Block copolymer composition, resin composition containing block copolymer composition, heat-shrinkable film

Abstract

To provide a block copolymer composition that makes it possible to obtain a heat-shrinkable film that can be separated by specific gravity using water even if the heat-shrinkable film is not foamed when obtaining a heat-shrinkable film from a resin composition containing the block copolymer composition.SOLUTION: Provided is a block copolymer composition containing one or more block copolymers that include a vinyl aromatic monomer unit and a conjugated diene monomer unit. When the total mass of the vinyl aromatic monomer units and the conjugated diene monomer units is taken to be 100 mass%, the block copolymer composition contains the vinyl aromatic monomer units in an amount from 52 mass% to 69 mass% inclusive. The block copolymer composition has a flexural modulus measured according to ISO 178 of 1000 MPa or more, and the block copolymer composition has at least one peak in the loss tangent (tan δ) range from 80°C to 110°C inclusive when dynamic viscoelasticity measurement is performed by a fixed three-point bending mode at a heating rate of 4°C / min, a frequency of 1 Hz, and a bend of 0.02% according to ISO 6721-1.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a block copolymer composition, a resin composition containing the block copolymer composition, and a heat-shrinkable film including a layer composed of the resin composition. [Background technology]

[0002] Heat-shrinkable films made from block copolymers obtained by polymerizing vinyl aromatic compounds and conjugated diene compounds have excellent heat shrinkability and finish after shrinkage, and can be adapted to various shapes and attachment methods of packaged items. As a result, they are widely used for shrink-wrapping, such as labels for PET bottled beverages.

[0003] In recent years, environmental issues caused by disposable plastics, such as microplastics, marine litter, and global warming due to the use of petroleum-derived materials, have become a major concern, and there is a demand for reducing the environmental impact in the shrink packaging field as well. For example, many PET bottles used for beverages and other products are collected and recycled, but if labels are mixed in with the collected PET bottles, the range of usable uses is limited and the recycling rate drops. Therefore, by using labels that can be easily separated from the PET bottle, the recycling rate of PET bottles can be improved, the amount of petroleum-derived materials used can be reduced, and environmental impact can be expected to be reduced.

[0004] Among methods for separating different materials, gravity separation, which utilizes the difference in specific gravity between the material and water, is known as a method with particularly good separation accuracy. Block copolymers, which are used in general heat-shrinkable films and are obtained by polymerizing vinyl aromatic compounds and conjugated diene compounds, have a higher specific gravity than water, just like PET bottles, making it difficult to separate the two using gravity separation. Patent Document 1 discloses a method in which the heat-shrinkable film is made into a foamed film, thereby lowering its specific gravity compared to water, thereby enabling PET bottles to be easily separated using gravity separation. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2005 / 005527 Summary of the Invention [Problem to be solved by the invention]

[0006] However, since foamed films have bubbles inside the film, they may have poor surface smoothness and transparency, which can cause problems with printing properties and appearance when used as labels.

[0007] An object of the present invention is to provide a block copolymer composition from which a heat-shrinkable film can be obtained that is capable of being gravity separated with water, even if the heat-shrinkable film is non-foamed, when the heat-shrinkable film is obtained from a resin composition containing the block copolymer composition. [Means for solving the problem]

[0008] As a result of intensive research by the present inventors, it has been found that the present invention provides a block copolymer composition containing one or more block copolymers containing vinyl aromatic monomer units and conjugated diene monomer units, wherein the block copolymer composition contains the vinyl aromatic monomer units in an amount of 52% by mass or more and 69% by mass or less when the total mass of the vinyl aromatic monomer units and the conjugated diene monomer units is taken as 100% by mass, the block copolymer composition has a flexural modulus of elasticity of 1000 MPa or more as measured in accordance with ISO 178, and a flexural modulus of elasticity of 1000 MPa or more as measured in accordance with ISO 6721-1. The present inventors have found that by using a block copolymer composition having a loss tangent (tan δ) that exhibits at least one peak in the range of 80°C or higher and 110°C or lower when dynamic viscoelasticity is measured in a fixed three-point bending mode under conditions of a heating rate of 4°C / min, a frequency of 1 Hz, and a strain of 0.02%, it is possible to obtain a block copolymer composition from which a heat-shrinkable film that can be gravity-separated with water can be obtained, even if the heat-shrinkable film is not foamed, can be obtained, and have completed the present invention.

[0009] That is, the present invention provides the following: [1] A block copolymer composition containing one or more block copolymers containing vinyl aromatic monomer units and conjugated diene monomer units, the block copolymer composition contains the vinyl aromatic monomer units in an amount of 52% by mass or more and 69% by mass or less, when the total mass of the vinyl aromatic monomer units and the conjugated diene monomer units is taken as 100% by mass; the block copolymer composition has a flexural modulus of 1000 MPa or more as measured in accordance with ISO 178; The block copolymer composition has at least one peak in loss tangent (tanδ) in the range of 80°C or higher and 110°C or lower when dynamic viscoelasticity is measured in a fixed three-point bending mode under conditions of a heating rate of 4°C / min, a frequency of 1 Hz, and a strain of 0.02% in accordance with ISO 6721-1. Block copolymer compositions. [2] The block copolymer composition according to [1], wherein the specific gravity of the block copolymer composition measured at 23°C is 0.950 or more but less than 1.000. [3] At least one of the one or more block copolymers contained in the block copolymer composition has a structure represented by any one of the following formulas (i) to (iv): (i) (S1) n -(B) m (ii) (S1) n -(B) m -(S2) (iii) (S1) n -(B) m -X (iv) (S1) n -(B) m -(S2)-X [In the formula, each of (S1) and (S2) is a polymer block having a vinyl aromatic monomer unit content of 85% by mass or more and 100% by mass or less, (B) is a polymer block having a conjugated diene monomer unit content of 60% by mass or more and 100% by mass or less, X is a coupling center, and each of n and m is an integer of 1 or more] Each of the block copolymers having the structures represented by the formulas (i) to (iv) contains, in 100% by mass of the block copolymer, (S1)1 to (S1) n The total mass of the above components is 40% by mass or more and 70% by mass or less, Each of the block copolymers having the structures represented by the formulas (i) to (iv) contains, in 100% by mass of the block copolymer, (B)1 to (B) m The total mass of the above components is 30% by mass or more and 48% by mass or less, Each of the block copolymers having the structures represented by the formulas (i) to (iv) contains 0% by mass or more and 12% by mass or less of (S2) in terms of mass relative to 100% by mass of the block copolymer, The one or more block copolymers contain a block copolymer having a structure represented by any one of the formulas (i) to (iv) in a total of 100% by mass, in an amount of 60% by mass or more and 100% by mass or less in total mass. The block copolymer composition according to [1] or [2]. [4] (S1) is a homoblock composed of vinyl aromatic monomer units or a random copolymer block composed of vinyl aromatic monomer units and conjugated diene monomer units, (B) is a homoblock composed of conjugated diene monomer units, (S2) is a homoblock composed of vinyl aromatic monomer units; [3] The block copolymer composition according to [3]. [5] The block copolymer composition according to any one of [1] to [4], wherein the vinyl aromatic monomer unit is a styrene monomer unit, and the conjugated diene monomer unit is a butadiene monomer unit. [6] A resin composition containing the block copolymer composition according to any one of [1] to [5], The resin composition contains 80% by mass or more and 100% by mass or less of the block copolymer composition based on 100% by mass of the resin composition. Resin composition. [7] A heat-shrinkable film comprising a layer made of the resin composition according to [6]. [8] A label using the heat-shrinkable film described in [7]. [9] A container equipped with the heat-shrinkable film described in [7].

