JPH02269035A - Soft multilayer film - Google Patents

Abstract

PURPOSE:To perform skin packaging by continuously heat-sealing a film without cooling said film by specifying the elastic recoveries to 50% and 100% tensile elongations at 100 deg.C. CONSTITUTION:A soft multilayer film is constituted at least of a thermoplastic resin layer 1 having rubber elasticity 1, an oxygen barrier layer 2, a heat seal layer 3 and, if necessary, an adhesive layer 4 and the elastic recoveries to 50% and 100% tensile elongations at 100 deg.C thereof are 70% or more in both longitudinal and lateral directions of the film. In order to obtain a film high in elastic recovery, a resin excellent in rubber elasticity is used as a main constitutional material to be set to a thickness 1/3 or more the total thickness and a soft vinyl cloride resin, polybutadiene, a butadiene/styrene copolymer and a mixture of these resins and an olefinic resin are used. By this method, a film excellent in oxygen barrier properties, sealability, flexibility and fittness and suitable for skinpackaging of a system continuously performing vacuum sealing after molding can be obtained.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention involves heating and forming a film using a concave sealer, and then
The present invention relates to a multilayer film for food packaging, which is flexible and has excellent fit to the contents, and is used in a method in which the film is continuously heat-sealed and skinned without cooling.

[Conventional technology]

Conventionally, packaging has been carried out using plastic films, and the most convenient method is to place the contents into a film that has been previously formed into a certain shape, and then seal it on all sides by covering it with another film.

For packaging foods such as processed meat and fish paste products, the method described above is called deep drawing packaging and is carried out using a continuous machine, but in the case of foods, there is no air inside to improve the preservation of the contents. So-called vacuum packaging, in which food is sealed in a vacuum, is generally used.In order to further improve shelf life, it is more effective to use a barrier film that does not allow the passage of oxygen, which promotes food oxidation and bacterial growth. A multilayer film using an ethylene-vinyl alcohol copolymer or a vinylidene chloride resin as an oxygen barrier layer has been considered and widely used.

However, deep drawing vacuum packaging is simple and convenient for items with a fixed shape, but for items with irregular shapes or sliced items arranged in a staggered manner, the size of the molded product becomes larger than the contents. Therefore, when vacuum packaging, the excess formed film wrinkles, which not only looks bad but also causes cranks and pinholes.Furthermore, the film that has been cooled to near room temperature after forming has a poor fit to the contents. Moisture accumulates between the film and the contents, resulting in poor appearance and even faster quality deterioration.

Therefore, instead of forming the film in advance, a method has been considered in which the film is heat-formed using a concave sealer in a vacuum box and then heat-sealed continuously without cooling the film. The fit to the contents was improved due to the close contact. However, since the size of the molded product with the sealer is larger than the content, the difference in film is left over and wrinkles occur.Therefore, as a film characteristic, the film is resistant to molding elongation in the molding sealing temperature range of 100 to 130°C. Rubber elastic molding is large and it is necessary to absorb the excess film, and conventionally used films mainly made of olefin resins and polyamide resins have a problem of poor rubber elasticity and wrinkles. .

[Problem to be solved by the invention]

The present invention aims to improve the rubber elasticity of various resins by adjusting the ratio of elastic return to tensile elongation (hereinafter referred to as elastic recovery rate) in order to create a multilayer film that can eliminate the wrinkles that occur during molding and sealing.
We studied the total elastic recovery rate, formability, and flexibility when multilayered, and completed the research.
The purpose is to provide a food packaging film suitable for a packaging method (hereinafter referred to as skin pack) in which the film is heat-formed with a concave sealer in a vacuum box and then heat-sealed continuously without cooling the film. There is a particular thing.

[Means to solve the problem]

The present invention is composed of at least a thermoplastic resin layer having rubber elasticity as the main constituent materials, an oxygen gas barrier layer, a heat sealing layer, and an adhesive layer as required.
% and the ratio of elastic return to 100% tensile elongation is 70% or more in both the longitudinal and lateral directions of the film.

In order to obtain a film with a high elastic recovery rate, a resin with excellent rubber elasticity is used as the main constituent material and at least one-third of the total thickness, and in the present invention, soft vinyl chloride resin, polybutadiene, butadiene-styrene copolymer, polyurethane , polyester elastomers, saturated thermoplastic elastomers obtained by hydrogenating styrene-butadiene-styrene or styrene-isoprene-styrene block copolymers, and mixtures of these with olefin resins.

As a soft vinyl chloride resin, the average degree of polymerization is 700 to 18.
00 vinyl chloride homopolymer, ethylene-vinyl chloride copolymer with an ethylene content of 10% or less, or ethylene-vinyl acetate-vinyl chloride graft copolymer with an ethylene-vinyl acetate copolymer content of 12% or less; The mixture is 100 parts by weight of the base resin, and the solubilizing agent is 40 to 70 parts by weight.
Parts by weight added or vinyl chloride ratio 70-40
% of ethylene-vinyl acetate-vinyl chloride graft copolymer and urethane-vinyl chloride copolymer can be used.

