Lithographic printing plate precursor

Abstract

The present invention relates to a lithographic printing plate precursor. Disclosed is a lithographic printing plate precursor comprising a support and a coating, said coating comprising (i) a photopolymerisable layer comprising a polymerisable compound and an optionally substituted trihaloalkylsulphone photoinitiator, and (ii) a top layer provided over said photopolymerisable layer; characterised in that said top layer comprises an infrared absorbing dye, said infrared absorbing dye being capable of forming a printed image upon exposure to heat and / or IR radiation.

Description

[0001] This application is a divisional application of the parent application with application number 201980032389.9. The application date of the parent application is May 13, 2019; the invention title is "Precursor for Offset Printing Plate". Technical Field

[0002] This invention relates to a novel lithographic printing plate precursor. Background Technology

[0003] Lithographic printing typically involves the use of a printing plate, such as a printing plate mounted on a cylinder of a rotary printing press. The plate has a lithographic image on its surface, and a printed product is obtained by applying ink to the image and then transferring the ink from the plate to a receiving material, typically paper. In conventional lithography, ink, along with an aqueous dampening solution (also called a dampening solution), is supplied to the lithographic image, which consists of oleophilic (or hydrophobic, i.e., ink-receptive and water-repellent) regions and hydrophilic (or oleophobic, i.e., water-receptive and ink-repellent) regions. In so-called waterless offset printing, the lithographic image consists of ink-receptive regions and ink-repellent regions, and in the waterless offset printing process, only the plate is supplied with ink.

[0004] Lithographic printing plates are typically obtained by image-wise exposure and processing of a radiation-sensitive layer on a lithographic support. Imaging and processing transform a so-called lithographic plate precursor into a printing plate or base. The radiation-sensitive coating is typically image-wise exposed to heat or light using a digitally modulated exposure device (such as a laser), triggering physical and / or chemical processes such as ablation, polymerization, insolubility through polymer crosslinking or particle coagulation of thermoplastic polymer latex, solubilization by disrupting intermolecular interactions, or by increasing the permeability of the developing barrier layer. While some plate precursors can produce a lithographic image immediately after exposure, the most popular lithographic plate precursors require wet processing because the exposure creates a difference in solubility or dissolution rate in the developer between the exposed and unexposed areas of the coating. In positive lithographic plate precursors, the exposed areas of the coating dissolve in the developer, while the unexposed areas remain resistant to the developer. In negative lithographic printing plate precursors, the unexposed areas of the coating dissolve in the developer, while the exposed areas remain resistant to the developer. Most lithographic printing plate precursors contain a hydrophobic coating on a hydrophilic support, such that the areas remaining resistant to the developer define the ink acceptance of the plate, thus defining the printing area, while the hydrophilic support is exposed through the dissolution of the coating in the developer in the non-printing areas.

[0005] Photopolymer printing plates rely on a working mechanism that typically involves a coating of a free-radical polymerizable compound that hardens upon exposure. "Hardening" refers to the coating becoming insoluble or non-dispersible in a developing solution and can be achieved through polymerization and / or crosslinking of the photosensitive coating upon exposure to light and / or heat. Photopolymer printing plate precursors can be sensitized to blue, green, or red light (i.e., wavelengths between 450 nm and 750 nm), to violet light (i.e., wavelengths between 300 nm and 450 nm), or to infrared light (i.e., wavelengths between 750 nm and 1500 nm). Optionally, a heating step is performed after the exposure step to enhance or accelerate the polymerization and / or crosslinking reactions.

[0006] Typically, a top layer or protective outer coating above the imageable layer is required to act as an oxygen barrier to provide the necessary sensitivity to the printing plate. The top layer usually comprises a water-soluble or water-swellable polymer, such as polyvinyl alcohol. In addition to acting as an oxygen barrier, the top layer should preferably be easily removable during processing and sufficiently transparent to photochemical radiation, for example, from 300 nm to 450 nm, or from 450 nm to 750 nm, or from 750 nm to 1500 nm.

[0007] The classic workflow for photopolymer printing plates involves an initial exposure step of the photopolymer plate precursor in a UV or infrared plate-making machine, followed by an optional preheating step, a washing step for the protective outer coating, an alkaline development step, and rinsing and sizing steps. However, significant progress has been made towards simplifying the workflow, where the preheating and / or washing steps are eliminated, and where processing and sizing are performed in a single step, or where processing is done with a neutral adhesive and then sizing is done in a second step. Alternatively, on-press processing has become very popular, where the plate is mounted on the printing press and the coating is developed by interacting with dampening solution and / or ink supplied to the plate during press operation. During the first run of the printing press, non-image areas are removed from the support, thus defining the non-printing areas of the plate.

[0008] To enable the evaluation of image quality, such as image resolution and detail rendering (typically measured with a densitometer), of lithographic printing plates before mounting them on a printing press, the plate precursor typically contains colorants, such as dyes or pigments, in its coating. After processing, these colorants provide contrast between the colorant-containing image areas and the hydrophilic support where the coating has been removed, allowing the end user to evaluate image quality and / or determine if the precursor has been exposed to light. Furthermore, in addition to allowing for image quality evaluation, high contrast between the image and the hydrophilic support is required to achieve good image registration (alignment) between different printing plates in multicolor printing, thereby ensuring image sharpness (resolution) and correct color rendering in the provided image.

[0009] However, for photopolymer lithographic printing plates that are processed on-machine and therefore not developed before being mounted on the printing press, it is impossible to pre-inspect and identify the plates containing colorants. A solution has been provided in the art by incorporating components into coatings that are capable of forming a so-called "printed image" (i.e., an image visible before processing) upon exposure. However, in these materials, the photoinitiating system is typically the reactive component, which induces the formation of the printed image upon exposure and thus reduces lithographic variability.

[0010] The formation of printed images of violet-sensitive photopolymer systems has been disclosed in, for example, US 3,359,109, US 3,042,515, US 4,258,123, US 4,139,390, US 5,141,839, US 5,141,842, US 4,232,106, US 4,425,424, US 5,030,548, US 4,598,036, EP 434 968, WO 96 / 35143 and US 2003 / 68575.

[0011] The formation of printed images is also known for thermophotopolymer lithographic printing plates. Such plates are typically exposed in an image-like manner by an IR laser and often contain, in addition to IR dyes as photothermal conversion compounds, dyes that absorb in the visible light wavelength range and change color upon heating. This color change can be obtained, for example, with thermally decomposable dyes that bleach upon heating, as disclosed in EP 897 134, EP 925 916, WO 96 / 35143, and EP 1300 241. Alternatively, this heat-induced color change can be a result of a maximum absorption shift of visible dyes, as disclosed in EP 1 502 736 and EP 419 095. When printed images are formed by a reduction in heat-induced visible light absorption or by a conversion from a highly tinted coating to a less tinted coating, a problem associated with these prior art materials is that the resulting printed images are characterized by only low contrast between exposed and unexposed areas, require large amounts of dye, and / or have an increased risk of contamination during development / washing.

[0012] Contrast-providing colorants derived from so-called leuco dyes are widely used in the field, these dyes changing color in response to changes in pH, temperature, UV, etc. Leuco dye technology involves the conversion between two chemical forms, one of which is colorless. If the color conversion is caused by, for example, pH or temperature, this conversion is reversible. Irreversible conversions are typically based on redox reactions.

[0013] Contrast-providing colorants, such as those described in US 7,402,374, US 7,425,406, and US 7,462,440, are obtained using leuco dyes that become colored in the presence of a hot acid-generating agent. Coloration of the printed area is initiated by pictorial exposure, thereby visualizing the image area prior to development of the plate precursor. However, this leuco dye technique yields only weak image contrast that diminishes over time, and requires high exposure energy to produce contrast.

[0014] EP 2 297 611 discloses an imaging element comprising an outer coating disposed on a photopolymerizable imageable layer, the photopolymerizable imageable layer comprising a water-soluble polymer binder and a composition capable of changing color upon exposure to infrared radiation, the composition comprising an acid-generating compound, an infrared radiation-absorbing compound, and optionally one or more compounds that generate color in the presence of an acid.

