JP2002167481A - Thermoplastic elastomer composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a new and cheap thermoplastic elastomer composition usable for a non-painted air-bag cover having a spring hardness of 40-98 without requiring a nylon-based net for reinforcing in air-bag covers. SOLUTION: This thermoplastic elastomer composition has, as a main component, an (a) component, as an ethylene-α-olefin copolymer, wherein a (b) component as a copolymer of propylene with a 2-8C α-olefin, and a (c) component as a propylene based thermoplastic elastomer are add-alloyed to improve a developing property at high and low temperatures, a scratching resistance and a moldability and to realize lowering in a unit price of material, and a (d) component as a silicone oil having a viscosity of 50,000 cst or above, improves the scratching resistance, a stickiness and a releasing property in injection- molding.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

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

[0003]

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

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

[0005]

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

[0006]

Means for Solving the Problems As a result of various studies, the present inventors have found that the main component is an ethylene / α-olefin copolymer as the component a, and propylene as the component b and propylene having 2 to 2 carbon atoms.
8 by adding a copolymer with α-olefin and c-component propylene-based thermoplastic elastomer to improve the development performance at high and low temperatures, scratch resistance and moldability, and reduce the unit cost of materials And the viscosity of the d component is 500
Scratch resistance by silicone oil of 00cst or more,
With the compounding design concept of improving stickiness and mold release during injection molding, it is possible to obtain an airbag cover with excellent deployability over a wide temperature range of -40 ° C to 90 ° C, and excellent splash resistance during deployment. , And the best combination of these,
-4 not only immediately after molding but also after high temperature aging test and weather resistance test
It has been found that an airbag cover which is excellent in deployability in a wide temperature range of 0 ° C. to 90 ° C. and which does not require painting which is excellent in splash resistance during deployment and which realizes a reduction in the unit cost of materials has been obtained, and completes the present invention. It has been reached.

That is, the present invention provides a thermoplastic elastomer composition excellent in high-temperature and low-temperature deployability suitable for an airbag cover, which is obtained by melting and kneading the components a, b, c and d according to the following claims and pelletizing. Is provided. (A) an ethylene / α-olefin copolymer composed of ethylene and an α-olefin having 4 to 12 carbon atoms 20 to 80% by weight (b) a copolymer of propylene and an α-olefin having 2 to 8 carbon atoms 0 80% by weight (c) Manufactured by a multistage polymerization method using a catalyst (a)
A propylene-based thermoplastic elastomer comprising a copolymer of propylene and an α-olefin having 3 to 30 carbon atoms and a copolymer of (ii) ethylene and propylene 0 to 80% by weight (d) Viscosity (JIS Z8803, 25 ° C) ) Is 5000
Silicone oil at 0 centistokes or more
1-10% by weight

The α-olefin of the ethylene / α-olefin copolymer is preferably octene-1, and the ethylene / α-olefin copolymer is substantially prepared by using a metallocene-based catalyst. Preferably, the copolymer is a linear copolymer.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The ethylene / α-olefin copolymer used as the component a in the present invention comprises ethylene and an α-olefin having 4 to 12 carbon atoms. As such α-olefins, for example, α-olefins having 4 to 12 carbon atoms include butene-1, pentene-1, hexene-1, 4-methyl-pentene-1, heptene-1, octene-1. , Nonene-1, decene-1, undecene-1, dodecene-1
And the like.

[0010] More preferably, when octene-1 is used as the α-olefin, further improvement in mechanical strength is expected.

The ethylene / α-olefin copolymer of the present invention is substantially linear and can be produced with a known metallocene catalyst.

Further, the ethylene / α-olefin copolymer which is substantially linear according to the present invention has a different polymerization catalyst as compared with a conventional one using a Ziegler catalyst or the like, and has a property of the obtained polymer. Also differs greatly from the conventional one. The characteristics of an ethylene / α-olefin copolymer which is substantially linear using a metallocene catalyst are listed as follows. Since the polymerization catalyst has an extremely high activity, the weight ratio of the α-olefin can be increased, and an elastomeric polymer having high flexibility can be obtained even without containing a plasticizer. 2. Uniform distribution of comonomer compared to Ziegler-based polymers. 3. Compared with Ziegler-based polymers, the molecular weight distribution is extremely sharp, the amount of low molecular weight components is extremely small, the mechanical strength and processability are excellent, and the quality is high. 4. Despite having a sharp molecular weight distribution, when a long-chain branch is introduced, the melt index (I10) at 190 ° C./10 kgf (about 98 N) defined by ASTM D1238 and 190 ° C./2.16 kg
The value of the ratio (I10 / I2) to the melt index (I2) at f (about 21 N) is large, and the workability is excellent. 5. Excellent weather resistance

