HU176118B - Composition for coating ceramics with glaze of high chemical resistance, and process for producing the glazes - Google Patents

Abstract

Compsns. for forming vitreous, transparent, coloured or opaque glazes on porous or compact ceramic articles, and having a mean linear thermal expansion coefft. 8.0 x 10-6/degrees C (20-400 degrees C) and >8.5 x 10-6/degrees C (20 degrees C to the glass transition pt.) comprise 65-75% SiO2 0-6% Al2O3 4-12% B2O3 and 8-12% PbO, 12-16% alkali metal oxides and 0-4%, alkaline earth oxides and/or fluorides SiO2 + Al2o3 being 67-75%, and the balance being 20-30% flux comprising 0-10% of various coloured oxides, soluble in the compsn., chosen pref. from CaO, CuO, NiO and Fe2O3, and 0-5 mol% of one or more of ZrO2, TiO2, SnO2, Nb2O5 and CeO2, 0-10 mole% coloured pigments, pref. spiral and 0-10 mol% flux. Glazes have an improved chemical stability, reduced tendency to release head, and are particularly suitable for glazing porous and impermeable ceramics, glass-ceramics and quartz or porous sintered articles leased on glass and scrap silicate, esp. having linear expansion coefft. >8.0 x 10-6/degrees C. The firing temp. of the glaze compsn. is 900 degrees C.

Description

FIELD OF THE INVENTION The present invention relates to a composition, solid or porous, at a temperature of from 20 to 400 ° C, from 8.5 to 10 ~ ⁶ degrees Celsius ^. for coating ceramics with a medium linear thermal expansion coefficient of high chemical resistance, in particular low loss of lead.

The present invention relates to the production of ceramic glazes having a colorable and / or opaque, translucent, increased chemical resistance, particularly with low loss of lead, on solid or porous ceramic tiles, in particular on sintered bodies made of glass and quartz, or on glass and silicone waste.

Coating ceramic tiles with both colorable and opaque translucent glazing, known as glaze, is one of the most important methods for finishing ceramic products. In order to achieve this breeding, it is usually a requirement that the glaze should lie firmly and faultlessly on the tile. Smooth adhesion of the vitreous topsheet to the ceramic object, 20

1. by coordinating the expansion coefficient of the tile with the glaze; and

2. can be achieved by sufficient drainage of the honey at the end of the burn.

In order to ensure good adhesion of the glaze to the pots, it was advantageous to apply the glaze while applying pressure. This is achieved mainly by using a glaze having a temperature range of 20 ° C to a softening point! has a mean linear expansion coefficient of 30 less than that of ceramic fired clay, tile, and has a linear linear expansion coefficient of the same temperature range, with the glazing softening being characterized in particular by the transition point.

Whereas it has now become possible to calculate the average linear expansion coefficients of glass, ceramic glaze and enamel with sufficient accuracy based on their chemical composition, [Steklo i Keram. 10 (1953), No. 1, 7-10. 10], the coordination of the thermal expansion coefficient of a ceramic glaze with the thermal expansion coefficient of the material being burned is practically without any difficulty.

In contrast, until now, it has generally not been possible to calculate the runoff of glasses, enamels, and glazes, characterized by their temperature-viscosity behavior, from their chemical composition, or to estimate with sufficient accuracy. However, it is known that an enamel frit can drain into a smooth glaze if its viscosity at a smooth firing temperature is around several thousand poises, preferably 2000 poises. [Bull. Soc. Franc. CERA. 1951, No. 11.4-13.0.]

Finally, their chemical stability is an essential feature of the quality of ceramic glazes. It is known that at present, the chemical resistance of glasses, glazes and enamels cannot be deduced from their chemical composition with sufficient accuracy.

A zománcfritteket having a medium thermal expansion coefficient within the temperature range 20-400 ° C (Ak _ _{2o. 4oo)} 8.0 · 10 ^-6 degrees ^_1 at the 20 ° C and moderate coefficient of thermal expansion within the transition point (Ak ₂₀ _ _Tg) and 8.5 · 10 ^-6 degrees smoothly flow out over larger ^_1 at 900 ° C, currently melting at higher temperatures zománcfrittek preparing a mixture component as smooth firing temperatures above 1000 ° C is used mainly folyasztóként grinding enamel suspensions made up with the best for zománcfrittek preparation. For this reason, they have so far been of little importance for the preparation of glazes by means of smooth firing below 900 ° C. This enamel frit includes the commercially available "lead monosilicate" PbO. SiO ₂ (I. fritt). Parmeolo describes two additional mixtures for the above mentioned coefficients of thermal expansion (frites II and III). [Parmeles, CW, Ceramic Glazes, 3rd edition, Chicago, Cahmers Publ. Comp. 1951]. The three lead-containing frites described in Table 1 give glassy coatings, which show a yellowish tint, in a suitable ceramic tile at a temperature of 800-850 ° C for 6 to 4 hours with a residence time.

