JPH0977883A - Heat shrinking film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a heat shrinking film excellent in low temperature shrinking property and preserving stability. SOLUTION: This heat shrinking film is produced by blending 100 pts.wt. block copolymer consisting of 70-95wt.% vinyl aromatic hydrocarbon with 30-5wt.% conjugated diene and 1-10wt.% solid plasticizer in an ambient temperature, and uniaxially stretching the obtained resin composition. As the block copolymer, the one containing two or more of the vinyl aromatic hydrocarbon block and the conjugated diene block is preferable. Also, one or more plasticizers selected from triethylene glycol dibenzoate and neopentyl glycol dibenzoate is preferable.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-shrinkable film which has excellent low-temperature shrinkability and good storage stability.

[0002]

2. Description of the Related Art Conventionally, a heat-shrinkable film using a block copolymer composed of a vinyl aromatic hydrocarbon and a conjugated diene could be used as a label for a glass bottle. It was difficult to put it into practical use as an easy-to-use PET bottle label. As a method for improving the low temperature shrinkability of the heat shrink film, JP-A-59-64331 proposes to use a block copolymer obtained by repeatedly polymerizing a styrene block and a butadiene block.

[0003]

However, although the low temperature shrinkability of the film was improved by this method, the storage stability of the obtained heat shrinkable film was inferior. On the other hand, Japanese Patent Application Laid-Open No. 2-206529 proposes a method of improving low-temperature shrinkability and storage stability by adding a plasticizer which is liquid at room temperature to this block copolymer. This method reduces the content of the conjugated diene contained in the block copolymer, and by adding a plasticizer that is liquid at room temperature,
The vinyl aromatic hydrocarbon moiety is plasticized to improve low temperature shrinkability and storage stability. Since the vinyl aromatic hydrocarbon portion is plasticized with a plasticizer that is liquid at room temperature, the low temperature shrinkability is improved, but the stretching begins to return at room temperature,
Natural shrinkage did not result in satisfactory storage stability.

Changing the structure of the block copolymer, changing the content of the conjugated diene contained in the block copolymer,
Attempting to improve the low-temperature shrinkability effect by adding a liquid plasticizer at room temperature has a mutual relationship that storage stability is deteriorated at the same time.

Therefore, there has been a demand for a heat-shrinkable film of a block copolymer system composed of a vinyl aromatic hydrocarbon and a conjugated diene, which has excellent low-temperature shrinkability and good storage stability.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a heat-shrinkable film which can be applied to labels of PET bottles and has excellent low-temperature shrinkability and storage stability.

[0007]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that a block copolymer consisting of a vinyl aromatic hydrocarbon and a conjugated diene is blended with a solid plasticizer at room temperature to carry out uniaxial stretching. Then, it was found that a film which is excellent in low-temperature shrinkability and is hard to shrink naturally at room temperature was obtained, and the present invention was completed. That is, the heat-shrinkable film of the present invention comprises 100 parts by weight of a block copolymer consisting of 70 to 95% by weight of vinyl aromatic hydrocarbon and 30 to 5% by weight of conjugated diene, and plasticizer 1 to be solid at room temperature. A resin composition containing 10 parts by weight is uniaxially stretched.

The present invention will be described in detail below.

The block copolymer used in the present invention comprises 70 to 95% by weight of vinyl aromatic hydrocarbon and 5 to 30% by weight of conjugated diene. Also preferably 75 to 90% by weight of vinyl aromatic hydrocarbon, and 10 to 2 of conjugated diene.
It is composed of 5% by weight.

