Heat-shrinkable film and container

Abstract

[Problem] To provide a heat-shrinkable film which has excellent wear resistance and impact resistance even when the heat-shrinkable film is thinned and a container which comprises the heat-shrinkable film. [Solution] One aspect of the present invention provides a heat-shrinkable film. The heat-shrinkable film is a stretched film which comprises not less than 50 mass% of a block copolymer composition that contains at least one block copolymer having a vinyl aromatic monomer unit and a conjugated diene monomer unit. The heat-shrinkable film has a thickness of 20-30 μm, has a thermal shrinkage of not less than 40% at 90°C and in 10 seconds, has a Young's modulus of not less than 1,100 MPa and an elongation at break of not less than 100% when the heat-shrinkable film is stretched at a tensile speed of 200 mm / min in the direction orthogonal to the stretching axis in a tensile test conforming to ISO 527-3:2018, and has an impact strength of not less than 0.7 J in an impact test conforming to ASTM D3420.

Description

Heat-shrinkable film and container

[0001] The present invention relates to a heat-shrinkable film and a container.

[0002] As a raw material for heat-shrinkable films used in shrink packaging, block copolymers having vinyl aromatic monomer units and conjugated diene monomer units are widely used (see Patent Document 1). In recent years, heat-shrinkable films used in shrink packaging are required to accommodate various shapes of packaged objects, mounting methods, and to achieve a film appearance with excellent design. Further, from the perspective of reducing environmental impact, efforts are being made to reduce the amount of raw materials used and the amount of carbon dioxide generated by thinning the heat-shrinkable film (hereinafter also referred to as "thinning"). For this reason, there is a demand for the development of a heat-shrinkable film having excellent abrasion resistance and impact resistance that can withstand actual use even when thinned.

[0003] Japanese Patent Application Laid-Open No. 2003-96262

[0004] In view of the above circumstances, the present invention aims to provide a heat-shrinkable film having excellent abrasion resistance and impact resistance even when thinned, and a container provided with such a heat-shrinkable film.

[0005] According to one aspect of the present invention, there is provided a heat-shrinkable film which is a stretched film containing at least 50% by mass of a block copolymer composition containing at least one block copolymer having vinyl aromatic monomer units and conjugated diene monomer units, having a thickness of 20 μm or more and 30 μm or less, having a heat shrinkage rate of 40% or more at 90°C for 10 seconds, and in a tensile test conforming to ISO 527-3:2018, having a Young's modulus of 1100 MPa or more and an elongation at break of 100% or more when stretched at a tensile speed of 200 mm / min in a direction perpendicular to the stretching axis, and having an impact strength of 0.7 J or more in an impact test conforming to ASTM D3420.

[0006] According to such an aspect, excellent abrasion resistance and impact resistance can be achieved even when thinned.

[0007] The heat-shrinkable film of this embodiment is a stretched film containing 50% by mass or more of a block copolymer composition containing at least one block copolymer having vinyl aromatic monomer units and conjugated diene monomer units. Such a heat-shrinkable film exhibits excellent abrasion resistance by having a predetermined Young's modulus and elongation at break, and excellent impact resistance by having a predetermined impact strength. Prior to describing the composition and physical properties of the heat-shrinkable film, the block copolymer composition used in the heat-shrinkable film will be described.

[0008] <Block Copolymer Composition> The block copolymer composition may contain at least one block copolymer having vinyl aromatic monomer units and conjugated diene monomer units, but from the viewpoint of ease of adjusting the physical properties of the heat-shrinkable film, it is preferable to contain multiple types of block copolymers. The block copolymer composition of this embodiment preferably contains 50 to 80 parts by mass of block copolymer (A) and 20 to 50 parts by mass of block copolymer (B).

[0009] <<Block Copolymer (A)>> It is preferable that the block copolymer (A) has vinyl aromatic monomer units and conjugated diene monomer units. Furthermore, it is preferable that the block copolymer (A) contains conjugated diene monomer units in an amount of more than 15% by mass and 25% by mass or less based on 100% by mass of the block copolymer (A), and contains blocks with a conjugated diene monomer unit content of 85% by mass or more and 100% by mass or less (hereinafter also referred to as "conjugated diene-rich blocks") in an amount of 7% by mass or more and 20% by mass or less based on 100% by mass of the block copolymer (A).

[0010] Vinyl aromatic monomer units are derived from vinyl aromatic hydrocarbons and have the function of imparting high rigidity to block copolymer (A). On the other hand, conjugated diene monomer units are derived from conjugated dienes and have the function of increasing the strength of block copolymer (A). Here, since block copolymer (A) contains a relatively large amount of vinyl aromatic monomer units, it can impart high rigidity (hardness) to the resulting film. Therefore, block copolymer (A) can be called a high-rigidity component in the block copolymer composition. Furthermore, by containing an appropriate amount of conjugated diene monomer units, block copolymer (A) can easily create molecular-level entanglement with block copolymer (B) which contains a large amount of conjugated diene monomer units.

[0011] Examples of vinyl aromatic hydrocarbons include styrene, o-methylstyrene, p-methylstyrene, p-tert-butylstyrene, 2,4-dimethylstyrene, 2,5-dimethylstyrene, α-methylstyrene, vinylnaphthalene, and vinylanthracene. Among these, styrene is preferred as the vinyl aromatic hydrocarbon. Examples of conjugated dienes include 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, and 1,3-hexadiene. Among these, 1,3-butadiene or isoprene is preferred as the conjugated diene.

[0012] The block copolymer (A) preferably contains the conjugated diene-rich block in an amount of approximately 9% to 18% by mass, and more preferably 11% to 16% by mass, based on 100% by mass of the block copolymer (A). This allows for maintaining high rigidity of the block copolymer (A) while further enhancing the effect of facilitating molecular-level entanglement with the block copolymer (B). The block copolymer (A) preferably contains conjugated diene monomer units in an amount of approximately 16% to 24% by mass, more preferably 17% to 23% by mass, and even more preferably 18% to 22% by mass, based on 100% by mass of the block copolymer (A). This further improves the above effect.

[0013] The block copolymer (A) is preferably represented by the general formula: S1-R1-R2-S2, where S1 and S2 are each blocks of vinyl aromatic monomer units. The presence of these S1 and S2 blocks can be confirmed, for example, by the molecular weight of the components obtained by osmium acid decomposition of the block copolymer (A) according to the literature (method described in I.M. KOLTHOFF, et al., Journal of Polymer Science, Volume 1, 429 (1946)). R1 ​​and R2 are each at least one block of vinyl aromatic monomer units and conjugated diene monomer units.

[0014] Methods for forming the R1 and R2 blocks include continuously feeding vinyl aromatic hydrocarbons and conjugated dienes to the active end at a constant rate ratio while maintaining a starvation state, and adding arbitrary amounts of vinyl aromatic hydrocarbons and conjugated dienes all at once. When the R1 and R2 blocks consist of both vinyl aromatic monomer units and conjugated diene monomer units, these blocks may be either random blocks or tapered blocks.

