Lithographic printing plate support, method of manufacturing the same, and presensitized plate

Abstract

A lithographic printing plate support in which surface unevenness due to surface treatment has been suppressed and a presensitized plate of excellent sensitivity are produced from an aluminum alloy plate containing iron, silicon, titanium and boron by specifying the state in which TiB2 particles are present in the surface layer and the width of the crystal grains, and by having specific indicators relating to the respective concentrations of iron and silicon in the surface layer following graining treatment fall within specific ranges. In a method of manufacturing the lithographic printing plate support, an aluminum alloy melt having specified alloying ingredients is subjected to a specified casting process to have the amount of the alloying ingredients in solid solution following cold rolling fall within specified ranges.

Description

[0001] The entire contents of documents cited in this specification are incorporated herein by reference. BACKGROUND OF THE INVENTION [0002] The present invention relates to lithographic printing plate supports obtainable using an aluminum alloy plate, and to presensitized plates for lithographic printing obtainable from such supports. The invention also relates to methods of manufacturing such lithographic printing plate supports and presensitized plates. [0003] Aluminum alloy plates are generally produced by using a semi-continuous casting process (direct chill casting) to cast a slab from an aluminum alloy melt, then subjecting the slab to homogenizing heat treatment, followed by hot rolling, cold rolling and, if necessary, annealing. [0004] To produce aluminum alloy plates continuously by a simpler process than semi-continuous casting, various continuous casting processes have been proposed which use a driven, or moving, mold that casts the plates directly from the aluminum allo...

AI Technical Summary

Benefits of technology

[0112] Most of the inadvertent impurities in the melt will originate from the aluminum ingot. If the inadvertent impurities in the melt are what is present in an ingot having an aluminum purity of 99.7 wt %, they will not compromise the intended effects of the invention. The inadvertent impurities may be, for example, impurities included in the amounts mentioned in Aluminum Alloys: Structure and Properties, by L. F. Mondolfo (1976).

[0113] The aluminum melt used in the continuous casting step contains at least 95 wt % aluminum, 30 to 5,000 ppm of iron, 300 to 2,000 ppm of silicon, and 1 to 500 ppm of copper.

[0115] Silicon is an element which is present in an amount of about 300 to 1,000 ppm as an inadvertent impurity in the aluminum ingot serving as the starting material for the aluminum melt. A very small amount of silicon is often intentionally added to prevent variations due to starting material differences. Part of the amount of silicon added enters into solid solution in the aluminum.

[0116] In the practice of the invention, the aluminum melt has a silicon content of preferably from 300 to 2,000 ppm. Generally, the stability of electrochemical graining treatment can be enhanced by increasing the amount of silicon to at least a given level. However, in the practice of this invention, by providing a lower limit in the amount of copper in solid solution which is based on the total amount of copper, an excellent electrochemical graining treatment uniformity is achieved even in a relatively low amount of silicon in solid solution. In the present invention, the amount of silicon is at least 300 ppm, and preferably at least 500 ppm.

[0117] The presence of too much silicon favors the formation of compounds with iron, which affects the amount of iron that enters into solid solution. Moreover, too much silicon will increase the amount of uncombined silicon. When anodizing treatment is carried out after graining treatment, the uncombined silicon causes defects to arise more easily in the anodized layer. Water retention at such defects is poor, and tends to result in scumming of the paper medium during printing. Accordingly, the amount of silicon in the invention is not more than 2,000 ppm, and preferably not more than 1,500 ppm. <Iron>

[0118] Iron increases the mechanical strength of the aluminum alloy, exerting a large influence on the strength of the support. In particular, it has a large heat softening resistance-enhancing effect. Moreover, although iron has until now been thought of as having relatively little influence on electrochemical graining treatment, when the amount of iron in solid solution is too small, the pits that are formed as a result of electrochemical graining treatment may undergo deformation.

Problems solved by technology

However, the inventors have made studies and as a result found that lithographic printing plate supports manufactured from aluminum alloy plates obtainable by these methods have surface unevenness caused by the surface treatment, and that presensitized plates manufactured from such supports have a poor sensitivity.

The inventors have made extensive studies to achieve the above objects and as a result found that the surface unevenness due to surface treatment in lithographic printing plate supports manufactured by continuous casting and the low sensitivity in presensitized plates produced using such supports are caused by factors having to do with the uniformity in the distribution of specific elements and the width of crystal grains at the surface of the aluminum alloy plate.

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