General information about photopolymer.

An Ultra Violet exposure unit is used to expose a light sensitive emulsion to Ultra Violet light. This particular emulsion is a photopolymer. A photopolymer is a plastic of which some properties change if exposed to light. An unexposed emulsion consists of "monomer" molecules without much cohesion. As soon as these monomers are exposed to light, they change into polymers which means that the molucules form links and chains with other molecules. A "monomer" molecule can be washed out easily with with a water/soda solution, while a "polymer" molecule appears to us as "hardened out" because of the links and chains it forms with other molecules, hence it cannot be washed out to easily with a water/soda solution.

The light sensitive emulsion can be applied to a plate in various ways;

• A liquid emulsion can be applied to a plate with an aerosol spray or with a brush. Another way is the use of a turntable; a drop of liquid is dropped on to the middle of the plate on the turntable. The centrifugal forces will distribute the liquid evenly over the plate. In this manner a very thin and even layer kan be accomplished.
• The light sensitive emulsion is also available as a film, on a roll. The sensitive layer is very fragile and is therefore protected on both sides with a transparant mylar layer. This film can be applied to the plate in different ways. (see instructions for ImagOn, ImagOn Ultra, Riston and Puretch).
• Also available are plates with a ready made layer of photopolymer on top (Toray, Solar plates). These plates are used in commercial (relief)printing as an alternative for the old lead clichés. Because of the thickness of the layer (appr. 0,5mm) these plates mainly used for relief printing. (Dianne Longley's "Printmaking with Photopolymer Plates" or Dan Welden's book "Printmaking in the Sun").

The sort of material to be used for the support of the polymer plate depends upon the final purpose. It is obvious that the support must be able to resist the pressure of an etching press. This already limits the choise to metal and some plastics. The "Toray plates" or "Solar plates" for example have a support made of a steel sheet of a few tenth's of a mm thickness.

• If a film can be laminated onto a plate, it is very important to realize this this allows the plate to be handled and printed like any other intaglio plate. Photopolymer films come in several thicknesses; For example the ImagOn (Ultra) films are about 50 microns (0,05mm) thick. This thickness makes these films very suitable for the "Non-etch-techniques".
  In a "non-etch-technique" the film is exposed in the contact frame through a transparant sheet of plastic that carries the image. In the next step the polymer is washed out in a water/soda solution. The unexposed areas in will be washed out and show up as grooves in the film. The exposed areas will not be washed out and remain intact. After drying the plate in a drying cabinet the plate can be inked and printed. After inking and wiping the "grooves" only contain ink, the same way as in "traditional" intaglio. The difference here is that the grooves are only present in the layer of photopolymer and not in the metal plate beneath it. The metal plate is therefore used only as support in order to keep the film and hence the image together.
• If the emulsion is applied on to the plate as a liquid, this results normally in a very thin layer. (5-20 micron). Some photopolymer films are also quite thin (Puretch or Blue Shot). If one uses these thin layers of film for a "non-etch-technique" there will be a problem when printing a dark black. The film is not thick enough to contain, when etched, enough ink in order to print a dark black. These thin layers are not to be used for non-etching-techniques. They are however very suitable for "etching-techniques". In these techniques the polymer is used as a resist. The preparation and exposure are more or less the same as with a "non-etch-technique" but the development times in the soda bath are longer. The unexposed area's are completely washed off from the plate. The exposed areas are hard and will remain intact. Next the plate is etched (in iron-per-chloride, ferric-chloride). The grooves and dots will not be created in the film, but in the copper or zinc plate. After etching the plate is cleaned in a more concentrated bath of water and soda. In this bath also the hardened polymer will also dissolve after about 10 minutes. The plate can now be inked and printed in the normal way. This technique also allows you to add to the plate other techniques like dry point or engraving. In the "etch-techniques" the support of the film becomes the forme to print from.

Use of the UV exposure unit

1. Use the exposure unit only in areas where direct daylight has no access. Daylight contains UV-light and can influence the photopolymer. Low intensity normal tube light is no problem.
2. Insert the plug into the mains. The UV-light will start, but first with a low intensity. After a few minutes full intensity is reached. Therefore, the lamp should be kept on during a session. The sliding shutter must be used to start and stop the exposure.
3. Open the glass cover of the contact frame (or vacuum-frame). Place the plate in the contact frame with the sensitive layer pointing upwards.
4. The transparant plastic sheet carrying the image is put on top of the plate with the image side pointing downwards. Close now the contact frame. It is very important that there is no space between the image on the sheet and the light sensitive layer. If there is space, it will probably lead to a fuzzy print.
5. Record the time. Decide when the shutter must be opened and closed. The exposure time depends upon many things but will probably be around 2 or 3 minutes. Carry out the exposure.
6. After exposure the contact frame is openened and the plate is taken out. The image can be seen vaguely on the film (ghost-image). The plate is now ready to be developed in the soda solution.

Points of attention:

• At this time only the contact frame of 25x30cm (10"x12") is available and comes with the exposure unit. For some printmakers this size is good enough, especially while learning to work with these techniques. For others however, bigger sizes are needed. Polymetaal will develop in the future a contact frame of 50x60cm. It is possible that it will have to become a vacuumframe. Check this page regularly to find out recent developments.
• The distance between the contact frame and the lamp is adjustable; therefore the smaller the print the shorter the distance as well as a shorter the exposure time. If one needs the full size of 50x60cm, the contact frame must be in the lowest position.