US3595762A - Plating process - Google Patents

Abstract

DEPOSITIN IN SAID STRATUM OF PARTICLES A CONDUCTIVE METAL LAYER CONTAINING SULFUR-FREE NICKEL HAVING AN EFFECTIVE THICKNESS LESS THAN THE MAXIMUM THICKNESS OF SAID STRATUM OF PARTICLES THEREBY FORMING A MATRIX WHEREIN SAID PARTILES ARE RETAINED AFFIXED TO SAID SURFACE IN FIXED POSITION IN SAID CONDUCTIVE METAL LAYER, AND AT LEAST SOME OF SAID PARTICLES INTERCEPT THE SURFACE OF SAID CONDUCTIVE METAL LAYER.

IN ACCORDACE WITH CERTAIN OF ITS ASPECTS, THIS IVENTION RELATES TO NOVEL COMPOSITIONS AND TO A PROCESS FOR PREPARING A METAL PLATE RECEPTIVE TO A DECORATIVE NOBLE METAL DEPOSIT, CHARACTERIZED BY THE PRESENCE OF MICROPOROUS AREAS AND MICROCRACKED AREAS OVER SUBSTANTIALLY THE ENTIRE SURFACE OF SAID NOBLE METAL PLATE, COMPRISING AFFIXING TO A BASIS MATERIAL BEARING A CONDUCTIVE METAL SURFACE A STRATUM OF PARTICLES HAVING A PARTICLE SIZE OF ABOUT 0.05-15 MICRONS AND A DENSITY ON SAID CONDUCTIVE METAL SURFACE OF ABOUT 100-5,000,000 PARTICLES/CM.2; AND

Description

July 27, 1971 ssm 3,595,162

PLATING PROCESS Filed Oct 16, 1968 United States Patent U5. Cl. 204-38R 21 Claims ABSTRACT OF THE DISCLOSURE In accordance with certain of its aspects, this invention relates to novel compositions and to a process for preparing a metal plate receptive to a decorative noble metal deposit, characterized by the presence of microporous areas and microcracked areas over substantially the entire surface of said noble metal plate, comprising aflixing to a basis material bearing a conductive metal surface a stratum of particles having a particle size of about 0.05-l microns and a density on said conductive metal surface of about l00-5,000,000 particles/cm. and depositing in said stratum of particles a conductive metal layer containing sulfur-free nickel having an effective tlm'ckness less than the maximum thickness of said stratum of particles thereby forming a matrix wherein said particles are retained afiixed to said surface in fixed position in said conductive metal layer, and at least some of said particles intercept the surface of said conductive metal layer.

This invention relates to a novel process for preparing a metal plate particularly characterized by its receptivity to noble metal plate, typified by a corrosion-resistant decorative electrodeposited chromium plate containing microcracked areas and microporous areas over substantially the entire surface of said chromium plate. This application is a continuation-in-part of application Ser. No. 509,267, filed Nov. 23, 1965 for Novel Plating Process.

As is well known to those skilled in the art, decorative noble metal plate typified by chromium plate may be obtained by e.g. electrodepositing chromium onto a surface of electrodeposited nickel. However, chromium plate ob tained in this manner may be subject to defects including gross cracking or crazing and excessive corrosion which decreases usefulness as decorative chromium.

Prior art processes have attempted to overcome the problem of gross cracking in chromium plate by including in the nickel plating bath (from which may be deposited the nickel undercoat for the chromium plate) a substance which produces a microporous condition in the chromium plate subsequently deposited.

However prior art methods have not succeeded, by employing additives in the nickel plating bath, in preventing gross cracking over all areas of the subsequently deposited chromium plate and thus it has not been possible to attain a chromium plate characterized by the presence of microcracked areas and microporous areas over substantially the entire surface of said chromium plate.

It is an object of this invention to permit attainment of a plate particularly characterized by its receptivity to a noble metal plate typlcally a decorative chromium plate.

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It is a further object of this invention to provide a chromium plate which is highly useful as a decorative chromium plate, and which contains microcracked areas and microporous areas over substantially the entire surface area of said chromium plate. Other objects will be apparent to those skilled in the art from inspection of the following description.

In accordance with certain of its aspects, the process of this invention for preparing a metal plate receptive to a decorative noble metal deposit, characterized by the presence of microporous areas and microcracked areas Over substantially the entire surface of said noble metal plate, comprises affixing to a basis material bearing a conductive metal surface a stratum of particles having a particle size of about 0.05-15 microns and a density on said conductive metal surface of about IOU-5,000,000 particles/cm. and depositing in said stratum of particles a conductive metal layer containing surfur-free nickel or sulfur-free nickel alloy having an effective thickness less than the maximum thickness of said stratum of particles thereby forming a matrix wherein said particles are retained afiixed to said surface in fixed position in said conductive metal layer, and at least some of said particles intercept the surface of said conductive metal layer.

As used herein the form sulfur-free is meant to include amounts of sulfur less than about 0.05 percent by weight of nickel (or nickel alloy) plate. Preferably, the amount of sulfur is less than about 0.02 percent by weight and most preferably less than 0.01 percent by weight. Optimum performance may be obtained by complete elimination of the sulfur content from the nickel (including nickel alloy) plate.

The basis material which may be treated according to this invention may include a basis metal such as iron, steel, brass, bronze, copper, zinc, aluminum, magnesium, nickel, etc., either pure or in the form of alloy. The preferred basis metal to be plated in accordance with this invention may be steel, zinc, or brass and most preferably steel, zinc, or brass which has been first plated with a conductive deposit such as a plate of bright nickel, typically preceded by a first plate of copper, bronze, or semi-bright nickel.

Other basis materials which may be treated by the process of this invention may include plastics and resins including acrylonitrile-butadiene-styrene, acetals, acrylics, alkyds, allyls, amines, cellulosics, chlorinated polyethers, epoxies, furanes, fiuorocarbons, isocyanates (urethanes), polyamides (nylons), phenoxys, phenolics, polycarbonates, polyesters, polyethylenes, silicones, polystyrenes, polyvinyls, and copolymers, etc. of these materials. When the basis material to be treated by process of this invention is a plastic or resin, the surface thereof will be treated as by deposition thereon of a conductive deposit, such as nickel deposit.

