JPWO2007032401A1 - Multi-layer film for top seal - Google Patents

Abstract

The present invention is a multilayer film for top seal used for a tray having a surface layer containing a polystyrene resin, and the multilayer film has at least a first layer and a second layer, (A) a copolymer comprising a conjugated diene and a vinyl aromatic compound, (b) a copolymer obtained by hydrogenating a copolymer comprising a conjugated diene and a vinyl aromatic compound, and (e) a conjugated diene and 50% by weight or more of at least one selected from the group consisting of a binder resin of a hydrogenated copolymer of a vinyl aromatic and an α-olefin copolymer, a mixture of branched low-density polyethylene, and the like. The multilayer film has a gel fraction of 0.5 to 50% by weight, a thickness of 70 μm or less, a tensile elastic modulus of 40 to 300 MPa in an arbitrary direction, and a thermal shrinkage at 200 ° F. any The multilayer film is 15 to 75% in the direction, package using a multilayer film, to provide a method of manufacturing a multi-layer film.

Description

  The present invention relates to a multilayer film used for a top seal. The present invention particularly relates to a multi-layer film for top seal packaging, a multi-layer film using a multi-layer film, and a multi-layer film using the multi-layer film for use in combination with a tray having a surface layer containing a polystyrene resin in order to store, transport and sell food. It is related with the manufacturing method.

  Conventionally, stretch packaging, shrink packaging, and the like using a packaging film have been performed for packaging using trays of various materials. In the stretch wrapping, since the tray is packaged while pulling the film, the film does not loosen after the obtained package is transported, and a good packaging appearance can be maintained. In shrink wrapping, particularly pillow shrink wrap, generally, an article to be packaged is packaged by the following method. In other words, the food items and other items to be packaged in the tray are gently wrapped with a film with a margin regardless of the shape and size of the items to be packaged, and then the heat roller system is used for the film on the back of the package. In addition, the film before and after the tray is sealed with a seal-and-cut method, and then the film is shrunk by applying heat to the package in a heat-shrinking tunnel for a very short time. Package the package. Therefore, in pillow shrink packaging, several types of trays can be packaged without changing the width of the film that wraps the tray. As a result, labor can be saved in the packaging process, and the packaging speed is faster than stretch packaging. It has the feature that it can.

  However, in any of the packaging methods described above, the entire contents including the tray are packaged. Therefore, in the above packaging method, for example, when transporting rough handling is performed when packaging raw meat or the like, the upper and lower sides of the packaging body are turned upside down, so that the gravy turns to the back of the tray and hygiene cannot be maintained. There was a problem.

  As a method for solving such problems of stretch packaging and shrink packaging, there is a top seal packaging in which a tray and a film are bonded or fused together at the peripheral edge of the upper surface of the tray and sealed. In this method, since the peripheral edge of the upper surface of the tray is securely bonded or fused, the moisture and oil from the contents such as raw meat turn to the back of the tray and the moisture and oil There is no leakage. The amount of film used is also small compared to stretch packaging and shrink packaging, and the packaging material can be reduced, which is an effective means for reducing waste.

  However, when sealing a tray made of polystyrene resin as a raw material with top-seal packaging, a film that uses an olefin resin for the surface layer that is normally used can be used for both hard and foamed trays. It cannot be sealed and cannot be sealed. For this reason, the tray may be multilayered or coated, and a multilayer tray in which an olefin-based resin layer is arranged at the seal portion of the tray may be used. However, in such a tray, since the polyolefin resin is laminated or coated on the polystyrene layer in the tray manufacturing process, not only the production process becomes complicated, but also two or more types of loss occur in the manufacturing process. Because it becomes a mixture of the raw materials, it is difficult to recycle. There is also a method of applying an adhesive to the peripheral edge of the tray. However, as described above, the tray production process becomes complicated and recycling becomes difficult.

  In order to solve these problems, Patent Document 1 discloses a layer mainly composed of an ethylene-based resin and / or an ethylene-α-olefin copolymer, at least two polymer blocks mainly made from a vinyl aromatic compound, and a conjugated diene. A stretch film in which at least one layer composed of at least one polymer block mainly made from the above is disposed on the surface layer is disclosed.

However, with this stretch film, the sealing property when the contents are raised more than the height of the tray, particularly the sealing property of the interstitial material, is insufficient, and after packaging, several to several tens of packages are placed in the cardboard box. When packed in single or several boxes, the lower package, particularly the lower package, is depressed by the pressure applied to the contents by the upper weight, and the film around the depressed package loosens. This looseness results in a poor appearance and reduces merchantability at the store.
JP-A-10-180951

  The present invention can be sealed with a tray having a surface layer containing a polystyrene-based resin, in particular, a foamed tray made of polystyrene-based resin as a raw material, and is broken during handling during storage during storage after transportation, It is an object of the present invention to provide a film that does not cause seal peeling and that satisfies a better packaging appearance at the same time, and a method for producing the film. In particular, an object of the present invention is to provide a film that satisfies the sealing performance, tear resistance, and good packaging appearance at the same time when the height of the package is raised from the height of the tray, and a method for producing the same. To do.

  If the packaged food is processed food such as sugar beet or meat, especially raw poultry meat, water, oil, or a water-oil mixture tends to adhere to the peripheral edge of the tray during the packaging process, reducing the sealing performance. Cause it. Another object of the present invention is to provide a top seal film that exhibits good sealing properties even when these interstitial materials are present and does not cause liquid leakage due to these interstices.

  The present inventors diligently studied to examine the above problems, and found that the above object can be achieved by the multilayer film and the method for producing the multilayer film described below, and have completed the present invention. That is, the object of the present invention has been achieved by the following multilayer film and multilayer film production method.

