JP2001001468A - Heat-shrinkable multilayered film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat-shrinkable multilayered film good in packaging machine aptitude and optical characteristics, having good heat seal characteristics to various heat seals such as fusion seal, surface seal or the like, reducing the deformation of content caused by the shrinkage of the film and especially excellent in heat sealability and packaging finish at the time of high speed packaging. SOLUTION: A heat-shrinkable multilayered film of three or more layers contains a surface layer (A) comprising linear low density polyethylene with a specific density and an inner layer (B) containing a mixed resin compsn. consisting of 50-90 wt.% of (a) linear low density polyethylene with a specific density, 5-40 wt.% of (b) high-pressure-processed low density polyethylene and 5-40 wt.% of (c) a copolymer such as an ethylene/vinyl acetate copolymer. In this case, this film has a specific gel ratio, a specific m.p. and specific heat shrinkage stress.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has good heat-sealing properties for various heat seals such as fusing seals and face seals.
The present invention also relates to a heat-shrinkable multilayer film which is less likely to deform its contents due to shrinkage of the film and is particularly excellent in heat-sealing properties and packaging finish during high-speed packaging.

[0002]

2. Description of the Related Art Conventionally, shrink wrapping (synonymous with shrink wrapping) is capable of rapidly and tightly packaging a plurality of products regardless of the shape and size of an object to be packaged, resulting in a package obtained. It is used for packaging foods and sundries because it has a beautiful appearance, exhibits a display effect, enhances product value, keeps the contents sanitary, and facilitates visual quality control. Such shrink wrapping is generally carried out by first wrapping the contents by heat sealing with a little room for the film, and then heat shrinking the film with hot air from a shrink tunnel, etc., and a tight and beautiful finish is obtained. . At this time, as a method of heat sealing, there are a bar sealing method, a hot roller method, a hot plate sealing method, a fusing sealing method, and the like. Here, the methods listed above are basically surface seals that are fusion-sealed between film surfaces, and are usually cut by a cutter almost simultaneously with heat sealing in the immediate vicinity of the seal surface, so-called seal-and-cut method, At the stage of primary packaging before shrinking, a method is employed in which the folded portion is heat-sealed with a hot plate in a state where the film is folded at the bottom of the article to be packaged (hereinafter, referred to as an overlap seal method). In addition, the above-mentioned fusing and sealing method does not require a separate cutter as in the above method, and is a method of instantaneously melting and cutting simultaneously with a melt seal by a hot blade, and widely used for various films for packaging as a simple method. Have been.

[0003] On the other hand, there are various types of primary packaging of the contents to be performed by appropriately using a heat sealing method before the film is thermally shrunk by hot air or the like in a shrink tunnel. There are packaging forms such as pillow packaging and stretch-like overlap packaging. What is important in any packaging form is that the integrity of the heat seal is maintained, the contents are not deformed, and a tight finish is obtained during shrinking and after the completion of the packaging including the heat sealing step. It is.

[0004] As described above, there are various packaging forms and heat sealing systems, and packaging is performed taking advantage of each feature. On the other hand, good packaging machine suitability and compatibility with various conditions as described above. It is desired to provide a film having excellent packaging finish.

In general, the properties required for a shrink wrapping film include shrinkage properties, heat sealing properties, optical properties, mechanical strength, and the like. Further, as the above-mentioned shrinkage characteristics, a suitable heat shrink force and high shrinkability for finishing tightly without deforming the packaged object and tightness are required. Thinner heat-sealing lines during sealing are preferred because they are more aesthetically pleasing.) Regarding good transparency and gloss of the film, especially after shrinkage, include the time of packaging and transportation and storage after packaging. It is required to have strength (tear, breakthrough, etc.) against various external loads. Until now, various studies have been made to provide a multilayer film that satisfies the above-mentioned required characteristics. Among such studies, there are many techniques relating to a multilayer film in which a polyethylene resin is disposed on a surface layer.

For example, JP-A-2-283445 discloses a resin having an olefin component and having a relatively low melting point (for example, ethylene vinyl acetate copolymer, ultra low density polyethylene, ethylene butyl acrylate copolymer). And a core layer composed of an ethylene methyl acrylate copolymer and an olefin component or polyester, and a resin having a relatively high melting point (eg, polyester, linear low-density polyethylene, low-density polyethylene, high-density polyethylene, Two outer layers comprising polypropylene and ethylene propylene copolymerized) having a maximum average transverse shrinkage of less than 300 pounds per square inch and a melting point at least about 10 ° C. higher than the melting point of the core layer material. A multilayer shrink film having is disclosed, the resulting film comprises: P because of the stomach contraction force and high free shrink
It also describes that packaging similar to that of a VC film can be performed and that no harmful odor or contaminating by-products are generated. JP-A-60-240451 discloses a crosslinked core layer containing a linear low-density polyethylene and a three-component blend of a linear low-density polyethylene, a linear medium-density polyethylene, and an ethylene-vinyl acetate copolymer. A shrink film comprising two cross-linked surface layers comprising:
It is described as having a new and improved combination of physical properties, such as high orientation or heat shrinkage, that is heat sealable and combined with good tear resistance with moderate elongation and elastic memory. JP-A-1-301251 discloses that the inner and outer layers and the intermediate layer have a density and a melt index (the same as the melt flow rate (hereinafter referred to as MFR) in the present invention) from the specified linear low-density polyethylene. A heat-shrinkable film in which the thickness ratio of the intermediate layer to all layers, and the thickness of the inner and outer layers is specified,
It describes that the low-temperature heat sealability is excellent.

[0007]

However, among the above prior arts, the heat shrinkable film obtained in JP-A-2-283445 can prevent the product to be packaged from being broken due to low shrinkage force. Difficult to seal,
In particular, there is a problem in the heat sealing property at the time of high-speed packaging. That is, in high-speed packaging (usually, a packaging speed of 50 packs / min or more), the heat sealing time itself is shortened, so that high-temperature heat sealing is employed. In such a case, the resin constituting the film is used. Due to the temperature characteristics of the surface seal, the core layer, that is, the inner layer, is softer and easier to melt than the outer layers, so that the heat seal portion of the film is fused to the seal bar, There is a problem that heat sealing failure such as heat seal breaking is likely to occur due to stretching. A crosslinked core layer comprising linear low-density polyethylene and a three-component blend of linear low-density polyethylene, linear medium-density polyethylene, and ethylene-vinyl acetate copolymer disclosed in JP-A-60-240451 are also disclosed. The shrink film comprising the two crosslinked surface layers comprises good tear resistance with moderate elongation and elastic memory, but the shrinkage stress of the heat shrink film is too high, In a series of flows in which the film is heat-sealed and shrink the film for tight packaging, the time from heat-sealing to entering the shrink tunnel during high-speed packaging is reduced, so the heat-sealed part is sufficient. When the film does not cool down, the contraction force of the film acts as a pulling force, so heat seal puncture is likely to occur, and at the same time, sheet materials such as notebooks and printing paper And it had a problem to be packaged will readily deform when included) for packaging those of bundles. Further, the film disclosed in JP-A-1-301251 is excellent in transparency and low-temperature heat sealability, but is inferior in heat resistance of the film because it is not subjected to a cross-linking treatment. There are restrictions on high-speed packaging, such as the seal temperature cannot be raised. Further, as in the case of the film disclosed in Japanese Patent Application Laid-Open No. 60-240451, the heat-shrinkable film has a high shrinkage stress, so that a heat-seal puncture is generated at the time of packaging, or the packaged object is easily deformed. Had a problem.

An object of the present invention is to provide a multilayer heat-shrinkable film in which a conventional polyolefin-based resin is disposed on a surface layer, in addition to excellent mechanical strength such as tear resistance and shrinkage properties, as well as disadvantages of the conventional film. Heat sealing properties, that is, good heat sealing properties for both fusing seals and face seals (stable heat sealing is possible, clean heat sealing is possible), especially excellent heat sealing properties at high speed packaging By providing a heat-shrinkable multi-layer film with good appearance finish including the heat-sealed part, it suppresses the deformation that has occurred when wrapping less rigid objects such as notebooks and printing paper. is there.

