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

Abstract

To provide a thermoplastic elastomer composition capable of forming a molded product excellent in appearance and flow mark around a tear line while maintaining rigidity.SOLUTION: A thermoplastic elastomer composition contains the following component (A), and has a minimum die swell ratio in a range of 60.80 / s to 6080 / s of a shear rate at a test temperature of 210°C in a capillary rheometer (see JIS K7199) of 1.30 or more. Component (A): a propylene block copolymer containing 50 to 97 mass% of propylene units and 3 to 50 mass% of ethylene units.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a thermoplastic elastomer composition, an injection-molded article made from this thermoplastic elastomer composition, and an airbag storage cover. [Background technology]

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

[0003] Various proposals have been made regarding the structure and materials of the airbag storage cover in airbag systems, so that it ruptures 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 a thermoplastic elastomer composition obtained by dynamically heat-treating a composition containing a specific amount of a specific propylene polymer, a specific olefin-based block copolymer, and a styrene-conjugated diene block copolymer and / or its hydrogenated product in the presence of an organic peroxide. Patent Document 2 also proposes a thermoplastic elastomer composition obtained by dynamically heat-treating a polypropylene block copolymer and an ethylene-α-olefin copolymer having an ethylene unit content of 5 to 50% by mass in the presence of an organic peroxide and a crosslinking aid. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2016-186041 [Patent Document 2] Japanese Patent Publication No. 2018-141092 [Overview of the project] [Problems that the invention aims to solve]

[0006] In recent years, concerns have arisen regarding the potential for airbag storage covers to break at low temperatures due to increased airbag deployment power. Therefore, materials with superior rigidity are desired from the perspectives of improved safety and design flexibility. Furthermore, while airbag storage covers have traditionally been manufactured through a painting process, the cost associated with this process, such as the need to add painting lines, has led to a demand for materials that can be manufactured without painting in order to reduce production costs. In addition, from an aesthetic standpoint, molded products with improved gloss unevenness and flow marks on the surface design side of the tear line portion of the airbag storage cover (the thin-walled portion of the airbag cover designed to tear open when the airbag deploys) are desired.

[0007] Detailed investigations by the present inventors revealed that the thermoplastic elastomer composition described in Patent Document 1 suffers from poor flow marking properties and an unsatisfactory appearance. Furthermore, while the thermoplastic elastomer composition described in Patent Document 2 improved design (flow marking properties), it was found to suffer from an unsatisfactory appearance around the tear line.

[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 that enables molded articles with excellent appearance around the tear line and flow markings while maintaining rigidity. [Means for solving the problem]

[0009] The inventors of the present invention have conducted extensive research to solve the above problems and have found that the above problems can be solved by having a thermoplastic elastomer composition containing a specific propylene-based block copolymer in which the minimum value of the die swell ratio in the range of 60.80 / s to 6080 / s at a test temperature of 210°C using a capillary rheometer (see JIS K7199) is 1.30 or higher.

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

[10] .

[0011] [1] A thermoplastic elastomer composition containing the following component (A), wherein the minimum value of the die swell ratio in a capillary rheometer (see JIS K7199) at a test temperature of 210°C and a shear rate in the range of 60.80 / s to 6080 / s is 1.30 or greater. Component (A): A propylene-based block copolymer having a propylene unit content of 50-97% by mass and an ethylene unit content of 3-50% by mass.

[0012] [2] The thermoplastic elastomer composition according to [1], wherein the ratio of the maximum to minimum die swell ratio in the range of 60.80 / s to 6080 / s at a test temperature of 210°C using a capillary rheometer (see JIS K7199) is 1.15 or less.

[0013] [3] The thermoplastic elastomer composition according to [1] or [2], further comprising the following component (B). Component (B): A propylene-based random copolymer consisting of propylene units, ethylene units, and / or α-olefin units other than propylene.

[0014] [4] A thermoplastic elastomer composition according to any of [1] to [3] further containing the following component (C) Component (C): An ethylene copolymer consisting of ethylene units and α-olefin units with 4 to 20 carbon atoms.

[0015] [5] The thermoplastic elastomer composition according to [4], wherein the α-olefin unit of component (C) has 4 or more carbon atoms and 8 or fewer carbon atoms.

[0016] [6] The thermoplastic elastomer composition according to [4] or [5], wherein component (C) has a crosslinked structure.

[0017] [7] Further comprising the following component (D), and the content of the following component (D) is 0.01 part by mass to 1.00 part by mass with respect to 100 parts by mass in total of the said component (A), component (B) and component (C). The thermoplastic elastomer composition according to [6]. Component (D): Organic peroxide

[0018] [8] Further comprising the following component (E), and the content of the following component (E) is 0.01 part by mass to 1.00 part by mass with respect to 100 parts by mass in total of the said component (A), component (B) and component (C). The thermoplastic elastomer composition according to [6] or [7]. Component (E): Crosslinking aid

[0019] [9] An injection molded article obtained by injection molding the thermoplastic elastomer composition according to any one of [1] to [8].

[0020]

[10] An airbag storage cover using the thermoplastic elastomer composition according to any one of [1] to [8].

Advantages of the Invention

[0021] According to the present invention, it is possible to provide a thermoplastic elastomer composition that enables an injection molded article excellent in appearance and flow mark properties around the tear line portion while maintaining rigidity. An airbag storage cover made of an injection molded article obtained by injection molding 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.

Embodiments for Carrying Out the Invention

[0022] Hereinafter, the present invention will be described in detail. However, the present invention is not limited to the following description, and can be arbitrarily modified and implemented without departing from the gist of the present invention. In this specification, when expressing by sandwiching numerical values or physical property values before and after using "~", it shall be used including the values before and after.

