JPH10129387A - Air bag cover - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an air bag cover to be manufactured through a simple process and besides be excellent in impact resistance, especially, impact resistance, wear resistance, and damage resistance at a low temperature. SOLUTION: An air bag comprises (A) 10-50 pts.wt. a block copolymer consisting of a polymer block (a) of styrene or its derivative and a polymer or a copolymer block (b) being an isoprene copolymer block or an isoprene butadien copolymer block, and an isoprene unit content amount of 40mol% or more combined at 1, 2-figure or 3, 4-figure based on a total isoprene unit; (B) 15-60 pts.wt. crystalline polyorefin resin; and (C) a total amount of components (A)-(C) 100 pts.wt. a thermoplastic elastomer composition containing an ethylene content being 75-88mol% an ethylene.α-olefin copolymer or 15-50 pts.wt. an ethylene.α-olefin.non-conjugate dien copolymer.

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 accommodating a vehicle collision safety device (airbag).
More specifically, the present invention relates to an airbag cover made of a thermoplastic elastomer composition.

[0002]

2. Description of the Related Art An airbag device for an automobile operates and deploys upon detecting a collision, an impact or the like. At this time, the airbag cover accommodating the airbag must be reliably deployed without scattering the debris that damages the occupant. In addition, it is a part that is always in touch with the public, and an excellent appearance is required.

[0003] Various structures and materials of such an airbag cover have been conventionally studied. For example, JP-A-50-127336 and JP-A-55-110643
In Japanese Patent Application Laid-Open No. H11-163, there is described an airbag cover which uses a polyurethane resin or the like and inserts a reinforcing material such as a net in addition to a portion to be broken to prevent scattering of fragments when deployed. However, the airbag cover having such a structure has a problem in that a process for accurately inserting a reinforcing material at the time of manufacturing is complicated, so that production efficiency is low and cost is high.

Further, Japanese Patent Application Laid-Open Nos.
JP-A-220946 describes an airbag cover in which a skin layer made of a soft resin giving a soft and soft feeling and a core layer made of a hard resin for maintaining strength are integrally formed. However, such an airbag cover has two problems.
There is a problem that layer forming must be performed and a complicated and expensive special molding machine is required.

In recent years, a single-layer type airbag cover which does not require such complicated steps has been provided. For example, JP-A-4-314648 and JP-A-6-1
No. 56178 describes an airbag cover made of an olefin-based and / or styrene-based thermoplastic elastomer. However, when the airbag cover is made of a material having high rigidity, the occupant cannot be given a soft feeling, and since the impact strength at low temperatures is low, debris may be scattered when the airbag is activated. There is a security problem. Further, when the rigidity is reduced to improve the feel and low-temperature impact resistance, it is easy to wear when the rigidity is reduced, and the scratch resistance is poor.

[0006]

SUMMARY OF THE INVENTION The present invention is intended to solve the problems associated with the prior art as described above, and can be manufactured in a simple one step, and has a high impact resistance, especially at low temperatures. It is an object of the present invention to provide an airbag cover which is excellent in impact resistance, is excellent in abrasion resistance and scratch resistance, and has a good appearance without coating.

[0007]

The present invention is the following airbag cover. (1) (A) a polymer block (a) of styrene or a derivative thereof and an isoprene polymer block or an isoprene-butadiene copolymer block, wherein the 1,2-position or the 3,4-position relative to all isoprene units A polymer or copolymer block (b) having an isoprene unit content of 40 mol% or more bonded with 10 to 50 parts by weight of an optionally hydrogenated block copolymer;
(B) 15 to 60 parts by weight of a crystalline polyolefin resin, and (C) an ethylene / α-olefin copolymer having an ethylene content of 75 to 88 mol%, or an ethylene content of 75 to 88 mol%.
15 to 50 parts by weight of an ethylene / α-olefin / non-conjugated diene copolymer [the total amount of components (A), (B) and (C) is 100 parts by weight. An airbag cover comprising a thermoplastic elastomer composition (hereinafter, referred to as a first airbag cover). (2) (A) a polymer block (a) of styrene or a derivative thereof and an isoprene polymer block or an isoprene / butadiene copolymer block, wherein the 1,2-position or the 3,4-position relative to all isoprene units; A polymer or copolymer block (b) having an isoprene unit content of 40 mol% or more bonded with 10 to 50 parts by weight of an optionally hydrogenated block copolymer;
(B) 15-60 parts by weight of a crystalline polyolefin resin,
(C) ethylene / α having an ethylene content of 75 to 88 mol%
-Olefin copolymer or ethylene content of 75-8
A crosslinked olefinic thermoplastic elastomer (D) comprising 15 to 50 parts by weight of an ethylene / α-olefin / non-conjugated diene copolymer of 8 mol%, and (D) a crystalline polyolefin resin and an olefinic rubber; ) 0-50
Parts by weight [dashi, components (A), (B),
The total amount of (C) and (D) is 100 parts by weight.] An airbag cover (hereinafter, referred to as a second airbag cover) comprising a thermoplastic elastomer composition. (3) The airbag cover according to the above (1) or (2), wherein the crystalline polyolefin resin (B) is polyethylene. (4) The crystalline polyolefin resin (B) has a density of 0.93
The airbag cover according to the above (3), wherein the airbag cover is polyethylene of 0 g / cm ³ or more. (5) The airbag cover according to any one of the above (1) to (4), wherein the ethylene / α-olefin copolymer (C) is an ethylene / butene-1 copolymer.

