Airbag storage cover and thermoplastic elastomer composition for airbag storage cover

Abstract

A thermoplastic elastomer composition containing a propylene polymer, an elastomer, and a colorant, and an airbag storage cover comprising a thermoplastic elastomer composition having a total light transmittance of 0.001-70% as measured by the following method. Lt; a total light transmittance determination method gt; the total light transmittance is measured on the basis of JIS K7136-1 with respect to a sheet-like test piece having a thickness of 1 mm and manufactured by injection molding the thermoplastic elastomer composition at a resin temperature of 200 DEG C and a mold temperature of 40 DEG C.

Description

Technical Field

[0001] The present invention relates to an airbag storage cover having moderate light transmittance and light diffusibility, and a thermoplastic elastomer composition for use therein. In addition, the present invention also relates to a molded body and a composite molded body using the thermoplastic elastomer composition for the airbag storage cover. Background Art

[0002] An airbag system for an automobile is a system that protects drivers and passengers during a collision of an automobile or the like, and is composed of a device that senses the impact during a collision and an airbag device. The airbag device is provided in a steering wheel, an instrument panel in front of a passenger seat, seats for a driver and a passenger, a front pillar, and a side pillar.

[0003] Regarding the airbag storage cover in the airbag device, there is a concern that when the airbag expands, fragments may scatter due to the destruction of the cover that houses it, or the cover may scatter due to the destruction of the cover mounting portion. Therefore, various proposals have been made regarding its structure and material in order to prevent the abnormal destruction and scattering of the cover.

[0004] Regarding the airbag storage cover itself, there is a concern that the output of the airbag deployment may increase, resulting in breakage in the low-temperature range and the high-temperature range. Therefore, from the viewpoints of enhancing safety and design freedom, it is desired to develop a thermoplastic elastomer composition as a material that improves low-temperature impact resistance and high-temperature strength.

[0005] As such a thermoplastic elastomer composition for an airbag, a composition using a propylene-based resin as a hard segment and an olefin-based rubber or a styrene-based elastomer such as ethylene / propylene elastomer (EPDM, EPR, etc.) as a soft segment is known (Patent Documents 1 and 2). Prior Art Documents Patent Documents

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2019-38925 Patent Document 2: Japanese Patent Application Laid-Open No. 2020-158615 Summary of the Invention Problems to be Solved by the Invention

[0007] In recent years, the functions of touch screen displays have been incorporated into the designs of some airbag storage covers. Such airbag storage covers are composed of a film surface layer serving as the touch screen display interface and an airbag storage cover layer in contact with the surface layer, and a light-emitting light source such as an LED module is embedded inside the airbag storage cover. In such a structure, in order to facilitate the user to see the light of the light source, the airbag storage cover needs to be made of a material that can transmit light. Therefore, the thermoplastic elastomer composition for the airbag storage cover layer not only needs to have the conventional low-temperature impact resistance and high-temperature strength, but also needs to have a light transmittance that allows the user to see the light of the light source. On the other hand, from a design perspective, it is desirable for the airbag storage cover to have an appropriate light transmittance so that the airbag stored inside the airbag storage cover is not clearly visible.

[0008] According to the detailed research of the present inventors, although the thermoplastic elastomer compositions for airbags described in Patent Documents 1 and 2 have good low-temperature impact resistance and high-temperature strength, they are not for achieving the above-mentioned appropriate light transmittance, so their light transmittance and light diffusion are not fully controlled.

[0009] The subject of the present invention is to provide an airbag storage cover having an appropriate light transmittance and light diffusion when irradiated with light. Means for Solving the Subject

[0010] The present inventors have found that in a thermoplastic elastomer composition containing a propylene-based polymer, an elastomer, and a colorant, by controlling the total light transmittance within a desired range, an airbag storage cover having an appropriate light transmittance and light diffusion can be provided, and the present invention has been completed.

[0011] The gist of the present invention lies in the following [1] to

[31] .

[0012] [1] An airbag storage cover, characterized in that it is composed of a thermoplastic elastomer composition containing a propylene-based polymer, an elastomer, and a colorant, and the total light transmittance (total light transmittance) of the thermoplastic elastomer composition measured by the following method is 0.001% or more and 70% or less. <Method for Measuring Total Light Transmittance> For a 1-mm-thick sheet test piece manufactured by injection molding the thermoplastic elastomer composition under the conditions of a resin temperature of 200 °C and a mold temperature of 40 °C, the total light transmittance is measured based on JIS K7136-1.

[0013] [2] The airbag storage cover according to [1], wherein the thermoplastic elastomer composition has an Izod impact strength at -40 °C based on ISO180 of 50 kJ / m 2 or more.

[0014] [3] The airbag storage cover according to [1] or [2], wherein the propylene-based polymer contains a propylene-based block copolymer.

[0015] [4] The airbag storage cover according to [3], wherein the propylene-based block copolymer is a propylene-based block copolymer having a propylene-based polymer component and an ethylene / propylene copolymer component.

[0016] [5] The airbag storage cover according to any one of [1] to [4], which is disposed at a visually confirmable position.

[0017] [6] The airbag storage cover according to [5], which is disposed on an instrument panel, a steering wheel, or a console panel.

[0018] [7] The airbag storage cover according to any one of [1] to [6], wherein at least one selected from a styrene-based elastomer and an ethylene / α-olefin copolymer is contained as the elastomer.

[0019] [8] The airbag storage cover according to [7], wherein a styrene-based elastomer is contained as the elastomer.

[0020] [9] The airbag storage cover according to [8], wherein the styrene-based elastomer is composed of a hydride (b1) of a styrene / conjugated diene block copolymer having a styrene unit content of 10% by mass or more and 15% by mass or less and a hydride (b2) of a styrene / conjugated diene block copolymer having a styrene unit content of 25% by mass or more and 35% by mass or less.

[0021]

[10] The airbag storage cover according to any one of [7] to [9], wherein the glass transition temperature of the styrene-based elastomer is -65°C or higher and -45°C or lower.

[0022]

[11] The airbag storage cover according to [7], wherein an ethylene / α-olefin copolymer is contained as the elastomer.

[0023]

[12] The airbag storage cover according to any one of [1] to

[11] , wherein the colorant is at least one selected from an organic pigment and an inorganic pigment.

[0024]

[13] The airbag storage cover according to

[12] , wherein 0.01 part by mass or more and 5 parts by mass or less of an organic pigment is contained as the colorant with respect to 100 parts by mass of the total amount of the propylene-based polymer and the elastomer.

[0025]

[14] The airbag storage cover according to

[12] , wherein, based on 100 parts by mass of the total amount of the propylene-based polymer and the elastomer, 0.001 part by mass or more and 0.5 part by mass or less of an inorganic pigment is contained as the colorant.

[0026]

[15] The airbag storage cover according to

[12] , wherein, based on 100 parts by mass of the total amount of the propylene-based polymer and the elastomer, 0.001 part by mass or more and 3 parts by mass or less of an organic pigment and an inorganic pigment in total are contained as the colorant.

[0027]

[16] The airbag storage cover according to any one of [1] to

[15] , wherein the melt flow rate of the thermoplastic elastomer composition at a temperature of 230 °C and a measurement load of 21.18 N is 1.0 g / 10 minutes or more and 50 g / 10 minutes or less based on JIS K7210 (1999).

[0028]

[17] The airbag storage cover according to any one of [1] to

[16] , wherein, in the thermoplastic elastomer composition, the content of the elastomer is 45 parts by mass or more and 250 parts by mass or less relative to 100 parts by mass of the propylene-based polymer.

[0029]

[18] The airbag storage cover according to any one of [1] to

[17] , wherein the total light transmittance is 0.001% or more and 20% or less.

[0030]

[19] A thermoplastic elastomer composition for an airbag storage cover, characterized in that it is a thermoplastic elastomer composition for an airbag storage cover containing a propylene-based polymer, an elastomer, and a colorant, the elastomer is at least one selected from styrene-based elastomers and ethylene / α-olefin copolymers, the colorant is at least one selected from organic pigments and inorganic pigments, the total light transmittance of the thermoplastic elastomer composition measured by the following method is 0.001% or more and 70% or less. <Method for measuring total light transmittance> For a 1-mm-thick sheet test piece manufactured by injection molding the thermoplastic elastomer composition under the conditions of a resin temperature of 200 °C and a mold temperature of 40 °C, the total light transmittance is measured based on JIS K7136-1.

[0031]

[20] The thermoplastic elastomer composition for an airbag storage cover according to

[19] , wherein, based on 100 parts by mass of the total amount of the propylene-based polymer and the elastomer, 0.01 part by mass or more and 5 parts by mass or less of an organic pigment is contained as the colorant.

[0032]

[21] The thermoplastic elastomer composition for an airbag storage lid according to

[19] , wherein, based on 100 parts by mass of the total amount of the propylene-based polymer and the elastomer, 0.001 part by mass or more and 0.5 part by mass or less of an inorganic pigment is contained as the colorant.

[0033]

[22] The thermoplastic elastomer composition for an airbag storage lid according to

[19] , wherein, based on 100 parts by mass of the total amount of the propylene-based polymer and the elastomer, a total of 0.001 part by mass or more and 3 parts by mass or less of an organic pigment and an inorganic pigment are contained as the colorant.

[0034]

[23] The thermoplastic elastomer composition for an airbag storage lid according to any one of

[19] to

[22] , wherein a styrene-based elastomer is contained as the elastomer.

[0035]

[24] The thermoplastic elastomer composition for an airbag storage lid according to

[23] , wherein the styrene-based elastomer is composed of a hydride (b1) of a styrene / conjugated diene block copolymer having a styrene unit content of 10% by mass or more and 15% by mass or less and a hydride (b2) of a styrene / conjugated diene block copolymer having a styrene unit content of 25% by mass or more and 35% by mass or less.

[0036]

[25] The thermoplastic elastomer composition for an airbag storage lid according to

[23] or

[24] , wherein the glass transition temperature of the styrene-based elastomer is -65°C or higher and -45°C or lower.

[0037]

[26] The thermoplastic elastomer composition for an airbag storage lid according to any one of

[19] to

[25] , wherein a propylene-based block copolymer is contained as the propylene-based polymer.

[0038]

[27] The thermoplastic elastomer composition for an airbag storage lid according to

[26] , wherein the propylene-based block copolymer is a propylene-based block copolymer having a propylene-based polymer component and an ethylene / propylene copolymer component.

