EP1960483A2

EP1960483A2 - Coating material for protecting metals, especially steel, from corrosion and/or scaling, method for coating metals and metal element

Info

Publication number: EP1960483A2
Application number: EP06828628A
Authority: EP
Inventors: Stefan Sepeur; Stefan Goedicke; Nicole Reuter
Original assignee: Nano X GmbH
Current assignee: Nano X GmbH
Priority date: 2005-12-12
Filing date: 2006-12-07
Publication date: 2008-08-27
Also published as: DE102005059614A1; WO2007076766A2; CN101360796B; RU2425853C2; US20100098956A1; WO2007076766A3; RU2008128466A; KR20110066970A; BRPI0619535A2; KR101169175B1; KR20080076991A; CN101360796A; JP2009518471A; JP5419457B2

Abstract

It was surprisingly found that when a suitable binder including a suitable filler is used during the high temperature treatment of a curing process, the coating materials of the invention change in such a manner that electrically conducting reactive layers are formed that allow welding and especially spot welding together with the metal substrate even after treatment at temperatures of more than 800 °C.

Description

DESCRIPTION

Coating material for the protection of metals, in particular steel, from corrosion and / or scaling, process for coating metals and metal element

The invention relates to a coating material for the protection of metals, in particular steel, against corrosion and / or scaling, a method for coating metals and a metal element.

Supporting steel parts, such as body parts in the automotive industry, are often made of high-strength tempered steels. The steel is transferred by annealing at temperatures above 800-900 ° C in the austenitic region, hot formed and then cooled again with a sufficiently large cooling rate to achieve the formation of a martensitic, high-strength microstructure. If the cooling and thus hardening takes place in the forming tool, this is called form hardening. With this method, high-strength components can be produced. For the production of larger components or components with complex geometry is increasingly a two-stage forming process with a preforming at room temperature (cold forming) with downstream hot working (molding) of the preferred Vorziehteils used. A general problem with hot forming is the scaling of the steel surface.

By scaling or scaling is meant the oxidation of metals by direct reaction with atmospheric oxygen at higher temperatures. The scale layer formed on the steel surface is hard and brittle and preferably bursts from the base material when cooled again.

The scale layer damages both the components and the forming tools, which must be cleaned of fallen scale after each forming step. With unprotected sheets therefore the form hardening of components with corresponding quantities of series operation is extremely difficult. In addition, the scale must be radiated to achieve adequate corrosion protection before further processing of the components, since it is not a suitable basis for subsequent processes such as phosphating and cataphoretic dip painting. Protective coatings for the corrosion protection of steel are known from the prior art. Metal coatings of aluminum or aluminum alloys and zinc or zinc alloys can be deposited by hot dip or galvanized on the steel.

The application EP 1 013 785 A1 describes the coating of hot-rolled sheet with a metal or a metal alloy. It is a layer of aluminum or an alloy of aluminum, iron and silicon, which is applied by hot dip (Feueralumierung). While such a protective layer provides effective protection against scaling on heating to austenitizing temperature, it is limited in its practical use in press-hardening, which is particularly noticeable when molding complex geometries. DE 102 46 614 A1 mentions that in the dipping method described in EP 1 013 785 A1 an intermetallic alloy phase would form during the coating process between the steel and the actual coating, which would be hard and brittle and would break during cold working. The resulting microcracks would cause the coating to detach from the base material and thus lose its protective function. From this description and practical experience in the forming of steel blanks or parts results that the fire aluminizing is not suitable for cold forming and thus not for a two-stage cold and hot forming process. In DE 102 46 614 Al these problems are to be solved by the application of a metallic protective layer with a galvanic process from an organic, non-aqueous solution. In this case layers of aluminum or an aluminum alloy or zinc or zinc alloy should be deposited. The galvanic deposition of aluminum on steel, however, is a very complicated and expensive process.

When using zinc and zinc alloys, however, the use in hot forming is also severely limited, since the zinc is largely oxidized during heating or evaporated under a protective gas atmosphere.

