EP3362293B1

EP3362293B1 - Supply system for an inkjet printer

Info

Publication number: EP3362293B1
Application number: EP16801573.3A
Authority: EP
Inventors: Gildo Bosi; Claudio Ricci
Original assignee: Sacmi Imola SC
Current assignee: Sacmi Imola SC
Priority date: 2015-10-16
Filing date: 2016-10-14
Publication date: 2019-08-07
Anticipated expiration: 2036-10-14
Also published as: PL3362293T3; CN108472962A; RU2687809C1; ES2744805T3; BR112018007362A2; BR112018007362B1; MX2018004551A; WO2017064665A1; ITUB20154980A1; PT3362293T; CN108472962B; EP3362293A1; MX391563B

Description

TECHNICAL FIELD

The present invention relates to a supply system, to an inkjet printer and to a method for printing.

BACKGROUND OF THE INVENTION

Decorative printing with piezoelectric inkjet heads is used in the sector of ceramic tiles and slabs for floors and walls.
This technology has a good level of flexibility (practically unlimited number of printable subjects) and of production stability and makes it possible to obtain a good print definition and high quality image.
The inks used in the ceramics sector have a characteristic feature that distinguishes them from conventional inks for digital applications on industrial products (paper, wood, textiles, etc.): they must be able to withstand the high firing temperatures to which the ceramic product is subjected after decoration. To achieve this, the inks are supplemented with large proportions of inorganic pigments (mixtures of chromophore metal oxides), reaching up to 40% by weight. These pigments, in the form of finely ground powders, have a much higher density than the vehicle in which they are dispersed (an organic or water-based solvent) and therefore have a tendency to sediment, i.e. precipitate in the liquid portion. Adequate counter measures must therefore be taken in the printing machines to avoid the danger of sedimentation. This danger is particularly noticeable at the heads which are the most noble and delicate part of the entire system.
Recently inkjet head manufacturers have developed specific models of head for use in ceramics (i.e. with inks with inorganic pigments), using suitable materials and providing the heads with inner ducts for recirculating the ink.
Patent application number WO2013/150396 describes (with particular reference to FIG 1 - the reference numerals indicated therein are shown hereinafter in brackets) an ink supply system comprising a supply element (31) to which the print heads (1) are fluidically connected. They also have a collection manifold (41), also connected to the print heads (1) and equipped with a pump (43); and a supply duct (3), which is provided with a respective pump (32) and is adapted to bring the ink from a reservoir (5) to the supply element (31) .
The patent application number US2010/214334 describes an inkjet print head. Such a head (for which use for ceramic substrates is not indicated) comprises: a pressure chamber; an actuator that expands and contracts the volume of the pressure chamber; an individual supply flow channel for guiding the ink to the pressure chamber; a nozzle that ejects the ink; a flow channel for guiding the ink from the pressure chamber to the nozzle; and an ink recovery flow channel connected to the nozzle.
The known printers and ink supply systems, however, have various drawbacks, among which: they are relatively complex; they do not ensure correct control of the internal pressure of the heads to prevent unwanted drips and to ensure ejection readiness status ("shot") when required; they do not guarantee that the nozzles of the print heads eject a large amount of ink (note that the ceramic substrates to which the ink has been applied are treated at high temperatures and that these conditions may lead to partial decomposition of the inks applied); they do not always enable sufficient limitation of the sedimentation of the ink particles.
The aim of the present invention is to provide a supply system, an inkjet printer and a method for printing, which can overcome, at least partially, the drawbacks of the prior art and are, at the same time, easy and economical to produce.

SUMMARY

According to the present invention, a supply system, an inkjet printer and a method for printing as specified in the independent claims below, and, preferably, in any one of the claims depending directly or indirectly on the independent claims, are provided.

BRIEF DESCRIPTION OF THE FIGURES

The invention will now be described with reference to the accompanying drawings, which illustrate a non-limiting embodiment thereof, in which:

figure 1 is a schematic lateral view of a printer according to the present invention;
figure 2 schematically illustrates a supply system according to the present invention and part of the printer in figure 1; and
figure 3 is a schematic cross-section of a detail in figure 2.

