably 85% or more, especially 90%
The above is preferable.

Furthermore, the melt index (according to JIS K-7210, measured at a temperature of 210°C and a load of 2.18 kg, hereinafter referred to as rML(2)J) is usually 0.1 to 50 g/
10 minutes, preferably 0.1 to 20 g/10 minutes, particularly preferably 0.5 to 20 g/10 minutes.

M I (2) is 0. If an ethylene-vinyl alcohol copolymer having an If/less than 10 minutes is used, moldability is not good when producing a multilayer laminate described later. On the other hand, 20g/10
If the ethylene-vinyl alcohol copolymer is used in excess of 50%, the moldability will be poor when producing a multilayer laminate, and a good laminate will not be obtained.

(C) Polyamide Furthermore, the substantially amorphous polyamide used between the gas barrier layer and the inner surface layer and/or outer surface layer in the present invention refers to the heat of crystal fusion measured by a differential scanning calorimeter. is less than 2 cal/g. The heat of crystal fusion is 2ca
If it exceeds l/g, the melting point of the amide resin is high, and when the molding temperature is raised to the melting temperature to mold this polyamide resin, the propylene polymer and ethylene-vinyl alcohol copolymer may be thermally degraded. There is. Further, it is important that the glass transition point measured with the same calorimeter is 80°C to 180°C. If a polyamide resin having a glass transition point of less than 80° C. is used, the barrier properties will be significantly reduced when the plastic container of the present invention is heat-treated for retort heat sterilization or the like.

On the other hand, when the temperature exceeds 180°C, moldability is significantly reduced.

The polyamide contains acids such as adipic acid, azelaic acid, terephthalic acid, isophthalic acid, cyclohexane-1,
4-dicarboxylic acids, etc., and as amines, 3'-dimethyl dicyclo-hexylenemethane, 4,4'-diamino-
Dicyclohexylene propane, isophorone diamine, and as lactams, caprolactam, laurolactam,
Furthermore, the isocyanate can be obtained by polycondensing 4,4'-diphenylmethane diisocyanate and tolylene diisocyanate. This polyamide resin is produced by two methods: a melt polymerization method and a solution polymerization method using these polycondensation components.

The solution polymerization method is basically a pressurized melt polymerization method similar to the production of normal nylon-6 and nylon-66.
In the case of polyamide resins, aromatic dicarboxylic acids are often used as the raw dicarboxylic acid, and the polymerization temperature is relatively high, so there is a problem that the polymer produced during melt polymerization tends to be colored or gelled. Therefore, various methods have been developed, such as adding phosphorus-based compounds during polymerization to prevent coloring and gelation, and performing two-step polymerization consisting of a pre-condensation step and a post-condensation step using terephthalic acid diester as a starting material. It is desirable to take some measures.

Furthermore, as the solution polymerization method, a decarboxylation condensation reaction between a diisocyanate and a dicarboxylic acid may be used.

In manufacturing the container of the present invention, 2
In order to prevent deterioration of barrier properties after long-term storage of about 18 months, a water vapor diffusion prevention layer is interposed between the polyamide layer and the ethylene-vinyl alcohol copolymer layer (gas barrier layer) as shown below. It is necessary.

(D) Water vapor diffusion prevention resin In addition, in the present invention, the water vapor diffusion prevention resin used to protect the barrier properties during long-term storage and bond the barrier layer and the polyamide layer to each other is an olefin-based heavy duty resin. It is obtained by graft polymerizing an unsaturated carboxylic acid or a derivative thereof to the polymer. This graft polymerization is generally carried out in the presence of a radical initiator as described below.

The olefin polymer may be an ethylene homopolymer, ethylene and carbon atoms having at most 12 carbon atoms (preferably 3 carbon atoms).
~8 pieces) with α-olefin (copolymerization ratio of α-olefin is usually 20% by weight or less, preferably 15% by weight or less, preferably 10% by weight or less) and ethylene as the main component ( Generally 65% by weight or more, preferably 70% by weight
(weight% or more) monomers having polar groups [e.g.
Examples include copolymers with vinyl acetate, (meth)acrylic acid or alkyl esters thereof, and the propylene-based polymers described above.

Melt index [JIS
Measured under conditions 4 according to K-7210, hereinafter rM I
(3) J] and propylene polymer M I
(1) is generally 0. O1~100g/1
0 minutes, preferably from 0.02 to 50 g/10 minutes, particularly preferably from 0.05 to 50 g/10 minutes. When a propylene polymer or an ethylene polymer having M I (1) or M I (3) below the lower limit is used, it is difficult to uniformly carry out the graft reaction. on the other hand,
If the amount exceeds the upper limit, the strength of the resulting adhesive resin will be poor, and the adhesive strength will also be poor.

