U.S. patent number 3,668,081 [Application Number 05/125,423] was granted by the patent office on 1972-06-06 for production of electrolytic metal.
This patent grant is currently assigned to The International Nickel Company, Inc.. Invention is credited to William Gerard Borner.
United States Patent |
3,668,081 |
Borner |
June 6, 1972 |
PRODUCTION OF ELECTROLYTIC METAL
Abstract
Metals such as nickel are electroformed upon a matrix or mandrel
having an epoxy resist pattern thereon to provide foraminous or
dividable electrodeposited metal separable from the matrix wherein
the matrix is prepared by depositing from 2 to 30 microinches of
standard chromium thereon and the desired resist pattern is applied
to the chromium-plated surface in the form of a thermoset epoxy ink
or paint containing dicyandiamide as a heat-curing agent and then
heat curing the resist pattern to provide a repeatedly reuseable
matrix.
Inventors: |
Borner; William Gerard
(Ringwood, NJ) |
Assignee: |
The International Nickel Company,
Inc. (New York, NY)
|
Family
ID: |
22419655 |
Appl.
No.: |
05/125,423 |
Filed: |
March 17, 1971 |
Current U.S.
Class: |
205/75; 204/281;
205/196 |
Current CPC
Class: |
C25C
7/02 (20130101) |
Current International
Class: |
C25C
7/00 (20060101); C25C 7/02 (20060101); C23b
007/02 (); B01k 001/00 (); C23b 007/00 () |
Field of
Search: |
;204/3,4,11,12,281
;106/1,2 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
T R. Bates, Photosensitive Resists for Electroforming; Plating
Magazine July 1965 pp. 673-676 .
G. R. Schaer, Electroformed Screens with Controlled Hole Size for
Battery Plaques, Plating Feb 1968 pp. 130-137.
|
Primary Examiner: Mack; John H.
Assistant Examiner: Tufariello; T.
Claims
1. In the electrorefining of nickel wherein nickel is
electrodeposited from an acid aqueous sulfate-chloride nickel
electrolyte upon a sheet-form cathode blank having interconnecting
areas of non-conductive resist material applied to said blank to
define conductive islands on the faces thereof and relatively heavy
dividable nickel deposits separable from said cathode blank are
formed thereon, the improvement which comprises producing
repeatedly reusable stainless steel cathode blanks by chromium
plating said cathode blank, applying a film of epoxy-base paint
cured by means of dicyandiamide to the resulting chromium surface
and heat-curing said paint film to form said interconnecting areas
of resist, whereby said epoxy-base paint film adheres strongly to
said chromium plated stainless
2. The process according to claim 1 wherein the chromium deposit is
removed from the conductive islands prior to the electrodeposition
of nickel
3. The process according to claim 1 wherein the chromium plate has
a
4. The process according to claim 1 wherein the pattern of
interconnecting areas of resist is applied to said stainless steel
blanks by silk screen
5. The process according to claim 1 wherein the epoxy paint
comprises in parts by weight of effective ingredients, about 12
parts of epoxy resin having a viscosity at 38.degree. C. of about
400 to 600 centipoise, up to
6. The process according to claim 5 wherein the pigment is titanium
dioxide
7. The process according to claim 1 wherein the conductive islands
are
8. The process according to claim 1 wherein the stainless steel
cathode blank has a pickled surface and the nickel deposit contains
about 0.005
9. The process according to claim 8 wherein said nickel deposit
contains
10. The process according to claim 1 wherein the stainless steel
cathode blank has a sandblasted surface and the nickel deposit is
essentially
11. In the electroforming of nickel upon a stainless steel matrix
having on the surface thereof a pattern of resist material, the
improvement for providing a strongly adherent pattern of said
resist material upon said matrix surface which comprises chromium
plating said surface, applying to said chromium plated surface a
resist pattern of an epoxy-base ink containing dicyandiamide as a
hardener, heat-curing said resist ink pattern and electrodepositing
nickel upon said matrix bearing said cured ink pattern whereby said
matrix may be employed repeatedly without damage
12. In the electrodeposition of a metal from the group consisting
of nickel, cobalt and iron from an acid aqueous electrolyte upon a
sheet-form cathode blank having a continuous pattern of
non-conductive resist material applied to said blank to define
conductive islands on the faces thereof and relatively heavy
dividable metal deposits separable from said cathode blank are
formed thereon, the improvement which comprises producing
repeatedly reusable cathode blanks made of a metal from the group
consisting of stainless steel, titanium, aluminum, iron and nickel
by chromium plating said cathode blank, applying a film of
epoxy-base paint cured by means of dicyandiamide to the resulting
chromium surface and heat-curing said paint film to form said
interconnecting lines of resist, whereby said epoxy-base paint film
adheres strongly to said chromium plated metal cathode blank during
said electrodeposition process.
