Ceramic tile and method for producing ceramic tiles

TECHNICAL FIELD

The present invention relates to a method for producing ceramic tiles, and ceramic tiles, particularly flooring or cladding tiles.

PRIOR ART

Ceramic tiles usually comprise a substantially panel-shaped body of ceramic material, having a decorative surface which may be glazed or unglazed.

The decorative surface may also have a decor, representing, for example, an imitation of wood, natural stone, marble, concrete, resin or any other design. The decorative surface of the tile may also comprise a relief structure, representing the grain of stone or wood, for example.

The relief structure is produced by pressing during the forming of the tile.

In practice, the powders forming the ceramic mixture are placed in a mould and pressed with a die having a structure corresponding to the negative of the relief structure of the tile. Pressing may take place in a continuous process or another process in which no mould is used, where the negative structure is applied to a compacting belt.

The need to use dies, or other preformed negatives, limits the variability of the relief structures that can be produced. The resulting products therefore tend to have an obviously artificial appearance, mainly due to the high repetition rate of the reliefs and printed decors.

Furthermore, in order to allow laying with reduced joints, or even in contact, the ceramic tiles are rectified after firing so as to have a substantially regular dimension. However, the rectification operation is relatively costly, due to the production of waste material and the consumption of abrasives.

With the aim of reducing the artificial appearance of a ceramic product, WO2019116132 proposes a method for the irregular machining of the edges of atile before the stage of decoration. The present invention proposes, in the first place, to provide an alternative method for producing ceramic tiles, which, according to some of its embodiments, is intended to resolve one or more of the problems arising from the prior art.

DISCLOSURE OF THE INVENTION

The present invention, according to its first independent aspect, proposes a tile having a lower face and an upper face and comprising a ceramic body and a decor on at least said upper face.

Said tile may have the characteristic that said lower face differs in its shape and/or dimension from said upper face, and in particular the shapes of the perimeters of said upper face and said lower face may differ.

Said tile may have the characteristic that said lower face has edges substantially in square with each other. Thus the tiles may be placed together with a reduced joint and preferably in contact with each other at the edges of the lower face. Preferably, said edges of the lower face are not rectified. “Substantially in square” is taken to mean that the angles between the edges of the lower face are substantially equal to each other. In particular, “substantially” is taken to mean that said angles may differ from each other by less than 2°, or preferably by less than 1°.

According to the preferred embodiment of the invention, the upper face of the tile has edges out of square with each other. “Out of square” is taken to mean that at least one of the angles between the edges of the upper face differs from the other angles, and preferably all the angles differ from each other. In particular, said angles of the upper face may differ from each other by at least 1°, or preferably by at least 2°. Thus the tiles may be brought together, possibly in contact, but the joints between the upper faces of the tiles will differ from each other, imparting a less artificial appearance to the tiled surface. Additionally, each tile will itself be less artificial. The body of the tile may comprise walls having a substantially vertical extension, where “vertical” is taken to mean orthogonal to the plane of the lower and upper faces. It should be noted that said upper and lower faces may preferably be parallel to each other. At least one of said vertically extending walls may have an inclination with respect to the horizontal plane, in other words with respect to the plane of the lower face, that differs from the inclination of the other walls. Preferably, the inclination of each wall differs from the others. It should be noted that the walls comprise an upper edge coinciding with the respective edge of the upper face and a lower edge coinciding with a respective edge of the lower face. Thus the upper face has a shape in plan view that differs, at least in its dimension, from the lower face, imparting an irregular and less artificial appearance to the tile.

In the preferred embodiment, at least one, preferably each, of the vertically extending walls exhibits a varying inclination along a longitudinal direction of said wall. It should be noted that said longitudinal direction is preferably parallel to the plane of the lower face. Thus the upper edge of said wall may have different angles of the walls located at the opposite ends. According to some embodiments, said walls may be curved.

Preferably, the edges of the upper surface are not rectified. In particular, it is preferable for the walls of the tile not to be rectified and/or machined with machine tools. The tile may have substantially any shape, preferably a polygonal shape. Preferred examples of said shapes may be rectangles, squares or hexagons.

