JPH0880565A - Multilayer shrink film - Google Patents

Abstract

PURPOSE: To provide a multilayered shrink film consisting of a surface layer, an inner layer composed of a specific ethylene/α-olefin copolymer and a layer composed of a specific polypropylene resin and made excellent in low temp. shrinkability by specifying the thickness ratio of the respective layers and also specifying the difference between the heat shrinkage factors of the respective layers and an average heat shrinkage factor, average heat shrinkage stress and heat shrinkage force. CONSTITUTION: A surface layer A composed of an ethylene/vinyl acetate copolymer, an inner layer B composed of an ethylene/α-olefin 2 copolymer with density of 0.850-0.930g/cm<2> and a melt flow rate of 0.2-3g/10min under load of 2.16kgf at 190 deg.C and a layer C composed of a polypropylene resin with a melt flow rate of 0.1-10g/10min under load of 2.16kgf at 230 deg.C are provided. The thickness ratios of the respective layers A, B, C occupying in all of layers are respectively set to 10-60%, 10-80% and 5-60% and, further, the heat shrinkage factor of a multilayered shrink film is 15% or more in one of longitudinal and lateral directions and the difference value between longitudinal and lateral heat shrinkage stresses at 80 deg.C and 100 deg.C is set to 30% or less and the heat shrinkage stress in longitudinal and lateral directions at 80 deg.C is set to 90g/mm<2> or more and heat shrinkage force at 80 deg.C is set to 110g/15mm width or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The film of the present invention is shrinkable as a packaging material (used as a synonym for "shrink").
It relates to a multilayer film having properties suitable for packaging and mainly used for food packaging applications.

[0002]

2. Description of the Related Art Conventionally, shrink wrapping has the feature that it can quickly and tightly package a plurality of products regardless of the shape and size of the packaged product, and the resulting packaged product has an appearance. It is often used for packaging foods, miscellaneous goods, etc. because it is beautiful, exhibits the display effect, enhances the product value, keeps the contents sanitary, and is easy to visually confirm the quality. In such shrink wrapping, the contents are first wrapped with a little room left in the film, and then the film is heat-shrinked by hot air or the like, or the film is wrapped in a tensioned state to some extent as in conventional stretch wrapping, and the end of the film is wrapped. Is folded to the bottom of the packaged object, and the overlapping portion of the film at the folded portion is adhered to the hot plate (this adhesion method is hereinafter referred to as bottom seal), and then heat shrink treatment is similarly performed. There are methods such as removing local wrinkles and wrinkles on the film (hereinafter referred to as stretch shrink), and all of them produce a tight and beautiful finish. As the properties required for films for these applications, first of all, the sealability is important, especially in the case of stretch shrink, bottom sealability is important.
Generally, a wide bottom seal temperature range is required. Here, the bottom seal temperature range means that if the seal temperature is low, it does not adhere (including heat adhesion due to melting of the surface layer here), and even if seemingly adheres, the adhered part easily peels off during heat shrinkage. If it is removed, the adhesion part may be peeled off during the subsequent handling (for example, during transportation), and if the sealing temperature is too high, the film may locally melt or whiten, resulting in heat shrinkage treatment. It refers to the proper sealing temperature range that does not have these problems, including the subsequent sealing state. In addition, as other required properties, since the object to be packaged often dislikes heat in general, it may be low-temperature shrinkability,
This is also effective in terms of energy cost. It also has mechanical strength such as tear resistance, puncture resistance, and drop weight impact strength, transparency, gloss, anti-fog property, etc., and distortion caused by various deformations applied to the film after packaging (transportation Vibrations in the inside, deformation of the contents due to changes in the environmental load such as the load applied to the stacked packages especially at the lower stage, or when pressed with fingers, etc., the lumps and wrinkles that occur on the film, and also the local dents ) Is to have a deformation multiplicity that recovers to the original state as quickly as possible, and to exhibit a stable packaging finish that is not affected by the temperature of the contents during packaging, and a film that comprehensively satisfies these Strongly desired.

By the way, conventionally, as a heat-shrinkable film, a film mainly composed of polyvinyl chloride, polypropylene, polyethylene or the like is known, but a single-layer film is not able to comprehensively satisfy the above-mentioned required characteristics. It is difficult, especially for heat-shrinkable films using polyvinyl chloride, plasticizers and heat stabilizers that are added and used in combination are not preferable for hygiene, and hydrogen chloride gas is used for heat sealing, disposal, and incineration. There is a problem in the work environment and environmental protection such as occurrence of.

On the other hand, as a multilayer heat-shrinkable film,
JP-A-59-158254 discloses a three-layer low-temperature shrinkable film having a surface layer made of an ethylene-vinyl acetate copolymer (hereinafter also referred to as EVA) and a core layer made of linear polyethylene. . However, although this film is excellent in transparency and tear strength, it has insufficient puncture strength, and there is a problem in packaging those having protrusions (for example, headed shrimp, crab, etc.). Further, there is a problem that the bottom sealing property has a narrow sealing temperature range (equal to the hot plate surface temperature). Further, this film also has an insufficient recovery from deformation after packaging. In addition, JP-A-60-1
Japanese Patent No. 54065 discloses a five-layer shrink film having EVA as a surface layer and a linear low-density polyethylene layer and an EVA layer as an inner layer. This film also has excellent transparency and tear strength, but has a bottom. The sealing temperature range is practically insufficient, and the deformation recovery property after shrink wrapping is also insufficient. Japanese Patent Publication No. 2-14898 discloses a multilayer film containing at least one specific mixed composition layer containing a soft elastomer, but it is excellent in transparency and bottom sealing property and also imparts antifogging property. It is easy, but the tear strength and the puncture strength are insufficient, and the deformation multiplicity after shrink wrapping is poor. Further, JP-A-3-215034, JP-A-3-220250, and JP-A-5-131.
Japanese Patent No. 599 discloses a multilayer shrink film using a specific linear low-density polyethylene or a specific ethylene α-olefin copolymer, and these films have good transparency and tear strength, If an anti-fog agent is added by the kneading method in order to impart anti-fog durability,
There are problems that the anti-fogging agent is poor in bleeding property and it is difficult to exhibit the anti-fogging property, the bottom sealing temperature range is narrow, and highly accurate maintenance of packaging conditions is required. Further, JP-A-5-318682 discloses a film in which the core layer is composed of an ethylene-propylene copolymer or an ethylene-butene-propylene copolymer, and both outer layers are a specific linear low density polyethylene. However, this film is inferior in anti-fogging property and insufficient in puncture strength and drop weight impact strength. JP-A-6-134945 discloses that the core layer is an ethylene-propylene copolymer or ethylene-butene-
A multilayer film made of a propylene copolymer, in which both outer layers are made of a mixture of a linear low-density polyethylene and an ethylene-ethyl acrylate copolymer, is disclosed, but the transparency and gloss are poor and the antifogging property is also exhibited. It is difficult and has poor piercing strength and falling weight impact strength.

As described above, at present, no film having the characteristics that comprehensively satisfy the requirements as a shrink wrapping film has been obtained, and the thinning of the film from the viewpoint of resource saving is also a big problem. Therefore, the emergence of a film satisfying these requirements is strongly desired.

[0006]

SUMMARY OF THE INVENTION The object of the present invention is to have high strength even with a thin wall, excellent sealing property, especially bottom sealing property in stretch shrink packaging, and practically sufficient transparency, gloss and anti-fogging property. It is an object of the present invention to provide a shrink film that exhibits excellent performance in shrink-wrapping, has good recovery from deformation of the film after packaging, and has excellent low-temperature shrinkability.

