Patent ID: 6383425
Filing Date: 2002-05-07
Classification: B29C,B29K,C08J,Y10T

Abstract:
A method for extruding foam sheet having improved surface appearance, comprising:extruding through a coathanger extrusion die: a foamable composition comprising a polypropylene resin, from about 0.05 to about 0.5 wt. % of a crystallization nucleating agent, from about 0.01 to about 5 wt. % of an inert solid bubble nucleating agent having a particle size of from about 0.3 to about 5 microns, and from about 0.1 to about 25 wt. % of a foaming agent, said extrusion die comprising a die land and an exit opening having a height t1 in fluid communication with said die land, the aperture of said die land having a minimum height t2, and widening along the extrusion axis of said die to the exit opening, thereby forming an expansion zone, the ratio t1/t2 lying in the range of from about 2 to about 5; forming a foamed polypropylene extrudate of given thickness; drawing said extrudate through finishing rolls to produce a foam sheet; and taking up said foam sheet.