Airbag storage cover

Abstract

The purpose of the present invention is to provide an airbag storage cover that excels in long-term heat resistance, long-term light resistance, and fogging resistance while maintaining high-temperature strength and low-temperature impact resistance. The present invention relates to an airbag storage cover comprising a thermoplastic elastomer composition containing 10-300 parts by mass of component (B) per 100 parts by mass component (A). Component (A): A propylene-based polymer. Component (B): An olefin-based block copolymer comprising an ethylene polymer block and an ethylene-1-octene copolymer block and satisfying the condition (X1). Condition (X1): In a proportion of triad monomer chains determined by 13C NMR measurement, the total of OOO, OOE, and EOO is 6.0-20.0% (provided that E represents an ethylene monomer unit, and O represents an octene monomer unit).

Description

Airbag storage cover

[0001] The present invention relates to an airbag storage cover that maintains high-temperature strength and low-temperature impact resistance, while also exhibiting excellent long-term heat resistance, long-term light resistance, and fogging resistance.

[0002] Automotive airbag systems are systems that protect the driver and occupants in the event of a collision, and consist of a device that senses the impact of a collision and an airbag device. This airbag device is installed in the steering wheel, the instrument panel in front of the passenger seat, the driver's and passenger's seats, the front and side pillars, etc.

[0003] In airbag systems, there are concerns that when the airbag inflates, the airbag storage cover may break, causing fragments to scatter, or the cover itself may break at the mounting points, leading to the cover flying off. Therefore, various proposals have been made regarding the structure and materials of the cover to prevent abnormal breakage and scattering of the cover across a wide temperature range from low to high temperatures.

[0004] As a material for airbag storage covers, for example, Patent Document 1 proposes a thermoplastic elastomer composition comprising a propylene resin and a specific amount of a particular ethylene-α-olefin block copolymer.

[0005] As an airbag storage cover made of an olefin-based thermoplastic elastomer, for example, Patent Document 1 discloses a thermoplastic elastomer composition that is excellent in high-temperature strength and low-temperature impact resistance, comprising a propylene-based resin and a specific amount of a specific ethylene-α-olefin block copolymer. Patent Document 2 discloses a thermoplastic elastomer composition that is excellent in low-temperature impact resistance, high-temperature strength, release properties, injection moldability, etc., comprising a specific amount of two types of specific propylene-based polymers with different copolymer components, a specific ethylene-α-olefin copolymer, and a styrene-conjugated diene block copolymer.

[0006] Japanese Patent Publication No. 2014-77128 Japanese Patent Publication No. 2019-38925

[0007] Automotive interior components, particularly airbag storage covers, are exposed to prolonged heat and ultraviolet radiation from direct sunlight due to their installation location. These components are likely to experience significant deterioration in their physical properties under these operating conditions.

[0008] Detailed studies by the present inventors have revealed that while the thermoplastic elastomer compositions used in airbag storage covers described in Patent Documents 1 and 2 exhibit good low-temperature impact resistance and high-temperature strength, there is room for improvement in their durability when exposed to heat and ultraviolet rays over long periods, i.e., long-term heat resistance, long-term light resistance, and fogging resistance.

[0009] The object of the present invention is to provide an airbag storage cover that maintains high-temperature strength and low-temperature impact resistance, while also being superior in long-term heat resistance, long-term light resistance, and fogging resistance.

[0010] The present inventors have discovered that an airbag storage cover comprising a composition consisting of a propylene polymer and an olefin block copolymer containing a block of a specific ethylene polymer and a block of ethylene-1-octene copolymer exhibits excellent long-term heat resistance, long-term light resistance, and fogging resistance, leading to the present invention.

[0011] In other words, the gist of this invention is as follows:

[0012] One aspect of the present invention relates to an airbag storage cover comprising a thermoplastic elastomer composition containing 10 to 300 parts by mass of component (B) per 100 parts by mass of component (A). Component (A): Propylene polymer Component (B): Olefin block copolymer comprising an ethylene polymer block and an ethylene-1-octene copolymer block, and satisfying the following condition (X1) Condition (X1): １３ The proportion of triad monomer chains determined by 13C NMR measurement is 6.0-20.0% in total for OOO, OOE, and EOO (where E represents an ethylene monomer unit and O represents an octene monomer unit).

[0013] Aspect 2 of the present invention relates to an airbag storage cover according to aspect 1, wherein component (B) satisfies the following condition (Y1). Condition (Y1): The crystal melting peak, which is the top temperature of the melting peak, is determined by differential scanning calorimetry (DSC), where the material is melted from 25°C to 200°C at a heating rate of 100°C / min, held at 200°C for 1 minute, crystallized to -90°C at a cooling rate of 1°C / min, held at -90°C for 10 minutes, and then measured at a heating rate of 10°C / min up to 200°C, and is between 110 and 125°C.

[0014] Aspect 3 of the present invention relates to an airbag storage cover according to aspect 1 or 2, wherein component (B) satisfies the following condition (Y2). Condition (Y2): The heat of fusion at the crystal melting peak at 110 to 125°C is 20 to 60 J / g, determined by differential scanning calorimetry (DSC) by melting from 25°C to 200°C at a heating rate of 100°C / min, holding at 200°C for 1 minute, crystallizing at a cooling rate of 1°C / min to -90°C, holding at -90°C for 10 minutes, and then measuring at a heating rate of 10°C / min to 200°C.

[0015] Aspect 4 of the present invention relates to an airbag storage cover according to any one of aspects 1 to 3, wherein component (B) satisfies the following condition (X2). Condition (X2): １３ The proportion of EEE in the triad monomer chain, as determined by 13C NMR measurement, is between 58.0% and 80.0%.

[0016] Aspect 5 of the present invention relates to an airbag storage cover according to any one of aspects 1 to 4, wherein component (B) satisfies the following condition (X3). Condition (X3): １３ The total amount of octenocomonomers, as determined by 13C NMR measurement, is between 5.0 and 40.0 mol%.

[0017] Aspect 6 of the present invention relates to an airbag storage cover according to any one of aspects 1 to 5, wherein component (A) is a propylene block copolymer obtained by polymerizing a propylene homopolymer in a first step and then polymerizing a propylene-ethylene copolymer in a second step.

[0018] Embodiment 7 of the present invention relates to an airbag storage cover according to any one of embodiments 1 to 6, wherein the melt flow rate of component (A) (measured at a temperature of 230°C and a measured load of 21.18 N) is 10 to 150 g / 10 min.

[0019] Aspect 8 of the present invention relates to an airbag storage cover according to any one of aspects 1 to 7, wherein the thermoplastic elastomer composition further comprises 10 to 300 parts by mass of the following component (C) per 100 parts by mass of component (A). Component (C): Ethylene α-olefin copolymer, which has a heat of fusion of crystals between 110°C and 125°C of less than 20 J / g, determined by differential scanning calorimetry (DSC) by melting from 25°C to 200°C at a heating rate of 100°C / min, holding at 200°C for 1 minute, crystallizing to -90°C at a cooling rate of 1°C / min, holding at -90°C for 10 minutes, and then measuring to 200°C at a heating rate of 10°C / min.

[0020] Aspect 9 of the present invention relates to an airbag storage cover according to aspect 8, wherein the melt flow rate of component (A) (measured at a temperature of 230°C and a measured load of 21.18 N) is 10 to 100 g / 10 min, and the melt flow rate of component (C) (measured at a temperature of 190°C and a measured load of 21.18 N) is 0.01 to 10 g / 10 min.

[0021] Embodiment 10 of the present invention relates to an airbag storage cover according to any one of embodiments 1 to 9, wherein the thermoplastic elastomer composition further comprises 1 to 150 parts by mass of the following component (D) per 100 parts by mass of component (A). Component (D): Styrene-conjugated diene block copolymer and / or hydrogenated thereof

[0022] Aspect 11 of the present invention relates to an airbag storage cover according to aspect 10, wherein the thermoplastic elastomer composition contains 30% by mass or more of component (A) relative to the total amount of components (A) to (D).

[0023] Aspect 12 of the present invention relates to an airbag storage cover according to any one of aspects 1 to 11, wherein the thermoplastic elastomer composition has a melt flow rate of 1 to 50 g / 10 min at a measurement temperature of 230°C and a measurement load of 21.18 N, in accordance with JIS K7210 (1999).

[0024] Aspect 13 of the present invention relates to an airbag storage cover according to any one of aspects 1 to 12, wherein the thermoplastic elastomer composition has a notched Izod impact strength of 70 kJ / m² at a temperature of -45°C in accordance with ISO 180 (2000). ２ That concludes the explanation regarding the airbag storage cover.