[0039]

[28] The thermoplastic elastomer composition for an airbag storage lid according to any one of

[19] to

[22] ,

[26] and

[27] , wherein an ethylene / α-olefin copolymer is contained as the elastomer.

[0040]

[29] A molded article, characterized in that it is composed of the thermoplastic elastomer composition for an airbag storage lid according to any one of

[19] to

[28] .

[0041]

[30] A composite molded body, characterized by having a first layer containing the thermoplastic elastomer composition for an airbag storage lid described in any one of

[19] to

[28] and a second layer made of a resin film.

[0042]

[31] The composite molded body according to

[30] , which is an airbag storage lid. Advantages of the Invention

[0043] According to the present invention, an airbag storage lid having appropriate light transmittance and light diffusibility when irradiated with light can be provided.

[0044] The airbag storage lid of the present invention can preferably be used for any one of an airbag storage lid for a driver's seat, an airbag storage lid for a front passenger seat, an airbag storage lid for a pedestrian, a knee airbag storage lid, a side airbag storage lid, a curtain airbag storage lid, etc.

[0045] In particular, since the airbag storage lid of the present invention has appropriate light transmittance and light diffusibility and is appropriately compounded with a film for a touch screen, it is also suitable for an airbag storage lid integrated with a touch screen type display. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 Figure 1 is a schematic view showing an example of an airbag storage lid, Figure 1 (a) is a front view, Figure 1 (b) is a rear view. Figure 2 Figure 2 is a schematic view showing the direction of light transmission from a light source to the airbag storage lid, and is a view magnifying and showing a cross section along the Figure 1 II-II line of (a). REFERENCE SIGNS LIST 1: Airbag storage lid 2: Light source (LED module) DETAILED DESCRIPTION OF THE INVENTION

[0047] The present invention will be described in detail below. The present invention is not limited to the following description and can be implemented with arbitrary modifications within the scope not departing from the gist of the present invention.

[0048] [Thermoplastic Elastomer Composition] First, the thermoplastic elastomer composition related to the present invention will be described.

[0049] The thermoplastic elastomer composition (hereinafter, sometimes referred to as "the thermoplastic elastomer composition of the present invention.") constituting the airbag storage lid of the present invention is a thermoplastic elastomer composition containing a propylene-based polymer, an elastomer, and a colorant, and is a composition having a total light transmittance of 0.001% or more and 70% or less as measured by the following method. ​​​​<Method for measuring total light transmittance> For a 1 mm thick sheet test piece manufactured by injection molding the thermoplastic elastomer composition under the conditions of a resin temperature of 200 °C and a mold temperature of 40 °C, the total light transmittance is measured based on JIS K7136-1.

[0050] <Mechanism> The thermoplastic elastomer composition constituting the airbag storage lid of the present invention has appropriate light transmittance when irradiated with light. In addition, it also has an effect suitable for compounding with a film for a touch screen. Although the details of the reason why the thermoplastic elastomer composition of the present invention exhibits such an effect are not determined, the reasons for exhibiting such an effect can be speculated as follows.

[0051] The propylene-based polymer and the elastomer affect the light transmittance of the airbag storage lid while controlling various properties such as moldability, low-temperature impact resistance, and high-temperature strength required for the airbag storage lid. The propylene-based polymer has a tendency to reduce the light transmittance, and the elastomer has a tendency to increase the light transmittance. Here, in addition to the propylene-based copolymer and the elastomer, by further blending a colorant having a light transmittance-reducing effect in a well-balanced manner, it is possible to control the light transmittance of the thermoplastic elastomer composition and further the airbag storage lid while having various properties such as moldability, low-temperature impact resistance, and high-temperature strength required for the airbag storage lid.

[0052] The thermoplastic elastomer composition of the present invention constituting the airbag storage lid in the preferred embodiment has excellent light diffusibility when irradiated with light. Therefore, the light from the light source diffuses and does not transmit linearly, and glare can be suppressed in terms of visual confirmation. In addition, since the shape of the light source cannot be visually recognized, the designability is also excellent. Thus, the airbag storage lid of the present invention also has an effect suitable for compounding with a film for a touch screen.

[0053] <Propylene-based polymer> The propylene-based polymer used in the thermoplastic elastomer composition of the present invention is a polymer having a propylene unit as a main component among all monomers of the propylene-based polymer. The lower limit of the propylene unit content rate of the propylene-based polymer is usually 50% by mass or more, and from the viewpoints of heat resistance and rigidity, it is preferably 85% by mass or more, and more preferably 90% by mass or more. On the other hand, the upper limit of the propylene unit content rate of the propylene-based polymer is not particularly limited, and from the viewpoint of low-temperature impact resistance, it is preferably 98% by mass or less, and more preferably 97% by mass or less. The propylene unit content rate in the propylene-based polymer can be determined by infrared spectroscopy. The propylene-based polymer is distinguished from the following ethylene / α-olefin copolymer as an elastomer by having a propylene unit as a main component.

[0054] The propylene-based polymer can be either a propylene homopolymer or a propylene copolymer. In the propylene copolymer, in addition to propylene units, it preferably contains 15% by mass or less, more preferably 10% by mass or less of ethylene units, α-olefin units other than propylene, monomer units other than ethylene and α-olefins, etc.

[0055] The propylene copolymer can be a propylene random copolymer or a propylene block copolymer.

[0056] In the present invention, from the viewpoint of light transmittance, a propylene random copolymer is preferably used as the propylene copolymer.

[0057] Examples of the α-olefin as the α-olefin unit other than propylene contained in the propylene random copolymer include α-olefins having 4 or more and 20 or less carbon atoms. Examples of the α-olefin having 4 or more and 20 or less 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, 2,2,4-trimethyl-1-pentene, etc. α-olefins having 4 or more and 10 or less carbon atoms are preferred, and 1-butene, 1-hexene, and 1-octene are more preferred. In the propylene random copolymer, it may contain only one of these α-olefin units and ethylene units, or may contain two or more.

[0058] Specific examples of the propylene random copolymer include 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, propylene / ethylene / 1-octene copolymer. Among these, a copolymer of at least one monomer selected from ethylene and α-olefins having 4 or more and 10 or less carbon atoms and propylene is preferred.

[0059] As a method for producing the propylene random copolymer, a known polymerization method using a known olefin polymerization catalyst can be used. For example, a multi-stage polymerization method using a Ziegler-Natta type catalyst can be cited. In this multi-stage polymerization method, a slurry polymerization method, a solution polymerization method, a bulk polymerization method, a gas phase polymerization method, etc. can be used, and two or more of these can also be combined.

[0060] In the present invention, from the viewpoint of light diffusion, a propylene block copolymer is preferably used as the propylene copolymer.

[0061] The propylene-based block copolymer is preferably a copolymer having a propylene-based polymer component and an ethylene / propylene copolymer component. In the propylene-based block copolymer having a propylene-based polymer component and an ethylene / propylene copolymer component, from the viewpoints of mechanical properties and rigidity, the content ratio of the propylene-based polymer component is preferably 30% by mass or more, more preferably 35% by mass or more, and further preferably 40% by mass or more, relative to the total amount of the propylene-based polymer component and the ethylene / propylene copolymer component. On the other hand, from the viewpoint of impact resistance, the content ratio of the propylene-based polymer component is preferably 99% by mass or less, more preferably 97% by mass or less, and further preferably 95% by mass or less, relative to the total amount of the propylene-based polymer component and the ethylene / propylene copolymer component.

[0062] In the propylene-based block copolymer having the above-mentioned propylene-based polymer component and ethylene / propylene copolymer component, from the viewpoints of mechanical properties and rigidity, the content ratio of propylene units in the propylene-based polymer component is preferably 90% by mass or more, more preferably 95% by mass or more, further preferably 97% by mass or more, and particularly preferably 100%. From the viewpoint of light diffusion, the content ratio of ethylene units in the ethylene / propylene copolymer component constituting the propylene-based block copolymer is preferably 31% by mass or more, more preferably 35% by mass or more, and further preferably 40% by mass or more. On the other hand, from the viewpoint of impact resistance, the content ratio of ethylene units in the ethylene / propylene copolymer component is preferably 70% by mass or less, more preferably 65% by mass or less, and further preferably 60% by mass or less. As the propylene-based block copolymer having a propylene-based polymer component and an ethylene / propylene copolymer component, for example, a propylene-based block copolymer obtained by polymerizing a propylene homopolymer in the first step and then polymerizing a propylene / ethylene copolymer in the second step can be exemplified.

[0063] The crystal melting peak temperature of the propylene-based block copolymer is desirably 155°C or higher and less than 175°C. Among the propylene-based block copolymers having a crystal melting peak temperature within the above range, since the crystal component is sufficiently present, good heat resistance, mechanical properties, and light diffusion properties can be imparted. Regarding the effect on light diffusion properties, since there is a difference in refractive index between the crystal part and the amorphous part contained in the propylene-based block copolymer, generally, the more the crystal part, the more light diffusion occurs inside the propylene-based block copolymer, and thus the light diffusion property tends to increase. From this viewpoint, the melting peak of the propylene-based block copolymer is preferably 160°C or higher. On the other hand, the upper limit of the melting peak of the propylene-based block copolymer is not particularly limited and is usually 170°C or lower. The propylene-based block copolymer satisfying such a crystal melting peak temperature may also contain a filler such as talc or a known nucleating agent as needed.

[0064] The crystallization melting peak temperature of the propylene-based block copolymer can be measured by the following method based on JIS K7121. That is, using a differential scanning calorimeter (DSC6220 manufactured by SII / Nanotechnology), the following steps (1) to (3) are sequentially carried out to measure the melting behavior of the propylene-based block copolymer. In each step, a graph is plotted with time as the horizontal axis and heat of fusion as the vertical axis to obtain a melting curve, and the peak top observed in step (3) is taken as the crystallization melting peak temperature. Step (1): Starting from room temperature, heat 5 mg of the sample from 40 °C to 200 °C at a rate of 100 °C / minute. After the heating is completed, hold for 3 minutes. Step (2): Cool from 200 °C to 40 °C at a rate of 10 °C / minute. After the cooling is completed, store for 3 minutes. Step (3): Heat from 40 °C to 200 °C at a rate of 10 °C / minute.

