JP5969310B2 - Heat shrinkable multilayer film and packaging bag using the same - Google Patents

Description

  The present invention relates to an easy-cut heat-shrinkable multilayer film and a packaging bag using the same.

  Conventionally, various types of plastic packaging containers have been developed and proposed for filling and packaging foods and drinks, pharmaceuticals, cosmetics, industrial members, chemical products, and other articles. In order to fill and package a plastic packaging container, it is necessary to seal the opening of the plastic packaging container with a film. And the request | requirement, such as protection of the quality of contents, such as food / beverage products, and the extension of a preservation | save period, requires that the film which seals an opening part is excellent in heat-sealability. It is also required that the film used for filling and packaging completely seals the contents.

  Examples of packaging methods for covering food products include household wrap packaging, overlap packaging, twist packaging, bag packaging, skin packaging, shrink packaging, stretch packaging, and pillow packaging. In particular, shrink wrapping, pillow wrapping, and top seal wrapping continuous wrapping machines have recently been on the development trend of higher speeds. Accordingly, films having various layer configurations and resin compositions have been developed and proposed for the required characteristics of films used in continuous packaging.

  In particular, frozen noodles and ramen noodles, such as frozen noodles and refrigerated noodles, are rigid and have no shrinkage due to microwave heating to prevent burns when cooked in a microwave. There is a demand for films that can be cut and have excellent straight-cut properties.

  For example, Patent Document 1 uses a medium-high density polyethylene as an intermediate layer as a film having rigidity and excellent heat shrinkage characteristics, and an ethylene-α-olefin copolymer as a heat seal layer as a surface layer. A heat shrinkable multilayer shrink film has been disclosed.

JP 2010-094967 A

  However, when the frozen noodles are heat-sealed with a general-purpose packaging machine using the film disclosed in Patent Document 1 and heated in a microwave oven and cut in the longitudinal direction, the film does not propagate straight. In addition, there is a case where it is split obliquely or laterally and a sufficient opening cannot be obtained.

  The problem to be solved by the present invention is that the shrinkage packaging capable of solving the problems in the prior art as described above is possible, and has excellent cutting properties even after heating with a microwave oven, etc. It is to provide a multilayer film.

  As a result of intensive investigations to solve the above problems, the present inventors have used a specific combination of resins, subjected to a crosslinking treatment so as to have a specific gel fraction, and have a specific heat shrinkage rate. The present inventors have found that a shrinkable multilayer film can solve the above-mentioned problems and completed the present invention.

That is, the present invention provides the following heat-shrinkable multilayer film and package.
[1] A heat-shrinkable multilayer film comprising a base material layer and a heat seal layer laminated on the base material layer, wherein the base material layer is 25 to 70% by mass of medium-density polyethylene and high-pressure method low-density polyethylene 5 It is a layer formed by subjecting a first resin composition containing ˜25% by mass and 25% to 60% by mass of a polypropylene resin to a crosslinking treatment, and the heat seal layer is one kind or two or more kinds of ethylene weight. It is a layer formed by subjecting the second resin composition containing coalesce to a crosslinking treatment, and the shrinkage rate at 100 ° C. in accordance with the measurement method ASTM D2732 is 10% or less, and the heat shrinkage rate at 140 ° C. is 60% or more. A heat shrinkable multilayer film having a gel fraction of 20% by mass or more.
[2] The heat-shrinkable multilayer film according to [1], wherein the medium-high density polyethylene has a density of 0.930 to 0.970 g / cm ³ .
[3] In the above [1] or [2], the second resin composition contains at least one ethylene-based polymer selected from the group consisting of high-pressure method low-density polyethylene and linear low-density polyethylene. The heat-shrinkable multilayer film as described.
[4] The heat-shrinkable multilayer film according to any one of [1] to [3], wherein the first resin composition further contains 0.1 to 5.0% by mass of a glycerin fatty acid ester.
[5] The heat-shrinkable multilayer film according to any one of [1] to [4], wherein the second resin composition further contains 0.1 to 5.0% by mass of a glycerin fatty acid ester.
[6] The heat-shrinkable multilayer film according to any one of [1] to [5], wherein the heat seal layer is laminated on both surfaces of the base material layer.
[7] The heat-shrinkable multilayer film according to any one of [1] to [6], having a thickness of 5 to 40 μm.
[8] A packaging bag using the heat-shrinkable multilayer film according to any one of [1] to [7].
[9] The packaging bag according to [8], which is for frozen noodles or refrigerated surface packaging.

  According to the present invention, it is possible to provide a heat-shrinkable multilayer film that can be shrink-wrapped and has excellent cut properties even after being heated by a microwave oven or the like, and a package using the heat-shrinkable multilayer film.

  Hereinafter, a mode for carrying out the present invention (hereinafter referred to as the present embodiment) will be described in detail. In addition, this invention is not limited to the following embodiment, It can implement by changing variously within the range of the summary.

  The heat-shrinkable multilayer film of the present embodiment (hereinafter sometimes simply referred to as “film”) includes a base material layer (I) and a heat seal layer (II) laminated on the base material layer (I). With. The base material layer (I) is obtained by subjecting the first resin composition containing 25 to 70% by mass of medium-high density polyethylene, 5 to 25% by mass of high-pressure low-density polyethylene, and 25 to 60% by mass of polypropylene resin to a crosslinking treatment. The heat seal layer (II) is a layer formed by subjecting a second resin composition containing one or more ethylene polymers to a crosslinking treatment.

  In the present embodiment, the shrinkage rate of the film based on the measurement method ASTM D2732 is 10% or less at 100 ° C. and 60% or more at 140 ° C. Moreover, the gel fraction of a film is 20 mass% or more.

  Hereinafter, the base material layer (I) and the heat seal layer (II) will be described in detail.

