JPH0251380B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a block copolymer and a heat-shrinkable film made of a block copolymer composition having excellent impact resistance, low-temperature stretchability, shrinkage characteristics, and environmental damage resistance. Shrink wrapping can neatly solve the bagging and wrinkles that were unavoidable with conventional packaging technology, and can quickly wrap products tightly or irregularly shaped items, so heat-shrinkable films for this purpose are suitable for food packaging. It is used for paper, stickers, labels, etc. Conventional raw materials for heat-shrinkable films include:
Vinyl chloride resin is widely used because it satisfies required properties such as shrinkage properties, transparency, mechanical strength, and suitability for packaging machines. However, there is a strong demand for substitutes for vinyl chloride resin due to hygienic problems caused by residual vinyl chloride monomers and plasticizers, and the problem of generation of hydrogen chloride during incineration. 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-49-102494 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. For this reason, methods for improving the low-temperature shrinkage properties of block copolymers are disclosed in Japanese Patent Application Laid-Open No. 57-25349 and Japanese Patent Application Laid-Open No. 57-25349.
An attempt was made in Publication No. 34921. These are all (S-B)n-S (S is styrene block, B
is a butadiene block. The low-temperature shrinkability is improved by using a block copolymer having a structure in which n=2 to 10). However, although the heat-shrinkable film obtained by the above method has good low-temperature shrinkability, it has poor environmental damage resistance.
When coated on a glass bottle or the like, there is a problem in that the film easily cracks and cannot be used. In view of the current situation, the inventors of the present invention have conducted intensive studies on a method for obtaining a heat-shrinkable film with excellent low-temperature shrinkability and environmental damage resistance. We have discovered that this objective can be achieved by using a block copolymer composed of a specific range of copolymer blocks that have a relatively high hydrogen content and a vinyl aromatic hydrocarbon blocking ratio, and have published this book. The invention was completed. That is, the present invention has at least one vinyl aromatic hydrocarbon polymer segment A and at least one vinyl aromatic hydrocarbon and conjugated diene copolymer segment B, and has at least one vinyl aromatic hydrocarbon and conjugated diene segment B. To produce a block copolymer having a weight ratio of 77/23 to 95/5 with the diene, 10 to 70% by weight of the total vinyl aromatic hydrocarbon used is used to form segment A; B
A mixture in which the weight ratio of vinyl aromatic hydrocarbon and conjugated diene exceeds 75/25 and is not more than 93/7 is prepared under conditions such that the blocking rate of vinyl aromatic hydrocarbon in segment B is 20 to 75% by weight. A heat ^- shrinkable block copolymer obtained by stretching a block copolymer obtained by polymerizing in The present invention relates to a heat-shrinkable film made of a block copolymer composition obtained by combining the above-mentioned block copolymer with another polymer. Since the block copolymer used in the present invention has excellent low-temperature stretchability, it can be easily uniaxially or biaxially stretched at low temperatures, and a film can be obtained with excellent low-temperature shrinkability. Since the heat-shrinkable film of the present invention has excellent shrinkability at low temperatures or short-term shrinkability even at high temperatures, it can be used for packaging articles that would deteriorate or deform if heated at high temperatures for a long period of time in the shrink wrapping process.
