JPH079640A - Shrinkable multilayer film - Google Patents

Abstract

PURPOSE:To obtain a multilayer film which has excellent adaptability for wrapping and surface display characteristic by using a mixed resin of ethylene-alpha- olefin copolymer and ethylene-vinyl acetate copolymer as a surface layer and using a polyethylene polymer layer having high pressure low density as an inner layer. CONSTITUTION:A surface layer and an inner layer made of two layers are provided. The surface layer consists of a mixed resin in which 10-90wt.% of ethylene-a-olefin copolymer and 10-90wt.% of a kind of copolymer selected out of EVA, ethylene-aliphatic unsaturated carboxylic acid copolymer, and ethylene-aliphatic unsaturated carboxylic ester copolymer are mixed. One layer out of them is a polymer layer which contains polyethylene of high pressure low density as a main component. At least other one layer is a polymer layer which contains ethylene-a-olefin copolymer as a main component. A shrinkable film is constituted of the four layers.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shrinkable multi-layer film made of an ethylene resin suitable for shrink wrapping and the like.

[0002]

2. Description of the Related Art Conventionally, shrink wrapping is characterized in that the appearance of the package is beautiful, it has a display effect, the product value is increased, the contents are kept hygienic, and the quality can be visually confirmed easily. In addition, since even irregularly shaped products and a large number of products can be quickly and tightly packaged, they are widely used for packaging foods, sundries and the like. With an automatic wrapping machine for shrink wrapping, the contents are wrapped with a slight margin, and the contents are passed through a shrink tunnel heated by a heater, etc. When heat is applied by a fan motor, the film shrinks and the product You can make a tight and tight packaging, and a tight and beautiful packaging. The properties required for films for this purpose are strength, shrinkage, sealing properties (especially fusing sealing properties), surface display properties such as transparency and anti-fog properties (especially foods), and heat resistance (microwave oven). The packaging characteristics such as the characteristics that can be used) are required comprehensively.

As a film suitable for shrink wrapping and the like, a thermoplastic film mainly containing polyethylene, polypropylene or polyvinyl chloride is generally known.
In a heat shrink film using polyvinyl chloride, plasticizers and heat stabilizers that are added and used in combination are not preferable for hygiene,
Disposal and incineration have problems in environmental protection and hygiene, and for these reasons, polyolefin-based shrink films have been favorably used in recent years.

As a shrinkable film for packaging, which is particularly used for foods, a linear low density polyethylene (hereinafter referred to as "LLDPE") is disclosed in JP-A-60-240451.
And 2 surface layers consisting of linear medium-density polyethylene and ethylene-vinyl acetate copolymer (hereinafter referred to as "EVA"), and L
A crosslinked film having a layer made of LDPE is disclosed, and JP-A-1-301251 discloses a density of 0.
870 to 0.915 g / cm ³ of two surface layers made of ethylene-α-olefin copolymer and a density of 0.915 to 0.
A biaxially stretched film having a core layer made of 930 g / cm ^{3 of} an ethylene-α-olefin copolymer is disclosed, and JP-A-3-138148 discloses a density of 0.9.
A multi-layer film having two surface layers consisting of an ethylene-α-olefin copolymer of 100 to 0.925 g / cm ³ and EVA and a core layer consisting of high-pressure low density polyethylene (hereinafter referred to as “LDPE”) (Including) are disclosed.

The film described in JP-A-60-240451 is characterized by having excellent heat-sealing properties and a gradual shrinkage-temperature curve, but the transparency, especially the transparency after shrinkage, Has the drawback of decreasing,
Further, the anti-fogging agent is inferior in bleeding property, and it is difficult to impart anti-fogging property. The film described in Japanese Patent Application Laid-Open No. 1-301251 is characterized by excellent low-temperature sealing property and good packaging suitability, but it is similarly insufficient in anti-fogging property and is extremely heat-resistant. It cannot be used in a microwave oven. If the film described in JP-A-3-138148 is crosslinked, it has sufficient heat resistance and is well-balanced in overall characteristics, but the film has a slightly weak strength and is practically used. On the other hand, when shrink-wrapping is performed, there is a problem that the film is torn from the air vent hole, and the running property is somewhat difficult depending on the type of the packaging machine.

