JP2013035888A - Thermoplastic elastomer composition and air bag housing cover - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermoplastic elastomer composition, having excellent appearance, low-temperature impact resistance, rigidity and the like which are satisfactory for a non-coated air bag housing cover.SOLUTION: The thermoplastic elastomer composition includes a specific propylene polymer, a specific ethylene-α-olefin copolymer rubber and a specific propylene-ethylene copolymer. Relative to 100 pts.wt. of the propylene polymer, the content of the ethylene-α-olefin copolymer rubber is 10-200 pts.wt., and the content of the propylene-ethylene copolymer is 10-100 pts.wt.

Description

  The present invention relates to a thermoplastic elastomer composition excellent in appearance, rigidity, low-temperature impact resistance, and the like, and an airbag storage cover comprising the same.

An automobile airbag system is a system that protects a driver or a passenger in the event of a collision with an automobile or the like, and includes a device that senses an impact during the collision and an airbag device. The airbag device is installed on a steering wheel, an instrument panel in front of a passenger seat, a driver seat and a passenger seat, or front and side pillars.
The airbag storage cover in the airbag device may cause injury to the driver or crew members when the airbag is inflated due to scattering of debris due to destruction of the cover storing the airbag, or scattering of cover due to destruction of the cover mounting portion. There is a risk of causing it. For this reason, various structures and materials have been proposed for the purpose of preventing the cover from being abnormally broken and scattered in a wide temperature range from low temperature to high temperature.

  For example, Patent Literature 1 proposes an airbag storage cover made of a hydrogenated styrene / conjugated diene block copolymer, a plasticizer for rubber, an olefinic resin, and an additive. Patent Document 2 proposes an airbag storage cover made of a hydrogenated product of a propylene-based copolymer resin, an α-olefin copolymer rubber, and a styrene / conjugated diene block copolymer. Further, Patent Document 3 proposes an injection-molded body comprising a thermoplastic elastomer composition comprising a propylene-based resin produced by multistage polymerization and ethylene-propylene-5-ethylidene-2-norbornene copolymer rubber. .

  However, in the resin compositions as described in Patent Documents 1 to 3, the appearance when formed into a molded body such as an airbag storage cover, particularly the appearance of the tear line portion of the airbag storage cover is poor. A problem has been found that it is not suitable for an unpainted airbag storage cover. Further, for improving the appearance of the airbag housing cover molded article, a thermoplastic elastomer composition comprising a propylene-based resin, a crystalline propylene-ethylene copolymer, and an ethylene-α-olefin copolymer rubber as disclosed in Patent Document 4. In particular, in the examples of Patent Document 4, ethylene-propylene-5-ethylidene-2-norbornene copolymer rubber is used among ethylene-α-olefin copolymer rubber. A composition is shown. However, the airbag storage cover preferably has high rigidity for horn operability and shape retention, and development of a non-coating material with improved balance between rigidity and low-temperature impact resistance is desired.

Japanese Patent Laid-Open No. 5-38996 Japanese Patent Laid-Open No. 10-265628 JP 2008-45037 A JP 2009-263471 A

Conventional injection molded articles made of an olefin-based thermoplastic elastomer composition have a poor appearance due to the occurrence of gloss unevenness on the surface design side of the tear line part, and a coating process is essential for improving the design. Further, high rigidity is desirable for the horn operability and shape retention of the airbag storage cover, and a material with an improved balance between rigidity and low-temperature impact resistance has been desired. Under such circumstances, the problems to be solved by the present invention are the appearance satisfactory as an unpainted airbag storage cover, low-temperature impact resistance, rigidity, deployment performance when used as an airbag storage cover, and the like. The object is to provide an excellent thermoplastic elastomer composition.

As a result of intensive studies to solve the above-mentioned problems, the present inventors have determined that a thermoplastic elastomer composition contains a specific amount of each of a specific polypropylene polymer, an ethylene-α-olefin copolymer rubber, and a propylene-ethylene copolymer. Excellent low-temperature impact resistance, rigidity suitable for airbag storage covers, deployment performance when used as airbag storage covers, and excellent appearance to satisfy even unpainted airbag storage covers And found the present invention. That is, the gist of the present invention resides in the following [1] to [5].
[1] The following components (A), (B) and (C) are contained, and 10 to 200 parts by weight of component (B) and 10 to 100 parts by weight of component (C) with respect to 100 parts by weight of component (A). A thermoplastic elastomer composition comprising a part.
Component (A): The following component (A-1) is polymerized in the first step, and then the following component (A-2) is polymerized in the second step, and component (A-1) and component (A- 2) Polypropylene polymer component (A-1) in which the content of component (A-1) is 70 to 95% by weight and the content of component (A-2) is 30 to 5% by weight ): Propylene-based polymer having a propylene unit content of 90 to 100% by weight Component (A-2): Ethylene-α-olefin copolymer component (B) having an ethylene unit content of 20 to 80% by weight ): The ethylene unit content is 50 to 80% by weight and the C4 to C8 α-olefin unit is the total amount of the ethylene unit content and the C4 to C8 α-olefin unit content. Ethylene-α-olefin copolymer rubber component having a content of 50 to 20% by weight ( C): The content of propylene units is 80 to 92% by weight, the content of ethylene units is 20 to 8% by weight, and the melt flow rate with respect to the total content of propylene units and ethylene units (Measurement temperature 230 ° C., measurement load 21.18 N) is 1 to 50 g / 10 min, and the density is 0.890 g / cm ³ or less [2] based on 100 parts by weight of the component (A) The thermoplastic elastomer composition according to [1], comprising 1 to 50 parts by weight of the following component (D).
Component (D): Styrene / conjugated diene block copolymer and / or hydrogenated product thereof [3] 1 to 50 parts by weight of the following component (E) with respect to 100 parts by weight of the component (A), The thermoplastic elastomer composition according to [1] or [2].
Component (E): Softener for hydrocarbon rubber [4] The thermoplastic elastomer composition according to any one of [1] to [3], which satisfies the following characteristics (1) to (3):
(1) Melt flow rate at a measurement temperature of 230 ° C. according to JIS K7210 and a measurement load of 21.18 N is 0.1 to 100 g / 10 minutes (2) Flexural modulus according to JIS K7203 is 100 MPa or more (3) JIS An airbag storage cover comprising the thermoplastic elastomer composition according to any one of [5] [1] to [4], having a notched Izod impact strength at a temperature of −40 ° C. according to K7110 of 50 kJ / m ² or more .

