US2250436A - Matrix for electrodeposition of foraminous sheet - Google Patents

Description

July 22, 1941. E. o. NoRRls 2,250,436

MATRIX FOR THE ELECTRDEPOSITION OIFFORAMNOUS SHEET Filed Oct. 6, 1939 2 Sheets-Sheet 2 ze Z7 50% 1775 Patented July 22, 1941 -`2,250,436 OFFICE MATRIX FOR. ELECTRODEPOSITION F FORAMINOUS SHEET Edward 0. Norris, Westport, Conn., assignor to Edward 0. Norris, Inc., New York, N. Y., a corporation of New York Application October 6, 1939, Serial No. 298,216

2 Claims.

The invention relates to matrices adapted to be employed as a cathode for the reception of a nonadherent electrolytic deposit in the form of foraminous sheet. The deposit-receiving surface of such a matrix comprises a network of electrically conductive material orat least of material capable of receiving an electrolytic deposit, the spaces delimited by said network being of electrically non-conductive material or at least of material that will not receive an electrolytic deposit. In matrices of this character, the insulated areas are produced by first creating a multitude of pits or depressions in a metal surface 4and then lling the pits or depressions with the insulating material, which may beBakelite, glass, enamel or other material having the propertyabove described. i

The foregoing and various other methods of producing such a matrix are described in my United States Patents Nos. 2,166,366, issued July 18, 1939, and 2,166,367, issued July- 18, 1939, and,

.as the details of themethod are not involved in the invention, they will not be further described. 'I'he invention deals with a special construction of a matrix of the general type above described but in which provision is made whereby the llings may be readily removed from the pits and the pits be again refilled. 'I'his is more important when the fillings consist of material that is insoluble or diilicultly soluble, since llings of this character cannot be removed except with the greatest difliculty, if at all. Although if the llings are-of soluble material they can to a certain extent be removed by dissolving them, even then it is diilicult to remove all of the material from certain shapes of pits which I will hereinafter describe.

Referring to the drawings, Fig. 1 is a perspective view of a fragment of a copper plate,provided with a multitude of pits in its surface; I Fig. 2 is a plan view of an obverse of the plate Fig. 3 is a view on the line 3 3 of Fig. 2;

Fig. 4 is a view showing two successive steps in the process:

Fig. 4a is a. detail view of a fragment of Fig. 4;.

Fig. 5 is a view in section of a base matrix;

Fig. 6 is a view-similar to Fig. 5 showing the pits of the base matrix of Fig. 5 filled with insulating material;

Fig. 7 is a perspective view of the base matrix `C of Fig. 5 shown however flat instead of curved;

Fig. 8` is a view in sectional elevation on a median plane passing through a row or a column ofpits but. inaddition; showing certain of the pits plated with copper and lled with insulating material;

Fig. 9 is a view in section showing several initial lsteps in producing a modied form of matrix;

(ci. 20a-,281)

It should be explained that the most practical use to which such a matrix is put is that of producing very "ne screen-say, from that having ifty apertures to the linear inch to that having several hundred. It is therefore not feasible to illustrate the matrix of my invention except on a very exaggerated scale. Of course. it is also to be appreciated that only a very small area of an actual matrix can be shown.

,' In practicing the invention, I prefer to em-` ploy a base matrix having special characteristics that function to retain the llings securely locked in place 'in the pits. The construction which I prefer for this purpose consists in so shaping the pits that, as viewed in vertical section, they appear to be slightly undercut to provide inwardly overhanging edges. ducing a matrix of this character will nowbe described, reference iirstl being made to Figs. 1-6, inclusive;

Fig. 1 shows a plate A which may be of any metal that lends itself to the process as I will describe it, but which is preferably of copper, the surface being provided with the pits Il isolated from each other by the walls l2, and it will be observed that the walls of each pi't nare slightly outwardlyas they approach the surface of the plate. Such a platevcan be produced by Several already known methods, but for a speciiic description of one method reference is again made to my two patents above referred to.

Briefly, an illustrative method consists in first applying a light-sensitive film, for example of light-sensitized .photographers glue, to the surface of the plate, and then photo-printing a reticulated pattern on the light-sensitive lm by projecting light upon it-through a screen exhibiting a multitude of opaque dotsa'rranged in rows and columns. After suiiicient exposure the iilm becomes hardened where exposed `to the light (i. e.. the light passing through the screen between the dots) and the unexposed portions (i. e., where the light is stopped off by the dots) being easily removableby washing. After washing, etching uid (e. g., ferric chloride) is applied to the plate, resulting in producing the pits Il where the copper surface is exposed.

