JPH11209559A - Elastomer composition and casing cover for air bag unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a thermoplastic elastomer excellent in scratch resistance on the surface of its molded product, flexibility, heat resistance, lower temperature characteristics, weather resistance, strength and moldability and useful for e.g. automobiles, home electric appliances or groceries, especially suitable for interior and exterior parts for automobiles needing a good exteriority as a product and among others suitable for casing covers for air bag devices. SOLUTION: This thermoplastic elastomer composition and injection-molded casing cover thereof for air bag devices comprises the following (a), (b) and (c). (a) 100 pts.wt. of 2 kinds of block copolymers with a specific structure obtained by hydrogenating a block copolymer which comprises a polymer block A mainly comprising a vinyl aromatic compound and a block copolymer B mainly comprising a conjugated diene compound; (b) 30 to 125 pts.wt. of polypropylene-based resin having a melt flow rate of 5 to 100 g/min.; and (c) 0 to 50 pts.wt. of hydrocarbon oil.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to various molded articles having excellent scratch resistance (scratch resistance) on the surface of molded articles, and excellent flexibility, heat resistance, low-temperature properties, weather resistance, strength, and moldability. The present invention relates to a thermoplastic elastomer composition that can be used as a material. In particular, the present invention relates to a storage cover of an airbag device designed to restrain an occupant in a seat and protect the occupant from a secondary collision with a steering device, an instrument panel, or the like in a collision accident or the like of a high-speed moving body such as an automobile. The present invention relates to an elastomer composition excellent for use and a storage cover for an airbag device.

[0002]

2. Description of the Related Art Thermoplastic elastomers having excellent productivity have been increasingly used for automotive parts, home electric parts, medical parts and miscellaneous goods, for which vulcanized rubber has hitherto been mainly used. Examples thereof include olefin-based elastomers composed of an ethylene-propylene copolymer and polypropylene, polyurethane elastomers, and soft polyvinyl chloride.

However, at present, these molding materials have drawbacks in terms of scratch resistance, flexibility, workability, economy, and recyclability. That is, olefin-based elastomers are relatively inexpensive and have excellent weather resistance and heat resistance, but are inferior in flexibility and scratch resistance. Although polyurethane elastomers are excellent in scratch resistance, they have drawbacks in that they are inferior in flexibility and weather resistance and are expensive. Soft vinyl chloride is relatively inexpensive and has excellent weather resistance and scratch resistance, but has the drawback of poor flexibility at low temperatures and poor recyclability.

Some proposals have also been made for elastomer compositions using hydrogenated derivatives of vinyl aromatic compound-conjugated diene compound block copolymers (hereinafter abbreviated as hydrogenated block copolymers). . For example, JP-A-50-14742, JP-A-52-65551,
JP-A-58-206644 discloses compositions in which a hydrogenated block copolymer is blended with a rubber softener and an olefin resin. However, these compositions, like the olefin-based elastomers, also had poor scratch resistance.

On the other hand, an airbag system is basically composed of a collision detecting device for detecting a collision of a high-speed moving object and an airbag device, and the latter airbag device is an airbag,
A gas generator that generates gas that inflates the airbag,
Storage cover for storing the airbag and gas generator, and mounting device (retainer) for mounting the gas generator and storage cover
Consists of The airbag device is attached to the front of the occupant moving at high speed, and when the collision detection device is activated by a collision,
Gas is instantaneously generated from the gas generator, and the gas is filled into the airbag which is folded and stored in the space formed by the gas generator, the storage cover and the fixture, and the airbag is filled with the gas. The storage cover is deployed by the pressure of the filled gas, and the airbag is instantaneously released and inflated from the opening obtained by the deployment toward the front of the occupant, thereby restraining the occupant to the seat side. Can be prevented from being injured by colliding with a steering device, an instrument panel, or the like.
Therefore, the storage cover of the airbag device is designed to unfold and release the bag instantaneously without scattering the debris that may injure the occupant when the gas generator is activated due to a collision accident or the like. Must-have.

As a storage cover for such an airbag device, Japanese Patent Application Laid-Open No. 50-127336 or Japanese Patent Application Laid-Open No.
Japanese Patent Publication No. 110643 proposes a storage cover for an airbag device molded from urethane resin in which a reinforcing net made of nylon is mainly placed.

[0007] Since the above-mentioned airbag storage cover uses a reinforcing nylon net, the problem that cracks are generated in the portion other than the cleaved portion at the time of deployment and that a part of the cover is scattered is solved. In addition, it takes time to incorporate the reinforcing net at the time of molding, and the position of the reinforcing net is displaced.

