A method for manufacturing ceramic tiles

Abstract

A method for manufacturing a ceramic tile (1) that comprises the steps of: - providing a green tile (100) having at least a green body (120) with an upper surface; - applying at least one structuring agent (130) on the upper surface of the green body (120) said first structuring agent (130) being adapted to determine at least a portion of a relief structure (10) on the ceramic tile (1); - after having applied said first structuring agent (130), providing at least a first surface covering (8) on said upper surface of the green body (120); and - firing said green tile (100) to obtain a ceramic tile (1) having a relief structure (10) on its upper surface; wherein the method further comprises the step of applying a colored substance (14) on said green body (120) before providing said first surface covering (8).

Description

[0001] A method for manufacturing ceramic tiles.

[0002] The present invention relates to a method for manufacturing ceramic tiles, and ceramic tiles, particularly flooring or cladding tiles. The invention further relates to a line for manufacturing ceramic tiles.

[0003] 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 have a decorative pattern, 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.

[0004] As it is known, relief structure in ceramic tiles is normally produced by pressing during the forming of the tile. In practice, the powders forming the ceramic mixture are placed in a mold and pressed with an embossing die having a relief corresponding to the negative of the relief structure of the tile. Pressing may take place in a continuous process, or another process in which molds are not used, where the relief structure is obtained via the use of embossing belts. The need to use dies, or other preformed negatives, limits the variability of the relief structures that can be produced. Furthermore, the negatives are subject to wear, due mainly to the hardness of the powders and the high production rate. The wear makes it necessary to regenerate or replace the negatives, which consequently increases costs, especially in the case of compacting belts. Furthermore, the substitution of the mold, which occurs every time that it is necessary to change the product or when the mod in use is worn, require time and causes the interruption of the production.

[0005] EP 4086235 Al, from the inventor of the present application, proposes a solution for providing a more flexible way for forming a relief structure on the surface of ceramic tiles, that involves applying a structuring agent directly on the surface of a green body (pressed powders of a ceramic mixture) before applying a glaze coating. The present invention proposes, in the first place, to provide an improved 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.

[0006] Thereto, the present invention, according to its first independent aspect, provides for a method for manufacturing a ceramic tile that comprises the steps of

[0007] - providing a green tile having at least a green body with an upper surface;

[0008] - applying at least one structuring agent on the upper surface of the green body said structuring agent being adapted to determine at least a portion of a relief structure on the ceramic tile;

[0009] - after having applied said structuring agent, providing at least a first surface covering on said upper surface of the green body; and

[0010] - firing said green tile to obtain a ceramic tile having a relief on its upper surface; wherein the method further comprises the step of applying a colored substance on said green body before providing said first surface covering.

[0011] The inventor has found that the application of the colored substance before applying the first surface covering gives the opportunity to hide the color of the green body. This is particularly of interest in case the relief generated in the first surface covering is so deep that the surface covering is substantially completely displaced, and the color of the green body become at least partially visible through the first surface covering. Moreover, in some cases, the colored substance can help increasing the contrast of the decorative surface in the position of the relief, so that the relief structure itself is more visible and / or appears deeper.

[0012] In a preferred embodiment of the invention, the colored substance is opaque. Preferably the colored substance can be white, grey, brown, beige or black. It is not excluded that the colored substance is of another color, but said colors are those that can be more efficient in covering the color of the green body and at the same time improve the contrast in a wide variety of possible decor. In particular, white color has been found the most versatile and most efficient one in maximizing the contrast with a decoration to be formed on the surface of the covering element. In this way, it may be possible to equip a colored substance application device with a limited number of colors, preferably a single color, for the production of a wide range of decorative surfaces. In some preferred embodiments, the colored substance can have substantially the same color of the first surface covering.

[0013] In the preferred embodiment, the colored substance is an ink, for example an ink adapted for being printed with an inkjet printer. Preferably, said ink comprises a pigment, said pigment preferably comprising metal oxides. It is also noted that said pigment should be adapted for being fired in a firing process of a ceramic tile, which normally occurs at a maximum temperature normally between 800 and 1300 °C. The ink can further comprise a liquid part that can be water-based (mainly, but not necessarily completely, formed by water) or organic based (mainly, possibly completely, formed by organic substances like, for example, fatty acid esters, glycol ester or mixture thereof).

[0014] Preferably, the colored substance can be applied on the surface of the green body according to a predetermined pattern. For example, said predetermined pattern of the colored substance can imitate or represent a wood or stone texture, like wood veins or pores. In the most preferred embodiment, said pattern of the colored substance can at least partially, preferably completely, correspond to a pattern of the structuring agent. In this way, it is possible to localize the colored substance in those areas where the higher contrast and the green tile color hiding effect needs to be maximized, thereby saving colored substance material and minimizing wastes.

[0015] In the context of the present application, the structuring agent is a substance that is adapted to interact with the surface coating provided on the surface of the green tile in such a way to generate a relief structure on the surface of the ceramic tile, in particular said relief being formed by excavations in the generally planar surface of the ceramic tile. Since the relief structure is obtained via an interaction between the structuring agent and the surface covering, it is noted that said excavation is at least partially preferably entirely formed in said surface covering. The structuring agent can be according to several possibilities, three of which are herein described without limitative intent. According to a first possibility, the structuring agent can be a repelling agent, i.e. a structuring agent that is able to repel the first surface covering, and displace it or prevent it to cover a certain area of the surface of the green tile where the structuring agent is provided, so to form an excavation. In particular, the structuring agent of the first possibility can be adapted to interact with the vehicle or solvent that is used to apply the first surface covering. The first surface covering can for example be applied in the so called “wet form”, i.e. in liquid form where the first surface covering material is in solution or in suspension in a solvent or vehicle. Said vehicle can be water or an organic substance. Thanks to this interaction the structuring agent of the first possibility can locally repel the vehicle of the first surface covering thereby forming an excavation or a protrusion in the surface of the tile. It is to be noted that in case said structuring agents of the first possibility are used, the relief structure can be at least partially formed, and be visible, in the green tile before the firing step. Said interaction can be caused, for example, by a low affinity between the vehicle or solvent of the first surface covering and the structuring agent, e.g. a different polarity, or a different surface tension. For example, in case the vehicle of the first surface covering is a polar substance, like water or a water-based substance, the physical structuring agent can be a non-polar substance or a substance with a low polarity, for example an oily substance or an organic substance. For example, in this first possibility the structuring agent can be or comprise a hydrophobic substance. Said interaction according to the first possibility can also be caused by different surface tension between the first surface covering and the structuring agent. In some embodiments, the structuring agent can be or comprise an hydrophobic silane-based substance.

