Calcium borate/amino carboxylate corrosion inhibitors

Abstract: A synergistic combination of a calcium borate and an amino carboxylate for use as a corrosion inhibitor in coating formulations. Preferably, the corrosion inhibitor is a powder formed by treating a calcium borate with an amino carboxylate.

Description: BACKGROUND OF THE INVENTION The present invention relates to a corrosion inhibitor for use in coating formulations such as primers or paints. The corrosion inhibitor comprises synergistic combinations of a calcium borate and an amino carboxylate. As is known in the art, corrosion inhibitors are incorporated into coating formulations to provide or enhance protection of underlying metal surfaces against oxidation and electrochemical corrosion. Known corrosion inhibitors include zinc chromate, strontium chromate, barium metaborate, calcium borate, zinc phosphate, calcium boro-silicate and zinc phospho oxide. These known inhibitors are all powdered pigments which are incorporated into coating formulations under high-shear agitation during the pigment grinding stage along with other common pigments such as titanium dioxide, calcium carbonate, clay, mice and barium sulfate. Calcium borates are known corrosion inhibitors. Corrosion inhibiting coating compositions containing calcium metaborate are described in U.S. Patent No. 3,380,836. However, when calcium borates are used by themselves in coating compositions they can cause the coating to be susceptible to blistering after being applied to a metal surface. See Example. The use as a liquid corrosion inhibitor of the COTROL 18-8 amino carboxylate product available from Cas Chem, Inc., or through resale from Buckman Laboratories, Inc., has recently been reported in the trade literature. Unlike traditional corrosion inhibitors which are in pigment or powder form, the amino carboxylate product, being a liquid, is not incorporated by itself into coating formulations during the pigment grinding stage, but rather during the subsequent let-down stage along with other liquid components, i.e., resin emulsions, dispersants, etc. When the amino carboxylate is used by itself to inhibit corrosion in a coating formulation, the coating formulation can be susceptible to softening of the final coating and loss of adhesion to the metal surface. Thus a coating formulation containing an amino carboxylate such as the COTROL 18-8 product might be scraped off the metal surface to which it is applied, leaving the surface unprotected. SUMMARY OF THE INVENTION It is an object of the present invention to provide a corrosion inhibitor which can give increased corrosion resistance to a coating formulation and can reduce the susceptibility of the coating to blistering, softening and loss of adhesion. It is a further object of the present invention to provide a corrosion inhibitor capable of having the above properties and which can be in a form easily and routinely handled, such as a pigment or powder. Additionally, it is an object of the present invention to provide (1) a coating formulation containing such a corrosion inhibitor, (2) a method of preventing or reducing corrosion of a surface susceptible to corrosion, such as a metal surface, comprising use of the corrosion inhibitor, and (3) a surface coated with a composition containing the corrosion inhibitor. The above objects can be accomplished with a corrosion inhibitor comprising synergistically effective amounts of a calcium borate and an amino carboxylate. Corrosion of a metal surface can be prevented or reduced by coating the metal surface with a coating formulation containing a corrosion-reducing amount of the corrosion inhibitor. DESCRIPTION OF THE INVENTION The corrosion inhibitor of the present invention comprises a combination of calcium borate and an amino carboxylate in a ratio of from 99:1 to 75:25. The synergistic combination can be achieved in at least two ways: 1) adding to a coating formulation the calcium borate and an amino carboxylate separately in the required ratio and 2) treating the calcium borate with an amino carboxylate to form a treated calcium borate pigment or powder, the calcium borate and the amino carboxylate being present in the required ratio. The calcium borate suitable for use may be of any available form such as, but not limited to, calcium borate, calcium orthoborate, calcium metaborate, calcium pyroborate, calcium sesquiborate or hydrates thereof. The preferred calcium borate is calcium metaborate or a hydrate thereof. Calcium metaborate is available from American Borate Company of Virginia Beach, Va and is sold as TURKISH COLEMANITE product. The amino carboxylate preferably employed in the invention is the COTROL 18-8 product, described above, which is sold by Cas Chem, Inc. and is available for resale from Buckman Laboratories, Inc. This liquid amino carboxylate was tested in coatings in conjunction with traditional calcium borate corrosion inhibitors to determine optimum use levels with lowest cost. Surprisingly, it was discovered that the use of the amino carboxylate in the presence of calcium borate can yield increased corrosion protection that is superior to that of either corrosion inhibitor used by itself and can also provide other performance benefits. A first embodiment of this invention is achieved by adding a calcium berate and an amino carboxylate separately to a coating composition but in a total count which is synergistically effective to prevent or at least reduce corrosion of the metal surface to be coated. The calcium borate is added during the pigment grinding stage; the amino carboxylate is added during the let-down stage when other liquids are added. A