NON-NEWTONIAN WATER COMPOSITION FOR OBTAINING CERAMIC GLAZES FOR HIGH-RESOLUTION DIGITAL APPLICATION

Description

P024065IT-01 Notarbartolo & Gervasi SpA “NON-NEWTONIAN WATER COMPOSITION FOR OBTAINING CERAMIC ENAMELS FOR HIGH-RESOLUTION DIGITAL APPLICATION” ***** ***** ***** FIELD OF INVENTION 5 The present invention relates to the sector of decoration of ceramic products through enamel printing with the achievement of a three-dimensional surface structure. The products and methods of the present invention are especially important in the production of tiles for use in construction; given the relevance of this application, reference will be made in the following text to it, but what has been described can also be applied to other types of ceramic artefacts. 10 STATE OF THE ART The introduction of digital inkjet printing technology as a method of decoration of ceramic tiles has allowed an evolution of the typology of products on the market, leading to a series of management, processing and product advantages. previous technologies (roller decoration, screen printing, ...) in fact had problems, for 15 example, low resolution of the design transferred onto the support or imperfections of the same due to the fact that the printing support is often not perfectly flat. To overcome these problems, in the last 2-3 decades, technologies have been introduced digital printing, in which the decoration of the ceramic support is obtained through the emission, by a microprocessor-controlled print head, of droplets of a 20 suspension containing the precursors of the decoration material. These digital systems for the decoration are based on high resolution DOD (Drop on Demand) technology (higher of 220 dpi) in which print heads are used that generate droplets of tens of picoliters at a frequency which, depending on the print head manufacturer, varies between 5-30 KHz; The best-known manufacturers of these types of printheads are, among others, Dimatix (Fujifilm), Xaar, 25 Seiko, K&M, Ricoh and Durst. With these techniques, decoration typically occurs using materials, mainly pigments, which have a granulometry D < 1.2 µm (i.e. a distribution granulometry such that all particles have a maximum size smaller than this value) P024065IT-01 Notarbartolo & Gervasi SpA and which can be sprayed with 50 micron nozzles up to a maximum weight of 25-30 g / m . There are numerous patent documents relating to digital enamels suitable for use with DOD technology; see for example US patent application 2015 / 291841 A1 relating to 5 for glazing ceramic tiles requiring a relatively low amount of glaze and a high resolution, to obtain the required aesthetic effects both in the pre- and post- phase decoration. When, due to the aesthetic and technical characteristics of ceramic tiles, it is it is necessary to apply a greater amount of enamel than that allowed by DOD technology 10 high resolution, it is necessary to use other techniques, among which the technique of digital inkjet printing with solenoid valve systems or that described in the patent applications EP 1972450 A2 and EP 2085225 A2, which feature larger print nozzles than those of normal DOD printers to allow the passage of larger quantities of products with larger particle sizes. The droplet size generated by these systems is many tens of thousands. 15 nanoliters, the print head discharge frequency is in the order of 1 KHz and the resolution of approximately 50 dpi. Another development in the industry has been the shift from organic solvent-based products to water-based products with appropriate additives, in order to reduce the environmental impact and above all the emission of odorous substances during the tile firing process. An example of 20 such systems is the patent application WO 2020 / 065429 A1, which describes additives in capable of guaranteeing a low emissions profile into the environment. Finally, a recent development dictated mainly by market demands is that of have tiles with a surface that is not perfectly smooth, but which reproduces the appearance of stones natural unpolished or wood grain parquet; a ceramic surface of this type 25 type, which reproduces the appearance and also the three-dimensional structure of material surfaces natural, it is defined as textured. Even for the production of tiles with textured surfaces it is important, if not necessary, respect the requirements indicated above for flat tiles, i.e. in particular the P024065IT-01 Notarbartolo & Gervasi SpA possibility of creating precise and high resolution decorations and the use of multi-purpose products low environmental impact possible, and which do not release (or release in the smallest quantities) possible) odorous substances during the heat treatments used in the production processes. Currently known products and methods are not able to satisfy all these needs. 