JPWO2005102695A1 - Heat shrinkable film - Google Patents

Abstract

The present invention mainly comprises a first layer containing a first polymer mainly composed of a thermoplastic polyester and a thermoplastic polyurethane, and a second polymer in which the repeating unit mainly comprises a halogen or hydrogen bond. A heat-shrinkable film is provided in which the first layer and the second layer are directly laminated.

Description

  The present invention relates to a heat-shrinkable film for shrink wrapping, and particularly to a film having a good appearance even after shrinkage treatment.

  Shrink wrap has a beautiful appearance, enhances product value, keeps the contents hygienic, makes it easy to visually confirm quality, and allows fast and tight fixation and packaging of atypical products and multiple products. It is often used for packaging miscellaneous goods. In particular, when a film is required to have impact strength or pinhole resistance, a film in which a resin having a strong structure having a hydrogen bond as a repeating unit, for example, a polyamide resin is laminated is widely known. On the other hand, a film excellent in gas barrier properties is required for packaging chemicals and electronic parts and the like mainly in the food field in order to suppress the deterioration and decay of the package and improve the storage period. As polymers having excellent gas barrier properties, there are vinylidene chloride copolymers and ethylene-vinyl alcohol copolymers (hereinafter referred to as EVOH), but the former contains chlorine, the latter contains hydroxyl groups in repeating units, and is highly polar. Therefore, there is a problem that they are strongly aggregated after stretching, and the resulting film has a low heat shrinkage rate. Furthermore, this film has advanced characteristics such as pinhole resistance, and as described above, studies have been made on multilayering with a polyamide resin layer (for example, Patent Document 1). However, since this polyamide resin (hereinafter referred to as PA) also forms hydrogen bonds in the same manner as EVOH, the thermal shrinkage rate is further suppressed. Thus, many of the conventional high-strength films and gas barrier shrink films have low thermal shrinkage rates. If the heat shrinkage rate is low, the display effect of the product is inferior, and in the case of packaging that adheres to the contents, the adhesion is poor, and when the contents are food, the freshness may not be sufficiently maintained.

  On the other hand, in order to solve the above-mentioned problem of EVOH, studies have been made to arrange a layer made of thermoplastic polyester (for example, Patent Document 2). This study makes it possible to achieve uniform stretching of the EVOH layer with the thermoplastic polyester layer, achieve low-temperature shrinkage, and have a certain interlayer adhesion, so that zigzag is generated due to insufficient shrinkage of the EVOH layer that is likely to occur during heat shrinkage. The whitening phenomenon can be eliminated. Zigzag whitening refers to a layer mainly composed of a resin having a small thermal shrinkage rate as shown in FIG. 1 (film cross-sectional view) when a laminate of a resin having a small shrinkage rate and a resin having a high shrinkage rate is laminated. It means a zigzag bent without being able to follow the shrinkage of a layer mainly composed of a large resin, and when the film is viewed from the surface, it is whitened and the transparency is lowered. However, when the inventor made additional trials in accordance with Patent Document 2, it was confirmed that zigzag whitening occurred because the difference in thermal shrinkage between the two could not be absorbed depending on the layer structure, the resin used, and the shrinkage conditions.

Further, a study of arranging a mixture of a thermoplastic polyester and a thermoplastic polyurethane (hereinafter referred to as TPU) on the surface layer, and disposing a PA layer and an EVOH layer on the inner layer through a modified polyolefin of the adhesive layer (for example, Patent Document 3) It has also been made. It is said that low temperature brittleness can be improved by mixing thermoplastic polyurethane in the surface layer. However, according to the inventor's follow-up test, it has been found that this cannot achieve a sufficient heat shrinkage rate under dry heat shrinkage conditions such as 120 ° C. for 5 seconds.
Japanese Patent No. 3418204 Japanese Patent Laid-Open No. 10-34836 JP-A-9-183200

  The present invention is a heat-shrinkable film excellent in optical properties without causing delamination or zigzag whitening even after sufficiently heat-shrinking in a wide range of shrinkage conditions even in a laminated film having a large difference in shrinkage ability for each layer The purpose is to provide.

  The inventors of the present invention have reached the present invention as a result of intensive studies to achieve the above object. That is, the present invention is as follows.

  1. A first layer including a first polymer mainly composed of thermoplastic polyester and thermoplastic polyurethane, and a second layer mainly composed of a second polymer whose main repeating unit has substantially a halogen or hydrogen bond. A heat-shrinkable film, wherein the first layer and the second layer are directly laminated.

2. Item 2. The heat-shrinkable film according to Item 1, wherein the second polymer is any one selected from the group consisting of the following (a) to (d).
(A) Polyamide (b) Ethylene-vinyl alcohol copolymer (c) Polyvinylidene chloride (d) A polar group-containing polyolefin and a mixture of any one of (a) to (c).

  3. Item 2. The heat-shrinkable film according to Item 1, wherein the crystallinity of the thermoplastic polyester is 30% or less.

  4. The heat-shrinkable film according to item 1, wherein the heat shrinkage rate at 120 ° C. in the dry heat treatment is 30% or more in one direction of MD or TD and 20% or more in the other direction.

  5. Item 2. The heat-shrinkable film according to Item 1, comprising a laminate in which the second layer, the first layer, and the second layer are directly laminated in this order.

  6). Item 2. The item 1, wherein the second polymer is a polyamide, the second layer including the first layer, and the second layer containing a gas barrier resin in this order. Heat shrinkable film.

  7. Use of the heat-shrinkable film of item 1 for a gas replacement package.

  8). The heat described in Item 1 for the package used in a method of covering the contents with a package, causing the package to adhere to the contents by depressurizing the interior of the package, and further heat shrinking the package. Use of shrinkable film.

  According to the present invention, a heat-shrinkable film excellent in optical properties without causing zigzag whitening even after sufficiently heat-shrinking under a wide range of shrinkage conditions even in a laminated film having a large difference in shrinkage ability for each layer. For example, a beautiful shrinkage can be obtained while satisfying required properties such as strength and barrier properties.

Film cross section showing an example of zigzag whitening

  The heat-shrinkable film of the present invention needs to have a first layer (hereinafter referred to as layer A) containing a first polymer mainly composed of thermoplastic polyester and thermoplastic polyurethane. The thermoplastic polyester is necessary for exhibiting the above-described effects described in Patent Document 2. Thermoplastic polyurethane has strong adhesive strength with layer B, which is directly laminated on layer A, which will be described later, and suppresses delamination after shrinkage even under conditions where shrinkage ability differs from other layers, and zigzag whitening after shrinkage Has an important effect of not generating.

  The thermoplastic polyester in the present invention is divided into an aromatic polyester and an aliphatic polyester depending on its chemical structure, and both are suitably used in the present invention. Examples of the aromatic polyester include polyethylene terephthalate, polybutylene terephthalate, and copolyester. Copolyesters are often employed because physical properties such as stretchability, shrinkage and optical properties can be changed depending on the constituent monomer species and their ratio. For example, when alcohol is used as a copolymerization component, ethylene glycol is generally used, but as other copolymerization components, propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6- Hexanediol, neopentyl glycol, polyethylene glycol such as diethylene glycol or triethylene glycol, polytetramethylene glycol, cyclohexane dimethanol, xylylene glycol, or other known diols, including ethylene glycol A combination with one of these diols or one that does not contain ethylene glycol and contains one of the other diols based on any one of the above diols. On the other hand, terephthalic acid is generally used as the acid component for copolymerization, but it also contributes to esterification reactions with isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, other aromatics, or aromatic rings. And dicarboxylic acids having substituents that do not. Further, it may contain at least one dicarboxylic acid selected from succinic acid, adipic acid, sebacic acid, other aliphatic dicarboxylic acids and the like, or other known ones. Further, a mixture of the above polyesters or a mixture of two or more kinds such as a mixture with other polyesters other than the above as long as it is thermoplastic may be used.

  Examples of the aliphatic polyester used in the present invention include polylactic acid resin, aliphatic polyester obtained by polycondensation of aliphatic dicarboxylic acid and aliphatic diol as main components, aliphatic polyester obtained by ring-opening polymerization of cyclic lactones, and synthetic fat. Aliphatic polyesters, aliphatic polyesters such as poly (hydroxyalkanoic acid) biosynthesized in cells, and aliphatic aromatic polyesters having a structure in which a part of these polyesters is substituted with an aromatic compound. Many of these are known as biodegradable resins in recent years.

  The polylactic acid polymer is a polylactic acid homopolymer and a copolymer containing 50% by weight or more of lactic acid monomer units, and is composed of a polylactic acid homopolymer, lactic acid, and other hydroxycarboxylic acid and lactone. It is a copolymer with a compound selected from the group. When the content of the lactic acid monomer unit is less than 50% by weight, the heat resistance and transparency of the film tend to be lowered. Preferably, it is a polylactic acid homopolymer and a copolymer containing 80% by weight or more of lactic acid monomer units, or a mixture of these copolymers, more preferably 90% by weight of polylactic acid homopolymer and lactic acid monomer units. % Of a copolymer or a mixture of these copolymers.