[0065] As a method for producing the propylene-based block polymer, a known polymerization method using a known olefin polymerization catalyst can be used. For example, a multi-stage polymerization method using a Ziegler-Natta catalyst can be cited. In this multi-stage polymerization method, a slurry polymerization method, a solution polymerization method, a bulk polymerization method, a gas phase polymerization method, etc. can be used, and two or more of these can also be combined.

[0066] In addition, as a method for producing the propylene homopolymer, a known slurry polymerization method, solution polymerization method, bulk polymerization method or gas phase polymerization method using a known Ziegler-Natta catalyst or a known complex catalyst such as a metallocene complex and a non-metallocene complex can be exemplified.

[0067] The melt flow rate (MFR) of the propylene-based polymer of the present invention is not limited, and is usually 0.1 g / minute or more. From the viewpoint of the appearance of the molded article, it is preferably 10 g / 10 minutes or more, more preferably 20 g / 10 minutes or more, further preferably 25 g / 10 minutes or more, and usually 200 g / 10 minutes or less. From the viewpoint of tensile strength, it is preferably 150 g / 10 minutes or less, more preferably 100 g / 10 minutes or less. The melt flow rate of the propylene-based polymer is measured under the conditions of a measurement temperature of 230 °C and a measurement load of 21.18 N based on JIS K7210 (1999).

[0068] The propylene-based polymer used in the thermoplastic elastomer composition of the present invention can also use commercially available corresponding products. As the propylene-based polymer, it can be purchased from the manufacturers listed below and appropriately selected. As commercially available products, for example, there are Prim Polypro (registered trademark) of Prime Polymer Co., Ltd., Sumitomo NOBLEN (registered trademark) of Sumitomo Chemical Co., Ltd., acrylic polymers of Sunallomer Co., NOVATEC (registered trademark) PP or WINTEC (registered trademark) of Nippon Polypro Co., Moplen (registered trademark) or Adflex (registered trademark) of Lyondell Basell Co., ExxonMobil PP of ExxonMobil Co., Formolene (registered trademark) of Formosa Plastics Co., Borealis PP of Borealis Co., SEETEC PP of LG Chemical Co., ASIPOLYPROPYLENE of A. Schulman Co., INEOSPP of INEOS Olefins & Polymers Co., Braskem PP of Braskem Co., Hanwha Total Petrochemical Random PP of Hanwha Total Co., Sabic (registered trademark) PP of Sabic Co., TOTALPETROCHEMICALS Polypropylene of TOTAL PETROCHEMICALS Co., and YUPLENE (registered trademark) of SK Co.

[0069] The thermoplastic elastomer composition of the present invention may contain only one type of acrylic polymer, or may contain two or more substances having different monomer compositions, physical properties, etc.

[0070] <Elastomer> As the elastomer, a known elastomer can be used. From the viewpoints of low-temperature impact resistance and high-temperature strength, as the elastomer, it is preferably to contain at least one selected from styrene-based elastomers and ethylene / α-olefin copolymers, and more preferably to contain styrene-based elastomers.

[0071] <Styrene-based elastomer> The styrene-based elastomer used in the thermoplastic elastomer composition of the present invention preferably has a glass transition temperature in the range of -65°C or higher and -45°C or lower. When the styrene-based elastomer has two or more glass transition temperatures, at least one glass transition temperature needs to be in the range of -65°C or higher and -45°C or lower. As long as it is a styrene-based elastomer having a glass transition temperature in the range of -65°C or higher and -45°C or lower, by combining with an acrylic polymer, a thermoplastic elastomer composition with moderate light transmittance, excellent low-temperature impact resistance, and high-temperature strength can be obtained. From the viewpoint of low-temperature impact resistance, the glass transition temperature of the styrene-based elastomer more preferably exists in the range of above -65°C and below -50°C. The glass transition temperature of the styrene-based elastomer is measured by the DSC method.

[0072] When using two or more styrene-based elastomers, the glass transition temperature of each styrene-based elastomer may be within or outside the above-mentioned range of the glass transition temperature. As the styrene-based elastomer, at least one glass transition temperature preferably exists in the range of above -65°C and below -45°C, and more preferably in the range of above -65°C and below -50°C.

[0073] In the present invention, as the styrene-based elastomer, specifically, a hydride of a styrene / conjugated diene block copolymer can be used.

[0074] From the viewpoints of low-temperature impact resistance, high-temperature strength, and light transmittance, the styrene-based elastomer used in the present invention preferably has a styrene unit content of 20% by mass or more and 35% by mass or less. From the viewpoints of strength and heat resistance, the styrene unit content of the styrene-based elastomer is more preferably 21% by mass or more. From the viewpoints of flexibility and impact resistance, the styrene unit content of the styrene-based elastomer is more preferably 30% by mass or less, further preferably 28% by mass or less, and particularly preferably 25% by mass or less. Here, the styrene unit content refers to the content of styrene units derived from the raw material styrene and introduced into the hydride of the styrene / conjugated diene block copolymer. The styrene unit content of the styrene-based elastomer can be measured by proton NMR using a nuclear magnetic resonance apparatus and calculated by quantifying the styrene characteristic groups.

[0075] When using two or more styrene-based elastomers, the styrene unit content can also be calculated proportionally based on the styrene unit content of each styrene-based elastomer and the compounding mass ratio of each styrene-based elastomer. In this case, the styrene unit content of each styrene-based elastomer may be within or outside the above-mentioned preferred range of the styrene unit content. It is only necessary that the styrene unit content of the total amount of the styrene-based elastomer calculated proportionally is within the above-mentioned preferred range of the styrene unit content.

[0076] For example, as a styrenic elastomer, by combining a hydrogenated product (b1) of a styrene / conjugated diene block copolymer having a styrene unit content of 10% by mass or more and 15% by mass or less and a hydrogenated product (b2) of a styrene / conjugated diene block copolymer having a styrene unit content of 25% by mass or more and 35% by mass or less in an amount such that the styrene unit content is 20% by mass or more and 35% by mass or less, particularly 20% by mass or more and 25% by mass or less, it is easy to balance high-temperature strength, low-temperature impact resistance, and light transmittance. The hydrogenated product (b1) of the styrene / conjugated diene block copolymer and the hydrogenated product (b2) of the styrene / conjugated diene block copolymer are each preferably a hydrogenated product of a styrene / conjugated diene / styrene block copolymer.

[0077] Preferred conjugated dienes in the hydrogenated product of the styrene / conjugated diene block copolymer as the styrenic elastomer are butadiene, isoprene, or a mixture thereof. Examples of the hydrogenated product of the styrene / conjugated diene block copolymer include a hydrogenated product of a styrene / butadiene block copolymer (hereinafter, sometimes simply referred to as "SEBS" alone).

[0078] As a styrenic elastomer, by using a hydrogenated product of a styrene / conjugated diene block copolymer, compared with a polymer having a double bond in its molecular structure such as a styrene / butadiene / styrene block copolymer (SBS), light resistance can be well maintained in a thermoplastic elastomer composition having moderate transmittance to visible light and ultraviolet light. In addition, in the aforementioned propylene-based polymer, by combining and using a hydrogenated product of a styrene / conjugated diene block copolymer having a styrene unit content of 20% by mass or more and 35% by mass or less, particularly 20% by mass or more and 25% by mass or less and having a glass transition temperature in the range of -65°C or higher and -45°C or lower, a thermoplastic elastomer composition excellent in low-temperature impact resistance and high-temperature strength and having moderate light transmittance can be obtained.

[0079] The styrenic elastomer used in the present invention is preferably a linear styrenic elastomer. As long as it is a linear styrenic elastomer, it is easily dispersed in the propylene-based polymer and the light transmittance is easily adjusted. Here, the linear styrenic elastomer means, for example, a hydrogenated product of a copolymer in which the conjugated diene portion of a styrene / conjugated diene block copolymer is butadiene, isoprene, or a mixture thereof. Specifically, a styrene / ethylene / butene / styrene copolymer as a hydrogenated product of a styrene / butadiene block copolymer can be cited.

[0080] In the hydrogenated product of a styrene / conjugated diene block copolymer as a styrene-based elastomer, the 1,2-microstructure analyzed by NMR method is preferably 60 mol% or less, more preferably 45 mol% or less. From the viewpoints of moldability and flexibility, a substance having a 1,2-microstructure of 60 mol% or less is preferred. In addition, from the viewpoint of weather resistance, the hydrogenation rate of the hydrogenated product of a styrene / conjugated diene block copolymer as a styrene-based elastomer is preferably 90 mol% or more, more preferably 95 mol% or more.

[0081] From the viewpoint of mold release property, the weight-average molecular weight (Mw) of the styrene-based elastomer is preferably 40,000 or more, more preferably 45,000 or more, and further preferably 48,000 or more. From the viewpoint of low-temperature impact resistance, the weight-average molecular weight (Mw) of the styrene-based elastomer is preferably 400,000 or less, more preferably 300,000 or less, and further preferably 250,000 or less.

[0082] The weight-average molecular weight (Mw) of the styrene-based elastomer is a value measured by gel permeation chromatography (GPC method). For example, it can be measured under the following conditions. Machine: "HLC-8220GPC(R)" manufactured by Tosoh Corporation Column: "TSKgel Super HM-M (6.0 mm I.D × 15 cm × 2 + G)" manufactured by Tosoh Corporation 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 conversion Calibration curve approximation formula: Cubic equation (hyperbola): Set the exclusion limit time to 12 minutes

[0083] When using two or more kinds of styrene-based elastomers, the weight-average molecular weight of the styrene-based elastomer can be obtained by measuring a mixture of the respective components of the styrene-based elastomer by the above GPC method. In this case, the weight-average molecular weight of each styrene-based elastomer can be within or outside the preferred range of the weight-average molecular weight of the styrene-based elastomer described above, as long as the mixture of the styrene-based elastomers is within the preferred range of the weight-average molecular weight of the styrene-based elastomer described above.

[0084] As a method for producing a styrenic elastomer, for example, a method described in Japanese Patent Publication No. 40-23798 can be cited. A styrene / conjugated diene block copolymer is synthesized using a lithium catalyst in an inert solvent, and then, for example, a method described in Japanese Patent Publication No. 42-8704, Japanese Patent Publication No. 43-6636, Japanese Patent Laid-Open No. 59-133203, or Japanese Patent Laid-Open No. 60-79005 is used to hydrogenate it in an inert solvent in the presence of a hydrogenation catalyst.

