Thermoplastic elastomer composition and molded body

Abstract

Provided is a molded body of an olefin-based thermoplastic elastomer from which is obtained an uncoated airbag-cover molded article having a better appearance with reduced tear-line gloss unevenness.　This thermoplastic elastomer composition is obtained by at least partially crosslinking 10-55 parts by mass of an ethylene / α-olefin copolymer (A), 40-70 parts by mass of a propylene-based polymer (B), and 2-30 parts by mass, excluding 30 parts by mass, of a styrene-based thermoplastic elastomer (C). The thermoplastic elastomer composition is characterized by satisfying requirement (1) and optionally further satisfying requirement (2).　Requirement (1): the ethylene / α-olefin copolymer (A) comprises, at least as a portion thereof, an ethylene / α-olefin copolymer (A1) having a density of 0.860-0.920 g / cm3.　Requirement (2): the styrene-based thermoplastic elastomer (C) has a loss tangent (tanδ) peak temperature of -45°C or lower.

Description

Thermoplastic elastomer composition and molded article

[0001] The present invention relates to a thermoplastic elastomer composition and a thermoplastic elastomer molded article having a good appearance made from the composition.

[0002] Olefin-based thermoplastic elastomers are widely used as energy-saving and resource-saving elastomers, particularly as a substitute for vulcanized rubber, in automotive parts, industrial machinery parts, electronic and electrical equipment parts, building materials, and other applications.

[0003] Olefin-based thermoplastic elastomers, made from ethylene-propylene-non-conjugated polyene copolymers (EPDM) and crystalline polyolefins such as polypropylene, have a lower specific gravity and superior durability compared to other thermoplastic elastomers, including resistance to heat aging and weathering.

[0004] Patent Document 1 discloses a thermoplastic elastomer composition for airbag covers comprising a propylene polymer component, an ethylene-α-olefin copolymer component, an ethylene-α-olefin-non-conjugated diene copolymer rubber, and a mineral oil-based softener, and states that this composition is excellent in appearance, fluidity, and mechanical strength.

[0005] Japanese Patent Publication No. 2012-224837 Public Relations

[0006] In recent years, the demand for improved performance has increased, and in particular for unpainted airbag covers, the tear line (a thin section) can sometimes have a higher gloss than the thick section, resulting in uneven gloss on the tear line and detracting from the appearance. One reason for the uneven gloss on the tear line is the physical protrusion of the tear line. Furthermore, in automotive interior material surfaces, the demand for shallow textures has increased from an aesthetic standpoint, making the uneven gloss on the tear line more noticeable than with conventional deep textures. These defects are difficult to hide even with painting, and may even be emphasized, potentially compromising the appearance quality.

[0007] The present invention provides a thermoplastic elastomer composition that, in the molding of an unpainted airbag cover, suppresses the physical protrusion of the tear line, thereby enabling a good appearance with reduced gloss unevenness of the tear line.

[0008] The present invention relates, for example, to the following [1] to

[15] . [1] A thermoplastic elastomer composition obtained by crosslinking at least a portion of 10 to 55 parts by mass of an ethylene-α-olefin copolymer (A), 40 to 70 parts by mass of a propylene polymer (B), and 2 parts by mass or more and less than 30 parts by mass of a styrene-based thermoplastic elastomer (C), (the total of the ethylene-α-olefin copolymer (A), the propylene polymer (B), and the styrene-based thermoplastic elastomer (C) being 100 parts by mass), and satisfying the following requirement (1). Requirement (1): The ethylene-α-olefin copolymer (A) has a density of 0.860 to 0.920 g / cm³. ３ It contains at least a portion of ethylene-α-olefin copolymer (A1).

[0009] [2] The thermoplastic elastomer composition described in [1] above, further satisfying the following requirement (2): Requirement (2): The styrene-based thermoplastic elastomer (C) has a loss tangent (tanδ) peak temperature of -25°C or lower. [3] The ethylene-α-olefin copolymer (A) has a density of 0.860 to 0.920 g / cm³. ３A thermoplastic elastomer composition according to either [1] or [2] above, comprising 30 to 100% by mass of an ethylene-α-olefin copolymer (A1). [4] A thermoplastic elastomer composition according to any one of [1] to [3] above, wherein the ethylene-α-olefin copolymer (A1) is a random copolymer. [5] A thermoplastic elastomer composition according to any one of [1] to [4] above, wherein the propylene polymer (B) is a propylene block copolymer. [6] A thermoplastic elastomer composition according to any one of [2] to [5] above, wherein the loss tangent (tanδ) peak temperature of the styrene-based thermoplastic elastomer (C) in requirement (2) is -70 to -35°C. [7] A thermoplastic elastomer composition according to any one of [1] to [6] above, wherein the styrene-containing unit content of the styrene-based thermoplastic elastomer (C) is 15 to 40% by mass.

[0010] [8] The thermoplastic elastomer composition according to any one of [1] to [7] above, further comprising a crosslinking agent (D) and obtained by dynamic crosslinking.

[0011] [9] The thermoplastic elastomer composition according to [8] above, wherein the crosslinking agent (D) is phenolic or organic peroxide.

[10] The thermoplastic elastomer composition according to either [8] or [9] above, wherein the crosslinking agent (D) is an organic peroxide crosslinking agent, and the amount blended with the ethylene-α-olefin copolymer (A), propylene polymer (B), and styrene thermoplastic elastomer (C) is 0.05 to 3.00 parts by mass per 100 parts by mass of the total.