The thermoplastic elastomer composition of the present invention can be molded using a normal injection molding machine, and a molded body excellent in fluidity, rigidity, low-temperature impact resistance, appearance and the like can be obtained. It is a useful cover that does not require a painting process and has excellent air bag deployment performance.

  Hereinafter, the present invention will be described in detail, but the present invention is not limited to the following description, and can be arbitrarily modified and implemented without departing from the gist of the present invention. In addition, in this specification, when expressing by putting a numerical value or a physical-property value before and behind using "-", it shall use as what includes the value before and behind.

[Thermoplastic elastomer composition]
The thermoplastic elastomer composition of the present invention contains the following components (A), (B) and (C), 10 to 200 parts by weight of component (B) per 100 parts by weight of component (A), and component (C 10 to 100 parts by weight.

Component (A): The following component (A-1) is polymerized in the first step, and then the following component (A-2) is polymerized in the second step, and component (A-1) and component (A- 2) Polypropylene polymer component (A-1) in which the content of component (A-1) is 70 to 95% by weight and the content of component (A-2) is 30 to 5% by weight ): Propylene-based polymer having a propylene unit content of 90 to 100% by weight Component (A-2): Ethylene-α-olefin copolymer component (B) having an ethylene unit content of 20 to 80% by weight ): The ethylene unit content is 50 to 80% by weight and the C4 to C8 α-olefin unit is the total amount of the ethylene unit content and the C4 to C8 α-olefin unit content. An ethylene-α-olefin copolymer rubber component having a content of 50 to 20% by weight C): The content of propylene units is 80 to 92% by weight, the content of ethylene units is 20 to 8% by weight, and the melt flow rate with respect to the total content of propylene units and ethylene units Propylene-ethylene copolymer having a measurement temperature of 230 ° C. and a measurement load of 21.18 N of 1 to 50 g / 10 min and a density of 0.890 g / cm ³ or less.

<Component (A)>
Component (A) is obtained by polymerizing the following component (A-1), followed by polymerization of the following component (A-2), and with respect to the total amount of component (A-1) and component (A-2), This is a propylene polymer having a component (A-1) content of 70 to 95% by weight and a component (A-2) content of 30 to 5% by weight.

Component (A-1): Propylene-based polymer having a propylene unit content of 90 to 100% by weight (provided that the entire component (A-1) is 100% by weight) Component (A-2): Ethylene The content of the unit is 20 to 80% by weight (provided that the whole component (A-2) is 100% by weight). The ethylene-α-olefin copolymer component (A-1) contains propylene units. Even if it is a propylene-type polymer whose amount is 90-100 weight% and it is a homopolymer of propylene, in addition to a propylene unit, it is 10 units of alpha-olefin units other than propylene, and monomer units other than alpha-olefins. A copolymer containing not more than wt% may be used. Examples of the α-olefin unit other than propylene include ethylene and an α-olefin having 4 to 20 carbon atoms. Examples of the α-olefin having 4 to 20 carbon atoms include 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, 1 -Tridecene, 1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-nonadecene, 1-eicocene, 3-methyl-1-butene, 3-methyl-1-pentene, 4-methyl Examples include -1-pentene, 2-ethyl-1-hexene, 2,2,4-trimethyl-1-pentene, and the like. Preferred are ethylene and α-olefins having 4 to 10 carbon atoms, and more preferred are ethylene, 1-butene, 1-hexene and 1-octene.

  The content of the propylene unit in the component (A-1) is 90 to 100% by weight, preferably 95 to 100% by weight, more preferably 98 to 100% by weight based on the whole component (A-1). 100% by weight. When the content of the propylene unit in the component (A-1) is equal to or more than the lower limit, the heat resistance and rigidity when the thermoplastic elastomer of the present invention is molded are improved. The content of the propylene unit can be determined by infrared spectroscopy.

  Examples of the propylene polymer of component (A-1) include propylene homopolymer, propylene-ethylene copolymer, propylene-1-butene copolymer, propylene-1-hexene copolymer, propylene-1-octene copolymer. Examples thereof include a polymer, a propylene-ethylene-1-butene copolymer, a propylene-ethylene-1-hexene copolymer, and a propylene-ethylene-1-octene copolymer. A propylene homopolymer, a copolymer of propylene and at least one monomer selected from ethylene and an α-olefin having 4 to 10 carbon atoms is preferable.

  The ethylene-α-olefin copolymer of component (A-2) is a copolymer having an ethylene unit and an α-olefin unit. The α-olefin unit of the component (A-2) includes propylene, 1-butene, 2-methylpropylene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 1 -C3-C8 alpha olefins, such as octene, can be illustrated. Preferably, it is a C3-C8 alpha olefin which has a double bond in terminal carbons, such as propylene, 1-butene, 1-hexene, and 1-octene. One or more of these are used.

  The content of the ethylene unit and α-olefin unit in the component (A-2) is such that the ethylene unit content is 20 to 80% by weight based on the total amount of the ethylene unit and α-olefin unit, and the α-olefin unit is contained. The amount is 80-20% by weight. By making content of an ethylene unit and a C4-C8 alpha olefin unit into a component (A-2) in the said range, the low temperature impact resistance of a thermoplastic elastomer will become favorable. The content of the ethylene unit in the component (A-2) is preferably 25% by weight or more, more preferably 30% by weight or more, and still more preferably 35%, based on 100% by weight of the whole component (A-2) % Or more, preferably 60% by weight or less, more preferably 50% by weight or less. On the other hand, the content of the α-olefin unit of the component (A-2) is preferably 75% by weight or less, more preferably 70% by weight or less, based on 100% by weight of the whole component (A-2). More preferably, it is 65 weight% or less. Further, the content of the α-olefin unit is preferably 40% by weight or more, and more preferably 50% by weight or more. The contents of ethylene units and α-olefin units can be determined by infrared spectroscopy.

