US2381911A - Electrodeposition - Google Patents

Description

I Patented Aug. 14, 1945 Bertram C. Kathe, Detroit, Mich.

No Drawing. Application September 16, 1940, Serial 'No. 357,009

20 Claims. (Cl. 204-30) This application is a continuation in part of my copending applications, Serial No. 92,044, filed July 22, 1936, Serial No. 202,674, filed April 18, 1938 nowabandoned, and Serial No. 231,349, filed September 23, 1938, now Patent No. 2,280,240 of April 21, 1942.

The present invention pertains to a novel method of imparting conductivity to the surface of non-conductive materials. In the art of electroty'ping and the allied art of electroforming, non-conductive plastic materials are used to obtain negative or female impressions of some surface of which a duplicate or duplicates is desired. Before electrodeposition can be effected some method of rendering the surface of-these materials conductive must be employed. At present a fair degree of conductivity is achieved by ap-.

plying a film of graphite to the surface of the impression, either by polishing finely divided dry graphite by hand or machine or by spraying the surface of the impression with a water-emulsion of finely divided graphite. A greater degree of conductivity is obtained when both methods are employed, that is, when the impression is first dry-polished then wet-leaded," and this is the combination most frequently employed.

Another method, less frequently used, is to sub- .stitute finely divided copper for the graphite and to apply it by either or both of the methods used for graphite.

Impression surfaces treated as described above are poor conductors, and while acceptable, still leave much to be desired, because, when placed in an electrolytic bath, deposition starts from the point or points of contact and grows very slowly over the treated surface.

Under the most favorable conditions from 15 to 25 minutes will be needed to attain coverage? on electro-type forms of the size usually used. In order to reduce this time element, various assisting means have been proposed and attempted. Most notable of these is the Knight process.

ing a film, consisting of a homogenous mixture of a reductant substance and a conductive substance, in a solution that acts both as the electrolyte of a battery and as a plating solution. The theory involved is that the minute particles of reductant substance, in tending to go into solution due to their solution pressureor electro-positive relation toward the electrolyte, generate an electro-motive force and cause a current of electricity After coverage" is attained, electro-deposition I,

is continued until the desired thickness of metal is built up.

The principal object of the present invention is to provide for obtaining a greater and more uniform conductivity, particularly on the walls of recesses, than is possible by methods now in use, thereby reducing to a minimum the time needed to attain coverage and to obviate the need of laborious chemical and mechanical assisting methods. r

According to the present invention, a chemito flow through the solution "and'hence back to themselves through minute inert conductive particles in intimate contact with themselves. This series of conditions causes the conductive particles to act as cathodes in relation to the solution, and since metallic-ions are present in the solution due to-the dissociation of a dissolved metallic salt, the metallic ions are neutralized and deposited upon the conductive particles, thereby forming a continuous metallic film over the treat- Experiment cor- I ed non-conductive surface. roborated this theory. It was found that the resultant metallic films were much more conductive than were the films produced by any other sists of fixing by impingement a mixture of about by weight of 200 mesh globular zinc and about 25% by weight of 200 mesh graphite to the surface of the impression material or other nonconductive surface. The zinc content, however, may vary from 10% to the' more practical ratios being above 20%, and the remainder to being graphite.

Another method according to the invention consists in fixing by impingement a mixture of a finely divided electro-positive metal such as zinc, aluminum or magnesium, or alloys of these, and a finely divided less electro-positive metal such as tin, lead, copper or antimony in approximately the above proportions. The advantages of the impingement method are described in detail below.

This treated surface is then brought into contact with a striking solution that is workable when it is approximately normal in zinc sulphate and approximately normal in copper sulphate. The film that results from this treatment will be an extremely thin film of copper. It is not necescally deposited film of metal is obtained by plac- 65 sary to apply current to the striking solution process that the electrical resistance between the.

two substances be an absolute minimum. On a flat wax surface sufllcient force can be applied by hand brushing with a velour powder puff or by using a moderate stiff short haired brush. The brushing must be continued until the surface has a bright metallic sheen. Before treating with the striking solution the unflxed, non-adhering material must be removed. This is best accomplished by washingwith a water spray.

