US3076734A

US3076734A - Protective coatings on metals

Info

Publication number: US3076734A
Application number: US40128A
Authority: US
Inventors: Kurt E Schimkus
Original assignee: Acme Steel Co
Current assignee: Acme Steel Co
Priority date: 1960-07-01
Filing date: 1960-07-01
Publication date: 1963-02-05
Anticipated expiration: 1980-02-05

Description

United States This invention relates to protective coatings for metals and to coating baths and coating methods for applying such protective coatings to metals.

Various coatings have been utilized heretofore to protect base metals, i.e., metals which corrode and discolor upon exposure to various operating conditions such as high humidity, salt water and the like. These coatings have been applied by many different methods using a large variety of coating baths and coating methods. It

"has been desirable in certain instances to provide coatings that are transparent whereby to leave substantially unchanged the color of the surface coated. On the other hand it is desirable in other instances to color the coated surface. I

A particular example of an application in which it is desired to impart a particular color to a metal surface is the use of steel strapping to bind aluminum ingots. It has been customary heretofore to provide a galvanized coating on the steel strapping but it has been found that the color of the galvanized steel is confusingly similar to the color of the aluminum ingots, whereby the steel strapping is often thrown into the storage bins with the aluminum ingots thereby to contaminate the aluminum.

There are disclosed in my co-pending application Serial No. 724,794, filed March 31, 1958 for Protective Coatings on Metals, now Patent No. 3,007,818, issued November 7, 196 1, protective coatings, and coating baths and methods of applying the coatings, which may be either substantially colorless and transparent or which may be colored in one of many ways." The invention of this application is an improvement upon the subject matter of the above application in that better coatings and more desirable colors can be provided thereby. Accordingly, it is an important object of the present invention to provide improved protective coatings for base metals and to provide improved coating baths and improved coating methods to apply the protective coatings to the base metals.

Another object of the invention is to provide an improved coating for base metals which has a'desirable predetermined color and particularly a color which contrasts with the color of galvanized coatings and aluminum.

Yet another object of the invention is to provide improved coating baths and coating methods which produce the colored protective coating of the present invention on a'base metal surface inasingle step process.

Still another object of the invention isto provide improved coatings of the type set forth which comprise a combination of different coating compounds on the metal surface being treated.

A further object of the invention is to provide an improved coating bath and method of applying the coating which can be operated at substantially room temperature utilizing simple equipment and simple and inexpensive operating procedures.

It has been found that good protective coatings can be applied to base metal surfaces by applying thereto a composition containing an anion of a phosphoric acid ester of cyclohexanol and a compound selected from the class consisting of zirconium salts and basic zirconium salts distributed in a suitable carrier. A preferred class of ester of cyclohexanol are those which are the anions of a phosphoric acid ester of hexahydroxycyclohexanol (inositol), the preferred anion being that of inositol hexaatent weight of free phytic acid to-provide a concentration in 3,076,734 Patented Feb. 5, 1963 phosphoric acid commonly called phytic acid; the phytic acid may be applied as the free acid or as a salt thereof, the sodium, potassium, cadmium and magnesium salts being particularly advantageous. The preferred 'zirconium compound for use in the present invention is zirconium oxychloride.

A preferred class of carriers useful in the present invention are hydrophilic carriers. For example, aqueous solutions, oil-water emulsions and wax-like compositions containing water and other hydrophilic materials can be used satisfactorily. In general any base metal that will react with an acid medium can be treated successfully to provide a protective coating thereon using this invention, the pH of the acid medium being from 0.8 to about 6.9.

The concentration in the carrier of the phytic acid or salt thereof used in the present invention is preferably from about 00001 mol/liter to about 0.1 mol/liter. The zirconium ion is preferably present in the carrier in a concentration from about 0.001 mol/liter to about 0.1- mol/liter; it further is desirable that the molar ratio between the zirconium ions and the phytate ions present he in the range from about 1 to about 50. It further is desirable in certain instances to provide coatings including a compound derived from chromic acid, dichromic acid and salts thereof in which case the chromate may be present in the carrier in a concentration of about 0.01 mol/liter to about 1.0 mol/liter.

By a proper choice of the composition and concentration of the ingredients and by the proper control of the pH, the time required to obtain a satisfactory coating upon application of the coating composition may be from a fraction of a second up to as much as 30 minutes or an hour or more.