DETAILED DESCRIPTION

In accordance with a first aspect of the present invention, in figure 2, reference numeral 1 indicates as a whole a supply system for an inkjet printer 2 (shown as a whole in figure 1) (in particular for ceramic substrates) comprising at least two (a plurality of print heads 3 (in particular, piezoelectric), each of which has at least one respective ejection 4 nozzle (figure 3).
The system 1 (figure 2) comprises a supply element (in particular, a manifold) 5, which is adapted to contain ink (indicated in figure 2 as number 55) and to which the nozzles 4 are fluidically connected; a plurality of connection ducts 6, each of which is arranged between the supply element 5 and a (respective) nozzle 4; a collection manifold 7, which is fluidically connected to said ejection nozzles 4; a plurality of connection ducts 8, each of which is arranged between a (respective) nozzle 4 and the collection manifold 7; and a suction assembly 9 to reduce the pressure in the supply element 5.
In particular, each nozzle 4 is able to eject small amounts of ink in the form of drops.
According to preferred embodiments, the suction assembly 9 comprises a vacuum generator 9a and a valve 9b, which connects the vacuum generator 9a to the supply element 5. Advantageously, the vacuum generator 9a comprises (more precisely, is) a venturi tube. Such an embodiment has the advantage of being two-way with respect to the atmosphere and of automatically compensating the change in the level of the fluid in the supply element 5.
Alternatively, the vacuum generator 9a comprises (more precisely, is) a positive displacement pump (for example of the blade type) with a throttled bypass to the atmosphere, with vacuum-breaker damping functions.
In particular, each connection duct 6 fluidically connects the supply element 5 and the respective nozzle 4; each connection duct 8 fluidically connects the respective nozzle 4 and the collection manifold 7.
According to some embodiments, each connection duct 6 extends from the supply element 5 to the respective nozzle 4. In addition or alternatively, each connection duct 8 extends from the respective nozzle 4 to the collection manifold 7.
In particular, the suction assembly 9 is connected to an upper area of the supply element 5 (more precisely, through an upper wall of the collection unit 5 itself).
Advantageously, the supply element 5 is (only) partially filled with ink, and the suction assembly 9 is connected in an area above the free surface (upper surface) of the ink inside the supply element 5.
The collection manifold 7 has two ends 10 and 11 fluidically connected to respective different positions of the supply element 5. In particular, the two ends 10 and 11 are directly (i.e. without crossing any print head 3 - more in particular, any nozzle 4) fluidically connected to the respective different positions of the supply element 5.
The system 1 further comprises a conveying device 12 (in particular a pump) for conveying (pushing) the ink from the end 11 through (from one end to the other) the supply element 5.
In this way, it is possible to achieve a significant reduction of the sedimentation of the solid part of the ink (it being possible to keep the ink in motion) with a relatively simple and inexpensive structure.
In this regard, it is to be noted that the flow rate required by the print heads 3 is in general too low to ensure sufficient speed in the supply element 5 (for the solid components not to precipitate). The passage of part of the ink contained inside the supply element 5 also through the collection manifold 7 makes it possible to increase the overall speed of the ink inside the supply element 5.
In particular, the system 1 also comprises a connection duct 13 (extending from the end 10 to the supply element 5) to fluidically connect the end 10 and the supply element 5; and a connection duct 14 (extending from the end 11 to the supply element 5) to connect the end 11 and the supply element 5.
More precisely, the conveying device 12 is adapted to convey the ink through the supply element 5 and the collection manifold 7 (and the connection ducts 13 and 14). In use, the conveying device 12 is operated continuously in order to obtain a continuous motion of the ink.
Advantageously, the supply element 5 has a greater inner volume than the inner volume of the collection manifold 7 (more precisely, greater than the sum of the inner volumes of the collection manifold 7 and of the connection ducts 13 and 14).
In particular, the transversal cross-section of the supply element 5 is 3 to 10 times the transversal cross section of the collection manifold 7.
