| 摘要 |
PURPOSE:To prevent background fog and to enhance image preservability by using 2,4'-dihydroxydiphenylsulfone with predetermined purity obtained by the dissolution under heating and cooling treatment in alcohol specified in the number of nitrogen atoms or an alchohol-water system as a developer forming a thermal color forming layer along with a leuco dye and a sensitizer. CONSTITUTION:As a developer, 2,4'-dihydroxydiphenylsulfone with purity of 97wt.% more obtained by a method wherein a crude compd. is dissolved in 1-4C alcohol, for example, methanol, isopropanol or an alcohol-water system under heating and subsequently cooled or partially distilled to remove the solvent and the obtained crystal is washed and dried is used. As the purity of this compd. is enhanced, background fog is prevented and preservability is enhanced. Therefore, one with purity of 98% or more is pref. used though the yield thereof is lowered. As a sensitizer, p-benzylbiphenyl is used. |
