Device for controlling a printing temperature of an ink in a printhead

Abstract

A device for controlling the printing temperature of an ink (5) in a printhead (3) of an inkjet printing system is described. It comprises a heat exchanger (2) with a first channel for ink (5) and a second channel for a temperature control fluid (4), a chiller (1) for heating and / or cooling the temperature control fluid (4), an ink circuit (100) configured to pump ink (5) through the heat exchanger (2) and into the printhead (3), and a temperature control fluid circuit (100) configured to pump the temperature control fluid (4) through the chiller (1) and the heat exchanger (2).The device is designed to heat and / or cool the temperature control fluid (4) by means of the chiller (1) in such a way that the temperature of the ink (5) is brought into and maintained within a predetermined temperature range, wherein at least one heating element (23, 24) is provided on the heat exchanger (2) which is designed to additionally heat the temperature control fluid (4) and the ink (5) by means of an electric current in order to bring the ink (5) into the predetermined temperature range more quickly.

Description

[0001] The invention relates to a device for controlling a printing temperature of an ink in a print head of an inkjet printing system.

[0002] In high-performance printing, particularly at high resolutions above 600 dpi and cutting-edge speeds, high-quality prints must be produced with low ink consumption. The high demands placed on ink performance can only be met if the ink is kept within a narrow, specified temperature range during the printing process. Experience has shown that the most advantageous ink properties can be achieved in a temperature range between 25 degrees Celsius and 38 degrees Celsius, and particularly between 30 degrees Celsius and 34 degrees Celsius. Even small deviations of 1 degree Celsius from the ideal temperature can lead to performance losses. Depending on the outside temperature, the room temperature, and heating effects from pump activity and electrical current, it is therefore necessary to heat or cool the ink.Since the room temperature of a room in which an inkjet printing system is located is usually less than 30 degrees Celsius, it is necessary in such cases to preheat ink that is in an ink circuit.

[0003] US 2010 / 0066785A1 discloses an inkjet printer that has a heat exchanger for heating and cooling the ink. This has channels for the various ink colors. The ink in the channels can be heated by means of a heater, which is shown as a plate in the figures and can be switched on and off. The heat exchanger also has a radiating section that can be pivoted to exchange heat with the channels. The radiating section is provided with a large surface area to cool the ink by radiating heat to the environment. The cooling is enhanced by an air flow designed to transport the heat away from the surface of the radiating section. A disadvantage of this is that cooling is no longer possible at an outside or room temperature above 34 degrees Celsius. Furthermore, the heater is not adjustable.Therefore, the heater's on and off times must be measured very precisely in order to really keep the ink within the narrow specified temperature range.

[0004] US 2019 / 0092017 A1 discloses an inkjet printer that has a heat exchanger for cooling and heating the ink. This heat exchanger has one or more ink channels and a temperature control channel. A temperature control fluid flows through the temperature control channel. This fluid can be cooled in a chiller. Furthermore, it can be heated by the residual heat from integrated circuits used to control the pumps, although this requires reversing the flow direction of the temperature control fluid.

[0005] US 2021 / 0023838 A1 discloses an inkjet printer that has a heat exchanger for cooling and heating the ink. This heat exchanger has an unspecified heater and a cooler, which can, for example, be a radiation cooler as in US 2010 / 0066785A1.

[0006] The invention is based on the object of maintaining the ink temperature more efficiently and precisely within the specified temperature range and reducing the preheating time required to bring the ink into the specified temperature range when the temperature is significantly below the specified temperature range. This can be particularly the case after extended downtimes.

[0007] This object is achieved by a device for controlling a printing temperature of an ink in a print head of an inkjet printing system according to claim 1. Advantageous embodiments emerge from the subclaims.

[0008] The device according to the invention comprises a heat exchanger. This heat exchanger has a first channel for ink and a second channel for a temperature control fluid, in particular water. A chiller is provided for heating and / or cooling the temperature control fluid. Furthermore, the device has an ink circuit configured to pump ink through the heat exchanger and the print head. It also has a temperature control fluid circuit configured to pump the temperature control fluid through the chiller and the heat exchanger. The device is configured to heat and / or cool the temperature control fluid by means of the chiller such that the temperature of the ink is shifted into and maintained within a predetermined temperature range.At least one heating element is provided on the heat exchanger, which is designed to additionally heat the temperature control fluid and the ink by means of an electric current in order to bring the ink into the predetermined temperature range more quickly.