[0009]

Means for Solving the Problems The present inventors have made intensive studies to achieve the above object, and as a result, have reached the present invention. That is, the present invention provides a density of 0.900 to 0.940.
g / cm < ³ > linear low-density polyethylene-containing surface layer (A), and (a) a density of 0.900 to 0.940 g / cm3.
Linear low density polyethylene 50 to 90 wt% of ^3, (b)
From 5 to 40% by weight of high-pressure low-density polyethylene and from 5 to 40% by weight of (c) at least one copolymer selected from ethylene-vinyl acetate copolymer and ethylene-aliphatic unsaturated carboxylic acid ester copolymer. A multilayer film comprising at least three layers containing at least one internal layer (B) containing a mixed resin composition comprising:
The gel fraction of all layers of the film is 0.1 to 10% by weight,
The relationship between the gel fraction and the layer ratio of the surface layer (A) and the inner layer (B) satisfies the following formula (I), and the melting point of at least one resin used for the inner layer (B) is ), And the maximum equilibrium heat shrinkage stress of the film at 80 to 140 ° C. measured in accordance with ASTM D-2838 is 200 g / mm ² or less in both the longitudinal and transverse directions. 140 measured
A heat-shrinkable multilayer film characterized in that the film has a heat-shrinkage ratio of 30% or more in at least one direction in the vertical and horizontal directions. GB × TB ≧ GA × TA (I) (wherein, in the above formula (I), GA and GB are the gel fractions of the surface layer (A) and the inner layer (B), respectively, and TA, TB
Represents the thickness ratio of the surface layer (A) and the inner layer (B), respectively. Hereinafter, the present invention will be described in detail.

First, the present invention is different from the prior art in that a specific resin composition containing a specific linear low-density polyethylene as an inner layer (B) in a surface layer (A) containing the linear low-density polyethylene. Are combined, the relationship between the gel fraction and the layer ratio of the layers (A) and (B) is defined, and the gel fraction and the maximum equilibrium heat shrinkage stress of the whole film are specified. The role of the constituent elements of the present invention, which is different from the above-mentioned prior art, is that, in addition to excellent suitability for packaging machine and shrinkage characteristics, heat sealing property at the time of performing face sealing (hereinafter referred to as face sealing) has been a conventional problem. ), Heat-sealing performance at the time of performing fusing-sealing (hereinafter referred to as fusing-sealing property), and particularly, stable heat-sealing property in high-speed packaging can be sufficiently ensured. A good finish can be realized by suppressing the deformation.

The linear layer used in the surface layer (A) of the present invention
The density of polyethylene is 0.900 to 0.940 g /
cm^Threebelongs to. Here, the density referred to in the present invention is J
23 ° C value measured according to IS-K-7112.
You. Role of polyethylene resin used for surface layer (A)
Has stable face sealing and fusing sealing properties.
First, the film is given a so-called waist to make it suitable for high-speed packaging machines.
Is expressed. Wire used for surface layer (A)
Low density polyethylene having a density of 0.940 g / cm^ThreeTo
If it exceeds, the stability of the heat seal decreases, and
In addition to lowering the transparency of the film, it is difficult to obtain low-temperature shrinkage
Become. On the other hand, the density is 0.900 g / cm ^ThreeLess than
The film does not exhibit the stiffness and the film surface
Poor packaging machine suitability due to sticky surface, especially high-speed packaging
Can not be done. The preferred density is 0.905 to 0.93
5g / cm^Three, More preferably 0.910 to 0.930
g / cm^ThreeIt is.

The content of the linear low-density polyethylene in the surface layer (A) of the present invention is preferably at least 50% by weight or more, more preferably at least 70% by weight. An ethylene-vinyl acetate copolymer and a partially saponified product thereof within a range not impairing the effects of the present invention,
Ethylene-aliphatic unsaturated carboxylic acid ester copolymer,
Ionomer resin, high-pressure method polyethylene, low-pressure method high-density polyethylene, highly branched polyethylene polymer polymerized by a transition metal catalyst (degree of branching: 5 to 110 groups / 10
(00 carbon), crystalline 1,2-polybutadiene, and other resins such as petroleum resins such as hydrogenated polyterpene and copolymers of propylene with ethylene or butene-1.

The role of the linear low-density polyethylene in the inner layer (B) is to ensure stable stretchability during stretch film formation,
The purpose is to impart practically sufficient strength physical properties such as tear strength and puncture strength to the entire film. Further, like the linear low-density polyethylene used for the surface layer (A), it also has a role of expressing a firmness regarding the suitability for the packaging machine.

The density of the linear low-density polyethylene used for the inner layer (B) of the present invention is 0.900 to 0.940 g /
cm ³ . If the density exceeds 0.940 g / cm ³ , the stretching itself becomes difficult, the transparency of the obtained film is reduced, and the low-temperature shrinkage is also difficult to obtain. On the other hand, if the density is less than 0.900 g / cm ³ , a so-called stiffness of the film cannot be exhibited, and the suitability for a packaging machine is inferior. In particular, high-speed packaging cannot be performed. The preferred density is 0.905 to 0.93
5 g / cm ³ , more preferably 0.910 to 0.930
g / cm ³ . Further, those having a melt flow rate (MFR) of 0.2 to 7 g / 10 min measured under the conditions of 190 ° C. and 2.16 kgf (hereinafter, the same conditions for linear low density polyethylene) are preferable. When it exceeds 7 g / 10 minutes, the stretching stability is reduced, the film is easily broken at the time of stretching, and unevenness in thickness is easily caused, and even if the film is obtained, the mechanical strength such as tear strength and piercing strength is poor. May be obtained, which is not preferable depending on the application. On the other hand, if the MFR is less than 0.2 g / 10 minutes, there may be a problem that the extrusion power at the time of extrusion molding increases, and a problem that the extrusion power decreases and the extrusion efficiency decreases and the productivity decreases. A more preferred MFR is 0.5 to 5 g / 10 min, and still more preferably 0.6 to 4 g / min.
10 minutes.

The linear low-density polyethylene used for the surface layer (A) and the inner layer (B) is known as an ethylene α-olefin copolymer, and these are ethylene and propylene, butene-1, pentene. It is a copolymer with at least one monomer selected from α-olefins having 3 to 18 carbon atoms, such as -1,4-methyl-pentene-1, hexene-1, and octene-1. From the viewpoints of mechanical strength such as impact strength, tear strength, piercing strength and the like, and stretch film forming properties, 4-methyl-pentene is used as α-olefin.
1, pentene-1, hexene-1, and octene-1 are preferred.

As the above linear low-density polyethylene,
A polymer (MSC) obtained using a conventional multi-site catalyst such as a Ziegler catalyst, or a polymer (comonomer distribution or the like) polymerized by a single-site catalyst such as a metallocene catalyst, and a molecular weight distribution by a conventional method. A more homogenized product (SSC) than a polymerized product (for example, a value represented by weight average molecular weight Mw / number average molecular weight Mn of 1.5
To 4.0, more preferably 1.7 to 3.5), and a mixture of both may be used, and at least one of them is used. The linear low-density polyethylene polymerized with the single-site catalyst may have a controlled long-chain branch, or in addition to the α-olefin, a monomer having a polar group or a styrene-based monomer. Other monomers may be copolymerized.
The high-pressure low-density polyethylene in the inner layer (B) has a role of forming a main gel during the crosslinking treatment in the inner layer and a role of preventing a drawdown phenomenon.

High-pressure polyethylene has a characteristic that it is relatively easy to crosslink at a low electron beam irradiation density compared to linear low-density polyethylene, and the gel fraction of the film cross-linking component depends on the mixing ratio of the high-pressure low-density polyethylene. Can be adjusted. Further, because of the high melt tension (melt tension), which is a characteristic of the high-density low-density polyethylene resin, it also plays a role in improving the film-forming properties of the raw film. That is,
The resin that composes each layer is melted by each extruder, co-extrusion is performed from a multilayer die, and the resin is drawn down. The film is immediately quenched and solidified to obtain a raw film. The film has a role of preventing a phenomenon (a so-called drawdown phenomenon) in which the film is pulled down by gravity more than expected due to the weight of the film and causes uneven thickness in the length direction of the film.

