A method for manufacturing ceramic tiles

Abstract

A method for producing ceramic tiles and / or slabs (21) comprising: - a step of preparing a ceramic mixture (10) comprising a specific moisture content; - a first drying step (S4) for reducing the moisture content of the mixture; - a step (S7) of forming a raw tile and / or raw slab (11) comprising said mixture, subsequent to said first drying step; - a second drying step (S8) suitable for further reducing the moisture content of the mixture subsequent to said forming step (S7); - optionally, one or more steps of application of one or more layers of coating and / or decoration (S9) on an upper surface of said raw tile and / or raw slab (11), - a step (S10) of firing said raw tile and / or raw slab (11) to obtain a ceramic tile and / or a ceramic slab (11), wherein at least one of said first and second drying steps (S4, S8) is performed by means of microwave radiation (MW) and / or radio frequency radiation (RF).

Description

[0001] A method for manufacturing ceramic tiles

[0002] The present invention relates to a method for producing ceramic tiles and / or slabs.

[0003] The invention further relates to a method for producing a ceramic mixture for producing ceramic tiles and / or slabs.

[0004] As is known, ceramic tiles and / or slabs are produced starting from a ceramic mixture formed from a blend of raw materials, and possibly semi-finished materials, suitably ground and homogenized. The grinding and mixing of the raw materials usually takes place in a wet process, i.e., in the presence of water, at the end of which a fluid suspension known in the industry as a slip is obtained. The slip is then atomized in such a way as to reduce the amount of water to the desired level and to obtain the formation of a ceramic mixture in granular form, where the granules are substantially spherical.

[0005] This method of producing the mixture has several advantages including, in particular, the effective homogenization and comminution of the mixture. These features, combined with the almost spherical shape of the atomized granules, make the resulting mixture particularly suitable for the industrial production of tiles, especially large-format tiles, and / or slabs in processes with high production capacities.

[0006] However, preparing the wet-processed mixture involves a high energy cost and high water consumption.

[0007] Alternative processes for producing the mixture involve dry grinding and subsequent granulation of the mixture. However, dry-processed mixtures are mainly used for the production of medium- and small-sized tiles, as they do not have the same homogeneity features typical of wet-processed mixtures. An object of the present invention is to propose a method for producing alternative ceramic tiles and / or slabs that allows one or more of the aforementioned drawbacks of the prior art to be overcome. A further object of the invention is to propose an alternative method for preparing mixtures for ceramic tiles and / or slabs. Such objects are achieved by the features of the invention as set out in the independent claim. The dependent claims outline preferred and / or particularly advantageous aspects of the invention.

[0008] In the context of the present invention, the terms “tile” and “slab” both indicate plate-shaped products, preferably of a square or rectangular shape, suitable for covering surfaces, in particular for covering walls and / or floors. The term “tile” and “slab” are therefore substantially interchangeable. However, the term “slab” is preferably used to refer to large-sized products, for example to products having at least a longitudinal or transverse dimension, preferably both, greater than or equal to 90 cm. Similarly, the term “tile” is preferably used to refer to small products, such as products having at least one longitudinal or transverse dimension, preferably both, less than 90 cm.

[0009] A first independent aspect of the invention provides a method for producing ceramic tiles and / or slabs comprising: a step of preparing a ceramic mixture, said mixture having a specific moisture content; a first drying step suitable for reducing the moisture content of the mixture; a step of forming a raw tile comprising said mixture after said first drying step; a second drying step suitable for further reducing the moisture content of the mixture after the forming step; optionally a step of decorating an upper surface of said raw tile; a step of firing said raw tile to obtain a ceramic tile, wherein at least one of said first and second drying steps is performed by means of microwave radiation (MW) and / or radio frequency radiation (RF). In this way it is possible to reduce the energy cost of the production process. The inventor has found that radio frequency or microwave radiation is particularly effective in said first and / or second drying steps, the components of the mixture being substantially transparent to said radiation, and the radiation being absorbed by the moisture- forming water. The inventor has also found that the use of radio frequency radiation poses less risk to the health of operators than microwave radiation, thus requiring simpler and less expensive systems. The inventor has also found that radio frequency and / or microwave radiation is particularly advantageous at the first drying step; in fact, in this step the mixture may be in a different state than in a solid and compact state as after forming, for example in particulate form, so that the evaporation of the water forming the moisture is particularly effective. Furthermore, at least in some embodiments of the invention, said first drying step may result in a greater decrease in moisture content than in the second drying step, so that the adoption of radio frequency and / or microwave irradiation in said first drying step is particularly advantageous.

