Foams of polyolefin/polystyrene resin mixture

Claim 1

A foam of a polyolefin/polystyrene resin mixture obtained by mixing a polyolefin resin and a polystyrene resin in the presence of a hydrogenated styrene/butadiene block copolymer, and subjecting the resultant mixed resinous composition to extrusion foaming, wherein; (1) said hydrogenated styrene/butadiene block copolymer comprises, as components before hydrogenation, 10 to 38% by weight of styrene based on the total weight of said block copolymer before hydrogenation and butadiene having 1,2-bond type butadiene of 20 to 50% by weight based on the total weight of butadiene, and; (2) said foam comprises a thin surface skin portion showing a value of 0.65 or more of the surface structural index S represented by the following formula: S=t/T≧0.65 wherein t and T each represent a total light-transmission evaluated according to the method of ASTM D1003 with respect to a surface skin layer and an inner layer defined below; said surface skin layer means a layer cut out from the surface of a foam (an original plate) at an inner side in the thicknesswise direction and in the thickness dimension of 3 times the dimension of an average cell diameter of said foam, and said inner layer means a layer cut out from a middle portion of said form excluding said surface skin layer in the thicknesswise direction and in the thickness dimension of 3 times the dimension of the average cell diameter of said foam; and said average cell diameter is determined by drawing a straight line having a length (L) measured in the thicknesswise direction of the middle portion of the foam, counting the number of cells across said straight line and making calculations based on the following formula, and is indicated by an average value obtained by repeating the calculations 10 times: Cell diameter (mm)=1.626×L mm÷cell number.