[0015] Thermochromic dye technology involves designing IR dyes containing thermally degradable groups, thereby achieving color shift upon exposure to heat and / or light. This technology provides enhanced lithographic contrast by increasing the concentration of the thermochromic dye or the exposure energy. However, this technology is particularly suitable for thermopolymer printing plates, i.e., plates comprising an image recording layer that functions through thermally induced particle aggregation of thermoplastic polymer latex, and does not work well in the photosensitive layer of photopolymer-based printing plates. In fact, barely acceptable contrast is feasible in such printing plates when exposed to very high laser energies and / or when significantly high concentrations of thermochromic dyes are incorporated into the coating.

[0016] In summary, there is still a need for photopolymer-based lithographic printing plates, which include coating formulations that provide improved contrast between image and background areas during imaging and are preferably designed for direct on-machine development. Summary of the Invention

[0017] Therefore, one object of the present invention is to provide a photopolymer-based negative printing plate that provides excellent visual contrast during imaging, and even before processing.

[0018] This objective is achieved by the printing plate precursor as defined in claim 1 and the preferred embodiments as defined in the dependent claims. A specific feature of the printing plate material of the present invention is that it comprises two coating layers, wherein the top layer contains an infrared-absorbing compound capable of forming a colored compound, thereby forming a printed image upon exposure to IR light and / or heat. The colored compound is a compound visible to the human eye, typically with wavelengths in the visible electromagnetic spectrum ranging from about 390 nm to 700 nm.

[0019] According to the present invention, it has been surprisingly found that by incorporating an infrared-absorbing compound capable of forming a colored compound into the top layer, a very high visual contrast is achieved. It has been observed that even at low exposure energy levels (e.g., below 150 mJ / m²), the coating according to the present invention exhibits excellent visual contrast when exposed to heat and / or light. 2 A clear printed image is also formed below.

[0020] Before development and after exposure, for example at 70 mJ / m 2 Up to 190 mJ / m 2 More preferably 75 mJ / m 2 Up to 150 mJ / m 2 The optimal value is 80 mJ / m 2 Up to 120 mJ / m 2 At the specified energy density, the CIE 1976 color distance ΔE measured between the exposed (image) area and the unexposed (non-image) area is preferably at least 2. As a result, effective plate inspection via a perforated bending machine and / or registration system is possible, eliminating the need for additional inkjet printing systems and / or laborious pre-control of the plate via, for example, acidic adhesives after imaging to obtain inkjet plate information.

[0021] Preferably, the precursor is treated with an adhesive solution; however, more preferably, development is performed by mounting the precursor on the printing cylinder of a lithographic printing press and rotating the printing cylinder while simultaneously feeding dampening solution and / or ink onto the precursor.

[0022] Another object of the present invention is to provide a method for preparing a lithographic printing plate, the method comprising the following steps: - A printing plate precursor including the coating as defined above is exposed to heat and / or IR radiation in an image manner, thereby forming a lithographic image consisting of image areas and non-image areas, and thereby inducing color changes in the imaging areas; - To develop the exposed precursor.

[0023] Other features, elements, steps, characteristics, and advantages of the invention will become more apparent from the following detailed description of preferred embodiments of the invention. Specific embodiments of the invention are also defined in the dependent claims. Detailed Implementation

[0024] Lithographic printing plate precursor The lithographic printing plate precursor according to the invention is negative-printed, meaning that after exposure and development, the unexposed areas of the coating are removed from the support and define hydrophilic (non-printing) areas, while the exposed coating is not removed from the support and defines oleophilic (printing) areas. The hydrophilic areas are defined by a support having a hydrophilic surface or being provided with a hydrophilic layer. The hydrophobic areas are defined by a coating that hardens upon exposure (optionally followed by a heating step). Areas with hydrophilic properties refer to areas that have a higher affinity for aqueous solutions than for oleophilic inks; areas with hydrophobic properties refer to areas that have a higher affinity for oleophilic inks than for aqueous solutions.

[0025] "Curing" refers to the coating becoming insoluble or non-dispersible in the developing solution, and can be achieved by polymerization and / or crosslinking of the photosensitive coating, optionally followed by a heating step to enhance or accelerate the polymerization and / or crosslinking reaction. In this optional heating step (hereinafter also referred to as "preheating"), the printing plate precursor is heated, preferably at a temperature of about 80°C to 150°C, and preferably during a dwell time of about 5 seconds to 1 minute.

[0026] The coating comprises a top layer and at least one layer comprising a photopolymerizable composition, also referred to as a "photopolymerizable layer". The top layer is provided on top of the photopolymerizable layer. The coating may also include other layers, such as intermediate layers, adhesion-improving layers, and / or other layers located between the support and the photopolymerizable layer and / or between the top layer and the photopolymerizable layer.

[0027] The coating of the printing plate precursor is preferably capable of being developed in an machine using dampening solution and / or ink.

[0028] The printing plate of the present invention is characterized in that it can be exposed at low energy densities (i.e., below 190 mJ / m²; preferably between 70 mJ / m² and 190 mJ / m²; more preferably between 75 mJ / m² and 150 mJ / m² and most preferably between 80 mJ / m² and 120 mJ / m²).

[0029] Top layer The coating comprises a top layer, preferably serving as an oxygen barrier layer, or a protective outer coating. Low molecular weight substances present in the air may degrade or even inhibit image formation, and therefore a top layer is applied to the coating. The top layer should preferably be easily removable during development, adhere sufficiently to the photopolymerizable layer of the coating, or optionally another layer, and should preferably not inhibit light transmission during exposure. The top layer is provided on top of the photopolymerizable layer.

[0030] The top layer contains an infrared-absorbing compound that is capable of forming a colored compound upon exposure to infrared light and / or heat, thereby forming a printed image. The infrared-absorbing compound capable of forming a colored compound is preferably an infrared-absorbing dye, also known as an IR dye. Coloring IR dyes are also referred to herein as thermochromic infrared-absorbing dyes or thermochromic IR dyes. Thermochromic IR dyes have predominant absorption in the infrared wavelength range of the electromagnetic spectrum (i.e., the wavelength range between about 750 nm and 1500 nm) and preferably have no significant light absorption in the visible wavelength range of the electromagnetic spectrum (i.e., the wavelength range between 390 nm and 700 nm). The thermochromic compound (preferably a dye) preferably contains at least one thermally pyrolytic group that transforms into a group that is a stronger electron donor through exposure to IR radiation or a heat-induced chemical reaction. As a result, the exposed thermochromic IR dye absorbs significantly more light in the visible wavelength range of the electromagnetic spectrum; in other words, the thermochromic IR dye undergoes a blue shift, thereby forming a visible image, also known as a printed image. The formation of this printed image differs significantly from existing methods, in which compounds are transformed from essentially colorless to light-colored to colored compounds. These compounds typically exhibit altered absorption across the UV wavelength range of the electromagnetic spectrum to the visible wavelength range, meaning they often exhibit a redshift. Compared to the aforementioned color-forming method of the thermochromic IR dyes of this invention, the printed image obtained by this method has much weaker contrast.

[0031] The contrast of a printed image can be defined as the difference between the optical density in the exposed area and the optical density in the unexposed area, and is preferably as high as possible. This allows the end user to immediately determine whether the precursor has been exposed and processed, to distinguish different color choices, and to check the image quality on the printing plate precursor. The contrast of the printed image preferably increases with increasing optical density in the exposed area and can be measured by reflectance using an optical densitometer equipped with several filters (e.g., cyan, magenta, yellow).

[0032] The concentration of the thermochromic IR dye relative to the total dry weight of the coating can be from 0.1% to 20.0% by weight, more preferably from 0.5% to 15.0% by weight, and most preferably from 1.0% to 10.0% by weight.

