Method for dry decoration of ceramic slabs

Abstract

The invention relates to a granular ceramic compound for decorating ceramic slabs, comprising a plurality of granules of ceramic material that are loose or incoherent with one another, characterised in that it comprises an adhesive in a catalysed, i.e. hardened state, distributed together with said granules of ceramic material. The invention further relates to a method for producing the ceramic compound and a method for decorating a ceramic slab, comprising the following steps: spreading a layer of granular ceramic compound according to the invention over a surface of the ceramic slab; activating the adhesive in predefined areas that define overall a decoration or graphic pattern; catalysing the adhesive again in said predefined areas so that, in said predefined areas, the granular ceramic compound adheres to the ceramic slab; removing the granular ceramic compound outside said predefined areas.

Description

[0001] Title

[0002] “METHOD FOR DRY DECORATION OF CERAMIC SLABS”

[0003] Description

[0004] The present invention relates to a method for decorating a ceramic slab.

[0005] In particular, the invention relates to a method for spreading a decorative layer of granular material on the surface of a ceramic slab.

[0006] The invention further relates to a method for producing a ceramic granular material, particularly suitable for creating surface decorations.

[0007] There are presently various known methods for decorating a ceramic slab, which use different technologies.

[0008] As is well known, the decoration of ceramic tiles substantially takes place with two main techniques.

[0009] A first technique envisages applying the decoration on a raw tile by means of ink jet printers. The decoration is applied on the tile after pressing and before firing.

[0010] A second technique envisages applying the decoration, again in a step preceding the firing of the tile, in the form of a granular or powder material.

[0011] In this second technique, the granular or powder material forming the decoration is deposited by means of devices of varying nature. To ensure that the layer of granular material defines the expected decoration and remains adherent to the ceramic slab after being deposited and until firing, the present technologies provide for the application, on the surface of the pressed ceramic slab, of an adhesive material, which has the purpose of holding the subsequently deposited granular material.

[0012] In particular, the adhesive material is applied digitally in a controlled manner, for example by means of ink jet printers, so as to define a trace of the desired decoration. In other words, the adhesive material defines the area on which the decoration will be created.

[0013] Following the application of the adhesive material, the granular material is deposited; this may take place in a more or less controlled manner. That is because, in any case, only the granular material which is deposited in contact with the adhesive will remain adherent to the surface of the ceramic slab. The part of the material that is not deposited on the adhesive can instead be removed by suction or blowing, so that only the granular material adherent to the adhesive remains on the surface of the ceramic slab.

[0014] Subsequently, the ceramic slab, complete with the decoration created with the granular material, can continue in the production cycle, receiving any further decorations, and to the final firing process, which sinters the entire body of the ceramic slab, including the decoration.

[0015] The technology summarised above poses several drawbacks.

[0016] First of all, the use of adhesive requires complex supply systems for the digital printer in order to prevent clogging and blockages of the print nozzles.

[0017] Furthermore, the granular material that may be used effectively must have a particle size within a rather limited range. This is because particles that are too fine or too coarse do not flow adequately and thus cannot be distributed in a sufficiently uniform manner.

[0018] The aim of the present invention is to offer a method for decorating a ceramic slab which allows the drawbacks of the presently available methods to be overcome.

[0019] One advantage of the method according to the present invention is that it does not require the application of adhesive on the surface of the ceramic slab to be decorated.

[0020] Another advantage of the method according to the present invention is that it does not impose limitations on the particle size of the granular material used for the decoration.

[0021] Additional features and advantages of the present invention will become more apparent from the detailed description that follows of one embodiment of the invention in question, illustrated by way of non-limiting example in the appended figures, in which:

[0022] - figure 1 schematically shows a first example of a granule (G) according to the invention;

[0023] - figure 2 schematically shows a second example of a granule (G) according to the present invention;

[0024] - figure 3 schematically shows a slab (L) provided with areas (D) on which the ceramic compound according to the present invention is deposited;

[0025] - figure 4 schematically shows a system for implementing the method according to the present invention.