Description
The electroforming art has struggled with the problem of providing
foraminous or dividable electrodeposits of nickel and other metals
for many years. For example, electroforming provides an economical
method for providing screen made of nickel, copper or other metals
on a continuous basis. In such an operation, a matrix or mandrel
having a pattern of non-conductive spots corresponding with the
openings desired in the electroformed screen is prepared. During
the course of the electrodeposition upon the matrix, metal is
electrodeposited upon the conductive areas of the matrix but does
not deposit upon the non-conductive spots, thus yielding a
foraminous metal sheet when the electrodeposit is stripped from the
matrix. When the mandrel or matrix is provide as a slowly rotating
cylindrical cathode in an electroplating bath, a continuous screen
of nickel or other metal can be provided. The preparation of such
matrices or mandrels in the past has been expensive since it had
been considered necessary, because of the strong tendency of the
electrodeposited metal to pull the non-conductive material with it
when the metal is stripped from the matrix, to provide a physical
anchoring of the non-conductive material in the face of the matrix.
A cheaper means for providing non-conductive areas upon the matrix
or mandrel which would enable the non-conductive material to adhere
strongly to the mandrel surface during electrodeposition and
stripping of the electrodeposited metal would be of great
assistance in this connection.
In another area; to wit, electrorefining, it has been considered
for years desirable to be able to provide the electrorefined metal
in a form which could be easily subdivided. Thus, absent a means
for providing the electrorefined metal, such as nickel, in a form
which could easily be divided, the only means for providing the
electroformed metal in physical forms smaller in dimension than
that of the cathode upon which the metal was deposited was by the
route of shearing the cathodes. Since many electrorefined metals,
including particularly nickel and copper, are tough and relatively
hard, the shearing operation was accomplished only at considerable
expense, and resulting sharp edges formed upon the sheared pieces
presented handling problems and were undesirable from the labor
standpoint. Traditionally, nickel has been electrorefined by a
method wherein thin metal starting sheets were first prepared, and
metal was deposited in the electrorefining cell on both sides of
the starting sheet to an appropriate thickness usually on the order
of about three-eighths of an inch. The Prescott U.S. Pat. No.
2,392,614 which utilized a slotted starting sheet and the Wesley et
al U.S. Pat. No. 2,773,816 which utilized interconnecting lines of
a resist material on the starting sheet represent prior endeavors
in the art to provide dividable electrorefined cathodes of copper
and of nickel, respectively. These prior attempts were
characterized by relatively high cost and by the fact that the
divided product produced thereby still presented sharp edges and
difficulties in separating the resulting cathode into component
pieces. Other workers have recognized that dividable electrorefined
metal could be provided by utilizing a flat mandrel of a metal such
as stainless steel bearing upon the faces thereof an
interconnecting pattern of resist lines. The electrodeposited metal
produced upon such mandrels could be separated from the mandrel and
divided along lines corresponding to the initial lines of resist
applied upon the faces of the mandrel. In order to apply such a
technique to commercial production in an electrorefinery on an
economic basis, it was speedily discovered that it was essential to
provide a mandrel which could be reused numerous times, e.g., 10
times or more, in the electrorefining bath without having to
replace or repair the lines of resist upon the faces thereof. It
was found, however, that under the conditions existing at the
cathode in an electrorefining process, the materials which could be
employed as the resist materials broke down speedily with the
result that it was necessary to repair or replace the resist
material each time the mandrel was returned to the process for
further plating. Thus, materials such as electroplaters tape,
rubber base and plastic paints and inks, etc., which had been used
as stop-offs in electroplating racks and the like, were found to be
inadequate to meet the severe demands of this service.
The present invention is directed to a means for providing highly
retentive resist areas upon an electroplating matrix or mandrel for
use in electroforming.
Broadly stated, the present invention is directed to a process for
electroforming metals, including nickel, cobalt and iron, upon a
mandrel which may be made of stainless steel, titanium, aluminum,
iron and nickel, etc., wherein the mandrel is prepared by chromium
plating faces thereof, applying to the chromium plated faces a
thermosetting epoxy ink or paint containing dicyandiamide as a
hardener in the desired pattern as by, for example, silk screen
printing, curing the ink or paint film by heating, and thereafter
electrodepositing metal thereupon. As noted hereinbefore, the ink
or paint film may be applied to any desired pattern and may, for
example, form a continuous pattern of interconnecting lines or
areas upon the face of the mandrel so as to define conductive areas
having the desired shape and size for the plated shapes to be
produced.
