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Long-Run Lithographic Plate without Development Step

IP.com Disclosure Number: IPCOM000103516D
Original Publication Date: 1990-Dec-01
Included in the Prior Art Database: 2005-Mar-18
Document File: 1 page(s) / 58K

Publishing Venue

IBM

Related People

Afzali-Ardakani, A: AUTHOR [+3]

Abstract

For the longest press runs, which comprise hundreds of thousands of copies, offset-lithographic plates are used which employ a thick metal substrate. The plate, which is usually made of aluminum, is put in intimate contact with a previously prepared photo-negative by use of vacuum, and is exposed to light through the photo-negative in a "plate-making machine". The metal plate is coated with a photosensitive layer so that, for "negative- working plates", the regions corresponding to light transmitted through the photo-negative become hydrophobic. The surface of these plates is specially roughened or "grained" for two reasons: 1. The developed hydrophobic regions are protected from wear on the press by the surrounding high peaks. 2.

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Long-Run Lithographic Plate without Development Step

      For the longest press runs, which comprise hundreds of
thousands of copies, offset-lithographic plates are used which employ
a thick metal substrate.  The plate, which is usually made of
aluminum, is put in intimate contact with a previously prepared
photo-negative by use of vacuum, and is exposed to light through the
photo-negative in a "plate-making machine".  The metal plate is
coated with a photosensitive layer so that, for "negative- working
plates", the regions corresponding to light transmitted through the
photo-negative become hydrophobic.  The surface of these plates is
specially roughened or "grained" for two reasons:  1. The developed
hydrophobic regions are protected from wear on the press by the
surrounding high peaks.  2. The channels associated with the rough
surface allow air to escape during pumpdown when the plate is being
readied for exposure.

      This conventional process can be modified so that the usual
photonegative is not used, but instead a special direct negative,
which is written under computer control by electro-erosion, is
employed.  This direct negative is placed in intimate contact with an
aluminum plate which is grained as usual, but which has a special
coating on it which permits avoidance of all wet processing
subsequent to exposure.

      One use of such a direct negative is its employment in a
conventional platemaking machine with a conventional photo- sensit...