[0023] In the present invention, "airbag storage cover" refers to the entire container for storing an airbag, and for example, in a container in which an airbag is stored, it refers to the opening through which the airbag deploys, or the entire container integrated with this opening.

[0024] [Thermoplastic elastomer composition] The thermoplastic elastomer composition of the present invention is a thermoplastic elastomer composition containing the following component (A), wherein the minimum value of the die swell ratio (hereinafter sometimes simply referred to as "die swell ratio") in the range of shear rates of 60.80 / s to 6080 / s at a test temperature of 210°C using a capillary rheometer (see JIS K7199) is 1.30 or higher. Component (A): A propylene-based block copolymer having a propylene unit content of 50-97% by mass and an ethylene unit content of 3-50% by mass.

[0025] <Dicewell ratio> Through the inventors' studies, it was found that in the thermoplastic elastomer composition of the present invention containing component (A), when the minimum die swell ratio in the shear rate range of 60.80 / s to 6080 / s is 1.30 or higher, the appearance around the tear line and flow markings are excellent. A die swell ratio greater than 1 in the shear rate range of 60.80 / s to 6080 / s means that a force acting perpendicular to the flow direction of the resin used for molding is acting on it. In the thermoplastic elastomer composition of the present invention, by setting the die swell ratio to 1.30 or higher, the flow leading edge of the resin flowing in the mold becomes stable at a wide range of molding speeds from low to high, and it is believed that the appearance around the tear line and flow markings are excellent. From the above viewpoint, the minimum die swell ratio of the thermoplastic elastomer composition of the present invention is preferably 1.31 or higher, more preferably 1.35 or higher, and even more preferably 1.40 or higher. There is no upper limit to the die swell ratio of the thermoplastic elastomer composition, but it is usually 2.00 or lower.

[0026] Furthermore, it is preferable that the ratio of the maximum to minimum die swell ratio in the shear rate range of 60.80 / s to 6080 / s is 1.15 or less, as this results in excellent appearance around the tear line. A small ratio of the maximum to minimum die swell ratio in the shear rate range of 60.80 / s to 6080 / s means that the thermoplastic elastomer composition of the present invention does not exhibit shear rate dependence from low to high speeds in its molten state. In areas where the mold thickness fluctuates significantly, such as around the tear line, the flow rate of the molten resin used for molding also fluctuates greatly. However, by using a thermoplastic elastomer composition such that the ratio of the maximum to minimum die swell ratio in the shear rate range of 60.80 / s to 6080 / s is 1.15 or less, stable mold texture transfer properties tend to be easily obtained even in such areas. From the above perspective, it is more preferable that the ratio of the maximum to the minimum die swell ratio in the shear rate range of 60.80 / s to 6080 / s be 1.10 or less.

[0027] In the present invention, the die swell ratio in a capillary rheometer (see JIS K7199) is a value measured during the extrusion process in which a sample is extruded under the following conditions using a Capillograph 1D (JIS K7199) manufactured by Toyo Seiki Seisakusho Co., Ltd., and is calculated by the following formula (I). Test temperature: 210℃ L / D: 10 (D=1mm) Shear rate: 60.80 / s ~ 6080 / s 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)

[0028] The die swell ratio of the thermoplastic elastomer composition of the present invention can be controlled by the rubber component used and the manufacturing conditions. For example, a composition containing components (A), (B), and (C) described below can be dynamically crosslinked using component (D) as a crosslinking agent and component (E) as a crosslinking aid (hereinafter sometimes referred to as "dynamic crosslinking"), and a desired die swell ratio can be obtained by controlling the crosslinking state.

[0029] By reducing the viscosity difference between the resin components (A) and (B) and the rubber component (C) during melting, or by using a component (C) with low viscosity (relatively high MFR), the dispersion of components (A) and (B) and component (C) can be brought closer to a co-continuous layer, thereby controlling the die swell ratio to increase. In this case, it is preferable to use a component (C) with high viscosity (relatively low MFR) in combination in order to control the physical properties, especially low-temperature impact resistance, without impairing them. Alternatively, the desired thermoplastic elastomer composition can be obtained by performing the dynamic heat treatment described later using components (D) and (E).

[0030] When dynamic crosslinking is performed using the organic peroxide of component (D), the -OO- bonds of component (D) are cleaved, and the resulting free radicals abstract hydrogen atoms from the polymer, generating polymer radicals. Here, if the polymer is a disintegrating polymer such as polypropylene, the polymer radicals generated by the abstraction of hydrogen atoms cause the molecular chains to break and decompose (polymer radical cleavage reaction), resulting in a significant decrease in high-temperature strength. In contrast, if the polymer is a crosslinking polymer, the polymer radicals recombine to form -CC- bonds, and crosslinking proceeds.

[0031] Furthermore, when a crosslinking aid of component (E) is used in combination, it is possible to promote the recombination of polymer radicals generated using component (D), and to suppress the polymer radical cleavage reaction of disintegrating polymers.

[0032] In the thermoplastic elastomer composition of the present invention, components (A) and (B) have the properties of the disintegrating polymer, and component (C) has the properties of the crosslinking polymer. Therefore, during dynamic crosslinking treatment, the amount and conditions of use of components (D) and (E) are controlled according to the properties of components (A) to (C) so as to appropriately crosslink component (C) while suppressing the decomposition of components (A) and (B). This makes it possible to form a dispersion morphology including a sea-island structure or co-continuity in which rubber domains of component (C) with an appropriate crosslinking density exist in a matrix of stably existing components (A) and (B), thereby obtaining a thermoplastic elastomer composition having a desired die swell ratio and low-temperature impact resistance.

