a method for manufacturing relief printing plates made of a photo - sensitive polymeric material , including the steps of providing a photographic negative having opaque areas and transparent areas defining a desired printing relief pattern , applying a layer of viscous photo - sensitive resin on the photographic negative , providing a flexible support base having a roughened surface , and applying it onto the layer of viscous resin with the roughened surface contacting the layer of resin , projecting ultra - violet radiation on the negative for hardening any of the resin which is exposed to the ultra - violet radiation through the transparent areas of the negative thereby forming the printing relief and causing the resin to adhere to the roughened surface during the hardening thereof , and removing the negative and recovering any of the resin which was behind the opaque areas of the negative and was not hardened .