JP2023084128A - Block copolymer, composition, heat shrinkable film, sheet and molding of sheet - Google Patents

Abstract

To provide a block copolymer having a high tensile elongation value and less in gel foreign material.SOLUTION: A block copolymer has a first vinyl aromatic block (S1), a second vinyl aromatic block (S2), and a copolymer block (B/S), wherein the (S1) and (S2) are each independently substantially composed of only the vinyl aromatic monomer unit, a weight average molecular weight of (S2) is not more than (S1), and the (B/S) is substantially composed only of vinyl aromatic monomer units and conjugated diene monomer units, and a content of the conjugated diene monomer units in (B/S) is 55 mass% or more and 82 mass% or less, when a total mass of the (S1) and (S2) is 100 mass%, a ratio of the (S1) is 50 mass% or more and 85 mass% or less, and a content of the (B/S) is 38 mass% or more and 60 mass% or less.SELECTED DRAWING: None

Description

The present invention relates to block copolymers, compositions, heat-shrinkable films, sheets and molded articles of sheets.

A heat-shrinkable film made from a block copolymer obtained by polymerizing a vinyl aromatic compound and a conjugated diene-based compound has excellent heat-shrinkability and excellent finish after shrinkage, and can be applied to various shapes and attachment methods of packaged objects. It is widely used for shrink wrapping because it can be used. It is also excellent in that it does not cause environmental pollution problems like polyvinyl chloride when it is disposed of. For example, Patent Document 1 discloses a heat-shrinkable film using a composition containing a block copolymer of styrene and butadiene.

In addition, the block copolymer is also used in sheets and molded products thereof. For example, in molded products such as food containers, polystyrene resins and poly(styrene-methacrylic acid A method of adding the block copolymer to a copolymer resin or the like is widely used.

Japanese Patent Laid-Open No. 11-158241

Impact resistance and rupture resistance are important properties of heat-shrinkable films, sheets, and molded products thereof, and the tensile elongation of the starting block copolymer or the composition containing the block copolymer is one of these properties. Used as an index. However, block copolymers with good tensile elongation and compositions thereof have the problem that gel foreign matter is likely to occur (fish eyes are likely to occur when made into films, sheets, etc.). It has been desired to achieve compatibility with gel contaminants.

The present invention has been made in view of such problems, and an object of the present invention is to provide a block copolymer having a high tensile elongation value, which is an index of mechanical strength and appearance quality, and less gel foreign matter. Invention. Furthermore, the provision of a composition containing the block copolymer, and a sheet, film, or heat-shrinkable film having high impact strength, tensile elongation, less fish eyes, and excellent appearance, using the composition as a raw material. The object of the present invention is to provide.

According to the present invention, a block copolymer having a first vinyl aromatic block (S1), a second vinyl aromatic block (S2), and a copolymer block (B/S), The first vinyl aromatic block (S1) is substantially composed only of vinyl aromatic monomer units, and the second vinyl aromatic block (S2) is substantially composed of vinyl aromatic monomer units. It is composed only of monomer units, has a weight average molecular weight equal to or less than the first vinyl aromatic block, and the copolymer block (B/S) is substantially composed of vinyl aromatic monomer units and conjugated diene units. The content of the conjugated diene-based monomer unit in the copolymer block is 55% by mass or more and 82% by mass or less, and the first vinyl aromatic block and the second When the total mass of the vinyl aromatic blocks is 100% by mass, the ratio of the first vinyl aromatic block is 50% by mass or more and 85% by mass or less, and the copolymer in the block copolymer The polymer block content is 38% by mass or more and 60% by mass or less, and dynamic viscoelasticity measurement was performed in accordance with ISO 6721-1 under the conditions of a temperature increase rate of 4° C./min, a frequency of 1 Hz, and a strain of 0.02%. A block copolymer having at least one peak in the range of −70° C. or more and −35° C. or less is provided.

The weight average molecular weight of the first vinyl aromatic block (S1) is preferably 30,000 or more and 100,000 or less.

When the total mass of the vinyl aromatic monomer unit and the conjugated diene monomer unit in the block copolymer is 100% by mass, the vinyl aromatic monomer unit in the block copolymer is preferably 64% by mass or more and 75% by mass or less.

Various embodiments of the present invention are illustrated below. The embodiments shown below can be combined with each other.
Preferably, the copolymer block (B/S) is a random copolymer block of vinyl aromatic monomer units and conjugated diene monomer units.
Preferably, it is linear, and the arrangement of polymer blocks is (S1)-(B/S)-(S2) or (S2)-(B/S)-(S1).

Another aspect of the present invention provides a composition comprising the block copolymer and further comprising a polymer different from the block copolymer.
Preferably, the content of the block copolymer is 15% by mass or more and 85% by mass or less.

Another aspect of the present invention provides a heat-shrinkable film comprising a layer composed of the above composition.

Another aspect of the present invention provides a sheet comprising a layer composed of the above composition.

According to another aspect of the present invention, there is provided a molded article obtained by molding the sheet.

Embodiments of the present invention will be described below. Various features shown in the embodiments shown below can be combined with each other. In addition, the invention is established independently for each characteristic item.

1-1. Block Copolymer A block copolymer according to one embodiment of the present invention comprises a first vinyl aromatic block (S1), a second vinyl aromatic block (S2), and a copolymer block (B/S). and have

The block copolymer is preferably a linear block copolymer. The linear block copolymer preferably has a first vinyl aromatic block (S1) at one end and a second vinyl aromatic block (S2) at the other end. The linear block copolymer is preferably a (S1)-(B/S )-(S2) or (S2)-(B/S)-(S1).

