Pellet, film, and method for producing pellet

Abstract

Provided is a pellet which is composed of a block copolymer composition, reduces occurrence of fish eyes when molded into a film, and is excellent in tensile elongation.　According to the present invention, there is provided a pellet composed of a block copolymer composition, the block copolymer composition containing 95% by mass or more of a linear block copolymer mainly composed of a vinyl aromatic monomer unit and a conjugated diene monomer unit, wherein: the content ratio of the conjugated diene monomer unit is 12%-27% by mass when the total of the vinyl aromatic monomer unit and the conjugated diene monomer unit in the block copolymer composition is taken as 100% by mass; and when a peak with the highest peak top molecular weight among peaks each having an area ratio of 20% or more with respect to the total peak area in a polystyrene-equivalent molecular weight pattern obtained by measuring the block copolymer composition through gel permeation chromatography is defined as a main peak, the peak top molecular weight of the main peak is 150,000 to 300,000, and the total area of peak portions included in the range corresponding to the molecular weight of 1.8 times to 2.2 times the peak top molecular weight of the main peak is less than 5% of the area of the main peak.

Description

Pellets, films, and methods for producing pellets

[0001] The present invention relates to pellets, films, and methods for producing pellets.

[0002] Styrene-butadiene block copolymer compositions are widely used in shrink film applications due to their excellent shrink properties.

[0003] JP 11-158241

[0004] In addition to a good heat shrinkage rate, the properties required for shrink film include high tensile elongation and few foreign matter (fish eyes). Fish eyes are mainly caused by gel-like foreign matter due to structural units derived from butadiene, and generally, the lower the butadiene percentage, the less likely fish eyes tend to occur. Also, if the molecular weight is too high, gelation easily occurs, making fish eyes more likely to occur. However, if the butadiene percentage or molecular weight is too low, the tensile elongation decreases.

[0005] The present invention has been made in view of the above circumstances, and provides pellets composed of a block copolymer composition, which have little fisheyes when formed into a film and have excellent tensile elongation.

[0006] As a result of intensive investigations to solve the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by containing a specific linear block copolymer in a predetermined amount or more and by satisfying specific conditions for the molecular weight and the peak area as measured by GPC, and have thus completed the present invention.

[0007] The following inventions are provided: [1] Pellets composed of a block copolymer composition, the block copolymer composition comprising 95% by mass or more of a linear block copolymer primarily composed of vinyl aromatic monomer units and conjugated diene monomer units, the content of the conjugated diene monomer units being 12 to 27% by mass when the total of the vinyl aromatic monomer units and the conjugated diene monomer units in the block copolymer composition is taken as 100% by mass, the polystyrene-equivalent molecular weight of the block copolymer composition is measured by gel permeation chromatography, and when the highest peak-top molecular weight among peaks having an area ratio of 20% or more to the total peak area is defined as a main peak, the peak-top molecular weight of the main peak is 150,000 to 300,000, and the total area of ​​peak portions falling within a range corresponding to a molecular weight 1.8 to 2.2 times the peak-top molecular weight of the main peak is less than 5% of the area of ​​the main peak. [2] The block copolymer composition is the pellet according to [1], comprising two or more types of the linear block copolymers. [3] The method for producing pellets according to [1] or [2], comprising a polymerization step and a pelletizing step, wherein in the polymerization step, a monomer raw material containing a vinyl aromatic monomer and a conjugated diene monomer is polymerized to obtain a polymerization solution containing the linear block copolymer, and in the pelletizing step, the polymerization solution is pelletized by a devolatilizing extrusion method, and when the resin temperature at the outlet of the extruder in the pelletizing step is T (°C), T satisfies the formula (1). (1) T≦−0.0129×B ２ -0.35 x B + 257 (B: content (mass%) of the conjugated diene monomer units when the total of the vinyl aromatic monomer units and the conjugated diene monomer units in the block copolymer composition is 100 mass%). [4] A film which is a molded product of a raw material containing the pellets according to [1] or [2].

[0008] Hereinafter, embodiments of the present invention will be described. Various features shown in the following embodiments can be combined with each other. Furthermore, each feature can be an invention independently. Furthermore, in the following embodiments, elements not specified in the claims are optional elements and can be omitted. Any number of "0"s (for example, one or two) may be added to the end of numerical values ​​disclosed in the following description. For example, one or two "0"s may be added after "1.4" to make it "1.40" or "1.400".

[0009] 1. Pellets Pellets according to one embodiment of the present invention are pellets made of a block copolymer composition. The pellets can be used as a raw material (or a part of a raw material) for films such as heat-shrinkable films, sheets, and various other molded products.

[0010] <Block Copolymer Composition> The block copolymer composition contains 95% by mass or more, preferably 98 to 100% by mass, and more preferably (substantially) 100% by mass of a linear block copolymer A mainly composed of vinyl aromatic monomer units and conjugated diene monomer units. Specific examples of the content of the linear block copolymer A include 95, 96, 97, 98, 99, and 100% by mass, and may be within a range between any two of the values ​​exemplified here. Furthermore, the block copolymer composition contains 95% by mass or more, preferably 98 to 100% by mass, and more preferably (substantially) 100% by mass of the linear block copolymer A relative to 100% by mass of the total polymers contained in the composition.

