JPH0679838A - Stretched film for food packaging - Google Patents

Abstract

PURPOSE:To provide a stretched film for food packaging with excellent transparency, luster, sight-through properties, stretch characteristics, deformation recoverability, suitability to packaging machines, workability, etc., and with no problem on disposal and food hygiene. CONSTITUTION:The title film is a laminated film consisting of a three-layered structure and the surface layers on both sides of the film consist of a compsn. wherein an ethylenic copolymer is a main ingredient and the copolymer consists of a multi-component copolymer consisting of ethylene, a radically polymerizable acid anhydride and other radically polymerizable comonomer and the ratio of the unit derived from the radically polymerizable acid anhydride in the copolymer is at least 0.1wt.% and at most 5wt.% and the ratio of the unit derived from the other radically polymerizable comonomers is at least 3wt.% and at most 50wt.% and the central layer consists of a compsn. wherein a crystalline polybutene-1 is a main ingredient.

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 packaging foods, and more particularly to a film obtained by laminating layers made of a specific composition, which has transparency, gloss, transparency,
The present invention relates to a stretch film for food packaging, which has excellent elongation properties, heat sealing properties, deformation recovery properties, etc., and has no waste disposal properties and food hygiene problems.

[0002]

2. Description of the Related Art Generally, a film for stretch-wrapping foods such as fruits and vegetables, fresh fish, fresh meat, and prepared foods directly or on a plastic tray is required to have the following characteristics. (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 for prevention of dryness and maintenance of freshness (4) Self-adhesiveness and heat sealability for maintaining tight packaging (5) Elongation property for uniform elongation and recovery to obtain tight packaging (6) Suitability for packaging machines to improve workability of stretch packaging

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 JP-B-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.
Further, a composition described in JP-A-63-41550 has been proposed. This composition satisfies some points necessary for a stretch film only by stretching, but the most important film is obtained. It has little elongation and deformation recovery when stretched, and is far from the characteristics required as a stretch film. Further, as a film, a film described in Japanese Examined Patent Publication No. 52624/1990 is proposed, but since this film is also a stretched film, it has little elongation and deformation recovery when the most important film is stretched, and as a stretch film. It is far from the required characteristics.

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 are laminated. Stretch films for food packaging have been proposed (Japanese Patent Laid-Open No. 55-8).
(See Japanese Patent No. 1155). However, with regard to this stretch film for food packaging, there is still a problem that the temperature range in which heat-sealing is possible in an automatic packaging machine is narrow, and therefore the film other than the heat-sealing portion is melted to cause perforation, and the automatic packaging machine is also used. There is a problem in that the cutting property of the film by the cutter blade and the slipping property with respect to the tray and the object to be packaged are poor, and the elasticity of rubber is poor, and the suitability for automatic packaging machines is poor.

Further, ethylene and α-containing 4 to 8 carbon atoms
A random copolymer of at least one α-olefin selected from olefins and propylene, wherein α
-Ethylene-acetic acid having a vinyl acetate unit content of 5 to 25 wt% on both sides of a resin-based layer having an olefin unit content of 4 to 19 wt% 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 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 uniform elongation property.

Further, a film for stretch packaging in which a layer containing an ethylene-vinyl acetate copolymer resin having a vinyl acetate content of 5 to 25% by weight is laminated on a layer containing a butene-1 resin as a main component. Has been proposed (see JP-A-61-89040). However, this stretch wrapping film has a relatively good balance of physical properties in the vertical and horizontal directions, but is inferior in transparency, gloss, and particularly transparency. As described above, a stretch film for food packaging, which satisfies the above-mentioned required characteristics and has no problems in waste disposal and food hygiene, has not yet been proposed.

[0009]

The problem to be solved by the present invention is that it is excellent in transparency, gloss, see-through property, elongation property, deformation recovery property, packaging machine suitability, workability and the like, and it is a problem in terms of waste disposal and food hygiene. It is to provide a stretch film for food packaging that does not have such a material.