When the total mass of the first vinyl aromatic block and the second vinyl aromatic block contained in the block copolymer is 100% by mass, the ratio of the first vinyl aromatic block (the first vinyl aromatic block The mass of the aromatic block/(the mass of the first vinyl aromatic block+the mass of the second vinyl aromatic block)×100) is 50 to 85% by mass. In other words, the ratio of the second vinyl aromatic block (mass of the second vinyl aromatic block/(mass of the first vinyl aromatic block + mass of the second vinyl aromatic block) x 100) is 15. ~50% by mass. When the ratio of the first vinyl aromatic block is in this range, the tensile elongation tends to be good, and the impact resistance and heat shrinkage when used as a raw material for a heat-shrinkable film tend to be good. When the two vinyl aromatic blocks have the same weight-average molecular weight (distinction cannot be made after dividing the blocks by decomposing the block copolymer block), 50% by mass (two blocks can be treated as having a mass ratio of 50/50).

The content of the copolymer block in the block copolymer is 38% by mass or more and 60% by mass or less, preferably 40% by mass or more and 55% by mass or less. When the copolymer block content is in this range, the balance between tensile elongation and the suppression of gel foreign matter (fish eyes) tends to be good, and the impact resistance when used as a raw material for heat-shrinkable films is high. likely to be good.

When the total mass of the vinyl aromatic monomer unit and the conjugated diene monomer unit in the block copolymer is 100% by mass, preferably the vinyl aromatic monomer unit in the block copolymer is 64 to 75% by mass, more preferably 68 to 72% by mass. When the ratio of the vinyl aromatic monomer unit in the block copolymer is within such a range, the balance between tensile elongation and suppression of gel foreign matter (fisheye) tends to be good, and heat-shrinkable film When used as a raw material, it tends to have good impact resistance and blocking resistance.

The weight average molecular weight of the block copolymer is preferably 100,000 or more and 200,000 or less. As a result, while physical properties such as tensile elongation are ensured, molding processability when molding a film or sheet tends to be good.

The block copolymer may be a mixture of two or more block copolymers satisfying the above requirements, and may contain other components as long as the effect of the present invention is not impaired. Other components are, for example, heat-deactivated products and coupling products generated during production of the block copolymer, additives, and the like.

1-2. First Vinyl Aromatic Block The first vinyl aromatic block is substantially composed only of vinyl aromatic monomer units. The phrase “substantially composed of only vinyl aromatic monomer units” means that, when the weight of the first vinyl aromatic block is 100% by mass, 98% by mass or more of the vinyl aromatic monomer unit is It is a monomeric unit, meaning that 2% by mass or less of unintended monomeric units may be present. Hereinafter, the expression "consisting substantially only of" has the same meaning. When the weight of the first vinyl aromatic block is 100% by mass, more preferably 99% by mass or more of the first vinyl aromatic block is a vinyl aromatic monomer unit, and more preferably 100% by mass is vinyl aromatic monomer units.

A vinyl aromatic monomer unit is a unit derived from a vinyl aromatic monomer used for polymerization. A vinyl aromatic monomer is a monomer having a vinyl group bonded to an aromatic ring. Vinyl aromatic monomers include, for example, styrene, o-methylstyrene, p-methylstyrene, p-tert-butylstyrene, 2,4-dimethylstyrene, 2,5-dimethylstyrene, α-methylstyrene, vinyl Examples include vinyl aromatic hydrocarbon monomers such as naphthalene and vinylanthracene. In one aspect, the vinyl aromatic monomer is preferably styrene. These monomers may be used alone or in combination of two or more.

The weight average molecular weight of the first vinyl aromatic block is preferably 30,000 or more and 100,000 or less, more preferably 35,000 or more and 70,000 or less. Also, the weight average molecular weight of the first vinyl aromatic block is greater than or equal to that of the second vinyl aromatic block. As a result, transparency tends to be good when used as a raw material for heat-shrinkable films and sheets.

1-3. Second Vinyl Aromatic Block The second vinyl aromatic block is substantially composed only of vinyl aromatic monomer units. When the weight of the second vinyl aromatic block is 100% by mass, more preferably 99% by mass or more of the second vinyl aromatic block is a vinyl aromatic monomer unit, and more preferably 100% by mass is vinyl aromatic monomer units. The vinyl aromatic monomer unit is the same as the first aromatic vinyl block. Also, the weight average molecular weight of the second vinyl aromatic block is less than or equal to that of the first vinyl aromatic block.

1-4. Copolymer Block The copolymer block is substantially composed only of vinyl aromatic monomer units and conjugated diene monomer units. When the weight of the copolymer block is 100% by mass, more preferably 99% by mass or more of the copolymer block is vinyl aromatic monomer units and conjugated diene monomer units, and more preferably 100% by mass is vinyl aromatic monomer units and conjugated diene monomer units.

The content of the conjugated diene-based monomer unit in the copolymer block is 55% by mass or more and 82% by mass or less when the total mass of the monomer units constituting the copolymer block is 100% by mass, It is preferably 60% by mass or more and 80% by mass or less. When the content of the conjugated diene-based monomer unit is in such a range, the balance between tensile elongation and gel foreign matter generation (fish eye) tends to be good, and when used as a raw material for heat-shrinkable film Good impact resistance and blocking resistance tend to be obtained.

