Lithographic printing plate precursors and methods of use

Abstract

An IR sensitive lithographic printing plate precursor provides stable printing using a unique IR sensitive image recording layer. The IR radiation sensitive layer includes: component (1) a free radical initiator composition; component (2) a radically polymerizable composition; and component (3) a color-changing compound of structure (I) having an indene structure in the conjugated chain between the aromatic end groups. A specific group, such as a halogen group, is directly or indirectly attached to the indene structure. The infrared radiation sensitive image recording composition and the infrared radiation sensitive image recording layer also contain one or more borate ions. After infrared imaging, these precursors exhibit desirable fresh or initial printings and printings after dark storage. The precursor may be on-press developable.

Description

Field of the Invention

[0001] The present invention relates to infrared radiation-sensitive lithographic printing plate precursors that can be imaged using infrared radiation to provide imaged lithographic printing plates. Such precursors include a unique infrared radiation-sensitive composition that provides a stable print-out image between exposed and unexposed areas in an imagewise exposed infrared radiation-sensitive image recording layer. The present invention also relates to methods of using these precursors to provide lithographic printing plates having excellent print-out images. Background of the Invention

[0003] In lithography, lithographic ink receiving areas (also referred to as image areas) are created on the hydrophilic surface of a flat substrate (e.g., an aluminum-containing substrate). When the printing plate surface is moistened with water and a lithographic ink is applied, the hydrophilic areas of the aluminum-containing substrate retain the water and repel the lithographic ink, and the lithographic ink receiving image areas accept the lithographic ink and repel the water. The lithographic ink is transferred to the surface of the material on which the image is to be reproduced, perhaps using a blanket roller in a printing press.

[0004] Negative-working lithographic printing plate precursors useful for preparing lithographic printing plates typically comprise a negative-working radiation-sensitive image-recording layer disposed over a hydrophilic surface of an aluminum-containing substrate. Such an image-recording layer comprises a radiation-sensitive component dispersible in a suitable polymeric binder material. After image-wise exposure of the precursor to suitable radiation to form exposed and unexposed areas in the image-recording layer, the unexposed areas are removed by suitable means, revealing the hydrophilic surface of the aluminum-containing substrate underneath. The exposed areas of the image-recording layer that are not removed are lithographic ink-receptive, and the hydrophilic aluminum-containing substrate surface revealed by the development process accepts water and aqueous solutions (e.g., fountain solution), and repels lithographic inks.

[0005] In recent years, there has been an increasing desire in the lithographic printing industry to simplify lithographic printing plate preparation by performing on-press development (identified herein as "DOP") using lithographic inks and / or fountain solutions to remove unexposed areas of the image-recording layer at the start of lithographic printing. After laser imaging, the on-press developable precursor can be sent directly to the printing press without any prior wet chemical step to remove the image-recording layer coating in the precursor in the non-printing areas.

[0006] It is therefore highly desirable that such imaged lithographic printing plate precursors have a different color or "contrast" between exposed and unexposed areas. This color difference or contrast is often referred to as the "print out" or "print out image". A strong print out will facilitate the operator's visual evaluation and identification of the imaged printing plate precursor so that the imaged printing plate precursor can be properly connected to the printing press unit.

[0007] Many approaches have been taken to enhance the printout and stability of prints that can be produced in press-developable printing plate precursors. It has been observed that all of them have certain weaknesses.

[0008] For example, printout in imaged precursors with imaging compositions comprising an acid generator and an acid-sensitive color precursor (e.g., a lactone-based leuco dye) is generally not strong enough, due to the limited efficiency of acid generation in imaging compositions designed for infrared radiation imaging and on-machine development. In addition, the concentration of protons generated during infrared radiation imaging is generally reduced after imaging by chemical equilibrium or other post-imaging chemical reactions. As a result, printouts based on proton-induced color changes generally fade after imaging. It has limited image stability.

[0009] U.S. Patent Application Publication 2021 / 0078350 (Viehmann et al.) describes efforts to increase printout by incorporating more sensitive color-forming compounds into infrared radiation-sensitive imaging compositions, which convert from a colorless form to a colored form at lower acid concentrations. Background color formation is suppressed by special additives to stabilize good contrast in the printout. The initial printout achieved is quite high, but there is still a need to improve the printout and its stability when using the described chemistry.

[0010] A different approach to producing printouts is based on the use of infrared (IR) decomposable dyes that contain thermally unstable groups and are capable of losing thermally unstable groups when exposed to infrared radiation or heat to form compounds of different colors with absorption spectra in the visible spectral region. This approach is described in U.S. Pat. Nos. 8,148,042 (Callant et al.) and 8,178,282 (Callant et al.) and U.S. Patent Application Publication No. 2010 / 0274023 (Callant et al.). Such IR decomposable dyes should generally be present in the imaging composition in relatively large amounts, or in lower amounts and require high infrared radiation exposure energy in order to produce sufficient printouts.

[0011] In addition, some IR decomposable dyes used in such chemical processes generate gaseous materials when decomposed, and these gaseous materials are generally harmful to the crosslinked negative plate-making compositions based on free radical polymerizable compounds in the presence of suitable free radical initiators, resulting in poor image durability during lithographic printing operations. In addition, according to the method generally referred to as ablation or partial ablation, the heat pulses generated from the exposure infrared radiation at high energy levels can generally damage the physical integrity of the imaging composition. Ablation or partial ablation generally results in poor image durability. For example, in U.S. Patent 8,148,042 (noted above), the printing plate precursors PPP34 and PPP35 described in the imaging composition containing IR decomposable dyes require 275mJ / cm 2 Imaging energies were set so as to produce cyan printouts (ΔOD) of 0.43 and 0.60. There is no teaching that such imaging compositions are useful for forming printing plates having sufficient durability of the infrared radiation exposed areas after development of any kind.

[0012] It is demonstrated in U.S. Patent Application Publication No. 2020 / 0147950 (Billiet) that the IR-decomposable dyes taught in U.S. Patent No. 8,148,042 (noted above) can be directly incorporated into polymerizable compositions at more practical exposure energies (e.g., 120 mJ / cm 2 or lower), where PPP04 using the IR-decomposable dye IR02 in combination with IR01 (as used in PPP03) produced very little improvement in printout relative to PPP03 (e.g. at 120 mJ / cm 2 ΔE: 2.99 vs 2.12). Billiet's ΔE parameter is similar to the ΔE parameter defined below.

[0013] To avoid the inefficiency of IR-decomposable dyes and their undesirable effects on negative-working printing plate precursors having polymerizable imaging compositions, WO 2019 / 219560 (Billiet et al.) teaches placing the IR-decomposable dye in a protective overcoat applied on top of an imageable layer comprising an IR-imageable composition. However, the presence of a protective layer in the lithographic printing plate precursor requires additional steps during manufacture, and when present, removal of the protective layer reduces the speed of development. In addition, when the printing plate precursor is developed on-machine, the protective layer can release polymeric or other materials into the fountain solution and cause lithographic operation failures. Furthermore, the printout generated using infrared radiation at typical exposure doses suitable for such IR-sensitive imageable compositions is still far below what is required.

[0014] U.S. Patent Application Publication 2019 / 0329545 (Shibamoto et al.) teaches the use of certain IR-decomposable dyes that, in their excited state, are capable of accepting electrons from an electron-donating initiator upon exposure to infrared radiation to form a first wave of free radicals from the electron-donating initiator, and are further capable of forming a second wave of free radicals from the IR-decomposable dye by further decomposition thereof or by further reaction with an electron-accepting initiator. The disclosure demonstrates the color-forming ability of such imaging compositions containing IR-decomposable dyes under the exposure conditions presented.

[0015] U.S. Patent Application Publication 2020 / 0117086 (Noshi et al.) describes certain IR-decomposable dyes in combination with certain color developers. As illustrated by Comparative Examples 1 and 2 thereof, the specified IR-decomposable dyes of this teaching do not have sufficient printout in the absence of the specified color developer.

[0016] U.S. Patent No. 8,084,182 (Munnelly et al.) teaches the use of certain IR-decomposable dyes in IR-sensitive polymerizable compositions. In Examples 1-3, Munnelly et al. demonstrate that at 300 mJ / cm 2 The invention discloses good printout (ΔE values ​​of 13.8-17.4) at high exposure doses in an imageable composition comprising an IR-decomposable dye containing a combined alkoxycarbonylamino group used in combination with a conventional acid-sensitive dye precursor. However, in the absence of the acid-sensitive dye precursor, Example 4 of Munnelly et al. shows much lower printout (ΔE of 6.6). Using the teachings from this patent to compare IR-decomposable dyes (which do not contain alkoxycarbonylamino groups), even in the presence of the acid-sensitive dye precursor, the printout was not significantly improved at 300 mJ / cm 2 Low printout was also provided at imaging energies (ΔE of 4.6). Furthermore, Munnelly et al. demonstrated only a brief press run of 200 copies, and it was not obvious whether printing plates derived from the Munnelly et al. precursor would have sufficient image durability during printing to satisfy consumers in the industry who would typically print far more than 200 copies in a typical press run.

