Thermoplastic elastomer composition, injection molded article, and airbag storage cover

Abstract

To provide a thermoplastic elastomer composition capable of realizing a molding excellent in flow mark property, while maintaining low temperature impact resistance and its injection molding.SOLUTION: A thermoplastic elastomer composition containing component (A): a propylene block copolymer, and component (B): an ethylene / α-olefin copolymer, and satisfying the following formula. An injection molding made by injection molding this thermoplastic elastomer composition. Formula: [Melt flow rate of component (B) measured at test temperature 230°C and load 21.18 N] / [Melt flow rate of component (A) measured at test temperature 230°C and load 21.18 N]≥0.5.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a thermoplastic elastomer composition excellent in low-temperature impact resistance and molding appearance, an injection-molded product made of this thermoplastic elastomer composition, and an airbag storage cover.

Background Art

[0002] An airbag system for automobiles is a system that protects drivers and passengers during collisions of automobiles and the like, and consists of a device that senses the impact during a collision and an airbag device. This airbag device is installed on the steering wheel, the instrument panel in front of the passenger seat, the seats of the driver's seat and the passenger seat, the front and side pillars, and the like.

[0003] Regarding the airbag storage cover in an airbag device, various proposals have been made regarding its structure and material so that it cleaves as designed when the airbag inflates.

[0004] As an airbag storage cover made of an olefin-based thermoplastic elastomer, for example, Patent Document 1 proposes one containing a specific propylene-based block copolymer with high fluidity and low molecular weight and a specific ethylene-α-olefin copolymer with low fluidity and high molecular weight.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

[0007] According to our detailed investigation, the thermoplastic elastomer composition described in Patent Document 1 had room for improvement in terms of flow marking properties.

[0008] This invention has been made in view of the problems of the prior art described above. Specifically, the object of this invention is to provide a thermoplastic elastomer composition, an injection-molded article thereof, and an airbag storage cover made of the thermoplastic elastomer composition, which enable molded articles with excellent flowmark properties while maintaining low-temperature impact resistance. [Means for solving the problem]

[0009] As a result of diligent research to solve the above problems, the inventors have found that the above problems can be solved by setting the relationship between the melt flow rate values ​​measured at a test temperature of 230°C and a load of 21.18N for the propylene-based block copolymer and the ethylene-α-olefin copolymer within a specific range in a thermoplastic elastomer composition containing a propylene-based block copolymer and an ethylene-α-olefin copolymer.

[0010] In other words, the gist of the present invention lies in the following [1] to [8].

[0011] [1] A thermoplastic elastomer composition comprising component (A): a propylene-based block copolymer and component (B): an ethylene-α-olefin copolymer, and satisfying the following formula. Formula: [Melt flow rate of component (B) measured at a test temperature of 230°C and a load of 21.18N] / [Melt flow rate of component (A) measured at a test temperature of 230°C and a load of 21.18N] ≥ 0.5

[0012] [2] The thermoplastic elastomer composition according to [1], wherein the melt flow rate (test temperature 230°C, load 21.18N) of the propylene-based block copolymer of component (A) is 1 to 20 g / 10 min.

[0013] [3] The thermoplastic elastomer composition according to [1] or [2], wherein the melt flow rate (test temperature 230°C, load 21.18N) of the ethylene-α-olefin copolymer of component (B) is 10 to 100 g / 10 min.

[0014] [4] The thermoplastic elastomer composition according to any one of [1] to [3], wherein the α-olefin of the ethylene-α-olefin copolymer of component (B) has 3 to 8 carbon atoms.

[0015] [5] Referring to ISO 180, an IZOD impact value of 60 kJ / m was measured in a -45°C atmosphere using a notched IZOD impact strength test specimen prepared. 2 The thermoplastic elastomer composition described in any of [1] to [4] above.

[0016] [6] A thermoplastic elastomer composition according to any one of [1] to [5], wherein the die swell ratio measured at a test temperature of 210°C and a shear rate of 243 / sec using a capillary rheometer (see JIS K7199) is 1.34 or higher.