Table 1

Features I. fritt II, frit III. frit SiO _{2 in} mole% 50.33 64.52 64.02 A1 ₂ O ₃ mole% 0.54 3.23 3.23 PbO in mole% 47.9 22.58 22.08 Na ₂ O in mole% 0.45 - 10.67 K ₂ O in mole% 0.74 9.67 - Tg at C ° 403 490 462 Ak ( ₅₀ 4 ₀₀ ) 9.9 9.0 9.9 · 10 ″ ⁶ degrees ^-1 Ak (5 ₀ 400) 10 9.5 ¹ 10.2 10 ⁶ fok-

The major disadvantage of these lead-containing frites is their low chemical resistance. I, II. and III. Table 2 shows the amount of glaze produced from frites designated as "Frit" in solid ceramic tiles at 825-850 ° C after suitable chemical treatment.

Table 2

Chemical treatment I. fritt II. frit III. frit 20.4% v / v HCl for 6 hours, followed by chloride-free washing and drying Weight loss mg / dm ² 60.2 464 256 In a solution of 16.4 g NaOH and 21.6 g Na ₂ CO _{3 in} 800 g water for 3 hours cooking, washing to neutral and drying Weight loss mg / dm ² 199 249 252

I, II. and III. Another major drawback of frites designated as "Frit" is that it is emitted when exposed to chemical agents. It is known that the lead-containing frites described in Table 1 are characterized by high levels of lead loss, which values are above the legal limits in most states. It is also known that in high lead-containing enamel nephrites, lead loss is primarily due to alkali metal oxides and / or boric oxide (Singer, F. und Singer, SS, Industrielle Keramik, 2 Band, Massen, Glasuren, Farbkörper, Herstellungsverfahren, Springer Verlag Berlin / 196) , [Sprechsaal, 105, (1972), No. 18, 739-742. page] increases noticeably. Therefore, the Frit I denotes 18.0 mg of dissolved lead per 1 dm ^{2 of} glazed surface, but still shows the smallest loss of lead from the above frites. [(TGL 14 934 Bl. 2, Test Method) and (Bér. Dr. Keram. Ges. 51 (1974), No. 6, pp. 169-171).] It is also known that there are no significant chemical improvements. is not achieved by the addition of other oxides, such as SiO ₂ and / or Al ₂ O ₃ or alkaline earth metal oxides, which are conventional in the preparation of enamel frites to achieve the thermal expansion and flow properties specified in the specification below. or III. frites. The above I to II. and

III. Products with a chemical composition similar to those described under Frites and having similar thermal expansion and flow properties are also commercially available. These are known to be used mainly in the preparation of frites for coatings and generally exhibit poor chemical resistance, in particular a high lead loss above 1 mg Pb / dm ² .

The thermal expansion and flow properties of enamel frites according to the invention are accomplished by some topcoat frites. These are mostly colored, predominantly glassy products, which are already burnt onto glassy ceramic compositions at about 750 ° C to 900 ° C by decorative firing. As is well known, top coat glazes that easily flow at ornamental firing temperatures react with the softening glaze underneath to develop the chemical resistance of the glaze.

The use of such topcoat coloring frites for the manufacture of glassy coatings is possible from both a scientific and a technical point of view, but the glazes thus obtained are known to have insufficient chemical resistance, in particular lead loss, above the permitted limit. Table 3 illustrates this fact with two typical examples (smooth firing temperature 800-825 ° C, residence time 2 hours, suitable ceramic tiles).

Table 3

Features colored frits for yellow glaze colored frits for blue glaze SiO _{2 in} mole% 42.3 35.1 B ₂ O ₃ mole% 12.5 10.6 Fe ₂ O ₃ mole% 5.6 7.6 PbO in mole% 27.9 28.0 ZnO mole% 5.5 ___ CoO mole% - 13.4 Na ₂ O in mole% 6.2 5.3 Ák ( ₂₀ 4oo) · 10 “ ⁶ degrees ¹ 8.2 8.5 20.4% v / v HCl for 6 hours, followed by chloride-free washing and drying Weight loss mg / dm ² completely completely loosened loosened

I for yellow glaze í for blue glaze j colored frit 1 colored frit

Cooking, washing to dry and drying in a solution of 16.4 g NaOH and 21.6 g Na ₂ CO _{3 in} 800 g water for 3 hours Weight loss mg / dm ² completely dissolved completely dissolved Loss of lead mg lead / dm ² 40.88 5.27