[0025] Aspect 14 of the present invention relates to an airbag storage cover according to any one of aspects 1 to 13, wherein the thermoplastic elastomer composition has a tensile breaking strength of 4.0 MPa or more at 85°C, referring to JIS K 6251 (1993).

[0026] The present invention provides an airbag storage cover that maintains high-temperature strength and low-temperature impact resistance, while also exhibiting excellent long-term heat resistance, long-term light resistance, and fogging resistance.

[0027] The airbag storage cover of the present invention can be suitably used as a driver's side airbag storage cover, passenger side airbag storage cover, pedestrian airbag storage cover, knee airbag storage cover, side airbag storage cover, curtain airbag storage cover, and the like.

[0028] Hereinafter, embodiments for carrying out the present invention will be described in detail. However, the present invention is not limited to the following description and can be arbitrarily modified and implemented without departing from the gist of the present invention. In this specification, when expressing a numerical value or a physical property value with "~" sandwiched before and after it, the values before and after it are used as including those values. Also, in this specification, for numerical ranges described step by step, the upper limit value or the lower limit value of a numerical range at a certain step can be arbitrarily combined with the upper limit value or the lower limit value of a numerical range at another step. Further, in the numerical ranges described in this specification, the upper limit value or the lower limit value of the numerical range can also be replaced with the values shown in the examples.

[0029] In this specification, the "airbag storage cover" means the entire container for storing the airbag. For example, in a container in which the airbag is stored, it is the opening when the airbag is deployed, or the entire container integrated with this opening.

[0030] [Thermoplastic elastomer composition] First, the thermoplastic elastomer composition according to an embodiment of the present invention will be described.

[0031] The airbag storage cover according to an embodiment of the present invention includes a thermoplastic elastomer composition containing 10 to 300 parts by mass of the following component (B) with respect to 100 parts by mass of the following component (A). Component (A): Propylene-based polymer component (B): An olefin-based block copolymer containing a block of an ethylene polymer and a block of an ethylene / 1-octene copolymer and satisfying the following condition (X1) Condition (X1): １３ In the ratio of triad monomer chains determined by 13C NMR measurement, the total of OOO, OOE, and EOO is 6.0 to 20.0% (where E means an ethylene monomer unit and O means an octene monomer unit).

[0032] [Mechanism] The thermoplastic elastomer composition according to an embodiment of the present invention exhibits an effect of being excellent in long-term heat resistance, long-term light resistance, and fogging resistance while maintaining high-temperature strength and low-temperature impact resistance. Although the details of the mechanism by which the thermoplastic elastomer composition according to an embodiment of the present invention exhibits such an effect are not clear, it is presumed as follows.

[0033] Regarding the airbag storage cover containing the thermoplastic elastomer composition according to an embodiment of the present invention, compared with those using conventional thermoplastic elastomers known from Patent Documents 1 and 2, etc., it exhibits an effect of being excellent in long-term heat resistance, long-term light resistance, and fogging resistance. The olefin block copolymer containing a block of an ethylene polymer and a block of an ethylene-1-octene copolymer in component (B) compared with the olefin block copolymer containing a block of an ethylene polymer and a block of an ethylene-1-octene copolymer described in Patent Documents 1 and 2 １３ In the ratio of the triad monomer chains determined by C NMR measurement, since the ratio of the octene monomer chains is high, it is considered that the molecular structure is stable and the crystallinity is also high. Therefore, even when exposed to high temperatures and ultraviolet rays from direct sunlight, the molecular motion is restricted, and decomposition by heat and oxygen is difficult to proceed. As a result, when an airbag storage cover is made using the thermoplastic elastomer composition containing component (A) and component (B), component (B) is considered to contribute to improving long-term heat resistance, long-term light resistance, and fogging resistance.

[0034] <Component (A)> The thermoplastic elastomer composition according to an embodiment of the present invention contains a propylene-based polymer as component (A). By including component (A), injection moldability is imparted to the thermoplastic elastomer according to an embodiment of the present invention, and effects such as improvement in high-temperature strength and rigidity are imparted to the airbag storage cover. The "propylene-based polymer" of component (A) means a polymer having a propylene unit content of 90% by mass or more as its constitutional unit.

[0035] Component (A) is a propylene polymer having a propylene unit content of 90 to 100% by mass. It may be a homopolymer of propylene, or a propylene copolymer containing 10% by mass or less of α-olefin units other than propylene (wherein "α-olefin" includes ethylene) or monomer units other than α-olefins, in addition to propylene units. Examples of α-olefin units other than propylene include ethylene and α-olefins having 4 to 20 carbon atoms. Examples of α-olefins having 4 to 20 carbon atoms include 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, 1-tridecene, 1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-nonadecene, 1-eicosene, 3-methyl-1-butene, 3-methyl-1-pentene, 4-methyl-1-pentene, 2-ethyl-1-hexene, and 2,2,4-trimethyl-1-pentene. Other α-olefins besides propylene are preferably ethylene and α-olefins having 4 to 10 carbon atoms, and more preferably ethylene, 1-butene, 1-hexene, and 1-octene.

[0036] Examples of the propylene-based polymer of component (A) include propylene homopolymer, propylene-ethylene copolymer, propylene-1-butene copolymer, propylene-1-hexene copolymer, propylene-1-octene copolymer, propylene-ethylene-1-butene copolymer, propylene-ethylene-1-hexene copolymer, and propylene-ethylene-1-octene copolymer. Preferably, it is a copolymer of propylene homopolymer, ethylene, and propylene with at least one monomer selected from α-olefins having 4 to 10 carbon atoms. Furthermore, the propylene-based polymer of component (A) may also be a polypropylene block copolymer. Particularly preferred as component (A) from the viewpoint of low-temperature impact resistance and high-temperature strength is a propylene block copolymer obtained by polymerizing a propylene homopolymer in the first step, followed by polymerizing a propylene-ethylene copolymer in the second step.

[0037] The propylene unit content of component (A) is 90 to 100% by mass, preferably 95 to 100% by mass, and more preferably 98 to 100% by mass, relative to the total amount of component (A). A propylene unit content of component (A) above the aforementioned lower limit ensures good heat resistance and rigidity of the airbag storage cover. The propylene unit content in component (A) can be determined by infrared spectroscopy.

[0038] The melt flow rate of component (A) (measured at a temperature of 230°C and a measured load of 21.18 N) is not limited, but is usually 0.1 g / min or more, preferably 10 g / 10 min or more, more preferably 20 g / 10 min or more, and even more preferably 30 g / 10 min or more, from the viewpoint of the appearance of the molded article. Also, the melt flow rate of component (A) (measured at a temperature of 230°C and a measured load of 21.18 N) is usually 200 g / 10 min or less, preferably 150 g / 10 min or less, and even more preferably 100 g / 10 min or less, from the viewpoint of tensile strength. In one embodiment, the melt flow rate of component (A) can be 10 to 150 g / 10 min, or 10 to 100 g / 10 min. The melt flow rate of component (A) is measured according to JIS K 7210 (1999) under conditions of a measurement temperature of 230°C and a measurement load of 21.18 N.

[0039] As a method for producing the propylene polymer of component (A), known polymerization methods using known olefin polymerization catalysts can be used. For example, a multi-stage polymerization method using a Ziegler-Natta catalyst can be used. This multi-stage polymerization method can include slurry polymerization, solution polymerization, bulk polymerization, gas-phase polymerization, etc., and two or more of these may be combined.

[0040] Furthermore, component (A) used in the thermoplastic elastomer composition according to the embodiment of the present invention can also be a commercially available product. Commercially available propylene polymers can be procured from the following manufacturers, etc., and can be selected as appropriate. Available commercially available products include: Prime Polypro® from Prime Polymer Co., Ltd., Sumitomo Noblen® from Sumitomo Chemical Co., Ltd., Polypropylene Block Copolymer from Sun Allomer Co., Ltd., Novatec® PP from Nippon Polypropylene Co., Ltd., Moplen® from Lyondell Basell, ExxonMobil PP from ExxonMobil, Formosa Plastics, Formolene® from Formosa Plastics, Borealis PP from Borealis, SEETEC PP from LG Chemical, and A. Examples include Schulman's ASI Polypropylene, INEOS Olefins & Polymers' INEOS PP, Braskem's Braskem PP, SAMSUNG TOTAL PETROCHEMICALS' Samsung Total, Sabic's Sabic® PP, TOTAL PETROCHEMICALS' TOTAL PETROCHEMICALS Polypropylene, and SK's YUPLENE®.

[0041] <Component (B)> Component (B) constituting the thermoplastic elastomer composition according to the embodiment of the present invention is an olefin-based block copolymer containing an ethylene polymer block and an ethylene-1-octene copolymer block.