[0011] The linear block copolymer A contains, when the total of the monomer units (structural units) contained in the linear block copolymer A is taken as 100% by mass, vinyl aromatic monomer units and conjugated diene monomer units in a total amount of, for example, 98% by mass or more, and preferably (substantially) 100% by mass.

[0012] The linear block copolymer A is a copolymer having a block structure, in which the block structure is formed in a linear chain. A block copolymer having vinyl aromatic monomer units and conjugated diene monomer units can be obtained, for example, by a living anionic polymerization reaction in an organic solvent using an organolithium compound or the like as a polymerization initiator. In living anionic polymerization, almost all of the vinyl aromatic monomers and conjugated diene monomers used in the polymerization reaction can be converted into polymers, so that block copolymers with any primary structure can be obtained by changing the amounts and order of addition of these monomers.

[0013] The linear block copolymer A has two or more blocks selected from the group consisting of a vinyl aromatic block (S), a conjugated diene block (B), and a copolymer block (S / B).

[0014] The linear block copolymer A has, for example, the following block structures: (S)-(S / B)-(S / B) (S)-(S / B) (S)-(S / B)-(S) (S)-(S / B)-(B)-(S) (S)-(B)-(S)

[0015] The vinyl aromatic block (S) contains more than 98% by mass of vinyl aromatic monomer units, more preferably 99% by mass or more, and preferably 100% by mass, of the total mass of the monomer units contained in the block taken as 100% by mass. The vinyl aromatic block (S) may be composed essentially of vinyl aromatic monomer units alone.

[0016] The conjugated diene block (B) contains conjugated diene monomer units in an amount of more than 98% by mass, more preferably 99% by mass or more, and preferably 100% by mass, where the total mass of the monomer units contained in the block is taken as 100% by mass. The conjugated diene block (B) may be composed substantially of conjugated diene monomer units alone.

[0017] The copolymer block (S / B) is a block containing vinyl aromatic monomer units and conjugated diene monomer units. The copolymer block (S / B) contains 2 to 98% by mass, preferably 5 to 80% by mass, and more preferably 7 to 60% by mass, of conjugated diene monomer units, assuming that the total mass of the monomer units contained in the block is 100% by mass. The copolymer block (S / B) may be a tapered type in which the composition of the vinyl aromatic monomer units and the conjugated diene monomer units changes continuously, or a random type in which the composition of the vinyl aromatic monomer units and the conjugated diene monomer units is approximately constant.

[0018] The vinyl aromatic monomer unit is a unit derived from the vinyl aromatic monomer used in the polymerization of the linear block copolymer A. The vinyl aromatic monomer is a monomer in which a vinyl group is bonded to an aromatic ring. Examples of the vinyl aromatic monomer include vinyl aromatic monomers such as styrene, o-methylstyrene, p-methylstyrene, p-tert-butylstyrene, 2,4-dimethylstyrene, 2,5-dimethylstyrene, α-methylstyrene, vinylnaphthalene, and vinylanthracene. The vinyl aromatic monomer is preferably styrene. These monomers may be used alone or in combination of two or more.

[0019] The conjugated diene monomer units are units derived from the conjugated diene monomer used in the polymerization of the linear block copolymer A. The conjugated diene monomer is a monomer having a conjugated chemical structure represented by C=C-C=C. Examples of the conjugated diene monomer include 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, and 1,3-hexadiene. The conjugated diene monomer is preferably 1,3-butadiene. These monomers may be used alone or in combination of two or more.

[0020] In the linear block copolymer A, the content of conjugated diene monomer units is preferably 6 to 45% by mass, where the total mass of the monomer units contained in the linear block copolymer A is taken as 100% by mass. When this range is satisfied, good tensile elongation and few fisheyes tend to be achieved simultaneously when the block copolymer A is formed into a film. Specific examples of the content of the conjugated diene monomer units include 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, and 45% by mass, and may be within a range between any two of the values ​​exemplified here.

[0021] The linear block copolymer A may have monomer units (other monomer units) derived from other monomers copolymerizable with the vinyl aromatic monomer and the conjugated diene monomer. When the total mass of the monomer units contained in the linear block copolymer A is taken as 100 mass%, the content of the other monomer units in the linear block copolymer A is, for example, 0 to 2 mass%, and preferably 0 mass%.

[0022] The content of the conjugated diene monomer units is 12 to 27% by mass, preferably 15 to 25% by mass, when the total of the vinyl aromatic monomer units and the conjugated diene monomer units in the block copolymer composition is taken as 100% by mass. In the block copolymer composition, the vinyl aromatic monomer units and the conjugated diene monomer units are present as structural units constituting a block copolymer such as linear block copolymer A. When the block copolymer composition contains two or more block copolymers, the content of these units is calculated based on the total amount of each monomer unit in these block copolymers. When this range is satisfied, the occurrence of fisheyes is reduced and the tensile elongation is excellent when molded into a film. In particular, by keeping the content of the conjugated diene monomer units at or below the upper limit, the occurrence of gel-like foreign matter resulting from thermal crosslinking of structural units derived from the conjugated diene monomers can be suppressed. The content of the conjugated diene monomer unit is specifically, for example, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, or 27% by mass, and may be within a range between any two of the values ​​exemplified here.

