Thermoplastic elastomer composition, molded body, and automotive component

Abstract

Provided is a thermoplastic elastomer composition wherein: the amount of a propylene-based block copolymer (A) having an MFR as measured under the conditions of 230°C and a 2.16 kg load in accordance with ASTM D1238 of 50 g / 10 min or less and having an ethylene-derived structural unit content of 6.0 mass% or more relative to all structural units is 30-55 mass%; the amount of an ethylene-based copolymer rubber (B) is 25-70 mass%; and the amount of an at least partially crosslinked ethylene-based copolymer rubber (C) is 0-20 mass% (provided that the total amount of the propylene-based block copolymer (A), the ethylene-based copolymer rubber (B), and the ethylene-based copolymer rubber (C) is 100 mass%). Also provided are a thermoplastic elastomer molded body and an automotive component.

Description

Thermoplastic elastomer composition, molded body, and automobile part

[0001] The present invention relates to a thermoplastic elastomer composition, a molded article, and an automobile part.

[0002] Olefin-based thermoplastic elastomers are made from ethylene copolymers and crystalline olefin-based polymers such as polypropylene, and are therefore lighter and easier to recycle than other thermoplastic elastomers. Furthermore, because they do not emit toxic gases when incinerated, they are widely used in automobile parts, industrial machinery parts, electrical and electronic parts, building materials, etc., particularly as a substitute for vulcanized rubber, from the viewpoints of energy conservation, resource conservation, and more recently, global environmental protection.

[0003] As a thermoplastic elastomer composition having good low-temperature tensile elongation, for example, Patent Document 1 discloses a thermoplastic elastomer composition containing 30 to 60 parts by mass of a propylene polymer (A), 32 to 65 parts by mass of an ethylene-α-olefin copolymer (B) composed of ethylene and an α-olefin having 4 to 20 carbon atoms, and 1 to 20 parts by mass of an at least partially crosslinked rubber (C) (the total amount of components (A), (B), and (C) is 100 parts by mass). Furthermore, as a thermoplastic elastomer composition having a good balance of required properties such as melt flowability during injection molding, releasability when releasing a molded body from a mold, low-temperature impact resistance of an airbag cover molded body obtained by injection molding, and weld physical properties, for example, Patent Document 2 discloses a thermoplastic elastomer composition comprising: component (A): a propylene-based polymer portion (a) obtained by polymerizing a monomer mainly composed of propylene polymerized in a first step and an ethylene-based copolymer portion (b) polymerized in a second step, and having an intrinsic viscosity [η] of 2.5 to 8.0; component (B): an ethylene-propylene-based copolymer rubber having a Mooney viscosity of 20 to 100; and component (C): a propylene-based copolymer rubber having a density of 0.860 to 0.910 g / cm ３ and an ethylene copolymer having a melt flow rate of 0.01 to 10 g / 10 min.

[0004] International Publication No. 2020 / 162382 Japanese Patent Application Laid-Open No. 2009-24054

[0005] Resin compositions used in automotive parts, such as airbag covers for automotive airbag systems, are required to have improved impact strength at lower temperatures so that they can withstand more severe usage environments, are required to prevent fragments of the airbag cover from flying when the airbag is deployed, and are required to be usable in a wide range of temperature environments, from low to high. Furthermore, since the molded body may be deformed by the ejector when removed from injection molding, a resin composition that is less likely to deform when molded by injection molding is required. Neither Patent Document 1 nor Patent Document 2 discusses the suppression of fogging.

[0006] The problem to be solved by one embodiment of the present invention is to provide a thermoplastic elastomer composition that can produce molded articles having excellent fogging suppression and low-temperature impact resistance. The problem to be solved by another embodiment of the present invention is to provide molded articles and automotive parts having excellent fogging suppression and low-temperature impact resistance.

[0007] Means for solving the above problems include the following aspects: <1> A thermoplastic elastomer composition having a melt flow rate (MFR) of 50 g / 10 min or less, measured in accordance with ASTM D1238 under conditions of 230°C and a load of 2.16 kg, and containing 30 to 55 mass% of a propylene-based block copolymer (A) having a content of structural units derived from ethylene of 6.0 mass% or more, based on the total mass of the copolymer, and having 25 to 70 mass% of an ethylene-based copolymer rubber (B), and having 0 to 20 mass% of an at least partially crosslinked ethylene-based copolymer rubber (C), wherein the total amount of the propylene-based block copolymer (A), the ethylene-based copolymer rubber (B), and the ethylene-based copolymer rubber (C) is 100 mass%. <2> The thermoplastic elastomer composition according to <1>, wherein the content of the ethylene-based copolymer rubber (C) is 1 to 20% by mass (provided that the total amount of the propylene-based block copolymer (A), the ethylene-based copolymer rubber (B), and the ethylene-based copolymer rubber (C) is 100% by mass). <3> The thermoplastic elastomer composition according to <1> or <2>, wherein the propylene-based block copolymer (A) has a melting point (Tm) of 145 to 170°C. <4> The thermoplastic elastomer composition according to any one of <1> to <3>, wherein the ethylene-based copolymer rubber (B) contains at least one of an ethylene-1-butene copolymer and an ethylene-1-octene copolymer. <5> A thermoplastic elastomer molded article, which is a molded article of the thermoplastic elastomer composition according to any one of <1> to <4>. <6> The thermoplastic elastomer molded article according to <5>, wherein the initial flexural modulus measured in accordance with ASTM D790 is 200 MPa or more. <7> An automobile part comprising the thermoplastic elastomer molded article according to <6>. <8> The automobile part according to <7>, which is an airbag cover.

