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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