The applications WO 2005/021820 A1, WO 2005/021821 A1 and WO 2005/021822 A1 describe processes for producing various hardened steel parts. In each case, a protective layer consisting of zinc is applied to the steel together with another oxygen-affine element (especially aluminum). This protective layer is described in WO 2005/021821 A1 in a hot-dip method, in WO 2005/021820 A1 and WO 2005/021822 Al applied in a hot dip or galvanic process. However, all of the coatings described here, which contain zinc as the main element, have in common that they are very sensitive to oxidation and evaporation in the austenitizing temperatures required for a mold hardening process and cause burn marks on the surface at the least contamination (eg dust) which lead to component rejects ,

From DE 100 39 404 A1 a process for the preparation of compositions containing pigments or fillers based on polysiloxanes by means of the sol-gel process is known in which, in a first step, epoxy-containing organosilanes (alkoxysilanes) are hydrolyzed to a sol and the SoI is gelated in a second step using pigments or fillers having an average particle diameter of at least 500 nm and optionally an aromatic polyol having an average molecular weight of at most 1,000.

DE 199 40 857 A1 describes a sol-gel coating material for single-layered or multi-layer coated substrates, in particular automobile bodyworks, which should in particular make it possible subsequently to apply a scratch-resistant coating to finished, already cured coatings in as short a time as possible without causing adhesion problems , For this purpose, a siloxane-containing paint formulation is modified with organic constituents. The sol-gel coating material contains as essential constituents an acrylate copolymer solution and a sol.

DE 198 13 709 A1 describes a process for protecting a metallic substrate against corrosion, in which a coating composition based on (hetero) polysiloxanes prepared by hydrolysis and condensation processes is applied to the substrate and cured, the coating composition comprising at least one Species Z, which reacts with the metal to form a species Y, which has a more negative enthalpy of formation than the species X, or interacts. The coating composition can be applied wet-chemically. Weldability or even spot weldability is not described.

From DE 101 49 148 Al a process for the coating of metallic surfaces with an aqueous composition is known which comprises at least one organic Film former containing at least one inorganic compound in particle form and at least one lubricant. In the composition of DE 101 61 383 A1, in addition to the organic film former, there is a content of cations and / or hexafluoro complexes of cations and at least one inorganic compound in particle form.

DE 101 41 687 Al describes a composition containing silicon compounds which is used essentially for the production of a coating on surfaces and as a raw material for paints. It contains as reaction mixture at least one alkyltialkoxysilane, at least one alkoxysilane and / or at least one tetraalkoxysilane, at least one hydrous silicic acid sol, at least one acid and at least one alcohol or at least one glycol.

DE 100 27 265 A1 discloses aluminum coils coated with multicoat color or effect coatings which have on at least one of their surfaces a combination effect layer which consists of a pigmented powder slurry, a clearcoat and a sealer based on organically modified ceramic materials.

EP 0 610 831 A2 describes a process for producing functional coatings with organofunctional silanes of a metal compound and low-volatility oxides, wherein a hydrolytic condensation is carried out, for which an organic crosslinkable prepolymer is added to the hydrolytic condensate and the coating solution thus obtained is applied to a substrate and then cured ,

WO 95/13326 A1 discloses a process for the preparation of compositions based on hydrolyzable silanes having epoxy groups, in which a prehydrolyzed silicon compound is added with a particulate material, preferably a nonionic surfactant or purely aromatic polyol, to give coatings having a high scratch resistance to obtain long-term hydrophilic properties, corrosion-inhibiting properties, good adhesion and transparency.

In the area of anticorrosion coatings to be applied wet-chemically, organic protective coatings are known, for example, protective coatings partially filled with zinc pigments. These provide preferably as an additional seal on a hot dipping process or galvanized steel surface good corrosion protection for low temperature applications, but can not be used for hot forming and molding processes above 800 ⁰ C due to their insufficient temperature resistance. The same applies to a large number of corrosion protection coatings on an organic or sol-gel basis.

In the state of the art currently no wet-chemically applied coating materials are known which protect steel against corrosion and / or scaling and are still weldable after heat treatment of the coated steel at temperatures above 600 ° C. This weldability includes in particular the suitability of a coated steel part after heat treatment for spot welding, for which a sufficient electrical conductivity of the layer in conjunction with the component is necessary even after said heat treatment.

It is therefore an object of the invention to provide a coating material which, after heat treatment of the steel coated therewith, still permits welding, in particular spot welding.

This object is achieved in that means for achieving a weldability, in particular by means of spot welding method, the applied coating material are provided, that the coating material can be applied wet-chemically, that the coating material changes in high-temperature processes of more than 600 ° C in its structure, and is suitable as a primer for other coating materials.