[0033] Thermochromic IR dyes are preferably represented by formula I, II or III: Formula I Formula II Formula III in Ar 1 Ar 2 and Ar 3 Independently representing an optionally substituted aromatic hydrocarbon group or an aromatic hydrocarbon group having an optionally substituted cyclic benzene ring. W 1 and W 2 Independently represent sulfur atoms, oxygen atoms, NR¨, where R¨ represents an optionally substituted alkyl group, NH or -CM. 10 M 11 Group, wherein M 10 and M 11 Independently, it is an optionally substituted aliphatic hydrocarbon group or an optionally substituted (hetero)aryl group, or wherein M is an optionally substituted aliphatic hydrocarbon group or a heteroaryl group. 10 and M 11 Together they contain the necessary atoms to form a ring structure, preferably a 5- or 6-membered ring; W 3 Represents a sulfur atom or -C(A) 3 )=C(A 4 )- group, W 4 Represents a sulfur atom or -C(A) 7 )=C(A 8 )- group, M 1 and M 2 Independently representing hydrogen, optionally substituted aliphatic hydrocarbon groups, or together containing the necessary atoms to form the optionally substituted cyclic structure, preferably M. 1 and M 2 Together they contain the necessary atoms to form an optionally substituted cyclic structure, which may contain an optionally substituted cyclic benzene ring, preferably a 5- or 6-membered ring, more preferably a 5-membered ring, and most preferably a 5-membered ring having 5 carbon atoms. M 3 and M 4 Independently represents an optionally substituted aliphatic hydrocarbon group; M 5 M 6 M 7 and M 8 M 16 and M 17 Independently representing hydrogen, halogen, or optionally substituted aliphatic hydrocarbon groups, A 1 To A 8 Independently representing hydrogen, halogen atoms, optionally substituted aliphatic hydrocarbon groups, or optionally substituted (hetero)aryl groups, or wherein A 1 and A 2 A 3 and A 4 A 5 and A 6Or A 7 and A 8 Each of them together contains the necessary atoms to form a ring structure, preferably a 5- or 6-membered ring; M 12 and M 13 and M 14 and M 15 Independently representing an optionally substituted aliphatic hydrocarbon group or an optionally substituted (hetero)aryl group, or wherein the M 14 M 15 A 5 Or A 7 The two components together contain the necessary atoms to form at least one ring structure, preferably a 5- or 6-membered ring; the M 12 M 13 A 2 Or A 4 The two together contain the necessary atoms to form at least one ring structure, preferably a 5- or 6-membered ring; M 9 It is transformed into a form that is more than M through exposure to IR radiation or thermally induced chemical reactions. 9 A group with a stronger electron donor; and the transition provides an increase in the integrated light absorption of the dye between 350 nm and 700 nm; And optionally one or more counterions to obtain an electrically neutral compound.

[0034] Thermochromic IR dyes can be neutral, anionic, or cationic dyes, depending on the type and number of substituents. In a preferred embodiment, dyes of formula I, II, or III contain at least one anionic or acidic group, such as -CO2H or -CONHSO2R. h -SO2NHCOR i -SO2NHSO2R j -PO3H2, -OPO3H2, -OSO3H, -S-SO3H or -SO3H groups or their corresponding salts, wherein R h R i and R j Independently, it is aryl or alkyl, preferably methyl, and said salt is preferably an alkali metal salt or ammonium salt, including mono-, di-, tri-, or tetra-alkylammonium salts. These anionic or acidic groups may be present in Ar. 1 Ar 2 Or Ar 3 On the aromatic hydrocarbon group or cyclic benzene ring, or present in M 3 M 4 Or M 12 To M 15 On an aliphatic hydrocarbon group, or present in M 12 To M15 It is attached to a heteroaryl group. Other substituents may be selected from halogen atoms, cyano groups, sulfone groups, carbonyl groups, or carboxylic acid ester groups.

[0035] In another preferred embodiment, M 3 M 4 Or M 12 To M 15 At least one of these groups is substituted at the end with at least one of these groups, more preferably with -CO2H, -CONHSO2-Me, -SO2NHCO-Me, -SO2NHSO2-Me, -PO3H2 or -SO3H groups or their corresponding salts, wherein Me represents methyl.

[0036] In a preferred embodiment, the thermochromic IR dye is represented by formula I, II, or III above, including M represented by one of the following groups. 9 : -(N=CR 17 )a-NR 5 -CO-R 4 , -(N=CR 17 b-NR 5 -SO2-R 6 , -(N=CR 17 c-NR 11 -SO-R 12 , -SO2-NR 15 R 16 and -S-CH2-CR 7 (H) 1-d (R 8 ) d -NR 9 -COOR 18 , in a, b, c, and d are independently 0 or 1; R 17 Represents hydrogen, an optionally substituted aliphatic hydrocarbon group, or an optionally substituted (hetero)aryl group, or wherein R 17 and R 5 Or R 17 and R 11 Together they contain the necessary atoms to form a ring structure; R 4 Indicates -OR 10 -NR 13 R 14 Or -CF3; Where R 10Indicates an optional substituted (hetero)aryl group or an optional branched aliphatic hydrocarbon group; R 13 and R 14 Independently representing hydrogen, an optionally substituted aliphatic hydrocarbon group, or an optionally substituted (hetero)aryl group, or wherein R 13 and R 14 Together they contain the necessary atoms to form a ring structure; R 6 Indicates an optionally substituted aliphatic hydrocarbon group or an optionally substituted (hetero)aryl group, -OR 10 -NR 13 R 14 Or -CF3; R 5 Indicates hydrogen, optionally substituted aliphatic hydrocarbon groups, SO3- groups, -COOR 18 A group or optionally substituted (hetero)aryl group, or wherein R 5 With R 10 R 13 and R 14 At least one of them together contains the necessary atoms to form a ring structure; R 11 R 15 and R 16 Independently representing hydrogen, an optionally substituted aliphatic hydrocarbon group, or an optionally substituted (hetero)aryl group, or wherein R 15 and R 16 Together they contain the necessary atoms to form a ring structure; R 12 Indicates an optionally substituted aliphatic hydrocarbon group or an optionally substituted (hetero)aryl group; R 7 and R 9 Independently representing hydrogen or optionally substituted aliphatic hydrocarbon groups, R 8 This indicates -COO- or -COOR 8' , where R 8' It represents hydrogen, alkali metal cations, ammonium ions, or mono-, di-, tri-, or tetra-alkylammonium ions; R 18 This indicates an optional substituted (hetero)aryl or α-branched aliphatic hydrocarbon group.

[0037] Suitable examples of thermochromic IR dyes used in this invention are described on pages 4 to 8 of EP 1 910 082, IRD-001 to IRD-101, and are incorporated herein by reference.

[0038] In a highly preferred embodiment, the thermochromic IR dye is represented by formula IV. Among them, Ar1 Ar 2 W 1 W 2 and M 1 To M 9 As specified above.

[0039] Most preferably, the thermochromic IR dye is represented by formula IV, wherein Ar 1 and Ar 2 Independently representing the optionally substituted aryl group; optionally cyclizing with the optionally substituted benzene ring. W 1 and W 2 It represents -C(CH3)2; M 1 and M 2 Together they contain the necessary atoms to form an optionally substituted 5-membered ring, which may contain an optionally substituted cyclic benzene ring; M 3 and M 4 Independently representing optionally substituted aliphatic hydrocarbon groups, M 5 M 6 M 7 and M 8 It represents hydrogen; M 9 express -NR 5 -CO-R 4 -NR 5 -SO2-R 6 -NR 11 -SO-R 12 -SO2-NR 15 R 16 Where R 4 R 5 R 6 R 11 R 12 R 15 and R 16 As specified above; And optionally one or more counterions to obtain an electrically neutral compound. Preferably, the IR dye contains at least one anionic or acidic group, such as -CO2H, -CONHSO2R. h -SO2NHCOR i -SO2NHSO2R j-PO3H2, -OPO3H2, -OSO3H, -SO3H or -S-SO3H groups or their corresponding salts, wherein R h R i and R j Independently, it is aryl or alkyl. More preferably, M 3 Or M 4 At least one of the aliphatic hydrocarbon groups is substituted at the end by at least one of the anionic group or acid group.

[0040] In a highly preferred embodiment, the thermochromic IR dye is represented by formula IV, wherein Ar 1 and Ar 2 Independently represents the aryl group with optional substitution; W 1 and W 2 It represents -C(CH3)2; M 1 and M 2 Together they contain the necessary atoms to form an optionally substituted 5-membered ring, which may contain an optionally substituted cyclic benzene ring; M 3 and M 4 Independently representing optionally substituted aliphatic hydrocarbon groups, M 5 M 6 M 7 and M 8 It represents hydrogen; M 9 express -NR 5 -CO-R 4 -NR 5 -SO2-R 6 in R 4 For -OR 10 , where R 10 For optional branched aliphatic hydrocarbon groups; R 5 Indicates hydrogen, an optionally substituted aliphatic hydrocarbon group, or an optionally substituted (hetero)aryl group. R 6 Indicates an optionally substituted aliphatic hydrocarbon group or an optionally substituted (hetero)aryl group; and Optionally, one or more counterions can be used to obtain an electrically neutral compound.

