Granule and process for preparing coloured ceramic articles

The invention relates to a granulate for producing colored ceramic shaped parts, and to its use, to a method for producing colored ceramic shaped parts and on colored ceramic shaped parts, and ceramic molding green compacts.

Colored ceramic shaped parts can be produced by sintering a granulate. Coloring particles become mixed with the ceramic powder and optionally sintering aids to form granules. Under color-producing particles are particles that have the desired color before sintering or the color you want to train only during the sintering process. The mixing of the components is carried out by a milling process or by precipitation from a solution. In both cases, the mixture then has to be dried, wherein the precipitation of a solution, the calcination of the powder mixture is often necessary. Shaping can be carried out by cold or hot isostatic pressing. After sintering is then obtained a monochromatic ceramic molding. These two old men of color are associated with considerable technical effort.

A specific method for producing ruby-colored aluminum oxide ceramic is described in the Czechoslovakian Patent CS 191 122. The granulate consists of a mixture of alumina ceramic powder and a binder. After mixing of this granulate is injection-molded. The coloring of the molded parts is carried out by impregnation with a chromium chloride solution after partial removal of the binder. The impregnated molding is sintered. A disadvantage, however, that when soaking and subsequent drying separation phenomena occur because the chromium chloride is predominantly absorbed at the surface, although the solvent fully penetrates into the molding. A homogeneous color distribution is therefore not accessible.

The object of the invention is therefore to provide a granulate for producing colored ceramic shaped parts. Furthermore, a process for producing colored ceramic shaped parts with good characteristics of color and color distribution, in particular provided a homogeneous color distribution. This procedure should be simple and flexible. Another object of the invention is to provide homogeneously colored ceramic moldings and ceramic molding green compacts.

The object is achieved by the provision of a granulate for the production of colored ceramic moldings, which granulate ceramic powder, binder and color-imparting particles. The proportion of binder in the molding composition is to be processed 30 vol% to 60 vol%. Color-producing particles are those particles which are colored already during the mixing of the granulate or color unfold during the manufacturing process, particularly during the sintering process. Preferred color-producing particles are metal powders, metal oxide powders, their precursor compounds, which form when heat metal oxides, pigments, or mixtures of these materials. Particularly preferred is the use of Lanthanides or their oxides, of metals of the group Co, Cr, Cu, Fe, Mn, Mo, Nb, Ni, Pb, Si, Sn, Ti, VW, or their oxides, in particular oxides of the group of CoO, Co₂O₃, Co₃O₄, Cr₂O₃, Cu₂O, CuO, Fe₂O₃, Fe₃O₄, MnO, Mn₂O₃, MnO₂, MoO₂, MoO₃, NbO, NbO₂, Nb₂O₅, NiO, PbO, PbO₂, SiO₂, SnO, SnO₂, TiO, Ti₂O₃, TiO₂, VO₂, V₂O₅, WO₂, W₂O₅, WO₃. Particularly preferred is also the use of metal salts or metal complexes, in particular, of carboxylates, carbonates, nitrates or acetylacetonates, are converted on sintering in the color-imparting oxides. Similarly colored pigments from the crystal structure classes Baddelleyt, hematite, cassiterite, corundum, olivine, rutile, sphene, spinel and zircon are preferred as color-producing particles. The granules may contain several different color-producing particles. This allows a variety of new colors will sprout pad. Color modifications can also be achieved, it is carried out with metal powders instead of metal oxide. The color after the sintering in an oxidizing atmosphere is often significantly brighter than in the use of the corresponding metal oxide powder with the use of metal powders.

Preferably, the color-producing particles have particle sizes below 10 microns, more preferably below 5 microns. The color-producing particles preferably have a weight content of the used granulate mass or to a feedstock composition for injection molding of 0.05% to 20%.

In another preferred embodiment, the ceramic powder of alumina, zirconium oxide, yttrium oxide, cerium oxide, magnesium oxide, SiC, Si₃N₄ or a combination or a mixture containing thereof. Here, the ceramic powder can also consist essentially of one of these materials. Thus, in the preparation can be an aluminum oxide or zirconium oxide ceramic is yttria or magnesia are added as stabilizing or sintering aid.

Preferred binders are polyacetals, in particular polyoxymethylenes and copolymers and homopolymers of polyoxymethylenes. It can also be a combination of several binders.

In addition to the binder, the injection molding material may also contain organic additives for dispersion and surface modification. In addition, also wetting agents, plasticizers or other additives that affect the rheological properties of the granules during the deformation, are added.

The object is to provide a granulate for producing colored ceramic shaped parts, is also achieved by a granulate consisting of a mixture of a first and a second granulate. It contains the first granular ceramic powder and binder, the second granular colorant particles and binder. Both granulates have the same volume filling in order to ensure the same shrink during the sintering process. These granules can be used in the master batch method in which a color-producing particles containing granulate is mixed as needed with granules with different ceramic powders. This can be combined in a simple manner, a plurality of dyes and ceramic powders.

According to the invention granules, contain the ceramic powder, binder and color-producing particles, used to prepare colored ceramic shaped parts by injection molding. Specifically, a granulated material is used according to one of claims directed to the granulate.

According to the method described in the claims ceramic powder, binder and color-producing particles are mixed and processed into granules of a particularly high homogeneity. From these granules form a green body (green sheet) is molded by injection molding, from which then the binder is removed. The binder-free green body is finally sintered to the use-enabled moldings. In this case, the granules are preferably used, as described above.

The molding by injection molding, debinding and sintering of ceramic granules is described in the European patents EP 413 231, EP 444 475, EP 465 940 and EP 446 708. The intended solely for processing by injection molding pellets in this case contains no color-producing particles. Surprisingly, it has now been found that an incorporation of coloring materials leads to a very homogeneous injection molding material that is suitable for the preparation of homogeneously colored ceramic parts. These parts exhibit a previously attainable only with significantly greater effort surface quality.

The mixture of these components is usually kneaded at temperatures of 115-200 ° C or extruded and subsequently cooled and granulated. The granules obtained can be conducted by conventional screw and piston injection molding machine into molds and deformed bar at temperatures 175-200 ° C and at pressures from 200 to 2000. The demolded green compacts are then subjected to binder removal.

The process of the removal of the binder, ie, the removal of the binder from the ceramic green body depends on the type of binder used. The distance from binders containing polyacetals, is preferably carried out in gaseous, acidic or boron trifluoride-containing atmosphere.

The sintering of the molded and binder-free ceramic moldings is preferably in air, in inert gas atmosphere, in a reducing atmosphere, in vacuum or at a certain oxygen partial pressure. In a preferred process variant, ceramic shaped parts of certain colors are produced by certain sintering conditions. By choosing the sintering atmosphere, a hue can be very varied significantly in nuances or. The latter is the case when the valence state of the metal cation is changed. So a dyed with Eisenzirkonsilikat pink green body is brown during sintering in the air while it is green for sintering in a reducing atmosphere. A colored with flesh-Mn₂O₃ green body is black in an inert gas atmosphere pink, in air.

The task homogeneous provide solid colored colored ceramic moldings is inventively achieved in that the ceramic parts are provided, which consist of a molded, binder removal and sintered pellets, as described above. the colored ceramic shaped parts are preferably made by a process as described in the method claims. These methods have already been described above. The colored ceramic shaped parts are preferably configured as decorative parts, in particular as components of watches, jewelry (rings, necklaces, cufflinks, brooches, tie pins, bracelets, etc.), writing implements, tools, household appliances, door hardware, lighters, vases, lamps, buttons, religious objects (crucifixes, statues of saints, rosaries) or as tiles.

According to the invention ceramic molding green compacts are provided which contains by molding a granulate, ceramic powder, binder and color-producing particles are produced by injection molding. In particular, they are prepared by forming a granulate according to one of claims directed to the granulate. These granules are described above.

example 1

An injection molding granulate comprised 1000 g of zirconia, stabilized with 3 mol% Y₂O₃. The average particle size was 0.3 microns. were mixed with 17 g of polyethylene glycol having a molecular weight of about 800, 23 g polybutanediol with a molecular weight of about 80,000 and 168 g of polyoxymethylene with 2 wt .-% butanediol. As the coloring material 5 g Cr₂O₃ were added. The sustaining mass was mixed in a kneader and mixed with 300 ml of butyl glycol. The mixture was further kneaded under heating, the solvent was evaporated slowly. one hour was subsequently kneaded at about 175 ° C, then cooled and the mixture granulated.

The resulting granules were injection molded into moldings, which were then debinded under acid catalysis. During sintering in an inert gas atmosphere at 1500 ° C, a dark green-colored molding was obtained with a density of about 6 g / ml.

example 2

An injection molding pellet was prepared as in Example 1st Instead Cr₂O₃ However 20g FeCrNi spinel (black) and in the second case 14 g CoAl spinel (blue) was added as a coloring material in the first case.

The moldings obtained were subjected to binder removal with gaseous oxalic acid at 130 ° C under acid catalysis. The subsequent sintering was performed at 1500 ° C even in air, and even in an argon atmosphere.

The sintering in air resulted in blue or black moldings. The use of an argon atmosphere, however, led to a much brighter shade of blue, while the black remained unchanged.

example 3

800 g of yttrium-stabilized zirconia was processed with 200 g of alumina and 50 g of Cr₂O₃ and the other binder components and additives as in Example 1 to form a granulate, injection molded and debinded. During sintering in air at 1600 ° C, a ruby-colored molded article was obtained.

example 4

700 g of alumina having a mean particle size of 0.8 microns was processed with 7 g of Co powder and 20 g CoAl₂O₄ and the other binder components and additives as in Example 1 to form a granulate, injection molded and debinded. During sintering in air at 1650 ° C, a blue molding was obtained in both cases, the use of cobalt powder to a brilliant blue, the use of CoAl₂O₄ to a considerably darker blue led.

example 5

1000 g of yttrium-stabilized zirconia was processed with 30 g of Mn₂O₃ and the other binder components and additives as in Example 1 to form a granulate, injection molded and debinded. During sintering in air at 1500 ° C, a brown-black-colored molding was obtained as a pink-colored molding was obtained in the sintering in an inert gas atmosphere at 1500 ° C.