plates are prone to distortion and shrinkage, in particular traditional molded
rubber plates that will shrink and stretch both in their length, width and thickness, usually in the range of 1.5 to 2%. This is very much determined by what
materials are included in the plate construction, the compounds themselves, the
plate thickness, and the size of cylinder or sleeve it is to be mounted onto.
Now, with photopolymer, shrinkage issues are generally disregarded as in theory
they should not shrink with the stabilization (polyester sheet) that is bonded
to the back of the photopolymer. This said, anyone that makes plates knows not
to expose and washout plates from the same job running around the plate length
and the across the plate width as a difference in tightly registered plates
will be seen as a slight mis-registration due in part to the different
alignment of the polymer strings which can cause a slightly different stretch
or apparent shrinkage difference.
This can even apply between plates that
consist of heavy solids and other plates that have little or no print areas, in
particular with thicker plates and deeper etched plates. This is why it is
critical to maintain a uniform depth when plates are washed out if photopolymer
and applies the same to metal molds if chemically etched. All plates will
distort( stretch) when wrapped around a curved surface and will elongate on the
outer surface and contract on the inner surface of the plate. For modern
photopolymer plates the standard calculation is 3.1416 x 2 times plate
thickness over its repeat length. Plates mounted on stickyback prior to
mounting on the print cylinder have much more surface stretch and distortion than
when mounting a plate onto the stickyback that has already been mounted on the
print cylinder or sleeve.