According to some preferred embodiments, the conveying device 12 is arranged between the end 11 and the supply element 5 (at the connection duct 14). In this way it is possible to achieve very low flow fluctuations in the supply element 5 thereby improving the stability of the pressure to the nozzles 4 and reducing the possibility that the solid components of the ink are deposited (this advantage is particularly relevant where the supply element 5 has a particularly high inner volume, which implies a relatively slow flow speed inside the supply element 5).
Advantageously, the system 1 further comprises a pressure sensor 15 to detect the pressure inside the supply element 5 (in particular, in an area above the supply element 5, more precisely above the ink inside the supply element 5); and a control device 16 for operating the suction assembly 9 on the basis of what is detected by the pressure sensor 15 (and to maintain the pressure within a given range).
According to some embodiments, the suction assembly is adapted to reduce the pressure in the area above the supply element 5 according to the following relationship: $p_{v} = - (ρ gh + Δp)$
where p_v is the pressure (negative, i.e. the difference with respect to atmospheric pressure) measured by the sensor 15, ρ is the ink density, g is the acceleration of gravity, h is the distance in height between the free surface of the ink and the nozzles 4.
Δp indicates a further depression required for the proper functioning of the ejection, typically in the range between 2.5 and 10 mbar.
According to some embodiments, the pressure applied by the suction assembly 9 (p_v) is about -20 to -50 mbar (more precisely, from -27 to -33 mbar, even more precisely, about -30 mbar).
In this way, the pressure generated by the piezometric charge of the ink column weighing on the print heads 3 is cancelled.
Advantageously, in use, the adjustment of the suction assembly 9 via the sensor 15 keeps the pressure p_v constant within ± 50 Pa (± 0.5 mbar or ± 5 mm water column), for a better functioning of the print heads 3.
Advantageously, the system 1 comprises a regulating device 17, which is designed to regulate the ink flow from the supply element 5 to the collection manifold 7 and is arranged between the supply element 5 and the end 10 of the collection manifold (more precisely at the connection duct (13). In particular, the regulating device 17 comprises (more precisely, is) a valve.
According to different embodiments, the regulating device 17 is of the manual or automatic type for a continuous and dynamic compensation of the pressure inside the print heads 3 (as a function of the amount of ink delivered by the print heads 3).
According to some embodiments, the system 1 comprises a treatment group 18 for treatment of the ink. In particular, such treatment group 18 is placed between the conveying device 12 and the supply element 5 (along the connection duct 14) and is suitable to purify the ink (which is supplied to the supply element 5).
It is to be noted that the particular positioning of the treatment group 18 enables the conveying device 12 to suitably overcome the pressure losses due to the passage of the ink through said treatment group 18.
In particular, the treatment group 18 comprises at least one filter 19. The filter 19 has the task of retaining the solid particles which are too large (typically larger than 5µm), which could obstruct the internal circuitry and / or nozzles 4 compromising print quality. In addition or alternatively, the treatment group 18 comprises a degasser 20. The degasser 20 has the task of removing any air bubbles or other gases dissolved in the ink. A possible accumulation of these small bubbles could reduce the "shot" efficiency of one or more nozzles 4. More precisely, a pump 21 connected to the degasser 20 and adapted to maintain an appropriate vacuum in said degasser 20 (in particular, a pressure of - 700mbar respect to atmospheric pressure) is also provided.
Advantageously, the system 1 comprises a supply assembly 22, which is suitable to supply the ("fresh") ink to the supply element 5. In particular, the system 1 also comprises a detecting device 23 to detect the ink level inside the supply element 5; and a control device 24 to activate the supply assembly 22 based on what has been detected by the detecting device 23. More precisely, in use, the supply assembly 22 is operated so as to maintain the ink level inside the supply element 5 below a maximum level and above a minimum level - in particular, substantially constant.