For example, it is suitable for packaging fresh foods, plastic molded products, etc. Moreover, the heat-shrinkable film of the present invention has excellent impact resistance and can be used as a coating for articles such as glass bottles that are likely to have fragments scattered when broken. Furthermore, the heat-shrinkable film 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 film of the present invention is left in an outdoor environment with severe temperature changes. . In particular, when the article to be coated is made of materials such as metal, porcelain, glass, and polyester resin, which have extremely different properties such as coefficient of thermal expansion and water absorption, conventional heat-shrinkable films cannot be used. The heat shrinkable film of the present invention does not have such problems and can be used in the natural environment for a long time. It can withstand being left in the ground. Therefore, the heat-shrinkable film of the present invention can be particularly suitably used for applications such as labels for containers made of the above-mentioned materials by taking advantage of these advantages. Furthermore, the heat-shrinkable film of the present invention has excellent colorability and printability. The present invention will be explained in detail below. The block copolymer used in the present invention has at least one vinyl aromatic hydrocarbon polymer segment A and at least one vinyl aromatic hydrocarbon and conjugated diene polymer segment B, and has at least one vinyl aromatic hydrocarbon polymer segment B. The weight ratio of hydrocarbon to conjugated diene is 77/
In producing a block copolymer having a ratio of 23 to 95/5, preferably 80/20 to 93/7, 10 to 70% by weight, preferably 15 to 60% by weight of the total vinyl aromatic hydrocarbon used is to form segment A, while for segment B, the weight ratio of vinyl aromatic hydrocarbon to conjugated diene is greater than 75/25 and less than or equal to 93/7, preferably greater than 80/20 and 90/25.
A block copolymer obtained by forming segment B by polymerizing a mixture having a molecular weight of 10 or less under conditions such that the block rate of vinyl aromatic hydrocarbon is in the range of 20 to 75% by weight, preferably 30 to 65% by weight. It is a combination. If the weight ratio of the vinyl aromatic hydrocarbon to the conjugated diene in the block copolymer is less than 77/23, the rigidity will be poor, and if it exceeds 95/5, the impact resistance will be poor, which is not preferred. Also, the amount of vinyl aromatic hydrocarbon used to form segment A is
If it is outside the range specified by the present invention, impact resistance will be poor, which is not preferable. If the weight ratio of the vinyl aromatic hydrocarbon and conjugated diene used to form segment B is less than 75/25, the rigidity will be poor and the weight ratio will be 93/25 or less.
If it exceeds 7, it becomes brittle and a good sheet or stretched film cannot be obtained. Furthermore, segment B
When the blocking rate of the vinyl aromatic hydrocarbon is 20% by weight, the rigidity will be poor, and if it exceeds 75% by weight, the environmental damage resistance will be poor, which is not preferable. In the present invention, the block rate of vinyl aromatic hydrocarbon in segment B means segment B
It is the value obtained by dividing the amount of the vinyl aromatic hydrocarbon homopolymer portion produced when forming the segment B by the amount of the vinyl aromatic hydrocarbon used to form the segment B. Blocking rate of vinyl aromatic hydrocarbon in segment B (weight%) = (weight of vinyl aromatic hydrocarbon polymer in segment B) / (weight of vinyl aromatic hydrocarbon in segment B) x 100 in segment B The blocking rate of the vinyl aromatic hydrocarbon can be determined by polymerizing only the segment B part of the block copolymer under the same polymerization conditions as in the case of obtaining the desired block copolymer. It can be determined by measuring the content of vinyl aromatic hydrocarbon and the content of vinyl aromatic hydrocarbon polymer in the corresponding polymer. The content of the vinyl aromatic hydrocarbon polymer was determined by oxidative decomposition (L.
M. KOLTHOFF, et, al., J. Polym. Sci. 1, 429
(1946)) by quantifying the vinyl aromatic hydrocarbon polymer component (however, the vinyl aromatic hydrocarbon polymer component with an average degree of polymerization of about 30 or less is excluded). can be grasped. Another method is to oxidize and decompose the finally obtained block copolymer using the same method as above and determine the weight of the vinyl aromatic hydrocarbon polymer.
The weight of the vinyl aromatic hydrocarbon polymer in segment B is calculated by subtracting the charged weight of the vinyl aromatic hydrocarbon used in the formation of segment A. It can be determined by dividing it by the weight of the preparation. In the present invention, the polymer structure has the general formula (a) (A-B)n (b) A-(B-A)n (c) B-(A-B)n (in the above formula, n is 1 or above, and generally an integer of 1 to 5.) 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, X represents, for example, 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.
and n is an integer of 1 or more. Generally, it is an integer from 1 to 5. ) or any mixture of these block copolymers can be used. In addition, the B segment part has 2
It may include repeating units of B segments or more. The number average molecular weight of these block copolymers is generally 50,000 to 500,000, preferably 100,000.
