Frit for ceramic glaze, glaze and tile thus produced, and method of manufacturing tiles

Abstract

The present invention relates to a frit for tile glaze, characterised in that it comprises, in mass percentage, with respect to the total mass of the frit: 11.5- 20.5 Al2O3; 7.0-10.0 CaO; 0.5-3.5 MgO; 55.5-63.0 SiO2; 1.0-5.5 ZnO and SrO in a proportion comprised between 1.0-9.0, to a glaze for tiles and to a tile comprising the glaze defined above. The invention also relates to a method of manufacturing a glaze-coated tile in which the application of liquid enamel derived from the defined frit is carried out in two steps: - a first veil application of the liquid enamel composition at high density on an unprocessed ceramic substrate, - a second veil application of the liquid enamel composition or an application using the airless technique at low density, obtaining a glaze-coated precursor tile piece which gives rise to a glaze-coated tile by firing and processing the previous precursor piece.

Description

[0001] DESCRIPTION

[0002] Frit for ceramic glazing, glaze and tile thus produced, and process for manufacturing tiles

[0003] TECHNICAL SECTOR

[0004] The present invention relates to a frit that produces a ceramic glaze, the final tile coated with said glaze, and a tile manufacturing process. It allows for the creation of a glaze with greater scratch resistance. It is a new family of polished, transparent glazes for porcelain stoneware tiles made from wet-applied enamels, with mechanical and aesthetic performance unattainable with current enamel compositions.

[0005] STATE OF THE ART

[0006] Glazed tile finishes are known in the prior art. These glazes have a smooth, silky matte texture, thus satisfying market demands, as this type of surface finish is one of the most sought-after today. However, currently available polished matte transparent glazes have low scratch resistance and low abrasion resistance. These technical shortcomings limit their use in products that will be exposed to high traffic.

[0007] Although there are currently polished, transparent matte glazes available for porcelain stoneware, they lack the combination of aesthetic and technical properties that the market demands, specifically: high resistance to scratching and abrasion, zero dirt retention, transparency, and a silky matte texture with high stretch. The term "high stretch" refers to a final surface that is completely uniform and smooth, without any roughness or irregularities.

[0008] Frits, compositions of sand and soda ash used in glassmaking, and employed in current transparent matte glaze compositions are based on high-Al₂O₃ systems of the AhCh-BaO (with or without ZnO) and AhCh-CaO-MgO (with or without ZnO) types. See the article by Partyka J.; Lesniak M.; Preparation of glass-ceramic glazes in the SiO₂-Al₂O₃-CaO-MgO-K₂O-Na₂O-ZnO system by variable content of ZnO., Ceramics International (2016), http: / / dx.doi.org / 10.1016 / j.ceramint.2016.02.077i; It refers to a glass-ceramic glaze, suitable for coating ceramic materials, prepared from a frit with a composition, in weight percentage, of SiO₂ / Al₂O₃ 6.06 for all cases, an example of a frit being: SiO₂ / Al₂O₃ 6.06, K₂O 2.41; Na₂O 2.46; CaO 8.14; MgO 5.60 and ZnO 3.74. However, these frits do not contain strontium oxide and the purpose of the study is only to analyze different contents of Zn oxide, highlighting its decorative capacity.Therefore, it cannot be deduced from the article that a tile coated with a glaze prepared with that frit achieves the objectives of the present invention, of greater resistance to scratching, soiling and abrasion.

[0009] The article by Lesniak M; Jastrzebski W.; Gajek M.; Partyka J.; Dorosz D.; Sitarz M., The structure of model glasses of the amorphous phase of glass-ceramic glazes from the SiO2-Al2O3-CaO-MgO-Nd2O-K2O-ZnO system, Journal of Non-Crystalline Solids 515 (2019) 125-132, discloses a glass-ceramic glaze, suitable for coating ceramic materials, prepared from a frit of composition, in weight percentage, as an example, SiO275.11; Al2O312.10; K2O 3.42; Na2O 1.68; CaO 3.52; MgO 1.42; ZnO 2.50. In this article the cited system is different from that of the present invention, since at least it is distinguished in that it does not comprise SrO, and it is not deduced that a tile coated with a glaze prepared with that frit, achieves the objectives of the present invention of greater resistance to scratching, soiling and abrasion.