[0042] [Condition (X1)] Component (B) satisfies the following condition (X1). Condition (X1): １３In the ratio of triad monomer chains determined by C NMR measurement, the total of OOO, OOE and EOO is 6.0 to 20.0% (where E means ethylene monomer unit and О means octene monomer unit). For example, OOO means a unit in which each monomer unit of -octene-octene-octene- is bonded, OOE means a unit in which each monomer unit of -octene-octene-ethylene- is bonded, and EOO means a unit in which each monomer unit of -ethylene-octene-octene- is bonded.

[0043] (Measurement conditions) Under the above conditions (X1) and the conditions (X2) and (X3) described below, １３ The measurement conditions of C NMR are as follows. Weigh 20 mg of the sample into an NMR sample tube with an outer diameter of 5 mm, add 0.53 mL of heavy orthodichlorobenzene (ODCB), heat it with a block heater at 120 °C, and dissolve it. A 13C NMR spectrum was measured using a Bruker AVANCE600 spectrometer. The resonance frequency was 150.9 MHz, the flip angle was 90°, the data acquisition time was 2.0 s, the pulse repetition time was 30 s, the number of integrations was 288, and the temperature was 120 °C. The reference for the chemical shift is that the signal of the polyethylene main chain is 30.0 ppm.

[0044] Further, from the viewpoints of long-term heat resistance and long-term light resistance, for the ratio of the above triad monomer chains, the total of OOO, OOE and EOO is more preferably 6.5% or more, even more preferably 7.0% or more, and particularly preferably 8.0% or more. On the other hand, from the viewpoints of crystallinity and moldability, 15.0% or less is more preferable, and 10.0% or less is even more preferable.

[0045] Component (B) preferably satisfies the following condition (X2). Condition (X2): １３ In the ratio of triad monomer chains determined by C NMR measurement, the ratio of EEE is 58.0 to 80.0%.

[0046] Furthermore, from the viewpoint of long-term heat resistance and long-term light resistance, the proportion of EEE in the above triad monomer chain is more preferably 58.5% or more, and even more preferably 59.0% or more. On the other hand, from the viewpoint of crystallinity and moldability, it is more preferably 70.0% or less, even more preferably 65.0% or less, and particularly preferably 60.0% or less.

[0047] [Condition (X3)] Component (B) preferably satisfies the following condition (X3). Condition (X3): １３ The total amount of octenocomonomers, as determined by 13C NMR measurement, is between 5.0 and 40.0 mol%.

[0048] Furthermore, from the viewpoint of low-temperature impact resistance, the total amount of octencomonomer is more preferably 10.0 mol% or more, and even more preferably 15 mol% or more. On the other hand, from the viewpoint of preventing fusion due to blocking, it is more preferably 30.0 mol% or less, even more preferably 25.0 mol% or less, and particularly preferably 20.0 mol% or less.

[0049] [Conditions (Y1) and (Y2)] Component (B) preferably satisfies at least one of the following conditions (Y1) and (Y2). Condition (Y1): The crystal melting peak, which is the top temperature of the melting peak, is determined by differential scanning calorimetry (DSC), where the material is melted from 25°C to 200°C at a heating rate of 100°C / min, held at 200°C for 1 minute, crystallized to -90°C at a cooling rate of 1°C / min, held at -90°C for 10 minutes, and then measured at a heating rate of 10°C / min up to 200°C, and the crystal melting peak is 110 to 125°C. Condition (Y2): The heat of fusion at the crystal melting peak between 110 and 125°C is determined by differential scanning calorimetry (DSC), where the material is melted from 25°C to 200°C at a heating rate of 100°C / min, held at 200°C for 1 minute, then crystallized to -90°C at a cooling rate of 1°C / min, held at -90°C for 10 minutes, and then measured at a heating rate of 10°C / min up to 200°C. The heat of fusion at the crystal melting peak between 110 and 125°C is 20 to 60 J / g.

[0050] Here, in component (B), the fact that the heat of fusion at the 110-125°C crystalline melting peak is 20-60 J / g is an indicator that the ethylene polymer blocks in component (B) are crystalline.

[0051] When component (B) satisfies at least one of the above conditions (Y1) and (Y2), component (B) typically has crystalline properties based on blocks of ethylene polymer, as well as amorphous properties based on blocks of ethylene-α-olefin copolymer. Having such a structure in component (B) provides the airbag storage cover according to the embodiment of the present invention with the effects of high-temperature strength and low-temperature impact resistance.

[0052] Regarding the above condition (Y1), the crystal melting peak of component (B) is preferably 110°C or higher, more preferably 115°C or higher, and even more preferably 120°C or higher, from the viewpoint of long-term heat resistance and long-term light resistance. On the other hand, the crystal melting peak of component (B) is preferably 125°C or lower, and more preferably 123°C or lower, from the viewpoint of moldability. Regarding the above condition (Y2), the heat of fusion of component (B) is preferably 20 J / g or higher, and more preferably 30 J / g or higher, from the viewpoint of high-temperature strength. Furthermore, the heat of fusion of component (B) is preferably 60 J / g or lower, and more preferably 50 J / g or lower, from the viewpoint of low-temperature impact resistance.

[0053] [Other Preferred Embodiments] The crystalline polymer block in component (B) is mainly composed of ethylene, but may also contain other monomer units in addition to ethylene. Examples of other monomer units include 1-propylene, 1-butene, 2-methylpropylene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene, etc. Preferably, it is an α-olefin having 3 to 8 carbon atoms and having an intercarbon double bond at the terminal carbon atoms, such as 1-propylene, 1-butene, 1-hexene, 1-octene. The α-olefin in component (B) may be copolymerized with ethylene by only one type, or by two or more types copolymerized with ethylene. Furthermore, component (B) may be used by only one type or by a combination of two or more types.

[0054] The ethylene-1-octene copolymer block of component (B) may have other monomer units in addition to ethylene units and 1-octene units. The other monomer units are α-olefins with 3 to 7 carbon atoms having an intercarbon double bond at the terminal carbon atom, such as 1-propylene, 1-butene, 2-methylpropylene, 1-pentene, 3-methyl-1-butene, 1-hexene, and 4-methyl-1-pentene. Component (B) may be used alone or in combination of two or more types.

[0055] The ethylene unit content of component (B) is preferably 50 to 80% by mass relative to the total amount of ethylene units, 1-octene units, and α-olefin units. A higher ethylene unit content is preferable to prevent fusion due to blocking of component (B), while a lower ethylene unit content is preferable from the viewpoint of low-temperature impact resistance when the thermoplastic elastomer according to the embodiment of the present invention is molded. The ethylene unit content of component (B) is more preferably 55% by mass or more, and even more preferably 60% by mass or more. Furthermore, the ethylene unit content is more preferably 75% by mass or less. The ethylene unit content and the carbon-4 to carbon-8 α-olefin unit content in component (B) can be determined by infrared spectroscopy, respectively.

[0056] The ethylene-1-octene copolymer of component (B) may have other monomer units in addition to ethylene units and 1-octene units, such as monomer units based on non-conjugated dienes (non-conjugated diene units). Examples of such non-conjugated dienes include linear non-conjugated dienes such as 1,4-hexadiene, 1,6-octadiene, 2-methyl-1,5-hexadiene, 6-methyl-1,5-heptadiene, and 7-methyl-1,6-octadiene; and cyclic non-conjugated dienes such as cyclohexadiene, dicyclopentadiene, methyltetrahydroindene, 5-vinylnorbornene, 5-ethylidene-2-norbornene, 5-methylene-2-norbornene, 5-isopropylidene-2-norbornene, and 6-chloromethyl-5-isopropenyl-2-norbornene. Preferably, it is 5-ethylidene-2-norbornene or dicyclopentadiene.

[0057] Furthermore, if component (B) contains other monomer units such as non-conjugated diene units, their content is usually 10% by mass or less, preferably 5% by mass or less, relative to the total content of component (B). The content of non-conjugated diene units and propylene units can be determined by infrared spectroscopy.

[0058] Component (B) has blocks of crystalline ethylene polymer, as well as amorphous properties due to blocks of ethylene-1-octene copolymer. This amorphous property is expressed by the glass transition temperature, which, according to the DSC method, is preferably -80°C or higher, more preferably -75°C or higher, while preferably -50°C or lower, and more preferably -60°C or lower.

