CA1174945A - Coating solution for metal surfaces - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

An acidic aqueous coating solution which contains a metal selected from the group consisting of zirconium, titanium, hafnium, and mixtures thereof, fluoride, and one or more of the following organic compounds: a surfactant or a poly-hydroxy compound having no more than 7 carbon atoms, or a mixture of said surfactant and said polyhydroxy compound, said solution being free of phosphate and boron when the organic compound is the polyhydroxy compound, and which solution is effective in forming on an aluminum surface a non-chromate, clear and colorless, corrosion resistant coating to which overlying siccative coatings adhere tightly.

Description

1~7~45 COAq`ING SOLUTION FOR METAL SURFACES
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Field of the Invention This invention relates to the application to metal surfaces of coatings which are corrosion resistant and to which overlying coatings such as those formed from paints, inks, and lacquers adhere ti~htly. ,~ore particularly, this invention relates to acid c aqueous coating solutions which are free of toxic materials such as chromates and ~erricyanide, and which form the af~rementioned types of coatings OII
aluminum surfaces.

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It is known to coat aluminum surfaces with aqueous coatings ~olutions that are ~ffective in forming thereon coatings which are corrosion resistant to thereby protect the surface from degradatian due to attack by corrosive materials. In general, the coatings formed from such coatings solutions should also have properties such that overlying coatings which are applied thereto adhere tightly and strongly. Such overlying coatings are decorative or functional in nature and are formed from materials such as paints, lacguers, inks, etc. (hereinafter referred to as "siccative coatings").

Certain aspects of the present invention will be described in connection with the coating of aluminum cans.
The invention has, nevertheless, broader applicability.
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Corrosion resistant coatings which are applied to aluminum cans should be uniformly clear and colorless so that the coated cans have the bright shiny natural appearance of the underlying aluminum. This bright shiny natural appearance is desired in the final product even thou~h portions of the can may be covered with overlying siccative coatings~ (It is noted that there are other aluminum coating operations in which it is desired that the corrosion resistant and adherent coating imparts to the aluminum surface a colored appearance, for example a yellowish to green tint. ~owever, this is not generally desired when coating aluminum cans~) The corrosion resistant coatings should also have properties such that the overlying coatings, which are decorative or functional in nature, adhere tigIltly and strongly thereto.

... . . ..
Another property that coated aluminum cans should have is the ability to resist discoloration when the coated can is subjected to moderately hot water, for example, water having a temperature within the range o~ about 140F to about 170P. This occurs in operations referred to in industry as "Pasteurization" of the cans. This treatment has a tendency to cause an uncoated or an inadequately coated aluminum surface to blacken or otherwise discolor thereby leaving the can with an unattractive appearance. The term "corrosion resistance"
is used herein, unless otherwise specifically stated, to mean , , , -2-. .
that the coated surface resists blackening or other discolor-ation when exposed to the aforementioned hot water or boiling water treatment. Such a coating will be referred to herein-after as a "corrosion-resistant coating".

A further property that is desirable in coated aluminum, cans is the ability of such cans to undergo a simple test to confirm the presence of such ccating. ~his property allows can manufactures to randomly sample cans from their line and by means of such test determine that the clear and colorless coating is actually present on the cans. One such test conventionally employed in the can industry is known as the "muffle test".

Coating solutions are p,resently ava~ilable which form on aluminum surfaces uniformly clear and colorless coatings.
One of the most widely used coating solutions, which forms such coatings, contains chromic acid, phosphoric acid and hydxofluoric acid. In recent years, however, there has been an industry-wide switch from hexavalent chromium-based coating compositions to coating compositions which do not contain this material, the use of which creates, in general, waste disposal problems.

This invention relates to the provision of an a~ueous coating solution which does not require the use of hexavalent chromium or similarly toxic materials, and which is capable ~1'74~4S

of forming a clear and colorless, corrosion-reSistant coating on an aluminum surface, which coating excellently adheres to overlying, siccative coatings.

PEPOR$ED DEVELOPMENTS

Recent developments in the industry are exe~plified by the disclosures of the following: pu~lished UK Patent Application GB 2,014,617 A; U.S. Patent Nos. 4~107r334 3,9~4,936; and 4,148,670, the last two mentioned being assigned to the same assignee as the present developmen~.
Compositions which are the subject of the aforementioned are described as being capable of forming non-chromate coatings on aluminum surfaces and each is acidic and includes, as essential ingredients, a fluoride-containing compound and variously either a zirconium-,titanium-,or hafnium-containing compound. Phosphate is described as an additional essential constituent o the composition of the '670 patent, while a polyhydroxy compound having six or fewei~ carbon atoms is described as an optional ingredient. Both phosphate and tannin are described as additional essential constituents of the composition of the '334 patent.

The presence of phosphate in the solution is said to contribute to the corrosion resistance and adherent properties of the coating, and to allow the coating to undergo the so-called "muffle test'' which may be used to 49~S

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confirm the presence of the coating on an aluminum surface.
However, phosphate has been found to cause a decrease in the adhesion of certain water-borne siccative coatings, and thus it would be desirable to produce a coating in which phosphate is not an essential ingredient.

BRIEF DESCRIPTION OF THE I~7ENTION

In accordance with the present invention there is provided an acidic aqueous coating solution that is capable of forming a non-chromate, clear ana colorless, corrosion-resistant coating on an aluminum surface and which solution contains at leàst about 0.5 x 10 3 mole/liter of a metal selected from the group consisting of zirconium, hafnium, titanium, and mixtures thereof, fluoride in an amount at least sufficient to combine with all of said metal, and characterized in that it contains one or more of the following organic compounds: at least about 10 ppm of a surfactant or at least about 0.025 x 10 3 mjl of a polyhydroxy compound having no more than 7 carbon atoms or a mixture thereof, said solution being free of phosphate and boron when the or~anic compound is the polyhydroxy compound.

The acidic aqueous coating solution of the invention can be used to treat a bright shiny aluminum surface in a manner such that the bright shiny appearance of the surface is not changed, while forming on the surface a uniformly colorless and clear coating which exhibits excellent corrosion resistance and to which overlying siccative coatings adhere tightly.

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The coating solutions of the present invention are capable of effectively forming the aforementioned type o coatings on an aluminum surface in the absence of toxic materials and materials of the type which create waste disposal problems, including, for example, hexavalent chromium and elements such as manganese, iron, cobalt, nickel, molybdenum and tungsten, and also materials such as ferricyanide and ferrocyanide.
Accordingly, it is not necessary to add to the coating solution of the present invention materials, which if added, would mandate that effluents comprising the solution be treated specially before the effluent is discharged to the environment or to a sewage disposal plant.

Several of the advantages which flow from the use of the present invention relate to the use of water-based compo-~lstions from which there aré forme'd the siccative coatings that ~overlie coatings formed from the composition of the present invention. By way of background, it is noted that there has been a relatively recent trend in the industry away from the use of organic solvent-based coating compositions and to the use of watér-based coating compositions. Industry experience has shown that coatings formed from water-based compositions do not tend to adhere as well to underlying coat-ings of the prior art Zr, Ti, or Hf type as coatings formed from organic solvent-based compositions. For example, siccative coatings formed from water-based compositions do not tend to adhere as well to underlying coatings formed from the phosphate-containing compositions described'in afore-mentioned U.S. Patent No. 4,148,670 as those formed from ' `"` ~17494S
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organic solvent-based compositions. The compositions of the present invention can be use~ to form on aluminum surfaces coatings that provide an excellent adherent base or siccative coatings formed from water-based compositions.

It has been observed that the corrosion resistance of coatings formed from acidic aqueous coating solutions of the invention in which the polyhydroxy compound is the organic compound may tend to vary, depending on the type of water used in preparing such compositions. The corrosion resistance properties are better when the coatings are formed from com-positions prepared from hard water than when they are formed from compositions prepared from soft water. As wili be described more fully below, it appears that the relatively low calcium concentration in soft water affects adversely ... . . . . .
the corrosion resistant properties of the coatings. To state it otherwise, the relatively high concentration of calcium in hard water improves the corrosion resistance of the coatings. ~his variatio in coating resistance with variation in water hardness is not expexienced when the 5urfactant or the mixture of the surfactant and t~e poly-hydroxy compound is the organic compound in the aqueous acidic coating solutions of the present invention.

