DE19955880A1 - Metal coating process, e.g. for steel parts used in vehicles, involves forming a coupling layer by plasma coating in inert gas and-or oxidizing gas containing organo-silicon compound and then applying organic coating - Google Patents

Abstract

A process for the production of coatings by forming a coupling layer on a substrate with a barrier discharge at 0.1-1.5 bar and then applying an organic coating involves using a metallic substrate and generating the discharge in a gaseous mixture or aerosol of inert carrier gas and/or oxidizing gas and organo-silicon compound(s) other than tetramethylsilane An Independent claim is also included for metal parts with a coating system obtained by this method.

Description

The invention relates to a method for producing inorganic Protective layers on metal surfaces through an at atmospheric pressure performed plasma coating. This coating serves as a pretreatment before painting and improves paint adhesion and corrosion protection compared to a painted metal that does not have such a pretreatment has undergone. The process therefore represents a wastewater-free process Alternative to the known pre-treatment processes such as Chromating, phosphating or another chromium-free Conversion coating.

In the following, the terms "corona discharge" and "barrier discharge" used synonymously.

DE-A-195 15 069 describes a process for the preparation of inorganic Layers known on solid surfaces, in which a high-frequency Corona discharge or a high-frequency pulsed chemical discharge Compounds are mixed in gaseous or as an aerosol and these at the from the corona treated surface primarily through the corona discharge below Process of a chemical conversion is a continuous solid inorganic Form a layer. Here, a high-frequency pulsed corona discharge or a high-frequency corona discharge, which only leads to a slight heating of Leads between one or more electrodes and the surface Solid surface burned in a gas mixture containing one or more contains chemical components. As chemical components, silicon  or organometallic compounds, metal halides and hydrides or in the Discharge-decomposable metal salts (aerosols) are used when using a oxygen-containing carrier gas converted to metal oxides on the surface become. If the layer-forming compound contains oxygen itself, it is Oxide formation also possible in an inert gas stream. This process can Normal pressure can be carried out. In one embodiment of DE-A-195 15 069 a mixture of 1 vol.% water vapor, 69 vol. Nitrogen and 30 vol .-% oxygen used, before mixing the Carrier gas components the nitrogen flow in an evaporator with 1 vol .-% Tetramethoxisilane then load us with the other components of the Carrier gas stream is mixed.

EP-A-622 474 describes a method for depositing silicon oxide known a fixed moving substrate, wherein the substrate in the presence exposed to a reactive atmosphere of a barrier discharge. The reactive Atmosphere has a pressure above 10,000 Pa and contains at least one silane and oxygen or a gas that can release oxygen and a carrier gas. The gas mixture is preferably at atmospheric pressure. As silanes Although pure silicon hydrogens are preferred, alkoxysilanes such as, for example However, tetraethoxysilane or hexamethyldisiloxane are also said to be used can be. Plastic films are used as the substrate for this treatment used. The goal of this treatment is the plastic surfaces to make it more wettable to make the films more printable or more adhesive for making adhesives.

These two prior art documents do not speak the task pretreatment for a layer system on a metallic substrate To provide, being between the substrate and an organic In a pre-treatment step, an adhesive layer is applied, which the adhesion of the organic coating as well as the corrosion protection effect improved.  

DE-C-195 05 449 describes a method for producing a Layer system consisting of an adhesive layer and an organic Coating, such as varnishes or adhesives, on a substrate, taking the Adhesive layer by means of a barrier discharge at a pressure of 0.1 to 1.5 bar generated and the substrate coated in this way provided with the organic coating. The method can be used to make electronic components such as for example chips, tracks made of metal, preferably aluminum, steel or to coat galvanized steel sheet as well as profits, profile tubes or wires. In the specified embodiments is made of tetramethylsilane Starting material made a silicon oxide layer. In this way coated flat chip precision resistors, which after coating with were coated with a varnish, showed in a climate test increased corrosion resistance compared to those not with the adhesive layer provided reference samples. When transferring this procedure to Large-area metallic substrates, however, become liable to corrosion and paint receive values for technical applications with increased corrosion load, for example in vehicle construction, is not sufficient.

The invention relates to a method for producing a layer system, consisting of an adhesive layer and an organic coating, on one Substrate, wherein the adhesive layer by means of a barrier discharge at a pressure is generated from 0.1 to 1.5 bar and the substrate coated in this way with a organic coating is provided, characterized in that the substrate is metallic and the barrier discharge in a gaseous mixture or an aerosol of at least one inert carrier gas and / or one oxidizing gas and at least one organosilicon compound that is not Tetramethylsilane is done.

