JP7622382B2 - Thermoplastic elastomer composition, injection molded product and airbag storage cover - Google Patents

Description

The present invention relates to a thermoplastic elastomer composition, and an injection-molded article and an airbag storage cover made from this thermoplastic elastomer composition.

An automobile airbag system is a system that protects the driver and passengers in the event of a collision, and consists of a device that detects the impact of the collision and an airbag device. This airbag device is installed in the steering wheel, the instrument panel in front of the passenger seat, the driver's and passenger's seats, the front and side pillars, etc.

Various proposals have been made regarding the structure and materials of the airbag storage cover in an airbag device so that it will tear as designed when the airbag inflates.

As an airbag storage cover made of an olefin-based thermoplastic elastomer, for example, Patent Document 1 proposes a thermoplastic elastomer composition obtained by dynamically heat treating a composition containing a specific propylene-based polymer, a specific olefin-based block copolymer, and a specific amount of a styrene-conjugated diene block copolymer and/or a hydrogenated product thereof in the presence of an organic peroxide.

JP 2016-186041 A

In recent years, there has been concern that airbag storage covers may break at low temperatures due to increased airbag deployment power, and therefore materials with excellent low-temperature impact resistance are desired from the standpoint of improving safety and freedom of design. In addition, airbag storage covers have traditionally been manufactured through a painting process, but there are issues with the cost of the painting process, such as the need to add painting lines, and in order to manufacture more cheaply, there has been a demand in recent years for materials that can be manufactured without painting. Furthermore, compared to unpainted airbag storage covers, from the standpoint of design, there is a demand for molded products with low gloss and improved flow mark properties.

According to detailed studies by the present inventors, it has been found that the thermoplastic elastomer composition described in the above-mentioned Patent Document 1 has problems such as poor flow mark resistance and insufficient appearance.
The present invention has been made in consideration of the above problems of the conventional technology. That is, an object of the present invention is to provide a thermoplastic elastomer composition which enables the production of molded products having low gloss and excellent flow mark properties while maintaining low-temperature impact resistance.

As a result of extensive research into solving the above problems, the present inventors have found that the above problems can be solved by setting the die swell ratio (test temperature 210°C, shear rate 243/s) in a capillary rheometer (JIS K7199) to 1.10 or more in a resin composition obtained by dynamically heat treating a composition containing a propylene-based block copolymer and an ethylene-α-olefin copolymer in the presence of a crosslinking agent and a crosslinking aid.

That is, the gist of the present invention lies in the following [1] to [9].

[1] A thermoplastic elastomer composition obtained by dynamically heat treating a composition containing the following components (A) and (B) in the presence of the following components (C) and (D), wherein the thermoplastic elastomer composition has a die swell ratio (test temperature 210°C, shear rate 243/s) of 1.10 or more as measured using a capillary rheometer (JIS K7199):
Component (A): Propylene-based block copolymer Component (B): Ethylene/α-olefin copolymer Component (C): Organic peroxide Component (D): Crosslinking aid

[2] The thermoplastic elastomer composition according to [1], wherein the α-olefin of component (B) has 4 to 8 carbon atoms.

[3] The thermoplastic elastomer composition according to [1] or [2], wherein the ethylene/α-olefin copolymer of component (B) is an ethylene/α-olefin block copolymer.

[4] The thermoplastic elastomer composition according to [3], wherein the ethylene/α-olefin block copolymer is an ethylene/α-olefin block copolymer containing a polymer block of ethylene and an ethylene/α-olefin copolymer block.

[5] The thermoplastic elastomer composition according to [4], in which the ethylene-α-olefin block copolymer has a crystalline melting peak at 110 to 125°C and a crystalline melting heat of 20 to 60 J/g.

[6] The thermoplastic elastomer composition according to any one of [1] to [5], further comprising the following component (E):
Component (E): Styrene-conjugated diene block copolymer and/or hydrogenated product thereof

[7] The thermoplastic elastomer composition according to any one of [1] to [6], further comprising the following component (F):
Component (F): Hydrocarbon-based rubber softener

[8] An injection-molded product obtained by injection molding a thermoplastic elastomer composition according to any one of [1] to [7].

[9] An airbag storage cover using the thermoplastic elastomer composition described in any one of [1] to [7].

According to the present invention, there is provided a thermoplastic elastomer composition which enables the production of molded articles having low gloss and excellent flow mark resistance while maintaining low-temperature impact resistance.
The airbag storage cover made of the molded product of the present invention can be suitably used as any of a driver's seat airbag storage cover, a passenger seat airbag storage cover, a pedestrian airbag storage cover, a knee airbag storage cover, a side airbag storage cover, a curtain airbag storage cover, etc.

The present invention will be described in detail below, but the present invention is not limited to the following description, and can be modified as desired without departing from the gist of the present invention. In this specification, when "~" is used to express a numerical value or physical property value before and after the value, the value before and after the value is included.

In the present invention, "airbag storage cover" refers to the container that stores an airbag in general, such as the opening in a container that stores an airbag when the airbag deploys, or the entire container that is integrated with this opening.

[Thermoplastic elastomer composition]
The thermoplastic elastomer composition of the present invention is a thermoplastic elastomer composition obtained by dynamically heat treating a composition containing the following components (A) and (B) in the presence of the following components (C) and (D), and has a die swell ratio (test temperature: 210°C, shear rate: 243/s) (hereinafter sometimes simply referred to as "die swell ratio") of 1.10 or more in a capillary rheometer (JIS K7199).
Component (A): Propylene-based block copolymer Component (B): Ethylene/α-olefin copolymer Component (C): Organic peroxide Component (D): Crosslinking aid

<Die swell ratio>
It has been found that the thermoplastic elastomer composition of the present invention tends to have good flow mark properties when the die swell ratio is 1.10 or more. It is believed that when the thermoplastic elastomer composition of the present invention has a die swell of 1.10 or more, the flow front in the mold during injection molding becomes stable, improving the flow mark properties. The die swell ratio of the thermoplastic elastomer composition of the present invention is preferably 1.13 or more, more preferably 1.15 or more. There is no upper limit to the die swell ratio of the thermoplastic elastomer composition, but it is usually 2.00 or less.