  Lactic acid has L-lactic acid and D-lactic acid as optical isomers, and polylactic acid obtained by polymerizing them contains about 10% or less of D-lactic acid unit and about 90% or more of L-lactic acid unit, Or a polylactic acid having an L-lactic acid unit of about 10% or less and a D-lactic acid unit of about 90% or more, an optical purity of about 80% or more, and a D-lactic acid unit of 10% to 90% It is known that there are polylactic acid having an L-lactic acid unit of 90% to 10% and amorphous polylactic acid having an optical purity of about 80% or less.

  As a monomer used as a copolymerization component with lactic acid, as hydroxycarboxylic acid, glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 3-hydroxyvaleric acid, 4-hydroxyvaleric acid, 6-hydroxycaproic acid Etc. Examples of the aliphatic cyclic ester include glycolide, lactide, β-propiolactone, γ-butyrolactone, δ-valerolactone, ε-caprolactone, and lactones substituted with various groups such as a methyl group. Examples of the dicarboxylic acid include succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, terephthalic acid, and isophthalic acid. Examples of the polyhydric alcohol include aromatic polyhydric alcohols such as bisphenol / ethylene oxide addition reaction products, Aliphatic polyhydric alcohols such as ethylene glycol, propylene glycol, butanediol, hexanediol, octanediol, glycerin, sorbitan, trimethylolpropane, neopentyl glycol, ether glycols such as diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, etc. Is mentioned.

  As a polymerization method of the polylactic acid resin, known methods such as a condensation polymerization method and a ring-opening polymerization method can be employed. Moreover, the method of increasing molecular weight using binders, such as a polyisocyanate, a polyepoxy compound, an acid anhydride, and polyfunctional acid chloride, can also be used.

  The weight average molecular weight of the polylactic acid resin is preferably in the range of 10,000 to 1,000,000. If the molecular weight is less than 10,000, it is difficult to obtain only a film having poor mechanical properties, and if it exceeds 1,000,000, the melt viscosity becomes high, and it is difficult to obtain a film having stable physical properties by an ordinary processing machine.

  Examples of aliphatic polyesters obtained by polycondensation of aliphatic dicarboxylic acid and aliphatic diol as main components include succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid and other aliphatic carboxylic acids, terephthalic acid One or more of aromatic carboxylic acids such as acid and isophthalic acid, and aliphatic diols such as ethylene glycol, 1,3-propion glycol, 1,4-butanediol, and 1,4-cyclohexanedimethanol The polycondensation chosen is an example.

  Examples of aliphatic polyesters obtained by ring-opening polymerization of cyclic lactones include ring-opening polymers selected from one or more cyclic monomers such as ε-caprolactone, δ-valerolactone, and β-methyl-δ-valerolactone. Can be mentioned.

  Examples of synthetic aliphatic polyesters include copolymers of succinic anhydride, cyclic acid anhydrides such as ethylene oxide and propylene oxide, and oxiranes.

  In addition, as poly (hydroxyalkanoic acid) biosynthesized in the microbial cells, poly (3-hydroxybutyric acid), poly (3-hydroxypropionic acid), poly (3-hydroxyvaleric acid), poly (3-hydroxybutyric acid) -3-hydroxyvaleric acid) copolymer, poly (3-hydroxybutyric acid-3-hydroxyhexanoic acid) copolymer, poly (3-hydroxybutyric acid-3-hydroxypropionic acid) copolymer, poly (3-hydroxy Examples include butyric acid-4-hydroxybutyric acid) copolymer, poly (3-hydroxybutyric acid-3-hydroxyoctanoic acid) copolymer, poly (3-hydroxybutyric acid-3-hydroxydecanoic acid) copolymer, and the like. .

  Examples of the aliphatic aromatic polyester include polybutylene succinic acid phthalic acid copolymer, polyethylene succinic acid phthalic acid copolymer, polybutylene adipic acid phthalic acid copolymer, polyethylene adipic acid phthalic acid copolymer, and polyethylene glutar. Examples include acid terephthalic acid copolymer, polybutylene glutaric acid terephthalic acid copolymer, polybutylene succinic acid adipic acid phthalic acid copolymer, and the like.

  The weight average molecular weight of the aliphatic polyester is preferably in the range of 20,000 to 500,000, more preferably in the range of 50,000 to 250,000. When the molecular weight is less than 20,000, it is difficult to sufficiently improve practical physical properties such as mechanical strength and impact strength, and when the molecular weight exceeds 500,000, molding processability may be inferior.

  Among these thermoplastic polyesters, copolymer aromatic polyesters and polylactic acid resins are preferred from the viewpoints of stretch processability, shrinkage properties, and optical properties. Among them, crystallinity as a raw material (by wide-angle X-ray diffraction method). Measurement) is preferably 30% or less, more preferably 20% or less, still more preferably 10% or less, still more preferably 5% or less, and particularly preferably substantially amorphous. A substantially amorphous material is preferable not only because it has the best stretch processability, shrinkage properties, and optical properties, but also enables low-temperature extrusion.

  Examples of such low crystallinity or substantially non-crystalline materials include, for example, those obtained by copolymerizing isophthalic acid in addition to terephthalic acid as an acid component, and other glycol glycol such as ethylene glycol as an alcohol component. Obtained by copolymerizing an alcohol component, for example, containing ethylene glycol as a main component as an alcohol component, 40 mol% or less of 1,4-cyclohexanedimethanol, and further copolymerized using terephthalic acid as an acid component Etc. In that case, a more preferable ratio of ethylene glycol and 1,4-cyclohexanedimethanol as an alcohol component is that of 1,4-cyclohexanedimethanol being 20 to 40 mol%, more preferably about 25 to 36 mol%. Examples of such amorphous aromatic polyester include Eastar PETG6763 copolyester (trade name) and Embrace copolyester (trade name) manufactured by Eastman Chemical Japan Co., Ltd. Examples include E-01-3 (trade name) of amorphous PET for extrusion manufactured by Kanebo Synthetic Co., Ltd.

Further, from the same viewpoint, the polylactic acid resin preferably has 3% to 97%, more preferably 4% to 96%, and most preferably 10% to 90% D-lactic acid units.

  As the thermoplastic polyurethane (TPU) used in the present invention, a polyaddition product of a polyol and an isocyanate can be used. As the polyol, polyether polyol such as polypropylene glycol and polytetramethylene ether glycol, polyester polyol such as adipate polyol, polycaprolactone polyol or polycarbonate polyol, polybutadiene polyol, acrylic polyol and the like can be used. These may be used alone or in combination of two or more. As the isocyanate, diphenylmethane diisocyanate, paraphenylene diisocyanate, dianisidine diisocyanate and the like can be used. These may be used alone or in combination of two or more. Furthermore, diol or triol can be used as a crosslinking chain extender. The melt viscosity can be adjusted by using a crosslinking chain extender.

  TPU is preferably an elastomer from the viewpoint of stretch processability. Specifically, Kuraray Co., Ltd. Kuramiran U (trade name) and TU polymer (trade name), Nippon Polyurethane Industry Co., Ltd. Miractolan (trade name), Dainichi Seika Kogyo Co., Ltd. Rezamin P (Trade name), Esten (trade name) manufactured by NOVEON. The behavior and melting behavior as an elastomer differ depending on the content of the isocyanate component. When the content of the isocyanate component is expressed in terms of nitrogen content, the nitrogen content contained in TPU is preferably 1 to 7% by weight, and particularly preferably 3 to 5% by weight. If it is less than 1% by weight, the melt viscosity is too small to obtain a sufficient viscosity, and if the nitrogen content exceeds 7% by weight, the melt viscosity becomes too large, which impedes the extrusion processability and stretch processability. It is because it may affect.

  Of the resin composition constituting the layer A of the present invention, TPU is preferably 5 to 60% by weight, more preferably TPU is 15 to 50% by weight, and most preferably TPU is 20 to 40% by weight. . If the ratio of the resin composition is within this range, the adhesiveness with the layer B is sufficiently expressed, and heat having excellent optical properties without causing zigzag whitening even after sufficiently heat shrinking under a wide range of shrinkage conditions. A shrinkable film can be provided. For example, a shrinkable article having good optical properties can be obtained while satisfying required properties such as strength and barrier properties. If the TPU is less than 5%, the adhesiveness with the layer B is weak, and zigzag whitening may occur depending on the heat shrinkage conditions. When TPU exceeds 60%, extrusion processability and stretch processability may become difficult.

