WO2023025670A1

WO2023025670A1 - Antimicrobial and/or catalytic glaze composition

Info

Publication number: WO2023025670A1
Application number: PCT/EP2022/073160
Authority: WO
Inventors: Jan Interwies
Original assignee: N-Tec Gmbh
Priority date: 2021-08-25
Filing date: 2022-08-19
Publication date: 2023-03-02
Also published as: DE102021004362A1

Abstract

The invention relates to a glaze composition having an antimicrobial and/or catalytic effect for surface finishing of a ceramic item, which glaze composition comprises at least one silicon compound, at least one aluminium compound and at least one antimicrobial and/or catalytic metal compound, wherein the metal of the at least one antimicrobial and/or catalytic metal compound is selected from the group consisting of zinc, tin, copper, calcium, strontium, lanthanum, cerium, iron, nickel, vanadium, molybdenum and tungsten. In the glaze composition, the weight ratio of aluminium to silicon is at least 0.30, the proportion of the metal of the at least one antimicrobial and/or catalytic metal compound in the glaze composition is at most 20 wt.% and an aqueous slurry of the glaze composition has a pH that deviates from pH 7 by at least 0.2. The invention also relates to a method for coating a ceramic item with the antimicrobially and/or catalytically acting glaze composition and to a coated ceramic item produced according to the method.

Description

ANTIMICROBIAL AND/OR CATALYTIC GLAZE COMPOSITION

The invention relates to a glaze composition that can be used to finish the surface of a ceramic object and impart antimicrobial and/or catalytic properties to the surface Roof tiles, a tile, a slab - i.e. a large panel with an edge length of at least 1.5 m, which is used as such or can be divided into smaller pieces -, a facade panel, fireclay, a chimney pipe, a kitchen worktop, a kitchen sink or similar. Surface finishing can be carried out on fired, partially fired or unfired ceramic substrates such as green ceramic bodies, clay or loam, as well as engobed, glazed or unglazed substrates. The glaze composition is particularly suitable for the surface finishing of fine stoneware. Since this is mostly not glazed, its surface has a high sensitivity to dirt, which should be reduced with the help of a surface treatment, also known as surface refinement.

Known surface finishes usually consist of a mixture of different metal oxides, which are present according to the Seger formula in such amounts to one another that the overall mixture has a neutral pH. In order to obtain the desired antimicrobial and/or catalytic properties, at least one metal compound with an antimicrobial effect, such as zinc oxide, is added to the metal oxide mixture. Such a composition and the corresponding surface finish are described, for example, in EP 3 053 902 A1. A key feature of this and similar metal oxide compositions is a very high proportion of zinc oxide, exceeding 35 percent by weight in the case of EP '902. However, investigations of such compositions by the applicant have shown that the corresponding surface finishes are only very slightly pronounced, despite the high proportion of zinc oxide possess antimicrobial and catalytic properties. In addition, the high proportion of zinc oxide means that only matt glazes are available, some of which are rough because the zinc oxide forms coarser particles on the surface

[0003] On the other hand, surface finishes that have pronounced antimicrobial and/or catalytic properties, can be applied very thinly and do not change the optical properties of the substrate surface to be finished are desirable. Accordingly, the object of the invention is to specify a glaze composition which gives a ceramic object treated therewith a surface finish with pronounced antimicrobial and/or catalytic properties without noticeably changing the optical properties of the ceramic object.

This object is achieved with the glaze composition according to claim 1 and the ceramic article according to claim 12, which is obtainable by the method according to claim 11, which is also part of the present invention. Preferred developments are described in the respective dependent claims.

In a first aspect, the invention thus relates to a glaze composition with an antimicrobial and/or catalytic effect for the surface finishing of a ceramic object, which comprises at least one silicon compound, at least one aluminum compound and at least one antimicrobial and/or catalytic metal compound, the metal of the at least an antimicrobial and/or catalytic metal compound selected from the group consisting of zinc, tin, copper, calcium, strontium, lanthanum, cerium, iron, nickel, vanadium, molybdenum and tungsten. The weight ratio of aluminum to silicon in the glaze composition is at least 0.30, and the proportion of the metal of the at least one antimicrobial and/or catalytic metal compound in the glaze composition is at most 20% by weight. In addition, the pH of an aqueous slurry of the glaze composition is in a non-neutral range, deviating by at least 0.2 from pH 7, i.e. it is either acidic (pH < 6.8) or alkaline (pH > 7 ,2).

[0006] Antimicrobial properties are understood in the context of the invention to mean, in particular, antibacterial, antiviral, fungicidal and algicidal properties. In the present case, an active metal compound or an antimicrobial metal refers accordingly to substances which are suitable for imparting antimicrobial properties to a surface finish produced using them. A catalytic effect is usually understood to mean influencing the kinetics of a chemical reaction, for example in order to start the latter, to accelerate it and/or to steer it in a specific direction. In the context of the invention, the catalytic action is primarily aimed at decomposing pollutants and/or pollutants, in particular Air pollutants, by means of the catalytic metal compound or the catalytic metal. A subcategory of catalytic action is photocatalytic action, in which the catalytic reactions take place under the influence of light. Accordingly, within the scope of the invention, a photocatalytic effect is to be understood as meaning a catalytic effect that takes place under the influence of light, and in particular the decomposition of dirt and/or (air) pollutants under the influence of light using at least one photocatalytic metal compound or one photocatalytic metal. The latter refer to substances that are able to achieve a photocatalytic effect. Catalytic or photocatalytic effects can be detected in a manner known in the prior art, for example by means of a methylene blue test. For the sake of simplicity, the antimicrobial and/or catalytic metal compound is referred to below as the “active metal compound”, and the antimicrobial and/or catalytic metal as the “active metal”. The antimicrobial and/or catalytic properties are summarized accordingly under "active properties".

