ITUB20150733A1 - DECORATION PROCEDURE ON PRESSED BUT NOT DRY CERAMIC TILES - Google Patents

Description

DESCRIPTION

TITLE: DECORATION PROCEDURE ON PRESSED BUT NOT DRY CERAMIC TILES

FIELD OF APPLICATION OF THE INVENTION

The present invention is applied exclusively to ceramic tiles obtained with the dry pressing process obtained by applying a strong specific pressure inside a mold.

STATE OF THE ART

The production technology of decorated ceramic tiles? has been in constant evolution since the dawn of civilization. At the beginning of the seventies it underwent a very strong acceleration with the invention of the fast mono-firing process in single-layer roller kilns, according to the teachings of patent IT1010205. This new technology has allowed to drastically reduce consumption, to accelerate production cycles, thus reducing? costs and making the glazed ceramic tile a very consumer product. World annual production? today estimated at over 12 billion square meters.

This technology consists of a series of successive processes that begin with the preparation of a slightly moist powder of a suitable ceramic mixture. This moist powder can? be obtained with different procedures, but? characterized by the fact that its humidity? ? generally between 4% and 10%, depending on whether it has been obtained through a dry or wet preparation process.

This slightly moist powder is then subjected to a forming process, through the application of strong pressure, inside a mold. This forming process is referred to as? Dry forming? as the percentage of humidity? in the dust? very low. The process of? Wet forming? instead, it refers to formulations of ceramic mixtures containing up to 16% of water, which are formed in the plastic state, as happens for tiles and bricks, and in some cases also for? drawn? like clinker and spaltplatten.

As said, the present invention is applied exclusively to ceramic tiles obtained with the dry pressing process obtained by applying a strong specific pressure inside a mold.

There are dry forming processes in which the ceramic piece is formed starting from low humidity powders, applying high specific pressures between two surfaces without lateral containment, or without the use of a mold, as taught in patents US7160092 and US7252489 .

These technologies are used to make a kind of compacted dough belt, which is subsequently cut to obtain the desired dimensions.

The present invention does not apply to strip or plate forming systems, for which specific decoration technologies have been developed, in some cases even directly on the just compacted strip.

Does the decoration on non-dried ceramic materials come already? used in some particular cases: for example, the tiles or bricks are often? dirty? with solutions or suspensions of salts or coloring metal oxides immediately after the drawing operation. In the drawing operation, the ceramic mixture? in the plastic state why? ? very humid, so it does not tend to absorb the water with which it is wet, it does not deform and does not break. The solution or suspension, which contains the coloring salts or oxides, drips onto the wet piece and produces a decorative effect as described in US2191106.

If such an operation were performed on an undried 10 mm thick raw tile dry pressed with 5% humidity, the surface wetted by the water contained in the suspension would greedily absorb the water, causing swelling, with consequent bending until the piece breaks under its own weight.

The application of glazes, engobes or decorations on a non-dried tile can? be done before pressing, depositing on the surface of the mixture powder that still has to be pressed the pigments or the enamel granules with the same humidity. of the dough to be pressed. During pressing, the components of the decoration interpenetrate with the body of the tile. This technology? It was introduced in the 80s, but then used only on particular productions and still today it is indicated with the technological term of? mono-pressing ?, according to the teachings contained in the patents EP0444730 and EP0492733 and subsequent improvements. An attempt was also made to print the decoration inside the mold, which is then transferred to the ceramic product during the pressing phase according to the teaching of patent US4501714.

The ceramic tiles obtained with the dry pressing process inside a mold represent almost all of them. of world production and the universally adopted technological protocol provides that, immediately after the forming operation in the mold and the subsequent extraction from the mold, the freshly pressed tile is subjected to a drying operation. These protocol don't? never been the subject of a patent, but it is part of the body of knowledge acquired over millennia of ceramic production.

The drying operation, inside suitable drying systems,? necessary to increase the mechanical resistance of the piece just formed, in order to make it resistant enough to pass the subsequent processing stages without being damaged. The dried tile achieves a mechanical resistance several times higher than that of the non-dried piece, and leaves the dryer at temperatures generally above 100 ° C. The piece ? therefore very hot and resistant enough to be able to withstand the subsequent processing phase.