5 at the same time. In order to obtain a textured surface it would be necessary to start from a flat surface one possibility would be to apply large amounts of enamel, with much higher weights than techniques using high-speed DOD technology resolution, reaching values ​​exceeding one kilogram per square meter. These 10 grammages can be achieved for example with the systems described in the questions of patent EP 1972450 A2 and EP 2085225 A2, in which however suspension drops are formed large dimensions, in the order of tens of nanoliters, and do not allow the obtaining of high resolution decorations. US Patent 9765228 B2 describes digital inks / glazes for these types of 15 inkjet printing systems, which have a liquid medium that is based on a mixture of water and polar solvents and a solid part which is characterized by the use of agents anti-sedimentants normally used in the formulation of traditional enamels applied with non-digital methods, such as bell, disk, waterfall, etc. These anti-settling agents are generally clays (montmorillonites, bentonites, etc.) and kaolins, although they can be 20 also used carbon black or colloidal oxides and hydroxides. All of these are solids and do not dissolve in a liquid medium consisting of water and polar solvents. All of these, moreover, they interact mainly with the molecules of the solvents that make up the liquid medium, without having a direct interaction with the solid particles of the glaze. In the case of clays and like kaolins, these materials incorporate the solvent molecules into their laminar structure. -1 25 When the enamel is at rest or subjected to a low shear force (Y < 10 s) the incorporation of solvent molecules by the clay or kaolin causes the viscosity of the enamel increases significantly, thus achieving the anti-sedimentation effect. Conversely, when the enamel is subjected to a high shear force, the incorporated molecules P024065IT-01 Notarbartolo & Gervasi SpA are released by reducing the viscosity of the enamel. In the case of colloidal oxides, the effect anti-sedimentation is due to the fact that they create three-dimensional networks in which the particles remain trapped solvent molecules, causing an increase in viscosity when the enamel is at rest or subject to low shear forces and a reduction in viscosity as the shear force increases 5 cut. Enamels that exhibit this behavior are commonly called enamels thixotropic or non-Newtonian glazes. The enamels described in US 9765228 B2 are not easy to manage when you want to use them in digital inkjet to proceed with the glazing or decoration of ceramic supports. The viscosity of a thixotropic digital enamel at the time of injection is 10 greater than that required in the inkjet technique, the drop does not form immediately, and they are several pulses are needed until the injection begins, which causes the effect known as delay. This effect results in the absence of enamel in the first moments of printing, and since Using digital systems, you generally print patterns that do not cover the entire piece (images, geometric shapes, etc.), the printing process is continuously started and stopped, 15 therefore the final result is a defective print with numerous enamel gaps on the surface of the part, which leads to a printed part that does not meet the minimum quality criteria required by the ceramic industry. Furthermore, all inkjet printing techniques are very demanding in terms of stability of the digital enamels that are intended to be used, since in industrial systems 20 distribution and emission of the suspensions there are numerous ducts and passages of small section, small diameter orifices, three-dimensional filters, corners, etc. where the enamel It can become stuck if it is not stable enough, causing clogs and printing problems. An additional difficulty in obtaining digital texturing enamels perfectly stable is the use of particles with relatively large dimensions (D < 50 μm), 25 compared to D < 1.2 μm that characterize high-resolution DOD digital enamels. To overcome some of the previously described drawbacks, some studies have also been carried out. completely stable digital enamels without the use of anti-settling agents (enamels Newtonian) with an evaporation weight loss value of less than 5% and with P024065IT-01 Notarbartolo & Gervasi SpA grain size D < 50 μm for digital glazing systems designed to apply weights greater than 200 g / m ; an example of enamels of this type is described in the application of US patent 2015 / 0353415 A1. However, these systems do not allow for good texturing of the ceramic substrate. 