This invention relates to a resin composition for heatsensitive transfer recording medium and a heat-sensitive transfer recording medium utilizing the resin composition for heat-sensitive transfer recording medium.
In the prior art, a heat-sensitive transfer recording medium comprises a colorant layer containing a fusible substance formed on the surface of a lengthy substrate sheet formed of, for example, a polyester. In most cases, the heat-sensitive transfer recording medium is shipped and stored under wound state. And, the heat-sensitive transfer recording medium under wound state, by, for example, heating the surface opposite to that of the substrate sheet where the above colorant layer is provided, melts a part of the above colorant layer and transfers the melted colorant layer onto the surface of a recording sheet such as paper in contact with the heat-sensitive transfer recording medium, thereby forming a printed image on the surface of the above paper.
However, in the heat-sensitive transfer recording medium of the prior art, in the case of performing heat-sensitive transfer with a thermal head, when transfer is effected with a thermal energy necessary to obtain sufficient printed image density, the so-called sticking phenomenon is caused in which the substrate sheet itself is fused to the thermal head, whereby there are involved problems such that running of the heat-sensitive transfer recording medium becomes impossible or that the heat-sensitive transfer recording medium is broken at that portion in an extreme case.
Also, since the heat-sensitive transfer recording medium of the prior art is stored under wound state as mentioned above, during storage thereof for a long term, the so-called blocking phenomenon may sometimes occur in which the back of the substrate sheet is adhered to the colorant layer. If blocking phenomenon has occurred, it becomes impossible to withdraw the heat-sensitive transfer recording medium under wound state for running.
For solving these problems, some attempts for providing heat-resistant protective layer as the backing layer on the back of the substrate sheet have been proposed.
For example, there have been proposed the method in which a metal layer or a silicon oxide layer as an abrasion resistant layer is provided on the back of the substrate sheet (see Japanese Unexamined Patent Publication No. 143152/1979 and No. 74195/1982), the method in which a heat-resistant resin layer such as of silicone or fluorine is provided (see Japanese Unexamined Patent Publication No. 7467/1980), the method in which a resin layer added with solid or semi-solid surfactant at normal temperature is provided (see Japanese Unexamined Patent Publication No. 129789/1982), or the method in which a layer containing a lubricating inorganic pigment in a heat-resistant resin is (see Japanese Unexamined Patent Publication No. 155794/1981).
However, the methods according to such proposals involve problems in that prevention of sticking phenomenon or prevention of blocking phenomenon is not satisfactory, or that special means requiring great production cost such as vapor deposition, cure aging, etc. may be necessary.
Also, the heat-sensitive transfer recording medium merely coated on the back of the substrate sheet with a heat-resistant resin layer such as of silicone or fluorine will be denatured in the colorant layer through migratability of the silicone or fluorine material itself, during storage for a long term or after exposed for a long time under high temperature. It has now been clarified by the study by the present inventors that transfer irregularity and defect of printed image are caused by receiving bad influences on the colorant layer from the migratable heat-resistant resin layer.
The present invention has been accomplished on the basis of the state of the art as described above.