In the present invention, a second layer (hereinafter referred to as layer B) mainly comprising a second polymer having a repeating unit mainly comprising a halogen or hydrogen bond is also required. The resin constituting this layer B has a strong polarity due to its structure, and they are more strongly aggregated after stretching, and are essential for improving the strength and developing the barrier property. Here, “substantially having a halogen or having a hydrogen bond” means that, among the repeating units constituting the polymer, the main repeating unit has a halogen or constitutes a hydrogen bond, and the chemical treatment In the case where a chemical group constituting a halogen or a hydrogen bond is added only to a terminal or a part of the molecular chain (less than 50 mol% in the repeating unit), it is insufficient to obtain the above-mentioned physical properties peculiar to the layer B. It is not included in the invention. Further, “mainly composed of a polymer having a halogen or a hydrogen bond” means that the layer B contains a polymer having a halogen or a hydrogen bond in an amount of 50% by weight or more. means.
The second polymer in which the main repeating unit substantially has a halogen or hydrogen bond is (a) polyamide, (b) ethylene-vinyl alcohol copolymer, (c) polyvinylidene chloride, or ( d) It is preferably composed of a mixture comprising a polar group-containing polyolefin and any one of (a) to (c). Hereinafter, the second polymer will be described in more detail.

  Examples of the resin having substantially halogen as the repeating unit include polyvinylidene chloride polymers, polyvinyl chloride polymers, polyvinylidene fluoride polymers, and polyvinyl fluoride. Among these, polyvinylidene chloride is included. It is preferably applied because the polymer is excellent in gas barrier properties. Examples of the vinylidene chloride-based polymer include copolymer resins of vinylidene chloride and 50 mol% or less of vinyl chloride, methyl acrylate, butyl acrylate, and the like.

  On the other hand, a hydrogen bond refers to a bond XH... Y in which atoms X and Y (nitrogen, oxygen, phosphorus, sulfur, halogen, etc.) that are more negative than hydrogen atoms are weakly bonded through hydrogen. Examples of the polymer having substantially repeating hydrogen bonds include PA, EVOH, polyvinyl alcohol (hereinafter referred to as PVA), cellulose, and derivatives thereof. Among these, high-strength PA and gas barrier EVOH are preferably used in the present invention. PVA is also preferably used when hydrophilicity is particularly required for the film.

  EVOH used in the present invention has an ethylene copolymerization ratio of less than 50%. From the viewpoint of gas barrier properties, those having 45 mol% or less of ethylene are preferred. Moreover, it is preferable that an ethylene copolymerization ratio is 25 mol% or more from a viewpoint of the balance of a moldability and gas barrier property.

  As the PVA used in the present invention, thermoplastic PVA whose thermoplasticity is improved by graft modification in addition to adjusting the saponification degree is suitably used. Specifically, low saponification degree PVA, Eco Synth AX (trade name) manufactured by Nippon Synthetic Chemical Industry Co., Ltd. (grafted product of polyoxyalkylene on vinyl alcohol / allyl alcohol copolymer), Kuraray Co., Ltd. Kuraray Poval (trade name) made by Kuraray and CP series (trade name) for hot melt molding, and Kuraray Co., Ltd. Exval (trade name) for melt molding (CP polymer) (trade name) Has been.

  Examples of PA used in the present invention include aliphatic polyamides and semi-aromatic polyamides. Specific examples include polycaproamide (nylon 6), polyhexamethylene adipamide (nylon 66), polycaproamide / polyhexamethylene adipamide copolymer (nylon 6/66), polytetramethylene adipamide (Nylon 46), polyhexamethylene sebamide (nylon 610), polyhexamethylene dodecamide (nylon 612), polycaproamide / polyhexamethylene adipamide / polydodecanamide copolymer (nylon 6/66/12) , Polyhexamethylene terephthalamide / polycaproamide copolymer (nylon 6T / 6), polyhexamethylene adipamide / polyhexamethylene terephthalamide copolymer (nylon 66 / 6T), polyhexamethylene adipamide / polyhexamethylene Isophthalamide Polymer (nylon 66 / 6I), polyhexamethylene adipamide / polyhexamethylene terephthalamide / polyhexamethylene isophthalamide copolymer (nylon 66 / 6T / 6I), polyhexamethylene terephthalamide / polyhexamethylene isophthalamide copolymer -(Nylon 6T / 6I), polyhexamethylene terephthalamide / poly (2-methylpentamethylene) terephthalamide copolymer (nylon 6T / M5T), polyhexamethylene terephthalamide / polyhexamethylene sebacamide / polycaproamide copolymer ( Nylon 6T / 610/6), polyhexamethylene terephthalamide / polydodecanamide / polyhexamethylene adipamide copolymer (nylon 6T / 12/66), polyhexamethylene tele Taramide / polydodecanamide / polyhexamethylene isophthalamide copolymer (nylon 6T / 12 / 6I), polyxylylene adipamide (nylon XD6), polyhexamethylene terephthalamide / polyhexamethylene isophthalamide (nylon 6T / 6I), And mixtures or copolymers thereof. Among the PAs, nylon 6/66 having a melting point of 200 ° C. or lower is preferable from the viewpoints of cost, extrudability, and stretchability. Further, in order to improve stretchability, it is preferable to mix nylon 6/66 with 20 to 100% and PA with a melting point of 180 ° C. or less and low crystalline or amorphous PA with 0 to 80% by weight. Examples of PA having a melting point of 180 ° C. or lower include nylon 6-69, nylon 6-12, nylon 6-66-610, nylon 6-66-12, nylon 6-66-610-12, and the like. Amorphous PA is a copolymer of aliphatic diamine / isophthalic acid and aliphatic diamine / terephthalic acid, an acid component comprising 40 to 98 mol% isophthalic acid component and 2 to 60 mol% terephthalic acid component, and hexamethylene. It consists of 50 to 99 mol% of diamine and optionally 0 to 50 mol% of bis (p-aminocyclohexyl) methane. These are non-crystalline nylons made of nylon 6I-6T, and a sealer made by Mitsui DuPont Co., Ltd. PA 3426 (trade name), Gripoly G21 (trade name) manufactured by EMS Co., Ltd., Mitsubishi Engineering Plastics Ltd. NOVAMID X21 are marketed as (trade name), in particular is preferably used, its preferred amount is from 10-40%, most preferably 20-30%. Of these, amorphous ones are most preferable, and when they have crystallinity, PA having no crystallization peak temperature within 15 ° C., more preferably within 20 ° C. in the vicinity of the stretching temperature is preferable from the viewpoint of stretchability. When it is necessary to impart gas barrier properties to the PA layer, nylon XD (for example, nylon MXD6 (trade name) manufactured by Mitsubishi Gas Chemical Company, Inc.) is preferably used mainly or as a mixture.

  Mixing the polar group-containing polyolefin with the layer B of the present invention is preferable because the adhesion with the layer A can be further improved. Examples of the polar group-containing polyolefin include an ethylene-vinyl ester copolymer, an ethylene-unsaturated carboxylic acid copolymer, an ionomer of an ethylene-unsaturated carboxylic acid copolymer, and an ethylene-unsaturated carboxylic acid ester copolymer. . Examples of the unsaturated carboxylic acid component include acrylic acid, methacrylic acid, fumaric acid, maleic acid monomethyl ester, maleic acid monoethyl ester, and maleic anhydride.

  Specifically, ethylene-vinyl acetate copolymer (EVA) as the ethylene-vinyl ester copolymer, ethylene-methyl methacrylate copolymer (EMMA), ethylene-acrylic acid as the ethylene-unsaturated carboxylic acid ester copolymer. Methyl copolymer (EMA), ethylene-ethyl acrylate copolymer (EEA), ethylene-unsaturated carboxylic acid copolymer, ethylene-methacrylic acid copolymer (EMAA), ethylene-acrylic acid copolymer (EAA) ), A modified olefin polymer obtained by graft-modifying an ethylene copolymer with maleic anhydride, glycidyl (meth) acrylate, or the like.

  The ionomer used in the present invention is a metal such as zinc, sodium, magnesium, lithium, or potassium in which at least a part of the carboxyl group of the ethylene / unsaturated carboxylic acid random copolymer such as an ethylene / (meth) acrylic acid copolymer is used. It is neutralized by 0.1 to 90% with ions. In the ionomer, the ethylene component is 75 to 95% by weight, particularly 80 to 90% by weight, and the unsaturated carboxylic acid component, that is, the unsaturated carboxylic acid and unsaturated carboxylate component is 5 to 25% by weight, particularly 10 to 20% by weight. %, And other unsaturated monomer components are preferably copolymerized in a proportion of 0 to 25% by weight, particularly 0 to 20% by weight. Two or more different unsaturated carboxylic acid components may be used as long as the sum satisfies the above requirements. The ethylene / unsaturated carboxylic acid random copolymer serving as the ionomer base polymer can be obtained by random copolymerization of each polymerization component under high temperature and high pressure. Other unsaturated monomer components include, for example, acrylic acid esters such as methyl (meth) acrylate, ethyl (meth) acrylate, isobutyl (meth) acrylate, n-butyl (meth) acrylate, and methacrylic acid. About 0 to 25% by weight of an ester or an unsaturated ester such as vinyl acetate may be copolymerized.

