JPH05254074A - Heat-shrinkable multilayered film - Google Patents

Abstract

PURPOSE:To improve stretching film forming properties and packing aptitude by setting the m.p. of the polymer of at least one layer of an internal layer to specific relation with respect to the m.p. of the polymer of a surface layer and devising a measure specifying the thickness ratios of respective polymer layers to all of layers. CONSTITUTION:In a multilayered film, two surface layers are constituted of a polymer (A) based on an ethylene/aliphatic unsaturated carboxylic acid copolymer and at least one layer of an internal layer is constituted of a copolymer (B) based on high-pressure low density polyethylene with density of 0.890-0.94g/cm<4>. In this case, the m.p. measured by a differential scanning calorimeter of the polymer (B) is 130 deg.C or lower and set to a value at least 5 deg.C higher than that of the polymer (A). The thickness ratios of the respective layers composed of the polymers (A), (B) to all of layers are set to 5-80% and 20-95% ad the film is set to a gel ratio due to crosslinking of 3-30% as a whole.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-shrinkable multi-layer film which is excellent in mechanical properties such as waist strength and tear strength, sealing properties and optical properties, and can be particularly preferably used for shrink wrapping.

[0002]

2. Description of the Related Art Various packaging methods such as household wrap packaging, overwrap packaging, twist packaging, bag packaging, skin packaging, shrink wrapping, stretch wrapping, etc. are available as film packaging methods by making use of their respective characteristics. Has been adopted. Among them, shrink wrapping is characterized by its beautiful appearance, high product value, hygienic contents, and easy visual quality confirmation. Since it can be fixed and packaged, it is often used for packaging foods, sundries, etc.

In recent years, shrinkage packaging (overlap shrink) excellent in high-speed packaging workability has been promoted due to the fact that production area packaging or centralized packaging has been advanced due to lack of work space in backyards of supermarket stores and difficulty in securing workers. , Pillow shrink, sleeve packaging, etc.), and in particular, any sealing method such as overlap seal, pillow shrink packaging, fusing seal, which is often used for sleeve packaging, can be applied. There is a strong demand for development of a film having wrapping suitability. On the other hand, in response to global environmental problems, the problem of plastic waste treatment has been particularly highlighted in recent years, and the thinning of films has been called out as a social need from the viewpoint of resource saving.

Conventionally, as a heat-shrinkable polymer film,
Films mainly composed of polyvinyl chloride, polypropylene, polyethylene and the like are known, but these films each have drawbacks.

A heat-shrinkable film using polyvinyl chloride has good gloss and transparency, and has a wide range of shrinkage temperature, and is used in many applications, but its sealing strength is rather weak, especially when fusing and sealing. There is a problem that the resin decomposes and harmful odorous gas is generated, and carbon adheres to the seal part and the sealer of the film to promote the decrease of the seal strength, and the toughness at low temperature is insufficient. is there. Furthermore, since it usually contains a large amount of plasticizers and stabilizers, its dimensions and physical properties tend to change over time, and disposal is also environmentally friendly and hygienic.
There's a problem.

The polypropylene-based heat-shrinkable film is inexpensive and flexible, and has a high shrinkage force, but it is inferior in overlap sealability, has a narrow range of suitable shrinkage conditions, and has insufficient toughness and transparency.

The polyethylene-based heat-shrinkable film is a low-density polyethylene, a so-called linear low-density polyethylene (hereinafter referred to as LLDPE) which is an ethylene-α-olefin copolymer, or an ultra-low-density polyethylene (hereinafter referred to as VLDPE). , Which has a relatively high seal strength and toughness,
The range of suitable shrinkage conditions is narrow, stress loss during shrinkage is likely to occur, transparency is slightly poor, and stretching film forming safety is poor and productivity is poor, and it is difficult to thin the film. is there.

As a multilayer film suitable for a heat-shrinkable film, JP-A-2-145336 discloses an ethylene- (meth) acrylic acid copolymer resin and an ethylene- (meth) acrylic acid ester copolymer resin in the intermediate layer. , Ethylene-
A low-temperature shrinkable multilayer shrink film made of a low-density polyethylene or an ethylene-α-olefin copolymer resin is used as an outer layer by using one or more blends of vinyl acetate copolymer resin (hereinafter referred to as EVA). Although disclosed, this film is still insufficient in stretch film-forming property,
A thin film, particularly a film having a thickness of 30 μm or less, has a large uneven thickness, and there are problems that a stable sealing strength cannot be obtained due to meandering of the film during packaging, and a finish defect occurs after shrinkage.