5 In view of these difficulties, the systems currently used to obtain surfaces textured and decorated at high resolution include two-step processes, where in the first phase the starting ceramic surface is textured, either directly when it is still in workable plastic dough form, or subsequently through selective deposition on the surface, according to a design and often in several successive deposition steps, of materials, 10 generally glues or grits, which give rise to the texturing and on which the finishing is then carried out the decoration; examples of this second approach are described in patent applications CN 102503386 A, CN 115403410 A and WO 2011 / 107610 A1. However, these methods have the disadvantage of requiring a dedicated work phase, separate from the decoration one, for the creation of the textured surface, lengthening 15 production times; furthermore, in the case of using glues, these generate during the heat treatments for firing glazes produce large quantities of odorous organic vapors. The problem of making a system available for the production of textured and decorated ceramic surfaces that is free from the above problems indicated, that is, which allows for the creation of texturing and decoration of a ceramic surface 20 in a single production step, which does not generate problems of sedimentation or occlusion of ducts and orifices of printing machines, and which does not give rise to the generation of high quantity of odorous substances in the production site. SUMMARY OF THE INVENTION This and other objects are achieved with the present invention, which relates to a 25 non-Newtonian water composition for obtaining ceramic glazes for application high resolution digital, said composition comprising, by weight: - between 50 and 55% of a mixture of ceramic raw materials, including frits, clays including kaolinites and bentonites as suspending agents, sodium feldspar, quartz and P024065IT-01 Notarbartolo & Gervasi SpA optionally ceramic pigments; - between 15 and 20% of an additive comprising organic compounds and optionally bentonite in a solvent consisting of a mixture of water and ethylene glycols; - between 30 and 40% water; 5 - optionally, between 1 and 4% of a carboxymethylcellulose-based glue. BRIEF DESCRIPTION OF THE FIGURES Figures 1 to 4 reproduce photographs taken of tiles produced with the glazes of the invention. DETAILED DESCRIPTION OF THE INVENTION 10 The composition of the invention has non-Newtonian behavior, that is, it is such that the Its viscosity varies as a function of the applied shear stress. This allows for a product that has relatively low viscosity during the emission phase from the orifices or nozzles of the print heads, so as not to cause problems of clogging of these heads or of delay in the emission of composition droplets with consequent printing defects; 15 After deposition, however, the composition has high viscosity and does not spread on the surface ceramic, being present only in the selective printing areas and thus allowing the texturing of the same surface. In the following description all percentages are by weight unless otherwise stated. otherwise specified. 20 The term “dry” refers to the sum of the weights of the ceramic raw materials and the organic, polymeric, preservative components and any bentonite of the additive. The composition of the invention comprises a mixture of ceramic raw materials, additives, and a liquid medium for suspending solids. The ceramic raw material mix includes the following necessary components: 25 - 10-30% of frit; - 15-25% clays, including kaolinite and bentonite; - 20-30% sodium feldspar; - 20-40% quartz. P024065IT-01 Notarbartolo & Gervasi SpA As known in the industry, frit is a mixture of silica powders and minerals that provide oxides to the composition. Clays useful for the present invention necessarily include clays of the type kaolinitic and bentonite. Kaolinitic clay is present in quantities equal to or greater than 8% and 5 less than 20%. Bentonite is present in the overall composition in quantities between between 0.5 and 1.5% of the dry weight; within this range, the amount of bentonite is higher in the case of compositions with a frit content higher than 15%. Even if present in small percentage, bentonite is a necessary component for the compositions of this invention because the inventors observed that it has a suspending effect which prevents the 10 sedimentation of the solid component, thus preventing the deposition of solids in the pipes and in the nozzles of inkjet deposition apparatus. Bentonite can optionally be present in the formulation of the additive; in this case, the quantity of this component must be distributed between ceramic raw materials and additive in such a way as to fall within the range above indicated. 