CA1108086A - Electrodeposition of copper sheet on separated cathode surfaces and extrusion of resulting particles - Google Patents

Abstract

Abstract Granules of copper are produced by deposition on a patterned electrode having cathode surfaces 7 separated by insulating material 9, 10. Deposition may be continued until the copper coheres into a continuous sheet, in which case the sheet is broken up along its lines of weakness.
The granules are fabricated by continuous friction-effected extrusion to obtain rod, wire or other elongate products.

Description

This ~nvention relates to the fabrication o~
copper in the ~orm of elongate bodies and especially but not exclusively to the ~abrication o~ elongate bodies o~ copper of electric conductor gradeJ which ~or avoidance o~ uncertain~y can be taken to mean copper with a conductivi~y o~ at least 101% I.A.C.S. When the copper contain~ impuriti~s of the usual kind, this corresponds to a total impurity level (counting oxygen as an impurity) in the re~ion o~ 0,05~ or below.
Copper o~ this quality is normally produced by electrolytic refining as flat9 approximately rectangular cathodes, and the conventional fabricatlon process involves melting the cathodes, casting (either continuously or discretel~) into bars and hot-working (by swaging, rolling, extrusion or more than one o~ these processes) to elongate shape. In most cases cold drawing and/or cold rolling ~ollows.
It has long been recognised that this process involves the provision o~ much expensive equipment and the use o~ large amounts o~ energy merely to raise the temperature of the copper to melt it and sub~equently to maintain a suitable hot-working temperature, and attempts have been made to pr.ovide a low-temperature ~abrication process ~or the production of elongate products from unmelted cathode copper.
Most such attempts have been based on modification of the electrolytic refining process to form an elongate product directly~ Though technically possible ~or some

- 2 --products, thi~ has 9~ ~ar proYed lmpr~ctieable and/or uneconomic ~or the manu~a~ture o~ eleotric conductcr~
(e~cept thin ~oil3) becau~e the area o~ th~ electrodes i~
not e~ficiently utili~ed i~ it~ component part~ (e.g. the turns o~ a spiral) are ~pac.ed gufficlentl~ to avoid rl~k of adhesion, irregular cro~-3ection, a~d con~equent fracture i~ ~ub~equent proce~3ing, and the additi~es required in the electrolytic bath to control ~he shape of the product may have a deleteriou~ e~ect on its electr~cal condu¢tivity and~or the rate o~ depo~ition~
Anether ~uch attemptJ wh~ ch reached commercial u~e ln the United Stat0~ of America on a mode~t ~cale in the 1930l9 or thereabollt~9 but ha~ ~ince fallen into disu~e~
produced a product known a~ "coalesoed Gopperl~. The coalesced copper proee~ wa~ in a broad 3en~e of the word, a ~powder metallurgic~ proce3~ as lt lnvolved the del~berats produ~tion o~ brittle cathodes whloh ware broken up into fragment3 whi~h might be as large as several centimetr.es 1n each of their ma~or dlmen3~0n~ and 5 nn~ thick. ~he~e ~ragments wera compre~ed lnto briquette~, ¢oale~ced by heating ~or a substantial period under relluc~ ondition~ Qt around 900C to effect

3~rface d0~xidatlon, sane other ~ icatlon and grain grGwth, and ~ub equently hot-e~ctruded to gi~e a solid pro*uct of electric ¢ondllctor grade.
We have rec0ntly discovered that the heat-treatment and c oale~en¢e step o~ thl3 known proces~ was nolther ns¢es~ary nor bene~i~ial and th~t fabricated productQ with ... , .. _ _ . ,, ., ... . , _,,, . ... ,. ., ... . . .. _, .. . .

