DESCRIPTION OF THE INVENTION 
The aim therefore is to provide ceramic frits which produce fault-free 
glazes after high-speed baking and also have good covering power and high 
gloss. 
The invention therefore relates to ceramic frits for producing glazes with 
white opacity and covering power through ceramic high-speed baking at 
temperatures between 980.degree. C. and 1150.degree. C., characterised in 
that the ceramic frits have the following composition: 
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SiO.sub.2 48-60 wt. % 
B.sub.2 O.sub.3 3-8 wt. % 
Al.sub.2 O.sub.3 4-8 wt. % 
Na.sub.2 O 0.2-2.0 wt. % 
K.sub.2 O 4-8 wt. % 
MgO 0-2 wt. % 
CaO 7.5-13 wt. % 
BaO 0-5 wt. % 
ZnO 7-12 wt. % 
ZrO.sub.2 0.3-2.5 wt. % 
TiO.sub.2 3.5-5.5 wt. % 
P.sub.2 O.sub.5 0-3 wt. % and 
Na.sub.2 O + K.sub.2 O 
4.5-8.5 wt. %. 
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Ceramic frits having the following composition are particularly preferred: 
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SiO.sub.2 52-60 wt. % 
B.sub.2 O.sub.3 
4-7 wt. % 
Al.sub.2 O.sub.3 
4-7 wt. % 
Na.sub.2 O 1-2 wt. % 
K.sub.2 O 4-6.5 wt. % 
MgO 1-2 wt. % 
CaO 9-11 wt. % 
ZnO 8-10 wt. % 
ZrO.sub.2 0.5-1.0 wt. % 
TiO.sub.2 4.5-5.5 wt. % 
P.sub.2 O.sub.5 
0.1-2.2 wt. and 
Na.sub.2 O + K.sub.2 O 
4.5-8.5 wt. %. 
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Surprisingly, the recrystallisation of TiO.sub.2, which determines the 
brightness, can be controlled by adding small quantities of ZrO.sub.2, 
which melts in the form of ZrSiO.sub.4 in the batch, thus critically 
improving the brightness of the glaze. ZrO.sub.2 must be added in a 
proportion of 0.3 to 2.5 wt. %, preferably 0.5 to 1.0 wt. %. 
Surprisingly, the recrystallisation of TiO.sub.2 and consequently the white 
opacity can also be critically controlled by varying the proportion of 
P.sub.2 O.sub.5. P.sub.2 O.sub.5 is incorporated by melting in a 
proportion of 0 to 3 wt. %, preferably 0.1 to 2.2 wt. %. The P.sub.2 
O.sub.5 can be introduced into the melt via the TiO.sub.2. 
By using ZrO.sub.2 and P.sub.2 O.sub.5 to influence the opacity, the 
TiO.sub.2 content of the frits according to the invention can be reduced 
to 3.5 to 5.5 wt. %. This advantageously affects the cost of manufacture, 
by simultaneously reducing the cost of the raw material and reducing the 
cost of melting owing to the ease of melting. 
The Na.sub.2 O content must be between 0.2 and 2 wt. %. As a result, the 
edge softening point of the frits is above 900.degree. C., i.e. they are 
extremely suitable for Monoporosa high-speed baking and, in the preferred 
range of application between 980.degree. and 1150.degree. C., give glazes 
having high surface smoothness, i.e. very little wrinkling and high gloss. 
When used in double high-speed baking (bicottura rapida), there is no 
undesirable migration of salts leading to surface faults during baking. 
The K.sub.2 O content is about 4 to 8 wt. %, and the sum of Na.sub.2 
O+K.sub.2 O is about 4.5 to 8.5 wt. %. The resulting thermal expansion 
coefficient for the frits according to the invention is in the range from 
55 to 75.multidot.10.sup.-6 K.sup.-1 between 20.degree. C. and 40.degree. 
C., which matches the thermal expansion of the ceramic body. 
The B.sub.2 O.sub.3 content is between 3 and 8 wt. %. Smaller quantities 
cause a loss of gloss, whereas higher proportions result in edge softening 
points which are too low for high-speed Monoporosa baking. 
The MgO content is 0 to 2 wt. %. A higher content results in dulling or 
reduction of gloss. If the CaO content is 7.5 to 13 wt. % and the ZnO 
content is 7 to 12 wt. %, the result is a high-gloss smooth glaze. If the 
proportions are lower, the viscosity of the frits in the claimed 
temperature range is too low, whereas higher proportions may result in a 
loss of gloss. 
The frits according to the invention do not contain the toxic element lead 
or the element fluorine, i.e. they are not a toxicological or ecological 
hazard. 