[Base material layer (I)]
In this Embodiment, base material layer (I) is 1st resin containing 25-70 mass% of medium density polyethylene, 5-25 mass% of high-pressure process low density polyethylene, and 25-60 mass% of polypropylene resin. It is a layer formed by subjecting the composition to a crosslinking treatment.

  When the first resin composition contains medium-high density polyethylene, it is possible to obtain a low-shrinkage film in which rigidity is imparted to the film and shrinkage during microwave heating is sufficiently prevented.

Polyethylene is classified by density according to JIS K 6922, and a density of 0.942 g / cm ³ or higher is a high density polyethylene (HDPE), and a range of 0.930 to 0.941 g / cm ³ is a medium density polyethylene (MDPE). The thing of the range of 0.910-0.929 g / cm < ³ > is made into a low density polyethylene (LDPE).

  In the present embodiment, the medium-high-density polyethylene is a high-density polyethylene and a medium-density polyethylene, and a density of 0.930 or more, a polymer of ethylene alone or a copolymer of ethylene and a C4-6 α-olefin. Indicates. Examples of the α-olefin include 1-butene and 1-hexene. The medium-high density polyethylene can be produced by a generally known method such as a Philips method, a standard method, or a Ziegler method.

In the present embodiment, it is necessary that the film has sufficient rigidity and can be easily stretched during production. From the viewpoint of having good rigidity and further preventing shrinkage during heating in the microwave oven, the density of the medium-high density polyethylene is preferably 0.930 to 0.970 g / cm ³ , more preferably 0.942 to 0.970 g / cm ³ , more preferably 0.942 to 0.966 g / cm ³ , and even more preferably 0.950 to 0.960 g / cm ³ . Moreover, it is preferable to use a high density polyethylene as a medium density polyethylene.

  In the present embodiment, “density” means a value measured according to JIS K 6922. Specifically, the density can be measured with a density gradient tube according to JIS K 6922.

  In the present embodiment, the melt flow rate of medium-high density polyethylene (hereinafter sometimes simply referred to as “MFR”) is preferably 0.2 to 7.0 g / 10 min, more preferably 0. .5 to 6.0 g / 10 min. A melt flow rate of 0.2 g / 10 min or more is preferable from the viewpoint of obtaining film strength, and 7.0 g / 10 min or less is preferable from the viewpoint of obtaining stability in the production process.

  In the present embodiment, the melt flow rate (MFR) is an index indicating the fluidity at the time of melting, and means a value measured according to JIS K 7210. Specifically, the MFR can be measured by a melt indexer according to JIS K 7210.

  In this Embodiment, when a 1st resin composition contains a high-pressure method low density polyethylene, it can be set as a stable film at a production process.

  The high-pressure low-density polyethylene is a polyethylene copolymer in which ethylene as a repeating unit is randomly bonded with a branch and has a long chain branch.

In the present embodiment, it is preferable that the density of the high-pressure low density polyethylene is 0.910~0.929g / cm ^3, more preferably 0.915~0.929g / cm ^3. When the density of the high-pressure method low-density polyethylene is 0.910 g / cm ³ or more, the film can be given rigidity and slackness of the film can be suppressed. When the density of the high-pressure method low-density polyethylene is 0.929 g / cm ³ or less, the practical level of the haze of the film can be maintained.

  As a method for producing the high-pressure method low-density polyethylene, generally known methods can be used. In general, high-pressure low-density polyethylene is produced by polymerizing ethylene and α-olefin in an autoclave or tube reactor in the presence of a free radical generator such as peroxide at a high temperature and high pressure of 100 to 300 ° C and 100 to 350 MPa. can do.

  In the present embodiment, the melt flow rate of the high-pressure method low-density polyethylene is preferably 0.1 to 5.0 g / 10 minutes, and more preferably 0.2 to 4.0 g / 10 minutes. A melt flow rate of 0.1 g / 10 min or more is preferable from the viewpoint of obtaining film strength, and 5.0 g / 10 min or less is preferable from the viewpoint of obtaining stability in the production process.

  In this Embodiment, it becomes possible to provide linear cut property by mix | blending a polypropylene-type resin with a 1st resin composition.

  As the polypropylene resin, a homopolypropylene, ethylene-propylene copolymer, block polypropylene, ethylene-butene-propylene terpolymer is used which has a melting point of 120 ° C. or higher, and is used to prevent shrinkage when heated in a microwave oven. Therefore, the melting point is more preferably 125 ° C. or higher. From the viewpoint of the compatibility of the first resin composition with other polyethylene resins, an ethylene-propylene copolymer obtained by copolymerizing a small amount of ethylene is more preferable than a homopolypropylene having high crystallinity.

  In this Embodiment, it is preferable that the melt flow rate of polypropylene resin is 0.1-20 g / 10min, More preferably, it is 0.2-10g / 10min.

  The proportion of the polypropylene resin in the first resin composition is preferably 60% by mass or less, more preferably 55% by mass or less, and still more preferably 50% by mass or less from the viewpoint of preventing tearing in the packaging machine. Further, from the viewpoint of imparting straight cut property, it is preferably 25% by mass or more, more preferably 28% by mass or more.

  In the first resin composition, the medium-high density polyethylene, the high-pressure method low-density polyethylene, and the polypropylene-based resin are contained in the medium-high density polyethylene from the viewpoint of increasing the rigidity of the film and facilitating stretching during production. Is 25 to 70% by mass, high-pressure low-density polyethylene is preferably 5 to 25% by mass, and polypropylene resin is preferably 25 to 60% by mass.

  In this Embodiment, it is preferable that the gel fraction of base material layer (I) is 10-60 mass%. When the gel fraction of the base material layer (I) is 10% by mass or more, the film exhibits excellent productivity and film strength and heat resistance. Moreover, when the gel fraction is 60% by mass or less, it is possible to impart a tenacity to the film strength and to further suppress the tearing of the film when subjected to an automatic packaging machine or the like. The gel fraction of the base material layer (I) is preferably 20 to 50% by mass, more preferably 25 to 40% by mass.

