Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Composite having voids in a component
Reexamination Certificate
2001-02-16
2003-08-19
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Composite having voids in a component
C428S040400, C428S041700, C427S147000, C427S229000, C427S256000, C427S385500
Reexamination Certificate
active
06607816
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to compositions suitable for colouring ceramic manufactured articles and to the relevant colouring process.
In particular, the compositions of the invention consist of water solutions or solutions of water and water-miscible solvents, of gold organic complexes compatible with other colouring cations optionally present in the solution releasing low quantities of corrosive vapours during the firing cycle.
Said solutions allow the obtainment of ceramic manufactured articles in shades from pink to purple to violet after a firing cycle ranging from 750° C. to 1,300° C.
STATE OF THE ART
The use of coloured ceramic manufactured articles as well as the compositions and process adopted to obtain the relevant colours have been known since long. One of the methods most commonly used consists in the addition of powdered pigments, in particular inorganic oxides and mineral colouring matters, to the ceramic mixture (vitrified stoneware) before firing. The ceramic manufactured article is thus coloured through its whole thickness, although with large consumption of colouring matter, which is the most expensive component.
According to a process used, the surface of the ceramic material is caused to absorb, either after partial firing (as disclosed e.g. in German patent 2,012,304) or simply after moulding and before firing (as disclosed e.g. in Swiss patent 575,894), a water solution of inorganic salts or metal complexes (as disclosed e.g. in Sprechsal, vol. 119, No. 10, 1986, in EP 0704411 and in patent PCT, WO 97/38952), which become stable colours at high temperature during the ceramic firing cycle.
The water solution is applied to the ceramic material before final firing. This process is particularly advantageous because it allows the colouring of very thin layers: therefore, it is widely used for flat manufactured articles (such as e.g. floor and wall tiles).
Another problem to be solved when using colours in a water solution is the obtainable depth of colour penetration into the ceramic material. In fact, it was experimentally found that the depth of penetration depends on several parameters, such as the viscosity and surface tension of the colouring solution, the application temperature, the quantity of water optionally sprayed on the manufactured article once the colouring solution has been applied. The water solution is applied to the ceramic manufactured article by immersion, spraying, disk, and silk-screen techniques.
Of cardinal importance is the application technique: in particular, the quantity of colouring solution that may be applied by disk and spraying techniques is as high as 400 to 600 g/m2; by silk-screen type techniques it usually amounts to 100 to 200 g/m2 and sometimes even to 400 g/m2, when thickened screens made of a small number of threads are used.
Silk-screen type techniques are very much in demand, being the only techniques allowing graphic decorations and drawings, which otherwise cannot be obtained, and requiring lower quantities of colouring matter. When said techniques are used, the colouring solutions are to be thickened with appropriate thickening agents, e.g. modified glucomannans, starch and modified starch derivatives, cellulose and modified cellulose derivatives, or other polymeric substances, soluble or dispersible in a water solution.
Colour penetration into the ceramic material before firing can be obtained by spraying relatively high quantities of water on the manufactured article after application of the colouring solution. However, the resulting colours are less intense than those obtained using other techniques.
Colour penetration into the material is particularly important in the case of “smoothed” vitrified stoneware tiles.
The term “smoothed” means that the vitrified stoneware surface has been abraded with diamond wheels by 0.8 to 1.5 mm and subsequently smoothed or polished with appropriate felt until obtaining a glassy surface.
It follows that colour penetration into stoneware articles to be smoothed after firing must reach a depth of 1.6 mm min.
Other methods have been developed for the smoothing of very thin (1 to 10 0) surface layers of the manufactured article.
PRIOR ART
The use of water solutions of gold compounds for the colouring also in-depth of ceramic manufactured articles is well known. The compounds disclosed in German patent 4,320,072 for said application substantially are gold chlorides also reported in the preceding literature (cf. “Encyclopedia der technischen Chemie”, F. Ullmann, 1929, vol. 4, pp. 837-838). However, the gold chloride solution suffers from the inconvenience of being strongly acid, as it contains hydrochloric acid. In the absence of excess hydrochloric acid, the solution is unstable and the gold compound hydrolyses easily with formation of insoluble compounds.
It follows that the solution is corrosive and impairs the apparatus used. In particular, in the case of silk-screen type technique, it rapidly impairs the printing screen.
WO 97/21646 discloses the use of gold sodium thiosulphate solutions, Na
3
Au(S
2
O
3
)
2
, stabilised with sodium sulphite, for ceramic surfaces colouring by water solution absorption.
From the compositions of solutions 1, 2, and 3 described therein, it is possible to calculate that 4.7 g SO
2
or 5.88 g SO
3
, or an intermediate value in the case of mixtures thereof is released per g Au deposited on the surface.
In both cases (use of gold chloride and gold thiosulphate), high amounts of strongly corrosive vapours rapidly impairing the heater metal structures, are released. Therefore, vapours are to be abated to prevent the emission of same into the environment.
The use of precious metals water solutions in high concentrations, in the form of thiol derivatives, to obtain thin metal films for decorative purposes, e.g. for dishes, or for electronic purposes, e.g. for printed circuits, is already known.
The following are examples of said use:
1. U.S. Pat. No. 5,545,452 discloses the use of Au thiolates water solutions with a metal content of 2 to 25% by wt. (column 3, rows 10 to 20) to obtain thin metal films for decorative purposes (column 1, rows 38 to 40);
2. EP No. 514,073, like the U.S. patent above, discloses the use of thiolates water solutions to obtain thin films made of Au or other precious metals to decorate the outer surface, and not the inside, of baked ceramic manufactured articles.
Technical Problem
Considering that it is very simple to colour ceramic materials by disk, spraying and silk-screen techniques, the ceramic industry is highly interested in the possibility of using colouring water solutions based on gold to be applied by said techniques, and offering the advantage of
releasing the lowest possible quantity of very noxious or corrosive vapours in the heater;
being compatible with water solutions of organic derivatives of other cations used for the superficial and in-depth colouring of ceramic manufactured articles.
Therefore, it is an object of the present invention to provide colouring formulations in the form of water solutions, which
release low quantities of corrosive vapours (≦2 g SO
2
/g Au deposited);
are compatible with water solutions of organic derivatives of other cations used for the superficial and in-depth colouring of ceramic manufactured articles;
colour the ceramic manufactured articles at their surface and to a depth of at least 1 mm.
The Applicant, who has full-fledged experience in the production and sale of colouring matters for ceramic tiles, has now found that water solutions or water mixtures with alcohols or other water-miscible organic solvents, of monovalent gold organic derivatives, can be used to obtain-after firing-colour shades varying from pink to purple to violet on manufactured articles consisting of a conventional ceramic mixture.
The water or hydroalcoholic solutions being an object of the present invention are particularly useful for colouring tiles of vitrified stoneware, either at their surface or to a depth of 1 to 3 mm from their surface.
In-depth colouring is essential f
Guizzardi Fabrizio
Vignali Graziano
Hedman & Costigan ,P.C.
Kiliman Leszek
Vignali Graziano
LandOfFree
Formulations based on water soluble gold compounds suitable... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Formulations based on water soluble gold compounds suitable..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Formulations based on water soluble gold compounds suitable... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3124393