WO2018007972A1

WO2018007972A1 - Process for obtaining large-format and thin thickness glazed ceramic slabs

Info

Publication number: WO2018007972A1
Application number: PCT/IB2017/054076
Authority: WO
Inventors: Claudio Fossaluzza
Original assignee: Target - S.R.L.
Priority date: 2016-07-07
Filing date: 2017-07-06
Publication date: 2018-01-11
Also published as: CN109476559A; IT201600071139A1; EP3481790A1

Abstract

The process for obtaining large-format and thin thickness glazed ceramic slabs comprises steps of: predisposing a flat support of vitrified ceramic material having desired dimensions and thickness, applying, on at least a surface portion of said support, a glaze having a fusible base and metal pigments having a glazing temperature (TV) lower than a vitrification temperature (TG) of said support, subjecting the product obtained to a heat treatment, conducted at a firing temperature (T2) equal to the glazing temperature (TV) of said glaze.

Description

TITLE

PROCESS FOR OBTAINING LARGE-FORMAT AND THIN THICKNESS

GLAZED CERAMIC SLABS.

Description

TECHNICAL FIELD OF THE INVENTION

[001] The present invention relates to a process for obtaining glazed flat ceramic elements having large dimensions and reduced thickness, such as slabs suitable for being advantageously used both as they are and also suitable for being used to obtain tiles of smaller dimensions and different shapes, for cladding surfaces such as for example floorings and walls, both internal and external.

BACKGROUND ART

[002] In recent years, the ceramic industry sector has evolved in order to meet market needs, and now offers ceramic slabs for cladding that are progressively of larger dimensions, while at the same time the thickness thereof is reduced so as to make them sufficiently light for transport and laying; in fact today glazed ceramic slabs are in production that have a surface extension of even greater than 3m² and a thickness comprised between about 3 and 1 1 mm, in particular between 3 and 6 mm.

[003] Slabs of these dimensions in fact enable cladding very large surfaces, such as for example building fagades, limiting the number of gaps between one element and another and thus producing a highly- appreciated uniform and minimalist aesthetic effect.

[004] Said slabs can also have glazed surfaces, i.e. surface-decorated thanks to the application of special ceramic glazes, i.e. compositions suitable for developing, generally at heat, a glassy surface, obtaining desired colouring or aesthetic effects.

[005] The traditional method for obtaining conventional glazed tiles, thus having a thickness of greater than 6-7 mm and modest dimensions, i.e. substantially less than 3m², known in the sector as "double-firing", consists in preparing a support made of a clayey material, subjecting it then to a first firing, at a temperature comprised between about 1050 - 1 100°C, so as to cause vitrification thereof, realising a vitrified ceramic product known as a "biscuit"; this product is then glazed using suitable ceramic glazes and then subjected to a further firing, at a temperature close to vitrification temperature, with the aim of obtaining the glazing of the surface glaze. In fact, the ceramic glazes generally used have a glazing temperature of a little lower than the vitrification temperature of the clayey support.

[006] However, this process is firmly inadvisable for realising large- dimension glazed slabs with reduced thickness, as during the second firing step there are frequently tensions between the underlying support and the glaze, which can lead to deformations, thus compromising the planarity of the final slab, or even fractures, making the slab effectively unusable.

[007] For the above-described reasons, the large-dimension slabs with reduced thickness at present available on the market are obtained with a process known as "single-firing", in which a single operation achieves both the firing of the preformed clayey mixture constituting the body of the slab and the surface glazing.

[008] In other words, the slab of unfired clayey material is surface- decorated by application of suitable glazes, and thereafter fired in a single cycle, in which temperatures of about 1 150 - 1200°C are reached, so as to cause, at the same time, firing of the clayey mixture, i.e. the vitrification thereof, and the glazing of the surface glaze. In this case too, clearly, the ceramic glazes generally used have a glazing temperature that is substantially equal to the vitrification temperature of the clayey support.

[009] Lastly, in another known process the unfired slabs are subjected to a single firing, at the vitrification temperature, and then decorated with suitable colours in the cold state, thus without any further need for firing; with this system however the surface decoration is rather delicate and absolutely not resistant to wear, and thus makes the slabs unsuitable for use as a cladding for floorings.

[0010] As regards, on the other hand, the type of decoration, in recent years great efforts have been made by producers for obtaining glazed slabs, creating, on the surface thereof, the aspect of natural materials, such as for example marble, stone, granite, wood etc.