[0017] Co-pending and co-assigned U.S. patent applications U.S. Serial Nos. 17 / 844,953 (filed by Simpson et al. on June 21, 2022) and 17 / 685,570 (filed by Simpson et al. on March 3, 2022) (and having priority from USSN 63 / 169,278 filed on April 1, 2021) disclose certain color-changing compounds for producing strong and stable printouts. These color-changing compounds are cyanine dyes characterized by a mesogenic group that can be decomposed by radiation. The decomposition is expected to involve removal of protecting groups such as trifluoromethanesulfonimide groups to produce strong and irreversible printouts, but the indene moiety in the cyanine core structure enhances the formation of phenylated byproducts as part of the color formation. The ratio of phenylated products to decomposition products depends on the amount of borate compound provided in the imaging chemistry. The pending patent applications noted do not disclose any other mesogenic groups that allow the formation of phenylated products. In one of the comparative examples described therein, cyanine dyes containing an indenyl core and a diphenylamino mesogenic group are shown to provide poor printout, indicating that in the absence of a specified decomposable mesogenic group, insufficient formation of phenylated products is achieved. Decomposable mesogenic groups typically contain unstable leaving groups and, upon loss of the leaving group, become stronger electron donating groups at the meso position of the cyanine dye, which results in a change in the absorption peak of the cyanine dye. These pending patent applications do not disclose that the phenylated byproducts themselves are sufficient to generate printout. In addition, cyanine dyes containing decomposable mesogenic groups require more complex synthetic procedures and expensive reagents, and are therefore more expensive to use in lithographic printing plate precursors.

[0018] Despite all the efforts described in the industry to provide adequate and stable printout in press-developable lithographic printing plates with excellent press run durability, there is a continuing need to provide press-developable lithographic printing plate precursors that not only have the necessary properties desired, such as fast imaging speed, good on-press developability, good lithographic durability and good shelf life, but also exhibit strong and stable printout using lower exposure energies as required for high productivity, and which printout is achieved using relatively low-cost materials in the imaging chemistry. SUMMARY OF THE INVENTION

[0020] The present invention provides a lithographic printing plate precursor comprising:

[0021] Aluminum-containing substrates, and

[0022] An infrared radiation-sensitive image-recording layer disposed on an aluminum-containing substrate, the infrared radiation-sensitive image-recording layer comprising the following components (1), (2) and (3):

[0023] (1) a free radical initiator composition capable of generating free radicals upon exposure to infrared radiation;

[0024] (2) a free radical polymerizable composition; and

[0025] (3) A color-changing compound represented by the following structure (I):

[0026]

[0027] in:

[0028] Ar1, Ar2 and Ar3 independently represent the atoms necessary to complete a substituted or unsubstituted aromatic ring or to complete a substituted or unsubstituted heteroaromatic ring;

[0029] Y represents an oxygen atom, a sulfur atom, or a 4 R 5 ) represented by a dialkylmethylene group, wherein R 4 and R 5 is independently a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms;

[0030] R 1 and R 2 are independently substituted or unsubstituted alkyl;

[0031] X represents a single bond or a divalent linking group, and the divalent linking group is -S- or -O-;

[0032] L represents -C(=O)-OR 7 Group, -SO2-R 3 Group, -SO2NR 8 R 9 groups and groups other than -NPh2, where Ph represents phenyl, R 7 Represents a compound having the same structure as -C(=O)OR 7 A substituted or unsubstituted alkyl group is a secondary or tertiary carbon to which the remainder of the group is attached; and R 3 , R 8 and R 9 independently represent substituted or unsubstituted alkyl, substituted or unsubstituted aryl, or substituted or unsubstituted heteroaryl; and

[0033] Za represents one or more counterions to balance the charge in the rest of the color-changing compound according to component (3) of structure (I),

[0034] wherein the infrared radiation-sensitive image-recording layer contains one or more borate anions represented by the following structure (IIa):

[0035] B(R l0 R 11 R 12 R 13 )-

[0036] Structure (IIa)

[0037] Where R 10 , R 11 , R 12 and R 13 are independently substituted or unsubstituted alkyl, or substituted or unsubstituted aryl, provided that R 10 , R 11 , R 12 and R 13 At least three are the same or different substituted or unsubstituted aryl groups, and the substituted aryl groups each have no more than two halogen substituents.

[0038] The present invention also provides a method for providing a lithographic printing plate, comprising:

[0039] A) image-wise exposing a lithographic printing plate precursor according to any embodiment of the invention as described herein to infrared radiation to provide exposed areas and unexposed areas in the infrared radiation sensitive image recording layer, and

[0040] B) On-press removal of the unexposed areas in the infrared radiation-sensitive image-recording layer from the substrate using a lithographic ink, a fountain solution or a combination of a lithographic ink and a fountain solution.

[0041] The present invention provides printout images generated in infrared radiation sensitive image recording layers in areas exposed to relatively low energy imaging infrared radiation. Such printouts are initially strong and do not fade significantly during dark storage. In addition, in many embodiments, the imaging chemistry used to provide excellent printout images does not adversely affect imaging speed, on-press development capability, or lithographic image durability. In addition, the present invention solves the problems noted above and provides significant printout advantages using less costly chemicals. Further details of the present invention and the results obtained therefrom are provided below. DETAILED DESCRIPTION OF THE INVENTION

[0043] definition

[0044] The term "infrared radiation absorber" as used herein refers to a compound or material that absorbs electromagnetic radiation in the near infrared (near IR) region and the infrared (IR) region of the electromagnetic spectrum, and it generally refers to a compound or material having a maximum absorption in the near IR region and the IR region (e.g., at 750 nm or longer wavelengths).

[0045] As used herein, the terms "near infrared region" and "infrared region" refer to radiation having a wavelength of at least 750 nm and longer. In most cases, the term is used to refer to the region of the electromagnetic spectrum of at least 800 nm and up to and including 1400 nm.

[0046] For the purposes of the present invention, the intensity of the printout is usually indicated by the parameter ΔE, which is the Euclidean distance in the CIE 1976 L*a*b* color space between the color of the radiation-exposed area and the color of the radiation-unexposed area measured from reflection in 45 / 0 geometry (unpolarized) using a CIE 2° observer and D50 as illuminant, according to EN ISO 11664-4 "Colorimetry-Part 4: CIE 1976 L*a*b*Colourspace" and other known references. Color measurements can be made using commercial instruments such as the Techkon SpectroDens instrument. In the CIE 1976 L*a*b color space, colors are expressed as three color values: L* - the lightness (or brightness) of the color, a* - the green-red component of the color, b* - the blue-yellow component of the color value.

[0047] For the purposes of the present invention, the visible spectral region refers to the spectral region of electromagnetic radiation having a peak wavelength of 400 nm - 700 nm.

[0048] As used herein, the terms "print out" and "print out image" are intended to refer to the same feature.

[0049] Unless otherwise indicated, the term "weight %" refers to the amount of a component or material based on the total solids of a composition, formulation or layer. Unless otherwise indicated, the percentages for a dry layer or the total solids of the layer or coating formulation or composition may be the same.

[0050] As used herein, the term "hydrophilic" refers to a surface, layer or material that is generally "water-loving" in that it is miscible with, soluble in or wetted by water, as opposed to a "hydrophobic" surface, layer or material that is generally water-repellent and soluble in oil-based solvents.

[0051] The terms "on-press developable" and "on-press developability" as used herein refer to the ability of a precursor according to the present invention to be developed after exposure to infrared radiation (imaging) by mounting the imaged precursor on a suitable printing press and developing it during the first few printing passes using a fountain solution, a lithographic ink, or a combination of a fountain solution and a lithographic ink.

[0052] use

[0053] The lithographic printing plate precursors according to the present invention are useful for providing lithographic printing plates that exhibit a satisfactory and stable printout after image-wise exposure. These lithographic printing plates can be used for lithographic printing during operation of a printing press. According to the present invention, on-press processing or off-press processing can be used to prepare lithographic printing plates. A lithographic printing plate precursor having a structure and components as described below is prepared.

[0054] Lithographic printing plate precursors

[0055] The precursor according to the present invention can be formed by suitably applying an infrared radiation-sensitive image recording composition (as described below) to a suitable hydrophilic aluminum-containing substrate (as described below) to form a negative-working infrared radiation-sensitive image recording layer. Generally speaking, the infrared radiation-sensitive image recording composition (and the resulting infrared radiation-sensitive image recording layer) comprises: component (1) a free radical initiator composition, which is capable of generating free radicals when exposed to infrared radiation; component (2) a free radical polymerizable composition; and component (3) a color-changing compound, which is represented by structure (I) described below. All of these components (1), (2) and (3) are defined in detail below, and these components are the only essential components necessary to achieve the advantages of the present invention. In addition, it is necessary that the infrared radiation-sensitive image recording layer contains one or more borate anions as described in detail below.

[0056] In some embodiments, the infrared radiation-sensitive image recording composition (and the resulting infrared radiation-sensitive image recording layer) may further comprise one or more of the following components (4), (5), and (6): component (4) an infrared absorbing material different from (3) a color-changing compound (or a mixture of two or more thereof); component (5) an acid-sensitive dye precursor different from all of components (1), (2), (3), and (4) (or a mixture of two or more thereof); and component (6) a non-radical polymerizable polymer material different from all of components (1), (2), (3), and (4) (or a mixture of two or more thereof). These components (4) to (6) are described below. In some very useful embodiments, the infrared radiation-sensitive image recording layer consists essentially of all of the indicated components (1) to (4) and component (6) to provide the desired lithographic printing plate precursor with desirable printout, as well as optimal overall imaging, on-press development, and printing properties.

[0057] There is typically only one infrared radiation-sensitive image-recording layer in each precursor. This layer is typically the outermost layer in the precursor, but in some embodiments, there may be an outermost protective layer (also referred to as a topcoat, overcoat, or oxygen barrier layer) as described below disposed above (or directly above and in contact with) the infrared radiation-sensitive image-recording layer.

[0058] Aluminum-containing substrates:

[0059] The aluminum-containing substrate used to prepare the precursor according to the present invention generally has a hydrophilic imaging side surface, or at least has a surface that is more hydrophilic than the applied infrared radiation-sensitive image recording layer. Therefore, it can also be identified as a "hydrophilic aluminum-containing substrate". The aluminum-containing substrate generally comprises an aluminum-containing support, which can consist of raw aluminum or a suitable aluminum alloy conventionally used for the preparation of lithographic printing plate precursors.