Among these olefinic polymers, low-density and high-density ethylene homopolymers, propylene homopolymers, copolymers of ethylene and propylene, and copolymers of ethylene or propylene with other α-olefins are preferred. .

The unsaturated carboxylic acids used in producing this graft copolymer are broadly classified into monobasic unsaturated carboxylic acids and dibasic unsaturated carboxylic acids. - The basic unsaturated carboxylic acid usually has at most 20 carbon atoms (preferably 15 or less), and representative examples thereof include acrylic acid and methacrylic acid. Furthermore, the number of carbon atoms in dibasic unsaturated carboxylic acids is generally at most 40.
(preferably 30 or less), typical examples of which include maleic acid, itaconic acid, nadecic acid and fumaric acid. Furthermore, examples of derivatives include esters, acid anhydrides, amides, imides, and metal salts of these monobasic unsaturated carboxylic acids and dibasic unsaturated carboxylic acids. Among these derivatives, for amides and imides, the number of carbon atoms in the amide group and imide group is usually at most 20 (preferably 15 or less). Further, the total number of carbon atoms in the ester is generally at most 40, and preferably 80 or less. Further, the metal of the metal salt generally includes alkali metals and metals of Group 2 of the periodic table, and representative examples thereof include sodium, potassium, zinc, magnesium, and calcium. Representative examples of these derivatives include methyl acrylate, dityl acrylate, butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, glycidyl acrylate, glycidyl methacrylate, and maleic acid. Monoethyl ester, maleic acid diethyl ester, fumaric acid monomethyl ester, fumaric acid dimethyl ester, itaconic acid monomethyl ester, itaconic acid diethyl ester, acrylamide, methacrylamide, maleic acid monoamide, maleic acid diamide, maleic acid-N-monoethylamide , maleic acid-N,N-diethylamide,
Maleic acid-N-monobutyramide, maleic acid N,N
-dibutylamide, fumaric acid monoamide, fumaric acid diamide, fumaric acid-N-monoethylamide, fumaric acid-N
, N-diethylamide, fumaric acid-N-monobutylamide, fumaric acid N-N, N-dibutylamide, maleimide, N-butylmaleimide, N-phenylmaleimide, sodium acrylate, sodium methacrylate, potassium acrylate, methacrylate Examples include acid potassium.

In addition, the decomposition temperature of the radical initiator used in this graft polymerization with a half-life of 1 minute is usually 100°C or higher, and 1
A temperature of 05°C or higher is preferred, and a temperature of 120°C or higher is particularly preferred. Representative examples of suitable radical initiators include dicumyl peroxide, benzoyl peroxide, di-tert-butyl peroxide, 2,5-dimethyl-2,5-di(tert-butyl-peroxy), etc. xane, 2,5-dimethyl-2,5-di(tertiary-butylperoxy)hexane-3, lauroyl peroxide,
Examples include organic peroxides such as tertiary-butyl peroxybenzoate.

The proportions of the unsaturated carboxylic acid and its derivatives and the radical initiator to 100 parts by weight of the olefin polymer are generally as follows.

For unsaturated carboxylic acids and derivatives thereof, the total amount thereof is 0.1 to 5.0 parts by weight, and 0.05 to 3.0 parts by weight.
0 parts by weight is preferred, and 0.1 to 2.0 parts by weight is particularly preferred. If the total amount of unsaturated carboxylic acids and derivatives used is less than 0.01 parts, the adhesion of the graft copolymer will be insufficient. On the other hand, if the amount exceeds 5.0 parts by weight, not only is there a risk that decomposition or crosslinking reactions will occur during the production of the graft copolymer, but the adhesiveness will actually decrease.

In addition, in the case of a radical initiator, the amount is 0.001 to 1.0 parts by weight, and 0.001 to 1.0 parts by weight. Preferably 1.0 parts by weight, especially 0
．． 01 to 0.5 parts by weight. When the proportion of the radical initiator used is less than 0.0 parts by weight, the modification effect is poorly exhibited and a long period of time is required to complete the modification.

On the other hand, if it exceeds 1.0 parts by weight, excessive decomposition or crosslinking reaction may occur, which is not preferable.