[11] The thermoplastic elastomer composition according to any one of [1] to

[10] above, further comprising a plasticizer (F).

[12] A thermoplastic elastomer molded article obtained by molding the thermoplastic elastomer composition according to any one of [1] to

[11] above.

[0012]

[13] An automotive part comprising the thermoplastic elastomer molded body described in

[12] above.

[14] An automotive part described in

[13] above, which is an airbag cover.

[15] An automotive part described in

[13] or

[14] above, which is an unpainted airbag cover.

[0013] The thermoplastic elastomer composition of the present invention exhibits excellent flexural elasticity, low-temperature impact resistance, and appearance. In particular, when molding an unpainted airbag cover, it can suppress the gloss of tear lines and achieve a good appearance.

[0014] Figure 1 is an explanatory diagram showing a molded body having a thickest portion with a thickness L1 and a thinnest portion with a thickness L2 in a direction perpendicular to the flow direction of the composition during molding.

[0015] The following describes specific embodiments of the present invention in detail. The following descriptions of the constituent elements may be based on representative embodiments of the present invention, but the present invention is not limited in any way to the following embodiments and can be implemented with appropriate modifications within the scope of the present invention. In this specification, a numerical range expressed using "~" means a range that includes the numbers written before and after "~" as the lower and upper limits. In this specification, when referring to the amount of each component in a composition, if there are multiple substances corresponding to each component in the composition, it means the total amount of the multiple substances present in the composition unless otherwise specified. In this specification, "~" indicating a numerical range means that the units written before or after it are the same unit unless otherwise specified. In this specification, a combination of two or more preferred embodiments is a more preferred embodiment.

[0016] The thermoplastic elastomer composition of the present invention is obtained by crosslinking at least a portion of 10 to 55 parts by mass of an ethylene-α-olefin copolymer (A), 40 to 70 parts by mass of a propylene polymer (B), and 2 parts by mass or more and less than 30 parts by mass of a styrene-based thermoplastic elastomer (C) (the total of the ethylene-α-olefin copolymer (A), propylene polymer (B), and styrene-based thermoplastic elastomer (C) being 100 parts by mass), wherein the ethylene-α-olefin copolymer (A) satisfies the following requirement (1). Requirement (1): Density of 0.860 to 0.920 g / cm³ ３ The present invention contains at least a portion of an ethylene-α-olefin copolymer (A1). The ethylene-α-olefin copolymer (A), propylene polymer (B), and styrene thermoplastic elastomer (C) of the present invention will be described in order below, and for convenience, they may be referred to as component (A), component (B), and component (C), respectively.

[0017] Component (A) The ethylene-α-olefin copolymer (hereinafter also referred to as "polymer of component (A)") that constitutes component (A), which is one of the components that make up the thermoplastic elastomer composition, is preferably a copolymer of ethylene and an α-olefin having 3 to 20 carbon atoms.

[0018] The α-olefin preferably has 3 to 20 carbon atoms, particularly 3 to 12, and more preferably 4 to 8 carbon atoms. Specific examples of such α-olefins include propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 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, 9-methyl-1-decene, 11-methyl-1-dodecene, and 12-ethyl-1-tetradecene. Among these, propylene, 1-butene, 1-hexene, and 1-octene are preferred, with 1-butene being particularly preferred. These α-olefins may be used individually or in combination of two or more.

[0019] In the copolymer of component (A), the content of structural units derived from ethylene is preferably 50 to 85 mol%, more preferably 50 to 80 mol%, provided that the sum of the structural units derived from ethylene and the structural units derived from α-olefin is 100 mol%. When the content of structural units derived from ethylene falls within the above range, a thermoplastic elastomer composition excellent in compatibility with the propylene-based polymer of component (B) can be obtained. Examples of such ethylene / α-olefin copolymers include ethylene / propylene copolymers, ethylene / 1-butene copolymers, ethylene / 1-hexene copolymers, ethylene / 1-octene copolymers, ethylene / propylene / 1-hexene copolymers, and ethylene / 1-butene / 1-hexene copolymers.

[0020] The copolymer of component (A) can be produced, for example, by copolymerizing ethylene and an α-olefin according to a conventionally known method using a vanadium catalyst, a Ziegler-Natta catalyst or a metallocene catalyst. From the viewpoint that a copolymer satisfying the above physical properties can be easily obtained, a synthesis method using a metallocene catalyst is preferred. Specifically, synthesis is carried out using a catalyst containing a metallocene compound and an aluminum-containing compound described in International Publication No. 2008 / 152935, or a catalyst comprising a metallocene compound described in Japanese Patent Laid-Open No. 9-40586 and an organoaluminum oxy compound or an ionized ionic compound, and such a method is more preferred.