1. A multilayer film for top seal used for a tray having a surface layer containing a polystyrene-based resin, the multilayer film having at least a first layer and a second layer, wherein the first layer (A) a copolymer comprising a conjugated diene and a vinyl aromatic compound, (b) a copolymer obtained by hydrogenating a copolymer comprising a conjugated diene and a vinyl aromatic compound, and (c) a conjugated diene and a vinyl aromatic compound. A binder resin of a hydrogenated copolymer and an α-olefin copolymer, (d) a binder resin of a hydrogenated copolymer of a conjugated diene and a vinyl aromatic and an α-olefin copolymer, A mixture of an ethylene / α-olefin copolymer, and (e) a mixture of a hydrogenated copolymer of a conjugated diene and a vinyl aromatic and an α-olefin copolymer, and a branched low-density polyethylene. Kara The multilayer film has a gel fraction of 0.5 to 50% by weight, a thickness of 70 μm or less, and a tensile modulus of elasticity in any direction. A multilayer film having a thermal shrinkage of 40 to 300 MPa and a thermal shrinkage at 200 ° F. of 15 to 75% in an arbitrary direction.
2. The second layer is made of high-density polyethylene, medium-density polyethylene, branched low-density polyethylene, ethylene / α-olefin copolymer, ethylene / methacrylic acid copolymer metal partial neutralized product, ethylene / vinyl acetate copolymer. Item 2. The multilayer film according to Item 1, containing at least 50% by weight of at least one selected from the group consisting of a polymer, a polypropylene polymer, and a polypropylene terpolymer.
3. Between the first layer and the second layer, a copolymer comprising a conjugated diene and a vinyl aromatic compound, an ethylene / vinyl acetate copolymer, an ethylene / methyl methacrylate copolymer, an ethylene / Metal partial neutralized product of methacrylic acid copolymer, ethylene / acrylic acid copolymer, ethylene / ethyl acrylic acid copolymer, ethylene / maleic anhydride copolymer, ethylene / ethylene acrylate / maleic anhydride copolymer, An ethylene / maleic acid-modified resin, a Vicat softening temperature of 50 to 68 ° C., an ethylene / α-olefin copolymer, a polypropylene-based polymer, and at least one selected from the group consisting of a polypropylene-based terpolymer Item 3. The multilayer film according to Item 1 or 2, comprising at least one layer of three.
4. The multilayer film according to any one of Items 1 to 3, wherein the first layer contains a polystyrene-based resin, and a total of styrene components in the first layer is 60% by weight or more.
5. Item 1 containing at least one additive selected from the group consisting of glycerin, fatty acid, polyhydric alcohol fatty acid ester, talc, oleate, amide-based lubricant, and mineral oil having a number average molecular weight of 250 to 480. The multilayer film of any one of -4.
6. The multilayer film according to any one of Items 1 to 5, wherein the gel fraction of the first layer is 0.5 to 15% by weight.
Item 7. The item according to any one of Items 1 to 6, which is used for top seal packaging of a hard tray or foamed tray having a surface layer containing a polystyrene-based resin containing at least one of processed food and raw poultry meat. Multilayer film.
8. A package having a tray having a surface layer containing a polystyrene resin and the multilayer film according to any one of Items 1 to 7, wherein the multilayer film top seals the tray.
9. The package according to Item 8, wherein the package is packaged with at least one of processed food and raw meat.
10. (a) a copolymer comprising a conjugated diene and a vinyl aromatic compound, (b) a copolymer obtained by hydrogenating a copolymer comprising a conjugated diene and a vinyl aromatic compound, and (c) a conjugated diene and a vinyl aromatic. A binder resin of a hydrogenated copolymer and an α-olefin copolymer, (d) a binder resin of a hydrogenated copolymer of a conjugated diene and a vinyl aromatic and an α-olefin copolymer, A mixture of an ethylene / α-olefin copolymer, and (e) a mixture of a hydrogenated copolymer of a conjugated diene and a vinyl aromatic and an α-olefin copolymer, and a branched low-density polyethylene. A first layer containing at least 50% by weight selected from the group consisting of: high density polyethylene, medium density polyethylene, branched low density polyethylene, ethylene / α-olefin copolymer, ethylene 50% by weight of at least one member selected from the group consisting of neutralized metal / methacrylic acid copolymer, ethylene / vinyl acetate copolymer, polypropylene polymer, polyethylene terpolymer, and polypropylene terpolymer Second layer contained above, and copolymer of conjugated diene and vinyl aromatic compound, ethylene / vinyl acetate copolymer, ethylene / methyl methacrylic acid copolymer, metal portion of ethylene / methacrylic acid copolymer Neutralized product, ethylene / acrylic acid copolymer, ethylene / ethyl acrylic acid copolymer, ethylene / maleic anhydride copolymer, ethylene / ethylene acrylate / maleic anhydride copolymer, ethylene / maleic acid modified resin, Vicat Ethylene / α-olefin copolymer with a softening temperature of 50 to 68 ° C., polypropylene polymerization A third layer containing at least 50% by weight of at least one selected from the group consisting of a body and a polypropylene-based terpolymer, and at least one layer of the first layer between the first layer and the second layer. A step of co-extrusion so as to sandwich the three layers to form a tubular parison, a step of cooling the tubular parison, and so that the gel fraction of the tubular parison is 0.5 to 50% by weight, The step of performing electron beam irradiation at 15 to 150 kGy from the first layer side, and the temperature at the stretching start point is set to 70 ° C. to 140 ° C., and the double bubble inflation method is performed so that the stretching ratio is 1.5 to 10 times. The manufacturing method of a multilayer film including the process to extend | stretch.

  By using the multilayer film of the present invention, packaging by a top seal packaging method for a tray having a surface layer containing a polystyrene resin is possible. Furthermore, the package using the multilayer film of the present invention has a good seal strength against impacts due to cargo handling and the like in the storage and transportation processes after packaging. As a result, it is possible to obtain a package that suppresses the occurrence of tearing in the film and can maintain a good appearance such as extremely little looseness of the film when the package is arranged on the storefront after transportation. . In particular, the packaging body using the multilayer film of the present invention exhibits a good sealing property when top-sealing an article to be packaged higher than the height of the tray, that is, when performing a top seal in a raised state. , Has a good packaging appearance.

  In addition, when performing top-seal packaging in which processed foods, raw meat, in particular poultry raw meat such as chicken, are to be packaged, water, oil, or water-oil is added to the peripheral edge of the tray in the packaging process. The mixture tends to adhere. The package using the multilayer film of the present invention can prevent the occurrence of liquid leakage even in the presence of these interstitial materials, and enables good sealing.

  The present invention will be described in detail below, particularly focusing on preferred embodiments thereof.

  The present invention relates to a top seal multilayer film used for a tray having a surface layer containing a polystyrene resin.

  Examples of the tray having a surface layer containing a polystyrene resin include a hard tray and a foam tray having a surface layer containing a polystyrene resin. As a specific form of this tray, a hard tray or foam tray made of polystyrene resin as a main raw material, or a single layer or laminated hard body or foam sealing surface formed from a raw material other than polystyrene resin is used. Examples include trays laminated with polystyrene resin.

  In the present invention, the “top seal packaging” is a packaging method in which the contents are sealed by sealing a film as a lid to the peripheral edge of the tray by means of heat fusion, impulse sealing or the like. The polystyrene resin as a material of the tray includes a homopolymer of a styrene compound, a copolymer of two or more styrene compounds, and a rubber polymer in a matrix made of the polymers of the styrene compounds. Examples thereof include rubber-modified styrene resins dispersed in the form of particles, and these may be used alone, or a mixture of two or more of these may be suitably used. In addition, pigments, recycled raw materials, other thermoplastic resins, and the like may be added to the tray. Here, the recycled raw material refers to a material that has been processed so that it can be used again after being subjected to processing such as cutting or pelletizing on a film loss portion generated in the film manufacturing process or the packaging process.

  The multilayer film of the present invention has at least a first layer and a second layer. In the following description, the first layer is referred to as “surface layer (1)”, and the second layer is referred to as “surface layer (2)”.

  In this invention, said specific resin component is used for surface layer (1), and the gel fraction of the whole film is specified. By using the surface layer (1) in contact with the tray, the sealing performance with the tray, especially when there is a jam, and the sealing performance when the packaged items are raised from the top surface of the tray are improved. In addition, it is possible to prevent tearing of the film and peeling of the seal due to impact, which occur during transportation of the package using the film, after handling, and during handling during storage.

  The surface layer (1) of the present invention comprises (a) a copolymer comprising a conjugated diene and a vinyl aromatic compound, (b) a copolymer obtained by hydrogenating a copolymer comprising a conjugated diene and a vinyl aromatic compound, (c ) Binding resin of hydrogenated copolymer of conjugated diene and vinyl aromatic and α-olefin copolymer, (d) Hydrogenated copolymer of conjugated diene and vinyl aromatic and α-olefin copolymer A mixture of a binder resin with a copolymer and an ethylene / α-olefin copolymer, and (e) a binder resin of a hydrogenated product of a copolymer of a conjugated diene and a vinyl aromatic and an α-olefin copolymer, and a branch 50% by weight or more of at least one selected from the group consisting of a mixture with a low-density polyethylene.