[0008] Japanese Patent Application Laid-Open No. Hei 1-2202550 discloses that a surface layer made of a soft material having a JIS K6301 A hardness of 30 to 70 and a core layer made of an elastic hard resin are integrally formed, and the core layer is cleaved. A storage cover having a structure provided with a slit for use has been proposed. Although the storage cover of the present proposal is preferable in that it has some rigidity and gives an occupant an appropriate feel, it requires two-layer molding of a core layer and a surface layer, and therefore requires two injection mechanisms. There is a problem that an expensive multilayer molding machine is required. In addition, since the soft material serving as the surface layer has poor surface scratch resistance (scratch resistance), it is necessary to paint the surface after forming two layers, which has a problem of high cost.

Japanese Patent Application Laid-Open No. 5-38996 discloses a JIS
A housing cover for an airbag device having a K6301 A hardness of 60 to 85 and molded from a thermoplastic elastomer composition mainly composed of a hydrogenated styrene-conjugated diene-based block copolymer has been proposed. The cover of this proposal is preferable in that it gives the occupant a moderately flexible feel and achieves adaptability in a wide temperature range, but the surface has poor scratch resistance (scratch resistance). Has to be painted, which has a problem of high cost.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional technical problems, and a hydrogenated block having excellent flexibility, weather resistance, heat resistance, low-temperature characteristics, strength and moldability has been developed. Disclosed is a thermoplastic elastomer composition having improved scratch resistance while utilizing the properties of a polymer, and a storage cover for a low-cost airbag device which does not require coating of a surface made of the elastomer composition. .

[0011]

That is, the present invention provides: (a) 100 parts by weight of a hydrogenated block copolymer mixture of the following (a-1) and (a-2): (a-1) at least two A block copolymer obtained by hydrogenating a block copolymer composed of a polymer block A mainly composed of a vinyl aromatic compound and a polymer block B mainly composed of at least one conjugated diene compound,
The number average molecular weight is more than 200,000 and not more than 400,000, and the polymer block A is 15 to 40% by weight of the copolymer.
(A-2) A polymer block A mainly composed of at least one vinyl aromatic compound and a polymer mainly composed of at least one conjugated diene compound. A block copolymer obtained by hydrogenating a block copolymer consisting of a united block B,
The above-mentioned hydrogenated block copolymer in which the number average molecular weight is more than 30,000 and not more than 140000, and the polymer block A constitutes 8 to 35% by weight of the copolymer: 40 to 90 parts by weight (b) The melt flow rate is 5 (C) hydrocarbon oil: 0 to 50 parts by weight, and a storage cover of an airbag device comprising the elastomer composition. It is.

Hereinafter, the present invention will be described in detail. Examples of the vinyl aromatic compound constituting the hydrogenated block copolymer as the component (a) of the present invention include styrene and α.
One or more of methylstyrene, vinyltoluene, p-tert-butylstyrene and the like can be selected;
Among them, styrene is preferred.

Examples of the conjugated diene compound include butadiene, isoprene, 1,3-pentadiene, 2,3
One or more of -dimethyl-1,3-butadiene and the like can be selected, and among them, butadiene, isoprene and a combination thereof are preferable. The polymer block B mainly composed of a conjugated diene compound before hydrogenation can be arbitrarily selected from microstructures in the block. For example, in the case of a polybutadiene block, a 1,2-vinyl bond structure is used. 20-50% by weight,
It is preferably from 25 to 45% by weight, and in the polyisoprene block, the 1,4-vinyl bond is at least 80% by weight, preferably at least 90% by weight.

In the present invention, the hydrogenated block copolymer comprises:
Two types (a-1) and (a-2) are used. The hydrogenated block copolymer (a-1) has a number average molecular weight of 20
More than 0000 and not more than 400,000, preferably 2200
00 or more and 350,000 or less, more preferably 2500
The polymer block A constitutes 15 to 40% by weight, preferably 20 to 35% by weight of the copolymer. If the number average molecular weight of the hydrogenated block copolymer is 200,000 or less, the strength and heat resistance of the elastomer composition are undesirably reduced. On the other hand, when the number average molecular weight of the hydrogenated block copolymer exceeds 400,000, the moldability (flowability) of the elastomer composition is lowered, and the appearance of the molded product is deteriorated (the generation of flow marks). Further, the polymer block A is 15% by weight of the copolymer.
If it is less than 10%, the strength and heat resistance of the elastomer composition are undesirably reduced. On the other hand, when the amount of the polymer block A exceeds 40% by weight of the copolymer, the scratch resistance and flexibility of the elastomer composition are decreased, and the moldability and low-temperature properties are undesirably decreased.

