Ink heating device and ink supply system for a printing apparatus

Abstract

An ink supply system for supplying ink to a drop-forming unit of a print-head in a printing apparatus includes a reservoir for holding or storing a volume of liquid ink to be supplied to a drop-forming unit in a print-head, and a heating device arranged upstream of the reservoir for heating the ink to an desired operating temperature. The heating device includes a heating body for transferring heat to the ink, wherein the heating body includes a plurality of channels which extend from an top side of the heating body to an bottom side of the heating body for conveying the ink to the reservoir, whereby the ink is heated via contact with walls of the channels. The heating body typically includes a substantially monolithic body of a highly thermally conductive material and the plurality of channels are substantially parallel channels which extend through the heating body. A print-head of a printing apparatus incorporating the ink supply system, and a heating device are also disclosed.

Claims

1. A heating device for heating liquid ink in an ink supply system of a printing apparatus, comprising: a heating body for transferring heat to liquid ink in contact with the heating body, wherein the heating body comprises an essentially solid body of thermally conductive material and includes a plurality of generally parallel channels formed therein which extend from a topside of the heating body to a bottom side of the heating body, wherein the heating body comprises a receptacle at the top side for receiving the liquid ink, wherein an inlet opening of each of the plurality of substantially parallel channels is formed in a base of the receptacle, wherein the heating device comprises a passage arranged separated from the receptacle and to provide a fluid connection between the top side and the bottom side of the heating body, which passage in operation provides pressure equalization between the top side and the bottom side of the heating body, and wherein the plurality of substantially parallel channels are arranged to, in operation, convey the liquid ink from the top side to the bottom side of the heating body whereby the ink is heated via contact with walls of the channels.

2. The heating device according to claim 1, wherein each of the plurality of substantially parallel channels has a length in the range of about 3 mm to about 10 mm.

3. The heating device according to claim 1, wherein each of the plurality of substantially parallel channels has a diameter in the range of about 0.2 mm to about 1.0 mm.

4. The heating device according to claim 1, wherein the number of the plurality of substantially parallel channels formed in the heating body is in the range of about 100 to about 500.

5. The heating device according to claim 1, wherein the passage is formed in the heating body.

6. An ink supply system for supplying ink to a drop-forming unit of a print-head in a printing apparatus, comprising: a reservoir for holding a volume of liquid ink to be supplied to a drop-forming unit in a print-head; and the heating device according to claim 1 arranged upstream of the reservoir for heating the ink to a desired operating temperature, the heating device comprising a heating body for transferring heat to the ink, wherein the heating body comprises a plurality of channels which extend from the top side of the heating body to the bottom side of the heating body for conveying the ink to the reservoir, whereby the ink is heated via contact with walls of the channels.

7. The ink supply system according to claim 6, wherein the heating body comprises a substantially monolithic body of a thermally conductive material and wherein the plurality of channels are substantially parallel channels which extend through the heating body.

8. The ink supply system according to claim 6, further comprising a filter device which is arranged between the heating device and the reservoir, wherein the filter device is arranged at the bottom side of the heating body and at an inlet of the reservoir.

9. A print-head of a printing apparatus, comprising: the ink supply system according to claim 6; and a drop-forming unit which is supplied with ink from an outlet of the reservoir.

10. The print-head according to claim 9, wherein the drop-forming unit comprises a MEMS; and/or wherein a second filtering device is provided to filter the ink from the ink supply system upstream of the drop-forming unit.

11. A printing apparatus comprising the ink supply system according to claim 6.

12. A printing apparatus comprising the print-head according to claim 9.

13. The heating device according to claim 2, wherein each of the plurality of substantially parallel channels has a diameter in the range of about 0.2 mm to about 1.0 mm.

14. The heating device according to claim 2, wherein the number of the plurality of substantially parallel channels formed in the heating body is in the range of about 100 to about 500.

15. The heating device according to claim 3, wherein the number of the plurality of substantially parallel channels formed in the heating body is in the range of about 100 to about 500.

16. The heating device according to claim 2, wherein the passage is formed in the heating body.

17. The heating device according to claim 3, wherein the passage is formed in the heating body.

18. The heating device according to claim 4, wherein the passage is formed in the heating body.

19. An ink supply system for supplying ink to a drop-forming unit of a print-head in a printing apparatus, comprising: a reservoir for holding a volume of liquid ink to be supplied to a drop-forming unit in a print-head; and the heating device according to claim 2 arranged upstream of the reservoir for heating the ink to a desired operating temperature, the heating device comprising a heating body for transferring heat to the ink, wherein the heating body comprises a plurality of channels which extend from the top side of the heating body to the bottom side of the heating body for conveying the ink to the reservoir, whereby the ink is heated via contact with walls of the channels.