[0060] The aluminum-containing support may be treated using techniques known in the art including some type of roughening by physical (mechanical) graining, electrochemical graining, or chemical graining, followed by one or more anodizing treatments. Each anodizing treatment is typically performed using phosphoric acid or sulfuric acid and conventional conditions to form the desired hydrophilic aluminum oxide (or anodic oxide) layer on the aluminum-containing support. There may be a single aluminum oxide (anodic oxide) layer, or there may be multiple aluminum oxide layers (e.g., an inner aluminum oxide layer and an outer aluminum oxide layer disposed above the inner aluminum oxide layer), each having a plurality of pores with varying depths and shapes of the pore openings. Such methods thus provide an anodized oxide layer or aluminum oxide layer beneath an infrared radiation-sensitive image-recording layer that may be provided as described below. Discussions of such holes and methods for controlling their width are described in, for example, U.S. Patent Publications 2013 / 0052582 (Hayashi), 2014 / 0326151 (Namba et al.), and 2018 / 0250925 (Merka et al.), as well as U.S. Patents 4,566,952 (Sprintschnik et al.), 8,789,464 (Tagawa et al.), 8,783,179 (Kurokawa et al.), and 8,978,555 (Kurokawa et al.), and EP 2,353,882 (Tagawa et al.).

[0061] In some embodiments, the aluminum-containing substrate may include a hydrophilic layer disposed directly on the grained, anodized, and post-treated aluminum-containing substrate, and such hydrophilic layer may include a non-crosslinked hydrophilic polymer having carboxylic acid side chains.

[0062] Alternatively, the anodized aluminum-containing substrate may be further treated using known post-anodization treatment methods, such as post-treatment using an aqueous solution of a hydrophilic material, to seal the anodic oxide pores and / or to hydrophilize its surface.

[0063] Particularly useful hydrophilic layer or coating materials for this purpose comprise: a compound having one or more ethylenically unsaturated polymerizable groups, one or more -OM groups (at least one of which is directly attached to a phosphorus atom), and a molecular weight of less than 2000 g / mol, wherein M represents a hydrogen atom, a sodium atom, a potassium atom, or an aluminum atom; and one or more hydrophilic polymers, at least one of which is a hydrophilic copolymer comprising at least (a) repeating units comprising amide units, and (b) repeating units comprising -OM' groups directly attached to a phosphorus atom, wherein M' represents a hydrogen atom, a sodium atom, a potassium atom, or an aluminum atom. Such a hydrophilic layer may be formed at a molecular weight of at least 0.0002 g / m 2 And up to and including 0.1g / m 2 The dry coverage is set above the outermost layer of aluminum oxide.

[0064] Infrared radiation sensitive image recording layer:

[0065] The infrared radiation-sensitive recording layer composition according to the present invention (and the infrared radiation-sensitive image-recording layer prepared therefrom) is designed to be "negative-working" as this term is known in the field of lithography. The infrared radiation-sensitive image-recording layer can be designed to have a certain combination of components to provide on-press developability to the lithographic printing plate precursor after exposure, for example, to enable on-press development using a fountain solution, a lithographic printing ink, or a combination of the two.

[0066] The present invention utilizes a component (1) free radical initiator composition that is capable of generating free radicals upon exposure to infrared radiation. Such a component (1) initiator composition may comprise one or more organic halogen compounds, such as bis(trihalomethyl)triazines and trihalomethyl aryl sulfones; or one or more onium salts, such as iodonium salts and sulfonium salts, many of which are known in the art to be capable of generating free radicals upon exposure to infrared radiation.

[0067] Representative compounds other than onium salts are described, for example, in

[0087] to

[0102] of U.S. Patent Application Publication 2005 / 0170282 (Inno et al., US '282) and U.S. Patent 6,309,792 (Hauck et al.), and also Japanese Patent Publication 2002 / 107916, and WO 2019 / 179995.

[0068] In some embodiments, component (1) free radical initiator composition should include one or more iodonium cations. Useful onium salts are described in, for example,

[0103] to

[0109] of US'282. For example, useful iodonium salts include at least one iodonium cation and a suitable anion in the molecule. Examples of iodonium salts include diaryl iodonium salts, such as diphenyl iodonium salts and derivatives thereof obtained by introducing one or more substituents into the phenyl ring of these compounds. Suitable substituents include, but are not limited to, alkyl, alkoxy, alkoxycarbonyl, acyl, acyloxy, chlorine, bromine, fluorine and nitro. Especially useful iodonium cations such as diaryl iodonium cations can have, for example, two substituted or unsubstituted phenyl groups.

[0069] Examples of anions in iodonium salts include, but are not limited to, halogen anions, ClO4 - PF6 - 、BF4 - 、SbF6 - 、CH3SO3 - CF3SO3 - 、C6H5SO3 - 、CH3C6H4SO3 - 、HOC6H4SO3 - 、ClC6H4SO3 - , and boron anions as described, for example, in U.S. Pat. No. 7,524,614 (Tao et al.). Representative useful iodonium salts are described in columns 6-7 of U.S. Pat. No. 7,524,614 (noted above), where the iodonium cation may contain various listed monovalent substituents "X" and "Y", or a carbocyclic or heterocyclic ring fused to the corresponding phenyl group.

[0070] In addition, the iodonium salts described in paragraphs

[0033] to

[0038] of the specification of Japanese Patent Publication No. 2002-082429 [or U.S. Patent Application Publication No. 2002-0051934 (Ippei et al.)] are useful. Representative iodonium borates are, for example, those listed in column 8 of U.S. Patent No. 7,524,614 (noted above). A particularly useful iodonium salt is diaryliodonium tetraphenylborate.

[0071] The component (1) free radical initiator composition is present in the infrared radiation-sensitive image recording layer in an amount (molar ratio or weight ratio) that will be readily apparent to a person skilled in the art of preparing press-developable lithographic printing plate precursors, and the minimum total amount and the maximum total amount are generally at least 1 wt. % and up to and including 20 wt. %, based on the total coverage (solids) of the infrared radiation-sensitive image recording layer.

[0072] Another essential feature of the infrared radiation sensitive image recording layer is component (2) a free radical polymerizable composition comprising one or more free radical polymerizable components, each of which contains one or more free radical polymerizable groups that can be polymerized using free radical initiation during infrared radiation exposure. In some embodiments, there are at least two free radical polymerizable components, which have the same or different numbers of free radical polymerizable groups in their respective molecules. Therefore, useful free radical polymerizable components may contain one or more free radical polymerizable monomers or oligomers, which have one or more polymerizable ethylenically unsaturated groups (e.g., two or more such groups). Similarly, crosslinkable polymers having such free radical polymerizable groups may also be used. Oligomers or prepolymers may be used, such as urethane acrylates and urethane methacrylates, epoxide acrylates and epoxide methacrylates, polyester acrylates and polyester methacrylates, polyether acrylates and polyether methacrylates, and unsaturated polyester resins. In some embodiments, the free radical polymerizable component comprises a carboxyl group.

[0073] The one or more free radical polymerizable components may have a sufficiently large molecular weight or have sufficient polymerizable groups to provide a cross-linkable polymer matrix that acts as a "polymer binder" for the other components in the infrared radiation-sensitive image-recording layer. In such embodiments, a different (6) non-free radical polymerizable polymer material (described below) is not required, but may still be present if desired.

[0074] Useful free radical polymerizable components include urea urethane (meth) acrylates or urethane (meth) acrylates having multiple (two or more) polymerizable groups. For example, urethane acrylates having two and up to six acrylate groups or even up to fifteen acrylate groups can be obtained by reacting a triisocyanate (e.g. N100 (Bayer Corp., Milford, Conn.)) or a diisocyanate (e.g., hexane-1,6-diisocyanate) is prepared by reacting hydroxyethyl acrylate, pentaerythritol triacrylate or dipentaerythritol pentaacrylate. Such urethane (meth) acrylate compounds or urea (meth) acrylate compounds have up to fifteen or more (meth) acrylate groups per molecule. Commercially available urethane acrylates having fifteen acrylate groups include U-15HA and UA-53H available from Shin-Nakamura Chemical Co. Ltd. These compounds having a large number of (meth) acrylates can be included in the (2) free radical polymerizable composition due to their high crosslinking efficiency.

[0075] Useful free radical polymerizable compounds include non-urethane (meth)acrylates and non-urea (meth)acrylates derived from polyfunctional alcohols, such as NK Ester A-DPH (dipentaerythritol hexaacrylate), available from Kowa American; and Sartomer SR399 (dipentaerythritol pentaacrylate), Sartomer 355 (di(trimethylolpropane) tetraacrylate), Sartomer SR295 (pentaerythritol tetraacrylate), Sartomer SR415 [ethoxylated (20) trimethylolpropane triacrylate], Sartomer SR494 (ethoxylated pentaerythritol tetraacrylate), available from Sartomer Company, Inc. These non-urethane (meth)acrylates and non-urea (meth)acrylates may also have a large number of (meth)acrylate groups per molecule.

[0076] For example, useful free radical polymerizable components are also described in EP 1,182,033A1 (Fujimaki et al.) (beginning at paragraph

[0170] ) and U.S. Pat. Nos. 6,309,792 (Hauck et al.), 6,569,603 (Furukawa), and 6,893,797 (Munnelly et al.). Other useful free radical polymerizable components include those described in U.S. Patent Application Publication No. 2009 / 0142695 (Baumann et al.), which include 1H-tetrazolyl groups.