  The ethylene-α-olefin copolymer of component (A-2) includes ethylene-propylene copolymer, ethylene-1-butene copolymer, ethylene-1-hexene copolymer, ethylene-1-octene copolymer. Examples thereof include a copolymer, an ethylene-propylene-1-butene copolymer, an ethylene-propylene-1-hexene copolymer, and an ethylene-propylene-1-octene copolymer. Preferably, it is a copolymer of ethylene and an α-olefin having 3 to 10 carbon atoms. In addition, the component (A-1) and the component (A-2) may contain other copolymerization components as long as the effects of the present invention are not impaired.

The content of the component (A-1) in the component (A) is 70% by weight or more, preferably 80% by weight or more, based on the whole component (A) as 100% by weight, from the viewpoint of the rigidity of the molded body. More preferably, it is 85% by weight or more. Further, the content of (A-1) is 95% by weight or less, preferably 93% by weight or less, based on 100% by weight of the whole component (A), from the viewpoint of low temperature impact resistance of the molded product.
The content of component (A-2) in component (A) is 5% by weight or more, preferably 7% or more, with 100% by weight of component (A) from the viewpoint of low temperature impact resistance of the molded product. is there. Further, the content of the component (A-2) is 30% by weight or less, preferably 20% by weight or less, more preferably 20% by weight or less, with the component (A) being 100% by weight from the viewpoint of the rigidity of the molded body. 15% by weight or less.

In addition, the analysis of the content ratio of the component (A-1) and the component (A-2) in the component (A) can be analyzed by a cross fractionation chromatograph (CFC), and the component (A-1) and the component ( It is possible to measure the weight ratio by separating A-2) and to measure the ethylene content by subsequent infrared spectroscopy.
The melt flow rate of component (A) (measuring temperature 230 ° C., measuring load 21.18 N) is not limited, but is usually 0.1 g / min or more, and preferably 10 g / 10 from the viewpoint of the appearance of the molded body. Min. Or more, more preferably 20 g / 10 min or more, and further preferably 30 g / 10 min or more. In addition, the melt flow rate of component (A) (measuring temperature 230 ° C., measuring load 21.18 N) is usually 200 g / 10 min or less, and preferably 150 g / 10 min or less from the viewpoint of tensile strength. More preferably, it is 100 g / 10 minutes or less. The melt flow rate is measured under the conditions of a measurement temperature of 230 ° C. and a measurement load of 21.18 N according to JIS-K7210.

As a method for producing the component (A) propylene-based resin, a known polymerization method using a known olefin polymerization catalyst is used. For example, a multistage polymerization method using a Ziegler-Natta catalyst can be mentioned. As the multistage polymerization method, a slurry polymerization method, a solution polymerization method, a bulk polymerization method, a gas phase polymerization method, or the like can be used, and two or more of these may be combined.
Moreover, the component (A) used for the thermoplastic elastomer composition of the present invention may be a commercially available product. A commercially available polypropylene copolymer (A) can be procured from the manufacturer etc. which are listed below, and can be selected suitably. Commercially available products include Prime Polymer's Prime Polypro (registered trademark), Sumitomo Chemical's Sumitomo Noblen (registered trademark), Sun Allomer's polypropylene block copolymer, Nippon Polypro's Novatec PP (registered trademark), LyondellBasel Moplen (R), ExxonMobil's ExxonMobil PP, Formosa Plastics' Formolene (R), Borealis's Borealis PP, LG Chemical's SEETEC PP, A. Schulman's ASI
POLYPROPYLENE, INEOS PP from INEOS Olefins & Polymers, Braskem PP from Braskem, Sumsung Total PETROCHEMICALS, SumicTOL TAPPAL from SABIC
PETROCHEMICALS Polypropylene, SK Corporation's YUPLENE (registered trademark), and the like.

<Component (B)>
Component (B) has an ethylene unit content of 50 to 80% by weight and a carbon number of 4 to 8 based on the total amount of ethylene unit content and α-olefin unit content of 4 to 8 carbon atoms. An ethylene-α-olefin copolymer rubber having an α-olefin unit content of 50 to 20% by weight.

Examples of the α-olefin having 4 to 8 carbon atoms used for the component (B) include 1-butene, 2-methylpropylene, 1-pentene, 3-methyl-1-butene, 1-hexene and 4-methyl-1- Examples include pentene and 1-octene. Preferably, 1-butene, 1
-It is a C4-C8 alpha olefin which has a carbon-carbon double bond in the terminal carbon atoms, such as hexene and 1-octene. The α-olefin of the component (B) may be one that is copolymerized with ethylene or two or more that are copolymerized with ethylene. In addition, the component (B) may be used alone or in combination of two or more.

  The ethylene-α-olefin copolymer rubber is an ethylene unit and an α-olefin unit having 4 to 8 carbon atoms, as well as other monomer units such as a monomer unit based on a non-conjugated diene (non-conjugated diene unit) or a propylene unit. You may have a body unit. Examples of the non-conjugated diene include 1,4-hexadiene, 1,6-octadiene, 2-methyl-1,5-hexadiene, 6-methyl-1,5-heptadiene, and 7-methyl-1,6-octadiene. Chain non-conjugated dienes; cyclohexadiene, dicyclopentadiene, methyltetrahydroindene, 5-vinylnorbornene, 5-ethylidene-2-norbornene, 5-methylene-2-norbornene, 5-isopropylidene-2-norbornene, 6- And cyclic non-conjugated dienes such as chloromethyl-5-isopropenyl-2-norbornene. 5-Ethylidene-2-norbornene and dicyclopentadiene are preferable.

  The content of the ethylene unit in the component (B) is 50% by weight or more and 80% by weight or less with respect to the total amount of the ethylene unit content and the α-olefin unit content. The content of the ethylene unit in the component (B) is preferably larger in order to prevent fusion due to blocking of the component (B), and is smaller from the viewpoint of low-temperature impact resistance when the thermoplastic elastomer of the present invention is molded. Is preferred. Content of the ethylene unit of a component (B) becomes like this. Preferably it is 55 weight% or more, More preferably, it is 60 weight% or more. The ethylene unit content is preferably 75% by weight or less.