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superior properties can be obtained without surface-deoxidation provide~ that the metal is never heated to the extent of allowing significant amounts of any impuri-ty present to dissolve in the copper, and have therefore proposed in the complete specification of our British Patent No. 1543440, a method of making an elongate body of copper of electric conductor grade comprising: electrodepositing copper in the form of brittle cathodes; breaking the cathodes into ~ragments with a mean specific surface area in the approximate range from 10 25 - 1,000 mm /g; feeding these fragments as such and without any high temperature treatment Eor purification or grain growth to a continuously acting friction-effected extrusion machine and by means of that machine working the fragments under pressure sufficiently to consolidate and bond the fragments into a continuous elongate body.
Brittle cathodes are likely to be of higher porosity than cathodes of conventional ductility and may therefore occlude greater amounts of electrolyte and possibly anode slime, leading in some cases to higher impurity levels 20 (especially for antimony, arsenic and sulphur) than for conventional coppers; such a higher impurity level may not in every circumstance be completely compensated by the control of impur.ity dissolution and is likely to result in a product with a lower conductivity than might have been obtained from a feed of ductile copper particles.
In accordance with the invention, a method of fabricating copper into an elongate product comprises:-(i) Electrodepositing copper onto an electrode having a plurality of cathode sur:Eaces substantially separated from one another by insulating material until the areas of copper deposited on the individual cathode surfaces cohere across the boun~aries o~ those areas in the form of a shee-t;
(ii) Stripping the deposited copper from the electrode;
(iii) Subse~uently fracturing the sheet in areas of weakness corresponding to at least some of those boun~aries to form particles of copper and (iv) Extruding those particles by a continuous friction-effected extrusion process to form an elongate product.
The particles preferably have volumes in the approximate range from 1 mm to 0.1 dm and par-ticles of these dimensions are hereaf-ter called "granules"; granules produced by the present invention wlll usually have at least one major dimension (their thickness) not greater than 10 mm but thicker granules could be produced if desired.
The electrode may be of any suitable conductive material; for conventional acid copper sulphate baths either titanium, stainless steel, or copper will usually be preferred;
if copper is used, a parting agent will usually he applied -to it. Normally the cathode areas will all be parts of the major surace(s) of an initially continuous sheet.
Normally electrodeposition will be part of an electro-refining process, and the conditions adopted are preferably such that ductile copper is deposited, standard refining conditions can be, and are preferably, ~-~0~

ueed .
The separation oR 1~h~ shset lnto distinct sathode area~ by in~la~in~ materlal may bs e~ected in variou~
waysO In particular the ln~ulating material ma~r be durable 30 a~ to ~urvlve ~tripping Or the copper and repaated uqe or~ i~ oheap enou~h, it may be di~po~able a~d be replaced a~tor each u9eo ~he pre~erred durable in3ulating material i~ an a~odic o:~cide layer f`orm0d on an elsctrode Or titanium ( or o tiher sui~able motal ) ,.
AlternR~ives include variouq organie in~ulating materlal~
prote¢ted ~rom mechani¢al damaga bg being re~essed into shallow grooves pro~lded in l~he surf`ace o~ the electrode;
suitable organic material~ ~or u8e in ~hi 9 way includs epoxy resln~ (thermo~ettine~ or coldsetting)J ~bbers (pre~erably vulcani~ed in itu) " and ethylene-vinyl acetate copolymers (thermopla~tic)O I~ po~abl0 insulating material i!~l ~eferrea, thi~ wlll u~ually be an organic materlal applied as a ~ a~e layer on a plain matal ~ur~a~eO ~he ~ ace layer may be a ~oating applied ~roro a ~luid ~ta~e9 or it may be a prefor~d por~orate sheet prsferably se¢urely bonded to ~he metal Or the eleotrode b~ ~el~ adhesion or by a separate adhe ~iYe but alte~nativ31~ ecurely Glamped to the metal ~o a~ to a~tabli3h a ~ub~tantiall~ ~luid-tight eontaotO Suita~le material~ include roorn-temperature vulcani3ing sllicone rubber con~:~o~i~ions applied in th~ ~ condition~ and poly~rln~l chloride applied in ~heet ~ormO
To enqure the produotion o~ a unl~orm p~odu¢t tha oathodic area~ ar3 pre~erably allke in ~hape and ~ize~ or .. . . . .... . .. .... . .