[0010] The document Non-isothermal crystallization kinetics of transparent glass-ceramic phosphors containing calcium magnesium aluminosilicate nanocrystals; J. Nanosci. Nanotechnol. 18, 6195-6200, 2018, describes a glass-ceramic enamel, prepared from a frit of composition, in mol percent 20CaO-15MgO-50SiO2-10Al2O3-5ZnO, which is doped with 0.5Eu 3+ / 0.1Sm 3+ , and which is expected to be used in the optical industry.

[0011] The crystalline phases devitrified from these conventional frits during heat treatment are primarily alkaline earth silicoaluminates, zinc silicates, and quartz allotropic phases, with crystal sizes on the order of 5 pm. The number and dimensions of these phases determine the technical and aesthetic performance of the final glaze. As with any crystallization process, devitrification from frits is affected by the heating and cooling rates of the thermal cycle to which they are subjected—in this case, the industrial firing cycle of the tiles they cover. In practice, the cooling stage of this cycle is poorly regulated, making it impossible to control the actual rate at which it occurs.This causes crystal formation to occur without any control, meaning that a given frit composition can devitrify a greater or lesser number of crystals, or crystals of varying sizes, in the same firing kiln. This effect is accentuated when different kilns are used, even if the thermal cycles are theoretically the same.

[0012] In current techniques, protective enamel is applied in three different ways: using a spray gun, a filler gun, or a low-pressure airless spray booth. With the spray gun, a curtain of enamel is formed and passed through the workpiece. Similarly, with the filler gun, a curtain of enamel is formed and passed through the workpiece. Both the spray gun and filler gun methods result in a higher density of enamel. Finally, with the low-pressure airless spray, the enamel is applied at a low density and sprayed onto the workpiece through nozzles.

[0013] The state-of-the-art tile manufacturing process consists of the following steps: i) Pressing the porcelain stoneware support (base on which all applications are made) to obtain raw pieces from an atomized composition.

[0014] i) Drying the porcelain stoneware substrate in a drying kiln to remove moisture from the pieces. iii) Application of the engobe / base, usually by spray gun and at high density, to cover the substrate and prevent degassing problems. iv) Application of digital decoration using digital decoration machines, if a neutral piece is not desired. v) Application of glaze, which can be done by spray gun, line gun, or airless spray booth, at low density (1.25-1.35 g / cm²). 3 ). vi) Firing and the rest of the tile processing.

[0015] The piece thus constructed is then treated in a kiln for the production of the tile.

[0016] According to the present invention, step v) of the procedure is divided into two steps: v1) first application of the enamel composition to a high-density nozzle; v2) second application of the enamel composition using the selected technique, either airless or nozzle. This double application, performed in steps v1) and v2), creates a double layer that reacts to give the final piece the desired mechanical properties.

[0017] In this technology, a density between 1.45-1.55g / cm³ is called "high density". 3 This distinguishes it from the "low density" application, which refers to a density between 1.15-1.25g / cc, and which is required by a type of machinery such as airless application with nozzles.

[0018] In the case of transparent matte glazes, it is necessary that the refractive indices of the crystalline phases present and the vitreous phase in which they are dispersed be very similar, so that the incident light is not deflected upon striking them, resulting in a diffuse reflection (opalescence / opacity), but rather passes through them without deviation, allowing the surface covered by the glaze to be seen. The difference in the refractive indices of the crystalline phases present and the vitreous phase should not exceed 2%.

[0019] To solve the prior art problems outlined above, it is necessary to design enamel compositions that produce transparent, matte glass-glass glazes through the devitrification of crystalline phases during industrial firing cycles, starting from the vitreous fraction (derived from the frits), with the following characteristics: a refractive index similar to that of the residual vitreous phase present in the glaze, and high microhardness and fracture toughness. Furthermore, the combination of residual vitreous phase and crystalline phases (number, size, and distribution) must not be subject to internal stresses that could be released as breakage when the glaze is subjected to any external mechanical action (impact, cutting, etc.).

[0020] The present invention provides a polished transparent glaze for porcelain stoneware tiles from wet-applied glazes, i.e., by the double application of a liquid glaze composition with granules.

