JPH09241445A - Thermoplastic resin composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a thermoplastic resin composition excellent in injection moldability, having well-balanced mechanical properties, and useful for molding thin-wall, large-sized products such as internal trim materials/facing materials for automotive parts, comprising a specific polypropylene resin, an elastomer component and talc. SOLUTION: This thermoplastic resin composition comprises comprises (A) 30-80wt.% of a polypropylene resin 20-150g/10min in melt flow rate (MFR), 0-2wt.% in copolymer portion and >=95% in isotactic pentad fraction, (B) 10-30wt.% of a styrene-based block copolymer elastomer of formula I (PS is a polystyrene block; PEB is a polyethylene-butene block; (m) is >=1) or formula II, with a MFR of 0.5-40g/10min and a polystyrene segment content of 10-30wt.%, and (C) 10-40wt.% talc <=5μm in average particle size.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermoplastic resin composition containing a specific polypropylene resin, a styrene block copolymer elastomer and talc, and having particularly excellent injection moldability and mechanical properties.

[0002]

2. Description of the Related Art Polypropylene is widely used in various fields because of its low density and good mechanical properties and moldability. However, since it is inferior in impact resistance and heat resistance, the ethylene-propylene block copolymer obtained by the multi-stage polymerization for the purpose of improving it has a rubber component such as ethylene-propylene copolymer rubber or ethylene-butene copolymer rubber. Various polypropylene-based resin compositions to which an inorganic filler such as talc and talc are added have been proposed.

For example, JP-A-1-149845 discloses that
(A) containing 5 to 12% by weight of a boiling xylene-soluble component having an ethylene content of 20 to 60% by weight, having an ethylene content of 1 to 7% by weight, and a melt flow rate of 15 to 15%;
Propylene-ethylene block copolymer 59 to 74% by weight, and (b) propylene content is 2 to 50 g / 10 min.
0-60% by weight and Mooney viscosity ML _{1 + 4} (100
C) of 35 to 20% by weight of an ethylene-propylene copolymer rubber having a specific surface area of 30000
Disclosed is a resin composition containing 3 to 6% by weight of talc having a mean particle size of 0.5 to 2.0 μm at a density of at least cm ² / g.

[0004]

In order to improve the impact resistance of conventional polypropylene, the content of the ethylene-propylene copolymer portion of the ethylene-propylene block copolymer as the polypropylene component was increased, Increasing the amount of a rubber component such as an ethylene-propylene copolymer rubber or an ethylene-butene copolymer rubber added later to the components causes a problem that the fluidity is deteriorated. Further, the addition of a large amount of a rubber component causes a problem that heat resistance and surface hardness are reduced.

[0005] On the other hand, in order to improve the production efficiency, the size and thickness of molded articles have been further developed, and there has been an increasing demand that molding materials have to have higher performance.

In order to meet such a demand, it is essential that the molding material has higher fluidity and higher performance.
In the conventional composite material of ethylene-propylene block copolymer and polyolefin elastomer, there is a limit to the improvement of the physical properties.

Accordingly, an object of the present invention is to provide a thermoplastic resin composition having excellent moldability and good mechanical properties.

[0008]

Means for Solving the Problems As a result of intensive research to solve the above problems, the present inventors have blended a polypropylene resin having specific physical properties, a specific styrene block copolymer elastomer and talc. By
The inventors have found that the problems of the present invention can be solved and completed the present invention.

That is, the thermoplastic resin composition of the present invention has (A) (1) a melt roll rate of 20 to 150 g /
10 minutes, (2) the content of the copolymer portion is 0 to 2% by weight and (3) 30 to 80% by weight of a polypropylene resin having an isotactic pentad fraction of 95% or more, (B) (1) Melt flow rate is 0.5-40g / 1
0 minutes and (2) the content of polystyrene part is 10 to 3
0 wt% and has the following formula (I) or (II):

[0010]

Embedded image

[0011]

Embedded image (In the above formula, PS is a polystyrene block, PE
B is a polyethylene-butene block and m ≧ 1) 10 to 30% by weight of a styrene block copolymer elastomer represented by (C) 10 to 40% by weight of talc having an average particle size of 5 μm or less.
And

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The thermoplastic resin composition of the present invention is
This will be described in detail below.