The graft copolymer of the present invention can be produced by known means for producing this type of graft copolymer.

A typical production method includes the olefinic polymer, unsaturated carboxylic acid or its derivative, and radical initiation in a solvent such as an aromatic hydrocarbon compound such as xylene or toluene, or an aliphatic hydrocarbon compound such as hexane or heptane. The olefinic polymer, the unsaturated carboxylic acid or its derivative, and the radical initiator are mixed in advance under essentially non-crosslinking conditions, and the resulting mixture is mixed in a screw extruder, Banbury, etc. Production methods include melt mixing using mixers, kneaders, and other mixers commonly used in the field of synthetic resins;
The latter method is preferred from the point of view of economy.

In the latter case, the temperature conditions for modification are appropriately selected in consideration of the deterioration of the olefin polymer, the decomposition of the unsaturated carboxylic acid or its derivative, the decomposition temperature of the organic peroxide, etc. ~350℃, 150℃
-350 degreeC is desirable, especially 150-300 degreeC is suitable.

Furthermore, in the present invention, this resin is ASTM P1
The water vapor permeability measured at a temperature of 40℃ using the method of 249 is 6.
It is necessary to have such a thickness that it is less than 0g/r+f·24hr. In the case of a water vapor diffusion prevention layer that only has a water vapor permeability of 60g/rd・24hr or more,
Alternatively, if a water vapor diffusion prevention layer is not provided, after retort processing, especially when stored under high temperature and high humidity, the moisture trapped in the polyamide layer will diffuse into the barrier layer, resulting in a loss of barrier properties. make worse.

On the other hand, the resin used for the water vapor diffusion prevention layer is placed between the inner surface and the polyamide and the outer surface and the polyamide.
Each may be interposed for the purpose of improving adhesiveness.

(E) Container and method for manufacturing the same The container of the present invention will be explained in more detail below with reference to the drawings.

FIG. 1 is a cross-sectional view of a typical container body of the present invention filled with contents 12 and sealed by a lid 14. Further, FIG. 2 is a partially enlarged sectional view of the bottom wall portion 11 of the sectional view shown in FIG. 1. Incidentally, the container body has a flange portion lO as seen in FIG. The container body consists of an inner surface layer made of a propylene polymer, an outer surface layer 2, and a gas barrier layer 3 made of an ethylene-vinyl alcohol copolymer interposed between these layers. Polyamide layers 4 and 5 are present between the gas barrier layer 3 and the outer surface layer 2 and the gas barrier layer 3, respectively. Furthermore, a water vapor diffusion prevention layer 7 is present between the gas barrier layer 3 and the polyamide layers 4 and 5. and 8 exist.

Further, an inner surface layer 1, an outer surface layer 2 and a polyamide layer 4
and 5, an adhesive layer 6.9 may be provided between them to improve adhesion.

The gas barrier layer (ethylene-vinyl alcohol copolymer layer 3) maintains practical gas barrier properties under normal conditions, so the thickness is generally 5 to 200 tons! n, particularly preferably 10 to 180.

In addition, the inner surface layer 1 and the outer surface layer are 50 μs to 2,
On+*, especially 60tln to 1.9mm
is desirable. Further, the thickness of the amorphous nylon layer interposed between the outer surface layer and the barrier layer and between the inner surface layer and the barrier layer is 10 to 800 t1m, particularly 20 to 800t1m.
200 stores is preferable.

A sectional view of the plastic container of the present invention is shown in FIG. 1, and a partially enlarged sectional view of the sectional view is shown in FIG.

In the container shown in FIG. 1, the thickness of the flange part 10, body wall part 13, and bottom wall part 11 is generally 0.3 to 2.
．． It has 0 fins.

To manufacture the container of the present invention, any molding method practiced in the field of general olefin polymers (such as a sheet method, an injection molding method, a blow molding method, etc.) may be applied. Typical examples of this molding method include forming an inner surface layer, a gas barrier layer, an outer surface layer, a water vapor diffusion prevention layer, or each of these layers and an adhesive resin layer into thin products (films, sheets) used in these fields. A laminated sheet is manufactured by forming a sheet or film in advance using a forming machine and adhering each of these thin materials. Then, a container may be manufactured from this sheet by vacuum forming, pressure forming, or press forming. Alternatively, the sheet may be produced by co-extrusion sheet molding of the inner surface layer, gas barrier layer, outer surface layer, water vapor diffusion prevention layer, or these layers and the polymer (resin) constituting the adhesive resin layer. good.