20. An ink supply system for supplying ink to a drop-forming unit of a print-head in a printing apparatus, comprising: a reservoir for holding a volume of liquid ink to be supplied to a drop-forming unit in a print-head; and the heating device according to claim 3 arranged upstream of the reservoir for heating the ink to a desired operating temperature, the heating device comprising a heating body for transferring heat to the ink, wherein the heating body comprises a plurality of channels which extend from the top side of the heating body to the bottom side of the heating body for conveying the ink to the reservoir, whereby the ink is heated via contact with walls of the channels.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a more complete understanding of the invention and the advantages thereof, exemplary embodiments of the invention are explained in more detail in the following description with reference to the accompanying drawing figures, in which like reference characters designate like parts and in which:

(2) FIG. 1 is a schematic cross-sectional side view of an ink supply system according to a preferred embodiment;

(3) FIG. 2 is a perspective view of a heating device according to a preferred embodiment;

(4) FIG. 3 is a cross-sectional perspective view of the heating device shown in FIG. 2;

(5) FIG. 4 is a graph comparing a maximum and minimum temperature of the ink with a wall temperature over a length of the channel in the heating body of a heating device according to a preferred embodiment;

(6) FIG. 5 is a cross-sectional perspective view of a print-head for a printing apparatus according to a preferred embodiment;

(7) FIG. 6 is a detailed cross-sectional perspective view of the heating device in the print-head of FIG. 5;

(8) FIG. 7 is a cross-sectional side view of a print-head for a printing apparatus according to another preferred embodiment; and

(9) FIG. 8 is a flow diagram that schematically illustrates a method of supplying ink to a drop-forming unit according to a preferred embodiment.

(10) The accompanying drawings are included to provide a further understanding of the present invention and are incorporated in and constitute a part of this specification. The drawings illustrate particular embodiments of the invention and together with the description serve to explain the principles of the invention. Other embodiments of the invention and many of the attendant advantages of the invention will be readily appreciated as they become better understood with reference to the following detailed description.

(11) It will be appreciated that common and/or well understood elements that may be useful or necessary in a commercially feasible embodiment are not necessarily depicted in order to facilitate a more abstracted view of the embodiments. The elements of the drawings are not necessarily illustrated to scale relative to each other. It will further be appreciated that certain actions and/or steps in an embodiment of a method may be described or depicted in a particular order of occurrences while those skilled in the art will understand that such specificity with respect to sequence is not actually required. It will also be understood that the terms and expressions used in the present specification have the ordinary meaning as is accorded to such terms and expressions with respect to their corresponding respective areas of inquiry and study, except where specific meanings have otherwise been set forth herein.

DETAILED DESCRIPTION OF EMBODIMENTS

(12) With reference firstly to drawing FIG. 1, an ink supply system 1 for supplying ink to a drop-forming unit (not shown) in a print-head 50 of a printing apparatus. The ink supply system 1 includes a reservoir 2 which is enclosed by a housing 3 for storing or holding a volume of liquid ink 4 to be supplied to the drop-forming unit of the print-head via an outlet 5 of the reservoir 2. The specific configuration of the reservoir 2 is not itself central to the concept of the ink supply system 1 in this embodiment and will therefore not be described here in detail. The ink supply system 1 further includes a heating device 10 which is arranged upstream of the reservoir 2 for heating the liquid ink 4 to a desired operating temperature.

(13) With reference now also to FIGS. 2 and 3 of the drawings, the heating device 10 comprises a heating body 11 for transferring heat to the liquid ink 4 in contact with the heating body 11. In this regard, the heating body 11 comprises an essentially solid body or block of a highly thermally conductive material, such as copper or aluminum or a respective alloy thereof. The heating body or block 11 includes an array of generally parallel channels 12 formed therein which extend from an top side 13 of the body 11 to an bottom side 14 of the body 11. Each of the channels 12 comprises a circular bore and all of the channels 12 have substantially the same dimensions; namely a diameter of about 0.5 mm and a length of about 5 mm. The heating body or block 11 of this embodiment has 300 channels 12 formed therein for conveying the liquid ink 4 from the top side 13 to the bottom side 14, with the ink being heated by contact with the heating body or block 11, and particularly with walls of the channels 12 as the liquid ink passes through the channels.

