EP1336480A1

EP1336480A1 - Method and device for decoration by silkscreen printing of ceramic tiles or the like

Info

Publication number: EP1336480A1
Application number: EP03425095A
Authority: EP
Inventors: Marco Sante Montipo'
Original assignee: Gruppo Concorde SpA
Current assignee: Gruppo Concorde SpA
Priority date: 2002-02-18
Filing date: 2003-02-18
Publication date: 2003-08-20
Also published as: ITFI20020029A1

Abstract

The device for silkscreen printing decoration by transfer comprises: a silkscreen printing screen (1); supporting means (3) to position an item to be decorated (P) in front of said silkscreen printing screen; means (7) to apply a silkscreen printing ink (I) to said silkscreen printing screen. To transfer the ink from the silkscreen printing screen to the tile or other item to be decorated a nozzle (5; 5X) is provided, positioned in front of said silkscreen printing screen on the opposite side from the item to be decorated. The nozzle produces an air jet which causes transfer of the silkscreen printing ink from the silkscreen printing screen to the item.

Description

Technical Field

The present invention relates to a device and a method for silkscreen printing decoration by transfer of items of various form and especially, although not exclusively, ceramic tiles or other rigid products.

State of the Art

Decoration of ceramic tiles using silkscreen printing by transfer is a technique that has been known and used for some time, both in the version with flat silkscreen printing screens or nets and with rotary cylindrical screens or nets.
It consists in transferring ceramic silkscreen printing inks from an accumulation zone over a silkscreen printing screen to one or more zones of the surface of a tile under the screen according to a diagram or pattern defined by the screen, constituted by a net fabric, the meshes of which are suitably sealed in some zones by polymerized photosensitive emulsion reproducing the pattern. In this way the silkscreen printing ink is distributed uniformly over the entire surface of the screen but is only transferred to the item to be decorated underneath in the zones in which meshes of the net fabric of the screen are not closed by the emulsion and in which the screen comes into contact with the surface of the tile or other item to be decorated, thus producing the desired decoration. Subsequent applications with screens in series make it possible to attain multicolor effects.
Transfer of ceramic silkscreen printing inks usually constituted by gelled solutions of metal compounds, mixtures of enamels and coloring pigments carried by more or less viscous liquids such as oils, glycols, greases, water or other suitable carrier liquids, or others, takes place using a suitable elastic doctor made of polymers or elastomers. The doctor, sliding in relation to the screen and exploring the entire useful upper surface, forces the ink spread on it to pass through the holes defined by the open meshes of the net forming the screen and to form a multitude of drops of ink on the lower surface, each of which corresponds to an open mesh of the screen. As the doctor exerts a downward pressure as it advances, that is towards the item to be decorated, the screen is deformed in a downward direction towards the surface to be decorated at the relative successive positions of the doctor. In this way each drop of ink which has passed through the screen comes into contact with the surface to be decorated and remains attached to it. Immediately after this, as the doctor has moved forward in relation to the point of contact with the item to be decorated, the screen retreats and is no longer in contact with the surface of the item, in order not to spoil the deposit which has just taken place.
Examples of silkscreen printing devices with rotary cylindrical screens of this type for the decoration of ceramic tiles and other items are described in EP-B-0836555, EP-A-1157832 and in EP-A-0974458.
A device for silkscreen printing decoration of items with a complex shape, such as plates or the like, is described in IT-B-1117838.
An example of a silkscreen printing device with a flat screen is described in EP-A-0909644.
When decorating ceramic tiles, the flatter and more regular the surface to be decorated is, the more accurate the transfer of ink will be. Particular uneven surfaces or those that are generally level but extremely rough, such as surfaces of tiles reproducing in relief the fracture surfaces of a natural split stone, are difficult to decorate as in the more recessed zones the pressure of the doctor on the screen is insufficient to bring the drops of ink into contact with the surface to receive them. The drops remain attached to the screen, accumulate during subsequent cycles until large drips are produced which then fall to stain and spoil the decoration.