[0007]

DISCLOSURE OF THE INVENTION As a result of intensive studies made by the present inventors to overcome the above-mentioned drawbacks of the prior art, EVA
In a multi-layer film having an ethylene-based copolymer as a surface layer, at least two layers of a specific resin layer are arranged as an inner layer, and a multi-layer film having specific physical properties is further provided, as compared with a conventional film, The inventors have found that the strength, sealing property, and deformation recovery property after shrink wrapping are remarkably improved even with a thin wall, and have reached the present invention.

That is, the present invention is at least one copolymer resin selected from ethylene-vinyl acetate copolymers, ethylene-aliphatic unsaturated carboxylic acid copolymers and ethylene-aliphatic unsaturated carboxylic acid ester copolymers. A multi-layer film consisting of at least 4 layers, each having at least one surface layer (A) consisting of the above, at least one layer (B) consisting of an ethylene α-olefin copolymer, and one layer (C) consisting of a polypropylene resin as an inner layer. In the layer (B)
The density of the ethylene α-olefin copolymer used in the above is 0.850 to 0.930 g / cm ³ ,
Melt flow rate (hereinafter, referred to as MFR) at 0.degree. C. and a load of 2.16 kgf is 0.2 to 3 g / 10 minutes, and the polypropylene resin used for the layer (C) is 230.degree. C. and a load of 2.16 kgf. Has an MFR of 0.
It is 1 to 10 g / 10 minutes, and the thickness ratio of each layer to all layers is 10 to 60% for the surface layer (A), 10 to 80% for the layer (B), and 5 to 60% for the layer (C). Furthermore, the heat shrinkage at 80 ° C. is 15% or more in at least one of the vertical and horizontal directions, and the difference in the average thermal shrinkage between the vertical and horizontal at 80 ° C. and 100 ° C. is 3
It is 0% or less, the average heat shrinkage stress of vertical and horizontal at 80 ° C. is 90 g / mm ² or more, and the heat shrinkage force at the same temperature is 110 g / 15 mm width or less. It is a shrink film. Hereinafter, the present invention will be described in detail.

The remarkable effect in the present invention cannot be manifested in a single layer of each of the above-mentioned layers constituting the film, and the same effect cannot be obtained if even one layer is missing. First, it is essential that the above is the configuration specified above. Surface layer (A) of the film of the present invention
Secures airtightness as a package by heat sealing, adhesion, etc., and reinforces mechanical strength such as tear strength, puncture strength, drop weight impact strength, etc. to exert a synergistic effect with the specific inner layer of the present invention. As a layer, it also plays a role as a surface layer for bleeding an antifogging agent as an additive, an antistatic agent, a lubricant, etc. by an internal addition method. It can also be used as a reinforcing layer and an additive retaining layer in terms of mechanical strength for the inner layer.

The resin constituting the surface layer (A) is ethylene-
It is at least one copolymer resin selected from a vinyl acetate copolymer, an ethylene-aliphatic unsaturated carboxylic acid copolymer, and an ethylene-aliphatic unsaturated carboxylic acid ester copolymer. The ethylene-vinyl acetate copolymer has a vinyl acetate group content of 5 to 26% by weight and MFR (190 ° C, 2.
16 kgf: The same applies to EVA hereinafter. ) Is 0.
It is preferably 3 to 10 g / 10 minutes. If the vinyl acetate group content is less than 5% by weight, the transparency is poor, and 26% by weight
Exceeding the above range will result in poor extrusion moldability, a strong odor of acetic acid and a reduction in commercial properties. In addition, a sticky phenomenon tends to occur and troubles may easily occur during packaging work. MFR is 0.3
If it is less than g / 10 minutes, there is a problem in melt processability such as an increase in extrusion power during extrusion molding, and the surface tends to be roughened during stretch film formation. Further, when MI exceeds 10 g / 10 minutes, the seal strength such as hot tacking property is lowered, and the synergistic effect with the specific internal layer in terms of mechanical strength becomes poor. A more preferable vinyl acetate group content is 7 to 20% by weight, and a further preferable MFR is 0.5 to 6 g / 10 minutes.

Next, as the ethylene-aliphatic unsaturated carboxylic acid copolymer and the ethylene-aliphatic unsaturated carboxylic acid ester copolymer, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, ethylene -Acrylic ester (selected from C1 to C8 alcohol components such as methyl, ethyl, propyl and butyl) copolymer, ethylene-methacrylic acid ester (C1 to C8 alcohol such as methyl, ethyl, propyl and butyl) And a copolymer or the like. These are multicomponent copolymers of three or more components to which other components are further added (for example, free terpolymers of three or more components selected from ethylene, aliphatic unsaturated carboxylic acid and the same ester, or modified ones). ) May be sufficient. The component to be copolymerized may be at least two or more multicomponent copolymers selected from the above or other components. The content of these carboxylic acid or carboxylic acid ester groups is usually 3 to
35% by weight is used. Considering the transparency of the film and the deterioration of the packaging workability due to blocking, lowering of the waist, etc., preferably 3 to 25% by weight, more preferably 3 to 2%.
0% by weight. MFR (190 ℃, 2.16kgf)
Is the same as the ethylene-vinyl acetate copolymer.

The resin constituting the layer (A) is at least one selected from the above resins. An ethylene-vinyl acetate copolymer is preferable in terms of optical properties and sealing properties. Further, the (A) layer may be optionally mixed with another resin within a range that does not impair the original characteristics thereof. As an example of the mixed resin, a portion of an ethylene-vinyl acetate copolymer is used. Saponified products, ionomer resins, ethylene α-olefin copolymers, high-pressure low-density polyethylene, high-density polyethylene, α- having a crystallinity of 30% or less by an X-ray method different from the above ethylene α-olefin copolymers. A soft resin made of an olefin copolymer, a polypropylene resin, a polybutene resin, a styrene-conjugated diene block copolymer and one obtained by hydrogenating at least a part of the block copolymer, and these resins are acid-modified. Modified materials, crystalline 1,2-polybutadiene and the like can be mentioned. These are within a range not exceeding 50% by weight, preferably 40% by weight or less, more preferably Properly it may be appropriately used in 30 wt% or less.

When the film of the present invention is used for food packaging, 0.1-5% by weight of the antifogging agent is added to at least one of the surface layers (A) (% by weight based on the surface layer to be added).
Is preferably contained, and more preferably 0.3 to 4% by weight. If it is less than 0.1% by weight, the antifogging effect is insufficient, and if it exceeds 5% by weight, bleeding may be contaminated and the sealing property may be deteriorated in some cases. Examples of the antifogging agent used, sorbitan fatty acid ester, glycerin fatty acid ester, glycerin fatty acid succinic acid ester, polyglycerin fatty acid ester, sorbitan-glycerin condensed fatty acid ester, sorbitan-diglycerin condensed fatty acid ester,
Partial polyhydric alcohol fatty acid ester such as pentaerythritol fatty acid ester and dipentaerythritol fatty acid ester, polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, polyethylene glycol fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene glycerin fatty acid ester Ethylene oxide adducts such as sorbitol, sorbitol derivatives obtained by adding propylene oxide and ethylene oxide to sorbitol and then esterifying, amines such as alkylamines, alkylamides, alkylethanolamines and fatty acid diethanolamides, amides and their ethylenes. One of oxide addition products, polyalkylene glycols, and other known compounds, or Used in combination with more species.

