| WO2009058746A1 | 2009-05-07 |
| US5348915A | 1994-09-20 |
| CLAIMS 1. A glaze composition for treating ceramics comprising: Frits from 12 to 48% by weight Mullites from 5 to 15% by weight Magnesium Aluminate from 5 to 15% by weight - Zirconium Silico Aluminate from 5 to 15% by weight - Silicas from 5 to 21% by weight, and - Feldspars from 3 to 20% by weight; wherein said Frits consist of Alkalis, Amphoterics and Acids and wherein the ratio Alkalis : Amphoterics : Acids is 1 : 0.383 - 1.596 : 2.605 - 0.603. 2. A glaze composition according to claim 1 , also comprising: - Inorganic Colorants from 2 to 8% by weight. 3. A glaze composition according to claims 1 or 2, wherein the ratio Alkalis Moles per Molecular Formula Compound Seger % by weight weight Moles formula Alkalis CaO 56.0774 0.1393 0.382 7.81 MgO 40.3044 0.0504 0.138 2.03 ZnO 81.408 0.1333 0.366 10.85 K20 94.2 0.0333 0.091 3.14 Na20 61.9789 0.0082 0.023 0.51 Sum of Alkali Moles 0.3645 1 Amphoterics A1203 101.96 0.0696 0.191 7.10 B203 69.6202 0.0700 0.192 4.87 Sum of Amphoteric Moles 0.1396 0.383 Acids Si02 60.68 0.8523 2.338 51.72 Zr02 123.218 0.0971 0.267 11.97 Sum of Acid Moles 0.9495 2.605 4. A glaze composition according to claim 1 or 2, wherein the ratio Alkalis : Amphoterics : Acids of said Frit is 1 : 1.596 : 0.603, said Frit comprising: Seger Molecular Formula Compound formula % by weight weight Moles Moles Alkalis CaO 56.0774 0.4833 1 27.10 Sum of Alkali Moles 0.4833 Amphoterics A1203 101.96 0.0469 0.097 4.78 B203 69.6202 0.7245 1.499 50.44 iphoteric Moles 0.7714 1.596 Acids 5. A glaze composition according to any of the preceding claims, wherein the ratio Alkalis : Amphoterics : Acids of said composition is 1 : 0.5223 - 0.5508 : 2.9374 - 2.7339. 6. A glaze composition according to claim 5, comprising: Alkalis Amphoterics A1203 101.96 0.1478 0.1700 0.4497 0.4784 15.07 17.33 B203 69.6202 0.0238 0.0257 0.0726 0.0724 1.66 1.79 Sum of Amphoteric 0.17161 0.1957: 0.5223 0.5508 Moles Acids for producing a white glaze. 7. A glaze composition according to any of the preceding claims, wherein said Inorganic Colorants are selected from among Zirconium Silicates, Iron Chrome Cobalt Spinels, Zirconium Silica Praseodymium, Zirconium Silica Iron, Zirconium Silica Vanadium, Iron Chrome Manganese Spinels and mixtures thereof. 1 8. A glaze composition according to any of the preceding claims, further comprising any colour achievable with the colour-opponent space "Color Space Lab" or "CIELAB", in particular any colour having: - L* from 6 to 90 - a* from 0 to 10 - b* from 0 to 10 wherein L* is the brightness and a* and b* are the colour-opponent dimensions for producing a coloured glaze. 9. A glaze composition according to any of the preceding claims, wherein the ratio SiO2 : Al2O3 is between 2.555 : 0.4784 and 2.760 : 0.4497. 10. A glaze composition according to any of the preceding claims, whose particle size is less than 40 microns. 1 1. A method of glazing a ceramic article comprising the steps of: a. preparing a ceramic article; b. preparing a glaze composition according to any of the preceding claims; c. mixing an amount of said glaze composition ranging between 100 kg and 15,000 kg with an amount of water equal to 45% of the weight of said amount of glaze composition in a grinding mill of the traditional type, said mill being coated with high- alumina, at a speed of 15-18 revolutions/minute, at a temperature of 20-25 °C and for a time period of 240-300 minutes, to obtain a homogeneous mixture and a specific granulometric curve; d. adding appropriate adhesives to the obtained homogeneous mixture, thereby obtaining a glaze to be applied on the surface of said ceramic article; e. applying said glaze on said ceramic article by spraying with a density not greater than 1.680 g/1, so as to obtain a uniform layer from 2,500 to 3,000 g/m2 of said glaze; f. letting the glazed ceramic article dry for at least 24 h; g. placing the ceramic article in a tunnel and/or static kiln for a cycle of 16-22 hours at a maximum temperature of 1,250 °C, with permanence at the temperature of 1,250 °C for 40-120 minutes; h. letting cool at room temperature until complete curing of the applied glaze. 