It also has been found that satisfactory coatings having a desired color can be achieved by utilizing a coating composition including an acidic hydrophilic carrier having incorporated therein a compound selected from the class consisting of zirconium salts and basic zirconium salts and a second compound selected from the class consistingof chromic acid and dichromic acid and salts thereof. In such compositions the zirconium compound is present in a concentration of from about 0.001 mol/liter to about 0.1 mol/liter and the chromium compound is present in a concentration from about 0.01 mol/liter to about 1.0 mol/liter, the molar ratio between the chromium and zirconium present being from about 0.1 to about 10; the pH is preferably in the range from about 0.8 to about 6.9 and the time necessary to apply the compositionto obtain a satisfactory coating may be from a fraction of a second up to as much as 30 minutes or an hour or more.

It further has been found that the corrosion protection afforded by all of the above compositions can be materially enhanced by incorporating therein a compound selected from the class consisting of salts of arsenic and oxides of arsenic and salts thereof, the arsenic compound being present in a concentration from about 0.001 mol/ liter to about 0.05 mol/ liter. The character of the coat ing can also be improved by incorporating in the compositions a cationic fatty amide derivative such as that sold under the trademark Protamine by the Procter Chemical Co., the fatty amide preferably being present in an amount from about 0.1 to 5 grams per liter.

The following specific examples of protective coatings, coating compositions and coating methods illustrate the application of the present invention and it is to be undere stood that these examples are not intended in any way to limit the scope of the present invention.

Example 1 A coating composition was prepared by adding to water an aqueous solution of phytic acid containing 70% by the coating solution of about 5 grams per liter of phytic acid. Sufiicient zirconium oxychloride octahydrate was added to provide a concentration thereof in the coating solution of about 5 grams 'per liter. The pH was then adjusted to 1.4 by adding concentrated nitric acid. A cleaned strip of galvanized mild carbon steel was provided and immersed in the coating solution for seconds toform a'coating thereon. The coated strip was then taken from thesolution and any excess coating solution removed. After drying, the coated steel strip was examined and found to have a brown protective coating of phytate and zirconium thereon. The coating provided good protection against humidity and salt water when subjected to humidity and salt water corrosion tests. The strip prepared exhibited better corrosion properties than a like strip having only a phytate protective coating thereon.

' The method of Example 1 above has been operated successfully when the concentration of the phytic acid in the coating solution has been increased to as much as 25 grams per liter or more and smaller concentrations of phytic acid can also be used but there results a coating which is much lighter in weight. The zirconium oxychloride has also been successfully increased to as much as 30 grams. per liter and decreased to as little as 0.3 gram per liter while'still providing a satisfactory color in the coating, it' being understood that the more zirconium oxychloride present the darker is the color of the resultant coating for like times of exposure. It further was found that the pH 'of the coating solution could be varied from approximately 1.0 to approximately 2.0 and still provide satisfactory coatings with the same exposure.

Example 2 The coating solution and method described above in Example 1 with respect to a. zinc surface were applied to a cadmium surface. A protective coating was formed on cadmium which had a desirable brown color and which provided good protection against corrosion by humidity and salt water.

Example 3 A mild carbon steel strip was provided and the coating solution and method described above in Example lwer'e applied thereto. A protective coating having a desired light brown color was obtained, the. coating providing good protection against corrosion by humidity and salt water. 7

Iri'general, any of the base metals that react with acidic mediums or solutions can be coated using the coating solution and method of Example 1, 'tin and copper being other specific. examples of metals on which the solution and methodof Example 1 have been successfully employed; The coating solution may contain, for exam ple, from about'0.000l mol/literof-phytate ion (empirical rdr'mfila'c n so r y to' about 0:1 moi/liter. and from about. 0.001 mol/liter to about 0.1 mol/liter of zirconium ion. When such concentrations'are used in an acid solution, the immersion time will be in the order. of- 10 to 20 seconds to provide. an'adequate. protective phytate and zirconium containing coating. In general, if the concentration of phytate and zirconium containing ions is lower, the amount of coating laid down during a given of time will be less. Conversely, if the concentration of phytate ion. and zirconium containing ion is increased, a heavier coating 'will be formed on the metal duringfa given period of time. The amount of coating laid down during a given period of time is less if the pH is higherv and is greater if the pH is lower. Those skilled in theart. will be able to ascertain satisfactory conditions forlaying down the desired weight. of coating from the above examples. i i

It has been found that it is also possible to co-deposit a chro mate coating. on the base metal with the phytate and zirconium coating obtained by the coating solution aud method of Example 1. The following is an example of a suitable coating solution and method for producing a combination coating including a chromate therein.

Example 4 The following ingredients were mixed to provide a liter of coating solution having the concentrations indicated.