Object and Summary of the Invention

The object of the present invention is to produce a device and a method which make it possible to produce silkscreen printing decorations even on surfaces which are extremely rough or in any case very uneven, such as the surfaces of tiles reproducing natural split stone, producing a high definition decoration.
The object of an improved embodiment of the invention is to produce a silkscreen printing method and device which allow high flexibility and make it unnecessary to have a silkscreen printing screen or net for each pattern one wishes to reproduce on the item to be decorated.
In substance, according to the method of the present invention the silkscreen printing ink is transferred through the silkscreen printing net or screen to the item to be decorated through the action of at least one air flow, the item to be decorated and the air flow having a relative movement parallel to the surface to be decorated of said item.
In practice, the ink to be transferred is distributed on one face of the silkscreen printing net or screen so that it fills the open meshes of the net fabric and is successively transferred towards the surface to be decorated because of the impact of the air flow. Transfer thus occurs without reciprocal contact between the screen and the surface to be decorated. The latter may thus have protrusions, roughness, unevenness or even considerable defects in its planarity, without this negatively influencing the quality of the decoration.
The method may be implemented either with a flat screen or with a rotary cylindrical screen.
In practice, the silkscreen printing ink may be applied by a doctor on the surface of the silkscreen printing screen, positioning the doctor directly upstream of the zone of action of the air jet.
In a first particularly-simple embodiment of the invention, the air flow or jet is created by a slotted nozzle, and thus has a laminar form. In substance, the air flow constitutes an aerodynamic doctor which replaces the mechanical doctor of traditional systems. The length of the slot is about equal to the useful width of the silkscreen printing screen. The latter has, in a per se known way, a pattern corresponding to the negative of the pattern to be reproduced on the tile or other item to be decorated. The meshes of the net fabric corresponding to zones of the item which are not to receive ink will be closed, while the meshes corresponding to zones which are to receive ink will be open to allow the ink to pass through owing to the effect of the air thrust.
According to an improved embodiment of the invention, on the other hand, an air flow is produced by a plurality of air jets, for example by a series of small nozzles placed side by side according to preferably transverse alignment in relation to the relative movement of the item to be decorated. In this case the air jets produced by the individual nozzles are controlled in a programmed manner, by means of a central control unit, to form the decoration, while the silkscreen printing screen has an active zone formed of a plurality of open meshes without a pattern, that is without closed meshes.
In substance, the silkscreen printing ink is in this case distributed so as to fill all the meshes of the screen and is projected onto the surface of the item to be decorated selectively by operating the nozzles in suitable time sequences synchronized with the relative movement between the item to be decorated and the nozzles. Combination of relative movement between the item to be decorated and nozzles on the one hand and controlled opening and closing of each single nozzle makes it possible to produced even complicated patterns without having to change the screen. In fact, the screen will be a universal screen. The different patterns will be attained simply by loading the control unit with the necessary program for correct control of nozzle opening and closing.
It is also possible to position the nozzles according to several side by side alignments to increase definition.
The object of the present invention is also a device for silkscreen printing decoration by transfer, comprising: a silkscreen printing net or screen; supporting means to position an item to be decorated in front of said silkscreen printing screen; means to apply a silkscreen printing ink to said silkscreen printing net or screen and to transfer it to said item. According to the invention, the device characteristically comprises at least one nozzle positioned in front of said silkscreen printing screen on the opposite side in relation to the item to be decorated, said nozzle producing an air jet which causes the silkscreen printing ink to transfer from the silkscreen printing screen to the item, the nozzle and the silkscreen printing screen being movable in relation to each other.
In a first embodiment, the nozzle has an elongated air outlet to produce an air jet of laminar form.
In an improved embodiment of the invention, the device comprises a plurality of nozzles which produce corresponding air jets and advantageously a control unit for timed control of their opening and closing as described above.
Further advantageous features and embodiments of the invention are indicated in the attached dependent claims.