[0016] According to a second possibility, the structuring agent can be a sinking agent. A sinking agent, in ceramic practice, is a substance that is able to interact with a glaze to a depression or excavation in the glaze. It is noted that in this second possibility, the structuring agent is able to interact with the substance of the first surface covering itself rather than with the vehicle or solvent thereof. For example, said interaction can be a chemical interaction. It is to be noted that in some cases said interaction of the structuring agent of the second possibility with the first surface covering can occur during said firing step, for example it can be activated during said firing step. In the preferred embodiment of the invention, where the first surface covering can be or comprise a glassy substance, for example a glaze, the structuring agent of said second possibility can be or comprise substances able to interact with the glassy structure of the first surface covering, for example can be or comprise metal oxides or metal complex. For example, the structuring agent of said second possibility can be configured to locally modify, preferably reduce, the viscosity of the glassy substance forming the first surface covering. The structuring agent of said second possibility can also cause a local increase of the density of the glassy substance. The local reduction of the viscosity, and / or of the density, can cause the glassy structure to collapse in correspondence of the portion of the uppers surface of the tile where the structuring agent has been provided thereby forming an excavation. In the most preferred embodiment, the structuring agent of the second possibility can comprise a bismuth oxide, for example bismuth vanadate, lead oxide, tin oxide, oxide of alkali metals, alkaline earth metal etc. Oxides of heavy metals are preferred like oxides of bismuth, vanadium lead and tin. Amongst the latter, oxides of bismuth are preferred because their low toxicity compared to the toxicity of lead.

[0017] According to a third possibility the structuring agent can be a combination of the structuring agent according to the first and the second possibility described above. For example, the structuring agent according to the third possibility can comprise a suspension of a metal oxide or of a metal complex for modifying the characteristic of the glassy structure into a water repellent vehicle or solvent.

[0018] Preferablu, only one structuring agent is provided on the surface of the green tile. In this case, it is preferred that the structuring agent is according to the first possibility. In fact, the inventors have found that structuring agent according to the first possibility is the most promising for maximizing the depth of the relief.

[0019] In alternative embodiments, the step of providing the structuring agent can involve applying at least two structuring agents, preferably different each other. For example, said at least two structuring agents can be respectively according to the first and to the second possibility. In this way, it is possible to combine the effects of the structuring agents according to both the first and second possibility thereby obtaining a structure with deeper excavations. Moreover, the combination of the two typologies of structuring agents permits to maximize the effect of formation of the relief structure and at the same permits to reduce or limit their drawbacks. The combination on the same tile of two different structuring agents may also allow to improve the definition and / or the variation of the relief structure on the tile. In fact, in this way it is possible to provide on different portions of the upper surface different structuring agent that can be differently effective in creating the relief structure.

[0020] In case the method involves applying at least two structuring agents, said predetermined patterns of the structuring agents can partially or completely correspond so that in the corresponding portions of the patterns there can be a synergic effect of the structuring agents. In other embodiments, said predetermined patterns can differ partially or completely, differences in said patterns may allow to obtain a higher variation of the characteristics of the relief structure, like for example variation of the depth thereof.

[0021] According to a special embodiment, in case multiple structuring agents are provided on the green tile, it is possible that one structuring agent is provided before providing the first surface covering and that a second structuring agent can be provided after that the first surface covering has been provided. In this case it is possible to further vary the interaction of between the structuring agents and the first surface covering so that, for example a relief structure having multiple depth can be achieved, one depth in correspondence of the first structuring agent and a second depth in correspondence of the second structuring agent. Preferably, said second structuring agent is according to the above mentioned second possibility. In this special embodiment, it is preferable that the first structuring agent is according to the above mentioned first possibility, whereas the second structuring agent is according to the above mentioned second possibility.

[0022] Preferably, said colored substance and said structuring agent can be applied by means of the same device. In the most preferred embodiment, the structuring agent and the colored substance can be applied by means of printing technique, preferably via digital inkjet printing. Digital inkjet printing allows providing the structuring agent and the colored substance according to a large variety of predetermined pattern and to quickly shift from one pattern to another pattern thereby increasing not only the offer of products on the market but also the flexibility of the entire tile manufacturing process. Digital inkjet printing of the structuring agent and the colored substance can be performed by means of an inkjet printer comprising one or more printheads. In the preferred embodiment the structuring agent can be printed with a resolution above 200 DPI, preferably above 300 DPI. The inkjet printer can be a single pass printer or a multi-pass printer, albeit single pass printers are preferred since allow higher production rate. Single pass printer comprises stationary printheads adapted to print on green tiles moving below said printheads in an advancing direction. Preferably, said printer comprises a first group of printheads adapted to print said structuring agent, and a second group of printheads adapted to print said colored substance, and wherein said first group of printheads is disposed upstream said second group of printheads along said advancing direction. By printing said colored substance and the structuring agent with the same printer, it is possible to maximize the alignment between the pattern of the structuring agent and the pattern of the colored substance so that it is ensured that the desired contrast is obtained in correspondence of the excavation.

[0023] In the preferred embodiment, said structuring agent is provided on the green body in an amount of at least 50 g / sqm (grams per square meter).

[0024] According to the preferred embodiment of the first independent aspect, the green body comprises at least a ceramic mixture suitable for the production, after firing, of a tile of ceramic material such as porcellaneous stoneware, monoporosa (also called single fired wall tile), white or red body ceramic, maiolica, or terracotta. The mixture comprises a mix of powders of raw materials such as clay, kaolin, feldspar, quartz, metal oxides, frits and other raw materials.

