JP2001233160A - Air bag cover - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an air bag storage cover having safety reliability, adaptability in a wide temperature range, durability, and desirable touch, and capable of realizing high productivity and low cost without being painted. SOLUTION: This air bag device storage cover is made of an injection molding of a thermoplastic elastomer and has an air bag storage recess on the inside and an expected rupture section of a fragile structure. The thermoplastic elastomer has the Shore D hardness of 20-70 and comprises (A) a polyurethane elastomer of 100 pts.wt. and (B) a specific polypropylene mixture of 5-900 pts.wt. including ethylene-propylene copolymer rubber with the average dispersion grain size of 2 μm or below and having the bending elastic modulus of 20-700 Mpa and the Shore D hardness of 20-60.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is designed so that a high-speed moving body such as an automobile restrains an occupant to a seat side in the event of a collision or the like and protects the occupant from a secondary collision with a control device or an instrument panel. And a storage cover for the airbag device.

[0002]

2. Description of the Related Art An airbag system is basically composed of a collision sensing device for detecting a collision of a high-speed moving object and an airbag device. The latter airbag device generates an airbag and gas for inflating the airbag. The gas generator includes a gas generator, an airbag and a storage cover for storing the gas generator, and a mounting device (retainer) for mounting the gas generator and the storage cover.

[0003] The airbag device is mounted in front of an occupant in a high-speed moving body, and when a collision detection device is activated due to a collision accident or the like, gas is instantaneously generated from a gas generator, and the gas generator, storage cover and mounting device are mounted. The gas is filled in the airbag which is folded and stored in the space formed by the tool, and the storage cover is expanded by the pressure of the gas filled in the airbag, and the air is opened from the opening obtained by the expansion. The instantaneous release and inflation of the bag toward the front of the occupant restrains the occupant to the seat side, thereby preventing the occupant from colliding with a steering device, an instrument panel, or the like and being injured.

Therefore, when the gas generator is operated due to a collision accident or the like, the storage cover of the airbag device is reliably deployed without splattering debris that may injure the occupant, and the bag is instantaneously opened. Must emit. JP-A-50-127336 and JP-A-55-110643 disclose a storage cover for such an airbag device.
JP-A-5-11637, JP-A-52-116537,
Various proposals have been made in, for example, JP-A-202550 or JP-A-5-038996.

JP-A-50-127336 and JP-A-55-110643 disclose a method in which a fiber net or a metal net or the like is formed from a urethane resin or an elastic material, and a portion other than a portion to be broken is provided. A storage cover having a structure in which a material is embedded has been proposed. In these proposals, since the resin material used is fragile, it is necessary to adopt a structure in which a reinforcing material is embedded in order to prevent fragments from being scattered when the airbag device is operated. It takes time to set, and it is difficult to obtain a molded body in which the reinforcing material is embedded at the expected position with high accuracy.
Furthermore, in the case of urethane resin by reaction injection molding, it is necessary to take time for the reaction to proceed sufficiently in the mold,
It has the disadvantage of low production rate and low production yield.

In particular, the production of automobiles reaches 10 million units a year, and it is fatal that the production speed and production yield are low. Japanese Patent Application Laid-Open No. 52-11637 discloses an embrittlement temperature.
50 ° C or less, flexural rigidity 1,000 to 3,000 kg / c
There has been proposed a storage cover formed of m ² thermoplastic elastomer and having a fragile structure at a portion to be broken. According to this proposal, productivity is improved because of the structure in which the reinforcing material is not embedded, but the bending rigidity of the material is 1,000.
Since it is as high as 3,000 kg / cm ² , performance in a low-temperature region is not sufficient, and when the device is developed at a low temperature, it is broken at a portion other than a portion expected to be broken, and the cover may be scattered, possibly damaging an occupant.

Japanese Patent Application Laid-Open No. Hei 1-2202550 discloses a JI
A storage cover having a structure in which a surface layer made of a soft resin having an SK6301-A type hardness of 30 to 70 and a core layer made of an elastic hard resin are integrally formed, and a slit for opening the cover is provided in the core layer has been proposed. ing. Although the proposed storage cover gives the occupant a moderately soft feel, it requires two-layer molding of the core layer and surface layer, which requires a complex and expensive molding machine with two sets of injection mechanisms. There are major drawbacks.

[0008] Japanese Patent Application Laid-Open No. 5-039996 discloses an airbag accommodating recess inside and a fragile structure to be broken, a hydrogenated styrene-conjugated diene block copolymer, a plasticizer for rubber, Consists of an olefin resin and additives, and has a JIS K6301A type hardness of 60 or more and 8
A storage cover for an airbag device, which is an injection-molded article of a thermoplastic elastomer composition having a particle size of 5 or less, has been proposed. The proposed storage cover gives the occupants a moderately soft feel and high productivity, but the bending stiffness at low temperatures is relatively large, and in some cases it may become brittle at low temperatures and lose the certainty of deployment performance. is there. Furthermore, the scratch resistance of the surface is not always good, and a hard urethane coating is required, which is not always advantageous in terms of cost.

[0009]

The first requirement that the storage cover of the airbag device should have is that it is reliably deployed and has safety. That is, when the airbag device is operated, the storage cover must be deployed without splattering debris that may hurt the occupant, and the bag must be released instantaneously.

The second is flexibility over a wide temperature range. In the case of a car, the temperature of the storage cover is often −40 ° C. to 90 ° C. depending on the region, season, and condition in which it is used, but it must not be brittle at low temperatures and lose its reliability, or must be softly deformed at high temperatures . Third is durability against heat and light. In the case of an automobile, the storage cover is often used by being attached to a portion irradiated with sunlight that enters through a windshield. Therefore, the storage cover must not deteriorate due to light degradation and lose its reliability.

Fourth, high productivity and low production cost. This requirement is particularly important in high volume automotive airbag systems. In particular, it is important to reduce the thickness of the cover in order to reduce the material cost, and for that purpose, there is a tendency that a material having a relatively high rigidity is desired. Fifth is feel. It is preferable that the occupant gives a moderately soft feeling when touching the storage cover, and thus has a great effect of producing psychological comfort important for safe driving. Sixth, there is a problem in appearance, that is, the surface is hardly damaged.

