Preparation of photopolymeric gravure printing plates

#The present invention relates to a process for the production of photopolymeric gravure printing plates which are to be developed with water or water/alcohol mixtures after imagewise exposure and have, arranged one on top of the other on a dimensionally stable substrate, a layer (A) which may be bonded to the dimensionally stable substrate by an adhesion-promoting layer and is crosslinkable by actinic radiation, a layer (B) sensitive to IR radiation, if required a parting layer arranged between layer (A) and layer (B), and a peelable protective film applied to the layer (B), and are suitable for digital information transfer, and gravure printing plates produced by this process.

#Photopolymeric gravure printing plates which can be developed with water or with an aqueous alcoholic medium consist of a photosensitive photopolymerizable layer which is soluble or dispersible in the developer and is applied to a dimensionally stable substrate, for example polyethylene terephthalate film or steel or aluminum sheet. In order to provide a firm bond, an adhesion-promoting layer may be applied between the photosensitive, photopolymerizable layer which can be developed with water or an aqueous alcoholic medium and the substrate.

#A release layer may also be present on the photosensitive, photopolymerizable layer which can be developed with water or an aqueous alcoholic medium, said release layer being required whenever said layer present underneath is so tacky that, when the photographic negative is placed on top, the air present in the vacuum printing frame cannot be uniformly removed and consequently vacuum errors occur during exposure.

#A water-soluble IR-sensitive layer (B) was produced by dissolving 2 parts of carbon black (eg. Printex® U from Degussa) and 6 parts of a polyvinyl alcohol (eg. Mowiol® 5-72 from Hoechst) in 80 parts of water and 20 parts of n-propanol. n-Propanol is used as leveling agent in order to achieve good wetting during casting of this solution on a polyethylene terephthalate sheet. After combination of the components, these were treated in a disperser (Ultra Turrax) for 2 hours in order to prepare a finely divided dispersion. The dispersion thus obtained was cast on a polyethylene terephthalate sheet (125 μm Mylar® from DuPont), this being done in such a way that the resulting film had a layer thickness of 8 μm and an optical density of 4.5 after drying.

#This layer was laminated with a commercial water-developable gravure printing plate on steel sheet, eg. nylograv® WSA 52 (manufacturer BASF Aktiengesellschaft) with the use of propanol/water (18:1) as a laminating solvent, after the protective film had been removed from this plate.

#After the protective film had been peeled off, the photosensitive recording material was mounted on a vacuum drum and exposed by means of an Nd-YAG laser (wavelength 1064 nm). The spot diameter of the IR beam was adjusted to 20 μm. This was an exposure unit from Baasel-Scheel. Thereafter, the plate was exposed uniformly to UV light of wavelength 320-400 nm without reduced pressure in an 80×107 nyloprint® exposure unit equipped with Philips TL 10R 40W tubes and was washed out with water in a nyloprint DW/DT 85 continuous unit, dried for 30 minutes at 100° C. and postexposed. A printing plate having an excellent gradation of well depths and a scatter of well depths with a constant exposure time of ±1 μm and giving excellent printed copies was obtained. The nonprinting parts were absolutely defect-free.