JPH0359923B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a block copolymer having excellent impact resistance, rigidity, low-temperature stretchability, and environmental damage resistance, and a method for producing the same. Block copolymers consisting of conjugated dienes and vinyl aromatic hydrocarbons exhibit elasticity similar to that of vulcanized natural rubber or synthetic rubber without vulcanization when the vinyl aromatic hydrocarbon content is relatively low. It has properties at room temperature and has the same processability as thermoplastic resins at high temperatures, so it is useful for footwear, plastic modification,
Widely used in asphalt, adhesive and other fields. In addition, when the vinyl aromatic hydrocarbon content is relatively high, a thermoplastic resin that is transparent and has excellent impact resistance can be obtained, so its usage has increased in recent years, mainly in the food packaging container field, and its applications have also expanded. It is becoming more diverse. Such a block copolymer has a two-phase structure consisting of a hard segment with a high glass transition temperature and a soft segment with a low glass transition temperature. The glass transition temperature of the soft segment is determined by using polymers with a glass transition temperature close to those of conjugated diene polymers (polybutadiene, polyisoprene, etc.) in order not to deteriorate the low-temperature properties of the block copolymer, such as flexibility and impact resistance at low temperatures. Block copolymers having polymers as soft segments are commonly used. Therefore, as the soft segment, a block copolymer incorporating a conjugated diene homopolymer or a copolymer of a conjugated diene and a vinyl aromatic hydrocarbon, the main component of which is a conjugated diene, is commonly used. Under such current circumstances, the present inventors found that the weight ratio of the vinyl aromatic hydrocarbon polymer segment to the vinyl aromatic hydrocarbon to the conjugated diene exceeds 75/25, which is completely different from the conventional knowledge. We have now completed the present invention by discovering that a block copolymer composed of the following copolymer segments has unique properties of excellent low-temperature stretchability and environmental damage resistance. That is, the present invention is a linear block compound whose polymer structure is represented by the general formula (a) (A-B) _o (b) A-(B-A) _o (c) B-(A-B) _o. Polymer (In the above formula, A indicates a vinyl aromatic hydrocarbon polymer segment. B indicates a vinyl aromatic hydrocarbon to conjugated diene weight ratio of more than 75/25, 93/
7 or less and which has a vinyl aromatic hydrocarbon blocking rate of 20 to 75% by weight represented by the following formula. Blocking rate (wt%) of vinyl aromatic hydrocarbon in segment B = [weight of vinyl aromatic hydrocarbon polymer in segment B]/[weight of vinyl aromatic hydrocarbon in segment B] x 100 n is 1 to It is an integer of 5. ), and the weight ratio of vinyl aromatic hydrocarbon to conjugated diene is 77/23 to 95/5, and the amount of vinyl aromatic hydrocarbon forming segment A is 10 to 70 of the total vinyl aromatic hydrocarbon. Weight%, number average molecular weight
The present invention relates to a block copolymer having a molecular weight of 50,000 to 500,000 and a method for producing the same. Since the block copolymer of the present invention has excellent low-temperature stretchability, it can be easily uniaxially or biaxially stretched at low temperatures, and a film with excellent low-temperature shrinkability can be obtained. Since the heat-shrinkable film obtained from the block copolymer of the present invention has excellent shrinkability at low temperatures and short-term shrinkability even at high temperatures, it may deteriorate or deform if heated at high temperatures for a long period of time in the shrink packaging process. Suitable for packaging of products that generate a large amount of heat, such as fresh foods and plastic molded products. Moreover, the above-mentioned heat-shrinkable film has excellent impact resistance and can be used as a coating for articles such as glass bottles that are likely to scatter fragments when broken. Furthermore, the above-mentioned heat-shrinkable film 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 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 obtained from the block copolymer of the present invention has the drawback of poor environmental damage resistance after coating, and cracks easily form in the film. It can withstand being left in the natural environment for long periods of time. Therefore, the above-mentioned heat-shrinkable film can be particularly suitably used for applications such as labels for containers made of the above-mentioned materials by taking advantage of such advantages. Furthermore, the block copolymer of the present invention can be processed by injection molding,
Various molded products can be made by injection blow molding. Furthermore, films and sheets formed from the block copolymer of the present invention by methods such as extrusion molding and inflation molding can be used as they are or by further secondary processing by methods such as pressure molding and vacuum molding for various uses. Can be used. In such uses, the block copolymer of the present invention is characterized by excellent colorability and printability. The present invention will be explained in detail below. The block copolymer of the present invention has the above-mentioned polymer structure consisting of a vinyl aromatic hydrocarbon polymer segment A and a copolymer segment B of a vinyl aromatic hydrocarbon and a conjugated diene. and the conjugated diene weight ratio is 77/23 to 95/