The basis material bearing a conductive surface, preferably a bright nickel plate, may be immediately treated after disposition of such plate or it may be water rinsed; or it may be rinsed, dipped in aqueous acid solution such as 0.5 %l0%, say 2%, by weight of sulfuric acid prior to further treatment. The so-treated material may be dried or it may be further treated as is. If drying has been permitted, the conductive surface may be cleaned as by cathodically treating in alkaline cleaner followed by rinsing in water or dipping in an acid solution before further treatment.

TABLE I Component Minimum Maximum Preferred Nickel sulfate, hydrated 200 500 300 Nickel chloride, hydrated 30 80 45 Boric acid 35 55 45 pH 3 5 4.

A typical sulfamate-type bath which may be used in practice of the process of this invention may include the following components in aqueous solution:

TABLE II Component Minimum Maximum Preferred Nickel sulfamate 330 400 375 Nickel chloride, hydrated 15 6 45 Boric acid 33 55 45 pH 3 4. O

A typical chloride-free, sulfate-type bath which may be used in practice of the process of this invention may include the following components in aqueous solution:

TABLE III Component Minimum Maximum Preferred Nickel sulfate, hydrated 300 500 400 Boric acid 35 55 45 pH 3 5 4. 0

A typical chloride-free, sulfamate-type bath which may be used in practice of the process of this invention may include the following components in aqueous solution:

TABLE IV Component Minimum Maximum Preferred Nickel sulfamate. 300 400 350 Boric acid 35 55 45 pH 3 5 4. O

A typical pyrophosphate-type which may be used in practice of the process of this invention may include the following components in aqueous solution:

TAB LE V Component Minimum Maximum Preferred Sodium pyrophosphate, hydrated 50 80 65 Nickel sulfate, hydrated 80 160 120 Sodium bisuifite 1. 5 2. 5 2 Sodium citrate, hydrated 50 70 60 Citric acid 20 Sodium chloride. 40 30 Ammonia (28%). 30 60 50 pH 7. 5 9 8. 5

A typical fluoborate-type bath which may be used in the practice of the process of this invention may include the following components in aqueous solution:

TABLE VI Component Minimum Maximum Preferred Nickel fluoborate, hydrated 250 400 300 Nickel chloride, hydrated 15 60 30 Boric acid 15 30 20 pH 2 4 3. 0

It will be apparent that the above baths may contain components in amounts falling outside the preferred minima and maxima set forth, but that most satisfactory and economical operation may normally be effected when the components are persent in the baths in the amounts indicated.

The plating baths may further contain brighteners or other additives such as sodium saccharate or wetting agents. High-foaming wetting agents such as sodium lauryl sulfate may be particularly useful when employed in conjunction with mechanical agitation; and low-foaming agents such as sodium dialkylsulfosuccinates may be particularly useful when employed in conjunction with air agitation.

In practice of this invention, the basis material preferably bearing a first plate (of e.g. copper) and a nickel or duplex nickel plate, may be further treated by aflixing thereto a stratum of particles having a particle size of about 0.05-15 microns.

Typically the particles may be finely-divided, naturallyoccurring or artifically prepared materials. They may be spherical, chunky, angular, ovular, elongated, plateletshaped, etc. Preferably they may be flat, i.e. have two dimensions substantially greater than the third dimension. The preferred particles may be platelets.

Typical particulate materials which may be employed may include talc; kaolin; wax; graphite; sulfides such as molybdenum disulfide and tungsten disulfide; pigments including barytes, chromium-cobalt green and cobalt-aluminum blue and oxides such as silica and alumina; particles of plastic e.g. polymers or copolymers of styrene, butadiene, acrylonitrile, vinyl acetate, vinyl chloride, etc.; diatomaceous earths; powdered aluminum; activated carbon; silicates e.g. sodium silicate; carbonates, e.-g. calcium carbonate; carbides; sulfur; etc., or mixtures of these materials.

There may also be present other additives such as polar organic compounds, e.g. amides, amines, long-chain alcohols, acetylenics, etc., to enhance the properties of adhesion, inhibition, or dispersion.

Application of particles may be effected by contacting the basis material with particles. The particles may be blown over the surface of the conductive metal surface of the basis material. The basis material may be dipped into a bed, preferably a fluidized bed of particles i.e. particles suspended in an upflowing stream of gas. Aflixing of particles may be effected by electrostatic or electrophoretic techniques on the basis metal piece. If desired, the basis metal may be wet to assist deposition thereon and adherence thereto of the particles.

The preferred particles may be used in the form of a bath i.e. a suspension, emulsion, dispersion or latex of the solid or semi-solid particles in a fluid, preferably a liquid. In one preferred embodiment, the particles may be particles of solid suspended in a liquid in concentration as low as 0.001%, typically, 0.1%2%, and preferably about 0.5%. Outstanding results may be obtained by use of baths containing 0.12% particles.

Typically the particles in the bath may be from commercially available materials: for example, talc may be obtained having particles ranging in size up to about 7 microns. 0.012% of talc may be added to water and dispersed as by milling in a ball mill or in a Waring Blendor or by stirring. Similar techniques may be employed to disperse wax, pigments, kaolin, etc.

The fluid, typically aqueous medium, in which the particles may be suspended may be water, but preferably is a bath having a composition substantially similar to the bath immediately preceding from which the basis material may have been removed after treatment, e.g. a waterrinse bath or a nickel-plating bath.

Air, mechanical, or ultrasonic agitation may be used to maintain the particles in suspension. Additives such as suspending agents including surfactants, dispersants, thixotropes, emulsifiers, etc., e.g. alginates, lignosulfonates, gelatin, etc., may be present, and if desired, electrolytes including sodium sulfate, heavy metal salts, acids, etc.

