JPH0432098B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to molded products such as heat-shrinkable films, sheets, tubes, etc. made of block copolymer mixtures having excellent low-temperature shrinkability, impact resistance, and environmental damage resistance. [Conventional technology] Shrink wrapping has recently been used particularly for food packaging because it can neatly eliminate the bagging and wrinkles that were unavoidable with conventional packaging techniques, and it can also quickly wrap products tightly or irregularly shaped items. is increasing. Conventionally, vinyl chloride resin has been mainly used as a material for shrink wrapping films, sheets, etc. because it satisfies required properties such as low-temperature shrinkability, transparency, and mechanical strength. However, vinyl chloride resin has hygienic problems due to vinyl chloride monomer and plasticizers.
There is a strong demand for a replacement product due to the problem of hydrogen chloride generation during depreciation. 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 are widely used as materials for food packaging containers. It is being done. However, conventionally known block copolymers are unsuitable as materials for heat-shrinkable packaging because of their high stretching temperatures and high shrinkage temperatures. For example, JP-A-49-10249 and JP-A-49-
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 a film cannot achieve sufficient shrinkage unless the heat shrinkage temperature is about 100°C or higher. Methods for improving the low-temperature shrinkability of such block copolymers are also disclosed in JP-A-50-6673 and JP-A-55-5544.
This is attempted in the Publication No. In the former method, by applying the tubular method to a linear copolymer, simultaneous biaxial orientation is achieved through expansion stretching in a temperature range where effective high degree of orientation occurs, resulting in good low-temperature heat shrinkability. This is a method of manufacturing film. however,
In this method, expansion and stretching is started in a very limited temperature range depending on the butadiene content of the raw resin, and the temperature in the stretching zone from the expansion start point to the expansion end point is strictly controlled. If the slope is not adjusted properly, a film having the desired low-temperature heat shrinkability cannot be obtained, and therefore, it is difficult to carry out the process easily. In the latter method, a styrene-butadiene block copolymer with a styrene content of 20-50% is added to a styrene-butadiene block copolymer with a styrene content of 65-90%.
This method produces a biaxially stretched film with low-temperature shrinkability by blending the two by weight; however, if the kneading conditions of both components are poor, sufficient low-temperature shrinkability cannot be achieved, and the kneading method requires advanced techniques. This method has the disadvantage that it requires a lot of time and is difficult to implement. [Problems to be Solved by the Invention] In view of the current situation, the present inventors have carried out extensive studies on a method for easily obtaining block copolymer films, sheets, etc. with excellent low-temperature shrinkability. The vinyl aromatic hydrocarbon polymer block constituting the block is a block copolymer having a molecular weight within a certain range, or such a block copolymer is combined with a low molecular weight vinyl aromatic hydrocarbon polymer or a normal high molecular weight vinyl aromatic polymer. It was discovered that a composition containing a hydrocarbon polymer could be stretched at a relatively low temperature, and the purpose was achieved, and Japanese Patent Application No. 56-22989,
Applications were filed for Japanese Patent Application No. 56-63325 and Japanese Patent Application No. 56-95314. After that, the present inventors further investigated the improvement, and found that by combining several types of specific block copolymers, the product had not only low-temperature shrinkability but also heat-shrinkability with excellent impact resistance and environmental damage resistance. The inventors have newly discovered that it is possible to obtain a molded article, and have completed the present invention. [Means for Solving the Problems] That is, the present invention has (A) a polymer block mainly composed of at least one vinyl aromatic hydrocarbon and a polymer block mainly composed of at least one conjugated diene. death,
A block copolymer having a vinyl aromatic hydrocarbon content of 75 to 95% by weight, and a number average molecular weight of the block copolymer of 100,000 to 350,000,
A block copolymer in which the vinyl aromatic hydrocarbon polymer block incorporated into the block copolymer has a number average molecular weight of 10,000 to 100,000, 30
~95 parts by weight, (B) having at least one vinyl aromatic hydrocarbon-based polymer block and at least one conjugated diene-based polymer block;
Block copolymer with a vinyl aromatic hydrocarbon content of more than 50% and less than 75% by weight, 70