  In the copolymer comprising (a) a conjugated diene and a vinyl aromatic compound used for the surface layer (1) of the present invention, the content of the vinyl aromatic compound in the copolymer is not particularly limited. The content of the copolymer (a) is preferably 50% by weight or more of the surface layer (1) from the viewpoint of film forming properties, and preferably 95% by weight or less from the viewpoint of the sealing property in the raised state. More preferably, it is 60 to 85 weight%.

  Conjugated dienes are olefinically unsaturated conjugated double bond-containing compounds such as 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3 butadiene, 1,3. -Pentadiene, 2-methyl 1,3-pentadiene, 1,3-hexadiene and the like. These may be used alone or in combination of two or more.

  The vinyl aromatic compound is a compound having a vinyl bond and having an aromatic group in the side chain. For example, styrene, o-methylstyrene, p-methylstyrene, m-methylstyrene, α-methylstyrene, ethylstyrene. , Α-methyl-p-methylstyrene, 2,4-dimethylstyrene, monochlorostyrene, p-methylstyrene, p-tert-butylstyrene, α-ethylstyrene and the like. These may be used alone or in combination of two or more.

  The copolymer (a) of the present invention includes 1) a random copolymer of a conjugated diene and a vinyl aromatic compound, 2) a block copolymer comprising a block of a conjugated diene and a vinyl aromatic block, 3) Block copolymer composed of vinyl aromatic compound block and conjugated diene / vinyl aromatic compound block 4) Vinyl aromatic compound block and conjugated diene / vinyl aromatic copolymer block and conjugated diene And a block copolymer comprising these blocks.

  Examples of the block copolymer 3) include a block copolymer in which a vinyl aromatic compound block is present on both ends, and a block copolymer in which a vinyl aromatic compound block is present on one end.

  Examples of the block copolymer 4) include a block copolymer composed of a vinyl aromatic block on one end and a conjugated diene block on the other end.

  Examples of the copolymer block of the conjugated diene / vinyl aromatic compound include those in which the conjugated diene and the vinyl aromatic compound are present at random, and those in which the vinyl aromatic compound is present in a tapered shape. Any of these structures can be used in the multilayer film of the present invention. In particular, when the slipperiness of the film is required, a block copolymer composed of a vinyl aromatic compound block and a conjugated diene / vinyl aromatic compound copolymer block may be used. Furthermore, among the block copolymers composed of vinyl aromatic compound blocks and conjugated diene / vinyl aromatic compound copolymer blocks, the vinyl aromatic compounds in the conjugated diene / vinyl aromatic copolymer block gradually increase. It is preferable to exist in a tapered shape.

  The weight average molecular weight of the copolymer (a) used in the present invention is not particularly limited, but is preferably 20,000 to 600,000, more preferably 20,000 to 400,000, and still more preferably 80,000. ~ 300,000. The weight average molecular weight of the copolymer (a) is preferably 20,000 or more from the viewpoint of film forming performance, and preferably 600,000 or less from the viewpoint of extrusion performance. The molecular weight distribution is preferably 10.0 or less, more preferably 1.1 to 5.0, and still more preferably 1.1 to 4.0 from the viewpoint of molding processing performance. All of the above characteristics are measured by gel permeation chromatography (hereinafter abbreviated as GPC).

  For the surface layer (1) of the present invention, a copolymer obtained by hydrogenating (b) a copolymer comprising a conjugated diene and a vinyl aromatic compound may be used. That is, the copolymer (a) comprising the conjugated diene and the vinyl aromatic compound may be hydrogenated. Examples of the copolymer (b) include a styrene / ethylene / butadiene block hydrogenated copolymer, a styrene / ethylene / butadiene block / styrene hydrogenated copolymer, a styrene / isoprene / butadiene block hydrogenated copolymer, and styrene. -Isoprene, butadiene block, styrene hydrogenated copolymer and the like.

  As the binding resin of (c) hydrogenated copolymer of conjugated diene and vinyl aromatic used in the surface layer (1) of the present invention and α-olefin copolymer, for example, polystyrene is used at one end, and the other side Examples thereof include a polymer having a crystal component structure of polyethylene at the terminal and an α-olefin copolymer therebetween, such as DYNARON 4600P: styrene / ethylene butylene / olefin crystal block copolymer of JSR Corporation.

  The binder resin (c) used for the surface layer (1) of the present invention is mixed with an ethylene / α-olefin copolymer or a branched low-density polyethylene in order to raise the stiffness of the film and suppress the stickiness of the film. May be. Usually, the mixture is used by mixing it with the binding resin of (c) so that it becomes 50% by weight or less of the total amount of the binding resin of (c) and the mixture, but the mixing ratio is not particularly limited. That is, the surface layer (1) of the present invention comprises (d) a binder resin of a hydrogenated copolymer of α-olefin copolymer and a copolymer of conjugated diene and vinyl aromatic, and an ethylene / α-olefin copolymer. A mixture and / or (e) a mixture of a hydrogenated product of a copolymer comprising a conjugated diene and a vinyl aromatic and an α-olefin copolymer, and a branched low-density polyethylene. Good.

  When the surface layer (1) used in the present invention contains a mixture of the binding resin (c) and (d), or a mixture of the binding resin (c) and (e) The total amount of the binder resin of the hydrogenated copolymer of conjugated diene and vinyl aromatic and the α-olefin copolymer may be 50% by weight or more of the total amount of the mixture.

  In the present invention, another resin may be added to one surface layer (1) in a range of 50% by weight or less. The resin to be added is not particularly limited, but a polystyrene resin is preferable from the viewpoint of sealing properties and film rigidity.

  The polystyrene resin includes a homopolymer of a styrene compound, a copolymer of two or more styrene compounds, and a rubbery polymer dispersed in a matrix made of a polymer of these styrene compounds. The rubber-modified styrene resin etc. which will be mentioned are mentioned, These can be used suitably also as a 2 or more types of mixture used independently. Among these, it is preferable to use a homopolymer of styrene.

  Specific examples of copolymers of two or more kinds of styrene compounds include styrene, o-methylstyrene, p-methylstyrene, m-methylstyrene, α-methylstyrene, ethylstyrene, Examples include α-methyl-p-methylstyrene, 2,4-dimethylstyrene, monochlorostyrene, p-methylstyrene, p-tert-butylstyrene, α-ethylstyrene, and the like. These may be used alone or in combination of two or more thereof.

  A method for producing the polystyrene-based resin is not limited, and examples thereof include bulk polymerization, solution polymerization, emulsion polymerization, and suspension polymerization. Examples of the three-dimensional structure of the polystyrene resin molecule include atactic, isotactic, syndiotactic and the like, and any of them can be suitably used. From the viewpoint of extrudability, the polystyrene resin has a melt flow rate (hereinafter referred to as MFR) of 2 to 50 g / 10 min. Are preferable, and 3 to 20 g / 10 min. Is more preferable.

  The method for polymerizing the rubber-modified styrene resin is not particularly limited. Generally, a rubbery polymer is dissolved in a styrene compound monomer, and under stirring, bulk polymerization, bulk suspension polymerization or solution polymerization is performed. It is obtained by precipitating a rubbery polymer and granulating it. Examples of the rubbery polymer include polybutadiene, styrene / butadiene copolymer, polyisoprene, butadiene / isoprene copolymer, and ethylene / propylene copolymer. Polybutadiene and styrene / butadiene copolymer are preferable, and those obtained by partially hydrogenating these are more preferable.

