Drying and gas or vapor contact with solids – Material treated by electromagnetic energy – Infrared energy
Patent
1999-04-02
2000-03-14
Gravini, Stephen
Drying and gas or vapor contact with solids
Material treated by electromagnetic energy
Infrared energy
34278, 1014241, 101488, F26B 334
Patent
active
060355484
DESCRIPTION:
BRIEF SUMMARY
This invention relates to UV dryers, in particular, for use with high speed printing machines.
UV dryers are frequently used in the printing industry for drying photopolymerisable inks. When used with high speed printing machines, a lamp or bank of lamps having a high UV output is required, in order to cure the inks during the short time when the sheets are passing the mouth of the dryer. Unfortunately, UV lamps also emit a substantial amount of heat and the larger or longer the lamp, the greater the amount of waste heat which needs to be disposed of. The present invention seeks to provide a solution to this problem.
U.S. Pat. No. 4,048,490 describes a UV dryer having a conventional parabolic reflector. A plurality of optically flat dichroic filters are mounted beyond the parabolic reflector and are arranged in conjunction with a reflective cusp to ensure that light rays from the UV lamp are reflected from at least two surfaces before reaching the surface to be irradiated.
U.S. Pat. No. 4,070,499 describes an array of UV lamps mounted within adjoining elliptical reflectors. The reflectors may be cooled by coolant media circulated through tubes in contact with the back surfaces of the reflectors.
EP-A-0134591 describes a UV dryer in which a lamp is mounted in a parabolic reflector and a cooling air flow is directed between the reflector surface and the lamp envelope.
According to one aspect of the present invention, there is provided a UV dryer for drying photopolymerisable ink on a web wherein a UV lamp is supported within a reflector housing, said housing including a reflector body having curved reflector surfaces disposed to reflect UV light onto a web, characterised in that each of the reflector surfaces comprises a thin, flexible heat conductive metal strip, bearing a dichroic film on one side which is adjacent the lamp and wherein the strip is deformed so that the opposite side is in close contact with said reflector body, said dichroic film exhibiting a high degree of transmission towards infra-red radiation and a high degree of reflection towards UV radiation and said reflector body having other surfaces spaced from said reflector surfaces and cooling means are provided for passing a cooling medium over said other surfaces to cool the reflector body.
The reflective surface of the reflector comprises a thin, flexible, polished metal strip of heat-conductive material e.g. stainless steel, having one surface disposed for reflecting UV light towards the printed sheets or web, and the other in close contact with the reflector housing. The reflector housing may be air or water cooled and, because the dicroic film is transmissive towards infra-red radiation, the underlying metal strip becomes hot and heat is conducted from the strip of sheet material to the reflector body member. By arranging for air-cooling fins or water-cooling passages to be positioned close to the surface of the reflective body member which is in close contact with the flexible substrate, efficient transfer of heat to the cooling medium is achieved. As a further aid to heat transfer, a heat-conductive paste may be applied to the back surface of the strip. The strip is fastened to the body member in such a way as to ensure close contact of the back surface of the strip with the corresponding surface of the body member. Where a paste is present, the fastening device ensures that the paste is squeezed between the contacting surfaces.
The provision of a reflector which is a thin flexible sheet material is advantageous because there are difficulties in coating dichroic films onto curved surfaces. In accordance with this invention, the dichroic film is coated onto a flat metal sheet which is then deformed to take up the same curvature as the reflector body member.
According to another feature of the invention, the UV dryer is preferably cooled using water. In one embodiment of the invention the UV dryer includes movable shutters to close off the reflector mouth when the web is stationary. Under such conditions, the shutters can become extrem
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GEW (EC) Limited
Gravini Stephen
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