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at least are o~ only a small number of di~erent hapes and/or sizes. We pre~er to use a regular pattern of squares, hexagons, rectangular strips~ or other polygons spaced by insulating strips of uniform width, except when pre~ormed insulating sheets are used, when it may be pre~era~le to use circular openingsJ poss~bly of two di~erent sizes to secure better space utilisation.
Rectangular strips may be as long as the electrode itsel~, lf desiredO Currently we pre~er that long strips should not be wider than 10 mm, or at the most 25 mm, and that more compact shapes should not exceed 100 mm square. Particular friction-ef~ected extrusion machines~
such as the prototypes currently in use~ may require smaller particles than this.
The cathodic areas will usually need to be spaced by a ~ew millimetres to ensure clear demarcation;
and we have ~ound that ror shest ~ormation the deposit thickness will usually need to be several times the spacing.
A~ter removal ~rom the electrolytic cell, the electrode with the deposited copper on lt will normally be washed to remove electrolyte, ~or convenience in subsequent handling. The copper may then be strippe~
broadly in the same way as copper start~ng sheets are stripped from blanks, that is by a blade ~orced along the electrode at a position slightly spaced ~rom the ~ 8 ~

electrode sur~ace and possibly (where applicable) by tearing after a corner or end has been separated. The continuous sheet so formed may be broken up ~ubsequently by any suitable type of mill~ u~u~lly one operating by impact and/or bendlng. Jaw mills, tooth millsg ball mills, ha~mer mills~ and tumblers may all be used.
A~ter stripping, and be~ore and/or a~ter ~ragmentakioll, the particulate copper is pre~erably washed again to minimise electrolyte contamination, and afterwards preferably dried. The copper is preferably screened to elim~nate any oversize particles (which may be returned to the fragmentation mill).
Continuous ~riction-effected extrusion processes, such as those known by the proprietary names "Conform", "Linex" and "Extrolling", operate without a closed billet Qhamber and the metal, instead o~ being ~orced into the extrusion die by a ram or by fluid pressure, is gripped by a member or members o~ the enclosure that are advanced towards the die mouthl where it upsets and extrudes thDough the die. (A fuller description o~ the Con~orm and Linex processes will be ~ound in Wire Journal~
April 1976, pp 64-69; the Con~orm process is the sub~ect o~ British Patents 1370894 and 14~4201 and the Line~
process the subject o~ British Patent 1488445).
Pre~erably the granules or other particles of copper are fed as such, without any pre-compaction9 to the 8~

friction-effected e~rusion operation and are caused to cohore by the ex~rusion proceqs it~el~; pro~erably alqo the temperature o~ the copper at no time e~ceads 700C~ so a~ to avoid any ~ub~tantial los~ of elactrical conductivity by di~solution o~ impurities that may be pre~ent in undissolved ~orm.
Optionally ths particles may be preheated be~ore e~trusion, to reduce the e~truslon pres ure requi~ed.
Preferably the prehoating temperature doe~ not exceed 450C, as otherwise there may be a risk that during the e~trusion proce~s a temperature Q~ 700C may be exceeded as a result o~ adiabatic he~ating. A reducing or neutral atmosphere, or the use o~ vacuum, may be desirable i~
preheating i3 uqed; cracked ammonia and ~team (preferabl~
~ree of air in both case3) are suitable.
I~ de~ired~ the extrusion tools ma~ be pre-heated~
at lsa8t ini~ially. ~he 3xposure time is ~o short that a protective atmosphere i~ not consid3red necessar~ in normal ca~e~. ~nles~ a porous product ls acceptable9 the extrusion ratio is pre~erably at lea~t 8:1, and reductions of around 9:1 to 20:1 are pref~erredO In s~e ca~e~ it may be bene~icial to e~trude two or more product~ s1multan eou~ly using a dual or multiple dia. E~trusion may be a~ial~ iOe. in the same direction ~ the material to ba o~truded approaches the dle, or it rnay be at right angle~, or another angle, to the a~cial direction.
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The extruded product may be haat-treated, i~ desired, to homogeni~e it~q ~trueture and/or modi~ machanical properties; pre~erQbly heat-treatment ls below 7OOC to avoid si~ni~icant grain growth and dis~qolution o~
impuritie~
me elongate product will ofte.n be ~wire rod~, that is round rod suitable ~or drawing into wire; alternati~ely it may be a finish3d product Or rectangular or other special qection9 includin~ hollow soctions which can be produced using bridge or porthole dies. Further it may be intermodiate (3a~ a square or re~tangular rod) ~or u3e as a ~eed to a qecond continuou~ friction-e~ected extru~ion procesq, a~d in ~qome ca~eq wire may be e~truded directly.
In the accompan~ing drawings each o~ ~igure~q 1-6 is a diagrammatic elevation (not to ~cale) o~ a di~erent electrode for use in the first step of the method o~ the invention.
The electrode o~ figure 1 comprises a stout metal sheet having an uppor area 1 that iq bare and .~erves ~or makin~ electrical connections, an intermediate area 2 that i~ coated with insulating matarlal and in use extends partly in th~ elect~olyte and partly in ths air above i~, and a main area 3 qer~ing ~or raception o~ electrodspoqited coppar. The edge~ 49494 o~ the main area ~r~ coated with insulating materi~l and both it3 ma~or sur.~aces ara ~ub-di~ided by diagonal strip~ ~,6 of i~ulating material into a multiplicity of diamo~d-~haped cathode 9urfaces 7.
Triangular or other undersize area9 8 ad~oining the edge3 of the 3~rip may be coatad ir uni~ormity o~ particl0 i~
re~uired, ..... , .. ,,--. . ...
2 ~