<< Block Copolymer (A) >> The block copolymer (A) used in the present invention comprises a polymer block (a) of styrene or a derivative thereof, a specific isoprene polymer or a specific isoprene-butadiene. It consists of a block (b) made of a copolymer and may be hydrogenated.

The polymer component constituting the block (a) is styrene or a derivative thereof. Specific examples of styrene derivatives include α-methylstyrene, 3-methylstyrene, 4-propylstyrene, 4-cyclohexylstyrene, 4-dodecylstyrene, 2-ethyl-4-benzylstyrene, and 4- (phenylbutyl). Styrene and the like. Styrene and α-methylstyrene are preferable as the polymer component constituting the block (a).

The polymer or copolymer constituting the block (b) is an isoprene polymer or an isoprene / butadiene copolymer, and is a 1,2-position or a 3,3-position represented by the following formula with respect to the entire isoprene unit. The content of isoprene units bonded at the 4-position is at least 40 mol%, preferably at least 45 mol%.

[0011]

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In the block copolymer (A), when the content of the isoprene unit bonded at the 1,2-position or the 3,4-position relative to all the isoprene units is 40 mol% or more, scratch resistance is excellent. Airbag cover can be obtained.

The proportion of the polymer block (a) of styrene or a derivative thereof in the block copolymer (A) is preferably 5 to 50% by weight, more preferably 10 to 45% by weight.
%, The proportion of the soprene polymer block or the isoprene-butadiene copolymer block (b) is preferably 95 to 50% by weight, more preferably 90 to 55% by weight.
Range.

The block copolymer (A) is preferably a hydrogenated block copolymer. When the hydrogenated block copolymer (A) is used, an airbag cover having more excellent weather resistance and heat resistance can be obtained.

The block copolymer (A) used in the present invention has a melt flow rate (MFR; ASTM D).
1238, 230 ° C, 2.16 kg load, the same applies hereinafter)
However, it is preferably in the range of 0.01 to 30 g / 10 min, more preferably 0.01 to 10 g / 10 min. When the block copolymer (A) having a melt flow rate in the above range is used, an airbag cover having excellent scratch resistance can be obtained.

The block form of the block copolymer (A) used in the present invention is most preferably a block (a) -block (b) -block (a) form.
It is not limited to this.

Such a block copolymer (A) can be produced, for example, by the following method. (1) A method in which styrene or a derivative thereof, isoprene or an isoprene-butadiene mixture is sequentially polymerized using an alkyllithium compound as an initiator. (2) A method of polymerizing styrene or a derivative thereof, followed by isoprene or a mixture of isoprene and butadiene, and coupling this with a coupling agent. (3) A method of sequentially polymerizing isoprene or an isoprene-butadiene mixture and then styrene or a derivative thereof using a dilithium compound as an initiator. Details of the method for producing the block copolymer (A) are described in, for example, JP-A-2-300250.

The hydrogenated block copolymer (A) is obtained by subjecting the block copolymer (A) obtained by the above method to a hydrogenation treatment by a known method. The block to be hydrogenated is an isoprene polymer block or an isoprene / butadiene copolymer block (b).

In the first thermoplastic elastomer composition for an airbag cover of the present invention, the blending ratio of the block copolymer (A) is such that the block copolymer (A), the crystalline polyolefin resin (B), And 10 to 50 parts by weight, preferably 15 to 45 parts by weight, more preferably 100 parts by weight of the total amount of the ethylene / α-olefin copolymer or ethylene / α-olefin / non-conjugated diene copolymer (C). Is 20 to 30 parts by weight.

In the second thermoplastic elastomer composition for an airbag cover according to the present invention, the mixing ratio of the block copolymer (A) is as follows: the block copolymer (A), the crystalline polyolefin resin (B), 10 to 50 based on 100 parts by weight of the total amount of the ethylene / α-olefin copolymer or ethylene / α-olefin / non-conjugated diene copolymer (C) and olefinic thermoplastic elastomer (D)
Parts by weight, preferably 15 to 45 parts by weight, more preferably 20 to 30 parts by weight. When the block copolymer (A) is used in the above-described mixing ratio, an airbag cover having excellent heat resistance and excellent scratch resistance can be obtained.

<< Crystalline Polyolefin Resin (B) >> The crystalline polyolefin resin (B) used in the present invention includes a homopolymer or copolymer of an α-olefin having 2 to 20 carbon atoms. Specific examples of such a crystalline polyolefin resin (B) include the following polymers or copolymers.