As shown in FIG. 1, after the container body thus manufactured is filled with the contents 12, the lid portion 14 is heat-sealed to the flange portion 10 for sealing. Lid part 14
is a laminate that forms a molded container body, for example, a laminate in which the inner surface layer of the lid 14 has a metal foil (for example, aluminum foil) on the outside of a resin that can be heat-sealed to the inner surface layer 1 of the container body. But that's fine.

The sealed container thus produced is subjected to retort heat sterilization (steam or heat sterilization) under conditions of time and temperature necessary to ensure complete commercial sterilization of the contents 12 (e.g. , for 30 minutes at a temperature of 125°C).

[Examples and comparative examples]

Hereinafter, the present invention will be explained in more detail with reference to Examples.

In addition, in the Examples and Comparative Examples, the oxygen permeability of each sample was measured using an oxygen permeation measuring device [Modern Control Co., Ltd.
(Model 0X-TRAN10150) manufactured by U.S.A.) was measured at a measurement temperature of 23° C., a relative humidity inside the container of 90%, and a relative humidity outside the container of 60%.

The water vapor permeability of the water vapor diffusion prevention resin was measured using a water vapor permeation measuring device [manufactured by Modern Control Co., Ltd. (USA), model PERM].
ATRAN-W TWIN) at a measurement temperature of 40℃,
Measurement was performed under conditions where the relative humidity was 9B%RH.

The types, manufacturing methods, physical properties, etc. of the propylene polymer, ethylene-vinyl alcohol copolymer, water vapor diffusion prevention resin, and amorphous polyamide used in Examples and Comparative Examples are shown below.

[(A) Propylene polymer]

As a propylene polymer, M I (1) is 1. og/
Propylene homopolymer [hereinafter [PP(A)]
], Ml(1) is 0.5 g/10 min, and the ethylene copolymerization ratio is 18% by weight.
85 parts by weight of propylene block copolymer [hereinafter referred to as rPP(B)J] and 0.2 g/1 M I (3)
Using an extruder with a screw diameter of 65 mm, 15 parts by weight of an ethylene homopolymer (hereinafter referred to as "PE (1)") with a density of 0.955 g/cd and a resin temperature of 220 ° C. The composition produced while kneading [pellets,
Hereinafter referred to as "composition (■)"], 60 parts by weight of the PP (B), 10 parts by weight of PE (1), and an average particle size of 5.0 μm.
m and has an aspect ratio of about 60.
A composition [pellets, hereinafter referred to as "composition (■)"] and PP (B
) 70 parts by weight of talc with an average particle size of 5.0 μm was melt-kneaded in the same manner to produce a composition [pellets, hereinafter referred to as composition (m)].

[(B) Ethylene-vinyl alcohol copolymer] Also,
A saponified product obtained by saponifying an ethylene-vinyl acetate copolymer having an ethylene copolymerization ratio of 38 mol% as an ethylene-vinyl alcohol copolymer [saponification degree 99%, M I (2) 4.0 g /10
, hereinafter referred to as rEVOHJ].

[(C) Water vapor diffusion prevention resin]

Furthermore, M I (1) is 0 as a water vapor diffusion prevention resin.
．． 100 parts by weight of a propylene homopolymer at a rate of 5 g/10 minutes, 0.3 parts by weight of maleic anhydride, and 0.2 parts by weight of benzoyl peroxide were triblended in advance for 5 minutes using a Henschel mixer. The resulting mixture was heated to a resin temperature of 220°C using a single screw extruder (diameter: 40mm).
Modified polypropylene 1 obtained by melt-kneading at a temperature of °C: M I (1) 25 g/1
0 minutes] was used.

Using a T-die film forming machine with a screw diameter of 40 m/nφ and a die width of 400 mm, at an extrusion temperature of 230°C,
Films with various thicknesses from μ to 120μ were molded and their water vapor permeability was measured. The results are shown in Table 1.

[(D) Amorphous polyamide resin]

In addition, as an amorphous polyamide resin, a mixture of terephthalic acid, trimethylhexamethylene diamine, and water is first heated to 110°C, a demethyl alcohol reaction is performed to remove methyl alcohol, and the resulting aqueous solution is heated to 240°C.
The mixture was subjected to pressure melt condensation polymerization at a temperature of 25 atmospheres to obtain a low polymer as a precursor. The low polymer was subjected to polycondensation using an extruder under reduced pressure at a temperature of 260°C. The obtained polymer [hereinafter referred to as "P A (a) J]" was heated to 25°C using dimethyl formaldehyde as a solvent.
The particle size average molecular weight measured by the method was approximately 20,000, and the heat of crystal fusion was 0.2 cal/g. Moreover, the glass transition point was 148°C. P as amorphous polyamide resin
A I used (a). For comparison, polycapramide produced by ring-opening polymerization of ε-caprolactam [glass transition point 48°C, heat of crystal fusion 16
cal/g% or less rPA(b)J] was used.