Grams/liter Sodium dichromate (Na Cr O -2H O) 10 Zirconium oxychloride (ZrOC1 -8H O) 5 Sodium phytate l The solution had the pH thereof adjusted to 1.4 and was heated to F. A galvanized steel strip was coated by immersing it for 10 seconds in the heated solution. The resultant coating had good adhesion, was light brown in color, and provided good corrosion resistance to both high humidity and salt water.

Other sources of chromium may be used instead of the sodium dichromate set forth in Example 4, i.e., chromic acid, dichromic acid, and other salts thereof, such, for example, as potassium dichromate can be used in place of sodium dichromate. The following is an example of the use of chromic acid as a source of chr0- mium:

Example 5 The following ingredients Were mixed in a liter of water to provide the concentrations indicated:

Grams/liter Chromic acid (CrO 6 Zirconium oxychloride (ZrOC1 -8H O) 10 Sodium phytate 2 The pH of this coating solution was adjusted to 1.4. A clean galvanized strip of steel was provided and was coated by dipping it in the solution at room temperature, i.e., about 75 F. A 10 second immersion produced a brown coating, and a 20 second immersion produced a brownish green coating. Both coatings exhibited good adhesion and gave good protection against high humidity and salt water. The solutions and methods of Examples 4 and 5 have also been applied successfully to tin and copper surfaces.

The following is an example of a production coating bath useful in coating galvanized steel strapping to provide thereon a combination coating including phytate, a zirconium compound and chromate.

Example 6 To 10 gallons of water were added 46.75 pounds of sodium dichromate, the solution being stirred until all of the sodium dichromate was dissolved. Nitric acid (70% solution in water by. weight) was then added in the amount of 4.0 gallons (15.16 liters). 10 pounds of zirconium oxychloride octahydrate were then added after which the volume of the solution was brought to 20 gallons by the addition of water. This solution was then stirred until all materials were completely dissolved whereby to provide a concentrate which can be subsequently diluted to provide the production coating solution. The production coating solution was prepared from the concentrate by diluting it 1:20 so that the 20 gallons of concentrate provided 400 gallons of solution to which was added 2.0 gallons (7.58 liters) of an aqueous solution of phytic acid. containing 70% by weight of phytic acid. The production coating solution contained the following concentrations of active ingredients.

Phytic acid 7.2 gms./l. (0.011 moi/liter). Zirconium oxychloride 3 gms./l. (0.00932 mol/liter). Sodium dichromate 14 gms./l. (0.047 mol/liter).

The coating solution will have a pH of 0.9 and the pH is maintained during operation in the range 0.9 to 1.3. The operating temperature of the coating solution is maintained at F.;+:5 F.

As an example of the use of the production coating solution, it was used in coating a galvanized steel strip having a width of 2 inches and a thickness of 0.011 inch which was galvanized on both sides to a thickness of 0.00004 inch. The galvanized strip was run through the heated coating solution in a continuous manner and each portion of the strip Was immersed in the coating bath for a period of from 9 to 13 seconds. There was produced on the strip an attractive brown coating having good adhesion and providing good protection against corrosion by high humidity and saltwater.

The zirconium concentration in the bath must be maintained at substantially the above stated level by substantially continuous replenishment and the control of the rate of addition of zirconium ion can be accomplished by watching the color of the coated strip, since the color is a good indication of the amount of zirconium ion present in the coating bath. The other constituents of the coating solution may be depleted by as much as 25% before replacement is required. The concentrate solution may be used to accomplish replacement but often the drag-out will be sufiicient so that the lost Solution must be replaced in an amount that will compensate substantially for the depletion of the active ingredients from the coating solution by deposition thereof on the galvanized strip. The coating solution must be discarded and replaced 'when the zinc concentration therein reaches 12 grams per liter.

The production run set forth in Example 6 above was successfully repeated using 1.5 grams per liter of zirconium oxychloride and 5 grams per liter of zirconium oxychloride in the coating bath. The coatings obtained therefrom possessed all of the desirable characteristics set forth above with respect to the coating obtained from Example 6, the only difference being in the color of the coating produced, the lower concentration providing a coating having a light brown color with a slight greenish tint and the higher concentration providing a coating having a golden brown or dark brown color.

Chromic acid and phytic acid may be utilized as in gredients in the same baths. The following is an example of the use of these ingredients.

Example 7 The following ingredientswere placed in a liter of water to provide .the indicated concentrations:

Grams per liter The pH of the solution was adjusted to 1.4 using concentrated nitric acid. A galvanized steel strip was coated by immersing the strip in the solution for 10 seconds at 120 F., and there was produced thereon a deep brown protective coating which had good adhesion and excellent resistance to corrosion by high humidity and salt water.