[0009] Because the at least one heating element is located directly on the heat exchanger, the heating by the at least one heating element and the heating of the ink by the temperature control fluid take place at the same location. This allows for faster heating of the ink and good temperature control. Furthermore, it is a cost-effective solution, as both heating elements, particularly heating foils or heating mats, and heat exchangers are commercially available at low cost and can be easily integrated together.

[0010] Preferably, at least two heating elements are provided. This advantageously allows additional heating to take place at various surface sections of the heat exchanger.

[0011] The at least one heating element is designed, in particular, as an electrically conductive coating on a carrier, which is sealed in polyester film or silicone. This is a particularly cost-effective and commercially available variant of a heating element.

[0012] The heat exchanger is preferably designed as a plate heat exchanger. Such heat exchangers are commercially available at low cost, easy to manufacture, and a heating element can be easily attached to them, especially if it is designed as a heating foil or heating mat. Plate heat exchangers typically have metal plates arranged in layers. These metal plates can be soldered or screwed together, for example. They are usually made of particularly thermally conductive, robust, and corrosion-resistant stainless steel. For example, a wave-like pattern of the metal plates can create gaps in which heat exchange then takes place.

[0013] It is particularly preferred if the flow direction of the temperature control fluid and the flow direction of the ink are cross-orthogonal to each other. Crossflow is particularly preferred if a fixed temperature is to be achieved, which is particularly consistent with the objective of the invention for temperature control of the ink.

[0014] However, it is also conceivable for the flow direction of the temperature control fluid and the flow direction of the ink to be cocurrent or countercurrent. The greatest conceivable heat exchange occurs in a countercurrent flow direction.

[0015] In a particularly advantageous embodiment, the heat exchanger is insulated from the outside. This is advantageous because it effectively limits heat conduction to the outside. This allows the specified temperature range of the ink to be better achieved and maintained. The insulation is preferably designed to be openable. This allows the at least one heating element to be advantageously installed within the insulation.

[0016] Preferably, a first heating element is mounted on an outermost metal plate of the plate heat exchanger in a first direction. Particularly preferably, a second heating element is mounted on an outermost metal plate of the plate heat exchanger in a second direction. This advantageously allows for particularly good heat transfer. In a particularly advantageous embodiment, the first and / or second heating element spans at least 80 percent of the surface of the outermost metal plate. This allows for further improvement in heat transfer.

[0017] It is conceivable that at least one heating element is glued, clamped, and / or screwed to the heat exchanger. This is not to be understood as a limitation.

[0018] The insulation of the heat exchanger preferably has a bore for supplying power to the at least one heating element. This is advantageous for controlling the at least one heating element.

[0019] The chiller can preferably be operated in both a cooling and a heating mode. This allows the temperature of the temperature control fluid to be controlled and / or regulated very precisely.

[0020] In an advantageous embodiment, the temperature control fluid circuit is configured to continue pumping the temperature control fluid through the print head. This allows for even more precise control of the ink temperature at the print head. This is especially necessary because heat is released at the print head during the printing process. If the ink temperature is within the specified range after passing through the heat exchanger, it can be heated to above the specified range as it passes through the print head. The temperature control fluid can therefore provide even more cooling here.

[0021] To be able to respond even better to heating of the print head, the device preferably has a valve configured to direct the temperature control fluid through the heat exchanger in a first position and to direct the temperature control fluid past the heat exchanger in a second position. This is particularly advantageous in cooling mode to more quickly counteract heating of the print head during a printing process by directing the temperature control fluid past it rather than through the heat exchanger, thus achieving a stronger cooling effect in the print head.

