HIGH MOLECULAR MASS, SATURATED HYDROCARBON ACID BASED CHEMICAL CONVERSION COATING COMPOSITION

Abstract

Disclosed is a method of using a high molecular mass, saturated hydrocarbon acid to generate a chemical conversion coating on light metal surfaces such as aluminum, magnesium, and titanium and their alloys.

Claims

1. A conversion coating prepared by a process comprising the steps of: (a) contacting a substrate comprising a metal selected from aluminum, magnesium, or titanium, with a saturated hydrocarbon acid having a molecular mass of at least about 340 Da; and then (b) heating the substrate of step (a) to a temperature at or above the melting point of the saturated hydrocarbon acid, for a time sufficient to yield a conversion coating on the substrate.

2. The conversion coating of claim 1, wherein the saturated hydrocarbon acid of step (a) has a molecular mass between about 340 Da and 2,000 Da.

3. The conversion coating of claim 1, wherein the saturated hydrocarbon acid of step (a) has a molecular mass between about 340 Da and 1,000 Da.

4. The conversion coating of claim 1, wherein the saturated hydrocarbon acid of step (a) has between 22 carbon atoms and 70 carbon atoms.

5. The conversion coating of claim 1, wherein the saturated hydrocarbon acid of step (a) has between 22 carbon atoms and 50 carbon atoms.

6. The conversion coating of claim 1, wherein the saturated hydrocarbon acid of step (a) has between 22 carbon atoms and 40 carbon atoms.

7. The conversion coating of claim 1, wherein the saturated hydrocarbon acid of step (a) has between 22 carbon atoms and 30 carbon atoms.

8. The conversion coating of claim 1, wherein the saturated hydrocarbon acid of step (a) is linear or branched.

9. The conversion coating of claim 1, wherein the saturated hydrocarbon acid of step (a) comprises two or more fused rings.

10. A method of creating a conversion coating, the method comprising: (a) contacting a substrate comprising a metal selected from aluminum, magnesium, or titanium, with a saturated hydrocarbon acid having a molecular mass of at least about 340 Da; and then (b) heating the substrate of step (a) to a temperature at or above the melting point of the saturated hydrocarbon acid, for a time sufficient to yield a conversion coating on the substrate.

11. The method of claim 10, wherein the saturated hydrocarbon acid of step (a) has a molecular mass between about 340 Da and 2,000 Da.

12. The method of claim 10, wherein the saturated hydrocarbon acid of step (a) has a molecular mass between about 340 Da and 1,000 Da.

13. The method of claim 10, wherein the saturated hydrocarbon acid of step (a) has between 22 carbon atoms and 70 carbon atoms.

14. The method of claim 10, wherein the saturated hydrocarbon acid of step (a) has between 22 carbon atoms and 50 carbon atoms.

15. The method of claim 10, wherein the saturated hydrocarbon acid of step (a) has between 22 carbon atoms and 40 carbon atoms.

16. The method of claim 10, wherein the saturated hydrocarbon acid of step (a) has between 22 carbon atoms and 30 carbon atoms.

17. The method of claim 10, wherein the saturated hydrocarbon acid of step (a) is linear or branched.

18. The method of claim 10, wherein the saturated hydrocarbon acid of step (a) comprises two or more fused rings.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0036] The method proceeds as follows: A high molecular mass saturated hydrocarbon acid is applied to the metal surface to be coated, preferably an aluminum, magnesium, or titanium workpiece, or a workpiece made of an alloy of any of these metals. The hydrocarbon acid may be applied neat or dissolved/dispersed in any suitable solvent (typically water or a low molecular mass hydrocarbon such as hexane). The molecular mass of the saturated hydrocarbon acid should be at least 340 Da. Thus, the smallest saturated hydrocarbon acid employed in the method is docosanoic acid (also known as behenic acid), which has 22 carbon atoms and a molecular mass of 340.59 Da, C.sub.21H.sub.43COOH (CAS No. 112-85-6). Larger saturated hydrocarbon acids include, but are not limited to, C.sub.23 tricosanoic acid CH.sub.3(CH.sub.2).sub.21COOH, C.sub.24 tetracosanoic acid CH.sub.3(CH.sub.2).sub.22COOH, C.sub.25 pentacosanoic acid CH.sub.3(CH.sub.2).sub.23COOH, C.sub.26 hexacosanoic acid CH.sub.3(CH.sub.2).sub.24COOH, etc. The analogous C.sub.70 saturated acid has a molecular mass of 1,013.85 Da. The analogous C.sub.140 saturated acid has a molecular mass of 1,995.71 Da. The preferred molecular mass, though, of the saturated hydrocarbon acid is between about 340 Da to about 1000 Da, thus from approximately C.sub.22 to approximately C.sub.70 saturated organic acids.