[0059] The melt flow rate of component (B) (measurement temperature 190°C, measurement load 21.18 N) is not limited, but is usually 10 g / 10 min or less, preferably 8 g / 10 min or less, more preferably 5 g / 10 min or less, and even more preferably 3 g / 10 min or less from the viewpoint of strength. Also, the melt flow rate of component (B) is usually 0.01 g / 10 min or more, preferably 0.05 g / 10 min or more, and even more preferably 0.10 g / 10 min or more from the viewpoint of fluidity. The melt flow rate of component (B) is measured according to ASTM D1238 under the conditions of a measurement temperature of 190°C and a measurement load of 21.18 N.

[0060] The density of component (B), measured at 23°C in accordance with ISO 1183-A, is preferably 0.88 g / cm³ from the viewpoint of low-temperature impact resistance. ３ The following, and more preferably 0.87 g / cm³ ３ The following applies. On the other hand, there is no particular restriction on the lower limit, but it is usually 0.85 g / cm³. ３ That's all.

[0061] Component (B) can be synthesized according to the methods disclosed in Japanese Patent Publication No. 2007-529617, Japanese Patent Publication No. 2008-537563, and Japanese Patent Publication No. 2008-543978. For example, it can be produced by preparing a composition containing a mixture or reaction product obtained by combining a first olefin polymerization catalyst, a second olefin polymerization catalyst capable of preparing a polymer with chemical or physical properties different from the polymer prepared by the first olefin polymerization catalyst under equivalent polymerization conditions, and a chain shuttle agent, and then contacting the above ethylene and α-olefin with the composition under addition polymerization conditions.

[0062] For the polymerization of component (B), a continuous solution polymerization method is preferably applied. In continuous solution polymerization, catalyst components, chain shuttling agents, monomers, and optionally solvents, auxiliary agents, scavengers, and polymerization aids are continuously supplied to the reaction zone, and the polymer product is continuously extracted from there. The length of the block can be changed by controlling the ratio and type of catalyst, the ratio and type of chain shuttling agent, the polymerization temperature, etc.

[0063] Furthermore, other conditions for the method of synthesizing the block copolymer are disclosed in Japanese Patent Publication No. 2007-529617, Japanese Patent Publication No. 2008-537563, and Japanese Patent Publication No. 2008-543978. In addition, a commercially available product is, for example, "Engage® 11677" manufactured by Dow Chemical Company. In the thermoplastic elastomer composition according to the embodiment of the present invention, "Engage® XLT8677" manufactured by Dow Chemical Company does not correspond to component (B) and is used as a comparative example in subsequent examples, but it may be combined and formulated together with component (B).

[0064] <Component (C)> The thermoplastic elastomer composition according to the embodiment of the present invention may further contain the following component (C), and preferably contains 10 to 300 parts by mass of the following component (C) per 100 parts by mass of component (A). Component (C): Ethylene α-olefin copolymer, which has a heat of fusion of crystals at 110°C to 125°C of less than 20 J / g, determined by differential scanning calorimetry (DSC) by melting from 25°C to 200°C at a heating rate of 100°C / min, holding at 200°C for 1 minute, crystallizing at a cooling rate of 1°C / min to -90°C, holding at -90°C for 10 minutes, and then measuring at a heating rate of 10°C / min to 200°C.

[0065] In the above component (C), it is preferable that the heat of fusion of crystals at 110 to 125°C is less than 20 J / g, as this results in low crystallinity of component (C) and a tendency towards amorphousness. By including component (C) in the thermoplastic elastomer composition, the low-temperature impact resistance of the airbag storage cover according to the embodiment of the present invention can be further improved.

[0066] Component (C) is a copolymer containing at least ethylene units and α-olefin units. Examples of α-olefins used in component (C) include 1-propylene, 1-butene, 2-methylpropylene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, and 1-octene. Preferably, the α-olefin used in component (C) is an α-olefin having 3 to 8 carbon atoms and having an intercarbon double bond at the terminal carbon atom, such as 1-propylene, 1-butene, 1-hexene, and 1-octene. In component (C), only one type of α-olefin may be copolymerized with ethylene, or two or more types may be copolymerized with ethylene. Furthermore, component (C) may be used alone or in combination of two or more types.

[0067] The ethylene unit content of component (C) is preferably 50 to 80% by mass relative to the total amount of ethylene units and α-olefin units. A higher ethylene unit content is preferable to prevent fusion due to blocking of component (C), while a lower ethylene unit content is preferable to improve the low-temperature impact resistance when the thermoplastic elastomer according to the embodiment of the present invention is molded. The ethylene unit content of component (C) is more preferably 55% by mass or more, and even more preferably 60% by mass or more. Furthermore, the ethylene unit content is more preferably 75% by mass or less. The ethylene unit content and the carbon-3 to carbon-8 α-olefin unit content in component (C) can be determined by infrared spectroscopy, respectively.

[0068] The amorphous ethylene-α-olefin copolymer of component (C) may have other monomer units, such as monomer units based on a non-conjugated diene (non-conjugated diene units), in addition to ethylene units and α-olefin units having 3 to 8 carbon atoms. Examples of such non-conjugated dienes include linear non-conjugated dienes such as 1,4-hexadiene, 1,6-octadiene, 2-methyl-1,5-hexadiene, 6-methyl-1,5-heptadiene, and 7-methyl-1,6-octadiene; and cyclic non-conjugated dienes such as cyclohexadiene, dicyclopentadiene, methyltetrahydroindene, 5-vinylnorbornene, 5-ethylidene-2-norbornene, 5-methylene-2-norbornene, 5-isopropylidene-2-norbornene, and 6-chloromethyl-5-isopropenyl-2-norbornene. Preferably, it is 5-ethylidene-2-norbornene or dicyclopentadiene.

[0069] Furthermore, other monomeric units of component (C), such as non-conjugated diene units, are typically 10% by mass or less, preferably 5% by mass or less, relative to the total amount of component (C). The content of non-conjugated diene units and propylene units can be determined by infrared spectroscopy.

[0070] Specific examples of component (C) include ethylene-1-butene copolymer rubber, ethylene-1-hexene copolymer rubber, ethylene-1-octene copolymer rubber, ethylene-propylene-1-butene copolymer rubber, ethylene-propylene-1-hexene copolymer rubber, and ethylene-propylene-1-octene copolymer rubber. These may be used individually or in combination of two or more. Among these, ethylene-1-butene copolymer rubber and ethylene-1-octene copolymer rubber are preferred.

[0071] The melt flow rate of component (C) (measurement temperature 190°C, measurement load 21.18 N) is not limited, but is usually 10 g / 10 min or less, preferably 8 g / 10 min or less, more preferably 5 g / 10 min or less, and even more preferably 3 g / 10 min or less from the viewpoint of strength. Also, the melt flow rate of component (C) is usually 0.01 g / 10 min or more, preferably 0.05 g / 10 min or more, and even more preferably 0.10 g / 10 min or more from the viewpoint of fluidity. In one embodiment, the melt flow rate of component (C) can be 0.01 g to 10 g / 10 min. The melt flow rate of component (C) is measured according to ASTM D1238 under the conditions of a measurement temperature of 190°C and a measurement load of 21.18 N.

[0072] In a preferred embodiment, the melt flow rate of component (A) may be 10 to 100 g / 10 min, and the melt flow rate of component (C) may be 0.01 to 10 g / 10 min.

[0073] The density of component (C), measured at 23°C in accordance with ISO 1183-A, is preferably 0.88 g / cm³ from the viewpoint of low-temperature impact resistance. ３ The following, and more preferably 0.87 g / cm³ ３ The following applies. On the other hand, there is no particular restriction on the lower limit, but it is usually 0.85 g / cm³. ３ That's all.

[0074] As a method for producing component (C), known polymerization methods using known olefin polymerization catalysts are used. For example, as olefin polymerization catalysts, complex catalysts such as Ziegler-Natta catalysts, metallocene complexes, and non-metallocene complexes can be used, and polymerization methods include slurry polymerization, solution polymerization, bulk polymerization, and gas-phase polymerization. It is also possible to use commercially available products. Examples of commercially available products include the Engage® series from Dow Chemical and the Tuffmer® series from Mitsui Chemicals, Inc.

[0075] <Component (D)> The thermoplastic elastomer composition according to the embodiment of the present invention may further contain the following component (D), and preferably contains 1 to 150 parts by mass of the following component (D) per 100 parts by mass of component (A). Component (D): Styrene-conjugated diene block copolymer and / or hydrogenated thereof

[0076] Suitable conjugated dienes in component (D) styrene-conjugated diene block copolymer and / or its hydrogenated product are butadiene, isoprene, or mixtures thereof. Examples include styrene-butadiene block copolymer (hereinafter sometimes simply abbreviated as "SBS") and / or its hydrogenated product. Examples of hydrogenated products of styrene-butadiene block copolymer include partially hydrogenated styrene-butadiene-butylene-styrene copolymer (SBBS) and substantially fully hydrogenated styrene-ethylene-butylene-styrene copolymer (SEBS). Examples also include styrene-ethylene-propylene-styrene copolymer (SEPS), which is a hydrogenated product of styrene-isoprene block copolymer (hereinafter sometimes simply abbreviated as "hydrogenated SIS"), and hydrogenated products of styrene-polyisobutylene-styrene block copolymer (hereinafter sometimes simply abbreviated as "hydrogenated SIBS").