Finally, the cost of producing glaze overcoats is much higher than the cost of known glazes on the market. Substantially increasing the chemical resistance of such enamel frites by adding oxides, such as SiO ₂ and / or Al ₂ O ₃ and / or alkaline earth metal oxides, which are customary in the preparation of enamel frites, is not achievable to the extent known in the invention. However, most metallic enamel frites have these thermal expansion and flow properties. These have an average linear expansion coefficient in the range of 20 ° C to 400 ° C, which is known to be greater than 10 · 10 ~ ⁶ degrees ^_1 . They are usually burned at temperatures in the range of about 750 ° C to about 850 ° C. However, metal enamel frites generally exhibit low chemical resistance to acids. For this reason, their use as glazing in ceramic tiles has not yet been realized. To illustrate these disadvantages of metal enamel frites, two commercially available enamel frites (frites IV and

V. fritt) are summarized in Table 4.

Table 4

Features ARC. frit V. frit SiO _{2 in} mole% 42.63 54.42 SiF at ₄ mol% 4.56 - A1 ₂ Oh ₃ mol% 7.2 4.9 A1F _{S in} mole% - 4.48 B ₂ O ₃ mole% 13.6 8.52 CaO in mole% 6.79 - CaF at ₂ mol% - 2.09 Na ₂ O in mole% 7.83 8.19 NaF mole% 9.14 13.45 K ₂ O in mole% 4.69 3.95 ZrO ₂ mole% 4.1 - Smooth firing temperature in C ° 825-850 825-850 Burning time in hours at smooth burning temperature 4-2 4-2 Α1 ^ 2ο-4α)) '1θ ^-6 degrees ^-1 woman 11.1 20.4% v / v HCl Cooking for 6 hours, followed by chloride-free washing and drying Weight loss mg / dm ² 2976 2015

Features! ARC. fritt | V. fritt ''. -Mr.

16.4 g NaOH and 21.6 g:

Na ₂ CO ₃ prepared with 800 g water;

made in solution for 3 hours cooking, j!

washing and drying to neutral Weight loss mg / dm ² 139 195

Finally, enamel frites with average linear expansion coefficients in the temperature range of 20 ° C to 400 ° C and 8.0 ° C to 10 ~ ⁶ degrees ^-I and medium linear expansion coefficients in the temperature range 20 ° C to Tg are also known. 8.5 · 10 ~ ⁶ degrees ^_I , but only ^goes well over 900 ° C. This includes, for example, enamel frites having a similar chemical composition to commercially available soda lime glass. Their smooth firing temperatures are known to be above 1050 ° C. Attempts have already been made to reduce the smooth annealing temperature by adding fluids known in the manufacture of enamel frites, such as boric oxide, while keeping the expansion coefficient constant. However, the chemical resistance of the frites so produced is also significantly reduced, as shown in Table 5.

Table 5

Features commercial soda lime glass of which developed enamel frit SiO _{2 in} mole% 71.30 59.23 A1 ₂ O ₃ mole% 1.01 1.37 B ₂ O ₃ mole% - 9.62 MgO mole% 4.17 3.25 CaO in mol / o 7.46 5.82 BaO mole% 0.81 1.83 Li ₂ O in mole% - 1.93 Na ₂ O in mole% 14.19 15.70 K ₂ O in mole% 1.06 1.25 Smooth firing temperature in C ° 1050-1100 800-825 Burning time in hours at the temperature of the burn 4-2 4-2 TGC ° 513 472 Ak (20-400) 10 ⁶ degrees ¹ 10.4 10.5 20.4% v / v HCl for 6 hours, followed by chloride-free washing and drying Weight loss mg / dm ² 2 1426 16.4 g NaOH and 21.6 g Na ₂ CO _{3 with} 800 g water i 1 3 hours cooking, neutral washing and drying Weight loss mg / dm ² 87 1 1 1 1 193

Until now, enamel frites with a smooth firing temperature of less than 900 ° C and satisfactory chemical resistance have not yet been produced.

German Patent Publication No. 2,352,829 discloses lead-containing, low-melting glass fluxes, and lead-containing, low-melting, tin-oxide-containing or tin-oxide-titanium-oxide-containing frit, for making decals and ceramic ornaments. These low-melting frites melt as described in the temperature range of about 430 ° C to 870 ° C, are highly resistant to acids and / or alkaline materials, and prevent the release of lead, cadmium and other toxic compounds. However, the disclosure does not disclose the magnitude of the amount of material dissolved from low melting frit; and, above all, it is not clear how large their lead losses are in the presence of higher amounts of alkali metal oxide.

