Abstract: An additive for a pigment based ink—jet printing composition which is used in conjunction with a printing head that comprises metallic components, is disclosed. The additive comprises a cationic component and an anionic component, and characterized in that the cationic component is a cationic surfactant. Preferred additives are those where the cationic component is C10-22alkyl trimethyl ammonium. Pigment-based ink—jet printing compositions comprising these additive are also described.

Abstract: An ink-jet print head suitable for use with pigment based inks having protective layers interdisposed between pairs of juxtaposed dissimilar metal surfaces having a relatively large electrochemical potential difference therebetween so as to substantially reduce the potential difference, thereby reducing clogging of the ink-jet nozzles. The ink-jet head further comprising a composite body formed with an array of ink jet nozzles for respectively emitting a train of ink droplets, each of said ink jet nozzles being associated with a piezoelectric transducer and adapted for flow communication with a source of pigment based ink via an ink duct.

Abstract: A method of operating for an ink jet printer having a printer head bearing a plurality of equi-distantly spaced ink jets for printing parallel lines of dots on a substrate in n passes of the print head over the substrate. Between each pass of the printer head over the substrate, the printer head is displaced in a direction perpendicular to the direction of the lines by a distance y that satisfies: (i) y=m1×a where m1 is a natural number equal to 2 or more and a is the separation gap between adjacent lines; (ii) y is not a multiple of the inter ink jet separation distance of the printer head; and (iii) m1 and n do not have a common factor except the factor with the value of 1. These conditions on y ensure that two adjacent lines are printed by different ink jets and that each line is printed by only one ink jet.

Abstract: A method and apparatus for direct production of photopolymeric printing plates. The method comprises forming a positive and/or negative image on a substrate by ink-jet printing with a photopolymeric ink composition, optionally preheated. The apparatus for carrying out the method of the invention comprises a rotatable drum adapted for retaining on its inner or outer surface the substrate to be printed; a carriage, displaceable axially in respect of the drum; a container for a photopolymeric ink composition; at least one nozzle communicating with the carriage for ejecting the photopolymeric ink composition; and a UV source located so as to expose the printed surface of the substrate to UV radiation.