[0010] The mixture may comprise a solid portion formed of a fine particulate, preferably formed of a blend of powders of ceramic raw materials, and water forming said moisture content.

[0011] Said radio frequency radiation (RF) may have a frequency lower than 0.100 GHz, preferably lower than 0.050 GHz, more preferably lower than 0.030 GHz. It is particularly preferred that the radio frequency radiation exhibits a frequency of approximately 0.027 GHz. At this frequency, the radiation may efficiently interact with the water molecules contained in the mixture, first causing the vibration and then evaporation thereof in a short time. Moreover, these frequencies do not present any particular critical problems in the interaction with the human body, so that using these frequencies may reduce risks for operators.

[0012] Said microwave radiation may have a frequency comprised between 0.9 and 300 GHz, preferably between 0.9 and 3 GHz. Internal investigations have shown that these frequencies are particularly effective in causing the mixture to dry.

[0013] In some embodiments, at the end of said first drying step, the mixture may have a moisture content lower than or equal to 7%, preferably lower than or equal to 4%, and / or higher than or equal to 2%, preferably higher than or equal to 3%. This moisture content may be sufficient to allow the mixture to compact during the forming step so as to form the raw tile. The inventor has found that a moisture content of the mixture of between 2 and 4% at the end of the first drying step may allow a mixture to be obtained that is sufficiently dry for subsequent processing, for example crushing, to be carried out, as will be better explained below, without requiring the removal of an excessive quantity of water from the mixture, resulting in excessive energy consumption.

[0014] Furthermore, in the context of the present invention, the moisture content is to be understood as expressed as the mass of water in relation to the total mass of the mixture.

[0015] Advantageously, the step of preparing the mixture may comprise a granulation step of the mixture that is separate from said first drying step. In this way, the features of the granulate may be modulated with greater independence with respect to atomization, in which the granulation and drying of the mixture take place in a single process. In practice, the effect of the drying on the features of the granulate may be reduced. For example, the inventor has found that by separating said granulation step from said first drying step, it is possible to obtain a granulate with a higher density so that a lower compaction force may be required during the forming step to obtain the desired compacted density or that, for the same compaction force, a compacted component with a higher density may be obtained which may, during the subsequent firing step, lead to a lower shrinkage. Furthermore, a higher density of the compacted component, due to a higher density of the granulate, may result in a higher breaking load of the compacted component so that lower consumption of tougheners may be required in preparation of the mixture, resulting in economic savings, especially for the production of large-sized slabs. Furthermore, a granulate with a higher density may cause a faster deaeration during the compaction step, with possible consequent increase in the compaction speed. In some embodiments, said granulation step results in an increase in the moisture content of the mixture. In this way, greater control over the final moisture content of the mixture may be allowed. Preferably, following said granulation step, the mixture may have a moisture content of between 4 and 10%, preferably between 4 and 8%. Preferably, said granulation may lead to the formation of substantially spherical granules. Substantially spherical granulates have good flowability and fluidity which, especially in the loading of molds of traditional presses, favors a rapid and homogeneous distribution of the mixture with consequent advantages in terms of pressing speed and uniformity of the shrinkage in firing. Preferably, said granules may have a maximum dimension of less than 2 mm.

[0016] According to the preferred embodiment, the step of preparing the mixture may comprise a step of wet grinding of a blend of raw materials and water. The wet grinding may allow a mixture having a solid portion formed of very fine particles to be obtained, which is particularly suitable, in the subsequent firing step, to allow the sintering of said mixture. In addition, wet grinding, compared to dry grinding techniques, may favor a better homogenization of the components of the mixture. In this way, the mixture may be particularly suitable for the production of large-format slabs. Preferably, said mixture may have a residue at 63 pm (i.e. a fraction of solid particulate having a size greater than 63 pm) of between 4 and 10% by weight with respect to the total weight of the solid portion of the mixture. Preferably at the end of said wet grinding, the moisture content of the mixture is greater than 30%, preferably greater than or equal to 35%. In these conditions, the mixture, before the drying step, is substantially in the form of an aqueous suspension of solid particles. Said suspension is also known in the industry as a slip.