It was further found that the coating produced could be improved as to adhesion and corrosion resistance by addingthereto cationic fatty amide derivatives of the type sold under the trademark Protamine by the Procter Chemical Co} The following is an example of such a coating solution.

A galvanized strip was coated using the above solution by immersing the strip for 10 seconds in the solution at room temperature, i.e., 75 F. The coating thus produced was adherent, had a brown color and gave good corrosion resistance againsthigh humidity and salt water. The coating was analyzed spectrographically and it was de- The following ingredients were added to water to provide the concentrations indicated:

Grams per liter Chromic acid (*CrO 4.8 Zirconium oxychloride (ZrOCI -SH O) 5 Sufficient nitric acid was added to reduce the pH to 1.4, approximately 10 cc. of concentrated nitric acid being required per liter of coating solution. A galvanized steel strip was coated by immersing the strip for 10 seconds in the coating solution at a temperature of 120 F. The resultant coating was a deep reddish brown, possessed adevquate adhesion and provided excellent corrosion resistance against high humidity and salt water.

The coating solution of Example 9 above can be prepared by substituting sodium dichromate for the chromic acid and by providing a much greater concentration of zirconium oxychloride as follows.

Example 10 These ingredients were added to water to provide the concentrations indicated: Grams per liter Sodium dichromate 50 Zirconium oxychloride 50 The pH of the sodium solution was 1.0. A galvanized steel strip was coated with this solution by immersing it in the solution at a temperature of 100 F. There resulted a protective coating having a deep brown'color. The solutions and methods of Examples 9 and 10 have also been used to provide protective coatings on tin and copper.

Even better corrosion resistance can be obtained from the coatings of the present invention if the coating solutions have added thereto a small amount of arsenic, for example, arsenic pentoxide (As O The following is an example of a bath incorporating arsenic therein.

Example 11 The following ingredients were added to water to provide the concentrations indicated:

Grams per liter Phytic acid 5 Zirconium oxychloride (ZrOCl -8H O) 5 Arsenic pentoxide (As O 5 'did the coating obtained by Example 1.

Arsenic can also be added advantageously to those coating solutions in which chromium is one of the active constituents. The following is an example using such a solution.

Example 12 The following ingredients were added to water to provide the concentrations indicated:

' Grams per liter Sodium dichromate (N21 Cr O -2H O) 14 Zirconium oxychloride (ZrCI -SH O) 3 Arsenic pentoxide (As O 5 Phytic acid 7 The pH of this solution was adjusted to 1.4 by the addition of concentrated nitric acid. A galvanized steel strip was coated by immersing the strip for 10 seconds in the solution at 120 F. The resultant coating was very adherent and provided excellent corrosion resistance against humidity and salt water. Higher concentrations of the arsenic pentoxide provided slightly less corrosion protection and lower concentrations of the arsenic pentoxide likewise provided less corrosion protection than the optimum value of grams per liter set forth in Example 12. However, all of the coatings formed using arsenic pentoxide as an ingredient in the coating solution showed improved corrosion protection over those coatings provided by identical solutions but omitting the arsenic pentoxide therefrom.

Arsenic is also useful in those coating compositions which include only sources of chromium and zirconium as the active constituents. The following is an example of such a coating composition.

Example 13 The following ingredients were added to water to provide the concentrations indicated:

Grams per liter Chromic acid (CrO' 4.8 Zirconium oxychloride (ZrOCl '8H O) 4.8 Arsenic pentoxide (As O 5 The pH of this solution was adjusted to 1.4 by the addition of approximately cc. of concentrated nitric acid per liter of solution. A galvanized steel strip was coated utilizing the solution of Example 13 and the resultant coating exhibited good adhesion, provided good corrosion protection and had a distinctive brown color.

The ingredients utilized in Example 6 above can also be incorporated in a hydrophilic wax-like base which can be used to provide a protective Coating on aluminum surfaces. The following is an example of the application of the principles of the present invention in this manner.

