EP3290543A1 - Method of treating metal surfaces with an aqueous composition and aqueous composition - Google Patents

Method of treating metal surfaces with an aqueous composition and aqueous composition Download PDF

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Publication number
EP3290543A1
EP3290543A1 EP17188548.6A EP17188548A EP3290543A1 EP 3290543 A1 EP3290543 A1 EP 3290543A1 EP 17188548 A EP17188548 A EP 17188548A EP 3290543 A1 EP3290543 A1 EP 3290543A1
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Prior art keywords
iron
aqueous composition
composition
range
metal surface
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EP17188548.6A
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German (de)
French (fr)
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EP3290543B1 (en
Inventor
Richard Johannes Van Der Net
Robin Arthur LANGELAAR
Roland Lambertus Maria van MEER
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Ad Productions BV
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Ad Productions BV
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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 Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
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Abstract

The invention relates to a method of treating a metal surface of iron or iron alloy using an aqueous composition for imparting corrosion resistance and bonding properties, as well as to the aqueous composition. The aqueous composition consists of:
Figure imga0001
 wherein the molar ratio of Cr3+to :F- ranges from 0.25-0.4, and wherein the pH ranges from 2.0-4.4.

Description

  • The invention relates to a method of treating metal surfaces with an aqueous composition and to an aqueous composition for treatment of metal surfaces.
  • Mechanical and chemical treatment of metal surfaces for enhancing corrosion resistance and/or improving bonding to a subsequently applied coating such as an adhesive layer, paint layer, lacquer layer or other finishing layer is well known in the art. E.g. mechanical treatment for example grid blasting has been used to remove scale and/or oxides from the metal surface and to improve adhesion, when chemical treatment steps were not practical to apply. Only waterborne cleaning of metal parts made of especially iron and iron alloys without any suitable chemical treatment will result in flash rusting (also known as "rapid corrosion"), if the parts are not painted within a few hours. Degreasing of oiled surfaces using a suitable solvent like thinner or heptane does not give rise to flash rusting. However, solvent degreasing offers considerable health and safety risks for personnel and the environment. Chemical treatment of metal surfaces of zinc (alloy) coated steel, mild steel, or aluminium and their alloys with aqueous chromate (chromium VI) solutions results in a so called "chromate conversion layer", which offers corrosion resistance and improved adhesion, and avoids the occurrence of flash rusting before painting.
  • It is also recognized that these chromate based aqueous solutions suffer from the toxicity of the Cr6+ component thereof. Cr6+ is classified as carcinogenic and will be banned from most industrial applications with high exposure risks for the co-workers. Disposal of the toxic treatment composition is also a problem, although to a lesser extent if it is converted into the comparatively innocuous trivalent chromium. However, such a conversion brings about additional costs and expenses.
  • Also 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.
  • Today the use of chromate-free (paint) primers has become more common. It has appeared that mechanical and chemical pre-treatments of metals become more important to guaranty corrosion protection performance of metal paint systems.
  • Ongoing legislation is also developed and comes gradually into force in order to reduce and ultimately abandon hexavalent chromium based metal treatment compositions.
  • Therefore, in the art there is a need for treatments that are substantially free of hexavalent chromium compounds, that offer corrosion resistance and bonding performance to the metal surfaces treated similar to those obtained by treating these metal surfaces with conventional solutions comprising hexavalent chromium.
  • Various proposals to satisfy this need have been disclosed in the patent literature. E.g. 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. These extraneous cations and anions will affect the formation to insoluble species negatively. Therefore the remaining unreacted solution should be rinsed from the substrate with tap or demineralised water resulting in an additional waste stream that requires disposal or other processing.
