Block copolymer and composition

Abstract

Provided is a block copolymer (I) having a polymer block A mainly composed of a vinyl aromatic monomer unit and a polymer block B mainly composed of a conjugated diene monomer unit, the content of the polymer block A being 3-40% by mass, the amount of vinyl bonds before hydrogenation of the polymer block B being 35-55 mol%, and the amount of vinyl bonds before hydrogenation of the polymer block B being 30-50 mol%. The hydrogenation rate of conjugated diene monomer units contained in the polymer block (B) is 30-90 mol%, and the weight-average molecular weight of the block copolymer (I) is 150,000-600,000.

Description

TECHNICAL FIELD

[0001] The present application relates to a block copolymer and a composition. BACKGROUND

[0002] Block copolymers using a vinyl aromatic compound and a conjugated diene compound have the same elasticity as natural rubber and synthetic rubber at normal temperature, and have the same molding processability as a thermoplastic resin at high temperature, and further have excellent weather resistance and heat resistance, and thus have been widely used as a resin modifier in the fields of automobile parts, tire parts, medical molding products, asphalt modifiers, shoe products, food container molding products, packaging materials, adhesive sheets, household electrical and industrial parts, and the like.

[0003] An airbag system for an automobile, which is an automobile part, is a system for protecting a driver and an occupant at the time of a collision of an automobile or the like, and is composed of a device for sensing an impact at the time of a collision and an airbag device. The airbag device is provided in a steering wheel, an instrument panel in front of a passenger seat, seats of a driver seat and a passenger seat, a front pillar, a side pillar, and the like. With respect to an airbag housing cover in the airbag device, in order to cause the airbag housing cover to be cracked as designed at the time of inflation of the airbag, various proposals have been made with respect to the structure and the material thereof.

[0004] For example, as a thermoplastic elastomer constituting a material for an airbag housing cover (the material uses a thermoplastic elastomer composition excellent in low-temperature impact resistance and heat resistance), a styrene-butadiene-styrene block copolymer, a propylene resin, an ethylene-a-olefin copolymer, and the like are proposed as a styrene-conjugated diene block copolymer (for example, see Patent Literature 1).

[0005] PRIOR ART DOCUMENTS

[0006] PATENT LITERATURE

[0007] Patent Literature 1: Japanese Patent Application Laid-Open No. 2022-109650 SUMMARY

[0008] PROBLEMS TO BE SOLVED BY THE INVENTION

[0009] In recent years, from the aspect of safety, the enlargement of an airbag is being promoted, and on the other hand, from the aspect of appearance, the miniaturization of an airbag device is being sought. Therefore, the relative output applied to an airbag housing cover at the time of deployment of the airbag is required to be increased, and the material for the airbag housing cover is required to have more excellent impact resistance at low temperature.

[0010] The thermoplastic elastomer composition disclosed in the above-described Patent Document 1 contains a propylene block copolymer, an ethylene-based polymer containing a polymer block formed of ethylene and an ethylene-a-olefin copolymer block, and a partially hydrogenated product of a styrene-conjugated diene block copolymer. It is described therein that the thermoplastic elastomer composition is excellent in low-temperature impact resistance at -45°C and is suitable as a material for an airbag housing cover of an airbag system.

[0011] However, the thermoplastic elastomer composition disclosed in Patent Document 1 has the following problem: at an extremely low temperature of around -70°C, there is room for improvement in impact resistance.

[0012] Therefore, an object of the present application is to provide a composition and a block copolymer for use in the above-described composition, which is particularly obtainable in practically sufficient elongation at break, rigidity, and excellent impact resistance at an extremely low temperature and low gloss as a material for an airbag housing cover.

[0013] Means for solving the problem

[0014] The present inventors have conducted intensive studies in order to solve the above-described problem, and as a result, have found that a composition containing a block copolymer having a specific structure can solve the above-described problem of the prior art, thereby completing the present application.

[0015] That is, the present application is as described below. [1]

[0017] A block copolymer (I) having a polymer block A having an ethylene-based aromatic monomer unit as a main component and a polymer block B having a conjugated diene monomer unit as a main component,

[0018] The content of the above-described polymer block A is 3 to 40 mass%,

[0019] The vinyl bond content of the above-described polymer block B before hydrogenation is 35 to 55 mol%,

[0020] The hydrogenation rate of the conjugated diene monomer unit contained in the above-described polymer block B is 30 to 90 mol%,

[0021] The weight average molecular weight is 150,000 to 600,000. [2]

[0023] The block copolymer (I) described in the above-described [1], wherein the hydrogenation rate of the conjugated diene monomer unit contained in the above-described polymer block B is 30 to 77 mol%. [3]

[0025] The block copolymer (I) as described in any one of the above [1] to [2], wherein the melt flow rate at a measurement temperature of 230°C and a measurement load of 2.16 kg according to ISO 1133 is less than 0.1 g / 10 minutes. [4]

[0027] The block copolymer (I) as described in any one of the above [1] to [3], which is a hydrogenated product of a coupled polymer represented by the following (1) having a coupling rate of 80% or more.

[0028] (A-B) n-X (1)

[0029] (In formula (1), A is a polymer block A having a vinyl aromatic monomer unit as a main component, B is a polymer block B having a conjugated diene monomer unit as a main component, n is an integer of 1 or more, and X is a residue of a coupling agent or a residue of a polymerization initiator.) [5]

[0031] The block copolymer (I) as described in any one of the above [1] to [4], which is any one selected from the group consisting of a pellet, a flake, and a powder. [6]

[0033] A composition for an airbag housing cover, comprising:

[0034] Component (I): 1 to 58 parts by mass of the block copolymer (I) as described in any one of the above [1] to [5];

[0035] Component (II): 11 to 68 parts by mass of an ethylene-based copolymer; and

[0036] Component (III): 100 parts by mass of a propylene-based polymer. [7]

[0038] An airbag housing cover formed of the composition as described in the above [6].

[0039] Effects of the Invention

[0040] According to the present invention, a composition having a good and extremely low elongation at break, rigidity, impact resistance at extremely low temperatures, and low glossiness, and a block copolymer used in the above composition can be obtained. DETAILED DESCRIPTION

[0041] Hereinafter, a specific embodiment of the present invention (hereinafter, referred to as "the present embodiment") will be described in detail.

[0042] Note that the present embodiment below is for illustrating the present invention, and the present invention is not limited to the following embodiment. The present invention can be implemented by being appropriately modified within the scope of the gist thereof.

[0043] [Block copolymer]

[0044] The block copolymer of the present embodiment is described in detail below.

[0045] The block copolymer (I) of the present embodiment has a polymer block A having a vinyl aromatic monomer unit as a main component and a polymer block B having a conjugated diene monomer unit as a main component,

[0046] The content of the polymer block A is 3 to 40 mass%,

[0047] The vinyl bond content of the polymer block B before hydrogenation is 35 to 55 mol%,

[0048] The hydrogenation rate of the conjugated diene monomer unit included in the polymer block B is 30 to 90 mol%,

[0049] The weight average molecular weight is 150,000 to 600,000.

[0050] In the present specification, with respect to the monomer unit constituting the polymer block, "as a main component" means that the object monomer unit is included in the object polymer block in an amount of 80 mass% or more and 100 mass% or less, and preferably in an amount of 90 mass% or more and 100 mass% or less.

[0051] The block copolymer (I) of the present embodiment has at least one polymer block A having a vinyl aromatic monomer unit as a main component and at least one polymer block B having a conjugated diene monomer unit as a main component.

[0052] By having the above-described configuration, a block copolymer capable of providing a composition excellent in elongation at break, rigidity, impact resistance at extremely low temperatures, and low glossiness in practical use can be obtained.

[0053] The block copolymer (I) of the present embodiment, for example, preferably has a structure represented by the following general formula.

[0054] In addition, the block copolymer (I) of the present embodiment can be a mixture including two or more of the following structures in any ratio.

[0055] (A-B) n

[0056] A-(B-A) n

[0057] A-B-A-B

[0058] B-A-B-A

[0059] B-(A-B) n

[0060] [(AB) n ] m -Z

[0061] [(BA) n ] m -Z

[0062] [(AB) n -B1] m -Z

[0063] [(BA) n -B2] m -Z

[0064] In each general formula representing the above block copolymers, A is a polymer block primarily composed of vinyl aromatic monomer units, and B is a polymer block primarily composed of conjugated diene monomer units. This clearly distinguishes polymer block A from polymer block B. The boundary between polymer block A and polymer block B does not necessarily need to be clearly distinguished.

[0065] The numbers B1, B2, etc. in the formula are used to distinguish each polymer block.

[0066] In addition, n is an integer greater than or equal to 1, and preferably an integer of 1-16.

[0067] m is an integer of 2 or greater, preferably an integer of 2-12, and more preferably an integer of 2-8.

[0068] Z represents a coupling agent residue. Examples of coupling agents include, but are not limited to, polyhalides and acid esters described below.

[0069] The structure of the block copolymer (I) of the present embodiment is preferably a structure obtained by hydrogenating a polymer having a coupled structure as shown in the following (1). The coupling rate is preferably 80% or more.

[0070] (AB) n-X (1)

[0071] (In formula (1), A is a polymer block A mainly composed of vinyl aromatic monomer units, B is a polymer block B mainly composed of conjugated diene monomer units, n is an integer greater than 1, and X is a residue of a coupling agent or a residue of a polymerization initiator.)

[0072] The block copolymer (I) having the above structure can be obtained, for example, by sequentially polymerizing the polymer block A and the polymer block B and hydrogenating the coupled polymer obtained by coupling them.