~350000. 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 polymer bonds, such as 1,
3-butadiene, 2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl-1,3-
Examples include butadiene, 1,3-pentadiene, 1,3-hexadiene, and particularly common ones 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 the present invention is prepared in a hydrocarbon solvent.
Obtained by polymerization using an organic lithium compound as an initiator. Examples of carbon hydrogen solvents include aliphatic dissolved hydrogen such as butane, pentane, hexane, isopentane, heptane, octane, isooctane, cyclopentane,
Alicyclic hydrocarbons such as methylcyclopentane, cyclohexane, methylcyclohexane, and ethylcyclohexane, or aromatic hydrocarbons such as benzene, toluene, ethylbenzene, and xylene can be used. Organolithium compounds are organic monolithium compounds in which one or more lithium atoms are bonded in the molecule, such as ethyllithium, n-propyllithium, isopropyllithium, n-butyllithium, sec-butyllithium, tert-butyllithium. , hexamethylene dilithium, butadienyl dilithium, isoprenyl dilithium, etc. In the block copolymer used in the present invention,
The blocking rate of vinyl aromatic hydrocarbon in segment B is determined by (i) continuously feeding a mixture of vinyl aromatic hydrocarbon and conjugated diene into the polymerization system, and adjusting the feeding rate, polymerization temperature, and/or polarity at that time. Adjustments can be made by adjusting the amount of compounds and randomizing agents used,
(ii) When polymerizing a mixture of a vinyl aromatic hydrocarbon and a conjugated diene by adding it all at once or by adding a portion of these monomers in several steps, use a polar compound or a randomizing agent to It can be adjusted by adjusting the amount used.
The most common method is to use a polar compound such as ethers, amines, thioethers, phosphines, phosphoramide, or a randomizing agent, and to adjust the amount used. Examples of suitable ethers are dimethyl ether diethyl ether, diphenyl ether and tetrahydrofuran, diethylene glycol dimethyl ether, diethylene glycol dibutyl ether. Examples of amines include tertiary amines, such as trimethylamine,
In addition to tetramethylethylenediamine, cyclic tertiary amines can also be used. Phosphines and phosphoramides include triphenylphosphine and hexamethylphosphoramide. Randomizing agents include potassium or sodium alkylbenzene sulfonate, potassium or sodium butoxide, and the like. These polar compounds or randomizing agents may be added before the start of the polymerization reaction, or may be added before the polymerization of the segment B portion. The above block copolymer (hereinafter referred to as component (A)) used in the present invention can be blended with other polymers as component (B) to improve rigidity, impact resistance, etc. . The polymer of component (B) that can be used in the present invention includes (i) a polymer block mainly composed of at least one, preferably two or more vinyl aromatic hydrocarbons and at least one conjugated diene; A block copolymer resin having a polymer block and having a weight ratio of vinyl aromatic hydrocarbon to conjugated diene of 60/40 to 95/5, preferably 65/35 to 90/10 (hereinafter referred to as block copolymer) (ii) It has at least one, preferably two or more polymer blocks mainly composed of vinyl aromatic hydrocarbons and at least one polymer block mainly composed of conjugated dienes, and has at least one polymer block mainly composed of vinyl aromatic hydrocarbons. A block copolymer elastomer (hereinafter referred to as a block copolymer elastomer) in which the weight ratio of hydrocarbon to conjugated diene is 10/90 or more and less than 60/40, preferably 15/85 to 55/45. Rubber-modified styrenic polymer (iv) At least one kind of polymer selected from rubber-modified styrenic polymers. In block copolymer resins and block copolymer elastomers, a polymer block mainly composed of vinyl aromatic hydrocarbons is one in which the content of vinyl aromatic hydrocarbons exceeds 75% by weight, preferably 80% by weight.