12. Method of glazing according to claim 1 1, wherein step b. provides the preparation of a glaze composition formulated with 48.00% by weight of Frits, 15.00% by weight of Mullites, 5.00% by weight of Magnesium Aluminate, 7.00% by weight of Zirconium Silico Aluminate, 15.00% by weight of Silicas, 3.00% by weight of Feldspars and 5% by weight of Inorganic Colorants; step c. provides the mixing of an amount of said glaze composition equal to 2.000 kg with an amount of water equal to 45% of the weight of said amount of glaze composition in a grinding mill of the traditional type, said mill being coated with high-alumina, to a speed of 15-18 revolutions/minute, at a temperature of 20* 25°C and for a period of time of 240-300 minutes, to obtain a homogeneous mixture and a specific granulometric curve characterized by sizes of between 0.02 and 2,000 microns. 13. A method of glazing according to claim 1 1 or 12, wherein said ceramic article is selected from wash-basins and sanitary fittings, shower bases, worktops, kitchen tops, kitchen sinks, hospital equipment, and the like. 14. A glazed ceramic article comprising a glaze composition according to any of claims 1 to 10. |
"Glaze composition for treating ceramics, method of glazing ceramic articles and glazed ceramic articles"
DESCRIPTION
The present invention relates to glaze compositions for treating ceramics.
More precisely, the present invention relates to glaze compositions for the glazing of articles on substrates of Vitreous China, Fire Clay, Fine Gres, linker, porcelain and/ or mixtures of same, as well as other types of substrates that can be used to make single-fired articles.
Still more precisely, the present invention relates to glaze compositions to be applied on substrates of ceramic articles such as, for example, wash-basins and sanitary fittings, shower bases, worktops, kitchen tops, kitchen sinks, hospital equipment, and the like, to confer anti-scratch, anti-stain, anti-abrasion and anti-slip properties.
The present invention also relates to a method of glazing ceramic articles.
It is known that in the manufacture of ceramics, specifically of the articles listed above, glazes obtained from raw materials which contain pollutants of various types (for example, impure water, iron, metals, their oxides, salts and compounds) are used; the presence of these pollutants is responsible for numerous defects that are found on the finished glazed ceramic articles.
The main defects caused by non-pure raw materials in glazes are:
a low resistance to attack by chemical substances, normally present in detergents used for cleaning; - a reduced hardness, which causes easy wear and abrasion;
- high porosity;
high stainability.
More precisely, the easy wear of the first ceramic layer and the porosity of the internal part of the common glaze used in ceramic processing determine a rapid penetration of soiling agents and mycobacteria into the glaze, with a consequent difficulty in removing stains and a build-up of bacteria.
In ceramic articles to which a layer of common glaze has been applied, the formation of cavities that penetrate from the surface through to the most internal part of the glaze is frequent and, in such cases, a slight abrasion is sufficient to undermine the thin surface layer of the glaze and penetrate into the innermost part characterized by the presence of empty spaces; therefore, a ceramic material treated with a common glaze, made from impure raw materials, is easily attacked by any soiling agent and subject to abrasion and scratches, since the raw materials used in common glazes do not easily bind or interact with other products, such as for example Calcined Alumina.
