METHOD FOR COATING A SUBSTRATE

Abstract

A method for coating a substrate is provided in that a plasma jet is produced from a working gas, at least one precursor material is fed to the working gas and/or the plasma jet and is reacted in the plasma jet and at least one reaction product of at least one of the precursors is deposited on at least one surface of the substrate and/or on at least one layer arranged on the surface. At least one of the deposited layers improve the optical transmission properties of the substrate.

Description

This nonprovisional application is a continuation of International Application No. PCT/DE2008/000886, which was filed on May 28, 2008, and which claims priority to German Patent Application No. 10 2007 025 152.3, which was filed in Germany on May 29, 2007, and which are both herein incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method for coating a substrate.

2. Description of the Background Art

Coating processes in which coating materials are deposited from a gas phase on a surface have been commonly used for some time to influence the surface properties of different substrates. In this case, a differentiation is made between chemical and physical gas phase depositions. In the chemical method, so-called precursors, i.e., precursor substances of the coating materials, are generally reacted by supplying energy, and the reaction products of the precursors are directed onto the surface and deposited there. The energy can be supplied, for example, by means of a flame treatment. The precursor exposed to the flame during its thermal reaction forms particles, particularly nanoparticles, which agglomerate even in the flame and then settle on the surface. A homogeneous and dense coating is possible in this way but with a high consumption of energy. Another option is a so-called low-pressure plasma technique, in which the precursor is reacted in a plasma source or in its spatial proximity on the surface to be coated to form thin layers. Although this method is advantageous in terms of energy, it nevertheless requires evacuated process chambers and is therefore costly and inflexible.

For some years, so-called normal-pressure plasma techniques have been known, in which the surfaces to be coated need not be placed in a vacuum. Particle formation in this case occurs even in the plasma. The size of the agglomerates forming thereby, and therefore the main properties of the coating, can be adjusted, inter alia, by the distance of the plasma source from the surface. The homogeneity of the deposited layers, presuming a suitable control of the substrate, is comparable to that achieved by flame treatment but the required energy input is much lower.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a method for coating a substrate, said method which enriches the prior art.

In a method of the invention for coating a substrate, particularly made of glass, a plasma jet is produced from a working gas. At least one precursor material is supplied to the working gas and/or the plasma jet and reacted in the plasma jet. At least one reaction product of at least one of the precursors is deposited on at least one surface of the substrate and/or on at least one layer arranged on the surface. In this case, at least one of the deposited layers is used to improve the transmission of the surface. This means that the reflection at the surface is reduced, so that more light is incident on the surface and can pass through the substrate. According to the invention, at least a first coating process of this type occurs on a hot or heated surface of the substrate. The first coating occurs subsequent to a substrate manufacturing process in which the substrate is formed with the aid of heat.

In particular, in the coating of glass, the coating process can occur immediately after a glass manufacturing process, if the glass leaves a float bath in a still hot state. The adhesion of a layer thus applied is especially good, because a fresh glass surface is especially reactive. Glass surfaces take up water, carbon dioxide, and other substances from the atmosphere relatively rapidly and thereby lose a considerable part of their reactivity. The coating of hot glass using a plasma process is advantageous in comparison with a flame treatment, because unlike a flame or its combustion gases, the plasma does not additionally heat the hot glass surface, and deformation, for example, wave formation, is thus avoided. Moreover, the energy expenditure is much lower than for a heat treatment, so that costs are reduced. In comparison with the simple spraying of a coating solution or the deposition of particles from a gas stream, in which the energy required for the reaction to form the layer is taken from the heat of the glass and thus, together with convection, leads to an undesired rapid cooling of the glass, the method of the invention is characterized in that in a plasma coating process the plasma supplies the reaction energy, on the one hand, and does not additionally heat the surface, on the other. Exclusion of air and water vapor or reaction products thereof is easily possible in a plasma coating process in contrast to flame treatment, for example, by suitable selection of the working gas. In this way, for example, air or oxygen can be kept away from the layers to be formed and from the surface. In contrast to a flame treatment, in a plasma coating process on a glass substrate subsequent to a glass manufacturing process in the float bath, the depositing of the coating substances formed from the precursor is not disrupted by the heat of the hot glass. The described method may also be used on a substrate already provided with at least one layer.

