US2287123A - Method of producing matrices for the electroforming of foraminous sheets - Google Patents

Description

Patented June 23,1942

METHOD OF PRODUCING MATRICES FOR THE ELECTROFORMING F FORAMINOUS SHEETS Edward 0. Norris, Westport, Comm, assignor to,-

Edward 0. Norris, Inc., New York, N. Y., a corpcration of New York Original application October 6, 1939, Serial No. 298,216. Divided and this application January 21, 1941, Serial No. 375,156 Y 3 Claims. (01. 204-11) This application is a division of my pendin application Ser. No. 298,216, filed October 6, 1939, Patent No. 2,250,436, July 22, 1941.

The invention relates to matrices adapted to be employed as a cathode for the reception of a non-adherent electrolytic deposit in the form of foraminous sheet. The deposit-receiving surface of such a matrix comprises a network of electrically conductive material or at 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 and then filling the pits or depressions with "the insulating material, which may be Bakelite, 'glass, enamel or other material having the property above described. --'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 the method are not involved in the invention, they will not be further described. T In order that the ultimate foraminous sheet to be produced shall be of as uniform construction as possible, including hole size, hole shape, and land cross-sectional shape, I find that it is desirable in the first place to produce what may be termed a skeleton screen, which is subsequently built up by a second electroforming step after the skeleton has been removed from the matrix. However, by the simple etching process employed in producing the pits, it is very difiicult to control the width of the lands of the matrix when this width gets to be very narrow, for the reason that in such cases the walls of adjoining pits are often broken down, which of course renclers the matrix useless. It is therefore the principal object of the invention to produce a matrix having much narrower lands or depositing areas than is possible with a simple etching process.

Referring to the drawing,

Fig. 1 is a perspective view of a fragment of a copper plate provided with a multitude of pi in its surface;

Fig. 2 is a plan view of an obverse of the plate I 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.

It should be explained that the most practical use to which such a matrix is put is that of producing very fine screen-say, from that having fifty apertures to the linear inch to that having several hundred. It is therefore not leasible to illustrate the matrix of my invention ex: cept on a very exaggerated scale. Of course, it is also to be appreciated that only a very small areaof an actual matrix can be shown.

In practicing the invention, I-prefer to employ a base matrix having special characteristics that function to retain the fillings 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. A suitable process of producing a matrix of this character will now be described, reference first 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 ll isolated from each other by the walls l2, and it will be observed that the walls of each pit flare slightly outwardly as'they approach the surface of the plate. Such a plate can be produced by several already known methods, but for a specific de scription 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 film by projecting light upon it through a screen exhibiting a multitude of opaque dots arranged in rows and columns. After sumcient exposure the film becomes hardened where exposed to the light (1. e., the light passing through the screen between the dots) and the unexposed portions (1. e., Where the light is stopped of! by the dots) being easily removable by washing. After washing, etching fiuid (e. g., ferric chloride) is applied to the plate, resulting in producing the pits I I where the copper surface is exposed. I r

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 nonadherent, the surface of the master plate may be coated with a stripping fihn, 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 sufficient quantity to cover the surface, and that the plate be heated in order 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 l3 and the valleys which are the obverse of the lands M of the master plate being indicated by the numeral l5.

After the plate of obverse pattern to that of the master plate (which I will indicateas 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 l5a, 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 3 is in turn used as a matrix for the electrolytic deposition of a third plate indicated as a whole by the letter C. First, however, a thin adherent deposit N3 of copper is applied to the patterned surface of the 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 to the action of (e. g.)-

(l) 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 lbs 2 Chronic acid lb 1 Water... gals 10 Neither, of these reagents will have any appreciable effect on the nickel if merely enough time is allowed for the reaction to remove the copper. If removed by deplating, conventional methods may be employed, the entire plate of Fig. 4 being simply employed as an anode in an electrolytic copper bath.

The pits [9 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 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 im'- portant thing in the selection of metals (besides other a high throwing power as above explained.

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 ofthe 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 regions I! and I1 than it is at the bottoms of the valleys as indicated at- IB and I8. The deposition is carried out to a sufficient extent to cause the areas indicated by H and H to approach each other, the ultimate result being that the dimension a. is less than the dimension D, but-yet the dimension b is much smaller than could be produced by simply etching pits in the original plate. The plate thus produced is illustrated in Fig. 4.

The plate C, of a metal difierent from copper-- e. g., nickel-is now deposited by electrodeposition' on the copper surface IS 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 l1. l1 than in the regions 18, I find that such is not the case and that the valleys become completely filled with nickel. I am not able to explainthis phenomenon except by the theory that it is due to the high throwing power of nickel, The plate B with it added copper film Nickel and copper have these contrasting properties but are noted merely by way of example,

although it may be said that thus far I have found that they answer my purposes more satisfactorily than any other combination.

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. In the method of producing a matrix for the electroforming of foraminous sheet with very narrow lands, the steps which comprise producing a multitude of pits in the surface of a metal plate, rendering the pitted surface including the surfaces of the pits capable ofreceiving an electrolytic deposit that is non-adherent thereto, producing from the said plate by electrodeposition a second metal plate with a surface that is the obverse of the pitted surface of the first-mentioned plate, building out the resulting protuberances on the said second plate laterally by electrodeposition to partially overhang and narrow the valleys that separate them, electroforming on the said second plate a third plate which is the electroforming of foraminous sheet with very narrow lands, which comprises producing a multitude of pitsin the surface of a metal plate,

rendering the pitted surface including the surfaces of the pits capable of receiving an electrolytic deposit that is non-adherent thereto, pro-- ducing from the said plate a second plate with a surface that is the obverse of the pitted surface of the first-mentioned plate, building out the resulting protuberances on the said second plate laterally to partially overhang and narrow the valleys that separate them, elect'roforming on the.

said secondplate a third plate, then removing the second plate from the third plate, and filling the pits in the third plate with material passive to electrolytic deposition.

3. In the method of producing a matrix for the electroforming of foraminous sheet with very narrow lands, the steps which comprise producing a metal plate from the surface of which a multitude of protuberances having electrically from the electroformed plate, and filling the pits in the electroformed plate which are the obverseof the protuberances with material passive to electrodeposition.

EDWARD O. NORRIS.

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