JPH01301433A - Surface skin member of plastics bumper - Google Patents

Abstract

PURPOSE:To enable a bumper to be durable against impact, temperature variation and other usage condition by using as the skin member of the bumper a molded product which contains olefinic thermoplastic resin, synthetic rubber and inorganic filler at the specified rates to obtain the material characteristics of both the specified longitudinally resilient coefficient and the specified linear expansion coefficient. CONSTITUTION:Styrene ethylene butadiene styrene (SEBS) rubber which is synthetic resin, potassium-whiskers titanate as inorganic filler are mixed at 30% and 15%, respectively in polypropylene a kind of olefinic thermoplastic resin and the surface skin 3 of a plastics bumper is formed by the extrusion molding method. The surface skin is characterized of 3,700kg/cm<2> in longitudinally resilient coefficient and 8.7X10<-5>mm/mm/ deg.C in linear expansion coefficient so that the surface skin will not generate a crack and permanent deformation against the collision of vehicle and has low possibility of a crack and deformation due to variation in temperature.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a skin member for automobile pants, particularly a plastic bumper, which has a good appearance when attached to an automobile, and which is resistant to shock loads such as light collisions and temperature. To provide a skin member that does not cause defects such as cracking and permanent deformation due to changes.

[Prior art and its problems]

BACKGROUND OF THE INVENTION In recent years, automobile bumpers have increasingly been made of plastic. In order to meet the demands for exterior styling and weight reduction, as well as safety standards in the United States in particular, their structures often consist of, for example, reinforcement as a strength member, foam as a shock absorbing member, and skin members. Can be seen. (Utility Model Publication No. 61-35465) The skin members of these bumpers have various physical properties required.
It was common to use urethane elastomers.

However, although the above materials satisfy the required physical properties, the cycle time for molding is long, many cracks occur, requiring man-hours for manual processing, and the defective rate is high. However, it had to be expensive.

[Object of the present invention]

An object of the present invention is to provide a skin member made of an inexpensive material that can withstand usage conditions such as shock and temperature changes, and is suitable for mass production. .

[Means for solving problems]

In order to overcome the problems of the prior art described above, in the present invention, the skin member of a plastic bumper is made by mixing a synthetic rubber and an inorganic filler in predetermined proportions into an olefin-based thermoplastic resin, so that the longitudinal elastic modulus is 2000. -5000
kg/cm2. Linear expansion coefficient 10XIO'mm/mm/℃
The molded article had the following physical properties.

By mixing an inorganic filler, the coefficient of linear expansion can be increased to 10.
The modulus of longitudinal elasticity can be reduced to 0 (units omitted below) or less by mixing synthetic rubber.
(20oo to 5000), and can cope with impact and temperature changes due to both physical properties.

〔Example〕

30LX of 5EBS (styrene-ethylene-butadiene-styrene) rubber, which is a synthetic rubber, to polypropylene, which is a type of olefin-based thermoplastic resin;

15% potassium titanate whisker, which is an inorganic filler.
%, a skin member with a thickness of 3 mm was produced by injection molding, and the longitudinal elastic modulus and linear expansion coefficient were measured, and the former was 3700 kg/crn2. The latter is 8.
A result of 7 x 10-5 mm/mm/'C was obtained.

Even when polyethylene, which is an olefin, was used as a substitute for polypropylene as the base resin, similar results were obtained.

Furthermore, if 20 to 50% by weight of EPM (ethylene propylene rubber) or EPDM (ethylene propylene terpolymer) is mixed in place of the synthetic rubber 5EBS, the effect of reducing the longitudinal elastic modulus is similar.

Furthermore, in order to reduce the coefficient of linear expansion (in order to reduce the linear expansion coefficient), replace the potassium titanate whiskers with glass fibers.

Talc, calcium carbonate, asbestos, etc. are effective.
Good results can be obtained by incorporating 10 to 20% by weight of these.

The structure of a plastic bumper to which the above skin member is applied is shown in FIGS. 1 to 3.

Reference numeral 1 denotes a car body, and a front bumper 2 is fixed to the front end of the car body. (A flyer bumper is fixed to the rear end, but is not shown.) 21 is the front part, and 22 is the side part.