Surprisingly, it has been found that it is quite possible to provide wet-chemically coatable coating material which offers good protection against scaling and, in addition, can be welded and is spot-weldable.

An embodiment of the invention is that in order to achieve weldability, an easily oxidized organic or inorganic-organic binder with easily oxidized organic fractions is connected to an electrically conductive metallic or non-metallic filler. By using a suitable binder with a suitable filler, the coating material according to the invention transforms during the high-temperature treatment of a curing process in such a way that electrically conductive reaction layers are formed which weld together with the metal substrate even after treatment at temperatures above 800 ° C. and in particular can be spot-welded. In the high temperature process, the binder is oxidized at a temperature greater than 600 ° C in a period of less than 10 minutes. The organic components burn to gaseous products as well as to electrically conductive carbon black. During the combustion of the organic constituents, a reducing atmosphere is created in the layer, which protects the metal pigments from oxidation during the high-temperature process. The metal pigments or non-metallic electrically conductive particles contained in the layer combine after the oxidative removal of electrically insulating layer components with the substrate surface to form an electrically conductive surface.

Compared to the layers which are known from the prior art and can not be applied wet-chemically, the coatings according to the invention also have the following advantages: The coatings are very diverse in their application possibilities since they are not only used in the coil coating process but also in other application processes such as curtain coating, spray painting, Dip coating, floods, etc. are applied and thus can be used in addition to coil or circuit boards on three-dimensional components. The coatings are multifunctional, i. In addition to the main function of scaling and / or corrosion protection, the coatings can also develop lubricity during cold and hot forming by incorporating tribologically active constituents and thus replace external lubricants. The layers can also be applied in very low layer thicknesses (in the lower micron range), which both improves the electrical conductivity and also brings material and thus cost savings. If an even higher electrical conductivity is desired after the hot forming process, a thin electrically conductive primer can also be applied to the layer.

The coating material may remain after the forming process or Hochtemperaturumformprozeß on the surface of the substrate and optionally fulfill an additional function, eg increase the scratch resistance, improve corrosion protection, aesthetic aspects meet (color, Antifingerprinteigenschaften), a tarnish (metal or PVD surfaces ) Offer, change the electrical conductivity (antistatic effect, insulating effect) and possibly serve as a substrate for the usual further processing steps (eg phosphating, cataphoretic dip coating).

Another embodiment of the invention is that to achieve weldability, an organic, inorganic or organic-inorganic binder matrix contains compounds which form a conductive phase when heated under reducing conditions at temperatures above 600 ° C, in particular metal salts, metal alkoxides, carbides and phosphides of iron, copper, tungsten and aluminum, electrically conductive oxides, in particular antimony tin oxide / ATO and indium tin oxide / ITO.

In the metal salts, those of the minor group metals are preferred.

A further embodiment of the invention is that to achieve weldability, the coating material contains electrically conductive compounds that are resistant to the oxidation processes at high temperatures, in particular stainless steel pigments, pigments or powders of precious metals, copper, tin, graphite and carbon black, high temperature resistant semiconductors like silicon carbide.

By the targeted addition of electrically conductive compounds that are resistant to the oxidation processes at high temperatures and thereby have the necessary before both during the curing process and the electrical conductivity required for spot welding, the weldability is ensured.

A further embodiment of the invention is that the coating material contains electrically conductive substances which are resistant to oxidation processes under reducing conditions in the layer, in particular pigments and powders of iron, aluminum, zinc, magnesium, graphite and carbon black.

The abovementioned reducing conditions in the layer can be induced in particular by the binder. It is within the scope of the invention that the coating material between 5 and 95 wt .-%, preferably from 10 to 75 wt .-% of binder and between 0 and 90 wt .-%, preferably from 25 to 75 wt .-% of pigments and / or contains fillers.

According to the invention it is provided that the binder organic compounds, especially polyurethanes, polyesters, epoxy resins, alkyd resins, phenolic resins, melamine resins, acrylates, methacrylates, organic-inorganic compounds, in particular oligo- and polysiloxanes from hydrolysis and condensation of alkylalkoxysilanes or alkoxysilanes or mixtures thereof or silicones or silicone resins or organically modified silicone resins, or purely inorganic compounds, in particular silicates, polyphosphates, aluminosilicates or metals, metal alkoxides and their condensation products, metal oxides and metal salts.

