JPH06270248A - Stretched film for food packing and production thereof - Google Patents

Abstract

PURPOSE:To provide a stretched film for food packing excellent in transparency, glossiness, see-through, elongation characteristics, packing machine aptitude and workability other than deformation recovery and safe from the aspect of waste disposal and food sanitation. CONSTITUTION:A stretched film for food packing is a laminated film composed of a three-layered structure and each of both surface layers (A) of the film are composed of a specific ethylenic copolymer or a compsn. containing the same and the center layer (B) of the film is composed of a compsn. selected from crystalline polypropylene (B1), crystalline polybutene-1(B2) and the surface layer (A) (B3) and respective mixing wt. ratios are 0.20<=(B1+B2)/(B1+B2+B 3)<=0.98, 0.1<=(B1)/(B1+B2+B3)<=0.49, 0.1<=(B2)/(B1+B2+B3)<=0.49 and 0.02<=(B3)/(B1+B2+B3)<=0.80. The shrinkage factor of the laminated film after inflation molding is 20% or less at.90 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stretch film for food packaging, and more particularly, it is a film obtained by laminating layers made of a specific composition, which is formed by an inflation method and then heat treated. The present invention relates to a stretch film for food packaging, which is excellent in waste disposal and has no problems in food hygiene.

[0002]

2. Description of the Related Art Generally, the following characteristics are required as a film for stretch-wrapping foods such as fruits and vegetables, fresh fish, meat, prepared foods directly or on a plastic tray. (1) Transparency, gloss and transparency for improving product value (display effect) (2) Breathability and anti-fog property for maintaining freshness and display effect of food containing a lot of water (3) Product Water vapor permeability to prevent dryness and maintain freshness (4) Self-adhesiveness and heat sealability to maintain tight packaging (5) Uniform elongation characteristics and deformation recovery to obtain tight packaging (6) Suitability of wrapping machine to improve workability of stretch wrapping

Conventionally, a plasticized polyvinyl chloride film has been used as a film satisfying such characteristics. However, since the plasticized polyvinyl chloride film uses a large amount of plasticizer, it has a large water vapor permeability, and there is a problem that the plasticizer easily migrates to the packaged item. Also,
Since it has poor cold resistance, it has a drawback that when the package is stored at a low temperature, the film becomes hard and brittle and is easily broken.

Further, regarding the post-use treatment of the film, in the plasticized polyvinyl chloride film, the plasticizer tends to flow out from the film after being discarded, and the plasticizer that has flowed out may pollute the sea or river. In addition, since hydrogen chloride gas is generated when incinerating at a garbage disposal site, a special treatment facility is required in the incinerator, and when incinerating at home, the toxic gas released is preferable for direct health. Furthermore, there was a problem that it contributed to the promotion of acid rain.

As a composition suitable for a stretch film which solves these problems, a composition described in Japanese Patent Publication No. 59-38976 has been proposed. However, in this composition, the most important transparency, gloss, and transparency are not sufficient in the inflation method, which is a conventionally known film forming method, and are not at a satisfactory level.
Moreover, the packaging workability is not sufficient. Further, JP-A-63-
The composition described in Japanese Patent No. 41550 has been proposed, but this composition satisfies some points necessary for a stretch film only by stretching, but elongation and deformation when stretching the most important film. With less recovery, the characteristics required as a stretch film are:
It's far apart. Also, as a film,
The one described in JP-B-2-52624 is proposed, but since this film is also a stretched film, the elongation and deformation recovery when the most important film is stretched is small, and the characteristics required as a stretch film are Are far apart.

Further, a layer made of an ethylene-vinyl acetate copolymer having a vinyl acetate unit content of 1 to 10% by weight and a layer made of an ethylene-vinyl acetate copolymer having a vinyl acetate unit content of 11 to 50% by weight. A stretch film for food packaging, which is formed by laminating the above-mentioned materials, has been proposed (Japanese Patent Laid-Open No. 55-8).
(See Japanese Patent No. 1155). However, for this food packaging film, the temperature range that can be heat-sealed in an automatic packaging machine is still narrow, so there is a problem that the film other than the heat-sealed portion is melted and perforated.
Further, there is a problem that the cutting property of a film by a cutter blade in an automatic packaging machine and the slipping property with respect to a tray and an object to be packaged are poor, and since it has rubber-like elasticity, it is inferior in suitability for an automatic packaging machine.

