Process for producing phosphate coatings
First Claim
1. An improved process for phosphating metal surfaces which comprises the steps of providing an activating composition comprising a mixture of about 60% to about 90% by weight of a particulated dried reaction product of a titanium-containing compound and a sodium phosphate compound containing at least about 0.005% by weight titanium and the balance comprising tetrasodium pyrophosphate, dispersing said activating composition in water at a concentration of about 0.1 to about 10 g/l to provide an activating solution, contacting a clean metal surface with said activating solution at a pH of about 7 to about 10 for a period of time of at least about 15 seconds to provide an activated metal surface, contacting the activated metal surface with an aqueous high-zinc phosphating solution for a period of time to produce a desired thickness of a zinc phosphate coating thereon, rinsing the zinc phosphate coating with a dilute aqueous solution containing chromium ions, and thereafter applying an electrophoretic organic coating to the rinsed zinc phosphate coating.
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Abstract
An improved process for activating metal surfaces prior to a phosphating treatment whereby relatively thin, dense, fine-sized and uniform crystalline adherent phosphate coatings are produced providing superior corrosion protection and paint adherence when coated substrates are subjected to cyclical temperature and ambient environments typifying normal service conditions. To prepare the aqueous activating solution, a dry activating composition is prepared which is adapted to be dispersed in water at a controlled concentration and which comprises a mixture of about 60 to about 90% by weight of a particulated dried reaction product of a titanium-containing compound and sodium phosphate compound containing at least about 0.005% by weight titanium with the balance comprising tetrasodium pyrophosphate. The dry activating composition is dispersed in the aqueous solution to provide a total concentration of from about 0.1 to about 10 g/l. In accordance with the process aspects of the present invention, the aqueous dispersion containing the activating composition is applied to cleaned metal surfaces such as steel, zinc and aluminum before the following zinc phosphating step whereby improved phosphating coatings are produced.
39 Citations
27 Claims
- 1. An improved process for phosphating metal surfaces which comprises the steps of providing an activating composition comprising a mixture of about 60% to about 90% by weight of a particulated dried reaction product of a titanium-containing compound and a sodium phosphate compound containing at least about 0.005% by weight titanium and the balance comprising tetrasodium pyrophosphate, dispersing said activating composition in water at a concentration of about 0.1 to about 10 g/l to provide an activating solution, contacting a clean metal surface with said activating solution at a pH of about 7 to about 10 for a period of time of at least about 15 seconds to provide an activated metal surface, contacting the activated metal surface with an aqueous high-zinc phosphating solution for a period of time to produce a desired thickness of a zinc phosphate coating thereon, rinsing the zinc phosphate coating with a dilute aqueous solution containing chromium ions, and thereafter applying an electrophoretic organic coating to the rinsed zinc phosphate coating.
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14. An improved process for phosphating metal surfaces which comprises the steps of providing an activating composition comprising a mixture of about 60% to about 90% by weight of a particulated dried reaction product of a titanium-containing compound and a sodium phosphate compound containing at least about 0.005% by weight titanium and the balance comprising tetrasodium pyrophosphate, dispersing said activating composition in water at a concentration of about 0.1 to about 10 g/l to provide an activating solution, contacting a clean metal surface with said activating solution at a pH of about 7 to about 10 for a period of time of at least about 15 seconds to provide an activated metal surface, contacting the activated metal surface with an aqueous high-zinc phosphating solution for a period of time to produce a desired thickness of a zinc phosphate coating thereon, post-treatment rinsing the zinc phosphate coating with a dilute post-treating solution to enhance the corrosion resistance of the zinc-phosphated surface, and thereafter applying an electrophoretic organic coating to the rinsed zinc phosphate coating.
- 15. An improved process for phosphating metal surfaces which comprises the steps of providing an activating composition comprising a mixture of about 60% to about 90% by weight of a particulated dried reaction product of a titanium-containing compound and a sodium phosphate compound containing at least about 0.005% by weight titanium and the balance comprising tetrasodium pyrophosphate, dispersing said activating composition in water at a concentration of about 0.1 to about 10 g/l to provide an activating solution, contacting a clean metal surface with said activating solution at a pH of about 7 to about 10 for a period of time of at least about 15 seconds to provide an activated metal surface, contacting the activated metal surface with an aqueous high-zinc phosphating solution for a period of time to produce a desired thickness of a zinc phosphate coating thereon, post-treatment rinsing the zinc phosphate coating with a dilute substantially chromium-free post-treating solution to enhance the corrosion resistance of the zinc-phosphated surface, and thereafter applying an electrophoretic organic coating to the rinsed zinc phosphate coating.
Specification