  The content of the α-olefin unit of the component (B) is 20% by weight or more and 50% by weight or less with respect to the total amount of the ethylene unit content and the α-olefin unit content. The content of the α-olefin in the component (B) is preferably larger from the viewpoint of low-temperature impact resistance when the thermoplastic elastomer of the present invention is used as a molded body, and prevents fusion due to blocking of the component (B). For this purpose, a smaller amount is preferable. The content of the α-olefin unit of the component (B) is preferably 25% by weight or more. Further, the content of the α-olefin unit of the component (B) is preferably 45% by weight or less, more preferably 40% by weight or less.

In addition, content of the ethylene unit in a component (B) and content of a C4-C8 alpha olefin unit can each be calculated | required by infrared spectroscopy.
The content of the non-conjugated diene unit or propylene unit in the component (B) is usually 0 to 10% by weight, preferably 0 to 5% by weight, based on the entire component (B). The content of non-conjugated diene units and propylene units can be determined by infrared spectroscopy.

The component (B) may contain other copolymerization components as long as the effects of the present invention are not impaired.
Specific examples of the component (B) used in the thermoplastic elastomer composition of the present invention include ethylene-1-butene copolymer rubber, ethylene-1-hexene copolymer rubber, ethylene-1-octene copolymer rubber, Examples thereof include ethylene-propylene-1-butene copolymer rubber, ethylene-propylene-1-hexene copolymer rubber, and ethylene-propylene-1-octene copolymer rubber. These may be used alone or in combination of two or more. Among these, ethylene-1-butene copolymer rubber and ethylene-1-octene copolymer rubber are preferable.

The melt flow rate of component (B) (measuring temperature 190 ° C., measuring load 21.18 N) is not limited, but is usually 10 g / 10 min or less, and preferably 5 g / 10 from the viewpoint of appearance.
Or less, more preferably 1 g / 10 min or less, and even more preferably 0.5 g / 10 min or less. Further, the melt flow rate of the component (B) is usually 0.01 g / 10 min or more, and from the viewpoint of fluidity, it is preferably 0.05 g / 10 min or more, more preferably 0.10 g / 10. More than a minute. The melt flow rate is measured in accordance with JIS K7210 under conditions of a measurement temperature of 190 ° C. and a measurement load of 21.18N.

  As a manufacturing method of a component (B), the well-known polymerization method using the well-known olefin polymerization catalyst is used. For example, as an olefin polymerization catalyst, a Ziegler-Natta catalyst, a complex catalyst such as a metallocene complex or a nonmetallocene complex can be used, and as a polymerization method, a slurry polymerization method, a solution polymerization method, a bulk polymerization method, a gas polymerization method, Examples thereof include a phase polymerization method. It is also possible to use commercially available products. Examples of commercially available products include Engage (registered trademark) series manufactured by Dow Chemical Company.

  The content of the component (B) is 10 parts by weight or more, preferably 30 parts by weight or more, more preferably 50 parts by weight with respect to 100 parts by weight of the component (A) from the viewpoint of low temperature impact resistance of the molded body. More preferably, it is 60 parts by weight or more. Moreover, content of a component (B) is 200 weight part or less with respect to 100 weight part of components (A) from a viewpoint of the rigidity of a molded object, Preferably it is 170 weight part or less, More preferably, it is 140 weight part Part or less, more preferably 120 parts by weight or less.

<Ingredient (C)>
Component (C) has a propylene unit content of 80 to 92% by weight and an ethylene unit content of 20 to 8% by weight with respect to the total content of propylene unit content and ethylene unit content, A propylene-ethylene copolymer having a melt flow rate (measuring temperature 230 ° C., measuring load 21.18 N) of 1 to 50 g / 10 min and a density of 0.890 g / cm ³ or less. Here, the component (C) does not include the component (A).

  The content of propylene units is 80% by weight or more, preferably 82% by weight or more based on the total content of propylene units and ethylene units in component (C), The content is 92% by weight or less, preferably 90% by weight or less. When the content of the propylene unit is equal to or higher than the lower limit value, poor fusion due to blocking is reduced, and when the content is equal to or lower than the upper limit value, the low-temperature impact resistance of the molded body is improved.

  Further, the content of the ethylene unit is 8% by weight or more, preferably 10% by weight or more, more preferably 12% by weight or more with respect to the total content of the propylene unit and the ethylene unit in component (C) On the other hand, it is 20% by weight or less, preferably 18% by weight or less. When the content of the ethylene unit is not less than the lower limit value, the molded article has good low temperature impact resistance, and when it is not more than the upper limit value, poor fusion due to blocking is reduced.

The content of propylene units and the content of ethylene units in component (C) can be determined by infrared spectroscopy.
In addition, the component (C) may contain other copolymerization components as long as the effects of the present invention are not impaired.
The melt flow rate of component (C) (measuring temperature 230 ° C., measuring load 21.18 N) is 1 g / 10 min or more, more preferably 2 g / 10 min or more, and further preferably 5 g / 10 min or more. . The melt flow rate (measuring temperature 230 ° C., measuring load 21.18 N) is 50 g / 10 min or less, preferably 40 g / 10 min or less, more preferably 30 g / 10 min or less, more preferably 20 g / 10 min or less. When the melt flow rate of the component (C) is equal to or higher than the lower limit value, the molded appearance is good, and when it is equal to or lower than the upper limit value, the mechanical strength is good.

The melt flow rate is measured according to JIS K7210 under the conditions of a measurement temperature of 230 ° C. and a measurement load of 21.18N.
The density of the component (C) is at 0.890 g / cm ³ or less, preferably 0.885 g / cm ³ or less, more preferably 0.880 g / cm ³ or less, more preferably 0.875 g / cm ³ or less. When the density of a component (C) is below the said upper limit, the low temperature impact resistance of a molded object becomes favorable. Further, the lower limit of the density of the component (C) is not particularly limited, but is usually 0.850 g / cm ³ or more, preferably 0.855 g / cm ³ or more, more preferably 0.860 g / cm ³ or more. is there.

  Examples of the method for producing component (C) include slurry polymerization method, solution polymerization method, bulk polymerization method, gas phase polymerization method using nonmetallocene complex catalyst such as heteroaryl ligand catalyst described in JP-T-2005-508416. Examples thereof include a phase polymerization method. Moreover, it is also possible to appropriately select from commercially available products such as Versify (registered trademark) series manufactured by Dow Chemical Company.