As mentioned in the introduction, the process of separating substances by means of a Corona discharge, which is also understood to be a barrier discharge, known in principle. In the cited documents DE-C-195 05 449, DE-A-195 15 069 and EP-A-622 474 describes this technique in more detail. In the present case the procedure is preferably that described in DE-C-195 05 449  is described in more detail. You ignite the corona discharge between one or several electrodes and the metallic conductive substrate. For example one works with a pulsed sinusoidal excitation of a frequency in Range from 50 Hz to 1 MHz, preferably from 10 to 100 kHz. Preferably moving the substrate through the zone of the corona discharge once or through it several times. It is also possible to go through the substrate one after the other to move several coating zones arranged one behind the other.

The static coating rate depends on the content of the Organosilicon compound in the gaseous mixture or aerosol. Under the concentration conditions listed below and at a Pressure of the gaseous mixture or the aerosol in the range of Atmospheric pressure, the static coating rate is in the range from 0.5 to 100 nm / sec. The one with a moving substrate such as moving Metal strips achievable layer supports depend on a given Movement speed depends on how long the zone of the corona discharge is or how many such discharge zones are installed one after the other. By Appropriate choice of these parameters can therefore be the desired layer overlay can be set.

The organosilicon compound is preferably selected from in molecular Form present silicon compounds with one to five silicon atoms per Molecule. So you can use molecular organosilicon compounds which contain one, two, three, four or five silicon atoms in the molecule. Compounds with three, four or five silicon atoms in the molecule can be linear or be cyclical. Those with four or five silicon atoms in the molecule can there is also a branched structure. Do the molecules contain two or more Silicon atoms, one preferably selects those compounds in which the Silicon atoms connected to each other via a nitrogen or an oxygen atom are.

Organosilicon compounds which have one are generally preferred Have a molecular weight of at least 150. For example, the  Organosilicon compound can be selected from hexamethyldisiloxane, Hexamethyldisilazane, tetraethoxysilane, tetramethoxysilane, decamethylcyclo pentasiloxane, hexamethylcyclotrisiloxane, methyltriethoxysilane, octa methylcyclotetrasilonxane, octamethyltrisiloxane, vinyltrimethoxysilane, vinyltri ethoxysilane, vinyltrimethylsilane, vinyltris (2-methoxyethoxy) silane, aminopropyl trimethoxysilane, aminopropyltriethoxysilane, mercaptopropyltrimethoxysilane, Mercaptopropyltriethoxysilane, methacryloxypropyltrimethoxysilane, methacryloxy ethoxytrimethylsilane, epoxycyclohexylethyltrimethoxysilane, glycidoxypropyl trimethoxysilane, isobutyltrimethoxysilane, ethyltriethoxysilane, dimethyldiethoxysilane.

Under an inert carrier gas is a gas or a mixture of gases understood that under the reaction conditions not with the Organosilicon compound or its secondary products react. Preferably you choose the carrier gas from nitrogen and noble gases or mixtures of these, argon being preferred as the noble gas. The oxidizing gas can be selected from oxygen and from other gases that are among the Eliminate reaction conditions oxygen, as well as mixtures thereof. For example, the following are suitable: water or methanol vapor or Nitrous oxide, nitrogen monoxide or carbon dioxide. It is also suitable Oxygen, which is preferred because of the simplicity of handling, and Nitrous oxide, carbon dioxide or a mixture of any composition from oxygen, nitrous oxide and carbon dioxide. Carrier gas and oxidizing However, gas can also be identical. For example, carbon dioxide can both can be used as a carrier gas as well as an oxidizing gas, since in the Plasma oxidizing species emerge. The same applies to nitrogen, on the one hand can act as a carrier gas, on the other hand in plasma in reactive fragments is split.

The proportion of the organosilicon compound in the gaseous is preferably Mixture or the aerosol 0.01 to 1, in particular 0.05 to 0.5 vol.%. Lies an aerosol in which the organosilicon compound in the form of If there are liquid droplets or solid particles, the proportion is calculated the organosilicon compound on the aerosol in such a way that the  Liquid droplets or the solid particles as completely evaporated and approximately the ideal gas law for the gas volume obtained applies. The proportion of the oxidizing gas in the gaseous mixture or the aerosol is preferably adjusted to 30 to 70% by volume, preferably to 40 up to 60 vol%. The rest is 100% by volume of the inert carrier gas.