According to the preferred embodiment, the tile may have a maximum dimension, that is to say a length of its longer edge, of less than 35 cm, preferably less than 30 cm, even more preferably less than 25 cm. This is because the inventors have surprisingly found that by limiting the dimension of the tile to less than said values it is possible to limit the shape defects that may occur during firing, thus making it unnecessary to rectify the edges of the lower face, or the walls of the tile more generally. The tile may also have a thickness of between 2 and 15 mm, preferably between 4 and 12 mm.

According to the preferred embodiment, the ceramic body may be made of porcelaneous stoneware. According to other embodiments, the body may be made of other materials such as monoporous ceramic, red stoneware, single-fired red body ceramic, clinker or terracotta.

The tile may preferably comprise a surface coating, preferably at least one glaze, capable of at least partially covering an upper surface of the body.

The surface coating may comprise a background coating which may form a base for the decor or the decor itself. Thus the base layer may cover the colour of the body while also waterproofing the body. Preferably, the base layer may comprise at least one glaze and/or one engobe. The base layer may have any colour, but it is preferable for the colour of the base layer to be selected in such a way as to reduce the amount of pigment required for forming the decor. The decor is preferably formed in the surface coating; for example, it may be formed in a decorative layer placed on top of the base layer. Preferably, the decor is formed by pigments printed according to a digital pattern. The decor may have any type of pattern which may be non- representational or may simulate an artificial or natural material. According to the preferred embodiment, the decor comprises characteristics representing defects and/or imperfections such as scratches, stains, changes of tone, etc.

The surface coating may comprise an upper layer placed over the decor and/or over the base layer. Preferably, said upper layer may be capable of protecting the decor itself from wear. In this case, advantageously, the upper layer may be transparent or translucent, so that the underlying decor remains visible. According to other embodiments, the upper layer lay comprise fillers and/or additives for imparting new functions and/or for improving the surface properties of the decorative layer, such as wear resistant, non-slip, anti-bacterial or non-staining properties. The upper layer may be configured to impart particular aesthetic characteristics to the tile, such as lustres, metallic effects, variations of gloss, etc. The upper layer may comprise a glazing element or a grit. In the preferred embodiment, the base layer and/or the upper layer has a thickness of more than 100 microns, preferably more than 200 microns, or even more preferably more than 500 microns.

The tile may comprise at least one relief structure on said upper face. Said relief structure may comprise a first structure formed in the surface coating. Advantageously, said first structure may be formed at least in the upper layer of the surface coating, so that the configuration of said first structure is not obscured by the superimposition of other layers and remains visible as designed, with high definition. Additionally, since it is formed in the upper layer, above the decor, the first structure may have characteristics corresponding to characteristics of the decor so as to create a synergistic effect between the structure and the decor, for example imparting greater depth to the decor and/or counteracting and/or amplifying the effects of light reflection in particular portions of the decor. According to a preferred embodiment, said first structure may be configured to simulate defects such as scratches, blisters, chipping or roughness. Preferably, said first structure may be composed of depressions or cavities in the upper face of the tile; for example, said upper layer may be capable of covering the upper surface of the body in a partial, or at least non- uniform, manner, so that a gap or cavity is formed where the structure is not present or is present to a lesser degree. Preferably, said first structure may be formed according to a digital pattern, and said digital pattern is preferably coordinated with the decor. In some embodiments, the first structure could be formed partially or entirely in the base layer. It is possible for the first structure to be could be formed partially in the base layer and partially in the upper layer in some embodiments. Said relief structure may comprise a second structure formed in the body. It should be noted that the relief structure may comprise both the first and the second structure, or only one of the two. The second structure is preferably made by pressing in the body and is then formed of concavities and/or depressions. However, according to other embodiments, the second structure may be made by additive methods in which some of the material forming the body is deposited on the upper surface of the body according to a predefined pattern. Preferably, the second structure has a greater depth than the first structure. Additionally, said second structure may preferably exhibit the coarser characteristics of the relief structure, while the first structure may comprise the more detailed characteristics of the relief structure. For example, the second structure may have depressions to make the upper surface of the body corrugated, thus providing areas of differing light reflection in the tile surface and imparting an irregular, less industrial appearance to the tile. To strengthen the impression of a hand-made quality in the tiles, it is preferable for the second structure not to be coordinated with the pattern, although in other embodiments it is possible that the second structure may have characteristics corresponding to characteristics of the decor.