  In the present embodiment, the base resin layer (I) can be obtained by subjecting the first resin composition to a crosslinking treatment so that the gel fraction falls within the above numerical range. The gel fraction can be measured by the method described later.

[Heat seal layer (II)]
In the present embodiment, the heat seal layer (II) is a layer formed by subjecting a second resin composition containing one or more ethylene polymers to a crosslinking treatment. With such a heat seal layer, the film has a wide heat seal temperature region and can exhibit stable heat seal properties.

  Examples of the ethylene polymer include high pressure method low density polyethylene and linear low density polyethylene. The second resin composition preferably contains at least one selected from the group consisting of a high pressure method low density polyethylene and a linear low density polyethylene.

  As the high-pressure method low-density polyethylene, the same ones as those described above as the high-pressure method low-density polyethylene constituting the first resin composition can be used. The same high pressure method low density polyethylene may be blended with the first resin composition and the second resin composition, or different high pressure method low density polyethylene may be blended.

  In the present embodiment, the linear low density polyethylene is a copolymer of ethylene and a C3-C18 α-olefin. The α-olefin is preferably selected from propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene and the like.

The density of the linear low-density polyethylene is 0.916 to 0.939 g / cm in that the rigidity of the film becomes an appropriate height as a packaging film and the adhesion between the films can be prevented by appropriate surface roughness of the film. ³ is preferable, and 0.920 to 0.930 g / cm ³ is more preferable. Low adhesion between the films is preferable in that the seal part in the automatic packaging machine is finished cleanly without any defects.

  The melt flow rate of the linear low density polyethylene is preferably from 0.1 to 10 g / 10 minutes, and more preferably from 1.0 to 8.0 g / 10 minutes. A melt flow rate of 0.1 g / 10 min or more is preferable in that good film strength can be obtained, and 10 g / 10 min or less is preferable in that stability in the production process can be obtained.

  The polymerization catalyst used for producing the linear low density polyethylene is not particularly limited, and may be any of a multisite catalyst, a single site catalyst, and the like.

(Additive)
In the present embodiment, from the viewpoint of improving slipperiness and antifogging property, a glycerin fatty acid ester can be added to the base material layer (I) and / or the heat seal layer (II) as an additive. Specifically, for example, by adding an additive to the first resin composition and / or the second resin composition, the additive is added to the base material layer (I) and / or the heat seal layer (II). Can be blended.

  In the present embodiment, the glycerin fatty acid ester is an ester of glycerin and a fatty acid. By allowing the glycerin fatty acid ester to be present on the film surface, antifogging properties can be imparted to the film.

  Hydrophilicity and lipophilicity can be adjusted by changing the degree of polymerization of glycerin, the type of fatty acid, and / or the degree of esterification. Examples of the glycerin fatty acid ester include glycerin fatty acid ester, diglycerin fatty acid ester, triglycerin fatty acid ester, polyglycerin fatty acid ester, and the like, for example, diglycerin oleate, diglycerin laurate, glycerin monooleate, or a mixture thereof. The main components such as are preferable from the viewpoint of the slipperiness and glossiness of the film and are easy to use.

Examples of glycerin fatty acid esters other than those mentioned above include glycerin monofatty acid esters, difatty acid esters, trifatty acid esters, polyfatty acid esters, and the like, and monoglycerin esters of saturated or unsaturated fatty acids having 8 to 18 carbon atoms. , Diglycerin ester, triglycerin ester, tetraglycerin ester and the like.
Specifically, glycerol monolaurate, glycerol monomyristate, glycerol monopalmitate, glycerol dipalmitate, glycerol monostearate, glycerol distearate, glycerol tristearate, glycerol diolate, glycerol trioleate, glycerol mono Linoleate, diglycerol myristate, diglycerol palmitate, diglycerol stearate, diglycerol linoleate, triglycerol laurate, triglycerol oleate, triglycerol stearate, tetraglycerol laurate, tetraglycerol oleate, tetraglycerol stearate Etc.

  In the present embodiment, in order to allow the glycerin fatty acid ester to be present on the film surface, the temperature setting of the extruder is set to 250 ° C. or higher, and the base layer (I) or the heat seal layer (II) is configured at a high shear rate. It is preferable to knead | mix with resin (1st resin composition or 2nd resin composition) to carry out, and it is suitable to carry out the fine dispersion of glycerol fatty acid ester at the time of kneading | mixing. Bleedout is an important factor with different effects depending on the amount and manner of existence. As a manner of existence, it is preferable that the glycerin fatty acid ester is present in the form of layers instead of droplets, that is, in a substantially continuous state on the surface of the film.

  Generally, the glycerin fatty acid ester contained in the base material layer (core layer) moves to the adjacent layer (outer layer) and promotes the bleed out of the outer layer, and the glycerin fatty acid ester itself is thought to bleed out to the surface. ing. Further, it is considered that the glycerin fatty acid ester can impart good antifogging properties to the film by shifting (bleeding out) to the film surface.

  Since the antifogging property of the film can be improved by adjusting the hydrophilicity and lipophilicity of the glycerin fatty acid ester, it is preferable to use a highly hydrophilic glycerin fatty acid ester, and the addition amount of the glycerin fatty acid ester The anti-fogging property of the film can also be improved by increasing the amount.

  In this Embodiment, it is preferable that a 1st resin composition contains 0.1-5.0 mass% of glycerol fatty acid ester from an antifogging viewpoint.

  Moreover, in this Embodiment, it is preferable that a 2nd resin composition contains 0.1-5.0 mass% of glycerol fatty-acid ester from a viewpoint of anti-fogging property and the slipperiness of a packaging machine and a film. .

  In addition to the above additives, talc or fatty acid amide may be added to the base material layer (I) and the heat seal layer (II) to prevent adhesion between the films.