(14) Referring now to drawing FIGS. 4 and 5 together with FIGS. 1 to 3, the liquid ink 4 having a first temperature (e.g. 110 C.) is delivered to the heating device 10 at the top side 13 of the heating body 11 from a melting device 20. In this regard, the melting device 20 includes a tapered tube 21 within which solid ink elements, such as spherical toner pearls (not shown), are heated to the first temperature such that they melt. The hot-melt ink 4 therefore flows down through a central cavity 22 of the heated tube 21 into a receptacle 15 which is provided the top side 13 of the heating body or block 11 in the form of a generally rectangular basin or trough. In particular, the rectangular basin or trough 15 can be seen in FIGS. 2 and 3 to be formed integrally with the generally solid body or block 11 of thermally conductive material. Because the heating body 11 is heated to a second temperature which is higher than the first temperature (e.g. 130 C.), when the ink 4 flows into the basin or trough 15 at the top side 13 and comes into contact with the heating body 11, it will begin to be heated further by the heating device 10. As can be seen in FIG. 2 and FIG. 3, each of the channels has a respective inlet opening 16 in a base of the trough 15, such that the ink may then flow directly into the channels 12.

(15) The graph in FIG. 4 plots the change in temperature of the ink (T_ink) as it passes along the length of each channel 12. In particular, FIG. 4 shows curves for both the minimum temperature of the ink (T_ink min) and the maximum temperature of the ink (T_ink max) tested for a constant wall temperature (T_wall) of 130 in each channel 12. Thus, even with the minimum or worst result, the heating device 10 of the ink supply system 1 still elevates the temperature of the liquid ink 4 to within 1.6 of the wall temperature, as summarised in Table 1 below.

(16) TABLE-US-00001 TABLE 1 Overview of heating device performance Overview Ink Temperature input T_ink_in 110 C. Ink Temperature output T_ink_out 128.4 C. Heat transfer effectiveness 92% Temperature error T_err C. Wall temperature T_wall C. Total channel length L_tot 1500 mm round Nusselt number Nu 3,657

(17) With particular reference now to FIGS. 5 and 6 of the drawings, it will be noted that the heating device 10 includes a passage or through-hole 17 to provide pressure equalization between the top side 13 and the bottom side 14 of the heating body or block 11. In this way, minimal pressure difference exists between the space above the heating block 1 and the space below the heating block 11, such that gravity or liquid column height of the ink in the basin or tough 15 acts as the driving force for ink flow through the channels 12.

(18) As is apparent from FIG. 1 and FIG. 5, the ink supply system 1 comprises a filter device 30 which is arranged between the heating device 10 and the reservoir 2. In particular, the filter device 30 comprises a filter member or mat 31 (e.g. comprised of stainless steel fibres or stainless steel wool) arranged at the bottom side 14 of the heating body or block 11 and extending across a full expanse of the heating block 11 immediately adjacent to an inlet 6 to the reservoir 2. As can be seen in FIG. 3 and FIGS. 5 and 6, the heating block 11 has a downwardly projecting rim 18 which cooperates with the housing 3 above the reservoir 2 to clamp or hold the filter member or mat 31 in position. The rim 18 also produces a small cavity 19 at the bottom side 14 of the block 11 which allows the ink to spread across the filter member 31. Accordingly, the filter device 30 acts to filter the hot-melt ink 4 before it enters the reservoir chamber 2 to prevent unwanted introduction of particles or contaminants into the reservoir 2. Because the heating device 10 elevates the temperature of the ink upstream of the filter device 30, the ink 4 has a relatively reduced viscosity and thus flows more readily through the filter device 30, enabling higher ink flow rates in the ink supply system 1 or a more compact construction of the heating device 10. By increasing the number of channels 12, the flow rate may also be increased and/or the device 10 can be made more compact. If the ink flow rate is increased, the ink supply system 1 becomes very suited to use with modern drop-forming units, and especially drop-forming units that employ micro-electro-mechanical systems (MEMS).