Further, it is insufficient to satisfy both the sealability, for example, the bottom sealability in the overlap shrink wrapping and the fusing sealability often used in the pillow shrink wrapping, etc., and there is also a problem in high-speed wrapping workability. Further, there is a drawback that additives (lubricants, antifogging agents, antistatic agents, etc.) used for improving the packaging property of the film are not bleeding effectively, so that they do not work effectively.

Further, Japanese Patent Laid-Open No. 3-69337 discloses that
For the purpose of substituting a PVC film for packaging, an overwrapping film manufactured by a specific process composed of ultra-low density polyethylene, EVA, ethylene- (meth) acrylic acid copolymer resin, etc. is disclosed. However, when this film is used as a heat-shrinkable film, since the film itself has low-temperature shrinkability, it cannot withstand storage in the summer when the temperature is high, the film roll easily shrinks in width, and hot-sticking occurs during sealing. (Heat adhesion of the film to the sealer) easily occurs,
In some cases, a sealing failure may occur, the waist is not sufficient, and high-speed packaging workability is poor.

Further, an ethylene-based crosslinked film is known as a heat-shrinkable film from a long time ago. For example, Japanese Patent Publication No. 37-18893 discloses a method for producing the film, but the electron beam crosslinked film obtained by this method is superior in strength and heat shrinkage property to the non-crosslinked film. However, it has the drawbacks of poor heat sealability and poor packaging workability.

Further, by forming the film into multiple layers,
A method for improving heat sealability, transparency, impact strength, etc. has been proposed. For example, JP-A-57-113066, JP-A-57-197161, JP-A-57-
As disclosed in 199626, it is a method of laminating resins having different crosslinking efficiencies. Specifically, LLDPE or the like having low crosslinking efficiency is used as the heat-sealing layer or surface layer, and EVA, ethylene-acrylic acid copolymer, ethylene-ethyl acrylate copolymer or the like having high crosslinking efficiency is used as the heat-resistant layer or core layer. By using it, it is intended to obtain heat sealability.

However, since this film uses a highly crystalline resin in the surface layer, the gloss and transparency after shrinking are deteriorated, and the bottom sealing property in the overlap shrink wrapping and the pillow shrink wrapping etc. It is insufficient to satisfy both of the frequently used fusing sealing properties.

Further, JP-A-59-158254 discloses a low-temperature shrinkable film having three layers, a surface layer made of EVA and a core layer made of LLDPE or the like.
Although this film has excellent transparency and toughness,
The LLDPE, which is the main component of the film, does not necessarily have good stretch film-forming property by itself, and is stretched under strict temperature control near the melting point.

For this reason, slight changes in the stretching temperature conditions are likely to affect the quality of the film, such as physical properties, and
Hot sticking (heat sticking of the film to the sealer) is likely to occur at the time of sealing, which may cause poor sealing, and the hot tack property (hot peel strength) required for high-speed packaging is not sufficient. is there. Also, E
When the thickness ratio of the VA layer is large, the waist and the tear strength may be lowered and the packaging workability may become a problem. Further, since the film itself has low-temperature shrinkability, it cannot withstand storage in the summer when the temperature is high, and the film roll has a width shrinkage.

[0016]

The object of the present invention is to provide excellent stretch film-forming properties, and excellent packaging suitability for overlap shrink, pillow shrink, sleeve packaging, etc., especially high-speed packaging suitability, sealing property, It is to provide a film having excellent mechanical properties such as waist and tear strength, and optical properties such as gloss and transparency.

[0017]

That is, the present invention is:
One surface layer is composed of a polymer (A) whose main component is an ethylene-aliphatic unsaturated carboxylic acid copolymer, and at least one of the inner layers has a density of 0.890 to 0.940 g / cm 3.
^At least three layers composed of a polymer (B) containing as a main component at least one polymer selected from high-pressure process low-density polyethylene, ethylene-α-olefin copolymer, and polybutene-1 polymer In the multi-layer film, the copolymer which is the main component of the polymer (B) has a melting point of 130 ° C. or less as measured by a differential scanning calorimeter and which is the main component of the polymer (A). At least 5 ° C. higher than the melting point of, and the thickness ratio of the (A) layer and the (B) layer to all layers is 5 to 80%, and 2 respectively.
The heat-shrinkable multilayer film is characterized by having a gel fraction of 0 to 95% and 3 to 30% by crosslinking as a whole.

The present invention will be described in detail below. First, the polymer used for the surface layer has an ethylene-aliphatic unsaturated carboxylic acid copolymer as a main component, and has a role as a seal layer having both tear strength and toughness. Examples of the ethylene-aliphatic unsaturated carboxylic acid copolymer include an ethylene-acrylic acid copolymer, an ethylene-methacrylic acid copolymer, and the like. These are three or more components containing other components. It may be a multi-component copolymer (for example, a free terpolymer of ternary or more selected from ethylene, an aliphatic unsaturated carboxylic acid and the same ester, or a modified one).