[0008] According to one embodiment of the present invention, there is provided a thermoplastic elastomer composition that suppresses the generation of volatile components (fogging) and that can produce molded articles that have excellent low-temperature impact resistance. Also, according to one embodiment of the present invention, there are provided molded articles and automotive parts that have excellent suppression of the generation of volatile components (fogging) and have excellent low-temperature impact resistance.

[0009] The present invention will be described in detail below. The following description of the constituent elements may be based on a representative embodiment of the present invention, but the present invention is not limited to such an embodiment. In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. When referring to the amount of each component in a composition, if multiple substances corresponding to each component are present in the composition, the total amount of the multiple substances present in the composition is referred to unless otherwise specified. In this specification, when a numerical range is indicated by "to," the units before or after the "to" refer to the same unit unless otherwise specified. In this specification, a combination of two or more preferred embodiments is a more preferred embodiment. Furthermore, in this specification, unless otherwise specified, each component in a composition or each structural unit in a polymer may be present alone or in combination of two or more types. The present invention will be described in detail below.

[0010] <Thermoplastic Elastomer Composition> The thermoplastic elastomer composition according to the present invention has a melt flow rate (MFR) of 50 g / 10 min or less, measured in accordance with ASTM D1238 at 230°C under a load of 2.16 kg, and contains 30 to 55 mass% of a propylene-based block copolymer (A) having a content of ethylene-derived structural units of 6.0 mass% or more based on all structural units, 25 to 70 mass% of an ethylene-based copolymer rubber (B), and 0 to 20 mass% of an at least partially crosslinked ethylene-based copolymer rubber (C) (wherein the total amount of the propylene-based block copolymer (A), the ethylene-based copolymer rubber (B), and the ethylene-based copolymer rubber (C) is 100 mass%). Each component of the thermoplastic elastomer composition will be described in detail below.

[0011] <<Propylene-Based Block Copolymer (A)>> The propylene-based block copolymer (A) is a propylene-ethylene block copolymer. The propylene-based block copolymer (A) is a copolymer mainly composed of structural units derived from propylene, and the content of the structural units derived from propylene is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 80% by mass or more, based on the total mass of the copolymer.

[0012] The content of the propylene-derived structural unit, the content of the ethylene-derived structural unit, the content of the α-olefin-derived structural unit, and the content of the non-conjugated polyene-derived structural unit are as follows: １３ It can be determined by calculation based on the results of measurement by C-NMR.

[0013] The propylene-based block copolymer (A) contains structural units derived from ethylene, and the content of the structural units derived from ethylene is 6.0% by mass or more, preferably 6.0 to 25% by mass, and more preferably 6.5 to 20% by mass, based on the total mass of the copolymer. When the content of the structural units derived from ethylene is within the above range, the generation of volatile (fogging) components is effectively suppressed.

[0014] The propylene-based block copolymer (A) may contain a structural unit derived from an α-olefin other than ethylene. The α-olefin other than ethylene is not particularly limited, and examples thereof include α-olefins having 4 to 20 carbon atoms. Examples of the α-olefins having 4 to 20 carbon atoms include 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-decene, 1-dodecene, 1-tetradodecene, 1-hexadodecene, 1-octadodecene, 1-eicosene, 4-methyl-1-pentene, 2-methyl-1-butene, 3-methyl-1-butene, 3-methyl-1-butene, 3,3-dimethyl-1-butene, diethyl-1-butene, trime Examples of the α-olefin include ethyl-1-butene, 3-methyl-1-pentene, ethyl-1-pentene, propyl-1-pentene, dimethyl-1-pentene, methylethyl-1-pentene, diethyl-1-hexene, trimethyl-1-pentene, 3-methyl-1-hexene, dimethyl-1-hexene, 3,5,5-trimethyl-1-hexene, methylethyl-1-heptene, trimethyl-1-heptene, ethyl-1-octene, and methyl-1-nonene. Among these, the α-olefin other than ethylene is preferably an α-olefin having 4 to 8 carbon atoms, and more preferably 1-hexene and 1-octene. These α-olefins may be used alone or in combination of two or more. The content of structural units derived from α-olefins other than ethylene is preferably 5% by mass or less, more preferably 1% by mass or less, based on the total mass of the copolymer, and even more preferably substantially free of such units.

[0015] The content of the propylene-based block copolymer (A) is 30 to 55 mass%, preferably 35 to 55 mass% (wherein the total amount of the propylene-based block copolymer (A), the ethylene-based copolymer rubber (B), and the ethylene-based copolymer rubber (C) is 100 mass%). When the content of the propylene-based block copolymer (A) is in the range of 30 to 55 mass%, the generation of volatile (fogging) components is suppressed and low-temperature impact resistance is excellent.

[0016] From the viewpoint of achieving better suppression of the generation of volatile (fogging) components, the content of the propylene-based block copolymer (A) is more preferably 35 to 50 mass%, and even more preferably 35 to 45 mass% (wherein the total amount of the propylene-based block copolymer (A), the ethylene-based copolymer rubber (B), and the ethylene-based copolymer rubber (C) is 100 mass%). The propylene-based block copolymer (A) may be one type or two or more types.

[0017] From the viewpoint of excellent flowability and excellent moldability of the resulting automotive interior material, the propylene-based block copolymer (A) has a melt flow rate (MFR) measured in accordance with ASTM D1238 under conditions of 230°C and a load of 2.16 kg of 50 g / 10 min or less, preferably 5 to 50 g / 10 min, 10 to 50 g / 10 min, and more preferably 15 to 45 g / 10 min.