A second independent aspect of the invention relates to a set of tiles in which one or more of the tiles are in accordance with the first independent aspect. Said tiles may comprise one or more of the tiles in accordance with the first independent aspect. According to the preferred embodiment of said second independent aspect, the lower faces of the tiles in the set have the same shape and/or dimension. Preferably, the edges of said lower faces are in square with each other. Additionally, according to the preferred embodiment of said second independent aspect, the upper faces of the tiles in the set may have different shapes and/or dimensions. Preferably, the edges of said upper faces are not in square with each other. Since the tiles may be installed with the edges of the lower face in contact with each other, installation is considerably faster than conventional installation, as there is no need to use cross spacers or distance pieces. Moreover, owing to the different shapes and/or dimensions of the upper faces, a joint or space is created between the edges of the tiles for receiving a grout for waterproofing the tiled surface. Furthermore, the variability of the upper faces imparts a substantially hand-made quality to the tiled surface.

A third independent aspect of the invention provides a method for producing ceramic tiles, where said tiles comprise a lower face and an upper face, said method comprising the steps of: preparing a mixture for ceramic materials; shaping said mixture into a panel-shaped body to produce a raw tile; providing a decor on the raw tile; firing said raw tile to produce the ceramic tile. The method may have the characteristic that, in said shaping step, the tile is shaped with a lower face that differs from the upper face in its shape and/or dimension. Preferably, the upper face has a different shape from the lower face. Preferably, the lower face has edges in square with each other, while the upper face has edges out of square. It should be noted that the method of the third independent aspect is capable of producing tiles in accordance with the first independent aspect. The tiles produced by the method according to the second independent aspect may comprise one or more of the characteristics described in relation to the first independent aspect.

Said mixture for ceramic materials is suitable for the production, after firing, of a tile of ceramic material such as porcelaneous stoneware, monoporous ceramic, white or red body ceramic, maiolica, or terracotta. The mixture comprises a mix of powders of raw materials such as clay, kaolin, feldspar, quartz, oxides and other minerals. According to the method of the invention, the body may be formed by compacting the mixture by continuous compaction and/or discontinuous pressing. There is no reason why the raw tile should not be produced by extrusion, in less preferred embodiments. Preferably, the compaction of the mixture is carried out with moulds and/or compacting belts comprising a structure which is the negative of the pattern of the second structure, so as to produce said second structure in the upper surface of the body.

In other embodiments, the body may be made by means of flat moulds or belts, and the second structure may be made by the controlled removal or deposition of part of the mixture from or on to the upper surface of the body. For example, the first structure may be made by a first procedure of printing, preferably digitally, a liquid substance such as an adhesive on the upper surface of the body according to a predefined pattern, after which the mixture is spread on the upper surface. The portion of mixture not adhering to the adhesive is then removed, by suction means for example. The remaining portion of mixture forms a relief in the upper surface of the body.

In the preferred embodiment, the forming step is carried out in a static press in which the mixture is compacted in a mould. Said mould comprises at least an upper wall and a lower wall for forming the respective surfaces of the body. The mould further comprises a plurality of side walls for containing the mixture in the mould during pressing. Said side walls are configured to define the shape of the edges of the upper and lower surfaces of the body and of the vertically extending walls of the body.

The method may comprise a drying step, to eliminate at least some of any residual moisture from the mixture, and to impart greater mechanical strength to the raw tile. The drying is preferably carried out at temperatures above 80°C, for example above 100°C. The drying is carried out after the pressing step, and may preferably be carried out before the step of forming the structure. Preferably, the raw tile after drying has a residual moisture content of less than 8%, for example less than 5%. The method may also comprise a step of applying at least one base layer, for example a glaze and/or an engobe, to the upper surface of the body. For example, the base layer may be applied wet, by pouring or airbrushing for example, so as to deposit a substantially uniform layer on the upper surface of the body. However, there is no reason why the base layer should not be applied by other methods, for example by digital printing, screen printing or flexography, or by dry application methods.