The density of the high-pressure low-density polyethylene used for the inner layer (B) of the present invention is not particularly limited, but is usually 0.910 to 0.928 g / cm ³ . Here, the density is a value at 23 ° C. measured according to JIS-K-7112. If the density exceeds 0.928 g / cm ³ , stretching itself becomes difficult, the transparency of the obtained film is lowered, and the role of preventing the drawdown phenomenon is lowered. On the other hand, if the density is less than 0.910 g / cm ³ , the resin is too soft, causing a decrease in the rigidity of the film,
Due to the so-called lack of rigidity of the film, the sliding property of the film deteriorates, so that the suitability for the packaging machine is deteriorated, and high-speed packaging in particular becomes impossible. The preferred density is 0.912 to 0.926 g / c
m ³ , more preferably 0.914 to 0.924 g / cm
³

The MFR of the high-pressure method low-density polyethylene used for the inner layer (B) of the present invention is measured at 190 ° C. under a condition of 2.16 kgf (hereinafter, the same applies to the high-pressure method low-density polyethylene). Although not particularly limited, it is usually 0.2 to 7 g / 10 minutes. In addition, MFR is 7 g / 1.
Beyond 0 minutes, the role of preventing the drawdown phenomenon decreases,
In addition to easily causing uneven thickness, even if a film is obtained, only a film having poor mechanical strength such as tear strength or piercing strength may be obtained. If the MFR is less than 0.2 g / 10 minutes, there may be a problem that the extrusion power at the time of extrusion molding increases and a problem that the extrusion power decreases and the extrusion efficiency decreases and the productivity decreases. More preferred MFR
Is 0.3 to 6 g / 10 min, more preferably 0.4 to 5 g
/ 10 minutes.

The role of the ethylene-fatty acid ester copolymer in the inner layer (B) is mainly to play a role of fine adjustment of gel fraction generation in a very low irradiation level region at the time of crosslinking treatment and to prevent a drawdown phenomenon. is there. Ethylene-fatty acid ester copolymers are relatively easy to crosslink at a low electron beam irradiation density compared to high-pressure low-density polyethylene and linear low-density polyethylene due to the properties of the resin. It has the property of cross-linking more gently with respect to the irradiation ratio than low-density polyethylene (the role of mitigating the effects of external environmental changes such as temperature and humidity on stabilizing product quality). It plays a role of fine adjustment of gel fraction generation in the linear level region.

The ethylene-fatty acid ester copolymer used in the inner layer (B) of the present invention includes ethylene-vinyl acetate copolymer, ethylene-aliphatic unsaturated carboxylic acid (ethylene-acrylic acid copolymer, Ethylene-methacrylic acid copolymer) and ethylene-aliphatic unsaturated carboxylic ester (ethylene-acrylate, ethylene-
A methacrylic acid ester, and ester species selected from the components of C1 to C8 alcohols such as methyl, ethyl, propyl, and butyl). They are,
Further, a multi-component copolymer to which other components are added (for example, a free copolymer selected from ethylene, an aliphatic unsaturated carboxylic acid and the same ester, and the like) may be used. The components to be copolymerized may be at least two or more multi-component copolymers selected from the above or other components. The content of these carboxylic acid or carboxylic acid ester groups is not particularly limited, but usually 3 to 35% by weight. From the viewpoint of the transparency of the film, it is more preferably 3 to 25% by weight, and still more preferably 3 to 20% by weight.

The ethylene-fatty acid ester copolymer used in the inner layer (B) of the present invention has a temperature of 190 ° C. and 2.16 kg.
The MFR measured under the condition of f (hereinafter, the same conditions for the ethylene-fatty acid ester copolymer) is not particularly limited, but is usually 0.2 to 10 g / 10 min. If the MFR exceeds 10 g / 10 minutes, the role of preventing the drawdown phenomenon is reduced, and thickness unevenness may easily occur. If the MFR is less than 0.2 g / 10 minutes, there may be a problem that the extrusion power at the time of extrusion molding increases and a problem that the extrusion power decreases and the extrusion efficiency decreases and the productivity decreases. A more preferred MFR is 0.3 to 8 g / 10 min, still more preferably 0.5 to 6 g / min.
10 minutes.

In the present invention, the component ratio of the linear low-density polyethylene, the high-pressure low-density polyethylene and the ethylene-fatty acid ester copolymer in the inner layer (B) is defined as follows.
Produces a film of uniform thickness without drawing down, generates a gel component for stable stretching in the temperature range above the melting point, and further satisfies the heat sealing properties of the obtained film Fine adjustment of the production amount of fine gel fraction, and in the physical properties of the resulting film, tear strength,
This is for imparting strength to the film with respect to strength physical properties such as piercing strength and suitability for a packaging machine.

The component ratio in the inner layer (B) of the linear low-density polyethylene is 50 to 90% by weight. If the component ratio in the inner layer (B) is less than 50% by weight, practically sufficient strength physical properties such as tear strength and puncture strength cannot be imparted to the entire film, and furthermore, a firmness regarding packaging machine suitability is exhibited. May not be possible. If the component ratio in the inner layer (B) exceeds 90% by weight, it becomes difficult to exert the role of other component resins such as high-pressure low-density polyethylene and ethylene-fatty acid ester copolymer. Preferably it is 55 to 85% by weight, more preferably 65 to 80% by weight. The component ratio in the inner layer (B) of the high-pressure low-density polyethylene is 5 to 40% by weight. Inner layer (B)
If the component ratio is less than 5% by weight, unevenness in thickness due to drawdown occurs when the film is formed. In addition, there are few crosslinking points for stretching at a temperature equal to or higher than the melting point, and stable stretching is difficult. If the component ratio in the inner layer (B) exceeds 40% by weight, it becomes difficult to express the role of other component resins such as linear low-density polyethylene and ethylene-fatty acid ester copolymer. Preferably 10 to 40
%, More preferably 15 to 30% by weight. The component ratio in the inner layer (B) of the ethylene-fatty acid ester copolymer is 5 to 40% by weight. If the component ratio in the inner layer (B) is less than 5% by weight, fine adjustment of the gel fraction, which is a delicate balance between the fusing characteristics and the stretching characteristics, cannot be performed, and severe electron beam crosslinking control must be performed.
If the component ratio in the inner layer (B) exceeds 40% by weight, the role of other component resins such as linear low-density polyethylene and high-pressure low-density polyethylene becomes difficult to express. Preferably it is 5 to 35% by weight, more preferably 5 to 20% by weight.

In the present invention, the gel fraction of the entire heat-shrinkable film, the relationship between the gel fraction of the surface layer (A) and the inner layer (B) and the layer ratio, and the inner layer (B) are used. The purpose of defining the relationship between the melting point of the resin and the melting point of the linear low-density polyethylene resin used for the surface layer (A) is to enable stable face sealing and fusing sealing.
The multilayer film of the present invention needs to be crosslinked from the viewpoint of heat resistance during shrinkage and sealing, and the gel fraction of all layers of the film is 0.1 to 10% by weight, preferably 0.1 to 10% by weight. It is 5 to 10% by weight, more preferably 1 to 10% by weight. If the gel fraction of all layers of the film exceeds 10% by weight, it is stable in the face seal if the gel fraction of the resin used for the surface layer (A) is lower than that of the resin composition used for the inner layer (B). However, in the case of the fusing seal, it is impossible to stabilize the fusing by the existing packaging machine, and it is necessary to modify the heat sealing part. Particularly at the time of high-speed packaging, it is necessary to remodel the heat sealing part of the existing packaging machine, such as changing the heat capacity, and use a special packaging machine.