The above described method is applicable only locities, possess the minimum viscous resistance and have no tendency to hold the oxide covered r'eductants in phase.

In experiments conducted along this line, it was found that practically the same percentage compositions suitable for brushing application were also suitable for air impingement application. It was found that the impact velocity had to be accommodated to the relative hardness or softness of the wax. The range used for the extreme conditions found in electrotype waxes was from 4,000 to 50,000 feet per minute. The reductant and conductant mixtures applied by this method produce excellent bright, highly conductive metallic films on all areas and surfaces after strikin in the usual "striking solution and are easily several thousand times as conductive as the graphite to flat or slowly curved wax surfaces and will I not work on indented surfaces such as are used in electrotyping because sufficient force cannot be applied to the indented parallel type face and the ,indented vertical type wall surfaces to insure the essential low resistance contacts. This method while being unquestionably novel is very laborious, unclean and of such limited application that it is not proposed to direct any of the claims of this application to its protection.

In seeking to overcome the limitation to flat surfaces of the above method, I attempted to use the principle of the electrotypers wet leading machine. This machine, widely used in the electrotyping industry to apply a conductive film of graphite to electrotype forms, operates by squirting jets of a water emulsion of graphite against the moving electrotype form. Extensive experiments were conducted looking to the determination of the proper relation of zinc-graphite percentage composition, zinc-graphite-water percentage composition and jet pressure. All prom films used in the electrotyping industry.

Suitable apparatus for the coating of electrotype molds is more fully'discussed in my co-pending application No. 231,349, now Patent No. 2,280,240 of April 21, 1942, which may be considered cogent to the present invention, although other impingement apparatus meeting the stated requirements may be used. If it is borne in mind that the action of this process is dependent upon ising combinations and conditions were used even up to the yield, or distortion point of the wax. No set of conditions was found to produce a,satisfactory film. While graphite could be deposited out of the emulsions under almost any condition of jet pressure or temperature, little if any of the zinc could be made to adhere under even the most extreme conditions. It was also found that the zinc-graphite mixtures decomposed rapidly when wet.

Confronted by the failure of the wet method, I concluded that since all finely divided metals, the cheapest powerful reductants, were covered with oxide films, these oxide films when wet were not only very friable, but also must possess a greater aflinity for water than for wax or guttapercha. It was also reasoned that the force tending to cause adherence was the impact velocity than the pressure of the impacting stream, and that the viscous resistence of any fluid medium would largely counteract the particles kinetic energy or impact velocity force, especially since at or kinetic energy of the individual particle rather the formation of a film consisting of billions of minute short-circuited cells, it will be apparent that the current density produced through the electrolyte will be the resultant of the number of anodes or reductant particles per unit area, the resistance of the short circuit, the reactivity of the reductant with the electrolyte, the resistivity of the electrolyte and the deposition potential of the desired metal ion upon the particular conductive particle used.

In producing conductivity upon wax electrotypes the number of anodes per unit area will be the resultant of the ratio of the reductant particles to the conductive particles, the size and shape of the reductant particles, the size, shape and nature of the conductive particles, the force or speed with which they are applied, and the inherent adhesiveness of the wax toward the reductant and the conductive particles. The latter factor is highly distinctive for every particular wax formula and for anygiven temperature of the particular wax. Only particles that are either flaked, amorphous or substantially globular adhere well to wax.

The resistance of the contact between the reductant particles and the conductive particle will tacts will be. Rosin and oil or grease present in or on the surface of the wax are highly inimical.

The reactivity of the reductant toward the electrolyte will of course depend upon the electrolytic potential of the reductant toward the the surface under treatment there would be eddy currents flowing at right angles to the direction of the impinging stream. v soned and noted that relatively tremendous hydraulic impact pressures do not correspond to very high impact velocities.