[0023] When the total of the monomer units contained in each polymer in the block copolymer composition is taken as 100% by mass, the content of the conjugated diene monomer units is preferably 12 to 27% by mass, more preferably 15 to 25% by mass. Specific examples of the content of the conjugated diene monomer units include 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, and 27% by mass, and may be within a range between any two of the values ​​exemplified here.

[0024] The content of conjugated diene monomer units can be calculated from the amounts of vinyl aromatic monomer units and conjugated diene monomers charged when producing each block copolymer, or it may be calculated using a known halogen addition method. A typical example of the halogen addition method involves dissolving the sample in a solvent capable of completely dissolving it, adding an excess amount of iodine monochloride / acetic acid solution to allow for sufficient reaction, adding potassium iodide solution, and titrating with a sodium thiosulfate / ethanol solution. The content of conjugated diene monomer units is calculated from the amount of double bonds obtained by the above-mentioned method. The content of vinyl aromatic monomer units is calculated by subtracting the content of conjugated diene monomer units from the total content of the sample.

[0025] The block copolymer composition may contain two or more types of linear block copolymers A that differ in monomer unit composition, molecular weight, etc. Furthermore, the block copolymer composition may contain a polymer other than the linear block copolymer A.

[0026] When the block copolymer composition is measured by gel permeation chromatography (GPC) in terms of polystyrene, the peak-top molecular weight of the main peak, which is the peak having the highest peak-top molecular weight among peaks having an area ratio of 20% or more to the total peak area, is 150,000 to 300,000, preferably 180,000 to 250,000. When this range is satisfied, the tensile elongation is excellent when the composition is molded into a film. In particular, when the molecular weight is too large, thermal crosslinking is likely to occur due to shear heating, and gelation may occur easily with fewer crosslinking cycles. Specific examples of the peak top molecular weight of the main peak are 150,000, 155,000, 160,000, 165,000, 170,000, 175,000, 180,000, 185,000, 190,000, 195,000, 200,000, 205,000, 210,000, 215,000, 220,000, 225,000, 230,000, 235,000, 240,000, 245,000, 250,000, 255,000, 260,000, 265,000, 270,000, 275,000, 280,000, 285,000, 290,000, 295,000, and 300,000, and may be within a range between any two of the numerical values ​​exemplified here.

[0027] In one embodiment, the total area of ​​the peak portions falling within a range corresponding to a molecular weight 1.8 to 2.2 times the peak top molecular weight of the main peak may be less than 5% of the area of ​​the main peak, preferably less than 4%, and more preferably less than 3%. Here, "the total area of ​​the peak portions falling within a range corresponding to a molecular weight 1.8 to 2.2 times the peak top molecular weight of the main peak" means that, regardless of whether the peak top falls within the range corresponding to a molecular weight 1.8 to 2.2 times, if even a portion of the peak falls within the range, the area of ​​that portion of the peak is included in the total area. Note that if the entire peak falls within the range, the area of ​​the entire peak is naturally included in the total area. When such a range is satisfied, fisheyes are less likely to occur when the film is molded. Dimers of the component corresponding to the main peak are primarily present in the range 1.8 to 2.2 times the peak top molecular weight of the main peak. The area of ​​the component having a peak top within the range 1.8 to 2.2 times can be controlled, for example, by molding conditions such as the resin temperature during pellet molding. The ratio of Area 1 to the area of ​​the main peak is specifically, for example, 0, 0.5, 1.0, 1.5, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.5, or 4.9%, and may be within a range between any two of the numerical values ​​exemplified here.

[0028] The method for producing the linear block copolymer A is not particularly limited, and for example, the linear block copolymer A can be obtained by a living anionic polymerization reaction of a monomer raw material containing a vinyl aromatic monomer and a conjugated diene monomer in an organic solvent using an organolithium compound as a polymerization initiator.

[0029] 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. Cyclohexane is a particularly preferred organic solvent.

[0030] 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. A particularly preferred organolithium compound is n-butyllithium.

[0031] In living anionic polymerization, block copolymers with any primary structure can be obtained by changing the amount and method of addition of the monomer raw materials. For example, the molecular weight can be adjusted by changing the ratio of the organolithium compound to the monomer raw materials, and the ratio of vinyl aromatic monomer units to conjugated diene monomer units in each block chain can be controlled by changing the addition method, such as the order of addition or the method of addition.