In the prior art, it has hitherto been customary to put together the glaze composition according to the Seger formula from three groups of metal oxides—the neutral, the base and the acid side—in such a way that the overall composition had a neutral pH. In the investigations on which the present invention is based, however, it has surprisingly been shown that significantly better active properties are achieved if this customary procedure is deviated from and the pH of the glaze composition is deliberately reduced by a value of at least by appropriate selection of the components contained in the glaze composition 0.2 is shifted to either the alkaline or the acidic range. The pH of the aqueous slurry of the glaze composition according to the invention preferably deviates by at least 0.3 or 0.4 or 0.5 or 0.6 or 0.7, in particular by at least 0.8 or 0.9 and particularly preferably by at least 1 .0 from the neutral pH value of 7. The pH value for the acidic range is therefore preferably at most 6.x, where x can be 0, 1, 2, 3, 4, 5, 6 or 7, or at most 5.y or 4.y, where y is 0 in each case , 1, 2, 3, 4, 5, 6, 7, 8 or 9. For the alkaline range, the pH is preferably at least 7.z, where z can be 3, 4, 5, 6, 7, 8 or 9, or at least 8.y or 9.y, where y is 0, 1, can be 2, 3, 4, 5, 6, 7, 8 or 9.

The glaze composition is chosen so that the pH value deviating from pH 7 is not only present in its aqueous suspension, but also remains either in the acidic or in the alkaline range after firing of the composition and accordingly also with the glaze composition finished surface of the ceramic object has a pH value as described above which is not neutral and in particular deviates from pH 7 by at least 0.2. The pH of the finished surface can be determined, for example, by means of an aqueous solution of bromothymol blue, which is suitably applied to the finished surface of the ceramic article. The bromothymol blue solution is known to be green at neutral pH, yellow in the acidic range and blue in the alkaline range. Of particular importance for the development of the positive properties of the glaze composition according to the invention is not only the pH, but also the weight ratio of aluminum to silicon, which are present in the form of at least one aluminum compound and at least one silicon compound in the glaze composition according to the invention. In contrast to what is customary in the prior art, a weight ratio based on the metal atoms is defined according to the invention, since the extensive investigations carried out within the scope of the invention have shown that, in order to achieve a good antimicrobial effect, it is evident that suitable mixed-crystal structures are produced on the surface of the finishing layer, which in turn requires a certain ratio of aluminum to silicon. This weight ratio of aluminum to silicon in the glaze composition is at least 0.3. This weight ratio is generally in excess of that found in conventional glaze compositions for making surface finishes. That is, the proportion of aluminum relative to silicon is generally higher in the glaze compositions of the present invention than comparable prior art glaze compositions. Thus, starting from a known glaze composition, this can be modified to a glaze composition according to the invention by adding an aluminum compound and optionally further compounds for adjusting the pH value and/or an active metal compound. In addition to 0.3 and >0.3, suitable ratios of aluminum to silicon are in particular >0.35, >0.4, >0.45, >0.5, >0.55 and >0.6. The weight ratio of aluminum to silicon in the glaze composition according to the invention is preferably in a range which is selected from the group consisting of from 0.30 to 5.0, from 0.30 to 4.0, from 0.30 to 3, 0, from 0.40 to 5.0, from 0.40 to 4.0, from 0.40 to 3.0, from 0.40 to 1.2, from 0.45 to 5.0, from 0, 45 to 4.0 and from 0.45 to 3.0.

On the other hand, the proportion of the active metal compound in the glaze composition according to the invention is comparatively low. It is added so that the metal content of the active metal compound is at most 20% by weight based on the total glaze composition. The calculation of the proportions by weight of the individual components of the glaze composition and accordingly the total weight of the glaze composition is carried out without taking any solvents into account. Of course, this does not rule out that individual, several or even all components of the glaze composition are added in dissolved or suspended form. In this case, however, the proportion of solvent in which the added component is dissolved or suspended is not included in the calculation of the proportion by weight or the proportion of solvent is deducted from the calculation of the proportion by weight of the corresponding component.

The comparatively small proportion of at least one active metal compound, hereinafter also simply referred to as metal compound, which is required to achieve the antimicrobial and/or catalytic effect is not only advantageous with regard to the reduced costs, but in fact, as a rule, also a prerequisite for achieving a sufficient effect in the first place. The investigations accompanying the invention surprisingly showed that precisely the high proportion of active metal compounds used in the prior art means that the surface treated with a corresponding glaze composition has a comparatively low antimicrobial and/or catalytic effect. The investigations carried out suggest that the metal compounds used, when used in larger amounts, act as fluxing agents in the glaze composition. As a result, they melt together with the other components of the glaze composition and become embedded in the vitreous melts that form. As a result, however, they are no longer present as active components on the surface of the coating formed and lose their catalytic activity almost completely. According to the investigations carried out, this effect practically always occurs when the proportion of the metal of the active metal compound in the glaze composition is over 20 percent by weight. Accordingly, in the glaze composition of the present invention, the active metal compound is added so that the content of the active metal is at most 20% by weight of the glaze composition. However, the proportion of the metal in the active metal compound is preferably lower and is, for example, at most 19, 18, 17, 16, 15, 14, 13, 12, 11 or 10 percent by weight, particularly preferably less than 9 or 8 percent by weight and in particular less than 7 or 6 or 5% by weight of the total glaze composition. If several active metal compounds are used, the amounts stated relate to the totality of the metals of all active metal compounds. In principle, any combination of the active metal compounds mentioned is possible. Combinations containing a zinc compound are particularly preferred.

It is believed that the reason why extremely high proportions of an active metal compound such as zinc oxide are used in the prior art can be seen in the fact that the proportion has been continuously increased due to the incorporation of the metal compound into a vitreous melt. in order to achieve a slight antimicrobial and/or catalytic effect at all, so that the proportion of zinc oxide ultimately came to more than 35 percent by weight. These extremely high proportions of zinc oxide then no longer melt completely, so that zinc oxide particles remain on the surface of the coating. However, this leads to the already mentioned disadvantages of a cloudy and possibly rough surface, the activity of which is still comparatively low. If a zinc compound such as zinc oxide is used in the glaze composition according to the invention, its proportion is preferably at most 10 percent by weight, particularly preferably less than 8 percent by weight and in particular 3 to 7 percent by weight of the entire glaze composition. Glaze compositions of this type generally lead to transparent, colorless glazes.