% or more by weight, and is composed of a vinyl aromatic hydrocarbon homopolymer block or a vinyl aromatic hydrocarbon homopolymer portion and a copolymer portion of a vinyl aromatic hydrocarbon and a conjugated diene. can be cited as a specific example. Further, a polymer block mainly composed of conjugated diene is a polymer block in which the content of conjugated diene is 25% by weight or more, preferably 50% by weight or more,
Specific examples include a conjugated diene homopolymer block, a copolymer block of a vinyl aromatic hydrocarbon and a conjugated diene, or a polymer block consisting of a combination thereof. In addition, these block copolymers have a polymer structure of the general formula: (a) (A'-B')n (b) A'-(B'-A')n (c) B'-(A'-B')n (In the above formula, A' is a polymer block mainly composed of vinyl aromatic hydrocarbons, and B' is a polymer block mainly composed of conjugated diene. A' block and B' block (n is an integer of 1 or more, generally an integer of 1 to 5.) ) [(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 represents, for example, 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. Generally, it is an integer from 1 to 5. ) or any mixture of these block copolymers can be used. Among these block copolymers, block copolymer resins can be used as stiffness improvers or impact resistance improvers, and generally have a number average molecular weight of 50,000 to 50,000.
500,000, preferably 80,000 to 350,000 can be used. Further, the book copolymer elastomer can be used as an impact resistance improver, and those having a number average molecular weight of 20,000 to 250,000, preferably 40,000 to 200,000 can be used. The non-rubber modified styrenic polymer used in the present invention is obtained by polymerizing the vinyl-substituted aromatic hydrocarbon compound or a monomer copolymerizable therewith. Monomers copolymerizable with vinyl-substituted aromatic hydrocarbon compounds include α
-Methylstyrene, acrylonitrile, acrylic esters, methacrylic esters, maleic anhydride, etc. Particularly preferred non-rubber modified styrenic polymers include polystyrene, styrene-α-methylstyrene copolymer, acrylonitrile-styrene copolymer, styrene-methacrylic acid ester copolymer, and styrene-maleic anhydride copolymer. These can be used alone or in a mixture of two or more. The rubber-modified styrenic polymer that can be used in the present invention is obtained by polymerizing a mixture of a vinyl-substituted aromatic hydrocarbon compound or a monomer copolymerizable therewith with an elastomer, and polymerization methods include suspension polymerization and emulsion polymerization. , bulk polymerization, bulk-
Suspension polymerization is commonly carried out. Examples of monomers copolymerizable with the vinyl-substituted aromatic hydrocarbon compound include α-methylstyrene, acrylonitrile, acrylic esters, methacrylic esters, and maleic anhydride. Further, as the elastomer, natural rubber, synthetic isoprene rubber, butadiene rubber, styrene-butadiene rubber, high styrene rubber, etc. are used. These elastomers are generally 2 to 70 parts by weight, more generally 3 to 50 parts by weight per 100 parts by weight of the vinyl-substituted aromatic hydrocarbon compound or a monomer copolymerizable therewith, or dissolved in the monomer. In latex form, it is subjected to bulk polymerization, bulk-suspension polymerization, emulsion polymerization, etc. Particularly preferred rubber-modified styrenic polymers include high impact rubber-modified styrenic polymers (HIPS). Non-rubber-modified styrenic polymers can be used as stiffness improvers, and rubber-modified styrenic polymers can be used as stiffness, impact resistance, and slip property improvers. In the present invention, the blending weight ratio of component (A) and component (B) is 30/70 or more, preferably 95/5 to 30/70, more preferably 90/10 to 40/60. If the amount of component (B) exceeds 70 folds, low-temperature stretchability, low-temperature shrinkability, etc. will be poor, which is not preferable. When obtaining a heat-shrinkable film that is well-balanced in terms of rigidity, impact resistance, low-temperature stretchability, low-temperature shrinkability, environmental damage resistance, and transparency by using component (B), (i) to (iv) 5 parts