Rigid thermoplastic resin foam and process for preparation thereof

Claim 1

A process for the preparation of a rigid thermoplastic resin foam, which comprises heating a foam of a rigid thermoplastic resin for at least one minute in hot water maintained at a temperature higher than 85° C. or a water vapor atmosphere maintained at a temperature higher than 85° C. to expand the foam, then contracting the foam so that the volume is less than 70% of the volume of the final foam, and aging and expanding the foam in a drying chamber at an ambient temperature (T) of 40° C.≦T< the softening point of the resin for at least 24 hours, whereby is obtained a foam having a density (D) of 3 Kg/m 3 ≦D≦17 Kg/m 3 , a multi-cellular structure including many wrinkles having one end in the boundary portion where at least 3 cells are adjacent to one another and extending toward the central portion of the cell wall, an average cell diameter (A) of A≦2.0 mm, a closed cell ratio (B) of B≧50%, a kinetic spring constant (K) of K≦40×10 6 N/m 3 , and a minimum value (C), among 60% compression set values determined with respect to three directions rectangular to one another, of C≦25%.