Further, a stretch film for food packaging has been proposed in which an ethylene-vinyl acetate copolymer is laminated on both sides of an intermediate layer containing a polypropylene resin and a low crystalline ethylene-α-olefin copolymer. (See JP-A-60-171148). However,
This multilayer film is still difficult to balance the physical properties in the vertical and horizontal directions, is inferior in cuttability, and does not have sufficient deformation recovery property.

Further, ethylene and α- having 4 to 8 carbon atoms
A random copolymer of at least one α-olefin selected from olefins and propylene, wherein α
-Ethylene having a vinyl acetate unit content of 5 to 25% by weight on both surfaces of a resin-based layer having an olefin unit content of 4 to 19% by weight and a melt flow rate of 1 to 10 g / 10 min. A stretch packaging film having a total thickness of 6 to 40 μm, in which a layer containing a vinyl acetate copolymer resin as a main component is laminated, has been proposed (JP-A-61-446).
35 gazette). However, this stretch wrapping film is inferior in transparency and gloss, is difficult to balance the physical properties of the film in terms of length and width, is inferior in cuttability, and does not have sufficient deformation recovery property.

Further, the layer containing butene-1 resin as a main component contains ethylene-containing vinyl acetate in an amount of 5 to 25% by weight.
There has been proposed a stretch packaging film obtained by laminating layers containing a vinyl acetate copolymer resin as a main component. (See Japanese Patent Laid-Open No. 61-89040). However, this stretch packaging film does not have transparency, luster, particularly transparency and sufficient deformation recovery, although the vertical and horizontal balance of film properties is relatively good.

As described above, many stretch wrapping films have been proposed, but no stretch wrapping film for food packaging which satisfies the above-mentioned required characteristics and has no problems in waste disposal and food hygiene has yet been proposed. is the current situation.

[0011]

The object of the present invention is not only excellent in deformation recovery, but also excellent in transparency, gloss, see-through property, elongation property, packaging machine suitability, workability, etc. An object of the present invention is to provide a stretch film for food packaging which has no problem in hygiene.

[0012]

Therefore, the present inventor has solved the above-mentioned problems of the conventional film, and in particular, has excellent deformation recovery property, has uniform elongation property of the film, and has transparency and gloss. It has excellent transparency, has a wide temperature range that can be heat-sealed by an automatic packaging machine, and has excellent packaging workability.
Moreover, the inventors have conducted extensive research to develop a stretch film that fully satisfies the requirements for stretch wrapping of foods and, in addition, does not cause environmental problems in the used treatment and has no food hygiene problems. As a result, it was found that a film obtained by molding a specific composition by an inflation method and then heat-treating the film is a film that meets the above-mentioned purpose. The present invention has been completed based on such findings.

That is, the present invention relates to a laminated film having a three-layer structure, the surface layers (A) on both sides of the film.
Are ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, ethylene-methyl acrylate copolymer, ethylene-acrylic acid copolymer, ethylene-ethyl acrylate copolymer, ethylene-methacrylic Methyl acid copolymer, ethylene-methacrylic acid copolymer,
At least one ethylene-based copolymer selected from ethylene-α-olefin copolymers having a density of 0.910 g / cm ³ or less and an ethylene unit content of 65 to 90% by weight, or a composition containing these, The central layer (B) is
The composition is selected from (B ₁ ) crystalline polypropylene, (B ₂ ) crystalline polybutene-1, and (B ₃ ) surface layer (A), and the mixing ratio of each is 0.20 ≦ (B ₁ + B ₂ )
/ (B ₁ + B ₂ + B ₃ ) ≦ 0.98; 0.1 ≦ (B ₁ ).
/ (B ₁ + B ₂ + B ₃ ) ≦ 0.49; 0.1 ≦ (B ₂ ).
/ (B ₁ + B ₂ + B ₃ ) ≦ 0.49; 0.02 ≦ (B
₃ ) / (B ₁ + B ₂ + B ₃ ) ≦ 0.80, and the shrinkage rate of the laminated film after inflation molding at 90 ° C. is 20% or less, which is a food packaging excellent in recovery from deformation. The present invention provides a stretch film.