  The content of the component (C) is 10 parts by weight or more, preferably 15 parts by weight or more, more preferably 20 parts by weight or more with respect to 100 parts by weight of the component (A) from the viewpoint of the appearance of the molded body. . Moreover, content of a component (C) is 100 weight part or less with respect to 100 weight part of a component (A) from a viewpoint of the low temperature impact strength of a molded object, Preferably it is 80 weight part or less, More preferably, it is 60 weight. Or less.

<Component (D)>
The thermoplastic elastomer composition of the present invention preferably further contains the following component (D) from the viewpoint of improving the appearance when formed into a molded article such as an airbag housing cover.
Component (D): Styrene / conjugated diene block copolymer and / or hydrogenated product thereof Suitable conjugated diene in the styrene / conjugated diene block copolymer and / or hydrogenated product of component (D) is butadiene, isoprene or It is a mixture of these. For example, a styrene-butadiene block copolymer (hereinafter sometimes simply referred to as “SBS”) and / or a hydrogenated product thereof (hereinafter simply referred to as “hydrogenated SBS”). Styrene / ethylene / butylene / styrene copolymer (SEBS) or hydrogenated styrene / isoprene block copolymer (hereinafter simply abbreviated as “hydrogenated S-I-S”). ) Styrene / ethylene / propylene / styrene copolymer (SEPS), hydrogenated product of styrene / butadiene / isoprene block copolymer (hereinafter simply referred to as “hydrogenated S-BI-S”) ).

  The styrene content of the styrene / conjugated diene block copolymer and / or its hydrogenated product (D) is not particularly limited, but is preferably 5% by weight or more, more preferably 8% by weight from the viewpoint of strength and heat resistance. It is above, More preferably, it is 10 weight% or more. The styrene content is preferably 50% by weight or less, more preferably 45% by weight or less, and still more preferably 40% by weight or less from the viewpoints of flexibility and impact resistance.

  The styrene / conjugated diene block copolymer of component (D) and / or the conjugated diene of the hydrogenated product has a 1,2-microstructure analyzed by NMR method of preferably 60% or less, more preferably 45% or less. If the 1,2-microstructure exceeds 60%, the moldability and flexibility tend to decrease. From the viewpoint of weather resistance, the component (D) is preferably a hydrogenated styrene / conjugated diene block copolymer, and the hydrogenation rate is preferably 90% or more, more preferably 95% or more.

The weight ratio (isoprene / butadiene) when the conjugated diene in the styrene / conjugated diene block copolymer of component (D) and / or its hydrogenated product is a mixture of isoprene and butadiene is generally 99/1 to 1/99, It is preferably 90 / 10-30 / 70, particularly preferably 80 / 20-40 / 60.
The weight average molecular weight of the hydrogenated styrene / conjugated diene block copolymer of component (D) and / or the hydrogenated product thereof is preferably 50,000 or more, more preferably from the viewpoint of product gloss and mechanical strength. Is 80,000 or more, more preferably 100,000 or more. The weight average molecular weight is preferably 1,000,000 or less, more preferably 800,000 or less, and still more preferably 500,000 or less, from the viewpoint of the appearance of the molded body.

  As a method for producing these styrene / conjugated diene block copolymers, for example, a styrene / conjugated diene block copolymer is produced in an inert solvent using a lithium catalyst by the method described in Japanese Patent Publication No. 40-23798. In addition, for the hydrogenated styrene / conjugated diene block copolymer, the styrene / conjugated diene block copolymer is synthesized as described above, and then, for example, Japanese Patent Publication No. 42-8704, Examples include the method of hydrogenation in the presence of a hydrogenation catalyst in an inert solvent by the methods described in JP-A-43-6636, JP-A-59-133203, and JP-A-60-79005. be able to. Hydrogenated S-BI-S is synthesized by, for example, a method described in JP-A-3-188114.

  The styrene / conjugated diene block copolymer and / or a hydrogenated product thereof can be obtained as a commercial product. Examples of the styrene / conjugated diene block copolymer include “Clayton (registered trademark) D” manufactured by Kraton Polymer Co., Ltd. Examples of hydrogenated styrene / conjugated diene block copolymers include “Clayton (registered trademark) G” manufactured by Kraton Polymer Co., Ltd., “Septon (registered trademark)” manufactured by Kuraray Co., Ltd., “Tuftec (registered trademark)” manufactured by Asahi Kasei Corporation Trademark) ”and the like.

From the viewpoint of appearance, the component (D) is preferably 1 part by weight or more, preferably 5 parts by weight or more, more preferably 10 parts by weight or more with respect to 100 parts by weight of the component (A). On the other hand, the component (D) is preferably 50 parts by weight or less, more preferably 40 parts by weight or less, and still more preferably from 100 parts by weight of the component (A) from the viewpoint of low temperature impact resistance of the molded product. Is 30 weight or less.

<Ingredient (E)>
The thermoplastic elastomer composition of the present invention preferably contains the following component (E) from the viewpoint of moldability of the airbag housing cover.
Component (E): Softener for hydrocarbon rubber The weight average molecular weight of component (E) is preferably 300 or more, more preferably 500 or more, from the viewpoint of preventing stickiness of the molded article of the airbag housing cover. The weight average molecular weight of component (E) is preferably 2,000 or less, more preferably 1,500 or less, from the viewpoint of moldability of the airbag housing cover.

Component (E) is generally a mixture of aromatic rings, naphthene rings, and paraffin rings, and the one in which the number of carbon atoms in the paraffin chain accounts for 50% or more of the total carbon is called paraffinic oil. Those having a naphthene ring carbon number of 30 to 45% are called naphthenic oils, and those having more than 30% aromatic carbon are called aromatic oils. Of these, paraffinic oil is preferably used from the viewpoint of weather resistance. The paraffinic oil preferably has a kinematic viscosity at 40 ° C. of 20 to 800 cst, and more preferably 50 to 600 cst. The pour point of paraffinic oil is usually 0 to -40 ° C, preferably 0 to -30 ° C. Flash point (COC) of paraffinic oil
Is usually 200 to 400 ° C, preferably 250 to 350 ° C.