That is, an object of the present invention is to have safety certainty, adaptability in a wide temperature range, durability, and a favorable feel,
An object of the present invention is to provide a storage cover that can achieve high productivity and low cost (thinning) and that is hardly damaged.

[0013]

As a result of intensive studies, the present inventors have found that a concave portion for storing an airbag is provided on the inner side, a fragile structure is to be broken, and a Shore D hardness of 20 is provided.
The present inventors have found that a storage cover obtained by molding a specific thermoplastic elastomer having a size of ~ 70 by an injection molding method solves the above-mentioned problems, and have completed the present invention.

That is, the present invention relates to a storage cover for an airbag apparatus comprising an injection molded article of a thermoplastic elastomer, which has an airbag storage recess inside and a fragile structure intended to be broken, An accommodating cover for an airbag device, wherein the elastomer is a thermoplastic elastomer composition having a Shore D hardness of 20 to 70, wherein the elastomer comprises the following components (A) and (B).

(A) Polyurethane elastomer: 100
Parts by weight (B) (B-1) a polypropylene-based polymer (propylene
(B-2) ethylene-propylene-based copolymer rubber (containing 75% by weight or less of propylene): 40 to 90% by weight, wherein ethylene in the mixture is 40 to 90% by weight. The average dispersion particle size of the propylene copolymer rubber is 2 μm or less, the flexural modulus of the mixture is 20 to 700 MPa, and the Shore D hardness is 2
Polypropylene mixture of 0 to 60: 5 to 900 parts by weight

Hereinafter, the present invention will be described in detail. The polyurethane elastomer (hereinafter abbreviated as TPU) as the component (a) of the present invention is classified according to the linear polyol to be used and includes polyester (caprolactone, adipate), polycarbonate, and polyether types. Both can be used. Of these, polycarbonates having high mechanical strength and a good balance of heat aging resistance and hydrolysis resistance are desirable.

As the polycarbonate-based polyurethane elastomer, a Shore D hardness of 20 to 70 obtained by copolymerizing the following components (a) and (b) and, if necessary, component (c):
Are preferred.

(A) A polycarbonate diol comprising a repeating unit of the following formula (1) and having a terminal group of a hydroxyl group (wherein R represents an aliphatic or alicyclic hydrocarbon group having 2 to 10 carbon atoms) .

[0019]

Embedded image

(B) Polyisocyanate (c) Chain extender having two active hydrogens capable of reacting with polyisocyanate

The polycarbonate diol used as the component (a) of the polyurethane elastomer of the present invention comprises:
Schell, Polymer Review No. 9
, Pages 9-20 (1964), from aliphatic and / or cycloaliphatic diols. Preferred diols include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, 2,3 -Butanediol, 1,5-pentanediol, 1,6-hexanediol, 2,5-hexanediol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol and the like.

In order to obtain a steering wheel having a good balance of hydrolysis resistance (sweat resistance), weather resistance and soft feeling, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol Is preferred.

In particular, polycarbonate diols suitable for the airbag cover of the present invention include 1,4-butanediol and / or 1,5-pentanediol,
A copolymerized polycarbonate diol synthesized from 1,6-hexanediol is preferable because the resulting airbag cover has excellent low-temperature characteristics. 1,4-butanediol and / or 1,4-butanediol which is a repeating unit in the polymer
The ratio of 5-pentanediol to 1,6-hexanediol is 10/90 to 90/10, preferably 20/90 to 90/10.
80-80 / 20, more preferably 30 / 70-70
/ 30.

The range of the average molecular weight of the polycarbonate diol used in the present invention is usually 500 in number average molecular weight.
~ 5000, preferably 1000 ~ 3000,
More preferably, those having a molecular weight of 1500 to 2500 are used, and it is desirable that the terminal of the polymer is substantially all hydroxyl groups.

In the present invention, in addition to the above-mentioned diols, compounds having three or more hydroxyl groups in one molecule, such as trimethylolethane, trimethylolpropane, hexanetriol, pentaerythritol,
Polyurethane using a polycarbonate which has been polyfunctionalized by using a small amount such as the above is also included.

Next, as the polyisocyanate used as the component (b) of the polyurethane elastomer of the present invention, for example, 2,4-tolylene diisocyanate, 2,6
-Tolylene diisocyanate and mixtures thereof (TD
I), diphenylmethane-4,4′-diisocyanate (MDI), naphthalene-1,5-diisocyanate (NDI), 3,3′-dimethyl-4,4′-biphenylene diisocyanate, crude TDI, polymethylene polyphenylisocyanate, Known aromatic diisocyanates such as crude MDI; xylylene diisocyanate (XD
I), known aromatic alicyclic diisocyanates such as phenylene diisocyanate; 4,4'-methylenebiscyclohexyl diisocyanate (hydrogenated MDI), hexamethylene diisocyanate (HMDI), isophorone diisocyanate (IPDI), cyclohexane diisocyanate (hydrogenated XDI) Known aliphatic diisocyanates, such as
And modified isocyanurates, carbodiimidations and biurets of these isocyanates.

Suitable chain extenders used as necessary as the copolymerization component (c) of the polyurethane elastomer of the present invention include those commonly used in the polyurethane industry. Supervised by Keiji Iwata Recent polyurethane application technology CMC 1985, pp. 25-27, including known water, low molecular polyol, polyamine and the like.
A known polyol may be used in combination with the aliphatic polycarbonate used in the present invention, depending on the use of the polyurethane, as long as the effects of the present invention are not impaired. Known polyols include known polyols such as polyester and polyether carbonate described in Yoshio Imai, Polyurethane Form Polymer Publishing Association, 1987, pp. 12-23.

Specifically, a diol having a molecular weight of 300 or less is usually used as the low-molecular polyol. For example, aliphatic diols such as ethylene glycol, 1,3-propylene diol, 1,4-butane diol, pentamethylene glycol, hexamethylene glycol, neopentyl glycol, decamethylene glycol and the like can be mentioned.

