Patent ID: 6952959

Claim:
A method of designing a heat seal width which comprises; (1) heat-sealing a test piece of a sheet to be heat-sealed at a temperature lower than the fusion temperature of a heat seal portion of the sheet, (2) heat-sealing another test piece of the sheet at a temperature at or higher than the fusion temperature, (3) pulling to peel a heat-sealed portion of each test piece, and measuring the pull strength variation with peel length, (4) calculating the peel energy in various peel lengths of the test piece heat-sealed at a temperature lower than the fusion temperature of the heat seal portion of the sheet by integrating the pull strength variation, (5) calculating the peel energy of the test piece heat-sealed at the temperature at or higher than the fusion temperature by integrating the pull strength variation up to rupture at the heat-sealed portion, and (6) setting the heat seal width at a peel length having a peel energy higher than the peel energy of the test piece heat-sealed at a temperature at or higher than the fusion temperature.