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
  • C23C22/36—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 containing also phosphates
  • C23C22/361—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 containing also phosphates containing titanium, zirconium or hafnium compounds
• • 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
  • C23C22/36—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 containing also phosphates
  • C23C22/364—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 containing also phosphates containing also manganese cations
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D139/00—Coating compositions based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a single or double bond to nitrogen or by a heterocyclic ring containing nitrogen; Coating compositions based on derivatives of such polymers
  • C09D139/04—Homopolymers or copolymers of monomers containing heterocyclic rings having nitrogen as ring member
  • C09D139/06—Homopolymers or copolymers of N-vinyl-pyrrolidones
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D7/00—Features of coating compositions, not provided for in group C09D5/00; Processes for incorporating ingredients in coating compositions
  • C09D7/40—Additives
  • C09D7/65—Additives macromolecular
• • 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

Definitions

• This invention relates to the field of the anti-corrosive treatment of vehicle bodies or domestic appliances, wherein an anti-corrosive coating is produced on selected non-ferrous surfaces. It is particularly suitable for metal components having surfaces of two or more different non-ferrous metals. A particular feature of the present invention is the fact that no toxic chromium has to be used.
• U.S. Pat. No. 5,129,967 discloses treatment baths for a no-rinse treatment (referred to there as “dried in place conversion coating”) of aluminum, containing:
• EP-B-8 942 discloses treatment solutions, preferably for aluminum cans, containing:
• an aqueous concentrate for regenerating the treatment solution containing:
• DE-C-24 33 704 describes treatment baths to increase paint adhesion and permanent corrosion protection on aluminum, among other materials, which may contain 0.1 to 5 g/l polyacrylic acid or salts or esters thereof and 0.1 to 3.5 g/l ammonium fluorozirconate, calculated as ZrO 2 .
• the pH of these baths may vary over a broad range. The best results are generally obtained when the pH is 6-8.
• U.S. Pat. No. 4,992,116 describes treatment baths for the conversion treatment of aluminum with a pH of between about 2.5 and 5, which contain at least three components:
• a molar ratio of about 2.5:1 to about 1:10 should be maintained between the fluoro acid and the phosphate.
• WO 92/07973 teaches a chromium-free treatment process for aluminum which uses as its main components 0.01 to about 18 wt. % H 2 ZrF 6 and 0.01 to about 10 wt. % of a 3-(N-C 1 -C 4 alkyl-N-2-hydroxyethylaminomethyl)-4-hydroxystyrene polymer in an acidic aqueous solution.
• Optional components are 0.05 to 10 wt. % dispersed SiO 2 , 0.06 to 0.6 wt. % of a solubility promoter for the polymer and surfactant.
• Vehicle bodies such as car bodies, are currently assembled from steel and/or other metallic materials, such as galvanised steel or aluminum. After assembly, the bodies are cleaned and subjected to a conversion treatment before painting, to achieve adequate corrosion protection and adequate paint adhesion. The bodies are then painted, generally these days by cathodic electrodeposition coating. Domestic appliances containing metal components, such as refrigerators, freezers, washing machines, tumble driers, cookers, microwave ovens or even metal furniture, may be subjected to a similar process. Owing to the lower corrosion protection requirements for these items, they are generally coated with a powder coating after the conversion treatment.
• Phosphating is widespread as a conversion treatment for domestic appliances.
• conversion treatment takes place exclusively as so-called “layer-forming” zinc phosphating.
• the vehicle bodies are contacted with an aqueous solution having a pH of about 2.5 to about 3.8, containing about 0.3 to 2 g/l zinc ions and about 10 to about 20 g/l phosphate ions.
• These phosphating solutions often also contain about 0.3 to 2 g/l manganese ions and often nickel or copper ions.
• a layer of crystalline zinc iron phosphates is formed on steel surfaces and a layer of crystalline zinc phosphates on zinc or aluminum surfaces.
• the actual phosphating step is accompanied by additional steps.
• the metal surfaces are first cleaned, generally in several steps, and then activated.
• the metal surfaces are contacted with a solution which mainly contains secondary alkali metal phosphates and suspended colloidal titanium phosphates.
• This step must be very carefully controlled in order to guarantee sufficient quality of the subsequent phosphating.
• the activating baths are consumed relatively quickly, so that they have to be renewed at short intervals of a few days to several weeks. The monitoring and care of the activation baths therefore represents a considerable proportion of the care and monitoring expenditure for a phosphating line.
