Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
  • C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
  • C23C22/34—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing fluorides or complex fluorides
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/82—After-treatment
  • C23C22/83—Chemical after-treatment
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C2222/00—Aspects relating to chemical surface treatment of metallic material by reaction of the surface with a reactive medium
  • C23C2222/10—Use of solutions containing trivalent chromium but free of hexavalent chromium

Definitions

• the invention relates to a method of treating metal surfaces with an aqueous composition and to an aqueous composition for treatment of metal surfaces.
• phosphate coatings have been used to improve adhesion of coatings, such as paint, and corrosion resistance of steel. Some major disadvantages of phosphate coatings are necessity of several rinsing steps, sludge disposal and power consumption. Additionally these coatings are often sealed with a hexavalent chromium solution for optimum adhesion and corrosion. Therefore these phosphate coatings suffer from several environmental, health and safety drawbacks.
• WO 2006/088518 has disclosed a process for preparing zirconium-chromium conversion coatings on iron and iron alloys to improve the corrosion resistance and adhesive bonding strength.
• This known method comprises treating iron and iron alloys with an acidic aqueous solution having a pH ranging from about 2.5 to 5.5, preferably 3.7-4.0 for steel surfaces.
• the acidic aqueous solution comprises, per litre of solution, from about 0.01 to 22 grams of a trivalent chromium compound, about 0.01 to 12 grams of a hexafluorozirconate, about 0.0 to 12 grams of at least one fluorocompound selected from the group consisting of tetrafluoroborate, hexafluorosilicate and mixtures thereof, from about 0.0 to 10 grams of at least one divalent zinc compound, from 0.0 to about 10 grams of at least one water soluble thickener and from 0.0 to about 10 grams of at least one water soluble surfactant.
• Above known treatment contains at least zirconium and the preferred soluble trivalent chromium species is containing a sulphate anion.
• WO 2006/088519 A1 discloses a similar treatment, wherein the solution also comprises a stabilizing compound selected from polyhydroxy and carboxylic compounds.
• a stabilizing compound selected from polyhydroxy and carboxylic compounds.
• these preparations are used at low concentrations of the effective species to avoid over-etching and flash rust during drying.
• low concentrations result in less dense protective layers on the metal surface and therefore might affect the protective and/or bonding performance.
• a no-rinse process for treating metal surfaces is known, particularly for the subsequent application of organic coating compositions, in which the metal surface is wetted with an aqueous bath solution having a pH in the range of 2-3 and containing 0.5-10 g/L of chromium-(III) ions, 0.55-11 g/L of fluoride ions, 0.6-12.5 g/L of phosphate and 0.15-5.0 g/L of an organic film-forming agent which is soluble or homogeneously dispersible in water, like a water-soluble acrylic polymer.
• An object is to provide a method of protecting an organic coated surface of iron or iron alloy against corrosion and/or improving durable adhesion properties of such an organic coating or an adhesive using a metal surface treatment solution.
• Another object of the invention is the provision of an alternative metal treatment method and solution based on trivalent chromium for protection of an organic coated surface of iron or iron alloy against corrosion and/or for improvement of the adhesion properties of such an organic coating or an adhesive using a metal surface treatment solution.
• Yet another object is to provide a dry-in-place metal treatment method and solution requiring no rinse step after application.
• Yet another object is to provide a dry-in-place metal treatment solution for use at room temperature on iron and iron alloys without flash rusting.
• Still another object is to provide a metal treatment method and solution for application to an already phosphated surface of iron and iron alloy replacing a conventional chromate seal on such surface.