[0015] In block R1, the mass ratio of vinyl aromatic monomer units to conjugated diene monomer units is preferably 100:0 or more and 85:15 or less, more preferably 97.5:2.5 or more and 82.5:17.5 or less, and even more preferably 95:5 or more and 80:20 or less. In block R2, the mass ratio of vinyl aromatic monomer units to conjugated diene monomer units is preferably 15:85 or more and 0:100 or less (particularly 0:100), but depending on the properties of the target block copolymer (A) and block copolymer composition, it can be approximately 12.5:87.5 or more and 2.5:97.5 or less, and can also be approximately 10:90 or more and 5:95 or less. The above effects can be further improved by adjusting the mass ratio of vinyl aromatic monomer units to conjugated diene monomer units in each of blocks R1 and R2. The block copolymer composition may contain one type of block copolymer (A) as described above, or it may contain two or more types.

[0016] <Block Copolymer (B)> Block copolymer (B) preferably has vinyl aromatic monomer units, conjugated diene monomer units, and residues of a polyfunctional coupling agent. Furthermore, this block copolymer (B) preferably contains conjugated diene monomer units in an amount of 26% to 50% by mass per 100% by mass of block copolymer (B), and preferably contains blocks (conjugated diene-rich blocks) with a conjugated diene monomer unit content of 85% to 100% by mass in an amount of 20% to 45% by mass per 100% by mass of block copolymer (B). Because block copolymer (B) contains a relatively large amount of conjugated diene monomer units, it can impart high strength (flexibility) to the resulting film. Therefore, block copolymer (B) can be called a high-reinforcing component in the block copolymer composition.

[0017] Furthermore, the presence of polyfunctional coupling agent residues allows these residues to couple, generating a branched-chain structure in the block copolymer (B). As a result, the film's rigidity (hardness) is maintained while its elongation under high-speed deformation is improved. Consequently, the film can be given excellent impact resistance. The vinyl aromatic monomer units and conjugated diene monomer units are the same as those described for block copolymer (A) above.

[0018] The block copolymer (B) preferably contains the conjugated diene-rich block in an amount of approximately 25% to 42.5% by mass, and more preferably 30% to 40% by mass, based on 100% by mass of the block copolymer (B). This allows for sufficient molecular-level entanglement with the block copolymer (A) containing a predetermined amount of the conjugated diene-rich block. As a result, the impact resistance of the resulting film can be improved. The block copolymer (B) preferably contains conjugated diene monomer units in an amount of approximately 30% to 50% by mass, more preferably 34% to 47.5% by mass, and even more preferably 38% to 45% by mass, based on 100% by mass of the block copolymer (B). This further improves the above effect.

[0019] The block copolymer (B) is preferably represented by the general formula: (S3-R3-R4-S4)nX. Here, S3 and S4 are each blocks of vinyl aromatic monomer units, similar to S1 and S2 described in block copolymer (A). R3 and R4 are each blocks of at least one of vinyl aromatic monomer units and conjugated diene monomer units, similar to R1 and R2 described in block copolymer (A). When the R3 block and R4 block are both blocks of vinyl aromatic monomer units and conjugated diene monomer units, these blocks may be either random blocks or tapered blocks. n is an integer of 1 or more, preferably an integer between 1 and 6, and more preferably an integer between 2 and 4. X is a residue of a polyfunctional coupling agent. Examples of polyfunctional coupling agents include silicon tetrachloride, epoxidized soybean oil, and organic carboxylic acid esters.

[0020] In the R3 block, the mass ratio of vinyl aromatic monomer units to conjugated diene monomer units is preferably 100:0 or more and 85:15 or less, more preferably 97.5:2.5 or more and 82.5:17.5 or less, and even more preferably 95:5 or more and 80:20 or less. In the R4 block, the mass ratio of vinyl aromatic monomer units to conjugated diene monomer units is preferably 15:85 or more and 0:100 or less (particularly 0:100), but depending on the properties of the target block copolymer (B) and block copolymer composition, it can be approximately 12.5:87.5 or more and 2.5:97.5 or less, and can also be approximately 10:90 or more and 5:95 or less. In each of the R3 block and the R4 block, the above effects can be further improved by adjusting the mass ratio of vinyl aromatic monomer units to conjugated diene monomer units. The block copolymer composition may contain one type of block copolymer (B) as described above, or it may contain two or more types.

[0021] Block copolymer (A) and block copolymer (B) (hereinafter, unless otherwise specified, they will be collectively referred to as "block copolymer") can be produced by polymerizing vinyl aromatic hydrocarbon monomers and conjugated diene monomers in a dehydrated organic solvent using an organolithium compound as an initiator, and optionally in the presence of a randomizing agent. As organic solvents, for example, aliphatic hydrocarbons such as butane, pentane, hexane, isopentane, heptane, octane, and isooctane; alicyclic hydrocarbons such as cyclohexane, methylcyclohexane, and ethylcyclohexane; and aromatic hydrocarbons such as benzene, toluene, ethylbenzene, and xylene can be used.

[0022] Organolithium compounds are compounds in which one or more lithium atoms are bonded to the molecule. Examples of such organolithium compounds include monofunctional organolithium compounds such as ethyllithium, n-propyllithium, n-butyllithium, sec-butyllithium, and tert-butyllithium, as well as polyfunctional organolithium compounds such as hexamethylenedisitium, butadienyldilinium, and isoprenyldilinium.

[0023] Tetrahydrofuran (THF) is primarily used as a randomizing agent. Other randomizing agents that can be used include, for example, ethers, amines, thioethers, phosphoramides, alkylbenzene sulfonates, and potassium or sodium alkoxides. Examples of ethers include dimethyl ether, diethyl ether, diphenyl ether, diethylene glycol dimethyl ether, and diethylene glycol dibutyl ether. Examples of amines include tertiary amines such as trimethylamine, triethylamine, and tetramethylethylenediamine, as well as macrocyclic amines. Other randomizing agents that can be used include triphenylphosphine, hexamethylphosphoramide, potassium or sodium alkylbenzene sulfonate, and potassium or sodium butoxide.

[0024] When using a randomizing agent, the amount added is preferably about 10 parts by mass or less, and more preferably 0.001 parts by mass or more and 8 parts by mass or less, per 100 parts by mass of total monomer added. The randomizing agent may be added before the start of the polymerization reaction or during the polymerization reaction. Additional additions may also be made as needed.

[0025] The block copolymer solution obtained in this way is inactivated by adding a polymerization inhibitor such as water, alcohol, or carbon dioxide. The amount of polymerization inhibitor added should be sufficient to deactivate the active ends. Methods for recovering the block copolymer from this solution include, for example, adding the solution to a poor solvent such as methanol to precipitate the block copolymer; evaporating the solvent using a heated roll or the like to precipitate the block copolymer (drum dryer method); concentrating the solution with a concentrator and then removing the solvent with a vented extruder; or dispersing the solution in water and removing the solvent by blowing in steam (steam stripping method).

[0026] When preparing a block copolymer composition by mixing block copolymer (A) and block copolymer (B), the mixing method can be one in which the desolvented block copolymer (A) and block copolymer (B) are melted and mixed together in an extruder, or one in which the solutions of the block copolymers before desolventing are solution-blended and then desolvented.