15 The mixture of ceramic raw materials may also include as additional optional components: - 1-3% alumina; - 1-2% zinc oxide; - 1-4% mullite; 20 - 1-6% calcium carbonate; - 1-10% wollastonite. Other materials can be added to the mixture of ceramic raw materials described above. components known in the industry, such as pigments, sands, zirconium silicates, carbonate barium, strontium carbonate, lithium carbonate, dolomite, feldspars other than feldspar 25 sodium, tin oxide, nepheline, bismuth oxide, boric products, colemanite, cerium oxide, cobalt oxide, copper oxide, iron oxide, aluminum phosphate, iron carbonate, oxide of manganese, sodium fluoride, chromium oxide, spodumene, talc, magnesium oxide, cristobalite, rutile, anatase, bismuth vanadate, vanadium oxide, ammonium pentavanadate P024065IT-01 Notarbartolo & Gervasi SpA and their mixtures. The mixture and percentage of each of the ceramic and frit raw materials are defined according to the final finish you wish to give to the enamelled surface of the ceramic tile after firing (transparent glossy, glossy, matt glossy, 5 opaque, etc.). To obtain different surface finishes (glossy, opaque, matt) the The main characteristics of the composition to be balanced are first of all the typology and the percentage of the frit used, and then the raw materials in the formula that allow for shift the balance more towards a glossy or matte finish. For example, starting from a average composition of digital enamel, to obtain a glossy finish a percentage is used 10 more transparent frit than opaque, a higher percentage of quartz, and it avoids the use of opacifiers such as alumina and mullite; obviously, adopting measures contrary to those indicated above, the composition moves towards obtaining opaque enamels. A typical composition for obtaining a polish for application with digital tools is as follows: 15 - 18% of fried; - 25% clay, of which 1% bentonite; - 23% sodium feldspar; - 20% quartz; - 6% alumina; 20 - 2.5% zinc oxide; - 2% calcium carbonate; - 3.5% wollastonite. The second component of the composition of the invention is a liquid additive including: 25 - 75-90% of one or more ethylene glycols; - 1-5% of sodium and / or ammonium acrylate or polyacrylate of molecular weight between between 100 and 500 g / mol; - 0.3-2% of a vinyl resin with a weight average molecular weight between P024065IT-01 Notarbartolo & Gervasi SpA 300,000 and 1,000,000 g / mol; - 0.1-0.5% antibacterial preservatives; - 5-15% water. The main component of the additive is ethylene glycols; these can be chosen 5 between monoethylene glycol, diethylene glycol and polyethylene glycols (the latter also known as chemistry with the abbreviation PEG); the glycols or polyglycols useful for the invention are those with molecular weight from 60 to 400 g / mol). Sodium and / or ammonium acrylate or polyacrylates have a fluidifying function; polyacrylates are chosen from those with a molecular weight between 100 and 500 g / mol. 10 The vinyl resin present in the additive has a suspending function. The additive also includes a small amount of antibacterials to prevent mold formation during storage, which would give rise to odorous emissions in the heat treatments to which the enamel is subjected in the production processes of ceramic articles. An antibacterial useful for the purposes of the invention is a commercial mixture of 5-chloro-2- 15 methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one, known as K athon. The inventors noted that the additive has optimal properties, useful for the purposes of the invention, when formulated to have a density between 1.13 and 1.14 g / mL. Finally, the additive may optionally include bentonite in such quantities that, when added together 20 to the quantity already present in the mixture of ceramic raw materials, the quantity total of this compound in the composition is in the range of 0.5-1.5% with respect to the dry weight. This additive is characterized by good lubricating power, slow drying and excellent suspending power which allows the preparation of glaze and engobe suspensions 25 stable over time. Optionally, between 1 and 4% of a liquid glue, which consists of an aqueous suspension of carboxymethylcellulose (CMC) concentration 6-7%. P024065IT-01 Notarbartolo & Gervasi SpA The liquid glue optionally added to the basic composition has the function of binder of the composition, to keep it stable and avoid mixing during all phases of tile production; this component also has a gripping effect on the material ceramic of the support to be decorated, avoiding slipping of the composition on said support 5 and thus allowing a faithful reproduction of the desired design. The addition of glue liquid also has the effect of delaying the drying of the composition, making it easier to apply of the applied enamel. The compositions described above are obtained by grinding the ceramic components in the additive, which together with the water forms the liquid medium in which the grinding takes place. 10 Liquid grinding medium is used in quantities between 35 and 60% by weight of the overall composition. The milling takes place in traditional tambourine mills, loading all three components (ceramic raw materials, additive and water) from the beginning. The compositions described above present a series of properties and characteristics that make them ideal for high-resolution digital printing with a texturizing effect. 