Printing – Planographic – Lithographic plate making – and processes of making or using...
Reexamination Certificate
1999-06-29
2002-03-12
Funk, Stephen R. (Department: 2854)
Printing
Planographic
Lithographic plate making, and processes of making or using...
C101S457000, C101S462000, C347S096000
Reexamination Certificate
active
06354209
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to methods for making lithographic printing plates. In particular, it relates to a method for directly making the lithographic printing plates by using hydrophobic polymer latex printing, which makes it possible to produce the lithographic plates directly from digital data output from computers, facsimiles, or the like without using any intermediate films.
BACKGROUND OF THE INVENTION.
Digitalization of information has made a rapid progress in recent years throughout the process from manufacturing a block copy, an upper stream process of printing, to manufacturing a printing plate, thereby putting to practical use for example, a photographic form system of characters, by which a block copy of manuscripts can be readily prepared, or a scanner which directly reads picture images. With this progress, there has arisen a demand for a direct plate-making method in which lithographic plates can be directly prepared from digital data output from computers, facsimiles, or the like without using a film for making printing plates.
As one example of the direct plate-making method, a method wherein an image or non-image portion is directly formed on a substrate by ink-jet printing is known to the art. The ink-jet printing system is a relatively rapid image output system and has a simple construction because it does not require any complex optical system. Therefore, the printing system makes an apparatus for making printing plates simple and the cost for making printing plates can be reduced since the maintenance labor is largely reduced.
As examples of the methods for preparing printing plates by using the ink-jet printing system, Japanese Kokai Publication 113456/1981 proposes the methods for preparing printing plates wherein ink-repelling materials (e.g. curable silicone) are printed on a printing plate by ink-jet printing. The printing plate obtained by this method is an intaglio printing plate in which the ink-repelling material formed on the surface of the substrate serves as a non-image part. As a result, the resolution of the printed images at shadow area or reversed lines is not so good. Moreover, a large amount of ink is needed in this method because the ink-repelling material must be deposited on the whole non-image part which occupies most of the surface of the printing plate.
U.S. Pat. No. 5,312,654 discloses a method for making lithographic printing plates comprising: forming an image on a substrate having an ink absorbing layer and a hydrophilized layer between the substrate and absorbing layer by ink-jet printing using a photopolymerizable ink composition, and exposing it to an active light in the wavelength region curing the image. The printing endurance of said printing plates is low.
EP-A- 533 168 discloses a method for avoiding ink spreading by coating the lithographic base with an ink absorbing layer which is removed after ink printing. This is an uneconomical and cumbersome method.
Research Disclosure 289118 of May 1988 discloses a method for making printing plates with the use of an ink jet wherein the ink is a hydrophobic polymer latex. However said printing plates have a poor ink acceptance and a low printing endurance.
OBJECTS OF THE INVENTION
It is an object of the invention to provide a method for making lithographic printing plates from a lithographic base having a hydrophilic surface image-wise imaged with a hydrophobic polymer latex which yields an excellent lithographic printing plate with a high printing endurance.
It is further an object of the present invention to provide a method for making lithographic printing plates without a wet development of the lithographic base in a rapid , economical and ecological way.
Further objects of the present invention will become clear from the description hereinafter.
SUMMARY OF THE INVENTION
According to the present invention there is provided a method for making a lithographic printing plate comprising the steps of dispensing in a predetermined pattern a latex of particles of a hydrophobic polymer onto an optionally modified hydrophilic surface of a lithographic base, characterized in that said hydrophobic polymer and the optionally modified hydrophilic surface of the lithographic base have mutually reactive groups.
DETAILED DESCRIPTION OF THE INVENTION
According to the present invention, the lithographic base may be an anodized aluminum support. A particularly preferred lithographic base is an electrochemically grained and anodized aluminum support. The anodized aluminum support may be treated to improve the hydrophilic properties of its surface. For example, the aluminum support may be silicated by treating its surface with sodium silicate solution at elevated temperature, e.g. 95° C. Alternatively, a phosphate treatment may be applied which involves treating the aluminum oxide surface with a phosphate solution that may further contain an inorganic fluoride. Further, the aluminum oxide surface may be rinsed with a citric acid or citrate solution. This treatment may be carried out at room temperature or may be carried out at a slightly elevated temperature of about 30 to 50° C. A further interesting treatment involves rinsing the aluminum oxide surface with a bicarbonate solution. Still further, the aluminum oxide surface may be treated with polyvinylphosphonic acid, polyvinylmethylphosphonic acid, phosphoric acid esters of polyvinyl alcohol, polyvinylsulphonic acid, polyvinyl-benzenesulphonic acid, sulphuric acid esters of polyvinyl alcohol, and acetals of polyvinyl alcohols formed by reaction with a sulphonated aliphatic aldehyde. It is further evident that one or more of these post treatments may be carried out alone or in combination. More detailed descriptions of these treatments are given in GB-A- 1 084 070, DE-A- 4 423 140, DE-A- 4 417 907, EP-A- 659 909, EP-A- 537 633, DE-A- 4 001 466, EP-A- 292 801, EP-A- 291 760 and U.S. PAT. No. 4,458,005.
According to another mode in connection with the present invention, the lithographic base with an optionally modified hydrophilic surface comprises a flexible support, such as e.g. paper or plastic film, provided with a cross-linked optionally modified hydrophilic layer. A particularly suitable cross-linked hydrophilic layer may be obtained from a hydrophilic binder cross-linked with a cross-linking agent such as a melamine-resin, formaldehyde, dialdehydes like glutaric dialdehyde glyoxal, polyisocyanate or a hydrolyzed tetra-alkylorthosilicate. The latter is particularly preferred.
As hydrophilic binder there may be used hydrophilic (co)polymers such as for example, homopolymers and copolymers of vinyl alcohol with as reactive functions hydroxyl groups, acrylamide with as reactive function an amide group, methylol acrylamide, methylol methacrylamide, acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxyethyl methacrylate, all with a hydroxyl function as reactive group, maleic anhydride with an anhydride as reactive group, maleic acid with a hydroxyl function as reactive group, maleic anhydride/vinylmethylether copolymers anhydride with an anhydride as reactive group. The hydrophilic binder can partially contain crosslinkable or reactive groups e.g. silanol modified polyvinylalcohol, vinylalcohol copolymer with crosslinkable acrylamides like N-(-methoxymethyl)-acrylamide, n-butoxymethyl acrylamide, n-butoxymethyl methacrylamide. The hydrophilicity of the (co)polymer or (co)polymer mixture used is preferably the same as or higher than the hydrophilicity of polyvinyl acetate hydrolyzed to an extent of at least 60 percent by weight, preferably at least 80 percent by weight.
The amount of crosslinking agent, in particular of tetraalkyl orthosilicate, is preferably at least 0.2 parts by weight per part by weight of hydrophilic binder, more preferably between 0.5 and 5 parts by weight, most preferably between 1.0 parts by weight and 3 parts by weight. The amount of cross-linking agent is not so high that no hydroxyl groups of the polyvinyl alcohol remain.
A cross-linked hydrophilic layer in a lithographic base used
Aert Huub Van
Oelbrandt Leo
Agfa-Gevaert
Breiner & Breiner L.L.C.
Funk Stephen R.
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