[0027] The content of block copolymer (A) in the block copolymer composition may be approximately 50 parts by mass or more and 80 parts by mass or less, but is preferably approximately 55 parts by mass or more and 75 parts by mass or less, and more preferably approximately 60 parts by mass or more and 70 parts by mass or less. On the other hand, the content of block copolymer (B) in the block copolymer composition may be approximately 20 parts by mass or more and 50 parts by mass or less, but is preferably approximately 25 parts by mass or more and 45 parts by mass or less, and more preferably approximately 30 parts by mass or more and 40 parts by mass or less. In this case, the resulting film can be given a good balance of excellent abrasion resistance and impact resistance.

[0028] The block copolymer composition preferably contains conjugated diene monomer units in an amount of approximately 19% to 30% by mass, more preferably 21% to 28% by mass, and even more preferably 23% to 26% by mass, based on 100% by mass of the total of vinyl aromatic monomer units and conjugated diene monomer units. By setting the content of conjugated diene monomer units above the lower limit, a decrease in the strength of the block copolymer composition is prevented, making film breakage less likely during film molding and providing favorable practical strength after packaging. Furthermore, by setting the content of conjugated diene monomer units below the upper limit, the rigidity of the block copolymer composition becomes appropriate, allowing for stable film molding. In addition, even when the film is thinned, it can be properly attached to the packaged object (e.g., the container body), which is also preferable.

[0029] The content of this conjugated diene monomer unit in the block copolymer composition is １ It can be measured using the 1H-NMR method. １ An example of the H-NMR method is to dissolve the block copolymer composition in a solvent such as deuterated chloroform, １ One method involves performing 1H-NMR measurements and calculating the content of conjugated diene monomer units from the obtained spectrum.

[0030] The block copolymer composition and the molecular weight of the block copolymer can be measured using gel permeation chromatography (GPC). In the molecular weight distribution of the obtained block copolymer composition, it is preferable to have at least one molecular weight peak originating from the block copolymer composed of vinyl aromatic monomer units and conjugated diene monomer units in each of the molecular weight ranges of 160,000 to 260,000 and 60,000 to 110,000, more preferably at least one of the above molecular weight peaks in each of the molecular weight ranges of 170,000 to 250,000 and 70,000 to 100,000, and even more preferably at least one of the above molecular weight peaks in each of the molecular weight ranges of 180,000 to 240,000 and 80,000 to 90,000.

[0031] In order to achieve a good balance of physical properties in the resulting film, it is preferable to use block copolymers with different conjugated diene monomer unit contents. In the molecular weight range of 160,000 to 260,000, it is preferable to use block copolymer (A) with a sufficiently low content of conjugated diene monomer units, and in the molecular weight range of 60,000 to 110,000, it is preferable to use block copolymer (B) with a higher content of conjugated diene monomer units than block copolymer (A). This makes it easier to impart superior abrasion resistance and impact resistance to the film.

[0032] Specifically, block copolymer (A) preferably has at least one molecular weight peak in its molecular weight distribution in the range of approximately 160,000 to 260,000 (particularly 170,000 to 250,000, or 180,000 to 240,000). On the other hand, block copolymer (B) preferably has at least one molecular weight peak in its molecular weight distribution in the range of approximately 60,000 to 110,000 (particularly 70,000 to 100,000, or 80,000 to 90,000). By using block copolymer (A) and block copolymer (B) having the above molecular weight peaks in combination, it is possible to more reliably impart excellent abrasion resistance and impact resistance to the resulting film.

[0033] Furthermore, when measuring the molecular weight distribution of block copolymer (A) alone and block copolymer (B) alone, and when measuring the molecular weight distribution of a block copolymer composition which is a mixture of block copolymer (A) and block copolymer (B), the position where the molecular weight peak is observed (peak top molecular weight) is considered to be basically the same. However, after coupling of block copolymer (B), for reasons that are not clear, the position of the molecular weight peak observed in the range of 60,000 to 110,000 molecular weights may shift by approximately +1,000 to +2,000 compared to the position of the molecular weight peak observed before coupling. In addition, after coupling of block copolymer (B), the position of the molecular weight peak of the double chain of block copolymer (B) may overlap with or be close to the position of the molecular weight peak of block copolymer (A), which may cause a slight shift in the position of the molecular weight peak observed in the range of 160,000 to 260,000 molecular weights.

[0034] A type A test specimen is prepared using the block copolymer composition in accordance with ISO 3167:1993. The flexural modulus of the type A test specimen, measured in accordance with ISO 178:2019, is preferably 1500 MPa to 2050 MPa, more preferably 1550 MPa to 2000 MPa, and even more preferably 1600 MPa to 1950 MPa. By setting the flexural modulus above the lower limit, the rigidity and elongation under high-speed deformation of the block copolymer composition are improved, enabling stable film formation. Furthermore, even when the film is thinned, it can be properly attached to the packaged object (e.g., the container body), which is preferable. By setting the flexural modulus below the upper limit, a decrease in the strength of the block copolymer composition is prevented, making film breakage less likely during film formation, which is also preferable in terms of practical strength after packaging.

[0035] While the block copolymer compositions described above are preferably used alone, their use is not particularly limited. For practical purposes, the block copolymer compositions may be used with at least one polymer selected from the group consisting of vinyl aromatic hydrocarbon polymers (a), copolymers of vinyl aromatic hydrocarbons and acrylic acid esters (b), and hydrogenated block copolymers of vinyl aromatic hydrocarbons and conjugated dienes (c), as long as their physical properties are not impaired. Examples of common vinyl aromatic hydrocarbon polymers (a) include polystyrene, poly-α-methylstyrene, and syndiotactic polystyrene.

[0036] Examples of acrylic acid esters used as monomers for copolymer (b) include methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, isoamyl acrylate, n-hexyl acrylate, (2-ethyl)hexyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, and (2-ethyl)hexyl acrylate. Examples of vinyl aromatic hydrocarbons used as monomers for copolymer (b) include styrene, o-methylstyrene, p-methylstyrene, p-tert-butylstyrene, 2,4-dimethylstyrene, 2,5-dimethylstyrene, α-methylstyrene, vinylnaphthalene, and vinylanthracene, with styrene being preferred among these.

[0037] Hydrogenated block copolymer (c) can be obtained by hydrogenating a block copolymer consisting of a vinyl aromatic hydrocarbon and a conjugated diene obtained by various polymerization methods, using at least one hydrogenation catalyst such as a titanocene compound or a reducing organometallic compound. By keeping the content of these polymers (a) to (c) in the block copolymer composition to about 30% by mass or less, deterioration of the strength, transparency, or both of the resulting film can be suitably prevented or reduced.

[0038] The block copolymer composition may contain fillers as needed. The effects obtained by adding fillers include, for example, increased strength, improved heat insulation, conductivity, insulation, reduced cost, coloring, and prevention of blocking. Depending on the purpose, inorganic fillers, organic fillers, or a combination of both can be used. One purpose of adding fillers in film applications is to prevent blocking.

