Abstract: A desensitizer for a lithographic printing plate, which contains:(i) at least one silicate represented by the general formulae (I), (II) and (III)M.sub.2 O.(SiO.sub.2).sub.n.qH.sub.2 O (I) ##STR1## wherein M represents an alkali metal atom; R.sup.1, R.sup.2, R.sup.3 and R.sup.4, which may be the same or different, each represents a hydrogen atom, an alkyl group or a hydroxyalkyl group; n represents a number of from 1 to 8.5; q represents a number of from 0 to 12; m represents a number of greater than 0 and up to 10; and p represents a number of from 4 to 5000;(ii) at least one wetting agent;(iii) a hydrophilic colloidal material; and(iv) water, anda process for preparing a lithographic printing plate using the desensitizer.

Abstract: A photopolymerizable composition comprising a polymerizable ethylenically unsaturated compound, optionally, a linear organic polymer, and a photopolymerization initiator comprising a combination of a compound represented by the general formula (I) ##STR1## wherein Z represents the non-metal atomic group necessary to form a nitrogen containing heterocyclic nucleus, R.sub.1 represents an alkyl group or a substituted alkyl group, and R.sub.2 represents an alkyl group or an aryl group having a comparatively high photopolymerization initiating ability; and a compound represented by the general formula (II) ##STR2## wherein X represents a halogen atom, Y represents --CX.sub.3, --NH.sub.2, --NHR.sup.1, --NR.sup.1.sub.2 or OR.sup.1, R.sup.1 represents an alkyl group or an aryl group and R represents an alkyl group, an alkyl group substituted with at least one chlorine atom, an aryl group, a substituted aryl group or a substituted alkenyl group.

Abstract: 2-Arylnaphtho[1,8-bc]furan-5-ones represented by general formula (I): ##STR1## wherein G represents a substituted phenyl group, an unsubstituted or substituted 1-naphthyl group and an unsubstituted or substituted 2-naphthyl group, with the substituents being selected from the group consisting of a straight chain or branched chain alkyl group having 1 to 5 carbon atoms, a straight chain or branched chain alkoxy group having 1 to 3 carbon atoms and a halogen atom; are disclosed as well as photopolymerizable compositions containing at least one of the above compounds as a photopolymerization initiator for addition polymerizable ethylenically unsaturated compounds.

Abstract: A step tablet in which density steps of a definite shape, each density step having a specific optical density, form a series of decreasing or increasing densities, in which any two density steps contiguous to each other are disposed with a boundary space of a specific shape between the density steps.

Abstract: A light-sensitive lithographic printing plate element suitable for the formation of negative and positive images, simultaneously, comprising a hydrophilic support having, in succession, a light-sensitive composition layer and a transparent cover film in which images for printing are formed by imagewise exposing through the cover film and peeling apart to remove, together with the cover film, the areas having a stronger adhesion to the cover film in the light-sensitive composition layer by utilizing the difference in adhesion to the support and to the cover film between the exposed areas and the unexposed areas of the light-sensitive composition layer, whereby the areas of the light-sensitive composition layer having a stronger adhesion to the support remain on the support, wherein the surface of the support adjacent the light-sensitive composition layer is treated with an aqueous solution containing at least one water soluble oxygen acid or water soluble oxygen acid salt selected from the group consisting of