The electrode of figure 2 differs only in that ~he insulating strips 9~10 on ~he main area ~ run vertically and horizontall~. This ensures uniformity of particle sizes withou~ loss of volume efficiency, but may produce a slightly less pure deposit as ~he horizontal upper edges of the initial copper deposits may tend to collect some particulate impurities ("sllmes").
The electrode o~ ~igure 3 has vertical in~ulating strips 9 onl~, and consequently has long narrow bare areas 11 for deposition o~ copper strips. Horizontal strips 10 could be used alone, as seen in figure 4, but this arrangement would also tend to produce a less pure product.
m e electrodes o~ figures 5 and 6 have their main areas 3 coated all over apart from circular areas 12~13, of one size in figure 5 and two di~ferent si~es in figure 6. This arrangement has a lower volume efficiency but the rounded shape o~ the particles may help them feed more satis~actorily to s-ome ~riction-ef~ected extrusion machines.
EXAMPLES
Electrodes, measuring 2~5 mm by 280 mm~ for use in a pilot electro-re~ining cell were prepared as follows:
Exam~le 1 A titanium sheet was coated on both sides with a photo-resist and exposed on each side in turn to actinic light under a negative having dark bands about 4 mm wide at 15 mm centres in a square grid pa~tern made by sticking strips of opaque material on a clear plastics sheet and photographing it. ~he unexposed grid pattern was removed by conventional development leaving a pattern o~ protected , l . _ . _ _ __ . . . .... , _ . .. ... . ... . . ... . . . .. . .... . .... . ..... .. . . . . ..

~ 6 squares o~ about 11 mm side. The plate was then anodised using a conventional technique to apply a durable oxide coating to the exposed metal; the remaining photoresist was then stripped off with a solvent to expose the metal in the unanodised area o~ the squares. (Pattern as figure 2).
Example 2 A copper sheet was divided into square grid patterns o~ various sizes ranging ~rom about 10 mm to 25 mm side using a room-temperature vulcanising silicone rubber composition, sold b~ Imperial Chemical Industries Limited under the trade mark Silcoset a~ Silcoset RTV No. 100, No. 101, or No. 105 (two-pack) or No. 151, No. 152 or No. 15~ (one-pack) applied to the clean dry surface of the sheet in a strip o~ about 5 mm wide, over a priming strip o~ the recommended primer OPl. (Pattern as ~igure 2). A conventional parting agent was then applied.
Example ~
An adhesive-backed pvc filmg about 1 mm thick~ sold as a pro~ective ~ilm ~or book covering, was punched with a square pattern o~ round holes each about 25 mm in diameter on 18 mm centres with smaller holes about 5 mm in diameter interposed diagonally between them and was stuck to the surface of a titanium sheet. (Pattern as figure 6).
Exam~le 4 "` `;
A resilien~ plasticised pvc sheetg about 5 mm thick, was punched with a hexagonal pattern of 20 mm holes on .