[0010]

Means for Solving the Problems The present inventors have solved the above-mentioned problems of conventional films, have uniform elongation characteristics of the film, and are excellent in transparency, gloss, and see-through property. Has a wide temperature range that can be heat-sealed and is excellent in packaging workability. Moreover, it satisfies the requirements for stretch wrapping of foods. Moreover, it does not cause environmental problems during post-processing treatment, which is a food hygiene problem. Research was repeated to develop a stretch film that does not have any As a result, it has been found that a laminate having a layer made of a specific composition is a film that serves the above 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, wherein the surface layers (A) on both sides of the film are multicomponent copolymers comprising ethylene, a radical-polymerizable acid anhydride and other radical-polymerizable comonomers. Is a polymer,
The proportion of the units derived from the radical-polymerizable acid anhydride in the copolymer is 0.1% by weight or more and 5% by weight or less, and the proportion of the units derived from other radical-polymerizable comonomers is 3% by weight or more and 50% by weight. % Or less of the ethylene-based copolymer (a) as a main component and the central layer (B) as a crystalline polybutene-1 as a main component. It provides a film.

The stretch film for food packaging of the present invention is basically a laminated film having a three-layer structure, and the surface layers on both sides thereof are the (A) layer and the central layer is the (B) layer. That is, the basic structure of the stretch film for food packaging of the present invention is (A) layer / (B) layer / (A) layer.

The surface layer (A) of the present invention is a multi-component copolymer comprising ethylene, a radical-polymerizable acid anhydride and a radical-polymerizable comonomer other than the above, and is used as a radical-polymerizable acid anhydride in the copolymer. Ethylene-based copolymer (a) in which the proportion of units derived from 0.1% by weight or more and 5% by weight or less, and the proportion of units derived from other radically polymerizable comonomer is 3% by weight or more and 50% by weight or less. It is composed of a composition containing as a main component.

The ethylene-based copolymer (a) used in the surface layer (A) of the present invention is a multi-component copolymer composed of ethylene, a radical-polymerizable acid anhydride and a radical-polymerizable comonomer. The radical-polymerizable acid anhydride referred to here is a compound having at least one radical-polymerizable unsaturated bond and at least one acid-anhydride group in the molecule, and capable of introducing an acid-anhydride group into the molecule by polymerization. Indicates. Specific examples of the compound include maleic anhydride, itaconic anhydride, endic acid anhydride, citraconic anhydride, 1-butene-3,4-
Examples include dicarboxylic acid anhydrides, alkenylsuccinic anhydrides having a double bond at the terminal having at most 18 carbons, and alkadienyl succinic anhydrides having a double bond at the terminal having at most 18 carbons. . These are 2
You can use more than one type at the same time. Of these, maleic anhydride and itaconic anhydride are particularly preferable.

Many compounds can be used as the radical-polymerizable comonomer. Specifically, they are ethylenically unsaturated ester compounds, ethylenically unsaturated amide compounds, ethylenically unsaturated acid compounds, ethylenically unsaturated ether compounds, and ethylene type unsaturated compounds. An unsaturated hydrocarbon compound etc. can be mentioned. If these are specifically described, examples of the ethylenically unsaturated ester compound include vinyl acetate, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, and (meth) acrylate. ) Hexyl acrylate, octyl acrylate (meth), (meth)
Examples thereof include lauryl acrylate and benzyl (meth) acrylate. Examples of the ethylenically unsaturated amide compound include (meth) acrylamide and N-methyl (meth)
Acrylamide, N-ethyl (meth) acrylamide,
N-propyl (meth) acrylamide, N-butyl (meth) acrylamide, N-hexyl (meth) acrylamide, N-octyl (meth) acrylamide, N, N-
Examples thereof include dimethyl (meth) acrylamide and N, N-diethyl (meth) acrylamide. Examples of the ethylenically unsaturated acid compound include (meth) acrylic acid. Ethylenically unsaturated ether compounds include methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether, butyl vinyl ether,
Examples thereof include octadecyl vinyl ether and phenyl vinyl ether. Ethylenically unsaturated hydrocarbon compounds and other compounds include styrene and α-
Methylstyrene, acrylonitrile, methacrylonitrile, acrolein, trimethoxyvinylsilane, triethoxyvinylsilane, vinyl chloride, vinylidene chloride and the like can be mentioned. Of these, particularly preferable compounds include (meth) acrylic acid esters and (meth) acrylic acid. If necessary, two or more kinds of these comonomers may be used in combination at the same time.

