JPH02227412A - Heat-shrinkable polymer film - Google Patents

Abstract

PURPOSE:To obtain the title film having a specific glass transition temperature, a specific crystallinity index, excellent heat shrinkability, weather resistance and water resistance by drawing a block copolymer containing a polymer block of vinyl aromatic compound, etc., and a polymer block such as conjugated diene, etc. CONSTITUTION:A block copolymer containing (A) a homopolymer of a vinyl aromatic compound or a copolymer of the vinyl aromatic compound and another vinyl aromatic compound or a conjugated diene or an adduct thereof with hydrogen and having >=50 deg.C glass transition temperature and (B) a homopolymer of a conjugated diene compound or a copolymer of the conjugated diene compound and another conjugated diene or the vinyl aromatic compound hydrogenated >=50mol% of unsaturated bond of conjugated diene-unit and having a crystallinity index at 25 deg.C of 15wt.% that of the polymer block B in the polymer chain, forming A-B-A block structure and having 10,000-100,000 weight-average molecular weight is uniaxially or biaxially orientated to give the aimed film having >=10% percentage of heat shrinkage.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a heat-shrinkable polymer film having excellent shrinkage characteristics, weather resistance, and water resistance.

[Prior art] Shrink packaging has recently become popular for food packaging because it eliminates the bagging and wrinkles that were unavoidable with conventional packaging technology, and it also allows for quick packaging of products and irregularly shaped items. Its use is increasing.

Conventionally, vinyl chloride resin has been mainly used as a material for films or sheets for shrink packaging due to its required properties such as low-temperature shrinkability, transparency, and mechanical strength.

[Problems to be solved by the invention] However, although vinyl chloride resin has the above-mentioned excellent properties, there are hygienic problems with vinyl chloride monomers and plasticizers,
There is a problem with the generation of hydrogen chloride during incineration, and there is a strong demand for an alternative.

On the other hand, block copolymer resins made of vinyl aromatic hydrocarbons and conjugated dienes do not have the above problems and have good transparency and impact resistance, so they have been widely used as materials for food packaging containers in recent years. However, these conventionally known block copolymers are unsuitable as materials for heat-shrinkable packaging because they require high stretching temperatures and also have high shrinkage temperatures.

For example, JP-A No. 49-102494 and JP-A No. 49-Sho.
Publication No. 108177 describes a packaging film obtained by biaxially stretching a block copolymer having a styrene hydrocarbon content of 50 to 95% by weight, and a composition in which the block copolymer is blended with a styrene resin. However, such films cannot obtain sufficient shrinkage unless the heat shrinkage temperature is about 100°C or higher, and furthermore, the block copolymer resin contains unsaturated bonds derived from the conjugated diene contained therein. It had problems such as poor weather resistance.

[Means and effects for solving the problem] As a result of intensive studies on heat-shrinkable polymer films, the present inventor found that a polymer film formed by stretching a block copolymer having a specific structure can be produced at a low heat-shrink temperature. The present invention was achieved based on the discovery that it exhibits a high shrinkage rate, has excellent transparency and weather resistance, does not require a plasticizer, and does not generate harmful gases during incineration.

That is, the present invention includes an A-B-A block structure consisting of at least A and B polymer blocks detailed below in the polymer chain, and has a weight average molecular weight of 10.000 to 1.
The present invention provides a heat-shrinkable polymer film having a heat shrinkage rate of 10% or more in the stretching direction, which is obtained by uniaxially or biaxially stretching a block copolymer having a molecular weight of 1,000,000.

Specific examples of the block copolymer structure used in the present invention include general formulas (a) (A-B) (b) B (A- B) (c) B (A-B) (d) [(A-B) (e) ((A-B) CD (B (A-B) (g) (B (A-B) A A A -B] X fl I A) X n I A) X n m A)

In the above formula, n is an integer of 1 or more and 10 or less, and m
is an integer of 2 or more and 10 or less, X is a terminal coupling agent, and each A block and each B block may have the same structure or different structures. The A block consists of a homopolymer of a vinyl aromatic compound, a copolymer of a vinyl aromatic compound and another vinyl aromatic compound, a copolymer of a vinyl aromatic compound and a conjugated diene compound, or a hydrogen adduct thereof. . When the A block is a copolymer, the copolymerization mode may be any copolymerization structure such as random copolymerization, alternating copolymerization, tapered copolymerization, etc., and is not particularly limited. In particular, when the A block is a copolymer of a vinyl aromatic compound and a conjugated diene compound or a hydrogen adduct thereof,
The preferred content of the vinyl aromatic compound or its hydrogen adduct is 10 weight percent or more. Further, the glass transition temperature of the A block must be 50°C or higher, preferably 65°C or higher and 250°C or lower, more preferably 80°C.
above and below 200°C. Glass transition temperature is 50℃
If it is less than this, natural shrinkage at room temperature will occur significantly, which is not preferable. Furthermore, if the glass transition temperature is too low, processing of the resin with a general-purpose plastic processing machine becomes difficult, which may be undesirable in some cases. Furthermore, the preferred if of the Shigenobu average molecule ω of A70 ivy (7IIGat.

