JP2011136548A - Polyolefin-based heat-shrinkable film excellent in shrink finish properties - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyolefin-based heat-shrinkable film which can obtain excellent low-temperature shrinking performance and heat resistance without carrying out cross linking, and can express advanced shrink finish properties required in packaging an expensive commercial product. <P>SOLUTION: In the polyolefin-based heat-shrinkable film, a film comprising at least three layers composed of surface layers comprising 10-60 pts.wt. of a polyolefin-based elastomer in which a melting peak temperature measured by a differential scanning calorimeter (hereinafter called as DSC) is in the range of 130-170°C a hardness (Shore A) is 60-90, and 40-90 pts.wt. of a propylene resin, and a core layer composed of an ethylenic resin is vertically and horizontally biaxially-stretched. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a shrink wrap material, and more particularly, to a polyolefin-based heat shrinkable film excellent in shrink finish.

Conventionally, polyvinyl chloride shrink film, polypropylene shrink film, polyethylene shrink film, and the like are known as heat shrinkable packaging materials, but polypropylene, in terms of low cost, easy disposal after use, etc. Polyolefin shrink films such as polyethylene are preferably used. However, although the polypropylene-based shrink film is excellent in heat resistance and the like, it has drawbacks such as low temperature shrinkage and poor tear resistance. On the other hand, the polyethylene-based shrink film has defects such as poor heat resistance, although it is excellent in low-temperature shrinkage and tear resistance.

In order to improve these drawbacks, a polyethylene-based crosslinked shrink film obtained by crosslinking an ethylene-based resin has been disclosed (Patent Document 1). These polyethylene-based cross-linked shrink films are excellent in low-temperature shrinkage, heat resistance, tear resistance, etc., but because they are cross-linked, it is difficult to reuse scrap generated in manufacturing processes and non-standard products. There are problems such as cost increase and resource saving.
Moreover, the polyolefin-type heat-shrinkable film (patent documents 2-7) which laminated | stacked propylene-type resin and ethylene-type resin on the surface layer and the inner layer individually or by the blend type | system | group is disclosed. These films still have insufficient low-temperature shrinkage, heat resistance, etc., and have a problem that the high shrinkage finish required for packaging expensive products such as cosmetics and drugs cannot be obtained. It was.

JP-A-5-84826 Japanese Patent Laid-Open No. 10-296932 JP 2005-144725 A JP 2008-036844 A JP 2008-149503 A JP 2009-039950 A JP 2009-101682 A

The present invention provides a polyolefin-based heat-shrinkable film that has excellent low-temperature shrinkage and heat resistance without crosslinking, and can exhibit the high degree of shrinkage finish required when packaging expensive products. It is an object to do.

The inventors of the present invention have arrived at the present invention as a result of intensive studies to solve such problems. That is, in the present invention, the melting peak temperature measured by a differential scanning calorimeter (hereinafter abbreviated as DSC) is in the range of 130 ° C. to 170 ° C., and the hardness (Shore A) is 60 to 90.
It consists of at least three layers of a surface layer composed of 10 to 60 parts by weight of a polyolefin-based elastomer and 40 to 90 parts by weight of a propylene-based resin, and a core layer composed of an ethylene-based resin.
This is an axially stretched polyolefin heat-shrinkable film.

The polyolefin-based heat-shrinkable film of the present invention is excellent in low-temperature shrinkage and tear resistance, a surface layer comprising a polyolefin-based elastomer excellent in low-temperature shrinkage and heat resistance, and a propylene-based resin excellent in heat resistance and the like. It consists of at least three core layers made of an ethylene-based resin, and has excellent low-temperature shrinkage and heat resistance by stretching biaxially in the vertical and horizontal directions, and has a high degree of shrinkage that is required when packaging expensive products. There is an effect that sex can be expressed.