~5 parts by weight (C) having at least one polymer block mainly composed of vinyl aromatic hydrocarbon and at least one polymer block mainly composed of conjugated diene,
Consisting of 5 parts by weight or more and 60 parts by weight or less of a block copolymer having a vinyl aromatic hydrocarbon content of 10 to 50% by weight, based on 100 parts by weight of the total amount of component (A) and component (B). , its bending modulus is 7000~18000Kg/ ^cm2
This invention relates to a heat-shrinkable molded product obtained by stretching a block copolymer mixture having a heat shrinkage rate of 10% or more at 90°C in the stretching direction. In the present invention, a heat-shrinkable molded article refers to a film, sheet, or tube-shaped molded article that has the property of shrinking when heated. Since the heat-shrinkable molded product of the present invention has excellent shrinkability at low temperatures, it can be used to package items that would deteriorate or deform if heated at high temperatures for a long period of time during the shrink-wrapping process, such as fresh foods and plastic molded products. Suitable for packaging. In addition, the heat-shrinkable molded product of the present invention has excellent environmental damage resistance, and has the feature that it is difficult to break even if an article coated with the heat-shrinkable molded product of the present invention is left in an outdoor environment with severe temperature changes. has. In particular, when the article to be coated is made of materials such as metal, porcelain, glass, or polyester resin, which have very different properties such as coefficient of thermal expansion and water absorption, conventional heat-shrinkable molded products However, when using the heat-shrinkable molded product of the present invention, there is no such problem and it can withstand long-term environmental damage. It can withstand being left in the ground. Therefore, by taking advantage of these advantages, the heat-shrinkable molded article of the present invention can be particularly suitably used for applications such as labels for containers made of the above-mentioned materials. The present invention will be explained in detail below. Component (A), component (B) or component (C) used in the present invention
Each of the block copolymers has at least one
It is a block copolymer having one, preferably two or more, vinyl aromatic hydrocarbon-based polymer blocks and at least one conjugated diene-based polymer block. Here, the polymer block mainly composed of vinyl aromatic hydrocarbons is a polymer block in which the vinyl aromatic hydrocarbon content exceeds 50% by weight, preferably 70% by weight or more. Furthermore, a polymer block mainly composed of conjugated diene is a polymer block in which the content of conjugated diene is 50% by weight or more, preferably 70% by weight or more, and more preferably 90% by weight or more. When a random copolymer portion of a vinyl aromatic hydrocarbon and a conjugated diene is present in a polymer block mainly composed of vinyl aromatic hydrocarbons or a polymer block mainly composed of conjugated dienes, the copolymerized vinyl aromatic Although the group hydrocarbons are uniformly distributed in the polymer block,
Alternatively, the distribution may be tapered (gradually decreasing). The block copolymer used in the present invention can basically be produced by conventionally known methods.
Publication No. 19286, Special Publication No. 14979, Publication No. 14979, Special Publication No. 14979
-36957 Publication, Special Publication No. 48-2423, Special Publication Sho
The method described in Japanese Patent No. 48-4106 and the like can be mentioned, but manufacturing conditions must be set so that each constituent polymer satisfies the requirements described below. All of the above-mentioned known methods involve block copolymerizing a conjugated diene and a vinyl aromatic hydrocarbon using an anionic polymerization initiator such as an organolithium compound in a hydrocarbon solvent. In the present invention, the polymer structure has the general formula: (a) (A-B) _o (b) A(-B-A) _o (c) B(-A-B) _o (In the above formula, A is vinyl B is a polymer block mainly composed of aromatic hydrocarbons, and B is a polymer block mainly composed of conjugated diene. The boundary between A block and B block does not necessarily need to be clearly distinguished. n is 1 ) or the general formula, (d) [(B-A) _o --] _n+2 ---X (e) [(A-B) _o --] _n+2 ---X (f) [(B-A) _o --B _n+2 ---X (g) [(A-B) _{o ---} A _n+2 --- X (In the above formula, A and B are the same as above, and
represents a residue of a coupling agent such as silicon tetrachloride or tin tetrachloride, or a residue of an initiator such as a polyfunctional organolithium compound. m and n are integers of 1 or more. ) or a mixture of these block copolymers with any polymer structure can be used. In the present invention, vinyl aromatic hydrocarbons include styrene, o-methylstyrene, p-methylstyrene, p-tert-butylstyrene, 1,3-dimethylstyrene, α-methylstyrene, vinylnaphthalene, vinylanthracene, etc. However, styrene is a particularly common one.