[0017] [7] An injection-molded article obtained by injection molding a thermoplastic elastomer composition described in any of [1] to [6].

[0018] An airbag storage cover using the thermoplastic elastomer composition according to any one of [8][1] to [6]. [[ID=(2)]]

Effect of the Invention

[0019] According to the present invention, it is possible to provide a thermoplastic elastomer composition that enables a molded product excellent in flow mark properties while maintaining low-temperature impact resistance. The airbag storage cover of the present invention using the thermoplastic elastomer composition of the present invention can be suitably used for 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.

Mode for Carrying Out the Invention

[0020] 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 this specification, when expressing numerical values or physical property values before and after using "~", the values before and after are used as including those values.

[0021] In the present invention, the "airbag storage cover" means the entire container for storing the airbag. For example, in the container in which the airbag is stored, it is the opening when the airbag is deployed, or the entire container integrated with this opening.

[0022] [Thermoplastic Elastomer Composition] The thermoplastic elastomer composition of the present invention contains a propylene-based block copolymer as component (A) and an ethylene-α-olefin copolymer as component (B), and the ratio of the melt flow rate values of component (A) and component (B) measured at a test temperature of 230°C and a load of 21.18 N satisfies the following formula. Formula: [Melt flow rate of component (B) measured at a test temperature of 230 °C and a load of 21.18 N] / [Melt flow rate of component (A) measured at a test temperature of 230 °C and a load of 21.18 N] ≥ 0.5

[0023] Hereinafter, the melt flow rate of component (A) measured at a test temperature of 230 °C and a load of 21.18 N may be denoted as "MFR(A)", the melt flow rate of component (B) measured at a test temperature of 230 °C and a load of 21.18 N may be denoted as "MFR(B)", and [Melt flow rate of component (B) measured at a test temperature of 230 °C and a load of 21.18 N] / [Melt flow rate of component (A) measured at a test temperature of 230 °C and a load of 21.18 N] may be denoted as "MFR(B) / MFR(A)". In the present invention, the melt flow rate (MFR) of component (A) and component (B) is a value measured at a test temperature of 230 °C and a load of 21.18 N in accordance with ISO 1133. From the viewpoint of appearance, MFR(B) / MFR(A) is preferably 0.7 or more, more preferably 0.9 or more. On the other hand, the upper limit of MFR(B) / MFR(A) is not particularly limited, but is usually 100 or less, and from the viewpoint of achieving both low-temperature impact resistance and appearance, it is preferably 70 or less, more preferably 30 or less, and still more preferably 15 or less.

[0024] <Mechanism> The molded article obtained from the thermoplastic elastomer composition of the present invention exhibits the effect of being excellent in flow mark property while maintaining low-temperature impact resistance. Although the details of the reason why the thermoplastic elastomer composition of the present invention exhibits such an effect are not clear, it is considered as follows. In order to achieve both moldability and low-temperature impact resistance, the mechanism of the generation of flow marks when a thermoplastic elastomer composition composed of a resin component with high fluidity (for example, a propylene-based block copolymer with high fluidity) and a rubber component with low fluidity (for example, an ethylene·α-olefin copolymer with low fluidity) is subjected to molding is considered as follows. Thermoplastic elastomer compositions consisting of a highly fluid resin component and a high molecular weight, low fluidity rubber component generally take on a sea-island structure, where the resin component forms the matrix and the rubber component forms the domains, due to the viscosity gap that occurs during compounding. In this case, because the rubber component tends to aggregate more easily than the resin component, the rubber component is not sufficiently finely dispersed within the resin matrix, and the domain shape tends to become larger. When such a thermoplastic elastomer composition is used for molding, the presence of large domains derived from the rubber component in the fluid during molding results in unstable fluidity and the occurrence of flow marks. To suppress the flow marks that occur in this way, it is conceivable to promote the fine dispersion of the rubber component within the resin component when compounding the resin component and the rubber component. To achieve this, it is effective to control the viscosity difference between the resin component and the rubber component to be small, or to control the rubber component to have a low molecular weight. By doing so, the shear stress generated during compounding makes it easier to disperse the rubber component, and it is thought that fine dispersion of domains consisting of rubber components present in the matrix consisting of resin components can be achieved. Specifically, in order to achieve the low-temperature impact resistance required for the application, the resin component is made high molecular weight to reduce its fluidity, while the rubber component is made low molecular weight to increase its fluidity. This allows for finer dispersion of the rubber component during compounding while maintaining low-temperature impact resistance, resulting in stable resin fluidity and excellent flowmark properties.

