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Method of Improving Press Life of Direct Offset Masters

IP.com Disclosure Number: IPCOM000119302D
Original Publication Date: 1991-Jan-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 2 page(s) / 67K

Publishing Venue

IBM

Related People

Afzali-Ardakani, A: AUTHOR [+4]

Abstract

Direct offset masters made by electro-erosion suffer from a problem which may usually be ignored in conventional photo-offset plates, namely severe wear of the plate surface during press operation. The wear process is associated with the non-imaged area, and manifests itself by the gradual uptake of ink in that region (scumming), until the point is reached where the print copies are judged unacceptable.

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Method of Improving Press Life of Direct Offset Masters

      Direct offset masters made by electro-erosion suffer from
a problem which may usually be ignored in conventional photo-offset
plates, namely severe wear of the plate surface during press
operation.  The wear process is associated with the non-imaged area,
and manifests itself by the gradual uptake of ink in that region
(scumming), until the point is reached where the print copies are
judged unacceptable.

      In direct masters the non-image area is associated with the
presence of a thin (20-30 nm) layer of aluminum which covers the
silica-in-binder baselayer.  When this aluminum layer is locally worn
away, the exposed hydrophobic base layer can accept ink.  The wear
process begins with tiny holes in the aluminum near the tops of the
"mountains" in the rough underlayer; these holes enlarge with
increasing wear until they are large enough to accept ink.  Depending
on press conditions, the tack of the ink used, and the stiffness and
morphology of the baselayer, between 2 and 5 thousand copies can be
expected before unacceptable scumming is observed.

      The fountain solution used in offset printing is acidic,
typically having a pH of about 4.  This environment can cause etching
of the aluminum film.  The aluminum removal proceeds faster on the
press in the presence of fountain solution, and is even faster when
ink as well as fountain solution is applied on the press in the
normal fashion for printing.

      Some imp...