Example 14 The following ingredients were mixed in the proportions indicated:

Gms. Cetyl alcohol 7 Stearyl alcohol 3 White. beeswax 4 Petrolatum 27 Glycerine 8 In a separate container the following materials were mixed in the proportions indicated:

' Gms. Sodium lauryl sulfate (saponifying agent) 1 Distilled water 50 Zephiran chloride (a germicide and preservative comprising a mixture of alkyldimethylbenzylammonium chlorides) 0.06

A quantity of the coating solution of Example 6 was treated to evaporate the major portion of the water therefrom whereby to form a paste. 25 gms. of the paste so formed were mixed together with the materials set forth above including the hydrophilic base, the saponifying agent and the preservative. The resultant mixture has a pH in the range 2.5 to 2.8. This coating composition was applied to aluminum by spreading a layer thereof on the aluminum surface to be protected. The coating was left in position for about 30 minutes and then wiped off. It was found that a protective coating had been formed on the aluminum surface which was highly resistant to corrosion as determined by humidity and salt water exposure tests.

Instead of using the solution of Example 6, compositions for coating aluminum have also been prepared by forming pastes from the solutions of Examples 1 to 5 and 7 to 13 and incorporating those pastes in the hydrophilic base of Example 14.

The phytic acid utilized in certain of the above examples was specified to be an aqueous solution containing approximately 70% by weight of phytic acid in a relatively pure state. It has been found that it is not necessary to use substantially pure phytic acid and, in fact, waste solutions called steep liquor resulting from the steeping of grain are sufficiently rich in phytic acid to work satisfactorily. These liquors contain about 10% to 30% of phytic acid by weight. The other impurities found therein also do not interfere with the coating action. The sodium phytate specified in certain of the examples is prepared by adding concentrated sodium hydroxide solution to a 70% by weight aqueous solution of phytic acid until the pH thereof is approximately 4.7. The concentration of the phytate ion in solutions made in accordance with the present invention may be in the range from about 0.0001 mol/liter to 0.1 mol/liter, a preferred range being 0.001 mol/ liter to about 0.05 mol/ liter. It is believed that the coatings formed on metal surfaces from solutions including the phytate ion contain as one of the constituents thereof a phytate compound of the metal of the surface, i.e., zinc surfaces including zinc phytate, steel surfaces including iron phytate, cadmium surfaces including cadmium phytate, tin surfaces including tin phytate, copper surfaces including copper phytate, aluminum surfaces containing aluminum phytate, etc.

In general, the zirconium in the coating compounds can be derived from any zirconium salt soluble in acidic aqueous media but preferably from the basic zirconium salts such as zirconium oxychloride. Other examples of sources of zirconium are zirconium ammonium fluoride, zirconium tetrachloride, zirconium nitrate, zirconium potassium fluoride and zirconium sulfate. The concentration of zirconium ion in the coating composition may be from 0.001 mol/liter toabout.0.1 mol/liter but preferably is in the range 0.003 to about 0.03 mol/ liter. It is believed that the zirconium in the coating formed on the metal surface is present as the corresponding zirconate (ZrO of the metal surface, i.e., zinc surfaces including in the coating zinc zirconate, steel surfaces including iron zirconate, cadmium surfaces including cadmium zirconate, aluminum surfaces including aluminum zirconate, tin surfaces including. tin zirconate, copper surfaces including copper zirconate, etc.

The chromium present in certain of the coating solutions may be derived from chromic acid, dichromic acid or salts thereof such as sodium dichromate, potassium dichromate, etc. The concentration of the chromium in the coating composition may be from about 0.01 mol/liter to about 1.0 mol/liter. It is believed that the coatings formed on metal surfaces from solutions including the chromate ion contain as one of the constituents thereof a chromate compound of the metal of the surface, i.e., zinc surfaces including zinc chromate, steel surfaces including iron chromate, cadmium surfaces including cadmium chromate, tin surfaces including tin chromate, copper surfaces including copper chromate, aluminum surfaces containing aluminum chromate, etc.

It further has been found that it is desirable in those compositions including both phytate ions and chromium that the molar ratio of chromium to phytate be from about 1 to about 50. In those compositions including both zirconium and chromium, it is preferred that the ratio of zirconium to chromium be about 0.1 to about 10. Further, in those compositions including both zirconium and phytate it is preferred that the ratio of zirconium to phytate be from about 1 to about 100.

The arsenic present in certain of the above examples may be derived from any of the salts of arsenic, from the oxides thereof or the salts thereof which are soluble in acidic aqueous media, the preferred source being arsenic pentoxide. Other suitable sources are ammonium dihydrogen orthoarsenate, potassium orthoarsenate, potassium 9 monohydrogen orthoarsenate, potassium dihydrogen orthoarsenate, sodium orthoarsenate, sodium monohydrogen orthoarsenate (both the heptahydrate and the dodecahydrate) sodium dihydrogen arsenate, and potassium arsenite. The preferred concentration of arsenic in the coating composition is from about 0.001 mol/liter to about 0.05 mol/liter.