In fact it is also known that, in common glazes, in order to bring about a reaction between alkali-bearing minerals, such as Calcium Oxide, Barium Oxide and Magnesium Oxide, and materials bearig AI2O3 and S1O2, such as Mullites, Silica and Feldspars, higher temperatures are required while the molar ratios S1O2/ AI2O3 have values ranging between 5-6; furthermore, in addition to the temperature factor, the reaction is affected by the time factor, in particular by the firing time. The surface characteristics of the common glazes with which ceramic articles are made on the basis of the substrates mentioned above are generally fairly hard, but are not as resistant to abrasion and wear.
To produce glazes able to confer superior characteristics of resistance to abrasion and wear, the materials bearing AI2O3 would have to be subjected to very high temperatures, and in any case well above the 1,250°C at which ceramic articles for sanitary ware are fired, in order to form crystals of Mullite and incorporate them into the glaze.
Furthermore, to produce glazes able to confer superior characteristics of resistance to abrasion and wear, the said materials bearing AI2O3 should also remain at temperatures far higher than 1,250°C for periods of time far longer than the usual 40-120 minutes, in cycles of 16-22 hours.
Therefore the need to improve the resistance to abrasion and wear of glazes used for glazing ceramic articles for sanitary ware on substrates of Vitreous and/or Fire Clay remains unsatisfied.
In the abrasives industry, the use of aggregates or calcined spinels at temperatures of 1,700-1,800°C and Frits fused at temperatures between 1,350-1,450°C is also known.
Moreover, in everyday use, common glazes can be subject to sudden changes in temperature, which may be responsible for the formation of crazing, i.e. cause breakage; it is believed that the occurrence of crazing can depend on the inability of the glaze to maintain cohesive bonds between the particles that compose it, because of sudden changes in temperature. According to the Harkort test, to ensure that articles are exempt from crazing or other damage for long periods, thermal shocks between 160°C and 180°C are tolerated.
We believe it is useful here to point out that by the term "crazing" we mean a fine, irregular cracking which, as well as causing a visual surface defect, determines a loss of impermeability in the glazed ceramic; furthermore, "immediate crazing" means cracking that appears at the end of the production cycle and "delayed or late crazing" means cracking that appears after a few days or even months after glazing.
In view of the above, therefore, the need to obtain glazed ceramic articles possessing excellent anti-scratch, anti-stain, anti-abrasion and anti-slip properties that are also resistant to thermal shocks, specifically sudden ones, remains unsatisfied.
The object of the present invention is to provide a glaze composition for the treatment of ceramics which overcomes the drawbacks of common glazes set forth above.
More precisely, the object of the present invention is to provide a glaze composition for the treatment of ceramics that confers on glazed ceramic articles a high resistance to attack by chemicals and elevated hardness, as well as low porosity and stainability, in other words elevated anti-abrasion, anti-scratch and anti-stain properties.
Another object of the invention proposed here is to provide a glaze composition for the treatment of ceramics that confers on glazed ceramic articles elevated anti-slip properties. Another object of the invention proposed here is to provide a glaze composition for the treatment of ceramics that bears significant temperature changes without forming crazing and other types of cracks.
Another object of the invention is to provide a glaze composition for the treatment of ceramics that uses pure raw materials that are readily available and economical.
Yet another object of the invention is to provide a method of glazing ceramic articles that is economical, simple, safe and reliable.
Yet another object of the invention is to provide glazed ceramic articles possessing excellent anti-scratch, anti-stain, anti-abrasion and anti-slip properties and are also resistant to thermal shock.
In view of these objects, the present invention provides a glaze composition for treating ceramics, a method of glazing ceramic articles and the glazed ceramic articles obtained by this method having, respectively, the features of the attached claims 1, 11 and 14, to which reference is hereby made for brevity.
Therefore, one specific object of the present invention is a glaze composition for treating ceramics comprising aggregates or spinels such as Mullites, Zirconium Silico Aluminates, Frits, AI2O3, S1O2 and raw materials such as Quartz and Feldspar and, optionally, Inorganic Colorants in such quantities as to give the desired properties.
Another object, possibly independent and autonomous, of the present invention with respect to other aspects of the invention, is a method of glazing ceramic articles. Another object, possibly independent and autonomous, of the present invention with respect to other aspects of the invention, is a glazed ceramic article.