[10] A container with a label as described in [8]. Regarding. [Effects of the Invention]

[0010] A heat-shrinkable film obtained from a resin composition containing the block copolymer composition of the present invention can be gravity separated by water even if it is not foamed. DETAILED DESCRIPTION OF THE INVENTION

[0011] <Terminology> In the present specification, for example, the expression "A to B" means A or more and B or less.

[0012] The following describes in detail the embodiments of the present invention. The present invention is not limited to these, and various modifications are possible without departing from the spirit of the invention. The various features shown in the following embodiments can be combined with each other. Furthermore, each feature can be an invention independently. In this specification, a block copolymer containing vinyl aromatic monomer units and conjugated diene monomer units may be simply referred to as a "block copolymer." Also, other polymers that are not block copolymers containing vinyl aromatic monomer units and conjugated diene monomer units may be simply referred to as "other polymers."

[0013] <Block copolymer composition> A block copolymer composition according to one embodiment of the present invention contains one or more block copolymers containing vinyl aromatic monomer units and conjugated diene monomer units. In one embodiment, the polymer contained in the block copolymer composition is only a block copolymer containing vinyl aromatic monomer units and conjugated diene monomer units. The block copolymer composition may also contain various additives within a range that does not impair the effects of the present invention.

[0014] <Block copolymer containing vinyl aromatic monomer units and conjugated diene monomer units> A block copolymer containing vinyl aromatic monomer units and conjugated diene monomer units according to one embodiment of the present invention is a block copolymer synthesized by block copolymerizing a vinyl aromatic monomer and a conjugated diene monomer, and has one or more block chains composed of vinyl aromatic monomer units and / or conjugated diene monomer units.

[0015] <Vinyl aromatic monomer unit> The vinyl aromatic monomer unit is a structural unit of the block copolymer derived from a vinyl aromatic monomer used in copolymerization of the block copolymer. Examples of the vinyl aromatic monomer include styrene monomers such as styrene, o-methylstyrene, p-methylstyrene, p-tert-butylstyrene, 2,4-dimethylstyrene, 2,5-dimethylstyrene, and α-methylstyrene, as well as vinylnaphthalene and vinylanthracene. In one embodiment, the vinyl aromatic monomer is preferably styrene. These monomers may be used alone or in combination of two or more.

[0016] <Conjugated diene monomer unit> The conjugated diene monomer unit is a structural unit of the block copolymer derived from a conjugated diene monomer used in copolymerization of the block copolymer. Examples of the conjugated diene monomer include butadiene monomers such as 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), and 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, and 1,3-hexadiene. In one embodiment, the conjugated diene monomer is preferably 1,3-butadiene or isoprene. These monomers may be used alone or in combination of two or more.

[0017] <Contents of vinyl aromatic monomer units and conjugated diene monomer units in block copolymers> The contents of the vinyl aromatic monomer units and the conjugated diene monomer units in the block copolymer according to one embodiment of the present invention are not particularly limited, but when the block copolymer is taken as 100% by mass, the vinyl aromatic monomer units are preferably 50 to 80% by mass and the conjugated diene monomer units are preferably 20 to 50% by mass, and more preferably 52 to 69% by mass and 31 to 48% by mass. The preferred content of the vinyl aromatic monomer unit in the block copolymer is, for example, 50, 55, 60, 65, 70, 75, or 80% by mass, where the block copolymer is taken as 100% by mass, and may be within a range between any two of the values ​​exemplified here. The content of the conjugated diene monomer units in the block copolymer is preferably 20, 25, 30, 35, 40, 45, or 50% by mass, for example, when the block copolymer is taken as 100% by mass, and may be within a range between any two of the values ​​exemplified here. When the content of the conjugated diene monomer units in the block copolymer is within the above range, the block copolymer is easily and uniformly miscible, and gel formation and a decrease in transparency are less likely to occur. When vinyl aromatic monomer units are used in combination, the content of vinyl aromatic monomer units means the total content of the vinyl aromatic monomer units used in combination. When conjugated diene monomer units are used in combination, the content of conjugated diene monomer units means the total content of the conjugated diene monomer units used in combination.

[0018] <Weight-average molecular weight of block copolymer containing vinyl aromatic monomer units and conjugated diene monomer units> The weight-average molecular weight of the block copolymer is preferably 40,000 to 500,000, more preferably 60,000 to 300,000, and even more preferably 70,000 to 200,000. A weight-average molecular weight of 40,000 or more provides sufficient rigidity and impact resistance for the block copolymer composition, while a weight-average molecular weight of 500,000 or less provides good processability for the block copolymer composition, which are preferred. The weight-average molecular weight of the block copolymer can be measured using a gel permeation chromatograph (hereinafter abbreviated as GPC).

[0019] <Structure of block copolymer containing vinyl aromatic monomer units and conjugated diene monomer units> At least one of the block copolymers containing one or more vinyl aromatic monomer units and conjugated diene monomer units contained in the block copolymer composition according to one embodiment of the present invention preferably has a structure represented by any one of the following formulas (i) to (iv): (i) (S1) n -(B) m (ii) (S1) n -(B) m -(S2) (iii) (S1) n -(B) m -X (iv) (S1) n -(B) m -(S2)-X [In the formula, each of (S1) and (S2) is a polymer block having a vinyl aromatic monomer unit content of 85% by mass or more and 100% by mass or less, (B) is a polymer block having a conjugated diene monomer unit content of 60% by mass or more and 100% by mass or less, X is a coupling center, and each of n and m is an integer of 1 or more] Here, each of the block copolymers having the structures represented by the formulas (i) to (iv) contains (S1)1 to (S1) n The block copolymers having the structures represented by the formulae (i) to (iv) each contain (B)1 to (B) m The total mass of (S2) is 30% by mass or more and 48% by mass or less. Each of the block copolymers having the structures represented by the formulae (i) to (iv) contains 0% by mass or more and 12% by mass or less of (S2) relative to 100% by mass of the block copolymer. By incorporating a block copolymer having a structure represented by any one of formulas (i) to (iv) into the block copolymer composition, the rigidity of a heat-shrinkable film obtained from a resin composition containing the block copolymer composition can be improved.

[0020] Each of the polymer blocks (S1) and (S2) is preferably a polymer block having a vinyl aromatic monomer unit content of 85% by mass or more and 100% by mass or less and a conjugated diene monomer unit content of 0% by mass or more and 15% by mass or less, and more preferably a polymer block having a vinyl aromatic monomer unit content of 90% by mass or more and 100% by mass or less and a conjugated diene monomer unit content of 0% by mass or more and 10% by mass or less.

[0021] The polymer block (B) is preferably a polymer block having a conjugated diene monomer unit content of 60% by mass or more and 100% by mass or less and a vinyl aromatic monomer unit content of 0% by mass or more and 40% by mass or less, and more preferably a polymer block having a conjugated diene monomer unit content of 70% by mass or more and 100% by mass or less and a vinyl aromatic monomer unit content of 0% by mass or more and 30% by mass or less.

[0022] Each of the block copolymers having the structures represented by formulas (i) to (iv) contains (S1)1 to (S1) n The total mass of these components is 40% by mass or more and 70% by mass or less, preferably 45% by mass or more and 66% by mass or less, and more preferably 45% by mass or more and 60% by mass or less.

[0023] Each of the block copolymers having the structures represented by formulas (i) to (iv) contains (B)1 to (B) m The total mass of these components is 30% by mass or more and 48% by mass or less, and preferably 32% by mass or more and 48% by mass or less.

[0024] Each of the block copolymers having the structures represented by formulas (i) to (iv) contains 0% by mass or more and 12% by mass or less of (S2) relative to 100% by mass of the block copolymer, and preferably 0% by mass or more and 10% by mass or less.