[0025] <Ingredient (A)> The thermoplastic elastomer composition of the present invention contains a propylene-based block copolymer as component (A). The propylene-based block copolymer of component (A) usually contains a propylene homopolymer component and other polymer components. The content of the propylene homopolymer component in component (A) is usually 50% by mass or more, preferably 60% by mass or more, and more preferably 75% to 92% by mass, relative to the total amount of component (A). When the content of the propylene homopolymer component in component (A) is above the lower limit, the heat resistance and rigidity tend to be good. When the content of the propylene homopolymer component in component (A) is below the upper limit, the low-temperature impact resistance tends to be good. When component (A) is composed of a mixture of two or more propylene-based copolymers with different compositions, the content of the propylene homopolymer component in the entirety of component (A) should be within the above numerical range.

[0026] The content of propylene homopolymer components in component (A), the content of copolymer components of propylene and ethylene and / or other α-olefins other than the propylene homopolymer components described later, and the content of ethylene units and α-olefin units in component (B) described later can each be determined by infrared spectroscopy.

[0027] Component (A) contains a propylene homopolymer component in the aforementioned preferred content relative to the entire component (A), and also contains a copolymer component of propylene and ethylene and / or an α-olefin other than propylene (hereinafter sometimes referred to as "other α-olefins"). Examples of the copolymer component of Component (A) other than the propylene homopolymer component include propylene-ethylene block copolymer, propylene-other α-olefin block copolymer, propylene-ethylene-other α-olefin block copolymer, or other propylene-based block copolymers.

[0028] The content of copolymer components of propylene and ethylene and / or other α-olefins in component (A), other than the propylene homopolymer component, is usually 50% by mass or less, preferably 40% by mass or less, and more preferably 8 to 25% by mass.

[0029] The propylene-other α-olefin block copolymer component or the other α-olefin units of the propylene-ethylene-other α-olefin block copolymer component contained in component (A) can be 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. Other α-olefins are preferably α-olefins having 4 to 10 carbon atoms, and more preferably 1-butene, 1-hexene, and 1-octene. These other α-olefin units may be present in component (A) as one type or as two or more types.

[0030] Examples of propylene-based block copolymers 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.

[0031] Preferably, the component (A) is a block copolymer of ethylene and propylene with at least one monomer selected from α-olefins 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, component (A) is particularly preferably 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.

[0032] The lower limit of the melt flow rate (230°C, load 21.18N) of component (A) is preferably 1g / 10min or more, more preferably 3g / 10min or more, and even more preferably 5g / 10min or more, from the viewpoint of balancing the low-temperature impact resistance and appearance of the resulting molded product. The upper limit of the melt flow rate (230°C, load 21.18N) of component (A) is preferably 20g / 10min or less, and more preferably 15g / 10min or less, from the viewpoint of low-temperature impact resistance. Component (A) may be composed of multiple types of components (A) with different MFRs, such that the melt flow rate (230°C, load 21.18N) of component (A) falls within the above numerical range.

[0033] As a method for producing the propylene-based block copolymer of component (A), known polymerization methods using known olefin polymerization catalysts can be used. For example, polymerization methods using Ziegler-Natta catalysts can be cited. These polymerization methods can include slurry polymerization, solution polymerization, bulk polymerization, gas-phase polymerization, etc., and two or more of these may be combined.

