Device for controlling printing temperature of ink in print head

Abstract

To control such that a temperature of an ink can be kept within a predetermined temperature range.SOLUTION: The invention provides a device for controlling a printing temperature of an ink in a print head of a system for inkjet printing. The system includes: a heat exchanger with a first channel for the ink and a second channel for a temperature control fluid; a chiller for heating / cooling the temperature control fluid; an ink circuit that is configured to pump the ink through the heat exchanger into the print head; and a temperature control fluid circuit that is configured to pump the temperature control fluid through the chiller and the heat exchanger. The device is configured to heat / cool the temperature control fluid with the chiller such that a temperature of the ink is set and kept within a predetermined temperature range. At least one heating element is provided at the heat exchanger and configured to heat the temperature control fluid and the ink with an electric current to set the ink within the predetermined temperature range.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to an apparatus for controlling the printing temperature of ink in a printhead of a system for inkjet printing.

[0002] In the field of high-performance printing, especially in the field of printing with high resolutions, exceeding 600 dpi, and speeds in the state-of-the-art range, high-quality printouts must be generated with low ink consumption. The high demands on the behavior of the ink can only be achieved if the ink is maintained within a narrow, predefined temperature range during the printing process. Experience has shown that the most favorable ink properties are achieved within a temperature range of 25° C. to 38° C., in particular 30° C. to 34° C. A deviation as small as 1° C. from the ideal temperature can lead to a loss of performance. Depending on the outside and room temperatures and the heating effects of the pump operation and the current, the ink must therefore be heated or even cooled. The room temperature in the room in which the system for inkjet printing is located is usually below 30° C., so in such cases it is necessary to preheat the ink present in the ink circuit.

[0003] US 2010 / 0066785 A1 discloses an inkjet printer with a heat exchanger for heating and cooling the ink. The inkjet printer has a number of passages for different ink colors. The ink in the passages can be heated by a heater, which is shown in the drawing as a plate and can be switched on and off. The heat exchanger further has a radiating section, which can be pivotally moved to exchange heat with the passages. The radiating section is provided with a large surface for cooling the ink by thermal radiation to the surroundings. The cooling is enhanced by an air flow, which is arranged to carry the heat away from the surface of the radiating section. The disadvantage here is that when the outside or room temperature exceeds 34 degrees Celsius, cooling is no longer possible. Furthermore, the heater is not adjustable. The on and off times of the heater must therefore be set very precisely to achieve keeping the ink within a very narrow predetermined temperature range.

[0004] US 2019 / 0092017 discloses an inkjet printer with a heat exchanger for cooling and heating ink. The inkjet printer has one or more ink passages and a temperature control passage. A temperature control fluid flows through the temperature control passage. The temperature control fluid can be cooled in a chiller. Furthermore, the temperature control fluid can be heated by residual heat of an integrated circuit used to control the operation of the pump, but this requires a reversal of the flow direction of the temperature control fluid.

[0005] US 2021 / 0023838 discloses an inkjet printer having a heat exchanger for cooling and heating ink, an unspecified heater, and a cooler, which may be a radiative cooler, for example as in US 2010 / 0066785.

[0006] The problem underlying the present invention is to more efficiently and more accurately maintain the temperature of the ink within a predetermined temperature range, and to reduce the preheat time to bring the ink within the predetermined temperature range when the temperature is significantly below the predetermined temperature range, which may be especially true after an extended period of downtime.

[0007] This problem is solved by a device for controlling the printing temperature of ink in a print head of a system for inkjet printing according to claim 1. Advantageous embodiments can be seen from the dependent claims.