Although certain preferred examples of the invention have been given for purposes of illustration, it is to be understood that various changes and modifications can be made thereon Without departing from the spirit and scope of the invention and it is intended to cover in the following claims all such changes and modifications that fall within the scope thereof.

I claim:

1. A composition for use in providing a protective coating on base metals consisting essentially of a first compound selected from the class consisting of phytic acid and salts thereof and ayseco-nd compound selected from the class consisting of acid soluble zirconium salts and basic zirconium salts, said first and second compounds being present in amounts equivalent to from about 0.0001 to about 0.1 mole of said first compound and from about 0.001 to about 0.1 mole of said second compound, the molar ratio of said second compound to said first compound being in the range from about 1 to about 50.

. 2. A composition for use in providing a protective coating on base metals consisting essentially of a first compound selected from the class consisting of phytic acid and salts thereof, a second compound selected from the class consisting of acid soluble zirconium salts and basic zirconium salts, and a third compound selected from the class consisting of chromic acid, dichromic acid and salts thereof, said compounds being present in amounts equivalent to from about 0.0001 to about 0.1 mole of said first compound and from about 0.001 to about 0.1 mole of said second compound and from about 0.01 to about 1.0 mole of said third compound, the molar ratio of said second compound to said first compound being in the range from about 1 to about 50, the molar ratio of said third compound to said second compound being in the range from about 0.1 to about 10.

3. A composition for use in providing a protective coating on base metals consisting essentially of a first compound selected from the class consisting of phytic acid and salts thereof, a second compound selected from the class consisting of acid soluble zirconium salts and basic zirconium salts, and a third compound selected from the class consisting of acid soluble salts of arsenic, oxides of arsenic and salts thereof, said compounds being present in amounts equivalent to from about 0.0001 to about 0.1 mole of said first compound and from about 0.001 to about 0.1 mole of said second compound and from about 0.001 to about 0.05 mole of saidthird compound, the

molar ratio of said second compound to said first compound being in the range from about 1 to about 50, the molar ratio of said first compound to said third compound being in the range from about 1 to about 100.

4. A composition for use in providing a protective coating on base metals consisting essentially of a first compound selected from the class consisting of phytic acid and salts thereof, a second compound selected from the class consisting of acid soluble zirconium salts and basic zirconium salts, ,a third compound selected from the class consisting of chromic acid and dichromic acid and salts thereof, and a fourth compound selected from the class consisting of acid soluble salts of arsenic, oxides of arsenic and salts thereof, said compounds being present in amounts equivalent to from about 0.0001 to about 0.1 mole'of said first compound and from about 0.001 to about 0.1 mole of said second compound and from about 0.01 to about 1.0 mole of said third compound and from about 0.001 to about 0.05 mole of said fourth compound, the molar ratio of said second compound to said first compound being in the range from about 1 to about 50,

the molar ratio of said third compound to said second compound being in the range from about 0.1 to about 10, and the molar ratio of said first compound to said fourth compound being in the range from about 1 to about 100.

5. A coating composition to provide a protective coating on base metals consisting essentially of an aqueous solution having a pH in the range from about 0.8 to about 6.9 and containing from about 0.0001 to about 0.1 mole per liter of phytate ion and from about 0.001 to about 0.1 mole per liter of a compound selected from the group consisting of acid soluble zirconium salts and basic zirconium salts.

6. A coating composition to provide a protective coating on base metals consisting essentially of an aqueous solution having a pH in the range from about 0.8 to about 6.9 containing from about 0.0001 to about 0.1 mole per liter of phytate ion, from about 0.001 to about 0.1 mole per liter of a compound selected from the group consisting of acid soluble zirconium salts and basic zirconium salts, and from about 0.01 to about 1.0 mole per liter of a compound selected from the group consisting of chromic acid and dichr-omic acid and salts thereof.

7. A coating composition to provide a protective coating on base metals consisting essentially of an aqueous solution having a pH in the range from about 0.8 to about 6.9 containing from about 0.0001 to about 0.1 mole per liter of phytate ion, from about 0.001 to about 0.1 mole per liter of a compound selected from the group consisting of acid soluble zirconium salts and basic zirconium salts, and from about 0.001 to about 0.05 mole per liter of a compound selected from the class consisting of acid soluble salts of arsenic, oxides of arsenic and salts thereof.