[0025] The block copolymer having the structure represented by formula (iii) or (iv) is (S1) n -(B) m Polymerization block of (S1) n -(B) mIt can be obtained by polymerizing the polymer block -(S2) and then coupling with a coupling agent. Examples of coupling agents include chlorosilane compounds such as dimethyldichlorosilane, silicon tetrachloride, 1,2-bis(methyldichlorosilyl)ethane, methyltrichlorosilane, and tetrachlorosilane; alkoxysilane compounds such as dimethyldimethoxysilane, tetramethoxysilane, tetraphenoxysilane, methyltrimethoxysilane, and tetraphenoxysilane; tin tetrachloride; polyhalogenated hydrocarbons; carboxylic acid esters; polyvinyl compounds; and epoxidized oils and fats such as epoxidized soybean oil and epoxidized linseed oil. Two or more coupling agents may also be used in combination. A particularly preferred polyfunctional coupling agent is epoxidized soybean oil.

[0026] <Content of Block Copolymer Having a Structure Represented by Any One of Formulas (i) to (iv)> Preferably, the total mass of the block copolymer having a structure represented by any one of the formulae (i) to (iv) is 60% by mass or more and 100% by mass or less, more preferably 70% by mass or more and 100% by mass or less, of 100% by mass of the block copolymer containing one or more vinyl aromatic monomer units and conjugated diene monomer units contained in the block copolymer composition according to one embodiment of the present invention. By including a block copolymer having a structure represented by any one of the formulae (i) to (iv) in an amount of 60% by mass or more and 100% by mass or less in total of 100% by mass of the block copolymers, the rigidity of the heat-shrinkable film obtained from the resin composition containing the block copolymer composition can be improved.

[0027] <Structure of (S1), (S2), and (B)> The polymer block (S1) is preferably a homoblock composed of vinyl aromatic monomer units or a random copolymer block composed of vinyl aromatic monomer units and conjugated diene monomer units, the polymer block (B) is preferably a homoblock composed of conjugated diene monomer units, and the polymer block (S2) is preferably a homoblock composed of vinyl aromatic monomer units.

[0028] (S1) may be a random copolymer block composed of vinyl aromatic monomer units and conjugated diene monomer units. By using (S1) as a random copolymer block, the Tg of the block copolymer composition, i.e., the peak temperature of the loss tangent (tanδ) in dynamic viscoelasticity measurement, can be controlled, and good shrinkage properties can be easily obtained when the composition is made into a heat-shrinkable film.

[0029] The random copolymer block can be obtained, for example, by adding a vinyl aromatic monomer and a conjugated diene monomer at a certain flow rate ratio and polymerizing them.

[0030] In one embodiment of the present invention, (S1) may be a polystyrene block or a random copolymer block composed of a styrene monomer and a butadiene monomer, (B) may be a polybutadiene block, and (S2) may be a polystyrene block. By adopting such a configuration, the rigidity and shrinkage properties of a heat-shrinkable film obtained from a resin composition containing the block copolymer composition can be further improved.

[0031] <Method for producing a block copolymer containing vinyl aromatic monomer units and conjugated diene monomer units> The method for producing the block copolymer according to one embodiment of the present invention is not particularly limited, and examples thereof include a method for polymerizing the vinyl aromatic monomer and the conjugated diene monomer in an organic solvent using an organolithium compound as an initiator.

[0032] 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; and aromatic hydrocarbons such as benzene, toluene, ethylbenzene, and xylene.

[0033] An organolithium compound is a compound having one or more lithium atoms bonded to the molecule. Examples of the organolithium compound include monofunctional organolithium compounds such as ethyllithium, n-propyllithium, isopropyllithium, n-butyllithium, sec-butyllithium, and tert-butyllithium, and polyfunctional organolithium compounds such as hexamethylenedilithium, butadienyldilithium, and isoprenyldilithium.

[0034] In so-called living anionic polymerization using an organolithium compound as an initiator, the vinyl aromatic hydrocarbon and conjugated diene subjected to the polymerization reaction can be almost entirely converted into a polymer.

[0035] A randomizer may also be added to control the polymerization state. Tetrahydrofuran (THF) is typically used as the randomizer, but other ethers, amines, thioethers, phosphoramide, alkylbenzenesulfonate, potassium or sodium alkoxides, etc. can also be used. Suitable ethers include THF, dimethyl ether, diethyl ether, diphenyl ether, diethylene glycol dimethyl ether, diethylene glycol dibutyl ether, etc. Amines that can be used include tertiary amines such as trimethylamine, triethylamine, and tetramethylethylenediamine, as well as cyclic amines. Other randomizers that can be used include triphenylphosphine, hexamethylphosphoramide, potassium or sodium alkylbenzenesulfonate, potassium or sodium butoxide, etc.

[0036] The amount of the randomizer to be added may be, for example, 0.001 to 10 parts by mass per 100 parts by mass of the total charged monomers. The addition is preferably made before the start of the polymerization reaction. Additional addition may also be made as necessary.

[0037] The block copolymer thus obtained is inactivated by adding a polymerization terminator such as water, alcohol, or carbon dioxide in an amount sufficient to inactivate the active terminals. The copolymer can be recovered from the resulting block copolymer solution by any of the following methods: (1) precipitation using a poor solvent such as methanol, (2) precipitation by evaporating the solvent using a heated roll or the like (drum dryer method), (3) concentrating the solution using a concentrator and then removing the solvent using a vented extruder, or (4) dispersion of the solution in water, blowing in steam to heat and remove the solvent, and recovering the copolymer (steam stripping method).

[0038] <Additives> The block copolymer composition according to one embodiment of the present invention may contain additives within the range that does not impair the effects of the present invention. Examples of such additives include various stabilizers, lubricants, processing aids, antiblocking agents, antistatic agents, antifogging agents, light resistance improvers, softeners, plasticizers, pigments, etc. Each additive may be added to the block copolymer solution, or may be blended with the recovered block copolymer and melt-mixed.

[0039] Examples of stabilizers include phenolic antioxidants such as 2-tert-butyl-6-(3-tert-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenyl acrylate, 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-di-tert-butyl-4-methylphenol, and phosphorus-based antioxidants such as trisnonylphenyl phosphite. Examples of antiblocking agents include organic fillers such as high-impact polystyrene and crosslinked beads of vinyl aromatic hydrocarbon copolymers, silica beads, and quartz beads. Examples of other additives include fatty acid amides, ethylene bisstearamide, sorbitan monostearate, saturated fatty acid esters of fatty alcohols, and pentaerythritol fatty acid esters. These additives are preferably used in an amount of 5% by mass or less relative to 100% by mass of the block copolymer composition.

[0040] <Vinyl aromatic monomer units in block copolymer composition> A block copolymer composition according to one embodiment of the present invention contains 52 to 69% by mass of vinyl aromatic monomer units, more preferably 55 to 66% by mass, and even more preferably 57 to 64% by mass of vinyl aromatic monomer units, relative to 100% by mass of the total mass of vinyl aromatic monomer units and conjugated diene monomer units. The preferred content of vinyl aromatic monomer units in 100% by mass of the total mass of vinyl aromatic monomer units and conjugated diene monomer units is specifically 52, 53, 55, 60, 65, 68, or 69% by mass, and may be within a range between any two of the values ​​exemplified here. When two or more block copolymers are used in combination, the content of the vinyl aromatic monomer unit means the total content of the vinyl aromatic monomer units contained in the block copolymers used in combination.

[0041] When the content of the vinyl aromatic monomer unit is 52% by mass or more, the rigidity of the heat-shrinkable film obtained from the resin composition containing the block copolymer composition can be made suitable for heat-shrinkable films, and when it is 69% by mass or less, the specific gravity separability by water of the heat-shrinkable film obtained from the resin composition containing the block copolymer composition can be further improved.

[0042] The content of the vinyl aromatic monomer units in the total of 100% by mass of the vinyl aromatic monomer units and the conjugated diene monomer units can be measured by the halogen addition method.