An obverse of the pitted surface of the plate just described which I will refer to as the master plate is then made by electrolytic deposition, the deposit being likewise preferably of copper. In order that the deposit shall be 4non-adherent, the surface of the master plate may be coated with a stripping film, for example a very thin film of a solution of carnauba wax in benzol. It is preferable that -the solution be applied sparingly, although of course in suicient quantity to cover -the surface, and that the' plate be heated in order A suitable process of pro to result in equal and complete distribution, and removal of the excess. Bronze powder such as is used by electrotypers may be then dusted over the waxed surface. Such a surface although conductive, is non-adherent to electrolytic deposition, and the result of this operation is illustrated in Figs. 2 and 3, the protuberances which are the obverse of the pits of the master plate being indicated by the numeral I3 and the valleys which are the obverse of the lands I4 of the master plate being indicated by the numeral I5.

After the plate of obverse pattern to that of the master plate (which I will indicate as a whole by the letter B) has been stripped from the master plate, it is formed into the shape of a hollow cylinder and its ends joined by any convenient means, such as by solder I5a, the protuberances being then located on the interior periphery of the cylinder. To clearly show this, it is possible to illustrate only a section of the cylinder in the region of the juncture. In point of fact, in the case of a cylinder of the curvature shown, protuberances would be almost, and in some cases actually microscopically small. The hollow cylinder formed from the plate B is in turn usedas a matrix for the electrolytic deposition of a third plate indicated as a whole by the letter C. First, however, a thin adherent deposit I6 of copper is applied to the patterned surface of the plate B by electrodeposition, and the result is that if this step be carried out under standard conditions of operation, the rate of growth in thickness of the deposit in the depths of the valleys I5 is slower than the rate of growth on more exposed portions of the protuberances. The effect produced is illustrated in detail in Fig, 4a, where, as may be observed, the copper is considerably thicker in the regionsl I'I and I1' than it is at the bottoms of the valleys as indicated at I8 and I8'. The deposition is carried out to a suicient extent to cause the areas indicated by II and I1' to* approach each other, the ultimate result being that the dimension a is less than the dimension b. The plate thus produced is illustrated in Fig. 4.

The plate C, of a metal different from coppere. g., nickel-is now deposited by electrodeposition on the copper surface I6 on the interior of the periphery of the cylinder. While it might appear that the nickel, like the copper, would grow in thickness more rapidly in the regions I1, I1 than in the regions I8, I nd that such -is not the case and the valleys become completely filled with nickel. I am not able to explain this phenomenon except by the theory that it is due to the high throwing power of nickel. The plate B with its added copper film I6 is then removed either by chemical action or by deplating electrolytically, resulting in the plate shown in Fig. 5. If the copper is to be removed chemically, it may be done by subjecting it tothe action of (e. g.)- (1) a solution of potassium cyanide or preferably (2) a mixture of chromic or sulphuric acid in water, suitable proportions being about as follows:

Sulphuric acid lb-- 2 Chromic acid- 1b l Water en! 10 The pits I9 of the plate C are then filled with Bakelite 20, cement or other substance electrically non-conductive or at least incapable of receiving an electrolytic deposit on its exposed surface. Bakelite is preferred.

It will be observed that, by virtue of the fact that the walls of each pit' converge slightly as they approach the surface, the fittings 2U are securely locked in place'and the cylinder of Fig. 6 with its fillings may serve as a matrix for the electrolytic production of foraminous sheet like screen or other fabric of reticulated pattern,

It is obvious from the foregoing that an important thing in the selection of metals (besides of course their adaptability for electrolytic deposition) is that one be passive to some kind of a corroding agent that has a destructive action on the other hand and that one have a low and the other a high throwing power as above explained. Nickel and copper have these contrasting properties but are noted merely by way of example, al though it may be said that thus far I have found that they answer my purposes more satisfactorily than any other combination.

Referring now to Figs. 7-10 of the drawings:

Fig. 7 shows a fragment of a matrix base similar to the 'matrix base C of Fig. 5 except that it is flat instead of cylindrical provided with the pits 26 arranged in rows and columns as shown, separated by the walls or ridges 2l running in one direction and the walls or ridges 28 running transversely of them, these walls merging at the corners 29. The lands 30 of the walls 21 and the -lands 3I of the walls 28 therefore present an electrically conductive surface of reticulated pattern capable of receiving an electrolytic deposit of corresponding pattern, if deposition on the surfaces of the pits be prevented.

