LED PRINT CURING APPARATUS

Abstract

A print curing apparatus comprising an LED array comprising a body; the body comprising a mounting area with one or more LED modules mounted thereon; at least one heat sink; and one or more cooling modules, adjacent to the or each heat sink. The one or more cooling modules comprises at least one water-cooled holder comprising at least one fluid inlet channel and at last one fluid outlet channel therethrough; at least one heat pipe held substantially within the or each water-cooled holder, wherein the or each water-cooled holder is shaped to hold at least one heat pipe.

Claims

1. A print curing apparatus comprising: an LED array comprising a body, the body comprising: a mounting area with one or more LED modules mounted thereon; at least one heat sink; and one or more cooling modules, adjacent to the at least one heat sink, wherein the one or more cooling modules comprise at least one water-cooled holder comprising at least one fluid inlet channel and at least one fluid outlet channel therethrough; and at least one heat pipe held substantially within the at least one water-cooled holder, wherein each of the at least one water-cooled holder is shaped to hold at least one of the at least one heat pipes.

2. The print curing apparatus according to claim 1 wherein the at least one water-cooled holder comprises a plurality of cylindrical openings therethrough.

3. The print curing apparatus according to claim 1, wherein the at least one fluid inlet channel and the at least one fluid outlet channel are separate from the at least one heat pipe.

4. The print curing apparatus according to claim 1, wherein each of the at least one heat pipe is clamped within its respective one of the at least one water-cooled holders.

5. The print curing apparatus according to claim 1, further comprising a plurality of LED modules, wherein each LED module is removably attached to three or more heat pipes.

6. The print curing apparatus according to claim 4, wherein the water-cooled holder is a shaped extrusion comprising at least two fluid inlet channels and at least two fluid outlet channels therethrough, at least four channels therethrough, or at least two fluid inlet channels and at least two fluid outlet channels.

7. The print curing apparatus according to claim 1, wherein each of the at least one inlet channel and each of the at least one outlet channel is an equal distance from the adjacent heat pipe, wherein each of the at least one inlet channel and each of the at least one outlet channel has an elongate cuboidal shape, wherein each of the at least one inlet channel and each of the at least one outlet channel has at least two finned walls, or wherein each of the at least one inlet channel and each of the at least one outlet channel has a cross-sectional width greater than about 2 mm.

8. The print curing apparatus according to claim 1, wherein the at least one inlet channel and the at least one outlet channel are configured such that a flow of water therethrough is turbulent.

9. The print curing apparatus according to claim 1, wherein the at least one water-cooled holder is block shaped for holding the at least one heat pipe in position, and wherein the at least one water-cooled holder comprising three or more mating parts.

10. The print curing apparatus according to claim 1, wherein the at least one inlet channel is closer to the heat sink than the one or more outlet channel is to the heat sink.

11. The print curing apparatus according to claim 1, wherein a pressure drop across the length of the print curing apparatus is negligible.

12. The print curing apparatus according to claim 1, wherein the at least one water-cooled holder comprises an inner block and two outer blocks, and wherein each block has a length substantially identical to the length of the print curing apparatus.

13. The print curing apparatus according to claim 12, wherein each of the inner and two outer blocks comprises at least two semi-cylindrical recesses each having a length that is substantially perpendicular to the length of the apparatus, wherein the inner block mates with each of the outer blocks to form the water-cooled holder having cylindrical openings therethrough, wherein the radius of each semi-cylindrical recess is equal to or less than the radius of the outer wall of a heat pipe held therein, or wherein the diameter of each cylindrical opening is equal to or less that the diameter of the outer wall of the heat pipe held therein.

14. The print curing apparatus according to claim 1, further comprising a plurality of LED modules, wherein each LED module is positioned adjacent to at least one cooling module, and wherein each cooling module comprises three heat pipes for each LED module.

Description

DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0079] The invention will now be described by way of example with reference to the accompanying drawings, in which:

[0080] FIG. 1 is a cross-sectional view through a cooling module of an LED print curing apparatus constructed according to the present invention;

[0081] FIG. 2 shows a perspective view from the side of a print curing apparatus, incorporating a plurality of cooling modules, in accordance with the present invention;

[0082] FIG. 3 shows an exploded perspective view of the print curing apparatus, showing the outer and central securing blocks of the water-cooled holder partially separated from the heat pipes;

[0083] FIG. 4 shows a cross-section through the water-cooled holder; and

[0084] FIG. 5 shows an exploded cross-sectional view through the outer and central blocks of the water-cooled holder with the heat pipes partially removed from the central block.

