US3390060A - Wax stopoff composition and process - Google Patents

Description

United States Patent 3,390,060 WAX STOPOFF COMPOSITION AND PROCESS Ram Dev Bedi, Cleveland, Ohio, assignor to M & T Chemicals Inc., New York, N.Y., a corporation of Delaware No Drawing. Filed Mar. 11, 1964, Ser. No. 351,240 Claims. (Cl. 204--) ABSTRACT OF THE DISCLOSURE A cathode having a selected area of high current density whereon plating is desired and pre-determined areas of low current density is protected against undesirable reactions during electroplating by applying to the areas of low current density a solution containing an inert organic solvent, chlorinated naphthalene wax having a melting point of at least 100 C., and microcrystalline wax having a melting point of at least 75 C.; and evaporating said solvent to form a wax film having a thickness of about -50 microns on said areas of low current density.

This invention relates to plating and more particularly to a technique for preventing undesirable reactions on cathodic areas of low or negligible current density during such plating.

As is well known to those skilled in the art, electroplating of various metals, typically nickel, copper, tin, zinc, or chromium may be effected in baths of varying acidity and composition; many of those baths may contain chloride or fluoride together with oxidizing agents which may be an integral part of the bath or present as an additive. During the plating of basis metals such as iron, steel, cast iron, copper, aluminum, zinc, etc. in such baths it is necessary to control current density over the areas to be plated. Because of differences in area or geometry or accessibility, there may be portions of the cathode which have a low current density, typically less than 1.6 amperes per square decimeter and frequently 0.3-1.0 a.s.d., or even no appreciable current whatsoever.

It has been found that undesirable chemical reactions, both electrolytic and non-electrolytic, may take place at such areas of low or negligible current density. For example, the low current density areas may be chemically etched by the plating solution. Electrolytic etching or other undesirable electrolytic reactions may also take place. These undesirable reactions may cause serious problems during the plating operation. For example, the dimensions of the plated product may be altered or its appearance spoiled. The problem of undesirable reaction may be present in various baths, typified by chromium plating baths, nickel plating baths, copper plating baths, tin plating baths, zinc plating baths and particularly in acid baths containing halides or halide-complexes and frequently containing oxidizing agents, etc. For purposes of convenience and illustration, reference will hereinafter be made to chromium plating baths.

As is well known to those skilled in the art, chromium plating may be effected by use of a bath containing e.g. chromic acid and sulfate, or sulfate together with other compounds which may be employed to effect various desirable results. Typical of these additive compounds may be fluorides or fluoride complexes.

Other illustrative chromium plating systems may include soluble catalyst systems containing e.g. chromic acid and a sulfate such as sulfuric acid in amount sufficient to give the desired concentration of sulfate ion, or self-regulating baths, typically those containing silicofluorides together with sulfate and chromic acid.

During chromium plating from baths typified by the foregoing, it is common to operate at a temperature "ice which may vary depending upon the speed of plating desired or other factors. Commonly however, the tempera ture of operation may be 34 C.-72 (3., typically 48 0-63 C. The cathodic current density may preferably be controlled to fall in the range of 8-100, and typically 12- 75 amperes per square decimeter (a.s.d.) on the selected areas of high current density whereon plating may occur. However, because of the irregular shape of many pieces which are to be chromium plated, it is not possible to maintain uniform desired current density over the entire piece. If the current be set to provide a current density as noted, there will be places, typically interior portions, end portions, back portions, or crevices where the current density may be considerably lower, for example 1.6 or less and frequently 0.3-1.0 a.s.d. or less.

It has been found that undesirable reactions may take place at these areas of low current density, e.g. they may be strongly etched during plating. Etching may be caused by ordinary chemical action or by electrolytic action and may be particularly pronounced when the bath is a chromium plating bath which contains the fluoride or silicofluoride ions which may be present in self-regulating high speed baths, soluble catalyst baths, or sparingly soluble catalyst chromium plating baths, and particularly when the basis metal is cast iron.