When the content of the conjugated diene in the block copolymer is less than 5% by weight, the heat shrinkable film finally obtained has insufficient flexibility and low temperature shrinkability. If it exceeds 30% by weight, the rigidity becomes poor and a so-called stiff film results. Examples of the vinyl aromatic hydrocarbon in the block copolymer include styrene, o-methylstyrene, p-methylstyrene, p-tert-butylstyrene, 1,3-dimethylstyrene, α-methylstyrene, vinylnaphthalene,
Although vinyl anthracene can be mentioned, styrene is particularly used among them. These substances may be used alone or in combination of two or more. The conjugated diene is preferably a diolefin having a pair of conjugated double bonds. Specifically, 1,3-butadiene,
2-methyl-1,3-butadiene (isoprene), 2,3-
Dimethyl-1,3-butadiene, 1,3-pentadiene,
1,3-hexadiene can be mentioned, among which 1,3
-Butadiene, isoprene are especially used. These substances may be used alone or in combination of two or more. The block copolymer is a vinyl aromatic hydrocarbon block,
It is preferable to include two or more conjugated diene blocks each. By polymerizing two or more of each block, low temperature shrinkability can be enhanced. However, it is not economically preferable to polymerize 5 or more of each block because the operation is difficult. It is preferable to use a block copolymer containing 2-3 blocks.

In the present invention, 1 to 10 parts by weight, preferably 1 to 3 parts by weight of a plasticizer which is solid at room temperature is added to 100 parts by weight of the block copolymer. If the amount is less than 1 part by weight, the resulting film has poor storage stability. If it exceeds 10 parts by weight, the transparency of the film is lowered and it is not suitable for use.

The plasticizer used in the present invention is a solid at room temperature and becomes a liquid when heated, and preferably has a melting temperature of 40 to 70 ° C. The melting temperature is a melting point, or a melting point without a melting point is a softening temperature. If the melting temperature is less than 40 ° C., natural shrinkage occurs at room temperature and storage stability becomes poor, and if it exceeds 70 ° C., low temperature shrinkability becomes poor.

By adding a plasticizer which is solid at room temperature, the natural shrinkage of the vinyl aromatic hydrocarbon moiety is reduced at room temperature to improve the storage stability. In addition, when shrink-labeling the heat-shrinkable film on a PET bottle or the like by heating, the added plasticizer is melted, so that the vinyl aromatic hydrocarbon portion is plasticized. Therefore, the film tends to shrink, and the low temperature shrinkability is improved.

As the plasticizer which is solid at room temperature, triethylene glycol dibenzoate (melting point 47 ° C.), neopentyl glycol dibenzoate (melting point 49 ° C.), polyester polyol having a melting temperature in the range of 40 to 70 ° C., etc. Can be mentioned.

These substances may be used alone or as a mixture of two or more kinds. As the polyester-based polyol, S-2010 (manufactured by Dainippon Ink and Co., Inc., softening temperature 60 ° C.)
Are commercially available. Of these, triethylene glycol dibenzoate and neopentyl glycol dibenzoate are particularly preferably used.

In the resin composition used in the present invention,
If necessary, a styrene homopolymer, a styrene-butadiene elastomer and an impact resistant styrene polymer can be mixed.

Further, the resin composition used in the present invention comprises an antioxidant, an antistatic agent, a stabilizer, a lubricant, a crosslinking agent,
It may contain a pigment, a dye, a filler, and an antiblocking agent. The method for producing the heat-shrinkable film is as follows. Block copolymerization of vinyl aromatic hydrocarbon and conjugated diene,
Vinyl aromatic hydrocarbon 70-95% by weight, conjugated diene 5
A block copolymer consisting of ~ 30% by weight is produced. A resin composition is prepared by adding 1 to 10 parts by weight of a plasticizer to 100 parts by weight of the block copolymer. The heat-shrinkable film is obtained by laterally uniaxially stretching or longitudinally uniaxially stretching after molding the obtained resin composition by extrusion molding, calendar molding or the like.

[0018]

Since the heat-shrinkable film of the present invention contains a plasticizer which is solid at room temperature, it has good low-temperature shrinkability and storage stability. Since this heat-shrinkable film has good low-temperature shrinkability, it shrinks even at low temperatures and can be used for labels for PET bottles. In addition to that, it has excellent storage stability, which reduces natural shrinkage even in the summer and makes the film convenient to handle.