As described above, at present, no shrink wrapping film has been obtained which satisfies all the properties required for efficiently packaging foods or the like in an automatic wrapping machine.

[0007]

SUMMARY OF THE INVENTION One of the objects of the present invention is to provide a polyethylene-based multilayer film satisfying the characteristics such as packaging suitability and surface display characteristics. It is an object of the present invention to provide a shrinkable multi-layer film having not only the characteristics but also heat resistance that can withstand the use of a microwave oven.

[0008]

That is, the present invention comprises 10 to 90% by weight of an ethylene-α-olefin copolymer,
EVA, ethylene-aliphatic unsaturated carboxylic acid copolymer,
10 to 90% by weight of at least one copolymer selected from ethylene-aliphatic unsaturated carboxylic acid ester copolymers
And a surface layer made of a mixed resin of, and an inner layer composed of at least two layers, at least one layer of which is a polymer layer containing high-pressure low-density polyethylene as a main component, and at least other layers. A shrinkable film, characterized in that one layer comprises at least four layers which are polymer layers containing an ethylene-α-olefin copolymer as a main component.

The present invention will be described in detail below.
Ethylene-α-olefin copolymer used for surface layer
Is a commonly known straight-chain ethylene and, for example, butene-
1, pentene-1, hexene-1, 4-methylpentene
-1, octene-1 etc. are selected from 3 to 18 carbon atoms
At least one α-olefin, preferably hexene
Copolymerization of -1,4-methylpentene-1 and octene-1
It was done. This ethylene-α-olefin copolymerization
Body density is 0.870-0.940g / cm ³Range of
And preferably 0.890 to 0.925 g / c
m³, And more preferably 0.905 to 0.915 g / cm
³Is. Density is 0.870g / cm³Less than
The film surface tends to be sticky,
It may cause blocking or similar causes during packaging work.
Trouble easily occurs, and the density is 0.94
0 g / cm³If it exceeds the limit, the compatibility with EVA will decrease.
And the transparency (especially after shrinkage) decreases.
It

EVA used in the surface layer of the present invention has a vinyl acetate group content of 5 to 26% by weight, preferably 7 to 2
It is in the range of 0% by weight, more preferably 10 to 17% by weight. A vinyl acetate content of less than 5% by weight is inferior in transparency, and a vinyl acetate content of more than 26% by weight is inferior in extrusion moldability.
The acetic acid odor tends to be strong, and stickiness tends to occur. Further, as the ethylene-aliphatic unsaturated carboxylic acid copolymer and the ethylene-aliphatic unsaturated carboxylic acid ester copolymer, an ethylene-acrylic acid copolymer, an ethylene-methacrylic acid copolymer, an ethylene-acrylic acid ester (C ₁ -such as methyl, ethyl, propyl, butyl, etc.
Arco of C ₈ - selected from the components of the Le) copolymer, ethylene-methacrylic acid ester (methyl, ethyl, propyl, selected from the components of the alcohol of C ₁ -C ₈ of butyl) copolymers can be mentioned To be These are multicomponent copolymers of three or more components to which other components are further added (for example, free terpolymers of three or more components selected from ethylene, aliphatic unsaturated carboxylic acid and the same ester, or modified ones thereof. What you did). The component to be copolymerized may be one of the above, or at least two or more multicomponent copolymers selected from other components. The content of these carboxylic acid or carboxylic acid ester groups is usually 3
The amount is ˜35% by weight, preferably 3 to 25% by weight, more preferably 3 to 20% by weight in consideration of the deterioration of the packaging work due to the blocking of the film and the lowering of the waist.

At least one selected from the ethylene-α-olefin copolymer (former), EVA, ethylene-aliphatic unsaturated carboxylic acid polymer, ethylene-aliphatic unsaturated carboxylic acid ester copolymer and the like for the surface layer of the present invention. The proportion of one polymer (latter) is 90 to 10% by weight of the former, and 10 to 90% by weight of the latter, preferably 80 to 90% by weight of the former.
The latter is 20 to 65% by weight with respect to 35% by weight. If the latter ratio is less than 10% by weight, for example, the kneadability with a surfactant and an antifogging agent and the bleeding property are poor, and the antifogging property is deteriorated. On the other hand, if the latter component is more than 90% by weight, the heat-sealing property, particularly the fusing and sealing property will be deteriorated.