[0022] The ink circuit preferably has a buffer tank that is partially filled with air or another gas and partially with ink. This allows good control of the pressure and temperature of the ink. A branch line of the ink circuit leads in particular from the buffer tank to the print head. The pressure in the buffer tank thus advantageously guides the ink to the print head. A partial ink circuit preferably leads from the buffer tank through a pump, through the heat exchanger and back to the buffer tank. This partial circuit advantageously serves to heat and / or cool the ink in the buffer tank via the heat exchanger. In particular, a valve is provided in the partial ink circuit that is designed to either guide the ink through the heat exchanger or bypass the heat exchanger.In this way, when the ink is passed past the heat exchanger, a heat exchange effect at the print head can be enhanced, which is particularly beneficial in cooling mode.

[0023] Further advantageous embodiments emerge from the following drawings and from the detailed description of the figures.

[0024] Brief summary of the drawings Fig. 1 schematically shows a flow diagram of a temperature control fluid circuit of a preferred embodiment of the device according to the invention; Fig. 2 schematically shows a flow diagram of an ink circuit of a preferred embodiment of the device according to the invention; Fig. 3 shows a schematic vertical-horizontal sectional view of a plate heat exchanger with two heating elements according to a preferred embodiment of the device according to the invention; Fig. 4 shows a further schematic vertical-horizontal sectional view of the plate heat exchanger from Fig. 3 ; Fig 5 shows a perspective view of the plate heat exchanger from the Fig. 3 and 4 . Detailed character description

[0025] In Fig. 1A flow diagram schematically shows a temperature control fluid circuit of a preferred embodiment of a device according to the invention, designated 100. This temperature control fluid circuit 100 is configured to pump a temperature control fluid 4 through a chiller 1, through a plate heat exchanger 2, and through a pressure head 3.

[0026] The chiller 1 is configured to heat and / or cool the temperature control fluid 4. It can be configured, for example, as a refrigeration machine, heat pump, or compression refrigeration or heating system to supply or remove heat from the temperature control fluid through a thermodynamic cycle. A design with Peltier element(s) or other known systems for heating and / or cooling fluids is also conceivable. The chiller 1 has an inlet 11 for the temperature control fluid 4 and an outlet 12 for the temperature control fluid 4. The temperature control fluid circuit 100 is configured to supply the temperature control fluid 4 to the chiller 1 through the inlet 11 and to discharge the heated or cooled temperature control fluid 4 through the outlet 12.

[0027] In this embodiment, a first Roman valve 101 is provided downstream of the outlet 12 of the chiller 1. The first Roman valve 101 is configured to either supply the temperature control fluid 4 from the chiller 1 to the plate heat exchanger 2 or to bypass the plate heat exchanger 2 in a first bypass 102.

[0028] The plate heat exchanger 2 is intended to heat or cool ink in an ink circuit using the temperature control fluid 4. However, this only occurs when the first Roman valve 101 is set so that the temperature control fluid 4 discharged from the chiller 4 is fed to the plate heat exchanger 2. For this purpose, the plate heat exchanger 2 has an inlet 21 and an outlet 22. In this embodiment, these are arranged on a common surface without restriction of generality. The plate heat exchanger has a first heating element 23 and a second heating element 24. The first heating element 23 is arranged on a surface of the plate heat exchanger 2 facing the inlet 21 and the outlet 22. The second heating element 24 is arranged on a surface of the plate heat exchanger facing away from the inlet 21 and the outlet 22. Further preferred features of the plate heat exchanger 2 will be described with reference to Figure 3-5described below.

[0029] In this embodiment, a T-connector 103 is arranged downstream of the plate heat exchanger. The T-connector 103 is configured to transfer temperature control fluid 4 coming from the outlet 22 of the plate heat exchanger 2 and temperature control fluid 4 coming from the first bypass 102 into a common temperature control fluid stream 104. In this way, depending on the position of the first Roman valve 101, the T-connector 103 either carries temperature control fluid from the plate heat exchanger 2 or carries temperature control fluid 4 from the first bypass 102.

