JP5997591B2 - Low temperature shrinkable overlap packaging film - Google Patents

Description

  The present invention relates to a cold shrinkable overlap packaging film.

  Conventionally, shrink wrapping (shrink wrapping) is used to wrap a plurality of products quickly and tightly at the same time, regardless of the shape and size of the package. Moreover, since the appearance of the obtained package is beautiful, the contents are kept hygienic, and visual quality control is easy, it is used for packaging foods.

  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, overlap shrink packaging, pillow packaging, and top seal packaging continuous packaging machines have been in the development trend of higher speeds in recent years. 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, as a method of packaging fresh food such as meat and fish, an overlap is placed by placing an object to be packaged such as meat or fresh fish in a foamed polystyrene tray (hereinafter sometimes referred to as “PSP tray”) and covering with a packaging machine. Shrink packaging is widely used.

  However, in recent years, due to increasing awareness of the environment, trays and the like have been used in which the expansion ratio of expanded polystyrene is increased to reduce the raw materials used. As a result, the rigidity and heat resistance of the tray itself are reduced, and the tray may be deformed or crushed during packaging.

  For example, Patent Document 1 discloses a film aimed at improving productivity and transparency, gloss, heat sealability, antifogging, and heat shrinkability.

  Further, for example, in Patent Document 2, a heat seal layer is laminated with a specific content of an ethylene-α-olefin random copolymer and an ethylene-α-olefin block copolymer having different density ranges. A multilayer film for shrink wrapping which aims to achieve both heat shrinkability and deformation recovery after shrink wrap by using as a layer is disclosed.

Patent 4919620 Japanese Patent No. 5074303

  However, when the PSP tray is packaged with a general-purpose overlap packaging machine using the film disclosed in Patent Document 1, the deformation recovery property after shrink wrapping is inferior. When the volume of the contents decreases, the film may not follow the volume change and may remain as wrinkles.

  Further, in the film disclosed in Patent Document 2, an ethylene-α-olefin random copolymer is used for the surface layer. If the pressure at the time of sealing is low, the film is folded due to the shrinkage of the film before sealing the bottom. Since the portion contracts and turns up, there may be cases where sufficient bottom sealing performance cannot be obtained.

  The problem to be solved by the present invention is to solve the problems in the prior art as described above, without causing container deformation or cracking at the time of packaging, good bottom sealability, and deformation recovery after packaging. Another object of the present invention is to provide a low-temperature shrinkable overlapping packaging film capable of obtaining a tight package.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that a low-temperature shrinkable overlapping packaging film comprising a core layer containing a plurality of ethylene-based copolymers having specific physical properties and both surface layers However, they have found that the above-mentioned problems can be solved and completed the present invention.

That is, the present invention provides the following low-temperature shrinkable overlap packaging film.
[1] Two surface layers (I) containing 50% by mass or more of an ethylene-vinyl acetate copolymer and an ethylene-α-olefin random copolymer (A) having a density of 0.880 to 0.939 g / cm ^3. Polyolefin resin (C) having an ethylene-α-olefin block copolymer (B) of 20 to 90% by mass and a melting peak temperature of 120 ° C. or less of 5 to 40% by mass and a melt tension at 190 ° C. of 60 to 200 mN. And a core layer (II) containing 5 to 40% by mass of a low-temperature shrinkable overlap packaging film composed of at least three layers.
[2] The polyolefin resin (C) includes at least one selected from the group consisting of an ethylene vinyl acetate copolymer having a vinyl acetate content of 5 to 40% and a high-pressure low-density polyethylene. The film for low temperature shrinkable overlap packaging as described.
[3] The low-temperature shrinkable overlapping packaging film according to [1] or [2], wherein the heat shrinkage stress at 100 ° C. is 250 g / cm ² or less.
[4] The film for cold shrinkable overlap packaging according to any one of [1] to [3], wherein at least one layer is crosslinked.

  According to the present invention, container deformation and cracking at the time of packaging do not occur, the bottom sealing property is good, the deformation recovery property is excellent even after packaging, and it is possible to obtain a tight packaging body for low temperature shrinkable overlap packaging A film can be provided.