5. Segment A with a block copolymer, preferably 80/20 to 93/7, using 10 to 70% by weight, preferably 15 to 60% by weight of the total vinyl aromatic hydrocarbon used. is formed, 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 less than or equal to 90/10; Blocking rate of vinyl aromatic hydrocarbons is 20-75
It is a block copolymer formed by polymerizing the segment B under conditions such that the amount by weight is preferably in the range of 30 to 65% by weight. 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 and therefore undesirable. 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
If the blocking rate of vinyl aromatic hydrocarbon is less than 20% by weight in the formation of
If it exceeds , it is not preferable because the environmental damage resistance is poor. In the present invention, the blocking 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 (wt%) of vinyl aromatic hydrocarbon in segment B = [weight of vinyl aromatic hydrocarbon polymer in segment B] / [weight of vinyl aromatic hydrocarbon in segment B] x 100 The blocking rate of the vinyl aromatic hydrocarbon corresponds to the segment B portion obtained by polymerizing only the segment B portion of the block copolymer under the same polymerization conditions as when obtaining the desired block copolymer. It can be determined by measuring the vinyl aromatic hydrocarbon content and the vinyl aromatic hydrocarbon polymer content in the polymer. The content of the vinyl aromatic hydrocarbon polymer is 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 to form 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) _o (b) A-(B-A) _o (c) B-(A-B) _o (in the above formula, n is 1 It is a linear block copolymer represented by: Note that the B segment portion may include two or more repeating units of B segments. The number average molecular weight of these block copolymers is from 50,000 to 500,000, preferably from 100,000 to 350,000. In the present invention, vinyl aromatic hydrocarbons include styrene, 0-methylstyrene, p-methylstyrene, p-tert-butylstyrene, 1,3-
Dimethylstyrene, α-methylstyrene, vinylnaphthalene, vinylanthracene, etc.
A particularly common example is styrene. These may be used not only alone, but also as a mixture of two or more. Conjugated dienes include diolefins having a pair of conjugated double bonds, such as 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl-1,
3-butadiene, 1,3-pentadiene, 1,3
-hexadiene, etc., 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. In addition, in the formation step of segment B of the present invention, when a mixture of a vinyl aromatic hydrocarbon and a conjugated diene is supplied to the polymerization system for polymerization, the supply form of the vinyl aromatic hydrocarbon and the conjugated diene is Any method may be used as long as a hydrocarbon and a conjugated diene are copolymerized to form segment B that satisfies the requirements specified in the present invention. For example, the vinyl aromatic hydrocarbon and the conjugated diene may be mixed in advance and the mixture may be supplied to the polymerization system, or the vinyl aromatic hydrocarbon and the conjugated diene may be supplied to the polymerization system from separate supply ports. However, these monomers may be mixed and copolymerized at the same time in the polymerization system, or after one monomer is supplied in its entirety into the polymerization system, the other monomer may be copolymerized until the polymerization of that monomer is completed. It may be supplied into the system for copolymerization. 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 hydrocarbon solvents include aliphatic hydrocarbons such as butane, pentane, hexane, isopentane, octane, and isooctane, alicyclic hydrocarbons such as cyclopentane, methylcyclopentane, cyclohexane, methylcyclohexane, and ethylcyclohexane, or benzene, toluene, Aromatic hydrocarbons such as ethylbenzene and xylene can be used. An organolithium compound is an organolithium compound in which one or more lithium atoms are bonded in the molecule. Examples include ethyllithium, n-propyllithium, isopropyllithium, n-butyllithium, sec-butyllithium, tert-butyllithium, hexamethylene dilithium, butadienyl dilithium, and isoprenyl dilithium. In the production of the block copolymer of 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; (ii) adjusting the supply rate, polymerization temperature, and/or amount of polar compound or randomizing agent used;
Methods of adjusting the amount of polar compounds and randomizing agents used when adding a mixture of vinyl aromatic hydrocarbon and conjugated diene all at once or adding a portion of these monomers in several portions during polymerization, etc. Accordingly, it can be adjusted to the range defined by the present invention. As polar compounds and randomizing agents, ethers,
Examples include amines, thioethers, phosphoramides, alkylbenzene sulfonates, potassium or sodium alkoxides, and the like. Examples of suitable ethers are dimethyl ether, diethyl ether, diphenyl ether and tetrahydrofuran, diethylene glycol dimethyl ether, diethylene glycol dibutyl ether. As the amines, in addition to tertiary amines such as trimethylamine, triethylamine, and 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. In order to adjust the blocking rate of styrene in segment B to the range specified in the present invention using a polar compound or randomizing agent, the amount used must be equal to the total amount of monomers used.