The inventive combination of the features of a suitable ratio of aluminum to silicon, the adjustment of the pH such that it is not neutral, and a suitable and comparatively small amount of an active metal compound in the glaze composition has the result that the metal compound does not lose its catalytic and/or antimicrobial activity when the glaze composition is fired, but is present in an active form on the surface of the finishing layer formed on the ceramic article. It is essential that the metal compound does not form a vitreous melt with other components of the glaze composition and is not embedded in such a melt. Rather, mixed crystals are formed on the surface of the finishing layer, in the crystal lattice of which metal atoms of the at least one active metal compound are incorporated. This mixed crystal formation is only possible if the parameters described above are observed at the same time. Neither the high proportion of aluminum in the glaze composition nor the adjustment of the pH value nor the small amount of the active metal/the active metal compound lead to the formation of the desired mixed crystals and surface finishes with the desired optical and active properties. The desired mixed crystal formation can be promoted in a targeted manner by a suitable choice of the components of the glaze composition. The selection is made in particular taking into account the conditions under which the firing process of the glaze composition is to take place on the ceramic object to be finished, in particular taking into account the firing temperature and the firing time. The components and in particular the active metal compound are expediently selected in such a way that, at the selected firing temperature and within the specified firing time, they form a melt from which crystallization and the formation of the desired mixed crystals can take place.

In the prior art, it has hitherto been customary to add metal compounds and in particular also the active metal such as zinc in the form of low-melting frits to the glaze composition. In these frits, the active metal is embedded in a pre-melted metal-containing glass. If the active metal compound is used exclusively in this form, the formation of mixed crystals in surface finishing is hardly possible, and glass-like melts are almost always formed in which the active metal compound has completely lost its activity. If the glaze composition then contains other fluxes such as alkali or alkaline earth metal compounds, the formation of mixed crystals is virtually impossible. Accordingly, in the present invention, it is not preferable to add the active metal compound in the form of a frit. However, this does not completely rule out the use of frits in the glaze composition according to the invention. Frits can be used, for example, to set a suitable viscosity in the melt of the glaze composition, which enables crystallization of the desired mixed crystals from the melt. In addition, it is possible and sometimes even advantageous to use frits containing at least one active metal in the glaze composition, and it has been observed that the antimicrobial and/or catalytic effect of the composition can thereby be even further improved. However, such term frits are preferably only used in addition to an active metal compound that is not present in the form of frits. For example, frits containing zinc can advantageously be used in combination with at least one zinc-containing compound which is not in the form of a frit in the glaze composition according to the invention. In contrast, the desired antimicrobial and/or catalytic effect cannot generally be achieved with zinc-containing frits alone.

The metal of the active metal compound used according to the invention is selected from the group consisting of zinc, tin, copper, calcium, strontium, lanthanum, cerium, iron, nickel, vanadium, molybdenum and tungsten. Among these, the tin compounds are those that can be used to produce glazing compositions and surface finishes whose pH is in the acidic range. Tin oxide, tin hydroxide and tin chloride or any mixtures thereof are used as preferred tin compounds. Tin hydroxide and tin chloride are converted into tin oxide during firing and, like tin oxide itself, together with other components of the glaze composition, form oxidic - i.e. oxygen-containing - mixed crystals which accumulate on the surface of the surface finish of a ceramic object treated with the glaze composition and are responsible for a high catalytic and/or or ensure antimicrobial activity of the finished surface. The other active metal compounds - i.e. those of zinc, copper, calcium, strontium, lanthanum, cerium, iron, nickel, vanadium, molybdenum and tungsten - are suitable for the production of basic glaze compositions, which lead to refined surfaces with an alkaline pH value. Among these, compounds of zinc, strontium, iron, copper and nickel are preferred, with zinc compounds being particularly preferred in the present invention. Combinations of the metal compounds mentioned can also be used. Combinations of zinc and strontium compounds, for example, produce very good results. Even tin compounds can be used to form alkaline glaze compositions when combined with a sufficient amount of alkaline components. However, this is not preferred according to the invention, also because tin compounds usually lead to clouding and thus to an optical impairment of the surface finish obtained.

If the pH of the glaze composition containing at least one of these metal compounds is to be in the alkaline range, the metal compounds are preferably selected from the group consisting of oxides, hydroxides, carbonates, nitrates, sulfates, chlorides or mixtures thereof. Sulfates and chlorides are preferably only used in combination with other naturally basic metal compounds in order to be able to reliably adjust the pH of the glaze composition to at least 7.2. Metal compounds which are particularly preferred according to the invention are zinc oxide, zinc hydroxide or zinc carbonate and mixtures thereof. As mentioned, these can also be combined with other active metal compounds, such as those of strontium, in particular strontium hydroxide and/or strontium carbonate, the latter also giving good results on their own—without zinc compounds. As in the case of Here, too, tin compounds are the metal compounds that are not initially present as oxides and are converted into oxides during the firing process. In addition to the metal compounds expressly mentioned, other metal compounds which can be converted into the corresponding oxides during firing, such as oxalates, can in principle also be used. Oxidic mixed crystals are formed from the oxides in combination with elements of the other components of the glaze composition during the firing process. Here, too, it can be seen that these mixed crystals accumulate on the surface of the finishing layer, where they develop a high catalytic effect.

It is also possible to add the components of the glaze composition at least partially in the form of naturally occurring rocks. These are ground up before addition and added in powder form. Carbonate minerals, for example, are suitable for use in a basic pH glaze composition. To set the desired aluminum-to-silicon ratio, rocks that are low in silicate and/or rocks that are rich in aluminum are preferably used, which are found among other things among igneous rocks. Suitable examples are bentonite, calcite, diabase, dolomite, foil syenite, kaolin, melilite, montmorillonite, mullite, nepheline, olive, plagioclase, pyroxene and syenite. The parameters pH value, Al:Si ratio and proportion of the active metal compound specified according to the invention can be adjusted by suitable selection of the minerals and their proportions by weight—if necessary by supplementing missing proportions by adding pure individual compounds.