It is a schematic cross section of the film for low temperature shrinkable overlap packaging which is one embodiment of the present invention.

  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 low-temperature shrinkable overlap packaging film of the present embodiment (hereinafter sometimes simply referred to as “film”) includes both surface layers (I) and a core layer (II). Both surface layers (I) contain 50% by mass or more of an ethylene-vinyl acetate copolymer. The core layer (II) has an ethylene-α-olefin random copolymer (A) having a density of 0.890 to 0.939 g / cm ^{3 and} an ethylene-α-olefin random copolymer (A) of 20 to 90% by mass and a melting peak temperature of 120 ° C. or less. It is a film containing 5 to 40% by mass of an α-olefin block copolymer (B) and 5 to 40% by mass of a polyolefin resin (C) having a melt tension at 190 ° C. of 60 to 200 mN.

  Hereinafter, both surface layers (I) and core layer (II) will be described in detail.

  FIG. 1 is a schematic cross-sectional view of a film for cold shrinkable overlap packaging which is an embodiment of the present invention. As shown in FIG. 1, the low-temperature shrinkable overlap packaging film 10 includes both surface layers (I) 2 and 3 on the upper surface and the lower surface, and a core layer (II) 1 sandwiched therebetween.

[Both surface layers (I)]
In this Embodiment, both surface layers (I) should just contain 50 mass% or more of ethylene-vinyl acetate copolymers. The ethylene-vinyl acetate copolymer is excellent in heat sealability derived from vinyl acetate and retention of the antifogging agent, and is suitable for use in the surface layer.

  In particular, in the present embodiment, it is preferable that the ethylene-vinyl acetate copolymer is contained in an amount of 50% by mass or more because heat sealability and antifogging properties are improved, and the content is preferably 60% by mass or more. Therefore, it is more preferable because heat sealability and antifogging properties are further improved. In addition, the upper limit value of the content ratio of the ethylene-vinyl acetate copolymer is preferably 100% by mass.

  The vinyl acetate content in the ethylene-vinyl acetate copolymer is preferably 1 to 40% by mass, more preferably 5 to 30% by mass, and still more preferably 10 from the viewpoint of achieving both heat sealability and antifogging properties. ˜20 mass%.

  The vinyl acetate content is determined by dissolving a sample in xylene according to JIS K 7192 and hydrolyzing the acetate group with an alcohol solution of potassium hydroxide. It can be measured by adding excess sulfuric acid or hydrochloric acid and back titrating the acid with a standard sodium hydroxide solution using phenolphthalein as an indicator.

  Both surface layers (I) may contain other flexible resins and modified resins in a range not exceeding 50 mass%. Examples of the flexible resin include ethylene-α-olefin random copolymers, high-pressure low-density polyethylene, and the like. When a resin having a melting point of 60 to 120 ° C. or less is used, from the viewpoint of heat sealability and packaging machine runnability. Preferably, it is 70-115 degreeC, More preferably, it is 80-110 degreeC.

[Core layer (II)]
In the present embodiment, the core layer (II) has an ethylene-α-olefin random copolymer (A) having a density of 0.880 to 0.939 g / cm ³ and 20 to 90% by mass, and a melting peak temperature of 120. 5 to 40% by mass of an ethylene-α-olefin block copolymer (B) having a temperature of not higher than ° C. and 5 to 40% by mass of a polyolefin resin (C) having a melt tension at 190 ° C. of 60 to 200 mN.

  In this Embodiment, mechanical strengths, such as the tensile strength of a film and tear strength, are improved by containing 20-90 mass% of ethylene-alpha-olefin random copolymers (A). The ethylene-α-olefin random copolymer 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 ethylene-α-olefin random copolymer (A) is 0.880 to 0.939 g / cm ³ because the rigidity of the film becomes an appropriate height as a packaging film. From the viewpoint of the waist and shrinkage of the film, it is more preferably 0.890 to 0.925 g / cm ³ , still more preferably 0.895 to 0.920 g / cm ³ .