Also, alicyclic diols such as 1,1-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, tricyclodecanedimethanol, xylylene glycol, bis (p-hydroxy) diphenyl, bis (p-hydroxy Phenyl) propane, 2,2-bis [4- (2-hydroxyethoxy) phenyl] propane, bis [4 (2-hydroxy) phenyl] sulfone,
1,1-bis [4- (2-hydroxyethoxy) phenyl] cyclohexane and the like. Preferably, ethylene glycol and 1,4-butanediol are used.

As a method for producing the polyurethane elastomer of the present invention, a urethanization reaction technique known in the polyurethane industry is used. For example, an NCO-terminated polyurethane prepolymer is produced by reacting the polyol with an organic polyisocyanate at room temperature to 200 ° C.

A thermoplastic polyurethane elastomer can be produced using the polyol, polyisocyanate and, if necessary, a chain extender. In the production of these, known polymerization catalysts represented by organic metal salts such as tertiary amines, tin, and titanium are described, for example, by Keiji Yoshida (polyurethane resin), published by Nihon Kogyo Shimbun, pp. 23-32 (1).
969) can be used. These reactions may be carried out using a solvent, and preferred solvents include dimethylformamide, diethylformamide, dimethylacetamide, dimethylsulfoxide, tetrahydrofuran, methylisobutylketone, dioxane, cyclohexanone, benzene, toluene, and ethylcellosolve. is there.

In producing the polyurethane elastomer of the present invention, a compound containing only one active hydrogen that reacts with an isocyanate group, for example, a monohydric alcohol such as ethyl alcohol and propyl alcohol, and a compound such as diethylamine and di-n-propylamine Secondary amines and the like can be used as terminal terminators.

The polyurethane elastomer using the polycarbonate polyol of the present invention is not only excellent in flexibility and elastic recovery but also extremely excellent in hydrolyzability as compared with other polyurethane elastomers. When used for a bag cover, it is suitable because of its excellent sweat resistance.

Next, the polypropylene mixture as the component (B) of the present invention is, for example, a propylene copolymer mixture obtained by sequential polymerization of at least two or more stages. In the first step, a propylene homopolymer or a copolymer of propylene and an α-olefin (propylene is 85% by weight)
(B-1) or an ethylene-propylene copolymer (containing 85% by weight or more of propylene).
From the next step, ethylene-propylene (containing 75% by weight or less of propylene) or ethylene-propylene.
A component (B-2) is produced by polymerizing a propylene-α-olefin (which may contain a small amount of diene) copolymer (containing 75% by weight or less of propylene).

[0035] In the polymerization of propylene in the first step, the isotactic index of the obtained polypropylene is 80% or more,
Preferably an amount of at least 85%, more preferably at least 90%, of ethylene or α-olefin, such as butene-1, pentene-1,4-methyl-pentene-
It can be performed in the presence of 1, hexene-1, and octene-1 or a combination thereof.

The monomers used to polymerize the ethylene-propylene copolymer or ethylene-propylene-α-olefin copolymer after the second step are propylene and ethylene and / or α-olefin (for example, butene-
1, pentene-1, 4-methyl-pentene-1, hexene-1, and octene-1 or a combination thereof). The polymerization of the copolymer after the second step is carried out by conjugated or non-conjugated dienes, for example, butadiene, 1,4-
It can be carried out in the presence of hexadiene, 1,5-hexadiene, and ethylene-norbornene-1. The diene, when present, is typically from 0.5 to 10% by weight, based on the weight of all monomers used in the second and subsequent steps.

The amount of (B-1) in the polypropylene composition of component (B) is from 10 to 60% by weight, preferably from 15 to 60% by weight.
50% by weight, the amount of (B-2) is 40 to 90% by weight, preferably 50 to 85% by weight.

Further, the total amount of ethylene copolymerized in the polypropylene mixture of the component (B) is 15 to 60% by weight, preferably 17 to 45% by weight, more preferably 20 to 3% by weight.
5% by weight. The amount of all α-olefins copolymerized in the polypropylene mixture (B) is 0 to 30% by weight, preferably 3 to 20% by weight, more preferably 5 to 5% by weight.
10% by weight.

The mixture (B) was subjected to differential scanning calorimetry (D
SC) shows at least one melting peak present at a temperature above 120 ° C., preferably above 140 ° C. Further, the mixture (B) has a flexural modulus of 20 to 700 MPa, preferably 50 to 300 MPa.
Mpa, more preferably 70-200 MPa. The mixture (B) has a Shore D hardness of 20 to 60,
Preferably it is 30-50.

The melt flow rate (measured according to ASTM D1238, 230 ° C., 2.16 kg load; hereinafter abbreviated as MFR) of the mixture (B) is 10 to 10.
60 g / 10 min, preferably 12 to 50 g / 10 min, more preferably 15 to 40 g / 10 min. If the MFR is less than 10 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 a molded product is deteriorated (the generation of flow marks). Further, the MFR is 10 g / 10
If the amount is less than minutes, the scratch resistance of the elastomer composition also decreases, which is not preferable. On the other hand, the MFR is 60 g / 10
If the amount exceeds minutes, the strength and heat resistance of the elastomer composition are undesirably reduced.

The ethylene-propylene copolymer rubber dispersed in the mixture (B) has an average dispersed particle size of 2 μm or less.
Preferably it is 1.5 μm or less. If the average dispersed particle size of the rubber exceeds 2 μm, the scratch resistance of the elastomer composition is extremely lowered, which is not preferable.

The catalyst used for the polymerization of the polypropylene mixture of component (B) is a Ziegler-Natta type catalyst.
Preferred catalysts are reaction products of a solid catalyst component containing a titanium compound and an electron donor compound (internal donor) supported on magnesium chloride with a trialkylaluminum compound and an electron donor compound (external donor). . As a method for preparing the catalyst and a method for polymerizing the component (B),
For example, JP-A-3-205439 and JP-A-6-2
No. 5367, JP-A-6-25489 and the like.

