Printing – Erasable plate
Reexamination Certificate
2001-05-03
2003-02-18
Funk, Stephen R. (Department: 2854)
Printing
Erasable plate
C101S458000, C101S467000
Reexamination Certificate
active
06520088
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a re-usable printing form with a printing surface, particularly for use in offset printing, and to a method for forming images on a re-usable printing form with a printing surface. An image is thus controllingly formable on the surface and erasable from the surface.
Lithographic printing is based upon exploiting the immiscibility of oil and water on a printing form; a lipophilic solution or a black or colored ink is retained by the image-forming regions, and the water or the hydrophilic solution is retained by the regions of the printing surface which do not form an image. When the suitably prepared printing surface is wetted with hydrophilic and lipophilic substance or solution, in particular water and black or colored ink, the regions not intended for image formation or imaging preferably retain the hydrophilic substances and repel the lipophilic substances, while the image-forming regions accept the lipophilic solution or black or colored ink and repel the hydrophilic substances. As a consequence, the lipophilic substance is then suitably transferred to the surface of a material whereon the image is to be fixed, such as paper, fabric, polymer, and the like.
For many years, aluminum has been employed as a base material for printing plates. Typically, the aluminum is first subjected to a granulation process and subsequently to an anodizing process. The anodizing serves to prepare an anodic oxide layer, the adhesion of which is improved by the granulation. The granulation enhances the hydrophilic properties of the background of the printing plate. In the anodizing process, a strong acid, such as sulfuric or phosphoric acid, is typically used, so that then by a further method, such as a thermal siliconizing process or so-called electrosiliconizing, the surface can be made hydrophilic.
The aluminum base or carrier is characterized by the fact that it has a porous, tear-resistant hydrophilic surface, which is quite particularly adapted to lithographic printing, especially in the case of long press runs. An additional use of hydrophilic barrier layers, especially comprising polyvinyl phosphoric acid, polyacrylic acid, silicates, zirconates, or titanates, is optional. A great many radiation-sensitive materials are known which are suitable for generating copies in the application of lithographic printing, as long as after being exposed to light and after a necessary or desirable development and fixing, they make an image region available that can be used for printing. For example, photopolymerizable substances can be used therefor.
The aforedescribed device is subjected to an image-forming or imaging exposure to light, by supplying energy selectively. This can be effected, for example, by an exposure to UV light through a mask, or by direct writing with a laser.
The lithographic printing plates of the aforedescribed type are conventionally treated with a developer solution, which is typically an aqueous alkaline solution with organic additives. The necessity for introducing considerable quantities of these substances and disposing of them has long been a special problem in the application of printing methods.
For this reason, for some time, efforts have been made to produce printing plates for which a wet-chemical developing process is unnecessary in order to create the image. To that end, ceramic oxides can be used, for example, in the form of coatings on a printing plate.
In the published European Patent Document EP 0 911 154 A1, TiO
2
and ZnO
2
are proposed as materials for the plate surface; they can be in ceramic form, either pure or also together with other metallic additives, in various mixture ratios. This surface is hydrophobic in the non-excited state and can be changed to a hydrophilic state by irradiation with ultraviolet light. By heating, this process of switching from one to the other can be reversed again. The imaging is then performed by illuminating the entire surface of the plate with ultraviolet light, and regions which are supposed to carry colored ink in printing are covered by a mask and film, respectively. For erasing the image, the image regions are thermally switched back or reversed, for example, with a laser beam.
U.S. Pat. No. 5,743,188 proposes the use of zirconate (ZrO
2
) in ceramically pure form or in a form provided with other additives as an active material in the surface. The surface is exposed pointwise or point-by-point to laser radiation or, in other words, melted, and as a result converted from a hydrophilic, stoichiometric state to a lipophilic, substoichiometric state. This conversion to the substoichiometric state is performed by ablation (removal) of small quantities of the surface of the ceramic. The printing form can be erased by thermally oxidizing the surface.
The use of ceramic oxides as a printing surface has considerable disadvantages, however. Because ceramic oxides are very much harder and more brittle than metals, stresses occur in and between the layers, which result in separation from the substrate, whether it is a metal foundation or a film, especially of a polymer. Bending of the substrate, in particular, can cause cracks and spalling.
Large-area ceramic oxide layers are produced by a relatively complex process. Standard methods, such as cathode ray sputtering and thermal vapor deposition, are performed in a high vacuum, which entails high costs and makes it difficult to achieve a high throughput of material. Deposition with the aid of pulsed laser radiation by the so-called PLD process (pulsed laser deposition) is limited to small substrate areas and is also again performed under vacuum conditions. In wet-chemical processes, such as the sol-gel process, for example, the components of the ceramic to be deposited are in dissolved form in a liquid, which is applied as a thin film. To expel the solvent afterwards, the layers are tempered. The requisite temperatures are above the melting point of aluminum, which is used as a standard base or foundation for printed originals, so that aluminum sheets cannot be coated in this manner. Layers that are applied by plasma spraying are at least several hundred micrometers thick and are too rough and nonhomogeneous to be used as a printing surface.
To be able to exploit special material effects of ceramic oxides, care must furthermore usually be taken that the ceramic is in the correct phase. Especially under thermal stress and when switching thermally back and forth between states, undesired phase transitions can occur.
Furthermore, in forming images on a zirconate surface by point-type ablation, indentations can remain behind in the image matrix even after the image has been erased. When the next image is printed, these indentations can be deleterious to the printed outcome, producing what is known as ghosting. The removal of material also means only a limited number of imaging processes will be possible.
Even more-economical printing with direct imaging printing presses, wherein the subject to be printed is imaged directly on a printing surface with the aid of a laser and CtP systems (computer-to-plate systems), respectively, require the use of a printing form which can be erased after the printing and whereon a new subject can be imaged again.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a re-usable printing form with a printing surface formed of a material having improved surface and processing properties, so that it is suitable for printing most varied images many times on the same printing surface. Costs are thereby lowered at the same time.
With the foregoing and other objects in view, there is provided, in accordance with one aspect of the invention, a re-usable printing form having a printing surface, comprising metallic titanium in the printing surface.
In accordance with another feature of the invention, the printing surface is on a carrier having therein at least one of aluminum, another metal, and plastic material.
In accordance with a further feature of the inve
Funk Stephen R.
Greenberg Laurence A.
Heidelberger Druckmaschinen AG
Locher Ralph E.
Stemer Werner H.
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