The copolymer block has a tapered type in which the composition of vinyl aromatic monomer units and conjugated diene monomer units changes continuously, and a copolymer block in which the composition of vinyl aromatic monomer units and conjugated diene monomer units changes continuously. Although there is a random type in which the composition is almost constant, random copolymer blocks are preferred in the present invention. A random copolymer block is formed, for example, by continuously adding a vinyl aromatic monomer unit and a conjugated diene monomer unit in a constant weight ratio to a polymerization system. In the random copolymer block, the composition of the vinyl aromatic monomer unit and the conjugated diene monomer unit is almost constant, so there are no regions where the composition ratio of the conjugated diene monomer unit is locally high. Therefore, the generation of fish eyes can be suppressed more than the tapered type. In addition, since there is no region where the composition ratio of the conjugated diene-based monomer unit is locally low, the conjugated diene-based monomer unit can efficiently contribute to impact resistance and fracture resistance, and these physical properties are improved. Good balance.

A conjugated diene-based monomer unit is a unit derived from a conjugated diene-based monomer used for polymerization. A conjugated diene-based monomer is a monomer having a chemical structure represented by C=C--C=C. Conjugated diene monomers include, for example, 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 1,3 - conjugated diene monomers such as hexadiene. In one aspect, the conjugated diene-based monomer is preferably 1,3-butadiene. These monomers may be used alone or in combination of two or more.

The molecular weight of each block can be calculated based on the measurement of the weight average molecular weight of the block copolymer and the charged amount of each monomer. Alternatively, it may be calculated based on measurement of the weight average molecular weight of the block copolymer and measurement of the weight average molecular weight after decomposition of the block copolymer.

For decomposition of the block copolymer, for example, an ozonolysis method described in a known document (Y. TANAKA, et al., "RUBBER CHEMISTRY AND TECHNOLOGY", p16 (1985)) can be used. . The first vinyl aromatic block and the second vinyl aromatic block composed only of vinyl aromatic monomers are not decomposed, and after decomposition, the first vinyl aromatic block and the second vinyl aromatic block It becomes possible to measure the molecular weights respectively, and to calculate their contents. Then, the weight average molecular weight and content of the copolymer block are calculated by subtracting the weight average molecular weights of the first vinyl aromatic block and the second vinyl aromatic block from the weight average molecular weight of the block copolymer before decomposition. can do.

1-5. Composition The composition according to one embodiment of the present invention preferably further contains a polymer (resin) different from the block copolymer, in addition to the block copolymer. Examples of polymers different from the above block copolymers include styrene-butadiene block copolymers, polystyrene, and poly(styrene-methyl methacrylate) copolymers, which are different from the above block copolymers. The block copolymer of the present invention has an excellent balance of impact resistance, breakage resistance, and fisheye suppression when used as a raw material for heat-shrinkable films and sheets. By forming a composition with a styrene-butadiene block copolymer having excellent stiffness and polystyrene having excellent rigidity, it is possible to obtain a heat-shrinkable film or sheet having a better balance of physical properties.

The content of the block copolymer in the composition is preferably 15% by mass or more and 85% by mass or less, more preferably 30% by mass or more and 70% by mass or less. Although the content of the polymer different from the block copolymer in the composition is not particularly limited, it is, for example, 15% by mass or more and 85% by mass or less, preferably 30% by mass or more and 70% by mass or less.

1-6. Physical properties of block copolymer and composition According to ISO6721-1, loss when dynamic viscoelasticity measurement of block copolymer is performed under conditions of temperature increase rate of 4 ° C./min, frequency of 1 Hz, and strain of 0.02% The tangent value (tan δ) has at least one peak in the range of -70 to -35°C. When the copolymer block is a random copolymer block and the content of the conjugated diene-based monomer unit in the copolymer block is within the above range, tan δ tends to be within the above range, resulting in impact resistance and breaking resistance. , the blocking resistance is well balanced, and the occurrence of fish eyes is easily suppressed. It is also preferred that the composition containing the block copolymer also has at least one peak in the same range.

1-7. Production method

The block copolymer according to one embodiment of the present invention can be synthesized by various methods, and can be obtained by a living anionic polymerization reaction using an organic lithium compound as a polymerization initiator in an organic solvent.

Examples of organic solvents include aliphatic hydrocarbons such as butane, pentane, hexane, isopentane, heptane, octane, and isooctane; alicyclic hydrocarbons such as cyclopentane, methylcyclopentane, cyclohexane, methylcyclohexane, and ethylcyclohexane; Aromatic hydrocarbons such as benzene, toluene, ethylbenzene, and xylene are included. The use of cyclohexane is particularly preferred.

Organolithium compounds are compounds with one or more lithium atoms bound in the molecule. Examples of organic lithium compounds include monofunctional organic lithium compounds such as ethyllithium, n-propyllithium, isopropyllithium, n-butyllithium, sec-butyllithium and tert-butyllithium, hexamethylenedilithium, butadienyl Polyfunctional organic lithium compounds such as dilithium and isoprenyldilithium can be used. The use of n-butyllithium is particularly preferred.

In living anionic polymerization, a block copolymer having an arbitrary primary structure can be obtained by changing the addition amount and addition method of monomers (vinyl aromatic monomer and conjugated diene monomer). For example, only a vinyl aromatic monomer is added, and after the vinyl aromatic monomer is completely consumed, a vinyl aromatic monomer and a conjugated diene monomer are simultaneously added at a predetermined rate. However, after these are completely consumed, only the vinyl aromatic monomer is added again and polymerized.