[0043] <Flexural Modulus of Block Copolymer Composition> The block copolymer composition according to one embodiment of the present invention has a flexural modulus of 1000 MPa or more, preferably 1050 MPa or more, and more preferably 1100 MPa or more, measured in accordance with ISO 178. Specific preferred flexural moduli of the block copolymer composition are 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, or 1800 MPa, and may be within a range between any two of the values ​​exemplified here.

[0044] When the flexural modulus is 1000 MPa, the rigidity of the heat-shrinkable film obtained from the resin composition containing the block copolymer composition can be made suitable for the heat-shrinkable film. The flexural modulus can be controlled, for example, by adjusting the structure of the block copolymer, and one example is to increase the flexural modulus by using a block copolymer having a structure represented by any one of formulas (i) to (iv). The flexural modulus can also be increased by increasing the amount of vinyl aromatic monomer units contained in 100% by mass of the total mass of vinyl aromatic monomer units and conjugated diene monomer units of the block copolymer composition.

[0045] Flexural modulus is measured according to ISO 178.

[0046] <Peak of loss tangent value (tanδ) when dynamic viscoelasticity measurement of block copolymer composition is performed> A block copolymer composition according to one embodiment of the present invention has a loss tangent (tan δ) measured in a fixed three-point bending mode according to ISO 6721-1 under conditions of a heating rate of 4°C / min, a frequency of 1 Hz, and a strain of 0.02%, and the loss tangent (tan δ) has at least one peak in the range of 80°C to 110°C, preferably at least one peak in the range of 82°C to 108°C, and more preferably at least one peak in the range of 84°C to 106°C. Specifically, the loss tangent (tan δ) has at least one peak at 80, 85, 90, 95, 100, 105, or 110°C, and may have one or more peaks within a range between any two of the values ​​exemplified here.

[0047] If there is one or more peaks in the loss tangent value (tanδ) between 80°C and 110°C, it is believed that a heat-shrinkable film obtained from a resin composition containing a block copolymer composition can have shrinkage properties suitable for a heat-shrinkable film. The temperature at which the peak of the loss tangent (tanδ) appears can be controlled, for example, by allowing a random copolymer block composed of a vinyl aromatic monomer unit and a conjugated diene monomer unit to exist in the block copolymer and adjusting the content ratio of the vinyl aromatic monomer unit and the conjugated diene monomer unit in the random copolymer block.

[0048] The loss tangent value (tanδ) is measured in accordance with ISO 6721-1 by performing dynamic viscoelasticity measurement using, for example, a dynamic viscoelasticity measuring device RSA-III (manufactured by TA Instruments) under conditions of a heating rate of 4°C / min, a frequency of 1 Hz, and a strain of 0.02% in a fixed three-point bending mode.

[0049] <Specific Gravity of Block Copolymer Composition> The specific gravity at 23° C. of the block copolymer composition according to one embodiment of the present invention is preferably 0.950 or more and less than 1.000, more preferably 0.950 or more and 0.999 or less, and even more preferably 0.960 or more and 0.997 or less. Specifically, the specific gravity of the block copolymer composition is 0.950, 0.960, 0.970, 0.980, 0.990, 0.991, 0.992, 0.993, 0.994, 0.995, 0.996, 0.997, 0.998, or 0.999, and may be within a range between any two of the values ​​exemplified here.

[0050] When the specific gravity of the block copolymer composition is less than 1.000, the heat-shrinkable film obtained from a resin composition containing the block copolymer composition can have excellent gravity separation properties with water. Note that the lower the specific gravity of the block copolymer composition, the better the gravity separation properties of the heat-shrinkable film with water. However, taking into account other properties such as the rigidity of the heat-shrinkable film, it is more practical to set the specific gravity to 0.950 or more. The specific gravity of the block copolymer composition can be controlled, for example, by adjusting the content of the vinyl aromatic monomer units when the total mass of the vinyl aromatic monomer units and the conjugated diene monomer units in the block copolymer composition is taken as 100 mass%.

[0051] The specific gravity of the block copolymer composition at 23°C can be measured according to the procedure described in JIS Z8807:2012.

[0052] <Method of producing block copolymer composition> A block copolymer composition according to one embodiment of the present invention can be obtained by mixing one or more block copolymers containing vinyl aromatic monomer units and conjugated diene monomer units with various additives as needed. The block copolymer and additives can be mixed by known methods. For example, they may be dry-blended using a Henschel mixer, ribbon blender, super mixer, V blender, or the like, or may be melted and pelletized in an extruder. In one embodiment, melt mixing is preferred. Alternatively, a method of mixing polymer solutions together and then removing the solvent can be used.

[0053] <Resin composition> A resin composition according to one embodiment of the present invention contains a block copolymer composition according to one embodiment of the present invention, which contains one or more block copolymers containing vinyl aromatic monomer units and conjugated diene monomer units.

[0054] A resin composition according to one embodiment of the present invention contains a block copolymer composition in an amount of 80% by mass or more and 100% by mass or less, preferably 85% by mass or more and 100% by mass or less, and more preferably 90% by mass or more and 100% by mass or less, based on 100% by mass of the resin composition. The content of the block copolymer composition in 100% by mass of the resin composition is specifically 80, 82, 85, 90, 95, 98, or 100% by mass, and may be within a range between any two of the values ​​exemplified here. In one embodiment, the resin composition may consist essentially of the block copolymer composition. By ensuring that the content of the block copolymer composition is 80% by mass or more, the heat-shrinkable film obtained from the resin composition containing the block copolymer composition exhibits good water-induced gravity separability and can have rigidity suitable for the heat-shrinkable film.

[0055] <Other polymers contained in the resin composition> The resin composition according to one embodiment of the present invention may contain other polymers that are not block copolymers containing vinyl aromatic monomer units and conjugated diene monomer units, as long as the effects of the present invention are not impaired. Such other polymers are polymers that do not contain block copolymers containing vinyl aromatic monomer units and conjugated diene monomer units. Specific examples of such other polymers include styrene polymers such as general-purpose polystyrene, high-impact polystyrene, and styrene-(meth)acrylic acid ester copolymer resins.

[0056] <Method of manufacturing resin composition> The resin composition according to one embodiment of the present invention can be obtained by mixing the block copolymer composition according to one embodiment of the present invention with, if necessary, additives and the other polymers described above. The resin composition may also be obtained by mixing one or more block copolymers with, if necessary, additives and other polymers without going through the block copolymer composition. The block copolymer composition, additives, and other polymers can be mixed by known methods, or the block copolymer, additives, and other polymers can be mixed by known methods. For example, they may be dry-blended using a Henschel mixer, ribbon blender, super mixer, V blender, or the like, or may be melted and pelletized in an extruder. In one embodiment, melt mixing is preferred. Alternatively, a method in which polymer solutions are mixed together and then the solvent is removed can be used.

[0057] <Heat-shrinkable film> A heat-shrinkable film according to one embodiment of the present invention is a heat-shrinkable film including a layer made of a resin composition containing a block copolymer composition including one or more block copolymers containing vinyl aromatic monomer units and conjugated diene monomer units, wherein the heat-shrinkable film is stretched in at least one of the MD and TD directions of the heat-shrinkable film. In the present invention, the MD direction of the heat-shrinkable film means the machine direction in which the film is fed out of the production line, and the TD direction of the heat-shrinkable film means the transverse direction perpendicular to the MD direction. Of the MD and TD directions in which the heat-shrinkable film is stretched, the direction in which it is stretched more is sometimes referred to as the main stretching direction.