[0032] 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 (polymerization solution) by any method, including (A) precipitation using a poor solvent such as methanol, (B) precipitation by evaporating the solvent using a heated roll or the like (drum dryer method), (C) concentrating the solution using a concentrator and then removing the solvent using a vented extruder (devolatilization extrusion method), or (D) dispersing the solution in water, blowing in steam to heat and remove the solvent, and recovering the copolymer (steam stripping method). Devolatilization extrusion method is particularly preferred.

[0033] A block copolymer composition according to one embodiment of the present invention can be obtained by mixing at least one block copolymer obtained by the above-described production method or the like with other additives as required.

[0034] Examples of other 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 copolymer and melt-mixed.

[0035] 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, antistatic agents, and lubricants 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 based on the block copolymer.

[0036] The block copolymer composition according to one embodiment of the present invention may contain two or more block copolymers. Known methods can be used to mix these block copolymers. For example, the block copolymers 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 (polymerization solutions) together and then removing the solvent can be used.

[0037] <Method for Producing Pellets> Pellets according to one embodiment of the present invention are granules composed of the block copolymer composition, and are obtained by molding the block copolymer composition or a polymer solution (polymerization solution) of the linear block copolymer A, which is a component of the block copolymer composition, into granules.

[0038] The method for producing pellets is not particularly limited as long as it does not impair the physical properties of the block copolymer composition constituting the pellets, and may be, for example, a method including a polymerization step and a pelletizing step. The method for producing pellets may also include a mixing step.

[0039] In the polymerization step, a monomer raw material containing a vinyl aromatic monomer and a conjugated diene monomer is polymerized to obtain a polymerization solution containing one or more linear block copolymers A. The polymerization of the monomer raw material can be carried out, for example, by the living anionic polymerization reaction described above. The polymerization solution is inactivated by adding a polymerization terminator.

[0040] In the mixing step, a mixed solution is obtained by mixing two or more polymerization solutions each containing one or more types of linear block copolymers A. For example, a polymerization solution containing one type of linear block copolymer A is mixed with a polymerization solution containing two types of linear block copolymers A to obtain a new polymerization solution (mixed solution) containing three types of linear block copolymers A.

[0041] In the pelletizing step, the inactivated polymerization solution (or mixed polymerization solutions) is pelletized by devolatilization extrusion. In devolatilization extrusion, the polymerization solution is concentrated using a concentrator and then the solvent is removed using a vented extruder. When the resin temperature at the extruder outlet during devolatilization extrusion is T (°C), pelletization is performed under conditions such that T satisfies the following formula (1), thereby suppressing dimerization (for example, the formation of a dimer of the component corresponding to the main peak due to thermal crosslinking) and achieving a low fisheye level. The resin temperature at the extruder outlet can be adjusted by the screw rotation speed of the extruder, the discharge rate, the temperature of the polymerization solution fed to the extruder, etc. (1) T≦−0.0129×B ２ −0.35×B+257 (B: content (% by mass) of the conjugated diene monomer units when the total of the vinyl aromatic monomer units and the conjugated diene monomer units in the block copolymer composition is 100% by mass)

[0042] 2. Film A film according to one embodiment of the present invention is a molded product of the pellets. The film is, for example, a heat-shrinkable film containing the block copolymer composition. The heat-shrinkable film can be obtained by uniaxially, biaxially, or multiaxially stretching a sheet or film extruded from the pellets by a known method, such as a T-die method or a tubular method. Biaxial stretching by a T-die method is particularly preferred.

[0043] The heat-shrinkable film according to one embodiment of the present invention can be a layer containing the block copolymer composition alone, but can also be a heat-shrinkable multilayer film by laminating another resin layer on at least one surface of the layer. 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 a resin composition (hereinafter, the unstretched film may be referred to as a "sheet" to distinguish it from the unstretched film) and stretched, or a multilayer sheet 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 for the other resin layer.

[0044] Examples of uniaxial stretching include a method of stretching an extruded sheet in a direction perpendicular to the extrusion direction (TD) using a tenter, and a method of stretching an extruded tubular film in the circumferential direction.

[0045] Examples of biaxial stretching include a method in which an extruded sheet is stretched in the extrusion direction (MD) with a roll and then stretched in a direction perpendicular to the extrusion direction (TD) with a tenter or the like, and a method in which an extruded tubular film is stretched simultaneously or separately in the extrusion direction and the circumferential direction.

[0046] The stretching temperature is preferably, for example, 60 to 120°C. By setting the temperature to 60°C or higher, the sheet is less likely to break during stretching, and by setting the temperature to 120°C or lower, the shrinkage characteristics and thickness precision of the resulting film are likely to be good. The stretching ratio is not particularly limited, but is preferably 1.5 to 8 times. By setting the stretching ratio to 1.5 times or higher, the heat shrinkability is likely to be good, and by setting the stretching ratio to 8 times or lower, the sheet is less likely to break during stretching. When these stretched films are used as heat-shrinkable labels or packaging materials, the heat shrinkage ratio at 80°C is preferably 20% or more. If the heat shrinkage ratio is less than 20%, high temperatures are required during shrinkage, which is undesirable as it will adversely affect the article to be covered. The film thickness is preferably 10 to 300 μm.