[0077] The styrene content of the styrene-conjugated diene block copolymer and / or its partially hydrogenated or fully hydrogenated product (D) is not particularly limited, but from the viewpoint of strength and heat resistance, it is preferably 5% by mass or more, more preferably 8% by mass or more, and even more preferably 10% by mass or more. Furthermore, from the viewpoint of flexibility and impact resistance, the styrene content is preferably 70% by mass or less, more preferably 55% by mass or less, and even more preferably 40% by mass or less.

[0078] In component (D), the conjugated diene has a 1,2-microstructure of 60 mol% or less, more preferably 45 mol% or less, as analyzed by NMR. Having a 1,2-microstructure below the above upper limit is preferable from the viewpoint of moldability and flexibility, and also from the viewpoint of not allowing the crosslinking reaction to proceed excessively by dynamic heat treatment. In component (D), from the viewpoint of utilizing the crosslinking reaction, if component (D) is a hydrogenated styrene-conjugated diene block copolymer, its hydrogenation rate is preferably 95% or less, more preferably 90% or less, and even more preferably 85% or less.

[0079] When the conjugated diene in component (D) is a mixture of isoprene and butadiene, the mass ratio (isoprene / butadiene) is generally 99 / 1 to 1 / 99, preferably 90 / 10 to 30 / 70, and particularly preferably 80 / 20 to 40 / 60.

[0080] The weight-average molecular weight (Mw) of component (D) is preferably 50,000 or more, more preferably 80,000 or more, and even more preferably 100,000 or more, from the viewpoint of release properties. Furthermore, the weight-average molecular weight (Mw) is preferably 500,000 or less, more preferably 450,000 or less, even more preferably 400,000 or less, and particularly preferably 350,000 or less, from the viewpoint of fluidity and dispersibility.

[0081] The weight-average molecular weight (Mw) of component (D) is measured by gel permeation chromatography (GPC), and can be measured, for example, under the following conditions: Instrument: Tosoh Corporation "HLC-8220 GPC(R)" Column: Tosoh Corporation "TSKgel Super HM-M (6.0 mm I.D × 15 cm × 2 + G)" Detector: Differential refractive index detector (RI / built-in) Solvent: Chloroform Temperature: 40°C Flow rate: 0.25 mL / min Injection volume: 0.1 mass% × 20 μL Calibration sample: Monodisperse polystyrene Calibration method: Polystyrene equivalent Calibration curve approximation formula: Cubic (hyperbola) Exclusion limit setting time: 12 minutes

[0082] As a method for producing the styrene-conjugated diene block copolymer of component (D), for example, the styrene-conjugated diene block copolymer may be synthesized in an inert solvent using a lithium catalyst by the method described in Japanese Patent Publication No. 40-23798. Furthermore, for the hydrogenated styrene-conjugated diene block copolymer, the styrene-conjugated diene block copolymer may be synthesized as described above, and then hydrogenated in an inert solvent in the presence of a hydrogenation catalyst by the method described in Japanese Patent Publication No. 42-8704, Japanese Patent Publication No. 43-6636, Japanese Patent Publication No. 59-133203, and Japanese Patent Publication No. 60-79005.

[0083] Component (D), the styrene-conjugated diene block copolymer and / or its hydrogenated product, is also available commercially. Examples of styrene-conjugated diene block copolymers include Kraton® D from Kraton Polymers. Examples of partially hydrogenated styrene-conjugated diene block copolymers include ToughTec® P from Asahi Kasei Corporation. Examples of hydrogenated styrene-conjugated diene block copolymers include Kraton® G from Kraton Polymers, Septon® from Kuraray Co., Ltd., and ToughTec® from Asahi Kasei Corporation.

[0084] <Formulation> From the viewpoint of the low-temperature impact resistance of the molded article, the content of component (B) is 10 parts by mass or more, preferably 30 parts by mass or more, more preferably 50 parts by mass or more, and even more preferably 60 parts by mass or more, per 100 parts by mass of component (A). Furthermore, from the viewpoint of the rigidity of the molded article, the content of component (B) is 300 parts by mass or less, preferably 200 parts by mass or less, more preferably 150 parts by mass or less, and even more preferably 120 parts by mass or less, per 100 parts by mass of component (A).

[0085] From the viewpoint of the low-temperature impact resistance of the molded article, the content of component (C) is preferably 10 parts by mass or more, more preferably 30 parts by mass or more, even more preferably 50 parts by mass or more, and particularly preferably 60 parts by mass or more, per 100 parts by mass of component (A). Furthermore, from the viewpoint of the rigidity of the molded article, the content of component (C) is preferably 300 parts by mass or less, more preferably 200 parts by mass or less, even more preferably 150 parts by mass or less, and particularly preferably 120 parts by mass or less, per 100 parts by mass of component (A).

[0086] From the viewpoint of high-temperature airbag deployment performance, the content of component (A) is preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 45% by mass or more, relative to the total amount of components (A) to (D). Furthermore, from the viewpoint of low-temperature impact resistance, the content of component (A) is preferably 70% by mass or less, more preferably 65% ​​by mass or less, and even more preferably 60% by mass or less, relative to the total amount of components (A) to (D).

[0087] Furthermore, from the viewpoint of airbag deployment performance under low and high temperature conditions, the content of component (B) is preferably 15% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more, relative to the total amount of components (A) to (D). Furthermore, from the viewpoint of injection moldability, the content of component (B) is preferably 70% by mass or less, more preferably 65% ​​by mass or less, and even more preferably 60% by mass or less, relative to the total amount of components (A) to (D).

[0088] <Other Components> In addition to the above components, the thermoplastic elastomer composition according to the embodiment of the present invention may contain optional components such as the following additives and polymers other than components (A) to (D) (hereinafter referred to as "other polymers"), as long as they do not significantly impair the effects of the present invention.

[0089] Other components include various additives such as colorants, antioxidants, heat stabilizers, light stabilizers, ultraviolet absorbers, neutralizing agents, lubricants, antifogging agents, antiblocking agents, slip agents, flame retardants, dispersants, antistatic agents, conductivity imparters, metal deactivators, molecular weight modifiers, antibacterial agents, and fluorescent whitening agents. For example, antioxidants are used in an amount of 0.01 to 0.5 parts by mass per 100 parts by mass of the total amount of components (A) to (D).

[0090] Other polymers that may be contained in the thermoplastic elastomer composition according to the embodiment of the present invention include ester polymers, amide polymers, styrene polymers, acrylic polymers, carbonate polymers, vinyl chloride polymers, and various other elastomers. The other polymers listed above may be contained individually or in combination of two or more. Furthermore, the thermoplastic elastomer composition according to the embodiment of the present invention may also contain a hydrocarbon-based rubber softener. In particular, when the thermoplastic elastomer composition according to the embodiment of the present invention uses a styrene-conjugated diene block copolymer and / or its hydrogenated product as component (D), it is preferable to use a hydrocarbon-based rubber softener.

[0091] Hydrocarbon-based rubber softeners are generally mixtures of aromatic rings, naphthenic rings, and paraffinic rings. Paraffinic oils are classified as follows: those with 50% or more carbon atoms in the paraffin chain are called paraffinic oils; those with 30-45% carbon atoms in the naphthenic ring are called naphthenic oils; and those with more than 30% carbon atoms in the aromatic ring are called aromatic oils. Among these, paraffinic oils are preferred from the viewpoint of weather resistance. Paraffinic oils preferably have a kinematic viscosity of 20-800 cst at 40°C, and more preferably 50-600 cst. The pour point of paraffinic oils is usually 0 to -40°C, preferably 0 to -30°C. The flash point (COC) of paraffinic oils is usually 200-400°C, preferably 250-350°C.

[0092] The weight-average molecular weight of the hydrocarbon-based rubber softener is preferably 300 or more, more preferably 500 or more, from the viewpoint of preventing stickiness of the molded airbag storage cover. Furthermore, the weight-average molecular weight of the hydrocarbon-based rubber softener is preferably 2,000 or less, more preferably 1,500 or less, from the viewpoint of the moldability of the airbag storage cover.

