JPS5914945A - Laminated film - 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 provides a laminated film, more specifically a laminated film suitable for packaging foods, etc., which has high gas barrier properties and maintains high heat-sealing strength even after high-temperature treatment with hot water. There are suggestions.

BACKGROUND ART Conventionally, heat-resistant food packaging has been put into practical use that can enclose cooked food and heat it with hot water or the like before eating. These food packagings have gas and water vapor barrier properties, heat resistance,
Heat-sealability, packaging machine suitability 1 Mechanical toughness, printability, etc. are required. In order to satisfy such performance, many laminated films have been proposed, and some of them have been put into practical use.

Conventionally, the common design concept of these heat-resistant laminated films for food packaging has been to arrange a barrier material layer with high barrier properties against gas, water vapor, etc. in the middle layer, and to arrange a reinforcing material on the surface side. The reason is.

If the barrier material layer is exposed on the surface, it may become moist due to hot water sterilization treatment, etc., and the barrier properties may deteriorate, and the barrier material layer may become wet during bag making, packaging, transportation, etc.
This is because damage occurs during handling, leading to a decrease in barrier properties, and the storage performance of the enclosed product is likely to decrease.

Specific examples of laminated films based on conventional design concepts are disclosed in JP-A No. 49-5187. )) The layer A is a reinforcing material, the layer B is a barrier material, and the layer 0 is a sealant material. but,
Although this laminated film can satisfy the above-mentioned required performance to some extent, it cannot necessarily be said that the performance is sufficient. In other words, the barrier layer B and the sealant layer C are arranged in contact with each other, and the sealant layer O and the reinforcing material A11l are not directly bonded to each other, so the reinforcing material does not affect the sealing strength and the sheet strength depends on the strength of the barrier material layer. This had the disadvantage that the high strength of the reinforcing material could not be utilized.

This invention was made in view of the above circumstances, and its gist is that the polyacrylonitrile film is composed of three layers laminated in this order: a polyacrylonitrile film, a reinforcing film, and a sealant material, and the polyacrylonitrile film has a high acrylonitrile content. The laminated film is a biaxially stretched film of a polymer having a weight of 85 mm or more.

In this laminated film, the sealant material and the reinforcing film are arranged in direct contact with each other, so the strength of the reinforcing film directly contributes to the sealing strength, and the sealing strength is high and maintains high sealing strength even when exposed to high temperatures such as hot water. Polyacrylonitrile films (hereinafter simply referred to as PAN films) have high gas and water vapor barrier properties, and even when the surface is exposed to moisture, the gas barrier properties do not deteriorate, and the laminated film exhibits high barrier properties. In addition, it has appropriate rigidity and slipperiness, has excellent mechanical properties for bag making and packaging machines, and is highly processable, as well as excellent transparency, gloss, and printability.

The PAN film used in this invention is a biaxially stretched film of a polymer having an acrylonitrile content of 85 or more.

If the acrylonitrile content is less than 85%, the above-mentioned required performance cannot be satisfied, and it is more preferably 90% or more.

Must be biaxially oriented film. Unstretched or uniaxially stretched films cannot satisfy the required performance, and are particularly poor in mechanical strength and prone to damage such as pinholes, making them unsuitable for disposing on the outer layer of a laminated film. The thickness is 5 μ to 50 μ, and if it is less than 5 μ, the barrier properties are insufficient, and if it is more than 50 μ, it is not required for practical use and is undesirable as it increases the cost. More preferably it is 10-60μ. For the PAN film, an acryloni(5) tolyl homopolymer or copolymer is used, and in the case of a copolymer, the comonomer is usually selected from acrylic acid ester, vinylidene chloride, vinyl acetate, styrene, etc. The biaxial stretching ratio is usually 0.4 in the vertical and horizontal directions.
~2.5, and the thickness of the film obtained by stretching is 0.4 or less, preferably 0.2 or less relative to the original film thickness,
For example, Special Publication No. 46-7458 or Special Publication No. 54
Obtained by the method described in No.-15069. Also PA
It is more preferable that the N film is heat-treated in advance to have a hot water resistance shrinkage rate of 2-2 or less and a boiling water treatment shrinkage rate of 5% or less for 30 minutes.