15 As mentioned, compositions have first of all non-Newtonian behavior, and therefore they have relatively low viscosity inside the system and in particular in the head at the time of the so-called “shot”, but reach a higher viscosity after the deposition avoiding that the composition “spreads” on the support; in particular, in the phase of 5 -1 “shot”, in which the cutting speed values ​​are in the order of 10 s, without exceeding the limit 20 of 10-20 mPa·s which would cause the nozzle to clog or cause unwanted discharge of larger amounts of nail polish than desired. The compositions of the invention also have the following additional characteristics: - grinding residue 2-2.5 g / 100 mL: this feature guarantees the printhead compatibility; 25 - density between 1.45 and 1.55 g / mL: these density values ​​guarantee good suspension of composition inside digital printers and, at the same time, a good structure and definition of the same when applied on the tile; at density values lower temperatures there is a risk of significant sedimentation of the suspension and loss of definition in P024065IT-01 Notarbartolo & Gervasi SpA application; - recirculating viscosity in the range 20 < η < 50 mPa·s at 40 °C and viscosity during shot in the range 10 < η < 30 mPa·s at 40 °C measured with Anton Paar MCR 92 Rheometer. These viscosity values ​​allow for optimal behavior both during the 5 permanence in the printing apparatus and during the firing from the head, both after the deposition on the ceramic support, as described above. The composition has a behavior pseudoplastic in the temperature range from 30°C to 45°C, with the viscosity decreasing as the shear rate increases. To perform the rheological measurements, the following measurement method: 10 - temperature setting at 25 °C; - homogenization, followed by a rest period; -1 - viscosity measurement at 25 °C with a shear rate of 0.25 s; - temperature setting at 40°C; - homogenization, followed by a rest period; -1 15 - viscosity measurement at 40 °C in a shear rate range of 0.1÷1500 s; -1 - hysteresis and interpolation measurements at 10, 100, 500 and 1000 s. - emission speed during shooting, with a distance of 3 mm between the head and the support ceramic, between 6 and 10 m / s, measured with a Drop Watcher zoom camera equipped with high-speed strobe light (JetXpert from ImageXpert). 20 - drying time between 90 and 180 s at a temperature between 65 and 70 °C, compatible with the transit speeds of the tiles in the production plants; -7 -1 - a coefficient of expansion in the range 60-80 × 10 °C; this value of expansion coefficient makes the enamel obtained with the compositions of the invention have during heat treatments an expansion compatible with that of the ceramic support 25 and any other components present on it, so as to avoid fractures due to differential expansions (dilatometric agreement). The invention will be further described through the following experimental part. INSTRUMENTS, METHODS AND EXPERIMENTAL CONDITIONS P024065IT-01 Notarbartolo & Gervasi SpA For rheological measurements on the glazes, the Anton Paar MCR 92 rheometer was used. To measure the granulometric distribution of the glazes, the granulometer was used Malvern 3000E model laser. For digital application, the conformity of Durst Phototechnik printheads was evaluated. TM 5 SpA via the Durst Rockjet Drop Watcher validation kit. EXAMPLE 1 This example refers to the production of a composition of the invention. This composition was produced by mixing and grinding as described above. following components: 10 - 52% of a mixture of ceramic components composed as follows: - 18% fried; - 25% clay, of which 1% bentonite; - 23% sodium feldspar; - 20% quartz; 15 - 6% alumina; - 2.5% zinc oxide; - 2% calcium carbonate; - 3.5% wollastonite. - 17% of additive composed as follows: 20 - 80% of a mixture of ethylene glycols; - 3% sodium polyacrylate with a molecular weight between 100 and 500 g / mol; - 2% of a vinyl resin with a weight average molecular weight between 300,000 and 1,000,000 g / mol; - 0.5% antibacterial preservatives; 25 - 14.5% water. - 31% water. The viscosity at 40 °C of this composition was measured, at different values ​​of velocity cutting. The test results are shown in the following table: P024065IT-01 Notarbartolo & Gervasi SpA -1 Shear rate (s ) Viscosity (mPa s) 10 80.4 100 27.1 500 19.8 1000 18.7 EXAMPLE 2 This example refers to the production of another composition of the invention. 