Hereinafter, the present invention will be described in detail.
In the present invention, the polyolefin elastomer used for the surface layer has a melting peak temperature measured by DSC in the range of 130 ° C. to 170 ° C. and a hardness (Shore A) of 60.
It must be ~ 90. When the melting peak temperature is less than 130 ° C, the heat resistance is insufficient, and when it exceeds 170 ° C, the low temperature shrinkage is insufficient. When the hardness (Shore A) is less than 60, the heat resistance is slightly insufficient, and the slipping property is also deteriorated. In other words, combining the aforementioned melting peak temperature range and hardness range is indispensable to achieve a high balance between low-temperature shrinkage and heat resistance, and the high shrinkage finish required when packaging expensive products. It leads to the expression of sex. An example of the polyolefin-based elastomer is Notio manufactured by Mitsui Chemicals Co., Ltd., whose crystal and amorphous structure are nano-order controlled. In addition, this polyolefin-based elastomer is a surface layer resin 1
It is necessary that 10 to 60 parts by weight are contained in 00 parts by weight. If the composition in the surface layer is less than 10 parts by weight, the low-temperature shrinkability is insufficient, and if it exceeds 60 parts by weight, the slipperiness and heat resistance are reduced. In both cases, the high degree required for packaging expensive products It is not possible to develop a good shrinkage finish.

Further, in the measurement using the DSC, the polyolefin elastomer of the surface layer has a total amount of heat absorbed from the melting start temperature to a temperature 20 ° C. lower than the melting peak temperature from the melting start temperature to the melting end temperature. It is desirable that it is 39% or less, preferably 30% or less, more preferably 20% or less of the total heat absorbed during the period. If it exceeds 40%,
The slipperiness tends to decrease.

The propylene-based resin used for the surface layer of the present invention is a polymer having a propylene content of 50 mol% or more, and produced by a metallocene catalyst, a Ziegler-Natta catalyst, or the like.
A polypropylene homopolymer, a copolymer of propylene and α-olefin, such as propylene-ethylene, propylene-butene copolymer, and propylene-ethylene-butene terpolymer. 40 in 100 parts by weight of the surface layer resin
It is contained in 90 parts by weight and mainly serves to impart heat resistance. When the composition of the surface layer of the propylene-based resin is less than 40 parts by weight, the heat resistance and slipperiness are lowered, and when it exceeds 90 parts by weight, the low-temperature shrinkage is lowered. In both cases, it is necessary for packaging expensive products. It is not preferable because it cannot exhibit the high shrinkage finishing property.

The propylene resin used for the surface layer has a melting peak temperature of 12 measured by DSC.
It is preferable that it is 0-165 degreeC and MFR is 0.3-10.0 g / 10min. If the melting peak temperature is less than 120 ° C, the heat resistance tends to be low, and if it exceeds 165 ° C, the low temperature shrinkage tends to be low, and if the MFR is less than 0.3 g / 10 min or 10.0 g / 10 min , Transparency tends to decrease.

The ethylene-based resin used for the core layer of the present invention is a polymer having an ethylene content of 50 mol% or more, and propylene, butene-1, pentene-1, hexene-1, heptene-
1, one or more α-olefins selected from the group consisting of octene-1, 4-methylpentene-1, copolymers of ethylene with ethylene-vinyl acetate, ethylene-aliphatic non-aliphatic Saturated carboxylic acid copolymer, ethylene-aliphatic unsaturated carboxylic acid ester copolymer,
Consisting of at least one selected from ionomer resins and polyethylene homopolymers,
Mainly acts to provide low temperature shrinkage and tear resistance.

When ethylene-based resin is not used for the core layer, low-temperature shrinkage and tear resistance are insufficient, and the high shrinkage finish required for packaging expensive products cannot be expressed. This is not preferable because problems such as easy breakage of the product occur.

The ethylene resin used for the core layer has a density of 0.865 to 0.925 g / cm ³ , M
It is preferable that it consists of 1 type, or 2 or more types of ethylene-alpha olefin copolymer of I0.5-4.0g / 10min. The density is more preferably 0.870 to 0.910 g / cm ³ . When the density is less than 0.865 g / cm ^3, the tensile elastic modulus of the film tends to be lowered and the running property in the packaging machine tends to be lowered. When the density exceeds 0.925 g / cm ³ , the low temperature shrinkage is lowered. It becomes easy. When MI is less than 0.5 g / 10 min, the motor load at the time of extrusion tends to increase, and when it exceeds 4.0 g / 10 min, stretching workability and heat resistance decrease, and pinholes and seals during fusing sealing Opening tends to occur.