  Rubber-modified styrene resins include copolymers of styrene units and methacrylate units, copolymers of styrene units and alkyl acrylate units, polybutadiene or styrene / butadiene copolymers in dispersed phase, styrene / methacrylate esters And a copolymer having a continuous phase mainly composed of. The rubber-modified styrene resin is not particularly limited, but the MFR is 2 to 50 g / 10 min. Is more preferable, and more preferably 3 to 20 g / 10 min. It is.

  When a polystyrene resin is added to the surface layer (1) of the multilayer film of the present invention, the total of styrene components in the surface layer (1) is preferably 60% by weight or more, more preferably 65% by weight or more. It is particularly preferably 75 to 93% by weight. If the styrene component in the surface layer (1) is within this range, the sealing property with the tray having the surface layer containing the polystyrene resin is improved. In addition, by making the amount of the styrene component as described above, the effect of improving the slip stability with the mechanical device and improving the film forming stability can be obtained without causing a significant decrease in transparency during film forming. .

  The multilayer film of the present invention needs to have a gel component. In the present invention, the gel component refers to a component that is formed from a high molecular weight component of a resin, a crosslinking component, and the like and does not dissolve even when attempted to dissolve with a solvent.

  If such a gel component is present, it is known in the prior art that the heat shrinkability is excellent but the heat sealability is lowered (Japanese Patent Laid-Open No. 2-99526). However, in the present invention, by specifying the resin constituting the surface layer (1) and further specifying the gel fraction of the entire film, sealing properties, in particular, interstitial materials such as moisture, oil and gravy are present on the sealing surface. However, the present inventors have found that sealing is ensured at the time of sealing, after sealing, during transportation, after transportation and after storage.

  The gel fraction of the multilayer film of the present invention needs to be 0.5 to 50% by weight from the viewpoint of the sealing strength in the presence of the interstitial material and the stretchability at the time of film formation, Preferably it is 1-45 weight%, More preferably, it is 2-40 weight%. In particular, in the case where a lot of contaminants are attached in the packaging process and it is difficult to seal, the gel fraction of the entire multilayer film is within the above range, and the gel fraction of the surface layer (1) is preferably By setting the content to 0.5 to 15% by weight, more preferably 1 to 12% by weight, and still more preferably 1.5 to 8% by weight, the sealing performance can be further improved. By making the gel fraction of the surface layer (1) within this range, the viscosity of the sealing layer at a high temperature can be increased, and the surface layer (1) can be prevented from being destroyed. Good sealability can be obtained.

  The multilayer film of the present invention needs to have a thickness of 70 μm or less, preferably 50 μm or less, more preferably 40 μm or less. By setting the thickness to 70 μm or less, the durability of the film cutting blade when applied to a packaging machine when performing long run packaging is improved. In order to prevent tearing of the film during transportation, the thickness of the multilayer film is preferably 5 μm or more, more preferably 8 μm or more.

  The tensile elastic modulus in the present invention is a value quantified by a 2% elastic modulus (an elastic modulus calculated from a stress when the strain is 2%). Tensile modulus of the multilayer film of the present invention from the viewpoint of recoverability of the film after packaging, storage, and transportation, and particularly from the viewpoint of sealability when packaging a swelled product that wraps the contents higher than the container Needs to be in the range of 40 to 300 MPa in an arbitrary direction, preferably 45 to 250 MPa, more preferably 50 to 230 MPa.

  The thermal contraction rate at 200 ° F. of the multilayer film of the present invention is arbitrary from the viewpoint of wrinkle generation after packaging, and particularly from the viewpoint of sealing properties when packaging a swelled product in which the contents are higher than the container. It is necessary to be 15 to 75% in the direction, preferably 15 to 60%, more preferably 18 to 50%. When top-sealed packaging is performed using the multilayer film of the present invention, for example, in order to remove wrinkles and the like of the film of the package, and to improve the packaging appearance as a result, heat is applied at around 200 ° F. after packaging. For this reason, it is necessary to define the thermal shrinkage rate of the multilayer film at 200 ° F.

  The state in which the film surface is raised when the top seal is performed refers to a top seal packaging form in which the height of an object to be packed in the tray is higher than the inner height of the tray. The multilayer film of the present invention can be usefully used even when the height of the article to be packaged is higher than the inner height of the tray. The multilayer film of the present invention is particularly effective for a bulge of 5 mm or more (when the height of the packaged object is 5 mm or more larger than the height inside the tray), and can be usefully used even in a bulge state of 10 mm or more. When the contents are raw meat, it can be usefully used even in a raised state of 20 mm or more.

  In the multilayer film of the present invention, the resin used in the surface layer (2) is high-density polyethylene, medium-density polyethylene, branched low-density polyethylene, ethylene / α-olefin copolymer, ethylene / methacrylic, from the viewpoint of film formation stability. 50% by weight or more of at least one selected from the group consisting of neutralized metal parts of acid copolymers, ethylene / vinyl acetate copolymers, polypropylene polymers, polyethylene terpolymers, and polypropylene terpolymers. Is preferred.

  Among them, ethylene / α-olefin copolymer, branched low-density polyethylene, and ethylene / α-olefin copolymer and branched from the viewpoint of long-run film-forming stability and tear resistance when the package is transported More preferably, it comprises a mixture of low density polyethylene. The ethylene / α-olefin copolymer is a random copolymer of ethylene and at least one monomer selected from α-olefins having 3 to 18 carbon atoms. As the α-olefin, propylene, butene-1, Examples include pentene-1, 4-methyl-pentene-1, hexene-1, octene-1, decene-1, dodecene-1.

  The ethylene content in the ethylene / α-olefin copolymer is preferably 40 to 95% by weight, more preferably 50 to 90% by weight, and still more preferably 60 to 85% by weight. The polymerization method of ethylene and α-olefin is not particularly limited, and examples thereof include a polymerization method using a multisite catalyst, a single site catalyst, or the like. When packaging contents that require transparency, it is preferable to use one that has been polymerized with a single-site catalyst. In that case, it is preferable to use one having a molecular weight distribution (Mw / Mn) measured by GPC of 3.5 or less because the transparency is particularly good.

The high-density polyethylene used in the surface layer (2) of the present invention is a homopolymer of ethylene or a copolymer of ethylene and 5 mol% or less of a 1-olefin monomer, and the density is 0.00. It refers to a resin of 942 g / cm ³ or more.

The medium density polyethylene used in the surface layer (2) of the present invention, among the homopolymer or the copolymer, a density of 0.930 g / cm ³ or more refers to 0.942 g / cm ³ less than the resin .

The density of the ethylene / α-olefin copolymer used in the surface layer (2) of the present invention is preferably 0.870 to 0.925 g / cm ³ . When the density is 0.870 g / cm ³ or more, the film is stretched and the running property on the packaging machine is improved, and when the density is 0.925 g / cm ³ or less, the transparency is improved.

The density of the branched low density polyethylene used in the surface layer (2) of the present invention is preferably 0.908 to 0.925 g / cm ³ . When the density is 0.908 g / cm ³ or more, the film is stretched and the running property on the packaging machine is improved, and when the density is 0.925 g / cm ³ or less, the transparency is improved.

  The MFR of the ethylene / vinyl acetate copolymer used in the surface layer (2) is 0.3 to 5.0 g / 10 min. And more preferably 0.5 to 3.5 g / 10 min. It is. The vinyl acetate content is preferably 5.5 to 20.0% by weight, more preferably 5.5 to 16.0% by weight from the viewpoint of preventing film breakage and preventing the smell of acetic acid.

  Examples of the polypropylene polymer used in the surface layer (2) include a homopolymer, a random copolymer with ethylene or butene, and the like. Among these, from the viewpoint of packaging appearance, a copolymer with ethylene or butene is preferable. The polypropylene terpolymer means an ethylene-butene-propylene or ethylene-propylene-diene ternary copolymer in which propylene is a main component.