[1] Composition Component (A) Polypropylene Resin (A) The polypropylene resin used in the present invention is
Homopolypropylene resin, which is a homopolymer of propylene, is not more than 2% by weight, preferably 1% by weight in the polymer.
The following propylene and α-olefins such as ethylene,
Butene-1, pentene-1, 4-methyl-pentene-
It may contain a crystalline random copolymer or a block copolymer with 1, 1, hexene-1, octene-1, etc.

The polypropylene resin (A) used in the present invention has (1) a melt flow rate (230 ° C., a load of 2.16 kg, hereinafter referred to as MFR) of 20 to 150 g.
/ 10 minutes, preferably 40 to 140 g / 10 minutes.
If the MFR is less than 20 g / 10 minutes, the fluidity of the composition will be insufficient, while if it exceeds 150 g / 10 minutes, the ductility will be reduced.

Further, the content of the (2) copolymer portion is 0.
˜2% by weight, preferably 0-1% by weight. When the content of the copolymer portion exceeds 2% by weight, the impact resistance at low temperature deteriorates and the embrittlement temperature increases, which is not preferable.

Further, (3) the isotactic pentad fraction (IPF) is 95% or more, preferably 97% or more. Isotactic pentad fraction (IPF)
Is less than 95%, the high crystallinity of the polypropylene resin is insufficient, and high rigidity, heat distortion temperature and the like are insufficient, which is not preferable.

By the way, the isotactic pentad fraction (IPF) is defined by A. Zambelli et al., Macromolecules, 6 ,
925 (1973) is an isotactic fraction in pentad units in a polypropylene molecular chain measured using a nuclear magnetic resonance spectrum ( ¹³ C-NMR) with isotope carbon. In other words, the isotactic pentad fraction is the fraction of propylene monomer units in which five propylene monomer units are continuously isotactically bonded. However, regarding the attribution of peaks, Macromolecules, 8 ,
687 (1975). Specifically, the isotactic pentad unit is measured with the intensity fraction of the mmmm peak in all the absorption peaks in the methyl carbon region of the ¹³ C-NMR spectrum. The isotactic pentad fraction (IPF) was measured for n-heptane insoluble matter according to the above method.

The polypropylene resin as described above can be manufactured by various methods. Among them, as a preferable method, for example, in the presence of a stereoregular catalyst, a known slurry polymerization method, a solution polymerization method, a liquid phase polymerization method using an olefin monomer as a medium, or a gas phase polymerization method can be used for production. it can.

An example of the production method is, for example, titanium trichloride,
A combination of a transition metal compound catalyst component such as titanium tetrachloride or a catalyst component obtained by supporting them on a carrier having magnesium halide such as magnesium chloride as a main component and an organoaluminum compound such as triethylaluminum or diethylaluminum cloyd. It is obtained by polymerizing propylene alone using a catalyst system, or by homopolymerizing propylene and then introducing a comonomer so that the content of the copolymer is 2% by weight or less and polymerizing the copolymer. The copolymer portion is a random copolymer and can be separated and quantified as a room temperature xylene-soluble portion.

Incidentally, an organic peroxide is added to polypropylene resin to lower the molecular weight by a melt extrusion reaction,
You may use what adjusted R to 20-150g / 10min.

(B) Styrenic Block Copolymer Elastomer The (B) styrenic block copolymer elastomer used in the present invention has the following structural formula (I) or structural formula (6). (II) It is shown.

[0022]

Embedded image

[0023]

[Chemical 6] (In the above formula, PS is a polystyrene block, PE
B is a polyethylene-butene block and m ≧ 1) Such a styrenic block copolymer is a monovinyl-substituted aromatic hydrocarbon, preferably styrene and a conjugated diene hydrocarbon, preferably 1.3-butadiene. It is a block-copolymerized product of hydrogenated products.

In the present invention, in particular, a block copolymer of a styrene polymer block and a 1.3-butadiene elastomer block is hydrogenated to produce a hydrogenated block copolymer. As described above, such a hydrogenated block copolymer has two or more blocks of a PS block and a PEB block, preferably a PS block and a PB block.
Those having 3 or more blocks of EB block and PS block are preferable as the physical properties used in the present invention.