[0085] Styrenic elastomers can also be obtained as commercial products. Examples of commercial styrenic elastomers include "Kraton (registered trademark) G" manufactured by Kraton Polymers, "SEPTON (registered trademark)" manufactured by Kuraray Co., Ltd., and "TUFTEC (registered trademark)" manufactured by Asahi Kasei Corporation.

[0086] The thermoplastic elastomer composition of the present invention may contain only one type of styrenic elastomer, or may contain two or more substances having different monomer compositions, physical properties, etc.

[0087] <Ethylene / α-olefin copolymer> From the viewpoint of light diffusibility, as the elastomer of the thermoplastic elastomer composition of the present invention, an ethylene / α-olefin copolymer such as an ethylene / α-olefin random copolymer or an ethylene / α-olefin block copolymer is preferably used.

[0088] In the ethylene / α-olefin copolymer, as the α-olefin unit, substances having propylene, 1-butene, 2-methylpropene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, or 1-octene as the constituent units can be exemplified. As the α-olefin, an α-olefin having 4 or more and 8 or less carbon atoms with a carbon-carbon double bond at the terminal carbon atom, such as propylene, 1-butene, 1-hexene, or 1-octene, is preferred. The ethylene / α-olefin copolymer may be a substance obtained by copolymerizing only one type of α-olefin with ethylene, or may be a substance obtained by copolymerizing two or more types of α-olefins with ethylene.

[0089] In order to prevent welding caused by the blocking of the ethylene / α-olefin copolymer, it is preferred that the ethylene unit content in the ethylene / α-olefin copolymer is relatively high. From the perspective of low-temperature impact resistance when forming the thermoplastic elastomer composition of the present invention, it is preferred that the ethylene unit content in the ethylene / α-olefin copolymer is relatively low. Specifically, the lower limit of the ethylene unit content in the ethylene / α-olefin copolymer relative to the total 100% by mass of the ethylene unit and the α-olefin unit is usually 50% by mass or more, preferably 55% by mass or more, more preferably 60% by mass or more, and further preferably 65% by mass or more. On the other hand, the upper limit of the ethylene unit content in the ethylene / α-olefin copolymer is usually 99% by mass or less, preferably 80% by mass or less.

[0090] The content of the ethylene unit, the content of the α-olefin unit, and the content of the non-conjugated diene unit described below in the ethylene / α-olefin copolymer can be determined by infrared spectroscopy, respectively.

[0091] In addition to the ethylene unit and the α-olefin unit, the ethylene / α-olefin copolymer may also have other monomer 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. Among these non-conjugated dienes, 5-ethylidene-2-norbornene and dicyclopentadiene are preferred.

[0092] When the ethylene / α-olefin copolymer has other monomer units such as non-conjugated diene units, its content relative to the total 100% by mass of the ethylene / α-olefin copolymer is usually 10% by mass or less, preferably 5% by mass or less.

[0093] The melt flow rate (MFR) of the ethylene / α-olefin copolymer is not limited and is usually 10 g / 10 min or less. From the perspective of strength, it is preferably 8.0 g / 10 min or less, more preferably 5.0 g / 10 min or less, and further preferably 3.0 g / 10 min or less. In addition, the melt flow rate of the ethylene / α-olefin copolymer is usually 0.01 g / 10 min or more. From the perspective of fluidity, it is preferably 0.05 g / 10 min or more, more preferably 0.10 g / 10 min or more. The melt flow rate of the ethylene / α-olefin copolymer is measured according to ASTM D1238 under the conditions of a measurement temperature of 190 °C and a measurement load of 21.18 N.

[0094] From the viewpoint of low-temperature impact resistance, the density of the ethylene / α-olefin copolymer is preferably 0.88 g / cm 3 or less. On the other hand, from the viewpoint of transparency, that is, refractive index, the density of the ethylene / α-olefin copolymer is preferably 0.86 g / cm 3 or more. The density of the ethylene / α-olefin copolymer can be measured by the ISO 1183-A method (measurement temperature: 23 °C).

[0095] The ethylene / α-olefin copolymer can be obtained as a commercial product. Examples of commercial products that meet the ethylene / α-olefin copolymer include "Engage (registered trademark)" and "INFUSE (registered trademark)" manufactured by Dow Chemical Company, "Solumer (registered trademark)" manufactured by SK Corporation, "LUCENE (registered trademark)" manufactured by LG Chem, "TAFMER (registered trademark)" and "Mitsui EPT" manufactured by Mitsui Chemicals, "DYNARON (registered trademark)" manufactured by ENEOS MATERIAL, "KEP-070P" manufactured by KmuhoPolychem, "Vistamaxx (registered trademark)" manufactured by ExxonMobil Chemical, etc.

[0096] The thermoplastic elastomer composition of the present invention may contain only one kind of ethylene / α-olefin copolymer, or may contain two or more substances having different monomer compositions, physical properties, etc.

[0097] <Preferred combination of propylene-based polymer and elastomer> From the viewpoint of light diffusion properties, in the preferred combination of the propylene-based polymer and the elastomer, the propylene-based polymer is a propylene-based block copolymer, and the elastomer is an ethylene / α-olefin copolymer. More preferably, it is a combination of a propylene-based block copolymer having a propylene content of 90% by mass or more and 100% by mass or less and an ethylene / propylene copolymer block having an ethylene content of 31% by mass or more and 70% by mass or less, and an ethylene / α-olefin copolymer.

[0098] <Colorant> The thermoplastic elastomer composition of the present invention contains a colorant. By containing the colorant, in the obtained airbag storage cover, compared with when the colorant is not contained, by making the transmitted white light more prominent, it has the effect of being easily recognizable by the human eye.

[0099] The colorant can be any one of organic pigments and inorganic pigments. Since the colorant has light-shielding properties, the light transmittance can be adjusted by the addition amount of the colorant. Generally, inorganic pigments have stronger light-shielding properties, while organic pigments have weaker light-shielding properties. Known substances can be used for organic pigments and inorganic pigments.

[0100] Examples of organic pigments include phthalocyanine green, phthalocyanine blue, disazo yellow, disazo pyrazolone orange, benzimidazolone, naphthol red, quinacridone red, quinacridone magenta, dioxazine violet, etc. Examples of inorganic pigments include carbon black, lampblack, titanium oxide, iron oxide yellow, iron oxide red, ultramarine, etc.

[0101] These can be used alone or in combination of two or more. That is, only one kind of organic pigment can be used, or two or more kinds can be used. In addition, only one kind of inorganic pigment can be used, or two or more kinds can be used. Further, one kind or two or more kinds of organic pigments can be mixed with one kind or two or more kinds of inorganic pigments.

[0102] <Nucleating agent for crystallization> The thermoplastic elastomer composition of the present invention may also contain a nucleating agent for crystallization. As the nucleating agent for crystallization, a diacetal-based nucleating agent is preferably used. By mixing the diacetal-based nucleating agent, the crystallization of the above-mentioned propylene-based polymer is promoted, and an improvement in light transmittance can be expected.

[0103] As the diacetal-based nucleating agent, known substances can be used. Commercially available products of the diacetal-based nucleating agent include GEL ALL (registered trademark) D, GEL ALL (registered trademark) MD, GEL ALL (registered trademark) DXR of Shin Nippon Rika Co., Ltd., Millad (registered trademark) 3988, Millad (registered trademark) NX8000, Millad (registered trademark) NX8000J, Millad (registered trademark) NX8000K, Millad (registered trademark) NX8000ECO of Milliken Japan Co., Ltd. (USA), SIPAX NA-2 of GCH TECHNOLOGY Co., Ltd. (China), etc. These can be used alone or in combination of two or more.

[0104] <Blending ratio> From the viewpoint of low-temperature impact resistance, in the thermoplastic elastomer composition, the lower limit of the elastomer content is preferably 45 parts by mass or more, more preferably 60 parts by mass or more, and still more preferably 80 parts by mass or more, based on 100 parts by mass of the propylene-based polymer. On the other hand, from the viewpoint of high-temperature strength, in the thermoplastic elastomer composition, the upper limit of the elastomer content is preferably 250 parts by mass or less, more preferably 220 parts by mass or less, and still more preferably 200 parts by mass or less, based on 100 parts by mass of the propylene-based polymer.

[0105] When a styrene-based elastomer is contained as the elastomer, from the viewpoint of low-temperature impact resistance, the lower limit of the styrene-based elastomer content is preferably 45 parts by mass or more, more preferably 60 parts by mass or more, and still more preferably 80 parts by mass or more, based on 100 parts by mass of the propylene-based polymer. On the other hand, from the viewpoint of high-temperature strength, the upper limit of the styrene-based elastomer content is preferably 250 parts by mass or less, more preferably 220 parts by mass or less, and still more preferably 200 parts by mass or less, based on 100 parts by mass of the propylene-based polymer.

[0106] When an ethylene / α-olefin copolymer is contained as the elastomer, from the viewpoint of low-temperature impact resistance, the lower limit of the ethylene / α-olefin copolymer content is preferably 45 parts by mass or more, more preferably 60 parts by mass or more, and still more preferably 80 parts by mass or more, based on 100 parts by mass of the propylene-based polymer. On the other hand, from the viewpoint of high-temperature strength, the upper limit of the ethylene / α-olefin copolymer content is preferably 250 parts by mass or less, more preferably 220 parts by mass or less, and still more preferably 200 parts by mass or less, based on 100 parts by mass of the propylene-based polymer.

[0107] When a styrene-based elastomer and an ethylene / α-olefin copolymer are used in combination as the elastomer, the lower limit of the styrene-based elastomer content ratio is preferably 10% by mass or more, more preferably 20% by mass or more, and still more preferably 30% by mass or more, based on the total amount of the styrene-based elastomer and the ethylene / α-olefin copolymer. On the other hand, the upper limit of the styrene-based elastomer content ratio is preferably 90% by mass or less, more preferably 85% by mass or less, and still more preferably 80% by mass or less, based on the total amount of the styrene-based elastomer and the ethylene / α-olefin copolymer.

[0108] Regarding the content of the colorant in the thermoplastic elastomer composition of the present invention, when an organic pigment, an inorganic pigment, or a mixture of an organic pigment and an inorganic pigment is used as the colorant, the compounding can be carried out as described below, respectively.