The surface layer and / or the core layer can be mixed with other resins as long as the object of the present invention is not affected. For example, the surface layer can be mixed with an ethylene resin, and the core layer can be used with a mixture of a polyolefin elastomer or propylene resin used in the surface layer. Adjustments can be made, and recycled resins such as trims and non-standard products can be mixed.

The layer structure of the present invention is a layer structure of at least three layers, for example, a three-layer structure of A / B / A,
A five-layer structure such as A / A + B / B / A + B / A, A / B / A + B / B / A, and the like can be given. Among them, the layer structure provided with the A + B layer is preferable because it is easy to adjust various physical properties and to mix and use recycled resins.
The mixing ratio of the polyolefin-based elastomer, the propylene-based resin and the ethylene-based resin in the A + B layer is not particularly limited as long as it does not hinder the object of the present invention.

Although it does not specifically limit about the thickness structural ratio of each layer of this invention, It is preferable that the thickness ratio of a core layer exists in the range of 40 to 80% with respect to the whole thickness. If the thickness ratio of the core layer is less than 40%, the tear resistance tends to be lowered, and if it exceeds 80%, the heat resistance tends to be lowered. Although the total thickness of the film is not particularly limited, it is preferably 7 to 35 μm as a heat shrinkable packaging material.

As long as it does not interfere with the object of the present invention, additives such as lubricants, antiblocking agents, antistatic agents, antifogging agents, and antioxidants should be used appropriately for the purpose of providing each effective action. Can do.

Next, the manufacturing method of the film of this invention is shown. The method for producing the film of the present invention using the above resin can be carried out by a known longitudinal and transverse biaxial stretching method.

Hereinafter, the case of three-layer laminated annular film-forming stretching will be described as an example.
First, a mixture of a polyolefin-based elastomer and a propylene-based resin is melt-kneaded with three extruders so that it becomes a surface layer and an ethylene-based resin as a core layer, and is co-extruded in a ring from a three-layer annular die, without stretching. Once rapidly solidified, a tube-shaped unstretched film is produced. The obtained tube-shaped unstretched film is supplied to a tubular stretching apparatus, and a highly orientable temperature range, for example, a temperature lower than 10 ° C. below the melting point of the core layer resin, preferably below 15 ° C. below the melting point.
By applying gas pressure to the inside of the tube at a lower temperature and expanding and stretching, both the longitudinal and lateral stretch ratios are 3
Causes simultaneous biaxial orientation at ~ 6 times. The film taken out from the stretching apparatus can be annealed as desired, and the natural shrinkage during storage can be suppressed by this annealing.

EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited to these Examples.
The measurement and evaluation methods and the raw materials used in Examples and Comparative Examples are shown below.

1. Film thickness: measured according to JIS-Z1709.

2. Thickness ratio: Measured by observing the cross section of the film with a microscope.

3. Haze: Measured according to JIS-K7105.

4). MI: Measured according to JIS-K7210 at 190 ° C. and 2.16 kg load condition.

5. MFR: Measured under conditions of 230 ° C. and 2.16 kg load according to JIS-K7210.

6). Melting peak temperature: Measured according to JIS-K7121 using a differential scanning calorimeter (DSC).

7). Hardness (Shore A): The instantaneous value was measured according to ASTM D2440.

8). Low-temperature absorption ratio: In measurement using DSC, (total amount of heat absorbed from the melting start temperature to a temperature 20 ° C. lower than the melting peak temperature) / (between the melting start temperature and the melting end temperature) The total amount of heat absorbed by the low-temperature-side absorbed heat led to the total amount of heat was measured.

