JPH06100018A - Stretched film for packing food - Google Patents

Abstract

PURPOSE:To provide a stretched film for packing of food which is excellent in transparency, luster, seeing through, elongation, recovery from deformation, adaptability for a packing machine, workability, etc., and further which is safe for waste disposal and hygienic for food. CONSTITUTION:This is a laminated film composed of at least three layers. The surfaces of both sides (A layer) of the film are composed of multi- dimensional copolymer (a) made of radical-polymeride acid anhydride with ethylene and other radical polymeride comonomer. The layer (B layer) inside the surface layers is a copolymer of crystalline polypropylene (B1) having melt flow rate of 0.1-10 g/10min. and a copolymer (B2) of ethylene with a kind of at least alpha-olefine selected from alpha-olefine with carbon number of 3-12, which includes 10-9 0% of alpha-olefine by weight and which is 0.910g/cm<3> or less in the density.

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stretch film for food packaging, and more particularly to a film obtained by laminating layers made of a specific composition, which is transparent, glossy, transparent, stretchable and heat sealable. The present invention relates to a stretch film for food packaging, which has excellent properties, deformation recovery, etc., and has no waste disposal property 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.
Moreover, the packaging workability is not sufficient. 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. Elongation when stretched and little recovery from deformation, the characteristics required as a stretch film are:
It's far apart. Also, as a film,
The one described in Japanese Patent Publication No. 52624/1990 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 are laminated. Stretch films for food packaging have 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 poor in suitability for an automatic packaging machine.

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 (Japanese Patent Laid-Open No. 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, particularly transparency and uniform elongation property of the film.

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 waste treatment or food hygiene problems has been proposed yet. Is the current situation.

[0010]

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.

[0011]

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 is a laminated film having at least a three-layer structure, wherein the surface layers (A layers) on both sides of the film are composed of ethylene, a radical-polymerizable acid anhydride and other radical-polymerizable comonomers. The ratio of the units derived from the radical-polymerizable acid anhydride in the copolymer is 0.1 wt% or more and 5 wt% or less, and the ratio of units derived from other radical-polymerizable comonomers. Is 3 wt% or more and 50 wt% or less, and the melt flow rate of the layer (B layer) closer to the center than the surface layer (A layer) is 0.1 to 10 g.
A crystalline polypropylene (B ₁ ) having a length of / 10 minutes and a copolymer of ethylene and at least one α-olefin selected from α-olefins having 3 to 12 carbon atoms, wherein the content of α-olefin is Provided is a stretch film for food packaging, comprising a composition with a copolymer (B ₂ ) having a density of 0.910 g / cm ³ or less and 10% by weight or more and 90% by weight or less. .

The stretch film for food packaging of the present invention is a laminated film having at least a three-layer structure, in which the surface layers on both sides are (A layer), and the layer on the center side of this (A layer) is (B layer). Is. That is, the basic structure of the stretch film for food packaging of the present invention is (A layer) / (B layer) /
Although it is (A layer), a plurality of layers may be provided between (A layer) and (B layer) or between (B layer).

The surface layer (A layer) of the present invention is a multi-component copolymer composed of ethylene, a radical-polymerizable acid anhydride and a radical-polymerizable comonomer other than this, and the radical-polymerizable acid anhydride in the copolymer. The ratio of units derived from is 0.1
If the proportion of units derived from other radically polymerizable comonomer is 3% by weight or more, 50% by weight or more and 5% by weight or less by weight%
It is composed of the following ethylene-based copolymer (a).

The ethylene-based copolymer (a) used in the surface layer (A layer) of the present invention is a multi-component copolymer comprising ethylene, a radical-polymerizable acid anhydride and a radical-polymerizable comonomer other than ethylene. 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-dicarboxylic acid anhydride, and at most 1 carbon atom.
Examples thereof include alkenylsuccinic anhydride having a double bond at the terminal of 8 and alkadienyl succinic anhydride having a double bond at the terminal having at most 18 carbon atoms. These may be used in combination of two or more kinds at the same time. Of these, maleic anhydride and itaconic anhydride are particularly preferable.

