The present invention relates to a thermal transfer receiving paper used in copier, printers and facsimiles by utilizing the thermal transfer method of thermal melting ink type. More particularly, it relates to a thermal transfer receiving paper useful for the cards or labels requiring high speed printing and high speed reading, such as passenger tickets, passes, airway tickets, POS labels, prepaid cards and the like.
Recently, accompanied with rapid developments in office automation and factory automation, copier, printers and facsimiles utilizing various recording methods such as electrography method and thermal transfer method have been used depending on each applications and, for example, widely used in CAD/CAM. Color materials are used for printing image in such a thermal transfer method and usually a color material is molten, vaporized or sublimed and transferred on a recording medium such as image-receiving paper, e.g., paper or film and thus an image is recorded on it by adhesion, adsorption or dyeing.
Among these recording methods, a thermal melting transfer method in which an ink film having a thermal melting ink layer constituted by color materials and waxes or resins is molten by the heat of a thermal head and the color material is transfered on a thermal transfer receiving paper to prepare a recorded image is noticed to be utilized in card papers such as passenger tickets, passes and airway tickets, labels such as POS labels and cards such as prepaid cards requiring reliability and security as it has advantages such that it requires only simple and compact equipments and is maintenance free. The thermal melting transfer method also has a feature that it can use plain papers as the recording medium.
However, even such thermal transfer method cannot give a satisfactory result when a plain paper is used as demands for full-color printing, high speed printing, clear image printing and higher resolution have been increased together with the improvement in the performance of the printing equipment in the same manner as in the other printing methods. For example, when the bar code on a label printed at high speed is read by a reader, if the image quality is poor and many missing of dots and discontinuity of line are observed, the bar code cannot be read in high precision and such a thermal transfer receiving paper fails. In tickets and cards combined with magnetic recording method, as the card is passed through an equipment including a magnetic head at a high speed and is used repeatedly for a long period, transferability and fastness become issue when the image transferred on the thermal transfer receiving paper is stained by rubbing and the ink is imperfectly transferred and the card becomes failed in its role.
For the purpose, a number of proposals has been made on the thermal transfer receiving paper. For example, they include a method in which the Beck smoothness of the surface of the image-receiving layer is specified (Japanese Laid-Open Patent Publication Nos. 133092 of 1982 and 187892 of 1984), a method in which a image-receiving layer containing specified emulsions and latices is provided (Japanese Laid-Open Patent Publication Nos. 158297 of 1986 and 158498 of 1986) and a method in which a image-receiving layer containing a specified pigment and binders such as polyvinyl alcohol and latex is provided (Japanese Laid-Open Patent Publication Nos.110489 of 1985, 192690 of 1985, 217289 of 1986, 266296 of 1986, 284486 of 1986, 32085 of 1987, 257888 of 1987 and 202293 of 1989). However, these conventional methods could not attain completely the improvement in ink transfer. Thus, they include difficulties including poor in representativity of edges of images and lack in the sharpness of images, peeling of the surface of the imaging layer together with the transfer ink by the pick during separating the ink film with the thermal transfer receiving paper in the thermal transfer process causing imperfect transfer of ink and discontinuity of line. Thus, at present no satisfactory printed image is yet obtained.
Also, recently gravure and offset printings are frequently made on the thermal transfer receiving paper and consequently the demands on the qualities such as smoothness and surface strength of the thermal transfer receiving paper and opacity have become more strict. Furthermore, there are troubles such as deterioration of the image quality due to the paper dust formed from the thermal transfer receiving paper and paper feeding or delivery trouble in the printer. The measures for eliminating these troubles are the pressing need of the hour.
An object of the present invention is to provide a thermal transfer receiving paper of high quality and high image quality which gives no transfer unevenness, nor discontinuity of line nor imperfect transfering of ink and is excellent in transferability and fastness of transferred image and has an excellent high speed printability to say nothing of full-color printing and also has an excellent printability.