When the bath is a latex bath, it may be formed from various resins. Illustrative resins which may be present in latices used in the instant invention include resins containing non-aromatic unsaturation in the repeating unit of the molecule formed from:

(a) Diene compositions including butadiene typically natural rubber; isoprene i.e. 2-methyl butadiene; chloroprene i.e. Z-chloro-butadiene; pentadiene-1-3; etc.

(b) Acrylate compositions including acrylate and methacrylate esters such as methyl acrylate; methyl methacrylate; ethyl acrylate; ethyl methacrylate; propyl acrylate; etc.

(c) Acrylonitrile compositions including acrylonitrile; methacrylonitrile; ethacrylonitrile; etc.

(d) Vinyl compositions including vinyl chloride; vinyl acetate; l-chloro-propene-l; styrene; o-, m-, and p-methyl styrenes; etc.

(e) Olefin compositions including ethylene; propylene; butylene; etc.

Typical compositions may include those formed from more than one of the above types, such as from two components including butadiene-styrene; butadiene-acrylonitrile; methyl acrylatestyrene; etc. or three components (terpolymers) including e.g. acrylonitrile-butadienestyrene; etc. Most preferably polymers of the noted compositions may be used in the form of copolymers with e.g. other noted compositions.

The above compositions may be modified and typically carboxylic-modified i.e. the molecule containing aliphatic unsaturation may be modified by the addition thereto of a carboxylic acid group. Typically this may be effected e.g. by reacting the composition with maleic anhydride in order to form carboxylic groups on the polymer molecule or by hydrolyzing a CN group to a carboxyl group.

It is a feature of the latices which may be employed in practice of the process of this invention that they may be readily available from natural sources e.g. natural rubber latex or that they may readily be formed by dispersion synthetic compositions in aqueous media e.g. butadiene-styrene polymer latices.

Illustrative specific commercially available synthetic latices which may be used in practice of this invention include:

(a) A water-based acrylic polymer latex having a nonionic emulsifier, a pH of 7, and an average particle size of 0.16 micron (such as that sold under the trademark Hycar 2601 by B. F. Goodrich Chemical Co.);

(b) A water-based copolymer of butadiene-styrene-carboxylic modified latex (i.e. a latex wherein butadiene-styrene copolymer is modified by the inclusion of COOH groups), including a synthetic emulsifier, a pH of 9, and an average particle size of 0.16 micron (such as that sold under the trademark Pliolite 491 by Goodyear Industrial Products Co.)

(c) A water-based hydrocarbon resin latex having a nonionic emulsifier, a pH of 8.8 and a maximum particle size of 1 micron (such as that sold under the trademark Piccopale N3 by Pennsylvania Industrial Chemical Corporation);

(d) A water-based vinyl acetate polymer latex having a non-ionic emulsifier, a pH of 4.0-5.5, and an average particle size of about 1 micron (such as that sold under the trademark Plyamul 40370 by Reichhold Chemical Co.);

(e) A Water-based vinyl acetate polymer latex having an anionic emulsifier, a pH of 3.55.5, and an average particle size of 0.5 micron (such as that sold under the trademark Gelva TS-30 by Shawinigan Resins Corp.);

(f) A Water-based copolymer of butadiene-styrene 50/50 latex having a synthetic emulsifier, a pH of 9.6, a non-staining anti-oxidant, and an average particle size of 0.6 micron (such as that sold under the trademark Pliolite 176 by Goodyear Industrial Products Co.);

(g) A water-based vinyl chloride polymer latex having a pH of 8.0, and an average particle size of 0.16 micron (such as that sold under the trademark Dow 700 by Dow Chemical Co.);

(h) A water-based vinyl acetate polymer latex having a pH of 4.05.0, an anionic emulsifier and a particle size of 0.053 microns (such as that sold under the trademark CL-102 by Celanese Corp. of America);

(i) A water-based copolymer of vinylidene chloride 5 acrylonitrile 85/15 latex having an anionic emulsifier, a pH of 6.0-7.0, and an average particle size of 0.2 micron (such as that sold under the trademark Saran Latex F122 A15 by Dow-Chemical Co.).

The preferred latices may be in the form of nonconductive latices in aqueous medium, typically containing 30-60%, say 40%, resin in the aqueous medium. Commonly these latices may be characterized by the presence of colloidal-size particles, typically less than about one micron and commonly of the order of 0.00050.2 micron. The most highly preferred latices which may be used in practice of this invention to permit attainment of the preferred chromium plate containing microcracked areas and microporous areas over substantially the entire area of the chromium plate include the carboxylic-modified butadiene copolymer latices containing particles of an average size of up to about 1 micron. Typical of such latices is (b) supra sold under the trademark Pilolite 491 in which the average particle size may be about 0.16 micron. Other latices may include vinylidene chloride copolymer latices such as the copolymer with acrylonitrile, as (i) supra sold under the trademark Saran Latex F122 A15 in which the average particle size may be about 0.2 micron. A preferred latext may for example be a polyvinyl chloride latex containing 0.5% by weight of polyvinyl chloride having a nominal particle size of about 0.16 micron, such as that sold under the trademark Dow 700 (g) supra). Additives including dispersants etc. may be present.

Typically the particles may be employed in the form of an aqueous dispersion having the following composition:

TABLE VII Parts by weight Minimum Maximum Preferred Particles 0.001 5 O. 5 Fluid '95 100 99. 5 Additive 0. 00005 0. 01 0.01

A preferred bath in the form of a dispersion which may be employed may include:

TABLE VIII Parts by weight Minimum Maximum Preferred Tale 0. 005 5 0. 5 100 100 0. 10 0. 01 0. 10 0. 01

Application of the particles onto the metal surface may preferably be effected by dipping the metal surface in an aqueous bath containing said particles. Dipping may be effected, preferably at ambient temperature of 10 C.- 40 C., and the surface may be retained therein for time sufficient to inundate the surface, typically 5-60 seconds, preferably about 30 seconds. Moderate agitation in this step may be preferred.

