JPH082363A - Pad for air bag device - Google Patents

Abstract

PURPOSE:To provide a pad for an air bag device that can be mounted on a vehicle without coating the design face. CONSTITUTION:A pad body 13 is formed of resin/elastomer blended material into a single layer. The blended ratio of the resin/elastomer blended material is PP/elastomer (weight ratio)=60/40-40/60. The elastomer is of a blended group of EPM/styrene group thermoplastic elastomer (weight ratio)=80/20-20/80. The polymerization specification of EPM is to satisfy propylene content ratio=21-40 mol%, 3mol% <=P-P<=12mol%, 35mol%<= E-P<=50mol% (where P-P and E-P signify the dyadic chain distribution (<13>C-NMR) of propylene-propylene binding and ethylene-propylene binding.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pad for covering an upper surface of an airbag device mounted on a steering wheel of an automobile or an instrument panel in front of a passenger seat, and more particularly to a thermoplastic elastomer which can be manufactured with good productivity. The present invention relates to a pad for an airbag device, which is a single-layer molded body (hereinafter abbreviated as “TPE”).

The following is a list of the main abbreviations for the polymers used in this specification.

TPE: thermoplastic elastomer PP: polypropylene EPM: amorphous ethylene propylene random copolymer TPS: styrene-based TPE hydrogenated SBR: styrene / ethylene / butylene copolymer SEBS: styrene / ethylene / butylene / styrene block copolymer Combined SEPS ... Styrene / ethylene / propylene / styrene block copolymer

[0004]

2. Description of the Related Art Conventional air bag device pads are usually manufactured as follows.

The above-mentioned pad is usually manufactured by using a polyurethane material for reaction injection molding (RIM) having a foaming formulation, in which a net insert is embedded and injection molding is performed. This net insert is for reinforcing the upper wall portion of the pad when the airbag is operated.

However, in the case of this manufacturing method, since the net insert is used, the setting work is required,
However, the number of production steps is increased, and the polyurethane material used for RIM molding is thermosetting, so that the material cannot be recycled.

Therefore, for example, Japanese Patent Laid-Open No. 4-31464
In Japanese Patent Laid-Open No. 8.5-38996, a pad for an airbag device formed by a single layer of a resin / elastomer blend material is proposed. Here, examples of the resin include an olefin resin and an elastomer.

[0008]

However, the pad having the above-mentioned structure has a soft specification in consideration of the embrittlement of the material at a low temperature (usually -40 ° C.).

Therefore, the design surface is apt to be sticky, and the scratch resistance and weather resistance are not sufficient.
It had to be painted before it could be installed in a real car.

In view of the above, an object of the present invention is to provide a pad for an airbag device which can be mounted on an actual vehicle without coating the design surface.

[0011]

An air bag device pad according to the present invention solves the above problems by the following constitution.

A pad for covering the upper surface of the airbag device, wherein the pad main body is formed of a single layer of a resin / elastomer blend material, and the upper wall portion can be expanded by breaking when the airbag is inflated. In the airbag device pad, the resin / elastomer blend material is PP
/ Elastomer (weight ratio) = blend ratio of 60/40 to 40/60, wherein the elastomer is EPM / TP
It is a blend system of S (weight ratio) = 80/20 to 20/80, and the polymerization specification of EPM is propylene content =
21-40 mol%, 3 mol% ≦ P−P ≦ 12 mol%, 38 mol%
≦ E−P ≦ 50 mol% is satisfied (however, P
-P: Propylene-propylene bond, E-P: Ethylene-propylene bond diad chain distribution ( ¹³ C-NM
R) is meant. ) Is characterized.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Next, an embodiment of the present invention will be described with reference to the drawings. Further, each data of the comparative example is shown in Table 2.

A. First, the basic configuration will be described.

That is, in the pad for covering the upper surface of the airbag device 11, the pad main body 13 is formed of a single layer of a resin / elastomer blend material, and is broken when the airbag 15 swells and the upper wall portion is broken. This is a configuration in which a deployment groove portion 19 capable of deploying 17 is continuously provided. Here, the entire continuous shape of the expansion groove portion 19 is not particularly limited, but is generally H-shaped as shown in FIG.

B. In the above configuration, the present application has the following characteristic configurations.

(1) The first characteristic constitution is that the resin / elastomer blend material is polypropylene (PP) / elastomer (weight ratio) = 60/40 to 40/60 (preferably 55/45 to 45/55). Is a blend ratio of.