In the present invention, the die swell ratio in a capillary rheometer (JIS K7199) is a value measured during the extrusion process of a sample under the following conditions using a Capillograph 1D (JIS K7199) manufactured by Toyo Seiki Seisakusho Co., Ltd., and is calculated by the following calculation formula (I).
Test temperature: 210°C
L/D: 10 (D=1mm)
Shear rate: 243/s
St=Dm/Dt (I)
St, Dm, and Dt indicate the following.
St: die swell ratio Dm: diameter (mm) of extruded sample measured at test temperature at a position 10 mm below the die exit
Dt: diameter of the capillary die measured at the test temperature (mm)

In order to obtain a thermoplastic elastomer composition having a die swelling ratio of 1.10 or more by subjecting a composition containing the above-mentioned components (A) and (B) to dynamic heat treatment in the presence of components (C) and (D), it is preferable to take the following measures, for example.
From the viewpoint of the manufacturing method, it is preferable to dynamically heat-treat a mixture of a part of component (A), component (B), component (C), and component (D), and if necessary, component (E) and component (F) described below to partially crosslink the mixture, and then add the remainder of component (A). In this way, the component (A) added later is less susceptible to molecular chain scission by radicals, the tensile strength of the composition can be maintained high, and the die swell ratio can be controlled to 1.10 or more. The part of component (A) and the remainder of component (A) may be one or more kinds as long as they correspond to the component (A) described below, and the part of component (A) and the remainder of component (A) may be the same or different.
As components to be added after partial crosslinking by dynamic heat treatment, it is considered that the die swell ratio can be increased by component (B), component (E) and component (F) in addition to component (A). Therefore, with regard to component (B), component (E) and component (F), one or more of these may be partially added and mixed before partial crosslinking by dynamic heat treatment, and the remainder may be added after partial crosslinking by dynamic heat treatment.

<Component (A)>
The thermoplastic elastomer composition of the present invention contains a propylene-based block copolymer as component (A). The propylene unit content of the propylene-based block copolymer of component (A) is usually more than 50% by mass, preferably 70 to 99% by mass, based on the entire component (A). When the propylene unit content of component (A) is equal to or more than the above lower limit, the heat resistance and rigidity tend to be good. When the propylene unit content of component (A) is equal to or less than the above upper limit, the low-temperature impact resistance tends to be good. When component (A) is constituted by mixing two or more propylene-based polymers having different compositions, the propylene unit content of component (A) as a whole may be within the above numerical range.

The propylene unit content and α-olefin unit content described below in component (A), and the ethylene unit content and α-olefin unit content described below in component (B) can each be determined by infrared spectroscopy.

Component (A) contains propylene units in the above-mentioned preferred content relative to the entire component (A), and also contains ethylene units other than propylene units, α-olefin units other than propylene (hereinafter sometimes referred to as "other α-olefins") units, monomer units other than ethylene and α-olefins, etc. Examples of the propylene-based block copolymer of component (A) include propylene-ethylene block copolymers, propylene-other α-olefin block copolymers, propylene-ethylene-other α-olefin block copolymers, and other propylene-based block copolymers.

The total content of ethylene units other than propylene units, other α-olefin units, and other monomer units in component (A) is preferably 1 to 30 mass%.

When component (A) is a propylene-other α-olefin block copolymer, the α-olefin units other than propylene can include α-olefin units having 4 to 20 carbon atoms. Examples of α-olefins having 4 to 20 carbon atoms include 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, 1-tridecene, 1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-nonadecene, 1-eicosene, 3-methyl-1-butene, 3-methyl-1-pentene, 4-methyl-1-pentene, 2-ethyl-1-hexene, and 2,2,4-trimethyl-1-pentene. The α-olefin other than propylene is preferably an α-olefin having 4 to 10 carbon atoms, more preferably 1-butene, 1-hexene, or 1-octene.
These other α-olefin units may be contained in component (A) either alone or in combination of two or more kinds.

Examples of the propylene-based block copolymer of component (A) include propylene-ethylene block copolymer, propylene-1-butene block copolymer, propylene-1-hexene block copolymer, propylene-1-octene block copolymer, propylene-ethylene-1-butene block copolymer, propylene-ethylene-1-hexene block copolymer, propylene-ethylene-1-octene block copolymer, and propylene-based block copolymers obtained by polymerizing a propylene homopolymer in the first step and then polymerizing a propylene-ethylene block copolymer in the second step.

Preferably, it is a block copolymer of propylene and at least one monomer selected from ethylene and an α-olefin having 4 to 10 carbon atoms, or 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. Among these, it is particularly preferable that component (A) is 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, from the viewpoint of low-temperature impact resistance and high-temperature strength.

The melt flow rate (230°C, load 21.18N) of component (A) is not limited, but is usually 0.1 g/10 min or more, and from the viewpoint of the appearance of the molded product, it is preferably 10 g/10 min or more, more preferably 20 g/10 min or more, and even more preferably 30 g/10 min or more. The melt flow rate (230°C, load 21.18N) of component (A) is usually 200 g/10 min or less, and from the viewpoint of tensile strength, it is preferably 150 g/10 min or less, more preferably 100 g/10 min or less. The melt flow rate (MFR) of component (A) is measured under conditions of 230°C and load 21.18 N in accordance with ISO 1133 (2011).
A plurality of components (A) having a melt flow rate (230° C., load 21.18 N) within the range of 0.1 to 200 g/10 min may be used.

The propylene-based block copolymer of component (A) can be produced by a known polymerization method using a known olefin polymerization catalyst. For example, a polymerization method using a Ziegler-Natta catalyst can be used. The polymerization method can be a slurry polymerization method, a solution polymerization method, a bulk polymerization method, a gas phase polymerization method, or the like, and two or more of these methods can be combined.

Component (A) may also be a commercially available product. Commercially available products of component (A) include, for example, "PrimPolypro (registered trademark)" manufactured by Prime Polymer Co., Ltd., "Sumitomo Noblen (registered trademark)" manufactured by Sumitomo Chemical Co., Ltd., "Polypropylene block copolymer" manufactured by SunAllomer Co., Ltd., "Novatec (registered trademark) PP" manufactured by Japan Polypropylene Corporation, "Moplen (registered trademark)" manufactured by LyondellBasell Co., Ltd., "ADFLEX (registered trademark)" manufactured by LyondellBasell Co., Ltd., "Hifax (registered trademark)" manufactured by LyondellBasll Co., Ltd., "ExxonMobil PP" manufactured by ExxonMobil Co., Ltd., "Formolene (registered trademark)" manufactured by Formosa Plastics Co., Ltd., "Borealis PP" manufactured by Borealis Co., Ltd., "SEETEC PP" manufactured by LG Chemical Co., Ltd., and A. Examples include "ASIPOLYPROPYLENE" manufactured by Schulman, "INEOS PP" manufactured by INEOS Olefins & Polymers, "Braskem PP" manufactured by Braskem, "Hanwha Total" manufactured by Hanwha TOTAL PETRO CHEMICALS, "Sabic (registered trademark) PP" manufactured by Sabic, "TOTAL PETRO CHEMICALS Polypropylene" manufactured by TOTAL PETRO CHEMICALS, and "YUPLENE (registered trademark)" manufactured by SK.

The propylene-based block copolymer of component (A) may be used alone or in the form of a mixture of two or more types having different copolymer component compositions, physical properties, etc.

<Component (B)>
The thermoplastic elastomer composition of the present invention contains an ethylene/α-olefin copolymer as component (B). When the sum of the ethylene unit content and the α-olefin unit content is taken as 100 mass%, the ethylene/α-olefin copolymer of component (B) preferably has an ethylene unit content of 50 to 80 mass% and an α-olefin unit content of 20 to 50 mass%. When the ethylene unit content is within the above range, the affinity with other components is good, and the fine dispersibility of the thermoplastic elastomer composition tends to be improved.

