Reference Book
Gravure printing unit
Gravure printing unit comprises of the printing cylinder running in a trough of
ink, a rubber immersed roller and a doctor blade to remove excess ink from
the surface of the cylinder.
Printing cylinder :- are generally one piece continuous cylinder containing
recessed screened image which has been produced either by etching or
engraving. The cylinders are designed to easily removable for quick change
over and to enable the cylinders to be proofed, prior to printing and whenever
necessary, stored for future use. At each unit the cylinder is immersed in the
ink fountain. As the cylinder turns, its tiny ink cells get filled with ink.
Impression cylinder :- An impression cylinder which is made up of rubber,
neoprene or other synthetic products usually applies pressure to transfer the
ink to the substrate.
Ink duct :- It is a part of complete circulating system where ink is pumped to
the tray from a bulk supply and surplus ink returned filtered and adjusted for
solvent balance, then repumped to the cylinder. The entire system should be
enclosed as far as possible to ensure cleanliness of the ink and to avoid
evaporation.
Doctor blade :- It is a thick blade made of stainless steel or plastic set at twenty
degree angle with the cylinder. Doctor blade is prepared to ride on the surface
of the printing cylinder and remove surplus ink without damaging the surface
of the printing image.
Electrostatic assist :- To improve the ink transfer to the substrate especially
when the surface is hard or has poor ink receptivity a power source feeds
electrical charges between the impression roller and the printing cylinder which
create a force that helps to release ink from the etched cells. This process is
called electrosatic assist.Cylinder preparation methods
Transferring the image to the cylinder is accomplished using electromechanical
engraving and laser beam engraving methods.
Electromechanical method :- Direct digital electromechanical engraving
produces the most reliable cylinders for the press. In this method the cylinder
is prepared using scanned data to drive an engraving machine. The scanner
and the engraver are electronically linked. The scanner reads the original copy
and converts it to electronic pulses and transfer it to the engraver. The engraver
prompts a diamond stylus cutting tool or a laser device to form tiny wells on
the image carrier surface.