The ceramic industry is increasingly seeking to produce porous or solid ceramic products at low temperatures in a short period of time. As a result, the use of energy and combustion auxiliaries per unit formulation can be greatly reduced. Finally, it has become possible to produce ceramic compositions having properties similar to porcelain at temperatures below 900 ° C (as required by REQUEST 114 TGL 7838). In particular, such products exhibit a significantly increased average linear expansion coefficient compared to known classical porcelain. The coefficient is 20-400 ° C temperature range by the phase composition tile which glassy and crystalline phases such as quartz is characterized by 9-10 degrees ^{_6 _í} (poor pot quartz) and 14,0 · 10 ^"6 degrees ^-1 (rich in quartz tiles). Such ceramic sintered products require improved chemical resistance enamel frites which, at temperatures below 900 ° C, drain and glaze into the tile. For this, these enamel frites have a mean linear expansion coefficient of 20 ° C to 400 ° C at 8.0 · 10 “at ⁶ degrees ^-1 , and an average linear expansion coefficient of 20 ° C to conversion point (Tg) of 8, It should be greater than 5 · 10 ^-6 degrees ^ 'and these frites should run smoothly at temperatures below 900 ° C during the normal firing time in the ceramic industry.

To overcome the disadvantages described in the prior art, a composition for coating with high chemical resistance, particularly low loss of lead, has been developed which has an average linear expansion coefficient in the temperature range of 20 ° C to 400 ° C, preferably greater than 8.5 · 10 ~ ⁶ degrees. for solid or porous tiles with a mean linear expansion coefficient in the range of 20 ° C to 400 ° C greater than 8.5 · 10 ~ ⁶ degrees ^-1 , and a process has been developed for ceramic glazes on solid or porous ceramic tiles, especially sintered glass for the manufacture of bodies or porous sintered glass products containing silicate wastes at a temperature between 750 ° C and 900 ° C by simple incineration during the normal firing time.

The composition according to the invention is characterized in that 20 to 60% by weight of enamel frit,

40% to 80% by weight of water or saturated aliphatic alcohol with a maximum carbon content,

0-18 weight percent kaolin,

0 to 4% by weight bentonite,

0-14% by weight of colored pigment,

0-14% by weight of bleach,

Contains 0-5% by weight of peptidizer plus total enamel frit, kaolin and bentonite

a) 65-74.9 mole% SiO ₂ ,

b) 0.1 to 5 mol% of Al ₂ O ₃ and optionally 0.1 to 5 mol% of a rare oxide such as ZrO ₂ and / or TiO ₂ and / or SnO ₂ , and / or CeO ₂ and / or Nb ₂ O ₅ ,

c) 4-12 mol% B ₂ O ₃ ,

d) 8-12 mol% PbO,

e) 12 to 16 mol% of alkali metal oxide,

(f) 0 to 4 mol% of alkaline earth metal oxide and / or fluoride, g to 0 to 10 mol% of glass soluble soluble oxide, such as CoO or CuO, and the total amount of the components:

(a) and bj 67 to 75 mol%,

c), d), e) and f) are from 25 to 33 mol%.

Said colored composition may also be used as a glazed colored frit or an embedded colored frit. The composition of the invention and the preparation of the glazes are exemplified.

Ceramic glazes of the compositions of the present invention, having the specified composition, have an incomparably better chemical resistance than the known glazes, except for rare oxides. The amounts soluble in the presence of acids (m ₀ ) remain below 30 mg, preferably below 20 mg, after boiling the mash in 20.4% v / v hydrochloric acid for 6 hours, followed by washing, drying and measuring to remove chloride. mázra dm ^2. Alkaline behatásnál glaze made from a composition according to the invention 250 mg, preferably 150 mg a, lose less per 1 dm ² mázra. The resistance of the ceramic glaze to alkaline influences is determined as follows: glaze 16.4 g NaOH and

A solution of 21.6 g of Na ₂ CO _{3 in} 800 g of water is refluxed for 3 hours and then washed to neutral, dried and weighed. Finally, treatment of glazes obtained according to the invention at room temperature for 24 hours 3% by weight of acetic acid to 1 dm ² calculated mázfelületről less than 1 mg, preferably less than 0.5 mg of lead dissolved from.

It has now been found that by reducing one of the ingredients of the composition of the invention, only glazes have been obtained which, while retaining the thermal expansion and flow properties required by this invention, exhibit a significantly lower chemical resistance than the composition of the present invention. Thus, it has also been shown that the increased chemical stability of the colorable and / or opaque translucent ceramic glazes is substantially achieved only by the use of the composition according to the invention.