[0018] The density of the propylene-based block copolymer (A) is preferably 0.85 to 0.95 g / cm from the viewpoint of excellent mechanical strength. ３ , more preferably 0.88 to 0.94 g / cm ３ , more preferably 0.90 to 0.93 g / cm ３ is.

[0019] From the viewpoint of excellent mechanical strength, the propylene-based block copolymer (A) preferably has an intrinsic viscosity [η] measured in decalin (decahydronaphthalene) at 135°C of 2.0 to 7.0 dl / g, more preferably 2.3 to 6.0 dl / g, and even more preferably 2.5 to 6.0 dl / g.

[0020] The melting point (Tm) of the propylene-based block copolymer (A) is preferably 145 to 170°C, more preferably 155 to 165°C. If the melting point (Tm) of the propylene-based block copolymer (A) is less than 145°C, the impact resistance at low temperatures will be improved but the rigidity will decrease. If the melting point (Tm) exceeds 170°C, the rigidity will increase but the impact resistance at low temperatures may deteriorate. The melting point (Tm) of the propylene-based block copolymer (A) can be determined by the measurement method described in the Examples below.

[0021] The propylene-based block copolymer (A) may be composed solely of fossil fuel-derived monomers, solely of biomass-derived monomers, or a combination of fossil fuel-derived monomers and biomass-derived monomers. Fossil fuels include petroleum, coal, natural gas, shale gas, or a combination thereof. Biomass includes any renewable natural raw material, such as a plant-derived or animal-derived material, including fungi, yeast, algae, and bacteria, and its residues.

[0022] <<Ethylene-Based Copolymer Rubber (B)>> The ethylene-based copolymer rubber (B) is a copolymer rubber containing structural units derived from ethylene as a main component, and is preferably a copolymer rubber of ethylene and an α-olefin having 3 to 20 carbon atoms. The ethylene-based copolymer rubber (B) and the ethylene-based copolymer rubber (C) described below are preferably copolymers having a crystallinity of less than 10% as determined by differential scanning calorimetry (DSC).

[0023] The content of the structural units derived from ethylene in the ethylene-based copolymer rubber (B) is preferably 50% by mass or more, more preferably 50 to 95% by mass, still more preferably 50 to 90% by mass, and particularly preferably 55 to 85% by mass, based on the total mass of the copolymer rubber (B).

[0024] Examples of the α-olefins having 3 to 20 carbon atoms include propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-decene, 1-dodecene, 1-tetradodecene, 1-hexadodecene, 1-octadodecene, 1-eicosene, 4-methyl-1-pentene, 2-methyl-1-butene, 3-methyl-1-butene, 3-methyl-1-butene, 3,3-dimethyl-1-butene, and diethyl-1-butene. Examples of the α-olefin include trimethyl-1-butene, 3-methyl-1-pentene, ethyl-1-pentene, propyl-1-pentene, dimethyl-1-pentene, methylethyl-1-pentene, diethyl-1-hexene, trimethyl-1-pentene, 3-methyl-1-hexene, dimethyl-1-hexene, 3,5,5-trimethyl-1-hexene, methylethyl-1-heptene, trimethyl-1-heptene, ethyl-1-octene, and methyl-1-nonene. Among these, the α-olefin is preferably an α-olefin having 3 to 8 carbon atoms, more preferably propylene, 1-butene, and 1-octene, and even more preferably 1-butene and 1-octene. The above α-olefins may be used alone or in combination of two or more.

[0025] The ethylene copolymer rubber (B) may contain structural units derived from monomers other than ethylene and α-olefins having 3 to 20 carbon atoms (hereinafter also referred to as "other monomers"), but it is preferable that it does not contain structural units derived from other monomers. The other monomers are not particularly limited, and examples thereof include non-conjugated polyenes described below.

[0026] The ethylene copolymer rubber (B) preferably has a composition different from that of the ethylene copolymer rubber (C) before crosslinking, which will be described later, and more preferably contains at least one of an ethylene-1-butene copolymer and an ethylene-1-octene copolymer, and further preferably an ethylene-1-butene copolymer and an ethylene-1-octene copolymer.

[0027] The melting point (Tm) of the ethylene copolymer rubber (B) measured by a differential scanning calorimeter (DSC) is preferably 30 to 120°C or no melting point is observed, more preferably 30 to 100°C or no melting point is observed, even more preferably 30 to 80°C or no melting point is observed, and particularly preferably no melting point is observed. The melting point (Tm) is determined by the measurement method described in the examples below.

[0028] The ethylene copolymer rubber (B) has a melt flow rate (MFR) measured in accordance with ASTM D1238 under conditions of 230°C and a load of 2.16 kg, of preferably 0.01 to 10 g / 10 min, more preferably 0.1 to 5 g / 10 min, and even more preferably 0.1 to 3 g / 10 min, from the viewpoint of excellent low-temperature impact resistance.

[0029] The ethylene copolymer rubber (B) may be a so-called oil-extended rubber, which is prepared by blending a softener, preferably a mineral oil-based softener, during its production. The mineral oil-based softener is not particularly limited, and known softeners can be used, such as paraffin-based process oil.