Brief description of the drawings

The finding shall now be better understood according to the description and attached drawing, which shows a non-limiting practical embodiment of the invention. In greater detail, in the drawing:
Figs. 1 and 2 show schematic sections of a device according to the invention with a rotary cylindrical silkscreen printing screen applied to the decoration of a smooth tile and a rough tile respectively;
Figs. 3 and 4 show schematic sections of a device according to the invention with a flat silkscreen printing screen applied to the decoration of a smooth tile and a rough tile respectively;
Fig.5 shows a section according to plane orthogonal to the axis of the cylindrical silkscreen printing screen, according to the line V-V in Fig.6, of a device according to the invention employing a specific type of blade nozzle;
Fig.6 shows a section according to VI-VI in Fig.5;
Fig.7 shows an improved device, with a rotary cylindrical screen, in a section according to a plane orthogonal to the axis of the screen, with the trace VII-VII in Fig.8; and
Fig.8 shows a section according to VIII-VIII in Fig. 7.

Detailed description of embodiments of the invention

Figs. 1 and 2 represent in a highly schematic way a first embodiment of the invention with the use of a rotary cylindrical silkscreen printing net or screen. Only the parts required to understand the invention are represented in the drawing, it being understood that the remaining parts of the device, and in particular of the silkscreen printing screen may be produced according to any known method. For example, the screen may be supported (cantilevered or with a support at both ends), stretched and made to rotate suitably for example with systems known to those skilled in the art. Analogously, known systems may be used to supply the silkscreen printing ink to the screen.
The screen is generically indicated with 1 and rotates around its horizontal axis A-A. It is constituted by a net fabric and has watertight zones 1A and zones 1B permeable to silkscreen printing ink. These permeable and watertight zones are obtained with known systems through the use of photosensitive emulsions.
Under the silkscreen printing screen is a transport system constituted by a conveyor 3 which may be composed of a series of parallel belts. The tiles P to be silkscreen printed are laid on the conveyor 3. The direction of advance of the tiles P, indicated by the arrow fP, is the same as the direction of rotation (arrow f1) of the silkscreen printing screen 1 around its axis A-A, so that in the zone in which the upper surface of the tile P to be decorated and the screen 1 are the closest to each other, the peripheral speed of the screen is substantially equal both in modulus and in direction.
Unlike the procedure in traditional systems, where decoration occurs through physical contact between the screen and the upper surface of the tile P or other item to be screen printed, in the present case there is no reciprocal contact between the screen and tile even in the zone in which they are closest to each other.
Housed inside the cylindrical volume defined by the screen 1 is a blade nozzle 5 which is supplied with compressed air through a duct 5A. The nozzle 5 extends for the entire useful width of the screen, in an orthogonal direction to the plane of the figure. The nozzle 5 outlet is in proximity to the internal surface of the cylindrical screen, in front of the zone closest to the conveyor 3 and therefore to the tile P to be decorated which travels under the screen.
Directly upstream of the nozzle 5, in relation to the direction of advance of the screen, and inside this screen, a fixed inking doctor 7 is positioned, supported, as is the nozzle 5, by a support coaxial to the screen, not shown in the drawing. The silkscreen printing ink I is deposited, via a duct not shown, in front of the inking doctor 7. As the screen 1 moves in front of the doctor 7 which touches its internal surface, the ink I wets the surface of the screen and fills all the open meshes of the screen, that is the zone not closed by the emulsion distributed in the zones 1A.
When a portion of the screen 1 wet with ink I travels in front of the laminar nozzle 5, the air flow emitted from the nozzle causes sufficient thrust on the ink trapped in the meshes of the screen to detach the ink and to project it against the surface of the tile P traveling under the screen, with a movement synchronized with the rotary movement of said screen.