It has also been found that the glazes according to the invention can only be blast-free in a temperature range of 750-900 ° C, preferably 800-875 ° C, during normal firing times in the ceramic industry if they are at least 25 mol% B ₂ O ₃ and / They contain PbO and / or alkaline earth oxide and / or alkaline earth metal iodide or fluoride flux. Particularly, it is preferred to have a smooth firing temperature of 800 to 850 ° C

1 (λ

28-33 mol% of said flux must be present (within the composition) in the glaze. Finally, it has also been found that the use of more than 35 mol% of said fluxing agent makes it impossible to obtain a glaze having the desired physical and chemical properties. The low alkali metal oxide or fluoride content of 0-4 mol%, respectively, "stretches" the translucent glazes according to the invention, which means that the decrease in viscosity decreases with increasing temperature. In addition, they improve their mechanical properties, such as hardness. While these alkaline earth metal compounds may be used in higher proportions, this has the disadvantage that glazes run smoothly above 900 ° C.

As noted below, the use of a proportion of poorly melting oxides such as SiO ₂ and / or Al ₂ O ₃ above 75 mol / / is no longer possible if the thermal expansion and flow properties required by the present invention are to be maintained. Above 75 mole percent of these molten oxides, at temperatures below 900 ° C, make the glazes dense so that smooth, smooth-spilled, glass-like coatings are not formed during the normal firing time. The use of more than 6 moles of Al ₂ O ₃ in the glazes of the present invention is no longer permitted. It has been found that the use of more than 6 mol% alumina in translucent ceramic glazes having excellent thermal expansion and flow properties can only be achieved by simultaneously significantly reducing the SiO ₂ content and by addition of said flux, but the chemical resistance of such glassy coatings reduced. It has been found to be particularly advantageous if 1-4 mole% Al ₂ O ₃ is incorporated in the translucent ceramic glazes of the present invention.

The given rare oxides can be used in small amounts as glazing agents, so that the thermal expansion and flow properties required in this invention are generally not substantially altered. Their use in the context of this invention is optional as it does not increase the chemical resistance of the glazes. Optional rare oxides up to 5 mol / o as glazing agents may be ZrO ₂ and / or TiO ₂ and / or SnO ₂ and / or Nb ₂ O ₅ and / or CeO ₂ , generally used in combination with ceramic dyes, such that the glazes retain their chemical resistance and, if necessary, improve the color development.

Transparent ceramic glazes fired on suitable ceramic tiles at 750-900 ° C, preferably 800-850 ° C, are solid and defect-free within the typical firing times of the ceramic industry. Ceramic tiles for both porous as well as solid products can be used if they are middle, linear coefficients of thermal expansion within a range of temperatures from 20 to 400 ° C greater than 8.5 · 10 ^{-1 6} degrees. Such porous products nowadays can be made from mixtures of glass and sand on the one hand and mixtures of glass and silicate wastes such as concrete and / or loam waste in the presence of a few% clay at temperatures below 900 ° C. Preferably, however, solid products such as sintered glass and quartz are surface-cured.

X-ray examinations of the glazes on said ceramic tiles, as well as microscopic examination of etched abrasions on glass tile fragments, have shown that the translucent ceramic glazes produced by the process of the invention are crystalline-free and do not induce phase rebuilding. process or ornamental firing on already shrunken pots. In particular, the etched sandings on the glazed tiles showed that the glazes produced according to the invention did not undergo any chemical reaction at the tile / glaze interface and did not undergo any crystalline phase re-formation and no tangential cracks. In a restrictive sense, the use of Li ₂ O as a flux in larger amounts (greater than about 5 mol%) produced crystalline precipitates at the tile / glaze phase boundary surface, which resulted in visible cracks. Therefore, in general, more than 4 mol% Li ₂ O should not be present in the transparent glazes produced by the process of the invention and this is advantageous in terms of cost.

The translucent glazes produced according to the invention can be colored and / or opaque, which greatly extends their application in the ceramic industry. Dyes and / or pigments and / or opacifiers known per se in the ceramic industry may be used for tinting and / or opacification. Among other things, it has been found that frites containing 2-10 mol% predominantly soluble coloring oxides, such as cobalt oxide or copper oxide, in the translucent glazes produced according to the invention exhibit color, brilliance and flawlessness during normal firing at temperatures of 750-900 and glazes with improved chemical stability were available. Finally, it was also possible to color the translucent glazes with 2 to 10 mol% of a pigment, in particular a spinel-type pigment. It has also been found that it is most advantageous to add the coloring pigments to the grinding additive during the preparation of the slurry, while the coloring oxides and their heat-convertible compounds (carbonates or nitrates) can also serve as additives in the production of frit.