These may be used not only alone, but also as a mixture of two or more. The conjugated diene is a diolefin having a pair of conjugated double bonds, for example, 1,3
-butadiene, 2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene, etc., but particularly common ones include Examples include 1,3-butadiene and isoprene.
These may be used not only alone, but also as a mixture of two or more. The block copolymer of component (A) used in the present invention has a number average molecular weight of 100,000.
~350,000, preferably 130,000 to 300,000, and the number average molecular weight of the vinyl aromatic hydrocarbon polymer block incorporated in the block copolymer is 10,000 to
100,000, preferably 15,000 to 70,000, and the vinyl aromatic hydrocarbon content is 75 to 95% by weight, preferably 77 to 90% by weight. The number average molecular weight of block copolymer (A) is
If the number average molecular weight is less than 100,000, the environmental damage resistance will be poor, and if the number average molecular weight is more than 350,000, the mixability with other components and the processability of the block copolymer mixture will be poor, which is not preferable. Furthermore, if the number average molecular weight of the vinyl aromatic hydrocarbon polymer block incorporated in the block copolymer is less than 10,000, the tensile strength and rigidity will be poor, and if it exceeds 100,000, the low-temperature stretchability and low-temperature shrinkage will be poor. It is not desirable because it has inferior properties. Furthermore, if the vinyl aromatic hydrocarbon content is less than 75% by weight, the tensile strength and rigidity will be poor, and if it exceeds 95% by weight, the impact resistance will be poor, which is not preferable. In addition, in the present invention, the number average molecular weight of a block copolymer is defined as the peak count number and the number average molecular weight of monodisperse polystyrene obtained by GPC of monodisperse polystyrene for gel permeation chromatography (hereinafter referred to as GPC). A calibration curve is prepared, and the number average molecular weight corresponding to the main peak count number of the GPC pattern of the block copolymer is read from the calibration curve. In addition, the number average molecular weight of the vinyl aromatic hydrocarbon polymer block incorporated into the block copolymer is determined by the oxidative decomposition of the block copolymer with di-tertiary butyl hydroperoxide using osmium tetroxide as a catalyst. methods (e.g. LMKOLTHOFF, etal.,
A vinyl aromatic hydrocarbon polymer block component obtained by the method described in J. Polym. Sci. ) is the value calculated by transferring the calibration curve created using monodisperse polystyrene for GCP and following a conventional method (for example, "Gel Chromatography <Basic Edition>" published by Kodansha).Next The block copolymer of component (B) used in the present invention has a vinyl aromatic hydrocarbon content of 50% by weight.
more than 75% by weight, preferably 60-73% by weight
It is. Vinyl aromatic hydrocarbon content is 50% by weight
In the following cases, the compatibility with component (A) will be insufficient and the environmental damage resistance will be poor, and if it exceeds 75% by weight, the environmental damage resistance will deteriorate. In the present invention, the number average molecular weight of the block copolymer (B) is preferably 80,000 to 250,000 in terms of improving environmental damage resistance.
Preferably, a block copolymer of 100,000 to 200,000 is used. There is no particular restriction on the number average molecular weight of the vinyl aromatic hydrocarbon polymer block incorporated into the block copolymer of component (B), but in order to obtain a molded article with better low-temperature shrinkability, Number average molecular weight is 10,000 to 100,000, preferably 15,000 to
It is recommended to use a block copolymer of 70,000. In the present invention, the block copolymer mixture of component (A) and component (B) has a vinyl aromatic hydrocarbon content of 10 to 50% by weight, preferably 15 to 45% by weight as component (C).
By blending and using a block copolymer in an amount of % by weight, impact resistance can be further improved without deteriorating low-temperature shrinkage properties and environmental damage resistance.