  The metal / neutralized product of ethylene / methacrylic acid copolymer used in the surface layer (2) of the present invention is a partially neutralized copolymer of ethylene and methacrylic acid with polyvalent metal ions such as sodium and zinc. This refers to a harmonized thermoplastic resin in which polymer chains are connected by ionic bonds.

  The above resin used in the surface layer (2) of the present invention may be contained in the surface layer (2) in an amount of 50% by weight or more, and the remaining resin of 50% by weight or less is not particularly limited. Used.

  In the present invention, it is preferable to have at least one third layer between the surface layer (1) and the surface layer (2). The third layer is a copolymer comprising a conjugated diene and a vinyl aromatic compound, an ethylene / vinyl acetate copolymer, an ethylene / methyl methacrylic acid copolymer, a metal partial neutralized product of an ethylene / methacrylic acid copolymer, Ethylene / acrylic acid copolymer, ethylene / ethyl acrylic acid copolymer, ethylene / maleic anhydride copolymer, ethylene / ethylene acrylate / maleic anhydride copolymer, ethylene / maleic acid modified resin, Vicat softening temperature is 50 It is preferable to contain at least 50% by weight of at least one selected from the group consisting of ˜68 ° C. ethylene / α-olefin copolymer, polypropylene polymer, and polypropylene terpolymer. By using a resin selected from these, it is possible to prevent delamination of the multilayer film in the packaging process, particularly when top-sealing contents with high excitement. From the viewpoint of extrudability, the MFR of the third layer is 0.3 to 5.0 g / 10 min. And more preferably 0.5 to 3.5 g / 10 min. It is.

  If the above-mentioned resin is contained in the third layer in an amount of 50% by weight or more, the remaining 50% by weight or less of the resin is not particularly limited, and any resin is used.

  Since the multilayer film of the present invention has a good packaging appearance without film tearing, glycerin, fatty acid, polyhydric alcohol fatty acid ester, talc, oleate, amide-based lubricant, and number average molecular weight of 250 to 480. It is preferable that at least one additive selected from the group consisting of mineral oils is included.

  The additive has an effect of imparting lubricity to the film and preventing the film from being caught in a part of the packaging machine and causing the film to be torn when the packaging speed is high in the packaging process. In addition, when a relatively heavy package is transported after packaging, it has the effect of improving the slipperiness between the film and the tray and preventing the film from being broken during transportation. Furthermore, there is an effect that the opening property at the time of forming the tubular parison is improved, the slipping property with the mechanical device is improved, and the film forming stability is improved. From such a viewpoint, it is preferable to add the above-mentioned additive at 10% by weight or less with respect to the entire surface layer (1) and / or surface layer (2).

  Examples of the fatty acid used in the present invention include capric acid, coconut oil fatty acid, oleic acid, sunflower oil fatty acid, caproic acid and the like.

  Examples of the polyhydric alcohol fatty acid ester include glycerin fatty acid ester, diglycerin fatty acid ester, polyglycerin fatty acid ester, and the like, all of which contribute to antifogging properties and film forming stability. From the viewpoints of film-forming stability, antifogging properties, etc., the amount of polyhydric alcohol fatty acid ester added should be 0.5-7 wt% with respect to the entire surface layer (1) and / or surface layer (2). Preferably, it is 0.7 to 5% by weight. When performing printing, it is preferable to set it as 0.8 to 3 weight% from a viewpoint of ink peeling.

  Examples of the oleate include sodium oleate, calcium oleate, potassium oleate and the like, and sodium oleate is particularly preferable from the viewpoint of film formation stability of the film.

  Examples of amide-based lubricants include erucic acid amide, oleic acid amide, stearic acid amide and the like. In order to satisfy transparency and lubricity at the same time, the amount of the amide-based lubricant added is preferably 0.1 to 2% by weight based on the entire surface layer (1) and / or surface layer (2).

  When using mineral oil in this invention, it is preferable that the number average molecular weight shall be 250-480. When the number average molecular weight is 250 or more, the effect of contributing to the film formation stability is high, and when it is 480 or less, the film formation stability is good and the seal strength is improved.

  Since these additives have different optimum values depending on the film forming conditions, one or two or more additives selected from the above substances can be selected as necessary.

  The multilayer film of the present invention is suitable for a top-seal packaging method in a state where the packaged items are raised from the tray, and thus is suitable for a tray application having a surface layer containing polystyrene resin containing, for example, raw poultry meat Can be used for At present, in the market, supermarkets and the like, raw poultry meat is marketed in a form in which a packaging film is overlapped on a polystyrene foam tray, or in a pillow shrink packaging. When packaging these packages with the top seal packaging method, meat oil or moisture tends to adhere to the peripheral edge of the tray during the packaging process, so the sealing performance, especially when the contents are raised, It becomes important. Since these problems can be solved by using the multilayer film of the present invention, the multilayer film of the present invention is most suitable for the above-mentioned use.

  The packaging body in which the multilayer film of the present invention is top-sealed on a tray having a surface layer containing a polystyrene-based resin has good sealing properties, particularly interstitial material sealing properties, so there is no liquid leakage from the packaging body. It is possible to prevent the film from being torn even during refrigeration or frozen transportation.

  When the contents are raw meat, particularly raw poultry meat, there are many liquids mainly composed of blood or the like that ooze out from the meat. By using the top seal package of the present invention, it is possible to prevent liquid leakage to the outside of the package during storage, during transportation, and after transportation even when an impact occurs during handling.

  Next, the example of the manufacturing method of the multilayer film of this invention is demonstrated.

  The film of the present invention is formed into a film by a single bubble inflation method, a double bubble inflation method, a triple bubble inflation method, a tenter method, or the like. From the viewpoint of shrinkability, the single bubble inflation method, the double bubble inflation method, the triple The bubble inflation method is preferable, and the double bubble inflation method is more preferable.

  Specifically, the raw materials used were melted for each of the surface layer (1), the surface layer (2), and the third layer with several types of extrusion machines, and each molten resin was passed through a screen changer and a polymer pipe. After that, each molten resin is guided to an annular die, and the molten resin to be each layer is laminated sequentially or simultaneously inside the annular die. ) Next, the tubular parison thus obtained is cooled by the following method.

  As a cooling method of the tubular parison, for example, cooling is performed using water as a cooling medium from the outside of the parison, cooling is performed using water as a cooling medium from the outside of the parison, and further inside the tubular parison is further performed. A cooling mandrel whose surface is blasted and roughened (the inside of the mandrel is flushed with water) is cooled from both the inside and outside of the tubular parison, and the parison is rapidly cooled and solidified. Any method may be used in the present invention.

  The position where the cooling mandrel is installed is important in controlling the thickness of the parison. From the viewpoint of operability and thickness control, the end of the cooling mandrel is preferably located at a position 10 to 70 mm away from the annular die surface of the annular die, and more preferably 20 to 60 mm. The length of the cooling mandrel is preferably 150 to 300 mm from the viewpoints of operability and cooling capacity. The diameter of the cooling mandrel is preferably 1.0 to 1.7 times, more preferably 1.05 to 1.35 times the annular die lip diameter of the annular die, from the viewpoint of operability and cooling capacity. .