Many compounds can be used as the radical-polymerizable comonomer, and specifically, an ethylenically unsaturated ester compound, an ethylenically unsaturated amide compound, an ethylenically unsaturated acid compound, an ethylenically unsaturated ether compound, an ethylene type 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 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 an apparatus for production. 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. Diacyl peroxide such as oxide, peroxycarbonate such as di-i-propylperoxycarbonate, di-2-ethylhexylperoxycarbonate; t-
Peroxyesters such as butylperoxypivalate, t-butylperoxylaurate; ketone peroxides such as methylethylketone peroxide, cyclohexanone peroxide; 1,1-bis-t-butylperoxycyclohexane, 2,2 Peroxyketals such as bis-t-butylperoxyoctane; hydroperoxides such as t-butylhydroperoxide, cumene hydroperoxide; azo compounds such as 2,2-azo-i-butyronitrile, etc. Is mentioned.

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 layer) of the present invention, the above resins can be used alone or as a composition of two or more kinds. Further, the surface layer (A layer) of the film is made of the above-mentioned resin composition, and further, in order to obtain appropriate slipperiness, self-adhesiveness, antistatic property and antifogging property, an additive is added. Can be blended. Specifically, sorbitan fatty acid ester, glycerin fatty acid ester, polyglycerin fatty acid ester, and other sorbitan monooleate, sorbitan monolaurate, sorbitan monobehenate, sorbitan monostearate, glycerin monooleate, glycerin monostearate, glycerin monolaurate. Rate, glycerin monobehenate, diglycerin monolaurate, diglycerin monostearate, diglycerin monooleate, tetraglycerin monooleate, tetraglycerin monostearate, hexaglycerin monolaurate, hexaglycerin monooleate, decaglycerin monolaurate Examples thereof include but are not limited to rates, 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 5.0% by weight, preferably 0.5 to
It is 3.0% by weight. If the added amount is less than 0.1% by weight,
If the effect of modifying the film is insufficient, and if it exceeds 5.0% by weight, the amount of protrusion to the film surface is large and the film becomes sticky, resulting in a marked decrease in workability and contamination of the packaged object. May cause problems such as

Next, the layer (B layer) closer to the center than the surface layer (A layer) has a melt flow rate of 0.1 to 10 g / 1.
A crystalline polypropylene (B ₁ ) having 0 minutes, and a copolymer of ethylene and at least one α-olefin selected from α-olefins having 3 to 12 carbon atoms,
It comprises a composition with a copolymer (B ₂ ) having an α-olefin content of 10% by weight or more and 90% by weight or less and a density of 0.910 g / cm ³ or less.

The first component, crystalline polypropylene (B
₁ ) is a copolymer with polypropylene or other resin unit produced by a conventionally known method, and has a melt flow rate at 230 ° C. of 0.1 to 10 g / 10 minutes, preferably 0.2 to 5 g. / 10 minutes, more preferably 0.5 to
It is 3.0 g / 10 minutes. If the melt flow rate at 230 ° C. is less than 0.1 g / 10 minutes, the molding stability will be problematic, and if it exceeds 10 g / 10 minutes, the strength of the film will be insufficient and molding stability will be problematic. Further, it is preferably a copolymer of ethylene and at least one α-olefin selected from α-olefins having 4 to 12 carbon atoms and propylene, and more preferably
It is a copolymer of ethylene or butene-1 and propylene. Here, the content of α-olefin is 10
Wt% or less, preferably 2 wt% or more and 10 wt% or less,
It is more preferably 4% by weight or more and 8% by weight or less. α
-If the olefin content exceeds 10% by weight, the heat sealability may deteriorate.

