DE19940458A1 - Process for changing coating materials - Google Patents

Abstract

The invention relates to a method for thermally modifying coating materials which are electrically at least semiconductive. According to said method, the coating materials in solid form are subjected to an electromagnetic alternating field which causes thermal modification as a result of their inductive heating. The invention also relates to an object with a coating consisting of a material which is electrically at least semiconductive, deposited on a base body which can only be slightly heated by eddy-current induction. The base body consists of a material which is, in particular, dimensionally stable and which remains unmodified only up to a predetermined temperature and the coating material has characteristics which enable it to be modified by being heated to a temperature which lies below said predetermined temperature.

Description

The present invention relates to a method for thermi electrical change at least semiconducting coating tion materials and an object with a coating made of electrically at least semiconducting material.

It has long been known that the properties of counter can be changed by the surfaces of the Ge objects are coated. Depending on the coating used tion material can reduce friction, reduced Ver wear, changed reflectivity, etc. can be obtained.

According to the variety and importance of coatings there are also a variety of different techniques for Apply the coating materials to one of them basic body. Among the techniques with which coatings on materials such as ceramics, glass, metal and / or combinations NEN same are applied, u. a. the spray pyro lysis (pyrolysis process), as described by M Mizuhashi, J. Non-Cristalline Solids 38 & 39 (1980), 329 and by J. Dutta, Thin Solid Films 239 (1994), 150; the gas phases deposition (PVD) and sputtering methods as described by L. Meng, Thin  Solid Films 237 (1994), 112; and CVD (Chemical Vaper Deposition) method as exemplified by D. J. Houl ton, A.C. Jones, P.W. Haycock, E.W. Williams, J. Bull, G. W. Critchlow, Chem. Vap. Deposition 1 (1995), 26, and from S. R. Vishawakarma, Thin Solid Films 176 (1989), 99. The aforementioned gas phase processes usually require egg considerable technical effort and accordingly high investment costs, especially in the coating large components.

It is also already known by means of wet chemical coating processing method, in particular on the basis of the sol-gel Process of applying coatings. With sol-gel processes are primarily ionic or molecular compounds Layer material precursors are present on the main body be reacted and appear as an amorphous layer store what the sol-gel layer of suspensions nanoscale Crystals differ. Published work on this stam For example, Y. Takahashi, Y. Wada, J. Electrochem. Soc. 137 (1) (1990), 267; J. Pütz; Diploma thesis, Institute for New Materials, February 1996; C. J. R. Gonzales-Olivier, J. Non- Crystalline Solids 82 (1986), 400, and S. Park, Thin Solid Films 258 (1995), 268. The sol-gel process is particularly popular reversible in the production of ceramic layers, layers of Glass and hybrid layers made of different materials such as glass and ceramics or inorganic and organic Fabrics are composed.

In wet chemical coating techniques, sol-gel Systems and / or coating suspensions of microstructure particles and / or nanoparticles, especially nanoparticles by dipping or spinning, spraying, printing, etc. applied what an inexpensive, especially large area Coating even structured layers allows.

The coatings applied by wet chemical processes however differ from those due to gas phase processes  manufactured in their properties, especially what the Size of the particles present in the layer as well as the Layer density is concerned. The density with the crystallization onsgrad has a significant impact on phy sical properties of the layer produced. So change refractive index, reflectivity, permittivity, susceptibility lity, electrical conductivity, permeability, etc. typically the electrical conductivity of coatings from ITO (indium tin oxide) and ATO (antimony tin Oxyd) lower if this is to be coated via wet chemical processing techniques are applied as if the coating be produced by vacuum processes. In addition, at the production of a layer usually more than one Layer parameters are taken into account. For example at the same time high or specifically adjustable Conductivities, high transparency, i.e. transmissivity for Visible light and thin layers desired, which we should be a few nanometers to a few micrometers thick. It is from G. Gasparro, J. Pütz, D. Ganz, M.A. Aegerter, EuroSun '96, Int. Symp. On Optical Materials Technology for Energy Ef ficiency and Solar Energy Conversion, 1996, known for an optimal functionality of the layer as high as possible Density that ideally corresponds to the theoretically possible value speaks, must be sought.

In addition to the density, the particle size also plays a considerable role role, because many particle properties depend on size gig. So change with the size of existing in a shift which particles have the catalytic properties of the layer, the electrical properties, the optical transparency, etc. There are even transitions from ferro to super paramagnetism observed when the to form multi-domain particles the required volume limit is undershot. The size of the Particles in a layer, however, depend on the manufacturer way, ie the chemical manufacturing process and the subsequent layer treatment, for example by heat drove for particle crystallization and / or sintering.  

