Tech Briefs

Thermographic Printing Using Organic Silver Salts

Light-sensitive and light-insensitive materials generate black and white images by the use of heat; no ink is required.

The materials presented allow the writing on a single sheet of these materials without ink, but only by heat, thereby revealing a black and white image. This process is called thermographic writing or printing.

altThe patent portfolio presented here comprises patents on thermographic recording materials both for light-sensitive and light-insensitive materials. Light-insensitive materials can be used to write by heat only, such as by thermal heads. Light-sensitive materials can be imaged with UV or IR laser light, whereafter the image is revealed by heating. All materials are based on organic silver salts. Finally, the patents also cover protective layers on top of the materials, which can be transparent or not.

The materials presented here can be used for thermographic printing. Black and white images are obtained without the use of ink, but by the use of heat only, applied by digitally controlled thermal heads. The heat causes a chemical reaction to occur between an organic silver salt and a reducer, resulting in a black silver image. All reagents are present in the material, which does not need any processing after the thermal contact. The process is therefore dry, clean, and suitable for office or hospital environments. Another version of the materials can be imaged with light (UV, IR laser light), whereby the image is revealed after a heating step.

A first version of these materials is light-insensitive and requires heating only in the specific spots where a black image is required. This is achieved by the use of digitally controlled thermal heads in contact with the material. This thermographic writing is commercialized for the production of medical hard-copies, e.g. digital X-ray images can be written to a hard copy in this way. Other applications such as inkless printing of labels or tags or any other image are feasible.

The materials all contain organic silver salts, which react with a reducing agent under the influence of the heat applied, whereby black metallic silver is generated imagewise. All the reagents are present in a single sheet, and the sheet needs no further processing after the contact with the thermal heads.

A second version of these materials is light-sensitive and requires light (UV light, IR laser sources) to write the image, which is only revealed after heating the material. This is achieved by using light-
sensitive silver halide, if necessary sensitized to the light source (IR), which acts as a catalyst for thermal development of the organic silver salts present.

In this way, an image is formed only on the spots that were illuminated by the light source. Again, no wet processing step is required for the material, and the heating step is sufficient to show the desired image.

All these materials, light-sensitive or not, have a protective layer on top to prevent sticking to the thermal heads or damaging the chemical composition. To this end, coatings have been developed that may or may not be transparent, depending on the application.

This technology is offered by AGFA-Gevaert NV. For more information, view the yet2.com TechPak at http://info.hotims.com/28059-154.