It is also possible to coat other substrates, for example, made of plastic, particularly transparent plastic, in the same or similar way.

In particular, in the coating of a substrate made of glass, the temperature of the surface to be coated is within a range of from 100° C. to 800° C., preferably within a range of from 300° C. to 800° C. The temperature of the surface to be coated may also be within a range from room temperature to 800° C.

The depositing of the layer can take place at atmospheric pressure (also called normal pressure). The normal-pressure plasma technique requires substantially lower technical effort, because a treatment of the surface to be coated in vacuum is eliminated. In the normal-pressure plasma method, the particles form in the plasma jet. The size of the agglomerates forming from these particles and therefore the main properties of the coating can be adjusted, inter alia, by the distance of the plasma source from the surface. The homogeneity of the deposited layers is comparable to that achieved by flame treatment but the required energy input is much lower. Alternatively, the method can also be performed at a slightly reduced normal pressure.

The generation of the plasma can occur in a free jet plasma source. In this method, a high-frequency discharge between two concentric electrodes is ignited, whereby the forming hollow cathode plasma is carried out by an applied gas stream as a plasma jet from the electrode arrangement usually several centimeters into free space and to the surface to be coated. The precursor can be introduced both before the excitation into the working gas (direct plasma processing) and also afterwards into the already formed plasma or into its vicinity (remote plasma processing).

Another possibility for generating plasma is the utilization of a dielectrically hindered discharge. In this case, the working gas, particularly air, acting as the dielectric is passed between two electrodes. The plasma discharge occurs between the electrodes, which are supplied with a high-frequency high voltage. Likewise, the glass substrate itself can be used as a dielectric by passing the gas stream between a metallic flat electrode and the flat glass substrate.

The precursor can be introduced in the gaseous state into the working gas or the plasma jet. Liquid or solid, particularly powdered precursors may also be used, but are preferably converted to the gaseous state before introduction, for example, by vaporization. Likewise, the precursor can be introduced first into a carrier gas, entrained thereby, and introduced together with said gas into the working gas or plasma jet.

The throughput of the working gas and/or of the precursor is preferably variable and controllable and/or adjustable. The throughputs of the working gas and precursor in particular are controllable and/or adjustable independent of one another. Apart from the distance of the plasma source to the surface to be coated, there is another means available to influence the layer properties, such as, for example, the layer thickness or the refractive index. Likewise, it is possible to realize gradient layers in this way. The following properties of the substrate, for example, can be changed selectively by suitable selection of these process parameters and the employed precursors: scratch resistance, self-healing ability, barrier behavior, reflection behavior, transmission behavior, refractive index, transparency, light scattering, electrical conductivity, antibacterial behavior, friction, adhesion, hydrophilicity, hydrophobicity, oleophobicity, surface tension, surface energy, anticorrosive action, dirt-repellent action, self-cleaning ability, photocatalytic behavior, antistress behavior, wear behavior, chemical resistance, biocidal behavior, biocompatible behavior, electrostatic behavior, electrochromic activity, photochromic activity, and gasochromic activity.

The deposited layer comprises preferably at least one of the components comprising silicon, silver, gold, copper, iron, nickel, cobalt, selenium, tin, aluminum, titanium, zinc, zirconium, tantalum, chromium, manganese, molybdenum, tungsten, bismuth, germanium, niobium, vanadium, gallium, indium, magnesium, calcium, strontium, barium, lithium, lanthanides, carbon, oxygen, nitrogen, sulfur, boron, phosphorus, fluorine, halogens, and hydrogen. The layers contain in particular oxide or/and nitride compounds of silicon, titanium, tin, aluminum, zinc, tungsten, and zirconium.

An organosilicon and/or an organotitanium compound are preferably used as a precursor, for example, hexamethyldisiloxane, tetramethylsilane, tetramethoxysilane, tetraethoxysilane, titanium tetraisopropylate, or titanium tetraisobutylate.

