US 3300333 A
Description (OCR text may contain errors)
United States Patent Office 3,300,333 Patented Jan. 24, 1967 3,300,333 METHOD OF AND MEANS FOR APPLYING CORROSION INHIBITING COATING Mary Anne Page, Minneapolis, Minn., assignor to Minnesota Mining and Manufacturing Company, St. Paul,
Minn., a corporation of Delaware No Drawing. Filed May 27, 1963,Ser. No. 283,564
6 Claims. (Cl. 117120) This invention relates to a novel method of and means for applying an extremely thin but effective corrosion-inhibiting coating to metal surfaces. It particularly relates to a simple means for the commercial applications of such coatings.
The manufacturers of sheet metal have long been faced with a problem of corrosion inhibition. A typical situation exists in a copper mill, where cupreous strips on the order of .030 inch thick and up to feet wide are produced and wound convolutely into coils several hundred feet long. Such coils are then sent to the plant of a copper fabricator where they may be further reduced in thickness and/ or formed into finished products. The lag between the time when the copper leaves the mill and the time when it is utilized by the fabricator may be six months or more.
Sheet copper is a strikingly attractive raw material but it is subject to numerous types of corrosion. It is deleteriously affected by salt, for example, and a fingerprint which is inadvertently left on a copper surface often proves to be the site of destructive corrosive attack. It is also discolored unattractively and irregularly by exposure to the atmosphere, especially when hydrogen sulfide is present. Before a fabricator can use discolored or corroded copper sheets, he is compelled to remove the blemish, usually by abrasion, generally simultaneously removing adjacent sound metal. The process is inconvenient, expensive, and wasteful, and it is thus common commercial practice to return sheet copper to the supplier if it contains serious visually detectable defects.
In an attempt to reduce the quantity of cupreous sheet metal which is returned, mills have resorted to numerous techniques to limit corrosion, none of which is universally satisfactory. For example, oil or grease reduces corrosion slightly, but it is messy and inconvenient to remove. Where the oil-in-water emulsion of rolling lubricant is allowed to remain, corrosion is reduced very little and irregular stains often appear on the metal strip.
Where the copper sheet is annealed before leaving the mill, the annealing scale is ordinarily removed by passing the sheet through a pickling tank. Subsequent to this operation the sheet may be passed through a tank containing acidified sodium chromate and various catalysts to apply a chromate conversion coating to the surface. Although this process employs inexpensive raw materials and is fairly effective, the resulting surface is often nonuniform because of uneven wetting, the high water marks themselves often providing the site for subsequent corrosion. In addition, the chromate conversion operation changes the color of the copper and increases the difficulty of further thickness reduction. Further, although this process is well-suited to operations where a wet scale removal treatment of the annealed copper is already necessary, it is expensive and inconvenient when the copper would not ordinarily be subjected to such an operation.
It has also been proposed to minimize the tarnishing of copper sheets by Wrapping them in paper or cloth impregnated with a vapor phase corrosion inhibitor. Al-
though theoretically sound, this process is inconvenient, expensive, and has not gained very wide acceptance.
In some instances fabricators have coated cupreous products, such as planters, teakettles, or copper-bottomed pans, with lacquer, but the lacquer itself may discolor, and frequently tarnish may appear unexplainably and spread beneath the lacquer, which then must be removed, at considerable inconvenience.
It is known to apply a corrosion inhibiting compound to a metal surface and then to rub the treated surface with a cloth, and it would not be surprising to find that a cloth could be periodically dipped in a solution of corrosion inhibitor and rubbed over a metal surface to leave a protective coating. Commercially, however, such procedures are contraindicated, since solvent removal is hazardous, extra equipment is needed, and it has been supposed that frequent retreatment of the cloth would be necessary and that degree of corrosion resistance would vary widely. Insofar as I am aware, then, no one has given any serious consideration to frictionally transferring a solvent-free corrosion-inhibiting compound from a treated fibrous structure to a metal workpiece.