Examples 1 to 9, Comparative Examples 1 to 8 As shown in Fig. 2, the inner and outer surface layers were a layer mainly composed of a propylene polymer whose type and thickness are shown in Table 2, and the intermediate layer was a layer with a thickness as shown in Table 2. The gas barrier layer (EVOH layer) made of ethylene-vinyl alcohol copolymer (EVOH) shown in Table 2, the thickness and type between the inner surface layer and the EVOH layer and between the outer surface layer and the EVOH layer, respectively. A polyamide layer is provided, and furthermore, EVOH
A water vapor diffusion prevention layer is provided between each layer and the polyamide layer, and a water vapor diffusion prevention resin layer is provided between the polyamide layer and the inner and outer surface layers with the thickness shown in Table 2. Nine-layer multilayer sheet manufacturing equipment (manufactured by Toshiba Machine Co., Ltd.)
A sheet was formed using a feed block type extruder (5 extruders with a screw diameter of 40 mm) (however, the values for the thickness of each layer in Table 2 indicate the thickness at the multilayer sheet stage).

Each sheet having such a configuration was molded to a diameter of 7 mm using a vacuum forming machine (manufactured by Asano Research Institute, model: F L V441).
6.8+nus depth is 45mm and capacity is 156cc
A container was manufactured. Each container obtained in this way was filled with water so that 5% of the total content was a space, and an aluminum foil with a thickness of 20 mm was interposed so that the thickness of both sides was 60 mm.
The temperature of the lid made of propylene polymer is 20℃.
Ring sealing was performed for 3 seconds at 0°C and a pressure of 2.5 kg/cd to produce a container filled with water. Each of the resulting containers was placed in a retort pot (manufactured by Daiwa Seikasha, pneumatic type,
The sample was placed in a retort processing apparatus) and subjected to retort processing at a temperature of 121'C for 20 minutes. The retort processing capacity and the oxygen permeability of the unretorted container were measured using an oxygen permeation measuring device. The results obtained are shown in Table 3.

It is clear from Table 3 that the barrier properties of the plastic containers of the present invention not only hardly change before and after retort treatment, but also that the barrier properties hardly change even when stored for a long period of time under high humidity.

Chapter 1 Table No. table ■) cc/1 atmosphere of oxygen.

24h "・pcs 30℃.

After being stored for 3 months at 90% RH, the plastic container of the present invention exhibits the following effects.

In other words, it not only has excellent gas barrier properties, but also
This is a thermoplastic resin container that does not cause spoilage, deterioration, or denaturation of the contents even if stored for a long time after retort heat sterilization.

The container obtained by the method of the present invention can be used in a wide variety of ways to achieve the above-mentioned effects. Typical uses are shown below.

(1> Various processed seasoning food containers (2) Various liquid food containers (3) Various food containers (4) Various industrial chemical containers

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of containers manufactured in Examples and Comparative Examples. Moreover, FIG. 2 is a partially enlarged sectional view of FIG. 1. 1...Inner surface layer 2...Outer surface layer 3...
Gas barrier layer 4.5... Polyamide resin layer 6.9... Adhesive resin layer 7.8... Water vapor diffusion prevention layer 10... Flange 12... Contents (water) 14... Lid 11...Bottom wall part 13...Body wall part

Claims (1)

[Claims] Formed by a laminate of a gas barrier layer made essentially of an ethylene-vinyl alcohol copolymer and inner and outer surface layers of a thermoplastic resin mainly composed of a propylene polymer, sandwiching the gas barrier layer. a multi-layered plastic container, in which there is a water vapor diffusion prevention layer having a water vapor permeability measured at 40° C. of less than 60 g/m^2·24 hr, which is sandwiched in contact with the gas barrier layer; and the heat of crystal fusion measured by a differential scanning calorimeter is less than 2.0 cal/g between the water vapor diffusion prevention layer and the inner surface layer and the outer surface layer,
and a substantially amorphous polyamide layer having a glass transition point of 80° C. to 180° C. as measured by the calorimeter.