  The melt flow rate of the ethylene-α-olefin random copolymer (A) is preferably 0.1 to 10 g / 10 min. 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. More preferably, it is 0.2-5.0 g / 10min, More preferably, it is 0.5-2.5 g / 10min.

  The ethylene-α-olefin random copolymer (A) is produced by a gas phase method, a solution method, or a high pressure method, but the polymerization catalyst to be used is not particularly limited, and may be any of a multi-site catalyst and a single-site catalyst. .

  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 (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, favorable deformation | transformation recoverability can be provided by containing 5-40 mass% of ethylene-alpha-olefin block copolymers (B).

  The melting point (melting peak temperature) of the ethylene-α-olefin block copolymer (B) is 120 ° C. or less from the viewpoint of the heat resistance and stretching stability of the film. Moreover, it is preferable that it is 80 degreeC or more from a viewpoint of the rigidity provision to a film.

  The ethylene-α-olefin block copolymer (B) is chemically defined as (x) a first olefin polymerization catalyst and (y) a polymer prepared by the first olefin polymerization catalyst under equivalent polymerization conditions. In the presence of a mixture obtained by combining a second olefin polymerization catalyst capable of adjusting polymers having different properties and (z) a chain shuttling agent, or a composition containing a reactive organism, ethylene and α- It is a block copolymer formed by polymerizing olefins.

  In the present embodiment, by containing a polyolefin resin (C) having a melt tension at 190 ° C. of 60 to 200 mN, sufficient orientation can be imparted to the original fabric before stretching. Even a cross-linking treatment results in a stable film in the production process.

  As the polyolefin-based resin (C), a polyethylene polymer having a long chain branch is preferable because ethylene of a repeating unit is randomly bonded with a branch, and it is preferable to give a stretch to the film. Process low density polyethylene is preferred. When it is desired to give flexibility to the film, an ethylene-vinyl acetate copolymer can be used. When it is desired to suppress deformation of the container in the primary packaging stage before heat shrinkage, (C) includes an ethylene-vinyl acetate copolymer. May be preferred.

  As the vinyl acetate content increases, the melting point of the resin decreases and the ethylene-vinyl acetate copolymer becomes flexible.

  In the present embodiment, the vinyl acetate content is preferably 5 to 40% by mass, more preferably 5 to 30% by mass, and even more preferably 7 to 20% by mass from the viewpoints of flexibility and thermal stability.

  The melt flow rate of the ethylene-vinyl acetate copolymer for imparting flexibility to the film is preferably 0.1 to 1.8 g / 10 minutes, more preferably 0.2 to 1.5 g / 10 minutes. It is. A melt flow rate of 0.1 g / 10 min or more is preferable from the viewpoint of obtaining film strength, and a melt flow rate of 1.8 g / 10 min or less is preferable from the viewpoint of obtaining stability in the production process.

In the present embodiment, is preferably, more preferably 0.915~0.925g / cm ³ density of the high-pressure low-density polyethylene as (C) is 0.910~0.929g / cm ³ . When the density of the high-pressure method low-density polyethylene is 0.910 g / cm ³ or more, rigidity is imparted to the film and slackness of the film is easily suppressed. When the density of the high-pressure method low-density polyethylene is 0.929 g / cm ³ or less, it becomes easy to maintain a practical level of haze of the film.

  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 1.8 g / 10 minutes, more preferably 0.2 in terms of extrusion stability and stretching stability. ~ 1.5 g / 10 min. A melt flow rate of 0.1 g / 10 min or more is preferable from the viewpoint of obtaining film strength, and a melt flow rate of 1.8 g / 10 min or less is preferable from the viewpoint of obtaining stability in the production process.

  Of the core layer (II), an ethylene-α-olefin random copolymer (A), an ethylene-α-olefin block copolymer (B), a polyolefin resin (C) having a melt tension at 190 ° C. of 60 to 200 mN. The content is in the range of 20 to 90% by mass of (A), 5 to 40% by mass of (B), and 5 to 40% by mass of (C) because stretching stability and deformation recovery are improved. .