The term "surfactant" is used herein to mean a material which when used in a small amount is capable of reducing markedly the surface tension of water. For example, the presence of as little as 2 ppm of surfactant dissolved in water can 9'~5 reduce the surface tension of water by more than one-third of its normal value. Of the various classes of surfactants that can be used (anionic, cationic, nonionic and amphoteric), the use of a nonionic surfactant is preferred in accordance with the present invention.

Detailed Description of the Invention The coating solution of the present invention can be used to coat surfaces of pure aluminum or alloys of aluminum, for example, aluminum alloys containing minor amounts of metals such as, for example, magnesium, manganese, copper and silicon. Presently, the most popular alloy used in the aluminum can industry is aluminum alloy 3004. It is believed that one of the widest uses of the coating solution of the present invention will be the coating of aluminum suxfaces which have a bright shiny appearance. Aluminum cans and aluminum strip are examples of articles that can be treated effectively with the composition of this invention.

The acidic aqueous coating solution can be prepared from a variety of compounds which contain the aforementioned essential ingredients (a metal selected from the group consisting of titanium, zirconium and hafnium compounds and mixtures thereof, a fluoride compound, and an organic compound selected from the group consisting of a polyhydroxy compound having no more than 7 carbon atoms, a surfactant, and a mixture li~49~5 of said polyhydroxy compound and said surfactant) and which are soluble in the solution. As to the source of the zirconium, titanium, or hafnium, there can be used soluble fluozirconate, fluotitanate or fluohafnate compounds such as, for example, acids ~fluozirconic, fluotitanic, and fluohafnio) thereof and ammonium and alkali metal fluozirccnates, fluotitanates, and fluohafnates. The coating solution can be prepared also from metallic fluorides such as zirconium fluoride ~ZrF4), titanium fluoride (TiF3, TiF4), and hafnium fluoride (HfF4).
In addition, the coating solutions can be prepared from a mixture of soluble compounds, one of which contains zirconium, titanium, or hafnium, and the other of which contains fluoride.
Examples of such compounds are water soluble salts comprising nitrates and sulfates of Zr, Ti or Hf (for example, zirconium nitrate, zirconium sulfate, titanium (iv) sulfate, hafnium .. , .,.~- .
nitrate), and hydrofluoric acid and water soluble salts thereof, for example, ammonium and alkali metal salts.

Satisfactory coatings can be formed from coating solutions D a~-t~ng as little as ab~ut 0.5 x 10 3 mDle/liter ("m/l") of either Ti, or Hf (about 0.05 g/l of Zr, about 0.02 g/l of Ti, and about 0.09 g/l of Hf). When utilizing a mixture of one or more of Zr, Ti or Hf, the total of the amounts of the metals should be at least about 0.5 x 10 m/l. However, as will be explained below, greater amounts of these ingredients may be required to produce satisfactory coatings depending on other parameters of the coating process.

_9_ , -1~74945 zirconium, titanium, or hafnium can be used in amounts up to their solubility limits in the acidic aqueous coating solution. The solubility limits of the inyredients will depend on other parameter3 of the coating solution, including particularly, the acidity of the coating solution, the amount of fluoride in the coating solution, and the amounts of optional ingredients that mi~ht be used. These parameters should be controlled so that the formation of zirconium, titanium, or hafnium precipitate is avoided. The formation of such precip-itate is undesirable for several reasons. Precipitation depletes the amounts of the ingredients. Also, the deposition on the coated aluminum surface of precipitate can adversely affect the coating properties. In addition, the formation and accumulation of any type o precipitate can tend to interfere with the application of the coating solution. For example, ~: . .... .
it can clog spray nozzles. If precipitation is encountered in a specific application, the pH of the coating sol~tion can be lowexed, and/or the amount of fluoride can be increased.

As to the fluoride concentration, the minimum concentration should be that which is sufficient to combine with all of the zirconium, titanium, or hafnium to form a soluble complex therewith, for example, a fluozirconate, fluotitanate, or fluohafnate. Accordingly, the minimum amount of fluoride is dependent on the amount o zirconium, titanium, or hafnium in the solution. In general, at least about 4 moles of fluoride per mole of Zr, Ti or Hf is necessary to prevent precipitation of such metals. Preferably, at least about six moles of fluoride are employed per mole of Zr, Ti or Hf.

, 11749~5 In situations wherein the coating solution is recycled or a bath of the solution is used continuously, there is a build-up in concentration of the aluminum dissolved by the solution,~hich build-up may adversely affect the coating process. Therefore, the coating solution should contain an amount of fluoride sufficient to complex the dissolved aluminum.

Thus, from a practical standpoint, the coating solutio~
should contain, when operating on an industrial scale, an excess of fluoride, that is, an amount above that complexed with aluminum and any other constituents in the solution that form complexes with the fluoride. Such excess fluoride is referred to herein as "availa~le fluoride" and the means for calculation thereo is well known in the art. A coating .;:. . . .
~olution which contains available fluoride is one in which fluoride is available to complex with aluminum. In order to avoid undue etching of the aluminum surface which tends to produce a aull and frosty surface and to avoid adverse affeats on corrosion resistance and adherent properties of the coating as well as precipitation of calcium or other such ions present in the solution, it is recommended that the available fluoride concentration be no greater than about 26.3 x 10 3 mole/liter, or no greater than about 500 ppm.

Any material which is soluble in the coating solution, which is a source of fluoride capable of complexing aluminum and which does not contain a constituent which adversely ~'74945 affects the coating process can be used. If fluorlde i5 added as a complex fluoride of titanium, zirconium, or hafnium, however, there should be added to the solution another material such as HF, salts thereof, NH4F-HF, alkali metal bifluorides, H2SiF6 or HBF4, which is a source of fluoride for complexing the aluminum that builds up during continuous use. HF and ~BF4 are particularly preferred sources o~ fluoride.

As mentioned above, it is preferred that the surfactant for use in the present invention be selected from the nonionic class of surfactants. Although in some cases noticeable improvements will be observed when using about 10 ppm of sur-factant, it is preferred to use the surfactant in an amount of about 20 to about 100 ppm. Higher amounts, for example, up to about 500 ppm, can be used, but in general, little or no additional improvements are realized at higher concentrations.

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As regards the polyhydroxy compound, any water soluble polyhydroxy compound having no more than seven carbon atoms or any compound soluble in the coating solution which when dissolved th~n yields polyhydroxy compounds having seven or fewer carbon atoms and which does not interfere with the ability of the coating solution to coat or provide coatings having the desired corrosion resistance and paint adherence may be used. Examples of such compounds include gluconic acid, salts of gluconic acid, sodium glucoheptonate, sorbitol, mannitol, dextrose, ethylene glycol, and glycerine. Particularly preferred polyhydroxy compounds are gluconic acid and alkali metal and 9'~S

ammonium salts thereof~ Any compound soluble in the coating solution which yields gluconate and/or gluconic acid may be used. Examples of such compounds are stable gluconolactones such as glucono-delta-lactone and glucono-gamma-lactone.

It has been found that the use of the polyhydroxy compound in the coating solution allows the user to conduct a simple test to confirm the presence of the coating on the aluminum surface even when the solution is free of phosphate. In an industrial operation which can involve the treatment of vast quantities of aluminum in a relatively shoxt time, it is helpful to have a simple test to confirm that the coating solution is forming a coating since the coating is not visible to the eye. An unnoticed change in the operating parameters of a bath of the coating solution which renders it ineffective ~, , .................. .. .~
may take place as a result of mechanical or human failure.
For example, improper replenishment of the coating solution may go unnoticed.
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It has been found that an aluminum surface coated with such a composition of the present invention containing the polyhydroxy compound of the invention and no phosphate changes in color varying from light golden brown to darker shades of brown or purple when subjected to a relatively high temperature for a relatively short period of time ! for example, 900F for S minutes. This test, referred to herein as the "muffle test", can be used to randomly sample treated aluminum 9urfaces to ~1749~5 determine whether or not the coating solution is depositing on the aluminum surface. If the coating is not being deposited, the aluminum surface has a dull greyish appearance after the muffle test. The ability of such surfaces to successfully undergo this test is quite surprising as heretofore it had been believed that the presence of phosphate was necessary to obtain a positive test.

