Thermographic printing on plain paper - using thermographic medium dampened or mixed with conductive salt soln.

摘要

The method of printing on an electrically insulating medium comprises applying to a selected portion of the medium a non-conductive heat sensitive material in the liq. state of the type that changes colour when heated above a threshold temp. in mixt. with a liq. electrolyte chemically non-reactive with the heat sensitive material; contacting the selected portion with a pair of closely spaced electrodes made of material non-corrodible by the electrolyte and applying an electrical potential difference across the electrodes the electric current flowing thereby producing a temp. higher than the threshold temp. for the colour change. The mixt. pref. comprises an indolinobenzo-spiro-pyran cpd., a Ca resinate, a cobalto-naphthenate, a polyvinyl alcohol, a nonionic surfact active agent and a conductive polymer in water. Thermographic printing systems of increased speed are produced. No corrosion or scaling of the electrodes is experienced and the electrodes can remain in contact with the paper without affecting the print resolution.