The features and advantages will become more apparent from the following description of preferred but not exclusive embodiments, given merely by way of non-limiting example.
With the glaze composition for treating ceramics according to the present invention, extraordinary anti-scratch, anti-stain, anti-abrasion and anti-slip properties are conferred on the glazed ceramic material, thus making the articles obtained more durable against wear and the consequent penetration of soiling agents and mycobacteria.
With the glaze composition for treating ceramics according to the present invention, therefore, excellent resistance to changes in temperature is conferred, thus rendering the obtained manufactured articles able to withstand, without damage, states of stress resulting from dimensional deformations induced by sudden changes in temperature, especially when the latter are repeated several times.
Moreover, with the method of glazing ceramic articles according to the present invention, which provides for the application and a single firing of the substrate and the glaze, the extraordinary properties conferred on the glazed ceramic material are stable and irreversible.
The inventive principle underlying the glaze composition for treating ceramics according to the present invention, which is the result of ongoing research carried out by the Applicant and proven by multiple laboratory tests and production tests, is the formulation comprising highly specialized materials, namely aggregates or spinels and Frits, suitable to confer on the ceramic articles an exceptional resistance to abrasion and wear, in addition to making possible the perfect incorporation of Mullite crystals in the ceramic glaze.
In particular, the aggregates or spinels used in the composition according to the present invention include Magnesium Aluminate and Zirconium Silico Alumina te.
In particular, the Frits used in the composition according to the present invention include Potassium Oxide, Sodium Oxide, Zinc Oxide, Calcium Oxide, Magnesium Oxide, Silicon Dioxide, Barium Oxide, Titanium Dioxide, Aluminium Oxide, Boron Oxide, Zirconium Oxide; said Frits allow to bring aluminium oxide and silica bound with high amounts of alkalis connected to each other that, unlike single elements, allow the formulation of glazes for the production of ceramic articles for sanitary ware that can be subjected to firing at a temperature range of between 1,153°C and 1,233°C so as to incorporate Mullites, Magnesium Aluminates and Zirconium Silico Aluminates and, optionally, Inorganic Colorants, in quantities greater than those that it would be possible to incorporate in a common glaze.
With the glaze composition according to the present invention, the surface characteristics of the finished products, such as hardness, resistance to abrasion, wear and soiling are substantially improved; furthermore, the obtaining of surfaces that are planar and soft to the touch, which are not obtained using common glazes, in particular those comprising Calcined Alumina, is of fundamental importance.
It is useful here to point out that by the term "Frits" we mean vitreous masses made from substances such as alkaline oxides and alkaline-earth oxides, borates, quartz and feldspars, which, after being premixed, are melted at temperatures between 1,350°C and 1,450°C in specific melting furnaces of the known type and, consequently, are combined in a homogeneous manner thus lowering the subsequent glass-forming temperature to 1,000-1,100°C.
According to the present invention, the glaze composition for treating ceramics includes:
Frits from 2 to 48% by weight Mullites from 5 to 15% by weight
Magnesium Aluminate from 5 to 15% by weight
Zirconium Silico Aluminate from 5 to 15% by weight
Silicas from 5 to 21 % by weight
Feldspars from 3 to 20% by weight, and optionally
Inorganic Colorants from 2 to 8% by weight, wherein said Frits consist of Alkalis (Sodium Oxide, Potassium Oxide, Zinc Oxide, Barium Oxide, Magnesium Oxide), Amphoterics (Alumina Oxide, Boron Oxide) and Acids (Silica Oxide, Titanium Oxide, Zirconium Oxide) preferably melted together and wherein the ratio Alkalis : Amphoterics : Acids is 1 : 0.383 - 1.596 : 2.605 - 0.603.
We wish to point out that in the present invention, the term "silica/ silicas" and the term "quartz/ quartzs" are used interchangeably to identify the silicon dioxide SiO 2 although, for accuracy, the quartz and its polymorphs are minerals that represent the most common natural physical state of silica, which is crystalline solid.