i, ooo ~1oo, ooo I like history, Kuha 3,0
The range is from 00 to 30,000. An excessively high molecular weight results in a high molecular weight of the 1q block copolymer, and thus a high melt viscosity, resulting in a decrease in processability3.
Also, if the molecular weight is too low, the heat shrinkage performance of the obtained film will deteriorate, probably because the phase separation structure of the A and B blocks of the block copolymer will collapse.

In addition, the B block consists of a homopolymer of a conjugated diene compound, a copolymer of a conjugated diene compound and a conjugated diene compound, or a copolymer of a conjugated diene compound and a vinyl aromatic compound, and the conjugated diene unit is unsaturated. At least 50% of the bonds are hydrogen adducts, and the crystallinity at 25° C. is at least 5% by weight of the B polymer block, preferably at least 50% by weight of the crystals. melts below the glass transition temperature of the A block. When the B block is a copolymer, its bonding mode may be any copolymerization mode such as random copolymerization, tapered copolymerization, etc., and is not particularly limited. In particular, when the B block is a hydrogen adduct of a copolymer of a conjugated diene compound and a vinyl aromatic compound, the preferred content of the hydrogen adduct of the conjugated diene and () is 70% by weight.
That's all.

In addition, 50 mol% or more of the unsaturated bonds in the conjugated diene unit must be hydrogen adducts, and the preferred hydrogen addition rate is 75
It is mol% or more, more preferably 95 mol% or more, and most preferably 98 mol% or more. If the hydrogen addition rate is less than 50 mol %, sufficient crystallinity cannot be imparted to the obtained block copolymer, and heat shrinkage performance will not be exhibited. Moreover, when the hydrogen addition rate is 98 mol % or more, the heat resistance and weather resistance of the obtained film are significantly improved, which is particularly preferable. 25 more
The crystallinity of the B block at °C must be 5% by weight or more, preferably 10% by weight or more, more preferably 30% by weight or more. When the degree of crystallinity is less than 5% by weight, the polymer exhibits remarkable rubber elasticity,
It becomes difficult to stretch the film. Further, it is preferable that at least 50% by weight of the crystals at 25° C. melt at a temperature lower than the glass transition temperature of the A block. More preferably, 80% by weight, particularly preferably 95% by weight, of the crystals melt below the glass transition temperature of the A block.

When the melting temperature of 50% by weight or more of the crystals exceeds the glass transition temperature of the A block, the shrinkage rate of the resulting heat-shrinkable polymer film decreases. The preferred weight average molecular weight of the B block is 2,000 to 500,000, more preferably 4.000 to 200,000. An excessively high molecular weight will increase the molecular weight and thus the melt viscosity of the resulting block copolymer, leading to a decrease in processability. Moreover, if the molecular weight is too low, the heat shrinkage performance of the obtained film will deteriorate, probably because the phase separation structure of the A and B blocks of the block copolymer will collapse.

The weight average molecular weight of the block copolymer as a whole is 10
．． Must be in the range 000-1.000.000. The preferred weight average molecular weight is 15.000 to 300,
000.

Particularly preferred is a range of 20,000 to 150,000.

Excessively high molecular weight increases melt viscosity and reduces processability. In addition, an excessively low molecular weight is undesirable because it deteriorates film properties such as strength and strength. In addition, regarding the composition ratio of A and B blocks, the content of A block is preferably 5 to 95% by weight, more preferably 20 to 9% by weight.
5% by weight, particularly preferably in the range from 40 to 90% by weight. If the composition ratio of blocks A and B is outside this range, sufficient heat shrinkage performance cannot be achieved.

n related to the number of blocks defining the structure of the block copolymer used in the present invention is 1 to IO1, preferably 1 to
5, and m, which indicates the number of branches in the star polymer, is 2.
~IO1 preferably ranges from 2 to 4. It goes without saying that n and m may be a mixture of polymers with different numbers.