8. A coating composition to provide a protective coating on base metals consisting essentially of an aqueoussolution having a pH in the range from about 0.8 to about 6.9 containing from about 0.0001 to about 0.1 mole per liter of phytate ion, from about 0.001 to about 0.1 mole per liter of a compound selected from the group consisting of acid soluble zirconium salts and basic zirconium salts, from about 0.01 to about 1.0 mole per liter of a compound selected from the class consisting of chromic acid and dichromic acid and salts thereof, and from about 0.001 to about 0.05 mole per liter of a compound selected from the class consisting of salts of arsenic, oxides of arsenic and salts thereof.

9. A coating composition to provide a protective coating on base metals consisting essentially of an aqueous solution having a pH in the range from about 0.8 to about 6.9 and containing from about 0.001 to about 0.05 mol/ liter of phytate ion, from about 0.003 to about 0.03 mol/ liter of a compound selected from the group consisting of acid soluble zirconium salts and basic zirconium salts and from about 0.01 to about 1.0 mol/liter of chromate ion.

10. A coating composition to provide a protective coating on base metals consisting essentially of an aqueous solution having a pH in the range from about 0.8 to about 6.9 and containing from about 0.001 to about 0.05 mol/ liter of phytate ion, from about 0.003 to about 0.03 mol/ liter of a compound selected from the group consisting of acid soluble zirconium salts and basiczirconium salts, from about 0.01 to about 1.0 moi/liter of chromate ion, and from about 0.001 to about 0.05 moi/liter of a compound selected from the class consisting of acid soluble salts of arsenic and oxides of arsenic and salts thereof.

11. A coating composition to provide a protective coating on base metals consisting essentially of an aqueous solution having a pH of about 1.4 and containing about 0.01 mol/liter of phytate ion, about 0.01 mol/liter of zirconium oxychloride and about0t5 incl/liter of dichromate ion.

12. A coating composition to provide a protective coating on base metals consisting essentially of an aqueous conium oxychloride, about 0.05 mol/liter of dichromate ion, and about 0.02 mol/liter of arsenic pentoxide.

13. The method of providing a protective coating on base metals comprising immersing the base metal in a coating composition comprising an acidic aqueous solution containing from about 0.0001 to about 0.1 mole per liter of phytate ion and from about 0.001 to about 0.1 mole per liter of a compound selected from the group consisting of acid soluble zirconium salts and basic zirconium salts.

14. The method of providing a protective coating on base metals comprising immersing the base metal in a coating composition comprising an acidic aqueous solution containing from about 0.0001 to about 0.1 mole per liter of phytate ion, from about 0.001 to about 0.1 mole per liter of a compound selected from the group consisting of acid soluble zirconium salts and basic zirconium salts, and from about 0.01 to about 1.0 mole per liter of acompound selected from the class consisting of chromic acid and dichromic acid and salts thereof.

15. The method of providing a protective coating on base metals comprising immersing the base metal in a coating composition comprising an acidic aqueous solution containing from about 0.0001 to about 0.1 mole per liter of phytate ion, from about 0.001 to about 0.1 mole per liter of a compound selected from the group consisting of acid soluble zirconium salts and basic zirconium salts, from about 0.01 to about 1.0 mole per liter of a compound selected from the class consisting of chromic acid and dichromic acid and salts thereof, and from about 0.001 to about 0.05 mole per liter of a compound selected from the class consisting of acid soluble salts of arsenic and oxides of arsenic and salts thereof.

16. The method of providing a protective coating on base metals comprising immersing the base metal in a coatingcomposition comprising an acidic aqueous solution containing from about 0.0001 to about 0.1 mole per liter of phytate ion, from about 0.001 to about 0.1 mole per liter of a compound selected from the group consisting of acid soluble zirconium salts and basic zirconium salts, and from about 0.001 to about 0.05 mole per liter of a compound selected from the class consisting of acid soluble salts of arsenic and oxides of arsenic and salts thereof.

17. The method of providing a protective coating on base metals comprising applying to the base metal a coating composition comprising an aqueous solution containing from about 0.001 to about 0.05 mol/liter of phytate ion, from about 0.003 to about 0.03 mol/liter of a compound selected from the group consisting of acid soluble zirconium salts and basic zirconium salts, and from about. 0.01 to about 1.0 mol/liter of dichromate ion, said composition having a pH in the range from about 0.8 to about 6.9.

18. The method of providing a protective coating on base metals comprising applying to the base metal a coating composition comprising an aqueous solution containing from about 0.001 to about 0.05 mol/liter of phytate ion, from about 0.003 to about 0.03 mol/liter of a compound selected from the group consisting of acid soluble zirconium salts and basic zirconium salts, from about 0.01 to about 1.0 mol/liter of dichromate ion, and from about 0.001 to about 0.05 mol/liter of a compound selected from the class consisting of acid soluble salts of arsenic and oxides of arsenic and salts thereof, said composition having a pH in the range from about 0.8 to about 6.9.