Preferably, the decor is printed, preferably by digital printing, inkjet for example, although other printing methods such as screen printing, flexography, offset and rotogravure are not ruled out. However, inkjet printing and contactless printing methods in general are preferred, because they enable the decor to be applied even to highly developed structures.

Advantageously, the method may also comprise a step of applying the upper layer, for example a glaze or a grit, to the upper surface of the body. In particular, according to the preferred embodiment of the invention, the upper layer may be applied after the application of said decor. Advantageously, the protective layer may be transparent or translucent. In some embodiments, the upper layer may be applied wet, by pouring or airbrushing for example, so as to deposit a substantially uniform layer on the upper surface of the tile. However, in the preferred embodiment, the protective layer is applied by dry application methods. In particular, in the preferred embodiment, the upper layer is applied by a first procedure of printing, preferably digitally, a liquid substance such as an adhesive on the upper surface of the body according to a predefined pattern, after which grit is spread on the upper surface. The portion of grit not adhering to the adhesive is then removed, by suction means for example. The remaining portion of grit forms a relief in the upper layer, creating the first structure. The first structure may also be formed in a similar way in the base layer.

The method also comprises the step of firing the tile at a temperature of more than 900°C, or preferably more than 1000°C, for example about 1200°C. The firing step follows the step of producing the structure, and preferably follows the steps of applying the background and protective coatings and the decor, so that the body and coatings are fired together.

According to the preferred embodiment of the invention, the method does not provide a procedure of squaring or rectifying the tiles.

Preferably, for each production batch, the method may be configured to produce a set of tiles in which the lower faces of said tiles have the same shape. Preferably, for each production batch, said method may be configured to produce a set of tiles in which the tiles have different upper faces. Preferably, at least four different shapes of the upper face, or preferably at least eight different shapes, may be identifiable in each production batch. Preferably, at least four different first structures, or preferably at least eight first structures, may be identifiable in each production batch. Preferably, at least four different decors, or preferably at least eight decors, or even more preferably at least twelve different decors, may be identifiable in each production batch. Preferably, at least four different second structures, or preferably at least eight second structures, or even more preferably at least twelve second structures, may be identifiable in each production batch. Preferably, the combination of the shape of the upper face, the first structure, the decor and/or the second structure may be random, so as create a large number of combinations, helping to impart a greater impression of hand-made quality to the product, particularly after the tiles have been laid.

Further characteristics and advantages of the invention will be apparent from a perusal of the following examples, provided by way of non-limiting example, with the aid of the figures appearing on the attached sheets.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is an axonometric view of a tile according to a first aspect of the invention; Figure 2 is a top view of a tile according to the first aspect of the invention;

Figure 3 is an enlargement of the cross section taken along the plane III-III of Figure 1;

Figure 4 is an enlargement of the area IV of Figure 5;

Figure 5 is a top view of a set of tiles according to the first aspect of the invention;

Figure 6 shows schematically a production line and some procedures of a method according to a further aspect of the invention.

BEST EMBODIMENT OF THE INVENTION

Figure 1 shows a ceramic tile 1 comprising a body 2 of ceramic material, for example porcelaneous stoneware. The tile 1 comprieses an upper face 3 having a decor 4, representing wood or stone for example. The tile 1 further comprises a lower face 5 opposite the upper face 3, and walls having a substantially vertical extension 6.

Figure 2 is a top view of a tile 1 according to the first aspect of the invention. In Figure 2 it should be noted that the lower face 5 of the tile 1 comprises edges 7, defining the lower edges of the vertically extending walls 6, which are in square with each other and define a substantially rectangular shape of the lower face 5. It should be noted that, in the context of the present invention, “vertical extension” is taken to mean that the walls 6 extend in a direction that cuts the plane of the lower face 5.