As component (C), block copolymers having a number average molecular weight of 20,000 to 250,000, preferably 40,000 to 200,000 can generally be used. In the present invention, the weight ratio of component (A) and component (B) is
The ratio is 30:70 to 95:5, preferably 50:50 to 90:10. If the blending amount of each component is outside this range, it is not preferable because the environmental damage resistance will be poor. Also component (C)
The blending amount is 5 parts by weight or more and 60 parts by weight or less, preferably 5 parts by weight or more and 50 parts by weight or less, based on 100 parts by weight of the total amount of component (A) and component (B). If the amount of component (C) exceeds 60 parts by weight, it is not preferable because tensile strength and rigidity are poor. In the present invention, the block copolymer mixture consisting of component (A), component (B), and component (C) has a flexural modulus of 7,000 to 18,000 Kg/cm ² , preferably 9,000 to 16,000.
Kg/ ^cm2 . If the flexural modulus is less than 7000 Kg/cm ² , the rigidity is poor, and when the heat-shrinkable molded product of the present invention, such as a film or tube, is used as a material for shrink packaging, it may sag during the packaging process and may not be properly packaged. The problem arises that it is difficult to
Moreover, if the flexural modulus exceeds 18,000, it is not preferable because the environmental damage resistance is poor. In the present invention, the flexural modulus refers to the flexural modulus of a block copolymer mixture consisting of component (A), component (B), and component (C).
Values measured based on JIS-K-7203. Particularly suitable block copolymer mixtures in the present invention have a vinyl aromatic hydrocarbon content of 77 to 90% by weight and a block copolymer number average molecular weight of 130,000.
300,000, the number average molecular weight of the vinyl aromatic hydrocarbon polymer block incorporated in the block copolymer is 15,000 to 70,000 as component (A), and the vinyl aromatic hydrocarbon content is 60-73
% by weight, the number average molecular weight of the block copolymer is
100,000 to 200,000, and the number average molecular weight of the vinyl aromatic hydrocarbon polymer block incorporated in the block copolymer is 15,000 to 70,000. The vinyl aromatic hydrocarbon content as component (C) is 15~
45% by weight, the number average molecular weight of the block copolymer is
This is a block copolymer mixture containing 40,000 to 200,000 block copolymers. Heat-shrinkable molded products using these materials have particularly excellent low-temperature shrinkability, with a heat shrinkage rate of 15% or more at 80°C in the stretching direction. In the above preferred embodiment, the ratio (/n) of the weight average molecular weight to the number average molecular weight of the vinyl aromatic hydrocarbon polymer block incorporated into the block copolymer further improves heat shrinkability. A value of less than 1.25 is recommended in terms of The block copolymer used in the present invention may be modified with hydroxyl groups by hydrogenation, halogenation, hydrogen halogenation, epoxidation, or chemical reaction within a range that does not impair its basic properties such as low-temperature shrinkability and rigidity. Modifications such as introduction of functional groups such as thiol groups, nitrile groups, sulfonic acid groups, carboxyl groups, and amino groups may also be performed. In the present invention, a block copolymer mixture (component (a)
A low molecular weight vinyl aromatic hydrocarbon polymer or copolymer (referred to as component (b)) may be blended with the material (referred to as component (b)) for the purpose of improving low-temperature stretchability and low-temperature shrinkability. In addition, for the purpose of further improving low-temperature stretchability, low-temperature shrinkability, and rigidity, the block copolymer may be combined with component (b) and a relatively high molecular weight vinyl aromatic hydrocarbon polymer or copolymer (with component (c)). ) may also be blended. Furthermore, component (c) 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 (c) used in the present invention include the above-mentioned vinyl aromatic hydrocarbon monomers or copolymers as well as the above-mentioned vinyl aromatic hydrocarbon polymers or copolymers. 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, etc. Contains copolymers. Particularly preferred are styrene homopolymers, styrene and α-methylstyrene copolymers, and styrene and methyl methacrylate copolymers. 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 5,000. Number average molecular weight is 20000
Exceeding this is not preferable because the effect of improving low-temperature shrinkage is lost. 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 70 parts by weight, based on 100 parts by weight of the block copolymer of component (a). weight part,
More preferably, it is 15 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 or more.
~1,000,000, more preferably 80,000~500,000. If the number average molecular weight of component (c) is less than 30,000, it is not preferable because the effect of improving rigidity is not sufficient. The blending amount of the vinyl aromatic hydrocarbon polymer or copolymer as component (c) is 5 to 80 parts by weight, preferably 10 to 60 parts by weight, based on 100 parts by weight of the block copolymer mixture of component (a). parts, more preferably 15 to 45 parts by weight. Various additives may be added to the block copolymer mixture used in the present invention or the block copolymer composition blended with the above vinyl aromatic hydrocarbon polymer or copolymer depending on the purpose. .