Component (E) is component (A) from the viewpoint of moldability when it is used as an airbag storage cover or the like.
The amount is preferably 1% by weight or more, more preferably 5% or more, and more preferably 10% by weight or more with respect to 100 parts by weight. On the other hand, the component (E) is preferably 50 parts by weight or less, more preferably 40 parts by weight or less, with respect to 100 parts by weight of the component (A), from the viewpoint of shape retention of the airbag storage cover and developability at high temperatures. 30 weight or less is more preferable.

<Other optional components>
Furthermore, in the thermoplastic elastomer composition of the present invention, the following additives and components (A) to (D) other than the above-described components are used in accordance with various purposes within a range that does not significantly impair the effects of the present invention. Arbitrary components, such as resin (henceforth "other resin"), can be mix | blended.
Optional ingredients include colorants, antioxidants, heat stabilizers, light stabilizers, UV absorbers, neutralizers, lubricants, anti-clouding agents, anti-blocking agents, slip agents, flame retardants, dispersants, antistatic agents. And various additives such as conductivity imparting agents, metal deactivators, molecular weight regulators, antibacterial agents and fluorescent brighteners. For example, the antioxidant is used in the range of 0.01 to 0.5 parts by weight per 100 parts by weight of the total amount of components (A) to (E).

  Examples of other resins that can be contained in the thermoplastic elastomer composition of the present invention include polyester resins, polyamide resins, styrene resins, acrylic resins, polycarbonate resins, polyvinyl chloride resins, and various other elastomers. Other resins mentioned above may contain only one type or two or more types.

[Method for producing thermoplastic elastomer composition]
The thermoplastic elastomer composition of the present invention comprises the above components (A), (B) and (C) and, if necessary, the components (D) and / or (E) as usual extruders, Banbury mixers, It can be produced by kneading by a conventional method using a roll, a Brabender plastograph, a kneader Brabender or the like. Among these production methods, it is preferable to use an extruder, particularly a twin screw extruder. When the thermoplastic elastomer composition of the present invention is produced by kneading with an extruder or the like, the thermoplastic elastomer composition can be usually produced by melt-kneading while being heated to 160 to 240 ° C, preferably 180 to 220 ° C. Furthermore, you may make it partially bridge | crosslink by mix | blending the following crosslinking agent and crosslinking adjuvant with the thermoplastic elastomer composition of this invention, and heat-processing dynamically.

As a crosslinking agent for partially crosslinking the thermoplastic elastomer composition of the present invention, an organic peroxide is preferably used, and 2,5-dimethyl-2,5-di (t-butylperoxy) hexane is preferably used. 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne-3, 1,3-bis (t-butylperoxyisopropyl) benzene, 1,1-di (t-
(Butylperoxy) 3,5,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di (peroxybenzoyl) hexyne-3, dicumyl peroxide and the like.

  Examples of crosslinking aids used for partial crosslinking with these organic peroxides include compounds having N, N′-m-phenylene bismaleimide, toluylene bismaleimide, P-quinone dioxime, nitrobenzene, Diphenylguanidine, trimethylolpropane, divinylbenzene, ethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, allyl methacrylate and other compounds having a radically polymerizable carbon-carbon double bond, and component (B) or component Examples thereof include compounds having a functional group that reacts with the carbon-carbon double bond or carbon straight-chain part of (D).

[Physical properties and uses of thermoplastic elastomer compositions]
The thermoplastic elastomer of the present invention is excellent in appearance, low-temperature impact resistance, rigidity and the like by containing a specific amount of the components (A) to (C). By using α-olefin units having 4 to 8 carbon atoms in the α-olefin copolymer rubber, for example, α-olefins having 3 carbon atoms as described in Examples of JP 2009-263471 A are used. Compared with the conventional products, the low temperature impact resistance is particularly improved. The reason why the low temperature impact resistance is particularly improved in the thermoplastic elastomer composition of the present invention is that, by using an α-olefin unit having 4 to 8 carbon atoms as the component (B), α having 3 carbon atoms can be obtained. -It is presumed that the branched chain of α-olefin was extended as compared with the case of using an olefin unit, and the interaction at the interface between molecules was enhanced.

The thermoplastic elastomer composition of the present invention preferably further satisfies the following physical properties.
The thermoplastic elastomer composition of the present invention usually has a melt flow rate of 0.1 g / 10 min or more at a temperature of 230 ° C. and a measurement load of 21.18 N in accordance with JIS K7210. From the viewpoint of fluidity, it is preferably 5 g / 10 minutes or more, more preferably 6 g / 10 minutes or more, and further preferably 7 g / 10 minutes or more. In addition, the melt flow rate is usually 100 g / 10 min or less, and from the viewpoint of preventing sink marks and burrs when forming the airbag housing cover, the melt flow rate is preferably 60 g / 10 min or less, more preferably It is 40 g / 10 min or less, more preferably 30 g / 10 min or less, particularly preferably 20 g / 10 min or less.

  In the thermoplastic elastomer composition of the present invention, the flexural modulus according to JIS K7203 is preferably 100 MPa or more, more preferably 200 MPa or more, and further preferably 250 MPa or more, from the viewpoint of load deflection. The flexural modulus is preferably 700 MPa or less, more preferably 600 MPa or less, further preferably 550 MPa or less, and further preferably 500 MPa or less, from the viewpoint of low-temperature impact resistance of the molded body.

The thermoplastic elastomer composition of the present invention preferably has physical properties such that the Izod impact strength at −40 ° C. according to JIS K7110 is 50 kJ / m ² or more. When the Izod impact strength is less than the above range, the low-temperature impact resistance tends to be low because the low-temperature impact resistance is inferior. On the other hand, the upper limit of the Izod impact strength of the thermoplastic elastomer composition of the present invention is not particularly limited, but is usually 150 kJ / m ² or less.

  The thermoplastic elastomer of the present invention is useful as a raw material for an airbag storage cover because it is excellent in appearance, low-temperature impact resistance, rigidity and the like, but its use is not limited to the airbag storage cover. Applications other than airbag storage covers include instrument panels, center panels, center console boxes, doors and rims, pillars, assist grips, automotive interior parts such as handles, automotive exterior parts such as malls, home appliance parts, building materials, furniture Etc.