The hydrogenated block copolymer (a-2) has a number average molecular weight of more than 30,000 to 140,000, preferably 50,000 to 120,000, more preferably 60,000.
000 to 90000, and the polymer block A constitutes 8 to 35% by weight of the copolymer, preferably 10 to 30% by weight, and more preferably 15 to 25% by weight. If the number average molecular weight of the hydrogenated block copolymer is 30,000 or less, the strength and heat resistance of the elastomer composition are undesirably reduced. On the other hand, the number average molecular weight of the hydrogenated block copolymer is 1
If it exceeds 40000, the molding processability (fluidity) of the elastomer composition is lowered, and the appearance of the molded product is deteriorated (flow mark generation), which is not preferable. Further, if the amount of the polymer block A is less than 10% by weight of the copolymer, the strength and heat resistance of the elastomer composition are undesirably reduced. On the other hand, if the polymer block A exceeds 35% by weight of the copolymer, the scratch resistance and flexibility of the elastomer composition are undesirably reduced.

The molecular weight distribution of the hydrogenated block copolymers (a-1) and (a-2) [the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) (Mw / Mn)] is 5 or less;
Preferably it is 2 or less, more preferably 1.5 or less. If the molecular weight distribution exceeds 5, the strength and heat resistance of the elastomer composition are not sufficient, which is not preferable. The molecular weight and the molecular weight distribution described in the present specification can be determined by, for example, GPC (Gel
It is measured by the Permeation Chromatography method. In GPC analysis, the molecular weight can be calculated using a calibration curve prepared with standard polystyrene.

The hydrogenated block copolymer used as the component (a-1) in the present invention comprises at least two polymer blocks A mainly composed of a vinyl aromatic compound and at least one conjugated diene compound mainly. And a block copolymer obtained by hydrogenating a block copolymer consisting of a polymer block B, for example, ABA, BAB-
A, ABABA, BABAB and the like.

The hydrogenated block copolymer used as the component (a-2) in the present invention comprises at least one polymer block A mainly composed of a vinyl aromatic compound and at least one conjugated diene compound. Is a block copolymer obtained by hydrogenating a block copolymer comprising a polymer block B mainly composed of, for example, AB, AB-
A, BABA, ABABA, BAB
-AB and the like.

Although a composition having good scratch resistance can be obtained with the AB type structure, at least two hydrogenated block copolymers (a-2) which are particularly preferable in terms of strength and heat resistance are obtained. A polymer block A mainly composed of a vinyl aromatic compound,
A block copolymer obtained by hydrogenating a block copolymer composed of at least one polymer block B mainly composed of a conjugated diene compound and, for example, ABA, B-
ABA, ABABA, BABAB
Etc.

In the present invention, (a-1) or (a-
2) The polymer block A mainly composed of a vinyl aromatic compound of the hydrogenated block copolymer used as the component, and the polymer block B mainly composed of the conjugated diene compound are each a vinyl aromatic compound or a vinyl aromatic compound in each polymer block. Conjugated diene compound distribution is random or tapered (the monomer component increases or decreases along the molecular chain)
Or, it may be partially block-shaped or an arbitrary combination thereof. When there are two or more polymer blocks A and B, each polymer block may have the same structure or different structure. It may be. As used herein, the expression "predominantly" means that the corresponding monomer unit is at least 5 of the polymer block.
0% by weight or more, preferably 70% or more.

The mixing ratio of the hydrogenated block copolymer (a-1) to the hydrogenated block copolymer (a-2) is such that the total amount of the hydrogenated block copolymer is 100 parts by weight. The polymer (a-1) is 10 to 60 parts by weight, the block copolymer (a-2) is 40 to 90 parts by weight, and more preferably the block copolymer (a-1) is 20 to 50 parts by weight. And the block copolymer (a-2) is 50 to 80 parts by weight. If the amount of the block copolymer (a-1) is less than 10 parts by weight, the strength and heat resistance of the elastomer composition are undesirably reduced. When the amount of the block copolymer (a-1) exceeds 60 parts by weight, the moldability (flowability) of the elastomer composition is obtained.
And the appearance of the molded article deteriorates (generation of flow marks), which is not preferred.