The hydrogenated block copolymer is a styrene-ethylene-butene block copolymer elastomer (hereinafter also referred to as SEBS) or styrene-
It is also called an ethylene-butene copolymer elastomer (hereinafter also referred to as SEB). The hydrogenation amount of this SEBS or SEB is 90 mol% or more, and preferably one having no unsaturated bond is preferable from the viewpoint of weather resistance, recyclability and the like.

The MFR of the (B) styrene block copolymer elastomer is 0.5 to 40 g / 10 minutes, preferably 0.5 to 30 g / 10 minutes. MFR is 0.
If it is less than 5, the fluidity is insufficient, the moldability is deteriorated, and the impact resistance is also insufficient. On the other hand, when the MFR exceeds 40 g / 10 minutes, ductility and impact resistance are insufficient, which is not preferable.

Further, the content of the polystyrene portion constituting the (B) styrene block copolymer elastomer is
It is 10 to 30% by weight, preferably 15 to 20% by weight. When the content of the polystyrene portion is less than 10% by weight, the impact resistance is deteriorated. On the other hand, when the content is more than 30% by weight, stretching becomes insufficient, which is not preferable.

(C) Talc The (C) talc used in the present invention has an average particle size of 5 μm measured by a laser diffraction / scattering particle size distribution analyzer.
m or less. If the average particle size of talc exceeds 5 μm, it is not preferable because rigidity and dimensional stability are insufficient. In addition, talc is preferably subjected to surface treatment with a modified silicone, a titanate coupling agent, or the like, because the rigidity and heat resistance of the composition can be further improved.

The thermoplastic resin composition of the present invention may be further oxidized with respect to a total of 100 parts by weight of the above-mentioned respective components (A), (B) and (C) depending on its use such as interior and exterior materials for automobiles. It is preferable to add about 0.05 to 2 parts by weight of each of the inhibitor, the heat stabilizer and the light stabilizer. If the amount of each component is less than 0.05 parts by weight, the respective effects are not sufficient, while if it exceeds 2 parts by weight, not only there is no further effect but also the physical properties of the composition are deteriorated, which is not preferable.

As the antioxidant used in that case,
Examples include phenol type and phosphorus type. Examples of phenol-based compounds include tetrakis [methylene-3
(3,5-di-t-butyl-4-hydroxyphenyl)
Propionate] methane, 2,6-di-t-butyl-4
-Methyl-phenol, tris (3,5-di-t-butyl-4-hydroxyphenyl) isocyanurate and the like.

Examples of phosphorus compounds include tris (2,4-di-t-butylphenyl) phosphite,
4,4'-butylidene-bis (3-methyl-6-t-butylphenyl-di-tridecyl) phosphite, 1,
1,3-tris (2-methyl-4-ditridecyl-phosphite-5-t-butyl) and the like.

Further, examples of the heat stabilizer include sulfur compounds such as distearyl thiopropionate and dilauryl thiopropionate.

Further, examples of the light stabilizer include bis (2,2,6,6-tetramethyl-4-piperziridine).
Sebacate, dimethyl-1 (2-hydroxyethyl)-
Condensation product of 4-hydroxyl-2,2,6,6-tetramethylpiperidine and succinic acid, poly [{6- (1,1,
3,3-Tetramethylbutyl) amino-1,3,5-triazine-2,4-diyl} {(2,2,6,6-tetramethyl-4-piperidyl) imino} hexamethylene {(2,2 , 6,6-Tetramethyl-4-piperidyl)
Imino}], N, N'-bis (3-aminopropyl) ethylenediamine-2,4-bis [N-butyl-N-
(1,2,2,6,6-pentamethyl-4-piperidyl) amino] -6-chloro-1,3,5-triazine condensate and the like.

For the purpose of modifying the thermoplastic resin of the present invention, other additives such as a releasing agent, an antistatic agent, a plasticizer, a flame retardant, a lubricant, an anticorrosive agent for copper, an organic or inorganic agent are used. The pigment and its dispersant can be added.

The above-mentioned various additives and pigments are generally added at the time of mixing the respective components, but a high-concentration masterbatch may be prepared in advance and blended after injection molding.