0.001 to 10 parts by weight per 100 parts by weight, preferably
It is 0.01 to 5 parts by weight. The polymerization temperature for producing the block copolymer of the present invention is generally -40°C to 150°C, preferably 40°C to 150°C.
℃ to 120℃. The time required for polymerization varies depending on the conditions, but is usually within 48 hours, particularly preferably 1 to 10 hours. Further, it is desirable to replace the atmosphere of the polymerization system with an inert gas such as nitrogen gas. The polymerization pressure is not particularly limited as long as it is within a pressure range sufficient to maintain the monomer and solvent in a liquid phase within the above polymerization temperature range. Furthermore, care must be taken not to introduce impurities such as water, oxygen, carbon dioxide gas, etc. that would inactivate the catalyst and living polymer into the polymerization system. The living block copolymer thus obtained is inactivated by adding a polymerization terminator such as water, alcohol, carbon dioxide, etc. in an amount sufficient to inactivate the active ends.
At this time, by appropriately selecting a polymerization terminator such as reacting with carbon dioxide, alkylene oxide, alkylene sulfide, etc., -OH, -SH, -COOH, -COCl, -SO ₃ H ,−
Block copolymers having various functional groups such as C≡N at their ends can be obtained. If necessary, various stabilizers can be added to the block copolymer for the purpose of improving heat resistance, weather resistance, etc. Methods for recovering the block copolymer from the obtained block copolymer solution include, for example, recovering the block copolymer by precipitation using a precipitant such as methanol, and heating the solution to evaporate the solvent. Any conventionally known method can be employed, such as a method of recovering the copolymer by dispersing the block copolymer solution in water, a method of dispersing the block copolymer solution in water, blowing in water vapor, and distilling off the solvent under heating to recover the copolymer. The block copolymer of the present invention has a vinyl aromatic hydrocarbon content of 60 to 60%, which is outside the range specified in the present invention.
A block copolymer resin of a vinyl aromatic hydrocarbon and a conjugated diene containing 95% by weight of a vinyl aromatic hydrocarbon, a block copolymer elastomer of a vinyl aromatic hydrocarbon and a conjugated diene having a vinyl aromatic hydrocarbon content of less than 60% by weight,
Polymers of the above-mentioned vinyl aromatic hydrocarbon monomers, the above-mentioned vinyl aromatic hydrocarbon monomers and other vinyl monomers, such as acrylics such as ethylene, propylene, butylene, vinyl chloride, vinylidene chloride, vinyl acetate, and methyl acrylate. Stiffness and impact resistance are achieved by blending at least one polymer selected from acid esters, methacrylic esters such as methyl methacrylate, copolymers with acrylonitrile, rubber-modified high-impact styrenic resins (HIPS), etc. etc. can be improved. Various additives can be added to the block copolymer of the present invention 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. Further, 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 aliphatic alcohols, pentaerythritol fatty acid esters, etc. Also, 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'-t-
Butylbenzoxazolyl-(2)]thiophene, etc.
Compounds described in "Practical Handbook of Additives for Plastics and Rubber" (Kagaku Kogyosha) can be used.