(1) Ethylene homopolymer (manufacturing method may be either low pressure method or high pressure method) (2) Ethylene and 10% by mole or less of other α-olefin or vinyl monomer such as vinyl acetate and ethyl acrylate (3) Propylene homopolymer (4) Random copolymer of propylene and 10 mol% or less of other α-olefin (5) Propylene and 30 mol% or less of other α-olefin Block copolymer (6) 1-butene homopolymer (7) Random copolymer of 1-butene and 10 mol% or less of other α-olefin (8) 4-methyl-1-pentene homopolymer ( 9) 4-methyl-1-pentene and up to 20 mol% of other α-
Random copolymer with olefin Specific examples of the α-olefin include ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene.

Among the above-mentioned crystalline polyolefin resins, ethylene homopolymer is preferable, and among them, the density is 0.9.
Particularly preferred is a polyethylene of 30 g / cm ³ or more. The crystalline polyolefin resin (B) as described above can be used alone or in combination.

The crystalline polyolefin resin (B) has a melt flow rate (MFR; ASTM D1238, 23).
0 ° C, 2.16 kg load, the same applies hereinafter).
01 to 100 g / 10 min, more preferably 0.3 to 7
It is in the range of 0 g / 10 minutes. The crystalline polyolefin resin (B) has a crystallinity of usually 5 to 5 determined by an X-ray method.
It is in the range of 100%, preferably 20-80%.

In the first thermoplastic elastomer composition for an airbag cover according to the present invention, the compounding ratio of the crystalline polyolefin resin (B) is such that the block copolymer (A), the crystalline polyolefin resin (B), And 15 to 60 parts by weight, preferably 20 to 55 parts by weight, based on 100 parts by weight of the total amount of the ethylene / α-olefin copolymer or ethylene / α-olefin / non-conjugated diene copolymer (C).
Parts by weight, more preferably 30 to 50 parts by weight.

In the second thermoplastic elastomer composition for an airbag cover according to the present invention, the compounding ratio of the crystalline polyolefin resin (B) is such that the block copolymer (A), the crystalline polyolefin resin (B), ethylene·
15 to 60 parts by weight, preferably 20 parts by weight, based on 100 parts by weight of the total amount of the α-olefin copolymer or the ethylene / α-olefin / non-conjugated diene copolymer (C) and the olefin-based thermoplastic elastomer (D) ５５55 parts by weight, more preferably 25-50 parts by weight.

When the crystalline polyolefin resin (B) is used in the above-mentioned mixing ratio, a thermoplastic elastomer composition excellent in moldability can be obtained, and an airbag excellent in scratch resistance and heat resistance can be obtained. A cover is obtained.

<< Ethylene / α-olefin copolymer or ethylene / α-olefin / non-conjugated diene copolymer (C) >> The ethylene / α-olefin copolymer or ethylene / α-olefin / non-ethylene copolymer used in the present invention is used. The ethylene content of the conjugated diene copolymer (C) is 75 to 88 mol%,
Preferably it is 77-85 mol%.

Examples of the α-olefin include α-olefins having 2 to 20 carbon atoms such as ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene and 1-octene.
-Olefin. Specific examples of the non-conjugated diene include dicyclopentadiene, 1,4-hexadiene, cyclooctadiene, methylene norbornene, and ethylidene norbornene.

The ethylene / α-olefin copolymer or ethylene / α-olefin / non-conjugated diene copolymer (C) has a Mooney viscosity [ML _{1 + 4} (100 ° C.)] of 1
It is desirably 0 to 250, preferably 30 to 150. The iodine value of the ethylene / α-olefin / non-conjugated diene copolymer (C) in which the non-conjugated diene is copolymerized is 2
It is preferably 5 or less.

In the first thermoplastic elastomer composition for an airbag cover according to the present invention, the blending ratio of the ethylene / α-olefin copolymer (C) is such that the block copolymer (A) and the crystalline polyolefin resin (B) and a total amount of ethylene / α-olefin copolymer or ethylene / α-olefin / non-conjugated diene copolymer (C) 100
15 to 50 parts by weight, preferably 20 to 4 parts by weight based on parts by weight
0 parts by weight, more preferably 25 to 40 parts by weight.

In the second thermoplastic elastomer composition for an airbag cover of the present invention, the blending ratio of the ethylene / α-olefin copolymer (C) is such that the block copolymer (A) and the crystalline polyolefin resin (B) 15 to 50 with respect to 100 parts by weight of the total amount of the ethylene / α-olefin copolymer or ethylene / α-olefin / non-conjugated diene copolymer (C) and the olefin-based thermoplastic elastomer (D). Parts by weight, preferably 20 to 40 parts by weight,
More preferably, it is 25 to 40 parts by weight.