The production method of these block copolymers is not limited as long as they have the above-mentioned structure. For example, a method using a lithium catalyst by a method described in Japanese Patent Publication No. 40-23798 is used. Thus, a vinyl aromatic compound-conjugated diene compound block copolymer before hydrogenation can be synthesized in an inert solvent.

Examples of the method of hydrogenation include, for example, Japanese Patent Publication No. 42-8704, Japanese Patent Publication No. 43-6636, Japanese Patent Application Laid-Open No. 60-220147, and Japanese Patent Application Laid-Open No.
3132 or JP-A-62-207303. At least 80%, preferably at least 90%, of the aliphatic double bonds derived from the conjugated diene compound are hydrogenated, while less than 20%, preferably less than 10%, of the vinyl aromatic compound is hydrogenated. To be selected. The hydrogenation rate of the hydrogenated block copolymer can be easily known by infrared spectroscopy or nuclear magnetic resonance analysis.

Next, the component (b) of the present invention is a polypropylene resin. As the polypropylene resin, propylene homopolymer or propylene and α-
It is a copolymer with an olefin (hereinafter abbreviated as propylene-based resin). In the case of a copolymer of propylene and an α-olefin having 2 to 8 carbon atoms, the α-olefin in the copolymer may be ethylene, butene-1, isobutene, pentene-1, hexene-1, 4-methylpentene- 1, octene-1 and the like. The proportion of α-olefin is 30% by weight or less. These propylene-based resins can be synthesized by a conventionally known method, for example, a propylene homopolymer synthesized using a Ziegler-Natta type catalyst, or a copolymer of random or block propylene and an α-olefin. Is raised. In order to obtain an elastomer composition having excellent heat resistance and moldability, it is preferable to use a polypropylene resin as the polyolefin resin.

The melt flow rate of these polypropylene resins (ASTM D1238, 230 ° C., 2.1
A value measured according to a 6 kg load. (Hereinafter abbreviated as MFR) is 5 to 100 g / 10 min, preferably 10 to 60 g.
/ 10 minutes. If the MFR is less than 5 g / 10 minutes, the melt viscosity of the elastomer composition is high, and the moldability (flowability) of the elastomer composition is lowered, and the appearance of the molded product is deteriorated (the generation of flow marks), which is not preferable. On the other hand, if the MFR exceeds 100 g / 10 minutes, the strength and heat resistance of the elastomer composition are undesirably reduced.

The flexural modulus of the polypropylene resin is 800
It is at least 900 MPa, preferably at least 900 MPa, more preferably at least 1000 MPa. If the flexural modulus of the polypropylene resin is less than 800 MPa, the hardness and heat resistance of the elastomer composition are undesirably reduced.

In the present invention, the blending amount of the polypropylene resin as the component (b) is 100
30 to 125 parts by weight, preferably 55 to parts by weight,
100 parts by weight. If the blending amount of the polypropylene resin is less than 30 parts by weight, the heat resistance and the moldability (flowability) of the elastomer composition are lowered, and the appearance of the molded product is deteriorated (the generation of flow marks). If the amount of the polypropylene-based resin exceeds 125 parts by weight, the flexibility of the elastomer composition is undesirably reduced.

The component (c) in the present invention is a hydrocarbon oil, which has the effect of improving the flexibility and processability of the resulting composition, and is a non-aromatic mineral oil or a liquid or low molecular weight oil. Synthetic softeners are suitable. As the non-aromatic mineral oil, generally known paraffin oils and naphthenic oils can be used. Among them, paraffin oils having an aromatic ring component of 10% by weight or less are preferable. The compounding amount of the hydrocarbon oil is 0 to 50 parts by weight, preferably 5 to 45 parts by weight, more preferably 10 to 40 parts by weight, based on 100 parts by weight of the hydrogenated block copolymer. If the blending amount of the hydrocarbon oil exceeds 50 parts by weight, the scratch resistance and heat resistance of the elastomer composition are undesirably reduced.

Further, the composition of the present invention may optionally contain an inorganic filler, a stabilizer, a lubricant, a coloring agent, a silicone oil, a flame retardant, and the like. As the inorganic filler, for example, calcium carbonate, talc, magnesium hydroxide, mica,
Barium sulfate, silicic acid (white carbon), titanium oxide, carbon black and the like can be mentioned. Stabilizers include hindered phenolic antioxidants, phosphorus heat stabilizers,
Hindered amine light stabilizer, benzotriazole U
V absorbent and the like. Stearic acid as a lubricant,
And stearic acid esters and metal salts of stearic acid.