The subsequent processing phase consists in the application of one or more? covering layers that serve to make the tile waterproof, easy to clean and, above all, attractive and decorative. The covering layers can also be multiple and are defined with a multitude of specific names of the technology: engobe, glaze, glaze, flaming, grit, etc. Most of these preparations are applied on an aqueous basis, in the form of suspensions of very fine powders dispersed in water. The heat contained in the tile just out of the dryer allows the water contained in the suspensions to evaporate.

If the tiles were cold, they would get soaked in water and crack under their own weight.

As soon as the layers of enamel have dried, we proceed with the decoration operation. For many years the decorations have been applied with the techniques of screen printing, engraving or pad printing, which involve contact between the printing medium and the surface to be decorated. In the last fifteen years, though, yes? the digital decoration technique that uses? ink-Jet? type heads has been established, thanks to which the printing medium does not come into contact with the surface to be decorated. I quote with respect the first patent on a ceramic ink for digital printing: US5407474; and the first patent of a digital printer for ceramic tiles: EP1038689 which was followed by many others.

The digital inkjet decoration technique has undergone a dizzying development, which has led it to supplant most of the previous techniques, but it has not solved one of the biggest problems. sneaky that afflicts the decoration of the tiles: that of stability? of the hue? decoration. Thanks to digital printers? today it is possible to faithfully reproduce any image directly on the surface of the tile, but? still difficult to reproduce from time to time the same image with the same shades? of color. Sometimes the hue? it changes from one production batch to another and also during the production of the same batch. One of the main reasons for the tonal variation? in digital printing? the variation of temperature and humidity? surface of the tiles during the decoration phase. The solution adopted today? that of inserting cooling systems before printing which, in addition to being an extremely inefficient solution from an energy point of view, sometimes represents a further element of variability.

Digital printers have greatly improved the sharpness of decoration, thanks to the development of print heads that reach exceptional resolutions, but suffer from variations in temperature and humidity. of the surface, why? the size of the drops applied by a digital printer? of a few tens of pico-liters. Even small variations in temperature and humidity superficial, lead to the variation of the color rendering. The image definition remains excellent, but the tonality changes. The human eye has the ability? to discriminate even very small variations of tonality? and this requires tile manufacturers to select the production batches so that they are the most? possible homogeneous as tonality. The variations of tonality? lead to the fragmentation of production batches in the warehouse with the consequent increase in need? of storage and reduction of flexibility? productive.

Organic solvents

According to the state of the art, using the single firing production protocol, the dried tiles, after being decorated, enter the firing kiln. According to the protocol currently used, the phase following the decoration is, in fact, directly the phase of simultaneous firing of the ceramic support and of the layers that make up the glaze, the decorations and the surface finishes. At this point, the organic liquids that made up the liquid phase of the inks, and which have been absorbed by the dried raw tile, are exposed to a sudden increase in temperature which can? cause radical transformations in their composition and chemical structure. Firing ovens for ceramic tiles are, in the vast majority of cases, fueled by gaseous fuels (natural gas or LPG) or liquid (naphtha), which must be mixed with large quantities? of air (one part of methane, 10 parts of air). Do they come like this? huge volumes of exhausted fumes are generated, which must be evacuated. The hot fumes from the cooking areas are used to pre-heat the pieces in the entrance, but not? possible to further lower the inlet temperature to the ovens, why? at temperatures pi? low starts the formation of acid condensation in the fans. These acid condensates will then be removed by the appropriate smoke filters.

In fact, at the entrance to the cooking ovens, the decorated tiles are hit by hot fumes at a temperature of over 300 ° C. This high temperature does not cause any problems for materials glazed and decorated with water-based suspensions, when the humidity? residual in the raw tiles? less than 1%. The residual water evaporates quickly while the temperature of the material rises very quickly.

When the tiles are decorated or even glazed with suspensions based on organic compounds, the situation changes radically. Even if the starting organic compounds are absolutely harmless, when subjected to violent heating, these molecules do not just evaporate, but break (cracking) and recombine (reforming) giving rise to new uncontrollable organic compounds, which can be strongly odorous and also strongly irritating and even toxic.