The process is preferably carried out in such a way that the adhesive layer obtained an average layer thickness in the range from 0.1 to 200, preferably from 1 to 100 nm having. This can be done in particular by the parameters: pressure of the Gas mixture, proportion of silicon compound in the gas mixture, Control the length of stay of a surface element in the discharge zone. The The coating obtained usually covers the substrate evenly nationwide. However, it is conceivable, especially with low coverages, that you get an island-like and not fully covering. The The term "average layer thickness" is intended to indicate that the extent of coverage of the substrate applies the layer thickness that would be obtained if the deposited layer the substrate everywhere with the same coating thickness covered. There are different ways of determining the average layer thickness Methods available. At higher layer thicknesses are gravimetric Appropriate methods, taking the substrate before and after coating weighs. Thinner coatings can be made using common methods of Surface analysis, for example, can be determined with ellipsometry. The mentioned average layer thicknesses lead to a favorable compromise with regard to corrosion protection and liability of a subsequently applied organic coating.

The organic coating to be applied to the adhesive layer can be very be designed differently. For example, it can be a paint act as explained in more detail below. However, it can also be a Act adhesive layer over which the coated substrate with others Materials is connected. For example, complex components can Be glued together, in which at least one component Has layer system produced according to the invention. Furthermore, the  Layered composite of substrate, adhesive layer and organic coating Represent component of a laminate.

The organic coating can also be a dye layer such as represent an ink. In this case, the adhesive layer serves the purpose of liability to improve the color on the base. Or the organic coating provides represents a primer layer.

As a material for the organic coating on the corona discharge deposited adhesive layer can be used in particular varnishes, as in coil coating of metals are common. For example, the organic coating containing polymers selected from polyesters, polymerized epoxy compounds, polymers or copolymers of Acrylic acid, methacrylic acid and maleic acid or derivatives (e.g. esters) of these, polyamides and polyurethanes. Organic coatings based on Polyacrylates are particularly preferred. The thickness of the organic coating is preferably in the range between 15 and 30 microns, for example in Range around 25 µm. Application techniques such as those used in the stand are suitable for this the technology for coil coating are common.

The chemical nature of the metallic substrate plays in the invention Procedure doesn't matter. However, the procedure is especially for such metallic substrates designed in the architectural field, in vehicle construction and used in the household appliance and furniture industry and which are often already from Provide the manufacturer of the tape material with an organic coating become. For example, the metallic substrate can be selected from steel, galvanized or alloy galvanized steel, aluminized or alloy-aluminized steel, magnesium and its alloys and made of Aluminum and its alloys.

It has been shown that for the different metallic substrates certain organosilicon compounds may be particularly suitable. For the Case that the metallic substrate is selected from galvanized or  Alloy galvanized steel is chosen as the silicon compound in the gaseous Mixture or the aerosol, preferably a tetraalkoxysilane, in particular Tetraethoxysilane, or a hexaalkyldisiloxane, preferably hexamethyldisiloxane. If, on the other hand, the metallic substrate is non-galvanized steel, one uses as an organosilicon compound in the gaseous mixture or aerosol preferably a hexaalkyldisiloxane, especially hexamethyldisiloxane.

The method according to the invention is more ongoing, in particular for the coating Metal straps provided. Accordingly, there is a special aspect of present invention in that the layer system is up to date Metal tape is applied. The parameters depend on the layer thickness achieved, Belt speed and length of the discharge zone depend on each other.

In a further aspect, the invention relates to a metal part comprising a Has layer system that can be obtained by the process according to the invention is and was obtained in particular by this method. Furthermore, the Invention the use of such a metal part in the architectural field, in in the furniture industry, in vehicle construction or in the appliance industry. in the Architecture, the coated metal parts can be used especially for roof, Facade or wall cladding or elements are used. in the Vehicle construction is particularly the use as a covering material or as Wall elements in the construction of ships, aircraft, road and Rail vehicles possible. In the furniture industry, in particular Manufacture of closets in question. In the device industry they can coated metal parts especially when building household appliances such as for example dishwashers and washing machines, refrigerators, stoves, Microwave devices and similar devices are used in which Metal sheets are used as flat cladding.