For example, barrier layers, which reduce permeability for gases and water, are realizable in this way.

In an embodiment, a first layer with a barrier effect and then at least one other layer as a functional layer, preferably with at least one of the aforementioned properties, are deposited on a lime-sodium-silicate glass (standard float glass). The barrier layer reduces, on the one hand, the passage of water, carbon dioxide, and other substances from the atmosphere to the surface of the glass substrate. On the other hand, migration particularly of sodium from the glass into the functional layer is reduced, so that its activity is retained. The functional layer in this case can be applied by means of the same method or by means of another coating process onto the still hot or already cooled glass.

Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein:

FIG. 1 shows transmission spectra of a glass substrate in an untreated state, treated with an atmospheric-pressure plasma, and coated with an atmospheric-pressure plasma;

FIG. 2 shows transmission spectra of substrates made of flat glass in an untreated state and coated by means of a free-jet plasma source at atmospheric pressure with layers having a different layer thickness;

FIG. 3 shows transmission spectra of substrates made of flat glass in an untreated state and coated by means of a blown corona, generated in a plasma source, at atmospheric pressure with layers having a different layer thickness;

FIG. 4 shows transmission spectra of substrates made of polycarbonate in an untreated state and coated by means of a blown corona plasma source at atmospheric pressure with layers having a different layer thickness; and

FIG. 5 shows transmission spectra of substrates made of flat glass in an untreated state and coated by means of plasma generated by a dielectrically hindered discharge at atmospheric pressure with layers having a different layer thickness.

DETAILED DESCRIPTION

FIG. 1 shows a transmission spectra of a glass substrate. A substrate made of float glass is coated by means of an atmospheric-pressure plasma torch. Plasma is generated in a nozzle, made as a hollow cathode, by means of high-frequency high-voltage discharge and is carried out by an air-gas stream, which is passed through the nozzle, from the same into a plasma jet 2 to 3 centimeters long. For operation, the hollow cathode is supplied with a high voltage of about 15 kV at a frequency of 20 kHz to 50 kHz. The wattage of this arrangement is, for example, about 200 W. The primary gas pressure of the air-gas stream is about 5 bar. If this air-gas stream is enriched with one or more precursors, with this type of arrangement thin layers can be deposited on substrates, which are located at a certain distance to the atmospheric-pressure plasma torch. Flat glass slides, whose surface is heated to about 550° C. by means of a conventional hot plate, are used as the substrate. The samples are carried under the downward-directed nozzle of the atmospheric-pressure plasma torch with the aid of an xy positioning table. The distance of the nozzle to the substrate is 10 mm. The travel speed is 150 mm/sec at a grid distance of 2 mm. Four passes are realized overall. In the air-gas stream, a precursor is metered in with a throughput of 0.5 L/min. In so doing, a layer is deposited on the surface of the substrate. The deposited layer has the following properties:

Thickness: ca. 190 nm

Refractive index: ca. n=1.47

FIG. 1 shows the transmission spectra of various slides. In this case, a transmission τ is plotted versus a wavelength λ. The transmission spectrum S1 characterizes an uncoated surface of the substrate. The transmission spectrum S2 is characteristic for a substrate having the aforementioned parameters but treated without the addition of precursors. The transmission spectrum S3 shows characteristics of a substrate having the mentioned parameters and treated and coated with the addition of precursors. It is clear from the figure that the transmission τ of the coated substrate versus the uncoated substrate and the substrate treated only with the plasma is considerably improved, so that an antireflective effect results.