• the invention provides a method of treating a metal surface of iron or iron alloy for providing corrosion protection, adhesion of coating and/or adhesive, which method comprises the application of an aqueous composition onto the metal surface of iron or iron alloy, which composition consists of: trivalent chromium (Cr 3+ ): 1.16-7.0 g/l total fluoride (F - ): 1.3-7.7 g/l organic corrosion inhibitor: up to 2.0 g/l water soluble polymers: 0-4.0 g/l water soluble surfactant 0-1.0 g/l organo functional silane and/or oligomer 0-4.0 g/l pH adjusting agent 0-1.0 g/l fluoride adjusting agent 0-1.0 g/l wherein the molar ratio of Cr 3+ to : F - ranges from 0.25-0.4, and wherein the pH ranges from 2.0-4.4.
• the invention provides an aqueous composition as defined above for treating a metal surface of iron or iron alloy.
• the aqueous composition according to the invention is free of hexavalent chromium and contains as main constituents trivalent chromium ions and fluoride ions in a molar ratio of Cr 3+ to : F - ranging from 0.25-0.4.
• a solution having a relatively simple composition regarding its components without the need of specific more complex (fluorometalate) compounds as a source of fluoride ions offers good results regarding corrosion resistance and adhesion.
• the metal surface may have a conventional phosphate conversion coating applied to it, before it is exposed to the composition according to the invention.
• the composition can be easily applied, even in repair and maintenance conditions such as outdoor pipeline field applications, ship-building, road work, offshore, industrial equipment and other (non-mobile) steel structures.
• the composition can be applied directly to the metal surface, after conventional mechanical and/or chemical pre-treatment, such as grit blasting, sanding and scuffing and degreasing/pickling respectively. Rinsing after application of the composition is not necessary.
• the treatment solution can be dried in air under prevailing conditions and does not require any special measures or apparatuses. However the treated metal substrate should be dry before subsequent painting or adhesive bonding processes are carried out.
• forced drying methods can be used for example oven-drying, infra-red drying and forced-air drying.
• the thus treated surface of iron or iron alloy can be coated with an organic paint, optionally including the pre-application of a paint primer, and/or with an adhesive bonding system.
• the layer formed from the composition enhances the adhesion of the subsequently applied coating such as a paint layer system or adhesive bonding system.
• the enhanced adhesion offers good corrosion resistance when the thus coated metal surface is exposed to corrosive conditions.
• the layer formed may allow to reduce the layer thickness of a conventional paint primer or to waive the conventional primer at all .
• Trivalent chromium is present in amount of 1.16-7.0 g/l. A preferred range is 3.0-6.0 g/l. Total fluoride is in the range of 1.3-7.7 g/l.
• the molar ratio of Cr 3+ to : F - is 0.25-4.0, preferably 0.30-0.36, more preferably 0.32-0.34, such as 1:3. It has been found that the stoichiometric ratio of CrF 3 or slightly above offer good results regarding corrosion resistance and/or bonding characteristics.
• the trivalent chromium can be obtained by reducing chromic acid (H 2 CrO 4 ) with chemical agents that can be oxidized by chromic acid like methanol or hydrogen peroxide leaving no residual products in the starting solution after heating.
• Another attractive source is using CrF 3 .4H 2 O as a starting material. This compound is hardly soluble in water, but accompanied by acidic components like HF and acidic homopolymers and copolymers it is.
• HF is preferably used as it does not introduce extraneous anions.
• the pH ranges from 2.0-4.4, preferably 2.7-3.8, in particular 2.7-3.4.
• the composition may contain pH adjusting agents, such as alkali metal hydroxide like sodium hydroxide, potassium hydroxide, and ammonia, in an amount of 0-1.0 g/l. It is believed that alkali metal ions do not - or to a substantially lesser extent-contribute to the formation of the protective layer and thus its protection and/or bonding properties.
• the molar ratio of fluoride to trivalent chromium is preferably equal to or slightly above the stoichiometric ratio of CrF 3 .
• Adjustment may be carried out by incorporating of fluoride adjusting agents that offer an additional source of fluoride anions. If present, these fluoride adjusting agents are present in an amount up to 1.0 g/l.
• Preferred examples include fluoric acid, fluorides of alkali metals and ammonium, in particular sodium fluoride and ammonium bi fluoride.