[0021] DESCRIPTION OF THE INVENTION

[0022] In this document, the term “glazed” refers to the enamel already integrated into the tile, that is, the layer that covers the tile, and “glaze” refers to the material applied to the porcelain stoneware substrate, which will create the glaze that covers the tile. In this document, when “percentage” is mentioned, even if the symbol does not appear, it should be understood that the numerical value is followed by “%”, for example: “percentages by mass: Al₂O₃ 1.5-20.5; CaO 7.0-10.0; MgO 0.5-3.5; SiO₂ 5.5-63.0; ZnO 1.0-5.5; and SrO” is equivalent to: Al₂O₃ 1.5-20.5%; CaO 7.0-10.0%; MgO 0.5-3.5%; SiO₂ 5.5-63.0%; ZnO 1,0-5.5%, and SrO 1, 0-9.0%”.

[0023] The present invention relates, firstly, to a frit for glazing tiles, characterized in that it comprises, in percentage by mass, with respect to the total mass of the frit: Al2O311 ,5-20.5; CaO 7.0-10.0; MgO 0.5-3.5; SiO255.5-63.0; ZnO 1.0-5.5, and SrO in a proportion between 1.0-9.0 with respect to the total mass of the frit.

[0024] All percentages indicated, unless explicitly stated otherwise, are percentages by mass relative to the total mass of the fried food.

[0025] According to additional particular embodiments, the frit for tile glazing comprises, in percentage by mass with respect to the total mass of the frit, also K2O, in a proportion between 1.0-7.5%.

[0026] According to additional particular embodiments, the frit for tile glazing comprises, in percentage by mass, with respect to the total mass of the frit: Al2O3 11.5-20.5; BaO 0-1.5; B2O3<0.5; CaO 7.0-10.0; SrO 1.0-9.0; P2O5<0.5; Fe2O3<0.5; Li2O <0.5; MgO 0.5-3.5; PbO <0.5; K2O 1.0-7.5; SiO2 5.5-63.0; Na2O 1.0-3.5; TiO2<0.5; ZnO 1.0-5.5 and ZrO2<1.0.

[0027] According to additional particular embodiments, the frit for tile glazing comprises, as a percentage by mass relative to the total mass of the frit: Al2O3 11.5 - 13.5; BaO <0.5; B2O3<0.5; CaO 8.0 - 10.0; SrO 1.0 - 2.0; P2O5<0.5; Fe2O3<0.5; Li2O <0.5; MgO 0.5 - 1.5; PbO <0.5; K2O 6.5 - 7.5; SiO2 61.0 - 63.0; Na2O 1.0 - 2.0; TiO2<0.5; ZnO 3.5 - 5.5 and ZrO2<0.5.

[0028] According to additional particular embodiments, the frit for tile glazing comprises, as a percentage by mass relative to the total mass of the frit: Al2O3 16.0 - 18.0; BaO <0.5; B2O3 <0.5; CaO 8.0 - 10.0; SrO 7.0 - 9.0; P2O5 <0.5; Fe2O3 <0.5; Li2O <0.5; MgO 2.5 - 3.5; PbO <0.5; K2O 1.0 - 2.0; SiO2 55.5 - 57.5; Na2O 1.0 - 2.0; TiO2 <0.5; ZnO 2.0 - 4.0 and ZrO2 <1.0.

[0029] According to additional particular embodiments, the frit for tile glazing comprises, as a percentage by mass relative to the total mass of the frit: Al2O3 18.5 - 20.5; BaO 0.5 - 1.5; B2O3 < 0.5; CaO 7.0 - 9.0; SrO 3.0 - 5.0; P2O5 < 0.5; Fe2O3 < 0.5; Li2O < 0.5; MgO 1.5 - 2.5; PbO < 0.5; K2O 4.0 - 5.0; SiO2 56.5 - 58.5; Na2O 2.5 - 3.5; TiO2 < 0.5; ZnO 1.0 - 2.0; ZrO2 < 1.0.

[0030] These frit compositions result in matte, transparent, polished, non-porous glass-crystalline glazes (for porcelain stoneware, the pore size should be less than 50 microns, and preferably there should be no pores at all) with microstructures that provide the necessary mechanical properties without compromising the chemical and staining resistance required for reliable use as a coating for porcelain stoneware tiles. Furthermore, they possess the appropriate thermal expansion to ensure proper bonding to the slip and substrate on which they will be deposited.