  • WO 2006/088519 A1 discloses a similar treatment, wherein the solution also comprises a stabilizing compound selected from polyhydroxy and carboxylic compounds. In practice, these preparations are used at low concentrations of the effective species to avoid over-etching and flash rust during drying. However, low concentrations result in less dense protective layers on the metal surface and therefore might affect the protective and/or bonding performance.
  • From EP 111897 A1 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.
  • Accordingly, in a first aspect 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 (Cr3+): 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 Cr3+ to :F- ranges from 0.25-0.4, and wherein the pH ranges from 2.0-4.4.
  • In a second aspect the invention provides an aqueous composition as defined above for treating a metal surface of iron or iron alloy.
  • Below the invention is explained first of all in terms of composition and components thereof. 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 Cr3+to :F- ranging from 0.25-0.4. Surprisingly it has been found that 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. These fluorometalate compounds as used in the prior art will introduce extraneous polyvalent metal ions and these are believed not to play a significant role regarding corrosion resistance and adhesion and could complicate the preparation of the composition regarding desired ratios of components. Contrary thereto the composition according to the invention can be easily prepared. Inorganic anions other than fluorides like phosphates are advantageously absent in the composition according to the invention. These other inorganic anions increase the solubility of the resulting conversion layer and affect its performance. Also stability and maintenance of the treatment bath might become more complicated. Metal surfaces that can be suitably treated with the composition according to the invention include iron and iron alloys such as cold rolled steel, mild steel and carbon steels. 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. Typically 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. In order to reduce process time forced drying methods can be used for example oven-drying, infra-red drying and forced-air drying. After the composition has been applied and sufficiently dried, 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. Furthermore, it has appeared that 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 Cr3+ 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 CrF3 or slightly above offer good results regarding corrosion resistance and/or bonding characteristics.
  • The trivalent chromium can be obtained by reducing chromic acid (H2CrO4) 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 CrF3.4H2O 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. In order to set the acidity at the required level 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.
  • As said, the molar ratio of fluoride to trivalent chromium is preferably equal to or slightly above the stoichiometric ratio of CrF3. 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. Thus 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. In addition the organic 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..
  • In addition to the above components the composition may comprise additional components from a selected group of optional compounds. These 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. These polymers improve wetting behaviour of the treatment composition, as well as adhesion of subsequently applied organic coatings. Too high concentrations will reduce wet adhesion of an organic coating. 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.
  • Yet another component that may be present, 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. Typically 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. Typically 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.
  • It has surprisingly been found that 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. Upon application of the composition according to the invention, in particular 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. Thus in an embodiment of 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.
  • The 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.
  • Advantageously the coating weight (after drying measured by XRF (X ray fluorescence)) ranges from 20 to 200 mg chromium/m2. 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.