[0058] <Structure of heat-shrinkable film> The heat-shrinkable film may be a single-layer film using only a layer containing the resin composition, or a heat-shrinkable multilayer film having another resin layer laminated on at least one surface thereof. To obtain a heat-shrinkable multilayer film, another resin layer may be laminated on a stretched heat-shrinkable film, another resin layer may be laminated on an unstretched film obtained by forming the resin composition into a film and stretching it, or a multilayer film obtained by laminating the resin composition and another resin by multilayer extrusion molding may be stretched. A styrene-based resin is preferably used as the resin used for the other resin layer. In one embodiment, the heat-shrinkable film is preferably non-foamed. To obtain a non-foamed film, all layers may be formed without using commonly used foaming methods, i.e., chemical foaming methods in which a resin is foamed using gas generated by thermal decomposition of a chemical foaming agent when the resin and the chemical foaming agent are melt-kneaded, or physical foaming methods in which a gas is injected into a molten resin in an extruder to foam the resin. For example, when the cross section of the heat-shrinkable film is observed with a laser microscope, the film can be considered to be non-foamed if the area ratio of bubbles to the cross-sectional area is 1% or less. The non-foamed heat-shrinkable film has good transparency and surface smoothness.

[0059] <Method for manufacturing heat-shrinkable film> A heat-shrinkable film according to one embodiment of the present invention is a film including a layer made of the resin composition according to one embodiment of the present invention. The heat-shrinkable film is obtained by stretching a sheet including a layer made of the resin composition according to one embodiment of the present invention. The method for producing the sheet is not particularly limited, and for example, a method of forming the sheet by extruding a resin composition can be used. Furthermore, during extrusion, the resin composition may be extruded together to form a sheet composed of multiple layers including a layer composed of the resin composition. In this specification, the terms "sheet" and "film" are not used to distinguish between thicknesses, but when the thickness changes (becomes thinner) through operations such as stretching, the material before it becomes thinner may be referred to as a "sheet."

[0060] The stretching may be uniaxial, biaxial, or multiaxial. Examples of uniaxial stretching include a method of stretching an extruded sheet in a direction perpendicular to the extrusion direction (TD) using a tenter, a method of stretching an extruded tubular film in the circumferential direction (TD), and a method of stretching an extruded sheet in the extrusion direction (MD) using a roll. Examples of biaxial stretching include a method of stretching an extruded sheet in the extrusion direction (MD) using a roll and then stretching it in a direction perpendicular to the extrusion direction (TD) using a tenter or the like, and a method of stretching an extruded tubular film in the extrusion direction (MD) and the circumferential direction (TD) simultaneously or separately.

[0061] The stretching temperature is preferably, for example, 60 to 120°C. A temperature of 60°C or higher makes the film less likely to break during stretching, and a temperature of 120°C or lower is preferred because a film with good shrinkage properties can be obtained. A particularly preferred temperature is within the range of Tg + 5°C to Tg + 20°C relative to the glass transition temperature (Tg) of the composition constituting the film. In the case of a multilayer film, a particularly preferred temperature is within the range of Tg + 5°C to Tg + 20°C relative to the Tg of the polymer composition of the layer with the lowest Tg. The glass transition temperature (Tg) can be determined, for example, from the temperature at the peak of the loss modulus.

[0062] The stretching ratio in the main stretching direction, which is the direction in which the film is stretched more than the other directions, is not particularly limited, but is preferably 1.5 to 8.0. A stretching ratio of 1.5 or more in the main stretching direction can provide a film with good shrinkage properties, while a stretched film can be easily produced by a stretching ratio of 8.0 or less, which is preferred.

[0063] <Heat-shrinkable film's specific gravity separation by water> The heat-shrinkable film according to one embodiment of the present invention has excellent water-specific gravity separation properties, which can be achieved, for example, by making the specific gravity of the heat-shrinkable film less than 1,000. The specific gravity of the heat-shrinkable film according to one embodiment of the present invention at 23°C is preferably, for example, 0.950 or more and less than 1.000. If the specific gravity of the heat-shrinkable film is less than 1.000, it will float on water and can be separated by specific gravity with water from films having a specific gravity of 1.000 or more, which is preferable. The specific gravity of the heat-shrinkable film can be controlled by incorporating a layer composed of the resin composition according to one embodiment of the present invention into the heat-shrinkable film or by adjusting the specific gravities of other layers. The specific gravity is measured at 23°C in accordance with, for example, JIS Z8807:2012.

[0064] <Shrinkage characteristics of heat-shrinkable film> The heat-shrinkable film according to one embodiment of the present invention can have shrinkage characteristics suitable for heat-shrinkable films. The shrinkage characteristics referred to here refer to, for example, the balance between the thermal shrinkage rate and the natural shrinkage rate. The thermal shrinkage rate and the natural shrinkage rate are generally in a trade-off relationship, but it is desirable to achieve a balance between them depending on the application.

[0065] <Heat shrinkage rate of heat shrinkable film> A heat-shrinkable film according to one embodiment of the present invention can have a heat shrinkage rate suitable for heat-shrinkable films. Specifically, for example, the heat shrinkage rate in at least one direction is preferably 60% or more at 100°C for 10 seconds, and 40% or more at 80°C for 10 seconds. Such a heat shrinkage rate does not require high temperatures during shrinkage, thereby minimizing the impact on the article to be covered. Below, we will explain a case where the heat shrinkage rate requirement is met in the main stretching direction (the direction in which the film is stretched more greatly) of the heat-shrinkable film, but the present invention is not limited to this. The heat shrinkage percentage of the heat shrinkable film according to one embodiment of the present invention means a value measured in the TD direction of the heat shrinkable film when the main stretching direction (the direction in which it is more stretched) of the heat shrinkable film is the TD direction, whereas when the main stretching direction of the heat shrinkable film is the MD direction, it means a value measured in the MD direction of the heat shrinkable film. The heat shrinkage rate is calculated, for example, by immersing a heat-shrinkable film in warm water for a certain period of time and calculating the difference in length between before and after shrinkage.

[0066] <Natural shrinkage rate of heat-shrinkable film> The heat-shrinkable film according to one embodiment of the present invention can have a natural shrinkage rate suitable for heat-shrinkable films. Specifically, for example, it is preferably 4% or less at 40°C for 7 days. If the natural shrinkage rate is 4% or less, shrinkage of the heat-shrinkable film during storage can be reduced, resulting in excellent storage properties. The natural shrinkage rate is calculated, for example, by leaving a heat-shrinkable film in an atmosphere at 40° C. for 7 days and calculating the difference in length before and after shrinkage.

[0067] <Heat-shrinkable film rigidity> The heat-shrinkable film according to one embodiment of the present invention can have a rigidity suitable for a heat-shrinkable film, and therefore has an appropriate stiffness, allowing the heat-shrinkable film to be attached to a container without any problems during processing or operation. The rigidity can be measured, for example, by the Young's modulus in the MD direction of the heat-shrinkable film. Specifically, if the Young's modulus in the MD direction at 23°C is 500 MPa or more, the heat-shrinkable film can be said to have a rigidity suitable for the heat-shrinkable film. The Young's modulus can be measured at 23°C, in an environment with a humidity of 50±5%, and at a tensile speed of 200 mm / min.

[0068] The thickness of the heat-shrinkable film according to one embodiment of the present invention is preferably 20 to 100 μm, and more preferably 50 to 95 μm.

[0069] The heat-shrinkable film according to one embodiment of the present invention can be attached to containers by taking advantage of its heat shrinkability, either as an unprinted film or as a label printed with a product name or the like, or as a cap seal or other packaging material, etc. For example, it can be used as a label to be attached to metal can containers made of tinplate, TFS, aluminum, etc. (three-piece cans, two-piece cans, bottle cans with lids, etc.), glass containers, or resin containers made of polyethylene terephthalate (abbreviated as PET), polyethylene, etc. [Example]

[0070] The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to these.

