Method for the preparation of planographic printing plates

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As is understood from the above given description, the method of the invention utilizes the principle that the pattern-wise photocuring of the photocurable organopolysiloxane composition is accompanied by the simultaneous transfer of the photocured organopolysiloxane layer from the base plate to the sheet and curing of the uncured organopolysiloxane composition left pattern-wise on the base plate is effected by exposure to light in a dose as large as desired with simultaneous increase of the adhesive bonding strength thereof to the base plate so as that the resultant printing plate is imparted with an unusually high durability in printing.
In the hitherto known positive type plate materials for peeling development, i.
e.
plate materials for pattern-wise exposure to light through a positive transparency, the silicone layer photocured by the pattern-wise exposure to light is firmly bonded to the adhesive layer on the base plate to form the non-image areas of the printing plate.
This effect is obtained by the increase in the adhesive bonding strength between the cured silicone layer and the adhesive layer on the base plate with the exposure dose so that the bonding strength between the cured silicone layer and the adhesive layer is sufficiently high after completion of plate making to endure an ordinary planographic printing process.
On the other hand, in negative type plate materials, i.
e.
plate materials for pattern-wise exposure to light through a negative transparency, for peeling development using a photocurable silicone, such as disclosed in Japanese Patent Disclosure No.
54-121804, the layer of the photocurable silicone must be so designed that it transfers by the pattern-wise exposure to light to the surface of the peeling sheet and adhesively bonded thereto as a layer of cured silicone.
In addition, the layer of the uncured silicone left on the base plate must be subsequently photocured to form the non-image areas with increased ink-repellency and, desirably, with increased adhesive bonding strength with the surface of the adhesive layer on the base plate by this second exposure to light