Cleaning and liquid contact with solids – Processes – Longitudinally traveling work of bar – strip – strand – sheet...
Reexamination Certificate
1999-04-06
2001-01-16
Stinson, Frankie L. (Department: 1746)
Cleaning and liquid contact with solids
Processes
Longitudinally traveling work of bar, strip, strand, sheet...
C134S020000
Reexamination Certificate
active
06174382
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to apparatuses and methods for cleaning printing ink and other materials from printing screens and frames used in screen printing, and specifically relates to low pressure-high volume water washoff for cleaning and reclaiming printing screens.
BACKGROUND OF THE INVENTION
Screen printing, also known as serigraphics, is the process of transferring an image to a substrate by the use of a printing screen through which ink is squeezed. The ink is then deposited in all places on the substrate except where the screen has been processed by a photographically applied image depicting the places where ink is not to be forced through the screen mesh. The images screen mesh is normally made of silk, plastic, or metal, and is held in place by a screen frame made of wood, plastic, or metal. The ink contains pigment or dye in an appropriate vehicle.
Screen cleaning and reclaiming requires the removal of all ink residue and emulsion (image, stencil or mould) from the screen and frame when the printing is completed. In that way, the screen may be reused for a different printing task. Methods currently utilized to clean printing screens involve spraying the screen with highly pressurized solvents and water from a nozzle or gun structure. Many such high pressure spraying techniques and apparatuses, however, require high power motors which deliver low amounts of water at very high pressures. The high power motors are expensive to purchase and maintain. Furthermore, such apparatuses generally require a long time to properly clean a screen, thus reducing efficiency and increasing the overall costs of the cleaning operation.
Several attempts have been made to develop a cleaning procedure and apparatus which efficiently and inexpensively cleans a screen. However, such attempts utilize high pressure spraying and therefore do not address the drawbacks of the prior art discussed above.
For example, U.S. Pat. Nos. 5,400,812; 5,223,041; 4,808,237; and 4,365,383 all disclose apparatuses and methods which utilize high pressure spraying at pressures of anywhere from 500 to 3,000 psi. Therefore, such devices will require expensive, high power pumps for delivering the necessary pressures.
U.S. Pat. No. 3,656,493 utilizes a single spray nozzle which is directed over one side of the screen by a control mechanism to spray a predetermined pattern. That is, each ink-removing step must be accomplished in a single station and requires monitoring to determine whether each successive step has been successful. As may be appreciated, such monitoring is time consuming and costly, and requires continuous worker supervision of the machine. Furthermore, the '493 patent does not address the problem of requiring high pressure spraying for cleaning of the screen.
Still further, U.S. Pat. No. 4,717,426 discloses a method of cleaning printing ink and printing mould wherein the ink and mould is loosened and thereafter flushed with high pressure water. U.S. Pat. No. 4,420,004 discloses an automatic printing screen cleaning apparatus which uses a high pressure water jet to remove the printing stencil. As such, existing devices have failed to address the drawbacks associated with high pressure and generally low volume spraying of screens for cleaning purposes.
Still further, many of the available apparatuses utilize single chambers which must be sequentially operated through the various different steps required to clean a printing screen. As such, screens can only be cleaned one at a time, and a cleaning process for the next successive screen cannot begin until the current screen has completed the cleaning process. As will be appreciated, the throughput for such devices is severely limited, thus reducing efficiency and increasing the overall cost of the screen cleaning process.
Additionally, various currently available screen cleaning apparatuses, as discussed above, also utilize a variety of different integrated systems which must be operably coupled together for proper screen cleaning. Such apparatuses utilize numerous adjustable or movable parts or elements that must be constantly maintained or replaced. Furthermore, as is the case with single chamber and single nozzle apparatuses, the operation of the nozzle must constantly be adjusted to provide proper coverage of the screen. The various separate systems which are coupled together for cleaning, as well as the large number of movable parts, increases the overall manufacturing and operating costs of the prior-art cleaning apparatuses.
Existing apparatuses also include elements or sections which must be constantly modified or adjusted to wash screens of different sizes. As may be appreciated, the necessity of adjusting or modifying the apparatuses for different size screens requires manual attention, and therefore, increases labor and operating costs. Additionally, the various adjustable mechanisms associated with such systems are more expensive to manufacture, thus increasing manufacturing costs.
Accordingly, and in view of the above background, there is a need for a screen cleaning and reclaiming apparatus which efficiently cleans a screen without the requirement of high water pressure for removing ink and other materials from the screen. There is also a need for a screen cleaning and reclaiming apparatus which does not require expensive, high power pumping equipment. There is also a need for an apparatus which reduces the time and manpower required for cleaning and reclaiming a screen and thus increases the throughput for the cleaning process and reduces the cost thereof. There is a need for an apparatus which is versatile, durable, reliable and which may be manufactured and subsequently used at a relatively low cost. Still further, it is desirable to have a screen cleaning and reclaiming apparatus that does not have to be repeatedly customized for different screen sizes. Further, it is desirable for such an apparatus to clean several screens in succession without requiring complete cleaning of one screen before another screen begins the cleaning process.
SUMMARY OF THE INVENTION
The above objectives and shortcomings of the prior art are addressed by the low pressure-high volume water washoff apparatus and process of the present invention. The apparatus comprises a cleaning device which defines a cleaning path wherein a screen is cleaned and reclaimed as it moves along the path. A series of low pressure-high volume water washoff stations are positioned successively along the path for cleaning and reclaiming the screen. More specifically, a washoff station for removal of ink and ink degradent is positioned along the cleaning path followed by a washoff station for emulsion removal downstream from the ink removal station, and a washoff station for degreaser removal further downstream along the cleaning path from the emulsion removal station. Each of the successive stations along the cleaning path directs a low pressure-high volume application of washoff fluid across the cleaning path to engage and wash a screen moving therealong. Preferably, water is used as a washoff fluid and is directed onto the screen from a row of nozzles positioned on either side of the path at each washoff station.
In accordance with the principles of the present invention, the nozzles deliver low pressure-high volume water washoff in the pressure range of approximately 40-400 psi with a water delivery rate of approximately 10-250 gallons per minute. Guide rails maintain the screen in a vertically upright position to intercept the low pressure streams or fans of water directed onto the screen by vertically positioned rows of nozzles at each station.
More specifically, a screen is positioned in the cleaning device on a conveyor element which moves along the cleaning path at approximately 12 feet per minute. After the screen is positioned in the screen loading area, it preferably passes by a row of nozzles which apply an ink degradent substance. Alternatively, the ink degradent substance might be manually applied to the screen. Following the applicat
Cord Albert B.
Cord Cameron W.
Jensen Gregory N.
Parr Ted K.
Intercontinental Chemical Corporation
Stinson Frankie L.
Wood Herron & Evans L.L.P.
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