With regard to the composition of the components of the glaze composition according to the invention, it has proven advantageous to select only those with a basic pH if a glaze composition is to be produced with a pH in the alkaline range, and - apart from the required Silicon compound - to avoid acidic and especially strongly acidic components if possible. Conversely, for a glaze composition with an acidic pH, if possible only those components are used which have an acidic pH, while alkaline and in particular strongly alkaline components are not used if possible - apart from the required at least one aluminum compound. In this respect, the invention deviates from the generally customary procedure in which, according to the Seger formula, components from the basic, neutral and acidic groups are put together in such a way that a neutral pH results. However, according to the investigations carried out, it is precisely this deviation from the usual procedure that leads to the formation of the desired mixed crystals on the surface of the finishing layer and thus to the significantly improved antimicrobial and/or catalytic properties.

The at least one aluminum compound which must be contained in the glaze composition according to the invention is preferably selected from the group consisting of aluminum oxide, aluminum hydroxide, aluminum nitrate and aluminum alcoholates. The latter can be in whole or in part be hydrolyzed. The alcohol residue is preferably selected from aliphatic saturated, branched or unbranched alcohol residues with 1 to 8 and in particular! up to 4 carbon atoms. Preferred examples are methanol, ethanol, n-propanol, isopropanol, n-, sec- or tert-butanol or mixtures thereof. The aluminum compound is particularly preferably selected from aluminum oxide or aluminum hydroxide. The at least one silicon compound that must also be present is expediently selected from the group consisting of frits, clay minerals and quartz powder, with the latter being less preferred.

In principle, it has been found in the tests carried out that the use of compounds with a small particle size can promote the formation of the desired mixed crystals in the production of the finishing layer. Accordingly, it is preferred to use the solid components of the glaze composition according to the invention in finely divided form. The metal compound therefore expediently has an average particle diameter D 50 of 1 nm to 30 μm, preferably 50 nm to 500 nm, particularly preferably 50 nm to 200 nm and in particular 50 to 100 nm. In the case of the at least one aluminum compound such as aluminum oxide or aluminum hydroxide this preferably has an average particle diameter D 50 of 1 nm to 30 μm and in particular of 1 to 6 μm. A maximum particle size of 30 μm for the aluminum compound is also preferred because with larger particle diameters the aluminum compound no longer forms eutectics with other components of the glaze composition under the usual firing conditions. However, the formation of a eutectic can lower the melting point of the glaze composition, which in turn affects the viscosity of the melt and thus the ability to form the desired mixed crystals. Above all, the interaction of aluminum compounds such as aluminum oxide with zinc compounds such as zinc oxide promotes mixed crystal formation.

As already mentioned several times, the formation of mixed crystals, in the crystal structure of which metal atoms of the at least one active metal compound are incorporated, is important in order to achieve high catalytic and/or antimicrobial activity of the surface finish of a ceramic object produced from the glaze composition according to the invention. Crystal formation can be promoted by suitably adjusting the viscosity of the melt formed during the firing process. A possibility of adjusting the viscosity of the melt, which is known per se, consists in a suitable choice of the concentration of the melt phase formers or fluxes in the glaze composition. It has already been mentioned that some of the glaze components used as active metal compounds, such as zinc oxide in higher amounts of, for example, more than about 8 and in particular more than 10 percent by weight, themselves act as fluxes. By suitably selecting the amount of the at least one active metal compound, in some cases it can therefore be achieved that no further fluxes have to be added to the glaze composition. In other cases, the glaze composition is additionally at least one Added melt phase former/flux. Preferred melt-phase formers/fluxes are, for example, alkali metal and/or alkaline earth metal compounds, since it has been found that they can also improve the catalytic effect of surface finishing. This is attributed to the fact that the alkali and alkaline earth metals, of which sodium, potassium, magnesium, calcium and barium are preferred, promote the formation of the mixed crystals and are incorporated into the crystal structure themselves to form active basic silicates, thereby increasing antimicrobial and catalytic properties evoke activity.

[0022] Which of these melt-phase formers/fluxes are actually used depends, among other things, on whether a glaze composition with an alkaline or an acidic pH value is to be produced. As already mentioned, it is preferable, if possible, to use acidic or at least neutral components for acidic glaze compositions, but preferably alkaline or at least neutral components for alkaline glaze compositions. For example, alkali metal and/or alkaline earth metal halides, in particular chlorides, are suitable. In the case of a basic glaze composition, suitable basic melt phase formers or fluxes are preferably selected from alkali metal or alkaline earth metal oxides, hydroxides, carbonates, phosphates, silicates or tungstates. Combinations of melt phase formers/fluxing agents can also be used. The quantity with which the melt phase former/the flux is added to the glaze composition is - as mentioned - selected in such a way that oxidic mixed crystals can form in the melt of the glaze composition at the selected firing temperature within the firing time, the dissolving of the active metal compound(s) in a glassy melt, on the other hand, is prevented. Excessively high proportions of melt-phase former/flux promote such an undesired dissolution of the active metal compound in the glass matrix. Appropriate amounts of melt phase former/fluxing agent can be readily determined by simple experimentation. They are usually at most 40% by weight, preferably up to 30% by weight and in particular at most 20% by weight or at most 15% by weight, based on the total glaze composition. Glaze compositions that are to be fired at a comparatively low temperature and/or in rapid firing generally require a higher proportion of melt phase formers/fluxes than those that are fired at a higher temperature.