[0073] Specifically, in the polymerization process, in the case of a block copolymer of a linear polymer triblock ABA type having a molecular weight of more than 150,000 by conventional living anionic polymerization, the amount of the polymerization initiator is very small, and the molecular weight can be greatly offset due to the influence of the trace inactivating components (impurities) contained in the solvent and the monomer, so there is a tendency for the yield to decrease. In order to avoid these problems, it is necessary to strengthen the purification of the solvent and the monomer, but there is an economically disadvantageous problem. In addition, in the hydrogenation reaction process, the diffusion efficiency of the hydrogen in the system tends to decrease, so in order to obtain the target hydrogenation rate, a long hydrogenation process is required, which has a problem of reduced productivity. In addition, in the desolvation process consisting of the conventional stripping process and the dehydration extrusion process, it is also possible that the phenomenon such as equipment damage caused by applying excessive load to the driving device, the molecular chain of the polymer is cut, and the fire caused by the situation may occur. In addition, since pellets are not formed after drying and most of them are pellets, flakes or powders, adhesion occurs in the process, which becomes the reason for yield reduction or pollution.

[0074] On the other hand, by providing the block copolymer (I) of the present embodiment with the coupled structure as described above, the molecular weight can be increased and, by adjusting the coupling ratio, the coupled branched polymer and the uncoupled polymer (AB) can coexist. This allows the composition obtained using the block copolymer (I) to have well-balanced improvements in terms of processability, compatibility with propylene-based polymers, and surface appearance.

[0075] When the block copolymer (I) of this embodiment is a hydrogenated product of the coupled polymer represented by the above formula (1), the coupling rate based on the coupling agent is preferably 80% or more, more preferably 82% or more, and even more preferably 84% or more.

[0076] When the coupling ratio in the block copolymer (I) is 80% or more, the processability and surface appearance of the obtained composition tend to be excellent.

[0077] It should be noted that the coupling rate can be controlled within the above numerical range by adjusting the amount of the coupling agent, the reaction time and the reaction temperature.

[0078] (Contents of polymer block A and polymer block B)

[0079] In the block copolymer (I) of this embodiment, the content of the polymer block A mainly composed of vinyl aromatic monomer units is 3 to 40% by mass, preferably 5 to 38% by mass, and more preferably 7 to 36% by mass.

[0080] When the content of the polymer block A in the block copolymer (I) of the present embodiment is 3% by mass or more, the tensile strength of the composition of the present embodiment described later tends to be excellent. When the content of the block polymer A is 40% by mass or less, the elongation at break of the composition of the present embodiment described later tends to be excellent.

[0081] Note that the content of the polymer block A and the polymer block B can be controlled within the above numerical range by adjusting the amount of monomers to be charged.

[0082] In the block copolymer (I) of the present embodiment, the content of the polymer block B described above, which has a conjugated diene monomer unit as the main component, is 60% by mass to 97% by mass, preferably 62% by mass to 95% by mass, and more preferably 64% by mass to 93% by mass.

[0083] The content of the polymer block A in the block copolymer (I) of the present embodiment can be calculated by a method (I. M. Kolthoff, et al., Polym. Sci. 1, 429 (1946) (hereinafter referred to as osmium tetroxide decomposition method)) in which the mass of the polymer having a vinyl aromatic monomer unit as the main component (excluding a vinyl aromatic compound having an average degree of polymerization of about 30 or less) is found by oxidizing and decomposing the block copolymer before hydrogenation with tert-butyl hydroperoxide using osmium tetroxide as a catalyst, and the content of the polymer block A in the block copolymer (I) is calculated using the found mass.

[0084] In addition, the content of the polymer block A in the block copolymer can be measured using the copolymer after hydrogenation (block copolymer (I)) by the method described in Y. Tanaka, et al., RUBBER CHEMISTRY and TECHNOLOGY 54, 685 (1981) using a nuclear magnetic resonance device (NMR).

[0085] The NMR method will be specifically described taking the case where the vinyl aromatic compound is styrene and the conjugated diene compound is 1,3-butadiene as an example.

[0086] 1H-NMR measurement is performed using a sample in which 30 mg of the block copolymer is dissolved in 1 g of deuterated chloroform, and the content of the polymer block A (in this case, polystyrene block) (Ns value) is found from the proportion of the integral value of the chemical shift of 6.9 ppm to 6.3 ppm to the total integral value.

[0087] Block styrene strength (b-St strength)

[0088] = (integral value of 6.9 ppm to 6.3 ppm) / 2

[0089] Random styrene strength (r-St strength)

[0090] = (7.5 ppm ~ 6.9 ppm of integral value) - 3 x (b-St)

[0091] Ethylene-butene strength (EB strength)

[0092] = Total integral value - 3 x {(b-St strength) + (r-St strength)} / 8

[0093] Polystyrene block content (Ns value) obtained by NMR method

[0094] = 104 x (b-St strength) / [104 x {(b-St strength) + (r-St strength)} + 56 x (EB strength)]

[0095] Here, there is a correlation between the content of the block polymer A in the copolymer (I') before hydrogenation (referred to as "Os value") determined by the osmium tetroxide decomposition method and the content of the block polymer A in the block copolymer after hydrogenation (referred to as "Ns value") determined by the NMR method, and the correlation is represented by the following equation.

[0096] Os value = -0.012 (Ns value) 2 + 1.8 (Ns value) - 13.0

[0097] (Vinyl bond content)

[0098] The vinyl bond content of the above polymer block B in the block copolymer (I) of the present embodiment before hydrogenation is 35 mol% to 55 mol%, preferably 36 mol% to 54 mol%, more preferably 37 mol% to 53 mol%, and further preferably 40 mol% to 50 mol%.

[0099] When the vinyl bond content of the above polymer block B in the block copolymer (I) of the present embodiment before hydrogenation is 35 mol% or more, the composition of the present embodiment described later using the block copolymer (I) of the present embodiment has a tendency to have excellent impact resistance at extremely low temperatures.

[0100] When the vinyl bond content of the above polymer block B before hydrogenation is 55 mol% or less, the composition of the present embodiment described later has a tendency to have excellent rigidity.

[0101] Note that in the present specification, the vinyl bonding amount refers to the total content of the 1,2-vinyl bonding amount (content of the conjugated diene introduced into the polymer as 1,2-bonding) and the 3,4-vinyl bonding amount (content of the conjugated diene introduced into the polymer as 3,4-bonding) with respect to the total conjugated diene (here, the 1,2-vinyl bonding content in the case of using 1,3-butadiene as the conjugated diene, and the 3,4-vinyl bonding content in the case of using isoprene as the conjugated diene).

[0102] The vinyl bonding amount of the polymer block B before hydrogenation can be measured using a nuclear magnetic resonance device (NMR). The microstructure (cis ratio, trans ratio, vinyl bonding amount) from the conjugated diene monomer unit in the block copolymer (I) of the present embodiment can be controlled within the above numerical range by using a polar compound or the like described later and by adjusting the amount.

[0103] (Hydrogenation rate)

[0104] In the block copolymer (I) of the present embodiment, the hydrogenation rate of the conjugated diene monomer unit contained in the above polymer block B is 30 mol% to 90 mol%, preferably 30 mol% to 85 mol%, more preferably 30 mol to 80 mol%, and further preferably 30 mol% to 77 mol%.

[0105] Since the hydrogenation rate affects the solubility parameter value, flowability, compatibility with propylene resin, and glass transition temperature of the block copolymer (I) of the present embodiment, the preferred hydrogenation rate is also set in consideration of the effects on them.

[0106] By setting the hydrogenation rate of the block copolymer (I) of the present embodiment to 30 mol% or more, in the composition of the present embodiment described later using the block copolymer (I) of the present embodiment, there is a tendency to have good compatibility with the propylene polymer (III), excellent elongation at break, and excellent heat resistance.

[0107] By setting the above hydrogenation rate to 90 mol% or less, there is a tendency to have excellent impact resistance at extremely low temperatures in the composition of the present embodiment described later.

[0108] The hydrogenation rate of the block copolymer (I) can be controlled within the above numerical range, for example, by adjusting the amount of the catalyst at the time of hydrogenation. The hydrogenation rate can be controlled, for example, by adjusting the amount of the catalyst, the amount of hydrogen charge, the time, the pressure, and the temperature, or the like at the time of hydrogenation.

[0109] The hydrogenation rate of the block copolymer (I) of the present embodiment can be measured by the proton nuclear magnetic resonance (1H-NMR) method.

[0110] (Weight average molecular weight)

[0111] The weight average molecular weight of the block copolymer (I) of the present embodiment is 150,000 to 600,000, preferably 200,000 to 600,000, more preferably 250,000 to 600,000, and even more preferably 300,000 to 600,000.

[0112] When the weight average molecular weight of the block copolymer (I) of this embodiment is 150,000 or more, the composition of this embodiment described later using the block copolymer of this embodiment tends to have excellent impact resistance at extremely low temperatures and low gloss.

[0113] In addition, in the composition of the present embodiment, the dispersion morphology of the block copolymer (I) changes to a sea-island structure (sea: component (II) and component (III); island: component (I)) depending on the weight-average molecular weight of the block copolymer. If the weight-average molecular weight of the block copolymer (I) is 150,000 or more, the dispersion morphology of the block copolymer in the composition using the block copolymer of the present embodiment changes from a co-continuous structure to a sea-island structure (sea: component (II) and component (II); island: component (I)). This morphological change reduces orientation (residual strain), thereby reducing the shrinkage of the composition after heating at 110°C for 1000 hours.

[0114] If the weight average molecular weight of the block copolymer (I) is less than 150,000, the dispersion form of the block copolymer in the composition containing the block copolymer becomes a co-continuous structure.

