Patent Application
20110285768
The invention relates to a printing system according to the preamble of claim 1 and to a printing device or machine according to the preamble of claim 15.
Printing systems or printing devices for printing containers using digital electrical print heads which operate according to the inkjet principle are fundamentally known. Also known in particular are printing systems or printing machines in which a plurality of printing positions for holding a respective container to be printed are formed on a container transport element which is driven in rotation about at least one vertical axis, in particular on a rotor which is driven in rotation about a vertical machine axis, at which printing positions the containers are printed using electronically actuated digital print heads which operate according to the inkjet principle. The print heads are in this case provided on a print head transport element which can likewise be driven in rotation about the at least one vertical axis and which is for example the container transporter or an independent transport element. In any case, the print heads are located on a moving part, for example a rotating part, of the respective printing device or machine. This arrangement of the print heads requires special measures which ensure a proper supply of the very fluid printing ink to the print heads, in particular which also ensure that the printing ink is fed to the print heads in each case at a pressure that is constant or as constant as possible and with a consistency and quality that remain constant. Only in this way is it possible to achieve the desired high-quality print on the containers.
The problem addressed by the invention is that of providing a printing system which ensures a high-quality print despite the print heads being arranged on a moving or rotating part of the printing system. In order to solve this problem, a printing system is configured according to claim 1. A printing device or printing machine forms the subject matter of claim 15.
One essential feature of the printing system according to the invention lies in the splitting of this system or of the printing ink supply into a stationary part and a moving, for example rotating, part which comprises the print heads, wherein the stationary part preferably contains at least one main tank for accommodating a sufficient stock of printing ink and in particular also elements for refilling the printing ink and/or for conditioning the printing ink, i.e. in particular controlling the temperature of and/or degassing and/or filtering the printing ink, while the moving or rotating part of the printing system comprises at least one auxiliary tank which forms an inlet tank for the print heads, but preferably also a second auxiliary tank which serves as an outlet tank for the print heads, and these tanks are arranged centrally in relation to the print heads and/or the movement path thereof and are controlled with regard to both the pressure and the filling level.
Further developments, advantages and possible uses of the invention will also become apparent from the following description of examples of embodiments and from the figures. All the features described and/or shown form in principle, per se or in any combination, the subject matter of the invention, regardless of the way in which they are combined in the claims or the way in which they refer back to one another. The content of the claims is also included as part of the description.
The invention will be explained in more detail below with reference to the figures and on the basis of an example of embodiment. In the figures:
In the figures, 1 is a printing device of the rotary type for printing bottles or similar containers 2 using digital print heads 3 operating according to the inkjet principle, having a plurality of nozzles 3.1 which are provided one after the other in a row in the vertical direction on each print head 3 and which can be electrically actuated individually. The application of the printing ink to the nozzles 3.1 takes place by appropriate actuation of electrodes or piezo elements.
In the illustrated embodiment, the printing device 1 consists of a rotor 4 which can be driven in rotation about a vertical machine axis MA and on the circumference of which a plurality of printing positions 4.1 are formed, each of the printing positions having a print head 3. The containers 2 to be printed are fed to the printing positions 4.1 via a container feed 6. The printed containers are removed from the respective printing position 4.1 at a container discharge 7.
In the illustrated embodiment, a print head 3 is provided at each printing position 4.1. The printing of the containers 2 takes place at the printing positions 4.1 in a line-by-line manner by a relative movement of the container 2 relative to the print head 3, namely in the illustrated embodiment in that each container 2, oriented with its container axis in the vertical direction, i.e. parallel to the axis of rotation of the rotor 4, is rotated in a controlled manner about its container axis during the printing operation.
One particular problem caused in particular by the print heads 3 being arranged on the rotor 4 which is driven in rotation about the vertical machine axis lies inter alia in the proper provision of the printing ink to the individual print heads 3. For instance, for trouble-free operation of the print heads 3 and in particular also for the quality of the print, it is necessary that the individual print heads 3 or the nozzles 3.1 thereof are not only supplied with a sufficient quantity of printing ink but rather the printing ink must reach the print heads or the nozzles thereof at a predefined pressure, namely in general at a slight underpressure or overpressure compared to the ambient pressure. Despite the rotating design of the printing device 1, this supply of printing ink to the print heads 3 is ensured in an optimal manner by the printing system 5 which will be described in more detail below in connection with
In principle, the printing system 5 according to the invention consists of two components, namely of the static part denoted 8 in
The static part 8 of the printing system comprises inter alia a main tank 11 for accommodating a stock of printing ink, as well as all the functional elements for conditioning the printing ink, i.e. inter alia a temperature module 12 for constantly controlling (heating or cooling) the temperature of the printing ink in the main tank 11 and a degasser 13 and a filter 14 in a first printing ink circuit for constantly controlling the temperature of, degassing and filtering the printing ink, said first printing ink circuit comprising a conveying and circulating pump 15 and including the main tank 11. The main tank 11, partially filled with the printing ink, is subjected to a controlled pressure P11 during the printing operation, namely for example, during normal printing operation, to a pressure P11 which is somewhat lower than the ambient or atmospheric pressure. An underpressure has the advantage that it aids the desired degassing of the media, in particular of the ink. A slight overpressure is also conceivable, but cannot be used in the variant shown.