[0026] The preparation of a granular ceramic compound according to the present invention provides for the following steps.

[0027] Initially, the method envisages a step of preparing a ceramic powder material, preferably a glaze, comprising a plurality of particles (P) of different shape and / or size.

[0028] The method envisages then producing a mixture of said ceramic material with an adhesive (C), and a step of granulating said mixture, that is, a step which produces granules (G) comprising particles partly or completely coated with adhesive, and / or aggregates comprising a number of particles joined together, partly or completely coated with adhesive. Preferably, the mixing step also comprises the step of granulating the mixture of ceramic material and adhesive.

[0029] In the part of the description that follows, reference will be made to the mixing step, it being understood that the granulating step is included therein.

[0030] The mixture of said ceramic material with an adhesive can be obtained by means of mixers adapted for homogeneous mixing of different powder and liquid materials. Such devices are capable of uniformly combining the different solid and liquid components to create a coherent mixture.

[0031] For example, it is possible to use high-performance planetary mixers, which are particularly suitable for mixing dry / wet powders and granulation with liquids and ensure high performance in the mixing and granulation process. Alternatively, it is possible to use twin shell mixers or double cone mixers. Such mixers, which are widely used in industry to mix powders and for granulation, are designed to combine different solid and liquid components in a homogeneous manner, thereby contributing to ensure the uniformity of the mixture. In a first possible embodiment of the method, the mixing step is configured so that, substantially, each particle is at least partly or completely coated with adhesive. In a second possible embodiment of the method, the mixing step is configured to join together a number of particles so as to form an aggregate, at least partly or completely coated with adhesive. In the following part of the description, particles at least partly or completely coated with adhesive, and aggregates of particles at least partly or completely coated with adhesive will both be called granules.

[0032] Preferably, the adhesive is a liquid or paste adhesive.

[0033] In the ceramic context, the adhesives may include organic and inorganic binders conventionally used for the preparation of ceramic powders and the formation of granulated materials.

[0034] After mixing, the method envisages fixing or catalysing the adhesive to obtain a hardening thereof.

[0035] The method described thus far produces a granular ceramic compound comprising ceramic material and adhesive in a catalysed, i.e. hardened state.

[0036] Preferably, the step of catalysing the adhesive is carried out in such a way that each particle (P) and / or each aggregate is coated, at least partly, by a layer of adhesive (C) in a hardened state.

[0037] In the first possible embodiment of the method, the particles (P) are at least partly or completely coated with adhesive (C) in a hardened state but are not bound together. In the second possible embodiment, the adhesive, in a hardened state, binds a number of particles so as to form aggregates, but such aggregates are separate from one another. This allows for the mixture to be substantially in an incoherent, granular form, i.e. it comprises a plurality of loose granules (G), each at least partly or completely coated by a layer of adhesive.

[0038] In a third possible embodiment of the method, the mixing step is configured to produce a mixture comprising granules both in the form of aggregates, made up of a number of particles joined together, and in the form of individual particles. The granules are at least partly or completely coated with hardened adhesive. In this third embodiment as well, the mixture is substantially in an incoherent granular form, i.e. it comprises a plurality of loose particles or aggregates, each at least partly or completely coated by a layer of adhesive.

[0039] The ceramic compound obtained thus comprises a plurality of granules of ceramic material that are loose or incoherent with one another, and an adhesive in a catalysed, i.e. hardened state, distributed together with said granules of ceramic material.

[0040] The adhesive at least partly or completely coats at least some of said granules of ceramic material, without binding them together.

[0041] The granular ceramic compound obtained with the method according to the present invention has numerous advantages.

[0042] First of all, thanks to the catalysed adhesive coating, each granule is more resistant compared to the granules of the granular ceramic compounds presently available. This enables an easier management of the compound, given that fewer protection measures are required.