The α-olefin constituting the ethylene-α-olefin copolymer of component (B) is not limited, but specific examples include propylene, 1-butene, 3-methyl-1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, and 1-decene. Component (B) may contain only one type of these α-olefin units, or two or more types. Among these, α-olefins having 4 to 8 carbon atoms are preferred, and 1-octene is more preferred. The ethylene-α-olefin copolymer contains 1-octene units as α-olefin units, resulting in good tensile strength.

Examples of the ethylene/α-olefin copolymer of component (B) include ethylene/α-olefin random copolymers and ethylene/α-olefin block copolymers. Among these, ethylene/α-olefin block copolymers, particularly ethylene/α-olefin block copolymers containing a polymer block of ethylene and an ethylene/α-olefin copolymer block, are preferred.

The ethylene/α-olefin block copolymer has a polymer block made of crystalline ethylene, and also has amorphousness due to the block containing an α-olefin. When component (B) has such a structure, the effect of high temperature strength and low temperature impact resistance is easily imparted to the obtained airbag storage cover.
Furthermore, it is believed that the polymer block made of ethylene is dynamically heat-treated in the presence of the organic peroxide of component (C) to reduce gloss and improve appearance.

The ethylene-α-olefin block copolymer of component (B) preferably has a crystalline melting peak at 110 to 125°C and a crystalline melting heat of 20 to 60 J/g. Here, component (B) having a crystalline melting peak at 110 to 125°C and a crystalline melting heat of 20 to 60 J/g calculated from the crystalline melting peak is an indicator that component (B) has a polymer block made of crystalline ethylene. From the viewpoint of high-temperature strength, the crystalline melting heat of component (B) is more preferably 30 J/g or more. Also, from the viewpoint of low-temperature impact resistance, the crystalline melting heat of component (B) is more preferably 50 J/g or less.

The amorphous nature of the α-olefin-containing blocks of the ethylene/α-olefin block copolymer of component (B) can be expressed by the glass transition temperature, and the glass transition temperature of component (B) measured by the DSC method is preferably -80°C or higher, more preferably -75°C or higher, while it is preferably -50°C or lower, more preferably -60°C or lower.

The crystalline melting peak temperature, crystalline melting heat, and glass transition temperature of component (B) can be determined by differential scanning calorimetry (DSC). The crystalline melting peak temperature is the top temperature of the melting peak obtained by a differential scanning calorimeter (DSC), and the crystalline melting heat can be determined from the area of the melting peak obtained by a differential scanning calorimeter. The glass transition temperature is the intersection point of the tangent at the inflection point and the baseline obtained by a differential scanning calorimeter.
The specific measurement conditions for determining these values are as follows:
That is, a 10 mg sample is taken and melted using a DSC at a heating rate of 100°C/min from 25°C to 200°C, held at 200°C for 1 minute, crystallized at a heating rate of 10°C/min to -130°C, held at -130°C for 10 minutes, and then measured at a heating rate of 10°C/min up to 200°C.

The polymer block made of ethylene in the ethylene-α-olefin block copolymer of component (B) is mainly made of ethylene units, but may contain other monomer units in addition to ethylene. Here, "mainly made up of" means that it accounts for 50% by mass or more of the total, particularly 60 to 100% by mass. Examples of other monomer units include propylene units, 1-butene units, 2-methylpropylene units, 1-pentene units, 3-methyl-1-butene units, 1-hexene units, 4-methyl-1-pentene units, and 1-octene units. Preferred are α-olefin units having 3 to 8 carbon atoms and a carbon-carbon double bond at the terminal carbon atom, such as propylene units, 1-butene units, 1-hexene units, and 1-octene units. The polymer block made of ethylene in component (B) may be one in which only one type of α-olefin is copolymerized with ethylene, or two or more types of α-olefins are copolymerized with ethylene.

The α-olefin-containing block in the ethylene-α-olefin block copolymer of component (B) may be exemplified by those having propylene units, 1-butene units, 2-methylpropylene units, 1-pentene units, 3-methyl-1-butene units, 1-hexene units, 4-methyl-1-pentene units, and 1-octene units as constituent units of the α-olefin units, and is preferably an α-olefin unit having 3 to 8 carbon atoms and a carbon-carbon double bond at the terminal carbon atom of a propylene unit, 1-butene unit, 1-hexene unit, 1-octene unit, etc. From the viewpoint of low-temperature impact resistance, it is preferable that the α-olefin-containing block in component (B) contains ethylene units in addition to α-olefin units. In this case, the α-olefin-containing block may be one in which only one type of α-olefin is copolymerized with ethylene, or two or more types of α-olefins are copolymerized with ethylene.

The α-olefin-containing block in the ethylene-α-olefin block copolymer of component (B) may contain, in addition to the α-olefin units and ethylene units described above, other monomer units such as monomer units based on non-conjugated dienes (non-conjugated diene units). Examples of the non-conjugated diene units include linear non-conjugated diene units such as 1,4-hexadiene units, 1,6-octadiene units, 2-methyl-1,5-hexadiene units, 6-methyl-1,5-heptadiene units, and 7-methyl-1,6-octadiene units; and cyclic non-conjugated diene units such as cyclohexadiene units, dicyclopentadiene units, methyltetrahydroindene units, 5-vinylnorbornene units, 5-ethylidene-2-norbornene units, 5-methylene-2-norbornene units, 5-isopropylidene-2-norbornene units, and 6-chloromethyl-5-isopropenyl-2-norbornene units. Among these, the dicyclopentadiene units and 5-ethylidene-2-norbornene units are preferred.

When the ethylene-α-olefin block copolymer of component (B) contains other monomer units such as non-conjugated diene units, the content thereof is usually 10% by mass or less, and preferably 5% by mass or less, based on the total amount of component (B).

Examples of the ethylene/α-olefin block copolymer of component (B) used in the thermoplastic elastomer composition of the present invention include ethylene/α-olefin block copolymers having a polymer block made of ethylene and an ethylene/α-olefin copolymer block. Specific examples include block copolymers containing a polymer block made of ethylene and an ethylene/α-olefin copolymer block such as an ethylene/1-butene copolymer, an ethylene/1-hexene copolymer, an ethylene/1-octene copolymer, an ethylene/propylene/1-butene copolymer, an ethylene/propylene/1-hexene copolymer, or an ethylene/propylene/1-octene copolymer.
Among these, from the viewpoint of tensile strength, it is preferable that component (B) is an ethylene/1-octene block copolymer containing a polymer block made of ethylene and an ethylene/1-octene copolymer block.

The melt flow rate (190°C, load 21.18N) of component (B) is not limited, but is usually 10 g/10 min or less, and from the viewpoint of strength, it is preferably 8.0 g/10 min or less, more preferably 5.0 g/10 min or less, and even more preferably 3.0 g/10 min or less. The melt flow rate (190°C, load 21.18N) of 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, and more preferably 0.10 g/10 min or more. The melt flow rate of component (B) is measured according to ASTM D1238 under the conditions of 190°C and load 21.18 N.

