Browse Prior Art Database

Dry Offset Masters by Electroerosion

IP.com Disclosure Number: IPCOM000119287D
Original Publication Date: 1991-Jan-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 2 page(s) / 102K

Publishing Venue

IBM

Related People

Cohen, MS: AUTHOR [+3]

Abstract

A conventional lithographic plate must consist of two kinds of areas: printing areas, which accept grease (ink) and repel water, and non-printing areas, which accept water and repel grease (ink). The wider the difference between the ink-grease activity of the image and the water-grease activity of the non-image areas, the better the plate and the easier it will run on the press. In conventional lithography, an aqueous fountain solution is used to prevent ink from wetting nonimaged areas of the printing plate.

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Dry Offset Masters by Electroerosion

      A conventional lithographic plate must consist of two
kinds of areas:  printing areas, which accept grease (ink) and repel
water, and non-printing areas, which accept water and repel grease
(ink). The wider the difference between the ink-grease activity of
the image and the water-grease activity of the non-image areas, the
better the plate and the easier it will run on the press.  In
conventional lithography, an aqueous fountain solution is used to
prevent ink from wetting nonimaged areas of the printing plate.

      Electroerosion printing can be used to make offset masters by
eroding selected areas of a thin conductive layer, typically,
evaporated aluminum film, in an electroerosion recording medium.
Usually, the medium contains a substrate or support layer, a base
layer, thin conductive layer, and a protective or lubricating
overlayer.

      In contrast with conventional lithography plates which require
a water-ink cycle, dry offset masters do not require the use of a
water-ink cycle on a printing press to define the inked regions,
thereby making press operations for high resolution printing easy.
Instead, the desired inked and non-inked areas are defined by
oleophilic and olephobic surfaces, respectively, that is by regions
of low and ultralow energies.

      Waterless printing masters with improved characteristics can be
obtained using electroerosion techniques where a lubricant overlay of
low surface energy is provided which comprises a silicone or
fluorocarbon polymer preferably containing a particulate conductive
material.  These materials have a large difference in wettability
between imaged and non-imaged regions with respect to oleophilic inks
and thereby permit high contrast printing.  This waterless printing
master typically comprises a support, a hard underlayer of an
oleophilic polymer, a layer of a conductive material, such as
aluminum, and the overcoat layer of a silicone or fluorocarbon
polymer containing a particulate conductive material.  These polymers
have sufficiently low surface energy and, accordingly, a low surface
tension, so that ink will not adhere thereto.  Therefore, non-image
(uneroded) areas are formed which inherently repel ink so that water
is not necessary during the printing process.

      The polymer surface layer is applied from dispersions of
fluorocarbon or silicone polymers, preferably with a...