In the film of the present invention, even if the gel fraction of all layers is 0.1% by weight or more and 10% by weight or less, the relationship between the gel fraction of each layer and the layer ratio is expressed as GB × TB ≧ GA × TA (GA And GB are the gel fraction of the surface layer (A) and the inner layer (B), respectively, and TA and TB are the surface layer (A) and the inner layer (B), respectively.
And the relationship between the melting point of the resin used for the inner layer (B) and the melting point of the surface layer (A) is that at least one of the melting points of the resin used for the inner layer (B) is Unless the melting point is higher than the melting point of the surface layer (A), stable face sealing and fusing sealing become difficult. For example, the layer ratio of the surface layer (A) and the thickness ratio of the inner layer (B) are equal, and the gel fraction of the resin used for the surface layer (A) is higher than that of the resin composition used for the inner layer (B). If high, the orientation of the surface layer is higher than the orientation of the inner layer, the radiant heat emitted from the hot blade before the hot blade and the film come into contact, the film begins to shrink, so the film will be rounded, Effective face sealing becomes difficult. When the melting point of the linear low-density polyethylene resin used for the surface layer (A) is higher than the melting point of any resin used for the inner layer (B), the inner layer softens and melts as compared with the surface layer. Therefore, there is a problem that the heat seal portion of the film is fused to the seal bar, or the heat seal portion is stretched at the time of sealing and cutting, so that a heat seal failure such as breakage of the heat seal easily occurs. Surface layer (A)
And gel fractions GA and GB in each layer of the inner layer (B)
Is preferably at most 70% by weight. If the gel fraction in each layer exceeds 70% by weight, it may be necessary to change the heat capacity or to modify the heat seal part of the existing packaging machine. It is preferably at most 60% by weight, more preferably at most 50% by weight. The thickness ratios TA and TB of the respective layers refer to the ratio of the total thickness of the surface layer (A) and the total thickness of the inner layer (B) when the thickness of all the layers is 1.

In the multilayer film of the present invention, it is sufficient that at least one surface layer, which is a sealing surface, satisfies the above-described requirements. desirable. The multilayer film of the present invention has a heat shrinkage at 140 ° C. of at least 30 in at least one direction in the vertical and horizontal directions in order to sufficiently perform tight packaging during shrink packaging.
% Or more. If the multilayer film has a heat shrinkage at 140 ° C. of less than 30% in at least one of the vertical and horizontal directions, the shrinkage is poor, and it is difficult to obtain a tightly wrapped package at the time of shrink wrapping. You can only get something with. More preferred heat shrinkage is 140 ° C
Has a heat shrinkage of 3 in at least one direction in the vertical and horizontal directions.
It is at least 5%, more preferably at least 40%.

In the multilayer film of the present invention, when the object to be packaged is weak in rigidity during shrink wrapping (for example, sheets such as notebooks and printed matter and bundles thereof), the shrinkage stress of the film causes , Easily deforms sleds,
From the viewpoint of preventing the packaged item from being damaged, AS
The maximum equilibrium heat shrinkage stress at 80 to 140 ° C. measured by TM D-2838 is 200 g in both the longitudinal and transverse directions.
/ Mm ² or less. If the equilibrium heat shrinkage stress of the multilayer film exceeds 200 g / mm ^{2 in} both the vertical and horizontal directions, the shrinkage stress of the film easily causes warpage or other deformation or breaks the packaged object. Preferably, the maximum equilibrium heat shrinkage stress is 190 g / mm ² or less in both the vertical and horizontal directions, and more preferably, the maximum equilibrium heat shrinkage stress is 180 g / mm ² or less in both the vertical and horizontal directions.

In the multilayer film of the present invention, the surface layer (A) and the inner layer (B) each contain at least 50% by weight, preferably 40% by weight, of one or more other resins within a range that does not impair the original properties. %, More preferably 30% by weight or less. Other resins are not particularly limited, for example, ethylene-vinyl acetate copolymer and its partially saponified product, ethylene-aliphatic unsaturated carboxylic acid ester copolymer, ionomer resin, high-pressure low-density polyethylene,
Low-pressure high-density polyethylene, highly branched ethylene polymer polymerized by a transition metal catalyst (branching degree: 5 to 110)
Group / 1000 carbons), a styrene-conjugated diene copolymer (block, random) and a product obtained by hydrogenating at least a part of the copolymer, a product obtained by modifying these resins by acid modification, and the like. , 2-polybutadiene, petroleum resins such as hydrogenated polydicyclopentadiene and hydrogenated polyterpene, and resins used in layers other than the layer to be mixed.

Similarly, a plasticizer, an antioxidant, a surfactant, an ultraviolet absorber, an inorganic filler, and the like are added to the surface layer (A) and the inner layer (B) of the present invention within a range that does not impair the original characteristics. It may contain an antifogging agent, an antistatic agent, an antiblocking agent, a lubricant, a crystal nucleating agent, a coloring agent, and the like.As a method of adding to the resin, knead and add directly to the target resin layer, or optionally prepare a master batch in advance. It may be prepared and diluted and added.

The multilayer film of the present invention comprises a total of at least three layers of the surface layer (A) and the inner layer (B). In some cases, a resin layer using the same resin as the surface layer (A) may be used. It may be added as a layer. As the arrangement of the layers, for example, in the case of three layers: A / B / A, in the case of five layers: A
/ B / A / B / A and the like. In addition, the case of six layers or more is included. In the film of the present invention, in addition to resins usable for the surface layer (A) and the inner layer (B) of the present invention, as well as known thermoplastic resins, as long as the effects of the present invention are not impaired. Another layer made of resin may be provided. In this additional layer, as a recovery layer,
A mixed composition layer composed of a resin used for each layer of the film is also included.

The thickness of the heat-shrinkable multilayer film of the present invention is not particularly limited, but is usually 5 to 80 μm, preferably 6 to 80 μm.
It is a thin region of 60 μm, more preferably 7 to 40 μm. If it is less than 5 μm, the stiffness of the film may be reduced, and the heat sealing strength may also be reduced. In addition, there may be a problem in workability at the time of packaging. In addition, when the thickness exceeds 80 μm, the stiffness of the film becomes too strong, and the fitting property deteriorates.
Responsiveness of shrinkage may be poor, or performance such as mechanical strength may be excessive.

Next, an example of a method for producing the heat shrinkable multilayer film of the present invention will be described. First, each layer (surface layer (A),
The resin constituting the inner layer (B) and other layers used as necessary) is melted by each extruder, and co-extruded and quenched and solidified by a multilayer die to obtain a raw film. As the extrusion method, a multi-layer T-die method, a multi-layer circular method, or the like can be used, and the latter is preferable. The film raw material thus obtained is subjected to a resin cross-linking treatment by electron beam irradiation, and subsequently, the film raw material is heated to a temperature equal to or higher than the melting point of the resin by heat transfer heating using hot air or radiation heating such as an infrastructure heater. While stretching the raw film in the machine flow direction at a speed ratio between two sets of nip rolls, air is injected into the raw film and also stretched in a direction perpendicular to the machine flow direction. Examples of the stretching method include a roll stretching method, a tenter method, an inflation method (including a double bubble method), and a method in which a film is formed by simultaneous biaxial stretching is more preferable than the stretchability and other rationality. Stretching is performed in at least one direction in an area stretching ratio of 4 to 81 times, preferably 6 to 6 times.
The film is stretched at 4 times, more preferably at 8 to 49 times, and is appropriately selected depending on the required heat shrinkage ratio and the like depending on the application. If necessary, post-processing, for example, heat setting for dimensional stability, surface treatment such as corona treatment or plasma treatment, printing treatment, lamination with other types of films, etc. may be performed. The crosslinking treatment is performed using an electron beam (for example, an acceleration voltage of
A conventionally known method such as irradiation with an energy beam of 1000 kV), irradiation of energy rays such as ultraviolet rays and γ rays, and use of a peroxide are used. For example, irradiation with an electron beam varies depending on the type of resin, but usually 1 to 4 Mrad is preferable for the packaging film used in the present invention. The reason why the raw film after the cross-linking treatment is heated to the melting point of the resin or higher is to adjust the heat shrinkage stress of the stretched film so as not to deform the packaged object at the time of packaging. Stretching below the melting point of the resin causes deformation or breakage of the packaged object. In order to stably perform stretching at or above the melting point of the resin, a crosslinking treatment is required. Without cross-linking treatment, the tension of the raw film before stretching is extremely reduced, making stretching difficult.