[0037] The organic acid is applied to the metal surface to be coated. As noted above, the acid can be applied neat or dispersed/dissolved in a suitable solvent or vehicle. The metal surface is then heated to melt the applied acid, which initiates the reaction that yields the conversion coating. The workpiece is then cooled to room temperature. Any excess hydrocarbon acid is removed with a suitable cleaning agent. The result is a chemical conversion coating on the metal surface. The restulting conversion coating is resistant to alkaline cleaning solutions and stripping agents such as benzene, toluene, and the like. The following examples illustrate the process:

EXAMPLE 1

[0038] A 3 inch4 inch (7.62 cm10.16 cm) sample of aluminum 0.0625 inches (15.8750 mm) thick was made the cathode in a electrochemical cell containing 5% potassium hydroxide in distilled water at 12 volts and 30 amps per square foot (929.03 cm.sup.2) for about ten seconds to remove any existing soil and/or existing oxides from the metal surface. The sample was then rinsed in distilled water, dried, weighed, and coated with a thin film of stearic acid (C.sub.18, molecular mass 284.5 Da). The sample was then gently heated until the stearic acid melted and then allowed to cool to room temperature. Any excess stearic acid was then dissolved off the sample with a strong alkaline cleaner. The sample was then rinsed in distilled water and dried. There was no increase in the mass of the metal or increase in the thickness of the metal sample as would be the case if a chemical reaction had taken place between the metal sample and the stearic acid. Treating the sample with boiling water quickly oxidized the metal surface.

EXAMPLE 2

[0039] A 3 inch4 inch (7.62 cm10.16 cm) sample of aluminum 0.0625 inches (15.8750 mm) thick was made the cathode in a electrochemical cell containing 5% potassium hydroxide in distilled water at 12 volts and 30 amps per square foot (929.03 cm.sup.2) for about ten seconds to remove any existing soil and/or existing oxides from the metal surface. The sample was then rinsed in distilled water, dried, weighed, and coated with a thin film of roccellic acid (C.sub.17, a dibasic acid with a molecular mass 300.43 Da). The sample was gently heated until the roccellic acid melted and cooled to room temperature. Any excess roccellic acid was then dissolved off the metal surface with a strong alkaline cleaner. The sample was then rinsed in distilled water and dried. There was no increase in the mass of the metal or increase in the thickness of the metal sample as would be the case if a chemical reaction had taken place between the metal and the roccellic acid. Treating with boiling water oxidized the metal surface.

EXAMPLE 3

[0040] A 3 inch4 inch (7.62 cm10.16 cm) sample of aluminum 0.0625 inches (15.8750 mm) thick was made the cathode in a electrochemical cell containing 5% potassium hydroxide in distilled water at 12 volts and 30 amps per square foot (929.03 cm.sup.2) for about ten seconds to remove any existing soil and/or existing oxides from the metal surface. The sample was then rinsed in distilled water, dried, weighed, and coated with a thin film of docosanoic acid (C.sub.22, molecular mass 340.57 Da). The sample was then gently heated to melt the docosanoic acid and allowed to cool to room temperature. Any excess docosanic acid was then dissolved off the metal sample with a strong alkaline cleaner. The metal was then rinsed in distilled water and dried. There was an increase in the mass of the metal and the thickness of the metal sample, indicating that a chemical reaction had taken place between the metal and the organic acid in question. Water beaded when applied to the surface of the sample. Treating the sample with boiling water did not oxidize the metal.

EXAMPLE 4

[0041] An aluminum sample was prepared as described previously. The sample was then coated with a thin film of lithocholic acid (C.sub.24, molecular mass 376.58 Da):

##STR00001##

The sample was gently heated until the lithocholic acid melted and cooled to room temperature. Excess lithocholic acid was then dissolved off the metal with a strong alkaline cleaner. The metal was then rinsed in distilled water and dried. There was an increase in the mass of the sample and an increase in the thickness of the sample, indicating that a chemical reaction had taken place between the metal and the lithocholic acid. Water beaded when applied to the surface of the sample. Treating with boiling water did not oxidize the metal.

EXAMPLE 5

[0042] An aluminum sample was prepared as described previously. The sample was then coated with a thin film of deoxycholic acid (C.sub.24, molecular mass 392.58):

##STR00002##

The sample was then heated to melt the deoxycholic acid and allowed to cool to room temperature. Any excess material was then dissolved off the metal with a strong alkaline cleaner. The metal was then rinsed in distilled water and dried. There was an increase in the mass of the metal and the thickness of the metal sample, indicating that a chemical reaction had taken place between the metal and the organic acid in question. Water beaded when applied to the surface of the sample. Treating the sample with boiling water did not oxidize the metal.