(19) The inlet 6 of the reservoir 2 includes valve means 7 (e.g. formed as a float-type check valve) for controlling admission of the ink 4 into the reservoir 2 and preventing back-flow of the ink during a purge of the reservoir 2. In this regard, the ball-float of the valve 7 can move vertically downwards to an open position (as shown) under the influence of a liquid ink head or column height above the valve means 7 to admit the ink 4 to the reservoir. Further, by increasing the pressure p applied to the reservoir 2 inside the housing 3 via a port 8 during a purge of the reservoir, the ball-float of the valve means 7 can move upwards to a closed position to prevent back-flow of the ink 4 through the inlet 6. A level sensor (not shown) may control the level of the ink in the reservoir 2 such that a free space 9 remains above the ink level 4 in the reservoir. Because the heating device 10 of this embodiment is arranged in the ink supply system 1 above the level of the reservoir 2, the possible presence of air bubbles in the ink 4 passing though the heating body or block 11 is not critical. Specifically, any air bubbles present in the ink will have an opportunity to escape into the free space 9 above the level of the ink 4 before the ink is conveyed via the outlet 5 to a drop-forming unit.

(20) Referring now to the embodiments of drawing FIG. 5 and FIG. 7, it will be noted that examples of print-heads 50 for printing apparatus are shown which combine the ink supply system 1 described above with a respective drop-forming unit 40. The drop-forming unit 40 in this embodiment includes an intermediate assembly 41 and microelectromechanical system (MEMS) arranged on a chip 42 for generating or issuing ink droplets. The drop-forming unit 40 is supplied with ink 4 from the ink supply system 1, and specifically from the outlet 5 of the reservoir 2. Because the ink was pre-heated in the heating device 10 and held at a desired temperature within the reservoir 2, the ink entering the drop-forming unit 40 is within a very narrow range of a desired operating temperature. The ink flow from the reservoir 2 may be split or divided by a channel 43 internally within the drop-forming unit 40 for delivery to a suitable location of the MEMS chip 42, which is configured to form the drops to be printed on a print medium in a manner known by those skilled in the art and not explained here in detail.

(21) Finally, with reference now to FIG. 8 of the drawings, a flow diagram is shown that schematically illustrates steps in a method of heating hot-melt ink in an ink supply system 1 according to an embodiment of the invention as described above with respect to FIGS. 1 to 7. In this regard, the first box i of FIG. 8 represents the step of providing liquid ink at a first temperature to a heating device 10 which comprises a monolithic heating body or block 11 having a plurality of channels 12 formed there-through. The second box ii represents a step of receiving the liquid ink an top side 13 of the heating body or block 11 in a receptacle 15 formed therein, wherein the heating body or block 11 is maintained at a second higher temperature which corresponds to a desired operating temperature for the ink. The third box iii then represents the step of passing or conveying the ink through the many channels 12 in the heating body or block 11 to raise the temperature of the ink to approach the second temperature. The final box iv in FIG. 8 represents the step of discharging the ink from the bottom side 14 of the heating body or block 11 and conveying the ink into the reservoir 2 via the inlet 6, preferably after passing a filter device 30.

(22) Although specific embodiments of the invention are illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations exist. It should be appreciated that the exemplary embodiment or exemplary embodiments are examples only and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents. Generally, this application is intended to cover any adaptations or variations of the specific embodiments discussed herein.

(23) It will also be appreciated that in this document the terms comprise, comprising, include, including, contain, containing, have, having, and any variations thereof, are intended to be understood in an inclusive (i.e. non-exclusive) sense, such that the process, method, device, apparatus or system described herein is not limited to those features or parts or elements or steps recited but may include other elements, features, parts or steps not expressly listed or inherent to such process, method, article, or apparatus. Furthermore, the terms a and an used herein are intended to be understood as meaning one or more unless explicitly stated otherwise. Moreover, the terms first, second, third, etc. are used merely as labels, and are not intended to impose numerical requirements on or to establish a certain ranking of importance of their objects.

LIST OF REFERENCE SIGNS

(24) 1 ink supply system 2 reservoir 3 housing 4 ink 5 reservoir outlet 6 reservoir inlet 7 valve means 8 port in the housing 9 free space 10 heating device 11 heating body or block 12 channel 13 top side of heating body 14 bottom side of heating body 15 receptacle, basin or trough 16 inlet opening of channel 17 passage 18 rim 19 cavity 20 melting device 21 tapered tube 22 central cavity of tube 30 filter device 31 filter member or mat 40 drop-forming unit 41 intermediate assembly 42 microelectromechanical system 43 channel 50 print-head