EP1899097A2

EP1899097A2 - Materials for coating ceramic bodies, processes for the preparation thereof, use thereof and ceramic articles including these materials

Info

Publication number: EP1899097A2
Application number: EP06777447A
Authority: EP
Inventors: Marco Bitossi
Original assignee: Colorobbia Italia SpA
Current assignee: Colorobbia Italia SpA
Priority date: 2005-06-23
Filing date: 2006-06-23
Publication date: 2008-03-19
Also published as: WO2006136610A3; WO2006136610A2; ITFI20050142A1

Abstract

Disclosed is a series of materials which can be applied as surface coating film to double-fired, porous single-fired, single-fired and porcelain stoneware ceramic objects. These materials can be in powder form, in a carrier suspension, in granular form, atomized, sintered, pelletized and the like, in the most suitable grain sizes.

Description

Materials for coating ceramic bodies, processes for the preparation thereof, use thereof and ceramic articles including these materials

Field of the invention The invention relates to ceramic materials to be used as coating films for ceramic articles produced with double-fired, porous single-fired, single-fired, porcelain stoneware, third- and fourth-fire technologies.

State of the art

As it is known in the ceramics industry to produce various articles a ceramic body (support) is used, composed of clay, feldspar and quartz and other raw materials depending on the type of article, which is then coated with films of materials of particular interest which, through firing, offer the final product suitable aesthetic and technical characteristics for commercial purposes.

The aforesaid materials are applied with various techniques, such as disc application, bell waterfall, dry application (during the phase to press the support or subsequently), screen printing, silicone roller technique and others.

More specifically, some of the aforesaid materials offer the final article an appearance similar to metals, enhancing the characteristics of surface shine typical of metals. Nonetheless, these materials always associate marked shine with other aesthetic characteristics which in any case offer a visual appearance typical of ceramic materials. In particular, a certain degree of surface glassiness typical of brilliant enamels can always be noted. Even in the case of non-brilliant surfaces a texture typical of mat or semi-mat ceramic enamels can nonetheless always be noted. These last-mentioned characteristics mean that, even to the less expert eye, the ceramic tile coated with the relevant materials currently in use can immediately be distinguished from a metal surface, such as steel, copper or other true metals.

The only exception is one range of materials, named "metal lustres", applied in the

"third and fourth firing", which effectively have a much more marked metal appearance but require "third or fourth firing" technology and can be attributed to a range of technological uses and related costs that cannot prevail over the technologies used and the objects of the present invention. Moreover, even for these, applications with the effect of steel are not know, but noble metals such as gold, platinum, silver and the like are used. DESCRIPTION OF THE INVENTION The present invention allows the aforesaid limits to be overcome, offering the ceramist a new range of materials for coating ceramic bodies which have ameliorative characteristics in aesthetic terms of metallic effect, with particular reference to steel, granting the article an appearance much more similar to true metal surfaces by using metal powders, both on their own and mixed with materials conventionally used to produce materials for coating ceramic bodies. According to the invention, materials for coating ceramic bodies are intended as: enamels, crystal glazes, frits, frit granules, ceramic paints, atomized, sintered, pelletized and granulated materials, enamels and crystal glazes for screen printing or silicone roller application, enamels and crystal glazes for dry application before, during and after pressing of the support, supplied dry and/or in a medium, in a wide range of grain sizes and suitable for all specific cases. By placing the materials forming the object of the present invention under and/or over layers of materials for coating ceramic bodies as defined above, variations are obtained in the colour or surface texture of the article, obtaining a diversification of the basic metallic effect and enlarging the range of possible final aesthetic results.

The use of these new materials with screen printing or silicone roller techniques also allows further diversification of the aesthetic offer as the traditional principles of ceramic decoration are valid. Materials for coating ceramic bodies according to the present invention are composed of metal powders with an extremely high metal content and an extremely low oxide content.

These materials are already widely known in the metallurgical sector, where they are normally defined as atomized powders, and are generally composed of iron, nickel, cobalt or copper based alloys and are used in various ways, such as in electric arc or oxy-acetylene torch welding processes.

Atomized powders produced by cooling the melted alloy in a flow of nitrogen or argon, according to processes well known in the metallurgic field, are particularly preferred, as their content of oxides is practically zero and because this technique allows the production of spherical particles which proves more efficient for the wanted result then the particles obtained by water cooling which show and irregular flake shape. Preferably the powders used according to the present application consists of a mixture of particles of different diameter, normally comprised between 50 and 150 micron.