[0025] In the method according to the invention, the green body may be formed by compacting the mixture by continuous compaction and / or discontinuous pressing. Preferably, the compaction of the mixture is carried out with molds, dies and / or compacting belts capable of producing a substantially smooth upper surface of the raw tile. However, in alternative embodiments, the mold, die and / or the compacting belt could comprise a structure that is the negative of a basic structure to be produced on the upper surface of the green body. In this case, it would be possible to produce a first basic structure in the green body during forming, and then, after the forming step, to execute a step for producing a second relief structure in the first surface covering according to the first independent aspect of the invention. In this way, the relief structure in the first surface covering may be limited to modifications and / or aspects of detail relative to the basic structure, so as to increase the variability of the structures. Said basic structure can have a detpth above 0,1 mm, more preferably above 0,5 mm, for example above 1mm. In this way it can be possible to have a deeper basic structure in the body of the tile and a more detailed, more variable and less deep structure in the surface covering. It is also possible that the method comprises the step of identifying the basic structure on the upper surface of the green body and the step of selecting the pattern of the structuring agent on the basis of the said identification. In this way it may be possible to coordinate the basic structure and the relief structure, in form of the pattern of the structuring agent, in order to optimize the aesthetic and the natural appearance of the final ceramic tile. The identification of the basic structure can be performed via a 3D scanner or via reading of a marker in the tile, for example with optical readers.

[0026] The method may comprise a drying step, to eliminate at least some of any residual moisture from the mixture forming the green body, and to impart greater mechanical strength to the green body itself. The drying is preferably carried out at temperatures above 80°C, for example above 100°C. The drying is carried out after the step of forming the green body, and is preferably carried out before the step of providing the first surface covering. Preferably, the raw tile after drying has a residual moisture content of less than 5%, or preferably less than 1%. In the preferred embodiment said drying step can be carried out before providing the structuring agent and / or the colored substance. Anyway, according to a special embodiment, the said drying step can be performed after said structuring agent and / or colored substance is provided, preferably between said step of providing the structuring agent and / or the colored substance and said step of providing the first surface covering. It is also not excluded that a first structuring agent and / or the colored substance is provided before drying and / or the colored substance and a second structuring agent is provided after drying.

[0027] In some embodiments the structuring agent and / or the colored substance can be provided after said drying step. In this case the method may also comprise the step of cooling down the upper surface of the green tile, at least of the green body thereof before applying the structuring agent and / or colored substance, in order to improve the printing performances and avoiding the risk of clogging the printheads.

[0028] In the preferred embodiment of the invention, the structuring agent and / or the colored substance can be applied directly onto the upper surface of the green body, i.e. without the interposition of any intermediate layer between the green body and the structuring agent.

[0029] In the preferred embodiment of the invention, the first surface covering can comprise a glaze or an engobe. Preferably, the first surface covering material comprises at least a frit and ceramic raw materials like clay, quartz, opacifiers, silica and / or pigments like metal oxides. In the preferred embodiment, the first surface covering is opaque (not transparent) and colored. Most preferably, the first surface covering has substantially the same color as the colored substance. In this way, the it is possible to provide a more continuous in the visual appearance of the ceramic tile. Most preferably, the first surface covering can be white, beige, or grey.

[0030] The first surface covering is provided on the upper surface of the green body after that the structuring agent and the colored substance have been provided. In the preferred embodiment the first surface covering may be applied wet, for example in the form of a slurry comprising a liquid solvent or vehicle, preferably water, and the surface covering material in powder form. The first surface covering material is preferably applied by spraying or airbrushing but, alternatively it can be applied, by pouring or via other techniques like, for examples, digital printing, screen printing or flexography, or by dry application methods. Spraying or airbrushing are preferred techniques for the application of the first surface covering because they allow a uniform and quick application of a relatively high quantity of first surface covering material, so to form a thicker surface covering in which a deeper relief structure can be formed. In some embodiments, valvejet printing or even inkjet printing can be used for providing the first surface covering. In case inkjet printing is used it is preferred to make use of high discharge printheads.

[0031] Preferably said slurry comprises a density of above 1300 g / 1, more preferably between 1300 g / 1 and 1700 g / 1, for example 1650 g / 1. A higher density of the slurry means a higher dry content thereof. In the context of the invention, it is preferrable to apply the first surface covering in the form of a highly dense slurry so that it is possible to apply a high quantity of first surface covering material while keeping short the time for the evaporation of the vehicle of the slurry which could harm subsequent passages of the method. The first surface covering can be applied in a dry weight above 200 g / sqm, more preferably above 500 g / sqm, for example between 200 and 1000 g / sqm, more preferably between 600 and 900 g / sqm. Preferably, the first surface covering is adapted to cover the entirety of the upper surface of the green body.

[0032] It should also be noted that the method may provide the step of applying a decorative pattern to the upper surface of the green tile. Preferably, the decor is printed by digital printing, inkjet for example, although in alternative embodiment other printing methods such as screen printing, flexography, offset and rotogravure are possible. However, inkjet printing is preferred, because it allows printing a high variety of decor with a relatively high resolution. For example, the decor can be printed with a resolution above 200 DPI, preferably above 300 DPI, for example 360. Preferably the pattern of the structuring agent, the colored substance and the decorative pattern can be printed with the same resolution. The decorative pattern preferably can imitate a wood, marble, natural stone, cement or metal decor. Of course, the decorative pattern can be according to any kind of design.

[0033] In the special embodiment wherein a first and a second structuring agent are provided, respectively before and after the first surface covering is provided, the second structuring agent can be preferably provided by the same device for providing the decorative pattern, especially by the same inkjet printer. Preferably, said inkjet printer comprises a first group of printheads adapted to print said decorative pattern, and a second group of printheads adapted to print said second structuring agent, and wherein said first group of printheads is disposed upstream said second group of printheads along said advancing direction. By printing said decorative pattern and the second structuring agent with the same printer, it is possible to maximize the alignment between the pattern of the second structuring agent and the decorative pattern so that it is ensured that the relief structure is at least partially matching the decorative pattern. In fact, between the application of the first structuring agent and the application of the decorative patent there may be some movements of the tile on the line so that the it could be difficult to obtain a perfect match between the relief structure and the decorative pattern; thereto, by applying the second structuring agent and the decorative pattern with the same device it is ensured that at least that part of the relief structure that is obtained by the second structuring agent matches the decorative pattern.

