Search Images Maps Play YouTube News Gmail Drive More »
Sign in
Screen reader users: click this link for accessible mode. Accessible mode has the same essential features but works better with your reader.

Patents

  1. Advanced Patent Search
Publication numberUS3887447 A
Publication typeGrant
Publication dateJun 3, 1975
Filing dateSep 27, 1973
Priority dateJul 9, 1971
Also published asCA1009606A1, DE2327764A1, DE2327764B2
Publication numberUS 3887447 A, US 3887447A, US-A-3887447, US3887447 A, US3887447A
InventorsSheasby Peter Geoffrey, Smith Alan Martin
Original AssigneeAlcan Res & Dev
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Process of electrograining aluminium
US 3887447 A
Abstract
In a process for electrograining aluminium by subjecting the aluminium to alternating current whilst immersed in an aqueous electrolyte containing 2 - 20 gms/litre hydrochloric acid the electrolyte is stabilised against the presence of sulphate ion contamination and the pit size is controlled to a value below about 10 microns by the addition to the electrolyte of defined quantities of phosphoric acid or chromic acid. Both for operational reasons and for avoidance of health hazards it is preferred to employ phosphoric acid in an amount of about 5 - 10 gms/litre.
Images(3)
Previous page
Next page
Claims  available in
Description  (OCR text may contain errors)

United States Patent [191 Sheasby et al.

[ June 3, 1975 PROCESS OF ELECTROGRAINING ALUMINIUM [75] Inventors: Peter Geoffrey Sheasby; Alan Martin Smith, both of Banbury, England [22] Filed: Sept. 27, 1973 [21] Appl. No.: 401,257

[52] US. Cl. 204/129.4; 204/l29.75; 204/129.95 [51] Int. Cl C23b 3/02 [58] Field of Search 204/1294, 129.9, 129.95,

[56] References Cited UNITED STATES PATENTS 2,721,835 10/1955 Axtell 204/12995 3,477,929 11/1969 Namikata et al. 204/12995 3,755,116 8/1973 Teral et al. 204/129.95

FOREIGN PATENTS OR APPLICATIONS 1,202,030 8/1970 United Kingdom 204/l29.95

831,954 4/"1960 United Kingdom 204/1294 1,441,928 5/1966 France 529,755 6/1955 Italy 204/ 129.4

Primary ExaminerT. Tung Attorney, Agent, or Firm-Cooper, Dunham, Clark, Griffin & Moran ABSTRACT In a process for electrograining aluminium by subjecting the aluminium to alternating current whilst immersed in an aqueous electrolyte containing 2 20 gms/litre hydrochloric acid the electrolyte is stabilised against the presence of sulphate ion contamination and the pit size is controlled to a value below about 10 microns by the addition to the electrolyte of defined quantities of phosphoric acid or chromic acid. Both for operational reasons and for avoidance of health hazards it is preferred to employ phosphoric acid in an amount of about 5 1O gms/litre.

2 Claims, No Drawings PROCESS OF ELECTROGRAINING ALUMINIUM The present invention relates to improvements in the process of electrograining (electroetching) aluminium.

Aluminium is commonly used for the production of lithographic printing plates. For this purpose it is desirable that it should have a roughened surface characterised by the presence of very fine pits.

One known way of producing a desirable fine, uniformly pitted surface with randomly oriented pits is by an electrograining technique, in which the aluminium is subjected to alternating current when immersed in dilute hydrochloric acid. The hydrochloric acid electrolyte generally incorporates 2-20 gms hydrochloric acid per litre.

In the alternating current electrograining of aluminium sheet in hydrochloric acid as a pretreatment for the production of lithographic plates it is conventional to employ a current density in the range of 20 to 60 amps/sq. ft. (2 to 6 amps/dm for a period of 4 to 15 minutes. The charge input involved is generally in the range of 15,000 50,000 coulombs/sq. ft.

The above conditions are typical for batch processes. Where a continuous process is employed, i.e., where moving strip material is moved past stationary electrodes, current densities of the order of 100 1,000 amps/sq. ft. (l0 100 amps/dm may be employed for treatment times of /2 3 minutes.

Whilst coarsely-pitted electrograined surfaces can readily be obtained with such electrolyte, it is found that considerable care must be exercised in order to obtain a finely pitted surface (pits below microns in diameter). In particular, it is found that the presence of sulphate ion in the electrolyte will usually lead to a coarsely pitted surface, in which the pits are larger than is desirable for optimum performance for lithographic purposes. Although it is possible to start up the process with electrolyte made up with deionised water, it is inevitable that the electrolyte will become increasingly contaminated with sulphate and other ions carried over from earlier stages of the process.

As conventionally performed the preparation of aluminium for use in lithographic printing comprises a three-stage process involving degreasing and pretreatment (usually etching in sodium hydroxide-based solutions) followed by electrograining and anodising. As explained above, electrograining is conventionally carried out by applying alternating current to the aluminium whilst immersed in dilute aqueous hydrochloric acid. Since it is economically necessary to wash the aluminium in normal tap water (deionised water being too expensive for wash purposes) after the pretreatment stages, it is inevitable that the electrograining electrolyte will become progressively contaminated by whatever ions may be present in the wash water, carried over on the surface of the aluminium. Most natural waters contain more than parts per million sulphate ion.