In addition to bleeding on the surface, an appropriate amount of the additive may be retained on the surface by a coating method. Further, known inorganic substances, acid amides and the like may be included as a lubricant, or one or both of the above may be coated on one side or both sides of the film in the same manner. Next, the multilayer film of the present invention has an inner layer having a density of 0.850 to 0.930 g / cm ³ and MFR.
(190 ° C., 2.16 kgf) is 0.2 to 3 g / 10 min. Layer (B) made of an ethylene α-olefin copolymer, and MFR (230 ° C., 2.16 kgf) is 0.1 to 10 g / Each layer has at least one layer (C) composed of a polypropylene resin for 10 minutes.

The layer (B) plays an important role in ensuring stable stretchability and imparting to the film a molecular orientation sufficient to exhibit a practically sufficient deformation recovery property after shrink-wrapping at the same time as low temperature shrinkability. Hold. Ethylene α used in this (B) layer
-Olefin copolymers include linear low-density polyethylene, ultra-low density (what is called VL and UL) polyethylene, and these are ethylene and propylene, butene-1, pentene-1, 4-methyl. -Α- having 3 to 18 carbon atoms such as pentene-1, hexene-1, octene-1
It is a copolymer with at least one kind of monomer selected from olefins, but from the viewpoint of mechanical strength such as tear strength, puncture strength, drop weight impact strength, and extensibility, 4-methyl is used as α-olefin. -Pentene-1, hexene-1, octene-1 are preferred. Density is 0.850 ~
It is in the range of 0.930 g / cm ³ . The density referred to in the present invention is a value at 23 ° C. measured according to JIS-K-7112. When the density exceeds 0.930 g / cm ³ , the transparency is lowered and the stretchability (especially the low temperature stretchability) is obtained.
And the transparency after shrinkage deteriorates. The density is 0.
If it is less than 850 g / cm ³ , the deformation recovery property after shrinkage is reduced and the bottom seal temperature range is narrowed. The preferable density is 0.860 to 0.925 g / cm ³ , and more preferably 0.870 to 0.920 g / cm ³ . Also,
MFR (190 ° C, 2.16kgf) is 0.2-3g /
10 minutes is essential, MFR is 0.2g / 1
If it is less than 0 minutes, the extrusion power at the time of extrusion molding will increase and the surface smoothness of the extruded raw material will decrease. Also, MFR is 3
When it exceeds g / 10 minutes, the stretching itself becomes difficult or the stability of the stretching decreases. Further, even if a film is obtained, only those having inferior mechanical properties such as tear strength and puncture strength can be obtained. Preferred MFR is 0.3-2.5
g / 10 minutes, more preferably 0.4 to 2 g / 10 minutes, still more preferably 0.5 to 1.5 g / 10 minutes.

The above ethylene α-olefin copolymer was polymerized with a metallocene catalyst typified by a so-called single-site catalyst in addition to a polymer obtained using a conventional catalyst such as a Ziegler catalyst. More homogenized (eg, weight average molecular weight / molecular weight distribution) than those polymerized by conventional methods
A polymer having a value represented by a number average molecular weight of 1.5 to 3.5, more preferably 1.5 to 3.0), or a polymer of another type of catalyst, and in addition to the above characteristics, is random. A copolymer which is highly copolymerizable and also has a controlled long-chain branch freely (for example, as an α-olefin, for example, octene-
1 is also included. Alternatively, in addition to these α-olefins, a monomer having a polar group, a styrene-based monomer, or the like may be freely copolymerized.

The layer (C) expands the sealing property, particularly the bottom sealing temperature range, and greatly improves the packaging workability such as the degree of freedom in selecting packaging conditions and the packaging speed. Further, it exhibits an effect of suppressing avatar-shaped shrinkage unevenness in a portion that comes into contact with the object to be packaged, which is caused by the temperature dependence of the heat shrinkage ratio becoming too large. Polypropylene resin is used for the (C) layer, and homopolypropylene, propylene having a propylene content of 70% by weight or more, and one or more kinds of other α-olefins (C2, C4 to C8). In addition to those copolymerized with conventional catalysts such as Ziegler-Natta catalysts, syndiotactic polypropylene and isotactic polypropylene polymerized with the above-mentioned metallocene catalysts etc. And at least one of these is used. Among them, the propylene content is 80 to 9 from the viewpoints of low temperature stretching, low temperature shrinkability, deformation multiplicity and falling weight impact strength.
It is a copolymer with 7% by weight of the other α-olefin and has a main melting peak temperature of 125 to 155 by DSC method.
Random copolymers in the range of ° C and polypropylene having a syndiotactic component polymerized with the above-mentioned metallocene catalyst or the like from the viewpoint of stretchability are preferable.
More preferably, it is polypropylene having the latter syndiotactic component. MFR of polypropylene resin used for this (C) layer (230 ° C, 2.16k
gf) is 0.1 to 10 g / 10 minutes. MFR is 0.
If it is less than 1 g / 10 minutes, the extrusion power at the time of extrusion molding will increase and the surface smoothness of the extruded raw material will deteriorate. Also,
When the MFR exceeds 10 g / 10 minutes, the stability of stretching is reduced, resulting in a film with large uneven thickness.
Mechanical properties such as tear strength, puncture strength, drop weight impact strength, etc. are reduced, and only those with poor deformation recovery after shrink wrapping can be obtained. The preferred MFR is 0.3 to 8 g / 10 minutes, more preferably 0.5 to 6 g / 10 minutes.

The layers (B) and (C) are each composed of ethylene α.
An olefin copolymer and a polypropylene resin are contained in an amount of 50% by weight or more, and may contain one or more other resins within a range that does not impair their original properties. The content of the ethylene α-olefin copolymer in the layer (B) and the content of the polypropylene resin in the layer (C) are preferably 60% by weight or more, more preferably 70% by weight.
That is all. Examples of other resins to be mixed include ethylene-vinyl acetate copolymers and partially saponified products thereof, ethylene-aliphatic unsaturated carboxylic acid copolymers, ethylene-
Aliphatic unsaturated carboxylic acid ester copolymer, ionomer resin, high-pressure low density polyethylene, ethylene α-olefin copolymer, styrene-conjugated diene block copolymer and at least a part of the block copolymer were hydrogenated And those obtained by modifying these resins by acid modification or the like, crystalline 1,2-polybutadiene, polybutene-1 type resin, petroleum resin, hydrogenated resin, terpene resin, hydrogenated resin and the like. The resin itself actually used in layers other than the layer to be mixed is also included. Of these, a polybutene-1 type copolymer or an ethylene α-olefin copolymer is preferable, and a more preferable ethylene α-olefin copolymer has a density of 0.850 to
Octene as α-olefin at 0.900 g / cm ³
1 is almost randomly copolymerized and also has a controlled long chain branching.