The material produced according to the invention has the advantage that it is formed and can be joined, for example, by gluing or flanging, without the Cover is damaged. Therefore, there is no or at least a reduced effort for a surface coating of the components after their assembly.  

For example, in the automotive industry, the usual Phosphating and cathodic electrocoating can be dispensed with.

Embodiments

The process was carried out on cold rolled steel (CRS) test specimens Tried and tested electrolytically galvanized steel (EG) with an area of 10 × 20 cm. Before these sample sheets were exposed to the corona discharge, EG- Sheets with a commercial alkaline cleaner (Ridoline® 1559, Henkel KGaA; 1% in deionized water, 55 ° C, 5 min.) And then for about 15 sec. each side first with city water and then with deionized water and blown dry with nitrogen. CRS sheets were cleaned in a wet chemical cleaning system. On Cleaning cycle included the following steps: alkaline cleaning in one Spray chamber, alkaline ultrasound-assisted cleaning, rinsing with demineralized water, weakly alkaline passivation, ultrasound-assisted Rinsing with deionized water in a triple cascade, drying first with circulating air at 110 ° C and then in vacuum. Between cleaning and The sheets were coated for max. Stored for 24 hours.

For the deposition of the adhesive layer by means of corona discharge, a laboratory system was used which is suitable for coating flat substrates up to a size of 100 × 35 cm ² . It had an open system with a flushing and suction device (gas curtain), a pair of stick electrodes with ceramic dielectric and process gas shower and was operated with pulsed sinusoidal MF excitation (20 to 50 kH). The process gas with the composition given in Table 1 was used at atmospheric pressure. The substrate was moved through the discharge zone at the speed shown in Table 1. A schematic representation of a system suitable for this purpose and, if necessary, further process parameters can be found in DE-C-195 05 449.

Those provided with the adhesive layer formed during the corona discharge Sheets were coated with a commercial coil coating varnish, which with applied with a squeegee and baked at 241 ° C for one hour. The Paint thicknesses ranged from 15 to 29 µm. An additional primer was added not used.

The adhesive strength was determined by means of a cross cut test (Gt test) in accordance with DIN 53151. In some investigations, a depression was also made in the cross-cut. The deformability of the painted sheet was determined using the tbend test according to ECCA T 20. Here, a sheet is folded through 180 ° (level: "t ₀ "), the bending radius of the lacquer layer approximately corresponding to the sheet thickness. Removed areas of lacquer are then removed from the coating edge with the help of a tape. The paint on the coating edge is assessed according to the following criteria:
0 = coating edge without cracks
1 = The delaminated area of the coating edge is approx. 5%
2 = surface of the coating edge is approx. 15%
3 = surface of the coating edge is approx. 35%
4 = surface of the coating edge is approx. 65%
5 = surface of the coating edge is approx. <65%
6 = surface area of the coating edge is 100%
(Total demolition, additional classification)

The corrosion stability was based on the salt spray test (500 hours, 1000 hours) to DIN 53167 or DIN 50021-SS using 2-3 test sheets each determined. The test panels were with a vertical scratch and one bevelled side. The criterion for the corrosion stability was the Infiltration of the lacquer layer on the scratch or on the edge is determined. For this the loose paint components were scraped off with a spatula and the mean the distance between the firmly adhering lacquer layer and the scratch or Edge determined.  

The results of the paint adhesion and corrosion tests are in Table 2 contain. The results show that a good corrosion protection effect with unsatisfactory paint adhesion can be connected (Examples 2 to 5). Such Materials will be used especially for applications where that Material is deformed little or not at all during production, but good Corrosion protection is desirable. Examples 1 and 6, however, show that also Let coating conditions be set, which to a good compromise of Lead paint adhesion and corrosion protection. Such material works well reshape and use for a purpose where the Corrosion protection requirements are less stringent (interior fittings, Furniture, household appliances).

For comparison, tests were carried out in which the sheets before Painting instead of with a deposition in a corona discharge with a technically customary wet chemical pretreatment processes (chromating or chrome-free passivation) have been pretreated. Here you get Paint adhesion and corrosion protection results that reflect current technical Represent standard. The examples according to the invention show that this technical standard can be largely achieved without wet chemical Procedures must be used that involve water consumption and Wastewater is associated with and in some cases toxic heavy metals (Chromate) can be used.  