The high-pressure low-density polyethylene used as the main component of the inner layer of the present invention is a commercially available ethylene homopolymer having a long-chain branch or a copolymer modified with a small amount of α-olefin. It includes. In addition, those which are usually used as modified polyethylene obtained by copolymerizing ethylene with 10% by weight or less of the following copolymerizable comonomer, for example, a vinyl acetate group content of 10
It contains EVA or the like in an amount of not more than wt%. “Mainly” means that the high-pressure low-density polyethylene has a ratio of at least 50% by weight or more, for example, high-density polyethylene, LLDPE, ultra-low density (“VLDP”).
E ", referred to as" ULDPE ") polyethylene, ethylene-aliphatic unsaturated carboxylic acid polymer, ethylene-aliphatic unsaturated carboxylic acid ester copolymer, α-olefin copolymer soft polymer ( For example, one or more α-olefins selected from ethylene and / or propylene and α-olefins having 4 to 12 carbon atoms, or a soft copolymer composed of a free combination thereof may be mentioned. Crystals thereof by X-ray method The degree of chemical conversion is generally 30% or less, which is different from the above-mentioned resin group), polypropylene, polybutene-based polymer, poly-4-methylpentene-based polymer, etc. It is contained in the range.

Next, the linear ethylene-α-olefin copolymer used as the main component in the other inner layer means ethylene and, for example, butene-1, pentene, similar to those used in the surface layer. -1, hexene-1, 4
-Methylpentene-1, octene-1, etc. have 3 to 10 carbon atoms.
A copolymer of at least one α-olefin selected from the group consisting of 18 and hexene-1,4-methylpentene-
A copolymer of 1, and octene-1 is more preferable. The density of this ethylene-α-olefin copolymer is 0.87.
It is in the range of 0 to 0.940 g / cm ³ , preferably 0.900 to 0.940 g / cm ³ , and more preferably 0.915 to 0.935 g / cm ³ . If the density is less than 0.870 g / cm ³ , the film strength, elastic modulus, stiffness, etc. are reduced and the density is 0.9.
If it is 40 g / cm ³ or more, the transparency (particularly the transparency after shrinkage) tends to be poor even when it is used as an inner layer. The linear ethylene-α-olefin copolymer, which is the main component, may be mixed with other polymers within a range that does not impair the original properties thereof, as in the case of the high-pressure low-density polyethylene as described above. Is.

The coexistence of the above-mentioned polymer layer mainly composed of the high-pressure low-density polyethylene and the polymer layer mainly composed of the ethylene-α-olefin copolymer as an inner layer makes it possible to obtain optical properties such as transparency and the like. Achieves stable stretch film-forming property while maintaining excellent properties such as anti-fogging property and sealing property, especially excellent film-forming stability in high-magnification biaxial stretching, and tearing from air holes during shrink wrapping Such problems as described above have been solved, the film has excellent runnability, and the finish after shrink-wrapping has no wrinkles at the corners, resulting in a marked improvement over conventional products.

The film of the present invention comprises 10 to 90% by weight of the ethylene-α-olefin copolymer forming the surface layer, ethylene-vinyl acetate copolymer, ethylene-aliphatic unsaturated carboxylic acid copolymer, ethylene-aliphatic. A resin layer (A) made of a mixed resin containing 10 to 90% by weight of at least one copolymer selected from unsaturated carboxylic acid ester copolymers,
And at least four layers of a total of a polymer layer (B) mainly composed of a high-pressure low-density polyethylene as an inner layer and an ethylene-α-olefin copolymer layer (C) as an inner layer, and the layer arrangement For example, in the case of 4 layers:
In the case of 5 layers such as A / B / C / A: A / B / C / B / A,
A / C / B / C / A, A / B / A / C / A, etc. 7 layers: A / B / A / C / A / B / A, A / B / A / B / C
/ B / A, A / B / C / A / C / B / A, A / C / B /
A / B / C / A, A / C / A / B / A / C / A, A / C
/ B / C / A / C / A, A / B / A / C / A / C / A,
A / B / A / B / A / C / A, A / B / C / A / B / C
/ A, A / B / C / B / A / C / A and the like, but not limited thereto, and also includes cases of 6 layers, 8 layers and more.