On the other hand, I discovered that a gaseous medium, such as air, offered a suspension medium that would permit very great impactve- It was further reaelectrolyte, the ionic density of the electrolyte, the temperature of the electrolyte, the tendency of the reductant to form protective oxide films and the inherent degree of passivity of the particular reductant in any given electrolyte.

The factorsaffecting resistance of electrolytes and deposition .potentials are well described in the literature of electro-deposition.

In view of the many factors affecting the reaction of this process it should be obvious that no-speciflc formula for the ratio of conductive particles to the reductant particles can be stated as being inevitably successful. The ratio must be adapted to the specific conditions of wax compo- I sition, wax temperature, solution composition, solution temperature, application velocity, etc.,

. thatit/is to be operated under. It will be found that if the current density is too great, hydrogen will be evolved from the treated surface upon immersion in the electrolyte and a spongy deposit of metal will result. This condition indicates too high a ratio of reductant to conductive particles. Should the current densitybe too low a very thinfilm of metal will be deposited that redissolves almost as fast as it is formed. This condition indicates too low a ratio of reductant to conductive particles.

Should the contacts between the reductant and conductive particles be of too high a resistance, simple chemical replacement will occur and a pulverant'film of metal of extremely low conductivitywill result. This condition indicates insufficient application velocity. The optimum ratio for a given set of conditions can easily be determined by the use of conductivity bridge measurements on'surfaces treated with compositions of different ratios.

When intelligently operated, as above outlined,-

. this process will yield conductivities hitherto unattainable by any prior art process.

When applied to electrotyping, my invention represents a distinctly major advance in that art, because 'it enables the attaining of results hitherto eitherextremely slow, laborious, expensive or impossible.

In the past electrotypers have had to content themselves either with the slow coverage that unassisted graphite films would give them or use a laborious assisting, process, known as the oxidizing or Knight process, which while producing good conductivity on the raised portions of the wax, produces little or noimprovement in conductivity on the side walls and type face 'surface that are recessed into the wax, the places where good conductivity is most desired. In the case of plates having fine lines or dots with considerable white area between them, the use of the so-called oxidizing process is distinctly disadvantageous, because the good conductivity of the raised wax surface robs the poorly conduc- 'tive recessed areas of the needed current. In-

numerable failures result from this peculiarity of the oxidizing process, and much costly time and labor are consumed in repeating the entire operation of molding, graphitizing, and deposition .or correcting undeposited areas by hand operations upon-the completed electrotype plate.

My invention, which is quickly performed by the expenditure of much less labor than the oxidizing process, yields a high uniform conductivity on the raised wax surfaces, the type side walls and the deeply recessed type face areas, gives almost instantaneous coverage, permits the reproduction of wax molding of fine line and dot detail heretofore impossible and reduces failures, because of non-conductive areas, to the vanishing point. Furthermore, by the use of this invention, nickel electrotypes may b rapidly deposited upon a bright metal film such as nickel, cadmium, cobalt or tin, thereby'adding greatly to the sales appeal of the finished electrotype.

The striking solutionvaries in its composition according to operating conditions and can readily be determined by persons skilled in the art.

the above described solution that is approximately normal in copper sulphate and approximately normal in zinc sulphate. In some cases an alkalin solution may be preferable. In any case, howeverfthe reductant has a higher solution pressure toward the strikingsolution that has the metal to be deposited or; in other words, the reductant material is higher in the electro-motive series than, or electropositive to, the metal to be deposited.

The preferred metalsto be used as the reductant are zinc, magnesium and aluminum because they are electropositive to the metals ordinarily vto-be deposited and are commercially available as.

well as stable in finely powdered form. Under some conditions these metals may be passive toward the striking solution. The passivity can be ofiset by using an alkaline bath or by alloying the metal with about 2% of an impurity such as tin, copper or zinc. Magnesium and zinc have however been used without alloying, and pure zinc powder mixed with graphite will deposit copper out of an acid copper sulphate solution.