In Figure 2 it should also be noted that the upper face 3 of the tile 1 comprises edges 8, defining the upper edges of the vertically extending walls 6, which are in square with each other and define a polygonal shape, preferably irregular, of the upper face 3. As may be seen in Figure 2, the lower face 5 and the upper face 3 are of different shapes. It may also be seen from Figure 2 that the vertically extending walls 6 vary their inclination with respect to the horizontal plane, in other words with respect to the plane of the lower face 5, along their longitudinal direction, where said longitudinal direction is substantially parallel to the plane of the lower face 5.

Figure 2 also shows that the tile has a maximum dimension L of less than 35 cm, preferably less than 30 cm, or even more preferably less than 25 cm.

Figure 3 shows that the tile 1 comprises a relief structure 5 formed in said body 2 and apparent on the upper surface 3. The relief structure 5 may represent the grain of wood or natural stone, and may have structural characteristics, such as recesses or protrusions, corresponding to characteristics of the decor 4.

Figure 3 shows that the tile 1 further comprises a relief structure 9 formed in the upper face 3. The tile 1 further comprises a surface coating 10 that covers an upper surface 11 of the body 2.

Figure 4 shows that the surface coating 10 comprises a base layer 12, a decorative layer 13 and an upper layer 14.

In the preferred example, the base layer 13 comprises a glaze that has a substantially uniform colour and is capable of acting as a background or base for the decor. In the example, the base layer 13 is distributed in a substantially uniform manner on the upper surface 11 of the body 2.

The decorative layer 13 comprises the decor 4 and is preferably produced by digital printing.

The upper layer 14, in the example, comprises a transparent glaze and is placed over the decorative layer 13. In the illustrated example, the upper layer 14 covers the upper surface 11 of the body 2 in a non-uniform manner. In the example, discontinuities in the upper layer 14 are represented by gaps 15. The alternation between the upper layer 14 and the gaps 15 creates a first structure 16 of the relief structure 9.

A second structure 17 of the relief structure 9 is produced in the body 2, by pressing for example. In the illustrated preferred example, the second structure 17 comprises depressions that are wider and less well defined than in the first structure 16, which can define detailed aspects of the relief structure 9.

Figure 5 shows a top view of a set 20 of tiles 1 as shown in Figures 1 to 4, in which said tiles 1 comprise lower faces 5 having substantially the same shape and dimensions, so that they can be laid next to each other, but the upper faces 3 have different shapes and dimensions. In particular, the irregularity of the shapes of said upper faces 3 creates joints 21 between the tiles with variable dimensions, thus strengthening the impression of a hand-made quality of the set 20.

Figure 6 shows some steps of a method for producing the tile 1 of Figure 1, according to a further independent aspect of the invention.

The method comprises a step SI of forming a raw tile 22, which in this step is substantially defined by the body 2, by compacting powders of a ceramic mixture. In practice, the powders are compacted in a compaction station 25, by means of a discontinuous press in the example, so as to impart a substantially panel-like shape to the body 2. Preferably, the press uses a mould 23 shaped to form the second structure 17 on the upper surface 11 of the body 2, and to define the shapes of the upper faces 3 and lower faces 5 of the tiles 1. The compaction station is preferably configured for producing at least 4, or preferably 8 different shapes of the upper faces 3 for each production batch. The compaction station is preferably configured for producing at least four, or preferably eight different second structures 17 for each production batch.

The body 2 advances along the line in a direction of advance D towards a drier 26 for removing moisture from the mixture of the body 2 in a drying step S2.

The dried body 2 then advances towards a coating station 27 in which, by means of a coating procedure S3, the raw tile 22 is provided with the base layer 12, by means of airless spraying or airbrushing for example. The coated raw tile 22 advances towards a decorating station 28 having an inkjet printer 29, in which the raw tile 22 is provided with the decor 4 by a printing step S4.

The raw tile 22, now decorated, advances towards a second coating station in which, by means of a second coating procedure S5, the raw tile 22 is provided with the upper layer 14.