[0034] In the most preferred, the decorative pattern may have characteristics corresponding to structural features of the relief structure and / or of the basic structure. For example, where the decorative pattern represents a pore of wood or stone, the relief structure may have a recess representing the pore. In this way the realism of the design may be improved. Moreover, in this way it may be possible to compensate phenomena of light scattering or reflectance that are typical for product with glassy surface like ceramic tile, in such a way to give the impression of an even deeper structure and / or in such a way to reduce the glassy and artificial appearance of the surface of the tile so to improve the similarity with the material imitated by the decor, for example wood, stone, cement or metal. For example, the decorative pattern can comprise darker area that may be printed at least partially in correspondence of excavation of the relief structure. To this aim it is possible that the pattern of the structuring agent at least partially, preferably completely corresponds to the decorative pattern.

[0035] With the aim of obtaining a precise correspondence between the pattern of the structuring agent and / or of the colored substance, and the decorative pattern, it is possible that the method comprises the step of identifying the basic structure and or the pattern of the structuring agent on the upper surface of the green tile when approaching the inkjet printer for printing the decorative pattern. In the preferred embodiment, an identification element is applied to the green tile and subsequently identified. Preferably, said identification element is a code readable by an optical reader, for example a barcode or a QR code. Said identification element can be applied to the green tile during, immediately before or immediately after the step of providing the structuring agent and / or the step of providing the colored substance. Preferably said identification element is printed on a surface of the green tile which is different from the upper surface, the most preferred embodiment, said reader is printed with an ink which is adapted to disappear during the firing step, so that the identification element cannot being confused with other ID applied on the product for other purposes, for example for storing purposes. For example, said identification element can be applied in form of an organic ink, preferably a UV ink. In case the structuring agent and / or of the colored substance are applied before the drying step, said ink forming the identification code can withstand a temperature up to 200°C, or up to 250°C. Preferably said identification element is read immediately before the step of printing the decorative pattern. The reader for reading the identification element can be connected to a control unit connected to the printer for printing the decorative pattern.

[0036] In some embodiments, the method may also comprise a step of applying a second surface covering, for example a glaze and / or grit, to the upper surface of the green tile. In particular, the second surface covering may be applied after the application of the first surface covering, and preferably after the application of said decor. Advantageously, the second surface covering may be transparent or translucent. The second surface covering may be preferably applied wet, by pouring or airbrushing for example, so as to deposit a substantially uniform layer on the upper surface of the tile. In alternative embodiments, the second surface covering can be applied by other methods, for example by digital printing, screen printing or flexography, or by dry application methods.

[0037] Preferably the second surface coating is applied wet rather than dry. In fact, wet application of the second surface covering material provides for thinner second surface covering compared to dry application of second surface covering material, so that the second surface covering can be sufficiently thin to adapt to the relief formed in the first surface covering in such a way that said relief manifest itself through the second surface covering and can be visibly and haptically perceived on the surface of the ceramic tile.

[0038] Preferably, the second surface covering is applied in dry weight amount below 30 g / sqm.

[0039] In some embodiments a second relief structure can be formed in said second surface covering. Preferably said second relief structure in the second surface covering can be formed according to multiple possibilities either alone or in combination each other, two of which are herein described.

[0040] According to a first possibility, said second relief structure can be formed by providing a structuring agent in or on said decor and subsequently providing said second surface covering so that said structuring agent interacts with the second surface covering. Said structuring agent can have the same characteristics as those described above for interaction with the first surface covering and can be applied in the same way. According to a preferred solution of this first possibility the structuring agent is printed by the same printer used for printing said decorative pattern. In this case, it is further preferable that the second surface covering can be applied wet.

[0041] According to a second possibility, said second relief structure can be formed by providing a liquid according to a pattern, to form at least a wet area on the surface of the tile; subsequently providing said second surface covering material, preferably in dry powder form, so that said second surface covering material at least partially sticks to wet portion; possibly removing the second surface covering material that doesn’t stick to said wet portion. In this way after firing, a partial second surface covering is formed, for example according to said pattern of wet area, to form elevation at the surface of the tile. Said liquid can be a glue or adhesive. According to a preferred solution of this first possibility the liquid is printed in form of an ink, preferably for inkjet printing. Preferably the liquid can be provided according to a pattern that can entirely or partially correspond, or not correspond at all, to the decor and / or to the pattern of the structuring agent provided before the first surface covering. According to a preferred solution, said pattern of the liquid is such that the wet areas at least partially surround the pattern of the structuring agent provided before the first surface covering. In this way the relief formed by elevation in the second surface covering surrounding the relief formed by excavation in the first surface covering can be combined to form a resulting relief structure in the tile with an increased thickness. According to a preferred solution of this first possibility the liquid can be printed by the same printer used for printing said decorative printer. It is noted that in this way said liquid can be printed according to the same printing file of the decorative pattern so that the decorative pattern and the relief structure can at least partially correspond and said correspondence can be, at least in part, obtained in an extremely easy and cheap way without taking any special measure.

[0042] 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 at or above 1200°C, preferably between 1200°C and 1250°C. The firing step follows the step of providing the first surface covering and of providing the structuring agent and preferably follows the steps of applying the second surface covering and the decor, so that the green tile, the green body and all the layers above its upper surface, can be fired in a unique process.