[0017] Said ceramic raw materials forming the mixture may comprise clays, kaolins, feldspar, frits, glass, calcium and / or magnesium carbonates, sand, calcium silicate, metal oxides, ceramic production waste (e.g. waste of raw or fired tiles of the same production process), talc and / or other minerals. Advantageously, the mixture is a mixture for the formation of vitrified ceramic, for example porcelain stoneware. According to the preferred embodiment, said mixture preparation step comprises a preliminary step of decreasing the moisture content of the mixture, preferably before said first drying step. Advantageously, in this preliminary step of decreasing the moisture content of the water, it does not evaporate but remains in the liquid state, simplifying the collection and recovery thereof, for example the reuse of the water for the production of another mixture. Furthermore, by virtue of said preliminary step, the amount of water to be dried may be substantially reduced, resulting in energy savings. According to the preferred embodiment, said preliminary step of decreasing the moisture content may preferably be performed mechanically, for example by filter pressing, sedimentation or centrifugation. Filter pressing is preferable to other techniques because it may allow an effective separation of the water in a relatively short time, therefore with high productivity, and with relatively economical facilities. Said preliminary step of decreasing the moisture content may result in a reduction of the moisture content of the mixture greater than 30%, preferably greater than 45%, for example 50%. In this way it is possible to obtain significant energy savings in the subsequent drying steps.

[0018] Advantageously, at the beginning of said preliminary step of decreasing the moisture content, the mixture is in the aforementioned form of a slip, i.e. it has a moisture content greater than 30%, preferably greater than or equal to 35%. At the end of said preliminary step, and preferably at the beginning of said first drying step, the mixture may comprise a moisture content of between 12 and 20%, for example between 15 and 20%.

[0019] Said preliminary step of decreasing the moisture content of the mixture may lead to the formation of one or more solid mixture aggregates. For example, the filter pressing may involve the formation of a so-called “cake” i.e. a compacted mixture. Advantageously, said step of preparing the mixture comprises one or more steps for crushing said aggregates. In this way, it may be returned to the powdered state or in any case be reduced into aggregates of reduced size so as to favor subsequent processing of said mixture. Advantageously, one or more of said crushing steps may be carried out dry, i.e., without further addition of water or other substances in a liquid phase. In fact, since the mixture is a simple aggregate of raw powders, dry grinding may be sufficient to obtain the desired crushing level. For example, said crushing steps may be carried out by means of one or more of the following devices: lump breakers, for example rotary-reel lump breakers, hammer mill, roller mill, pin mill.

[0020] According to the preferred embodiment, the method may comprise a first of said crushing steps before said first drying step. In this way, the mixture may be crushed to such a size as to favor drying. In fact, since a smaller size allows water to escape from the aggregates more easily, drying efficiency and / or productivity may be increased.

[0021] Advantageously, the method may comprise a second of said crushing steps before and / or after said first drying step. In this way, the mixture may be brought back to the fine particulate state, prior to the formation of the aggregate, and is suitable for the formation of the granule. In particular, said second crushing, if carried out after said first drying step, may result in better micronization, i.e. crushing to form a fine particulate, since in the presence of lower moisture content of the mixture the aggregation capacity of the latter is reduced so that the crushing is more effective.

[0022] The forming step comprises the compaction of said mixture. Said forming step may take place by means of a discontinuous, continuous or semi-continuous compaction process. According to the preferred embodiment, the forming step takes place by continuous compaction, for example in moldless compactors. Said processes and compactors are particularly suitable for the production of large slabs. Said compaction step may include the distribution of granulate to form a continuous strip and may comprise a cutting step, preferably on the fly, of said strip in order to obtain said first raw tile or slab. In this case, the width of the strip may correspond to said transverse side, and the cut is made to define the length of said longitudinal side. In said compaction step a pressure greater than 200 kg / cm2may be applied, for example greater than 300 kg / cm2. In particular, in the event of continuous compaction said pressure is usually less than 400 kg / cm2, for example less than 350 kg / cm2. Therefore, in the event of continuous compaction, the pressure is relatively low and results in lower density in the compacted mixture of the raw tile or slab. This lower density may correspond to a higher shrinkage during the subsequent firing step, whereby the use of a denser granulate obtained from granulation separated from the drying of the mixture, as described above, is particularly advantageous in combination with continuous compaction.