The surface may then be removed from the bath bearing a stratum of particles which cling evenly distributed thereon-probably held in place by surface tension and adsorptive forces. The particles may be affixed to the surface by these forces and may be uniformly distributed thereover. Typically there may be 100-5,000,000 particles on each square centimeter of surface, and commonly 5,0002,000,000 particles/cm? The surface so-attained may, if desired, be allowed to dry, or it may be water-washed, or it may be further processed as is, e.g. bearing a thin film of adherent liquor.

The surface bearing the stratum of affixed particles may then be further treated. There may be deposited on said surface and in said stratum, a conductive layer containing sulfur-free nickel or sulfur-free nickel alloy having an effective thickness less than the maximum thickness of the stratum of particles whereby a high portion of the upper surfaces of the particles remain uncovered.

The conductive layer may contain sulfur-free nickel. Typically, the sulfur-free nickel deposit may contain less than about 0.05% sulfur, and typically less than 0.02%, say 0.01% (typically bright nickel may normally contain 0.05 %0.l sulfur; and semi-bright may typically contain 0.002-0.02% sulfur). The nickel deposit may be deposited from baths using brighteners as in a bright nickel bath or in a semi-bright nickel bath. Preferably, it may be bright nickel and be produced from a bath such as those of Tables I-IV to which may have been added brighteners such as e.g. 1,2-dichloropropenyl pyridinium chloride; 1,2- dibromopropenyl pyridinium bromide; etc.

In one embodiment, the conductive layer may contain bright sulfur-free nickel. Typically, such a layer may be obtained from a bath such as the baths of Tables I-IV containing a primary brightener and a secondary brightener. Typically primary brighteners present in amount of 0.1 g./l.1.0 g./l., say about 0.7 g./l., may include watersoluble acetylenics including for example butyne-l,3-diol.

In the preferred embodiment of this invention, the conductive layer may contain sulfur-free nickel. It may contain nickel together with a nickel-alloying metal such as copper, tin, cobalt, etc. In the preferred embodiment the conductive layer may contain a sulfur-free alloy of nickel and cobalt. Preferably, in this alloy, cobalt may be present in amount of 1-20 parts, say parts and nickel may be present in amount of 8099 parts, say 90 parts. Typical layers which may be employed may include 35 parts of nickel and 65 parts of tin; 60 parts of nickel and 40 parts of copper; etc. Preferably, the layer may include 90 parts of nickel and 10 parts of cobalt.

The alloy plate may be deposited from the following illustrative baths wherein the parts noted are parts by weight per volume of aqueous solution, e.g. grams per liter of aqueous solution (except for the pH which is electrometric) TABLE IX Component: G./l. Nickel sulfate, hydrated 240 Nickel chloride, hydrated 30 Cobalt sulfate 4.5 Boric acid 3O Ammonium sulfate 0.75 Formaldehyde 2.5 Nickel formate 45 pH 2.3-3.7

Typical operation of the above bath at 65 C. and cathode current density of 3-5 a.s.d. for 1 minute will yield a deposit containing 5% cobalt and 95% nickel. Deposit containing 18% may be obtained by use of a bath containing g./l. of cobalt sulfate.

In the preferred embodiment, nickel may be deposited from any of the baths hereinbefore noted. Plating may be carried out at 15 C.60 C., say 54 C. The average cathode current density may typically be 1.0-15 amperes per square decimeter (a.s.d.), preferably 5 a.s.d. When the pyrophosphate bath supra is used, the temperature may typically be 20 C.35 C. and the cathode current density 0.22 a.s.d.

Plating may typica ly be carried out to produce a conductive layer preferably having an effective thickness less than the maximum thickness of the stratum of particles whereby said particles are retained in fixed position in the conductive layer and at least some of said particles penetrate the surface of the layer. Typically the effective thickness may average 0.02-3 microns, preferably 0.2 micron. There will thus be formed a matrix of particles in a conductive layer of metal, i.e. a heterogeneous matrix deposit. Microscopic inspection of the matrix deposit may readily reveal that the particles may be retained in fixed position in a matrix of the conductive layer. It will also be observed (as by dark field illumination in a microscope or by the Dubpernell test) that the particles may traverse the conductive layer and may be observed above the upper surfaces thereof.

Inspection of the stratum of particles in which the conductive layer has been deposited will clearly indicate that when the conductive layer is deposited in effective thickness less than the maximum thickness of the stratum of particles, there may be formed a matrix wherein the particles affixed to the metal surface are retained in fixed position in the conductive layer and at least some of the particles intercept the surface of the conductive layer. When the particles in the conductive layer are substantially spherical particles having more-or-less uniform size, the resulting matrix cross-section may appear to be essentially as set forth in FIG. 1 of the drawing. Here the effective thickness of the conductive layer may be 50%60% of the thickness of the stratum of particles and the particles more-or-less uniformly intercept the surface of the conductive layer in which they are retained in fixed position.

In FIG. 2, there is shown a typical illustrative crosssection through the surface of a conductive layer having an elfective thickness less than the maximum thickness of the stratum of particles. In this FIG. 2, the particles are heterogeneously sized; as will be apparent, varying proportions of different sized particles intercept the surface of the conductive layer in which the particles are retained in position.

In FIG. 3 is shown a typical cross-section of a matrix formed by first afiixing a plurality of fiat platelets of heterogeneous size to the basis metal and thereafter depositing a conductive layer in the stratum. As will be apparent from inspection of this FIG. 3, the effective thickness of the conductive layer is less than the actual thickness of the stratum of particles, i.e. in spite of the bridging effect, the upper portion or surface of at least some of the platlet particles is not covered by the deposited conductive layer. It will be noted, however, that the actual thickness of the conductive layer may be greater than the actual thickness of the stratum by as much as half the average width of the typical platelet particle.