The static part 8 of the printing system furthermore comprises a refilling valve 16, via which the refilling of printing ink into the printing system 5 from cartridges 17 is possible. Via a multiway valve 18, which is arranged in the printing ink circuit of the static part 8 in the flow direction downstream of the filter 14 and upstream of the main tank 11, and via a line 19 connected to the valve 18 and a rotary connection 20, the static part 8 of the printing system 5 is connected to a flow line or supply line 21 of the rotating part 10 of the printing system 5, said line containing a valve 22.
The rotating part 10 of the printing system comprises inter alia two auxiliary tanks 23 and 24, of which the auxiliary tank 23 serves as an inlet tank 23 or as a source for the printing ink supplied to the print heads 3, and of which the auxiliary tank 24 serves as an outlet tank or as a drain for receiving the printing ink which is not required during printing and which has flowed through the print heads 3. The two auxiliary tanks 23 and 24 are each of circular shape and are provided centrally, i.e. coaxial to the machine axis MA and arranged one above the other in the vertical direction on the rotor 4, namely with the auxiliary tank 23 above the auxiliary tank 24. The individual print heads 3 are arranged in a manner distributed around the auxiliary tanks 23 and 24. The supply line 21 opens via the valve 22 into the auxiliary tank 23. The auxiliary tank 23 is respectively connected via a line 25 to a connection terminal of the respective print head 3, said connection terminal serving as inlet. A connection terminal of each print head 3 which serves as outlet is connected via a line 26 containing a pressure reducer 27 to a multiway valve 28, via which optionally a connection of the line 26 to the auxiliary tank 24, a connection between the auxiliary tank 24 and the line 21 or via the rotary connection 20 to the line 19 or else a connection between the line 26 and the line 21 or via the rotary connection to the line 19 is possible. In normal printing operation, the valve 28 is controlled in such a way that a connection between the line 26 and the auxiliary tank 24 exists via this valve. In the illustrated embodiment, the two auxiliary tanks 23 and 24 are moreover of identical design.
Each auxiliary tank 23 and 24 comprises means by which the pressure in the auxiliary tank 23 and 24, which is in each case partially filled with the printing ink during the printing operation, and in particular also the pressure in the lines 25 and 26 and thus at the connection terminals of the print heads 3 is precisely set so that the pressure P23 in the auxiliary tank 23 is somewhat greater than the pressure P24 in the auxiliary tank 24, but the pressure P23 is for example slightly lower than the atmospheric pressure. This pressure control means on the one hand that the printing ink flows through the print heads 3 during the printing operation, i.e. the quantity of printing ink supplied to each print head 3 via the line 25 but not required for the printing operation is discharged from the print head 3 via the line 26 thereof. The volume flow of printing ink to each print head 3 from the auxiliary tank 3 and also from each print head 3 to the auxiliary tank 24 can be set by an appropriate choice of pressures P23 and P24.
In order to achieve conditions which are independent or substantially independent of the rotational speed of the rotor 4 during the printing operation, not only are the two auxiliary tanks 23 and 24 provided centrally on the rotor 4 and the print heads 3 provided in each case around the auxiliary tanks 23 and 24 at the same radial distance from said auxiliary tanks, but also the lines 25 and 26 leading to the print heads 3 and provided individually for each print head 3 are installed on the rotor 4 in the same way for all the print heads 3, for example in such a way that these lines run radially or substantially radially relative to the vertical machine axis MA.
The auxiliary tanks 23 and 24 are furthermore equipped with means which ensure an exact filling level of the printing ink in each auxiliary tank 23 and 24 during operation of the printing device 1. In the illustrated embodiment, these means are formed by providing a circular barrier or an overflow 29 in the interior of each circular auxiliary tank 23 and 24, which barrier or overflow concentrically surrounds the machine axis and separates the tank interior 23.1 or 24.1 serving to accommodate the printing ink from a circular collecting chamber 23.2 or 24.2 which is likewise formed in each auxiliary tank 23 and 24 and which serves for collecting excess printing ink. The collecting chambers 23.2 and 24.2 are provided internally, i.e. are surrounded by the associated tank interior 23.1 or 24.1.