I have now found a novel, simple, and unexpected means for and method of imparting excellent corrosion resistance to cupreous and other metal surfaces. The appearance of the surface remains unchanged, and treated sheet can be readily rolled, soldered, or lacquered after only the conventional degreasing operation. The method of my invention is particularly adapted to industria plants, where unskilled persons are able to obtain consistently good results for extended periods of time.
In accordance with my invention I apply to a metal surface an extremely thin layer of an organic corrosioninhibiting compound which is capable of becoming bound to the metal by chemisorption.
In applying the corrosion-inhibiting compound, I employ a rotary porous fibrous rubbing element, such as a buffing wheel, which contains at its working surface and for a substantial distance inwardly therefrom on the order of 0.005 to 0.1 part of a solvent-free corrosion inhibiting compound per part of fiber. I have found that such a rubbing element may be used continuously through-out an 8-hour shift with no detectable wear and with only an unimportant decrease in the degree of corrosion resistance imparted. Even after treating thousands of lineal feet of metal, the treated fibrous rubbing element is readily restored to full functional efficiency by lightly dressing or combing the surface, thereby removing any matted fibers and oxidized metal which may be adhering thereto. The rate of wear, is in fact, so infinitesimal that the amount of corrosion-inhibiting compound transferred to the metal surface has been calculated to have an effective thickness far below 500 Angstrom units, or less than one-tenth the wave length of the lower limit of the visible light spectrum.
Among the attractive commercial aspects of my novel process are the facts that it can be put into effect very quickly and easily in almost any metal strip finishing line, that the equipment is simple, inexpensive, and compact, and that there is very little criticality of adjustment, and that, as indicated, the treated fibrous rubbing element needs only-the most perfunctory attention. The process is entirely dry, involving no immersion tanks, drying facilities or expensive and hazardous solvents. Cost of the treating materials themselves is almost insignificant, and the saving on metal which must be refinished or returned to the mill overwhelmingly outweighs any costs resulting from use of the process.
My invention will be further illustrated by means of several non-limiting examples set forth below in which all parts are by weight unless otherwise noted.
Example Three twenty-ply sections of /92 muslin (No. 2 sheeting, 4 sq. yds./ 1b.), each having a 9 inch diameter, 1% inch centerhole, and four rows of concentric machine sewing /2 inch apart, were immersed in and allowed to absorb all of a solution of 6.5 g. of alpha-mercaptostearic acid in 400 ml. of acetone. The sections were then removed from the solution and slowly rotated until the acetone evaporated. The average level of treatment thus attained was 2.24 g. of alpha-mercaptostearic acid per sq. yd. of cloth, or 2% of the weight of the cloth. The three sections were then axially ganged between a pair of /2 inch diameter side plates and driven at 1700 r.p.m. Three 1" x 3 x copper samples, previously cleaned abrasively, Were now treated by hand, the operator quickly moving the piece so that one entire major surface contacted the periphery of the wheel. Three identical copper samples were similarly buffed with a control wheel which contained no alpha-mercaptostearic acid but was otherwise identical. These six samples, all identical in appearance, were exposed to an atmosphere of 100 p.p.m. H 8 and 100% relative humidity at room temperature for 2 hours. The control samples were stained a dark blue-green and red whereas the test samples showed only a slight brown tarnish around the edges.