  At least selected from the group consisting of glycerin, fatty acids, polyhydric alcohol fatty acid esters, oleates, silicone lubricants and mineral oils having a number average molecular weight of 250 to 480, depending on the temperature in the production room during or after cooling the parison Preferably one additive is applied to the inside of the tubular parison. Examples of the coating method include a method of spraying and applying the substance from the inside or outside of the tube-shaped parison, a method of applying the substance liquid in the tube-shaped parison, and applying a certain amount while squeezing with a roll. When using a spraying method, the method of applying from the inside is preferable because it is simple in operation.

  Next, the cooled and solidified tubular parison is guided into a stretching machine, and stretching is performed by injecting air between nip rolls provided with a speed difference while heating the stretching start point between 70 to 140 ° C. From the viewpoint of stretching stability, the stretching ratio is preferably 1.5 to 10 times, more preferably 2 to 7 times with respect to each of the flow direction (MD) and the width direction (TD). Do. The stretching start point refers to the position where the TD direction of the parison begins to swell due to the internal pressure of the bubble.

  By controlling the stretching start temperature to be 70 ° C to 140 ° C and the stretching ratio to be 1.5 to 10 times in any of the MD and TD directions, the tensile modulus of elasticity can be obtained in any direction. Of 40 to 300 MPa and a heat shrinkage rate of 15 to 75% at 200 ° F. can be obtained.

  From the viewpoint of long-run film formation stability, sealing properties, in particular, interstitial material sealing properties, and heat resistance, the tubular parison may be subjected to a crosslinking treatment with an electron beam. The electron beam cross-linking treatment may be performed either before stretching or after stretching, but is preferably performed before stretching because a relatively small crosslinking apparatus can be used.

  The film of the present invention has a sealing ratio when there is a contaminant between the tray and the film, and from the viewpoint of stretching stability, so that the gel fraction of the entire film is 0.5 to 50% by weight, The electron beam irradiation is preferably 15 to 150 kGy, and more preferably 25 to 120 kGy. In order to create a gel component, there is a method of adding a crosslinking agent in a multilayer film to chemically create a crosslinking point, but in this case, the crosslinking reaction starts in the extruder, and the extrusion performance may be lowered. . Then, it is preferable to perform said electron beam process to the tubular parison after extrusion, or the film after extending | stretching, and to produce a gel component.

  The electron beam irradiation may be totally transmitted through the tubular parison. In particular, when it is necessary to seal a tray having a large amount of contaminants such as oil and gravy on the sealing surface, and when strong contaminant sealability is required, an electron beam is irradiated from the surface (1) side of the tubular parison. It is preferable. By irradiating from the surface layer (1) side, it becomes easy to control the gel component ratio in the surface layer (1), and it is possible to improve the sealing property of the foreign matter at the time of sealing.

  It is preferable to subject the stretched film to surface treatment such as corona treatment, ozone treatment, or flame treatment because a film suitable for printing applications can be obtained. The obtained raw film is slit into a predetermined size to obtain a packaging film.

  Moreover, you may add antioxidant, a plasticizer, etc. in the multilayer film of this invention to such an extent that the original characteristic is not impaired. Further, the multilayer film of the present invention may contain a petroleum-based resin, and high pressure method low density polyethylene or the like may be blended in a layer necessary as a processing aid as long as the original properties are not impaired. When using hydrogenated petroleum resin (Arcon (Arakawa Chemical Co., Ltd .: trade name)) or hydrogenated terpene resin (Clearon (Yasuhara Chemical Co., Ltd .: trade name)), the content is 0 of the entire multilayer film. When the content is from 1 to 10% by weight, shrinkage and transparency are good, which is preferable.

  Hereinafter, although an embodiment of the invention is described in detail based on an example, the present invention is not limited to these examples. In addition, the measurement of each physical property in this invention was performed with the following method.

(1) Elastic modulus The elastic modulus was determined according to JIS-K7127.

(2) Heat shrinkage rate The heat shrinkage rate is obtained by putting the 100 mm square film in an air oven type high temperature bath set at 200 ° F., and determining the amount of shrinkage of the film after heat treatment for 1 minute and dividing by the original size. It was expressed as a percentage of the value. In addition, this heat shrinkage rate set arbitrary three places in the TD direction about the obtained film, calculated | required the heat shrinkage rate of each location with the said method, and made it the average value of those heat shrinkage rates.

(3) Measuring method of gel fraction A film is extracted in boiling p-xylene for 12 hours, filtered through a 150-mesh size mesh, the insoluble part weight is measured, and the ratio is expressed by the following equation.
Gel fraction (% by weight) = (weight of insoluble part after extraction / weight of film before extraction) × 100

(4) Vicat softening temperature The Vicat softening temperature was determined according to JIS-K7206.

(5) Component amount of styrene in surface layer (1) The component amount of styrene was determined by an ultraviolet spectrophotometer method. When a copolymer comprising a hydrogenated conjugated diene and a vinyl aromatic compound is used, it can be determined by a nuclear magnetic resonance apparatus method (NMR method).

(6) MFR of resin used
1) Copolymer comprising polystyrene resin and conjugated diene and vinyl aromatic compound:
It calculated | required according to JIS-K6871.
2) Ethylene vinyl acetate copolymer:
It calculated | required according to JIS-K6730.

(7) Amount of vinyl aromatic compound in copolymer comprising conjugated diene and vinyl compound Using NMR method, using apparatus: VARIAN INOVA AS600 according to the method described in RUBBER CHEMISTRY AND TECHNOLOGY 54, 685, (1981) ¹ H-NMR spectrum ( ¹ H single pulse method ( ¹ H uses 45 ° pulse)) and ¹³ C-NMR spectrum ( ¹ H decoupling method per ¹³ C gate ( ¹³ C Can be obtained from those values using 45 ° pulses)))

(8) Weight average molecular weight and molecular weight distribution (Mw / Mn)
1) Weight average molecular weight and molecular weight distribution in a copolymer comprising a conjugated diene and a vinyl compound:
Using GPC (GPC apparatus HLC-8020 (trademark) manufactured by Tosoh Corporation), the column was measured using Tosoh TSK series, the solvent was tetrahydrofuran, the column temperature was 40 ° C., the flow rate was 1 ml / min, and the concentration was 3 mg / ml. . The weight average molecular weight and molecular weight distribution (Mw / Mn) were determined from the weight average molecular weight (Mw) and the number average molecular weight (Mn) converted from the composition curve of standard polystyrene.
2) Weight average molecular weight and molecular weight distribution of polyethylene resin:
Using GPC (GPC device 150C type manufactured by Nippon Waters Co., Ltd.), using TSK GMH-6 made by Tosoh, using orthodichlorobenzene (ODCB) as a solvent, temperature 135 ° C., flow rate 1 mL / min, concentration 10 mg / 10 mL. It was measured. The weight average molecular weight and molecular weight distribution (Mw / Mn) were determined from the weight average molecular weight (Mw) and the number average molecular weight (Mn) converted from the composition curve of standard polystyrene.

(9) Density of polyethylene resin It calculated | required according to JIS-K6760.

(10) Evaluation method of packaging appearance of multilayer film In the center of a foamed polystyrene tray having a length of 220 mm, a width of 160 mm, and a height of 20 mm, an article to be packaged (100 mm in length, 50 mm in width, 50 mm in height) , 100 mm in length, 50 mm in width, 20 mm in height with polystyrene foam placed), and after the operation of coating chicken juice once on the tray edge with gauze, each multilayer film of Examples and Comparative Examples Using top seal packaging. Thereafter, a multilayer film at a location 20 mm from the center of the peripheral edge in the horizontal direction toward the center of the packaging film is pushed in by about 20 mm with a piece of wood having a diameter of 10 mm, and after 5 minutes, the occurrence of looseness / wrinkles is evaluated. The evaluation criteria were as follows.
○: The indentation mark is completely recovered and no looseness / wrinkle is observed.
Δ: Indentation remains slightly and looseness / wrinkle is observed.
X: A state in which a circular or oval indentation of about 10 mm remains strong, and there are many slacks and wrinkles in that part and the periphery.