The chromium plating, which is essential in accordance with the
invention, can be accomplished in any standard chromium plating
bath. As is known, chromium plating baths are usually aqueous and
contain at least about 50 grams per liter (gpl) of chromic acid
(CrO.sub.3) and a catalyst such as sulfuric acid, with the weight
ratio of chromic acid to sulfuric acid being about 50:1 to about
250:1, e.g., 100:1. A satisfactory aqueous chromium plating bath,
for purposes of the invention, contains about 250 gpl of chromic
acid and 2.5 gpl of sulfuric acid. Chromium can be deposited upon
the face of the mandrel at a cathode current density from about 80
to about 200 amperes per square foot with a bath temperature of
about 100.degree. F. to about 120.degree. F. being employed. The
chromium deposit may be from about 2 to about 30 microinches in
thickness. The chromium deposit may be left upon the exposed areas
of the mandrel with beneficial effects in connection with the
electroforming of relatively thin foraminous materials, e.g.,
screen, which usually are plated to a thickness range of about
0.0001 to about 0.001 inches. In such a case the epoxy ink or paint
pattern would be discontinuous, e.g., a system of dots. When the
electroforming is part of a nickel electrorefining operation and
the mandrel material is stainless steel or titanium, the chromium
deposit advantageously is removed from the exposed areas of the
mandrel prior to electrodeposition of metal thereon. This may be
accomplished, for example, by anodic dissolution in an alkaline
solution, e.g., sodium carbonate or sodium hydroxide water
solution. As an example, an aqueous solution containing about 20 to
about 50 gpl of sodium hydroxide may be employed and current may be
passed from the mandrel as anode at a current density of about 10
to about 60 amperes per square foot. In this way, a mandrel can be
produced on which adhesion of heavy deposits, e.g., at least about
3/8 inches thick of, for example, nickel, is facilitated.
Any of the standard acid, aqueous nickel electroplating or
electrorefining baths, e.g., the sulfate-chloride (Watts) bath, the
all-chloride bath, the sulfamate bath, the sulfate-sulfamate bath,
etc., may be employed in carrying out the invention. These baths
usually are buffered with boric acid and are operated within the pH
range of about two to about four, at temperatures of about
110.degree. to about 150.degree. F. and at cathode current
densities of about 20 to about 50 amperes per square foot (a.s.f.).
The baths may contain usual brightening or leveling agents, e.g.,
hydracrylonitrile in the amount of about 15 milligrams to about 75
milligrams per liter, and may contain agents to incorporate a small
amount of sulfur in the nickel deposited, e.g., about 0.005 to
about 0.025 grams per liter (g.p.l.) of sulfur dioxide, amounts
which will provide about 0.005 to about 0.025 percent of sulfur in
the deposited nickel. Alloy deposits may also be produced, e.g.,
nickel-cobalt alloy deposits, again using standard bath
compositions for this purpose. Standard cobalt and iron plating
solutions may also be used, as disclosed in Modern Electroplating,
edited by F. A. Lowenheim, John Wiley and Sons, Inc., (1963).
A problem encountered in carrying out the invention in the
production of electrolytic metal having substantial thickness,
e.g., at least 0.25 inch, is that of lifting or separation of the
electrolytic metal from the exposed metal mandrel surfaces when the
stress level becomes excessive. The use of a small amount of sulfur
co-deposited with the nickel provides a controlled stress level in
a nickel deposit produced from the sulfate-chloride bath. Thus, a
sulfur content of about 0.01 percent to about 0.02 percent in
electrolytic nickel, provided through the incorporation of about
0.01 percent to about 0.02 percent of sulfur dioxide in the
electrolyte, will usually provide a stress level of preferably .+-.
5,000 pounds per square inch in the nickel. Such nickel is useful
as nickel electroplating material because of its high chemical and
electrochemical activity, as is discussed in the Renzoni et al U.S.
Pat. No. 3,437,571. When such nickel is deposited in an
electroplating or electrorefining operation upon a stainless steel
mandrel having a pickled surface, good adherence of the deposited
nickel and of the resist film to the stainless steel surface is
obtained. However, when it is desired to produce sulfur-free nickel
in substantial thickness, from, e.g., the sulfate-chloride bath,
the metal, e.g., stainless steel, mandrel must first be roughened
by means of a sand blasting operation using grit at least as coarse
as "No. 2" , having an average particle size in excess of 30
mesh.
In order to give those skilled in the art a better appreciation of
the advantages of the invention, the following example is given.