FIG. 2 shows the transmission spectra of substrates made of flat glass. A substrate made of float glass is coated by means of a free jet plasma torch at atmospheric pressure. Plasma is generated in a nozzle, made as a hollow cathode, by means of a high-frequency high-voltage discharge and is carried out by an air-gas stream, which is passed through the nozzle, from the same into a plasma jet 2 to 3 centimeters long. For operation, the hollow cathode is supplied with a high voltage of about 15 kV at a frequency of 20 kHz to 50 kHz. The wattage of this arrangement is, for example, about 200 W. The primary gas pressure of the air-gas stream is about 5 bar. If this air-gas stream is enriched with one or more precursors, with this type of arrangement thin layers can be deposited on substrates, which are located at a certain distance to the free jet plasma torch. Flat glass slides are used as the substrate. For example, polycarbonate or silicon disks can also be coated. The samples are carried under the downward-directed nozzle of the free jet pressure plasma torch with the aid of an xy positioning table. The distance of the nozzle to the substrate is 10 mm. The travel speed is 150 mm/sec at a grid distance of 2 mm. Two passes are realized overall. In the air-gas stream, a precursor is metered in with a throughput of 0 to 0.5 L/min. In so doing, a layer, whose layer thickness depends on the throughput, is deposited on the surface of the substrate. Hexamethyldisiloxane was used as the precursor. The deposited layers accordingly contain substantially silicon oxide.

FIG. 2 shows the transmission spectra of various substrates. In this case, a transmission τ is plotted versus a wavelength λ. The transmission spectrum S1 characterizes an uncoated surface of the substrate. The transmission spectra S2, S3, S4, and S5 show characteristics of substrates with layers with a layer thickness in each case of: 68.5 nm, 69.5 nm, 90 nm, and 126 nm, which were deposited using the described method. It is clear from the figure that the transmission τ of the coated substrates, characterized by the transmission spectra S2, S4, and S5, is considerably improved compared with the uncoated substrate at a wavelength λ of ca. 550 nm.

FIG. 3 shows the transmission spectra of substrates made of flat glass. A substrate made of float glass is coated by means of a plasma torch at atmospheric pressure. In this case, the plasma is generated in an electrode head between two high-voltage electrodes by means of a dielectrically hindered discharge. The distance between the high-voltage electrodes is about 10 mm. Compressed air, which is provided by means of a blower and is blown out between the electrodes, is used as the dielectric and working gas. The spray discharges arising thereby are carried out of the electrode head with the working gas. The working width of the electrode head is 60 mm; the electrodes are supplied with high voltage at a frequency of 20 kHz. For example, 3-mm thick flat glass is used as the substrate. For example, polycarbonate can also be coated. The samples are passed under the electrode head of the plasma torch with the aid of an xy positioning table. The distance of the nozzle to the substrate is about 20 mm. The travel speed is 150 mm/sec. A different number of passes is realized, whereby layers of different layer thicknesses result. In the air-gas stream, hexamethyldisiloxane is metered in as a precursor with a throughput of 2 L/min. The deposited layers accordingly contain substantially silicon oxide.

FIG. 3 shows the transmission spectra of various substrates. In this case, a transmission τ is plotted versus a wavelength λ. The transmission spectrum S1 characterizes an uncoated surface of the substrate. The transmission spectra S2, S3, and S4 show characteristics of substrates with layers with a layer thickness in each case of: 47 nm, 77 nm, and 90 nm, which were deposited using the described method. It is clear from the figure that the transmission τ of the coated substrates, characterized by the transmission spectra S2, S3, and S4, is considerably improved compared with the uncoated substrate at a wavelength λ of ca. 550 nm.

FIG. 4 shows transmission spectra of substrates made of polycarbonate, which were coated using the method described for FIG. 3. The transmission spectrum S1 characterizes an uncoated surface of the substrate. The transmission spectra S2, S3, and S4 show characteristics of substrates with layers with a layer thickness in each case of: 18 nm, 32 nm, and 42 nm, which were deposited using the described method. It is clear from the figure that the transmission τ of the coated substrates, characterized by the transmission spectra S2, S3, and S4, is considerably improved compared with the uncoated substrate at a wavelength λ of ca. 550 nm.