  Among these ionomers, zinc ionomers are particularly preferably used for PA and EVOH. Zinc ionomers are preferred because they form coordinate bonds with amino groups and have a high affinity for PA. Examples of this include High Milan AM7315 (trade name) and High Milan 1706 (trade name) manufactured by Mitsui DuPont Polychemical Co., Ltd. In addition to its properties, some amino groups have increased affinity for EVOH, and these are also preferably used for EVOH. As this, for example, High Milan AM79261 (trade name) manufactured by Mitsui DuPont Polychemical Co., Ltd. may be mentioned. Furthermore, since sodium ionomer has a strong electrostatic interaction with a hydroxyl group, it is also preferably used for PA and EVOH. Examples of this include High Milan S1856 (trade name) manufactured by Mitsui DuPont Polychemical Co., Ltd.

  The effect of the present invention is particularly apparent in a film exhibiting a high shrinkage rate, and the heat shrinkage rate is 120 ° C. dry heat in the vertical direction (the line direction during film formation is the vertical direction, hereinafter referred to as MD). Alternatively, in the heat-shrinkable film, one of the transverse direction (transverse direction with respect to the line direction during film formation, hereinafter referred to as TD) is 30% or more, and the other is 20% or more. In general, the upper limit of the shrinkage rate of the heat shrink film is 90%, and in many cases 80%. In order to obtain such a high heat shrinkage rate, the crystallinity of the thermoplastic polyester used in the layer A is preferably 30% or less, more preferably 20% or less, still more preferably 10% or less, and even more preferably 5%. In the following, it is particularly preferable that it is substantially amorphous. The low crystalline resin facilitates a high draw ratio and realizes a high shrinkage ratio in a practical shrinkage temperature region above the glass transition point without waiting for melting of the crystal component.

  Regarding the arrangement of the layer A and the layer B in the present invention, any of A / B, A / B / A, B / A / B, A / B / A / B, and the like can be exhibited. The heat-shrinkable film of the present invention is preferably composed of a laminate (in this specification, referred to as layer B / layer A / layer B) in which layer B, layer A, and layer B are directly laminated in this order. In particular, when two or more kinds of layers B, for example, a layer B in which the second polymer is a polyamide, a layer B containing a gas barrier resin, and a layer A are composed of three or more layers, the heat shrinkage of the present invention The conductive film is preferably composed of a laminate in which the second polymer is a polyamide layer B, a layer A, and a layer B containing a gas barrier resin in this order. Moreover, as resin which has gas-barrier property, resin containing EVOH is mentioned, for example. Layer B is strongly polar and strongly agglomerates after stretching, resulting in a low heat shrinkage rate of the film or a zigzag whitening due to a small heat shrinkage rate of the specific layer. This is because they are arranged separately on both sides and directly and efficiently act on and supplement each layer B by the adjacent layers A. By taking such a layer arrangement, a film having both pinhole resistance and gas barrier properties can be obtained without causing delamination and zigzag whitening. In this specification, “adjacent” and “directly stack” have the same meaning.

Moreover, in this invention, the oxygen absorption layer which provided the oxygen absorption function in the gas barrier resin layer or the layer by the side of food from it can be provided preferably. The oxygen barrier resin has an oxygen permeability (cc · 25.4 microns / m ² · 24 hr · atm, 25 ° C., 0RH%) of 50 or less, preferably 10 or less, more preferably 2 or less, most preferably 1 or less. Is. Specific examples include EVOH, vinylidene chloride resin, nylon XD, polyglycolic acid, polyglycolic acid-lactic acid copolymer, etc., but EVOH, vinylidene chloride resin, and polyglycolic acid are preferable from the viewpoint of barrier properties. Furthermore, EVOH is preferable from the viewpoint of coextrusion.

  As the constituent of the oxygen absorbing layer, there can be used a method of mixing or coating an inorganic substance / organic substance imparting a deoxygenating function to a resin, or a resin itself having an oxygen absorbing ability. Examples of inorganic / organic substances include iron powder, aluminum powder, ascorbic acid, activated carbon, hindered phenol, polyphenol, and unsaturated fats and oils. Resins with oxygen-absorbing ability include those with double bonds in the molecule and those containing tertiary hydrogen, and in combination with transition metals such as cobalt and silver, and their salts and oxides in the presence of appropriate catalysts. This promotes auto-oxidation. Of these, those having a double bond and less likely to lower the molecular weight of the resin due to oxidative decomposition are, for example, those having a double bond in the cyclic structure of the side chain (for example, ethylene / methyl described in JP 2003-521552 A). An acrylate / cyclohexene-methyl acrylate copolymer or the like is preferably used.

  In the present invention, a seal layer is preferably provided.

  The resin that mainly constitutes the sealing layer is not particularly limited as long as it is a heat-sealable thermoplastic resin, but polyolefin resins and polystyrene resins are preferably used from the viewpoint of the sealing temperature. .

  In the present invention, the polyolefin resin used for the seal layer is specifically shown below.

  Ethylene-based polymers are polymerized by a single site catalyst or a multi-site catalyst, and include ordinary low density, medium density, high density polyethylene, linear low density polyethylene, and ultra low density polyethylene. Ethylene and propylene, 1-butene , 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene and the like and a copolymer with an α-olefin having 3 to 18 carbon atoms.

  As the propylene polymer, a copolymer of propylene and another α-olefin is preferable. In particular, a copolymer of propylene and another α-olefin obtained by a metallocene catalyst has a melting point close to that of a polyethylene resin and is preferably used. Specific examples of this include Wintech (trade name, manufactured by Nippon Polychem Co., Ltd.).

  Examples include olefin-vinyl ester copolymers, olefin-unsaturated carboxylic acid copolymers, ionomers of olefin-unsaturated carboxylic acid copolymers, and olefin-unsaturated carboxylic acid ester copolymers. It is done. Examples of the unsaturated carboxylic acid component include acrylic acid, methacrylic acid, fumaric acid, maleic acid monomethyl ester, maleic acid monoethyl ester, and maleic anhydride. Specifically, ethylene-vinyl acetate copolymer (EVA) as the ethylene-vinyl ester copolymer, ethylene-methyl methacrylate copolymer (EMMA), ethylene-acrylic acid as the ethylene-unsaturated carboxylic acid ester copolymer. Methyl copolymer (EMA), ethylene-ethyl acrylate copolymer (EEA), ethylene-unsaturated carboxylic acid copolymer, ethylene-methacrylic acid copolymer (EMAA), ethylene-acrylic acid copolymer (EAA) ), A modified olefin polymer obtained by graft-modifying an ethylene copolymer or a propylene copolymer with maleic anhydride, glycidyl (meth) acrylate, or the like. Further, at least part of the carboxyl group of an ethylene / unsaturated carboxylic acid random copolymer such as an ethylene / (meth) acrylic acid copolymer called an ionomer is 0 by a metal ion such as zinc, sodium, magnesium, lithium, or potassium. Examples include those neutralized by 1 to 90%. In the ionomer, the ethylene component is 75 to 95% by weight, particularly 80 to 90% by weight, and the unsaturated carboxylic acid component, that is, the unsaturated carboxylic acid and unsaturated carboxylate component is 5 to 25% by weight, particularly 10 to 20% by weight. %, And other unsaturated monomer components are preferably copolymerized in a proportion of 0 to 25% by weight, particularly 0 to 20% by weight. Two or more different unsaturated carboxylic acid components may be used as long as the sum satisfies the above requirements. The ethylene / unsaturated carboxylic acid random copolymer serving as the ionomer base polymer can be obtained by random copolymerization of each polymerization component under high temperature and high pressure. Other unsaturated monomer components include, for example, acrylic acid esters such as methyl (meth) acrylate, ethyl (meth) acrylate, isobutyl (meth) acrylate, n-butyl (meth) acrylate, and methacrylic acid. About 0 to 25% by weight of an ester or an unsaturated ester such as vinyl acetate may be copolymerized.