DETAILED DESCRIPTION OF THE INVENTION

[0085] Referring to FIG. 1 and FIG. 2, the present invention relates to a print curing apparatus 1 comprising an array of LED modules 8 (not shown), wherein each LED module 8 is a unit containing one or more LEDs. In use, each LED is a radiation source for curing print or a coating on a substrate (not shown). It is understood that the LED modules 8 form a linear radiation source to direct radiation continually onto a substrate during curing. That is, there are no additional components between the LED modules 8 so that the radiation source is a continual, uninterrupted array along the apparatus. The LED modules 8 comprise boards that rest on a heat sink sandwiching a thermal compound therebetween. Electrical connections are made by terminals from the side to the top of the LED board.

[0086] In use, the LEDs are arranged to emit radiation from an outer, substrate-facing side of the LED modules 8 through a curing window onto a substrate (not shown) to be cured. In alternative embodiments of the present invention, the curing window comprises a lens or reflector. The print curing apparatus 1 is an elongate shape and can be fitted directly onto a machine, or is a slideable cassette which, in use, is slideable into a housing. When inserted into the housing, the LED modules form a solid radiation emitting face.

[0087] Referring to FIGS. 1, 2 and 3, in use, heat is transferred away from the inner face of the LED modules 8 by one or more cooling modules 13, wherein heat is transferred from heat pipes 7 into one or more water-cooled holders 15.

[0088] In a preferred embodiment shown in FIG. 3, the cooling module 13, comprising the heat pipes 7 fitted into a respective water-cooled holder 15, which is an elongate body along substantially the full length of the radiation emitting face of the LED modules 8. Each heat pipe 7 is directly held by the water-cooled holder 15 to improve thermal contact therebetween.

[0089] In an optional embodiment of the present invention, heat is transferred away from the LED modules by multiple cooling modules 13 (comprising heat pipes 7 sitting in water-cooled holders 15), which form an elongate body along substantially the full length of the radiation emitting face of the LED modules 8.

[0090] Referring to FIG. 3, the or each cooling module 13 comprises heat pipes 7, which fit into the water-cooled holder 15. In a preferred embodiment of the invention, the water-cooled holder 15 is an extrusion made from aluminium. As shown in FIG. 3, the water-cooled extrusion comprises a central, elongate block 15a and two outer, securing, elongate blocks 15b. In alternative embodiments of the present invention, the water-cooled extrusion 15 comprises two blocks into which the heat pipes 7 are fitted.

[0091] Each of the central block 15a and the outer, securing blocks 15b have semi-cylindrical recesses 20; that is, the recesses 20 have the shape of a longitudinal half of a cylinder. The central block 15a has multiple semi-cylindrical recesses 20 in each of the longer, outer-facing sides. Each of the outer, securing blocks 15b has multiple semi-cylindrical recesses 20 in one of its longer sides, which is facing inwardly. In use, the central block 15a mates with the two outer securing blocks 15b, whereby the multiple semi-cylindrical recesses 20 each hold a heat pipe 7 in place. The securing blocks 15a, 15b secure the heat pipes in a tight clamping arrangement, or by a push-fit connection. The semi-cylindrical recesses 20 are undersizedi.e. each have an inner radius that is less than the outer radius of the heat pipe 7. This ensures that each heat pipe 7 is firmly held in place and that the heat transfer is as efficient as possible from each heat pipe 7 to the surrounding water-cooled block/holder 15. Furthermore, the arrangement of the present invention allows for the cooling modules 13, including the LED modules 8 and heat sink 2, to be built off-site and conveniently installed on site; for example, during an on-site repair without requiring on-site replacement of individual LED modules.

