January 2017
e-VIBES
January 2017
Role of water in printing
Invariably, in every press, quality of water is paid the least attention.‘ What is there in water’ is the casual attitude, because it is available and contributes the minimal addition to the cost. It is forgotten that usage of unsuitable water for the printing leads to high waste cost and produces bad reproduction. It is generally known that the water simply keeps the non-printing area clean. But the role played by water( Dampening) is highly complex. The water and dampening chemistry contributes to printing in the following ways:
Keeps the non-printing area clean
Retards wearing of the plates
Reduces the temperature of the plates and rollers.
Prevents rusting of the plates.
Prevents foaming.
Reduces the surface tension of the water.
Controls and stabilizes the ph and conductivity.
Prevents formation of fungal and bacteria in the water.
Keeps the non-printing area sensitized for long.
Sharpens the dots and hence ensures better printing.
Aids the ink to release from the plates and blankets.
Prevents emulsification.
For us to appreciate the importance of water and dampening solution let us see how the water with the solution achieves the above said assignments. The plate surface is impregnated with two different chemistries in the printing and non-printing areas. Though these two areas are different, in contrary to our belief, both the areas can accept both ink and water. If the plate is allowed to run too dry the ink can catch-up in the non-printing areas. This is because that if adequate water is not provided to wet the surface, the aluminum plate accepts water. Likewise water also wets even the image areas initially and the ink sits on the top of it. The difference is, in the non-image areas it spreads thinly and in the image areas it bleeds. This facilitates the ink to get released from the plate to off-set to the paper. However excess and strong chemistry of the dampening solution causes the printing areas water-receptive and“ blinds” the plate. Also ink release must happen quickly.( In web machines of even with modest speed, the time span for the water between reaching the plate and to the printing nip is just
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