  In the present invention, the polystyrene resin used for the seal layer is a homopolymer or copolymer of at least one styrene monomer selected from the group consisting of styrene and its derivatives, or styrene and its derivatives. And a copolymer of at least one styrene monomer selected from the group consisting of and other vinyl monomers. In the case of a copolymer, it may be a random copolymer or a block copolymer. The polystyrene resin must be able to be extruded and stretched. Examples of the styrene monomer include styrene, α-methyl styrene, o-methyl styrene, m-methyl styrene, p-methyl styrene, halogenated styrene, t-butyl styrene, vinyl toluene, vinyl xylene, divinyl benzene, and the like. Can be given. Among these, styrene, α-methylstyrene, and p-methylstyrene are preferable, and styrene and α-methylstyrene are particularly preferable. The styrene monomer is usually 25 to 100% by weight, preferably 50 to 100% by weight, and more preferably 55 to 98% by weight, as a proportion of the total amount of monomers used as a polymerization raw material for the polystyrene resin. Is desirable.

  The other vinyl monomer copolymerized with the styrene monomer is not particularly limited as long as it is a vinyl compound copolymerizable with the styrene monomer. Such other vinyl monomers include: olefins such as ethylene and propylene; polyenes such as butadiene and isoprene; acrylonitrile monomers such as acrylonitrile, methacrylonitrile and α-chloroacrylonitrile; methyl methacrylate and ethyl methacrylate. (Meth) acrylic acid alkyl ester monomers such as methyl acrylate, ethyl acrylate and n-butyl acrylate; maleimide monomers such as n-phenylmaleimide, n-methylphenylmaleimide, n-cyclohexylmaleimide and n-ethylmaleimide Examples thereof: Unsaturated carboxylic acid derivatives such as maleic anhydride, acrylic acid, and methacrylic acid. These monomers can also be used individually by 1 type, and can also be used in combination of 2 or more type. These are marketed, for example, asaflex (trade name) manufactured by Asahi Kasei Corporation.

  A rubber-like polymer may be mixed in the polystyrene resin. Examples of the rubbery polymer include polybutadiene, isoprene / butadiene copolymer, styrene / butadiene copolymer, acrylonitrile / butadiene copolymer, ethylene / propylene copolymer, and ethylene / propylene / diene copolymer. . These include, for example, Tough Tech (trade name) from Asahi Kasei Co., Ltd., Dynalon (trade name) from JSR Corporation, Clayton (trade name) from Shell, Hibler (trade name) from Kuraray Co., Ltd. Product name). A polystyrene resin can also be used individually by 1 type, and can also be used in combination of 2 or more type.

  Moreover, the aliphatic polyester shown below can also be used for a heat seal layer.

  For example, aliphatic polyesters obtained by polycondensation of aliphatic dicarboxylic acid and aliphatic diol as main components include aliphatic carboxylic acids such as succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid, and dodecanedioic acid. , One or more of aromatic carboxylic acids such as terephthalic acid and isophthalic acid, and aliphatic diols such as ethylene glycol, 1,3-propion glycol, 1,4-butanediol and 1,4-cyclohexanedimethanol The polycondensation chosen is an example.

  Examples of aliphatic polyesters obtained by ring-opening polymerization of cyclic lactones include ring-opening polymers selected from one or more cyclic monomers such as ε-caprolactone, δ-valerolactone, and β-methyl-δ-valerolactone. Can be mentioned.

  Examples of synthetic aliphatic polyesters include copolymers of succinic anhydride, cyclic acid anhydrides such as ethylene oxide and propylene oxide, and oxiranes.

  The weight average molecular weight of the aliphatic polyester is preferably in the range of 20,000 to 500,000, more preferably in the range of 50,000 to 250,000. When the molecular weight is less than 20,000, it is difficult to sufficiently improve practical physical properties such as mechanical strength and impact strength, and when the molecular weight exceeds 500,000, molding processability may be inferior.

  The outer surface layer of the present invention, that is, the layer of the surface layer that does not contact the contents is not particularly limited, and may be any of a seal layer, a polyester layer, a polyamide layer, and a barrier resin layer. good. When requesting printability, the polar group-containing polyolefin, polyester resin, and polyamide resin exemplified above can be mainly used. When the surface wear resistance is required, a polyamide resin can be mainly used. When the outer surface layer is used as the seal layer, the same resin as that of the seal layer can be mainly used. When the outer surface layer is a polyolefin-based resin, when an additive is mixed, the glass transition point is not higher than room temperature, so that it can be appropriately bleed out and various surface characteristics can be adjusted according to the application. Furthermore, in the case of a polyethylene-based resin, it is possible to impart so-called sealing heat resistance, that is, prevention of fusion to the seal bar during sealing by crosslinking.

In the case where the heat-shrinkable film of the present invention is subjected to a palm-clad heat sealing process that requires a heat seal layer only on one side, in the resin where the seal surface layer and the non-seal surface layer can be crosslinked by an electron beam such as a polyethylene resin, It is preferable that the seal surface layer and the non-seal surface layer satisfy the following formula.
10 ≦ G (non-seal surface) ≦ 70 (I)
0 ≦ G (seal surface) ≦ 30 (II)
G (non-seal surface) ≧ 1.2 × G (seal surface) (III)
However, G (non-seal surface layer) and G (seal surface layer) represent the gel fraction (weight%) by bridge | crosslinking of a non-seal surface layer and a seal surface layer, respectively.

  In this case, the non-sealed surface layer has a role as a heat-resistant layer at the time of joint heat sealing. Moreover, it has the effect | action which improves the stretchability of the film containing PA layer and gas barrier resin layer which are difficult to stretch. The gel fraction G (non-sealed surface layer) of the non-sealed surface layer is preferably 10% by weight or more and 70% by weight or less. When the gel fraction is 10% by weight or more, the effect as the heat resistant layer and the stretchability improving effect tend to be large, and when the gel fraction is 70% by weight or less, the effect as the heat resistant layer and the stretchability tend to be good. On the other hand, the gel fraction G (seal surface layer) of the heat seal surface layer is preferably 30% by weight or less. This is preferably 20% by weight or less, more preferably 10% by weight or less. Most preferably, it is substantially uncrosslinked and has a gel fraction of 0%. When the gel fraction exceeds 30% by weight, sealing tends to be difficult and the sealing strength tends to be insufficient.

  Further, the relationship between the non-seal surface layer and the gel fraction resulting from crosslinking of the seal surface layer is preferably G (non-seal surface layer) ≧ 1.2 × G (seal surface layer). In the case of G (non-sealing surface layer) <1.2 × G (sealing surface layer), the effect of the heat-resistant layer of the non-sealing surface layer on the side to which the heat is applied for sealing is no longer exerted on the sealing layer, and heat sealing In addition to the longer time required for packaging, packaging defects become more noticeable.

  It should be noted that the thickness of the non-seal surface layer is not particularly limited regardless of the presence or absence of crosslinking, and even if it is as thin as 1 micron, it is satisfactory in many cases. If necessary, it is preferably 5 microns or more, more preferably 8 microns or more, and most preferably 10 microns or more.

  In the present invention, the layer A and the layer B are provided directly adjacent to each other without interposing other layers, but an adhesive layer can be provided as necessary in combination with other layers. As the adhesive layer, the above-mentioned polar group-containing polyolefin can be used.

  As long as the effects of the present invention are not impaired, known additives in any resin layer, for example, antioxidants (for example, 2,2-thiobis (4methyl-6-t-butylphenol) ), Light stabilizers (for example, 2-hydroxy-4-octoxybenzophenone), processing aids (for example, calcium stearate), lubricants (for example, erucic acid) Amide, oleic acid amide, stearic acid amide, behenic acid amide, etc.), anti-blocking agent (for example, natural silica, synthetic silica, or average particle diameter (Coulter counter method) 10 μm or less, preferably 1 to 4 μm PMMA beads), anti-fogging agents (for example, diglycerin monolaurate, diglycol Serine monooleate, diglycerin distearate, polyoxyalkylene ether, polyoxyethylene alkylene ester, etc.), antistatic agent (for example, polyglycerin ester, etc.), other sealing property improving functions Such as alicyclic saturated hydrocarbon resin (Arakawa Chemical Industries, Ltd., Alcon (trade name), etc.), hydrogenated terpene resin (Yasuhara Chemicals, Inc., Clearon) (Trade name, etc.), terpene resin (manufactured by Yasuhara Chemical Co., Ltd., YS resin (trade name), etc.), liquid paraffin (manufactured by Matsumura Oil Research Co., Ltd., Moresco White (trade name), etc.), rosin, Rosin ester, coumarone indene resin, etc.) may be mixed in. Also, known surface treatments such as Corona discharge treatment, flame treatment, radiation processing including electron-plasma, etc., can be an ion etching process and the like.