MFI of these polymers (190 ° C., 21
60 g) is usually appropriately selected within the range of 0.1 to 10.
Moreover, these can be used individually or in a mixed system of 2 or more types. The content of the aliphatic unsaturated carboxylic acid in the ethylene-aliphatic unsaturated carboxylic acid copolymer is usually 1 to 2.
Although the content of 0 mol% is used, it is preferably 1 to 15 mol%, more preferably 1 to 1 in view of the deterioration of the packaging workability due to the occurrence of blocking of the film, the lowering of the waist and the like.
It is 0 mol%, more preferably 1 to 6 mol%.

As other components, at least one kind of miscible resin is mixed within a range not exceeding 50% by weight, as long as the characteristics are not significantly deteriorated, and the ethylene-aliphatic unsaturated carboxylic acid copolymer is mixed. You may comprise the surface layer which has a polymer as a main component. The preferable amount of the other miscible resin is 40% by weight or less, more preferably 30% by weight or less, and further preferably 20% by weight or less.

For example, as an example of the resin to be mixed, EV
A, ethylene-unsaturated unsaturated carboxylic acid ester copolymer, for example, ethylene-acrylic acid ester (selected from C _{1 to} C ₈ alcohol components such as methyl, ethyl, propyl and butyl) copolymer, ethylene- Methacrylic acid ester (C ₁ such as methyl, ethyl, propyl, butyl, etc.
Selected from alcohol components -C _8. ) There are copolymers and the like.

Ethylene-vinyl alcohol copolymers (for example, those having an ethylene content of 55 to 95 mol%), partially saponified products or modified products thereof, ionomer resins, ethylene and carbon monoxide, or vinyl in addition to these. A copolymer containing an ester component, or a resin obtained by converting at least a part of the resin into a hydroxyl group, crystalline 1,2-polybutadiene, an ethylene-based resin other than the above (including those used for the internal layer described later), Examples include soft polymers composed of α-olefin copolymers, propylene-based resins, and the like,
At least one kind may be selected from these.

Next, in the film of the present invention, at least one of the inner layers has a density of 0.890 to 0.940 g / cm ^3.
And the melting point measured by a differential scanning calorimeter is 130 ° C.
The following and at least 5 ° C. higher than the melting point of the ethylene-unsaturated unsaturated carboxylic acid ester copolymer, at least selected from high-pressure process low-density polyethylene, ethylene-α-olefin-based copolymer, and polybutene-1-based polymer 1
It is composed of a polymer containing two polymers as main components.

This layer is a heat-resistant layer for ensuring the stability required for packaging machine suitability and workability, especially for high-speed wrapping, stable sealing performance in overlap seals and gas-sealing seals, and also the role to exert toughness. have. When the density of the polymer as the main component is less than 0.890 g / cm ^{3, the} rigidity to give sufficient packaging machine suitability and workability is insufficient, and high speed packaging suitability is poor. Also, the density is 0.940
If it exceeds, the rigidity of the film tends to be excessive, and the transparency after heat shrinking decreases. The preferred density is 0.90
0 to 0.935 g / cm ³ , more preferably 0.905
Is about 0.930 g / cm ³ .

If the melting point of the polymer as the main component, measured by a differential scanning calorimeter, is less than the melting point of the ethylene-aliphatic unsaturated carboxylic acid copolymer + 5 ° C., the heat resistance is lowered, resulting in overheating. In lap sealability and gas palm seal, the film may melt and puncture may occur,
Sealing properties, especially troubles during high-speed packaging. Similarly, when the melting point exceeds 130 ° C., the temperature condition in the fusing seal becomes high, which accelerates the deterioration and accumulation of the dust adhered to the sealer, causing troubles and shortening the life of the sealer.

The preferred melting point is the melting point of the ethylene-aliphatic unsaturated carboxylic acid copolymer + 10 ° C. to 130 ° C., and the more preferred melting point is the melting point of the ethylene-aliphatic unsaturated carboxylic acid copolymer + 15 ° C. As described above, the temperature is 130 ° C. or lower. The high-pressure low-density polyethylene used in the present invention is usually a homopolymer of ethylene having a long chain branch, a copolymer of ethylene and 5 mol% or less of 1-olefin monomer, and ethylene and a functional group. Means a copolymer with 1 mol% or less of a non-olefin monomer having only carbon, oxygen and hydrogen atoms, and a density of 0.910 or more, 0.930 g / c
It is less than m ³ .

