Background Art Various known processes exist for decorating ceramic tiles before or after firing.

Each of these processes involves the use of a matrix reproducing the profile of the decoration to be transferred onto the tile. The matrix, usually a screen, is a flat surface exhibiting holes according to predetermined shapes, and is in effect a filter between the colorant and the surface of the tile to be decorated. The screen allows passage of the colorant only at determined points, so the colorant passing through deposits onto the tile and reproduces the desired figure thereon.

One process arranges the screen in contact with the tile surface to be decorated by means of a doctor which slides on the screen itself. The spreading action of the doctor, which occurs with considerable pressure on the screen, pushes the colorant and forces it through the screen at the points where the screen is permeable, thence depositing on the tile. Due to the pressure with which the doctor slides on the screen and the relative sliding motions both elements are subject to, both the screen and the doctor suffer from abrasion and wear. Also, the colorant used must have characteristics of density, adhesion and lubrication which can be attained only through the addition of oil to the other components.

Oil glazes are rather expensive with respect to other types of colorants and are also not very ecological. This means that special attention has to be paid to the

disposal of the residues of this process, as well as to the vapours and fumes generated during the glazing and firing processes.

Another decoration process involves the colorant being spread on the screen with a doctor, but the screen is not placed in contact with the tile, but rather is in front of and at a certain distance therefrom. The tile and the screen can be set in relative motion until they reach an aligned position at which a jet of compressed air is directed onto the screen, causing the colorant to cross the screen at the points where it is permeable, thence depositing on the tile. Though the intensity of the mechanical interaction between the doctor and the screen is less with respect to the above-described process, as the pressure on the colorant is exerted by the compressed air, there are however abrasion phenomena of a not- inconsiderable relevance. This process, like the one described above, involves the use of expensive and polluting oil glazes because the colorants have to exhibit a density sufficient not to drip through the screen once they have been spread thereon.

The main aim of the present invention is to provide a process for decorating tiles and a device for carrying out the process, which obviate the drawbacks in the prior-art processes.

An advantage of the invention is that the screen is not subject to wear as there is no contact either with the tile or with other moving parts.

A further advantage of the invention is that it can be operated using water-based glazes and not oil-based colorants.

Disclosure of Invention Further characteristics and advantages of the present invention will better emerge from the detailed description that follows, of a process for decorating tiles and a device for carrying out the process, illustrated purely by way of example in the figures of the drawings, in which:

figure 1 is a schematic view in vertical elevation of a device according to the present invention; figure 2 is a view in section of the device of figure 1 according to line A-A; figure 3 is an enlarged-scale view of a detail of the device of figure 1.

The process comprises the following stages: - arranging a screen reproducing the profile of a decoration in a frontal position with respect to the surface to be decorated of a tile, and distanced therefrom; - spraying a glaze on the screen from a nozzle arranged on an opposite side of the screen with respect to the tile so that the glaze passes through the screen selectively by effect of a pressure with which the glaze is sprayed and deposits on the tile, reproducing the profile of the decoration.

The screen is constituted by a surface on which one or more through-holes are afforded, reproducing the profile of the decoration. Traditionally the screen is made of a metal grid, the holes of which are specially widened at points where the profile of the decoration is to be made. Other types of screen are obtained using metal strips (or other materials) on which one or more openings are made to reproduce the profile of the decoration. The glaze sprayed from the nozzle towards the tile is filtered by the screen, which allows only a selective passage there-through, through the predetermined zones which reproduce the decoration to be made on the tile. The glaze passes through the screen not by effect of gravity, i. e. the glaze does not drip through the screen, but passes by effect of the pressure with which it is sprayed and the characteristics of the nozzle. These two parameters influence the dimensions of the drops of glaze, making possible a passage thereof through the spaces in the screen.

In a preferred embodiment of the process the tile and the screen are arranged on parallel planes and are in relative motion, with respect to the nozzle, so as to transit in the zone in which the glaze is sprayed. The tile and the screen are

arranged frontally and parallel at a separation distance which is comprised between about 1 and 5 mm and are in motion, in a same direction and at a same speed, in a transversal direction with respect to the fixed nozzle which is arranged at a distance from the screen which is comprised between about 20 and 40 cm.

