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Development of High-Rigidity Polypropylene Material and Clear Coat for Lightweight Bumper Fascia

Article of Honda R&D Technical Review Vol.28 No.2

Summary

A polypropylene material and clear coat were developed for the purpose of reducing bumper fascia weight.
In order to reduce bumper fascia weight, a polypropylene material was developed that would make it possible to thin the average wall thickness of 3.0 mm down to 2.0 mm. The developed material has high flowability to enable injection at 2.0 mm, and steps were taken to augment its rigidity by making it a high-rigidity material. At the same time, attention was also paid to the reduction in impact resistance caused by the higher rigidity, and to the fact that it would be further reduced after coating. That reduction in impact resistance was therefore limited by developing not only a material but also a coating for the purpose. Of the primer, base, and clear layers that make up the bumper fascia coating, the origin of cracking is in the clear layer. The main component of the clear layer is acrylic resin, and the glass transition temperature of this resin was raised while also adding an admixture of resin particles with a diameter of 0.1 µm or less. This was done to make the coating hard and brittle, increasing the number of cracks in order to distribute the stress.
As a result, a weight reduction of 23% or more relative to preceding materials was achieved in the bumper fascia of the 2016 model CIVIC.

Reference

(1) Asano, C., To, K., Hara, M., Onishi, M.: Development of High Stiffness PP for Bumper Fascias, Mazda Technical Review, No. 30, p. 191-194, (2012)
(2) Moore, Edward P., Jr., ed., Yasuda, T., Sakuma, M.: Shogekikairyo PP, Polypropylene handbook, Kiso kara Yotokaihatsu made, Kogyo Chosakai Publishing Co., Ltd., p. 258, (1998) (in Japanese)
(3) JIS K5600-5-3: 1999, Testing methods for paints – part 5: Mechanical property of film, Section 3: Falling-weight test
(4) ASTM D790-10: 2010, Standard Test Method for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials

Author (organization or company)

Emi NOMI(Automobile R&D Center)、Ken NAKANE(Automobile R&D Center)

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