In general, any method known in the art for blending polymer components may be used to prepare the elastomeric composition of the present invention.
In order to obtain the most homogeneous blend, a method of melt-kneading using various kinds of kneading machines such as commonly used mixing rolls, kneaders, Banbury mixers and extruders is desirable. Before melt-kneading, these compounds are dry-blended in advance using a mixer such as a Henschel mixer, tumbler or ribbon blender, and the mixture is melt-kneaded to obtain a homogeneous elastomer composition.

As the molding method of the elastomer composition of the present invention, injection molding, extrusion molding, compression molding and the like can be applied, but it has a feature that it is particularly excellent in moldability at the time of injection molding. When performing injection molding, a normal plastic molding machine can be used, and an injection molded product can be obtained in a short time. In addition, the elastomer composition has an advantage that the sprue portion and the runner portion can be recycled because of its excellent thermal stability.

As a method of further molding the obtained composition into a storage cover of an airbag device, injection molding is suitably used. The storage cover of the airbag device can be obtained in a short time by supplying the airbag device to an injection molding machine having a mold for the storage cover and performing injection molding. In addition, since the present elastomer has excellent thermal stability, it has an advantage that the sprue portion and the runner portion can be recycled. To ensure that the storage cover of the airbag device unfolds and release the airbag instantaneously,
It is desirable to provide a tear line designed in advance on the cover. The tear line is designed in an H shape, a U shape, or the like in consideration of the position of the passenger, the installation position of the airbag device, the direction in which the bag is released, the shape of the cover, and the like. Further, the tear line can be provided by reducing the thickness of other portions, such as a V-shaped groove and a U-shaped groove, along the portion to be broken.

Although it is economically advantageous to form the airbag cover of the present invention into a single layer by the injection molding method, it is combined with other plastics for the purpose of reinforcing the mounting portion and increasing the rigidity of the molded product. Can also be used. In the case of compounding, an injection multilayer molding method or a method of bonding using an adhesive can be used. However, since the present elastomer composition has excellent scratch resistance, it can be suitably used as a skin material.

[0034]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the examples and comparative examples, the test methods used for various evaluation methods are as follows. (1) Hardness [-]: JIS K6301, A type, 2
Measured at 3 ° C. (2) Tensile strength [kgf / cm ² ]: JIS K630
No. 1 and No. 3 dumbbells and 2 mm thick pressed sheets were used as samples. (3) Elongation [%]: JIS K6301, No. 3 dumbbell, 2 mm thick pressed sheet was used as a sample.

(4) Heat sag [mm]: A test piece having a length of 110 mm, a width of 12.5 mm and a thickness of 2 mm was molded by an injection molding machine. It was left for 24 hours or more in an atmosphere at a temperature of 23 ° C. and a relative humidity of 50%. A square iron pole having a height of 80 mm was placed on a horizontal iron plate, and one of the test pieces was fixed on the upper surface of the square iron pole so that the overhang length was 80 mm (the fixed part was set horizontally). The sample was placed in an oven that had been kept at a constant temperature of 110 ° C. in advance, and was taken out after being left for 1 hour. The height between the front end portion opposite to the fixing portion and the horizontal iron plate surface was measured before and after placing in the oven, and the difference was shown as a result. (5) Melt flow rate (MFR) [g / 10 min]:
ASTM D1238 was measured at 230 ° C. under a load of 2.16 kg.

(6) Scratch resistance and gloss retention [%]: A flat plate having a smooth surface was formed by injection molding. Place the plate horizontally and place a cotton cloth with a load of 40 g / cm ²
Reciprocated twice. The glossiness of the friction surface is determined according to JIS K7105.
(E1), and the retention ratio from the glossiness (E0) before friction; (E1 / E0) × 100 (%) was determined. Grain drop test: A flat plate with a surface grain (matte, edging depth about 20 microns) was formed by injection molding. 10 flat plates
It was left in an oven at 0 ° C. for 168 hours. After being taken out of the oven, the surface condition was visually observed, and those having no change were evaluated as ○, slightly glossy as Δ, and glossy as ×.