In other words, in practice, the supply assembly 22 has the function of keeping the amount of ink constant and, therefore, reducing pressure perturbations inside the supply element 5, while the ink itself is used by the print heads 3.
In the embodiment shown, the control devices 24 and 16 coincide. It is to be noted however that, according to alternative embodiments, the control devices 24 and 16 are mutually separate and independent.
Advantageously, the supply assembly 22 is placed between the collection manifold 7 and the conveying device 12 (along the connection duct 14). In other words, the conveying device 12 is placed between the supply assembly 22 and the supply element 5. In this way, the flow rate of the ink to the supply element 5 is controlled (and stable) not undergoing uncontrolled fluctuations due to the ink coming from the supply assembly 22.
According to some embodiments, the supply assembly 22 comprises a reservoir 25 and a conveying device (in particular, a pump) 26 to bring the ink to the supply element 5 (more precisely to the connection duct 14). Advantageously, inside the reservoir 25, an agitator 27 is provided to reduce the possibility that inside said reservoir 25 solid deposits of material should form.
Advantageously, the system 1 also comprises a regulating device (valve) 28 placed along a duct 29, which extends from the reservoir 25 to the connection duct 14 (and along which the conveying device 26 is placed). In use, the regulating device 28 is opened when new ink is to be supplied to the supply element 5 (and, therefore, the conveying device 26 is activated). Typically, the supply assembly 22 is adapted to supply (through the regulating device 28) a flow of ink from 0 to 0.50 1/min (in particular, about 0.15-0.25 1/min, more precisely, about 0.20 1/min).
In some cases, the regulating device 28 is a three-way valve connected to a further duct 30 leading to the reservoir 25. It is thus possible to achieve (keeping the conveying device 26 constantly active) the continuous recirculation of the ink of the reservoir 25 (even when filling is not performed). In this way the risk of sedimentation in the duct 29 is reduced.
According to some embodiments, the system 1 also comprises a three-way valve 31 (placed at the connection duct 14). Under normal conditions, the valve 31 places the conveying device 12 in communication with the supply element 5, for normal printing operations. In use, in the case of extraordinary maintenance or changing the ink, the valve 31 is switched to place the conveying device 12 in communication with the reservoir 25 through a duct 31a, allowing a drainage flow and thus emptying the circuit. The duct 31a extends from the valve 31 to the reservoir 25 (more precisely, to the duct 30).
Advantageously, system 1 further comprises a pump 32, which is used to initialize the print heads 3 through the purge operation, generally carried out when turning on the printer 2 or following a change of ink. In use, to carry out initialization a valve 33 is opened which connects the pump 32 to the supply element 5, (simultaneously closing the valve 9b) thus imposing inside the containment element an inner pressure (positive) of about 200 mbar. In this way the ink is forced to enter the print heads 3 causing forced dripping and completely filling the inner circuits. After initialization, the valve 33 is closed, the valve 9b is opened and the pump 32 is turned off.
According to some embodiments, the supply element 5 is an oblong shape. In particular, the print heads 3 are arranged in succession along the supply element 5.
Advantageously, the system 1 further comprises a pressure sensor 34 to estimate the pressure inside the collection manifold 7.
According to some embodiments, the sensor 34 (detecting the pressure) is arranged downstream, considering the flow direction of the ink, of the regulating device 17 (in the collection manifold 7 and / or in the connection duct 14 and / or in the connection duct 13).
In particular, the conveying device 12 is suitable to activate depending on what is detected by the sensor 34. More precisely, a control device 41 (for example coinciding with the control devices 16 and / or 24 or a control device separate from and independent thereof) controls the conveying device 12 on the basis of what is detected by the sensor 34 (so to maintain inside the collection manifold 7 a predetermined pressure - and thus a given flow).
According to some embodiments, the control device 41 is suitable to control the conveying device 12 according to what is detected by the sensor 34 so as to maintain the pressure inside the collection manifold 7 between a minimum and a maximum.
