I was going through some of my old notes from a class and found this on platemaking. feeling a bit nostalgic since this platemaker isn’t there anymore or anything else from PAL 😦
Within the Print Applications Laboratory, located within Bay 3 is the plate making facilities for the entire lab. We had a chance to view the processes of plate making first hand and watch the creation of a lithography plate.
The plate making process is broken up into seven linear steps; prepress of content, imaging of the plate, pre-baking, development of image and non image areas, cleaning of residual cleaner, checking for quality and finally sending the plate to press.
The other serves as a multipurpose device to allow for web integration and storage For the prepress part of the workflow, once the file is received it is processed using the software Workshop, which is part of the Prinergy workflow. The pages of the files are refined, converted, trapping is set in place and optimized. After the Workshop software, the file is sent to Preps, which again will refine the PDF to the specifications of the output – the plate. Preps allows you to define your media size and imposition on the plate. Each imposed signature is sent as individual separations (CMYK).
Next, the each of the separations is sent to be imaged on a plate it is referred to as plate setting. The process of exposure is the thermal method using an infrared laser. The laser will write the halftones and dots that will make up the image. The plate is imaged on a steal drum using two lasers, the first is to actually image the plate while the second checks the drum for the height of plate to ensure that the plate is in correct alignment with the other plates so that on press all the image areas will be aligned. The plate maker is capable of a resolution of 2400 x 2400 dpi at 250 rotations per minute.
After the plate has been imaged it enters the plate oven. The oven initiates the hardening of the imaging area. The plate oven runs at about three feet per minute and the temperature should be around 248 degrees. If the plate oven is over or under temperature, it could cause problems with the hardening of the image areas. Baking also helps the plate to be more resistant to cleaning solvents.
Directly from the oven, plate goes into a development tank. It is there that the plate is developed in Kodak MX1919 Regenrator Solution and then is washed out in a water bath. A velvet roller will agitate the chemistry and with the water to insure that, no residual chemical is left on the plate. Once the plate is washed, Gum Arabic or plate finisher is then applied as a coating to protect the plate against oxidation, fingerprints and general use on press. Any dark green areas are the image areas and the silver colored areas represent non-image areas.
Finally, the plate is inspected for quality. Using the IC Plate2 by X-rite, you can measure the dot of the plate. This device is self-calibrating and helps to determine whether dots are in the correct range of +/- 2 % of tolerance. If they are not this may mean the plate has been over or under exposed. After evaluating the measure of the dot, a densitometer is also used. The densitometer is not as accurate as the IC Plate2 because it takes into account the measures for light reflectance of the metallic plate. However, a densitometer is very consistent in its measurements and allows the operator another way to track exposure.
Software: Creo Prinergy PDF Workflow – including Workshop
Plate maker: Creo 5080 Trendsetter VLF Quantum with 40 watt V-speed Laser
Plate: KPG Gold Thermal plate, Electrochemically grained and anodized aluminum substrate
Oven: Kodak Polychrome Graphics
Processor: Kodak CTP 850 Quartz Plate Processor
Chemicals Used: Kodak MX1919 Plate Regenerator, Kodak MX1591 Prebake Solution, Kodak 8505 Plate Finisher
Negative or Positive Plate?
The plate that we created for this lab is a planographic, negative working plate. The plate is negative working because within the specification sheet of the plate, Kodak labels it as such. However, if that sheet were not available, you would know by the process used to image what type it is. In this method of exposure, the image areas are exposed to light and non-image areas are left unexposed, much like producing a photographic print with a negative in the darkroom. With the use of film for exposure decreasing, the plate we worked with in lab was exposed using an infrared laser. The caveat when dealing with negative working plates is that because we must use an infrared laser to harden the photopolymer, exposure is everything and the smallest error could render the plate useless.