[0047] The heat-shrinkable film can be used as a heat-shrinkable label, a heat-shrinkable cap seal, etc. In addition, it can be used as a packaging film, etc.

[0048] The present invention will be described in more detail below with reference to examples, but these examples are merely illustrative and are not intended to limit the scope of the present invention.

[0049] [Production of Block Copolymer Composition and Pellets] Pellets (P-1) to (P-8) were produced by the following procedure.

[0050] <Pellets (P-1)> (Polymerization Step 1-1) Preparation of Block Copolymer Polymerization Solution (S-1) (1) 467 kg of cyclohexane was charged into a reaction vessel. (2) While stirring at an internal temperature of 30°C, 1,380 mL of n-butyllithium (10% by mass cyclohexane solution) was added, followed by the addition of 8.0 kg of styrene, and the temperature was raised to 80°C to allow polymerization. (3) After complete consumption of the styrene, while maintaining the internal temperature at 80°C, a total of 110.0 kg of styrene and a total of 10.0 kg of 1,3-butadiene were simultaneously added at constant addition rates of 143.0 kg / h and 13.0 kg / h, respectively, and this state was maintained for a sufficient period of time after the completion of addition. (4) After complete consumption of the styrene, the internal temperature was lowered to 70°C, and 22.0 kg of 1,3-butadiene was added, followed by the temperature being raised to allow polymerization. (5) After the 1,3-butadiene was completely consumed, the internal temperature was increased to 60°C, and 50.0 kg of styrene was added and polymerized. (6) After the styrene was completely consumed, 220 g of water was added to inactivate the mixture, thereby obtaining a block copolymer polymerization solution (S-1).

[0051] (Polymerization Step 1-2) Preparation of Block Copolymer Polymer Solution (S-2) (1) 467 kg of cyclohexane was charged into a reaction vessel. (2) While stirring at an internal temperature of 30°C, 2480 mL of n-butyllithium (10% by mass cyclohexane solution) was added, followed by the addition of 40.0 kg of styrene, and the temperature was raised to 80°C to allow polymerization. (3) After complete consumption of styrene, while maintaining the internal temperature at 80°C, a total of 36.0 kg of styrene and a total of 8.0 kg of 1,3-butadiene were simultaneously added at constant addition rates of 120.0 kg / h and 26.7 kg / h, respectively, and this state was maintained for a sufficient period of time after the completion of addition. (4) After complete consumption of styrene, the internal temperature was lowered to 50°C, and 66.0 kg of 1,3-butadiene was added, and the temperature was raised to allow polymerization. (5) After complete consumption of 1,3-butadiene, the internal temperature was lowered to 60°C, and 50.0 kg of styrene was added and allowed to polymerize. (6) After the styrene was completely consumed, 390 g of water was added to inactivate the mixture, thereby obtaining a block copolymer polymerization solution (S-2).

[0052] (Mixing Step 1) Polymerization solution S-1 and polymerization solution S-2 were mixed so that the weight ratio of (S-1):(S-2) was 66.7:33.3, thereby obtaining mixed solution 1.

[0053] (Pelletization Step 1) The mixed solution 1 was molded in a devolatilizing extruder to obtain pellets P-1. The resin temperature at the extruder outlet was 238°C. The block copolymer composition constituting pellets P-1 has a linear block copolymer content of substantially 100% by mass. The block copolymer composition may contain, in addition to the linear block copolymer, a lithium salt derived from an organolithium compound, etc., but this amount is so small relative to the mass of the linear block copolymer that the linear block copolymer content can be considered to be substantially 100% by mass. The same applies to other examples.

[0054] <Pellets (P-2)> (Polymerization step 2-1) Preparation of block copolymer polymerization solution (S-2) A block copolymer polymerization solution (S-2) was obtained by carrying out the same operation as in (Polymerization step 1-2).

[0055] (Polymerization Step 2-2) Preparation of Block Copolymer Polymerization Solution (S-3) (1) 467 kg of cyclohexane was charged into a reaction vessel. (2) While stirring at an internal temperature of 30°C, 1,000 mL of n-butyllithium (10% by mass cyclohexane solution) was added, followed by the addition of 40.0 kg of styrene, and the temperature was raised to 80°C to allow polymerization. (3) After complete consumption of the styrene, while maintaining the internal temperature at 80°C, a total of 102.0 kg of styrene and a total of 18.0 kg of 1,3-butadiene were simultaneously added at constant addition rates of 153.0 kg / h and 24.0 kg / h, respectively, and this state was maintained for a sufficient period of time after the completion of addition. (4) After complete consumption of the styrene, the internal temperature was raised to 60°C, and 40.0 kg of styrene was added, followed by the temperature being raised to allow polymerization. (5) After complete consumption of the styrene, 150 g of water was added to inactivate the mixture, thereby obtaining a block copolymer polymerization solution (S-3).

[0056] (Mixing Step 2) Polymerization solution S-2 and polymerization solution S-3 were mixed so that the weight ratio of (S-2):(S-3) was 33.3:66.7, thereby obtaining mixed solution 2.