In some cases, in use, the conveying device 12 and the regulating device 17 (and the suction assembly 9) are adjusted so that the difference between the pressures detected by the sensors 15 and 34 is greater than (or approximately equal to) a given pressure. According to specific embodiments, the difference between the pressures detected by the sensors 15 and 34 is about 47-53 mbar (in particular, around 50 mbar).
Typically, in practice the minimum (and maximum or optimum) values of the ink flow rate through the supply element 5 and the collection manifold 7 are defined so as to substantially avoid the formation of sediments. The sum of these two flows identifies the pressure which must be applied using the conveying device 12 (and, therefore, detected by the sensor 34). The conveying device 12 is made to work as a function of this parameter (with the feedback control of the sensor 34) and the regulating device 17 is thus commanded so as to achieve the desired flows through the supply element 5 and the collection manifold 7.
Once the system 1 is set in this manner, the suction assembly 9 is actuated and while the conveying device 12 works substantially continuously (in order to reduce the sedimentation), the print heads 3 can be activated so as to perform the printing.
Figure 3 shows schematically the structure of a non-limiting embodiment of a print head 3 with a corresponding plurality of nozzles 4. As can be seen, each nozzle 4 is connected to common connection ducts 6 and 8.
In accordance with a second aspect of the present invention, a method is provided for supplying ink to the print heads 3. The method provides for the use of a supply system 1 according to the first aspect of the present invention and for the ink to be kept in motion in the supply element 5 and in the collection manifold 7 by means of the conveying device 12. In particular, according to the method, a space inside the supply element 5 is maintained between the ink and an upper end of the supply element 5.
Advantageously, the pressure exerted by the conveying device 12 is greater than the pressure reduction created by the suction assembly 9.
In accordance with a third aspect of the present invention (figure 1), an inkjet printer 2 is provided. The printer comprises at least two print heads 3, each of which is provided with at least one respective ejection nozzle 4, and a supply system 1 according to the first aspect of the present invention.
According to the embodiment shown, the printer 2 comprises a conveyor 35 for the substrates (in particular, ceramic; more precisely, tiles) 36, said conveyor 35 extending under the print heads 3.
Advantageously, the printer 2 also includes a sensor 37 to detect the presence of the substrate 36 in input.
Typically, the printer 2 has one or more (in this case four) print bars 38, each of which has a plurality of print heads 3. Each print bar 38 is adapted to apply a different colour. The print heads 3 are mounted at a given distance from the surface of the substrate which is to be decorated and which passes under them so as to avoid contact.
Advantageously, the printer 2 further comprises a control system 39 with an operator interface 40 for controlling the printer 2 and selecting the images to be printed. According to some embodiments, the control system 39 comprises the control devices 16, 24 and 41.
In accordance with a fourth aspect of the present invention, a method is provided for printing, which provides for the use of a printer 2 according to the third aspect of the present invention and for the ink to be kept in motion (substantially continuously) in the supply element 5 and in the collection manifold 7 by means of the conveying device 12. In particular, the method is realized in such a way that there is space inside the supply element 5 between the ink and an upper end of said supply element 5. The method comprises an application step during which ink is applied to a substrate 36, in particular a tile, by means of the print heads 3.
Advantageously, the pressure exerted by the conveying device 12 is greater than the vacuum exerted by the suction assembly 9.
According to some embodiments, the printer 2 comprises a supply assembly 22, which is adapted to supply the ink to the supply element 5; and a detecting device 23 for detecting the level of ink inside the supply element 5. During the application step, the ink is continuously supplied to the supply element 5, in particular so as to compensate the amount of ink ejected by each ejection nozzle 4.