The tile and the screen are"synchronized"so that there is no relative motion between them, and as they translate they pass into the zone in which the glaze is sprayed. The indicated distances between tile and screen and between nozzle and screen can vary within wider ranges in relation to special working needs.

By regulating the distance between the screen and the nozzle and between the screen and the tile it is possible to obtain different decorative effects. By reducing the distances very high definition is obtained, and by increasing the distances nuances can be obtained. The same effects can also be obtained by varying the sliding speed of the screen and tile; at slower speeds decorations obtained are more well-defined or intense, whereas at greater speeds the decorations are more vague. Other special effects can be obtained by varying the direction of the tile and screen motion, for example crossing them over and aligning them in parallel directions, perpendicular or in some way arranged at the nozzle position in which the glaze is sprayed.

The characteristics of the process according to the present invention enable the process to carried out using a glaze made of a mixture of water and coloured clays instead of the oil colours normally used. The glaze does not need to have special characteristics relating to density and consistence because, as described, it passes through the screen thanks to the size of the sprayed drops. The use of non-oily glazes enables easy and simple washing of all the parts and in particular of the screen which can be rapidly readied for subsequent decorations using different colours. The proposed process can, however, also be used for oil-based glazes or indeed other types of glaze besides.

With reference to the figures of the drawings, the device of the invention comprises: a mobile transport plane 2 predisposed for positioning tiles 30; a nozzle 4 predisposed for spraying on command a glaze in the direction of the mobile transport plane 2; a screen 3, reproducing the profile of a decoration, arranged in a frontal position and distanced with respect to the mobile transport plane 2 and the tiles 30 so that the screen 3 is at least partially positioned between the nozzle 4 and the tiles 30 located on the mobile transport plane 2.

In a preferred embodiment of the device, the screen 3 is moving with respect to the nozzle 4 and, at least for a predetermined time interval, the screen 3 and the mobile transport plane 2 move parallel and at a same speed along a transport direction x. Preferably the screen 3 is cylindrically shaped and rotates on command about a longitudinal axis y which is parallel to the mobile transport plane 2 and transversal to the transport direction x. At working speed the screen 3 has a peripheral velocity which is the same as the speed of the mobile transport plane 2.

The screen 3 is constrained at ends thereof to two support rings 9 provided with a plurality of shaped pivots 10 which extend in a distancing direction from the screen 3 and are arranged parallel to the longitudinal axis y. Each shaped pivot 10 of a support ring 9 is coaxial to a corresponding shaped pivot 10 of the other support ring 9. The shaped pivots 10 are predisposed to house in respective shaped seatings 11 which are associated to two crowns 12. Each of the crowns 12 faces a respective support ring 9 and is constrained in rotation to a support structure 70.

The shaped seatings 11 are conformed in such a way as to constrain the shaped pivots 10 with respect to the rotation of the crowns 12 about the longitudinal axis y, and, in a predetermined angular position of the screen 3, and to enable a contemporaneous disengagement of the shaped pivots 10 upon effecting a rolling

rotation of the support rings 9 on a plane which is parallel to the mobile transport plane 2. Each shaped pivot 10 exhibits, at a free end thereof, a conical expansion 10a which prevents displacements of the pivot along the longitudinal axis y in a distancing direction from the shaped seating 11. At least one of the crowns 12 can be commanded to make small displacements along the longitudinal direction y between a maximum distance position and a minimum distance position with respect to the other crown 12. At the maximum distance position between the two crowns 12 the pivots 10 are subject to a traction force across the respective conical expansions 10a so that the screen 3 is solidly connected to the crowns 12, while at the position of minimum distance between the two crowns 12 the shaped pivots 10 can be disengaged from the respective shaped seatings 11.

Each shaped pivot 10 can be inserted in the respective seating 11 through a notch 1 la which is transversal with respect to the longitudinal axis y. The shaped pivot 10 is made to slide along the notch 1 la in a transversal direction with respect to the longitudinal axis y up until it reaches a correct position internally of the shaped seating 11 at which position the pivot 10 is laterally in contact with the shaped seating 11 itself. The notches 11 a are arranged in such a way that, at a given angular position of the screen 3, the notches 11 a are about parallel and facing a same way. At this given angular position of the screen 3 two shaped pivots 10 are in a lower position with respect to the other shaped pivots 10.