When two or more layers (A), (B) or (C) are provided, the resins constituting those layers may be the same or different, and The (A) layer is a multilayer of different polymers (copolymerization components of each resin, copolymerization ratio, mixed composition, etc.), for example, A
It may be ₁ / A ₂ or the like, and the same applies to the (B) layer or the (C) layer. At this time, there is no particular limitation on the method for forming a multilayer, and any conventionally used method such as a coextrusion method, a laminating method, or a coating method may be used, but the coextrusion method is particularly preferable. Is preferred.

Further, at least one layer composed of other resin may be used in the film as long as the characteristics of the film of the present invention are not impaired.

These layers may have gas barrier properties of ethylene-vinyl alcohol type copolymers, polyamide type polymers, polyester type polymers and acrylonitrile type polymers, and these gas barrier resins may be used. A combination of layers and an adhesive layer may be used.

In order to obtain a heat-shrinkable film, it is preferable to orient it in a stretched state, and depending on the shrinkability required according to a commonly used method, it is about 2 to 10 times in each direction of uniaxial or biaxial. Stretching is preferred.
The commonly used methods include roll stretching method, tenter method,
There is no particular limitation such as a bubble stretching method, but a method of forming a film by simultaneous biaxial stretching is preferable. Also, if necessary, after processing,
For example, heat setting or lamination with another film may be performed.

The thickness of the heat-shrinkable film of the present invention is not particularly limited, but when it is used as a sheet, it is usually 100 to 1000 μm, and when it is used as a film, its thickness is 5 to 100 μm. More preferably, it is from 7 to 80 μm, and if it is less than 5 μm, there is a problem in workability during packaging, such that the film tends to have insufficient rigidity and is easily torn. The thickness of the (A) layer on the surface is preferably 5 to 60% of the entire film,
It is preferably 10 to 50%. When it is 5% or less, the seal strength is low and the transparency is lowered, and when it is 60% or more, the performance is excessive. The thickness of the layer (B), which is one of the intermediate layers, is suitably used in the range of 10 to 80%, preferably 20 to 60%. If it is 10% or less, stretching stability, uneven thickness, and low-temperature shrinkability are poor. Furthermore, the thickness of the (C) layer is suitably used in the range of 10 to 80%, preferably 20 to 60%. If it is 10% or less, the mechanical strength such as tear strength and elastic modulus of the film is poor.

As a preferred method of imparting heat resistance in addition to heat shrinkability, crosslinking treatment is carried out either before or after stretching, or both so that the gel fraction of the film becomes 1 to 50%. preferable. As a cross-linking method,
First, energy ray irradiation can be mentioned. Examples of energy rays include ionizing radiation such as ultraviolet rays, electron rays, X rays, α rays, γ rays and neutron rays, and electron rays are preferable. It is also possible to add a cross-linking agent and heat it above the decomposition temperature of the cross-linking agent to carry out the cross-linking, which may be combined with energy beam irradiation, and other known cross-linking methods are used.
At that time, preferably, electron beam (energy: 100 KV
It is possible to freely crosslink the surface layer (one or both), the inner layer or the like at a level of 1 MV). In that case, the gel fraction is 1 to 3 in total.
It is more preferably 5% by weight. Further, the polymer layer of the present invention may contain a surfactant and an antifogging agent to the extent that they do not impair the original properties of each, and for example, polyhydric alcohol moieties such as sorbitan fatty acid ester, glycerin fatty acid ester, and polyglycerin fatty acid ester. Of ethylene oxide such as fatty acid ester of polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, polyethylene glycol fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene glycerin fatty acid ester, alkylamine, alkylamide, alkylethanol Amines, amines such as alkylethanolamides, amides, polyalkylene glycols, granidine derivatives, phosphate-containing ion activators, sulfonic acid derivatives, quaternary ammonium , Pyridinium salts, other imidazoline derivatives, polyvinyl alcohol, hydrophilic polymers of acrylic acid,
It may be a polymer having a pyrrolidinium ring in the main chain, or a mixture containing at least one or more of silica sol, alumina sol and the like. 2 to 5% by weight, preferably 0.4 to 4% by weight,
If it is less than 0.2% by weight, the effects such as antifogging property and antistatic property are not sufficient, and if it is more than 5% by weight, the kneading property is deteriorated and the surface is contaminated. It is preferable to add it also to at least one layer. In particular, in order to exhibit properties such as antifogging property and antistatic property at an early stage and to improve its durability, it is preferable to add a large amount to the inner layer rather than the surface layer. It is preferable to add 0.5 to 6% by weight to the above. In addition, in some cases, in addition to the above (or in addition to the above), the surface layer may be subjected to various coating treatments with a known treatment agent containing the above-mentioned additives by a known method.