[0093] When using a hydrocarbon-based rubber softener, from the viewpoint of moldability when forming an airbag storage cover, the content of the hydrocarbon-based rubber softener is preferably 1 part by mass or more, more preferably 5 parts by mass or more, and more preferably 10 parts by mass or more, per 100 parts by mass of component (A). On the other hand, from the viewpoint of shape retention and expandability at high temperatures of the airbag storage cover, the content of the hydrocarbon-based rubber softener is preferably 100 parts by mass or less, more preferably 80 parts by mass or less, even more preferably 60 parts by mass or less, and particularly preferably 40 parts by mass or less, per 100 parts by mass of component (A).

[0094] <Method for Manufacturing Thermoplastic Elastomer Composition> The thermoplastic elastomer composition according to the embodiment of the present invention can be manufactured by kneading the above components (A) and (B), components (C) and (D) as needed, and other components using conventional methods with a conventional extruder, Banbury mixer, roll, Brabender plastograph, kneader-brabender, etc. Among these manufacturing methods, it is preferable to use an extruder, particularly a twin-screw extruder. When manufacturing the thermoplastic elastomer composition by kneading with an extruder, etc., it can usually be manufactured by melt kneading at a heated temperature of 160 to 240°C, preferably 180 to 220°C. Furthermore, the thermoplastic elastomer composition may be partially crosslinked by dynamically heat-treating it with the following crosslinking agents and crosslinking aids.

[0095] As a crosslinking agent for partially crosslinking the thermoplastic elastomer composition according to the embodiment of the present invention, it is preferable to use an organic peroxide, such as 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexyn-3, 1,3-bis(tert-butylperoxyisopropyl)benzene, 1,1-di(tert-butylperoxy)3,5,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(peroxybenzoyl)hexyn-3, dicumyl peroxide, etc.

[0096] Examples of crosslinking aids used when partially crosslinking with these organic peroxides include compounds having N,N'-m-phenylenebismaleimide, toluenebismaleimide, etc., compounds having radically polymerizable carbon-carbon double bonds such as P-quinone dioxime, nitrobenzene, diphenylguanidine, trimethylolpropane, divinylbenzene, ethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, allyl methacrylate, etc., and compounds having functional groups that react with the carbon linear portion of component (B) and / or component (C).

[0097] <Physical Properties> The thermoplastic elastomer composition according to the embodiment of the present invention, by containing specific amounts of component (A) and component (B), exhibits excellent long-term heat resistance, long-term light resistance, and fogging resistance, as well as excellent injection moldability, high-temperature strength, room-temperature strength, low-temperature impact resistance, etc.

[0098] In this specification, the melt flow rate (MFR) measured at a temperature of 230°C and a measurement load of 21.18 N according to JIS K 7210 (1999) is used as an indicator of the injection moldability of the thermoplastic elastomer composition. The thermoplastic elastomer composition according to the embodiment of the present invention preferably has an MFR of 1 to 50 g / 10 min in order to be excellent in injection moldability. An MFR of 1 g / 10 min or more of the thermoplastic elastomer composition is preferable because it has excellent fluidity and facilitates injection molding. Furthermore, an MFR of 50 g / 10 min or less is preferable because it can suppress the generation of burrs and the like during injection molding. From the viewpoint of fluidity, it is more preferable to have an MFR of 5 g / 10 min or more, and even more preferably 10 g / 10 min or more. On the other hand, from the viewpoint of suppressing burrs and the like during injection molding, the MFR of the thermoplastic elastomer composition is more preferable to have an MFR of 40 g / 10 min or less, even more preferably 30 g / 10 min or less, and particularly preferably 20 g / 10 min or less. Furthermore, the MFR of thermoplastic elastomers tends to increase as the amount of component (A), which is a highly fluid component, increases, and conversely, it tends to decrease as the amount of component (B), which is a less fluid component, increases. Also, when component (C) is included, the MFR of the thermoplastic elastomer composition tends to decrease as the amount of component (D) increases.

[0099] In this specification, the notched Izod impact strength at -45°C in accordance with ISO 180 (2000) is used as an indicator of low-temperature impact resistance. The notched Izod impact strength at -45°C in accordance with ISO 180 (2000) of the thermoplastic elastomer composition according to the embodiment of the present invention is preferably 50 kJ / m ２ The above is preferable to 60 kJ / m ２ The above is preferable, and more preferably 71 kJ / m ２ That concludes the explanation. On the other hand, there is no particular upper limit to the notched Izod impact strength, but it is usually 150 kJ / m２ The following applies:

[0100] In this specification, the tensile fracture strength at 85°C, referring to JIS K 6251 (1993), is used as an indicator of high-temperature strength. The tensile fracture strength at 85°C, referring to JIS K 6251 (1993), of the thermoplastic elastomer composition according to the embodiment of the present invention is preferably 4.0 MPa or higher, more preferably 4.5 MPa or higher, and even more preferably 5.0 MPa or higher. On the other hand, there is no particular upper limit to the tensile fracture strength, but it is usually 30.0 MPa or lower.

[0101] In this specification, the tensile fracture strength at 23°C, referring to JIS K 6251 (1993), is used as an indicator of strength at room temperature. The tensile fracture strength at 23°C of the thermoplastic elastomer composition according to the embodiment of the present invention, referring to JIS K 6251 (1993), is preferably 5.0 MPa or higher, more preferably 6.0 MPa or higher, and even more preferably 8.0 MPa or higher. On the other hand, there is no particular upper limit to the tensile fracture strength, but it is usually 50.0 MPa or lower. Furthermore, the tensile fracture elongation is preferably 100% or higher, more preferably 200% or higher, and even more preferably 300% or higher. There is no particular upper limit to the tensile fracture elongation, but it is usually 1500% or lower. In this specification, a characteristic feature is that the rate of change from the initial results is small even after heat resistance tests and light resistance tests have been performed. For this reason, in this specification, it is particularly important that there is little change in physical properties even after heat resistance tests and light resistance tests.

[0102] In this specification, referring to ISO 6452 Method A (glass cooling method), a fogging tester WSF-2 manufactured by Suga Test Instruments Co., Ltd. was used, and the heating layer temperature was set to 100°C, and the temperature of the cooling plate placed on top of the glass plate for haze value measurement (110 mm x 110 mm x 3 mm, visible light transmittance of 98% or more) was set to 20°C and heated for 16 hours. After the test, the glass plate was left at standard conditions (23°C, 50% RH) for 1 hour, and then the diffuse light transmittance (Td.%) and total light transmittance (Tt.%) in the center of the haze were measured using an NDH8000 (integrating sphere type light transmittance measuring device) manufactured by Nippon Denshoku Industries, Ltd., and the haze value (haze number) was calculated using the following formula. The haze value (haze number) of the glass plate is used as an indicator of fogging resistance. The haze value is preferably 20% or less, more preferably 8% or less, and even more preferably 1.5% or less. There is no specific lower limit, but it is usually 0% or higher.

[0103] (Calculation formula for haze value) Haze value (%) = H = Td / Tt × 100 [In the formula, Td represents the diffuse light transmittance (%), and Tt represents the total light transmittance (%).]

[0104] The above thermoplastic elastomer composition can be used as an airbag storage cover by forming a molded body using a conventional injection molding method, or, if necessary, various molding methods such as gas injection molding, injection compression molding, or short-shot foam molding. In particular, the airbag storage cover according to the embodiment of the present invention is preferably manufactured by injection molding, and the molding conditions when performing injection molding are as follows. The molding temperature when injection molding the airbag storage cover is generally 150 to 300°C, preferably 180 to 280°C. The injection pressure is usually 5 to 100 MPa, preferably 10 to 80 MPa. The mold temperature is usually 0 to 80°C, preferably 20 to 60°C. The airbag storage cover obtained in this way is suitably used as an airbag storage cover for an airbag system that activates when a high-speed moving object such as an automobile senses the impact or deformation during a collision, and inflates and deploys to protect the occupants.

[0105] The present invention will be described in more detail below using examples, but the present invention is not limited to the following examples unless it exceeds its gist. The various manufacturing conditions and evaluation result values ​​in the following examples have meaning as preferred upper or lower limits in embodiments of the present invention, and the preferred range may be defined by a combination of the aforementioned upper or lower limits and the values ​​in the following examples or between examples.

