Plastic and nonmetallic article shaping or treating: processes – Outside of mold sintering or vitrifying of shaped inorganic... – Shaping or treating of multilayered – impregnated – or...
Patent
1998-10-08
2000-10-17
Derrington, James
Plastic and nonmetallic article shaping or treating: processes
Outside of mold sintering or vitrifying of shaped inorganic...
Shaping or treating of multilayered, impregnated, or...
264600, 264601, 264602, 264644, 264678, 264680, C04B 3334
Patent
active
061326720
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to compositions for colouring ceramic products and the relevant colouring process.
In particular the compositions according to the present invention consist of aqueous or hydroalcoholic solutions of an inorganic salt or organic derivative of chromium in combination with an inorganic salt or organic derivative of a metal selected from antimony, zinc, zirconium, manganese, which allow the obtainment of ceramics in a particular colour, by using ceramic supports which contain some amount of TiO.sub.2 added as such to the ceramic mass before the molding. Furthermore, said solutions may also be used in combination with solutions of other metallic cations to obtain particular shades.
STATE OF THE ART
The use of coloured ceramics as well as the compositions and processes meant for obtaining said colours have been known since long. One of the most common methods is based on the addition of powdered pigments, in particular inorganic oxides and mineral colouring matters, to the ceramic mass (vitrified stoneware) before firing. The ceramic product obtained is coloured through its whole thickness, with considerable consumption of colouring matter, which is the most expensive component.
Considering that colouring inside ceramic articles is superfluous, the material being not transparent, studies were conducted to develop methods for colouring the ceramics surface only, with a considerable saving of costly materials.
A method developed to this end is based on pigments addition to the surface of ceramics (in particular tiles), already in the mold, before final pressing and firing.
Said technique is especially used for vitrified stoneware tiles as it produces a 2 to 3 mm thick surface layer that may also be smoothed. Said method is material-saving, the colour being imparted only to a thin layer of the ceramic product; however, it is hardly viable as it requires devices for metering and feeding, in the molds for ceramics, the amounts and types of pigments needed for obtaining the desired products. Moreover, it does not allow the obtainment of particularly complex products.
Another process consists in causing the surface of the ceramic material to absorb an aqueous solution of inorganic salts or of metal organic derivatives (as described, e.g., in Sprechsal, vol. 119, No. 10, 1986 and in EPA 0 704 411) after partial firing (as disclosed, e.g., in German patent No. 2,012,304) or simply after molding and before firing (as disclosed, e.g., in Swiss patent No. 575,894), said inorganic salts and metal organic derivatives being transformed into colourants, stable at a high temperature, during ceramic firing. The aqueous solution is applied to the ceramic material e.g. by dipping or spraying or disk treatment or silk-screen process.
The aqueous solution is applied to the ceramic material before final firing.
A colouring of this type is particularly advantageous as it allows the obtainment of very thin coloured layers. It is widely used in the case of flat articles (such as for example tiles for floors and walls).
A further problem set by the use of colours in aqueous solution is the depth to which the colouring matter penetrates into the ceramic material. In fact, experimental evidences have been provided that the penetration depth depends on various parameters, such as the colouring solution viscosity and surface tension, the application temperature, the quantity of water sprayed on the manufacture after application of the colouring solution, the application technique.
This last parameter, i.e. the application technique, is of great importance: in fact, whereas the amount of colouring solution that 10 may be applied by disk treatment or spraying may be as high as 400 to 600 g/m2, by silk-screen techniques it may generally be 100 to 200 g/m2.
Silk-screen techniques are particularly asked for being the only ones allowing the obtainment of graphics, drawings and decorations, and requiring lower amounts of colourant. Colourant penetration into the ceramic material before firing
REFERENCES:
patent: 3651184 (1972-03-01), Everhart et al.
Chemical Abstracts, vol. 94, No. 4, Jan. 26, 1981, Abstract 19564-2, A. Villatoro, Coloration System for Ceramic Products.
Derwent Publications Ltd, Class A97, AN-115348, Apr. 1992.
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