[0030] The content of the ethylene copolymer rubber (B) (when two or more types of ethylene copolymer rubbers (B) are contained, the total content thereof) is 30 to 70 mass%, preferably 35 to 65 mass%, more preferably 40 to 60 mass%, and even more preferably 45 to 55 mass% (however, the total amount of the propylene block copolymer (A), the ethylene copolymer rubber (B), and the ethylene copolymer rubber (C) is 100 mass%). When the content of the ethylene copolymer rubber (B) is within the above range, the generation of volatile (fogging) components is suppressed and low-temperature impact resistance is excellent. The ethylene copolymer rubber (B) may be contained alone or in combination of two or more types.

[0031] The ethylene copolymer rubber (B) may be composed only of monomers derived from fossil fuels, or may be composed only of monomers derived from biomass, or may contain a combination of monomers derived from fossil fuels and monomers derived from biomass.

[0032] The method for producing the ethylene copolymer rubber (B) is not particularly limited, and any known production method can be used.

[0033] <<Ethylene-Based Copolymer Rubber (C)>> The at least partially crosslinked ethylene-based copolymer rubber (C) (hereinafter, may also be simply referred to as "ethylene-based copolymer rubber (C)") is preferably a copolymer of ethylene and an α-olefin having 3 to 20 carbon atoms. The α-olefin having 3 to 20 carbon atoms is not particularly limited, and examples include the α-olefins having 3 to 20 carbon atoms in the ethylene-based copolymer rubber (B) described above. From the viewpoints of suppressing the generation of volatile (fogging) components and achieving excellent low-temperature impact resistance, among the α-olefins having 3 to 20 carbon atoms, the α-olefin is preferably an α-olefin having 3 to 8 carbon atoms, more preferably propylene and 1-butene, and even more preferably propylene.

[0034] The content of the structural units derived from ethylene in the ethylene-based copolymer rubber (C) is preferably 50% by mass or more, more preferably 50 to 95% by mass, still more preferably 50 to 90% by mass, and particularly preferably 55 to 85% by mass, based on the total mass of the copolymer rubber (C).

[0035] The ethylene copolymer rubber (C) may be a copolymer rubber of ethylene, an α-olefin having 3 to 20 carbon atoms, and a non-conjugated polyene. The non-conjugated polyene is not particularly limited, and examples thereof include linear non-conjugated dienes such as 1,4-hexadiene, 3-methyl-1,4-hexadiene, 4-methyl-1,4-hexadiene, 5-methyl-1,4-hexadiene, 4,5-dimethyl-1,4-hexadiene, 7-methyl-1,6-octadiene, 8-methyl-4-ethylidene-1,7-nonadiene, and 4-ethylidene-1,7-undecadiene; methyltetrahydroindene, 5-ethylidene-2-norbornene, 5-methylene-2-norbornene, 5-isopropylidene-2-norbornene, and the like. Examples thereof include cyclic non-conjugated dienes such as bornene, 5-vinylidene-2-norbornene, 6-chloromethyl-5-isopropenyl-2-norbornene, 5-vinyl-2-norbornene, 5-isopropenyl-2-norbornene, 5-isobutenyl-2-norbornene, cyclopentadiene, and norbornadiene; and trienes such as 2,3-diisopropylidene-5-norbornene, 2-ethylidene-3-isopropylidene-5-norbornene, 2-propenyl-2,2-norbornadiene, and 4-ethylidene-8-methyl-1,7-nonadiene. Among these, 5-ethylidene-2-norbornene, 5-vinyl-2-norbornene, cyclopentadiene and 4-ethylidene-8-methyl-1,7-nonadiene are preferred as non-conjugated polyenes, and 5-ethylidene-2-norbornene is more preferred.

[0036] From the viewpoint of excellent low-temperature impact resistance, the ethylene-based copolymer rubber (C) is preferably an ethylene-propylene-non-conjugated polyene copolymer rubber or an ethylene-1-butene-non-conjugated polyene copolymer rubber, more preferably an ethylene-propylene-non-conjugated polyene copolymer rubber, and even more preferably an ethylene-propylene-5-ethylidene-2-norbornene copolymer rubber. From the viewpoint of suppressing the generation of volatile (fogging) components and excellent low-temperature impact resistance, the ethylene-based copolymer rubber (C) preferably has a composition different from that of the above-mentioned ethylene-based copolymer rubber (B).

[0037] The ethylene copolymer rubber (C) may be composed only of fossil fuel-derived monomers, or may be composed only of biomass-derived monomers, or may contain a combination of fossil fuel-derived monomers and biomass-derived monomers.

[0038] When the ethylene copolymer rubber (C) is an ethylene-α-olefin-non-conjugated polyene copolymer rubber, the iodine value is preferably 1 to 30 g / 100 g, more preferably 3 to 25 g / 100 g. （１＋４） 100°C) is preferably 10 to 250.

[0039] From the viewpoint of excellent mechanical strength and oil resistance, the ethylene copolymer rubber (C) before crosslinking preferably has an intrinsic viscosity [η] of 2.0 to 7.0 dl / g, more preferably 3.0 to 7.0 dl / g, and even more preferably 3.3 to 7.0 dl / g, measured in decalin (decahydronaphthalene) at 135° C. When the ethylene copolymer rubber (C) is an oil-extended ethylene copolymer rubber oil-extended with a softener (E) described below, the intrinsic viscosity [η] refers to a value measured on the ethylene copolymer rubber (C) alone, which has been degreased before the measurement of the intrinsic viscosity [η].

[0040] The ethylene copolymer rubber (C) may be a so-called oil-extended rubber, which is prepared by blending a softener (E), preferably a mineral oil-based softener, into the ethylene copolymer rubber (C) during its production. The softener (E) (preferably a mineral oil-based softener) is not particularly limited, and any known softener may be used, such as paraffin-based process oil.