A first preferred formulation of the above glaze composition provides the use of a first Frit having the ratio Alkalis : Amphoterics : Acids equal to 1 : 0.383 : 2.605; a second preferred formulation of the above glaze composition foreseesprovides the use of a second Frit having the ratio Alkalis : Amphoterics : Acids equal to 1 : 1.596 : 0.603.
We wish to point out here that the ratios mentioned above are expressed as "Seger formulas".
It is known to a person skilled in the field of the present invention, but it is worth reiterating here, that the German scientist and chemical ceramist Herman Seger was a pioneer of the scientific study of glazes and it was he who first introduced the molecular approach to glazes, i.e. the idea of using the ideal formula in glaze compositions in order to be able to express and compare the molecular formulas of different glazes; the reason why the ideal formula was introduced resides in the fact that many materials that are found in nature have a relatively constant composition and that, once their main components have been identified, any minor impurities, although always present, can be ignored (for example, the ideal formula of Potassium Feldspar is K2O.AI2O3.6S1O2, wherein the ratio of the main oxides is 1 : 1 : 6).
In order to better clarify Seger' s idea, which was to express the glazes as a method of comparison, we deem it useful to provide a numerical example; a special glaze for high temperatures can be expressed thus:
K2O O.27 CaO O.73 AI2O3 O.4I Si0 2 3.72
and this expression is known as a "Molecular Unit".
The important aspect is that the fluxes K2O and CaO are mathematically related to the other components of the glaze, i.e., the stabilizer AI2O3 and the glass former S1O2, in such a way that their sum, that is the sum of K2O and CaO, is equal to one (1); this allows a precise comparison with the other elements of the glaze and is the reason it is called a "Unit".
Returning to the glaze composition according to the present invention, said first Frit having the following Seger formula:
Alkalis Amphoterics Acids
1 0.383 2.605 comprises:
Moles per
Molecular formula
Compound Seger % by weight
weight Moles
formula
Alkalis
CaO 56.0774 0.1393 0.382 7.81
MgO 40.3044 0.0504 0.138 2.03
ZnO 81.408 0.1333 0.366 10.85 20 94.2 0.0333 0.091 3.14
Na20 61.9789 0.0082 0.023 0.51
Sum of Alkali Moles 0.3645 1
Amphoterics
A1203 101.96 0.0696 0.191 7.10
B203 69.6202 0.0700 0.192 4.87 Bum of Amphoteric Moles 0.1396 0.383
Acids
To express this as a Seger formula, the sum of the alkali moles must be unified to 1 and the number obtained is used to multiply the amphoteric moles and the acid moles, singly or by category totals.
The followin calculations are shown b wa of verification
Again with reference to the glaze composition according to the present
comprises:
Seger
Molecular formula
Compound formula % by weight
weight Moles
Moles
Alkalis CaO 56.0774 0.4833 1 27.10
Sum of Alkali Moles 0.4833
Amphoterics
A1203 101.96 0.0469 0.097 4.78
B203 69.6202 0.7245 1.499 50.44
Sum of Amphoteric Moles 0.7714 1.596
Acids
Si02 60.68 0.2914 0.603 17.68
Sum of Acid Moles 0.2914 0.603
The sum of the Alkali Moles is equal to 0.4833 for which we obtain:
The followin calculations are shown b wa of verification
Additional compositions of Frits suitable for use in the present invention comprise:
g/mol
% by weight (Seger formula)
CaO 0.382 7.81 MgO 0.138 2.03 ZnO 0.366 10.85
and:
g/mol
ger formula)
Preferably the compositions mentioned above are used in combination; in particular, the last composition confers on the Frit elevated expansion properties and a reduction of the glass-forming temperature, which is comprised between 680°C and 780°C.
The glaze composition according to the present invention has an Alkalis : Amphoterics : Acids ratio equal to 1 : 0.5223 - 0.5508 : 2.9374 - 2.7339.
A glaze composition as per those indicated above, in particular for the
Molecular % by formula
Compound formula Moles formula Seger Moles
weight weight
Alkalis
Amphoterics
Acids
The sum of the minimum for the Alkali Moles is equal to 0.3286 for which we obtain:
1 0.3286 = 3.0429 The followin calculations are shown b wa of verification
The sum of the maximum for the Alkali Moles is equal to 0.3553 for which we obtain:
The followin calculations are shown b wa of verification
Preferably, the glaze composition according to the present invention also comprises Inorganic Colorants, which have the purpose of conferring the desired colour to the glazes.
