METHOD FOR PRODUCING SHEET
Provided is a method for producing a foamable sheet with a convenient process. The method for producing a sheet includes the steps of: molding a resin composition including a thermoplastic resin and inorganic substance particles in a ratio of 80:20 to 20:80 and further including a foaming agent into a sheet-like product and stretching the sheet after being molded. The foaming agent preferably includes a polyethylene resin as a carrier resin and a hydrogencarbonate as an active component that acts as a thermally decomposable foaming agent serving as a foam nucleating agent.
1 . A method for producing a sheet, the method comprising the steps of:
molding a resin composition including a thermoplastic resin and inorganic substance particles in a ratio of 80:20 to 20:80 and further including a foaming agent into a sheet-like product; and
stretching the sheet after being molded.
2 . The method according to claim 1 , wherein the foaming agent is a thermally decomposable foaming agent that acts as a foam nucleating agent and includes a crystalline polyethylene resin as a carrier resin and a hydrogencarbonate as an active component.
3 . The method according to claim 1 , wherein the amount of the hydrogencarbonate in the foaming agent is 0.04% by mass to 1% by mass relative to the total mass of the resin composition.
4 . The method according to claim 1 , wherein the step of molding into a sheet-like product includes the step of extruding the resin composition at a temperature of 30° C. to 45° C. higher than the decomposition temperature of a polyethylene resin in the foaming agent.
5 . The method according to claim 1 , wherein the sheet after being molded is stretched in a ratio of 1.2 times to 5 times in a longitudinal direction and/or a transverse direction.
6 . The method according to claim 1 , wherein the inorganic substance particles include calcium carbonate particles.
7 . The method according to claim 1 , wherein the method is a method for producing a sheet for cardboard.
8 . The method according to claim 1 , wherein the method is a method for producing a sheet for building decoration.
9 . The method according to claim 8 , wherein the method is a method for producing a sheet including no backing paper.
10 . The method according to claim 1 , further comprising the step of applying a clay latex-based coating liquid or a coating liquid suitable for digital printing onto a surface of the sheet after stretching.
11 . A method for producing a foamed sheet, the method comprising the steps of:
kneading a resin mixture including a thermoplastic resin and inorganic substance particles having an average particle diameter of 1 μm to 15 μm in a ratio of 80:20 to 20:80 and further including additives including a lubricating agent to provide kneaded pellets; and
adding a thermally decomposable foaming agent that acts as a foam nucleating agent and includes a polyethylene resin as a carrier resin, in an amount of 0.04% to 1% relative to the resin in terms of a hydrogencarbonate as an active component, and kneading and extrusion-molding the resultant mixture at a temperature of 30° C. to 45° C. higher than the decomposition temperature of the foaming agent.
12 . A method for stretching the sheet obtained by the method as claimed in claim 11 in a ratio of 1.2 times to 5 times in a longitudinal direction and/or a transverse direction.
13 . The method for producing a sheet according to claim 11 , wherein the thermoplastic resin, the inorganic substance particles, and the additives including the lubricating agent are directly charged into a kneading-extrusion-molding apparatus, the thermally decomposable foaming agent as claimed in claim 11 is added during the process of kneading, and the sheet is formed not through the form of mixed pellets.