In practice such deposition is prevented by filling the pits with some non-conductive material such as glass, enamel, sealing wax, Bakelite or the like, leaving however the lands 30 and 3I exposed. However, a matrix of the foregoing description is, as has been before briefly noted, subject to several objections, the most serious of which and the one with which my invention chiefly deals being that the fillings become loose and drop out or become disintegrated after comparatively limited use or are pulled out in stripping a deposited sheet. As the production of such matrices fromvthe initial step of producing the pits is an expensive operation not only on account of the eilort involved but on account of delaying operations in a producing plant, commercial production on such simple matrices at a reasonable cost is impossible. It is one of the purposes of my invention to produce a matrix of such a character that the fillings can be quickly and easily removed, leaving intact original metallic matrix base. Since refilling the pits in such a matrix base is a comparatively easy operation, the practical objections which I have above referred to are mainly, if not wholly, removed.

Continuing the description from the matrix base of Fig. 7, the next step is to line the entire surfaces of the pits and also to cover the lands with a thin coating 32 of copper, care being taken-that the entire surfaces are completely coated and that no nickel is exposed. 'I'his step may be conveniently carried out by eleetrolytic deposition. I should,` however, state at this point that in specifying copper tol be plated on a base of nickel, I select these metals merely because they are cheap and because there are available common etching agents that react on copper to the exclusion of nickel. If the matrix base were of copper, the coating might be of chromium or any other combination of two metals, one of which is capable of being removed by a chemical reagent or by electrolytic deplatingY or other means to the exclusion of the other could be used. In other words, nickel and copper are selected merely as examples of preferred mlaterials for producing my matrix and` not as exclusive of other combinations.

'Ihe plating with copper having been completed as is illustrated'in Fig. 8, the pits are then filled with Bakelite or other suitable insulating material such as has been above referred to. The Bakelite in plastic form may be introduced into the pits by spreading a quantity over the surface, then squeegeeing or brushing r until thoroughly worked into the holes and, when dry, rubbing off until the deposit-receiving surfaces are clean and bright and capable of receiving a deposit when the matrix is employed as a cathode in an electrolytic bath. It may now be assumed thatfrom one cause or another, such as physical violence, chemical action or wear, it is desired to remove the fillings and re-fill the matrix. If the matrix base be of nickel with a copper plating thereon as suggested, a suitable reagent for the purpose is a solution of chromic acid and sulphuric acid in water, a workable formula being, for example, as follows:

be less than the corresponding diameter of the mouth of the pit with the lining absent.

'I'he method of producing pits with overhanging edges has been described in connection with Figs. 1-5, both inclusive.

The matrix of Fig. 8 is not however my preferred form since the fillings are not as securely locked in position as they preferably should be, and they are very liable to be pulled out in the ordinary use of the matrix.

4The preferred form of matrix and method of producing it is shown in Figs. 9 and 10 and the explanation will proceed from the .point at which the nickel matrix base has been plated Igvviitha copper as described' in connection with Taking up the description therefore from that point, the next step which I follow is to mask the surfaces of the pits against electrolytic deposition, which may be accomplished by introducing into them by squeegeeing, brushing or otherwise a small quantity of a readily soluble substance suitable for the purpose; such as shellac,

Per cent Sulphuric acid 16 Chromic acid 8 Water '76 der ordinary conditions in a comparatively brief time. When the reaction has been entirely completed, the iillings can, as will be apparent, be

removed by such methods as scrubbing, rolling a sticky roller over it or making it cathodic in a dilute sulphuric acid solution. After the loosened fillings have been removedV and the surface including'the pits has been properly cleaned, there remains the matrix base restored to the original condition as shown in Fig. 1. To resurface or re-fill, it is simply necessary to proceed as before to produce the structure of Fig. 8, and this procedure may be repeated a great many times in case of any given matrix base.

It is preferable, although not essentially involved in the invention, that the side walls of the pits be undercut as shown in the drawings but nnly to an extent sufficient to permit the fillings to readily drop out when the lining is removed. In-other words, thegreatest diameter of the lining should be only such that the filling can pass through the mouth of the pit when the lining is removed; for example, if-the mouth of the pit (before applying the copper lining) have a diameter of .015", the greatest corresponding diameter of the filling should be less than .015" so that the overhanging Walls of the pit will not obstruct the removal of the filling when the lining has been removed. To state the matter in another way, it is preferable that the greatest asphaltum or the like. The masking material may be applied freely and should cover the walls of the pits to their intersection with the copper covered lands.

In practice it is necessary that surplus masking material be 'thoroughly cleaned from the lands forming the screen pattern before further steps are taken.

lThe masking material, especially in the case of shellac, tapers in thickness as shown in crosssection (Fig. 9) to the rims of the pits. After the shellac (if it be used) has been introduced, the partially finished matrix is preferably subjected as a cathode to electrolytic deposition in a copper bath, with the result that an additional coating 33 of copper is laid-on the copper coating previously applied but only on the lands and slightly down over the shellac or whatever masking material may be employed. In the drawing Y a line of demarcation is Ashownbetween the copper coating first applied and the second coating, although in point of fact the second coating would be closely adherent to the first, and in most cases no actual line of demarcation would be apparent.

