JPH0612039U - Multi-layer plastic container - Google Patents

Abstract

(57) [Summary] [Purpose] To obtain a container having a multi-layer plastic laminated structure, which is excellent in gas barrier properties, heat insulating properties, and heat resistance. A multi-layer plastic container in which a heat-resistant resin layer is provided on both sides of a gas barrier layer containing an ethylene-vinyl alcohol copolymer, wherein at least the heat-resistant resin of the outer surface layer of the container is formed of foam. A multi-layered plastic container characterized in that

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention is a container in which a gas barrier layer made of an ethylene-vinyl alcohol copolymer is used as an intermediate layer of a container, a heat-resistant resin is provided on both surfaces of the gas barrier layer, and at least an outer surface layer is formed of a foam. The present invention relates to a multi-layer plastic container having a gas barrier property and a heat insulating property suitable for containing cold-processed foods or high-temperature processed foods such as boiling water and having suitability for containers for retort foods.

[0002]

[Prior art]

 Conventionally, as a multi-layer plastic container, a gas barrier layer containing an ethylene-vinyl alcohol copolymer is sandwiched on both sides with a heat-resistant resin such as polyethylene, polypropylene, or polyester, and is formed into a packaging container such as a bottle or a cup. The product is known.

However, the ethylene-vinyl alcohol copolymer has a reduced gas barrier due to the influence of water absorption, and a container of this type has an ethylene-vinyl alcohol copolymer of an intermediate layer during retort heating sterilization after filling various foods, for example. As a means for preventing the deterioration of the gas barrier performance caused by the absorption of water by the vinyl alcohol copolymer, a method of laminating a low water-absorbing resin (Japanese Utility Model Publication No. 47-23353), or a forced drying after retort heat sterilization treatment. Those which reduce the water content of ethylene-vinyl alcohol copolymers (Japanese Patent Laid-Open No. 60-159043) have been proposed. However, these containers have the drawback of lacking heat insulation. In the latter case, the drying process and the heat energy used at that time are required.

[0004]

[Problems to be solved by the device]

 The present invention solves the above drawbacks by providing an ethylene-vinyl alcohol copolymer having excellent gas barrier performance as an intermediate layer of a laminate used for packaging and a heat-resistant resin foam layer as an outer surface layer. In addition, we have developed a multi-layer plastic container that has both moisture resistance and heat insulation properties by providing a foamed or non-foamed layer of heat-resistant resin on the inner surface layer of the container, and completed the present invention.

[0005]

[Means for Solving the Problems]

 That is, the present invention is a multi-layer plastic container in which a heat-resistant resin layer is provided on both sides of a gas barrier layer containing an ethylene-vinyl alcohol copolymer, and at least the heat-resistant resin of the outer surface layer of the container is a foam. It is a multilayer plastic container characterized by being formed.

[0006]

[Action and Example]

 FIG. 1 shows a multi-layer plastic container having a foam layer 1 made of a heat-resistant resin as an outer layer, a gas barrier layer 3 of an ethylene-vinyl alcohol copolymer as an intermediate layer, and a non-foam 2 made of a heat-resistant resin as an inner layer. 5 is a side sectional view of FIG.

FIG. 2 is a side view of a multilayer plastic container 5 in which a foam layer 1 made of a heat-resistant resin is provided on the outer and inner layers and a gas barrier layer 3 of an ethylene-vinyl alcohol copolymer is provided on the intermediate layer. FIG.

Further, FIG. 3 is a cross-sectional view of the sheet in which the adhesive layer 4 is provided between the gas barrier layer 3 and the foam layer 1 and the non-foam layer 2 of FIG.

In the laminated structure of ethylene-vinyl alcohol copolymer, when the retort sterilization treatment was performed at 120 ° C. for 30 minutes, the ethylene-vinyl alcohol copolymer layer was sandwiched by the heat resistant resin layer. However, it is recognized that the oxygen permeation amount of the packaging container after the sterilization treatment reaches 30 times as much as that of the untreated product in the same container.