One of the most popular vector fluids? used in ceramic inks for digital printers? propylene glycol, which is universally recognized as absolutely non-toxic and safe, to the point that? used in the preparation of injectable pharmaceutical products (Diazepam?), cosmetic products (Nivea Visage?) and as a food additive (E1520). However ? known that, following thermal degradation processes at temperatures above its boiling temperature, it leads to the formation of propionaldehyde (propanal) which? a corrosive and irritating chemical compound [1]. If, on the other hand, the propylene glycol remains below the temperature of 188 ° C, it evaporates without decomposing.

Another typical example of suspending liquid found in digital printer ink? ethylene glycol ether (ethylene glycol ether). This organic compound evaporates without decomposing at a temperature of 135 ° C. But when are these compounds, when are they exposed to lower temperatures? high undergo a process of pyrolysis, their molecules break and recombine giving rise to dimers and oligomers with properties? unpredictable.

A typical example? the DGBE (dyethylene glycol buthyl ether), which at room temperature? considered absolutely safe but above 170 ° C it decomposes into an uncontrollable mixture that contains aldehydes, ketones, and organic acids. [2]

According to the teachings of the US20150037501 patent, a ceramic ink for digital printers can? be prepared with ethylene glycol. Ethylene glycol? by itself? toxic, and if ingested can? be fatal with only 30 milliliters. The vapors of ethylene glycol are however very dangerous and it is absolutely necessary to avoid contact with the skin and eyes. From a document available online from DOW Chemical [3] which supplies the product, it appears that the thermal degradation of ethylene glycol leads to the formation of oxalic acid and formic acid, both of which are extremely toxic. The boiling point for ?,? 197? C, so below this temperature it evaporates without degrading. However, the vapors remain irritating and, if in high concentrations, even toxic.

According to the teachings of the US7803221 patent, a ceramic ink for digital printers can? be prepared using PGMEA (PolyGlycolMonoMetilEtherAcetate) as solvent. From the safety data sheet (MSDS) of the PGMEA [4] it is clear that the PGMEA emits toxic fumes in the event of a fire, ie in the event of very rapid overheating, but which evaporates at 140 ° C. The vapors of this chemical compound are irritating, but they are not toxic.

This situation is generating a strong concern in the bodies in charge of environmental control (ARPA; EPA), which are evaluating the need? to put a limit on the use of these substances when they are exposed to high temperatures, until a solution is developed that allows to definitively control this type of emissions.

The state of the art for the elimination of dangerous organic substances from the emissions of industrial plants consists of a post-combustion phase of the fumes from the ovens: raising the temperature of the fumes over 800 ° C causes the complete combustion of all organic residues. originally present in the gaseous effluents, reducing the emission to carbon dioxide and water. However, this solution? very difficult to implement, why? involves a very high cost in terms of energy consumption. A current medium-sized kiln for firing tiles emits several tens of thousands of cubic meters of exhaust gas into the atmosphere every hour. The temperature of these gases, after the abatement operations necessary to eliminate dust and acid condensates, yes? lowered to about 120? C. Reheating these volumes of gas up to 800? C means increasing the energy consumption associated with the cooking phase by at least 50-70%.

EXPOSURE AND ADVANTAGES OF THE FOUND

A purpose of the present invention? that of providing the technique with a decoration process on pressed but not dried ceramic tiles as part of a solution that improves their performance.

Another object of the invention? the reduction of organic compounds in the gaseous effluents of the firing ovens of ceramic tiles decorated with organic-based inks.

Does it follow that with the procedure in question there is an improvement in stability? of tones in the production of ceramic tiles.

These and other objects are achieved thanks to the characteristics of the invention reported in independent claim 1. The dependent claims outline preferred and / or particularly advantageous aspects of the invention.

Said objects and advantages are all achieved by the process of decorating pressed but not dried ceramic tiles, object of the present invention, which is characterized by the provisions of the following claims.

BRIEF DESCRIPTION OF THE FIGURES

This and other characteristics will become more evident from the following description of some embodiments illustrated, purely by way of non-limiting example in the accompanying drawing tables.

- Figure 1: illustrates the trend of the tile flexion with determination of the speed? of bending as a function of time and temperature,

- Figure 2: illustrates a plant scheme implementing the process object of the invention.