According to a particular embodiment of the invention the fraction of particles having dimension higher then 100 micron is comprised between 20 - 40 % wt on the total of the powder, this embodiment allows the formation in the final product of aesthetic effects (so called "peacock tail" effects) which are particularly appreciated.

The powders are normally kept in suspensions using the suitable rheological measures. By way of example, metal powders useful according to the invention can have the following composition percentages indicated in weight in relation to the total weight of the powder: iron based alloys: Fe 50 - 90%; Cr 4 - 35%; Ni 4 - 11 nickel based alloys: Ni 75 - 96%, Cr 6 - 15%, Fe 1 - 4; cobalt based alloys: Co 50 - 68%; Cr 20 - 30%, Ni 2 - 25% copper based alloys: Cu 75 - 92%; Ni 1 - 5%; Fe 1 - 3 %

Moreover said powders can also contain, for example, B, Si, C, W, Mo, Mn, Al, Ni,

Nb, Sn, Zn normally in small quantities.

Examples of metal powders used in the present application are: Fe 67% Cr 17%, Ni 12%, Mo 2,5% Mn 1 ,5%

Cr 26%, Ni 10%, Mo 5%, Si 1 ,5%, C 2 Cu 89% AI 10% Fe 1%

Cu 89,1%, Al 7,3%, Zn 2,7%, Sn 0,3%, Ni 0,2%, Fe 0,4% (mint alloy) Co 27, 1%, Cr 31 ,6%, Ni 23,90%, Cu 0,4%, Fe 2,2%, Mn 0,5%, W 14,3% (stellite having extremely high resistance to abrasion and corrosion). Co 36% Cr 26% W 12,5% Ni 22,5% Si 1 ,2% C 1 ,7% For the objects according to the invention the metal powders above can be applied dry to the surface of the ceramic body creating the desired decoration by means of a suitable mechanical system. The ceramic body will be subjected to the usual drying and firing operations at the temperatures and for the times and cycles normally required.

Alternatively, the powders can be mixed with common materials conventionally used in ceramics, such as frits, feldspars, kaolins, clays, zirconium silicates, alumina-silica minerals containing alkaline and/or alkaline earth elements, metal oxides, ceramic pigments and others normally used to prepare materials for coating ceramic bodies as defined above according to the invention, preferably prepared separately before mixing.

The aforesaid mixes are prepared adding metal powders to other materials conventionally used in ceramics as indicated above in a dry mixer or other machine suitable for the type of material to be mixed, to obtain homogenization. The mix thus obtained is applied to the ceramic body, if necessary with the aid of the usual media (i.e. polyethylene glycol or water) and this is then fired at the normal temperatures and for the times and cycles required. If desired, after firing the ceramic article can be smoothed and polished with suitable tools, as already known in the art for products coated with conventional materials, or also uncoated products.

By performing the aforesaid operations the desired metallic effect is enhanced. According to a particular embodiment of the invention, the cooling phase of the fired article can be performed in furnaces with a flow of nitrogen or argon to reduce any surface oxidation processes which can occur during said cooling phase. It must be noted that the powders are mixed with the other conventional materials mentioned above in high percentages which reach values ranging from 35% to 85% in weight in relation to the total weight of the mixture, so that the percentage of metals Fe, Cu or Co present in the semi-finished product ready for ceramic use is very high. In particular, it must be considered that in screen printing media forms a rheological limit is reached above which it is difficult to maintain the metal particles in suspension, said particles tending to precipitate to give rise to unstable solid- liquid mixtures, for percentages of powders of over 80-90%, even using Theological additives such as bentonite and/or chemical suspending agents. On the contrary, in the case of dry applications, as there are no Theological limits, it is possible to use the powders as is (100%). In these cases the metal part binds stably to the ceramic support using the vitreous component present on the surface of the ceramic support or of the layer of conventional enamel applied to the support, during softening of the vitreous phase underneath the characterizing component, which takes place during firing. It must be noted how the materials for coating metallic or metallized ceramic bodies used to date have much lower percentages of metals and are usually introduced as oxides and not as metal in elementary state.