(Additive)
In this Embodiment, it is preferable to mix | blend glycerol fatty acid ester with both surface layer (I) and / or core layer (II) as an additive from a viewpoint of improving slipperiness and anti-fogging property.

  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 component such as is preferable because it is easy to use from the viewpoint of the slipperiness and glossiness of the film.

  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 190 ° C. or higher, and both surface layers (I) or the core layer (II) are configured at a high shear rate. It is preferable to knead with the resin, and it is preferable to finely disperse the glycerin fatty acid ester when kneading. 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.

  In general, it is considered that the glycerin fatty acid ester contained in the core layer migrates to both adjacent surface layers to promote bleed out and the glycerin fatty acid ester itself bleeds out to the surface. 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 to contain 2.0-5.0 mass% of glycerol fatty acid ester in both surface layers (I) from a viewpoint of anti-fogging property.

  Moreover, in this Embodiment, it is preferable to contain 0.1-2.0 mass% of glycerin type fatty acid ester in core layer (II) from a viewpoint of anti-fogging property and the slipperiness of a packaging machine and a film.

  In the present embodiment, the following additives may be included in both surface layers (I) and core 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.

In the present embodiment, both surface layers (I) and / or core 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 a good compatibility with the resin composition constituting both the surface layers (I) or the core layer (II). It is preferable.

  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 both surface layers (I) or core layer (II) is effective for imparting film moldability and antifogging properties.

  In addition to the above additives, talc and fatty acid amide may be added to both surface layers (I) and core layer (II) to prevent adhesion between films.

  In the low-temperature shrinkable overlap packaging film of the present embodiment, in order to suppress softening deformation of the tray due to heating during heat shrinkage, it is necessary to shrink at a low temperature as much as possible to obtain a tight finish. The shrinkage in the TD direction at 100 ° C. is preferably 10% or more, and preferably 60% or less in order to suppress cracking of the tray.

In addition, the heat shrinkage stress in the TD direction at 100 ° C. is preferably 250 g / mm ² or less in view of preventing deformation of the PSP tray or the like that is a packaged object during heat shrinkage in an automatic packaging machine, and is tight. In order to obtain shrinkage, it is preferably 100 g / mm ² or more.

  In the low-temperature shrinkable overlap packaging film of the present embodiment, an intermediate layer (III) may be provided between both surface layers (I) and the core layer (II) as long as the characteristics are not impaired. Good. The intermediate layer (III) is (i) as an anti-fogging agent retaining layer for maintaining anti-fogging properties, (ii) to improve the adhesion between both surface layers and the core layer, and to suppress 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 original properties are impaired due to the reasons (i), (ii) and (iii) above. As long as there is no resin, additives other than those used for both the surface layer (I) and the core layer (II), additives, and the like 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 (III) to the film of the present embodiment is not particularly limited as long as the characteristics are not impaired, but is preferably 40% or less, more preferably 30% or less, Preferably it is 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 the present embodiment, the arrangement of both surface layers (I) and the core layer (II) is not particularly limited as long as the core layer (II) is laminated between the both surface layers (I). Although not intended, for example, in the case of three layers consisting of (I) and (II): (I) / (II) / (I), consisting of all four layers using one intermediate layer (III) : (I) / (III) / (II) / (I), in the case of all five layers using two intermediate layers: (I) / (III) / (II) / (III) / (I), Both surface layers can also be used in combination with an intermediate layer (IV) different from the intermediate layer (III), and can be composed of 7 layers, 8 layers, or more layers.

  In the film for low temperature shrinkable overlap packaging of the present embodiment, the thickness is preferably 5 to 40 μm, more preferably 8 to 30 μm. If the thickness is in the range of 5 to 40 μm, it is difficult to break even for a packaged object having heavy objects or protrusions, and stable production is possible. The thickness of the film can be adjusted to a desired value depending on the discharge amount or stretching ratio of each layer extruder during production.

  In this Embodiment, it is preferable that the thickness ratio of core layer (II) is 50 to 90% from a viewpoint of the intensity | strength of a film, More preferably, it is 60 to 85%.