[0034]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present description will be described in more detail with reference to embodiments. The measurement and evaluation method used in the present invention is as follows. (1) Optical properties (haze, gloss) Haze is ASTM-D-1003, and gloss is ASTM-
The measurement was performed according to each of D-2457. (2) Thermal shrinkage rate A 100 mm square film sample was placed in an air oven type constant temperature bath set at 140 ° C.
After 0 minute treatment, the shrinkage of the film was determined, and the value obtained by dividing by the original dimension was expressed as a percentage. The measurement was performed in the vertical direction (M
D) and in the transverse direction (TD).

(3) Fusing Sealability (3-1) Fusing Seal Starting Temperature TP701 Heat Seal Tester manufactured by Tester Sangyo Co., Ltd.
A fusing blade of mR × 280 mmL was attached, and fusing sealing was performed by changing the temperature in various manners under the conditions of an air pressure of 3 kg / cm ² (air cylinder diameter: 50 mmφ) and a heat sealing time of 1 second. At this time, the temperature at the tip of the fusing blade was actually measured with a contact-type thermometer, and the measured value was used as a value for each temperature condition. The above-mentioned test was performed with each of the measurement films in a state of being folded in two and being overlapped with each other with a width dimension having a margin for the fusing blade, and the minimum of 90% or more (252 mm or more) of the fusing blade was blown. The temperature was defined as the fusing seal starting temperature. It should be noted that the lower the fusing seal starting temperature, the more suitable for high-speed packaging conditions, and is also preferable from the viewpoint of energy saving.

(3-2) Finishing of the fusing seal For the fusing seal that is about 10 ° C. higher than the starting temperature of the fusing seal specified in (3-1) above, the finishing of the fusing seal is based on the following criteria. evaluated. ：: The heat seal is complete and has no defects, and there is almost no stringing and the finish of the melted surface is clean. Δ: Heat sealing is almost complete, but slight stringing is observed, and there is a slight problem in productability. X: A state in which obvious stringing is seen in several places, or a heat seal portion has a heat seal defect such as a local opening, and there is a problem as a product.

(4) Surface Sealability (4-1) Surface Seal Start Temperature The surface seal start temperature was measured using an actual tray and simulating a push-up type packaging machine. A film is bent into a tubular shape along the vertical direction of a commercially available polypropylene tray (approximate dimensions: vertical 150 mm, horizontal 115 mm, height 23 mm) having a metal plate of 100 g adhered to the inner bottom, and both ends are formed with this film. Wrap the tray so that about half the area at the bottom of the tray overlaps without dubbing the film, and then do not dub both ends of the remaining film without being bent along the horizontal direction of the tray And folded at the bottom of the tray. At this time,
At the bottom of the tray, two or five layers are formed. The tray thus prepared was placed on a hot plate for 2 seconds to seal the bottom of the tray. The temperature at this time was measured on a hot plate with a contact-type thermometer, and the measured value was used as a value for each temperature condition. Thereafter, the heat-sealed end of the film was lightly pulled, and the temperature at which the film did not peel was defined as the surface sealing start temperature. In addition,
The lower the face seal starting temperature, the more suitable for high-speed packaging conditions, and it is also preferable from the viewpoint of energy saving.

(4-2) Finish of Face Seal The temperature of the face seal starting temperature specified in (4-1) above is about 1
The surface seal finished at 0 ° C. higher temperature was evaluated for the finish of the surface seal according to the following criteria. ：: The face seal on the bottom of the tray was completely heat-sealed for both the two sheets and the five sheets, no defects were observed, and the finish of the face seal was clean. Δ: The surface seal on the bottom of the tray is almost complete, but slightly
The sheet part is easily peeled off and the two parts are slightly whitened. A state where there is a problem with the merchantability. ×: A state in which the film was melted and a hole was formed in the case where two face seals were formed on the bottom of the tray, and the face seal was not clearly sealed in the case of five face seals. There is a problem with the merchantability.

(5) Tear strength According to JIS-P-8116, using a light load tear tester (manufactured by Toyo Seiki), the longitudinal direction (MD) and the transverse direction (TD) are used.
It measured about each. In addition, although the reading of the measured value here is performed so that it may fall in the range of 20 to 60 on the scale, when there is a difference depending on the measurement range, the higher value is measured. (6) Maximum equilibrium heat shrinkage stress The equilibrium heat shrinkage stress of the heat shrinkable film is ASTM D-2.
It was measured according to 838. Equilibrium heat shrinkage stress is 80-1
It is the value of the shrinkage stress after 60 seconds from the start of the measurement time at 40 ° C., and the maximum equilibrium heat shrinkage stress is the maximum value of the equilibrium heat shrinkage stress measured from 80 ° C. to 20 ° C.

(7) Gel fraction of all layers of the film, surface layer (A), and inner layer (B) The gel fraction (% by weight) of the entire layer of the film was determined by using a sample in p-xylene obtained by boiling all the layers of the film. (12 hours)
The ratio to the insoluble portion was calculated. This value was used as a measure of the degree of crosslinking.

Gel fraction (% by weight) = (sample weight after extraction / sample weight before extraction) × 100 Gel fraction GA (% by weight) of surface layer (A) and gel fraction GB of inner layer (B) (% By weight) was 14
Put in an air oven type thermostat set at 0 ° C., shrink freely, cut out the film of each layer in a state where the film thickness is increased, and in the boiling p-xylene, as in the gel fraction measurement of all the film layers The sample was extracted by and the ratio to the insoluble portion was calculated.

(8) Melting point 6 to 8 mg of the measurement data was collected and packed in an aluminum pan, and was subjected to a DSC method using a differential scanning calorimeter (DSC-7) manufactured by Perkin Elmer Co. under a nitrogen gas flow at 10 ° C. Once the temperature is raised to 200 ° C at a heating rate of 1 minute and held for 1 minute,
It was cooled again to 0 ° C. at a rate of 10 ° C./min. Thereafter, the temperature was maintained at 0 ° C. for 1 minute, and the temperature was raised again at a rate of 10 ° C./min for measurement, and the highest endothermic peak at that time was taken as the melting point.

(9) Suitability for high-speed packaging Using a FP-280 universal automatic packaging machine manufactured by Ibaraki Seiki Co., Ltd., a rectangular parallelepiped wooden piece (approximate dimensions: 150 × 100 × 35 m)
m) was packed at a packing speed of 60 packs / min for 2 minutes, for a total of 120 pieces. The used packaging machine employs, as a heat sealing method, a face seal using a hot roller method at a center seal portion, and then a fusing seal at a cutter seal portion, and the following evaluation was made. The shrinkage was performed by passing the package through a hot air shrink tunnel in about 5 seconds. In addition, appropriate conditions were changed so that the temperature of each heat seal portion and the hot air at the time of shrinkage became the optimum conditions of each film. ◎: There is no running trouble of the film due to fusion or adhesion at each heat seal part during packaging, and there is no defect such as breakage at each heat seal part even in the package after shrinking, and the appearance of each heat seal part is good. Good productability. ○: There is no running trouble of the film due to fusion or adhesion at each heat seal part during packaging, and even after shrinkage, there are no defects such as tears in each heat seal part, but more than half of the packages are blown and sealed. In the portion, there is a partial defect (whitening or a very small partial heat sealing defect) in the threading surface seal portion, and the appearance defect is slightly recognized. However,
An acceptable range of merchantability. Δ: Fusion and adhesion of the film to the sealer were observed in each heat-sealed portion during packaging, and the running property of the film was unstable. In addition, most packages after shrinking have stringing at the fusing seal portion and poor heat sealing at the surface seal portion, and have poor appearance or have a defective portion such as a tear in the heat seal portion of the package. Things are
1 to 10 are allowed. ×: Trouble due to fusion and adhesion of the film to the sealer occurred at each heat seal portion of the package, making it difficult to run the film continuously. Alternatively, in the package after shrinking, 11 or more defects having a defect such as tear in the heat seal portion are observed.