[0033] <Ingredient (A)> The thermoplastic elastomer composition of the present invention contains a propylene-based block copolymer as component (A), having a propylene unit content of 50 to 97% by mass and an ethylene unit content of 3 to 50% by mass. By including component (A), a thermoplastic elastomer composition with excellent rigidity can be obtained.

[0034] The lower limit of the propylene unit content of the propylene-based block copolymer of component (A) is usually 50% by mass or more, preferably 70% by mass or more, relative to the total amount of component (A). On the other hand, the upper limit of the propylene unit content of the propylene-based block copolymer of component (A) is usually 97% by mass or less, preferably 95% by mass or less. When the propylene unit content of component (A) is above the lower limit, the heat resistance and rigidity tend to be good. When the propylene unit content of component (A) is below the upper limit, the low-temperature impact resistance tends to be good. When component (A) is composed of two or more propylene-based block copolymers with different compositions, the propylene unit content of component (A) as a whole should be within the above numerical range.

[0035] The lower limit of the ethylene unit content of the propylene-based block copolymer of component (A) is usually 3% by mass or more, preferably 5% by mass or more, relative to the total amount of component (A). On the other hand, the upper limit of the ethylene unit content of the propylene-based block copolymer of component (A) is usually 50% by mass or less, preferably 40% by mass or less. When the ethylene unit content of component (A) is above the lower limit, it tends to have good compatibility with component (C). When the ethylene unit content of component (A) is below the upper limit, it tends to have good heat resistance and rigidity. When component (A) is composed of two or more propylene-based block copolymers with different compositions, it is sufficient if the ethylene unit content of component (A) as a whole is within the above numerical range.

[0036] The content of propylene units and ethylene units in component (A) and the content of α-olefin units described later, the content of propylene units and ethylene units in component (B) described later and the content of α-olefin units described later, and the content of ethylene units and α-olefin units in component (C) can each be determined by infrared spectroscopy.

[0037] Component (A) contains propylene units and ethylene units in the aforementioned preferred proportions relative to the total component (A), and may also contain α-olefin units other than propylene units and ethylene units (hereinafter sometimes referred to as "other α-olefins"), monomer units other than α-olefins, etc. Examples of propylene-based block copolymers of component (A) include propylene-ethylene block copolymers and propylene-ethylene-other α-olefin block copolymers.

[0038] The total content of ethylene units other than propylene units, other α-olefin units, and other monomer units in component (A) is preferably 3 to 50% by mass.

[0039] If component (A) is a propylene-ethylene-other α-olefin block copolymer, then α-olefin units other than propylene 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. The α-olefins other than propylene 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.

[0040] Examples of propylene-based block copolymers of component (A) include propylene-ethylene 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.

[0041] 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.

[0042] The melt flow rate (MFR) of component (A) (230°C, load 21.18N) is not limited, but is usually 0.1g / 10min or more, preferably 3g / 10min or more, more preferably 5g / 10min or more, and even more preferably 8g / 10min or more, from the viewpoint of the appearance of the molded article. Also, the melt flow rate (MFR) of component (A) (230°C, load 21.18N) is usually 200g / 10min or less, preferably 150g / 10min or less, and more preferably 100g / 10min or less, from the viewpoint of tensile strength. The melt flow rate (MFR) of component (A) is measured under conditions of 230°C and a load of 21.18N, in accordance with ISO 1133 (2011). Component (A) may consist of multiple components with melt flow rates (230°C, load 21.18N) within the range of 0.1 to 200 g / 10 min.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] <Ingredient (B)> The thermoplastic elastomer composition of the present invention preferably contains a propylene-based random copolymer consisting of propylene units and ethylene units and / or α-olefin units other than propylene as component (B). The propylene-based random copolymer of component (B) improves the compatibility between component (A) and component (B), and reduces the crystallinity of component (A), thereby improving transferability to the mold.

[0047] In the propylene-based random copolymer of component (B), the propylene unit content is preferably 60 to 99% by mass, and more preferably 80 to 98% by mass. This is preferable because the propylene unit content of component (B) tends to fall within the melting peak temperature range described later.

[0048] The propylene-based random copolymer of component (B) has ethylene units and / or α-olefin units other than propylene units as constituent units other than propylene units. Examples of constituent units other than propylene units that component (B) may contain include ethylene units, 1-butene units, 1-pentene units, 1-hexene units, 1-heptene units, 1-octene units, 1-nonene units, 1-decene units, 1-undecene units, 1-dodecene units, 1-tridecene units, 1-tetradecene units, 1-pentadecene units, 1-hexadecene units, 1-heptadecene units, 1-octadecene units, 1-nonadecene units, 1-eicosene units, 3-methyl-1-butene units, 3-methyl-1-pentene units, 4-methyl-1-pentene units, 2-ethyl-1-hexene units, and 2,2,4-trimethyl-1-pentene units. These may contain only one type or two or more types. The ethylene units and / or α-olefin units other than propylene that component (B) contains in addition to propylene units are preferably ethylene units, 1-butene units, and the like.

[0049] In the propylene-based random copolymer of component (B), the content of ethylene units and / or α-olefin units other than propylene is preferably 1 to 40% by mass, and more preferably 2 to 20% by mass. This is preferable because the content of ethylene units and / or α-olefin units other than propylene in component (B) tends to fall within the range of the melting peak temperature described later.

[0050] The melt flow rate (MFR) of component (B) (230°C, load 21.18N) is not limited, but is usually 0.1g / 10min or more, preferably 0.5g / 10min or more, and more preferably 1g / 10min or more, from the viewpoint of moldability. Also, the melt flow rate (MFR) of component (B) (230°C, load 21.18N) is usually 200g / 10min or less, preferably 150g / 10min or less, and more preferably 100g / 10min or less, from the viewpoint of tensile strength. The melt flow rate (MFR) of component (B) is measured under conditions of 230°C and a load of 21.18N, in accordance with ISO 1133 (2011). Component (B) may consist of multiple components with melt flow rates (230°C, load 21.18N) within the range of 0.1 to 200 g / 10 min.