The properties of a coating are therefore greatly reduced depending on whether the layers consist of a suspension, dispersion, by means of solvents, by vacuum deposition, etc. be put.

It is therefore possible to change layers by heat treatment other. This is beneficial when you are working from very small layers forming particles, d. H. Nanoparticles runs out to thin To form layers; per se this is especially the case with very thin ones Layers advantageous because here too there is still a large number of Particles lie on top of each other, which causes certain layer defects medically and largely results in homogeneous layers. Based on such nanostructures, ge targeted heat supply achieves a change in properties the.

So it is possible wet chemical layers made of particulate densify systems by sintering. Such Densification by sintering usually requires temperatures which, especially with ceramic coating materials, about 1,000 ° C. In addition to the change caused by sintering is also a change in properties only by crystallization in the case of wet chemistry, in particular using the sol-gel method provided layers possible because the crystallization at ge lower temperatures than the compression and / or sintering tion takes place. Through targeted heat and precisely metered heat The degree of crystallization, density, porosity, Adjust pore size and other material properties. At Thursday tation of the layer-forming particles can by a Nachkri stallization even a transport of the doping on specific lattice positions are achieved, which is the material property also sets. Such a transport of the dopants materials on suitable lattice sites can be Often do not stop precipitation processes, at least not I agree.  

It is known to densify by sintering in an oven to carry out, provided with the coating material a body with this in an oven until the Materials are thermally changed as required.

However, this is disadvantageous, especially with large and massive ones Base bodies with appropriately dimensioned stoves required are the ratio of energy used to heating of the basic body and the energy required to change the Coating material is bad and moreover ther Mix sensitive base body at most little and inadequate let it warm up.

The object of the present invention is to create something new to provide for commercial use.

The solution to this problem is claimed independently. Before drawn embodiments can be found in the dependent claims chen.

A basic idea of the present invention is thus included see that the initially low conductivity of the wet mixed layers is used to generate energy ductively, i.e. by creating eddy currents, selectively in to deposit the layer. Thereby the knowledge is given useful that despite the thermi treatment to increase electrical conductivity of the particulate, that is to say having and / or representing nanoparticles from existing and / or sol-gel coating material and the fact that the coating material is usually on a basic body only in very thin layers of example applied a few µm thick and made of nanoparticles det, especially with high-frequency electromagnetic Alternating fields is possible to generate such strong eddy currents conditions that the desired thermal change of the Be layering material.  

The heat treatment according to the invention also enables Removal of organic solvents that are known in the art Technology must be burned out, a solidification of anor ganic binders, respectively a debinding and / or Process Aid Removal. For the removal of foreign matter fen is advantageous in that the heating does not go from the outside inside is done like in conventional ovens, but the whole Layer is warmed up practically at the same time and so you increase in temperature when the outer layers begin to heat up is prevented, which would otherwise result in outgassing respectively Could prevent expulsion of unwanted process aids.

The high-frequency electromagnetic fields are in the Range from a few kilohertz to a maximum of a few megahertz gen. The use of frequencies in the range is preferred 100 to 500 kilohertz, because this frequency range sufficiently strong alternating electromagnetic fields with low Let effort generate and the energy through the skin effect can be deposited well in thin layers. The times sintering is typically only a little at normal performance seconds. This may also take place before sintering a crystallization.

The application of a high-frequency electromagnetic The alternating field generates the desired one by induction thermal change, in particular up to a compression tion as can be continued by conventional sintering. The heat treatment according to the present invention is carried out so fast that a quick thermal healing of Defects, a so-called "rapid thermal annealing" enables light becomes. Such treatment was previously only through Infrared flashes are known, but which are particularly in the In Do not allow the red absorbent body to be used.

It is sufficient to only electrically semiconductive particulate To use material as a coating material, in particular  special doping for the material to achieve the Semiconductors can be used.

In particular, indium tin Oxide, fluorine-doped tin oxide, antimony-tin oxide, zinc oxide, Nitrides, carbides, borides, titanates, niobates, tantalates in general my perovskite, iron oxides, TiN, TiC, Ti (CN), TaC, AlN as well Precursors of the aforementioned substances, as well as semiconductors of the III-IV and / or III-V type in question. In particular fluordo The doped tin oxide also has a nanoparticle sufficient conductivity. Similar allocations are also possible with Ito, for example.

Ceramic coating material can also be used who the like electrically conductive, especially metals and / or intermetallic compounds as long as the conductivity is off is enough to conduct eddy currents.

The coating material will typically get to the bottom body applied in a thin layer, typically usually wet chemical, i.e. with a fluid, for example Dip and / or spin coating, spraying, printing, in particular re offset and / or screen printing, knife coating, casting and rolling and / or combinations of these methods.

