A multilayer polyethylene resin fuel tank for off-road motorcycles and All-Terrain Vehicles (ATVs) has been developed to comply with U.S. EPA gasoline permeation control regulations. Motorcycles and ATVs employ complex saddle-shaped tanks with weld-molded insert parts and requirements for exterior design, and the following four issues were therefore identified and addressed for the multilayer blow molding process. To enable the saddle shape to be molded, pre-blowing and depressuring were employed in the blow molding process in order to achieve a uniform wall thickness. A temperature range that balanced resistance to drawdown in the parison, resistance to melting damage in the insert parts, and adhesion of the insert parts enabled the adhesive strength of the insert parts to be increased. Changes to the design of the modified polyethylene adhesive used to bond the EVOH, which forms a gasoline permeation barrier, have increased the resistance of the insert parts to delamination as a result of impact. The employment of a mold surface treatment producing a surface roughness able to conceal mold transfer defects has enabled the external design requirements for the tank to be satisfied.
Article of Honda R&D Technical Review Vol.21 No.1 (137 - 143)