EP1972450A2

EP1972450A2 - A printing head for tile decoration

Info

Publication number: EP1972450A2
Application number: EP08075107A
Authority: EP
Inventors: Gian Mario Guidotti
Original assignee: Ingegneria Ceramica Srl
Current assignee: Ingegneria Ceramica Srl
Priority date: 2007-03-20
Filing date: 2008-02-11
Publication date: 2008-09-24
Also published as: ITMO20070098A1; EP1972450A3

Abstract

The invention relates to a printing head (1) for decorating tiles (11), comprising at least a hollow element (2), internally of which a conduit (3) is afforded, destined to contain pressurised glaze (4). The conduit (3) exhibits at least an outlet nozzle (6) for the glaze (4). An obturator (9) is associated to each nozzle (6) and is mobile between a closed position of the nozzle (6) and an open position of the nozzle (6). The obturator (9) is activated by a relative piezo-electric actuator (10), arranged internally of the conduit (3), to which it is solidly constrained.

Description

Description.

The invention relates to a printing head for tile decoration.
In particular, the invention can be applied in printing using ceramic glazes.
The printing head of the present invention is preferably applicable in decoration in the ceramic sector.
The prior art has for a long time included techniques for printing or tile decoration, such as for example silk screening, rotary printing, flexography, etc.
These techniques include use of special coloured ceramic glazes, or suspensions made up of a liquid part, internally of which a quantity of mineral powders are dispersed, which provide special resistance to abrasion, as well as brilliancy and shininess, for the decorated surface of the tile.
In the case of the techniques most commonly used at present, apart from the very well known silk screening and flexographic techniques, a further very widely used method is the intaglio technique, in which the glaze is deposited on the surface of the tile by means of rollers made of an elastomer material on a smooth and elastically deformable surface of which the intaglio matrix of the design to be reproduced is cut.
The matrix is constituted by a plurality of miniscule cells which, specially filled with glaze by the action of at least a doctor, which has the task of scraping, cleaning the smooth surface off, in which the cells are cut, release the glaze when the roller comes into contact with the tile to be decorated.
This machinary exhibits some basic drawbacks, having their roots in the very technology of printing used, and which are briefly listed here.
Printing is done via contact (the roller presses on the surface of the tile) so although the roller is "soft", some specific problems of ceramic decoration remain unresolved.
Indeed the tiles are never completely flat, so it is difficult to adjust the roller pressure, which if not sufficient may leave some tile zones undecorated, while if over-adjusted will be too strong and will risk breaking the tile during the printing operation.
Often the tiles to be decorated exhibit a "structured" surface (with three-dimensional reliefs and grooves, and therefore not "smooth"), in order to simulate natural stone. In this case it is impossible for the roller to decorated the bas-reliefs, which will contact the printing matrix only with some difficulty.
In any case, for all the techniques using cylindrical matrices or rollers, in order to decorate a tile satisfactorily in the chromatic sense, at least four printing rollers are necessary, one for each different colour, with the matrix on each roller bearing the graphic design associated to that colour. This being true for each type of decoration (and every ceramic industry has hundreds if not thousands of different decoration graphics), it is clear that the total quantity of rollers a tile producers must have available is truly enormous - and lead to the following drawbacks.
The investment for buying the printing means (rollers) is very high, considering the single cost for each roller (virgin roller + the matrix having to be cut into the roller according to the graphic design of the decoration).
A not inconsiderable level of capital outlay is bound up in this investment. Also true is that for small production batches, a roller might be used for a number of applications which is much lower than its working life would permit.
Further, large spaces must be made available for storing the rollers, leading to high storage costs.
It is also impossible to use "just in time" techniques on the production line, i.e. realise different decorations, as in order to do this the matrix has to be replaced; nor is it possible to realise low-cost printing tests, considering the cost involved in manufacturing a single matrix.
In the light of these considerations it is obvious that all the techniques which include use of a printing means (for example rollers, as illustrated above) are not flexible for programming the production of tiles on the basis of the real demand, which ever more often is subject to strong variability inasmuch as it is characterised by ever-smaller batches.
In order to solve these problems, in recent years machines have been developed for the decoration of tiles which use the technique of common ink-jet printers, conventionally used in other sectors such as printing on paper and cardboard.
These machines include the use of heads which are controlled by special electronic switchboards and which release drops of pigment according to the desired printing sequence. In this way the motif to be printed can be changed, easily and rapidly, simply via the control panel by directly selecting the desired graphic files.
The holes in the heads used are very small, generally in the order of a few tenths of millimetres, in order for high printing definition to be obtained.
The above machines have however shown themselves to have obvious use limitations in the ceramic field, especially in connection with the use of coloured ceramic glazes (suspensions), described herein above and commonly used in traditional decoration methods.
In these machines the nozzle size and its poor resistance to abrasion and wear prevent use of ceramic glazes containing microparticles of minerals, whose granulometry, commonly variable in a range between 0 and 40 µm, inevitably causes obturation and erosion of the nozzle itself.
A further use limitation of these ink-jet machines is connected to an intrinsic characteristics of all the suspensions, which leads to natural depositing, over time, of the solid part and to division thereof from the liquid part.
The aim of the present invention is to reolve the problems encountered in the prior art by providing a printing head for tile decorations which is absent from the above-cited drawbacks, in reference to both roller-type decoration and ink-jet decoration.
In more detail, an aim of the present invention is to realise a printing head which :