[0115] When the weight average molecular weight of the block copolymer (I) is 600,000 or less, the composition using the block copolymer of the present embodiment tends to have excellent processability and appearance.

[0116] The weight average molecular weight of the block copolymer (I) can be determined by using a calibration curve obtained by measurement of commercially available standard polystyrene (prepared using the peak molecular weight of standard polystyrene) for the peak molecular weight of a chromatogram measured by gel permeation chromatography (GPC) by the method described in the Examples below.

[0117] The shape of the molecular weight distribution of the block copolymer measured by GPC is not particularly limited, and the block copolymer may have a multimodal molecular weight distribution with two or more peaks or a unimodal molecular weight distribution with one peak.

[0118] The weight average molecular weight of the block copolymer (I) can be controlled within the above numerical range by adjusting the amount of monomers added, the amount of reaction initiator added, the polymerization time, and the polymerization temperature during the polymerization step.

[0119] (Melt flow rate)

[0120] The block copolymer (I) of the present embodiment preferably has a melt flow rate (MFR; in accordance with ISO 1133; 230°C, 2.16 kg load) of less than 0.1 g / 10 min, more preferably 0.01 g / 10 min or less, and even more preferably NF (Non-Flow).

[0121] When the MFR of the block copolymer (I) of the present embodiment is less than 0.1 g / 10 minutes, the impact resistance and low gloss of the composition of the present embodiment described below tend to be improved, and the shrinkage rate after heating the composition at 110° C. for 1000 hours tends to be reduced.

[0122] The melt flow rate of the block copolymer can be measured by the method described in the Examples below and can be controlled within the above numerical range by adjusting the amount of monomer added, the amount of reaction initiator added, the amount of polymerization additive, the polymerization time, and the polymerization temperature during the polymerization step.

[0123] (form)

[0124] The form of the block copolymer (I) of the present embodiment is preferably any one selected from the group consisting of pellets, flakes, pellets, and powder, and more preferably flakes, pellets, and powder.

[0125] When the block copolymer (I) of this embodiment is in the form of flakes, pellets, or powder, the specific surface area is larger than that of pellets, the solvent is more easily volatilized, the residual amount of cyclohexane, etc. can be reduced, and the VOC of the composition of this embodiment described later can be reduced.

[0126] The morphology of the block copolymer (I) of the present embodiment can be controlled by adjusting the weight average molecular weight and performing the step of separating the block copolymer after polymerization from the solvent.

[0127] [Method for producing block copolymer]

[0128] The block copolymer (I) of the present embodiment can be produced, for example, by polymerizing an organic alkali metal compound as a polymerization initiator in an organic solvent to obtain a block copolymer, and then performing a hydrogenation reaction to produce the block copolymer.

[0129] The polymerization method may be batch polymerization, continuous polymerization, or a combination thereof. Batch polymerization is preferred from the perspective of obtaining a block copolymer with a narrow molecular weight distribution.

[0130] The polymerization temperature is usually 0°C to 150°C, preferably 20°C to 120°C, more preferably 40°C to 100°C, and further preferably 40°C to 80°C.

[0131] The polymerization time varies depending on the target block copolymer, but is usually within 24 hours, preferably 0.1 hour to 10 hours. From the viewpoint of obtaining a block copolymer having a narrow molecular weight distribution and high strength, more preferably 0.5 hour to 3 hours.

[0132] The polymerization pressure is not particularly limited as long as it is a pressure range sufficient to maintain nitrogen and the solvent in the liquid phase.

[0133] It is preferable that no impurities that deactivate the polymerization initiator and the living polymer, such as water, oxygen, carbon dioxide, and the like, be present in the polymerization system.

[0134] As the organic solvent, aliphatic hydrocarbons such as n-butane, isobutane, n-pentane, n-hexane, n-heptane, n-octane, and the like; alicyclic hydrocarbons such as cyclohexane, cycloheptane, methylcyclopentane, and the like; and aromatic hydrocarbons such as benzene, xylene, toluene, ethylbenzene, and the like can be given, but are not limited thereto.

[0135] As the organic alkali metal compound belonging to the polymerization initiator, an organolithium compound is preferable.

[0136] As the organolithium compound, an organic monolithium compound, an organic dilithium compound, an organic multilithium compound can be used, but are not limited thereto.

[0137] As the organolithium compound, ethyllithium, n-propyllithium, isopropyl lithium, n-butyllithium, sec-butyllithium, t-butyllithium, phenyllithium, hexamethylenedilithium, butadienyllithium, isopropenyllithium, and the like can be given, but are not limited thereto. Among these, from the viewpoint of polymerization activity, n-butyllithium, sec-butyllithium are preferable.

[0138] The amount of the organic alkali metal compound as the polymerization initiator varies depending on the molecular weight of the target polymer, but is usually preferably in the range of 0.01 phm to 0.5 phm (parts by mass per 100 parts by mass of the monomer), more preferably in the range of 0.03 phm to 0.3 phm, and further preferably in the range of 0.05 phm to 0.15 phm.

[0139] The total amount of the 1,2-linkage and the 3,4-linkage of the conjugated diene monomer unit of the polymer block B of the block copolymer (I) before hydrogenation can be controlled by using a Lewis base (for example, an ether, an amine, and the like). The amount of the Lewis base is adjusted by the ratio of the target 1,2-linkage and 3,4-linkage. In addition, by adding the Lewis base and the metal alkoxide described later under two or more conditions, a block copolymer (I) having polymer blocks B with different ratios of 1,2-linkage and 3,4-linkage can be produced.

[0140] As the Lewis base, there can be mentioned, but not limited to, for example, an ether compound, an ether compound having 2 or more oxygen atoms, a tertiary amine compound, and the like.

[0141] As the tertiary amine compound, there can be mentioned, but not limited to, for example, pyridine, N,N,N',N'-tetramethylethylenediamine, tributylamine, tetramethylpropylenediamine, 1,2-dipiperidinylethane, bis[2-(N,N-dimethylamino)ethyl]ether, and the like. They can be used only one kind alone, or two or more kinds in combination.

[0142] As the tertiary amine compound, a compound having 2 amines is preferable. Further, among these, a compound having a structure showing symmetry within a molecule is more preferable, and N,N,N',N'-tetramethylethylenediamine, bis[2-(N,N-dimethylamino)ethyl]ether, 1,2-dipiperidinylethane are further preferable.

[0143] In the production process of the block copolymer (I) of the present embodiment, the polymerization can be performed in the presence of the above-mentioned Lewis base, the organolithium compound, and the alkali metal alkoxide. Here, the alkali metal alkoxide is a compound represented by the general formula MOR (wherein M is an alkali metal, and R is an alkyl group).

[0144] As the alkali metal of the alkali metal alkoxide, from the aspects of higher 1,2- and 3,4-linkage ratios, a narrow molecular weight distribution, and a higher polymerization rate, sodium or potassium is preferable.

[0145] As the alkali metal alkoxide, there can be mentioned, but not limited to, for example, sodium alkoxide, lithium alkoxide, potassium alkoxide having an alkyl group having 2 to 12 carbon atoms, and more preferably sodium alkoxide, potassium alkoxide having an alkyl group having 3 to 6 carbon atoms, and further preferably sodium tert-butoxide, sodium tert-amylate, potassium tert-butoxide, potassium tert-amylate. Among these, further more preferably, sodium tert-butoxide, sodium tert-amylate as sodium alkoxide.

[0146] In the production process of the block copolymer (I) of the present embodiment, the method of hydrogenation is not particularly limited, and for example, the block copolymer obtained as described above can be subjected to hydrogenation by supplying hydrogen in the presence of a hydrogenation catalyst, whereby a block copolymer in which the double bond residues of the conjugated diene monomer units are hydrogenated is obtained.

[0147] In the case where the polymerization process and the hydrogenation process are performed in an inert hydrocarbon solvent, for example, the inert hydrocarbon solvent can be removed to isolate the block copolymer.

[0148] As the specific method of removing the solvent, there can be mentioned, but not limited to, for example, stripping. By performing stripping, a water-containing pellet is obtained, and the obtained water-containing pellet is dried, whereby the block copolymer can be obtained.

[0149] In the stripping, a surfactant is preferably used as a granulating agent. As such a surfactant, there is no particular limitation, and for example, the same anionic surfactants, cationic surfactants, nonionic surfactants as described above can be mentioned. These surfactants can generally be added at 0.1 ppm to 3000 ppm relative to the water in the stripping. In addition, in addition to the surfactant, a water-soluble salt of a metal such as Li, Na, Mg, Ca, Al, Zn, or the like can be used as a dispersion aid for the granules.

[0150] The concentration of the granulated block copolymer (I) dispersed in water obtained by the polymerization step of the block copolymer (I) and the above-described stripping is generally 0.1 mass% to 20 mass% (relative to the water in the stripping). If it is in this range, no operational trouble occurs, and granules having a good particle size can be obtained. It is preferable to adjust the water content to 1 mass% to 30 mass% by dehydrating the granules of the block copolymer (I), and then to dry until the water content reaches 1 mass% or less.

[0151] In the dehydration step of the above-described granules, dehydration can be performed using a roll, a Banbury-type dehydrator, a screw extruder-type press dehydrator, or the like, or using a conveyor belt, a box-type hot-air dryer, or the like, and these dehydration and drying can be performed simultaneously.

[0152] In the production method of the block copolymer (I) of the present embodiment, a process of deashing a metal such as a polymerization initiator or the like can be employed as necessary.