9. Tensile modulus: measured according to JIS-Z7127.

10. 100 ° C. heat shrinkage ratio: 10 pieces of a film cut into a square of 100 mm each in length and width
After being immersed in a glycerin bath at 0 ° C. for 10 seconds, it was rapidly cooled in water, the lengths in the vertical and horizontal directions were measured, and the thermal shrinkage rates of MD and TD were calculated from the formula (1).

11. Shrink packaging finish: Kyowa Denki Co., Ltd. L-type seal type half-fold automatic packaging machine (model: AT-
500), pre-wrap a cosmetic bottle container on the market with a margin of 20%, and stay in the shrink tunnel set at 5 ° C before the heat resistance limit of the film for 5 seconds. Five were randomly selected and evaluated according to the following criteria.
<Evaluation criteria>
○: The corners of the four corners of the packaging sample are extremely small, there are almost no wrinkles, and the appearance is good.
Δ: Corners and wrinkles at the four corners of the packaging sample are slightly noticeable.
X: The corners and wrinkles at the four corners of the packaging sample are clearly noticeable and the appearance is remarkably impaired. Or the film causes poor running at the time of packaging, and scratches and the like are damaged.

A1;
Polyolefin elastomer (Notio PN-3560 manufactured by Mitsui Chemicals, Ltd., melting peak temperature 159 ° C., hardness (Shore A) 70, low temperature absorption ratio 6%)
A2;
Polyolefin elastomer (Mitsui Chemicals Co., Ltd. Notio PN-0040, melting peak temperature 160 ° C., hardness (Shore A) 86, low temperature absorption ratio 17%)
A3;
Polyolefin elastomer (Tafmer A4085S, Mitsui Chemicals, Ltd., melting peak temperature 66 ° C., hardness (Shore A) 86)
B1;
Propylene-ethylene random copolymer (melting peak temperature 145 ° C, MFR = 2.3g / 10min)
B2;
Propylene-ethylene random copolymer (melting peak temperature 125 ° C, MFR = 2.0g / 10min)
B3;
Propylene-ethylene random copolymer (melting peak temperature 145 ° C, MFR = 0.5g / 10min)
C1;
Ethylene-octene-1 copolymer (density = 0.905g / cm3, MI = 0.8g / 10min)
C2;
Ethylene-octene-1 copolymer (density = 0.920g / cm3, MI = 1.0g / 10min)
C3;
Ethylene-octene-1 copolymer (Density = 0.870g / cm3, MI = 1.0g / 10min)

Example 1
As shown in Table 1, a resin composition composed of 25 parts by weight of A1 and 75 parts by weight of B1 is used as both surface layers, C1 is used as a core layer, and after melt-kneading with three extruders, the thickness ratio is 1. The extrusion amount of each extruder was set so as to be / 5/1, and coextrusion was performed downward with a three-layer annular die. The formed three-layered tube was cooled by passing through a water tank while the outer surface of a cylindrical cooling mandrel in which cooling water circulated was slid, and was taken out to obtain an unstretched film. The obtained unstretched tube was guided to a tubular biaxial stretching apparatus and stretched at 90 to 110 ° C. by 5 times in the longitudinal and lateral directions to obtain a laminated biaxially stretched film having a film thickness of 15 μm. The evaluation results of the obtained film were as shown in Table 1 and were good characteristics.

Example 2
In Example 1, a laminate having a film thickness of 15 μm was prepared in the same manner as in Example 1 except that the resin composition consisting of 25 parts by weight of A2 and 75 parts by weight of B1 was used as both surface layers and C2 was used as the core layer. A biaxially stretched film was obtained. The evaluation results of the obtained film were as shown in Table 1 and were good characteristics.

Example 3
In Example 1, a laminate having a film thickness of 15 μm was prepared in the same manner as in Example 1 except that the resin composition consisting of 10 parts by weight of A1 and 90 parts by weight of B2 was used as both surface layers and C3 was used as the core layer. A biaxially stretched film was obtained. The evaluation results of the obtained film were as shown in Table 1 and were good characteristics.

