JPH08143722A - Thermoplastic olefin elastomer composition for air bag cover material - Google Patents

Abstract

PURPOSE: To obtain a thermoplastic olefin elastomer composition which can give an air bag cover capable of being broken without fail at the time of operation without sattering of broken fragment by using a specified olefin polymer. CONSTITUTION: This composition comprises 10-50wt.% propylene/ethylene random copolymer having a melt flow rate (at 230 deg.C under a load of 2.16kg) of 10-120g/10min and an ethylene content of 2.0-4.5wt.%, 5-40wt.% low-density polyethylene, 10-50wt.% propylene/ethylene copolymer (C) comprising a crystalline propylene polymer and an amorphous propylene/ethylene copolymer and containing 20wt.% or above amorphous propylene/ethylene copolymer, and 20-75wt.% ethylene copolymer rubber (D) of a Mooney viscosity (ML1+4 , 100 deg.C) of 20-120. It is desirable that the crystalline propylene polymer is the one containing 3.0-4.5wt.% ethylene.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an olefinic thermoplastic elastomer composition for an air bag cover material mounted on a vehicle as a safety device. More specifically,
It is attached to the steering wheel and the instrument panel part to store the airbag that protects the driver or passenger in the passenger seat by inflating it in the event of a vehicle collision. The present invention relates to an olefin-based thermoplastic elastomer composition for an air bag cover material, which is free from damage pieces and has excellent surface characteristics suitable for mounting in a vehicle, vibration damping property, and elongation at break at high temperature and breaking strength.

[0002]

2. Description of the Related Art An air bag system for protecting a driver or a passenger in a passenger seat in the event of a vehicle collision comprises a collision sensing device and an air bag device.
The latter air bag device is composed of an air bag, a device for generating gas for inflating the air bag, and a cover for housing them, and the cover is attached to a steering wheel in front of the driver or an instrument panel portion in front of the passenger seat.

When a sensing device is activated in a collision accident, gas is generated instantaneously from the gas generator, and the thin wall portion or the like provided in advance on the storage cover is destroyed by the pressure of the gas filling the inside of the air bag, and the passenger boarding. The airbag can be inflated and released over the entire surface of the person, restraining the occupant to the seat side, and preventing or reducing an injury accident due to a collision with a steering wheel or other control device, windshield, instrument panel, or the like.

The characteristics required for an air bag cover material are that it is instantaneously and reliably crushed by the gas pressure in the air bag at the time of a collision, that no fragments will injure the occupant during the crushing, It has the appearance characteristics suitable for being mounted on a vehicle, has the strength to withstand use in a wide temperature range, and has the damping property for reducing the vibration transmitted from the vehicle body.

Various structures and materials have been proposed for the air bag storage cover, but a reinforcing material is usually used for the purpose of preventing scattering of fragments during crushing. For example, there is one in which a reinforcing material such as a net is embedded in an area other than a portion of a material such as foamed polyurethane that is supposed to be broken, to form the entire cover (Japanese Patent Laid-Open Nos. 50-127336 and 5-56).
(No. 5-110643), the manufacturing process for accurately embedding the reinforcing material in the entire cover except for the fractured part is complicated, resulting in low production efficiency and high cost.

Therefore, a two-layer type storage cover has been proposed which comprises a core layer (inner layer) capable of maintaining the strength and shape required for an air bag device, and a surface layer capable of giving a soft and soft feeling. For example, one comprising a core layer containing an olefinic rubber and a surface layer of a thermoplastic resin (Japanese Patent Application Laid-Open No. 2-22
No. 0946), which comprises a core layer of an olefin resin and a surface layer containing styrene rubber as a main component (JP-A-3-189252).
No. 4), which comprises an olefin elastomer and a core layer of an elastomer or resin having a tensile strength higher than that of the surface layer material thereof (Japanese Patent Laid-Open No. 4-15145), a core layer of a polyurethane thermoplastic elastomer and a styrene or olefin thermoplastic For example, there is one having an elastomer surface layer (JP-A-5-286399).