[0043] According to the most preferred embodiment of the invention the method comprises the steps of: - providing a green tile having at least a green body with an upper surface, said upper surface being flat; - inkjet printing a first structuring agent on the upper surface of the green body according to a first pattern with a first printer, said first structuring agent being adapted to determine at least a part of a relief structure on the ceramic tile; wherein said first structuring agent comprises a hydrophobic substance; - applying a colored substance on said green body according to a pattern corresponding to the first pattern of the first structuring agent; said colored substance being a white ceramic ink printed by means of the said first printer; - after having applied said first structuring agent and said colored substance, providing at least a first surface covering on said upper surface of the green body; wherein said first surface covering is applied in form of a water-based suspension of an engobe, preferably white; said first surface covering being spread over the entirety of the upper surface of said green body and being repelled by the first structuring agent so that excavations are formed at said first pattern; - after having provided said first surface covering, printing a decorative pattern by means of a second inkjet printer adapted to jet a plurality of colored ceramic inks, optionally said decorative pattern being partially or entirely corresponding to said first pattern of the first structuring agent; - applying a second structuring agent according to a second pattern by means of said second inkjet printer, said second pattern being partially, preferably entirely corresponding to said decorative pattern; said second structuring agent comprising a sinking agent adapted to form an excavation in said first surface covering; - firing said green tile to obtain a ceramic tile having a relief on its upper surface. Said method can further comprise drying said green tile before or after said first structuring agent is provided. This embodiment is particularly relevant since the second structuring agent being applied with the same printer of the decorative printer ensures a precise matching between the decorative pattern itself and at least a part of the relief structure, while that part of the relief structure which is obtained by means of the first structuring agent is enhanced by means of the colored substance so that the finally obtained ceramic tile shows an enhanced three-dimensional appearance on its decorative surface, and results more realistic when imitating a natural stone, a marble, a wood or another material.

[0044] It is to be noted that a second independent aspect of the invention can relate to a line for manufacturing a ceramic tile in accordance with the method of the first independent aspect. Thereto the line of the second independent aspect comprises at least: a first device for applying a first structuring agent on an upper surface of a green tile; a second device disposed downstream the first device along an advancing direction, said second device being configured for applying a first surface covering on the surface of the green tile; a firing kiln for firing said green tile into a ceramic tile. With the characteristic that said line comprises a further device for applying a colored substance on the surface of the said green tile, said further device being disposed upstream said second device. Preferably said further device being the same first device for providing the structuring agent, more preferably said first device being a first inkjet printer. Said second device comprising a coating device adapted to spread the first surface covering on the entire upper surface of the green tile. Said line further comprising a second printer for printing a decorative pattern on the surface of the green tile, said second printer being disposed downstream said second device. Preferably, said line further comprises means for applying a second structuring agent on the surface of the green tile, said means being disposed downstream said second device. Preferably, said means being the second printer for printing the decorative pattern. It is noted that any of the device, means, printer, kiln, dryer can comprise any of the feature described above in connection with the first independent aspect and / or being configured for carrying on any of the steps of the method of the first independent aspect.

[0045] It is noted that the fact that an identification element can be applied to the green tile, said identification element being adapted to identify the pattern of the structuring agent and that said identification element can be detected so that a decorative pattern to be printe on the green tile can be selected on the basis of said selection, for example to obtain a good matching between the pattern of the relief structure and the decorative pattern can be achieved, can constitute an inventive aspect independently from the first independent aspect and, in particular, form the fact that the first colored substance is applied on the green tile. Thereto according to its third independent aspect the invention can relate to a method for manufacturing a ceramic tile that comprises the steps of: - providing a green tile having at least a green body with an upper surface; applying at least a first structuring agent on the upper surface of the green body, said first structuring agent being adapted to determine at least a part of a relief structure on the ceramic tile, wherein said first structuring agent is printed according to a first predetermined pattern in a first printing step; after having applied said first structuring agent, providing at least a first surface covering on said upper surface of the green body; after having provided said first surface covering, printing a decorative pattern on said green tile in a second printing step; firing said green tile to obtain a ceramic tile having a relief structure on its upper surface; wherein the method comprises the step of applying an identification element on the green tile, said identification element being adapted to identify the first predetermined pattern; and wherein the method comprises the step of detecting said identification element and selecting the decorative pattern to be printed on the green tile in said second printing step. Preferably wherein said identification element degrades, preferably disappear, during said firing step. According to an important aspect of said third independent aspect, the method can comprise a drying step between said first printing step and the step of applying said first surface covering. Preferably, in said important embodiment said identification element is formed by a substance that isa able to withstand the drying temperature, said drying temperature being at least 200°C, preferably at least 250°C. It is noted that the method of the third independent aspect can comprise anyone of the characteristics described above in relation to the first independent aspect.

[0046] With the intention of better showing the characteristics of the invention, in the following, as an example without any limitative character, several preferred forms of embodiments are described with reference to the accompanying drawings, wherein:

[0047] Figure 1 is an axonometric view of a tile produced by the method according to the invention;

[0048] Figure 2 is an enlargement of the cross section taken along the plane II-II of Figure 1;

[0049] Figure 3 is an enlargement of the area III of Figure 2;

[0050] Figure 4 shows schematically a production line and some steps of a method according to a first possible implementation of the invention;

[0051] Figure 5 is an enlargement of the area V of Figure 4;

[0052] Figures from 6 to 9 respectively show, schematically, the view of Figure 3 of a tile during some steps of the method of figure 4.

[0053] Figure 1 shows a ceramic tile 1 comprising a body 2 of ceramic material, porcelaneous stoneware for example, and an upper surface 4 having a decorative pattern 6, representing wood or stone for example.

[0054] As shown in Figure 2, the tile 1 comprises a first surface covering 8 covering the upper surface of the body 2, said first surface covering 8 comprising a glaze or an engobe. The first surface covering 8 is opaque and comprises a color which is preferably white, or alternatively brown, beige, grey or black. The tile 1, further comprises a relief structure 10 on its upper surface 4 that is realized in the first surface covering 8. The relief structure 10 is formed by excavation or recesses in the generally flat surface of the surface covering 8, above a flat upper surface of the body 2.

[0055] Figure 3 shows that the tile 1 further comprises a second surface covering 12, preferably transparent, that is disposed above the first surface covering 8 and adapted to protect the decorative pattern 6. In the preferred embodiment, the second surface covering 12 comprises a transparent glaze.

[0056] Figure 3 further shows that the relief structure 10 comprises structural features that correspond to structural features of the decorative pattern 6. For example, the relief structure 10 comprises recesses where the decorative pattern 6 represents recessed grains of a wood or of a stone.

