US3552993A - Process for rinsing chromium plated parts - Google Patents

Abstract

BY THIS PROCESS AND THROUGH THE USE OF THIS PRODUCT ONE MAY ENHANCE THE RINSING OF OBJECTS WHICH ARE WETTED WITH DILUTE CHROMIC ACID. A PRIMARY EXAMPLE WOULD INVOLVE RINSING CHROMIUM PLATED OBJECTS IN WHICH THE LUSTER THEREOF IS TO BE PRESERVED AND WATER SPOTTING IS TO BE AVOIDED. BY THIS PRACTICE, ONE MAY INSURE THAT WASTE RINSE WATERS ARE FREE OF CONTAMINATION BY THE TOXIC HEXAVALENT CHROMIUM ION WHICH FORMELY DEVELOPED IN SUCH RINSING. IN AT LEAST ONE WATER RINSE HEREIN, ONE MAY COMBINE A REDUCING AGENT WITH BUFFER AND SURFACTANT HEREIN. THIS

REDUCES CHROMIC ACID STAINING AND DEVELOPS AT THE SAME TIME AN ANTI-POLLUTANT WASTE RINSE WATER. ESSENTIALLY, THE PROCESS MAY BE DEFINED AS CHEMICALLY RINSING OBJECTS WHICH HAVE BEEN WETTED WITH CHROMIC ACID SOLUTION, WITH AN ADDITIVE COMPRISING:

(A) A CHROMIC ACID REDUCING AGENT (B) A BUFFER TO STABILIZE THE AGENT AND (C) A SURFACTNT TO INSURE RINSE WETTING.

MOREOVER, THE PROCESS HAS EVEN WIDER UTILITY IN REDUCING THE HEXAVALENT CHROMIUM IONS IN SOLUTION FROM ANY SOURCE WHATSOEVER, VIZ: "ETCH" BATH; CHROMIC ACID PLATING BATH, ETC.

Description

Jan- 5, 1971 H. w. BUCHANAN PROCESS FOR RINSING CHROMIUM PLATED PARTS Filed June 9, 1969 @rfi @QSVI NNS m llllllll lllllll f llwillli@ v.

ATTORNEY United States Patent O Maine Filed June 9, 1969, Ser. No. 831,346 Int. Cl. B44d 1/44 U.S. Cl. 117--62 5 Claims ABSTRACT OF THE DISCLOSURE By this process and through the use of this product one may enhance the rinsing of objects which are wetted with dilute chromic acid. A primary example would involve rinsing chromium plated objects in which the luster thereof is to be preserved and water spotting is to be avoided. By this practice, one may insure that waste rinse waters are free of contamination by the toxic hexavalent chromium ion which formerly developed in such rinsing. In at least one water rinse herein, one may combine a reducing agent with buffer and surfactant herein. This reduces chromic acid staining and develops at the same time an anti-pollutant waste rinse water. Essentially, the process may be delined as chemically rinsing objects which have been wetted with chromic acid solution, with an additive comprising:

(a) a chromic acid reducing agent (b) a buffer to stabilize the agent and (c) a surfactant to insure rinse wetting.

Moreover, the process has even wider utility in reducing the hexavalent chromium ions in solution from any source,

BACKGROUND OF THE INVENTION Chromium plated objects are particularly susceptible to loss of luster, Water spotting, etc., during rinsing as there is generally a reluctance to use adequate rinse water, because of waste disposal problems. Most known surfactants which facilitate improved rinsing also are attacked by chromic acid and lose effectiveness. For example, various uorocarbon surfactants have been employed in chromic acid plating baths to reduce drag-out, but these are considered too expensive to be used to reduce the surface tension of rinse baths.

In the related eld of electroless plating of plastic objects, where subjected to an etch bath, chemical rinsing is important, precedent to sensitizing and activating as will be described.

SUMMARY OF THE INVENTION In one form of invention, chromic acid plating solution herein is rinsed from plated objects by contacting them with a dilute aqueous solution, containing sodium hydrosulfite, an alkaline buffer such as sodium carbonate, and preferably a surfactant such as nonionic or anionic wetting or dispersing agent. The plated objects are rinsed without loss of luster, without water spotting, and without producing waste rinse waters contaminated with toxic hexavalent chromium ions. The rinsing processes of the present invention thus permit the use of chromic acid sensitive surfactants as rinse aids, because the rinse water is always kept free of hexavalent chromium ions. At room temperature or lower the present preferred surfactant inhibits oc formation from the trivalent chromium hydroxide. Thus the rinsing can be accomplished in the presence of a considerable amount of trivalent chromium 3,552,993 Patented Jan. 5, 1971 ICC hydroxide without encountering the dulling effect of a dried-on lm. Noteworthy is the fact that the process and product are useful though lacking in a surfactant, per se, as will be explained herein.