The cross-sectional structure of the front part 21 is shown in FIG. 2, where 3 is a skin member and 4 is a reinforcement, which is a steel plate.

It is made of aluminum, FRP, etc.
(not shown) to the vehicle body 11. Reference numeral 5 denotes a buffer material, which is made of urethane foam, styrofoam, or the like.

Further, the cross-sectional structure of the side portion 22 is as shown in FIG.
It is composed of a skin member 3 and a buffer body 5.

As a whole, the front bumper 2 is fixed to the vehicle body 1 at the front part 21 via the reinforcement 4 as described above, and in addition, the skin member 3 is directly attached to the vehicle body 1 at the rear end of the side part 22. It is fastened.

[Effect]

If we consider the case where the automobile shown in FIG. 3, a large deformation occurs. At this time, if the material of the skin member 3 is soft, it will be easily deformed and will have restorability, but if it is hard (having a high modulus of longitudinal elasticity), permanent deformation or cracking will easily occur. Tests were conducted on skin members with various modulus of longitudinal elasticity under the impact loads that can occur in practical situations in automobiles, and it was found that those with a modulus of longitudinal elasticity exceeding 5000 kg/cm2 would remain damaged after a collision, which would be undesirable for practical use. The results were obtained.

If the weight is less than 2000 kg/cm2, it is too soft and causes problems such as vibration due to the undulating surface, making it undesirable as a product.

Next, the climate conditions for car use are -40°C to +8°C.
A temperature of 0°C is considered, and within this temperature range, permanent deformation, cracking, discoloration, etc. must not occur in the skin member. According to experiments, the coefficient of linear expansion is 10. OX 10 mm/mm/℃
If it exceeds this amount, abnormal deformation of the skin member at a part of the corner of the bumper (near the boundary between the front part 21 and the side part 22) will occur, resulting in a problem. This means that the car body stretches due to temperature changes (
The coefficient of linear expansion of steel is approximately 1.0×10).
This is because the side portion 22 fixed at the rear end becomes abnormally deformed because the elongation of the skin member 3 is about 10 times that of the previous one.

With a linear expansion coefficient of 8.7 x 10-5, no problems occur in the above temperature range.

〔effect〕

The present invention provides a skin member of a plastic bumper consisting of a skin member and an internal member for strength retention and shock absorption, which is made by mixing a synthetic rubber and an inorganic filler into an olefin thermoplastic resin in predetermined proportions, respectively. Longitudinal elastic modulus 20
00~5000kg/cm2゜Coefficient of linear expansion 10 x 1
Since the molded product has physical properties of 0 mm/mm/'C or less, problems such as cracking and permanent deformation of the skin member will not occur even under the load of a car collision (
Furthermore, the above-mentioned problems do not occur even when the temperature changes from low to high temperatures.

In addition, since the base resin is an olefin-based thermoplastic resin, the material can be obtained at low cost, injection molding is possible, cycle time can be shortened, and defects such as cracks are less likely to occur (such as rework and defective products). This makes it possible to obtain practical products suitable for mass production, such as minimizing the amount of waste.

[Brief explanation of the drawing]

The drawings illustrate embodiments of the invention. FIG. 1 shows a partial perspective view of an automobile equipped with a bumper having a skin member of the present invention. FIG. 2 is a longitudinal sectional view of the front part of the same bumper, and FIG. 3 is a longitudinal sectional view of the side part of the same bumper. [Explanation of main symbols] 1...Vehicle body, 2...Front bumper. 21... Same front part, 22... Same side part. 3...Skin member, 4...Reinforcement. 5...Buffer

Claims (1)

[Claims] (1) In the skin member of a plastic bumper, which consists of a skin member and an internal member for strength maintenance and shock absorption, synthetic rubber and inorganic filler are mixed in predetermined proportions into an olefin-based thermoplastic resin. Elastic modulus 2000~
5000kg/cm^2, linear expansion coefficient 10x10^-^
A skin member for a plastic bumper, characterized in that it is a molded body having physical properties of 5 mm/mm/°C or less.