[Heat shrink multilayer film]
The heat-shrinkable multilayer film of the present embodiment is a heat-shrinkable multilayer film comprising a base material layer (I) and a heat seal layer (II) laminated on the base material layer (I). I) is a layer obtained by subjecting a first resin composition containing 25 to 70% by mass of medium-high density polyethylene, 5 to 25% by mass of high-pressure low-density polyethylene, and 25 to 60% by mass of a polypropylene resin to a crosslinking treatment. The heat seal layer (II) is a layer obtained by subjecting the second resin composition containing one or more ethylene polymers to a crosslinking treatment, and is 100 based on the measurement method ASTM D2732. The heat shrinkable multilayer film has a shrinkage rate at 10 ° C. of 10% or less, a heat shrinkage rate at 140 ° C. of 60% or more, and a gel fraction of 20% by mass or more.

  The heat-shrinkable multilayer film of this embodiment has a heat shrinkage rate of 10% or less at 100 ° C. in that it does not cause seal puncture during microwave heating and exhibits stable heat seal strength. Accordingly, in order to obtain a tight packaging bag when shrinkage at the time of packaging is required, the heat shrinkage rate at 140 ° C. is 60% or more.

  The heat-shrinkable multilayer film may contain the following additives in the base material layer (I) and the heat seal layer (II) in order to impart good antifogging properties and slipperiness. Examples of additives include fatty acid esters of polyhydric alcohols, polyoxyethylene alkyl ethers, polyalkylene glycol fatty acid esters, and the like.

  Examples of fatty acid esters of polyhydric alcohols include mono-fatty acid esters, di-fatty acid esters, tri-fatty acid esters, poly-fatty acid esters of polyhydric alcohols, etc., and polyhydric alcohols of saturated or unsaturated fatty acids having 8 to 18 carbon atoms. Examples include esters. Examples of polyhydric alcohols include sorbitan, and specific examples of sorbitan esters include sorbitan laurate, sorbitan myristate, sorbitan palmitate, sorbitan monostearate, sorbitan distearate, sorbitan tristearate, sorbitan monooleate. Sorbitandiolate, sorbitan trioleate, sorbitan linoleate and the like. These additives can be added to the base material layer (I) and / or the heat seal layer (II), for example, by containing them in the first resin composition and / or the second resin composition.

In the present embodiment, the base material layer (I) and / or the heat seal layer (II) may contain liquid paraffin. As liquid paraffin, the kinematic viscosity in 40 degreeC measured based on JISK2283 is 10-10000 (mm < ² > / s) normally. The liquid paraffin is a liquid paraffin having a kinematic viscosity of 50 to 3000 (mm ² / s) and good compatibility with the resin composition constituting the base material layer (I) or the heat seal layer (II). Preferably there is.

  A liquid paraffin may be used individually by 1 type, and may be used in combination of 2 or more type. Addition of liquid paraffin to the base material layer (I) or the heat seal layer (II) is effective for imparting film moldability and antifogging property.

  In the present embodiment, from the viewpoint of film moldability and antifogging properties, the resin composition constituting the base layer (I) or the heat seal layer (II) contains 0.1 to 5.0% by mass of liquid paraffin. For this reason, it is preferable that the first resin composition and / or the second resin composition contain 0.1 to 5.0% by mass of liquid paraffin.

  The heat-shrinkable multilayer film of the present embodiment may include an intermediate layer between the base material layer (I) and the heat seal layer (II) as long as the characteristics are not impaired. The intermediate layer (i) serves as an antifogging agent retaining layer for maintaining the antifogging property, and (ii) improves the adhesion between the heat seal layer and the base material layer and suppresses delamination (iii) ) It is preferably provided for reasons such as a recovered layer of the film in which the recovered resin is re-pelletized by an extruder, and the range does not impair the original characteristics for the reasons (i), (ii) and (iii) above. Thus, other resins and additives other than the resin used for the base material layer (I) and the heat seal layer (II) may be blended at 60% by mass or less.

  Although it will not specifically limit if it is resin collect | recovered when manufacturing a film as collect | recovered resin, The resin etc. which are obtained by melting again the film of this Embodiment are mentioned.

  The thickness ratio of the intermediate layer to the entire heat-shrinkable multilayer film is not particularly limited as long as the properties are not impaired, but is preferably 40% or less, more preferably 30% or less, and still more preferably. 25% or less. When the thickness ratio of the intermediate layer is 40% or less, it is preferable from the viewpoint of stretching stability.

  In this embodiment, the arrangement of the base material layer (I) and the heat seal layer (II) is not particularly limited as long as the heat seal layer (II) is laminated on the base material layer (I). Although not intended, for example, in the case of two layers consisting of a base material layer (I) and a heat seal layer (II): (II) / (I), both surface layers consist of a heat seal layer (II) In the case of three layers: (II) / (I) / (II), when the intermediate layer (hereinafter sometimes simply referred to as (B)) is composed of three layers: (II) / ( B) / (I), (II) / (I) / (B), when both surface layers are composed of a heat seal layer (II) and one intermediate layer is composed of all four layers: (II) / ( B) / (I) / (II), when there are four intermediate layers using two intermediate layers: (II) / (B) / (I) / (B) Consists Toshiru layer (II), etc. may become an intermediate layer of two layers using all five layers (II) / (B) / (I) / (B) / (II) can be mentioned. It is also possible to use an intermediate layer different from the intermediate layer (B) (hereinafter sometimes simply referred to as (D)) in combination, (II) / (B) / (I) / (D) , (II) / (D) / (I) / (B), (II) / (D) / (B) / (I), (II) / (B) / (D) / (I) 4 layers, (II) / (D) / (B) / (I) / (II), (II) / (B) / (I) / (D) / (II), (II) / (B) / (D) / (I) / (II) 5 layers, (II) / (B) / (D) / (I) / (B) / (II) 6 layers, (II) / It can also be composed of 8 layers or more, such as 7 layers consisting of (B) / (D) / (I) / (B) / (D) / (II).

