Printing – Planographic – Copying apparatus
Patent
1998-10-09
1999-12-14
Asher, Kimberly L.
Printing
Planographic
Copying apparatus
101170, 101153, 399168, 399115, B41L 700, B41F 900, B41F 110, G03G 1502
Patent
active
060003332
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION OF THE PRIOR ART
This invention relates to gravure printing and in particular to apparatus for use in a gravure press and for a method of gravure printing. Our European Patent Application No. 88304242.6, published as EP-A-0294042, discloses an electrostatic assist (ESA) gravure press, as illustrated in FIGS. 1 and 2 of the accompanying drawings, in which laterally spaced electrical contacts, contacting the surface of the impression roller, are used to supply an electric charge to the surface of the impression roller. Each of the electrical contacts comprises a multiplicity of deflectable electrically-conductive filaments, made for example from stainless steel. This represented an improvement on the arrangement previously disclosed in WO84/03068, in which there were laterally spaced stainless steel wiper blades, urged under spring action against the impression roller surface, instead of the bristles or other filaments, because there was less wear on the impression roller, and there was a lower build up of dust on the impression roller.
Such electrostatic assist systems apply an electric field across the nip of a gravure press unit, between the impression roller and the print cylinder. This electric field assists the transfer of the ink from the cylinder cells to the web. The impression roller has a conductive surface which is insulated from the roller core, and hence from the printing unit. The surface resistivity of the impression roller is critical in the successful implementation of the electrostatic assist system. A power supply is connected to the charge transfer mechanism, i.e. to the electrical contacts in the case of the system described in our European Patent Application No. EP-A-0294042 referred to above. It is this transfer of charge which raises the potential of the roller surface to a voltage suitable to produce and to maintain the necessary electric field at the nip. By suitable control of the power supply, the magnitude of the nip electric field can be controlled.
The impression roller in the printing press acquires a coating of the various contaminants, visible and invisible, present in such an environment. Among these could be dust from the paper and the ink and their constituents and from other sources. The roller surface can be permanently affected by such contamination and need re-grinding or similar processing to return it to its original condition.
The effect of this contaminant when no ESA printing is being done is negligible as the contamination tends to be evenly deposited over the roller surface and the impression roller pressure (the main influence on non-ESA print) is negligibly affected.
The application of ESA to a suitable impression roller contaminated as above would, again, be minimal. The slight variation in roller surface conductivity is easily compensated for in the ESA control system electronics.
This all assumes that the contamination is even over the surface. When this condition is not maintained a "pattern" may build up on the surface. Patterning on the surface of the impression roller is due to a non-uniform charge being applied to the surface as well as, in the case of a contact charge system, non-uniformity of the charge transfer contacts themselves. Again the non-ESA impression roller print is largely unaffected. Only when the contamination is particularly bad does this pattern transfer to the print.
However, because of this effect, ESA roller conductivity will vary locally across the surface corresponding with the pattern. As a result, when the ESA system is switched on, the ESA effect will vary locally across the roller surface reflecting the variation in roller surface conductivity. The effect of this is to induce, in the areas of greater or lesser ESA transfer, a developed pattern on the printed material.
In an ESA system the charge transfer mechanism itself contributes to the patterning on the roller surface, the resulting pattern reflecting discontinuities and unevenness in the charge transfer process.
OBJECTS OF THE INVENTION
Accordingly, the
REFERENCES:
patent: 4440082 (1984-04-01), Carey et al.
patent: 4494857 (1985-01-01), Ueno et al.
patent: 4697514 (1987-10-01), George et al.
patent: 4766460 (1988-08-01), Yamamoto et al.
patent: 4958563 (1990-09-01), Lewis et al.
Asher Kimberly L.
Presstech Controls Limited
LandOfFree
Apparatus for use in a gravure printing press does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus for use in a gravure printing press, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus for use in a gravure printing press will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-854343