JPS633813Y2 - - Google Patents

Description

[Detailed explanation of the idea]

The present invention is used as a bottom material for deep-drawn vacuum packaging, and is suitable for obtaining a package that has excellent content preservation and adhesion to the content, and has minimal curl at the sealing part with the lid material. Regarding composite film. Deep drawing vacuum packaging is a process in which the bottom film is formed into a shape similar to the contents using a vacuum or pressure forming machine.
A packaging method in which a package is obtained by filling the contents and sealing it with a lid under vacuum. The composition of composite films that are currently widely used as bottom films for deep-drawn vacuum packaging is saponified ethylene-vinyl acetate copolymer (hereinafter referred to as saponified EVA) layer/polyamide resin (hereinafter referred to as Ny) layer/polyethylene.
There is a sealing layer made of polyethylene resin (hereinafter referred to as PE resin) such as ethylene vinyl acetate copolymer or ionomer, and the bottom material with this structure is combined with a sealing layer made of a lid material such as OPP/K coated cellophane/PE resin. When sealed and used as a package, there were no particular problems with the storage stability and adhesion of the contents to the contents, but when this package was stored in a show case, the sealed portion curled and did not look good. The reason why the seal part of the package curls is that the Ny layer and saponified EVA layer in the composite film for the bottom material have a high tensile modulus of elasticity, and the dimensional changes due to moisture absorption are large. It was found that this occurs due to the loss of balance with the lid material, which has little dimensional change because the PE resin layer of the sealing layer cannot be suppressed, but the EVA saponified layer has excellent barrier properties, so the preservation of the contents is improved. In terms of
Although it is essential, the Ny layer has a large dimensional change due to moisture as shown in Figures 2 and 3, so it may not be necessary in cases where pinhole resistance is of paramount importance, but in light packaging where this is not the case. The inventors of the present invention found that it is better to have a structure that does not include the Ny layer because it is the main factor that causes curling in the package.
As a result of investigating whether there is a structure that includes an EVA saponified layer in the composition of the composite film and prevents the sealing part with the lid material from curling during storage, we found that the EVA in the surface layer
The saponified layer 1 is made as thin as possible to reduce the effect of moisture absorption, has a high tensile modulus, and suppresses dimensional changes in the EVA saponified layer due to moisture absorption, thereby reducing dimensional changes as a bottom material film. The middle layer is layer 2, which has a certain rigidity, and the sealing layer 3 is made of PE that can be sealed with the lid material.
It has been found that by using a structure with a resin layer, a package can be obtained in which the balance with the lid material is maintained and the seal portion does not curl during storage. this is
The tendency of the EVA saponified layer to expand due to moisture absorption is suppressed by a rigid layer that has a large tensile modulus and has the power to suppress the expansion by the EVA saponified layer.If this is replaced with a force balance, it can be expressed as an equation. It will look like this: β _E t _E (L _E −L _T )=σ _S t _S L _T +σ _A t _A L _T ……(1), L _T = β _E t _E L _E /σ _S t _S +σ _A t _A +β _E t _E ……(2) where t _E : Thickness composition ratio of EVA saponified layer t _S : Thickness composition ratio of PE resin layer t _A : Thickness composition ratio of rigid resin layer β _E : EVA saponification Compressive modulus of the layer σ _S : Tensile modulus of the PE resin layer σ _A : Tensile modulus of the rigid resin layer L _E : Assuming no influence from other layers
Dimensional change rate due to moisture absorption of the EVA saponified layer L _T : Indicates the dimensional change rate of the composite film bottom material for deep-drawn packaging. The aforementioned lid material (OPP/K-coated cellophane/
In the case of PE resin), the dimensional change rate at 90% relative humidity (RH) is 0.2%, and the smaller the difference between this dimensional change rate and the dimensional change rate of the bottom material film, the better the seal between the lid material and the bottom material. Almost no curling occurs due to moisture absorption. In other words, it has been found that the closer L _T for the bottom material is to 0.2% at 90% RH, the more curl-free packaging can be obtained. As can be seen from equation (2) above, in order to reduce _L One way is to increase the composition ratio, but making the EVA saponified layer thinner will reduce gas barrier properties and storage stability.
If the tensile modulus of PE resin is increased, the adhesion to the contents and the sealing performance with the lid material will be reduced, and if the tensile modulus of the rigid resin layer is increased, problems will arise in the adhesion to the contents. As a result of various experiments conducted by the present inventors to achieve this goal, the dimensional change rate of the composite film for the bottom material ( We found that it is possible to reduce L _T ). Note that the storage conditions for sliced ham packaging, in which the composite film for bottom material of the present invention is mainly used, are often stored in an atmosphere with a relative humidity (RH) of 70 to 90%; The equilibrium moisture content changes with respect to relative humidity as shown in Figure 2, and the dimensional change rate corresponding to each equilibrium moisture content changes as shown in Figure 3. At 90%RH, the size of EVA saponified material changes. The rate of change L _E is 0.96%. Currently, the thickness of the bottom material for deep-drawn packaging is mainly 75 to 200μ, but in the case of the composite film for the bottom material of the present invention, the thickness composition ratio of the EVA saponified layer 1 is 4.
The experimental results showed that ~30% is desirable. As mentioned above, when the thickness composition ratio of the EVA saponified layer is less than 4%, the barrier properties deteriorate, and when it is more than 30%, the rate of dimensional change due to moisture absorption increases. In order to reduce the dimensional change rate due to moisture absorption of the EVA saponified layer, it was found that the higher the tensile elastic modulus and the larger the thickness composition ratio of the rigid resin layer 2, as mentioned above, the more effective it is, but it is more effective than necessary. In order to reduce the difference in the dimensional change rate between the lid material and the lid material to 0.2%, which prevents the packaging from curling, the tensile modulus of the rigid resin layer must be between 120 and 400 Kg/ ^mm2. Within this range, its thickness composition ratio is 0.75 to 2.5 times the thickness composition ratio of the EVA saponified layer, and its composition ratio is 40 times the total thickness.
The experimental results of the present inventors revealed that it is effective if the amount is less than %. Furthermore, if the moisture absorption rate of this resin layer is 0.4 or less, it can be said that the dimensional change rate is very small and negligible compared to the dimensional change rate of the EVA saponified layer. The moisture absorption rate is the value obtained by dividing the weight change before and after moisture absorption by the weight before moisture absorption. Furthermore, it is better to place the rigid resin layer in the middle layer since the outer layer has poor adhesion to the contents. Tensile modulus is 120-400Kg/mm, moisture absorption rate is ^2nd place
Rigid PVC is used as a rigid resin of 0.4% or less.
There are GP/PS, HI/PS, BS, AS, ABS, MMA resin, etc. Seal layer 4 has a tensile modulus of elasticity of 50 Kg/mm ² since the other layers are made of relatively stiff resins, so from the viewpoint of the balance of the layer structure, the layer must be as stiff as possible or its adhesion to the contents will be poor. The following resins are desirable, and the resins include LDPE, EVA, and ionomer resins. Next, the dimensional change rate ( _L
The calculation is as follows. Conventional composite film

