JPH0689216B2 - Bumper composition with excellent paintability - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Industrial Field of the Invention The present invention comprises a thermoplastic composition comprising a special hydrogenated block copolymer, polyolefin and ethylene-propylene rubber, and is easily injection-moldable and It is intended to obtain a bumper having the same flexibility and other characteristics as a polyurethane bumper.

(Prior art and its problems) In recent years, plastics have been adopted as bumper materials for automobiles for the purpose of weight reduction and simplification of the process by integration.
As an example, a thermosetting resin such as polyurethane is used for a highly flexible bumper especially for high-class vehicles, but since it is thermosetting, it has problems in reworkability of the material and process simplification.

(Means for Solving Problems) That is, the present inventor has completed the present invention by discovering the following composition as a result of earnest research for solving the above-mentioned problems of the prior art. That is, (1) a carboxylic acid is added to a hydrogenated product of a block copolymer having at least one polymer block A mainly containing a vinyl aromatic compound and at least one polymer block B mainly containing a conjugated diene compound. Modified block copolymer 30 to which a molecular unit containing a group or its derivative group is bound
-40% by weight (2) Polyolefin 30-55% by weight (3) Composition consisting of 40-5% by weight of ethylene / propylene rubber has the same flexibility, impact resistance and paintability as polyurethane bumpers, and injection molding It was found that the bumper molding can be performed easily. Each component will be described below.

Representative examples of the components A and B constituting the hydrogenated block copolymer are as follows. A component is styrene, α-methylstyrene, vinyltoluene, p-tert-butylstyrene, etc., and B component is butadiene, isoprene, 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, etc. Can be given.

The hydrogenation rate of the hydrogenated block copolymer is preferably 25% or less in the block A portion and 95% or less in the block B portion.

If the hydrogenation rate of part A exceeds 25%, the mechanical strength of the composition,
The impact resistance tends to decrease, and the hydrogenation rate of part B is 95
If it is less than%, heat resistance and weather resistance tend to deteriorate.

The modified hydrogenated block copolymer has a number average molecular weight of 5,00.
0 to 1,000,000, preferably 30,000 to 500,000 is suitable. When the number average molecular weight is less than 5,000, the mechanical strength and impact resistance of the composition are lowered, and when it exceeds 1,000,000, the flow characteristics of the composition are remarkably lowered.

In the present invention, a modified copolymer obtained by binding a block copolymer with a molecular simple substance containing a carboxylic acid group or its derivative group in a hydrogenated product is used for improving the coating property and impact resistance of the composition of the present invention. It is a useful essential ingredient.

Examples of the molecular body containing a carboxylic acid group or a derivative group thereof include maleic acid, fumaric acid, itaconic acid, halogenated maleic acid, cis-4-cyclohexene-1,2-dicarboxylic acid, endo-cis-bicyclo [ 2,2,1] -5-
Examples thereof include heptene-2,3-dicarboxylic acid and the like, acid anhydrides, esters, amides and imidized products of these dicarboxylic acids, acrylic acid and methacrylic acid, and esters and amidated products of these monocarboxylic acids. These are 1
It is possible to use not only one kind but also a mixture of two or more kinds. Of these, unsaturated dicarboxylic acids or derivatives thereof are preferable, and maleic anhydride is particularly preferable.

The amount of binding is 0.05 to 15 parts by weight, preferably 0.1 to 10 parts by weight, and more preferably 0.5 to 5 parts by weight, based on 100 parts by weight of the modified block copolymer. If the amount added exceeds 15 parts by weight, a large amount of unreacted unsaturated carboxylic acid or its derivative contained in the resulting modified hydrogenated block copolymer will remain, resulting in a severe irritating odor and a reddish brown hue. It is not preferable, and it is not preferable because it may cause a decrease in adhesive strength due to residual monomers. Also
If the added amount is less than 0.05 part by weight, the effect of improving the paintability and impact resistance, which are the features of the composition of the present invention containing the modified hydrogenated block copolymer obtained, cannot be obtained.

The content of the modified hydrogenated block copolymerization component in the composition is preferably 30 to 40% by weight.

If less than 30% by weight, the flexibility and impact resistance are poor, and 40% by weight
If it exceeds, the flexibility is too good and the dimensional stability is lost.

As the polyolefin, a homopolymer of propylene, a copolymer with ethylene (random type or block type), polyethylene and the like are preferable. Other Japanese Patent Application Sho 59-
The polyolefins described in 155434, page 23, line 5 from the bottom are used.

The content of polyolefin is preferably 30 to 55% by weight. 30
If it is less than wt%, the flexibility is too good and the dimensional stability is poor. 55
When it exceeds the weight%, flexibility and impact resistance deteriorate.

As the ethylene / propylene rubber, a type having no diene-based third component used for vulcanized rubber is preferable,
What is commercially available as a thermoplastic pellet for so-called plastic blends is most suitable. Among them, those having a melt flow index of 0.5 g / 10 minutes (2.16 kg load at 230 ° C.) or more are preferable in terms of fluidity.

The content of ethynylene / propylene rubber is preferably 40 to 5% by weight. If it exceeds 40% by weight, impact resistance and paintability are deteriorated. If it is less than 5% by weight, the mechanical strength of the composition tends to be low.

Other than the above, the composition of the present invention includes a plasticizer, a drop agent, a pigment, a foaming agent, a filler, and the like. If necessary, compounds generally used in the rubber and plastic fields may be blended.

(Example) The compounds shown in the table below were blended with a Henschel mixer, mixed with an extruder (65 mmφ, twin-screw extruder), and pelletized.
Using this pellet, an injection molding machine was used to obtain a bumper-shaped molded product shown in FIG. Reference numeral 1 is a main body, and 2 is a reinforcing rib.

Impact Energy Measurement: Drop Weight Tester, Leohitrichs -40 ℃, 11m /
sec Judgment of coatability: Urethane coating without primer treatment (Kansai Paint, Retan PG-80) After baking at 60 ° C for 15 minutes, a crepe test. ○ 100
% No peeling, △ 50% peeling.

Extrusion conditions: Temperature Hopper part 170 ℃ Die part 180 ℃ Rotation speed 50rpm Injection molding conditions: Temperature Hopper part 230 ℃ Nozzle part 250 ℃ Mold part 65 ℃ Cooling time 25 seconds Cycle 40 seconds (effect) Composition of the present invention By using, the bumper can be easily molded, and the obtained bumper has the flexibility and other characteristics comparable to those of the urethane bumper.

[Brief description of drawings]

FIG. 1 is a perspective view of an example of an automobile bumper formed by using the composition of the present invention. 1 ... Main body, 2 ... Reinforcing ribs.

Claims (3)

[Claims] 1. A carboxylic acid is added to a hydrogenated product of a block copolymer having at least one polymer block A mainly containing a vinyl aromatic compound and at least one polymer block B mainly containing a conjugated diene compound. Block copolymer with a molecular unit containing a group or its derivative group bonded 30-40% by weight 2. Polyolefin 30 to 55% by weight 3. A bumper composition comprising 40% to 5% by weight of ethylene / propylene rubber and having excellent coatability.