5 The test of Example 1 was repeated, with the difference that the mixture of components ceramics was composed as follows: - 10% fried; - 25% clay, of which 1.5% bentonite; - 30% sodium feldspar; 10 - 25% quartz; - 3% mullite; - 2% zinc oxide; - 5% calcium carbonate. The results of the viscosity test as a function of shear rate are reported in the 15 following table: -1 Shear rate (s ) Viscosity (mPa s) 10 120.3 100 58.7 500 25.1 1000 24.9 Compared to the formulation of Example 1, in this composition there is an increase in P024065IT-01 Notarbartolo & Gervasi SpA ratio between clay and frit components, and therefore the plasticity of the glaze. EXAMPLE 3 (COMPARATIVE) This example refers to the production of a composition not of the invention. The test of Example 1 was repeated, with the difference that the mixture of components 5 ceramics was composed as follows: - 30% fried; - 5% clay, of which 1.5% bentonite; - 30% sodium feldspar; - 25% quartz; 10 - 3% alumina; - 3% mullite; - 2% zinc; - 5% calcium carbonate. The results of the viscosity test as a function of shear rate are reported in the 15 following table: -1 Shear rate (s ) Viscosity (mPa s) 10 22.8 100 16.0 500 14.7 1000 14.4 Compared to the formulation of Example 1, in this composition there is a decrease of the relationship between the clay and frit components, and therefore of the plasticity of the glaze. From the values ​​obtained, it can be seen that at low shear rates the composition of this example has 20 a viscosity lower than the permitted range, therefore there are problems of sedimentation and resulting in defects in shooting quality. EXAMPLE 4 This example refers to the production of another composition of the invention. P024065IT-01 Notarbartolo & Gervasi SpA The test of Example 1 was repeated, leaving the composition of the ceramic component but adding in this case 1% of CMC-based glue (CMC concentration in glue 6%) to improve the lubrication of digital enamel and in order to give it sufficient adhesive power towards the ceramic support 5 or more previously applied layers. The addition of 1% glue compensated. with a corresponding decrease in the percentage of additive. The results of the viscosity test as a function of shear rate are reported in the following table: -1 Shear rate (s ) Viscosity (mPa s) 10 88.3 100 37.4 500 19.7 1000 19.6 10 The rheological values ​​of this enamel are within the working parameters of the technology and the addition of 1% liquid glue gives better application properties from the point of view ceramic. EXAMPLE 5 (COMPARATIVE) This example refers to the production of another composition of the invention. 15 The test of Example 4 was repeated, but in this case using 5% of glue. CMC base; the addition of glue was compensated by reducing the percentage of ceramic components at 50%, the percentage of the additive at 15% and the percentage of water at 30%. The results of the viscosity test as a function of shear rate are reported in the 20 following table: -1 Shear rate (s ) Viscosity (mPa s) 10 140.0 P024065IT-01 Notarbartolo & Gervasi SpA 100 51.5 500 25.8 1000 24.3 From the values ​​obtained, it can be seen that at low cutting speeds (10 - 100 mPa s), the enamel digital has a viscosity higher than the permitted range, and therefore problems arise in the drop creation (delay in triggering the on-demand shot). EXAMPLE 6 5 This example refers to the production of a ceramic tile with a surface textured produced using the composition of Example 2. Some tiles, with different structured designs, have been produced by pressing mold of a standard ceramic support. After drying, each tile was applied by spraying an engobe (industry standard composition) with a density of 1450 – 10 1500 g / L with a weight of approximately 370 g / m . The composition of the Example has been applied below 2, the graphics were printed and finally a final polish (“top coat”) was applied, (industry standard composition) at a density of 1350 – 1400 g / L with a weight of approximately 210 g / m . Figures 1 to 4 show photographs of the resulting tiles. COMMENT ON THE RESULTS 15 Based on the examples given, it can be noted that: - it is necessary to work with clay percentages ≥ 8%, but never higher than 25%. Percentages higher temperatures cause an increase in viscosity that is higher than the range allowed; - the percentage of plastic component must be balanced with the percentage content 20 of frit. In Example 3, where the clay-frit ratio is 1:6, the following values ​​are recorded: viscosity values ​​below the permitted range, which causes problems suspension; - the best condition is represented by Example 4, in which the formulation 1% liquid glue was added to the standard liquid. This is because the glue 25 improves the lubrication of the digital enamel and gives it sufficient power P024065IT-01 Notarbartolo & Gervasi SpA adhesive towards the ceramic support or other previously applied layers applied; - the maximum amount of liquid glue that can be added to the digital polish is equal to 4%. By increasing the percentage of glue above this value, a 5 increase in viscosity (higher than the permitted values, see Example 5) which it generates problems both in the recirculation phase and in the firing phase; - the percentage of liquid glue added to the digital polish must be adjusted accordingly based on the plastic component of the compound: therefore it will depend on the ratio between the part clayey and amorphous and / or the nature of the clays used.

