Printing – Planographic – Lithographic printing plates
Reexamination Certificate
2001-07-03
2002-12-17
Funk, Stephen R. (Department: 2854)
Printing
Planographic
Lithographic printing plates
C148S439000, C420S532000, C420S535000, C420S544000, C420S550000, C428S650000, C428S687000
Reexamination Certificate
active
06494137
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a support for a lithographic printing plate and a presensitized plate, particularly to a presensitized plate that can be processed into a lithographic printing plate having longer press life and higher resistance to dot ink stain and a support for a lithographic printing plate used for the presensitized plate.
BACKGROUND OF THE ART
Photosensitive lithographic printing plates using aluminum alloy plates as supports are extensively used in offset printing. Such lithographic printing plates are prepared by processing presensitized plates. Generally, the presensitized plate is made by graining the surface of an aluminum alloy plate, anodizing it, applying a photosensitive solution, and drying the applied coat to form a photosensitive layer. The presensitized plate is exposed imagewise, whereupon the exposed areas of the photosensitive layer change in physical properties. The photosensitive layer is then treated with a developer solution so that it is removed from the exposed areas (if the presensitized plate is positive-acting) or from the unexposed areas (if the presensitized plate is negative-acting). The areas from which the photosensitive layer has been removed are hydrophilic non-image areas and the areas where the photosensitive layer remains intact are ink-receptive image areas. Thus, presensitized plates are processed into lithographic printing plates using the changes in the physical properties of the photosensitive layer that take place upon exposure.
The lithographic printing plate is then mounted on the plate cylinder for printing. In printing, an ink and a fountain solution are supplied to the surface of the plate. The ink adheres only to the image areas of the plate and the image is transferred to the blanket cylinder, from which it is transferred to the substrate such as paper, thereby completing the printing process.
Aluminum alloy plates are conventionally grained by three known techniques, mechanical (e.g. ball graining and brush graining), electrochemical (electrolytic etching with a liquid electrolyte based on hydrochloric acid, nitric acid, etc.; this technique is also hereunder referred to as “electrolytic graining”), and chemical (etching with an acid or alkali solution). Since the plate surfaces prepared by electrolytic graining have homogeneous pits and exhibit better printing performance, it is common today. In order to produce further uniform grained surface, it is also common today to combine the electrolytic graining method with another method such as mechanical graining or chemical graining.
The nonuniformity of the roughened surfaces of supports for lithographic printing plates have considerable effects on press life and other parameters to the printing performance of lithographic printing plates. In order to deal with this problem, many proposals have been made that try to eliminate the nonuniformity. Particularly, in the electrochemical graining method, many proposals have been made try to produce uniform grained surface by changing the aluminum alloy composition of the plates and many proposals have also been made concerning the waveform and frequency of the power supply for electrolytic graining.
With a view to producing uniform grained surfaces on supports for lithographic printing plates, it has been proposed that streak occurrence be restrained and uniform graining by electrolytic etching be ensured by incorporating 0.05-0.1 wt % of Cu in an aluminum alloy support containing 0.05-1 wt % of Fe and 0.01-0.15 wt % of Si (JP-A-11-99763, the term “JP-A” as used herein means an “unexamined published Japanese patent application”).
According to another proposal, it is described that the Fe, Si and Cu levels in an aluminum alloy plate are adjusted to the ranges of 0.05-1 wt %, 0.015-0.2 wt % and ≦0.001 wt %, respectively, with the distributed elemental Si level in the metal structure being regulated to 0.015 wt % or more and the uniformity in surface graining by electrolytic etching, fatigue strength and burning characteristics are improved (JP-A-11-99764).
According to yet another proposal, it is described that the Fe, Si and Cu levels in an aluminum alloy plate are adjusted to the ranges of 0.05-1 wt %, 0.015-0.2 wt % and 0.001-0.05 wt %, respectively, with the distributed elemental Si level in the metal structure being regulated to 0.015 wt % or more and no streaks occur and uniformity in surface graining by electrolytic etching, fatigue strength and better burning characteristics are improved (JP-A-11-99765).
According to a further proposal, it is described that the Fe, Si and Ti levels in an aluminum alloy plate are adjusted to 0.20-0.6 wt %, 0.03-0.15 wt % and 0.005-0.05 wt %, respectively, with part or all of these elements forming intermetallic compounds and the number of the grains of said intermetallic compounds present on the surface and of a size between 1 and 10 &mgr;m being regulated to 1000-8000 grains/mm
2
and pits can be formed by a short period of electrolytic graining treatment without producing unetched areas and uniform pits can be formed by graining treatment even if they are shallow (JP-A-11-115333).
However, if the Cu content of aluminum alloy supports is zero or very small (≦0.001 wt %) as proposed in JP-A-11-115333 and JP-A-11-99764, supra, no deep enough pits are generated and the supports have short press life and low ink stain resistance. Also problematic is the micro-streaking (unevenness in the form of very fine streaks) that results from low Cu levels.
Conversely, if aluminum alloy supports contain Cu in large amounts (≧0.05 wt %) as proposed in JP-A-11-99763, there is no problem of “micro-streaking” which occurs in the case of low Cu content but, on the other hand, no uniform electrolytic graining can be achieved and “yet-to-be etched”, or undergrained, areas are prone to occur, leading particularly to poor ink stain resistance.
The aluminum alloy support proposed in JP-A-11-99765, supra has such a large content (≧0.015 wt %) of elemental Si (which is one of the forms in which Si occurs in aluminum alloy supports) that defects will readily develop in the anodized layer, leading to poor resistance to aggressive ink staining. The term “aggressive ink staining” will be explained later in detail and suffice it here to say that when printing is done with the occurrence of many interruptions, the non-image areas of the lithographic printing plate have so much increased ink receptivity on the surface that stain appears as spots or rings in the print (e.g. paper) and this stain is referred to as “aggressive ink staining”.
The Assignee previously proposed that an aluminum alloy support containing 0.05-0.5 wt % of Fe, 0.03-0.15 wt % of Si, 0.006-0.03 wt % of Cu and 0.010-0.040 wt % of Ti, with at least one of 33 elements including Li, Na, K and Rb being contained in an amount of 1-100 ppm and with the purity of Al being regulated to 99.0 wt % or higher, should be subjected to graining treatments including electrolytic graining so as to produce a support for lithographic printing plates that has been grained with high efficiency to give a very high degree of uniformity in the grained surface (JP-A-2000-37965).
This is not a prior art, but the Assignee filed Japanese Patent Application No. 11-349888 and taught that when the aluminum alloy support disclosed in JP-A-2000-37965, namely, the one containing specified amounts of Fe, Si, Cu, Ti and at least one of 33 elements including Li, Na, K and Rb, was modified by further incorporating a very small amount of Mg, a surface of a support for a lithographic printing plate could be uniformly grained by electrochemical graining, and also filed Japanese Patent Application No. 2000-91197 wherein an aluminum alloy support exhibits improved resistance to aggressive ink stain of the foregoing support.
However, according to these supports, if particularly sharply inclined portions locally exist on the wavy surface of supports, and when these particularly sharply inclined portions are located within non-image areas of the lithographic
Sawada Hirokazu
Uesugi Akio
Burns Doane , Swecker, Mathis LLP
Fuji Photo Film Co. , Ltd.
Funk Stephen R.
LandOfFree
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