As already mentioned, a frit can also be added to the glaze composition. This can take place as an alternative to or in addition to the addition of the melt phase former. A frit containing the metal of the at least one active metal compound is preferably added. The frit then serves not only to adjust the viscosity of the melt, but is also suitable for improving the antimicrobial and/or catalytic effect of the surface finish produced. The frit will usually be present in the glaze composition in an amount of up to 65% by weight, in particular at most 60, 50, 40, 30 or 25% by weight. Here, too, the appropriate amount can easily be determined by simple experiments. In all cases is when adding other compounds, care must be taken to ensure that the specified ratio of aluminum to silicon of at least 0.3 is not shifted outside the specified range as a result of the addition

The invention may also be practiced by modifying glaze compositions known in the art to have the above-described properties of a suitable aluminum to silicon ratio, a pH differing from pH 7 by at least 0.2, and have a proportion of metal of at least one active metal compound of at most 20 percent by weight, so that they are able to form the desired mixed crystals and thus a high catalytic and/or antimicrobial activity on the ceramic object to be refined during the firing process. Usually this will mean increasing the proportion of aluminum by adding a suitable aluminum compound such as aluminum oxide or aluminum hydroxide. At the same time, a shift in the pH value into the alkaline range can also be achieved in this way. Aluminum compounds such as aluminum oxide in particular also have an influence on the viscosity of the melt of the glaze composition formed during firing and prevent the melt from melting too early or being too liquid, in which crystallization and formation of the desired mixed crystals cannot take place. If necessary, the proportion of the active metal compound can be reduced by increasing the other components of the glaze composition, whereby a suitable viscosity of the melt can also be set using components such as fluxes in order to promote the formation of the mixed crystals, if this should be necessary.

Depending on the selection of the at least one active metal compound, the active properties of the surface finishing layers produced using the glaze composition according to the invention can be adjusted in such a way that the catalytic or the antimicrobial properties predominate. The use of calcium compounds enhances the catalytic properties, while zinc compounds provide both catalytic and antimicrobial properties. Compounds of the metals zinc, lanthanum, molybdenum and tungsten can impart not only antimicrobial and/or catalytic but also photocatalytic properties to the glaze composition according to the invention. It is thus possible to produce surfaces with photocatalytic properties even without the addition of a titanium compound that is otherwise commonly used. With regard to the potentially health-endangering and in particular carcinogenic properties discussed for titanium dioxide, this is another great advantage of the present glaze compositions and the products contained with them.

The glaze composition according to the invention can in principle be applied in any manner known in the prior art. The glaze composition is preferably slurried in a suitable solvent before application to the substrate surface to be finished. Aqueous solvents such as water-alcohol mixtures and in particular pure water are preferred. The slurry can be applied to the substrate surface in any suitable manner be, for example by steam atomization, pouring, centrifuging, flooding, dipping, rolling or printing or, which is preferred according to the invention, by spraying. By spraying, particularly even applications can be achieved with a very small layer thickness. Because of the high activity of the glaze composition according to the invention, very small layer thicknesses are already sufficient, and these have the advantage that they are practically no longer visible on the substrate surface after baking and accordingly do not change the visual impression of the substrate. The spraying can take place, for example, by means of airless or HVLP spraying. The airless spraying method is carried out, for example, with a membrane pump and a pressure of up to 300 kPa or also with high pressure of up to 30,000 or 40,000 kPa, the slurry being applied to the substrate without the action of an atomizing agent. In the HVLP (High Velocity Low Pressure) process, the atomization pressure is generally in the range of 700 to 1300 kPa and in particular around 1000 kPa. The basic procedure is known to those skilled in the art. Since only a small layer thickness has to be achieved, a single spraying process is usually sufficient. However, if necessary, several spraying processes can be carried out one after the other.

[0027] It is generally applied to a ceramic object that has not yet been fired (green compact) or to a pre-fired ceramic object, for example after biscuit firing. It is also possible to finish the surface of a ceramic object that has already been completely fired, but this is not preferred from the point of view of costs, since when applied to a green compact or a pre-fired ceramic object, the object and the glaze composition can be fired simultaneously, thus saving energy. In accordance with the method of the present invention, the glaze composition slurry applied to the surface of the ceramic article to be finished is then fired. If desired, the application can be dried beforehand, but this is not usually necessary since the small amounts of the aqueous solvent in the kiln evaporate very quickly at the beginning of the kiln process. The firing process itself takes place in a manner customary in the prior art for glaze compositions and generally at a temperature between 650 and 1350°C, preferably at 800 to 1250°C. The glaze composition can be fired both in short firing and in long firing, with the duration of firing usually being between 0.5 and 5 hours for short firing and between 5 and 40 hours for long firing.

In principle, the glaze composition according to the invention is suitable for finishing practically any conceivable ceramic object whose surface is to be given improved surface properties, so that it offers protection against aggressive environmental or chemical influences, for example, is water, dirt or lime-repellent or easy to clean becomes. The surface can be completely or only partially provided with a surface finish. The surface finish can be applied to fired, partially fired or unfired ceramic substrates such as green ceramic bodies, clay or loam, as well as engobed, glazed or unglazed 1

substrates are made. Suitable ceramic substrates come from the field of sanitary ceramics, building ceramics or laboratory ceramics. Concrete examples are roof tiles, tiles (both for floors and walls), slabs, facade panels, fireclay, chimney pipes, kitchen worktops, kitchen sinks or the like. A particularly preferred ceramic substrate is fine stoneware, for example in the form of wall or floor tiles, which - like the other coated ceramic objects - is given a hard-wearing and in particular dirt-repellent surface thanks to the surface finishing layer according to the invention, which is also self-cleaning due to its catalytic or photocatalytic properties.

The antimicrobial, catalytic or photocatalytic properties of the surface finishing layer produced using the glaze composition according to the invention are based primarily on the formation of mixed crystals of the metal of the active metal compound with silicon and/or aluminum and oxygen. If alkali or alkaline earth metal-containing compounds were also added to the glaze composition as melt phase formers or fluxes, the mixed crystals formed also contain the corresponding alkali or alkaline earth metal elements in the crystal lattice. If the active metal compound is a zinc compound, mixed crystals are formed that correspond to the formula 2 ZnO • SiO ₂ , with other metal atoms such as the alkali or alkaline earth metals already mentioned being incorporated into the crystal lattice, depending on the overall composition of the glaze composition . During the firing process, mixed crystals of different composition are usually formed, distributed over the surface finishing layer. The formation of uniform mixed crystals of the same composition over the entire surface is rather the exception. When the metal of the active metal compound is zinc, various zinc silicon aluminum oxide crystals and/or alkali/alkaline earth zinc silicon aluminum oxide crystals form . Alternatively or additionally, zinc silicon aluminum hydroxide crystals and/or alkali metal/alkaline earth zinc silicon aluminum hydroxide crystals are also formed.