The film of the present invention is basically a laminated film having a three-layer structure, the surface layers on both sides of which are (A) layers,
The central layer is the (B) layer. That is, the basic structure of the film of the present invention is (A) layer / (B) layer / (A) layer. Ethylene used in the surface layer (A) of the present invention
Vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, ethylene-methyl acrylate copolymer, ethylene-acrylic acid copolymer, ethylene-ethyl methacrylate copolymer, ethylene-methyl methacrylate copolymer The content of the monomer other than the ethylene unit in the polymer and the ethylene-methacrylic acid copolymer is not particularly limited, but is preferably 5 to 25% by weight, more preferably 10 to 20% by weight. If this content is less than 5% by weight, flexibility, transparency, and deformation recovery tend to be low, and 25% by weight
If it exceeds, the strength characteristics may deteriorate.

The physical properties of these copolymers are not particularly limited, but the melt flow rate at 190 ° C. is preferably 0.1-10 g / 10 minutes, more preferably 1-5.
g / 10 minutes. Melt flow rate is 0.1 g /
If it is less than 10 minutes, not only the elongation property is deteriorated but also the extrudability tends to be problematic, and if it exceeds 10 g / 10 minutes, the strength property may be deteriorated.

Further, it is a comonomer in the ethylene-α-olefin copolymer having a density of 0.910 g / cm ³ or less and an ethylene unit content of 65 to 90% by weight, which is used in the surface layer (A) of the present invention. As the α-olefin, those having 3 to 12 carbon atoms such as 1-propene, 1-butene, 1-hexene, 1-octene, and 4-methyl-1-pentene are preferable. The physical properties of these copolymers are not particularly limited, but the density is preferably 0.860 to
0.910 g / cm ³ , more preferably 0.870 to
The melt flow rate at 0.900 g / cm ³ and 190 ° C. is preferably 0.1 to 10 g / 10 minutes, more preferably 1 to 5 g / 10 minutes. The ethylene unit content is 65 to 90% by weight, preferably 70 to 8
It is 5% by weight. When the density is more than 0.910 g / cm ³ , non-uniform elongation occurs when the film is stretched during packaging, and the transparency is significantly reduced. further,
If the melt flow rate is too small, not only the elongation properties will deteriorate, but also the extrudability will be prone to problems. On the contrary, if it is too large, problems such as deterioration of strength properties and deterioration of molding stability may occur.

The surface layer (A) of the present invention can be formed by using the above resins alone or as a mixture of two or more kinds, or as a composition containing them, preferably an ethylene-vinyl acetate copolymer. , Density is 0.910g / cm
An ethylene-α-olefin copolymer having an ethylene unit content of ^{3 to 3 and} having a content of 65 to 90% by weight, a mixture thereof, or a composition containing these as the main components.

The layer (A), which is the surface layer of the film, is composed of the above-mentioned resin composition, and further, in order to obtain proper slipperiness, self-adhesiveness, antistatic property and antifogging property. , Additives can be blended. Specifically, sorbitan fatty acid ester, propylene glycol fatty acid ester, glycerin fatty acid ester, polyglycerin fatty acid ester, polyoxyethylene glycerin fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyethylene glycol fatty acid ester, polypropylene glycol fatty acid ester, polyoxyethylene Examples thereof include, but are not limited to, aliphatic alcohols and polyoxyethylene alkylphenyl ethers. These additives are used alone or as a mixed composition, and the addition amount is usually 0.1-5.
It is 0% by weight, preferably 0.5 to 3.0% by weight. If the amount added is too small, the modifying effect of the film is not sufficient, while if too large, the amount of protrusion to the film surface is large, the film becomes sticky, and as a result, the workability is significantly reduced. Problems such as contamination of the packaged item may occur.

Next, the central layer (B) of the stretch film of the present invention has a composition selected from (B ₁ ) crystalline polypropylene, (B ₂ ) crystalline polybutene-1 and (B ₃ ) surface layer (A). It is a mixed composition of products. It is the first component (B
₁ ) is crystalline polypropylene, which is a polypropylene or a copolymer with another resin unit produced by a conventionally known method. A copolymer with ethylene, 1-butene or the like or another α-olefin is preferable, and a propylene-ethylene random copolymer having an ethylene unit content of 4 to 15% by weight, more preferably 6 to 12% by weight is more preferable. It is a polymer. For its physical properties,
Although there is no particular limitation, it is preferable that the melt flow rate at 230 ° C. is 0.1 to 15 g / 10 minutes. If the unit content of the α-olefin is too small, the flexibility tends to be impaired. On the contrary, if the unit content is too large, the effect of improving the heat sealability on the hot plate cannot be sufficiently expected. Further, if the melt flow rate is small, the elongation characteristics deteriorate, and if it is large,
The strength may be reduced, which is not preferable.