Likewise, it is advantageous that the coating material contains metal pigments, in particular the metals aluminum, zinc, iron, tin, copper, magnesium, stainless steel, as well as silver and other noble metals or metal salts.

These serve to improve the corrosion protection and / or to avoid high-temperature corrosion (scale formation).

It may also be expedient that the coating material contains lubricants, in particular natural and synthetic waxes, oils, polymers such as polytetrafluoroethylene or fluorinated ethylene propylene, thermoplastics, in particular polyethylene and polyamide, stearates, aluminum, zinc, magnesium and lithium soaps, higher fatty acids, Organic compounds of chlorine, phosphorus and sulfur, fluorides of calcium or barium, phosphates, oxides, hydroxides and sulfides of calcium and zinc and metals, in particular lead, copper, tin, silver, gold, indium and nickel.

Furthermore, it is part of the invention that the coating material contains solid lubricants, in particular inorganic solid lubricants, preferably graphite, carbon black, boron nitride, titanium nitride, molybdenum disulfide and tungsten disulfide.

These solid lubricants are particularly suitable for processes that are carried out at higher temperatures. It is also part of the invention that the coating material one or more anti-corrosion pigments or corrosion inhibitors, in particular silicates, polyphosphates, tannin derivatives, basic sulfonates of alkali and alkaline earth metals, zinc salts of organic nitrogen acids, phosphates, chromates, Molybdate of calcium, magnesium, zinc or aluminum , contains.

This improves the corrosion protection properties.

The invention also provides a process for coating metals, in particular steel, with coating material material according to the invention, wherein the coating material is applied to a substrate by a wet-chemical coating process such as knife coating, dipping, spray painting, rolling, flooding or curtain coating and by a hardening step firmly the surface of the substrate is tied.

In this case, it is provided in a variant of the invention that the curing step at room temperature to 800 ° C, preferably at temperatures from room temperature to 300 ° C, wherein the elevated temperature by hot air or by irradiation in the range NIR, IR, UV, electron beam or inductive is initiated.

It is possible that the coating material already has sufficient electrical conductivity to be weldable already after simple drying or a curing step as described above.

Another variant of the invention is that after application of the coating material to the substrate in a high-temperature process step, the composite coating material / substrate to a temperature between 600 ° C and 1300 ° C, preferably between 840 ° C and 1000 ⁰ C, heated.

The thermal treatment leads to the fact that the coating material changes its chemical structure and usually has a technical importance for the metal, for example, the formability by pressing, forging, etc. is improved or the thermal treatment is part of a with or without forming performed hardening process. It is achieved by the resulting structure having sufficient electrical conductivity has to be weldable with the usual welding methods, in particular spot welding. In addition, the coating material is deformable in all common cold and hot forming processes.

Furthermore, it is expedient that the high-temperature process step lasts between one second and several hours, preferably between one second and 30 minutes.

It is part of the invention that the metallic substrate steel, a steel alloy or with a metallic coating, in particular of aluminum, zinc, magnesium, tin or corresponding alloys of these metals such as aluminum-silicon, aluminum-iron, zinc-iron, zinc Silicon, zinc-aluminum-aluminized aluminum.

According to the invention it is provided that coils or plates or other components, in particular profiles, rods, wire, pipes, fittings, forgings, castings are used as a steel substrate.

Finally, a metal element provided with a coating material according to the invention is also within the scope of the invention.

Such metal elements may in particular be parts of motor vehicles (e.g., body or engine parts), trains or aircraft, machinery, industrial equipment, agricultural equipment, metal parts used in construction or mining

The invention will be explained in more detail with reference to three exemplary embodiments.