• the actual phosphating step is generally followed by so-called post-passivation.
• post-passivation As a result of this post-passivation, any pores remaining in the crystalline phosphate layer are closed and corrosion protection and paint adhesion are improved.
• the phosphated metal surfaces are contacted with an aqueous solution which may contain various components.
• post-passivation solutions based on hexavalent chromium, complex fluorides of titanium and/or hafnium, reactive polymers of vinyl phenol derivatives or copper ions are in practical use. These post-passivation baths also have to be checked and adjusted regularly.
• a conversion treatment in the form of phosphating therefore generally requires, in addition to cleaning, at least three treatment baths for activation, phosphating and post-passivation, all of which have to be regularly checked and, if necessary, adjusted or renewed.
• These at least three baths that are required and the additional rinsing baths between them mean that a large space and high investments are required, thus increasing costs for the manufacture of vehicle bodies and domestic appliances.
• car bodies generally contain surfaces of steel, often in conjunction with surfaces of aluminum and/or galvanised or alloy-galvanised steel.
• car bodies and domestic appliances apart from plastics parts, may be assembled in such a way that the metal surfaces thereof represent exclusively non-ferrous surfaces. Examples of these non-ferrous surfaces are surfaces of zinc (by the use of galvanised steel), aluminum, magnesium or alloys of these elements with one another or with other metals. Even for the anti-corrosive treatment of items of this type, the phosphating described above is used exclusively at present.
• An object of the present invention is to reduce the cost of anti-corrosive treatment for car bodies or domestic appliances compared with the prior art.
• the present invention is based on the knowledge that the complex process sequence for phosphating may be made shorter if the metal surfaces of the car bodies or domestic appliances have virtually no iron surfaces.
• the present invention relates to a process for the anti-corrosive treatment of vehicle bodies or domestic appliances which, at least in part, have a metal surface and wherein this metal surface consists of at least 90%, based on the metal surface, zinc, aluminum and/or magnesium and/or alloys of these metals with one another or with other alloying elements, wherein the vehicle bodies or domestic appliances are cleaned, passivated and painted, characterised in that, for the purpose of passivation, the vehicle bodies or domestic appliances are contacted with an aqueous solution having a pH of 1 to 12 and containing complex fluorides of Ti, Zr, Hf, Si and/or B in a quantity such that the content of Ti, Zr, Hf, Si and/or B is 20 to 500 mg/l, and 50 to 2000 mg/l organic polymers, the composition of the aqueous solution being selected such that no crystalline zinc-containing phosphate layer is formed on the metal surface.
• the complex fluorides of the above elements may be introduced into the aqueous solution in the form of the corresponding fluoro acids or the alkali metal and/or ammonium salts thereof.
• complex fluorides of titanium or zirconium are formed by the reaction of oxides or salts of these elements with hydrofluoric acid.
• the aqueous solution may contain free fluoride, for example in the form of hydrofluoric acid or alkali metal or ammonium fluorides.
• the content of free fluoride may, for example, be from 0.001 to 1 g/l. This addition of free fluoride increases the pickling action of the aqueous solution and thus the rate of formation of the conversion coating, particularly in the case of hot-dip galvanised steel or aluminum.
• the present process is preferably used for those car bodies and domestic appliances which have no surfaces of uncoated steel.
• the steel surface it is not impossible for the steel surface to be bare at cut edges, weld points or grinding points even when coated steel, such as galvanised steel, pre-phosphated steel or organically pre-coated steel, is used.
• a proportion of at least 90%, preferably 95% and particularly preferably 99% of the metal surface should consist of the above-mentioned metals, zinc surfaces generally being surfaces of galvanised steel.
• Non-metallic surfaces, such as plastics surfaces or surfaces of pre-phosphated or organically pre-coated steel, are not included in this area relation.
• the present process has the great advantage that, compared with conventional phosphating, the activation and post-passivation steps may be omitted. This means that the pre-treatment line is shorter and the time spent on caring for the baths and disposing of them is reduced. This simplifies the process control, reduces the costs and decreases the burden on the environment.