The first component, crystalline polypropylene (B
₁ ) plays an important role in solving the problem of melting and piercing during heat-sealing in an automatic packaging machine. It is important to mix. That is, the content of the crystalline polypropylene (B ₁ ) in the composition forming the layer (B layer) depends on other components, but is preferably 10% by weight or more and 50% by weight or less. When the content of the crystalline polypropylene (B ₁ ) is less than 10% by weight,
There is a possibility that the effect of improving heat sealability may not be sufficiently obtained, and the appropriate temperature range in which heat seal is possible is narrow, so when heat sealing with a hot plate of an automatic packaging machine, the film partially melts and holes are formed. There is a problem of openness, and in order to prevent this, there is no choice but to change the temperature condition in accordance with the change in the weight of the contents, and the workability may be significantly reduced. On the other hand, if it exceeds 50% by weight, the elongation property of the film is deteriorated, the tray is deformed during stretch wrapping, and there is a problem that a tight wrapping cannot be obtained. Furthermore, when the film is stretched, it is uneven. There is a risk of causing wrinkles in the packaging due to the excessive stretching.

Next, the copolymer (B ₂ ) as the second component is
A copolymer having a density of 0.910 g / cm ³ or less and ethylene and at least one α-olefin selected from α-olefins having 3 to 12 carbon atoms, and in some cases, a smaller amount of a polyene structure. Hydrocarbons having, for example, dicyclopentadiene, 1,4-hexadiene, ethylidene norbornene and the like may be further copolymerized. Examples of the α-olefin used here include propylene, butene-1, hexene-1, heptene-1,
4-methyl-1-pentene, octene-1 and the like.
The content of α-olefin in the copolymer (B ₂ ) is preferably 10% by weight or more and 90% by weight or less. If it is less than 10% by weight or more than 90% by weight, the film may not have sufficient deformation recovery properties and elongation properties.

The second component, the copolymer (B ₂ ), plays an important role in enhancing the flexibility of the film and obtaining the finish of a tight package. Further, the film tears or heat during stretching. It is important to mix within a certain range to avoid the problem of melting and puncturing during sealing. That is, depending on the component of the crystalline polypropylene (B ₁ ), it is preferably 50% by weight or more and 90% by weight or less. If the content of the copolymer (B ₂ ) is less than 50% by weight, the flexibility of the film may be insufficient and the effect of improving the deformation recovery may not be sufficiently obtained.
If it exceeds the range, the film is likely to be broken during packaging, and the heat resistance of the film is insufficient, so that the temperature range in which heat sealing is possible is narrowed, and there is a possibility that a problem may occur in which the film is melted and punctured during heat sealing.

Further, the copolymer (B ₂ ) which is the second component
Is a copolymer (B ₂₁ ) having an α-olefin content of 70% by weight or more and 90% by weight or less, and a copolymer (B ₂₁ ) having an α-olefin content of 10% by weight or more and 70% by weight or less.
₂₂ ). More preferably, the copolymer (B ₂₁ ) has an α-olefin content of 75.
The content of the α-olefin in the copolymer (B ₂₂ ) is 25% by weight or more and 60% by weight or less. The blending ratio of the copolymer (B ₂₁ ) and the copolymer (B ₂₂ ) is such that the copolymer (B ₂₁ ) is 40% by weight or more and 90% by weight or less, and the copolymer (B ₂₂ ) is 10% by weight or more 60% by weight or more. It is preferably less than or equal to weight%.

The layer (B layer) of the present invention comprises the above-mentioned resin composition, and further has appropriate slipperiness, self-adhesiveness, antistatic property and antifogging property against these resin components. In order to obtain the same, the same additive as that of the surface layer (A layer) can be blended.

In the present invention, the surface layer (A layer) on both sides of the film is provided with a layer composed of the ethylene copolymer (a), and the layer (B layer) closer to the center than the (A layer) is crystalline polypropylene. The main purpose of providing the layer composed of the composition of (B ₁ ) and the copolymer (B ₂ ) is to obtain the ethylene-based copolymer (a).
This is because the single film made of does not have satisfactory heat-sealing property and strength. On the contrary, the single film made of the composition of crystalline polypropylene (B ₁ ) and the copolymer (B ₂ ). Then, the flexibility, transparency, gloss, see-through property, self-adhesion property, deformation recovery property, etc. of the film cannot be obtained sufficiently. These problems are caused by providing a layer made of the ethylene-based copolymer (a) on both surface layers (A layer) of the film, and adding a crystalline polypropylene (B layer) to the layer (B layer) on the center side of the (A layer). _This can only be solved by laminating a layer composed of the composition of ₁ ) and the copolymer (B ₂ ).