(8) Formability: Injection molding machine has a thickness of 5 mm and a portion to be broken (tier line) has a thickness of 0.5.
A storage cover of an airbag device for a driver's seat having a thickness of 2.5 mm and a hinge portion having a thickness of 2.5 mm was formed under the following conditions. Observe the appearance of flow mark, gloss, etc. of the molded body by visual inspection, and mark ○: good, ○ ~ △: slightly defective, △: slightly defective, ×: defective, extremely poor X
X. Cylinder temperature C1: 180 ° C, C2: 190 ° C, C
3: 190 ° C, nozzle temperature: 200 ° C, injection speed: low speed, mold temperature: 40 ° C

(9) Deployment performance of the storage cover: The airbag and the storage cover are attached to an iron fitting (retainer), and a gas generator is further attached to assemble the airbag device. Next, the airbag device was deployed at the deployment temperature (-4
(0 ° C., 23 ° C., and 90 ° C.) and left for one hour after the internal temperature is stabilized. Then, the airbag device is taken out, attached to a stand, and energized and deployed. (Electricity is supplied within 1 minute after taking out from the thermostat.) If the storage cover is torn at the portion to be broken without generating broken pieces and the airbag is deployed, the deployability is determined to be good.

The components used in the examples and comparative examples are as follows. Component (a-1) -1 having a structure of ABA, having a number average molecular weight of 270000,
Molecular weight distribution 1.2, bound styrene content 31% by weight, 1,2-vinyl bond content of polybutadiene part before hydrogenation was 38
A hydrogenated block copolymer of a styrene / butadiene block copolymer having a hydrogenation rate of 99% by weight and a polybutadiene portion of 99% was synthesized by the method described in JP-A-60-220147.

Component (a-1) -2 having the structure of ABA, having a number average molecular weight of 220,000,
Molecular weight distribution 1.1, bound styrene content 32% by weight, polybutadiene moiety before hydrogenation had 1,2-vinyl bond content of 37
A hydrogenated block copolymer of a styrene / butadiene block copolymer having a hydrogenation rate of 99% by weight and a polybutadiene portion of 99% was synthesized by the method described in JP-A-60-220147.

Component (a-1) -3 having the structure of ABA, having a number average molecular weight of 290000,
Molecular weight distribution 1.2, bound styrene content 28% by weight, 1,4-bond content of polyisoprene portion before hydrogenation 94% by weight, 3,4-bond content 6% by weight, hydrogenation rate of polyisoprene portion A hydrogenated block copolymer of 99% styrene / isoprene block copolymer was obtained by
No. 47 was synthesized.

Component (a-1) -4 having the structure of BABA and having a number average molecular weight of 25,000
Styrene / butadiene block copolymer having a molecular weight distribution of 1.2, a bound styrene content of 34% by weight, a 1,2-vinyl bond content of the polybutadiene portion before hydrogenation of 36% by weight, and a hydrogenation rate of the polybutadiene portion of 99%. Was synthesized by the method described in JP-A-60-220147.

Component (a-1) -5 having the structure of ABA, having a number average molecular weight of 250,000,
Molecular weight distribution 1.2, bound styrene content 45% by weight, 1,2-vinyl bond content of the polybutadiene portion before hydrogenation was 36
A hydrogenated block copolymer of a styrene / butadiene block copolymer having a hydrogenation rate of 99% by weight and a polybutadiene portion of 99% was synthesized by the method described in JP-A-60-220147.

Component (a-1) -6 having the structure of BABA and having a number average molecular weight of 17000
Styrene / butadiene block copolymer having a molecular weight distribution of 1.2, a bound styrene content of 33% by weight, a 1,2-vinyl bond content of the polybutadiene portion before hydrogenation of 38% by weight, and a hydrogenation rate of the polybutadiene portion of 99%. Was synthesized by the method described in JP-A-60-220147.

Component (a-2) -1 having the structure of ABA, having a number average molecular weight of 90000, a molecular weight distribution of 1.10, an amount of bound styrene of 21% by weight, and 1,2 of the polybutadiene portion before hydrogenation. 38 vinyl bonds
A hydrogenated block copolymer of a styrene / butadiene block copolymer having a hydrogenation rate of 99% by weight and a polybutadiene portion of 99% was synthesized by the method described in JP-A-60-220147.

Component (a-2) -2 having the structure of BABA and having a number average molecular weight of 6,500
0, molecular weight distribution 1.13, bound styrene content 30% by weight,
A hydrogenated block copolymer of a styrene / butadiene block copolymer having a 1,2-vinyl bond content of 36% by weight in the polybutadiene portion before hydrogenation and a hydrogenation rate of 99% in the polybutadiene portion is disclosed in JP-A-60-220147. It was synthesized by the method described in the gazette.