EXAMPLE 6

[0043] An aluminum sample was prepared as described previously. The sample was then coated with a thin film of a synthetic saturated hydrocarbon acid (molecular mass 700 Da). and then heated to its melting point and then allowed to cool below its melting point. Any excess acid was then dissolved off the metal with a strong alkaline cleaner. The metal was then rinsed in distilled water and dried. There was an increase in the mass of the metal and the thickness of the metal sample, indicating a chemical reaction had taken place between the metal and the organic acid in question. Water beaded when applied to the surface of the sample. Treating the sample with boiling water did not oxidize the metal. In addition, conventional lacquer paint exhibited excellent adhesion to the treated metal surface.

EXAMPLE 7

[0044] An aluminum sample was prepared as described previously. The sample was then coated with a thin film of a synthetic saturated hydrocarbon wax acid (molecular mass 993 Da). The sample was heated until the wax melted and was then cooled to room temperature. Any excess was was then dissolved off the metal with benzene followed by cleaning the metal with a strong alkaline cleaner. The metal was then rinsed in distilled water and dried. There was an increase in the mass of the sample and the thickness of the sample, indicating that a chemical reaction had taken place between the metal and the organic wax. Water beaded when applied to the surface of the sample. Treating the sample with boiling water did not oxidize the metal. In addition, conventional lacquer paint exhibited excellent adhesion to the treated metal surface.

EXAMPLE 8

[0045] A 3 inch8 inch (7.62 cm20.32 cm) aluminum alloy 5052, 0.030 inches (0.76 mm) was made the cathode in a electrochemical cell containing 5% potassium hydroxide in distilled water at 12 volts and 30 amps per square foot (929.03 cm.sup.2) for about ten seconds to remove any existing soil and/or existing oxides from the metal surface. The sample was then rinsed in distilled water, dried, weighed, and coated with a thin film of stearic acid (molecular mass 284.5 Da). The sample was gently heated until the stearic acid melted allowed to cool to room temperature. Any excess stearic acid was then dissolved off the metal with a strong alkaline cleaner. The metal was then rinsed in distilled water and dried. There was no increase in the mass of the metal or increase in the thickness of the metal sample as would be the case if a chemical reaction had taken place between the metal and the stearic acid. Treating the sample with boiling water caused oxidation of the surface.

EXAMPLE 9

[0046] A sample was prepared as in Example 8 and coated with a thin film of heneicosanoic acid (molecular mass 326.56 Da). The sample was then heated to melt the acid and allowed to cool to room temperature. Any excess heneicosanoic acid was then dissolved off the metal with a strong alkaline cleaner. The metal was then rinsed in distilled water and dried. There was no increase in the mass of the metal or increase in the thickness of the metal sample as would be the case if a chemical reaction had taken place between the metal and the heneicosanoic acid. Treating the sample with boiling water caused oxidation of the surface.

EXAMPLE 10

[0047] A sample was prepared as in Example 8 and then coated with a thin film of docosanoic acid (molecular mass 340.38). The sample was heated to melt the acid and allowed to cool to room temperature. Any excess docosanoic acid was then dissolved off the metal with a strong alkaline cleaner. The metal was then rinsed in distilled water and dried. There was an increase in the mass of the metal and the thickness of the metal sample, indicating a chemical reaction had taken place between the metal and the organic acid. Water beaded when applied to the surface of the sample. Treating the sample with boiling water did not oxidize the metal.

EXAMPLE 11

[0048] A sample was prepared as in Example 8 and then coated with a thin film of a synthetic saturated hydrocarbon acid having a molecular mass of 700 Da. The sample was then heated to melt the hydrocarbon and allowed to cool to room temperature. Any excess hydrocarbon acid was then dissolved from the sample surface with a strong alkaline cleaner. The sample was then rinsed in distilled water and dried. There was an increase in the mass of the metal and the thickness of the metal sample, indicating that a chemical reaction had taken place between the metal and the hydrocarbon acid. Water beaded when applied to the surface of the sample. Treating the sample with boiling water did not oxidize the metal. In addition, conventional lacquer paint exhibited excellent adhesion to the treated metal surface.

