1、中文 2490 字 Digital printing Phil Green Digital printing is currently the most rapidly growing print sector, and one which is opening up new possibilities of short-run color work. It is also enabling entirely different relationships between the purchaser and supplier of printed products and making pos
2、sible all kinds of new products. The conventional printing processes described earlier in this chapter are mature technologies. The technological development of these processes will continue, but will tend to deliver only incremental improvements in performance. Digital printing, by comparison, is s
3、till at an early stage in its development and will continue to develop rapidly, opening up new markets and making increasing inroads into the conventional process. In the medium term at least, it is highly unlikely that digital printing will entirely replace the conventional processes. This is for t
4、wo fundamental reasons: The cost of colorants used makes unit prices too high to compete on longer runs； Modern printing equipment is designed around production economies of scale, with high speeds, large formats and inline processes such as folding and coating, and it will be some time before manuf
5、acturers build digital presses that can compete on high production volumes. The strength of digital printing is therefore largely in shorter print runs. However, the short-run market is expanding fast as print runs for all types of product are falling, and new products are made possible by integrate
6、d digital production. A direct cost comparison between digital and conventional printing may not be relevant in every case as digital printing can often provide a better solution to a communication problem, adding value and generating savings elsewhere in the production cycle, for example, in admini
7、stration or distribution costs. This logic also applies to the print buyers when thinking of incorporating digital printing into their own operations, adding them to their existing design and prepress operations. To take a example in retailing, instore printing facilities linked to install and run t
8、han purchasing from external suppliers, but the marketing benefits may outweigh the additional costs. The point at which digital and conventional printing breaks even tends to be at a run length of around 1000 copies(more for black and white and less for color). Run lengths that do not fall automati
9、cally into the province of conventional or digital will be decided by the added value of the process: for digital printing this includes distributed printing and the ability to vary the image with each copy, while for conventional processes such as litho it will include the higher quality levels, th
10、e greater range of substrates that can be printed, and the availability of inline processes such as coating. Digital printing technologies Digital printers currently fall into four basic types: Page printers that print flat sheets of paper, usually in A4 format but sometimes up to A3 (these range fr
11、om desktop printers to high -speed copier/printers like DocuTech, and include high-quality continuous tone printers used mostly for proofs and presentation materials)； Large-format devices that print on continuous rolls, mainly for short-run posters； Overprinting heads for adding product codes (main
12、ly for packaging) that are mounted onto conventional presses or finishing equipment, or on packaging lines； Reel-fed machines that print at speeds comparable to conventional printing presses. A digital printer has two fundamental components: a marking engine that transfers colorant to the paper, and
13、 a front-end that prepares the data used to drive the marking engine. The front end will include a RIP and a memory buffer. The page data is transferred directly to the front end without the need for films and plates, so there are large potential savings in costs. Because the digital printing device
14、 is driven by data and requires no plates, the image can be changed for each successive print. This variable image printing concept has great potential interest to publishers and advertisers who are interested in tailoring their communications more closely to what is known about their audience, ofte
15、n in conjunction with sophisticated marketing databases. Digital printing systems that operate at high speeds or high resolutions require dedicated front ends and large memory buffers, but low-end devices such as desktop printers can make use of software-based printer drivers that sit on the users h
16、ost computer. The most widely-used technologies in marking engines are ink jet, laser and dye sublimation. Ink jet Ink jet printers deploy an array of nozzles to project ink droplets onto the paper surface. The nozzles are relatively cheap to produce, and wider arrays that can image a moving web of
17、paper are currently in development. Ink jet print heads are found in all the types of digital printer listed earlier, and dominate the large-format and overprinting markets. They can print on the widest range of substrates (including cheaper grades such as part mechanicals). Laser Laser printers tra
18、nsfer toner to the paper surface electro-statically. An image is created on a photoconductive surface by adding or removing an electrical charge, and toner is attracted to the charged areas on this imaging surface (laser printers are perhaps more accurately known as electrostatic printers, since other energy sources such as electron beams can also be used to alter the conductive properties of the imaging surface). Most systems use