Softening agents for soft vinyl chloride resin include phthalic acid-based, phosphoric acid-based,
Use known fatty acid-based, polyester-based, trimellitic acid-based, and pyromellitic acid-based materials, and add other known materials such as stabilizers, lubricants, processing aids, secondary softeners/stabilizers, etc. be able to.

In addition, polybutadiene has a crystallinity of 10 to 40% and is 1.2
Syndiotac 1,2-polybutadiene containing 70% or more of bonds and having an average molecular weight of 100,000 or more is used, and preferably has a crystallinity of 15 to 35% from the viewpoint of processability and flexibility.

Butadiene-styrene copolymer has a Vicat softening point of 50℃
The following Schitzer hardness is 55 degrees or less on the D scale, 300%
A material with a tensile stress of 40 kgf/c4 is used.

The polyurethane used is ester-based or ether-based, and preferably has a Schitzer hardness of 55 degrees or less on the D scale.The polyester elastomer has a hard segment that is a condensation unit of terephthalic acid or isophthalic acid and a dihydric alcohol, and terephthalic acid. A saturated polyester is used, which is a block copolymer of a soft segment made by condensation polymerization of acid or isophthalic acid and a dihydric alcohol having an ether bond, and has a melting point of 170°C or less and a Schitzer hardness of 55° or less on the D scale. is preferred.

The saturated thermoplastic elastomer obtained by hydrogenating styrene-butadiene-styrene or styrene-isoprene-ethylene block copolymer has a styrene content of 30% or less, and the olefin resin to be mixed with it is polypropylene, ethylene-α-olefin. Copolymers are preferred.

Vinylidene chloride resin is a binary or multi-component copolymer of 60 to 9 parts of vinylidene chloride and an unsaturated monomer such as vinyl chloride, alkyl acrylate, acrylic acid, acrylonitrile, etc. Solubilizers, stabilizers, etc. can be added.

The ethylene-vinyl alcohol copolymer used has an ethylene content of 32 to 47 mol% and a Young's modulus of 130 kgf/-8 or less.

Ethylene resins for the sealing layer include low density polyethylene, linear low density polyethylene, ethylene-vinyl acetate copolymer, ethylene-α olefin copolymer, ethylene-acrylic acid copolymer, ethylene-alkyl acrylate copolymer, Ionomer resin etc. can be used.

The adhesive layer is made of resin such as low density polyethylene, linear low density polyethylene, ethylene-α-olefin copolymer, ethylene-propylene copolymer, high-density polyethylene, ethylene-vinyl acetate copolymer, polypropylene, etc., and acrylic acid, Monobasic unsaturated fatty acids such as methacrylic acid or dibasic unsaturated fatty acids such as maleic acid, fumaric acid, itaconic acid, and those obtained by chemically combining these anhydrides, vinyl acetate content 15% More than ethylene-
Vinyl acetate copolymer, ethylene-maleic anhydride copolymer, and ethylene-methyl methacrylate-glycidyl acrylate terpolymer can be used alone or in combination of two or more.

The multilayer film of the present invention can be manufactured using known methods such as coextrusion and dry lamination, but in order to impart balanced elastic recovery to MD and TD, coextrusion inflation method or coextrusion may be used. It is preferable that the film produced by the T-die method be biaxially stretched or uniaxially stretched in the transverse direction by a known method to obtain a film with small anisotropy of physical properties.

[For production]

Since the film of the present invention is mainly composed of a resin with rubber elasticity, it has a high rate of elastic recovery in the film sealing temperature range, and even when the contents are in an irregular shape, the softened film remains elastic during skin pack. It shrinks and fits along the contents, making it possible to produce skin pack packaging that looks good and does not cause wrinkles or film walnuts. However, among the layers having these functions, especially the oxygen gas barrier layer, the above-mentioned vinylidene chloride resin or ethylene-vinyl alcohol copolymer is used. Since these have poor rubber elasticity, the elastic recovery rate of the total film is significantly reduced, but this can be compensated for by setting the ratio of the rubber elastic resin to 60% or more.

In addition, although there are cases where it is not possible to increase the ratio of rubber elastic resin due to productivity, economical and manufacturing technology issues, it is possible to use soft vinyl chloride resin and polybutadiene, which have particularly excellent elastic recovery power among rubber elastic resins. Even with a ratio of 30% to 50%, a multilayer film with good elastic recovery can be obtained.

〔Example〕

The films of Examples 1 to 4 and Comparative Examples 1 to 3 were made by melting the resin using five extruders, forming a film by T-die coextrusion, and then continuously stretching 20% in the transverse direction at 80°C. was manufactured. In addition, the films of Example 5 and Comparative Example 4 were produced by a coextrusion inflation silane method using three extruders, and the film of Example 6 was produced by a T-die coextrusion method using five extruders. did. The thickness of all the obtained films was 100μ.

Table 1 shows the composition and evaluation results of each film.

Details of each evaluation are as follows.

1. Cut the elastic recovery rate sample into strips with a width of 10 m and a length of 150 m.
Mark the marked lines at 0 kaku intervals.