[0041] Preferably, the thermochromic IR dye contains at least one anionic group or acid group, such as -CO2H, -CONHSO2R. h -SO2NHCORi -SO2NHSO2R j -PO3H2, -OPO3H2, -OSO3H, -SO3H or -S-SO3H groups or their corresponding salts, wherein R h R i and R j Independently, it is aryl or alkyl. More preferably, M 3 Or M 4 At least one of the aliphatic hydrocarbon groups is substituted at the terminal by at least one of the anionic group or acid group. The salt is preferably an alkali metal salt or an ammonium salt, including mono-, di-, tri-, or tetra-alkylammonium salts.

[0042] To obtain an electrically neutral compound, the optional counterion may be selected from, for example, halogens, sulfonates, perfluorosulfonates, toluenesulfonates, tetrafluoroborates, hexafluorophosphates, arylborates, arylsulfonates; or cations, such as alkali metal salts or ammonium salts, including mono- or di- or tri- or tetra-alkylammonium salts.

[0043] The most preferred thermochromic IR dyes are represented by one of the following formulas V to XII: Formula V Style VI in X - This indicates halogen, sulfonate, perfluorosulfonate, toluenesulfonate, tetrafluoroborate, hexafluorophosphate, arylborate, or arylsulfonate; and R 3 R 3' Independently representing an optionally substituted alkyl group, preferably methyl or ethyl; or an ether group, preferably -CH2-CH2-O-CH3.

[0044] Equation VII Formula VIII Formula IX in M + =Li + Na + K + NH4 + 、R'R''R'''NH + , where R', R'', and R''' independently represent hydrogen, an optional substituted alkyl or aryl group; Formula X Formula XI Formula XII The aforementioned thermochromic IR dyes can also be coupled to each other or to other IR dyes to form IR dye dimers or oligomers. In addition to covalent coupling between two or more thermochromic IR dyes, supramolecular complexes containing two or more thermochromic IR dyes can also be formed through ionic interactions. Dimers composed of two different IR dyes can be formed, for example, through interactions between cationic and anionic IR dyes, as described in, for example, WO / 2004069938 and EP 1 466 728. IR dyes can also be ion-bonded to polymers, as described, for example, in EP 1582 346, where an IR dye containing two to four sulfonate groups is ion-bonded to a polymer containing covalently linked ammonium, phosphonium, and sulfonium groups.

[0045] Supramolecular complexes containing two or more thermochromic IR dyes can also be formed through hydrogen bonding or dipole-dipole interactions.

[0046] The color difference between the exposed and unexposed areas of the coating, calculated from the L*a*b* value of the image area (exposed area) and the L*a*b* value of the non-image area (unexposed area) of the coating, is expressed as ΔE. When the coating of the present invention is exposed to even low energy densities (e.g., 70 mJ / m² to 190 mJ / m², more preferably 75 mJ / m² to 150 mJ / m², most preferably 80 mJ / m² to 120 mJ / m²), a printed image with a CIE 1976 color difference ΔE of at least 2, more preferably at least 2.5, and most preferably at least 3 is formed. According to the present invention, at very low exposure energy (e.g., below 150 mJ / m²), a CIE 1976 color difference ΔE is formed. 2 Under these conditions, a CIE 1976 color difference ΔE of at least 2 is obtained. ΔE is the CIE 1976 color distance ΔE, which is defined by the pairwise Euclidean distance of the CIE L*a*b* color coordinates. The CIE L*a*b* color coordinates are obtained by reflectance measurements using a 45 / 0 geometry (unpolarized), a CIE 2° observer, and a D50 light source. More details are described in CIE S 014-4 / E:2007 Colorimetry – Part 4: CIE 1976 L*a*b* Colour Spaces and CIE publications and CIE S 014-1 / E:2006, CIE Standard Colourmetric Observers.

[0047] The CIE 1976 color coordinates L*, a*, and b* discussed in this article are part of the well-known CIE (Commission Internationale de l'Eclairage) system of three-color coordinates, which also includes the constraint C* = [(a*, b ... 2 + (b) 2 ] 1 / 2 The other chromaticity value is C*. The CIE 1976 color system is described, for example, in "Colorimetry, CIE 116-1995: Industrial Colour Difference Evaluation" or "Measuring Colour" (RWG Hunt, 2nd edition, edited by Ellis Horwood Limited, UK, 1992).

[0048] The CIE L*a*b* values ​​discussed and reported in this article were measured according to the ASTM E308-85 method.

[0049] The top layer may also include an adhesive. A preferred adhesive for the top layer is polyvinyl alcohol (PVA). The PVA preferably has a degree of hydrolysis ranging from 74 mol% to 99 mol%, more preferably from 80 mol% to 98 mol%. The weight-average molecular weight of the PVA can be measured by the viscosity of a 4 wt% aqueous solution at 20°C as defined in DIN 53 015, and the viscosity value is preferably between 2 and 26, more preferably between 2 and 15, and most preferably between 2 and 10.

[0050] The outer coating may optionally contain other components such as inorganic or organic acids, matting agents, surfactants, (organic) waxes or wetting agents, as disclosed in EP 2 916 171, which is incorporated herein by reference.

[0051] The thickness of the top coating is preferably 0.10 g / m. 2 and 1.75 g / m 2 Between 0.20 g / m 2 and 1.3 g / m 2 Between, more preferably between, 0.25 g / m 2 and 1.0 g / m 2 The optimal value is between 0.30 g / m 2 and 0.80 g / m 2 Between. In a more preferred embodiment of the invention, the top layer has 0.25 g / m. 2 Up to 1.75 g / m 2The coating thickness, and contains polyvinyl alcohol with a degree of hydrolysis ranging from 74 mol% to 99 mol% and a viscosity value ranging from 3 to 26 as defined above.

[0052] Hydrophilic polymers in the protective outer coating can cause a problematic increase in the viscosity of printing chemicals such as dampening solutions and / or developers. Therefore, the thickness of the protective outer coating should preferably not be too high, for example, exceeding the range given above.

[0053] Definition Aliphatic hydrocarbon groups are preferably alkyl, cycloalkyl, alkenyl, cycloalkenyl, or ynyl; suitable groups are described below. Aromatic hydrocarbon groups are preferably hetero(aryl) groups; suitable hetero(aryl) groups (i.e., suitable aryl or heteroaryl groups) are described below.

[0054] The term "alkyl" as used herein refers to all possible variations for each number of carbon atoms in the alkyl group, namely methyl, ethyl; for three carbon atoms: n-propyl and isopropyl; for four carbon atoms: n-butyl, isobutyl, and tert-butyl; for five carbon atoms: n-pentyl, 1,1-dimethyl-propyl, 2,2-dimethylpropyl, and 2-methyl-butyl, etc. Examples of suitable alkyl groups are methyl, ethyl, n-propyl, isopropyl, n-butyl, 1-isobutyl, 2-isobutyl and tert-butyl, n-pentyl, n-hexyl, chloromethyl, trichloromethyl, isopropyl, isobutyl, isopentyl, neopentyl, 1-methylbutyl and isopentyl, 1,1-dimethyl-propyl, 2,2-dimethylpropyl and 2-methyl-butyl, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, and methylcyclohexyl. Preferably, the alkyl group is a C1 to C6 alkyl group.

[0055] Suitable alkenyl groups are preferably C2 to C6-alkenyl groups, such as vinyl, n-propenyl, n-butenyl, n-pentenyl, n-hexenyl, isopropenyl, isobutenyl, isopentenyl, neopentenyl, 1-methylbutenyl, isohexenyl, cyclopentenyl, cyclohexenyl and methylcyclohexenyl.

[0056] Suitable alkynyl groups are preferably C2 to C6-alkynyl groups; suitable aralkyl groups are preferably phenyl or naphthyl groups comprising one, two, three or more C1 to C6-alkyl groups; suitable alkylaryl groups are preferably C1 to C6-alkyl groups comprising aryl, preferably phenyl or naphthyl groups.