The ethylene-α-olefin copolymer means ethylene and propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, which has substantially no long-chain branching. The carbon number of 1-octene is 3-1
8 is a copolymer with at least one kind of monomer selected from α-olefins and is different from the above high-pressure low-density polyethylene (however, including general medium- and low-pressure medium-density polyethylene). ..

Further, as the polybutene-1 type polymer,
Butene-1 content 80 mol% or more crystalline is of high molecular weight which also includes a copolymer with other monomer (carbon number C _2, C _3, alkene of C ₅ ~C _8), liquid and It is different from waxy low molecular weight ones. The MFI (190 ° C., 2160 g) of these polymers is usually appropriately selected within the range of 0.1 to 10.

These can be used alone or in a mixture of two or more, and other resins can be blended in
The same applies to the case of the layer (A) (however, the amount and type are the same as the main resin of the layer (A)).

The film of the present invention has two surface layers (A).
And at least one of the internal layers is a layer (B), and the thickness ratio of the layers (A) and (B) to all layers is 5 to 80% and 20 to 20%, respectively. 95
%. Here, the thickness of the (A) layer refers to the total thickness of the (A) layer used for the surface layer, and simply refers to the total thickness of the (B) layer.

The thickness ratio of the layer (A) to all layers is 5%.
When it is less than the above range, the heat sealability, particularly the sealability in overlap seals and gas-sealing seals is deteriorated, and the stretchability is also deteriorated. On the other hand, if the ratio exceeds 80%, the performance required as the seal layer becomes excessive, but the rigidity becomes weak, and the effect of the (B) layer as the heat-resistant layer also decreases, resulting in poor workability in packaging. The thickness ratio of the layer (A) to all layers is preferably 10 to 70%, more preferably 15 to 60%.

When the thickness ratio of the layer (B) to all layers is less than 20%, the effect of the layer (B) as a heat-resistant layer is reduced and the rigidity tends to be insufficient. If the ratio exceeds 95%, the stretchability will decrease, making stable film formation difficult. In addition, the heat sealability is relatively lowered, which is a practical problem. The thickness ratio of the layer (B) to all layers is preferably 30 to 90%, more preferably 40 to 85%.

The film of the present invention has two surface layers (A).
Although it is a layer, the resins constituting the respective surface layers may be the same or different, and the same applies when the layer (B) has two or more layers. In addition to the surface layer (A)
The layers may be arranged as inner layers. Further, at least one layer composed of another resin may be freely used inside, as long as the characteristics of the film of the present invention are not impaired.

These layers may have gas barrier properties such as ethylene-vinyl alcohol copolymers, polyamide polymers, polyester polymers, acrylonitrile polymers, and the like. A combination of a barrier resin layer and an adhesive layer may be used.

Next, the film of the present invention comprises 3
It has a gel fraction of -30%. If the gel fraction is less than 3%, troubles due to hot stick (heat adhesion of the film to the sealer) are likely to occur during heat sealing, the stretchability is lowered, and the finish after shrinkage is poor. When the gel fraction exceeds 30%, the heat sealability is deteriorated, and the seal strength is lowered and the fusing seal temperature is increased. There is also a problem that the tear strength is lowered.

The gel fraction is preferably 5 to 25%, more preferably 5 to 20%. Further, the gel fraction of the (A) layer constituting each surface layer is determined by the seal strength, the fusing seal strength,
It is preferably in the range of 3 to 40%, more preferably 5 to 30% in view of hot stick property, tear strength, stretchability and the like, and the gel fraction values of the respective surface layers may be the same or different.

The gel fraction referred to in the present invention is brought about by crosslinking, and a typical example of the crosslinking method is energy irradiation. The energy rays refer to ionizing radiation such as ultraviolet rays, electron rays, X-rays, α rays, β rays, γ rays and the like, and preferably electron rays. As the irradiation method, either a uniform irradiation dose or a non-uniform irradiation dose in the thickness direction of the film can be adopted depending on the purpose, and a known method is used.

As another cross-linking method, a cross-linking agent is added, or if necessary, a cross-linking auxiliary agent is also used, and the kind, combination, and addition amount thereof are appropriately adjusted according to the purpose, and the decomposition temperature of the cross-linking agent is adjusted. It is also possible to crosslink by heating above.
It may be combined with energy beam irradiation.

Further, the film of the present invention may contain a plasticizer, an antioxidant, a surfactant, a colorant, an ultraviolet absorber, a lubricant, an inorganic filler, etc. within a range not impairing the original purpose. Further, in order to impart antifogging property, antistatic property, adhesiveness, lubricity or the like to one surface or both surfaces of the film of the present invention, surface modification such as corona treatment and plasma treatment as group (1), or Surfactants as group (2),
It may be coated with antifogging agent, antistatic agent, etc., or added to the resin to cause bleeding.
Known adhesives and pressure-sensitive adhesives may be treated in the same manner as (3).