[0030] The temperature control fluid flow 104 from the T-connector 103 is configured to be directed into the print head 3. In this embodiment, the ink is additionally heated and / or cooled here. This is particularly advantageous when the temperature of the ink in the print head rises due to a printing process. In this case, the chiller can be switched to cooling mode. Furthermore, the first Roman valve 101 can be adjusted so that the temperature control fluid 4 flows from the chiller's outlet 12 into the first bypass 102, thus preventing heating in the plate heat exchanger 4 and allowing the full cooling effect of the temperature control fluid 4 to occur directly at the print head 3. This allows for a very rapid response to heating of the print head. Downstream of the print head, the temperature control fluid 4 flows directly back into the inlet 11 of the chiller 1 in this embodiment.

[0031] In Fig. 2An ink circuit of a preferred embodiment of a device according to the invention is schematically illustrated in a flow diagram and designated 200. This ink circuit 100 has a buffer tank 201. This buffer tank 201 is partially filled with ink 5 and partially with air 6. In this way, an overpressure in the buffer tank 201 can be very precisely adjusted. A branch line 206 leads from the buffer tank 201 to the print head 3.

[0032] A sub-circuit 202 of the ink circuit 200 is configured in this embodiment to pump ink 5 through a plate heat exchanger 2 by means of a pump 2021 and to feed it back into the buffer tank 201. The plate heat exchanger 2 is configured to cool or heat the ink 5 passing through it by means of a temperature control fluid 4. In this way, the temperature of the ink 5 in the buffer tank can be controlled. An exemplary temperature control fluid circuit 100 is described above with reference to Fig. 1described. The pump is arranged downstream of the buffer tank 201. A second Roman valve 2022 is arranged downstream of the pump. The second Roman valve is designed to direct the ink 5 onward to the plate heat exchanger 2 in a first position and to direct the ink 5 back to the buffer tank 201 in a second bypass 2025 in a second position. In the event that the second Roman valve 2022 is in the first position, a 5µm filter is arranged downstream of the second Roman valve 2022. A degasser 2024 is arranged downstream of the 5µm filter 2024. In this way, it can be ensured that no clumps or gas bubbles enter the plate heat exchanger 2. Gas bubbles could reduce heat conduction and clumps could clog the plate heat exchanger 2. The plate heat exchanger 2 is arranged downstream of the 5µm filter 2024. The ink is returned to the buffer tank 201 from an ink outlet of the plate heat exchanger 2.

[0033] In the Fig. 3 to 5 a plate heat exchanger from a preferred embodiment of a device according to the invention is shown in two sectional views and one perspective view and designated by 2.

[0034] The plate heat exchanger 2 has an ink supply 25 and a temperature control fluid supply 21. Furthermore, the plate heat exchanger 2 has an ink discharge 26 and a temperature control fluid discharge 22. An exemplary temperature control fluid circuit 100 is described with reference to Fig. 1 described above. An exemplary ink circuit 200 is described with reference to Fig. 2 described above. The plate heat exchanger 2 comprises metal plates 27 formed in layers and forming spaces or chambers. An ink control fluid chamber 28 and an ink chamber 29 are arranged alternately one after the other. Fig. 3In this way, six ink control fluid chambers 28 and five ink chambers 29 are shown. Particularly advantageously, the plate heat exchanger is designed to vary the volume by adding additional metal plates 27 and chambers.

[0035] A first heating element 23 is arranged at a first end of the plate heat exchanger 2. A second heating element 24 is arranged at a second end of the plate heat exchanger 2. The plate heat exchanger 2 terminates at each end with a mounting plate 29b. In this embodiment, the outer mounting plates 29b are connected by means of screw connections 29a. In this way, the chambers of the plate heat exchanger 2 can be advantageously kept sealed, with a variation of the volume of the plate heat exchanger being easily possible by sliding additional metal plates 27 between them and sealing them using the screw connections 29a and mounting plates 29b.

[0036] The first heating element 23 and the second heating element 24 are designed as heating foils and each span more than 80% of the surface area of ​​the outer metal plates of the heat exchanger. This allows for particularly good additional heat dissipation. By varying the voltage, the heat output of the heating foils can be modified.

[0037] In the sectional view of Fig. 4 Above the plate heat exchanger 2, the arrangement of the first Roman valve 101, the bypass 102 and the T-connector 103 is shown. Fig. 1 By means of the first Roman valve 101, it is advantageous to adjust whether the temperature control fluid 4 from the chiller 1 (see Fig. 1 ) through the plate heat exchanger 2 or through the bypass 102.