[0077] The total amount of one or more components of the free radical polymerizable composition of component (2) present is generally at least 10 wt % or at least 20 wt %, and up to and including 50 wt % or up to and including 70 wt %, all based on the total coverage (solids) of the infrared radiation-sensitive image recording layer.

[0078] The third essential component of the infrared radiation-sensitive image recording composition and the infrared radiation-sensitive image recording layer according to the present invention is component (3) a color-changing compound or a mixture of two or more thereof, each of which is represented by the following structure (I):

[0079]

[0080] Wherein Ar1, Ar2 and Ar3 independently represent the atoms necessary to make the substituted or unsubstituted aromatic ring complete or to make the substituted or unsubstituted heteroaromatic ring complete.Therefore, in general, for any or all of Ar1, Ar2 and Ar3, it is necessary to have an appropriate number of carbon atoms to make the substituted or unsubstituted aromatic ring complete, such as to make benzene (benzo) ring or naphthalene (naphtho) ring complete.In addition, for any or all of Ar1, Ar2 and Ar3, it is necessary to have an appropriate number of carbon atoms and one or more heteroatoms to make the substituted or unsubstituted heteroaromatic ring complete, such as to make the following complete: pyridine-2-yl, pyridine-3-yl, pyridine-4-yl, pyridazine, pyrimidine-2-yl, pyrimidine-4-yl, pyrimidine-5-yl or pyrimidine-6-yl, pyrazine, triazine, pyrrole, furan, thiophene, pyrazole or oxazole, imidazole, thiazole or triazole ring.

[0081] In many useful embodiments of the present invention, Ar1 and Ar2 are the same atoms necessary for making substituted or unsubstituted aromatic rings, such as identical substituted or unsubstituted aromatic rings such as substituted or unsubstituted benzene (benzo) rings complete. In addition, one or both of the complete aromatic rings by the atom of Ar1 and Ar2 can be replaced by, for example, the following groups: one or more identical or different optionally substituted alkyl, alkoxy, halogen groups (such as one or two identical or different halogen groups), cyano,-COOR' groups,-SO3R' groups or-SO2R' groups, wherein R' represents substituted or unsubstituted alkyl, which can be identical or different for each indicated group. For one or both of the complete aromatic rings by the atom of Ar1 and Ar2, it is particularly useful to be replaced by one or two halogen groups (such as chloro groups) which can be identical or different groups. It is also desirable that Ar3 represents the carbon atom and hydrogen atom required for making the benzene (benzo) rings complete in structure (I).

[0082] Furthermore, in structure (I), Y represents an oxygen atom, a sulfur atom, or a moiety consisting of>C(R 4 R 5 ) represented by a dialkylmethylene group, wherein R 4 and R 5 is independently a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms. In many useful embodiments of the present invention, each representation of Y is the same or different dialkylmethylene group, or even the same dialkylmethylene group, wherein R 4 and R 5 is the same unsubstituted alkyl radical having 1 or 2 carbon atoms. A skilled chemist will be able to prepare numerous compounds in which Y is varied among the possible radicals, including the many possible dialkylmethylene radicals.

[0083] In structure (I), R 1 and R 2Independently substituted or unsubstituted alkyl groups each have 1 to 12 carbon atoms, and in many embodiments one or both of such alkyl groups may contain the same or different ether or ester linkages which interrupt the carbon chain or, in the case of an ester group, which may serve to terminate the alkyl chain.

[0084] Further, in structure (I), X represents a single bond or a divalent linking group selected from -S- and -O-. In a particular embodiment used in the present invention, X represents a single bond.

[0085] In structure (I), L represents a group other than -C(=O)-OR 7 Group, -SO2-R 3 Group, -SO2NR 8 R 9 groups and groups other than -NPh2, where Ph represents phenyl, R 7 represents a substituted or unsubstituted alkyl group having a -C(=O)OR 7 The rest of the group is attached to 1-8 carbon atoms including the secondary or tertiary carbon atom. 3 , R 8 and R 9 Independently represents a substituted or unsubstituted alkyl group having 1 to 12 carbon atoms, a substituted or unsubstituted aryl group having 6 or 10 carbon atoms in the aromatic ring, or a substituted or unsubstituted heteroaryl group. Under typical imaging conditions, L is stable and does not undergo a decomposition reaction that results in cleavage of the L group from X. L is typically an electron withdrawing group.

[0086] In some embodiments, the (3) color-changing compound is that represented by structure (Ia) below.

[0087]

[0088] Among them, Ar1, Ar2, Ar3, R 1 , R 2 , Y and Za are the same groups as described above for structure (I), and A is selected from -SR 14 、-OR 14 , chloro, bromo, iodo, fluoro, nitro, cyano, trichloromethyl, tribromomethyl, trifluoromethyl, alkylammonium, dialkylammonium and trialkylammonium groups, wherein the same or different alkyl groups each contain 1 to 10 carbon atoms and may be optionally substituted, and R 14 It is an optionally substituted aryl group or an optionally substituted heteroaryl group or an optionally substituted alkyl group. In view of the convenience of synthesis, it is particularly preferred that A is a halogen group (such as a chloro group) or -SR 14 OR 14 , where R 14is optionally substituted alkyl, optionally substituted aryl or optionally substituted heteroaryl. Wherein A is -SR 14 The color-changing compound according to structure (Ia) of the group can be easily derived from the compound according to structure (Ia) in which A is a chloro group by reaction with a suitable compound having an -SH group or an -OH group. Compounds having -SH groups are generally used as free radical co-initiators, accelerators or stabilizers. Examples of such compounds include 3-mercapto-1H-1,2,4-triazole (CAS No.3179-31-5), 2-mercaptobenzothiazole (CAS No.149-30-4) and 5-methyl-1,3,4-thiadiazole-2-thiol (CAS No.29490-19-5). Compounds having phenolic OH groups are generally used as free radical initiators or as thermal stabilizers. Examples of free radical initiators with phenolic OH groups include 4-hydroxyphenyl tribromomethyl sulfone as described in U.S. Patent Application Publication 201 1 / 0,315,034A (Heylen et al.). When a compound having one or more -SH groups or one or more -OH groups is included in an infrared radiation-sensitive image recording layer which also contains a color-forming compound according to structure (Ia) wherein A is a halogen group (e.g. a chloro group), wherein A is -SR 14 OR 14 The new color-forming compound according to structure (Ia) can be formed by dehydrohalogenation in situ in the coating solution, or during coating, drying or storage of the precursor. The compound having one or more -SH groups is formed by R 14 -SH stands for, where R 14 is a substituted or unsubstituted alkyl, a substituted or unsubstituted aryl, or a substituted or unsubstituted heteroaryl. In order to avoid premature color formation in the infrared radiation-sensitive image recording layer of the lithographic printing plate precursor before exposure to infrared radiation, it is preferred that R 14 The group does not contain an -NH- subgroup.

[0089] Useful compounds having one or more -SH groups include, but are not limited to, 2-mercaptobenzothiazole, 2-mercaptobenzoxazole, 2,2'-dithiobis(benzothiazole), 1-phenyltetrazole-5-thiol, 5-mercapto-1-methyltetrazole, 5-tert-butylthio-1,3,4-thiadiazole-2-thiol, 5,5'-dithiobis(1-phenyl-1H-tetrazole), 3-mercapto-4-methyl-1,2,4-triazole, N-tert-butyl-2-benzothiazolesulfenamide, and 4-methyl-5-phenyl-4H-1,2,4-triazole-3-thiol.

[0090] R 14A useful example is shown below:

[0091]

[0092]

[0093] Finally, in structure (I), Za represents one or more counterions to balance the charge in the remainder of the color-changing compound according to structure (I). When the remainder of the color-changing compound according to structure (I) is positively charged, Za represents an anion. Many useful anions are known in the art, such as halogen anions, ClO4 - PF6 - 、BF4 - 、SbF6 - 、CH3SO3 - CF3SO3 - 、C6H5SO3 - 、CH3C6H4SO3 - 、HOC6H4SO3 - 、ClC6H4SO3 - ; and boron-containing anions as described in, for example, U.S. Patent 7,524,614 (noted above). Useful boron-containing anions include tetraaryl borate anions (e.g., tetraphenyl borate) as described above for electron-donating agents. In some embodiments, Za can be supplied by an electron-donating agent in (1) a radical initiator composition. When the remainder of the color-changing compound (3) according to structure (I) is negatively charged, Za represents a cation. Useful cations are known in the art, such as alkali metal ions, alkaline earth metal ions, tertiary ammonium ions, and quaternary ammonium ions; and onium ions, such as iodonium ions, sulfonium ions, or phosphonium ions. In some embodiments, Za can be supplied by an onium compound in the radical initiator composition of component (1) as described above.

[0094] While not wishing to be bound by a particular theory, it is believed that Ar3 in structure (I) affects the geometry of the polymethine chain in the component (3) color-changing compound and thus renders it more reactive in the presence of an organic borate anion according to structure (IIa) as described below. For example, in the presence of a tetraphenylborate anion, a compound according to structure (I) [inventive color-changing compound 2 or ICCC-2 shown below] can undergo a chemical reaction (shown below) to form a phenylated product ICCC 2-Ph during or after irradiation of the infrared radiation-sensitive image recording layer by a suitable infrared source. It is also possible to phenylate the component (3) color-changing compound by reacting with a triphenylalkyl borate such as triphenyl-n-butyl borate and tris(3-fluorophenyl)-n-butyl borate.

[0095]

[0096] The phenylated product such as ICCC 2-Ph in the infrared radiation exposed area of ​​the infrared radiation sensitive image recording layer is stable at room temperature for at least one week and thus provides a stable printout to the infrared radiation exposed lithographic printing plate precursor. In addition, in the presence of a sufficient amount of a borate anion according to the following structure (IIa), the phenylated product can be formed at a much lower infrared radiation energy input than that normally required for a decomposition reaction involving cleavage of a leaving group as described in many prior arts listed in the background of the invention section above.