As the reinforcing film, polyester, nylon, polypropylene film, etc. can be used. Among them, biaxially stretched films of polyester and nylon have excellent heat resistance and mechanical strength, and are used as heat-resistant laminated films for food packaging.
Suitable for improving heat resistance and sealing strength. Its thickness is 5-30μ, more preferably 10=20μ.

(4) Sealant materials include polyethylene, polypropylene, ionomer, polyethylene-propylene copolymer, polybutene-1, polyethylene-vinyl acetate copolymer, polyethylene-acrylic acid ester copolymer, etc.
It can be selected from those conventionally used as heat sealing materials. Its thickness is 20-100μ, more preferably 25-70μ.

In producing this laminated film, conventional means such as dry, wet, or extrusion lamination methods are selectively employed to bond and laminate each layer. It goes without saying that, if necessary, an adhesive or anchor agent such as urethane-modified polyester, polyethyleneimine, or organic titanate may be applied to the interface, or corona treatment or oxidation treatment may be applied.

This will be explained below with reference to examples.

Example 1 96wt% acrylonitrile and 4wt% methyl acrylate
% copolymer (molecular weight 80,000) wet process! ! ! ! Apply dry laminating adhesive (urethane-modified polyester resin) to a thickness of about 2μ on one side of a PAN film (25μ completely heat-set, hot water shrinkage rate 0.8 inch) obtained by biaxially stretching with dry heat. A biaxially oriented polyester film (PET) (12μ, manufactured by Toyobo Co., Ltd.) was pressure-bonded and laminated using a heated roll at 70°C.

Next, another dry laminate adhesive (urethane adhesive) is roll-coated to a thickness of about 2μ on the polyester film surface of this laminate film, and an unstretched polypropylene film (OFF) (5oμ) is applied on top of this. were crimped and laminated in the same way. As shown in Table 1, even after boiling and hot water treatment for 50 minutes, this three-layer laminate film showed no significant deterioration in its gas barrier properties, transparency, mechanical strength, etc. As a comparative example, a six-layer laminate film of polyester/adhesive/polyacrylonitrile/adhesive/#i-stretched polypropylene was prepared using the same film as above, and a polyvinylidene chloride coated 2/7) axially oriented polyester ( A two-layer laminate film of 12μ) (KPIT)/adhesive/unstretched polypropylene (50μ) was produced in the same manner and compared. As a result, no difference was observed in transparency or gas barrier properties, but in the heat seal strength test, breakage of the polyacrylonitrile film was observed between the layers of the PAN film and polypropylene film in the comparative example. However, KInT coated with polyvinylidene chloride was devitrified by hot water treatment and the 08 gas permeability decreased.

/ / / / / 2, ~″′, /” 7,′ 7/ /2″,,,,z /″′ (8) Example 2 Acrylonitrile/ with different acrylonitrile contents
Six types of polyacrylonitrile films (25μ) obtained by forming films using a methyl acrylate copolymer in the same manner as in Example 1 and biaxially stretching were prepared using the same polyacrylonitrile/polyester/unstretched film as in Example 1. A three-layer laminate film of polypropylene was produced and evaluated in the same way.

The results were not satisfactory, as shown in Table 2, when the acrylonitrile content was low, the gas barrier properties deteriorated and the film contracted significantly after hot water treatment.

Table 2

Claims (1)

[Claims] (1) Consisting of three layers: polyacrylonitrile film, reinforcing film, and sealant material, laminated in order.
A laminated film characterized in that the polyacrylonitrile film is a biaxially stretched film of a polymer having an acrylonitrile content of 85 weight or more.