It is possible to control the physical properties of the block copolymer by changing the amount and method of addition. For example, the molecular weight can be controlled by the ratio of the organolithium compound and the monomer, and the storage elastic modulus and loss tangent (tan δ) can be controlled by the ratio of the vinyl aromatic monomer unit and the conjugated diene monomer unit in each block chain. can.

The block copolymer thus obtained is deactivated by adding a polymerization terminating agent such as water, alcohol or carbon dioxide in an amount sufficient to deactivate the active ends. Methods for recovering the copolymer from the resulting block copolymer solution include (A) a method of precipitating with a poor solvent such as methanol; method), (C) a method of concentrating the solution with a concentrator and then removing the solvent with a vented extruder (devolatilization extrusion method), (D) dispersing the solution in water and blowing steam to remove the solvent by heating. Any method such as a method of recovering the copolymer (steam stripping method) can be employed. A devolatilizing extrusion method is particularly preferred.

A composition according to an embodiment of the present invention is obtained by mixing the block copolymer obtained by the above production method or the like with other block copolymers, polymers, or additives as necessary. be done.

Other additives include, for example, various stabilizers, lubricants, processing aids, antiblocking agents, antistatic agents, antifog agents, light resistance improvers, softeners, plasticizers, pigments and the like. Each additive may be added to the block copolymer solution, or may be blended with the recovered copolymer and melt-mixed.

Stabilizers include, for example, 2-tert-butyl-6-(3-tert-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenylacrylate, 2-[1-(2-hydroxy-3, 5-di-tert-pentylphenyl)ethyl]-4,6-di-tert-pentylphenyl acrylate, octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate and 2,6- Phenolic antioxidants such as di-tert-butyl-4-methylphenol, phosphorus antioxidants such as trisnonylphenyl phosphite, and the like. Examples of antiblocking agents, antistatic agents, and lubricants include fatty acid amides, ethylenebisstearic acid amides, sorbitan monostearate, saturated fatty acid esters of fatty alcohols, and pentaerythritol fatty acid esters. These additives are preferably used in an amount of 5 mass % or less based on the block copolymer.

The composition according to one embodiment of the present invention may contain a plurality of types of polymers such as the above block copolymer and other polymers, and as a method for mixing these polymers, a known method is employed. be able to. For example, they may be dry-blended using a Henschel mixer, a ribbon blender, a super mixer, a V-blender, or the like, or may be melted and pelletized using an extruder. In one aspect, melt mixing is preferred. A method of removing the solvent after mixing the polymer solutions can also be used.

2. Heat Shrinkable Film/Sheet/Molded Article of Sheet The heat shrinkable film or sheet according to one embodiment of the present invention comprises a layer composed of the above composition.

Sheets ("sheets" can also be referred to as "films", but hereinafter referred to as "sheets" to distinguish them from "heat-shrinkable films") can be produced using the above composition by known methods such as the T-die method, It can be obtained by extrusion by a tubular method.

A heat-shrinkable film can be obtained by uniaxially, biaxially or multiaxially stretching an extruded sheet. In particular, a method of extruding with a T-die method and biaxially stretching is preferred.

The heat-shrinkable film or sheet according to one embodiment of the present invention may have a structure including only a layer composed of the above composition, but by laminating another resin layer on at least one surface thereof, It can be a heat-shrinkable film or sheet with a multilayer structure. In order to make the heat-shrinkable film into a multilayer structure, another resin layer may be laminated on the layer composed of the composition after stretching, and the unstretched film obtained by forming the composition may be Another resin layer may be laminated and stretched, or a multilayer film obtained by laminating the above composition and another resin by multilayer extrusion molding may be stretched. A styrene-based resin is preferable as the resin used for the other resin layer.

Examples of uniaxial stretching include a method of stretching an extruded sheet with a tenter in a direction perpendicular to the extrusion direction (TD), a method of stretching an extruded tubular film in the circumferential direction, and the like.

Examples of biaxial stretching include a method of stretching an extruded sheet in the direction of extrusion (MD) with rolls and then stretching in a direction perpendicular to the direction of extrusion (TD) with a tenter or the like, and an extruded tubular sheet. are stretched simultaneously or separately in the extrusion direction and the circumferential direction.

The stretching temperature is preferably 60 to 120° C., for example. When the temperature is 60° C. or higher, the sheet is less likely to be broken during stretching, and when the temperature is 120° C. or lower, the heat shrinkage rate and thickness accuracy of the obtained film tend to be good. The draw ratio is not particularly limited, but is preferably 1.5 to 8 times. When it is 1.5 times or more, the heat shrinkability tends to be good, and when it is 8 times or less, the sheet is less likely to break during stretching. When the heat-shrinkable film is used as a heat-shrinkable label or packaging material, the heat-shrinkage ratio at 80°C is preferably 20% or more. If it is less than 20%, a high temperature is required during shrinkage, which adversely affects the article to be coated. The thickness of the film is preferably 10-300 μm.

A heat-shrinkable film can be used as a heat-shrinkable label, a heat-shrinkable cap seal, and the like. In addition, it can be used as a packaging film or the like. By using such a heat-shrinkable film as a label, a label-attached container such as a PET bottle can be obtained.

A molded article according to one embodiment of the present invention is a molded article obtained by molding a sheet into an arbitrary shape.