[0057] As visible in figure 3, the tile 1 comprises a colored substance 14 between the body 2 and the first surface covering 8, which is present in the tile in a pattern that corresponds to the relief structure 10. In practice the colored substance 14 is present below the recesses of the relief structure 10.

[0058] Figure 4 shows some steps of a method and a line 20 for manufacturing the tile 1 of Figure 1. The method shown in figure 4 is better understood with the help of figures from 5 to 9.

[0059] The method comprises a step SI of forming a green tile 100, which in this step is substantially defined by a green body 120, by compacting powders of a ceramic mixture. In practice, in a compaction station 22 the powders are compacted, by means of a discontinuous press in the example, so as to impart a substantially panel-like shape to the green body 120.

[0060] After step SI, the green body 120 advances along the line 20 in an advancing direction D, for example by means of transport elements T, towards a drier 24 for removing moisture from the mixture of the green body 120 in a drying step S2. In the example, after the drying step, the body has a residual moisture content of less than 5%.

[0061] The green body 120 advances in the direction D towards a first printing station 26 for providing a structuring agent 130 and the colored substance 14 on the green body 20 in a first printing step S3. In the preferred and illustrated example, the first printing station 26 comprises a first inkjet printer 28, preferably a single pass printer. The step S3 is better explained with the help of figures 5 and 6.

[0062] Figure 5 shows that the first inkjet printer 28, in this embodiment, is a single pass inkjet printer comprising a plurality of printing bars 30, 32 wherein each printing bar comprises a plurality of printheads and wherein each printing bar 30, 32 is dedicated to print a respective ink. Said printing bars 30, 32 are disposed one after the other along the advancing direction D. In the example said printing bars 30, 32 comprises a first printing bars 30 destined to print a first structuring agent 130, for forming said relief structure 10, and second printing bars 32 dedicated to print the colored substance 14. As showed in figure 5, each first printing bar 30 for printing the structuring agent precedes one second printing bar 32 for printing the colored substance 14 in the advancing direction D.

[0063] Figure 5 further shows that the first printing station 26 comprises also a lower printer 34 for printing an identification element, not shown, on the lower surface of the green body 120. Said identification element is, preferably, a barcode or a QR code related to information connected to the pattern in which the first structuring agent 130 and / or the colored substance 14 are printed. Said identification code is preferably printed using UV inks being able to withstand a temperature of at least 200 °C, more preferably 250°C. In the embodiment said lower printer 34 is controlled by a first control unit ICU. In the example, the first control unit ICU is adapted to control also the first inkjet printer 28.

[0064] Figure 6 shows that the first structuring agent 130 and the colored substance 14 are printed directly on the upper surface of the green body 120. In the embodiment, the first structuring agent 130 is, for example, polymer- or silane-based and is or comprises preferably a water repellent substance. The colored substance 14 comprises a metal oxide and is preferably white or of the same color as the first surface covering 8. As shown also in figure 6, the first structuring agent 130 is printed according to a first pattern and the colored substance 14 is printed according to a pattern that substantially coincide to the first pattern of the first structuring agent 130. Going back to Figure 4 and following the stream of the method, after the step S3 the green tile 100 reaches a first coating station 36 for providing the first surface covering 8 on the upper surface of the green body 120 and above the first structuring agent 130 and the colored substance 14, in a first coating step S4. In the example, the coating station 36 comprises a sprayer 38. The first surface covering 8 is provided in form of a slurry, in particular of a water suspension of powder of engobe precursor. Preferably said slurry comprises a density of above 1300 g / 1, more preferably between 1300 g / 1 and 1700 g / 1, for example 1650 g / 1.

[0065] As shown in figure 7, the slurry for forming the first surface covering 8 is at least partially repelled by the first structuring agent 130 so that the thickness of the first surface covering 8 is lower or even absent in correspondence of the first pattern of the first structuring agent 130 and the relief structure 10 is partially generated, in form of excavation, immediately after the application of the first surface covering 8. In any case, thanks to the colored substance 14 it is ensured that in case in a certain areas the first surface covering 8 is completely removed, or its thickness is so thin that it may become partially transparent or translucent, the color of the green body 120 is not visible and that it is given enough image contrast that the relief structure 10 is enhanced.

[0066] Going back to figure 4, the green tile 100 is moved to a second printing station 40, preferably comprising a second inkjet printer 42, in particular single pass, for printing the decorative pattern 6 on the green tile 100 in a second printing step S5. The second inkjet printer 42 is configured to jet a plurality of colored ceramic inks for printing said decorative pattern 6. As shown in figure 8, the decorative pattern 6 at least partially coincides to the first pattern of the first structuring agent 130.

[0067] In the example, the second inkjet printer 42 is further configured for printing a second structuring agent 132 according to a respective second pattern. In the example, the second structuring agent 132 is an ink comprising a sinking agent, for example a vanadium- based or bismuth-based sinking agent. The second pattern according to which the second structuring agent 132 is printed is at least partially corresponding to the decorative pattern 6. In the example, the second pattern according to which the second structuring agent 132 is printed differs from the first pattern of the first structuring agent 130. Additionally, it is noted that in the example the colored substance 14 is not printed in correspondence of said second pattern according to which the second structuring agent 132 is printed.

[0068] The second printing station 40 comprises an optical reader 44 connected with a second control unit IICU, that in the example is further configured to control the second inkjet printer 42. The second control unit IICU is adapted to select the decorative pattern 6 to be printed by the second printer 42 on the basis of the identification element read by the optical reader 44.

[0069] After the second printing step S5, the green tile 100 reaches a second coating station 46 for providing the second surface covering 12 on the green tile 100 in a second coating step S6. The second coating station 46 comprises a sprayer 48 that sprays the second surface covering 12 in form of a slurry on top of the first surface covering 8 and of the printed decorative pattern 6 as shown in figure 9.

[0070] The green tile 100 is then subjected to a firing step S7 in a kiln 50, for example a continuous roller kiln, at a maximum temperature of approximately 1220°C, so as to produce the tile 1.

