Various information processing systems have been developed as a result of the rapid changes which have taken place in the information industry in recent years. Methods of recording and apparatus compatible with new information processing systems have been developed and adopted. Thermal transfer recording methods use apparatus which is light and compact, has little noise, and has excellent operability and maintenance characteristics. Moreover, since thermal transfer also allow coloring to be achieved easily, these methods are widely used.
Thermal transfer recording methods can be broadly classified into two types, namely mass transfer types and dye transfer types. The latter case relates to a recording method in which a thermal dye transfer donating material (hereinbelow, "dye-donor") is constucted of a substrate with a dye layer containing dyes having heat transferability. The material is brought into contact with a thermal dye transfer receiving material (hereinbelow, "dye receptor"). The dye donor material is selectively heated with a thermal printing head provided with a plurality of juxtaposed heat-generating resistors. The heating is in response to an information signal defining a pattern or image. Dye from the selectively heated regions of the dye donor is transferred to the dye receptor and forms a pattern thereon. The shape and the density of the patern forms an image in accordance with the pattern and the intensity of heat applied to the dye-donor.
A dye receptor usually comprises a support coated with a dye receiving layer. The dye coming from the dye donor can thermally and properly diffuse into that layer. An intermediate layer, useful as cushioning layer, porous layer or dye diffusion preventing layer, may be provided between the support and the receiving layer.
The dye donor may be a monochrome dye layer or it may comprise a sequence of different colored and discrete areas of, for example, cyan, magenta, yellow, and optionally black hue. When a dye-donor containing said sequenced two, three or more primary color areas is used, a multicolor image can be obtained by sequentially performing the dye transfer process steps for each color. The dye receptors of the prior art are commonly manufactured by coating organic solvent solutions of polymers and other ingredients, involving expensive, polluting and hazardous processes. To reduce risks of fire, explosions and other accidents, special precautions and expensive manufacturing apparatus are needed in handling the organic solvent solutions used in that type of manufacture.
The image fastness given by the prior art dye receptors is quite limited and still not competitive with conventional photographic image fastness.
To bypass the use of organic solvents, JP Patent Appls. 57/137,191 or 60/038,192 claims dye receptors obtained by coating a blend of polyesters or vinylic latices that however still give the disadvantage of limited image fastness, including significant photofading.
European Appl. 363,989 describes dye receptors based on water soluble polymers in which polymeric dye accepting compounds are dispersed, and wherein said water soluble polymers are hardened by a hardening agent.
Similarly, JP Patent Appl. 02/025,393 describes dye receptors based primarily on polymer solutions as a primary binder and vinyl styrene or ethylvinylacrylate particles as a secondary ingredient.
EP 351,075 is another prior art example of aqueous dye receptors, using a silica dispersion and a melamine and formaldehyde condensation resin. In EP 300,505 a polyolefin latex is used to coat a receptor underlayer. The dye receiving layer is obtained by coating an organic solvent solution of polymer.
In JP Patent Appl. 61/266,296, aqueous receptors are obtained by using aqueous solutions of water soluble polymers such as polyvinyl alcohol or substituted celluloses as a binder for porous and non-porous fillers.
In JP Patent Appl. 63/315,283, aqueous solutions of polyvinyl alcohol and/or other water soluble resins are used as receptor binders. In EP 364,900 a polyester receptor layer is obtained by polycondensation of polyfunctional acids and alcohols and curing of the aqueous coated solution of reactants to crosslink them.
In DE 3,934,014 copolymers of styrene and acrylic compounds are used as latices for obtaining the underlayer. The dye receiving layer is coated over the latex underlayer.
JP 02/122,992 discloses a receiving layer comprising an aqueous solution or dispersion of polymeric resin in combination with silica particle and modified silicone oil, the layer having improved antisticking properties.
JP 01/038,277 discloses a composition for a receiving layer obtained from an aqueous dispersion of modified polyester containing hydrophilic groups.
In JP 01/004,391 aqueous latices with a Tg&gt;50.degree. C. are involved in the preparation of dye receptors in combination with colloidal silica.
JP 63/011,392 discloses an oil solution of resin dispersed in water and then coated.
In JP 62/238,790 a solution or dispersion of polyester having solubilizing groups is combined with a water solution or dispersion of resins and of crosslinking compounds to increase the adhesion of the receiving layer.
In JP 62/146,693 a latex is coated as an underlayer (cushioning layer) on which the receiving layer is coated.
Accordingly, there is at present continuous work to obtain aqueous dye receptors with improved qualities which reduce the above mentioned problems.