[0039] Examples of fillers having anti-blocking properties include organic fillers such as high-impact polystyrene (HIPS), cross-linked beads of vinyl aromatic hydrocarbon-(meth)acrylic acid ester and / or (meth)acrylic acid copolymer, and cross-linked beads of vinyl aromatic hydrocarbon copolymer, as well as inorganic fillers such as silica beads and quartz beads. To obtain good transparency, it is preferable to use HIPS, cross-linked beads of vinyl aromatic hydrocarbon-(meth)acrylic acid ester and / or (meth)acrylic acid copolymer, and cross-linked beads of vinyl aromatic hydrocarbon copolymer. The blending ratio of such fillers is preferably about 10 parts by mass or less, more preferably about 0.05 parts by mass or more and 5 parts by mass or less, and even more preferably about 0.1 parts by mass or more and 3 parts by mass or less, per 100 parts by mass of the block copolymer composition.

[0040] Block copolymer compositions may contain various additives as needed. Examples of additives include plasticizers, antioxidants, weather resistant agents, lubricants, anti-blocking agents, antistatic agents, anti-fogging agents, and pigments.

[0041] Examples of antioxidants 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, and n-octadecyl-3-(4-hydroxy-3,5-di-tert-butylphenyl)propionate, and phosphorus-based antioxidants such as 2,2'-methylenebis(4,6-di-tert-butylphenyl)octylphosphite and tris(2,4-di-tert-butylphenyl)phosphite.

[0042] Examples of the weathering agent include benzotriazole-based ultraviolet absorbers such as 2-(2-hydroxy-3-tert-butyl-5-methylphenyl)-5-chlorobenzotriazole, and hindered amine type weathering agents such as tetrakis(2,2,6,6-tetramethyl-4-piperidyl)-1,2,3,4-butanetetracarboxylate. Further, as the weathering agent, white oil, silicone oil, etc. can be added.

[0043] Examples of the lubricant include fatty acids, fatty acid esters, fatty acid amides, glycerin fatty acid esters (glycerides), sorbitan fatty acid esters, pentaerythritol fatty acid esters, sucrose fatty acid esters, propylene glycol fatty acid esters, polyethylene wax, polyolefin wax such as polypropylene, paraffin wax, microcrystalline wax, petrolatum, etc.

[0044] As the antistatic agent, for example, surfactants such as nonionic surfactants, anionic surfactants, cationic surfactants, and amphoteric surfactants are mainly used. The antistatic agent may be kneaded into the block copolymer composition in advance and then used, or may be surface-coated after the block copolymer composition is formed into various films.

[0045] The heat-shrinkable film of the present embodiment can be obtained by stretching a film base material (sheet base material) extruded by, for example, a T-die method, a tubular method, etc. in a uniaxial or multiaxial direction using the block copolymer composition as described above. That is, the heat-shrinkable film of the present embodiment is a stretched film containing 50% by mass or more of a block copolymer composition containing at least one block copolymer having a vinyl aromatic monomer unit and a conjugated diene monomer unit. The stretched film only needs to be stretched in at least one axial direction, and may be uniaxially stretched or biaxially stretched.

[0046] Examples of uniaxial stretching include, for example, a method of stretching an extruded film substrate in a direction perpendicular to the extrusion direction with a tenter, a method of stretching an extruded film substrate in the same direction as the extrusion method, a method of stretching an extruded tubular film substrate in the circumferential direction, and a method of stretching an extruded tubular film substrate in the same direction as the extrusion direction. Examples of biaxial stretching include, for example, a method of stretching an extruded film substrate in the extrusion direction with a roll and then stretching it in a direction perpendicular to the extrusion direction with a tenter, a method of simultaneously biaxially stretching an extruded film substrate with a tenter, a method of simultaneously or separately stretching an extruded tubular film substrate in the extrusion direction and the circumferential direction, and the like.

[0047] The thermally shrinkable film can be obtained by using the block copolymer composition as described above alone or mainly in at least one layer. That is, the thermally shrinkable film includes a layer containing 50% by mass or more of the block copolymer composition. The layer structure of the film may be a single layer or a multilayer. It is preferable to use the block copolymer composition as described above mainly. Such a thermally shrinkable film is excellent in abrasion resistance and impact resistance. Here, when the thermally shrinkable film has a single-layer structure, the content of the block copolymer composition in the thermally shrinkable film may be about 50% by mass or more, but is preferably about 60% by mass or more, more preferably about 70% by mass or more, further preferably about 80% by mass or more, particularly preferably about 90% by mass or more, and may be 100% by mass. In this case, the abrasion resistance and impact resistance of the obtained thermally shrinkable film can be sufficiently enhanced.

[0048] The thickness of the heat-shrinkable film is not particularly limited. For example, in the case of shrink labels used for packaging PET bottles, considering general printing equipment, printing methods, and application methods, the thickness is preferably around 20 μm to 30 μm, for example, around 25 μm. It is preferable that the heat shrinkage rate of the heat-shrinkable film at 70°C for 10 seconds is 5% or more. Specifically, it is preferable that the heat shrinkage rate in the main shrinkage direction after immersing the heat-shrinkable film in 70°C hot water for 10 seconds is 5% or more. It is also preferable that the heat shrinkage rate in the main shrinkage direction after immersing the heat-shrinkable film in 100°C hot water for 10 seconds is 50% or more, and it is more preferable that it is 10% or more at 70°C and 60% or more at 100°C. With a heat-shrinkable film having such a heat shrinkage rate, application defects are less likely to occur regardless of the shape of the packaged object.

[0049] Furthermore, for similar reasons, it is preferable that the heat shrinkage rate of the heat shrinkable film at 90°C for 10 seconds (the heat shrinkage rate in the main shrinkage direction after immersing the heat shrinkable film in 90°C hot water for 10 seconds) be about 40% or more, more preferably about 50% or more, even more preferably about 60% or more, and particularly preferable about 70% or more. Moreover, it is preferable that the heat shrinkage rate of the heat shrinkable film at 80°C for 10 seconds (the heat shrinkage rate in the main shrinkage direction after immersing the heat shrinkable film in 80°C hot water for 10 seconds) be about 20% or more, more preferably about 30% or more, even more preferably about 40% or more, and particularly preferable about 50% or more.

[0050] In a tensile test of a heat-shrinkable film in accordance with ISO 527-3:2018, the Young's modulus when stretched at a tensile speed of 200 mm / min in a direction perpendicular to the stretch axis is preferably around 1100 MPa or higher, more preferably around 1200 MPa or higher, even more preferably around 1300 MPa or higher, and particularly preferably around 1400 MPa or higher. The upper limit of the Young's modulus is usually around 1900 MPa. Therefore, the Young's modulus can be, for example, between 1100 MPa and 1900 MPa. In general shrink packaging, a tubular heat-shrinkable film is placed over the container body, so the heat-shrinkable film is required to have sufficient rigidity to withstand the stress during placement. When using a thin film of heat-shrinkable film with a thickness of about 25 μm, setting the Young's modulus of the heat-shrinkable film within the above range makes it easier to prevent fitting defects such as the heat-shrinkable film bending when placed over the container.

[0051] In this case, the elongation at break of the heat-shrinkable film is preferably 100% or more, more preferably 150% or more, and even more preferably 200% or more. The upper limit of the elongation at break is usually around 250%. Therefore, the elongation at break can be, for example, between 100% and 250%. By setting the elongation at break of the heat-shrinkable film within the above range, it is possible to effectively prevent the heat-shrinkable film from breaking during use, for example, due to ink solvents during printing.