The blending amount of the polypropylene mixture of the component (B) in the thermoplastic elastomer composition of the present invention is TPU
5 to 900 parts by weight, preferably 15 to 500 parts by weight, more preferably 30 to 500 parts by weight, per 100 parts by weight of component (A).
200 parts by weight. If the amount of the polypropylene mixture of the component (B) exceeds 900 parts by weight, the rubber elasticity decreases and the low-temperature characteristics deteriorate, which is not preferable. Also,
If the blending amount of the polypropylene mixture of the component (B) is less than 5 parts by weight, the high-temperature properties of the thermoplastic elastomer composition deteriorate, and the appearance of the molded product deteriorates (flow marks are generated), which is not preferable.

As the polypropylene mixture of the component (B) used in the present invention, Adflex, Hifax
(Manufactured by Montell, Catalloy TPO series) or the like.

Further, the elastomer composition of the present invention comprises:
If necessary, a polyolefin-based resin can be added. Specific examples of polyolefin resins that can be added include polyethylene resins and polypropylene resins. Examples of the polyethylene resin include low-density polyethylene, linear low-density polyethylene, high-density polyethylene, and a copolymer of ethylene and an α-olefin having 3 to 8 carbon atoms. In the case of a copolymer of ethylene and an α-olefin having 3 to 8 carbon atoms, the α-olefin in the copolymer may be propylene, butene-1, isobutene, pentene-
1, hexene-1, 4-methylpentene-1, octene-1 and the like. The ratio of α-olefin is 3
What is 0% by weight or less is used.

The polypropylene resin is a propylene homopolymer or a copolymer of propylene and an α-olefin having 2 to 8 carbon atoms (hereinafter abbreviated as propylene 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 ratio of α-olefin is 3
What is 0% by weight or less is used. 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.

As additives used in the present invention, it is desirable to use at least an antioxidant, a light stabilizer and a heat stabilizer. Examples of these antioxidants include aliphatic, aromatic or alkyl-substituted aromatic esters of phosphoric acid and phosphorous acid, hypophosphorous acid derivatives, phenylphosphonic acid, phenylphosphinic acid, diphenylphosphonic acid, polyphosphonates, dialkylpentaerythritol diacids. Phosphite,
Phosphorus compounds such as dialkylbisphenol A diphosphite; phenol derivatives, especially compounds containing sulfur such as hindered phenol compounds, thioethers, dithioates, mercaptobenzimidazoles, thiocarbanilides, thiodipropionates; tinmalate, dibutyltin mono Tin compounds such as oxides can be used.

These may be used alone or in combination of two or more. The addition amount of these stabilizers is based on 100 parts by weight of the polyetherester block copolymer.
0.01 to 5 parts by weight, preferably 0.1 to 3 parts by weight, more preferably 0.2 to 2 parts by weight. Generally, antioxidants can be divided into primary, secondary and tertiary antiaging agents. Particularly, as a hindered phenol compound as a primary anti-aging agent, Irganox 1010 (trade name:
Ciba-Geigy), Irganox 1520 (trade name: Ciba-Geigy) and the like are preferable. Phosphorus compounds as secondary aging inhibitors are PEP-36, PEP-24G,
HP-10 (all trade names: manufactured by Asahi Denka Co., Ltd.)
afos168 (trade name: Ciba-Geigy) is preferred. Further, as the sulfur compound as the tertiary aging inhibitor, thioether compounds such as dilauryl thiopropionate (DLTP) and distearyl thiopropionate (DSTP) are preferable.

Examples of the ultraviolet absorber and light stabilizer include benzotriazole compounds and benzophenone compounds. As the light stabilizer, a radical scavenging light stabilizer such as a hindered amine compound is suitably used.

Further, a plasticizer may be added to the composition obtained as required. Examples of such plasticizers include phthalic acid esters such as dioctyl phthalate, dibutyl phthalate, diethyl phthalate, butyl benzyl phthalate, di-2-ethylhexyl phthalate, diisodecyl phthalate, diundecyl phthalate, diisononyl phthalate: tricresyl phosphate, triethyl phosphate, Phosphate esters such as tributyl phosphate, tri-2-ethylhexyl phosphate, trimethylhexyl phosphate, tris-chloroethyl phosphate, tris-dichloropropyl phosphate: octyl trimellitate, isodecyl trimellitate, trimellitate, Dipentaerythritol esters, dioctyl adipate, dimethyl adipate, di-2-ethylhexyl aze Over DOO, dioctyl azelate, dioctyl sebacate, di-2
Fatty acid esters such as ethylhexyl sebacate and methyl acetyl ricinocate: pyromellitic esters such as octyl pyromellitic acid: epoxidized soybean oil,
Epoxy plasticizers such as epoxidized linseed oil and epoxidized fatty acid alkyl esters: polyether plasticizers such as adipic acid ether ester and polyether: liquid NB
R, liquid rubber such as liquid acrylic rubber, liquid polybutadiene, etc .;

These plasticizers can be used alone or in combination of two or more. The addition amount of the plasticizer is appropriately selected according to the required hardness and physical properties, but is preferably 0 to 50 parts by weight per 100 parts by weight of the composition.

Further, kaolin, as long as the physical properties are not impaired,
Silica, mica, titanium dioxide, alumina, calcium carbonate, calcium silicate, clay, kaolin, diatomaceous earth, asbestos, barium sulfate, aluminum sulfate, calcium sulfate, basic magnesium carbonate, molybdenum disulfide, graphite, glass fiber, carbon fiber, etc. Fillers and reinforcements: Lubricants or mold release agents such as zinc stearate and bis-amide amide: carbon black for coloring, ultramarine, titanium white, zinc white, zinc oxide,
Dyeing pigments such as navy blue, azo pigments, nitro pigments, lake pigments, phthalocyanine pigments, etc .: Flame retardants such as octabromodiphenyl, tetrabromobisphenol polycarbonate, etc.
Blowing agent: Thickener such as epoxy compound or isocyanate compound: Various known additives such as silicone oil and silicone resin can be used.