A preferred additive is 30 parts by weight or less of coumarone.
Examples include softeners and plasticizers such as indene resin, terpene resin, and oil. In addition, various stabilizers,
Pigments, antiblocking agents, antistatic agents, lubricants, etc. can also be added. In addition, anti-blocking agents, lubricants,
Examples of antistatic agents include fatty acid amide, ethylene bisstearamide, sorbitan monostearate, saturated fatty acid esters of fatty acid alcohols, pentaerythritol fatty acid esters, and ultraviolet absorbers include pt-butyl phenyl salicylate. , 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 2-(2'-hydroxy-3'-t-butyl-5'-methylphenyl)
-5-chlorobenzotriazole, 2,5-bis-[5'-t-butylbenzoxazolyl-(2)]thiophene, etc., are listed in "Practical Handbook of Additives for Plastics and Rubber" (Kagaku Kogyosha). These compounds are generally used in a range of 0.01 to 5% by weight, preferably 0.1 to 2% by weight. In the present invention, block copolymerization of component (A), component (B), and component (C) can be used. The combined mixture and other additives can be mixed by any conventionally known compounding method.For example, an open roll, intensive mixer, internal mixer, co-kneader, or continuous kneader with a twin-screw rotor. , a melt-kneading method using a general mixing machine such as an extruder, a method of dissolving or dispersing each component in a solvent, or heating and removing the solvent after mixing, etc. To obtain heat-shrinkable molded articles from the composition,
Basically, the methods used to impart heat-shrinkability to films made of vinyl chloride resin can basically be used, but the heat-shrinkable molded products obtained can be heated at 90°C.
Thermal shrinkage rate is 10% or more, preferably 15-99
%, more preferably 20-80%. 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 makes it impossible to package such items and reduces shrink-wrapping processing capacity. In addition, in the present invention, 90°C
The heat shrinkage rate of a uniaxially stretched or biaxially stretched molded product is the value obtained when the molded product is immersed for 5 minutes in a heating medium such as 90°C hot water, silicone oil, or glycerin that does not affect the properties of the molded product. This is the heat shrinkage rate in each stretching direction. In order to obtain a heat-shrinkable uniaxially or biaxially stretched molded article from the block copolymer mixture or block copolymer composition described above, the block copolymer mixture or block copolymer composition is processed by a conventional T-die or From annular die to flat or tube shape 150~
Extrusion molding is carried out at 250°C, preferably 170 to 220°C, and the resulting unstretched product is uniaxially or biaxially stretched.
For example, in the case of uniaxial stretching, in the case of a film or sheet, it is stretched in the extrusion direction using a calendar roll, etc., or in the direction perpendicular to the extrusion direction using a tenter, etc., and in the case of a tube shape, it is stretched in the extrusion direction of the tube or in the circumferential direction. Stretch. In the case of biaxial 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 tenter, etc., and in the case of tube-shaped storage, the extruded film or sheet is stretched in the extrusion direction of the tube. and simultaneously or separately in the circumferential direction of the tube, that is, in the direction perpendicular to the tube axis. The heat-shrinkable film or tube of the heat-shrinkable molded article of the present invention obtained in this way generally has a thickness in the range of 5 to 500μ, preferably 10 to 200μ, and more preferably 30 to 100μ. be adjusted. In the present invention, it is preferable to stretch at a stretching temperature of 60 to 120°C, preferably 80 to 110°C, and a stretching ratio of 1.5 to 8 times, preferably 2 to 6 times, in the machine direction and/or the transverse direction. If the stretching temperature is less than 60°C, breakage will occur during stretching, making it difficult to obtain the desired heat-shrinkable molded product, and if it exceeds 120°C, it will be difficult to obtain a product with good low-temperature shrinkability. The stretching ratio is selected within the above range to correspond to the shrinkage ratio required depending on the application, but if the stretching ratio is less than 1.5 times, the heat shrinkage ratio is low and it is not suitable for use in heat-shrinkable packaging. A stretching ratio of more than 8 times is not preferable in terms of stable production in the stretching process. In the case of biaxial stretching,
The stretching ratios in the machine direction and the transverse direction may be the same or different. After uniaxial stretching or 2
The heat-shrinkable molded product after axial stretching is then heated to 60 to 105°C, preferably 80 to 95°C, immediately after cooling if necessary.
for a short time, e.g. 3-60 seconds, preferably 10-40 seconds.