[0109] When the colorant is an organic pigment, from the viewpoint of moderate hiding power, it is preferably 0.01 part by mass or more, more preferably 0.1 part by mass or more, and still more preferably 0.2 part by mass or more with respect to 100 parts by mass in total of the acrylic polymer and the elastomer. There is no regulation on the upper limit of the content of the organic pigment, and it is usually 5 parts by mass or less.

[0110] When the colorant is an inorganic pigment, it is preferably 0.001 part by mass or more, more preferably 0.01 part by mass or more, and still more preferably 0.03 part by mass or more with respect to 100 parts by mass in total of the acrylic polymer and the elastomer. On the other hand, the content of the inorganic pigment is preferably 0.5 part by mass or less, more preferably 0.3 part by mass or less, and still more preferably 0.15 part by mass or less.

[0111] When the colorant contains both an organic pigment and an inorganic pigment, the total amount of the organic pigment and the inorganic pigment is preferably 0.001 part by mass or more, more preferably 0.01 part by mass or more, and still more preferably 0.03 part by mass or more with respect to 100 parts by mass in total of the acrylic polymer and the elastomer. On the other hand, the total content of the organic pigment and the inorganic pigment is preferably 3 parts by mass or less, more preferably 1 part by mass or less, and still more preferably 0.5 part by mass or less. In addition, when an organic pigment and an inorganic pigment are used in combination, from the viewpoint of moderate hiding power, 10 to 5000 parts by mass, particularly 30 to 3000 parts by mass of the organic pigment is preferably used with respect to 100 parts by mass of the inorganic pigment.

[0112] By making the thermoplastic elastomer composition of the present invention contain an acrylic polymer, an elastomer, and a colorant, on the basis of having the characteristics required for the airbag storage lid, from the viewpoint of the thermoplastic elastomer composition and further effectively obtaining the desired translucency of the airbag storage lid, the total content ratio of the acrylic polymer, the elastomer, and the colorant in the whole thermoplastic elastomer composition of the present invention is preferably 80% by mass or more, more preferably 85% by mass or more, and still more preferably 90% by mass or more.

[0113] When the thermoplastic elastomer composition of the present invention contains a crystal nucleating agent, preferably a diacetal-based crystal nucleating agent, the content of the crystal nucleating agent in the thermoplastic elastomer composition of the present invention is preferably 0.05 part by mass or more and 5.0 parts by mass or less, more preferably 0.05 part by mass or more and 1.0 part by mass or less with respect to 100 parts by mass in total of the acrylic polymer and the elastomer.

[0114] <Other components> In the thermoplastic elastomer composition of the present invention, in addition to the above-mentioned propylene-based polymer, styrene-based elastomer, ethylene / α-olefin copolymer, colorant, and crystal nucleating agent, within the range where the effects of the present invention are not significantly impaired, the following additives, inorganic fillers (excluding inorganic pigments), organic fillers, or polymers other than the propylene-based polymer, styrene-based elastomer, and ethylene / α-olefin copolymer (hereinafter referred to as "other polymers") and other optional components can be compounded according to various purposes.

[0115] Examples of the additives include various additives such as antioxidants, heat stabilizers, light stabilizers, ultraviolet absorbers, neutralizing agents, slip agents, antifogging agents, anti-blocking agents, lubricants, flame retardants, dispersants, antistatic agents, conductivity imparting agents, metal deactivators, molecular weight regulators, antibacterial agents, fluorescent brighteners, and silicone oils. Among these additives, each additive can generally be compounded and used in the range of 0.01 part by mass or more and 2 parts by mass or less based on 100 parts by mass of the total amount of the propylene-based copolymer and the elastomer.

[0116] Examples of the other polymers that the thermoplastic elastomer composition of the present invention may contain include low-density polyethylene, polyester elastomer, polyurethane elastomer, polyester, polyamide, polyurethane, styrene polymer, polycarbonate, vinyl chloride polymer, and various elastomers other than the above (excluding those belonging to the styrene-based elastomer and ethylene / α-olefin copolymer). The above-listed other polymers may contain only one type or two or more types.

[0117] When the thermoplastic elastomer composition of the present invention contains other polymers, in order to fully obtain the effects brought by containing the propylene-based polymer, elastomer, and colorant, the content rate of the other polymers is preferably 20% by mass or less, more preferably 15% by mass or less, and further preferably 10% by mass or less based on the total amount of the thermoplastic elastomer composition.

[0118] <Manufacturing method of thermoplastic elastomer composition> The thermoplastic elastomer composition of the present invention can be manufactured by kneading the above-mentioned propylene-based polymer, elastomer, colorant, and other components used as needed using a conventional extruder, Banbury mixer, roll press, Brabender plastograph, kneader Brabender, etc. by a conventional method. Among these manufacturing methods, an extruder, particularly a twin-screw extruder, is preferably used.

[0119] <Physical properties> The thermoplastic elastomer composition of the present invention is a composition having the properties required for an airbag storage lid and having the appropriate translucency desired for an airbag storage lid in addition to the thermoplastic elastomer composition.

[0120] The thermoplastic elastomer composition of the present invention is preferably used for an airbag storage cover. In the present invention, the "airbag storage cover" means: the general term for a container that stores an airbag. For example, in a container that stores an airbag, the opening part when the airbag is deployed, or the entire container integrated with the opening part. In such applications, the thermoplastic elastomer composition of the present invention preferably has the following physical properties.

[0121] (Total light transmittance) For the thermoplastic elastomer composition of the present invention, from the viewpoint of visual confirmation when light is irradiated from the back surface of the molded product, for a 1 mm thick sheet test piece manufactured by injection molding the above thermoplastic elastomer composition under the conditions of a resin temperature of 200 °C and a mold temperature of 40 °C, the total light transmittance (total light transmittance) measured based on JIS K7136-1 is preferably 0.001% or more and 70% or less, more preferably 60% or less, further preferably 50% or less, and particularly preferably 20% or less. By setting the total light transmittance of the thermoplastic elastomer composition of the present invention within such a numerical range, when used as an airbag storage cover, light can be recognized without pressure when irradiated from the back surface.

[0122] (Izod impact strength) In the present invention, the Izod impact strength at -40 °C, -45 °C, and -50 °C according to ISO180 is used as an index of low-temperature impact resistance. The Izod impact strength of the molded body of the thermoplastic elastomer composition of the present invention is preferably 50 kJ / m 2 or more, more preferably 70 kJ / m 2 or more. There is no particular limitation on the upper limit of the Izod impact strength of the thermoplastic elastomer composition of the present invention, and it is usually 150 kJ / m 2 or less.

[0123] (MFR) In the present invention, the melt flow rate (MFR) based on JIS K7210 (1999) at a temperature of 230 °C and a measurement load of 21.18 N is used as an index of the injection moldability of the thermoplastic elastomer composition. For the thermoplastic elastomer composition of the present invention, in order to obtain a composition with excellent injection moldability, its melt flow rate is preferably 1.0 g / 10 min or more and 50 g / 10 min or less. When the MFR of the thermoplastic elastomer composition for airbags is 1.0 g / 10 min or more, the fluidity tends to be good. When the MFR of the thermoplastic elastomer composition for airbags is 50 g / 10 min or less, it is easy to suppress burrs and the like during molding, so it is preferred. From the viewpoint of fluidity, the MFR of the thermoplastic elastomer composition for airbags is more preferably 2.0 g / 10 min or more, and further preferably 2.5 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 preferably 40 g / 10 min or less, further preferably 20 g / 10 min or less, particularly preferably 17 g / 10 min or less, and especially preferably 15 g / 10 min or less.

[0124] (Elongation at break at normal temperature / Tensile strength at break) From the viewpoint of material strength, the elongation at break of the thermoplastic elastomer composition of the present invention based on JIS K6251 at 23 °C is preferably 300% or more, and more preferably 350% or more. When the elongation at break at 23 °C is above the above lower limit, the elongation of the material is good, so the deployability of the airbag storage lid made of the thermoplastic elastomer composition of the present invention tends to be good. The upper limit of the elongation at break of the thermoplastic elastomer composition of the present invention is not particularly limited, and is usually 1500% or less.

[0125] For the same reason, when measuring the elongation at break, the measured tensile strength at break is preferably 10 MPa or more, and more preferably 12 MPa or more. When the tensile strength at break at 23 °C is above the above lower limit, the material strength is high, so the deployability of the airbag storage lid made of the thermoplastic elastomer composition of the present invention tends to be good. The upper limit of the tensile strength at break of the thermoplastic elastomer composition of the present invention is not particularly limited, and is usually 25 MPa.

[0126] (Tensile strength at break at high temperature) From the viewpoint of material strength, the tensile strength at break of the thermoplastic elastomer composition of the present invention based on JIS K6251 at 85 °C is preferably 4.5 MPa or more, more preferably 5.0 MPa or more, and further preferably 5.5 MPa or more. When the tensile strength at break at 85 °C is above the above lower limit, the material strength is high, so the deployability of the airbag storage lid made of the thermoplastic elastomer composition of the present invention tends to be good. The upper limit of the tensile strength at break of the thermoplastic elastomer composition of the present invention is not particularly limited, and is usually 8 MPa or less.

[0127] (Flexural modulus) The bending modulus of the thermoplastic elastomer composition of the present invention, measured at 23°C based on JIS K7203, is preferably 600 MPa or less, particularly 200 MPa or more and 550 MPa or less. When the bending modulus of the thermoplastic elastomer composition is below the above upper limit, the low-temperature impact resistance tends to be good. When the bending modulus of the thermoplastic elastomer composition is above the above lower limit, the rigidity tends to be excellent.

[0128] (Light diffusion rate) From the viewpoint of controlling the light diffusibility of the thermoplastic elastomer composition of the present invention, for a composition obtained by removing only the colorant from the constituent components of the thermoplastic elastomer composition and containing only a propylene-based polymer, an elastomer, and other components used as needed (hereinafter, sometimes referred to as "colorant-free composition"), the light diffusion rate measured according to DIN5036 is preferably 10% or more, more preferably 14% or more, further preferably 20% or more, and particularly preferably 25% or more. The upper limit of the light diffusion rate of the colorant-free composition is not particularly limited, and is preferably 95% or less. Here, the light diffusion rate (reference DIN5036) of the colorant-free composition can be measured using a variable-angle photometer GC5000L manufactured by Nippon Electric Decoration Co., Ltd. In addition, the calculation formula of the light diffusion rate is as described below. Light diffusion rate (%) = ((Brightness value at 20° + Brightness value at 70°) / (Brightness value at 5° × 2)) × 100

[0129] As described above, in order to achieve such light diffusibility, a preferred combination of the propylene-based polymer and the elastomer is a combination in which the propylene-based polymer is a propylene-based block copolymer and the elastomer is an ethylene / α-olefin copolymer, and more preferably a combination of a propylene-based block copolymer having a propylene-containing block with a propylene content of 90% by mass or more and 100% by mass or less and an ethylene / propylene copolymer block with an ethylene content of 31% by mass or more and 70% by mass or less, and an ethylene / α-olefin copolymer.