When the ethylene / α-olefin copolymer or the ethylene / α-olefin / non-conjugated diene copolymer (C) is used in the above-mentioned mixing ratio, air having excellent scratch resistance and excellent flexibility is used. A bag cover is obtained.

<< Olefin-based thermoplastic elastomer (D) >> In the present invention, an olefin-based thermoplastic elastomer (D) can be blended in order to reduce the surface gloss and obtain an excellent appearance. The olefin-based thermoplastic elastomer (D) used in the present invention is composed of a crystalline polyolefin resin (c) and an olefin-based rubber (d).

As the above-mentioned crystalline polyolefin resin (c), the same resins as the above-mentioned crystalline polyolefin resin (B) can be used. In the olefin-based thermoplastic elastomer (D), the crystalline polyolefin resin (c) is added in an amount of 1 to 100 parts by weight of the total amount of the crystalline polyolefin resin (c) and the olefin-based rubber (d).
0 to 90 parts by weight, preferably 10 to 80 parts by weight, more preferably 20 to 70 parts by weight.

When the olefinic thermoplastic elastomer (D) in which the crystalline polyolefin resin (c) is blended in the above ratio is used, an airbag cover having excellent scratch resistance and excellent heat resistance can be obtained.

Examples of the olefin rubber (d) include an amorphous random elastic copolymer having an α-olefin having 2 to 20 carbon atoms and a content of 50 mol% or more. As such an elastic copolymer, an α-olefin copolymer composed of two or more α-olefins, an α-olefin / non-conjugated diene copolymer composed of two or more α-olefins and a non-conjugated diene Specific examples thereof include the following rubbers in addition to the copolymer exemplified as the component (C). Propylene / α-olefin copolymer rubber [propylene / α-olefin (molar ratio) = about 90/10 to 50/5
0] Butene / α-olefin copolymer rubber [butene / α-olefin (molar ratio) = about 90/10 to 50/50]

Specific examples of the α-olefin include ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene and the like. Specific examples of the non-conjugated diene include dicyclopentadiene, 1,4-hexadiene, cyclooctadiene, methylene norbornene, and ethylidene norbornene.

Olefinic thermoplastic elastomer (D)
Mooney viscosity [ML] of the copolymer rubber used as the rubber
_{1 + 4} (100 ° C)] is from 10 to 250, preferably from 30 to
Preferably it is 150.

In the present invention, an olefin rubber (d) and a rubber (e) other than the olefin rubber can be used in combination as long as the object of the present invention is not impaired. Examples of the rubber (e) other than the olefin rubber include diene rubbers such as styrene-butadiene rubber (SBR), nitrile rubber (NBR), natural rubber (NR), and butyl rubber (IIR), and polyisobutylene rubber. Is raised.

Olefinic thermoplastic elastomer (D)
In the above, the olefin-based rubber (d) is used in an amount of 10 to 90 parts by weight, preferably 20 to 90 parts by weight, and more preferably 100 parts by weight of the total amount of the crystalline polyolefin resin (c) and the olefin-based rubber (d). Is used in a proportion of 30 to 80 parts by weight.

When the olefin rubber (d) and the rubber (e) other than the olefin rubber are used in combination,
The rubber (e) other than the olefin rubber is 40 parts by weight or less, preferably 5 parts by weight, based on 100 parts by weight of the total amount of the crystalline polyolefin resin (c) and the olefin rubber (d).
It is used in a proportion of up to 20 parts by weight.

When the olefin-based rubber (d) or the olefin-based rubber (d) and the rubber (e) other than the olefin-based rubber are used in the above proportions, an airbag having excellent scratch resistance and excellent flexibility. A cover is obtained.

The olefin-based thermoplastic elastomer (D) used in the present invention may contain a mineral oil-based softening agent, a heat stabilizer, an antistatic agent, a weather stabilizer, an antioxidant, a filler, a coloring agent, if necessary. Additives such as agents and lubricants can be blended within a range that does not impair the purpose of the present invention.

The olefinic thermoplastic elastomer (D) preferably used in the present invention comprises a crystalline polypropylene resin as the crystalline polyolefin resin (c) and an ethylene / α-olefin copolymer as the olefinic rubber (d). Rubber or an ethylene / α-olefin / non-conjugated diene copolymer rubber, wherein these components are present in the olefin-based thermoplastic elastomer (D) in a partially crosslinked state, and are composed of a crystalline polypropylene resin and an olefin. 70/30 to 10/9 by weight compounding ratio with crystalline rubber (crystalline polypropylene resin / olefin rubber)
It is in the range of 0.

More specific examples of the olefin-based thermoplastic elastomer (D) preferably used in the present invention include 60 to 10 parts by weight of a crystalline polypropylene resin as the crystalline polyolefin resin (c) and an olefin-based rubber (d). ) As ethylene-propylene copolymer rubber or ethylene-propylene-diene copolymer rubber 40 to 90
Parts by weight [the total amount of the crystalline polypropylene resin and the olefin-based rubber is 100 parts by weight] and 5 to 100 parts by weight of a rubber (e) other than the olefin-based rubber and / or 5 to 100 parts by weight of a mineral oil-based softener. And an olefin-based thermoplastic elastomer in which the olefin-based rubber (d) is partially crosslinked.