[0031] The grinding and sieving of the developed frits results in granules. Granules and granite are terms used interchangeably in this document.

[0032] The frits are transformed into granules / granules to be one of the components of a liquid enamel composition that is transformed into the glaze that covers the glazed tile of the invention.

[0033] The present invention also relates to a transparent, matte, glass-crystalline glaze comprising a frit as defined above.

[0034] The present invention also relates to a matte, transparent, glass-crystalline glaze obtained from a frit as defined above. The glaze is the final layer that covers the surface of the tile.

[0035] The present invention also relates to a tile comprising the glaze defined above.

[0036] The present invention also relates to a manufacturing process for a glazed tile comprising: a) obtaining a frit as defined above, b) grinding and sieving the frit obtained, obtaining granules, c) preparing a liquid glaze composition comprising the granules obtained in the previous step and water, d) carrying out a first filleting application onto a raw ceramic support of a liquid glaze composition obtained, at high density, f) carrying out a second filleting application of a liquid glaze composition, at high density, or an application by means of the “airless” technique at low density, obtaining a precursor piece of a glazed tile, and g) firing and processing the previous precursor piece, obtaining a glazed tile.

[0037] In addition to the granules and the glaze, the liquid glaze composition comprises water and, optionally, additives.

[0038] These additives are conventional additives normally used in this technology, suitable for keeping the granules in suspension, suitable for achieving a good and homogeneous application, and which do not cause porosity problems after the piece is baked.

[0039] Examples of additives may include one or more dispersing agents, binding agents, thickening agents, anti-sedimentation agents, leveling agents, wetting agents, crosslinking agents, anti-foaming agents, coalescing agents, or mixtures thereof.

[0040] The composition of the liquid enamels obtained in step c) according to the invention is as follows:

[0041] - Granites (produced from the new frit / s developed): 45-50%

[0042] - Water: 40-50%

[0043] - Additives: 0-5%.

[0044] According to specific realizations, in stage c) the enamel composition obtained comprises, with respect to the total mass of the composition:

[0045] - grains produced from the frit: 45-50%

[0046] - water: 40-50%

[0047] - Additives: 0-5%.

[0048] According to specific embodiments, once the granules are available, the liquid glaze composition is prepared (step c)) comprising: glaze, granules, water, and optionally, additives. According to specific embodiments, first, granules / granite are produced from the developed frit by grinding the frit (step b), for example, in mills that break the frit to a specific size or granulometry (125-80 microns) or even (125-0 microns) to obtain the desired final granules. Optionally, this involves a deferrization process to ensure the absence of tamper-evident particles, thus achieving a specific granulometry. Once the granules are available, the liquid glaze composition is prepared (step c)) comprising glaze, granules, water, and optionally, additives.

[0049] To obtain the liquid enamel (step c)), according to specific procedures, each of the enamel components is added in a specific order to allow them to homogenize over a predetermined time, depending on the mixture being prepared, until a homogeneous mixture with the appropriate density and viscosity parameters is obtained. Before the material is discharged from the facility, the mixture is sieved to prevent lumps and ensure that it is completely homogeneous.

[0050] The appropriate density and viscosity will be the values ​​of these parameters that are usual in the technique, and that allow the subsequent application of the liquid enamel according to the defined stages d) and f).

[0051] For example, for the application of an enamel using the filera technique, the viscosity can be between 30 and 40 seconds measured in a 4 m Ford Cup.

[0052] Glazes are prepared with the frits defined according to the invention, for the first and second application on the ceramic support, since the combination of glazes also provides the final properties sought.

[0053] The glazes used in each of these applications corresponding to stages d) and f) - first application and second application - comprise a mixture of the developed frit, transformed into granite of the required granulometry and additives.

[0054] The enamels for the first and second coats can be the same or different. Both contain the components listed above, and these components can be in the proportions indicated above. If they differ in composition, the enamels for the first and second coats can be in various ratios to each other. For example, they can be in any weight ratio between 1:99 and 99:1, such as 50:50, 40:60, 30:70, 20:80, or 10:90.

[0055] The first stage of applying the enamel composition to the filler according to the procedure of the invention is carried out by applying the composition at a density between 1.45-1.55 g / cm 3 , called “high density”:

[0056] The second stage of applying the enamel composition can be done by applying the composition in a thin stream at a density between 1.45-1.55g / cm 3 , or by the “airless” technique at a density between 1.15-1.25g / cc.