[0021] As the copolymer of component (A), commercially available products may also be used, examples of which are as follows: That is, "DF605" (density: 0.861 g / cm ３ ), "DF610" (density: 0.862 g / cm ３ ), "DF740" (density: 0.870 g / cm ３ ), and "DF110" (density: 0.905 g / cm ３ ), "Engage 8842" (density: 0.857 g / cm ３ ) "Engage 8150" (density: 0.868 g / cm ３) “Engage8100” (density 0.870g / cm ３ ) "Engage7447" (density 0.865g / cm ３ ) "Engage8003" (density 0.885g / cm ３ ) "Engage8480" (density 0.902g / cm ３ ) "KS240T" manufactured by Nippon Polyethylene Co., Ltd. (density 0.880 g / cm³) ３ ), “KS571” (density 0.907g / cm ３ Examples include:

[0022] In the present invention, component (A) must satisfy the following requirement (1): Requirement (1): Density of 0.860 to 0.920 g / cm³ ３ It contains at least a portion of ethylene-α-olefin copolymer (A1). Therefore, if requirement (1) is met, from the viewpoint of impact resistance and appearance, component (A) has a density of 0.860 to 0.920 g / cm³. ３ It is required to contain at least a portion of ethylene-α-olefin copolymer (A1). The density of component (A1) is preferably 0.861 to 0.900 / cm³. ３ The most preferred concentration is 0.862 to 0.880 / cm². ３ Most preferably 0.865 to 0.875 / cm ３ Component (A) has a density of 860 g / cm³. ３ By including at least a portion of the ethylene-α-olefin copolymer (A1) described above, for example, the orientation of the rubber (component (A)) at the tear line of the airbag is suppressed, and the morphological difference between the normal part and the tear line part is reduced. The difference in shrinkage in the thickness direction between the normal part and the tear line part is reduced, and the bulging of the tear line part can be suppressed. As a result, uneven gloss is suppressed. On the other hand, the density of component (A1) is 0.920 g / cm³. ３ By doing the following, a molded body with good impact resistance can be obtained.

[0023] Furthermore, the melt flow rate (MFR) of component (A) is preferably 0.1 to 50.0 g / 10 min, more preferably 0.2 to 40.0 g / 10 min, and particularly preferably 0.3 to 10.0 g / 10 min, from the viewpoint of improving impact resistance. If it is 0.1 g / 10 min or more, the miscibility with the propylene polymer (B) is good, and if it is 50.0 g / 10 min or less, a molded article with better low-temperature impact resistance can be obtained. Here, the MFR is a value measured in accordance with ASTM D1238, and the measurement conditions are 190°C and a 2.16 kg load. Component (A) may also contain copolymers other than copolymer (A1). In that case, the content of copolymer (A1) in component (A) is preferably 30% by mass or more of the total of component (A), more preferably 40% by mass, and particularly preferably 50% by mass or more. Being within the above range is preferable from the viewpoint of impact resistance. Furthermore, the ethylene-α-olefin copolymer (A1) may be a block copolymer or a random copolymer, but the random copolymer is preferred because it has good compatibility and dispersibility with the propylene polymer (B), high melt flow stability, and has the advantage of suppressing tear line buildup and appearance defects. A suitable example of the ethylene-α-olefin copolymer (A1) is a random copolymer that does not have a melt peak. (The absence of a DSC melt peak means that, in accordance with JIS K7121 (2012), when a sample pellet is heated at 280°C for 10 minutes using a differential scanning calorimeter (DSC), then cooled from 280°C to -50°C at a rate of 10°C / min, held at -50°C for 1 minute, and then heated again at a rate of 10°C / min, no crystal melting peak is observed in the DSC curve obtained by this heating (no crystal melting peak of 20 J / g or more is observed).)

[0024] Component (B) The propylene polymer constituting component (B) is not particularly limited and may be a propylene homopolymer or a copolymer of propylene and an α-olefin other than propylene (hereinafter also referred to as "other α-olefin"). It may also be a block copolymer or a random copolymer. From the viewpoint of improving the impact resistance of the thermoplastic elastomer composition, the propylene polymer is preferably a propylene block copolymer. The propylene block copolymer is, for example, a block copolymer of propylene and another α-olefin, preferably a block copolymer of propylene and another α-olefin in an amount of 30 mol% or less, and more preferably a block copolymer of propylene and another α-olefin in an amount of 15 mol% or less. Examples of the other α-olefin include ethylene, 1-butene, 1-pentene, 1-hexene, etc. Among these, ethylene is particularly preferred.

[0025] Component (B) preferably has a melt flow rate (MFR) of 20.0 g / 10 min or more at 230°C and a load of 2.16 kg, as measured in accordance with ISO 1133, and more preferably 30.0 to 70.0 g / 10 min, and more preferably 30.0 to 60.0 g / 10 min. When the melt flow rate (MFR) is 20.0 g / 10 min or more, a molded article with an excellent balance of moldability and low-temperature impact resistance can be obtained. Furthermore, when the melt flow rate (MFR) is 70 g / 10 min or less, the low-temperature impact resistance is further improved.

[0026] As for the propylene-based block copolymers described above, any known ones can be used without limitation. For example, EG8150 and EG8200 from Dow Chemical, J709QG from Prime Polymer, BC05B from Nippon Polypropylene, J817U from Prime Polymer, and P739ET from SCG Chemicals are preferably used. These copolymers may be used individually or in combination of two or more types.

[0027] Component (C) Component (C) is one or more types of styrene-based thermoplastic elastomers. The styrene-based thermoplastic elastomer is an elastomer containing styrene as a monomer unit. The proportion of monomer units derived from styrene in the styrene-based elastomer may be 5% by mass or more, 10% by mass or more, 80% by mass or less, 30% by mass or less, or 20% by mass or less, based on the total mass of the styrene-based elastomer. That is, the proportion of monomer units derived from styrene can preferably be 5% by mass to 80% by mass, more preferably 5% by mass to 30% by mass, even more preferably 5% by mass to 20% by mass, and particularly preferably 10% by mass to 20% by mass. The styrene-based thermoplastic elastomer may be a hydrogenated product in which some or all of the unsaturated bonds derived from monomers such as alkadienes (usually excluding the unsaturated bonds of the benzene ring derived from styrene) are converted to saturated bonds by hydrogenation. Hydrogenation tends to improve heat resistance.

