JPH10212381A - Thermoplastic elastomer composition for air bag cover and air bag cover - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a thermoplastic elastomer compsn. excellent in resistances to scratch and low-temp. impact by compounding a polypropylene resin, a hydrogenated arom. vinyl-conjugated diene block copolymer or an ethylene-α-olefin copolymer rubber, and a specific block copolymer comprising a specific combination of a vinylarom. polymer block, a conjugated diene polymer block or a vinylarom.-conjugated diene random copolymer block, and a vinylarom.- conjugated diene taper block. SOLUTION: This compsn. comprises 20-70wt.% polypropylene resin, 5-60wt.% hydrogenated arom. vinyl-conjugated diene block copolymer or 5-60wt.% ethylene-α-olefin copolymer rubber, and 5-50wt.% A-B, A-B-C, or A-B-A type block copolymer wherein A is a vinylarom. polymer block, B is a conjugated diene block or a vinylarom.-conjugated diene random copolymer block, and C is a vinylarom.-conjugated diene taper block.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a thermoplastic elastomer composition for an airbag cover and an airbag cover. More specifically, the present invention relates to a thermoplastic elastomer composition having excellent scratch resistance, low-temperature impact resistance, and moldability, and an airbag cover using the thermoplastic elastomer composition.

[0002]

2. Description of the Related Art In recent years, automobiles equipped with airbags have been increasing in order to protect occupants of automobiles from the impact of a collision. The airbag is normally housed in an airbag cover, and a thermoplastic elastomer composition is generally used for the airbag cover.

Conventionally, the air bag cover is generally coated on a molded product in order to supplement the appearance and scratch resistance during use. However, in recent years, the air bag cover has been coated for the purpose of simplifying the process and reducing the cost. Non-painting, in which molded products are used directly as airbag covers, is in progress. For this reason, there is an increasing demand for thermoplastic elastomers to have high fluidity, scratch resistance, low-temperature impact resistance and the like during molding to improve the appearance of molded articles.

JP-A-52-116537 and JP-A-4-314648 disclose airbag covers using a crosslinked olefin-based thermoplastic elastomer composition and a styrene-based thermoplastic elastomer composition. I have. However, the airbag covers obtained by these methods are not always satisfactory in terms of appearance and scratch resistance.

In recent years, hydrogenated diene copolymers compatible with polypropylene have been developed.
No. 191 discloses a thermoplastic resin composition having excellent impact resistance comprising a hydrogenated diene copolymer, a polyolefin resin and an ethylene-α-olefin random copolymer.
JP-A-7-188508 discloses a thermoplastic elastomer composition comprising a hydrogenated diene-based copolymer, a polyolefin-based resin and a styrene-based block copolymer and having excellent flexibility and high elasticity.

[0006]

SUMMARY OF THE INVENTION In view of the above situation, an object of the present invention is to provide a thermoplastic elastomer composition having excellent scratch resistance, low-temperature impact resistance and moldability, and the thermoplastic elastomer composition. An object of the present invention is to provide an airbag cover using an object.

[0007]

That is, one aspect of the present invention relates to the following (a) 20 to 70% by weight, (b) 5 to
60% by weight and (c) 5 to 50% by weight (however, (a)
+ (B) + (c) = 100% by weight. ) Comprising a thermoplastic elastomer composition for an airbag cover. (A): Polypropylene resin (B): (B-i) or (B-ii) (B-i): Polymer block composed of at least two aromatic vinyl compounds and at least one conjugated diene compound A hydrogenated aromatic vinyl-conjugated diene compound block copolymer obtained by hydrogenating a block copolymer consisting of a polymer block consisting of ii): ethylene-α-olefin copolymer rubber (c): (A)-(B) block copolymer, (A)-
(B)-(C) block copolymer or (A)-(B)-
(A) a block copolymer [where (A) is a vinyl aromatic compound polymer block, (B) is a conjugated diene polymer block or a vinyl aromatic compound-conjugated diene random copolymer block, and (C) is a vinyl copolymer block. The aromatic compound shows a gradually increasing vinyl aromatic compound-conjugated diene taper block, and these block copolymers may have a polymer molecular chain extended or branched via a coupling agent residue.) The block copolymer satisfying the following conditions (1) to (3) is hydrogenated, 80% or more of the double bond of the conjugated diene portion is saturated, and the number average molecular weight is 500.
Hydrogenated diene-based copolymer having a molecular weight of 00 to 600,000 (1): the weight ratio of vinyl aromatic compound / conjugated diene is 5/95 to 60/40 (2): all monomers constituting the block copolymer (A) The amount of the vinyl aromatic compound in the block (A) is 3
% By weight, and the total bonding amount of the vinyl aromatic compounds in the (A) block and the (C) block is 50% by weight or less. Must exceed 50%