by weight or more of at least one kind of polymer selected from the above polymers, the amount of (i) is 70 parts by weight or less, and the amount of each of (ii) to (iv) is 30 parts by weight. It is recommended that the amount be less than or equal to 1. In addition, when improving slipperiness by blending the polymer (iv), the effect can be exhibited even when the blending amount is 0.5 to 5 parts by weight. In the block copolymer and block copolymer composition used in the present invention, the block copolymer of component (A) has a number average molecular weight of 120,000 to 500,000, preferably 120,000 to 350,000 as defined in the present invention. 5 to 95% by weight, preferably 10 to 90% by weight of a block copolymer,
Number average molecular weight is 50,000 or more and less than 120,000, preferably 5
Block copolymer defined by the present invention of 95,000 to 100,000
It is particularly recommended to use a mixture comprising 5% to 5% by weight, preferably 90 to 10% by weight, in order to obtain a heat-shrinkable film with excellent impact resistance, low-temperature stretchability, and shrinkage properties. Various additives can be added to the block copolymer and block copolymer composition used in the present invention depending on the purpose. A suitable additive is
Examples include softeners and plasticizers such as coumaron-indene resin, terpene resin, and oil in an amount of 30 parts by weight or less. Further, various stabilizers, pigments, antiblocking agents, antistatic agents, lubricants, etc. can also be added. In addition, as anti-blocking agents, lubricants, and antistatic agents,
For example, fatty acid amide, ethylene bisstearamide, sorbitan monostearate, saturated fatty acid ester of aliphatic alcohol, pentaerythritol fatty acid ester, etc., and as ultraviolet absorbers,
pt-butylphenyl salicylate, 2-
(2'-hydroxy-5'-methylphenyl)benzotriazole, 2-(2'hydroxy-3'-t-butyl-5'-methylphenyl)-5-chlorobenzotriazole, 2,5-bis-[5'- Compounds described in "Practical Handbook of Additives for Plastics and Rubber" (Kagaku Kogyo Co., Ltd.), such as t-butylbenzoxazolyl-(2)]thiophene, can be used. These are generally used in a range of 0.01 to 5% by weight, preferably 0.1 to 2% by weight. To obtain a heat-shrinkable uniaxially or biaxially oriented film from the block copolymer or block copolymer composition described above, the block copolymer or block copolymer composition is processed into a conventional T-die or annular die. The unstretched material is extruded into a flat or tube shape at 150 to 250°C, preferably 170 to 220°C, and the resulting unstretched product is substantially 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 with a calender roll, or in the direction perpendicular to the extrusion direction with a tenter, and in the case of a tube shape, it is stretched in the extrusion direction of the tube shape or in the circumferential direction. Stretch to. 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 a tube shape, the extruded film or sheet is stretched in the longitudinal direction with a tenter, etc. They are stretched simultaneously or separately in the circumferential direction of the tube, that is, in the direction perpendicular to the tube axis. In the present invention, it is preferable to stretch at a stretching temperature of 60 to 110°C, preferably 80 to 100°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 occurs during stretching, making it difficult to obtain a desired heat-shrinkable film, and if it exceeds 110°C, it is difficult to obtain a film with good shrinkage properties. 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 heat-shrinkable packaging. Further, a stretching ratio exceeding 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 biaxial stretching, the heat-shrinkable film 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. In order to use the heat-shrinkable film obtained in this way as a heat-shrinkable packaging material or a heat-shrinkable label material, the heat shrinkage rate at 80°C in the stretching direction is 15% or more, preferably 20-20%. It should be 70%, more preferably 30-80%. If the heat shrinkage rate at 80°C in the stretching direction is less than 15%, the shrinkage characteristics are 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.