[0028] The melt flow rate (MFR) of component (C) is preferably 0.1 to 50.0 g / 10 min, more preferably 1.0 to 40.0 g / 10 min, particularly preferably 2.0 to 10.0 g / 10 min, and most preferably 3.0 to 5.0 g / 10 min, from the viewpoint of impact resistance. If it is 0.1 g / 10 min or more, the miscibility with the propylene polymer (B) is good, and if it is 50.0 g / 10 min or less, a molded article with better low-temperature impact resistance can be obtained. Here, the MFR is a value measured in accordance with ASTM D1238, and the measurement conditions are 190°C and a 2.16 kg load.

[0029] The styrenic thermoplastic elastomer may be, for example, a block copolymer composed of a polystyrene block and a polyolefin block formed of monomer units derived from an alkadiene having 4 to 10 carbon atoms, or a hydrogenated product thereof. From the viewpoint of compatibility with a propylene-based polymer and impact resistance, the polyolefin block may contain at least one alkadiene selected from isoprene and butadiene as a monomer unit. In the present specification, an elastomer containing styrene and ethylene as monomer units is classified as a styrenic thermoplastic elastomer. The styrenic thermoplastic elastomer may be a diblock-type copolymer composed of a polystyrene block and a polyolefin block bonded thereto, or may be a triblock-type copolymer composed of polystyrene blocks arranged at both terminals and a polyolefin block arranged between the polystyrene blocks. The triblock-type copolymer can contribute to improving impact resistance.

[0030] In the block copolymer as the styrenic thermoplastic elastomer, the proportion of the polyolefin block may be 95% by mass or less, or 90% by mass or less, based on the mass of the block copolymer, and may be 20% by mass or more, 70% by mass or more, or 80% by mass or more. When the styrenic thermoplastic elastomer contains the polyolefin block in an appropriate proportion, the impact resistance and rigidity of the thermoplastic elastomer composition blended therewith are improved. Preferable specific examples of the styrenic thermoplastic elastomer include a hydrogenated product of a styrene-butadiene-styrene block copolymer, a hydrogenated product of a styrene-isoprene-styrene block copolymer, and a hydrogenated product of a styrene-isoprene-butadiene-styrene block copolymer.

[0031] As the styrenic thermoplastic elastomer, the following copolymers, for example, can be produced by conventional methods such as anionic polymerization and cationic polymerization. Styrene-ethylene-butene-styrene block copolymer (SEBS), styrene-ethylene-propylene-styrene block copolymer (SEPS), styrene-butadiene-styrene copolymer (SBS), hydrogenated styrene-butadiene-styrene copolymer (hydrogenated styrene-butadiene rubber) (HSBR), styrene-ethylene-propylene-styrene block copolymer (SEPS), styrene-isoprene-styrene block copolymer (SIS), styrene-isobutylene-styrene copolymer (SIBS), styrene-isobutylene copolymer (SIB), styrene-ethylene-butene-styrene-styrene copolymer (SEBSS)

[0032] Further, the following are exemplified as commercial products of styrenic thermoplastic elastomers. SEBS Tuftec H manufactured by Asahi Kasei Chemicals Corporation SEBS Kraton manufactured by Kraton Corporation SEPS Septon manufactured by Kuraray Co., Ltd.

[0033] The styrenic thermoplastic elastomer used is one in which, in terms of dynamic viscoelasticity in torsion mode at a measurement frequency of 1 Hz, the value of loss tangent (tan δ) preferably has a maximum point at -25°C or lower. Among these, the maximum point of loss tangent (tan δ) is more preferably in the range of -70°C to -25°C, and still more preferably in the range of -70°C to -35°C. It is derived from the polyolefin component of component (C). Use of such a styrenic thermoplastic elastomer provides better results from the perspective of low-temperature impact strength. There is no particular limitation as long as it is a styrenic thermoplastic elastomer as described above, and examples thereof include the following.

[0034] SEBS: Trade name H1062, loss tangent (tan δ) peak temperature -49°C, styrene content 18% by mass (manufactured by Asahi Kasei Corporation)

[0035] Thus, by using component (C) in combination, and in particular by using SEBS in combination, the fluidity and dispersibility of the micro-crosslinked rubber are improved. As a result, for example, in the application of unpainted airbag covers, it is effective in preventing uneven gloss at the tear line, and the homogenization of the surface skin layer is thought to suppress the bulging of the tear line and contribute to an improved appearance.

[0036] Method for producing a thermoplastic elastomer composition The thermoplastic elastomer composition of the present invention can be obtained by dynamically heat-treating component (A), component (B), and component (C). As a method for dynamic heat treatment, a method of melt-kneading the above-mentioned components (A), component (B), and component (c) in the presence of a crosslinking agent is preferred. The blending ratio of components (A), component (B), and component (C) is 10 to 55 parts by mass for component (A), 40 to 70 parts by mass for component (B), and 2 parts by mass or more and less than 30 parts by mass for component (C). Among these, the blending ratio of component (A) is preferably 15 to 50 parts by mass, and more preferably 15 to 40 parts by mass. The blending ratio of component (B) is preferably 45 to 65 parts by mass, and more preferably 50 to 65 parts by mass. From the viewpoint of improving the appearance of the molded article, the blending ratio of component (C) is preferably 2 to 28 parts by mass, more preferably 5 to 28 parts by mass, even more preferably 10 to 28 parts by mass, particularly preferably 10 to 25 parts by mass, and most preferably 10 to 20 parts by mass. (However, the total of components (A), (B), and (C) shall be 100 parts by mass.)