[0051] The melting peak temperature of component (B) is preferably 50°C or higher, more preferably 75°C or higher, even more preferably 100°C or higher, and particularly preferably 125°C or higher. On the other hand, the melting peak temperature of component (B) is preferably 155°C or lower, more preferably 154°C or lower, and even more preferably 153°C or lower. A melting peak temperature of component (B) above the lower limit is preferable from the viewpoint of heat resistance. A melting peak temperature of component (B) below the upper limit is preferable from the viewpoint of appearance performance.

[0052] The melting peak temperature of component (B) can be measured according to JIS K7121 by the following method. Specifically, the melting behavior of component (B) is measured by sequentially performing the following steps (1) to (3) using a differential scanning calorimeter (DSC6220 manufactured by SSI Nanotechnology). In each process, time is plotted on the horizontal axis and the amount of heat of fusion on the vertical axis to obtain a melting curve, and the peak top of the peak observed in process (3) is defined as the melting peak temperature. Step (1): Heat 5 mg of the sample from room temperature at a rate of 100°C / min from 40°C to 200°C, and hold the temperature for 3 minutes after the heating is complete. Step (2): Cool the temperature from 200°C to 40°C at a rate of 10°C / min, and hold the temperature for 3 minutes after the cooling is complete. Step (3): Increase the temperature from 40°C to 200°C at a rate of 10°C / min.

[0053] The propylene-based random copolymer of component (B) is particularly preferred if it has a melting peak temperature of 100°C to 155°C and a melt flow rate (230°C, 21.2N) of 0.1 to 200 g / 10 min.

[0054] As a method for producing the propylene-based random copolymer of component (B), 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.

[0055] Ingredient (B) can also be obtained as a commercially available product. Commercially available products that fall under these categories include: Prime Polymer's "Prim Polypro®," Sumitomo Chemical's "Sumitomo Noblen®," Nippon Polypropylene's "Novatec® PP," LyondellBasell's "Moplen®," ExxonMobil's "ExxonMobil PP," Formosa Plastics' "Formolene®," Borealis' "Borealis PP," LG Chemical's "SEETEC PP," A. Schulman's "ASI POLYPROPYLENE," INEOS Olefins & Polymers' "INEOS PP," Braskem's "Braskem PP," Samsung Total Petrochemicals' "Samsung Total," Sabic's "Sabic® PP," and TOTAL PETROCHEMICALS' "TOTAL PETROCHEMICALS Materials such as "Polypropylene" and SK Corporation's "YUPLENE (registered trademark)" are available, and these can be appropriately selected and combined for use.

[0056] <Ingredient (C)> The thermoplastic elastomer composition of the present invention preferably contains an ethylene-based copolymer consisting of an ethylene unit and an α-olefin unit having 4 to 20 carbon atoms as component (C).

[0057] In the ethylene copolymer of component (C), it is preferable that the ethylene unit content is 50 to 80% by mass and the α-olefin unit content is 20 to 50% by mass, when the sum of the ethylene unit content and α-olefin unit content is taken as 100% by mass. When the ethylene unit and α-olefin 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 improve. Furthermore, in embodiments in which component (C) has a crosslinked structure due to dynamic heat treatment in the presence of the organic peroxide of component (D) described later, the gloss tends to decrease and the appearance tends to improve, which is preferable.

[0058] The α-olefins constituting the ethylene copolymer of component (C) are not limited, but specifically include 1-butene, 3-methyl-1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, and 1-decene. Component (C) may contain only one of these α-olefin units, or two or more. Among these, α-olefins with 4 to 8 carbon atoms are preferred, and 1-octene is more preferred. The inclusion of 1-octene units as α-olefin units in the ethylene-α-olefin copolymer results in good tensile strength.

[0059] Specific examples of component (C) 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.

[0060] The melt flow rate (MFR) of component (C) (190°C, load 21.18N) is not limited, but is usually 80g / 10min or less, preferably 50g / 10min or less, and more preferably 40g / 10min or less, from the viewpoint of strength. Also, the melt flow rate (MFR) of component (C) (190°C, load 21.18N) is usually 0.01g / 10min or more, preferably 0.05g / 10min or more, and more preferably 0.10g / 10min or more, from the viewpoint of fluidity. The melt flow rate (MFR) of component (C) is measured under conditions of 190°C and a load of 21.18N, according to ASTM D1238.

[0061] From the viewpoint of having excellent low-temperature impact resistance and excellent appearance and flow mark resistance around the tear line, it is preferable to use a combination of a low viscosity component (Cl) (with a relatively high MFR) and a high viscosity component (C2) (with a relatively low MFR) as component (C). In this case, the lower limit of the melt flow rate of component (C1) (190°C, load 21.18N) is preferably 3g / 10 min or more, more preferably 5g / 10 min or more, and even more preferably 7g / 10 min or more. The upper limit of the melt flow rate of component (C1) (190°C, load 21.18N) is preferably 200g / 10 min or less, more preferably 100g / 10 min or less, and even more preferably 80g / 10 min or less. On the other hand, the lower limit of the melt flow rate (190°C, load 21.18N) of component (C2) is preferably 0.01 g / 10 min or more, more preferably 0.05 g / 10 min or more, and even more preferably 0.1 g / 10 min or more. The upper limit of the melt flow rate (190°C, load 21.18N) of component (C2) is preferably less than 3g / 10min, more preferably 2g / 10min or less, and even more preferably 1g / 10min or less. The ratio of the melt flow rate of component (C1) (190°C, load 21.18N) to the melt flow rate of component (C2) (MFR of component (C1) / MFR of component (C2)) is preferably greater than 1 and 20,000 or less, more preferably 5 or more and 2,000 or less, and even more preferably 7 or more and 800 or less.

