Coating apparatus – Projection or spray type – With projector heating – cleaning or conditioning
Reexamination Certificate
2000-05-30
2003-04-08
Crispino, Richard (Department: 1734)
Coating apparatus
Projection or spray type
With projector heating, cleaning or conditioning
C118S612000, C118S050000, C239S139000, C239S424000
Reexamination Certificate
active
06544336
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to pressurized spray systems. Specifically, the invention relates to a spray system used to apply a polymer to the surface of a printing plate.
BACKGROUND OF THE INVENTION
In general, the surface of a commercial printing plate is coated with reactive materials. The layer of reactive material applied to the plate is capable of being imaged (frequently the imaging process involves laser light) and is also capable of retaining the image on the plate. The image bearing plate may subsequently be used in a printing press to impart the image onto a printing surface. Recently, “direct-to-press” technology has permitted printing plates to be imaged directly on the printing press. The reactive materials used to coat printing plates are typically light or heat sensitive polymers, which are sprayed onto the printing plate through some sort of pressurized spray nozzle. Throughout this application, the word “polymer” is used to describe the reactive material sprayed on a printing plate. However, the word “polymer” should not be construed in a limiting sense, as the invention would apply to any material used to coat printing plates. In addition, the spray nozzle that is the subject of this invention may be used to temporarily spray other materials used in plate preparation, such as cleaning agents, stripping agents, water and other chemicals. For simplicity, use of the word “polymer” should also be understood to incorporate these other materials temporarily sprayed on a printing plate surface.
Many types of spray nozzles exist in the prior art and they disclose various techniques for spraying different kinds of materials. U.S. Pat. No. 5,360,165 discloses a spray paint nozzle with a conical shroud, used to contain the sprayed paint, and a “recirculation mechanism”, used to reclaim leftover paint that does not adhere to the target surface. U.S. Pat. No. 5,441,201 discloses a liquid spray device for use in agricultural applications that is equipped with a shroud and uses hot air to break up conical sheets of sprayed liquid into droplets. U.S. Pat. No. 5,285,967 teaches a high velocity thermal spray gun for spraying high temperature melted powdered plastics, which also involves a shroud and a mechanism for cooling the melted powder down prior to reaching the target. U.S. Pat. No. 4,218,019 involves an “air shroud”, which contains the sprayed liquid and directs it toward the target. Finally, U.S. Pat. No. 5,057,342 discloses an apparatus for improving the feathering of the output from an “airless” spray nozzle. While these prior art inventions teach techniques that may be generally applicable to spray nozzles, none of them address concerns particularly related to the application of polymer to the surface of printing plates.
In order to ensure the quality of the printed image the application of the polymers to a printing plate must be “complete” (i.e. a coating on the entire imaging area of the plate) and “uniform” (i.e. a consistently even layer in all imaging areas of the plate). An additional consideration that is important to the spraying of polymers onto printing plates is the actual transfer efficiency of the spraying process. As the polymers used on printing plates are expensive, it is obviously beneficial to maximize the amount of polymer transferred from the nozzle to the plate and minimize the amount of wastage. These criteria of completeness, uniformity and transfer efficiency are most easily achieved when the polymer is sprayed in an atomized mist, in a fashion similar to commercially available “spray-paint” canisters. Unfortunately, the molecules of polymers used on commercial printing plates tend to become entangled with one another, making the polymer difficult to atomize, substantially reducing the effectiveness of conventional low-pressure spraying techniques. Accordingly, a spraying apparatus is required to obtain a complete, uniform coating of relatively entangled polymer on a printing plate with a high transfer efficiency.
In addition to the above requirements, the spraying of polymers onto printing plates involves a number of additional complications. Typically, the polymers used on printing plates are comprised of two or more reagents that must be mixed prior to spraying. The mixing process initiates a chemical reaction, similar to that of epoxy resin, which causes the polymer to cure and harden. Consequently, the mixing must be done immediately prior to spraying to avoid premature curing. In addition, any excess polymer that is mixed but not sprayed is wasted because it cures and is no longer sprayable. As such, an apparatus is required to mix the polymer's constituent reagents immediately prior to spraying in a manner that will minimize the amount of polymer that is wasted by being mixed, but not sprayed.
Excess wastage is also a problem when applying polymer to a plate that is already mounted on the drum of a printing press. This process is common in today's “direct-to-press” technology. Since part of the drum surface (referred to in this application as the “plate-mounting gap” or “gap”) is used to mount the plate and does not require a coating of polymer, any polymer sprayed into the plate-mounting gap is wasted. As such, an apparatus is required to minimize the amount of polymer sprayed into the plate-mounting gap.
A final consideration is the need for cleaning of the spray nozzle apparatus. If the polymer collects in the nozzle mechanism, it may cure and impair the functionality of the device. Consequently, an apparatus is required to facilitate the efficient cleaning of the spray apparatus.
SUMMARY OF THE INVENTION
The invention herein disclosed concerns an apparatus for a spray system operative to spray a substantially liquid polymer onto the surface of a printing plate. A fluid nozzle receives the polymer from the internal features of the spray system and ejects the polymer in a substantially liquid state. Surrounding the fluid nozzle, there is a conduit, which carries heated, high pressure air. The air heats the polymer, prior to its ejection from the fluid nozzle. The conduit also ejects the heated air, in such a manner that the air physically interacts with, and atomizes, the substantially liquid polymer, creating a mist of polymeric matter. The heating of the polymer by the air in the conduit makes it easier to atomize the polymer.
The apparatus also comprises a solid shroud surrounding the fluid nozzle and extending toward the printing plate. The shroud is equipped with at least one aperture attached to a vacuum source, such that the shroud, aperture and vacuum source act in combination to remove excess polymer that does not adhere to the printing plate. A fast shut-off valve, which controls the ejection of the polymer from the fluid nozzle, is located proximate to the fluid nozzle. In this manner, the amount of wasted polymer due to non-required ejection is minimized. The apparatus may also include a mixer operative to thoroughly and homogeneously mix the polymer from a number of constituent reagents. As with the shut-off valve, the mixer is located proximate to the fluid nozzle, so as to minimize the amount of the polymer, which is mixed, but not ejected.
Finally, the apparatus may comprise a cleaning mechanism. The cleaning system itself consists of a plurality of switches, which arrest the flow of the constituent reagents (if required) and permit at least one cleaning fluid to flow through (and simultaneously clean) the mixer, fast shut-off valve and fluid nozzle. The cleaning system also comprises a cleaning arm equipped with a source of vacuum suction. The cleaning arm moves, by either translation or rotation, between an active position (directly external to the fluid nozzle) and a non-intrusive position (out of the way, so as not to interfere with the ejected polymer). During cleaning, the cleaning arm is in the active position, directly external to the fluid nozzle. In this manner, the cleaning arm collects cleaning fluid, left-over polymer and any other materials ejected from the fluid nozzle.
Adv
Creo Inc.
Crispino Richard
Oyen Wiggs Green & Mutala
Tadesse Yewebdar T
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