Shore D of the thermoplastic elastomer of the present invention
The hardness is preferably from 20 to 70, more preferably from 25 to 70.
The range is 50. If the Shore D hardness is less than 20, it is not preferable because the developing performance at high temperatures and the scratch resistance are poor. On the other hand, if the Shore D hardness is more than 70, the resulting airbag cover has poor low-temperature deployment performance and soft feeling, which is not preferable.

Further, the melt flow rate of the thermoplastic elastomer of the present invention (at 230 ° C. under a load of 2.16 kg,
(Hereinafter abbreviated as MFR) is 0.5 to 100 g / 10 min, preferably 5 to 50 g / 10 min, more preferably 10 to 3 g.
0 g / 10 minutes. If the MFR is less than 0.5 g / 10 minutes, the injection moldability is poor and short shots are caused, which is not preferable. On the other hand, if the MFR exceeds 100 g / 10 minutes, not only mechanical properties (breaking strength, breaking elongation, etc.) and abrasion, etc., are deteriorated, but also the developing performance is unfavorably deteriorated.

The thermoplastic elastomer composition constituting the storage cover of the airbag device of the present invention is melt-kneaded and granulated by various extruders, Banbury mixers, kneaders, rolls, and combinations thereof. In the form of pellets. By molding the thermoplastic elastomer composition with a general-purpose simple injection molding machine used for molding a general thermoplastic resin or thermoplastic elastomer, a storage cover can be obtained with high productivity.

Next, the structure of the storage cover of the present invention will be specifically described with reference to the drawings. FIG. 1 is a perspective view showing an example of a storage cover of a driver airbag device according to the present invention. FIG. 5 is a perspective view showing an example of a storage cover of the passenger airbag device according to the present invention. FIG. 8 is a schematic diagram showing a cross section similar to FIG. 6 showing another example of the storage cover of the passenger airbag device according to the present invention. FIG. 9 is a schematic diagram showing a cross section similar to FIG. 7 of the storage cover shown in FIG.

The top surface of the storage cover is H as shown in FIG.
It can be set in a U-shape, a U-shape as shown in FIG. Further, the side wall of the storage cover can be set as shown in FIGS. The vulnerable portion of the fragile structure may be provided with a V-shaped groove, a U-shaped groove, a U-shaped groove, a groove having another cross-sectional shape, or another groove at a portion along the set expected line of the storage cover. This can be realized by making the thickness thinner than the thickness of the portion or by providing slits or cuts intermittently. In addition, the surface of the storage cover is subjected to graining to further improve the scratch resistance of the surface.

[0058]

The present invention will be described in more detail with reference to the following Examples and Comparative Examples, but the present invention is not limited thereto. <Evaluation Method> First, physical property evaluation items used in Examples and Comparative Examples and evaluation methods thereof will be described below.

[Melt Flow Rate (MFR)] After about 5 g of pellets of each thermoplastic elastomer composition was vacuum-dried in a vacuum dryer at 70 ° C. for about 12 hours, immediately
With an orifice of 2.090 mm in diameter and 8 mm in length,
MFR under L condition with load of 2.16 kg and measurement temperature of 230 ° C
Was measured.

[Surface hardness] The Shore D hardness was measured at 25 ° C.

[Flexural modulus (MPa)] JIS K720
According to 3, length 125mm x width 12.5mm x length 3
mm injection molding test piece, at a bending speed of 2 mm / min, -50 ° C, -40 ° C, -25 ° C, 0 ° C, 23 ° C,
The flexural modulus was measured at each temperature of 100 ° C.

[Breaking strength (MPa), breaking elongation (%)]
According to JISK6301, length 20mm x width 3mm x
The measurement was performed by performing a tensile test at 25 ° C. under a condition of a head speed of 20 mm / min using an injection-molded test piece having a thickness of 2 mm.

[Surface Scratch Resistance] The pencil hardness (9B to 9H) was evaluated with a load of 340 g.

[Sweat Resistance] An injection test piece was subjected to artificial sweat liquid (artificial sweat liquid composition; 7 g of NaCl, 500 cc of methyl alcohol,
Urea 1g, lactic acid 4g, distilled water 500cc) at room temperature
Dipped for 0 days. The test piece was taken out, and the appearance after the abrasion test (the appearance after the test using a JIS K7204 wear wheel) was evaluated in 3 grades. 3: no scratches due to worn wheels were observed at all 2: scratches due to worn wheels were slightly observed 1: scratches caused by worn wheels were clearly observed

[Expansion Performance of Storage Cover] The airbag and the storage cover were attached to an iron mounting bracket (retainer).
Furthermore, an airbag device is assembled by attaching a gas generator. Next, this airbag device is placed in an air thermostat at a deployment temperature (-40 ° C., room temperature or 90 ° C.). After the internal temperature is stabilized, the air bag is left for another 2 hours, and then the air bag is taken out. (Turn on the power within one minute after removing the air bag device from the air oven.) If the storage cover ruptures at the part to be ruptured without generating fragmentation and the airbag is deployed, the deployability of the storage cover is ○. The case was evaluated as x.

[Molding processability] Injection molding machine, length 15
A flat plate having a thickness of 0 mm, a width of 100 mm and a thickness of 2 mm was formed under the following conditions. The appearance of the molded product was visually observed such as flow mark and gloss, and a good one was evaluated as ○, a slightly poor one as Δ, and a poor one as ×. Cylinder temperature C1: 20
0 ° C, C2: 210 ° C, C3: 210 ° C, nozzle temperature:
200 ° C., injection speed: low, mold temperature: 40 ° C. A method for synthesizing an aliphatic copolycarbonate diol is shown below as a reference example.

