Anti-Corrosion Coating for Metals

This invention relates to anti-corrosion coatings and particularly such coatings for fabricated steel parts.

In the manufacture of automobiles and the like, there is a tendency for fabricated metal parts, such as steel parts, to corrode even after painting especially in the inside areas where portions of the metal are folded into close proximity to other portions and not painted.

Accordingly, among the objectives of the invention are to provide anti-corrosion compositions for metal which will protect the metal surfaces against corrosion even when portions of the part are folded on one another.

Basically, the anti-corrosion composition embodying the invention comprises a mixture of aluminum paste or zinc paste, microcrystalline wax, aromatic hydrocarbon resin, chlorinated rubber, natural barium sulfonate, chlorinated solvent, aromatic hydrocarbon solvent and mineral spirits.

Aluminum paste is well known material comprising 65-75% aluminum flake, by weight, and 25-35% solvent such as mineral spirits, by weight. Typical aluminum pastes are sold by Aluminum Company of America under the designations Standard Paste Nos. 6221 and 6240.

Zinc paste is a well known material comprising zinc flake and solvent such as mineral spirits. Typical zinc pastes are sold by United States Bronze Powders, Inc., under the designation Zinc Flake Paste 751.

The term microcrystalline wax is well understood in the art. A typical microcrystalline wax is sold by Shell Chemical Company under the trademark SHELLMAX 500 and has the following properties:

Another microcrystalline wax that has given satisfactory results is made by Mobil Oil Corporation and sold under the trademarks Mobilwax 2305 and Mobilwax 2305 BR having the following properties:

Aromatic hydrocarbon resins are low molecular weight, nonpolar, amber-colored thermoplastic resins produced from petroleum derived monomers. Typical resins are sold by Hercules Incorporated, Wilmington, Del., under the trademark PICCO.

Satisfactory results have been achieved utilizing resins sold by Hercules Incorporated under the trademark PICCO and having the following properties:

Chlorinated rubber is a rubber that contains 66+% combined chlorine. Typical chlorinated rubbers are manufactured by Hercules Incorporated, Wilmington, Del., and sold under the trademark Parlon and having the following properties:

The petroleum distillate may be one of the various types preferably having a boiling point ranging from 350.degree. to 380.degree. F.

A typical petroleum distillate is generally known in the trade as Solvent 140. For example, such a solvent is sold by Shell Chemical Company under the designation Shell Sol 140 having the following properties:

A similar solvent is sold by Grow Solvent Company, Inc., under the designation Solvent GS 140 and has the following properties:

Chlorinated solvent may comprise any one of the number of well-known solvents such as perchloroethylene.

A typical perchloroethylene is such as sold by The Dow Chemical Company under the designation "Special Vapor Degreasing Grade" having the following specifications and properties:

A typical barium sulfonate is manufactured by Witco Chemical Corporation, New York, N.Y., under the trademark Neutral Barium Petronate 50-S and is a synthetic barium sulfonate having the following typical tests:

The compositions embodying the invention may have the following range of compositions by weight:

The compositions embodying the invention and utilizing aluminum may have the following ranges of composition by weight:

In the above aluminum compositions, the chlorinated solvent is preferably perchloroethylene and the aromatic hydrocarbon solvents are preferably toluene ranging from 8-14% by weight and xylene ranging from 15-28% by weight.

The compositions embodying the invention and utilizing zinc may have the following ranges of compositions by weight:

In the above zinc compositions, the chlorinated solvent is preferably perchloroethylene and the aromatic hydrocarbon solvents are preferably toluene ranging from 11-16% by weight and xylene ranging from 11-16% by weight.

Specific examples of the compositions are as follows:

The various compositions heretofore described have been tested and have been found to provide good corrosion resistance on bare steel panels in a salt cabinet for over 360 hours, humidity resistance for over 500 hours, no blistering, partial immersion salt solution resistance for at least 260 hours, partial immersion detergent solution resistance for at least 260 hours, and good adhesion.