The film of the present invention is an antioxidant, an ultraviolet absorber, a plasticizer, an antiblocking agent, which is usually used for plastic films, within the range not impairing the original purpose.
If desired, slip agents, lubricants, antistatic agents, inorganic fillers, etc. may be contained. These are contained in at least one of the resin layers constituting the film of the present invention. If it is necessary to prevent sliding and blocking with the packaged product while maintaining the above, it is also effective to use an anti-blocking agent, slip agent, lubricant, etc. only on one surface layer on the side that contacts the packaged product. is there.

The film of the present invention is mainly suitable for packaging materials, especially shrink wrapping, but it is also a film that can be used as a household or commercial wrap film.

[0024]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

The measuring methods and evaluating methods in the examples are as follows. (1) Gel Fraction A sample is extracted with boiling p-xylene, and the proportion of the insoluble portion is shown by the following equation (1), which is used as a measure of the degree of crosslinking.

[0026]

[Formula 1] However, a polymer which is not cross-linked and which is not completely dissolved in boiling p-xylene is replaced with p-xylene, and the solvent is appropriately changed to a solvent that can be completely dissolved during boiling for measurement. (2) Film-forming stability The stability during inflation film formation of the film was evaluated according to the following criteria according to the size of the uneven thickness of the film.

⊚: Bubbles that do not fluctuate when the thickness deviation is less than ± 10% ○: Bubbles that fluctuate slightly when the thickness is ± 10 to 20% △: Bubbles that fluctuate more than ± 20% and have a large fluctuation : Non-inflationable (3) Anti-fogging property Cover a beaker containing water at 20 ° C for 3 days after film formation, leave it in the refrigerator at 5 ° C for 1 hour, and then check the state of the water attached to the film. The following criteria were used for evaluation.

5: A water film formed in a mirror surface 4: A water film with a slight unevenness 3: A film with spread water drops 2: A film with small water drops 1: White and cloudy Things that cannot be confirmed (4) Tensile elastic modulus It was measured according to the ASTM-D-882-81 method. (5) Tear strength According to JIS-P-8116, it measured using the light load tearing tester (made by Toyo Seiki). The value was the average value of the tear strength in the machine direction and the transverse direction. In addition, the reading of the measurement here is
The measurement was carried out so that the scale was in the range of 20 to 60, but if there was a difference in the measured values depending on the measurement range, the higher value was adopted. (6) Fusing seal strength 0.5mmR × 280mm for sentinel heat sealer
Attach L fusing blade, 140 ~ 240 ℃, 30psi,
Two layers of 15 mm width film were fused and sealed under the condition of 0.5 seconds, and immediately after that, one end of the film was fixed and a load was applied to the other end to measure the load at intervals of 20 ° C. The maximum load was defined as strength. (7) Haze after Shrinking The film was shrunk at an area shrinkage of 30% using a hot air tunnel, and then measured by the ASTM-D-1003 method. In addition,
As the temperature, the lowest temperature (90 to 150 ° C.) at which the above shrinkage can be achieved in 5 seconds through the hot air tunnel was adopted. (8) Suitability for packaging machine Using a linear packaging machine (manufactured by Omori Machinery Co., Ltd.), a packaging test was conducted under the conditions of 40 packs / minute using a bento case and chopsticks as contents. This packaging machine supplies the contents at a constant pitch from the film into a tubular shape through a former,
The center seal is continuously performed, then the top seal is performed, the rough packaging is performed, and then the film is contracted by hot air to tightly package the film. The air holes were formed by a mechanical drilling method using a pin having a sharp tip of about 0.4 mmφ. The packaging suitability was evaluated according to the following criteria.