[0153] In addition, in the production method of the block copolymer of the present embodiment, a process of adding an antioxidant, a neutralizing agent, a surfactant, or the like can be further employed as necessary.

[0154] As the antioxidant, for example, a hindered phenol-based compound, a phosphorus-based compound, a sulfur-based compound, or the like can be mentioned, but is not limited thereto, and one kind thereof can be used alone, or two or more kinds thereof can be used in combination.

[0155] Examples of hindered phenol compounds include, but are not limited to, 2,6-di-tert-butyl-4-methylphenol, n-octadecyl-3-(4'-hydroxy-3',5'-di-tert-butylphenyl) propionate, [octadecyl-3-(3,5-dibutyl-tert-butyl-4-hydroxyphenyl) propionate], 2,2'-methylenebis(4-methyl-6-tert-butylphenol), 2,2'-methylenebis(4-ethyl-6-tert-butylphenol), 2,4-bis[(octylthio)methyl]-o-cresol, 2-tert-butyl-6-(3-tert-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenyl acrylate, 2,4-di-tert-amyl-6-[1-(3,5-di-tert-amyl-2-hydroxyphenyl)ethyl]phenyl acrylate, and 2-[1-(2-hydroxy-3,5-di-tert-amylphenyl)]acrylate.

[0156] Examples of the phosphorus-based compounds and sulfur-based compounds include, but are not limited to, 3,3'-thiodipropionate, 2-mercaptobenzimidazole, 4,6-bis(octylthiomethyl)-o-cresol, thiodiethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], dilaurylthiodipropionate, laurylstearylthiodipropionate, pentaerythritol tetrakis(6-laurylthiopropionate), tris(nonylphenyl)phosphite, and tris(2,4-di-tert-butylphenyl)phosphite.

[0157] The amount of the antioxidant added is preferably 0.01 to 1 part by mass, more preferably 0.05 to 0.5 parts by mass, and even more preferably 0.1 to 0.4 parts by mass, relative to 100 parts by mass of the block copolymer (I).

[0158] Examples of the neutralizing agent include, but are not limited to, various metal stearates, hydrotalcite, and benzoic acid.

[0159] Examples of the surfactant include, but are not limited to, anionic surfactants, nonionic surfactants, and cationic surfactants.

[0160] Examples of the anionic surfactant include, but are not limited to, fatty acid salts, alkyl sulfate ester salts, and alkyl aryl sulfonates.

[0161] Examples of the nonionic surfactant include, but are not limited to, polyoxyethylene alkyl ethers and polyoxyethylene alkylaryl ethers.

[0162] Examples of the cationic surfactant include, but are not limited to, alkylamine salts and quaternary ammonium salts.

[0163] In order to prevent blocking, the block copolymer (I) of the present embodiment may contain an anti-blocking agent in its pellets as needed.

[0164] As the anti-blocking agent, for example, calcium stearate, magnesium stearate, zinc stearate, polyethylene, polypropylene, ethylene bis-stearamide, talc, amorphous silica, and the like can be mentioned, but are not limited thereto.

[0165] As the mixing amount of the anti-blocking agent, 500 to 10,000 ppm, more preferably 1,000 to 7,000 ppm, relative to the block copolymer (I) is preferable. The anti-blocking agent is preferably mixed in a state of being attached to the surface of the granules, but a part thereof can be contained inside the granules.

[0166] Note that the block copolymer (I) of the present embodiment also includes a case where the above-described additive is mixed.

[0167] [Composition]

[0168] The composition of the present embodiment contains the block copolymer (I) of the present embodiment, the following component (II), and component (III).

[0169] That is, the composition of the present embodiment contains:

[0170] Component (I): 1 to 58 parts by mass of the block copolymer (I) of the present embodiment;

[0171] Component (II): 11 to 68 parts by mass of an ethylene-based copolymer; and

[0172] Component (III): 100 parts by mass of a propylene-based polymer.

[0173] (Component (II): Ethylene-based Copolymer)

[0174] The composition of the present embodiment contains an ethylene-based copolymer as component (II).

[0175] In the ethylene-based copolymer of component (II), there is no particular limitation as long as the content of ethylene units is 50% by mass or more relative to the total monomer units, and an ethylene-a-olefin copolymer is preferable.

[0176] In the ethylene-a-olefin copolymer, when the total content of ethylene units and a-olefin units is set to 100% by mass, the content of ethylene units is preferably 50 to 80% by mass, and the content of a-olefin units is preferably 20 to 50% by mass. If the content of ethylene units is within the above range, the affinity of component (II) of the composition of the present embodiment to other components is good, the differential dispersibility of the composition of the present embodiment is improved, and there is a tendency that the rigidity, elongation at break, and impact resistance are excellent.

[0177] Examples of the α-olefin constituting the ethylene·α-olefin copolymer include, but are not limited to, 1-propylene, 1-butene, 2-methylpropylene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, and 1-octene.

[0178] Component (II) may contain only one of these α-olefins or two or more of them.

[0179] Among these, the α-olefin is preferably an α-olefin having 4 to 8 carbon atoms, and more preferably 1-octene.

[0180] When the ethylene·α-olefin copolymer contains 1-octene units as α-olefin units, the elongation at break of the composition of the present embodiment tends to be good.

[0181] Examples of the ethylene·α-olefin copolymer include ethylene·α-olefin random copolymers and ethylene·α-olefin block copolymers. Among these, ethylene·α-olefin block copolymers are preferred, particularly ethylene·α-olefin block copolymers comprising a polymer block composed of ethylene and an ethylene·α-olefin copolymer block.

[0182] The ethylene-based copolymer of component (II) used in the composition of the present embodiment preferably has a crystal melting peak at 110 to 125° C., and a crystal melting heat of 20 to 60 J / g.

[0183] Here, in component (II), having a crystalline melting peak at 110 to 125°C and a crystalline melting heat of 20 to 60 J / g is an indicator that component (II) has a polymer block composed of crystalline ethylene. From the perspective of the high-temperature strength of the composition of this embodiment, the crystalline melting heat of component (II) is preferably 20 J / g or more, more preferably 30 J / g or more. In addition, from the perspective of the impact resistance of the composition of this embodiment at very low temperatures, the crystalline melting heat of component (II) is preferably 60 J / g or less, more preferably 50 J / g or less.

[0184] The component (II) preferably has a non-crystalline structure based on an ethylene-α-olefin copolymer block in addition to a polymer block composed of crystalline ethylene.

[0185] This amorphous property can be expressed by the glass transition temperature. The glass transition temperature of component (II) by DSC method is preferably -80°C or higher, more preferably -75°C or higher, and is preferably -50°C or lower, more preferably -60°C or lower.

[0186] When component (II) has such a structure, the composition of the present embodiment tends to be excellent in rigidity and impact resistance at extremely low temperatures.

[0187] The values ​​of the crystal melting peak, the heat of crystal melting, and the glass transition temperature of component (II) can be measured by differential scanning calorimetry (DSC).

[0188] The crystalline melting peak is the highest temperature of the melting peak obtained by differential scanning calorimetry.

[0189] The heat of crystal melting can be determined from the area of ​​the melting peak obtained by a differential scanning calorimeter.

[0190] The glass transition temperature is the intersection of a base line obtained by a differential scanning calorimeter and a tangent line at an inflection point.

[0191] The specific measurement conditions for obtaining these values ​​are as follows.

[0192] That is, a 10 mg sample was taken and, using DSC, the temperature was raised from 25°C to 200°C at a heating rate of 100°C / min to melt the sample. The sample was then held at 200°C for 1 minute, then cooled to -130°C at a cooling rate of 10°C / min to crystallize the sample. The sample was then held at -130°C for 10 minutes, then heated to 200°C at a heating rate of 10°C / min to perform measurement, and these values ​​were obtained.

[0193] The ethylene-based copolymer as the component (II) is a component mainly composed of ethylene units, and may have other monomer units in addition to the ethylene units.

[0194] Here, "mainly" means occupying 50% by mass or more of the whole, and particularly preferably 60 to 100% by mass.

[0195] Examples of other monomers include α-olefins such as 1-propylene, 1-butene, 2-methylpropylene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, and 1-octene, with 1-propylene, 1-butene, 1-hexene, and 1-octene being preferred.

[0196] When component (II) contains α-olefin units having 3 to 8 carbon atoms and having a carbon-carbon double bond at their terminal carbon atoms, only one α-olefin may be copolymerized with ethylene, or two or more α-olefins may be copolymerized with ethylene.

[0197] In the case where the component (II) is an ethylene-a-olefin copolymer, it can have other monomer units such as monomer units based on a non-conjugated diene (non-conjugated diene units) in addition to ethylene units and a-olefin units. As the above non-conjugated diene, there can be mentioned chain-like non-conjugated dienes such as 1,4-hexadiene, 1,6-octadiene, 2-methyl-1,5-hexadiene, 6-methyl-1,5-heptadiene, 7-methyl-1,6-octadiene; cyclic non-conjugated dienes such as cyclohexadiene, dicyclopentadiene, methyltetrahydroindene, 5-vinyl-norbornene, 5-ethylidene-2-norbornene, 5-methylene-2-norbornene, 5-isopropylidene-2-norbornene, 6-chloromethyl-5-isopropenyl-2-norbornene, and the like. Preferred are 5-ethylidene-2-norbornene and dicyclopentadiene.

[0198] The content of the ethylene units in the component (II) is preferably 50 to 80% by mass relative to the entire component (II). In order to prevent fusion due to blocking of the component (II), it is preferred that the content of the ethylene units in the component (II) be large, and from the viewpoint of the impact resistance of the composition of the present embodiment at very low temperatures, it is preferred that the content of the ethylene units in the component (II) be small.