This is undesirable because it becomes impossible to package articles that are subject to deterioration or deformation at high temperatures, and shrink wrapping ability decreases. In addition, in the present invention, the heat shrinkage rate at 80°C refers to the heat shrinkage rate at 80°C for a uniaxially stretched or biaxially stretched film at 80°C.
This is the heat shrinkage rate in each stretching direction of a molded product when immersed for 5 minutes in a heat medium such as hot water, silicone oil, or glycerin that does not inhibit the properties of the molded product. Further, the uniaxially stretched or biaxially stretched heat-shrinkable film of the present invention has a tensile modulus in the stretching direction of 5000 Kg/cm ² or more, preferably 7000 Kg/cm ² or more, and more preferably 10000 Kg/cm ^{2 or} more. Some things are necessary as heat shrink packaging materials. If the tensile modulus in the stretching direction is less than 5000 Kg/cm ² , it is not preferable because it causes sagging during the shrink wrapping process and normal packaging cannot be performed. When using the uniaxially stretched or biaxially stretched film of the present invention as a heat-shrinkable packaging material, in order to achieve the desired heat shrinkage rate,
A few seconds to a few minutes at a temperature of ~250℃, preferably 1~
It can be heat-shrinked by heating for 60 seconds, more preferably 2 to 30 seconds. The heat-shrinkable film of the present invention is superior in terms of hygiene compared to conventional vinyl chloride resin-based films.
Taking advantage of its properties, it can be used for various purposes, such as packaging for fresh foods, frozen foods, 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 the film 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 uniaxially stretched heat-shrinkable film of the present invention has excellent shrinkage characteristics and environmental damage resistance, so it has excellent thermal expansion coefficient and water absorption, as well as heat-shrinkable label material for plastic molded products that deform when heated to high temperatures. Materials that are extremely different from the block copolymer of the present invention, such as metal, porcelain, glass, paper, polyolefin resins such as polyethylene, polypropylene, and polybutene, polymethacrylic acid ester resins, polycarbonate resins, polyethylene terephthalate, and It can be suitably used as a heat-shrinkable label material for containers using at least one member selected from polyester resins such as butylene terephthalate and polyamide resins as a constituent material.
In addition to the resins mentioned above, the materials constituting the plastic container in which the heat-shrinkable film of the present invention can be used include polystyrene, rubber-modified high-impact polystyrene (HIPS), styrene-acrylonitrile copolymer, and styrene-anhydrous. Maleic acid copolymer, acrylonitrile-butadiene-styrene copolymer (ABS), methacrylic acid ester-butadiene-styrene copolymer (MBS), polyvinyl chloride resin, polyvinylidene chloride resin, phenol resin, urea resin, Examples include melamine resin, epoxy resin, unsaturated polyester resin, and silicone resin. These plastic containers may be a mixture of two or more types of resins, a laminate, or a container made of a combination of various materials. In addition, when using a heat-shrinkable film obtained by uniaxially stretching the block copolymer or block copolymer composition defined in the present invention as a heat-shrinkable label material, 80% in the direction orthogonal to the stretching direction is used. The heat shrinkage rate at °C is preferably less than 15%, preferably 10% or less, more preferably 5% or less. Therefore, in the present invention, substantially uniaxial stretching for heat-shrinkable labels means stretching in the stretching direction.
Stretching is performed so that the heat shrinkage rate at 80°C is 15% or more and the heat shrinkage rate at 80°C in the direction orthogonal to the stretching direction is less than 15%. In addition, in the present invention, the thickness of the film is generally 10
~300μ, preferably adjusted to a range of 30 to 100μ. 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. Examples 1 to 5 and Comparative Examples 1 to 7 In the first stage, ₁ part by weight of S styrene was substantially completely polymerized using n-butyllithium as a catalyst in a cyclohexane solvent. After that, in the second stage, ₂ parts by weight of S styrene and ₁ part by weight of B butadiene were added to substantially complete polymerization to produce a block copolymer having an A-B type polymer structure. . The blocking rate of styrene in the second stage was adjusted by adding tetrahydrofuran to the cyclohexane solvent before the start of the first stage polymerization, and adjusting the amount of the added amount. To illustrate the amount of tetrahydrofuran used, in Examples 1 and 2, about 1.8 parts by weight of tetrahydrofuran was used based on 100 parts by weight of the total monomers used. Each block copolymer contained 2,6-di-tert-butyl-4-methylphenol and trisphenyl phosphate as stabilizers, respectively.