[0130] <Formed bodies such as airbag storage covers> Using the thermoplastic elastomer composition of the present invention, a formed body such as an airbag storage cover can be obtained by generally using a conventional injection molding method, or various molding methods such as gas injection molding, injection compression molding, and short-shot foaming molding as needed. It is particularly preferred to obtain a formed body such as an airbag storage cover by injection molding the thermoplastic elastomer composition of the present invention. The molding conditions during injection molding are as described below.

[0131] When injection molding the thermoplastic elastomer composition, the molding temperature is usually 150 °C or higher and 300 °C or lower, preferably 180 °C or higher and 280 °C or lower. The injection pressure is usually 5 MPa or higher and 100 MPa or lower, preferably 10 MPa or higher and 80 MPa or lower. The mold temperature is usually 0 °C or higher and 80 °C or lower, preferably 20 °C or higher and 60 °C or lower.

[0132] As the average thickness of the design part of the airbag storage cover of the present invention composed of the thermoplastic elastomer composition of the present invention, it is usually 6 mm or less, preferably 5 mm or less, more preferably 4 mm or less. In addition, for the lower limit of the thickness, it is usually 0.5 mm or more, preferably 0.8 mm or more, more preferably 1 mm or more. The thickness of the airbag storage cover itself can have various different thickness parts, and even if there are thickness parts outside the above average thickness range, it is not a problem. By making the thickness of the airbag storage cover within the above preferred range, the effect of moderate light transmittance brought by using the thermoplastic elastomer composition of the present invention can be obtained more effectively, so it is preferred.

[0133] <Thermoplastic Elastomer Composition for Airbag Storage Cover> As one of the embodiments of the thermoplastic elastomer composition of the present invention, it is a thermoplastic elastomer composition for an airbag storage cover containing a propylene-based polymer, an elastomer, and a colorant, and a thermoplastic elastomer composition for an airbag storage cover having a total light transmittance of 0.001% or more and 70% or less measured by the aforementioned method can be cited. For the above propylene-based polymer, the description of <propylene-based polymer> in the thermoplastic elastomer composition of the present invention is applicable. The above elastomer is at least one selected from styrene-based elastomers and ethylene / α-olefin copolymers, and the descriptions of <elastomer>, <styrene-based elastomer>, and <ethylene / α-olefin copolymer> in the thermoplastic elastomer composition of the present invention are applicable.

[0134] Among the above colorants, the colorant is at least one selected from organic pigments and inorganic pigments. Preferably, when the colorant is an organic pigment, it contains 0.01 parts by mass or more and 5 parts by mass or less relative to 100 parts by mass of the total amount of the above propylene-based polymer and elastomer; when the colorant is an inorganic pigment, it contains 0.001 parts by mass or more and 0.5 parts by mass or less; when the colorant contains an organic pigment and an inorganic pigment, based on the total amount of the organic pigment and the inorganic pigment, it contains 0.001 parts by mass or more and 3 parts by mass or less. For this colorant, the description of <colorant> in the thermoplastic elastomer composition of the present invention is applicable.

[0135] For the blending ratio and other details in the thermoplastic elastomer composition for the airbag storage lid, the blending ratio and other descriptions in the thermoplastic elastomer composition of the present invention are applicable.

[0136] <Composite molded body> The composite molded body of the present invention having a first layer made of the thermoplastic elastomer composition for the airbag storage lid of the present invention and a second layer made of a resin film is preferably used as an airbag storage lid. That is, the thermoplastic elastomer composition for the airbag storage lid of the present invention can be integrated with a resin film to form a composite molded body. The composite molded body of the present invention having a first layer containing the thermoplastic elastomer composition for the airbag storage lid of the present invention and a second layer made of a resin film is preferably used as an airbag storage lid.

[0137] By using such a composite molded body, it is possible to composite a resin film incorporating the operation function or design of a touch screen with an airbag storage lid.

[0138] Examples of the resin film include, for example, a film made of polypropylene, a film made of polyethylene, a film made of a polyolefin-based thermoplastic elastomer, and a film made of polyester.

[0139] The thickness of the above resin film that forms the second layer is usually 3 mm or less, preferably 2 mm or less, more preferably 1.5 mm or less, and further preferably 1 mm or less. There is no limit to the lower limit of the thickness of the above resin film, and it is usually 0.01 mm or more. Regarding the thickness of the airbag storage lid of the present invention, as described above. In the airbag storage lid of the present invention which is a composite molded body having a first layer made of the thermoplastic elastomer composition for the airbag storage lid of the present invention and a second layer made of the above resin film, the thickness of the first layer is usually 6 mm or less, preferably 5 mm or less, more preferably 4 mm or less, usually 0.5 mm or more, preferably 0.8 mm or more, and more preferably 1 mm or more. By making the thicknesses of the first layer and the second layer within the above preferred ranges, the effect of appropriate translucency brought about by using the thermoplastic elastomer composition of the present invention can be obtained more effectively, and thus it is preferred.

[0140] The composite molded body of the present invention can be formed by an insert molding method. In the insert molding method, a resin film is pre-added into the mold before molding, and then by filling the thermoplastic elastomer composition for the airbag storage lid of the present invention into the mold, a composite molded body of the present invention having a first layer made of the thermoplastic elastomer composition for the airbag storage lid of the present invention and a second layer made of a resin film can be obtained.

[0141] <Use> The thermoplastic elastomer composition of the present invention is excellent in high-temperature strength and low-temperature impact resistance, has moderate light transmittance, and can preferably be used as a molding material for an airbag storage cover. In particular, in such an airbag storage cover, for example, it is preferably an airbag storage cover of an airbag system that is triggered by sensing an impact or deformation when a high-speed moving object such as an automobile collides, and protects the occupants by expanding and deploying. In particular, due to its moderate light transmittance, the airbag storage cover of the present invention is preferably an airbag storage cover disposed at a position where a touch screen display or the like can be visually confirmed. As a visually confirmable position, for example, positions that can be visually confirmed by the occupant in the driver's seat and the occupant in the front passenger seat can be cited. Specifically, the instrument panel, the steering wheel, and the console can be cited.

[0142] Reference Figure 1 、 2 、 an example of an embodiment in the case of an airbag storage cover to which the thermoplastic elastomer composition of the present invention is applied and disposed at a position where a touch screen display or the like can be visually confirmed will be described. Figure 1 (a) is a front view schematically showing an example of an airbag storage cover, Figure 1 (b) is a rear view of the same figure. Figure 2 is an enlarged view showing a cross section along the Figure 1 II-II line of (a).

[0143] A light source (LED module) 2 is provided on the back side of the airbag storage cover 1. The light ( Figure 2 the arrow in) from this light source 2 needs to pass through the airbag storage cover 1 and can be visually confirmed by the occupant. Therefore, at least the light-transmitting portion 1A corresponding to the light source 2 of the airbag storage cover 1 is made of the thermoplastic elastomer composition of the present invention. For other portions 1B other than the light-transmitting portion 1A, they can be made of the thermoplastic elastomer composition of the present invention or can be made of a conventional thermoplastic elastomer composition without light transmittance. In this way, by making at least the light-transmitting portion 1A corresponding to the light source 2 of the airbag storage cover 1 made of the thermoplastic elastomer composition of the present invention, good visual confirmability can be obtained while obtaining moderate internal concealment even in an airbag storage cover provided with a touch screen display. Examples

[0144] Hereinafter, the content of the present invention will be further specifically described using examples. The present invention is not limited to the following examples as long as it does not exceed its gist. The values of various manufacturing conditions and evaluation results in the following examples are preferred values of the upper limit or the lower limit in the embodiments of the present invention, and the preferred range can also be a range defined by a combination of the above upper limit or lower limit values and the values in the following examples or between the examples.

[0145] <Raw materials> [Polypropylene-based polymer] (A-1): NOVATEC (registered trademark) PP MG03E manufactured by Nippon Polypro Co., Ltd. Random copolymer of propylene / ethylene MFR (JIS K7210 (1999)): 30 g / 10 min (measurement conditions: 230 °C, load 21.18 N (2.16 kgf)) Crystalline melting peak temperature: 146 °C Propylene unit content: 96 mass% (A-2): NOVATEC (registered trademark) PP BC03B manufactured by Nippon Polypro Co., Ltd. Propylene block copolymer A substance obtained by polymerizing a propylene homopolymer in the first step and then polymerizing an ethylene / propylene copolymer in the second step MFR (JIS K7210 (1999)): 30 g / 10 min (measurement conditions: 230 °C, load 21.18 N (2.16 kgf)) Crystalline melting peak temperature: 169 °C Content of propylene homopolymer component: 84 mass% Content of ethylene / propylene copolymer component: 16 mass% Ethylene unit content in the ethylene / propylene copolymer component: 55 mass% (A-3): NOVATEC (registered trademark) PP MA3 manufactured by Nippon Polypro Co., Ltd. Propylene homopolymer MFR (JIS K7210 (1999)): 11 g / 10 min (measurement conditions: 230 °C, load 21.18 N (2.16 kgf)) Crystalline melting peak temperature: 159 °C Propylene unit content: 100 mass% (A-4): NOVATEC (registered trademark) PP BC06NCA manufactured by Nippon Polypro Co., Ltd. Propylene block copolymer A substance obtained by polymerizing a propylene homopolymer in the first step and then polymerizing an ethylene / propylene copolymer in the second step MFR (JIS K7210 (1999)): 60 g / 10 min (measurement conditions: 230 °C, load 21.18 N (2.16 kgf)) Crystalline melting peak temperature: 164 °C Content ratio of propylene homopolymer component: 92% by mass Content ratio of ethylene / propylene copolymer component: 8% by mass Content ratio of ethylene units in ethylene / propylene copolymer component: 46% by mass (A-5): A mixture obtained by mixing the following propylene random copolymer (A-5-1) and the following propylene random block copolymer (A-5-2) in a ratio of (A-5-1):(A-5-2) = 67% by mass:33% by mass in the total amount of 100% by mass of the mixture of (A-5-1) and (A-5-2) (A-5-1): Propylene / ethylene random copolymer WINTEC (registered trademark) WFX4M manufactured by Nippon Polypro with an ethylene unit content of 3.1% by mass MFR (JIS K7210 (1999)): 7 g / 10 min (measurement conditions: 230 °C, load 21.18 N (2.16 kgf)) Crystalline melting peak temperature: 124 °C (A-5-2): Propylene / ethylene random block copolymer Adflex (registered trademark) Q100F manufactured by Lyondell Basell A substance obtained by polymerizing a propylene / ethylene random copolymer in the first step and then polymerizing a propylene / ethylene random copolymer in the second step MFR (JIS K7210 (1999)): 0.6 g / 10 min (measurement conditions: 230 °C, load 21.18 N (2.16 kgf)) Crystalline melting peak temperature: 143 °C Content ratio of propylene / ethylene random copolymer component obtained in the first step: 32.9% by mass Content ratio of propylene / ethylene random copolymer component obtained in the second step: 67.1% by mass Content ratio of ethylene units in propylene / ethylene random copolymer component obtained in the second step: 25.6% by mass

