I'm assuming that the question on two sided plates is in reference to
aluminum lithographic plates. While two sided plates are available, they are
not commonly used due to a variety of problems. Using them can be very time
consuming and generally not worth the effort involved, especially in light of
the cost of plate matieral versus the other costs or potential costs such as
a ruined print job or downtime associated with a plate remake.
Their use presents some challenges because the integrity of the plate
material can be compromised due to bending and mounting. This can lead to
breaking, cracking, and movement. If a job is to be reprinted and the plate
rebent again, it will produce additional stresses on the plate thus leading
to cracking, breaking, and other plate movement.
Additional care must be taken to prevent damage to the imaged area or
unimaged area (whatever the case may be). If the plate cylinder is undercut,
then the packing material must be clean, undamaged, and frequently changed.
If packing material is not necessary, then the plate cylinder must be
extremely clean and undamaged. This requires the use of more cleaning solvent
than that required for single sided plates.
The use of the second side of the plate is generally limited to single color
jobs because holding registration and maintianing image integrity can be
compromised because the plate had previously been bent, mounted and then
rebent and remounted which promotes plate stress and breakage. If
registration can not obtained and/or the plate breaks throught the course of
a run, this causes more waste and downtime than what is anticipated to be
prevented by using double sided plates.
I hope the above answered your question. If you need some additional
information, please let me know.