[0199] The lower limit of the content of the ethylene units in the component (II) is more preferably 55% by mass or greater, and further preferably 60% by mass or greater.

[0200] On the other hand, the upper limit of the content of the ethylene units in the component (II) is more preferably 75% by mass or less. Note that the content of the ethylene units and the content of the a-olefin units in the component (II) can each be found by infrared spectroscopy.

[0201] In addition, in the case where the component (II) has other monomer units such as non-conjugated diene units, the content thereof is generally 10% by mass or less, and preferably 5% by mass or less, relative to the entire component (II).

[0202] The content of the non-conjugated diene units can also be found by infrared spectroscopy.

[0203] As the component (II) used in the composition of the present embodiment, specifically, there can be exemplified ethylene-based block copolymers including a polymer block composed of ethylene and including ethylene-1-butene copolymer, ethylene-1-hexene copolymer, ethylene-1-octene copolymer, ethylene-propylene-1-butene copolymer, ethylene-propylene-1-hexene copolymer, ethylene-propylene-1-octene copolymer, and the like ethylene-a-olefin copolymer block as preferred.

[0204] In the component (II), these ethylene-a-olefin copolymer blocks can include one, or two or more in combination.

[0205] Among these, component (II) is most preferably an ethylene-based block copolymer comprising a polymer block composed of ethylene and an ethylene-1-octene copolymer block.

[0206] The melt flow rate of component (II) is not limited, and is usually 10 g / 10 minutes or less, and from the viewpoint of the strength of the composition of the present embodiment, it is preferably 8.0 g / 10 minutes or less, more preferably 5.0 g / 10 minutes or less, and further preferably 3.0 g / 10 minutes or less.

[0207] In addition, the melt flow rate of component (II) is usually 0.01 g / 10 minutes or more, and from the viewpoint of the flowability of the composition of the present embodiment, it is preferably 0.05 g / 10 minutes or more, and more preferably 0.10 g / 10 minutes or more.

[0208] The melt flow rate (MFR) of component (II) is measured in accordance with ASTM D1238 at a measurement temperature of 190°C and a measurement load of 21.18 N.

[0209] From the viewpoint of the impact resistance at extremely low temperatures of the composition of the present embodiment, the density of component (II) is preferably 0.880 g / cm 3 and more preferably 0.875 g / cm 3 or more. On the other hand, the lower limit thereof is not particularly limited, and is usually 0.850 g / cm 3 or more.

[0210] The density of component (II) is measured in accordance with ISO 1183-A method at a measurement temperature of 23°C.

[0211] Component (II) can be synthesized according to the methods disclosed in Japanese Patent Application Publication No. 2007-529617, Japanese Patent Application Publication No. 2008-537563, and Japanese Patent Application Publication No. 2008-543978.

[0212] For example, it can be manufactured by preparing a composition comprising a mixture or reaction product obtained by combining a first olefin polymerization catalyst, a second olefin polymerization catalyst capable of producing a polymer having chemical or physical properties different from a polymer produced using the first olefin polymerization catalyst under equivalent polymerization conditions, and a chain shuttling agent, and contacting the above-described ethylene and α-olefin with the above-described composition under addition polymerization conditions.

[0213] A continuous solution polymerization method is preferably used in the polymerization of component (II).

[0214] In the continuous solution polymerization method, catalyst components, a chain shuttling agent, monomers, and, if necessary, a solvent, an auxiliary agent, a scavenger, and a polymerization aid are continuously supplied to a reaction zone, and a polymer product is continuously withdrawn.

[0215] In addition, the length of the polymer block can be controlled by adjusting the ratio and type of the above-mentioned catalysts, the ratio and type of the chain shuttling agent, the polymerization temperature, and the like.

[0216] In the method for synthesizing the ethylene-based copolymer of component (II), other conditions can be applied to the conditions disclosed in JP-A-2007-529617, JP-A-2008-537563, and JP-A-2008-543978.

[0217] As component (II), commercially available products may be used, for example, Engage (registered trademark)-XLT series and INFUSE (registered trademark) series manufactured by The Dow Chemical Company.

[0218] It should be noted that among component (II), regarding components having ethylene-octene copolymer blocks, the INFUSE (registered trademark) series and the Engage (registered trademark)-XLT series were commercially produced by The Dow Chemical Company in 2007 and 2011, respectively, and were not available as products before then.

[0219] The composition of the present embodiment may contain only one type of component (II), or may contain two or more types of components (II) having different monomer unit compositions, physical properties, and the like.

[0220] (Component (III): Propylene-based polymer)

[0221] The composition of this embodiment contains component (III): a propylene-based polymer.

[0222] The propylene-based polymer of component (III) refers to a polymer in which the content of propylene units relative to all monomer units is greater than 50% by mass.

[0223] That is, component (III) is a polypropylene-based resin having a propylene unit content of more than 50% by mass and 100% by mass or less.

[0224] The propylene polymer as component (III) is not particularly limited in type and may be a propylene homopolymer or a propylene copolymer containing propylene units and α-olefin units other than propylene (wherein the “α-olefin” mentioned here also includes ethylene) and / or monomer units other than α-olefins.

[0225] As the propylene-based copolymer, any of a propylene-based random copolymer and a propylene-based block copolymer can be used.

[0226] Among the components (III), the propylene-based polymer component contributes to the rigidity and heat resistance of the composition of the present embodiment.

[0227] Examples of the α-olefin units other than propylene contained in the propylene-based copolymer include ethylene and α-olefin units having 4 to 20 carbon atoms.

[0228] Examples of the α-olefins having 4 to 20 carbon atoms include 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, 1-tridecene, 1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-nonadecene, 1-eicosene, 3-methyl-1-butene, 3-methyl-1-pentene, 4-methyl-1-pentene, 2-ethyl-1-hexene, and 2,2,4-trimethyl-1-pentene.

[0229] As the α-olefin other than propylene, ethylene and α-olefins having 4 to 10 carbon atoms are preferred, and ethylene, 1-butene, 1-hexene, and 1-octene are more preferred.

[0230] Examples of the propylene polymer of component (III) include propylene homopolymers, propylene / ethylene copolymers, propylene / 1-butene copolymers, propylene / 1-hexene copolymers, propylene / 1-octene copolymers, propylene / ethylene / 1-butene copolymers, propylene / ethylene / 1-hexene copolymers, and propylene / ethylene / 1-octene copolymers. Preferred are propylene homopolymers and copolymers of propylene and at least one monomer selected from ethylene and α-olefins having 4 to 10 carbon atoms.

[0231] From the perspective of the impact resistance and elongation at break of the composition of this embodiment at extremely low temperatures, a particularly preferred component (III) is a polypropylene block copolymer obtained by polymerizing a propylene homopolymer in the first step and then polymerizing an ethylene-propylene copolymer in the second step.

[0232] The content of the propylene unit in the component (III) is greater than 50% by mass and less than or equal to 100% by mass, preferably 70 to 100% by mass, and more preferably 90 to 100% by mass, relative to the entire component (III).

[0233] When the content of the propylene unit of the component (III) is equal to or greater than the above lower limit, the rigidity and heat resistance of the composition of the present embodiment tend to be good.

[0234] The content of α-olefin units such as propylene units and ethylene in the component (III) can be determined by infrared spectroscopy.

[0235] From the perspective of the appearance of the molded article of the composition of this embodiment, the melt flow rate of component (III) is preferably 1 g / 10 min or more, more preferably 5 g / 10 min or more, further preferably 10 g / 10 min or more, and even more preferably 20 g / 10 min or more.

[0236] The melt flow rate of component (III) is usually 150 g / 10 min or less, and preferably 130 g / 10 min or less, more preferably 100 g / 10 min or less, from the viewpoint of tensile strength.

[0237] The melt flow rate (MFR) of the component (III) was measured in accordance with ISO 1133 at a measurement temperature of 230° C. and a measurement load of 21.18 N.

[0238] When the component (III) is a blend of propylene-based polymers having different MFRs, the MFR of the component (III) can be calculated by the following formula.

[0239] log(MFR blend)

[0240] =w1log(MFR1)+w2log(MFR2)+………+wilog(MFRi)+…+wnlog(MFRn)…(formula)

[0241] Where wi is the mass fraction of component i, MFRi is the MFR of component i, and n is the total number of components in the blend. w1+w2+…+wi+…wn=1.

[0242] As a method for producing the propylene-based polymer of component (III), a known polymerization method using a known olefin polymerization catalyst can be adopted.

[0243] For example, a multistage polymerization method using a Ziegler-Natta catalyst can be mentioned.

[0244] The multistage polymerization method may be a slurry polymerization method, a solution polymerization method, a bulk polymerization method, a gas phase polymerization method, or the like, or a combination of two or more of these methods may be used.

[0245] Alternatively, a commercially available corresponding product may be used as component (III).

[0246] The propylene-based polymer in the component (III) can be purchased from the following manufacturers and can be appropriately selected.

[0247] As commercially available products that can be obtained, for example, there are PrimPolypro (registered trademark) of PRIME POLYMER Co., Ltd., Sumitomo Noblen (registered trademark) of Sumitomo Chemical Co., Ltd., polypropylene block copolymer of SunAllomer Co., Ltd., NOVATEC (registered trademark) PP of Japan Polypropylene Co., Ltd., Moplen (registered trademark), Hifax X (registered trademark) of LyondellBasell Industries N.V., ExxonMobil PP of ExxonMobil Corporation, Formolene (registered trademark) of Formosa Plastics Corporation, Borealis PP of Borealis, SEETEC PP of LG Chemical, ASI POLYPROPYLENE of A. Schulman, INEOS PP of INEOS Olefins & Polymers, Braskem PP of Braskem, Sumsung Total of SAMSUNG TOTAL PETROCHEMICALS, Sabic (registered trademark) PP of Sabic, TOTAL PETROCHEMICALS Polypropylene of TOTAL PETROCHEMICALS, YUPLENE (registered trademark) of SK, and the like.