  The thickness of the heat-shrinkable multilayer film in the present embodiment is preferably 5 to 40 μm, more preferably 8 to 30 μm. If the thickness of the heat-shrinkable multilayer film is in the range of 5 to 40 μm, it is difficult to cause tearing even on an object to be packaged having heavy objects or protrusions, and stable production is possible. The thickness of the heat-shrinkable multilayer film can be adjusted to a desired value depending on the discharge amount or stretching ratio of each layer extruder at the time of production.

  In the heat-shrinkable multilayer film, the thickness ratio of the base material layer (I) is preferably 50 to 90%, more preferably 60 to 85%, from the viewpoint of film strength.

  In the heat-shrinkable multilayer film, the thickness ratio of the heat seal layer (II) is preferably 50 to 10%, more preferably 40 to 15%, from the viewpoint of expressing stable heat seal strength.

[Method for producing heat-shrinkable multilayer film]
Examples of the method for producing the heat-shrinkable multilayer film of the present embodiment include a direct inflation method, a double bubble inflation method, a triple bubble inflation method, and a tenter method.

  In the inflation method, a predetermined resin is melted and kneaded using a heated extruder and extruded with an annular die. Quench with cooling water and extract the unstretched material. Extrusion is not particularly limited and can be obtained by a method using a multilayer T die or a multilayer circular die, but a method using a multilayer circular die is preferred.

  Next, this raw fabric is subjected to a crosslinking treatment, and then the raw fabric is heated to a melting point or higher by heat transfer heating with hot air or radiation heating such as an infrastructure heater, and then the raw fabric is given a speed ratio between two nip rolls. While stretching in the flow direction (MD), air is injected into the tube to stretch in the vertical direction (TD).

  Since the heat-shrinkable multilayer film of the present embodiment needs heat resistance so that it can be used under high temperature conditions in a microwave oven, the base material layer (I) and the heat seal layer (II) are subjected to crosslinking treatment. ing.

  In the method for producing the heat-shrinkable multilayer film in the present embodiment, generally known methods can be used as the crosslinking method. Examples thereof include a method of adding a crosslinking agent and heating to a temperature higher than the decomposition temperature of the crosslinking agent, and a method of irradiating ionizing radiation such as α rays, β rays, γ rays, neutron rays, and electron beams.

  By performing the crosslinking treatment, the haze and gloss after shrinkage of the film can be improved. Moreover, when it heats and shrinks more than melting | fusing point of resin which comprises a film, there is also an aim which prevents the tear by melting of a film.

  Since the heat-shrinkable multilayer film of the present embodiment is appropriately cross-linked, stable stretching can be performed even at a temperature equal to or higher than the melting point of the resin constituting the film, and a film having a high heat shrinkage rate can be obtained. it can. That is, by crosslinking, the stretching temperature and the stretching ratio can be easily adjusted, and a film having a high heat shrinkability and a low heat shrinkage stress can be produced. In addition, most of the film does not shrink in the heat seal temperature range, and a stable heat seal property can be exhibited.In the temperature range of the hot air shrink tunnel, the optimum heat shrinkage rate and heat shrink stress for shrink wrapping are achieved. It becomes possible to have.

  In the present embodiment, it is preferable to irradiate the ionizing radiation so that the gel fraction of the whole film is 20 to 80% by mass. In consideration of mechanical unevenness, the irradiation dose is 40 to 120 kGy. Is preferred. An irradiation dose of 40 kGy or more is preferable from the viewpoint of haze and glossiness after heat shrinkage of the film, and an irradiation dose of 120 kGy or less is preferable from the point of heat shrinkage stress. The relationship between the degree of irradiation and the degree of crosslinking differs depending on the type of resin.

  In the present embodiment, the heat seal layer (II) has a gel fraction of 20% by mass or less from the viewpoint of fluidity of the heat seal resin and shrinkage stress of the film. In the base material layer (I), the gel fraction is preferably 20% by mass or more from the viewpoint of film rigidity and productivity.

[Packaging bag]
An example of a process for obtaining a packaging bag using the heat-shrinkable multilayer film of the present embodiment as a packaging film will be described. There are various methods for covering an article to be packaged with a film, such as pillow packaging or stretch packaging, and any method can be selected. However, here, a method of continuous packaging with pillow packaging will be described.

  Examples of packages include frozen noodles such as ramen and udon or refrigerated noodles.

  Examples of pillow packaging include the following methods. Seal both ends of the film to form a cylinder. Put an item to be packaged in a cylinder, seal it before and after, and separate it to obtain each package. When this is shrunk to obtain a tight package, a tightly finished package can be obtained by thermally shrinking the film with a hot-air shrink tunnel whose temperature is adjusted to 140 to 170 ° C. in advance.

  The packaging speed of the continuous wrapping machine is such that about 20 pieces are packed in one minute, but in the case of a recent high-speed continuous wrapping machine, about 30 to 80 pieces are packed in one minute. Therefore, the packaging film is strongly required to have suitability for the packaging speed, for example, slipperiness, hot tack sealability, and heat shrinkage characteristics.

  The heat-shrinkable multilayer film of the present embodiment is a film excellent in slipperiness, hot tack sealability, and heat-shrinkability as a packaging film.

  The sealing method includes impulse sealing, heat sealing, fusing sealing, and the like, and any method that is generally used may be selected according to the film. In addition, these sealing methods may be used in combination in a timely manner. However, a high-speed continuous packaging machine often employs a method that is sealed with a short heat seal.