It is surprising and advantageous for a pronounced antimicrobial and/or catalytic activity that the mixed crystals are generally formed with a concentration gradient of the active metal elements, which are essentially concentrated in an area pointing towards the outer surface of the layer The concentration of the metal atoms then decreases in the lower-lying areas from about 1 gm depth of the finishing layer. This means that the catalytically active metal elements in the mixed crystals are present exactly where they are supposed to develop their activity, namely on the outermost surface of the finished ceramic object. The cause of this concentration gradient of the active metal is assumed to be that during the firing process the material on the surface of the ceramic object initially forms a vitreous layer with components of the glaze composition. A dedicated layer boundary between the surface of the ceramic object and the finishing layer can hardly or not at all be discerned in the finished ceramic object. For this on the surface of the ceramic The vitreous layer formed by the object then grows out the active mixed crystals and accumulates with the active metal during the crystallization process. The height at which the mixed crystals grow out of the vitreous layer is usually at most 100 μm, in particular at most 50 μm and predominantly not more than 25 μm, measured perpendicularly to the surface of the ceramic object.

The invention will be explained in more detail below with reference to some exemplary embodiments. The exemplary embodiments relate only to a few preferred exemplary embodiments of the invention, without the invention being restricted to these. Unless expressly stated otherwise, all percentages are percentages by weight.

Example 1 - Calcium Containing Active Glaze Composition

Starting from a calcium-containing glaze composition (Protecta) of the following composition:

SiO ₂ 55.6%

Al2O3 23.3% CaO 10.0%

Na ₂ O 4.5%

_K2O

MgO

modified it first by adding a flux (magnesium oxide) and then by adding an active metal compound (zinc oxide) to give the following modified glaze compositions: a) Glaze composition modified with MgO

_SiO2 50.0%

Al ₂ O ₃ 21.0% CaO 9.0%

Na ₂ O 4.0%

_K2O 3.0%

MgO 13.0%

After being slurried in water, the glaze composition a) is applied to the surface of a ceramic object to finish its surface and, after firing, results in a finish with a basic pH value (pH>8, measured with an aqueous bromothymol blue solution) and catalytic properties.

Glaze composition a) can be further modified by adding a zinc compound: b) Glaze composition additionally modified with zinc oxide

SiO ₂ 47.6%

Al ₂ O ₃ 20.0%

CaO 8.5%

Na ₂ O 3.8%

_K2O 2.8%

MgO 9.5%

ZnO 7.8%

After being slurried in water, the glaze composition b) is applied to the surface of a ceramic object to finish it and, after firing, results in a finish with a basic pH value (pH>8, measured with an aqueous bromothymol blue solution) and antimicrobial and catalytic properties.

Example 2 - Calcium Containing Active Glaze Composition

In this example of another glaze composition containing calcium, the active metal compound is added in the form of zinc carbonate:

_SiO2 50.0%

Al ₂ O ₃ 21.0%

CaO 9.0%

Na ₂ O 4.0%

_K2O 3.0%

ZnCO ₃ 13.0%

The zinc carbonate converts to zinc oxide during firing. Surfaces with antimicrobial, catalytic and photocatalytic properties are formed.

Example 3 - Calcium Containing Active Glaze Composition

The calcium-containing glaze composition (Protecta) of Example 1 is first modified by adding 9.7% calcium carbonate to an active glaze composition according to the invention and, after being slurried in water, applied to the surface of a ceramic article to finish it. Firing results in a coating with a basic pH value (pH > 8, measured with an aqueous bromothymol blue solution) and catalytic properties.

Example 4 - Barium and calcium containing active glaze composition

Starting from a barium and calcium containing glaze composition, which also contains zinc in the form of a zinc containing frit and which has the following components: SiO ₂ 47.9%

Al2O3 20.2% BaO 18.1%

ZnO 4.3%

Na ₂ O 4.2%

_K2O 3.2%

CaO 2.1%, an active glaze composition is prepared by adding a zinc compound that is not in the form of a frit. Specifically, 6% zinc oxide is added, which leads to an active glaze composition with the following ingredients:

SiO ₂ 45.0%

Al ₂ O ₃ 19.0%

BaO 17.0%

ZnO 10.0% (of which approx. 4% from frit containing zinc)

Na ₂ O 4.0%

_K2O 3.0%

CaO 2.0%

A surface finish made using this glaze composition exhibits high antimicrobial, catalytic and photocatalytic activity.

Example 5 - Barium and calcium containing active glaze composition

A glaze composition corresponding to Example 4 can also be obtained when zinc carbonate is used instead of zinc oxide. Such a glaze composition has, for example, the following components:

SiO ₂ 45.0% Al ₂ O ₃ 19.0% BaO 17.0% ZnO 4.0% Na ₂ O 4.0%

K ₂ O 3.0% CaO 2.0% ZnCO ₃ 6.0%

Example 6 - Barium and calcium containing active glaze composition

Starting from a barium- and calcium-containing glaze composition, which contains zinc in the form of a zinc-containing frit and, in addition, magnesium oxide and which has the following components: SiO ₂ 45.0% Al2O3 19.0% BaO 17.0% ZnO 4.0% Na ₂ O 4.0%

K ₂ O 3.0% CaO 2.0% MgO 6.0% an antimicrobial, catalytic and photocatalytic glaze composition is prepared by adding a zinc compound, which is not in the form of a frit glaze composition with the following components:

SiO ₂ 41.3% Al ₂ O ₃ 17.4% BaO 15.6% ZnO 8.3% Na ₂ O 3.7%

K ₂ O 2.8% CaO 1.8% MgO 9.1%

The components of the glaze compositions mentioned in the above examples do not necessarily have to be added in the form of the oxides mentioned. Alternatively, one, several or all of the components mentioned can be added in the form of other metal compounds, which can be converted into the corresponding oxides during the firing process. Examples of suitable metal compounds have already been mentioned in the previous description, in particular carbonates, halides, hydroxides, nitrates, phosphates, sulfates, etc. It is also possible to add the components of the glaze composition at least partially in the form of naturally occurring rocks that have previously been ground into powders. For example, carbonate rocks and silicate-poor and/or aluminum-rich rocks, in particular igneous rocks such as bentonite, calcite, diabase, dolomite, foidsyenite, kaolin, melilite, montmorillonite, mullite, nepheline, olive, plagioclase, pyroxene and syenite are suitable. These are used in amounts such that conversion into the oxides gives the percentages given in the examples.