For this purpose the following can be used:
a) Zirconium Silicates to obtain white glazes; more or less white glazes will be obtained according to the percentage used;
b) Inorganic Colorant Oxides to obtain a range of the following colours:
• grey and black scale: Iron Chrome Cobalt Spinels,
• yellow scale: Zirconium Silica Praseodymium,
• pink scale: Zirconium Silica Iron,
• blue scale: Silica Zirconium Vanadium, • brown scale: Iron Chrome Manganese Spinels.
These Inorganic Colorants optionally added to the glaze composition according to the present invention are selected, therefore, from among Zirconium Silicates (to obtain different shades of white glazes), Iron Chrome Cobalt Spinels (for grey and black glazes), Zirconium Silica Praseodymium (to obtain yellow glazes), Zirconium Silica Iron (to obtain pink glazes), Zirconium Silica Vanadium (to obtain blue glazes), Iron Chrome Manganese Spinels (to obtain brown glazes).
To obtain the full range of colours, mixtures of Zirconium Silicates and Inorganic Colorant Oxides are used.
It is important to note that the Inorganic Colorants, Zirconium Silicates included, do not dissolve in glazes, but remain incorporated without changing the original composition of the bases of the ceramic glazes in which they can be included in order to impart the desired colour to the ceramic glazes.
Preferably, in the present invention, the aluminium oxide (AI2O3) is brought by Frits, Mullites, Magnesium Aluminate and Magnesium Silico Aluminate.
Preferably, in the present invention, the Magnesium Aluminate is a refractory material of the type commonly used in the electronics industry; the following table shows the values related to the content of Magnesium Oxide and Aluminium Oxide present in the Magnesium Aluminate:
Compound % by weight
MgO 28.31
A1 2 0 3 71.69
Preferably, in the present invention, the Zirconium Silico Aluminate is an advanced ceramic of the type commonly used for the production of doors for glass melting furnaces; hereunder is the content of Aluminium Oxide, Silicon Oxide and
Zirconium Oxide in the Zirconium Silico Aluminate:
Compound g/mol % by weight
Al 2 O 3 1.000 40.00
SiO 2 ! 0.848 20.00
ZrO 2 0.827 40.00
Preferably, in the present invention, the Zirconium Oxide (Zr0 2 ) is brought by Zirconium Silico Aluminate and possibly integrated with commercially available Zirconium Silicates.
Preferably, in the present invention, the Silica (S1O2) over and above that brought by Frits and Zirconium Silico Aluminate, is integrated with commercially available common quartz.
The glaze according to the present invention can be produced in an infinite range of colours, without said colouring penalizing in any way the extraordinary characteristics of the glaze itself.
Thus, if a coloured glaze is desired, the composition according to the present invention also comprises any colour obtainable with a colour-opponent space "Lab color space" or "CIELAB", in particular any colour having: L* from 6 to 90
a* from 0 to 10
b* from 0 to 10 wherein L* is the brightness and a* and b* are the colour-opponent dimensions. As mentioned above, to achieve the intended objects it is necessary that the molar ratio Si0 2 : Al 2 O 3 be between 2.555 : 0.4784 and 2.760 : 0.4497.
The value of the Ionic Potential of the glaze composition according to the present invention is preferably between 32.7 and 35.4.
The bases/ acids ratio value according to Lengersdorff of the glaze composition according to the present invention is preferably between 36.8 and 34.8.
The theoretical melting temperature of the glaze composition according to the present invention is preferably between 1,213°C and 1,233°C.
A further requirement to be met in order to obtain glazes suitable to obtain the desired results is the particle size, which must be d(0.1) 0.9-1 microns d(0.5) 7.5-8.5 microns d(0.9) 26-27 microns, preferably less than 40 microns.