Another advantage derived from the polyhydroxy compound, and one also experienced with the surfactant, is that it en-~lances the ability of coatings formed from coating solutions containing this ingredient to withstand blackening or other discoloration for a period of at least 5 minutes and up to as long as 15 minutes when subjected to water having a temperature within the range of about 140F to about 170~F. As noted above, aluminum cans are sometimes treated in this manner when subjected to so-called "pasteurization" procedures.

It has been found also that the use of the polyhydroxy compound contributes to the corrosion resistance and adherent properties of the coatings, particularly coatings formed from a coating solution having a pH below about 3~5. In addition, it has been found that overlying siccative coatings, particularly water-borne coatings, adhere very well to coatings which contain polyhydroxy compounds. While organic-borne siccative coatings adhere well to coatings containing phosphates, certain water-borne coatings have not been found to adhere nearly as well to such coatings.

11749~5 Coated aluminum cans having a high level of water stain resistance and capable of discoloring when subjected to the aforementioned muffle test have been produced from coating compositions containing as little as about 0.025 x 10 3 mole/liter of the polyhydroxy compound. Preferably, such coating compositions contain from about 0.3 x 10 mole/liter to about 1.75 x 10 3 mole/iiter of the polyhydroxy compound.
Higher amounts, for example, up to about 2.5 x 10 mole/liter, can be used, but in general, little or no additional improve-ments are realized at higher concentrations.

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When the polyhydroxy compound is employed in the solutions of the present invention along with the surfactant, it is recommended tnat at least about 40 ppm of the polyhydroxy compound be used. Although higher amounts can be used, it is recommended that the polyhydroxy compound be present in an amaunt no greater than about 1000 ppm. Preferably about 40 to about 400 ppm of the polyhydroxy compound are used~

The pH of the coating solution can vary over a wide range, for example, about 1.5 to about S. Improvements in corrosion resistance attributed to the surfactant, when present in the solutions of the present invention, are observed particularly at a pH within the range of about 3.5 to about 4.5. Improve-ments in corrosion resistance attributed to the polyhydroxy compound, when present in the solutions of the present invention, ~1749~5 .

are observed particularly at a pH within the range of about 3.0 to about 5.0, and preferably, a pH within the range of a~out 3.0 to about 4.0 is used. The p~ of the solution may be adjusted by using appropriate amounts of nitric acid or ammonium hydroxide. Although nitric acid and ammonium hydroxide are recommended as pH adjusters, any acid or base which will not interfere with the coating process can be used. For example, perchloric acid or sul~uric acid can be used.

The coating solution of the present invention should be free of chromium, iron cyanides, and any materials that form in the solution solids which tend to precipitate.

Examples of other materials which can be optionally added to the coating solution of the present invention are , . . . .
those which have been reported heretofore as being useful in Zr, Ti, or Hf and fluoride-containing compositions For example, aforementioned U.S. Patent No. 3,964,936 discloses the use of materials which are a source of boron in an amount of at least about 10 ppm and ranging up to about 200 ppm.
When a boron compound is added to the acidic aqueous coating solutions of the present invention which contain surfactant, it is particularly preferred that the boron compound be added as boric acid in the aforementioned amounts. Boron compounds are not added to the solutions of the present invention that do not contain the surfactant~ Tannin is another optional ingredient that can be added to the solution in concentrations of at least about 25 ppm and ranging up to about 10 g/l (see U.S. Patent No. 4,017,334 and U.K. Patent Application GB 2,014,617).

ll'~g9~5 When using organic solvent-based coating compositions to form the overlying siccative coating, the solution of the present invention can Optionally include phosphate in an amount of about 10 ppm to about 1000 ppm, as described in U.S. Patent No. 4,148,670, except when the solution contains the poly-hydroxy compound and does not contain the surfactant.

Still other materials which can be optionally added to the coating solution of the present invention are various .
other acids including, for example, glutaric, ascorbic, maleic, and salicylic. Such acids can be used in amounts of at least about 5 ppm and preferably within the range of about 100 to about 500 ppm to realize various advantages, including improving the adhesive properties of coatings formed from the solution.

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Amount xanges for ingredients comprising the composition of the present invention have been described above. Consider-ations should be taken into account in formulating specific compositions for spécific applications while working within the aorementioned ranges. When operating at a relatively high pH, relatively small amounts of zirconium, titanium and/or hafnium should be used to deter precipitation. When contacting the aluminum surface with the coating solution for a relativeiy short time, relatively high amounts of the aforementioned metals should be used. Similarly, when the temperature of contact between the coating solution and the aluminum $urface is relatively low, relatively high amounts of ingredients should be used.

9~5 One preferred embodiment of the present invention ~herein-after "preferred embodiment A") has a pH within the range of about 3.4 to about 4 and contains:

Approximate Concentration Ingredient in Moles~Liter Zr 0.5 x 10 3 to 1.75 x 10 3 Polyhydroxy Compound 0.3 x 10 3 to 1.75 x 10 3 Available Fluoride -0.5 x 10 3 to 2r5 x 10 3 The preferred source of Zr in preferred em~odiment A is ammonium fluozirconate, and the preferred polyhydroxy compound is gluconic acid. Preferably hydrofluoric acid is used as the source of available fluoridej and nitric acid is used to adjust the pH.

When hafnium is added to preferred embodiment A, it is preferably added in an amount of from about 0.5 x 10 mole~liter to about 1.75 x 10 3 moles/liter. The preferred source of hafnium i5 HfF4. Other preferred ingredients and amounts thereof which may be employed in the preferred Zr-containing solution of preferred embodiment A have been previously desaribed.

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Another preferred embodiment of the present invention ~hereinafter "preferred embodiment B") has a pH within the range of about 3.5 to about 4.5 and contains about 0.75 x 10 3 to about 2 x 10 3 m/l of zirconium and about 10 ppm to about 500 ppm of surfactant and, most preferably,a pH within the range of about 3.7 to about 4.3 and contains 1 x 10 3 to ~i749~5 .

about 1.75 x 10 3 m/l of zixconium and about 20 to about 100 ppm of surfactant, each of the aforementioned containing enough fluoride to complex all of the Zr and the dissolved aluminum present in the solution.

The preferred source of both Zr and fluoride in the make-up composition of preferred embodiment B is fluozirconic acid and nitric acid is preferably used to adjust the pH.

The coating solution of the present invention can be prepared con~eniently by diluting an aqueous concentrate of the ingredients with an appropriate amount of water. For example, with regard to preferred embodiment A, a concentrate should be such that when a coating solution contains about 0 5 to about 10 weight percent of the concentrate, the amounts o ingredients present in the coating solution are: ~A) at least about 0.5 x 10 mole /liter of zirconium and/or hafnium; (B) at least about 0.025 x 10 3 mole /liter of polyhydroxy compound, and (C) fluoride in an amount at least sufficient to combine with substantially all of the zirconium or hafnium to form a complex therewith, and the pH of the coating solution is within the range of about 3 to about 5.
More preferably, the concentrate is such that when the coating solution comprises about 0.5 to about 10 weight percent of the concentrate, the coating solution comprises: (A) about 0.5 x 10 3 moles/liter to about 1.75 x 10 3 moles/liter of zirconium, added as a fluozirconate such as sodium or potassium 1~74945 fluozirconate, most preferably ammonium fluozirconate; (B) about 0.3 x 10 3 mole /liter to about 1.75 x 10 (~ole /liter A of polyhydroxy compound added as gluconic acid; ~t about 0.5 x 10 3)mole /liter to about 2.50 x 1.0 3 mole /liter of HF; and ~e~ nitric acid in an amount such that the pH of the coating solution is within the range of about 3.4 to about 4.
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By way of further example, with regard to. preferred embodiment B, the concentrate should be such that when a coating solution comprises about 0.5 to about 10 wei~ht percent of the concentrate, the amounts of ingredients present in the coating solution are: (A) at least about 0.5 x 10 3 m/l of one or more of zirconium, titanium, and ha.fnium; and (B) fluoride in an amount at least sufficient to combine with ~ubstantially all of the Zr, Ti, or Hf to form a complex ~ . . . -~ .
therewith, and (C) at least about 10 ppm of surfactant.