Thanks to the parallel arrangement of the notches 11 a, by rotating the screen 3 about the axis of the shaped pivots 10 which are in a lower position, the other shaped pivots 10 are contemporaneously disengaged from the shaped seatings 11. Once the other pivots 11 have been disengaged, the shaped pivots 11 in the lower position can be disengaged.

Each crown 12 is rotatingly constrained to the support structure 70 by means of three ball bearing supports 13 which are solidly constrained to the support

structure 70 and which each comprise a ball 13a predisposed to contact the crown 12 at a position corresponding to an annular race afforded in a surface of the crown 12 facing towards an opposite side of the screen 3. Each crown 12 also exhibits a further annular race afforded in the face turned towards the screen 3 predisposed to contact with three balls 19a which are associated to the support structure 70 by means of respective supports 19. Each ball 19a is aligned parallel to the longitudinal axis y, with a respective ball 13 a arranged on the opposite side of the crown 12. The distance between two aligned balls can be regulated for example by a screw, passing through the relative ball bearing support 13, parallel to the longitudinal axis y, which enables the force with which the balls grip the crown 12 to be controlled.

The crowns 12 are further rotated on command by a motor. Each crown 12 is solidly constrained to a cogwheel 14, coaxial to the longitudinal axis y, which is mechanically connected to a rotating actuator, for example an electric motor, by means of a cogged chain 15. In the preferred embodiment the electric motor, of known type and not illustrated in the figures of the drawings, transmits the rotary motion to a shaft 20 which is parallel to the longitudinal axis y. The shaft 20 is supported rotatingly to the support structure 70 and is provided at ends thereof with two sprockets 21 which are about co-planar to the cogwheels 14. The cogged chains 15 transmit motion from the sprockets 21 to the cogwheels 14.

The support structure 70 is associated to a frame 60 by first guides 71 and second guides 72 on which it is mobile with respect to the mobile transport plane 2, respectively along the longitudinal axis y and in a perpendicular direction with respect to the mobile transport plane 2.

The nozzle 4 is arranged internally of the screen 3 and is constrained to the frame 60 by guides of known type and not shown in the figures, on which the nozzle 4 is slidable in a perpendicular direction to the mobile transport plane 2. The nozzle

4 receives the colorant through a supply conduit and atomizes it into drops small enough to pass through the screen.

The device is further provided with means for cleaning, arranged internally of the screen 3, which comprise: a conveyor 5, connected to an aspiration device of known type and not illustrated in the figures, which device is provided with an elongate aspiration aperture 6 which is arranged parallel to the longitudinal axis y; a scraper 7, connected to the conveyor 5 in proximity of an edge of the aspiration aperture 6, which scraper 7 is arranged in contact with the screen 3 downstream of the aspiration aperture 6 with respect to the rotation direction of the screen 3; a spray humidifier 8, solidly constrained to the conveyor 5, which is predisposed to spray a cleaning liquid onto an area of the screen 3 which is upstream of the aspiration aperture 6 with respect to the rotation direction of the screen 3; a collector element 16, solidly constrained to the conveyor 5, which collector element 16 is provided with a scraper 18, arranged in contact with the screen 3 upstream of the spray humidifier 8 with respect to the rotation direction of the screen 3, and a collection channel 17, arranged below the scraper 18. The function of the means for cleaning is to remove an excess of colorant which deposits on the screen and which can obstruct passage of the colorant sprayed by the nozzle 4. The colorant deposited on the screen 3 is diluted with the cleaning liquid sent by the spray humidifier 8. As the colorant is water-based, the cleaning liquid can be water. The size of the mesh of the screen 3 is'such that the diluted colorant cannot drip down by force of gravity through the screen 3. The aspiration aperture 6 and the scraper 7 both face upwards and are arranged in a zone which is about diametrically opposite the area on which the colorant is sprayed and upstream of the vertical plane passing through the nozzle 4. In this way the diluted colorant entering into contact with the scraper 7 drips downwards and towards the aspiration aperture 6, through which it is trapped in the conveyor