[0106] <Raw Materials> The components used in the examples and comparative examples are shown below. Here, "crystal melting peak temperature" refers to the top temperature of the melting peak obtained by differential scanning calorimetry (DSC) using a Discovery DSC 25 manufactured by TA Instruments, Inc., where the material is melted from 25°C to 200°C at a heating rate of 100°C / min, held at 200°C for 1 minute, crystallized to -90°C at a cooling rate of 1°C / min, held at -90°C for 10 minutes, and then measured up to 200°C at a heating rate of 10°C / min. Furthermore, "calorific value of crystalline melting" refers to the amount of heat at the crystalline melting peak between 110 and 125°C, determined by differential scanning calorimetry (DSC) by melting the material from 25°C to 200°C at a heating rate of 100°C / min, holding it at 200°C for 1 minute, crystallizing it at a cooling rate of 1°C / min to -90°C, holding it at -90°C for 10 minutes, and then measuring it at a heating rate of 10°C / min up to 200°C.

[0107] [Component (A)] (A-1): Propylene-based block copolymer (manufactured by Nippon Polypropylene Co., Ltd., trade name "Novatec® PP BC03B", obtained by polymerizing a propylene homopolymer in the first step, followed by polymerizing an ethylene-propylene copolymer in the second step) MFR (JIS K 7210 (1999)): 30 g / 10 min (measurement conditions: 230°C, load 21.18 N (2.16 kgf)) Content of propylene homopolymer block: 84% by mass Content of ethylene-propylene copolymer block: 16% by mass Ethylene unit content in ethylene-propylene copolymer block: 55% by mass

[0108] (A-2): Propylene-based block copolymer (manufactured by Nippon Polypropylene Co., Ltd., trade name "Novatec® PP BC3B", obtained by polymerizing a propylene homopolymer in the first step, followed by polymerizing an ethylene-propylene copolymer in the second step) MFR (JIS K 7210 (1999)): 10 g / 10 min (measurement conditions: 230°C, load 21.18 N (2.16 kgf)) Content of propylene homopolymer block: 83% by mass Content of ethylene-propylene copolymer block: 17% by mass Ethylene unit content in ethylene-propylene copolymer block: 41% by mass

[0109] (A-3): Propylene-based block copolymer (manufactured by Lyondell Basell, trade name "Hifax X1956A", obtained by polymerizing a propylene homopolymer in the first step, followed by polymerizing an ethylene-propylene copolymer in the second step) MFR (JIS K 7210 (1999)): 1.1 g / 10 min (measurement conditions: 230 °C, load 21.18 N) Content of propylene homopolymer block: 70% by mass Content of ethylene-propylene copolymer block: 30% by mass Ethylene unit content in ethylene-propylene copolymer block: 65% by mass Melting temperature: 162 °C

[0110] (A-4): Propylene-based block copolymer (manufactured by Lyondell Basell, trade name "Adflex Q300F", obtained by polymerizing a propylene homopolymer in the first step, followed by polymerizing an ethylene-propylene copolymer in the second step) MFR (JIS K 7210 (1999)): 0.65 g / 10 min (measurement conditions: 230°C, load 21.18 N) Content of propylene homopolymer block: 39% by mass Content of ethylene-propylene copolymer block: 61% by mass Ethylene unit content in ethylene-propylene copolymer block: 58% by mass Melting temperature: 162°C

[0111] [Component (B)] (B-1): Ethylene-1-octene block copolymer (manufactured by Dow Chemical Company, trade name "Engage® 11677", a block copolymer having blocks of ethylene polymer and blocks of ethylene-1-octene copolymer) Total proportion of OOO, OOE and EOO in the proportion of triad monomer chains ( １３ (C NMR measurement): 8.9% proportion of EEE in the triad monomer chain ( １３ ¹¹¹ NMR measurement): 59.6% Total amount of octenocomonomer ( １３ ¹³C NMR measurement): 18.5 mol% Crystal melting peak temperature: 121°C Heat of crystal melting: 38 J / g Glass transition temperature (DSC method): -67°C MFR (ASTM D1238): 0.5 g / 10 min (Measurement conditions: 190°C, load 21.18 N (2.16 kgf)) (Catalog value) Density (ISO 1183-A method): 0.872 g / cm³ ３ (Measurement temperature: 23℃)

[0112] [Component (B') (for comparative example)] (B'-1): Ethylene-1-octene block copolymer (manufactured by Dow Chemical Company, trade name "Engage® XLT8677", a block copolymer having blocks of ethylene polymer and blocks of ethylene-1-octene copolymer) Total proportion of OOO, OOE and EOO in the proportion of triad monomer chains ( １３ (C NMR measurement): 5.8% proportion of EEE in the triad monomer chain ( １３ ¹¹¹ NMR measurement): 57.9% Total amount of octenocomonomer ( １３ ¹³C NMR measurement): 18.4 mol% Crystal melting peak temperature: 116°C Heat of fusion: 37 J / g Glass transition temperature (DSC method): -67°C MFR (ASTM D1238): 0.5 g / 10 min (Measurement conditions: 190°C, load 21.18 N (2.16 kgf)) (Catalog value) Density (ISO 1183-A method): 0.872 g / cm³ ３ (Measurement temperature: 23℃)

[0113] [Component (C)] (C-1): Ethylene-1-butene random copolymer (manufactured by Mitsui Chemicals, Inc., trade name "Tafmer® A1050S") Crystal melting peak temperature: No peak between 110 and 125°C Heat of crystal melting: 0 J / g MFR (ASTM D1238): 1.2 g / 10 min (measurement conditions: 190°C, load 21.18 N (2.16 kgf)) (catalog value) Density (ISO 1183-A method): 0.862 g / cm³ ３ (Measurement temperature: 23℃)

[0114] [Component (D)] (D-1): Styrene-butadiene-styrene block copolymer (manufactured by LCY, trade name "Globalprene® 3411") Styrene unit content: 30% by mass (catalog value) Conjugated diene unit content: 70% by mass (catalog value) Density: 0.94 g / cm³ ３ 1,2-microstructure of conjugated diene: 30 mol% Weight-average molecular weight (Mw): 240,000

[0115] <Evaluation Method> 1) Measurements were taken in accordance with MFR JIS K 7210 (1999) under conditions of a temperature of 230°C and a load of 21.18 N.

[0116] 2) Low-temperature impact resistance (Izod impact strength) Using an in-line screw-type injection molding machine (manufactured by Sumitomo Electric Industries, Ltd., product name "SE180"), a test piece measuring 4 mm thick x 10 mm wide x 80 mm long was molded to measure the Izod impact strength at an injection pressure of 100 MPa, an injection speed of 27 mm / s, a cylinder setting temperature of 220°C, and a mold temperature of 40°C. Then, a notch was made in the dumbbell (the dimensions and evaluation method of the notch conformed to ISO 180 (2000)), and the measurement was taken at a temperature of -45°C. A higher Izod impact strength value was evaluated as indicating superior low-temperature impact resistance.

[0117] 3) High-temperature strength and room-temperature strength (tensile fracture test) Using an inline screw-type injection molding machine (Sumitomo Electric Industries, Ltd., product name "SE180"), test specimens for tensile testing (sheets with a thickness of 2 mm, a width of 120 mm, and a length of 80 mm) were molded at an injection pressure of 100 MPa, an injection speed of 27 mm / s, a cylinder setting temperature of 220°C, and a mold temperature of 40°C. Then, test specimens for tensile testing were punched out according to JIS K 6251 (1993) (JIS-3 dumbbell). For these punched test specimens, the tensile fracture strength (unit: MPa) was measured at a pulling speed of 500 mm / min and in an atmosphere of 85°C using a Shimadzu Corporation Autograph precision universal testing machine "AG-X" according to JIS K 6251 (1993), in accordance with ISO 37-1A. Furthermore, room-temperature strength was measured using the same method as for high-temperature strength, except that tensile fracture strength was measured in an atmosphere of 23°C. A higher tensile fracture strength value was considered to indicate superior strength.

[0118] 4) Long-term heat resistance (heat resistance test) The test specimens obtained in 2) or 3) above were placed in an oven (manufactured by ESPEC Corporation, product name "Perfect Oven") and left to stand at 110°C for 1000 hours. After that, the test specimens were removed and left to stand in a room temperature environment and used as test specimens for the heat resistance test. A tensile test was performed at a temperature of 23°C in the same manner as the measurement of room temperature strength in 3) above. The higher the retention rate of tensile strength and tensile elongation after the heat resistance test, the better the long-term heat resistance was evaluated.

[0119] 5) Long-term lightfastness (lightfastness test) The test specimen obtained in 2) or 3) above is placed in an ultraviolet carbon arc lightfastness tester (manufactured by Suga Test Instruments Co., Ltd., product name "Fedometer U-48HB" (compliant with JIS K 7102), with a black panel temperature of 83°C ± 3°C and an irradiance of 365 W / m²). ２ The samples were exposed to light at 300-400 nm and 50 ± 5% RH for 500 hours. Tensile tests were conducted at 23°C in the same manner as the room-temperature strength measurement described in 3) above. Samples with higher retention rates of tensile strength and tensile elongation after the lightfastness test were evaluated as having superior long-term lightfastness.