[0057] A cyclic group or cyclic structure includes at least one ring structure and can be a monocyclic or polycyclic group, meaning a single ring or multiple rings fused together.

[0058] Suitable examples of aryl groups can be represented by, for example, optionally substituted phenyl, benzyl, tolyl, or o-, m-, or p-xylyl, optionally substituted naphthyl, anthracene, phenanthryl, and / or combinations thereof. The heteroaryl group is preferably a monocyclic or polycyclic aromatic ring containing a carbon atom and one or more heteroatoms in its ring structure, preferably one to four heteroatoms independently selected from nitrogen, oxygen, selenium, and sulfur. Preferred examples include optionally substituted furanyl, pyridinyl, pyrimidinyl, pyrazolyl, imidazolyl, oxazolyl, isoxazolyl, thienyl, tetrazolyl, thiazolyl, (1,2,3)triazolyl, (1,2,4)triazolyl, thiadiazolyl, thiofenyl, and / or combinations thereof.

[0059] A cyclic group or cyclic structure includes at least one ring structure and can be a monocyclic or polycyclic group, meaning a single ring or multiple rings fused together.

[0060] Halogens are selected from fluorine, chlorine, bromine or iodine.

[0061] The term "substituted," in the case of substituted alkyl groups, means that the alkyl group can be replaced by atoms other than those normally present in such groups (i.e., carbon and hydrogen). For example, substituted alkyl groups can include halogen atoms or thiol groups. Unsubstituted alkyl groups contain only carbon and hydrogen atoms.

[0062] The optional substituents on alkyl, cycloalkyl, alkenyl, cycloalkenyl, alkynyl, aralkyl, alkylaryl, aryl and heteroaryl groups are preferably selected from -Cl, -Br, -I, -OH, -SH, -CN, -NO2, alkyl (such as methyl or ethyl), alkoxy (such as methoxy or ethoxy), aryloxy, carboxylic acid or its alkyl ester, sulfonic acid or its alkyl ester, phosphonic acid or its alkyl ester, phosphate or ester (such as alkyl ester, such as methyl or ethyl ester), thioalkyl, thioaryl, thioheteroaryl, -SH, thioether (such as thioalkyl or thioaryl), ketone, aldehyde, sulfoxide, sulfone, sulfonate, sulfonamide, amino, vinyl, alkenyl, alkynyl, cycloalkyl, alkylaryl, aralkyl, aryl, heteroaryl or heterocycloalkyl and / or combinations thereof.

[0063] Support The lithographic printing plate used in this invention includes a support having a hydrophilic surface or being provided with a hydrophilic layer. The support is preferably a roughened and anodized aluminum support known in the art. Suitable supports are disclosed, for example, in EP 1843 203 (paragraphs

[0066] to

[0075] ). The surface roughness obtained after the roughening step is generally expressed as an arithmetic mean centerline roughness Ra (ISO 4287 / 1 or DIN 4762) and can vary between 0.05 μm and 1.5 μm. The Ra value of the aluminum substrate of this invention is preferably from 0.1 μm to 1.4 μm, more preferably from 0.3 μm to 1.0 μm, and most preferably from 0.4 μm to 0.9 μm. The lower limit of the Ra value is preferably about 0.1 μm. More details regarding the preferred Ra values ​​for the roughened and anodized aluminum support surface are described in EP 1 356 926. Anodizing of the aluminum support forms an Al2O3 layer, and the anodized weight (g / m³) is... 2 Al2O3 formed on the aluminum surface at 1 g / m 2 and 8 g / m 2 The anode weight is preferably ≥2.0 g / m³. 2 More preferably ≥2.5g / m 2 And the optimal value is ≥3.0 g / m 2 .

[0064] The roughened and anodized aluminum support can be subjected to so-called post-anodizing treatments, such as treatment with polyvinylphosphonic acid or derivatives thereof, treatment with polyacrylic acid or derivatives thereof, treatment with potassium fluorozirconate or phosphate, treatment with alkali metal silicates, or combinations thereof. Enlargement or sealing of the micropores of the anodized aluminum can be performed as disclosed in JP2001-253181A or JP2001-322365A. Alternatively, the support can be treated with adhesion-promoting compounds, such as those described in EP 1 788 434

[0010] and WO 2013 / 182328. However, for precursors optimized for use without a preheating step, it is preferable to use a roughened and anodized aluminum support without any post-anodizing treatment.

[0065] In addition to aluminum supports, plastic supports, such as polyester supports, can also be used, which are provided with one or more hydrophilic layers, as disclosed in, for example, EP 1 025 992.

[0066] Photopolymer coating Photopolymerizable compound The coating has at least one layer comprising a photopolymerizable composition, also referred to as a "photopolymerizable layer". The coating may include an intermediate layer located between the support and the photopolymerizable layer.

[0067] The photopolymerizable layer comprises at least one polymerizable compound and optionally a binder. The coating thickness of the photopolymerizable layer is preferably in the range of 0.2 g / m². 2 and 5.0 g / m 2 Between, more preferably between 0.4 g / m 2 and 3.0 g / m 2 The optimal value is between 0.6 g / m 2 and 2.2 g / m 2 between.

[0068] According to a preferred embodiment of the invention, the polymerizable compound is a polymerizable monomer or oligomer containing at least one terminal olefinically unsaturated group, hereinafter also referred to as a "radically polymerizable monomer". Polymerization involves linking the radically polymerizable monomers together. Suitable radically polymerizable monomers include, for example, polyfunctional (meth)acrylate monomers (such as ethylene glycol, trimethylolpropane, pentaerythritol, ethylene glycol, ethoxylated trimethylolpropane (meth)acrylates, urethane (meth)acrylates) and oligomeric amine di(meth)acrylates. In addition to the (meth)acrylate group, the (meth)acrylate monomer may also have other olefinically unsaturated groups or epoxy groups. The (meth)acrylate monomer may also contain acidic functional groups (such as carboxylic acids or phosphoric acids) or basic functional groups (such as amines).

[0069] Suitable free radical polymerizable monomers are disclosed in

[0042] and

[0050] of EP 2 916 171, and are incorporated herein by reference.

[0070] Initiator The lithographic printing plate precursor of the present invention contains a trihaloalkyl sulfone initiator, also known as a "TBM-initiator".

[0071] A TBM initiator is a compound that, upon exposure, optionally in the presence of a sensitizer, is capable of generating a free radical. The TBM initiator is preferably an optionally substituted trihaloalkyl sulfone compound, wherein the halogen is independently represented as fluorine, bromine, chlorine, or iodine, and the sulfone is a compound containing a sulfonyl functional group attached to two carbon atoms. Tribromomethylphenyl sulfone is the most preferred initiator. Further details regarding such initiators can be found in paragraphs

[0029] to

[0040] of the unpublished co-pending application EP 18163285.2.

[0072] It was found that coatings including TBM initiators resulted in significantly improved image sharpness (resolution) on printed sheets compared to coatings including prior art initiators. Furthermore, it was found that by using TBM initiators in a photopolymerizable layer in combination with thermochromic dyes in the top layer, image sharpness (resolution) on printed sheets was further improved and / or contrast (i.e., color difference between exposed and unexposed areas) remained remarkably stable during processing and / or storage under, for example, conventional white office light (800 lux).

[0073] The TBM initiator is an optionally substituted trihaloalkylaryl or heteroaryl sulfone compound. The optionally substituted aryl group is preferably a substituted phenyl, benzyl, tolyl, or ortho-, meta-, or para-xylyl, naphthyl, anthracene, phenanthrene, and / or combinations thereof. The heteroaryl group is preferably a monocyclic or polycyclic aromatic ring containing a carbon atom and one or more heteroatoms in its ring structure, preferably one to four heteroatoms independently selected from nitrogen, oxygen, selenium, and sulfur. Preferred examples include optionally substituted furanyl, pyridinyl, pyrimidinyl, pyrazolyl, imidazolyl, oxazolyl, isoxazolyl, thiophene, tetrazolyl, thiazolyl, (1,2,3)triazolyl, (1,2,4)triazolyl, thiadiazolyl, thiophene, and / or combinations thereof. The optionally substituted heteroaryl group is preferably a five- or six-membered ring substituted with one, two, or three oxygen atoms, nitrogen atoms, sulfur atoms, selenium atoms, or combinations thereof. Examples include furan, thiophene, pyrrole, pyrazole, imidazole, 1,2,3-triazole, 1,2,4-triazole, tetrazolium, oxazole, isoxazole, thiazole, isothiazole, thiazolium, thiazolium, thiadiazole, oxadiazole, pyridine, pyridazine, pyrimidine, pyrazine, 1,3,5-triazine, 1,2,4-triazine or 1,2,3-triazine, benzofuran, benzothiophene, indole, indazole, benzoxazole, quinoline, quinazoline, benzimidazole or benzotriazole.