Claims

A supply system for an inkjet printer (2) for ceramic substrates comprising at least two print heads (3), each of which is provided with at least one respective ejection nozzle (4); the supply system (1) comprises a supply element (5), which is adapted to contain ink and to which the ejection nozzles (4) are fluidically connected; a plurality of first connection ducts (6), each of which is arranged between the supply element (5) and one of said nozzles (4); a collection manifold (7), which is fluidically connected to said nozzles (4); a plurality of second connection ducts (8), each of which is arranged between one of said nozzles (4) and the collection manifold (7); and a suction assembly (9) for reducing the pressure inside the supply element (5);
the collection manifold (7) having a first and a second end (10, 11), which are fluidically connected to respective different positions of the supply element (5);
the supply system (1) comprising, furthermore, a conveying device (12) (in particular, a pump), which is adapted to convey the ink from the second end (11) through the supply element (5); also a third connection duct (13) to fluidically connect the first end (10) and the supply element (5); and also a fourth connection duct (14) to connect the second end (11) and the supply element (5).
A system according to claim 1, wherein the third connection duct (13) extends from the supply element (5) to the first end (10); the fourth connection duct (14) extends from the second end (11) to the supply element (5).
A system according to claim 1 or 2, and comprising a regulating device (17), which is designed to regulate the ink flow from the supply element (5) to the collection manifold (7) and is arranged between the supply element (5) and the first end (10) of the collection manifold (7); in particular, the regulating device (17) being arranged along the third connection duct (13).
A system according to claim 3, and comprising a treatment assembly (18) to treat ink, which is arranged between the conveying device (12) and the supply element (5) and is designed to purify ink; in particular, it comprises at least one filter (19).
A system according to any one of the preceding claims, and comprising a supply assembly (22), which is designed to supply ink to the supply element (5); a detecting device (23) to detect the ink level inside the supply element (5); and a control device (24) to activate the supply assembly (22) based on what has been detected by the detecting device (23) (in particular, so as to keep the ink level inside the supply element (5) below a maximum level and above a minimum level).
A system according to claim 5, wherein the supply assembly (22) is arranged between the collection manifold (7) and the conveying device (12).
A system according to any one of the preceding claims, wherein the supply element (5) has an oblong shape; the print heads (3) being arranged one after the other along the supply element (5).
A system according to any one of the preceding claims, and comprising a first pressure sensor (15), which is adapted to detect the pressure inside the supply element (5), in particular in an area above the ink contained in the supply element (5) itself; and a control device (16) to activate the suction assembly (9) based on what has been detected by the first pressure sensor (15).
A system according to any one of the preceding claims, wherein between the supply element (5) and the collection manifold (7), in the area of the supply element (5) and in the area of the collection manifold (7), there are no further conveying means adapted to set the ink in motion, in particular pumps, in addition to the conveying device (12).
A system according to any one of the preceding claims, wherein each second connection duct (8) extends from the respective nozzle (4) to the collection manifold (7).
A system according to any one of the preceding claims, wherein the first and the second ends (10, 11) are fluidically connected without crossing any print head (3) (in particular any nozzle (4)) to the respective different positions of the supply element (5).
System according to any one of the preceding claims, wherein the conveying device (12) (in particular a pump) is suitable to push the ink from the second end (11) through the supply element (5).
An inkjet printer, comprising at least two print heads (3), each of which is provided with at least one respective ejection nozzle (4), and a supply system (1) according to any one of the preceding claims.
A printer according to claim 13, and comprising a conveyor (35) for tiles (36) which extends, at least partially, under the print heads (3).
A printing method, which involves the use of a printer (2) according to claim 13 or 14 and requires that the ink is kept in motion (substantially continuously) in the supply element (5) and in the collection manifold (7) by means of the conveying device (12) and, in particular, that there is a space inside the supply element (5) between the ink and an upper end of the supply element (5) itself; the method comprises an application step, during which ink is applied to a substrate (36), in particular a tile, by means of the print heads (3).
A method according to claim 15, wherein the pressure exerted by the conveying device (12) is greater than the vacuum exerted by the suction assembly (9).
A method according to claim 15 or 16, wherein the printer (1) comprises a supply assembly (22), which is adapted to supply ink to the supply element (5); and a detecting device (23) to detect the ink level inside the supply element (5); during the application step, the ink being continuously supplied to the supply element (5), in particular so as to compensate for the amount of ink ejected by each ejection nozzle (4).