The first component (B ₁ ) plays an important role in solving the problem of melting and perforation during heat sealing with a hot plate in an automatic packaging machine,
Furthermore, it is important to mix within a specific range so as not to cause uneven elongation during stretching. That is,
The mixing ratio of (B ₁ ) is 10 to 49% by weight, preferably 20 to 45% by weight. The mixing ratio of (B ₁ ) is 10
If the content is less than 10% by weight, the effect of improving the heat-sealing property on the hot plate cannot be sufficiently obtained, and the appropriate temperature range in which heat-sealing is possible is narrow. In order to prevent this, the temperature condition has to be changed in accordance with the change in weight of the contents, and the workability is significantly reduced. Further, when it is 50% by weight or more, although it has a relationship with other resin components, the elongation property of the film is deteriorated, the tray is deformed during stretch wrapping, and a tight wrapping cannot be obtained. Problems can arise and can also cause wrinkling problems in the package due to uneven elongation when the film is stretched.

The second component (B ₂ ) is crystalline polybutene-1, having a density of 0.880 to 0.920 g /
cm ³ , preferably 0.885 to 0.915 g / cm
³ , Melt flow rate at 190 ℃ is 0.1-1
Butene at 0 g / 10 minutes, preferably 1 to 5 g / 10 minutes
1 is a homopolymer or a butene-1-α-olefin copolymer having an α-olefin unit content of 1.5 to 20% by weight such as ethylene or propylene. If the density is too low, the effect of improving the cuttability in the lateral direction of the film will not be sufficient, and if it is too high, the flexibility may decrease. Further, if the melt flow rate is too low, the mixing property with other resins and the extrudability are insufficient, and if it is too high, the strength characteristics may deteriorate.

The second component (B ₂ ) plays an important role in improving the cuttability in the automatic packaging machine, smoothing the feeding of the tray, and the ability to easily cut by hand in the lateral direction. It is important to mix in a specific range in order to prevent uneven elongation during stretching. That is, the mixing ratio of (B ₂ ) is
It is 10 to 49% by weight, preferably 20 to 45% by weight. If the mixing ratio of (B ₂ ) is less than 10% by weight, the effect of improving cuttability cannot be sufficiently obtained, smooth packaging cannot be obtained in an automatic packaging machine, and workability is significantly reduced. Further, in the case of 50% by weight or more, there is a relationship with other resin components,
The elongation property of the film deteriorates, the problem that the tray is deformed when stretch-wrapping is performed and a tight packaging cannot be obtained, and further, uneven stretching occurs when the film is stretched, the wrinkling of the packaging occurs. May cause problems with entering.

Thus, the first component (B ₁ ) and the second component (B ₂ ) have different expected improvement effects,
The same problem occurs when the mixing ratio exceeds a specific range. Therefore, (B ₁ ) and (B
The total mixing ratio of ₂ ) is 20 to 98% by weight, preferably 35 to 90% by weight, more preferably 35 to 50% by weight.
Is. If the total mixing ratio of (B ₁ ) and (B ₂ ) is less than 20% by weight, it is difficult to obtain a mixing ratio satisfying both heat sealability and cuttability, and if more than 98% by weight, it is difficult to stretch. May cause uneven elongation.

Further, the third component (B ₃ ) is a composition selected from the surface layer (A), and the composition used for the surface layer (A) may be used. Other composition selected from the layer (A) may be used. It is preferable to use the composition used for the surface layer (A) in consideration of recycling the non-product portion at the time of molding to the central layer.

The third component (B ₃ ) plays an important role in improving flexibility and elongation characteristics and obtaining a tightly bound package. Furthermore, it is important to mix with (B ₁ ) and (B ₂ ) in a specific range so as not to deteriorate the heat-sealing property. That is, the mixing ratio of (B ₃₎ is 2 to 80% by weight, preferably 10 to 65 wt%, more preferably 50 to 65 wt%. If the mixing ratio of (B ₃ ) is less than 2% by weight, the flexibility and elongation properties cannot be sufficiently improved, and if it exceeds 80% by weight, the heat-sealing property is deteriorated and the strength is lowered. There is a fear.