[0146] [Styrenic elastomer] (B-1): Kraton (registered trademark) G1652 manufactured by Kraton Polymers Hydrogenated styrene / butadiene block copolymer (styrene / ethylene / butene / styrene copolymer (SEBS)) Weight average molecular weight (Mw): 70,000 Content ratio of styrene units: 30% by mass Glass transition temperature: -55 °C (B-2): Kraton (registered trademark) G1657 manufactured by Kraton Polymers LLC Hydride of styrene / butadiene block copolymer (styrene / ethylene / butene / styrene copolymer (SEBS)) Weight-average molecular weight (Mw): 110,000 Styrene unit content: 13 mass% Glass transition temperature: -55 °C

[0147] [Ethylene / α-olefin copolymer] (C-1): Engage (registered trademark) 8100 manufactured by The Dow Chemical Company Ethylene / 1-octene random copolymer MFR (ASTM D1238): 1 g / 10 min (measurement conditions: 190 °C, load 21.18 N (2.16 kgf)) Density (ISO 1183 - Method A): 0.87 g / cm 3 (Measurement temperature: 23 °C) (C-2): Engage (registered trademark) XLT8677 manufactured by The Dow Chemical Company Ethylene / 1-octene block copolymer Crystalline melting peak temperature: 119 °C Heat of crystalline melting: 37 J / g MFR (ASTM D1238): 0.5 g / 10 min (measurement conditions: 190 °C, load 21.18 N) (guideline value) Density (ASTM D792): 0.870 g / cm 3 (Guideline value) (C-3): Mitsui EPT3092PM manufactured by Mitsui Chemicals, Inc. Ethylene / propylene / ethylidene norbornene copolymer Mooney viscosity ML(1+4) 125 °C (ASTM D1646): 61 (guideline value) Ethylene unit content (ASTM D3900): 65 mass% (guideline value) Ethylidene norbornene unit content (ASTM D6047): 4.6 mass% (guideline value)

[0148] [Colorant] [Organic pigment] (D-1): HCM1560 Green manufactured by Dainichi Seika Color & Chemicals Mfg. Co., Ltd. Phthalocyanine green masterbatch Pigment concentration in masterbatch: 20 mass% Carrier: Polyethylene

[0149] <Inorganic pigment> (D-2): Lamp Black 101 manufactured by ORION ENGINEERED CARBONS Lamp black masterbatch Pigment concentration in masterbatch: 40% by mass Carrier: Polyethylene (D-3): PC40C manufactured by Dainichi Seika Co., Ltd. Carbon black masterbatch Pigment concentration in masterbatch: 40% by mass Carrier: Polyethylene

[0150] <Evaluation method> In the evaluations of the following 1) to 3), 5) to 8), the thermoplastic elastomer composition particles obtained in each example were used, and injection molding was performed into sample test sheets for each test at an injection pressure of 50 MPa, a cylinder set temperature of 190 °C (resin temperature 200 °C), and a mold temperature of 40 °C using an in-line screw injection molding machine ("IS130" manufactured by Toshiba Machine Co., Ltd.).

[0151] 1) Total light transmittance For the injection-molded sheet with a thickness of 1 mm × width of 100 mm × length of 100 mm, the total light transmittance was measured based on JIS K7136-1.

[0152] 2) Visual confirmation evaluation when irradiating light from the back For the injection-molded sheet with a thickness of 1 mm × width of 100 mm × length of 100 mm, light was irradiated from the back of the sheet, and a sensory evaluation of visual confirmation was performed. A flashlight with an intensity of 19 lumens was used as the light source, and the sheet was placed at a position 10 cm away from the light source, and a sensory test was conducted to confirm how the light passing through the sheet looked, and it was evaluated according to the following criteria. ◎: The light looks very comfortable. 〇: The light looks moderately comfortable. Δ: Although within the allowable range, it looks a bit dazzling. ×A: Too dazzling to look directly at. ×B: The light does not pass through at all.

[0153] 3) Visual shielding property of the content For the injection-molded sheet with a thickness of 3 mm × width of 100 mm × length of 100 mm, a sensory evaluation was performed to confirm whether the reverse side of the sheet could be seen when observing through the sheet, and it was evaluated according to the following criteria. ◎: The reverse side of the sheet cannot be seen at all. 〇: A little of the reverse side of the sheet can be seen. Δ: A certain degree can be seen on the reverse side of the sheet. ×: The reverse side of the sheet is completely visible.

[0154] 4) Injection moldability: Melt flow rate (MFR) Measured based on JIS K7210 (1999) under the conditions of a temperature of 230 °C and a load of 21.18 N.

[0155] 5) Low-temperature impact resistance: Izod impact strength Through injection molding, a test piece for measuring Izod impact strength with a notch of 10 mm in thickness × 4 mm in width × 80 mm in length is molded. Based on ISO180 (2010), it is measured at temperatures of -40 °C, -45 °C, and -50 °C. In addition, in the Izod impact test, those that do not break are designated as "P", those that are about to break and only have one remaining skin are designated as "H", and those that break are designated as "C". The larger the value of the Izod impact strength and the more the sample is "P" (not broken), the better the low-temperature impact resistance is evaluated.

[0156] 6) Flexural modulus (23 °C) Measured based on JIS K7203 under the conditions of a span of 64 mm and a bending speed of 1 mm / min.

[0157] 7) Elongation at break / tensile strength at break at normal temperature (23 °C): Tensile fracture test (JIS-No. 3 dumbbell, tensile speed 500 mm / min) Based on JIS K6251 (JIS-No. 3 dumbbell), a test piece for punching and tensile test (a sheet with a thickness of 2 mm × a width of 120 mm × a length of 80 mm) is blanked. For this blanked test piece, based on JIS K6251, the elongation at break and the tensile strength at break are measured in an atmosphere of 23 °C. The larger the values of the elongation at break and the tensile strength at break, the better the evaluation.

[0158] 8) Tensile strength at break at high temperature (85 °C): Tensile fracture test (JIS-No. 3 dumbbell, tensile speed 500 mm / min) (unit: %) Based on JIS K6251 (JIS-No. 3 dumbbell), a test piece for punching and tensile test (a sheet with a thickness of 2 mm × a width of 120 mm × a length of 80 mm) is blanked. For this blanked test piece, based on JIS K6251, the tensile strength at break is measured in an atmosphere of 85 °C. The larger the value of the tensile strength at break, the better the evaluation. In the following Tables 1 to 4, the numerical values of the tensile strength at break at 85 °C with ">" indicate that the measured strength reached the upper limit of the machine and thus did not break. The numbers represent the stress at which the upper limit of the machine was reached. In this evaluation, this stress can be regarded as the same as the fracture stress.

[0159] <Examples / Comparative Examples> [Example 1] As shown in Table-1, except for 100 parts by mass of (A-1), 50 parts by mass of (b-1), 50 parts by mass of (b-2), and 0.5 part by mass of (D-1), 0.4 part by mass of a diacetal-based crystal nucleating agent (Millad (registered trademark) NX8000 manufactured by Milliken Japan), 0.15 part by mass of an antioxidant (IRGASTAB (registered trademark) FS301FF manufactured by BAS Japan), 0.2 part by mass of a light stabilizer (SABOSTAB (registered trademark) UV119 manufactured by SONGWON), 0.1 part by mass of an ultraviolet absorber (TINUVIN (registered trademark) 326 manufactured by BASF Japan), and 0.2 part by mass of a silicone oil (KF96-100CS manufactured by Shin-Etsu Chemical Co., Ltd.) were compounded relative to a total of 100 parts by mass of the propylene-based polymer and the elastomer, and the mixture was mixed for 1 minute using a Henschel mixer. The above mixture was fed into a co-rotating twin-screw extruder (TEM-26SS manufactured by Toshiba Machine Co., Ltd., L / D = 48.5, number of barrels: 12) at a rate of 25 kg / h, and the temperature was raised within the range of 160°C or higher and 210°C or lower for melt-kneading to produce thermoplastic elastomer composition pellets. For the obtained thermoplastic elastomer composition pellets, the evaluations of 1) to 8) above were carried out. These evaluation results are shown in Table-1.

[0160] [Examples 2 to 29 and Comparative Examples 1 to 15] Except for using the formulations shown in Tables 1 to 5, thermoplastic elastomer composition pellets were obtained in the same manner as in Example 1. For the diacetal-based crystal nucleating agent, antioxidant, light stabilizer, ultraviolet absorber, and silicone oil, the same formulations as in Example 1 were used. For the obtained thermoplastic elastomer composition pellets, the evaluations of 1) to 8) above were carried out. These evaluation results are shown in Tables 1 to 5. In addition, in the evaluation result columns of Tables 1 to 5, "-" indicates that there is no data and no evaluation was performed. In Tables 1 to 5, the pigment concentration in the thermoplastic elastomer composition refers to the content of the pigment relative to a total of 100 parts by mass of the propylene-based polymer and the elastomer.