Next, in the film of the present invention, the thickness ratio of each layer to all layers is 10 to 60% for the surface layer (A), 10 to 80% for the inner layer (B), and 5 for the inner layer (C). It is important to be -60%. When the ratio of the surface layer (A) is less than 10%, the antifogging property and the seal strength are deteriorated and the practicality becomes poor. On the other hand, if it exceeds 60%, the mechanical strength such as tear strength, puncture strength, drop weight impact strength and the like will decrease. on the other hand,
When the ratio of the inner layer (B) is less than 10%, the stretchability is deteriorated, and in addition, the mechanical strength and the deformation multiplicity after contraction are significantly deteriorated. On the other hand, if it exceeds 80%, the stability at the time of extruding the original fabric decreases, and the variation in the thickness and width of the original fabric becomes large,
The subsequent stretching tends to be difficult. In addition, the obtained film tends to have excessively strong shrinkage force, and the periphery thereof including the sealing portion during the sealing work is extremely shrunk, resulting in extremely poor packaging finish, and in the case of bottom sealing. The seal part may peel off when contracting. Regarding the inner layer (C), when the ratio of the layer is less than 5%, the bottom seal temperature range is narrowed and the effect of suppressing the temperature dependence of the heat shrinkage cannot be exhibited. On the other hand, when the ratio of the layer exceeds 60%, the drawability is lowered and the drawing temperature is increased, resulting in loss of the low temperature shrinkability. In addition, the layer ratio that can be taken by the other layers is lowered, and the antifogging property, the sealing property, the mechanical strength such as tear strength, the deformation multiplicity after shrinkage, etc. become insufficient. However, even if the ratio of the layer (C) is 5% or more, the thickness of the layer itself is 0.5.
If the thickness is not more than μm, the above effect may be difficult to obtain,
The lower limit of the thickness of the (C) layer is preferably 0.5 μm.
The preferable value of the thickness ratio of the (A) layer in all layers is 15
-50%, more preferably 20-45%. Also,
The preferable layer ratio of the inner layer (B) is 15 to 70%, more preferably 20 to 60%. Similarly, the inner layer (C)
The preferred layer ratio is 10 to 50%, more preferably 1
It is 0 to 40%.

The film of the present invention is composed of at least 4 layers in total, that is, the (A) layer forming the surface layer, the (B) layer as the inner layer, and the (C) layer.
For example, 4 layers: A / B / C / A, 5 layers: A
/ C / B / C / A, A / B / C / B / A, A / B / A /
For 7 layers such as C / A: A / C / B / A / B / C / A,
A / C / A / B / A / C / A, A / C / B / C / A / C
/ A, A / B / A / C / A / C / A, A / B / A / B /
A / C / A, A / B / C / A / B / C / A, A / B / C
/ B / A / C / A, A / C / B / C / B / C / A, A /
B / C / B / C / B / A etc. are mentioned. 6 layers,
Includes cases of 8 layers and more.

When two or more layers (A), (B) or (C) are provided, the resins constituting these layers may be the same or different. Further, the layer (A) may be a multilayer of resins having the same or different monomer components, for example, A1 / A2, etc., and the same applies to the layer (B) or the layer (C). In addition, the film of the present invention further comprises (A) of the present invention as an inner layer within a range that does not impair its original properties.
In addition to the resin that can be used for each of the layers (B) and (C), another layer composed of a known thermoplastic resin may be arranged. This added layer also includes, as a recovery layer, a mixed composition layer made of the resin used in each layer of the film. What is used for these other layers is, for example, a 4-methyl-pentene-1 type polymer, a polypropylene type resin, a polybutene type resin, but any of them contains a copolymer. Further, ionomer resins, high-pressure low-density polyethylene, medium-density polyethylene, high-density polyethylene, soft resins made of α-olefin copolymers different from those usable in the (B) layer, styrene-conjugated diene block copolymers. Further, hydrogenated at least a part of the block copolymer, crystalline 1,2 polybutadiene, polyamide, thermoplastic polyester, ethylene-vinyl alcohol copolymer and the like can be mentioned, and at least one of them is used. Layers made of these resins are (A) layer, (B)
Layer, each internal layer of (C) layer, or (A) layer and (B) layer,
The layers may be arranged between the layers (B) and (C) and between the layers (A) and (C), and an adhesive layer made of another known adhesive resin may be provided between the layers as necessary. May be. Such adhesive resin includes ethylene-vinyl acetate copolymer, ethylene-
At least 2 of an aliphatic unsaturated carboxylic acid copolymer, an ethylene-aliphatic unsaturated carboxylic acid ester copolymer, or a free combination of ethylene and each of the above-mentioned copolymerizable monomers.
Multi-component copolymer of species, partially saponified ethylene-vinyl acetate copolymer, at least one α having 2 or more carbon atoms
-Copolymer composed of at least three kinds of monomers consisting of olefin and carbon monoxide and at least one kind of monomer selected from vinyl acetate, aliphatic unsaturated carboxylic acid and aliphatic unsaturated carboxylic acid ester Examples thereof include coalesce, thermoplastic polyurethane, and the above-described resins and acid-modified polyolefin resins.

Furthermore, the film of the present invention has a heat shrinkage ratio at 80 ° C. of 1 in at least one of the vertical and horizontal directions.
5% or more and 80 of the average heat shrinkage ratio of vertical and horizontal
The difference between the values at 30 ° C and 100 ° C is 30% or less, and the average heat shrinkage stress between vertical and horizontal at 80 ° C is 90 g /
Thermal shrinkage force of 110 g / 1 at mm ² or more and at the same temperature
It is essential to have a value of 5 mm width or less.

The reason why the heat shrinkage characteristics are the above values is that the main purpose of the present invention is low temperature shrinkability, excellent sealing properties, particularly stable and clean bottom sealing in stretch shrink packaging is achieved, and packaging finishes, For example, it is necessary in order to suppress the generation of avatar-shaped shrinkage spots and the deformation of the tray and the container in the portion that comes into contact with the object to be packaged such as food, and to exhibit the practically sufficient deformation recovery property after the packaging.

At least one of vertical and horizontal at 80 ° C.
If the heat shrinkage in the direction is less than 15%, the low-temperature shrinkage is basically poor, and the fitability after shrinkage during shrink-wrapping becomes insufficient, which may cause wrinkles and lumps after packaging. Further, when the tray or the container is wrapped, the corner portion is likely to remain as a shrinkage defect, which lowers the commercial property. A preferable heat shrinkage ratio at 80 ° C is at least 1 of vertical and horizontal.
20% or more in the direction. The upper limit is almost determined within a range that does not adversely affect the dimensional change in the storage and distribution process (in the case of a roll-shaped roll, the difference in the width between the winding core and the outside is a problem), and is usually 60% or less. , Preferably 50% or less.

The average heat shrinkage ratio of vertical and horizontal is 80 ° C.
When the difference between the values at 100 ° C. and 100 ° C. exceeds 30%, unevenness is likely to occur in the folded portion of the film when bottom sealing is performed, flatness cannot be obtained, the finish is significantly deteriorated, Poor adhesion is likely to occur. Further, during shrink-wrapping, avatar-like shrinkage unevenness is likely to occur at a portion that comes into contact with an object to be packaged such as food. The preferred value of the difference between the average thermal shrinkages at 80 ° C. and 100 ° C. is 25% or less, more preferably 20% or less. The smaller this difference is, the smaller the change in shrinkage rate with respect to temperature change, the better the bottom sealability, and the less likely that avatar-like shrinkage unevenness occurs, which is preferable.

On the other hand, if the average heat shrinkage stress of vertical and horizontal at 80 ° C. is less than 90 g / mm ² , the fit property and the cohesive force become insufficient as in the above case, and especially the deformation recovery property after packaging is poor. Becomes The preferable average heat shrinkage stress at 80 ° C. is 100 g / mm ² or more, more preferably 110 g / mm ² or more. The upper limit is naturally limited to the range in which the shrinkage force of the film as a whole including the thickness factor of the film does not exceed the value specified in the present invention.

Further, the heat shrinkage force of the film of the present invention at 80 ° C. is 110 g / 15 mm width or less,
When the width exceeds g / 15 mm, when the fusing seal is performed, the hot peeling property of the fusing seal portion may occur immediately after the sealing or at the time of contraction, and the seal may be opened, or the film may be folded in the bottom seal. When the lapped portion shrinks, peeling is likely to occur, and the tightening force for the object to be packaged becomes too strong, and the tray or container is likely to be deformed. This heat shrinkage force needs to be 110 g / 15 mm width or less for both vertical (MD) and horizontal (TD), but the preferable heat shrinkage force is 100 g / 15 m.
m width or less, more preferably 90 g / 15 mm width or less. The lower limit is naturally limited within the range not exceeding the value of the heat shrinkage stress defined above.