From the viewpoint of low-temperature impact resistance, the density of component (B) is preferably 0.880 g/cm3 or ^less , more preferably 0.870 g/cm3 ^or less. On the other hand, the lower limit is not particularly limited, but is usually 0.850 g/cm3 or ^more . The density of component (B) can be measured by ASTM D792.

The ethylene-α-olefin block copolymer of component (B) can be synthesized according to the methods disclosed in JP-A-2007-529617, JP-A-2008-537563, and JP-A-2008-543978. For example, the ethylene-α-olefin block copolymer can be produced by preparing a composition containing a mixture or reaction product obtained by combining a first olefin polymerization catalyst, a second olefin polymerization catalyst capable of preparing a polymer having different chemical or physical properties from the polymer prepared by the first olefin polymerization catalyst under the same polymerization conditions, and a chain shuttling agent, and then contacting the composition with the ethylene and α-olefin under addition polymerization conditions.

A continuous solution polymerization method is preferably used for the polymerization of the ethylene-α-olefin block copolymer of component (B). In the continuous solution polymerization method, the catalyst components, the chain shuttling agent, the monomers, and optionally the solvent, the auxiliary agent, the scavenger, and the polymerization aid are continuously fed into the reaction zone, and the polymer product is continuously removed therefrom. In this case, the length of each block of the ethylene-α-olefin block copolymer can be changed by controlling the ratio and type of the catalyst, the ratio and type of the chain shuttling agent, the polymerization temperature, etc.

Component (B) may be a commercially available product. Examples of commercially available products of component (B) include the "Engage (registered trademark)-XLT" series and "INFUSE (registered trademark)" series manufactured by Dow Chemical Company, the "Solumer (registered trademark)" series manufactured by SK Corporation, the "Tafmer (registered trademark)" series and "Mitsui EPT" manufactured by Mitsui Chemicals, Inc., "JSR EPR" manufactured by JSR Corporation, "Esprene (registered trademark)" manufactured by Sumitomo Chemical Company, Ltd., and "Keltan (registered trademark)" manufactured by LANXESS Corporation.

The ethylene-α-olefin copolymer of component (B) may be used alone or in the form of a mixture of two or more types having different copolymer component compositions, physical properties, etc.

<Component (C)>
In the thermoplastic elastomer composition of the present invention, the organic peroxide of component (C) acts as a crosslinking agent in dynamic heat treatment, which can reduce the gloss of molded articles such as airbag storage covers made of the thermoplastic elastomer composition of the present invention, resulting in a particularly good appearance.

As the organic peroxide of component (C), either an aromatic organic peroxide or an aliphatic organic peroxide can be used. Specific examples of the peroxides include dialkyl peroxides such as di-t-butyl peroxide, t-butylcumyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 2,5-dimethyl-2,5-di(t-butylperoxy)-3-hexyne, 1,3-bis(t-butylperoxyisopropyl)benzene, and 1,1-di(t-butylperoxy)-3,3,5-trimethylcyclohexane; peroxy esters such as t-butyl peroxybenzoate, t-butylperoxyisopropyl carbonate, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, and 2,5-dimethyl-2,5-di(benzoylperoxy)-3-hexyne; and hydroperoxides such as acetyl peroxide, lauroyl peroxide, benzoyl peroxide, p-chlorobenzoyl peroxide, and 2,4-dichlorobenzoyl peroxide. Among these, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane is preferred. These may be used alone or in combination of two or more.

<Component (D)>
In the thermoplastic elastomer composition of the present invention, component (D) acts as a crosslinking aid in the dynamic heat treatment.

Examples of crosslinking aids for component (D) include peroxide aids such as sulfur, p-quinone dioxime, p-dinitrosobenzene, and 1,3-diphenyl guanidine; polyfunctional vinyl compounds such as divinylbenzene, triallyl cyanurate, triallyl isocyanurate, and diallyl phthalate; and polyfunctional (meth)acrylate compounds such as ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, and allyl (meth)acrylate. These may be used alone or in combination of two or more.

<Component (E)>
The thermoplastic elastomer composition of the present invention may contain a styrene-conjugated diene block copolymer and/or a hydrogenated product thereof as component (E).

Suitable conjugated dienes in the styrene-conjugated diene block copolymer and/or its hydrogenated product of component (E) are butadiene, isoprene, or a mixture thereof. Examples of component (E) include styrene-butadiene block copolymer and/or its hydrogenated product. Examples of hydrogenated styrene-butadiene block copolymer include partially hydrogenated styrene-butadiene-butylene-styrene copolymer (SBBS) and substantially completely hydrogenated styrene-ethylene-butylene-styrene copolymer (SEBS). Examples of component (E) include styrene-ethylene-propylene-styrene copolymer (SEPS), which is a hydrogenated product of styrene-isoprene block copolymer, and hydrogenated products of styrene-butadiene-isoprene block copolymer.

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

The conjugated diene in component (E) has a 1,2-microstructure analyzed by NMR, which is preferably 60 mol % or less, more preferably 45 mol % or less. It is preferable that the 1,2-microstructure is equal to or less than the above upper limit from the viewpoints of moldability and flexibility, and also from the viewpoint of not excessively proceeding with the crosslinking reaction due to dynamic heat treatment. From the viewpoint of utilizing the crosslinking reaction in component (E), when component (E) is a hydrogenated product of a styrene-conjugated diene block copolymer, the hydrogenation rate is preferably 95% or less, more preferably 90% or less, and even more preferably 85% or less.

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

From the viewpoint of releasability, the weight average molecular weight (Mw) of component (E) is preferably 50,000 or more, more preferably 80,000 or more, and even more preferably 100,000 or more. From the viewpoint of fluidity and dispersibility, the weight average molecular weight (Mw) of component (E) is preferably 500,000 or less, more preferably 450,000 or less, even more preferably 400,000 or less, and particularly preferably 350,000 or less.

The weight average molecular weight (Mw) of the component (E) is measured by gel permeation chromatography (GPC), and can be measured, for example, under the following conditions.
Equipment: Tosoh Corporation "HLC-8220GPC(R)"
Column: "TSKgel Super HM-M (6.0 mm I.D. x 15 cm x 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% x 20 μL
Calibration sample: Monodisperse polystyrene Calibration method: Polystyrene equivalent Calibration curve approximation: Cubic equation (hyperbola)
Exclusion limit setting time: 12 minutes

A method for producing the styrene-conjugated diene block copolymer of component (E) is, for example, a method described in JP-B-40-23798, in which a styrene-conjugated diene block copolymer is synthesized in an inert solvent using a lithium catalyst. A method for producing a hydrogenated product of a styrene-conjugated diene block copolymer is, for example, a method for synthesizing a styrene-conjugated diene block copolymer by the above method, and then hydrogenating the copolymer in an inert solvent in the presence of a hydrogenation catalyst by the methods described in JP-B-42-8704, JP-B-43-6636, JP-A-59-133203, and JP-A-60-79005.