The olefin thermoplastic elastomer (D) used in the present invention is obtained by dynamically preparing a blend containing a crystalline polyolefin resin (c) and an olefin rubber (d) in the presence of an organic peroxide. To a heat treatment.

Specific examples of the organic peroxide include dicumyl peroxide, di-tert-butyl peroxide, 2,2
5-dimethyl-2,5-di- (tert-butylperoxy) hexane, 2,5-dimethyl-2,5-di- (tert-butylperoxy)
Hexin-3, 1,3-bis (tert-butylperoxyisopropyl) benzene, 1,1-bis (tert-butylperoxy) -3,3,5-trimethylcyclohexane, n-butyl-4,4-
Bis (tert-butylperoxy) valerate, benzoyl peroxide, p-chlorobenzoyl peroxide, 2,
4-dichlorobenzoyl peroxide, tert-butyl peroxybenzoate, tert-butyl perbenzoate, t
ert-butyl peroxyisopropyl carbonate, diacetyl peroxide, lauroyl peroxide, tert-
Butyl cumyl peroxide and the like.

Among these, 2,5-dimethyl-2,5-di- (tert-butylperoxy) hexane and 2,5-dimethyl-2,5-di-, in terms of odor and scorch stability. (Tert-butylperoxy) hexyne-3,1,3-bis (tert-butylperoxyisopropyl) benzene, 1,1-bis (tert-butylperoxy) -3,3,5-trimethylcyclohexane, n-butyl-4 1,4-bis (tert-butylperoxy) valerate is preferred, and 1,3-bis (tert-butylperoxyisopropyl) benzene is most preferred.

The organic peroxide is a total amount of the crystalline polyolefin resin (c) and the olefin rubber (d) of 100
0.05 to 3% by weight, preferably 0.1 to 3% by weight
２2% by weight.

In the partial crosslinking treatment with the above organic peroxide, sulfur, p-quinonedioxime, p, p'-dibenzoylquinonedioxime, N-methyl-N-4-dinitrosoaniline,
Peroxy crosslinking aids such as nitrosobenzene, diphenylguanidine, and trimethylolpropane-N, N'-m-phenylenedimaleimide; or divinylbenzene, triallyl cyanurate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, and polyethylene glycol dimethacrylate And polyfunctional methacrylate monomers such as trimethylolpropane trimethacrylate and allyl methacrylate; and polyfunctional vinyl monomers such as vinyl butyrate and vinyl stearate.

In the partial crosslinking treatment with an organic peroxide,
By using the compound as described above, a uniform and mild crosslinking reaction can be expected. Among the above compounds, divinylbenzene is most preferred. Divinylbenzene is easy to handle, has good compatibility with the crystalline polyolefin resin (c) and the olefin rubber (d), which are the main components of the object to be crosslinked, and solubilizes the organic peroxide. Since it has an action and acts as a dispersant for an organic peroxide, a crosslinking effect by heat treatment is uniform, and an olefin-based thermoplastic elastomer (D) having a good balance between fluidity and physical properties can be obtained.

It is desirable that the crosslinking aid or the polyfunctional vinyl monomer is used in an amount of 0.1 to 3% by weight, preferably 0.3 to 2% by weight, based on the whole of the object to be crosslinked. When the blending ratio of the crosslinking aid or the polyfunctional vinyl monomer is within the above range, the obtained olefin-based thermoplastic elastomer (D) has the crosslinking aid and the polyfunctional vinyl monomer remaining as unreacted monomers in the elastomer. Therefore, there is no change in physical properties due to heat history during processing and molding, and the fluidity is excellent.

The term "dynamically heat-treating" means that the above components are kneaded in a molten state. Dynamic heat treatment
The mixing is performed using a kneading device such as a mixing roll, an intensive mixer (for example, a Banbury mixer, a kneader), or a single-screw or twin-screw extruder, but is preferably performed in a non-open type kneading device. The dynamic heat treatment is preferably performed in an inert gas such as nitrogen.

The kneading is preferably performed at a temperature at which the half-life of the organic peroxide used is less than 1 minute. The kneading temperature is usually 150 to 280C, preferably 170 to 24.
0 ° C., and the kneading time is 1 to 20 minutes, preferably 1 to
5 minutes. The shearing force applied during kneading is usually 10 to 10 ⁴ sec ⁻¹ , preferably 10 ² to 10 sec at a shear rate.
It is determined within the range of 10 ⁴ sec ⁻¹ .

