Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making printing plates
Reexamination Certificate
2000-11-09
2002-07-02
Hamilton, Cynthia (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making printing plates
C430S273100
Reexamination Certificate
active
06413700
ABSTRACT:
FIELD OF THE INVENTION
The invention is directed to conventional and waterless printing plate intermediates that contain an imaging mask. The invention is also a method of imaging same using imaging devices. The method involves the direct formation of a resinous image pattern on a planographic plate employing digital image information and digitally driven printer heads.
BACKGROUND OF THE INVENTION
In conventional planographic printing, a printing plate bearing as oleophilic, ink receptive, image is first dampened with an aqueous fountain solution to prevent the ink from wetting the hydrophilic, non-image bearing, area of the printing plate. Afterwards, an oil-based ink is rolled over the pate to selectively coat the now printable image. Conventional planographic printing has a number of problems inherent to having both an oleophilic ink and an aqueous fountain solution conjoined on the same press. First, the fountain solution applied to the printing plate flows back into the train of inking rollers on the press, causing emulsification of the ink. Second, it is difficult to maintain control of the delicate balance needed between the amount of ink and the amount to fountain solution one needs to apply to the printing plate. Consequently, image fidelity and uniformity is difficult to maintain. Third, the fountain solution tends to flow forward over the offset cylinder, moistening the copy paper and causing it dimensional changes. Finally, in those cases where the printing is imaged directly by electrophotography, the plate must be subjected to an etching treatment which makes the printing operation more complicated.
Considerable effort has been applied in the industry toward the development of printing plates that overcome some of the foregoing problems. A significant portion of that effort has been directed toward the development of planographic plates that do not require a fountain solution circulating in the printing apparatus to accomplish the printing function. These printing plates are referred to herein as “waterless” is plates to distinguish them from conventional printing plates that employ aqueous fountain solution during printing operations. With waterless plates, the use of fountain solution is avoided by employing printing methods and plate compositions that do not rely on inducing hydrophilicity to a portion of the plate in order to distinguish the oleophilic image surface from the non-oleophilic non-image surface.
U.S. Pat. No. 4,342,820 teaches a negative working waterless plate that does not require dampening (i.e. fountain solution) for use in printing. The plate comprises a base substrate; a light releasing photosensitive layer, overlaying the base substrate; and a silicone rubber layer, overlaying the photosensitive layer. When the printing plate is exposed through a negative film and treated with a developer, only the silicone rubber layer overlaying the exposed photosensitive layer is removed, while the photosensitive layer remains as is to form the image area.
U.S. Pat. No. 3,894,873 teaches a positive working waterless plate comprising a base substrate; a light sensitive photoadhesive layer, overlaying a base substrate; and a silicone rubber layer, overlaying the photoadhesive layer. When the printing plate is exposed through a positive transparency and treated with a developer, only the silicone rubber layer overlaying the unexposed photoadhesive layer is removed, while the photoadhesive layer remains as is to form the image area.
The waterless plates described in the foregoing patents are contact speed as opposed to camera speed plates. The term “camera speed” indicates that the light-sensitive material is photographically sensitive enough to is permit imagewise exposure by focusing an original onto the light-sensitive layer of the printing plate forming material through an image-focusing lens system or other high sensitivity of digitized imaging devices. On the other hand, the term “contact speed” means that a light-sensitive material has sensitivity such that it can be exposed through a negative or positive transparency placed in contact with it. Camera speed materials are photographically sensitive to relatively low energy levels of light while contact speed materials require relatively high light energy levels for exposure. However, regardless of the speed or light sensitivity of the plate, photographic plate making is time consuming and requires the facilities and equipment adequate to support the necessary chemistry. To circumvent these shortcomings, a number of electronic or digitized alternatives to photographic plate imaging have been developed.
Lithography and offset printing methods have long been combined in a compatible marriage of great convenience for the printing industry for economical, high speed, high quality image duplication in small runs and large. Known art available to the industry for image transfer to a lithographic plate is voluminous but dominated by the photographic process wherein a hydrophilic plate is treated with a photosensitive coating, exposed via a film image and developed to produce a printable, oleophilic image on the plate.
While preparing lithographic plates by photographic image transfer is relatively efficient and efficacious, it is a multi-step, indirect process of constrained flexibility. Typically, a photographically presensitized (PS) plate is prepared from a hydrophilically surface treated aluminum. A positive or negative film image of an original hard copy is prepared and the pre-sensitized plate exposed to the film image, developed, washed and made ready for print operations. Any desired changes in the film image must be made by first changing the original hard copy and repeating the photographic process; hence, the constrained flexibility. As sophisticated and useful as it is to prepare plates by photographic image transfer, the need for a lithographic plate fabricating process that obviates the above problems associated with the photographic process has long been recognized. Clearly, it would be highly beneficial to the printing industry to directly produce a quality printable image on a plate without proceeding through a multi-step photographic process. It would also be highly efficacious if a process were developed whereby changes could be made in an original image in some predetermined manner without incurring the need to correct hard copy and repeat the photography, particularly if those changes could be made “on line”.
Progress in digital technology now enables printers to use direct to plate digital plate makers. The high speed of text printing provides considerable productivity improvements over the conventional analog mode of plate preparation. Digitally controlled devices alter the ink-receptivity of the plate in a pattern representative of the image to be printed. Electromagnetic radiation pulses produced by one or more laser or ink-jet sources that directly deposit ink repellent/accepting materials on the plate.
Image forming by digital computer aided design of graphical material or text is well known. Electronically derived images of words or graphics presented on the cathode ray tube (CRT) of a digital computer system can be edited and converted to final hard copy by direct printing with impact printers, laser printers or ink jet printers. This manner of printing or producing hard copy is extremely flexible and useful when print runs of no more than a few thousand are required but the print process is not feasible for large runs measured in the tens or hundreds of thousands of pieces. For large runs, printing by lithographic plate is still the preferred process with such plates prepared by the process of photographic image transfer.
It is known that digitized image information can be used in plate making wherein a film is made to express the image according to the image information digitization and an image is formed on the plate by exposure and development. While this method augments flexibility by permitting editing of a digitized image, the method does not overcome the problems associat
Hallman Robert W.
Pappas S. Peter
Shimazu Ken-Ichi
Zhu Hui
Hamilton Cynthia
Kodak Polychrome Graphics LLC
Ratner & Prestia
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