(1) Running stability (running failure was evaluated as the one that develops as a variation in the fusing seal interval.) ◎: The fusing seal interval is constant and stable ○: The fusing seal interval is slightly variable Item △: Large variation in fusing seal spacing ×: Film tearing during packaging (2) Sliding property ◎: Film is machine, good content and slippage ○: Film is caught on the machine Noise: △: Film is caught by the machine and packaging loss is 5% or more ×: Same as above Loss is 10% or more (3) Flat (seal opens when heated with hot air or tears starting from air holes) ◎: No punctures ○: Punctures less than 3% when heated with hot air △: Punks of 3% or more and less than 10% when heated with hot air ×: All punctured after fusing and sealing ( Four ) Finish (wrinkles, tears) ◎: Tight packaging without wrinkles or tears on the film ○: Packaging with some looseness or rare tears △: Some wrinkles or tears on the package × : Package Wrinkled or Ripped Next, the resins used in Examples and Comparative Examples are described below.

VLDPE-1: ethylene-α-olefin copolymer (density = 0.910 g / cm ³ , MI = 3.
6 g / 10 minutes, comonomer = 4-methylpentene) VLDPE-2: ethylene-α-olefin copolymer (density = 0.890 g / cm ³ , MI = 3.3 g / 10
Min, comonomer = 1-octene) LLDPE-1: ethylene-α-olefin copolymer (density = 0.930 g / cm ³ , MI = 2.1 g / 10
Min, comonomer = 4-methylpentene) LLDPE-2: ethylene-α-olefin copolymer (density = 0.920 g / cm ³ , MI = 2.1 g / 10
Min, comonomer = 1-octene LLDPE-3: ethylene-α-olefin copolymer (density = 0.926 g / cm ³ , MI = 2.0 g / 10
Min, comonomer = 1-octene) LLDPE-4: acid-modified ethylene-α-olefin copolymer (density = 0.920 g / cm ³ , MI = 3.5 g /
10 minutes, comonomer = 1-octene LDPE-1: High pressure method low density polyethylene (density = 0.
919 g / cm ³ , MI = 2.0 g / 10 minutes) LDPE-2: High pressure method low density polyethylene (density = 0.
928 g / cm ³ , MI = 0.5 g / 10 min) LDPE-3: High pressure method low density polyethylene (density = 0.
920 g / cm ³ , MI = 0.4 g / 10 minutes) EVA-1: ethylene-vinyl acetate copolymer (density =
0.920 g / cm ³ , vinyl acetate content = 15% by weight, MI = 2.3 g / 10 minutes) EVA-2: ethylene-vinyl acetate copolymer (density =
0.930 g / cm ³ , vinyl acetate content = 10% by weight, MI = 1.3 g / 10 minutes) EVA-3: ethylene-vinyl acetate copolymer (density =
0.940 g / cm ³ , vinyl acetate content = 18% by weight, MI = 2.5 g / 10 minutes) EMA-1: ethylene-methyl acrylate copolymer (density = 0.940 g / cm ³ , methyl acrylate) Content =
8.9% by weight, MI = 3.0 g / 10 minutes) EAA-1: ethylene-acrylic acid copolymer (density =
0.920 g / cm ³ , acrylic acid content = 6.4% by weight, MI = 3.5 g / 10 minutes) EVOH-1: ethylene-vinyl alcohol copolymer (density = 1.140 g / cm ³ , ethylene content) Amount = 3
3.3 wt%, MFI = 3.5 g / 10 minutes) EVOH-2: ethylene-vinyl alcohol copolymer (density = 1.170 g / cm ³ , ethylene content = 2)
8.1% by weight, MFI = 3.5 g / 10 minutes) PA-1: Nylon-6 (density = 1.140 g / c)
m ³ ) (Examples 1 to 12, and Comparative Examples 1 to 5) A mixture of 40% by weight of VLDPE-1 and 60% by weight of EVA-1 was added to the surface layer extruder in the extruder for the inner layer (1). LDPE-1
, LLDPE-1 was fed to the extruder for the inner layer (2),
By co-extruding using a 5-layer die and quenching, surface layer / inner layer (1) / inner layer (2) / inner layer (1) / surface layer = 70 μ / 110 μ / 90 μ / 110 μ / 70 μ, total 450 μ The tubular film of was molded. At that time, diglycerin monooleate as a nonionic surfactant was injected into the extruder in an amount of 2% by weight based on the surface layer and 3% by weight based on the inner layer (1), and kneaded. This tube-shaped film was flattened, and irradiation crosslinking was carried out by an electron beam irradiation device having an acceleration voltage of 500 KV. At this time, the degree of cross-linking was adjusted so that the gel fraction of all layers was 20%, and then the temperature at the stretching start point was heated to 150 ° C.
The film is stretched 6.8 times and TD 6.6 times to obtain a film having a thickness of 10 μm, which is referred to as Example 1.

