JPH0686109B2 - Composite film laminate for retort sterilization packaging materials - Google Patents

Description

TECHNICAL FIELD The present invention relates to a composite film laminate for retort sterilization packaging materials.

2. Description of the Related Art As is well known, in recent years, the number of pre-prepared foods and retort sterilized foods that are premised on normal temperature distribution and normal temperature long-term storage has been increasing in recent years from the viewpoint of consumer convenience and energy saving. Especially curry as a retort food,
Many different foods are used. Also, in the heat sterilization and cooking of packaged foods, there is a tendency that high-temperature short-time treatment is carried out so as not to impair the taste, flavor, and appearance of the food contents, and polypropylene film is used as the innermost sealant layer. At present, the composite film used is becoming the mainstream in this field.

Since it can be stored and distributed in a cold region of 0 ° C. or lower even though it is distributed at room temperature and stored for a long time at room temperature, the composite film is required to have heat resistance as well as cold resistance. From such a request, the film includes an ethylene-propylene block copolymer, or a blend of an ethylene-propylene random copolymer with ethylene-propylene copolymer rubber (EPR), or an ethylene-propylene copolymer rubber with a propylene homopolymer. Films composed of blends of (EPR) are used. That is, these films include a film based on an ethylene-propylene block copolymer and an ethylene-propylene copolymer rubber (EP
R) is a blended film.

On the other hand, retort food packaging materials can be roughly classified into transparent packaging materials and opaque packaging materials. Generally, a transparent packaging material has a constitution of polyethylene terephthalate film / unstretched nylon film / polypropylene film, and in many cases, ethylene-propylene copolymer rubber is blended with ethylene-propylene random copolymer or propylene homopolymer as polypropylene film. The film formed by the above method is used.

The opaque packaging material generally has a constitution of polyethylene terephthalate film / aluminum foil / polypropylene film, and the polypropylene film is formed by blending ethylene-propylene copolymer rubber with ethylene-propylene random copolymer or propylene homopolymer. Both films formed and films formed from ethylene-propylene block copolymers have been used.

That is, ethylene-propylene copolymer rubber is
A transparent film formed by blending with a propylene random copolymer or a propylene homopolymer can be used as a packaging material in both transparent and opaque fields.
However, an opaque film formed by molding an ethylene-propylene block copolymer can be used as a packaging material in an opaque field, but cannot be used in a field requiring transparency.

Problems to be Solved by the Invention As described above, the conditions of the retort are shortened at high temperature and shorter time, but today, even when processing a large amount of products, the condition of the retort is further shortened at high temperature and short time. It's starting. However, ethylene, which is currently used in the largest amount,
A transparent film formed by blending a propylene copolymer rubber with an ethylene-propylene random copolymer causes fusion between the films at a high retort temperature, which is a serious obstacle in practical use or appearance. Furthermore, a film formed from an ethylene-propylene block copolymer having poor transparency is also used as an ethylene-propylene copolymer rubber.
It has been the actual situation until now that a film formed by blending with a propylene random copolymer cannot be used as a transparent packaging material for high temperature short time sterilization.

Therefore, as described above, a film formed by molding a conventional ethylene-propylene block copolymer or a film formed by blending an ethylene-propylene copolymer rubber with an ethylene-propylene random copolymer is a high temperature short film that meets the needs of the times. Since it cannot be used as a transparent packaging material for time sterilization, the present inventors have conducted earnest research to develop a transparent packaging material composite polypropylene film capable of sterilization at high temperature for a short time and its laminate from such a viewpoint. Of.

MEANS FOR SOLVING PROBLEMS AND EFFECTS THEREOF According to the present invention, (i) polypropylene or ethylene-
A first layer composed of a propylene random copolymer, (ii) a second layer composed of a blend of an ethylene-propylene block copolymer, a rubber component in the block copolymer and a polyolefin polymer having good compatibility, and iii) A composite film laminate for a retort sterilization packaging material is provided which comprises a transparent base film and a third-layer composite film comprising a polypropylene homopolymer or an ethylene-propylene random copolymer.

The first and third layer films of the composite film of the present invention are formed from polypropylene and an ethylene-propylene random copolymer. Although it is not specified as polypropylene, MFI (JIS-K-67
According to 58, it is preferably 0.5 to 20) measured at 230 ° C. As the ethylene-propylene random copolymer,
From the viewpoint of heat resistance against retort treatment, it is necessary that the melting point is 145 ° C. or higher, and the concentration of ethylene forming the copolymer is desirably 3% by weight or less.