For example, as the group (2), partial fatty acid ester of polyhydric alcohol such as sorbitan fatty acid ester, glycerin fatty acid ester and polyglycerin fatty acid ester; polyoxyethylene alkyl ether,
Ethylene oxide adducts such as polyoxyethylene alkyl phenyl ether, polyethylene glycol fatty acid ester, polyoxyethylene sorbitan fatty acid ester, and polyoxyethylene glycerin fatty acid ester;
Amines, amides such as alkylamines, alkylamides, and alkylethanolamines;

Polyalkylene glycol, granidine derivative, phosphate-containing anion activator, sulfonate derivative,
Quaternary ammonium salt, pyridinium salt, imidazoline derivative, dimethyl silicone oil, methylphenyl silicone oil, polyether modified silicone oil, alkyl modified silicone oil, and various other modified silicone oils; polyvinyl alcohol, acrylic acid-based hydrophilic polymers, pyrrolidinium Examples thereof include polymers having a ring in the main chain, and silica sol and alumina sol.

The group (3) includes mineral oil, liquid polybutene, oils and fats not included in the former, and viscous liquids (500 centipoise or more) and the like, which are used alone or in combination. Moreover, you may combine freely the additive of each said process or each group. The total thickness of the film of the present invention is 5 to 50 µ, preferably 5 to 3
0 μ. If the thickness is less than 5 μ, the film has insufficient rigidity and is easily torn, which causes a problem in workability during packaging. Further, if the thickness exceeds 50 μ, the performance becomes excessive, which deviates from one object of the present invention to provide a thin film.

The total thickness of the (A) layer used as the surface layer is
It is 0.6 to 40 μ, preferably 1 to 20 μ, and more preferably 1 to 16 μ. The total thickness of the layer (B) is 2
-40 mu, preferably 4-20 mu, and more preferably 5-
16μ. The upper and lower limits of the layers (A) and (B) are
As described above, there are limitations in terms of sealing property, elasticity, stretchability, and excessive performance.

The film of the present invention has an area shrinkage at 60 ° C. of less than 10% and an area shrinkage at 120 ° C. of 40% or more, preferably 50% or more. If the area shrinkage ratio at 60 ° C. is 10% or more,
Dimensional changes become a problem in the distribution process, including the storage of films. Further, the area shrinkage ratio at 120 ° C. is 40
If it is less than%, the fit property after shrinkage becomes insufficient, which may cause wrinkles and lumps after packaging.

Next, an example of the method for producing the multilayer film of the present invention will be described, but the invention is not limited thereto. First, two surface layers made of a polymer (A) containing an ethylene-aliphatic unsaturated carboxylic acid copolymer as a main component,
High density, having a density of 0.890 to 0.940 g / cm ³ , a melting point of 130 ° C. or less as measured by a differential scanning calorimeter, and at least 5 ° C. higher than the melting point of the ethylene-aliphatic unsaturated carboxylic acid copolymer. Method A low-density polyethylene, an ethylene-α-olefin-based copolymer, a polymer comprising at least one polymer selected from polybutene-1-based polymers (B) to form a multilayer film including a layer comprising a polymer The polymer of each layer is melted in each extruder, coextruded with a multi-layer die, rapidly cooled to obtain a multi-layer film raw material, and then the obtained multi-layer film raw material is irradiated with ionizing radiation for crosslinking treatment. To do.

An electron beam is preferably used as the ionizing radiation, and the irradiation dose is usually in the range of 0.5 to 30 Mrad. Then, the raw material of the multilayer film is heated and stretched. Stretching is performed in at least one direction by an area stretching ratio of 5 to 60 times, preferably 7 to 50 times,
It is appropriately selected according to the heat shrinkage required depending on the application.

The stretching method is not particularly limited, such as a roll stretching method, a tenter method and a bubble method, but a method of forming a film by simultaneous biaxial stretching is preferable. Also, if necessary, post-treatment,
For example, heat setting, lamination with a multilayer film, or the like may be performed. The film of the present invention is mainly suitable for a packaging material, especially shrink wrapping, but it is also a film that can be used as a wrap film for household and business use.

The present invention will be described in more detail with reference to examples, but the present invention is not limited thereto. The measurement and evaluation methods in the present invention and examples will be described below. (1) Density: According to ASTM D1505.

(2) Melting point: Using a differential scanning calorimeter (DSC), the temperature was once raised to 190 ° C., cooled to room temperature or lower at a temperature lowering rate of 20 ° C./min, and again raised to 10 ° C./min. Was measured, and the main endothermic peak temperature at that time was taken as the melting point.
However, with respect to the polybutene-1 type polymer, one that was annealed at 40 ° C. or higher for 24 hours or more was used, and the main endothermic peak temperature at the first temperature rise (10 ° C./min) was taken as the melting point.