Further, according to Example 1 according to the kind and blending ratio of the resin, the kind and addition amount of the nonionic surfactant, and the gel fraction as shown in Tables 1, 2 and 3. Similarly, a film was obtained. This will be referred to as Examples 2 to 12 and Comparative Examples 1 to 5.

Explaining these films, Examples 1 to 9 and 11 are five-layer films having respective layer ratios, and Example 10 is a surface layer / inner layer (1) / inner layer (2).
/ Inner layer (3) / Inner layer (2) / Inner layer (1) / Surface layer = 67.5μ / 67.5μ / 67.5μ / 45μ / 6
7.5μ / 67.5μ / 67.5μ, total 450μ
Is a 7-layer film in which a tube-shaped film is prepared, subjected to electron beam irradiation treatment in the same manner as in Example 1, and then stretched to form a film. Further, in Example 12, the surface layer / inner layer (1) / inner layer (2)
/ Inner layer (3) / Inner layer (2) / Inner layer (1) / Surface layer = 67.5 μ / 90 μ / 45 μ / 45 μ / 45 μ / 90
Example 1 except that a tube-shaped film of μ / 67.5 μ, a total of 450 μ was prepared and no electron beam irradiation treatment was performed.
A film having a thickness of 20 μm was formed by stretching in the same manner as in. Comparative Examples 3, 4, and 5 correspond to the prior art, respectively.
138148, JP-A-1-301251,
A film corresponding to JP-A-60-240451, wherein surface layer / inner layer (1) / surface layer = 1.5 μ / 7 μ
It is a 3-layer film with a total of /1.5μ and 10μ. Tables 1, 2 and 3 show film-forming stability, anti-fogging property, transparency after shrinkage, and tensile elastic modulus, tear strength and fusing seal, which are important characteristic values when performing mechanical packaging for these films. The strength and suitability for packaging machines are also described.

[0033]

[Table 1]

[0034]

[Table 2]

[0035]

[Table 3] The films of Examples 1 and 2 of the present invention had excellent stretch film-forming properties, that is, high productivity, and little variation in film thickness. In addition, the film is flexible, and a nonionic surfactant that has the effect of a slip agent and an antifogging agent is moderately bleeding, so running stability and slipperiness are good, and a fusing seal can be firmly performed. It was a thing. In the packaging test, the film was able to be stably packaged, tightly packed without wrinkles and tears, and extremely excellent in packaging workability.

In Comparative Example 1, the fusing sealing property is good because the surface layer is only VLDPE, but the antifogging property is poor and the transparency after shrinkage is poor, and it is difficult to use as a film. It was Regarding the suitability for a packaging machine, the nonionic surfactant did not bleed so badly that the running stability and slipperiness were inferior, and the packaged film had wrinkles and transparency.

In Comparative Example 2, since the surface layer was only EVA, the bleeding of the nonionic surfactant was good, and the transparency and antifog property after shrinkage were good, but the fusing seal strength was low.
Since the fusing seal strength was lower than the shrinkage stress at the time of shrinking after packaging with a margin, the seal was almost peeled off and the package could not be packaged. The problem was that the seal would peel off during packaging.

The film of Comparative Example 3 is good in stretch film-forming property, fusing sealing strength, transparency after shrinkage, and antifogging property, but is inferior in tear strength, so that air is removed when shrinking depending on the size of the bento container. Some of the films were torn from the holes used for, and Comparative Examples 1 to 3 were inferior in packaging workability and were difficult to use.

