Patent ID: 6984445

Claim:
A manufacturing method of a multi-layer sheet comprising the steps of: producing a modified thermoplastic resin by adding a multifunctional monomer to a thermoplastic resin so as to have the thermoplastic resin reacted with the multifunctional monomer, forming an expandable sheet by adding a pyrolysis foaming agent to the modified thermoplastic resin so as to melt and mix the resin at a temperature lower than a temperature of decomposition of the pyrolysis foaming agent, thereafter forming an expandable multi-layer sheet by layering a sheet for reinforcement on at least one side of the expandable sheet; said sheet for reinforcement being made of a non-woven fabric in which non-meltable fibers and thermoplastic resin fibers are interwound with one another, covering and concealing the sheet for reinforcement all over by layering on the sheet for reinforcement of the expandable multi-layer sheet a surface sheet made of a thermoplastic resin which is compatible with the thermoplastic resin fibers of the sheet for reinforcement, a melt index of the thermoplastic resin fibers of the sheet for reinforcement being 30 to 60 g/10 minutes and a melt index of the thermoplastic resin of which the surface layer is made being 20 g/10 minutes or less, thereafter foaming the expandable multi-layer sheet to obtain from the expandable sheet a thermoplastic resin foam sheet having an aspect ratio Dz/Dxy of bubbles of 1.2 or more, and an expansion ratio of 5 to 50 cc/g by heating the expandable multi-layer sheet at a temperature higher than a temperature of reaction of multi-functional monomer and than a temperature of decomposition of pyrolysis foaming agent, and binding the non-meltable fibers together by melting the thermoplastic resin fibers of the sheet for reinforcement, wherein the surface sheet is melted and entered into the sheet for reinforcement to be integrated with the thermoplastic resin foam sheet.