Metal treatment – Process of modifying or maintaining internal physical... – Processes of coating utilizing a reactive composition which...
Patent
1996-04-26
1998-07-07
Silverberg, Sam
Metal treatment
Process of modifying or maintaining internal physical...
Processes of coating utilizing a reactive composition which...
148254, C23C 2280
Patent
active
057762651
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention is an improved method for providing a phosphate conversion coating on a metal substrate.
BACKGROUND OF THE INVENTION
A variety of compositions and processes have been used to provide an adherent, uniform phosphate coating on a metal surface. The phosphate coating is applied to enhance the adhesion of subsequently applied coatings and to provide for improved corrosion resistance of the coated metal substrate.
Phosphate coating processes (known as phosphating or phosphate conversion coating processes) are well known in the art. Generally, the phosphating process comprises contacting the metal surface with a acidic phosphate solution. The phosphating solution generally contains ions of metals such as zinc, nickel, manganese, copper, chromium and other metals which are known to provide conversion coatings on metal substrates in an acidic phosphate solution.
The metal substrate can be contacted with the acidic phosphate solution by immersion, spraying, roller coating, flowing and other means known for contacting a metal with an aqueous solution. Acidic phosphate conversion coating solutions are well known in the art and have been found very useful for providing a base for application of a protective coating to the metal substrate.
As disclosed in U.S. Pat. No. 2,310,239 to Jernstedt, U.S. Pat. No. 2,874,812 to Cavanagh and Maurer and in U.S. Pat. No. 4,539,051, to Hacias, conversion coatings can be improved if, prior to contacting the metal to be phosphate coated with the acidic phosphate solution, the metal surface is first activated by contact with an aqueous activating composition. The aqueous activating compositions are generally mixtures comprising water with a reaction product of a titanium compound and a phosphate. The aqueous activating compositions are at an alkaline pH, generally in the range of about 7 to about 11 and preferably in the range of from about 8 to about 10. Titanium compound-phosphate compound reaction products generally contain from about 0.005 to about 25% by weight titanium. As is disclosed in the cited references, a cleaned metal substrate is contacted with an aqueous activating composition to assist in providing an even coating with low coating weight and small crystal morphology in the phosphate conversion coating step.
It is well known in the art that after the aqueous activating composition is prepared by mixing a dry activating composition with water, the aqueous activating composition loses its activating ability as time passes and the aqueous composition ages. The activating ability of the aqueous activating composition declines with time even if the composition has not been exhausted by contact with metal substrates. It would be useful to be able to extend the useful life of the aqueous activating compositions. The time period since preparation of the aqueous activating composition is known as the aging period or aging.
Contacting the metal substrate with the aqueous activating composition provides for a phosphate conversion coating which has a small crystal size, optimal coating weight and a more even coating than substrates which have been contacted with acidic phosphate solutions without prior contact with the aqueous activating composition.
Before the metal substrate is contacted with the aqueous activating composition and conversion coated, it is important that the metal substrate be clean. Cleaning of the metal substrate is generally accomplished by contacting the metal substrate with an acidic or an alkaline cleaning composition. Generally, the alkaline compositions are preferred since the activating composition is at an alkaline pH. However, as long as the metal substrate is rinsed of the cleaning solution, an acidic cleaning solution can be utilized.
A BRIEF SUMMARY OF THE INVENTION
According to the present invention, an improved phosphate conversion coating can be formed on a metal substrate by the process by contacting an aqueous activating composition used to activate the metal substrate with ultrasonic vibration energy.
REFERENCES:
patent: 2459847 (1949-12-01), Jernstedt
patent: 4529451 (1985-07-01), Otrhalek
patent: 4531978 (1985-07-01), Otrhalek
Dunn Robin M.
Giles Terrence R.
Kramer Linda S.
Miller Robert W.
Henkel Corporation
Jaeschke Wayne C.
Ortiz Daniel S.
Silverberg Sam
Szoke Ernest G.
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