The TiO.sub.2 frits according to the invention have considerable advantages 
over white frits based on precipitation of ZrSiO.sub.4 and hitherto used 
on a large industrial scale. On the one hand the frits according to the 
invention melt much more easily and do not tend to precipitate in the 
melting furnaces as in the case of frits containing ZrSiO.sub.4 which can 
result in considerable difficulties in production. On the other hand, 
owing to their ZrSiO.sub.4 lower viscosity (particularly at higher 
temperatures), they give smoother surfaces on baking, resulting in 
considerably higher gloss. 
The frits according to the invention are used for producing glazes on 
ceramic substrates. 
For wet application it is conventional to use a glaze slip consisting of at 
least 65 wt. % of one or more of the frits according to the invention 
together with one or more substances from the following group: kaolin, 
bentonite, China clay, quartz, aluminum oxide, molochite, feldspar, talc, 
pigments and opacifiers. 
It is preferable to use glaze slips containing at least 85 wt. % of one or 
more of the frits according to the invention, in order to obtain a 
high-gloss fault-free surface. The frits according to the invention or the 
glaze slips are preferably used in the temperature range between 
980.degree. C. and 1150.degree. C. for coating ceramic tiles after 
high-speed Monoporosa baking or high-speed double baking. 
The frits are also suitable as component of a glaze slip for high-speed 
single baking on sealing-tight bodies at elevated temperature. 
Of course, the frits according to the invention can also be used in 
conventional baking (not high-speed; 3 to 48 hours). In addition to the 
tile sector, there are applications to sanitary ceramics and the crockery 
industry. 
The frits according to the invention, therefore, when applied to bodies for 
glazing, can be in the form of a ceramic slip applied when wet. 
Alternatively, powder electrostatic dry application is advantageous, or 
dry application in the form of a granulated product after suitable 
processing. 
The invention will be explained in detail with reference to the following 
examples. 
EXAMPLES 
Example 1 
94 parts by weight of frit A, 6 parts by weight of kaolin and 60 parts by 
weight of water were ground in a ball mill for 2 hours to form a ceramic 
slip. After spraying onto a porous unbaked body, drying and baking at 
1085.degree. C. for 41 minutes, the product was a high-gloss smooth white 
glaze with higher covering power and a faultless surface. 
Example 2 
99.85 parts by weight of frit A and 0.15 g of a mixture of polymethyl 
hydrogen siloxanes having the formula: 
##STR1## 
with n=5 to 50 were ground in a ball mill until the particle-distribution 
maximum was below 50 .mu.m and less than 10 wt. % of the grains were 
larger than 100 .mu.m and 100 wt. % were smaller than 150 .mu.m. 
The resulting powder was electrostatically applied to a porous unbaked body 
at 50 kV. 
After baking at 1085.degree. C. for 41 minutes, the product was a 
high-gloss glaze with high covering power and brightness and a faultfree 
surface. 
Example 3 
96 parts by weight of frit B, 4 parts by weight of kaolin and 35 parts by 
weight of water were ground in a ball mill for 2 hours to form a ceramic 
slip. After pouring onto a pre-baked ceramic body, drying and baking at 
1030.degree. C. for 40 minutes, the product was a white glaze with high 
gloss. There were no observable surface faults such as dents, pits or 
pin-holes. 
Example 4 
96 parts by weight of frit C, 4 parts by weight of kaolin, 0.4 parts by 
weight of sodium carboxymethyl cellulose and 50 parts by weight of water 
were ground in a ball mill to obtain a ceramic slip. After spraying onto a 
porous unbaked ceramic body, drying and high-speed baking at 1120.degree. 
C. for 50 minutes, the product was a high-gloss white glaze with a 
fault-free surface. 
Example 5 
The process was as in Example 4 except that frit D was used. After spraying 
onto a porous ceramic unbaked body, drying and high-speed baking at 
1150.degree. C. for 35 minutes, the product was a white glaze with high 
covering power, high gloss and excellent surface quality. 
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Frit A Frit B Frit C Frit D 
Composition 
[wt. %] [wt. %] [wt. %] [wt. %] 
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SiO.sub.2 
54.2 53.2 51.2 50.9 
B.sub.2 O.sub.3 
5.4 6.4 6.4 6.4 
Al.sub.2 O.sub.3 
6.1 6.1 6.1 7.1 
Na.sub.2 O 
1.5 1.5 1.5 0.5 
K.sub.2 O 
6.1 6.1 6.1 7.6 
MgO 1.6 1.6 1.6 1.6 
CaO 10.0 10.0 10.0 10.0 
ZnO 8.9 8.9 8.9 8.4 
TiO.sub.2 
5.0 5.0 5.0 5.0 
ZrO.sub.2 
1.0 1.0 1.0 0.3 
P.sub.2 O.sub.5 
0.2 0.2 2.2 2.2. 
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