The film of Example 3 was prepared by adding a mixture of oleic acid amide: erucic acid amide = 1: 1 to the surface layer resin for the purpose of improving peelability and slipperiness, and other than that, Example 1 was used. It is a stretched film formed by the same method as above.The stretched film forming property of this film is good, and the fusing seal strength is excellent, and particularly the film and the lunch container are excellent in slipperiness and peeling property, and thus the film can be easily formed. It was a film that could be opened.

A stretched film was produced in the same manner as in Example 1 except that a tubular film was formed by the same method as in Example 1 with the resin and nonionic surfactant composition shown in Tables 1 and 2. Examples 4 to 9 and 11. Examples 4-9 and 11
Has excellent film-forming stability, high productivity, excellent transparency and antifogging property, and has a high display effect during packaging. Further, the film was excellent in fusing seal strength and tear strength, and had good running stability and slipperiness in a packaging test, and a tight packaging without wrinkles or tears could be achieved.

Regarding Comparative Examples 4 and 5 corresponding to the prior arts of JP-A-1-301251 and JP-A-60-240451, the fusing seal strength was reasonable, but the transparency of the film was poor, In particular, the antifogging property was poor and the surface display property was poor. Further, in the packaging test, the running stability and slipperiness were poor due to poor bleeding of the nonionic surfactant, many wrinkles were observed after packaging, and the packaging workability was poor.

Examples 10 and 12 which are 4-kind 7-layer film
The film was excellent in film-forming property, surface display property, and fusing seal strength, and could be stably packaged without wrinkles or tears in the packaging test. Further, since the resin having excellent gas barrier property is used for the inner layer, the film has high gas barrier property.

(Example 13) A stretched film was prepared in the same manner as in Example 3 except that 0.1% by weight of dimethylpolysiloxane was added to the surface layer of the resin. Similar to Example 3, this film was also excellent in film forming property (⊚), surface display property, and fusing seal strength. Also, since the film is excellent in slipperiness and adhesion, it can be packaged stably without wrinkles or tears even in the packaging test, and the film can be easily opened without the lunch case and the film coming into close contact with each other. there were.

(Example 14) Stretching was carried out in the same manner as in Example 3 except that fine powder silica was used in combination with 0.1% by weight of the surface layer resin as an additive used in the surface layer. The membrane was made. Stretched film formation is stable (◎), especially in the subsequent packaging test, there is almost no tearing from air holes or wrinkles, excellent workability for continuous packaging, and openability after packaging the bento case. It was excellent.

Example 15 Using the same resin as in Example 1 for each surface layer resin, one more surface layer extruder was added, and 0.4% by weight of finely powdered silica and 0.4% by weight of silica were added as additives to the extruder. A surface layer on one side was formed with a composition containing 1.5% by weight of diglycerin monooleate, and 1.5% by weight of diglycerin monooleate as an additive was added to the other surface layer extruder, A five-layer tubular film was formed in the same manner as in Example 1 except that each surface layer was formed, and then a film having a thickness of 10 μm was stably obtained in the same manner. The film was subjected to a packaging test with the silica-added surface layer in contact with the lunch box container. The result was that the finish was extremely good, the gloss and transparency were excellent, and the film had an appropriate anti-fog property (4). However, it was also excellent in openability.

[0046]

INDUSTRIAL APPLICABILITY The film of the present invention has a high degree of suitability for packaging machines such as slipperiness and mechanical strength, and is excellent in surface display characteristics such as transparency and anti-fog property. It is a multi-layered film and gives a beautifully finished package.

Claims (1)

[Claims] 1. An ethylene-α-olefin copolymer 10
To 90% by weight and at least one copolymer selected from ethylene-vinyl acetate copolymer, ethylene-aliphatic unsaturated carboxylic acid copolymer, ethylene-aliphatic unsaturated carboxylic acid ester copolymer 10 A surface layer formed of a mixed resin of 90% by weight, and an inner layer composed of at least two layers in addition to the above, at least one layer of which is a polymer layer containing high-pressure low-density polyethylene as a main component. A shrinkable multilayer film comprising at least four other layers, wherein at least one other layer is a polymer layer containing an ethylene-α-olefin copolymer as a main component.