(10) Sectional Layer Structure (Ratio of Each Layer Thickness) A 100 mm square film sample was placed in a silicon oil thermostat set at 140 ° C. and shrink-treated by free shrinkage. (OLYMPUS OPTIC with photography function PM-10AK
AL CO. , LTD. MODEL CHT). The notation is expressed as a percentage by dividing the thickness of each layer by the thickness of the entire film, and the notation is expressed as:
It was described in the order of the inner layer (B) / the outer layer (A). When the thickness of all the layers is 1, the ratio of the total thickness of the surface layer (A) is TA, and the ratio of the total thickness of the inner layer (B) is TB.
And

Next, the resins used in Examples and Comparative Examples are described below. LL1: Linear low density polyethylene (MFR (190 ° C.,
2.16 kgf) = 1.0 g / 10 min, density = 0.91
2 g / cm ³ , α-olefin = octene-1: MS
C), melting point = 121 ° C. LL2: Linear low density polyethylene (MFR (190 ° C.,
2.16 kgf) = 2.0 g / 10 min, density = 0.92
6 g / cm ³ , α-olefin = octene-1: MS
C), melting point = 123 ° C. LL3: Linear low density polyethylene (MFR (190 ° C.,
2.16 kgf) = 1.8 g / 10 min, density = 0.92
1 g / cm ³ , α-olefin = hexene-1: SS
C), melting point = 119 ° C. LL4: Linear low density polyethylene (MFR (190 ° C.,
2.16 kgf) = 2.0 g / 10 min, density = 0.91
2 g / cm ³ , α-olefin = hexene-1: MS
C), melting point = 121 ° C. LL5: Linear low density polyethylene (MFR (190 ° C.,
2.16 kgf) = 1.7 g / 10 min, density = 0.92
8 g / cm ³ , α-olefin = hexene-1: SS
C), melting point = 121 ° C. LL6: Linear low density polyethylene (MFR (190 ° C.,
2.16 kgf) = 0.5 g / 10 min, density = 0.92
6 g / cm ³ , α-olefin = hexene-1: MS
C), melting point = 124 ° C. LL7: Linear low density polyethylene (MFR (190 ° C.,
2.16 kgf) = 4.0 g / 10 min, density = 0.91
6 g / cm ³ , α-olefin = octene-1: MS
C), melting point = 123 ° C. LL8: Linear low density polyethylene (MFR (190 ° C.,
2.16 kgf) = 0.5 g / 10 min, density = 0.86
8 g / cm ³ , α-olefin = octene-1: SS
C), melting point = 55 ° C. LL9: Linear low density polyethylene (MFR (190 ° C.,
2.16 kgf) = 2.5 g / 10 min, density = 0.94
1 g / cm ³ , α-olefin = octene-1: SS
C), melting point = 127 ° C. LL10: Linear low density polyethylene (MFR (190
° C, 2.16 kgf) = 1.0 g / 10 min, density = 0.
885 g / cm ³ , α-olefin = octene-1: S
SC), melting point = 91 ° C. LL11: Linear low density polyethylene (MFR (190
° C, 2.16 kgf) = 1.0 g / 10 min, density = 0.
920 g / cm ³ , α-olefin = octene-1: M
SC), melting point = 122 ° C. LL12: Linear low density polyethylene (MFR (190
° C, 2.16 kgf) = 2.5 g / 10 min, density = 0.
935 g / cm ³ , α-olefin = octene-1: M
SC), melting point = 125 ° C. LL13: Linear low density polyethylene (MFR (190
° C, 2.16 kgf) = 1.0 g / 10 min, density = 0.
890 g / cm ³ α-olefin = hexene-1: MS
C), melting point = 116 ° C. LL14: Linear low density polyethylene (MFR (190
° C, 2.16 kgf) = 2.0 g / 10 min, density = 0.
920 g / cm ³ , α-olefin = octene-1: M
SC), melting point = 123 ° C. LD1: high-pressure low-density polyethylene (MFR (190
° C, 2.16 kgf) = 0.4 g / 10 min, density = 0.
920 g / cm ³ ), melting point = 110 ° C. LD2: high-pressure low-density polyethylene (MFR (190
° C, 2.16 kgf) = 3.0 g / 10 min, density = 0.
922 g / cm ³ ), melting point = 112 ° C. EVA1: ethylene-vinyl acetate copolymer (MFR (1
90 ° C., 2.16 kgf) = 1.0 g / 10 min, density =
0.935 g / cm ³ , comonomer content = 15%),
Melting point = 94 ° C. EVA2: Ethylene-vinyl acetate copolymer (MFR (1
90 ° C., 2.16 kgf) = 5.5 g / 10 min, density =
0.930 g / cm ³ , comonomer content = 6%), melting point = 109 ° C. EVA3: ethylene-vinyl acetate copolymer (MFR (1
90 ° C., 2.16 kgf) = 1.0 g / 10 min, density =
0.924 g / cm ³ , comonomer content = 3.5
%), Melting point = 115 ° C.

[0046]

EXAMPLE 1 Linear low-density polyethylene (LL1) was used as the surface layer (A), 70% by weight of (a) linear low-density polyethylene (LL2) was used as the inner layer (B), and (b) Using a mixed resin composition consisting of 20% by weight of polyethylene (LD1) and 10% by weight of (c) ethylene-vinyl acetate copolymer (EVA1), a 32 mm extruder (L
/ D = 22) Using a 40 mm extruder (L / D = 24), melt extruded from an annular die into three layers consisting of two surface layers and one internal layer (extrusion rate 20 kg).
/ H). Immediately after that, the molten extrudate was quenched and solidified with cold water to form a tubular raw material having a uniform thickness accuracy of each layer having a folding width of 200 mm and a thickness of 540 μm. At that time, the thickness ratio (%) of each layer was 15/70 /
It was adjusted to be 15. The surface layer (A) includes
0.25% by weight of finely ground feldspar (average particle size: 4.5 μm: Shiroishi Kogyo “Minex7”) as antiblocking agent, 1.0% by weight of erucamide as lubricant, and glycerin monostearate 1 as antistatic agent 0.0% by weight was added. The obtained tubular raw material is irradiated with an electron beam accelerated at an accelerating voltage of 500 KV by 2 to 3 Mrad, cross-linking treatment is performed, and then radiant heating by an infra heater is performed to heat the tubular raw material to a melting point or more, According to the speed ratio of two pairs of differential nip rolls, the machine flow direction (M
By injecting air into the tube-shaped raw material 6 times in D), the film is simultaneously biaxially stretched 6 times in the direction perpendicular to the machine flow direction (TD), and cool air is applied to the bubble formed by the air ring. The stretching was cooled and fixed to obtain a multilayer film having a thickness of 15 μm. The obtained film was evaluated by the above method. Table 1 shows the results.

As is clear from Table 1, the obtained film was excellent in both face sealing property and fusing sealing property, and had excellent suitability for high-speed packaging. In addition, because of its high shrinkability and low maximum equilibrium heat shrinkage stress, it not only showed a finished package, but also had excellent physical properties such as optical properties and tear strength.

[0048]

Example 2 A film was obtained in the same manner as in Example 1 except that the linear low-density polyethylene used for the surface layer (A) was changed to LL3. Table 1 shows the layer structure of the film and the evaluation results. As in Example 1, all of the obtained films were excellent in face sealability and fusing sealability, suitable for high-speed packaging, high in shrinkage, and excellent in physical properties such as optical properties and tear strength. Was.

[0049]

Examples 3 to 5 The composition of the resin mixed layer used for the inner layer (B) was as follows: Example 3 (a) 80% by weight of linear low density polyethylene (LL2); LD1) 10% by weight, (c) ethylene-vinyl acetate copolymer (EVA1) 10% by weight, as Example 4, (a) 55% by weight of linear low density polyethylene (LL2),
(B) 10% by weight of high-pressure low-density polyethylene (LD1), (c) ethylene-vinyl acetate copolymer (EVA1)
35% by weight, (a) 55% by weight of linear low-density polyethylene (LL2), (b) 35% by weight of high-pressure low-density polyethylene (LD1), and (c) ethylene-vinyl acetate copolymer (EVA1) ) A film was obtained in the same manner as in Example 1 except that the amount was changed to 10% by weight. Table 1 shows the layer structure of the film and the evaluation results. As in Example 1, all of the obtained films were excellent in face sealability and fusing sealability, suitable for high-speed packaging, high in shrinkage, and excellent in physical properties such as optical properties and tear strength. Was.