In the illustrated example, the second coating station 30 comprises an inkjet printer 31 for printing an adhesive according to a predetermined pattern, and a distribution device 32 for spreading a grit, or a dry glaze, on the upper surface of the body 2 so that some of said grit adheres to the adhesive according to the pattern. The second coating station 30 further comprises a removal device 33, a suction device for example, for removing the excess grit not adhering to the adhesive, thus creating the gaps 15 in the upper layer 14.

The raw tile 9 is then subjected to a firing step S6 in a kiln 34, for example a continuous roller kiln, at a maximum temperature of approximately 1200°C, so as to produce the tile 1.

It should be noted that the method does not include procedures for rectification or squaring after firing.

The invention thus conceived is susceptible of numerous modifications and variations, all of which fall within the scope of the inventive concept.

Furthermore, all the details may be replaced with other technically equivalent elements. In practice, the materials used, as well as the contingent shapes and dimensions, may be any, according to requirements, without thereby departing from the protective scope of the following claims.

Additionally, as is apparent from the content of the description, the present invention relates to one or more of the articles listed below and numbered 1 to 48:

1.- A tile having a lower face and an upper face and comprising a ceramic body and a decor on at least said upper face.

2.- Tile according to Article 1, wherein said lower face differs in its shape and/or dimension from said upper face, and in particular the perimeters of said upper face and said lower face may differ in their shapes.

3.- Tile according to Article 1 or 2, wherein said lower face has edges in square with each other, and preferably said edges of the lower face are not rectified.

4.- Tile according to any of the preceding articles, wherein the upper face of the tile has edges out of square with each other.

5.- Tile according to any of the preceding articles, wherein the body of the tile comprises walls extending in a substantially vertical direction, and at least one of said walls preferably has an inclination with respect to the horizontal plane, in other words with respect to the plane of the lower face, that differs from the inclination of the other walls; or, even more preferably, the inclination of each wall differs from the others.

6.- Tile according to Article 5, wherein the walls comprise an upper edge coinciding with the respective edge of the upper face, and a lower edge coinciding with a respective edge of the lower face. 7.- Tile according to Article 5 or 6, wherein at least one, preferably each, of the vertically extending walls shows a varying inclination along its longitudinal direction.

8.- Tile according to any of Articles 5 to 7, wherein the edges of the upper surface are not rectified; in particular, it is preferable for the walls of the tile not to be rectified and/or machined with machine tools.

9.- Tile according to any of the preceding articles, wherein the tile may have substantially any shape, preferably a polygonal shape, preferred examples of said shapes possibly being rectangles, squares or hexagons.

10.- Tile according to any of the preceding articles, having a maximum dimension, that is to say a length of its longer edge, of less than 35 cm, preferably less than 30 cm, even more preferably less than 25 cm.

11.- Tile according to any of the preceding articles, having a thickness of between 2 and 15 mm, preferably between 4 and 12 mm.

12.- Tile according to any of the preceding articles, wherein the ceramic body is made of porcelaneous stoneware.

13.- Tile according to any of the preceding articles, comprising a surface coating, preferably at least one glaze, capable of at least partially covering an upper surface of the body.

14.- Tile according to Article 13, wherein the surface coating comprises at least one base layer, the base layer preferably having a colour selected in such a way as to reduce the amount of pigment required for forming the decor.

15.- Tile according to Article 13 or 14, wherein the decor is preferably formed in the surface coating, the decor preferably being formed in a decorative layer placed on top of the base layer.

16.- Tile according to any of the preceding articles, wherein the decor is formed by pigments printed according to a digital pattern.

17.- Tile according to any of the preceding articles, wherein the decor comprises characteristics representing defects and/or imperfections such as scratches, stains, or changes of tone.

18.- Tile according to any of Articles 13 to 17, wherein the surface coating comprises an upper layer placed over the decor and/or over the base layer, said upper layer preferably being capable of protecting the decor from wear. 19.- Tile according to Article 18, wherein the upper layer is transparent or translucent.20.- Tile according to Article 18 or 19, wherein the base layer and/or the upper layer has a thickness of more than 100 microns, preferably more than 200 microns, or even more preferably more than 500 microns.

