Electrolysis: processes – compositions used therein – and methods – Electrolytic erosion of a workpiece for shape or surface... – Gap maintenance or defined tool-workpiece gap
Reexamination Certificate
2000-02-24
2001-12-04
Valentine, Donald R. (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic erosion of a workpiece for shape or surface...
Gap maintenance or defined tool-workpiece gap
C205S658000, C205S704000, C204S206000
Reexamination Certificate
active
06325912
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to an apparatus and method for electrolytic treatment which comprises etching a metal web electrolytically using alternating waveform current continuously, and particularly, relates to an apparatus and method for electrolytic treatment suitable for electrolytic etching of aluminum web during manufacturing a support for planographic printing plate.
Electrolytic etching of a surface of aluminum, iron or the like is widely utilized, and alternating waveform current is generally used due to required quality and the improvement in reaction efficiency. For example, Japanese Patent KOKOKU 56-19280 discloses an electrolytic etching treatment which can provide excellent roughening as a support for an offset printing plate by using an alternating waveform current impressed so that the electric voltage at anode is made greater than the electric voltage at cathode in electrolytic roughening of an aluminum plate.
In general, electrolytic etching is carried out at a current density of 10 to 100 A/dm
2
in an acidic electrolytic solution, such as 1 to 5% nitric acid or hydrochloric acid. Upon treating electrolytically an aluminum plate as the metal web, Al →Al
3+
+3e dissolution reaction occurs at an anode period, and H
+
+e→(1/2)H
2
↑ hydrogen gas generation reaction and Al
3+
+30H→Al(OH)
3
aluminum hydroxide smut formation reaction occur simultaneously at a cathode period on the aluminum plate.
These reactions occur alternately according to the frequency of power supply, and, in general, it is possible to obtain a required roughened surface by adjusting these fundamental reactions by controlling electrolytic conditions, such as the type and concentration of electrolytic solution, temperature conditions, current density and charged quantity of electricity.
Hereupon, in the case of using alternating waveform current, there are differences between the treatment initiating part by the dissolution reaction and the terminating part caused by the current cycle on entering a metal web into an electrolytic bath and on going out of the bath, and shadow unevenness (uneven treatment) occurs in the cross direction to the traveling direction of the metal web. The uneven treatment generates according to the frequency of a power supply. For example, in the case of a treating speed of 50 m/min and a frequency of power supply of 60 Hz, the uneven treatment generates at an interval (pitch) of 1.39 cm in the longitudinal direction of the metal web. In view of massproduction, a higher treating speed and a higher current density treating speed and a higher current density treatment are desired. In the case of high strength aluminum support containing manganese or the like which recently increases, there is a tendency to manufacture a high quality support for planographic printing plate by lowering frequency.
On the other hand, the degree of the above mentioned ununiformity according to the frequency of power supply becomes stronger by higher treating speed, higher current density or lower frequency due to its generation mechanism.
In this regard, Japanese Patent KOKAI 1-230800 discloses an electrolytic apparatus which can remove the uneven treatment by providing low current density zones at the front end and rear end of an electrode, and making the remaining portion a constant current density zone. Japanese Patent KOKAI 4-289200 discloses a roughening method using a power supply frequency of 1 to 30 Hz.
However, according to the conventional methods mentional above, the uneven treatment according to the frequency cannot be removed entirely in the case of high treating speed, high current density or variation of electrolytic solution conditions.
SUMMARY OF THE INVENTION
An object of the invention is to provide an electrolytic treatment apparatus and an electrolytic treatment method which remove the uneven treatment according to the frequency and can achieve high treating speed and high current density treatment. The inventors investigated eagerly as to the uneven treatment generated on metal web, and as a result, they found that the uneven treatment occurs particularly strongly at the upstream end of the rear electrode in the traveling direction of the metal web in an indirect electric power supply cell. They further found that the uneven treatment is generated caused by the existence of untreating zone between the electrodes, and by a very high current density at that part caused by the electric resistance of the metal web.
Thus, the present invention provides a method for electrolytic treatment which comprises passing a metal web through an apparatus for electrolytic treatment which comprises a drum roller around which a metal web is wound, arc-shaped electrodes allocated on the outside of the drum roller concentrically with a space, and an electrolytic solution put in the space, and electrolyzing the metal web by applying an electric current to the electrodes, wherein the electrolyzing is carried out in a state that the drum roller has been moved upward from the concentric point.
By making the drum roller movable, the current density at the ends of the electrodes can be controlled so as to become optimum. When the drum roller is moved upward from the concentrical point, the distance from the ends of electrodes is lengthened to decrease the current density around the end portions of electrodes. The above ends are produced by separating an electrode. A suitable moving range is 10 to 100%, preferably 10 to 40%, more preferably 20 to 40% of the distance between the drum roller and the arc-shaped electrodes upon being located concentrically.
REFERENCES:
patent: 4747923 (1988-05-01), Oda
patent: 4929326 (1990-05-01), Uesugi et al.
patent: 5066370 (1991-11-01), Andreshak et al.
patent: 5094733 (1992-03-01), Kaneko et al.
patent: 387 750 (1990-09-01), None
patent: 475 026 (1992-03-01), None
Hirokawa Tsuyoshi
Yamazaki Toru
Fuji Photo Film Co. , Ltd.
Sughrue Mion Zinn Macpeak & Seas, PLLC
Valentine Donald R.
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