In a continuous coating operation, fluoride and the metal are consumed and tt~se ingredients as well as others are additionally depleted a9 a result of drag-out of the.solution on the aluminum surface. The rate of depletion is related to the shape of the surface being coated as well as the means of application of the coating solution to the surface. In addition to this depletion, there is a build-up in concentration of dissolved aluminum as noted above. Therefore, in a continuous coating operation, the ingredients should be replenished.

- -11~ 5 Replenishment may be effected by monitoring each ingre-dient and adding an additional amount thereof as it is depleted but preferably replenishment is accomplished by adding an aqueous concentrate containing the ingredients to be replenished in amounts effective to maintain said ingredients in the solution in effective operating amounts. The replenishing composition preferably contains a relatively high proportion of fluoride when aluminum build-up is experienced in the coating solution.
Preferred sources of available fluoride for use in replenishing are HF or ammonium bifluoride or a mixture thereof or HBF4.

Thus by way of example and with reference to preferred embodiment A, the following is a recommended aqueous concentrate for replenishing the coating solution of preferred embodiment A.
~A) about 31 x 10 3 mole/liter to about 251 x 10 3 mole/liter of zirconium and/or hafnium;
(B) about 19 x 10 3 mole/liter to about 148 x 10 3 mole/liter of the polyhydroxy compound; and (C) a material which is a source of about 90 x 10 3 mole/liter to about 695 x 10 3 mole/liter of available fluoride, preferably HF or ammonium bifluoride or a mixture thereof.

By way of further example and with reference to preferred embodiment B, the following is a recommended aqueous concentrate for repleni5hing the coating solution of preferred embodiment B.
(A) about 0.05 mole/liter to about O.S mole/liter of zirconium, titanium and/or hafnium;
(B) about 0.2 mole/liter to about 10 moles/liter of fluoride; and (C) about 1 to about 100 g/l of surfactant.

The coating solutions of the present invention should be applied to a clean aluminum surface. Available cleaning compositions such as alkaline or acid cleaning sol~ltions can be used to clean the aluminum surface according to conventional techniques.

When coating drawn and ironed aluminum cans it is preferred to subject the cans to a cleaning solution comprising an acidic aqueous solution of a mixture of HF, H2SO4 and surfactant, for example, solutions such as those described in U.S. Patent Nos. 4,009,115; 4,116,853; and 4,124,407, each assigned to the same assignee as the present invention, and the disclosures of which are incorporated herein by reference.

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The coating solution can be applied to the alumin~m surface by any suitable method. For example, the solution can be applied by spraying the aluminum surface, or the aluminum surface can be immersed in the solution, or it can be applied by roll or flow coating techniques or misting techniques.
The solution can be used to coat individual articles such as, for example, cans, or it can be used to coat forms of aluminum, such as aluminum strip, which are subsequently fabricated into articles.

, The temperature of the coating solution should be such that the reactive ingredients of the solution bond to the aluminum surface. For example, with a solution such as 1~7~345 preferred embodiment A, a temperature of at least about 110F
is generally required to produce the desired degree of corrosion resistance and preferably such coating solution should have a temperature of about 130F to about 150F. With a solution such as preferred embodiment B, a temperature of at least about 90F is generally required to produce the desired degree of corrosion resistance and temperatures of up to about 140F
can be used, preferably about 110F to about 130F.

If the temperature of the coating solution is too high, problems such as a dull and frosty appearing surface may be encountered. The temperature at which this occurs depends on various of the parameters of the coating operation, including~
for example, the time of contact of the solution with the aluminum surface and the reactivity of the solution which ., .
depends on pH and concentration of ingredients in the solution.
By way of further example, with solutions such as preferred embodiment A, precipitation of zirconium and/or hafnium oxides.at temperatures in excess of about 160F may become a problem if the p~ of the coating solution rises above about 4.5.

Desired coatings can be formed by contacting the coating solution and the aluminum surface for at least about 5 seconds, preferably at least about 15 seconds. The lower the temperature o the coating solution, the longer should be the contact time, and the higher the temperature of the solution, the shorter 1174~45 the contact time required. In general, it will be unnecessary to contact the surface with the coating solution for more than one minute After the coating solution has been applied to the aluminum surface, it should be water rinsed, including a final deionized water rinse. Rinsing with water that contains a small amount of dissolved solids may lead to a coating wh~ich does not adhere well to a subsequently applied siccative coating. In utilizing the present invention, it is not necessary to rinse the coated surface with an aqueous solution of chromium such as, for example, a hexavalent chromium solution.

After the coated surface has been water rinsed, or otherwise treated as described above, the coating should be dried. This can be done by any practical means, such as, for example, oven drying or forced circulation of hot air.
Other available drying methods can be used.

After the coating has been applied, it can be subjected to sanitary or decorative coating operations which include, for example, applying to the coated surface siccative coatings.
These coatings are usually applied after the aluminum surface has been coated, water-rinsed, and dried. In some applications the sanitary c~ating is applied after the water rinse and both the coating of the present invention and the sanitary coating are dried simultaneously.

Siccative coatings which comprise the functional and/or aesthetic coatings which overlie the coatings formed from the coating solution of the present invention are well known, of course, and can be formed from either water-based or organic solvent-based compositions.

By way of example, it is noted that in an application where aluminum cans are to be filled with beer, the cans are treated with the coating solution of the present invention and then sanitary and/or decora~ive coatings are applied.
Thereafter, the cans are filled with beer and sealed; after which the beer-filled cans are subjected to pasteurization.

It is believed that the zirconium, titanium, or hafnium present in the coating solution of the presént invention is .. . . ..
present in a complexed form which is both soluble in the solution and reactive with the aluminum surface to form thereon a coating containing such metal without affecting the bright shiny appearance of the aluminum surface. Accordingly, the solution should be free of constituents which combine with the aforementioned metals to form compounds and/or complexes which precipitate from the solution and/or compounds or com-plexes which are not reactive with the aluminum surface or which are reactive, but in a mannér such that the bright shiny appearance of the aluminum surface is altered.

EX~PLES

The following examples present illustrati~e but non-limiting embodiments of the present invention. Comparative examples are also set forth.

Unless stated otherwise, the aluminum surfaces treated with the solutions identified in the examples were drawn and ironed aluminum cans which were first degreased, a~ necessary, in an acidic aqueous cleaner containing sulfuric acid, hydro-fluoric acid and detergent. Unless stated otherwise, the coating solutions were applied by spraying for about 20 seconds at the temperatures set ~orth below. After treatment with the solutions identified in the examples, the aluminum surfaces were rinséd with tap water and then with deionizea water, and thereafter dried in an oven for 3.5 minutes at about 400F.

.
Thereafter, the aluminum cans were tested for corrosion resistance by subjecting them to a water stain resistance test simulating can exposure during commercial pasteurization processes. The test consisted of immersing the cans for a period of 30 minutes in a hot solution of distilled or deionized water containing 0.22 g/l of sodium bicarbonate, 0.082 g/1 of sodium chloride, and 2.18 g/l of a water con-ditioner ~Dubois 915, a proprietary product, supplied by Dubois Chemical Inc., which exhibits a total alkalinity of 5.8% Na2O
and on analysis contains NaNO3, carbonate, triethanolamine and dodecylphenyl polyethylene glycol). The solution was maintained at 150- 5F during the test. After immersion, the cans were rinsed with tap water, dried wlth a paper towel and then examined ~or staining. A cleaned-only aluminum surface, when subjected to this test, turns black or brown after a few minutes. It will be seen from examples set forth below that prior treat-ment of aluminum surfaces with coating solutions of the present invention can result in the provision of coated surfaces which are not blackened or otherwise discolored or which xesist blackening or other discoloration. The aluminum surfaces were rated as follows: 5, perfect - identical to a treatea but untested suxface; 4.5 - very slight diminishing of the bright appearance of the suxface; 4.0 - very slight discoloration;
3.5 - light discoloration, but commercially acceptable; 3.0 -discoloration that is considered not commexcially acceptable;
" ..~
0 - total failure, characterized by severe blackening.