Although the application of this invention to the art of electrotyping has been dealt with at length herein, it is not my intent to limit it to that field.

. preferred embodiments of my invention, it is to be definitely understood that I do not desire to limit the application of the invention thereto, and any change orchanges may be made in the materials used and in the steps and operations involved in assembling and applying the same, within the spirit of the invention and the scope of the subjoined claims.

. What I claim is:

1. The method of producing a highly conductive'metallic film of a continuous crystalline structure on an electrically non-conductive surface, comprising first embedding in said surface a film composed of a mixture of finely divided reductant substance of good electrical. conductivity and finely divided conductive substance of lowe: electrolytic potential than said reductant substance, by impinging at high velocity an air suspension of said mixture against said non-conductive surface, removing the excess non-adhering material, then bringing said treated surface in contact with an aqueous metal solution toward which the reductant substance has a higher electrolytic potential than the metal or metals in solution.

-2. The method of producing a highly conduc-' tive metallic film of a continuous crystalline structure on an electrically non-conductive surface, comprising first embedding in said surface a film composed of a mixture of finely divided reductant substance of good electrical conductivity and finely divided conductive substance, by impinging at high velocity an air suspension of said mixture against said non-conductive surface, removing the excess non-adhering material, then bringing said treated surface in contact; with an aqueous metal solution in which said conductive substance is in- For 'examplepin depositing copper on a surface treated with powdered zinc and graphite, an acid copper sulphate solution may be'used instead of ert and toward which the reductant substance has a higher electrolytic potential than the metal or metals in solution.

3. The method of producing a highly conducture on an electrically non-conductive surface,

comprising first embedding in said surface a film composed of a mixture of finely divided reductant substance of good electrical conductivity and finely divided graphite, by impinging at high velocity an air suspension of said mixture against said non-conductive surface, removing the excess non-adhering material, then bringing said treated surface in contactwith an aqueous metal solution toward which the reductant substance has a higher electrolytic potential than the metal or metals in solution.

4. The method of producing a highly conductive metallic film of a continuous crystalline structure on an electrically non-conductive surface. comprising first embedding in said surface a film composed of a mixture of finely divided reductant substance of good electrical conductivity and finely divided conductive substance of lower electrolytic potential than said reductant substance,

I by impinging at high velocity an air suspension of said mixture against said non-conductive surface, removing the excess non-adhering material, then bringing said treated surface in contact with an aqueous metal solution without application of extemal current, toward which solution the reductant substance has a higher electrolytic potential than the metal or metals in solution.

5. The method of producing a highly conductive metallic film of a continuous crystalline structure on an electrically non-conductive surface, comprising first embedding in said surface a, film composed of a mixture of finely divided metal alloy and finely divided conductive sub: stance of lower electrolytic potential than said metal alloy, by impinging at high velocity an air suspension of said mixture against said non-conductive surface, removing the excess non-adhering material, thenbringing said treated surface in contact with an aqueous metal solution in which said alloy is electrolytically active and toward which the alloy particles have a higher electrolytic potential than the metal or metals in solution.

6. The method of producing a highly conductive metallic film of a continuous crystalline structure on an electrically non-conductive surface, comprising first embedding in said surface a film composed of a mixture of finely divided I treated surface in contact with an aqueous metal solution in which said alloy is electrolytically active and toward which the alloy particles have a higher electrolytic potential than the metal or metals in solution.

8. The method of producing a highly conductive metallic film of a continuous crystalline structure on an electrically non-conductive surface, comprising first embedding in said surface a film composed of a mixture of finely divided metal alloy and finely divided conductive substance, the alloy consisting of aluminum and an activating ingredient, by impinging at high velocity an air suspension of said mixture against said nonconductive surface, removing the excess nonadhering material, then bringing said treated surface in contact with an aqueous metal solution in which said alloy is electrolytically active and toward which the alloy particles have a higher electrolytic potential than the metal or metals in solution.