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

[Method for producing film for low-temperature shrinkable overlap packaging]
Examples of the method for producing the low-temperature shrinkable overlap packaging 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, extruded from an annular die, rapidly cooled with cooling water, and an unstretched original fabric is collected. 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).

  In the low-temperature shrinkable overlap packaging film of the present embodiment, it is preferable that at least one of the surface layers (I) and the core layer (II) is subjected to a crosslinking treatment in order to impart stretch stability. .

  In the method for producing a low-temperature shrinkable overlap packaging 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.

  The low-temperature shrinkable overlap packaging film of the present embodiment can be stably stretched at a temperature equal to or higher than the melting point of the resin constituting the film by being appropriately crosslinked, and has a high heat shrinkage rate. Since it can be set as a film, it is preferable. That is, by crosslinking, the stretching temperature and the stretching ratio can be easily adjusted, and a film having a high heat shrinkage stress and a low shrinkage stress can be produced.

  In this embodiment, it is preferable that the ionizing radiation is irradiated so that the gel fraction is 1 to 60% by mass in the whole film, and the irradiation dose is 30 to 90 kGy considering mechanical unevenness. Is preferred. The irradiation dose is more preferably 35 kGy or more from the viewpoint of haze and glossiness after heat shrinkage of the film, and more preferably 80 kGy or less from the point of heat shrinkage stress.

  Depending on the type of resin, the relationship between the degree of irradiation and the degree of cross-linking differs, and the cross-linking treatment improves stretchability and improves the deformation recovery after packaging. May be impaired.

  The gel fraction of the entire film is preferably from 3 to 50% by mass, more preferably from 5 to 50% by mass, in terms of stretching stability and bottom sealing during packaging, container deformation prevention, deformation recovery after packaging, and the like. 45% by mass.

  The gel fraction can be measured by the method described later.

[Packaging]
In this embodiment, an example of a packaging process by an automatic packaging machine will be described.

  Examples of the overlap packaging include the following methods. Put both ends of the film together to form a cylinder. Put an object to be packaged (such as meat and fresh fish stored in a PSP tray) in a cylinder and fold the front and back to the bottom side while cutting the front and back to obtain each package. By thermally shrinking the film in a hot-air shrink tunnel whose temperature is adjusted to 80 ° C. to 140 ° C. in advance, wrinkles at the top of the package can be removed, and the film can be stretched to make a tight package.

  In recent high-speed continuous packaging machines, the packaging speed is about 80 to 120 pieces per minute. For this reason, the packaging film is strongly required to be suitable for the packaging speed, for example, slipping property, bottom sealing property, and heat shrinkage property.

  As an example of the bottom sealing method, it is preferable that the bottom sealing is performed by folding the film to the bottom side and passing it over a preheated hot plate while holding it with a sponge holding belt.

  When the heat shrinkage treatment is performed after packaging, hot air, steam, hot water or the like can be used, 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

[100 ° C. thermal shrinkage]
The heat shrinkage rate was measured according to ASTM D2732. The film was sampled to be 10 cm × 10 cm in the flow (MD) direction and the width (TD) direction, respectively, and was freely shrunk for 30 minutes using a hot air dryer set at 100 ° C. The measurement was performed three times, and the thermal shrinkage rate of TD was measured three times, and the average value was obtained.

[Maximum heat shrinkage stress at 100 ° C]
The maximum heat shrinkage stress (heat shrinkage stress) was measured according to ASTM D2838. The film was cut into a size having a width of 10 mm and a length of 50 mm, immersed in an oil bath kept at 100 ° C., and the maximum heat shrinkage stress in the TD direction was measured three times to obtain an average value.