19. The method of coating galvanized and cadmium plated steel strips which. consists in immersing the strip in an acidic aqueous solution containing from about 0.0001 to about 0.1 mole per liter of phytate ion, from about 0.001 to about 0.1 mole per liter of a compound selected from the group consisting of acid soluble zirconium salts and basic zirconium salts and a mineral acid.

20. The method of coating galvanized and cadmium plated steel strips which consists in immersing the strip in an acidic aqueous solution containing from about 0.0001 to about 0.1 mole per liter of phytate ion, from about 0.001 to about 0.1 mole per liter of a compound selected from the group consisting of acid soluble zirconium salts and basic zirconium salts, and from about 0.001 to about 0.05 moles per liter of a compound selected from the class consisting of acid soluble salts of arsenic and oxides of arsenic and salts thereof, and a mineral acid.

21. A base metal containing a metal selected from the group consisting of aluminum, cadmium, copper, iron, tin and zinc and having a protective coating thereon comprising a phytate compound of the base metal and a compound of the base metal with an ion consisting of atoms selected from the group consisting of zirconium and oxygen.

22. A base metal containing a metal selected from the group consisting of aluminum, cadmium, copper, iron, tin and zinc and having a protective coating thereon comprising a phytate compound of the base metal, a compound of the base metal With an anion consisting of chromium and oxygen, and a compound of the base metal with an ion consisting of atoms selected from the group consisting of zirconium and oxygen.

23. A base metal containing a metal selected from the group consisting of aluminum, cadmium, copper, iron, tin and zinc and having a protective coating thereon comprising a phytate compound of the base metal, a compound of the base metal with an anion consisting of chromium and oxygen, and a compound of the base metal with an ion consisting of atoms selected from the group consisting or zirconium and oxygen, the ratio between the chromium and zirconium in said coating being approximately 2 to 1 by weight.

24. A zinc containing metal member having a coating comprising zinc phytate and a compound of zinc with an ion consisting of atoms selected from the group consisting of zirconium and oxygen.

25. A zinc containing metal member having a coating comprising zinc phytate, zinc chromate, and a compound of zinc with an ion consisting of atoms selected from the group consisting of zirconium and oxygen.

26. An aluminum containing metal member having a coating comprising aluminum phytate and a compound of aluminum with an ion consisting of atoms selected from the group consisting of zirconium and oxygen.

27. An aluminum containing metal member having a coating comprising aluminum phytate, aluminum chromate, and a compound of aluminum with an ion consisting of atoms selected from the group consisting of zirconium and oxygen.

28. An iron containing metal member having a coating comprising iron phytate and a compound of iron with an ion consisting of atoms selected from the group consisting of zirconium and oxygen.

29. An iron containnig metal member having a coating comprising iron phytate, iron chromate, and a compound of iron with an ion consisting of atoms selected from the group consisting of zirconium and oxygen.

30. A tin containing metal member having a coating comprising tin phytate and a compound of tin with an ion consisting of atoms selected from the group consisting of zirconium and oxygen.

31. A tin containing metal member having a coating comprising tin phytate, tin chromate, and a compound of tin with an ion consisting of atoms selected from the group consisting of zirconium and oxygen.

32. A copper containing metal member having a coating comprising copper phytate and a compound of copper with an ion consisting of atoms selected from the group consisting of zirconium and oxygen.

33. A copper containing metal member having a coating comprising copper phytate, copper chromate, and a compound of copper with an ion consisting of atoms selected from the group consisting of zirconium and oxygen.

References Cited in the file of this patent UNITED STATES PATENTS Sch-amberger June 6, 1939

Claims

13. THE METHOD OF PROVIDING A PROTECTIVE COATING ON BASE METALS COMPRISING IMMERSING THE BASE METAL IN A COATING COMPOSITION COMPRISING AN ACIDIC AQUEOUS SOLUTION CONTAINING FROM ABOUT 0.001 TO ABOUT 0.1 MOLE PER LITER OF PHYTATE ION AND FROM ABOUT 0.0001 TO ABOUT 0.1 MOLE PER LITER OF A COMPOUND SELECTED FROM THE GROUP CONSISTING OF ACID SOLUBLE ZIRCONIUM SALTS AND BASIC ZIRCONIUM SALTS.