EXAMPLE 12

[0049] A 2 inch2 inch (5.08 cm10.16 cm) sample of magnesium 0.035 inches (0.889 mm) thick was made the cathode in a electrochemical cell consisting of 5% potassium hydroxide in distilled water solution at twelve volts and thirty amps per square foot for 30 seconds to remove any existing soil and/or existing oxides from the sample, rinsed in distilled water, dried, weighed and then coated with a thin film of a synthetic saturated hydrocarbon acid (molecular mass 700 Da). The sample was then heated to melt the hydrocarbon acid and allowed to cool to room temperature. Any excess hydrocarbon acid was then dissolved off the metal with a strong alkaline cleaner. The sample was then rinsed in distilled water and dried. There was an increase in the mass of the metal and the thickness of the metal sample, indicating a chemical reaction had taken place. Water beaded when applied to the surface of the sample. Treating the sample with boiling water did not oxidize the metal. In addition, conventional lacquer paint exhibited excellent adhesion to the treated metal surface.

EXAMPLE 13

[0050] A sample was prepared as in Example 12 and then coated with a thin film of roccellic acid (molecular mass 300.43 Da). The sample was heated to melt the roccellic acid and allowed to cool to room temperature. Any excess roccellic acid was then dissolved off the metal with a strong alkaline cleaner. The sample was then rinsed in distilled water and dried. There was no increase in the mass of the metal or increase in the thickness of the metal sample as would be the case if a chemical reaction had taken place between the metal and the organic acid in question. Treating the sample with boiling water quickly oxidized it.

EXAMPLE 14

[0051] A sample was prepared as in Example 12 and then coated with a thin film of heneicosanoic acid (molecular mass 326.56), then heated to its melting point and allowed to cool to room temperature. Any excess heneicosanoic acid was then dissolved off the metal with a strong alkaline cleaner. The metal was then rinsed in distilled water and dried. There was no increase in the mass of the metal or increase in the thickness of the metal sample as would be the case if a chemical reaction had taken place between the metal and the organic acid in question. Treating with boiling water quickly oxidized the sample surface.

EXAMPLE 15

[0052] A sample was prepared as in Example 12 and then coated with a thin film of docosanoic acid. The sample was then heated to melt the acid and allowed to cool to room temperature. Any excess docosanoic acid was then dissolved off the metal with a strong alkaline cleaner. The metal was then rinsed in distilled water and dried. There was an increase in the mass of the metal and the thickness of the metal sample, indicating a chemical reaction had taken place. Water beaded when applied to the surface of the sample. Treating the sample with boiling water did not oxidize the metal.

EXAMPLE 16

[0053] A 4 inch4.5 inch (10.16 cm11.43) sample of magnesium alloy AZ91 D 0.035 inches thick was made the cathode in a electrochemical cell consisting of 5% percent potassium hydroxide in distilled water solution at twelve volts and thirty amps per square foot for 30 seconds to remove any existing soil and/or existing oxides from the metal's surface, rinsed in distilled water, dried, weighed and then coated with a thin film of a synthetic saturated hydrocarbon acid (molecular mass 700 Da). The sample was then heated melt the hydrocarbon and cooled to room temperature. Any excess hydrocarbon acid was then dissolved off the metal with a strong alkaline cleaner. The metal was then rinsed in distilled water and dried. There was an increase in the mass of the metal and the thickness of the metal sample, indicating chemical reaction had taken place between the metal and the organic acid in question. Water beaded when applied to the surface of the sample. Treating the sample with boiling water did not oxidize the metal. In addition, conventional lacquer paint exhibited excellent adhesion to the treated metal surface.

EXAMPLE 17

[0054] A sample was prepared as in Example 16 and then coated with a thin film of stearic acid (molecular mass 284.5). The sample was the heated to melt the stearic acid and allowed to cool to room temperature. Any excess stearic acid was then dissolved off the metal with a strong alkaline cleaner. The metal was then rinsed in distilled water and dried. There was no increase in the mass of the metal or increase in the thickness of the metal sample as would be the case if a chemical reaction had taken place. Treating with boiling water quickly oxidized the metal.

EXAMPLE 18

[0055] A sample was prepared as in Example 16 and then coated with a thin film of a synthetic saturated hydrocarbon wax acid (molecular mass 993). The sample was heated to melt the wax and then cooled to room temperature. Any excess wax was then dissolved off the metal with benzene followed by cleaning the metal with a strong alkaline cleaner. The metal was then rinsed in distilled water and dried. There was an increase in the mass of the metal and the thickness of the metal sample, indicating a chemical reaction had taken place. Water beaded when applied to the surface of the sample. Treating the sample with boiling water did not oxidize the metal. In addition, conventional lacquer paint exhibited excellent adhesion to the treated metal surface.