In the present invention, (B ₁ ), (B ₂ ),
The mixed composition of (B ₃ ) is used as the central layer (B), and the surface layers (A) on both sides thereof are ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, ethylene-methyl acrylate copolymer. , Ethylene-acrylic acid copolymer, ethylene-ethyl methacrylate copolymer, ethylene-methyl methacrylate copolymer, ethylene-methacrylic acid copolymer, ethylene unit with a density of 0.910 g / cm ³ or less The main purpose of laminating a layer comprising at least one ethylene copolymer selected from the ethylene-α-olefin copolymers having a content of 65 to 90% by weight or a composition containing these is (B ₁ ), This is because the flexibility, transparency, luster, self-adhesiveness, deformation recovery, etc. of the film cannot be sufficiently obtained with the single film composed of the mixed composition of (B ₂ ) and (B ₃ ). Conversely, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, ethylene-
Methyl acrylate copolymer, ethylene-acrylic acid copolymer, ethylene-ethyl methacrylate copolymer, ethylene-methyl methacrylate copolymer, ethylene-methacrylic acid copolymer, density 0.910 g / ethylene having an ethylene unit content of 65 to 90% by weight at cm ³ or less
A single film composed of at least one ethylene-based copolymer selected from α-olefin copolymers or a composition containing these cannot provide sufficiently satisfactory heat sealability, strength, etc. on a hot plate. Is. These problems are caused by using a mixed composition of (B ₁ ), (B ₂ ), and (B ₃ ) as the central layer (B) and at least one of the polymers of the above-mentioned surface layer (A) on both sides of the central layer (B). This can be solved for the first time by laminating layers composed of the ethylene copolymer or the composition containing them.

The film of the present invention is a film having a three-layer structure in which the above-mentioned (A) layer is used as the surface layers on both sides and the (B) layer is used as the central layer, and the surface layers on both sides of the (B) layer ( A)
The same composition may be used, or a composition belonging to the category of the above composition but having a different component composition may be used.

The laminated film composed of the above composition is usually formed by the inflation method, but it is desirable to heat-treat it after the formation, and the film after heat treatment is treated at 90 ° C.
20% in both vertical and horizontal directions
It is necessary that the content is below, preferably 10% or less, and more preferably 5% or less. When the shrinkage ratio after heat treatment exceeds the above range, the effect of heat treatment is not sufficiently exhibited, and therefore improvement in deformation recovery may not be expected.

Further, the laminated film of the present invention is formed by a blow-up method with a blow-up ratio of 3 to 12, preferably 5 to 12, more preferably 8 to 10, and then 35 to 110 ° C., preferably 40 to 100. C., more preferably 50 to 80.degree. C., for heat treatment. In the inflation method, when the blow-up ratio is less than the above range, the physical properties in the vertical and horizontal directions are unbalanced, and uniform elongation properties cannot be obtained, and when it exceeds the above range, stable molding may be difficult.

Further, after the inflation molding, heat treatment can improve the deformation recovery of the film. If the temperature of the heat treatment is less than 35 ° C, the effect of the heat treatment cannot be sufficiently obtained, and if it exceeds 110 ° C, the handling of the film may become difficult. The method of heat treatment is not particularly limited, but may be performed before the winding step at the time of molding, or after heat treatment of the tube-shaped raw material or the raw material wound and cut and wound, the desired width and length are obtained. You may rewind.

The thickness of the laminated film of the present invention is usually 8 to 30 μm, preferably 10 to 20 μm.
Is. When the thickness of the film is less than 8 μm, the handleability of the film is significantly deteriorated due to the deterioration of the strength and stiffness of the film, and when it exceeds 30 μm, the stress at the time of stretching the film becomes large and the tray or the packaged product is deformed. There is a risk that it will happen.

Furthermore, the thickness of the film center layer (B) is
It is preferably 20% or more and 85% or less of the total thickness of the film, specifically, 2.0 to 25.0 μm, preferably 4.0 to 1
The thickness of 8.0 μm is preferable. Here, if the thickness of the central layer is less than 20% of the total thickness of the film, the effect of improving heat sealability and cuttability cannot be expected, and if it exceeds 85%, uniform elongation properties may be impaired.