[0062] From the viewpoint of low-temperature impact resistance, the density of component (C) is preferably 0.880 g / cm³. 3 The following, and more preferably 0.870 g / cm³ 3 The following applies. On the other hand, there is no particular restriction on the lower limit, but it is usually 0.850 g / cm³. 3 That concludes the explanation. The density of component (C) can be measured according to ASTM D792.

[0063] As a method for producing component (C), known polymerization methods using known olefin polymerization catalysts are used. For example, as olefin polymerization catalysts, complex catalysts such as Ziegler-Natta catalysts, metallocene complexes, and non-metallocene complexes can be used, and polymerization methods include slurry polymerization, solution polymerization, bulk polymerization, and gas-phase polymerization.

[0064] Component (C) may be a commercially available product. Examples of commercially available components (C) include the "Engage(registered trademark)-XLT" series and "INFUSE(registered trademark)" series from Dow Chemical, the "Solumer(registered trademark)" series from SK Chemicals, the "Tafmer(registered trademark)" series and "Mitsui EPT" from Mitsui Chemicals, "JSR EPR" from JSR, "Esplen(registered trademark)" from Sumitomo Chemical, and "Keltan(registered trademark)" from LANXESS.

[0065] The ethylene-α-olefin copolymer with 4 to 20 carbon atoms in component (C) may be used alone, or two or more copolymers with different copolymer component compositions and physical properties may be mixed and used.

[0066] <Ingredient (D)> In the thermoplastic elastomer composition of the present invention, the organic peroxide of component (D) acts as a crosslinking agent in dynamic heat treatment. This dynamic heat treatment causes component (C) to have a crosslinked structure, which reduces the gloss of molded articles such as airbag storage covers made from the thermoplastic elastomer composition of the present invention, resulting in a particularly good appearance.

[0067] As component (D), either aromatic organic peroxides or aliphatic organic peroxides can be used. Specifically, examples 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-hexine, 1,3-bis(t-butylperoxyisopropyl)benzene, and 1,1-di(t-butylperoxy)-3,3,5-trimethylcyclohexane; peroxyesters 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-hexine; 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 individually or in combination of two or more.

[0068] <Ingredient (E)> In the thermoplastic elastomer composition of the present invention, component (E) acts as a crosslinking aid in dynamic heat treatment.

[0069] Examples of crosslinking aids for component (E) include peroxide aids such as sulfur, p-quinone dioxime, p-dinitrosobenzene, and 1,3-diphenylguanidine; 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 individually or in combination of two or more.

[0070] <Composition Ratio> The blending ratio of the raw materials for the thermoplastic elastomer composition of the present invention is described below.

[0071] The content of component (B) in the thermoplastic elastomer composition of the present invention is usually 5 parts by mass or more, preferably 10 parts by mass or more, and more preferably 15 parts by mass or more, per 100 parts by mass of component (A), from the viewpoint of molded appearance and low-temperature impact resistance. Furthermore, from the viewpoint of rigidity and tensile strength of the molded product, it is usually 100 parts by mass or less, preferably 90 parts by mass or less, and more preferably 85 parts by mass or less.

[0072] The content of component (C) 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, when the total of components (A) and (B) is 100 parts by mass, from the viewpoint of low-temperature impact resistance. On the other hand, from the viewpoint of rigidity and tensile strength of the product, it is usually 200 parts by mass or less, preferably 150 parts by mass or less, and more preferably 120 parts by mass or less.

[0073] The content of component (D) in the thermoplastic elastomer composition of the present invention is usually 0.01 parts by mass or more, preferably 0.05 parts by mass or more, and more preferably 0.10 parts by mass or more, when the total of components (A), (B), and (C) is 100 parts by mass, from the viewpoint of low gloss. On the other hand, from the viewpoint of low-temperature impact resistance and molded appearance, it is usually 1.00 part by mass or less, preferably 0.80 parts by mass or less, and more preferably 0.60 parts by mass or less.

[0074] The content of component (E) in the thermoplastic elastomer composition of the present invention is usually 0.01 parts by mass or more, preferably 0.05 parts by mass or more, and more preferably 0.075 parts by mass or more, when the total of components (A), (B), and (C) is 100 parts by mass, from the viewpoint of low gloss. On the other hand, from the viewpoint of flow marking, it is usually 1.00 part by mass or less, preferably 0.80 parts by mass or less, and more preferably 0.60 parts by mass or less.

[0075] <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.

[0076] Other components may include, for example, resins such as thermoplastic resins and elastomers other than components (A), (B), and (C), antioxidants, fillers, heat stabilizers, weathering aids, light stabilizers, ultraviolet 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.

[0077] 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 and polyolefin resins (excluding those corresponding to components (A) and (B)). Examples of elastomers other than component (C) include styrene elastomers; polyester elastomers; and polybutadiene.

[0078] Examples of antioxidants include phenolic antioxidants, phosphite antioxidants, and thioether antioxidants. When using antioxidants, they are typically used in an amount of 0.01 to 3.0 parts by mass per 100 parts by mass of the total of components (A), (B), and (C).

[0079] 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), (B), and (C).

[0080] [Method for producing thermoplastic elastomer compositions] The thermoplastic elastomer composition of the present invention is produced by dynamically heat-treating a composition containing predetermined amounts of component (A), component (B), component (C), and other components in the presence of component (D) or component (D) and component (E).

