Photopolymer Plates

What are Photopolmer Plates?
Photopolymer is photosensitive material in sheet form that is exposed to UV lights through a negative film. The light shines through the clear sections of the film and hardens the polymer. The plate is washed out with water. The exposed areas are left to form the relief and the unexposed is washed away. The plate is dried and exposed to UV one
more time to complete the process. The plate image and text will be in reverse so when mounted onto the base system in the press, it will be inked and print right-reading onto the paper. The polymer of a plate is connected either to a steel-backed plate (which then connects to a magnetic base) or to double-stick adhesive (which then connects to
a non-magnetic base like the Boxcar Base).

Making a Film
To create a photopolymer plate, you’ll want to work with images comprised of linework or from halftone. It’s not possible to print a gradient or greyscale if not made up of lines or dots. You’ll need to create a negative film for exposing your image onto the plate. There are several ways to do this:

SERVICE BUREAU

You can use a line drawing, or halftone image and have a film made at a service bureau. One local bureau is Media Fusion. You can upload your order on line from their website: http://www.mfiprepress.com/

CREATE YOUR OWN FILM

You can create your own film using either Pictorico, specialized film for the Epson printer, or from doubled up acetate laser-printed at Alphagraphics. If you go this route you’ll want to use the light table to line up the two images and carefully tape them together on the edges.

WORKING DIRECTLY ONTO ACETATE OR FILM MATERIAL

You can also work directly onto film material using ink or paint that is opaque enough to block out the UV light. Remember to invert your image and reverse it so the emulsion side of the film is right-reading, which goes face down on the plate, and non-emulsion side is reversed.

Halftone Image Guidelines

Open image in Photoshop.
Go to image, mode, greyscale.
Go to Image, adjustments, brightness/contrast. (you want a strong black and white image)
Go to image, mode, select bitmap
Output: 300 dpi, select halftone screen
Frequency: Play with it until it looks good to you. Probably not above 40...
Angle: 45
Shape: round, or other if you want
Save. You can scale this up now to any size.

Exposing the Plate
The exposure time depends on the type of image. If it’s a bold graphic with large solid areas, it will take less time than if it’s an image made up of delicate hair lines. It’s a good idea to do a test strip using a small piece of photopolymer plate through a critical area of your image, to make sure your exposure time is right before investing in a larger piece. The times tend to run from 1-3 minutes. It can be useful to use a Stauffer Scale, a test strip for exposing and seeing a greyscale range.