It has been shown by practical printing trials that very finely grained surfaces lead to extended plate life and better image definition in lithographic printing. We have however found that contamination of the hydrochloric acid electrograining electrolyte by more than about 10 15 parts per million sulphate ion leads to a much more irregular and coarsely pitted surface, with the result that lithographic printing plates of relatively poor quality result from electrolyte made up from tap present in an amount of 1.5 l5 gms/litre, whilst chromic acid (calculated as CrO may be present in an amount of L5 2.0 gms/litre.

It is greatly preferred to employ phosphoric acid to chromic acid, for reasons of economics, lesser criticality of concentration and far lower health hazards involved.

With 'both materials it is found desirable to hold down the quantity of alkali metal ion, since this is also found to lead to the formation of large, irregular pits during electrograining, although it is tolerable in much larger proportions than is sulphate ion. A very suitable concentration of orthophosphoric acid is 5 l0 gms/litre.

The invention is hereinafter further described with reference to the following examples:

EXAMPLE 1 A hydrochloric acid, containing 6 gms hydrochloric acid per litre, electrolyte was made up with deionised water 1 litre) and 5 gms orthophosphoric acid per litre was added. mm X 50 mm (3 in. X 2 in.) panels of 99.7 percent aluminium were electrograined in this solution at room temperature with a 75 mm X 75 mm (3 in. X 3 in.) graphite counterelectrode placed 50 mm (2 in.) away from it. An ac voltage of 8 volts was applied for 6 minutes and a finely pitted surface was produced with the average pit size about 3 microns. Varying the hydrochloric acid concentration between 6 gms and 9 gms per litre had no effect on the fineness of the surface produced, although the current passing varied from about 4 amps to 5 amps under these conditions (about 70 amps/sq. ft. at the treated face of the panel).

EXAMPLE 2 A 8 gms per litre hydrochloric acid electrolyte was made up, using tap water containing about ppm. of sulphate ion, and 8 gms per litre phosphoric acid was added. When panels of 99.7 percent aluminium were processed under the same conditions as Example 1, a finely pitted surface with pits ranging from l-5 microns in diameter were produced. A similar electrolyte was then made up without the addition of phosphoric acid and this produced a relatively irregular and coarsely pitted surface with pit sizes ranging from about 10 to 30 microns.

EXAMPLE 3 Trials were carried out in a 50-gallon tank containing 8 gms/litre hydrochloric acid electrolyte made up with tap water containing about 100 ppm. of sulphate ion. A 99.7 percent aluminium sheet 480 mm X mm (19 in. X 5 in.), electrograined at room temperature at a constant current of amps (about 200 amps/sq. ft. at the treated face of the panel) with the applied ac. voltage rising from 10 to 12 volts over the 2-minute electrograining period, produced a surface with pits up to 20 by 30 microns in size. After addition of 8 gms/litre orthophosphoric acid to the same electrolyte, processing a similar panel under the same con- 3 ditions gave a surface with pits ranging from 1 5 microns in size.

In these tests the aluminium plates were connected as one electrode of the system with a graphite electrode. However both electrodes may be formed of aluminium plates to be electrograined. The process may also be carried out on a continuous scale. A continuous strip of aluminium is drawn through a two-compartment cell, in each of which is a counterelectrode connected to an a.c. source, so that current flows between the counterelectrodes through the aluminium strip which is passed through an aperture in the partition between the two compartments and through the electrolyte between the electrodes and the adjacent portion of the strip. By using this method, which has long been known for continuous anodising, contact between the strip and an electrode is avoided and arcing problems are avoided.

We claim:

1. In the process of electrograining aluminum for the production of lithographic printing plates which comprises subjecting the aluminum to alternating current while immersed in an aqueous electrolyte containing 2 20 gms/liter hydrochloric acid the improvement which comprises the addition to the electrolyte of L5 l5 gms/liter phosphoric acid whereby to maintain the pit size below about l0 microns in the presence of contaminant sulphate ion in the electrolyte.