In order to eliminate these problems, it has been common to cover the low current density areas of articles to be plated with lacquer, tape, or thick deposits of wax, typically of the order of 1-8 mm. thick. Prior art use of lacquers, tapes, and waxes has not been completely satisfactory. Tapes must be carefully placed and removed, since any spaces not completely covered will be severely etched. Lacquer coatings are removed with considerable difficulty. Waxes have been applied in a molten state which requires that they and the article to be treated be heated, thus presenting problems of burns, flammability, toxic fumes, time-consuming labor, and expense. Thick deposits of wax have been used to ensure a non-porous coating and protection throughout the plating operation, and their production requires the application of a number of coats. These thick wax deposits which have heretofore been believed necessary may flake or chip from the article to be plated. They may present adhesion problems, especially when applied to a relatively smooth surface and without suflicient preheating. Wax which flakes, chips, or otherwise separates from the article may contaminate the plating bath. Such thick deposits must be removed from the plated part after plating, and their removal may be difficult. Also, their use is expensive because of the large amounts of wax which must be employed.

Various other techniques to minimize low current density etching of cathodes in the noted plating baths have not been uniformly successful and there is today no generally used, economical etch preventive system which is completely satisfactory under all circumstances.

It is an object of this invention to provide a technique for preventing undesirable reactions at low curent density areas in plating operations. It is a further object to provide novel compositions useful for treating cathodes to prepare them for plating. Other objects will be apparent to those skilled in the art on inspection of the following description.

In accordance with certain of its aspects, this invention provides a process for protecting against undesirable reactions during electroplating a cathode having selected areas of high current density whereon plating is desired and predetermined areas of low current density, which comprises applying to said predetermined areas of low current density a solution comprising an inert organic solvent, chlorinated naphthalene wax having a melting point of at least about C., and microcrystalline wax having a melting point of at least about 75 C.; and evaporating said solvent thereby forming on said areas of low current density a wax film having a thickness of about 2.5-50 microns.

The cathode may be protected from undesirable reactions by treating the predetermnied areas thereof of low or negligible current density. The areas of low current density may be those at which the current density is less than 1.6 a.s.d., and typically between 0.3 and 1.0 a.s.d., or less. In accordance with this invention, the low current density areas of the cathode may be treated with a solution of chlorinated naphthalene wax and microcrystalline wax. The waxes which may be employed in the practice of this invention may be microcrystalline wax having a melting point of at least about 75 C., say 75-90" C. and chlorinated naphthalene wax having a melting point of at least about 100 C., say 100-190 C., and which are resistant to decomposition in the plating bath.

Microcrystalline waxes are waxes having an average molecular weight of about 490-800 which may be obtained e.g. as by-products in the recovery of petrolatum and crude oil and typically from dewaxing of lube oil stock. The most preferred microcrystalline waxes are those having a moderately high degree of plasticity, a melting point of about 75-90 C., and a needle penetration (100 g./5 see/25 C.) of about 7-25 as determined on a Universal Penetrometer (No. 14). Typical of such waxes are those sold under the trademarks Be Square 170/ 175, Be Square 180/185, Superla Light Yellow, Petrosene A, Be Square White, and Sun 12-90.

Other illustrative microcrystalline waxes which may be employed in the practice of this invention include the following.

Chlorinated naphthalene waxes are wax-like materials prepared by chlorinating naphthalene to a final chlorine content of about 40-70% by weight. The chlorinated naphthalenes obtained commercially may typically be mixtures of tri-, tetra-, penta-, hexaand octachloronaphthalene isomers. Melting points may be about 100-190 C. The most preferred chlorinated naphthalene waxes may be those having a melting point of about 120-140 C. and a chlorine content of about 55-65% by weight.

Illustrative preferred chlorinated naphthalene waxes which may find use in the practice of this invention include chlorinated naphthalene having a chlorine content of 62% and a melting point of 137 C. sold under the trademark Halowax 1014; chlorinated naphthalene having a chlorine content of 59% and a melting point of 130-134 C. sold under the trademark Nibren Wax D130; and chlorinated naphthalene having a chlorine content of 65% and a melting point of 120-125 C. sold under the trademark Seekay 123.

In accordance with certain more preferred embodiments of this invention, the wax employed may be a mixture of a microcrystalline wax and a chlorinated naphthalene wax. The mixture may typically comprise about 3-20 parts by weight of microcrystalline wax and about 2-20' parts by weight of chlorinated naphthalene wax. Preferably the mixture may comprise about 6-12 parts by weight of microcrystalline wax and about 6-12 parts by weight of chlorinated naphthalene wax. Most preferably, it may comprise 7-8 parts of microcrystalline wax and 6-7 parts of chlorinated naphthalene wax.

