Thermal Printing

Laser thermal transfer uses similar dyes, but a semiconductor infrared laser supplies the energy, which is converted to heat by an IR absorber in the transfer ribbon [7,10], 

The ultimate aim of D2T2 is application in digital photography [11], This could provide a multibillion-euro outlet. However, this market is being captured by photorealistic ink-jet printers because of their lower cost, versatility, and higher speed. 

Yellow Dyes. A yellow D2T2 dye is probably the easiest to obtain both in terms of color and properties. The leading transfer-printing yellow dyes for textiles, such as quinophthalones and azophenols, are inadequate, as are typical photographic yellows such as azamethines. Two of the most widely used dye classes are methine (12) and especially azopyridones (13) [7,11,12], 

Magenta Dyes. As for silver halide photography, a magenta dye is more difficult to produce than a yellow dye, both in terms of color and properties. Anthraqui-nones are the leading textile transfer-printing dyes, but these are red rather than magenta and are tinctorially weak (low print optical densities). However, they 

Black dyes are not normally used in D2T2. A black color is obtained by overprinting the yellow, magenta, and cyan dyes to produce a so-called composite black. 

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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). 

Thermal printing usually involves passing materials over a full-width array of electronically controlled heaters (a thermal printhead). This marks thousands of spots simultaneously, so pages print relatively quickly. Image data to control the printhead usually come from computer systems. Black-and-white and full-color systems are both practical. Color is slower and more cosdy to purchase and use, primarily because this involves three or four successive printing operations, one for each color used. 

H. Schofield, 5th Mnnual European ICG Conference on Thermal Printing Technology, Amsterdam, Nethedands, 1989. 

On-line pervaporation, 18 518 On-line probes, for fermentation, 11 39 On-line vapor permeation, 18 518 On/off feedback controllers, 20 691 Onstream analyzers, 20 682 On-tank leak detection systems, 24 311 Onyx thermal printing process, 19 321 Oocytes, retroviral infection of, 12 457 Oolitic limestone, 15 28 Opacification, colorants for ceramics, 7 344-345... 

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]. 

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. 

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. 

This topic is covered in detail in Section 5.6, but a brief mention of ink-jet printing is warranted in order to compare and contrast the colorants and technology to laser printing and thermal printing. 

R. Bradbury, Thermal Printing in Chemistry and Technology of Printing and Imaging Systems, P. Gregory (ed.), Blackie, London, 1996. 

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

Overprinting is usually carried out with one or other of the following printing processes hot foil stamping, flexographic, letterpress, tampon, thermal printing, and stamp debossing. 

Detail on printing and decoration as applied to planar surfaces such as paper and board can be found in many textbooks. However, the decoration and printing of packs, packaging materials and packaging components, many of which are non-planar surfaces, involves processes additional to the conventional ones. This chapter therefore briefly discusses these many processes, which continue to increase (comparatively recent additions include inkjet, laser and thermal printing). 

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