[0057] The pipe application is more convenient than the bell application because it has more parameters to control the material's flow, such as pressure and opening, while the bell application depends more on gravity.

[0058] Firing is the stage in which the precursor piece of the glazed tile, that is, the ceramic support with the liquid enamel composition, applied twice beforehand, after being dried, is subjected to a specific heating cycle at a certain temperature and time, to obtain the final ceramic tile.

[0059] Cooking times will depend on the specific requirements of the final product. For example, cooking cycles can range from 50 to 70 minutes with maximum cooking temperatures between 1180 and 1220°C. It is also important to note that regulating the cooling stage (making it faster) can promote greater scratch resistance.

[0060] After firing, the operation called “processing” refers to a process of polishing the ceramic tile to obtain a polished tile.

[0061] One of the innovations of the procedure lies in the double wet application of the enamel compositions. The expression "wet" refers to the double application of the enamel composition.

[0062] The invention achieves specific microstructures to attain this combination of technical and aesthetic properties, for which it is essential to be able to accurately measure the mechanical properties of the glazed surfaces. Since this is not possible using conventional methods, it is necessary to resort to other tests to understand the true behavior of the glazes under mechanical stress. This allows for their design according to rigorous technical criteria and enables the evaluation of the relationship between their composition, nature, and microstructure, and their mechanical performance under typical usage conditions. Different measurement methods have been studied to obtain values ​​that allow us to determine scratch resistance. Of all the methods tested, the dynamic indentation method, following the test procedure of standard EN1071-3:2005, has been considered the most suitable.

[0063] Obtaining enamel compositions according to the present invention results in transparent matte glass-glass glazes with scratch and abrasion resistance similar to that of so-called "technical" porcelain stoneware and, therefore, far superior to that of currently available transparent matte glazes. Furthermore, the developed procedure for applying the final product allows for achieving the aforementioned technical properties: scratch resistance similar to polished / unpolished porcelain, high chemical resistance, and low porosity.

[0064] As an example, a series of wet-applied glaze compositions (granules / granules) have been formulated (granules being another term for granite or granules). These compositions result in polished, transparent, matte, non-porous, glass-glass glazes with microstructures that provide the appropriate mechanical properties without compromising the chemical and soiling resistance required for reliable use as a coating for porcelain stoneware tiles.

[0065] According to the present invention, a homogeneous material is obtained with large quartz particles and other crystals such as mullite embedded in a glassy matrix. These crystals impart hardness to the glaze and reduce scratch propagation and narrow the scratch widths.

[0066] Brief description of the figures

[0067] Figure 1 shows micrographs of the following materials: 1a) marble lb) granite lc) polished technical porcelain ld) polished technical porcelain (II) le) matte enamel lf) gloss enamel lg) P1T2 (1205°C-60') (piece according to the invention, test 1, T2 in table 1)

[0068] Figure 2 shows the scratch patterns obtained during the scratch test for the samples:

[0069] Figure 2a): TEST 2 T1 ,

[0070] Figure 2b): 2T2 TEST,

[0071] Figure 2c): TEST 2 T3,

[0072] Figure 2d): TEST 2 T4,

[0073] Figure 2e): TEST 2 T5,

[0074] Figure 2f): TEST 2 T6 and

[0075] Figure 2g): TEST 2 T7:

[0076] MODES OF REALIZING THE INVENTION

[0077] The prepared specific enamel compositions, called ML, comprising the frits according to the invention, broken like granite by grinding and sieving to obtain granites with a granulometry between 125 and 0 microns, and specific additives for wet application with specific characteristics.

[0078] The following describes various ways of carrying out the invention, as an illustrative and non-limiting example thereof.

[0079] The frits were prepared following standard procedures. The frit was formulated with oxides according to the examples and melted in a laboratory setting to obtain the frit. This frit was then broken into a granular material.

[0080] The fries corresponding to “examples 1, 2 and 3” were prepared with the composition shown in table 1:

[0081] These proportions have been developed as optimal for the purpose of providing the desired crystallization conditions and good surface appearance in the Zn-Al-Ca-Mg gloss glaze system.