Typically the actual thickness of the conductive layer which yields an effective thickness less than the maximum thickness of the stratum of particles may vary from typically about 20%30% of the thickness of the stratum to as much as 200% of the thickness of the stratum. For example, when the particles are irregular or highly porous, the actual thickness of the conductive layer may be as little as 20%. When the particles are substantially spherical and uniformly sized, the actual thickness of the conductive layer may be 50%-60%. When the particles are heterogeneously sized platelets, the actual thickness of the conductive layer may be 50%200% or more typically of the maximum thickness of the stratum of particles.

Under each of these conditions, the effective thickness of the conductive layer is less than the maximum thickness of the stratum of particles, i.e. the conductive layer forms a matrix wherein the particles of said stratum are retained in fixed position in the conductive layer and at least some of said particles traverse the conductive layer and intercept or penetrate the surface of said conductive layer. In each of these embodiments, it will be observed that the particles in the matrix remain aflixed to and appear to be in contact with the metal surface of the basis material.

The product so prepared may typically thus include a metal plate (receptive to a noble metal plate, such as a decorative chromium plate, characterized by the presence of microporous or microcracked areas over substantially the entire surface of said chromium plate) comprising a basis material bearing a conductive metal surface, and affixed thereto 100-5,000,000 particles/cmP, each particle having a size of about 0.05l microns, said particles being fixed in a matrix containing a conductive metal layer, at least some of said particles traversing said conductive metal layer and intercepting the surface thereof.

The basis metal plated with matrix plate, as hereinabove set forth, may then be further plated with a decorative noble metal deposit, typically chromium. Chromium plating may be effected at temperature of 30-60 C., say 43 C., and current density of 550 a.s.d., say a.s.d., for 0.5 minutes, say 5 minutes, from a bath containing 10()500 g./l., say 250 g./l. of chromic acid and 1-5 g./l., say 2.5 g./l. of sulfate ion, typically derived from sodium sulfate. Other components including other chromium plating catalysts, e.g. fluoride or silicofluoride, self-regulating strontium ion-containing composi tions, fume suppressants, etc. may be present in the chromium plating bath.

The chromium plate prepared by the process of this invention may be obtained in thickness of at least 0.02 micron, typically in decorative thickness of less then about 1 micron, and may be further particularly characterized by its bright decorative appearance, its high corrosion resistance, and by its microcracked and microporous structure. The chromium plate, which lies over the matrix plate containing particles which may partially protrude above or intercept the surface of the conductive layer, may possess microcracking and microporosity over substantially the entire area of its surface.

The microcracked surface area of the chromium plate prepared by the process of this invention may be found to have at least 100 microcracks per linear centimeter at 40 mm. from the high current density end of a standard Hull Cell panel plated with 10 amperes for 5 minutes at 43 C., compared to 510 microcracks per inch for the same chromium on the typical prior art nickel plate. This unexpectedly high degree of microcracking is suffi cient to obtain microcracked areas over all thicknesses of chromium plated in the high and intermediate current density areas. The high degree of microcracking extends sufiiciently over the surface of the chromium plate so as to be essentially contiguous with the microporous areas which are characteristic of the low current density areas of the chromium plate on the matrix surface.

This product may be inspected under a microscope and found to contain a microporous surface in the low current density areas of the standard Hull Cell panel. Typically it may possess a plurality of pores, typically about one hundred to two or three million (at a chromium thickness of less than about 0.5 micron) more-or-less uniformly distributed over the surface of the metal. Chromium deposited, on e.g. a nickel plate, prepared by the process of this invention may thus be found to contain micro porous areas or microcracked areas over the entire surface. Because of the presence, over all areas of the chromium plate, of microperforated areas (i.e. either micro porous areas or microcracked areas), it is possible to attain the novel benefits herein set forth.

When chromium plating is applied to the heterogeneous matrix-stratum described herein unexpected benefits are derived. Other factors being constant, the cracking of a chromium plate will depend on its thickness. Such fac tors as concentration of chromic acid, concentration of catalyst materials, temperature of plating, etc.; all have an effect. It is characteristic of prior art chromium deposits generally that no cracking appears throughout the first stage of deposition, up to about 0.5 micron. As the thickness is increased in the undesirable second stage, e.g., in the range of 0.5-1.0 micron, gross cracking may develop; in the undesirable third stage, e.g., about 1.0-1.5 micron, spangle-type cracking, i.e., microcracking interspersed in gross cracking, may develop. In the fourth stage, microcracking alone may develop. The undesirable intermediate stages, i.e., stages two and three, may be objectionable in appearance in the as-plated condition and particularly so after the initiation of corrosion has emphasized the presence of the cracks. Micropores and microcracks are not objectionable because the fineness of structure is not perceived by the eye except with aid of magnification. Furthermore the presence of these microperforations over the entire plate, permits attainment of the outstanding corrosion-resistant properties hereinafter set forth.

It has been unexpectedly found in the practice of this invention that microporosity is produced in stage one and microcracking is facilitated so that the undesirable stages two and three, i.e., gross and spangle-type cracking, do not appear. Thus a final plated chromium part may have microporosity where low current densities occur and microcracking in higher current density areas with no objectionable gross cracking or spangle.

The preferred thickness of the bright decorative electroplated chromium plate may be 0.025.0 microns, say 0.5 micron. The degree of microcracking (attained at thickness greater than about 0.5 micron) over a typical matrix nickel plate may be at least 100 microcracks per linear centimeter.

In the following series of exampes, unless otherwise specifically noted, basis metal panels were plated with a bright nickel plate in a standard commercial bright nickel plating bath. The bright nickel-plated panel was (1) water rinsed, (2) dipped into 2% by weight sulfuric acid, (3) water rinsed, and thereafter (4) dipped into a dispersion bath containing the suspended particles designated in Tabel X. The basis metal plate was maintained in this bath for about 30 seconds to form thereon a stratum of particles, removed, and (5) passed to a matrix bath wherein a conductive layer of sulfur-free nickel plate was deposited thereon. The nickel plating bath (treated from time to time with active carbon and filtered to maintain the solution free of impurities and insolubles) contained 300 g. of nickel sulfate heptahydrate, 60 g. of nickel chloride hexahydrate, g. of boric acid, and water to make up on liter-pH 4.0.