It has been found that the addition of 2-10 mol% dye pigment does not substantially change the smooth firing temperature of the translucent enamel frit used. In contrast, said coloring oxides act as more or less strong fluxes, so that when added, the translucent enamel frites used generally have a reduced firing temperature. It has been found to be advantageous if the reduced combustion temperatures thus reduced are generally not by increasing the SiO ₂ and / or Al ₂ O ₃ content, but by rare oxides such as ZrO ₂ and / or TiO ₂ and / or SnO ₂ and / or It was compensated by the addition of up to 5 mol% of Nb ₂ O ₅ and / or CeO ₂ , while for the reasons mentioned above, no more than 75 mol% of poorly melting oxides were added to the glaze. The compounds listed above can be added both to the preparation of the mixture, the preparation of the frit and the preparation of the slurry. However, the effect of rare oxides is not only limited to influencing the temperature dependence of the viscosity of the glaze, but also allows the chemical stability of the slightly colored glaze to be slightly corrected by the addition of coloring oxides.

Finally, the colored glossy ceramic glazes produced according to the present invention can also be used as overcoat glazes based on their improved chemical resistance. It is also possible, especially for colored enamel frites flowing smoothly between 850 and 900 ° C, to be used as an embedded dye optionally. The use of a coloring oxide or coloring pigment in an amount greater than 5 mol% is permitted for coloring the translucent glazes. However, as a result, the physical properties of such glassy coatings are generally not significantly improved, however, the economy is reduced by the incomparably high cost of dye oxides or pigments.

The opaque ceramic glazes of the present invention may be opacified or opacified by known opacifying agents. It has been found that the bleaching agents known per se are preferably added to the grinding additive at a concentration of 10 mol% in the slurry formulation. Particularly suitable as opacifying agents are zirconium silicate (ZrSiO ₄ ) or TiO ₂ or SnO ₂ , preferably 8 to 10 mol%. Quantitative X-ray examinations of the opaque glazes show that the amount of said opacifying agents in the glazes remains substantially unchanged. The translucent glazes may also be clouded by the addition of 8 to 15 mol% calcium fluoride to the mixture.

According to the invention, the glaze is prepared by preparing a slurry of molten, frit, and milled to 40µιη-ηέ1 enamel frit and additives such as clay, kaolin and / or bentonite and / or peptide at temperatures between 1250 and 1400 ° C. Pepticizers are used to stabilize the suspension, such as sodium hydroxide, water glass, boric acid, etc.), and the suspension is then applied and burned until smooth. For the above-mentioned technical operations, standard machine units 35 can be used in the ceramic industry. Rotary frying ovens are particularly suitable for melting and frying glaze builders.

The invention is further illustrated by the following embodiments, but the scope of the invention is not limited to those described in the examples.

Example 1

93.5 parts by weight of a mixture of Na ₂ CO ₃ , 183 parts by weight of K ₂ CO ₃ , 290 parts by weight of Pb ₃ O ₄ , 530 parts by weight of SiO ₂ and 95 parts by weight of H ₃ BO _{3 at} 1320 ° C to 1350 ° C. ° fused and fried. From the enamel frit thus obtained, which has the following chemical composition (mole%): SiO ₂ = 70.32, 50 B ₂ O ₃ = 5.15, PbO = 10.18, Na ₂ O = 7.33 and K ₂ O = 7.02; thermal properties: conversion point (Tg) = 470C °, softening point (T _soft ) = 599 C °, average linear expansion coefficient (Ak ₃₀ _ _{40 <} ) in the temperature range 50-400 ° C = 9.9 · 10 ⁶ degrees ^The average linear expansion coefficient (Ak ₅₀ _ _Tg ) for the temperature range of ¹ to 50 ° C to 55 ° C is 10.9 x 10 ⁶ degrees ¹ , after which the alcoholic suspension is prepared. This slurry is immersed in each half of a cylindrical ceramic body, the surface of the bodies varying in size from 17 cm ² to 22 cm ² , the immersion bodies are dried and suspended in an electrically heated jacketed oven at 800-825 ° C for 3 to 4 hours. we burn it over time. In this way, translucent ceramic glaze is obtained, 65 = 11.7 mg / dm ² , = 215 mg / dm ² , which shows the following chemical resistance values: m ₀ after proper acid treatment m ₀ after proper alkaline treatment m ₀ result of the lead loss test

0.5 mg Pb / dm ² .