The present invention will be described in more detail with reference to the following examples. Moreover, these are all examples, and do not limit the content of the present invention.

[Production of block copolymer]
By the following operations, block copolymers P1 to P8 were produced as Examples 1 to 4 and Comparative Examples 1 to 4 (Table 1).

<Polymerization of block copolymer P1>
(1) 500.0 kg of cyclohexane and 75.0 g of tetrahydrofuran (THF) were placed in a reactor.
(2) 2000 mL of a 10% by mass cyclohexane solution of n-butyllithium was added as a polymerization initiator solution to the solution, and the temperature was maintained at 30°C.
(3) 20 kg of styrene was added to anionically polymerize styrene. The internal temperature rose to 42°C.
(4) After the styrene was completely consumed, the internal temperature of the reaction system was raised to 80°C, and while maintaining the internal temperature, a total of 40 kg of styrene and a total of 60 kg of 1,3-butadiene were added at 40 kg/h each. , were added simultaneously at a constant addition rate of 60 kg/h.
(5) After styrene and 1,3-butadiene were completely consumed, the internal temperature of the reaction system was lowered to 55° C., and 80 kg of styrene was added all at once to anionically polymerize the styrene. The internal temperature rose to 93°C.
(6) Finally, all polymerization active terminals were deactivated with water to obtain a polymerization liquid containing a block copolymer having polystyrene blocks and random blocks of styrene and butadiene.
(7) This polymerization liquid was devolatilized and melted and pelletized by an extruder to obtain a block copolymer P1.

<Polymerization of block copolymer P2>
(1) 500.0 kg of cyclohexane and 75.0 g of tetrahydrofuran (THF) were placed in a reactor.
(2) 2000 mL of a 10% by mass cyclohexane solution of n-butyllithium was added as a polymerization initiator solution to the solution, and the temperature was maintained at 30°C.
(3) 25.6 kg of styrene was added to anionically polymerize the styrene. The internal temperature rose to 45°C.
(4) After the styrene is completely consumed, the internal temperature of the reaction system is raised to 80°C, and while maintaining the internal temperature, a total of 34.4 kg of styrene and a total of 60 kg of 1,3-butadiene are added to each 34 4 kg/h and 60 kg/h were added simultaneously at constant addition rates.
(5) After styrene and 1,3-butadiene were completely consumed, the internal temperature of the reaction system was lowered to 55° C., and 80 kg of styrene was added all at once to anionically polymerize the styrene. The internal temperature rose to 93°C.
(6) Finally, all polymerization active terminals were deactivated with water to obtain a polymerization liquid containing a block copolymer having polystyrene blocks and random blocks of styrene and butadiene.
(7) This polymerization solution was devolatilized and melted and pelletized with an extruder to obtain a block copolymer P2.

<Polymerization of block copolymer P3>
(1) 500.0 kg of cyclohexane and 75.0 g of tetrahydrofuran (THF) were placed in a reactor.
(2) 2000 mL of a 10% by mass cyclohexane solution of n-butyllithium was added as a polymerization initiator solution to the solution, and the temperature was maintained at 30°C.
(3) 50 kg of styrene was added to anionically polymerize the styrene. The internal temperature rose to 49°C.
(4) After the styrene was completely consumed, the internal temperature of the reaction system was raised to 80°C, and while maintaining the internal temperature, a total of 40 kg of styrene and a total of 60 kg of 1,3-butadiene were added at 40 kg/h each. , were added simultaneously at a constant addition rate of 60 kg/h.
(5) After styrene and 1,3-butadiene were completely consumed, the internal temperature of the reaction system was lowered to 60° C., and 50 kg of styrene was added all at once to anionically polymerize styrene. The internal temperature rose to 81°C.
(6) Finally, all polymerization active terminals were deactivated with water to obtain a polymerization liquid containing a block copolymer having polystyrene blocks and random blocks of styrene and butadiene.
(7) This polymerization solution was devolatilized and melted and pelletized by an extruder to obtain a block copolymer P3.

<Polymerization of block copolymer P4>
(1) 500.0 kg of cyclohexane and 75.0 g of tetrahydrofuran (THF) were placed in a reactor.
(2) 2000 mL of a 10% by mass cyclohexane solution of n-butyllithium was added as a polymerization initiator solution to the solution, and the temperature was maintained at 30°C.
(3) 60 kg of styrene was added to anionically polymerize the styrene. The internal temperature rose to 56°C.
(4) After styrene was completely consumed, the internal temperature of the reaction system was raised to 80°C, and while maintaining the internal temperature, a total of 16 kg of styrene and a total of 64 kg of 1,3-butadiene were added at 16 kg/h each. , were added simultaneously at a constant addition rate of 64 kg/h.
(5) After styrene and 1,3-butadiene were completely consumed, the internal temperature of the reaction system was lowered to 60° C., and 60 kg of styrene was added all at once to anionically polymerize styrene. The internal temperature rose to 81°C.
(6) Finally, all polymerization active terminals were deactivated with water to obtain a polymerization liquid containing a block copolymer having polystyrene blocks and random blocks of styrene and butadiene.
(7) This polymerization solution was devolatilized and melted and pelletized with an extruder to obtain a block copolymer P4.