[0052] In impact tests of heat-shrinkable films in accordance with ASTM D3420, the impact strength is preferably around 28 kJ / m or more (0.7 J or more), more preferably around 32 kJ / m or more (0.8 J or more), even more preferably around 36 kJ / m or more (0.9 J or more), and particularly preferably around 40 kJ / m or more (1 J or more). The upper limit of the impact strength is usually around 52 kJ / m (1.3 J). Therefore, the impact strength can be, for example, around 28 kJ / m or more (0.7 J or more) and 52 kJ / m or less (1.3 J or less). A heat-shrinkable film having such an impact strength can be judged to have excellent impact resistance.

[0053] The natural shrinkage rate of the heat-shrinkable film is preferably about 2% or less, and more preferably about 1.6% or less, when the heat-shrinkable film is stored at 40°C for 7 days. In this case, for example, when the heat-shrinkable film is stored in a high-temperature environment without temperature control, it is less likely to develop appearance defects such as warping. Furthermore, the haze value (degree of cloudiness) of the heat-shrinkable film is preferably about 10% or less, more preferably about 8% or less, and even more preferably about 6% or less. In this case, the appearance of the heat-shrinkable film can be improved.

[0054] Heat-shrinkable film can be used in various packaging forms, such as heat-shrinkable labels, heat-shrinkable cap seals, and overpack films. The container of this embodiment comprises a container body and a heat-shrinkable film attached to the container body. The container body is not particularly limited and is, for example, a PET bottle. Furthermore, it may be provided in the following embodiments.

[0055] (1) A heat-shrinkable film comprising 50% by mass or more of a block copolymer composition containing at least one block copolymer having vinyl aromatic monomer units and conjugated diene monomer units, having a thickness of 20 μm or more and 30 μm or less, a heat shrinkage rate of 40% or more at 90°C for 10 seconds, a Young's modulus of 1100 MPa or more and elongation at break of 100% or more when stretched at a tensile speed of 200 mm / min in a direction perpendicular to the stretch axis in a tensile test in accordance with ISO 527-3:2018, and an impact strength of 0.7 J or more in an impact test in accordance with ASTM D3420.

[0056] (2) A heat-shrinkable film as described in (1) above, wherein the molecular weight distribution of the block copolymer composition has at least one molecular weight peak derived from the block copolymer consisting of vinyl aromatic monomer units and conjugated diene monomer units in each of the ranges of 160,000 to 260,000 and 60,000 to 110,000.

[0057] (3) A heat-shrinkable film according to (1) or (2) above, wherein the block copolymer composition contains the conjugated diene monomer units in an amount of 19% by mass or more and 30% by mass or less based on 100% by mass of the total of the vinyl aromatic monomer units and the conjugated diene monomer units.

[0058] (4) In the heat-shrinkable film described in any one of (1) to (3) above, the block copolymer composition contains 50 parts by mass or more and 80 parts by mass or less of block copolymer (A) and 20 parts by mass or more and 50 parts by mass or less of block copolymer (B), wherein the block copolymer (A) has vinyl aromatic monomer units and conjugated diene monomer units, and the conjugated diene monomer units are contained in an amount of more than 15% by mass and 25% by mass or less based on 100% by mass of the block copolymer (A), and the content of the conjugated diene monomer units is 85% by mass or more and 100% by mass or less of block copolymer (A) A heat-shrinkable film comprising: 7% to 20% by mass of the block copolymer (A) relative to 100% by mass of the block copolymer (B); the block copolymer (B) having vinyl aromatic monomer units, conjugated diene monomer units, and residues of a polyfunctional coupling agent; the conjugated diene monomer units comprising 26% to 50% by mass of the block copolymer (B) relative to 100% by mass of the block copolymer (B); and blocks with a content of 85% to 100% by mass of the conjugated diene monomer units comprising 20% ​​to 45% by mass of the block copolymer (B) relative to 100% by mass of the block copolymer (B).

[0059] (5) A heat-shrinkable film as described in (4) above, wherein the block copolymer (A) is represented by the general formula: S1-R1-R2-S2 (wherein S1 and S2 are blocks of vinyl aromatic monomer units, and R1 and R2 are blocks of at least one of vinyl aromatic monomer units and conjugated diene monomer units), and in the R1 block, the mass ratio of the vinyl aromatic monomer units to the conjugated diene monomer units is 100:0 or more and 85:15 or less, and in the R2 block, the mass ratio of the vinyl aromatic monomer units to the conjugated diene monomer units is 15:85 or more and 0:100 or less, a heat-shrinkable film.

[0060] (6) A heat-shrinkable film according to (4) or (5) above, wherein the block copolymer (B) is represented by the general formula: (S3-R3-R4-S4)nX (wherein S3 and S4 are each blocks of the vinyl aromatic monomer unit, R3 and R4 are each blocks of at least one of the vinyl aromatic monomer unit and the conjugated diene monomer unit, n is an integer of 1 or more, and X is a residue of the polyfunctional coupling agent), wherein in the R3 block, the mass ratio of the vinyl aromatic monomer unit to the conjugated diene monomer unit is 100:0 or more and 85:15 or less, and in the R4 block, the mass ratio of the vinyl aromatic monomer unit to the conjugated diene monomer unit is 15:85 or more and 0:100 or less, a heat-shrinkable film.

[0061] (7) A container comprising a container body and a heat-shrinkable film described in any one of (1) to (6) above attached to the container body. Of course, this is not limited to this.

[0062] Finally, while various embodiments relating to this disclosure have been described, these are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be implemented in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents.

[0063] The block copolymer compositions and heat-shrinkable films will be described in more detail below based on the examples, but are not limited to these examples.

[0064] 1. Production of Block Copolymer (A) 1-1. Production of Block Copolymer (A1) (1) 467 kg of cyclohexane and 84 g of tetrahydrofuran (THF) were charged into the reaction vessel. (2) While stirring at an internal temperature of 30°C, 1250 mL of n-butyllithium (10% by mass cyclohexane solution) was added, and 8.0 kg of styrene monomer was added and the temperature was raised to complete the polymerization. (3) While maintaining the internal temperature at 80°C, a total of 106.0 kg of styrene monomer and a total of 12.0 kg of butadiene monomer were added simultaneously at constant addition rates of 144.5 kg / h and 16.4 kg / h, respectively, and this state was maintained for a sufficient time after the addition was completed. (4) The internal temperature was raised to 60°C, and 24 kg of butadiene monomer was added and polymerization was carried out. (5) The internal temperature was raised to 55°C, and 50 kg of styrene monomer was added to complete the polymerization. (6) This polymerization solution was pre-concentrated and then defoliated and extruded using a twin-screw extruder with a vacuum vent to obtain the target pellet-shaped block copolymer (A1).

[0065] 1-2. Production of Block Copolymer (A2) (1) 467 kg of cyclohexane and 84 g of tetrahydrofuran (THF) were charged into the reaction vessel. (2) While stirring at an internal temperature of 30°C, 1540 mL of n-butyllithium (10% by mass cyclohexane solution) was added, and 8.0 kg of styrene monomer was added and the temperature was raised to complete the polymerization. (3) While maintaining the internal temperature at 80°C, a total of 106.0 kg of styrene monomer and a total of 12.0 kg of butadiene monomer were added simultaneously at constant addition rates of 144.5 kg / h and 16.4 kg / h, respectively, and this state was maintained for a sufficient time after the addition was completed. (4) The internal temperature was raised to 60°C, and 24 kg of butadiene monomer was added and polymerization was carried out. (5) The internal temperature was raised to 55°C, and 50 kg of styrene monomer was added to complete the polymerization. (6) This polymerization solution was pre-concentrated and then defoliated and extruded using a twin-screw extruder with a vacuum vent to obtain the desired pelletized block copolymer (A2).