[0043] Furthermore, the granular ceramic compound obtained with the method according to the invention can be made with powders having a much smaller particle size compared to the compounds presently available for similar applications (commonly known in the sector as “grits”).

[0044] The possibility of varying the particle size of the compound as desired, from very small values to larger values, enables management of the final roughness of the product, making it possible, for example, to avoid brushing steps or another surface finishing of the product after firing.

[0045] The step of catalysing the adhesive is obtained as a function of the type of adhesive used. For example, catalysation of the adhesive is obtained by means of at least one of the following steps: drying; exposure to UV radiation; heating; cooling.

[0046] For example, cooling can be used when the adhesive is in a high- temperature liquid form and solidifies below a given temperature. The given temperature can be reached by means of an adhesive cooling device.

[0047] The granular ceramic compound according to the present invention is particularly advantageous for decorating ceramic slabs. In particular, the decoration of a ceramic slab can be achieved by carrying out the following steps.

[0048] Ceramic slab is understood to mean a semi-finished product obtained with a forming process, known in the sector, which substantially entails spreading a layer of ceramic material in granular or powder form, having a pre-established thickness, on a substrate and compacting or pressing the layer by means of a pressing device known in the sector. A compacted or pressed slab (L) is schematically represented in figure 3. The slab (L) has a top surface (F), intended to remain in view and to receive a decoration, and a bottom surface, opposite the top surface, and intended to serve as a surface for laying. Hereinafter in the description, the top surface of the slab intended to receive the decoration will be indicated simply as surface, or surface to be decorated.

[0049] After compacting or pressing, the ceramic slabs can undergo one or more decorating steps with the surface application of glazes, using technologies known in the sector. At the end of the decorating steps provided for, the slab undergoes a firing step.

[0050] The method according to the present invention is particularly effective for decorating ceramic slabs in a step preceding the final firing, and in particular in a step between the compacting or pressing and firing.

[0051] Following the preparation of a ceramic slab, the method according to the present invention envisages spreading, on the surface to be decorated of the ceramic slab, a layer of granular ceramic compound according to the present invention, i.e. obtained with the above-described method for preparing a granular ceramic compound. As explained previously, the granular ceramic compound comprises a plurality of particles of ceramic material, at least partly or completely coated with adhesive in a catalysed, i.e. hardened state, and / or a plurality of aggregates of particles of ceramic material, each of which is at least partly or completely coated with adhesive in a catalysed, i.e. hardened state.

[0052] Preferably, but not necessarily, the spreading of the layer of granular ceramic compound is carried out in a controlled manner, or in such a manner as to reproduce pre-established patterns or decorations. Alternatively, it is possible to spread the layer of ceramic compound evenly over the surface of the ceramic slab.

[0053] Once the layer of granular ceramic compound according to the present invention has been spread on the surface to be decorated, it is possible to reactivate the adhesive in predefined areas (D) that define overall a decoration or graphic pattern. In the text that follows, the word “decoration” is understood to mean any image or graphic pattern it is desired to reproduce on a surface of the ceramic slab. The step of activating the adhesive brings the adhesive back into a liquid or paste state, which favours the adhesion of the granular ceramic compound to the surface of the ceramic slab, as well as the reciprocal adhesion of the granules making up the granular ceramic compound itself.

[0054] The method of activating the adhesive in predefined areas substantially depends on the type of adhesive used, as will be better explained below in the description.

[0055] Following the activation, the adhesive is catalysed again in said predefined areas, so that, in said predefined areas, the granular ceramic compound adheres to the ceramic slab. In this manner, the part of granular ceramic compound comprised in the areas (D) that define overall the decoration, stably adheres to the ceramic slab. In contrast, the part of granular ceramic compound outside the areas that define overall the decoration, that is, the excess with respect to the decoration, remains loose, i.e. incoherent both internally and with respect to the surface of the slab. The above-described steps can be carried out in a system schematically represented in figure 4. The system is configured to carry out the steps of the method in line, i.e. it is configured to carry out the steps of the method on slabs (L) fed forward on a conveyor device along a feed direction (X).