Another aspect of the present invention relates to an airbag cover obtained by using the above-mentioned thermoplastic elastomer composition.

[0009]

DETAILED DESCRIPTION OF THE INVENTION The component (A) of the present invention is a polypropylene resin. As a polypropylene resin,
Polypropylene or propylene and α having 2 or more carbon atoms
-Copolymers with olefins are preferred. Examples of the α-olefin having 2 or more carbon atoms include ethylene, 1-
Butene, 1-pentene, 3-methyl-1-butene, 1-
Hexene, 1-decene, 3-methyl-1-pentene, 4
-Methyl-1-pentene, 1-octene and the like are preferable, and ethylene is preferable, and these may be any type of random and block.
The melt flow rate of the polypropylene resin is usually 0.1.
1 to 100 g / 10 min, preferably 1 to 70 g / min.
The range is 10 minutes.

The component (b) of the present invention is (b-i) or (b-ii).

The component (b-i) of the present invention comprises at least 2
Obtained by hydrogenating a block copolymer consisting of a polymer block consisting of two aromatic vinyl compounds and a polymer block consisting of at least one conjugated diene compound, wherein the conjugated diene portion has a vinyl bond content of 50% The following is a hydrogenated aromatic vinyl-conjugated diene compound block copolymer.

Specific examples of the aromatic vinyl compound (b-i) include styrene, α-methylstyrene, p-methylstyrene, vinylxylene, monochlorostyrene,
Examples thereof include dichlorostyrene, monobromostyrene, dibromostyrene, ethylstyrene, and vinylnaphthalene. Among them, styrene is preferred from the viewpoint of industrialization.

Specific examples of the conjugated diene compound (b-i) include butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2-neopentyl-1,3 butadiene, 2-chloro-1,3 butadiene, -Cyano 1,3-butadiene and the like, and among them, butadiene or isoprene is preferred from the viewpoint of industrialization.
The vinyl bond content of the conjugated diene portion is below 50%. Here, the vinyl bond amount of the conjugated diene portion refers to the ratio of the amount of 1, 2 bonds and / or 3, 4 bonds in the polymerized portion of the conjugated diene.

Aromatic vinyl compound in component (b-i)
The weight ratio of the conjugated diene compound is from 10/90 to 50/50.
And more preferably 10/90 to 35/75. If the ratio is too low, the tensile strength of the thermoplastic elastomer composition may be low, or the low-temperature impact resistance may be low.On the other hand, if the ratio is too high, the flexibility of the thermoplastic elastomer composition may be poor, Low-temperature impact resistance may decrease. The vinyl bond content of the conjugated diene portion is 50
%, The low-temperature impact resistance is reduced.

The component (b-i) has a number average molecular weight of 1,000.
It is preferably 0 or more and 150,000 or less, more preferably 20,000 or more and 120,000 or less.
If the molecular weight is too large, the dispersed particle size in the thermoplastic elastomer composition may be large, resulting in poor impact resistance or low fluidity.

The component (b-ii) of the present invention is ethylene-α-
It is an olefin copolymer rubber. Examples of the ethylene-α-olefin copolymer rubber include an ethylene-α-olefin copolymer rubber and an ethylene-α-olefin-nonconjugated diene copolymer rubber.

The α-olefin in the ethylene-α-olefin copolymer rubber is, for example, a compound having 3 to 3 carbon atoms.
12, propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-decene and the like, among which propylene is preferred. Examples of the non-conjugated diene include chain non-conjugated dienes such as 1,4-hexadiene, dicyclopentadiene, and 5-ethylidene-2.
-Cyclic non-conjugated dienes such as norbornene.