(3) Gel fraction: A sample was extracted with boiling p-xylene and the proportion of the insoluble portion was expressed by the following formula, which is used as a measure of the degree of crosslinking.

[Equation 1]

(4) Thermal shrinkage: The area shrinkage when a 100 mm square film sample is treated for 30 seconds in a silicone oil bath uniformly heated to a predetermined temperature. (5) Tensile elastic modulus: Performed according to ASTM-D882-67 and expressed as a value obtained by converting stress at 2% elongation to 100%.

(6) Tear strength: ASTM-D-1922
It was measured according to. (7) Haze after shrinkage: After shrinking the film at an area shrinkage ratio of 30% using hot air of 120 ° C., ASTM-D-1
It measured according to 003-52.

(8) Film-forming stability: The continuous stability of the film (continuous stability of the stretching bubble) and the thickness unevenness of the finished film when heat-stretched by a predetermined method were evaluated. Symbol ⊚: Stretching pattern of the film (stretching bubble) hardly changed, and continuous stability was good. ◯: Film thickness unevenness is within ± 15%. Δ: The stretching start position is somewhat unstable. Thickness variation exceeds ± 15% and within ± 25%. ×: Film broke or bubble puncture occurred frequently. Or even if stretching is possible, the variation of the stretching start position is large and the thickness unevenness is ±
Over 25%.

(9) Fusing sealing property: A 0.5R × 280L (mm) fusing blade was attached to a sentinel heat sealer, and a 250 mm wide two-layer film was fused and sealed under the conditions of 30 psi and 0.5 seconds. The lower limit temperature of fusing seal was evaluated from the following viewpoints. ◎: Those that could be completely melted at 180 ° C or less, ○: Those that could be melted at temperatures above 180 ° C and 200 ° C, △: Those that could be melted by 80% or more in the width direction at 200 ° C, ×: At 200 ° C The fusing is less than 80% in the width direction, and fusing sealing is difficult.

(10) Packability: Condition 1: Overlap / shrink wrapping machine (SP-30 manufactured by Ibaraki Seiki Co., Ltd.)
0) and OPS tray (size: 190 x 100 x
25 mm) containing about 200 g of clay was used as an article to be packaged, and 100 pieces were packaged at a packaging speed of 50 pieces / minute, and the wrapping property was evaluated from the following viewpoints. Condition 2: Pillow shrink packaging machine (manufactured by Ibaraki Seiki Co., Ltd .:
EP-280) was used, two cucumbers were used as the articles to be packaged, and 100 pieces were packaged at a packaging speed of 40 pieces / minute, and evaluated from the following viewpoints. ◎: Rupture of film, breakage or peeling of seal part, generation of wrinkles and sagging 0/100 pieces ○: Same as above 1-5 / 100 pieces △: Same as above 6-20 / 100 pieces ×: Same as above 21 or more / 100 pieces

Next, the resins used in Examples and Comparative Examples will be described below. a ₁ : ethylene-acrylic acid copolymer (acrylic acid content: 1.6 mol%, MFR (190 ° C., 2160 g):
2. Melting point: 104 ° C.) a ₂ : Ethylene-acrylic acid copolymer (acrylic acid content: 3.7 mol%, MFR (190 ° C., 2160 g):
1.5. Melting point: 100 ° C. a ₃ : Ethylene-methacrylic acid copolymer (methacrylic acid content: 1.2 mol%, MFR (190 ° C., 2160)
g): 2. (Melting point: 103 ° C)

A ₄ : ethylene-methacrylic acid copolymer (methacrylic acid content: 2.7 mol%, MFR (190
C., 2160 g): 3. Mp; 99 ℃) a _5: ethylene - methacrylic acid copolymer (methacrylic acid content: 3.7 mol%, MFR (190 ℃, 2160
g): 7. Melting point: 95 ° C.) b ₁ : High pressure method low density polyethylene (density: 0.922 g
/ Cm ³ , melting point: 106 ° C, MI (190 ° C, 2160
g): 2. )

B ₂ : High-pressure low-density polyethylene (density:
0.920 g / cm ³ , melting point: 105 ° C., MI (190
℃, 2160g): 0.4) b 3: medium density polyethylene (density: 0.935 g / cm
³ , melting point: 122 ° C, MFR (190 ° C, 2160
g): 1.8) b _4: high density polyethylene (density: 0.950 g / cm
³ , melting point: 127 ° C, MFR (190 ° C, 2160
g): 0.8)