The metallocene-based catalyst comprises a cyclopentadienyl derivative of a Group IV metal such as titanium or zirconium and a co-catalyst, and is not only highly active as a polymerization catalyst, but also a conventional catalyst such as a Ziegler-based catalyst. Compared to,
The molecular weight distribution of the obtained polymer is narrow, the distribution of α-olefins having 4 to 12 carbon atoms, which is a comonomer of the copolymer, is uniform, and the catalyst species are uniform.
In the case of an olefin copolymer which is a copolymer of ethylene and an α-olefin using a Ziegler catalyst, the melt index ratio (I10 / I2) and the molecular weight distribution show a substantially linear proportional relationship, and the melt index ratio is The molecular weight distribution tends to increase with the increase. The molecular weight distribution is about 3 to 10. On the other hand, in the case of the metallocene-based olefin copolymer, the molecular weight distribution is a sharp value of less than 3.0, and the low molecular weight component is extremely small, regardless of the value of the melt index ratio. For this reason,
The ethylene / α-olefin copolymer used in the present invention has excellent mechanical strength and processability, and is of high quality.

The molecular weight distribution was calculated by gel permeation chromatography (GPC). The GPC apparatus and the measuring method are not particularly limited, but the present inventors used the following apparatus and measuring method. Apparatus Waters 150C isothermal chromatography column Laboratories 103, 104,
105,106 Solvent 1,2,4-trichlorobenzene Measurement temperature 140 ° C Standard substance Polystyrene

The "substantially linear" ethylene / α-olefin copolymer of the present invention is defined as a backbone of the polymer having a length of from 0.01 long chain branches per 1000 carbons to 3 carbons per 1000 carbons. It means that it is substituted by a long-chain branch, and the above-mentioned melt index ratio (I1
0 / I2) is as large as 5 or more, and gives good extrusion molding. As used herein, long chain branching is defined as a chain length of at least about 6 carbons and is defined as 13C nuclear magnetic resonance (NM
R) Measure long chain branching using spectroscopy and
all method (Rev. Macromol. Chem.
Phys. , C29 (2 & 3), pages 285-297). In contrast, the term "on-line" olefin copolymer means that the olefin copolymer does not contain long chain branches.

In addition, the ethylene / α-olefin copolymer which is substantially linear according to the present invention can be used as a suitable constrained geometry catalyst among metallocene catalysts during polymerization.
(dgeometry catalysts). The monocyclopentadienyl transition metal olefin polymerization catalyst taught in U.S. Pat. No. 5,026,798 is also disclosed in the present invention, provided that the reaction conditions are as specified below. Suitable for use in plastic elastomer compositions. Co-catalysts suitable for use in preparing the substantially linear ethylene / α-olefin copolymers of the present invention include, but are not limited to,
Examples include polymeric or oligomeric aluminoxanes, especially methylaluminoxane, as well as inert, compatible, non-coordinating, ion-generating compounds. Suitable cocatalysts are non-coordinating inert boron compounds.

The ethylene / α which is substantially linear in the present invention
-The polymerization conditions suitable for producing the olefin copolymer are generally those which are effective in a solution polymerization method, but the application of the present invention is not limited thereto. Slurry and gas phase polymerization methods are also effective provided appropriate catalysts and polymerization conditions are used. In the preparation of the ethylene / α-olefin copolymer which is substantially linear according to the present invention, a multiple reactor polymerization method, for example, US Pat.
No. 342 can also be used. The reactors can be operated in series or in parallel using at least one constrained geometry catalyst in one of the multiple reactors. The ethylene / α-olefin copolymer of the component (a) is 20 to 80% by weight, preferably 3 to 80% by weight.
0 to 70% by weight. If the amount of the component (a) is less than 20% by weight, the impact resistance at low temperatures is significantly reduced.
Good deployment performance cannot be exhibited when the airbag cover is deployed at 0 ° C. If the amount of the component (a) exceeds 80% by weight, it is not possible to exhibit heat-resistant shape retention and good deployment performance when the airbag cover is deployed at 90 ° C.