In either case, the broken portion is thinned or a groove or slit is provided in the outer layer or in the inner layer in order to surely perform the breaking during operation. Since it is manufactured by integral molding, a reinforcing material is embedded. It has the advantages of higher production efficiency, better crushability, better appearance and feel, and easier strength adjustment. However, since it is necessary to perform two-layer molding of the core layer and the surface layer by using two or more kinds of materials, there is still a problem in productivity, and since the physical properties of both layers are different, there is a problem during or during molding. There is also a problem that deformation and cracks may occur due to use for a period of time.

Therefore, in recent years, a single-layer type cover that does not use a reinforcing material has also been proposed. For example, it is made of various thermoplastic elastomers such as polyester-based, polyolefin-based, polyurethane-based, polyamide-based, etc., and forms a thin portion along the portion of the surface portion that should be broken when the airbag is operated, and the thin portion of the surface portion The thickness of the cover is changed so that the portion close to the wall is thin and the outer peripheral portion is thick (JP-A-4-151348).
Hardness (JIS K6301) 70 or more, flexural modulus (JIS K720
3) consisting of olefin-based and / or styrene-based thermoplastic elastomer having a weight of 5000 kg / cm ² or less (JP-A-4-31
4648), and hydrogenated styrene-conjugated diene polymer (SEBS), rubber plasticizer (paraffinic oil) and olefinic resin having a fragile structure (slit, groove, thin portion, etc.) to be broken. JIS A hardness (JI) consisting of (polypropylene) and additives (such as antioxidants)
There is an injection-molded article (Japanese Patent Laid-Open No. 5-38996) of a thermoplastic elastomer having S K6301) of 60 to 85.

Among these compositions, those using a styrene thermoplastic elastomer (styrene-butadiene block copolymer hydrogenated product, SEBS) have insufficient impact strength at low temperatures. Further, SEBS easily forms a microphase-separated structure, and the styrene component tends to have a rod-shaped lamella structure. Therefore, it is considered that the orientation of the styrene lamella becomes unbalanced in the longitudinal direction and the lateral direction during the injection molding, the mechanical properties are likely to be different, and uniform fracture is unlikely to occur. Further, in the composition using this SEBS, the mechanical loss tangent (tan δ), which is an index of vibration damping property,
The dispersion peak of does not exist near room temperature, and the vibration damping property is insufficient.

Therefore, an object of the present invention is to use an olefin for an air bag cover material, which basically uses a material of a polyolefin composition which is easy to mold, so that the cover is surely destroyed during operation and the fragments are not scattered. To provide a thermoplastic elastomer composition. Further, another object of the present invention is excellent in surface properties such as appearance, texture, vibration damping and touch (flexibility), and weather resistance that can be used in a wide range of temperature conditions from cold regions to tropical regions. It is an object of the present invention to provide an olefin-based thermoplastic elastomer composition for an air bag cover material, which has an improved breaking elongation particularly at high temperature and is excellent in breaking strength. Further, another object of the present invention is to provide an olefin-based thermoplastic elastomer composition having excellent moldability, capable of efficiently producing an air bag cover material, and recyclable after use.

[0011]

[Means for Solving the Problems] The inventors of the present invention have conducted extensive studies on an olefin-based thermoplastic elastomer composition for a airbag cover material, which comprises a polyolefin and an olefin-based elastomer, and as a result, propylene-ethylene random copolymer And low-density polyethylene, a composition comprising a propylene-ethylene copolymer consisting of a crystalline propylene-based polymer part and a non-crystalline propylene-ethylene copolymer part, and an ethylene-based copolymer rubber is mechanical. It has excellent properties, especially elongation at break and strength at high temperature, low flexural modulus, small orientation during molding and uniform fracture cleavage, and mechanical loss tangent (tan δ).
The present inventors have completed the present invention by discovering that the dispersion peak of 1 exists near room temperature and the vibration damping property is good.