[0037] The term "dynamic heat treatment" above refers to kneading each of the above components in a molten state. Dynamic heat treatment is carried out using a kneading device such as a mixing roll, an intensive mixer (e.g., a Banbury mixer, a kneader), or a single-screw or twin-screw extruder, but it is preferable to carry it out in a closed-type kneading device. Furthermore, dynamic heat treatment is preferably carried out under an inert gas atmosphere such as nitrogen.

[0038] The mixing should preferably be carried out at a temperature at which the half-life of the organic peroxide used is less than 1 minute. The mixing temperature is usually 150°C to 280°C, preferably 170°C to 240°C. The mixing time is usually 1 to 20 minutes, preferably 1 to 5 minutes. The shear force applied during mixing is usually a shear rate of 10 to 10,000 sec. －１ Preferably 100 to 10,000 seconds －１ It will be determined within the range.

[0039] In the present invention, it is desirable that the melt-mixing of components (A), (B), and (C) above be carried out in the presence of a crosslinking agent.

[0040] Crosslinking agent (D) Examples of crosslinking agents that can be used include phenolic and organic peroxide compounds, as well as hydrosilicone compounds, amino resins, quinones or their derivatives, amine compounds, azo compounds, epoxy compounds, isocyanate compounds, etc. Among these, phenolic and organic peroxide crosslinking agents are preferred, and organic peroxide crosslinking agents are more preferred.

[0041] Organic peroxide crosslinking agents The organic peroxide crosslinking agents may be aromatic or aliphatic. One type may be used, or two or more types may be used. Examples of organic peroxide crosslinking agents include dialkyl peroxides such as di-t-butyl peroxide, t-butylcumyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hexyn-3, 1,3-bis(t-butylperoxyisopropyl)benzene, and 1,1-di(t-hexylperoxy)-3,3,5-trimethylcyclohexane; t-butylperoxybenzoate, t- Examples include peroxyesters such as butyl peroxyisopropyl monocarbonate, n-butyl-4,4-bis(t-butylperoxy)valerate, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, and 2,5-dimethyl-2,5-di(benzoylperoxy)hexyn-3; and diacyl peroxides such as diacetyl peroxide, lauroyl peroxide, dibenzoyl peroxide, p-chlorobenzoyl peroxide, and 2,4-dichlorobenzoyl peroxide.

[0042] Among these, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane and 2,5-dimethyl-2,5-di(t-butylperoxy)hexyn-3 are preferred from the viewpoint of the degree of crosslinking of the resulting composition. For organic peroxide-based crosslinking agents, a 1-minute half-life temperature of 140 to 230°C is preferred from the viewpoint of easily obtaining a good degree of crosslinking and dispersibility of the resulting composition.

[0043] When thermally treated, the content of the organic peroxide-based crosslinking agent in the thermoplastic elastomer composition of the present invention is preferably 0.05 to 3.0 parts by mass, more preferably 0.07 to 0.32 parts by mass, and even more preferably 0.08 to 0.20 parts by mass, based on 100 parts by mass of the total of components (A), (B), and (C). A content of the organic peroxide-based crosslinking agent within this range is preferable because it provides an excellent balance between the flexibility and mechanical strength of the thermoplastic elastomer composition of the present invention.

[0044] Phenolic Crosslinking Agents Generally, thermally crosslinkable phenolic resins are used as phenolic crosslinking agents. Examples of phenolic resin crosslinking agents include phenolic resins produced by the condensation of substituted or unsubstituted phenols with aldehydes, phenolic resins produced by the condensation of bifunctional phenol dialcohols, and halogenated phenolic resins. Substituted phenols are preferably alkyl-substituted compounds having 1 to 10 carbon atoms. Furthermore, the aldehyde used in the condensation with substituted or unsubstituted phenols is preferably formaldehyde.

[0045] As a phenolic crosslinking agent, commercially available phenolic resins can be appropriately selected and used, such as Tackirol 201 (alkylphenol formaldehyde resin, manufactured by Taoka Chemical Industry Co., Ltd.), Tackirol 250-I (brominated alkylphenol formaldehyde resin with a bromination rate of 4%, manufactured by Taoka Chemical Industry Co., Ltd.), and Tackirol 250-III (brominated alkylphenol formaldehyde resin, manufactured by Taoka Chemical Industry Co., Ltd.). Among these, brominated alkylphenol formaldehyde resin is preferred in terms of the degree of crosslinking.

[0046] When thermally treated, the content of the phenolic crosslinking agent in the thermoplastic elastomer composition of the present invention is preferably 1 to 10 parts by mass, more preferably 2 to 8 parts by mass, and even more preferably 3 to 6 parts by mass, based on 100 parts by mass of the total of components (A), (B), and (c). It is preferable that the content of the phenolic crosslinking agent is within the above range because it improves the oil resistance and rubber elasticity of the resulting composition.

