JP2870031B2 - Transparent heat-resistant container - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a transparent heat-resistant container made of a gas-barrier multi-layer plastic, and more particularly, to the above-mentioned transparent food material having excellent transparency without shrinkage or deformation due to boiling sterilization. Related to heat-resistant containers.

[Prior Art] A multilayer plastic container having a gas barrier layer is excellent in ease of use, lightness, cost, storage stability and the like, and is widely used as a food packaging container. Preserving the food filled in such a packaging container, usually after filling the contents for distribution at normal temperature, a sterilization step is provided, as a sterilization method is performed at 110 ~ 120 ° retort sterilization, Heat sterilization such as boiling sterilization performed at 80 to 95 ° C is common.

In particular, fruits such as oranges, kiwis and pineapples, and foods such as honey beans and jelly have a low pH or a high sugar content. Therefore, the above sterilization is preferably performed by boil sterilization at 95 ° C or less. Furthermore, for the containers used for these foods, there is a great demand for the transparency of glass-like in order to improve the commercial properties, and containers that do not lose the transparency to the heat sterilization as described above have been desired. .

As a plastic material having such glass-like transparency, polystyrene, polycarbonate, and polyester may be mentioned as typical examples, but these have inferior heat resistance and disadvantages such as high cost.
It was difficult to use such a food container.

[Problems to be Solved by the Invention] Among the plastic materials having glass-like transparency, the most versatile plastic materials include polyester, particularly polyethylene terephthalate.

However, since the container made of unstretched polyethylene terephthalate has poor heat resistance as described above, it undergoes deformation and shrinkage when subjected to boil sterilization at about 95 ° C., further crystallization proceeds, and the transparency of the glass-like material is not lost. , Causing whitening.

Accordingly, an object of the present invention is to provide a skeleton made of a multilayer gas barrier plastic using transparent and highly versatile polyethylene terephthalate. It is an object of the present invention to provide a transparent heat-resistant container which can maintain the food properties and further maintain the long-term preservability of food.

Means and Action for Solving the Problems The present inventors have made intensive studies in view of the above problems, and as a result, the object of the present invention is to provide a thermoplastic resin on both surfaces of a saponified ethylene-vinyl acetate copolymer layer. It has polyethylene terephthalate layers (1) and (2) via an adhesive resin layer, and further has polyarylate layers (3) and (4) on each of the polyethylene terephthalate layers (1) and (2). This has been achieved by providing a transparent heat-resistant container, which is a multilayer container, wherein each layer of the container satisfies the following formulas (I) to (III).

(However, x ₁ polyarylate layer thickness (3) ([mu] m),
x ₂ polyarylate layer (4) thickness ([mu] m), y ₁ denotes the thickness of the polyethylene terephthalate layer (1) ([mu] m), y ₂ is the thickness of the polyethylene terephthalate layer (2) ([mu] m), 1 represents the total thickness (μm) of the transparent heat-resistant container. Hereinafter, the present invention will be described in more detail.

The polyarylate constituting the polyarylate layer used in the present invention refers to an aromatic polyester composed of terephthalic acid, isophthalic acid and bisphenol A, and includes a polymer alloy obtained by blend modification with polyethylene terephthalate. Polyarylate, like polyethylene terephthalate, has glass-like transparency, has a deformation temperature of 100 ° C. or higher, and has high heat resistance such that transparency is not impaired at all by heating by boiling sterilization .

In addition, since polyarylate has melt adhesion to polyethylene terephthalate without an intervening adhesive layer, it is suitable to be disposed on an upper layer of polyethylene terephthalate and used as a material for imparting heat resistance to polyethylene terephthalate as in the present invention.

In the present invention, as described above, polyarylate is used as a material for imparting heat resistance to polyethylene terephthalate, and the ratio of the thickness of the polyarylate to the total thickness of the container is adjusted as in the above formula (I), thereby making it possible to sterilize boil. Deformation and shrinkage can be improved. That is, if the sum of the thicknesses of both polyarylate layers is less than 10% of the total thickness,
Deformation and shrinkage are not sufficiently improved.