The above-mentioned thermoplastic elastomer composition is generally used for an air bag by using a general injection molding method or, if necessary, various molding methods such as a gas injection molding method, an injection compression molding method, and a short shot foam molding method. A storage cover can be formed.
In particular, the molding conditions for injection molding the airbag storage cover are as follows. The molding temperature when the airbag housing cover is injection-molded is generally 150 to 300 ° C, preferably 180 to 280 ° C. The injection pressure is usually 5 to 100 MPa, preferably 10 to 80 MPa. The mold temperature is usually 0 to 80 ° C., preferably 20 to
60 ° C.

  The airbag storage cover thus obtained is an airbag system that operates by sensing the impact and deformation of a high-speed moving body such as an automobile in the event of a collision accident and protects the occupant by inflating and deploying. Used as an airbag storage cover.

  EXAMPLES Hereinafter, although the content of this invention is demonstrated more concretely using an Example, this invention is not limited by a following example, unless the summary is exceeded. The values of various production conditions and evaluation results in the following examples have meanings as preferred values of the upper limit or lower limit in the embodiments of the present invention, and preferred ranges are the above-described upper limit or lower limit values and the following values: It may be a range defined by a combination of values of the examples or values of the examples.

The raw materials and the evaluation methods used in the following examples and comparative examples are as follows.
<Raw materials>
・ Ingredient (A)
a-1: Commercially available polypropylene block copolymer (obtained by polymerizing component (A-1) in the first step and then polymerizing component (A-2) in the second step).
MFR = 60 g / 10 min (measuring temperature 230 ° C., measuring load 21.18 N), content of component (A-1) = 92 wt%, content of component (A-2) = 8 wt%, component (A -1) propylene unit content = 100 wt%, component (A-2) ethylene unit content = 43 wt%, propylene unit content 57 wt%, melting temperature = 163 ° C

・ Ingredient (B)
b-1: Enage (registered trademark) 7487 manufactured by Dow Chemical Company
Ethylene-butene copolymer, ethylene unit content = 70 wt%, 1-butene unit content = 30 wt%, MFR = 0.2 g / 10 min (measuring temperature 190 ° C., measuring load 21.18 N), density = 0.86 g / cm ³

・ Ingredient (C)
c-1: Versify (registered trademark) 3401 manufactured by Dow Chemical Co., Ltd.
Propylene-ethylene copolymer, MFR = 8 g / 10 min (measuring temperature 230 ° C., measuring load 21.18 N), density = 0.864 g / cm ³ , ethylene unit content = 16 wt%, propylene unit content = 84% by weight
c-2: Versify (registered trademark) 3300 manufactured by Dow Chemical Co., Ltd.
Propylene-ethylene copolymer, MFR = 8 g / 10 min (measuring temperature 230 ° C., measuring load 21.18 N), density = 0.866 g / cm ³ , ethylene unit content = 14% by weight, propylene unit content = 86% by weight

・ Ingredient (D)
d-1 Kraton Kraton (registered trademark) G1651H
Hydrogenated styrene / butadiene block copolymer (styrene / ethylene / butylene / styrene copolymer (SEBS)), weight average molecular weight 264,000, styrene content 33%, conjugated diene component 1,2-microstructure 30%

・ Ingredient (E)
e-1: Idemitsu Kosan PW90
Paraffin oil (kinematic viscosity at 40 ° C 95.54 cSt (centistokes), pour point -15 ° C, flash point 272 ° C)

-Component (A) to be compared a-2: Novatec (registered trademark) PP MA1B manufactured by Nippon Polypro Co., Ltd.
Propylene homopolymer, MFR = 20 g / 10 min (measuring temperature 230 ° C., measuring load 21.18 N), content of component (A-1) = 100 wt%, content of component (A-2) = 0 weight %, Propylene unit content of component (A-1) = 100 wt%, melting temperature = 164 ° C.

-Component (B) comparison target b-2: EP57C manufactured by JSR
Ethylene-propylene-5-ethylidene-2-norbornene copolymer rubber, Mooney viscosity (ML1 + 4, 125 ° C.) = 61, ethylene unit content = 69 wt%, propylene unit content 31 wt%, ethylene unit and propylene unit Ethylidene norbornene content with respect to 100 parts by weight in total = 4.8 parts by weight, weight average molecular weight in terms of polypropylene (PP) 333,000, density = 0.86 g / cm ³

Component (C) for comparison c-3: Novatec (registered trademark) PP MG03B manufactured by Nippon Polypro Co., Ltd.
Random polypropylene, MFR: 30 g / 10 min (measurement temperature 230 ° C., measurement load 21
. 18N), density = 0.890 g / cm ³ , ethylene unit content = 3 wt%, propylene unit content = 97 wt%

<Evaluation method>
In the following measurements (2) to (4), an in-line screw type injection molding machine (“IS130” manufactured by Toshiba Machine Co., Ltd.) was used for bending at an injection pressure of 50 MPa, a cylinder temperature of 220 ° C., and a mold temperature of 40 ° C. An elastic modulus test piece was formed into a test piece having a thickness of 4 mm, a width of 10 mm, and a length of 80 mm, and a test piece for Izod impact strength was made to have a notch thickness of 4 mm × width of 12.7 mm × length of 64 mm. The test piece was molded into a test piece, and a sheet (thickness 2 mm × width 120 mm × length 80 mm) was formed and punched and used according to JIS K6251 (JIS-3 dumbbell). In the evaluation of the molding appearance of (5), an inline screw type injection molding machine (“SE180” manufactured by Sumitomo Machinery Co., Ltd.) was used, with the injection pressure of 80 MPa, the cylinder temperature of 220 ° C., and the mold temperature of 40 ° C. A test piece having a thickness of 3 mm, a width of 200 mm, and a length of 200 mm having a thickness of 0.7 mm was used.

1) Melt flow rate (MFR, unit: g / 10 min)
According to JIS K7210, the measurement was performed under the conditions of a measurement temperature of 230 ° C. and a measurement load of 21.18N.
2) Flexural modulus (unit: MPa)
According to JIS K7203, the measurement was performed under the conditions of a span interval of 64 mm and a bending speed of 1 mm / min. It shows that rigidity is excellent, so that the value of a bending elastic modulus is high.