Reference Example 1 970 g of ethylene carbonate (EC) was placed in a 3 liter flask equipped with a 10 mm diameter, 300 mm length distillation column filled with Dickson packing 3φ and having a length of 300 mm, a thermometer and a stirrer.
(11 mol), 1,6-hexanediol (HDL) 6
50 g (5.5 mol) and 570 g (5.5 mol) of 1,5-pentanediol (PDL) were added, and 20 torr was added.
The mixture was heated and stirred under reduced pressure, and the internal temperature was controlled to 150 ° C. The reaction was carried out for 20 hours while distilling EC having an azeotropic composition and ethylene glycol (hereinafter abbreviated as EG) from the top of the distillation column. Next, the distillation column was removed, the degree of vacuum was reduced to 7 torr, and unreacted EC and diol were recovered. After the completion of the distillation of unreacted substances, the internal temperature is set to 190 ° C,
By distilling out the diol while maintaining the temperature, a self-condensation reaction was performed to increase the molecular weight. Four hours later, G
A polymer having a molecular weight of 2000 was obtained by PC analysis. The yield was 740 g and the hydroxyl value was 56 mgKOH / g. This polymer is abbreviated as pc-a.

Reference Examples 2 and 3 1,4-butanediol (BDL) as the diol,
Aliphatic copolycarbonate diol (pc-pc) was prepared in the same manner as in Reference Example 1 except that 1,5-pentanediol and 1,6-hexanediol were used and the amounts shown in Table 1 were used.
b, pc-c). Table 1 shows the respective molecular weights.

[0069]

[Table 1]

Raw materials used in Examples and Comparative Examples,
And the evaluation method is as follows. 1. Polyurethane elastomer (hereinafter abbreviated as TPU) component (A) -1 (TPU-1): pc-a2 obtained in Reference Example 1
00g and 67.2g of hexamethylene diisocyanate were charged into a reactor equipped with a stirrer, a thermometer, and a condenser.
The reaction was carried out at 00 ° C. for 4 hours to obtain a prepolymer having a terminal NCO. 30 g of 1,4-butanediol as a chain extender was added to the prepolymer, and 0.2 g of dibutyltin dilaurate was used as a catalyst.
Universal extruder for lab with built-in kneader (Kasamatsu Chemical Industries, Ltd. LABO universal extruder KR-
(Type 35) at 140 ° C. for 60 minutes, and then pelletized by an extruder. Shore D hardness of urethane elastomer is 3
9, MFR was 24.

(A) -2 (TPU-2): except that pc-b was used as the polycarbonate diol,
Polymerization was performed in the same manner as in the synthesis method 1 to obtain a urethane elastomer. The resulting urethane elastomer has a Shore D hardness of 4
0, MFR was 20.

(A) -3 (TPU-3): except that pc-c was used as the polycarbonate diol,
Polymerization was performed in the same manner as in the synthesis method 1 to obtain a urethane elastomer. The resulting urethane elastomer has a Shore D hardness of 4
3, MFR was 23.

(A) -4 (TPU-4): Polycaprolactone polyol (manufactured by Daicel, Placcel 220, molecular weight 2,000) was used instead of polycarbonate diol.
Except using 0), it synthesize | combined by the method similar to the synthesis method of TPU-1. The resulting urethane elastomer had a Shore D hardness of 45 and an MFR of 27.

(A) -5 (TPU-5): Miractran E190 (manufactured by Nippon Miractran Co., Ltd., MDI / adipate TPU), Shore D hardness 45, MFR: 28

Component (B): Preparation of solid catalyst; MgCl ₂
Was completely dissolved, 49.5 g of anhydrous MgCl ₂ and 49.5 g of absolute ethanol, 100 ml of petrolatum oil and 100 ml of silicone oil were stirred at 120 ° C. in a nitrogen atmosphere. The mixture was then filled with 1500 ml of pre-filled 150 ml of petrolatum oil and 150 ml of silicone oil.
after transfer to an autoclave at 120 ° C., 3000
The mixture was stirred at rpm for 3 minutes. The mixture is cooled n
-Added under stirring in 1000 ml of heptane,
spherical solid l ₂ · 3EtOH was precipitated (average particle size 3
0-150 μm). Further, the obtained solid was dried under a nitrogen atmosphere while increasing the temperature from 50 ° C. to 100 ° C.
The H / MgCl ₂ molar ratio was adjusted to 1.27. The obtained solid had a porosity of 0.139 cc / g and a surface area of 9.1 m ² / g.
g, bulk density 0.564 g / cc.

25 g of this solid (carrier) was mixed with TiCl ₄ 6
25 cc in an autoclave with stirring and containing
C. under a nitrogen atmosphere. Further, the temperature of the autoclave was raised to 100 ° C. over 1 hour. When the temperature reached 40 ° C. in the heating process, diisobutyl phthalate was added at a molar ratio of 1/8 of magnesium. 100 ℃
After stirring for 2 hours, the mixture was allowed to stand at the same temperature to precipitate a solid.
The supernatant was removed by suction with a siphon. TiCl ₄ 5
50 ml was newly added, and the mixture was stirred at 120 ° C. for 1 hour and allowed to stand. After the supernatant was removed by suction with a siphon, the remaining solid was washed with 200 ml of anhydrous hexane six times at 60 ° C. and three times at room temperature. After drying in vacuum, it was used as a catalyst for polymerization of component (B).

The components (B) -1 and (B) -2 were polymerized by the following method. The polymerization was carried out continuously in a series of reactors equipped with a device for transferring sequentially from one reactor to the next. In a 22 liter stirred autoclave, consist of 16 liters of liquid propylene at 20 ° C. and a mixture of about 0.15 g of the above-mentioned solid catalyst, 75 ml of a 10% hexane solution of triethylaluminum and cyclohexylmethyldimethoxysilane (CMMS). A polymerization catalyst (Al / CMMS molar ratio 7.5) was added,
For 24 minutes. The prepolymer was then sent to a first reactor in the gas phase where propylene homopolymerization was performed. Further, the polymer was transferred to a second reactor, where copolymerization of ethylene and propylene was performed. Table 2 shows the polymerization conditions of the first and second reactors and the properties of the final product obtained.

[0078]

[Table 2]

Component (B) -3: Cataloy Adflex KS-084P, manufactured by Montell, MFR 30 g / 10
Minutes. Flexural modulus 108 MPa, Shore D hardness 44, average dispersed particle size of rubber 0.4 μm.

