| abstract |
A solution of a substantially colorless dye precursor in an organic solvent preferably boiling at above 180 DEG C is emulsified as droplets, and polymer microcapsule walls are formed therearound; the glass transition point (loss elastic modulus/storage elastic modulus) of the walls is 60-200 DEG C. The latter is achieved by selection of the polymer-forming components, e.g. a polyol or polyamine and a polyisocyanate, or by addition of a transition point modifier, preferably in the organic solution. The modifier can be a carbamic acid ester, aromatic methoxy compound or organic sulfonamide compound. The microcapsules are mixed with a color developer, e.g. a phenolic compound or organic acid, usually with a polymeric binder, and the mixture is coated onto a support of paper or a synthetic film. Coloration on heating, e.g. in a high speed thermal printer, occurs by permeation of coloration reactants through the capsule walls. |