  An example of the method for producing the heat shrinkable film of the present invention will be described. First, the resin constituting each layer is melted in each extruder, coextruded with a multilayer die, and rapidly solidified to obtain a multilayer film original fabric. As the extrusion method, a multilayer T-die method, a multilayer circular method or the like can be used, but the latter is preferable. The multilayer film original fabric thus obtained is heated to 50 to 200 ° C. for stretching. Examples of the stretching method include a roll stretching method, a tenter stretching method, inflation (including a double bubble method), and the like. A method of forming a film by biaxial stretching is preferable. Stretching is at least 1 to 10 times in one direction and 1 to 50 times in terms of area magnification, and this stretching ratio is appropriately selected depending on the required heat shrinkage rate and the like. Insufficient stretching may cause “residual shrinkage” due to insufficient shrinkage, which may prevent beautiful packaging. In the case of obtaining a film having a high shrinkage rate, a stretching ratio of 4 times or more in the longitudinal direction and the lateral direction is preferable, and more preferably a stretching ratio in which one is 4 times or more and the other is 4.5 times or more. The area magnification is also preferably 16 times or more, more preferably 18 times or more, and most preferably 20 times or more.

  In addition, after treatment, for example, heat setting for dimensional stability, lamination with various films may be performed.

  In particular, heat setting is performed when the shrinkage force needs to be reduced. In many cases, the processing temperature is selected from 60 ° C to 100 ° C. In order to relieve stress, the treatment is preferably performed at a temperature higher than the glass transition point of the polyamide, and in order to prevent film fusion, the temperature is preferably lower than the melting point of the surface resin. Furthermore, when suppressing the reduction | decrease of shrinkage, it is preferable to process at the temperature below the glass transition point of a polyester resin. In the case of tray packaging to be described later, it is particularly effective to reduce the shrinkage force in the lateral direction. In this case, dimensional relaxation of 0 to 30% is positively taken in the lateral direction during heat setting. Further, in this case, −20% to + 20% is selected as the dimensional relaxation rate in the vertical direction. In the case of tray packaging, it is possible to achieve both a high shrinkage ratio and a low shrinkage force by combining the above-described high stretch ratio and heat setting under specific conditions. In this case, the preferred heat shrinkage rate is 120% at a dry heat and either MD or TD is 30% or more, the other is 20% or more, and more preferably both MD and TD are 30% or more. Preferably, either MD or TD is 35% or more, and the other is 30% or more. Further, the preferable shrinkage stress is that the maximum stress (average value of MD and TD) when immersed in an oil bath at 120 ° C. is 3.0 MPa or less, more preferably 2.5 MPa or less, and most preferably 2.0 MPa or less.

  The film of the present invention is preferably used so as to be thermally shrunk by dry heat treatment such as hot water or shrink tunnel. For example, the heat-shrinkable film of the present invention is used in a method in which the contents are covered with a packaging body, the inside of the packaging body is depressurized to bring the packaging body into close contact with the contents, and the packaging body is further thermally contracted. It is preferable to use it for a package. Thereby, the package which is tightly adhered to the contents can be obtained. Another use is to use a horizontal pillow shrink wrapping machine without bringing the film into close contact with the entire contents, and place the contents on a tray to obtain a package that is thermally shrunk in a shrink tunnel. In particular, when the heat-shrinkable film of the present invention has gas barrier properties, it is preferably used for a gas replacement package. Above all, the air inside the package is replaced with an inert gas, that is, nitrogen, carbon dioxide and a mixture thereof, or a gas mixed with oxygen at a partial pressure of 20% or less or 21% or more as necessary. It is preferably used for the body.

  Although the thickness of the packaging film of the present invention can be set according to the purpose, it is usually 5 to 50 μm, more preferably 15 to 40 μm when used for tray packaging. In the case of using for the above, preferably 20 to 100 μm, more preferably 30 to 70 μm is used.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further in detail, this invention is not specifically limited to an Example. In addition, the measuring method and evaluation method in an Example are as follows.

(1) Dry heat treatment A margin rate of 30% x width 20%, that is, an air oven type thermostatic chamber in which a film sample of length 13 cm x width 12 cm is attached to a 10 cm square frame, and this is set to a predetermined temperature (100 ° C or higher). And processed for 30 minutes. The margin ratio was 20% horizontal x 30% vertical.
The margin rate (X) is expressed by the following formula.
Margin ratio (%) = 100 × (film length to be attached to frame−frame length) / frame length

(2) Warm water treatment A margin ratio of 30% length x 20% width, that is, a film sample of length 13 cm x width 12 cm is attached to a 10 cm square frame, and this is put in a warm water tank set at a predetermined temperature (95 ° C. or less), Treated for 4 seconds. The margin ratio was 20% horizontal x 30% vertical.

(3) Interlayer adhesion Under the conditions of (1) or (2) above, the shrinkage temperature is reduced by 10 ° C in increments of 80 ° C to 160 ° C. Then, after visually confirming the void from the surface of the film for the presence or absence of delamination at the time after treatment, the film cross-section is peeled off by tweezers or by hand as the interlaminar adhesion, and it is easy to peel off when trying to peel off the entire surface Evaluation was performed based on the following criteria. The evaluation was based on the worst result among the above conditions. When the thermal shrinkage rate did not reach 30% on one side and 20% on the other side, the sample was subjected to free shrinkage at that temperature.
AA: Delamination cannot be confirmed on the film. It is extremely difficult to peel the entire surface with tweezers.
A: Delamination cannot be confirmed on the film. The entire surface can be peeled off with tweezers, but it shows resistance.
B: Delamination can be partially confirmed on the film, and the entire surface can be peeled by hand without using tweezers and exhibits a slight resistance.
C: A considerable part of the film is delaminated, and even if tweezers are not used, the entire surface is easily peeled off and hardly exhibits resistance.

(4) Zigzag whitening When a 10 cm square film sample is put in an air oven type thermostatic bath set to a predetermined temperature and treated for 30 minutes in a freely shrinking state, the film is taken out and whitened with or without visual whitening. In each case, cross-sectional observation was performed with an optical microscope to confirm the presence or absence of bending of the layer, and evaluation was performed based on the following criteria. The shrinkage temperature was thermally shrunk in steps of 10 ° C. from 80 ° C. to 160 ° C., and the evaluation was based on the worst result among the above conditions.
AA: Almost no whitening of the film and bending of the layer B are observed.
A: Bending of layer B is slightly observed, but there is little or no whitening, and there is no practical hindrance B: Bending of layer B is clearly recognized, causing slight whitening and practically May be a problem.
C: The bending of the layer B is severe and the transparency is remarkably lowered by whitening.

(5) Heat shrinkage rate The film after passing through a hot air shrink tunnel MODEL MS8441 (trade name, manufactured by K & U System Co., Ltd.) set to a temperature of 120 ° C. in a state in which a 10 cm square film sample freely shrinks. The amount of vertical and horizontal shrinkage was determined and expressed as a percentage of the value divided by the original dimension. The maximum wind speed at the center was 4.5 m / sec and the passage time was 5 seconds.

(6) Crystallinity (Xc)
The degree of crystallinity is calculated from the heat of fusion (hereinafter referred to as ΔH (J / g)) by the DSC method. A sample (film) for measurement was set in an about 10 mg DSC apparatus, held at −10 ° C. for 1 minute, then heated at 10 ° C./minute, and an endothermic peak derived from the corresponding resin was used. The crystallinity is obtained from the following equation as g). When crystallization is performed during the temperature rise, the degree of crystallinity before the temperature rise is obtained by subtracting the exothermic amount corresponding to the crystallization from the crystal melting endotherm.
Crystallinity (Xc,%) = 100 × ΔH / H
In the case of a copolymer, H of the homopolymer having the most components is used as a numerical value. The theoretical crystal melting heat of the resin is as follows.
Thermoplastic polyester = 144 J / g
Among the thermoplastic polyesters, the specific resin is determined as follows.
Polylactic acid = 100 J / g

 The crystallinity shown in the examples in the present invention is that the layer A is composed of a mixture of a thermoplastic polyester and a thermoplastic polyurethane, but the thermoplastic polyurethane used in the examples of the present invention has substantially no heat of fusion. Since the heat of fusion obtained by measuring layer A with DSC was divided by the mixing ratio of the thermoplastic polyester to obtain the heat of fusion of the thermoplastic polyester, the degree of crystallinity of the thermoplastic polyester was determined.