[0248] In the composition of the present embodiment, the component (III) can include only one kind, or two or more kinds of component (III) that differ in the monomer unit composition, physical properties, and the like.

[0249] (Inclusion ratio)

[0250] In the composition of the present embodiment, the content of the above component (I) is 1 part by mass or more, preferably 5 parts by mass or more, more preferably 10 parts by mass or more, further preferably 15 parts by mass or more, further more preferably 20 parts by mass or more, relative to 100 parts by mass of the component (III), from the viewpoint of the impact resistance at extremely low temperatures, the elongation at break, and the heat resistance of the obtained molded body. In addition, the content of the component (I) is 58 parts by mass or less, preferably 50 parts by mass or less, more preferably 45 parts by mass or less, further preferably 40 parts by mass or less, further more preferably 35 parts by mass or less, relative to 100 parts by mass of the component (III), from the viewpoint of the impact resistance at extremely low temperatures and the heat resistance of the obtained molded body.

[0251] In the composition of this embodiment, from the perspective of low-temperature properties and heat resistance of the resulting molded article, the content of component (II) is 11 parts by mass or more, preferably 15 parts by mass or more, more preferably 20 parts by mass or more, even more preferably 25 parts by mass or more, and even more preferably 30 parts by mass or more, relative to 100 parts by mass of component (III). Furthermore, from the perspective of heat resistance of the resulting molded article, the content of component (II) is 68 parts by mass or less, preferably 65 parts by mass or less, more preferably 60 parts by mass or less, even more preferably 55 parts by mass or less, and even more preferably 50 parts by mass or less, relative to 100 parts by mass of component (III).

[0252] (Other ingredients)

[0253] In addition to the above-mentioned components, the composition of the present embodiment may further contain optional components such as the following additives, inorganic fillers, organic fillers, and resins other than components (I) to (III) (hereinafter referred to as "other resins") according to various purposes, within a range that does not significantly impair the effects of the present invention.

[0254] Examples of additives include colorants, antioxidants, weathering agents, heat stabilizers, light stabilizers, ultraviolet absorbers, neutralizers, lubricants, antifogging agents, antiblocking agents, slip agents, flame retardants, dispersants, antistatic agents, conductivity-imparting agents, metal deactivators, molecular weight regulators, antibacterial agents, fluorescent brighteners, and the like.

[0255] These additives can be generally blended in an amount of 0.01 to 2 parts by mass per 100 parts by mass of the total of components (I) to (III).

[0256] Examples of other resins that may be contained in the composition of this embodiment include polyester elastomers, urethane elastomers, polyester resins, polyamide resins, polyurethane resins, styrene resins (excluding substances corresponding to component (I)), acrylic resins, polycarbonate resins, polyvinyl chloride resins, polypropylene resins and other polyolefin resins (excluding substances corresponding to component (II) and component (III)), and various elastomers other than those mentioned above.

[0257] The other resins listed above may be contained alone or in combination of two or more.

[0258] (Method for producing composition)

[0259] The composition of the present embodiment can be produced by kneading components (I) to (III) and other components by a conventional method using a common extruder, Banbury mixer, roll, Brabender plastometer, Brabender kneader, or the like.

[0260] Among these production methods, it is preferred to use an extruder, particularly a twin-screw extruder.

[0261] The composition of the present embodiment can be produced by kneading using an extruder or the like and melt-kneading while heating to generally 160 to 240° C., preferably 180 to 220° C. The composition of the present embodiment can also be partially crosslinked by mixing the following crosslinking agent and crosslinking aid into the composition and subjecting it to a dynamic heat treatment.

[0262] As a crosslinking agent for partially crosslinking the composition of the present embodiment, an organic peroxide is preferably used. Examples of the organic peroxide include 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, 2,5-dimethyl-2,5-di(tert-butylperoxy)-3-hexyne, 1,3-bis(tert-butylperoxyisopropyl)benzene, 1,1-di(tert-butylperoxy)-3,5,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(benzoylperoxy)-3-hexyne, and dicumyl peroxide.

[0263] Examples of crosslinking aids used when partially crosslinking with these organic peroxides include compounds having a free radical polymerizable carbon-carbon double bond, such as N,N'-m-phenylenebismaleimide, tolylenebismaleimide, p-quinonedioxime, p-dinitrosobenzene, 1,3-diphenylguanidine, trimethylolpropane triacrylate, divinylbenzene, ethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, and allyl methacrylate, and compounds having a functional group reactive with the carbon linear portion of component (II).

[0264] [Airbag storage cover]

[0265] The composition of the present embodiment can be formed into a desired molded article by applying a conventional injection molding method or, if necessary, applying various molding methods such as gas injection molding, injection compression molding, and short shot foaming.

[0266] The composition of this embodiment is suitable as a material for an airbag storage cover.

[0267] The airbag storage cover of the present embodiment is preferably manufactured by injection molding, and the molding conditions during injection molding are as follows.

[0268] The molding temperature during injection molding of the airbag storage cover is generally 150 to 300°C, preferably 160 to 280°C.

[0269] The injection pressure is usually 5 to 100 MPa, preferably 10 to 80 MPa.

[0270] The mold temperature is usually 0 to 80°C, preferably 20 to 60°C.

[0271] The airbag storage cover thus obtained is suitable for use as an airbag storage cover of an airbag system that senses impact or deformation and activates and inflates and deploys an airbag when a high-speed moving object such as an automobile is involved in a collision accident.

[0272] The airbag housing cover of the present embodiment can be suitably used for driver's seat airbag housing covers, passenger's seat airbag housing covers, pedestrian airbag housing covers, knee airbag housing covers, side airbag housing covers, curtain airbag housing covers, and the like.

[0273] Example

[0274] The present embodiment will be described in further detail below with reference to specific examples and comparative examples, but the present invention is not limited to the following examples.

[0275] First, evaluation methods and physical property measurement methods applied to Examples and Comparative Examples are described below.

[0276] [Method for specifying the structure of a block copolymer and method for measuring physical properties]

[0277] (Peak molecular weight, weight average molecular weight and coupling ratio of block copolymers)

[0278] Each molecular weight was measured by gel permeation chromatography (GPC) [apparatus: manufactured by Waters] under the following measurement conditions.

[0279] The molecular weight of the peak top of the block copolymer (in the case of a coupled structure, corresponding to the uncoupled diblock component in the block copolymer) was determined from the obtained chromatogram using a calibration curve obtained by measurement of commercially available standard polystyrene (created using the peak molecular weight of the standard polystyrene).

[0280] Furthermore, a base line including all the peaks was set, and the weight average molecular weight of the entire block copolymer was calculated in the same manner.

[0281] <Measurement Conditions>

[0282] GPC; ACQUITY APC system (manufactured by Waters Corporation, Japan)

[0283] System (measurement and analysis) software: Empower3

[0284] Detector; Differential Refractive Index (RI) detector

[0285] Refractive index unit full scale: 500μRIU

[0286] Output full scale: 2000mV

[0287] Sampling rate: 10 points / second

[0288] Column: ACQUITY APC XT125 (4.6mm×150mm); 1 piece

[0289] ACQUITY APC XT200 (4.6mm×150mm); 1 piece

[0290] ACQUITY APC XT900 (4.6mm×150mm); 1 piece

[0291] ACQUITY APC XT450 (4.6mm×150mm); 1 piece

[0292] Solvent: Tetrahydrofuran (THF)

[0293] Flow rate: 1.0mL / min

[0294] Concentration: 0.1 mg / mL

[0295] Column temperature: 40°C

[0296] Injection volume: 20μL

[0297] <Coupling rate>

[0298] The coupling ratio was calculated from the ratio of the area of ​​the unreacted diblock component and the other coupled components to the total area by vertically dividing the inflection point of each inter-peak curve obtained by GPC in the coupled block copolymer.

[0299] (Content of vinyl aromatic monomer units in block copolymer)

[0300] A certain amount of the block copolymer was dissolved in chloroform and measured using an ultraviolet spectrophotometer (manufactured by Shimadzu Corporation, UV-2450). The content of the vinyl aromatic monomer unit (styrene) was calculated using a calibration curve based on the peak intensity at the absorption wavelength (262 nm) attributed to the vinyl aromatic compound component (styrene).

[0301] In addition, the content of the conjugated diene monomer unit in the block copolymer is calculated by (100-the content of all vinyl aromatic monomer units).

[0302] (Ratio of 1,2-bond and 3,4-bond in conjugated diene monomer unit contained in polymer block B in block copolymer (vinyl bond amount))

[0303] The proportion of 1,2-linkage and 3,4-linkage (vinyl bond amount) in the conjugated diene monomer unit in the block copolymer was determined using a nuclear magnetic resonance device (NMR) under the following measurement conditions.

[0304] After the completion of the entire reaction (after the completion of the hydrogenation reaction in the case of the hydrogenated block copolymer), a large amount of methanol was added to the reaction solution, whereby the block copolymer was precipitated and recovered. The recovered block copolymer was then extracted with acetone, and the extract was vacuum-dried and used as a sample for 1H-NMR measurement.

[0305] The conditions for 1H-NMR measurement were as follows.

