Drying and gas or vapor contact with solids – Material treated by electromagnetic energy – Ultraviolet energy
Patent
1993-03-09
1994-09-06
Bennet, Henry A.
Drying and gas or vapor contact with solids
Material treated by electromagnetic energy
Ultraviolet energy
34 60, 34611, F26B 328
Patent
active
053436296
DESCRIPTION:
BRIEF SUMMARY
This invention relates to U.V. dryers.
U.V. dryers are used widely in the printing industry for drying photopolymerisable inks. In conventional ultra-violet dryers, the U.V. lamp is disposed transversely to the direction of feed of the printed web or sheets and the U.V. lamp and its housing are conventionally cooled with a combination of air and water. Typically, the lamp reflector is provided with a water jacket through which water is passed, and a separate feed of compressed air is provided to provide a stream of cooling air over the lamp. While water cooling is effective, this is achieved at high cost and imposes further disadvantage of increased weight and complexity. Also, the cooling is relatively inflexible which results in difficulties in maintaining lamp stability at low powers.
According to one aspect of the present invention there is provided an ultra-violet, air-cooled dryer for drying or curing printing inks and other photopolymerisable coatings or layers, wherein a U.V. lamp is supported in the reflector housing for directing U.V. light onto printed sheets or webs, said dryer including air cooling means comprising outlets for pressurised air adapted to bathe said lamp in a stream of cooling air and a tubular heat barrier disposed between the lamp and the path of said sheets or web, said barrier being relatively transparent to U.V. light, but restricting passage of heat by virtue of passing a stream of air along said tubular barrier.
Preferably, the heat barrier comprises one or more tubes which extend longitudinally of the lamp and are connected to a source of filtered air so that cooling air is passed axially along the tube or tubes. The tubes may be manufactured from quartz, which is relatively transparent to U.V. light. Surprisingly, the passage of cooling air axially along the tube or tubes cuts down the transmission of heat across said tubular barrier by a substantial proportion. The outlets for providing the stream of air over the lamp are preferably incorporated in the reflector housing by incorporating a conduit extending longitudinally of the lamp in the reflector adjacent to the lamp, and forming said conduit with axially spaced slots or holes so as to direct a plurality of air streams transversely of the lamp.
Additional passageways are preferably provided for conducting air over the surface of the reflector remote from the lamp and the back surface of the reflector is preferably provided with fins to increase the heat transmission from the reflector to the air stream.
In order to maintain cooling to the web or sheets fed past the U.V. dryer, additional conduit or conduits may be formed in the outer lip of the reflector so as to direct a stream of air onto the sheets or webs which pass beneath the dryer.
An air stream or streams over the reflector and through the tubular heat barrier is preferably induced by applying suction to a housing for the lamp and conducting the cooling air or other gas over and through the components to be cooled. By providing suitable baffles and air passages, higher air pressures can be developed in some parts of the housing and relatively lower pressures in others. This feature can be taken advantage of by, for example, inducing a lower pressure below a table over which the web or printed sheets are passed, thus controlling the web or sheets and preventing curling during drying.
Use of air streams to cool both the lamp and reflector as well as to reduce the infra-red component reflected towards the web by passage through the tubular heat barrier has a further advantage. This is that the ozone which is inevitably produced by the lamp is rapidly diluted in the cooling stream well below safe working limits. In contrast, in conventional dryers in which air cooling is generally confined to the lamp, constant monitoring of the ozone level is necessary.
The infra-red content of the radiation which passes through the tubular heat barrier can be further reduced by applying an IR filter to the surface of the tubular heat barrier. A thin dielectric film may be appl
REFERENCES:
patent: 5117562 (1992-06-01), Dulay et al.
Bennet Henry A.
G.E.W. (EC) Limited
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