[0041] The ethylene copolymer rubber (C) may be completely crosslinked, provided that at least a portion of the copolymer is crosslinked. Preferably, the ethylene copolymer rubber (C) is at least partially crosslinked by dynamically crosslinking the ethylene copolymer rubber (C). "Dynamic crosslinking" refers to a process of forming a crosslinked structure in at least a portion of the ethylene copolymer rubber (C) by melt-kneading a mixture containing the ethylene copolymer rubber (C) and necessary components while applying a shear force.

[0042] The timing of crosslinking the ethylene-based copolymer rubber (C) before crosslinking is not particularly limited. For example, at least a portion of the ethylene-based copolymer rubber (C) may be (dynamically) crosslinked before mixing with the propylene-based block copolymer (A), or at least a portion of the ethylene-based copolymer rubber (C) may be (dynamically) crosslinked after or while mixing with the propylene-based block copolymer (A). When the ethylene-based copolymer rubber (C) has a high degree of crosslinking, the oil resistance and rubber elasticity of the molded article obtained from the thermoplastic elastomer composition are good, even if the hardness of the thermoplastic elastomer composition is low.

[0043] [Method for Producing Ethylene-Based Copolymer Rubber (C)] Examples of the method for producing the ethylene-based copolymer rubber (C) include a method in which the propylene-based block copolymer (A), the ethylene-based copolymer rubber (C), a crosslinking agent described below, and, if necessary, other additives are mixed together and dynamically crosslinked.

[0044] The apparatus used for the melt-kneading is not particularly limited, and examples thereof include conventionally known mixing / kneading apparatuses such as a Banbury mixer, a mixing roll, a Henschel mixer, a kneader, a single-screw or twin-screw extruder, etc. The order of adding the components during mixing / kneading is not particularly limited, but when two or more crosslinking agents are used, it is preferable that these crosslinking agents are added simultaneously.

[0045] Dynamic crosslinking is preferably carried out in a non-open type device, and is preferably carried out in an inert gas atmosphere such as nitrogen or carbon dioxide gas. The heating temperature in dynamic crosslinking is usually 125 to 280°C, preferably 145 to 240°C, and the mixing / kneading time is usually 1 to 30 minutes, preferably 3 to 20 minutes. The shear force applied during the mixing / kneading process is, for example, a maximum shear rate of 10 to 100,000 sec. －１ , preferably 100 to 50,000 seconds －１ , more preferably 1,000 to 10,000 seconds －１ , more preferably 2,000 to 7,000 seconds －１ Examples of shear forces include:

[0046] Examples of the crosslinking agent include known crosslinking agents used for dynamic crosslinking, such as organic peroxides, phenolic resins, sulfur, hydrosilicone compounds, amino resins, quinones or derivatives thereof, amine compounds, azo compounds, epoxy compounds, isocyanates, thermosetting elastomers, etc. Among these, from the viewpoint of the balance between fluidity and physical properties, organic peroxides are preferred as the crosslinking agent.

[0047] Specific examples of organic peroxides include 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(t-hexylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(t-hexylperoxy)cyclohexane, 1,1-bis(t-butylperoxy)cyclododecane, 1,1-bis(t-butylperoxy)cyclohexane, 2,2-bis(t-butylperoxy)octane, n-butyl-4,4-bis(t-butylperoxy)butane, and n-butyl-4,4-bis(t peroxyketals such as di-t-butyl peroxide, dicumyl peroxide, t-butylcumyl peroxide, α,α'-bis(t-butylperoxy-m-isopropyl)benzene, α,α'-bis(t-butylperoxy)diisopropylbenzene, 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane, and 2,5-dimethyl-2,5-bis(t-butylperoxy)hexyne-3; acetyl peroxide, isobutyryl peroxide, diacyl peroxides such as octanoyl peroxide, decanoyl peroxide, lauroyl peroxide, 3,5,5-trimethylhexanoyl peroxide, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, and m-trioyl peroxide; t-butyl peroxyacetate, t-butyl peroxyisobutyrate, t-butylperoxy-2-ethylhexanoate, t-butyl peroxylaurate, t-butyl peroxybenzoate, and di-t-butyl peroxide; peroxyesters such as t-butylperoxyisophthalate, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, t-butylperoxymaleic acid, t-butylperoxyisopropyl carbonate, and cumylperoxyoctate; and hydroperoxides such as t-butyl hydroperoxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide, 2,5-dimethylhexane-2,5-dihydroperoxide, and 1,1,3,3-tetramethylbutyl peroxide.

[0048] Among the above compounds, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, di-t-butyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane, and 2,5-dimethyl-2,5-bis(t-butylperoxy)hexyne-3 are preferred, and 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane is more preferred, from the viewpoint of thermal decomposition temperature, crosslinking performance, etc. The organic peroxide is preferably used in an amount of 1 to 20 parts by mass, more preferably 5 to 15 parts by mass, per 100 parts by mass of the ethylene copolymer rubber (C), from the viewpoint of molding flowability.

[0049] From the viewpoint of making the crosslinking reaction uniform, a crosslinking aid may be used in combination in the dynamic crosslinking reaction. The crosslinking aid is not particularly limited, and examples thereof include divinyl compounds such as divinylbenzene; oxime compounds such as p-quinone dioxime and p,p'-dibenzoylquinone dioxime; nitroso compounds such as N-methyl-N-4-dinitrosoaniline and nitrosobenzene; maleimide compounds such as trimethylolpropane-N,N'-m-phenylenedimaleimide; and sulfur, diphenyl guanidine, triallyl cyanurate, etc. Other examples of the crosslinking aid include polyfunctional methacrylate monomers such as ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, and allyl methacrylate; and polyfunctional vinyl monomers such as vinyl butyrate and vinyl stearate.

