In lithography the printing and non-printing elements are on the very same level. The excellence of the printing areas is the fact that they are ink-accepting, and the non-printing plate areas are ink-repellent. This situation is created by physical, inter-facial surface phenomena.
Lithographic printing might be subdivided to:
- Stone lithography (straight printing technique utilizing a stone printing plate),
- collotype (direct printing method),
- Offset printing (indirect printing process), and
- Di-litho (direct printing process with offset printing plate).
Lithography was created by Alois Senefelder in 1796. The image to be printed was drawn on the stone by using a special ink. The stone was moistened right before it was up, after which the non-image zones of the stone surface did not take on ink.
Collotype is a second lithography technology. A light-sensitive level of gelatin is exposed on a glass base above a negative and after that developed. Parts having diverse swelling characteristics in relation to water are generated. When printing plate has been dampened, differentiated color shade absorption characteristics are produced. Just like stone lithography, collotype is only utilised for artistic printed products or services (and having very short print runs).
Offset printing is the greatest lithographic technology. It is an indirect lithographic technique, a situation where the ink is first transferred from the printing plate into a adaptable intermediate carrier – the blanket – and after that onto the substrate.
To get an ink-repellent result on the printing plate (distinctive interaction of printing plate surface and ink), there are two commonly utilised technologies :
– Conventional offset printing technology: Dampening of the printing plate with dampening solution (water along with additives). The dampening solution is put on the plate in a very thin film by dampening rollers. The non-image zones of the plate are hydrophilic, and that is, water-receptive additionally the ink accepting surfaces are oleophilic, and they are almost wholly unreceptive to water. The film of dampening solution inhibits the transport of ink. Because offset lithography is by far almost certainly the most widespread, the repellent result among the ink and dampening solution is regularly often linked to “offset printing”. For this cause, inking and dampening units are required for “offset printing.”
-Waterless offset printing technology: The printing plate surface is mainly ink-repellent, for instance, due to an appropriate layer of silicone. The ink-receptive base region is exposed by the deliberate interruption of the layer of silicone (nearly 2 microns thick). This processes is named “waterless offset” (very frequently as “dry offset”).
Suitable printing plates and special inks need to be used for each of these techniques.
The di-litho technology, a lithographic technology in which the printing plate prints directly onto the printing substrate, was uniquely created for newspaper printing. The benefit from this technology was that conventional letterpress rotary printing presses could be used. The printing units of these presses have been modified by the installing of a dampening unit. Printing was done with conventional printing plates, however a special coating needed to be applied to them because of the very high tension because of the direct contact with the paper and the high stability with the full print run necessary in newspaper printing. This technology only played short-time role. When new investment was made in newspaper printing organisations, this technical solution was altered by web offset presses, which print onto the substrate via a blanket cylinder.
Advantages of Lithographic Printing
- consistently high-image quality.
- much quicker and much easier production of printing plates.
- longer life of printing plates because they only come in contact with the printing blanket, which is much softer and less abrasive than paper.
- offset lithography gives most inexpensive production on excellent quality images in big quantities.
Disadvantages of Lithographic Printing
- expensive cost for small quantities.
- the image quality printed with offset lithography is excellent for commercial purpose however not as good as rotogravure or photogravure printing.
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