Xerographic Devices

Attempts to transfer and so print images have been made previously. In the past there has not been a successful attempt to provide a single universal material, which can be used both in xerographic photocopiers, laser printers and the like and also permit transfer of full-color images from one surface to another without the use of intermediate means, such as adhesive materials and without loss of definition or color tones or image quality. 

With state of the art copiers and laser printers, it is possible to produce mirror images in the copiers themselves and for those mir- 

A transfer material has been developed for transferring monochrome and full-color images produced by a xerographic process or a dry toner printing onto a substrate. The process requires the use of a film from TPX as the transfer material. This material is used to transfer the xerographic or dry toner image onto the substrate with the application of heat and pressure (27). 

It has been discovered that the use of TPX not only allows the problem of distortion to be overcome, but also allows transfer of full-color images to be effected directly or indirectly from a photocopier or printer onto any desired suitable surface. 

The use of TPX permits complete transfer of the toner from its initial carrier onto many other surfaces including of paper, card, cardboard, all of which may be uncoated or coated with many different types of finish, and of glass, ceramics, woods, metals, plastics, etc. TPX has sufficient thermal stability to be useful within the range of temperatures at which the material can be used for effecting image transfer. 

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Law, K. Y, Tarnawsky, J. I. W. and Popovic, Z. D. (1994). Azo pigments and their intermediates—a study of the structure-sensitivity relationship of photogenerating bisazo pigments in bilayer xerographic devices. J. Imag. Sci. Technol, 38, 118-24. [204]... 

Use In xerographic devices from PCs to high speed lasers, color copies, and latest digital multifunction machines. 

The absorption, emission, and redox properties of squaraines make them highly suited for applications as photosensitizers. In view of this, the early studies on squaraines were focused on thin photovoltaic and semiconductor photosensitization properties [1,4,5,91-97], Champ and Shattuck [98] first demonstrated that squaraines could photogenerate electron-hole (e-h) pairs in bilayer xerographic devices. Subsequently, extensive work has been carried out on the xerographic properties of squaraines [2,24,34,47,48,99,100], and these properties have been reviewed recently [11]. In an extensive smdy on the correlation s between cell performance and molecular structure in organic photovoltaic cells, squaraines were found to have much better solar energy conversion efficiencies than a variety of other merocyanine dyes [4,5]. 

The xerographic gain (fj) is defined as the quantum yield of e-4i pair formation after illumination of the xerographic device and can be expressed as [40] ... 

Figure 10.9 shows a typical spectral response curve of a phthalocyanine based xerographic device. It exhibits flat and high photoresponses from 600 to 850 ran. The sensitivity between 450 and 550 nm is rather poor due to the lack of optical absorption. On the... 

The xerographic properties of squaraines are summarized in Table 10.4. Although all the results were obtained from bilayer xerographic devices, quantitative comparisons should be exercised with caution because they were obtained from different laboratories. Similar to phlhalocyanines, impurities are shown to be responsible for the dark decay variation too [142]. The structural effect on the photosensitivity is quite large Eo s values ranging from 2.9 to 1000 ergs/cm are observed. Factors that may contribute to the sensitivity variation are impurities, particle size, morphology... 

The photoconductivity of USq-5 to -15 have been studied in bilayer xerographic devices [179]. Although fabrication effect, purity and hole-injection efficiency have been shown to be important factors that influence the photoconductivity, USq-13 was identified as the most outstanding squaraine so far. Specifically, USq-13 is shown to have a low dark-decay value (—15 V/s) and high sensitivity in xerographic devices, where Eo values of 3.1 and 1.9 ergs/cm at 600 nm and 790, respectively, are obtained [181]. The sensitivity appears to surpass all squaraines reported in the literature (Table 10.4). In fact, the sensitivity performance of USq-13... 

Data obtained from bilayer xerographic devices the CGLs are fabricated by a vacuum-deposition technique, 0.1-0.3 pm. White light exposure, 400-700 nm. 

Figure 10.21. Spectral response curves of perylene pigments XlXb and XXa in bilayer xerographic devices. (Reproduced from ref. 235, Copyright 1989, The Society for Imaging Science and Technology.)...

In a bilayer xerographic device such as that shown in Figure 10.3, excitation of the photoconductor formally results in the generation of e-h pairs in the CGL. The... 

Figure 10.28. A proposed photogeneration mechanism for phthalocyanine photoconductors in bilayer xerographic devices.

Figure 10.34. Plot of the quantum yield of photogeneration for trisazo pigment XVI in bilayer xerographic devices as a function of the oxidation potential of the charge transporting molecule. (Reproduced from ref 329, Copyright 1993, The American Chemical Society.)...

One of the key parameters in the photodischarge of a xerographic device is the residual potential (Fr). A high Fr value lowers the contrast potential of the photodischarge process, which leads to low image-development latitude and poor copy quality. More significantly, electrons of space charges that remain in the device... 

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