[0050] The amount of the crosslinking aid added can be appropriately set depending on the desired purpose. For example, the amount of the crosslinking aid added is preferably 0.5 to 5 parts by mass, more preferably 0.5 to 3 parts by mass, per 100 parts by mass of the ethylene copolymer rubber (C).

[0051] In the dynamic crosslinking, additives other than the crosslinking agent and crosslinking aid (hereinafter simply referred to as "additives") may be added within a range that does not impair the object of the present invention. Examples of additives include plasticizers such as polyethylene glycol and phthalate esters such as dioctyl phthalate (DOP); heat stabilizers such as 2,6-di-t-butyl-4-methylphenol and n-octadecyl-3-(3,5'-di-t-butyl-4-hydroxyphenyl)propionate; and antioxidants such as trisnonylphenyl phosphite and distearyl pentaerythritol diphosphite. The amount of the additives added can be adjusted appropriately within a range that does not impair the object of the present invention.

[0052] The content of the ethylene copolymer rubber (C) is 0 to 20% by mass, preferably 0 to 15% by mass, more preferably 0 to 10% by mass, and even more preferably 0 to 8% by mass (wherein the total amount of the propylene block copolymer (A), the ethylene copolymer rubber (B), and the ethylene copolymer rubber (C) is 100% by mass). When the content of the ethylene copolymer rubber (C) is within the above range, the low-temperature impact resistance is excellent.

[0053] The content of the ethylene copolymer rubber (C) is preferably 1 to 20% by mass, more preferably 1 to 15% by mass, and even more preferably 2 to 8% by mass (wherein the total amount of the propylene block copolymer (A), the ethylene copolymer rubber (B), and the ethylene copolymer rubber (C) is 100% by mass). When the content of the ethylene copolymer rubber (C) is within the above range, a thermoplastic elastomer composition that is excellent in suppressing the generation of volatile (fogging) components can be obtained. The ethylene copolymer rubber (C) may be contained alone or in combination of two or more types.

[0054] [Other Components] The thermoplastic elastomer composition may contain components (hereinafter also referred to as "additives") other than the propylene-based block copolymer (A), the ethylene-based copolymer rubber (B), the ethylene-based copolymer rubber (C), and the softener (E) as long as the effects of the present invention are not impaired. The additives are not particularly limited, but include resins other than the propylene-based block copolymer (A), the ethylene-based copolymer rubber (B), and the ethylene-based copolymer rubber (C); acid acceptors, ultraviolet absorbers, antioxidants, heat stabilizers, antioxidants, light stabilizers, weather stabilizers, antistatic agents, metal soaps, aliphatic amides, lubricants such as wax, and crystal nucleating agents, all of which are known additives used in the field of polyolefins. The content of the other additives is not particularly limited as long as the object of the present invention is not impaired.

[0055] The amount of the additives to be added is not particularly limited as long as the effects of the present invention are achieved. However, the total amount of the other additives is usually 5 parts by mass or less, preferably 0.5 to 3.0 parts by mass, per 100 parts by mass of the total amount of the propylene-based block copolymer (A), the ethylene-based copolymer rubber (B), and the ethylene-based copolymer rubber (C).

[0056] [Method for Producing Thermoplastic Elastomer Composition] The thermoplastic elastomer composition can be produced by mixing the propylene-based block copolymer (A), the ethylene-based copolymer rubber (B), and the ethylene-based copolymer rubber (C), and, if necessary, the softener (E) and other additives, using a known method, for example, a Henschel mixer, a V-blender, a ribbon blender, a tumbler blender, etc., or by mixing and then melt-kneading the mixture using a single-screw extruder, a multi-screw extruder, a kneader, a Banbury mixer, etc., followed by granulation or pulverization. After mixing, the components may be further melt-kneaded using a single-screw extruder, a multi-screw extruder, a kneader, a Banbury mixer, etc., followed by granulation or pulverization.

[0057] <Thermoplastic elastomer molded article> The thermoplastic elastomer molded article according to the present invention (hereinafter sometimes simply referred to as "molded article") is an article molded from the thermoplastic elastomer composition described above. The molded article can be molded into various types of molded articles by known molding methods such as injection molding, extrusion molding, inflation molding, blow molding, extrusion blow molding, injection blow molding, press molding, vacuum molding, calendar molding, and foam molding.

[0058] Of the above molding methods, injection molding is particularly preferred. In this case, the molding temperature is preferably 170 to 260°C, more preferably 180 to 250°C, from the viewpoints of flowability, mold transferability and oxidation degradation of the resin component.

[0059] The molded article according to the present invention is particularly suitable for use as automobile parts such as automobile skin materials and automobile airbag cover materials, because of its excellent impact resistance at low temperatures.

[0060] The molded article according to the present invention has an initial flexural modulus, measured in accordance with ASTM D 790, of preferably 200 MPa or more, more preferably 200 to 500 MPa, and even more preferably 220 to 450 MPa. The initial flexural modulus can be determined by the method described in the examples below.

[0061] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0062] [Melt Flow Rate (MFR)] Measured in accordance with ASTM D1238 at 190°C under a load of 2.16 kg.

