Claims
- 1. An apparatus for coating a metal substrate with an inorganic phosphate coating, the apparatus comprising:
- a first bath containing a first composition in which the metal substrate is immersed for formation of the phosphate coating on the substrate, the first composition including a halohydrocarbon, a solubilizing solvent alcohol capable of solubilizing phosphoric acid in the halohydrocarbon and present in the composition in an amount between 25 volume percent and a level corresponding to the flammable concentration of the alcohol, a phosphatizing proportion of phosphoric acid, and water in an amount exceeding a portion of phosphoric acid, while being sufficient for the composition to deposit on the metal substrate a phosphate coating of substantial water insolubility while retaining continuous liquid phase homogeneity; and
- a second bath containing a second composition, the second bath situated such that vapors from the second composition are commingled with vapors of the first composition forming a vapor zone, the second composition including a level of alcohol such that vapors produced from the second composition when commingled with the vapors from the first composition produce a vapor with an alcohol content that is not flammable.
- 2. The apparatus of claim 1 wherein the halohydrocarbon is trichlorotrifluoroethane.
- 3. The apparatus of claim 1 wherein the solubilizing solvent alcohol is isopropanol.
- 4. The apparatus of claim 1 wherein zinc is present in the first bath.
- 5. The apparatus of claim 4 wherein the zinc is present in the form of elemental zinc, zinc salts, or cation-contributing compounds.
- 6. A process for depositing a phosphate coating, the process comprising: contacting a metal substrate with a first liquid composition comprising a halohydrocarbon, a solubilizing solvent alcohol capable of solubilizing the phosphoric acid in the halohydrocarbon and present in the composition in an amount between 25 volume percent and a level corresponding to the flammable concentration of the alcohol, a phosphatizing proportion of phosphoric acid, and water in an amount exceeding the proportion of phosphoric acid, while being sufficient for the composition to deposit on the metal substrate a phosphate coating of substantial water insolubility while retaining continuous liquid phase homogeneity; and
- providing a second liquid composition in proximity to the first liquid composition so that vapors from the second composition are commingled with vapors from the first composition, the second composition including a level of alcohol so that the vapors from the second composition when commingled with vapors from the first composition produce a vapor having an alcohol content that is not flammable.
- 7. The process of claim 6 wherein the halohydrocarbon is trichlorotrifluoroethane.
- 8. The process of claim 6 wherein the solubilizing solvent alcohol is isopropanol.
- 9. The process of claim 6 wherein the zinc is present in the first bath.
- 10. The process of claim 9 wherein the zinc is in the form of elemental zinc, zinc salts or zinc cation-contributing compounds.
- 11. The process of claim 6 wherein the second liquid composition has no more than 15 percent alcohol.
- 12. The process of claim 11 wherein the second liquid composition is a degreasing composition.
- 13. The process of claim 11 wherein the second liquid composition is used as a rinse.
REFERENCE TO CO-PENDING APPLICATION
This application is a continuation-in-part of pending application Ser. No. 07/095,739 filed on Sept. 11, 1987 now abandoned.
This invention is directed to a process for depositing an inorganic phosphate coating in a substrate using a high water and high alcohol content in a phosphatizing bath and a vapor zone associated with the bath that is not flammable.
Phosphate coatings are widely employed in the metal finishing industry for reducing corrosion and improving adhesion of topcoats, primers and paints on metal surfaces. Typically, either iron phosphate or zinc phosphate coatings are used, with the choice being determined largely by the end use of the metal article. Articles intended for interior use under controlled environments are generally treated with iron phosphate coatings, while those to be subjected to severe use under hostile environments are usually zinc phosphate coated.
Currently, a variety of solvent-based iron phosphatizing processes are available. For example, U.S. Pat. No. 3,524,749, assigned to DuPont, discloses compositions containing at least 85% by volume of a chlorinated hydrocarbon solvent, such as trichlorethylene or perchlorethylene, between 5 ppm and 5% by volume of phosphoric acid, and from 2%-10% by volume of a C.sub.3-8 alcohol as a solubilizer.
U.S. Pat. No. 4,008,101, assigned to Diamond-Shamrock Corporation of Cleveland, Ohio, provides solvent-based iron phosphatizing compositions which contain methylene chloride, a phosphatizing amount of phosphoric acid and a solubilizing solvent, usually an alcohol having less than 6 carbon atoms, capable of solubilizing phosphoric acid in methylene chloride. That iron phosphating composition further contains water in excess of the amount of phosphoric acid, such that the composition maintains liquid phase homogeneity.
U.S. Pat. No. 4,102,710, also assigned to Diamond-Shamrock, is directed to solvent-based iron phosphatizing compositions similar to those of U.S. Pat. No. 4,008,101, additionally containing phenolic stabilizers to further enhance the substantial water insolubility of the phosphate coatings and to assure topcoat adhesion.
U.S. Pat. No. 4,118,253, assigned to Diamond-Shamrock, discloses an iron phosphatizing composition wherein the relative amounts of the halogenated organic solvent, phosphoric acid solubilizer, phosphoric acid and water are so selected that the composition maintains a continuous, homogeneous liquid phase and is non-flammable.
U.S. Pat. No. 4,029,523, assigned to Diamond-Shamrock, discloses a liquid phosphatizing composition containing organic solvent, such as 1,1,1-trichlorethane or trichlorofluoromethane, a phosphatizing proportion of phosphoric acid, a solubilizing liquid capable of solubilizing phosphoric acid in the organic solvent, and water in an amount exceeding the proportion of phosphoric acid. The iron phosphatized coatings deposited onto metal surfaces from solvent-based compositions such as those disclosed in the above-cited patents assigned to DuPont and to Diamond-Shamrock, are all said to demonstrate at least substantial water insolubility, a degree of corrosion resistance over untreated metal and provide a surface for adhesion of paint or other finish coatings.
A method and an apparatus for depositing an inorganic phosphate coating on a metal substrate includes providing a first composition in a first phosphatizing bath having a high alcohol content and a second composition in a second bath having a low alcohol content.
The first composition includes a halohydrocarbon, solubilizing solvent alcohol capable of solubilizing phosphoric acid in the halohydrocarbon and present in the composition in an amount between 25 volume percent and a level corresponding to the flammable concentration of the alcohol, and water in an amount exceeding the proportion of phosphoric acid, while being sufficient for the composition to form on the metal substrate a phosphate coating of substantial water insolubility and while retaining continuous liquid phase homogeneity. If a zinc phosphate coating is desired, then zinc in an amount sufficient to saturate the composition is added.
The second composition includes a level of alcohol such that when the vapor from the second composition is commingled with vapor from the first composition, the commingled vapor is not flammable.
The metal substrate is immersed in the first composition in the first bath for formation of the phosphate coating on the substrate and then removed from the first bath and held in the commingled vapors of the first and second composition until substantially all liquid on the substrate has evaporated.
US Referenced Citations (9)
Continuation in Parts (1)
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Number |
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95739 |
Sep 1987 |
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Patent Grant
4931109