[0008] The device according to the invention comprises a heat exchanger, which has a first passage for ink and a second passage for a temperature control fluid, in particular water. A chiller is provided for heating and / or cooling the temperature control fluid. The device further comprises an ink circuit configured to pump the ink through the heat exchanger and the print head. The device further comprises a temperature control fluid circuit configured to pump the temperature control fluid through the chiller and the heat exchanger. The device is configured for the chiller to heat and / or cool the temperature control fluid such that the temperature of the ink is placed and maintained within a predetermined temperature range. The heat exchanger is provided with at least one heating element, which is configured for additionally heating 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] Due to the presence of the at least one heating element directly in 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, which combines a faster heating of the ink with a good temperature control. Moreover, this is a low-cost solution, since both the heating elements, in particular the heating films or heating mats, as well as the heat exchanger are commercially available at low cost and can be easily assembled together.

[0010] Preferably, at least two heating elements are provided, so that advantageously additional heating can take place at different surface sections of the heat exchanger.

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

[0012] Preferably, the heat exchanger is configured as a plate heat exchanger. Such heat exchangers are commercially available at low cost, can be easily manufactured, and can be easily fitted with heating elements, especially when the heating elements are configured as heating films or heating mats. Plate heat exchangers usually have several metal plates, which are configured in layers. The metal plates can be soldered or screwed to one another, for example. The metal plates mostly consist of a particularly thermally conductive, robust and corrosion-resistant special steel. A number of intermediate chambers can be provided, for example by a corrugated pattern of the metal plates, in which the heat exchange takes place.

[0013] It is particularly preferred if the flow direction of the temperature control fluid and the flow direction of the ink are crossed at right angles to each other. Cross flows are particularly preferred when it is desired to achieve a defined temperature, which is particularly in accordance with the objective of the present invention to temperature control the ink.

[0014] However, the flow directions of the temperature control fluid and the ink can be parallel or countercurrent to each other, with the greatest possible heat exchange occurring when the flow directions are countercurrent.

[0015] In a particularly advantageous embodiment, the heat exchanger is insulated against the outside. This is advantageous, since the heat transfer to the outside is thus effectively limited. Thus, a predefined temperature range of the ink can be achieved and maintained better. The insulation is in this case preferably designed to be releasable. Thus, the at least one heating element can advantageously be assembled inside the insulation.

[0016] Preferably, the first heating element is attached in a first direction to the outermost metal plate of the plate-type heat exchanger. Particularly preferably, the second heating element is attached in a second direction to the outermost metal plate of the plate-type heat exchanger. In this way, advantageously, a particularly good heat transfer can be achieved. In a particularly advantageous embodiment, the first and / or the second heating element is / are stretched over at least 80 percent of the surface of the outermost metal plate. In this way, the heat transfer can be further improved.

[0017] The at least one heating element can be glued and / or clamped and / or screwed to the heat exchanger, without this being to be construed as limiting.

[0018] The insulation of the heat exchanger preferably has holes for the current supply of the at least one heating element, which is advantageous for controlling the operation of the at least one heating element.

[0019] The chiller can preferably be operated in both cooling and heating modes, thus allowing the temperature of the temperature control fluid to be open-loop and / or closed-loop controlled with great accuracy.

[0020] In an advantageous embodiment, the temperature control fluid circuit is configured to pump the temperature control fluid further through the print head. In this way, control of the temperature of the ink in the print head can be performed even more accurately. This is necessary, among other things, because heat is released in the print head during the printing process. When the temperature of the ink is within a predetermined range after passing through the heat exchanger, the ink may heat up beyond the predetermined range as it passes through the print head. The temperature control fluid can now thus provide even more cooling.

[0021] To be able to react even better to the increase in temperature of the print head, the device preferably comprises a valve which in a first position directs the temperature control fluid through the heat exchanger and in a second position directs the temperature control fluid around the heat exchanger, which is advantageous in order to counteract the increase in temperature of the print head during the printing process more quickly, especially in the cooling mode, since the temperature control fluid is not still directed through the heat exchanger but instead bypasses it, and thus a stronger cooling effect can be generated in the print head.

