Exposure equipment is used to expose photopolymer plates or films to UV-light. Photopolymer will harden out when exposed to UV-light.
This technique is used in various printing techniques; such as screen printing, intaglio printing and relief printing, but also in the electronics industry for making printed circuit boards.
Traditionally, large exposure devices have a UV lamp and a vacuum system. They are still found in some printshops.
There is a discussion going on about the light source. Some claim that it is necessarily a "point of light". Others claim that fluorescent tubes with UV work just as well. We have tested one and the other and there appeared to be no significant difference between "one-lamp" (such as the Osram lamp) and tubes with UV light. In the circuit board industry technicians use UV-tube systems, with great precision, so it is likely that UV-tubes do the job as well as "point light sources".
Then there is also the discussion about the vacuum system. The vacuum system must ensure that the image carrier (transparent) is in direct contact with the photopolymer, in order to make the image transfer as accurately as possible. A vacuum system is well suited for that, but makes the system costly. For small sizes, a layer of foam can also be used. In these systems the foam is sitting in the lid (cover) of the exposure unit. If the image carrier and the photopolymer are in direct contact, without air layers, then it is alright, wether that is achieved with a foam layer or with a vacuum.
In the past, the HPR-lamp (with ballast) was very popular, especially for screenprinting. Unfortunately, this lamp is no longer available in good quality The Osram lamp (tanning lamp) is a reasonable alternative.
Henrik Boegh (Danish photographer-printmaker) developed a DIY (do it yourself) exposure cabinet based on an Ikea kitchen cabinet, a vacuum pump (old compressor from a fridge), a homemade vacuum frame and a lamp in the middle. Everyone is free to make such a device, but it will be clear that this equipment does not meet safety standards.
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