Printing – Planographic – Dampeners
Reexamination Certificate
1999-03-01
2001-12-11
Hilten, John S. (Department: 2854)
Printing
Planographic
Dampeners
C118S315000, C118S704000, C101S484000
Reexamination Certificate
active
06327974
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to printing machines and more particularly to a spray dampening system for a printing press.
RELATED TECHNOLOGY
In modern printing processes, including offset lithographic processes, a wetting solution and ink are applied to certain rollers of a printing press. The ink is subsequently transferred to a printed medium, such as paper. The wetting solution is applied in sufficient quantities to the rollers to facilitate the printing process and aid in proper application of the ink to the paper. The wetting solution, which is typically a water-based solution which repels the ink, adheres to blank portions of an image plate and helps prevent the application of ink to the blank areas.
Control of the amount and distribution of the applied wetting solution is critical. Insufficient wetting tends to encourage the ink to migrate to improper portions of the plate and thereby be transferred to corresponding areas of the paper which are not to be printed. Excess wetting results in waste which must be collected and removed from the system, and may even cause wetting of the paper to be printed. A smooth, even application of the wetting solution without excess is desirable.
Spray dampening systems, such as that described in Switall et al., U.S. Pat. No. 4,649,818, have been developed which employ solenoid-operated spray nozzles to apply the wetting fluid to a roller. The spray nozzles are typically arranged on a spray bar. Such spray dampening systems meter wetting fluid flow rates by cycling the solenoid-operated spray nozzles at various frequencies and duty cycles. The resulting periodic, non-continuous application of wetting solution to a roller results in periodic variations in the distribution of wetting solution on the roller. If the variations are too large, defects in the printed product may occur.
Two approaches have been attempted with prior dampening systems to reduce variations in the distribution of wetting solution on a roller. One approach increases the frequency of cycling of the spray nozzles to more closely approximate a continuous application of wetting solution to a roller. However, improvements achievable with this approach are limited, as it is difficult and expensive to increase the spray nozzle cycling frequency. This upper limit exists due to current nozzle technology and physical limitations. Also, higher spray nozzle cycling frequencies can lead to problems such as “misting” of wetting solution, resulting in its deposition in unwanted areas of the image plate. A second approach is to design and employ a dampener roll which filters out variations in the applied spray, producing a more continuous, uniform distribution of wetting solution. This approach may require unwieldy dampener rolls which are both difficult to package and prohibitively expensive.
SUMMARY OF THE INVENTION
The present invention provides a spray dampening device for a printing apparatus, the spray dampening device comprising a plurality of spray nozzles for applying spray bursts to a surface of a target of the printing apparatus. Each of the spray nozzles is cycled at a predetermined frequency and at an individual nozzle phase shift, the individual nozzle phase shifts being synchronized so that an effective frequency of spray bursts applied to the surface is greater than the predetermined frequency.
The present invention also provides method for spray dampening a printing device, the method comprising spraying a dampening solution in spray bursts through a plurality of spray nozzles to a surface of a target apparatus, and cycling each of the spray nozzles at a predetermined frequency and at an individual nozzle phase shift. The individual phase shifts are synchronized so that an effective frequency of spray bursts applied to the surface is greater than the predetermined frequency.
The present invention thus may provide increased effective dampening spray burst frequencies beyond limits approached by individual nozzles. Dampening system performance may be improved without the implementation of new individual nozzle technology. The benefits of a pulsed dampener system may be maintained while system performance approaches that of a continuous dampener.
REFERENCES:
patent: 4064801 (1977-12-01), Switall
patent: 4198907 (1980-04-01), Switall
patent: 4211258 (1980-07-01), Switall
patent: 4465714 (1984-08-01), Petro, IV
patent: 4469024 (1984-09-01), Schwartz et al.
patent: 4649818 (1987-03-01), Switall et al.
patent: 4708058 (1987-11-01), Smith
patent: 4815375 (1989-03-01), Switall et al.
patent: 4899653 (1990-02-01), Michl et al.
patent: 5038681 (1991-08-01), Hultberg
patent: 5887521 (1999-03-01), Nakamura et al.
patent: 35 45 535-A1 (1987-07-01), None
patent: 0 325 381 (1989-07-01), None
patent: 0 341 384 (1989-11-01), None
Belanger James Richard
Dawley Douglas Joseph
Grohusky Leslie J.
Heidelberger Druckmaschinen AG
Hilten John S.
Kenyon & Kenyon
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