Example 2 Three muslin'sections of the type described in Example 1 were immersed in and allowed to absorb all of a solution of 7 g. of Nalcamine G-39M corrosion inhibitor (3. semi-solid mixture of compounds having the structure:
/NCH2 RC N-CH2 CHzCHzNHz wherein R is a l7-carbon alkyl chain having one or two double bonds) in 400 ml. of acetone and slowly rotated while being allowed to dry. The average level of treatment thus attained was 2.41 g./sq. yd. of fabric or 2.16% of the weight of the cloth. The sections were then mounted and driven as in Example 1 and used to treat 1" x 3" samples of sheet copper, brass and steel as in Example 1. The treated samples were then tested by placing 5 drops of a 0.5% sodium chloride solution on the surface and timing the appearance of the first tarnish or rust. The results were as follows:
Minutes Untreated copper 22 Treated copper 2500 Untreated brass 31 Treated brass 495 Untreated steel 5 Treated steel 18 Example 3 Three muslin sections, as in Example 1, were immersed in and allowed to absorb all of a solution of 6 g. of nonylphenoxyacetic acid (a viscous corrosion-inhibiting liquid obtained from Geigy Co.) in 400 ml. of acetone and rotated until the acetone evaporated. The average level of treatment thus attained was 2.07 g./sq. yd. of fabric or 1.85% of the weight of the cloth. This wheel was used as in Example 1 to treat samples of copper, brass and steel, which were then tested for corrosion resistance as in Example 2. The results were:
Minutes Untreated copper 22 Treated copper 360 Untreated brass 31 Treated brass 870 Untreated steel 5 Treated steel 90 Example 4 Three muslin sections, as in Example 1, were immersed in and allowed to absorb all of a solution of 10 g. of cyclohexylamine nitrite in 500 ml. of methanol and 4 rotated while being allowed to dry. The average level of treatment thus attained was 3.45 g./sq. yd. of the fabric or 3.1% of the weight of the cloth. This wheel was used as in Example 1 to treat samples of copper and brass, which were then tested for corrosion resistance as in Example 2. The results were:
Minutes Untreated copper 22 Treated copper 360 Untreated brass 31 Treated brass 165 Example 5 Three muslin sections, as in Example 1, were immersed in and allowed to absorb all of a solution of 10 g. of octadecylamine in 500 ml. of acetone and rotated while being allowed to dry. The average level of treatment thus attained was 3.45 g./sq. yd. of the fabric or 3.1% of the weight of the cloth. This wheel was used, as in Example 1, to treat copper, brass, steel and silver samples. The copper, brass and steel samples were then tested for corrosion resistance as in Example 2. The results were:
Minutes Untreated copper 22 Treated copper 3700 Untreated brass Treated brass Untreated steel 5 Treated steel 18 The silver samples were tested in an H S atmosphere, as in Example 1, for six hours. After this exposure the control sample was tarnished -to a brown color whereas the treated sample remained bright silver.
Example 6 A nonwoven web (3.47 sq. yd./lb.) for-med from scrap cotton threads bonded with regenerated viscose xanthate was uniformly roll coated with g./square yard (wet weight) of a 5% solution of octadecylmercaptan in toluene. The web was then dried and 12 inch diameter discs having a 1% inch centerhole were died therefrom, the level of treatment thus attained being 5 -g./sq. yd. of the fabric or 3.8% of the weight of the cloth. Twelve such discs were stapled together to form a section and a Wheel was made from two usch sections. This wheel was used, as in Example 1, to treat two samples of copper, which were then exposed to an H S atmosphere, as in Example 1, for two hours. An untreated control sample became tarnished to a dark blue-green and red color whereas the treated samples remained untarnished.
Example 7 Fifty 9-inch diameter discs having a l flt-inch centerhole were died from a web (5.6 sq. yd./lb.) of nonwoven cotton fibers lightly bonded with Hycar 1571 butadienezacrylonitrile copolymer latex, and axially ganged. The resultant wheel was immersed in and allowed to absorb all of a solution of 10 g. of octadecylmercaptan in 800 ml. of acetone and then rotated while being allowed to dry. The level of treatment thus attained was 4.15 g./sq. yd. of the fabric or 5.1% of the weight of the cloth. This wheel was mounted :between side plates and used, as in Example 1, to treat two samples of copper which were then exposed to an atmosphere of H 8, as in Example 1, for 2 hours. A control sample became tarnished with :a dark blue-green and red color while the treated samples remained as bright copper.