The component (ii) is preferably an ethylene-propylene copolymer rubber from the viewpoint of low-temperature impact resistance.

The component (c) of the present invention comprises (A)-(B) block copolymer, (A)-(B)-(C) block copolymer or (A)-(B)-(A ) Block copolymer [where (A) is a vinyl aromatic compound polymer block,
(B) shows a conjugated diene polymer block or a vinyl aromatic compound-conjugated diene random copolymer block, and (C) shows a vinyl aromatic compound-conjugated diene taper block in which a vinyl aromatic compound is gradually increased. The polymer may have a polymer molecular chain extended or branched via a coupling agent residue].
The block copolymer satisfying the condition (3) is hydrogenated, and 80% or more of the double bonds of the conjugated diene portion are saturated,
It is a hydrogenated diene copolymer having a number average molecular weight of 50,000 to 600,000.

(1): The weight ratio of vinyl aromatic compound / conjugated diene is 5/95 to 60/40. (2): Vinyl aromatic in (A) block with respect to all monomers constituting the block copolymer. Group 3 compound amount
% By weight, and the total bonding amount of the vinyl aromatic compounds in the (A) block and the (C) block is 50% by weight or less. Must exceed 30%

The weight ratio of the vinyl aromatic compound / conjugated diene of the block copolymer in the component (c) is 5/95.
６０60/40, preferably 5/95 to 15/85
It is. If the proportion is too small, the tackiness of the component (c) increases, and the operability during production may be poor. On the other hand, if the proportion is too large, the hardness of the component (c) increases, resulting in flexibility and impact resistance. May decrease.

The amount of the vinyl aromatic compound in the block (A) is 3% by weight or more, preferably 4 to 10% by weight, based on all the monomers constituting the block copolymer in the component (C). If the amount is too small, the tackiness of the component (c) increases, and the operability during production may be poor.

The total amount of the vinyl aromatic compound in the block (A) and the block (C) of the block copolymer in the component (c) is 50% by weight or less, preferably 4 to 10% by weight. If the amount is excessive, the hardness of the component (c) increases, and the flexibility and impact resistance may decrease.

The amount of vinyl bonds in the conjugated diene portion in the block (B) of the block copolymer in the component (c) is 5
It is more than 0%, preferably 60% or more. If the amount is too small, the flexibility and scratch resistance of the thermoplastic elastomer composition may deteriorate.

The component (c) is a component in which at least 80% of the double bonds in the conjugated diene portion of the block copolymer are saturated, preferably at least 90%.
If the saturation ratio is too low, heat resistance and weather resistance may be poor.

The number average molecular weight of the component (c) is from 50,000 to
600,000, preferably 100,000 to 500
000. If the molecular weight is too small, the molded product may be sticky or the impact resistance may be poor, while if the molecular weight is too large, the fluidity of the thermoplastic elastomer composition may be low. .

The thermoplastic elastomer composition of the present invention comprises:
(A) 20 to 70% by weight, (B) 5 to 60% by weight and (C) 5 to 50% by weight (however, (A) + (B) +
(C) = 100% by weight. ), Preferably (A) 25 to 55% by weight, (B) 15 to
50% by weight and (c) 15 to 45% by weight. (B) If the component is too small, heat resistance, fluidity,
If the component (a) is in excess, the flexibility and impact resistance are poor. When the amount of the component (b) is too small, the low-temperature impact resistance is poor. On the other hand, when the amount of the component (b) is too large, the fluidity and the scratch resistance are reduced. If the component (c) is too small, the scratch resistance is poor. If the component (c) is too large, the low-temperature impact resistance may be poor, and the rigidity of the molded product may be insufficient.

The thermoplastic elastomer composition of the present invention comprises:
The flexural modulus measured in accordance with JIS K7203 is 3
It is preferably 000kg / cm ² or less, more preferably 200 kg / cm ² or more, 2200 kg / cm ²
It is as follows. If the flexural modulus is too high, low-temperature impact resistance,
The scratch resistance may be poor.

The thermoplastic elastomer composition of the present invention may further comprise, if necessary, an antioxidant,
Heat stabilizers, weathering agents, UV absorbers, lubricants, antistatic agents,
A pigment, a filler, and a flame retardant may be blended.