9. The method of producing a highly conductive metallic film of a continu'ous crystalline metal alloy and-finely divided conductive substance, the alloy consisting of a, metal normally passive in the solution to which it isto be subjected, alloyed with an activating ingredient, by j impinging at high velocity an air suspension of said mixture against said non-conductivesurface,

removing the excess non-adhering material, then bringing .said treated-surface in contact with an aqueous metal solution in which said alloy is electrolytically active and toward which the alloy particles have a higher electrolytic potential than the metal ormetals in solution. v a s -7.1 The method ofiproducing a highly conductive metallic film of; a; continuous crystalline structure on an ,electrically no onductive surface, comprising firstembedding in "aid fs'urface metal alloy and j finely divided;- conductive substance, the alloy consistingfof -a .metal normally l" passive in the solution to which'it, is to be subagainst said non-conductive surface, removing the, excess non-adhering material; then bringing, said structure on an electrically non-conductive surface, comprising first embedding in said surface a film composed of a mixture of finely divided metal alloy and finely ,divided conductive substance, the alloy consisting of aluminum and approximately two (2%) per cent of an activating ingredient, by impinging at high velocity an air suspension of said mixture against said nonconductive surface, removing the excess non-adhering material, then bringing said treated surface in contact withan aqueous metal solution in which said alloy is electrolytically active and toward which the alloy particles have a higher electrolytic potential than the metal or metals in solution.

10. The method of producing a highly conductive metallic film of a continuous crystalline structure on a electrically non-conductive surface, comprising first embedding in said surface a'film composed of a mixture of finely divided magnesium and finely divided conductive substance, by impinging at high velocity an air suspension of said mixture against said non-conductive surface, removing the excess non-adhering material, then bringing said treated surface in contact with an aqueous solution of a metal or metals having a lower electrolytic potential than magnesium.

11. The method of producing a highly conductive metallic film of a continuous crystalline structure on an electrically non-conductive surface, comprising first embedding in said surface a-film composed of a mixture of finely divided magnesium and finely divided graphite, by impinging atv high velocity an air suspension of said mixture against said non-conductive surface, removing the excess non-adhering material, then bringing said treated surface in contact with an aqueous solution of a metal or metals having a lower electrolytic potential than magnesium,

:12. The method of producing a highly conductive metallic filmof a continuous crystalline struccomprising first embedding in said surface a film composed of a mixture of finely divided zinc and finely'divided conductive substance, by imping- 7 iin'g'at high velocity an. air {suspension of said rn xture against "said non-conductive surface, 7 removing the excess non-adhering material, then bringing'jsaid treated surface in contact with an aqueous solution of a-metal or metals having a lower relectrolytic potential than zinc.

structure on an electrically non-conductive sur- I face, comprising first embedding in said surface a film composed of a mixture of finelydivided zinc and finely divided graphite, by impinging at high velocity an air suspension of said mix ture against said non-conductive surface, removing the excess non-adhering material, then bringing said treated surface in contact with an aqueous solution of a metal or metals having a lower electrolytic potential than zinc.

14. The method of producing a highly conductive metallic film of a continuous crystalline structure on an electrically non-conductive surface, comprising first embedding in said surface a film composed of an experimentally determined mixture of. finely divided reductant substance of good electrical conductivity and finely divided conductive substance of lower electrolytic potential than said reductant substance, by impinging at high velocity an air suspension of saidmixtureagainst said non-conductive surface, remov with the kinetic energy of a particle of 200 mesh surface with the kinetic energy 'of a particle of 200 mesh and a density of approximately 1.5 at

a velocity of at least 4,000 feet per minute, re-

moving the excess non-adhering material, then bringing said treated surface in contact with an aqueous metal solution toward which the reductant substance has a higher electrolytic potential than the metal or metals in solution.