Example 8 A 9-inch diameter lambs wool 'bonnet approximately 1 inch thick was immersed in and allowed to absorb all of a solution of 7 g. of octadecylmercapta-n in 200' ml. of heptane and then dried. The level of treatment was approximately 0.11 g./cu. in. of lambs wool. This bonnet was then mounted on the head of a portable disc sander driven at 1500 r.p.m. and used to treat an 8 x 10 inch copper panel. After testing by exposure to an H 8 atmosphere, as in Example 1, a control sample of copper became darkly tarnished whereas the treated panel showed no signs of tarnish.
Example 9 Two l7-inch diameter Jackson Airway buff sections having a 7-inch centerhole, each made from 3.89 square yards of 86/93 count jeans cloth (2.6 sq. yd./lb were immersed in and allowed to absorb all of a solution of 9 g. of alpha-mercaptosteric acid in 600 ml. of acetone and rotated while being allowed to dry. This gave a level of treatment of 2.31 g./sq. yd. of the fabric or 1.32% of the weight of the cloth. The two buff sections were then ganged between flanges, driven at 1700 r.p.m., a-nd used to treat one-half of an 8 x 10 inch copper panel. After being exposed to an H S atmosphere, as in Example 1, for two hours, the untreated half of the copper panel showed a dark tarnish streak whereas the treated half showed no discoloration.
Example 10 Jeans cloth webs having a 96/ 92 count (2.6 sq. yd./ lb.) were roll coated with 100 grams/square yard of various percentages of octadecylmercaptan (ODM) in toluene. Levels of treatment obtained were as given in the following table:
Web Percent ODM in G. ODM/sq. yd. Percent ODM in olntion Cloth Forty 9-inch diameter discs having l fit-inch centerholes were then stamped from each of the treated webs and six wheels formed. Each wheel was used at 170 0 r.p.m. to treat two copper samples and two brass samples. After exposure in an H S atmosphere, as in Example 1, for two hours appearance of the samples was as given in the The other set of samples was tested by placing on the metal a drop of a 0.5% sodium sulfide solution and timing the appearance of the first discoloration. The results were as follows:
Treatment Level in Brass Samples Copper Samples Wheel-Weight Percent Control (none) 30 sec... sec.
0.057 2 min 3 min.. 30 sec. 0.11-t 4 IXllIL, 30 sec 4 min, 40 sec. 0.57-. 5 min., 30 see 5 min, 5 sec. 2.86 17 min, 20 secmin., 55 sec. 5.7 53 min 25 min.. 30 sec. 11.4 100 min, 30 sec 60 mm, 15 sec.
Example 11 A copper-bottom pan was buffed to a bright finish using a plai-n cloth buff and grease stick with tripoli. Lime dusting was used to remove excess grease, and onehalf of the copper bottom was then color buffed using a cloth buff containing alpha-mercaptostearic acid. Fingerprints were deliberately placed on both halves. After 48 hours exposure to air in an industrial laboratory, the fingerprints on the untreated half had caused discoloration of the copper whereas on the treated half all visible traces could be easily wiped off with tissue. This pan was then partially filled with water which was brought to a boil during 10 minutes and boiled for 20 minutes on a hot plate. The untreated half showed tarnish due to heat oxidation, whereas the treated half maintained a good appearance except at the site of the fingerprints. Even after two more heating sequences the treated half was superior in appearance to the untreated half.
