Search

KR-20260065827-A - Multistage method for applying a corrosion protection coating to parts having a steel surface

KR20260065827AKR 20260065827 AKR20260065827 AKR 20260065827AKR-20260065827-A

Abstract

The present invention relates to a multi-stage method of first providing an elemental Zr and/or Ti-based conversion layer to a series of parts each having a steel surface, and subsequently dip-coating, wherein a rinsing stage follows after the conversion treatment stage, in which at least the steel surface of each part is brought into contact with an aqueous composition containing hydrogen peroxide. In the method according to the present invention, excellent corrosion protection on the steel surface is achieved even under adverse process conditions that typically promote corrosion defects on the steel surface and have an overall negative effect on corrosion protection.

Inventors

  • 브로우버, 얀-빌렘
  • 필라렉, 프랑크-올리버
  • 바프너, 크리슈토프
  • 아놀드, 안드레아스
  • 레사노 아르탈레호, 페르난도 호세
  • 앙게넨트, 크리스티나
  • 밀리스, 나딘 이자벨

Assignees

  • 헨켈 아게 운트 코. 카게아아

Dates

Publication Date
20260511
Application Date
20240906
Priority Date
20230908

Claims (14)

  1. A corrosion-protection treatment method for a series of parts including a steel surface, wherein each of the series of parts undergoes continuous treatment stages i) - iii): i) a. A fluoro complex of elemental Zr and/or Ti in an amount of at least 0.05 mmol/kg, calculated as the amount of elemental Zr and/or Ti, and b. A certain amount of free fluoride A conversion treatment stage comprising contacting with an acidic aqueous composition containing; ii) a rinsing stage comprising one or more immediately following rinsing steps, wherein at least one rinsing step is performed by contacting an aqueous composition having a pH greater than 4.00 containing at least 20 mg/kg of hydrogen peroxide; iii) A coating stage comprising dip-coating by contacting an aqueous dispersion of an organic binder.
  2. A method according to claim 1, characterized in that the wet film attached to the surface of the steel immediately after the rinsing stage ii) contains an amount of hydrogen peroxide preferably at least 10 mg/kg, particularly preferably at least 50 mg/kg, and particularly preferably at least 100 mg/kg based on the mass of the attached wet film.
  3. A method according to claim 1 or 2, wherein the rinsing stage ii) comprises a plurality of rinsing stages immediately following each other to bring each of a series of parts into contact with an aqueous composition stored in a system tank of each rinsing stage, wherein preferably, at least a partial volume of the aqueous composition stored in the system tank of the last rinsing stage is supplied back to the system tank of the first rinsing stage of rinsing stage ii), which is replaced by at least an equally large partial volume of the aqueous composition in the system tank of the last rinsing stage of rinsing stage ii), wherein such aqueous composition to replace the partial volume supplied back to the system tank of the first rinsing stage preferably has a non-conductivity of less than 20 μScm⁻¹ .
  4. In any one of claims 1 to 3, the aqueous composition of the sole or last rinse step of rinse stage ii), preferably the aqueous composition of each of all rinse steps of rinse stage ii), (a) Compounds of metals Bi, Ni, Co and/or Cu dissolved in water in each case, calculated as the amount of each element in the aqueous composition, less than 10 mg/kg, preferably compounds of these metals dissolved in water, having a standard reduction potential greater than -0.40 V (SHE) in each case, calculated as the amount of each element in the aqueous composition, (b) a surfactant of less than 1000 mg/kg in total, preferably less than 100 mg/kg, particularly preferably less than 50 mg/kg, preferably a surface-active organic compound, particularly preferably an organic compound, (c) a total of less than 100 mg/kg, preferably less than 10 mg/kg, of organosilanes and/or siloxanes, preferably a compound of elemental silicon dissolved in water, (d) Compounds of elemental Zr and/or Ti dissolved in water at a total of less than 100 mg/kg, preferably less than 20 mg/kg, particularly preferably less than 5 mg/kg, (e) total sodium and/or potassium ions of less than 50 mg/kg each, preferably less than 10 mg/kg, (f) Total zinc ions less than 50 mg/kg, preferably less than 10 mg/kg and/or, (g) Water-soluble phosphate, preferably water-soluble phosphorus-containing compound, with a total of less than 100 mg/kg, preferably less than 10 mg/kg A method characterized by containing
  5. A method according to any one of claims 1 to 4, characterized in that the wet film attached to the surface of the steel during contact with the first aqueous composition of the treatment stage iii) is reduced by at least 50%, preferably at least 80%, and particularly preferably at least 90% based on the mass of the wet film in each case compared to the wet film attached to the surface of the steel immediately after the rinsing stage ii).
  6. A method according to any one of claims 1 to 5, wherein the transfer of each part from the rinsing stage ii) to the processing stage iii) takes at least twice the time required for each part to pass through the rinsing stage ii) (rinsing stage duration), preferably said time (rinsing stage duration), particularly preferably at least three times; and particularly preferably, the transfer of each part from the rinsing stage ii) to the processing stage iii) takes more than 120 seconds, preferably more than 150 seconds, particularly preferably more than 180 seconds.
  7. A method according to any one of claims 1 to 6, characterized in that the drying step is performed before the processing stage iii) and after the rinsing stage ii).
  8. A method according to any one of claims 1 to 7, characterized in that the aqueous composition of the rinsing step having the highest hydrogen peroxide concentration among the rinsing steps ii) contains at least 100 mg/kg, preferably at least 400 mg/kg, particularly preferably at least 1000 mg/kg, but preferably 5000 mg/kg or less of hydrogen peroxide.
  9. A method according to any one of claims 1 to 8, characterized in that the pH of the aqueous composition of the rinsing step having the highest hydrogen peroxide concentration among the rinsing steps ii) is greater than 4.50, preferably greater than 5.00, particularly preferably greater than 5.50, particularly preferably greater than 6.00, but preferably 8.00 or less, particularly preferably 7.50 or less.
  10. A method according to any one of claims 1 to 9, characterized in that a part comes into contact with the aqueous composition(s) of rinse stage ii) by immersion into the system tank of each rinse stage containing each aqueous composition or by spraying each aqueous composition stored in the system tank.
  11. A method according to claim 10, characterized in that the part is contacted by spraying, preferably by atomizing, the aqueous composition stored in the system tank of the rinsing step, in a rinsing step ii) in which the part is contacted with an aqueous composition having the highest concentration of hydrogen peroxide.
  12. A method according to any one of claims 1 to 11, characterized in that a series of parts are first cleaned and/or degreased before the conversion processing stage i).
  13. In any one of claims 1 to 12, a series of parts has a zinc surface in addition to a steel surface, and each of the series of parts first undergoes an alkali treatment stage before a conversion treatment stage i), wherein in at least one treatment stage within the alkali treatment stage, the steel and zinc surfaces of the series of parts are, (a) at least 50 mg/kg, preferably at least 100 mg/kg of iron(III) ions, (b) contacted with an alkaline aqueous composition containing at least 100 mg/kg of phosphate ions, and A method characterized in that the alkaline aqueous composition has at least 1 point of free alkalinity and at least 10.5 pH.
  14. A method according to any one of claims 1 to 13, characterized in that a series of parts have a surface of aluminum and/or zinc, preferably aluminum and zinc, in addition to a steel surface.