In the stretch film for food packaging of the present invention, a layer comprising the ethylene copolymer (a) is provided on both surface layers (A layer) of the film, and a layer (B) closer to the center than this (A layer) is provided. A layered film having at least a three-layer structure in which a layer made of a composition of crystalline polypropylene (B ₁ ) and a copolymer (B ₂ ) is provided in the layer), and the surface layers (A layers) on both sides are 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. 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 thickness of the stretch film for food packaging of the present invention is usually 8 to 30 μm, preferably 10 to 20 μm. The thickness of the film is 8 μm
If it is less than the above, the handling property of the film is remarkably deteriorated due to the deterioration of the strength and stiffness of the film, and if it exceeds 30 μm, the stress during stretching of the film becomes large and the tray or the packaged object may be deformed. is there.

Furthermore, the thickness of the layer (B layer) of the stretch film for food packaging of the present invention is 20% of the total thickness of the film.
It is preferably not less than 85% and specifically, 1.0 to 2
A thickness of 5.0 μm, preferably 2.0 to 17.0 μm is suitable. Here, if the thickness of the layer (B 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.

[0035]

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 layer), ethylene-
A methyl methacrylate-maleic anhydride terpolymer was used. This copolymer utilizes equipment of a high-pressure low-density polyethylene plant and has a polymerization temperature of 240 ° C. and a polymerization pressure of 19
It was manufactured under the condition of 00 Kg / cm ² . Melt flow rate of copolymer (hereinafter abbreviated as MFR) (JIS-K72
10,190 ° C., load = 2.16 Kg, all MFR conditions are 15.0 g / 10 minutes, except for temperature, the content of units derived from methyl methacrylate is 16% by weight,
The unit 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 ) 99.5
A composition composed of 1% by weight and 0.5% by weight of diglycerin monooleate was used as the resin for the surface layer (A layer).

Next, a propylene-ethylene random copolymer (ethylene content 4% by weight, MFR 1.0 g / 10 min at 230 ° C.) was used as a resin for the (B layer) on the center side of the surface layer (A layer). Composition 30: 30% by weight, ethylene-propylene copolymer (ethylene content 30% by weight, density 0.870 g / cm ³ ): 70% by weight
A composition consisting of 7% by weight and 3.0% by weight of diglycerin monooleate was used. MFR of this composition at 230 ° C
Was 0.5 g / 10 minutes.

These resins are used with a diameter of 50 mm and L / D26
2 extruders and an inflation molding machine consisting of a 100 mm annular three-layer die were molded at a resin temperature of 210 ° C. and a blow-up ratio of 5.0, and the thickness of each layer was 5 μm / 5.
A film having a thickness of μm / 5 μm and a total thickness of 15 μm 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 2) As the resin for the surface layer (A layer), as in Example 1, an ethylene copolymer (a ₁ ) 99.5 was used.
% Of diglycerin monooleate, and a propylene-ethylene random copolymer (ethylene content is used as a resin for the layer (B layer) closer to the center than the surface layer (A layer) is used. 4% by weight, MFR at 230 ° C. 1.0 g / 10 minutes): 40% by weight, ethylene-propylene copolymer (ethylene content 20% by weight, density 0.880 g / cm ³ ): 45% by weight, ethylene-propylene copolymer Polymer (ethylene content 70% by weight, density 0.
880 g / cm ³ ): 97% by weight of a composition consisting of 15% by weight and 3.0% by weight of diglycerin monooleate were used.

Example 1 except that these compositions were used
The thickness of each layer is 5μm / 5μm / 5
A film having a thickness of 15 μm and a total thickness of 15 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 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 ).

The procedure of Example 1 was repeated except that this copolymer (a ₂ ) was used, and the thickness of each layer was 5 μm / 5 μ.
A film having a thickness of m / 5 μm and a total thickness of 15 μm 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 4) The same resin as in Example 1 was used for both the surface layer (A layer) and the layer on the center side of this (B layer), and a film ( The same procedure as in Example 1 is performed except that the scrap layer) is provided, and the thickness of each layer is (A layer) / (scrap layer) / (B layer) /
(A layer), a film having a thickness of 4 μm / 2 μm / 5 μm / 4 μm and a total thickness of 15 μm was obtained. (Scrap layer) collects and crushes the part that does not become a product during film formation,
It was thrown in as it was. The scrap recovery rate is
It was 13%. 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.

