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Phosphate Conversion Coating Composition and Process

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Phosphate Conversion Coating Composition and Process Europa,schesP_ MM M II M Mill I M Ml M M M I II J European Patent Office ***** Att nt © Publication number: 0 610 421 B1 Office europeen- desj brevets^ . © EUROPEAN PATENT SPECIFICATION © Date of publication of patent specification: 27.12.95 © Int. CI.6: C23C 22/36, C23C 22/44 © Application number: 92924113.1 @ Date of filing: 28.10.92 © International application number: PCT/US92/08982 © International publication number: WO 93/09266 (13.05.93 93/12) &) PHOSPHATE CONVERSION COATING COMPOSITION AND PROCESS ® Priority: 01.11.91 US 786694 (73) Proprietor: HENKEL CORPORATION 140 Germantown Avenue, @ Date of publication of application: Suite 150 17.08.94 Bulletin 94/33 Plymouth Meeting, PA 19462 (US) © Publication of the grant of the patent: @ Inventor: BOULOS, Mervet Saleh 27.12.95 Bulletin 95/52 4395 Stonehenge Court Troy, Ml 48098 (US) © Designated Contracting States: AT BE DE DK ES FR GB IT NL SE © Representative: Jonsson, Hans-Peter, Dr. et al References cited: Patentanwalte EP-A- 0 015 020 EP-A- 0 287 133 von Krelsler Seltlng Werner, EP-A- 0 361 375 EP-A- 0 448 130 Bahnhofsvorplatz 1 (Delchmannhaus) EP-A- 0 454 361 FR-A- 2 347 459 D-50667 Koln (DE) 00 CO Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid (Art. 99(1) European patent convention). Rank Xerox (UK) Business Services (3. 10/3.09/3.3.3) EP 0 610 421 B1 Description This invention relates to a composition and process for forming a phosphate conversion coating on active metal surfaces in order to increase the corrosion resistance of the surfaces, either as treated or after 5 subsequent conventional overcoating of the conversion coating layer formed by an organic based protective coating such as a paint or lacquer. Unlike many of the other compositions known for this general purpose, a composition according to this invention is well adapted to treating any of a variety of base metals, including at least steel and galvanized steel, zinc and zinc based alloys, aluminum and aluminum based alloys, and magnesium and magnesium based alloys. The composition and method of the invention are therefore io especially well adapted to treating objects having surfaces including more than one type of active metal to be protected against corrosion. A wide variety of phosphate conversion coating compositions and processes are already described in the art. Those believed to be most closely related to the present invention are described below. U. S. A 4,865,653 teaches the use of hydroxylamine or agents that react in water to produce 75 hydroxylamine in zinc phosphating solutions to expand the range of zinc concentrations over which the most desirable coating morphology for a zinc phosphate Conversion coating can be obtained. Ferrous, zinciferous, and aluminum surfaces can all be coated with the compositions and processes taught by this reference. U. S. 4,637,838 teaches zinc phosphating solutions optionally containing nitrobenzene sulfonate, 20 nitrilotriacetate, fluoride and complex fluoride anions, and/or chelators such as citrate and tartrate. U. S. A 4,149,909 teaches using a combination of accelerators including an oxidizing agent such as a chlorate or bromate in conjunction with a reducing agent such as hydroxylamine sulfate to phosphate ferrous metal surfaces at low temperatures to produce an iron phosphate coating with good salt spray corrosion resistance. 25 U. S. A 4,148,670 teaches treating aluminum with an aqueous composition comprising a zirconium or titanium compound which may be the fluozirconate or fluotitanate, a fluoride compound which may also be the noted complex fluoride compounds, and phosphate ions. U. S. A 3,619,300 teaches zinc phosphate conversion coating compositions containing zinc, phosphate, nitrate, and nitrite ions along with a combination of fluoride and bifluorides of sodium and potassium and 30 teaches that such compositions are useful for treating aluminum, iron, and/or zinc based surfaces. EP-A-0 287 133 and EP-A-0 015 020 teach phosphating processes and compositions comprising, in its embodiments phosphate, simple and/or complex fluorides, hydroxylamine, and iron chelating agents. These compositions also contain very substantial amounts of divalent and/or trivalent metal cations, particularly zinc. 35 A commercial product of Henkel Corporation sold for phosphate conversion coating processes more than one year before this application contains phosphate ions, nitrobenzene sulfonate ions, hydroxylam- monium sulfate, sodium xylene sulfonate, the monobutyl ether of diethylene glycol {i.e., HO-(CH2)2-0- (CH2)2-0-(CH2)3CH3}, and surfactant. Another commercial product of Henkel Corporation sold for more than one year before this application for