[0022] The ink circuit preferably has a buffer tank, which is partly filled with air or other gas and partly filled with ink. This allows a good management 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. Due to the pressure in the buffer tank, the ink is thus advantageously guided to the print head. A partial ink circuit preferably runs from the buffer tank through the pump, through the heat exchanger and back again to the buffer tank. This partial circuit is advantageously used for heating and / or cooling the ink in the buffer tank by means of the heat exchanger. In particular a valve is provided in the partial ink circuit, which is configured to guide the ink through the heat exchanger or to guide it around the heat exchanger. Thus, when the ink is guided around the heat exchanger, the heat exchange effect at the print head can be intensified, which is advantageous in particular in the cooling mode.

[0023] Further advantageous embodiments can be seen from the following drawings and detailed description of the drawings. [Brief description of the drawings]

[0024] [Figure 1] 1 is a schematic flow diagram of a temperature control fluid circuit of a preferred embodiment of the device according to the present invention. [Diagram 2] 2 is a schematic flow diagram of the ink circuit of a preferred embodiment of the device according to the present invention. [Diagram 3] FIG. 1 is a schematic vertical-horizontal section of a plate-type heat exchanger having two heating elements according to a preferred embodiment of the device according to the invention. [Figure 4] FIG. 4 is another schematic vertical-horizontal cross-sectional view of the plate heat exchanger shown in FIG. [Diagram 5] FIG. 5 is a perspective view of the plate heat exchanger shown in FIGS. 3 and 4.

[0025] Detailed Description of the Drawings 1 shows, in schematic flow diagram form, a temperature control fluid circuit of a preferred embodiment of the apparatus according to the present invention, generally designated 100. The temperature control fluid circuit 100 is configured to pump a temperature control fluid 4 through a chiller 1, a plate-type heat exchanger 2 and a print head 3.

[0026] The chiller 1 is configured to heat and / or cool a temperature control fluid 4. The chiller 1 can also be configured to supply heat to or remove heat from the temperature control fluid by a thermodynamic cycle, for example as a refrigerator or a heat pump or a compression cooling or heating system. It can also be formed using one or more Peltier elements or using other known systems for heating and / or cooling fluids. The chiller 1 has a supply 11 for the temperature control fluid 4 and a discharge 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 supply 11 and to discharge the heated or cooled temperature control fluid 4 through the discharge 12.

[0027] Arranged downstream of the discharge 12 of the chiller 1 is in this embodiment a first Roemer valve 101 which is configured to either feed the temperature control fluid 4 from the chiller 1 to the plate heat exchanger 2 or to guide it in a first bypass 102 around the plate heat exchanger 2.

[0028] The plate-type heat exchanger 2 is arranged to heat or cool the ink in the ink circuit by means of the temperature control fluid 4. This is, however, only done when the first rheometer valve 101 is adjusted so that the temperature control fluid 4 discharged from the chiller 4 is supplied to the plate-type heat exchanger 2. For this purpose, the plate-type heat exchanger 2 has a supply part 21 and a discharge part 22. The supply part 21 and the discharge part 22 are arranged in this embodiment on one common surface, but this does not limit the generality. The plate-type heat exchanger has a first heating element 23 and a second heating element 24. The first heating element 23 is arranged on the surface of the plate-type heat exchanger 2 facing the supply part 21 and the discharge part 22. The second heating element 24 is arranged on the surface of the plate-type heat exchanger opposite the supply part 21 and the discharge part 22. Further preferred features of the plate-type heat exchanger 2 are explained further below with reference to figures 3 to 5.

[0029] Arranged downstream of the plate heat exchanger is in this embodiment a T-connector 103 which is designed to transfer the temperature control fluid 4 coming from the discharge 22 of the plate heat exchanger 2 and the temperature control fluid 4 coming from the first bypass 102 into one common temperature control fluid stream 104. It is thus achieved that depending on the position of the first lehmer valve 101, the T-connector 103 either passes the temperature control fluid from the plate heat exchanger 2 or passes the temperature control fluid 4 from the first bypass 102.