[0033]

The present invention will be described in more detail with reference to Examples and Comparative Examples. Examples 1 to 3 As the resin for the surface layer (A), (a ₁ ) ethylene-vinyl acetate copolymer (vinyl acetate content 15% by weight, 190
Melt flow rate at ℃ 2.0g / 10 minutes),
(A ₂ ) ethylene-1-butene copolymer (density 0.88
0 g / cm ³ , melt flow rate at 190 ° C. 3.5 g / 10 min), (a ₃ ) (a ₁ ) 50% by weight,
(A ₂ ) A mixed resin composition comprising 50% by weight. further,
2 parts by weight of diglycerin monooleate is mixed with 98 parts by weight of each resin of (a ₁ ) to (a ₃ ) and pelletized to prepare a resin composition (a ₁₁ ) to (a ₃₁ ) for the surface layer (A). ). Next, as a resin for the central layer (B), (B ₁₁ ) propylene-ethylene random copolymer (ethylene content 7% by weight, melt flow rate at 230 ° C. 2.0 g / 10 minutes) (B ₂₁ ) polybutene-1 (Density 0.900 g / cm ³ ,
Melt flow rate at 190 ° C 1.0g / 10
Min) consisting of the same ethylene-vinyl acetate copolymer as (B ₃₁ ) (a ₁ ) (vinyl acetate unit content 15% by weight, melt flow rate at 190 ° C. 2.0 g / 10 min), (B ₁₁ ). Was mixed with 25 parts by weight, (B ₂₁ ) with 35 parts by weight and (B ₃₁ ) with 40 parts by weight, and pelletized to obtain a resin composition (b ₁ ) for the central layer (B). The composition of Example 1 was obtained by using an annular 3-layer die using two extruders each having an aperture of 50 mm and L / D26.
(A ₁₁ ) / (b ₁ ) / (a ₁₁ ), Example 2 (a ₂₁ ) /
(B ₁ ) / (a ₂₁ ), Example 3 (a ₃₁ ) / (b ₁ ) /
(A ₃₁ ), the resin temperature was 190 ° C., the blow-up ratio was 8.0, and inflation molding was carried out. The internal temperature was 50 ° C. in which two rolls before the winding process were surrounded by a chamber.
The thickness of each layer is 5
μm / 5 μm / 5 μm; a film having a total thickness of 15 μm was obtained.

Using this film, meat, fish, prepared foods, fruits and the like were placed on a tray made of expanded polystyrene and packaged by a stretch automatic packaging machine. The properties of the film and the measurement results are shown in Tables 1 and 2.

The physical properties of each item were measured and evaluated by the following methods. 1) Melt flow rate; JIS K7210 2) Density; JIS K6760 3) Haze (transparency); JIS K7105 4) Gloss (gloss); JIS K7105 5) Clarity (transparency); Murakami Color Research Laboratory Clarity Meter Measured with a slit width of 1 mm 6) Breaking strength; JIS Z1702 7) Elongation; JIS Z1702 8) Deformation recovery property: A sample piece having a width of 15 mm and a length of 100 mm is extended to 200 mm and immediately released 30 seconds later, The length was measured and indicated by the returned length of the sample piece. 9) Elongation characteristics: It was examined whether or not necking occurred when the film was stretched. 10) Self-adhesiveness: Two pieces of 100 mm in length and width were overlapped, the ends of each film were fixed to the upper and lower plates with tape, and peeled up and down to measure. 11) Anti-fogging property; 10 ml of water at 20 ° C in a 300 ml beaker
When 0 ml was placed and covered with a film and stored in a refrigerator at 1 ° C., the degree of cloudiness of the film was visually evaluated on a 5-point scale.
(The best value is 5.) 12) Heat-sealing property: The heater temperature of the hot plate of the automatic packaging machine is set to 50 to 160 ° C., the stretch-wrapped tray is allowed to stand on the hot plate for several seconds, and the tray bottom The seal strength and the presence / absence of perforations were evaluated, and the results were shown in the temperature range in which good sealing was possible. 13) Suitability for automatic wrapping machine: It was judged whether stretch wrapping is possible without problems such as wrinkles, cracks and distortions in trays, feedability of film, and cuttability. 14) Cuttability; sensory evaluation of the cuttability by hand in the lateral direction,
Those that were cut straight in the lateral direction were rated as 5, and those that were not cut or were bent and cut were rated on a scale of 5 according to their degree. 15) Heat shrinkage rate: A film having a width of 10 mm and a length of 150 mm (between the marked lines 100 mm) was dipped in a water bath at 90 ° C. for 20 seconds, immediately dipped in cold water, and then measured and expressed as a percentage of the shrunk length.

