The present application is a national stage filing and claims priority under 35 U.S.C. § 119 of International patent application Serial No. PCT/EP01/05594, filed 16 May 2001, and published in English and Great Britain Serial No. 0011916.4, filed 17 May 2000, the content of which is hereby incorporated by reference in its entirety.
The present invention relates to printing and in particular to printing using a multi-printhead ink jet printer formed from a plurality of printheads and which is wide enough to print across the full width of a continuous substrate.
A multi-printhead printer may be used in so-called “drop-on-demand” ink jet printing to print on to a continuous substrate, for example to print directly onto packaging in a production line. In this case, the printer may be arranged opposite a transport mechanism for the substrate, such as a part of the production line. Such printing is particularly attractive in the production of packaging because it is possible to package items from the same production run into packaging with a different appearance without stopping the packaging line. Thus, for example, the packaging printer may print packaging in one language for the first hundred units and then switch to print packaging in a different language for the next hundred units. Alternatively, the printer may switch from printing the packaging bearing one customer's trade marks to printing those of another. In either case, it is not necessary for a continuous production line to stop for the outer packaging to be changed, and this saves time and therefore money in the production process.
A multi-printhead ink jet printer comprises a very large number of densely packed nozzles through which ink is ejected onto the printing substrate to form the printed image. The spacing between nozzles can be around 140 microns to give a pixel density of 180 dpi. It is important that the ink jet nozzles are accurately located relative to each other, as a very small misalignment of even one nozzle can produce a noticeable effect on the printed image. In order to achieve a desired print density, the ink jet nozzles may be interleaved, i.e. one row of nozzles may be arranged to print pixels between the pixels printed by a second row of nozzles.
If it is desired to print in colour, separate nozzles are provided for each of the different coloured inks and the location of these nozzles must be coordinated with the required degree of accuracy. Many different coloured inks may be used for a full colour industrial printing process, and even in simple situations several colours may be used.
A multi-printhead ink jet printer can be made up of a plurality of printheads in the form of cartridges which fit together to form the whole printer. Such printheads are available from XaarJet Limited of Cambridge, United Kingdom. Such a multi-printhead printer has the advantage that failed ink jet printheads can be replaced without replacing the whole printer. In order that the whole printer is wide enough to cover the width of a desired substrate, the printheads are “stitched” together, so that the printheads overlap in the direction perpendicular to the direction of transport of the substrate.
Thus, in a multi-printhead printer the printheads must be accurately aligned to ensure acceptable printing results. In addition, it is desirable for the printer to be relatively compact in order to fit into standard production lines.
For ink jet printing, it is important that the temperature of the ink at the ink jet nozzles is controlled carefully to ensure reliable printing. Often, the printhead is run at a temperature sufficiently higher than ambient that cooling of the nozzles is not required. In other situations, it is not possible to operate at such temperatures and some form of cooling or heating is required.
Furthermore, the temperature profile across an array of ink jet nozzles should also be relatively uniform. However, in a multi-printhead printer where the cartridges are stitched together, there is very limited space in which to locate a device that is able to regulate the temperature of all the ink jet nozzles.
The present invention seeks to provide an arrangement for the temperature control of a stitched printhead cartridge.
According to the present invention, there is provided a cartridge for a multi-printhead ink jet printer, the cartridge comprising at least one array of ink jet nozzles and a heat sink for controlling the temperature of the nozzles, wherein the heat sink comprises a block of thermally conductive material having formed therein a passageway for a thermally conductive fluid, and wing regions of thermally conductive material extending from said block substantially parallel to said array of nozzles, and wherein the block and the wing regions are in thermal contact with the array of ink jet nozzles and the wing regions have an extent in a direction perpendicular to the array of nozzles which is smaller than the extent of the block in the same direction.
In accordance with the invention, the heat sink for the printhead cartridge has thin wing regions and a thicker block. The thin wing regions allow the cartridges to be stitched while maintaining the required temperature control. The thicker block allows a connection to be made to a coolant circuit of thermally conductive fluid, and increases the overall thermal capacity of the heat sink to maintain thermal stability.