enables use of means for printing (rollers) to be avoided;
perfectly decorates the tile surface, even in a case where it is not perfectly flat, or is structured (with zones in low relief), thanks to the fact that the print is not done via direct contact;
uses traditional ceramic glazes (suspensions), giving the printed graphic motif good abrasion-proof qualities, while at the same time preventing clogging and erosion of the nozzles;
flexibly programmes production of the tiles on the basis of the real demand, and enables the printing motif to be changed according to needs.

These aims and more besides, which will better emerge during the course of the following description, are substantially attained by a printing head for decorating tiles, according to what is described and claimed in the present invention.
Further characteristics and advantages will better emerge from the detailed description of a preferred but not exclusive embodiment of a printing head for decorating tiles, according to the present invention. The description will be made here below with reference to the accompanying figures of the drawings, which are provided by way of non-limiting example, and in which:

figure 1 is a section view of a portion of a printing head, in rest position, according to the present invention;
figure 2 is a section view of a portion of a printing head, in work position, according to the present invention;
figure 3 is a plan view of a printing head of the present invention.

With reference to the accompanying figures of the drawings, 1 denotes in its entirety a printing head for decorating tiles 11, according to the present invention.
In particular, though not exclusively, the head of the invention can be applied in in-line decorating of ceramic tiles.
The printing head 1 substantially comprises at least a hollow element 2, in which a conduit 3 containing a pigmented glaze 4 is afforded, preferably a ceramic glaze, which is maintained at a constant pressure. Generally the pressure is slightly above atmospheric pressure, preferably comprised between 50 mbar and 500 mbar.
In particular, the hollow element 2 is made of two shells, an upper shell 2a and a lower shell 2b. A continuous gasket 5 is interposed between the two shells 2a and 2b, which gasket 5 is specially shaped to ensure the seal of the conduit 3.
The upper shell 2a, which is internally hollow, defines the majority of the conduit 3 internally of which the coloured glaze 4 flows, and the lower shell 2b, also internally hollow, exhibits at least an outlet nozzle 6 of the drops of pigment 4.
A plurality of outlet nozzles 6 is preferably aligned to one another, each being provided with an outlet hole 7 having a diameter comprised between 100 µm and 300 µm, advantageously between 150 µm and 250 µm.
The nozzles are generally made of hard metal or ceramic material, such as adequately to resist the erosion produced by the microparticles of minerals dispersed in the glaze.
The nozzles 6 are applied to the lower shell 2b, and are easily replaceable such as to be able to equip the head 1 with the nozzles having a diameter which is suitable for the application to be performed and the glaze to be used.
The printing head 1 further comprises a closed-circuit supply system 8, schematically represented and associated limitedly to a single element in figure 2, which causes the pressurised ceramic glaze 4 to continuously circulate internally of the conduit 3.
The closed-circuit supply system 8 comprises a supply channel of the glaze to the conduit 3, a discharge channel and means for moving and pressurising the glaze in the conduit.
The glaze is released in the form of small drops which are launched through the holes 7 of the outlet nozzles 6. The drop intercepting and launching system comprises at least an obturator 9 associated to each nozzle 6.
The obturator 9 is a block of material which is resistant to wear and abrasion, which exhibits a first base surface 9a which rests against the internal surface 6a of the nozzle, such as to completely close the outlet hole 7 and ensure a perfect mechanical seal.
A second base surface 9b, opposite the first 9a, is solidly connected to a piezo-electric actuator 10 which, following deformation thereof, moves the obturator 9. The obturator 9 is mobile between a closed position of the outlet hole 7 of the nozzle 6, at which the piezo-electric actuator 10 presses the obturator 9 against the internal surface 6a of the nozzle 6, and an open position of the outlet hole 7 of the nozzle 6, at which the piezo-electric actuator 10 distances the obturator 9 from the nozzle 6.
In detail, the piezo-electric cactuator 10 is electrically connected to a tension generator, not illustrated, located externally of the conduit 3.
The piezo-electric actuator 10 is generally a bar, inserted transversally internally of the conduit 3. In the rest position the bar is perpendicular both to the longitudinal axis of the nozzle 6 and to the longitudinal axis of the conduit 3.
The piezo-electric actuator 10 is fixed at two points along its length, and is held elastically by the gasket 5 positioned between the two shells 2a and 2b of the element 2: in particular, a first connection point is located at a first end 10a of the bar, while a second connection point is in an intermediate position 10c of the bar.
The second end 10b of the bar, to which the electric connections arrive from the tension generator, is thus still external of the conduit 3, in an easily-accessible and clean zone.
An electronic switchboard, not illustrated, controls the tension generator in accordance with the printing sequence set; the tension generator activates the piezo-electric actuator 10, causing it to oscillate at a suitable frequency.
In particular, in the work position the piezo-electric bar 10 arches upwards such that the concavity thereof faces the nozzle 6.
Following this deformation, the piezo-electric bar 10 raises the obturator 9 and thus opens the outlet hole 7 of the nozzle 6.
The raising of the obturator 9 and the pressure in the conduit cause the glaze 4 to flow between the nozzle 6 and the obturator 9, below the first base surface 9a of the obturator 9 and into the hole 7 of the nozzle 6.