Under the severe conditions as described above, the amount of water vapor permeation of the heat resistant resin becomes abnormally large, and the ethylene-vinyl alcohol copolymer layer absorbs a large amount of water and is further exposed to high temperature. It is believed that this causes changes in the internal chemical structure (eg loss of intermolecular hydrogen bonds).

The multi-layer plastic container 5 of the present invention is provided with the foam layer 1 made of a heat-resistant resin on the outer surface layer so that the foam layer 1 made of the heat-resistant resin of the outer surface layer is permeated during, for example, retort sterilization treatment. Moisture absorbed by the ethylene-vinyl alcohol copolymer as the gas barrier layer 3 is effectively diffused or evaporated by the foam layer 1 made of the heat-resistant resin as the outer surface layer.

As a result, the multi-layer plastic container 5 of the present invention effectively recovers the reduction in the gas barrier property of the gas barrier layer 3 made of the ethylene-vinyl alcohol copolymer after the retort sterilization treatment. The process of forcibly drying after the treatment and the heat energy used at that time are unnecessary.

In addition, the multilayer plastic container 5 of the present invention has a heat insulating effect because the outer surface layer is foamed. Therefore, it is possible to omit the foaming step even for a shrinkable base material that requires heat insulating properties of the container.

The ethylene-vinyl alcohol copolymer used in the gas barrier layer 3 of the present invention includes ethylene or ethylene as a main component, a unit containing a small amount of olefin such as propylene, and a vinyl ester unit such as vinyl acetate. Copolymers with vinyl alcohol units obtained by saponification are used.

This ethylene-vinyl alcohol copolymer contains 40 to 80 mol%, particularly preferably 50 to 75 mol% of vinyl alcohol units from the viewpoint of gas barrier property and moisture resistance, The content of the residual vinyl ester unit is preferably 4 mol% or less, more preferably 1 mol% or less.

The ethylene-vinyl alcohol copolymer preferably has a sufficient molecular weight to form a film, and is generally measured at 30 ° C. in a mixed solvent of 85:15 by weight of phenol: water. It is preferable to have a viscosity of 0.01 dl / g or more, especially 0.05 dl / g or more.

The heat-resistant resin used for the foam layer 1 and the non-foam layer 2 of the present invention is a polyester resin, particularly polyethylene terephthalate, polyethylene terephthalate / isophthalate, polytetramethylene terephthalate, polyethylene / tetramethylene terephthalate. And polybisphenol A / terephthalate / isophthalate.

Other heat resistant resins include polyethylene resins such as low, medium or high density polyethylene, isotactic polypropylene, crystalline propylene-ethylene copolymer and crystalline propylene-butene-1 copolymer. Polymers and olefin-based resins such as crystalline polypropylene-butene-1-ethylene terpolymers, ethylene vinyl acetate copolymers, ion-crosslinked olefin copolymers (ionomers), etc. Further, polystyrene resin is advantageously used in terms of economy and mechanical properties.

As the foaming agent used for the heat-resistant resin of the present invention, a chemical foaming agent, a physical foaming agent or various foaming agents are used as long as they do not adversely affect the resin and the contents.

Examples of suitable chemical blowing agents include azodicarbonamide, dinitropentamethylenetetramine, azodiisobutyronitrile and hydrazine series, and examples of physical blowing agents include butane, heptane and Examples include hydrocarbons such as hexane, CFCs such as dichlorodifluoromethane, and nitrogen and carbon dioxide.

The expansion ratio of the foam varies depending on the compounding ratio of the raw material resin and the foaming agent, but the expansion ratio is usually 1.2 to 50 times, preferably 2.0 to 10 times.

The heat-resistant resin layer and the heat-resistant resin of the foam layer 1 and the non-foam layer 2 may contain a nucleating agent such as an inorganic fine powder and a coloring agent, as well as rubbers and carboxylic acid metal salts, if necessary. It can also be added as appropriate.

Next, in the multi-layer plastic container 5 of the present invention, it is more preferable to provide an adhesive layer 4 between the gas barrier layer 3 and the foam layer 1 and the non-foam layer 2 in order to increase the adhesive strength. .

