Browse Prior Art Database

Long-Run Direct Master for Electro-Erosion Printer

IP.com Disclosure Number: IPCOM000119299D
Original Publication Date: 1991-Jan-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 3 page(s) / 118K

Publishing Venue

IBM

Related People

Afzali Ardakani, A: AUTHOR [+3]

Abstract

Offset printing plates can be fabricated using electro-erosion writing. The offset plate is made by coating on a water-resistant substrate (e.g., specially treated paper on plastics like MYLAR* a hydrophilic base coat comprised of a hydrophilic film forming resin and a hard pigment (such as silicon or aluminum) and a radiation absorbant, such as carbon black, graphite or organic dyes. The hydrophilic matrix must be crosslinked so that the dry film will not dissolve in water. The purpose of the hard pigment is to provide the necessary hardness and surface roughness to the base coat.

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Long-Run Direct Master for Electro-Erosion Printer

      Offset printing plates can be fabricated using
electro-erosion writing. The offset plate is made by coating on a
water-resistant substrate (e.g., specially treated paper on plastics
like MYLAR* a hydrophilic base coat comprised of a hydrophilic film
forming resin and a hard pigment (such as silicon or aluminum) and a
radiation absorbant, such as carbon black, graphite or organic dyes.
The hydrophilic matrix must be crosslinked so that the dry film will
not dissolve in water.  The purpose of the hard pigment is to provide
the necessary hardness and surface roughness to the base coat.  The
black pigments or dyes are included in the base coat so that after
evaporation of the metal onto the hydrophilic base coat and
electro-erosion writing, the image area (exposed black undercoat) can
be selectively treated to become hydrophobic and thus ink receptive.

      After electro-erosion writing two distinct regions are formed:
the image areas which are black and light (heat) absorbing and the
metallized non-imaged areas which reflect the light.  At this stage
both imaged and non-imaged areas are hydrophilic.  In order to render
the black images area hydrophobic and ink receptive, a transparent
thin substrate (polystyrene, polyester, etc.) is coated with a
hydrophobic thermoplastic resin and pressed onto the electroroded
plate in such a way that the coated side of the transparent substrate
(transfer sheet) faces the metallized surface of the plate and the
composite is passed through a thermofax machine (or illuminated with
intense incandescent light). Due to adsorption of the radiation by
the black imaged region of the recording sheet, these areas are
heated, causing the thermoplastic resin of the transfer sheet to melt
locally with subsequent reduction in velocity that facilitates its
release at the imaged regions. This renders the imaged regions
hydrophobic and, therefore, ink receptive.

      The non-imaged areas which have a hydrophilic aluminum surface
reflect most of the light and do not undergo an appreciable change in
surface temperature.  Thus, the contacting thermoplastic resin layer
of the transfer sheet remains unaffected and non-transferrable in
these areas. When the plate is run on the print press, the treated
image areas absorb the ink and the electroded image areas are printed
directly on the paper.  Although the aluminum layer of the non-imaged
areas is worn off after 500-l000 copies, the black composite base
coat underneath these areas is still hydrophilic and repels the ink.
Since the base coat is relatively thick, several thousand copies can
be reproduced using this long-run master.

      The transfer sheet composite has the following characteristics:
 a)  The thermoplastic resin coatings have a good release property
from the supporting substrate which can be polypropylene, low density
polyethylene, high density polyethylene or MYLAR.
 b)  The trans...