Printing – Planographic – Lithographic printing plates
Patent
1996-09-20
1999-10-19
Funk, Stephen R.
Printing
Planographic
Lithographic printing plates
101458, 101459, 101465, 427453, B41N 108, B41N 304, C23C 410
Patent
active
059670479
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a thermal process for applying hydrophilic ceramic layers to substrates for printing plates. Owing to the achievable surface topography, this hydrophilized substrate is particularly suitable for coating with photosensitive layers which can be converted into printing plates which, after exposure to light and development, give printing plates which have uniform topography, permit long print runs and ensure good transport of damping solutions.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The most frequently used printing plates for the offset printing process usually consist of a substrate on which a photosensitive layer is firmly applied. This layer is exposed to light, after which the nonimage part must be removed completely from the surface. By means of the hydrophobic layer which remains behind (image part), ink can be applied to the product to be printed, which however is ensured only when water is present in the region of the nonimage parts. The wettability with water (hydrophilic property) in the region of the nonimage parts is of decisive importance for a high-quality printed image. It is known that alumina has such properties.
2. Description of the Related Art
It is therefore obvious to use aluminum substrates, to roughen the latter in order to improve anchoring of the printed image and to oxidize the surfaces. Chemical or electrochemical processes, also in combination with mechanical processes, for roughening pure aluminum have been disclosed, for example, in DE-A-34 13 899.
The multistage processes require a uniform aluminum composition at the substrate surface in order to ensure that, in a controlled chemical process, a uniform surface topography free of grains is obtained. The disposal of the baths and of the resulting solid are to be regarded as negative factors.
German Auslegeschrift 1,300,579 has disclosed a process in which a plasma is generated by means of an electric arc between a heat-resistant electrode and a metallic substrate in an inert gas mantle, with the aid of which plasma printing plates are roughened with small amounts of waste, and the surface can be modified by adding materials in such a way that it has improved hydrophilic properties. However, this process is difficult to realize in practice since it is very dependent on the intensities of the transmitted arcs, which are determined by a plurality of factors.
German Auslegeschrift 2,348,717 has disclosed a further process for applying damping solution-conveying layers to printing plates for the offset printing process. Layers of sparingly soluble or insoluble carbonates, silicates or quartz are provided, said layers being applied to roughened substrates by the plasma-spraying process method and then being ground to produce the suitable roughness. The image area is obtained by partially removing the coating. However, this process is very expensive owing to the machining and the etching process for removal of the layer.
SUMMARY OF THE INVENTION
It was the object of the present invention to provide a thermal coating process for rendering surfaces hydrophilic, in which not only aluminum substrates but also other metals, such as steels and other nonferrous metals and alloys, or even plastics can be reliably treated and can be firmly coated. The residues are to be reduced to a minimum and should be obtained in such a form that they can be readily reused.
The object is achieved, according to the invention, by a process of the generic type which is stated at the outset and whose defining features comprise producing a surface roughness R.sub.a in the range from 0.3 to 1.5 .mu.m on the surface of the substrate film by mechanical microroughening in a first treatment step and then providing the substrate film with a durably firmly adhering hydrophilic coating by thermal-spraying processing of pulverulent oxides and/or oxidic mixtures and compounds having a mean particle size in the range from -40 to +1 .mu.m.
For the purposes of the present invention, stated particle sizes of the type from -40 to +1
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patent: 4526839 (1985-07-01), Herman et al.
patent: 4596189 (1986-06-01), Halpern et al.
patent: 5382964 (1995-01-01), Schneider
patent: 5432046 (1995-07-01), Wanat et al.
patent: 5454318 (1995-10-01), Hirt et al.
Bos Ulrich
Frass Werner
Jaculi Dieter
Kuhn Heinrich
Pliefke Engelbert
Agfa-Gevaert AG
Funk Stephen R.
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