This invention relates to a cooling system for ink curing apparatus.

Ink curing apparatus comprising a housing containing a lamp partially surrounded by reflectors to direct UV light onto a substrate to cure ink are well known. The lamps used in ink curing produce UV radiation and infra-red radiation. Such apparatus requires highly efficient cooling systems due to the intense heat that is emitted from the lamp. Without sufficient cooling the life of the ink curing lamps is significantly reduced and the running parameters of the apparatus are more difficult to control.

It is know to use air circulation to cool the components of an ink curing apparatus. In such air-cooled systems, redundant hot air from the lamp is removed from the apparatus and passed through a heat exchanger built within a large separate cooling unit. It is also known to utilise water cooling systems that require a network of pipes, the apparatus requiring multiple inlets and outlets to provide a flow of water across the components of the apparatus. Such a water-cooled system is described in the Applicant's earlier British patent application no. GB0624086.5, wherein water-cooling is used in combination with a fan to direct air around the apparatus. Existing water-cooled systems also use large external heat exchangers or "chillers" to exhaust air which has been heated by the ink curing apparatus.

It has been found that even with the existing combination of water and air-cooling, the power level of the lamps used in UV print curing is limited by the amount of heat produced. Existing external heat exchangers exhaust a large volume of hot air to the atmosphere, are complex to set up and take up a significant amount of space. The present invention seeks to provide an improved cooling system that is fully self-contained within a single housing and which eliminates the need for an air exhaust from the system.

Accordingly, in one aspect there is provided an ink curing apparatus having a fully self-contained cooling system, the apparatus comprising a housing with two interconnected chambers, the first chamber housing a UV light source and the second chamber housing a water-cooled heat exchanging means, wherein a fan is provided at at least one end of the housing to circulate air over water-cooled surfaces between the UV light source and the heat exchanging means.

By water cooling the heat exchanger the air can be cooled and reused within the system without the need to exhaust any air from the apparatus.

Preferably, the heat exchanging means comprises one or more fins.

More preferably, the heat exchanging means comprises a series of fins extending radially from the centre of the second chamber.

Preferably, each fin is serrated.

A series of serrated fins provides the maximum possible surface area in contact with the heated air, which is circulating between the lamp and the heat exchanging means, and so provides maximum efficiency of heat exchange.

Preferably, the first and second chambers are connected by at least one duct.

Preferably, the fan is provided at one end of the housing. Optionally, a fan is provided at both ends of the housing.

For longer lamp housings, it has been found that improved cooling is provided by two fans, wherein each fan directs air from an end of the housing towards the centre.

Preferably, the cooled surfaces include surfaces of at least one reflector which at least partially surrounds the lamp.

Preferably, the water-cooled surfaces are cooled by water channelled through one or more pipes extending along the length of the housing.

Optionally, the or each pipe includes inner and outer discrete channels.

Preferably, the outer wall of the second chamber comprises at least one cavity.

By providing a "double-skinned" wall, the outer wall of the second chamber is cool enough for a user to touch without risk of injury.

One embodiment of the present invention will now be described by way of example with reference to the accompanying drawing, which is a schematic cross-sectional view of an ink curing apparatus incorporating a cooling system, constructed in accordance with the present invention.

The apparatus comprises a single housing 10 with an upper chamber 14 and a lower chamber 12. The lower chamber 12 houses at its lower end a UV lamp 16, which is partially surrounded by reflectors 18, 20. In use, a substrate 22 which carries ink for curing/drying is transported through the apparatus directly beneath the lamp 16. When the reflectors 18, 20 are in an open position, UV light is directed onto the substrate 22 for a period of time sufficient to dry/cure the ink on the substrate 22.

The ancillary parts of the apparatus within the lower chamber 12, including the surfaces of each reflector 18, 20 are water-cooled. Cold water enters the lower chamber 12 through a first end plate and is directed along an inlet pipe 24, which runs parallel to the longitudinal axis of the lamp 16. The cold water is directed past each reflector 18, 20 to the second end plate of the lower chamber 12. The water, heated by the surface of each reflector 18, 20 is directed through the second end plate and returned along an outlet pipe 26 to an output in the first end plate.

Alternatively the water-cooling of the lower chamber 12 can be achieved by means of a "parallel system". In such a system the water pipes include inner and outer channels. In use, cold water is directed into the apparatus through the inner channels of the pipes before being reversed such that the water, once hot, is directed out of the apparatus via the outer channels of the pipes.

The upper chamber 14 houses a heat exchanger system, which is connected to the lower chamber 12 housing the lamp 16 by a series of ducts 28. The upper chamber 14 has a double thickness wall around its periphery with a cavity between the inner and outer walls, such that only the inner wall is heated by the air passing through the chamber 14. The heat exchanger system comprises a fan (not shown) at one or both ends of the chamber 14. If a single fan is used and housed at one end of the housing 10, then air will be directed to the opposite end of the housing 10. If a fan is used at each end of the housing 10, air will be directed from each end of the housing 10 towards the centre of the housing 10. A series of substantially radial fins 30 are extruded within the upper chamber 14 and run along the length of the upper chamber 14. The fins 30 are serrated and extend radially outwards from at least two pipes 32, 34. The two pipes comprise an inlet pipe 32 and an outlet pipe 34 which are centrally positioned and run parallel to the length of the heat exchanger chamber 14.

In use, chilled water is passed along the inlet pipe 32 at a predetermined temperature. The fan at one or each end of the housing 10 directs air over the UV lamp 16 in the direction shown by the arrows and upwards to the heat exchanger chamber 14. The air, which has been heated by the lamp 16, passes along the length of the heat exchanger chamber 14 and as the fan directs the air along the length of the chamber 14 the air is also pulled towards the water-cooled centre of the heat exchanger along the radial fins 30. As the air passes along the heat exchanger, the temperature decreases progressively. The cooled air is then directed back into the lower chamber 12 through the open sections/ducts 28 in the upper chamber 14. The cooled air passes back along the length of the lower chamber 12 and is re-used to cool the lamp 16 and the reflectors 18, 20.

The upper chamber 14 is shown in this embodiment to be fitted directly above the lamp housing lower chamber 12. However, it is envisaged that the heat exchanger could be fitted to any of the walls of the lamp housing and could be remote from the lamp housing provided that the heat exchanger and housing are connected by a duct arrangement.

During use, the lamp 16 emits heat at around 750 ⁰ C. The UV heat is directed onto the substrate 22. A portion of the infra-red heat is absorbed into the surfaces of the reflectors 18, 20. The remaining infrared is drawn upwardly through the housing 10 via the fan. The path of the infra-red is shown by arrows in the Figure. On its way to the upper chamber 14, the air is drawn over the top surfaces of the reflectors 18, 20, which are kept cool via the water pipes 24, 26.

The apparatus is designed to direct the hot air from the lamp 16 over as many cooled surfaces of the ancillary components as possible. Hot air is known to travel from hot surfaces to cooled surfaces. Thus, by running chilled water along the centre of the heat exchanger chamber 14, the hot air is drawn over the maximum possible surface area of the cooled radial fins 30. Tests have shown that by the time air emitted from the lamp 16 has travelled over the cooled surfaces of the lower chamber 12 and the heat exchanger chamber 14 it has reduced significantly in temperature.

The present cooling system is an entirely closed arrangement whereby the air circulating around the apparatus is continuously re-used. Heat is exhausted from the system via the water outputted from the system.

It will be appreciated that the foregoing is merely exemplary of one embodiment of the cooling system according to the present invention and of just one form of ink curing apparatus with which it may be used. The skilled reader will understand that modifications can readily be made thereto without departing from the true scope of the invention.