[0071] <Preparation of Block Copolymer> <Preparation of Block Copolymer: (P-1)> (1) 467 kg of cyclohexane and 70 g of tetrahydrofuran (THF) were placed in a reaction vessel. (2) 2100 mL of a 10% by mass solution of n-butyllithium in cyclohexane was added thereto as a polymerization initiator solution, and the temperature was maintained at 30°C. (3) 8 kg of styrene was added and anionic polymerization of styrene was carried out. The internal temperature rose to 32°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, 114 kg of styrene and 9 kg of 1,3-butadiene were added simultaneously at constant addition rates of 148.2 kg / h and 11.7 kg / h, respectively. (5) After styrene and 1,3-butadiene were completely consumed, the internal temperature of the reaction system was lowered to 50°C, and 61 kg of 1,3-butadiene was added. The internal temperature rose to 97°C. (6) After the 1,3-butadiene was completely consumed, the internal temperature of the reaction system was lowered to 75°C, and 8 kg of styrene was added to carry out anionic polymerization of styrene. The internal temperature rose to 77°C. (7) After the styrene was completely consumed, all of the polymerization active terminals were finally quenched with water to obtain a polymerization solution containing a block copolymer with a polystyrene block, a random block of styrene and 1,3-butadiene, a poly-1,3-butadiene block, and a polystyrene block. (8) This polymerization solution was pre-concentrated and then extruded with a twin-screw extruder equipped with a vacuum vent to remove volatiles, thereby obtaining the desired block copolymer (P-1) in pellet form.

[0072] <Preparation of Block Copolymer: (P-2)> (1) 467 kg of cyclohexane and 70 g of tetrahydrofuran (THF) were placed in a reaction vessel. (2) 2100 mL of a 10% by mass solution of n-butyllithium in cyclohexane was added thereto as a polymerization initiator solution, and the temperature was maintained at 30°C. (3) 50 kg of styrene was added and anionic polymerization of styrene was carried out. The internal temperature rose to 56°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, 45 kg of styrene and 5 kg of 1,3-butadiene were added simultaneously at constant addition rates of 135.0 kg / h and 15.0 kg / h, respectively. (5) After styrene and 1,3-butadiene were completely consumed, the internal temperature of the reaction system was lowered to 50°C, and 66 kg of 1,3-butadiene was added. The internal temperature rose to 101°C. (6) After the 1,3-butadiene was completely consumed, the internal temperature of the reaction system was lowered to 70°C, and 34 kg of styrene was added to carry out anionic polymerization of styrene. The internal temperature rose to 84°C. (7) After the styrene was completely consumed, all of the polymerization active terminals were finally quenched with water to obtain a polymerization solution containing a block copolymer with a polystyrene block, a random block of styrene and 1,3-butadiene, a poly-1,3-butadiene block, and a polystyrene block. (8) This polymerization solution was pre-concentrated and then extruded with a twin-screw extruder equipped with a vacuum vent to remove volatiles, thereby obtaining the desired block copolymer (P-2) in pellet form.

[0073] <Preparation of Block Copolymer: (P-3)> (1) 467 kg of cyclohexane and 70 g of tetrahydrofuran (THF) were placed in a reaction vessel. (2) 3300 mL of a 10% by mass solution of n-butyllithium in cyclohexane was added thereto as a polymerization initiator solution, and the temperature was maintained at 30°C. (3) 126 kg of styrene was added and anionic polymerization of styrene was carried out. The internal temperature rose to 89°C. (4) After the styrene was completely consumed, the internal temperature of the reaction system was lowered to 45°C, and 66 kg of 1,3-butadiene was added. The internal temperature rose to 96°C. (5) After 1,3-butadiene was completely consumed, the internal temperature of the reaction system was lowered to 75°C, and 6 kg of styrene was added. The internal temperature rose to 77°C. (6) After the styrene was completely consumed, the internal temperature of the reaction system was lowered to 75°C, and 377 g of epoxidized soybean oil as a coupling agent was added, followed by reaction at 75°C for 10 minutes. (7) Finally, all of the polymerization active terminals were deactivated with water to obtain a polymerization solution containing a block copolymer in which block chains having polystyrene blocks, poly-1,3-butadiene blocks, and polystyrene blocks were coupled. (8) This polymerization solution was pre-concentrated and then extruded with a twin-screw extruder equipped with a vacuum vent to remove volatiles, thereby obtaining the desired block copolymer (P-3) in pellet form.

[0074] <Preparation of Block Copolymer: (P-4)> (1) 467 kg of cyclohexane and 70 g of tetrahydrofuran (THF) were placed in a reaction vessel. (2) 2100 mL of a 10% by mass solution of n-butyllithium in cyclohexane was added thereto as a polymerization initiator solution, and the temperature was maintained at 30°C. (3) 6 kg of styrene was added and anionic polymerization of styrene was carried out. The internal temperature rose to 32°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, 96 kg of styrene and 16 kg of 1,3-butadiene were added simultaneously at constant addition rates of 144.6 kg / h and 20.6 kg / h, respectively. (5) After the styrene and 1,3-butadiene were completely consumed, 14 kg of styrene and 64 kg of 1,3-butadiene were added simultaneously at constant addition rates of 14.0 kg / h and 64.0 kg / h, respectively, while maintaining the internal temperature of the reaction system at 80°C. (6) After the styrene and 1,3-butadiene were completely consumed, the internal temperature of the reaction system was lowered to 75°C, and 6 kg of styrene was added to carry out anionic polymerization of styrene. The internal temperature rose to 77°C. (7) After the styrene was completely consumed, all of the polymerization active terminals were finally quenched with water to obtain a polymerization solution containing block copolymers with polystyrene blocks, random blocks of styrene and 1,3-butadiene, random blocks of styrene and 1,3-butadiene, and polystyrene blocks. (8) This polymerization solution was pre-concentrated and then extruded with a twin-screw extruder equipped with a vacuum vent to remove volatiles, thereby obtaining the desired block copolymer (P-4) in pellet form.

[0075] <Preparation of Block Copolymer: (P-5)> (1) 467 kg of cyclohexane and 70 g of tetrahydrofuran (THF) were placed in a reaction vessel. (2) 2100 mL of a 10% by mass solution of n-butyllithium in cyclohexane was added thereto as a polymerization initiator solution, and the temperature was maintained at 30°C. (3) 100 kg of styrene was added and anionic polymerization of styrene was carried out. The internal temperature rose to 81°C. (4) After the styrene was completely consumed, the internal temperature of the reaction system was lowered to 80°C, and while maintaining the internal temperature, 16 kg of styrene and 78 kg of 1,3-butadiene were added simultaneously at constant addition rates of 13.6 kg / h and 65.0 kg / h, respectively. (5) After the styrene and 1,3-butadiene were completely consumed, the internal temperature of the reaction system was lowered to 75°C, and 6 kg of styrene was added to carry out anionic polymerization of styrene. The internal temperature rose to 77°C. (6) After the styrene was completely consumed, all of the polymerization active terminals were finally quenched with water to obtain a polymerization solution containing a block copolymer with a polystyrene block, a random block of styrene and 1,3-butadiene, and a polystyrene block. (7) This polymerization solution was pre-concentrated and then extruded with a twin-screw extruder equipped with a vacuum vent to remove volatiles, thereby obtaining the desired pellet-like block copolymer (P-5).

[0076] <Preparation of Block Copolymer: (P-6)> (1) 467 kg of cyclohexane and 70 g of tetrahydrofuran (THF) were placed in a reaction vessel. (2) 2100 mL of a 10% by mass solution of n-butyllithium in cyclohexane was added thereto as a polymerization initiator solution, and the temperature was maintained at 30°C. (3) 126 kg of styrene was added and anionic polymerization of styrene was carried out. The internal temperature rose to 89°C. (4) After the styrene was completely consumed, the internal temperature of the reaction system was lowered to 45°C, and 66 kg of 1,3-butadiene was added. The internal temperature rose to 96°C. (5) After 1,3-butadiene was completely consumed, the internal temperature of the reaction system was lowered to 75°C, and 6 kg of styrene was added. The internal temperature rose to 77°C. (6) After the styrene was completely consumed, all polymerization active terminals were finally quenched with water to obtain a polymerization solution containing a block copolymer having a polystyrene block, a poly-1,3-butadiene block, and a styrene block. (7) This polymerization solution was pre-concentrated and then extruded with a twin-screw extruder equipped with a vacuum vent to remove volatiles, thereby obtaining the desired block copolymer (P-6) in pellet form.