[0034] In addition, commercially available components (A) may be used. Examples of commercially available components (A) include "PrimPolypro®" manufactured by Prime Polymer, Inc., "Sumitomo Noblen®" manufactured by Sumitomo Chemical Co., Ltd., "Polypropylene Block Copolymer" manufactured by Sun Allomer Co., Ltd., "Novatec® PP" manufactured by Nippon Polypropylene Co., Ltd., "Moplen®" manufactured by LyondellBasell, Inc., "ADFLEX®" manufactured by LyondellBasell, Inc., "Hifax®" manufactured by LyondellBasell, Inc., "ExxonMobilPP" manufactured by ExxonMobil, Inc., "Formolene®" manufactured by Formosa Plastics, Inc., B Examples include "BorealisPP" from orealis, "SEETECPP" from LGChemical, "ASIPOLYPROPYLENE" from A. Schulman, "INEOSPP" from INEOSOlefins & Polymers, "BraskemPP" from Braskem, "HanwhaTotal" from HanwhaTotalPetroChemicals, "Sabic(registered trademark)PP" from Sabic, "TOTALPETROCHEMICALSPolypropylene" from TOTALPETROCHEMICALs, and "YUPLENE(registered trademark)" from SK.

[0035] The propylene-based block copolymer of component (A) may be used alone, or two or more types with different copolymer component compositions and physical properties may be mixed and used.

[0036] <Ingredient (B)> The thermoplastic elastomer composition of the present invention contains an ethylene-α-olefin copolymer as component (B). Preferably, when the sum of the ethylene unit content and α-olefin unit content of component (B) is taken as 100% by mass, the ethylene unit content is 50-80% by mass and the α-olefin unit content is 20-50% by mass. When the ethylene unit content is within the above range, the affinity with other components is good, and the fine dispersibility of component (B) in the thermoplastic elastomer composition tends to improve.

[0037] Examples of ethylene-α-olefin copolymers for component (B) include ethylene-α-olefin random copolymers and ethylene-α-olefin block copolymers.

[0038] The α-olefins constituting the ethylene-α-olefin copolymer of component (B) are not limited, but specifically 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 of these α-olefin units, or two or more.

[0039] Among these, α-olefins with 4 to 8 carbon atoms are preferred, and 1-octene is more preferred. The ethylene-α-olefin copolymer exhibits good tensile strength when it contains 1-octene units as α-olefin units.

[0040] The ethylene-α-olefin copolymer of component (B) may have other monomer units in addition to the α-olefin units described above, such as monomer units based on non-conjugated dienes (non-conjugated diene units). Examples of such 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, dicyclopentadiene units and 5-ethylidene-2-norbornene units are preferred.

[0041] If the ethylene-α-olefin block copolymer of component (B) has other monomer units such as non-conjugated diene units, the content of these units is usually 10% by mass or less, preferably 5% by mass or less, relative to the total amount of component (B).

[0042] Specific examples of component (B) used in the present invention include ethylene-1-butene copolymer rubber, ethylene-1-hexene copolymer rubber, and ethylene-1-octene copolymer rubber. These may be used individually or in combination of two or more. Among these, ethylene-1-butene copolymer rubber and ethylene-1-octene copolymer rubber are preferred.

[0043] The lower limit of the melt flow rate (230°C, load 21.18N) of component (B) is preferably 10g / 10min or more, more preferably 12g / 10min or more, and even more preferably 14g / 10min or more, from the viewpoint of balancing the low-temperature impact resistance and appearance of the resulting molded product. The upper limit of the melt flow rate (230°C, load 21.18N) of component (B) is preferably 100g / 10min or less, more preferably 90g / 10min or less, and even more preferably 80g / 10min or less, from the viewpoint of moldability.

[0044] Component (B) may be a commercially available product. Examples of commercially available components (B) include the "Engage®" series, "Engage®-XLT" series, and "INFUSE®" series from Dow Chemical Company, the "Solumer®" series from SK Chemical Company, the "Tafmer®" series, "Mitsui EPT" from Mitsui Chemicals, "JSR EPR" from JSR Corporation, "Esplen®" from Sumitomo Chemical Corporation, and "Keltan®" from LANXESS.