Examples 4 to 6 The resin for the surface layer (A) was (a ₁₁ ), and the resin for the center layer (B) was (B ₁₂ ) propylene-ethylene random copolymer (ethylene content 4% by weight, Melt flow rate at 230 ° C. 2.0 g / 10 min) (B ₁₃ ) Propylene-ethylene random copolymer (ethylene content 12% by weight, melt flow rate at 230 ° C. 8.0 g / 10 min) (B ₂₂ ) Polybutene -1 (density 0.895 g / cm ³ ,
Melt flow rate at 190 ° C 3.0 g / 10
Min) (B ₂₃ ) polybutene-1 (density 0.915 g / cm ³ ,
Melt flow rate at 190 ° C 2.0g / 10
Min) (B ₃₁ ) ethylene-vinyl acetate copolymer (vinyl acetate unit content 15% by weight, melt flow rate at 190 ° C. 2.0 g / 10 min), (B ₁₂ ) 15 parts by weight, ₂₃ ) 15 parts by weight and (B ₃₁ ) 70 parts by weight are mixed and pelletized, and the resin compositions (b ₂ ) and (B ₁₃ ) for the central layer (B) are 45 parts by weight and (B ₂₃ ). Is mixed with 45 parts by weight, (B ₃₁ ) is mixed with 10 parts by weight, and the mixture is pelletized to obtain 30 parts by weight of the resin composition (b ₃ ) and (B ₁₁ ) for the central layer (B) and 30 parts by weight of (B ₂₂ ). Parts by weight, 15 parts by weight of (B ₂₃ ) and 25 parts by weight of (B ₃₁ ) are mixed and pelletized to obtain the resin composition (b) for the central layer (B).
₄ )

Each of these compositions has a diameter of 50 mm,
Using two L / D26 extruders, from an annular three-layer die,
Layer construction for Examples _{4~6 (a 11) / (b} 2 ~ 4)
/ (A ₁₁ ), the resin temperature was 190 ° C., the blow-up ratio was 10.0, and inflation molding was carried out. The internal temperature of the two rolls before the winding process was surrounded by a chamber.
Heat treatment was performed through a heat treatment step portion at 0 ° C. to obtain a film having a thickness of each layer of 5 μm / 5 μm / 5 μm and a total thickness of 15 μm.

Using this film, meat, fish, prepared foods, fruits and the like were placed on a tray made of expanded polystyrene and packaged by a stretch automatic packaging machine. The properties of the film and the measurement results are shown in Tables 1 and 2.

Example 7 As in Example 6, inflation molding was carried out at a resin temperature of 190 ° C. and a blow-up ratio of 10.0 so that (a ₁₁ ) / (b ₄ ) / (a ₁₁ ), without heat treatment. The tube was loosely wound into a tube and stored in a room kept at 45 ° C for 24 hours, and then rewound by a slitter so that each layer has a thickness of 5
μm / 5 μm / 5 μm; a film having a total thickness of 15 μm was obtained. Using this film, meat, fish, side dishes, fruits, etc. were placed on a polystyrene foam tray and packaged by a stretch automatic packaging machine. The properties of the film and the measurement results are shown in Tables 1 and 2.

Comparative Example 1 30% by weight of ethylene-vinyl acetate copolymer (vinyl acetate unit content 15% by weight, melt flow rate at 190 ° C. 2.0 g / 10 minutes) in the central layer; polybutene-1
(Density 0.915 g / cm ³ , melt flow rate at 190 ° C. 2.0 g / 10 minutes) A resin composition consisting of 70 wt% was used, and the surface layer was an ethylene-vinyl acetate copolymer (vinyl acetate unit content 15 wt. %, Melt flow rate at 190 ° C. 2.0 g / 10 minutes) 98.5% by weight; sorbitan monooleate 1.5% by weight to form a film in the same manner as in Example 1, and the thickness of each layer. , 5 μm / 5 μm / 5 μm; a film having a total thickness of 15 μm was obtained. This film was used for packaging. The properties of the film and the measurement results are shown in Tables 3 and 4. The physical properties of each item were measured and evaluated in the same manner as in the examples.