In some of the examples the aluminum cans, aftex txeatment with the indicated solutions, were also tested for paint adhesion. After the treated surface was dried, as described above, a portion of the surface was painted with a waterborne white base coat (No. CE3179-2 white polyester sold by PPG
Industries Inc.) and the other portion of the surface was painted with a waterborne overvarnish (Purair* S145-121 sold by Inmont Corp.). After tne paint was cured, the painted surface was immersed in boiling water for 15 minutes. After removing the painted surface from the solution, it was cross .
* "Purair" is a registered trademark li7'~9~5 hatched, using a sharp metal object to expose lines of aluminum which showed through the paint or lacquer, and tested for paint adhesion. This test included applying Scotch** transparent tape No. 610 firmly over the cross hatched area and then drawing the tape back against itself with a rapid pulling motion such that the tape was pulled away from the cross hatched area. The results of the test were rated as follows: 10, perfect, when the tape did not peel any paint ~rom th~ surface;
8, acceptable; and 0, total failure.

Examples 1-15, and Comparative Examples Cl-C3 The following acidic aqueous concentr~te wasprepared for use in connection with the first group of examples.
g~
fluozirconic acid (100~) 10.5 aqueous ammonia (29 wt. %) 5.9 nitric acid (70 wt. ~) 9 deionized water to make 1 liter The above composition was prepared by combining an aqueous solution of 23.4 grams of 45 wt. % fluozirconic acid with a portion of the water, and thereafter the aqueous ammonia was added to the resulting solution. A white precipitate was formed, but it dissolved upon addition of nitric acid.

** "Scotch" is a registered trademark of the 3M Co.

.. . . ..

117~9~5 The resulting clear solution was diluted to 1 liter with deionized water resulting in a concentrate that was used to prepare treatment solutions at 2.5~ by volume in water comprising

2 parts deionized water and 1 part hard water. ~In the examples, the term "hard water" refers to tap water rom Ambler, Pennsylvania, which inclu~es about 80 to about lOb ppm of calcium and has a conductivity o about 400 to about 600 mhos.) To this soluti~n, there was added, in the amounts indicated in Table 1 below, a nonionic surfactant sold under the trademark Surfonic LF-17 by Jefferson Chemical Co., Inc. and which is reported to be a low-foaming alkyl polyethoxylated ether.
Solutions of varying acidity were prepared by adjusting the pH of the aforementioned base composition with appropriate amounts of an aqueous solution of 15~ (w/v) ammonium carbonate or dilute nitric acid.

.. .

The water-stain resistance of aluminum cans coated with the compositions is reported in Table 1 below.

~i'7~9~

T~ble I

Cbnc. of p~l 3'esiS~rce E:c. No.Sur~., F~ of ~nq Solu~
~1 5 3.5 3.3 S 3.~ 3.6 2 10 3.5 3.6

3 20 3.5 4.1 ? 40 3.5 S 80 3.5 4.2 C-2 o 4 3.7 6 5 4 4.4 7 10 4 4,7 8 20 ~ ~1.5 9 40 4 4.5 - 10 80 4 4.6 C-3 0 4.5 ~.
~1 5 4.5 4.4 12 10 4.5 4.7 . 13 20 1.S 4.8 14 40 4.5 . 4.7 ~S 80 4.5 ~.

The improvements in corrosion resistance achieved over the pH range of 3.5 to 4.5 for the compositions evaluated in Table I
are clearly shown. Other tests show that for the particular type of composition evaluated in Table 1, the water-stain resistance of coatings formed from compositions with and without surfactant were about the same when the pH of the composition was about 2.5.
Still other tests showed that for the particular type of composition evaluated in Table I, but prepared from deionized water only and containing 20 ppm of surfactant, improvements in water-stain resistance were achieved when the pH of the composition was in excess of 3.5, with substantial improvements being achieved at a pH of about 4.

11'749~5 Examples 16-39, and Comparative Examples C4-C6 .
The next group o examples shows the use of compositions of the type described in Examples 1-15 and Comparative Examples Cl-C3 but including also 0.1 g/l of gluconic acid which is effective in improving the water-stain resistance of the coated surface. Compositions of varying acidity and containing either the surfactant used in the compositions of the first group of examples or another surfactant were evaluated. Said other surfactant was a modified polyethoxylated straight chain alcohol which is considered to be a low-foaming material and which is sold under the trademark Triton DF-16 by Rohm and Haas Company. The specific compositions evaluated and the results of the testing are set forth in Table II below.
't: _ Example ~0 Table III below shows the effect of gluconic acid concentration on water stain resistance of coatings applied at varying temperatures from 90F to 150F. Zirconium was present in each solution in the form of ammonium fluozirconate ~(NH4)2ZrF6) at a concentration of 1.25 x 10 3 m/l, and each solution was adjusted to a pH of 3.8 by the addition of concentrated nitric acid. Two cans were employed in determining the water stain resistance rating of each solution.

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~lL1'745~'~5 Example 41 Table IV below also shows the effect of gluconic acid con-centration on water stain resistance, as well as on the adhesion of water-borne siccative coatings, at two different pH and temperature levels. Once again, zirconium was present in each solution in the form of ammonium fluozirconate ~NH4)2ZrF6) at a concentration of 1.25 x 10 3 mole/liter, and the pH of each solution was adjusted by the addition of concentrated nitric acid. Two cans were employed in determing each paint adhesion rating ("Adhesion") while each watex stain resistance rating ("Resistance") represents the average rating of six cans.

TABLE IY

~rr-ot or Cluoonlo Aold Conoontrotlon on Hotor Stoln RoolJt~noo und Adhoolon Or ~utorborno Slooutlvo Co-tln6o t 1,25 x 10 3M ~NH4)2Zr~6Conoontrutlon _ _ _ _ Oluoonlo Aol~ Adhoolon 8-~Dl- No. Cono. ~ x 10 3)~HromD. ~P) Roolotonou CL3179-2 S145-121 1 0 3.5 125 110, 10 10, 7 2 0 3.5 135 2-2/310, 10 10, 8 3 0 4.25 125 410, 10 10, 10

4 0 4.25 135 2-2/310, 8 10, 8 0.5 3.5 125 510, 10 10, 10 6 0.5 3.5 135 510, 10 10, 10 7 0.5 4.25 125 4-2~310, 10 10, 10 ô 0.5 4.25 135 4-2/310, 9 10, 10 9 1.25 3.2 125 4-1/610, 10 10, 10 1.25 3.5 135 510, 10 10, 10 11 1.254.25 125 510, 10 10, 10 12 1.254.25 135 510, 10 10, 10 13 2.5 3.5 125 1-1/610, 10 10, 10 14 2.5 3.5 135 2-2/310, 8 10, 10 2.5 4.25 125 1-2/310, 10 lo, 10 16 2.5 ~.25 135 4-2/39, 9 10, 10 Examples 42-45 An aqueous concentrate of the tupe used to formulate the compositions of Examples 1-15 was diluted with a sufficient amount of water (two parts deionized water and one part hard `Sd,~
i'i-~1'7'~4S

water ~to yield) a coating solution containing 2.5% by volumeof the concentrate, to which was added 20 ppm of Surfonic LF-17.
Four solutions were thus prepared, to each of which was added 0.1 g/l of one of the following ingredients: glutaric acid, asorbic acid, maleic acid or salicylic acid. The pH of each of the compositions was 3.5 and each was used in treating aluminum cans in the manner described above in connection with the preceding examples. For all of the cans treated in this way, water stain resistant ratings were above 3.5 and improved adhesion was exhibited when the cans were painted with either PPG CE 3179-2 or Inmont S145-121, water-based coating compo-sitions, or with Clements P1099-7A or Clements P550-G, organic solvent based coating compositions.

Examples 46-49 Other compositions were formulated by including 0.5 x 10 3 m/1 gluconic acid in each of the compositions of Examples 42-45 above. Coatings formed from such compositions exhibited improved adhesion with respect to top coats formed from various water-based resin coating compositions.