The resin layers (A), (B), and (C) of the present invention are plasticizers, antioxidants, surfactants, colorants, and ultraviolet absorbers, as long as the original characteristics are not impaired. , May include a lubricant, an inorganic filler, etc.,
One or both surfaces of the film of the present invention may be subjected to a coating treatment in order to impart antifogging property, antistatic property, lubricity, adhesiveness and the like. As the treatment agent used for coating, in addition to the various antifogging agents already described, sucrose ester, various silicone emulsions,
Silicone oil, granidine derivative, phosphate-containing anion activator, sulfonate derivative, quaternary ammonium salt,
Pyridinium salts, imidazoline derivatives, polyvinyl alcohol, acrylic acid-based hydrophilic polymers, polymers having a pyrrolidinium ring in the main chain, silica sol, alumina sol, etc., mineral oil, liquid polybutene, fats and oils not included in the above, etc. There are known treatment agents such as viscous liquids (100 centipoise or more) and the like, and at least one or two or more of these treatment agents can be used in combination, but diluted with an appropriate solvent (for example, water or alcohol). May be used. Further, the above layers (A), (B) and (C) are mixed with petroleum resin, hydrogenated petroleum, natural rosins, esterified rosins, terpene resin (containing hydrogenated resin) and the like. The polymer plasticizing effect, stretchability, surface characteristics, and other properties may be improved. Furthermore, the above (A), (B),
Surface treatment such as corona treatment and plasma treatment can be applied to the layer (C), which is used separately or in combination with the above coating treatment.

The thickness of the heat-shrinkable multilayer film of the present invention is
The thickness is usually 5 to 80 μm, preferably 6 to 60 μm, and more preferably 7 to 40 μm, but it is in the thin region of 7 to 20 μm that the effects of the present invention are particularly exerted. If the thickness is less than 5 μm, the rigidity of the film is insufficient and the sealing property is deteriorated, which causes a problem in workability during packaging. Also,
If it exceeds 80 μm, the film becomes too stiff and the fit is poor, and the response of shrinkage is poor, or the overall shrinkage is too strong, and the tray or container is deformed and the finish is easily damaged. . In addition, performance such as mechanical strength becomes excessive.

Next, an example of the method for producing the heat-shrinkable multilayer film of the present invention will be described. First, each layer ((A), (B),
The resin constituting the layer (C) and other layers used as necessary) is melted by each extruder, coextruded by a multilayer die and rapidly solidified to obtain a multilayer film original fabric. As the extrusion method, a multi-layer T-die method, a multi-layer circular method or the like can be used, but the latter is preferable. The multi-layer film stock thus obtained is heated and stretched under a temperature condition suitable for imparting orientation. As the stretching temperature, the stretching start point of the film (in the case of the inflation method,
The surface temperature at the position (expansion start as a bubble) is usually 120 ° C. or lower, preferably 100 ° C. or lower, more preferably 80 ° C. or lower, and further preferably 60 ° C. or lower. It is preferable because the properties are exhibited more. However, the lower limit of the stretching temperature is preferably 40 ° C. from the viewpoint of dimensional stability of the stretched film.

As the stretching method, there are a roll stretching method, a tenter method, an inflation method (including a double bubble method) and the like, but a method of forming a film by simultaneous biaxial stretching is preferable from the viewpoint of stretchability and rationality. Further, the stretching is performed in at least one direction by an area stretching ratio of 3 to 50 times, preferably 4 to 40 times, and is appropriately selected according to the heat shrinkage ratio required depending on the application. Further, if necessary, post-treatment, for example, heat setting for dimensional stability, or lamination with another kind of film may be performed.

Further, in the film of the present invention, at least one layer may be crosslinked, and in this case, even if the degree of crosslinking in the thickness direction is substantially uniform, the specific layer is mainly crosslinked. Also, in the case where one surface layer is main and gradually changes in the thickness direction, both surface layers may be main or may have a timely distribution in the thickness direction. This cross-linking treatment can be performed freely before and after the stretching film formation by electron beam (for example, 50 to 10).
(With energy of 00 kV), ultraviolet rays, X-rays, α rays,
Irradiation with energy rays such as γ-rays on one side or both sides, and cross-linking distribution in the thickness direction, with the same inclination (for example, one surface layer cross-links)
Such as irradiation, or a heat treatment after addition of peroxide or the like (in some cases, a combination of a crosslinking aid in the specific layer and a crosslinking retarder in the specific layer may be used),
Alternatively, the modification treatment may be carried out by a known method in addition to the combination of both methods, and is preferably an electron beam (for example, 50 to
The method according to (1) controlling the depth of penetration with an energy of 1000 kV) is clean.

By the cross-linking treatment, heat resistance, heat sealing property, especially sealing property in high-speed packaging are improved, and stretching film forming stability (necking suppression, thickness uniformity, stretching ratio improvement, stretching temperature condition range expansion). Etc.) can be improved and used as necessary.

[0034]

EXAMPLES The present invention will be described in more detail with reference to examples below. The measurement and evaluation methods used in the present invention are as follows. (1) Stretching stability of film formation When the film was heated and stretched according to a predetermined method, the continuous film formation stability of the film (continuous bubble formation stability of the inflation method) and the thickness unevenness of the finished film were evaluated. . Here, the thickness unevenness of the film is a total of 50 points or more, using a dial gauge, at least 25 points at equal intervals in the entire width (horizontal) direction of the film, and at least 25 points at 5 cm intervals in the flow (vertical) direction. Is measured, and the average value is first calculated. Next, half the difference between the maximum and minimum values
The value of is expressed as a percentage with respect to the average value calculated above, and is displayed with a ± sign.

⊚: The stretching start position of the film (stretching bubble in the inflation method) is substantially constant, the stretching pattern is extremely stable (in the case of stretching bubble, there is almost no shaking), and the continuous stability is good. ◯: A slight variation was observed in the stretching pattern, and the film thickness unevenness was within ± 15%. Δ: The stretching start position fluctuates or the stretching pattern is unstable.

X: Film broke, bubble punctures occurred frequently. Alternatively, even if the stretching is possible, the variation of the stretching start position is large, and the thickness unevenness exceeds ± 25%. (2) Heat Shrinkage A film sample of 100 mm square was placed in an air oven type thermostatic chamber set to a predetermined temperature and shrunk freely to 1
After treatment for 0 minutes, the amount of shrinkage of the film was determined and expressed as a percentage of the value divided by the original dimension. In the case of uniaxial stretching, the value in the stretching direction was used, and in the case of biaxial stretching, the average of the measured values in the vertical and horizontal directions was used. (3) Heat shrink force and heat shrink stress (OR in the text below
Abbreviated as S) A film is sampled in the shape of a strip with a width of 15 mm, and it is placed on a chuck with a strain gauge and the distance between chucks is 50 m.
Set it to m without loosening, and immerse it in silicone oil heated to 80 ° C to reduce the shrinkage force generated vertically,
The film was detected for each horizontal side, and the value after 1 minute of immersion was defined as the shrinkage force of the film. Further, a value obtained by dividing this value by the initial cross-sectional area of the film before immersion was taken as ORS. (4) Tear strength According to JIS-P-8116, it measured using the light load tearing tester (made by Toyo Seiki). The value was the average of the tear strengths in the vertical and horizontal directions. In addition, the reading of the measurement here is performed so as to be in the range of 20 to 60 on the scale, but if there is a difference in the measured value depending on the measurement range, the higher value is adopted. (5) Puncture strength In accordance with Article 10 of the Agriculture and Forestry Standard, the film has an internal size of 125
It is fixed to a wooden frame of mm × 125 mm, and a needle with a diameter of 1.0 mm and a tip shape of 0.5 mmR is 50 ± 5 mm in the center.
Puncture at a speed of / minute, the maximum load until the needle penetrated was measured, and the value was defined as the puncture strength. (6) Drop Weight Impact Strength It was measured according to ASTM-D-1709. (7) Anti-fogging property Using a film that has been stored for 3 days after film formation, the beaker containing water at 20 ° C is covered and hermetically sealed and left in a refrigerator at 5 ° C for 1 hour. The following criteria were used for visual judgment and evaluation.