DESCRIPTION OF THE FOUND

The present invention consists of a new technological decoration process which provides for the decoration of the tiles formed by dry pressing inside a mold, directly on the tiles just extracted from the mold, when they are still cold, and therefore have very low mechanical resistance and of very strong aptitude to absorb water.

At first glance, this might seem like an application of techniques already? notes, simply applied in a different order. This might seem like an obvious solution for an experienced technician in the field. In reality? ? a solution so new and unheard of that, if submitted to a technician expert in the sector, it would be considered madness: everyone knows that the tiles at the exit of the press, before being dried, cannot be glazed and decorated, why? are too weak and why? they would absorb too much water, bending and breaking.

We have surprisingly found that the freshly pressed tile 1 can? be subjected to an operation of application of a covering enamel using traditional methods of application (veil, sprinkling or spray 2) and can? also be decorated using the digital printing technique 3.

We have surprisingly found that the water contained in the preparations of the ceramic covering glazes is absorbed by the raw tile just pressed with a very precise kinetics. Using the absolute optical flexometer, of the type described in patent application ITPR2013A000064, yes? was able to follow the trend of the tile flexion and determine the speed? of bending as a function of time and temperature. See Fig.1. The experiment? was carried out by applying 0.1 grams of water per square centimeter on a freshly pressed raw tile with a thickness of 10 mm. The flexion after 1 minute from wetting? equal to 0.5% of the sample length. Does this mean that a piece of the size of 60cm x 60cm will sag? 3 mm in 60 seconds. Following these studies, we came to the conclusion that the initial wetting caused by the application of the enamel leads to a bending of the piece which? pi? what proportional to the quantity? of water applied. If the quantity? of water ? very small, the flexion progressively slows to a halt. There is a short period of time during which the flexion occurs in a very limited way. If within this time interval, the piece is heated, the flexion is reabsorbed without any damage. The time interval allowed for carrying out the decoration operations can? vary according to the characteristics of the dough and therefore should be determined from time to time. In a very general line, you can? establish that? less than 60 seconds.

The teaching of the present invention therefore consists in this processing protocol:

- Conventional pressing of the tiles with a hydraulic or mechanical press 1 using powders, presses and molds already? known

- Application on the freshly pressed tile of the covering layer consisting of engobe and glaze, or only glaze, using conventional techniques of sprinkling, veil or airless spray 2, in quantity? such as not to exceed a total amount of water on the surface of the piece equal to 0.1 grams per square centimeter

- Alternatively, the cover layer can? be applied using specific preparations for the InkJet 3 application with digital printing

- Application of the decoration with multiple inkjet print heads 3

- Application of the finishing layer with an airless spray application system 4 or with specific preparations for digital inkjet printing 3. Even the water contribution of this finishing layer must be included in the total water count of less than 0.1 g / cm2. If this doesn't? possible, the application of the final finishing layer can? be done after drying the piece.

- The maximum time to perform these operations? depending on the behavior of the ceramic mixture just pressed, and must be determined for each composition of the mixture. As a rough indication you can? indicate that the time interval between the application of the first covering layer and the passage to the subsequent drying phase 5? of the order of 60 seconds.

Unexpectedly, therefore, the technique of decorating directly on the pieces just pressed, object of the present invention, provides amazing results with productive, economic and environmental implications that go far beyond the initial objectives.

The aesthetic result? identical to that of decorated tiles after drying, but the stability? of the tone of the decoration is enormously improved, why? the piece ? cold and the decoration is not affected by surface temperature variations. The decoration with digital printers on glazed tiles before being dried does not affect the level of resolution of the digital print, but it definitely improves its stability.

Pi? in detail, the teaching of the present invention consists in the fact that the freshly pressed tiles 1 and glazed with a? glaze ?, or with engobe and conventional glaze 2 and subsequently decorated with the use of digital inks 3 do not enter directly into the cooking, but go through a drying phase 4, necessary to remove the water contained in the freshly pressed dough. This heating phase does not represent an additional heat treatment, since, according to the technological protocol of single firing, the tiles are in any case dried 5 before entering the firing kiln 9. So there is no? no increase in energy consumption. The drying can take place in a conventional dryer for unfired tiles. The difference with respect to traditional single firing consists in the fact that this drying phase is carried out after the decoration. These dryers normally operate with maximum temperatures around 150-180 ° C.