[0097] Even in the presence of a sufficient amount of the borate compound, Ar3 in structure (I) is still necessary. In the absence of Ar3, the phenylation reaction will be inefficient, if it occurs at all.

[0098] The amount of the color-changing compound (single or a mixture of two or more thereof) of component (3) represented by structure (I) in the infrared radiation-sensitive image recording layer is usually at least 0.5 wt % or at least 1 wt %, and up to and including 10 wt % or up to and including 15 wt %, based on the total weight of the infrared radiation-sensitive image recording layer.

[0099] In addition, it is essential that the infrared radiation-sensitive image-recording layer according to the present invention contains one or more borate anions represented by the following structure (IIa):

[0100] B(R 10 R 11 R 12 R 13 )-

[0101] Structure (IIa)

[0102] Where R 10 , R 11 , R 12 and R 13 are independently substituted or unsubstituted alkyl, or substituted or unsubstituted aryl, provided that R 10 , R 11 , R 12 and R 13At least three are the same or different substituted or unsubstituted aryl groups, and the substituted aryl groups each have no more than two halogen substituents. One or more borate anions may be provided to the infrared radiation sensitive image recording layer in various ways. For example, one or more borate anions may be provided as part of one or more iodonium salts in the component (1) free radical initiator composition. Alternatively, one or more borate anions may be provided as one or more Za counterions in structure (I) or as part of the component (4) infrared absorbing material described below. Still further, one or more borate anions may be provided as separate borate salts in the component (1) free radical initiator composition.

[0103] As noted above, in some embodiments, one or more iodonium cations may be provided as part of the component (1) free radical initiator composition for the infrared radiation-sensitive image recording layer. Since the borate compound present in the infrared radiation-sensitive image recording layer may participate in the reaction with the iodonium cation to produce free radical generation, as well as the reaction with the component (3) color-changing compound represented by structure (I), the amount of borate compound available for the phenylation reaction depends on both the amount of the borate compound and the amount of the iodonium cation. Therefore, in order to obtain a high-performance infrared radiation-sensitive image recording layer at low exposure energy (e.g., 110 mJ / cm 2 ) to produce sufficient printout and image durability under conditions of high sensitivity, the infrared radiation-sensitive image recording layer contains sufficient one or more iodonium cations and one or more borate anions such that the molar ratio of one or more borate anions to one or more iodonium cations is at least 0.25:1, or at least 0.5:1, or even at least 0.8:1, and up to and including 2:1, or up to and including 4:1.

[0104] Although not necessary, it is highly desirable that the infrared radiation-sensitive image recording layer according to the present invention may also include a component (4) infrared absorbing material (one or a mixture of two or more thereof) different from the component (3) color-changing compound described above. The component (4) infrared radiation absorber provides the desired infrared radiation sensitivity and / or converts the radiation into heat. Useful infrared radiation absorbers may be pigments or, in particular, infrared radiation absorbing dyes. Suitable dyes of this type are those described, for example, in U.S. Pat. Nos. 5,208,135 (Patel et al.), 6,153,356 (Urano et al.), 6,309,792 (Hauck et al.), 6,569,603 (Furukawa), 6,797,449 (Nakamura et al.), 7,018,775 (Tao), 7,368,215 (Munnelly et al.), 8,632,941 (Balbinot et al.) and U.S. Patent Application Publication 2007 / 056457 (Iwai et al.). In some infrared radiation-sensitive embodiments, it is desirable that at least one component (4) infrared radiation absorber in the infrared radiation-sensitive image recording layer is a cyanine dye comprising a suitable cationic cyanine chromophore and a tetraarylborate anion (e.g., tetraphenylborate anion). Examples of such dyes include those described in U.S. Patent Application Publication No. 2011 / 003123 (Simpson et al.).

[0105] The total amount of component (4) infrared radiation absorber is at least 0.5 wt% or at least 1 wt% and up to and including 15 wt% or up to and including 30 wt% based on the total weight of the infrared radiation-sensitive image recording layer.

[0106] Another optional but desirable component of the infrared radiation sensitive image recording layer is component (5) acid-sensitive dye precursor (e.g., a single species or a combination of two or more thereof). Useful component (5) acid-sensitive dye precursor is a colorless or almost colorless compound in a neutral form, and the compound is converted into a colored form when protonated. Many leuco dyes are known for this purpose, including those described in, for example, EP 3,418,332A2 (Inasaki et al., corresponding to U.S. Patent Application Publication 2018 / 0356730)

[0209] to

[0222] and EP2,018,365B1 (Nguyen et al., corresponding to U.S. Patent 7,910,768)

[0044] to

[0046] . These component (5) acid-sensitive dye precursors are different from all components (1), (2), (3) and (4) defined above.

[0107] In some embodiments, the weight ratio of component (5) acid-sensitive dye precursor to component (3) color-changing compound represented by structure (I) in the infrared radiation-sensitive image-recording layer is less than 1, or even less than 0.8.

[0108] For example, in some embodiments, at least one of the component (5) acid-sensitive dye precursors comprises a lactone substructure. More particularly, useful component (5) acid-sensitive dye precursors can be represented by one or more of the following structures (C1) and (C2):

[0109]

[0110] Where R 11 To R 19 Be independently hydrogen, unsubstituted or substituted alkyl or unsubstituted or substituted aryl.This type of substituted or unsubstituted alkyl can have 1-20 carbon atom, and possibly, one or more substituents can include but not limited to halogen, alkyl, aryl, alkoxy and phenoxy.Useful substituted or unsubstituted aryl can be aromatic carbocyclic ring or aromatic heterocyclic ring, and this type of group can have two or more condensed rings.Useful substituents for aryl ring can include but not limited to those described above for alkyl.But, skilled chemists can use this instruction about structure (C1) and structure (C2) to design other useful component (5) acid-sensitive dye precursors as guidance.

[0111] As indicated above, such component (5) acid-sensitive dye precursors may optionally be present in any desired amount of at least 0.5 wt% and up to and including 10 wt% based on the total coverage (solids) of the infrared radiation-sensitive image recording layer.

[0112] In many embodiments of the present invention, it is also optional but desirable that the infrared radiation-sensitive image-recording layer further comprises a component (6) non-radical polymerizable polymer material (or polymer binder), or a mixture of two or more thereof, each of which lacks any functional group that, if present, would enable the polymer material to undergo free radical polymerization. Thus, such component (6) non-radical polymerizable polymer material is different from all of the components (1), (2), (3) and (4) described above.

[0113] The weight average molecular weight (M) of the non-free radically polymerizable polymeric material of useful component (6) is as determined by gel permeation chromatography (polystyrene standards). w ) is typically at least 2,000 g / mol or at least 20,000 g / mol and up to and including 300,000 g / mol or up to and including 500,000 g / mol.

[0114] Such component (6) non-radical polymerizable polymer materials can be selected from polymer binder materials known in the art, including polymers comprising repeating units having side chains comprising polyoxyalkylene segments, such as those described in, for example, U.S. Pat. No. 6,899,994 (Huang et al.). Other useful polymer binders include two or more types of repeating units having different side chains comprising polyoxyalkylene segments, such as described in, for example, WO Publication 2015-156065 (Kamiya et al.). Some of such polymer binders may further include repeating units having cyano side groups, such as those described in, for example, U.S. Pat. No. 7,261,998 (Hayashi et al.).

[0115] Such component (6) non-free radical polymerizable polymeric material may also have a backbone comprising a plurality (at least two) of urethane moieties and pendant groups comprising polyoxyalkylene segments.

[0116] Useful component (6) non-radical polymerizable polymer material may be present in particulate form, i.e., in the form of discrete particles (non-agglomerated particles). Such discrete particles may have an average particle size of at least 10 nm and up to and including 1500 nm or typically at least 80 nm and up to and including 600 nm, and are typically uniformly distributed in the infrared radiation-sensitive image recording layer. The average particle size may be determined using various known methods and nanoparticle measuring equipment, including measuring the particles in an electron scanning microscope image and taking the average of a certain number of measurements.

[0117] Component (6) non-radical polymerizable polymer material may be present in an amount of at least 10 wt % or at least 20 wt % and up to and including 50 wt % or up to and including 70 wt % based on total coverage (solids) of the infrared radiation-sensitive image recording layer.

[0118] The infrared radiation-sensitive image-recording layer used in the present invention may also optionally include crosslinked polymer particles, such materials having an average particle size of at least 2 μm, as described, for example, in U.S. Pat. Nos. 9,366,962 (Hayakawa et al.), 8,383,319 (Huang et al.), and 8,105,751 (Endo et al.).

[0119] The infrared radiation-sensitive image-recording layer may also include conventional amounts of various other optional addenda, including, but not limited to, dispersants, humectants, biocides, plasticizers, surfactants for coatability or other properties, tackifiers, pH adjusters, desiccants, defoamers, development aids, rheology modifiers, or combinations thereof, or any other addenda commonly used in the lithographic coating art.

[0120] Overlay:

[0121] Although the infrared radiation-sensitive image-recording layer may be the outermost layer with no layers disposed thereon, it is possible that the inventive precursor may be designed with an overcoat layer disposed above (or directly on) the negative-working infrared radiation-sensitive image-recording layer that can be developed on-press (with no intervening layers between the two layers). When present, the overcoat layer is typically the outermost layer of the precursor and may be hydrophilic or hydrophobic in nature.

[0122] Can be at least 0.1g / m 2 or at least 0.15g / m 2 And up to and including 2.5g / m 2 But less than 4g / m 2 In some embodiments, the dry coating coverage is as low as 0.1 g / m 2 And up to and including 1.5g / m 2 , or at least 0.1g / m 2 And up to and including 0.9g / m 2 , so that the cover layer is relatively thin.