Example 1:

To 100 g of a 60% silicone polyester solution (for example, available in xylene under the trade name Silikoftal) 10 g of graphite powder (particle size <10 microns) are added and dispersed well with a dissolver. To the mixture are added 70 g of ethanol, 10 g of carnauba wax dispersion (solids content 20% by weight in white spirit), 50 g of aluminum pigment paste (eg Decomet high gloss, Al 1002/10, Schlenk) and 20 g of zinc paste (eg Zinkflake GTT, Eckart) and several more Stirred homogeneously with a paddle stirrer at low shear. After thorough dilution with butylglycol, the finished lacquer is coated with a flow cup spray gun (eg Sata Jet, nozzle 1.2 mm) onto an alkaline degreased steel substrate or, with suitable substrate geometry (flat sheet or blank), applied with a doctor blade so that a wet film thickness of about 10-40μm is achieved. The lacquer layer is cured for about 10 minutes at a surface temperature of 220 ° C. The paint can also be applied in the roll (eg coil coating) on the sheet and is baked at a PMT (peak Mean Temperature) of 230-240 ⁰ C.

Example 2:

To 100 g of a 60% silicone polyester solution (for example, available in xylene under the trade name Silikoftal) 30 g of graphite powder (particle size <10 microns) are added and dispersed well with a dissolver. 70 g of xylene, 10 g of carnauba wax dispersion (solids content 20% by weight in white spirit) and 30 g of aluminum pigment paste (for example Decomet high gloss, Al 1002/10, Schlenk) are added to the mixture and stirred in homogeneously with a small blade at a high speed for several hours.

After thorough dilution with butylglycol, the final varnish is applied to a grease-free galvanized steel substrate using a gravity-cup spray gun (eg Sata Jet, nozzle 1.2 mm) or, if the substrate geometry is suitable (flat sheet or blank), applied with a doctor blade so that a wet film thickness is achieved of about 10-40μm is achieved. The lacquer layer is cured for about 10 minutes at a surface temperature of 220 ° C. The paint can also be applied to the galvanized steel sheet by roller coating (for example coil coating) and is baked at a PMT (Peak Mean Temperature) of 230-240 ° C.

Example 3:

To 100 g of a 60% silicone-polyester solution (in xylene, for example sold under the trade name Silikoftal), 50 g of butylglycol and 85 g of an iron pigment paste (for example STAPA TA Ferricon 200, Eckart) are added and stirred in homogeneously with low shearing. The finished lacquer is applied to an alkaline degreased steel substrate by means of a flow cup spray gun (eg Sata Jet, nozzle 1.4 mm) or, with suitable substrate geometry (flat sheet or blank), applied with a doctor blade so that a wet film thickness of about 10 40μm is achieved. The lacquer layer is cured for 10 minutes at a surface temperature of 250 ° C.

Example 4:

To 100 g of polyester resin solution (available, for example, under the trade name Desmotherm VP LS 2218), 250 g of a suitable solvent (for example, Solvesso 150 aromatic mixture) are added and stirred homogeneously. To the diluted polyester resin is added 80 g of a vesicular copper powder (for example, STAKDART copper powder fine grind GTT, Eckart) and stirred homogeneously with a paddle stirrer at a low shear. 10 g of graphite powder (particle size <10 μm) and 10 g of carnauba wax dispersion (solids content 20% by weight in white spirit) are added to the mixture and dispersed well.

The finished lacquer is applied to an alkaline degreased steel substrate by means of a flow cup spray gun (eg Sata Jet, nozzle 1.4 mm) or, with suitable substrate geometry (flat sheet or blank), applied with a doctor blade so that a wet film thickness of about 10 40μm is achieved. The lacquer layer is cured for 10 minutes at a surface temperature of 180.degree. The paint can also be applied by roller coating (eg coil coating) to the sheet and is baked at a PMT (peak metal temperature) of 230-240 ⁰ C.

Claims

1. coating material for the protection of metals, in particular steel, against corrosion and / or scaling, characterized in that means for achieving a weldability, in particular by means of spot welding, the applied coating material are provided, that the coating material can be applied wet-chemically, that the Coating material is changed in its structure at high temperature processes of more than 600 ° C and is suitable as a primer for other coating materials.

2. Coating material according to claim 1, characterized in that to achieve the weldability, an easily oxidized organic or inorganic-organic binder with easily oxidized organic portions is connected to an electrically conductive metallic or non-metallic filler.

3. Coating material according to claim 1, characterized in that to achieve weldability, an organic, inorganic or organo-inorganic binder matrix contains compounds which form a conductive phase when heated under reducing conditions at temperatures above 600 ⁰ C, in particular metal salts, metal alkoxides, carbides and phosphides of iron, copper, tungsten and aluminum, electrically conductive oxides, in particular antimony tin oxide / ATO and indium tin oxide / ITO.