An additional extraordinary and unexpected benefit that you get? that, at these temperatures, the organic solvents evaporate without undergoing cracking and reforming phenomena and escape from the flue of the dryer 6 without being transformed into dangerous compounds.

What if organic liquids do not have by themselves? characteristics of danger? or odor, such as propylene glycol, the fumes emitted from the flue of the dryer 6 are in any case not dangerous, as these organic components of the digital inks have not reached the temperatures that cause them to decompose into toxic, corrosive or simply annoying, as unpleasant as a smell.

The application of the present invention allows to obtain further advantages, thanks to the application of another teaching already? known and already? in use in other industrial sectors: the recovery of the solvent, already? known according to the teachings of patents US4788776A, EP0839569 and many others.

The volumes of hot air emitted by a dryer are enormously lower than those emitted by a cooking oven and are free of acid condensation. This allows to adopt some artifices, such as for example the insertion after the chimney of the dryer 6 of a condenser 7 to capture and condense the solvents, how? already? become common in other industrial sectors. The condensation and recovery of the solvent, instead of representing an industrial cost, can you? transform into a recovery of resources with the consequent reduction of the industrial cost in total respect of the environment. A drying system can? be specifically designed to optimize solvent recovery. In this case ? It is advisable to use radiant heating systems, in order to drastically reduce the volumes of hot gases that must be cooled to condense volatile compounds. Radiant heating? pi? expensive compared to convection, but the economic benefits of solvent recovery can quickly balance the income statement.

The possibility? to recover the solvents opens the way to the possibility? to use the digital technique also for the application of the covering enamel (? Enamelbbio) and of the final finishing layer (? crystalline? or? matting enamel? or other) using the digital technique 3. The possibility? to control in a precise way the phase of application of the covering layer allows to obtain a further improvement of the stability? of tones.

Preparations for digital printing contain about 50% solvents. Applying 300 grams on a dry basis per m <2> of components for digital decoration, the quantity? of solvents used equals the dry fraction by weight. A typical modern production line produces 2.5 million m2 per year. Considering 300 grams per square meter of solvents, the potential recovery can? reach the impressive number of 750,000 kg per year, for a value at least equal to the same number in Euros. Even in the assumption that the quality? of the recovered solvent is not sufficient to allow its direct reuse in the preparation of the same inks, the remarkable result would be obtained of avoiding the release into the atmosphere of 750 tons of organic molecules which, in some cases, are certainly not dangerous, but which they could undergo transformations such as to make them dangerous later on. Suffice it to recall the case of fluorinated solvents, apparently harmless to humans, but which have shown their danger? for the whole planet a few decades after their reckless use on a global scale, due to a series of then completely unknown chemical reactions.

EXAMPLE N? 1

Production of tiles in 30x60 cm size, 10 mm thick, classified according to the ISO10545 standard in class BIa, following the production protocol known as? Glazed porcelain ?. Are the pressed pieces 1 extracted from the cavities? of the molds and sent, by means of suitable conveying systems, to a decoration line with belt conveyor, consisting of an application of? in aqueous suspension by means of a spray applicator 2, according to the known technique of the? airless? application, equal to 300 grams per square meter, followed by a belt conveyor with 8 high resolution ink-jet 3 head bars fed with ceramic pigments in suspension in an organic liquid based on polyols and esterified polyols.

The deposition of the covering layer and the decoration layer takes less than 60 seconds. Immediately after the decoration phase, the piece has not yet dried but already? completely decorated, it is transferred to a roller conveyor which transports it inside a heated multi-layer 5-layer roller dryer, with direct introduction of hot air generated by a series of gas burners. The inlet temperature to the roller dryer? of 120? C, the maximum temperature reaches 180? C and the permanence? 30 minutes. The hot and humid fumes coming out of the chimney of the dryer 6 contain the vapors of the organic components that made up the liquid phase of the enamel and of the digital inks. These organic compounds are still in their original molecular form, as they have not undergone molecular degradation processes that occur at a higher temperature. high. Since these are materials generally used in the cosmetic, pharmaceutical and food industries, they are classified as non-harmful, non-irritating and non-allergenic materials. Therefore even their vapors, extremely diluted in large volumes of humid fumes, remain harmless.