[0082] As can be seen in Table 1 above, the newly created microstructures correspond to Zn-Al-Ca-Mg-Sr systems, with the contribution of other oxides. However, Zn-Al-Ca-Mg-Sr are the major oxides, apart from silica, and are key to achieving the ultimate goal of high scratch resistance.

[0083] With the new formulations, granites were obtained through a milling and sieving process with a specific granulometry between 125 and 80 microns.

[0084] The procedure to obtain the granules consisted of grinding each of the frits using mills and then sieving them to obtain the necessary granulometry (125-80 mieras or 125-0 mieras).

[0085] After milling and sieving, a deferrization process was carried out to ensure the absence of tamper-evident particles. Glazes were then prepared according to step c) defined and the given compositions for the component proportions. The frits from example 1 and example 2 in Table 1 above were used to obtain the glazes.

[0086] Obtaining glazes of the invention and tile scratching experiments

[0087] Samples obtained according to the invention, called “Test”!” and “Test2”, were used. The “Test”!” sample was prepared by applying an enamel made from the frit of Example 1 in Table 1, and then applying the frit material according to Example 2 in Table 1.

[0088] In the sample “Test2” the glaze was first used according to example 2 of frit in the table

[0089] 1, and then example 1.

[0090] As shown in Table 2, 3 cooking cycles were tested for test 1: the first two were one hour long (the first at 1200°C and the second at 1205°C), and the third cycle was 50 minutes long at 1200°C.

[0091] As shown in Table 2, a one-hour cooking cycle at 1195°C, a second 50-minute cooking cycle at 1200°C, and slow cooling were tested.

[0092] 2.

[0093] The remaining data in the "cooking condition" column are interpreted similarly for cooking tests.

[0094] Table 2 below shows the results of the scratch width and critical breaking load tests for two control samples and vapor tests of the glaze examples obtained from the frits in Table 1 above:

[0095] Table 2:

[0096] LC3 corresponds to the breaking load of the material when performing the scratch resistance test.

[0097] Of the samples listed in Table 2, those that best exceeded the critical breaking load value are samples: TEST2 T4, TEST2 T6, and TEST2 T7. Figure 2 shows the scratch patterns obtained during the scratch test for samples: TEST 2 T1, TEST 2 T2, TEST 2 T3, TEST 2 T4, TEST 2 T5, TEST 2 T6, and TEST 2 T7.

[0098] Comparative scratching and abrasion tests

[0099] Comparative scratching and abrasion tests were also carried out with the materials prepared in TEST 1 and TEST 2, considering as reference materials two porcelain samples, one polished and the other unpolished, whose scratch width and critical breaking load values ​​are indicated below in Table 3:

[0100] Table 3 Critical breaking load values ​​Lc(3)N and line amplitude (m) of the reference samples And they were compared with the following glazes defined as TEST 1 and TEST 2, according to the invention, to obtain the required scratch and abrasion technical properties, table 4:

[0101] Table 4: Glazing according to the invention

[0102] On one hand, a background called HT80-55865 was developed that allows for good chromatic development and good coupling with the support.

[0103] Tests were carried out with the samples called TEST1 and TEST2 applying the background and the successive layers 1 a and 2 a according to Table 4 shown.

[0104] The first layer of enamel was 10 g over a surface of 10x20 cm.

[0105] The second layer of glaze was 10 g over a surface of 10x20 cm

[0106] Comparative results of tiles analyzed with state-of-the-art materials

[0107] Samples supplied by Esmalglass were analyzed.

[0108] Images of stripes were obtained from different pieces made with the frits and glazes of the invention, and were compared with images of these materials, such as marble, granite, and enamel.

[0109] Figure 1 shows photographs of the following materials: a) marble lb) granite lc) polished technical porcelain ld) polished technical porcelain (II) le) matte enamel lf) gloss enamel lg) P1T2 (1205°C-60') (piece according to the invention, test 1, T2 in table 1)

[0110] To obtain data from the sample called “Granite”, an additional scratch test was performed.

[0111] Table 5 shows the properties of the materials analyzed.

[0112] LC3 corresponds to the breaking load of the material when performing the scratch resistance test.

Claims

CLAIMS 1. Frit for glazing tiles, characterized in that it comprises, in mass percentage, Al2O3 11.5-20.5; CaO 7.0-10.0; MgO 0.5-3.5; SiO2 5.5-63.0; ZnO 1.0-5.5 and SrO in a proportion between 1.0-9.0, with respect to the total mass of the frit.