It is also possible to carry out a heat treatment for a second to prevent natural shrinkage at room temperature. When using the uniaxially stretched or biaxially stretched molded product of the present invention as a heat-shrinkable packaging material, the temperature is preferably 150 to 300°C in order to achieve the desired heat shrinkage rate.
At a temperature of 180-250℃ for several seconds to several minutes, preferably 1
It can be heat-shrinked by heating for ~60 seconds, more preferably 2-30 seconds. The uniaxially or biaxially stretched molded products of the present invention are superior in terms of hygiene compared to conventional vinyl chloride resin-based products, and their properties can be utilized for a variety of applications, such as fresh foods, frozen foods, and confectionery. kind of packaging,
It can be used for packaging clothing, stationery, toys, etc. As a particularly preferred application, after printing characters or designs on a uniaxially stretched film of the block copolymer mixture or block copolymer composition defined in the present invention,
It can be used as a so-called heat-shrinkable label material, which is used by heat-shrinking it to adhere tightly to the surface of a packaged object such as a plastic molded product, metal product, glass container, or porcelain. In particular, the film of the uniaxially stretched heat-shrinkable block copolymer mixture or composition of the present invention has excellent low-temperature shrinkability, impact resistance, and environmental damage resistance, so it is suitable for plastics that deform when heated to high temperatures. In addition to heat-shrinkable label materials for molded products, materials with thermal expansion coefficients and water absorption properties that are extremely different from those of the heat-shrinkable molded products of the present invention, such as metals, porcelain, glass, and polyolefin resins such as polyethylene, polypropylene, and polybutene. , polymethacrylic acid ester resin, polycarbonate resin, polyester resin such as polyethylene terephthalate, polybutylene terephthalate, and polyamide resin as a constituent material. Suitable for use as a heat-shrinkable label material for containers. can. In addition to the above-mentioned resins, the materials constituting the plastic container to which the heat-shrinkable molded product of the present invention can be applied include polystyrene, rubber-modified high-impact polystyrene (HIPS), styrene-acrylonitrile copolymer, and styrene-acrylonitrile copolymer. Maleic anhydride copolymer, acrylonitrile-butadiene-styrene copolymer (ABS), methacrylic acid ester-butadiene-styrene copolymer (MBS), polyvinyl chloride resin, polyvinylidene chloride resin, phenolic resin, urea resin , melamine resin, epoxy resin, unsaturated polyester resin, silicone resin, etc. These plastic containers may be a mixture of two or more resins or may be a laminate. In addition, when a heat-shrinkable film obtained by uniaxially stretching the block copolymer mixture defined in the present invention is used as a heat-shrinkable label material, the heat shrinkage rate at 90°C in the direction orthogonal to the stretching direction is is preferably less than 10%, preferably 5% or less, more preferably 3% or less. Examples of the present invention will be shown below to explain the present invention in more detail, but it goes without saying that the content of the present invention is not limited to these Examples. In the following examples, a styrene-butadiene block copolymer having the polymer structure, styrene content, number average molecular weight of the block copolymer, and number average molecular weight of the polystyrene block as shown in Table 1 was used with cyclohexane or n- n in hexane
- Polymerization using butyllithium as an initiator was used.

[Table] Examples 1 and 2, Reference Example 1 and Comparative Example 1 Each block copolymer mixture was formed into a sheet using a 40 mmφ extruder according to the formulation method shown in Table 2, and then expanded to about 3 times its size. Monoaxially stretched to a thickness of approximately 80μm
A film was produced. The performance of each film is
Shown in the table. The heat-shrinkable film of the present invention not only has excellent low-temperature stretchability, low-temperature shrinkability, container covering performance, and environmental damage resistance, but also has improved impact resistance and heat resistance by incorporating component (C). It can be seen that it is suitable as a material for shrinkable labels. In addition, in the uniaxially stretched films of Examples 1 and 2, the 90°C heat shrinkage rate in the direction orthogonal to the stretching direction was less than 5%.