Comparative Example 2 30% by weight of ethylene-vinyl acetate copolymer (vinyl acetate unit content: 15% by weight, melt flow rate at 190 ° C .: 2.0 g / 10 minutes) in the central layer; propylene-ethylene random copolymer (Ethylene unit content 7% by weight,
Melt flow rate at 230 ° C 2.0 g / 10
Min) 70% by weight, and the surface layer is an ethylene-vinyl acetate copolymer (vinyl acetate unit content 15% by weight, melt flow rate at 190 ° C. 2.0 g / 1
0 minutes) 98.5% by weight; diglycerin monooleate 2.
A composition containing 0% by weight was formed in the same manner as in Example 1 to obtain a film having a thickness of each layer of 5 μm / 5 μm / 5 μm and a total thickness of 15 μm. This film was used for packaging. The properties of the film and the measurement results are shown in Tables 3 and 4. The physical properties of each item were measured and evaluated in the same manner as in the examples.

Comparative Examples 3 and 4 Under the same conditions except that the heat treatments of Examples 1 and 6 were not performed, the thickness of each layer was 5 μm / 5 μm / 5 μ.
m: A film having a total thickness of 15 μm was obtained. This film was used for packaging. The properties of the film and the measurement results are shown in Tables 3 and 4. The physical properties of each item were measured and evaluated in the same manner as in the examples.

Comparative Examples 5 and 6 Inflation molding was attempted with the same resin and construction as in Example 1 but with a blow-up ratio of 12.5, but the stability of bubbles was poor and a film could not be obtained. Further, the product formed with a blow-up ratio of 2.5 has a poor physical balance in the vertical and horizontal directions, and particularly when stretched in the horizontal direction, necking easily occurs, so that it cannot be used as a stretch film.

[0044]

[Table 1]

[0045]

[Table 2]

[0046]

[Table 3]

[0047]

[Table 4]

[0048]

INDUSTRIAL APPLICABILITY As described above, the stretch film for food packaging according to the present invention is particularly excellent in recovery from deformation, transparency,
It has excellent gloss and transparency, has uniform elongation characteristics when the film is stretched, has excellent heat sealability in an automatic packaging machine, is suitable for packaging machines, and has excellent workability. In addition, the physical properties required for stretch films for food packaging, such as air permeability, antifogging property, water vapor permeability, and self-adhesiveness, are good. Further, there is no problem of disposal treatment after use, such as the conventional plasticized polyvinyl chloride stretch film, and there is no problem in food hygiene at all. Therefore, the stretch film for food packaging of the present invention is expected to be widely used as a film for stretch-wrapping various foods such as fruits and vegetables, fresh fish, meat, and prepared foods.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toyo Shinoda Oita City, Oita Prefecture, No. 2 in Oita, Showa Denko Co., Ltd. (72) Inventor Satoshi Iwamoto No. 2, Naka, Oita, Oita Prefecture Showa Electric Works Co., Ltd. Oita Research Center

Claims (2)

[Claims] 1. A laminated film having a three-layer structure, wherein the surface layers (A) on both sides of the film have ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, ethylene-methyl acrylate. Copolymer, ethylene-
Acrylic acid copolymer, ethylene-ethyl methacrylate copolymer, ethylene-methyl methacrylate copolymer,
Ethylene-methacrylic acid copolymer, density 0.910
It comprises at least one ethylene-based copolymer selected from ethylene-α-olefin copolymers having an ethylene unit content of 65 to 90% by weight at g / cm ³ or less, or a composition containing these, and the central layer (B ) Is (B ₁ ) crystalline polypropylene, (B ₂ ) crystalline polybutene-1, (B
₃ ) It is a composition selected from the surface layer (A), and the mixing ratio is 0.20 ≦ (B ₁ + B ₂ ) / (B ₁ + B _2).
+ B ₃ ) ≦ 0.98; 0.1 ≦ (B ₁ ) / (B ₁ + B ₂
+ B ₃ ) ≦ 0.49; 0.1 ≦ (B ₂ ) / (B ₁ + B ₂
+ B ₃ ) ≦ 0.49; 0.02 ≦ (B ₃ ) / (B ₁ + B
₂ + B ₃ ) ≦ 0.80, and the shrinkage rate of the laminated film after inflation molding at 90 ° C. is 20%
A stretch film for food packaging excellent in deformation recovery, characterized in that: 2. The method for producing a stretch film for food packaging excellent in deformation recovery according to claim 1, wherein the film is inflation-molded with a blow-up ratio of 3-12 and then heat-treated at a temperature of 35-110 ° C. .