Component (B) -4: manufactured by Montell, Cataloy Adflex KS-359P, MFR 12 g / 10
Minutes. Flexural modulus 83 MPa, Shore D hardness 41, average dispersed particle size of rubber 0.6 μm.

Examples 1 to 5 (A) -1, (A) -2, (A) -3,
(A) -4, (A) -5, (B) -1 as a polypropylene mixture, thermoplastic elastomer component 1
1 part by weight of carbon black master pellet (Royal Black RB 9005) per 100 parts by weight, Ir
ganox1010 to 0. 1 part by weight of dilauryl thiopropionate (DLTP, manufactured by Yoshitomi Pharmaceutical Co., Ltd.)
After adding 15 parts by weight and 0.1 part by weight of TINUVIN 327 (manufactured by Ciba Geigy), blending with a Henschel mixer, and melt-kneading at 220 ° C. with a 20 mm diameter co-axial twin screw extruder to obtain an elastomer composition. A pellet was obtained. Tables 3 and 4 show physical properties and evaluation results. Next, injection molding was performed using the above elastomer composition to obtain storage covers for a plurality of driver airbag devices. The molding cycle was 80 seconds, and the airbag device assembled using the obtained storage cover at −40 ° C., normal temperature,
The development performance at 90 ° C. is summarized in Tables 3 and 4.

FIGS. 1 to 4 show the shape of the storage cover according to the first embodiment.
This will be specifically described below with reference to FIG. FIG. 1 is a perspective view showing an example of a storage cover of a driver airbag device according to the present invention. FIG. 2 is a schematic diagram showing a cross section of the storage cover taken along line II-II in FIG. FIG. 3 is a schematic view showing an enlarged cross section of a V-shaped groove of the storage cover of FIG. FIG. 4 is a schematic view showing an enlarged cross section of a U-shaped groove of the storage cover of FIG.

As shown in FIG. 1, the storage cover has a flange 5 around the periphery of which has a bolt hole for attaching to a retainer (not shown). 1 is formed in a box shape, and a fragile structure 3 to be broken is arranged on the top surface 2 in an H shape as shown by a dotted line in FIG. The hinge part 4 is provided as shown by a dashed line.

As shown in FIGS. 2 and 3, the breakable portion 3 is formed by a V-shaped groove 6 having a V-shaped broken shape on the back side of the top surface 2. As shown in FIGS. 2 and 4, the hinge portion 4 is formed by a U-shaped groove 7 having a U-shaped cross section on the back side of the top surface 2. When the airbag (not shown) is inflated, the storage cover 1 is broken at the portion 3 to be broken, the two doors 2a and 2b are respectively deployed around the hinges 4, and the airbag is released and expanded.

The size of the portion 3 to be broken is 12 cm for a portion corresponding to two vertical bars in an H shape, 15 cm for a portion corresponding to a horizontal bar, the thickness of the portion to be broken is 0.5 mm, and the hinge The thickness of the portion is 1.9 mm, and the other portions are 3 mm. The storage cover of the first embodiment has a maximum clamping force of 150 k.
g / cm ² , the above-mentioned mold for the storage cover was attached to a general-purpose injection molding machine having a maximum injection pressure of 60 kg / cm ² , and an operating temperature of 20 g / cm ² .
Molded at 0-230 ° C. Further, in the first embodiment, the inner volume 6
A 0 liter airbag was used, and one gas generator having a gas generation amount of about 1 mol was used.

Examples 6 to 8 Using (A) -1 as the TPU and (B) -2, (B) -3 and (B) -4 as the polypropylene mixture,
In the same manner as in Example 1, pellets of the elastomer composition were obtained. The evaluation of the physical properties and the evaluation of the airbag were performed in the same manner as in Example 1. The results are shown in Table 4.

Examples 9 to 11 Using (A) -1 as the TPU and (B) -1 as the polypropylene mixture, pellets of the elastomer composition were obtained in the same manner as in Example 1. The evaluation of the physical properties and the evaluation of the airbag were performed in the same manner as in Example 1. Table 5 shows the results.

[0088]

[Table 3]

[0089]

[Table 4]

[0090]

[Table 5]

Examples 12 to 15 Thermoplastic elastomer composition pellets were obtained in the same manner as in Example 1 except that (A) -1 and (A) -2 were used as TPUs and (B) -1 was used as a polypropylene mixture. next,
The storage covers of a plurality of passenger airbag devices were obtained by injection molding. The molding cycle was 65 seconds. -40 of the airbag device assembled using the obtained storage cover
The developability at 90 ° C., normal temperature and 90 ° C. was all good.

FIG. 5 is a perspective view showing an example of a storage cover of the passenger airbag apparatus according to the present invention. FIG. 6 shows FIG.
FIG. 6 is a schematic diagram showing a section of the storage cover taken along line VI-VI of FIG. FIG. 7 is a schematic diagram showing a section of the storage cover taken along line VII-VII in FIG.

The shape of the storage cover according to the ninth embodiment is shown in FIGS. 5, 6, and 7. FIG. That is, the storage cover 11 includes the top plate 12 and the four side walls 18. Top plate 12 is side wall 1
The outer wall 8 has an eave-like shape, and the side wall is provided with a collar 15 on the outer periphery at the lower end. The storage cover 11 is a side wall 18
Can be attached to a retainer (not shown) by using a hole 19 arranged in the hole, and a gas generator (not shown) is attached to the retainer.

An airbag (not shown) can be stored in a space formed by the top plate 12, the side wall 18, the retainer, and the gas generator of the storage cover. The to-be-fractured portions 13, 13 'of the fragile structure are disposed inside the side wall 18 of the top surface 12 as shown in FIGS. 5, 6, and 7, and the hinge portion 14 is provided as shown in FIGS. It is arranged. Expected break 1
3 and 13 'are arranged as shown in FIGS.

As shown in FIGS. 6 and 7, the portions 13, 13 'to be broken are V-shaped grooves 1 having a V-shaped cross section on the back side of the top plate 12.
6, 16 '. The hinge part 14 is shown in FIG.
As shown in the figure, the cross-sectional shape on the back side of the top plate 12 is formed by a U-shaped U-shaped groove 17.

