Provided are an offset printing plate, an offset printing apparatus, and an offset printing method, which are capable of printing a high-definition image by waterless offset printing.

The offset printing plate comprises: a cylindrical plate base material; a silicon resin layer formed on the cylindrical plate base material; and a resist pattern part formed on the silicon resin layer, in which the silicon resin layer serves as a non-printing area, and the resist pattern part serves as a printing area. The silicon resin layer is preferably formed on the cylindrical plate base material seamlessly.

An infrared-sensitive color developing composition develops colors in a high density with an infrared exposure and does not significantly discolor when aged. A lithographic printing plate precursor which has extremely excellent plate-inspecting properties and favorable storage stability and is capable of maintaining favorable color-developing properties is provided, as is a plate making method for a lithographic printing plate in which the lithographic printing plate precursor is used. A new compound that can be preferably used as an infrared-sensitive color developer is also provided. An infrared-sensitive color developing composition of the invention includes a compound represented by Formula (1) (Component A). In addition, the compound in the present invention is represented by Formula (1). ##STR00001##

Provided is a planographic printing plate precursor including: a support; and an image recording layer formed on the support, in which the content of fine particles per unit area in a region on a plate surface on the image recording layer side from an end portion of the planographic printing plate precursor to a portion inside the end portion by 5 mm is greater than the content of the fine particles per unit area in a region other than the region by an amount of 10 mg/m.sup.2 or greater, edge stains are not generated therein, and transferring of the image recording layer is prevented even in a case where planographic printing plate precursors are stored in a stacked state. Further, provided are a method of producing the same and a printing method using the same.

An on-press development type lithographic printing plate precursor including a support, and an image-recording layer on the support, in which the image-recording layer contains an infrared absorber, a polymerization initiator, a polymerizable compound, and one or more compounds selected from the group consisting of a compound represented by Formula (1) and a compound represented by Formula (2) (in Formula (1) and (2), Ra.sub.1 and Ra.sub.2 represent an alkyl group, Rb.sub.1 and Rb.sub.3 represent an alkyl group, Rb.sub.2 and Rb.sub.4 represent an alkyl group, and EDG's each independently represent a hydrogen atom or an electron-donating group, provided that at least one of the four EDG's in Formula (1) represents an electron-donating group).

An on-press development type lithographic printing plate precursor includes a support, and an image-recording layer on the support, in which the image-recording layer contains an infrared absorber, a polymerization initiator, a polymerizable compound, and at least one compound selected from the group consisting of a compound represented by Formula (1) and a compound represented by Formula (2) (in Formulae (1) and (2), Ra.sub.1 and Ra.sub.2 represent an alkyl group, Rb.sub.1 and Rb.sub.3 represent an alkyl group, Rb.sub.2 and Rb.sub.4 represent an alkyl group, and EWG's each independently represent a hydrogen atom or an electron-withdrawing group, provided that at least one of the four EWG's in Formula (1) represents an electron-withdrawing group).

Lithographic printing plate precursors are prepared with a unique substrate and one or more radiation-sensitive imageable layers. The substrate is prepared by two separate anodizing processes to provide an inner aluminum oxide layer having an average dry thickness (T.sub.i) of 650-3,000 nm and a multiplicity of inner micropores having an average inner micropore diameter (D.sub.i) of 15 nm. A formed outer aluminum oxide layer comprises a multiplicity of outer micropores having an average outer micropore diameter (D.sub.o) of 15-30 nm; an average dry thickness (T.sub.o) of 130-650 nm; and a micropore density (C.sub.o) of 500-3,000 micropores/m.sup.2. The ratio of D.sub.o to D.sub.i is greater than 1.1:1, and D.sub.o in nanometers and the outer aluminum oxide layer micropore density (C.sub.o) in micropores/m.sup.2, are further defined by the outer aluminum oxide layer porosity (P.sub.o) according to the following equation:

0.3P.sub.o0.8

where P.sub.o is 3.14(C.sub.o)(D.sub.o.sup.2)/4,000,000.

A lithographic printing plate precursor has a support and an image-recording layer on the support. 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.nPFormula (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.PnP) is 1 or less.

Provided is a planographic printing plate precursor including: a support; and an image recording layer formed on the support, in which a region on the plate surface on the image recording layer side from an end portion of the planographic printing plate precursor to a portion inside the end portion by 5 mm contains a polymer containing a functional group represented by the following Formula (A), and the content of the polymer per unit area in the region is greater than the content of the polymer per unit area in a region other than the above-described region by an amount of 10 mg/m.sup.2 or greater.
Si(X).sub.m(R.sup.3).sub.n(A)

Negative-working, IR-sensitive dry printing plates utilize an oleophobic topmost layer, a nitrocellulose-based imaging layer ablatable by laser discharge, and a grained metal substrate with no heat-insulating layer intervening between the imaging layer and the substrate.

A negative type photosensitive resin composition includes a polymer compound which contains a linking group represented by Formula A-1 in a main chain and an ethylenically unsaturated group; and a polymerization initiator. In Formula A-1, R.sup.1 and R.sup.2 each independently represent a hydrogen atom or a monovalent organic group, and X.sup.1 represents a linking group represented by any of Formulae A-2 to A-6.

A negative type planographic printing plate precursor includes an image recording layer containing the negative type photosensitive resin composition.

A method of preparing a planographic printing plate includes, in order, an exposure step of image-exposing the negative type planographic printing plate precursor; and a development step of performing development by removing a non-exposed portion of the exposed negative type planographic printing plate precursor using a developer.

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