WO2013039886A1

WO2013039886A1 - Print system for reducing pressure fluctuations

Info

Publication number: WO2013039886A1
Application number: PCT/US2012/054619
Authority: WO
Inventors: Daniel Beedon; Pietro Lostumbo; Brian Kaspari; Scott BENIGNI; Xuedong Zhan; Paul Sage
Original assignee: Videojet Technologies Inc.
Priority date: 2011-09-13
Filing date: 2012-09-11
Publication date: 2013-03-21

Abstract

A print system includes an ink source, a print head including a nozzle for ejecting ink onto a substrate, and a fluid line providing fluid communication from the ink source to the print head. A traversing mechanism moves the print head in a lateral direction with respect to a production line. A pressure damping device is disposed in the fluid line adjacent the print head for reducing pressure fluctuations in the fluid line.

Description

PRINT SYSTEM FOR REDUCING PRESSURE FLUCTUATIONS BACKGROUND

[0001] The present disclosure relates to a system for reducing pressure fluctuations in an ink jet print head.

[0002] Pressure variations are a common problem in most hydraulic applications. In the application of continuous ink jet printing (CIJ) this issue is of particular importance as pressure changes result in velocity changes for ejected ink droplets, which affect drop placement on the substrate, resulting in poor print quality. When using a traversing print head, the inertia changes associated with moving the print head causes pressure fluctuations, resulting in reduced print quality. Although in some cases the print quality may be improved by using a larger font size, in many cases this is not desirable or even feasible.

BRIEF SUMMARY

[0003] The present disclosure provides a system for reducing pressure fluctuations in a traversing ink jet print head. The concept of the system is to restrict the fluid supply at or near the print nozzle such that pressure variations are reduced or eliminated. The disclosed embodiments provide for reduction of pressure variations to ensure constant ink velocity and higher print quality.

[0004] In one aspect, a print system includes an ink source, a print head including a nozzle for ejecting ink onto a substrate, and a fluid line providing fluid communication from the ink source to the print head. A traversing mechanism moves the print head in a lateral direction with respect to a production line. A plurality of restrictors is disposed in the fluid line adjacent the print head for reducing pressure fluctuations in the fluid line.

[0005] In another aspect, a print system includes an ink source and a continuous inkjet print head. The print head includes a nozzle for ejecting ink onto a substrate, a charge electrode for charging ink droplets ejected from the nozzle, deflection electrodes for controlling placement of the charged ink droplets, and a gutter for collecting unused ink droplets. A fluid line provides fluid communication from the ink source to the print head. A traversing mechanism moves the print head in a lateral direction with respect to a production line. A pressure damping device is disposed in the fluid line adjacent the print head for reducing pressure fluctuations in the fluid line

[0006] In another aspect, a method of operating a print system includes providing an ink source and a print head. The print head includes a nozzle for ejecting ink onto a substrate. Fluid communication is provided from the ink source to the print head. The print head is moved in a lateral direction with respect to a production line. A plurality of restrictors in the fluid line adjacent the print head reduces pressure fluctuations in the fluid line

[0007] The foregoing paragraphs have been provided by way of general introduction, and are not intended to limit the scope of the following claims. The presently preferred embodiments, together with further advantages, will be best understood by reference to the following detailed description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] FIG. 1 is a schematic view of an embodiment of a print system.

[0009] FIG. 2 is a graph showing the pressure variation of ink in the print head of a fixed (non-traversing) print head.

[0010] FIG. 3 is a graph showing the pressure variation of ink in the print head of a traversing print head.

[0011] FIG. 4 shows an embodiment of a print head with a pressure damping device.

[0012] FIG. 5 is a perspective view of the print head of FIG. 4.

[0013] FIG. 6 shows an embodiment of a pressure damping device.

[0014] FIG. 7 shows another embodiment of a pressure damping device.

DETAILED DESCRIPTION

[0015] The invention is described with reference to the drawings in which like elements are referred to by like numerals. The relationship and functioning of the various elements of this invention are better understood by the following detailed description. However, the embodiments of this invention as described below are by way of example only, and the invention is not limited to the embodiments illustrated in the drawings.

[0016] The present disclosure provides a system for reducing pressure fluctuations in the fluid supply to a traversing print head. The concept of the system is to dampen the hydraulic pressure of the fluid supply at or near the print nozzle such that pressure variations are reduced or eliminated. The disclosed embodiments provide for reduction of pressure variations to ensure constant ink velocity and higher print quality. The preferred embodiments eliminate moving components and potential failures of these components, although alternate methods may also be effective. Although the disclosed embodiments are particularly effective for traversing print head systems, they are also useful in other systems where pressure fluctuations occur in the ink supply for other reasons.