[0011] For this purpose, for application of the glaze on the surface of the slabs, at present digital printing systems are used, which include the use of one or more printing heads, suitable for directly dispensing, on the surface of the slab, special pigmented inks in the form of small drops, and able to continuously realise, on the whole slab surface, a plurality of identical elementary graphic units, i.e. pixels, the distribution of which enables the creation of complex forms and figures.

[0012] These printing systems use a four-colour method, or a possibly a six-colour method, and load four or six conventional colour inks on the printing heads that if mixed in various percentages give various tones and nuances.

[0013] While in order to create surface decorations creating the effect of natural materials these printing systems function in an overall satisfactory way, the same cannot be said for the realising of slabs having a uniform surface colouring, i.e. a "single-tone" finish.

[0014] In fact, as is known to an expert in the field, obtaining a homogeneously-glazed slab in a uniform colour requires the use of a large quantity of ink, which is not dispensable using a digital printing system; further, as a four-colour method is used, the same colour might be slightly different from slab to slab, making the final effect unacceptable. Further, certain colours, such as for example green, are very difficult to obtain.

[0015] For the creation of relief decorations, for example in order to obtain a glazed slab exhibiting a wood-grain surface, at present appropriate profiled dies are predisposed on the surface of the still-unfired clayey support, so as to impress thereon the desired relief decoration before proceeding with firing and glazing.

[0016] However, this system is poorly flexible as it is necessary to realise and to keep a plurality of dies in the storehouse, each bearing a specific relief decoration, with a consequent increase in costs.

SUMMARY OF THE INVENTION

[0017] The main task of the object of the present invention is to obviate the drawbacks in the prior art, by providing a process for obtaining slabs with glazed ceramic coatings having large dimensions and reduced thickness while enabling a planarity thereof to be maintained and preventing formation of fractures.

[0018] With regard to the above-described task, an aim of the present invention is to provide a process for realising ceramic cladding slabs which can be surface-decorated according to a user's requirements, possibly also realising "single-tone" colourings.

[0019] A further aim of the invention is to obtain a process that is simple to realise, versatile and reliable, and which does not require particular instrumentation or equipment, and is therefore easily industrialisable.

[0020] The above-mentioned task, and other aims which will more fully emerge in the following description, are attained by a process as defined in claim 1 ; further characteristics are defined in the following dependent claims.

DETAILED DESCRIPTION OF THE INVENTION

[0021] A process according to the present invention enables realising flat slabs made of surface-glazed vitrified ceramic material, i.e. surface areas of up to more than 3m², with a reduced thickness, preferably comprised about between 3 and 6 mm and, more generally, between 3 and 1 1 mm, suitable for being used for cladding floors or walls, either with their original size or reduced to elements having smaller dimensions.

[0022] A process according to the present invention is particularly advantageous for obtaining glazed slabs with a single colouring, which is homogeneous over the whole extension of the slab and uniform for all the slabs obtained using the process. However, as explained in the following in greater detail, with a process according to the present invention it is possible also to obtain glazed slabs provided with surface decorations recreating complex figures, patterns or relief decorations.

[0023] A first step a) of the process according to the present invention consists in predisposing a vitrified slab support having desired dimensions and thickness.

[0024] This slab support is preferably obtained by pouring a suitable mixture formed by essentially clayey components internally of a suitable and conventional die, then subjecting the mixture to a pressing by action of suitable ceramic presses.

[0025] Once the unfired support has been realised, it is subjected to a first heat treatment, or first firing, at a temperature T1 that is substantially equal to the vitrification temperature TG of the clayey material which the support is formed in, essentially comprised between about 1 150°C and 1200°C for obtaining vitrification thereof.

[0026] It is specified that in the present description, when it is stated that the support is "vitrified", this means that it has completed the vitrification process, and has then also cooled to ambient temperature.

[0027] In fact, the vitrified support is a semi-finished piece that can be stored and also transported for restricted distances, like any other ceramic product.

[0028] For the sake of precision, while it is important that between the pressure-forming step of the unfired support and the first firing step the latter should not travel long distances, because of the fragility thereof caused by the reduced thickness, the vitrified support has in fact sufficient resistance to be sent, using conventional work lines, to the following operating steps, in particular to the following step b) of surface glazing.

[0029] Possibly, if necessary, before step b) of glazing the vitrified support, the support can be subjected to a cutting step, in which it is appropriately cut, preferably by use of diamond cutting heads, following the most suitable geometries and dimensions on the basis of specific use requirements.