• Aqueous treatment solutions that may be used for the present process are known in principle in the prior art. Examples are mentioned in the introduction. Up to the present, treatment baths of this type have been used for treating less complex components, such as metal strips, metal sheets or metal cans. For complex components, such as car bodies or domestic appliances, these treatment baths have not been used up to now as the sole conversion treatment before painting. In particular, these treatment baths have not been used up to now in processes in which complex metal components were coated by electrodeposition or with a powder coating immediately after the conversion treatment.
• the aqueous solution used for passivation in the process sequence according to the present invention preferably contains the complex fluorides of Ti, Zr, Hf, Si and/or B in a quantity such that the content of Ti, Zr, Hf, Si and/or B is 50 to 400 mg/l.
• the aqueous solution preferably contains 100 to 1000 mg/l organic polymers.
• the organic polymers may, for example, be selected from epoxy resins, amino resins, tannins, phenol-formaldehyde resins, polycarboxylic acids, polymeric alcohols and/or the esterification products thereof with polycarboxylic acids, poly-4-vinylphenol compounds, amino group-containing homo- or co-polymer compounds and polymers or copolymers of vinyl pyrrolidone.
• epoxy resins amino resins, tannins, phenol-formaldehyde resins, polycarboxylic acids, polymeric alcohols and/or the esterification products thereof with polycarboxylic acids, poly-4-vinylphenol compounds, amino group-containing homo- or co-polymer compounds and polymers or copolymers of vinyl pyrrolidone.
• the organic polymers may, for example, be selected from poly-4-vinylphenol compounds corresponding to general formula (I):
• n represents a number between 5 and 100
• x independently represents hydrogen and/or CRR 1 OH groups wherein R and R 1 represent hydrogen, aliphatic and/or aromatic radicals having 1 to 12 carbon atoms.
• the organic polymers may be selected from amino group-containing homo- or co-polymer compounds, comprising at least one polymer selected from the group consisting of (a), (b), (c) or (d), wherein:
• (a) comprises a polymer material having at least one unit of the formula:
• R 1 to R 3 independently for each of the units, are selected from the group consisting of hydrogen, an alkyl group having 1 to 5 carbon atoms or an aryl group having 6 to 18 carbon atoms;
• Y 1 to Y 4 are selected from the group consisting of hydrogen, —CR 11 R 5 OR 6 , —CH 2 Cl or an alkyl or aryl group having 1 to 18 carbon atoms or Z:
• R 5 to R 12 independently for each of the units, are selected from the group consisting of hydrogen, an alkyl, aryl, hydroxyalkyl, aminoalkyl, mercaptoalkyl or phosphoalkyl group;
• R 12 may also be —O ( ⁇ 1) or —OH;
• W 1 is selected from the group consisting of hydrogen, an acyl, an acetyl, a benzoyl group; 3-allyloxy-2-hydroxypropyl; 3-benzyloxy-2-hydroxypropyl; 3-butoxy-2-hydroxypropyl; 3-alkyloxy-2-hydroxypropyl; 2-hydroxyoctyl; 2-hydroxyalkyl; 2-hydroxy-2-phenylethyl; 2-hydroxy-2-alkylphenylethyl; benzyl; methyl; ethyl; propyl; alkyl; allyl; alkylbenzyl; haloalkyl; haloalkenyl; 2-chloropropenyl; sodium; potassium; tetraarylammonium; tetraalkylammonium; tetraalkylphosphonium; tetraarylphosphonium or a condensation product of ethylene oxide, propylene oxide or a mixture or a copoly
• (b) comprises:
• R 1 to R 2 independently for each of the units, are selected from the group consisting of hydrogen, an alkyl group having 1 to 5 carbon atoms or an aryl group having 6 to 18 carbon atoms;
• Y 1 to Y 3 are selected from the group consisting of hydrogen, —CR 4 R 5 OR 6 , —CH 2 Cl or an alkyl or aryl group having 1 to 18 carbon atoms or Z:
• R 4 to R 12 independently for each of the units, are selected from the group consisting of hydrogen, an alkyl, aryl, hydroxyalkyl, aminoalkyl, mercaptoalkyl or phosphoalkyl group; R 12 may also be —O ( ⁇ 1) or —OH;
• W 2 independently for each of the units, is selected from the group consisting of hydrogen, an acyl, an acetyl, a benzoyl group; 3-allyloxy-2-hydroxypropyl; 3-benzyloxy-2-hydroxypropyl; 3-alkylbenzyloxy-2-hydroxypropyl; 3-phenoxy-2-hydroxypropyl; 3-alkylphenoxy-2-hydroxypropyl; 3-butoxy-2-hydroxypropyl; 3-alkyloxy-2-hydroxypropyl; 2-hydroxyoctyl; 2-hydroxyalkyl; 2-hydroxy-2-phenyleth
