Compositions: ceramic – Ceramic compositions
Reexamination Certificate
1999-02-26
2001-08-07
Marcheschi, Michael (Department: 1755)
Compositions: ceramic
Ceramic compositions
C501S141000, C501S145000, C501S150000, C106S439000, C106S441000, C264S006000, C264S600000, C264S601000, C264S602000, C264S644000
Reexamination Certificate
active
06271157
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to compositions suitable for colouring ceramic manufactured articles and the relevant colouring process.
In particular, the compositions of the invention consist of aqueous solutions of salts or organic complexes of titanium and chromium, combined with antimony or tungsten or mixtures thereof, which allow the obtainment of ceramic manufactured articles with shades ranging from light yellow to orange yellow to mustard.
Furthermore, to obtain particular shades, said solutions may be mixed with solutions of other cations.
STATE OF THE ART
The use of coloured ceramic manufactured articles as well as the compositions and procedures adopted to obtain the relevant colours have been known since long. One of the methods most commonly used is based on 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 used procedure, the surface of the ceramic material is caused to absorb, either after partial burning (as disclosed e.g. in German patent 2,012,304) or simply after press moulding and before burning (as disclosed e.g. in Swiss patent 575,894), an aqueous 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 firing cycle of the ceramic manufactured article.
The aqueous solution is applied to the ceramic material, e.g. by immersion, spraying, disk techniques, and silk-screen techniques.
The aqueous solution is applied to the ceramic material before final firing. This procedure 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 an aqueous 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 sprayed on the manufactured article once the colouring solution has been applied, the application technique.
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, and requiring lower quantities of colouring matter. By using said techniques, 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 an aqueous solution.
The colour penetrates into the ceramic material before firing by using relatively high quantities of water 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 smoothing very thin surface layers of the manufactured article, in the order of 1 to 10 micron.
TECHNICAL PROBLEM
Considering that it is very simple to colour ceramic materials by disk techniques, spraying and silk-screen techniques, the ceramic industry is highly interested in finding new substances to be used therewith.
As concerns said new substances, the following technical problems are to be solved. The substances must become stable colours at a high temperature; the manufactured article has to be coloured in the desired shades, on its surface and to a depth of 1.6 mm min from its surface, without too high consumption of colouring matter.
Unfortunately, very few are the colours available so far. In particular, the lack of yellows and orange yellows, obtainable in the presence of other colours, is deeply felt, especially by the industry of vitrified stoneware, which must propose ever new aesthetic solutions.
In fact, as disclosed in patent application PCT WO 97/38952, the whole range of yellows, oranges, orange beiges may be obtained using antimony/chromium, zirconium/chromium, zinc/chromium, manganese/chromium solutions, exclusively on supports modified by the addition of 0.5 to 10% by wt. titanium oxide, preferably 1% by wt. min. However, titanium oxide heavily affects the development of colours not included in the aforesaid range of yellows and oranges, which may be obtained with the already known aqueous solutions of iron, cobalt, nickel, vanadium, chromium, manganese, copper, ruthenium, palladium, zirconium, gold, and mixtures thereof, especially when used in low concentrations, or by the silkscreen technique, to obtain pale colours.
By way of example, Table 1 illustrates some tests carried out to prove the main effects that titanium oxide addition to the ceramic mixture exerts on the development of the (typical) colours of the aforesaid cations.
All tests were performed according to the following procedure:
a) drying six 33×33 cm supports (two of mixture A, two of mixture B and two of mixture C) at 100° C. to a water residue of 0.5% by wt. max.;
b) cooling said supports to room temperature;
c) letting fall an amount of mg 185+/−15 of colouring solution in a single point, within an area of approx. 10 cm2, of each support;
d) equalizing the supports at room temperature for 2 h and in a thermo-ventilated oven at 60° C. for 2 additional h to homogenize the solutions absorption;
e) kiln firing according to a standard ceramic cycle;
f) smoothing each support of mixtures A, B and C;
g) recording the support colour before and after smoothing.
TABLE 1
*Colour before smoothing
*Colour after smoothing
Test
Solution
Mixture
**C M Y K values**
**C M Y K values**
No.
(% as element)
type
***L*; a*; b* values
***L*; a*; b* values
1
0.4% Gold
A
Garnet
Parma red
25-70-65-25
17-47-39-7
37.5; 14.6; 10.3
56.5; 13.5; 2.1
2
0.4% Gold
B
Reddish violet
Cobalt violet
25-57-49-19
22-47-40-12
63.4; 8.3; 3.6
3
0.4% Gold
C
Violet
Violet
30-64-57-27
27-49-40-18
41.9; 12; 4.8
51.4; 7.4; 0.6
4
8% Vanadium
A
Grey beige
Lightgrey beige
30-31-44-18
15-19-29-4
56.4; 2.2; 6.4
69.3; 2.9; 9.9
5
8% Vanadium
B
Ocher brown
Dark beige
25-31-47-14
15-25-42-5
62.7; 3.9; 17.2
6
8% Vanadium
C
Pozzuoli red
Ocher brown
30-50-69-27
19-45-68-15
45.1; 8.1; 17.6
54.5; 9.1; 20.8
7
10% iron
A
Havana brown
Burnt umber
29-57-22-25
22-46-64-18
39.7; 13.8; 15.5
46.8; 9.8; 21.1
8
10% Iron
B
Burntumber
Raw sienna
29-53-61-26
15-54-85-22
48.6; 9.1; 26.9
9
10% Iron
C
Chocolate
Tobacco brown
33-54-71-31
28-44-73-27
38.9; 8.4; 20.4
46.3; 5.8; 23.1
10
5.8% Cobalt
A
indigo
Light ultramarine blue
62-67-22-25
59-13-9-7
34.7; −3.0; −20.9
42.9; −4.1; −27.4
*Colour before smoothing
*Colour after smoothing
Test
Solution
Mixture
**C M Y K values**
**C M Y K values**
No.
(% as element)
type
***L*; a*; b*
***L*; a*; b*
11
5.8% Cobalt
C
Manganese blue
Turquoise blue
65-49-22-24
37-24-27-11
39.7; −8.3; −20
55.9; −6.3; &m
Guizzardi Fabrizio
Vignali Graziano
Hedman & Costigan ,P.C.
Marcheschi Michael
Vignali Graziano
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