[0030] Further, in a case in which it is desired to give greater resistance to the cladding slabs obtained at the end of the process, in particular when the slabs are used in those conditions, thus having significant dimensions, it can be advantageous to apply a net reinforcing structure on the opposite surface of the support to the surface which will be subjected to glazing in said step b).

[0031] According to a particular feature of the present invention, at least a surface portion of the vitrified flat support obtained during said step a) is subjected to a step b) of glazing, in which glazes, i.e. substances in liquid or paste or powder form, are used that have a composition such as to develop a glassy surface at a determined temperature.

[0032] In particular, according to an advantageous characteristic of the present invention, the glazes applied during the glazing step b) of a process according to the present invention are selected from among those having a fusible base and metal pigments having a glazing temperature TV that is lower than the vitrification TG temperature of the support, and preferably comprised between about 600°C and about 900°C and, still more in particular, between 600° C and 830° C.

[0033] Following the application of said glaze on at least a surface portion of said vitrified flat support, it is subjected to a step c) of heat treatment, or firing, able to obtain the vitrification of the glaze placed on the surface thereof.

[0034] The firing temperature T2 reached in said step c) is essentially equal to, or at least close to, the above-mentioned glazing temperature TV of the glaze and this therefore preferably comprised between about 600°C and 900°C, on the basis of the dimensions of the support and the type of glaze used.

[0035] The temperature T2 is advantageously sufficient for obtaining the glazing of the applied glaze without however altering the support, as it is already vitrified, and in any case has a much high firing temperature. In this way, tensions are advantageously not created between the two materials, and consequently no fractures or deformations of the slab occur, which remains perfectly flat notwithstanding the significant dimensions thereof.

[0036] Step c) is preferably carried out using suitable single-layer roller kilns, taking care to maintain the temperature as constant as possible.

[0037] Said glazing step b) can be carried out with various techniques, known and conventional, selected on the basis of the type of decoration which is desired on the slab. For example, in order to obtain a decorated slab with "a single-tone" colouring which is uniform and homogeneous, the use of a screen printing method is particularly advantageous; in this case the glazes used will preferably be in paste form.

[0038] The different colourings that are to be used in the decoration of the slab, not present on the market, are therefore possibly prepared by mixing suitable quantities of glazes of different colours, up to obtaining the desired tone.

[0039] The screen printing method initially comprises preparation of a special screen comprised in a frame substantially formed by an external metal frame, on which screening mesh yarns are applied and stretched so as to form a large-mesh fabric.

[0040] This screen is then positioned at the portion of the surface of the vitrified support which is to be decorated, and is kept more or less raised with respect to the support on the basis of the quantity of colouring paste that is to be deposited.

[0041] The glaze in paste form is then poured onto the fabric of the screen frame and distributed with a doctor, on the portion of the surface of the slab which is to be decorated; by doing this it is possible to apply the glaze in paste form in a very uniform and precise way and in the right quantity on the surface that is to be glazed.

[0042] Instead, in a case in which it is desired to obtain, with the screen printing method, a special decoration creating figures or patterns that are more or less complex, it is necessary to selectively occlude the meshes of the fabric of the screen mesh in the zones in which glaze of a certain colour is not intended to pass through, while allowing the glaze to permeate into the zones defining the desired decoration.

[0043] To do this, a water-soluble photo-emulsion is suitably applied, which is then dried; a film is then created for screening, bearing the positive of the final decoration on a substantially high-density black background, and is placed in close contact with said emulsion, at the side destined to go into contact with the surface of the slab to be decorated, thus exposing it to ultra-violet rays.

[0044] The rays cause the hardening of the underlying emulsion exclusively in the free areas defined by the film; the portions of film realised in high-density black, on the other hand, prevent passage of the ultraviolet rays, thus preventing the hardening of the underlying emulsion, which will therefore remain water-soluble.

[0045] A subsequent washing of the fabric has the effect of removing the non-hardened emulsion, revealing the open areas of the screen material, which thus allows passage of the glaze in paste form towards the underlying surface to be decorated.

[0046] The screen printing method further enables obtaining glazed decorations in relief, without however requiring the realisation of reliefs or incisions obtainable with dies in the material forming the support; in fact, by acting on the quantity of emulsion applied on the fabric and on the distance between the frame and surface to be decorated, it is possible to define areas in which a greater quantity of glaze in paste form can be applied with respect to surrounding areas, thus creating decorations in relief with respect to the bottom.

