JP2002173575A - Thermoplastic elastomer composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new and inexpensive thermoplastic elastomer composition used for a noncoated airbag cover having 40-98 spring hardness without requiring a reinforcing nylon-based net in the airbag cover. SOLUTION: Flexibility and moldability are improved by including (a) component of a styrene-based elastomer known as a hydrogenated block copolymer and especially having >=70,000 number-average molecular weight as a main component and adding and alloying (b) component of a paraffinic oil therewith. Developability at a high and a low temperature, damage resistance and moldability are improved and a unit cost of the material is reduced by adding and alloying (c) component of a copolymer of propylene and a 2-8C α-olefin and (d) component of a propylene-based thermoplastic elastomer therewith. Damage resistance, stickiness and releasability when subjected to injection molding are improved by adding (e) component of a silicone oil having >=50,000 cSt viscosity thereto.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an airbag cover for an airbag system used as a safety device for automobiles and the like, which is excellent in the deployability of the airbag, the splash resistance at the time of deployment, does not require painting, and is inexpensive. The present invention relates to a novel thermoplastic elastomer composition.

[0002]

2. Description of the Related Art Conventionally, an airbag cover has been made of urethane having a reinforcing nylon net inserted therein, and there is no reinforcing nylon net due to inflation and deployment of an airbag folded and stored inside. It is designed to burst at the thin part. However, in the case where such an airbag cover does not use a reinforcing nylon-based net, there is a problem that a crack is generated in a portion other than a thin-walled rupture portion at the time of rupture, or the cover is scattered. In the case of using a nylon net for reinforcement, although the problem of tearability when deploying the airbag is solved, when molding the airbag cover,
It takes time to align the reinforcing net. There are drawbacks such as an increase in the defective rate due to misalignment of the reinforcing nylon net or a decrease in productivity due to urethane RIM molding.

[0003]

A number of airbag covers made of a thermoplastic resin which does not contain a reinforcing nylon net have also been studied.
With a softness that humans do not feel unpleasant as automobile interior parts of ~ 98, airbags are reliably deployed at temperatures of -40 ° C to 90 ° C, and when the airbags are deployed, the airbag cover cracks other than at the cracks, It was very difficult for the debris to never fly. Among them, in some polyolefin-based thermoplastic resins, in the state immediately after molding, although having good development performance at a temperature of -40 to 90 ° C., a crystal of the polyolefin-based thermoplastic resin after a high-temperature aging test or a weather resistance test Due to a change in physical properties accompanying a change in the phase structure such as a change in degree of aging, the temperature after these high-temperature aging test and weather resistance test is -40 ° C to 90 ° C.
At present, the deployability of airbags at 0 ° C and the anti-scattering property during deployment are not satisfactory.

Further, most of the air bag covers which are currently under study are coated in order to suppress discomfort such as scratches due to nails and clothes, unpleasant touch such as stickiness, and discoloration due to sunlight. -An airbag cover that does not require painting has been demanded from the viewpoint of economy. Up to now, organic lubricants such as higher fatty acids, higher fatty acid esters, and higher fatty acid amides, and low-viscosity silicone oil have been added to improve the scratch resistance or to prevent stickiness, and to increase the surface slipperiness of molded products. Attempts have been made to improve it. However, since these materials are remarkably transferred to the surface with the passage of time or heat, there is a problem that the appearance of the molded product is impaired or the scratch resistance is reduced.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an airbag cover for an airbag system used as a safety device for automobiles or the like, which does not require a nylon-based reinforcing net and has a spring hardness (hardness) of JIS K6253. An object of the present invention is to provide a novel thermoplastic elastomer composition used for an unpainted airbag cover of 40 to 98.

[0006]

As a result of various studies, the present inventors have found that among styrene-based elastomers known as hydrogenated block copolymers of the component a, those having a number average molecular weight of 70,000 or more are particularly desirable. As a main component, the flexibility and moldability are improved by alloying with the paraffinic oil of the component b, and the propylene of the component c and carbon number 2 to 2 are improved.
8 by adding a copolymer with α-olefin and a d-component propylene-based thermoplastic elastomer to improve alloying performance at high and low temperatures, scratch resistance and moldability, and reduce the unit cost of materials And the viscosity of component e is 500
Scratch resistance by silicone oil of 00cst or more,
With the compounding design concept of improving stickiness and mold release during injection molding, it is possible to obtain an airbag cover with excellent deployability over a wide temperature range of -40 ° C to 90 ° C, and excellent splash resistance during deployment. , And the best combination of these,
-4 not only immediately after molding but also after high temperature aging test and weather resistance test
It has been found that an airbag cover which is excellent in deployability in a wide temperature range of 0 ° C. to 90 ° C. and which does not require painting which is excellent in splash resistance during deployment and which realizes a reduction in the unit cost of materials has been obtained, and completes the present invention. It has been reached.