second and preferred embodiment involves physically combining a calcium borate and an amino carboxylate into one product prior to addition to a coating formulation. This embodiment advantageously allows both inhibitors to be added to coating formulations as a single corrosion inhibitor in a pigment or powder form. The single corrosion inhibitor can have the properties of normal dry pigmented products and can be handled and processed like traditional corrosion inhibiting pigments. The corrosion inhibitor of this second embodiment is advantageously added to a coating formulation in the pigment grinding stage as is routinely done in the art. This corrosion inhibitor can be prepared using conventional liquid/powder mixing techniques such as spray/tumble mixing, spray-drying, or other conventional techniques. The corrosion inhibitors according to both embodiments of the invention comprise synergistically effective amounts of a calcium borate and an amino carboxylate for reduction or prevention of surface corrosion, namely in a ratio ranging from 99:1 to 75:25. In both embodiments, and particularly the second embodiment above, the components are combined in a more preferred ratio ranging from about 99:1 to about 80:20. The most preferred ratio of the calcium borate to amino carboxylate is 90:10 for both embodiments. Depending on the intended use of the surface to be coated, the corrosion inhibitor of the invention may be added to a coating formulation in an amount preferably ranging from about 0.5 to about 50 percent by weight of the coating formulation. Increased amounts of the corrosion inhibitor in the coating formulation are highly preferred where the surface to be coated will be used in an environment conducive to corrosion. The corrosion inhibitor of the present invention can be used in conventional latex-based and oil-based coating formations such as primers or paints. The corrosion inhibitor can be compatible with conventional resins employed in such coating formulations. The following example is intended to illustrate, not limit, the present invention. EXAMPLE A white long-oil alkyd primer coating formulation was prepared according to the formulation set forth in Table 1. This formulation was divided into three parts and to each was added 5.0 percent by weight of a corrosion inhibitor. Coating formulation 1 contained calcium metaborate, TURKISH COLEMANITE product, as the sole corrosion inhibitor. The amino carboxylate, COTROL 18-8 product, was incorporated as the sole corrosion inhibitor in coating formulation 2. In formulation 2, the amino carboxylate was added in the second step along with the other liquids. Coating formulation 3 contained a corrosion inhibitor comprising a synergistically effective amount of calcium metaborate, the TURKISH COLEMANITE product, and the amino carboxylate, COTROL 18-8 product, according to the first embodiment of the invention. Each of the coating formulations was applied as self-primed white long-oil alkyd primers onto cold-rolled steel Q-panels. White Long-Oil Alkyd Primer Formulation lbs./100 Gal. % By weight Beckosol P-470-70 (10-060) Alkyd Resin 214.0 18.8 Mineral Spirits Solvent 50.0 4.4 Soya Lecithin Dispersant 3.0 0.3 Bentone 38 Gel Thickener 25.0 2.2 Corrosion Inhibitor 57.0 5.0 Ti-Pure R-900 Titanium Dioxide 250.0 22.0 Nytal 300 Talc 220.0 19.3 Grind on High Speed Mill, then add the following: Beckosol P-470-70 (10-060) Alkyd Resin 214.0 18.8 6% Zirco Drier 6.0 0.5 6% Cobalt Naphthalene Drier 1.0 0.1 ASA Antiskimming Agent 2.0 0.2 Mineral Spirits Solvent 102.0 8.4 1144.0 100.0 Table 2 shows the corrosion resistance of coating formulations after 425 hours of salt-spray exposure according to ASTM B117. The ratings were made according to ASTM D 610 with 10 being no corrosion and 0 being corrosion over entire coating surface. Coating No. Inhibitor Corrosion Rating 1 5% Calcium borate 7 2 5% Amino carboxylate 7 3 4.5% Calcium borate 0.5% Amino carboxylate 9 Table 3 shows the blister resistance of the coating formulations after 425 hours of salt spray exposure according to ASTM B117. Ratings were made according to ASTM D714 with 10 being no blisters and 0 being large blisters; F = few, M = medium, MD = medium dense, D = dense. Coating No. Inhibitor Blister Resistance Rating(s) 1 5% Calcium borate 4M 2 5% Amino carboxylate 7MD 3 4.5% Calcium borate + 0.5% Amino carboxylate 10 Table 4 shows the coating integrity of the coating formulations after 425 hours of salt-spray exposure according to ASTM B117. Coating No. Inhibitor Coating Integrity 1 5% calcium borate Hard Film/Good Adhesion 2 5% amino carboxylate Softer film can be scratched from panel 3 4.5% calcium borate + 0.5% amino carboxylate Hard film/Good adhesion As seen from the above results, the coating containing the corrosion inhibitor of the present invention provided better corrosion protection to the steel panels than either of the coatings containing the calcium metaborate or the amino carboxylate corrosion inhibitors separately. The synergistic corrosion inhibitor of this invention not only yielded superior corrosion protection but also provided other improvements over either or the single inhibitors: (1) the synergistic combination of inhibitors did not cause blistering of the coating when exposed to a corrosive salt-fog environment, whereas calcium borate when used by itself does demonstrate the disadvantage of causing blister formulation; and (2) the synergistic combination did not cause film softening or a reduction in adhesion of the coating's film to the metal surface after exposure to salt-fog, whereas the amino carboxylate by itself did show some softening and reduction in adhesion.