[0045] The ethylene-α-olefin copolymer of component (B) may be used alone, or two or more copolymers with different copolymer component compositions and physical properties may be mixed and used.

[0046] <Content ratio> The thermoplastic elastomer composition of the present invention contains component (A) and component (B). When the total of component (A) and component (B) is 100% by mass, the lower limit of the content of component (A) is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more, from the viewpoint of low-temperature strength. On the other hand, the upper limit of the content of component (A) is preferably 80% by mass or less, more preferably 70% by mass or less, and even more preferably 60% by mass or less, from the viewpoint of moldability. The lower limit of the content of component (B) is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more, from the viewpoint of moldability. On the other hand, the upper limit of the content of component (B) is preferably 80% by mass or less, more preferably 70% by mass or less, and even more preferably 60% by mass or less, from the viewpoint of low-temperature strength.

[0047] <Other ingredients> The thermoplastic elastomer composition of the present invention may contain other components as needed, provided that the effects of the present invention are not impaired.

[0048] Other components may include, for example, resins such as thermoplastic resins and elastomers other than components (A) and (B), antioxidants, fillers, heat stabilizers, weathering aids, mold release agents, light stabilizers, UV absorbers, neutralizing agents, lubricants, antifogging agents, antiblocking agents, slip agents, dispersants, colorants, flame retardants, antistatic agents, conductivity imparters, metal deactivators, molecular weight modifiers, antibacterial agents, antifungal agents, fluorescent whitening agents, and various other additives. These may be used individually or in combination of two or more.

[0049] Examples of thermoplastic resins other than components (A) and (B) 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 homopolymer and polyoxymethylene copolymer; polymethyl methacrylate resins, styrene elastomers; polyester elastomers; polybutadiene and polyolefin resins (excluding those corresponding to components (A) and (B)).

[0050] Examples of antioxidants include phenolic antioxidants, phosphite antioxidants, and thioether antioxidants. When using antioxidants, 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 components (A) and (B).

[0051] Examples of fillers include glass fibers, hollow glass spheres, carbon fibers, talc, calcium carbonate, mica, potassium titanate fibers, silica, metal soaps, titanium dioxide, and carbon black. When using fillers, they are typically used in amounts of 0.1 to 50 parts by mass per 100 parts by mass of the total of components (A) and (B).

[0052] <Method for producing thermoplastic elastomer compositions> The thermoplastic elastomer composition of the present invention can be manufactured by conventional methods using a conventional extruder, Banbury mixer, rolls, Brabender plastograph, kneader-brabender, etc., to knead components (A) and (B), and other components as needed. Among these manufacturing methods, the use of an extruder, particularly a twin-screw extruder, is preferred. When manufacturing the thermoplastic elastomer composition of the present invention by kneading with an extruder, etc., it can usually be manufactured by melt kneading at a heated temperature of 160 to 240°C, preferably 180 to 220°C.

[0053] <Properties of thermoplastic elastomer compositions> (MFR) In the thermoplastic elastomer composition of the present invention, the lower limit of the melt flow rate (MFR), measured in accordance with ISO 1133 (2011) at a temperature of 230°C and a load of 21.18 N, is usually 0.5 g / 10 min or more, preferably 1 g / 10 min or more, and more preferably 5 g / 10 min or more. On the other hand, the upper limit is usually 50 g / 10 min or less, preferably 45 g / 10 min or less, more preferably 40 g / 10 min or less, and particularly preferably 35 g / 10 min or less. By setting the MFR of the thermoplastic elastomer composition within the above numerical range, it tends to exhibit excellent moldability, low-temperature impact resistance, and appearance.