  • 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 various features of the treatment composition as discussed above are equally applicable to the method according to the invention.
  • 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..
  • The thus pre-treated, treated and organic coated surfaces were subjected to adhesion tests and corrosion tests according to quality regulations prescribed GSB and Qualitysteelcoat: Adhesion Cross cut adhesion pull-off EN ISO 16276-2; ASTM D3359
  • Adhesion Reversed impact ASTM D2794 or EN ISO 6272-1 and
  • 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. 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(III), Fluoride 4 HF 1 :3 divalent, phthalate (200) 3.0
    Ex6 Cr(III), Fluoride 4 HF 1: 3 propargyl alcohol (20) 2.9
    Comp 1 dissolved CrF3*4aq 1,5 CrF3*4aq 1 :3 PAA (200) 3.0
    Comp 2 Cr(III), Fluoride 0,28 HF 1 : 3 3.1
    Comp 3 Cr(III), Fluoride 4 HF + ABF 2 :7 3.4
    Comp 4 Cr(III), Fluoride 4 HF 1 :3 Plurafac LF PAA(100), PVA (50) 3.0
    Comp 5 DiChromiumTriSulphate 4 H2ZrF6 1 :6 caprylic acid (50) 3.0
    Comp 6
    Comp 7 Cr(III), Fluoride 4 HF 1 :3 PAA (100), PVA (50) 2.9
    Comp 8
    HF Hydrogen Fluoride
    ABF Ammonium bi Fluoride
    CrF3.4H2O Chromium Trifluoride
    H2ZrF6 HexafluoroZirconium Acid
    Dodicor (Clariant) commercial blend of corrosion inhibitors: benzyl quaternary amine imidazoline salt and propynol
    Plurafac LF (BASF) commercial branched and linear ethoxylated fatty alcohol
    PAA Poly acrylic acid (Mw = 100000 g/mol)
    PVA Poly vinyl alcohol (Mw = 60000 g/mol)
    Tabel 2. Examples method and results
    Examples Metal substrate Pretreatment Application room temperature Discoloration / flash rust during unforced drying Coating wt (mg Cr/m2) Type of organic coating Adhesion test #cut impact < 2mm Corrosion after x hours
    Ex5 CRS alk cleaned immersion 3 min no flash rust 80 coil coat pass 500
    Comp 1 CRS alk cleaned immersion 3 min slightly yellow stains 50 coil coat pass n/a
    Comp 2 CRS alk cleaned immersion 3 min yellow/ orange stains 40 coil coat failed n/a
    Comp 3 CRS alk cleaned immersion 3 min slightly yellow stains 120 coil coat pass 240
    Comp 4 CRS alk cleaned immersion 3 min slightly yellow stains 60 coil coat pass 240
    Comp 5 CRS alk cleaned immersion 3 min no flash rust 40 coil coat failed <168
    Ex6 C-steel grid blasted spray 2 min no flash rust 90 epoxy powder pass 1000
    Comp 6 C-steel grid blasted no flash rust epoxy powder pass <500
    Comp 7 C-steel grid blasted spray 2 min slightly yellow stains 75 powder pass 500
    Comp 8 C-steel grid blasted no flash rust powder pass <240
    CRS Oiled cold rolled steel
    C steel Low carbon steel DC-1
    alkaline cleaned alkaline cleaning (pH =10) during 3 minutes at 52 °C
    grid blasted mechanical roughening and removal of rust and oxides
    coil coat liquid polyester coating (7 micrometres)cured at 240° C in 40 - 60 seconds
    epoxy powder epoxy primer powder coating (300 micrometres) cured at room temperature in 2 weeks
    powder powder coating (80 micrometres) cured at 175oC in 15 minutes
    corrosion test SST is neutral salt spray test according to ASTM B117
    Table 3: Test results
    Carbon steels with mill scale or rusted/oxidized surfaces
    Example Inv Com p Comp Inv Comp Inv Comp Inv Comp Inv Comp
    Mechanical removal of rust and mill scale
    Dry abrasive grit blast cleaniing x x x x x x x x
    Scuffing disc/followed by grit blasting x x
    Chemical Treatment
    Commercial alkaline cleaned surface x x x
    Commercial iron phosphated surface x x x
    Ex1 spray application (2 min) x x x
    Ex2 wipe application x x
    Commercial Zr treated spray application x
    Organic Coating
    Type wet wet powder powder powder wet wet wet wet powder powder
    Coating thickness (µm) 95 95 60 60 60 1500 1500 1500 1500 90 90
    Adhesion test
    Adhesion cross-cut 1 mm + tape
    Corrosion
    NEN en ISO 92227 Neutral Salt Spray Test (ASTM B117)
    Creepage from the scribe (ISO 4628-8)
    After 500 hrs exposure (mm) 4 0 >50 1.5 3.4 2.3 3.7
    After 1000 hrs exposure (mm) 3 >20 2 14
    Table 4. Test results
    Slightly oiled mild steel substrate without oxide/mill scale
    Without solvent degreasing x x x x
    Solvent degreasing by wiping x x x
    Wipe/brush application of treatment compostion
    Comp 7 x
    Comp 4 x x
    Ex5 x
    Ex3 x
    Properties after treatment
    Wetting pretreatment n/a n/a poor good good poor good
    Flash rust during drying no no yes yes yes no no
    Wetting of powder paint (100 µm) very poor poor good good good good good
  • From the above examples and test results it appears that the 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.