Example 50 Table V below shows the effect of ammonium fluozirconate concentration on water stain resistance of coatings applied at varying temperatures from 90F to 150F. Gluconic acid was present in each solution at a concentration of 0.5 x 10 3 mole/
liter, and each solution was adjusted to a pH of 3.8 by the addition of concentrated nitric acid. Two cans were employed in determining the water stain resistance rating of each solution.

1 ~'J~ 345 TA~LE V
Erfect Or (NH4)2ZrF6 Conoentratlon on Water Staln Reslstance at 0.5 x 10-3M Gluconlc Acld Concentratlon and pH of 3.8 ~ater Staln Sample No. (NH4)2zrF6cono. Temp. (~F) ~eslstanoe 0 90 o, O
2 0 110 0, 0 3 0 130 o, 0 4 o 150 0 0.1go o o 6 0.1110 0, 0 7 0.1130 0, 0 8 0.1150 0, 0 9 0.2590 -0.25110 0, o 11 0.25130 3, 3 12 0.25150 3, 3 13 0.5090 0, 0 14 0.50110 2 2 0.50130 3 3 16 0.50150 4, 4 17 0.7590 2, 2 18 0.75110 2, 2 19 0.75130 3, 3 0.75150 4, 4 21 1.2590 22 1.25110 2, 2 23 1.25130 3, 3 24 1.25150 4, 4 1.7590 1, 1 26 1.75110 2 2 27 1.75130 4 4 28 1.75150 5, 5 29 2.2590 1, 1 2.25110 2, 2 ~1 2.25130 4, 4 32 2.25150 5, 5 33 5 0 9 2, 2 34 5.0110 2, 2

5.0130 4, 4 36 5.0150 4, 4 Example 51 Table V~ below shows the effect of ammonium fluozirconate concentration on water stain resistance, as well as on the adhesion of waterborne siccative coatings, at three different pH and two different temperature levels. Again, gluconic acid was present in each solution at a concentration of 0.5 x 10 3 mole/liter, and the pH of each solution was adjusted by the addition of concentrated nitric acid. Two cans were employed in determining each paint adhesion rating while each water stain resistance rating represents the average of six cans.

T~aLE VI
Erroot o~ (NH4)2ZrF6 Conoontrotlon on ~ater Stoln Ro~lat~no~ and Adhoalon Or ~at~rborno Sloo~tlv~
Co-t~ng~ at 0.5 1 10 3~ Gluoonlo Aoid Conoontratlon (NN )2ZrF ~at~r St~ln Adb~ion ~ample No. ~ono. (M ~6 lo~3) PH Temv. ~F)~oalatano~ CE3179-2 S145-121 1 0.75 3.5 125 4-2~310, 8 10, 10 2 0.75 3.5 135 5 10, 10 10, 10 3 0.75 4.o 125 4-s~6 9, 9 lo, lo 4 0.75 4.0 135 4-2/3 10 8 10, 10 0.754.25 125 4 lo 1~ 10 o

6 0.754.25 135 4 10, ô 9 9

7 1.25 3.5 125 5 10 10 10, lo

8 1.25 3.5 135 5 10 10 lo lo

9 1.25 4.0 125 5 10, 10 10 10 1.25 4.0 135 5 10, 8 l~o 9 11 1.254.25 125 4-2/3 10, 10 10 10 12 1.254.25 135 4-1~3 10 9 10 10 13 1.75 3.5 125 4 lo 10 10 8 14 1.75 3.5 135 4 lo, 8 9, 9 1,75 4.0 125 4 10, lo 10 10 16 1.75 4.0 135 4 10, 10 10 10 17 1.754.25 125 4 10 10 10 10 18 1.754.25 135 4 10 10 10 10 19 - - - - - - - Cl~an~d Only - - - - - - - - - - - - - - O 10, 9 10, 10 Example 52 Table VII below illustrates the water stain resistance of coatings formed from a solution of hafnium tetrafluoride, ~ydrofluoric acid and gluconic acid at varying temperatures from 90F to 150F. The solution contained 1.25 x 10 mole/liter of hafnium tetrafluoride, 2.5 x 10 mole/liter of gluconic acid. For comparative purposes, coatings were also formed from a like solution free of gluconic acid. The pH of both solutions were adjusted to 3.8 by the addition of concentrated nitric acid. Two cans were employed in determining the water stain resistance rating of the solutions.

1~4~3~S

TA~LE VII
~at~r St~ln Re~lstano~ ot C~atlngs Form~d Fro~ A Sol~tlon or N~rnlum T~trorluorlde, ~ydro~luorlc Acld ~nd Gluoonlo Aold ~rF4 HF Gluoonlc Acld ~t~r ~t~ln sa~Dlo No. ~M ~ 1~ 3~ M ~ 10 3) pN Te~ ~ F) Ro~latnnco_ 1 1.25 2.5 0 3.~90 0 2 1.25 2.5 0 3.~110 3 -1.25 2.5 0 3.ô130 4 1.25 2.5 0 3. B 150 2 1.25 2.5 0.5 3.890 6 1.25 2.5 0 5 3.8110 7 1.25 2.5 0.5 3.8130 5 8 1.25 2.5 ~.5 3.8150 5 Examples 53-56 Tables VIII, IX and X illustrate the effect of pH and temperature on the water stain resistance of coatings formed from a solution of ammonium fluozirconate and gluconic acid, as well as on the adhesion of water-borne siccative coatings to such coatings. The solution employed contained 1.25 x 10 3 mole/liter of the ammonium fluozirconate and 0.5 x 10 3 mole/
liter of the gluconic acid. For comparative purposes, coatings were also formed from a like solution free of gluconic acid.

The pH of both solutions was adjusted to the values shown in the tables by the addition of concentrated nitric acid. Such solutions were then applied at varying temperatures from 90F
to 160F. Two cans were employed in determining each water stain resistance rating and one can was employed in determining each paint adhesion rating at each pH and temperature value.
The condition of each solution (clear or cloudy) at each pH and temperature level employed is also set forth. As can be seen from Tables X and XI, the presence of gluconic acid is important at pH 4.5 and 5.0 in maintaining a clear solution and preventing pr~cipitation.

