The invention provides a dyeing solution for lithographic printing plates and a dyeing method for waterless lithographic printing plates that show stable plate inspection characteristics with little decrease in dye concentration and less dyeing unevenness even when used for bulk plate processing. The dyeing method for waterless lithographic printing plates is designed so that when used to dye an image area formed on a waterless lithographic printing plate with a dyeing solution containing an organic solvent, the relation of |β−α|<5 (cal/cm.sup.3).sup.1/2 is held wherein β is the SP value of the polymer compound included in the image area and α is the SP value of the organic solvent. The dyeing solution for lithographic printing plates contains (a) a dye, (b) a specific anionic surface active agent, and (c) an organic solvent containing at least one selected from ethers and alcohols.

According to aspects of the embodiments, there is provided a method of determining the amount of fountain solution employed in a digital offset lithography printing system. Fountain solution thickness is determined by examining optical density of some halftone or solid patch versus laser current level. The apparatus and method uses a variable current signal to dither or perturb the laser imaging system to irradiate a fountain solution layer to create patches at different laser current levels. An aptly programmed controller then process optical density measurements to indirectly estimate fountain solution level.

According to aspects of the embodiments, there is provided a method of determining the amount of fountain solution employed in a digital offset lithography printing system. Fountain solution thickness is determined by examining optical density of some halftone or solid patch versus laser current level. The apparatus and method uses a variable current signal to dither or perturb the laser imaging system to irradiate a fountain solution layer to create patches at different laser current levels. An aptly programmed controller then process optical density measurements to indirectly estimate fountain solution level.

An optical light reflectance measurement system above an imaging member surface measures fountain solution surface light reflectance interference on reflective substrate portions of the imaging member surface in real-time during a printing operation. The measured light reflectance interference corresponds to a thickness of the fountain solution layer and may be used in a feedback loop to actively control fountain solution layer thickness by adjusting the volumetric feed rate of fountain solution added onto the imaging member surface during a printing operation to reach a desired uniform thickness for the printing. This fountain solution monitoring system may be fully automated.

An optical light reflectance measurement system above an imaging member surface measures fountain solution surface light reflectance interference on reflective substrate portions of the imaging member surface in real-time during a printing operation. The measured light reflectance interference corresponds to a thickness of the fountain solution layer and may be used in a feedback loop to actively control fountain solution layer thickness by adjusting the volumetric feed rate of fountain solution added onto the imaging member surface during a printing operation to reach a desired uniform thickness for the printing. This fountain solution monitoring system may be fully automated.

A negative-working lithographic printing plate precursor includes (i) a support having a hydrophilic surface or which is provided with a hydrophilic layer, and (ii) a coating including a photopolymerisable layer including a photoinitiator and a polymerizable compound, and the photoinitiator includes at least one structural moiety including an oligo- or poly(alkyleneglycol).

A negative-working lithographic printing plate precursor includes (i) a support having a hydrophilic surface or which is provided with a hydrophilic layer, and (ii) a coating including a photopolymerisable layer including a photoinitiator and a polymerizable compound, and the photoinitiator includes at least one structural moiety including an oligo- or poly(alkyleneglycol).

Lithographic printing plates are provided by imagewise exposing negative-working lithographic printing plate precursors having one or more radiation-sensitive imageable layers, followed by contacting with a processing solution that contains up to 10 weight % of one or more compounds represented by Structure (I) shown as follows:

R.sup.1—C(═O)—N(R.sup.2)—R.sup.3   (I)

wherein R.sup.1, R.sup.2, and R.sup.3 independently represent hydrogen or a substituted or unsubstituted hydrocarbon group, or two or three of R.sup.1, R.sup.2, and R.sup.3 are combined to form one or more cyclic rings, and the total number of carbon atoms in the Structure (I) molecule is at least 7 and up to and including 33. Both negative-working and positive-working lithographic precursors can be imaged and processed using this processing solution using one or more successive applications of the same or different processing solution. The processing solution can be derived from a corresponding processing solution concentrate that can also be used for replenishment.

An intermediate roller positioned between a fountain solution vapor supply and an imaging member decouples fountain solution vapor deposition from the surface of the imaging member. The intermediate roller may be temperature controlled. A uniform layer of fountain solution condenses onto the surface of the temperature controlled intermediate roller regardless of the imaging blanket temperature. The fountain solution condensate layer deposited onto the intermediate roller splits and deposits a thin uniform layer of fountain solution liquid onto the imaging member surface. This liquid layer split may be independent of the temperature of the imaging member surface, resulting in a uniform layer of fountain solution on the imaging blanket for better imaging quality. Remotely locating the vaporizing chamber away from the imaging member prevents undesired heat transfer from a hot vaporizing chamber/baffle to the imaging member surface.

An intermediate roller positioned between a fountain solution vapor supply and an imaging member decouples fountain solution vapor deposition from the surface of the imaging member. The intermediate roller may be temperature controlled. A uniform layer of fountain solution condenses onto the surface of the temperature controlled intermediate roller regardless of the imaging blanket temperature. The fountain solution condensate layer deposited onto the intermediate roller splits and deposits a thin uniform layer of fountain solution liquid onto the imaging member surface. This liquid layer split may be independent of the temperature of the imaging member surface, resulting in a uniform layer of fountain solution on the imaging blanket for better imaging quality. Remotely locating the vaporizing chamber away from the imaging member prevents undesired heat transfer from a hot vaporizing chamber/baffle to the imaging member surface.