[0012]

That is, the present invention comprises: (a) Melt flow rate (230 ° C., 2.16 kg load) 10 to 120 g / 10
%, 10 to 50% by weight of a propylene-ethylene random copolymer having an ethylene content of 2.0 to 4.5% by weight, (b) 5 to 40% by weight of low-density polyethylene, (c) a crystalline propylene polymer part and an amorphous 10 to 50% by weight of a non-crystalline propylene-ethylene copolymer part, wherein the amorphous propylene-ethylene copolymer part is 20% by weight or more, and (d) Mooney viscosity (ML).
_{(1 + 4} , 100 ° C.) 20 to 120% by weight of ethylene copolymer rubber 20 to 75% by weight, and an olefinic thermoplastic elastomer composition for an air bag cover material are provided.

[0013]

[Composition Components] The olefinic thermoplastic elastomer composition for air bag cover materials of the present invention will be described below. The olefin-based thermoplastic elastomer composition for an air bag cover material of the present invention comprises (a) a propylene-ethylene random copolymer, (b) a low-density polyethylene, (c) a crystalline propylene-based polymer part, and an amorphous material. It contains a propylene-ethylene copolymer consisting of a propylene-ethylene copolymer part, and (d) an ethylene-based copolymer rubber.

The propylene-ethylene random copolymer as the component (a) is a crystalline propylene-ethylene copolymer obtained by randomly copolymerizing propylene and ethylene in the presence of a stereoregular polymerization catalyst. Is 2.0 ~
4.5% by weight, preferably 2.5 to 3.5% by weight, and a melt flow rate (MFR) (230 ° C, 2.16 kg load) of 10
It is 120 g / 10 minutes. The low density polyethylene as the component (b) is a polymer of ethylene having a density of 0.910 to 0.945 g / cm ³ , and has an MFR (230 ° C, 2.16 kg load).
0.05 g / 10 minutes or more, preferably 10-100 g / 10
Minutes. This polymer also includes linear low density polyethylene (LLDPE).

The propylene-ethylene copolymer as the component (c) comprises a crystalline propylene-based polymer part and a non-crystalline propylene-ethylene copolymer part, and the non-crystalline propylene-ethylene copolymer part is 20 parts. It is contained by weight% or more, preferably 20 to 80% by weight. It is preferable that the crystalline propylene polymer part contains 3.0 to 4.5% by weight of ethylene. Further, in addition to the propylene and ethylene components, a small amount of other α-olefin, diene-based monomer or the like may be contained. If the content of the non-crystalline propylene-ethylene copolymer in the component (c) is less than 20% by weight, mechanical properties such as flexibility and impact strength will be insufficient. Further, it is desirable that ethylene is present in the crystalline propylene polymer part in the above range from the viewpoint of mechanical properties such as flexural modulus.

Such a propylene-ethylene copolymer can be produced by a method such as batch polymerization or multistage polymerization of propylene and ethylene in the presence of a Ziegler catalyst or the like. For example, in multi-stage polymerization, first, propylene is polymerized in the presence of a Ziegler catalyst or the like to produce a crystalline propylene-based polymer, and in the next step, a mixture of propylene and ethylene is polymerized to form an amorphous propylene-polymer.
An ethylene copolymer part is produced. The content of the non-crystalline propylene-ethylene copolymer part here is 2
It is determined by measuring the amount of a component soluble in n-decane at 3 ° C.

In the present invention, by using the propylene-ethylene copolymer as the component (c), the crystalline propylene-based polymer part and the amorphous propylene-ethylene copolymer part are (a) propylene. -Since it plays a role of connecting the interface between the ethylene random copolymer and (b) low-density polyethylene and the (d) ethylene-based copolymer rubber, simply (a) a propylene-ethylene random copolymer and (d) ethylene. Mechanical loss tangent (t), which has improved breaking strength, excellent flexibility, high impact strength, and is an index of vibration damping property, as compared with a mixture with a system copolymer rubber.
Since a particularly large shoulder exists in the dispersion curve of an δ) from 0 to 30 ° C., a composition having a further improved vibration damping property can be obtained.

