The present invention relates to an image-receiving sheet for dye transfer-type thermal transfer recording.
Dye transfer-type thermal transfer recording is a recording system in which a color sheet for transfer recording is heated by a heating means such as thermal head to transfer the dye onto an image receiving sheet for transfer recording. The color sheet comprises a base sheet and a coloring layer disposed on one side thereof, and composed of a vaporable or thermally diffusible dye and a binder resin. The image receiving sheet comprises a substrate, and an image receiving layer containing a resin having dyeing property and formed on the surface thereof.
In the said dye transfer-type thermal transfer recording, the image receiving layer of the image-receiving sheet is demanded to satisfy the following performance requirements:
(1) The color sheet won't be fused to the image-receiving layer during the transfer recording operations and can be easily separated after recording, and there can be obtained record with excellent gradation. PA1 (2) The image receiving layer has good dyeing property and is capable of high-density recording. PA1 (3) The storage stability such as light resistance, darkening and fading resistance, bleeding resistance, migrating resistance, etc., of the records are excellent. PA1 a substrate, and PA1 an image receiving layer formed on the surface of the said substrate, and composed of a resin having dyeing property and an aliphatic ester having 24 or more carbon atoms per one ester group, a hydrocarbon oil, a fatty acid ester of a polyhydric alcohol or a mixture thereof.
For satisfying these performance requirements for image receiving sheet, preparation and selection of the resin and adjuncts forming the image receiving layer are important. But it is difficult with the conventional preparation and selection techniques to obtain an image receiving sheet with satisfactory quality and performance.
In order to attain an enhancement of recording sensitivity and density in the conventional thermal transfer recording method, it is necessary to improve the dye diffusion characteristics of the image receiving layer of the image receiving sheet so as to facilitate a transfer of the dye and to minimize the risk blotting of the image, shading-off of the image or back-transfer (which is a phenomenon that the once transferred dye is brought back to the color sheet on the occasion of lapping-transfer of the next dye).
For this purpose, it is practiced in the art to add an additive having an action to lower the glass transition point (Tg) of the polymeric material of the image receiving layer to an appropriate level.
As the additive to be added to the image-receiving layer, there are known a phthalic acid ester as a plasticizer (for example, Japanese Patent Application Laid-Open (KOKAI) Nos. 274990/86, 19138/85 and 80291/90). This plasticizer, however, is too active and tend to induce excessive diffusion of the dye during storage of the image, to deteriorate a blotting resistance and a migrating property of the image, and to cause shading-off of the image or back-transfer, thereby making it unable to obtain the well-balanced image qualities of the image receiving layer.
Thus, an offer of a high-quality image receiving layer which can meet both requirements for storage stability and dyeing property, that is, which is improved in dyeing property without impairing the storage stability of the image and capable of high-density recording, is demanded.
As a result of strenuous studies on the subject matter, it has been found that an image receiving sheet for thermal transfer recording obtained by incorporating an aliphatic ester having 24 or more carbon atoms per one ester group, a hydrocarbon oil, a fatty acid ester of a polyhydric alcohol or a mixture thereof in an image receiving layer composed of a resin having dyeing property and formed on a substrate surface, has an excellent dyeing property and is capable of high-density recording and excellent in storage stability. The present invention has been achieved on the basis of this finding.