Thermo-sensitive multi-color recording material and process for preparation thereof

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of a multi-color thermo-sensitive recording material comprises two thermo-sensitive coloring layers capable of forming different colors respectively at different temperatures, which are formed one over the other on a support member, and a decoloring layer disposed between the two thermo-sensitive coloring layers.
Particularly, in this embodiment, at least the upper thermo-sensitive coloring layer comprises a colorless or light-colored leuco dye and a phenolic material or acidic material and the decoloring layer consists essentially of a decoloring agent capable of decoloring color-forming materials of the upper thermo-sensitive coloring layer, and a binder agent which is a water soluble resin of a self cross-linking type.
The self cross-linking type water soluble resins are organic polymeric compounds having two or more atoms or atomic groups that can react with each other in one polymeric molecule and become insoluble in water when reacted with each other.
As the self cross-linking type water soluble resins, the following can be employed: initial condensed compounds of aminoplasts (amino resin), methylolurethanated polyvinyl alcohol, polyamides having epoxy groups or methylol groups at the ends of the molecules or at the side chains, and hydrocarbon resins having methylol groups at the ends of the molecules or at the side chains.
As the initial condensed compounds of aminoplasts, the following can be employed: formaldehyde resins of dimethylolmelamine, dimethyltrimethylolmelamine, trimethylolmelamine, tetramethylolmelamine, tetramethylpentamethylolmelamine, tetramethylhexamethylolmelamine, pentamethylpentamethylolmelamine, pentamethylhexamethylolmelamine, and the other alkylated melamines; ureaformaldehyde resin, anilineformaldehyde resin; thiourea formaldehyde resin; and cyanamide formaldehyde resin.
Polyamides having epoxy groups at the ends of the molecules are, for example, compounds represented by the following general formula: ##STR1## Hydrocarbon resins having methylol groups at the side chains are, for example, compounds represented by the following general formula: ##STR2## As the additives for promoting the cross-linking in the discoloring layer, compounds, such as ammonium nitrate, sodium nitrate, ammonium chloride and ammonium phosphate can be added to the decoloring layer