Added 0.5% by weight. The number average molecular weight of each block copolymer was in the range of 150,000 to 300,000. The obtained block copolymer was formed into a sheet with a thickness of 0.25 mm at 200°C using a 40 mmφ extruder, and then uniaxially stretched horizontally to a thickness of about 5 times using a tenter.
A 60μ film was produced. At this time, the temperature in the tenter was set at the lowest temperature at which a uniaxially stretched film could be stably produced from each block copolymer without breaking during stretching. Next, the tensile modulus of the heat-shrinkable film of each block copolymer in the stretching direction, puncture strength, and heat shrinkage rate at 80°C in the stretching direction were measured. As a result, it was revealed that the heat-shrinkable film of the present invention exhibits good rigidity, impact resistance, and shrinkage rate. Incidentally, all of these heat-shrinkable films had a heat shrinkage rate of less than 5% at 80°C in the direction orthogonal to the stretching direction. Moreover, all of them were transparent films. Next, after printing letters and patterns on the heat-shrinkable film of each block copolymer obtained as described above, the stretched direction is the circumferential direction, and the non-stretched direction is the longitudinal direction. A cylindrical heat-shrinkable label was produced using an automatic Shrink label machine, placed over a glass bolt, and passed through a shrink tunnel controlled at a temperature of approximately 180°C to be heat-shrinked. The time taken to pass through the shrink tunnel was controlled so that each heat-shrinkable label was in tight contact with the glass bottle surface, but labels with a lower heat shrinkage rate at 80°C took a longer time. In addition, the heat-shrinkable films of Comparative Examples 1, 4, and 5 had low rigidity;
A good coated product could not be obtained. When the environmental damage resistance of the thus obtained heat-shrinkable film-covered glass bottle products was examined, all of the heat-shrinkable film-covered products of the present invention had good performance.

【table】

[Table] Examples 6 to 10 and Comparative Example 8 Using the polymers shown in Table 3 as component (B), block copolymer compositions were produced according to the formulation method shown in Table 2. Each sample was formed into a sheet using an extruder, and then uniaxially stretched approximately 4 times to produce a film with a thickness of approximately 50 μm.The stretching temperature was set to the lowest temperature at which each sample could be stretched. The performance of each film is shown in Table 2. In addition, in the uniaxially stretched films of Examples 6 to 10, the heat shrinkage rate at 80° C. in the direction orthogonal to the stretching direction was less than 5%.

【table】

[Table] Examples 11 to 14 The same block copolymer compositions as in Examples 2 and 4 and the same block copolymer compositions as in Examples 7 and 10 were each molded into a sheet using a 40 mm extruder, and then
A biaxially stretched film having a thickness of approximately 40 μm was produced by biaxially stretching the film by a factor of 3 in both the vertical and horizontal directions using a biaxial stretching device. Table 4 shows the performance of the approximately biaxially stretched film obtained. The stretching temperature was set to the same temperature as in the case of uniaxial stretching.