The block copolymer used in the heat-shrinkable polymer film of the present invention can be obtained by applying known techniques. For example, Japanese Patent Publication No. 40-23798, Japanese Patent Publication No. 40-24914, or Japanese Patent Publication No. 4B-39
According to the method shown in Publication No. 90 etc., monomers selected from the corresponding vinyl aromatic compounds and conjugated diene compounds or mixtures thereof are sequentially polymerized by an anionic polymerization method etc., and various polymer reactions are performed as necessary. For example, JP-A-58-109515 or JP-A-63-
It can be obtained by carrying out a hydrogenation reaction on an unsaturated bond according to the method shown in Japanese Patent No. 484.

Examples of preferable vinyl aromatic compounds used in producing these block copolymers include styrene, α-methylstyrene, p-methylstyrene, m-methylstyrene, 0-methylstyrene, p-1ert-butylstyrene, Mention may be made of dimethylstyrene, vinylnaphthalene, and diphenylethylene. Examples of preferable conjugated diene compounds to be used include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, and 2,4-hexadiene.

A particularly preferred vinyl aromatic compound is styrene.

A particularly preferred conjugated diene compound is 1,3-butadiene, and 80% or more of the bonding modes of l,3-butadiene are 1,4-bonds.

Due to its structure, the block copolymer used in the heat-shrinkable polymer film of the present invention exhibits the following temperature dependence in each temperature range.

That is, (1) at a temperature exceeding the glass transition temperature of the A block, the polymer as a whole is in a completely melted and softened state and exhibits plastic fluidity. Therefore, block copolymers can be easily processed using various general-purpose plastic processing machines, especially sheet processing.

(if) In a temperature range below the glass transition temperature of the A block and in which most of the crystals in the B block melt, the block copolymer has a phase-separated structure, the B block remains in the molten rubber phase, and the A block is converted into a resin and acts as a crosslinking point to network the polymer chains of the rubber phase. Therefore, in this temperature range, the polymer as a whole exhibits crosslinked rubber-like properties, and the strain caused by stretching is substantially completely maintained without being alleviated. (iii) At the temperature at which most of the B blocks crystallize, each block of the polymer will crystallize or vitrify, and the polymer as a whole will exhibit hardened resinous properties, and the strain will be frozen. .

Therefore, for example, in the heat-shrinkable polymer film of the present invention, the block copolymer having the above-mentioned specific structure is processed into a desired film shape at a temperature exceeding the glass transition temperature of the A block, preferably at a temperature higher than the glass transition temperature of the A block. 5 of the crystal at 25°C below the glass transition temperature of the A block, preferably below the glass transition temperature of the A block and at 25°C of the B block.
The temperature at which 0% or more of the crystal melts, more preferably 90% of the crystal
It is obtained by uniaxially or biaxially stretching at a temperature above which % or more melts, and cooling to room temperature while maintaining the stretching. When the thus obtained heat-shrinkable polymer film is heated again to a temperature at which most of the crystals of the B block melt, the frozen strain is released and the film is heat-shrinked.

In the heat-shrinkable polymer film of the present invention, it is generally preferable to use the above-mentioned block copolymer alone, but an A-B-A block structure is incorporated into the polymer chain produced during the production of the block copolymer. It is also possible to include an incomplete block copolymer that does not contain an incomplete block copolymer, for example, a polymer consisting only of A blocks or B blocks, or an AB or B-A-B type block copolymer. However, even in this case, unless at least 30% by weight of the block copolymer specified in the claims of the present invention is contained, the heat shrinkage performance aimed at by the present invention cannot be sufficiently exhibited.

Furthermore, the block copolymer used in the present invention may contain blocks or functional groups other than those specified in the claims in the polymer chain, as long as the purpose of the present invention is not impaired. . Specifically, hydroxyl groups, thiol groups, nitrile groups, sulfonic acid groups, carboxyl groups, amino groups, etc. are formed by halogenation, hydrogen halogenation, epoxidation, or chemical reactions within a range that does not impair low-temperature shrinkability, rigidity, etc. Modifications such as introduction of functional groups may also be performed.

In the present invention, a low molecular weight vinyl aromatic hydrocarbon polymer or copolymer is added to the block copolymer (component (a)) for the purpose of improving low-temperature stretchability and low-temperature shrinkability.
) may also be blended.

In addition, for the purpose of further improving low-temperature stretchability, low-temperature shrinkability, and rigidity, a block copolymer may be combined with component (b) and a relatively high molecular weight vinyl aromatic hydrocarbon polymer or copolymer (component (C)). ) may also be blended. Furthermore, component (e) alone may be blended into the block copolymer for the purpose of improving rigidity.

