US2852450A - Method of copper plating - Google Patents

Description

Sept 16, 1958 E. H. MUNDELL 2,8 52-,450

METHOD oF COPPER PLATING Filed June 10, 1954 2 ShetS-Sheet 1 afveysl Sept.. .16, i958 E. H. MUNDELL 2,852,450

l METHOD oF COPPER PLATIN@ Filed June 10, 1954 2 Sheets-Sheet 2 zz f5 United States ,Patent O NIETHOD F COPPER PLATING Elmore H. Mundell, Gary, .Ind., assignor to R. ;-R.,`.Don nelley & Sons,.Company,a,corporation of Delaware Applicationllune 10, 1954, Serial'No. 435,807

1 Claim. `(CLIM-52) This invention relates to` an apparatus and method for copper plating a rotogravure cylinder, and in particular 1t relates to the copper plating of rotogravure cyllnders using an insoluble anode.

The principal object of the invention is to improve the copper plating of rotogravure cylinders so as to reduce the cost both of the electroplating equipment and the eX- pense of processing a rotogravure cylinder.

It has been common practice in the past to copper plate rotogravure cylinders by rotating them while partially submerged in an electroplating bath. Insofar as applicant is aware the apparatus has always included a copper anode which is spent during the plating process; and in order to support the copper bars forming the anode with a material which would not contaminate the electrolyte, the copper bars were customarily supported upon a chemical lead slab.

There were a number of objections to the customary electroplating process. In the rst place, it is essential to the production of a copper film of even thickness that the spacing between the anode and the adjacent cylinder surface be substantially equal throughout the length of the cylinder. In View of the fact that the copper bars forming the anode entered into the electrolytic action, and the electrolysis did not proceed evenly, it was very diflicult to keep the required uniformity of spacing between the anode mass and the cylinder. Unevenness in the spacing which developed with anode corrosion resulted in uneven plating of the cylinder. Since the cylinder surface must be very true and even, any unevenness in plating had to be corrected by grinding the plated surface. Thus, the time and expense of preparing a inished rotogravure cylinder was greatly increased by reason of the use of a copper anode.

Another ditiiculty with the previously known apparatus was that the lead support for the copper bars of the anode was easily distorted by the weight of the copper bars; and furthermore there was a tendency for a non-conducting sulphate film to form on the lead, reducing conductivity between the lead and the copper and causing excessive plating time.

In accordance with the present invention an anode is employed which is not disintegrated by the electrolytic action, so that it enters into the electroplating action solely as an electric conductor member. Preferably the anode is fabricated from conventional electrotype metal. The level of copper in the electrolyte is maintained by the addition of a copper salt from time to time in accordance with the amount of copper deposited upon the rotogravure cylinder.

It has been found that an anode formed from electrotype metal has much less tendency to sulphate and disintegrate with use than have the conventional lead supports previously used for copper bars. Since the anode does not enter into the electroplating action, there is no change in the surface shape of the anode so that a very even deposition of copper on the rotogravure cylinder is obtained and very little grinding of the surface is required.

Anodes, of electrotype metal have been-used experi- Amentallyfor many months with nosign o'f'any deteriora- ,tion of such magnitude as Lto 'alter-theeiclencyfof-the ...cated alongthe line`2-2 of1Fig.i4; Fig..3 is a-fragmentary section taken along theline ,3-3'of Fig. 4; and -Figf4 is a section taken as indicated along theline-f-elcf Fi 1.

'eferring to-the drawings ingreater detailfand-referring first to Fig. 4, the vapparatusincludes an electroplating tank indicated generally at 10 which has end walls 11, side walls 12 and a bottom 13. As best seen in Figs. 1 and 4, the end walls 11 of the tank are provided with aligned pillow blocks 14 on which are `supported rotatable sleeves indicated generally at 15 which have central openings to receive the stub shafts 17 of a rotogravure cylinder 18. The tank 10 is filled with an electrolyte 19 to a level such that the lower portion of an electrotype cylinder 18 mounted in the sleeves 15 is immersed in the electrolyte.

The sleeves 15 are provided with commutators 20, and one sleeve has on its outer face a pinion 21 which may mesh with a gear (not shown) for the purpose of rotating the cylinder 18 on the pillow blocks 14. A cathode lead 22 is electrically connected to a current carryingbuss bar 23 which extends in parallel spaced relation to one side wall 12 of the tank and part way across the two end Walls 11 upon which it is supported by means of insulating supports 24. At each end of the buss bar 23 is a contact brush 25 which bears upon one of the commutators 20 so as to make the rotogravure cylinder 18 a cathode of the electroplating circuit.

Along the wall of the tank opposite the buss bar 23 is an anode buss bar 26 which has a lead 27 by means of which it is made a part of the electroplating circuit, and the buss bar 26 has inclined arms 28 at the ends of the tank which are electrically connected to the ends o-f an internal buss bar 29 which is supported in the slots 30 in the end walls 11 of the tank. A series of anode contact clamps 31 are secured to the interior buss bar 29 and, as best seen in Fig. 2, the clamps 31 support an anode 32. As seen in Figs. 2 and 4, the anode 32 has an arcuate portion 33 which is submerged in the electrolyte 19 and which is concentric with the rotogravure cylinder 18 throughout the entire length of the cylinder. Wooden brace members 34 for the anode extend across the tank and are supported upon angle members 35 on the side walls 12.

The principal components of the electrolyte 19 are preferably 30 ounces of copper sulphate and 10 ounces of sulphuric icid per gallon of water in the solution. The anode 32 is preferably fabricated from electrotype metal of a common type which is 94% lead, 3% tin and 3% anti-mony. The electrotype metal is sufficiently rigid that it will hold its shape, particularly after it is age hardened. Since it does not enter into the electrolytic action there is no effective disintegration of the anode as is the case where copper anodes are employed, and it has only little tendency to sulphate in the electroplating process.

In carrying out the electroplating operation in the apparatus here described, the sleeves 15, which are-loosely supported upon the pillow blocks 14, are mounted upon bath so as to provide current density of 2 amperes per square inch between the anode and the cathode. The deposition of copper upon the rotogravure cylinder 18 reduces the copper in solution in the electrolyte, and the copper is replenished by adding copper carbonate to the electrolyte. Preferably the copper carbonate is added to the electrolyte at a rate which is slightly in excess of that theoretically required to replace exactly the copper plated out of the electrolyte. In practice, l0 pounds of copper carbonate are added for each 80 ounce shell plated.

The foregoing detailed description is given for clearness of understanding only andino unnecessary limitations are to be understood therefrom, as some modifications will be obvious to those skilled in the art.

I claim:

A method of copper plating which comprises immersing an article to be plated in an electrolyte containing a dis- 4 solved copper'salt, establishing an electric circuit through said article as a cathode and through an insoluble anode consisting of 94% copper, 3% tin and 3% antimony, and replenishing the copper as it is plated out of the electrolyte.

References Cited in the le of this patent UNTED STATES PATENTS 852,438 Lamb May 7, 1907 1,601,694 Merritt Sept. 28, 1926 1,820,204 Wilkins Aug. 25, 1931 1,918,627 Ballard July 18, 1933 2,340,400 Mantell Feb. 1, 1944 2,411,674 Wilson Nov. 26, 1946 2,435,872 Coulson Feb. 10, 1948 2,666,029 De Quasie et al. Jan. l2, 1954

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