The fluid usually becomes an organic substance, i.e. H. on organic solvent and / or water and preferred the coating material becomes particularly the same to achieve moderate results before exposure to the electroma gnetfeld at least pre-dried, which is due to warm air, sticking out etc. can be done.

The base body can be made of heat-sensitive and / or isolie material. Examples are particular Glass, such as silicate glass, ceramics, ceramic glasses, as well as plastics, in particular PMMA, PE, PET.  

The base body will preferably conduct significantly worse than the coating materials. To the energy of the electromagnetic table alternating field particularly completely in the Beschich it is particularly preferred if the basic body for this is at least two orders of magnitude lower electrical conductivity than that at least half has conductive coating material. To guarantee this Most, in particular for the purpose of increasing conductivity tated coating material can be selected. The comparison low conductivity ensures that the base body un depending on the penetration depth of the electromagnetic altern selfeldes, which is determined by the skin effect, energy primarily obtained from the heated coating material. Since the coating material with thin layers only a ge rings has heat capacity and accordingly very quickly to thermal change, which prefers a sin heating, densification and / or crystallization leaves, it is ensured that the base body is already due very little of the different heat capacities and al if necessary locally near the surface by the transgressor Heat flow is heated. Such warming is also at Plastic base bodies and the like in particular therefore even desirable because it adheres to the coating mate rials on the base body, especially through diffuse mate rial exchange, d. H. by "diffusion bonding" ver can improve. Protection is also provided for bodies of this type seen coating claimed.

It is thus possible to apply the coating materials locally Warm temperatures that are well above that tempera ture, the basic body as a whole without deformity on and / or decomposition could be exposed. The nanopart Chen allow sintering even at temperatures and / or times in which the base body also at high Sensitivity to heat remains unchanged.  

The invention is described below by way of example only ben.

A basic body made of PMMA, an electrical non-conductor Plastic, is by spraying with an organic Be stratification suspension, the ITO (indium tin oxide) nanoparticles contains, coated and dried at room temperature. After this The PMMA base body is dried together with the dried one Coating a high frequency electromagnetic change exposed field, causing inductive eddy currents in the indium Tin oxide coating can be excited, causing the coating material inductively heated. This does not dry out yet organic or unbound organic residues completely expelled.

At the same time, the PMMA body carrying the coating remains as an electrical non-conductor in which no eddy currents indu can be decorated, practically at room temperature. The change selfeld is chosen with a strength sufficient to in to couple the ITO layer so much energy that it permanently sintered. The alternating field becomes like this strongly chosen that the sintering quickly in a very short zen period takes place in which no significant heat can flow into the PMMA. After the ITO Coating material thermally induced by the vortex streams has been permanently compressed, the supply of high-frequency electromagnetic energy ended, whereupon the coated body that is only in and very close to the very thin layer was heated up, almost instantly Room temperature.

It is important with this heating technology that the thermi change almost exclusively requires energy in the coating material without influencing the basic body pers is coupled. This selective local absorption of energy required for heating allows a quick and ho he compression of the coating material without or with all  if moderate substrate heating. This enables indium Tin oxide, the compression temperature far above the typi the thermal load limit of the PMMA is as kerami layer with a given density, pore size, porosity etc. to be provided on a heat-sensitive carrier.

The coated PMMA body obtained has a solid Ver bond to the indium tin oxide coating on it is particularly durable. There are also no significant ones Stresses due to different coefficients of expansion body and coating.

In a further exemplary embodiment, commercially available Borosilicate glass, as used for window panes, coated with a suspension of ATO nanoparticles and there after dried. With the subsequent coupling of high frequency electromagnetic energy is the energy, d. H. the field strength and the frequency of the incoming alternating field the time varies. Since with the frequency also the penetration depth of the electromagnetic field in the coating changed there is a locally controlled energy supply via the Coating away. Accordingly, it varies across the layer also the degree of compaction, so that a gradient layer is obtained will. It can be anticipated that the method will also apply to al potash-containing glasses gives good results.

It should be mentioned that the layer condition at the thermal change can be detected optically, for example to regulate the energy supply.

It should be mentioned that the coating to be changed thermally materials are not necessarily already on a basic body must be applied, but also treated as a molding can be.