In addition, the present inventors, regarding the problem of clouding due to crystallization of polyethylene terephthalate such as boil sterilization, transparency reduction such as whitening, the configuration and arrangement of the polyarylate layer, the saponified ethylene-vinyl acetate copolymer layer. It has been found that the thickness of the polyarylate and polyethylene terephthalate layers on each side of the two sides influences. That is, the crystallization of polyethylene terephthalate proceeds at a heating temperature equal to or higher than the glass transition point, but when the water content of the surroundings and polyethylene terephthalate itself is low, the crystallization rate is low, for example, in a dry condition of about 95 ° C. There is not much transparency below. However, under high humidity, that is, when the water content of polyethylene terephthalate is high, the crystallization speed is high, and clouding and whitening occur immediately after boiling sterilization at about 95 ° C. For this reason, in the present invention, a non-crystalline polyarylate layer is disposed on both outermost layers to form a water vapor barrier layer, thereby suppressing the moisture content of the polyethylene terephthalate layer to a range that does not cause whitening by boiling sterilization. .

The water content of the polyethylene terephthalate layer is proportional to the amount of water vapor entering through the polyarylate layer, that is, inversely proportional to the thickness of the polyarylate layer, and is inversely proportional to the diffusion of water vapor, that is, the thickness of the polyethylene terephthalate layer.

The present inventors have conducted experiments on this relationship, and as a result of further intensive studies, it has been found that if the above-mentioned formulas (II) and (III) are satisfied, it is possible to prevent the polyethylene terephthalate layer from fogging and whitening during boil sterilization. Was found.

The thicknesses of the polyethylene terephthalate layer and the polyarylate layer are arbitrary as long as they satisfy the formulas (I), (II) and (III), respectively.
m, 10 to 500 μm.

In the present invention, the above (I), (II) and (II)
The relationship shown in equation I) is the relationship between the body, bottom,
It is enough if you are satisfied with the part where you observe the contents,
It is not always necessary that the flange portion, the mouth portion, and the like serving as the sealing portion of the container satisfy these relationships.

The polyethylene terephthalate constituting the polyethylene terephthalate layer used in the present invention is a polyester containing ethylene terephthalate as a main constituent unit and containing at least 80 mol% of an ethylene terephthalate unit, and a dicarboxylic acid other than terephthalic acid or a glycol other than ethylene glycol. Components can be included.

The saponified ethylene-vinyl acetate copolymer used in the present invention has an ethylene content of 20 to 60 mol% and a saponification degree of 90%.
% Or more, and the thickness of the layer is preferably 5% or more.
200200 μm. Further, as the thermoplastic adhesive resin used in the present invention, an olefin-based acid-modified product or an ester-based acid-modified product are preferably exemplified, and the thickness of the layer is arbitrary, for example, 2 to 100 μm. .

As a method for obtaining the transparent heat-resistant container of the present invention, a laminated sheet is obtained by, for example, an extrusion lamination package, a co-extrusion lamination method, a co-extrusion sheet preparation method (for example, a feed block method or a multi-manifold method) and the like. Examples thereof include methods obtained by molding by vacuum molding, pressure molding, or a thermoforming method using them in combination.

The shape of the transparent heat-resistant container is not particularly limited, and may be any of a tray shape, a cup shape, a bowl shape, and the like. Further, after filling the food or the like into the transparent heat-resistant container of the present invention, as a method of sealing the mouth, winding of a metal lid such as Al, heat fusion of a plastic molded lid, heat fusion of a plastic multilayer laminate film, It can be used in any method such as heat fusion of a metal foil or a plastic laminated film including a metal vapor deposition layer, or a method in which these are combined.

The transparency of the transparent heat-resistant container of the present invention is preferably 10 or less in haze value.