As a method for obtaining the thermoplastic elastomer composition of the present invention, melt kneading using a twin-screw extruder, a Banbury mixer or the like can be mentioned. The thermoplastic elastomer composition of the present invention can be obtained by a so-called simple blend without requiring a complicated production step such as dynamic crosslinking, and is advantageous from the viewpoint of production cost.

The thermoplastic elastomer composition of the present invention comprises:
It is processed into an airbag cover by utilizing the above excellent features. The airbag cover is characterized by having excellent scratch resistance and low-temperature impact resistance.

[0032]

The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited by the following examples.

[I] Raw Materials The following raw materials were used to obtain the compositions of Examples and Comparative Examples. (A) Polypropylene resin a-1: MI at 230 ° C. under a load of 2.16 kg of 65 (g)
/ 10 min), and a block polypropylene containing 17 wt% of an ethylene-propylene random copolymer having an ethylene content of 40 wt% A-2: MI at 230 ° C. and a load of 2.16 kg of 31 (g)
/ 10 min), and a block polypropylene (b-i) hydrogenated aromatic vinyl-conjugated diene compound block copolymer containing 13 wt% of an ethylene-propylene random copolymer having an ethylene content of 25 wt% b-1: hydrogenated styrene- Butadiene-styrene block copolymer (SEBS) Clayton G1657 manufactured by Shell Chemical Co. (number average molecular weight 80,000, styrene content 13) b-2: Hydrogenated styrene-isoprene-styrene block copolymer (SEPS) Septon 20 manufactured by Kuraray Co., Ltd.
63 (MI of 22 at 200 ° C., 10 kg load: 22, styrene content 13%) (b-ii) Ethylene-α-olefin copolymer rubber b-3: Mooney viscosity (ML _{1 + 4} 121 ° C.) 33,
Ethylene propylene rubber having a propylene content of 27% (C) Hydrogenated diene copolymer C-1: Hydrogenated styrene-butadiene rubber (h-SBR)
Dynalon 1320P (230 ° C,
2. MI of 3.5 with 16 kg load, styrene content 10
%)

[II] Formulation of additives In any of the following Examples and Comparative Examples, the formulation of the additives is constant as follows. Antioxidant: Sumilizer BP-101 (manufactured by Sumitomo Chemical Co., Ltd.) 0.1% Weathering agent: SANOL LS770 (Ciba
Geigy) 0.05% UV absorber: Sumisorb 300 (Sumitomo Chemical)
0.1% lubricant: erucamide 0.15% For the resulting composition, cylinder temperature 220 ° C,
A test piece was prepared by injection molding at a mold temperature of 50 ° C., and the physical properties were evaluated.

[III] Evaluation and measurement method

Various properties described in the examples and comparative examples were measured by the following methods. (1) Melt flow rate (MFR): JIS K71
12 (Temperature 230 ° C., Load 2.16 kgf) (2) Hardness: ASTM D2240 (3) Bending test: JIS K7203 (4) Tensile test: JIS K6301 (Using a No. 3 dumbbell, pulling speed 200 (mm / min) (5) Izod impact test: ASTM D256 (Test specimen was 12 mm thick and notched.) (6) Scratch resistance test: Tribogear (Shinto Kagaku) Was scratched by scratching a 2 mm-thick pressed sheet of the sample at a constant speed with a scratching needle loaded with a load of 500 g. The scratch depth was measured with a contact type surface roughness meter Surfcom (manufactured by Tokyo Seimitsu) on a scale of μm order. (7) Airbag cover deployment test: The following are methods for evaluating the airbag cover. That is, the airbag cover material is formed by injection molding, and the airbag and the airbag cover are attached to the mounting bracket.
Next, a gas generator is attached, and the air bag device is placed in an air bath at the developing temperature (-35 ° C., 85 ° C.). This is a quick deployment test. If the airbag cover is torn at the portion to be broken without generating fragments and the airbag is deployed, the deployability of the airbag cover is good.

<Embodiment 1> Block PP 50 of A-1
wt%, b-1 SEBS 25 wt%, c-1 h-
SBR 25 wt% and additives at cylinder temperature 200
The mixture was kneaded with a twin-screw extruder set at ℃ to prepare pellets. The obtained composition was subjected to injection molding to prepare test pieces, and the physical properties were evaluated. Table 1 shows the results. From these results, it was found that 85 ° C. and −35 ° C.
It is expected that any deployment test at 0 ° C would be good.

