Trivalent Chromium-Containing Composition for Use in Corrosion Resistant Coatings on Metal Surfaces

• US 20100132843A1
• Filed: 05/10/2007
• Published: 06/03/2010
• Est. Priority Date: 05/10/2006
• Status: Active Grant

• Current Assignee: Henkel AG & Co KGaA
• Original Assignee: Henkel AG & Co KGaA
• Inventors: Kramer, Kirk
• Granted Patent: US 9,487,866 B2
• Time in Patent Office: Days
• US Class Current: 148/247
• CPC Class Codes: B32B 15/017 one layer being formed of aluminium or an aluminium alloy, another layer being formed of an alloy based on a non ferrous metal other than aluminium
• CPC Class Codes: B32B 15/043 of metal B32B15/01 takes precedence
• CPC Class Codes: B32B 15/20 comprising aluminium or copper B32B15/016 and B32B15/017 take precedence
• CPC Class Codes: B32B 2307/752 Corrosion inhibitor
• CPC Class Codes: C23C 22/34 containing fluorides or complex fluorides
• CPC Class Codes: C23C 22/83 Chemical after-treatment
• CPC Class Codes: C23C 2222/10 Use of solutions containing trivalent chromium but free of hexavalent chromium
• CPC Class Codes: C23C 8/04 Treatment of selected surface areas, e.g. using masks
• CPC Class Codes: C23C 8/42 only one element being applied

Abstract

A low sludge trivalent chromium based conversion coating bath is provided which forms corrosion resistant coatings on aluminum and aluminum alloys by immersion in aqueous solutions containing trivalent chromium ions and fluorometallate ions followed by optional rinsing. Trivalent chromium coated aluminum also serves as an effective base for paint primers.

Claims

1. A composition for coating a metal surface, said composition comprising water and:

(A) a component of fluorometallate anions, each of said anions consisting of;

(i) at least four fluorine atoms; and

(ii) at least one atom of an element selected from the group consisting of titanium, zirconium, hafnium, silicon, aluminum, and boron, and, optionally, one or both of

(iii) at least one ionizable hydrogen atom; and

(iv) at least one oxygen atom;

(B) a component of water soluble chromium fluoride;

said composition being substantially free of hexavalent chromium and storage stable at ambient temperature for at least 2 weeks.

2. The composition according to claim 1, wherein the fluorometallate anions are selected from the group consisting of fluorosilicate, fluorotitanate, and fluorozirconate anions.

3. The composition according to claim 1, wherein the fluorometallate anions include fluorozirconate anions in a concentration within a range from about 0.4 to 100 g/kg;

water soluble chromium fluoride in a concentration within a range from about 4 to 100 g/l and said liquid composition comprising not more than 0.06% of dispersed silica and silicates.

4. The composition according to claim 1, wherein trivalent chromium and zirconium are present in a ratio of trivalent chromium to zirconium in a range of 0.725:

1 to 39;

1.

5. The composition according to claim 1, wherein said composition dried in place on an aluminum substrate provides corrosion resistance such that less than about 3 pits per 24 square inches develop when said substrate is subjected to 5% neutral salt spray at 95°

F. ASTMB-117 for at least 336 hours.

6. The composition according to claim 1, wherein:

the fluorometallate anions include fluorozirconate anions;

the concentration of fluorozirconate anions is within a range from about 1 to about 10 g/kg;

the concentration of chromium fluoride is within a range from about 4 g/l to about 100 g/l and

the ratio of trivalent chromium to zirconium is in the range of 7 to 17.

11. A process for coating or touching up or both coating and touching up a surface, said surface comprising at least one area of bare metal, at least one area of coating over an underlying metal substrate, or both of at least one area of bare metal and at least one area of coating over an underlying metal substrate, said process comprising operations of:

(I) covering the surface to be coated, touched up, or both coated and touched up with a layer of a liquid composition of claim 1; and

(II) drying the liquid layer formed in operation (I) to form a coated surface.

12. The process according to claim 11, wherein the surface comprises at least one area of bare metal and at least one area of coating over an underlying metal substrate;

and in operation (I), the liquid layer is formed over the at least one area of bare metal.

13. The process according to claim 11, wherein, in said liquid composition used in operation (I):

the fluorometallate anions are selected from the group consisting of fluorosilicate, fluorotitanate, and fluorozirconate anions.

14. The process according to claim 11, wherein, in said liquid composition used in operation (I):

the fluorometallate anions include fluorozirconate anions;

the concentration of fluorozirconate anions is within a range from about 1 to about 10 g/kg;

the concentration of chromium(III) ions is greater than 0 and not more than 100 g/l.

15. The process according to claim 14, wherein:

the surface comprises at least one area of bare metal adjacent to at least one area of coating over an underlying metal substrate,

said at least one area of coating over an underlying metal substrate comprising a first portion and a second portion,

in operation (I), the liquid layer is formed over both the area of bare metal and at least the first portion of said adjacent area of coating over an underlying metal substrate; and

the coating over an underlying metal substrate is selected from the group consisting of a phosphate conversion coating, a chromate conversion coating, and a conversion coating produced by contacting a surface consisting predominantly of iron, titanium, aluminum, magnesium and/or zinc and alloys thereof with an acidic treating solution comprising at least one of fluorosilicate, fluorotitanate, and fluorozirconate.

16. The process according to claim 13, wherein, in the liquid composition used in operation (I):

the fluorometallate anions include fluorozirconate anions;

the concentration of fluorozirconate anions is within a range from about 1 to about 8 g/kg;

the concentration of chromium fluoride is within a range from about 4 g/l to about 100 g/l; and

a concentration of hydrofluoric acid is present within a range from about 0.70 to about 1.3 ppt.

17. An article of manufacture having at least one portion that comprises the coated surface of claim 11.

18. The article of manufacture of claim 17 wherein the at least one portion comprises aluminum or aluminum alloy.

19. The article of manufacture of claim 17 said coated surface being essentially free of hexavalent chromium and having corrosion resistance properties characterized by less than about 3 pits per 24 square inches when subjected to 5% neutral salt spray at 95°

F. ASTMB-117 for at least 336 hours.

7. A storage stable composition made by mixing together a first mass of water and at least the following components:

(A) a second mass of a water-soluble source of fluorometallate anions to provide in the composition from about 1 to about 100 g/kg of the fluorometallate anion, each of said anions consisting of;

(i) at least four fluorine atoms; and

(ii) at least one atom of an element selected from the group consisting of titanium, zirconium, hafnium, silicon, aluminum, and boron, and, optionally, one or both of

(iii) at least one ionizable hydrogen atom; and

(iv) at least one oxygen atom;

(B) a third mass in an amount of 23 g/l to about 100 g/l of a water soluble source of trivalent chromium cations;

(C) an optional fourth mass of water-soluble source of fluorine anions;

(D) an optional fifth mass of a component of surfactant and/or water soluble thickener;

said composition being free of water-soluble organic corrosion inhibitor and water-soluble organic stabilizing agents and storage stable at ambient temperature for at least 2 weeks.

8. The composition according to claim 7, wherein said liquid composition comprises not more than 0.06% of dispersed silica and silicates.

9. The composition according to claim 7, wherein:

the second mass comprises fluorozirconate anions in an amount that corresponds to a concentration, in said composition, that is within a range from about 1 to about 8 g/kg; and

there is mixed into said composition a fifth mass of fluorinated alkyl ester surfactant molecules that corresponds to a concentration, in said composition, that is within a range from about 0.070 to about 0.13 ppt.

10. The composition according to claim 7, wherein the third mass is selected from the group consisting of nitrates, sulfates, and fluorides of chromium (III).