[0074] The preferred TBM initiator is an optionally substituted trihalomethylaryl sulfone; more preferably, it is a tribromomethylaryl sulfone; and most preferably, it is an optionally substituted tribromomethylphenyl sulfone.

[0075] The term "alkyl" herein refers to all possible variations in the number of carbon atoms per alkyl group, namely methyl, ethyl, for three carbon atoms: n-propyl and isopropyl; for four carbon atoms: n-butyl, isobutyl, and tert-butyl; for five carbon atoms: n-pentyl, 1,1-dimethyl-propyl, 2,2-dimethylpropyl, and 2-methyl-butyl, etc. Preferably, the alkyl group is C1 to C6 alkyl. Most preferably, the alkyl group is methyl.

[0076] The term "substituted," in the case of substituted alkyl groups, means that the alkyl group can be replaced by atoms other than those normally present in such groups (i.e., carbon and hydrogen). For example, substituted alkyl groups can include halogen atoms or thiol groups. Unsubstituted alkyl groups contain only carbon and hydrogen atoms.

[0077] Optional substituents represent alkyl, cycloalkyl, alkenyl or cycloalkenyl, alkynyl or heteroaryl, alkylaryl or aralkyl, alkoxy or aryloxy, thioalkyl, thioaryl or thioheteroaryl, hydroxyl, -SH, carboxylic acid group or its alkyl ester, sulfonic acid group or its alkyl ester, phosphonic acid group or its alkyl ester, phosphate group or its alkyl ester, amino, sulfonamide, amide, nitro, nitrile, halogen or combinations thereof.

[0078] Suitable alkenyl groups are preferably C2-C6 alkenyl groups, such as vinyl, n-propenyl, n-butenyl, n-pentenyl, n-hexenyl, isopropenyl, isobutenyl, isopentenyl, neopentenyl, 1-methylbutenyl, isohexenyl, cyclopentenyl, cyclohexenyl and methylcyclohexenyl.

[0079] Suitable alkynyl groups are preferably C2 to C6-alkynyl groups; suitable aralkyl groups are preferably phenyl or naphthyl groups comprising one, two, three or more C1-C6 alkyl groups; suitable alkylaryl groups are preferably C1-C6-alkyl groups comprising aryl groups (preferably phenyl or naphthyl groups).

[0080] A cyclic group or cyclic structure includes at least one cyclic structure and can be a monocyclic or polycyclic group, meaning one or more rings fused together.

[0081] The amount of TBM-initiator relative to the total dry weight of the components of the photopolymerizable composition typically ranges from 0.1 to 30% by weight, preferably 0.5 to 10% by weight, and most preferably 2 to 7% by weight.

[0082] Optionally, any radical initiator capable of generating free radicals upon direct exposure or in the presence of a sensitizer may be further used. Suitable examples include onium salts, carbon-halogen compounds (such as [1,3,5]triazines with trihalomethyl groups), organic peroxides, aromatic ketones, thio compounds, azo polymerization initiators, azide compounds, ketoxime esters, hexaaryl diimidazoles, metallocenes, active ester compounds, borates, and quinone diazides. Of these, onium salts, particularly iodonium and / or sulfonium salts, are preferred from the viewpoint of storage stability.

[0083] More specific optional free radical initiators include, for example, derivatives of acetophenone (such as 2,2-dimethoxy-2-phenylacetophenone and 2-methyl-1-[4-(methylthio)phenyl-2-morpholinopropyl-1-one); benzophenone; benzoin; coumarin ketones (such as 3-benzoyl-7-methoxycoumarin and 7-methoxycoumarin); xanthones; thioxanthones; benzoin or alkyl-substituted anthraquinones; onium salts (such as diaryliodonium hexafluoroantimonyate, diaryliodonium trifluoromethanesulfonate, 4-(2-hydroxytetradecyloxy)hexafluoroantimonyate). (-phenyl)phenyliodonium, triarylsulfonium hexafluorophosphate, triarylsulfonium p-toluenesulfonate, (3-phenylprop-2-one)triarylphosphonium hexafluoroantimonylate, and N-ethoxy(2-methyl)pyridinium hexafluorophosphate, as well as ononium salts as described in U.S. Patent Nos. 5,955,238, 6,037,098, and 5,629,354; borates (such as tetrabutylammonium triphenyl(n-butyl)borate, tetraethylammonium triphenyl(n-butyl)borate, diphenyliodonium tetraphenylborate, diphenyliodonium tetraphenylborate, wherein the phenyl group of the iodonium salt is included. Substitution of at least six carbon atoms, and triphenylsulfonium triphenyl(n-butyl)borate, and borates as described in U.S. Patent Nos. 6,232,038 and 6,218,076; halogenated alkyl-substituted s-triazines (such as 2,4-bis(trichloromethyl)-6-(p-methoxy-styryl)-s-triazine, 2,4-bis(trichloromethyl)-6-(4-methoxy-naphthyl-1-yl)-s-triazine, 2,4-bis(trichloromethyl)-6-piperyl-s-triazine and 2,4-bis(trichloromethyl)-6-[ [4-ethoxy-ethyleneoxy)-phenyl-1-yl]-s-triazine and s-triazine as described in U.S. Patent Nos. 5,955,238, 6,037,098, 6,010,824, and 5,629,354; and cyclopentadiene titanium (bis(ethyl9-2,4-cyclopentadien-1-yl)bis[2,6-difluoro-3-(1H-pyrrolo-1-yl)phenyl)titanium). Onium salts, borates, and s-triazines are preferred radical initiators. Diaryliodoonium salts and triarylsulfonium salts are preferred onium salts. Triarylalkylborates are preferred borates. Trichloromethyl-substituted s-triazines are preferred s-triazines. These initiators can be used alone or in combination.

[0084] Very high sensitivity can be achieved by combining fluorescent whitening agents and polymerization initiators as sensitizers.

[0085] The photopolymerizable layer may also contain a co-initiator. Typically, the co-initiator is used in combination with a free radical initiator. Suitable co-initiators for photopolymer coatings are disclosed in US 6,410,205, US 5,049,479, EP 1 079 276, EP 1369 232, EP 1 369 231, EP 1 341 040, US 2003 / 0124460, EP 1 241 002, EP 1 288 720 and in the reference book including the cited literature: Chemistry & Technology UV & EB formulation for coatings, inks & paints - Volume 3 - Photoinitiators for Free Radical and Cationic Polymerisation, KK Dietliker - PKT Oldring edit - 1991 - ISBN 0 947798161. As described in EP 107 792, a specific co-initiator may be present in the photopolymerizable layer to further increase sensitivity. Preferred co-initiators are disclosed in EP 2 916 171

[0051] and are incorporated herein by reference.

[0086] Very high sensitivity can be achieved by including a sensitizer (such as a fluorescent whitening agent) in the coating. Suitable examples of fluorescent whitening agents as sensitizers are described on page 24, lines 20 to 39 of WO 2005 / 109103. Useful sensitizers may be selected from the sensitizing dyes disclosed in US 6,410,205, US 5,049,479, EP 1 079 276, EP 1 369 232, EP 1 369 231, EP 1341 040, US 2003 / 0124460, EP 1 241 002 and EP 1 288 720.