Description

Multistage method for applying a corrosion protection coating to parts having a steel surface The present invention relates to a multi-stage method for first providing an elemental Zr and/or Ti-based conversion layer to a series of parts each having a steel surface, and subsequently dip-coating the same, wherein a rinsing stage follows the conversion treatment stage in which at least the steel surface of each part is brought into contact with an aqueous composition containing hydrogen peroxide. In the method according to the present invention, excellent corrosion protection on the steel surface is achieved even under adverse process conditions that typically promote corrosion defects on the steel surface and have an overall negative effect on corrosion protection. In the pretreatment of corrosion protection for parts with surfaces made of steel, galvanized steel, and/or aluminum materials, thin-film passivation based on amorphous transition layers derived from oxides and hydroxides of elements Zr and/or Ti has been widely established as an alternative to phosphating, in which crystalline coatings are formed during the treatment process. Efforts to further develop this type of transition coating substantially aim to form resource-saving and chromium-free passivations that provide an excellent primed base for subsequently applied paint systems, particularly dip-coating, with the goal of achieving corrosion protection equivalent to that of tricationic zinc phosphate. In particular, for amorphous thin films produced from transition treatments in acidic aqueous solutions containing water-soluble compounds of elements Zr and/or Ti, controlled film formation and growth of coatings with as few defects as possible are critical. To this end, prior art, on the one hand, focuses on influencing the kinetics of layer formation as presented in WO 2023/275270 and proposes sequentially forming a conversion layer in multiple wet-chemical process steps to produce hydroxide and oxide-based layer deposits of elemental Zr and/or Ti so that, for example, in a fluorine complex-based conversion treatment of elemental Zr and/or Ti, the conversion is as complete as possible. This is intended to prevent fluoride from remaining in the thin film, which can cause localized film defects upon contact with a corrosive medium. In contrast, another procedure for forming a conversion layer, described as an example in EP 1 455 002 A1, aims to reduce the proportion of fluoride during the conversion coating and to improve corrosion behavior and paint adhesion to subsequently applied electrodeposited coatings. To this end, EP 1 455 002 A1 proposes adding magnesium, calcium, Si-containing compounds, zinc, or copper to the conversion solution, and alternatively or in combination, drying the conversion coating or post-rinsing it with an alkaline aqueous composition. On the other hand, continuous corrosion protection pretreatment in industrial paint lines is problematic for corrosion protection, paint adhesion, and the appearance of the paint finish, whether the drying of the conversion coating on parts having steel surfaces occurs intentionally after the conversion treatment stage or is simply inevitable due to the spatial conditions of each paint line when transferring the parts to the dip-coating stage; it has been accurately shown that the latter disadvantage is due to the formation of flash rust, particularly during drying and/or longer transfer times or temporary plant downtimes. Based on the prior art, the object of the present invention is to establish a method for providing a transition coating on a metal surface, particularly a steel surface, that is as defect-free as possible and provides a high degree of robustness against corrosion damage during the transfer of parts from the transition processing stage to the deep-coating stage during the industrial pretreatment and deep-coating of a number of parts. The objective of the method is to produce a transition coating that is particularly resistant to flash rust formation on steel and thus can be deep-coated without any loss of corrosion protection even upon drying. Ideally, fluctuations in corrosion protection performance and the appearance of the deep-coated parts are prevented during exceptionally long transfer times from the transition processing zone to the painting zone, for example, during temporary plant downtime. The method must also be suitable for effectively protecting parts made of different metals, particularly a mixture of metallic steel, zinc, and aluminum, from corrosion. This objective is achieved by a multi-stage method for corrosion-protecting a series of parts including steel surfaces, wherein each of the series of parts undergoes continuous processing stages i) through iii): i) a. A fluorocomplex of at least 0.05 mmol/kg of elemental Zr and/or Ti, calculated as the amount of elemental Zr and/or Ti, and b. A certain amount of free fluoride A conversion treatment stage comp