At the exit of the dryer, the pieces are completely dried and free of the organic component of the liquid phase that was contained in the products for digital printing. At the exit of the dryer, the pieces, still very hot at a temperature of over 100 ° C, are conveyed on a belt conveyor line and subjected to a further decoration phase, with the application of a thick layer of enamel covering. in aqueous suspension 8, which allows the final polishing phase (lapping) which is carried out after firing. The water contained in the covering glaze evaporates quickly, as normally happens in the glazing processes on dried material typical of single firing.

The pieces are then sent to the subsequent processing phases following the conventional protocol: firing 9, possible rectification, possible lapping, possible brushing, selection, packaging and palletization.

Following the complete evaporation of the organic component during the first drying phase at low temperature before insertion into the oven, the fumes coming out from the chimney of the cooking oven 10 do not contain odorous or harmful organic compounds deriving from the thermal degradation process of the compounds. organic content in digital printing inks.

EXAMPLE N? 2

Production of 25x75 cm wall tiles with a thickness of 8 mm, classified according to the ISO10545 standard in class BIII, with porous mixture following the production protocol known by the technological term? Monoporous ?.

The freshly pressed tiles 1, immediately after extraction from the mold, are conveyed onto a conveyor belt. On the conveyor belt it passes under a digital printing machine 3 equipped with six ink-jet printing bars equipped with ink-jet heads with high-volume ejection nozzles. These heads are fed with a suspension of covering enamel called? Engobe ?. The suspending fluid? consisting of a mixture of esters and glycols. Subsequently the material passes under a series of 6 printing bars equipped with high resolution ink-jet 3 heads for color printing. The pigments are inorganic in nature according to the state of the art. The suspending fluids consist of a mixture of esters and glycols.

The deposition of the covering layer and the decoration layer takes less than 45 seconds. Immediately after the decoration phase, the piece has not yet dried but already? completely decorated, it is transferred onto a roller conveyor which transports it inside a drying rack 5 heated with a gas burner and integrated with hot air coming from a heat exchanger installed in the cooling area of the cooking oven. The inlet temperature to the rack dryer? of 80? C, the maximum temperature reaches 170? C and the permanence? 45 minutes. The hot and humid fumes coming out of chimney 6 from the dryer contain the vapors of the organic components that made up the liquid phase of the enamel and of the digital inks. These organic compounds are still in their original molecular form, as they have not undergone thermal degradation processes that occur at lower temperatures. high. Since these are materials generally used in the cosmetic, pharmaceutical and food industries, they are classified as non-harmful, non-irritating, non-allergenic materials. So even their vapors, extremely diluted in large volumes of humid fumes, remain harmless and do not generate disturbance, why? they do not contain odorous substances.

The next stage of processing, after leaving the dryer, consists in the application of a thick covering layer of a glossy and transparent enamel ground in aqueous suspension (crystalline). The dried tiles leave the dryer at a temperature of 120 ° C. The first phase of application consists in spraying finely nebulized water on the already surface. previously decorated. This application of water 8? essential to improve the adhesion of the next layer of enamel, which, in this way, finds a surface already? humid. As soon as the development of steam, caused by the application of water, ceases, the covering glaze is applied, using a veil application device 8. This covering glaze reaches its complete fusion in the subsequent heat treatment that takes place in the firing oven 9 and gives the product a shiny and bright appearance, which enhances the underlying decoration and gives depth? to the drawing.

Operating according to the teachings of this invention, the fumes emitted from the chimney of the cooking oven 10 do not contain organic compounds deriving from the thermal degradation of the organic products used as suspending agents in inks and enamels for digital printing. The fumes coming from the oven are subjected to the treatments of dedusting and abatement of the acid inorganic components (HF, HCl, H2SO4) required by the environmental regulations in force, but they are completely free from organic composites with an uncontrollable composition, which could derive from the thermal degradation of the inks. for digital printing.

EXAMPLE 3

Production of red-body floor tiles, classifiable according to ISO10545 in class BII, with the technique known as single-fired floor tiles with dry grinding.