Suitable examples of the adhesive depend largely on the combination of the resin layers. For example, when a polyethylene terephthalate resin is used as the heat-resistant resin to adhere to the ethylene-vinyl alcohol copolymer, various adhesives are used. Copolyester adhesives can be used, for example, copolyesters containing a combination of terephthalic acid and isophthalic acid and / or an aliphatic dibasic acid as an acid component, and ethylene glycol and / or butanediol as a diol component. Copolyesters containing combinations with diols containing long-chain alkylene groups and / or alkyleneoxyalkylen groups; polyesteramides or polyester / polyamide blends containing amide-reversing units and ester-repeat units in the polymer chain Etc. can be mentioned.

Further, when a polyolefin resin is used as the heat-resistant resin to adhere to an ethylene-vinyl alcohol copolymer, an ethylene-acrylic acid copolymer, an ion-crosslinked olefin copolymer, a maleic anhydride grafted polyethylene is used. One or more combinations of maleic anhydride graft polypropylene, acrylic acid grafted polyolefin, ethylene-vinyl acetate copolymer, copolyester, copolyamide and the like can be mentioned.

When manufacturing this type of container, there is the problem of regrind (scrap) reuse. In other words, when manufacturing packaging containers using general plastic materials, burrs due to pinch-off in blow molding of bottles, etc., and regrind (scrap) such as punched scraps in the case of cup molding from sheets or films. Is inevitably generated, and its reuse is usually performed from the viewpoint of resource saving and low cost. The regrind generated in the present invention can be mixed with a heat resistant resin before use.

The thickness of each layer of the multi-layer plastic container of the present invention differs depending on the application, but the thickness of the foam layer 1 and the non-foam layer 2 and the gas barrier layer 3 forming the inner and outer surface layers of the container. The ratio ranges from 2: 1 to 1000: 1, preferably 3: 1 to 500: 1.

Next, the thickness of the adhesive layer 4 interposed between the gas barrier layer 3 and the foam layer 1 and the non-foam layer 2 is at least 1 μm, preferably 5 to 30 μm.

The method for manufacturing a multi-layer plastic container of the present invention is such that, when molding from a sheet or film, it is melt-kneaded by an extruder corresponding to each resin layer and then a multi-layer multi-die such as T-die or circular die. It is possible to employ a method of extruding through or laminating the sheet and film by a lamination method such as dry lamination, sandwich lamination, extrusion coating, heat lamination, extrusion lamination and the like.

Then, the container is molded using the above-mentioned film or sheet, or directly molded from a bottle forming parison, a pipe or the like to obtain a cup-shaped, tray-shaped or bottle-shaped packaging container.

[0031]

[Effect of device]

 The multi-layer plastic container of the present invention removes the water contained in the ethylene-vinyl alcohol copolymer after heat sterilization or hot filling from the heat-resistant resin foam of the outer surface layer more quickly so that the barrier does not require heat treatment. In addition to recovering the deterioration of properties at an early stage and providing heat insulation by using a heat-resistant resin as a foam, it has the suitability for storing high-temperature processed foods such as frozen or chilled foods or hot water, and container suitability for retort foods. It has characteristics suitable for the intended use.

[Brief description of drawings]

FIG. 1 is a side sectional view of a multi-layer plastic container according to the present invention having an outer surface layer provided with a foam layer.

FIG. 2 is a side sectional view of a multi-layer plastic container 5 according to the present invention, in which a foam layer is provided on an outer surface layer and an inner surface layer.

3 is a cross-sectional view of the sheet of the present invention having an adhesive layer between the gas barrier layer and the foam layer and the non-foam layer of FIG. 1;

[Explanation of symbols]

 1 Foam Layer Wall 2 Non-Foam Layer 3 Gas Barrier Layer 4 Adhesive Layer 5 Container

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] September 3, 1993

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Correction target item name] All drawings

[Correction method] Change

[Correction content]

[Figure 3]

[Figure 1]

[Fig. 2]

Claims (1)

[Scope of utility model registration request] 1. A multi-layer plastic container having a heat-resistant resin layer on both sides of a gas barrier layer containing an ethylene-vinyl alcohol copolymer, wherein the heat-resistant resin of at least the outer surface layer of the container is a foam. A multi-layered plastic container characterized by: