Device and method for electrophoretic deposition with a movable electrode

The present invention relates to an apparatus and a method for production of a mold, in particular of a dental mold, by means of electrophoretic deposition of particles from a suspension. The invention also relates to a system having an apparatus such as this and a suspension of particles which can be deposited electrophoretically, to a computer program for controlling an apparatus such as this, and to a data storage medium having a computer program such as this.

Electrophoretic deposition of particles is a well-established method for production of ceramic, metallic or metal-ceramic parts or glass bodies. In recent years, the electrophoretic deposition of particles has been brought ever more sharply into focus for the production of ceramic parts, in particular in the field of fuel cell development and in the field of dentistry. The reason for this can be seen in the capability to produce homogeneous and dense particle packings in which, furthermore, the layer thickness can be adjusted in a defined manner.

In recent years, methods supported by a potential (methods in which an electrical field is applied in order to assist or accelerate the process) have become established for production of dental ceramics since, in contrast to dye-casting methods, these allow higher green densities and higher homogeneity. For example, the shrinkage during sintering can be minimized, thus allowing production closer to the final contours than can be achieved by dye casting. Furthermore, the sample shrinks isotropically because of the homogeneity. The suspensions on which these methods are based offer the advantage that reprocessing and thus reuse are possible after production of the mold.

Zirconium oxide, in particular, has been proven to be highly suitable for use as a material for production of dental ceramics. This has the advantage, in addition to the very high strength of the green bodies and molds, that very good translucency is also possible, which means that this material has the optical characteristics of a real tooth, or comes very close to this.

EP 0 200 242 A2 and EP 0 196 717 A1 have disclosed a method for production of a glass body in which a porous green body is formed from an aqueous suspension with a highly dispersed solid content, and this is then cleaned and sintered, with the green body being produced by separation of the phases of the suspension by means of electrophoresis.

DE 103 19 300 A1 discloses a method for production of a silica glass body. In this case, silicon dioxide particles are deposited on an electrically non-conductive membrane from an aqueous dispersion.

DE 103 20 936 A1 discloses a method for production of a completely ceramic green body, in particular for the dental field, in which ceramic particles are deposited on a porous mold from a suspension, with one electrode being arranged within the porous mold and one electrode being arranged outside it. This means that, when using water as a dispersant or suspension agent, no gas bubbles which occur as a result of electrolytic decomposition are enclosed in the green body.

DE 101 20 084 A1 discloses a method in which dental molds are produced on a model by means of electrophoretic deposition. The outer surface, facing away from the model, of the ceramic body which is obtained in this case is processed with ceramic material being removed.

DE 100 49 974 A1 discloses a dental ceramic being produced from at least one ceramic powder with the addition of a metallic powder, with the green body preferably being produced by electrophoretic deposition. During sintering in an oxidizing atmosphere, the metal is reduced, and this is used to compensate for the sintering shrinkage.

DE 100 49 971 A1 discloses a method in which a green body for a dental ceramic is deposited electrophoretically on an electrode, with the green body and the suspension from which it is deposited containing ceramic fibers and/or nanocrystalline particles.

“Creation and Optical Property of Microphotonic Crystals by Electrophoretic Deposition Method using Micro-counter Electrode” (J.-I. Hamagami, K. Hasegawa and K. Kanamura, Mat. Res. Soc. Symp. Proc. 797 (2004) 151-156) describes a method in which a microelectrode is arranged opposite a flat electrode in order to allow locally limited electrophoretic deposition.

The often-stated advantage of electrophoretic deposition of allowing homogeneous layers also represents a restriction, however, on the known methods. The largely uniform deposition of the particles over the entire electrode or the entire deposition element and over the deposited mold altogether means that the entire deposited mold has an essentially uniform layer thickness of deposited particles. This uniform layer thickness makes it necessary to provide for post-processing of the deposited body, for example by milling, in the case of the known methods, in order to achieve desired differences in the layer thickness in the deposited mold. Particularly in the dental field, it is frequently necessary or desirable to produce molds with a varying wall thickness, for example for crowns.

DE 102 51 369 A1 and DE 103 34 437 A1 teach the provision of an electrode which is specifically shaped and has areas of different conductivity for production of a desired three-dimensional shape of a deposited green body, that is to say for deposition of layers of different thicknesses. In this case, it has been found to be disadvantageous that the specific shape of the deposition electrode can be determined only empirically. The effect of a predetermined shape of the deposition electrode in conjunction with areas of different conductivity on the three-dimensional shape of the deposited layer can be predicted only roughly, if at all.

Rapid prototyping methods have become established for the production of small batches and for the construction of prototypes and individual structures, in the dental field as well. Their major advantage is their flexibility, since the tool is not only suitable for producing a specific geometry but also ensures shape flexibility. Most known embodiments are based on layers (or films) of ceramic powder which are fixed in layers on a position-selective basis. The excess, unfixed powders are generally thrown away.

One fixing option is selective laser sintering (SLS), in which a large amount of excess material is used. This must be processed again in complicated steps. In the case of laminated object manufacturing (LOM), in which tailor-made films with a thickness of about 130 μm are laminated to one another and are then sintered, excess material is likewise produced, and cannot be reprocessed.

EP 1 021 997 A2 discloses a method in which tooth replacement and dental accessories are produced by means of laser sintering. In this case, a bio-compatible material is selectively irradiated, thus resulting in sintering taking place at these points.

DE 102 19 983 A1 discloses a method in which a laser beam is passed selectively over a powder accumulation composed of metallic or non-metallic powders, such that a geometry can be formed layer by layer by reduction of the already sintered or molten structure. This has the disadvantage that the geometry, in particular an existing weak point, must be post-processed mechanically.

The result of successive sintering, generally layer-by-layer, is inferior, with respect to the homogeneity of the material, than a body which is sintered as an entity and is deposited, for example, by means of electrophoresis.

The known methods in which (electrophoretic) deposition is used make it possible to define a surface of the mold to be produced sufficiently accurately, specifically the surface of the mold which rests on that surface of the mount structure on which deposition takes place. Desired variation of the thickness of the mold and thus specific adjustment of the three-dimensional shape of the mold are feasible only to a very restricted extent, and are possible only with poor reproducibility.

Known rapid prototyping methods admittedly allow a desired three-dimensional shape to be produced specifically, but the particular homogeneity of electrophoretic deposition is not achieved in the process. Furthermore, significant material losses resulting from production scrap cannot be avoided with the known methods.

One object on which the present invention is based is to specify an apparatus and a method for production of a mold, in particular of a dental mold, by means of electrophoretic deposition of particles from a suspension, in which case a predetermined three-dimensional shape can be produced deliberately in order in this way to produce a mold which is as close as possible to the final dimensions and the final contour. A further aim is to produce the molds at low cost, with efficient use of resources, quickly and as simply as possible, with good reproducibility of the method being desirable in order to achieve a low scrap rate. According to a further aspect, a corresponding system (having an apparatus according to the invention and a suspension of particles which can be deposited electrophoretically), a computer program for controlling an apparatus such as this and a data storage medium having a computer program such as this will be specified.

According to the invention, in order to achieve the object, an apparatus is proposed for production of a mold, in particular of a dental mold, by means of electrophoretic deposition of particles from a suspension, having a chamber for holding the suspension, a first electrode which is associated with the chamber, a second electrode which is associated with the chamber, a mount structure, which is associated with the chamber and on which particles can be deposited, with the mount structure being formed by the second electrode and/or by a deposition element which is arranged between the first electrode and the second electrode, and a voltage source for production of an electrical potential difference between the first electrode and the second electrode, in which case the apparatus has a positioning element for carrying out a relative movement between the first electrode and the mount structure along a first predetermined path during the electrophoretic deposition.

Furthermore, the invention relates to a method for production of a mold, in particular of a dental mold, by means of electrophoretic deposition of particles from a suspension, having the following steps: provision of a suspension of particles which can be deposited electrophoretically, production of an electrical potential difference between a first electrode and a second electrode, with one of the two electrodes being arranged at least partially in the suspension, and with the other of the two electrodes making electrical contact with the suspension, and electrophoretic deposition of particles from the suspension on a mount structure, with the mount structure being formed by the second electrode and/or by a deposition element which is arranged between the first electrode and the second electrode, in which case the first electrode and/or the mount structure are/is moved relative to one another along a predetermined path during the electrophoretic deposition.