That is, the present invention provides a thermoplastic elastomer excellent in high-temperature and low-temperature deployability suitable for an airbag cover, which is obtained by melt-kneading and pelletizing the components a, b, c, d and e described in the following claims. A composition is provided. (A) A hydrogenated block copolymer comprising at least two terminal polymer blocks A mainly composed of a vinyl aromatic compound and at least one intermediate polymer block B mainly composed of a conjugated diene compound The obtained hydrogenated block copolymer has a spring hardness (JIS K6253) of 99 or less and a number average molecular weight of 70,000 or more.
45% by weight (b) Paraffinic oil 5 to 30% by weight (c) Copolymer of propylene and α-olefin having 2 to 8 carbon atoms 5 to 35% by weight (d) Manufactured by a multistage polymerization method using a catalyst. (A)
Propylene thermoplastic elastomer composed of a copolymer of propylene and an α-olefin having 3 to 30 carbon atoms and a copolymer of (ii) ethylene and propylene 5 to 90% by weight (e) Viscosity (JIS Z8803, 25 ° C) ) Is 5000
Silicone oil at 0 centistokes or more
1-10% by weight

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The hydrogenated block copolymer used as the component a in the present invention comprises at least two terminal polymer blocks A mainly composed of a vinyl aromatic compound and at least one intermediate polymer block B mainly composed of a conjugated diene compound. Which is obtained by hydrogenating a block copolymer consisting of
It is a hydrogenated vinyl aromatic compound-conjugated diene compound block copolymer having a structure represented by the following general formula. A- (BA) n (1 ≦ n ≦ 5) In order to obtain a hydrogenated block copolymer elastomer composition, a hydrogenated block copolymer having a hardness of 99 or less, preferably 90 or less is used. Therefore, when the vinyl aromatic compound is contained in an amount of 5 to 50% by weight, preferably 10 to 40% by weight, and the block structure is mentioned, the terminal polymer A mainly composed of the vinyl aromatic compound is A compound polymer block or a copolymer block of a vinyl aromatic compound containing more than 50% by weight, preferably 70% by weight or more of a vinyl aromatic compound and a hydrogenated conjugated diene compound, Further, the intermediate polymer block B mainly composed of a hydrogenated conjugated diene compound is used as a hydrogenated conjugated diene compound polymer block or a hydrogenated conjugated diene compound. The emissions Compound 5
It has a structure of a copolymer block of a hydrogenated conjugated diene compound and a vinyl aromatic compound containing more than 0% by weight, preferably 70% by weight or more. When there are two or more polymer blocks mainly composed of a vinyl aromatic compound and two or more polymer blocks mainly composed of a hydrogenated conjugated diene compound, each of the polymer blocks may have the same structure or may be different. It may have a structure.

As the vinyl aromatic compound constituting the hydrogenated block copolymer, one or more of styrene, α-methylstyrene, vinyltoluene, p-tert-butylstyrene and the like can be selected. Among them, styrene is preferred. As the conjugated diene compound before hydrogenation constituting the hydrogenated conjugated diene compound, for example, one or more selected from butadiene, isoprene, 2.3-dimethyl-1.3-butadiene and the like are selected. Among them, butadiene, isoprene and a combination thereof are preferred. Further, the molecular structure of the hydrogenated block copolymer may be linear, branched, radial, or any combination thereof. The number average molecular weight (Mn) of the hydrogenated block copolymer of the component a used in the present invention is 70.
The molecular weight distribution Mw / Mn is 10 or less (Mw: weight average molecular weight), preferably 5 or less, more preferably 2 or less. When the number average molecular weight is less than 70,000,
Sufficient strength cannot be provided. 1 molecular weight distribution
If it exceeds 0, the strength decreases. The amount of the component a is 5 to 45% by weight, preferably 25 to 35% by weight. If the amount of the component a is less than 5% by weight, sufficient strength or impact resistance cannot be imparted at low temperatures,
If the content exceeds 45% by weight, the fluidity is remarkably reduced, so that a molded article having a good appearance cannot be obtained immediately after molding. In addition, since the hydrogenated block copolymer of the component a has a large number average molecular weight, a product to which a paraffinic oil has been added in advance can be appropriately used for improving workability.