(7) Gel fraction It calculated | required by operation shown below based on ASTMD2765. A sample sampled about 50 mg from a predetermined place is weighed on a balance having an accuracy of 0.1 mg or less (Sg). A 150 mesh SUS screen pouch that has been soaked in acetone for 24 hours to remove the oil and the sample are combined and weighed on the same balance (W1 g). Wrap the sample in a pouch. The pouch-wrapped sample is kept in boiling paraxylene for 12 hours using a separable flask and condenser. The sample wrapped in the pouch is dried to a constant weight by a vacuum dryer. The sample wrapped in the pouch is weighed on the same balance (W2g). The gel fraction is calculated by the following formula: gel fraction (% by weight) = [1- (W1-W2) / S] × 100. In addition, the sample uses what peeled off the specific surface layer part of an original fabric, or cut out the section which occupies 80% or more of the thickness of a surface layer part when peeling is difficult. Alternatively, in some cases, the predetermined layer may be produced as a single layer film and used instead. About the film after extending | stretching, what was heat-shrinked and returned to the original fabric state can be used as a sample similarly to the above. If it is difficult to fuse and peel the surface layer and the inner layer of the film, separately, the inner layer resin has a poor adhesion to the surface layer and the density is as much as possible. After producing the raw material having the surface layer thickness, the irradiation experiment is repeated under the same conditions, and after peeling, the gel fraction is measured, and this can be used as the gel fraction of the film. For uncrosslinked resins other than polyethylene that are not completely dissolved in boiling paraxylene and do not have a gel fraction of 0%, a solvent that can be completely dissolved and the gel fraction can be selected as 0% can be selected.

The resin used is described below.
PES1: Copolymerized aromatic amorphous polyester, Eastar PETG6763 copolyester (Eastman Chemical Japan Co., Ltd.)
PES2: Copolymerized aromatic polyester, Belpet IFG8L (manufactured by Kanebo Gosei Co., Ltd.)
PES3: Aromatic polyester, EFG85A (manufactured by Kanebo Gosei Co., Ltd.)
PES4: Polylactic acid, Lacty # 5000 (manufactured by Shimadzu Corporation)
PES5: Polylactic acid (amorphous), Lacty # 9800 (manufactured by Shimadzu Corporation)
PES6: Polybutylene succinate adipate, Bionore # 3001 (manufactured by Showa Polymer Co., Ltd.)
PES7: Polybutylene succinate, Bionore # 1001 (manufactured by Showa Polymer Co., Ltd.)
PES8: Copolymerized aromatic amorphous polyester, E-03 (manufactured by Kanebo Gosei Co., Ltd.)
TPU1: Thermoplastic polyurethane, Kuramiron U1195 (manufactured by Kuraray Co., Ltd.)
TPU2: Thermoplastic polyurethane, E598 (manufactured by Nippon Polyurethane Industry Co., Ltd.)
TPU3: Thermoplastic polyurethane, ESTEN 58277 NAT021 (manufactured by NOVEON)
EVOH: ethylene-vinyl alcohol polymer, XEP915 (manufactured by Kuraray Co., Ltd.)
Ny1: Polyamide polymer, Novamid 2430 (manufactured by Mitsubishi Engineering Plastics)
Ny2: polyamide polymer, Novamid X21 (Mitsubishi Engineering Plastics Co., Ltd.)
Ny3: polyamide polymer, UBE nylon 7028B (manufactured by Ube Industries, Ltd.)
PVDC1: Vinylidene chloride-vinyl chloride copolymer (vinyl chloride component 22 wt%)
PVDC2: Vinylidene chloride-methyl acrylate copolymer (methyl acrylate component 10 wt%)
PVA: polyvinyl alcohol polymer, Ecomaty AX400TNG (manufactured by Nippon Synthetic Chemical Industry Co., Ltd.)
IR: Ionomer resin, High Milan AM79261 (Mitsui / DuPont Polychemical Co., Ltd.)
EMA: ethylene-methyl acrylate copolymer, Lexpearl RB3240 (manufactured by Nippon Polyolefin Co., Ltd.)
EVA: ethylene-vinyl acetate copolymer, Ultrasen 635 (manufactured by Tosoh Corporation)
MPO1: acid-modified polyolefin resin Admer NF731 (manufactured by Mitsui Chemicals, Inc.)
MPO2: acid-modified polyethylene resin Admer NF587 (manufactured by Mitsui Chemicals, Inc.)
MPO3: Mixture of 75% acid-modified polyethylene resin Ubebond F3000 (manufactured by Ube Industries) and 25% linear low density polyethylene, Umerit 2040F (manufactured by Ube Industries) MPO4: Acid-modified polyethylene resin A mixture of 50% Ubebond F3000 (manufactured by Ube Industries, Ltd.) and 50% low-density polyethylene, Suntec LD 1920F (manufactured by Asahi Kasei Chemicals) EEA: ethylene-ethyl acrylate copolymer, EVAFLEX 703A (Mitsui / Dupont Polychemical) (Corporation)
VL1: linear low density polyethylene, Umerit 1520F (manufactured by Ube Industries, Ltd.)
VL2: linear low density polyethylene, ULTZEX 2022L (manufactured by Mitsui Chemicals, Inc.)
VL3: linear low density polyethylene, affinity FP1140 (manufactured by Dow Chemical Japan Co., Ltd.)
VL4: linear low density polyethylene, kernel KF270 (manufactured by Nippon Polyethylene Co., Ltd.)
PP1: Polypropylene polymer, Wintech WFX4TA (manufactured by Nippon Polychem Co., Ltd.)
PP2: Polypropylene polymer, Sun Allomer PF621S (manufactured by Sun Allomer Co., Ltd.)
Petroleum resin: alicyclic saturated hydrocarbon resin, Alcon P115 (manufactured by Arakawa Chemical Industries, Ltd.)

  In VL1-4 and PP2, polyoxyethylene (5 mol) lauryl ether = 0.6%, diglycerin laurate = 1.2%, and glycerin monooleate = 0.2% as antifogging agents in advance. What was added to was used.

[Example 1]
Using the resin shown in Table A, two extruders were used, a two-layer tube was melt-extruded from an annular die, the tube was quenched using a water cooling ring, and an unstretched tube having a thickness of 220 μm was formed. Obtained.

  The obtained unstretched tube is heated so that the unstretched tube by radiation is heated by an infrastructure heater so that the temperature immediately before the bubble formation (bubble neck portion) becomes the maximum temperature, and this temperature (this is referred to as the stretching temperature). While heating up to 100 ° C, air is injected into the tubular parison to form bubbles and stretched 5.0 times in the vertical direction and 4.4 times in the horizontal direction, and cooled by applying cooling air from the air ring to the bubbles. did. Thereafter, the stretched film was folded and then slit to a predetermined width to obtain a shrink film having a thickness described in Table A.

  Next, the shrinkage film was evaluated for interlayer adhesion and zigzag whitening described in the text. The results are shown in Table A. As a result, the obtained shrinkable film did not cause delamination or zigzag whitening even after heat shrinkage, and was excellent in appearance and excellent in commercial value.

[Comparative Example 1]
Using the resin having the configuration shown in Table A, the same experiment as in Example 1 was repeated. Next, the shrinkage film was evaluated for interlayer adhesion and zigzag whitening described in the text. The results are shown in Table A. As a result, the resulting shrink film was inferior in commercial value due to delamination and zigzag whitening after heat shrinkage. From this experiment, it is understood that the addition of thermoplastic polyurethane is essential to the thermoplastic polyester resin in the present invention.

[Comparative Example 2]
Using the resin having the configuration shown in Table A, the same experiment as in Example 1 was repeated. Here, however, three extruders were used to obtain an unstretched tube having a thickness of 330 μm. Next, the obtained shrink film was evaluated for interlayer adhesion and zigzag whitening described in the text. The results are shown in Table A. As a result, even in MPO1, which is used as an adhesive resin for polyester resin of non-shrinkage or low shrinkage film, delamination after heat shrinkage is possible by hand for the obtained shrink film this time. Zigzag whitening was observed and the product value was inferior. This experiment shows that in the present invention, it is necessary that the thermoplastic polyester resin to which the thermoplastic polyurethane is added is adjacent to a resin having a hydrogen bond such as nylon.

[Example 2]
Using the resin having the configuration shown in Table A, the same experiment as in Comparative Example 2 was repeated. However, the unstretched tube thickness was set to 308 μm and stretched 5.0 times in length and 4.4 times in width. Next, the obtained shrink-wrap film was evaluated for interlayer adhesion and zigzag whitening described in the text. The results are shown in Table A. As a result, the obtained shrink film did not cause delamination even after heat shrinkage, and the layer B was slightly curved but was practically free of problems.

[Example 3]
The same experiment as in Example 2 was repeated using the resin having the structure shown in Table A. Next, the shrinkage film was evaluated for interlayer adhesion and zigzag whitening described in the text. The results are shown in Table A. As a result, the obtained shrink film was excellent in appearance and product value without delamination or zigzag whitening even after heat shrinkage.

  When Example 2 and Example 3 are compared, when there are two layers B, it can be seen that it is preferable for zigzag whitening to place layer A between two layers B.

[Example 4]
The same experiment as in Example 2 was repeated using the resin having the structure shown in Table A. However, here, seven extruders were used, and the thickness of the unstretched tube was 550 μm. Next, the shrinkage film was evaluated for interlayer adhesion and zigzag whitening described in the text. The results are shown in Table A. As a result, the obtained shrink film was excellent in appearance and product value without delamination or zigzag whitening even after heat shrinkage.