[0023] According to some embodiments, the method may provide for making a relief on the upper surface of the raw tile. Said relief may be achieved during the compaction step, for example by means of structured plates or strips.

[0024] Preferably, said second drying step, suitable for drying the raw tile or slab, results in the reduction in the amount of moisture of the mixture to a value of less than 5%, preferably less than 2%.

[0025] According to the preferred embodiment of the invention, said decoration step may comprise at least a first glazing step to coat the upper surface of the unfired tile with a first glaze. Preferably, said first glaze is opaque. In some embodiments, the decoration step may comprise a second glazing step for coating the upper surface of the raw tile with a second glaze. Preferably, said second glaze is transparent or translucent. Usually, said second glazing step may be performed after said first glazing step, for example said second glaze may be the final upper layer of the tile or slab.

[0026] The decoration step may comprise a digital inkjet printing step for printing a decoration. Advantageously, said printing step may follow the first glazing step so that said opaque glaze provides a base color for the printed decoration. Preferably, said second glazing step follows the printing step, so that said transparent glaze forms a protective layer for the printed decoration. In some embodiments, the method may comprise further decoration sub-steps, for example for the application of reliefs and / or material effects, such as for example metallic and / or luster effects. Said further decoration sub-steps may for example comprise the application of granules.

[0027] The firing step may take place according to a firing cycle which comprises a heating step and a firing step. Said firing cycle may have a maximum temperature higher than 700°C, preferably higher than 1000°C, for example higher than 1200°C. The firing step may preferably be performed in a continuous oven, preferably a roller oven.

[0028] After the firing step, the ceramic tile or slab may undergo one or more finishing steps, for example lapping, polishing and / or squaring.

[0029] According to a second independent aspect, the invention relates to a method for producing a ceramic mixture for the production of ceramic slabs that comprises a step of preparing a ceramic mixture comprising a specific moisture content and a drying step suitable for reducing the moisture content of the mixture, wherein said drying step is performed by means of microwave radiation (MW) and / or radio frequency radiation (RF). It should be noted that said method for producing the mixture may comprise one or more of the features indicated above relating to the preparation of the mixture. In particular, said method for producing the mixture may comprise one or more of the steps described above up to the granulation of the mixture. The invention is of particular interest when applied to a method for producing ceramic slabs, preferably having a longitudinal and transverse dimension greater than or equal to 90 cm, comprising the following steps. Preparing a ceramic mixture suitable for the production of porcelain stoneware comprising a specific moisture content. Said step of preparing the mixture comprises a step of wet grinding of a blend of ceramic raw materials in water, in which the water content (i.e. the moisture content of the mixture) is greater than 30% by weight of the total weight of the mixture. After grinding, the mixture comprises a solid portion in suspension in water, said solid portion being in the form of fine particulate having a residue at 63 pm of between 4 and 10%. The method comprises a preliminary step of decreasing the moisture content of the mixture by mechanical means, preferably by filter pressing, which involves a decrease in the moisture content of the mixture by 30%, for example by 50%, and the formation of first mixture aggregates, called “cakes,” having a moisture content between 15 and 20%. After said preliminary step of decreasing the moisture content, the method comprises a first step of dry-crushing said first aggregates to obtain second aggregates of smaller size, preferably by means of a rotary-reel lump breaker. The method therefore comprises a first drying step for decreasing the moisture content of the mixture, in the form of said second aggregates, by means of radio frequency radiation (RF), preferably with radiation having a frequency of 0.027 GHz. The first drying step results in the reduction of the moisture content of the mixture to a value lower than 7%, preferably 3%. The method comprises a second step of dry-crushing said second aggregates to obtain the mixture in the form of a fine particulate, preferably by means of pin mills. The method comprises a step of granulating the mixture with the addition of water, in order to obtain substantially spherical granulates having a moisture content of between 4 and 8% and a maximum dimension of less than 2 mm. The method comprises compacting said mixture, in the form of granulates, in a continuous compacting machine to form raw slabs. In this compaction step a pressure of less than 400 kg / cm2is applied. The raw slab is dried in a second drying step, preferably by means of radio frequency radiation, to bring the moisture content below 2%. Optionally, the method comprises one or more steps of decorating the upper surface of the raw slabs. Firing the raw slabs in a continuous oven with a firing cycle with maximum temperatures greater than 1000°C.