After nickel plating, the panel was (6) rinsed with water, and then (7) chromium plated in a bath containing 250 g./l. of chromic acid, 2.5 g./1. of sulfate (added as sodium sulfate) at 43 C.

Table X sets forth the dispersed material employed. Table XI sets forth the dispersant, details of operation and results. The f otnotes to Table X and Table XI indicate variations in the standard procedure. The footnotes follow Table XI.

TABLE X Nominal particle Percent Designation of dispersed I size Example Type of dispersed material (w./w.) material Supplier i 1 Latex-polyvinyl chloride O. 5 Dow 700 Dow Chemical Co 0.16. 2 Co trol 3 Latex-polyvinyl acetate P1ya1nul40370 Reichhold Chemical Inc 4% A 5 Plyamul 40-370. Reichhold Chemical Inc. 6. Gelva. TS30 Shawinigan Plastics Corp 7 Shawinigan Resins Corp 9 Con r0 10 MOS powder 1.0 11 WS; powder 1. 0 Submicron W82... 12 d0 1.0

. Firestone Plastics Co- TABLE X-Continued Nominal particle Percent Designation of dispersed size Example Type of dispersed material (w./w.) material Supplier (microns) 0. 8 Mistron ZSC Sierra Talc & Chemical Co d 0.445. 0. 8 o 0. 8

1. 1. 0 1. 0 0. 1 0. 4 l. 6 do 1. 0 Atlas Chemical Industries Inc 1. 0 do 1.0 do 1. 0 Ferro Corp. 6 0.5. 1. 0 do 5 0.5. 1. 0 -do u 0.5. do 1.0 5 do- 0.5. 30 WS powder plus Cr-Co pigment 1. 0 Submicron W82 and V7687 Bemol, Inc. and Ferro Corp 0 4 WS;; 61nd 0.6 r- C0. 31 .do 1.0 do do 04WS and 6 05 Cr- 00. 32 Castor oil wax 1. 0 Aldosterse 00-200 Glyco Chem. Inc

ale 0. l5 Mistron Monomix- Sierra Talc dz Chemicals Inc 6 1.0-6. do 0. (1 do 5 1.0-6 do 0. .d0 1.0-6 .do .4 d0 1.0-6 Calcium carbonate .2 Harry T. Campbell Sons Corp 6 10. Colloidal sulfur 0.03 Prepared by pouring hot, saturated alcohol solution of sulfur into water No'rE.See footnotes at end of Table XI.

TABLE XI Matrix bath Chromium bath Number of Chromium Time C.D Time C.D. Number of microcracks thickness, Example Aqueous phase (dispersant) (sec.) (a.s.d-) (sec.) (a.s.d.) pores/cm. per cm. microns 1. Electrolyte like matrix 60 0. 65 60 3. 25 5, 000 0. 032 60 3. 25 0. 032 180 4.0 60 20 7,000 0. 20 60 20 0 0. 20 180 4.0 60 20 7,000 0.20 300 4.0 60 20 20,000 0. 20 300 1. 3 60 6. 5 15, 000 0.065 300 1. 3 60 6. 5 16, 00 0. 065 60 6. 5 0. 065 1. 3 60 6. 5 100,000 0.065 10 7. 0 60 35 20, 000 0.35 10 2.0 60 10 3, 000, 000 0. 10 10 10 60 50 400 0. 50 10 7.0 60 35 15,000 0.35 10 1. 3 60 6. 5 15,000 0. 065 60 50 10 0.50 10 7.0 60 35 20, 000 0. 035 10 2. 9 60 14. 5 10,000 0. 014 10 5. 2 60 26 15, 000 0. 026 4.8 120 15. 5 I 00 0. 31 15 4. 8 120 15.5 14, 000 0. 31 15 4. 8 120 15.5 37, 000 0. 31 10 7 60 35 3, 000 0. 35 10 4 60 20 2, 0. 20 10 3 15 1, 000 0. 15 10 10 60 50 300 0. 50 10 5.2 60 26 70, 000 0. 26 10 1O 60 50 300 0. 50 10 5. 2 60 26 200, 000 0. 26 10 1O 60 50 400 0. 50 10 5. 2 60 26 80, 000 0. 26 10 7.0 60 35 5,00 0.35 15 4.8 120 15. 5 60,000 0.31 15 4. 8 240 15. 5 51, 00 0. 62 15 4.8 480 15.5 460 1. 24 15 4. 8 120 15.5 130, 000 0. 31 15 2. 2 60 14. 5 96, 000 0. 145 120 5. 2 60 76 280, 000 0. 76

1 Example 2No dip in dispersion.

2 Example 4-Directly to chromium plate from basis nickel plate.

3 Example 5-Eliminate steps (1), (2), and (3) in standard sequence. 4 Example 9-Directly to chromium plate from basis nickel plate.

5 Example 16-Direetly to chromium plate from basis nickel plate.

0 Maximum.

From Examples l-38, it will be apparent that the novel process permits attainment of unexpected results. For example by comparison of Example 8 with control Example 9, it will be observed that the product chromium plate prepared in practice of this invention exhibits 16,000 pores per square centimeter, while the control exhibited no pores. It is entirely unexpected that a chromium plate having a thickness of 0.065 micron would have this degree of microporosity; a normal commercial or prior art chr0- mium plate of this thickness deposited over a bright nickel plate would exhibit a microporosity of essentially zero. A microporous chromium deposit is characterized by substantially improved corrosion resistance.

It will also be apparent, from a comparison of Example 13 with control Example 16 that it may be possible to produce a chromium deposit of 0.5 micron thickness which is characterized by the presence of 400 microcracks per centimeter-the control Example 16 (typical of a normal prior art plate) exhibited 10 gross cracks per centimeter and no microcracks. A chromium plate char- 113 acterized by the presence of at least about 100 microcracks per centimeter possesses substantially improved corrosion resistance.