[0077] <Preparation of Block Copolymer: (P-7)> (1) 467 kg of cyclohexane and 70 g of tetrahydrofuran (THF) were placed in a reaction vessel. (2) 2100 mL of a 10% by mass solution of n-butyllithium in cyclohexane was added thereto as a polymerization initiator solution, and the temperature was maintained at 30°C. (3) 50 kg of styrene was added and anionic polymerization of styrene was carried out. The internal temperature rose to 56°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, 40 kg of styrene and 60 kg of 1,3-butadiene were added simultaneously at constant addition rates of 40.0 kg / h and 60.0 kg / h, respectively. (5) After the styrene and 1,3-butadiene were completely consumed, the internal temperature of the reaction system was lowered to 60°C, 50 kg of styrene was added, and the styrene was anionically polymerized. The internal temperature rose to 87°C. (6) After the styrene was completely consumed, all of the polymerization active terminals were finally quenched with water to obtain a polymerization solution containing a block copolymer with a polystyrene block, a random block of styrene and 1,3-butadiene, and a polystyrene block. (7) This polymerization solution was pre-concentrated and then extruded with a twin-screw extruder equipped with a vacuum vent to remove volatiles, thereby obtaining the desired pellet-like block copolymer (P-7).

[0078] <Preparation of Block Copolymer: (P-8)> (1) 467 kg of cyclohexane and 70 g of tetrahydrofuran (THF) were placed in a reaction vessel. (2) 2000 mL of a 10% by mass solution of n-butyllithium in cyclohexane was added thereto as a polymerization initiator solution, and the temperature was maintained at 30°C. (3) 4 kg of styrene was added and anionic polymerization of styrene was carried out. The internal temperature rose to 31°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, 144 kg of styrene and 12 kg of 1,3-butadiene were added simultaneously at constant addition rates of 144.0 kg / h and 12.0 kg / h, respectively. (5) After styrene and 1,3-butadiene were completely consumed, the internal temperature of the reaction system was lowered to 70°C, and 36 kg of 1,3-butadiene was added. The internal temperature rose to 83°C. (6) After the 1,3-butadiene was completely consumed, the internal temperature of the reaction system was lowered to 75°C, and 4 kg of styrene was added to carry out anionic polymerization of styrene. The internal temperature rose to 76°C. (7) After the styrene was completely consumed, all of the polymerization active terminals were finally quenched with water to obtain a polymerization solution containing a block copolymer with a polystyrene block, a random block of styrene and 1,3-butadiene, a poly-1,3-butadiene block, and a polystyrene block. (8) This polymerization solution was pre-concentrated and then extruded with a twin-screw extruder equipped with a vacuum vent to remove volatiles, thereby obtaining the desired pellet-like block copolymer (P-8).

[0079] <Block structure of block copolymer> The block structures of the resulting block copolymers (P-1) to (P-8) are shown in Tables 1 and 2. The block structure of the block copolymer can be determined by the procedure for adding each monomer, and the content of each block structure in the block copolymer and the content of the monomer unit in each block structure can be calculated from the amount of the raw material monomer charged.

[0080] <Physical properties of block copolymers> The resulting block copolymers (P-1) to (P-8) were measured for various physical properties according to the following procedures. The measurement results are shown in Tables 1 and 2.

[0081] <Weight average molecular weight> The weight average molecular weight was measured by GPC under the following conditions. Device name: HLC-8220GPC (Tosoh Corporation) Column: Four Shodex GPCKF-404 columns (Showa Denko KK) were connected in series. Temperature: 40℃ Detection: UV-visible spectroscopy (254 nm) Solvent: tetrahydrofuran Concentration: 2% by mass Calibration curve: Created using standard polystyrene (manufactured by VARIAN).

[0082] [Table 1]

[0083] [Table 2]

[0084] <Production of Block Copolymer Composition> [Raw materials used] Block copolymers: (P-1) to (P-8) obtained by the above polymerization Anti-blocking agent: E640N (high impact polystyrene, manufactured by Toyo Styrene Co., Ltd.)

[0085] Example 1 100% by mass of the block copolymer (P-1) was dry-blended with 1.3% by mass of E640N, and then melted and pelletized in an extruder to obtain a block copolymer composition (RA-1).

[0086] <Examples 2 to 4, Comparative Examples 1 to 3> Block copolymer compositions (RA-2) to (RA-4) and (RB-1) to (RB-3) were obtained by pelletizing 100% by mass of the block copolymer measured according to the block copolymer and blending ratio shown in Table 3 in the same manner as in Example 1.

[0087] <Physical properties of block copolymer composition> The obtained block copolymer compositions (RA-1) to (RA-4) and (RB-1) to (RB-3) were measured for various physical properties according to the following procedures. The measurement results are shown in Table 3.

[0088] <Content of vinyl aromatic monomer units when the total mass of vinyl aromatic monomer units and conjugated diene monomer units is taken as 100% by mass> The content of styrene monomer units was measured and calculated by the following halogen addition method, assuming that the total mass of styrene monomer units and 1,3-butadiene monomer units was 100% by mass. (A1) After dissolving the sample in a solvent (such as carbon tetrachloride) capable of completely dissolving the sample, an excess amount of iodine monochloride / carbon tetrachloride solution was added and the reaction was allowed to proceed sufficiently. Unreacted iodine monochloride was titrated with 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 butadiene content (rubber content) was calculated. The styrene content was calculated by subtracting the butadiene content from the total content of the sample.

[0089] <Flexural modulus> Measurements were performed according to ISO178.

[0090] <Peak of loss tangent value (tanδ)> In accordance with ISO 6721-1, dynamic viscoelasticity measurements were performed in a fixed three-point bending mode using a dynamic viscoelasticity measuring device RSA-III (manufactured by TA Instruments) under conditions of a heating rate of 4°C / min, a frequency of 1 Hz, and a strain of 0.02%. If a peak was present in the range of 80°C to 110°C in the obtained graph, the temperature at which the peak appeared is shown in Table 3. If no peak was present in the range of 80°C to 110°C, the temperature at which the highest peak appeared is shown in Table 3.

[0091] <Specific gravity> The specific gravity at 23°C was measured in accordance with JIS Z8807:2012.

[0092] [Table 3]

[0093] <Production of heat-shrinkable film> [Raw materials used] Resin composition: The above-mentioned block copolymer compositions (RA-1) to (RA-4) and (RB-1) to (RB-3) were used as they were as resin compositions.

[0094] A method for producing a heat-shrinkable film using the resin composition according to Example 1 will be described below.

[0095] (1) Extrusion of the sheet before stretching The resin composition of Example 1 was melted and extruded into a sheet using an extruder equipped with a T-die with a lip width of 300 μm, which is capable of extruding a sheet. The extruder that melted the resin and fed it to the T-die was a 65 mmφ short-screw extruder, and the set temperature was 200°C. The set temperature of the T-die was 180°C. The thickness of the obtained sheet was 0.30 mm.

[0096] (2) Stretching the pre-stretched sheet The obtained pre-stretched sheet was passed through a longitudinal stretching machine having two rolls with different rotation speeds at 80°C so as not to be stretched in the MD direction (i.e., the stretching ratio was 1.0 times), and then passed through a tenter-type transverse stretching machine and stretched 4.5 times in the TD direction at 90°C, finally obtaining a 70 μm thick heat-shrinkable film using the resin composition of Example 1.