  When performing heat shrinkage treatment after packaging, it is possible to prevent swelling during heating of the microwave oven by previously opening a small hole in the packaging film using either a needle, a hot needle or a laser. Besides, a tightly finished shrink package can be obtained by removing air from the packaging film bag during heat shrinkage. Hot air, steam, hot water, or the like can be used for heat shrinkage of the packaging film, but hot air is preferably used.

  The preferred embodiment of the present invention has been described above, but the present invention is not limited to the above embodiment.

  Hereinafter, the present embodiment will be described more specifically with reference to examples and comparative examples. However, the present embodiment is not limited to only these examples. The evaluation method used in the present embodiment is as follows.

[Gel fraction]
A sample was extracted for 12 hours in boiling p-xylene, and the proportion of the insoluble portion was calculated by the following formula. Used as a measure of the degree of crosslinking of the film.
Gel fraction (mass%) = (mass of sample after extraction / mass of sample before extraction) × 100

[Heat shrinkage at 100 ° C or 140 ° C]
In accordance with ASTM D2732, the measurement was performed by shrinking at temperatures of 100 ° C. and 140 ° C. A film having a size of 120 mm × 120 mm was marked with three points at intervals of 50 mm in the vertical direction. Subsequently, two points were marked at intervals of 50 mm in the horizontal direction starting from each of these points. The film was heat treated in a hot air drier maintained at the above temperature for 1 minute, and the thermal shrinkage was calculated from the length between each point.

[Maximum heat shrinkage stress at 140 ° C]
The maximum heat shrinkage stress at 140 ° C. was measured according to ASTM D2838.

[Hot tack seal strength]
Based on ASTM F1921-98, the measurement was performed using a Hotler HotTack measuring instrument. A V-shaped heat seal die was used, the temperature was 150 ° C., and the width of the test piece was 25 mm. The hot tack seal strength which peeled and changed with time was plotted on the order of 1/1000 second, and the evaluation was performed with the seal strength of 0.25 second after the start of peeling.
(Evaluation criteria)
A: The hot tack seal strength is 2.0 N / 15 mm width or more and less than 5.0 N / 15 mm width.
C: The hot tack seal strength is less than 2.0 N / 15 mm width, or 5.0 N / 15 mm width or more.

[Tear propagation strength]
In accordance with JIS-K-7128, each film was measured in the machine direction and transverse direction using a light load tear tester manufactured by Toyo Seiki Co., Ltd., and this was taken as the tear propagation strength.

[Evaluation of straight cut performance of packaging bags]
The obtained film is slit to a predetermined width, the flow direction of the film is matched with the longitudinal direction of the frozen udon with a weight of 200 g, the film is sealed with a heat sealer, a center seal portion is created, and a cylindrical packaging bag Got. Heat sealing was performed in the short direction of the frozen udon so as to be perpendicular to the center seal portion, and end seal portions were formed at both ends to obtain a three-side sealed packaging bag. The obtained three-side sealed packaging bag was stored in a freezer at −40 ° C. for 4 hours, and a microwave oven (manufactured by National, NE-EH21A) was set to output 500 W, 2 minutes 30 seconds, and heated. With the center seal part of the packaging bag after heating in front, pinch a 4cm part to the right from the center seal part with the left thumb and index finger, pinch with the thumb and index finger of the right hand, and pull the right hand downward toward you. The packaging bag was opened.
(Evaluation criteria)
AA: The film was torn straight in the longitudinal direction and was torn and propagated to the end seal portion on the opposite side, and a large opening was obtained.
A: The tear propagation distance was ½ or more of the packaging bag, and an opening sufficient for taking out the heated udon was obtained.
C: The tear propagation distance was less than ½ of the packaging bag, and a sufficient opening for taking out the heated udon was not obtained.

[Applicability to automatic packaging machines]
The obtained film was slit to a width of 300 mm, and 30 frozen udon (200 g) were each packaged using “FW-3451A-αV (trade name)” manufactured by Fujikikai Co., Ltd. As an evaluation of film breakage, when the film was unwound, a hole for steam removal at the time of microwave cooking was opened, and it was evaluated whether the breakage propagated from this hole. The case where no tear propagated from the vapor vent hole was designated as A, and the case where even one piece of tear propagated was designated as C. As the evaluation of the shape of the seal part, A was used when the seal part was free from wrinkles, and C was used when the films were in close contact and the seal part was wrinkled.
(Comprehensive judgment)
A case where all the above evaluations were A was comprehensively judged as A. In addition, a case where there was one or more C in the evaluation was comprehensively determined as C.

Resins, additives, and film production methods used in Examples and Comparative Examples are as follows.
[Base material layer (I)]
Medium High Density Polyethylene / HD1 High Density Polyethylene (Density = 0.952 g / cm ³ , MFR = 0.8 g / 10 min) (Suntech (registered trademark) HD S362, manufactured by Asahi Kasei Chemicals)
HD2 high density polyethylene (density = 0.966 g / cm ³ , MFR = 5.5 g / 10 min) (Suntech (registered trademark) HD J240 manufactured by Asahi Kasei Chemicals)
HD3 high-density biomass polyethylene (density = 0.935 g / cm ³ , MFR = 2.2 g / 10 min) (Green Polymer Biopolymer SGE7252 manufactured by Braschem)
High-pressure low-density polyethylene LD1 High-pressure low-density polyethylene (density = 0.922 g / cm ³ , MFR = 0.2 g / 10 min) (Suntech (registered trademark) LD M2004, manufactured by Asahi Kasei Chemicals)
Ethylene-α-olefin copolymer / LL1 Multisite linear low-density polyethylene (α-olefin comonomer = octene, density = 0.926 g / cm ³ , MFR = 2.0 g / 10 min) (manufactured by Dow Chemical Co., Ltd.) DOWLEX (registered trademark) 2032)
LL2 single-site linear low-density polyethylene (α-olefin comonomer = hexene, density = 0.926 g / cm ³ , MFR = 2.0 g / 10 min) (Evolue (registered trademark) SP2520 manufactured by Prime Polymer Co., Ltd.)
LL4 linear low-density biomass polyethylene (α-olefin comonomer = butene / hexene, density = 0.918 g / cm ³ , MFR = 1.0 g / 10 min) (Green Polymer Biopolymer SLH118 manufactured by Braschem)
Polypropylene resin / PP1 ternary copolymer PP (melting point: 135 ° C., MFR = 5.5 g / 10 min) (Lyondell Basell, Adsyl 5C30F)
PP2 ethylene-propylene copolymer (melting point 142 ° C., MFR = 7.5 g / 10 minutes) (Sun Allomer PC630S)
PP3 ethylene-propylene copolymer (melting point 150 ° C., MFR = 9.5 g / 10 min) (Sun Allomer PC724S)
PP4 homopolypropylene (melting point 161 ° C., MFR = 3.3 g / 10 min) (Sun Allomer PL500A)

