According to aspects of the embodiments, there is provided a method of measuring the amount of fountain solution employed in a digital offset lithography printing system. Fountain solution thickness is measured by using phase shifted monochromic light to produce optical path differences through the fountain solution film. The intensity of the reflected light through the fountain solution film is very sensitive due to the phase shifted light so interference fringes are easier to delineate and fountain solution thickness measurement more reliable.

A lithographic printing plate precursor includes an image recording layer on a support, in which the lithographic printing plate precursor has projections which are discontinuously formed on a surface of an outermost layer on a side where the image recording layer is provided, and a melting point of each projection is in a range of 70° C. to 150° C. A method of producing a lithographic printing plate includes a step of image-wise exposing the lithographic printing plate precursor to form an exposed portion and an unexposed portion, and a step of supplying at least one of printing ink or dampening water to remove the unexposed portion.

A system for preparing a photopolymer printing plate includes exposure unit comprising a plurality of UV light emitting diodes (UV LEDs), a holder comprising a UV translucent material configured to receive the printing plate, and a controller configured to activate the plurality of UV LEDs. The UV LEDs include a plurality of stationary back UV LEDs configured to emit UV radiation toward the non-printing back side of the printing plate through the holder with the printing plate disposed in a stationary position on the holder, the plurality of stationary back UV LED sources together defining at least one back array having a collective irradiation field covering an area at least coextensive with the lateral length and lateral width of the plate.

A negative-working lithographic printing plate precursor includes a coating including vinylogous vitrimer particles. The vinylogous vitrimer particles include a resin having at least one moiety of formula (I), (II), and/or (III): ##STR00001##

The invention provides a waterless offset lithographic printing plate precursor that is mountable on a magnet type printing cylinder and has high durability and halftone dot reproducibility. The waterless offset lithographic printing plate precursor contains at least a heat-sensitive layer and a silicone rubber layer disposed on a substrate, the substrate being of a ferromagnet material.

Provided is a lithographic printing plate recursor having a support and an image-recording layer on the support, in which the image-recording layer contains an infrared absorber, a polymer A that has a weight-average molecular weight of more than 15,000 and 150,000 or less, and a polymerizable compound B that has a weight-average molecular weight of 1,000 or more and 15,000 or less, and the polymer A is a polymer represented by Formula (I).

A.sup.P-(B.sup.P).sub.nP  Formula (I)

In Formula (I), A.sup.P represents an nP-valent organic group having a hydrogen bonding group, B.sup.P represents a group having 2 or more Polymerizable groups, nP represents an integer of 2 or more, and weight-average molecular weight of A.sup.P/(molecular weight of B.sup.P×nP) is 1 or less.

IR-sensitive lithographic printing plate precursors provide a stable print-out image using a unique IR radiation-sensitive composition in an infrared radiation-sensitive image-recording layer. This IR radiation-sensitive composition includes: (1) a free radical initiator composition that comprises an electron-donating agent; (2) a free radically polymerizable composition; and (3) a color-changing compound that is represented by the Structure (I) having a conjugated carbon chain between the aromatic terminal groups. The compound also has a —SO.sub.2—R.sup.3 group wherein R.sup.3 represents alkyl, aryl or heteroaryl groups. After IR imaging, these precursors exhibit desirable printout images both fresh and after dark storage. The precursors can be developed off-press or on-press.

A lithographic printing plate precursor is disclosed including a support and a coating including a polymerisable compound, an optionally substituted trihaloalkyl sulfone initiator, a leuco dye and a specific infrared absorbing compound including a six membered ring in the central position.

A lithographic printing plate precursor including an image recording layer on a hydrophilic support, in which the image recording layer includes a polymerization initiator, an infrared absorbent, a polymerizable compound, and an acid color former, and the infrared absorbent includes a compound represented by Formula 1, as well as a method of preparing a lithographic printing plate by use of the lithographic printing plate precursor. In Formula 1, at least one of Ar.sub.1 or Ar.sub.2 has a group represented by —X, where X represents a halogen atom, —C(═O)—X.sub.2—R.sub.11, —C(═O)—NR.sub.12R.sub.13, —O—C(═O)—R.sub.14, —CN, —SO.sub.2N.sub.15R.sub.16, or a perfluoroalkyl group, X.sub.2 represents a single bond or an oxygen atom, R.sub.11 and R.sub.14 each independently represents an alkyl group or an aryl group, and R.sub.12, R.sub.13, R.sub.15 and R.sub.16 each independently represents a hydrogen atom, an alkyl group, or an aryl group: ##STR00001##

Provided is a lithographic printing plate precursor having an aluminum support, an image-recording layer, and a water-soluble overcoat layer in this order, in which the image-recording layer contains an infrared-absorbing polymethine colorant having HOMO of −5.2 eV or less, a polymerization initiator, a polymerizable compound, and a polymer, and the polymer has a constitutional unit formed of an aromatic vinyl compound and a constitutional unit formed of an acrylonitrile compound. Also provided are a method for preparing a lithographic printing plate using the lithographic printing plate precursor.