[0081] In the present invention, "dynamic heat treatment" means kneading in a molten or semi-molten state in the presence of component (D) or component (D) and component (E). This dynamic heat treatment is preferably carried out by melt kneading, and suitable mixing and kneading equipment for this purpose includes, for example, a closed-type Banbury mixer, mixing rolls, a kneader, and a twin-screw extruder. Among these, the use of a twin-screw extruder is preferred. A preferred embodiment of the manufacturing method using this twin-screw extruder is to supply each component to the raw material supply port (hopper) of a twin-screw extruder having multiple raw material supply ports and perform the dynamic heat treatment.

[0082] The temperature during dynamic heat treatment is typically 80 to 300°C, preferably 100 to 250°C. The duration of the dynamic heat treatment is typically 0.1 to 30 minutes.

[0083] When performing dynamic heat treatment of the thermoplastic elastomer composition of the present invention using a twin-screw extruder, it is preferable to extrude while maintaining the relationship shown in formula (1) below between the barrel radius R (mm), screw rotation speed N (rpm), and discharge volume Q (kg / hour) of the twin-screw extruder, and more preferably while maintaining the relationship shown in formula (2) below. 2.6 <NQ / R3<22.6 …(1) 3.0 <NQ / R3<20.0 …(2)

[0084] For efficient production of thermoplastic elastomer compositions, it is preferable that the relationship between the barrel radius R (mm), screw rotation speed N (rpm), and discharge rate Q (kg / hour) of a twin-screw extruder is greater than the lower limit. On the other hand, it is preferable that the relationship is smaller than the upper limit because it suppresses heat generation due to shear and reduces the generation of foreign matter that causes defects in appearance.

[0085] [Molded products] <Forming 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 articles using conventional injection molding or, if necessary, various molding methods such as gas injection molding, injection compression molding, and short-shot foam molding. Among these, it is preferable to manufacture the articles by injection molding, and the molding conditions when performing injection molding are as follows. The molding temperature when injection molding molded products 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.

[0086] <Application> The molded product obtained in this way can be used, for example, as an airbag storage cover. As an airbag storage cover, it is preferably 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.

[0087] [Physical properties of thermoplastic elastomer compositions and molded articles] <mfr> The thermoplastic elastomer composition of the present invention also exhibits excellent moldability. Specifically, the melt flow rate (MFR) at a temperature of 230°C and a measurement load of 21.18 N in accordance with ISO 1133 (2011) is typically 0.5 to 50 g / 10 min, preferably 1 to 40 g / 10 min, and more preferably 2 to 30 g / 10 min.

[0088] <Tensile strength at break> The thermoplastic elastomer composition of the present invention also exhibits excellent tensile strength. Specifically, the tensile strength at break, measured using a 1A dumbbell as described in ISO 37 (2011) at a tensile speed of 500 mm / min and in an atmosphere of 23°C, is usually 5 MPa or higher, preferably 7 MPa or higher, and more preferably 8 MPa or higher. The tensile strength at break is specifically measured by the method described in the Examples section below.

[0089] <Elongation at break> The thermoplastic elastomer composition of the present invention also exhibits excellent elongation at break. Specifically, the elongation at break measured using a 1A dumbbell as described in ISO 37 (2011) at a tensile speed of 500 mm / min and in an atmosphere of 23°C is usually 500% or more, preferably 600% or more, and more preferably 700% or more. The elongation at break is specifically measured by the method described in the Examples section below.

[0090] <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. Flexural modulus correlates with low-temperature impact resistance, and excellent low-temperature impact resistance can be achieved by keeping the flexural modulus below 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 rigidity and shape retention characteristics of molded products, the lower limit of the flexural modulus is preferably 130 MPa or more, more preferably 150 MPa or more, and even more preferably 200 MPa or more. The flexural modulus is specifically measured by the method described in the Examples section below.

[0091] <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. The Izod impact strength at -45°C is specifically measured by the method described in the Examples section below. [Examples]

[0092] The present invention will be described in more detail below using examples, but the present invention is not limited to the following examples unless it exceeds its gist. The various manufacturing conditions and evaluation result values ​​in the following examples have meaning as preferred upper or lower limits in embodiments of the present invention, and the preferred range may be defined by a combination of the aforementioned upper or lower limits and the values ​​of the following examples or the values ​​of the examples themselves.

[0093] [Raw materials for the manufacture of thermoplastic elastomer compositions] <Ingredient (A)> A-1: Propylene-based block copolymer (obtained by polymerizing a propylene homopolymer in the first step, followed by polymerizing a propylene-ethylene copolymer in the second step) Novatec® PP BC3B, manufactured by Nippon Polypropylene Co., Ltd. Propylene unit content: 92.5% by mass Ethylene unit content: 7.5% by mass MFR (JIS K7210 (1999)): 9g / 10 min (Measurement conditions: 230℃, load 21.18N (2.16kgf))

[0094] 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 (registered trademark) PP BC03B, manufactured by Nippon Polypropylene Co., Ltd. Propylene unit content: 91.2% by mass Ethylene content: 8.8% by mass MFR (JIS K7210): 30g / 10min (Measurement conditions: 230℃, load 21.18N (2.16kgf))

[0095] 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. Propylene unit content: 96% by mass Ethylene content: 4% by mass MFR (JIS K7210): 60g / 10 min (Measurement conditions: 230℃, load 21.18N (2.16kgf))