[0030] The temperature control fluid flow 104 from the T-connector 103 is arranged to be led into the print head 3. Here, in this embodiment, additional heating and / or cooling of the ink takes place. This is particularly advantageous when the temperature of the ink in the print head is rising due to the printing process. In this case, the chiller can be switched to a cooling mode. Furthermore, the first lehmer valve 101 can be adjusted so that the temperature control fluid 4 from the outlet 12 of the chiller flows into the first bypass 102, so that no heating takes place in the plate-type heat exchanger 4, but the full cooling action of the temperature control fluid 4 takes place directly in the print head 3. Thus, a very rapid reaction to a rise in the temperature of the print head is possible. After the print head, the temperature control fluid 4 flows in this embodiment directly into the inlet 11 of the chiller 1 again.

[0031] 2 shows, in a schematic flow diagram, the ink circuit of a preferred embodiment of the device according to the invention, designated 200. The ink circuit 100 comprises a buffer tank 201, which is partly filled with ink 5 and partly filled with air 6. In this way, the positive pressure in the buffer tank 201 can be very well regulated. A branch line 206 leads from the buffer tank 201 to the print head 3.

[0032] The partial circuit 202 of the ink circuit 200 is configured in this embodiment to pump the ink 5 through the plate-type heat exchanger 2 by means of a pump 2021 and guide it back into the buffer tank 201 again. In this case, the plate-type heat exchanger 2 is configured to cool or heat the ink 5 guided 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 has been described above with reference to FIG. 1. Arranged downstream of the buffer tank 201 is a pump. Arranged downstream of the pump is a second rheometer valve 2022. The second rheometer valve is configured in this case to guide the ink 5 further to the plate-type heat exchanger 2 in a first position and to guide the ink 5 back into the buffer tank 201 in a second bypass 2025 in a second position. When the second rheometer valve 2022 is in the first position, a 5 μm filter is arranged downstream of the second rheometer valve 2022. The 5 μm filter 2024 is followed by a deaerator 2024. In this way, it is possible to prevent condensates or air bubbles from reaching the plate heat exchanger 2. Air bubbles can reduce the heat transfer, and condensates can block the plate heat exchanger 2. The 5 μm filter 2024 is followed by the plate heat exchanger 2. From the ink outlet of the plate heat exchanger 2, the ink is guided back into the buffer tank 201.

[0033] 3 to 5 show a plate heat exchanger from a preferred embodiment of the device according to the invention in two cross-sectional views and one perspective view, which is designated by the number 2.

[0034] The plate-type heat exchanger 2 has an ink supply 25 and a temperature control fluid supply 21. Furthermore, the plate-type heat exchanger 2 has an ink discharge 26 and a temperature control fluid discharge 22. An exemplary temperature control fluid circuit 100 has been described above with reference to FIG. 1. An exemplary ink circuit 200 has been described above with reference to FIG. 2. The plate-type heat exchanger 2 has a number of metal plates 27 which are formed in layers and form intermediate spaces or chambers. In this case, one ink control fluid chamber 28 and one ink chamber 29 are arranged alternately with one another. Thus, six ink control fluid chambers 28 and five ink chambers 29 are shown in FIG. 3. Particularly advantageously, the plate-type heat exchanger is formed in such a way that the volume can be changed by adding further metal plates 27 and chambers.

[0035] At a first end of the plate heat exchanger 2, a first heating element 23 is arranged. At a second end of the plate heat exchanger 2, a second heating element 24 is arranged. The plate heat exchanger 2 is closed at both ends by one mounting plate 29b each. The outer mounting plates 29b are connected in this embodiment by means of screw connections 29a. In this way, the chambers of the plate heat exchanger 2 can be advantageously kept tight, and a change in the volume of the plate heat exchanger is easily possible, since a further metal plate 27 can be inserted between them and sealed by means of the screw connections 29a and the mounting plates 29b.

[0036] The first heating element 23 and the second heating element 24 are here configured as heating films and are each stretched over more than 80% of the surface of the outer metal plate of the heat exchanger. In this way, a particularly good additional heat dissipation is achieved. By changing the voltage, the heat output of the heating film in particular can be changed.