[0054] (Dicewell ratio) From the viewpoint of improving flow markability, it is preferable that the die swell ratio of the thermoplastic elastomer composition of the present invention, measured and calculated using a Capillograph 1D (JIS K7199) manufactured by Toyo Seiki Seisakusho Co., Ltd. under the following conditions, be 1.34 or higher. A die swell ratio of 1.34 or higher ensures stable flow behavior when the composition flows from the molding nozzle into the mold. From this viewpoint, it is more preferable that the die swell ratio of the thermoplastic elastomer composition of the present invention be 1.40 or higher. On the other hand, there is no upper limit to the die swell ratio, but it is usually 2.00 or lower. Test temperature: 210℃ L / D: 10 (D=1mm) Shear rate: 243 cubic feet / sec The Dicewell ratio was calculated using the following formula (I). St = Dm / Dt (I) St, Dm, and Dt represent the following: St: Dicewell ratio Dm: Diameter (mm) of the extruded sample measured at the test temperature, 10 mm below the die exit. Dt: Diameter of the capillary die measured at the test temperature (mm)

[0055] (Low temperature impact resistance) The thermoplastic elastomer composition of the present invention exhibits excellent low-temperature impact resistance. In the present invention, low-temperature impact resistance is evaluated by the Izod impact strength at -45°C, as shown in the examples below. In the present invention, the Izod impact strength at -45°C is 50 kJ / m 2 It is preferable that the value be 60 kJ / m³ or higher. 2 It is more preferable that it be greater than or equal to 70kJ / m³ 2 It is even more preferable that the above conditions are met.

[0056] <Forming method> The thermoplastic elastomer composition of the present invention can be molded into a molded product using a conventional injection molding method or, if necessary, various molding methods such as gas injection molding, injection compression molding, and short-shot foam molding, thereby enabling the manufacture of the airbag storage cover of the present invention. In particular, the airbag storage cover of the present invention is preferably manufactured by injection molding, and the molding conditions when performing injection molding are as follows.

[0057] The molding temperature when injection molding an airbag storage cover is generally 150 to 300°C, preferably 160 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.

[0058] [Airbag storage cover] The airbag storage cover of the present invention, molded as described above using the thermoplastic elastomer composition of the present invention, is suitably used as an airbag storage cover for an airbag system that activates and inflates when it senses the impact or deformation of a high-speed moving object such as an automobile during a collision. The airbag storage cover of the present invention can be suitably used as a driver's side airbag storage cover, passenger side airbag storage cover, pedestrian airbag storage cover, knee airbag storage cover, side airbag storage cover, curtain airbag storage cover, and the like. [Examples]

[0059] The present invention will be described in more detail below with reference to examples and comparative examples. However, the present invention is not limited to the following examples unless it exceeds the gist of the invention. The various manufacturing conditions and evaluation result values ​​in the following examples are intended to represent preferred upper or lower limits in embodiments of the present invention, and the preferred range may be defined by a combination of the aforementioned upper or lower limits and the values ​​of the following examples or between examples.

[0060] [Raw materials for thermoplastic elastomer compositions] <Ingredient (A)> (A-1): Propylene-based block copolymer (obtained by polymerizing a propylene homopolymer in the first step, followed by polymerizing an ethylene-propylene copolymer in the second step) Novatec® PP BC3B, manufactured by Nippon Polypropylene Co., Ltd. MFR (ISO 1133): 10g / 10min (Measurement conditions: 230℃, load 21.18N) (A-2): Propylene-based block copolymer (obtained by polymerizing a propylene homopolymer in the first step, followed by polymerizing an ethylene-propylene copolymer in the second step) Novatec® PP BC03B, manufactured by Nippon Polypropylene Co., Ltd. MFR (ISO 1133): 30g / 10min (Measurement conditions: 230℃, load 21.18N) (A-3): Propylene-based block copolymer (obtained by polymerizing a propylene homopolymer in the first step, followed by polymerizing an ethylene-propylene copolymer in the second step) Novatec® PP BC06NCA, manufactured by Nippon Polypropylene Co., Ltd. MFR (ISO 1133): 60g / 10min (Measurement conditions: 230℃, load 21.18N)