The copolymer of propylene and an α-olefin having 2 to 8 carbon atoms, which is used as the component b of the present invention, is effective for improving the processability and heat resistance of the resulting composition. Α-olefin random or block copolymers, specifically propylene-ethylene copolymers, propylene-1-hexene copolymers, propylene-4-methyl-1pentene copolymers, and poly-4
-Methyl-1-pentene, polybutene-1 and the like, among which ethylene-propylene block copolymers are preferable, among which ethylene content is 2 to 30% by weight.
Are preferred. Further, a nucleating agent is preferably added in order to suppress a change in physical properties in a high-temperature aging test and a weather resistance test. The melt flow rate of this copolymer of propylene and an α-olefin having 2 to 8 carbon atoms (ASTM-D-1
(238L conditions, 230 ° C.) in the range of 0.1 to 60 g / 10 min, particularly 0.5 to 50 g / 10 min can be suitably used. If the melt flow rate is less than 0.1 g / 10 min, the fluidity during molding deteriorates, and the melt flow rate is reduced to 60 g / 10 min.
If it is larger than this, heat resistance is undesirably reduced. The amount of the component b is from 0 to 80% by weight, preferably from 30 to 80% by weight. If the amount of the component (b) exceeds 80% by weight, the impact resistance at low temperatures is remarkably reduced, so that good deployment performance cannot be exhibited when the airbag cover is deployed at -40 ° C.

The propylene-based thermoplastic elastomer used as the component c in the present invention improves the processability and heat resistance of the resulting composition, improves the airbag expandability at -40 ° C, and the scratch resistance, and reduces the gloss and the material. It is effective in reducing the unit price,
Regarding the production method, a multi-stage polymerization method using a catalyst (Japanese Unexamined Patent Publication No.
97408). The melt flow rate of this propylene elastomer (ASTM-D-1)
(238L condition, 230 ° C) is 0.5 to 40g / 10mi
n is preferred, and more preferably 1 to 30 g / 10 min. Melt flow rate is 0.5g
If the flow rate is less than 40 g / m, the fluidity during molding deteriorates.
If it exceeds in, the heat resistance is undesirably reduced. c
The amount of the component is from 0 to 80% by weight, preferably from 30 to 50% by weight. If the amount of the component (c) exceeds 80% by weight, the impact resistance at low temperatures is remarkably reduced, so that good deployment performance cannot be exhibited when the airbag cover is deployed at -40 ° C.

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

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

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

[0023]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. The components blended in the following Examples and Comparative Examples are as follows. <Component a> Ethylene / α-olefin copolymer: Ethylene / octene-1 copolymer (referred to as EOR) Ethylene / octene-1 composition ratio of a copolymer produced by a method using a metallocene-based catalyst 75/25 (weight ratio), density; 0.87 g / cm 3, MFR: 0.5 g /
10 min (190 ° C. × 2.16 kg) <Component b> Tokuyama MS650: ethylene-propylene block copolymer: melt flow rate 10 g / 10
min (JIS K7210) <Component c> Cataloy KS-084P manufactured by Montelusque Sunrise Co., Ltd .: (B) a copolymer of (a) propylene and an α-olefin having 3 to 30 carbon atoms and (b) ethylene produced by a multistage polymerization method Propylene-based thermoplastic elastomer comprising a copolymer of propylene and propylene: melt flow rate 30 g / 10 min (ASTM-D-12
38) <Component d> Silicone made by Dow Corning Toray Silicone
Concentrate BY27-001: straight silicone oil: PP = 50: 50, viscosity 100,000c
st or higher (25 ° C.), melt flow rate 16.4 (2
30 ° C, 2.16 kg)

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

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

The results are shown in Examples 1 to 5 and Comparative Examples 1 to 5. From these results, it can be seen that the airbag cover formed from the composition obtained in the present invention has a hardness of 40 to 98 and is excellent in airbag deployability at −40 to 90 ° C.

[0027]

[Table 1] 1) wt%

[0028]

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

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08L 83/04 C08L 83/04

Claims (3)

[Claims] 1. A thermoplastic elastomer composition comprising the following (a) to (d). (A) an ethylene / α-olefin copolymer composed of ethylene and an α-olefin having 4 to 12 carbon atoms 20 to 80% by weight (b) a copolymer of propylene and an α-olefin having 2 to 8 carbon atoms 0 80% by weight (c) Manufactured by a multistage polymerization method using a catalyst (a)
A propylene-based thermoplastic elastomer comprising a copolymer of propylene and an α-olefin having 3 to 30 carbon atoms and a copolymer of (ii) ethylene and propylene 0 to 80% by weight (d) Viscosity (JIS Z8803, 25 ° C) ) Is 5000
Silicone oil at 0 centistokes or more
1-10% by weight 2. The thermoplastic elastomer composition according to claim 1, wherein the α-olefin of the ethylene / α-olefin copolymer is octene-1. 3. The thermoplastic elastomer composition according to claim 1, wherein the ethylene / α-olefin copolymer is a substantially linear copolymer produced using a metallocene catalyst.