Metal treatment – Process of modifying or maintaining internal physical... – Processes of coating utilizing a reactive composition which...
Reexamination Certificate
2001-11-28
2003-11-11
Sheehan, John (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Processes of coating utilizing a reactive composition which...
C148S254000, C148S255000, C148S256000, C148S262000, C148S273000, C427S419100, C427S419300, C210S688000, C210S805000
Reexamination Certificate
active
06645316
ABSTRACT:
This invention relates to a process for post-passivation of a phosphated metal surface and thus falls within the general area of phosphating of metals. The process may be used to treat phosphatable metal surfaces, for example surfaces made from steel, galvanized or alloy-galvanized steel, aluminum, aluminized or alloy-aluminized steel. A preferred embodiment of the process contemplates that active components, such as divalent metal ions and phosphate ions, are concentrated by membrane filtration (nanofiltration, reverse osmosis) out of the post-passivation solution overflow or out of the rinsing water subsequent to post-passivation and transferred into the phosphating solution.
Phosphating, which precedes the post-passivation process according to the present invention, may be carried out as layer-forming or non layer-forming phosphating. In the case of non layer-forming phosphating, also known as iron phosphating, the phosphating solution does not contain any cations, which are incorporated into the generally X-ray amorphous phosphate and oxide layer which is being formed. Instead, the protective layer on the metal surfaces produced by non layer-forming phosphating contains only cations, which originate from the metal surface itself. Non layer-forming phosphating processes of this type are known from the prior art, for example from DE-A-44 17 965.
Non layer-forming phosphating is suitable for use as pretreatment prior to lacquer coating of metal articles of which no excessively stringent requirements are specified with regard to corrosion resistance. Examples thereof are agricultural machinery, as well as domestic appliances, such as refrigerators and washing machines, and pieces of steel equipment.
Layer-forming phosphating is commonly used as a pretreatment prior to lacquer coating of metal articles of which higher demands are made with regard to corrosion protection, such as automotive bodywork. In this embodiment, crystalline metal phosphate layers are generally deposited. The treatment solution for layer-forming phosphating contains cations which are incorporated into the phosphate layer. Particular examples are zinc ions and manganese and/or nickel ions.
The aim of layer-forming phosphating of metals is to produce on the metal surface strongly adhering metal phosphate layers which in themselves improve corrosion resistance and, in conjunction with lacquers and other organic coatings, contribute towards a substantial increase in adhesion and resistance to creepage on exposure to corrosion. Such phosphating processes have long been known in the art. Low-zinc phosphating processes, in which the phosphating solutions have relatively low contents of zinc ions of, for example, 0.5 to 2 g/l, are particularly suitable for pretreatment prior to lacquer coating. An essential parameter of these low-zinc phosphating baths is the weight ratio of phosphate ions to zinc ions, which is usually in a range >12 and may be up to 30.
It has been found that phosphate layers having distinctly improved corrosion protection and lacquer adhesion properties may be formed by also using polyvalent cations other than zinc in the phosphating baths. For example, low-zinc processes with the addition of, for example, 0.5 to 1.5 g/l of manganese ions and, for example, 0.3 to 2.0 g/l of nickel ions are widely used as so-called trication processes for preparing metal surfaces for lacquer coating, for example for cathodic electrocoating of automotive bodywork.
Prior to phosphating, in particular prior to layer-forming phosphating, the metal articles, such as automotive bodywork, are generally cleaned and activated in an activating bath, which conventionally contains colloidal titanium phosphate particles, for subsequent phosphating. After this cleaning and prior to activation or phosphating, the metal articles are conventionally rinsed with water. The phosphating stage is generally followed by post-passivation, the purpose of which is to improve further the corrosion protection obtained by phosphating. Examples of suitable post-passivation solutions are acidic chromate-containing solutions. However, the use of chromate-containing post-passivation solutions is problematic from the point of view of environmental protection and industrial safety. There has, therefore, been no shortage of attempts to find post-passivation solutions for the post-treatment of phosphated metal surfaces, which do not exhibit the disadvantages of chromate-containing solutions. Post-passivation solutions currently used in practice are those which contain as the active components thereof polyvinyl phenol compounds, hexafluorotitanates or zirconates and/or copper ions. The post-passivation solutions thus generally contain active components which are not used in the phosphating solution itself. It is therefore necessary in practice to take care that components of the post-passivation solution are not entrained into the phosphating solution.
It is known from DE-A-34 00 339 to use nickel-containing solutions for the post-passivation of phosphate layers. The nickel salt used is preferably the acetate. However, acetate ions should not be entrained into the phosphating solution, since, once therein, they become acetic acid and cause a severe odor nuisance.
In contrast, an object of the present invention is to provide a post-passivation solution which contains only active components which are also used in a phosphating solution. This is one facet of the broader object of minimizing the active substances used in the overall phosphating process and restricting water consumption.
DESCRIPTION OF THE INVENTION
The present invention relates to a process for post-passivation of a phosphated metal surface, characterized in that the phosphated metal surface is treated with an aqueous post-passivation solution which contains from 50 to 500 mg/l of nickel ions and from 200 to 1500 mg/l of phosphate ions.
Treatment of the phosphated metal surface with the post-passivation solution may be effected in such a way that the phosphated metal surface is sprayed with the post-passivation solution or dipped in the post-passivation solution. The post-passivation solution preferably contains a larger proportion, by weight, of phosphate ions than of nickel ions. The anions of phosphoric acid present in the post-passivation solution are treated for the purposes of calculation as if they were present wholly as tertiary phosphate ions. In actual fact, however, the corresponding protolysis equilibrium of the phosphate ions is established depending on the pH of the post-passivation solution. Since the pH of the post-passivation solution is preferably between 3 and 6 and in particular between 3.5 and 4.5, in practice the anions of phosphoric acid are present extensively as dihydrogen phosphate ions. For calculation of the weight ratios, this may however in practice be disregarded, since the mass of the protons contributes very little to the total mass of the anions of the phosphoric acid. It is preferable for such a weight ratio between nickel ions and phosphate ions to be established that the mass of the phosphate ions amounts to 2 to 5 times the mass of the nickel ions.
The process according to the present invention is preferably carried out in such a way that the aqueous post-passivation solution exhibits a temperature of between about 10 and about 50° C. The temperature is preferably between 15 and 30° C. The post-passivation solution may, for example, be at room temperature, i.e. a temperature between 18 and 25° C.
The phosphated metal surface is contacted with the aqueous post-passivation solution preferably for a period of from about 10 seconds to about 5 minutes, in particular between about 30 seconds and 2 minutes. This means that the metal surface is dipped in the post-passivation solution or sprayed therewith or both procedures are carried out one after the other. The phosphated, post-passivated metal surfaces are then rinsed with water. Completely deionized water is preferably used for this purpose.
The process according to the present invention may be used
Brouwer Jan-Willem
Kuhm Peter
Harper Stephen D.
Henkel Kommanditgesellschaft auf Aktien
Murphy Glenn E. J.
Oltmans Andrew L.
Sheehan John
LandOfFree
Post-passivation of a phosphatized metal surface does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Post-passivation of a phosphatized metal surface, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Post-passivation of a phosphatized metal surface will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3153757