Example 7 - Application and Firing of the Glaze Compositions

Before application, the glaze compositions are suspended in water. About 0.2 to 5.0, preferably 0.4 to 3.0, in particular 0.5 to 1.8 parts by volume of water are added per part by volume of glaze composition. A raw and unfired green tile body produced in a manner customary in the prior art is dried until its water content is at most 1 to 8%. Subsequently, optionally after application of a decoration, the glaze composition according to the invention as a slurry is applied to the green tile compact. The application is done in a single layer. A multi-layer application is possible, but - apart from sanitary glazes - not preferred in order to obtain the thinnest possible layer. The temperature of the green tile compact during application is 15 to 150°C, preferably 40 to 80°C. The slurried glaze composition is applied by spraying according to the following parameters:

Spraying: spraying pressure 100 - 1000 kPa, preferably 400 - 700 kPa

Needle variable, diameter 0.3 to 2.5 mm, preferably 0.5 to 1.5 mm

The amount of the composition is 10 to 350 g/m ² , preferably 150 to 250 g/m ² .

After application of the glaze composition, the green body is optionally dried again, in which case it is then heated to a temperature in the range from room temperature (20°C) to 300°C, preferably from 35 to 150°C. Drying and heating of the green body is not necessary, especially in cases where the furnace has a drying zone in the heating zone at the beginning of the furnace section. The green body is transported into a kiln in a heated state or alternatively at room temperature to be fired. The burning process takes place in a manner that is customary in the prior art, for example in accordance with one of the following alternatives:

Short firing: Temperature: 1050° C. to 1280° C., preferably 1120° C. to 1250° C. Time (entrance to exit): 0.5 h to 5 h, preferably 0.5 h to 2 h

Long firing: Temperature: 1000° C. to 1300° C., preferably 1100° C. to 1250° C. Time (entrance to exit): 10 h to 40 h, preferably 12 h to 24 h

After leaving the oven, the tile is ready and can be packaged, optionally after allowing it to cool to room temperature. In all of the examples described, the height at which the mixed crystals protrude over the adjacent surface is less than 25 μm. The finishing layer cannot be seen with the naked eye and, in comparison to an unfinished tile, does not cause any visual impairment.

Elemental analyzes of the crystalline surface by means of energy-dispersive X-ray spectroscopy (EDRS, EDX) were carried out for some surface finishing layers produced according to the invention. The results for the various glazes A to H are summarized in Table 1 below. Table 1

Electron micrographs, which are attached as FIGS. 5 to 14, were taken of the outer surfaces of surface finishing layers produced according to the invention. For comparison, FIGS. 1 to 4 show electron micrographs of conventional surface finishes. In the recordings, the image section corresponds to 150 pm by 100 pm in the actual surface structure. Show in detail:

1 shows a conventional barium-containing glaze;

Fig. 2 shows another example of a conventional barium-containing glaze;

Fig. 3 shows a conventional calcium-containing glaze;

4 shows a conventional sanitary glaze;

5 shows a surface treatment according to the invention from a calcium-containing glaze composition with zinc carbonate;

6 shows a surface finishing according to the invention from a further calcium-containing glaze composition with zinc carbonate;

7 shows a surface treatment according to the invention from a calcium-containing glaze composition with zinc oxide;

8 shows a surface finishing of a barium-containing glaze composition with zinc oxide according to the invention;

9 shows a surface finish according to the invention from a further barium-containing glaze composition with zinc oxide;

10 shows a surface finish of yet another barium-containing glaze composition with zinc oxide according to the invention; 11 shows a sanitary glaze made from a glaze composition according to the invention with zinc oxide and

12 shows another sanitary glaze made from a glaze composition according to the invention with zinc oxide.

[0042] At first glance, the recordings show that the surface structure of conventional surface finishes is very smooth. In contrast to this, the photographs of the surface finishes according to the invention show a strong crystallization which is caused by the mixed crystals formed according to the invention. These mixed crystals are structures of the formula _{2ZnO.SiO.sub.2} and other oxygen-containing crystals which, in addition to silicon and zinc, contain the other metals contained in the glaze composition incorporated into the crystal lattice. In particular, these are zinc silicon aluminum oxide crystals, alkali metal/alkaline earth metal zinc silicon aluminum oxide crystals, zinc silicon aluminum hydroxide crystals and/or alkali metal/alkaline earth metal zinc silicon aluminum hydroxide crystals. In general, mixed crystals of different compositions are distributed side by side over the finished surface. These structured and differentiated surfaces are held responsible for the outstanding antimicrobial, catalytic and, with appropriate doping, also photocatalytic properties of the surface finishing of ceramic objects according to the invention.