~ L~

TALLE YIII
er~ot Or Somperaturo on ~ater Staln Rosi~tanoe Or Coatlng~ Formod From a Solution Or 1.25 ~ 10 3N (NN4)2ZrF6 and 0.5 ~ 10 3H Cluoonlo Aold at a pH Or 3.0, ~nd on the Adhe~ion or ~atorborno Sloo~tlve Coatln~a to Suoh Coatln~s Gluoonlo Aold ~ater StalnAdhe~lon Solu~lon Sample_No. Cono. (M x 10 3) SeQD. (P) ~e~l~tanco Ce3179-2 Condltlon 1 090 2,2lrJ Clear 2 D100 2,210 Clear 3 0110 1,110 Cloar 4 0120 1,110 Cl~ar 0130 1,110 Clear 6 0140 2 210 Clear 7 0150 3 310 Clear 8 0160 3,310 Cle~r 9 0-590 3,310 Cle~r o.5 100 3~3 10 Clear 11 0.5 110 3~3 10 Clear 12 0.5 120 4 4 10 Cl~ar 13 0.5 130 4 4 10 Clear 14 0.5 140 5,5 10 Ciear 0.5 150 5,5 __ Cloar 16 0.5 160 5,5 7 (hoavy Cloar palnt) ~ TAOLE IX
Erroot Or S--poraturr on ~ator Staln ~o~l~tanoe or Coatln6~ Formod From a Solutlon Or 1.25 % 10 3M (NH4)2ZrP6 and 0.5 ~ 10 3M Gluoonlo Aold at a pH Or 3.5, and on the Adbe~lon Or ~atorborno Slooatlve CoatlnEs to Suoh Co~tln~
aluoonlo Aold ~ater StalnAdhoslon Solutlon samDlo Uo.Cono. (M x 10 3) Tomp. (~F~Posl~tanoo CE3179-2 Condltlon 1 090 0,0 10 Cl~ar 2 0100 0 0 10 ClAar 3 0110 0 0 10 Cloar 4 0120 0,0 10 Clear 0130 1 1 10 Cloar 6 0140 2 3 10 Cloar 7 0150 2,3 10 Clear 8 0160 2 3 10 Cloar 9 0.5 90 2 2 10 Clear 0.5 100 2,2 10 Cloar 11 0.5 110 3,3 10 Clear 12 0.5 120 3,4 10 Cloar 13 0.5 130 ll~4 10 Cloar 14 0.5 140 5,5 10 Clear 0.5 150 5 5 10 Ciear 16 0.5 160 5 5 10 Cloar ~1 7 .~ ~3 4 5 ShSLE X
Erroot Or Somporaturo on Wator Staln R~al~tanoo Or Co~tln~ Por~od Fro~ a Solutlon Or 1 25 ~ 10 3N (NH4)2ZrF6 and 0 5 ~ 10 3M Oluconlo Aold at a pN or 4 5, and ln tho Adboolon Or Watorborno Slooatl~e Coatlng~ to Suoh Coatln~
aluoonlo Aoid 3 ~ater StalnAdhoolon 901utlon 9a~plo No Cono ~N ~ 10 ) TOrD. 1 F~ Roolatanoe CE3179-2 Condltlon 1 0 90 0,0 10 Cloar 2 0 100 0,0 10 Sll~ht Naz~
3 0 110 0,0 10 Falnt Nazo 4 0 120 3,1 10 Cloudy 0 130 2,1 10 Cloudy 6 0 140 2,2 10 Cloudy 7 0 150 2,2 10 Cloudy ô 0 160 2,3 10 ~ory Cloudy 9 0 5 90 0,0 10 Cloar 0 5 100 0,1 10 Cloar 11 0 5 110 2,1 10 Cloar 12 0 5 120 3,1 10 Cl~r 13 0 5 130 4 4 10 Cl~ar 14 0 5 140 4,4 10 Cloar 0 5 150 4,4 10 Cloar 16 0 5 160 4,4 10 Cloar SANLE XI
Ett-ot ot Souporaturo on W~tor Staln Roalatanoo Or Co~tlnza For~od Fron Solutlon or 1 25

10 3N (hN4)2ZrF6 and 0 5 ~ lD 3N Oluoonlo Aold at a pH Or 5 0, and on tho Adboalr,n Or ~-torborno 9100-tl~ Coatlnga to 9uoh Coatlnga aluoonlo Aold Wator ~talnAdhoaloD Solutlon SanDlo No Cono(N ~ 10 3)So~P ( F)RoJlatanoo CE3179-2 Condltlon 1 0 90 2,Z 10 Cloudy 2 0 100 2,2 10 Cloudy 3 0 110 3,3 10 Cloudy 4 0 120 4,3 10 Cloudy 0 130 4,3 10 Cloudy 6 0 160 4,3 10 Cloudy 7 0 5 90 3,2 10 Cloar ô 0 5 100 3~3 10 Cloar 9 0 5 110 3,3 10 Clo-r 0 5 120 4,3 10 Cloar

11 0,5 130 4 3 10 Cloar

12 0 5 140 4 3 10 Clo-r

13 0 5 150 4,3 10 Cloar

14 0 5 160 4,2 10 Cloar lnltl-lly, oloudy artor otandln~ tor,Jl hr 'X

Exsmple 57 Table XII below shows how the addition of phosphate to an ammonium fluozirconate solution adversely affects the adhesion of water~orne siccative coatings to coatings formed from such solutions. The concentration of phosphate and ammonium fluo-zirconate in each of the solutions prepared is shown in the table. The phosphate was added as phosphoric acid. The pH
of the solutions varied as shown in the table. Once again, nitric acid was employed to adjust the pH. The solutions were applied at a temperature of 130F. Two cans were employed in determining each paint adhesion rating of each solution.

erroot Or Phosphato Conoontratlon On Adhoslon Or ~atorborn~
Sloaatlv~ Coatlng~ to Coatlnt~ Forood rron Fluozlroonate ~olutlona (~4)2ZrF6 PhoJphato Adhoslon S ~Dlo No.~M x 10 3) ~H x 10 3) DH CE179-2 S145-121 1 0.5 0 3.5 10, 9 9,6 2 0.5 0 4.0 10,10 8,7 3 0.5 0.1 3.5 10, 5 8,6 4 0.5 0.1 4.0 10, 5 7.0 0.5 0.25 3.5 O, 0 9,6 6 0.5 0.25 4.0 O, O ~,7 7 1.25 0 3.5 10,10 9,6 8 1.25 0 4.0 10, 9 8,7 9 1.25 0.1 3.5 7, 0 8,7 1.25 0.1 4.0 6, 5 10,0 11 1.25 0.25 3.5 O, 0 7,7 12 1.25 0.25 4.0 O, 0 8,0 13 2.5 0 3.5 10,10 10,8 14 2.5 0 4.5 10, 9 9,6 2.5 0.1 3.5 0, 0 10,9 16 2.5 0.1 4.0 9, 8 8,8 17 2.5 0.25 3.5 7, 5 8,5 18 2.5 0.25 4.0 O, 0 9,5 19- - - - - -Cloanod Only- - - - - - - - - - - - - - -10,10 10,8 ," !
.l'~ ` .

s Example 58 Table XIII below shows how the addition of phosphate and gluconic acid to ammonium fluozirconate solutions affects the adhesion of waterborne siccative coatings to coatings formed from such solutions. The concentration of each of these materials in each of the solutions prepared is shown in the table. The phosphate was added as phosphoric acid. The pH
of the solutions was varied as shown in the table and concen-trated nitric acid was employed to adjust the pH. The solutions were applied at the temperatures indicated. Two cans were employed in determining each paint adhesion rating of each solution.

TABLE XIII

Erroot Or Phooph-to nnd Cluoonlo ~old Conoontratlon on Adhonlon Or ~atorborno Slooatlvo Co-tlngo to Co-tlnga Yor-od rro- Fluozlroon~to Solutlono ~NH4)2zrF6 Phoophatc aluoonlo ~old ~h-~lon 90~Dlo No, ~H ~ 10 3) ~H x 10 3) ~H ~ 10 3) DH ~ L~l CE3179-2 S145-121 1 0.25 0 0 4.0 110 10,10 10, 8 2 0.25 0 0 4.0 130 10,10 8, 8 3 0.25 0.1 0 4.0 110 10, 8 10,10 4 0.25 0.1 0 4.0 130 7, 7 10 ô

0.25 0 0.5 4.0 110 10,10 10 10 6 O.Z5 0 0.5 4.0 130 10,10 10,10 7 0.25 0.1 0.5 4.0 110 ~ 6 10,10 8 0.25 0.1 0.5 4.0 130 0 0 10, 7 9 0.25 0 0 3.5 110 10 10 10 10 0.25 0 0 3.5 130 10 10 10 10 11 0.25 0.1 0 3.5 110 5, 5 10, 7 12 0,25 0.1 0 3.5 130 0 5 0, 0 13 0.25 0 0.5 3.5 llo lo lo lo,lo 14 0.25 0 0.5 3.5 130 10,10 lo,lo 0.25 0.1 0.5 3:5 110 10 7 7, 6 16 0.25 0.1 0.5 3.5 130 t 7 7, 7 17 1.25 0 0 3.5 110 10 10 10 7 la 1.25 0 0 3.5 130 10 10 9 7 1,25 0.1 0 3.5 110 10,10 10,10 1.25 0.1 0 3.5 130 0, 0 7, 5 21 1.25 0 0.5 3.5 110 10,10 10, 8 22 1.25 0 0.5 3.5 130 10, 8 10, 8 23 1.25 0.1 0.5 3.5 110 10 7 5 5 24 1.25 0.1 0.~ 3.5 130 10 8 7 0 25- - - - - -Cloanod Only- - - - - - - - - - - - - - - - - - - - - - - - - - 10,10 10,10 ~r ~p.