[Heat seal layer (II)]
Linear low-density polyethylene / LL1 Multisite linear low-density polyethylene (α-olefin comonomer = octene, density = 0.926 g / cm ³ , MFR = 2.0 g / 10 min) (DOWLEX made by Dow Chemical Co., Ltd.) Registered trademark) 2032)
LL2 single-site linear low-density polyethylene (α-olefin comonomer = 1-hexene, density = 0.926 g / cm ³ , MFR = 2.0 g / 10 min) (Evolue (registered trademark) SP2520 manufactured by Prime Polymer Co., Ltd.) )
LL3 Single-site linear low-density polyethylene (α-olefin comonomer = 1-hexene, density = 0.913 g / cm ³ , MFR = 2.0 g / 10 min) (Ube Maruzen Co., Ltd. Umerit (registered trademark) 1520F )
High-pressure low-density polyethylene / LD2 High-pressure low-density polyethylene (density = 0.920 g / cm ³ , MFR = 0.4 g / 10 min) (Suntech (registered trademark) LD M2004, manufactured by Asahi Kasei Chemicals)

[Additive]
Ad1 Glycerol monooleate (Riquemar (registered trademark) OL-100, manufactured by Riken Vitamin Co., Ltd.)
Ad2 diglycerin oleate (Rikenmar (registered trademark) O-71D manufactured by Riken Vitamin Co., Ltd.)
・ Ad3 liquid paraffin (Sumoyl (registered trademark) P70 manufactured by Matsumura Oil Co., Ltd.)

[Additive 1]
・ Ad1 / Ad2 / Ad3 = 1/1/1
[Additive 2]
・ Ad1 / Ad2 = 1/1

[Film Production Method]
The heat-shrinkable multilayer films in Examples and Comparative Examples were produced by the following method. That is, the resin for forming the substrate layer (I) is supplied to the extruder for the substrate layer (I), and the heat seal layer (II) is formed for the extruder for the heat seal layer (II). In each extruder, mixing and melting were performed while injecting a predetermined amount of a predetermined additive with an injection pump. Each of the mixed and melted resins was supplied to an annular die, laminated with the die, and coextruded. Immediately below the annular die, the molten resin discharged from the die was first cooled with cooling water and pinched with a pinch roll while forming a first bubble, and an unstretched raw material was collected.

  The original fabric was adjusted to have a desired thickness and layer ratio. This original fabric was subjected to a crosslinking treatment using an electron beam irradiation apparatus having an acceleration voltage of 750 kV. At this time, adjustment was performed so that the gel fraction of each layer was within a desired value. By heating the processed raw fabric in a heating furnace maintained at an atmospheric temperature of 170 ° C., and injecting air into the tube 5 to 7 times in the flow direction by the speed ratio between the two sets of nip rolls. The film was stretched 5 to 7 times in the direction perpendicular to the flow direction of the machine, and cooled by applying cold air from the air ring to the maximum diameter part of the bubble. Thereafter, it was folded to obtain a heat-shrinkable multilayer film having a thickness of 5 to 40 μm.

  Below, each Example and a comparative example are explained in full detail.

[Example 1]
29% by mass of HD1, 20% by mass of high-density low-density polyethylene LD1, 50% by mass of PP1, and a 1: 1: 1 ratio of glycerol monooleate Ad1, diglycerol oleate Ad2, and liquid paraffin Ad3 as additives. The resin composition containing 1.0% by mass of additive 1 mixed in step 1 was used as the first resin composition for forming the base layer (I). Further, an additive 1 in which 99% by mass of single-site linear low-density polyethylene LL1 and glycerin monooleate Ad1, diglycerin oleate Ad2, and liquid paraffin Ad3 are mixed at a ratio of 1: 1: 1 is 1. The resin composition containing 0% by mass was used as the second resin composition for forming the heat seal layer (II). Using these first resin composition and second resin composition, each layer thickness ratio of heat seal layer (II) / base material layer (I) / heat seal layer (II) is 15/70/15%. Extruded using an annular die.

  Thereafter, it was cooled and solidified with cooling water, and a tube-shaped stretched original fabric having a width of 130 mm and a thickness of 550 μm and a uniform thickness accuracy was collected. Next, this stretched raw fabric is guided to an electron beam irradiation apparatus of 750 kV, subjected to crosslinking treatment with an absorbed dose of 100 kGy, heated in a heating furnace maintained at an atmospheric temperature of 170 ° C., and the speed between the two sets of nip rolls. By injecting air into the tube at a ratio of 6.0 times, the film was stretched 6.2 times in the machine flow direction (MD) and the vertical direction (TD) to obtain a film having a thickness of 15 μm.

  Table 4 shows the evaluation results of the obtained film. Since the obtained film had high hot tack seal strength and high tear strength in the lateral direction, the straight-cut property of the packaging bag was good and the film was highly practical. There was no propagation of tears in the automatic wrapping machine, and there was no defect in the seal part.

