Thermal transfer printing receiver sheet and method

Details Thermal transfer printing receiver sheet and method Thermal transfer printing receiver sheet and method

1994-06-06

1995-07-04

Hess, B. Hamilton

Record receiver having plural interactive leaves or a colorless

Having plural interactive leaves

428195, 428328, 428523, 428913, 428914, 430200, 430945, B41M 5035, B41M 538

Patent

active

054300037

DESCRIPTION:

BRIEF SUMMARY
This invention relates to a thermal transfer printing method and to an imaged receiver sheet produced by the method.
Thermal transfer printing is a printing process in which a dye is caused, by thermal stimuli, to transfer from a dyesheet to a receiver sheet. In such processes, the dyesheet and receiver sheet are placed in intimate contact, the thermal stimuli are applied to the dyesheet and the dyesheet and receiver sheet are then separated. By applying the thermal stimuli to pre-determined areas in the dye-sheet, the dye is selectively transferred to the receiver to form the desired image.
The thermal stimuli were originally provided by means of mechanical print heads incorporating small electrical heaters. More recently, however, the thermal stimuli have been provided by heat inducing light, for example a laser.
Receiver sheets conventionally comprise a substrate with a dye-receiving polar surface on one side, into which a dye is thermally transferable and retainable. Where the substrate is itself polar and capable of receiving a dye, the dye may be transferred directly to a surface of the substrate. However receiver sheets typically comprise a substrate supporting a receiver layer specifically tailored to receive the dye. Receiver sheets may also comprise a backcoat to impart desirable characteristics including improved handling properties and to provide for improved ease of lamination. It is known to use polar polymers, for example, polyester and polyvinyl alcohol/polyvinylchloride copolymer, in the receiver layer as such polymers provide for good dye compatibility.
By "polar polymers" we mean a polymer comprised of monomeric units which have a significant dipole moment.
Dye sheets conventionally comprise a substrate having on one side thereof, a dye layer comprising a thermally transferable dye dissolved and/or dispersed in a polymeric binder, which again is a polar polymer. Where heat inducing light is to be employed, it is necessary to employ a light-absorbing material which may be present in the dye coat or may be present in a separate layer preferably located between the dye coat and the substrate in order to allow absorption of the inducing light.
However, as the dyesheet and receiver sheet are in intimate contact during the printing process and high temperatures are employed, problems with the polar substrate or receiver layer ant the dyesheet bonding together at least temporarily, have been encountered. A consequence of this bonding is that further undesirable transfer of dye from the dyesheet to the receiver sheet may occur in addition to the desired dye transfer causing loss of tone control and, in extreme cases where other components of the dye coat transfer, production of a half tone rather than a continuous tone image.
This problem has been addressed by employing a further component in the receiver layer to act as a release agent to facilitate the separation of the polar surface of the receiver sheet and the dye sheet at the required time, thus reducing the risk of unwanted dye transfer. Examples of release agents include silicone polymers for example siloxanes.
The provision of a receiver layer on the substrate allows a release agent to be incorporated in the dye-receptive surface but may lead to an increase in the cost of production of receiver sheets. Further, the presence of a release agent as an extra component in a receiver layer may also complicate the formulation and coating of the receiver layer onto the substrate.
An increasing use of thermal transfer printing is in the preparation of prints from images generated by a colour video camera. Clearly , it is important that the quality of such prints be equal to that of prints provided by conventional silver halide photographic methods. In particular, a reflective optical density of at least 1.6 is required for commercial acceptance. In addition, it is advantageous if a thermal transfer print has the same feel as a photographic print.
It is well known that photographic prints are produced on paper having a surface coating of a polyol

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