The ethylene copolymer rubber as the component (d) used in the present invention is an amorphous random elastic copolymer containing ethylene as a main component, for example, ethylene-propylene copolymer rubber (EPR). , Ethylene-1-butene copolymer rubber (EBR), ethylene-propylene-non-conjugated diene copolymer rubber (EPDM).

Here, the non-conjugated diene monomer of EPDM is a non-conjugated diene having 5 to 20 carbon atoms.
1,4-pentadiene, 1,4-hexadiene, 1,5
-Hexadiene, 2,5-dimethyl-1,5-hexadiene and 1,4-octadiene, and cyclic dienes such as 1,4-cyclohexadiene, cyclooctadiene and dicyclopentadiene, for example 5-ethylidene-2
-Norbornene, 5-butylidene-2-norbornene,
Examples thereof include alkenyl norbornenes such as 2-methallyl-5-norbornene and 2-isopropenyl-5-norbornene. Among the above rubbers, EPR, EBR and EPDM are preferable, and EPDM using ethylidene norbornene as a non-conjugated diene is particularly preferable from the viewpoint of providing a composition having excellent tensile properties and impact resilience.

The proportion of comonomer composing EPDM is
Ethylene content is 50-80% by weight, preferably 55-
70% by weight, propylene content is 20 to 50% by weight, preferably 25 to 40% by weight, diene compound content is 1 to
It is 20% by weight, preferably 2 to 10% by weight. The iodine value is preferably 3 to 70. Also, the Mooney viscosity (ML
_{1 + 4} , 100 ° C.) is 20 or more, preferably 20-120. Low molecular weight EPDM with Mooney viscosity less than 20
However, sufficient breaking strength at high temperatures cannot be obtained, and if it exceeds 120, the formability deteriorates.

In the present invention, in addition to the above components, other components can be blended if desired. For example, by incorporating a fatty acid-based lubricant such as stearic acid amide, erucic acid amide, oleic acid amide, methylenebisstearamide, ethylenebisstearamide and a mixture thereof, it is possible to improve the peeling property during processing and molding. Therefore, by adding carbon black, good weatherability can be obtained at the same time as coloring. Further, by adding a filler such as calcium carbonate, talc, kaolin, mica, glass fiber or synthetic fiber, it is possible to improve dimensional stability during molding, releasability and the like. In addition, UV absorbers, processing aids, heat stabilizers, light stabilizers, flame retardants,
Additives used in the field of resin compositions for molding such as antistatic agents and nucleating agents can be appropriately blended in usual proportions.

[0022]

[Blending Ratio of Each Component] The ratio of each component is (a) 10 to 50% by weight of a propylene-ethylene random copolymer,
(B) Low-density polyethylene 5 to 40% by weight, (c) propylene-ethylene copolymer 10 to 50% by weight, and (d) ethylene-based copolymer rubber 20 to 75% by weight.

When the content of the component (a) is less than 10% by weight, the thermoplastic elastomer obtained has a low fluidity, so that the moldability is deteriorated, and when it exceeds 50% by weight, the mechanical strength becomes too high and the cover is expected to break. Since it is necessary to reduce the thickness of the product, it becomes difficult to perform the molding process, and the appearance becomes plastic-like due to the occurrence of gloss, and the tactile feel deteriorates. When the content of the component (b) is less than 5% by weight, the effect of improving the physical properties does not appear, and 4
If it exceeds 0% by weight, mechanical properties such as flexural modulus will increase, and it will be difficult to break the cover when the airbag is expanded, when the airbag is inflated. When the component (c) is less than 10% by weight, the effect of improving the physical properties does not appear,
If it exceeds 50% by weight, mechanical properties such as breaking strength and tear strength will be increased, and gloss and touch will be deteriorated, and it will be difficult to tear the cover when the airbag is inflated when the airbag is expanded. . If the content of the component (d) is less than 20% by weight, the mechanical strength will be too high and the physical properties such as impact strength at low temperature will be deteriorated, and if it exceeds 75% by weight, the fluidity will be low and the moldability will be deteriorated.