By using a glaze composition according to the present invention it is possible to confer on a ceramic article treated therewith exceptional properties, as follows:
SCRATCH resistance defined according to standard UNI4543, point 4.6: the abrasion resistance test showed a weight loss of the sample ceramic article, glazed according to the present invention, of 0.18 g, a much lower value compared to the average weight loss for common glazed ceramic articles, which is 0.25 g;
ABRASION resistance defined according to standard, UNI4543 point 4.6: the abrasion resistance test showed a weight loss of the sample ceramic article, glazed according to the present invention, of 0.18 g, a much lower value compared to the average weight loss for common glazed ceramic articles, which is 0.25 g;
STAIN resistance defined according to standard UNI4543, points 4.1 and 4.4: the test for resistance to acid attack and stains on the sample ceramic article glazed according to the present invention, has proven that there has been no loss of glossiness and that all the staining agents can be removed with water with the exception of Potassium Permanganate, which was removed through the use of acidic cleaning agents; and
SLIP resistance defined according to standard DIN51097.1992: by means of an instrument for measuring the critical degree of inclination, or slip meter, it was possible to determine the slipperiness of a sample walkable ceramic article, specifically a shower base, glazed according to the present invention; more specifically, the test consists of having a person walk barefoot, forwards and backwards, on the test sample, while the gradient is increased by about 1 degree per second; the gradient angle at which the person is no longer in conditions of safety, is defined as the slip angle. The surface is continuously wetted with a solution (1 g/1 of a wetting agent + water). The average slip angle of the ceramic article glazed according to the present invention is 19.2° [B rating: (A+B)]. It is well known that in order to obtain a suitable anti-slip effect on a ceramic article glazed with common products and then fired, decals or grits are applied that, with a second firing at low temperatures, between 800°C and 1050°C, do not guarantee resistance of their application to the article. On a walkable ceramic article glazed according to the present invention, elevated anti-slip properties are obtained through a single firing at high temperatures. The above will be shown in the examples provided hereunder.
Example V. composition of white glaze
To obtain a white glaze, an example of a composition according to the present invention comprises:
- Frits 48.00 % by weight, Mullites 15.00 % by weight,
Magnesium Aluminate 5.00 % by weight,
Zirconium Silico Aluminate 7.00 % by weight,
Quartz 15.00 % by weight,
Potassium/ Sodium Feldspar 3.00 % by weight,
Zirconium Silicate 7.00 % by weight.
Example 2: composition of coloured glaze
To obtain a coloured glaze, an example of a composition according to the present invention comprises:
Frits 48.00 % by weight,
Mullites 10.04 % by weight,
Magnesium Aluminate 5.33 % by weight,
Zirconium Silico Aluminate 6.67 % by weight,
quartz 20.33 % by weight,
potassium Feldspar 3.00 % by weight,
Iron Chrome Cobalt Spinel 3.08 % by weight,
Iron Chrome Manganese Spinel 2.80 % by weight,
Silica Zirconium Praseodymium 0.76 % by weight
By using a glaze composition according to Example 1 it is possible to confer on a ceramic article treated therewith the following properties:
Test Standard RESULT Standard RESULT
UNI 4543,
io visible loss of glossiness
POINT 4.1
no visible loss of glossiness or permanent stains; all staining, agents are removed with water
UNI 4543,
with the exception of potassium POINT 4.4 \permanganate, which was removed
.through the use of acidic cleaning agents
UNI 4543/2,
Average weight loss: 0.18 g
POINT 4.6 DIN 51097: 1992 Average slip angle: 19.2° rating: B
i
HARKORT TEST SEE TABLE HEREUNDER
Table showing the results of the thermal shock resistance tests:
Another and different aspect of the present invention relates to a method of glazing a ceramic article, which comprises the following steps:
- preparing a ceramic article;
- p) eparing a composition of white or coloured glaze as described above;
- mixing an amount of said glaze composition varying between 100 kg and 15,000 kg with an amount of water equal to 45% of the weight of said amount of glaze composition in a grinding mill of the conventional type coated in high-alumina, at a speed of 15-18 revolutions/ minute, at a temperature of 20-25°C and for a period of time of 240-300 minutes, to obtain a homogeneous mixture and a specific granulometric curve that, as mentioned above, must be d(0.1) 0.9-1 microns d(0.5) 7.5-8.5 microns d(0.9) 26-27 microns, preferably less than 40 microns;
- adding appropriate adhesives to the homogeneous mixture obtained, thereby obtaining a glaze to be applied on the surface of said ceramic article;
- applying the glaze on the ceramic article by spraying with a density not exceeding 1.680 g/1, so as to obtain a uniform layer from 2,500 to 3,000 g/ m 2 of said glaze;
- letting the glazed ceramic article dry for at least 24 hours;
- placing the ceramic article in a runnel and/ or static kiln, in a cycle of 16-22 hours at a maximum temperature of 1,250°C, with a permanence at a temperature of 1,250°C of 40-120 minutes;
- letting the article cool at room temperature until curing of the applied glaze is complete.