2. The process of claim 1 wherein the aqueous electrolyte contains 5 l0 gms/liter phosphoric acid.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US2721835 *Jul 7, 1951Oct 25, 1955Shwayder Bros IncSurface treatment of aluminum articles
US3477929 *Apr 14, 1967Nov 11, 1969Fujitsu LtdMethod of etching aluminum foil in the manufacturing of aluminum electrolytic condensers
US3755116 *Apr 5, 1972Aug 28, 1973Sumitomo Light Metal IndProcess for the production of aluminum base offset printing plates
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US4072589 *Apr 13, 1977Feb 7, 1978Polychrome CorporationProcess for electrolytic graining of aluminum sheet
US4087341 *Nov 4, 1976May 2, 1978Nippon Light Metal Research Laboratory Ltd.Process for electrograining aluminum substrates for lithographic printing
US4140599 *Mar 1, 1978Feb 20, 1979Fujitsu LimitedEtching with hydrochloric acid and chromium trioxide
US4198278 *Jun 1, 1978Apr 15, 1980Toyo Aluminum Kabushiki KaishaMethod for producing anode aluminum foils for electrolytic condensers
US4279714 *Sep 15, 1980Jul 21, 1981Sprague Electric CompanyAlternating current electrolysis
US4279715 *Sep 15, 1980Jul 21, 1981Sprague Electric CompanyEtching of aluminum capacitor foil
US4294672 *May 30, 1980Oct 13, 1981Fuji Photo Film Co., Ltd.Electrolytic etched aluminum plate
US4301229 *Mar 27, 1979Nov 17, 1981Fuji Photo Film Co., Ltd.Electrolytically grained aluminum support for making a lithographic plate and presensitized lithographic printing plate
US4332651 *May 20, 1981Jun 1, 1982Sprague Electric CompanyAC Etching of aluminum capacitor foil
US4336113 *Jun 26, 1981Jun 22, 1982American Hoechst CorporationLithographic printing plates
US4477317 *Oct 31, 1983Oct 16, 1984Polychrome CorporationAluminum substrates useful for lithographic printing plates
US4547275 *Jan 28, 1985Oct 15, 1985Showa Aluminum Kabushiki KaishaPre-etching treatment with an aqueous solution of hydrochloric acid and chromic acid or a chromate, nitric acid treatment, and post-etching treatment with hydrochloric acid
US4576686 *Sep 26, 1984Mar 18, 1986Fuji Photo Film Co., Ltd.Electrolytic graining of surface, assymetric wave form
US4581996 *Mar 15, 1982Apr 15, 1986American Hoechst CorporationAluminum support useful for lithography
US4600482 *Apr 23, 1985Jul 15, 1986Hoechst AktiengesellschaftProcess for the electrochemical roughening of aluminum for use as printing plate supports, in an aqueous mixed electrolyte
US4618405 *Apr 23, 1985Oct 21, 1986Hoechst AktiengesellschaftProcess for the electrochemical roughening of aluminum for use as printing plate supports, in an aqueous mixed electrolyte
US4626328 *Apr 23, 1985Dec 2, 1986Hoechst AktiengesellschaftProcess for the electrochemical roughening of aluminum for use as printing plate supports, in an aqueous mixed electrolyte
US4655136 *Feb 6, 1984Apr 7, 1987Hoechst AktiengesellschaftAluminum or alloy thereof
US4661219 *Feb 4, 1986Apr 28, 1987Hoechst AktiengesellschaftProcess for the electrochemical roughening of aluminum for use in printing plate supports
US4666576 *Feb 4, 1986May 19, 1987Hoechst AktiengesellschaftProcess for the electrochemical roughening of aluminum for use in printing plate supports
US4671859 *Sep 19, 1986Jun 9, 1987Hoeschst AktiengesellschaftProcess for the electrochemical graining of aluminum for use as printing plate supports
US4824535 *Oct 13, 1987Apr 25, 1989Hoechst AktiengesellschaftProcess for the electrochemical graining of aluminum for use in printing plate supports
US4840713 *May 25, 1988Jun 20, 1989Hoechst AktiengesellschaftProcess for the electrochemical roughening of aluminum for use in printing plate supports
US4976198 *Jan 23, 1987Dec 11, 1990Fuji Photo Film Co., Ltd.Grain structure for lithographic printing plate supports
US5152877 *Oct 5, 1990Oct 6, 1992Fuji Photo Film Co., Ltd.Method for producing support for printing plate
US5156723 *Jan 22, 1991Oct 20, 1992Hoechst AktiengesellschaftUsing alternating current and electrolyte comprising sulfate ions and chloride ions
US5288372 *Jul 7, 1992Feb 22, 1994Alumax Inc.Altering a metal body surface
US5304298 *Sep 1, 1992Apr 19, 1994Hoechst AktiengesellschaftElectrochemical surface treatment; anodizing
USRE31743 *Aug 19, 1981Nov 20, 1984Sprague Electric CompanyAlternating current
EP0268790A2Oct 7, 1987Jun 1, 1988Hoechst AktiengesellschaftProcess for electrochemically modifying support materials of aluminum or aluminum alloys, which have been grained in a multi-stage process and use of these materials in the manufacture of offset-printing plates
EP0689096A1Jun 13, 1995Dec 27, 1995Eastman Kodak CompanyLithographic printing plates utilizing an oleophilic imaging layer
Classifications
U.S. Classification205/658, 205/682, 101/459
International ClassificationB41N3/03, B41N3/08, C25F3/04, B41N3/00, C25F3/00
Cooperative ClassificationC25F3/04, B41N3/08, B41N3/034
European ClassificationB41N3/03E, C25F3/04, B41N3/08