[0306] <Measurement Conditions>

[0307] Measurement device: JNM-LA400 (manufactured by JEOL)

[0308] Solvent: deuterated chloroform

[0309] Sample concentration: 50 mg / mL

[0310] Observation frequency: 400 MHz

[0311] Chemical shift reference: TMS (tetramethylsilane)

[0312] Pulse delay: 2.904 seconds

[0313] Number of scans: 64

[0314] Pulse width: 45°

[0315] Measurement temperature: 26°C

[0316] The proportion of 1,2-linkage and 3,4-linkage (vinyl bond amount) in the conjugated diene monomer unit in the block copolymer was determined using a nuclear magnetic resonance device (NMR) under the following measurement conditions.

[0317] (Content of Polymer Block A in the Block Copolymer)

[0318] The content of the polymer block A, which is the main body of the vinyl aromatic monomer unit, was determined using a nuclear magnetic resonance device (NMR) (Y. Tanaka, et al., RUBBER CHEMISTRY and TECHNOLOGY 54, 685 (1981). Hereinafter, referred to as "NMR method") using the block copolymer before hydrogenation.

[0319] (Hydrogenation rate of conjugated diene monomer unit included in polymer block B in block copolymer)

[0320] The hydrogenation rate of double bonds in the conjugated diene monomer unit included in polymer block B in the block copolymer was determined using a nuclear magnetic resonance device (NMR) under the same conditions as the determination method of (1,2-bonding and 3,4-bonding ratio) described above.

[0321] The hydrogenation rate of double bonds in the conjugated diene monomer unit included in polymer block B in the block copolymer was determined by calculating the proportion of the hydrogenated 1,2-bonding and hydrogenated 3,4-bonding and hydrogenated 1,4-bonding peak total area in the conjugated diene monomer unit to the total peak (1,2-bonding, 3,4-bonding, 1,4-bonding) related to the double bonds in the conjugated diene monomer unit.

[0322] (MFR of block copolymer)

[0323] The MFR of the block copolymer was determined according to JIS K7210 under the conditions of a temperature of 230°C and a load of 2.16 kg.

[0324] [Manufacture of composition]

[0325] (Component (I))

[0326] Preparation of hydrogenation catalyst

[0327] In the examples and comparative examples described later, the hydrogenation catalyst used for the production of the block copolymer was prepared by the following method.

[0328] A reaction vessel equipped with a stirring device was subjected to nitrogen replacement, and 1 L of dried and purified cyclohexane was added thereto. Then, 100 mmol of bis(η5-cyclopentadienyl) titanium dichloride was added. While stirring it sufficiently, 200 mmol of a solution of trimethylaluminum in n-hexane was added, and the reaction was carried out at room temperature for about 3 days to obtain a hydrogenation catalyst.

[0329] Manufacture of block copolymer ((I-1) to (I-26))

[0330] The polymerization conditions, structure, and properties of the block copolymer are shown in Tables 1 to 3.

[0331] Block copolymer (I-1)

[0332] A tank-type reactor with a stirring device and a jacket having a content of 100 L was cleaned, dried, and subjected to nitrogen replacement, and batch polymerization was performed as follows to produce the block copolymer (I-1).

[0333] As the 1st step, after a cyclohexane solution containing cyclohexane 38 L and styrene monomer 20.0 parts by mass was charged, N,N,N',N'-tetramethylethylenediamine (hereinafter also referred to as "TMEDA") was added at 0.58 mol relative to 1 mol of n-butyllithium (hereinafter also referred to as "Bu-Li").

[0334] As the 2nd step, after adjustment to a temperature of 40°C, Bu-Li was added at 0.090 parts by mass relative to 100 parts by mass of the total monomers, and polymerization was performed for 30 minutes under conditions of a temperature of 60°C in the reactor.

[0335] As the 3rd step, a cyclohexane solution containing conjugated diene monomer (butadiene monomer) 80.0 parts by mass was charged, and further polymerization was performed for 60 minutes while adjusting the reaction temperature to 80°C.

[0336] As the 4th step, tetramethoxysilane (hereinafter also referred to as "TMS") was added at a molar ratio of Si to Li (Si / Li) of 0.30 mol, and after stirring for 20 minutes, methanol was added at 0.1 mol relative to 1 mol of Bu-Li, to obtain a styrene-butadiene coupled polymer.

[0337] As the 5th step, the obtained coupled polymer was continuously hydrogenated at 95°C using a hydrogenation catalyst prepared as described above. The amount of hydrogenation catalyst was 100 ppm, the hydrogen pressure in the hydrogenation polymerizer was 0.95 MPa, and the average residence time was 90 minutes. After the end of the reaction, an antioxidant (octadecyl-3-(3,5-dibutyl-tert-butyl-4-hydroxyphenyl)propionate) was added at 0.25 parts by mass relative to 100 parts by mass of the block copolymer (I-1), to obtain a block copolymer (I-1).

[0338] The properties of the obtained block copolymer (I-1) are shown in Table 1.

[0339] <Block copolymers (I-2, 3, 4, 16, 19, and 20)>

[0340] The block copolymers (I-2, 3, 4, 16, 19, and 20) were obtained in the same manner as the block copolymer (I-1) described above, except that the addition amount of TMEDA in the 1st step and the addition amount of Bu-Li in the 2nd step were adjusted as shown in Tables 1 to 3 below.

[0341] <Block copolymers (I-5, 6, and 21)>

[0342] The block copolymers (I-5, 6, and 21) were obtained in the same manner as the block copolymer (I-1) described above, except that the addition amount of styrene monomer in the 1st step and the addition amount of butadiene monomer in the 3rd step were adjusted as shown in Tables 1 to 3 below.

[0343] <block copolymer (I-7, 8, 9, 10, 22, 23, and 24)>

[0344] The block copolymers (I-7, 8, 9, 10, 22, 23, and 24) were obtained in the same manner as in the block copolymer (I-l) except that the amount of TMEDA added in the first step was adjusted as shown in Tables 1 to 3 below.

[0345] <block copolymer (I-11, 12, 13, 14, 25, and 26)>

[0346] The block copolymers (I-11, 12, 13, 14, and 25) were obtained in the same manner as in the block copolymer (I-l) except that the average residence time at the time of the hydrogenation reaction in the fifth step was adjusted as shown in Tables 1 to 3 below.

[0347] Note that the block copolymer (I-25) was not subjected to the reaction of the fifth step.

[0348] <block copolymer (I-15, 17, 18)>

[0349] The block copolymers (I-15, 17, and 18) were obtained in the same manner as in the block copolymer (I-l) except that the amount of TMS added in the fourth step was adjusted as shown in Tables 1 and 2 below.

[0350] <block copolymer (I-16)>

[0351] A tank-type reactor having a stirring device and a jacket with a content volume of 100 L was cleaned, dried, and replaced with nitrogen, and batch polymerization was performed as follows to produce the block copolymer (I-16).

[0352] As the first step, after a cyclohexane solution containing cyclohexane 38 L and styrene monomer 10.0 parts by mass was charged, N,N,N',N'-tetramethylethylenediamine (hereinafter also referred to as "TMEDA") was added at 0.62 mol per 1 mol of n-butyllithium (hereinafter also referred to as "Bu-Li").

[0353] As the second step, after adjustment to a temperature of 40°C, Bu-Li was added at 0.021 parts by mass per 100 parts by mass of the total monomers, and polymerization was performed for 30 minutes under conditions in which the temperature in the reactor was 60°C.

[0354] As the third step, a cyclohexane solution containing conjugated diene monomer (butadiene monomer) 80.0 parts by mass was charged, and further polymerization was performed for 80 minutes while adjusting the reaction temperature to 80°C.

[0355] As the fourth step, a cyclohexane solution containing 10.0 parts by mass of styrene monomer was added and polymerized at an internal temperature of 80° C. for 30 minutes. Then, 0.1 mol of methanol was added per mol of Bu—Li to obtain a styrene-butadiene-styrene polymer.

[0356] As the 5th step, using the hydrogenation catalyst prepared as described above, the obtained polymer is continuously hydrogenated at 95 DEG C. The amount of hydrogenation catalyst is 100ppm, the hydrogen pressure in the hydropolymerizer is 0.95MPa, and the average residence time is 90 minutes. After the reaction is completed, an antioxidant (octadecyl-3-(3,5-dibutyl-tert-butyl-4-hydroxyphenyl) propionate) is added to 100 parts by mass of block copolymer to obtain block copolymer (I-16). The characteristics of the obtained block copolymer (I-16) are shown in Table 2 below.

[0357] (ingredient (II))

[0358] (II-1): Engage (registered trademark) XLT8677 manufactured by The Dow Chemical Company (an ethylene-based block copolymer having a polymer block composed of ethylene and an ethylene-1-octene copolymer block)

[0359] Crystallization melting peak temperature: 119℃

[0360] Crystallization melting heat: 37J / g

[0361] Glass transition temperature (DSC method): -67°C

[0362] MFR (ASTM D1238): 0.5g / 10min

[0363] (Measurement conditions: 190°C, load 21.18N (2.16kgf)) (Product catalog value)

[0364] Density (ISO 1183-A method): 0.872 g / cm 3 (Measurement temperature: 23°C)

[0365] (Component (III))

[0366] (III-1): Propylene-based block copolymer (obtained by polymerizing a propylene homopolymer in the first step and then polymerizing an ethylene-propylene copolymer in the second step)

[0367] MFR (ISO 1133): 65 g / 10 min (measurement conditions: 230°C, load 21.18 N (2.16 kgf))

[0368] Propylene polymer content: 92% by mass

[0369] Ethylene-propylene copolymer content: 8% by mass

[0370] Ethylene unit content in the ethylene-propylene copolymer component: 43% by mass

[0371] (III-2): HifaxX (registered trademark) 1956A manufactured by Lyondell Basell

[0372] (Product obtained by polymerizing a propylene homopolymer in the first step and then polymerizing an ethylene-propylene copolymer in the second step)

[0373] MFR (ISO 1133): 1.1 g / 10 minutes (measurement conditions: 230°C, load 21.18 N (2.16 kgf))

[0374] Content of propylene polymer component: 70% by mass

[0375] Ethylene-propylene copolymer content: 30% by mass,

[0376] Ethylene unit content in the ethylene-propylene copolymer component: 65% by mass

[0377] [Method of kneading the composition]

[0378] According to the compounding contents shown in Tables 4 to 6 below, the respective components were mixed using the materials and methods described below to obtain compositions.

