Direct thermal imaging method using a protected heat-sensitive r

Details Direct thermal imaging method using a protected heat-sensitive r Direct thermal imaging method using a protected heat-sensitive r

1996-05-02

1998-01-20

Hess, Bruce H.

Record receiver having plural interactive leaves or a colorless

Having a colorless color-former, developer therefor, or...

Heavy metal reactant

430338, 430567, 430608, 430619, 503202, 503226, B41M 528

Patent

active

057100950

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the invention
The present invention relates to a recording material suited for use in direct thermal imaging. More in particular the present invention relates to a recording material based on a heat induced reaction between a substantially light-insensitive organic silver salt and a reducing agent.
2. Background of the Invention
In thermography two approaches are known: of a recording material containing matter that by chemical or physical process changes colour or optical density. by transfer of a coloured species from an imagewise heated donor element onto a receptor element.
Thermal dye transfer printing is a recording method wherein a dye-donor element is used that is provided with a dye layer wherefrom dyed portions of incorporated dye is transferred onto a contacting receiver element by the application of heat in a pattern normally controlled by electronic information signals.
As described in "Handbook of Imaging Materials", edited by Arthur S. Diamond--Diamond Research Corporation--Ventura, Calif., printed by Marcel Dekker, Inc. 270 Madison Avenue, New York, N.Y. 10016 (1991), p. 498-499 in thermal printing operating with a thermal head image signals are converted into electric pulses and then through a driver circuit selectively transferred to the thermal printhead. The thermal printhead consists of microscopic heat resistor elements, which convert the electrical energy into heat via the Joule effect. The electric pulses thus converted into thermal signals manifest themselves as heat transferred to the surface of the thermal recording material wherein the chemical reaction resulting in colour development takes place.
The optical density of transparencies produced by thermal transfer of dyes or dye forming ingredients is rather low and in most of the commercial systems--in spite of the use of donor elements specially designed for printing transparencies--only reaches 1 to 1.2 (as measured by a Macbeth Quantalog Densitometer Type TD 102). However, for many application fields a considerably higher transmission density is asked for. For instance in the medical diagnostical field a maximal transmission density of at least 2.5 is desired.
High optical densities can be obtained using a recording material comprising on a support a heat-sensitive layer comprising a substantially light-insensitive organic silver salt and a reducing agent. Such recording material can be image-wise heated using a thermal head causing a reaction between the reducing agent and the substantially light-insensitive organic silver salt leading to the formation of a black image containing metallic silver. To obtain a good thermosensitivity heating is carried out by contacting the thermal head with the heat-sensitive layer. The density level may be controlled by varying the amount of heat applied to the recording material. This is generally accomplished by controlling the number of heat pulses generated by the thermal head. An image having a grey scale is thus obtained.
Because said recording material can yield a high-density image it is in principle suitable for use in medical diagnosis. However, it has been found that image deformations occur due to friction problems between the thermal head and the recording material. This problem could be solved by providing a lubricant e.g. a silicone oil in or on top of the heat-sensitive layer.
But even with the use of a lubricant uneveness of density arises in a number of successively printed images in which also white lines appear in areas that have to be completely black.
3. Summary of the Invention
It is an object of the present invention to improve the quality of images obtained by direct thermal imaging of a recording material comprising on a support in thermal working relationship (i) a substantially light-insensitive organic silver salt and (ii) a reducing agent.
A further object of the present invention is to provide a thermosensitive recording material suited for use in direct thermal imaging, wherein said material has in its structure a protec

REFERENCES:
patent: 3107174 (1963-10-01), Wartman
patent: 4741992 (1988-05-01), Przezdziecki
patent: 5424182 (1995-06-01), Horsten et al.

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