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What are PS plates
Jan 03, 2019

What are PS plates?

What are PS plates, you might ask? They look like this:


PS (Pre-Sensitized, lithographic) plates are a main component in offset printing, which is used in the majority of medium to large-scale printing tasks today. In offset printing, the image to be printed comes from a coated aluminium sheet, placed around the printing cylinder. The aluminium is treated so that its surface is hydrophilic (attracts water), while the developed coating is hydrophobic. Water and oil-based ink are used to transfer the image from the plate to a rubber roller, which then transfers the image onto the paper. The image below shows the printing process:


PS plates are made from large rolls of high quality aluminium. In a first process step, the rolls are run through several steps of electro-chemical processes to clean and roughen the surface. This roughening, called graining, creates microscopic pits on the surface, which can hold water. An enlarged view of the surface is shown in the next image:


The aluminium is then anodized to harden it, and coated with a photo-sensitive polymer, then dried for some time. Up to this point this is a continuous process, i.e. the roll runs through these steps as a continuous band. Next, the roll is cut into large sheets, which are inspected for imperfections. A percentage of the sheets are rejected, good sheets are stored in the intermediate product store. Based on roll width and thickness, the details of the processing and coating, and the cut length, around 300 intermediate products are created in this process.