[2] Mixing ratio The mixing ratio of the various components as described above is 30 to 80% by weight, preferably 50 to 80% by weight of the polypropylene resin (A).
% By weight, (B) styrene block copolymer elastomer is 10 to 30% by weight, preferably 10 to 25% by weight, and (C) talc is 10 to 40% by weight, preferably 10 to 30% by weight. Is.

When the polypropylene resin (A) is less than 30% by weight, the rigidity, heat resistance, hardness and the like of the resulting composition are likely to be lowered, while when it exceeds 80% by weight, the strength and ductility are lowered.

If the content of the (B) styrene block copolymer elastomer is less than 10% by weight, the impact resistance tends to decrease, while if it exceeds 30% by weight, the strength, rigidity, heat resistance,
The hardness etc. will decrease.

Further, if the talc (C) is less than 10% by weight, the rigidity and heat resistance are lowered, while if it exceeds 40% by weight, the ductility is lowered.

[3] Manufacturing Method The thermoplastic resin composition of the present invention is preliminarily dry-blended with the above-mentioned various components and then supplied to a single-screw extruder, a twin-screw extruder, a Banbury mixer, a kneader, etc. ~ 30
It can be produced by melt-kneading at 0 ° C, preferably 190 to 210 ° C.

[0041]

EXAMPLES Examples and comparative examples will be shown below, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded. The following resins, talc and additives were used as raw materials.

[1] Polypropylene Resin (PP) Table 1 Physical Properties PP-1 PP-2 PP-3 PP-4 PP-5 MFR ⁽¹⁾ 40 70 90 140 40 IPF ⁽²⁾ 97.7 98.0 97.6 97.6 95.0 Cv ^{( 3)} 0 0 0 0 0 Table 1 (continued) Physical properties PP- 6 PP-7 PP-8 PP-9 MFR ⁽¹⁾ 85 160 85 20 IPF ⁽²⁾ 97.0 97.5 97.0 97.3 Cv ⁽³⁾ 2 0 9 0 (Note) (1) MFR: Measured by ASTM D1238 at 230 ° C. under a load of 2.16 kg (unit: g / 10 minutes). (2) IPF: Isotactic pentad fraction (unit:%) measured using ¹³ C-NMR. (3) Cv: Content of copolymer portion (at room temperature xylene-soluble portion) in polypropylene resin (unit: wt%).

[2] SEBS and other elastomers Table 2 Physical properties SEBS-1 SEBS-2 SEBS-3 SEBS-4 SEBS-5 MFR ⁽³⁾ 2 30 12 5 160 PS ⁽⁴⁾ 29 20 20 30 30 Table 2 (Continued) Physical properties SEPS ⁽¹⁾ EPR ⁽²⁾ MFR ⁽³⁾ 0.5 0.8 PS ⁽⁴ ) 13-(Note) (1) SEPS: Styrene-ethylene-propylene-styrene block copolymer elastomer. (2) EPR: ethylene-propylene copolymer rubber (ethylene content 77% by weight). (3) MFR: 230 ° C according to ASTM D1238,
2. Measured under a load of 16 kg (unit: g / 10 minutes). (4) PS: Content of polystyrene portion in SEBS and SEPS (unit: weight%)

[3] Talc Talc: [Fuji Talc Co., Ltd., LMS300, average particle size 1.2 μm]

[4] Additive (1) Antioxidant-1: [Ciba Geigy Co., Irga
nox 1010] (2) Antioxidant-2: [Asahi Denka Co., Ltd., Mark 2112
] (3) Thermal stabilizer: [Sumitomo Chemical Co., Ltd., Sumilizer TPS] (4) Light stabilizer: [Ciba Geigy Co., Ltd., Chim
assorb 944]

Examples 1 to 10 and Comparative Examples 1 to 5 The above raw materials were blended in the proportions shown in Table 3, and in this case, 100 parts by weight of each blend was added with antioxidants-1 and 2, and heat stability. Each 0.2 parts by weight of the stabilizer and the light stabilizer are dry-blended with a super mixer and then charged into a twin-screw extruder (PCM-45 manufactured by Ikegai, L / D = 32) at 200 ° C. and a rotation speed of 200 rpm. Were melt-kneaded and extruded under the conditions of to obtain pellets.

