JPS60158056A - Multilayer structure for packaging - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a multilayer structure for packaging that has excellent oxygen barrier properties, moisture proof properties, and good deep drawing formability, and is particularly suitable for use in molded containers for food packaging. The present invention provides a multi-layered structure.

Since ethylene vinyl alcohol copolymers have excellent gas barrier properties such as low oxygen permeability, various food packaging materials are made using this as a barrier layer. However, the oxygen barrier properties of ethylene vinyl alcohol copolymers are a function of humidity, and as the humidity increases, the amount of oxygen permeation increases.
When the relative humidity is 60% RH or more, the amount of oxygen permeation increases rapidly, so there is a drawback that the oxygen barrier property is extremely reduced under high humidity. For this reason, it is necessary to form moisture-proof inner and outer layers on both sides of the central layer made of ethylene vinyl alcohol copolymer, and for example, polyolefins such as polypropylene or polyethylene are provided as the inner and outer layers. There is. Although the oxygen barrier property of such a multilayer structure is slightly improved, it is insufficient, and the moldability is poor, so that it is unsatisfactory for producing containers by deep drawing or the like.

As a result of various studies on ways to eliminate the influence of the oxygen barrier properties of the above-mentioned ethylene vinyl alcohol copolymer on humidity and to obtain a packaging material with excellent moldability, the inventors surprisingly found that ethylene vinyl alcohol copolymer By covering both sides of the polymer with a layer of hard vinyl chloride,
It has been discovered that it is possible to eliminate the influence of humidity, maintain the high oxygen barrier properties of an ethylene vinyl alcohol copolymer, and obtain a multilayer film with good deep drawability.

In the present invention, the center layer made of ethylene vinyl alcohol copolymer preferably has a thickness of 30 μm or more in order to have sufficient oxygen barrier properties, and if it is too thick, it is disadvantageous in terms of economic efficiency and processing suitability. 100μm
It is desirable that the thickness be as follows.

The thickness of the hard vinyl chloride placed on both sides of the center layer made of ethylene-vinyl alcohol copolymer is set to 3.5 mm to prevent the center layer from being affected by humidity and to obtain sufficient deep drawing formability.
The thickness is preferably 00 to 500 μm.

In the multilayer structure for packaging according to the present invention, it is essential that both the inner and outer layers are made of hard vinyl chloride.
standards of the PVC Food Sanitation Council and the standards of the PVC Food Sanitation Council
) A material that meets the standards and is suitable for dust and food packaging, and a vinyl chloride having an average degree of polymerization of about 600 to 800 is used.

Further, the ethylene vinyl alcohol copolymer used in the present invention has an ethylene content of 25 to 50 mo1% and a saponification degree of 90 degrees or more.

The multilayer film of the present invention can be easily produced by a lamination method or a coextrusion method.

In addition, polyethylene (PE) and ethylene vinyl acetate copolymer (EVA) are added to the outer side of the hard vinyl chloride layer on one side.
), ionomer (IONOMER), etc. can be provided with a layer having excellent heat sealability.

Incidentally, an isocyanate-based adhesive or the like may be used to laminate the center layer of ethylene vinyl alcohol with the inner and outer layers of hard vinyl chloride.

Furthermore, an isocyanate-based adhesive or the like can also be used between the hard vinyl chloride layer and a layer with excellent heat-sealing properties that is optionally formed outside the hard vinyl chloride layer.

In the case of coextrusion, ethylene-vinyl acetate copolymer (E
VA), low density polyethylene (LDPE), high density polyethylene (HDPE), polypropylene (PP),
An adhesive in which a functional group such as a carboxyl group is introduced into a non-polar polyolefin such as EVA is used.

The multilayered structure obtained as described above can be processed into a deep drawing machine or the like to make containers for food packaging. The top lid of the container may be made of the same material as the container, or may be made of other barrier material such as aluminum foil.

The multilayer structure for packaging according to the present invention has excellent moldability, and
When a deep-drawn container or the like is produced, a container with good wall uniformity can be obtained. Furthermore, even under high humidity conditions, the oxygen barrier properties of the ethylene vinyl alcohol copolymer in the center layer are maintained, and food products with excellent preservability can be obtained.

Examples and comparative examples showing that the products of the present invention are excellent in moldability and food storage stability will be described below.

Examples and Comparative Examples EVAL E made by Kuraray was used as the ethylene vinyl alcohol (EVAL), and this was used as the center layer, and inner and outer layers of hard vinyl chloride (abbreviated as PVC) were provided on both sides. A multilayer structure was created using an extrusion method.

The PVC used was one with a formulation suitable for food packaging that complied with PL standards, contained a PVC impact strengthener, a processing aid, etc., and had an average degree of polymerization (P) of 700.

The thickness of PvC is 350 μm for both the inner and outer layers, and the EVAL
The thickness of the center layer was 75 μm and 50 pm. Further, as the adhesive between EVAL and 270, a maleic anhydride grafted product of EVA, for example, ER-200V-3 manufactured by Showa Denko ■ was used.

The two types of films created in this way are applied to a deep-drawing machine to create a deep-drawn container as a molded cup, filled with miso, the space replaced with nitrogen gas, and made of the same material as the container body. It was sealed with the top lid.

In addition, as a comparative example, a container was made in the same manner as in the example, using polypropylene (pp) or polystyrene (pst) as one or both of the inner and outer layers provided on both sides of the center layer of EvAL, and filled with miso.

Regarding the inventive product and comparative product created as described above,
Table 1 shows the moldability and food storage stability of the filled miso based on the discoloration test. Discoloration test of miso) is 4 at 30℃.
The samples that had been left for 0 days were examined.

From the results shown in Table 1, it can be seen that the product of the present invention is superior to the comparative product in that both moldability and storage stability are good.

Claims (2)

[Claims] (1) A multilayer structure for packaging, characterized by comprising an inner and outer layer made of hard vinyl chloride on both sides of a central layer made of ethylene vinyl alcohol copolymer. (2) The core layer made of ethylene vinyl alcohol copolymer has a thickness of 30 to 100 μm, and each of the inner and outer layers made of hard vinyl chloride has a thickness of 300 to 500 μm. Multilayer structure for packaging.