[0056] The system comprises one or more dispensing units (10) adapted to spread, on the surface to be decorated of the ceramic slab, a layer of granular ceramic compound according to the present invention, i.e. obtained with the above-described method for preparing a granular ceramic compound. Preferably, but not necessarily, the one or more dispensing units are configured to spread the layer of ceramic compound in a controlled manner, or in such a manner as to reproduce pre-established patterns or decorations. Alternatively, it is possible to spread the layer of ceramic compound evenly over the surface of the ceramic slab.

[0057] The system further comprises an activator device (1 1 ), adapted to reactivate the adhesive in said predefined areas (D) that define overall a decoration. The activator device is adapted to bring the adhesive back into a liquid or paste state, which favours the adhesion of the granular ceramic compound to the surface of the ceramic slab, as well as the reciprocal adhesion of the granules forming the granular ceramic compound itself. Relative to the feed orientation of the slabs (L) along the feed direction (X), the activator device (1 1 ) is located downstream of the dispensing units (10) present. For example, the activator device (1 1 ) comprises a dispensing system, by way of example an inkjet printer, for dispensing a solvent and / or one or more sources of luminous radiation.

[0058] The system also comprises a catalyser device (12), adapted to catalyse the adhesive in said predefined areas (D), so that, in said predefined areas, the granular ceramic compound adheres to the slab (L). As explained previously, the part of granular ceramic compound comprised in the areas (D) that define overall the decoration stably adheres to the ceramic slab. In contrast, the part of granular ceramic compound outside the areas that define overall the decoration, that is, the excess, with respect to the decoration, remains loose, i.e. incoherent both internally and with respect to the surface of the slab. Relative to the feed orientation of the slabs (L) along the feed direction (X), the catalyser device (12) is located downstream of the activator device (11 ). For example, the catalyser device comprises UV lamps and / or heat sources.

[0059] Subsequently, it is possible to remove the granular ceramic compound outside said predefined areas, so that only the granular ceramic compound comprised in the areas that define overall the decoration remains on the surface of the ceramic slab.

[0060] The removal of the granular ceramic compound outside said predefined areas, that is, the excess, with respect to the decoration, can take place in various ways. For example, the removal can be achieved by suction, brushing, mechanical removal or another method.

[0061] With reference to the system schematically represented in figure 4, a removal device, not represented, would be located downstream of the catalyser device, relative to the feed orientation of the slabs (L) along the feed direction (X).

[0062] As previously highlighted, the activation of the adhesive substantially depends on the type of adhesive used. For example, the activation of the adhesive comprises at least one of the following steps: dispensing a solvent on said predefined areas; exposing said predefined areas to luminous radiation.

[0063] Advantageously, the dispensing of solvent can be achieved by means of a digital printer according to a predefined image. This allows the solvent to be dispensed with great flexibility and precision, in order to create detailed, complex decorations. Furthermore, the dispensing of a solvent makes it possible to use digital printers which are widely available in the sector, without the need to provide complex adaptations to the fluid supply circuits.

[0064] The solvent that may be used depends on the type of the adhesive employed. For example, for certain types of adhesive, a solvent that may be used is water, or a water-based solution. In combination with or as an alternative to dispensing a solvent on said predefined areas, the activation of the adhesive can be achieved by exposing it to luminous radiation emitted by a punctiform digital source, comprising for example a plurality of LEDs. This enables said predefined areas to be illuminated in a precise and effective manner.

[0065] As mentioned previously, following the activation the adhesive is again catalysed in said predefined areas, so that, in said predefined areas, the granular ceramic compound adheres to the ceramic slab. The re- catalysation of the adhesive is obtained according to the type of adhesive employed. For example, the catalysation of the adhesive is obtained by means of at least one of the following steps: drying; exposure to UV radiation; heating; cooling.