The purpose of adding the other ceramic raw materials mentioned is to make these new materials vitrifiable in the correct way and compatible with heat treatment subsequent to application to the support of the article, to obtain films provided with functional performances suitable for the use. This requirement, not always necessary, makes it possible also to use the components indicated above as is, when the firing temperatures, such as for porcelain stoneware, are sufficiently high to allow softening and adhesion to the support. The metallic characteristics visible after firing are provided by the aforesaid metal powders. Some examples are provided hereunder to allow a better understanding and appreciation of the present invention. Example 1

10 kg of metal powder 316L manufactured by Cogne Acciai Speciali Spa with the following grain size ranging from 50 to 150 micron are mixed with 10 kg of ceramic enamel for porcelain stoneware (previously ground with average grain size of 40 micron, and dried) with the following composition: Glass-ceramic frit with Ca Mg Al Si 27 %

Crystal frit 14 %

Kaolin 5 % Dolomite 2 %

Corundum 150 mesh 5 %

Nepheline 39 % Bentonite 8 %

100 parts of metal enamel thus obtained (METAL ENAMEL 1) are added to 50 parts in weight of commercial screen printing medium (polyethylene glycol or the like).

The homogenized suspension is ready for application which is performed on porcelain stoneware support in the following way:

1st Ceramic enamel 1 with water Disc application 500 g / sqm application as medium

2^nα application METAL ENAMEL 1 with Screen printing 27 wires / cm with screen printing medium as application screen of increased described thickness

The tiles obtained are dried and then fired in a single-layer roller kiln for porcelain stoneware with a maximum temperature of 1200⁰C and overall time cycle of 50 minutes.

Smoothing and polishing of the tile according to known techniques made the desired metallic effect even more evident, the final effect of the tile is very similar to a steel surface. The high percentage of iron present on the surface confirms the metallic effect. Example 2

7 kg of metal powders composed of 316 L and CU 90 IN PROPORTIONS OF 60% AND 40% RESPECTIVELY manufactured by Cogne Acciai Speciali SpA and with a grain size ranging from 50 to 150 microns are mixed with 3 kg of the following ceramic enamel for single-firing (previously ground with an average grain size of 40 microns, and dried) with the following composition: Lead-free flux frit 3 %

Calcium carbonate 8 %

Kaolin 6 %

Dolomite 5 % Sodium feldspar 34 %

Quartz 4 % Petalite 4 %

Wollastonite 11 %

Alumina 4 %

Corundum 150 mesh 7 %

Zinc oxide 6 %

Bentonite 8 %

100 parts of enamel thus obtained (METALLIC ENAMEL 2) are added to 50 parts in weight of commercial screen printing medium (polyethylene glycol or the like). The homogenized suspension is ready for application which is performed on porcelain stoneware support in the following way:

1st ceramic enamel 2 with water Disc application 500 g / sqm application as medium

2^nα application METAL ENAMEL 2 with Screen printing 27 wires / cm with screen printing medium as application screen of increased described thickness

The tiles obtained are dried and then fired in a single-layer roller kiln for single- firing with a maximum temperature of 118O⁰C and overall time cycle of 40 minutes.

Smoothing and polishing of the tile according to known techniques made the desired metallic effect even more evident, the final effect of the tile is very similar to a bronze surface. The high percentage of iron and copper present on the surface confirms the metallic effect.

Example 3

7 kg of metal powder 316 L manufactured by Cogne Acciai Speciali SpA and with a grain size ranging from 50 to 150 microns are mixed with 3 kg of the frit granules for porcelain stoneware (previously granulated starting from frit with a grain size of

50-140 microns, and dried) with the following composition:

CaO 14 %

K2O 2 % Na2O 3 %

ZnO 6% AI2O3 18 %

SiO2 54 %

ZrO2 3 %

The metal granules thus obtained (METAL GRANULES 1 ) are ready for application, which is performed on a porcelain stoneware support in the following way:

Smoothing and polishing of the tile according to known techniques made the desired metallic effect even more evident, the final effect of the tile is very similar to a steel surface. The high percentage of iron present on the surface confirms the metallic effect.

Example 4

The metal powder FE23C manufactured by Cogne Acciai Speciali SpA is applied dry, creating a design through a suitable mechanical system on the surface of the pre-pressed or soft mixture upstream of final pressing of the tile.

Smoothing and polishing of the tile according to known techniques made the desired metallic effect even more evident.

The high percentage of iron present on the surface confirms the metallic effect.

As proof of the vast possibilities of use of metal powders, results analogous to those indicated in the aforesaid examples were also obtained with the use of the following metal powders: 304 L, 630, 304CB, FE12V, IN825, NI50, CO1 FS, in combination with various materials for coating ceramic bodies known in the art.

Claims

1. Materials for coating of ceramic bodies comprising or consisting of metal powders.

2. Materials as claimed in claim 1 , wherein said materials for coating of ceramic bodies are chosen in the group consisting of: frits, frit granules, ceramic paints, atomized, sintered, pelletized and granulated materials, enamels and crystal glazes for screen printing or silicone roller application, enamels and crystal glazes for dry application before, during and after pressing of the support, supplied dry and/or in a medium, in a wide range of grain sizes and suitable for all specific cases.

3. Materials as claimed in claims 1 and 2, wherein said metal powders are atomized powders composed of iron, nickel, cobalt or copper based alloys.

4. Materials as claimed in claim 3, wherein said atomized powders are produced by cooling the alloy in a flow of nitrogen or argon so that the particles forming the powder have spherical shape and an extremely low metal oxide content.

5. Materials as claimed in Claims 1 - 4 wherein the powder consists of a mixture of particles of different diameter.

6. Materials according to Claim 5 wherein the particles dimensions are comprised between 50 and 150 micron.

7. Materials according to Claim 6 wherein the fraction of particles having dimensions higher then 100 micron is comprised between 20 - 40 % wt on the total of the powder.

8. Materials as claimed in claims 1 to 7, wherein said metal powders have the following compositions in which the percentages are indicated in weight in relation to the total weight of the material:

Fe 50 - 90%; Cr 4 - 35%; Ni 4 - 11%;

Ni 75 - 96%, Cr 6 - 15%, Fe 1 - 4;

Co 50 - 68%; Cr 20 - 30%, Ni 2 - 25%;

Cu 75 - 92%; Ni 1 - 5%; Fe 1 - 3 %; and optionally B, Si, C, W, Mo, Mn, Al, Ni, Nb, Sn, Zn.

9. Materials as claimed in claim 8, wherein said metal powders have the following compositions: Fe 67% Cr 17%, Ni 12%, Mo 2,5% Mn 1 ,5% Cr 26%, Ni 10%, Mo 5%, Si 1 ,5%, C 2 Cu 89% AI 10% Fe 1%

Co 36% Cr 26% W 12,5% Ni 22,5% Si 1 ,2% C 1 ,7% Cu 89,1%, Al 7,3%, Zn 2,7%, Sn 0,3%, Ni 0,2%, Fe 0,4% (mint alloy)

Co 27, 1%, Cr 31 ,6%, Ni 23,90%, Cu 0,4%, Fe 2,2%, Mn 0,5%, W 14,3%

10. Materials as claimed in claims 1 to 9, composed of metal powders as defined in the previous claims in combination with other materials conventionally used in ceramics.

11. Materials as claimed in claim 10, wherein said other materials conventionally used in ceramics are chosen from the group composed of: frits, feldspars, kaolins, clays, zirconium silicates, alumina-silica minerals containing alkaline and/or alkaline earth elements, metal oxides.

12. Materials as claimed in claims 10 and 11 , wherein the metal powders are present in percentages ranging from 35 to 95% in weight calculated on the weight of the material.

13. Method for preparing materials as claimed in claims 10 to 12, wherein: the metal powders are added to other the materials conventionally used in ceramics as indicated above in a dry mixer or other machine suitable for the type of material to be mixed, to obtain homogenization.

14. Use of materials as claimed in claims 1 to 12 for the coating of the ceramic body of ceramic articles.

15. Use as claimed in claim 14, wherein said ceramic articles are double-fired, porous single-fired, single-fired, porcelain stoneware, third- and fourth-fired ceramic objects.

16. Ceramic articles with metallic effect composed of double-fired, porous single- fired, single-fired and porcelain stoneware ceramic objects comprising a coating obtained with the materials as claimed in claims 1 to 12.

17. Ceramic articles as claimed in claim 16, wherein said materials are composed of metal powders applied dry.

18. Ceramic articles as claimed in claims 16 and 17, wherein said objects are tiles.

19. Method for producing ceramic articles as claimed in claims 16 to 18, wherein: - the metal powders are applied dry to the surface of the ceramic body creating the desired decoration by means of a suitable mechanical system;

- the ceramic body is subjected to the usual drying and firing operations, at the temperatures and for the times and cycles normally required.

20. Method for producing ceramic articles as claimed in claims 16 to 18, wherein:

- materials as claimed in claims 10 to 12 are applied to the ceramic body, if necessary with the aid of the usual media;

- the ceramic body is subjected to firing at the normal temperatures and for the times and cycles required.

21. Method for producing ceramic articles as claimed in claims 19 and 20 wherein the cooling of the fired article is performed in furnaces with a flow of nitrogen.

22. Method as claimed in claims 19 to 21 , wherein the cooled ceramic article is smoothed and polished.