[0017] FIG. 1 shows a schematic layout of a print system 10. The print system 10 includes an ink source 12, a fluid line 14, and a print head 16. The fluid line 14 provides fluid communication from the ink source 12 to the print head 16. The print head 16 includes a nozzle 40 (shown in FIG. 4) for ejecting ink onto a substrate. The print head 16 may be disposed over or along side a production line, such as a conveyer 18. A traversing mechanism 20 moves the print head 16 in a lateral direction with respect to the production line 18. Products 30 are conveyed by conveyer 18 and printed on by the print head to provide a printed product 32.

[0018] FIG. 2 shows the pressure variation of ink in the print head of a fixed (non-traversing) print head. It can be seen that the variation is quite small, on the order of 0.1 psi at a pressure of around 43 psi. FIG. 3 shows the pressure variation of ink in the print head of a traversing print head. It can be seen that there are significant pressure variations compared to the non-moving print head, on the order of 0.5 psi peak to trough. Such large pressure variations have been found to adversely affect the print quality.

[0019] It has been found that using a pressure damping device 22 in the fluid line 14 adjacent the print head 16 reduces pressure fluctuations in the fluid line 14. In one embodiment, the print head 16 is a continuous ink jet print head, and includes a charge electrode 42 for charging ink droplets ejected from the nozzle 40, deflection electrodes 44, 46 for controlling placement of the charged ink droplets, and a gutter 48 for collecting unused ink droplets. An example of a suitable print head 16 is shown in US 20100238209 entitled "Ink Jet Printer head Assembly" and assigned to Videojet Technologies Inc., the contents of which are hereby incorporated by reference.

[0020] FIGS. 4 and 5 show a modification to a Videojet 1000 series print head 16 to include the pressure damping device 22. Ink line 24 (which is in fluid

communication with ink line 14) is routed to damping device 22 (instead of directly to heater module 28). Another fluid line 26 conveys ink from pressure damping device 22 to heater module 28. Thus, pressure damping device 22 is able to be positioned within the existing print head assembly with only minor modifications. The pressure damping device 22 is preferably located close to the nozzle 40 in order to effectively reduce the pressure variation. In one embodiment, the pressure damping device 22 is located less than 10 inches, preferably less than 5 inches, from the nozzle 40.

[0021] A variety of suitable arrangements for the pressure damping device 22 are possible. In one embodiment, the pressure damping device 22 includes a plurality of restrictors. Each restrictor may include an orifice. In one embodiment, the diameters of the orifices may be between 10 micron and 150 micron. In one embodiment, the restrictor orifices are between 80 micron and 120 micron. In a preferred embodiment, three, four, or five restrictors are disposed in series. The restrictors act to smooth out the flow variations that occur in the traversing print head 16 as fluid squeezes through the restriction in the line. Without intending to be bound by theory, it is believed that the orifices even out the flow irregularities caused by inertial effects. When this effect happens multiple times in series, the result is an averaging of the fluid velocity which improves print quality. The pressure damping device 22 preferably does not include any moving mechanical parts.

[0022] A suitable embodiment of a pressure damping device is shown in FIG. 6. Pressure damping device 22 includes inlet 50 and outlet 52 at opposite ends of major body 60. Inlet 50 and outlet 52 may be of any suitable construction and may include barbed ends for securing a flow line or tube. Disposed within major body 60 is a plurality of flow restrictors 54. In the embodiment shown, five restrictors are disposed in series, but the number used may be more or less. Each restrictor includes an internal orifice 56 with a diameter smaller than the inner diameter 51 of the inlet 50. In one embodiment, the inner diameter of the orifices is 120 micron. Fittings 58 and 62 are disposed at either end of the series of restrictors 56 to hold them in place within the major body 60.

[0023] In another embodiment, the pressure damping effect is provided by a standpipe, either alone or in addition to restrictors. A standpipe provides a 'cushion' of air or other gas in a vertical pipe connected to the ink line 14. The gas cushion reduces pressure fluctuations in the ink line.

[0024] In another embodiment the system includes a diaphragm type pressure damper, either alone or in combination with the restrictors. A schematic embodiment 70 of such a damper is shown in FIG. 7 for illustrative purposes. The damper 70 includes inlet 72, outlet 74, and flexible diaphragm 76. The flexible diaphragm 76 isolates an air cushion 78 from the fluid volume 80 to prevent absorption of the air pocket by the fluid (compared to the previously described standpipe). The damper 70 reduces pressure fluctuations in the ink line - when the fluid pressure is high, diaphragm 76 moves to expand the fluid area 80 and decrease the air cushion area 78. Although FIG. 7 illustrates one embodiment of a damper, such devices are known in the art and any suitable version may be used in the present application. For example, the area enclosing the air cushion may be either open or closed, depending on the desired properties, and the design of the damper with a diaphragm may be of any suitable type known in the art.

[0025] In another embodiment, the pressure damping effect is provided by a hydraulic back pressure regulating type device. This device is a fast acting fluid regulator that simply dumps excess pressure back to a return line that is connected to the ink supply source 12.