[Table] Example 15 Cylindrical heat-shrinkable labels were prepared from the uniaxially stretched films of Examples 1 to 10 with the stretched direction in the circumferential direction and the unstretched direction in the longitudinal direction. high impact polystyrene (HIPS),
The mixture was placed over containers made of polypropylene, polycarbonate, polybutylene terephthalate, nylon 66, and paper, and passed through a shrink tunnel controlled at a temperature of 180 to 200°C to undergo heat shrinkage. As a result, all of these heat-shrinkable labels had no bagging or wrinkles, were in tight contact with the container surface, and had good environmental damage resistance. Example 16 Using the same polymerization method as in Example 2, 20 parts by weight of styrene was polymerized in the first stage, and 61 parts by weight of styrene and 14 parts by weight of butadiene were polymerized in the second stage. In the third stage, 5 parts by weight of styrene was polymerized to obtain a block copolymer having an ABA structure. This block copolymer had the same excellent performance as Example 2. Example 17 50 parts by weight of a block copolymer with a number average molecular weight of 180,000 produced in the same manner as in Example 2 except for changing the amount of n-butyllithium used, and a block copolymer with a number average molecular weight of 65,000 In Example 2, a block copolymer mixture containing 50 parts by weight of
A heat-shrinkable film was obtained by uniaxial stretching in the same manner as above. The minimum stretching temperature was 80°C. The tensile modulus of this heat-shrinkable film is 11000Kg/
cm ² , puncture impact value 2500 Kg·cm/cm, and shrinkage rate at 80°C was 61%. Example 18 In Example 7, the same block copolymer mixture as used in Example 17 was used in place of block copolymer A-2 to prepare a block copolymer composition. The minimum stretching temperature during uniaxial stretching of this block copolymer composition is 80°C.
The tensile modulus of the resulting heat-shrinkable film is
11500Kg/ ^cm2 , puncture impact value 30000Kg・
cm/cm, the shrinkage rate at 80°C was 55%.

Claims (1)

[Claims] 1. At least one vinyl aromatic hydrocarbon polymer segment A and at least one copolymer segment B of vinyl aromatic hydrocarbon and conjugated diene.
10 to 70% by weight of the total vinyl aromatic hydrocarbon used to produce a block copolymer having a weight ratio of vinyl aromatic hydrocarbon to conjugated diene of 77/23 to 95/5. Segment A is formed by using a mixture of vinyl aromatic hydrocarbon and conjugated diene in segment B, and a mixture in which the weight ratio of vinyl aromatic hydrocarbon and conjugated diene is more than 75/25 and not more than 93/7 is formed in segment B. Block rate is 20~
It is made by stretching a block copolymer obtained by polymerizing under conditions of 75% by weight, and at 80°C in the stretching direction.
A block copolymer heat-shrinkable film having a heat shrinkage rate of 15% or more and a tensile modulus in the stretching direction of 5000 Kg/cm ² or more. 2 (A) having at least one vinyl aromatic hydrocarbon polymer segment A and at least one vinyl aromatic hydrocarbon and conjugated diene copolymer segment B; To produce a block copolymer having a weight ratio of 77/23 to 95/5, 10 to 70% by weight of the total vinyl aromatic hydrocarbon used is used to form segment A, while segment B is A mixture in which the weight ratio of vinyl aromatic hydrocarbon and conjugated diene is more than 75/25 and less than 93/7 is polymerized under conditions such that the vinyl aromatic hydrocarbon blocking ratio in segment B is 20 to 75% by weight. (B)(i) a polymer block mainly composed of at least one vinyl aromatic hydrocarbon and a polymer mainly composed of at least one conjugated diene; (ii) a block copolymer resin having a block and having a weight ratio of vinyl aromatic hydrocarbon to conjugated diene of 60/40 to 95/5; A block copolymer elastomer having a polymer block mainly composed of a coalescing block and at least one conjugated diene, and having a weight ratio of vinyl aromatic hydrocarbon to conjugated diene of 10/90 or more and less than 60/40 ( iii) a non-rubber modified styrenic polymer; (iv) a block copolymer composition comprising 70 to 5 parts by weight of at least one polymer selected from rubber modified styrenic polymers; The heat shrinkage rate at 80℃ in the direction is 15%
The tensile modulus in the stretching direction is 5000Kg/cm ²
The above is a heat-shrinkable film.