The subsequent return movement into the rest position of the piezo-electric bar 10 pushes the obturator 9 downwards causing the exit of the glaze through the nozzle 6. During the descent stage, the obturator 9 pushes the underlying portion of glaze into the hole 7, impressing sufficient energy onto the glaze to project drops of pigment 20 in an external wise direction at a very high speed against the underlying tile 11.
We note that each nozzle 6 is associated to a relative obturator 9 and a respective piezo-electric actuator 10.
Thus each piezo-electric actuator 10 is controlled independently of another, and according to the length of the impulse received from the control switchboard, can proportionally generate drops of various sizes.
The opening time of the obturator preferably varies between 0.2 and 2 ms.
With a printing head 1 such as the one described above, the "variable dot" technique can be realised. This technique includes the dropping of drops of glaze having different sizes according to nuances and tone intensity to be achieved in the various parts of the motifs to be printed.
The overall graphic effect depends, apart from the reciprocal position of the deposited drops, on their size too, and thus the quantity of colour released from each drop.
Normally each conduit 3 (or cavity), designed to contain pressurised glaze 4, comprises a plurality of nozzles 6, each provided with an obturator 9 with a relative piezo-electric actuator 10, the nozzles 6 being aligned at equal distances from one another.
A printing head 1 comprises a plurality of hollow elements 2 arranged partially side-by-side and inclined in a fishbone arrangement, each hollow element 2 being provided with a plurality of reciprocally aligned outlet nozzles 6. The hollow elements 2 are located side-by-side and inclined such that the projection of the distance between the axes of any two contiguous nozzles of each hollow element 2 in a predetermined direction is less, according to a fixed ratio, than the distance itself. The direction is none other than the motion direction relative to the support to be printed on or decorated by the head.
The elements 2 are arrayed in a fishbone-arrangement, such as to reduce the distance between the nozzles 6 of adjacent elements 2, and thus to cover the surface 11 a of the tile 11 to be decorated as uniformly as possible. On the basis of the dimensions of the tile 11, the printing head 1 has a larger or smaller number of elements 2 coupled to one another.
The nozzle 6 and the obturator 9 are made of an abrasion-resistant material, such as to resist the erosive action of the ceramic powders present in the glaze 4.
Further, the mechanical coupling between the obturator 9 and the internal surface 6a of the nozzle 6, achieved simply with a pressure of the base surface 9a of the obturator 9 against the internal surface 6a of the nozzle 6, without any interference, joint or insertion of one in the other, prevents both further rubbing and wear on the surfaces and unpleasant drawbacks due for example to the delay in opening the nozzle 6 due to the presence of granules along the walls of the hole 7, which obstruct the relative sliding between the obturator 9 and the hole 7.
The printing head 1 of the present invention exhibits the great advantage of being both mechanically and electronically adjustable, so that the head is extremely flexible and versatile, and adaptable to various desired applications, and to various ceramic glazes at present available and in use, exhibiting various physical-chemical characteristics.
The adjustments that can be made influence the final graphic effect, and offer the chance to obtain the best functionality of the head in the most various operating situations.
Firstly, the size of the hole can be varied, by mounting a nozzle with a suitable diameter to the application to be effect or the glaze to be used. Thus on the basis of the granulometry of the powders suspended in the glazes which are most commonly used, it is possible to apply a nozzle having a larger or smaller diameter, avoiding the unpleasant drawback of obstruction of the nozzle. Further, by acting on the closed circuit supply system, the pressure at which the glaze is maintained in circulation intnerally of the conduit of the head can be adjusted. In this way the quantity of glaze exiting from the nozzle can be varied, thus by consequence varying the size of the drops, all according to the density and viscosity of the glaze.
The supply system also enables a modification of the speed of circulation of the glaze internally of the conduit; the continuous motion of the glaze prevents sedimentation of the mineral powder contained in the suspension, a vital condition for good functioning of the head.
The supply tension of the piezo-electric actuator influences the dimension of the opening and closing run of the obturator, modulating the size of the drops according to the passage hole, apart from the opening time of the nozzle. It is thus possible to perform this modulation in agreement with the physical-chemical characteristics of the glaze.
Obviously in relation to the motif to be printed, the opening time of each single zone can be regulated point by point, independently of the opening time of the other nozzles. Thus, as drops of various sizes can be obtained, this has a positive effect on the final graphic effect obtained.
The perfect adjustment of the size of the drops, independently of the characteristics of the glaze used, which is a characteristic of the present technology, lends maximum flexibility of use of the invention in the ceramic field.
This technique can be advantageously used not only for decoration, but thanks to the generous sizes of the drops of glaze which can be obtained it can also be employed in full-surface glazing.
The depositing of a greater thickness of glaze with respect to the above-described ink-ject machines using heads with micro-nozzles, contributes to an aesthetic result which renders the colours more natural and produces a particularly fine and effect, particularly appreciated in the ceramics field.