[Examples 5 to 10]
The experiment was repeated by replacing PES1 of Example 4 from PES2 to PES7, and replacing EEA with MPO2, to give Examples 5 to 10, respectively. However, for PES4 to PES7, the stretching temperature was 80 ° C. In Examples 5 to 10, the thickness of the unstretched tube was 360 μm, the stretch ratio was 4.1 times in length, and the width was 3.5 times. In any case, the obtained shrink film was excellent in appearance and product value without delamination or zigzag whitening even after heat shrinkage. The heat of fusion of Examples 4 to 10 was measured to determine the crystallinity of the thermoplastic polyester resin, and the thermal shrinkage at 120 ° C. was measured and described in Table B.

[Examples 11 to 12]
The experiment was repeated by replacing TPU1 of Example 4 with TPU2 or TPU3. The resulting shrink film was excellent in appearance and product value without delamination or zigzag whitening even after heat shrinkage.

[Example 13]
The same experiment as in Example 2 was repeated using the resin having the structure shown in Table A. However, here, the thickness of the unstretched tube was 940 μm, and the longitudinal and lateral stretching ratios were 5.0 times and 4.0 times, respectively. The stretching temperature was 75 ° C. Next, the shrinkage film was evaluated for interlayer adhesion and zigzag whitening described in the text. The results are shown in Table A. As a result, the obtained shrink film was excellent in appearance and product value without delamination or zigzag whitening even after heat shrinkage.

[Comparative Example 3]
The same experiment as in Example 13 was repeated by setting the fourth layer of Example 13 to 100% PES5. Next, the shrinkage film was evaluated for interlayer adhesion and zigzag whitening described in the text. The resulting shrink film was inferior in commercial value due to delamination and zigzag whitening after heat shrinkage.

  After side-sealing each film of Example 13 and Comparative Example 3, after 5 kg of pork was placed and vacuum-packed, delamination and zigzag whitening after immersing in warm water at 80 ° C. for 4 seconds were confirmed. Example 12 was AA in interlayer adhesion and zigzag whitening, and Comparative Example 3 was interlayer adhesion C and B in zigzag whitening.

[Examples 14 to 15]
The experiment was repeated by replacing PVDC1 of Example 12 with PVDC2 (Example 14) and PVDC1 (80%) + EVA (20%) (Example 15), and the resulting shrink film was delaminated or zigzag even after heat shrinkage. Whitening did not occur and it was excellent in appearance and excellent in commercial value.

[Examples 16 to 17]
The experiment was repeated with the mixing ratio of PES1 and TPU1 of Example 4 changed as shown in Table A. It can be seen that the amount of TPU can be cited as a main factor of the results of delamination and zigzag whitening after heat shrinkage of the obtained shrink film.

[Examples 18 to 20]
The experiment was repeated in the same manner as in Example 4 with the layer configuration shown in Table A. The obtained shrink film did not cause delamination or zigzag whitening even after heat shrinkage, and was excellent in appearance and product value.

[Example 21]
An unstretched tube (thickness: 450 microns) obtained in the same manner as in Example 4 with the same layer structure as in Example 18 was accelerated with an electron beam irradiation device (trade name, CURETRON, manufactured by NHV Corporation). Irradiation was performed so that the irradiation dose was 150 keV and the irradiation dose was 90 kGy. In addition, since it was a tube-shaped original fabric, it irradiated from both sides of the folded tube so that the irradiation dose would be 90 kGy on the entire outer peripheral surface of the tube.

  Next, the unstretched tube is heated by radiation with an infrastructure heater, adjusted so that the temperature immediately before the bubble formation (bubble neck) reaches the maximum temperature, and air is injected into the tubular parison while heating the temperature to 100 ° C. Bubbles were formed and stretched 4.6 times in the vertical and horizontal directions, respectively, and cooled by applying cooling air from the air ring to the bubbles. Then, after folding the stretched film, the film was further reheated to a film temperature of 78 ° C., heat set so that the dimensional relaxation rate was 15% in the lateral direction, and slit to a predetermined width. A shrink film having the same thickness as that was obtained. The gel fraction by boiling paraxylene according to ASTM-D2765 was 15% on the average of the first layer and the second layer, and the sixth layer and the seventh layer were 0%. The resulting shrink film was excellent in appearance and product value without delamination or zigzag whitening even after heat shrinkage. In addition, the thermal contraction rate of 120 degreeC of this film was length / width = 35/31%. Moreover, the maximum value of the shrinkage stress by immersion in an oil bath at 120 ° C. was vertical / horizontal = 1.9 / 1.5 MPa.

[Example 22]
Using six extruders, the same experiment as in Example 21 was repeated with the layer configuration shown in Table A. The resulting shrink film was excellent in appearance and product value without delamination or zigzag whitening even after heat shrinkage.

[Example 23]
Using five extruders, the same experiment as in Example 1 was repeated with the layer structure shown in Table A. The resulting shrink film was excellent in appearance and product value without delamination or zigzag whitening even after heat shrinkage.

[Example 24]
Using four extruders, the same experiment as in Example 1 was repeated with the layer configuration shown in Table A. The resulting shrink film was excellent in appearance and product value without delamination or zigzag whitening even after heat shrinkage. In addition, the heat shrinkage rate of this film at 120 ° C. was vertical / horizontal = 38/44%.

[Comparative Example 4]
Using four extruders, the same experiment as in Example 1 was repeated with the layer configuration shown in Table A. The obtained shrink film was the same as in Comparative Example 2, and after the heat shrinkage, delamination and zigzag whitening occurred and the commercial value was inferior. In addition, the heat shrinkage rate of this film at 120 ° C. was vertical / horizontal = 53/55%.

The solid tray Q-15-11 (trade name) (manufactured by Chuo Pearl Co., Ltd.) is used with a gas pack shrink wrapping machine CFP-3000 (trade name) (manufactured by Ibaraki Seiki Co., Ltd.) and the margin ratio is 30 The film of Example 21 and Example 24 and the film of Comparative Example 4 were wrapped so that the width was 20%. At this time, the filling gas was nitrogen. It passed through a shrink tunnel with a hot air temperature of 150 ° C. At this time, the transit time was 5 seconds. When the delamination and zigzag whitening of the packaged product at this time were evaluated, the films of Example 21 and Example 24 were AA for both items and C for both of the comparative examples 4. The results were the same even if the same experiment was repeated with the margin ratio 20% vertical and 30% horizontal.

  Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.

  The present application is a Japanese patent application filed on April 27, 2004 (Japanese Patent Application No. 2004-132023), a Japanese patent application filed on April 27, 2004 (Japanese Patent Application No. 2004-132024), and an application filed on April 27, 2004. This is based on a Japanese patent application (Japanese Patent Application No. 2004-132025), the contents of which are incorporated herein by reference.

  The shrinkable film of the present invention eliminates the resin having poor stretchability / shrinkability by the arrangement of the thermoplastic polyester resin layer, and also zigzag whitening and delamination after sufficiently heat shrinking under a wide range of shrinkage conditions. It is a practical high-strength, high-barrier and highly-shrinkable film that does not cause such problems and can be suitably used as a packaging film.

Claims (8)

  A first layer including a first polymer mainly composed of thermoplastic polyester and thermoplastic polyurethane, and a second layer mainly composed of a second polymer whose main repeating unit has substantially a halogen or hydrogen bond. A heat-shrinkable film, wherein the first layer and the second layer are directly laminated. The heat-shrinkable film according to claim 1, wherein the second polymer is any one selected from the group consisting of the following (a) to (d).
(A) Polyamide (b) Ethylene-vinyl alcohol copolymer (c) Polyvinylidene chloride (d) Polar group-containing polyolefin and a mixture of any one of (a) to (c)   The heat shrinkable film according to claim 1, wherein the crystallinity of the thermoplastic polyester is 30% or less.   2. The heat shrinkable film according to claim 1, wherein the heat shrinkage rate in a 120 ° C. dry heat treatment is 30% or more in one direction of MD or TD and 20% or more in the other direction.   The heat-shrinkable film according to claim 1, comprising a laminate in which the second layer, the first layer, and the second layer are directly laminated in this order.   The said 2nd polymer consists of a laminated body which laminated | stacked directly the said 2nd layer containing this 2nd layer containing 1st layer which is polyamide, this 1st layer, and resin which has gas barrier property in this order. Heat shrinkable film.   Use of the heat-shrinkable film according to claim 1 for a gas replacement package. The package according to claim 1, wherein the package is used for a method of covering the contents with a package, causing the package to adhere to the contents by depressurizing the inside of the package, and further thermally shrinking the package. Use of heat shrinkable film.