As a result, the ink is transferred to the tile P because of the air jet according to a pattern which reproduces the pattern on the silkscreen printing screen 1. As the ink is expelled from the net because of the air current produced by the nozzle 5, no physical contact between the tile P and the external surface of the screen 1 is required.
Each portion of the silkscreen printing screen from which the ink was expelled by the air current produced by the nozzle 5 is once more loaded with ink as soon as it travels in front of the doctor 7 to allow decoration of the subsequent tile.
Fig. 2 shows the same device as Fig. 1, used to decorate the surface of a tile P1 which is not smooth like the example in Fig.1, but extremely uneven, as is typically the case in tiles with surfaces imitating natural split stone. The opportunity offered by the device, to transfer ink without physical contact between the screen and the tile, makes high definition decoration of this type of product possible.
Figs. 3 and 4 schematically show the same inventive concept applied to a flat silkscreen printing screen or net. In this case also the two figures differ solely as concerns the nature of the surface to be decorated. In Fig.3 this is a substantially smooth and flat surface, while in Fig.4 it is an uneven surface. The silkscreen printing screen is again indicated with 1, the nozzle with 5, the air supply duct with 5A and the tile to be decorated with P and P1. The nozzle 5 moves in the direction of the arrow f5 in relation to the screen and in relation to the tile P or P1. The nozzle 5 is carried by moving equipment 4 on which the doctor 7 is also carried. This may be provided with a lifting movement so as not to interfere with the screen 1 during its return movement. Alternatively, two inking doctors may also be provided, disposed on opposite sides of the nozzle 5 and carried in the operating position alternately, so as to distribute the ink in the mesh of the silkscreen printing screen 1 both with a movement according to the arrow f5, and with a movement in the opposite direction, thus increasing productivity of the device.
The nozzle 5 may be a nozzle formed by two converging plates to form a chamber with a V-section as indicated schematically in Figs. 1 to 4, if necessary it being possible to adjust the distance between the output edges of the plates. Nonetheless, nozzles of different configuration may also be used, such as of the type commonly used to produce air curtains.
A nozzle of this type is schematically indicated in the embodiment in Figs. 5 and 6. It may be for example a blower of the type marketed by CER srl, Italy, with the trade name of ARTX Air Curtain. These systems are commonly utilized to remove water, debris or other items from plates, plastic films, conveyors and the like, to create isolating curtains between consecutive phases in industrial processes, to cool semi-finished products and for similar applications.
In Figs. 5 and 6 equivalent or corresponding parts to those in Figs. 1 and 2 are indicated with the same reference numbers. The nozzle 5 has an outlet 5B emitting an air current with moderate flow rate, which continues to adhere to the profile of the nozzle, undergoing a downward deflection until it produces an air curtain C with a much higher flow rate to the one emitted from the outlet 5B, thanks to the drawing effect on the surrounding air. The nozzle 5 and the inked doctor 7 are supported by a supporting beam 9 parallel to the axis A-A of the screen 1.
Figs. 7 and 8 show, in analogous views and sections to Figs. 5 and 6, an improved embodiment. Equivalent numbers indicate equivalent or corresponding parts to those in the embodiment in Figs. 5 and 6.
This further embodiment differs from the previous one in that the single elongated nozzle 5 forming an air curtain is replaced by a series of small nozzles 5X side by side to one another and aligned along a direction parallel to the axis A-A of the cylindrical screen 1. Each nozzle 5X is controlled by a programmable control unit, represented schematically and indicated with 11, which also controls the forward movement of the conveyor 3 and the rotary motion of the silkscreen printing screen 1. The control unit 11 is capable of synchronizing opening and closing of the single nozzles 5X with the rotary movement of the silkscreen printing screen 1 and with the forward movement of the tiles P, according to a memorized program.