[0071] As shown in figure 9, during the firing step S7 the first structuring agent 130 may degrade. Moreover, in figure 9, it is shown that the second structuring agent 132 is effective during firing so that the excavation formed by the second structuring agent 132 itself is noticeable, visually and haptically, after firing. Eventually, the relief structure 10 is composed by the excavations formed by the first structuring agent 130 and by the second structuring agent 132.

[0072] The invention thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the inventive concept.

[0073] 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.

[0074] Further, as is clear from the content of the description, the present invention relates to one or more of the items as listed below.

[0075] 1.- A method for manufacturing a ceramic tile (1) that comprises the steps of:

[0076] - providing a green tile (100) having at least a green body (120) with an upper surface;

[0077] - applying at least one structuring agent (130) on the upper surface of the green body (120) said first structuring agent (130) being adapted to determine at least a portion of a relief structure (10) on the ceramic tile (1);

[0078] - after having applied said first structuring agent (130), providing at least a first surface covering (8) on said upper surface of the green body (120); and

[0079] - firing said green tile (100) to obtain a ceramic tile (1) having a relief structure (10) on its upper surface; wherein the method further comprises the step of applying a colored substance (14) on said green body (120) before providing said first surface covering (8).

[0080] 2.- The method according to item 1, wherein the colored substance (14) is white, grey, brown, beige or black.

[0081] 3.- The method according to any of the preceding items, wherein said first surface covering (8) is colored.

[0082] 4.- The method according to item 3, wherein the colored substance (14) has substantially the same color of the first surface covering (8).

[0083] 5.- The method according to any of the preceding items, wherein the first surface covering (8) is opaque.

[0084] 6.- The method according to any of the preceding items, wherein colored substance (14) is an ink. 7.- The method according to item 6, wherein said ink of the colored substance (14) comprises a pigment, said pigment preferably comprising metal oxides.

[0085] 8.- The method according to item 6 or 7, wherein said colored substance (14) is applied via inkjet printing.

[0086] 9.- The method according to any of the preceding items, wherein said colored substance (14) and said first structuring agent (130) are applied according to respective patterns.

[0087] 10.- The method according to item 9, wherein the pattern of said colored substance (14) and the pattern of said first structuring agent (130) are at least in part, preferably completely, coinciding.

[0088] 11. - The method according to any of the preceding items, wherein said colored substance (14) and said first structuring agent (130) are applied by a same device.

[0089] 12.- The method according to any of the preceding items, wherein said device is a first inkjet printer (28).

[0090] 13.- The method according to item 12, wherein said first inkjet printer (28) is a single pass printer and comprises stationary printheads adapted to print on green tiles (100) moving below said printheads in an advancing direction (D).

[0091] 14.- The method according to item 13, wherein said first inkjet printer (28) comprises a first group of printheads adapted to print said colored substance (14), and a second group of printheads adapted to print said first structuring agent (130), and wherein said first group of printheads is disposed upstream said second group of printheads along said advancing direction (D).

[0092] 15.- The method according to any of the preceding items, comprising the step of printing a decorative pattern (6) on the upper surface of said green tile (100). 16.- The method according to item 15, wherein said step of printing the decorative pattern (6) is performed after that said first surface covering (8) is provided.

[0093] 17.- The method according to item 15 or 16, wherein said step of printing the decorative pattern (6) involves jetting at least one or more colored inks by means of a second inkjet printer (42).

[0094] 18.- The method according to any of items from 15 to 17, wherein said decorative pattern (6) at least partially corresponds to a pattern of said colored substance (14) and / or of at least said first structuring agent (130).

[0095] 19.- The method according to any of the preceding items, wherein said first surface covering (8) is applied by means of spry coating technique, a valve-jet printing technique or an inkjet printing technique.

[0096] 20.- The method according to any of the preceding items, wherein said first surface covering (8) is adapted to cover the entirety of the upper surface of the green body (120).

[0097] 21.- The method according to any of the preceding items, wherein said first structuring agent (130) comprise a hydrophobic substance and wherein said first surface covering (8) is a water-based suspension or solution.

[0098] 22.- The method according to any of the preceding items, comprising the step of applying a second structuring agent (132) after said first surface covering (8) is provided.

[0099] 23.- The method according to item 23, wherein said second structuring agent (132) comprises a sinking agent and wherein said first surface covering (8) is a glaze or an engobe.

[0100] 24.- The method according to anyone of item 22 or 23, wherein said second structuring agent (130) is applied by means of a second inkjet printer (42). 25.- The method according to item 24, wherein said second inkjet printer (42) is further used for printing a decorative pattern (6) on said green tile (100).

[0101] 26.- The method according to item 25, wherein said second structuring agent (132) is printed according to a second pattern being at least partially corresponding to said decorative pattern (6)

[0102] 27.- A method for manufacturing a ceramic tile (1) that comprises the steps of:

[0103] - providing a green tile (100) having at least a green body (120) with an upper surface;

[0104] - applying at least a first structuring agent (130) on the upper surface of the green body, said first structuring agent (130) being adapted to determine at least a part of a relief structure (10) on the ceramic tile (1), wherein said first structuring agent (130) is printed according to a first predetermined pattern in a first printing step (S3);

[0105] - after having applied said first structuring agent (130), providing at least a first surface covering (8) on said upper surface of the green body (120);

[0106] - after having provided said first surface covering (6), printing a decorative pattern (6) on said green tile (100) in a second printing step (S5);

[0107] - firing said green tile (100) to obtain a ceramic tile (1) having a relief structure (10) on its upper surface (4);

[0108] - wherein the method comprises the step of applying an identification element on the green tile (100), said identification element being adapted to identify the first predetermined pattern; and

[0109] - wherein the method comprises the step of detecting said identification element and selecting the decorative pattern (6) to be printed on the green tile (100) in said second printing step (S5).

[0110] 28.- The method according to item 27, wherein the identification element is a barcode or a QR code.

[0111] 29.- The method according to item 27 or 28, wherein the identification element is printed by means of an inkjet printer (34). 30.- The method according to any of items from 27 to 29, wherein the identification element is applied to a surface of the green body (120) that is different from the upper surface of the green tile (100).