【table】

[Table] Example 3 and Reference Examples 2 and 3 The block copolymer mixture was formed into a sheet using a 40 mmφ extruder according to the formulation shown in Table 3, and then the stretching ratio was determined using a biaxial stretching device (Iwamoto Seisakusho). Biaxial stretching was performed at 3x. The extrusion temperature conditions of the extruder are cylinder temperature 150℃~200℃, T die 200℃
℃, and the sheet extruded from the T-die was stretched through a biaxial stretching device. The stretching temperature was set to the same temperature as the lowest possible stretching temperature in uniaxial stretching. The performance of each film is shown in Table 3.

【table】

〔Effect of the invention〕

The heat-shrinkable molded article of the present invention has excellent shrinkability at low temperatures and is extremely effective for packaging perishable foods and the like that cannot be heated at high temperatures for long periods of time during the shrinking process. Furthermore, since it has excellent impact resistance and environmental damage resistance, it is easy to handle and has great industrial value.

Claims (1)

[Scope of Claims] 1 (A) A polymer block containing at least one vinyl aromatic hydrocarbon and at least one polymer block mainly consisting of a conjugated diene, and containing a vinyl aromatic hydrocarbon. A block copolymer in which the amount is 75 to 95% by weight, and the number average molecular weight of the block copolymer is 100,000 to 100,000.
350,000, 30 to 95 parts by weight of a block copolymer in which the vinyl aromatic hydrocarbon polymer block incorporated in the block copolymer has a number average molecular weight of 10,000 to 100,000; (B) at least one vinyl It has a polymer block mainly composed of an aromatic hydrocarbon and a polymer block mainly composed of at least one conjugated diene,
Block copolymer with a vinyl aromatic hydrocarbon content of more than 50% and less than 75% by weight, 70
~5 parts by weight (C) having at least one polymer block mainly composed of vinyl aromatic hydrocarbon and at least one polymer block mainly composed of conjugated diene,
Consisting of 5 parts by weight or more and 60 parts by weight or less of a block copolymer having a vinyl aromatic hydrocarbon content of 10 to 50% by weight, based on 100 parts by weight of the total amount of component (A) and component (B). , its bending modulus is 7000~18000Kg/ ^cm2
A heat-shrinkable molded product obtained by stretching a block copolymer mixture that has a heat shrinkage rate of 10% or more at 90°C in the stretching direction. 2 (A) It has at least one polymer block mainly composed of vinyl aromatic hydrocarbon and at least one polymer block mainly composed of conjugated diene, and the vinyl aromatic hydrocarbon content is 75 to 95% by weight. %, and the number average molecular weight of the block copolymer is 100,000 to 100,000.
350,000, 30 to 95 parts by weight of a block copolymer in which the vinyl aromatic hydrocarbon polymer block incorporated in the block copolymer has a number average molecular weight of 10,000 to 100,000; (B) at least one vinyl It has a polymer block mainly composed of an aromatic hydrocarbon and a polymer block mainly composed of at least one conjugated diene,
Block copolymer with a vinyl aromatic hydrocarbon content of more than 50% and less than 75% by weight, 70
~5 parts by weight (C) having at least one polymer block mainly composed of vinyl aromatic hydrocarbon and at least one polymer block mainly composed of conjugated diene,
Consisting of 5 parts by weight or more and 60 parts by weight or less of a block copolymer having a vinyl aromatic hydrocarbon content of 10 to 50% by weight, based on 100 parts by weight of the total amount of component (A) and component (B). , its bending modulus is 7000~18000Kg/ ^cm2
A heat-shrinkable film for a uniaxially stretched label made of a block copolymer mixture, characterized in that the block copolymer mixture is uniaxially stretched and has a heat shrinkage rate of 10% or more at 90°C in the stretching direction. 3 Suitable for labeling containers whose constituent material or part thereof is at least one selected from metal, porcelain, glass, polyolefin resin, polymethacrylate resin, polycarbonate resin, polyester resin, and polyamide resin. A heat-shrinkable film for uniaxially stretched labels according to claim 2.