Agfa-gevaert

Agfa Gevaert Nv

Agfa Graphics Nv

Agfa-gavaert

Wim Sap

Marc Irene Van Damme

Joan T Vermeersch

Johan August Loccufier

Huub Van Aert

Thomas Nouwen

A method is disclosed for accurate reproduction of high-quality halftone images comprising microdots by means of lithographic plate materials which comprise a heat-sensitive positive-working coating that requires wet processing. Such microdots have a dot size &#x2266;25 &#x3bc;m and may be obtained by stochastic screening or by amplitude-modulated screening at a ruling of not less than 150 lpi. It has been established that the 'physical right exposure energy density' (physical REED) lies in the range from CP to 1.5*CP, wherein the physical REED is defined as the energy density at which the physical area on the plate, occupied by a microdot corresponding to a 50% halftone in the image data, coincides with the 50% target value; and wherein CP is the clearing point of the plate which is defined as the minimum energy density that is required to obtain, after processing, a dissolution of 95% of the coating. An accurate reproduction of microdots can therefore be achieved by exposing the material with light having an energy density in the range from CP to 1.5*CP. Loss of microdots by overexposure is thereby avoided.

Method for accurate exposure of small dots on a heat-sensitive positive-working lithographic printing plate material

A heat-sensitive lithographic printing plate precursor is disclosed comprising a polymer which is soluble in an aqueous alkaline solution and which comprises at least one chromophoric moiety having a light absorption maximum in the wavelength range between 400 and 780 nm. Such materials show no dye stain after processing in areas where the coating has been removed by an alkaline developer.

Heat-sensitive lithographic printing plate precursor

A negative-working heat-sensitive material for making a lithographic printing plate by direct-to-plate recording is disclosed. The material comprises in the order given a lithographic base having a hydrophilic surface, an oleophilic imaging layer and a cross-linked hydrophilic upper layer which comprises an organic compound derived from sulfonic acid, sulfuric acid, phosphoric acid or phosphonic acid. Materials according to the invention are characterized by an increased water-acceptance in the non-printing areas, which allows a rapid start-up of the press.

Processless lithographic printing plate

A negative-working heat-sensitive material for making a lithographic printing plate by direct-to-plate recording is disclosed which comprises in the order given a lithographic base having a hydrophilic surface, an oleophilic imaging layer and a cross-linked hydrophilic upper layer, characterize in that the oleophilic imaging layer comprises at least one transition metal complex of an organic acid. Materials according to the invention are characterized by an increased run length and can be used as a printing plate immediately after exposure.

According to the present invention there is provided an imaging element for making a lithographic printing plate comprising on a support having a hydrophilic surface a photosensitive layer and a thermosensitive layer, said thermosensitive layer being opaque to light for which said photosensitive layer has spectral sensitivity and said thermosensitive layer being capable of rendered transparent upon exposure to laser light characterised in that an intermediate layer being soluble or swellable in an aqueous medium is provided between said photosensitive layer and said thermosensitive layer.

Growing community of inventors

Bruges, Belgium

Wim Sap