[0096] A-4: Propylene-based block copolymer (obtained by polymerizing a propylene homopolymer in the first step, followed by polymerizing a propylene-ethylene copolymer in the second step) LyondellBasell HIFAX® X1956A Propylene unit content: 90.1% by mass Ethylene content: 9.9% by mass MFR (ISO 1133): 1.1g / 10min (Measurement conditions: 230℃, load 21.18N (2.16kgf), catalog value)

[0097] <Ingredient (B)> B-1: Sun Allomer PC630A Propylene-ethylene random copolymer MFR (JIS K7210 (1999)): 7.5g / 10min (Measurement conditions: 230℃, load 21.18N (2.16kgf))

[0098] B-2: Novatec® PP MG03E, manufactured by Nippon Polypropylene Co., Ltd. Propylene-ethylene random copolymer MFR (JIS K7210 (1999)): 30g / 10 minutes (measurement conditions: 230℃, load 21.18N (2.16kgf))

[0099] <Ingredient (C)> C-1: Engage® 8842, manufactured by Dow Chemical Company. Ethylene-1-octene copolymer rubber Density: 0.857g / cm 3 (Catalog value) MFR (ASTM D1238): 1.0g / 10min (Measurement conditions: 190℃, load 21.18N) (Catalog value)

[0100] C-2: Toughmer (registered trademark) A0550S, manufactured by Mitsui Chemicals, Inc. Ethylene-1-butene copolymer rubber Density: 0.861g / cm 3 (Catalog value) MFR (ASTM D1238): 0.5 g / 10 min (Measurement conditions: 190 °C, load 21.18 N) (Catalog value)

[0101] C-3: Engage® 8180 manufactured by The Dow Chemical Company Ethylene-1-octene copolymer rubber Density: 0.863 g / cm 3 (Catalog value) MFR (ASTM D1238): 0.5 g / 10 min (Measurement conditions: 190 °C, load 21.18 N) (Catalog value)

[0102] C-4: Engage® 8100 manufactured by The Dow Chemical Company Ethylene-1-octene copolymer rubber Density: 0.870 g / cm 3 (Catalog value) MFR (ASTM D1238): 1.0 g / 10 min (Measurement conditions: 190 °C, load 21.18 N) (Catalog value)

[0103] C-5: Tafmer® A4050S manufactured by Mitsui Chemicals, Inc. Ethylene-1-butene copolymer rubber Density: 0.864 g / cm 3 (Catalog value) MFR (ASTM D1238): 3.6 g / 10 min (Measurement conditions: 190 °C, load 21.18 N) (Catalog value)

[0104] C-6: Engage® 8200 manufactured by The Dow Chemical Company Ethylene-1-octene copolymer rubber Density: 0.870 g / cm 3 (Catalog value) ]>MFR (ASTM D1238): 5.0 g / 10 min (Measurement conditions: 190 °C, load 21.18 N) (Catalog value)

[0105] C-7: Engage® 8407, manufactured by Dow Chemical Company. Ethylene-1-octene copolymer rubber Density: 0.870g / cm 3 (Catalog value) MFR (ASTM D1238): 30.0 g / 10 min (Measurement conditions: 190°C, load 21.18 N) (Catalog value)

[0106] <Ingredient (D)> D-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 Nuurion Pharmaceuticals.

[0107] <Ingredient (E)> E-1: Acryester TMP (trimethylolpropane trimethacrylate) manufactured by Mitsubishi Chemical Corporation

[0108] E-2: Divinylbenzene manufactured by Wako Pure Chemical Industries, Ltd. (a mixture of 55% by mass of divinylbenzene and 45% by mass of ethylvinylbenzene)

[0109] <Other ingredients> F-1: Antioxidant (BASF Japan product name: Irganox® 1010) F-2: Antioxidant (BASF Japan product name Irgaphos® 168) F-3: Release agent (Product name CRODAMIDE (registered trademark) VRX-BE-(HU) manufactured by Croda Japan Co., Ltd.) F-4: Black pigment (manufactured by Dainichi Seika Kogyo Co., Ltd., product name PC40C (carbon concentration 40% by mass))

[0110] [Method for evaluating thermoplastic elastomer compositions] 1) Melt flow rate (MFR) Measurements were taken in accordance with ISO 1133 (2011) at 230°C and under a load of 21.18N.

[0111] 2) Tensile strength and elongation at break Using an inline screw-type injection molding machine (Sumitomo Electric Industries, Ltd. "SE180DU"), test specimens for tensile testing (sheets 2 mm thick x 120 mm wide x 80 mm long) were molded from a thermoplastic elastomer composition at an injection speed of 30 mm / s, a cylinder temperature of 220°C, and a mold temperature of 40°C. These specimens were then punched out according to ISO 37 (2011) (1A dumbbell). The tensile strength at break (unit: MPa) and elongation at break (unit: %) of these punched specimens were measured at a tensile speed of 500 mm / min in an atmosphere of 23°C using a Shimadzu Corporation Autograph precision universal testing machine "AG-XPlus".

[0112] 3) Flexural modulus Using an inline screw-type injection molding machine (Sumitomo Electric Industries, Ltd. "SE180DU"), a multi-purpose evaluation test specimen A (a dumbbell 180 mm in length) was molded from a thermoplastic elastomer composition in accordance with ISO 3167 (2002) at an injection speed of 30 mm / s, a cylinder setting temperature of 220°C, and a mold temperature of 40°C. The end of the dumbbell was cut off to create a test specimen for measuring the flexural modulus (4 mm thick x 10 mm wide x 80 mm long). The flexural modulus was measured using a Shimadzu Corporation Autograph precision universal testing machine "AG-XPlus" in accordance with ISO 178 (2010) at a speed of 2 mm / min.

[0113] 4) 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., and calculated using the following formula (I). Test temperature: 210℃ L / D: 10 (D=1mm) Shear rate: 60.80 / s ~ 6080 / s 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)

[0114] 5) 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 specified, it indicates "Complete break".)