[Examples 2 to 11]
A film having a thickness of 12 to 25 μm was obtained in the same manner as in Example 1 except that the resin for forming each layer and the ratio thereof were changed as shown in Tables 1 and 2. In addition, the draw ratio was made the same as Example 1, and the thickness of the film was suitably adjusted with the thickness of the tube-shaped extending original fabric before extending | stretching.

  The evaluation results of the obtained film are shown in Table 4 and Table 5. All of the obtained films had high hot tack seal strength and high tear strength in the transverse direction, and thus the straight cut property of the packaging bag was good and the film was highly practical. There was no propagation of tears in the automatic wrapping machine, and there was no defect in the seal part.

[Example 12]
The packaging bag obtained in Example 1 was passed through a shrink tunnel heated to 160 ° C. for 3 seconds to form a shrink packaging bag, and then heated in a microwave oven to evaluate linear cut performance. Regardless of the shrinkage treatment in the shrink tunnel, the film was torn straight and excellent in straight cut.

[Comparative Example 1]
A 15 μm film was obtained in the same manner as in Example 1 except that the resin for forming each layer and the ratio thereof were changed as shown in Table 3.

  Table 6 shows the evaluation results of the obtained film. Although the hot tack seal strength was good, the tear strength in the transverse direction was low, and the linear cut property was not sufficient. Furthermore, since the density of the heat seal layer resin is low and the films easily adhere to each other, wrinkles easily enter the seal portion.

[Comparative Example 2]
A 15 μm film was obtained in the same manner as in Example 1 except that the resin for forming each layer and the ratio thereof were changed as shown in Table 3.

  Table 6 shows the evaluation results of the obtained film. The heat shrinkage rate at 120 ° C. was high, and the tear strength in the transverse direction was low. There was no problem with the density of LL of the heat seal layer, and the resins were difficult to adhere to each other, but the straight cut property was inferior and sufficient openings could not be obtained.

[Comparative Example 3]
A 15 μm film was obtained in the same manner as in Example 1 except that only the substrate layer (I) was used. Table 6 shows the evaluation results of the obtained film. It was inferior in hot tack sealing property, and the sealed part opened by microwave heating after packaging, and the contents spilled out of the bag.

[Comparative Example 4]
A 15 μm film was obtained in the same manner as in Example 1 except that the resin for forming each layer and the ratio thereof were changed as shown in Table 3.

  Table 6 shows the evaluation results of the obtained film. Since there was little PP resin of base material layer (I), the tearing strength of the horizontal direction was low, it was inferior to a straight cut property, and sufficient opening part was not obtained.

[Comparative Example 5]
A 15 μm film was obtained in the same manner as in Example 1 except that the resin for forming each layer and the ratio thereof were changed as shown in Table 3.

  Table 6 shows the evaluation results of the obtained film. Since the PP resin of the base material layer (I) is large, the tear strength is low in both the vertical direction and the horizontal direction, the straight cut property is inferior, and sufficient openings cannot be obtained.

[Comparative Example 6]
A 15 μm film was obtained in the same manner as in Example 1 except that the resin for forming each layer and the ratio thereof were changed as shown in Table 3.

  Table 6 shows the evaluation results of the obtained film. Since the PP resin of the base material layer (I) has a high melting point, the tear strength is low in both the vertical direction and the horizontal direction, the straight cut property is inferior, and sufficient openings cannot be obtained.

[Comparative Example 7]
The packaging bag obtained in Comparative Example 1 was passed through a shrink tunnel heated to 160 ° C. for 3 seconds to form a shrink packaging bag, and then heated in a microwave oven to evaluate linear cut performance. Regardless of the shrinkage treatment in the shrink tunnel, the film was torn diagonally and the straight cut property was not sufficient.

  The heat-shrinkable multilayer film of the present invention has excellent linear cutting properties and excellent balance of heat-shrinkage characteristics, so that it can be used for microwave cooking of frozen noodles and refrigerated noodles regardless of the heat-shrinking process after packaging. It can be suitably used as a packaging material.

Claims (9)

A heat shrinkable multilayer film comprising a base material layer and a heat seal layer laminated on the base material layer,
The base material layer is subjected to a crosslinking treatment on a first resin composition containing 25 to 70% by mass of medium density polyethylene, 5 to 25% by mass of high pressure low density polyethylene, and 25 to 60% by mass of polypropylene resin. The layer
The heat seal layer is a layer obtained by subjecting a second resin composition containing one or more ethylene polymers to a crosslinking treatment,
The shrinkage rate at 100 ° C. according to the measurement method ASTM D2732 is 10% or less, and the thermal shrinkage rate at 140 ° C. is 60% or more,
A heat-shrinkable multilayer film having a gel fraction of 20% by mass or more.   The heat-shrinkable multilayer film according to claim 1, wherein the density of the medium-high density polyethylene is 0.930 to 0.970 g / cm3.   The heat-shrinkable multilayer according to claim 1 or 2, wherein the second resin composition contains at least one ethylene polymer selected from the group consisting of a high-pressure process low-density polyethylene and a linear low-density polyethylene. the film.   The heat-shrinkable multilayer film according to any one of claims 1 to 3, wherein the first resin composition further contains 0.1 to 5.0% by mass of a glycerin fatty acid ester.   The heat-shrinkable multilayer film according to any one of claims 1 to 4, wherein the second resin composition further contains 0.1 to 5.0% by mass of a glycerin fatty acid ester.   The heat-shrinkable multilayer film according to any one of claims 1 to 5, wherein the heat seal layer is laminated on both surfaces of the base material layer.   The heat-shrinkable multilayer film according to any one of claims 1 to 6, which has a thickness of 5 to 40 µm.   The packaging bag using the heat-shrink multilayer film as described in any one of Claims 1-7. The packaging bag of Claim 8 which is an object for packaging frozen noodles or refrigerated noodles .