In this embodiment, the screen 1 is wholly constituted by a fabric the meshes of which are open. In other words, it does not have a pattern constituted by closed meshes and open meshes, reproducing in negative the pattern to be silkscreen printed on the tiles.
In fact, the pattern is produced in this case by synchronized control of opening and closing of the nozzles 5X and of the forward movement of the silkscreen printing screen and of the tiles. Each mesh of the screen 1 is filled with ink I in the zone of action of the inking doctor 7. When the inked zone of the screen passes in front of the nozzles 5X, some meshes are struck by air jets produced by the nozzles which are opened and the ink is projected from said meshes onto the tile P underneath. Other meshes, which travel in front of nozzles which are not opened, withhold the ink inside them. When, after completing a rotation of the screen, the meshes travel again under the zone of action of the inking doctor 7, all the meshes are loaded with fresh ink. Those previously emptied because of transfer onto the item below are simply filled with new ink. Vice versa, those meshes that were not previously hit by the air jet emitted by the nozzles pass under the inking doctor 7 and receive new ink, discharging the ink received during the previous cycle to the outside. An external doctor blade 8 collects the unused ink to recycle it and prevent it from falling onto the tiles to be decorated.
To guarantee exchange of ink in the meshes that are not hit by the air jet of the nozzles 5X all the meshes may be cleaned by an elongated nozzle analogous to the one in the previous embodiments, positioned in an inactive zone of the screen's travel, for example directly upstream of the zone of action of the doctor 7. A recovery tray, positioned externally to the screen may be used to collect and recycle the silkscreen printing ink. In this case the doctor blade 8 may be omitted.
By suitably coordinating opening and closing of the single nozzles the desired pattern may thus be produced on each tile, using an entirely featureless screen, that is without any decoration.
On the one hand this permits extremely high flexibility, as it is possible to produce in sequence a high number of patterns on tiles which are made to travel in succession under the silkscreen printing screen 1, the number of patterns being in substance limited only by the calculation and storage capacities of the control unit 11. On the other hand, each pattern no longer requires to be reproduced on a specific silkscreen printing screen or net, but simply memorized on a specific storage medium, while there is only one screen which may be used for any pattern. This results in an increase, not only in the versatility and flexibility of the machine, but also in its productivity, as it is no longer necessary to change the screen each time the pattern changes. The screen must only be changed when it becomes necessary to modify the dimension of the meshes and/or the dimension of the threads which form the screen or net, in order to change the quantity of ink transferred to the item to be decorated.
Also from the standpoint of warehouse management, there is a considerable advantage in being able to eliminate all the pattern screens currently required to reproduce each decoration.
To increase the resolution of the pattern it is possible to distribute the nozzles 5X according to two or more alignments, preferably parallel to the axis A-A of the screen 1 and staggered from one another.
The solution shown in Figs. 8 and 9 for a device with a rotary silkscreen printing screen may also be adopted with the appropriate modifications for a device with a flat screen with analogous advantages.
It is understood that the drawing shows only one practical embodiment of the invention, the forms and layouts of which may vary without however departing from the scope of the underlying concept of the invention. Any reference numbers in the attached claims are provided for the purpose of facilitating reading thereof in the light of the description and of the attached drawings and do not limit the scope of protection of the claims.