[0123] Preparation of lithographic printing plate precursors:

[0124] The lithographic printing plate precursor according to the present invention can be provided in the following manner. The infrared radiation-sensitive image recording layer formulation comprising the essential components (1), (2), (3) described above, and the required one or more iodonium cations and one or more borate anions, and the optional components (4), (5), (6) and other optional additives can be applied to the hydrophilic surface of a suitable aluminum-containing substrate (which is usually in the form of a continuous web) as described above using any suitable equipment and procedures. Typically, once the infrared radiation-sensitive image recording layer formulation is applied at a suitable wet coverage, it is dried in a suitable manner known in the art to provide the desired dry coverage as indicated below, thereby providing an infrared radiation-sensitive continuous web or infrared radiation-sensitive continuous article.

[0125] The manufacturing method generally comprises mixing the various components required for the infrared radiation-sensitive image recording layer in a suitable organic solvent or a mixture thereof containing water or water, applying the resulting infrared radiation-sensitive image recording layer formulation to a continuous aluminum-containing substrate web, and removing the solvent by evaporation under suitable drying conditions.

[0126] After suitable drying, the dry coverage of the infrared radiation-sensitive image-recording layer on the aluminum-containing substrate may be at least 0.1 g / m 2 or at least 0.4g / m 2 , and up to and including 2g / m2 or up to and including 4 g / m 2 , but other dry coverage amounts may be used as necessary to provide the desired dry coverage.

[0127] As described above, in some embodiments, a suitable overcoat formulation (described above) may be applied to the dried infrared radiation-sensitive image-recording layer using known coating and drying conditions, equipment, and procedures.

[0128] Imaging (exposure) conditions

[0129] During use, the infrared radiation-sensitive lithographic printing plate precursor of the present invention may be exposed to a suitable infrared radiation source, depending on the infrared radiation absorber present in the infrared radiation-sensitive image recording layer. In some embodiments, one or more infrared radiation-emitting lasers (which emit significant infrared radiation in the range of at least 750 nm and up to and including 1400 nm, or at least 800 nm and up to and including 1250 nm) may be used to image the lithographic printing plate precursor to produce exposed and unexposed areas in the infrared radiation-sensitive image recording layer. Such infrared radiation-emitting lasers may be used for such imaging in response to digital information provided by a computing device or other digital information source. Laser imaging may be digitally controlled in a suitable manner known in the art.

[0130] Thus, imaging can be performed using imaging or exposing infrared radiation from a laser (or an array of such lasers) that produces infrared radiation. Imaging can also be performed simultaneously using imaging radiation at multiple infrared (or near IR) wavelengths, if desired. The laser used to expose the precursor is typically a diode laser due to the reliability and low maintenance of diode laser systems, but other lasers, such as gas lasers or solid-state lasers, can also be used.

[0131] The infrared imaging apparatus can be configured as a flatbed recorder or a drum recorder in which the infrared radiation sensitive lithographic printing plate precursor is mounted to the inner cylindrical surface or the outer cylindrical surface of the drum. Examples of useful imaging apparatus are available as the following models: KODAK 囤 Trendsetter plate setter (Eastman Kodak Company) and NEC AMZISetter X-series (NEC Corporation, Japan). Other suitable imaging devices include Screen PlateRite 4300 series or 8600 series plate setters (available from Screen USA, Chicago, IL) operating at a wavelength of 810 nm or thermal CTP plate setters from Panasonic Corporation (Japan).

[0132] When using an infrared radiation imaging source, the imaging intensity may be at least 30 mJ / cm 2 and up to and including 500 mJ / cm 2 , and usually at least 50 mJ / cm 2 and up to and including 300 mJ / cm 2 .

[0133] On-press washing (development) and printing

[0134] After imagewise exposure as described above, the exposed infrared radiation-sensitive lithographic printing plate precursor having exposed and unexposed areas in the infrared radiation-sensitive image-recording layer can be processed on-press to remove the unexposed areas (and any hydrophilic protective layer over such areas). During this processing and during lithographic printing, the exposed aluminum-containing substrate surface repels ink, while the remaining exposed areas accept lithographic ink.

[0135] Thus, the negative-working lithographic printing plate precursors of the present invention can be developed on-press using a lithographic ink, a fountain solution, or a combination of a lithographic ink and a fountain solution. In such embodiments, the imaged (exposed) infrared radiation-sensitive lithographic printing plate precursor according to the present invention is mounted on a printing press and a printing operation is started. When the initial printing run is prepared, the unexposed areas in the infrared radiation-sensitive image-recording layer are removed by a suitable fountain solution, a lithographic ink, or a combination of the two. A representative example of a fountain solution is Varn Litho Etch 142W + Varn PAR (alcohol sub) (available from Varn International, Addison, IL).

[0136] In a typical press start-up using a sheet-fed printing press, the dampening rollers are first engaged and dampening solution is supplied to the mounted imaged precursor to swell the exposed infrared radiation-sensitive image recording layer at least in the unexposed areas. After a few rotations, the inking rollers are engaged and they supply lithographic ink to cover the entire printing surface of the lithographic printing plate. Typically, within 5-20 rotations after the inking rollers are engaged, the printing sheet is supplied to remove the unexposed areas of the infrared radiation-sensitive image recording layer from the lithographic printing plate and the material on the blanket cylinder (if present) using the formed ink-fountain solution emulsion.

[0137] The present invention provides at least the following embodiments and combinations thereof, but as those skilled in the art will appreciate from the teachings of this disclosure, other feature combinations are considered to be within the present invention:

[0138] 1. A lithographic printing plate precursor comprising:

[0139] Aluminum-containing substrates, and

[0140] An infrared radiation-sensitive image-recording layer disposed on an aluminum-containing substrate, the infrared radiation-sensitive image-recording layer comprising the following components (1), (2) and (3):

[0141] (1) a free radical initiator composition capable of generating free radicals upon exposure to infrared radiation;

[0142] (2) a free radical polymerizable composition; and

[0143] (3) A color-changing compound represented by the following structure (I):

[0144]

[0145] in:

[0146] Ar1, Ar2 and Ar3 independently represent the atoms necessary to complete a substituted or unsubstituted aromatic ring or to complete a substituted or unsubstituted heteroaromatic ring;

[0147] Y represents an oxygen atom, a sulfur atom, or a 4 R 5 ) represented by a dialkylmethylene group, wherein R 4 and R 5 is independently a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms;

[0148] R 1 and R 2 are independently substituted or unsubstituted alkyl;

[0149] X represents a single bond or a divalent linking group, and the divalent linking group is -S- or -O-;

[0150] L represents -C(=O)-OR 7 Group, -SO2-R 3 Group, -SO2NR 8 R 9 groups and groups other than -NPh2, where Ph represents phenyl, R 7 Represents a compound having the same structure as -C(=O)OR 7 A substituted or unsubstituted alkyl group is a secondary or tertiary carbon to which the remainder of the group is attached; and R 3 , R 8 and R 9 independently represent substituted or unsubstituted alkyl, substituted or unsubstituted aryl, or substituted or unsubstituted heteroaryl; and

[0151] Za represents one or more counterions to balance the charge in the rest of the color-changing compound according to component (3) of structure (I),

[0152] wherein the infrared radiation-sensitive image-recording layer contains one or more borate anions represented by the following structure (IIa):

[0153] B(R 10 R 11 R 12 R 13 ) -

[0154] Structure (IIa)

[0155] Where R 10 , R 11 , R 12 and R 13 are independently substituted or unsubstituted alkyl or substituted or unsubstituted aryl, provided that R 10 , R 11 , R 12 and R 13 At least three are the same or different substituted or unsubstituted aryl groups, and the substituted aryl groups each have no more than two halogen substituents.

[0156] 2. The lithographic printing plate precursor of embodiment 1, wherein the color-changing compound of component (3) is represented by structure (Ia):

[0157]

[0158] Among them, Ar1, Ar2, Ar3, R 1 , R 2 , Y and Za are the same groups as described above for structure (I), and A is selected from -SR 14 、-OR 14 , chloro, bromo, iodo, fluoro, nitro, cyano, trichloromethyl, tribromomethyl, trifluoromethyl, alkylammonium, dialkylammonium and trialkylammonium groups, wherein the same or different alkyl groups each contain 1 to 10 carbon atoms and may be optionally substituted, and R 14 is optionally substituted alkyl, optionally substituted aryl or optionally substituted heteroaryl.

[0159] 3. The lithographic printing plate precursor of embodiment 2, wherein A represents a halogen group or -SR 14 , where R 14 represents optionally substituted alkyl, optionally substituted aryl or optionally substituted heteroaryl.

[0160] 4. The lithographic printing plate precursor according to embodiment 2 or 3, wherein A represents a chloro group.

[0161] 5. The lithographic printing plate precursor of embodiment 2 or 3, wherein A represents -SR14 , where R 14 represents optionally substituted alkyl, optionally substituted aryl or optionally substituted heteroaryl.

[0162] 6. A lithographic printing plate precursor as described in any of embodiments 1-5, wherein component (1) the free radical initiator composition comprises one or more iodonium cations, and the amount of the iodonium cations is such that the molar ratio of one or more borate anions to one or more iodonium cations is at least 0.4:1.

[0163] 7. The lithographic printing plate precursor of any of embodiments 1 to 6, wherein the infrared radiation-sensitive image-recording layer further comprises a component (4) infrared absorbing material different from the component (3) color-changing compound.

[0164] 8. The lithographic printing plate precursor of any of embodiments 1-7, wherein Ar3 represents the carbon and hydrogen atoms required to complete the benzene ring.