5: A transparent water film having a mirror-like water film. 4; Water film with slight unevenness, but with little trouble in checking the contents. 3; Spreading water droplets are attached, but the contents can be confirmed and there is no practical problem. 2; Small water droplets are attached, and the shape of the contents can be seen, and it is difficult to check the details.

1; White and cloudy, and the presence of contents could not be confirmed. (8) Bottom seal temperature range and finish of seal part after shrinkage General commercially available P with 100 g metal plate attached to the inner bottom part
P tray (approximate dimensions; vertical 150 mm, horizontal 115 m
m, height 23 mm) with various films so that there is no dove in the vertical direction and the horizontal direction, and the bottom folding length is 50 mm at each end in the vertical direction, 2 sheets overlapped part and 3 sheets,
Both ends were folded into the lower part of the tray so that a stack of 5 sheets was formed, and the plates were placed on a hot plate adjusted to each temperature for 2 seconds to perform bottom sealing. With the lower limit of the temperature at which the edge of the film is gently pulled and it does not peel off, the film melts even at one place, holes are formed, whitening occurs to the extent that commerciality is lost, and the film shrinks, making sealing difficult. Was set as the bottom seal temperature range. In addition, after bottom sealing at a temperature almost in the middle of the bottom sealing temperature range, the finish of the bottom sealing part was evaluated under the following conditions by passing through a tunnel of hot air heating system under a wide and wide range of temperature conditions (80 to 160 ° C). .

◯: The tunnel temperature range is 30 ° C. or higher in which the end of the seal portion is not peeled off even if it is lightly pulled and unevenness due to partial curling or shrinkage does not occur. Δ: When the temperature range above is 10 ° C or higher and lower than 30 ° C. X: When the temperature range above is less than 10 ° C. (9) Deformation recovery The outer dimensions of the hollowed-out through state is 180 x 180 m.
m wooden frame as a film supporting base, and a box-shaped wooden mold having an outer dimension of 82 × 82 mm at the center of the supporting base so that each side of the supporting base is kept parallel to each other. 15 mm was projected, and in this state, the film was covered and fixed to the edge of the film support base with double-sided tape. At this time, the tension of the film was minimal, and the film was carefully fixed so as not to cause tarmi. Then, in this state, the film was shrunk by passing through a hot air tunnel at 90 ° C. for 3 seconds.
After passing through the tunnel, after standing at room temperature (about 23 ° C.) for about 3 minutes, the box-shaped wooden mold was taken out from the film support, and 1 minute later, the state of the surface of the film fixed on the support was observed. Good seldom wrinkles or wrinkles or local dents and excellent in commercialability ◎, Talmi or wrinkles, or those with slight local dents but no problem in commerciality ○, clearly Talmi or wrinkles, The case where there was a local dent and there was a problem in commerciality was marked with x, and the case of an intermediate level between ○ and × was marked with Δ. (10) Abata-like shrinkage unevenness In place of the iron pieces when shrink-wrapped in the evaluation of the bottom sealability, the shrimp preserved at about 5 ° C is put in a tray to a degree of slightly rising, and shrink-wrapped in the same manner, and the shrimp shrimp The contracted state of the film in the portion in contact with was observed. The case where there was almost no avatar-like shrinkage unevenness was marked with ◯, and the case where the avatar-like shrinkage unevenness occurred at most of the contact portions and there was a problem in commercial property was marked with x. In addition, the middle of the two was set as Δ. (11) Haze after shrinkage The film on the tray of the package obtained by the evaluation of the bottom sealability was cut out and measured according to ASTM-D-1003-52. (12) Gel Fraction A sample was extracted in boiling p-xylene (12 hours), and the proportion of the insoluble portion was expressed by the following formula, which was used as a measure of the degree of crosslinking.

Gel fraction (% by weight) = (sample weight after extraction / sample weight before extraction) × 100 However, a polymer which has not been subjected to crosslinking treatment and which is not completely dissolved in boiling p-xylene is p -Instead of xylene, change to a solvent that can be completely dissolved during boiling and perform the measurement. Next, the resins used in Examples and Comparative Examples are described below. EVA1: ethylene-vinyl acetate copolymer (vinyl acetate content = 15% by weight, MFR (190 ° C., 2.16 kg
f) = 2.2 g / 10 minutes) EVA2: ethylene-vinyl acetate copolymer (vinyl acetate content = 15 wt%, MFR (190 ° C., 2.16 kg)
f) = 1.5 g / 10 minutes) EVA3: ethylene-vinyl acetate copolymer (vinyl acetate content = 18% by weight, MFR (190 ° C., 2.16 kg)
f) = 1.0 g / 10 minutes) EM1: ethylene-methyl acrylate copolymer (methyl acrylate content = 9% by weight, MFR (190 ° C., 2.1)
6 kgf) = 3.0 g / 10 minutes) EA1: ethylene-acrylic acid copolymer (acrylic acid content = 6.5% by weight, MFR (190 ° C., 2.16 kg)
f) = 3.5 g / 10 min) VL1: ethylene α-olefin copolymer (having long chain branch polymerized by the improved single-site catalyst, density = 0.870 g / cm ³ , MFR (190 ° C., 2 .16
kgf) = 1.0 g / 10 min, I10 / I2 = 7.5, comonomer = octene-1 (24% by weight)) where I10
/ I2 is the MFR value (I10) at 190 ° C and a load of 10 kg and the MF at 190 ° C and a load of 2.16 kg.
It represents the ratio of the values of R (I2). VL2: ethylene α-olefin copolymer (polymerized with an improved single-site catalyst, having a long-chain branch and having a weight average molecular weight / number average molecular weight value of 2.0 and a sharp molecular weight distribution, density = 0.902 g / Cm ³ , MFR = 1.
0 g / 10 minutes, I10 / I2 = 9.0, comonomer = octene-1 (12% by weight)) VL3: ethylene α-olefin copolymer (density = 0.
890 g / cm ³ , MFR (190 ° C, 2.16 kg
f) = 4.0 g / 10 min, comonomer = butene-1) VL4: ethylene α-olefin copolymer (having long chain branch polymerized by the improved single-site catalyst, density = 0.895 g / cm ³ , MFR (190 ° C, 2.16
kgf) = 1.6 g / 10 min, I10 / I2 = 10.2,
Comonomer = octene-1) LL1: ethylene α-olefin copolymer (density = 0.
912 g / cm ³ , MFR (190 ° C, 2.16 kg
f) = 0.8 g / 10 minutes, comonomer = hexene-1) LL2: ethylene α-olefin copolymer (density = 0.
912 g / cm ³ , MFR (190 ° C, 2.16 kg
f) = 1.0 g / 10 minutes, comonomer = octene-1) LL3: ethylene α-olefin copolymer (density = 0.
912 g / cm ³ , MFR (190 ° C, 2.16 kg
f) = 3.3 g / 10 min, comonomer = octene-1) LL4: ethylene α-olefin copolymer (density = 0.
920 g / cm ³ , MFR (190 ° C, 2.16 kg
f) = 1.0 g / 10 min, comonomer = octene-1) LL5: ethylene α-olefin copolymer (density = 0.
935 g / cm ³ , MFR (190 ° C, 2.16 kg
f) = 2.1 g / 10 minutes, comonomer = 4-methyl-pentene-1) PP1: polypropylene resin (ethylene and butene-1)
Copolymer having MFR (230 ° C., 2.
16 kgf) = 5 g / 10 min, mp = 131 ° C.) PP2: polypropylene resin (copolymer with ethylene as a comonomer, MFR (230 ° C., 2.16 kgf)
= 1.8 g / 10 min, mp = 140 ° C.) PP3: polypropylene resin (syndiotactic polypropylene polymerized by a metallocene catalyst, weight average molecular weight / number average molecular weight value is 2.1, MFR (23
0 ° C., 2.16 kgf) = 2.5 g / 10 minutes, mp = 1
49 ° C) PP4: Polypropylene resin (homopolymer, MFR
(230 ° C., 2.16 kgf) = 4.0 g / 10 minutes, m
p = 160 ° C) PP5: polypropylene resin (homopolymer, MFR
(230 ° C., 2.16 kgf) = 11 g / 10 minutes, mp
= 161 ° C)

