Patent ID: 6296727
Filing Date: 2001-10-02
Classification: B29C,B29K,B29L,B42F,Y10T

Abstract:
A method of making a cover comprising a pair of welded thermoplastic polymer sheets having therebetween a stiffener, said method comprising the steps of:(a) providing a stiffener having a leading edge, a trailing edge and two side edges and defining a cover;(b) positioning a pair of thermoplastic polymer sheets on opposite sides of said stiffener; said thermoplastic polymer sheets each having two side edges substantially parallel to the side edges of said stiffener, the thermoplastic polymer being selected from the group consisting of polypropylene and a copolymer of ethylene or butene and propylene, the weight percent of ethylene or butene being between about 1 wt. % to about 10 wt. %, and containing a sufficient amount of a nucleating agent to raise the recrystalization temperature to between about 100.degree. C. to about 140.degree. C.;(c) ultrasonically welding together said thermoplastic polymer sheets around the periphery thereof; and(d) cutting said polymer sheets to form a leading edge and trailing edge of the thermoplastic polymer sheets which are substantially parallel to the leading edge and trailing edge of said stiffener and to form a cover in which the two thermoplastic polymer sheets have substantially the same length and width as the stiffener;(e) the thermoplastic polymer being a member selected from the group consisting of polypropylene and a copolymer of ethylene or butene and propylene, the weight percent of ethylene or butene being between about 1 wt. % to about 10 wt. %, and containing a sufficient amount of a nucleating agent to raise the recrystalization temperature to between about 100.degree. C. to about 140.degree. C.