[Applicability to automatic packaging machines]
The obtained film was slit to a width of 380 mm, and “STC-N2 (trade name)” manufactured by Omori Machine Industry Co., Ltd. was used to place chicken in a PSP tray (Eco FLB-A15-35 W manufactured by FP Corporation). 30 pieces each containing 200 g) were packaged.
(1) Cut-back property For evaluation of cut-back property at the time of film cutting, ○ when the film cut part is folded and adhered closely, △ when the tip is curled △, the film cut part is greatly swollen What is being marked as x.
(2) Bottom sealability As an evaluation of the bottom sealability, the bottom seal was performed by passing over a hot plate heated to 150 ° C. while suppressing only a film cut portion that was not turned up after packaging and suppressing it with a belt. The ones that were completely sealed were marked with ◯, the ones that were partially sealed were marked with △, and the ones that could be easily peeled off were marked with ×.
(3) Evaluation of tray deformation After the package completed up to the bottom seal was passed through a hot-air shrink tunnel set at a temperature of 115 ° C. for 1.5 seconds, it was evaluated whether the tray was cracked. The tray is not cracked and the deformation of the tray is less than 5% of the width of the tray. ○, the tray is not cracked but the deformation is 5% or more, and the tray is cracked. Was marked with x.

[Comprehensive evaluation of suitability for automatic packaging machines]
A total evaluation was given with A indicating that all of the above evaluations were A, B indicating one or more Δs, and C indicating one or more Xs.

[Deformation recovery of package]
At the center of the package obtained by the evaluation of the suitability of the automatic packaging machine, a metal round bar with a diameter of 15 mm (a hemisphere with a radius of 7.5 mm at the tip) is placed at a constant speed of 1000 mm / min from the top of the tray to a depth of 20 mm. Pushed in and pulled out at the same speed. The time required for disappearance of the indentation caused by the indentation immediately after the withdrawal was taken as the restoration time. The contents used were clay placed in the corner of the tray so as not to hinder the indentation.

  The case where the indentation mark disappeared within 30 seconds was marked with ◯, the case where the indentation mark disappeared within 30 seconds to 300 seconds was marked with Δ, and the case where wrinkles did not disappear after 300 seconds or more was marked with ×.

  Resins, additives, and film production methods used in Examples and Comparative Examples are as follows.

[Both surface layers (I)]
"Ethylene-vinyl acetate copolymer"
EVA1 NUC3758 (vinyl acetate content = 15% by mass, MFR = 2.2 g / cm ³ ) (manufactured by Nihon Unicar)
"Ethylene-α-olefin random copolymer"
・ LLDPE1 Umerit 0520F (α-olefin comonomer = hexene, density = 0.905 g / cm ³ , MFR = 2.0 g / 10 min) (manufactured by Ube Maruzen Polyethylene)

[Core layer (II)]
Ethylene-α-olefin random copolymer (A)
LLDPE2 ethylene-α-olefin random copolymer (α-olefin comonomer = hexene, density = 0.903 g / cm ³ , MFR = 1.0 g / 10 min) (Evolue SP0510 (trade name) manufactured by Prime Polymer Co., Ltd.)
LLDPE3 ethylene-α-olefin random copolymer (α-olefin comonomer = octene, density = 0.905 g / cm ³ , MFR = 0.8 g / 10 min) (Atein 4203 (trade name) manufactured by Dow Chemical Company)
LLDPE4 ethylene-α-olefin random copolymer (α-olefin comonomer = octene, density = 0.926 g / cm 3, MI = 2.0 g / 10 min) (Dow Rex 2032 (trade name) manufactured by Dow Chemical Company)
B-LLDPE ethylene-α-olefin random copolymer (biomass) (α-olefin comonomer = butene / hexene, density = 0.918 g / cm ³ , MFR = 1.0 g / 10 min) (Green Polyethylene, manufactured by Braskem) Biopolymer SLH118 (trade name))
VLDPE1 ethylene-α-olefin random copolymer (α-olefin comonomer = octene, density = 0.868 g / cm 3, MI = 0.5 g / 10 min) (Affinity EG8150 (trade name) manufactured by Dow Chemical Company)