FIG. 5 shows the transmission spectra of substrates made of flat glass. A substrate made of float glass is coated by means of a plasma torch at atmospheric pressure. In this case, the plasma is generated by means of a dielectrically hindered discharge between two horizontally arranged planar high-voltage electrodes, about 5 cm×10 cm in size. One of the two high-voltage electrodes, for example, the upper one, is glued to an insulating ceramic plate, about 1 mm thick, which is used as the dielectric. There is an air gap, which can be a few millimeters thick, between the upper high-voltage electrode, which is supplied with a high-frequency high voltage, and the lower high-voltage electrode, which is connected to ground or grounded. A planar plasma, which is formed of many small discharge channels, forms in this gap after application of the voltage. The high-voltage electrode comprises a gas supply system, through which a precursor-containing working gas can be supplied through a slit in the ceramic plate to the plasma space. If a recess is formed in the lower high-voltage electrode to accommodate planar substrates, such as, for example, made of flat glass, then coatings on planar substrates can be produced in this way. For this purpose, the lower high-voltage electrode can be mounted on an xy sliding unit, which is located at the suitable distance to the upper high-voltage electrode. The moving back and forth of the lower high-voltage electrode provided with the substrate below the upper high-voltage electrode results in the formation of the dielectrically hindered discharge during their passing, as well as in the reaction of the constantly available precursor-containing gas. For example, 3-mm thick flat glass is used as the substrate. The samples are carried under the upper high-voltage electrode with the aid of an xy positioning table. The distance of the high-voltage electrode to the substrate is about 1 mm. The travel speed is 60 mm/sec. 20 passes are realized. Various layer thicknesses were achieved by varying the throughput of the precursor-containing gas between 0 and 0.4 L/min. Hexamethyldisiloxane was used as the precursor. The deposited layers accordingly contain substantially silicon oxide.

FIG. 5 shows the transmission spectra of various substrates. In this case, a transmission τ is plotted versus a wavelength λ. The transmission spectrum S1 characterizes an uncoated surface of the substrate. The transmission spectra S2 and S3 show characteristics of substrates with layers with a layer thickness in each case of: 15 nm and 76 nm, which were deposited using the described method. It is clear from the figure that the transmission τ of the coated substrate, characterized by the transmission spectrum S3, is considerably improved compared with the uncoated substrate at a wavelength λ of ca. 550 nm.

The mentioned parameters are exemplary and are not to be understood as being limiting.

Other materials, particularly plastic, ceramic, glass ceramic, or metals can be used as a substrate. Likewise, an already coated substrate can be coated.

The coating process can be performed subsequent to a manufacturing process of the substrate on the still hot surface of the substrate. In the case of a glass substrate produced in a float bath, its coating can occur immediately thereafter.

The temperature of the surface is within a range of from 100° C. to 800° C., particularly in a range of from 300° C. to 800° C. It is also possible as an alternative to use the method when the temperature of the surface is within a range of from room temperature to 800° C. or, particularly when substrates made of plastic are used, within a range of from room temperature to 100° C. or 200° C.

The method is carried out under pressure conditions which result from the ambient atmospheric pressure and the flow relationships generated by the unit, particularly of the carrier gas stream and the exhaust gas removal.

The method can be carried out at a pressure greater than 800 mbar, particularly at atmospheric pressure.

A free jet plasma source or a dielectrically hindered discharge or microwave excitation can be used to generate the plasma.

The precursor can be introduced as a gas into the working gas or into the plasma. If the precursor is liquid or solid, it is preferably converted to the gaseous state before introduction into the working gas or into the plasma jet.

The throughput of the working gas and/or of the precursor can be variable and controllable and/or adjustable. The throughputs of working gas and precursor are in particular controllable and/or adjustable independent of one another. A layer can be deposited as a gradient layer in this way.

Alternatively or in addition to a transmission-improving layer, the deposited layers can also change the following properties of the substrate: scratch resistance, self-healing ability, barrier behavior, refractive index, transparency, light scattering, electrical conductivity, antibacterial behavior, friction, adhesion, hydrophilicity, hydrophobicity, oleophobicity, surface tension, surface energy, anticorrosive action, dirt-repellent action, self-cleaning ability, photocatalytic behavior, antistress behavior, wear behavior, chemical resistance, biocidal behavior, biocompatible behavior, electrostatic behavior, electrochromic activity, photochromic activity, and gasochromic activity.