[0165] 9. The lithographic printing plate precursor of any of embodiments 1-8, wherein Za comprises a tetraarylborate anion.

[0166] 10. The lithographic printing plate precursor of any of embodiments 1 to 9, wherein the free radical initiator composition of component (1) comprises an organic borate represented by the following structure (II):

[0167] [B(R 10 R 11 R 12 R 13 ) - ] n M n+

[0168] Structure (II)

[0169] Where R 10 , R 11 , R 12 and R 13 As defined for structure (IIa), n is an integer equal to or greater than 1, and M n+ It is an n-valent cation.

[0170] 11. The lithographic printing plate precursor of embodiment 10, wherein R of structure (II) and structure (IIa) 10 , R 11 , R 12 and R 13 All are the same or different substituted or unsubstituted aryl groups.

[0171] 12. The lithographic printing plate precursor of embodiment 10 or 11, wherein R in structure (IIa) and structure (II) 10 , R 11 , R 12 and R 13 All are the same substituted or unsubstituted phenyl groups.

[0172] 13. The lithographic printing plate precursor of any of embodiments 7 to 12, wherein the infrared radiation-sensitive image-recording layer further comprises a component (5) acid-sensitive dye precursor different from all components (1), (2), (3) and (4) defined above.

[0173] 14. The lithographic printing plate precursor of any of embodiments 1-13, wherein component (1) the free radical initiator composition comprises a diaryliodonium tetraphenylborate.

[0174] 15. The lithographic printing plate precursor described in embodiment 13 or 14, wherein the weight ratio of component (5) acid-sensitive dye precursor to component (3) color-changing compound represented by the following structure (I) in the infrared radiation-sensitive image recording layer is less than 1.

[0175] 16. A lithographic printing plate precursor as described in any of embodiments 7-15, wherein the infrared radiation sensitive image recording layer further comprises component (6) a non-radical polymerizable polymer material, which is different from all components (1), (2), (3) and (4) defined above and is present in particulate form.

[0176] 17. The lithographic printing plate precursor of any of embodiments 1 to 16, wherein the infrared radiation sensitive image recording layer is the outermost layer.

[0177] 18. A lithographic printing plate precursor as described in any of embodiments 1-17, wherein the color-changing compound of component (3) represented by structure (I) is present in the infrared radiation-sensitive image recording layer in an amount of coverage of at least 0.5 wt. % and up to and including 15 wt. %, based on the total weight of the infrared radiation-sensitive image recording layer.

[0178] 19. A method for providing a lithographic printing plate, comprising:

[0179] A) image-wise exposing a lithographic printing plate precursor according to any of embodiments 1 to 18 to infrared radiation to provide exposed areas and unexposed areas in the infrared radiation-sensitive image recording layer, and

[0180] B) On-press removal of the unexposed areas in the infrared radiation-sensitive image-recording layer from the substrate using a lithographic ink, a fountain solution or a combination of a lithographic ink and a fountain solution.

[0181] The following examples are provided to further illustrate the practice of the present invention and are not intended to be limiting in any way. Unless otherwise noted, the materials used in the examples were obtained from the various commercial sources indicated, although other commercial sources may also be utilized.

[0182] The aluminum-containing substrate for the lithographic printing plate precursor was prepared as follows:

[0183] Hydro 1052 aluminum alloy strips or meshes with a thickness of 0.28 mm (available from Norsk Hydro ASA, Norway) were used as aluminum-containing "plate" raw materials or supports. Both the pre-etching step and the post-etching step were carried out in alkaline solutions under known conditions. The etched aluminum support was roughened (or etched) by electrochemical means in a hydrochloric acid solution at about 23° C. to obtain an arithmetic mean roughness (Ra) of 0.5 μm on the surface of the aluminum-containing support. Thereafter, the aluminum-containing support was subjected to two separate anodizing treatments. The first anodizing treatment was carried out using phosphoric acid as the electrolyte to form a pore having an average micropore diameter (D o ) and an average dry thickness (T o ) of aluminum oxide outer layer. Then a second anodization treatment was performed using phosphoric acid as electrolyte to form an average micropore diameter (D i ) and an average dry thickness (T i ). The two anodization steps are carried out as a continuous process on a typical manufacturing line used to make lithographic printing plate precursors. The aluminum-containing support thus prepared is coated with an aqueous solution of polyacrylic acid to give an aqueous solution of 0.03 g / m 2 Dry thickness.

[0184] A negative-working infrared radiation-sensitive image recording layer was then formed on the aluminum-containing substrate as described by individually coating the infrared radiation-sensitive composition formulations having the components and amounts shown in Tables I, II and III below using a bar coater to provide 0.9 g / m 2 of each of the inventive precursors and comparative precursors described below after drying at 50° C. for 60 seconds. 2 The raw materials indicated in Table I are identified in Table II below, and the amounts of the various components are shown in Table III. These materials can be obtained from one or more commercial sources of chemicals or prepared using known synthetic methods and raw materials.

[0185] Table I

[0186] Components Amount (g) Polymer dispersions [containing non-free radically polymerizable polymeric materials] 1.056 Hydroxypropyl methylcellulose 0.60 Monomer 1 (free radical polymerizable component) 0.501 Monomer 2 (free radical polymerizable component) 0.249 Infrared absorber (see Table III) 0.03 Acid-sensitive dye precursors (see Table III) 0.035 Color-changing compounds (see Table III) 0.035 Surfactant 1 0.069 Initiator composition (see Table III) 0.09 M compound (see Table III) 0.015 1-Propanol 4.94 2-Butanone 2.40 1-Methoxy-2-propanol 4.22 δ-Butyrolactone 0.14 water 0.66

[0187] Table II

[0188]

[0189] Table II (continued)

[0190]

[0191] Table II (continued)

[0192]

[0193] Table III

[0194]

[0195] *B - / I + [mol / mol] represents the molar ratio of one or more borate anions to one or more iodonium cations, and the one or more borate anions are represented by the above structure (IIIa).

[0196] **inf represents infinite cases due to zero denominator.

[0197] The following properties were evaluated for each of the inventive and comparative lithographic printing plate precursors as described below: "On-Press Developability" (DOP), "Imaging Speed", "Print Out" (PO), and "Dark Fade". The measured scores for these properties are summarized in Table IV below.

[0198] On-press development capability (DOP):

[0199] By using Trendsetter 3244x at 15-150mJ / cm 2 Each lithographic printing plate precursor was image-wise exposed to evaluate the on-press developability. Each image-wise exposed lithographic printing plate precursor was then mounted on a MAN Roland Favorite04 printing press without development (rinsing). Fountain solution (Varn Supreme 6038) and lithographic ink (GansCyan) were supplied and lithographic printing was performed. On-press development occurs during printing and is evaluated by counting the number of printed sheets required to receive a clean background, and one of the following qualitative values ​​is given based on the number of printed sheets used to achieve a clean background. For this test parameter, + and 0 evaluation values ​​are acceptable.

[0200] +<10 sheets of printed paper

[0201] 0 10-30 sheets of printed paper

[0202] -> 30 sheets of printed paper

[0203] Imaging speed:

[0204] Each lithographic printing plate precursor was exposed and developed as described above. The imaging speed was measured on paper after 1000 impressions by determining the ink density of solids exposed to different energies. The inflection point of the ink density with respect to the exposure energy was considered a measure of the imaging speed. The following qualitative values ​​are given as the results of separate experiments, where lower imaging energies are desirable. For this parameter, + and 0 evaluation values ​​are acceptable.

[0205] + Imaging speed<30mJ / cm 2

[0206] 0 Imaging speed = 30-60mJ / cm 2

[0207] - Imaging speed>60mJ / cm 2

[0208] Prints out:

[0209] A Trendsetter 800 III Quantum TH 1.7 (available from Eastman Kodak Company) was used at 90 mJ / cm 2 Each lithographic printing plate precursor was imagewise exposed to provide exposed areas and unexposed areas in the negative-working IR-sensitive image recording layer. For each imagewise exposed lithographic printing plate precursor, the color difference between the exposed areas and the unexposed areas was measured within 10 minutes from the completion of the imagewise exposure by determining the ΔE value using a Techkon Spectro Dens spectrodensitometer, calculating the Euclidean distance of the measured L*a*b values, and giving the following qualitative values ​​immediately after exposure.

[0210]

[0211] Dark Fade:

[0212] Each lithographic printing plate was imagewise exposed as described above and then stored in the dark for 24 hours.ΔE measurements were then carried out as described above and the following qualitative values ​​are given.

[0213]

[0214]

[0215] Table IV

[0216] Example DOP Imaging speed Print Dark Fade Comparison 1 0 0 0 - Invention 1 0 0 ++ ++ Comparison 2 0 0 0 - Comparison 3 0 0 - - Comparison 4 0 0 ++ - Invention 2 0 0 +++ +++ Comparison 5 0 0 - - Comparison 6 0 - - - Comparison 7 0 - +++ +++ Invention 3 0 0 ++ ++ Invention 4 0 0 +++ +++ Invention 5 0 0 +++ +++ Invention 6 0 0 +++ +++

[0217] The results shown in Table IV support many conclusions. The data for Comparative Example 1 show that conventional acid-sensitive leuco dyes based on lactones (e.g., ASDP-1) typically provide moderate or acceptable printouts immediately after exposure without any long-term storage, but after storing the image, the printout becomes poorer (e.g., considering dark fading results). In Comparative Example 4, in which the highly acid-sensitive dye precursor ASDP-2 based on lactones is used, strong printouts are obtained immediately after exposure without any long-term storage, but after storing the image, the printout deteriorates. In Comparative Example 5, neither conventional acid-sensitive dye precursors based on lactones nor any other color-changing compounds are present. The corresponding precursors also show poor printouts immediately after exposure.