The preferred microcrystalline waxes may be the moderately highly plastic Waxes hereinbefore described having a melting point of about 75-90 C. and a needle penetration of about 7-25, say 20. The preferred chlorinated naphthalene may be a mixture of pentachloronaphthalene and hexachloronaphthalene having a melting 4 point of about 120-140 C. and containing about 55-65% by weight chlorine.

The thin, protective films formed in accordance with this invention which comprise microcrystalline wax together with chlorinated naphthalene are highly superior in their film-forming and protective qualities. Since these two materials may not be compatible in the desired proportions in a melt, they cannot readily be produced by prior art hot dip techniques. It is a particular feature that these novel composite films may be readily and conveniently produced by use of the novel solutions of this invention which comprises a solution of a microcrystalline wax and a chlorinated naphthalene in an inert organic solvent.

The organic solvent may preferably be inert, i.e. not chemically reactive toward the cathode and the wax employed. The inert organic solvents employed may preferably have a boiling point of 45-150 C. and most preferably 60-120 C. It is also desirable that the solvent be relatively non-toxic and that it not present extreme flammability hazards. The inert organic solvent may typically be a hydrocarbon solvent or a substituted hydrocarbon. Aromatic hydrocarbon solvents and chlorinated hydrocarbon solvents may be preferred. Examples of suitable inert organic solvents include benzene, toluene, cyclohexane, petroleum ether, gasoline, trichloroethylene, carbon tetrachloride, etc.

The novel solutions of this invention may be prepared by dissolving the microcrystalline wax and the chlorinated naphthalene wax in the organic solvent. It has been found most convenient to dissolve first the entire quantity of microcrystalline wax in the organic solvent and subsequently to dissolve the chlorinated naphthalene wax in the resultant solution. Moderate agitation may be used to facilitate dispersion. Mild heating may improve the rate of dissolution. Preferably, the wax may he added to the solvent in a divided form such as shavings, small lumps, etc. If desired, the wax may be melted and added in the molten state, preferably dropwise. The resultant solutions may possess good stability and may be stored prior to use.

The wax solution which may be employed in the practice of this invention may comprise parts by weight of an inert organic solvent and at least about 5 parts by weight of the waxes employed. Preferably 5-35 parts by weight of wax per 100 parts by weight of solvent may be employed. In the most preferred embodiments of this invention, 10-20, say 15 parts by weight of wax may be employed.

Where the wax used is the hereinbefore described preferred combination of microcrystalline wax and chlorinated naphthalene wax, the novel solutions may typically comp-rise 100 parts by weight of organic solvent, 3-20 parts by weight of microcrystalline wax, and 2-20 parts by weight of chlorinated naphthalene wax. Preferably the novel solution may comprise 100 parts of organic solvent, 6-12 parts of microcrystalline wax and 6-12 parts of chlorinated naphthalene wax. The most preferred solutions may comprise 100 parts of organic solvent, 7-8 parts of microcrystalline wax and 6-7 parts of chlorinated naphthalene.

The wax solutions employed in accordance with this invention may typically have a viscosity of 1-1000 centipoises at about 25 C,-40 C. and may, therefore, be readily and conveniently applied to the cathode. The novel solutions containing both microcrystalline and chlorinated naphthalene waxes are especially desirable because the thin films which they produce have outstanding adhesion, freedom from holes or discontinuities, resistance to decomposition in the plating bath, etc. Furthermore, they exhibit a relatively high viscosity and a rapid increase in viscosity with increasing concentration. Application of these solutions is especially convenient because of a minimum of dripping or flow. Because the viscosity increases rapidly as solvent evaporates, the wax film may rapidly become resistant to deformation and the treated cathodes may be readily handled shortly after treatment. It is a further advantage that the solutions herein described produce films which are continuous and free of holes, thus allowing satisfactory protection at very thin film thicknesses.

The wax solution may be applied to the low current density areas of the cathode by spraying, brushing, dipping, etc. Typically, a single-coat application may be sufiicient to give the desired thickness of about 2.5-50 microns and preferably 7.5-25, say 17.5 microns. Preferably, the cathode and the wax solution may be maintained at about 2540 C. during application. Higher or lower temperatures may be used but no substantial apparent advantage may be observed. After application the cathode may be air-dried, typically at room temperature, say 20-25 C. until the solvent evaporates, typically in about 3-60, say 4-15 minutes. If desired, evaporation of the solvent may be effected at higher or lower temperatures.