[0050]

Examples 6 and 7 The linear low density polyethylene LL2 used for the inner layer (B) is LL4 in Example 6, and L in Example 7 is L.
A film was obtained in the same manner as in Example 1 except that the film was changed to L5. Table 2 shows the layer structure of the film and the evaluation results. As in Example 1, all of the obtained films were excellent in face sealability and fusing sealability, suitable for high-speed packaging, high in shrinkage, and excellent in physical properties such as optical properties and tear strength. Was.

[0051]

Examples 8 to 9 The linear low-density polyethylene LL2 used for the inner layer (B) is LL6 in Example 8, and L in Example 9 is L.
A film was obtained in the same manner as in Example 1 except that the film was changed to L7. Table 2 shows the layer structure of the film and the evaluation results. As in Example 1, all of the obtained films were excellent in face sealability and fusing sealability, suitable for high-speed packaging, high in shrinkage, and excellent in physical properties such as optical properties and tear strength. Was.

[0052]

Example 10 Example 1 was repeated except that the high pressure method low density polyethylene LD1 used for the inner layer (B) was changed to LD2.
A film was obtained in the same manner as described above, and this was designated as Example 10. Table 2 shows the layer structure of the film and the evaluation results.
As in Example 1, all of the obtained films were excellent in face sealability and fusing sealability, suitable for high-speed packaging, high in shrinkage, and excellent in physical properties such as optical properties and tear strength. Was.

[0053]

Example 11 A film was obtained in the same manner as in Example 1, except that the ethylene-fatty acid ester copolymer EVA1 used for the inner layer (B) was changed to EVA2. Table 3 shows the layer structure of the film and the evaluation results. As in Example 1, all of the obtained films were excellent in face sealability and fusing sealability, suitable for high-speed packaging, high in shrinkage, and excellent in physical properties such as optical properties and tear strength. Was.

[0054]

Embodiments 12 and 13 The thickness of a tubular raw material was measured in Embodiment 1.
Sample No. 2 was adjusted to 290 μm, and Example 13 was adjusted to 900 μm. Similarly, a film was obtained in the same manner as in Example 1 except that the thickness of the obtained film was changed to 8 μm for Example 12 and 25 μm for Example 13. Table 3 shows the evaluation results of the obtained films. The obtained films are all excellent in face sealability and fusing sealability, and have high-speed packaging suitability.
It was also excellent in physical properties such as shrinkage and optical properties.

[0055]

Examples 14 and 15: Surface layer (A) and internal layer (B)
In Example 14, the layer composition ratio (%) A / B / A =
7.5 / 85 / 7.5, Example 15 shows the layer composition ratio (%) A
A film was obtained in the same manner as in Example 1, except that / B / A was changed to 25/50/25. Table 3 shows the evaluation results of the obtained films. The obtained film was excellent in face sealability and fusing sealability as in Example 1, and suitable for high-speed packaging, and also excellent in physical properties such as high shrinkage, optical properties and tear strength.

[0056]

Examples 16 and 17 Except that the type of the additive added to the surface layer (A) was changed, a tubular raw material having the same layer constitution and layer ratio as in Example 1 was produced, and the same procedure was followed. A film was obtained. In Example 16, a finely ground feldspar product (average particle size: 4.5 μm: Shiraishi Kogyo “Minex”) was used for the surface layer (A).
7 ") 0.25% by weight, erucamide 1.0% by weight
And an antistatic agent which is a mixture of glycerin fatty acid ester and alkyldiethanolamide (Toho Chemical "CB-2
74 ") 1% by weight, and similarly to Example 17, 1.5% by weight of a mixture of glycerin monooleate and diglycerin laurate in a weight ratio of 2: 1 was added. Table 4 shows the evaluation results of the obtained films. The obtained film is excellent in face sealing property and fusing sealing property as in Example 1, has high-speed packaging suitability, high shrinkage,
It was also excellent in physical properties such as optical properties and tear strength. The film obtained in Example 17 had excellent antifogging properties. (As an evaluation of anti-fog properties, cover the top open container filled with water at 20 ° C with a film and then store it in a refrigerated showcase at 5 ° C to observe the state of water droplets on the film surface. , The one with no water drop and good transparency has excellent anti-fog properties.)

[0057]

Example 18 The linear low-density polyethylene used for the surface layer (A) was LL1 (87.98% by weight) + LD1 (9.
A film was obtained in the same manner as in Example 1 except that the mixing system was changed to 77% by weight. Table 4 shows the layer structure of the film and the evaluation results. As in Example 1, all of the obtained films were excellent in face sealability and fusing sealability, suitable for high-speed packaging, high in shrinkage, and excellent in physical properties such as optical properties and tear strength. Was.

[0058]

Comparative Examples 1 to 3 Using the resin used for the inner layer (B), only each resin ratio was replaced with a resin ratio outside the scope of the present invention. Comparative Example 1 was (a) 40% by weight of linear low-density polyethylene (LL2), (b) 35% by weight of high-pressure low-density polyethylene (LD1), and (c) 25% by weight of ethylene-vinyl acetate copolymer (EVA1). Comparative Example 2 was (a) 70% by weight of linear low density polyethylene (LL2),
(B) 3% by weight of high-pressure low-density polyethylene (LD1),
(C) Ethylene-vinyl acetate copolymer (EVA1) 27
Comparative Example 3 shows (a) a linear low-density polyethylene (L
L2) 75% by weight, (b) high-pressure method low-density polyethylene (LD1) 22% by weight, (c) ethylene-vinyl acetate copolymer (EVA1) 3% by weight, except that the method was the same as that in Example 1. In Comparative Examples 1 to 3, a film was obtained.
And In Comparative Example 1, the resin ratio of the linear low-density polyethylene used for the inner layer (B) was out of the range of the present invention, and in Comparative Example 2, the resin ratio of the high-pressure method low-density polyethylene was also out of the range of the present invention. In Comparative Example 3, the resin ratio of the ethylene-vinyl acetate copolymer was also out of the range of the present invention.

Table 4 shows the layer structure of the film and the evaluation results.
And Table 5. The film obtained in Comparative Example 1 was not flexible, had poor sliding properties, was poor in packaging machine suitability, and was difficult to package at high speed. In addition, strength physical properties such as tear strength and piercing strength were poor. In Comparative Example 2, the drawdown was intense when forming the raw film, and the thickness of the raw film was uneven, making it difficult to form a stable film. Further, the whole film was whitish and slightly inferior in optical characteristics. In Comparative Example 3, fine adjustment of the gel fraction was difficult, and severe electron beam crosslinking control was required, and it was difficult to form a sample having a low gel fraction. The fusing sealing property was measured on the film obtained by barely obtaining, but the film had a slightly high gel content due to insufficient fine adjustment of the gel fraction, and was a film having poor fusing characteristics.

[0060]

Comparative Examples 4 and 5 The linear low-density polyethylene LL2 used for the inner layer (B) was outside the technical scope of the present invention.
A film was obtained in the same manner as in Example 1 except that the film was changed to 8, LL9, and Comparative Examples 4 to 5 were obtained. LL8 used in Comparative Example 4 is the density of the linear low-density polyethylene used for the inner layer (B), the melting point of the resin used for the surface layer (A), and the melting point of the resin used for the inner layer (B). The relationship is out of the technical range of the present invention, and the density of the linear low-density polyethylene used in the inner layer (B) of LL9 used in Comparative Example 5 is out of the range of the present invention.

Table 5 shows the layer structure of the film and the evaluation results.
Shown in The film obtained in Comparative Example 4 could not exhibit the so-called stiffness of the film, was poor in suitability for a packaging machine, and was particularly difficult to package at high speed. In the film of Comparative Example 5, stretching itself became difficult, and stable film formation was difficult. The barely obtained film has excellent so-called waist sliding properties,
Although the film was suitable for high-speed packaging, it was whitish, poor in transparency, and poor in low-temperature shrinkage. Further, in the film obtained in Comparative Example 4, the inner layer was softened and melted more easily than the surface layer in the surface sealing property, and the heat-sealed portion of the film was fused to the seal bar, or the heat-sealed portion was sealed and cut at the time of cutting. It was easy to cause heat seal failure such as heat seal breakage due to stretching. Further, the film tended to be rounded by the heat of the fusing blade, so that an effective face sealing could not be performed.