According to a preferred embodiment of the present invention, the above method of glazing a ceramic article, provides
preparing a glaze composition formulated with 48.00% by weight of Frits, 15.00% by weight of Mullites, 5.00% by weight of Magnesium Aluminate, 7.00% by weight of Zirconium Silico Aluminate, 15.00% by weight of Silicas, 3.00% by weight of Feldspars, and 5% by weight of Inorganic Colorants; and - mixing an amount equal to 2,000 kg of said glaze composition with an amount of water equal to 45% of the weight of said amount of glaze composition in a grinding mill of the conventional type coated in high-alumina, at a speed of 15-18 revolutions/minute, at a temperature of 20-25°C and for a period of time of 240-300 minutes, to obtain a homogeneous mixture and a specific granulometric curve characterized by sizes between 0.02 and 2,000 microns. To achieve the desired granulometric characteristics, the grinding bodies of the mill must all be of the same size and preferably of 40 mm in a mill with a 2,000 mm diameter.
The adhesives added to the homogeneous mixture obtained can be, for example, CMC Carboxyl Methyl Cellulose with a low sodium content; said adhesives are added to the homogeneous mixture obtained in an amount equal to 0.1% - 0.5%.
The ceramic articles that can be glazed according to the above method of glazing may be wash-basins and sanitary fittings, shower bases, worktops, kitchen tops, kitchen sinks, hospital equipment, and the like, on substrates in Vitreous China, Fire Clay, Fine Gres, Klinker, porcelain and/ or mixtures of same, as well as other types of substrates that can be used to make single-fired articles.
As already stated, with the above method of glazing, which provides for the application and a single firing of the substrate and the glaze, the extraordinary properties conferred on the glazed ceramic material are stable and irreversible.
Another and different aspect of the present invention relates to glazed ceramic articles, in respect of which it is considered useful to specify that said ceramic articles are raw glazed with the glaze according to the present invention, and that said ceramic articles and said glaze are fired simultaneously at high temperatures, preferably at about 1,250°C, thus resulting in a single casting of the glaze on the ceramic article, called single firing.
Always with regard to the glazed ceramic articles according to the present invention we wish to point out that their main property, which lies, as mentioned above, in their resistance to abrasion and wear, determines their opacity with an exceptional flatness.
The use of aggregates and Frits according to the present invention, which add the "righ " amount of AI2O3, S1O2 and alkalis to the glaze composition, allows the achieving of a total melting of the components of the glaze, incorporating crystals of calcined Mullite at a very high temperature, without leaving rough, un-flat or unsightly surfaces.
In conclusion, therefore, the glaze composition according to the present invention and its application on ceramic articles provides end products distinguished by an excellent evenness of the glaze, which enhances the beauty of the ceramic surface and allows it to withstand abrasion, scratching, wear and attack by any chemical agent.
Naturally, variations of the glaze composition for treating ceramics according to the present invention and the corresponding method of glazing are possible, for example through use of commercial products or devices different from those mentioned here, without this affecting the composition technical specifications and the firing cycle parameters and the established application rules to ensure the optimum performance of the glazed ceramics as defined above.
It is intended that what is described above has been described by way of non- limiting example, so any possible variant is deemed to fall within the scope of the present technical solution, as described above and claimed hereinafter.