21.- Tile according to any of the preceding articles, comprising at least one relief structure in said upper face.

22.- Tile according to Article 21, wherein said relief structure may comprise a first structure formed in the surface coating, said first structure preferably being formed at least in the upper layer of the surface coating.

23.- Tile according to Article 22, wherein the first structure has characteristics corresponding to characteristics of the decor.

24.- Tile according to Article 22 or 23, wherein said first structure may be configured to simulate defects such as scratches, blisters, chipping or roughness.

25.- Tile according to any of Articles 22 to 24, wherein said first structure is composed of depressions or cavities in the upper face of the tile; for example, said upper layer can cover the upper surface of the body in a partial, or at least non- uniform, manner.

26.- Tile according to any of Articles 21 to 25, wherein said relief structure may comprise a second structure formed in the body.

27.- Tile according to Article 26, wherein the second structure is preferably made by pressing in the body, being formed of concavities and/or depressions, for example.

28.- Tile according to Article 26 or 27, wherein the second structure exhibits the coarser characteristics of the relief structure, while the first structure may comprise more detailed characteristics of the relief structure.

29.- Tile according to any of Articles 26 to 28, wherein the second structure comprises depressions for making the upper surface of the body corrugated.

30.- Tile according to any of Articles 26 to 29, wherein said second structure is not coordinated with the pattern.

31.- A set of tiles wherein one or more of the tiles are in accordance with any of the preceding articles.

32.- Set according to Article 31, wherein the lower faces of the tiles of the set have the same shape and/or dimension. 33.- Set according to Article 31 or 32, wherein the edges of said lower faces are in square with each other.

34.- Set according to any of Articles 31 to 33, wherein the upper faces of the tiles of the set may have different shapes and/or dimensions.

35.- Set according to any of Articles 31 to 34, wherein the edges of said upper faces are not in square with each other.

36.- A method for producing ceramic tiles, wherein said tiles comprise a lower face and an upper face, the method comprising the steps of: preparing a mixture for ceramic materials; shaping said mixture into a panel-shaped body to produce a raw tile; providing a decor on the raw tile; firing said raw tile to produce the ceramic tile.

37.- The method according to Article 36, having the characteristic that, in said shaping step, the tile is shaped with a lower face that differs from the upper face in its shape and/or dimension, and/or the upper face has a different shape from the lower face, and/or the lower face has edges in square with each other, while the upper face has edges out of square.

38.- The method according to Article 36 or 37, wherein said tile is in accordance with any of Articles 1 to 30.

39.- The method according to any of Articles 36 or 38, wherein the body is formed by compacting the mixture by continuous compaction and/or discontinuous pressing.

40.- The method according to Article 39, wherein the forming step is carried out in a static press in which the mixture is compacted in a mould.

41.- The method according to Article 40, wherein said mould comprises at least an upper wall and a lower wall for forming the respective surfaces of the body and a plurality of side walls for containing the mixture within the mould during pressing, and wherein said side walls are configured to define the shape of the edges of the upper and lower surfaces of the body and of the vertically extending walls of the body.

42.- The method according to any of Articles 36 or 41, comprising a drying step to eliminate at least some of any residual moisture from the mixture, and to impart greater mechanical strength to the raw tile. 43.- The method according to any of Articles 36 or 42, comprising a step of applying the base layer, for example a glaze and/or an engobe, to the upper surface of the body.

44.- The method according to any of Articles 36 or 43, wherein the decor is printed, preferably by digital printing, for example inkjet printing.

45.- The method according to any of Articles 36 or 44, comprising a step of applying the upper layer, for example a glaze and/or a grit, to the upper surface of the body.

46.- The method according to Article 45, wherein the upper layer is applied by dry application methods. 47.- The method according to Article 46, wherein the upper layer is applied by a first procedure of printing, preferably digitally, a liquid substance such as an adhesive on the upper surface of the body according to a predefined pattern, after which grit is spread on the upper surface. The portion of grit not adhering to the adhesive is then removed, by suction means for example. 48.- The method according to any of Articles 36 or 47, not including a procedure of squaring or rectification of the tiles.