Examples of PP in the present invention include propylene homopolymers, copolymers of propylene and α-olefins such as propylene-ethylene block copolymers and mixtures thereof. Of the various PP mentioned above,
A crystalline propylene-ethylene block copolymer is preferred.

If the amount of PP is too large, it is difficult to impart a soft feeling (soft texture) to the pad body and it becomes difficult to obtain cold resistance (low temperature impact resistance) (see Comparative Examples 1 and 6).
Further, when the amount of the elastomer is excessive, the pad body has insufficient scratch resistance, stickiness tends to occur (see Comparative Example 7), and further, the shape retention ability becomes insufficient and the fluidity becomes low, Single-layer molding of the pad body by injection molding becomes difficult.

(2) The second characteristic constitution is that the elastomer is an ethylene propylene random copolymer (EPM).
/ TPS (weight ratio) = 80/20 to 20/80 (desirably 30/70 to 70/30).

Here, if the EPM is excessive, the scratch resistance of the pad body is not sufficient and stickiness is likely to occur as in the case of the elastomer (see Comparative Example 2).
Also, if TPS is too much, cold resistance (low temperature impact resistance)
Is difficult to obtain (see Comparative Example 3).

As the above-mentioned TPS, the soft segment may be SBS type which is polybutadiene and SIS type which is isoprene.
EBS-based, SEPS-based, and hydrogenated SBR, which do not have a double bond between molecules, have weather resistance, abrasion resistance,
It has excellent heat resistance and is desirable.

(3) The third characteristic constitution is that the polymerization specification of EPM is that the propylene content = 21-40 mol% (desirably 23-35 mol%), 3 mol% ≦ P-P ≦ 12 mol% (desirably). , 6 mol% ≦ P−P ≦ 10 mol%), 35 mol% ≦ E
−P ≦ 50 mol% (preferably 38 mol% ≦ E−P ≦ 45
mol%) requirement is satisfied (however,
P-P: Propylene-propylene bond, E-P: Ethylene-propylene bond diad chain distribution ( ¹³ C-NM
R) is meant. ).

When the EPM satisfies the above range, the low temperature physical properties are remarkably improved despite the high hardness of the compound material, and there is no problem even in the inflation test at -40 ° C.

If the EPM is out of the above range, it is difficult to obtain cold resistance (low temperature impact resistance) (see Comparative Examples 4 and 5). Also, P
If the P content exceeds 40 mol%, pelletization becomes difficult.

C. The method for manufacturing the pad is not particularly limited, but is performed as follows, for example.

The resin / elastomer blend material (PP / TPS / EPM compound) is used as a molding material in a molding die for injection molding. In the above, it is not necessary to coat the pad surface with a weather resistant paint or the like, and the product can be used as it is.

D. The pad 13 is attached to an inflator 25 to which an airbag 15 is mounted above a boss (not shown) of a steering wheel and is attached to a retainer 2
Then, the rivet 29 is fixed via the 7 and fixedly assembled.

E. The present invention is as shown in FIG.
It is also applicable to the airbag device M that does not have the deployment groove portion.

That is, an air bag 1 which is inflated at a predetermined time, a case 2 for accommodating the air bag 1, and a gas discharge port (not shown) are arranged in the case 2 for inflating the air bag 1 and are held by the case 2. The inflator 6 and the lid member 7 fixed to the case 2 to cover the airbag 1 are provided. In this airbag device M, the case 2 is connected and fixed to the main body of the vehicle so that the lid member 7 is located in the opening O of the instrument panel P.
The case 2 is formed of sheet metal, has an opening 2a that opens in a substantially rectangular shape in the upper part, and a bracket 3 to which a plurality of bolts 4 are fixed in the horizontal direction is welded to the outer peripheral surface. In the illustrated example, W is a windshield.

[0031]

As described above, the pad for an airbag device of the present invention uses PP as a resin / resin / elastomer blend material, and as an elastomer.
By using a blended system of TPS / EPM and using a EPM having a specific polymerization specification as a single layer, the following actions and effects are exhibited.

As shown in the test examples described below, the airbag device pad, which is a single-layer molded product of the present invention, has sufficient scratch resistance and no stickiness on the design surface without finishing coating. In addition, it has sufficient cold resistance so that no problems occur in the deployment performance when the pad swells at low temperatures.

Therefore, the air bag device pad of the present invention is a single-layer molded product that can be mounted on an actual vehicle without coating the design surface, and the productivity is greatly increased.

[0034]

[Test Example] Hereinafter, a test example performed for confirming the effect of the present invention will be described.