[0066] 1-3. Production of Block Copolymer (A3) (1) 467 kg of cyclohexane and 84 g of tetrahydrofuran (THF) were charged into the reaction vessel. (2) While stirring at an internal temperature of 30°C, 1000 mL of n-butyllithium (10% by mass cyclohexane solution) was added, and 8.0 kg of styrene monomer was added and the temperature was raised to complete the polymerization. (3) While maintaining the internal temperature at 80°C, a total of 106.0 kg of styrene monomer and a total of 12.0 kg of butadiene monomer were added simultaneously at constant addition rates of 144.5 kg / h and 16.4 kg / h, respectively, and this state was maintained for a sufficient time after the addition was completed. (4) The internal temperature was raised to 60°C, and 24 kg of butadiene monomer was added and polymerization was carried out. (5) The internal temperature was raised to 55°C, and 50 kg of styrene monomer was added to complete the polymerization. (6) This polymerization solution was pre-concentrated and then defoliated and extruded using a twin-screw extruder with a vacuum vent to obtain the desired pelletized block copolymer (A3).

[0067] 1-4. Production of Block Copolymer (A4) (1) 467 kg of cyclohexane and 84 g of tetrahydrofuran (THF) were charged into the reaction vessel. (2) While stirring at an internal temperature of 30°C, 1660 mL of n-butyllithium (10% by mass cyclohexane solution) was added, and 8.0 kg of styrene monomer was added and the temperature was raised to complete the polymerization. (3) While maintaining the internal temperature at 80°C, a total of 106.0 kg of styrene monomer and a total of 12.0 kg of butadiene monomer were added simultaneously at constant addition rates of 144.5 kg / h and 16.4 kg / h, respectively, and this state was maintained for a sufficient time after the addition was completed. (4) The internal temperature was raised to 60°C, and 24 kg of butadiene monomer was added and polymerization was carried out. (5) The internal temperature was raised to 55°C, and 50 kg of styrene monomer was added to complete the polymerization. (6) This polymerization solution was pre-concentrated and then defoliated and extruded using a twin-screw extruder with a vacuum vent to obtain the desired pelletized block copolymer (A4).

[0068] 1-5. Production of Block Copolymer (A5) (1) 467 kg of cyclohexane and 84 g of tetrahydrofuran (THF) were charged into the reaction vessel. (2) While stirring at an internal temperature of 30°C, 900 mL of n-butyllithium (10% by mass cyclohexane solution) was added, and 8.0 kg of styrene monomer was added and the temperature was raised to complete the polymerization. (3) While maintaining the internal temperature at 80°C, a total of 106.0 kg of styrene monomer and a total of 12.0 kg of butadiene monomer were added simultaneously at constant addition rates of 144.5 kg / h and 16.4 kg / h, respectively, and this state was maintained for a sufficient time after the addition was completed. (4) The internal temperature was raised to 60°C, and 24 kg of butadiene monomer was added and polymerization was carried out. (5) The internal temperature was raised to 55°C, and 50 kg of styrene monomer was added to complete the polymerization. (6) This polymerization solution was pre-concentrated and then defoliated and extruded using a twin-screw extruder with a vacuum vent to obtain the desired pelletized block copolymer (A5).

[0069] 2. Production of Block Copolymer (B) 2-1. Production of Block Copolymer (B1) (1) 467 kg of cyclohexane and 84 g of tetrahydrofuran (THF) were charged into the reaction vessel. (2) While stirring at an internal temperature of 30°C, 3370 mL of n-butyllithium (10% by mass cyclohexane solution) was added, and 50.0 kg of styrene monomer was added and the temperature was raised to carry out polymerization. (3) While maintaining the internal temperature at 80°C, a total of 69.4 kg of styrene monomer and a total of 6.6 kg of butadiene monomer were added simultaneously at constant addition rates of 148.7 kg / h and 14.1 kg / h, respectively, and this state was maintained for a sufficient time after the addition was completed. (4) The internal temperature was raised to 40°C, and 70.0 kg of butadiene monomer was added and polymerization was carried out. (5) The internal temperature was raised to 75°C, and 4.0 kg of styrene monomer was added and polymerization was carried out. (6) The internal temperature was set to 75°C, and 343 g of epoxidized soybean oil (ADEKA Corporation, "ADEKA Sizer O-130P") was added. The mixture was then stirred at 75°C for 10 minutes to complete the polymerization. (7) This polymerization solution was pre-concentrated and then devolatilized and extruded using a twin-screw extruder with a vacuum vent to obtain the desired pelletized block copolymer (B1).

[0070] 2-2. Production of Block Copolymer (B2) (1) 467 kg of cyclohexane and 84 g of tetrahydrofuran (THF) were charged into the reaction vessel. (2) While stirring at an internal temperature of 30°C, 4460 mL of n-butyllithium (10% by mass cyclohexane solution) was added, and 50.0 kg of styrene monomer was added and the temperature was raised to carry out polymerization. (3) While maintaining the internal temperature at 80°C, a total of 69.4 kg of styrene monomer and a total of 6.6 kg of butadiene monomer were added simultaneously at constant addition rates of 148.7 kg / h and 14.1 kg / h, respectively, and this state was maintained for a sufficient time after the addition was completed. (4) The internal temperature was raised to 40°C, and 70.0 kg of butadiene monomer was added and polymerization was carried out. (5) The internal temperature was raised to 75°C, and 4.0 kg of styrene monomer was added and polymerization was carried out. (6) The internal temperature was set to 75°C, and 454 g of epoxidized soybean oil (ADEKA Corporation, "ADEKA Sizer O-130P") was added. The mixture was then stirred at 75°C for 10 minutes to complete the polymerization. (7) This polymerization solution was pre-concentrated and then devolatilized and extruded using a twin-screw extruder with a vacuum vent to obtain the desired pelletized block copolymer (B2).

[0071] 2-3. Production of Block Copolymer (B3) (1) 467 kg of cyclohexane and 84 g of tetrahydrofuran (THF) were charged into the reaction vessel. (2) While stirring at an internal temperature of 30°C, 2610 mL of n-butyllithium (10% by mass cyclohexane solution) was added, and 50.0 kg of styrene monomer was added and the temperature was raised to carry out polymerization. (3) While maintaining the internal temperature at 80°C, a total of 69.4 kg of styrene monomer and a total of 6.6 kg of butadiene monomer were added simultaneously at constant addition rates of 148.7 kg / h and 14.1 kg / h, respectively, and this state was maintained for a sufficient time after the addition was completed. (4) The internal temperature was raised to 40°C, and 70.0 kg of butadiene monomer was added and polymerization was carried out. (5) The internal temperature was raised to 75°C, and 4.0 kg of styrene monomer was added and polymerization was carried out. (6) The internal temperature was set to 75°C, and 266 g of epoxidized soybean oil (ADEKA Corporation, "ADEKA Sizer O-130P") was added. The mixture was then stirred at 75°C for 10 minutes to complete the polymerization. (7) This polymerization solution was pre-concentrated and then devolatilized and extruded using a twin-screw extruder with a vacuum vent to obtain the desired pelletized block copolymer (B3).