As described above, the olefin-based rubber (d)
Crosslinked olefinic thermoplastic elastomer (D)
Can be obtained. Here, "partially crosslinked"
The term "when" means that the gel content (cyclohexane-insoluble matter) measured by the following method is, for example, 10% by weight or more, particularly 20% by weight or more and less than 98% by weight. In the present invention, the gel content is preferably 30% by weight or more.
“Completely crosslinked” means that the gel content (cyclohexane insoluble matter) measured by the following method is 98% by weight or more and 100% by weight. When the olefin-based thermoplastic elastomer (D) within the above range is used, the obtained thermoplastic elastomer composition has good fluidity during molding, and an airbag cover excellent in mechanical strength and heat resistance can be obtained.

[Measurement Method of Gel Content (Cyclohexane Insolubles)] A sample of the olefin-based thermoplastic elastomer (D) was weighed in an amount of about 100 mg and weighed 0.5 mm × 0.5 mm ×
It was cut into 0.5 mm strips, and the resulting strips were placed in 30 ml of cyclohexane in a closed vessel at 23 ° C. for 48 hours.
Soak for hours.

Next, this sample is taken out on a filter paper and dried at room temperature for at least 72 hours until the weight becomes constant. The value obtained by subtracting the weight of the cyclohexane-insoluble components (fibrous fillers, fillers, pigments, etc.) other than the polymer component from the weight of the dried residue is referred to as “corrected final weight (Y)”.

On the other hand, the value obtained by subtracting the weight of the cyclohexane-soluble component (eg, softener) other than the polymer component and the weight of the cyclohexane-insoluble component (fibrous filler, filler, pigment, etc.) other than the polymer component from the weight of the sample is given by:
This is referred to as “corrected initial weight (X)”.

The gel content (cyclohexane-insoluble content) is determined by the following equation.

## EQU1 ## Gel content [% by weight] = [corrected final weight]
(Y)] ÷ [corrected initial weight (X)] × 100

In the second thermoplastic elastomer composition for an airbag cover of the present invention, the blending ratio of the olefin-based thermoplastic elastomer (D) is such that the olefin-based thermoplastic elastomer (D) and the block copolymer (A) ),
Crystalline polyolefin resin (B) and ethylene / α
-Olefin copolymer or ethylene / α-olefin /
The amount is 0 to 50 parts by weight, preferably 15 to 45 parts by weight, more preferably 20 to 40 parts by weight, based on 100 parts by weight of the total amount of the non-conjugated diene copolymer (C). When the olefin-based thermoplastic elastomer (D) is used in the above-described mixing ratio, an airbag cover having excellent heat resistance and excellent scratch resistance can be obtained.

<< Other Components >> In the present invention, a known softening agent, heat stabilizer, or the like may be added to the thermoplastic elastomer composition for an airbag cover, if necessary, as long as the object of the present invention is not impaired. Additives such as an anti-aging agent, a weather resistance stabilizer, an antistatic agent, a filler, a colorant, and a lubricant can be added.

As the above-mentioned known softening agents, those usually used for rubbers are suitable. Specifically, process oils, lubricating oils, paraffin, liquid paraffin, polyethylene wax, polypropylene wax, petroleum asphalt, petrolatum Coal tars such as coal tar and coal tar pitch; fatty oils such as castor oil, linseed oil, rapeseed oil, soybean oil, and coconut oil; tall oil;
Waxes such as beeswax, carnauba wax and lanolin; fatty acids such as ricinoleic acid, palmitic acid, stearic acid, 12-hydroxystearic acid, montanic acid, oleic acid and erucic acid or metal salts thereof; petroleum resins and cumarone indene resins And synthetic polymers such as atactic polypropylene and the like; ester plasticizers such as dioctyl phthalate, dioctyl adipate and dioctyl sebacate; and other examples include microcrystalline wax, liquid polybutadiene or a modified or hydrogenated product thereof, and liquid thiocol.
Known heat stabilizers, anti-aging agents, and weather stabilizers include phenol-based, sulfite-based, phenylalkane-based, phosphite-based, and amine-based stabilizers.

<< Preparation of Thermoplastic Elastomer Composition >> The thermoplastic elastomer composition used in the present invention comprises the block copolymer (A), the crystalline polyolefin resin (B), and the ethylene / α-olefin copolymer. Or ethylene / α-olefin / non-conjugated diene copolymer (C)
And, if necessary, an olefin-based thermoplastic elastomer (D) at the above-mentioned specific ratio, and can be prepared by performing a dynamic heat treatment in the absence of an organic peroxide.

As the above-mentioned dynamic heat treatment performed in the production of the thermoplastic elastomer composition, the same dynamic heat treatment as in the production of the olefin-based thermoplastic elastomer (D) is desirable.

As the components used in the present invention, those having the above-mentioned respective physical property values in the above-mentioned general range can be used, but the components having all the above-mentioned physical property values in the preferable ranges are most preferable. However, components having specific physical property values within a preferred range and other physical property values within a general range can also be used as preferred. Further, the components used in the present invention can be mixed in the above-mentioned general range, but it is most preferable to mix all components in a preferable range. However, it is also preferable that the mixing ratio of a specific component is in a preferable range and the mixing ratio of another component is in a general range.