.. . .. .

8~

mm centres, clamped to a titanium sheet and held ~mderpressure applied at many points across its surface. (Pattern as Figure 5).
Example 5 A thick tltanium sheet had a diagonal square pattern o grooves 3 mm square an~ on 15 mm centres cut into it on each face by a circular saw. (Pattern as Figure 1). These grooves were filled by pouring in a cold-setting synthetic resin composition comprising, in parts by weight:
Low-viscosity Bisphenol-A type expoxy resin sold under the trade mark "Araldite"
as "Araldite MY 750" 50 Talc 40 Polyoxypropylene diamine of molecular weight about 2000, sold under the trade mark "Jeffamine" as "Jeffamine 2000", a bonding agent 10 Hardener, sold under the trade mark "Jeffamine" as "Jeffamine D230" and described as the bis 2-aminopropyl ether of a diol, with molecular weight 230 14 Proprietary curing promoter sold as "Accelerator 398" 5 (Jeffamine D2000, Jeffamine D230 and Accelerator 398 are all obtainable from Jefferson Chemical Company, Houston, Texas, U.S.A.).
After the resin had hardened the surfaces of the electrode were smoothed by sandlng.
Example 6 This was the same as Ex~ample 5 except -that the grooves were on 8 mm centres, leaving deposition areas 5 mm square.

Example 7 This was similar to example 2 except that the shee~ was o~ ~itanium and the insulating material was the asphalt-based material sold under the trad~mark "Mexphalte" applied by brushing or by printing with a patterned rubber roll.
Ea¢h o~ the electrodes prepared as descr~bed in examples 1-7 was ~ade cathodio ~n the electrolytic cell using conventional anode copper cut to 235 mm x 254 mm and conventional electrolyte and circulation procedure.
The current density was maintained at approximately the .
conventional level (the ef~ective area is initially less than ~or ~ plain cathode o~ the same overall size but rises as deposition proceeds and may in some cases exceed the area of a plai~ cathode for part o~ the time when copper is being deposited on the edges o~ separate blocks already deposited). The electrodes oP Examples 1, 5 and could be re-used without being ~reshly prepared.

This was similar to E~ample 1 exoept that the negative was made with only one set of parallel dark bands and consequently rectangular copper ~krips extending the full length o~ the electrode were produced. (Pattern as ~igure 3).
All the electrodes could be used to produce ~rangible sheets of ductile copper by continuing deposition to various thicknesses ln the region o~ 10 mm.
Granular copper produced by depositing on the ~ .. . ....... . . . . . . . . .. ... . . .. . . . . .. . .. . .

~18~

electrode o:f example 6 to a thickness o:f 5 mm, washing and stripping was re-washedg dried and pre-heated to 275C;
the roughly cubic granules were ~ed ~o a small "Con~orml' ~riction-ef~ected extrusion machine (a laboratory prototype with a groove about 9 mm square~ and extruded at a ratio o~ 8:1 to ~orm round rod 3.~ mm in diameter. After drawing into wire 0.5 mm ln diameter and annealing the product had an elongation of 26%, tensile strength 2~5 MN/m2, and electrical conductivity 101.8% IACS.
Similar results can be expected ~rom extruding granules deposited on the electrodes o~ the other examples or made by fracturing sheets deposited thereon, but a larger ~riction-e~ected extrusion machine will be required to accept the larger granules.

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Claims (3)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of fabricating copper into an elongate product comprising:
(i) Electrodepositing copper onto an electrode having a plurality of cathode surfaces substantially separated from one another by electrically insulating material until the areas of copper deposited on the individual cathode surfaces cohere across the boundaries of those areas in the form of a sheet;
(ii) Stripping deposited copper from the electrode;
(iii) Subsequently fracturing the sheet in areas of weakness corresponding to at least some of those boundaries to form particles of copper;
and (vi) Extruding those particles by a continuous friction-effected extrusion process to form an elongate product.

2. A method as claimed in Claim 1 in which the electrodeposition is part of an electrorefining process.

3. A method as claimed in Claim 1 in which the temperature of the copper at no time exceeds 700°C.