[0379] With respect to 100 parts by mass of the total of the above-mentioned components (I), (II), and (III), 0.2 parts by mass of an antioxidant (0.1 parts by mass of a fine mesh (trade name IRGANOX (registered trademark) 1010, manufactured by BASF Japan) and 0.1 parts by mass of (trade name Irgafos (registered trademark) 168, manufactured by BASF Japan), 0.2 parts by mass of a weathering aid (trade name Tinuvin (registered trademark) XT855FF, manufactured by BASF Japan), and 1.5 parts by mass of a colorant (black pigment, product with a carbon concentration of 40% by mass) were mixed for 1 minute using a Henschel mixer. The mixture was then fed into a co-rotating twin-screw extruder ("TEX30α", L / D = 45) at a rate of 20 kg / hr, and the mixture was heated within a range of 180 to 210°C and melt-kneaded to produce pellets of the composition.

[0380] Then, an ISO long dumbbell-shaped test piece (length 80 mm, width about 10 mm, thickness about 4 mm) for measuring physical properties was obtained by injection molding (cylinder setting temperature 210° C., mold temperature 40° C.).

[0381] [Evaluation method of composition]

[0382] (elongation at break)

[0383] The injection molded test pieces obtained in the above [Method of Kneading Composition] were subjected to a tensile test using a tensile testing machine (Minebea, TG-5kN) at 23°C and a crosshead speed of 500 mm / min in accordance with JIS K 6251. The elongation at break was measured and evaluated according to the following criteria.

[0384] ○: Elongation at break is 600% or more

[0385] △: Elongation at break is 300% or more and less than 600%

[0386] ×: Elongation at break less than 300%

[0387] (rigidity)

[0388] The ends of the ISO long dumbbell-shaped test piece obtained in the above [Method for Kneading Composition] were cut, and the parallel portion was formed into a long test piece with a length of approximately 80 mm, a width of approximately 10 mm, and a thickness of approximately 4 mm. The flexural modulus was calculated using the secant method from the strain-stress curve obtained by the three-point bending test, and evaluated according to the following criteria.

[0389] ○: Flexural rigidity is 300 MPa or more

[0390] △: Flexural rigidity is 250 MPa or more and less than 300 MPa

[0391] ×: Flexural rigidity less than 250 MPa

[0392] (Impact resistance at low temperatures (-45°C, -70°C))

[0393] The notched Charpy impact strength was measured in accordance with JIS K 7111-1 and evaluated based on the following criteria.

[0394] As for the test piece, the injection-molded ISO dumbbell-shaped test piece obtained in the above [Method for Kneading Composition] was cut at both ends, and the parallel portion was made into a long strip test piece with a length of about 80 mm, a width of about 10 mm, and a thickness of about 4 mm. The notch shape was A, and the impact direction was lateral.

[0395] The measurement temperature is -45°C and -70°C. The unit is kJ / m 2 .

[0396] <-45℃>

[0397] ○: Impact strength is 8kJ / m 2above

[0398] △: Impact strength is 3kJ / m 2 Above and less than 8kJ / m 2

[0399] ×: Impact strength less than 3 kJ / m 2

[0400] <-70℃>

[0401] ◎: Impact strength is 5kJ / m 2 above

[0402] ○: Impact strength is 3kJ / m 2 Above and less than 5kJ / m 2

[0403] △: Impact strength is 1kJ / m 2 Above and less than 3kJ / m 2

[0404] ×: Impact strength less than 1 kJ / m 2

[0405] (Low gloss)

[0406] The composition obtained by the above-mentioned [Composition Kneading Method] was used to produce a mirror-finished molded plate by injection molding (cylinder setting temperature 210°C, mold temperature 40°C). The gloss value (glossiness) was measured at an incident angle of 60° in accordance with ISO 7668 and evaluated according to the following criteria.

[0407] ○: Gloss value less than 20

[0408] △: Gloss value is 20 or more and less than 40

[0409] ×: Glossiness value is 40 or more

[0410] (Shrinkage after heating)

[0411] The injection molded test piece obtained by the above-mentioned [Method of Kneading Composition] was exposed to heat at 110° C. for 1000 hours, and then the dimensional change (MD direction) before and after heating was measured and evaluated according to the following criteria.

[0412] ○: Shrinkage rate less than 0.5%

[0413] △: Shrinkage is 0.5% or more and less than 2.0%

[0414] ×: Shrinkage rate is 2.0% or more

[0415] (Surface appearance)

[0416] The injection molded test pieces obtained in the above-mentioned [Method of Kneading Composition] were visually observed for the presence of flow marks and uneven gloss, and the surface appearance was evaluated according to the following criteria.

[0417] The surface appearance evaluation was performed by 5 people, and the evaluation results were consistent among all of them.

[0418] ◯: Neither flow marks nor gloss unevenness were observed on the test piece.

[0419] △: Flow marks and gloss unevenness of the test piece were slightly observed.

[0420] ×: Flow marks and gloss unevenness of the test piece were clearly observed.

[0421] (VOC (residual cyclohexane))

[0422] The cyclohexane remaining in the block copolymer prepared as described above was dissolved in chloroform at 5 g / 50 mL as a measurement sample, and methanol was added for precipitation. The solution was measured using a gas chromatograph (GC7820A / 7890A manufactured by Agilent) to evaluate VOC according to the following criteria.

[0423] ○: Cyclohexane content is less than 500ppm

[0424] △: Cyclohexane content is 500 ppm or more and less than 1500 ppm

[0425] ×: Cyclohexane content is 1500 ppm or more

[0426] The production methods and physical properties of the block copolymers (Production Examples 1 to 18, Comparative Production Examples 19 to 26) are shown in Tables 1 to 3 below, and the compositions and properties of the compositions using the block copolymers are shown in Tables 4 to 6 below.

[0427]

[0428]

[0429]

[0430]

[0431]

[0432]

[0433] As can be seen from Tables 4 to 6, Examples 1 to 21 were evaluated as excellent in terms of impact resistance at very low temperatures, elongation at break, rigidity, low gloss, and balance of properties, with no x in each evaluation and ○ or △.

[0434] As apparent from Tables 4 to 6, in Comparative Examples 1 to 10, any one of the evaluations of impact resistance at extremely low temperatures, elongation at break, rigidity, low gloss, and balance of properties was marked as ×, and was evaluated as poor.

[0435] This application is based on Japanese patent application No. 2023-031542 filed with the Japan Patent Office on March 2, 2023, the contents of which are incorporated herein by reference.

[0436] Industrial Applicability

[0437] The block copolymers and compositions of the present invention exhibit excellent impact resistance, elongation at break, rigidity, low gloss, and a balance of these properties at extremely low temperatures. These block copolymers have industrial applicability as materials for automotive interior components such as airbag covers, instrument panels, center panels, center consoles, door trims, pillars, armrests, and handles; automotive exterior components such as fender grommets; home appliance components; building materials; and furniture. They are particularly suitable as materials for airbag covers in airbag systems that inflate and deploy by sensing impact or deformation in collisions, such as those involving high-speed moving objects like automobiles, to protect passengers.

Claims

1. A block copolymer (I), wherein The block copolymer (I) comprises a polymer block A mainly composed of vinyl aromatic monomer units and a polymer block B mainly composed of conjugated diene monomer units. The content of the polymer block A is 3% to 40% by mass. The vinyl bond content of the polymer block B before hydrogenation is 35 mol% to 55 mol%, The hydrogenation rate of the conjugated diene monomer units contained in the polymer block B is 30 mol% to 90 mol%. The weight average molecular weight of the block copolymer (I) is 150,000 to 600,000.

2. The block copolymer (I) according to claim 1, wherein The hydrogenation rate of the conjugated diene monomer units contained in the polymer block B is 30 mol% to 77 mol%.

3. The block copolymer (I) according to claim 1, wherein The melt flow rate measured under the conditions of a measurement temperature of 230° C. and a measurement load of 2.16 kg in accordance with ISO 1133 is less than 0.1 g / 10 minutes.

4. The block copolymer (I) according to claim 1, which is a hydrogenated product of a coupled polymer represented by the following (1) having a coupling rate of 80% or more, (A-B) n-X (1) In formula (1), A is a polymer block A mainly composed of vinyl aromatic monomer units, B is a polymer block B mainly composed of conjugated diene monomer units, n is an integer greater than 1, and X is a residue of a coupling agent or a residue of a polymerization initiator. The block copolymer (I) according to claim 1 , which is in the form of any one selected from the group consisting of pellets, flakes and powder.

6. A composition for an airbag storage cover, comprising: Component (I): 1 to 58 parts by mass of the block copolymer (I) according to any one of claims 1 to 5; Component (II): 11 to 68 parts by mass of an ethylene copolymer; and Component (III): 100 parts by mass of propylene-based polymer. 7 . An airbag storage cover formed from the composition according to claim 6 .

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