[0041]

Example 1 Ethylene-vinyl acetate copolymer; EVA1
(Vinyl acetate content = 15% by weight, MFR (190 ° C.,
2.16 kgf) = 2.2) containing 1.5% by weight of diglycerin monolaurate in the surface layer and 1 in the inner layer
First, ethylene α-olefin copolymer; LL1 (density = 0.912 g / cm ³ , MFR (190 ° C., 2.16).
kgf) = 0.8 g / 10 min, comonomer = hexene-
1) in a further inner layer, polypropylene-based resin; P
P1 (copolymer having ethylene and butene-1 as a comonomer, MFR (230 ° C., 2.16 kgf) = 5 g / 10
Min, mp = 131 ° C), and the layer arrangement is EVA1 / L
After extruding using an annular five-layer die to form five layers of L1 / PP1 / LL1 / EVA1, it is rapidly cooled and solidified with cold water to have a folding width of 190 mm and a thickness of about 110 μm. Fabricated. At this time, a 6% sodium oleate aqueous solution was enclosed inside the tube, and the inner surface was coated by squeezing with a nip roll. The thickness of each layer is 16.5 from the outside of the tube.
μm / 27.5 μm / 2 2 μm / 27.5 μm / 16.
It was adjusted to be 5 μm.

Then, this raw fabric is passed between two pairs of differential nip rolls and heated to about 48 ° C. (equal to the stretching temperature) in the heating zone, and then air is forced into the stretching zone to form bubbles. Continuous drawing is performed in the cooling zone 1
A cold air of 8 ° C. was blown to obtain a film having a thickness of 10 μm, which was biaxially stretched at a stretching ratio of 3.7 times in the vertical direction and 3.0 times in the horizontal direction. The evaluation results of the film are shown in Table 1, and the stretching film-forming stability of the film is extremely good (⊚), excellent in mechanical strength such as tearing, piercing, drop weight impact strength and the like. MD) 27g, Horizontal (T
D) 11 g, which is a low value in the horizontal direction in balance,
In actual packaging, it is often required to have film cutability in the horizontal direction, which is also advantageous, and it has low temperature shrinkability, excellent transparency, and excellent bottom sealability. The film had a good finish without shrinkage unevenness. The resulting package had extremely good recovery from deformation, and the antifogging property was at a level of 4 out of 5 points, which was sufficient for practical use. As described above, even with a thin film having a thickness of 10 μm, individual mechanical properties and shrink wrapping, particularly, the sealing property and finish in the overlap shrink wrapping represented by the stretch shrink are excellent, and thus, in a comprehensive manner as well. A high-performance film is a film that has never existed before.

[0043]

Examples 2 to 4 By the same method as in Example 1, five-layer films shown in Table 1 were obtained. Each surface layer contained the same diglycerin monolaurate as in Example 1 in an amount of 1.5% by weight, and
A 6% aqueous solution of sodium oleate was enclosed inside the raw fabric tube, and the same treatment was performed. Stretching temperature is 46
Each of them was biaxially stretched at a stretching ratio of 2.2 to 3.8 times in the vertical and horizontal directions. As a result, the stretched film-forming stability was good, and as in Example 1, the film was high in strength, excellent in low-temperature shrinkability and transparency, and excellent in sealing property, packaging finish, elastic recovery property and the like.

[0044]

Comparative Examples 1 to 8 Using the resins used in Examples 1 and 2, extruded raw fabrics having a layer constitution ratio outside the range of the present invention were prepared in the same manner as in Example 1 and Stretch film formation was performed in the same manner. The results are shown in Table 2 as Comparative Examples 1 to 4. The stretching temperature is 48 to 52 in all cases.
Performed in the range of ° C. The layer composition ratio is a percentage of the surface layer (A): ethylene α-olefin copolymer (B) layer: polypropylene-based resin (C) layer, and Comparative Example 1 is 30:70:
0, Comparative Example 2 is 5:55:40, Comparative Example 3 is 70: 1.
0:20, Comparative Example 4 is 45: 5: 50.

Further, based on the layer structure similar to that of Example 2, a raw material having the same thickness was prepared by using a resin layer outside the scope of the present invention, and an attempt was made to perform stretch film formation. The stretching temperature was the same as in Comparative Examples 1 to 4. These are shown in Table 3 as Comparative Examples 5-8. In Comparative Examples 5 and 6, the MFR of the ethylene α-olefin copolymer is out of the range, in Comparative Example 7, the density of the ethylene α-olefin copolymer is out of the range, and in Comparative Example 8, the MFR of the polypropylene resin is in the range. Outside.

In each of these comparative examples, 1.5% by weight of diglycerin monolaurate was added to each surface layer.
First, in Comparative Example 1, the stretching stability was relatively good,
The temperature dependence of the shrinkage rate was large, avatar-like shrinkage unevenness was observed during packaging when it came into contact with a cold packaged object, and the finish of the seal part was slightly uneven and the productability was slightly inferior. . The puncture strength and falling weight impact strength were at an insufficient level. Further, in Comparative Example 2, the stretchability was unstable, the bottom sealing property and the finish were insufficient, and the antifogging property was at a level that could not be practically used.
In Comparative Examples 3 and 4, the mechanical strength such as tear strength was insufficient, and the deformation recovery property after shrinkage was poor.

Further, in Comparative Examples 5, 6 and 8, the stretching was unstable and the uneven thickness was large (± 21%), and the film was evaluated by selecting the portions having relatively small uneven thickness. In comparison with Comparative Example 6, there was a problem in the finish at the time of packaging, and in Comparative Example 8, mechanical strength such as tear strength was insufficient, and a practical bottom sealing temperature was obtained. The range was narrow, and the finish of the seal part after shrinkage was poor. In Comparative Example 7, the stretchability was extremely poor and a film could not be obtained.