The freshly pressed tiles starting from dry ground mix powders and humidified with the addition of 6% of water, immediately after extraction from the mold 1 are conveyed on a conveyor belt. The conveyor belt passes under a digital printing machine 3 equipped with six inkjet printing bars equipped with ink-jet heads with high ejection volume nozzles. These heads are fed with a suspension of cover enamel called "EnamelBB". The suspending fluid? consisting of a blend of polyesters, according to the teachings of the patent WO2012116878. Subsequently, the material passes under a series of 6 print bars equipped with high resolution inkjet heads for color printing. The pigments are inorganic in nature according to the state of the art. Suspension fluids consist of a blend of polyesters and other chemical additives. Immediately afterwards the material passes under 2 bars equipped with digital printing heads with high discharge volume for the application of the final finishing layer. This complete glazing and decoration operation takes less than about 30 seconds.

As soon as the decoration application phase, which includes all the decoration layers, is finished, the tile is sent to a drying system 5 equipped with infrared heating and a vapor cooling system 7. The vapors containing the aqueous component coming from from the drying of the freshly pressed tiles, and the organic solvents, coming from the inks used for digital printing, are passed through a plate exchanger 7, which causes condensation of the liquid components.

Considering a production of 8000 m <2> per day, with the application of 300 dry grams of inks containing 50% of organic solvents, the system of condensation of the fumes of the dryer? potentially capable of recovering up to 2400 kg per day of organic solvents. The efficiency of the condensation recovery? strongly influenced by the affinity? chemistry between solvent molecules and water. In any case, organic solvents are not released into the atmosphere.

Documents cited

[1] Mechanisms of Propylene Glycol and Triacetin Pyrolysis Teodoro Laino, * ,? Christian Tuma ,? Philippe Moor,

Elyette Martin,

Steffen Stolz,

,?

and Alessandro Curioni?

? IBM Research? Zurich, Sa? Umerstrasse 4, 8803 Ru? Schlikon, Switzerland

Philip Morris International R&D, Quai Jeanrenaud 5, 2000 Neucha? Tel, Switzerland

? University of Twente, Faculty EEMCS, P.O. Box 217, 7500 AE Enschede, The Netherlands]

[2] The DOW Chemical Company - Form No. 233-00262-MM-1214X - Product Safety Assessment: Diethylene Glycol Butyl Ether

Revised: December 23, 2014

[3]

Claims (9)

CLAIMS 1. Process of decorating on ceramic tiles characterized by the fact that it involves decorating with digital printers on dry-pressed glazed tiles before their drying. 2. Process according to claim 1, characterized by the fact that the pressed tiles 1, glazed 2 and decorated with the use of digital inks 3 do not enter directly into the baking oven but pass through a drying phase 4, necessary to remove the? water contained in the freshly pressed dough; said drying step being carried out after decoration, with maximum temperatures not exceeding 200 ° C. 3. Process according to claim 1, characterized in that the decoration of the tiles takes place directly on the tiles removed from the mold and when they are still cold. 4. Process according to claim 1, characterized in that it provides for carrying out: to. A conventional dry pressing of the tiles with a hydraulic or mechanical press (1) b. The application, on the freshly pressed tile, of the covering layer consisting of engobe and glaze, or only glaze, using the. sprinkling techniques, veil or airless spray (2), in quantity? such as not to exceed a total amount of water on the surface of the piece equal to 0.1 grams per square centimeter ii. specific preparations for InkJet application (3) with digital printing c. The application of at least one decoration on said freshly pressed tile, with multiple inkjet print heads (3) 5. Process according to claim 4, characterized in that it further provides for the application of at least one finishing layer with an airless spray application system (4) or with specific preparations for digital inkjet printing (3); and where the water contribution of this finishing layer must be less than 0.1 gr / cm2 in the total water count; if this not? possible, the application of the final finishing layer? done after drying the piece. 6. Process according to claim 4, characterized in that the time interval between the application of the first covering layer and the passage to the subsequent drying step 5? of the order of 60 seconds. 7. Process according to claim 4, characterized in that the maximum time for carrying out the operations? depending on the behavior of the ceramic mixture just pressed,? determined for each mixture composition. 8. Process according to claim 4, characterized in that it further provides for the condensation and recovery of the solvent which evaporates during said drying step. 9. Process according to claim 4, characterized in that said drying step uses radiant heating systems, reducing the volumes of hot gases that must be cooled to condense the volatile compounds.