[0097] Films were formed in the same manner as in Example 1 using the resin compositions of Examples 2 to 4 and Comparative Examples 1 to 3.

[0098] <Evaluation of heat-shrinkable film> The physical properties of the heat-shrinkable film thus obtained were evaluated as follows.

[0099] <Heat shrinkage rate> The heat shrinkage at 70, 80, 90 and 100°C was calculated by immersing the stretched film in warm water adjusted to the respective temperatures for 10 seconds and using the following formula. Heat shrinkage rate (%) = (L1-L2) / L1 x 100 L1: Length before shrinkage L2: Length after contraction

[0100] <Natural shrinkage rate> The stretched film was left standing in an atmosphere at 40°C for 7 days, and the elastic modulus was calculated using the following formula. Natural shrinkage rate (%) = (L1-L2) / L1 x 100 L1: Length before shrinkage L2: Length after contraction

[0101] <Young's modulus> The Young's modulus was measured at 23°C in the TD and MD directions of the heat-shrinkable film in an environment of humidity 50±5% at a tension speed of 200 mm / min.

[0102] <Stretch> The elongation was calculated by the following formula after a tensile test was carried out under the same conditions as those for the Young's modulus. Elongation (%) = L2 / L1 x 100 L1: Distance between chucks before tensioning L2: Distance between chucks at break

[0103] <Specific gravity> The specific gravity at 23°C was measured in accordance with JIS Z8807:2012.

[0104] <haze> Measurement was carried out in accordance with ASTM D-1003 using a haze meter (NDH-2000) manufactured by Nippon Denshoku Industries Co., Ltd.

[0105] <Floating / Sinking Judgment> In the above-mentioned specific gravity measurement at 23°C, samples that floated on the water were judged as "floating" and samples that sank were judged as "sinking."

[0106] [Table 4]

[0107] <Consideration> The heat-shrinkable films molded using the block copolymer compositions and resin compositions according to the examples of the present invention had specific gravities of less than 1,000 at 23° C., and therefore had excellent specific gravity separation properties with water. It was confirmed that the heat-shrinkable films molded using the block copolymer composition and resin composition according to the examples of the present invention have a Young's modulus in the MD direction of 500 MPa or more and have rigidity suitable for heat-shrinkable films. Therefore, the heat-shrinkable films have appropriate stiffness, and the operation and processing of attaching the heat-shrinkable films to containers can be carried out without any problems. Furthermore, it was confirmed that the heat-shrinkable films molded using the block copolymer compositions and resin compositions according to the examples of the present invention have shrinkage properties suitable for heat-shrinkable films. Because high temperatures are not required during shrinkage, the effects on the coated article can be minimized. Furthermore, the heat-shrinkable film has excellent storage properties because it can reduce shrinkage of the heat-shrinkable film during storage.

[0108] In particular, it was confirmed that the heat-shrinkable films molded using the block copolymer compositions and resin compositions according to the examples of the present invention can have excellent water-based specific gravity separation properties, as described above, even when molded without foaming.

[0109] On the other hand, when a block copolymer composition or resin composition having a flexural modulus of less than 1000 MPa was used, the film was soft and difficult to form (poor rigidity). Furthermore, when the total mass of the vinyl aromatic monomer units and conjugated diene monomer units in the block copolymer was taken as 100 mass%, heat-shrinkable films obtained using block copolymer compositions or resin compositions having a vinyl aromatic monomer unit content of more than 69 mass% had a specific gravity of 1.000 or more at 23°C.

[0110] When dynamic viscoelasticity measurement of a block copolymer composition was performed in a fixed three-point bending mode, the peak of the loss tangent (tanδ) did not have a peak in the range of 80°C to 110°C, but only in the temperature range above 110°C. In the case of using a block copolymer composition and a resin composition, it was difficult to form a film under general film-forming temperature conditions. [Industrial Applicability]

[0111] The block copolymer composition according to the present invention can provide a heat-shrinkable film that is capable of being separated by specific gravity with water, even if the heat-shrinkable film is not foamed, when the heat-shrinkable film is obtained from a resin composition containing the block copolymer composition. The resin composition containing the block copolymer composition according to the present invention can provide a heat-shrinkable film that is excellent in the specific gravity separation property with water, and has industrial applicability.< / haze>

Claims

1. A block copolymer composition containing one or more block copolymers containing vinyl aromatic monomer units and conjugated diene monomer units, the block copolymer composition contains the vinyl aromatic monomer units in an amount of 52% by mass or more and 69% by mass or less, when the total mass of the vinyl aromatic monomer units and the conjugated diene monomer units is taken as 100% by mass; the block copolymer composition has a flexural modulus measured in accordance with ISO 178 of 1000 MPa or more; The block copolymer composition has at least one peak in loss tangent (tan δ) in the range of 80°C or higher and 110°C or lower when dynamic viscoelasticity is measured in a fixed three-point bending mode in accordance with ISO 6721-1 under conditions of a heating rate of 4°C / min, a frequency of 1 Hz, and a strain of 0.02%. Block copolymer compositions.

2. The block copolymer composition according to claim 1 , wherein the block copolymer composition has a specific gravity measured at 23° C. of 0.950 or more but less than 1.

000.

3. At least one of the one or more block copolymers contained in the block copolymer composition has a structure represented by any one of the following formulas (i) to (iv): (i) (S1) ｎ -(B) ｍ (ii) (S1) ｎ -(B) ｍ -(S2) (iii) (S1) ｎ -(B) ｍ -X (iv) (S1) ｎ -(B) ｍ -(S2)-X [In the formula, each of (S1) and (S2) is a polymer block having a vinyl aromatic monomer unit content of 85% by mass or more and 100% by mass or less, (B) is a polymer block having a conjugated diene monomer unit content of 60% by mass or more and 100% by mass or less, X is a coupling center, and each of n and m is an integer of 1 or more] Each of the block copolymers having the structures represented by the formulas (i) to (iv) contains, in 100% by mass of the block copolymer, (S1) １ ~ (S1) ｎ The total mass of the above components is 40% by mass or more and 70% by mass or less, Each of the block copolymers having the structures represented by the formulas (i) to (iv) contains, in 100% by mass of the block copolymer, (B) １ ~ (B) ｍ The total mass of the above components is 30% by mass or more and 48% by mass or less, Each of the block copolymers having the structures represented by the formulas (i) to (iv) contains 0% by mass or more and 12% by mass or less of (S2) based on 100% by mass of the block copolymer, the total mass of the block copolymer having the structure represented by any one of the formulas (i) to (iv) is 60% by mass or more and 100% by mass or less, based on a total of 100% by mass of the one or more block copolymers; The block copolymer composition according to claim 1 or 2.

4. (S1) is a homoblock composed of vinyl aromatic monomer units or a random copolymer block composed of vinyl aromatic monomer units and conjugated diene monomer units, (B) is a homoblock composed of conjugated diene monomer units, (S2) is a homoblock composed of vinyl aromatic monomer units; The block copolymer composition of claim 3 .

5. 3. The block copolymer composition according to claim 1, wherein the vinyl aromatic monomer unit is a styrene monomer unit, and the conjugated diene monomer unit is a butadiene monomer unit.

6. A resin composition containing the block copolymer composition according to claim 1 or 2, The resin composition contains 80% by mass or more and 100% by mass or less of the block copolymer composition based on 100% by mass of the resin composition. Resin composition.

7. A heat-shrinkable film comprising a layer formed from the resin composition according to claim 6.

8. A label using the heat-shrinkable film according to claim 7.

9. A container fitted with the heat-shrinkable film according to claim 7.

10. A container equipped with the label according to claim 8.

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