1. Field of the Invention
The present invention relates to an image receiving sheet for sublimation-type thermal image transfer and also to a sublimation-type thermal recording method using the image receiving sheet, utilizing a different running speed mode.
2. Discussion of Background
Recently the demand for full color printers is increasing year by year. Typical recording methods for full color printers now available include an electrophotographic method, an ink-Jet method, and a thermosensitive image transfer method. Of these methods, the thermosensitive image transfer method is most widely employed because of its advantages over the other methods in that the maintenance is easy and the operation is noiseless.
The thermosensitive image transfer recording method can be classified into two types, a thermal fusing image transfer method and a sublimation-type thermal image transfer recording method.
The thermal fusing image transfer type recording method is carried out by (i) superimposing (a) an image transfer sheet provided with an ink layer which comprises a thermofusible material and a coloring agent which is dispersed in the thermofusible material on (b) an image receiving sheet, and (ii) applying heat imagewise to the image transfer sheet to fuse the ink layer imagewise and to transfer the ink layer imagewise to the image receiving sheet, thereby recording transferred images on the image receiving sheet.
The sublimation-type thermal image transfer recording method is carried out by (i) superimposing (a) an image transfer sheet provided with an ink layer which comprises a sublimable dye or thermal transferable dye, which is hereinafter referred to a sublimable dye for simplicity, on (b) an image receiving sheet, and (ii) applying heat imagewise to the image transfer sheet to sublime or transfer imagewise the dye contained in the ink layer onto the image receiving sheet, thereby recording transferred images on the image receiving sheet.
The sublimation-type thermal image transfer recording method is generally more suitable for recording full color images than the thermal fusing recording method in view of the performance of faithful color tone reproduction by the sublimation-type image transfer recording method.
As the sublimation-type thermal image transfer recording method, a different running speed mode (n-times use mode) recording method is recently employed, in which both an image receiving sheet for sublimation image transfer (hereinafter simply referred to as the image receiving sheet) and a sublimation-type thermal image transfer sheet (hereinafter referred to as the image transfer sheet) are caused to run with the running speed of the image receiving sheet being made n (n&gt;1) times the running speed of the image transfer sheet in order to perform repeated multiple recording.
In the conventional sublimation-type thermal image transfer recording method, there is employed an image receiving sheet which consists of a substrate (paper, synthetic paper, plastic film, etc.) end a dye receiving layer formed thereon, which dye receiving layer comprises a thermoplastic polyester resin or the like, which can be well dyed with a sublimation-type dye.
The above image receiving sheet, however, cannot be smoothly released from the image transfer sheet after the thermal image transfer recording is completed. Especially, when the different running speed mode recording method is employed, a strong friction works between the image transfer sheet and the image receiving sheet when image recording is performed, so that the two sheets tend to stick to each other or to be damaged.
Furthermore, in the different running speed mode recording method, when an image receiving sheet including a dye receiving layer with a gel percentage of less then 70 wt. % is employed, the dye receiving layer tends to be easily fused so that high energy cannot be applied thereto and accordingly images with high density cannot be obtained.
On the other hand, when an image receiving sheet including a dye receiving layer with a gel percentage of 100 wt. % is employed, the dye receiving layer is not fused so that high energy can be applied thereto and accordingly images with a single color having high density can be obtained. However, it is difficult for the dye transferred to be dispersed in the dye receiving layer because of the high gel percentage of the dye receiving layer so that the transferred dye stays near the surface of the dye receiving layer. As a result, a first dye transferred to the image receiving sheet is transferred back to the image transfer medium, so that images with high density, particularly, black images, cannot be obtained by subtractive mixing.