Browse Prior Art Database

High Optical Density Masterplate/Negatives for Offset Printing

IP.com Disclosure Number: IPCOM000036327D
Original Publication Date: 1989-Sep-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 3 page(s) / 16K

Publishing Venue

IBM

Related People

Hoekstra, JP: AUTHOR [+2]

Abstract

A technique is described whereby a fabrication process produces high optical density for negatives and longer life masterplates as used in electro-erosion printers and offset printing processes.

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 43% of the total text.

Page 1 of 3

High Optical Density Masterplate/Negatives for Offset Printing

A technique is described whereby a fabrication process produces high optical density for negatives and longer life masterplates as used in electro- erosion printers and offset printing processes.

Typically, electro-erosion writing utilizes electrical current sent through a resistive contact located between the writing electrode and a thin metal layer. The density of the electrical current is generally high so that the melting occurs rapidly, enabling the metal to be partially removed physically (boiling), as well as through evaporation. So as to obtain high current density, the contact area is made small, by roughing up the surface of the metal, to a point contact smaller than the diameter of the electrode. The metal layer is kept thin so that the writing process can take place. However, the optical density of this film is marginally sufficient to qualify the plate as a masterplate for offset printing.

Although the above process yields acceptable results for readable print, it has shortcomings when used for offset printing. Each dot removed in this fashion has an irregular shape and leaves residue in the center. The irregular shape causes a lack of resolution which must be compensated. The residue remaining in the center of the dot causes a change of density, which in turn effects the printing image. In order to obtain a clear dot, a mild etch cycle is generally required to remove the residue. This reduces the overall aluminum thickness, adversely affecting the optical image.

The concept described herein implements a multi-layered structure that can be applied to existing masterplate/negatives. Instead of depositing a single metal layer with a lubricant top layer, an oxide layer is deposited as an adhesion layer, followed by aluminum with an oxide layer on top and covered with an aluminum layer.

The plate used in the multi-layered structure consists of a smooth MYLAR* base coated with 100 angstroms of silicon monoxide, or tin oxide, to be used as an adhesion promoter for the next layer. Next, 400 angstroms of aluminum are deposited, followed by another 100 angstroms of silicon monoxide, or tin oxide. The resulting layer electrically insulates the 400 angstroms of aluminum, which is deposited next.

Instead of using a resistive contact, as was previously done, a capacitive discharge is created instead. The capacitive discharge takes place between the aluminum layers on top and underneath the oxide. The electrode makes contact with the top aluminum layer. When the charge has become sufficiently high under the electrode, the oxide breaks down, resulting in an electrical short, allowing current to flow (avalanche). The metal and oxide under the electrode are removed using the techniques of the previous process.

The capacitive discharge method is faster than the previously used resistance heated process and the area of contact is not of great significance now. Because the su...