[0057] (Pelletization step 2) The mixed solution 2 was molded in a devolatilizing extruder to obtain pellets P-2. The resin temperature at the extruder outlet was 242°C. The block copolymer composition constituting the pellets P-2 had a linear block copolymer content of substantially 100% by mass.

[0058] <Pellets (P-3)> (Polymerization Step 3-1) Preparation of Block Copolymer Polymerization Solution (S-4) (1) 467 kg of cyclohexane was charged into a reaction vessel. (2) While stirring at an internal temperature of 30°C, 1,450 mL of n-butyllithium (10 mass% cyclohexane solution) was added, and 122.0 kg of styrene was added, and the temperature was raised to 80°C to polymerize. (3) After the styrene was completely consumed, the internal temperature was raised to 50°C, and 46.0 kg of styrene and 32.0 kg of 1,3-butadiene were simultaneously added all at once, and the temperature was raised to polymerize. (4) After the styrene and 1,3-butadiene were completely consumed, 230 g of water was added to inactivate the mixture, thereby obtaining a block copolymer polymerization solution (S-4).

[0059] (Polymerization Step 3-2) Preparation of Block Copolymer Polymerization Solution (S-5) (1) 467 kg of cyclohexane was charged into a reaction vessel. (2) While stirring at an internal temperature of 30°C, 1,180 mL of n-butyllithium (10% by mass cyclohexane solution) was added, and 32.0 kg of styrene was added. The temperature was raised to 80°C and polymerization was carried out. (3) After the styrene was completely consumed, the internal temperature was raised to 50°C, and 67.0 kg of styrene and 9.0 kg of 1,3-butadiene were simultaneously added in one lump, and the temperature was raised and polymerization was carried out. (4) After the styrene and 1,3-butadiene were completely consumed, the internal temperature was raised to 50°C, and 67.0 kg of styrene and 25.0 kg of 1,3-butadiene were simultaneously added in one lump, and the temperature was raised and polymerization was carried out. (4) After the styrene and 1,3-butadiene were completely consumed, 190 g of water was added to inactivate the mixture, and a block copolymer polymerization solution (S-5) was obtained.

[0060] (Mixing Step 3) Polymerization solution S-4 and polymerization solution S-5 were mixed so that the weight ratio of (S-4):(S-5) was 30:70, thereby obtaining mixed solution 3.

[0061] (Pelletization step 3) The mixed solution 3 was molded in a devolatilizing extruder to obtain pellets P-3. The resin temperature at the extruder outlet was 238°C. The block copolymer composition constituting pellets P-3 had a linear block copolymer content of substantially 100% by mass.

[0062] <Pellets (P-4)> (Polymerization step 4-1) Preparation of block copolymer polymerization solution (S-4) A block copolymer polymerization solution (S-4) was obtained by carrying out the same operation as in (Polymerization step 3-1).

[0063] (Polymerization Step 3-2) Preparation of Block Copolymer Polymerization Solution (S-6) (1) 467 kg of cyclohexane was charged into a reaction vessel. (2) While stirring at an internal temperature of 30°C, 3720 mL of n-butyllithium (10% by mass cyclohexane solution) was added, and 50.0 kg of styrene was added. The temperature was raised to 80°C and polymerization was carried out. (3) After the styrene was completely consumed, the internal temperature was raised to 35°C, and 60.0 kg of styrene and 90.0 kg of 1,3-butadiene were simultaneously added in one lump, and the temperature was raised and polymerization was carried out. (4) After the styrene and 1,3-butadiene were completely consumed, 620 g of water was added to inactivate the mixture, thereby obtaining a block copolymer polymerization solution (S-6).

[0064] (Mixing Step 4) Polymerization solution S-4 and polymerization solution S-6 were mixed so that the weight ratio of (S-4):(S-6) was 66.7:33.3, thereby obtaining mixed solution 4.

[0065] (Pelletization Step 4) The mixed solution 4 was molded in a devolatilizing extruder to obtain pellets P-4. The resin temperature at the extruder outlet was 234°C. The block copolymer composition constituting pellets P-4 had a linear block copolymer content of substantially 100% by mass.

[0066] <Pellets (P-5)> (Polymerization step 5-1) Preparation of block copolymer polymerization solution (S-1) A block copolymer polymerization solution (S-1) was obtained by carrying out the same operation as in (Polymerization step 1-1).

[0067] (Polymerization Step 5-2) Preparation of Block Copolymer Polymer Solution (S-2) A block copolymer polymer solution (S-2) was obtained by carrying out the same operation as in (Polymerization Step 1-2).

[0068] (Mixing Step 5) The polymerization solution S-1 and the polymerization solution S-2 were mixed so that the weight ratio of (S-1):(S-2) was 66.7:33.3, thereby obtaining a mixed solution 5.

[0069] (Pelletization step 5) The mixed solution 5 was molded in a devolatilizing extruder to obtain pellets P-5. The resin temperature at the extruder outlet was 247°C. The block copolymer composition constituting pellets P-5 had a linear block copolymer content of substantially 100% by mass.