Next, the obtained pellets were injected into an injection molding machine (TOSHIBA MACHINE IS-90B / cylinder temperature 210 ° C.,
A test piece for measuring physical properties was obtained by injection molding with a mold (50 ° C.). The following tests were carried out on the test pieces thus obtained, and the results are shown in Table 4.

Table 3 Composition (wt%) Example 1 Example 2 Example 3 Example 4 Example 5 Type of PP PP-1 PP-2 PP-2 PP-3 PP-4 Compounding amount 57 58 57 57 57 SEBS type SEBS-1 SEBS-1 SEBS-1 SEBS-1 SEBS-1 Compounding amount 23 22 23 23 23 Talc compounding amount 20 20 20 20 20 Table 3 (continued) Composition (wt%) Example 6 Example 7 Example 8 Example 9 Example 10 Type of PP PP-5 PP-6 PP-1 PP-1 PP-1 Blend amount 58 59 59 60 58 Type of SEBS SEBS-1 SEBS-1 SEBS-2 SEBS-3 SEBS-4 compounding amount 22 21 21 20 22 Talc compounding amount 20 20 20 20 20 Table 3 (continued) Composition (wt%) Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 PP type PP- 7 PP-8 PP-9 PP-1 PP-1 Compound amount 57 62 60 57 57 SEBS type SEBS-1 SEBS-1 SEBS-5 SEPS EPR compound amount 23 18 20 23 23 Talc compound amount 20 20 20 20 20

Table 4 Physical Properties Example 1 Example 2 Example 3 Example 4 Example 5 MFR ⁽¹⁾ 22 37 34 27 31 Tensile strength ⁽²⁾ 230 235 229 226 233 Elongation at break ⁽³⁾ 600 400 500 600 500 Flexural modulus ⁽⁴⁾ 21400 21900 21200 22500 24500 Bending strength ⁽⁵⁾ 346 345 335 347 369 Izod impact strength ⁽⁶⁾ @ 23 ℃ 42 29 38 36 28 @ -30 ℃ 4.1 3.8 4.0 4.1 3.6 Heat distortion temperature ^{(7 )} 73 74 73 74 77 Rockwell hardness ⁽⁸⁾ 75 74 72 76 79 Embrittlement temperature ⁽⁹⁾ -20 -12 -15 -15 -13 Table 4 (continued) Physical properties Example 6 Example 7 Example 8 Implementation Example 9 Example 10 MFR ⁽¹⁾ 22 36 33 26 21 Tensile strength ⁽²⁾ 266 226 238 241 264 Elongation at break ⁽³⁾ 450 500 400 600 450 Flexural modulus ⁽⁴⁾ 22800 21300 23000 21300 22500 Bending strength ⁽⁵⁾ 388 379 352 355 384 Izod Impact strength ⁽⁶⁾ @ 23 ° C 23 37 26 33 22 @ -30 ° C 3.7 3.8 3.6 3.8 3.6 Heat distortion temperature ⁽⁷⁾ 75 72 74 75 74 Rockwell hardness ⁽⁸⁾ 74 70 72 72 76 brittle temperature ⁽⁹⁾ -13 -12 -12 -20 -12 table 4 (continued) product of Comparative example 1 Comparative example 2 Comparative 3 Comparative Example 4 Comparative Example ^{5 MFR (1) 33 33 37} 11.5 13.6 Tensile strength ⁽²⁾ 231 230 256 220 235 elongation at break ⁽³⁾ 100 600 100 30 600 Flexural modulus ⁽⁴⁾ 23900 23400 21400 24000 23100 flexural strength ^{( 5)} 366 348 367 360 368 Izod Impact strength ⁽⁶⁾ @ 23 ℃ 21 26 9 7 22 @ -30 ℃ 3.9 3.0 2.1 2.5 3.5 Heat distortion temperature ⁽⁷⁾ 77 74 70 75 77 Rockwell hardness ⁽⁸⁾ 79 76 74 78 72 Embrittlement temperature ⁽⁹⁾ -15 -10 -40 -3 (Note) (1) MFR: measured by ASTM D1238 at 230 ° C and 2.16 kg load (unit: g / 10 minutes). (2) Tensile strength: Measured by ASTM D638 (unit: kg / cm ² ). (3) Elongation at break: Measured according to ASTM D638 (unit:%). (4) Flexural modulus: measured by ASTM D790 (unit: kg / cm ² ). (5) Bending strength: Measured by ASTM D790 (unit: kg / cm ² ). (6) Izod impact strength: Measured at 23 ° C and -30 ° C according to ASTM D256 (unit: kg · cm · cm). (7) Heat distortion temperature (HDT): Measured by ASTM D648 at 18.6 kg / cm ² (unit: ° C). (8) Rockwell hardness: measured by ASTM D785 (scale is R). (9) Brittleness temperature: measured by ASTM D746 (unit: ° C).