[Table] The dimensional change rate of the lid material (OPP/K-coated cellophane/PE resin) is 0.2%, so the difference is
Curl occurred in the seal portion at 1.07−0.2=0.87%, which was greater than the limit of 0.6% that would not cause curl in the seal portion. Composite film of this invention

[Table] The difference in dimensional change rate with the lid material is 0.37−0.2=0.17%
The curling was very small and no curling was observed at the sealing part. Next, Table 2 shows examples of the composite film of the present invention. Furthermore, if the composition ratio of the rigid resin was too high, there was a problem in adhesion.

【table】

【table】 [Brief description of the drawings]

FIG. 1 is a diagram showing the structure of the composite film of the present invention. Figure 2 shows relative humidity vs. equilibrium moisture content. Figure 3 shows equilibrium moisture content vs. dimensional change rate.

Claims (1)

[Scope of claim for utility model registration] The seal layer is a polyethylene resin layer with a tensile modulus of 50 kg/mm ² or less, and the intermediate layer has a tensile modulus of 120 to 400.
Rigid resin layer with kg/mm ² and moisture absorption rate of 0.4% or less,
and a composite film whose surface layer is a saponified ethylene-vinyl acetate copolymer layer, each thickness composition ratio is t _E (0.75 to 2.5) = t _A , t _A ≦40/100T, t _E ≦4 to 30/ 100T (t _E : thickness composition ratio of saponified ethylene vinyl acetate copolymer layer t _A : thickness composition ratio of rigid resin layer T: thickness of composite film) .