Example 4
In Example 3, a laminated biaxially stretched film having a film thickness of 15 μm was obtained in the same manner as in Example 3 except that the thickness ratio was 1/4/1 and the longitudinal and lateral stretching ratios were respectively 4 times. The evaluation results of the obtained film were as shown in Table 1 and were good characteristics.

Example 5
In Example 1, a laminated biaxially stretched film having a film thickness of 15 μm was obtained in the same manner as in Example 1 except that the resin composition consisting of 60 parts by weight of A1 and 40 parts by weight of B1 was used as both surface layers. It was. The evaluation results of the obtained film were as shown in Table 1 and were good characteristics.

Example 6
In Example 1, a laminated biaxially stretched film having a film thickness of 15 μm was obtained in the same manner as in Example 1 except that the resin composition consisting of 60 parts by weight of A1 and 40 parts by weight of B3 was used as both surface layers. It was. The evaluation results of the obtained film were as shown in Table 2 and were good characteristics.

Comparative Example 1
In Example 1, a laminated biaxially stretched film having a film thickness of 15 μm was obtained in the same manner as in Example 1 except that the resin composition consisting of 75 parts by weight of A1 and 25 parts by weight of B1 was used as both surface layers. It was. The evaluation results of the obtained film were as shown in Table 1, and the slipperiness and heat resistance were lowered, and the shrink-wrapped finish was inferior.

Comparative Example 2
In Example 1, a laminated biaxially stretched film having a film thickness of 15 μm was obtained in the same manner as in Example 1 except that the resin composition consisting of 5 parts by weight of A1 and 95 parts by weight of B1 was used as both surface layers. It was. The evaluation results of the obtained film were as shown in Table 1. The low-temperature shrinkability was insufficient and the shrink-wrapped finish was inferior.

Comparative Example 3
In Example 1, a laminated biaxially stretched film having a film thickness of 15 μm was obtained in the same manner as in Example 1 except that the resin composition comprising 25 parts by weight of A3 and 75 parts by weight of B1 was used as both surface layers. It was. The evaluation results of the obtained film were as shown in Table 1. The heat resistance was insufficient and the shrink-wrapped finish was inferior.

The heat-shrinkable packaging material of the present invention is a polyolefin-based heat-shrinkable material that has excellent low-temperature shrinkability and heat resistance, and can exhibit a high degree of shrinkage finish required when packaging expensive products. It can be suitably used as a film.

Claims (5)

The melting peak temperature measured by a differential scanning calorimeter (hereinafter abbreviated as DSC) is 130.
A surface layer composed of 10 to 60 parts by weight of a polyolefin elastomer having a hardness (Shore A) of 60 to 90 and 40 to 90 parts by weight of a propylene resin, and a core layer composed of an ethylene resin. A polyolefin-based heat-shrinkable film comprising at least three layers of The melting peak temperature measured by DSC of the surface layer propylene-based resin is 120 to 165 ° C.
2. The polyolefin heat-shrinkable film according to claim 1, wherein MFR is 0.3 to 10.0 g / 10 min. The core layer ethylene-based resin has a density of 0.865 to 0.925 g / cm ³ and an MI of 0.5 to 4.0 g.
The polyolefin-based heat-shrinkable film according to any one of claims 1 to 2, wherein the polyolefin-based heat-shrinkable film is composed of one kind or two or more kinds of ethylene-α olefin copolymers for / 10 minutes. The core layer ethylene-based resin has a density of 0.870 to 0.910 g / cm ³ and MI of 0.5 to 4.0 g.
The polyolefin-based heat-shrinkable film according to any one of claims 1 to 3, wherein the polyolefin-based heat-shrinkable film is composed of one kind or two or more kinds of ethylene-α olefin copolymers for / 10 minutes. When the polyolefin elastomer used for the surface layer is measured using DSC, the total amount of heat absorbed between the melting start temperature and the temperature 20 ° C. lower than the melting peak temperature is from the melting start temperature to the melting end temperature. The polyolefin-based heat-shrinkable film according to any one of claims 1 to 4, which is 39% or less, preferably 30% or less, more preferably 20% or less of the total amount of heat absorbed in between. .