When the protective coating has dried, the cathode may be subjected to a cleaning operation prior to electroplating. During the cleaning step, high temperatures, i.e. prolonged exposure to temperatures greater than about 75 C., and organic solvents, e.g. trichloroethylene, may preferably be avoided to prevent premature removal of the protective film. A typical cleaning operation may comprise vapor blasting, water rinsing, hot alkaline cleaning, water rinsing, and acid dip. Alternatively, the cathode may be cleaned before applying the protective coating of wax to the low current density areas.

The cleaned cathode may then be plated by maintaining it, as cathode, in an electroplating bath, typically a chromium plating bath. During the plating step, it may be found that the areas of low current density, i.e., areas at which the current density is less than about 1.6 a.s.d., may be substantially completely protected from undesirable reactions, including chemical etching, electrolytic etching, etc. and that said areas of low or negligible current density may be substantially unaffected during plating.

After the plating operation, the protective coating may, if desired, be removed from the plated cathode, typically by hot (greater than about 80 C.) water immersion, vapor degreasing, etc. It is a feature of this invention that the very thin film of protective coating may not require removal and that it may be allowed to remain on the cathode to provide lubricity, corrosion protection, etc.

Practice of this invention according to certain of its aspects and the unexpected advantages obtained thereby may be observed from the following examples.

Example 1 A solution was prepared in accordance with this in vention by melting parts by weight of microcrystalline wax having a melting point of 77 C., a penetration reading (25 C.) of 20, an acid number of nil and a saponification number of nil, sold under the trademark Be Square 170/175, and adding the molten wax dropwise to 100 parts by weight of toluene with agitation. When the microcrystalline wax was completely dispersed, 10 parts by weight of chlorinated naphthalene wax having a chlorine content of 62%, a specific gravity (25 C.) of 1.78, and a melting point of 137 0, sold under the trademark Halowax 1014, was added dropwise-and dispersed in the toluene solution.

For purposes of comparison, a control solution of 35 parts by weight of the chlorinated naphthalene wax alone in 100 parts by weight of toluene and a second control solution of parts by weight of the microcrystalline wax alone in 100 parts by weight of toluene were prepared by the same technique.

Pieces of polished cast iron piston ring were treated with the three solutions by immersing them for several seconds, withdrawing them, and allowing them to drain and dry. The physical appearance of the film produced was noted.

When the films had dried completely, each of the treated pieces was immersed for several hours in a chromium plating bath containing 225 g./l. chromic acid,

1.19 g./l. sulfate ion (derived from strontium sulfate), and 2.3 g./l. silicofluoride ion (derived from potassium silicofluoride), said bath being maintained at C. during the immersion. The results of the comparative tests are shown in Table I.

lene wax alone. and crystalline in apparent in numerappearance. ous places.

Microcrystalline wax+ Uniform smooth film No chemical etching chlorinated having a thickness apparent; subnaphthalene wax. of about 20 strate completely microns. protected.

As may be seen from these comparisons, practice of this invention produces thin protective films which afford outstandingly superior protection of metal surfaces against chemical etching.

Example 2 A solution of 8.5 parts by weight of microcrystalline wax having a melting point of 77 C., a penetration reading (25 C.) of 20, an acid number of nil and a saponification number of nil, sold under the trademark Be square 170/175, and 8.5 parts by weight of chlorinated naphthalene wax having a chlorine content of 62%, a specific gravity (25 C.) of 1.78, and a melting point of 137 C., sold under the trademark Halowax 1014, in parts by Weight of toluene was prepared according to the procedure of Example 1. A solution of 15 parts by weight of the microcrystalline wax alone in 100 parts by weight of toluene was prepared for purposes of comparison.

Pieces of polished cast iron piston ring were coated by immersing them in the solutions, withdrawing them, and allowing them to drain and dry.

In order to ensure that the coated pieces would represent low current density areas during electrolysis in a plating bath, they were mounted inside a steel tube having a length of about 7.5 cm. and an inside diameter of about 1.3 cm. The coated pieces were maintained in contact with the interior surface of the tube.