[0047] Other Additives The thermoplastic elastomer composition of the present invention may contain (E) a crosslinking aid, as well as phenolic crosslinking agents, slip agents, antioxidants, ultraviolet absorbers, light stabilizers, conductivity imparters, antistatic agents, dispersants, antibacterial agents, acid acceptors, colorants, and the like. Each of these other additives may be used individually or in combination of two or more.

[0048] If the above-mentioned other additives are included, it is preferable that the proportion of the other additives used is 0.1 to 3.0 parts by mass, particularly 0.3 to 2.0 parts by mass, based on 100 parts by mass of the total of components (A), (B), and (C).

[0049] (E) Crosslinking aids Crosslinking aids can also be used from the viewpoint of making the effect of organic peroxide-based crosslinking agents uniform. Specific examples of crosslinking aids 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 others such as sulfur, diphenylguanidine, and triallyl cyanurate.

[0050] In the present invention, it is preferable to use divinylbenzene. Divinylbenzene has good compatibility with the above components (A) and (B), and has the effect of solubilizing organic peroxides and acting as a dispersant for organic peroxides. As a result, the effect of dynamic heat treatment is uniformly expressed, and a thermoplastic elastomer composition with a good balance of fluidity and physical properties is obtained.

[0051] The crosslinking aid and other compounds described above are preferably in an amount of 0.02 to 3.0 parts by mass, more preferably 0.03 to 2.0 parts by mass, and even more preferably 0.04 to 0.2 parts by mass, based on 100 parts by mass of the total of components (A), (B), and (C). By performing the dynamic heat treatment described above, at least a portion of the polymers constituting components (A) and (B) in the thermoplastic elastomer composition may be crosslinked. As a result, even if the hardness of the thermoplastic elastomer composition is relatively low, the resulting molded article tends to have good oil resistance and rubber elasticity.

[0052] Activators for Phenolic Crosslinking Agents: When the phenolic crosslinking agent is not halogenated, it may be used together with an activator. Examples of halogen donors that can be used as activators include stannous chloride, ferric chloride, chlorinated paraffin, chlorinated polyethylene, and chlorosulfonated polyethylene. However, if the phenolic crosslinking agent is halogenated, a halogen donor may not be necessary.

[0053] When a halogen donor is added as an activator along with a phenolic crosslinking agent, the amount of halogen donor added is preferably 1 to 100 parts by mass of halogen donor, more preferably 2 to 50 parts by mass of halogen donor, relative to 100 parts by mass of phenolic crosslinking agent.

[0054] As acid acceptors, iron oxide, titanium oxide, magnesium oxide, silicon dioxide, zinc oxide, etc., can be used. When an acid acceptor is used, the amount of acid acceptor added is preferably 1 to 100 parts by mass, more preferably 2 to 50 parts by mass, of the phenolic crosslinking agent.

[0055] (F) Plasticizers The compositions of the present invention preferably use plasticizers for purposes such as adjusting fluidity and hardness. Specific examples of plasticizers include petroleum-based plasticizers such as process oil, lubricating oil, paraffin, liquid paraffin, polyethylene wax, polypropylene wax, petroleum asphalt, and petrolatum; fatty oil-based plasticizers such as castor oil, linseed oil, rapeseed oil, soybean oil, and coconut oil; tall oil; sub(factis); waxes such as beeswax, carnauba wax, and lanolin; and fatty acids such as ricinoleic acid, palmitic acid, stearic acid, barium stearate, calcium stearate, and zinc laurate. Examples include salts; naphthenic acid; pine oil, rosin or its derivatives; synthetic polymer plasticizers such as terpene resins, petroleum resins, coumarone indene resins, and atactic polypropylene; ester-based softeners such as dioctyl phthalate, dioctyl adipate, and dioctyl sebacate; microcrystalline wax, liquid polybutadiene, modified liquid polybutadiene, liquid polyisoprene, terminally modified polyisoprene, hydrogenated terminally modified polyisoprene, liquid thiocol, and hydrocarbon-based synthetic lubricants. Among these, process oils are preferred.

[0056] The plasticizer may be used, for example, when melting and mixing components (A), (B), and (C), or it may be added later during the subsequent dynamic heat treatment.

[0057] When the thermoplastic elastomer composition of the present invention contains a plasticizer, the proportion of the plasticizer is preferably 0.05 to 3.0 parts by mass, more preferably 0.07 to 0.32 parts by mass, and even more preferably 0.08 to 0.20 parts by mass, based on 100 parts by mass of the total of components (A), (B), and (C). A plasticizer content within this range is preferable because it results in a composition with excellent extrusion moldability and low hardness.

[0058] Specifically, the thermoplastic elastomer composition of the present invention preferably has a Type D hardness (after 5 seconds) of 35 or higher, and more preferably 35 to 60, in accordance with JIS K6253.

[0059] By utilizing the above-described properties of the thermoplastic elastomer composition of the present invention, various thermoplastic elastomer molded articles with excellent performance can be obtained from the thermoplastic elastomer composition of the present invention.

[0060] Examples of molding methods include extrusion molding, press molding, injection molding, calendering, and hollow molding, with injection molding being particularly preferred among these. Examples of thermoplastic elastomer molded articles include automobile parts, civil engineering and construction materials, electrical and electronic components, satellite products, films and sheets, etc. Among these, automobile parts are particularly preferred because the aforementioned performance of the thermoplastic elastomer composition of the present invention is suitably expressed.