These generally range from 0.01 to 5% by weight, preferably 0.1%
It is used in a range of 2% by weight. The block copolymer of the present invention is transparent and has excellent impact resistance, and can be used as a molding material for various molded products. That is, the block copolymer of the present invention can be processed into extrusion molded products such as sheets and films, and heated by vacuum, compressed air, etc., by the same processing means as ordinary thermoplastic resins, either as they are or after being colored. It can be used in a wide range of container and packaging material fields, including molded products, specifically food containers and packaging, printer packaging materials, fruits and vegetables, and confectionery packaging films. In addition, it can be used in applications where ordinary general-purpose thermoplastic resins are used, such as in the fields of toys, daily necessities, food packaging containers, miscellaneous goods, and light electrical parts manufactured by injection molding and blow molding methods. A particularly preferred application is to print characters or designs on a uniaxially stretched film of the block copolymer specified in the present invention, and then apply heat shrinkage to the surface of a packaged object such as a plastic molded product, metal product, glass container, or porcelain. It can be used as a material for so-called heat-shrinkable labels, which are used in close contact with each other. In particular, the uniaxially stretched heat-shrinkable film obtained from the block copolymer of the present invention has excellent shrinkage characteristics 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. other,
Materials whose coefficient of thermal expansion and water absorption are extremely different from those of the block copolymer of the present invention, such as metals, porcelain, glass, paper, polyolefin resins such as polyethylene, polypropylene, and polybutene, polymethacrylate ester resins, and polycarbonate resins. It can be suitably used as a heat-shrinkable label material for containers using at least one member selected from resins, polyester resins such as polyethylene terephthalate and polybutylene terephthalate, and polyamide resins. In addition to the above-mentioned resins, the materials constituting the plastic container in which the heat-shrinkable block copolymer film of the present invention can be used include
Polystyrene, rubber modified high impact polystyrene (HIPS), styrene-acrylonitrile copolymer, styrene-maleic anhydride copolymer, acrylonitrile-butadiene-styrene copolymer (ABS), methacrylic acid ester-butadiene-
Styrene copolymer (MBS), polyvinyl chloride resin, polyvinylidene chloride resin, phenol resin, urea resin, melamine resin, epoxy resin,
Examples include unsaturated polyester resins and silicone resins. These plastic containers may be a mixture of two or more resins or may be a laminate. EXAMPLES The present invention will be described in more detail with reference to Examples below, but it goes without saying that the scope of the present invention is not limited thereto. Examples 1 to 5 and Comparative Examples 1 to 10 Block copolymers having a polymer structure of AB were produced according to the process shown in Table 1 using n-butyllithium as a catalyst in a cyclohexane solvent. 400 parts by weight of cyclohexane, about 1.8 parts by weight of tetrahydrofuran, and ₁ part by weight of styrene S were placed in a stainless steel polymerization vessel equipped with a stirrer and the interior was purged with nitrogen gas, and after setting the internal temperature to about 65°C, n-butyllithium was added. 0.045 parts by weight was added and polymerized. After the styrene has substantially completely polymerized, the internal temperature is approximately 85℃
Into the polymerization system, ₂ parts by weight of S styrene and ₁ part by weight of B butadiene were further added and polymerized. After these monomers have been substantially completely polymerized, 20 parts by weight of methanol is added to the polymerization solution to stop the polymerization, and then 2,6-di-tert-butyl-4- as a stabilizer is added.
Methylphenol and trisnonylphenyl phosphorite were each added in an amount of 0.5 parts by weight. In this way, block copolymer A-1 was obtained. The molecular weight of block copolymer A-1 determined by gel permeation chromatography was approximately 190,000 (using a calibration curve prepared using monodisperse polystyrene, GPC of the block copolymer The molecular weight was read from the main peak position of the pattern). Block copolymer A-
2 to A-4 and A-6 to A-12 were manufactured. still,
The blocking rate of polystyrene in segment B was adjusted mainly by varying the amount of tetrahydrofuran. The molecular weight of the obtained block copolymer is approximately 15
They ranged from 10,000 to 300,000. Block copolymer A-5 was produced as follows. Into the same polymerization vessel as above, 180 parts by weight of cyclohexane was charged, and after setting the internal temperature to about 65°C, 0.04 parts by weight of n-butyllithium was added and polymerized. After the styrene has substantially completely polymerized, reduce the internal temperature to approximately 80
A mixture consisting of 220 parts by weight of cyclohexane, 45 parts by weight of styrene, and 10 parts by weight of butadiene was added over 1 hour using a metering pump while maintaining the temperature at 0.degree. C. for polymerization. After these monomers were substantially completely polymerized, the same post-treatment as above was carried out to obtain block copolymer A-5. The molecular weight of block copolymer A-5 was approximately 210,000. 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 each block copolymer film 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 film obtained from the block copolymer of the present invention exhibited good stiffness, impact resistance, and shrinkage. All of these 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 each block copolymer film obtained as above, it is shaped into a cylindrical film with the stretched direction being the circumferential direction and the unstretched direction being the longitudinal direction. A heat-shrinkable label was produced, placed on a glass bottle using an automatic Shrink label machine, 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. The films of Comparative Examples 1, 4, and 5 had low rigidity, and good coated products could not be obtained. In this way, when the environmental damage resistance of glass bottle coating products made from the block copolymer was investigated, all of the film coating products made from the block copolymer of the present invention showed good performance. had.