[0030] It should be noted that the fact that the mixture may be prepared by means of wet grinding and subsequent drying separated from a granulation step, regardless of the fact that the drying takes place by means of exposure to radio frequency radiation or microwaves, may represent a further independent aspect of the present invention. In particular, it may be relevant to use a mixture thus prepared for the production of ceramic slabs, preferably having at least one side greater than or equal to 90 cm, which are traditionally prepared by an atomized mixture, widely considered the only one suitable for producing large-sized slabs with high-productivity processes. Therefore, according to a third independent aspect, the invention relates to a method for preparing a ceramic mixture comprising a step of grinding ceramic raw materials in water to obtain a mixture provided with a specific moisture content, a step of drying the ground mixture and a step of granulating the mixture, wherein said granulation step and said drying step are separated. Furthermore, the method for preparing a ceramic mixture according to the third independent aspect may be comprised in a method for producing ceramic tiles and / or slabs, comprising a step of, a step of forming a raw tile comprising said mixture, optionally one or more steps of applying one or more layers of coating and / or decoration on an upper surface of said raw tile, and a step of firing said raw tile to obtain a ceramic tile. It should be noted that the method of the third independent aspect may have one or more of the features described above in relation to the first and second independent aspect.

[0031] Furthermore, the invention according to a fourth independent aspect relates to a line for producing a ceramic mixture comprising a radio frequency dryer and / or a microwave dryer. Preferably, the line comprises a wet mill upstream of the dryer. The line may comprise a device configured to mechanically reduce the moisture content of the mixture, preferably a filter press. Advantageously, the line comprises one or more crushers upstream and / or downstream of the dryer. Preferably, said crushers are dry-type crushers, preferably rotary-reel lump breakers and / or pin mills. The line further comprises a granulating device, preferably of the type downstream of said dryer.

[0032] Further features and advantages of the invention will become apparent from the following non-limiting examples given by way of example with the aid of the figures shown in the accompanying drawings.

[0033] Fig. l is a diagram of some steps of a method for producing a mixture for ceramic slabs according to the second independent aspect of the invention. Fig. 2 is a diagram of some steps of a method for producing slabs according to the first independent aspect of the invention

[0034] Fig. 1 shows some steps in a method for producing a ceramic mixture according to a second independent aspect of the invention. The method comprises a first step SI of grinding and mixing ceramic raw materials RM according to a predetermined recipe. In the preferred example, the raw materials RM are selected and dosed appropriately, according to a suitable recipe or formulation, to form a mixture suitable for the production of porcelain stoneware. Raw materials RM for example comprise: clays, kaolin, one or more feldspars, sand, calcium and / or magnesium carbonate, frits, ceramic recycling material. During the grinding step, the raw materials RM according to the recipe are ground in a continuous wet W mill 1 with the addition of water, so as to obtain a slip 2 comprising a moisture content of 32% with a residue at 63 pm between 4 and 10%, for example 6%. In practice, the slip 2 is a suspension in water W of fine particulate P of ground raw materials.

[0035] After the grinding step, the slip 2 is subjected to a step of decreasing the moisture content S2 mechanically, in a filter press 3 in which the moisture content of the mixture is reduced by approximately 50%. At the end of the filter pressing step, the mixture is in the form of first solid aggregates 4 with a moisture content of 16%. Said first aggregates 3 are called “cakes” and are substantially formed of compacted, fine, wet particulate P. The water W that is separated from the slip during the step of decreasing the moisture content S2 may be collected and advantageously reused for the grinding step S 1.

[0036] The method then comprises a first crushing step S3 of said first aggregates 4, preferably in rotary -reel lump breakers 5. Following said first crushing step S3, second aggregates 6 are obtained which have a variable size, preferably with a maximum dimension of less than 10 cm. The second aggregates 6 of the mixture are dried in a first drying step S4, by means of radio frequency radiation. In the example, the radio frequency radiation has a frequency of approximately 0.027 GHz, and is applied to a continuous dryer 7. At the end of said first drying step S4, the mixture has a moisture content of 3%.