[0115] 6) Tearline exterior The appearance of the tear lines was assessed by molding a test piece for confirming the molded appearance 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 in-line 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 near the top of the tear lines was visually observed and judged according to the following criteria. (Judgment criteria) ×: The tear lines are very noticeable, and the appearance is very poor. △: The tear line is easily visible. ○: The tear line is not noticeable.

[0116] 7) Flow mark appearance The flow mark appearance was assessed by molding a test piece 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, cylinder setting temperature of 230°C, and 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 very noticeable, and the appearance is very poor. △: Flow marks are visible. ○: No flow marks were observed.

[0117] [Example 1] Component (A-1): 30 parts by mass, Component (A-4): 10 parts by mass, Component (B-1): 10 parts by mass, Component (C-3): 25 parts by mass, Component (C-6): 25 parts by mass, (D-1): 0.2 parts by mass, (E-1): 0.1 parts by mass, and for a total of 100 parts by mass of components (A-1), (A-4), (B-1), (C-3), and (C-6), component (F-1): 0.1 parts by mass, (F-3): 0.05 parts by mass. Parts by mass of (F-4): 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 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.

[0118] [Examples 2-5, Comparative Examples 1-5] Thermoplastic elastomer pellets were obtained in the same manner as in Example 1, except for the raw material formulations shown in Tables 1 and 2. However, for Comparative Examples 3, 4, and 5, after melting and kneading components other than component (F-4) to form pellets, component (F-4) was blended in before injection molding. The obtained thermoplastic elastomer compositions were evaluated in the same manner as in Example 1. The evaluation results are shown in Tables 1 and 2.

[0119] [Table 1]

[0120] [Table 2]

[0121] Discussion: From Table 1, it can be seen that Examples 1-5, where the minimum die swell value is 1.30 or higher at a test temperature of 210°C and a shear rate in the range of 60.80 / s to 6080 / s using a capillary rheometer (see JIS K7199), exhibit good tear line appearance and remarkably excellent follow-mark properties. Furthermore, the values ​​of the flexural modulus also indicate excellent rigidity.

[0122] In contrast, as shown in Table 2, Comparative Examples 1-3 and 5, in which the minimum die swell value in the range of 60.80 / s to 6080 / s at a test temperature of 210°C using a capillary rheometer (see JIS K7199) did not meet the requirement of 1.30 or higher, exhibited inferior tear line appearance and flow mark appearance. Furthermore, while Comparative Example 4, which does not contain component (A), satisfies the above-mentioned die swell performance and exhibits good tear line and flow mark appearance, its rigidity is extremely low. For example, it is easily foreseeable that the fixing points between the resin cover and the car body or steering wheel fittings may break when the airbag deploys, or that it may tear from parts other than the tear line. Therefore, it is difficult to meet the performance requirements for applications where rigidity is needed, such as as an airbag cover. [Industrial applicability]

[0123] The thermoplastic elastomer composition of the present invention makes it possible to obtain injection molded products with remarkably excellent tear line and flow mark appearances while maintaining rigidity, and can be suitably used in various applications. The thermoplastic elastomer composition of the present invention is useful, for example, as automotive interior parts such as airbag storage covers, instrument panels, center panels, center console boxes, door trims, pillars, assist grips, and steering wheels; automotive 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 when a high-speed moving object such as an automobile senses the impact or deformation during a collision, and protects the occupants by inflating and deploying.< / mfr>

Claims

1. A thermoplastic elastomer composition containing the following components (A), (B), and (C), wherein the minimum die swell ratio in a capillary rheometer (see JIS K7199) at a test temperature of 210°C and a shear rate in the range of 60.80 / s to 6080 / s is 1.30 or greater. The aforementioned component (C) is a thermoplastic elastomer composition comprising an ethylene-1-octene copolymer, a component (C1) having a melt flow rate (190°C, load 21.18 N) of 3 g / 10 min or more and 200 g / 10 min or less, and a component (C2) having a melt flow rate (190°C, load 21.18 N) of 0.01 g / 10 min or more and less than 3 g / 10 min. Component (A): A propylene-based block copolymer having a propylene unit content of 50-97% by mass and an ethylene unit content of 3-50% by mass. Component (B): A propylene-based random copolymer consisting of propylene units, ethylene units, and / or α-olefin units other than propylene. Component (C): An ethylene copolymer consisting of ethylene units and α-olefin units having 4 to 20 carbon atoms.

2. The thermoplastic elastomer composition according to claim 1, wherein the ratio of the maximum to minimum die swell ratio in the range of 60.80 / s to 6080 / s at a test temperature of 210°C using a capillary rheometer (see JIS K7199) is 1.15 or less.

3. The thermoplastic elastomer composition according to claim 1 or 2, wherein the α-olefin unit of component (C) has 4 to 8 carbon atoms.

4. The thermoplastic elastomer composition according to any one of claims 1 to 3, wherein the component (C) has a crosslinked structure.

5. The thermoplastic elastomer composition according to claim 4, further comprising the following component (D), wherein the content of component (D) is 0.01 parts by mass to 1.00 parts by mass relative to 100 parts by mass of the total of components (A), (B), and (C). Component (D): Organic peroxide

6. The thermoplastic elastomer composition according to claim 4 or 5, further comprising the following component (E), wherein the content of component (E) is 0.01 parts by mass to 1.00 parts by mass relative to 100 parts by mass of the total of components (A), (B), and (C). Ingredient (E): Crosslinking agent

7. An injection-molded article obtained by injection molding a thermoplastic elastomer composition according to any one of claims 1 to 6.

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

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