Abstract: Relief plates and printing plates are produced by a positive-working process, using a photopolymerizable layer which contains one or more photopolymerizable, olefinically unsaturated compounds, one or more photoinitiators which can be activated by UV light, and a combination of a phenothiazinium, phenoxazinium, phenazinium or acridinium dye with a mild reducing agent which, on exposure to visible light, is capable of reducing the dye in the excited electronic state. The photopolymerizable layer is exposed imagewise to light having a wavelength longer than 450 nm, and simultaneously or subsequently exposed uniformly to light having a wavelength of from 300 to 420 nm, after which the unpolymerized areas of the layer are removed.

Abstract: To close the gaps (6) which result between the end or edge sections (7) of the gravure printing plates (2) when the latter are clamped on form cylinders (1) of rotary gravure presses, the gap (6) is covered with a cover element (8) in which at least that surface region which lies on the end or edge sections (7) of the gravure printing plate (2) and covers the gap (6) is deformable under pressure and can therefore be matched up with the surface contour in the gap region, the cover element is pressed onto the surface of the gravure printing plate, the resulting gap cavity is filled with a curable filling compound and, when curing of the filling compound is complete, the cover element is removed.

Abstract: The gap formed between the end sections of a gravure printing plate anchored in a groove in a forme cylinder is covered with a plate, and the resulting gap cavity is filled with plastic, curable material. When the filling has been cured, the plate is removed. In order to position the plate exactly on the gap, the plate is held, in such a way that it can be rotated and lowered, by means of a pair of guide rails mounted on the forme cylinder axle; the said pair of rails can be connected to a means for centering on the gap, this means likewise being rotatable about the said axle.

Abstract: Gravure printing plates comprising a plastic printing layer applied on a printing plate base are produced by a method wherein a solid photosensitive layer (L) firmly bonded on the printing plate base is exposed imagewise to actinic light, and the exposed layer is washed out with a developer and then subjected to thermal hardening to form the plastic printing layer. In this process, the photosensitive layer (L) employed contains, as the photosensitive component, a compound possessing two or more aromatic and/or heteroaromatic o-nitrocarbinol ester groups, and a compound which effects crosslinking and possesses two or more reactive groups which are capable of reacting with --COOH groups under the action of heat to form a covalent chemical bond.

Abstract: Gravure printing plates which are highly abrasion-resistant and scratch-resistant can be produced rapidly and simply from a photosensitive recording material by exposing the latter through a photographic positive, washing out the unexposed areas and drying the resulting gravure printing plate, if the photosensitive recording material employed, which comprises a photopolymerizable and/or photocrosslinkable layer (L) applied to a dimensionally stable base, contains finely divided, hard, abrasive particles in the layer (L), the surface of this layer, which subsequently constitutes the surface of the printing plate, has a peak-to-valley height of <2 .mu.m, and the materials of this layer are chosen so that, after exposure and development, it has a Vickers hardness of not less than 10 N/mm.sup.2, measured under load.

Abstract: Gravure printing plates which are highly abrasion-resistant and scratch-resistant can be produced rapidly and simply from a photosensitive recording material by exposing the latter through a photographic positive, washing out the unexposed areas and drying the resulting gravure printing plate, if the photosensitive recording material employed, which comprises a photopolymerizable and/or photocrosslinkable layer (L) applied to a dimensionally stable base, contains finely divided, hard, abrasive particles in the layer (L), the surface of this layer, which subsequently constitutes the surface of the printing plate, has a peak-to-valley height of <2 .mu.m, and the materials of this layer are chosen so that, after exposure and development, it has a Vickers hardness of not less than 10 N/mm.sup.2, measured under load.

Abstract: Photosensitive recording materials which are suitable for the production of printing plates and relief plates and possess a photopolymerizable relief-forming layer which can be developed with water and is based on a polyvinylalcohol/monomer mixture contain, as a binder in the said layer, a polyvinylalcohol derivative which is obtained by reacting polyvinylalcohol with an acylating agent which has groups which are polymerizable by free radicals, the reaction being carried out in the heterogeneous phase, in an aprotic dispersant, using the acylating agent in an amount which corresponds to not less than twice the molar amount required to achieve the desired degree of acylation.

Abstract: The gap (15) formed between the end portions (5) of a gravure printing plate (3) which is anchored in a groove (2) of a printing cylinder (1) on which the plate is mounted is covered with a sheet (6) which overlaps the end portions. The gap cavity (9) thus formed is then filled with a thermoplastic and/or hardenable material and when this has hardened the cover is removed.

Abstract: Multi-layer photopolymer elements, which are suitable for the production of relief printing plates and contain photosensitive polyvinyl alcohol/monomer layers which can be developed with water, can be improved in respect of their production, drying and shelf life by the application of a thin layer of a highly hydrolyzed low molecular weight polyvinyl alcohol.

Abstract: A photopolymerizable recording composition which comprises a mixture, containing a photoinitiator, of (a) a photopolymerizable olefinically unsaturated monomer and (b) an organic polymeric binder, wherein the photoinitiator is an acylphosphine oxide compound of the formula R.sup.1 R.sup.2 PO--CO--R.sup.3, where R.sup.1 and R.sup.2 are certain organic radicals and R.sup.3 is tert.-alkyl or a cyclic radical with two substituents in the ortho-position to the carbonyl group. The recording compositions have a high reactivity when irradiated with UV light and are used in particular for the preparation of printing plates, relief plates and photo-resists.

Abstract: A laminate suitable for the production of printing plates and relief plates, and possessing a photosensitive layer, which is soluble in water or in an aqueous solution, and contains a hydrophilic polymeric binder, applied to a base, contains, between the base and the photosensitive layer, an intermediate layer which consists of a mixture of a polymeric binder which is compatible with the polymeric binder of the photosensitive layer and contains at least 30% by weight of a reaction product of a polyvinyl alcohol with acrylic anhydride and/or methacrylic anhydride, with at least one monomer which is compatible therewith and selected from the group consisting of the hydroxyalkyl acrylates and methacrylates and the diacrylates and dimethacrylates containing urethane groups. After application to the base, the intermediate layer is cured at 110.degree.-220.degree. C. before the photosensitive layer is applied.

Abstract: A photopolymerizable recording composition which comprises a mixture, containing a photoinitiator, of (a) a photopolymerizable olefinically unsaturated monomer and (b) an organic polymeric binder, wherein the photoinitiator is an acylphosphine oxide compound of the formula R.sup.1 R.sup.2 PO-CO-R.sup.3, where R.sup.1 and R.sup.2 are certain organic radicals and R.sup.3 is tert.-alkyl or a cyclic radical with two substituents in the ortho-position to the carbonyl group. The recording compositions have a high reactivity when irradiated with UV light and are used in particular for the preparation of printing plates, relief plates and photoresists.