4. Coating material according to claim 1, characterized in that for

Achieving weldability the coating material contains electrically conductive compounds that are resistant to the oxidation processes at high temperatures, in particular stainless steel pigments, pigments or powders of precious metals, copper, tin, graphite and carbon black, high temperature resistant semiconductors such as silicon carbide.

5. Coating material according to claim 1, characterized in that the

Coating material contains electrically conductive substances which are resistant to oxidation processes under reducing conditions in the layer, in particular pigments and powders of iron, aluminum, zinc, magnesium, graphite and carbon black.

6. Coating material according to claim 1, characterized in that the coating material between 5 and 95 wt .-%, preferably from 10 to 75 wt .-% of binder and between 0 and 90 wt .-%, preferably from 25 to 75 wt. % Pigments and / or fillers.

7. Coating material according to claim 1, characterized in that the binder organic compounds, in particular polyurethanes, polyesters, epoxy resins, alkyd resins, phenolic resins, melamine resins, acrylates, methacrylates, organic-inorganic compounds, in particular oligo- and polysiloxanes from hydrolysis and condensation of alkylalkoxysilanes or Alkoxysilanes or mixtures thereof or silicones or silicone resins or organically modified silicone resins, or purely inorganic compounds, in particular silicates, polyphosphates, aluminosilicates or metals, metal alkoxides and their condensation products, metal oxides and metal salts.

8. Coating material according to claim 1, characterized in that the coating material contains metal pigments (aluminum, zinc, iron, tin, copper, magnesium, stainless steel, silver, precious metals, etc.) or metal salts.

9. Coating material according to claim 1, characterized in that the coating material contains lubricants, in particular natural and synthetic waxes, oils, polymers such as polytetrafluoroethylene or fluorinated ethylene propylene, thermoplastics, in particular polyethylene and polyamide, stearates, aluminum, zinc, magnesium and lithium soaps , higher fatty acids, organic compounds of chlorine, phosphorus and sulfur, fluorides of calcium or barium, phosphates, oxides, hydroxides and sulfides of calcium and zinc and metals, in particular lead, copper, tin, silver, gold, indium and nickel.

10. Coating material according to claim 1, characterized in that the coating material contains solid lubricants, in particular inorganic solid lubricants, preferably graphite, carbon black, boron nitride, titanium nitride, molybdenum disulfide and tungsten disulfide. l l. Coating material according to Claim 1, characterized in that the coating material comprises one or more anticorrosion pigments or corrosion inhibitors, in particular silicates, polyphosphates, tannin derivatives, basic sulfonates of alkali and alkaline earth metals, zinc salts of organic nitrogen acids, phosphates, chromates, molybdate of calcium, magnesium, zinc or aluminum.

12. A method for coating metals, in particular steel, with coating material material according to any one of claims 1 to 9, characterized in that the coating material is applied by a wet chemical coating process such as doctoring, dipping, spray painting, rolling, flooding or curtain coating on a substrate and by a curing step is firmly tied to the surface of the substrate.

13. A method for coating metals according to claim 10, characterized in that the curing step at temperatures from room temperature to 800 ⁰ C, preferably at room temperature to 300 ° C, wherein the elevated temperature by hot air or by irradiation in the range NIR, IR, UV, electron beam or inductively initiated.

14. A process for coating metals according to claim 10, characterized in that after application of the coating material to the substrate in a high-temperature process step, the composite coating material / substrate to a temperature between 600 ° C and 1300 ⁰ C, preferably between 840 ° C and 1000 ^0th C, is heated.

15. A method for coating metals according to claim 12, characterized in that the high-temperature process step takes between one second to several hours, preferably between one second and 30 minutes.

16. A method for coating metals according to claim 10, characterized in that the metallic substrate steel, a steel alloy or a metal coating, in particular of aluminum, zinc, magnesium, tin or corresponding alloys of these metals such as aluminum-silicon, Aluminum-iron, zinc-iron, zinc-silicon, zinc-aluminum-silicon, plated steel is.

17. A method for coating metals according to claim 10, characterized in that coils or boards or other components, in particular profiles, rods, wire, pipes, moldings, forgings, castings are used as a steel substrate.

18. With a coating material according to claims 1 to 9 provided metal element.