Claims

A method of silkscreen printing decoration by transfer, wherein a silkscreen printing ink (I) is applied to a first surface of a silkscreen printing screen (1) and transferred to an item to be decorated (P) positioned in front of a second surface of the silkscreen printing screen,
characterized in that said silkscreen printing ink is transferred through the silkscreen printing screen to the item to be decorated through the action of at least one air flow.
Method as claimed in claim 1, characterized in that the silkscreen printing ink is transferred to the item to be decorated without reciprocal contact between the silkscreen printing screen and said item.
Method as claimed in claim 1 or 2, characterized in that the silkscreen printing ink is distributed by means of a doctor (7) on said first surface of the silkscreen printing screen.
Method as claimed in claim 1, 2 or 3, characterized in that an air flow of laminar form is produced, of a length at least equal to the useful width of the silkscreen printing screen, which has a pattern corresponding to a decoration to be produced on the item to be decorated, said pattern being defined by a distribution of open and closed meshes of the silkscreen printing screen.
Method as claimed in claim 1, 2 or 3, characterized in that an air flow composed of a plurality of air jets is produced and said air jets are controlled in a programmed manner to form the decoration, the silkscreen printing screen having an active zone composed of a plurality of open meshes without a pattern.
Method as claimed in claim 5, characterized in that said air jets are positioned according to at least one preferably rectilinear alignment.
Method as claimed in one or more of the previous claims, characterized in that a rotary cylindrical screen is used and means to produce said air flow are positioned inside thereof.
Method as claimed in claim 7, characterized in that a doctor to apply ink is positioned inside said rotary cylindrical screen, said doctor being placed directly upstream of the zone of action of the air flow in relation to the movement of the silkscreen printing screen.
Method as claimed in one or more of the previous claims, characterized in that said item to be decorated is a ceramic tile.
Method as claimed in claim 9, characterized in that the surface of said ceramic tile to be decorated is geometrically uneven.
Method as claimed in one or more of the previous claims, characterized in that the residual silkscreen printing ink is eliminated from the meshes of the silkscreen printing screen after each application to an item to be decorated and before loading new ink into said meshes.
A device for silkscreen printing decoration by transfer, comprising: a silkscreen printing screen (1); supporting means (3) to bring an item to be decorated (P) in front of said silkscreen printing screen; means (7) to apply a silkscreen printing ink (I) to said silkscreen printing screen,
characterized in that it comprises at least one nozzle (5; 5X) positioned in front of said silkscreen printing screen on the opposite side from the item to be decorated, said nozzle producing an air jet which causes transfer of the silkscreen printing ink from the silkscreen printing screen to said item, the nozzle and the silkscreen printing screen being movable in relation to each other.
Device as claimed in claim 12, characterized in that said at least one nozzle has an elongated air outlet to produce an air jet of laminar form.
Device as claimed in claim 12, characterized in that it comprises a plurality of nozzles (5X) which produce corresponding air jets aligned with one another.
Device as claimed in claim 14, characterized in that said nozzles are aligned with one another according at least to a preferably rectilinear alignment extending transversely in relation to the direction of reciprocal movement between the nozzles and the silkscreen printing screen.
Device as claimed in claim 14 or 15, characterized in that: said nozzles are associated with opening and closing means controlled by a programmable unit (11); said screen has at least one active zone formed by open meshes, without a pattern; and said nozzles are opened and closed in a controlled manner by said programmable unit to transfer the silkscreen printing ink to said item in order to form a pattern.
Device as claimed in one or more of the claims from 12 to 16, characterized in that it comprises a doctor (7) to apply and distribute the silkscreen printing ink on the silkscreen printing screen.
Device as claimed in claim 16, characterized in that said silkscreen printing screen is a rotary cylinder, positioned inside which are said at least one nozzle and said doctor, said doctor being positioned directly upstream of said nozzle in relation to the movement of the silkscreen printing screen.
Device as claimed in one or more of the claims from 12 to 18, characterized in that the distance between the supporting means and the silkscreen printing screen is regulated so that the item to be decorated does not touch the silkscreen printing screen.
Device as claimed in one or more of the claims from 12 to 19, characterized in that it comprises collection means (8) to collect the excess silkscreen printing ink from the face of the silkscreen printing screen facing the item to be decorated.
Device as claimed in claim 20, characterized in that said collection means comprise a doctor blade (8).
Device as claimed in claims 16 and 20, characterized in that said collection means comprise a laminar nozzle and a collection tray, positioned on opposite sides of the screen and upstream of said doctor (7), in relation to the relative movement between the screen and said nozzle.