Component (a-2) -3 having the structure of ABA, having a number average molecular weight of 55,000, a molecular weight distribution of 1.1, an amount of bound styrene of 25% by weight, and a polyisoprene part of 1,1 before hydrogenation. 4- 94% by weight of binding;
A hydrogenated block copolymer of a styrene / isoprene block copolymer having a 3,4-bond content of 6% by weight and a hydrogenation rate of the polyisoprene portion of 99% was prepared by the method described in JP-A-60-220147.
The synthesis was carried out according to the method described in Japanese Patent Publication No.

Component (a-2) -4 having the structure of ABA, having a number average molecular weight of 25,000, a molecular weight distribution of 1.14, an amount of bound styrene of 21% by weight, and 1,2 of the polybutadiene portion before hydrogenation. 38 vinyl bonds
A hydrogenated block copolymer of a styrene / butadiene block copolymer having a hydrogenation rate of 99% by weight and a polybutadiene portion of 99% was synthesized by the method described in JP-A-60-220147.

Component (a-2) -5 having the structure of BABA and having a number average molecular weight of 7,000
Styrene / butadiene block copolymer having a molecular weight distribution of 1.1, a bound styrene content of 39% by weight, a 1,2-vinyl bond content of a polybutadiene portion before hydrogenation of 36% by weight, and a hydrogenation rate of the polybutadiene portion of 99%. Was synthesized by the method described in JP-A-60-220147.

Component (b) -1 Shaw Allomer MK511 (block type polypropylene) made by JPO, MFR 15 g / 10 min, Curve elastic modulus 1
250 MPa. Component (b) -2 Showaromer M1700 (homopolypropylene), manufactured by JPO, MFR 31 g / 10 min, flexural modulus 1600 MP
a. Component (b) -3 Manufactured by JPO, Show Allomer E7100 (block type polypropylene), MFR 0.5 g / 10 min, flexural modulus 1450 MPa. Component (c) Idemitsu Kosan, paraffin oil. Diana Process Oil PW-380. (Kinematic viscosity: 380 cSt).

Examples 1 to 8 (a-1) -1 and (a-
2) Using -1 and (b)-as a polyolefin resin
1 and (c) as a hydrocarbon oil, blended in a Henschel mixer at the respective ratios shown in Tables 1 and 2, and then melt-kneaded at 220 ° C. in a 45 mm-diameter twin-screw extruder. Then, pellets of the elastomer composition were obtained. Next, the pellets of this elastomer composition were injection molded to obtain storage covers for a plurality of driver airbag devices. This was evaluated by the above test method, and the results are shown in Tables 1 and 2. From these results, it is clear that the elastomer of the present invention is excellent in scratch resistance, strength and heat resistance, has good melting properties, and is excellent in injection moldability. Also, -40
The developability at 23 ° C, 90 ° C, and 23 ° C was all good.

The shapes of the storage covers of Examples 1 to 8 are shown in FIGS.
This will be described below with reference to FIG. As shown in FIG. 1, the storage cover 1 has a flange 5 around which a bolt hole 9 for attaching to a retainer (not shown) is provided, and one side is opened to allow a space 8 in which an airbag can be stored. A broken portion 3 of a fragile structure is disposed on the top surface 2 in an H shape as shown by a dotted line in FIG. A hinge portion is provided as shown by a chain line.

The section 3 to be broken is formed by a groove 6 having a V-shaped cross section on the back side of the top surface 2 as shown in FIGS. 2 and 3, and the hinge portion is formed as shown in FIGS. Top surface 2
Is formed by a U-shaped groove 7. Storage cover 1 when airbag (not shown) is inflated
Is broken at the portion 3 to be broken, the two doors 2a and 2b are respectively developed around the hinges 4 and the airbag is released.

The dimensions of the portion 3 to be broken are 120 mm for a portion corresponding to two H-shaped bars, and 1 mm for a portion corresponding to a horizontal bar.
The thickness of the portion to be broken is 0.5 mm, the thickness of the hinge portion is 2.5 mm, and the other portions are 5 mm.

[0055]

[Table 1]

[0056]

[Table 2]

Comparative Examples 1 to 8 (a-1) -1, (a-
1) -6, using (a-2) -1, using (b) -1 as a polyolefin-based resin, and using (c) as a hydrocarbon oil, at each ratio shown in Tables 3 and 4. Kneading and evaluation were performed in the same manner as in the methods of Examples 1 to 8. The results are shown in Tables 3 and 4. From these results, it is clear that a composition outside the scope of the present invention is inferior in any physical properties or developing performance.