[0067]

The airbag cover of the present invention comprises a specific block copolymer, a crystalline polyolefin resin, and a specific amount of an ethylene / α-olefin copolymer or an ethylene / α-olefin / non-conjugated diene copolymer. Since it is made of a thermoplastic elastomer composition, it can be manufactured in one simple step, and has excellent impact resistance, especially at low temperatures, and has excellent abrasion and scratch resistance. Good appearance without it.

The airbag cover of the present invention, which is composed of a composition obtained by further blending an olefinic thermoplastic elastomer with the above thermoplastic elastomer composition, has more excellent scratch resistance and flexibility, and has better appearance.

[0069]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited to these examples. The raw materials of the thermoplastic elastomer composition used in each example are described below.

Block copolymer (A) (A-1) Hydrogenated product of styrene / isoprene / styrene block copolymer 1) Styrene content: 20% by weight 2) 1,2-position or 3 with respect to all isoprene units , 4
Content of isoprene units bonded at the-position: 55 mol% 3) MFR (ASTM D 1238-65T, 230 ° C, 2.16 kg load):
2.0g / 10min

Crystalline polyolefin resin (B) (B-1) Propylene block copolymer 1) Ethylene content: 8 mol% 2) MFR (ASTM D 1238-65T, 230 ° C., 2.16 kg load):
20 g / 10 min 3) Crystallinity determined by X-ray method: 73% (B-2) Polyethylene 1) MFR (ASTM D 1238-65T, 190 ° C, 2.16 kg load):
10 g / 10 min 2) Density (ASMT D 1505): 0.965 g / cm ³

Ethylene / α-olefin copolymer (C) (C-1) Ethylene / butene-1 copolymer 1) Ethylene content: 81 mol% 2) Mooney viscosity [ML _{1 + 4} , 100 ° C.]: 59 (C-2) Ethylene / propylene / 5-ethylidene-2-norbornene copolymer rubber 1) Ethylene content: 78 mol% 2) Iodine value: 14 3) Mooney viscosity [ML _{1 + 4} , 100 ° C]: 72

Olefinic thermoplastic elastomer (D) (D-1) Olefinic thermoplastic elastomer produced by the following method: Polypropylene as crystalline polyolefin resin (c) [MFR: 13 g / 10 min, determined by X-ray method] Crystallinity: 72%] and 40 parts by weight of ethylene-propylene / 5-ethylidene-2-norbornene copolymer rubber [ethylene content: 70 mol%, iodine value: 12, Mooney as olefin rubber (d)] Viscosity (ML _{1 + 4} , 100 ° C): 1
20] 60 parts by weight were kneaded at 180 ° C. for 5 minutes in a nitrogen atmosphere using a Banbury mixer, and the obtained kneaded material was passed through a roll to form a sheet, which was cut with a sheet cutter to form square pellets. Manufactured.

Then, 100 parts by weight of the square pellets were
After stirring and mixing 0.3 parts by weight of 1,3-bis (tert-butylperoxyisopropyl) benzene and 0.5 parts by weight of divinylbenzene with a Henschel mixer, the obtained mixture was subjected to L / D = 30, screw Extrusion was performed at 220 ° C. in a nitrogen atmosphere using a single screw extruder having a diameter of 50 mm to produce pellets of the olefin-based thermoplastic elastomer (D-1). The gel content of the obtained olefin-based thermoplastic elastomer (D-1) was 84%.

Example 1 30 parts by weight of pellets of a hydrogenated product (A-1) of a styrene / isoprene / styrene block copolymer, 40 parts by weight of pellets of a propylene block copolymer (B-1), and ethylene / butene 1 copolymer (C-1) was thoroughly mixed with 30 parts by weight, L / D = 30, screw diameter 50.
The mixture was extruded at 220 ° C. in a nitrogen atmosphere using a twin-screw extruder of 2 mm to produce pellets of the thermoplastic elastomer composition.

Further, a sample for an IZOD impact test and a square plate (150 mm × 150 mm × 3 mm) were formed from the thermoplastic elastomer composition pellets using an injection molding machine.
mm) at 220 ° C. and tested for IZOD impact strength, abrasion and scratch resistance by the following methods. Table 1 shows the results.

<< IZOD Impact Strength Test >>: ASTM D
It carried out at -30 degreeC according to 256. << Taber abrasion test >>: According to JIS K7204.
Wear wheel; H-22, load; 1000 g, rotation; 1000
Rotation, number of revolutions: 60 rpm << Scratch resistance test >>: A 20 mm square felt cloth is placed on the obtained square plate, and a weight is placed on the felt cloth so that a pressure of 200 g / cm ² is applied, and the corner is turned 100 times. The plate was reciprocated on the plate, and the scratch resistance was evaluated based on the surface state after the reciprocating operation. (5 levels of scratch resistance) A: The scratch is hardly noticeable B: The scratch is slightly noticeable C: The scratch is noticeable D: The scratch is noticeable E: The surface is whitened

Example 2 In Example 1, the propylene block copolymer (B
Pellets 4 of polyethylene (B-2) instead of -1)
Pellets of the thermoplastic elastomer composition were produced in the same manner as in Example 1 except that 0 parts by weight was used. Then
From the pellets of the thermoplastic elastomer composition, a sample and a square plate were formed in the same manner as in Example 1, and the IZOD impact strength, abrasion resistance and scratch resistance were evaluated. Table 1 shows the results.

