Patent ID: 8398904

Claim:
A preparation method of a microcellular foam comprising the steps of: a) mixing a plasticized thermoplastic polymer resin with a foaming agent using an extruder; b) forming micropores by passing the plasticized mixture through a pressure drop region; and c) cooling the melted mixture in which the micropores have been formed by passing it through a cooling region, wherein a temperature change region is between the pressure drop region and the cooling region, wherein the temperature at the beginning of the temperature change region is 160 to 177° C., and the temperature at the end of the temperature change region is 45 to 77° C.; wherein a temperature difference at the end of the pressure drop region and the beginning of the cooling region is 30 to 200° C.; wherein the temperature at the end of the pressure drop region is 150 to 250° C., and the temperature at the beginning of the cooling region is 40 to 150° C.; the temperature changes from the beginning to the end of the pressure drop region and the temperature changes from the beginning to the end of the cooling region are maintained to be within ±5° C. the microcellular foam comprises a skin layer having porosity of below 5% and a core layer having porosity of at least 5%, which is defined in Equation 1 below, and the thickness of the skin layer accounts for 5 to 50% of the entire thickness of the foam: Porosity(%)=(ρ N −ρ F )/ρ N ×100 [Equation 1] where ρ N is the density of a non-foamed portion and ρ F is the density of a foamed portion; and wherein the core layer has pores having an average diameter of 0.1 to 30 μm; the overall porosity of the foam is from 15 to 30%; and the impact absorption energy of the foam measured by a rheometric drop test in accordance with ASTM D4226, the elongation of the foam measured in accordance with ASTM D638, the tensile strength of the foam measured in accordance with ASTM D638 are at least 70% of that of a non-foamed counterpart prepared under comparable conditions, respectively.