[0010] The paraffinic oil used as the component b in the present invention is an essential component having an effect of adjusting the hardness of the resulting composition and imparting flexibility. In general, a softening agent for mineral oil rubber called process oil or extender oil used for softening, increasing the volume of rubber, and improving processability is a mixture of an aromatic ring, a naphthene ring, and a paraffin chain. Those having 50% or more of the total number of carbon atoms in the paraffin chain are called paraffinic, those having 30 to 45% naphthenic ring carbon are naphthenic, and those having more than 30% aromatic carbon are aromatic. System. The oil used as the component b in the present invention is preferably a paraffinic oil in the above category, and a naphthenic or aromatic oil is not preferred in terms of dispersibility and solubility. The paraffin-based softener for rubber has a kinematic viscosity at 37.8 ° C. of 2
0 to 500 cst, pour point is -10 to -15 ° C, and flash point is 170 to 300 ° C. The amount of the paraffinic oil of the component b is 5 to 30% by weight, preferably 1 to 30% by weight.
0 to 25% by weight. If the amount of the component (b) is less than 5% by weight, the fluidity is remarkably reduced, so that a molded article having a good appearance cannot be obtained immediately after molding. If the amount exceeds 30% by weight, the impact resistance at low temperatures is remarkably low. -40 ° C to lower
Good deployment performance cannot be exhibited when the airbag cover is deployed.

The copolymer of propylene and α-olefin having 2 to 8 carbon atoms used as the component c of the present invention is effective for improving the processability and heat resistance of the resulting composition. Α-olefin random or block copolymers, specifically propylene-ethylene copolymers, propylene-1-hexene copolymers, propylene-4-methyl-1pentene copolymers, and poly-4
-Methyl-1-pentene, polybutene-1 and the like, among which ethylene-propylene block copolymers are preferable, among which ethylene content is 2 to 30% by weight.
Are preferred. Further, a nucleating agent is preferably added in order to suppress a change in physical properties in a high-temperature aging test and a weather resistance test. The melt flow rate of this copolymer of propylene and an α-olefin having 2 to 8 carbon atoms (ASTM-D-1
(238L conditions, 230 ° C.) in the range of 0.1 to 60 g / 10 min, particularly 0.5 to 50 g / 10 min can be suitably used. If the melt flow rate is less than 0.1 g / 10 min, the fluidity during molding deteriorates, and the melt flow rate is reduced to 60 g / 10 min.
If it is larger than this, heat resistance is undesirably reduced. The amount of the component c is 5 to 35% by weight, preferably 15 to 25% by weight. 5% by weight of component c
If it is less than 35%, sufficient strength or impact resistance cannot be imparted at a high temperature, and if it exceeds 35% by weight, the impact resistance at a low temperature is remarkably reduced. Deployment performance cannot be demonstrated.

The propylene-based thermoplastic elastomer used as the component (d) in the present invention improves the processability and heat resistance of the resulting composition, improves the airbag expandability at -40 ° C. and the scratch resistance, and reduces the gloss and the material. It is effective in reducing the unit price,
Regarding the production method, a multi-stage polymerization method using a catalyst (Japanese Unexamined Patent Publication No.
97408). The melt flow rate of this propylene elastomer (ASTM-D-1)
(238L condition, 230 ° C) is 0.5 to 40g / 10mi
n is preferred, and more preferably 1 to 30 g / 10 min. Melt flow rate is 0.5g
If the flow rate is less than 40 g / m, the fluidity during molding deteriorates.
If it exceeds in, the heat resistance is undesirably reduced. d
The amount of the component is 5 to 90% by weight, preferably 10 to 60% by weight. If the amount of the d component is less than 5% by weight, sufficient strength or impact resistance cannot be imparted at high temperatures, and if the amount of the d component exceeds 90% by weight, the impact resistance at low temperatures becomes remarkably high. -4 to drop
Good deployment performance cannot be exhibited when the airbag cover is deployed at 0 ° C.