Example 59 ~ 4S

In order to demonstrate that aluminum surfaces coated with a coating solution containing gluconic acid, zirconium and fluoride undergo the so-called "muffle test", while aluminum surfaces coated with a like coating solution free of gluconic acid do not, a number of aluminum cans were coated with solutions having the compositions shown in Table XIV below.
The coated cans were then heated at a temperature of 900F for 5 minutes and the color of the cans was observed. The results observed are set forth below in Table XIV. The solutions employed each had a pH of 4.25, obtained by addition of con-centrated nitric acid, and were supplied at the temperatures shown in Table XIV.

TA~LE XIII
Huttlo Tont Ronultn or Cootod Alumlnuo Surraol~r (NN4)2Zrr6 Oluoonlo Aald 8urr~loo Color At~or Ro~tlnB
Dl- NO, ~IS X 10 3) (1~X 10 3) _ TO~ID. ~F) t 900F rOr 5 ~lnut-o 1. 25 0 125 ~llvor 2 1.25 0 135 811v-r 3 1.25 O.S 125 llght goldon bro~ln 4 1.25 0.5 135 llght gold-r brolln Cl-on-d Orly 811v-r In summary, it can be said that the present invention provides the means for forming on an aluminum surface a non-chromate coating which is colorless and clear without modifying the appearance of the aluminum surface. The coated surface exhibits improved corrosion resistance, as exemplified by the test results reported above, and exhibits excellent adhesion to overlying siccative coatings formed from either water-based or organic-solvent based coating compositions.

.;' j

Claims (32)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An acidic aqueous coating solution capable of forming a non-chromate, clear and colorless, corrosion-resistant coating on an aluminum surface and containing at least about 0.5 x 10-3 mole/liter of a metal selected from the group consisting of zirconium, hafnium, titanium, and mixtures thereof, fluoride in an amount at least sufficient to combine with all of said metal, and characterized in that it contains one or more of the follow-ing organic compounds: at least about 10 ppm of a surfactant, or at least about 0.025 x 10-3 mole/liter of a polyhydroxy compound having no more than 7 carbon atoms, or a mixture of said surfactant and said polyhydroxy compound, said solution being free of phosphate and boron when the organic compound is the polyhydroxy compound.

2. The coating solution of claim 1 wherein the pH of said solution is about 1.5 to about 5.

3. The coating solution of claim 1 wherein the amount of fluoride is at least about 4 moles per mole of said metal.

4. The coating solution of any one of claims 1-3 including also nitric acid.

5. The coating solution of claim 1 wherein said metal is zirconium and the organic compound is said surfactant, said zirconium being present in an amount of about 0.75 x 10-3 to about 2 x 10-3, said surfactant being present in an amount of about 10 ppm to about 500 ppm, said solution having a pH of about 3.5 to about 4.5.

6. The coating solution of claim 5 wherein the pH of said solution is about 3.7 to about 4.3, the amount of zirconium is about 1 x 10-3 to about 1.75 x 10-3 mole/liter and the amount of surfactant is about 20 to about 100 ppm.

7. The coating solution of claim 1 or 5 wherein the surfactant is selected from the group consisting of low-foaming alkyl polyethoxylated ethers and low-foaming polyethoxylated straight chain alcohols.

8. The coating solution of claim 6 wherein the surfactant is a nonionic surfactant.

9. The coating solution of claim 1 or 5 including one or more of glutaric, ascorbic, maleic, or salicylic acid.

10. The coating solution of claim 1 or 5 including also tannin.

11. The coating solution of claim 5, 6 or 8 including also at least about 0.025 x 10-3 mole/liter of said polyhydroxy compound.

12. The coating solution of claim 5, 6 or 8 including also at least about 10 ppm of a boron compound.

13. The coating solution of claim 5, 6 or 8 including also at least about 10 ppm of boric acid.

14. The coating solution of claim 1 wherein the metal is zirconium, the organic compound is said polyhydroxy compound, and the pH of the solution is about 3 to about 5.

15. The coating solution of claim 5 or 14 wherein the source of the zirconium is a compound selected from the group consisting of ammonium fluozirconate and fluozirconic acid.

16. The coating solution of claim 14, wherein the solution contains about 0.5 x 10-3 to about 1.75 x 10-3 mole/liter of zirconium and about 0.3 x 10-3 to about 1.75 x 10-3 mole/liter of said polyhydroxy compound.

17. The coating solution of claim 14 or 16, wherein the pH
of the solution is about 3 to about 4.

18. The coating solution of claim 1, wherein the poly-hydroxy compound is selected from the group consisting of gluconic acid, salts of gluconic acid, sorbitol, mannitol, dextrose, ethylene glycol, glycerine, and glucoheptonate.

19. The coating solution of claim 18 wherein the poly-hydroxy compound is selected from the group consisting of gluconic acid and salts of gluconic acid.

20. The coating solution of claim 19 wherein the source of said polyhydroxy compound is glucono-delta-lactone or glucono-gamma-lactone.

21. A process for forming a non-chromate, corrosion-resistant coating on an aluminum surface characterized by contacting said surface, for at least about 5 seconds with the acidic aqueous coating solution according to claim 1.

22. The process of claim 21 wherein the surface is contacted with the coating solution by spraying.

23. The process of claim 21 including applying to said coating an overlying siccative coating.

24. The process of claim 23 wherein said siccative coating is a water-borne coating.

25. The process of claim 24 wherein the water-borne coating is a polyester coating.

26. The process of claim 21 wherein the aluminum surface is contacted, at a solution temperature of at least about 110°F, with the coating solution of claim 5 or 6, said solution including also at least about 0.025 x 10-3 mole/liter of said polyhydroxy compound.

27. The process of claim 21 wherein the aluminum surface is contacted with the coating solution of claim 5 or 6 at a solution temperature of at least about 90 F to about 140°F.

28. An aluminum surface having a non-chromate, corrosion resistant coating formed thereon according to the process of claim 21, 22 or 25.

29. A continuous process for forming a non-chromate, corrosion resistant coating on an aluminum surface comprising contacting said surface, for at least about 5 seconds, at a solution temperature of at least about 110°F, with the coating solution of claim 5 or 6, said solution including also at least about 0.025 x 10-3 mole/liter of said polyhydroxy compound, and replenishing the coating solution as necessary with aqueous replenishing concentrate so as to maintain the concentrations of ingredients in the coating solution, said replenishing concentrate containing about 31 x 10-3 to about 251 x 10-3 mole/liter of zirconium, about 19 x 10-3 to about 148 x 10-3 mole/liter of polyhydroxy compound, and a material which is a source of about 90 x 10-3 to about 695 x 10-3 mole/liter of uncomplexed available fluoride.

30. A continuous process for forming a non-chromate, corrosion resistant coating on an aluminum surface comprising contacting said surface, for at least about 5 seconds, at a solution temperature of at least about 90°F to about 140°F, with the coating solution of claim 5 or 6, and replenishing the coating solution as necessary with aqueous replenishing concentrate so as to maintain the concentrations of ingredients in the coating solution, said replenishing concentrate contain-ing about 0.05 to about 0.5 mole/liter of zirconium, about 0.2 to about 10 mole/liter of fluoride, and about 1 to about 100 g/l of surfactant.

31. An aqueous concentrate such that an aqueous coating solution containing about 0.5 to about 10 weight percent of the concentrate has a pH within the range of about 3 to about 5 and consists essentially of at least about 0.5 x 10-3 mole/liter of zirconium or hafnium or a mixture thereof, at least about 0.025 x 10-3 mole/liter of a water soluble poly-hydroxy compound having no more than 7 carbon atoms, and at least sufficient fluoride to combine with and form a soluble complex with all of the zirconium and hafnium present in the solution, said coating solution being free of phosphate and boron and capable of forming a uniformly colorless and clear non-chromate coating on an aluminum surface.

32. An aqueous concentrate such that an aqueous coating solution containing about 0.5 to about 10 weight percent of the concentrate is effective in forming a non-chromate coating on aluminum, is acidic and consists essentially of: (A) at least about 0.5 x 10-3 m/l of one or more of zirconium, titanium, and hafnium; (B) fluoride in an amount at least sufficient to combine with substantially all of the Zr, Ti, or Hf to form a complex therewith; and also (C) at least about 10 ppm of surfactant.