In the following examples, panels may be bright nickel plated, water rinsed, acid dipped, water rinsed, as were mium plate which, at all normal decorative thicknesses, possesses either a desired microcrack pattern or a desired microporosity. This continuity of microcracking and microporosity permits attainment, over the entire area, of a chromium plate having an unexpectedly high the panels for the first series of examples supra. The resistance to corrosion. panels may then be dipped into an aqueous dispersion of The following examples serve to illustrate the adtalc (Mistron Monomix brand supplied by Sierra Talc vantages in corrosion resistance obtained by practice of and Chemicals Inc.) having a maximum particle size of this invention. 6 microns and a median particle size of 1 micron. The 10 Steel panels were copper plated and buffed to probasis metal, removed from the dispersion, and bearing a duce a final layer of buffed copper of about 7.5 microns stratum of talc was then plated for 10 seconds in a thick. They were then plated in a bright nickel plating standard commercially available .bright nickel system. bath to produce a thickness of microns. Except for Current density (C.D.) at varying points on the cathode the control which was water rinsed and plated in chrowas determined. 15 mium, the others were dipped in the noted dispersion, The matrix nickel plate containing talc particles was plated in a matrix bath of Watts nickel for 10 seconds then withdrawn from the bright nickel plating bath, water at 3 a.s.d. and then plated in chromium. After 48 hours rinsed, and chromium plated for 60 seconds in a standard corrosion testing (CASS) the ratings were noted.

TABLE XIII Chromium thickness (microns) 1 1 Dispersion 0.125 0.25 0.50

44 0.1% talc-Mistron Monomix (supra) in water 700,000 pores/cm. 7,000,000 pores/emf.-- 300 cracks/cm.

After 48 hours CASS 10/10 10 10 10. 45 1.6% graphite-Asbury No. 5530 (supra) in water. 37,000 pores/cm. 37,000 pores/em. 100 cracks/cm.

After 48 hours CASS 10/10 9 9 10 46 Control 10 cracks/em.

After 48 hours OAS ..r /9.

chromium plating bath containing 240 g./l. of chromium acid, 1.5 g./l. of sulfate (supplied as sodium sulfate), and 2 g./l. of silicofiuoride SiF (supplied as the sodium salt).

The product chromium plate was observed and the number of microcracks/cm. or the number of pores/cm. was determined by standard techniques.

In Table XII infra, the noted procedure was followed for Example 39. Example was conducted in a manner similar to Example 39, except that the basis metal bearing the stratum of particles was rinsed after the dip in the dispersion. In Example 42, there was added to the dispersant 0.0012% of Hallcomid M-lS-Ol (80% N,N- dimethylolamide), C. P. Hall Co. of Illinois. In Example 43, the procedure of Example 39 was followed except that no matrix deposit was applied over the stratum of particles, this example thus serving as a control.

From Table XII, it will be apparent that practice of the process of this invention permits attainment of product chromium plate characterized by microcracking in desired amount at selected thickness and by microporosity at selected thickness. More significantly, Table XII shows that it is possible to plate an entire panel over a wide range of current densities and to obtain a chro- In Table XIII, the CASS rating is given as a pair of numbers wherein the first number indicates the degree of basis metal corrosion and the second number indicates the appearance. In each case, over a Scale of 0 to 10, the higher numbers indicate a better rating; and values greater than 7-8 may be acceptable. Thus the control row, which is illustrative of the range of thicknesses occurring over a normal decorative plate, is unsatisfactory because over the 0.125 and 0.25 micron areas the corrosion ratings are 2/2 and 3/3 which are unacceptable. At the 0.50 micron thickness, the undesirable gross cracking attained makes the plate unsatisfactory. In contrast, in the other two examples, the micro-perforations permit attainment of satisfactory plate at all thicknesses over the plated piece.

It was observed that improved corrosion resistance was obtained when sulfur-free nickel (including nickel alloy) electrodeposits were employed in the foregoing examples.

Although this invention has been illustrated by reference to specific examples, numerous changes and modifications thereof which clearly fall within the scope of the invention will be apparent to those skilled-in-the-art.

What is claimed is:

l. A process for preparing a metal plate receptive to a decorative noble metal deposit, characterized by the presence of microporous areas and microcracked areas over substantially the entire surface of said noble metal plate, comprising aflixing to a basis material bearing a conductive metal surface a stratum of particles having a particle size of about 0.05-15 .microns and a density on said conductive metal surface about 5,000,000 particles/cmfi; and then depositing in said stratum of particles a conductive metal layer free of said particles containing sulfur-free nickel having an effective thickness less than the maximum thickness of said stratum of particles thereby forming a matrix wherein said particles are retained affixed to said surface in fixed position n said conductive metal layer, and at least some of said particles intercept the surface of said conductive metal layer.

2. A process for preparing a metal plate receptive to a decorative noble metal deposit, characterized by the presence of microporous areas and microcracked areas over substantially the entire surface of said nobel metal plate as claimed in claim 1 wherein said conductive metal surface is a nickel surface.

3. A process for preparing a metal plate receptive to a decorative noble metal deposit, characterized by the presence of microporous areas and microcracked areas over substantially the entire surface of said noble metal plate as claimed in claim 1 wherein said density of said particles is 5,000-2,000,000 particles/cm.

4. A process for preparing a metal plate receptive to a decorative noble metal deposit, characterized by the presence of microporous areas and microcracked areas over substantially the entire surface of said noble metal plate as claimed in claim 1 wherein said particles are platelet-shaped.

5. A process for preparing a metal plate receptive to a decorative noble metal deposit, characterized by the presence of microporous areas and microcracked areas over substantially the entire surface of said noble metal plate as claimed in claim 1 wherein said particles are aflixed to said conductive metal surface from a bath.

6. A process for preparing a metal plate receptive to a decorative noble metal deposit, characterized by the presence of microporous areas and microcracked areas over substantially the entire surface of said noble metal plate as claimed in claim 1 wherein said particles are affixed to said conductive metal surface by dipping said basis metal into a fluidized bed of said particles.

