What is the principle of offset printing process?
The answer any printing professional would give is “Oil and water do not mix with each other readily”. Oil refers to the oil-based ink. Offset is a planographic process. The image areas and non-image areas lie on the same plane just that image areas are oleophilic (oil receptive) and non-image areas are hydrophilic (water receptive).The major task for the operator of an offset machine is to achieve the ink and water balance on the plate so that ink remains only on the image areas. If the water supply is low the ink will enter the non-image area whereas if it is high the ink leaves the image areas. So, it is critical to achieve an appropriate balance between ink and water.The water has to desensitise the non-image areas, clean the plate during the press starts, lubricate the plate and the blanket and control the emulsification of ink and water. Also, it must rapidly spread over the plate. Water requires certain additives like acid, desensitiser, buffering agents, biocides, wetting agents (alcohol), defoamers, corrosion inhibitors etc. to work efficiently on the plate. The composition of these additives and water (95-98%) is called a dampening solution or fountain solution.The dampening solution should have a pH value in the range of 4.8 to 5.5 and hardness level between 8o to 12o dH.Ideally fountain solution has to be used on the press but most printers use water alone. It not only affects the quality of impressions but also decreases the life of the plate.
In India, the suppliers for dampening solutions are TechNova Imaging Systems, Bromide Color Chemicals, Nulith Graphics, Newstech India, Bottcher India and Max Flex Imaging.
10 May 2013, Vol VI Issue 1
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