The styrene-conjugated diene block copolymer and/or its hydrogenated product of component (E) may be commercially available. Examples of commercially available styrene-conjugated diene block copolymers include "Kraton (registered trademark) D" manufactured by Kraton Polymers, Inc. and "Globalprene (registered trademark)" manufactured by LCY Corporation. Examples of partially hydrogenated styrene-conjugated diene block copolymers include "Tuftec (registered trademark) P" manufactured by Asahi Kasei Corporation. Examples of fully hydrogenated styrene-conjugated diene block copolymers include "Kraton (registered trademark) G" manufactured by Kraton Polymers, Inc., "Septon (registered trademark)" manufactured by Kuraray Co., Ltd., and "Tuftec (registered trademark)" manufactured by Asahi Kasei Corporation.

Component (E) may be a styrene-conjugated diene block copolymer and/or a hydrogenated product thereof, and may be a mixture of two or more types having different copolymer component compositions, physical properties, etc.

<Component (F)>
From the viewpoint of improving moldability, the thermoplastic elastomer composition of the present invention preferably contains a hydrocarbon-based rubber softener as component (F).

Examples of the hydrocarbon-based rubber softener of component (F) include mineral oil-based softeners and synthetic resin-based softeners, but mineral oil-based softeners are preferred in terms of compatibility with other components. Mineral oil-based softeners are generally mixtures of aromatic hydrocarbons, naphthenic hydrocarbons, and paraffinic hydrocarbons, and those in which 50% or more of the total carbon atoms are paraffinic hydrocarbons are called paraffinic oils, those in which 30-45% of the total carbon atoms are naphthenic hydrocarbons, and those in which 35% or more of the total carbon atoms are aromatic hydrocarbons are called aromatic oils. Of these, it is preferable to use paraffinic oils in the present invention.

The kinematic viscosity (ASTM D 445/JIS K2283) of the hydrocarbon rubber softener of component (F) at 40°C is not particularly limited, but is preferably 20 cSt or more, more preferably 50 cSt or more, and is preferably 800 cSt or less, more preferably 600 cSt or less. The flash point (COC method) of the hydrocarbon rubber softener is preferably 200°C or more, more preferably 250°C or more.

The hydrocarbon rubber softener of component (F) may be a commercially available product. Examples of commercially available products of component (F) include the Nippon Oil Polybutene (registered trademark) HV series manufactured by JX Nippon Oil & Energy Corporation and the Diana (registered trademark) Process Oil PW series manufactured by Idemitsu Kosan Co., Ltd., and any of these may be appropriately selected and used.

The hydrocarbon-based rubber softener of component (F) may be used alone or in combination of two or more types.

<Mixing ratio>
The blending ratio of the raw materials for the thermoplastic elastomer composition of the present invention will be described below.

The content of component (B) in the thermoplastic elastomer composition of the present invention is usually 40 parts by mass or more, preferably 50 parts by mass or more, and more preferably 60 parts by mass or more, per 100 parts by mass of component (A) from the viewpoint of low-temperature impact resistance. Also, from the viewpoint of rigidity and tensile strength of the molded article, the content is usually 200 parts by mass or less, preferably 150 parts by mass or less, and more preferably 120 parts by mass or less.

The content of component (C) in the thermoplastic elastomer composition of the present invention is usually 0.01 part by mass or more, preferably 0.05 part by mass or more, more preferably 0.10 part by mass or more, from the viewpoint of low gloss, when the total amount of components (A) and (B) is 100 parts by mass, while it is usually 1.00 part by mass or less, preferably 0.80 part by mass or less, more preferably 0.60 part by mass or less, from the viewpoint of low temperature impact resistance and flow mark resistance.
In the case where the thermoplastic elastomer composition of the present invention further contains component (E) and/or component (F), the above-described content of component (C) may be applied based on the total amount of components (A), (B), (E), and (F) being 100 parts by mass.

The content of component (D) in the thermoplastic elastomer composition of the present invention is usually 0.01 part by mass or more, preferably 0.05 part by mass or more, more preferably 0.10 part by mass or more, from the viewpoint of low gloss, when the total amount of components (A) and (B) is taken as 100 parts by mass, while from the viewpoint of flow mark resistance, it is usually 1.00 part by mass or less, preferably 0.80 part by mass or less, more preferably 0.60 part by mass or less.
In the case where the thermoplastic elastomer composition of the present invention further contains component (E) and/or component (F), the above-described content of component (D) may be applied based on the total amount of components (A), (B), (E), and (F) being 100 parts by mass.

When the thermoplastic elastomer composition of the present invention contains component (E), the content thereof is usually 1 part by mass or more, preferably 5 parts by mass or more, and more preferably 10 parts by mass or more, per 100 parts by mass of component (A) from the viewpoint of low-temperature impact resistance. Also, from the viewpoint of rigidity and tensile strength of the molded article, the content thereof is usually 100 parts by mass or less, preferably 80 parts by mass or less, and more preferably 60 parts by mass or less.

When the thermoplastic elastomer composition of the present invention contains component (F), the content thereof is usually 1 part by mass or more, preferably 5 parts by mass or more, and more preferably 10 parts by mass or more, per 100 parts by mass of component (A), from the viewpoints of low-temperature impact resistance, fluidity, and flow mark resistance. Also, from the viewpoints of rigidity, tensile strength, and oil bleeding of the molded product, the content thereof is usually 100 parts by mass or less, preferably 80 parts by mass or less, and more preferably 60 parts by mass or less.

<Other ingredients>
The thermoplastic elastomer composition of the present invention may contain other components as required within the range that does not impair the effects of the present invention.

Examples of other components include resins such as thermoplastic resins and elastomers other than components (A), (B), and (E), antioxidants, fillers, heat stabilizers, weathering aids, light stabilizers, UV absorbers, neutralizing agents, lubricants, antifogging agents, antiblocking agents, slip agents, dispersants, colorants, flame retardants, antistatic agents, conductivity imparting agents, metal deactivators, molecular weight regulators, antibacterial agents, antifungal agents, and fluorescent brighteners. These may be used alone or in combination of two or more.

Examples of thermoplastic resins other than component (A) include polyphenylene ether resins; polyamide resins such as nylon 6 and nylon 66; polyester resins such as polyethylene terephthalate and polybutylene terephthalate; polyoxymethylene resins such as polyoxymethylene homopolymers and polyoxymethylene copolymers; polymethyl methacrylate resins, and polyolefin resins (excluding those that fall under component (A) or component (B)). Examples of elastomers other than components (B) and (E) include styrene elastomers (excluding those that fall under component (E)); polyester elastomers; and polybutadiene.

Examples of antioxidants include phenol-based antioxidants, phosphite-based antioxidants, and thioether-based antioxidants. When antioxidants are used, they are usually used in the range of 0.01 to 3.0 parts by mass per 100 parts by mass of the total of component (A), component (B), and optionally used components (E) and (F).

Examples of fillers include glass fiber, hollow glass spheres, carbon fiber, talc, calcium carbonate, mica, potassium titanate fiber, silica, metal soap, titanium dioxide, and carbon black. When a filler is used, it is usually used in an amount of 0.1 to 50 parts by mass per 100 parts by mass of the total of component (A), component (B), and optionally used components (E) and (F).