• the composition according to the invention contains an organic corrosion inhibitor in amount up to 2.0 g/l, preferably 0.0001-2.0, more preferably 0.1-1.0 g/l.
• the organic corrosion inhibitor is a required component of the composition according to the invention.
• the organic corrosion inhibitor can act as a flash corrosion inhibitor, which inhibits so called "flash rusting" during drying of the applied treatment composition on iron and iron alloys surfaces.
• flash corrosion inhibitor is thought to contribute to the final corrosion resistance after application of a coating like paint.
• the organic corrosion inhibitor should be slightly soluble in water or miscible therewith.
• Examples include: N,N- dimethyl propylene urea, tolytriazole, zinc phthalate, imidazolinemaleate, caprylic acid, phtalic acid, phosphonic acid alkylesters, n-butyric acid, benzotriazole, tolytriazole, phthalate divalent salts, nitrobenzoate, 1-octanol, tannic acid, nitro maleate divalent salts, 2-mercaptobenzimidazole, propargyl alcohol, propargyl alcohol ethoxylates, iso nitro phtalate zinc salt, 2-butyn 1,4 diol, 2-butyn 1,4 diol alkoxylates, alkanolamine salt of a nitrogenous organic acids, quaternary amines and combinations thereof.
• Concentration and the nature of the organic corrosion inhibitor or a mixture of corrosion inhibitors should be chosen in a way that it will not block the trivalent chromium deposition on the metal during treatment..
• the composition may comprise additional components from a selected group of optional compounds.
• optional compounds include water soluble homopolymers and copolymers that preferably are based on the following monomers: acrylic acid, methacrylic acid, vinylalcohol, vinylether, maleic acid, vinylphosphonic acid, vinylsulphonic acid, methyl vinylether and combinations thereof, up to 4.0 g/l, preferably 0.01-4.0 g/l, more preferably 0.1-1 g/l.
• Another optional compound is a water soluble surfactant, which may be present in an amount up to 1.0 g/l.
• a preferred concentration range is 0.001-0.5 g/l, while a more preferred concentration ranges from 0.01-0.1 g/l.
• Surfactant that can be used in the composition according to the invention include acid stable low foaming anionic and non-ionic surfactants like alkaryl sulfonates and poly ethylene glycol fatty amines. The surfactant provides uniform wetting of the substrate and efficient removal of oil and dirt. If the amount of surfactant is too high, it can cause excessive foaming in the process.
• an organo functional silane and/or a hydrolysed oligomer thereof is an organo functional silane and/or a hydrolysed oligomer thereof. If present, the concentration ranges up to 4.0 g/l.
• the reactive functional group is at least one selected from a mercapto group, an amino group, a vinyl group, an epoxy group and a methacryloxy group, advantageously in an amount of 1 to 40 mg/l based on Si.
• the method of treating a metal surface of iron or iron alloy for providing corrosion resistance and adhesion of a coating and or adhesive comprises a step of applying the aqueous composition according to the invention and outlined hereinabove to the metal surface.
• the metal surface to be treated with the composition according to the invention is pre-treated using known mechanical or chemical pre-treatment processes or acombination thereof for obtaining a better wettable surface, which typically requires the surface to be roughened and to be substantially free of rust, scale and oxides, fat, oil and the like.
• Mechanical pre-treatment processes comprise dry grit blasting, sanding, scuffing and abrading.
• Chemical pre-treatment include (acidic/alkaline/solvent) degreasing and pickling.
• a chemical pre-treatment is followed by a rinsing step using tap water or demineralised water. Combinations of mechanical pre-treatment and chemical pre-treatment in any order is also possible.
• the composition according to the invention can also replace degreasing using a solvent on oiled surfaces of iron or iron alloy, that are free of scale and oxides.
• a present composition containing a surfactant on such surfaces removal of oil, fat and dirt and building of the conversion layer occur simultaneously, rendering a preceding solvent degreasing step superfluous.