[0092] In a preferred embodiment, as shown in FIG. 3, the cooling module 13 comprises a single elongate water-cooled holder 15 that comprises three securing blocks 15a, 15b along the length of the apparatus. Alternatively, the cooling module 13 comprises two securing blocks. To set up the cooling module 13, multiple modular heat sinks 2, each having three heat pipes 7 attached thereto, are each positioned along the block so that each heat pipe is received in a semi-cylindrical recess 20 in the central, elongate block 15a. The outer, securing blocks 15b are then brought into engagement with the central block 15a so that each heat pipe is also fitted within a respective semi-cylindrical recess 20 in an outer block 15b to clamp the heat pipes 7 in place. In an alternative embodiment of the present invention, the inner and outer securing blocks 15a, 15b are brought together and individual cooling modules are attached to the water-cooled holder 15 by inserting heat pipes into the cylindrical recesses of the water-cooled holder 15.

[0093] Referring to FIG. 3, the central block 15a and two outer securing blocks 15b are clamped or push-fit to form a removable pinch grip and hold the multiple heat pipes 7 in place, whilst allowing for removal of the heat pipes 7 for repair and replacement, as required. The holder 15 is secured in place around the heat pipes by screws. For known devices, the heat pipes 7 are spaced at increments of 2.5 cm for a range of lengths from 2.5 cm to 250 cm.

[0094] Referring to FIGS. 1, 3, 4 and 5, each of the three blocks 15a, 15b, which form the water-cooled holder 15, further comprises an inlet channel 17 and an outlet channel 19. The inlet and outlet channels 17, 19 are substantially parallel to the length of the apparatus 1. In a modular system, comprising multiple water-cooled blocks 15, the inlet and outlet channels 17, 19 of each block are connected to form channels 17, 19 that run along the full length of the apparatus 1.

[0095] Referring to the preferred embodiment of FIG. 3, in use, a source of cooled water is fed into the inlet channels 17, such that cooled water flows along the length of the apparatus 1 to carry heat away from the water-cooled block 15, which is carrying heat away from the heat pipes 7. In use, heated water is carried away from the apparatus through outlet channels 19. The heated water output from the apparatus 1 is cooled before it is re-fed back to the inlet channels 17. The water flowing through the water-cooled holder 15 does not come into direct contact with the heat pipes 7, the heat sink 2, or the LED modules 8.

[0096] Referring to FIGS. 1, 2 and 3, the heat pipes 7 of the present invention use known heat pipe technology to take up heat generated by the LED modules 8. In use, when the apparatus 1 is switched on and the LEDs are radiating to cure a substrate, heat generated by the LEDs is transferred away from the rear, inner face of each LED module 8 to a copper heat sink 2. Heat is carried away from the LEDs by the heat pipe/s 7 and is then carried away from the heat pipes 7 by the respective water-cooled holder 15. On heating, the liquid held within the core of the heat pipe 7 is vaporised and the heat is carried away before the liquid re-condenses and the wick transports the liquid back to the base of the heat pipe 7. Heat is rapidly transferred from the LED modules to the heat pipes 7 and to the water-cooled holder 15.

[0097] The heat pipes 7 transfer heat away from the rear, inner face of the LED modules 8 over the length of each of the heat pipes 7 to the water-cooled holder 15. The arrangement of multiple heat pipes 7, wherein each heat pipe 7 is substantially U-shaped has been found to be particularly advantageous in improving the efficiency of heat transfer away from the LED array. Referring to FIG. 4, the U-shaped heat pipes 7 of the present invention each have a curved base section adjacent to the LED modules 8 and the upstanding sections of the heat pipes 7 are substantially perpendicular to the length of the apparatus 1.

[0098] The embodiment described above comprises water inlet channels 17 that are adjacent to the evaporator section 7a of the heat pipes, which are closest to the heat-generating LED modules 8 and the heat sink 2. The water inlet channels 17 do not directly contact the heat pipe 7, the LED modules 8, or the heat sink 2. The water outlet channels 19 are adjacent to the condenser section 7b of the heat pipes, which are furthest from the LED modules 8. It has been found that the efficiency of cooling is also improved by having two water-cooled inlet channels 17 adjacent to each of the upstanding sections of the heat pipe 7, such that each heat pipe 7 is effectively cooled around most of its outer surface.