[0047] Step b) of glazing can advantageously also be carried out by spray- printing; in this case, the glaze will preferably be in the form of liquid ink, or alternatively dry-printing with powder glazes.

[0048] The glazes might possibly also be applied on the surface of the vitrified support by using one or more methods among which those described in the foregoing, on the basis of the specific effect that is to be obtained.

[0049] Lastly, in a case in which the slabs obtained with a process according to the present invention are destined to form the cladding of a flooring, the glazes used, whether in liquid, powder or paste form, can be added-to by a determined quantity of powders of specific materials, suitable for giving the glazed surface of the slab a strong resistance to wear.

[0050] Further, the process of the invention can be configured in a plurality of embodiments, in which not only can the glazing be realised according to the various above-described ways, but it can also be combined in multiple ways with various decoration methods, including known ways, with the aim of obtaining special effects on the product.

[0051] In detail, the invention can also include, in combination with one or more of the different glazing modalities, decoration using digital inkjet printing and/or depositing of grits.

[0052] In a first version, first a glazing of the support can be done, then to proceed with a decoration using digital printing.

[0053] For example, a single-tone glaze coating can be realised and then, before or following the glaze hardening process, digital decoration can be carried out, creating a nuanced effect, or designs or different effects, proceeding with a re-firing at a temperature comprised between 600°C and 900°C.

[0054] In fact, it is known that decoration by digital printing is not able to realise single-tone backgrounds on the support that are truly uniform, and on a large format.

[0055] The invention therefore enables, in a surprising way with respect to the present knowledge and practice in the sector, realising a completely new product that is not at present obtainable.

[0056] In another embodiment of the process of the invention, by way of non-limiting example, the glaze can be spread in such a way as to define a "structure", then, before or after the glaze hardening process, to proceed to a digital decoration using digital inkjet printing, with a re-firing at a temperature comprised between 600°C and 900°C.

[0057] By "structure" is meant, in the present context, a decoration using reliefs and recesses, which implies the use of a significant quantity of material for this type of application, which cannot be obtained using digital printing.

[0058] In fact, digital decoration enables easily obtaining an infinite variety of two-dimensional decorations, but cannot deposit sufficient material for creating appreciable three-dimensional effects.

[0059] For this reason, at present ceramic companies are forced to use supports that are already structured from the outset, i.e. having a structure impressed during the forming step.

[0060] The supports are however very expensive and the use thereof is justified only in the case of production of large volumes of finished products.

[0061] As already explained, the reliefs can be realised by spreading coats of glaze using a spatula, for obtaining very natural effects, or by using print screens, for obtaining special patterns or special textures.

[0062] Digital decoration also contributes to the finished product because of its great precision and the chromatic variety of the decorations.

[0063] In this way, same or better results are obtained with respect to the known system, but with much lower costs and with the possibility of customising even for a single client, which would not be economically viable with the known systems.

[0064] In a further version of the invention the glazing is done before net screens are used to apply grits and create a decoration in relief.

[0065] In a further embodiment, glazing is done first, before application of glass flakes.

[0066] Further, the process of the invention can enable glazing only in one or more portions of the support, then decorating the other portions with different methods, for example by digital printing; consider for example an affixing of gold or other metals using digital printing methods flanked by glazed portions, for enriching the decoration.

[0067] To summarise, according to the present invention a process for obtaining a glazed cladding slab having large dimensions and reduced thickness, suitable for surface cladding for floorings or walls, comprises following steps:

a) predisposing a flat support of vitrified ceramic material having desired dimensions and thickness, said support preferably having previously been subjected to a step of heat treatment at a temperature (T1 ) equal to the vitrification temperature (TG) of the material, preferably comprised between 1 150°C and 1200°C;

b) applying, on at least a surface portion of said vitrified support, a glaze having a fusible base and metal pigments having a glazing temperature (TV) lower than a vitrification temperature (TG) of the material forming the vitrified support, and preferably comprised between 600°C and 900°C;

c) subjecting the product obtained at step b) to a heat treatment, conducted at a firing temperature (T2) substantially equal to or essentially proximal to the glazing temperature (TV) of said glaze, and therefore preferably comprised between 600°C and 900°C, for obtaining a glazed ceramic slab.

[0068] The application of the glaze of step b) of the process can advantageously be carried out using a screen printing method, and/or possibly with spray-printing.