(11) Evaluation method of sealing property of interstitial material of multilayer film Create a package similar to the method used in (10), put the package in a container filled with water, hold the inner lid, and put it in the water. The container was further dipped, and the container was further capped. The capped container was depressurized to 300 mmHg, and the sealing performance was evaluated based on whether or not water entered the package. The evaluation criteria were as follows.
○: The edge around the tray is all well sealed, and water does not enter the package at all.
X: There is a hole in a part of the peripheral edge of the tray, or there is a part with a poor seal, and water enters the inside of the package.

(12) Evaluation of film tearing Implemented after placing five pieces of tempura as contents in a foamed polystyrene tray with a length of 200 mm, a width of 150 mm, and a height of 20 mm, and applying tempura oil to the periphery of the tray Top seal packaging was performed using the surface layer (1) side of each multilayer film of Examples and Comparative Examples as the sealing surface.
In addition, about 300 g of chicken is put in another tray, and a chicken oil-water mixed liquid (mixed in a 1: 1 ratio of chicken drip solution and water commercially available in a tray pack) is placed at the periphery of the tray. After performing the operation of coating with gauze, top-seal packaging was performed at 170 ° C. using the multilayer films of Examples and Comparative Examples.
In any of the above, the distance from the upper surface of the tray to the highest position of the contents was about 20 mm, and the multilayer film was in a raised state.
The two types of packaging obtained above are each arranged in three layers on a cardboard box, transported by truck for a distance of about 200 km, and after transportation, the cardboard box is dropped twice from a height of 1 m, The state of the seal, the tearing of the film, the state of wrinkles generated in the film, and the state of leakage of liquid from the inside of the top seal package were visually confirmed.

[Resins used in Examples and Comparative Examples]
-Copolymer comprising conjugated diene and vinyl aromatic compound (SB1: Styroflex 2G66 (BASF)):
Copolymer composed of butadiene as conjugated diene and styrene as vinyl aromatic compound and having a weight molecular weight of 150,000 and Mw / Mn of 1.3. Copolymer composed of conjugated diene and vinyl aromatic compound (SB2: SOE) SS-9000 (Asahi Kasei Chemicals)):
Polymerized using butadiene as the conjugated diene and styrene as the vinyl aromatic compound, and then hydrogenated, a hydrogenated copolymer having a weight molecular weight of 210,000 and Mw / Mn of 2.2. From the conjugated diene and the vinyl aromatic Bonding resin of hydrogenated copolymer and α-olefin copolymer (SB3: DYNARON 4600P (JSR)):
Styrene content 20%, MFR = 5.6 g / 10 min.
・ Polyethylene resin (PE1):
α-olefin = hexene-1, density = 0.905 g / cm 3, MFR = 2.5 g / 10 min
-Ethylene-vinyl acetate copolymer (EVA1):
Vinyl acetate content = 15% by weight, MFR = 1.0 g / 10 min
-Ethylene-vinyl acetate copolymer (EVA2):
Vinyl acetate content = 6% by weight, MFR = 2.5 g / 10 min
-Polypropylene terpolymer (PP1: Adsyl 5C37F (Sun Allomer)):
Propylene-ethylene-butene copolymer, MFR = 5.5 g / 10 min
Polypropylene resin (PP2: Adflex C200F (Sun Allomer)):
Propylene-ethylene copolymer, MFR = 7.0 g / 10 min.
・ Polystyrene resin (PS1):
Styrene homopolymer, MFR = 15 g / 10 min.
[Example 1]

Three extruders were used, SB1 was introduced into the extruder for the surface layer (1), PE1 was introduced into the extruder for the surface layer (2), and extrusion for the intermediate layer (third layer) EVA1 was thrown into the machine, and a three-kind three-layer parison was extruded using an intra-die-bonded annular die.
The obtained tubular parison is cooled from the outside of the parison using water as a cooling medium, and also cooled from the inside of the parison by placing the inside of the parison along a rough cooling mandrel that has been blasted with water inside. The tube-shaped parison having a width of 180 mm and a thickness of 400 μm was prepared by cooling and solidifying from both inside and outside of the tube-shaped parison.
This tubular parison was guided to an electron beam irradiation apparatus, irradiated with an electron beam from the surface layer (1) side, and subjected to crosslinking treatment so that the absorbed dose was 80 kGy.
The parison after the crosslinking treatment was induced in a stretching machine and reheated, passed between two pairs of differential nip rolls, and bubbles were formed by air injection. The temperature in the vicinity of the stretching start point was about 98 ° C. Stretching is performed so that the magnification is 5 times in the longitudinal direction and 4 times in the transverse direction, and a multilayer film having a thickness of about 20 μm is obtained by a winder.
When winding the film with a winder, cut both ends, cut out to a size of 535 mm wide, make each of the two films into one film, and each film on the two winder shafts of the winder Each of the attached paper tubes was wound up by 200 m to obtain a multilayer film for evaluation.
[Example 2]

Except that SB2 was charged into the extruder for the surface layer (1), the same operation as in Example 1 was performed to obtain a film having a thickness of about 20 μm.
[Example 3]

A resin mixture obtained by mixing SB1 and PS1 was put into an extruder for the surface layer (1). Resin was mixed so that the styrene component of surface layer (1) might be 76 weight%. The mixing ratio was set to SB1: PS1 = 70 wt%: 30 wt%. Otherwise by performing the same operations as in Example 1, a film having a thickness of about 20 μm was obtained.
In addition, the styrene component in surface layer (1) in a present Example was 76 weight%.
[Example 4]

SB3 (70% by weight) + PE1 (30% by weight) is put into the extruder for the surface layer (1), and sodium oleate is put in the tube of the tubular parison so that it gets wet in the circumferential direction inside the parison. A certain amount of iron was applied. This tubular parison was guided to an electron beam irradiation apparatus, irradiated with an electron beam from the surface layer (2) side, and subjected to a crosslinking treatment so that the absorbed dose was 80 kGy.
[Example 5]

A film having a thickness of about 20 μm was obtained by performing the same operation as in Example 1 except that PP1 was charged into the extruder for the surface layer (2).
[Example 6]

PP2 (20% by weight) + EVA2 (80% by weight) was charged into the extruder for the surface layer (2) and PP1 (20% by weight) + EVA2 (80% by weight) into the extruder for the intermediate layer, and the thickness was about 20 μm. Film was obtained.
[Example 7]

A film having a thickness of about 20 μm was obtained in the same manner as in Example 1 except that the material (PE1) constituting the surface layer (2) contained 1.5% by weight of diglycerin fatty acid ester.
[Example 8]

The material constituting the surface layer (1) (SB1) contains 0.5% by weight of talc (Talc PKP81 (Fuji talc industry)), and the material constituting the surface layer (2) (PE1) contains 1.5 diglycerin fatty acid ester. A film having a thickness of about 20 μm was obtained in the same manner as in Example 1 except that the content was% by weight.
[Example 9]