As is clear from Table 4, Examples 1-10
The composition (1) has a good fluidity and an MFR value, and also has a good balance of mechanical properties. In contrast, the composition of the comparative example has a polypropylene resin MFR of 150 g.
If it exceeds / 10 minutes, the ductility decreases, and if the content of the copolymer portion in the polypropylene resin exceeds 2% by weight, the impact resistance at low temperature deteriorates and the embrittlement temperature increases, which is not preferable.

If the SEFR MFR is out of the range of the present invention or if an elastomer such as SEPS or EPR is used, ductility and impact resistance are deteriorated, and the brittle temperature becomes high, which is not preferable.

[0052]

EFFECT OF THE INVENTION The thermoplastic resin composition of the present invention is excellent in moldability and has a good balance of mechanical properties. Therefore, the range of injection molding conditions can be widened, which facilitates the molding of thin and large-sized products.

Therefore, it is useful in products obtained by injection molding of industrial materials such as interior / exterior materials for automobile parts and home electric appliance parts.

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[Procedure amendment]

[Submission date] April 25, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

Embedded image

Embedded image (In the above formula, PS is a polystyrene block, PE
B is a polyethylene-butene block, and m ≧ 1) 10 to 30% by weight of a styrene block copolymer elastomer represented by (C) 10 to 40% by weight of talc having an average particle size of 5 μm or less.
A thermoplastic resin composition containing:

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0014

[Correction method] Change

[Correction contents]

The polypropylene resin (A) used in the present invention has (1) a melt flow rate (230 ° C., load 2.16 kg, hereinafter referred to as MFR) of 20 to 150 g.
/ 10 minutes, preferably 40 to 140 g / 10 minutes.
If the MFR is less than 20 g / 10 minutes, the fluidity of the composition will be insufficient, while if it exceeds 150 g / 10 minutes, the ductility will be reduced.
In addition, polypropylene resin with high MFR is normally polymerized.
Can also be obtained by, but in terms of productivity
For example, peroxide is added to low polypropylene resin.
By molecular weight adjustment processing (CR processing) such as kneading
It is preferably prepared by

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0042

[Correction method] Change

[Correction contents]

[1] Polypropylene resin (PP) ^*) PP-2 to 4 and PP-7 CR-process PP-1
Prepared for each MFR. (Note) (1) MFR: 230 ° C according to ASTM D1238,
2. Measured under a load of 16 kg (unit: g / 10 minutes). (2) IPF: Isotactic pentad fraction (unit:%) measured using ¹³ C-NMR. (3) Cv: Content of copolymer portion (at room temperature xylene soluble portion) in polypropylene resin (unit: weight%).

Claims (1)

[Claims] 1. A melt flow rate of (A) (1) is 20.
~ 150 g / 10 minutes, the content of (2) copolymer part is 0
~ 2 wt% and (3) 30-80 wt% polypropylene resin with an isotactic pentad fraction of 95% or more
And (B) (1) the melt flow rate is 0.5 to 40 g / 1.
0 minutes and (2) the content of polystyrene part is 10 to 3
0% by weight and having the following formula (I) or (II): Embedded image (In the above formula, PS is a polystyrene block, PE
B is a polyethylene-butene block, and m ≧ 1) 10 to 30% by weight of a styrene block copolymer elastomer represented by (C) 10 to 40% by weight of talc having an average particle size of 5 μm or less.