Ethylene-α-olefin block copolymer (B)
OBC1 ethylene-α-olefin block copolymer (olefin block copolymer) (α-olefin comonomer = octene, density = 0.866 g / cm 3, MFR = 0.5 g / 10 min, melting point = 120 ° C.) (Dow Chemical Company) (Infuse D9000 (trade name))
OBC2 ethylene-α-olefin block copolymer (olefin block copolymer) (α-olefin comonomer = octene, density = 0.866 g / cm 3, MFR = 1.0 g / 10 min, melting point = 120 ° C.) (Dow Chemical Company) (Infuse D9107 (trade name))

Polyolefin resin (C)
LD1 High pressure method low density polyethylene (density = 0.922 g / cm ³ , MFR = 0.2 g / 10 min, melt tension at 190 ° C. = 175 mN) (Suntech LD M2102 (trade name) manufactured by Asahi Kasei Chemicals)
LD2 high pressure method low density polyethylene (density = 0.922 g / cm ³ , MFR = 1.5 g / 10 min, melt tension at 190 ° C. = 80 mN) (Asahi Kasei Chemicals Suntech LD M2115 (trade name))
EVA1 ethylene-vinyl acetate copolymer (vinyl acetate content = 15 mass%, MFR = 2.2 g / cm 3, melt tension at 190 ° C. = 55 mN) (NUC3758 (trade name) manufactured by Nihon Unicar)
EVA2 ethylene-vinyl acetate copolymer (vinyl acetate content = 15 mass%, MFR = 1.0 g / cm 3, melt tension at 190 ° C. = 115 mN) (NUC8452D (trade name) manufactured by Dow Chemical Co., Ltd.)

  The melt tension was measured as follows. Capillograph 1C (trade name) manufactured by Toyo Seiki Seisakusho Co., Ltd. is attached to the tip of the barrel with a capillary having a length of 8.0 mm and a nozzle diameter of 2.095 mm, the barrel temperature is set to 190 ° C., and the sample pellets are made several times. Separately, it was filled in the barrel while sufficiently venting air and melted. The resin melted from the capillary was extruded in the form of a strand with the piston speed set to 10 mm / min, and this strand was wound on a tension detection pulley having a diameter of 5 mm installed directly below the lower surface of the capillary 60 cm and wound at a constant winding speed. . The winding speed was increased stepwise to 1, 3, 5, 10, 20, 30 m / min, and data was captured for 20 seconds when the tension reached a steady state at each winding speed. At each winding speed, the same measurement was performed three times, the average value was the tension at the winding speed, and the maximum tension among the obtained tensions was the melt tension. When the strand was cut before the winding speed reached 30 m / min, the measurement was terminated there, and the maximum tension obtained was adopted as the melt tension.

[Additive 1]
・ Ad1 / Ad2 = 1/1
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.)

[Additive 2]
・ Ad1 / Ad2 / Ad3 = 4/5/1
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 polyoxyethylene alkyl ether (Rikenmar (registered trademark) B-205, manufactured by Riken Vitamin Co., Ltd.)

[Film Production Method]
The low-temperature shrinkable overlap packaging films in Examples and Comparative Examples were produced by the following method. That is, a resin for forming both surface layers (I) is supplied to the extruder for both surface layers (I), and a core layer (II) is formed for the extruder for the core layers (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 500 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 150 ° C., and injecting air into the tube 5 to 7 times in the flow direction depending on 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, the film was folded to obtain a film having a thickness of 5 to 40 μm.

Below, each Example and a comparative example are explained in full detail.
[Example 1]
A resin composition containing 97% by mass of EVA1 and 3.0% by mass of additive 1 in which glycerin monooleate Ad1 and diglycerin oleate Ad2 were mixed at a ratio of 1: 1 as an additive was added to both surface layers (I). It was set as the 1st resin composition for forming. Moreover, as (A), the ethylene-α-olefin random copolymer LLDPE2 is 59% by mass, (B) is the ethylene-α-olefin block copolymer OBC1 is 20% by mass, and (C) is a low pressure method. A resin composition containing 1.0% by mass of additive 1 in which 20% by mass of density polyethylene EVA2 and glycerin monooleate Ad1 and diglycerin oleate Ad2 are mixed at a ratio of 1: 1 is used as the core layer (II). It was set as the 2nd resin composition for forming. Using these first resin composition and second resin composition, the layer thickness ratio of surface layer (I) / core layer (II) / surface layer (I) 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 device of 500 kV and subjected to crosslinking treatment with an absorbed dose of 60 kGy, which is 8.0 times by the speed ratio between the two sets of nip rolls, and air is injected into the tube. 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 11 μm.

