Making pad printing plates in-house saves time and money and can be easily accomplished with the right machinery. Pad printing uses photo polymer plates, in which the image is etched into the surface by a photographic process. Numerous commercial machines are available with many timesaving and effort-reducing features, but plates can be successfully processed with an inexpensive standard platemaker. Homemade platemakers may suffice, but pad printing plates usually require the precise and repeatable control that commercial platemakers offer.
- Skill level:
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Things you need
- Film positive
- Photopolymer pad-printing plate, water-rinse type
- Halftone pad-printing plate screen
- Water basin
- Soft bristle brush
- Toaster oven or plate dryer
Cut the film positive to fit the plate size. Films must be right-reading (the image or letters are not reversed when viewed), emulsion side down, for proper image-to-plate contact. Laser vellum prints can be substituted for film, but they must be printed in reverse, so that when the vellum is placed on the plate, the toner is against the plate, and the image is right-reading.
Peel off the protective coating from the plate; inspect the plate for surface defects. The surface should be free of bubbles, scratches, indents or other imperfections. The protective cover serves no other purpose and may be recycled or discarded.
Place the film over the plate; place the plate and film into position on the platemaker. The film will be placed on the side from which the protective cover was removed, right-reading side up, Most small platemakers use a plate platform with hinged glass; more expensive platemakers use a vacuum blanket under the glass, and all air must be released before inserting the plate.
Close the glass over the plate, taking care that the film remains in position on the plate, and latch the glass (if equipped). If a vacuum frame is used, turn the vacuum on. On vacuum-frame units, the exposure will start automatically when the vacuum reaches proper draw (air) pressure.
Turn on the platemaker and expose the plate. Plate exposure times will vary according to the plate manufacturer, platemaker and film type, but they're usually about one minute for clear film to two minutes for vellum. Consult your platemaker and plate material user guide for specific information.
Remove the film positive from the plate and place a halftone exposure screen over the plate. Halftone exposure screens will vary according to the job type and will be from 70 to 300 lines. Halftone screens limit the depth of the plate etching, which regulates the amount of ink entering the etched area. Consult your plate manufacturer for recommendations on halftone screens.
Close the platemaker glass over the plate and halftone film; expose for an additional 40 seconds.
Remove the plate from the platemaker; set the halftone film aside.
Place the plate into a container of room-temperature water and rub lightly with fingers or a very soft-bristled brush. The plate-washing will be finished when the image is visibly etched into the polymer surface and when no trace of the slippery polymer is evident when you rub your finger over the plate surface.
Place the plate in a toaster oven or plate dryer set at about 21.1 degrees Celsius for about 15 minutes. Check with your plate supplier for specific information.
Expose the plate in the platemaker for an additional 15 minutes. This post-exposure will harden the polymer surface.
Remove the finished plate from the platemaker---it's now ready for use.
Tips and warnings
- Always experiment with platemaking before committing to a job. The manufacturer of the platemaker and plate material will likely be happy to offer specific advice.
- Most platemakers come with built-in timers or light integrators (found on more expensive units). Avoid using rotary dial timers, even if your platemaker includes one. An inexpensive digital kitchen timer is more accurate and will yield repeatable results.
- Log every plate into a notebook, noting the type of plate, exposure time and halftone screen, for future reference.
- Make sure you know the plate's washing type. While most common pad-printing plates for hobby and light commercial use are of the water-rinse variety, there are also alcohol- and chemical-rinse plates on the market. These plates won't rinse with water and may result in frustration and ruined plates.
- Polymer pad-printer plates are metal-backed. Although the metal edges are smoothed, they are thin and can cause lacerations if handled improperly.
- Wear eye protection when washing plates to protect against polymer chemical splashing.
- Follow the plate manufacturer's recommendations for disposing of used plate wash water; don't allow pets or children near the contaminated water container.
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