[0069] From the foregoing it is clear that the present invention achieves the set task and attains the set aims. In fact a process has been invented for obtaining ceramic and glazed cladding slabs, having large dimensions and reduced thickness which, thanks to the application of a suitable type of glaze, in particular, having a glazing temperature comprised between 600 and 900°C, and to the subsequent firing at a much lower temperature than the vitrification temperature of the material forming the support and essentially equal to the glazing temperature of the applied glaze, enables maintaining the planarity of the slabs, also preventing the formation of fractures which would compromise use thereof.

[0070] A process according to the present invention advantageously enables obtaining glazed and surface-decorated ceramic cladding slabs according to the requests of the user, possibly also simply realising any "single-tone" colouring in a perfectly uniform and homogeneous way.

[0071] Further, as will be evident to an expert in the field, a process according to the present invention is very versatile and at the same time reliable, as it requires not particular instrumentation or equipment, and is therefore easily industrialisable.

[0072] Naturally the present invention is susceptible to numerous applications, modifications or variants without thus forsaking the protective scope thereof, as defined in the following claims.

[0073] Further, the materials and equipment used for realising the present invention, as well as the forms and dimensions of the single components, might be the most suitable according to specific requirements.

Claims

1. A process for obtaining large-format and thin thickness ceramic slabs, comprising steps of:

a) predisposing a flat support of vitrified ceramic material having desired dimensions and thickness;

b) applying, on at least a surface portion of said support, a glaze having a fusible base and metal pigments having a glazing temperature (TV) lower than a vitrification temperature (TG) of said support;

c) subjecting the product obtained at step b) to a heat treatment, conducted at a firing temperature (T2) equal to or essentially proximal to the glazing temperature (TV) of said glaze.

2. The process according to claim 1 , wherein said flat support as in step a) is obtained by pouring a mixture formed by essentially clayey components internally of a die, then subjecting the mixture to a pressing and a first heat treatment conducted at a firing temperature (T1 ) equal to the vitrification temperature (TG) of the clayey material.

3. The process according to at least one of the preceding claims, wherein said vitrification temperature (TG) is comprised between about 1 150°C and 1200°C.

4. The process according to any one of the preceding claims, wherein said step c) is conducted at a firing temperature (T2) comprised between 600°C and 830°C.

5. The process according to any one of claims 1 to 3, wherein said step c) is conducted at a firing temperature (T2) comprised between 600°C and 900°C.

6. The process according to any one of the preceding claims, wherein said flat support also has surface extension that is greater than 3m² and a thickness about comprised between 3 mm and 6 mm.

7. The process according to any one of claims 1 to 5, wherein said flat support also has surface extension that is greater than 3m2 and a thickness about comprised between 3 mm and 1 1 mm.

8. The process according to any one of the preceding claims, wherein said step b) is carried out using a screen printing method, said glaze being in a paste form.

9. The process according to any one of the preceding claims, wherein said step b) is carried out using a spray dispensing method, said glaze being in a liquid or powder form.

10. The process according to any one of the preceding claims, wherein powders are added to said glaze, which powders are able to give said ceramic slab a greater resistance to wear.

11. The process according to any one of the preceding claims, wherein corundum powder is added to said glaze, so as to give said ceramic slab a greater resistance to wear.

12. The process according to any one of the preceding claims, wherein between said step a) and said step b), a net reinforcing structure is applied at a surface of said vitrified support that is opposite a surface of application of said glaze.

13. The process according to any one of the preceding claims, wherein steps b) and c) are actuated before and/or following one of following steps: decoration obtained by digital inkjet printing and/or decoration by affixing of grits and/or affixing of glass flakes.

14. The process according to the preceding claim, wherein following steps b) and c) a decoration is made using said digital printing.

15. The process according to the preceding claim, wherein a single-tone coating is obtained by means of steps b) and c) and a nuanced effect decoration is realised using digital printing.

16. The process according to claim 13, wherein a coating with reliefs and/or recesses is obtained by means of steps b) and c) and, thereafter, a decoration is applied using the above-mentioned digital printing.

17. The process according to at least one of claims 13 to 16, wherein during steps b) and c) one or more portions of the support are coated with glaze, leaving one or more portions uncovered by glazing, which are decorated by means of digital inkjet printing and/or decoration by affixing of grits and/or by affixing of glass flakes.

18. A glazed ceramic slab for cladding obtained using a process according to any one of preceding claims from 1 to 17.