[0024]

[Production Method of Composition] The olefinic thermoplastic elastomer composition for air bag cover material of the present invention is produced by blending and kneading the respective components in the above proportions and other additives as appropriate. be able to. Specifically, it can be produced by a method using a twin-screw extruder and a strand cutter or a hot cutter, or a method using a feeder ruder, a single-screw extruder and a hot cutter after kneading with a kneader or a Banbury mixer.

The olefinic thermoplastic elastomer composition of the present invention used as an air bag cover material is
Breaking elongation at 85 ° C (JIS K6301, 500 mm / min) is 600% or more, breaking strength at 85 ° C (JIS K6301) is 5
It is preferably 0 kg / cm ² or more, and particularly preferably a flexural modulus (JIS K7203) of 1000 to 5000 kg / cm ² .

When the breaking elongation at 85 ° C. is less than 600% or the breaking strength at 85 ° C. is less than 50 kg / cm ² , cracks are generated in the notch portion due to aging such as fatigue deterioration when used as an air bag cover. Otherwise, it will break at a position other than the notch during operation (when breaking and breaking). Further, if the hardness is low, deformation is likely to occur, resulting in poor shape retention, and if the flexural modulus is high, it is difficult to break the cover by tearing when the airbag is inflated.

The olefinic thermoplastic elastomer composition for an air bag cover material of the present invention may be molded into a cover for accommodating an air bag by a commonly used method. The thin portion is molded by a general molding method such as injection molding using a mold whose inner surface becomes a recess having an H shape, for example.

[0028]

The present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following description. In each of the examples and comparative examples, the following resin raw materials were used.

(A) Propylene-ethylene random copolymer (RPP): MFR (230 ° C., 2.16 kg load) 30
g / 10 minutes, ethylene content 3.1% by weight. (B-1) Low density polyethylene (LDPE): MFR (230 ° C, 2.
16 kg load) 65 g / 10 minutes, density 0.915 g / cm ³ . (B
-2) Linear low density polyethylene (LLDPE): MFR
(230 ℃, 2.16kg load) 50g / 10min, density 0.926
g / cm ³ . (C) Propylene-ethylene copolymer (RTPO): M
FR (230 ° C, 2.16kg load) 25g / 10 minutes, ethylene content of crystalline polypropylene polymer part 3.8% by weight,
Amorphous propylene-ethylene copolymer part 40% by weight. (D) Ethylene-propylene-non-conjugated diene copolymer (EPDM): propylene content 28% by weight, iodine value 1
5, Mooney viscosity (ML _{1 + 4} , 100 ° C.) 88. (E) Styrene-butadiene block copolymer hydrogenated product (SEBS): styrene content 30% by weight, MFR (2
30 ℃, 2.16kg load) 10g / 10min.

Example 1 The respective components in the proportions shown in Table 1 were melt-kneaded at a resin temperature of 220 ° C. with a twin-screw extruder and cut with a hot cutter to obtain an olefinic thermoplastic elastomer composition. This composition was molded to prepare a sample for measuring physical properties, and physical properties (MFR, breaking strength (23 ° C
And 85 ° C.), elongation at break, flexural modulus, damping property, and moldability) were measured. The measurement results are shown in Table 1 together with the blending ratio of each component.

Examples 2 to 5, Comparative Examples 1 to 4 Using the respective components in the proportions shown in Table 1, the same procedure as in Example 1 was carried out to obtain an olefinic thermoplastic elastomer composition for an air bag cover material. It was A sample for measuring physical properties was prepared from this composition, and each physical property was measured. The results are shown in Table 1 together with the blending ratio of each component.