The vinyl aromatic hydrocarbon polymers or copolymers of components (b) and (e) used in the present invention include homopolymers or copolymers of the above-mentioned vinyl aromatic hydrocarbon monomers,
The above vinyl aromatic hydrocarbon monomers and other vinyl monomers, such as ethylene, propylene, butylene, vinyl chloride, vinylidene chloride, vinyl acetate, acrylic esters such as methyl acrylate, methacrylic esters such as methyl methacrylate, acrylonitrile Copolymers with etc. are included. Particularly preferred are styrene homopolymers, copolymers of styrene and α-methylstyrene, and copolymers of styrene and methyl methacrylate.

The number average molecular weight of the low molecular weight vinyl aromatic hydrocarbon polymer or copolymer as component (b) used in the present invention is 20.
000 or less, preferably 200 to 10,000, more preferably 300 to 6,000. Number average molecular weight is 2
If it exceeds 0.000, the effect of improving low-temperature shrinkability is lost, which is not preferable. Particularly preferred are those having a number average molecular weight of 300 or more and less than 500, and such low molecular weight polymers or copolymers have an extremely good effect of improving low-temperature shrinkage properties. The amount of the low molecular weight vinyl aromatic hydrocarbon polymer or copolymer of component (b) is 5 to 100 parts by weight, preferably 10 to 100 parts by weight, based on 100 parts by weight of the block copolymer of component (a). 70 parts by weight, more preferably 1
It is 5 to 55 parts by weight.

The number average molecular weight of the relatively high molecular weight vinyl aromatic hydrocarbon polymer or copolymer used as component (C) in the present invention is 30.000 or more, preferably 50.000 to 50.000.
1.000.000, more preferably 80.000~
It is 500.000. The number average molecular weight of component (e) is a
If it is less than o or ooo, the effect of improving rigidity is not sufficient, which is not preferable. The blending amount of the vinyl aromatic hydrocarbon polymer or copolymer of component (C) is 5 to 80 parts by weight, based on 100 parts by weight of the block copolymer of component (a).
Preferably 10 to 60 parts by weight, more preferably 15 to 4 parts by weight
It is 5-layer tanbe.

Various additives can be added to the block copolymer used in the present invention or the block copolymer composition blended with the vinyl aromatic hydrocarbon polymer or copolymer as described above, depending on the purpose. Suitable additives include 30 parts by weight or less of coumaron-indene resins, terpene resins, softeners such as oils, and plasticizers. In addition, various stabilizers,
Pigments, antiblocking agents, antistatic agents, lubricants, etc. can also be added. In addition, examples of antiblocking agents, lubricants, and antistatic agents include fatty acid amide, ethylene bisstearamide, sorbitan monostearate, saturated fatty acid esters of fatty alcohols, and pentaerythritol fatty acid esters, and as ultraviolet absorbers. , p-t-butylphenyl salicylate, 2-(2'-hydroxy-5
' -methylphenyl)benzotriazole, 2-(2
'-Hydroxy-3'-t-butyl-5'-methylphenyl)-5-chlorobenzotriazole, 2.
5-bis-[5'-t-butylbenzoxazolyl-(2
)] Compounds such as thiophene listed in "Practical Handbook of Additives for Plastics and Rubber" (Kagaku Kogyo Co., Ltd.) can be used. These are generally used in a range of 0.01 to 5% by weight, preferably 0.1 to 2ffi%.

In the present invention, a block copolymer (component (a)) or a block copolymer composition consisting of component (a) and component (b), or a block copolymer composition consisting of component (a), component (b) and component (C) A block copolymer composition consisting of component (a) and component (
The block copolymer composition consisting of c) is JIS K-
Melt flow measured according to 6970 (200 °C, 5
kg load) from 0.001 to 70, preferably from 0.01 to
50, more preferably 0.1 to 30 g/10 min. A block copolymer or block copolymer composition having a melt flow within this range has excellent film formability.

In the present invention, component (a), component (a) and component (b),
or component (a), component (b) and component (C), or component (
The method of mixing a) and component (C) or these and other additives can be produced by any conventionally known blending method. For example, melt-kneading methods using general kneading machines such as open rolls, intensive mixers, internal mixers, continuous kneaders with a kneader and single twin-screw rotor, and extruders, and after dissolving or dispersing each component in a solvent. A method of removing the solvent by heating, etc. is used.

In order to obtain a heat-shrinkable stretched film from the above-mentioned block copolymer or block copolymer composition, the basic method used is the method conventionally used to improve the heat-shrinkability of films such as vinyl chloride resin. However, the resulting heat-shrinkable film has a heat shrinkage rate of 10% or more at 90°C.
Preferably 15-90%, more preferably 20-70%
Must.

If the heat shrinkage rate at 90℃ is less than 10%, low-temperature shrinkability is poor, so it is necessary to adjust the shrink packaging process to a high temperature and uniformity, or to heat it for a long time, which may cause deterioration or deformation at high temperatures. This is undesirable because it becomes impossible to package such items and shrink-wrapping processing capacity decreases. In addition, in the present invention, the heat shrinkage rate at 90°C means that a uniaxially stretched or biaxially stretched film is heated with 90°C hot water, silicone oil,
5 in a heat medium that does not inhibit the properties of molded products such as glycerin.
This is the heat shrinkage rate in each stretching direction of the molded product when immersed for minutes.

To obtain a heat-shrinkable uniaxially or biaxially stretched film from the block copolymer or block copolymer composition,
The block copolymer or block copolymer composition is extruded into a flat or tubular shape from a normal T die or annular die at 150 to 250°C, preferably 170 to 220°C, and the resulting unstretched product is Axial or biaxial stretching. For example, in the case of uniaxial stretching, in the case of a film or sheet, it is stretched in the extrusion direction with a calender roll, or in the direction perpendicular to the extrusion direction with a tender, and in the case of a tube, it is stretched in the extrusion direction of the tube or in the circumferential direction. Stretch. 2
In the case of axial stretching, in the case of a film or sheet, the extruded film or sheet is stretched in the longitudinal direction with a metal roll, etc., and then stretched in the transverse direction with a tender, etc., and in the case of a tube, the extrusion direction of the tube and the tube The tubes are stretched simultaneously or separately in the circumferential direction of the tube, that is, in a direction perpendicular to the tube axis.

The heat-shrinkable film of the present invention made in this way is
The thickness is adjusted to be in the range of 5 to 300μ, preferably 10 to iooμ, and more preferably 30 to 70μ.

In the present invention, it is preferred that the stretching temperature be from room temperature to 120°C, preferably from 40 to 110°C, and at a stretching ratio of 1.5 to 8 times, preferably 2 to 6 times, in the machine direction and/or the transverse direction. When the stretching temperature exceeds 120°C, it is difficult to obtain a film with good low-temperature shrinkability. The stretching ratio is selected within the above range to correspond to the shrinkage rate of 1° required for the application, but if the stretching ratio is less than 1°5 times, the heat shrinkage ratio is small and heat-shrinkable packaging is used. Furthermore, a stretching ratio of more than 8 times is unfavorable for stable production in the stretching process.

In the case of biaxial stretching, the stretching ratio C in the longitudinal direction and the transverse direction may be the same or different. The heat-shrinkable film after uniaxial stretching or biaxial stretching is then cooled and heated directly to 60 to 10 b℃, preferably 80 to 9
at 5°C for a short time, e.g. 3-60 seconds, preferably 10-60 seconds.
It is also possible to take measures to prevent natural shrinkage after heat treatment for 40 seconds and then cooling to room temperature. The uniaxially stretched or biaxially stretched heat-shrinkable film of the present invention has a tensile modulus in the stretching direction of 1.000 kg/cd or more, preferably 1.500 kg/cI# or more, more preferably 2.
000 kg/cd or more is preferable as a heat-shrinkable packaging material. Tensile modulus in stretching direction is 1.000kg
/cd or more is preferable because normal packaging can be performed without causing dents in the shrink packaging process.

When using the heat-shrinkable polymer film of the present invention as a heat-shrinkable packaging material, in order to achieve the desired heat-shrinkage rate,
It can be heat-shrinked by heating at a temperature of 50 to 300°C, preferably 180 to 250°C, for several seconds to several minutes, preferably for 1 to 60 seconds, and more preferably for 2 to 30 seconds.

The heat-shrinkable polymer film of the present invention is superior in terms of hygiene compared to conventional vinyl chloride resin-based films, and its properties can be utilized for a variety of applications, such as fresh foods, frozen foods,
It can be used for packaging confectionery, clothing, stationery, toys, etc. Particularly preferred applications include printing characters or designs on a uniaxially stretched film of the block copolymer or block copolymer composition defined in the present invention, and then printing it on plastic molded products, metal products, glass containers, porcelain, etc. It can be used as a so-called heat-shrinkable label material, which is used by being brought into close contact with the surface of a package by heat-shrinking.