• a surfactant on such surfaces removal of oil, fat and dirt and building of the conversion layer occur simultaneously, rendering a preceding solvent degreasing step superfluous.
• the method according to the invention involves contacting an oiled, but scale and oxide free surface of iron or iron alloy with the present composition.
• composition according to the invention allows also to replace a conventional chromate seal on an already phosphated surface of iron and iron alloy.
• the way of applying the composition according to the invention to the metal surface is not limited. However, homogeneity and uniformity of the applied wet film on the substrate before drying will be advantageous. Suitable application methods include spraying, dipping, wiping, brushing, roll coating and the like. Excess of treatment fluid on parts with intricate geometries can be removed with compressed air before drying. After application it is not necessary to perform a rinsing step to remove unreactive and/or unreacted species from the formed layer. Instead thereof the metal surface to which the composition according to the invention is applied can be allowed to dry immediately, e.g. in air optionally at elevated temperature like an oven having conditioned air.
• the coating weight (after drying measured by XRF (X ray fluorescence) ranges from 20 to 200 mg chromium/m 2 . Higher coating weights will reduce adhesion properties of subsequently applied organic coating layers. At lower coating weights no beneficial effect in corrosion protection has been measured.
• XRF X ray fluorescence
• a subsequently applied paint system and/or adhesive bonding system can be applied using conventional methods and equipment, such as spraying, brushing and roll coating.
• the invention is illustrated by the following examples according to the invention and comparative examples.
• the trivalent chromium compound "Cr(III) Fluoride" as indicated in the below Tables was obtained by reducing a chromic acid solution in a stoichiometric ratio chromium to fluoride 1 to 3.
• the fluoride source was an aqueous solution of hydrogen fluoride.
• Methanol in water was used as a reducing agent. After 4 hours of reduction at 80 °C no hexavalent chromium could be detected by using a s-diphenylcarbazide test method (detection limit for Cr(VI) is smaller than 0.03 ppm). Methanol and oxidation products of methanol like formalin and formic acid could not be detected by TOC (total organic carbon) measurements.
• Aqueous metal surface treatment liquids having a composition as indicated in Table 1 were prepared and applied to metal surfaces as indicated in Tables 2-4..
• Corrosion tests Accelerated corrosion testing according to ASTM B117 Neutral Salt Spray for iron, iron alloys and zinc coated steels .
• Tables 2 -4 summarize the test results. Table 1.
• Table 1. Examples composition Example Chromium compound (source) Concentration [Cr] g/L Fluoride source Molair ratio Cr :F Organic corrosion inhibitor (content mg/L) Surfactant Watersoluble polymer (content, mg/L) pH Ex1 dissolved CrF3*4aq 1,5 CrF3*4aq 1 :3 divalent, phthalate (200) PAA (200) 3.4 Ex2 dissolved CrF3*4aq 1,5 CrF3*4aq 1 :3 divalent, phthalate (200) Plurafac LF PAA (200) 3.4 Ex3 Cr(III), Fluoride 4 HF 1 :3 Dodicor (200) Plurafac LF PAA (200) 3.3 Ex4 Cr(III), Fluoride 4 HF 1 :3 Dodicor (200) 3.3 Ex5 Cr
• compositions according to the invention present better performance with respect to coating adhesion, wettability, flash rust inhibition and corrosion resistance than the comparative examples, that fail in one or more of these aspects or are worse.

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• Chemical & Material Sciences (AREA)
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• Chemical Kinetics & Catalysis (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Chemical Treatment Of Metals (AREA)

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Citations (4)

• 2016
  • 2016-08-31 NL NL2017398A patent/NL2017398B1/nl not_active IP Right Cessation
• 2017
  • 2017-08-30 EP EP17188548.6A patent/EP3290543B1/fr active Active
  • 2017-08-30 PL PL17188548T patent/PL3290543T3/pl unknown
  • 2017-08-30 ES ES17188548T patent/ES2865428T3/es active Active

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