The printing system is operated in such a way that, in each auxiliary tank 23 and 24, a given flow of printing ink constantly flows from the tank interior 23.1 or 24.1 via the overflow 29 into the associated collecting chamber 23.1 or 24.1. The collecting chambers 23.2 and 24.2 are connected to the main tank 11, namely, in the illustrated embodiment, in such a way that the collecting chamber 23.2 is connected via a line 30 and a pressure reducer (not shown) to the collecting chamber 24.2 and the latter is connected via a line 31, via the rotary connection 20 and via a control valve 34 to the main tank 11.
During operation, the printing system is furthermore controlled, namely inter alia by appropriate actuation of the pump 15 and of the valves 18, 22 and 34, in such a way that not only is the main tank 11 partially filled with the printing ink in a filling level-controlled manner, i.e. printing ink is refilled from the cartridge 17 connected to the refilling valve, via this refilling valve, the pump 15, the degasser 13, the filter 14 and the valve 18, into the main tank 11 when the printing ink level in the main tank 11 falls below a predefined level, but rather the system is also operated in such a way that each collecting chamber 23.2 and 24.2 is also filled with printing ink in a filling level-controlled manner. To this end, filling level sensors 35 (main tank 11) and 36 (collecting chambers 23.2 and 24.2) are provided both on the main tank 11 and on the collecting chambers 23.2 and 24.2.
In order to empty the auxiliary tanks 23 and 24 or the tank interiors 23.1 and 24.1, each tank is provided with an emptying valve 32, via which the tank interior 23.1 or 24.1 can be connected to the outlet of the associated collecting chamber 23.2 or 24.2 or to the corresponding line 30 or 31, said emptying valve nevertheless being closed during normal operation of the printing device. During printing operation of the printing device 1, the printing ink circulates in the printing system 5 in two circuits, namely in the first printing ink circuit of the static or stationary part 8, which includes the pump 15, the degasser 13, the filter 14 and the main tank 11, and in a second printing ink circuit which includes the static part 8 and the rotating part 10 of the printing system and also the print head 3.
In this second printing ink circuit, therefore, the printing ink flows for example from the auxiliary tank 23, through the print heads 3, then passes back via the valve 28 to the auxiliary tank 24 and from this auxiliary tank via the overflow 19 and via the collecting chamber 24.2 to the main tank 11, from which the printing ink is then fed back to the auxiliary tank 23 via the pump 15, the degasser 13, the filter 14 and the appropriately set valve 18, the connected line 19, the rotary connection 20 and the line 21. Both printing ink circuits thus include the temperature-controlled main tank 11, the degasser 13 and the filter 14, so that the printing ink in these printing ink circuits is constantly conditioned, i.e. inter alia is kept at a quality and temperature level required for optimal printing. The printing device 1 or the printing system 5 of this machine may be controlled in such a way that, during the printing operation, the printing ink flows simultaneously through both printing ink circuits. However, it is also possible to control the printing system 5 in such a way that, during the printing operation, only the second printing ink circuit, which includes the static part 8 and the rotating part 10, is activated at least primarily, while the first printing ink circuit of the printing system is activated for a quicker and more intensive conditioning of the printing ink when no additional printing ink has to be conveyed to the auxiliary tank 23.
The two-part design of the printing system, i.e. the separation into the static part 8 and the rotating part 10, has considerable advantages:
In order to achieve conditions which are independent of the rotational speed of the rotor 4 in the region where the printing ink is diverted from the respective collecting chamber 23.2 or 24.2 via the line 30 or 31, the lines 30 and 31 and the connections thereof are in each case arranged coaxial to the machine axis MA. The auxiliary tanks 23 and 24 once again form respectively the radially outer tank interior 23.1 and 24.1 in relation to the machine axis MA and the inner collecting chamber 23.2 and 24.2 in relation to the machine axis MA.
Of course, it is possible to flush and to clean the print heads 3 or the nozzles 3.1 in a maintenance cycle. To this end, by suitably actuating the printing system 5 and in particular also the various valves, printing ink is pumped or conveyed at increased pressure through the print heads 3, namely from the static part 8 via the line 19 and via the rotary connection 20 to the rotating part 10 and there for example via the line 26 to the individual print heads 3, at the nozzles 3.1 of which there exits at least some of the printing ink conveyed at high pressure for flushing and cleaning purposes.