[0043]

[Table 1]

[0044]

[Table 2]

In Tables 1 and 2, the physical properties of each item 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 having a width of 15 mm and a length of 100 mm is extended to 200 mm and immediately released 30 seconds later to measure 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 Ethylene-vinyl acetate copolymer (vinyl acetate unit content 15% by weight, MFR 2.0 g / 1 at 190 ° C.) as a resin for the layer on the center side (layer B)
0 minutes) 30% by weight; propylene-ethylene random copolymer (ethylene unit content 7% by weight, MFR at 230 ° C. 2.0 g / 10 minutes) 70% by weight of a composition for a surface layer (layer A) Ethylene-vinyl acetate copolymer as resin (vinyl acetate unit content 15% by weight, 190
MFR 2.0 g / 10 minutes at ℃) 98.5 wt%;
Using a composition consisting of 1.5% by weight of diglycerin monooleate, a film was formed in the same manner as in Example 1 to obtain a film having a thickness 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 below.

Comparative Example 2 A propylene-ethylene random copolymer (ethylene unit content 4% by weight, MFR 1.0 g at 230 ° C.) as a resin for the layer on the center side (layer B)
/ 10 min) 70% by weight; butene-1-ethylene copolymer (butene-1 content 97% by weight, density 0.895 g / c
m ^3, 190 MFR0.2g / 10 min at ° C.) 30
Using a composition composed of 10% by weight, ethylene-vinyl acetate copolymer (vinyl acetate unit content 15% by weight, MFR 2.0 g / 1 at 190 ° C.) as a resin for the surface layer (A layer)
0 minutes) 98.5% by weight; diglycerin monooleate 1.
A film containing 5% by weight of the composition was formed in the same manner as in Example 1 to obtain a film having a thickness 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 below.

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

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[Table 3]

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

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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 foods such as various 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 (5)

[Claims] 1. A laminated film having at least a three-layer structure, wherein the surface layers (A layers) on both sides of the film are multicomponent copolymers comprising ethylene, a radical-polymerizable acid anhydride and other radical-polymerizable comonomers. It is a polymer, and the ratio 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 ratio 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), and the layer (B layer) closer to the center than the surface layer (A layer) has a melt flow rate of 0.1 to 10 g / 10 min. Crystalline polypropylene (B ₁ ) which is ethylene, ethylene and a carbon number of 3 to ₁
A copolymer with at least one α-olefin selected from the α-olefins of 2, wherein the content of the α-olefin is 10% by weight or more and 90% by weight or less, and the density is 0.910 g / cm ³ or less. A stretch film for food packaging, comprising a composition with a certain copolymer (B ₂ ). 2. The crystalline polypropylene (B) of the layer (B layer).
₁ ) is a copolymer of ethylene and at least one α-olefin selected from α-olefins having 4 to 12 carbon atoms and propylene, wherein the content of the α-olefin is 10% by weight or less, and the melt Flow rate is 0.1
It is 10 g / 10 minutes, The stretch film for food packaging of Claim 1 characterized by the above-mentioned. 3. The food packaging according to claim 1, wherein the content of the crystalline polypropylene (B ₁ ) in the composition forming the layer (B layer) is 10% by weight or more and 50% by weight or less. Stretch film. 4. The copolymer (B ₂ ) of the layer (B layer) comprises a copolymer (B ₂₁ ) having an α-olefin content of 70% by weight or more and 90% by weight or less and an α-olefin content. 10
The stretch film for food packaging according to claim 1, which is a composition with a copolymer (B ₂₂ ) in an amount of from 70% by weight to 70% by weight. 5. The crystalline polypropylene (B) of the layer (B layer).
_The stretch film for food packaging according to claim 1, wherein the composition of ₁ ) and the copolymer (B ₂ ) has a melt flow rate of 0.1 to 10 g / 10 minutes. [0001]