[0058]

[Table 3]

[0059]

[Table 4]

Examples 9 to 14 (a-1) -1 and (a-
1) -2, (a-1) -3, (a-1) -4, (a-
2) -1, (a-2) -2, (a-2) -3, (b) -1 and (b) -2 as polyolefin resins, and (c) as hydrocarbon oil. It was kneaded and evaluated at the respective ratios shown in Tables 5 and 6 in the same manner as in Examples 1 to 8. The results are shown in Tables 5 and 6. From these results, it is clear that the elastomer of the present invention is excellent in scratch resistance, strength and heat resistance, has good melting properties, and is excellent in injection moldability. -40 ° C, 23 ° C, 90 ° C
The developability at ° C was all good.

[0061]

[Table 5]

[0062]

[Table 6]

Comparative Examples 9 to 12 (a-1) -1, (a-
1) -5, (a-2) -1, (a-2) -4, (a-
2) -5, using (b)-as a polyolefin resin
Using (b) -3, (c) as a hydrocarbon oil, and kneading in the respective ratios shown in Table 7, kneading was performed in the same manner as in Examples 1 to 8, and evaluated. The results are shown in Table 7. From this result, it is clear that a composition outside the scope of the present invention has poor physical properties or developability.

[0063]

[Table 7]

[0064]

The elastomer composition obtained by the present invention is excellent in scratch resistance, strength, heat resistance, flexibility, and moldability, so that it can be suitably used in the fields of automobile parts, home electric parts, toys, miscellaneous goods and the like. However, it can be suitably used for automobile interior parts such as instrument panels, armrests, handles, horn pads, etc., and automobile exterior parts such as window moldings and bumpers which require a product appearance because of particularly excellent scratch resistance. . Further, the storage cover of the airbag device obtained by the elastomer composition of the present invention,
In a wide temperature range from −40 ° C. to 90 ° C., good deployability can be obtained without cracking other than at the cracked portion and without scattering of the cover when the airbag is deployed. Further, since the surface of the molded article is excellent in scratch resistance and molding workability, the coating step which has been conventionally required can be eliminated, so that high productivity and low cost can be realized.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an example of a storage cover of an airbag device for a driver's seat according to the present invention.

FIG. 2 is a sectional view of the storage cover taken along line II-II in FIG.

FIG. 3 is an enlarged cross-sectional view of a storage cover V-shaped groove in FIG. 2;

FIG. 4 is an enlarged sectional view of a storage cover U-shaped groove in FIG. 2;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Storage cover 2 Top plate 3 Expected break part 4 Hinge part 6 V-shaped groove 7 U-shaped groove

Claims (6)

[Claims] (A) The following (a-1) and (a-2)
100 parts by weight of a hydrogenated block copolymer mixture of (a-1): a polymer block A mainly composed of at least two vinyl aromatic compounds and a polymer block B mainly composed of at least one conjugated diene compound A block copolymer obtained by hydrogenating a block copolymer consisting of
The number average molecular weight is more than 200,000 and not more than 400,000, and the polymer block A is 15 to 40% by weight of the copolymer.
(A-2) a polymer block A mainly composed of at least one vinyl aromatic compound and a polymer mainly composed of at least one conjugated diene compound. A block copolymer obtained by hydrogenating a block copolymer consisting of a united block B,
The above-mentioned hydrogenated block copolymer in which the number average molecular weight is more than 30,000 and not more than 140000, and the polymer block A constitutes 8 to 35% by weight of the copolymer: 40 to 90 parts by weight (b) The melt flow rate is 5 An elastomer composition comprising: 100 to 10 g / 10 min of a polypropylene resin: 30 to 125 parts by weight (c) hydrocarbon oil: 0 to 50 parts by weight. 2. The method according to claim 1, wherein the vinyl aromatic compound is styrene,
The conjugated diene compound is butadiene or isoprene or a combination thereof.
The elastomer composition according to any one of the preceding claims. 3. A propylene homopolymer having a bending elastic modulus of at least 800 MPa and / or a polypropylene resin.
2. The elastomer composition according to claim 1, wherein the elastomer composition is a copolymer of propylene and an α-olefin having 2 to 8 carbon atoms. 4. The elastomer composition according to claim 1, wherein the hydrocarbon oil is a non-aromatic mineral oil. 5. The elastomer composition according to claim 1, wherein the amount of the hydrocarbon oil is 10 to 40 parts by weight. 6. A storage cover for an airbag device comprising the elastomer composition according to claim 1, 2, 3, or 4.