[0037] The second aggregates 6, after the first drying step S4, are subjected to a second crushing step S5, preferably dry crushing in a pin mill 8, suitable for breaking said second aggregates 6 to bring the mixture into the form of a fine particulate P, i.e. substantially the fine particulate obtained after grinding SI. In particular, it is preferable that after this second crushing, the fine particulate matter has a residue at 63 pm of between 4 and 10%, for example 6%.

[0038] After said second crushing S5, the mixture, in the form of dry fine particulate P, is subjected to a granulation step S6 in a granulator 9. In the example, the granulator is an oblique-walled granulator, for example a Madirex granulator produced by Manfredini & Schianchi. The granulation step S6 involves adding water W to the mixture to favor the adhesion of the fine particulate particles P and to define the moisture content of the mixture that is useful for the subsequent steps.

[0039] In the example, the moisture content of the mixture at the end of said granulation S6 is approximately 6%. Advantageously, at the end of the granulation S6 the mixture is in the form of granules 10 having a substantially spherical shape with a maximum size less than 2 mm.

[0040] At the end of said granulation step S6 the mixture is substantially ready to be used in a method for producing ceramic slabs, as illustrated in Fig. 2. Pending its use, the mixture may be stored in special silos.

[0041] It should be noted that the method of Fig. 1 may comprise one or more screening operations downstream of one or more of the operations described above, for example downstream of the crushing, granulation, and / or grinding operations. Fig. 2 shows some steps in a method for producing ceramic slabs according to a second independent aspect of the invention.

[0042] The method comprises a first step S7 of compacting the ceramic mixture obtained in the method of Fig. 1 to form a raw slab 11. In the preferred embodiment shown in the figures, in said compaction step S7, the mixture, in the form of granulates 10, is distributed on a conveyor belt 12, by means of one or more distributors 13.

[0043] The mixture is compacted by means of a continuous compacting machine 14 into a continuous compacted strip which is subsequently cut by means of a cutting device 15 in a direction transverse to the length of the compacted strip (said length coinciding with the feed direction of the conveyor belt) to obtain the raw slab 11. In said compaction step S7, the continuous compacting machine 14 applies a pressure of approximately 300 kg / cm2to the mixture.

[0044] The raw slab 11 is then dried to remove the residual moisture during a second drying step S8. In the illustrated example, said second drying step S8 is carried out by exposure of the raw slab 11 to radio frequency radiation RF, preferably with a frequency of 0.027 GHz, in a continuous dryer 16.

[0045] The raw slab 11, after drying, is subjected to a decoration step S9. In the example, the decoration step S9 comprises a first glazing step S9A by means of an airless sprayer 17 for the deposition of a first glaze layer, for example having a solid color, preferably white. In the example, the decoration step S9 comprises the printing S9B of a decoration by means of an inkjet printer 18 on the first layer of glaze. In the example, the decoration step S9 comprises a second glazing step S9C by means of an airless sprayer 19 for the deposition of a second, preferably transparent, glaze layer.

[0046] The method proceeds with a firing step S10 of the raw slab 11 in an oven 20, by means of a firing cycle having a maximum temperature greater than 1200°C to obtain a ceramic slab 21.

[0047] The present invention is in no way limited to the embodiments described above, but said methods may be implemented according to different variants without thereby departing from the scope of the present invention.

[0048] The invention is further defined by each of the following articles:

[0049] 1.- A method for producing ceramic tiles (and / or slabs) comprising:

[0050] - a step of preparing a ceramic mixture comprising a specific moisture content;

[0051] - a first drying step for reducing the moisture content of the mixture;

[0052] - a step of forming a raw tile (and / or slab) comprising said mixture, subsequent to said first drying step;

[0053] - a second drying step suitable for further reducing the moisture content of the mixture subsequent to said forming step;

[0054] - optionally, one or more phases of application of one or more layers of coating and / or decoration on an upper surface of said raw tile (and / or slab),

[0055] - a step of firing said raw tile to obtain a ceramic tile (and / or slab), wherein at least one of said first and second drying steps is performed by means of microwave radiation (MW) and / or radio frequency (RF) radiation.