[0061] [Component (B)] (B-1): Ethylene-1-octene copolymer rubber Engage 8407, manufactured by Dow Chemical. MFR (ISO 1133): 70g / 10min (Measurement conditions: 230℃, load 21.18N) (B-2): Ethylene-1-octene copolymer rubber Engage 8200 manufactured by Dow Chemical MFR (ISO 1133): 10g / 10min (Measurement conditions: 230℃, load 21.18N) (B-3): Ethylene-1-octene copolymer rubber Engage 8100 manufactured by Dow Chemical MFR (ISO 1133): 2g / 10min (Measurement conditions: 230℃, load 21.18N) (B-4): Ethylene-1-octene copolymer rubber Engage (manufactured by Dow Chemical) 8150 MFR (ISO 1133): 1g / 10min (Measurement conditions: 230℃, load 21.18N)

[0062] [Method for evaluating thermoplastic elastomer compositions] (1) Low-temperature impact resistance (Izod impact strength) A thermoplastic elastomer composition was molded into an Izod impact strength test specimen measuring 4 mm thick x 10 mm wide x 80 mm long using an in-line screw-type injection molding machine (Sumitomo Electric Industries, Ltd. "SE180DU") at an injection speed of 30 mm / s, a cylinder temperature of 220°C, and a mold temperature of 40°C. A notch was then made in the dumbbell (the notch dimensions and evaluation method conformed to ISO 180 (2013)), and the measurement was performed at -45°C. In the table, (P) indicates "partial break." If not indicated, it indicates "complete break."

[0063] (2) Flow marking properties Flow mark properties were assessed by molding a test specimen with tear lines (a sheet measuring 3 mm thick x 100 mm wide x 350 mm long, with tear lines placed at 5 cm, 12.5 cm, 20 cm, and 27 cm from the gate, with the thinnest part having a thickness of 0.7 mm) from a thermoplastic elastomer composition using an inline screw-type injection molding machine (Sumitomo Electric Industries, Ltd. "SE180DU") at an injection speed of 20 mm / s, a cylinder setting temperature of 230°C, and a mold temperature of 40°C. The appearance of the parallel sections excluding the tear lines was visually observed and judged according to the following criteria. Judgment criteria ×: Flow marks are noticeable, resulting in a poor appearance. △: Flow marks are observed, but they are within market acceptable limits. ○: No flow marks were observed.

[0064] (3) Dicewell ratio The measurements were taken 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℃ L / D: 10 (D=1mm) Shear rate: 243 cubic feet / sec The Dicewell ratio was calculated using the following formula (I). St = Dm / Dt (I) St, Dm, and Dt represent the following: St: Dicewell ratio Dm: Diameter (mm) of the extruded sample measured at the test temperature, 10 mm below the die exit. Dt: Diameter of the capillary die measured at the test temperature (mm)

[0065] [Example 1] To a total of 100 parts by mass of component (A-1): 50 parts by mass and component (B-1): 50 parts by mass, 0.1 parts by mass of antioxidant (BASF Japan product name Irganox® 1010), 0.1 parts by mass of antioxidant (BASF Japan product name Irgaphos® 168), 0.1 parts by mass of mold release agent (Croda Japan product name CrodamideVRX®), and 1.5 parts by mass of black pigment (carbon concentration 40% by mass) were blended in a Henschel mixer for 1 minute. The mixture was then fed into a co-screw extruder (Kobe Steel "TEX30α", L / D=45, number of cylinder blocks: 13) from the first feed port at a speed of 30 kg / hr, heated to a temperature in the range of 180~210°C, melt-kneaded, and then pelletized to produce a thermoplastic elastomer composition. The evaluation results of the obtained thermoplastic elastomer composition are shown in Table 1.

[0066] [Example 2, Comparative Examples 1-4] A thermoplastic elastomer composition pellet was obtained in the same manner as in Example 1, except that the raw material formulation 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. Table 1 also shows the MFR(B) / MFR(A) calculated from the MFR(A) values ​​of component (A) and component (B).