Claims: Claims for the following Contracting States : AT, BE, CH, DE, DK, FR, GB, GR, IT, LI, LU, NL, SE A corrosion inhibitor comprising a calcium borate and an amino carboxylate wherein the ratio of said calcium borate to amino carboxylate is from 99:1 to 75:25. The corrosion inhibitor of claim 1 wherein said calcium borate is a powder and said calcium borate is treated with said amino carboxylate. The corrosion inhibitor of claim 1 wherein said ratio is from 99:1 to 80:20. The corrosion inhibitor of claim 3 wherein said ratio is about 90:10. The corrosion inhibitor of claim 1 wherein said calcium borate is calcium metaborate. A method of reducing the corrosion of a metal surface comprising coating said surface with a corrosion-reducing amount of the corrosion inhibitor of claim 1. A coating formulation comprising as corrosion inhibitors a calcium borate and an amino carboxylate wherein the ratio of said calcium borate to amino carboxylate is from 99:1 to 75:25. A coating formulation according to claim 7 comprising a corrosion inhibitor according to any of claims 1 to 6. The coating formulation of claim 7 wherein the corrosion inhibitors are added to said coating formulation in the amount of about 0.5 to about 50 percent by weight of said coating formulation. The coating formulation of claim 7 wherein said coating formulation is a paint. A method of reducing the corrosion of a metal surface comprising coating said surface with a corrosion-reducing amount of a coating formulation according to any one of claims 7 to 10. A surface coated with a coating formulation according to any one of claims 7 to 10. Claims for the following Contracting State : ES A method of reducing the corrosion of a metal surface comprising coating said surface with a corrosion-reducing amount of a corrosion inhibitor comprising a calcium borate and an amino carboxylate wherein the ratio of said calcium borate to amino carboxylate is from 99:1 to 75:25. The method of claim 1 wherein said calcium borate is a powder and said calcium borate is treated with said amino carboxylate. The method of claim 1 wherein said ratio is from 99:1 to 80:20. The method of claim 3 wherein said ratio is about 90:10. The method of claim 1 wherein said calcium borate is calcium metaborate. A method of reducing the corrosion of a metal surface comprising coating said surface with a corrosion-reducing amount of a coating formulation comprising as corrosion inhibitors a calcium borate and an amino carboxylate wherein the ratio of said calcium borate to amino carboxylate is from 99:1 to 75:25. The method of claim 6 wherein said calcium borate is a powder and said calcium borate is treated with said amino carboxylate. The method of claim 6 wherein said ratio is from 99:1 to 80:20. The method of claim 8 wherein said ratio is about 90:10. The method of claim 6 wherein said calcium borate is calcium metaborate. The method of claim 7 wherein the corrosion inhibitors are added to said coating formulation in the amount of about 0.5 to about 50 percent by weight of said coating formulation. The method of claim 7 wherein said coating formulation is a paint.

Inventors: DALTON DENNIS L, DALTON, DENNIS L.
Applicants: BUCKMAN LABOR INC, BUCKMAN LABORATORIES INTERNATIONAL, INC.
Application year: 1991
Main classification: C09D5
IPC codes: C23F11, C09D5