Stock material or miscellaneous articles – All metal or with adjacent metals – Having composition – density – or hardness gradient
Reexamination Certificate
1999-09-29
2001-02-27
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Having composition, density, or hardness gradient
C428S687000, C428S472200, C101S459000, C420S551000, C420S552000, C420S550000, C420S548000, C420S529000, C420S528000, C420S537000, C420S538000
Reexamination Certificate
active
06194082
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a support for a lithographic printing plate, and particularly to a support for a lithographic printing plate in which electrolytically graining (surface roughened) pits are uniformly and efficiently formed by electrochemically graining treatment (i.e., electrochemically surface roughening treatment) to give excellent printing performance.
BACKGROUND OF THE INVENTION
Previously, aluminum alloy plates have been used as supports for lithographic printing plates, and graining treatment is applied to the aluminum alloy plates for imparting adhesion with light-sensitive layers and water retention of non-image areas. A method of the graining treatment (i.e., the surface roughening treatment) hitherto known include mechanically graining processes such as ball graining and brush graining, electrochemically graining processes of electrolytic solutions mainly composed of hydrochloric acid or nitric acid, and electrochemically graining processes of etching a surface of aluminum alloy plate with acid solutions. In recent years, a combination of the electrochemically graining processes and other graining processes has come to constitute the mainstream, because the roughened surfaces obtained by the electrochemically graining processes have homogeneous pits (unevenness) and are excellent in printing performance.
However, even the electrochemically graining treatment is low in treating efficiency or produce the difference in the forming state of pits to cause failure to obtain homogeneous roughened surfaces in some cases, depending on the aluminum alloy plates used.
Then, for improving the efficiency of electrochemically graining treatment and equalizing roughened surfaces, the aluminum alloy composition has been variously studied. For example, JP-A-9-316582 (the term “JP-A” as used herein means an “unexamined published Japanese patent application publication”) discloses an aluminum alloy plate containing 0.02% to 0.6% by weight of Fe, 0.03% to 0.1% by weight of Si, 0.04% to 0.1% by weight of Zn and 0.03% by weight or less of Cu, and having a concentration ratio of Zn to Fe (Zn/Fe) of 0.2 or more. Further, JP-A-9-279272 discloses an aluminum alloy plate containing 0.02% to 0.6% by weight of Fe, 0.03% to 0.15% by weight of Si, 0.005% to 0.05% by weight of Ti and 0.005% to 0.20% by weight of Ni, and an intermetallic compound of the above-mentioned elements having 20% to 30% by weight of Ni in addition to Al. Furthermore, JP-A-3-177528 discloses an aluminum alloy plate containing 0.03% to 0.30% by weight of Si, 0.1% to 0.5% by weight of Fe, 0.001% to 0.03% by weight of Cu, 0.005% to 0.002% by weight of Ga, 0.001% to 0.03% by weight of Ni and 0.002% to 0.05% by weight of Ti.
The alloy composition of surface layer portions (regions of from a surface to a depth of about several micron meters) of aluminum alloy plates has also been studied. For example, JP-A-10-204567 discloses an aluminum alloy plate containing 0.20% to 0.6% by weight of Fe, 0.03% to 0.15% by weight of Si and 0.005% to 0.05% by weight of Ti, wherein the Si concentration of a surface layer portion of from a surface to a depth of 3 &mgr;m is 0.01% to 0.17% higher than that of the whole plate, and the surface layer portion contains 0.05% to 0.2% by weight of Si.
However, when the aluminum alloy compositions are specified as described above, it is necessary to add effective elements such as Zn and Ni in large amounts for obtaining the desired effects. Further, the necessity of adding plural kinds of elements causes increased cost. Furthermore, when the Si concentration of the surface layer portions of the aluminum alloy plates is increased, ink stains are liable to occur in non-image areas to raise a problem with regard to image quality.
Further, in the electrochemically graining treatment, the size, form and distribution of pits formed varies depending on electrolytic conditions such as supply electrical quantity, so that it is also necessary to strictly regulate and control the optimum electrolytic conditions.
SUMMARY OF THE INVENTION
In view of such situations, the present invention has been made, and an object of the present invention is to provide a support for a lithographic printing plate in which uniform pits can be efficiently formed by electrochemically graining treatment, always independently of electrolytic conditions to give excellent printing performance.
The above-mentioned object is attained by a support for a lithographic printing plate of the present invention comprising an aluminum alloy plate containing 0.05% to 0.5% by weight of Fe, 0.03% to 0.15% of Si, 0.006% to 0.03% by weight of Cu and 0.010% to 0.40% by weight of Ti, wherein the Cu concentration of a surface layer portion of from a surface to a depth of 2 &mgr;m of the aluminum allowy plate is at least 20 ppm higher than that of a region deeper than the above-mentioned surface layer portion.
In the support for a lithographic printing plate of the present invention, the aluminum alloy plate used has the specified alloy composition, and the Cu concentration of the surface layer portion is at least 20 ppm higher than that of the region deeper than the surface layer portion. Accordingly, reaction starting points of the pitting reaction in the electrochemically graining treatment are sparsely dispersed, and even if the pitting reaction is continued to proceed, the growth of pits exceeding the necessity is inhibited to form uniform pits, because the Cu concentration is low in the region deeper than the surface layer portion. Moreover, such inhibition of the growth of pits is similarly performed, independently of electrolytic conditions.
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described in detail below.
In the supports for lithographic printing plates of the present invention, Fe is added in an amount of 0.05% to 0.5% by weight. Fe greatly exerts an influence on the strength of the supports. Accordingly, a content of less than 0.05% by weight results in the liability of plate breakage when the supports are attached as the lithographic printing plates to plate cylinders of printing machines (i.e., printing press), because of too low the mechanical strength thereof. In particular, when the mechanical strength is regarded as important, the Fe content is preferably 0.2% or more by weight.
On the other hand, a content of more than 0.5% by weight results in high strength exceeding the necessity to lead to poor fitness in attachment to plate cylinders of printing machines as the lithographic printing plates, which unfavorably causes the liability of plate breakage in printing. The preferred upper limit is 0.4% by weight. However, in the case of printing plates used for proof printing, the restrictions in terms of these fitness and strength become unimportant.
Si is contained in an Al base metal, a raw material, as an inevitable impurity, so that it is often intentionally added in trace amounts for preventing the variation due to the difference in content between raw materials. In that case, it has been known that too high the Si content results in the increased ration of Si existing in the form of the single substance Si, which causes ink stains to be liable to occur in non-image areas of the printing plates. In the present invention, when the Si content exceeds 0.15% by weight, the non-image areas become liable to stain.
On the other hand, 0.03% or more by weight of Si is already contained according to the raw material in some cases, a content of less than that is not realistic. Further, Si has the effect of forming Al—Fe—Si metal compounds to equalize electrolytically graining. Accordingly, a content of less than 0.03% by weight does not provide this effect. Furthermore, for maintaining a content of less than 0.03% by weight, expensive high-purity Al base metals are required, so that this is not realistic also from this viewpoint.
Accordingly, the Si content is from 0.03% to 0.15% by weight, and preferably from 0.06% to 0.10% by weight.
Ti is an element added for making finer a crystal st
Sakaki Hirokazu
Sawada Hirokazu
Boss Wendy
Burns Doane , Swecker, Mathis LLP
Fuji Photo Film Co. , Ltd.
Jones Deborah
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