B ₅ : ethylene-α-olefin copolymer (comonomer: 1-butene, density: 0.885 g / cm
³ , melting point: 113 ° C, MFR (190 ° C, 2160
g): 0.8) b ₆ : ethylene-α-olefin copolymer (comonomer: 1-butene, density: 0.900 g / cm ³ , melting point 1)
15 ° C., MFR (190 ° C., 2160 g): 0.8) b ₇ : ethylene-α-olefin copolymer (comonomer: 1-hexene, density: 0.912 g / cm ³ , melting point: 117 ° C., MFR (190 C., 2160 g): 2.
0)

B ₈ : ethylene-α-olefin copolymer (comonomer: 1-octene, density: 0.926 g / c
m ³ , melting point: 121 ° C., MFR (190 ° C., 2160
g): 1.0) b _9: ethylene -α- olefin copolymer (comonomer: 4-methyl-1-pentene, density: 0.930 g /
cm ³ , melting point: 122 ° C., MFR (190 ° C., 2160
g): 1.3) b ₁₀ : polybutene (density: 0.915 g / cm ³ , melting point 125 ° C., MFR (190 ° C., 2160 g): 2.
0)

B ₁₁ : polybutene (density: 0.910 g
/ Cm ³ , melting point: 112 ° C, MFR (190 ° C, 216
0 g): 1.0) b ₁₂ : polypropylene resin (ethylene content: 2.
7 mol%, density: 0.90 g / cm ³ , melting point: 139
° C, MFR (190 ° C, 2160 g): 7. )

C ₁ : ethylene-vinyl acetate copolymer (vinyl acetate content: 5.0 mol%, MFR (190 ° C., 2
160 g): 2. , Melting point: 91 ° C. c ₂ : ethylene-methyl methacrylate copolymer (methyl methacrylate content: 3.0 mol%, MFR (19
0 ° C., 2160 g): 7. , Melting point: 100 ° C.)

(Examples 1 to 3 and Comparative Examples 1 and 2) The ethylene-methacrylic acid copolymer (a
₄ ), ethylene-α-olefin copolymer (b ₉ ) is used as the inner layer resin, each resin is melted by an extruder and extruded using an annular multi-layer die (3 layers), followed by quenching with cold water. When solidified, the layer structure is a ₄ / b ₉ / a ₄ = 90 μ / 4
A tube-shaped original fabric having a size of 20 μ / 90 μ was formed. At this time, 3 wt% of diglycerin monooleate as a nonionic surfactant was injected and mixed into the surface layer from the extruder cylinder.

This tube-shaped raw material was flattened and crosslinked to a gel fraction of 10% by an electron beam irradiation device, and then the original material was passed between two pairs of differential nip rolls and heated in a heating zone for 12 hours.
By heating to 5 ℃ and injecting air into the original fabric tube, it is stretched 7 times vertically and 6.6 times horizontally, and has a thickness of 13μ.
I got a film. This is Example 1.

[0065]

[Table 1]

As shown in Table 1, various films were obtained in the same manner as in Example 1 except that the thickness composition ratio of each layer and the gel fraction by electron beam irradiation were changed. These are Examples 2 and 3 and Comparative Examples 1 and 2. Table 2 shows the evaluation results of the film characteristics.
Shown in.

[0067]

[Table 2]

The film of the present invention had good stretch film-forming stability and was excellent in suitability for various shrink wrappings, but was not subjected to crosslinking treatment (Comparative Example 1).
Is inferior in stretch film-forming property, and it is particularly difficult to stably obtain a thin film having a thickness of 30 μm or less. As a result, poor uneven thickness also affects the sealing workability such as occurrence of troubles in the seal part. It was inferior.

Further, Comparative Example 2 is a case where highly cross-linked beyond the scope of the present invention. In this case, although the stretched film-forming property is relatively good, the resulting film has a fusion-cutting sealing property and the like. The sealing property of No. 1 was deteriorated and the packaging property was poor.

(Examples 4 to 13) Predetermined tubular raw fabrics were prepared in the same manner as in Example 1 (total thickness 600 µ in Examples 4 to 9 and total thickness 400 µ in Examples 10 to 13).
Was prepared, and similarly subjected to appropriate crosslinking treatment by an electron beam irradiation device to obtain films having layer constitutions shown in Tables 3 to 4 [Note that
Examples 7 to 10 are dimethyl silicone oil (50 cs
-25 [deg.] C.), and the others contain the same additives as in Example 1 in an amount of 1 to 3 wt% with respect to each surface layer].

