Successive corrosion-protecting pre-treatment of metal surfaces in a multiple-step process
First Claim
1. A method for anticorrosion pretreatment of metal surfaces in a processing sequence comprising a conversion treatment stage (D) with an aqueous composition (1) containing in total at least 50 ppm of one or more of elements B, Si, Ti, Zr and Hf in the form of water-soluble compounds at a pH value of 3 to 5.5, wherein the metallic surfaces pass in succession through at least treatment stages of:
- (A) optionally degreasing and cleaning;
(B) optionally rinsing with process water optionally containing part of the aqueous composition of the degreasing and cleaning stage (A);
(C) prerinsing with water containing in total at least 10 ppm of elements B, Si, Ti, Zr and/or Hf in the form of water-soluble compounds;
(D) conversion treatment with the aqueous composition (1);
(E) postrinsing with water containing part of the aqueous composition (1) of treatment stage (D);
(F) optionally second postrinsing with water containing part of the aqueous composition of postrinsing stage (E),wherein the aqueous composition (1) of the conversion treatment stage (D) contains a proportion of fluorine bound in the form of fluoro complexes of the one or more elements B, Si, Ti, Zr and Hf or fluorine in excess and unbound in the form of free fluoride, and wherein pH value in the prerinsing stage (C) is in a range from 5 to 7.0, andwherein a cascaded recirculation of aqueous medium from the final rinsing stage to the first rinsing stage proceeds such that in total at least 10 ppm of the elements B, Si, Ti, Zr and/or Hf in the form of water-soluble compounds are present in the prerinsing stage (C).
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Abstract
The present invention relates to a method for improving the corrosion-protecting pre-treatment of metal surfaces and using rinse water in a manner to conserve resources in such a corrosion-protecting pre-treatment, comprising a conversion treatment step using an aqueous composition comprising at least 50 ppm of the elements B, Si, Ti, Zr and/or Hf in the form of water-soluble compounds at a pH value of 3 to 5.5, wherein a minimum fraction of 10 ppm of the elements B, Si, Ti, Zr and/or Hf in the form of water-soluble compounds is present in the last pre-rinse step and a portion of the aqueous composition of the conversion treatment step is contained in the first post-rinse step. The resource-conserving use of the rinse water is accomplished according to the invention by way of a cascaded return of rinse water from the last rinse step to the first rinse step. The present invention also relates to a metallic component treated using the method according to the invention and to the use thereof in a process for applying a multi-coating system, in particular a paint system containing an organic binder, in industrial manufacturing.
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Citations
17 Claims
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1. A method for anticorrosion pretreatment of metal surfaces in a processing sequence comprising a conversion treatment stage (D) with an aqueous composition (1) containing in total at least 50 ppm of one or more of elements B, Si, Ti, Zr and Hf in the form of water-soluble compounds at a pH value of 3 to 5.5, wherein the metallic surfaces pass in succession through at least treatment stages of:
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(A) optionally degreasing and cleaning; (B) optionally rinsing with process water optionally containing part of the aqueous composition of the degreasing and cleaning stage (A); (C) prerinsing with water containing in total at least 10 ppm of elements B, Si, Ti, Zr and/or Hf in the form of water-soluble compounds; (D) conversion treatment with the aqueous composition (1); (E) postrinsing with water containing part of the aqueous composition (1) of treatment stage (D); (F) optionally second postrinsing with water containing part of the aqueous composition of postrinsing stage (E), wherein the aqueous composition (1) of the conversion treatment stage (D) contains a proportion of fluorine bound in the form of fluoro complexes of the one or more elements B, Si, Ti, Zr and Hf or fluorine in excess and unbound in the form of free fluoride, and wherein pH value in the prerinsing stage (C) is in a range from 5 to 7.0, and wherein a cascaded recirculation of aqueous medium from the final rinsing stage to the first rinsing stage proceeds such that in total at least 10 ppm of the elements B, Si, Ti, Zr and/or Hf in the form of water-soluble compounds are present in the prerinsing stage (C). - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. A method for the anticorrosion pretreatment of metal surfaces in a processing sequence comprising a conversion treatment stage (D) with an aqueous composition (1) containing in total at least 50 ppm of the elements B, Si, Ti, Zr and Hf in the form of water-soluble compounds at a pH value of 3 to 5.5, wherein the metallic surface passes in succession through at least the following treatment stages of:
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(A) optionally degreasing and cleaning; (B) optionally rinsing with process water optionally containing part of the aqueous composition of the degreasing and cleaning stage (A); (C) prerinsing with water containing in total at least 10 ppm of the elements B, Si, Ti, Zr and/or Hf in the form of water-soluble compounds; (D) conversion treatment with the aqueous composition (1); (E) postrinsing with water containing part of the aqueous composition (1) of treatment stage (D); and (F) optionally second postrinsing with water containing part of the aqueous composition of postrinsing stage (E), wherein the aqueous composition (1) of the conversion treatment stage (D) contains a proportion of fluorine bound in the form of fluoro complexes of the elements B, Si, Ti, Zr and/or Hf or fluorine in excess and unbound in the form of free fluoride and wherein the pH value in the prerinsing stage (C) is in a range from 5 to 7.0; and wherein the final rinsing stage is supplied with deionized water and a cascaded recirculation of aqueous medium from the final rinsing stage to the first rinsing state proceeds such that in total at least 10 ppm of the elements B, Si, Ti, Zr and/or Hf in the form of water-soluble compounds are present in the prerinsing stage (C), the treatment stage (D) being excepted from the cascaded recirculation and aqueous medium not being fed indirectly and directly into the treatment stage (D) from the final rinsing stage. - View Dependent Claims (17)
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Specification