[0063] [Intrinsic Viscosity] The intrinsic viscosity [η] (dl / g) was measured using a fully automatic intrinsic viscometer manufactured by Rigo Co., Ltd. at a temperature of 135° C. in a measurement solvent of decalin.

[0064] [Melting Point] The melting points of the propylene-based block copolymer (A) and the ethylene-based copolymer rubber (B) described below were measured using a differential scanning calorimeter (DSC) in accordance with JIS K 7121. Specifically, pellets of the ethylene-based copolymer rubber (B) were heated at 230°C for 10 minutes, then cooled to 30°C at a rate of 10°C / min, held at that temperature for 1 minute, and then heated at a rate of 10°C / min. The temperature at which the maximum amount of heat absorption was measured in the DSC curve was taken as the melting point.

[0065] [Density] The density of the propylene-based block copolymer (A) described below was measured in accordance with ASTM D1505.

[0066] The thermoplastic elastomer compositions in the following examples and comparative examples were prepared using the following raw materials. <<Propylene-based block copolymer (A)>> PP-1: This product is commercially available and has a melt flow rate (ASTM D1238, 230°C, 2.16 kg load) of 55 g / 10 min and a density (ASTM D1505) of 0.91 g / cm ３ This is a block polypropylene equivalent to a comparative example, with an initial flexural modulus (ASTM D790) of 1,200 MPa. The ethylene content is 3.8% by mass. The intrinsic viscosity [η] measured by the above method was 6.0 (dl / g). This copolymer has a melting point of 163°C as measured by DSC. PP-2: This product is commercially available, with a melt flow rate (ASTM D1238, 230°C, 2.16 kg load) of 15 g / 10 min and a density (ASTM D1505) of 0.91 g / cm. ３ It is a block polypropylene with an initial flexural modulus (ASTM D790) of 1000 MPa. It is a copolymer with a melting point of 162°C as measured by DSC. The ethylene content was 9.6% by mass. The intrinsic viscosity [η] measured by the above method was 2.7 (dl / g). PP-3 This product is commercially available and has a melt flow rate (ASTM D1238, 230°C, 2.16 kg load) of 45 g / 10 min and a density (ASTM D1505) of 0.91 g / cm. ３It is a block polypropylene with an initial flexural modulus (ASTM D790) of 1500 MPa. It is a copolymer with a melting point of 163°C as measured by DSC. The ethylene content was 6.8% by mass. The intrinsic viscosity [η] measured by the above method was 2.6 (dl / g). PP-4: This product is commercially available and has a melt flow rate (ASTM D1238, 230°C, 2.16 kg load) of 15 g / 10 min and a density (ASTM D1505) of 0.91 g / cm. ３ It is a block polypropylene with an initial flexural modulus (ASTM D790) of 1600 MPa. It is a copolymer with a melting point of 163°C as measured by DSC. The ethylene content was 8.0% by mass. The intrinsic viscosity [η] measured by the above method was 2.5 (dl / g). PP-5: This product is commercially available and has a melt flow rate (ASTM D1238, 230°C, 2.16 kg load) of 25 g / 10 min and a density (ASTM D1505) of 0.91 g / cm. ３ The copolymer is a block polypropylene having an initial flexural modulus (ASTM D790) of 1000 MPa. It is a copolymer having a melting point of 163°C as measured by DSC. The ethylene content was 14.7% by mass. The intrinsic viscosity [η] measured by the above method was 2.8 (dl / g).

[0067] <<Ethylene-based copolymer rubber (B)>> EBR-1: ethylene / 1-butene copolymer This product is a commercially available copolymer composed of ethylene and 1-butene, having an ethylene content of 69% by mass and a melt flow rate (ASTM D1238, 190°C, 2.16 kg load) of 0.5 g / 10 min, and in which substantially no melting point peak is observed by DSC.

[0068] EOR-1: Ethylene-1-octene copolymer This product is commercially available and is a copolymer composed of ethylene and 1-octene, with an ethylene content of 55% by mass, a melt flow rate (ASTM D1238, 190°C, 2.16 kg load) of 0.5 g / 10 min, and a melting point measured by DSC of 55°C.

[0069] EOR-2: Ethylene-1-octene copolymer. This product is commercially available and is a copolymer consisting of ethylene and 1-octene, with an ethylene content of 80% by mass, a melt flow rate (ASTM D1238, 190°C, 2.16 kg load) of 1.0 g / 10 min, and a melting point of 38°C as measured by DSC.

[0070] <<Ethylene-based Copolymer Rubber (C)>> TPV-1 50 parts by mass of the following oil-extended ethylene-propylene-5-ethylidene-2-norbornene copolymer rubber (E), 50 parts by mass of the above block polypropylene (PP-2), 0.3 parts by mass of an organic peroxide (2,5-dimethyl-2,5-bis(t-butylperoxy)hexane) (product name "Perhexa 25B" manufactured by NOF Corporation) as a crosslinking agent, 0.3 parts by mass of divinylbenzene as a crosslinking aid, and 0.1 parts by mass of a phenol-based antioxidant (product name "Irganox 1010" manufactured by BASF Corporation) as an antioxidant were thoroughly mixed in a Henschel mixer, and the mixture was extrusion-kneaded under the conditions described below to perform dynamic crosslinking. [Dynamic crosslinking conditions] Extruder: Model number KTX-46, manufactured by Kobe Steel, Ltd. Cylinder temperature: C1 to C2 120°C, C3 to C4 140°C, C5 to C14 200°C Die temperature: 200°C Screw rotation speed: 400 rpm Extrusion rate: 80 kg / h

[0071] Oil-extended ethylene-propylene-5-ethylidene-2-norbornene copolymer rubber (E) This product is a commercially available product, and has an ethylene-derived structural unit content of 64% by mass, an iodine value of 13 g / 100 g, and an intrinsic viscosity [η] measured in decalin at 135°C of 3.4 dl / g. This oil-extended rubber is prepared by blending 40 parts by mass of a softener (Diana Process Oil PW-380, manufactured by Idemitsu Kosan Co., Ltd.) with 100 parts by mass of the ethylene-propylene-5-ethylidene-2-norbornene copolymer rubber.