18. The method of producing a highly con ductive metallic film of a continuous crys alline structure on an electrically non-conductive surface, comprising first fixing to said'surface a filmcomposed of an experimentally determined mix.- ture of finely divided reductantsubstance of good electrical conductivity and finely divided conductive substance of lower electrolytic potential than said reductant substance, by impinging at high velocity an air suspension of said mixture against said non-conductive, surface, the final velocity of the particles ofsaidsubstances being such that said particles are impinged against said surface and a density of approximately 1t5 at a velocity ing the excess non-adhering material, then bringing said treated surface in contact with an aqueous metal solution toward which the me ductant substance has a higher electrolytic potential than the metal or metals in solution. 15. The method of producing a highly. conductive metallic film of a continuous crystalline structure on an electrically non-conductive surface,'comprising first embedding in said surface a film composed of an experimentally determined mixture of finely divided reductant substance of good electrical conductivity and finely divided conductive substance, by impinging at high velocity an air suspension of said mixture against said non-conductive surface, removing the excess non-adhering material, then bringing said treated surface in contact with an aqueous metal solution in which said conductive substance .is inert and toward which the reductant substance has a higher electrolytic potential than the metal or metals in solution.

16. The method of producing a. highly con.- ductive metallic film of a continuous crystalline structure on an electrically non-conductive surface, comprising first embedding in said surface a film composed of an experimentally determined mixture of finely divided reductant substance of good electrical conductivity and finely divided graphite, by impinging at high velocity an air suspension of said mixture against. said nonconductive surface, removing the excess nonadhering material, then bringing said treated surface in contact with an aqueous metal solution toward which the reductant substance has a higher electrolytic potential than the metal or metals in solution.

17. The method of producing a highly conductive metallic. film of. a continuous crystalline structure on an electrically non-conductive surface, comprising first fixing to said surface a film composed of an experimentally determined mixture of finely divided reductant substance of good electrical conductivity and finely divided conductive substance of lower electrolytic potential than said reductant substance, by impinging at high velocity an air suspension of said mixture against said non-conductive surface, the final velocity of the particles of said substancesv being such that said particles are impinged against said of 4,000 to 50,000 feet per minute, removing the treated surface in contact with an aqueous metal solution toward which the reductant substance has a higher electrolytic potential than the metal or metals in solution.

19. The method of producing a highly conductive metallic film of a continuous crystalline structure on an electrically non-conductive surface, comprising first fixing to said surface a film composed of an experimentally determined mixture of finely divided reductant substance of good electrical conductivity and finely divided conductive substance of lower electrolytic potential than said reductant substance, by impinging at high velocity an air suspension of said mixture against said non-conductive surface, the final velocity of the particles of said substances being such that said particles are impinged against said surface with the kinetic energy of a particle of 200 mesh and a density of approximately 1.5 at a velocity of at least 4,000 feet per minute, removing the excess non-adhering material, then bringing said treated surface in contact with an aqueousmetal vsolution toward which-the reductant substance has a higher electrolytic potential thanthe metal or metalsin solution.

20. The method of producing a highly conductive metallic film of a continuous crystalline structure on an electrically.non-conductive surface, comprising first fixing to said surface a film composed of an experimentally determined mixture of finely'd-ivided reductant substance of good electrical conductivity and finely divided conductive substance of lower electrolytic potential than said reductant substance, by impinging at high velocity an air suspension of said'mixture against said non-conductive surface, the final ve: locity of the particles of said substances being such that said particles are impinged against said surface with the kinetic energy of a particle of 200 mesh and a density of approximately 1.5 at

a velocity of 4,000 to 50,000 feet per minute, removing the excess non-adhering material, then bringing said treated surface in contact with an aqueous metal solution toward which the reductant substance has a higher electrolytic po-. tential than the metal or metals in solution.

. BERTRAM C. KATHE.