[0048]

Examples 5 to 12 By the same method as in Example 1, five-layer films shown in Tables 4 and 5 were obtained. Each surface layer contained 1.5% by weight of diglycerin monooleate, and 20% by weight of 38% sugar ester (sucrose laurate) aqueous solution and dimethyl silicone emulsion were placed inside the raw tubes of Examples 5 to 7. A mixture of 80% by weight and 6% sodium oleate aqueous solution was enclosed in the raw tube of each of Examples 8 to 12 and the same treatment was performed. The stretching temperature was 47 ° C. and 51 in order from Example 5.
℃, 49 ℃, 83 ℃, 49 ℃, 50 ℃, 77 ℃, 90 ℃
And the biaxial stretching was carried out within the stretching ratios of 2.1 to 5.2 times in the vertical and horizontal directions, respectively.

All of them have good stretch film-forming stability, are transparent and have anti-fog properties and are low-temperature shrinkable films as in Example 1, and those stretched at a low temperature are more excellent in elastic recovery. In addition, the film had a good balance of mechanical properties, sealing properties, packaging finish, and the like, and was a film that yielded a package having excellent commercial properties.

[0050]

Comparative Examples 9 to 12 In order to compare the effect of the present invention with the prior art, a film was obtained according to the disclosed technology as a method corresponding to Japanese Patent Publication No. 2-14898 (stretching temperature 47 ° C.). This was designated as Comparative Example 9. Similarly, a film obtained by performing stretch film formation (stretching temperature 97 ° C.) according to the technique disclosed in JP-A-5-318682 is Comparative Example 1
It was set to 0 and shown in Table 6. In each of Comparative Examples 9 and 10, 1.5% by weight of diglycerin monooleate was press-mixed into the surface layer from the tip of the extruder. In addition, a commercially available polypropylene resin multilayer shrink film; commercially available product 1
(Linear low density PE / (Linear low density PE and polypropylene random copolymer mixture) / Polypropylene random copolymer / (Linear low density PE and polypropylene random copolymer mixture) / Linear low density PE 5 layer film,
Similarly, a commercially available linear low-density polyethylene-based multilayer shrink film having a thickness of 12 μm was used as Comparative Example 11, and a commercial product 2 (ultra-low-density linear PE (VL) / linear low-density PE (L)
L) / VL three-layer film, thickness 13 μm) in Comparative Example 1
And 2. The evaluation results of these films are also shown in Table 6.
It was shown to.

First, Comparative Example 9 has low temperature shrinkability, excellent transparency, and good packaging finish, but is inferior in mechanical strength such as tear strength and puncture strength and deformation recovery, and Comparative Example 10 And 11 are poor in puncture strength, impact resistance and bottom sealability, poor in antifogging property, and insufficient in deformation recovery property. In addition, Comparative Example 12 also has problems in bottom sealability and anti-fogging property, has a puncture strength at an insufficient level, and has poor recovery from deformation at 90 ° C. shrinkage treatment, resulting in low temperature shrinkage and deformation. The film could not satisfy the recoverability at the same time.

[0052]

[Examples 13 to 15] A 7-layer die was used, and in the same manner as in Example 1, the thickness was 10 to 12 µm in a 4-layer, 7-layer structure shown in Table 7.
I got a film of. At this time, Example 13 and Example 1
In No. 5, diglycerin monolaurate was added to the surface layer in an amount of 1.0% by weight, and diglycerin monooleate 1.
1% by weight was added. In Example 14, 1.5% by weight of diglycerin monooleate was added only to the surface layer.
In each of the examples, 10% is contained inside the original tube.
The same treatment was performed by enclosing each of the aqueous sodium oleate solutions. The stretching temperature was in the range of 48 to 53 ° C.

In all cases, the stretched film-forming stability was good, the mechanical properties were good as in Example 1, the heat-sealing property and the packaging finish were good, and the elastic recovery property and anti-fog property were also excellent. It was a film.

[0054]

Example 16 A tube-shaped original fabric was produced in the same manner as in Example 1 except that the thickness of each layer (the same applies to the original fabric thickness) was changed. The thickness of each layer of the raw fabric at this time is 36 μm / 60 μm / 48 μm / 60 μm / 36 μ in order from the outside of the tube.
It was m. This tube-shaped raw fabric was irradiated with an electron beam at an accelerating voltage of 150 kV and treated so that the gel fraction of one surface layer was 21% and the gel fraction of the other surface layer was 3%. . This raw fabric was stretched at a stretching temperature of 58 ° C. in the same manner as in Example 1 to stably obtain a film having a thickness of 12 μm. The obtained film has a vertical and horizontal average heat shrinkage ratio of 31% at 80 ° C. and 54% at 100 ° C., a vertical and horizontal average shrinkage stress of 195 g / mm ² , and a heat shrinkage force of 44 g vertical and 26 g horizontal. It has a high tear strength of 15 g and a puncture strength of 320 g, and is suitable for stretch shrink wrapping. In addition, as a pillow shrink wrap, the surface layer with a gel fraction of 2% is the heat seal layer. When used for packaging with the side that comes in contact with the seal bar as a high-crosslinking layer, the problems such as tears and wrinkles at the seal part that have conventionally occurred when increasing the packaging speed are eliminated. , High-speed packaging workability has been significantly improved.

[0055]

[Table 1]

[0056]

[Table 2]

[0057]

[Table 3]

[0058]

[Table 4]

[0059]

[Table 5]

[0060]

[Table 6]

[0061]

[Table 7]

[0062]

The film of the present invention is a packaging film,
In particular, it is a high-performance film that is extremely comprehensive and well-balanced, which has never been achieved as a shrink-wrapping film. That is, the stretch film forming stability is excellent, tear resistance and puncture resistance even with a thin wall, a film having transparency of low-temperature shrinkability excellent in mechanical properties such as impact resistance, further heat sealability, In particular, the bottom sealability in stretch shrink packaging and the finish of the seal part are very good even after shrink wrapping, and in addition to good packaging finish and excellent deformation and multiplicity, it is possible to easily exhibit anti-fogging property. Therefore, the product has a remarkably commercial value that has never been seen before.

The film of the present invention can be used not only for various shrink-wrapping applications other than stretch shrink, but also for various packaging materials such as household and commercial wrap films.

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display area B29K 105: 02 B29L 9:00

Claims (1)

[Claims] 1. A surface layer comprising at least one copolymer resin selected from ethylene-vinyl acetate copolymer, ethylene-aliphatic unsaturated carboxylic acid copolymer and ethylene-aliphatic unsaturated carboxylic acid ester copolymer. (A) and at least one layer (B) made of an ethylene α-olefin copolymer as an inner layer and at least one layer (C) made of a polypropylene resin, in a multilayer film made of at least four layers, The density of the ethylene α-olefin copolymer used in the layer (B) is 0.850 to 0.
930 g / cm ³ , 190 ° C., load 2.16 k
Melt flow rate in gf is 0.2 to 3 g / 10
And the polypropylene resin used in the layer (C) has a melt flow rate of 0.1 to 10 g / 10 minutes at 230 ° C. and a load of 2.16 kgf, and the thickness of each layer in all layers. As a ratio, the surface layer (A) is 1
0-60%, layer (B) 10-80%, layer (C) 5
60%, and the heat shrinkage rate at 80 ° C is 15% or more in at least one of the vertical and horizontal directions,
Also, the difference between the average heat shrinkage ratio between the vertical and horizontal at 80 ° C and 100 ° C is 30% or less, and the average thermal shrinkage stress between the vertical and horizontal at 80 ° C is 90 g / mm ² or more, and the same. A multilayer shrink film having a heat shrinkage force at a temperature of 110 g / 15 mm width or less.