[0072] (Examples 1 to 8 and Comparative Examples 1 to 3) Each material was weighed out in the amount shown in Table 1, and 0.1 part by mass of a phenolic antioxidant (Irganox 1010, manufactured by BASF Corporation) as a heat stabilizer and 0.1 part by mass of a diazo-based weather stabilizer (Tinuvin 326, manufactured by BASF Corporation) as a weather stabilizer were added to 100 parts by mass of the mixture of the materials, and the mixture was thoroughly mixed in a Henschel mixer. The mixture was extrusion-kneaded under the following conditions to obtain pellets of a thermoplastic elastomer composition. [Kneading conditions] Extruder: Model No. KTX-46, manufactured by Kobe Steel, Ltd. Cylinder temperature: C1 to C2 120°C, C3 to C4 140°C, C5 to C14 200°C Die temperature: 200°C Screw rotation speed: 400 rpm Extrusion rate: 80 kg / h

[0073] The pellets prepared above were used to prepare test pieces for each evaluation as follows. The obtained test pieces were used to carry out the following evaluations. <Injection molding machine> Model number NEX140 (manufactured by Nissei Plastic Industrial Co., Ltd.) Cylinder temperature (injection molding temperature): 220°C Mold temperature: 40°C

[0074] [Inhibition of Volatile Components (Fogging)] Using the pellets prepared above, fogging (FOG) was measured in accordance with the German Association of the Automotive Industry standard VDA 278 (measurement of organic compound emission amount by thermal desorption-GC / MS method). The measurement results are shown in Table 2. The lower the amount of volatile components (μg / g), the better the inhibition of volatile components (fogging).

[0075] [Initial flexural modulus] A test piece having a thickness of 3.2 mm for measuring the initial flexural modulus was prepared by injection molding from the thermoplastic elastomer composition under the above conditions, and the initial flexural modulus was measured by carrying out a test in an atmosphere at a temperature of 23° C. The results are shown in Table 2. It can be said that the larger the value obtained by measuring the initial flexural modulus, the more resistant to deformation and the more excellent the elasticity.

[0076] [Low-Temperature Impact Resistance] The Izod impact test was carried out in accordance with ASTM D256. The thermoplastic elastomer composition was injection molded under the above conditions to prepare a 3.2 mm thick test piece with a notch for Izod impact strength, and the test was carried out in an atmosphere at a temperature of -40°C. The low-temperature impact resistance was evaluated based on the state of fracture of the test piece after the test, using the following evaluation criteria. An evaluation result of PB indicates that the test piece is less likely to break into pieces and is preferable. - Evaluation Criteria - PB: The test piece was only partially broken, and the shape of the test piece was maintained. B: The test piece was broken, and the shape of the test piece could not be maintained.

[0077]

[0078]

[0079] In the table, "-" means that the corresponding component is not contained. As shown in Table 2, it can be seen that the molded articles obtained from the thermoplastic elastomer compositions of Examples 1 to 8 have a better balance between suppressing the generation of volatile (fogging) components and low-temperature impact resistance than the molded articles obtained from the thermoplastic elastomer compositions of Comparative Examples 1 to 3.

Claims

1. A thermoplastic elastomer composition having a melt flow rate (MFR) of 50 g / 10 min or less, measured according to ASTM D1238 under conditions of 230°C and a load of 2.16 kg, and containing 30 to 55 mass% of a propylene-based block copolymer (A) having a content of structural units derived from ethylene of 6.0 mass% or more based on the total mass of the copolymer, containing 25 to 70 mass% of an ethylene-based copolymer rubber (B), and containing 0 to 20 mass% of an at least partially crosslinked ethylene-based copolymer rubber (C) (wherein the total amount of the propylene-based block copolymer (A), the ethylene-based copolymer rubber (B) and the ethylene-based copolymer rubber (C) is 100 mass%).

2. The thermoplastic elastomer composition according to claim 1, wherein the content of the ethylene-based copolymer rubber (C) is 1 to 20% by mass or more (wherein the total amount of the propylene-based block copolymer (A), the ethylene-based copolymer rubber (B) and the ethylene-based copolymer rubber (C) is 100% by mass).

3. The thermoplastic elastomer composition according to claim 1, wherein the melting point (Tm) of the propylene-based block copolymer (A) is 145 to 170°C.

4. The thermoplastic elastomer composition according to claim 1, wherein the ethylene copolymer rubber (B) comprises at least one of an ethylene / 1-butene copolymer and an ethylene / 1-octene copolymer.

5. A thermoplastic elastomer molded article, which is a molded article of the thermoplastic elastomer composition according to any one of claims 1 to 4.

6. The thermoplastic elastomer molded article according to claim 5, which has an initial flexural modulus of 200 MPa or more as measured in accordance with ASTM D790.

7. An automobile part comprising the thermoplastic elastomer molded article according to claim 6.

8. The automotive part according to claim 7, which is an airbag cover.