<Polymerization of block copolymer P5>
(1) 500.0 kg of cyclohexane and 75.0 g of tetrahydrofuran (THF) were placed in a reactor.
(2) 2000 mL of a 10% by mass cyclohexane solution of n-butyllithium was added as a polymerization initiator solution to the solution, and the temperature was maintained at 30°C.
(3) 4 kg of styrene was added to anionically polymerize the styrene. The internal temperature rose to 35°C.
(4) After the styrene was completely consumed, the internal temperature of the reaction system was raised to 80°C, and while maintaining the internal temperature, a total of 51 kg of styrene and a total of 7 kg of 1,3-butadiene were added at 153 kg/h each. , were added simultaneously at a constant addition rate of 21 kg/h.
(5) After styrene and 1,3-butadiene are completely consumed, the internal temperature of the reaction system is lowered to 60° C., 46 kg of 1,3-butadiene is added all at once, and 1,3-butadiene is anionically polymerized. rice field. The internal temperature rose to 94°C.
(6) After 1,3-butadiene was completely consumed, the internal temperature of the reaction system was lowered to 65° C., and 34 kg of styrene was added all at once to anionically polymerize styrene. The internal temperature rose to 79°C.
(7) Finally, all polymerization active terminals were deactivated with water to obtain a polymerization solution containing block copolymers having polystyrene blocks, polybutadiene blocks, and random blocks of styrene and butadiene.
(8) This polymerization solution was devolatilized and melted and pelletized with an extruder to obtain a block copolymer P5.

<Polymerization of block copolymer P6>
(1) 500.0 kg of cyclohexane and 75.0 g of tetrahydrofuran (THF) were placed in a reactor.
(2) 2000 mL of a 10% by mass cyclohexane solution of n-butyllithium was added as a polymerization initiator solution to the solution, and the temperature was maintained at 30°C.
(3) 74 kg of styrene was added to anionically polymerize the styrene. The internal temperature rose to 66°C.
(4) After styrene was completely consumed, the internal temperature of the reaction system was lowered to 45° C., and 100 kg of 1,3-butadiene was added all at once to anionically polymerize 1,3-butadiene. The internal temperature rose to 112°C.
(5) After 1,3-butadiene was completely consumed, the internal temperature of the reaction system was lowered to 70° C., and 26 kg of styrene was added all at once to anionically polymerize the styrene. The internal temperature rose to 78°C.
(6) Finally, all polymerization active terminals were deactivated with water to obtain a polymerization solution containing a block copolymer having polystyrene blocks and polybutadiene blocks.
(7) This polymerization solution was devolatilized and melted and pelletized with an extruder to obtain a block copolymer P6.

<Polymerization of block copolymer P7>
(1) 500.0 kg of cyclohexane and 75.0 g of tetrahydrofuran (THF) were placed in a reactor.
(2) 2000 mL of a 10% by mass cyclohexane solution of n-butyllithium was added as a polymerization initiator solution to the solution, and the temperature was maintained at 30°C.
(3) 65 kg of styrene was added to anionically polymerize the styrene. The internal temperature rose to 54°C.
(4) After styrene was completely consumed, the internal temperature of the reaction system was raised to 80°C, and while maintaining the internal temperature, a total of 22 kg of styrene and a total of 48 kg of 1,3-butadiene were added at 22 kg/h each. , were added simultaneously at a constant addition rate of 48 kg/h.
(5) After styrene and 1,3-butadiene were completely consumed, the internal temperature of the reaction system was lowered to 60° C., and 65 kg of styrene was added all at once to anionically polymerize styrene. The internal temperature rose to 86°C.
(6) Finally, all polymerization active terminals were deactivated with water to obtain a polymerization liquid containing a block copolymer having polystyrene blocks and random blocks of styrene and butadiene.
(7) Block copolymer 7 was obtained by devolatilizing this polymerization liquid and melting and pelletizing it with an extruder.

<Polymerization of block copolymer P8>
(1) 500.0 kg of cyclohexane and 75.0 g of tetrahydrofuran (THF) were placed in a reactor.
(2) 2000 mL of a 10% by mass cyclohexane solution of n-butyllithium was added as a polymerization initiator solution to the solution, and the temperature was maintained at 30°C.
(3) 10 kg of styrene was added to anionically polymerize the styrene. The internal temperature rose to 36°C.
(4) After styrene was completely consumed, the internal temperature of the reaction system was raised to 80°C, and while maintaining the internal temperature, a total of 16 kg of styrene and a total of 64 kg of 1,3-butadiene were added at 16 kg/h each. , were added simultaneously at a constant addition rate of 64 kg/h.
(5) After styrene and 1,3-butadiene were completely consumed, the internal temperature of the reaction system was lowered to 50° C., and 110 kg of styrene was added all at once to anionically polymerize styrene. The internal temperature rose to 103°C.
(6) Finally, all polymerization active terminals were deactivated with water to obtain a polymerization liquid containing a block copolymer having polystyrene blocks and random blocks of styrene and butadiene.
(7) This polymerization liquid was devolatilized and melted and pelletized by an extruder to obtain a block copolymer P8.

[Analysis of block copolymer]
<Content ratio of vinyl aromatic monomer unit/conjugated diene monomer unit>
The contents of vinyl aromatic monomer units (styrene) and conjugated diene monomer units (butadiene) in the block copolymer were measured and calculated by the following halogen addition method.
(A1) After dissolving the sample in a solvent (such as carbon tetrachloride) that can completely dissolve the sample, an excess amount of iodine monochloride/carbon tetrachloride solution is added and allowed to react sufficiently, and unreacted monochloride Iodine was titrated with a sodium thiosulfate/ethanol solution to calculate the amount of double bonds.
(A2) Based on the amount of double bonds obtained by the method of (A1), the content of butadiene (rubber content) was calculated.
The styrene content was calculated by subtracting the butadiene content from the total sample.