SB2 was used as the surface layer (1), PP1 was used as the surface layer (2), and a film was obtained by the double bubble inflation method. As the die, a parison was extruded using an in-die bonded annular die. The obtained tubular parison is cooled from the outside of the parison using water as a cooling medium, and also cooled from the inside of the parison by placing the inside of the parison along a rough cooling mandrel that has been blasted with water inside. The tube-shaped parison having a width of 180 mm and a thickness of 350 μm was prepared by cooling and solidifying from both inside and outside of the tube-shaped parison.
This tubular parison was guided to an electron beam irradiation apparatus, irradiated with an electron beam from the surface layer (1) side, and subjected to crosslinking treatment so that the absorbed dose became 35 kGy.
The parison after the crosslinking treatment was induced in a stretching machine and reheated, passed between two pairs of differential nip rolls, and bubbles were formed by air injection. The temperature in the vicinity of the stretching start point was about 110 ° C. Stretching is performed so that the magnification is 5 times in the longitudinal direction and 4 times in the transverse direction, and a multilayer film having a thickness of about 18 μm is obtained by a winder.
When winding the film with a winder, cut both ends, cut out to a size of 535 mm wide, make each of the two films into one film, and each film on the two winder shafts of the winder Each of the attached paper tubes was wound up to 200 m to obtain a multilayer film for evaluation.
[Comparative Example 1]

The same operation as in Example 9 was performed except that the electron beam crosslinking treatment was not performed in Example 9, and an attempt was made to obtain a multilayer film having a thickness of about 18 μm. The results obtained in Examples 1 to 9 and Comparative Example 1 are shown in Table 1. Note that “ND ¹ ” in the table means that the evaluation was not possible because the sealing performance was poor and could not withstand transportation.

  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.

  This application is based on and is based on a Japanese patent application filed on September 13, 2005 (Japanese Patent Application No. 2005-265703), the contents of which are incorporated herein by reference.

  The multilayer film of the present invention can be suitably used as a top seal packaging film. In particular, it is suitable as a processed food, raw meat, among them processed food using a tray with a polystyrene resin on the surface, and a top seal package for poultry raw meat such as chicken.

Claims (10)

A multilayer film for top seal used for a tray having a surface layer containing a polystyrene-based resin,
The multilayer film has at least a first layer and a second layer,
The first layer comprises:
(A) a copolymer comprising a conjugated diene and a vinyl aromatic compound,
(B) a copolymer obtained by hydrogenating a copolymer comprising a conjugated diene and a vinyl aromatic compound,
(C) a binding resin of a hydrogenated copolymer of a conjugated diene and a vinyl aromatic and an α-olefin copolymer,
(D) a mixture of a hydrogenated product of a copolymer of a conjugated diene and a vinyl aromatic and an α-olefin copolymer and an ethylene / α-olefin copolymer, and (e) a conjugated diene and a vinyl aromatic. 50% by weight or more of at least one selected from the group consisting of a mixture of a hydrogenated product of a copolymer and a binder resin of an α-olefin copolymer and a branched low-density polyethylene,
The multilayer film has a gel fraction of 0.5 to 50% by weight, a thickness of 70 μm or less, a tensile elastic modulus of 40 to 300 MPa in an arbitrary direction, and an arbitrary thermal shrinkage at 200 ° F. A multilayer film that is 15-75% in the direction of.   The second layer is made of high-density polyethylene, medium-density polyethylene, branched low-density polyethylene, ethylene / α-olefin copolymer, ethylene / methacrylic acid copolymer metal partial neutralized product, ethylene / vinyl acetate copolymer. The multilayer film according to claim 1, comprising at least 50% by weight of at least one selected from the group consisting of a polypropylene polymer and a polypropylene terpolymer.   A copolymer comprising a conjugated diene and a vinyl aromatic compound, an ethylene / vinyl acetate copolymer, an ethylene / methyl methacrylic acid copolymer, or an ethylene / methacrylic acid between the first layer and the second layer. Copolymer partially neutralized product, ethylene / acrylic acid copolymer, ethylene / ethyl acrylic acid copolymer, ethylene / maleic anhydride copolymer, ethylene / ethylene acrylate / maleic anhydride copolymer, ethylene / acrylic acid copolymer A third acid containing at least one selected from the group consisting of a maleic acid-modified resin, an ethylene / α-olefin copolymer having a Vicat softening temperature of 50 to 68 ° C., a polypropylene polymer, and a polypropylene terpolymer. The multilayer film according to claim 1 or 2, comprising at least one layer.   The multilayer film according to any one of claims 1 to 3, wherein the first layer contains a polystyrene-based resin, and a total of styrene components in the first layer is 60% by weight or more.   It contains at least one additive selected from the group consisting of glycerin, fatty acid, polyhydric alcohol fatty acid ester, talc, oleate, amide-based lubricant, and mineral oil having a number average molecular weight of 250 to 480. 5. The multilayer film according to any one of 4 above.   The multilayer film according to any one of claims 1 to 5, wherein the gel fraction of the first layer is 0.5 to 15% by weight.   The multilayer according to any one of claims 1 to 6, which is used for top seal packaging of a hard tray or foamed tray having a surface layer containing a polystyrene resin containing at least one of processed food and raw poultry meat. the film.   A package having a tray having a surface layer containing a polystyrene-based resin and the multilayer film according to any one of claims 1 to 7, wherein the multilayer film top seals the tray.   The package according to claim 8, wherein the package is packaged with at least one of processed food and raw meat. (A) a copolymer comprising a conjugated diene and a vinyl aromatic compound, (b) a copolymer obtained by hydrogenating a copolymer comprising a conjugated diene and a vinyl aromatic compound, and (c) comprising a conjugated diene and a vinyl aromatic. A binder resin of a hydrogenated copolymer and an α-olefin copolymer, (d) a binder resin of a hydrogenated copolymer of a conjugated diene and a vinyl aromatic and an α-olefin copolymer, ethylene · a mixture of an α-olefin copolymer, and (e) a mixture of a hydrogenated product of a copolymer of a conjugated diene and a vinyl aromatic, a binding resin of an α-olefin copolymer, and a branched low-density polyethylene. A first layer containing at least 50% by weight of at least one selected from the group;
High-density polyethylene, medium-density polyethylene, branched low-density polyethylene, ethylene / α-olefin copolymer, ethylene / methacrylic acid copolymer partially neutralized metal, ethylene / vinyl acetate copolymer, polypropylene polymer, polyethylene A second layer containing at least 50% by weight of at least one selected from the group consisting of a system terpolymer and a polypropylene terpolymer, and
Copolymer comprising conjugated diene and vinyl aromatic compound, ethylene / vinyl acetate copolymer, ethylene / methyl methacrylic acid copolymer, neutralized metal partial product of ethylene / methacrylic acid copolymer, ethylene / acrylic acid copolymer Copolymer, ethylene / ethyl acrylic acid copolymer, ethylene / maleic anhydride copolymer, ethylene / ethylene acrylate / maleic anhydride copolymer, ethylene / maleic acid modified resin, ethylene / maleic acid-modified resin with Vicat softening temperature of 50 to 68 ° C. a third layer containing at least 50% by weight of at least one selected from the group consisting of an α-olefin copolymer, a polypropylene-based polymer, and a polypropylene-based terpolymer,
Forming a tubular parison by co-extrusion to sandwich at least one third layer between the first layer and the second layer;
Cooling the tubular parison;
Subjecting the tubular parison to electron beam irradiation at 15 to 150 kGy from the first layer side so that the gel fraction of the tubular parison is 0.5 to 50% by weight; and
The manufacturing method of a multilayer film including the process of extending | stretching by the double bubble inflation method so that the temperature of an extending | stretching start point shall be 70 to 140 degreeC, and a draw ratio may be 1.5 to 10 times.