[0112] 31.- The method according to item 29 or 30, wherein said identification element is printed using UV inks.

[0113] 32.- The method according to any of items from 27 to 31, wherein said identification element degrades, preferably disappear, during said firing step.

[0114] 33.- The method according to item any of items from 27 to 32, comprising a drying step between said first printing step and the step of applying said first surface covering.

[0115] 34.- The method according to item 33, wherein said identification element is formed by a substance that is able to withstand the drying temperature.

[0116] 35.- The method according to item 34, wherein said identification element is formed by a substance that is able to withstand a temperature of at least 200°C, preferably at least 250°C.

[0117] 36.- A line (20) for manufacturing a ceramic tile (1), whether or not in accordance with any of items from 1 to 26, that comprises at least: a first device (28) for applying a first structuring agent (130) on an upper surface of a green tile (100); a second device (36) disposed downstream the first device (28) along an advancing direction (D), said second device (36) being configured for applying a first surface covering (8) on the surface of the green tile (100); a firing kiln (50) for firing said green tile (100) into a ceramic tile (1); wherein said line comprises a further device for applying a colored substance on the surface of the said green tile (100), said further device being disposed upstream said second device (36). 37.- The line according to item 36, wherein said further device being the same first device (28) for providing the structuring agent (130), more preferably said first device being a first inkjet printer.

[0118] 38.- The line according to item 36 or 37, wherein said second device (36) comprises a coating device adapted to spread the first surface covering (8) on the entire upper surface of the green tile (100).

[0119] 39.- The line according to any of items from 36 to 38, wherein it comprises a second printer (42) for printing a decorative pattern (6) on the surface of the green tile (100), said second printer (42) being disposed downstream said second device (36).

[0120] 40.- The line according to any of items from 36 to 39, wherein it comprises means for applying a second structuring agent (132) on the surface of the green tile (100), said means being disposed downstream said second device (36).

[0121] 41.- The line according to items 39 and 40, wherein said means being the second printer (42) for printing the decorative pattern.

Claims

Claims1.- A method for manufacturing a ceramic tile (1) that comprises the steps of:- providing a green tile (100) having at least a green body (120) with an upper surface;- applying at least one structuring agent (130) on the upper surface of the green body (120) said first structuring agent (130) being adapted to determine at least a portion of a relief structure (10) on the ceramic tile (1);- after having applied said first structuring agent (130), providing at least a first surface covering (8) on said upper surface of the green body (120); and- firing said green tile (100) to obtain a ceramic tile (1) having a relief structure (10) on its upper surface; wherein the method further comprises the step of applying a colored substance (14) on said green body (120) before providing said first surface covering (8).2.- The method according to claim 1, wherein the colored substance (14) is white, grey, brown, beige or black.3.- The method according to any of the preceding claims, wherein said first surface covering (8) is colored, preferably opaque.4.- The method according to claim 3, wherein the colored substance (14) has substantially the same color of the first surface covering (8).5.- The method according to any of the preceding claims, wherein colored substance (14) is an ink applied via inkjet printing, preferably said ink of the colored substance (14) comprising a pigment, said pigment preferably comprising a metal oxide.6.- The method according to any of the preceding claims, wherein said colored substance (14) and said first structuring agent (130) are applied according to respective patternspreferably wherein the pattern of said colored substance (14) and the pattern of said first structuring agent (130) are at least in part, preferably completely, coinciding.7.- The method according to any of the preceding claims, wherein said colored substance (14) and said first structuring agent (130) are applied by a same device, preferably said device being a first inkjet printer (28).8.- The method according to any of the preceding claims, comprising the step of printing a decorative pattern (6) on the upper surface of said green tile (100), preferably , wherein said step of printing the decorative pattern (6) involves jetting at least one or more colored inks by means of a second inkjet printer (42).9.- The method according to claim 8, wherein said step of printing the decorative pattern (6) is performed after that said first surface covering (8) is provided.10.- The method according to claim 8 or 9, wherein said decorative pattern (6) at least partially corresponds to a pattern of said colored substance (14) and / or of at least said first structuring agent (130).11.- The method according to any of the preceding claims, wherein said first structuring agent (130) comprise a hydrophobic substance and wherein said first surface covering (8) is a water-based suspension or solution.12.- The method according to any of the preceding claims, comprising the step of applying a second structuring agent (132) after said first surface covering (8) is provided, preferably wherein said second structuring agent (132) comprises a sinking agent and wherein said first surface covering (8) is a glaze or an engobe.13.- The method according to claim 12, wherein said second structuring agent (130) is applied by means of a second inkjet printer (42), and wherein said second inkjet printer (42) is further used for printing a decorative pattern (6) on said green tile (100).14.- The method according to claim 13, wherein said second structuring agent (132) is printed according to a second pattern being at least partially corresponding to said decorative pattern (6)15.- A line (20) for manufacturing a ceramic tile (1), whether or not in accordance with any of the preceding claims, that comprises at least: a first device (28) for applying a first structuring agent (130) on an upper surface of a green tile (100); a second device (36) disposed downstream the first device (28) along an advancing direction (D), said second device (36) being configured for applying a first surface covering (8) on the surface of the green tile (100); a firing kiln (50) for firing said green tile (100) into a ceramic tile (1); wherein said line comprises a further device for applying a colored substance on the surface of the said green tile (100), said further device being disposed upstream said second device (36).16.- The line according to claim 15, wherein said further device being the same first device (28) for providing the structuring agent (130), more preferably said first device being a first inkjet printer.17.- The line according to claim 15 or 16, wherein said second device (36) comprises a coating device adapted to spread the first surface covering (8) on the entire upper surface of the green tile (100).18.- The line according to any of claims from 15 to 17, wherein it comprises a second printer (42) for printing a decorative pattern (6) on the surface of the green tile (100), said second printer (42) being disposed downstream said second device (36).19.- The line according to any of claims from 15 to 18, wherein it comprises means for applying a second structuring agent (132) on the surface of the green tile (100), said means being disposed downstream said second device (36).20.- The line according to claims 15 and 19, wherein said means are the second printer (42) for printing the decorative pattern (6).

Images