Table 1

Coating tests (comparative tests wet-chemical, examples according to the invention with corona discharge)

Table 2

Paint adhesion and corrosion protection results (2 to 3 test panels)

Claims (17)

1. A process for producing a layer system consisting of an adhesive layer and an organic coating on a substrate, the adhesive layer being produced by means of a barrier discharge at a pressure of 0.1 to 1.5 bar and the substrate coated in this way with an organic coating is provided, characterized in that the substrate is metallic and the barrier discharge takes place in a gaseous mixture or an aerosol of at least one inert carrier gas and / or an oxidizing gas and at least one organosilicon compound which is not tetramethylsilane. 2. The method according to claim 1, characterized in that the Organosilicon compound is selected from present in molecular form Silicon compounds with one to five silicon atoms per molecule. 3. The method according to claim 2, characterized in that the Organosilicon compound has a molecular weight of at least 150. 4. The method according to claim 2, characterized in that the Organosilicon compound is selected from hexamethyldisiloxane, Hexamethyldisilazane, tetraethoxysilane, tetramethoxysilane, Decamethylcyclopentasiloxane, hexamethylcyclotrisiloxane, methyltriethoxysilane, Octamethylcyclotetrasilonxane, octamethyltrisiloxane, vinyltrimethoxysilane, Vinyltriethoxysilane, vinyltrimethylsilane, vinyltris (2-methoxyethoxy) silane, Aminopropyltrimethoxysilane, aminopropyltriethoxysilane, Mercaptopropyltrimethoxysilane, mercaptopropyltriethoxysilane, Methacryloxypropyltrimethoxysilane, methacryloxyethoxytrimethylsilane, Epoxycyclohexyl-ethyltrimethoxysilane, glycidoxypropyltrimethoxysilane, isobutyltrimethoxysilane, ethyltriethoxysilane, dimethyldiethoxysilane.   5. The method according to one or more of claims 1 to 4, characterized characterized in that the inert carrier gas is selected from noble gases, preferably argon, and from nitrogen. 6. The method according to one or more of claims 1 to 5, characterized characterized in that the oxidizing gas is oxygen, nitrous oxide, Carbon dioxide or a mixture of any composition Represents oxygen, nitrous oxide and carbon dioxide. 7. The method according to one or more of claims 1 to 6, characterized characterized in that the proportion of the organosilicon compound in the gaseous mixture or the aerosol 0.01 to 1, preferably 0.05 to 0.5% by volume is, in the case of the aerosol, the liquid droplets or imagines the solid particles as completely evaporated and for that obtained gas volume approximately applies the ideal gas law. 8. The method according to one or more of claims 1 to 7, characterized characterized in that the proportion of the oxidizing gas in the gaseous Mixture or the aerosol 30 to 70 vol%, preferably 40 to 60 vol% is. 9. The method according to one or more of claims 1 to 8, characterized characterized in that the adhesive layer has an average layer thickness in the range of 0.1 to 200, preferably from 1 to 100 nm. 10. The method according to one or more of claims 1 to 9, characterized characterized in that the organic coating is a varnish, an adhesive layer, represents a primer layer or a dye layer. 11. The method according to claim 10, characterized in that the organic Coating contains polymers selected from polyesters polymerized Epoxy compounds, polymers or copolymers of acrylic acid, Methacrylic acid and maleic acid or derivatives thereof, polyamides  and polyurethanes. 12. The method according to one or more of claims 1 to 11, characterized characterized in that the metallic substrate is selected from steel, galvanized or alloy galvanized steel, aluminized or alloy-aluminized steel, magnesium and its alloys and made of Aluminum and its alloys. 13. The method according to claim 12, characterized in that in the event that the metallic substrate is selected from galvanized or alloy galvanized steel, the organosilicon compound in the gaseous Mixture or the aerosol is a tetraalkoxysilane, preferably Tetraethoxysilane, or a hexaalkyldisiloxane, preferably Hexamethyldisiloxane. 14. The method according to claim 12, characterized in that in the event that the metallic substrate is non-galvanized steel, the organosilicon compound in the gaseous mixture or aerosol Hexaalkyldisiloxane, preferably hexamethyldisiloxane. 15. The method according to one or more of claims 1 to 14, characterized characterized in that the layer system on a running metal belt is applied. 16. Metal part which has a layer system which according to a method one of claims 1 to 15 is available. 17. Use of a metal part according to claim 16 in the architectural field in which Furniture industry, in vehicle construction or in the appliance industry.