5. From the conveyor 5 the colorant can be sent on to disposal or can be re-used after special treatments which restore it to its original density. The collector element 16, the scraper 18 of which is arranged upstream of the spray humidifier 8 with respect to the rotation direction of the screen 3, has the function of collecting the majority of the excess colorant from the screen 3. The colorant enters into contact with the scraper 18, which is arranged vertically, and descends along the scraper 18, depositing in the collection channel 17. The colorant collected in the collection element 16 is not diluted by the cleaning liquid sent from the spray humidifier 8 which is dried by the action of the aspirated air in the conveyor 5. For these reasons the colorant deposited in the collection channel 17 can be directly sent back to the nozzle 4 through known-type piping arrangements, not shown in the figures, with no need for the colorant to undergo control and/or density-restoring treatments.

The conveyor 5 is constrained to the frame 60 by means of known-type guides (not illustrated) on which the conveyor 5 is slidable in a perpendicular direction to the mobile transport plane 2.

The device functions in an extremely simple and effective way. During operation the tiles 30 move at a constant speed on the mobile transport plane 2 and the screen 3 rotates about the longitudinal axis y at a rotation speed at which the screen 3 has a peripheral velocity which is the same as the speed of the mobile transport plane 2. Though there is no contact between the screen 3 and the tiles 30, the screen 3 effectively rotates without dragging on the tiles 30, i. e. with no change in relative velocity. Advantageously the device can therefore be used for decoration of tiles having a structured surface, i. e. a non-flat configuration. As the decoration is made without contact between the tile 30 and the screen 3, the presence of crests and/or dips in the surface to be decorated is not in any way influential on the correct functioning of the device. The rotation of the screen 3

is also synchronised with the motion of the tiles 30 so that the decoration to be deposited faces the tiles 30 at the very moment in which they transit beneath the screen 3 and the nozzle 4. The colorant sprayed through the nozzle 4 passes through the screen 3 and is deposited on the tiles 30 in a similar way to what occurs with silk screening process, where there is, however, contact between the decorating roller and the tiles. The means for cleaning continuously remove the excess of colorant deposited on the screen 3 so that the screen 3 is perfectly permeable to selective passage of the colorant sprayed by the nozzle 4 on passage of each single tile 30. The distance and alignment of the screen 3 with respect to the mobile transport plane 2 can be regulated thanks to the presence of the first guides 71 and the second guides 72. In particular the screen 3 can slide on the first guides 71 between an operative position, in which it is aligned on the mobile transport plane 2 and envelops the nozzle 4 and the means for cleaning, and a non-operative position, in which it is aligned with respect to the mobile transport plane 2 and does not envelop the nozzle 4 and the means for cleaning, so that the nozzle 4 and means for cleaning are accessible. The means for cleaning and the nozzle 4 can translate solidly with the screen 3 in a direction which is perpendicular to the mobile transport plane 2, thanks to the respective guides with which they are connected to the frame 60. The vertical distances between the screen 3 and the tiles 30 and the nozzle 4 and the screen 3 influence the characteristics of the decoration which is reproduced on the tiles 30; the smaller the distances, the greater the definition of the decoration. The device is further provided with electronic means of known type which comprise some sensors connected to a circuit which detects the presence and position of the tiles 30 and synchronises, by acting on the various actuator, the rotation of the screen 3 with the motion of the tiles 30 and the spray of the colorant through the nozzle 4.

The process and device of the present invention offer important advantages.

Firstly, the screen is not subject to wear inasmuch as it is not in contact with the tile or the other parts in motion, as occurs with processes and devices in the prior art, but only with the scrapers of the means for cleaning. The screen 3 is therefore not subject to mechanical wear and therefore has a practically unlimited working life. The process and device of the invention also enable use of water-based colours and not oil-based colours, so that the production process is not highly pollutant and is simple and economical to actuate. The device is particularly simple and reliable to manage and maintain as it can be washed with water during the production cycle, with no need for shut-downs or pauses. All of the operative components are easily accessible for any type of operation and the screen can be dismounted with a simple and safe operation, which contributes to making maintenance of the device even more rapid and economical.