Example 12 A Jackson Airway cotton buff section having an outer diameter of 12 inches and a fluted /6. inch wide face was saturated with a 7 /2% solution of ODM in xylol and the solvent evaporated, leaving a deposit of 4.3% octadeeylmercaptan based on the cotton cloth. This wheel was then mounted on an arbor, driven at 1750 r.p.m., and forced against the outer surface o-f a 7-foot x 4-inch copper band mounted on an inflated auto tire and rotated at 4 r.p.m. This setup continuously transferred ODM from the treating wheel to the surface of the copper band, an operator continuously removing the ODM from the copper by alternate wiping with a solvent-dipped rag and a clean rag. From time to time the effectiveness of the wheel was tested by forcing 1" x 3" copper and brass coupons against the wheel, applying a drop of 0.5% Na s solution to the thus-treated coupons, and noting the time required for a stain to develop. Surprisingly, no stain developed within 60 minutes on either type of coupon until the treating wheel had run for yell over 10 hours. In contrast, untreated copper coupons stained in 30 seconds and untreated brass coupons in 65 seconds.
After the treated wheel had been used for 12 hours, some matting and discoloration was noted, and ability to impart corrosion resistance was declining. Combing the periphery with a conventional rake for buffing wheels quickly restored the original appearance and effectiveness.
The foregoing examples are intended to illustrate, but not to limit, the scope of my invention, and many variations will readily occur to those skilled in the art. To illustrate, there are numerous other organic corrosioninhibiting compounds capable of being bound to a metallic surface by chemisorption (i.e., having a functional group which reacts with the surface); thus the other mercaptans in the C C chain length, and compounds having metalreactive groups other than those I have named may be employed. Likewise the specific fibrous rotary rubbing element may take the form of a band entrained over one or more supporting wheels, although such embodiments tend to have shorted useful life after treatment than those of the preceding examples.
What I claim is:
1. The method of imparting corrosion-resistance to the surface of a normally corrodible cupreous metal which comprises contacting said surface with the working face of a rapidly rotating resilient rubbing element while maintaining both said face and said surface in dry condition, said element comprising a porous structure formed from organic fibers uniformly provided at its working face and for a substantial distance inwardly therefrom with a substance selected from the class consisting of organic compounds which are capable of being bound to cupreous metal by chemisorption and which inhibit the corrosion of cupreous metal when applied to the surface thereof, the working face of said element containing on the order of 0.005 to 0.1 part of said substance per part of fiber, whereby said substance is frictionally transferred to said surface to provide a uniform coating having a thickness significantly less than the wave length of visible light.
2. The process of claim 1 wherein the organic compound is further selected from the class consisting of mercapto-aliphatic compounds having a chain length of about 16 to 22 carbon atoms, viscous alkyl phenoxy carboxylic acids, and cyclohexylamine nitrite.
3. The process of claim 2 in which the cupreous metal is copper.
4. The process of claim 2 in which the cupreous metal is brass.
5. The method of imparting corrosion-resistance to the surface of a normally corrodible metal which comprises contacting said surface with the working face of a rapidly rotating resilient rubbing element while maintaining both said face and said surface in dry condition, said element comprising a porous structure formed from organic fibers uniformly provided at its working face and for a substantial distance inwardly therefrom with a substance selected from the class consisting of organic compounds which are capable of being bound to said metal by chemisorption and which inhibit the corrosion of said metal when applied to the surface thereof, the working face of said element containing on the order of 0.005 to 0.1 part of said substance per part of fiber, whereby said substance is frictionally transferred to said surface to provide a uniform coating having a thickness significantly less than the wave length of visible light.
6. A flexible, soft, dry solvent-free rotative rubbing element formed from organic fibers, suitable for practicing the process of claim 1, said rubbing element being impregnated with 0.005 to 0.1 part per part of fiber of a corrosion inhibiting compound selected from the class consisting of actadecyl mercaptan and alpha-mercapto stearic acid.
References Cited by the Examiner UNITED STATES PATENTS 2,257,750 10/1941 Lincoln et al 252395 X 2,807,584 9/1957 Rushton 25291 2,896,242 7/1959 Winch 15506 3,062,612 11/1962 Le Boucher. 3,117,012 7/1964 Alder et a1 1063 X RALPH S. KENDALL, Primary Examiner.
RICHARD D. NEVIUS, Examiner.
J. R. BATTEN, JR., Assistant Examiner.