[0019]

Embodiments of the present invention will be described below in detail.

Example 1 100 parts by weight of styrene-butadiene block copolymer (styrene content 85% by weight, butadiene content 15% by weight, 2 styrene blocks, 2 butadiene blocks), triethylene glycol dibenzoate (melting point 47 ° C.) Two
Parts by weight were mixed to obtain a resin composition. The resin composition was extruded with a T-die to obtain a T-die extrusion molded sheet having an average thickness of 200 μm, and then stretched 4 times using a transverse uniaxial stretching machine to obtain a transverse uniaxially stretched heat-shrinkable film. The resulting film was immersed in oil at 80 ° C for 5 minutes,
Low temperature shrinkage was evaluated by measuring the shrinkage. Separately from this, the film was left in an oven at 30 ° C. for 30 days, and the shrinkage ratio (%) was measured to evaluate the storage stability. Table 1 shows the measurement results. Example 2 A film was produced in the same manner as in Example 1 except that triethylene glycol dibenzoate was 5 parts by weight, and the low temperature shrinkability and the storage stability of the obtained film were evaluated. Table 1 shows the measurement results. Example 3 100 parts by weight of styrene-butadiene block copolymer (styrene content: 85% by weight, butadiene content: 15% by weight, 3 styrene blocks, 3 butadiene blocks), polyester-based polyol (S-2010: Dainippon Ink and Chemicals, Inc.) (Softening temperature 60 ° C.) 2 parts by weight were mixed to obtain a resin composition. A film was produced in the same manner as in Example 1, and the low temperature shrinkability and storage stability of the obtained film were evaluated. Table 1 shows the measurement results. Example 4 S-2010 was set to 5 parts by weight, and other conditions were used in Example 3.
A film was produced in the same manner as above, and the low temperature shrinkability and storage stability of the obtained film were evaluated. Table 1 shows the measurement results. Comparative Example 1 A film was produced in the same manner as in Example 1 from only 100 parts by weight of a styrene-butadiene block copolymer (styrene content 85% by weight, butadiene content 15% by weight, 2 styrene blocks, 2 butadiene blocks). Then, the low temperature shrinkability and the storage stability of the obtained film were evaluated. Table 1 shows the measurement results. Comparative Example 2 A film was produced in the same manner as in Example 1 from only 100 parts by weight of a styrene-butadiene block copolymer (styrene content 85% by weight, butadiene content 15% by weight, 3 styrene blocks, 3 butadiene blocks). Then, the low temperature shrinkability and the storage stability of the obtained film were evaluated. Table 1 shows the measurement results.

[0021]

[Table 1]

As shown in Table 1, the heat-shrinkable films of Examples 1 to 4 are superior to the films of Comparative Examples 1 and 2 (without addition of a plasticizer) in low temperature shrinkability and storage stability.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication B29K 105: 02 (72) Inventor Takayoshi Kinan 1 Higashiwada, Kamisu-cho, Kashima-gun, Ibaraki Shin-Etsu Chemical Industrial Co., Ltd.

Claims (3)

[Claims] 1. 100 parts by weight of a block copolymer consisting of 70 to 95% by weight of vinyl aromatic hydrocarbon and 30 to 5% by weight of conjugated diene, and 1 to 10 of a plasticizer solid at room temperature.
A heat-shrinkable film, wherein a resin composition containing 1 part by weight is uniaxially stretched. 2. The heat-shrinkable film according to claim 1, wherein the block copolymer contains two or more vinyl aromatic hydrocarbon blocks and conjugated diene blocks. 3. The heat-shrinkable film according to claim 1, wherein the plasticizer is at least one kind of plasticizer selected from triethylene glycol dibenzoate and neopentyl glycol dibenzoate.