The silicone oil used in the component e of the present invention is a component that imparts scratch resistance, prevents stickiness peculiar to elastomers, and improves mold releasability during injection molding. The type of the substituent to which the siloxane main chain is bonded in the molecular structure of the silicone oil is not particularly limited, but among them, dimethyl silicone oil, methylphenyl silicone oil, or alkyl-modified silicone oil is preferably used. The viscosity of the silicone oil as the component e is at least 50,000 cst, preferably at least 100,000. If the viscosity of the silicone oil is less than 50,000 cst, the initial scratch resistance and stickiness are improved, but the transfer to the molded product surface due to aging or heat is remarkable, which is not preferable. The amount of component e is 0.1 to 10% by weight, preferably 0.1 to 3% by weight.
% By weight. If it is less than 0.1% by weight, the abrasion resistance and stickiness cannot be sufficiently improved, and if it exceeds 10% by weight, a molded appearance cannot be obtained, resulting in an increase in cost. When using the silicone oil, it is possible to use a silicone oil which has been kneaded in advance with a thermoplastic resin in order to improve the dispersibility and workability of the silicone oil.

In addition to the above components (a) to (e), the composition of the present invention may further contain an inexpensive resin such as an inorganic filler and a polystyrene resin, if necessary. These not only have the benefit of reducing product costs as extenders, but also have a positive effect on quality improvement (inorganic fillers: heat-resistant shape retention, flame retardancy, etc., polystyrene resins: processability improvement, etc.). There is also an advantage of giving. Examples of the inorganic filler include calcium carbonate, carbon black, talc, magnesium hydroxide, mica, barium sulfate, natural silicic acid, synthetic silicic acid (white carbon), titanium oxide, and the like. As carbon black, channel black, furnace black Black or the like can be used. Of these inorganic fillers, talc and calcium carbonate are economically advantageous and preferred. Further, as the polystyrene resin usable for this purpose, those obtained by a radical polymerization method or an ionic polymerization method can be suitably used, and the number average molecular weight thereof is 5,000 to 500,000, preferably 10,000.
２００200,000, and the molecular weight distribution Mw /
Mn is preferably 5 or less. Further, if necessary, a nucleating agent, an outer lubricant, an inner lubricant, an ultraviolet absorber, a hindered amine light stabilizer, a hindered phenol antioxidant, a coloring agent, and the like may be added.

The method for producing the composition of the present invention includes:
A general method used for producing a usual resin composition or rubber composition can be employed. Basically, it is a mechanical melt-kneading method, in which a single-screw extruder, a twin-screw extruder, a Banbury mixer, various kneaders, Brabender, rolls and the like are used. At this time, the order of addition of each component is not limited.For example, all components are pre-mixed by a mixer such as a Henschel mixer or a blender and melt-kneaded by the above-described kneader, or any component is pre-mixed by master batch. It is possible to employ an addition method in which the components are melt-kneaded, the remaining components are added, and the mixture is melt-kneaded. At this time, the melting and kneading temperature is 1
It can be suitably selected from 70 ° C to 300 ° C. The hydrogenated block copolymer composition obtained here is further supplied to an injection molding machine equipped with a mold for an airbag cover, and injection molded in a short time to obtain an airbag cover. Also,
Unnecessary burrs, runner portions, and spool portions of the injection-molded product can be recycled because the composition of the present invention is thermoplastic, and can be reused as a material for an airbag cover.

[0016]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. The components blended in the following Examples and Comparative Examples are as follows. <Component a> Asahi Kasei Tuftec H1272: Polystyrene-hydrogenated polyisoprene-polystyrene structure, bound styrene content 35% by weight, number average molecular weight of about 120,000 (paraffin oil (Idemitsu Kosan Diana Process Oil PW- 380 [paraffinic process oil, kinematic viscosity: 381.6 cst (40 ° C.), 30.1
(100 ° C.), average molecular weight 746, ring analysis value: CA = 0
%, CN = 27%, CP = 73%]) 35% by weight oil-added product) <Component b> Diana Process Oil PW-3 manufactured by Idemitsu Kosan
80: paraffinic process oil, kinematic viscosity: 381.
6 cst (40 ° C.), 30.1 (100 ° C.), average molecular weight 746, ring analysis: CA = 0%, CN = 27%, CP =
73% <Component c> MS650 manufactured by Tokuyama: ethylene-propylene block copolymer: melt flow rate 10 g / 10
min (JIS K7210) <Component d> Cataloy KS-084P manufactured by Montelus d'Sunrise: a copolymer of (a) propylene and an α-olefin having 3 to 30 carbon atoms and (b) ethylene produced by a multistage polymerization method Propylene-based thermoplastic elastomer comprising a copolymer of propylene and propylene: melt flow rate 30 g / 10 min (ASTM-D-12
38) <Component e> Silicone made by Dow Corning Toray Silicone
Concentrate BY27-001: straight silicone oil: PP = 50: 50, viscosity 100,000c
st or higher (25 ° C.), melt flow rate 16.4 (2
30 ° C, 2.16 kg)