The precursors are selected in particular such that the deposited layer contains at least one of the components comprising silicon, silver, gold, copper, iron, nickel, cobalt, selenium, tin, aluminum, titanium, zinc, zirconium, tantalum, chromium, manganese, molybdenum, tungsten, bismuth, germanium, niobium, vanadium, gallium, indium, magnesium, calcium, strontium, barium, lithium, lanthanides, carbon, oxygen, nitrogen, sulfur, boron, phosphorus, fluorine, halogens, and hydrogen.

Used as a precursor are organosilicon and/or organotitanium compounds.

Air or another gas can be used as the working gas.

Multiple layers can be deposited one after another. For example, a first layer with a barrier effect can be deposited and then another layer.

The methods shown in the exemplary embodiments provide a coating from above. The coating, however, can also occur from below or from the side in the case of a vertical or an inclined substrate. In particular, a coating from several sides simultaneously is also possible, in the case of a planar substrate, for example, from above and below.

The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.

Claims

1. A method for coating a substrate, the method comprising:

generating a plasma jet from a working gas;

supplying at least one precursor material to the working gas and/or the plasma jet, the at least one precursor material being reacted in the plasma jet; and

depositing at least one reaction product having at least one precursor material on at least one surface of the substrate and/or on at least one layer arranged on the surface,

wherein at least one of the deposited layers improves an optical transmission of the substrate and/or reduces a reflection,

wherein the substrate at least for a first coating is hot or is heated,

wherein the first coating occurs subsequent to a substrate manufacturing process in which the substrate is formed with the aid of heat, and

wherein the generation of the plasma occurs in a free jet plasma source.

2. The method according to claim 1, wherein the coating of a substrate is made of glass, plastic, glass ceramic, ceramic, or metal.

3. The method according to claim 1, wherein a temperature of the substrate, at least on one substrate surface, is within a range of from 300° C. to 800° C.

4. The method according to claim 1, wherein the depositing of the layer takes place at a pressure, which results from an ambient atmospheric pressure and a flow relationships predominating in the unit.

5. The method according to claim 4, wherein the depositing of the layer takes place at atmospheric pressure.

6. The method according to claim 1, wherein the generation of the plasma occurs via a dielectrically hindered discharge or by microwave excitation.

7. The method according to claim 1, wherein a gaseous precursor is used.

8. The method according to claim 1, wherein, via at least one of the deposited layers, at least one of the properties of the substrate is changed, the properties including scratch resistance, self-healing ability, barrier behavior, reflection behavior, transmission behavior, refractive index, transparency, light scattering, electrical conductivity, antibacterial behavior, friction, adhesion, hydrophilicity, hydrophobicity, oleophobicity, surface tension, surface energy, anticorrosive action, dirt-repellent action, self-cleaning ability, photocatalytic behavior, antistress behavior, wear behavior, chemical resistance, biocidal behavior, biocompatible behavior, electrostatic behavior, electrochromic activity, photochromic activity, and/or gasochromic activity.

9. The method according to claim 1, wherein the deposited layer contains at least one of the components comprising silicon, silver, gold, copper, iron, nickel, cobalt, selenium, tin, aluminum, titanium, zinc, zirconium, tantalum, chromium, manganese, molybdenum, tungsten, bismuth, germanium, niobium, vanadium, gallium, indium, magnesium, calcium, strontium, barium, lithium, lanthanides, carbon, oxygen, nitrogen, sulfur, boron, phosphorus, fluorine, halogens, or hydrogen.

10. The method according to claim 1, wherein an organosilicon and/or organotitanium compound is used as the precursor.

11. The method according to claim 1, wherein air or a gas or vapor is used as the working gas.

12. The method according to claim 11, wherein oxygen, nitrogen, noble gases, hydrogen, carbon dioxide, gaseous hydrocarbons, or a mixture of at least two of the aforementioned working gases is used as the working gas.

13. The method according to claim 1, wherein at least one of the layers is deposited as a gradient layer.

14. The method according to claim 1, wherein a first layer with a barrier effect and then at least one other layer are deposited.

15. The method according to claim 3, wherein a temperature of the substrate at least on one substrate surface is within a range of from room temperature to 800° C., instead of within a range between 300° C. and 800° C.