Moreover, the process and product are equally useful in the plating of substrates which are of either metal or plastic, the latter having been prepared with a nickel plate base. As indicated, the process has its widest utility in the broad reduction of the hexavalent chromium ions in solution from any source whatsoever. For example, the etch bath, usually comprises a strong solution of chromic acid and sulfuric acid. Following the initial bath with the acid combination complete rinsing hereby is essential to successful sensitizing with stannous chloride and activating with palladous chloride. In this treatment of plastic objects a combination sodium hydrosulte and sodium carbonate solution is prepared without surfactant.

BRIEF DESCRIPTION OF THE DRAWINGS The ligure is a ow sheet, diagrammatically depicting one form of the process employed in the present invention.

DESCRIPTION OF THE PREFERRED 4EMBODIMENTS The present method is so devised that no toxic hexavalent chromium ions can enter the sewage system.

Reference the figure, as in the art, one employs broadly a saveall rinse tank (Tank II) as a first rinse. Make-up for the plating tank (Tank I) is continuously drawn from the saveall tank and then fresh soft water is added to replenish the saveall tank. Thus chrome values are recovered in the plating tank and the chromium content of the saveall is controlled at a low level. In the operation of the chemical rinse tank (Tank III), it is important that the chrome-reducing rinse aid formulation, defined hereinafter, be added at such a rate that there is always an excess of reducing power. Periodic additions are thus made, based upon tests for excess reducing power. The preferred method of testing for excess reducing power is a titration of a sample from the rinse tank by a standardized solution of rubine dye. The endpoint for the titration is the appearance of a stable pink color. Water is also added to the chemical rinse tank either continuously or periodically to keep the level of colloidal chromium sesquioxide from building up too high. A low concentration thereof should be maintained in the rinse for optimum effectiveness in obtaining maximum brightness on the plated parts. Too much rinse water not only entails high water costs, but also increases the requirement for the chrome-reducing rinse aid needed to maintain reducing conditions in the rinse. Following the chemical rinse, a conventional cold water rinse (Tank IV) may be em- -ployed to rinse away any chromium sesquioxide carried over from chemical rinse (Tank II). Optionally, a hot rinse in mineral-free water facilitates rapid drying of the plated parts and assures a spotless surface thereon.

As indicated, the rinsing of chrome plated parts herein reduces chromic acid staining and eliminates the problem of disposing of highly dilute waste waters containing the toxic hexavalent chromium ion. The process is thus one of chemical rinsing, in which the undesired contaminant which is to be rinsed away, is immediately converted to a less undesirable substance.

Specifically, chrome-plated parts wetted with chromic acid plating solution (Tank I) may be sequentially contacted (Tank III) with a buffered solution of sodium hydrosulfite at a temperature not exceeding F. The additive hydrosulte solution is a dilute aqueous solution preferably of a strength of about 0.025% comprising: a powder made by mechanically blending these three ingredients: A

(A) 42.8% Sodium hydrosullite (B) 52.2% Sodium carbonate (C) 5.0% Triton CF-54 The lower limit for the rinse aid concentration would be that point Where there is insuiiicient reducing power. Practically, the rinse aid lever should thus be maintained so that the rinse tank could effectively reduce at least one part per million of added chromic acid. By keeping the concentration low, one also minimizes losses of reducing power due to the slow spontaneous decomposition of the sodium hydrosulite in aqueous solutions.

Reduction of the chromic acid (Tank III) is essentially instantaneous, even when the hydrosulite content of the rinse bath is less than ten parts per million. Chromium sesquioxide that is formed is then in a dispersed, colloidal state and rinses from the metal easily (Tank IV). It is preferred though not essential that the rinse water (Tank IV) contain a surfactant which not only acts as a dispersing agent for the sesquioxide but also ensures that the chrome plated parts leave the rinse bath (Tank IV) in a water-break-free state. Now, the surfactant, as indicated, may take one of several nonionic or anionic forms or mixtures thereof. Included among suitable nonionics are the nonylphenol polyethylene glycol ethers, tridecyl polyethylene glycol ethers, and Triton CF-54 (a terminated ethoxylated phenol compound manufactured by the Rohm and Haas Co.)- Suitable anionic surfactants include the disodium salt of dioctylsulfosuccinic acid, sodium lauryl sulfate, and sodium dodecylbenzene sulfonate.