[0218] Compared to those results for Inventive Example 1, the results for Comparative Example 2 show that the presence of the specified -XL group in the (3) color-changing compound of Structure (I) or the presence of the specified -A group in Structure (Ia) provides improvements in printout and dark fading. Compounds such as the comparative color-changing compound CCC-2, which have an indene ring attached to a diphenylamino group rather than a chloro group, generally provide moderate or acceptable printout immediately after imaging, but the printout image becomes poor after dark fading storage. The difference between Comparative Example 2 and Inventive Example 1 demonstrates that, in addition to the Ar3 group in Structure (I) or Structure (Ia), the specified -XL group or -A group is also important for the efficiency of the phenylation reaction used to form the stable colored species explained above. CCC-2 has a diphenylamino group as the -XL group or as the -A group and therefore falls outside the scope of Structure (I) or Structure (Ia) as described above.

[0219] The results of Comparative Example 3 show lower printout both immediately after imaging and after dark storage relative to Inventive Example 1. These differences demonstrate that the presence of the (3) color-changing compound CCC-1 having an indene ring in the conjugated chain (benzene as AR3 in structure I) provides an improvement in printout compared to the comparative color-changing compound CCC3 having a cyclopentene ring in the conjugated chain according to structures (I) and (Ia). The differences between Comparative Example 3 and Inventive Example 1 demonstrate that Ar3 in structures (I) and (Ia) affects the geometry of the polymethine chain of the color-changing compound and therefore affects the efficiency of the phenylation reaction with the tetraphenylborate anion to form a stable colored phenylated product as explained above. In addition to the ΔE difference, it is also noted that the exposed areas of Inventive Example 1 have a reddish tint, which may be attributed to the phenylated product. The lithographic printing plate precursors in the other Inventive Examples also have a reddish tint in the infrared radiation exposed areas.

[0220] The results for Inventive Example 2 show that the printed images are slightly higher both immediately after imaging and after dark storage relative to the results for Inventive Example 1. This difference is believed to be caused by the reaction of the color-changing compound CCC-1 with the thiol compound M-1 to produce the new inventive color-changing compound CCC-1 / M-1 as shown below.

[0221]

[0222] The results from Inventive Example 2 show that CCC-1 / M-1 is even more effective than CCC-1 in the phenylation reaction with tetraphenylborate anion.

[0223] Inventive Examples 4 to 6 demonstrate that M compounds other than M-1 can also react with the meso-chloro group of CCC-1 to form a thioether bond and enhance the printout image compared to the printout image obtained in Inventive Example 1.

[0224] Inventive Example 3 demonstrates that when the color-shifting compound according to the present invention provides sufficient infrared radiation absorption to the printing plate precursor, a separate infrared radiation absorber can be omitted while maintaining good print-out image and imaging speed.

[0225] Comparative Example 6 illustrates that when a suitable borate compound according to the present invention is not present, the printout image can be poor even in the presence of a specific color-changing compound. Comparative Example 7 illustrates that a strong printout image can be obtained even in the absence of a suitable onium cation (e.g., diaryliodonium), but the imaging speed is poor. Therefore, in order to obtain both good imaging speed and a good printout image, both a suitable borate anion and an onium cation (e.g., diaryliodonium) are required.

Claims

1. A lithographic printing plate precursor comprising: Aluminum-containing substrates, and An infrared radiation-sensitive image recording layer disposed on the aluminum-containing substrate, the infrared radiation-sensitive image recording layer comprising the following components (1), (2) and (3): (1) a free radical initiator composition capable of generating free radicals upon exposure to infrared radiation; (2) a free radical polymerizable composition; and (3) A color-changing compound represented by the following structure (I): in: Ar1, Ar2 and Ar3 independently represent the atoms necessary to complete a substituted or unsubstituted aromatic ring or to complete a substituted or unsubstituted heteroaromatic ring; Y represents an oxygen atom, a sulfur atom or a >C(R 4 R 5 ) represented by a dialkylmethylene group, wherein R 4 and R 5 is independently a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms; R 1 and R 2 are independently substituted or unsubstituted alkyl; X represents a single bond or a divalent linking group, wherein the divalent linking group is -S- or -O-; L represents -C(=O)-OR 7 Group, -SO2-R 3 Group, -SO2NR 8 R 9 groups and groups other than -NPh2, where Ph represents phenyl, R 7 represents a compound having the same 7 A substituted or unsubstituted alkyl group is a secondary or tertiary carbon to which the remainder of the group is attached; and R 3 , R 8 and R 9 independently represent substituted or unsubstituted alkyl, substituted or unsubstituted aryl, or substituted or unsubstituted heteroaryl; and Za represents one or more counterions to balance the charge in the rest of the color-changing compound of component (3) according to structure (I), wherein the infrared radiation-sensitive image-recording layer comprises one or more borate anions represented by the following structure (IIa): B(R 10 R 11 R 12 R 13 )- Structure (IIa) Where R 10 , R 11 , R 12 and R 13 are independently substituted or unsubstituted alkyl or substituted or unsubstituted aryl, provided that R 10 , R 11 , R 12 and R 13 At least three of them are the same or different substituted or unsubstituted aryl groups, and the substituted aryl groups each have no more than two halogen substituents.

2. The lithographic printing plate precursor of claim 1, wherein the color-changing compound of component (3) is represented by structure (Ia): Among them, Ar1, Ar2, Ar3, R 1 , R 2 , Y and Za are the same groups as described above for structure (I), and A is selected from -SR 14 、-OR 14 , chloro, bromo, iodo, fluoro, nitro, cyano, trichloromethyl, tribromomethyl, trifluoromethyl, alkylammonium, dialkylammonium and trialkylammonium groups, wherein the same or different alkyl groups each contain 1 to 10 carbon atoms and may be optionally substituted, and R 14 is optionally substituted alkyl, optionally substituted aryl or optionally substituted heteroaryl.

3. The lithographic printing plate precursor of claim 2, wherein A represents a halogen group or -SR 14 , where R 14 represents optionally substituted alkyl, optionally substituted aryl or optionally substituted heteroaryl.

4. A lithographic printing plate precursor as claimed in claim 2 or 3, wherein A represents a chloro group.

5. The lithographic printing plate precursor according to claim 2 or 3, wherein A represents -SR 14 , where R 14 represents optionally substituted alkyl, optionally substituted aryl or optionally substituted heteroaryl.

6. A lithographic printing plate precursor as described in any one of claims 1 to 5, wherein the component (1) free radical initiator composition comprises one or more iodonium cations, and the amount of the iodonium cations is such that the molar ratio of the one or more borate anions to the one or more iodonium cations is at least 0.4:

1.

7. The lithographic printing plate precursor according to any one of claims 1 to 6, wherein the infrared radiation-sensitive image-recording layer further comprises a component (4) infrared absorbing material different from the component (3) color-changing compound.

8. A lithographic printing plate precursor as claimed in any one of claims 1 to 7, wherein Ar3 represents the carbon atoms and hydrogen atoms required to complete the benzene ring.

9. The lithographic printing plate precursor of any one of claims 1 to 8, wherein Za comprises a tetraarylborate anion.

10. The lithographic printing plate precursor of any one of claims 1 to 9, wherein the component (1) free radical initiator composition comprises an organic borate represented by the following structure (II): [B(R 10 R 11 R 12 R 13 ) - ] n M n+ Structure (II) Where R 10 , R 11 , R 12 and R 13 As defined for structure (IIa), n is an integer equal to or greater than 1, and M n+ It is an n-valent cation.

11. The lithographic printing plate precursor of claim 10, wherein R 10 , R 11 , R 12 and R 13 All are the same or different substituted or unsubstituted aryl groups.

12. The lithographic printing plate precursor of claim 10, wherein R in Structure (IIa) and Structure (II) 10 , R 11 , R 12 and R 13 All are the same substituted or unsubstituted phenyl groups.

13. The lithographic printing plate precursor of any one of claims 7 to 12, wherein the infrared radiation-sensitive image recording layer further comprises a component (5) acid-sensitive dye precursor different from all of the components (1), (2), (3) and (4) defined above.

14. The lithographic printing plate precursor of any one of claims 1 to 13, wherein the component (1) free radical initiator composition comprises a diaryliodonium tetraphenylborate.

15. The lithographic printing plate precursor of claim 13 or 14, wherein the weight ratio of the component (5) acid-sensitive dye precursor to the component (3) color-changing compound represented by the following structure (I) in the infrared radiation-sensitive image recording layer is less than 1.

16. The lithographic printing plate precursor of any one of claims 7 to 15, wherein the infrared radiation sensitive image recording layer further comprises a component (6) a non-radical polymerizable polymer material which is different from all of the components (1), (2), (3) and (4) defined above and is present in particulate form.

17. The lithographic printing plate precursor of any one of claims 1 to 16, wherein the infrared radiation-sensitive image recording layer is the outermost layer.

18. A lithographic printing plate precursor as described in any one of claims 1 to 17, wherein the color-changing compound of component (3) represented by structure (I) is present in the infrared radiation-sensitive image recording layer in an amount of at least 0.5 wt. % and up to and including 15 wt. % coverage, based on the total weight of the infrared radiation-sensitive image recording layer.

19. A method for providing a lithographic printing plate, comprising: A) image-wise exposing a lithographic printing plate precursor according to any one of claims 1 to 18 to infrared radiation to provide exposed areas and unexposed areas in the infrared radiation-sensitive image recording layer, and B) removing the unexposed areas in the infrared radiation sensitive image recording layer from the substrate on-press using a lithographic ink, a fountain solution or a combination of a lithographic ink and a fountain solution.

Images