The rotating part 10a of the printing system once again comprises the two auxiliary tanks 23 and 24, although only the auxiliary tank 23 or the tank interior 23.1 thereof is connected to the single input of each print head 3a via a respective line 25 and a multiway valve 37 additionally provided in this line. Also connected to the valve 37 is the line 26 containing the pressure reducer 27, which in this embodiment is connected directly to the line 21 or else is connected via the rotary connection 20 directly to the line 19. In this embodiment, the auxiliary tank 24 does not serve as a drain for receiving printing ink fed back from the print heads, but rather only the collecting chamber 24.2 of the auxiliary tank 24 is used to receive the excess printing ink from the collecting chamber 23.2 and to divert this printing ink to the main tank 11 of the stationary part 8a.
Two printing ink circuits are also possible in the printing system 5a, namely a first circuit within the static part 8a, which once again includes the pump 15, the degasser 13, the filter 14 and the main tank 11, and a second printing ink circuit which includes the static part 8a and the rotating part 10a. This second printing ink circuit then extends for example from the tank interior 23.1 of the auxiliary tank 23, via the overflow 19 therein, into the collecting chamber 23.2, from there into the collecting chamber 24.2, from there into the main tank 11 and from the latter via the pump 15, the degasser 13, the filter 14 and the lines 19 and 21 back to the auxiliary tank 23 and to the tank interior 23.1 therein.
Also in the pressure system 5a, therefore, the printing ink is constantly conditioned, i.e. degassed, filtered and temperature-controlled, i.e. either heated or cooled according to the respective requirements, not only in the first printing ink circuit which runs only in the static part 8a, but also in the second circuit which includes both the static part 8a and the rotating part 10a of the printing system 5a.
It has been assumed above that the two auxiliary tanks 23 and 24, which are of identical design and of circular shape, are provided in a manner offset from one another in the vertical direction, i.e. in the machine axis.
Of course, other embodiments are also conceivable. For instance,
Changing pressure conditions brought about by a varying rotational speed of the rotor are adapted or compensated by regulating the pressures P23b and P24b in the auxiliary tanks 23b and 24b and the differential pressure between said auxiliary tanks, so that a constant flow rate of the printing ink through the print heads 3 is achieved, as well as a constant pressure, for example a constant or stable underpressure (meniscus underpressure) at the nozzles 3.1 of the print heads 3.
It has been assumed above that the respective printing device 1 comprises a printing system 5, 5a or 5b which allows the printing of the containers 2 with a single printing ink, i.e. with printing ink of one single color. In order to produce a multicolor print using several sets of colors, a plurality of printing devices 1 are then provided one after the other in an installation, wherein one set of colors of the respective multicolor print is then produced in each printing device. At least in the further printing devices following the first printing device, the printing positions 4.1 for orienting the respective container 2 are formed at a marking provided on or applied to the container prior to the actual start of printing, in order thus to ensure that the individual sets of colors forming the multicolor print are applied in the correct position.
In principle, it is also possible to provide on a single printing device a plurality of printing systems 5, 5a or 5b for a plurality of printing inks of different color, in order thus to provide the container 2 with a multicolor print in its entirety at each printing position 4.1 and/or with multiple sets of colors of a multicolor print which is completed on a further printing device.
Unlike the previous diagrams,
The path through the lines which is indicated by arrows with a round end represents normal operation in which the pump 39 conveys into the auxiliary container 23 and the excess ink runs through the print head 3 and then into the auxiliary tank 24. The path through the lines which is indicated by the arrows with a polygonal end represents the flushing process in which the pump 39 conveys through a pressure reducer 41, which is provided in the line path 42, directly into the print head 3. In this way, an increased conveying power and a higher pressure is produced, as a result of which the nozzles 3.1 are flushed.
The invention has been described above on the basis of examples of embodiments. It will be understood that numerous changes and modifications are possible without thereby departing from the inventive concept on which the invention is based.
It has been assumed above that the rotating part 10, 10a, 10b of the printing system is located above the static part 8, 8a of the printing system. In principle, in order to achieve a design that is as compact as possible, it is also possible to configure the static part of the printing system in such a way that it entirely or almost entirely surrounds the moving or rotating part of said system, so that ultimately only the print heads protrude above the upper side of the printing system.
It has also been assumed above that the print heads 3 or 3a are also provided on the rotor 4, which firstly forms the transport element for the containers 2, i.e. the container transporter, that is to say the rotor 4 is at the same time also the transport element that moves the print heads 3 or 3a. However, other embodiments are also conceivable in which the print heads 3 or 3a for in each case at least one color or set of colors of a multicolor print are provided on a dedicated transport element (print head transport element) which is moved or rotated about the vertical machine axis MA.
In particular, the pressures P23 and P24 are controlled for example also as a function of the rotational speed and/or acceleration of the rotor 4, so that centrifugal forces exerted on the printing ink are compensated by the pressure regulation.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2009 020 702.3 | May 2009 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2010/002867 | 5/10/2010 | WO | 00 | 7/25/2011 |