The second layer film of the composite film of the present invention is formed from a blend of an ethylene-propylene block copolymer, a rubber component in the block copolymer and a polyolefin resin having good compatibility. As the ethylene-propylene block copolymer, the higher the ethylene concentration is, the better in order to maintain the cold resistance, but it is preferably 20% by weight or less in terms of molding and extraction of the solvent.

The present inventors have found that the transparency of the film can also be improved by blending the ethylene-propylene block copolymer with a rubber component in the block copolymer and a polyolefin resin having good compatibility.

That is, according to the knowledge of the present inventors, the ethylene-propylene block copolymer was found to have rubber components scattered therein as well as on the surface. The particle size of this rubber component is 0.8
.About.3 .mu..phi. And the wavelength of light larger than 0.4 to 0.65 .mu. Causes refraction and reflection of the light passing through the film, and reduces the amount (energy) of the light passing through the entire film. For this reason, the transparency (internal haze) of the ethylene-propylene block copolymer film was not always sufficient. That is, such a phenomenon can be eliminated by reducing the particle size of the rubber component. In order to reduce the particle size by polymerization, a method such as reducing the molecular weight of the rubber component can be considered, but reducing the molecular weight of the rubber component decreases the low temperature impact resistance of the film together with the molecular weight. It is not preferable because it is unsuitable for use. Therefore, the present inventors have conducted a study to reduce the particle size of the rubber component without lowering the molecular weight of the rubber component, and as a result, the compatibility with the rubber component is better than that of the surrounding propylene polymer, and It has been found that such a purpose can be achieved by melt blending a polymer having a viscosity lower than that of the rubber component with the ethylene-propylene block copolymer.

Preferred examples of the blending component include low density polyethylene having MI of 5 or more, high density polyethylene, ethylene-propylene copolymer rubber, ethylene-vinyl acetate copolymer and the like. The melt blending method may be as simple as passing through an ordinary extruder. The blending ratio of the blending component to the ethylene-propylene block copolymer is not particularly limited, but for example, an example of blending a high-flow low-density polyethylene with an ethylene-propylene block copolymer is SEM (scanning electron microscope). Observed in the photograph, the rubber component particle size decreases with increasing blending amount, and when the blending amount is 10% by weight or more, the rubber component particle size averages 0.4 μφ below the wavelength of light.
It was confirmed that It is best to blend up to an amount equal to the amount of rubber in the ethylene-propylene block copolymer. However, when blended more than that, the transparency tends to decrease. This is because the amount exceeds the amount that can be mixed into the rubber component, and it is considered that the surplus polymer remains in the polypropylene phase and has poor compatibility with polypropylene, and thus the transparency of the polypropylene part main body is reduced.

As the base film used for the transparent base film, for example, a transparent and high-gloss film such as a plain film such as a PET film, a nylon film, an Eval film or a composite film of two or more kinds of films can be used. The composite film composed of the first layer, the second layer, and the third layer can be compounded with a base film via an adhesive by an arbitrary method such as a dry laminating method.

In this way, the present inventors have found that polypropylene or ethylene-propylene copolymer is provided on both outer surfaces of a layer obtained by blending an ethylene-propylene block copolymer, a rubber component in the block copolymer and a polyolefin-based polymer having good compatibility. By forming a film of the united product with a coextrusion die, or by laminating it on a transparent base film layer through an adhesive by a method such as dry lamination,
They succeeded in obtaining a transparent high retort composite polypropylene film or a transparent retort film (including boil).

Due to the high temperature at the time of retort sterilization, the film often whitens, but since the rubber particles themselves of the composite film of the present invention have a particle size equal to or less than the wavelength of light, there are also defects at the interface due to the progress of secondary crystallization. It does not affect the light transmission so much and has the same degree of transparency as the propylene homopolymer, and is more transparent than the commercially available ethylene-propylene random copolymer blended with the ethylene-propylene copolymer rubber. Are better. When manufacturing the composite film, the method of joining the layers may be any of a coextrusion method, a lamination method, a bonding method with an adhesive, etc.
The coextrusion method is preferable because of its excellent productivity.