[0026] The present system is particularly suited for print heads that traverse at a high speed. In one embodiment, the print head traverses at a speed of at least 250 ft/min, more preferably at least 300 ft/min. Even at these high traverse speeds the present system is capable of reducing pressure fluctuations to prevent deterioration of print quality.

[0027] The pressure of ink in the fluid line is generally between 20 psi and 80 psi. The present system preferably reduces pressure fluctuations to less than 1 psi, more preferably less than 0.5 psi, and most preferably less than 0.25 psi. In one embodiment, the pressure damping device reduces the pressure variation by at least 50% compared to the same system without a pressure damping device. Thus, for example, if the normal pressure variation in a traversing system is 1 psi, the present system preferably reduces that to less than 0.5 psi. The pressure damping device more preferably reduces the pressure variation by at least 60%, 70%, or 80%. A restrictor design including five 66 micron orifices of equal in series was capable of reducing pressure variation by 68%, to 0.13 psi from 0.41 psi.

[0028] The described and illustrated embodiments are to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiments have been shown and described and that all changes and modifications that come within the scope of the inventions as defined in the claims are desired to be protected. It should be understood that while the use of words such as "preferable", "preferably", "preferred" or "more preferred" in the description suggest that a feature so described may be desirable, it may nevertheless not be necessary and

embodiments lacking such a feature may be contemplated as within the scope of the invention as defined in the appended claims. In relation to the claims, it is intended that when words such as "a," "an," "at least one," or "at least one portion" are used to preface a feature there is no intention to limit the claim to only one such feature unless specifically stated to the contrary in the claim. When the language "at least a portion" and/or "a portion" is used the item can include a portion and/or the entire item unless specifically stated to the contrary.

Claims

Claims What is claimed is:

1. A print system comprising:

an ink source;

a print head, the print head including a nozzle for ejecting ink onto a substrate; a fluid line providing fluid communication from the ink source to the print head;

a traversing mechanism for moving the print head in a lateral direction with respect to a production line;

a plurality of restrictors disposed in the fluid line adjacent the print head for reducing pressure fluctuations in the fluid line.

2. The print system of claim 1 wherein the print head is a continuous ink jet print head.

3. The print system of claim 1 wherein the print head further comprises a charge electrode for charging ink droplets ejected from the nozzle, deflection electrodes for controlling placement of the charged ink droplets, and a gutter for collecting unused ink droplets.

4. The print system of claim 1 wherein the restrictors include orifices with openings between 80 and 140 micron.

5. The print system of claim 1 further comprising a pressure damping device.

6. The print system of claim 5 wherein the pressure damping device does not include any moving mechanical parts.

7. The print system of claim 5 wherein the pressure damping device comprises a damper comprising a diaphragm.

8. The print system of claim 1 wherein the plurality of restrictors reduces the pressure variation by at least 50% compared to the same system without a pressure damping device.

9. The print system of claim 1 wherein the print head traverses at a speed of at least 300 ft/min.

10. The print system of claim 1 wherein the plurality of restrictors is located less than 10 inches from a nozzle of the print head.

11. The print system of claim 1 wherein the plurality of restrictors is located less than 5 inches from a nozzle of the print head.

12. The print system of claim 1 wherein the pressure of ink in the fluid line is between 20 psi and 80 psi.

13. A print system comprising:

an ink source;

a continuous ink jet print head, the print head comprising:

a nozzle for ejecting ink onto a substrate;

a charge electrode for charging ink droplets ejected from the nozzle; deflection electrodes for controlling placement of the charged ink droplets; and

a gutter for collecting unused ink droplets;

a fluid line providing fluid communication from the ink source to the print head;

a traversing mechanism for moving the print head in a lateral direction with respect to a production line; and

a pressure damping device disposed in the fluid line adjacent the print head for reducing pressure fluctuations in the fluid line.

14. The print system of claim 13 wherein the pressure damping device comprises a plurality of restrictors.

15. The print system of claim 13 wherein the pressure damping device is located less than 5 inches from the nozzle of the print head.

16. The print system of claim 13 wherein the pressure of ink in the fluid line is between 20 psi and 80 psi.

17. The print system of claim 13 wherein the pressure damping device comprises a damper comprising a diaphragm.

18. A method of operating a print system comprising

providing an ink source and a print head, the print head including a nozzle for ejecting ink onto a substrate;

providing fluid communication from the ink source to the print head;

moving the print head in a lateral direction with respect to a production line; and

using a plurality of restrictors in the fluid line adjacent the print head to reduce pressure fluctuations in the fluid line.

19. The method of claim 18 wherein the pressure damping device reduces the pressure variation by at least 50% compared to the same system without a pressure damping device.

20. The method of claim 18 comprising traversing the print head at a speed of at least 300 ft/min.

21. The method of claim 18 wherein the pressure damping device is located less than 5 inches from the nozzle of the print head.