[0032]

[Table 1]

The measurement and evaluation methods of each physical property shown in Table 1 are as follows. (1) MFR (g / 10 minutes): Measured at 230 ° C and 2.16 kg load. (2) Breaking strength (kg / cm ² ): ^{2 according to} JIS K6301
Measured at 3 ° C and 85 ° C. (3) Elongation at break (%): Measured at 85 ° C according to JIS K6301. (4) Flexural modulus (kg / cm ² ): Measured according to JIS K7203. (5) Moldability: The moldability was evaluated according to the following criteria by the viscosity measured during high-speed shearing at 220 ° C. (measured with a capillary rheometer (manufactured by Toyo Seiki Seisakusho at a shear rate of 1000 / sec)). ⊚: 900 poise or less, ◯: 900 poise to 1200 poise or less, Δ: 1200 poise to 1500 poise or less, ×: 1500 poise or more.

(6) Damping property: With a solid viscoelasticity measuring device,
1 Hertz (H) every 5 ° C in the range of -150 ° C to 200 ° C
The constant frequency of z) was applied to the composition, the storage elastic modulus and the loss elastic modulus at each temperature were measured, and the dispersion loss obtained by the mechanical loss tangent (tan δ) and the temperature was calculated according to the following criteria. . ◯: A dispersion curve of tan δ is in the temperature range of −5 to 30 ° C., ×: Dispersion curve of tan δ is outside the temperature range of −5 to 30 ° C.

As can be seen from Table 1, those obtained by adding the propylene-ethylene copolymer as the component (c) (Examples 1 to 5) had high breaking strength and breaking elongation at high temperature (85 ° C.). Improved, flexural modulus, moldability, and vibration damping properties also showed good values, and the propylene-ethylene copolymer as the component (c) was not added (Comparative Example 3). Out of range (Comparative Example 2) and SE as rubber component
It can be seen that the physical properties are well balanced as compared with those using BS (Comparative Example 1).

[0036]

The olefinic thermoplastic elastomer composition for an air bag cover material of the present invention comprises (a) a melt flow rate (230 ° C., 2.16 kg load) of 10 to 120 g /
10 minutes, propylene with an ethylene content of 2.4 to 4.5% by weight
An ethylene random copolymer, (b) low-density polyethylene, and (c) a crystalline propylene-based polymer part and a non-crystalline propylene-ethylene copolymer part, and a non-crystalline propylene-ethylene copolymer part. Of 20% by weight or more, and (d) an ethylene copolymer rubber having a Mooney viscosity (ML _{1 + 4} , 100 ° C.) of 20 to 120 are blended and kneaded. is there. The composition for an air bag cover material of the present invention uses only the olefin-based thermoplastic resin composition, and the air bag cover created by this is reliably destroyed during operation, without using auxiliary materials such as a net. Even if it does not scatter, it operates reliably in a wide temperature range, maintains flexibility, and has excellent surface properties and moldability. Further, no brittleness is observed even at a low temperature of -50 ° C, mechanical properties at a high temperature are excellent, and temperature adaptability is also good. Furthermore, in addition to being superior in vibration damping in a temperature range (10 to 25 ° C.) in which the frequency of use is high, the olefin resin composition is used as compared with a conventional styrene thermoplastic elastomer (SEBS, etc.). Therefore, it can be efficiently produced and can be recycled after use.

Claims (1)

[Claims] 1. A melt flow rate (230 ° C.,
2.16kg load) 10-120g / 10min, ethylene content
2.0 to 4.5% by weight of propylene-ethylene random copolymer 10 to 50% by weight, and (b) low density polyethylene 5
-40% by weight and (c) a crystalline propylene-based polymer part and an amorphous propylene-ethylene copolymer part,
20% by weight of non-crystalline propylene-ethylene copolymer part
10 to 50% by weight of the above propylene-ethylene copolymer, and (d) Mooney viscosity (ML _{1 + 4} , 100 ° C.) 2
0-120 ethylene copolymer rubber 20-75% by weight
An olefinic thermoplastic elastomer composition for an air bag cover material, which comprises: