Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Treating substrate prior to coating
Reexamination Certificate
2000-04-21
2003-03-18
Wong, Edna (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Treating substrate prior to coating
C205S208000, C205S209000, C205S213000, C205S214000, C205S219000, C205S220000, C205S324000
Reexamination Certificate
active
06533917
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for producing an aluminum support which is used as a support for lithographic printing plates.
The present invention also relates to a method for producing an aluminum support, including surface roughening of an aluminum support which is used as a support for lithographic printing plates, more specifically, the present invention relates to a method suitable for the surface roughening of an aluminum plate prone to generation of rush mat-like wrinkles called streaks ascribable to the difference in the orientation of crystal grains or generation of granular treatment unevenness called plane quality unevenness, which are readily occur in conventional chemical etching treatments.
Furthermore, the present invention relates to a method for producing an aluminum support for lithographic printing plates, which can attain uniform surface roughening of an aluminum plate containing many impurities and having bad graining property.
BACKGROUND OF THE INVENTION
The surface roughening of an aluminum support for lithographic printing plates is generally performed by an AC etching method where an ordinary sinusoidal AC current or a special alternating waveform current such as rectangular waveform current is used. Using a suitable electrode such as graphite as a counter electrode, the surface roughening of the aluminum plate is usually performed by a single treatment. However, the depth of pits obtained is generally shallow and the resulting aluminum support has a short press life. Therefore, various methods have been heretofore proposed so as to obtain an aluminum plate having a grained surface suitable for printing plates, where pits having a depth larger than the diameter thereof are uniformly and densely present. Known examples of these methods include a surface roughening method using a special electrolytic power source waveform (see, JP-A-53-67507 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”)), a ratio between the quantity of electricity at an anode time and the quantity of electricity at a cathode time in an electrolytic surface roughening using AC (see, JP-A-54-65607), a power source waveform (see, JP-A-56-25381), a combination with the quantity of current passed per the unit area (see, JP-A-56-29699).
On the other hand, with respect to the method for producing an aluminum support, an aluminum support prepared as follows has been used as a support for lithographic printing plates. An aluminum ingot melted and held is cast into a slab (thickness: from 400 to 600 mm, width: from 1,000 to 2,000 mm, length: from 2,000 to 6,000 mm). The slab obtained is subjected to a surface-cutting step where an impurity structure portion on the slab surface is cut off by from 3 to 10 mm using a surface cutting machine and then to a soaking treatment step where the slab is kept in a soaking pit at a temperature of from 480 to 540° C. for from 6 to 12 hours so as to remove stress inside the slab and make the structure uniform. Thereafter, the slab is hot-rolled at a temperature of from 480 to 540° C. into a thickness of from 5 to 40 mm and then cold-rolled at room temperature into a predetermined thickness. Furthermore, in order to have a uniform structure, the slab is annealed, thereby homogenizing the rolled structure. The thus-treated slab is then subjected to cold rolling into a predetermined thickness and corrected to obtain a plate having good flatness.
From the standpoint of energy savings and effective use of resources, it is demanded to use, as an aluminum support for lithographic printing plates, a general-purpose aluminum plate or an aluminum plate prepared by omitting the intermediate annealing treatment or soaking treatment from the production process of the aluminum plate.
However, when an aluminum support for lithographic printing plates is prepared using the above-described aluminum plate, streaking or treatment unevenness called plane quality unevenness is readily generated. This is considered to occur because the aluminum dissolving rate varies depending on the crystal orientation in the progress of a chemical dissolution reaction or the reaction of aluminum varies depending on the crystal orientation in the progress of electrochemical pitting reaction.
In other words, irregularities formed due to the difference in the dissolving rate in a chemical dissolution reaction or variations in the pitting reaction (e.g., number of pits, difference in the size) depending on the crystal orientation are viewed as streaking or plane quality unevenness.
SUMMARY OF THE INVENTION
The present invention relates to a method for producing an aluminum support for lithographic printing plates, which is free from generation of failures called streaking or plane quality unevenness, and also relates to a method for producing an aluminum support for lithographic printing plates, which is improved in the surface shape.
Furthermore, the present invention relates to a method for producing an aluminum support for lithographic printing plates, which has a surface shape free from generation of failures called streaking or plane quality unevenness.
Still further, the present invention relates to a method for surface roughening a lithographic printing plate aluminum support having an improved surface shape free from generation of failures called streaking or plane quality unevenness, and also relates to a method for producing an aluminum support for lithographic printing plates.
As a result of extensive investigations, the present inventors have found that when an aluminum plate subjected to an electrochemical surface roughening treatment, which is in a state such that smuts mainly comprising aluminum hydroxide are formed on the surface, is heat treated, streaking is difficult to occur in the afterward etching treatment.
Furthermore, the present inventors have found that when an aluminum plate is preliminarily surface-roughened in an aqueous hydrochloric acid solution before an electrochemical surface roughening treatment in an aqueous nitric acid solution, uniform honeycomb pits are formed. The present inventors have also found that when an electrochemical surface treatment in an aqueous hydrochloric acid solution is performed after an electrochemical surface roughening treatment in an aqueous nitric acid solution, an aluminum support for lithographic printing plates, having excellent printing capability can be obtained. The present inventors have also found that although an auxiliary anode is used in an electrochemical surface roughening treatment using AC so as to prevent the main electrode from dissolving, when an aqueous neutral salt solution is used as an electrolytic solution in the moiety using the auxiliary anode, dissolving of the aluminum plate takes place and the treatment steps can be reduced as compared with conventional systems involving chemical etching.
Still further, the present inventors have found that when an aluminum plate is subjected to a preliminary surface roughening treatment with an electricity quantity of from 1 to 300 C/dm
2
using AC having a frequency of from 50 to 500 Hz and then subjected to an electrochemical surface treatment, streaking is difficult to occur in the afterward etching treatment.
Still further, the present inventors have found that when an aluminum plate is subjected to a preliminary surface roughening treatment with an electricity quantity of from 1 to 300 C/dm
2
using AC having a frequency of from 50 to 500 Hz and then subjected to a desmutting treatment and further to an electrochemical surface roughening treatment, streaking is difficult to occur in the afterward etching treatment. The present inventors have also found that in a method where an aluminum support is preliminarily subjected to an electrochemical surface roughening treatment in an aqueous solution mainly comprising hydrochloric acid and then to a desmutting treatment in an acidic aqueous solution, when the desmutting treatment is performed while treating the aluminum plate by cathodic electrolys
Masuda Yoshitaka
Nishino Atsuo
Uesugi Akio
Fuji Photo Film Co. , Ltd.
Sughrue & Mion, PLLC
Wong Edna
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