At this point the partially finished matrix is again subjected cathodically to electrolytic deposition but this time in a nickel bath resulting in the deposit of the nickel layer 34 over the copper. The surface of this nickel deposit becomes the depositing surface of the matrix for the production of foraminous product referred to.

It should be explained that the copper deposit 33 is not essential to the structure, it being quite possible to apply the nickel deposit 34 directly to the ridges without the interposition of the copper deposit 33. However, a copper deposit is more adherent to a copper surfaced than is a nickel deposit, and, since the lands are very narrow, it is desirable that the nickel deposit be as adherent as possible. The interposition of the copper deposit 33 helps greatly in accomplishing these objects by increasing the area of nickel-copper contact. Another reason for interposing the copper deposit 33 isV that the slight gassing that takes place in depositing nickel has diameter of the pit with the lining present should posit 33, the nickel 34 is deposited only on copper, and therefore the shellac is protected from the destructive effect of the evolution of gases which takes place as an incident to depositing' nickel.

The reason for this apparently rather complicated procedure is as follows: The particular type of lresinoid which We now use was arrived at after trying, unsuccessfully, a great many materials, but it has no resistance to plating solutions until it isy baked, and when it has once been baked an additional layer of resinoid Will not stick to it and the original layer cannot be dissolved out, so it is necessary to use a material like shellac for the lock-forming filling and then dissolve it out, applying the resinoid as one complete filling.

The next step comprises removing the masking material, for example, by the application of a suitable solvent. In the case of shellac, alcohol, as is well known, satisfactorily serves this purpose, and its action may be assisted by applying it with a spray accompanied by brushing and, if

necessary, by some form of agitation of the matrix.

After the shellac or other masking material has been completely removed and the entire surface including the Walls of the pits has been cleaned as thoroughly as possible, the matrix is then filled with an insulating material or s. material that is incapable of taking an electrolytic deposit and capable of resisting the action of hot plating solutions and mechanical wear, and Bakelite may be used as in the case of the matrix of Fig. 8. The fillings are indicated by the numeral 35 in Fig. 10, and it will be observed that, by virtue of the overhanging layers of copper and nickel, respectively, the fillings are securely locked in place. Even such llings however are liable to breakage, disintegration by` chemical action, wear and other causes, and therefore it is necessary that such a matrix be from time to time re-filled, as in the case of the matrix of Fig. 8. This may be accomplished, as in the case of Fig. 8, by the application of the solution of sulphuric and chromic acids above referred to. While in this type of matrix there is no exposed copper, I find nevertheless that in some way the solution reaches the copper plating 32 and 33 Without affecting the nickel 34. In view of the fact that all copper surfaces are apparently sealed by the Bakelite fillings, I am unable to give a dependable explanation as to why this should be so, but it may be that the solution has the property of being able to permeate through the Bakelite, or it may be that it creeps between the Bakelite and the metal surfaces to which it contacts in spite of the fact that the Bakelite appears to be very adherent to the metal. These, however, are merely theories, and I am obliged to confine myself to a statement that the phenomenon takes place. In any event the effect of the action of the solution is to disintegrate the copper, whereupon the nickel layer'34 and the fillings can be readily removed. r

Still another method is to deplate the nickel coating 34 by subjecting the entire matrix anodically to electrolytic action in a 5% HCI solution, the sides and bottom being preferably masked beforehand.

I have described above certain embodiments of my invention and a preferred process with certain modifications thereof, but I wish it to be understood that these are illustrative and not limitative of my invention and that I reserve the right to make various changes in form, construction, and arrangement of parts and also to make various changes in process of manufacture falling within the spirit and scope of my invention, as set forth in the claims.

I claim:

1. A matrix for the electrolytic production o foraminous sheet, comprising a nickel plate provided in its surface with a multitude of pits having constricted orifices, said pits being lined with copper, the said copper lining partially enclosing a solid body of material passive to electrolytic deposition, the thickness of the copper lining being great enough so that in its absence the said solid body may pass without disintegration from said pits through said orifices.

2. A matrix for` the electrolytc production of foraminous sheet, comprising a nickel plate provided in its surface with a multitude of pits, the Walls of which have transversely constricted zones, said pits being lined with copper, the said lining partially enclosing a solid body of electrically non-conductive material and leaving an area thereof exposed at the orifices of the pits, the thickness of the lining being great enough so that in its absence the said solid body may pass Without disintegration from said pits past the constricted zones.

EDWARD O. NORRIS.

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