[0061] Examples of automotive parts include weatherstrips, bumper moldings, side moldings, air spoilers, air duct hoses, wire harness grommets, rack and pinion boots, suspension cover boots, glass guides, inter-belt line seals, corner moldings, glass enclosures, hood seals, glass run channels, secondary seals, various gaskets, hoses, airbag covers, and the like.

[0062] The airbag cover has a thick section and a thin section called a tear line. The tear line is a linear section in which the cover tears when the airbag deploys. In unpainted airbag covers, the tear line tends to appear glossier than the thick section, but in airbag covers manufactured from the thermoplastic elastomer composition of the present invention, the gloss of the tear line can be suppressed, so the difference in gloss between the tear line and the thick section is reduced, and a good appearance can be achieved. For this reason, an unpainted airbag cover can be cited as a particularly preferred example of a thermoplastic elastomer molded article.

[0063] Figure 1 shows an example of a molded article having a thick-walled portion and a thin-walled portion. The direction from left to right in Figure 1 is the flow direction of the composition during molding. The curved arrows in Figure 1 indicate the path through which the composition flows during molding. In a molded article having a thick-walled portion and a thin-walled portion manufactured from the thermoplastic elastomer composition of the present invention, the ratio (L1 / L2) of the thickness L1 of the thickest portion to the thickness L2 of the thinnest portion in a direction perpendicular to the resin flow direction is preferably 2 or more and 50 or less, and more preferably 2 or more and 20 or less. When the ratio (L1 / L2) is 2 or more and 50 or less, the molded article has a good appearance with suppressed gloss in the thin-walled portion.

[0064] The present invention will be described below with reference to examples, but the present invention is not limited to these examples. The raw materials used in the examples and comparative examples are listed below.

[0065] <Component (A): Ethylene-α-olefin copolymer> Component (A-1): Engage EG8842 Dow Chemical melt flow rate (MFR, 190℃): 1 g / 10 min, Density: 0.857 g / cm³ ３

[0066] <Ethylene-α-olefin copolymer (A1) contained in component (A)> Component (A1-1): EG8150 Dow Chemical melt flow rate (MFR, 190℃): 1 g / 10 min, Density: 0.868 g / cm³ ３ Components (A1-2): EG8100 Dow Chemical melt flow rate (ISO 1133, 190°C, 2.16 kg load): 1.0 g / 10 min, Density: 0.870 kg / m³ ３ Ingredients (A1-3): EG8200 Dow Chemical Meltflow Rate (MFR, 190°C): 5 g / 10 min, Density: 0.870 g / cm³ ３

[0067] <Component (B): Propylene polymer> Component (B-1): Block PP, manufactured by Prime Polymer, J817U, Melt flow rate (MFR, 230℃): 30g / 10min, Component (B-2): Block PP, manufactured by SCG Chemicals, P739ET, Melt flow rate (MFR, 230℃): 55g / 10min,

[0068] <Component (C): Styrene-based thermoplastic elastomer> Component (C-1): SEBS (product name H1062, manufactured by Asahi Kasei Corporation) tanδ peak temperature: -49°C, Styrene content: 18% by mass Melt flow rate (MFR, 230°C): 4g / 10min A hardness (10s, ISO 7619): 63 Component (C-2): ToughTec H1041, manufactured by Asahi Kasei Corporation Loss tangent (tanδ) peak temperature: -44°C, Styrene content: 30% by mass, Durometer A hardness (10s, ISO 7619): 71 Component (C-3): ToughTec H1221, manufactured by Asahi Kasei Corporation Loss tangent (tanδ) peak temperature: -30°C, Styrene content: 12% by mass, Durometer A hardness (10s, ISO 7619): 30 *The loss tangent (tanδ) peak temperature was measured using the solid dynamic viscoelasticity measurement method (torsional mode, 1 Hz).

[0069] <Ingredient (D): Crosslinking agent> Ingredient (D-1): Organic peroxide 2,5-dimethyl-2,5-di-(tert-butylperoxy)hexane (Perhexa 25B, manufactured by Nippon Oil & Fats Co., Ltd.)

[0070] <Ingredient (E): Crosslinking agent> Ingredient (E-1): Divinylbenzene (manufactured by Wako Pure Chemical Industries, Ltd., DVB810)

[0071] <Ingredients (F): Plasticizer> Ingredients (F-1): Paraffin-based oil (Product name "Diana Process Oil PW-100", manufactured by Idemitsu Kosan Co., Ltd.)

[0072] Example 1 The components were thoroughly mixed in a Henschel mixer according to the composition and mixing ratios listed in Table 1, and kneaded under the following conditions to obtain a thermoplastic elastomer composition. (Kneading conditions) Extruder: Model KTX-30, manufactured by Kobe Steel, Ltd. Cylinder temperature: C1-C8: 100°C, C9: 120°C, C10: 160°C, C11: 180°C, C12-C21: 200°C Die temperature: 200°C Screw rotation speed: 600 rpm Extrusion rate: 60 kg / h

[0073] Examples 2-4 and Comparative Examples 1-4: Thermoplastic elastomer compositions were obtained in the same manner as in Example 1, except that the amounts of each component were changed as shown in Table 1. The following physical properties were measured using the thermoplastic elastomer compositions obtained above. The results are shown in Table 1. The injection molding plates, test pieces, molded plates, and molded bodies used in the following physical property measurements were produced from the thermoplastic elastomer compositions obtained above using an injection molding machine (NEX140, manufactured by Nissei Plastic Industrial Co., Ltd.) at a composition temperature of 220°C.