Claims

CLAIMS 1. A non-Newtonian water composition for obtaining ceramic glazes for high-resolution digital application, said composition comprising by weight: - between 50 and 55% of a mixture of ceramic raw materials, including frits, clays including bentonites as suspending agents and kaolinites, sodium feldspar, quartz and optionally ceramic pigments; - between 15 and 20% of an additive comprising organic compounds and optionally bentonite in a solvent consisting of a mixture of water and ethylene glycols; - between 30 and 40% of water; - optionally, between 1 and 4% of a carboxymethylcellulose-based glue.

2. Composition according to claim 1, wherein the total quantity of bentonite present in the mixture of ceramic raw materials and / or in the additive is between 0.5 and 1.5% based on the dry weight.

3. Composition according to any of claims 1 or 2, wherein said mixture of ceramic raw materials comprises as necessary components: - 10-30% frit; - 15-25% clays, of which an amount equal to or greater than 8% and less than 20% consists of kaolinitic clays; - 20-30% sodium feldspar; - 20-40% quartz.

4. A composition according to any preceding claim, wherein said mixture of raw materials further comprises: - 1-3% alumina; - 1-2% zinc oxide; - 1-4% mullite; - 1-6% calcium carbonate; - 1-10% wollastonite. P024065IT-01 Notarbartolo & Gervasi SpA 5. A composition according to any preceding claim, wherein said mixture of ceramic raw materials further comprises pigments, sands, zirconium silicates, barium carbonate, strontium carbonate, lithium carbonate, dolomite, feldspars other than sodium feldspar, tin oxide, nepheline, bismuth oxide, boric products, colemanite, cerium oxide, cobalt oxide, copper oxide, iron oxide, aluminum phosphate, iron carbonate, manganese oxide, sodium fluoride, chromium oxide, spodumene, talc, magnesium oxide, cristobalite, rutile, anatase, bismuth vanadate, vanadium oxide, ammonium pentavanadate and mixtures thereof.

6. A composition according to any preceding claim, wherein said liquid additive comprises: - 75-90% of one or more ethylene glycols; - 1-5% of sodium and / or ammonium acrylate or polyacrylate with a molecular weight of between 100 and 500 g / mol; - 0.3-2% of a vinyl resin with a weight average molecular weight of between 300,000 and 1,000,000 g / mol; - 0.1-0.5% of an antibacterial preservative; - 5-15% of water; - optionally bentonite.

7. Composition according to any of the preceding claims, wherein said ethylene glycols are selected from monoethylene glycol, diethylene glycol and polyethylene glycols with a molecular weight from 60 to 400 g / mol.

8. Composition according to any of claims 6 or 7, wherein said sodium polyacrylate has a molecular weight between 100 and 500 g / mol.

9. A composition according to any of claims 6 to 8, wherein said antibacterial preservative is a mixture of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl4-isothiazolin-3-one.

10. A composition according to any of the preceding claims, further comprising between 1 and 4% of a liquid glue consisting of an aqueous suspension of P024065IT-01 Notarbartolo & Gervasi SpA carboxymethylcellulose at a concentration of 6-7%.

11. Ceramic article with a textured surface obtained by deposition on a ceramic substrate, using a digital printing technique, of a composition of any of the preceding claims, and subsequent heat treatment to transform the composition into a glaze.