phosphate conversion coating contains phosphate, hydroxylam- 40 monium sulfate, sodium molybdate, sodium sulfate, surfactants, an antifoam agent, and a siliceous desiccant. However, neither of these two commercial products contains any simple or complex fluorides or any organic compounds containing two or more hydroxide and/or carboxyl functional groups. In this description, except in the working examples and claims and wherever expressly indicated to the contrary, all numerical specifications of amounts of materials or conditions of reaction or use are to be 45 understood as modified by the term "about" in describing the broadest scope of the invention. Practice of the invention within the exact numerical limits given is generally preferred. A composition according to this invention is an aqueous liquid composition comprising, or preferably consisting essentially of, still more preferably consisting of, water and: (A) a water soluble component providing in aqueous solution dissolved complex fluoride ions selected 50 from the group consisting of fluoborate (BF^-2), fluohafnate (HfFG-2), fluosilicate (SiFG-2), fluotitanate (TiFG-2), fluozirconate (ZrFG-2), and mixtures thereof; (B) a water soluble component providing in aqueous solution ions selected from the group consisting of fluoride (F~), bifluoride (HF2~), and mixtures thereof; (C) a water soluble iron chelating agent component selected from molecules each of which contains at 55 least two, and preferably at least three, moieties selected from the group consisting of -COOH, -OH, and mixtures thereof; (D) a water soluble component source of dissolved hydroxylamine in aqueous solution; (E) a water soluble source of dissolved phosphate ions; and 2 EP 0 610 421 B1 (F) a water soluble component providing in aqueous solution dissolved oxidizing agents selected from the group consisting of nitroaromatic organic compounds, molybdate ions having the general formula MonO(3n+1)-2 where n represents a positive integer, tungstate ions, and mixtures thereof; wherein the concentration of any of Zn+2, Ni+2, Mn+2, Co+2 Cu+2, Fe+2, Ca+2,Mg+2 and any metal cations with 5 a valence of 3 or higher in the composition is not greater than 0.9 g/l. A process according to this invention comprises at a minimum a step of contacting a metal surface to be treated with a composition according to the invention for a sufficient time to form on the metal surface a detectable conversion coating. The compositions according to this invention, when they contain adequate amounts and types of surfactant component (G) as is usually preferred, are especially well suited to treating io metal surfaces that have not been subjected to any prior chemical cleaning or conventional "activation" (e.g., contact with a suitably prepared aqueous dispersion of colloidal titanium compounds), but conven- tional metal surface cleaning and/or activation steps before contact between the metal to be treated and the compositions according to the invention may be used if desired as part of a process according to this invention. is A process according to the invention also may, and usually preferably does, include conventional steps subsequent to the contact between the metal surface to be treated and the compositions according to the invention. These subsequent steps, e.g., may include rinsing with water, any conventional reactive post treatments, e.g., with compositions according to the teachings of U. S. A 4,963,596 or with chromate containing solutions, and painting or otherwise protecting the surface with an outer coating of an organic 20 based solid material. With increasing preference in the order given and with independent preference for each noted component, compositions according to the invention contain no more than 0.9, 0.5, 0.2, 0.07, or 0.01 grams per liter (hereinafter "g/L") of cations selected from the group consisting of Zn+2, Ni+2, Mn+2, Co+2, Cu+2, Fe+2, Ca+2, Mg+2, and all metal cations with a valence of 3 or higher. 25 Preferred sources for component (A) as described above are the acids and the alkali metal and ammonium salts having the anions noted. In a composition ready for use in a process according to this invention (briefly denoted hereinafter as a "working composition"), it is preferred, with increasing preference in the order given, that the concentration of component (A), calculated as the anion(s) present, be in the range from 0.05 to 1.0, 0.10 to 0.70, or 0.30 to 0.50 g/L. 30 However, for economy in shipment, it is often preferable to prepare a concentrated composition according to the invention, suitable for dilution with water, and optionally with addition of acid or base for pH control, at the point of use to prepare a working composition with a concentration of component (A) in the range given above and of other components in the ranges given below.
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