3) Izod impact strength (unit: kJ / m ² )
The temperature was measured at -40 ° C according to JIS K7110. The case where it was not destroyed was indicated as “NB”.
4) Tensile test (JIS-3 dumbbell, tensile speed 500mm / min)
According to JIS K6251, the tensile breaking strength (unit: MPa) and the tensile breaking elongation (unit:%) were measured. It shows that it is excellent in the expansion | deployment performance of an airbag storage cover, so that the value of a tensile fracture test is high.

5) Evaluation of molding appearance The appearance of the injection-molded article was visually observed, and the state of occurrence of the flow mark and the state of uneven gloss of the tear line portion were evaluated as follows.
Flow mark occurrence state:
“◯”: Good (no flow mark confirmed visually)
"X": Defect (a flow mark was confirmed visually)
State of gloss on the tear line:
“◎”: Very good (nearly uneven luster in the tear line portion was confirmed)
“Good”: Good (no noticeable glossy irregularities were found in the tear line part)
“×”: Defect (a gloss unevenness that was noticeable in the tear line portion was confirmed.)
6) Ethylene unit content of c-1 and c-2, propylene unit content (unit: wt%)
About c-1 and c-2, it measured by the infrared spectroscopy (FT / IR-60 by JASCO).

<Examples 1-4 and Comparative Examples 1-4>
[Example 1]
100 parts by weight of the above-mentioned a-1, 80 parts by weight of b-1, and 20 parts by weight of c-1 are further blended, and further 100 parts by weight of the total of a-1, b-1 and c-1 above. 0.1 parts by weight of an antioxidant (trade name Irganox 1010 manufactured by BASF) and 1.5 parts by weight of a black pigment (carbon concentration 40% product) were blended for 1 minute in a Henschel mixer, and the same direction twin screw extruder ( Kobe Steel “TEX30α”, L / D = 45, number of cylinder blocks = 13) is charged at a rate of 20 kg / h, heated in the range of 180-210 ° C., melt-kneaded, pelletized, and thermoplastic elastomer A composition was prepared. Evaluation of said 1) -5) was implemented about the obtained thermoplastic elastomer composition. The evaluation result of the obtained molded body is shown in Table-1.

[Examples 2 to 4 and Comparative Examples 1 to 4]
A thermoplastic elastomer was produced in the same manner as in Example 1 except that the materials shown in Table 1 were used. The evaluation result of the obtained molded body is shown in Table-1.

[Evaluation of results]
In Examples 1 to 3, the components (A) to (C) were blended, whereby the rigidity and low temperature impact resistance were excellent, and the glossiness of the tear line portion was good. In Example 4, in addition to the components (A) to (C), the component (D) and the component (E) were blended, whereby the glossiness of the tear line portion was further improved.

  Moreover, although the comparative example 1 mix | blended b-2 without mix | blending a component (B), it was inferior to low temperature impact resistance. In Comparative Example 2, (a-2) was blended without blending the component (A), but the impact resistance was inferior, and the state of occurrence of flow marks and the state of uneven luster of the tear line were poor. . In Comparative Example 3, c-3 was blended without blending the component (C), but the low temperature impact resistance and tensile strength were inferior and the glossiness of the tear line portion was poor. Although the comparative example 4 did not mix | blend a component (C), the glossiness state of the tear line part was bad.

  The thermoplastic elastomer composition of the present invention is very useful as an airbag storage cover because it is excellent in rigidity, low-temperature impact resistance, deployment performance when used as an airbag storage cover, and the like. Moreover, since the thermoplastic elastomer composition of the present invention is excellent in appearance when molded, it can also be used as a non-coated airbag housing cover that is advantageous in terms of cost. The thermoplastic elastomer composition of the present invention further includes an instrument panel, a center panel, a center console box, a door and a rim, a pillar, an assist grip, a car interior part such as a handle, a car exterior part such as a mall, a home appliance part, a building material, It is also useful for furniture.

Claims (5)

The following components (A), (B) and (C) are contained, and 10 to 200 parts by weight of component (B) and 10 to 100 parts by weight of component (C) are included with respect to 100 parts by weight of component (A). Thermoplastic elastomer composition.
Component (A): The following component (A-1) is polymerized in the first step, and then the following component (A-2) is polymerized in the second step, and component (A-1) and component (A- 2) Polypropylene polymer component (A-1) in which the content of component (A-1) is 70 to 95% by weight and the content of component (A-2) is 30 to 5% by weight ): Propylene-based polymer having a propylene unit content of 90 to 100% by weight Component (A-2): Ethylene-α-olefin copolymer component (B) having an ethylene unit content of 20 to 80% by weight ): The ethylene unit content is 50 to 80% by weight and the C4 to C8 α-olefin unit is the total amount of the ethylene unit content and the C4 to C8 α-olefin unit content. Ethylene-α-olefin copolymer rubber component having a content of 50 to 20% by weight ( C): The content of propylene units is 80 to 92% by weight, the content of ethylene units is 20 to 8% by weight, and the melt flow rate with respect to the total content of propylene units and ethylene units Propylene-ethylene copolymer having a measurement temperature of 230 ° C. and a measurement load of 21.18 N of 1 to 50 g / 10 min and a density of 0.890 g / cm ³ or less. The thermoplastic elastomer composition according to claim 1, comprising 1 to 50 parts by weight of the following component (D) with respect to 100 parts by weight of the component (A).
Component (D): Styrene / conjugated diene block copolymer and / or hydrogenated product thereof The thermoplastic elastomer composition according to claim 1 or 2, comprising 1 to 50 parts by weight of the following component (E) with respect to 100 parts by weight of the component (A).
Component (E): Hydrocarbon softener The thermoplastic elastomer composition according to any one of claims 1 to 3, which satisfies the following characteristics (1) to (3):
(1) Melt flow rate at a measurement temperature of 230 ° C. according to JIS K7210 and a measurement load of 21.18 N is 0.1 to 100 g / 10 minutes (2) Flexural modulus according to JIS K7203 is 100 MPa or more (3) JIS Notched Izod impact strength at a temperature of −40 ° C. according to K7110 is 50 kJ / m ² or more   An airbag storage cover comprising the thermoplastic elastomer composition according to any one of claims 1 to 4.