[0087] As described in EP 107 792, a specific co-initiator may be present in the photopolymerizable layer to further increase sensitivity. Preferred co-initiators are sulfur compounds, especially thiols, such as 2-mercaptobenzothiazole, 2-mercaptobenzoxazole, 2-mercapto-benzimidazole, 4-methyl-3-propyl-1,2,4-triazolin-5-thione, 4-methyl-3-n-heptyl-1,2,4-triazolin-5-thione, 4-phenyl-3-n-heptyl-1,2,4-triazolin-5-thione, 4-phenyl-3,5-dimercapto-1... 2,4-Triazole, 4-decyl-3,5-dimercapto-1,2,4-triazole, 5-phenyl-2-mercapto-1,3,4-oxadiazole, 5-methylthio-1,3,4-thiadiazolin-2-thione, 5-hexylthio-1,3,4-thiadiazolin-2-thione, mercaptophenyltetrazol, pentaerythritol mercaptopropionate, 3-mercapto-neopentyl butyrate, pentaerythritol tetra(thioglycolate). Other preferred co-initiators are polythiols disclosed in WO 2006 / 048443 and WO 2006 / 048445. These polythiols can be used in combination with the aforementioned thiols (such as 2-mercaptobenzothiazole).

[0088] The photopolymerizable layer may optionally contain an infrared-absorbing dye as a sensitizer, said infrared-absorbing dye absorbing light between 750 nm and 1300 nm, preferably between 780 nm and 1200 nm, more preferably between 800 nm and 1100 nm. A particularly preferred sensitizer is heptamethrin dye disclosed in paragraphs

[0030] to

[0032] of EP 1 359 008.

[0089] Binder The photopolymerizable layer preferably includes an adhesive. The adhesive can be selected from a wide range of organic polymers. Combinations of different adhesives can also be used. Useful adhesives are described, for example, in paragraph

[0013] of EP 1 043 627. Particulate polymers are also included, comprising homopolymers or copolymers prepared from monomers such as ethylene, styrene, vinyl chloride, methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, acrylonitrile, vinyl carbazole, acrylates, or methacrylates, or mixtures thereof.

[0090] Thermally reactive polymer particles contain thermally reactive groups (such as olefinic unsaturated groups, cationic polymerizable groups, isocyanate groups, epoxy groups, ethylene oxide groups) and functional groups with active hydrogen atoms, carboxyl groups, hydroxyl groups, amino groups, or acid anhydrides.

[0091] The average particle size of the polymer particles is preferably from 0.01 mm to 3.0 mm. Particulate polymers in the form of microcapsules, microgels or reactive microgels are suitable, as disclosed in EP 1 132 200, EP 1 724 112, and US 2004 / 106060.

[0092] Other ingredients The photopolymerizable layer may also contain particles that increase the coating’s resistance to artificial or mechanical damage. These particles may be inorganic, organic, or fillers, as described, for example, in US 7,108,956. Further details of suitable spacer particles described in EP 2 916 171

[0053] through

[0056] are incorporated herein by reference.

[0093] The photopolymerizable layer may also contain inhibitors. Specific inhibitors for use in photopolymer coatings are disclosed in US 6,410,205, EP 1 288 720 and EP 1 749 240.

[0094] The photopolymerizable layer may also contain adhesion-promoting compounds. Adhesion-promoting compounds are compounds capable of interacting with the support, preferably compounds having addition-polymerizable olefinic unsaturated bonds and functional groups capable of interacting with the support. "Interaction" is understood to be any type of physical and / or chemical reaction or process that forms a bond between the functional group and the support, said bond being a covalent bond, ionic bond, complex bond, coordinate bond, or hydrogen bond, and can be formed through adsorption processes, chemical reactions, acid-base reactions, complex formation reactions, or reactions of chelating groups or ligands. The adhesion-promoting compounds described in EP 2 916171

[0058] are incorporated herein by reference.

[0095] Various surfactants can be added to the photopolymerizable layer to allow or enhance the developability of the precursor; particularly developability with a gel solution. Both polymeric surfactants and small molecule surfactants, such as nonionic surfactants, are preferred. Further details are described in EP 2 916 171

[0059] , and are incorporated herein by reference.

[0096] According to the present invention, a method for manufacturing a negative lithographic printing plate is also provided, the method comprising the steps of: exposing a printing plate precursor in an image manner, and then developing the image-exposed precursor such that unexposed areas dissolve in a developing solution. Optionally, after the imaging step, a heating step is performed to enhance or accelerate the polymerization and / or crosslinking reaction. The lithographic printing plate precursor can be prepared by (i) applying a coating as described above onto a support and (ii) drying the precursor.

[0097] Exposure step The printing plate precursor is preferably exposed in an image-like manner by a laser that emits IR light. Preferably, the image-like exposure step is performed outside the printing press in a plate-making machine, which is an exposure device adapted to expose the precursor in an image-like manner using a laser (such as a laser diode emitting at about 830 nm or an NdYAG laser emitting at about 1060 nm) or by conventional exposure through contact with a mask. In a preferred embodiment of the invention, the precursor is exposed in an image-like manner by a laser that emits IR light.

[0098] Preheating step Following the exposure step, the precursor can be preheated in a preheating unit, preferably at a temperature of about 80°C to 150°C, and preferably for a dwell time of about 5 seconds to 1 minute. This preheating unit may include heating elements, preferably IR lamps, UV lamps, heated air, or heated rollers. Such a preheating step can be used for printing plate precursors containing photopolymerizable compositions to enhance or accelerate polymerization and / or crosslinking reactions.

[0099] Developing step Following the exposure or preheating step, when a preheating step is present, the printing plate precursor can be processed (developed). A pre-rinsing step can be performed before developing the imaging precursor, particularly for negative lithographic printing precursors with a protective oxygen barrier or outer coating. This pre-rinsing step can be performed in a separate apparatus or manually by rinsing the imaging precursor with water, or the pre-rinsing step can be performed in a washing unit integrated into the processing machine for developing the imaging precursor. The washing solution is preferably water, more preferably tap water. Further details regarding the washing step are described in EP 1 788 434

[0026] .

[0100] During the developing step, at least partially, the unexposed areas of the image recording layer are removed, while the exposed areas are not substantially removed. The processing solution, also known as the developer, can be applied to the printing plate by hand or in an automated processing apparatus, for example, by rubbing with an immersion pad, by immersion, dipping, coating, spin coating, spraying, or pouring. Treatment with the processing solution can be combined with mechanical friction (e.g., by a rotating brush). During the developing step, it is preferable to also remove any water-soluble protective layer present. Development is preferably carried out in an automated processing unit at a temperature between 20°C and 40°C.

[0101] In a highly preferred embodiment, the processing steps described above are replaced by on-press processing, wherein the imaging precursor is mounted on the printing press and processed on the printing press by rotating the printing cylinder while simultaneously feeding dampening solution and / or ink to the coating of the precursor to remove unexposed areas from the support. In a preferred embodiment, only dampening solution is supplied to the printing plate during printing press startup, and the ink supply is also activated after the printing cylinder has rotated a certain number of times. In an alternative embodiment, the supply of dampening solution and ink begins simultaneously, or only ink can be supplied during a certain number of rotations before the supply of dampening solution is activated.

[0102] The processing steps can also be performed by combining the above-described embodiments, for example, by combining development with processing solution with development on a printing press by applying ink and / or dampening solution.

[0103] Processing liquid The processing solution can be an alkaline developer or a solvent-based developer. Suitable alkaline developers are described in US2005 / 0162505. An alkaline developer is an aqueous solution with a pH of at least 11, more usually at least 12, and preferably 12 to 14. Alkaline developers typically contain an alkaline agent to achieve the high pH value, which can be an inorganic or organic alkaline agent. The developer may contain ionic surfactants, nonionic surfactants, and amphoteric surfactants (up to 3% by weight of the total composition); biocides (antimicrobial and / or antifungal agents), defoamers or chelating agents (such as basic gluconate), and thickeners (water-soluble or water-dispersible polyhydroxy compounds, such as glycerol or polyethylene glycol).

[0104] Preferably, the processing solution is an adhesive solution, thereby removing the non-exposed areas of the photopolymerizable layer from the support during the development step and applying adhesive to the printing plate in a single step. Developing with an adhesive solution has the additional advantage that, due to the residual adhesive in the non-exposed areas of the printing plate, no additional adhesive application step is required to protect the support surface in the non-printing areas. As a result, the precursor is processed and coated in a single step, leading to a simpler developing apparatus compared to developing apparatuses that include a developer tank, a rinsing section, and an adhesive application section. The adhesive application section may include at least one adhesive application unit or may include two or more adhesive application units. These adhesive application units may be configured as a cascaded system, i.e., when a supplemental adhesive solution is added to a second adhesive application unit or when the adhesive solution in the second adhesive application unit is used only once (i.e., when only the initial adhesive solution is used to develop the precursor in this second adhesive application unit, preferably by spray or jet technology), the adhesive solution used in the second adhesive application unit and present in the second tank overflows from the second tank to the first tank. Further details regarding this adhesive development are described in EP1 788444.