Ten type 304 stainless steel blanks, about 29 inches wide by 40
inches long by 0.125 inches thick and having a pickled finish were
prepared by subjecting them to cathodic alkaline cleaning and water
rinsing, and were then plated with about 10 microinches of chromium
by passing current thereto for about 21/2 minutes at 1 ampere per
square inch in a chromium plating bath containing 250 gpl chromic
acid and 2.5 gpl sulfuric acid. The temperature of the chromium
plating bath was 113.degree. F. The chromium plated blanks were
then hot water rinsed and dried. The dried blanks were then silk
screen printed to define a pattern of uncoated, conductive circular
areas about five-eighths inch in diameter in staggered rows with a
minimum spacing of three-eighths inch between the circular areas
using as a resist material an epoxy ink containing in parts, by
weight of effective ingredients, about 12 parts of diglycidyl ether
of bisphenol A (epoxy resin), about 7 parts of 20 weight per cent
titanium dioxide, 80 weight per cent calcium carbonate pigment and
about 1 part of dicyandiamide hardener. The silk screened blanks
were oven-cured at about 350.degree. F. for about 40 minutes to set
the epoxy resin. The chromium was removed from the exposed areas of
the mandrels by exposing them as anode for about 10 minutes in an
aqueous solution containing 45 gpl sodium hydroxide at an anode
current density of 10 asf. The blanks were then plated in an
electrorefining cell containing an aqueous sulfate-chloride nickel
electrolyte to build upon on each face thereof a thickness of
nickel of about three-eighths inch. The plating bath contained
about 55 gpl nickel, 20 gpl sodium, 50 gpl chloride, 20 gpl boric
acid, 85 gpl sulfate and 0.02 gpl sulfur dioxide. The plating
process proceeded for about ten days and the nickel deposit
contained about 0.025 percent sulfur. No adherence problem arose in
plating. After plating, the blanks were removed from the tanks, and
the nickel deposit in the form of circular segments was stripped
from each face thereof. The blanks were returned for further
plating without overhaul of the epoxy resin film pattern. The
process was repeated about 10 times without overhaul of the epoxy
film pattern being necessary.
In comparison to the successful results obtained when the stainless
steel starting blanks were chromium plated prior to silk screen
printing with the epoxy ink, it was found that films produced
identically directly on the surface of the same stainless steel
(without chromium plating) failed quickly with the result that the
prepared blanks could not be reused without repair or replacement
of the cured epoxy film. In this connection it is to be recognized
that electrodeposited metal such as nickel will penetrate even
microscopic pores in a stop-off film with resulting damage to the
film when the deposit is stripped. This factor has made it
extremely difficult to find any type of film forming pattern
material which would resist the severe service encountered in
exposure of the film to conditions existing at the cathode in an
electroplating bath during operation. Thus, many types of inks and
paints which yield a film which appears sound to the eye or even
under the microscope fail rapidly in this service.
Not only is the chromium plating necessary to secure requisite
adhesion of the epoxy film pattern to the cathode blank; but,
further, it appears that only epoxy ink or paint formulations,
wherein the epoxy resin is cured, hardened or "dried" by
dicyandiamide, are satisfactory. These formulations are especially
satisfactory for silk screen printing, since they are cured by
heating at temperatures of at least about 350.degree. F. and,
hence, remain liquid in the silk screen printer even for times as
long as a week or more. Ink formulations hardened by aliphatic or
aromatic polyamines, anhydrides, etc., are not satisfactory.
The epoxy resin used in the ink formulation, which is a mixture of
glycidyl ethers of bis-phenol, should itself have a viscosity in
the range of about 400 to about 600 centipoise at 38.degree. C.
since, as those skilled in the art known, viscosity of the resin is
a useful indirect measure of the epoxide content.
The pigment component of the ink performs a useful function in that
pigmented films assist in inspection of the blanks for film damage.
The pigment is preferably titanium dioxide, which may be extended
with, for example, calcium carbonate. The pigment is not essential
to the performance of the epoxy resist material. It is to be
appreciated that the electrodeposited metal grows across the resist
material during plating. Thus, in order to yield a deposit which is
readily separable into segments, the minimum width of the resist
areas should not be substantially less than the thickness of the
electrodeposited metal to be plated. The ink may contain a small
amount of colloidal silica ("Aerosil") to provide a thixotropic
effect.
Although the present invention has been described in conjunction
with preferred embodiments, it is to be understood that
modifications and variations may be resorted to without departing
from the spirit and scope of the invention, as those skilled in the
art will readily understand. Such modifications and variations are
considered to be within the purview and scope of the invention and
appended claims.
* * * * *