When the air bag is inflated, the storage cover 11
Is to be broken at scheduled break portions 13 and 13 '
A portion 12a surrounded by the hinge portions 3 and 13 'is deployed around the hinge portion 14, and the airbag is released and inflated. The dimensions of the storage cover 11 are as follows: (a) the top plate 12 has a long side 34 cm, a short side 14 cm, a thickness 3 mm,
(B) The long side of the side wall 18 is about 28 cm, the short side is about 10 cm, the height is about 6.8 cm, the thickness is about 3 mm, (c) the wall thickness of the part to be broken is 0.5 mm, and (d) the wall thickness of the hinge part is 1 0.9 mm.

The storage covers of Examples 12 to 15 had a maximum mold clamping force of 215 kg / cm ² and a maximum injection pressure of 60 kg / cm ² .
The above mold for a storage cover was attached to a general-purpose injection molding machine of cm ² , and molded at an operating temperature of 200 to 230 ° C. In Examples 12 to 15, an airbag having an inner volume of 120 liters was used, and two gas generators each generating about 1 mol of gas were used.

Comparative Examples 1 to 3 (A) -1 was used as TPU, (B) -1 was used as a polypropylene mixture, and TP of an extrusion blend type was used.
Santopre O (PP / EPDM blend)
ne 203-40 (flexural modulus 80 MPa, Shore D
Hardness 40, MFR 8g / 10min, dispersed particle size of rubber 9μ
m), and kneaded at the respective ratios shown in Table 6 in the same manner as in Examples 1 to 4, and evaluated. The results are shown in Table 6. From this result, it is clear that the composition outside the range of the present invention has any bad physical properties.

[0099]

[Table 6]

[0100]

As described above, the present invention employs the molding of a specific thermoplastic elastomer composition by an injection molding method, and the provision of a fragile structure intended to be broken provides durability. It has excellent feel, excellent feel, and can be reliably deployed in a wide temperature range, as well as high productivity,
An airbag storage cover that does not require painting and achieves low cost has been 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 schematic diagram showing a cross section of the storage cover taken along line II-II in FIG.

FIG. 3 is a schematic diagram showing an enlarged cross section of a V-shaped groove of the storage cover of FIG. 2;

FIG. 4 is a schematic view showing an enlarged cross section of a U-shaped groove of the storage cover of FIG. 2;

FIG. 5 is a perspective view showing an example of a storage cover of the passenger airbag device according to the present invention.

FIG. 6 is a schematic view showing a cross section of the storage cover taken along line VI-VI in FIG. 5;

FIG. 7 is a schematic view showing a cross section of the storage cover taken along line VII-VII in FIG. 5;

FIG. 8 is a perspective view of a passenger airbag device according to the present invention;
FIG. 7 is a schematic diagram illustrating a cross section similar to FIG. 6 illustrating another example of a cover.

FIG. 9 is a schematic diagram showing a cross section similar to FIG. 7 of the storage cover shown in FIG. 8;

[Explanation of symbols]

 1, 11, 21 ... Storage cover 2 ... Top surface 2a ... Door 3, 13, 13 ', 23, 23' ... Breaking scheduled part 4, 14, 24 ... Hinge part 5. ..Flanges 6, 16, 16 ', 26, 26' ... V-grooves 7, 7 ', 17, 27 ... U-grooves 8 ... Spaces 9 ... Holes 12, 22 ... Top plate 12a: Opening of top plate 18: Side plate 19: Hole

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3D030 DB47 3D054 AA02 AA03 AA13 AA14 BB02 BB09 BB23 BB30 FF01 FF02 FF04 FF18 4J002 BB142 BB152 BB153 CK031 EE036 EU176 EV046 EV086 EV136 EW066 FD126 FD056

Claims (4)

[Claims] 1. A storage cover for an airbag device comprising an injection molded article of a thermoplastic elastomer having an airbag storage recess inside and a rupture scheduled portion having a fragile structure, wherein the thermoplastic elastomer comprises: Shore D hardness 2 characterized by comprising the components (A) and (B)
A storage cover for an airbag device, which is a thermoplastic elastomer composition of 0 to 70. (A) polyurethane elastomer: 100 parts by weight (B) (B-1) polypropylene-based polymer (propylene is 85
(B-2) ethylene-propylene-based copolymer rubber (containing 75% by weight or less of propylene): 40 to 90% by weight, wherein ethylene in the mixture is 40 to 90% by weight. The average dispersion particle size of the propylene copolymer rubber is 2 μm or less, the flexural modulus of the mixture is 20 to 700 MPa, and the Shore D hardness is 2
Polypropylene mixture of 0 to 60: 5 to 900 parts by weight 2. The airbag device according to claim 1, wherein the polyurethane elastomer is a polyurethane elastomer obtained by copolymerizing the following components (a), (b) and, if necessary, component (c). Storage cover. (A) a polycarbonate diol comprising a repeating unit represented by the following formula (1) and having a terminal group of a hydroxyl group (wherein R
Represents an aliphatic or alicyclic hydrocarbon group having 2 to 10 carbon atoms). Embedded image (B) Polyisocyanate (c) Chain extender having two active hydrogens capable of reacting with polyisocyanate 3. The polycarbonate diol comprises a repeating unit of the following formulas (2) and (3), and includes an aliphatic polycarbonate diol having a hydroxyl group as a terminal group,
The ratio of the above (2) and (3) is (2) / (3) = 10/9
The airbag device according to claim 2, wherein the polyol is a high molecular polyol (where n is an integer of 4 and / or 5), which is 0 to 90/10 (molar ratio). Storage cover. Embedded image Embedded image 4. A heat obtained by blending 0.01 to 5 parts by weight of at least one additive selected from a heat stabilizer, an ultraviolet absorber and a light stabilizer with respect to 100 parts by weight of a thermoplastic elastomer. 4. The storage cover for an airbag device according to claim 1, wherein the storage cover is a plastic elastomer.