| 摘要 |
PROBLEM TO BE SOLVED: To make sensitivity very high and to lessen the energy to be supplied to a thermal head by a method wherein a film for thermal stencil printing is constituted of an L-lactic acid polymer and the ratio of an L-lactic acid in this L-lactic acid polymer is set to be a specified one or above. SOLUTION: An L-lactic acid of 80 parts and a hydroxycaproic acid of 20 parts are put in a reactor equipped with an agitator and agitated for four hours at 145 deg.C and under 6000Pa, while water is distilled off. Tin of 0.05 parts being added then, agitation is conducted further for three hours under the conditions of 145 deg.C and 4000Pa and thereby an oligomer is obtained. Tin of 0.2 parts and diphenyl ether of 200 parts being added to this oligomer, an azeotropic dehydration reaction is conducted under the conditions of 148 deg.C and 4400Pa and it is conducted for 30 hours, while water and a solvent being distilled are separated by a water separator and the solvent alone is returned to the reactor, whereby an L-lactic acid polymer is obtained. The ratio of an L-lactic acid in this L-lactic acid polymer is made 75mol% or above. By this method, the energy to be supplied to a thermal head can be lessened and the thermal head is given a long life. |