[0120] 6) Using a fogging-resistant inline screw-type injection molding machine (manufactured by Sumitomo Electric Industries, Ltd., product name "SE180"), a sheet measuring 2 mm thick x 120 mm wide x 80 mm long was molded at an injection pressure of 100 MPa, an injection speed of 27 mm / s, a cylinder setting temperature of 220°C, and a mold temperature of 40°C. The fogging test was performed using a fogging tester WSF-2 manufactured by Suga Test Instruments Co., Ltd., referring to ISO 6452 Method A (glass cooling method), with the heating layer temperature set to 100°C and the temperature of the cooling plate placed on top of the glass plate for HAZE value measurement (110 mm x 110 mm x 3 mm, visible light transmittance of 98% or more) set to 20°C, and heated for 16 hours. After the test, the glass plate was left at standard conditions (23°C, 50% RH) for one hour. Then, the diffuse light transmittance (Td.%) and total light transmittance (Tt.%) in the center of the haze area were measured using an NDH8000 (integrating sphere type light transmittance meter) manufactured by Nippon Denshoku Industries, Ltd., and the haze value was calculated using the following formula. A lower haze value was considered to indicate superior resistance to fogging.

[0121] (Calculation formula for haze value) Haze value (%) = H = Td / Tt × 100 [In the formula, Td represents the diffuse light transmittance (%), and Tt represents the total light transmittance (%).]

[0122] [Example 1] 100 parts by mass of component (A-1), 34 parts by mass of component (B-1), and 38 parts by mass of component (C-1), along with other components including 0.1 parts by mass of antioxidant (BASF Japan Ltd., trade name "Irganox® 1010"), 0.1 parts by mass of antioxidant (BASF Japan Ltd., trade name "Irgaphos® 168"), and 0.2 parts by mass of weather stabilizer (BASF Japan Ltd., trade name "Chinubin XT855FF"), were blended in a Henschel mixer for 1 minute. The mixture was then fed into a co-screw extruder (Kobe Steel Ltd., "TEX30α", L / D = 45, number of cylinder blocks = 13) at a speed of 20 kg / h, heated to a temperature of 180 to 210°C, and melt-kneaded to produce pellets of a thermoplastic elastomer composition. The obtained thermoplastic elastomer composition pellets were evaluated according to items 1) to 6) above. The evaluation results are shown in Table 1.

[0123] [Example 2 and Comparative Examples 1-2] Pellets of thermoplastic elastomer composition were obtained in the same manner as in Example 1. The obtained thermoplastic elastomer composition pellets were evaluated according to 1) to 6) above. The evaluation results are shown in Table 1.

[0124]

[0125] [Evaluation Results] As shown in Table 1, in a comparison of the combinations of Example 1 and Comparative Example 1, and Example 2 and Comparative Example 2, in which component (B-1) and component (B'-1) were used as components in the thermoplastic elastomer composition, the thermoplastic elastomer composition containing component (B-1) showed superior changes in tensile fracture elongation at room temperature after heat resistance and light resistance tests, and also superior fogging resistance.

[0126] Although various embodiments have been described above, it goes without saying that the present invention is not limited to these examples. It is clear to those skilled in the art that various modifications or alterations can be conceived within the scope of the claims, and these will naturally also fall within the technical scope of the present invention. Furthermore, the components in the above embodiments may be combined in any way without departing from the spirit of the invention.

[0127] The thermoplastic elastomer composition of the present invention exhibits excellent low-temperature impact resistance and dimensional stability, and can be suitably used in various applications in addition to airbag storage covers. For example, the thermoplastic elastomer composition of the present invention is useful as automotive interior parts such as instrument panels, center panels, center console boxes, door trims, pillars, assist grips, and steering wheels; automotive exterior parts such as mudguards and chromes; home appliance parts; building materials; and furniture. Among these, the thermoplastic elastomer composition of the present invention is particularly useful as an airbag storage cover, and among these airbag storage covers, it is suitable, for example, as an airbag storage cover for an airbag system that activates and inflates to protect occupants when it senses the impact or deformation of a high-speed moving object such as an automobile during a collision.

Claims

1. An airbag storage cover comprising a thermoplastic elastomer composition containing 10 to 300 parts by mass of component (B) per 100 parts by mass of component (A). Component (A): Propylene polymer Component (B): Olefin block copolymer comprising an ethylene polymer block and an ethylene-1-octene copolymer block, and satisfying the following condition (X1) Condition (X1): １３ The proportion of triad monomer chains determined by 13C NMR measurement is 6.0-20.0% in total for OOO, OOE, and EOO (where E represents an ethylene monomer unit and O represents an octene monomer unit).

2. The airbag storage cover according to claim 1, wherein component (B) satisfies the following condition (Y1). Condition (Y1): The crystal melting peak, which is the top temperature of the melting peak, is determined by differential scanning calorimetry (DSC), where the material is melted from 25°C to 200°C at a heating rate of 100°C / min, held at 200°C for 1 minute, crystallized to -90°C at a cooling rate of 1°C / min, held at -90°C for 10 minutes, and then measured at a heating rate of 10°C / min up to 200°C, and is between 110 and 125°C.

3. The airbag storage cover according to claim 1 or 2, wherein component (B) satisfies the following condition (Y2). Condition (Y2): The heat of fusion at the crystal melting peak at 110 to 125°C is 20 to 60 J / g, determined by differential scanning calorimetry (DSC) by melting from 25°C to 200°C at a heating rate of 100°C / min, holding at 200°C for 1 minute, crystallizing at a cooling rate of 1°C / min to -90°C, holding at -90°C for 10 minutes, and then measuring at a heating rate of 10°C / min to 200°C.

4. The airbag storage cover according to claim 1 or 2, wherein component (B) satisfies the following condition (X2): １３ The proportion of EEE in the triad monomer chain, as determined by 13C NMR measurement, is between 58.0% and 80.0%.

5. The airbag storage cover according to claim 1 or 2, wherein component (B) satisfies the following condition (X3): １３ The total amount of octenocomonomers, as determined by 13C NMR measurement, is between 5.0 and 40.0 mol%.

6. The airbag storage cover according to claim 1 or 2, wherein component (A) is a propylene block copolymer obtained by polymerizing a propylene homopolymer in a first step and then polymerizing a propylene-ethylene copolymer in a second step.

7. The airbag storage cover according to claim 1 or 2, wherein the melt flow rate of component (A) (measured at a temperature of 230°C and a measured load of 21.18 N) is 10 to 150 g / 10 min.

8. The airbag storage cover according to claim 1 or 2, wherein the thermoplastic elastomer composition further comprises 10 to 300 parts by mass of the following component (C) per 100 parts by mass of component (A). Component (C): Ethylene α-olefin copolymer, which has a heat of fusion of crystals at 110°C to 125°C of less than 20 J / g, determined by differential scanning calorimetry (DSC) by melting from 25°C to 200°C at a heating rate of 100°C / min, holding at 200°C for 1 minute, crystallizing at a cooling rate of 1°C / min to -90°C, holding at -90°C for 10 minutes, and then measuring at a heating rate of 10°C / min to 200°C.

9. The airbag storage cover according to claim 8, wherein the melt flow rate of component (A) (measured at a temperature of 230°C and a measured load of 21.18 N) is 10 to 100 g / 10 min, and the melt flow rate of component (C) (measured at a temperature of 190°C and a measured load of 21.18 N) is 0.01 to 10 g / 10 min.

10. The airbag storage cover according to claim 1 or 2, wherein the thermoplastic elastomer composition further comprises 1 to 150 parts by mass of the following component (D) per 100 parts by mass of component (A). Component (D): Styrene-conjugated diene block copolymer and / or hydrogenated thereof 11. The airbag storage cover according to claim 10, wherein the thermoplastic elastomer composition contains 30% by mass or more of component (A) relative to the total amount of components (A) to (D).

12. The airbag storage cover according to claim 1 or 2, wherein the thermoplastic elastomer composition has a melt flow rate of 1 to 50 g / 10 min at a measurement temperature of 230°C and a measurement load of 21.18 N, in accordance with JIS K7210 (1999).

13. The thermoplastic elastomer composition has a notched Izod impact strength of 70 kJ / m² at -45°C in accordance with ISO 180 (2000). ２ The airbag storage cover according to claim 1 or 2.

14. The airbag storage cover according to claim 1 or 2, wherein the thermoplastic elastomer composition has a tensile breaking strength of 4.0 MPa or more at 85°C, referring to JIS K 6251 (1993).

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