[Method of producing thermoplastic elastomer composition]
The thermoplastic elastomer composition of the present invention is preferably produced by dynamically heat treating a composition containing predetermined amounts of component (A), component (B), and optionally used components (E), (F), and other components, in the presence of component (C) and component (D).

In the present invention, "dynamic heat treatment" means kneading in a molten or semi-molten state in the presence of component (C) and component (D). This dynamic heat treatment is preferably carried out by melt kneading, and the mixing and kneading device used for this purpose may be, for example, a non-open type Banbury mixer, a mixing roll, a kneader, or a twin-screw extruder. Of these, it is preferable to use a twin-screw extruder.

A preferred embodiment of the production method using a twin-screw extruder is a method in which a mixture containing a part of component (A), component (B), component (C), component (D), component (E), component (F) used as necessary, and other components is melt-kneaded while being fed into a cylinder from a raw material feed port (hopper) (hereinafter sometimes referred to as "first hopper") on the more upstream side of a twin-screw extruder having multiple raw material feed ports, and the remaining amount of component (A) is fed into the cylinder from a raw material feed port (hopper) (hereinafter sometimes referred to as "second hopper") located on the more downstream side separate from the first hopper and further heat-treated to produce a partially crosslinked thermoplastic elastomer. Here, the second hopper that feeds the remaining amount of component (A) is preferably a raw material feed port located downstream of L/2, where L is the length from the most upstream raw material feed port (usually the first hopper) to the most upstream mixture outlet. However, if the second hopper is located too far downstream, the component (A) supplied from the second hopper will not be sufficiently dispersed, and therefore, it is preferable that the second hopper be located at least L/10 upstream of the outlet of the mixture.
The raw material supplied from the second hopper may also be at least a portion of components (B), (E) and (F) in addition to the remainder of component (A).

In this way, by dynamically heat treating a mixture of a portion of component (A), component (B), component (C), component (D), component (E) and component (F) to partially crosslink the mixture, and then adding the remainder of component (A), component (A) added later is less susceptible to molecular chain scission by radicals, resulting in a thermoplastic elastomer composition with increased tensile strength and an improved die swell ratio.

From the viewpoint of improving the mechanical strength and die swell ratio of the resulting composition, the initial charge amount of component (A) (amount fed from the first hopper) is preferably 90 parts by mass or less, more preferably 80 parts by mass or less, and even more preferably 70 parts by mass or less, assuming that the total amount of component (A) is 100 parts by mass. On the other hand, from the viewpoint of production stability during manufacturing, the initial charge amount of component (A) (amount fed from the first hopper) is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and even more preferably 30 parts by mass or more. Even when components (B), (E), and (F) are fed in portions, it is preferable to feed them in portions in the same ratio as component (A).

The temperature during dynamic heat treatment is usually 80 to 300°C, preferably 100 to 250°C. The time during which dynamic heat treatment is performed is usually 0.1 to 30 minutes.

When the thermoplastic elastomer composition of the present invention is produced by performing dynamic heat treatment using a twin-screw extruder, it is preferable to extrude the composition while maintaining the relationship represented by the following formula (1) between the barrel radius R (mm), the screw rotation speed N (rpm), and the discharge rate Q (kg/h) of the twin-screw extruder, and it is more preferable to extrude the composition while maintaining the relationship represented by the following formula (2).
2.6<NQ/ ^R3 <22.6...(1)
3.0<NQ/ ^R3 <20.0...(2)

In order to efficiently produce a thermoplastic elastomer composition, it is preferable that the relationship between the barrel radius R (mm), screw rotation speed N (rpm), and discharge rate Q (kg/hour) of the twin-screw extruder is greater than the lower limit value. On the other hand, it is preferable that the relationship is smaller than the upper limit value, since this suppresses heat generation due to shear and reduces the occurrence of foreign matter that causes poor appearance.

[Molded products]
<Ingredients and Method>
A molded article can be obtained by molding the thermoplastic elastomer resin composition of the present invention.
The thermoplastic elastomer composition of the present invention can be molded into a molded article by a normal injection molding method or, if necessary, by various molding methods such as gas injection molding, injection compression molding, short shot foam molding, etc. Among them, it is preferable to produce a molded article by injection molding, and the molding conditions when performing injection molding are as follows.
The molding temperature when injection molding a molded product is generally 150 to 300° C., preferably 160 to 280° C. The injection pressure is generally 5 to 100 MPa, preferably 10 to 80 MPa. The mold temperature is generally 0 to 80° C., preferably 20 to 60° C.

<Applications>
The molded article thus obtained can be used, for example, as an airbag storage cover, which is suitably used as an airbag storage cover for an airbag system that is activated and inflated upon sensing the impact or deformation of a high-speed moving object such as an automobile in a collision accident or the like.
The airbag storage cover of the present invention can be suitably used as any of a driver's seat airbag storage cover, a passenger seat airbag storage cover, a pedestrian airbag storage cover, a knee airbag storage cover, a side airbag storage cover, a curtain airbag storage cover, etc.

[Physical properties of thermoplastic elastomer composition and molded product]
<Low gloss>
According to the thermoplastic elastomer composition of the present invention, a molded article having low gloss and excellent appearance can be obtained. The degree of low gloss is preferably 50% or less as the glossiness measured at an incidence angle of 60° for an injection molded article of the thermoplastic elastomer composition of the present invention. If the glossiness is equal to or less than the upper limit, the desired design can be obtained without painting. The upper limit of the glossiness is more preferably 40% or less, and even more preferably 35% or less.
The gloss level is measured by the method described in the Examples section below.

According to the thermoplastic elastomer composition of the present invention, the above-mentioned low gloss can be obtained by subjecting a composition containing the above-mentioned components (A) and (B) to dynamic heat treatment in the presence of the above-mentioned components (C) and (D).

<Flexural modulus>
From the viewpoint of low-temperature impact resistance, the thermoplastic elastomer composition of the present invention preferably has a flexural modulus of 700 MPa or less. The flexural modulus is correlated with low-temperature impact resistance, and excellent low-temperature impact resistance can be achieved by having the flexural modulus be equal to or less than the above upper limit. From the viewpoint of low-temperature impact resistance, the upper limit of the flexural modulus is more preferably 600 MPa or less, and even more preferably 500 MPa or less. On the other hand, from the viewpoint of shape retention of a molded article, the lower limit of the flexural modulus is preferably 100 MPa or more, more preferably 150 MPa or more, and even more preferably 200 MPa or more.
The flexural modulus is measured by the method described in the Examples section below.

In the thermoplastic elastomer composition of the present invention, the above-mentioned flexural modulus can be achieved by using the above-mentioned components (A) and (B) in the above-mentioned preferred combination.

<MFR>
The thermoplastic elastomer composition of the present invention also has excellent moldability. Specifically, the melt flow rate (MFR) at a temperature of 230°C and a measurement load of 21.18 N according to ISO 1133 (2011) is usually 0.5 to 50 g/10 min, preferably 1 to 40 g/10 min, and more preferably 2 to 30 g/10 min.