2. Frit for glazing tiles, according to claim 1, characterized in that it further comprises, by mass percentage, K2O, in a proportion between 1.0-7.5 with respect to the total mass of the frit.

3. Frit for tile glazing, according to claim 1, characterized in that it comprises, as a percentage by mass relative to the total mass of the frit: Al₂O₃ 1.5-20.5; BaO 0-1.5; B₂O₃ <0.5; CaO 7.0-10.0; SrO 1.0-9.0; P₂O₅ <0.5; Fe₂O₃ <0.5; Li₂O <0.5; MgO 0.5-3.5; PbO <0.5; K₂O 1.0-7.5; SiO₂ 5.5-63.0; Na₂O 1.0-3.5; TiO₂ <0.5; ZnO 1.0-5.5 and ZrO₂ <1.0 4 Frit for tile glazing, according to claim 1, characterized in that it comprises, as a percentage by mass with respect to the total mass of the frit: Al2O3 11.5 - 13.5; BaO <0.5; B2O3<0.5; CaO 8.0 - 10.0; SrO 1.0 - 2.0; P2O5<0.5; Fe2O3<0.5; Li2O <0.5; MgO 0.5 - 1.5; PbO <0.5; K2O 6.5 - 7.5; SiO2 61.0 - 63.0; Na2O 1.0 - 2.0; TiO2<0.5; ZnO 3.5 - 5.5 and ZrO2<0.

5. 5 Frit for tile glazing, according to claim 1, characterized in that it comprises, as a percentage by mass with respect to the total mass of the frit: Al2O3 16.0 - 18.0; BaO <0.5; B2O3 <0.5; CaO 8.0 - 10.0; SrO 7.0 - 9.0; P2O5 <0.5; Fe2O3 <0.5; Li2O <0.5; MgO 2.5 - 3.5; PbO <0.5; K2O 1.0 - 2.0; SiO2 55.5 - 57.5; Na2O 1.0 - 2.0; TiO2 <0.5; ZnO 2.0 - 4.0 and ZrO2 <1.

0.

6. Frit for tile glazing, according to claim 1, characterized in that it comprises, as a percentage by mass with respect to the total mass of the frit: Al2O3 18.5 - 20.5; BaO 0.5 - 1.5; B2O3 < 0.5; CaO 7.0 - 9.0; SrO 3.0 - 5.0; P2O5 < 0.5; Fe2O3 < 0.5; Li2O < 0.5; MgO 1.5 - 2.5; PbO < 0.5; K2O 4.0 - 5.0; SiO2 56.5 - 58.5; Na2O 2.5 - 3.5; TiO2 < 0.5; ZnO 1.0 - 2.0; ZrO2 < 1.

0.

7. Tile glaze, comprising a frit defined in one of the claims 8. A tile comprising the glaze defined above in claim 7.

9. A method for manufacturing a glazed tile comprising: a) obtaining a frit as defined in one of the preceding claims, b) grinding and sieving the frit obtained, obtaining granules, c) preparing a liquid glaze composition comprising the granules obtained in the previous step and water, d) carrying out a first filleting application onto a raw ceramic support of a liquid glaze composition obtained in step c), at high density, f) carrying out a second filleting application of a liquid glaze composition obtained in step c), at high density, or an application by means of the “airless” technique at low density, obtaining a precursor piece of a glazed tile, and g) firing and processing the previous precursor piece, obtaining a glazed tile.

10. The process according to claim 9, wherein in step c) the enamel composition obtained comprises, with respect to the total mass of the composition: - grains produced from the frit: 45-50% - water: 40-50% - Additives: 0-5%.

11. The process according to claim 9, wherein after step b) of grinding the frit to obtain granite, and before step c), a deferrization process is carried out to ensure the removal of tamper-evident particles.

12. The process according to claim 9 or 11, wherein the mixture prepared in step c) is sieved to avoid the presence of lumps and to ensure that it is homogeneous.

13. The process according to any one of claims 9 to 12, wherein one enamel is prepared for the first application of step d) and a different enamel is prepared for the second application of step f).

14. Tile characterized in that it has been produced by the process of one of claims 9 to 13.

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