Thermographic sheet with double protective resin coating - as thickener to increase chemical and storage stability without impairing copy

摘要

Thermographic sheet consists of a substrate with a thermographic layer contg. a leuco dyestuff and developer and a protective coating of at least 2 layers. The first protective coating is prepd. from a liq. for which there is a difference of max. 20% between the solids concn. at which the Brookfield viscosity is 100 cPs at 60 rpm and 20 deg.C. and the concn. at which the viscosity is 10000 cP.s. Pref. the liq. for the first protective coating is based on a resin (I) with a max. elongation of 100% or more (JIS K7113 test method). The liq. for the second protective coating contains 20-80% (I) w.r.t. total resin content and also a Zr or Zn cpd.. (I) is soluble or dispersible in water. The difference in solids concns. is 10% or less. The protective coatings are applied wet-on-wet. ADVANTAGE - The chemical and storage stability are improved, without impairing the copy quality. The sheet is useful in facsimile copies, registering equipment, instruments and labelling.