[0067] [Table 1]

[0068] [Discussion of evaluation results] As shown in Table 1, Examples 1 and 2, which correspond to the thermoplastic elastomer composition of the present invention, exhibited excellent low-temperature impact resistance and flowmark performance. On the other hand, while Comparative Example 1 had excellent low-temperature impact resistance, flow marks were clearly visible, indicating inferior flow mark resistance. Comparative Examples 2-4 exhibited excellent flow mark resistance but poor low-temperature impact resistance. [Industrial applicability]

[0069] The thermoplastic elastomer composition of the present invention is suitable for various applications because it exhibits excellent low-temperature impact resistance and flowmark properties. For example, the thermoplastic elastomer composition of the present invention is useful as an interior part of automobiles such as airbag storage covers, instrument panels, center panels, center console boxes, door trims, pillars, assist grips, and steering wheels; an exterior part of automobiles such as mudguards and chromes; a home appliance part; a building material; and furniture. Among these, the thermoplastic elastomer composition of the present invention is particularly useful as an airbag storage cover, and among these airbag storage covers, it is suitable, for example, as an airbag storage cover for an airbag system that activates and inflates to protect occupants when it senses the impact or deformation of a high-speed moving object such as an automobile during a collision.

Claims

1. The compound contains component (A): a propylene-based block copolymer and component (B): an ethylene-α-olefin copolymer, and satisfies the following formula: The aforementioned component (B) is ethylene-1-octene copolymer rubber, When the sum of component (A) and component (B) is 100% by mass, the content of component (A) is 20% by mass or more and 80% by mass or less. Using a notched IZOD impact strength test specimen prepared in reference to ISO 180, the IZOD impact value measured in a -45°C atmosphere was 60 kJ / m ２ That's all. A thermoplastic elastomer composition having a die swell ratio of 1.34 or higher when measured using a capillary rheometer (see JIS K7199) at a test temperature of 210°C and a shear rate of 243 / sec. Formula: [Melt flow rate of component (B) measured at a test temperature of 230°C and a load of 21.18 N] / [Melt flow rate of component (A) measured at a test temperature of 230°C and a load of 21.18 N] ≥ 0.5

2. The thermoplastic elastomer composition according to claim 1, wherein the melt flow rate (test temperature 230°C, load 21.18 N) of the propylene-based block copolymer of component (A) is 1 to 20 g / 10 min.

3. The thermoplastic elastomer composition according to claim 1 or 2, wherein the melt flow rate (test temperature 230°C, load 21.18 N) of the ethylene-α-olefin copolymer of component (B) is 10 to 100 g / 10 min.

4. The thermoplastic elastomer composition according to any one of claims 1 to 3, wherein the α-olefin of the ethylene-α-olefin copolymer of component (B) has 3 to 8 carbon atoms.

5. An injection-molded article obtained by injection molding a thermoplastic elastomer composition according to any one of claims 1 to 4.

6. An airbag storage cover using the thermoplastic elastomer composition according to any one of claims 1 to 4.

7. The compound contains component (A): a propylene-based block copolymer and component (B): an ethylene-α-olefin copolymer, and satisfies the following formula: The aforementioned component (B) is ethylene-1-octene copolymer rubber, When the sum of component (A) and component (B) is 100% by mass, the content of component (A) is 20% by mass or more and 80% by mass or less. An airbag storage cover made of a thermoplastic elastomer composition having a die swell ratio of 1.34 or higher when measured with a capillary rheometer (see JIS K7199) at a test temperature of 210°C and a shear rate of 243 / sec. Formula: [Melt flow rate of component (B) measured at a test temperature of 230°C and a load of 21.18 N] / [Melt flow rate of component (A) measured at a test temperature of 230°C and a load of 21.18 N] ≥ 0.5

8. The airbag storage cover according to claim 7, wherein the melt flow rate (test temperature 230°C, load 21.18 N) of the propylene-based block copolymer of component (A) is 1 to 20 g / 10 min.

9. The airbag storage cover according to claim 7 or 8, wherein the melt flow rate (test temperature 230°C, load 21.18 N) of the ethylene-α-olefin copolymer of component (B) is 10 to 100 g / 10 min.

10. The airbag storage cover according to any one of claims 7 to 9, wherein the α-olefin of the ethylene-α-olefin copolymer of component (B) has 3 to 8 carbon atoms.

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