【table】

[Table] Examples 6 and 7 Injection molded products were produced using block copolymers A-1 and A-2, and the physical properties of the obtained molded products were
Shown in the table.

[Table] Examples 8 and 9 40 mmφ from block copolymers A-1 and A-3
A sheet with a thickness of 1.2 mm was produced at 200°C using an extruder, and then a cylindrical cup with a diameter of 50 mmφ and a height of 40 mm was formed using a vacuum forming device. Each cup-shaped molded product obtained was filled with 50 ml of water and allowed to fall naturally onto a concrete surface from a height of 1 m, but the cup did not break. Example 10 In the first stage using the same polymerization method as Example 2,
Polymerize 20 parts by weight of styrene, and in the second stage
After 61 parts by weight of styrene and 14 parts by weight of butadiene were polymerized, 5 parts by weight of styrene was further polymerized in the third stage to obtain a block copolymer having an ABA structure. This block copolymer had the same excellent performance as Example 2.

Claims (1)

[Claims] 1. A linear polymer whose structure is represented by the general formula (a) (A-B) _o (b) A-(B-A) _o (c) B-(A-B) _o Block copolymer (In the above formula, A indicates a vinyl aromatic hydrocarbon polymer segment. B indicates a vinyl aromatic hydrocarbon to conjugated diene weight ratio exceeding 75/25, 93/
7 or less and which has a vinyl aromatic hydrocarbon blocking rate of 20 to 75% by weight represented by the following formula. Blocking rate (wt%) of vinyl aromatic hydrocarbon in segment B = [weight of vinyl aromatic hydrocarbon polymer in segment B]/[weight of vinyl aromatic hydrocarbon in segment B] x 100 n is 1 to It is an integer of 5. ), and the weight ratio of vinyl aromatic hydrocarbon to conjugated diene is 77/23 to 95/5, and the amount of vinyl aromatic hydrocarbon forming segment A is 10 to 70 of the total vinyl aromatic hydrocarbon. Weight%, number average molecular weight
A block copolymer with a molecular weight of 50,000 to 500,000. 2 In a hydrocarbon solvent, using an organolithium compound as an initiator, the polymer structure has the general formula: (a) (A-B) _o (b) A-(B-A) _o (c) B-(A-B) Linear block copolymer represented by _o (In the above formula, A represents a vinyl aromatic hydrocarbon polymer segment. B represents a copolymer segment of a vinyl aromatic hydrocarbon and a conjugated diene.
n is an integer from 1 to 5. ), and the weight ratio of vinyl aromatic hydrocarbon to conjugated diene is 77/23 to 95/5, and the number average molecular weight is
50,000 to 500,000, (a) 10 to 500,000 of the total vinyl aromatic hydrocarbons used;
70% by weight to form segment A; (b) segment B, on the other hand, uses a mixture of vinyl aromatic hydrocarbon and conjugated diene in which the weight ratio is greater than 75/25 and less than 93/7, and is a polar compound; Alternatively, by polymerizing using a randomizing agent in an amount of 0.001 to 10 parts by weight based on 100 parts by weight of the total monomers used, the block rate of vinyl aromatic hydrocarbon in segment B represented by the following formula can be increased to 20 to 75% by weight. Blocking rate (wt%) of vinyl aromatic hydrocarbon in segment B = [Weight of vinyl aromatic hydrocarbon polymer in segment B] / [Weight of vinyl aromatic hydrocarbon in segment B] x 100 A method for producing a characteristic block copolymer. 3. Production of a block copolymer according to claim 2, characterized in that during polymerization of segment B, a mixture of a vinyl aromatic hydrocarbon and a conjugated diene is continuously supplied to the polymerization system for polymerization. Method.