The cylindrical ceramic bodies were prepared as follows: 204 parts by weight of hydrocyclone sludge from kaolin digestion and 296 parts by weight of shredded soda-lime in a vibratory mill were dry-ground for 24 hours with the addition of AlF ₃ · 0.5 H ₂ O. This gives the product of the following particle size distribution: 99.5% by weight below 40 μπι, 93% by weight below 20 μηι, 72% by weight below 10 μπι.

0.08 parts by weight of water and 0.008 parts by weight of water-soluble polyvinyl alcohol are added to 1 part by weight of this mixture and the mixture is thoroughly mixed. Subsequent homogenization is carried out by pressing the mixture through a 0.5 mm mesh sieve. The mixture is pressed into a roller having a diameter of 35 mm on a hydraulic press of 600 kg / cm ² . These extruded articles are dried at 100 ° C and then provided with holes 3 mm wide. These ceramic semi-finished products are fired at a temperature of 750-875 ° C over a residence time of 4-1 hours.

Example 2 parts by weight of Na ₂ CO ₃ , 180 parts by weight of K ₂ CO ₃ , 290 parts by weight of Pb ₃ O ₄ , 520 parts by weight of SiO ₂ , 95 parts by weight of H ₃ BO ₃ and 20 parts by weight of Al ₂ O The mixture of ₃ was melted and fritted at 1350 ° C. From the enamel frit thus obtained, which has the following chemical composition (in moles): SiO ₂ = 69.25, Al ₂ O ₃ = 1.55, B ₂ O ₃ = 5.33, PbO = 10.37, Na ₂ O = 6 , 96, and K ₂ O = 6.54; thermal properties: Tg = 475 ° C, T _soft = 640 ° C, Ak ₍₃₀ _ ₄₀₀₎ = = 9.9 · 10 ⁶ degrees ^_1 and Ak ₍₅₀ _ _Tg) = 10.6 - 10 ^ degrees ¹ after grinding an alcoholic suspension is prepared. This suspension is applied by immersion on each half of a cylindrical ceramic body having the size and method of preparation described in Example 1. The immersed bodies are dried and suspended in an electrically heated shell oven at a temperature of 825-850 ° C for a residence time of 3 to 2 hours. In this way, a translucent ceramic glaze is obtained which has the following chemical resistance values:

m ₀ after suitable acid treatment m ₀ after suitable alkaline treatment m ₀ lead loss test = 11,0 mg / dm ² = 162 mg / dm ² = 0,21 mg Pb / dm ² .

Example 3

After melting at a temperature of 1320-1350 ° C, the mixture of the composition of Example 2 is prepared as a frit having the following chemical composition (mole%): SiO ₂ = 68.67, Al ₂ O ₈ = 3.52, B ₂ O _b = 5.55, PbO = 9.63, Na ₂ O = 6.48, and K ₂ O = 6.15. From 100 g of enamel frit thus prepared and crushed to a particle size of less than 40 μπι,

7.5 g of standard kaolin and 1 g p. the. A suspension of boric acid in water (150 g) is prepared by immersion in cylindrical ceramic bodies over their entire surface. The ceramic cylindrical bodies are the same as in Example 1 and are made as described there.

The immersed bodies are dried and suspended in an electrically heated encased oven at a temperature of 835-865 ° C for a residence time of 2-3 hours. In this way, a translucent ceramic glaze is obtained which has the following chemical resistance values:

m ₀ after proper acid treatment = 11.2 mg / dm ² m0 after proper alkaline treatment = 156 mg / dm ² m0 lead loss test result = 0.2 mg Pb / dm ² .

Example 4 Slurry of Na ₂ CO ₃ , 175 parts of K ₂ CO ₃ , 290 parts of Pb ₃ O ₄ , 496 parts of SiO ₂ , 160 parts of H ₃ BO ₃ and 18 parts of Al ₂ O The mixture of ₃ was melted and fritted at 1360 ° C. From the enamel frit thus obtained, which has a chemical composition (in moles) of SiO ₂ = 66.07, Al ₂ O ₃ = 1.69, B ₂ O ₃ = 9.89, PbO = 10.03, Na ₂ O = 6, 43 and K ₂ O = 5.89; Thermal properties: Tg = 492C °, Ak _{(50 00 _4)} = 8.8 · 10 ^-6 degrees ^-1 and Ak ₍₅₀ _t _g) = 9.6 10 ^{6 -1} degrees after auger aqueous suspension is prepared. This suspension is immersed

The cylindrical ceramic bodies produced in Example 1 are applied over the entire surface. The immersed bodies are dried and suspended in an electrically heated shell oven at a temperature of 825 to 850 ° C for a residence time of 4 to 3 hours. In this way, translucent ceramic glaze is obtained which has the following chemical resistance values: m ₀ after suitable alkaline treatment = 110 mg / dm ² m ₀ lead loss test = 0.19 mg Pb / dm ² .