<Tensile strength at break>
The thermoplastic elastomer composition of the present invention is also excellent in tensile strength. Specifically, the tensile strength at break measured using a 1A dumbbell as specified in ISO 37 (2011) at a pulling speed of 500 mm/min in an atmosphere of 23° C. is usually 10 MPa or more, preferably 13 MPa or more, and more preferably 15 MPa or more.

<Elongation at break>
The thermoplastic elastomer composition of the present invention also has excellent elongation at break. Specifically, the elongation at break measured using a 1A dumbbell as specified in ISO 37 (2011) at a tensile speed of 500 mm/min in an atmosphere of 23° C. is usually 500% or more, preferably 600% or more, and more preferably 700% or more.

<Low temperature impact resistance>
The thermoplastic elastomer composition of the present invention has excellent low-temperature impact resistance. In the present invention, the low-temperature impact resistance is evaluated by the Izod impact strength at -45°C by the method shown in the Examples below. In the present invention, the Izod impact strength at -45°C is preferably 50 kJ/ ^m2 or more, more preferably 60 kJ/ ^m2 or more, and even more preferably 70 kJ/m2 or ^more .

<Flow mark resistance>
Molded articles obtained from the thermoplastic elastomer composition of the present invention are excellent in resistance to flow marks, with almost no flow marks being observed.
As described above, the thermoplastic elastomer composition of the present invention tends to have good flow mark properties when the die swell ratio is large. That is, it is considered that a large die swell ratio of 1.10 or more contributes to the stability of the flow front in the mold during injection molding, thereby improving the flow mark properties.

The present invention will be explained in more detail below using examples, but the present invention is not limited to the following examples as long as it does not exceed the gist of the invention. The values of various manufacturing conditions and evaluation results in the following examples are meant as preferred upper or lower limit values in the embodiments of the present invention, and the preferred range may be a range defined by a combination of the above-mentioned upper or lower limit values and the values of the following examples or values between the examples.

[Raw materials for producing thermoplastic elastomer composition]
<Component (A)>
A-1:
Propylene block copolymer (obtained by polymerizing a propylene homopolymer in the first step, followed by polymerizing a propylene-ethylene copolymer in the second step)
Novatec (registered trademark) PP BC06NCA manufactured by Japan Polypropylene Corporation
MFR (ISO 1133 (2011)): 60g/10min (measurement conditions: 230°C, load 21.18N)
Propylene unit content: 96% by mass
Ethylene unit content: 4% by mass

<Component (B)>
B-1:
Ethylene/1-octene block copolymer (a block copolymer having a polymer block made of ethylene and a block of an ethylene/1-octene copolymer)
Dow Chemical Company Engage® XLT8677
Crystal melting peak temperature: 119°C
Heat of crystal fusion: 37 J/g
MFR (ASTM D1238): 0.5 g/10 min (measurement conditions: 190°C, load 21.18 N) (catalog value)
Glass transition temperature (DSC method): -67°C
Density (ASTM D792): 0.870 g/cm ³ (catalog value)

B-2:
Ethylene-propylene-ethylidene norbornene terpolymer rubber Mitsui Chemicals, Inc. Mitsui EPT3092PM
Mooney Viscosity ML(1+4) 125℃ (ASTM D1646): 61 (catalog value)
Ethylene unit content (ASTM D3900): 65% by mass (catalog value)
Ethylidene norbornene unit content (ASTM D6047): 4.6 mass% (catalog value)

B-3:
Ethylene/1-octene random copolymer: Engage (registered trademark) 8180 manufactured by Dow Chemical Company
Crystal melting peak temperature: No peak at 110 to 125°C. Crystal melting heat: 0
MFR (ASTM D1238): 0.5 g/10 min (measurement conditions: 190°C, load 21.18 N) (catalog value)
Density (ASTM D792): 0.863 g/cm ³ (catalog value)

<Component (C)>
C-1:
Trigonox 101-40C (a mixture of 40% by mass of 2,5-dimethyl-2,5-di(t-butylperoxy)hexane and 60% by mass of calcium carbonate) manufactured by Nouryon Chemical Industries, Ltd.

<Component (D)>
D-1:
Mitsubishi Chemical Corporation Acrylate TMP (trimethylolpropane trimethacrylate)
D-2:
Divinylbenzene (mixture of 55% by mass of divinylbenzene and 45% by mass of ethylvinylbenzene) manufactured by Wako Pure Chemical Industries, Ltd.

<Component (E)>
E-1:
Styrene-butadiene-styrene block copolymer Kraton (registered trademark) D1101J manufactured by Kraton Polymers
Weight average molecular weight (Mw): 160,000
Styrene unit content: 31% by mass (catalog value)
Conjugated diene unit content: 69% by mass (catalog value)
1,2-microstructure of conjugated diene component: 12 mol%
Hydrogenation rate: 0%

<Component (F)>
F-1:
Paraffin-based oil: Idemitsu Kosan Diana (registered trademark) Process Oil PW90
Kinematic viscosity at 40°C: 95.54 cSt
Pour point: -15°C
Flash point: 272°C

[Method of evaluating thermoplastic elastomer composition]
1) Melt flow rate (MFR)
Measured in accordance with ISO 1133 (2011) at 230°C and a load of 21.18N.

2) Tensile strength at break and elongation at break Using an in-line screw type injection molding machine ("SE100DU" manufactured by Sumitomo Wiring Systems, Ltd.), a test piece for tensile testing (a sheet having a thickness of 2 mm x width of 120 mm x length of 80 mm) was molded from the thermoplastic elastomer composition at an injection speed of 30 mm/s, a cylinder set temperature of 220°C, and a mold temperature of 40°C, and then punched out in accordance with ISO 37 (2011) (1A dumbbell). The tensile strength at break (unit: MPa) and elongation at break (unit: %) of this punched test piece were measured at a pulling speed of 500 mm/min and an atmosphere of 23°C using an autograph precision universal testing machine "AGS-H" manufactured by Shimadzu Corporation.

3) Flexural modulus Using an in-line screw type injection molding machine ("SE100DU" manufactured by Sumitomo Wiring Systems, Ltd.), a multipurpose evaluation test piece A (180 mm long dumbbell) was molded from the thermoplastic elastomer composition in accordance with ISO 3167 (2002) at an injection speed of 30 mm/s, a cylinder set temperature of 220°C, and a mold temperature of 40°C. The ends of the dumbbell were cut off to prepare a test piece for measuring flexural modulus (thickness 4 mm x width 10 mm x length 80 mm). The flexural modulus was measured at a speed of 2 mm/min according to ISO 178 (2010) using a Pentograph B-2 manufactured by Toyo Seiki Co., Ltd.