<Weight average molecular weight and content of each block>
The weight average molecular weight of each block is determined by the following formula ( 1) to (3). Also, the content of each block was determined by the following formulas (B4) to (B6).
(B1) (weight average molecular weight of first vinyl aromatic block) = M x W1/(W1 + W2 + W3)
(B2) (weight average molecular weight of second vinyl aromatic block) = M x W2/(W1 + W2 + W3)
(B3) (weight average molecular weight of copolymer block) = M x W3/(W1 + W2 + W3)
(B4) (content of first vinyl aromatic block) = W1/(W1+W2+W3) x 100 [%]
(B5) (Content of second vinyl aromatic block) = W2/(W1+W2+W3) x 100 [%]
(B6) (content rate of copolymer block) = W3/(W1 + W2 + W3) x 100 [%]
(W1: Weight of charged monomer for first vinyl aromatic block [kg], W2: Weight of charged monomer for second vinyl aromatic block [kg], W3: Weight of charged monomer for copolymer block [kg])

Further, the weight-average molecular weights of the first vinyl aromatic block and the second vinyl aromatic block are obtained from a known document (Y. TANAKA, et al., "RUBBER CHEMISTRY AND TECHNOLOGY", p. 16 ( 1985)), after decomposing the conjugated diene-based monomer units by the ozonolysis method described in, GPC measurement can be performed. In that case, the weight average molecular weight of the copolymer block is obtained by subtracting the weight average molecular weight of the first vinyl aromatic block and the second vinyl aromatic block from the weight average molecular weight of the block copolymer before decomposition measured by GPC measurement. Calculated by subtracting
<GPC measurement>
The molecular weight of the block copolymer was measured using the following GPC measuring apparatus and conditions, and was calculated as a polystyrene-equivalent molecular weight based on a calibration curve using standard polystyrene.
Device name: HLC-8220GPC (manufactured by Tosoh Corporation)
Column: 4 ShodexGPCKF-404 (manufactured by Showa Denko) connected in series Temperature: 40°C
Detection: Differential refractive index Solvent: Tetrahydrofuran Concentration: 2% by mass
Calibration curve: prepared using standard polystyrene (manufactured by VARIAN).

<Ratio of conjugated diene-based monomer unit in copolymer block>
The ratio of the conjugated diene-based monomer unit (butadiene) in the copolymer block is the "content of the copolymer block" obtained by the above formula (B6), and the "conjugated diene-based monomer (B7) (Ratio of conjugated diene-based monomer unit in copolymer block) = (Conjugated diene-based monomer unit content)/ (Content rate of copolymer block) x 100 [%]

<Ratio of first vinyl aromatic block: S1/(S1+S2)>
The ratio of the first vinyl aromatic block (S1) and the second The ratio “S1/(S1+S2)” of the 2-vinyl aromatic block (S2) is the “content of the first vinyl aromatic block” in the above formula (B4) and the “second vinyl aromatic block” in the above formula (B5). Each was calculated using the "content rate of family system block".
Ratio of first vinyl aromatic block = mass of first vinyl aromatic block/(mass of first vinyl aromatic block + mass of second vinyl aromatic block) x 100 [% by mass]

<Measurement of loss tangent value>
The loss tangent value (tan δ) of the block copolymer was measured by the dynamic viscoelasticity measurement method described below.
(1) Using pellets of the block copolymer, a molded product with a thickness of 4 mm and a width of 10 mm was produced by injection molding, and a test piece of an appropriate size was cut from this molded product and It was then stored for 48 hours and subjected to curing treatment.
(2) Using a dynamic viscoelasticity measuring device RSA III manufactured by TA Instruments, in accordance with ISO 6721-1, a heating rate of 4 ° C./min, a measurement frequency of 1 Hz, a strain of 0.02%, and a fixed three-point bending mode- The storage modulus (E′) and loss modulus (E″) were measured in the temperature range of 120 to 120° C., and tan δ in the above temperature range was calculated by the following formula.
tan δ=E″/E′

<Tensile elongation>
In accordance with JIS K 7161, a dumbbell-shaped molded piece injection-molded using pellets was used to measure the nominal strain at tensile break at a tensile speed of 50 mm / min using Shimadzu Autograph AG-Xplus. Elongation value.

<Fisheye level>
The occurrence of gel contaminants in the block copolymer was evaluated as the fisheye level. The fish-eye level was measured by using a sheet extruder equipped with a T-die to prepare a non-stretched sheet with a thickness of about 50 μm from pellets of each block copolymer, and foreign matter of 0.2 mm or more in 3.3 m ² was evaluated by measuring the score of using an image recognition device. When the number of foreign matter was 300 or more, it was judged as "fail"; Table 1 shows the evaluation results of each example and comparative example. In Comparative Example 2, although a non-stretched sheet was produced, the molding operation was difficult, and there was a problem in moldability.

[Preparation of heat-shrinkable film]
For the production of the heat-shrinkable film, 50% by mass of the block copolymer P1 to P8 pellets are dry blended with 50% by mass of the resin composition (DP) described in Example 4 of Japanese Patent No. 6000939. A composition melt-kneaded at 200° C. using a screw extruder was used. As Comparative Example 9, a heat-shrinkable film was also produced using only DP pellets.