• At least a fraction of the above part is polymerised with one or more monomers which are selected, independently for each unit, from the group consisting of acrylonitrile, methacrylonitrile, methyl acrylate, methyl methacrylate, vinyl acetate, vinyl methyl ketone, isopropenyl methyl ketone, acrylic acid, methacrylic acid, acrylamide, methacrylamide, n-amyl methacrylate, styrene, m-bromostyrene, p-bromostyrene, pyridine, diallyldimethylammonium salts, 1,3-butadiene, n-butyl acrylate, t-butylaminoethyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, n-butyl vinyl ether, t-butyl vinyl ether, m-chlorostyrene, o-chlorostyrene
• (d) comprises a condensation polymer of the polymeric materials (a), (b) or (c), wherein a condensable form of (a), (b), (c) or a mixture thereof is condensed with a second compound which is selected from the group consisting of phenols, tannins, novolak resins, lignin compounds, together with aldehydes, ketones or mixtures thereof, to produce a condensation resin product wherein the condensation resin product, by adding “Z” to at least a part thereof, then reacts further by reaction of the resin product with (1) an aldehyde or ketone (2) a secondary amine to form a final adduct which may react with an acid.
• a condensation resin product by adding “Z” to at least a part thereof, then reacts further by reaction of the resin product with (1) an aldehyde or ketone (2) a secondary amine to form a final adduct which may react with an acid.
• the polymer described above is characterised in that at least a fraction of the groups Z of the organic polymer has a polyhydroxyalkylamine functionality, which results from the condensation of an amine or ammonia with a ketose or aldose having 3 to 8 carbon atoms.
• the organic polymer may represent a condensation product of a polyvinylphenol having a molecular weight of 1000 to 10000 with formaldehyde or paraformaldehyde and with a secondary organic amine.
• This secondary organic amine is preferably selected from methylethanolamine and n-methylglucamine.
• the organic polymer represents polycarboxylic acid or the anions thereof, it is preferably selected from polymers or copolymers of acrylic acid, methacrylic acid or the esterification products thereof with lower alcohols, for example having 1 to 4 carbon atoms.
• the solutions or suspensions of these polycarboxylic acids may additionally contain polymeric alcohols, such as polyvinyl alcohol, and/or the esterification products thereof with polymeric alcohol and the polycarboxylic acid may be present together. When the coating is dried, they then cross-link with one another by at least partial ester formation.
• the aqueous solution may contain polymers or copolymers of vinyl pyrrolidone. Suitable as homo- or co-polymers of vinyl pyrrolidone are, for example, the polymers listed in Table 1 or polymers of the monomers listed there.
• the application solution preferably has a pH of 1 to 6, narrower ranges possibly being preferred depending on the substrate, the type of application and the time of exposure.
• a pH of 2 to 4 is preferably selected and for the treatment of zinc or galvanized steel, a pH of 3 to 5.
• the process sequence according to the present invention may also be applied to car bodies or domestic appliances which have some surfaces of pre-phosphated or organically pre-coated steel or correspondingly pre-coated galvanised steel or aluminum.
• the pH of the aqueous solution is preferably adjusted to about 3 to about 10.
• a pH of about 3.5 to about 5 may be preferred.
• the anti-corrosive coating already present is not attacked by this process and is even partly reinforced in its anti-corrosive effect.
• the aqueous solution may additionally contain 0.001 to 2, preferably 0.005 to 0.5, g/l in each case, of ions of one or more of the metals Mn, Ce, Li, V, W, Mo, Mg, Zn, Co and Ni.
• the metals Mn, Ce, Li, V, W, Mo, Mg, Zn, Co and Ni may be used.
• These additional metal ions may further improve the anti-corrosive effect and paint adhesion.
• the aqueous solution may additionally contain 0.001 to 1.5, preferably 0.1 to 1 g/l each of phosphoric acid, phosphorous acid, phosphonic acid and/or the respective anions and/or their respective esters thereof.
• the esters should be selected such that they are water-soluble or water-dispersible. These additives also improve the anti-corrosive effect and paint adhesion.