In particular, the heat-shrinkable polymer film of the present invention has excellent low-temperature shrinkability and environmental damage resistance, so it can be used as a heat-shrinkable label material for plastic molded products that deform when heated to high temperatures, as well as for thermal expansion coefficient and water absorption. Materials whose properties are significantly different from those of the heat-shrinkable block copolymer of the present invention, such as metals, porcelain, glass, polyolefin resins such as polyethylene, polypropylene, and polybutene, polymethacrylate ester resins, polycarbonate resins, and polyethylene terephthalate. , polyester resin such as polyethylene terephthalate, and polyamide resin as a constituent material, it can be suitably used as a heat-shrinkable label material for containers. Furthermore, the uniaxially stretched heat-shrinkable block copolymer film of the present invention, by taking advantage of its excellent water whitening resistance, does not require sterilization treatment with hot water at 60°C or higher, more generally at 75°C or higher. It can be used as a heat-shrinkable label material for glass bottles, metal containers, plastic containers, etc. that contain food products. In addition to the above-mentioned resins, the materials constituting the plastic container in which the heat-shrinkable polymer film of the present invention can be used include polystyrene, rubber-modified high-impact polystyrene (H
IPS), styrene-acrylonitrile copolymer, styrene-maleic anhydride copolymer, acrylonitrile-butadiene-styrene copolymer (ABS), methacrylic acid ester-butadiene-styrene copolymer (MBS),
Examples include polyvinyl chloride resin, polyvinylidene chloride resin, phenol resin, urea resin, melamine resin, epoxy resin, unsaturated polyester resin, and silicone resin. These plastic containers may be a mixture of two or more resins or may be a laminate.

In addition, when using a heat-shrinkable copolymer film obtained by uniaxially stretching the block copolymer defined in the present invention as a heat-shrinkable label material, heat shrinkage at 90°C in the direction orthogonal to the stretching direction is performed. rate is less than 10%, preferably less than 5%,
More preferably, it is 3% or less.

[Effects of the Invention] Since the heat-shrinkable polymer film of the present invention has excellent shrinkability at low temperatures, it can be used to package items that would undergo deterioration or deformation if heated at high temperatures for a long time in the shrink-wrapping process, such as fresh foods. Suitable for packaging plastic molded products, etc. In addition, since the heat-shrinkable block copolymer film of the present invention has excellent water whitening resistance, it does not become cloudy even if an article coated with the film is kept in contact with the film for a long time at room temperature or treated with hot water of 70 to 80°C or higher. Transparency is lost (so-called watermarking)
There is no such problem. Therefore, it can be used in fields of application that require exposure to such conditions, such as applications that require sterilization treatment with hot water. Furthermore, the heat-shrinkable polymer film of the present invention has excellent resistance to environmental damage, and does not easily break even when an article coated with the heat-shrinkable polymer film of the present invention is left in an outdoor environment with severe temperature changes. It has the following characteristics.

In particular, when the article to be coated is made of materials such as metal, porcelain, glass, or polyester resin, which have extremely different properties such as coefficient of thermal expansion and water absorption, conventional heat-shrinkable polymers cannot be used. Films had the disadvantage of poor environmental damage resistance after coating and cracks easily formed in the film, but when the heat-shrinkable polymer film of the present invention is used, such problems do not occur. Can withstand being left in the natural environment for long periods of time. Therefore, taking advantage of these advantages, the heat-shrinkable polymer film of the present invention can be particularly suitably used for applications such as labels for containers made of the above-mentioned materials.

[Examples] The present invention will be specifically explained below with reference to Examples, but the scope of the present invention is not limited thereto.

First, the method for producing the polymer used will be explained.

(1) The polymers of Examples 1 to 3 were produced using a mixed monomer L of α-methylstyrene and styrene by an anionic polymerization method using butyllithium using cyclohexane as a solvent.
By sequentially polymerizing S-butadiene, a mixed monomer of α-methylstyrene and styrene again, and performing a hydrogenation reaction on the unsaturated bonds in the olefin part of the resulting polymer, it corresponds to the A-B-A structure. A linear pro-Tsuku copolymer was obtained.

(2) The polymer of Comparative Example 1 was prepared in the same manner as in Examples 1 to 3 except that a mixed solvent of cyclohexane and tetrahydrofuran was used as the solvent, and a linear block copolymer corresponding to the amorphous A-B-A structure was prepared. Obtained union.

(3) In the polymer of Comparative Example 2, the polymerization order of the monomers was changed to 1.
．． Example 1~ except that 3-butadiene, a mixed monomer of α-methylstyrene and styrene, and l,3-butadiene were used.
A linear block copolymer corresponding to the B-A-B structure was obtained in the same manner as in 3.