Claims

A printing head for decorating tiles, comprising:
at least a hollow element (2), internally of which a conduit (3) (or cavity) is afforded, destined to contain pressurised glaze (4);

at least an outlet nozzle (6) for the glaze (4) from the conduit (3) (or cavity);

at least an obturator (9), associated to each nozzle (6) and mobile between a closed position of the nozzle (6) and an open position of the nozzle (6);

at least a piezo-electric actuator (10), arranged internally of the conduit (3) (or cavity), which controls movement of the obturator (9) to which it is solidly constrained.
The printing head of claim 1, characterised in that it comprises a closed-circuit supply system (8) for promoting a constant-pressure continuous circulation of the glaze (4) internally of the conduit (3).
The printing head of claim 2, characterised in that the closed-circuit supply system (8) comprises a supply channel of the glaze (4) to the conduit (3), and means for moving and pressurising the glaze (4).
The printing head of one of the preceding claims, characterised in that each nozzle (6) has an outlet hole (7) having a diameter comprised between 100 µm and 300 µm, preferably between 150 µm and 250 µm.
The printing head of claim 1, characterised in that the piezo-electric actuator (10) comprises a bar (10), electrically supplied by a tension generator, which in the rest position is perpendicular to the longitudinal axis (6b) of the nozzle (6) and the longitudinal axis (3a) of the conduit (3).
The printing head of claim 5, characterised in that the bar (10) is fixed elastically internally of the conduit (3) at two points (10a, 10c), such that, in the work position, the bar (10) takes on an arched shape, a concavity of which faces towards the nozzle (6).
The printing head of one of the preceding claims, characterised in that each conduit (3) (or cavity), destined to contain pressurised glaze (4), comprises a plurality of the nozzles (6), each provided with an obturator (9) with a piezo-electric actuator (10), which nozzles (6) are consecutively aligned at equal distances from one another.
The printing head of claim 7, characterised in that it comprises a plurality of hollow elements (2) arranged partially side-by-side and inclined in a fishbone arrangement, each being provided with a plurality of outlet nozzles (6) which are aligned to one another; the hollow elements (2) being side-by-side and inclined in the fishbone arrangement such that a projection of a distance between axes of any two contiguous nozzles of each hollow element (2) along a predetermined direction is less than a distance thereof, in a predetermined ratio.
A printer for decorating tiles, characterised in that it comprises at least a printing head as in one or more of claims from 1 to 8.