7. A process for preparing a metal plate receptive to a decorative noble metal deposit, characterized by the presence of microporous areas and microcracked areas over substantially the entire surface of said noble metal plate as claimed in claim 1 wherein said particles are particulate material selected from the group consisting of talc, kaolin, wax, graphite, sulfides, pigments, plastics, diatomaceous earths, powdered aluminum, activated carbon, silicates, carbonates, carbides, sulfur, and mixtures of these materials.

8. A process for preparing a metal plate receptive to a decorative noble metal deposit, characterized by the presence of microporous areas and microcracked areas over substantially the entire surface of said noble metal plate as claimed in claim 7 wherein said particulate material is talc.

9. A process for preparing a metal plate receptive to a decorative noble metal deposit, characterized by the presence of microporous areas and microcracked areas over substantially the entire surface of said noble metal plate as claimed in claim 7 wherein said particulate material is graphite.

10. A process for preparing a metal plate receptive to a decorative noble metal deposit, characterized by the presence of microporous areas and microcracked areas over substantially the entire surface of said noble metal plate as claimed in claim 7 wherein said particulate material is molybdenum disulfide.

11. A process for preparing a metal plate receptive to a decorative noble metal deposit, characterized by the presence of microporous areas and microcracked areas over substantially the entire surface of said noble metal plate as claimed in claim 7 wherein said particulate material is tungsten disulfide.

12. A process for preparing a metal plate receptive to a decorative noble metal deposit, characterized by the presence of microporous areas and microcracked areas over substantially the entire surface of said noble metal plate as claimed in claim 7 wherein said particulate material is latex plastic.

13. A process for preparing a metal plate receptive to a decorative noble metal deposit, characterized by the presence of microporous areas and microcracked areas over substantially the entire surface of said noble metal plate as claimed in claim 12 wherein said latex plastic is selected from the group consisting of butadiene-styrene 1 5 copolymer, vinyl chloride polymer, vinyl acetate polymer and vinylidene chloride-acrylonitrile copolymer.

14. A process for preparing a metal plate receptive to a decorative noble metal deposit, characterized by the presence of microporous areas and microcracked areas over substantially the entire surface of said noble metal plate as claimed in claim 12 wherein said latex plastic is acrylonitrile-butadiene-styrene terpolymer.

15. A process for preparing a metal plate receptive to a decorative noble metal deposit, characterized by the presence of microporous areas and microcracked areas over substantially the entire surface of said noble metal plate as claimed in claim 1 wherein said conductive metal layer is selected from the group consisting of nickel, nickel-tin, cobalt, nickel-cobalt, silver, rhodium, platinum, copper, bronze, brass, zinc, cadmium and manganese.

16. A process for preparing a metal plate receptive to a decorative noble metal deposit, characterized by the presence of microporous areas and microcracked areas over substantially the entire surface of said metal plate as claimed in claim 15 wherein said conductive metal layer is nickel.

17. A process for preparing a metal plate receptive to a decorative noble metal deposit, characterized by the presence of microporous areas and microcracked areas over substantially the entire surface of said noble metal plate as claimed in claim 1 wherein said effective thickness of said conductive metal layer is 0.02-3 microns.

18. A process for preparing a metal plate receptive to a decorative noble metal deposit, characterized by the presence of microporous areas and microcracked areas over substantially the entire surface of said metal plate as claimed in claim 1 wherein the acutal thickness of said conductive metal layer is 20%-200% of the maximum thickness of said stratum of particles whereby said effective thickness of said conductive metal layer is less than said maximum thick-ness of said stratum of particles.

19. A process for preparing a metal plate receptive to a decorative noble metal deposit, characterized by the presence of microporous areas and microcracked areas over substantially the entire surface of said noble metal plate as claimed in claim 1 comprising aflixing to a basis material bearing a conductive nickel surface a stratum of latex plastic particles having a particle size of about 0.0545 microns and a density on said conductive nickel surface of about 5,000-2,000,000 particles/cm and then depositing in said stratum of latex plastic particles a conductive sulfur-free nickel layer free of said particles having an effective thickness of 0.02-3 microns, which effective thickness is less than the maximum thickness of said stratum of latex plastic particles thereby forming a matrix wherein said latex plastic particles are retained afiixed to said surface in fixed position in said conductive layer, and at least some of said particles intercept the surface of said conductive nickel layer.

20. A metal plate receptive to a decorative noble metal deposit characterized by the presence of microporous areas and microcracked areas over substantially the entire surface of said noble metal plate, prepared by affixing to a basis rnaterial bearing a conductive metal surface a stratum of particles having a particle size of about 0.05- 15 microns and a density on said conductive metal surface of about 5,000,000 particles/cm. and then depositing in said stratum of particles a conductive metal layer free of said particles containing sulfur-free nickel having an effective thickness less than the maximum thickness of said stratum of particles thereby forming a matrix wherein said particles are retained affixed to said surface in fixed position in said conductive metal layer, and at least some of said particles intercept the surface of said conductive metal layer.

21. A metal plate receptive to a decorative noble metal deposit as claimed in claim 20 wherein said conductive metal layer is selected from the group consisting of nickel.

References Cited UNITED STATES PATENTS 5 3/1959 Ferrand 204-16 4/1961 Larson 204-38X 9/1961 Eitel et a1 204-34 6/1962 Cox et a1 204-38 10 10/1962 Hirakis 29194 10/1962 Grazen 20416X 7/1965 Dudek et a1. 204-40X 5/1966 Jung et a1. 204-38X 12/1967 Brown et a1 29--194 15 4/1968 Duke et a1. 2'0416X *8/ 1968 Webb 204-16X 10/ 1964 Thomaszewski et a1. 20441 9/ 1967 Schwedhelm et a1 29194 2/1969 Du Rose et a1 29183.5

6/ 1969 'Odekerken 204-41 9/1969 Chessin et a1 204-29 FOREIGN PATENTS 5/1966 Great Britain.

US. C1. X.R.

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