Direct Thermal Printing

Increasingly there is a requirement for the printing of digital images in full colour. Whilst some progress has been claimed for direct thermal printing, e.g. the Thermo Autochrome from Fuji, the complexity of the multilayer papers means that they are very unlikely to ever compete effectively with inkjet printers. 

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Xanthene dyes are used as colour formers. These so-called fluorans usually contain amino groups sited para and meta to the central carbon atom. Such a substitution pattern gives rise to broad absorption bands and leads to almost black colour production the lactone 6.200 is a typical example. This xanthene derivative finds use in direct thermal printing [36]. The chemistry of fluoran leuco dyes has been reviewed [78]. 

Thermochromic dyes change color with temperature (heat). The effect may be due to a single dye or a composite system, and the color change may be reversible or irreversible. Thermochromic dyes find use in direct thermal printing and as temperature sensors, as well as in clothing and novelties. 

In direct thermal printing, a color former (colorless) and a developer (acidic) are brought into contact in the presence of heat, to... 

There are two main approaches to thermal printing, direct thermal and transfer thermography. Some examples of direct thermal printing were discussed, above, in the section on thermally developed silver systems. Current applications for this technology are for the most part... 

Thermal Printing. Thermal printing is a generic name for methods that mark paper or other media with text and pictures by imagewise heating of special-purpose consumable media. Common technologies are direct thermal thermal, ie, wax, transfer and dye-sublimation, ie, diffusion, transfer. Properties and preferred appHcations are diverse, but apparatus and processes are similar (87—89). 

A more recent application for silicas is in the specialty papers used for inkjet printing. Silica gels and precipitated silicas offer superior absorption of water-based inks, which allows for high resolution printing. Silica may be also found in high-quality direct thermal papers because of its superior insulation and absorption properties. 

E. Ozkol, J. Ebert, K.. Uibel, A.M. Watjen, and R. Telle, Development of High Solid Content Aqueous 3Y-TZP Suspensions for Direct Inkjet Printing Using a Thermal Inkjet Printer, 7. Ear. Ceram. Soc., 29,403-09 (2009). 

Photo/Thermal Reactions. The fifth basic class of photopolymer chemistry that can be used in commercial applications is based more on physical changes in a polymer-based matrix than on chemical reactions. A recent application of this technology is the laser ablation (77) of an organic coating on a flat support to directly produce a printing plate. The availability of newer high energy lasers will allow more applications to be based on the photo/thermal mechanism. 

The web passes the screen vertically into the drier above the drying or pre-gelling of the print is by means of hot air blown on both sides of the web, the air being heated by thermal oil or, more usually, by direct gas firing. The volume of air circulated and its temperature are controlled and can be varied. After drying or pre-gelling the web must be cooled so that it will not carry heat to the next screen, and this is done by passing it round two water-cooled cylinders. 

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