[0070] <Pellets (P-6)> (Polymerization step 6-1) Preparation of block copolymer polymerization solution (S-4) A block copolymer polymerization solution (S-4) was obtained by carrying out the same operation as in (Polymerization step 3-1).

[0071] (Polymerization step 6-2) Preparation of block copolymer polymerization solution (S-5) A block copolymer polymerization solution (S-5) was obtained by carrying out the same operation as in (Polymerization step 3-2).

[0072] (Mixing Step 6) Polymerization solution S-4 and polymerization solution S-5 were mixed so that the weight ratio of (S-4):(S-5) was 30:70, thereby obtaining mixed solution 6.

[0073] (Pelletization Step 6) The mixed solution 6 was molded in a devolatilizing extruder to obtain pellets P-5. The resin temperature at the extruder outlet was 250°C. The block copolymer composition constituting pellets P-6 had a linear block copolymer content of substantially 100% by mass.

[0074] <Pellets (P-7)> (Polymerization Step 7-1) Preparation of Block Copolymer Polymerization Solution (S-7) (1) 467 kg of cyclohexane was charged into a reaction vessel. (2) While stirring at an internal temperature of 30°C, 1560 mL of n-butyllithium (10% by mass cyclohexane solution) was added, followed by the addition of 8.0 kg of styrene, and the temperature was raised to 80°C to allow polymerization. (3) After complete consumption of the styrene, while maintaining the internal temperature at 80°C, a total of 98.0 kg of styrene and a total of 10.0 kg of 1,3-butadiene were simultaneously added at constant addition rates of 147.0 kg / h and 15.0 kg / h, respectively, and this state was maintained for a sufficient period of time after the completion of addition. (4) After complete consumption of the styrene, the internal temperature was raised to 60°C, 50.0 kg of 1,3-butadiene was added, and the temperature was raised to allow polymerization. (5) After the 1,3-butadiene was completely consumed, the internal temperature was increased to 60°C, and 34.0 kg of styrene was added and polymerized. (6) After the styrene was completely consumed, 250 g of water was added to inactivate the mixture, thereby obtaining a block copolymer polymerization solution (S-7).

[0075] (Pelletization Step 7) The polymerization solution S-7 was molded using a devolatilizing extruder to obtain pellets P-7. The resin temperature at the extruder outlet was 235°C. The block copolymer composition constituting pellets P-7 had a linear block copolymer content of substantially 100% by mass.

[0076] <Pellets (P-8)> (Polymerization step 8-1) Preparation of block copolymer polymerization solution (S-3) A block copolymer polymerization solution (S-3) was obtained by carrying out the same operation as in (Polymerization step 2-2).

[0077] (Pelletization step 8) The polymerization solution S-3 was molded using a devolatilizing extruder to obtain pellets P-8. The resin temperature at the extruder outlet was 245°C. The block copolymer composition constituting pellets P-8 had a linear block copolymer content of substantially 100% by mass.

[0078] <Pellets (P-9)> (Polymerization step 9-1) Preparation of block copolymer polymerization solution (S-2) A block copolymer polymerization solution (S-2) was obtained by carrying out the same operation as in (Polymerization step 1-2).

[0079] (Polymerization Step 9-2) Preparation of Block Copolymer Polymerization Solution (S-9) (1) 467 kg of cyclohexane was charged into a reaction vessel. (2) While stirring at an internal temperature of 30°C, 1800 mL of n-butyllithium (10% by mass cyclohexane solution) was added, followed by the addition of 8.0 kg of styrene, and the temperature was raised to 80°C to allow polymerization. (3) After complete consumption of the styrene, while maintaining the internal temperature at 80°C, a total of 110.0 kg of styrene and a total of 10.0 kg of 1,3-butadiene were simultaneously added at constant addition rates of 143.0 kg / h and 13.0 kg / h, respectively, and this state was maintained for a sufficient time after the completion of addition. (4) After complete consumption of the styrene, the internal temperature was lowered to 70°C, and 22.0 kg of 1,3-butadiene was added, followed by the temperature being raised to allow polymerization. (5) After the 1,3-butadiene was completely consumed, the internal temperature was increased to 60°C, and 50.0 kg of styrene was added and polymerized. (6) After the styrene was completely consumed, 290 g of water was added to inactivate the mixture, thereby obtaining a block copolymer polymerization solution (S-9).

[0080] (Mixing Step 9) Polymerization solution S-2 and polymerization solution S-9 were mixed so that the weight ratio of (S-2):(S-9) was 33.3:66.7, thereby obtaining mixed solution 9.

[0081] (Pelletization Step 9) The mixed solution 9 was molded in a devolatilizing extruder to obtain pellets P-9. The resin temperature at the extruder outlet was 237°C. The block copolymer composition constituting pellets P-9 had a linear block copolymer content of substantially 100% by mass.