It should also be mentioned that the coating materials relate to nano-particles not necessarily on a basic body  must be applied, but also in a base body, d. H. can be embedded in a basic matrix and / or treated in a liquid or other fluid that can. The nanoparticles can act as energy couplers act through which eddy current energy in the body can be coupled. This procedure can also be used the coating materials or nanoparticles in change their properties. The nanoparticle density in the Ma trix can be varied to achieve a desired absorption of the electromagnetic energy in the body or in the To achieve matrix and / or the depth of penetration selectively change. Like applying a thin layer and de subsequent sintering, density change, etc. is from crucial that selective heating of the Nanoparticles occur while they are in thermal contact with a surrounding medium of much larger mass and thus higher their thermal capacity. You get a selek again tive heating, but unlike sealing sintering it can be desired to heat the nanoparticles as long and as far men that the total matrix also a total of a tempera experienced increase in door. So nanoparticles can act as energy couplers and so-called hotspots can be used. These nanoscale Energy and heat couplers allow for their installation in Base bodies, matrices and / or their introduction into liquids targeted heatability through electromagnetic fields to make. When designed for specified electromagnetic Frequencies can also be an electromagnetic Ab achieve shielding effect. In the latter applications it does not matter that a thermal change achieved change is permanently effected, but rather here Warming as a thermal change itself sought.

Claims (24)

1. Process for the thermal change of electrically at least semiconducting coating materials, characterized in that the coating materials are acted upon in solid form with an alternating electromagnetic field until the thermal change is brought about by their inductive heating. 2. The method according to the preceding claim, characterized ge indicates that as an electrical coating material semiconducting material is used. 3. The method according to the preceding claim, characterized ge indicates that as an electrically semiconducting coating tion material used a semiconductively doped material becomes. 4. The method according to any one of the preceding claims, characterized characterized in that a kerami as coating material material is used.   5. The method according to any one of the preceding claims, characterized characterized in that the coating material is selected and / or is combined from the group ITO (indium tin Oxide), ATO (arsenic tin oxide), FTO, ZnO, nitrides, carbi the, borides and / or III-IV and / or III-V semiconductors. 6. The method according to claim 1, characterized in that as Coating material used an electrically conductive becomes. 7. The method according to any one of the preceding claims, characterized characterized in that a metal as the coating material and / or an intermetallic compound is used. 8. The method according to any one of the preceding claims, characterized characterized in that the coating material before its thermal change applied to a base body becomes. 9. The method according to the preceding claim, characterized ge indicates that the coating material gets to the bottom body is applied in a thin layer. 10. The method according to any one of claims 8 or 9, characterized ge indicates that the coating material together with a fluid is applied to the base body. 11. The method according to the preceding claim, characterized ge indicates that the coating material gets to the bottom body by dipping and / or spinning, spraying, Printing in particular offset and / or screen printing, squeegees and / or casting applied and / or a structured Surface is generated during application. 12. The method according to any one of claims 10 or 11, characterized ge indicates that the fluid is an alcoholic and / or  organic solvents and / or water and / or aqueous solvent is / are used. 13. The method according to any one of the preceding claims, characterized characterized in that the coating material before the egg property-changing inductive heating dried is, especially at temperatures below thermal change required. 14. The method according to any one of claims 8 to 13, characterized ge indicates that a base body made of heat-sensitive Material is used. 15. The method according to any one of claims 8 to 14, characterized ge indicates that a base body made of glass, in particular silicate-containing glass, glass ceramics, ceramics and / or art fabric, especially PMMA, PE, PET is used. 16. The method according to any one of the preceding claims, characterized characterized in that the coating materials by ih re inductive heating sintered and / or compressed and / or be crystallized and / or that Temperature treatment the electrical conductivity duration imprisoned. 17. The method according to any one of claims 14 to 16, characterized ge indicates that the coating materials are local Temperatures are warmed above those of the reason physical stability. 18. The method according to any one of claims 8 to 17, characterized ge indicates that a basic body is used, the Conductivity lower than that of the electrical at least semiconducting coating material. 19. The method according to any one of the preceding claims, characterized characterized in that the electrical conductivity in particular  especially for the induction of eddy currents of the basic body pers at least two orders of magnitude less than that of electrically at least semiconducting coating material is. 20. The method according to any one of the preceding claims, characterized characterized in that at the local coating material Heating the base body up to the surface so far is heated that between base material and Beschich tion material improved liability, in particular through diffusive material exchange. 21. Item with a coating of electrical at least semiconducting material on an eddy current inductor on at least slightly heatable body, thereby characterized in that the basic body from only up to heatable at a predetermined temperature, there is in particular dimensionally stable material, and the Be layering material by heating to temperature un below the specified changed properties has. 22. Object according to the preceding claim, characterized ge indicates that the property of the coating material than, which by heating to a temperature above the density has been permanently changed and / or electrical conductivity and / or the crystalline ne structure and / or the porosity of the coating material rials is. 23. Object according to one of the preceding claims, since characterized in that the basic body one by lo cal heating of the coating changed near the surface Area.   24. Object according to the preceding claim, characterized ge indicates that the area of the near-surface changes change of the base body is at most a few µm thick.