[0072] 2-4. Production of Block Copolymer (B4) (1) 467 kg of cyclohexane and 84 g of tetrahydrofuran (THF) were charged into the reaction vessel. (2) While stirring at an internal temperature of 30°C, 4940 mL of n-butyllithium (10% by mass cyclohexane solution) was added, and 50.0 kg of styrene monomer was added and the temperature was raised to carry out polymerization. (3) While maintaining the internal temperature at 80°C, a total of 69.4 kg of styrene monomer and a total of 6.6 kg of butadiene monomer were added simultaneously at constant addition rates of 148.7 kg / h and 14.1 kg / h, respectively, and this state was maintained for a sufficient time after the completion of addition. (4) The internal temperature was raised to 40°C, and 70.0 kg of butadiene monomer was added and polymerization was carried out. (5) The internal temperature was raised to 75°C, and 4.0 kg of styrene monomer was added and polymerization was carried out. (6) The internal temperature was set to 75°C, and 503 g of epoxidized soybean oil (ADEKA Corporation, "ADEKA Sizer O-130P") was added. The mixture was then stirred at 75°C for 10 minutes to complete the polymerization. (7) This polymerization solution was pre-concentrated and then devolatilized and extruded using a twin-screw extruder with a vacuum vent to obtain the desired pelletized block copolymer (B4).

[0073] 2-5. Production of Block Copolymer (B5) (1) 467 kg of cyclohexane and 84 g of tetrahydrofuran (THF) were charged into the reaction vessel. (2) While stirring at an internal temperature of 30°C, 2300 mL of n-butyllithium (10% by mass cyclohexane solution) was added, and 50.0 kg of styrene monomer was added and the temperature was raised to carry out polymerization. (3) While maintaining the internal temperature at 80°C, a total of 69.4 kg of styrene monomer and a total of 6.6 kg of butadiene monomer were added simultaneously at constant addition rates of 148.7 kg / h and 14.1 kg / h, respectively, and this state was maintained for a sufficient time after the completion of addition. (4) The internal temperature was raised to 40°C, and 70.0 kg of butadiene monomer was added and polymerization was carried out. (5) The internal temperature was raised to 75°C, and 4.0 kg of styrene monomer was added and polymerization was carried out. (6) The internal temperature was set to 75°C, and 235 g of epoxidized soybean oil (ADEKA Corporation, "ADEKA Sizer O-130P") was added. The mixture was then stirred at 75°C for 10 minutes to complete the polymerization. (7) This polymerization solution was pre-concentrated and then devolatilized and extruded using a twin-screw extruder with a vacuum vent to obtain the desired pelletized block copolymer (B5).

[0074] 3. Preparation of Block Copolymer Compositions 3-1. Preparation of Block Copolymer Composition (R11) 50.0 parts by mass of block copolymer (A1) and 50.0 parts by mass of block copolymer (B1) were thoroughly pelletized (dry blended), and then melt-mixed at a melting temperature of 200°C using a single-screw extruder (manufactured by Tabata Machinery Industry Co., Ltd., screw diameter: 40 mm, dalmaged type). This obtained block copolymer composition (R11). 3-2. Preparation of Block Copolymer Compositions (R12) to (R15) and (R21) to (R24) Block copolymer compositions (R12) to (R15) and (R21) to (R24) were prepared in the same manner as block copolymer composition (R11) by appropriately changing the type and / or amount of block copolymer.

[0075] 4. Preparation of Heat Shrinkable Film (Example 1) A block copolymer composition (R11) was extruded using a T-die type single-screw extruder (manufactured by Tanabe Plastic Machinery Co., Ltd., screw diameter: 65 mm, Dalmeage type) while melting at 200°C to produce a film substrate with an average thickness of approximately 0.14 mm. Subsequently, the film substrate was stretched 1.2 times in the flow direction (hereinafter also referred to as "MD") while heating to the stretching temperature. Furthermore, it was stretched 4.5 times in a direction perpendicular to the flow direction (hereinafter also referred to as "TD") using a tenter stretcher while heating at the stretching temperature (preheating / stretching / fixing = 110°C / 85°C / 70°C) to obtain a heat shrinkable film with an average thickness of 25 μm.

[0076] (Examples 2-5) Heat-shrinkable films were prepared in the same manner as in Example 1, except that block copolymer compositions (R12) to (R15) were used instead of block copolymer composition (R11). (Examples 6 and 7) Heat-shrinkable films were prepared in the same manner as in Example 1, except that a film substrate was prepared using a mixture of block copolymer composition (R12) and general-purpose polystyrene (GPPS) (manufactured by Toyo Styrene Co., Ltd., "G200C"), and the TD stretching temperature was changed.

[0077] (Example 8) A heat-shrinkable film was prepared in the same manner as in Example 1, except that a three-layer film substrate was prepared. The film substrate had a central layer, a surface layer provided on the surface side of the central layer, and a back layer provided on the back side of the central layer. The layer ratio of surface layer / central layer / back layer was 1 / 6 / 1 by volume. The central layer was composed of a block copolymer composition (R12), and the surface layer and back layer were composed of styrene-butadiene copolymer (SBC) (manufactured by Denka Co., Ltd., "440L"), respectively. (Example 9) A heat-shrinkable film was prepared in the same manner as in Example 8, except that glycol-modified polyethylene terephthalate (PETG) (manufactured by Eastman Chemical Company, "GN001") was used instead of styrene-butadiene copolymer (SBC), and the TD stretching temperature was changed.

[0078] (Comparative Examples 1-4) Heat-shrinkable films were prepared in the same manner as in Example 1, except that block copolymer compositions (R21) to (R24) were used instead of block copolymer composition (R11). When block copolymer composition (R24) was used, it was not possible to prepare a film substrate. (Comparative Example 5) A heat-shrinkable film was prepared in the same manner as in Example 1, except that a film substrate was prepared using a mixture of block copolymer composition (R12) and GPPS, and the TD stretching temperature was changed.

[0079] 5. Measurement and Evaluation 5-1. Measurement of the content of conjugated diene monomer units The content of conjugated diene monomer units in block copolymers and block copolymer compositions is: １ The peak area was determined by calculation using 1H-NMR measurements and the peak area derived from vinyl aromatic monomer units and conjugated diene monomer units. The measurement device used was the AVANCE-III manufactured by BRUKER.

[0080] 5-2. Measurement of the content of conjugated diene monomer units in blocks R1 to R4 The content of conjugated diene monomer units in blocks R1 to R4 was calculated from the amount of monomer used when producing each block copolymer.