(4) The polymer of Example 4 was obtained by sequentially polymerizing a mixed monomer of α-methylstyrene and styrene, 1,3-butadiene, by an anionic polymerization method using butyl lithium using cyclohexane as a solvent, and then performing a terminal coupling reaction with diphenyl carbonate. , by performing a hydrogenation reaction on the unsaturated bonds of the olefin moiety of the obtained polymer (A-B) 3X
A star-shaped block copolymer corresponding to the structure was obtained.

(5) The polymer of Example 5 was obtained by polymerizing a mixed monomer of styrene and butadiene by an anionic polymerization method using butyllithium using cyclohexane as a solvent, and then polymerizing a mixed monomer of styrene and butadiene again. By performing a hydrogenation reaction on the unsaturated bonds of the olefin moiety of B, which has a tapered copolymer structure,
A linear block copolymer corresponding to the -ABA structure was obtained.

(6) The polymer of Example 6 consists of a polystyrene macromer having an aromatic vinyl group at one end of the polymer chain, 2% by weight of isoprene, and 98% by weight of 1,3-butadiene, using cyclohexane as a solvent. A conjugated diene-based mixed monomer is anionically polymerized with butyllithium using barium-di-tert-butoxide as a cocatalyst, and a hydrogenation reaction is performed on the unsaturated bonds in the olefin portion of the resulting polymer, thereby producing a graft corresponding to A type of block copolymer was obtained.

Table 1 shows the analysis results of the structure and properties of the block polymer obtained above.

(The following is a blank space) Analysis and measurement conditions (a) The weight content of the block copolymer having the target structure and its molecular weight were determined by peak processing of the GPC measurement data.

(b) The weight fraction of the A block was determined by processing data measured by an infrared spectrophotometer of the pre-hydrogenated polymer using the Normpton method*.

(c) The average heavy metal molecules of A block and B block were determined from GPC measurement data and polymer composition data.

(d) Glass transition temperature, crystallinity, and crystal melting temperature were determined using a differential thermal analyzer.

(e) The 1,2-bond content of the butadiene moiety was determined by subjecting infrared spectrophotometer data of the pre-hydrogenated polymer to Hampton method processing.

(f) The hydrogen addition rate was analyzed by proton NMR.

*R,R,IIAMPTON,Analytlca
l Chemistry.

Vol, 21. Sou 8.1949゜Examples 1 to 6 and Comparative Examples 1 to 3 The block copolymers shown in Table 1 were each formed into a sheet using a 40mmφ extruder, and then uniaxially stretched to about 5 times. A film with a thickness of about 50 μm was produced.

The stretching temperature was set at room temperature or the lowest temperature at which each sample could be stretched (hereinafter referred to as the lowest temperature at which stretching is possible).

The performance of each 5F film is shown in Table 2.The heat-shrinkable film of the present invention has excellent low-temperature stretchability, rigidity, impact resistance, low-temperature shrinkability, and environmental damage resistance, and is suitable for heat-shrinkable labels, etc. It can be seen that it is a suitable material.

In addition, in the uniaxially stretched films of Examples 1 to 6, the heat shrinkage rate at 90° C. in the direction orthogonal to the stretching direction was less than 5%.

(Left below) (Note 1) Stretched at a stretching speed of 1.0m/win (Note 2)
Based on JIS K-8732 (Note 3) JIS P-8
134 (Note 4) A stretched film was immersed in silicone oil at 80°C for 5 minutes, and calculated using the following formula.

fI = Length before shrinkage g': Length after shrinkage (Note 5) A cylindrical seal is processed with the stretched direction in the circumferential direction and the direction orthogonal to the stretched direction in the vertical direction, and this is sealed into a glass Attach it to the bottle and go through the shrink process (approximately 200
The material was heat-shrinked in a shrink tunnel (with a hot air heat source at ℃) to tightly adhere it to a glass bottle. The obtained coated product was left in an outdoor natural environment for 4 weeks, and it was observed whether microcracks or cracks were generated in the coated film.

○: No microcracks or cracks are observed.

×: Microcracks and/or cracks are observed.

Examples 7 to 9 Block copolymer compositions were prepared by blending polystyrene and/or thermoplastic elastomer with the block copolymer composition according to the formulation shown in Table 3, and Examples 1 to 9 were prepared.
A uniaxially stretched heat-shrinkable film having a thickness of approximately 60 μm was prepared in the same manner as in Example 6. The performance of each film is shown in Table 3.