A preferred composition for use as a chrome-reducing rinse aid (Tank III) has the following formuation:

Reducing agent-42.8% Sodium hydrosult'ite (powdered) Buffer- 52.2% Sodium carbonate (light soda ash) Surfactant1-5.0% Triton CF-54 (Rohm & Hass) 1 May be excluded altogether. Although the percentages are not critical in the performance of the product suitable ranges would be:

Percent Reducing agent -90 Buffer 9-69 Surfactant1 1-10 1 May be excluded altogether.

The sodium carbonate serves as a buffer to stabilize the reducing activity of the rinse and increase the stability of the sodium hydrosulte to storage. Triton CF-54 is shown in the above formulation, any of the common nonionic or anionic wetting or dispersing agents would perform the function desired in promoting free rinsing and dispersing the colloidal chromium hydroxide. However, Triton CF-54 was chosen for our work because it was known to have optimum performance as a rinse aid in rinsing chrome plated parts. Other suggested surfactants would include the nonylphenol polyethylene glycol ethers, tridecyl polyethylene glycol ethers, the dioctyl ester of sodium sulfosuccinic acid, and sodium dodecylbenzene sulfonate. Alternatively, other alkaline buffers may be employed in place of the sodium carbonate such as trisodium phosphate, or sodium tripolyphosphate. The surfactant functions as a rinse aid by assuring good wetting of the chrome plated parts. It has a dispersing action on chromium sesquioxide and also renders the product relatively dust-free, thus reducing handling problems.

In carrying out the process of the present invention, it is preferred to maintain a low temperature in the rinse (Tank III), as heat tends to cause the chromium sesquioxide colloidal particles to flocculate. Such flocculation adversely leads to large oc particles that adhere to the chrome plated parts and tend to reduce the reflectivity of the plated surface. Heat also promotes rapid drying between rinses causing lioc particles to become so strongly attached to the plated surface that they are not removed during subsequent rinses. Whereas the process becomes rapidly inoperative at temperatures above F., very satisfactory results, however, can be obtained at 70 F.

Because impurities in the Water used in the rinse (Tank III) notably oxygen, react with sodium hydrosulite slowly under the conditions employed in said rinse, require that an excess be employed, it will thus take about fifteen (15) parts of the above recommended formulation, to reduce one part by weight of chromium from the hexavalent to the trivalent state. The 'theoretical quantity is 11.7 parts, but in practice, it is found that a moderate excess will be required. For example, it will take at least about fifteen (15) parts of the formulation per part of chromium to maintain a reducing condition in the rinse bath.

EXAMPLE I A fty-ve gallon, unheated chemical rinse was installed in a chrome plating line between the vcustomary saveall and first cold water rinse. From time to time, several ounces of a chrome-reducing rinse were added to the chemical rinse tank to maintain the rinse in a reducing condition. The formulation for the additive was 66% sodium hydrosulfite, 33% sodium carbonate, and 1% Triton CF-54. As plated parts from the saveall were rinsed iu the chemical rinse tank, a green color initially developed, due to the dispersed chromium sesquioxide. Following a subsequent cold water rinse, no evidence of any dulling film developed on any of the plated parts on continued operation.

EXAMPLE II A fifty-five gallon chemical rinse was operated at a temperature of 150-160 F. using the chrome-reducing rinse aid composition as in Example I. Chromium sesquioxide, formed from added chromic acid, at first appeared to -be colloidal but soon iiocculated to large green floc clumps. The floc was not readily removable by settling because of a very slow settling rate and the voluminous nature of the iioc. The lioc could be readily removed however, by circulating the rinse water through a lter. When in a short time the flow through the iilter slowed down greatly, it was calculated that a square foot of filter surface could be used practically for the removal of the chromium sesquioxide formed from onehalf ounce of chromic acid. During the test, it was demonstrated that the iioc was adherent to chromium surfaces and that it was not readily rinsed away if it was allowed to dry on the surface. Floc contamination reduced the brightness of the pladed surface.