[0071]

[Table 3]

[0072]

[Table 4]

Here, A ₁ : (a ₄ : 80% by weight +
c _1: 20 _{wt%) A 2: (a 4} : 80 wt% + c _2: 20 _{wt%) B 1: (b 9} : 75 wt% + b _2: 25 _{wt%) B 2: (b 11} : 70 by weight % + B ₁₂ : 30% by weight)

As for the draw ratio, Examples 4 to 6 had a length of 7 times and a width of 6.6 times, and Examples 7 to 11 had a length of 6.7 times and a width of 6 times.
The film formation was carried out under the conditions that the vertical length was 5.2 times and the horizontal width was 5.1 times in Examples 12 and 13. The evaluation results of the obtained film are shown in Tables 5-6.

[0075]

[Table 5]

[0076]

[Table 6]

In all cases, the stretch film-forming property was good, the heat shrinkage property, the optical property and the mechanical property were excellent, and the packaging property was also good. (Comparative Examples 3 to 8) Predetermined tubular raw fabrics (all having a total thickness of 600 μm) were produced in the same manner as in Example 1, subjected to the same crosslinking treatment, and then stretched to form a film.
To 8 are obtained, and the films having the layer structure shown in Comparative Examples 3 to 8 are obtained.
(Note that each surface layer contains 3 w of the same additive as in Example 1)
t% included).

Comparative Examples 3 to 6 are those in which the density or melting point of the resin constituting the internal layer (B) specified in the present invention is out of the range, and Comparative Examples 7 and 8 are the surface layer (A) and the internal layer. Each thickness ratio (to all layers) of (B) is out of the range, and in Comparative Example 9, an ethylene-vinyl acetate copolymer (C ₁ ) is used as the surface layer resin. In Comparative Examples 5 to 7, the film-forming stability was poor and the thickness unevenness was large, and samples were barely obtained. The results are shown in Table 9.

[0079]

[Table 7]

[0080]

[Table 8]

[0081]

[Table 9]

When the wrapping properties of the obtained films were evaluated, peeling, tearing, wrinkles and the like were observed at the seal portion, and the wrapping properties of both conditions 1 and 2 were not satisfied.

(Examples 14 to 18) In the same manner as in Example 1, using a three-kind five-layer die, a predetermined tubular raw material (Examples 14 to 16 had a total thickness of 400 μm, Example 17, Sample No. 18 had a total thickness of 60 μm, was subjected to the same cross-linking treatment, and was then subjected to stretch film formation to obtain a film having a layer constitution shown in Table 10 (each surface layer has the same addition as Example 1). 3% by weight of the agent). The draw ratio is Examples 14 to 16
Was 4.7 times the horizontal and 4.3 times the horizontal, and Examples 17 and 18 were the vertical 7 times and the horizontal 6.6 times. Table 11 shows the evaluation results of the obtained film.

[0084]

[Table 10]

Here, D ₁ : copolymer nylon 6/66
(Nylon 66 content: 15% by weight, in 95% sulfuric acid solution (2
Relative viscosity measured at 5 ° C .: 3.0) D ₂ : ethylene-vinyl alcohol copolymer [ethylene content: 44 mol%, saponification degree: 99% or more, MFR (2
10 ° C., 2160 g): 3.5] B ₃ : (b ₇ : 75% by weight + a ₄ : 25% by weight)

[0085]

[Table 11]

All of them are excellent in stretch film-forming property and wrapping property, and those having a thin barrier resin layer are particularly useful as a barrier shrink film and a barrier wrap film.

[0087]

INDUSTRIAL APPLICABILITY The multi-layer film of the present invention has excellent stretch film-forming properties, in particular, a thin film can be stably obtained, and has excellent heat-shrinkability as well as optical properties such as transparency, waist and tear. It has good mechanical properties such as strength, and is particularly excellent in various sealing properties such as overlap seals, gastric seals, fusing seals, etc. Very useful for packaging materials.

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Claims (1)

[Claims] 1. Two surface layers are composed of a polymer (A) whose main component is an ethylene-aliphatic unsaturated carboxylic acid copolymer, and at least one of the inner layers has a density of 0.890 to 0.9.
40 g / cm ³ of a high-pressure low density polyethylene, an ethylene-α-olefin-based copolymer, a polymer (B) containing at least one polymer selected from polybutene-1-based polymers as a main component In a multilayer film of at least three layers, the melting point of the polymer, which is the main component of the polymer (B), is 130 ° C. or less as measured by a differential scanning calorimeter and is the main component of the polymer (A). It has a value at least 5 ° C. higher than the melting point of the copolymer, and the thickness ratio of the (A) layer and the (B) layer to all layers is 5 to 80% and 20 to 95%, respectively.
And a gel fraction due to crosslinking of 3 to 30% as a whole, a heat-shrinkable multilayer film.