The composition embodying the invention is preferably made by first separately mixing a wax emulsion, a chlorinated rubber emulsion, and an aromatic hydrocarbon resin emulsion. In a typical example, the mixing is as follows:

Procedure: Heat and emulsify wax in mineral spirits. When dissolved and clear, add perchloroethylene, Igepal and Neutral Barium Petronate. Heat until clear. Cool.

Procedure: Dissolve at room temperature until clear.

Procedure: Dissolve at room temperature until clear.

Place all solvents by weight in container. Place premixed resin emulsion in solvent mixture. Place premixed wax emulsion in solvent mixture. Place premixed Parlon emulsion in solvent mixture. Stir for a maximum of 2 minutes.

Add aluminum pigment and stir. Do not shake.

Add AL 161 Syloid and AL 1 Syloid.

Add cellusolve acetate.

The following results are from tests administered on bare steel:

1. Flash point--not less than 11.7.degree. C. (53.degree. F.).

2. Storage stability--composition remains stable after 6 months at 23.8.degree. C. (75.degree. F.).

3. Sprayability--composition is sprayable without sagging or build up at bottom of panel.

4. High temperature flow point--composition does not sag, separate, or degenerate when exposed to temperatures up to 200.degree. F.

5. Toxicity--composition is not toxic when applied or in the dry state.

6. Viscosity--12-15 seconds in Fisher #2 cup after 10 minute agitation.

7. Salt spray corrosion resistance--withstands 360 hours exposure without base metal corrosion, adhesion loss, blisters or wrinkles.

8. Salt solution partial immersion test--withstands 7 days partial immersion in 5% salt tap water solution in an enclosed jar without corrosion, adhesion loss, blisters, or wrinkles. Immersion jar is placed inside a high-humidity cabinet, 100% relative humidity at 100.degree. F. to maintain constant temperature.

9. Detergent solution partial immersion test--withstands 7 days in solution composed of 10 grams of DuPont #7 car wash compound per gallon of tap water without corrosion, adhesion loss, blisters or wrinkles.

10. Environmental corrosion--withstands 10 cycles without corrosion, adhesion loss, blisters or wrinkles.

11. Humidity resistance--withstands 500 hours humidity exposure. Humidity cabinet is maintained at 100% relative humidity at 100.degree. F. Composition does not develop corrosion, adhesion loss, blisters or wrinkles.

12. Cold impact--withstands 2.8 joules (25 inch pounds) reverse impacts at -30.degree. C. (-20.degree. F.) without showing separation of wax from the substrate.

13. The anti-corrosion coating is removable from any topcoat surface without staining or discoloring the topcoat (painted surface).

The use of perchloroethylene is very important because it cleans and dissolves any oil present on the surface and allows the coating to make good contact with the surface. If bare steel is to be coated, I recommend that it be cleaned with perchloroethylene first. If the surface is contaminated with oil or grease, perchloroethylene will facilitate the adhesion process. The Parlon provides water and detergent resistance and helps prevent rust from starting. The wax and barium sulfonate keep the coating soft and prevent rust and moisture from creeping in. The aluminum pigment forms a protective finishing layer over the other ingredients.

This invention, when properly applied to a clean surface, will provide rust prevention especially in crevices and hard to reach places for all metals. This coating should not be oven dried. Up to 200.degree. F. may be applied to the surface and sagging will not occur. It will air dry in 5-10 minutes at room temperature. This composition is primarily for automobiles, inside the entire body, and especially for crevices, bottoms of doors, around plate glass, behind bumpers, on all frames, and all sheet metal whether galvanized or not. It has an advantage over zinc in that it requires less aluminum pigment and provides equal if not more protection. It provides good protection on bare, zinc-coated, or prime steel. I believe that the above compositions will provide good protection for pre-rusted surfaces such as highway bridges, for steel frames, cracked surfaces between steel frames and cement, and for water towers and other surfaces which retain moisture, detergent residue, or salt and are prone to rust.