Stretched thermoplastic resin foam sheet and process for production of the same

A method for producing a stretched thermoplastic resin foam sheet, comprising

• a stretching step for stretching a thermoplastic resin foam sheet in a width direction thereof which is to be carried out for a plurality of times, the thermoplastic resin foam sheet being obtained by heating a foamable thermoplastic resin sheet containing a thermoplastic resin and a pyrolytic foaming agent to the decomposition temperature of the pyrolytic foaming agent or higher,
• wherein
• the method comprises the steps of:
• a first stretching step for stretching the thermoplastic resin foam sheet by a stretching ratio of 1.1 to 2.0 times at a temperature at least 10° C. higher than a melting point or a softening point of the thermoplastic resin foam sheet;
• a second stretching step for stretching the thermoplastic resin foam sheet by a stretching ratio of 1.1 to 5.0 times at a temperature in a range from the temperature 50° C. lower than the melting point or the softening point of the thermoplastic resin foam sheet to the temperature 10° C. higher than the melting point or the softening point of the thermoplastic resin foam sheet, the second stretching step being carried out once or more than once after the first stretching step;
• and
• an annealing step not for stretching the thermoplastic resin foam sheet in the width direction thereof at a temperature in the range from the temperature 50° C. lower than the melting point or the softening point of the sheet to the temperature 10° C. higher than the melting point or the softening point of the sheet, the annealing step being carried out after each stretching step.

A method for producing a stretched thermoplastic resin foam sheet, the method comprising the steps of

• a first stretching and cooling step including:
• a first stretching step for stretching a thermoplastic resin foam sheet in a width direction thereof by a stretching ratio of 1.1 to 2.0 times at a temperature at least 10° C. higher than a melting point or a softening point of the thermoplastic resin foam sheet, the thermoplastic resin foam sheet being obtained by heating a foamable thermoplastic resin sheet containing a thermoplastic resin and a pyrolytic foaming agent to the decomposition temperature of the pyrolytic foaming agent or higher;
• an annealing step not for stretching the thermoplastic resin foam sheet in the width direction thereof at a temperature in the range from the temperature 50° C. lower than the melting point or the softening point of the thermoplastic resin foam sheet to the temperature 10° C. higher than the melting point or the softening point of the thermoplastic resin foam sheet, the annealing step being carried out after the first stretching step;
• and
• a cooling step for cooling the thermoplastic resin foam sheet, the cooling step being carried out after the annealing step, and
• a second stretching and cooling step including:
• a second stretching step for stretching the thermoplastic resin foam sheet in a width direction thereof by a stretching ratio of 1.1 to 5.0 times at a temperature in the range from the temperature 50° C. lower than the melting point or the softening point of the thermoplastic resin foam sheet to the temperature 10° C. higher than the melting point or the softening point of the thermoplastic resin foam sheet;
• an annealing step not for stretching the thermoplastic resin foam sheet in the width direction thereof at a temperature in the range from the temperature 50° C. lower than the melting point or the softening point to the temperature 10° C. higher than the melting point or the softening point, the annealing step being carried out after the second stretching step;
• and
• a cooling step for cooling the thermoplastic resin foam sheet, the cooling step being carried out after the annealing step,
• the second stretching and cooling step being carried out once or more than once.