[0037] The cross-sectional view of Figure 4 shows the arrangement of the first rhema valve 101, the bypass 102 and the T-connector 103 shown in Figure 1 on the plate heat exchanger 2. The first rhema valve 101 advantageously determines whether the temperature control fluid 4 from the chiller 1 (see Figure 1) is led 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. By the means described herein, it can be achieved quickly and at low cost to bring the ink 5 within a predefined printing temperature range. Furthermore, it can be achieved very accurately and at low cost to maintain the printing temperature of the ink 5 within this predefined range. Furthermore, good adaptability and variability to different ink volumes is achieved. [Explanation of symbols]

[0039] 1 Chiller 2 Plate heat exchanger 3 Print Head 4 Temperature Control Fluid 5. Ink 6. Air 11 Supply of temperature-controlled fluid to the chiller 12 Discharge of temperature control fluid from chiller 21 Temperature-controlled fluid supply for plate-type heat exchangers 22 Temperature controlled fluid outlet for plate type heat exchanger 23 First Heating Element 24 Secondary Heating Element 25 Ink supply for plate type heat exchanger 26 Ink discharge section for plate type heat exchanger 27 Metal Plate 28 Temperature Controlled Fluid Chamber 29 Ink chamber 29a Mounting plate 29b Screw for mounting plate 100 Temperature Control Fluid Circuit 101 First Rhema Valve 102 First Bypass 103 T type connector 104 Temperature Controlled Fluid Flow 200 Ink Circuit 201 Buffer Tank 202 Partial ink circuit 206 Branch Pipe 2021 Pump 2022 Second Rema Valve 2023 5μm filter 2024 Deaerator 2025 Second Bypass

Claims

1. 1. An apparatus for controlling the printing temperature of ink (4) in a print head (3) of a system for inkjet printing, said system comprising: A heat exchanger (2), a first passage for ink (5); A second passage for a temperature control fluid (4); A heat exchanger (2) having a chiller (1) for heating and / or cooling the temperature control fluid (4); an ink circuit (100) configured to pump ink (5) through said heat exchanger (2) and into said 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); Equipped with the device is configured to heat and / or cool the temperature control fluid (4) by means of the chiller (1) such that the temperature of the ink (5) is placed and maintained within a predetermined temperature range, the heat exchanger (2) is provided with at least one heating element (23, 24) configured 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) more quickly within the predetermined temperature range, Device.

2. 2. The device according to claim 1, wherein at least two heating elements (23, 24) are provided.

3. 3. The device according to claim 1 or 2, wherein at least one of the heating elements (23, 24) is formed as a heating film, in particular as an electrically conductive coating on a carrier, which is encapsulated in a polyester film or silicone.

4. 4. The device according to claim 1, wherein the heat exchanger (2) is configured as a plate heat exchanger (2) with metal plates, in particular made of stainless steel.

5. 5. The device according to claim 1, wherein the heat exchanger (2) is insulated against the outside.

6. 6. The device according to claim 1, wherein a first heating element (23) is attached to an outermost metal plate (27) of the plate-type heat exchanger (2) in a first direction and further preferably a second heating element (24) is attached to the outermost metal plate (27) of the plate-type heat exchanger (2) in a second direction and further preferably the first heating element (23) and / or the second heating element (24) are extended over at least 80 percent of the surface of the outermost metal plate.

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

8. 8. The apparatus of claim 1, wherein the temperature control fluid circuit (100) is further configured to pump the temperature control fluid (5) additionally through the print head (3).

9. 9. The device according to claim 1, wherein the temperature control fluid circuit (100) comprises a valve configured to, in a first position, direct the temperature control fluid (4) through the heat exchanger (2) and, in a second position, direct the temperature control fluid (4) bypassing the heat exchanger (2), the valve being preferably formed as a first rhema valve (101).

10. 10. The device according to claim 1, wherein the ink circuit (200) comprises a buffer tank (201) partly filled with air (6) or other gas and partly filled with ink (5), and preferably a branch line (206) of the ink circuit (200) leads from the buffer tank (201) to the print head (3).

Images