(1) The compound materials shown in Tables 1 and 2 were used to mold the pads of Examples and Comparative Examples. Each EP
The specifications of M are as shown in Table 3, and the specifications of each TPS are as follows.

TPS1 ... Styrene content 29 wt%, melt viscosity (in 20% toluene solution at 25 ° C.) 500 c
SEBS TPS2 of Ps ... Styrene content 13 wt%, MFR (200 ° C
SEBS TPS3 ... styrene content 10 wt%, MFR (230 ° C)
× 2.16kg) Hydrogenated SBR TPS4 3.5g / 10min. Styrene content 30wt%, MFR (230 ° C
Hydrogenated SBR TPS5 ... Styrene content 30 wt%, MFR (230 ° C.)
The specifications of the SEPS (2) pad for 0.7 g / 10 minutes are as follows.

Upper wall average wall thickness: 3 mm, development groove remaining wall thickness: 0.8 mm (3) Then, the following items were tested for each pad. The scratch resistance and stickiness were sensory-tested by 5 test subjects (adult males).

Scratch resistance: The surface of the product was scratched by a surface scratch tester ("HEIDON" manufactured by Shinto Kagaku Co., Ltd.) in accordance with JIS K 6718, and the surface condition of scratches was visually judged according to the following criteria.

Scratches are not conspicuous (4 or more out of 5) ∘ Scratches are conspicuous (4 or more out of 5) ... Χ The judgment is divided ... △ Stickiness: The surface of the product was judged by touch with the following criteria.

No stickiness (4 or more out of 5 people) ... ○ Stickiness (4 or more out of 5 people) ... Χ The judgment was divided ... △ Inflation test (cold resistance): When the product was mounted on an actual vehicle Equipping the same airbag device, low temperature (-4
An inflation test was performed in an atmosphere of 0 ° C., and the developed state of the pad was visually determined according to the following criteria.

Cleanly developed ... ○, cracks occurred in part of the pad ... △, pad scattered ... Χ, (4) The results are displayed, but the product performance of each example is
It was found that there was no problem in any of the scratch resistance, stickiness, and inflation test, whereas each comparative example has a problem in any item.

(5) In Tables 1 and 2, the physical property data of each material used are shown for reference. Each physical property data is
The test piece was prepared and measured.

[0043] Test Method of the properties data, respectively, the hardness (JIS A), tensile strength (T _B), tensile elongation (E _B),
Low temperature tensile strength (-35 ° C), high temperature tensile strength (+ 85 ° C)
All are in accordance with JIS K 6301, and the tan δ peak temperature is static strain 1 using Rheology's "DVE-V4".
It is obtained from the temperature dependence of the viscoelastic properties (E ′, E ″) measured under the conditions of 00 g, dynamic strain 100 g (constant load), and frequency of 20 Hz.

[0044]

[Table 1]

[0045]

[Table 2]

[0046]

[Table 3]

[Brief description of drawings]

FIG. 1 is a semi-longitudinal sectional view showing a manner of mounting a pad on an airbag device according to an example of the present invention;

FIG. 2 is a plan view of the pad of FIG.

FIG. 3 is a longitudinal sectional view of a mounting mode showing an example of another airbag device to which the pad of the present invention can be applied.

[Explanation of symbols]

 1 Airbag 2 Case 7 Lid Material (Pad) M Airbag Device 11 Airbag Device 13 Pad Main Body 15 Airbag 17 Upper Wall of Pad Main Body 19 Groove for Deployment

Claims (3)

[Claims] 1. A pad for covering the upper surface of an airbag device, wherein the pad body is formed of a single layer of a resin / elastomer blend material, and the upper wall portion can be expanded when the airbag is expanded. In the device pad, the resin / elastomer blend material is polypropylene / elastomer (weight ratio) = 60/40 to 40/60.
Is a blend ratio of the ethylene propylene random copolymer (EPM) / styrene-based thermoplastic elastomer (T
PS) (weight ratio) = 80/20 to 20/80, and the EPM polymerization specification is propylene content = 2.
1-40 mol%, 3 mol% ≦ P−P ≦ 12 mol%, 35 mol% ≦
It satisfies E−P ≦ 50 mol% (however, P−
P: propylene-propylene bond, EP: ethylene-
Dyad chain distribution of propylene bond ( ¹³ C-NMR)
Means ) A pad for an airbag device characterized by the following. 2. The pad for an airbag device according to claim 1, wherein the upper wall portion has a groove for deployment. 3. The TPS according to claim 1,
Is a hydrogenated TPS, a pad for an airbag device.