Ethylene copolymer (a) relating to the present invention
The proportion of the units derived from the radical-polymerizable acid anhydride and the other radical-polymerizable comonomer in each is preferably 0.1 to 5% by weight and 3 to 50% by weight, and more preferably 0.5 to 5% by weight. It is 4% by weight and 5 to 30% by weight. When the proportion of the radical-polymerizable acid anhydride is less than 0.1%, the self-adhesiveness and the deformation recovery are insufficient, and when the proportion exceeds 5%, the handling of the resin becomes difficult. When the proportion of the other radically polymerizable comonomer is less than 3%, the flexibility, transparency, gloss and deformation recovery of the ethylene-based copolymer (a) are low, and when it exceeds 50%, the handling of the resin becomes difficult. Along with that, the strength characteristics deteriorate.

Ethylene copolymer (a) relating to the present invention
In the production of, the usual low-density polyethylene production equipment and technology can be basically used. Generally, it is bulk polymerization, and is produced by radical polymerization under a pressure of 700 to 3000 atm in a temperature range of 100 to 300 ° C. The preferred polymerization pressure and polymerization temperature range are 1000 to 2500 atm, and the average temperature in the reactor is 1.
It can be 50 to 270 ° C.

When the pressure is less than 700 atm, the polymer has a low molecular weight, and the moldability and the resin properties of the composition are deteriorated. 3000
Pressures above atmospheric are essentially meaningless and only increase manufacturing costs. When the average polymerization temperature is 100 ° C. or lower, the polymerization reaction is not stable, the conversion rate to the copolymer is lowered, and there is a problem in economic efficiency. If the temperature exceeds 300 ° C, the molecular weight of the copolymer decreases, and at the same time, there is a risk of a runaway reaction.

It is desirable to use a vessel type reactor as the manufacturing apparatus. In particular, since radical-polymerizable acid anhydrides have poor polymerization stability, a high degree of homogenization within the reactor is required. If necessary, a plurality of reactors may be connected in series or in parallel to carry out multi-stage polymerization. Further, by dividing the inside of the reactor into a plurality of zones, it is possible to perform more precise temperature control.

Ethylene copolymer (a) used in the present invention
Is carried out in the presence of at least one free radical initiator under the above reaction conditions. Examples of the free radical initiator include oxygen; dialkyl peroxides such as di-t-butyl peroxide, t-butyl cumyl peroxide and dicumyl peroxide; acetyl peroxide, i-butyl peroxide, octanoyl peroxide. , Peroxycarbonates such as diacyl peroxide, di-i-propylperoxycarbonate, di-2-ethylhexylperoxycarbonate; and peroxycarbonates such as t-butylperoxypivalate, t-butylperoxylaurate, etc. Oxyesters; ketone peroxides such as methylethylketone peroxide and cyclohexanone peroxide; peroxyketals such as 1,1-bis-t-butylperoxycyclohexane and 2,2-bis-t-butylperoxyoctane; t -Butyl hydro Okishido, cumene hydroperoxide, hydroperoxide and the like; 2,2-azo -i- butyronitrile,
And other azo compounds, and the like.

In the polymerization, various chain transfer agents can be used as a molecular weight modifier. Examples of chain transfer agents include olefins such as propylene, butene and hexene, paraffins such as ethane, propane and butane, carbonyl compounds such as acetone, methyl ethyl ketone and methyl acetate, and aromatic hydrocarbons such as toluene, xylene and ethylbenzene. Etc. can be mentioned.

In the surface layer (A) of the present invention, the above resins can be used alone or as a composition of two or more kinds. The (A) layer, which is the surface layer of the film, contains the above-mentioned resin composition as a main component, and in order to adjust flexibility, deformation recovery, and molding stability, ethylene-ethyl acrylate Rubber made of polymer, ethylene-acrylic acid copolymer, ethylene-vinyl acetate copolymer, high-pressure low-density polyethylene, linear low-density polyethylene, ethylene-propylene copolymer, ethylene-butene-1 copolymer, etc. Further, in order to obtain appropriate slipperiness, self-adhesiveness, antistatic property and antifogging property, additives can be added. Specifically, sorbitan fatty acid ester, glycerin fatty acid ester, polyglycerin fatty acid ester and the like sorbitan monooleate, sorbitan monolaurate, sorbitan monobehenate, sorbitan monostearate, glycerin monooleate, glycerin monostearate,
Glycerin monolaurate, glycerin monobehenate, diglycerin monolaurate, diglycerin monostearate, diglycerin monooleate, tetraglycerin monooleate, tetraglycerin monostearate, hexaglycerin monolaurate, hexaglycerin monooleate, deca Examples thereof include, but are not limited to, glycerin monolaurate, decaglycerin monostearate, decaglycerin monooleate, and the like. These fatty acid esters are used alone or as a mixed composition, and the addition amount is usually 0.1 to 0.1%.
It is 5.0% by weight, preferably 0.5 to 3.0% by weight. If the addition amount is less than 0.1% by weight, the effect of modifying the film is not sufficient, and if it exceeds 5.0% by weight, the amount of protrusion on the film surface is large and the film becomes sticky.
As a result, workability is significantly reduced, and there is a possibility that problems such as contamination of the object to be packaged may occur.

Next, the central layer (B) of the present invention comprises a composition containing crystalline polybutene-1 as a main component.
The crystalline polybutene-1 in the present invention means butene-1.
It shows a homopolymer or a copolymer of butene-1 and other α-olefin, for example, a density of 0.880 to 0.9.
20 g / cm ³ , preferably 0.890 to 0.915 g
/ Cm ³ , the melt flow rate at 190 ℃ is 0.
A butene-1 homopolymer having a content of 1 to 10 g / 10 minutes, preferably 1 to 5 g / 10 minutes or a butene-1-ethylene copolymer having an ethylene unit content of 1.5 to 10% by weight is preferable. If the density is less than 0.880 g / cm ³ , the longitudinal and lateral strength of the film may be out of balance,
If it exceeds 20 g / cm ³ , the flexibility may be reduced. Furthermore, the melt flow rate is 0.1 g / 10
If it is less than 10 minutes, the extrudability is not sufficient, and if the melt flow rate exceeds 10 g / 10 minutes, the strength characteristics may be deteriorated.

The central layer (B) contains crystalline polybutene-1.
In addition, crystalline polypropylene, ethylene-α-olefin copolymer, ethylene-vinyl acetate copolymer, and ethylene copolymer similar to the surface layer (A) are used in order to adjust flexibility, elongation characteristics, longitudinal and lateral strength balance, and heat sealability. At least one resin component selected from the polymer (a),
It is preferably blended in the range of 15% by weight or more and 50% by weight or less based on the total amount of the crystalline polybutene-1.

Crystalline polypropylene is a copolymer of polypropylene or other 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 2 to 25% by weight, more preferably 6 to 25% by weight is more preferable. Is. 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 ethylene unit content is less than 2% by weight, the flexibility tends to be impaired,
If it exceeds 25% by weight, the effect of improving the heat sealing property cannot be expected sufficiently. Further, if the melt flow rate at 230 ° C. is less than 0.1 g / 10 minutes, the elongation property will deteriorate, and
If it exceeds g / 10 minutes, the strength is lowered, which is not preferable.

Further, the ethylene-α-olefin copolymer is selected from ethylene and α-olefins having 3 to 8 carbon atoms, for example, propylene, butene-1, hexene-1,4-methylpentene-1, octene-1 and the like. A copolymer with at least one α-olefin, wherein α
It is preferable that the olefin content is 5 to 18% by weight and the melt flow rate at 190 ° C. is 0.1 to 10 g / 10 minutes.

Further, the ethylene-vinyl acetate copolymer preferably has a vinyl acetate content of 5 to 25% by weight and a melt flow rate at 190 ° C. of 0.1 to 10 g / 10 minutes.

Further, the same ethylene-based copolymer (a) as the surface layer (A) may use the same composition as that of the surface layer (A), or may belong to the category of the above composition. Alternatively, compositions having different component compositions may be used. Furthermore, in order to obtain appropriate slipperiness, self-adhesiveness, antistatic property and antifogging property with respect to these resin components, the same additives as in the surface layer (A) can be blended.

Here, the central layer (B) is a layer made of a composition containing crystalline polybutene-1 as a main component, and the surface layers (A) on both sides thereof are mainly composed of an ethylene copolymer (a). The main purpose of laminating the layer made of the composition is to provide a single film made of the composition containing crystalline polybutene-1 as a main component, in the case of film flexibility, transparency, gloss, see-through property, self-adhesiveness, deformation recovery property, etc. Is not obtained enough,
On the contrary, a single film made of a composition containing the ethylene-based copolymer (a) as a main component cannot provide a film having satisfactory heat sealability and strength. These problems are caused by the fact that the central layer (B) is a layer made of a composition containing crystalline polybutene-1 as a main component, and a surface layer made of a composition containing an ethylene-based copolymer (a) as a main component on both sides of the layer ( A)
It is the first problem to be solved by stacking.

The stretch film for food packaging of the present invention is a film having a three-layer structure in which the above-mentioned (A) layer is a surface layer on both sides and the (B) layer is a center layer, and (B)
The surface layer (A) on both sides of the layer may use the same composition, or compositions belonging to the category of the above composition but having different component compositions. As a method for producing such a laminated film, the above-mentioned respective compositions can be laminated by a conventional method, specifically, an inflation method, a T-die method, an extrusion laminating method or the like. Of these, the inflation method is preferable because it has a good balance of vertical and horizontal physical properties.

The total thickness of the stretch film for food packaging of the present invention is usually 8 to 30 μm, preferably 10 to 20 μm. 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 during stretching of the film becomes large and the tray or the packaged product is deformed. There is a possibility that the problem will occur.

Further, the thickness of the central layer (B) of the stretch film for food packaging is 20% or more of the total thickness of the film 8
5% or less is preferable, and specifically 1.0 to 12.0 μ
m, preferably 2.0 to 8.0 μm. Here, if the thickness of the central layer (B) is less than 20% of the total thickness of the film, the effect of improving the heat-sealing property and the strength balance in the vertical and horizontal directions cannot be expected, and if it exceeds 85%, uniform elongation properties may be impaired. .

[0033]

EXAMPLES Next, the present invention will be described in more detail with reference to Examples and Comparative Examples. (Example 1) As the resin for the surface layer (A), an ethylene-methyl methacrylate-maleic anhydride terpolymer was used. This copolymer utilizes equipment of a high-pressure process low-density polyethylene plant and has a polymerization temperature of 240 ° C. and a polymerization pressure of 190.
It was manufactured under the condition of 0 Kg / cm ² . Melt flow rate of copolymer (hereinafter abbreviated as MFR) (JIS-K7
210, 190 ℃, load = 2.16Kg, below MFR is all 15.0g / 10 minutes under this condition except temperature),
The content of units derived from methyl methacrylate was 16% by weight, and the content of units derived from maleic anhydride was 2.2% by weight. The composition of the comonomer was determined by infrared absorption spectrum. This ethylene copolymer (a ₁ ) 99.
A composition comprising 5% by weight and 0.5% by weight of diglycerin monooleate was used as the resin for the surface layer (A).

As the resin for the central layer (B), crystalline polybutene-1 (density 0.910 g / cm ³ , MFR 1.0 g / 10 min at 190 ° C.): 60% by weight, propylene-ethylene random copolymer (containing ethylene) Amount 7% by weight, MFR at 230 ° C. 2.0 g / 10 min): 20
% By weight, ethylene-methyl methacrylate-maleic anhydride terpolymer (MFR at 190 ° C. 15.0 g
/ 10 minutes, the content of units derived from methyl methacrylate is 16% by weight, the units derived from maleic anhydride is 2.2% by weight): 97% by weight of a composition consisting of 20% by weight of (a ₁ ), diglycerin A composition consisting of 3.0% by weight of monooleate was used.

These resins have a diameter of 50 mm and L / D26
Using an inflation molding machine consisting of two extruders of No. 3 and an annular three-layer die of 100 mm, the resin temperature was 190 ° C. and the blow-up ratio was 5.0, and the thickness of each layer was 3/6/3.
A film having a thickness of 12 μm and a total thickness of 12 μm was obtained. Using this film, on a tray made of expanded polystyrene, meat,
Fish, side dishes, fruits, etc. were placed and packaged with an automatic stretch wrapping machine. The properties of the film and the measurement results are shown in Table 1 below.
And shown in Table 2.

(Example 2) A composition containing 98.5% by weight of an ethylene copolymer (a ₁ ) and 1.5% by weight of diglycerin monooleate as the resin for the surface layer (A) as in Example 1. As a resin for the central layer (B), crystalline polybutene-1 (density 0.910 g / cm ³ , MFR 1.0 g / 10 min at 190 ° C.): 50% by weight, ethylene-α-olefin copolymer (ethylene and hexene- 1 copolymer, density 0.917 g / cm ³ , MFR 2.0 g / 10 min at 190 ° C.): 20% by weight, ethylene-methyl methacrylate-maleic anhydride terpolymer (MFR 15.90 at 190 ° C.). 0 g / 10 minutes, the content of units derived from methyl methacrylate is 16% by weight, and the units derived from maleic anhydride is 2.2% by weight): (a ₁ ).
A composition comprising 99% by weight of a composition comprising 30% by weight and 1.0% by weight of diglycerin monooleate was used. The same procedure as in Example 1 was carried out except that these compositions were used, and the thickness of each layer was 3/6/3 μm and the total thickness was 12 μm.
m film was obtained. Using this film, meat, fish, side dishes, fruits, etc. 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 below.

Example 3 As an ethylene-based copolymer,
An ethylene-n-butyl acrylate-maleic anhydride terpolymer was used. The copolymer was produced under the conditions of a polymerization temperature of 240 ° C. and a polymerization pressure of 1900 Kg / cm ² using the equipment of a high pressure low density polyethylene plant. The MFR of the copolymer was 10, the content of units derived from n-butyl acrylate was 12% by weight, and the unit derived from maleic anhydride was 1.8% by weight. The composition of the comonomer was determined by infrared absorption spectrum. This copolymer was designated as (a ₂ ). A film having a thickness of each layer of 3/6/3 μm and a total thickness of 12 μm was obtained in the same manner as in Example 1 except that this ethylene copolymer (a ₂ ) was used. Using this film, meat, fish, side dishes, fruits, etc. 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 below.

(Example 4) The thickness of the central layer (B) was set to 6 μm.
m, and a film was obtained in the same manner as in Example 1 except that the thickness of both surface layers (A) was 6 μm. 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 below.

(Example 5) The thickness of the central layer (B) was 3 μm.
m, and a film was obtained in the same manner as in Example 1 except that the thickness of both surface layers (A) was 3 μm. 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 below.

[0040]

[Table 1]

[0041]

[Table 2]

Physical properties of each item in Tables 1 and 2 were measured and evaluated by the following methods. 1) MFR; JIS K7210 2) Density; JIS K6760 3) Haze (transparency); JIS K6714 4) Gloss (gloss); JIS K7105 5) Clarity (transparency); Murakami Color Research Laboratory Clarity Meter slit Measured with a width of 1 mm 6) Breaking strength; JIS Z1702 7) Elongation; JIS Z1702 8) Deformation recovery property: A sample piece with a width of 15 mm and a length of 100 mm is extended to 200 mm and immediately released 30 seconds later, the length of the sample piece It 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.

Comparative Example 1 As the resin for the central layer (B), ethylene-vinyl acetate copolymer (vinyl acetate unit content 15% by weight, MFR at 190 ° C. 2.0 g / 10)
Min) 30% by weight; polybutene-1 (density 0.915 g /
cm ³ , MFR at 190 ° C. 2.0 g / 10 min) 7
0% by weight of the composition was used as a resin for the surface layer (A), ethylene-vinyl acetate copolymer (vinyl acetate unit content 15% by weight, MFR at 190 ° C. 2.0 g / 1
0 minutes) 98.5% by weight; sorbitan monooleate 1.5
Films were formed in the same manner as in Example 1 using the composition of wt% to obtain a film having a thickness of each layer of 3 μm / 6 μm / 3 μm and a total thickness of 12 μm. This film was used for packaging. The properties of the film and the measurement results are shown in Tables 3 and 4 below.

Comparative Example 2 A commercially available plasticized polyvinyl chloride stretch film (thickness: 15 μm) was used in Example 1.
It was packaged in the stretch automatic packaging machine in the same manner as. The properties of the film and the measurement results are shown in Tables 3 and 4 below.

[0045]

[Table 3]

[0046]

[Table 4]

In Tables 3 and 4, the physical properties of each item were measured and evaluated in the same manner as in the examples.

[0048]

As described above, the stretch film for food packaging of the present invention is excellent in transparency, gloss and transparency,
It has uniform elongation properties when the film is stretched,
It is excellent in heat sealability in an automatic packaging machine, has sufficient elongation and deformation recovery, is suitable for packaging machines, and has excellent workability. In addition, the breathability, anti-fog property, water vapor permeability, required for stretch films for food packaging,
It has good physical properties such as self-adhesiveness. Further, there is no problem of disposability after use such as the conventional stretch film made of plasticized polyvinyl chloride, 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, fresh meat and prepared foods.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Satoshi Iwamoto, Oita City, Oita Prefecture 2 Nakanozu, Showa Denko Co., Ltd. Oita Research Co., Ltd. (72) Inventor Shinoda Toyoumi, Oita City, Oita Prefecture 2 Nakanozu Showa Denko Co., Ltd. Company Oita Research Center

Claims (4)

[Claims] 1. A laminated film having a three-layer structure, wherein the surface layers (A) on both sides of the film are multi-component copolymers comprising ethylene, a radical-polymerizable acid anhydride and other radical-polymerizable comonomers. If the proportion of the units derived from the radical-polymerizable acid anhydride in the copolymer is 0.1% by weight or more and 5% by weight or less, and the proportion of the units derived from other radical-polymerizable comonomers is 3% by weight or more. A food package comprising a composition containing 50% by weight or less of an ethylene-based copolymer (a) as a main component, and the central layer (B) containing a composition containing a crystalline polybutene-1 as a main component. Stretch film for. 2. The crystalline polybutene-1 of the central layer (B) is a butene-1 homopolymer or a copolymer of butene-1 and another α-olefin.
The stretch film for food packaging described. 3. The central layer (B) is 20% of the total film thickness.
The stretch film for food packaging according to claim 1, wherein the stretch film is 85% or less. 4. The stretch film for food packaging according to claim 1, wherein the total thickness of the film is 8 to 30 μm.