• the aqueous solution also contains one or more components which are known in the technical field of phosphating as so-called phosphating accelerators.
• phosphating accelerators have the main task, during phosphating, of preventing the formation of bubbles of elemental hydrogen on the metal surface. This effect is also referred to as the depolarisation effect. As with conventional phosphating, this also has the result in the present process that the formation of the conversion coating takes place more rapidly and that it is formed more uniformly. Accordingly, it is preferred for the aqueous solution to contain one or more phosphating accelerators selected from:
• the aqueous solution is free from chromium.
• additions of chromium compounds to the aqueous solution could, in individual cases, have a positive effect on the corrosion protection, the corrosion protection that may be achieved using the present process is adequate even without the use of chromium compounds in the area of application in question.
• Car bodies are often made from different materials.
• steels galvanised in different ways may be combined with one another or with components of aluminum and/or magnesium or the respective alloys thereof.
• a particular strength of the present process lies in the fact that, even in these cases, effective corrosion protection is created on the different materials during the passivation.
• a specialised embodiment of the present invention is characterised in that the vehicle bodies or domestic appliances have surfaces of at least two materials selected from zinc, aluminum, magnesium, alloys of these metals with one another or with other alloying elements.
• the aqueous solution used in the passivation step of the process sequence according to the present invention preferably has a temperature between ambient temperature (about 15 to 20° C.) and about 70° C. A temperature of 25 to 40° C. is preferred.
• the car bodies or domestic appliances may be contacted with the aqueous solution by spraying with the aqueous solution or by dipping in the aqueous solution. Spray processes are preferred.
• the aqueous solution is left in contact with the car bodies or domestic appliances for a period of about 1 to about 5 minutes for the passivation step. A period of 1 to 3 minutes is preferred in spray processes and a period of 2 to 5 minutes in dip processes.
• the passivation step is followed by painting the vehicle bodies or domestic appliances with a dipping paint suitable for electrodeposition or with a powder coating.
• a dipping paint suitable for electrodeposition or with a powder coating is preferred.
• electrodeposition particularly cathodic electrodeposition
• Modern, lead-free or low-lead electrodeposition paints capable of being deposited cataphoretically are suitable for this purpose, i.e. dipping paints containing less than 500 mg lead per kg dry solids in the paint suspension.
• Domestic appliances may also be coated by electrodeposition.
• powder coating is preferred for this application for reasons of cost.
• the process sequence according to the present invention is therefore characterised by the essential steps of cleaning, passivation and painting. Between these essential process steps, one or more rinsing stages with process water, tap water or deionised water may be provided. For the rinsing steps, spray or dip methods may be employed.
• the examples show a typical process sequence. These are laboratory tests, however, where a longer period of time elapses between passivation and painting than in the industrial manufacture of car bodies or domestic appliances. For this reason, the test sheets were dried after passivation and rinsing by blowing with compressed air and storing in a drying cabinet. In industrial applications, this drying is necessary if painting is to be carried out using a powder coating after passivation. If painting is carried out using electrodeposition, it is not necessary to dry the components after passivation and rinsing before they are introduced into the paint dipping bath.
• HDG hot-dip galvanised steel sheets
• test sheets were subjected to the following process operation, all steps being carried out by the dipping method:
• Test product Composition Test product 1 75 mg/l Ti as TiF 6 2 ⁇ 125 mg/l condensation product of a polyvinylphenol having a molecular weight of 1000 to 10000 with formaldehyde and n -methylglucamine
• Test product 2 75 mg/l Ti as TiF 6 2 ⁇ 250 mg/l vinyl pyrrolidone-vinyl caprolactam copolymer
• Test product 3 400 mg/l Zr as ZrF 6 2 ⁇ 750 mg/l modified polyacrylic acid (Acumer R 1510, Rohm and Haas) Test product 4 400 mg/l Zr as ZrF 6 2 ⁇ 250 mg/l modified vinyl pyrrolidone-vinyl caprolactum copolymer
• Test product 5 150 mg/l Ti as TiF 6 2 ⁇ 200 mg/l condensation product of a polyvinylphenol having a molecular weight of 1000 to 10000 with formaldehyde and n -methylglucamine 350 mg/l phosphate 200 mg/l Mn

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• 2000
  • 2000-03-04 DE DE10010758A patent/DE10010758A1/de not_active Withdrawn
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