The heat sink may be made of any suitable material and in the preferred embodiment the material is copper. Similarly, the thermally conductive fluid may be any suitable fluid, and is water in the preferred embodiment.
The passageway for the thermally conductive fluid may extend into the wing regions of the heat sink, in which case the passageway may be thinner in the wing regions than in the block.
An embodiment of the invention will now be described by way of example only and with reference to the accompanying drawings in which:
a, b shows schematically the heat sink of the cartridge of
The printer comprises a chassis 4, to which each cartridge is mounted in a precise location. The chassis 4 comprises an outer, rectangular frame 5 across which run a plurality of horizontal bars 6 to which the cartridges are mounted. The bars 6 are perpendicular to the direction of movement of the substrate (the z-direction) when the printer is in the position of use. On each bar 6, adjacent the location of each cartridge is provided a stop 7 which limits the movement of the cartridge in the direction along the bar 6 (the x-direction). The support 2 of each cartridge is urged against the respective stop 7 by a resilient member 8 represented schematically in
As shown most clearly in
In order for printing to be possible across the full width of the printer, adjacent rows of cartridges are “stitched”, i.e. arranged with an overlap in the x-direction. The overlap allows the whole width of the substrate to be covered continuously by the ink jet nozzles even though the width of the printheads 1 is greater than the width of the array 3 of ink jet nozzles that they carry.
The arrangement of cartridges shown in
In order for the ink jet nozzles 3 to operate correctly their temperature must be carefully controlled. The temperature of the nozzles 3 is controlled by a respective heat sink 9 provided in thermal contact with the outer surface of each of the printheads 1.
Referring to
The channel 13 is closed by a back plate 14 which is soldered to the bottom plate 12. The bottom plate 12 is detailed such that it can be soldered to the back plate 14 with plumbing solder to form an effective water seal around the channel 13. During the soldering operation great care is taken to ensure the flatness of the bottom plate 12 is maintained, so that good thermal contact can be made with the array 3 of nozzles, when the heat sink 9 is fitted with the closed end of the fluid pathway flush with the backplate of the printhead 1, which is in itself in good thermal contact with the nozzle array 3.
The channel 13 is in fluid communication with the holes 11 in the block so that coolant water can circulate therethrough to remove heat from the array 3 of nozzles. The lead-in to the tapped holes 11 is such that the flow is not greatly impaired compared with the channel 13. The cold side of the coolant water is fed directly to the end of the channel 13 with a fluid pathway that passes over the warm return path.
The heat sink is supplied with 2.6 litres/minute of water at the minimum operating temperature for the ink and at a pressure of greater than 1 bar. It has been calculated that the maximum heat sink temperature, at the end of the thin wings regions, is approximately 5° C. higher than the water temperature, assuming a required thermal dissipation of 40 W. In practice, the measured temperature difference has been found to be even smaller than the calculated value, which is based on pessimistic assumptions.
As can be seen from
In summary, a printhead cartridge for a multi-printhead ink jet printer includes an array 3 of ink jet nozzles and a heat sink 9 for controlling the temperature of the nozzles 3. The heat sink 9 is made up of a copper block 10 and thinner copper wing regions 12 extending from the block 10 parallel to the array 3 of nozzles. A passageway 11 for coolant water is formed in the block 10 and extends into the wings 12 as a thinner channel 13. The block 10 and the wing regions 12 are mounted in thermal contact with the array 3 of ink jet nozzles. The heat sink 9 has the advantage that it allows the cartridges in the printer to be stitched together to cover the full width of a substrate.
Number | Date | Country | Kind |
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0011916.4 | May 2000 | GB | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP01/05594 | 5/16/2001 | WO | 00 | 6/25/2003 |
Publishing Document | Publishing Date | Country | Kind |
---|---|---|---|
WO01/87620 | 11/22/2001 | WO | A |
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Number | Date | Country | |
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20040021721 A1 | Feb 2004 | US |