In heat-sensitive recording papers, a recording image is obtained by a physical or chemical change of substances caused by heat energy, and a number of such thermal processes are known.
Recently, the heat-sensitive recording papers have been used to record the output of a facsimile or coomputer output, which provide primary color formation with no requirement of development. Such dye type papers are disclosed in Japanese Patent Publication Nos. 4160/68 and 14039/70 and Japanese Patent Application (OPI) No. 27253/80 (corresponding to U.S. Pat. No. 4,283,458) (The term "OPI" as used herein refers to a "published unexamined Japanese Patent Application".)
Generally, when a heat-sensitive recording paper is used as a recording paper, the advantage of a small and light recording apparatus is obtained. Accordingly, such papers have become widely used. On the other hand, conventional heat-sensitive recording papers have the disadvantage that the recorded image can be erased by adhesion of various chemicals or oils, and the paper are easily fogged. Since these faults are serious problems in practical use, improvement has been attempted and in particular it is common to provide a protective layer on a heat-sensitive layer.
In Japanese Patent Publication No. 27880/69, is disclosed a layer containing a non-sticky lubricant melting at a temperature lower than the operation temperature and dispersed in a water soluble polymer such as polyvinyl alcohol. The layer is provided on a heat-sensitive color forming layer to prevent fouling of the surface of the mark (heat) during heating. However in this process, resistance to various chemicals or oils and resistance to water are insufficient.
Further, it has the disadvantage of sticking when used for facsimiles.
In order to remedy the above-described problems of heat-sensitive recording papers having a protective layer, by improving resistance to various chemicals, water resistance, sticking, pressure fog or adhesion of scums, it has been proposed to use hydrophobic polymeric substances and various water soluble polymers which can be used together with water proofing agents or with fillers. (Japanese Patent Application Nos. (OPI) 30437/73, 31958/73, 19840/78, 14751/79, 53545/79, 11837/79, 128349/79, 126193/81, 139993/81, 10530/82 (corresponding to U.S. Pat. No. 4,346,343), 29491/82, 1053925/82, 115391/82 (corresponding to U.S. Pat. No. 4,415,627), 144793/82 (corresponding to U.S. Pat. No. 4,444,819), 107884/82, 53484/83 and 193189/83).
However, these processes have the drawbacks that resistance to various chemicals, oils and water remains insufficient, sensitivity is reduced, sticking properties are insufficient, blocking, for example adhesion in case of interpoosition of water between surface/surface or surface/back face, is caused, and complicated production steps are required, thus increasing the cost. Consequently, they are not on the whole acceptable in industrial use.