In Examples 1 to 5 and Comparative Examples 1 to 7, after the components having the mixing ratios shown in the table were sufficiently dry-blended, the mixture was melted using a twin-screw kneader under the condition that the resin temperature was 170 to 230 ° C. It was kneaded and extruded to pelletize. The following evaluation was performed using this pellet. (1) Hardness (JIS K6253): A press sheet was prepared from the pellets and measured. (2) Appearance: Using an injection molding machine, a molded product of an airbag cover having a thickness of 0.5 mm at the split portion of the airbag cover and a thickness of 2 to 5 mm other than the split portion of the airbag bar is prepared from the pellets, and visually observed. The appearance such as flow mark and gloss was observed immediately after molding and after a high-temperature aging test at a temperature of 110 ° C. for 400 hours. (3) Heat-resistant shape retention: This airbag cover molded product is heated to a temperature of 1
A heat-resistant shape retention test was performed in an environment of 10 ° C. After 24 hours, the sample having good shape retention and no sagging, etc. was evaluated as ○, and the sample having sagging, etc. was evaluated as ×.

(4) Deployment test: (4) -1. Normal condition: This airbag cover molded product is subjected to environmental temperature of 90 ° C, 23 ° C and -40 ° C.
An airbag deployment test was performed. If the airbag cover is better developed than the airbag cover, the crack is generated at the airbag cover other than the airbag cover, or the cover is scattered.
A sample in which the airbag did not deploy well was marked as x. (4) -2. After high-temperature aging test: This molded airbag cover was subjected to a high-temperature aging test in an environment at a temperature of 110 ° C. After 400 hours of high temperature aging test, environmental temperature 90 ° C, 23 ° C and -4
An airbag deployment test was performed at 0 ° C. A sample that satisfactorily expanded from the cleaved portion of the airbag cover was rated as ○, and a sample that cracked or scattered the cover other than the cleaved portion of the airbag cover, and a sample that did not deploy the airbag satisfactorily was rated as x. (5) Scratch resistance test: The upper surface of this airbag cover molded product was subjected to a vertical load of 100 gf and a contact area with the molded product surface of about 1 square centimeter using Kanakin No. 3 cloth.
A reciprocating distance of 100 millimeters was reciprocated 10 times at 100 millimeters per second. The surface of the molded article after the test was visually observed, and those with scarcely noticeable scratches were evaluated as ○, and defective as x.

The results are shown in Examples 1 to 5 and Comparative Examples 1 to 7. In addition, the numerical value of the component a in the table is% by weight excluding the oil-extended oil component in the component a. When the component a is used, the numerical value of the component b in the table is a number obtained by adding the weight% of the oil-extended oil component in the component a to the weight% of the component b. From these results, the airbag cover formed from the composition obtained in the present invention has a hardness of 40 to 98 and a temperature of −40 to 90 ° C.
It can be seen that the airbag is excellent in deployability.

[0020]

[Table 1] 1) wt%

[0021]

As described above, the airbag cover molded from the composition of the present invention can provide a good airbag deployment without cracking or scatter of the cover other than cracking when the airbag is deployed at -40 to 90 ° C. . In addition, it has excellent long-term reliability such as high-temperature aging resistance and weather resistance. In addition, the usefulness is very large, as compared with the conventional urethane and reinforcing nylon-based nets, it has better moldability, good productivity, simple color matching, and low material cost.

Claims (1)

[Claims] 1. A thermoplastic elastomer composition comprising the following (a) to (e). (A) A hydrogenated block copolymer comprising at least two terminal polymer blocks A mainly composed of a vinyl aromatic compound and at least one intermediate polymer block B mainly composed of a conjugated diene compound The obtained hydrogenated block copolymer has a spring hardness (JIS K6253) of 99 or less and a number average molecular weight of 70,000 or more.
45% by weight (b) Paraffinic oil 5 to 30% by weight (c) Copolymer of propylene and α-olefin having 2 to 8 carbon atoms 5 to 35% by weight (d) Manufactured by a multistage polymerization method using a catalyst. (A)
A propylene-based thermoplastic elastomer composed of a copolymer of propylene and an α-olefin having 3 to 30 carbon atoms and a copolymer of (b) ethylene and propylene 5 to 90% by weight (e) Viscosity (JIS Z8803, 25 ° C) ) Is 5000
Silicone oil at 0 centistokes or more
1-10% by weight