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Admiral Explains: The basics of Litho Printing

Most people know that ink is involved in the lithographic printing process but not many know how that ink gets onto the paper.

So how does Lithographic printing work?

  • It’s based on the principal that ink and water don’t mix.
  • The graphics you provide are transferred onto a printing plate by a laser. The plates have a roughened texture, and are coated with a thermal emulsion.
  • The plates are then chemically treated to remove the exposed part of the emulsion from the plate.
  • When the printing plate is finished, the image area is rendered hydrophobic and grease receptive (so it repels water and attracts ink). The areas on the plate that are non-printed are rendered hydrophilic (they attract water but repel ink).
  • The plates are affixed on a cylinder on the press and they rotate.
  • Through each rotation the plate is passed over dampening rollers which flood the plate with water, which adheres to the rough surface, or negative parts of the image.
  • Then the plate is presented to rollers coated with ink, which adheres to the smooth or positive portions of the plate surface.
  • If at this point the image was transferred directly to paper, the paper would be dampened, so a cylinder with a rubber surface called a blanket is rolled over the plate. It squeezes the water away, but picks up the ink. In doing so, the image is transferred from the plate to the blanket, hence the term “offset” Litho.
  • The image is then transferred from the blanket to the paper.

If you would like to know more about the lithographic printing process and other processes used by the team at Admiral Design and Print please give us a call on 01933 44 34 55 or contact us.

Posted by The Admiral (not verified)

on

Fri 31st January 2014

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