In detail, Figures 5 and 6 show surface finishes that were produced from calcium-containing glaze compositions that were modified by the addition of zinc carbonate. In the finished finish, the zinc content in the surface finish shown in FIG. 5 is 11.2% by weight and the composition corresponds overall to glaze B in Table 1, while FIG. 6 shows a composition corresponding to glaze E with 8.9% by weight zinc . FIG. 7 shows a surface finish made from a zinc oxide modified calcium-containing glaze composition and having the composition of glaze F of Table 1. FIG. Figures 8 through 10 are illustrations of surface finishes of barium containing zinc oxide modified glaze compositions, in which the final finish shown has the composition of glazes A, C and D of Table 1, respectively. FIGS. 11 and 12 show sanitary glazes whose composition corresponds to glazes G and H in Table 1. They were made from glaze compositions of the invention modified with zinc oxide. In all cases, the crystal structures seen in Figures 5 to 12 have grown out of a vitreous layer which is formed during the firing process by reaction of the glaze composition with components of the surface of the ceramic article. The height at which the mixed crystals that form grow out of the vitreous layer and protrude over the vitreous layer in the finished surface finish is in all cases below 100 μm and is generally less than 50 μm and in particular at most 25 μm, measured in a vertical direction Direction to the surface of the ceramic object.

Claims

PATENT CLAIMS

1 . Glaze composition with an antimicrobial and/or catalytic effect for the surface finishing of a ceramic object, which comprises at least one silicon compound, at least one aluminum compound and at least one antimicrobial and/or catalytic metal compound, the metal of the at least one antimicrobial and/or catalytic metal compound being selected from the group , consisting of zinc, tin, copper, calcium, strontium, lanthanum, cerium, iron, nickel, vanadium, molybdenum and tungsten, characterized in that the weight ratio of aluminum to silicon in the glaze composition is at least 0.30, that the proportion of metal of the at least one antimicrobial and/or catalytic metal compound in the glaze composition is at most 20% by weight and that an aqueous slurry of the glaze composition has a pH which deviates from pH 7 by at least 0.2.

2. Glaze composition according to any one of the preceding claims, characterized in that the weight ratio of aluminum to silicon in the glaze composition is in a range selected from the group consisting of from 0.30 to 5.0, from 0.30 to 4.0, from 0.30 to 3.0, from 0.40 to 5.0, from 0.40 to 4.0, from 0.40 to 3.0, from 0.40 to 1.2, from from 0.45 to 5.0, from 0.45 to 4.0 and from 0.45 to 3.0. Glaze composition according to claim 1 or 2, characterized in that the pH of the slurry is in the alkaline range and in particular is greater than 7.2, preferably greater than 7.5 and particularly preferably greater than 8. Glaze composition according to claim 3, characterized in that the metal of the metal compound is selected from zinc, strontium, iron, copper and nickel and preferably zinc. Glaze composition according to claim 3 or 4, characterized in that the at least one metal compound is selected from the group consisting of oxides, hydroxides, carbonates, nitrates, sulfates, chlorides or mixtures thereof, and preferably zinc oxide, zinc hydroxide or zinc carbonate, where optionally the zinc compound is zinc oxide and with a maximum of 10% by weight, preferably with 3 to 7 % by weight contained in the glaze composition Glaze composition according to one of claims 3 to 5, characterized in that it further contains at least one of the following components: a) a basic flux, preferably an alkali or alkaline earth metal salt, in particular an alkali or Alkaline earth oxide, hydroxide, carbonate, phosphate, silicate or tungstate, the basic flux optio nal is contained in the glaze composition in an amount of at most 40% by weight, b) a frit, preferably a frit, which contains the metal of the at least one antibacterial metal compound, the frit optionally being present in an amount of up to 65% by weight. % is contained in the glaze composition Glaze composition according to claim 1 or 2, characterized in that the pH of the slurry is in the acidic range and in particular is less than 6.8, preferably less than 6 and particularly preferably less than 5. Glaze composition according to claim 7, characterized in that the metal is tin and the metal compound is selected in particular from tin oxide, tin hydroxide and tin chloride. Glaze composition according to one of the preceding claims, characterized in that the at least one aluminum compound is selected from the group consisting of aluminum oxide, aluminum hydroxide, aluminum nitrate and aluminum alcoholates, which can optionally be at least partially hydrolyzed, the alcohol residue preferably being selected from aliphatic saturated ones , Branched or unbranched alcohol residues having 1 to 8 and in particular 1 to 4 carbon atoms, in particular methanol, ethanol, n-propanol, isopropanol, n-, sec- or tert-butanol or mixtures thereof, and/or that the at least one silicon compound is selected from the group consisting of frits, clay minerals and quartz flour. Glaze composition according to claim 9, characterized in that the aluminum compound is aluminum oxide or aluminum hydroxide and has an average particle diameter D 50 of 1 nm to 30 μm, in particular from 1 to 6 μm, and/or the metal compound has an average particle diameter D 50 of 1 nm to 30 pm, preferably 50 nm to 500 nm, particularly preferably 50 nm to 200 nm, and in particular from 50 to 100 nm. Process for finishing the surface of a ceramic object with an antimicrobial surface finish, characterized in that an aqueous slurry of the glaze composition according to any one of claims 1 to 10 is applied to a surface of the ceramic object and then fired. Ceramic object obtainable by the method according to claim 11, characterized in that it is a sanitary ceramic, building ceramic, in particular a roof tile, a tile, a slab, a facade panel, fireclay, a chimney pipe, a kitchen worktop or kitchen sink, or tableware acts. Ceramic object according to claim 12, characterized in that the coating has at least one of the following properties:

- it contains mixed crystals of the metal of the active metal compound with silicon and/or aluminum and oxygen, with optional

• the mixed crystals, if the metal is zinc, are those of 2 ZnO • SiO ₂ , optionally with alkali or alkaline earth metals built into the crystal lattice,

• the mixed crystals, if the metal is zinc, are in particular zinc silicon aluminum oxide crystals and/or alkali/alkaline earth zinc silicon aluminum oxide crystals,

• the mixed crystals, if the metal is zinc, are in particular zinc silicon aluminum hydroxide crystals and/or alkali/alkaline earth zinc silicon aluminum hydroxide crystals,

• the mixed crystals have a height, measured perpendicularly to the surface of the ceramic object, of at most 100 μm, preferably no more than 50 μm and in particular at most 25 μm,

- in the case of a glaze composition according to any one of claims 3 to 6, 9 and 10, the surface of the coating has a basic pH, or

- in the case of a glaze composition according to any one of claims 7 to 10, the surface of the coating has an acidic pH.