Radiant energy – Irradiation of objects or material
Patent
1997-09-15
1999-08-31
Anderson, Bruce C.
Radiant energy
Irradiation of objects or material
250504R, G01J 100
Patent
active
059456809
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method for activating photoinitiators in photosensitive substrates like for instance printing inks, lacquers, and glue which set by radiation with UV light, and in which the photosensitive substrate and a light unit are moved relative to each other at a predetermined rate, the light unit comprising a UV light source placed in a lamp housing with a reflector for directing the UV light towards the substrate through an outlet opening, and in which the light emission is controlled by means of a control unit emitting a signal to an electronic ballast for the UV light source depending on the mutual travel speed between the light unit and the substrate and other predetermined parameters. The invention also comprises an apparatus for curing such substrates by use of the method.
Varnishes and lacquers which set by means of photoinitiators activated by UV light are used within many fields. A common feature for all the ways of using UV light for activating photoinitiators is that the quality of the curing depends on the light intensity being sufficiently strong and that light dosage--power multiplied with time per unit area, measured in joule per cm.sup.2 --is sufficiently strong.
The latest technology within the field of printing machines, which is an important field of use for the present invention, has up till now been limited to the mounting of simple lamp housings with reflectors and powerful UV lamps on the printing machine, so that the paper web after having been passed by a printing unit passes under a lamp housing with constant light intensity. As the speed of the paper web has to be high in order to make the printing machine pay off in an economically justifiable way, very powerful UV lights or several lamps after each other are used in order to obtain a sufficient thorough curing of the printing ink and to make it so dry, that the paper web may be rolled without any setoff of the colour. In this connection problems arise in respect of high temperature on the paper with subsequent thermal expansion, which gives inaccuracies in case of several printing proceedings following each other with different colours in a number of printing machines, or a blackcolouring of thermally sensitive paper which is used in thermoprinters.
In the new lamp constructions measures have been taken to remove some of the heat radiation, as only the UV part of the light is actively used by the photoinitiators. U.S. Pat. No. 4,563,589 discloses a method for removal of infrared radiation by a cold light mirror and a glass tube with an air based cooling system. Other systems are known, in which part of the infrared heat radiation is absorbed by the reflectors which are cooled strongly by air and water.
It is admittedly possible to increase the amount of photoinitiators in the printing ink to forward the curing process with a given light dosage. However, the photoinitiators shade one another, which primarily improves the curing in the surface, whereas it becomes worse in the depth, where the light intensity is reduced. The price of photoinitiators is moreover high compared with traditional alternatives like for instance printing inks based on ethyl alcohol. The use of printing inks based on ethyl alcohol, which inks are dried by means of hot air, does, however, entail other drawbacks, as they cause considerable environmental problems on account of the big amount of solubilizing agent released. A corresponding environmental problem does not arise by use of printing inks which are cured by means of UV light.
Environmental problems in form of too big amounts of ozone may, however, arise by using UV light, in particular where air cooled lamp housings are used, in which part of the oxygen of the air is transformed into ozone by means of the most short-waved part of the UV light with a wave length of 185 nm.
It has been realized that the photoinitiators in order to work effectively, have to receive UV light of an intensity which exceeds a certain critical level during the passage of the lamp housing. It is kn
REFERENCES:
patent: 3733709 (1973-05-01), Bassemir et al.
patent: 4033263 (1977-07-01), Richmond
patent: 4048490 (1977-09-01), Troue
patent: 4055769 (1977-10-01), Sander
patent: 4084490 (1978-04-01), Doherty
patent: 4563589 (1986-01-01), Scheffer
patent: 4644899 (1987-02-01), Glaus
patent: 4798960 (1989-01-01), Keller
patent: 5051666 (1991-09-01), Jensen
patent: 5150253 (1992-09-01), Watanuki
patent: 5163750 (1992-11-01), Natori
patent: 5204534 (1993-04-01), Dubuit
Anderson Bruce C.
Niels Lang Mathiesen and Knud Andreasen
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