  Tables 5 and 6 show the evaluation results of the obtained films. The obtained film had no problem in the evaluation of suitability for automatic packaging machines, and the overall evaluation was A evaluation. Moreover, the deformation recovery was excellent.

[Examples 2 to 12]
A film having a thickness of 10 to 15 μm was obtained in the same manner as in Example 1 except that the resin, additives, and ratio thereof for forming each layer 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.

  Tables 5 and 6 show the evaluation results of the obtained films. The obtained film had no problem in the evaluation of suitability for automatic packaging machines, and the overall evaluation was A evaluation. Moreover, the deformation recovery was excellent.

[Examples 13 to 14]
A film having a thickness of 11 μm was obtained in the same manner as in Example 1 except that the irradiation dose was changed to the conditions described in Table 6. Table 6 shows the evaluation results of the obtained film.

[Comparative Examples 1-8]
An 11 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 Tables 3 and 4. In Comparative Examples 5 to 8, since the stretching was not stable under the same crosslinking conditions as in claim 1, the crosslinking treatment was performed with an irradiation dose of 100 kGy.

  Tables 7 and 8 show the evaluation results of the obtained films.

  The film of Comparative Example 1 was inferior in suitability for automatic packaging machines because it did not use an ethylene-vinyl acetate copolymer for the surface layer and its bottom sealing property was insufficient.

  The film of Comparative Example 2 was inferior in suitability for an automatic packaging machine because the amount of the ethylene-vinyl acetate copolymer in the surface layer was small and the bottom sealing property was insufficient.

  In the film of Comparative Example 3, the density of the ethylene-α-olefin random copolymer in the core layer is low, the shrinkage rate at 100 ° C. is too high, and the film shrinks due to heat at the bottom sealing, and the bottom sealing property Was not sufficient, the shrinkage at 100 ° C. was high, and tray cracking occurred.

  The film of Comparative Example 4 did not use the ethylene-α-olefin block copolymer of (B), resulting in poor deformation recovery after packaging. In addition, the films of Comparative Examples 5 to 8 had a high degree of crosslinking and insufficient bottom sealability.

  According to the present invention, container deformation and cracking at the time of packaging do not occur, the bottom sealing property is good, the deformation recovery property is excellent even after packaging, and it is possible to obtain a tight packaging body for low temperature shrinkable overlap packaging A film can be provided.

  DESCRIPTION OF SYMBOLS 1 ... Core layer (II), 2, 3 ... Both surface layers (I), 10 ... Cold shrinkable overlap packaging film.

Claims (3)

Both surface layers (I) containing 50% by mass or more of an ethylene-vinyl acetate copolymer;
20-90 mass% of ethylene-α-olefin random copolymer (A) having a density of 0.880-0.939 g / cm ^{3 and} an ethylene-α-olefin block copolymer having a melting peak temperature of 120 ° C. or lower. (B) is composed of at least three layers of 5 to 40% by mass and a core layer (II) containing 5 to 40% by mass of a polyolefin-based resin (C) having a melt tension at 190 ° C. of 60 to 200 mN ,
At least one layer is cross-linked,
A film for low-temperature shrinkable overlap packaging , wherein the gel fraction of the entire film is 3 to 50% by mass .   2. The low temperature according to claim 1, wherein the polyolefin resin (C) contains at least one selected from the group consisting of an ethylene vinyl acetate copolymer having a vinyl acetate content of 5 to 40% and a high-pressure low-density polyethylene. Shrinkable overlap packaging film. The film for low temperature shrinkable overlap packaging according to claim 1 or 2, wherein the heat shrinkage stress at 100 ° C is 250 g / cm ² or less.

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