[0082] [Monomer Unit Proportion] The contents of vinyl aromatic monomer units (styrene monomer units) and conjugated diene monomer units (1,3-butadiene monomer units) in the block copolymer composition were measured and calculated by the halogen addition method. (A1) 0.2 g of sample was dissolved in a solvent (such as carbon tetrachloride) capable of completely dissolving the sample, and then 15 ml of Wiess's reagent (0.1 mol / L iodine monochloride / acetic acid solution) was added and allowed to react thoroughly. 20 ml of 4% potassium iodide solution was added, and the mixture was titrated with a 0.1 mol / L sodium thiosulfate / ethanol solution to calculate the amount of double bonds. (A2) The butadiene monomer unit content (rubber content) was calculated based on the amount of double bonds obtained by the method in (A1). The styrene content was calculated by subtracting the butadiene content from the total content of the sample. The content of the conjugated diene monomer units when the total of the vinyl aromatic monomer units (styrene monomer units) and the conjugated diene monomer units (1,3-butadiene monomer units) in the block copolymer composition is taken as 100 mass % is shown in Table 2.

[0083] [GPC Measurement] GPC measurement of the block copolymer composition was carried out using the following GPC measurement apparatus and conditions. The peak top molecular weight of each component and the area of ​​each peak were calculated based on the measurement results. The results are shown in Table 2. Apparatus name: HLC-8220GPC (manufactured by Tosoh Corporation) Column: Four Shodex GPCKF-404 (manufactured by Showa Denko K.K.) connected in series Temperature: 40°C Detection: Differential refractive index Solvent: Tetrahydrofuran Concentration: 2% by mass Calibration curve: Prepared using standard polystyrene (manufactured by VARIAN).

[0084] [Evaluation of molding conditions] When the resin temperature at the extruder outlet is T (°C), if T satisfies the following formula (1), it is evaluated as "Good", and if it does not, it is evaluated as "Poor". (1) T≦-0.0129×B ２ −0.35×B+257 (B: content (% by mass) of the conjugated diene monomer units when the total of the vinyl aromatic monomer units and the conjugated diene monomer units in the block copolymer composition is 100% by mass)

[0085] [Examples 1 to 4 and Comparative Examples 1 to 5] Each pellet was evaluated for tensile elongation and fisheye level during film production.

[0086] <Tensile Elongation> In accordance with JIS K 7161, a dumbbell-shaped molded piece was injection molded using the pellets, and the nominal tensile strain at break was measured at a tensile speed of 50 mm / min using an autograph AG-Xplus manufactured by Shimadzu Corporation, and this was taken as the tensile elongation value. The tensile elongation was then evaluated according to the following criteria. The evaluation results for each example and comparative example are shown in Table 2. ○: 10% or more ×: less than 10%

[0087] <Fisheye Level> Using a sheet extruder equipped with a T-die, an unstretched film was produced at a temperature of 220°C. ２ The number of foreign matters of 0.2 mm or more present in the sample was counted using an image recognition device and evaluated according to the following criteria. The evaluation results for each example and comparative example are shown in Table 2. ○: Less than 150 pieces ×: 150 pieces or more

[0088] In Table 2, "total area of ​​peak portions in a predetermined range" means "total area of ​​peak portions included in the range corresponding to a molecular weight 1.8 to 2.2 times the peak top molecular weight of the main peak."

[0089]

[0090]

Claims

1. A pellet composed of a block copolymer composition, wherein the block copolymer composition contains 95% by mass or more of a linear block copolymer mainly composed of vinyl aromatic monomer units and conjugated diene monomer units, and when the total of the vinyl aromatic monomer units and the conjugated diene monomer units in the block copolymer composition is 100% by mass, the content of the conjugated diene monomer units is 12 to 27% by mass. When measured by gel permeation chromatography for the polystyrene-equivalent molecular weight of the block copolymer composition, when the peak with the highest peak top molecular weight among the peaks with an area ratio of 20% or more to the total peak area is defined as the main peak, the peak top molecular weight of the main peak is 150,000 to 300,000, and the total area of the peak portions included in the range corresponding to a molecular weight of 1.8 to 2.2 times the peak top molecular weight of the main peak is less than 5% of the area of the main peak. A pellet.

2. The pellet according to claim 1, wherein the block copolymer composition contains two or more of the linear block copolymers.

3. The method for producing pellets according to claim 1 or claim 2, comprising a polymerization step and a pelletization step, wherein in the polymerization step, a monomer raw material containing a vinyl aromatic monomer and a conjugated diene monomer is polymerized to obtain a polymerization solution containing the linear block copolymer, and in the pelletization step, the polymerization solution is pelletized by a devolatilization extrusion method, and when the resin temperature at the outlet of the extruder in the pelletization step is T (°C), T satisfies the formula (1). (1) T ≤ -0.0129 × B ２ -0.35 × B + 257 (B: the content rate (mass%) of the conjugated diene monomer unit when the total of the vinyl aromatic monomer unit and the conjugated diene monomer unit in the block copolymer composition is 100 mass%) 4. A film which is a molded article of a raw material containing the pellet according to claim 1 or claim 2.

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