[0056] 2.- Method according to article 1, wherein said radio frequency (RF) radiation has a frequency of less than 0.100 GHz, preferably less than 0.050 GHz, more preferably less than 0.030 GHz.

[0057] 3.- Method according to article 1 or 2, wherein said microwave radiation has a frequency between 0.9 and 300 GHz, preferably between 0.9 and 3 GHz.

[0058] 4.- Method according to any one of the preceding articles, wherein at the end of said first drying step, the mixture has a moisture content of less than or equal to 7%, preferably less than or equal to 4%, and / or greater than or equal to 2%, preferably greater than or equal to 4%.

[0059] 5.- Method according to any one of the preceding articles, wherein said mixture preparation step comprises a granulation step of the mixture separate from said first drying step.

[0060] 6.- Method according to article 5, wherein said granulation step comprises an increase in the moisture content of the mixture, preferably said moisture content of the mixture after said granulation step is between 4 and 8%.

[0061] 7.- Method according to any one of the preceding articles, wherein said mixture preparation step comprises a wet milling step of a mixture of materials and water, preferably wherein the moisture in said mixture is greater than 30%, preferably greater than or equal to 35%.

[0062] 8.- Method according to article 7, wherein said mixture preparation step comprises a preliminary step of decreasing the moisture content of the mixture (also said step of separating the water from the mixture), preferably by mechanical means, for example by filter pressing, prior to said first drying step.

[0063] 9.- Method according to article 8, wherein said preliminary step results in a reduction of the moisture content of the mixture by at least 30%, preferably at least 40%.

[0064] 10.- Method according to article 7 or 8, wherein said preliminary step comprises the formation of one or more solid mixture aggregates, and wherein said step of preparing the mixture comprises one or more crushing steps of said aggregates.

[0065] 11.- Method according to article 10, wherein the crushing is carried out dry. 12.- Method according to article 11, wherein said crushing is carried out by means of one or more of the following devices: lump breakers, hammer mill, roller mill, pin mill.

[0066] 13. - A method for the production of a ceramic mixture for the production of ceramic slabs that comprises a step of preparing a ceramic mixture comprising a specific moisture content and a drying step suitable for reducing the moisture content of the mixture, wherein said drying step is performed by means of microwave radiation (MW) and / or radio frequency radiation (RF).

[0067] 14.- Method according to article 13, comprising a preliminary step of decreasing the water moisture content by mechanical means.

[0068] 15.- Method according to article 14, wherein said mechanical means comprises one or more of the following operations: filter pressing, centrifugation, sedimentation.

[0069] 16.- Method according to article 14 or 15, wherein said mechanical means results in a reduction in the moisture content of the mixture of at least 30%, preferably 50%.

[0070] 17.- Method according to any one of articles 14 to 16, wherein said mechanical means involves the formation of one or more solid mixture aggregates, and wherein the method comprises one or more steps of crushing said aggregates.

[0071] 18.- Method according to article 17, wherein the crushing is carried out dry.

[0072] 19.- Method according to article 17 or 18, wherein said crushing is carried out by means of one or more of the following devices: lump breakers, hammer mill, roller mill, pin mill. 20.- Method according to any one of articles 17 to 19, comprising a first and a second crushing wherein said first crushing is carried out before said drying and said second crushing is carried out downstream of said drying.

[0073] 21.- Method according to any one of articles 13 to 20, comprising, upstream of said drying step, a wet grinding step, preferably at the end of which the mixture is in the form of a suspension in water of solid fine particulate.

[0074] 22.- Method according to any one of articles 13 to 21, comprises a granulation step of the mixture that is separate from said first drying step.

[0075] 23.- Method according to article 22, wherein said granulation step results in an increase in the moisture content of the mixture.

[0076] 24.- A line for the production of a ceramic mixture, preferably according to the method in accordance with each of articles 13 to 23, which comprises a radio frequency dryer and / or a microwave dryer.

[0077] 25.- Line according to article 24, comprising a wet mill upstream of the dryer.

[0078] 26.- Line according to article 24 or 25, comprising a device configured to mechanically reduce the moisture content of the mixture, preferably a filter press.

[0079] 27.- Line according to any one of articles 24 to 26, comprising one or more crushers upstream and / or downstream of the dryer, preferably said crushers are of the dry type, e.g., hammer and / or roller type, and / or piston type, and / or lump breakers.