For example, as will be described in the following Examples, the polypropylene or ethylene-propylene random copolymerization is applied to both surfaces of a film obtained by blending one or more kinds of the thus obtained ethylene-propylene block copolymer and a compatible polyolefin polymer. Three-layer composite film obtained by laminating a united product or a composite film obtained by laminating the three-layer composite film with a transparent base resin film such as nylon or polyethylene terephthalate, with the film according to the present invention as the inner surface, a three-sided seal of 13 cm × 17 cm Make a bag and salad oil
After injecting 150 ml of a blend solution of 20 / water 80 and heat-sealing the remaining one, sterilizing the retort at 135 ° C for 20 minutes, and observing the appearance and the transparency of the contents. The devitrification was small, the appearance was not changed, and the state was extremely good as compared with the currently commercially available film made by blending the ethylene-propylene random copolymer rubber with the propylene random copolymer. Further, by using an ethylene-propylene block copolymer,
Cold resistance in the extremely low temperature range of 10 ° C or less was also improved, the drop bag breakage rate as a practical physical property was reduced, and the safety as a packaging material was increased.

Examples Examples of the present invention will be described below, but it goes without saying that the scope of the present invention is not limited to these examples. In the following examples, “%” represents “% by weight” unless otherwise specified.

Example 1 15% of low density polyethylene (L-LDPE) having an MFR of 15 (measured according to JIS-K-6758 at 230 ° C.) of 1.5 and an ethylene-propylene block copolymer having an ethylene content of 12% was used. Pre-blended resin is used as a base layer and MF is applied to both sides.
A two-kind three-layer film composed of polypropylene in which R was 10 was molded by a T-die molding machine at a die temperature of 250 ° C. to obtain a 70 μ-thick composite film.

Example 2 A composite film was formed in the same manner as in Example 1 except that L-LDPE having an MFR of 15 in Example 1 was replaced by an ethylene-propylene copolymer rubber (EPR) having an MFR of 6.

Example 3 A composite film was formed in the same manner as in Example 1 except that the L-LDPE having an MFR of 15 in Example 1 was replaced with a high-density polyethylene having an MFR of 8.

Example 4 Substituting propylene homopolymer with MER = 10 of Example 1 for M
A composite film was molded in the same manner as in Example 1 using an ethylene-propylene random copolymer having FR of 10.

Comparative Example 1 An ethylene-propylene block copolymer having an MFR of 1.5 and an ethylene content of 12% was alone molded by a T-die molding machine having a die temperature of 250 ° C to obtain a film having a thickness of 70µ.

Comparative Example 2 An ethylene-propylene random copolymer was blended with 15% of ethylene-propylene rubber to form a monolayer film.

Comparative Example 3 An ethylene-propylene block copolymer having an MFR of 1.5 and an ethylene content of 12% was used as a base layer, and MFR was 10 on both sides of the base layer.
A 2-kind 3-layer film composed of the polypropylene homolayer (8μ) is molded with a T-die molding machine at a die temperature of 250 ° C to obtain a thickness of 7
A 0 μ film was obtained.

The various 3-layer films of Examples 1-5 and Comparative Examples 1-2 were formed into a multilayer film by a T-die forming machine having a 2-kind 3-layer die, and the physical properties thereof were measured, and a nylon film and a urethane adhesive were used. 170mm after dry lamination
Create a three-way heat-sealing pouch with a size of 130 mm under a pressure of 3 kg / cm ² at 250 ° C. for 0.5 sec, fill it with 180 ml of a mixture of water and salad oil, and heat seal the other opening. High temperature heating retort sterilization treatment was performed at ℃ × 15 minutes. After the retort sterilization treatment, the appearance was observed and the bag was dropped in an atmosphere in which the temperature of the filling liquid was −5 ° C.

The results are as shown in Table 1.

(Table 1 footnote) * 1: Impact is measured using a film impact tester manufactured by Toyo Seiki Co., Ltd. Low temperature is -5 ° C and room temperature is 23 ° C.
The measurement was performed in an atmosphere.

* 2: Retort permeability is four-way heat-sealing with composite polypropylene films stuck together.
After performing retort sterilization treatment at 135 ° C for 30 minutes, observe the fusion state of the films in the four-way heat seal.

* 3: A low temperature drop bag is a pouch with a size of 130 mm x 170 mm, filled with 150 ml of a liquid of 50/50 blended with water and salad oil, and sealed. After that, concrete is poured from a height of 1.0 m in an atmosphere of -20 ° C. It was dropped vertically on the surface and the bag breaking rate at that time was taken.

Claims (1)

[Claims] 1. A first layer comprising (i) a polypropylene or an ethylene-propylene random copolymer, (ii) an ethylene-propylene block copolymer and a polyolefin-based polymer having good compatibility with a rubber component in the block copolymer. For a retort sterilization packaging material obtained by laminating a composite film of a second layer composed of a blend with a polymer and (iii) a third layer composed of a polypropylene homopolymer or an ethylene-propylene random copolymer on a transparent base film. Composite film laminate.