[0081] 5-3. Measurement of Molecular Weight The molecular weight of the block copolymer and block copolymer composition was measured using the following GPC measuring instrument and under the following conditions. Instrument name: High-speed GPC instrument HLC-8220 (manufactured by Tosoh Corporation) Column: Three PL gel MIXED-B columns in series Temperature: 40°C Detection: Differential refractive index Solvent: Tetrahydrofuran Concentration: 2% by mass Calibration curve: Prepared using standard polystyrene (manufactured by PL Co., Ltd.), and the molecular weight of the peaks observed in the range of 160,000 to 260,000 and the range of 60,000 to 110,000 in polystyrene equivalent values ​​was measured. When producing block copolymer (B) having coupling agent residues, a small amount of polymer liquid was withdrawn from the reaction vessel before step (6) above, and the molecular weight of that polymer was also measured.

[0082] 5-4. Measurement of flexural modulus Using the block copolymer compositions of each example and comparative example, Type A test specimens were prepared in accordance with ISO 3167:1993. The flexural modulus of these Type A test specimens was then measured in accordance with ISO 178:2019.

[0083] 5-5. Measurement of Heat Shrinkage The heat shrinkage rate was measured by the following method: (1) A test piece with an MD width of 100 mm and a TD width of 100 mm was cut from the heat-shrinkable film. (2) This test piece was completely immersed in 100°C hot water, 90°C hot water, 80°C hot water, or 70°C hot water for 10 seconds, then removed, thoroughly wiped dry, and the length L (mm) of TD was measured. (3) The heat shrinkage rate was calculated using the following formula: Heat shrinkage rate (%) = {(100.0 - L) / 100.0} × 100

[0084] 5-6. Tensile Test In accordance with ISO 527-3:2018, the heat-shrinkable film was stretched at a tensile speed of 200 mm / min in a direction perpendicular to the stretch axis. The Young's modulus (MPa) and elongation at break (%) were then measured.

[0085] 5-7. JSPS Abrasion Test A test specimen (MD: 200 mm × TD: 25 mm) was cut from a heat-shrinkable film, and a JSPS-type abrasion test was performed. Specifically, the test specimen was fixed to a specimen holder, and a friction element with a piece of cardboard or a heat-shrinkable film corresponding to the test specimen attached to its tip was moved back and forth under the conditions of a load of 500 gf, 1000 reciprocations, and a reciprocating speed of 30 reciprocations / minute. The number of reciprocations at which the test specimen broke was then checked and evaluated according to the following criteria. Other test conditions conformed to JIS P8136:1994. ○ (Good): The test specimen did not break even after 500 reciprocations. × (Poor): The test specimen broke by the 500th reciprocation.

[0086] 5-8. Measurement of Impact Strength A test specimen (100 mm x 100 mm) was cut from a heat-shrinkable film, and an impact strength test was performed. Specifically, the test specimen was fixed to the specimen stand of an impact tester (manufactured by Tester Sangyo Co., Ltd.), and the measurement was performed in accordance with ASTM D3420 using a triangular pyramidal impactor. The energy at which the test specimen was fractured was measured, and the value of that energy (J) divided by the thickness of the film was converted to (kJ / m). The size of the opening (inner diameter) of the specimen stand was 60 mm. The mass of the impactor was 13 g, and the sides of the impactor (isosceles triangle) were between 1.5 cm and 2.0 cm, and the base was between 2.5 cm and 3.0 cm. These results are shown in Tables 1 to 5 below.

[0087]

[0088]

[0089]

[0090]

[0091]

[0092] The results in Tables 4 and 5 show that the heat-shrinkable films of each example exhibit excellent abrasion resistance and impact resistance. In contrast, the heat-shrinkable films of each comparative example are inferior in either abrasion resistance or impact resistance, or both. Therefore, the heat-shrinkable films of each example can be made into thin films of 25 μm and are suitable for packaging various containers.

Claims

1. A heat-shrinkable film comprising 50% by mass or more of a block copolymer composition containing at least one block copolymer having vinyl aromatic monomer units and conjugated diene monomer units, having a thickness of 20 μm or more and 30 μm or less, a heat shrinkage rate of 40% or more at 90°C for 10 seconds, a Young's modulus of 1100 MPa or more and elongation at break of 100% or more when stretched at a tensile speed of 200 mm / min in a direction perpendicular to the stretch axis in a tensile test in accordance with ISO 527-3:2018, and an impact strength of 0.7 J or more in an impact test in accordance with ASTM D3420.

2. A heat-shrinkable film according to claim 1, wherein the molecular weight distribution of the block copolymer composition has at least one molecular weight peak derived from the block copolymer composed of vinyl aromatic monomer units and conjugated diene monomer units in each of the molecular weight ranges of 160,000 to 260,000 and 60,000 to 110,000.

3. A heat-shrinkable film according to claim 1, wherein the block copolymer composition contains the conjugated diene monomer units in an amount of 19% by mass or more and 30% by mass or less based on 100% by mass of the total of the vinyl aromatic monomer units and the conjugated diene monomer units.

4. In the heat-shrinkable film according to claim 1, the block copolymer composition contains 50 parts by mass or more and 80 parts by mass of block copolymer (A) and 20 parts by mass or more and 50 parts by mass of block copolymer (B), wherein the block copolymer (A) has vinyl aromatic monomer units and conjugated diene monomer units, the conjugated diene monomer units are contained in an amount of more than 15% by mass and 25% by mass or less based on 100% by mass of block copolymer (A), blocks with a content of 85% by mass or more and 100% by mass or less of conjugated diene monomer units are contained in an amount of 7% by mass or more and 20% by mass or less based on 100% by mass of block copolymer (A), the block copolymer (B) has vinyl aromatic monomer units, conjugated diene monomer units and residues of a polyfunctional coupling agent, the conjugated diene monomer units are contained in an amount of 26% by mass or more and 50% by mass or less based on 100% by mass of block copolymer (B), A heat-shrinkable film comprising blocks containing the conjugated diene monomer units in an amount of 85% by mass or more and 100% by mass or less, in an amount of 20% by mass or more and 45% by mass or less relative to 100% by mass of the block copolymer (B).

5. A heat-shrinkable film according to claim 4, wherein the block copolymer (A) is represented by the general formula: S1-R1-R2-S2 (wherein S1 and S2 are blocks of vinyl aromatic monomer units, and R1 and R2 are blocks of at least one of vinyl aromatic monomer units and conjugated diene monomer units), the mass ratio of the vinyl aromatic monomer units to the conjugated diene monomer units in the R1 block is 100:0 or more and 85:15 or less, and the mass ratio of the vinyl aromatic monomer units to the conjugated diene monomer units in the R2 block is 15:85 or more and 0:100 or less.

6. A heat-shrinkable film according to claim 4, wherein the block copolymer (B) is represented by the general formula: (S3-R3-R4-S4)nX (wherein S3 and S4 are each blocks of the vinyl aromatic monomer unit, R3 and R4 are each blocks of at least one of the vinyl aromatic monomer unit and the conjugated diene monomer unit, n is an integer of 1 or more, and X is a residue of the polyfunctional coupling agent), the mass ratio of the vinyl aromatic monomer unit to the conjugated diene monomer unit in the R3 block is 100:0 or more and 85:15 or less, and the mass ratio of the vinyl aromatic monomer unit to the conjugated diene monomer unit in the R4 block is 15:85 or more and 0:100 or less, a heat-shrinkable film.

7. A container comprising a container body and a heat-shrinkable film according to any one of claims 1 to 6 attached to the container body.

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