Using an autograph, stretch the sample at a speed of 5001/min. When the distance between the marked lines has expanded to 150 - (at 50% stretching), move the autograph backwards and change the distance between the marked lines when the load becomes 0 to It was measured using the following formula.

When stretched to 100%, the distance between the marked lines was calculated to be 200 m5. The measurement was carried out after the sample was left in an atmosphere of 100° C. for 5 minutes, and the measurements were carried out in the longitudinal and lateral directions of the film.

2 Oxygen gas permeation amount measurement MOCON company 0XTRAN method 3, skin back method Omori Machinery Co., Ltd. F V-6300 machine as a sealer and mold 180 x 135 cm, depth 12 spaces, four corners 1O
The R-shaped product was installed under the conditions of a sealing temperature of 130°C, a sealing time of 1 second, and a vacuum time of 4.0 seconds, and was skin-packed using the films of Examples and Comparative Examples as lid materials, and it was examined whether wrinkles remained. .

The bottom material is 120μ hard vinyl chloride sheet and 30μ ethylene-vinyl acetate copolymer with 10% vinyl acetate content.
The contents are dry laminated with a thickness of 2
Three pieces of sliced ham with a diameter of 100 square meters were arranged in a staggered manner.

No wrinkles left on O-pack products X Wrinkles appear on the bag item The resins used are as follows.

・Soft vinyl chloride resin: PVC average degree of polymerization 1300 Vinyl chloride homopolymer 100 parts by weight Solubilizer 50 parts by weight polyester with a molecular weight of 1800 Epoxidized linseed oil 5 parts by weight Polybutadiene: PBD density
0.9) g/cj Vicat Softening Point 52℃ Crystallinity 2
0% shear hardness (D scale) 40 degrees, butadiene-styrene copolymer: BS density 0
．． 91g/cd Vicat softening point 47℃ 300% tensile stress 30 kgf/d Sitzur hardness (D scale) 31 degrees Polyurethane: PU ester system
Density 1.19 g/d Shear hardness (D scale) 50 degrees / Acid-modified ethylene-vinyl acetate copolymer: AD-1 Manufactured by Mitsubishi Yuka ■ Modic E300 H / Acid-modified ethylene-α-olefin copolymer AD-II Mitsui Petrochemical Co., Ltd. Atmer AT469 C/vinylidene chloride resin I: pvDc-vinylidene chloride 7
Copolymer density: 8 parts by weight, 22 parts by weight of vinyl chloride Density: 1.65 g/cd Melting point: 140°C Vinylidene chloride resin 1: PVDC-II 92 parts by weight of vinyl chloride phosphoric acid Copolymer density: 8 parts by weight of acrylic acid 1.70g/d Melting point 155℃ ・Ethylene-vinyl alcohol copolymer ■: EVOH
-1 Ethylene content 44 mol% Melting point 164°C Young's modulus 110 kgf/ma” Ethylene-vinyl alcohol copolymer ■: EVOH-If Ethylene content 44 mol% Melting point 164°C Young’s modulus 150 kgf/1III ethylene-vinyl acetate copolymer Combined (vinyl acetate content 25%): EVA-25 Evaflex P250C manufactured by Mitsui Dupont Polychemical ■ Ethylene-vinyl acetate copolymer (vinyl acetate content 17%) jEVA-17 Evaflex manufactured by Mitsui Dupont Polychemical ■ V527-4 Ethylene-methyl methacrylate copolymer (methyl methacrylate content 18%): EMMA-18 Sumitomo Chemical (acryph) W H303 ionomer
: [HIMILAN 1856 manufactured by DuPont Mitsui Polychemical ■ [Effects of the invention] According to the present invention, oxygen gas barrier properties, sealing properties, flexibility,
It is possible to obtain a film that has excellent fit and is suitable for skin pack packaging that is continuously vacuum-sealed after forming.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a multilayer film showing an embodiment of the present invention.

Claims (1)

[Scope of Claims] 1. Consisting of at least a thermoplastic resin layer having rubber elasticity as the main constituent materials, an oxygen gas barrier layer, a heat sealing layer, and an adhesive layer if necessary, 50% and 100% at 100°C A flexible multilayer film characterized in that the ratio of elastic recovery to tensile elongation (elastic recovery rate) is 70% or more in both the longitudinal and lateral directions of the film. 2. Claim 1, wherein the oxygen gas barrier layer is the central layer, the outer layer is a thermoplastic resin layer having rubber elasticity, and the inner layer is a heat-sealing layer, which are laminated via an adhesive layer as necessary. The flexible multilayer film described. 3. Claim 1 or 2, wherein the oxygen gas barrier layer is a vinylidene chloride resin or an ethylene-vinyl alcohol copolymer having a Young's modulus of 130 kgf/mm^2 or less
The flexible multilayer film described in Section 1. 4. Claim 1, wherein the thermoplastic resin having rubber elasticity is a soft vinyl chloride resin or 1,2-polybutadiene with a crystallinity of 10 to 40% and an average molecular weight of 80,000 or more.
The flexible multilayer film according to any one of Items 2 and 3.