EXAMPLE III The chemical rinse bath was simulated on a laboratory scale by adding small increments from time to time of the formulation,

Percent Sodium hydrosullite 42.8 Sodium carbonate 52.2 Triton CPL-54 5.0

alternately with small quantitiesof a diluted chrome plating bath to a liter of water. The presence of hexavalent chromium gave the bath a yellow to green coloration, depending upon the amount of colloidal chromium sesquioxide present. In the absence of hexavalent chromium, the colloidal chromium sesquioxide gave the bath a distinct bluish coloration. Excess reducingcapacity due to a surplus of the sodium hydrosulfite formulation was readily measured by titration of a sample with a standardized solution of rubine dye. Thus the bath could readily be controlled so as to maintain excess reducing capacity. After repeated additions of the reducing formulation and the diluted chrome plating bath over a period of several days, it was noted that the average pH had remained relatively constant at 9.0'i0.8. This finding indicates that the proportion of sodium carbonate in the formulation is adequate for pH control.

EXAMPLE IV The composition described in Example I was again used to clean up a quantity of chromic acid plating solution that was accidentally spilled on the oor. The reduction of the hexavalent chromium was immediate, thus preventing any of the toxic material from entering the sewer.

I claim:

1. In the chromium plating of objects, an improved method comprising the steps of (A) initially chrome plating the object by exposure thereof to a chromic acid plating solution,

(B) sequentially chemically rinsing the initially rinsed plated object with a dilute aqueous solution f a formulated mixture comprising:

(B1) a sodium hydrosulfite chromic acid reducing agent;

(B2) a buifer to stabilize the reducing agent; and

(B3) a non-cationic surfactant to ensure rinse setting of the object, the rinsing being conducted at such a rate as to ensure an excess of reducing effectiveness.

2. In the chromium plating of objects, an improved method comprising the steps of (A) initially chrome plating the object by exposure thereof to a chromic acid plating solution, sequentially (B) chemically rinsing the initially rinsed plated object with an aqueous solution containing an additive comprising:

(B1) a chromic acid reducing agent of dilute aqueous hydrosulite;

(B2) a buffer of sodium carbonate to stabilize the reducing agent; and

(B3) a non-ionic wetting agent surfactant to ensure rinse wetting of the object, the rinsing being conducted at such a rate as to ensure an excess of reducing eifectiveness.

3. The method according to claim 2 in which the aqueous solution is a dilute solution of a formulated mixture comprising the following in percentage by weight:

(A) sodium hydrosulte 35 %-50%;

(B) sodium carbonate 45 %60%;

(C) nonionic wetting agent 1%-10%.

4. In the chromium plating of objects, an improved method comprising the steps of:

(A) initially chrome plating the object by exposure thereof to a chromic acid plating solution;

(B) sequentially, fresh water rinsing the plated object, while simultaneously withdrawing portions of the fresh water rinse and supplementing the chromic acid plating solution therewith;

(C) sequentially chemically rinsing the initially rinsed plated object with a dilute aqueous solution additive comprising:

(C1) a hydrosulte chromic acid reducing agent;

(C2) a sodium carbonate buier to stabilize the reducing agent; and

(C3) a non-ionic surfactant to ensure rinse Wetting of the metal body.

5. The method according to claim 4 in which the aqueous solution is a dilute solution of a formulated mixture comprising the following in percentages by weight:

(A) sodium hydrosulte L7a-50%;

(B) sodium carbonate %-60%;

(C) nonionic wetting agent 1%-10=%.

References Cited UNITED STATES PATENTS 2,811,466 10/1957 Samuel 117-22 2,829,059 4/1958 Eisenberg et al 106-1 2,871,550 2/1959 Weinberg et al. 29-l83.5 2,997,444 8/ 1961 Martin 252-188X 3,030,281 4/1962 Moy 204-52.1X 3,041,257 6/1962 Cope et al. 204-51 3,203,876 8/1965 Deyrup 204-13 3,207,694 9/1965 Gogek 252-188X 3,340,073 9/ 1967 Zirngiebl et al. 106-1 3,438,798 4/ 1969 Baudrand et al. 117-47 FOREIGN PATENTS 36,063 5/ 1965 Germany 204-35 RALPH S. KENDALL, Primary Examiner U.S. Cl. X.R. 117-430; 204-35 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 ,552 ,993 Dated January 5 19j] In\'entor(s) Harry W- Buchanan It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column S line 19, "hydrosulfte Chromic" should read hydrosulfite-chromic Signed and sealed this 29th day of June 1971.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E. SCHUYLER, JR. Attesting Officer Commissioner of Patents FORM PO1050 (1o-69) uscoMM-DC soave-1

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