[0062]

Comparative Example 6 A film was obtained in the same manner as in Example 1 except that the resin used for the surface layer (A) was changed to LL10, which is outside the scope of the present invention. .
Table 5 shows the layer structure of the film and the evaluation results. The film obtained in Comparative Example 6 could not exhibit the so-called stiffness of the film, was inferior in packaging machine suitability, and could not be particularly packaged at high speed.

[0063]

Comparative Example 7 A film was obtained in the same manner as in Example 1 except that the resin used for the surface layer (A) and the inner layer (B) was not stretched but stretched at a temperature equal to or lower than the melting point of the resin. Was designated as Comparative Example 7. The stretching temperature is closely related to the orientation of the film, that is, the heat shrinking force, and the purpose of making the stretching temperature below the melting point is to make the value of the maximum equilibrium heat shrinkage stress of the film larger than that of the film stretched at the temperature above the melting point. That is the purpose.

Table 5 shows the layer structure of the film and the evaluation results.
Shown in Each of the obtained films was excellent in physical properties such as optical properties and tear strength as in Example 1. However, since the value of the maximum equilibrium heat shrinkage stress of the film was large, the packaging was not performed during high-speed packaging. After heat sealing with a machine, the time required to enter the shrink tunnel was shortened, and a large shrinkage stress due to film shrinkage was applied to the heat sealing portion before the heat sealing portion was sufficiently cooled, so that heat seal puncture occurred frequently. Observation of the package which was barely heat-sealed punctured revealed that the packaged product was greatly deformed due to a large shrinkage stress at the time of shrink wrapping, and the commercial value was in an absolute state.

[0065]

Comparative Examples 8 and 9 In Comparative Example 8, a film was obtained in the same manner as in Example 1 except that the electron beam irradiation amount was changed to 6 to 7 Mrad. Further, in Comparative Example 9, a cross-linking treatment was performed at an electron beam irradiation amount of 6 to 7 Mrad, similarly to Comparative Example 8, except that 3500 ppm of an antioxidant was added to the inner layer (B) of Example 1. Table 6 shows the layer structure of the film and the evaluation results. Comparative Example 8 is excellent in surface sealability, optical properties, and physical properties such as tear strength, but cannot be sealed by fusing due to the high gel fraction of the film, and is not suitable for packaging machines employing the fusing seal. I didn't know. In addition, since the maximum equilibrium heat shrinkage stress was slightly higher with an increase in the gel fraction, the article to be packaged was slightly deformed during shrink packaging. However, it did not mean that there was no commercial value. In Comparative Example 9, since a large amount of an antioxidant was added to the inner layer (B), the gel fraction of the film of Comparative Example 8 was lower than that of all the layers, and the gel composition distribution in the film was such that the surface layer (A) had The gel fraction was high and the inner layer (B) had a gel composition distribution with a low gel fraction. Each of the obtained films was excellent in physical properties such as optical properties and tear strength as in Example 1, but in the face sealing property, the inner layer was softened and melted more easily than the surface layer. The heat seal portion was likely to be fused to the seal bar, or the heat seal portion was stretched at the time of sealing and cutting, and heat seal defects such as heat seal breakage were likely to occur. Further, the film tended to be rounded by the heat of the fusing blade, so that an effective face sealing could not be performed.

[0066]

Comparative Examples 10 to 12 In order to compare the effect of the present invention with that of the prior art, it is assumed that, corresponding to JP-A-2-283445, a surface layer made of LL11 and an inner layer made of EVA3 are used according to the disclosed technique. 3 layers (25/50
/ 25) was obtained.
0 was set. According to the technology disclosed in JP-A-60-240451, a surface layer composed of LL11 (50% by weight), LL12 (25% by weight) and EVA3 (25% by weight) and an inner layer composed of LL11 are provided. A three-layer (25/50/25) shrink film was obtained, and this film was used as Comparative Example 11. Also, Japanese Patent Application Laid-Open No. 1-3012
No. 51, a three-layer (15/75/15) shrink film composed of a surface layer composed of LL13 and an inner layer composed of LL14 was obtained according to the disclosed technology.
This film was used as Comparative Example 12. Table 6 shows the layer constitution and evaluation results of the obtained film. In Comparative Example 10, the product to be packaged can be prevented from being broken due to low shrinkage force. However, in the face sealing property, the core layer, that is, the inner layer is softened and melted more easily than both outer layers. The seal portion was likely to be fused to the seal bar, or the heat seal portion was stretched at the time of sealing and cutting, and heat seal failure such as breakage of the heat seal was liable to occur. Particularly, at the time of high-speed packaging, there were many troubles in the face seal portion. Comparative Example 11 has good tear resistance with moderate elongation and elastic memory, but in a series of flows of heat-sealing the films and shrinking the film for tight packaging, At the time of high-speed packaging, since the time from heat sealing to entering the shrink tunnel becomes shorter, the heat-sealed part is pulled by the shrinkage stress of the film, so heat seal puncture is likely to occur, and even when heat sealing is successful If the rigidity of the packaged object is weak,
The package was easily deformed. A similar phenomenon occurred in the face sealing property, and it was difficult to achieve stable face sealing. Comparative Example 12 was excellent in transparency and low-temperature fusing sealability, but was inferior in heat resistance of the film because it was not subjected to cross-linking treatment. It was narrow. Further, similarly to Comparative Example 11, since the heat shrinkage stress of the heat shrinkable film was high, heat seal puncture was easily generated, and the packaged object was easily deformed.

[0067]

[Table 1]

[0068]

[Table 2]

[0069]

[Table 3]

[0070]

[Table 4]

[0071]

[Table 5]

[0072]

[Table 6]

[0073]

According to the present invention having the above-described structure, a high-performance heat-shrinkable film which is extremely well-balanced and which cannot be obtained by conventional shrink-wrapping films can be provided. That is, a stable film can be formed by defining the physical properties of the film and the inner layer (B) based on the specific resin and the mixing ratio, the surface layer (A) based on the specific resin, and the suitability for a packaging machine. Good optical properties, good heat sealing properties for various sealing forms such as fusing and face sealing properties, little content deformation due to film shrinkage, especially heat sealing properties at high speed packaging And a heat-shrinkable multilayer film having excellent packaging finish.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4F100 AK05B AK63A AK63B AK63C AK68B AK70B AL05B BA03 BA06 BA10A BA10C BA15 GB90 JA03 JA13A JA13B JA13C JK03 JL12 JN30 YY00 YY00A YY00B YY00C

Claims (1)

[Claims] 1. Density 0.900 to 0.940 g / cm ³
A surface layer (A) containing a linear low-density polyethylene,
(A) 50 to 90% by weight of linear low-density polyethylene having a density of 0.900 to 0.940 g / cm ³ , (b) 5 to 40% by weight of high-pressure low-density polyethylene, and (c) ethylene-vinyl acetate copolymer At least one internal layer (B) containing a mixed resin composition comprising 5 to 40% by weight of at least one copolymer selected from a copolymer and an ethylene-aliphatic unsaturated carboxylic acid ester copolymer. A multilayer film composed of three layers, wherein the gel fraction of all layers of the film is 0.1 to 10% by weight, and the relationship between the gel fraction of the surface layer (A) and the inner layer (B) and the layer ratio is as follows. Satisfies the formula (I), that the melting point of at least one resin used for the inner layer (B) is equal to or higher than the melting point of the surface layer (A), and that 80 to 14 as measured by ASTM D-2838.
The maximum equilibrium heat shrinkage stress of the film at 0 ° C. is 200 g / mm ² or less in both the longitudinal and transverse directions; and
The heat shrinkage of the film at 140 ° C. measured in accordance with ASTM D-2732 is 30% in at least one of the vertical and horizontal directions.
A heat-shrinkable multilayer film characterized by the above. GB × TB ≧ GA × TA (I) (wherein, in the above formula (I), GA and GB are the gel fractions of the surface layer (A) and the inner layer (B), respectively, and TA, TB
Represents the thickness ratio of the surface layer (A) and the inner layer (B), respectively. )