[0161] [Table 1] <Table-1>

[0162] [Table 2] <Table-2>

[0163] [Table 3] <Table-3>

[0164] [Table 4] <Table-4>

[0165] [Table 5] <Table-5>

[0166] [Evaluation Results] In Examples 1 to 29 of the thermoplastic elastomer composition belonging to the present invention, the high-temperature strength, low-temperature impact resistance, and visual confirmability are all good. In Comparative Examples 1 to 3, 8, and 13, which are formulations without pigments, too much light passes through, and they are evaluated as being too dazzling in the evaluation of visual confirmability. In Comparative Examples 4 to 7, 9 to 12, and 14 to 15, since the total light transmittance is 0, it is evaluated that light cannot be recognized even when light is irradiated from the back.

[0167] [Example 30] An insert molding was performed using the thermoplastic elastomer composition particles obtained in Example 7 and a polypropylene film to produce a composite molded body. Specifically, NOVATEC (registered trademark) PP MG03E manufactured by Nippon Polypro was pressed into a film with a thickness of 0.5 mm and cut into a square with a side length of 100 mm, and it was placed in a mold of 100 mm × 100 mm × 3 mm, and the above-mentioned particles were injection-molded. By this method, a composite molded body in which the first layer made of the thermoplastic elastomer composition and the second layer made of the polypropylene film are integrally welded can be obtained. The total light transmittance of this composite is 0.05%, and in the evaluation of visual confirmability when light is irradiated from the back, the light looks very comfortable, and the result is judged as "◎".

[0168] [Experimental Examples 1 to 9: Light Diffusion Experiment] For the purpose of confirming the influence of components other than the colorant on visual confirmability, an experiment for confirming the influence on light diffusion and visual confirmability was conducted with the component combinations shown in Table-6. Without using pigments, except for the formulations shown in Table-6, thermoplastic elastomer composition (composition without colorant) particles were obtained in the same manner as in Example 1. For the acetal-based crystal nucleating agent, antioxidant, light stabilizer, ultraviolet absorber, and silicone oil, the same formulations as in Example 1 were used. For the obtained thermoplastic elastomer composition particles, the light diffusivity (reference: DIN5036) was measured using the evaluations 1) to 3) described above and a variable-angle photometer GC5000L manufactured by Nippon Electric Decoration Co., Ltd. These evaluation results are shown in Table-6. In addition, the calculation formula for the light diffusivity is as described below. Light diffusivity (%) = ((Brightness value at 20° + Brightness value at 70°) / (Brightness value at 5° × 2)) × 100

[0169] [Table 6]

[0170] From the results in Table-6, the following can be known. The light diffusivities in Experimental Example 1 and Experimental Examples 7 to 9 are all relatively low. When the light diffusivity is so low, since the light emitted from the light source penetrates straight, it is too dazzling in terms of visual confirmation, and the shape of the light source is directly visible, so the design evaluation is poor. Compared with Experimental Example 1 and Experimental Examples 7 to 9, the light diffusivities in Experimental Examples 2 to 6 are all relatively large values. In this way, when the light diffusivity is large, the light emitted from the light source diffuses rather than penetrates straight, glare can be suppressed in terms of visual confirmation, and since the shape of the light source cannot be seen, the design is also evaluated as excellent. From the above experimental results, it was confirmed that by using an acrylic block copolymer as the propylene copolymer and an ethylene / α-olefin copolymer as the elastomer, or by combining an acrylic block copolymer as the propylene copolymer and an ethylene / α-olefin copolymer as the elastomer, the light diffusivity tends to increase and the evaluation of visual confirmation tends to give good results.

[0171] Although the present invention has been described in detail in a specific manner, it is obvious to those skilled in the art that various changes can be made within the scope of the inventive effect. This application is based on Japanese Patent Application 2022-204498 filed on December 21, 2022, and the whole of it is incorporated herein by reference.

Claims

1. An airbag storage cover, characterized in that, It is composed of a thermoplastic elastomer composition containing an acrylic polymer, an elastomer, and a colorant, and the total light transmittance of the thermoplastic elastomer composition measured by the following method is 0.001% or more and 70% or less. Method for measuring the total light transmittance: For a 1-mm-thick sheet test piece manufactured by injection molding the thermoplastic elastomer composition under the conditions of a resin temperature of 200 °C and a mold temperature of 40 °C, the total light transmittance is measured based on JIS K7136-1.

2. The airbag storage cover according to claim 1, wherein, The thermoplastic elastomer composition has an Izod impact strength of 50 kJ / m² at -40 °C based on ISO 180 2 or more.

3. The airbag storage cover according to claim 1 or 2, wherein, It contains an acrylic block copolymer as the acrylic polymer.

4. The airbag storage cover according to claim 3, wherein, The acrylic block copolymer is an acrylic block copolymer having an acrylic polymer component and an ethylene / propylene copolymer component.

5. The airbag storage cover according to claim 1 or 2, which is arranged at a visually confirmable position.

6. The airbag storage cover according to claim 5, which is arranged on the instrument panel, steering wheel or console.

7. The airbag storage cover according to claim 1 or 2, wherein, It contains at least one selected from styrenic elastomers and ethylene / α-olefin copolymers as the elastomer.

8. The airbag storage cover according to claim 7, wherein, It contains a styrenic elastomer as the elastomer.

9. The airbag storage cover according to claim 8, wherein, The styrenic elastomer is composed of a hydride b1 of a styrene / conjugated diene block copolymer having a styrene unit content of 10% by mass or more and 15% by mass or less and a hydride b2 of a styrene / conjugated diene block copolymer having a styrene unit content of 25% by mass or more and 35% by mass or less.

10. The airbag storage cover according to claim 8 or 9, wherein, The glass transition temperature of the styrenic elastomer is -65 °C or more and -45 °C or less.

11. The airbag storage cover according to claim 7, wherein, It contains an ethylene / α-olefin copolymer as the elastomer.

12. The airbag storage cover according to claim 1 or 2, wherein, The colorant is at least one selected from organic pigments and inorganic pigments.

13. The airbag storage cover according to claim 12, wherein, Relative to 100 parts by mass of the total amount of the acrylic polymer and the elastomer, 0.01 part by mass or more and 5 parts by mass or less of an organic pigment is contained as the colorant.

14. The airbag storage cover according to claim 12, wherein, Relative to 100 parts by mass of the total amount of the acrylic polymer and the elastomer, 0.001 part by mass or more and 0.5 part by mass or less of an inorganic pigment is contained as the colorant.

15. The airbag storage cover according to claim 12, wherein, Relative to 100 parts by mass of the total amount of the acrylic polymer and the elastomer, a total of 0.001 part by mass or more and 3 parts by mass or less of an organic pigment and an inorganic pigment is contained as the colorant.

16. The airbag storage cover according to claim 1 or 2, wherein, The melt flow rate of the thermoplastic elastomer composition based on JIS K7210 in 1999 is 1.0 g / 10 minutes or more and 50 g / 10 minutes or less at a temperature of 230 °C and a measurement load of 21.18 N.

17. The airbag storage cover according to claim 1 or 2, wherein, In the thermoplastic elastomer composition, relative to 100 parts by mass of the acrylic polymer, the content of the elastomer is 45 parts by mass or more and 250 parts by mass or less.

18. The airbag storage cover according to claim 1 or 2, wherein, The total light transmittance is 0.001% or more and 20% or less.

19. A thermoplastic elastomer composition for an airbag storage cover, characterized in that, It is a thermoplastic elastomer composition for an airbag storage lid containing an acrylic polymer, an elastomer, and a colorant. The elastomer is at least one selected from styrenic elastomers and ethylene / α-olefin copolymers. The colorant is at least one selected from organic pigments and inorganic pigments. The total light transmittance of the thermoplastic elastomer composition measured by the following method is 0.001% or more and 70% or less. Method for measuring the total light transmittance: For a 1-mm-thick sheet test piece produced by injection molding the thermoplastic elastomer composition at a resin temperature of 200°C and a mold temperature of 40°C, the total light transmittance was measured based on JIS K7136-1.

20. The thermoplastic elastomer composition for an airbag storage lid according to claim 19, wherein, As the colorant, 0.01 part by mass or more and 5 parts by mass or less of an organic pigment is contained relative to 100 parts by mass in total of the propylene-based polymer and the elastomer.

21. The thermoplastic elastomer composition for an airbag storage lid according to claim 19, wherein, As the colorant, 0.001 part by mass or more and 0.5 part by mass or less of an inorganic pigment is contained relative to 100 parts by mass in total of the propylene-based polymer and the elastomer.

22. The thermoplastic elastomer composition for an airbag storage lid according to claim 19, wherein, As the colorant, 0.001 part by mass or more and 3 parts by mass or less of an organic pigment and an inorganic pigment in total are contained relative to 100 parts by mass in total of the propylene-based polymer and the elastomer.

23. The thermoplastic elastomer composition for an airbag storage lid according to claim 19, wherein, A styrenic elastomer is contained as the elastomer.

24. The thermoplastic elastomer composition for an airbag storage lid according to claim 23, wherein, The styrenic elastomer is composed of a hydrogenated product b1 of a styrene / conjugated diene block copolymer having a styrene unit content of 10 mass% or more and 15 mass% or less and a hydrogenated product b2 of a styrene / conjugated diene block copolymer having a styrene unit content of 25 mass% or more and 35 mass% or less.

25. The thermoplastic elastomer composition for an airbag storage lid according to claim 23 or 24, wherein, The glass transition temperature of the styrenic elastomer is -65°C or higher and -45°C or lower.

26. The thermoplastic elastomer composition for an airbag storage lid according to claim 19, wherein, A propylene-based block copolymer is contained as the propylene-based polymer.

27. The thermoplastic elastomer composition for an airbag storage lid according to claim 26, wherein, The propylene-based block copolymer is a propylene-based block copolymer having a propylene-based polymer component and an ethylene / propylene copolymer component.

28. The thermoplastic elastomer composition for an airbag storage lid according to claim 19, wherein, An ethylene / α-olefin copolymer is contained as the elastomer.

29. A molded article, characterized in that, It is composed of the thermoplastic elastomer composition for an airbag storage lid according to claim 19 or 26.

30. A composite molded article, characterized in that, It has a first layer containing the thermoplastic elastomer composition for an airbag storage lid according to claim 19 or 26 and a second layer composed of a resin film.

31. The composite molded article according to claim 30, which is an airbag storage lid.

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