[0099] The present invention is arranged such that the coldest areas of the water-cooled holder 15, which are adjacent to the water inlet channel 17, are near to the hottest part of the heat pipe 7 to maximise the rate of condensation and increase the rate of heat flow away from the LEDs 8 to be carried away by the water. There is a thermal gradient along the condenser section 7b, from the coolest area furthest from the LED modules 8 to the hottest area closest to the LED modules 8.

[0100] The print curing apparatus 1 comprises a plurality of LED modules 8, wherein each of the LED modules 8 is adjacent to three heat pipes 7. The multiple heat pipes 7 are clamped in position by the three elongate blocks 15a, 15b of the water-cooled holder 15. In alternative embodiments of the present invention, it is envisaged that the water-cooled holder 15 is also modular; comprising multiple central elongate blocks 15a and multiple outer securing blocks 15b. A modular water-cooled holder 15 is secured together by securing means, such as flanges and O-rings.

[0101] Referring to FIGS. 3, 4 and 5, when the water-cooled holder 15 is positioned around the heat pipes 7, the heat pipes 7 are held within the cylindrical recesses 20 formed by the mating parts 15a, 15b of the water-cooled holder 15. The water-cooled holder 15 when fitted around the heat pipes 7 further comprises three water inlet channels 17, which are formed in the lower part of the holder 15 and are substantially parallel to the longitudinal axis of the apparatus 1. Three return/outlet water channels 19 are formed in the upper part of the holder 15 and are also substantially parallel to the longitudinal axis of the apparatus 1.

[0102] In alternative embodiments, there may be two or more inlet and outlet channels. It is understood that the lower part of the holder 15 is the part closest to the LED modules 8 and heat sink 2; the upper part of the holder 15 is the part furthest from the LED modules 8 and the heat sink 2; and the longitudinal axis of the apparatus 1 is the axis parallel to longest length of the apparatus 11. In a preferred embodiment of the present invention, the water-cooled holder 15 forms a slideable cassette, which is slideably inserted into and removable from the print curing apparatus 1 in a direction parallel to the longest length of the apparatus. In alternative embodiments of the present invention, the water-cooled holder 15 is a fixed component of the print curing apparatus 1 and is not a slideable cassette.

[0103] In alternative embodiments of the present invention, the water-cooled holder 15 may comprise two water-flow channels, through which water flows. In this embodiment, water is supplied at one end of both water-flow channels and is output at the opposing end of each channel.

[0104] As shown in FIGS. 1, 3, 4, and 5, in a preferred embodiment of the present invention, each channel 17, 19 is an elongate cuboidal shape and comprises two opposing, finned walls. The cooling effect of the water-cooled holder 15 is improved by increasing the surface area for heat transfer to and from the walls of the water inlet and outlet channels 17, 19; that is, by providing finned walls or projections from the walls which protrude into the channel 17, 19 through which water flows.

[0105] Each inlet and outlet channel 17, 19 is between a first end plate and a second end plate. The first end plate is connected to a source of chilled water (not shown) and an outlet for heated water (not shown).

[0106] In use, cold water enters the apparatus 1 through inlets in the first end plate and flows along each of the three inlet channels 17 through the lower part of the water-cooled holder 15. The chilled water is heated by the heat generated by the LED modules 8, which is carried away from the LED modules 8 by the heat pipes 7, with the heat pipes 7 rapidly drawing heat away from the LED modules 8 and the heat sink 2. When the cold water has passed along the full length of the inlet channels 17 and so, along the full length of the apparatus 11 to the second end plate, the heated water returns through the three return channels 19 and is removed from the system through outlets in the first end plate.

[0107] Referring to FIG. 3, to access the heat pipes 7 for maintenance or repair, the screws securing the water-cooled holder 15 around the heat pipes 7 are removed. The connection between the outer securing blocks 15b can then be separated from the central block 15a. The water flow through the water-cooled holder 15 can easily be disconnected and there is no risk of disturbing water flow when accessing the heat pipes 7, because water flow is separated and fully contained within the water-cooled holder 15.

[0108] Within this specification, the term about means plus or minus 20%; more preferably, plus or minus 10%; even more preferably, plus or minus 5%; most preferably, plus or minus 2%.

[0109] The above described embodiment has been given by way of example only, and the skilled reader will naturally appreciate that many variations could be made thereto without departing from the scope of the claims.