[0074] (1) Melt flow rate (MFR) The melt flow rate (MFR) was measured in accordance with ISO 1133, at 190°C for ethylene-based materials and 230°C for propylene-based materials, with a load of 2.16 kg in both cases.

[0075] (2) Initial bending modulus test In accordance with ASTM D790, test specimens obtained by injection molding were used, and the measurement was taken at 23°C for test specimens that had been left at 23°C for 24 hours or more after molding.

[0076] (3) Izod Impact Test The Izod impact test was performed using test specimens in accordance with ASTM D256. Test specimens with a thickness of 3.2 mm and notches for Izod impact strength were prepared by injection molding from the thermoplastic elastomer composition and tested in an atmosphere at a temperature of -45°C. The Izod impact resistance was evaluated from the fracture state of the test specimens after the test according to the following criteria. Note that in the example where the measurement at -40°C was "CB", the test was not performed at -45°C. Since it was "CB" at -40°C, the more severe condition of -45°C also resulted in a "CB" evaluation. CB: Complete fracture → The test specimen fractures into two or more fragments HB: Hinge fracture → Incomplete fracture where only the thin surface layer in a hinge-like structure, which has lost its bending rigidity, remains as one piece and does not separate PB: Partial fracture → Incomplete fracture that does not meet the definition of hinge fracture NB: Non-destructive → No fracture

[0077] (4) Molding shrinkage rate The molding shrinkage rate [%] in the longitudinal (MD) and transverse (TD) directions of the rectangular plates obtained by injection molding was measured in the following manner, and the absolute value of the surface shrinkage rate (S) was determined. "A 3 mm thick rectangular plate with markings spaced 10 mm apart in the longitudinal and transverse directions was injection molded, and the distance between the markings of the rectangular plate, which had been cured at room temperature for 48 hours or more after molding, was measured, and the shrinkage rate was determined."

[0078] (5) Appearance A molded body having a thick section with L1 = 3 mm and a thin section with L2 = 0.5 mm, as shown in Figure 1, was produced by injection molding from the thermoplastic elastomer composition. The appearance was evaluated by observing the gloss unevenness occurring in the tear line area that appears in the thin section of the molded body. ○: No gloss unevenness was observed between the tear line area and the thick section. △: Slight gloss unevenness was observed between the tear line area and the thick section. ×: Gloss unevenness was clearly observed between the tear line area and the thick section.

[0079]

Claims

A thermoplastic elastomer composition obtained by crosslinking at least a portion of 10 to 55 parts by mass of an ethylene-α-olefin copolymer (A), 40 to 70 parts by mass of a propylene polymer (B), and 2 parts by mass or more and less than 30 parts by mass of a styrene-based thermoplastic elastomer (C), (with the total of the ethylene-α-olefin copolymer (A), propylene polymer (B), and styrene-based thermoplastic elastomer (C) being 100 parts by mass), wherein the thermoplastic elastomer composition satisfies the following requirement (1). 　 Requirement (1): The ethylene-α-olefin copolymer (A) has a density of 0.860 to 0.920 g / cm³. ３ It contains at least a portion of ethylene-α-olefin copolymer (A1). 　 Furthermore, the thermoplastic elastomer composition according to claim 1 that satisfies the following requirement (2). 　 Requirement (2): The styrene-based thermoplastic elastomer (C) has a loss tangent (tanδ) peak temperature of -25°C or lower. 　 The ethylene-α-olefin copolymer (A) has a density of 0.860 to 0.920 g / cm³. ３ A thermoplastic elastomer composition according to claim 1 or claim 2, comprising 30 to 100% by mass of an ethylene-α-olefin copolymer (A1). 　 The thermoplastic elastomer composition according to claim 1, wherein the ethylene-α-olefin copolymer (A1) is a random copolymer. 　 The thermoplastic elastomer composition according to claim 1, wherein the propylene polymer (B) is a propylene block copolymer. 　 The thermoplastic elastomer composition according to claim 2, wherein the loss tangent (tanδ) peak temperature of the styrene-based thermoplastic elastomer (C) in requirement (2) is -70 to -35°C. 　 The thermoplastic elastomer composition according to claim 1 or claim 2, wherein the styrene-containing unit content of the styrene-based thermoplastic elastomer (C) is 15 to 40% by mass. 　 The thermoplastic elastomer composition according to claim 1 or claim 2, further comprising a crosslinking agent (D) and obtained by dynamic crosslinking. 　 The thermoplastic elastomer composition according to claim 8, wherein the crosslinking agent (D) is phenolic or organic peroxide-based. 　 The thermoplastic elastomer composition according to claim 8, wherein the crosslinking agent (D) is an organic peroxide-based crosslinking agent, and the amount blended with the total of ethylene-α-olefin copolymer (A), propylene polymer (B), and styrene-based thermoplastic elastomer (C) is 0.05 to 3.00 parts by mass. 　 Furthermore, the thermoplastic elastomer composition according to claim 1 or claim 2, comprising a plasticizer (F). 　 A thermoplastic elastomer molded article obtained by molding the thermoplastic elastomer composition according to claim 1 or claim 2. 　 Automotive part comprising a thermoplastic elastomer molded article as described in claim 12. 　 The automotive part according to claim 13, which is an airbag cover. 　 The automotive part according to claim 14, which is an unpainted airbag cover.

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