Claims (15)

  1. 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 (Cr3+): 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 Cr3+ to :F- ranges from 0.25-0.4, and wherein the pH ranges from 2.0-4.4.
  2. The method according to claim 1, wherein the concentration trivalent chromium (Cr3+) in the aqueous composition is in the range of 3.0-6.0 g/L.
  3. The method according to claim 1 or 2, wherein the mol ratio Cr3+: F- in the aqueous composition is in the range of 0.30-0.36, preferably 0.32-0.34 and more preferably 1:3.
  4. The method according to any one of the preceding claims, wherein the composition comprises dissociated CrF3.4H2O.
  5. The method according to any one of the preceding claims, wherein the concentration organic corrosion inhibitor in the aqueous composition is in the range of 0.0001-2.0, preferably 0.1-1.0 g/L.
  6. The method according to any one of the preceding claims, wherein the concentration of the water soluble polymers in the aqueous composition ranges from 0.01-4.0, preferably 0.1-1.0 g/L.
  7. The method according to any one of the preceding claims, wherein the concentration of the water soluble surfactant in the aqueous composition is in the range of 0.001-0.5, preferably 0.01-0.1 g/L.
  8. The method according to any one of the preceding claims, wherein the pH ranges from 2.7-3.8, preferably from 2.7 to 3.4.
  9. The method according to any one of the preceding claims, wherein the coating weight, measured by XRF after drying, is in the range of 20-200 mg chromium/m2.
  10. The method according to any one of the preceding claims, wherein the metal surface is selected from a solvent degreased metal surface of iron or iron alloy, a metal surface of iron or iron alloy from which scale and oxides have been removed mechanically, a metal surface of iron or iron alloy that has already been provided with a phosphate conversion coating, and an oiled metal surface of iron and iron alloy that is free from scale and oxides.
  11. An aqueous composition for treating a metal surface of iron or iron alloy, in particular for use in the method according to any one of the preceding claims, which composition consists of: trivalent chromium (Cr3+): 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 Cr3+ to :F- ranges from 0.25-0.4, and wherein the pH ranges from 2.0-4.4.
  12. The composition according to claim 11, wherein the concentration trivalent chromium (Cr3+) is in the range of 3.0-6.0 g/L
  13. The composition according to claim 11 or 12, wherein the mol ratio Cr3+: F- is in the range of 0.30-0.36, preferably 0.32-0.34 and more preferably 1:3.
  14. The composition according to any one of the preceding claims 11-13, wherein the concentration organic corrosion inhibitor is in the range of 0.0001-2.0, preferably 0.1-1.0 g/L.
  15. The composition according to any one of the preceding claims 11-14, wherein the concentration of the water soluble polymers in the aqueous composition ranges from 0.01 - 4.0, preferably 0.1-1.0 g/L; and/or the concentration of the water soluble surfactant in the aqueous composition is in the range of 0.001-0.5, preferably 0.01-0.1 g/L; and/or the pH is in the range of 2.7-3.8, preferably 2.7-3.4.
EP17188548.6A 2016-08-31 2017-08-30 Method of treating metal surfaces with an aqueous composition and aqueous composition Active EP3290543B1 (en)

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0111897A1 (en) * 1982-12-23 1984-06-27 Gerhard Collardin GmbH Process for the treatment of metal surfaces, especially aluminium, aluminium alloy and steel ones, and aqueous bath solutions suitable therefor
EP0337411A2 (en) * 1988-04-12 1989-10-18 SurTec GmbH Process for preparing an acidic passivating bath for zinc, zinc alloys an cadmium surfaces, containing chromium III and fluoride
US20050103229A1 (en) * 2002-01-11 2005-05-19 Kazuya Tanaka Aqueous agent for treating substrate, method for treating substrated and treated substrate
US20110100513A1 (en) * 2009-11-04 2011-05-05 Bulk Chemicals, Inc. Trivalent chromium passivation and pretreatment composition and method for zinc-containing metals

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0111897A1 (en) * 1982-12-23 1984-06-27 Gerhard Collardin GmbH Process for the treatment of metal surfaces, especially aluminium, aluminium alloy and steel ones, and aqueous bath solutions suitable therefor
EP0337411A2 (en) * 1988-04-12 1989-10-18 SurTec GmbH Process for preparing an acidic passivating bath for zinc, zinc alloys an cadmium surfaces, containing chromium III and fluoride
US20050103229A1 (en) * 2002-01-11 2005-05-19 Kazuya Tanaka Aqueous agent for treating substrate, method for treating substrated and treated substrate
US20110100513A1 (en) * 2009-11-04 2011-05-05 Bulk Chemicals, Inc. Trivalent chromium passivation and pretreatment composition and method for zinc-containing metals

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