Examples Example-1 U polymer (U 8000) as polyarylate (PAR)
(Manufactured by Unitika) and NEH 2070 (manufactured by Unitika) as polyethylene terephthalate (PET).
Admer AT 469C (manufactured by Mitsui Petrochemical Industries, Ltd.) as a thermoplastic adhesive resin (Tie) and EVAL EP-F 101A as a saponified ethylene-vinyl acetate copolymer (EVOH)
(Manufactured by Kuraray Co., Ltd .: ethylene content 32 mol%, saponification degree 99.6%), each of which was co-extruded by a feed block method to prepare a multilayer sheet shown below.

PAR / PET / Tie / EVOH / Tie / PET / PAR Each layer thickness (100μ) (350μ) (25μ) (50μ) (25μ)
(350μ) (100μ) (total thickness 1000μ) Using the obtained multilayer sheet, a circular bowl-shaped container with a metal cover that can be tightened by the vacuum pressure forming method with plug assist (drawing ratio 0.6, internal volume 230cc) Molded. The container was glass-like transparent (haze value 5.0).

Also, was confirmed the thickness distribution of the vessel, the total thickness in the thinnest part (l) is 300μ, the innermost layer, the thickness of the outermost layer of the PAR (x _1, x ₂₎ Any 30μ, thickness of the PET The values (y ₁ , y ₂ ) were all 100 μm.

The molded container was filled with water, wound and immersed in a 95 ° C. warm bath for 30 minutes. After that, it was sufficiently cooled with tap water and the condition of the container was confirmed.
Glass-like transparency was also maintained (haze value 5.
0).

In Example 1, each of Example 2, Comparative Example 1, Comparative Example 1 was carried out in the same manner as in Example 1 except that the thickness of each layer constitution or the polyarylate layer and the polyethylene terephthalate layer were changed as shown in Table 1. 2 and Comparative Example-3 were performed. As a result, as shown in Table 1, in Comparative Example 1, shrinkage occurred entirely, and in Comparative Examples 2 and 3, all or part of the container was whitened. Further, the molded container obtained in Example 1 was filled with orange and pineapple syrup, rolled up, and boiled at 95 ° C for 30 minutes at 25 ° C, 65 ° C.
After storing under 3% RH environment and opening after 3 months and 6 months respectively, the color tone and sensory evaluation of the contents
There was almost no change after the boil.

[Effects of the Invention] As described in detail above, the present invention makes it possible to obtain
Even without boil sterilization for minutes, without deformation and shrinkage,
A transparent heat-resistant container capable of maintaining the transparency of glass-like and further maintaining the long-term preservability of food can be provided, and the marketability of the product has been improved.

Continuation of front page (72) Inventor Kiyoshi Sawada 1-5-1, Taito, Taito-ku, Tokyo Toppan Printing Co., Ltd. (72) Inventor Yasuhiko Yamano 1-5-1, Taito, Taito-ku, Tokyo Toppan Printing Co., Ltd. (56) References JP-A-2-162040 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B32B 1/00-35/00

Claims (1)

(57) [Claims] 1. A saponified ethylene-vinyl acetate copolymer layer having polyethylene terephthalate layers (1) and (2) on both sides via thermoplastic adhesive resin layers, respectively, and further comprising the polyethylene terephthalate layer (1). And (2) each having a polyarylate layer (3) and (4) on the multilayer container, wherein the thickness of each layer of the container is represented by the following formula (I):
A transparent heat-resistant container characterized by satisfying (III). (X ₁ + x ₂ ) /l≧0.1 (I) x ₁ y ₁ ≧ 2000 (II) x ₂ y ₂ ≧ 2000 (III) (where x ₁ is the thickness (μm) of the polyarylate layer (3),
x ₂ polyarylate layer (4) thickness ([mu] m), y ₁ denotes the thickness of the polyethylene terephthalate layer (1) ([mu] m), y ₂ is the thickness of the polyethylene terephthalate layer (2) ([mu] m), l represents the total thickness (μm) of the transparent heat-resistant container. )