In addition, in the uniaxially stretched films of Examples 7 to 9, the heat shrinkage rate at 90°C in the direction orthogonal to the stretching direction was less than 5%.

(Left below) Examples 10 to 13 The same block copolymers as in Examples 2.4.5 and 6 were
After forming each sheet into a sheet using an a+saφ extruder, 2
Biaxial stretching was performed using an axial stretching device at a stretching ratio of 3 times to produce a film with a thickness of about 40 μm. The stretching temperature was set to room temperature or the same temperature as the lowest possible stretching temperature in uniaxial stretching. The performance of each film is shown in Table 4.

(Margins below) Formulation ff1 for the table (overlapping area) Component (a) Block copolymer component of Example-2 (b) α-methylstyrene polymer component with number average molecule ff12000 (C) Number average molecule fi12 10,000 Styrene Polymer Example 14 A block copolymer composition was prepared by blending 10 parts by weight of polystyrene having a number average molecular weight of about 400 with 100 parts by weight of the block copolymer of Example 2. A uniaxially stretched film was produced in the same manner as in Example 6.

The lowest stretchable temperature of this block copolymer composition was room temperature, and the resulting film had a heat shrinkage rate of 70% at 90°C.

Example 15.18 After printing characters and patterns on the uniaxially stretched films of Examples 2 and 4, they were heat-shrinked into a cylindrical shape with the stretched direction in the circumferential direction and the unstretched direction in the longitudinal direction. A plastic label was prepared, placed over a cylindrical cup made of high-impact polystyrene, and passed through a shrink tunnel controlled at a temperature of 180 to 200° C. to be heat-shrinked. As a result, all of these heat-shrinkable labels had a colorful finish without any stickiness or wrinkles.

Next, heat-shrinkable labels similar to those described above were placed over containers made of polycarbonate, polybutylene terephthalate, and nylon 66, respectively, and heat-shrinked. In all cases, the finish and finish were good.

Claims (1)

[Claims] 1. At least A and B specified below in the polymer chain
Contains an A-B-A block structure consisting of polymer blocks, and has a weight average molecular weight of 10,000 to 1,000,00
A heat-shrinkable polymer film having a heat shrinkage rate of 10% or more in the stretching direction, which is obtained by uniaxially or biaxially stretching a block copolymer in the range of 0. Here, the block is a homopolymer of a vinyl aromatic compound, a copolymer of a vinyl aromatic compound and another vinyl aromatic compound, a copolymer of a vinyl aromatic compound and a conjugated diene compound, or a hydrogen adduct thereof. consisting of 5
This block is characterized by having a glass transition temperature of 0° C. or higher. B block is a homopolymer of a conjugated diene compound or a copolymer of a conjugated diene compound and another conjugated diene compound,
Or, it consists of a copolymer of a conjugated diene compound and a vinyl aromatic compound, and 50 of the unsaturated bonds of the conjugated diene unit
The polymer block is characterized in that mol% or more of the polymer block is a hydrogen adduct and the crystallinity at 25°C is 5% by weight or more of the B polymer block. Furthermore, each A block may have the same structure or different structures. 2. The crystallinity of the B polymer block at 25°C is 5% by weight or more of the B polymer block, and at least 50% by weight of the crystals melt below the glass transition temperature of the A block. The heat-shrinkable polymer film according to claim 1. 3. The block copolymer has a chain block structure represented by the general formula (a) (A-B)_nA (b) B(A-B)_nA or (C) B(A-B)_nA-B. The heat-shrinkable polymer film according to claim 1 or 2, characterized in that the film has a heat-shrinkable polymer film. Here, n is an integer of 1 or more and 10 or less, and each A block and each B block may have the same structure or different structures. 4. The block copolymer has the general formula (d) [(A-B)_n]_mX (e) [(A-B)_nA]_mX (f) [B(A-B)_nA]_mX or (g ) [B(A-B)_nA]_mX Claim 1 characterized in that it has a star-shaped block structure represented by
Or the heat-shrinkable polymer film according to claim 2. Here, n is an integer of 1 or more and 10 or less, m is an integer of 2 or more and 10 or less, X is a terminal coupling agent, and each A block and each B block may have the same structure or a different structure. But it doesn't matter. 5. Heat shrinkability according to claim 1 or claim 2, wherein the block copolymer has a graft-type block structure represented by the general formula (h) ▲ Numerical formula, chemical formula, table, etc. ▼ Polymer film. Here, n is an integer of 1 or more and 10 or less, and each A block and each B block may have the same structure or different structures.