<Examples 2 to 9 and Comparative Examples 1 to 5>
Except for the formulation shown in 2 and 3, the procedure was the same as in Example 1.

The following can be understood from the results. All examples satisfying the requirements of the present invention are flowability, low temperature impact resistance,
The results all show satisfactory results such as scratch resistance. On the other hand, Comparative Examples lacking the requirements of the present invention are unsatisfactory as follows. Comparative Examples 1 and 2 in which (C) which is an essential component of the present invention was not used were inferior in scratch resistance, and (B)
Comparative Examples 3 and 4 in which no was used were inferior in low-temperature impact resistance,
Comparative Example 5 in which (c) was not used was inferior in flexibility.

[0040]

[Table 1]

[0041]

[Table 2]

[0042]

[Table 3]

[0043]

[Table 4]

[0044]

[Table 5]

[0045]

[Table 6]

(Note) The table is noted as follows. (1) MI is a value at a temperature of 230 ° C. and a load of 2.16 kgf. (2) In the Izod impact strength, “NB” means “test piece breakage”, and “B” means “test piece breakage”.

[0047]

As described above, the present invention provides a thermoplastic elastomer composition having excellent scratch resistance, low-temperature impact resistance, and moldability, and an airbag cover using the thermoplastic elastomer composition. be able to.

Claims (8)

[Claims] 1. The following (A) 20 to 70% by weight, (B) 5
-60% by weight and (c) 5-50% by weight (however,
(A) + (b) + (c) = 100% by weight. A) a thermoplastic elastomer composition for an airbag cover. (A): Polypropylene resin (B): (B-i) or (B-ii) (B-i): Polymer block composed of at least two aromatic vinyl compounds and at least one conjugated diene compound A hydrogenated aromatic vinyl-conjugated diene compound block copolymer obtained by hydrogenating a block copolymer consisting of a polymer block consisting of ii): ethylene-α-olefin copolymer rubber (c): (A)-(B) block copolymer, (A)-
(B)-(C) block copolymer or (A)-(B)-
(A) a block copolymer [where (A) is a vinyl aromatic compound polymer block, (B) is a conjugated diene polymer block or a vinyl aromatic compound-conjugated diene random copolymer block, and (C) is a vinyl copolymer block. The aromatic compound shows a gradually increasing vinyl aromatic compound-conjugated diene taper block, and these block copolymers may have a polymer molecular chain extended or branched via a coupling agent residue.) The block copolymer satisfying the following conditions (1) to (3) is hydrogenated, 80% or more of the double bond of the conjugated diene portion is saturated, and the number average molecular weight is 500.
Hydrogenated diene-based copolymer having a molecular weight of 00 to 600,000 (1): the weight ratio of vinyl aromatic compound / conjugated diene is 5/95 to 60/40 (2): all monomers constituting the block copolymer (A) The amount of the vinyl aromatic compound in the block (A) is 3
% By weight, and the total bonding amount of the vinyl aromatic compounds in the (A) block and the (C) block is not more than 50% by weight. (3): The vinyl bonding amount of the conjugated diene portion in the (B) block. Must exceed 50% 2. The thermoplastic elastomer composition according to claim 1, wherein the aromatic vinyl compound (b) is styrene. 3. The thermoplastic elastomer composition according to claim 1, wherein the conjugated diene compound (b-i) is butadiene or isoprene. 4. The thermoplastic elastomer composition according to claim 1, wherein the weight ratio of the aromatic vinyl compound / conjugated diene compound (b-i) is from 10/90 to 50/50. 5. The number average molecular weight of (II) is 15,000.
The thermoplastic elastomer composition according to claim 1, which is 0 or less. 6. The thermoplastic elastomer composition according to claim 1, wherein (b) is an ethylene-propylene copolymer rubber. 7. The flexural modulus measured according to JIS K7203 is 3000 kg / cm ² or less.
The thermoplastic elastomer composition as described in the above. 8. An airbag cover obtained by using the thermoplastic elastomer composition according to claim 1.