4) Die Swell Ratio: The die swell ratio was measured during the extrusion process of the thermoplastic elastomer composition under the following conditions using a Capillograph 1D (JIS K7199) manufactured by Toyo Seiki Seisakusho Co., Ltd.
Test temperature: 210°C
L/D: 10 (D=1mm)
Shear rate: 243/s
The die swell ratio was calculated according to the following formula (I).
St=Dm/Dt (I)
St, Dm, and Dt indicate the following.
St: die swell ratio Dm: diameter (mm) of extruded sample measured at test temperature at a position 10 mm below the die exit
Dt: diameter of the capillary die measured at the test temperature (mm)

5) Glossiness A test piece for measuring glossiness (a sheet having a thickness of 2 mm, a width of 120 mm, and a length of 80 mm) was molded from the thermoplastic elastomer composition using an in-line screw type injection molding machine ("SE100DU" manufactured by Sumitomo Wiring Systems, Ltd.) at an injection speed of 30 mm/s, a cylinder temperature setting of 220°C, and a mold temperature of 40°C. The glossiness was measured at an incidence angle of 60° in accordance with ISO 2813.

6) Low temperature impact resistance (Izod impact strength)
The thermoplastic elastomer composition was molded into a test piece for Izod impact strength having a thickness of 4 mm, a width of 10 mm, and a length of 80 mm using an in-line screw type injection molding machine ("SE100DU" manufactured by Sumitomo Wiring Systems, Ltd.) at an injection speed of 30 mm/s, a cylinder set temperature of 220° C., and a mold temperature of 40° C. After that, a notch was made in the dumbbell (the notch dimensions and evaluation method were in accordance with ISO 180 (2013)) and measurement was performed under the condition of -45° C.

7) Flow Mark Property The flow mark property was evaluated by molding a test piece for measuring gloss (a sheet having a thickness of 2 mm, a width of 120 mm, and a length of 80 mm) from the thermoplastic elastomer composition using an in-line screw type injection molding machine (SE100DU manufactured by Sumitomo Wiring Systems, Ltd.) at an injection speed of 30 mm/s, a cylinder temperature setting of 220° C., and a mold temperature of 40° C., and visually observing the appearance of the test piece.
Criterion 1: Flow marks are noticeable and the appearance is very poor.
2: Flow marks are noticeable and the appearance is poor.
3: Flow marks are observed.
4: A few flow marks are observed.
5: No flow marks observed.

[Example 1]
A portion of component (A-1): 20 parts by mass, component (B-1): 50 parts by mass, component (C-1): 0.40 parts by mass, and component (D-1): 0.40 parts by mass were blended with 100 parts by mass of the total of components (A-1) and (B-1) together with 0.1 parts by mass of an antioxidant (manufactured by BASF Japan Ltd., trade name Irganox (registered trademark) 1010) and 2 parts by mass of a black pigment (carbon concentration 40% by mass) in a Henschel mixer for 1 minute, and the resulting mixture was mixed with the above mixture. The mixture was fed into a two-way twin-screw extruder ("TEX30α" manufactured by Kobe Steel, L/D=45, number of cylinder blocks: 13) from the first feed port at a rate of 14 kg/hr, heated to a temperature range of 180 to 210°C, melt-kneaded, and simultaneously, the remaining component (A-1): 30 parts by mass was fed from the second feed port provided midway through the extruder cylinder at a rate of 6 kg/hr, kneaded, and then pelletized to produce a thermoplastic elastomer composition. The evaluation results of the obtained thermoplastic elastomer composition are shown in Table 1.
The first supply port is provided in the most upstream cylinder block of the co-rotating twin-screw extruder, and the second supply port is provided in the ninth cylinder block from the upstream.

[ Example 4 , Reference Examples 2 to 3, Comparative Examples 1 to 7]
Pellets of a thermoplastic elastomer composition were obtained in the same manner as in Example 1, except that the raw material composition was as shown in Table 1. The obtained thermoplastic elastomer composition was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1.

In Table 1, "A-1 (*1)" is the amount of component (A-1) added from the first supply port, and "A-1 (*2)" is the amount of component (A-1) added from the second supply port. Also, "-" in the raw material composition column indicates that the component was not used.

[Discussion]
From Table 1, it can be seen that Examples 1 and 4, which have a die swell ratio of 1.10 or more and correspond to the thermoplastic elastomer composition of the present invention, have low gloss and are remarkably excellent in terms of flow mark resistance. It can also be seen that they are excellent in low temperature impact resistance.

In contrast, Comparative Examples 1 and 2, which do not use components (C) and (D), have a large die swell ratio but a high gloss.
In Comparative Examples 3 to 6, components (A) to (D) were used, but because component (A) was added all at once, the die swell ratio was not 1.10 or more, and the flow mark resistance was poor. Among these, Comparative Examples 4 and 5 also showed significantly poor low-temperature impact resistance.
In Comparative Example 7, component (A) was added in portions, a die swell ratio of 1.10 or more was achieved, and the flow mark resistance was excellent, but component (D) was not used, and the gloss level was high.

The thermoplastic elastomer composition of the present invention has low gloss, is remarkably excellent in terms of flow marks, and is also excellent in terms of low-temperature impact resistance, and can be suitably used in various applications. The thermoplastic elastomer composition of the present invention is useful, for example, as automobile interior parts such as airbag storage covers, instrument panels, center panels, center console boxes, door trims, pillars, assist grips, and handles, automobile exterior parts such as mudguards and grommets, home appliance parts, building materials, and furniture. Among these, the thermoplastic elastomer composition of the present invention is particularly useful as an airbag storage cover, and among airbag storage covers, it is suitable as an airbag storage cover for an airbag system that activates upon sensing the impact or deformation of a high-speed moving body such as an automobile in a collision accident, and protects the occupant by inflating and deploying.

Claims (8)

A thermoplastic elastomer composition obtained by dynamically heat-treating a composition containing the following components (A) and (B) in the presence of the following components (C) and (D), the thermoplastic elastomer composition having a die swell ratio (test temperature: 210°C, shear rate: 243/s) of 1.10 or more as measured by a capillary rheometer (JIS K7199), and containing 40 to 200 parts by mass of component (B): ethylene-α-olefin copolymer per 100 parts by mass of component (A): propylene-based block copolymer.
Component (A): A propylene-based block copolymer having a propylene unit content of 70% by mass or more and 99% by mass or less.
Component (B): An ethylene/α-olefin block copolymer containing a polymer block made of ethylene and an ethylene/α-olefin copolymer block.
Component (C): Organic peroxide Component (D): Crosslinking aid The thermoplastic elastomer composition according to claim 1, wherein the α-olefin of component (B) has 4 to 8 carbon atoms. The thermoplastic elastomer composition according to claim 1 or 2 , wherein the ethylene/α-olefin block copolymer has a crystalline melting peak at 110 to 125° C. and a crystalline melting heat of 20 to 60 J/g. The thermoplastic elastomer composition according to any one of claims 1 to 3, wherein the α-olefin of component (B) is 1-octene. The thermoplastic elastomer composition according to any one of claims 1 to 4, further comprising the following component (E):
Component (E): Styrene-conjugated diene block copolymer and/or hydrogenated product thereof The thermoplastic elastomer composition according to any one of claims 1 to 5, further comprising the following component (F):
Component (F): Hydrocarbon-based rubber softener An injection molded article obtained by injection molding the thermoplastic elastomer composition according to any one of claims 1 to 6. An airbag storage cover using the thermoplastic elastomer composition according to any one of claims 1 to 6.