A biaxial stretching apparatus by a T-die method was used for producing heat-shrinkable films for various measurements and evaluations. Pellets of the block copolymer composition were extruded into a sheet having a thickness of about 0.3 mm at a temperature of 210°C using a sheet extruder equipped with a T-die, and a line speed of 10 m/min was applied to 85 sheets using a longitudinal stretching machine. °C in the machine direction (MD) and then by a transverse stretching machine at 95 °C in the direction perpendicular to the machine direction (TD) by 4.5 times, resulting in an average thickness of about 50 µm. Heat-shrinkable films were prepared as Examples 5-8 and Comparative Examples 5-9. In Comparative Example 2, an attempt was made to form a film using pellets of the block copolymer P6, but the film could not be formed.

The heat-shrinkable films produced were analyzed and evaluated below.
<Measurement of heat shrinkage>
The heat shrinkage rate of the film was measured by the following method.
(1) A test piece having an MD width of 100 mm and a TD width of 100 mm was cut out from a heat-shrinkable film.
(2) This test piece was completely immersed in warm water of 80° C. or 100° C. for 10 seconds, then taken out, thoroughly wiped off, and the length L (mm) of TD was measured.
(3) The thermal shrinkage rate was calculated by the following formula.
Thermal shrinkage rate (%) = {(100-L) / 100} x 100

<Measurement of tensile elongation>
The tensile elongation of the film was measured by the following method.
(1) A strip-shaped sample piece having an MD width of 200 mm and a TD width of 10 mm was cut out from a heat-shrinkable film.
(2) Using a Tensilon universal material testing machine manufactured by Orientec Co., Ltd., the cut sample piece was subjected to MD tension at a measurement temperature of 23° C. and a tensile speed of 200 mm/min to measure the tensile elongation.

<Measurement of natural shrinkage>
The natural shrinkage rate of the heat-shrinkable film was measured by the following method.
(1) A sample piece having an MD width of 100 mm and a TD width of 350 mm was cut out from a heat-shrinkable film.
(2) Marked lines were placed in the center of the test piece so that the TD marked line interval was 300 mm, stored in an environmental tester at 40 ° C., and the marked line interval N (mm) after storage for 7 days was measured. .
(3) Natural shrinkage was measured by the following formula.
Natural shrinkage rate (%) = {(300-N) / 300} x 100

<Measurement of Impact Strength>
The impact strength of the heat-shrinkable film was measured according to ASTM D3420 using an impact tester (manufactured by Tester Sangyo Co., Ltd.) using an R25 tip.

<Fisheye level>
The fish-eye level of the heat-shrinkable film was obtained by cutting out 22 films of 50 cm in the MD direction and 30 cm in the TD direction from the stretched film, and visually checking the number of fish-eyes with a major axis of 0.2 mm or more using a loupe with a scale. It was measured. 300 or more fish eyes per 3.3 m ² were evaluated as "fail", 50 or more and less than 300 as "acceptable", and less than 50 as "good".

Claims (10)

A block copolymer having a first vinyl aromatic block (S1), a second vinyl aromatic block (S2), and a copolymer block (B/S),
The first vinyl aromatic block (S1) is
substantially composed only of vinyl aromatic monomer units,
The second vinyl aromatic block (S2) is
substantially composed only of vinyl aromatic monomer units,
weight-average molecular weight is equal to or less than the first vinyl aromatic block;
The copolymer block (B/S) is
substantially composed only of vinyl aromatic monomer units and conjugated diene monomer units,
The content of the conjugated diene-based monomer unit in the copolymer block is 55% by mass or more and 82% by mass or less,
When the total mass of the first vinyl aromatic block and the second vinyl aromatic block is 100% by mass, the ratio of the first vinyl aromatic block is 50% by mass or more and 85% by mass or less. and
The content of the copolymer block in the block copolymer is 38% by mass or more and 60% by mass or less,
According to ISO6721-1, the loss tangent value (tan δ) when performing dynamic viscoelasticity measurement under the conditions of a temperature increase rate of 4 ° C./min, a frequency of 1 Hz, and a strain of 0.02% is -70 ° C. or higher and -35 ° C. or lower. A block copolymer having at least one peak in the range of . 2. The block copolymer according to claim 1, wherein the first vinyl aromatic block (S1) has a weight average molecular weight of 30,000 or more and 100,000 or less. When the total mass of the vinyl aromatic monomer unit and the conjugated diene monomer unit in the block copolymer is 100% by mass, the vinyl aromatic monomer unit in the block copolymer The block copolymer according to claim 1 or 2, wherein the ratio of is 64% by mass or more and 75% by mass or less. 4. The copolymer block (B/S) according to any one of claims 1 to 3, wherein the copolymer block (B/S) is a random copolymer block of vinyl aromatic monomer units and conjugated diene monomer units. block copolymer. Any one of claims 1 to 4, which is linear and the arrangement of polymer blocks is (S1)-(B/S)-(S2) or (S2)-(B/S)-(S1). or the block copolymer according to item 1. A composition comprising the block copolymer according to any one of claims 1 to 5 and further comprising a polymer different from the block copolymer. 7. The composition according to claim 6, wherein the content of the block copolymer is 15% by mass or more and 85% by mass or less. A heat-shrinkable film comprising a layer composed of the composition according to claim 6 or 7. A sheet comprising a layer composed of the composition according to claim 6 or 7. A molded article obtained by molding the sheet according to claim 9 .