Example 5

100 g of comminuted enamel frit of the composition described in Example 1 and prepared in the same manner as described therein were thoroughly mixed with 5 g of Co ₂ O ₃ and a commercially available brown colorant of the spinel type. An aqueous suspension is prepared from this mixture. This slurry is immersed over the entire surface (between 17 cm ² and 22 cm ² ) of cylindrical ceramic bodies. The immersed bodies are dried and hung in an electrically heated shell oven. The physical and chemical stability values of the glazes are given in Table 6: The chemical resistance values are given in Table 6 in mg dissolved quantities.

Table 6

Features blue glaze brown glaze Smooth firing temperature in C ° 775-825 800-850 Length of stay in hours 4-2 4-1 m ₀ after appropriate acid treatment mg / dm ² 29.4 18.4 m ₀ after suitable alkaline treatment mg / dm ^{2 178} 105

Cylindrical ceramic bodies are produced as follows:

g of crushed quartz sand and 40 g of baking soda lime in a disk-rolling mill for 10 minutes are further comminuted and mixed. The particle size distribution of the mixture thus prepared is as follows: 98.5% by weight below 40 μηι, 90% by weight less than 20 μιη and 75% by weight less than 10 μπι. To one part by weight of this mixture, 0.15 parts by weight of water is added and evenly distributed. The mixture was further homogenized by passing it through a 0.5 mm mesh screen. The resulting granules were formed, dried and drilled as in Example 1.

Claims (2)

Patent claims A composition ^{comprising a} ceramic having a high linear resistance to glazing, particularly low lead ^{loss ,} with ceramic materials having a medium linear coefficient of expansion greater than 8.5 to ¹⁰ degrees Celsius ^, at a temperature of between 20 ° C and 400 ° C, characterized in that: 20-60% by weight of enamel frit, 40 to 80% by weight of water or saturated monovalent, not more than Aliphatic alcohol with 3 carbon atoms, 0-18 weight percent kaolin, 0 to 4% by weight bentonite, 0-14% by weight of colored pigment, 0-14% by weight of bleach, Contains 0-5% by weight of peptidizer plus total enamel frit, kaolin and bentonite a) 65-74.9 mole% SiO ₂ , b) 0.1 to 5 mol% of Al ₂ O ₃ and optionally 0.1 to 5 mol% of a rare oxide such as ZrO ₂ and / or TiO ₂ and / or CeO ₂ and / or Nb ₂ O ₅ and / or SnO ₂ , c) 4-12 mol% B ₂ O ₃ , d) 8-12 mol% PbO, e) 12 to 16 mol% of alkali metal oxide, f) 0 to 4 mol% of alkaline earth metal oxide and / or fluoride (g) 0 to 10 mol% soluble in a glass melt, colored oxides such as CoO or CuO and the total content of the components: a) and b) from 67 to 75 mol%, c), d), e) and f) are from 25 to 33 mol%. 2. A process for the production of ceramic glazes having a colorable and / or opaque, translucent, enhanced chemical resistance, particularly with low loss of lead, characterized in that: 20 to 60% by weight of enamelled frit melted and fused between 1250 and 1400 ° C and shredded to a particle size of 40 μιη-ηάΐ, 40 to 80% by weight of water or saturated monovalent aliphatic alcohol with less than 3 carbon atoms, 0-18% by weight of kaolin, 0 to 4% by weight of bentonite, 0-14% by weight of colored pigment, 0-14% by weight of a opacifying agent and An aqueous or alcoholic suspension of 0-5% by weight of the peptidizer is prepared and the total amount of enamel frit, kaolin, and bentonite a) 65-74.9 mole% SiO ₂ , b) 0.1 to 5 mol% of Al ₂ O ₃ and optionally 0.1 to 5 mol% of a rare oxide such as ZrO ₂ and / or TiO ₂ and / or SnO ₂ and / or CeO ₂ and / or Nb ₂ O _s , c) 4-12 mol% B ₂ O ₃ , d) 8-12 mol% PbO, e) 12 to 16 mol% of alkali metal oxide, f) 0 to 4 mol% of alkaline earth metal oxide and / or fluoride; (g) 0 to 10 mol% of a soluble colored oxide, such as CoO or CuO, soluble in glass and the total proportion of the components: aj and b) 67 to 75 mol%, c), d), e) and f) 25-33 mol%, the slurry is applied to the molded crude ceramic pieces, then dried and incinerated at a temperature of 750 to 900 ° C.