Example 3 In Example 1, the ethylene / butene-1 copolymer (C
Ethylene / propylene / 5-ethylidene instead of -1)
Pellets of 2-norbornene copolymer rubber (C-2)
Pellets of the thermoplastic elastomer composition were produced in the same manner as in Example 1 except that 0 parts by weight was used. Then
From the pellets of the thermoplastic elastomer composition, a sample and a square plate were formed in the same manner as in Example 1, and the IZOD impact strength, abrasion resistance and scratch resistance were evaluated. Table 1 shows the results.

Example 4 25 parts by weight of pellets of a hydrogenated product of a styrene / isoprene / styrene block copolymer (A-1), 30 parts by weight of pellets of polyethylene (B-2) and ethylene / butene-1 Pellets of a thermoplastic elastomer composition were produced in the same manner as in Example 1 using 25 parts by weight of the polymer (C-1) and 20 parts by weight of pellets of the thermoplastic elastomer (D-1). Next, a sample and a square plate were formed from the thermoplastic elastomer composition pellets in the same manner as in Example 1, and the IZOD impact strength, abrasion resistance, and scratch resistance were evaluated. Table 1 shows the results.

Comparative Example 1 5 parts by weight of pellets of a hydrogenated product (A-1) of a styrene / isoprene / styrene block copolymer, 70 parts by weight of pellets of a propylene block copolymer (B-1), Example 1 was mixed with 25 parts by weight of 5-ethylidene-2-norbornene copolymer rubber (C-2).
In the same manner as in the above, pellets of the thermoplastic elastomer composition were produced. Next, a sample and a square plate were formed from the thermoplastic elastomer composition pellets in the same manner as in Example 1, and the IZOD impact strength, abrasion resistance, and scratch resistance were evaluated. Table 1 shows the results.

Comparative Example 2 A sample and a square plate were molded from pellets of the olefinic thermoplastic elastomer (D-1) in the same manner as in Example 1, and the IZOD impact strength, abrasion resistance and scratch resistance were evaluated. Table 1 shows the results.

[0083]

[Table 1] * 1: Performed at -30 ° C. NB; not destroyed

Claims (5)

[Claims] (A) a polymer block (a) of styrene or a derivative thereof and an isoprene polymer block or an isoprene / butadiene copolymer block, wherein the 1,2-position or 3,4 with respect to all isoprene units; 10 to 50 parts by weight of an optionally hydrogenated block copolymer comprising a polymer or a copolymer block (b) having a content of isoprene units bonded at the -position of not less than 40 mol%, (B 15) to 60 parts by weight of a crystalline polyolefin resin, and (C) ethylene / α having an ethylene content of 75 to 88 mol%.
-Olefin copolymer or ethylene content of 75-8
It contains 15 to 50 parts by weight of an ethylene / α-olefin / non-conjugated diene copolymer of 8 mol% [however, the total amount of components (A), (B) and (C) is 100 parts by weight. ] An airbag cover comprising a thermoplastic elastomer composition. 2. A polymer block (a) of styrene or a derivative thereof and an isoprene polymer block or an isoprene / butadiene copolymer block, wherein the 1,2-position or 3,4 with respect to all isoprene units. 10 to 50 parts by weight of an optionally hydrogenated block copolymer comprising a polymer or a copolymer block (b) having a content of isoprene units bonded at the -position of not less than 40 mol%, (B ) Crystalline polyolefin resin 15 to 60 parts by weight, (C) ethylene.α having an ethylene content of 75 to 88 mol%
-Olefin copolymer or ethylene content of 75-8
(D) a crosslinked olefin-based thermoplastic elastomer (D) containing 15 to 50 parts by weight of an ethylene / α-olefin / non-conjugated diene copolymer and (D) a crystalline polyolefin resin and an olefin-based rubber ) Containing 0 to 50 parts by weight [the amount of components (A), (B), (C) and (D) is 100
Parts by weight]. An airbag cover comprising a thermoplastic elastomer composition. 3. The airbag cover according to claim 1, wherein the crystalline polyolefin resin (B) is polyethylene. 4. The crystalline polyolefin resin (B) has a density
0.930 g / cm ^ThreeThe above polyethylene
The airbag cover according to claim 3, wherein: 5. The airbag cover according to claim 1, wherein the ethylene / α-olefin copolymer (C) is an ethylene / butene-1 copolymer.