The entire assembly was placed in a chromium plating bath containing 225 g./l. chromic acid, 1.19 g./l. sulfate ion (derived from strontium sulfate), and 2.3 g./l. silicofiuoride ion (derived from potassium silicofiuoride). It was chromium plated for 2 hours at a temperature of 55 C. and a current density of about 3.1 a.s.d. (based on exterior surface). Following electrolysis, the pieces were removed and examined. The results of this comparison are reported in Table II.

TABLE 11 Wax used: Appearance after plating microcrystalline was alone Film flaked off in spots; surface of cast iron heavily corroded. microcrystalline wax-l-chlorinated naphthalene wax Film substantially unaffected; no corrosion, plating, or etching of coated surface.

As may be seen from this comparison, the thin wax films of this invention provide exceptional protection of metal surfaces from undesirable reactions during electroplating.

Although this invention has been illustrated by reference to specific example, 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. The process for protect-ing against undesirable reactions during electroplating a cathode having selected areas of high current density whereon plating is desired and predetermined areas of low current density, which comprises applying to said predetermined areas of low current density a solution comprising an inert organic solvent, chlorinated naphthalene wax having a melting point of at least 100 C., and microcrystalline wax having a melting point of at least 75 C.; and evaporating said solvent thereby forming on said areas of low current density a wax film having a thickness of about 2.5-50 microns.

2. The process for protecting a cathode as claimed in claim 1 wherein said solution contains at least about parts by weight of wax per 100 parts by weight of inert organic solvent.

3. The process for protecting a cathode as claimed in claim 1 wherein said chlorinated naphthalene wax has a melt-ing point of about 120-140" C. and a chlorine content of about 55-65% by weight.

4. The process for protecting a cathode as claimed in claim 1 wherein said microcrystalline wax has a melting point of about 7590 C., and a needle penetration of about 7-25.

5. The process for protecting a cathode as claimed in claim 1 wherein said inert organic solvent is selected from the group consisting of aromatic hydrocarbon solvents and chlorinated hydrocarbon solvents having a boiling point of 45-150 C.

6. The process for protecting against undesirable reactions during electroplating a cathode having selected areas of high current density whereon plating is desired and predetermined areas of low current density, which comprises applying to said predetermined areas of low current density a sol-ution comprising 100 parts by weight of an inert organic solvent; 2-20 parts by weight of chlorinated naphthalene wax having a melting point of about 120-140 C. and a chlorine content of about 55-65% by weight; and 3-20 parts by weight of microcrystalline wax having a melting point of about 75-90 C. and a needle penetration of about 7-25; and evaporating said solvent thereby forming on said areas of low current density a wax film having a thickness of about 2.5-50 microns.

7. The process for protecting a cathode as claimed in claim 6 wherein said inert organic solvent is selected from the group consisting of aromatic hydrocarbon solvents and chlorinated hydrocarbon solvents having a boiling point of -150 C.

8. The process for protecting a cathode as claimed in claim 6 wherein said solution contains 6-12 parts by weight of said chlorinated naphthalene wax and 6-12 parts by weight of said microcrystalline wax.

9. The process for electroplating a plate metal onto a cathode having selected areas of high current density, whereon plating is desired and predetermined areas of low current density which comprises applying to said predetermined areas of low current density a solution comprising an inert organic solvent, chlorinated naphthalene wax having a melting point of at least 100 C., and microcrystalline wax having a melting point of at least 75 C.; and evaporating said solvent thereby forming on said areas of low current density a wax film having a thickness of about 2.5- microns; and plating the plate metal onto said selected areas of said cathode, the said predetermined areas of low cathode current density remaining substantially free of etching during said plating.

10. The process of claim 9 wherein said plate metal is chromium.

References Cited UNITED STATES PATENTS 1,953,904 6/1931 Bowyer et al 102-12 2,070,918 2/1937 Peterson 2881 2,185,031 12/1939 MacLaren 134-5 2,635,093 4/1953 Miller et al 26092.1 3,084,128 4/1963 Sillwagon 260-4 FOREIGN PATENTS 483,307 4/1938 Great Britain.

OTHER REFERENCES The Condensed Chemical DictionarySixth edition, Reinhold Co., pp. 871, 262 and 1224-1225 relied on.

HOWARD S. WILLIAMS, Primary Examiner.

JOHN H. MACK, ROBERT K. MIHALEK, Examiners.

W. VAN SISE, Assistant Examiner.