[0038] In particular, a device according to the invention is provided for each ink color. The measures described in this document allow for a quick and cost-effective adjustment of ink 5 to a predetermined printing temperature range. Furthermore, a very precise and cost-effective maintenance of the printing temperature of ink 5 within this predetermined range can be achieved. Furthermore, good adaptability and variability to different ink volumes can be achieved. List of reference symbols

[0039] 1 Chiller 2 Plate heat exchanger 3 Print head 4 Temperature control fluid 5 Ink 6 Air 11 Temperature control fluid supply to the chiller 12 Temperature control fluid discharge from the chiller 21 Temperature control fluid supply for the plate heat exchanger 22 Temperature control fluid discharge for the plate heat exchanger 23 First heating element 24 Second heating element 25 Ink supply for the plate heat exchanger 26 Ink discharge for the plate heat exchanger 27 Metal plate 28 Temperature control fluid chamber 29 Ink chamber 29a Mounting plate 29b Fitting for mounting plate 100 Temperature control fluid circuit 101 First Roman valve 102 First bypass 103 T-connector 104 Temperature control fluid flow 200 Ink circuit 201Buffer tank 202Partial ink circuit 206Branch line 2021Pump 2022Second Roman valve 20235 µm filter 2024Degasser 2025Second bypass

Claims

1. A device for controlling a printing temperature of an ink (4) in a print head (3) of an inkjet printing system, comprising: - a heat exchanger (2) with: - a first channel for ink (5); - a second channel for a temperature control fluid (4); - a chiller (1) for heating and / or cooling the temperature control fluid (4); - an ink circuit (100) configured to pump ink (5) through the heat exchanger (2) and into the print head (3); - a temperature control fluid circuit (100) configured to pump the temperature control fluid (4) through the chiller (1) and the heat exchanger (2);wherein the device is designed to heat and / or cool the temperature control fluid (4) by means of the chiller (1) in such a way that a temperature of the ink (5) is placed into a predetermined temperature range and maintained therein, wherein at least one heating element (23, 24) is provided on the heat exchanger (2), which heating element is designed to additionally heat the temperature control fluid (4) and the ink (5) by means of an electric current in order to place the ink (5) more quickly into the predetermined temperature range.; 2. Device according to claim 1, wherein at least two heating elements (23, 24) are provided.

3. Device according to claim 1 or 2, wherein the at least one heating element (23, 24) is designed as a heating foil, in particular as an electrically conductive coating on a carrier, which is welded into polyester foil or silicone.

4. Device according to one of the preceding claims, wherein the heat exchanger (2) is designed as a plate heat exchanger (2), in particular with metal plates made of stainless steel.

5. Device according to one of the preceding claims, wherein the heat exchanger (2) is insulated from the outside.

6. Device according to one of the preceding claims, wherein a first heating element (23) is mounted on an outermost metal plate (27) of the plate heat exchanger (2) in a first direction, more preferably a second heating element (24) is mounted on an outermost metal plate (27) of the plate heat exchanger (2) in a second direction, more preferably the first heating element (23) and / or the second heating element (24) spans at least 80 percent of a surface of the outermost metal plate.

7. Device according to one of the preceding claims, wherein the chiller (2) can be operated both in a cooling mode and in a heating mode.

8. Device according to one of the preceding claims, wherein the temperature control fluid circuit (100) is further configured to additionally pump the temperature control fluid (5) through the print head (3).

9. Device according to one of the preceding claims, wherein the temperature control fluid circuit (100) has a valve which is configured to direct the temperature control fluid (4) through the heat exchanger (2) in a first position and to direct the temperature control fluid (4) past the heat exchanger (2) in a second position, wherein the valve is preferably designed as a first Roman valve (101).

10. Device according to one of the preceding claims, wherein the ink circuit (200) has a buffer tank (201) which is partly filled with air (6) or another gas and partly with ink (5), wherein preferably a branch line (206) of the ink circuit (200) leads from the buffer tank (201) to the print head (3).

Images