[0080] 28.- Line according to any one of articles 24 to 27, comprising a granulator device downstream of said dryer.

Claims

Claims1.- A method for producing ceramic tiles and / or slabs (21) comprising:- a step of preparing a ceramic mixture (10) comprising a specific moisture content;- a first drying step (S4) for reducing the moisture content of the mixture;- a step (S7) of forming a raw tile and / or slab (11) comprising said mixture, subsequent to said first drying step;- a second drying step (S8) suitable for further reducing the moisture content of the mixture subsequent to said forming step (S7);- optionally, one or more phases of application of one or more layers of coating and / or decoration (S9) on an upper surface of said raw tile and / or slab (11),- a step (S10) of firing said raw tile and / or slab (11) to obtain a ceramic tile and / or slab (21), wherein at least one of said first and second drying steps (S4, S8) is performed by means of microwave radiation (MW) and / or radio frequency (RF) radiation.2.- Method according to claim 1, wherein said radio frequency (RF) radiation has a frequency of less than 0.100 GHz, preferably less than 0.050 GHz, more preferably less than 0.030 GHz.3.- Method according to claim 1 or 2, wherein said microwave radiation has a frequency between 0.9 and 300 GHz, preferably between 0.9 and 3 GHz.4.- Method according to any one of the preceding claims, wherein at the end of said first drying step (S4), the mixture has a moisture content of less than or equal to 7%, preferably less than or equal to 4%, and / or greater than or equal to 2%, preferably greater than or equal to 4%.5.- Method according to any one of the preceding claims, wherein said mixture preparation step comprises a step (S6) of granulating the mixture that is separate from said first drying step.6.- Method according to claim 5, wherein said granulation step (S6) results in an increase in the moisture content of the mixture, preferably said moisture content of the mixture after said granulation step is between 4 and 8%.7.- Method according to any one of the preceding claims, wherein said mixture preparation step comprises a wet milling step (SI) of a mixture of materials (RM) and water (W), preferably wherein the moisture in said mixture is greater than 30%, preferably greater than or equal to 35%.8.- Method according to claim 7, wherein said mixture preparation step comprises a preliminary step (S2) of decreasing the moisture content of the mixture, preferably by mechanical means, for example by filter pressing, preferably prior to said first drying step (S4).9.- Method according to claim 8, wherein said preliminary step (S2) results in a reduction of the moisture content of the mixture by at least 30%, preferably at least 40%.10.- Method according to claim 7 or 8, wherein said preliminary step (S2) comprises the formation of one or more solid mixture aggregates (4), and wherein said step of preparing the mixture comprises one or more steps (S3, S5) of crushing said aggregates.11.- Method according to claim 10, wherein said crushing (S3, S5) is carried out dry.12.- A method for the production of a ceramic mixture (10) for the production of ceramic tiles and / or slabs (21) that comprises a step of preparing a ceramic mixture comprising a specific moisture content and a drying step suitable for reducing the moisture content of the mixture, wherein said drying step is performed by means of micro wave (MW) radiation and / or radio frequency (RF) radiation.13.- Method according to claim 12, comprising a preliminary step (S2) of decreasing the water moisture content by mechanical means.14.- Method according to claim 13, wherein said mechanical means comprises one or more of the following operations: filter pressing, centrifugation, sedimentation.15.- Method according to claim 13 or 14, wherein said mechanical means results in a reduction in the moisture content of the mixture (10) of at least 30%, preferably 50%.16.- Method according to any one of claims 13 to 15, wherein said mechanical means involves the formation of one or more solid mixture aggregates, and wherein the method comprises one or more steps (S3, S5) of crushing said aggregates.17.- Method according to claim 16, wherein said crushing (S3, S5) is carried out dry.18.- Method according to any one of claims 16 to 17, comprising a first and a second crushing, wherein said first crushing is carried out before said drying and said second crushing is carried out downstream of said drying.19.- Method according to any one of claims 12 to 18, comprising, upstream of said drying step, a wet grinding step, preferably at the end of which the mixture is in the form of a suspension in water of solid fine particulate.20.- Method according to any one of claims 12 to 19, comprising a step of granulating the mixture that is separate from said first drying step.

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