[0066] The method according to the present invention offers important advantages compared to the prior art.

[0067] First of all, the necessary stabilisation of the decoration, defined by spreading a layer of granular ceramic compound according to the invention, the activation of the adhesive in predefined areas that define overall the decoration, the subsequent catalysation of the adhesive in said predefined areas and the removal of the granular ceramic compound outside said predefined areas, is obtainable without the need to dispense adhesive. This makes it possible to eliminate, or drastically reduce, the complex solutions adopted in the prior art to enable the dispensing of adhesive.

[0068] Furthermore, the use of a granular ceramic compound according to the invention, comprising a catalysed adhesive, i.e. in a hardened state, makes it possible to obtain decorations having a much more complex and well- defined structure than those obtainable by the prior art. This is thanks to the possibility of selecting, in a much more precise and defined manner, by applying a solvent and / or luminous radiation, the areas in which one desires the consolidation of the granular ceramic compound, in the areas intended to define the decoration itself.

Claims

CLAIMS1) A method for decorating a ceramic slab, comprising the following steps: preparing a ceramic slab; spreading a layer of a granular ceramic compound comprising ceramic material and adhesive in a catalysed, i.e. hardened state over a surface of the ceramic slab; activating the adhesive in predefined areas that define overall a decoration or graphic pattern; catalysing the adhesive again in said predefined areas so that, in said predefined areas, the granular ceramic compound adheres to the ceramic slab.2) The method according to claim 1 , wherein in the step of spreading a layer of a granular ceramic compound over a surface of the ceramic slab, said compound comprises a plurality of granules of ceramic material, at least partly or completely coated with adhesive in a catalysed, i.e. hardened state.3) The method according to claim 2, wherein said granules comprise particles of ceramic material, each of which is at least partly or completely coated with adhesive in a catalysed, i.e. hardened state, and / or a plurality of aggregates of particles of ceramic material, each of which is at least partly or completely coated with adhesive in a catalysed, i.e. hardened state.4) The method according to one of the preceding claims, comprising a step of removing the granular ceramic compound outside said predefined areas, i.e. removing the granular ceramic compound that has not adhered to the surface of the ceramic slab.5) The method according to one of the preceding claims, wherein the step of activating the adhesive in predefined areas comprises at least one of the following steps: dispensing a solvent on said predefined areas; exposing said predefined areas to luminous radiation.6) The method according to claim 5, wherein the step of dispensing a solvent on said predefined areas takes place by means of a digital printer.7) The method according to one of the preceding claims, wherein the step of catalysing the adhesive again is achieved by means of at least one of the following steps: drying; exposure to UV radiation; heating; cooling.8) A method for preparing a granular ceramic compound, comprising the following steps: preparing a ceramic powder material, comprising a plurality of particles; preparing a mixture of said ceramic powder material with an adhesive; catalysing said adhesive to obtain a hardening thereof and obtain granules comprising particles and / or aggregates of particles and adhesive, maintaining the granules substantially separated.9) The method according to claim 8, wherein said step of preparing a mixture partly or completely coats each particle with adhesive, and / or joins together a number of particles so as to form an aggregate, at least partly or completely coated with adhesive.10) The method according to claim 8 or 9, wherein the step of catalysing the adhesive is obtained by means of at least one of the following steps: drying; exposure to UV radiation; heating; cooling.11) A granular ceramic compound for decorating ceramic slabs, comprising: a ceramic material; adhesive in a catalysed, i.e. hardened state.12) The ceramic compound according to claim 11 , comprising a pluralityof granules, wherein each granule comprises: a particle of ceramic material, at least partly or completely coated with adhesive in a catalysed, i.e. hardened state; and / or an aggregate of particles of ceramic material, at least partly or completely coated with adhesive in a catalysed, i.e. hardened state.13) The granular ceramic compound according to claim 12, wherein said granules are loose or incoherent with one another.

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