[0105] The adhesive solution is typically an aqueous liquid containing one or more surface-protective compounds that protect the lithographic image on the printing plate from contamination, such as oxidation, fingerprints, grease, oil, or dust, or from damage, such as scratching during plate handling. Suitable examples of such surface-protective compounds are film-forming hydrophilic polymers or surfactants. The layer retained on the printing plate after treatment with the adhesive solution preferably contains 0.005 g / m³. 2 and 20 g / m 2 Between, more preferably between, 0.010 g / m 2 and 10 g / m 2 The optimal value is between 0.020 g / m 2 and 5 g / m 2 The surface protective compounds in the adhesive solution. More details about the surface protective compounds in the adhesive solution can be found on page 9, line 3 to page 11, line 6 of WO 2007 / 057348. Because the developed plate precursor is developed and coated in one step, the finished plate requires no post-processing.

[0106] The adhesive solution preferably has a pH value of 3 to 11, more preferably 4 to 10, even more preferably 5 to 9, and most preferably 6 to 8. Suitable adhesive solutions are described, for example, in EP 1 342 568

[0008] to

[0022] and WO 2005 / 111727. The adhesive solution may further comprise inorganic salts, anionic surfactants, wetting agents, chelating compounds, antibacterial compounds, defoaming compounds and / or ink absorbers and / or combinations thereof. Further details regarding these additional components are described on page 11, line 22 to page 14, line 19 of WO 2007 / 057348.

[0107] Drying and baking step After the processing steps, the printing plate can be dried in a drying unit. In a preferred embodiment, the printing plate is dried by heating it in a drying unit, which may include at least one heating element selected from IR lamps, UV lamps, heated metal rollers, or heated air.

[0108] After drying, the printing plate may optionally be heated in a baking unit. More details about heating in a baking unit can be found on page 44, line 26 to page 45, line 20 of WO 2007 / 057348.

[0109] The resulting printing plate can be used in conventional so-called wet offset printing, where ink and aqueous dampening solution are supplied to the printing plate. Another suitable printing method uses so-called single-fluid inks without dampening solution. Suitable single-fluid inks have been described in US 4,045,232, US 4,981,517, and US 6,140,392. In a most preferred embodiment, the single-fluid ink comprises an ink phase (also called a hydrophobic or oleophilic phase) and a polyol phase, as described in WO 00 / 32705. Example

[0110] Example 1 1. Preparation of printing plate precursors Preparation of aluminum support S-01 A 0.3 mm thick aluminum foil was degreased by spraying it with an aqueous solution containing 26 g / L NaOH at 65 °C for 2 seconds, followed by rinsing with demineralized water for 1.5 seconds. Then, it was subjected to a temperature of 37 °C and approximately 100 A / dm³. 2 At current densities containing 15 g / L HCl and 15 g / L SO4 2- Ions and 5 g / L Al 3+ The foil was electrochemically roughened over 10 seconds using alternating current in an aqueous solution containing ions. It was then decontaminated by etching for 2 seconds with an aqueous solution containing 5.5 g / L NaOH at 36°C, followed by rinsing with demineralized water for 2 seconds. This was subsequently repeated at 50°C and 17 A / dm². 2 The foil was anodized for 15 seconds in an aqueous solution containing 145 g / L sulfuric acid at a current density, then washed with demineralized water for 11 seconds and dried at 120°C for 5 seconds.

[0111] The resulting support is characterized by a surface roughness Ra of 0.35 μm to 0.4 μm (measured using an NT1100 interferometer) and an oxide weight of 3.0 g / m². 2 .

[0112] Photopolymerizable layer The photosensitive composition as defined in Table 1 was applied to the support S-01 described above. The components were dissolved in a mixture of 35 vol% MEK and 65 vol% Dowanol PM (1-methoxy-2-propanol, commercially available from DOW CHEMICAL Company). The coating solution was applied to a wet coating thickness of 30 μm and then dried in a circulating oven at 120°C for 1 minute.

[0113] Table 1: Composition of the photosensitive layer (g / m³) 2 ) 1) FST 510 is the reaction product of 1 mole of 2,2,4-trimethylhexamethylene diisocyanate and 2 moles of hydroxyethyl methacrylate, and is commercially available from AZ Electronics as an 82% by weight solution in MEK; 2) CN 104 is an epoxy acrylate oligomer, commercially available from Arkema; 3) Initiator-01 is 4-hydroxyphenyltribromomethyl sulfone. 4) S2539 is an infrared absorbing dye, commercially available from FEW Chemicals, and has the following structure: 5) Ruco Coat EC4811 is a polyether polyurethane, commercially available from Rudolf Chemistry; 6) Tegoglide 410 is a surfactant and is commercially available from Evonik Tego Chemie GmbH; 7) Sipomer PAM 100 is a phosphonate methacrylate, commercially available from Rhodia; 8) Albritect CP 30 is a copolymer of vinylphosphonic acid and acrylic acid, and is commercially available from Rhodia as a 20% by weight aqueous dispersion.

[0114] Protective top layer An aqueous solution having the composition defined in Table 2 was coated (40 μm) onto the photosensitive layer and dried at 110 °C for 2 minutes.

[0115] Table 2: Composition of the protective layer (g / m³) 2 ) 1) Mowiol 4-88 TM And Mowiol 4-98 TM It is partially hydrolyzed polyvinyl alcohol, which is commercially available from Kuraray; 2) Exceval AQ4104 is a fully hydrolyzed ethylene-vinyl alcohol copolymer, commercially available from Kuraray; 3) IR-01 is an infrared absorbing dye with the following formula: 4) Lutensol A8™ is a surfactant that is commercially available from BASF.

[0116] Obtain PPP-01 to PPP-04 (Table 3).

[0117] 2. Imaging Using a High Power Creo 40W TE38 heat treatment machine TM (200 lpi Agfa Balanced Screening (ABS)) imaging of printing plate precursors PPP-01 to PPP-04 at 2400 dpi, the thermal plate setter being commercially available from Kodak and equipped with an 830 nm IR laser diode at an energy density of 50 mJ / cm². 2 and 200 mJ / cm 2 Between. Obtain printed versions PP-01 to PP-04.

[0118] 3. ΔE measurement Laboratory measurements were performed using a GretagMacBeth Spectro Eye reflectance spectrophotometer with the following settings: D50 (emitter), 2° (observer), no filter; commercially available from GretagMacBeth. The total color difference ∆E is a single value that takes into account the difference between the L, a*, and b* values ​​of the image and non-image areas. The higher the total color difference ∆E, the better the contrast. The contrast between image areas and non-image areas determines the appearance of the printed image.

[0119] 4. Results Table 3: Results of total color difference ∆E The results in Table 3 show that for the printing plates of the present invention, which include an outer coating containing dyes according to the present invention, the printed image is strong (total color difference ∆E equal to or greater than 2).

[0120] Example 2 1. Comparative preparation of printing plate PP-05 Photopolymerizable layer The photopolymerizable layer PL-01, as defined in Table 4, was coated onto the aforementioned support S-01 (see Example 1). The components were dissolved in a mixture of 35 vol% MEK and 65 vol% Dowanol PM (1-methoxy-2-propanol, commercially available from DOW CHEMICAL Company). The coating solution was applied to a wet coating thickness of 30 μm and then dried in a circulating oven at 120°C for 1 minute.

[0121] Table 4: Composition of the photosensitive layer (g / m²) 1) FST 510 is the reaction product of 1 mole of 2,2,4-trimethylhexamethylene diisocyanate and 2 moles of hydroxyethyl methacrylate, and is commercially available from AZ Electronics as an 82% by weight solution in MEK; 2) CN 104 is an epoxy acrylate oligomer, commercially available from Arkema; 3) Initiator-02 is 4-hydroxyphenyl-tribromomethyl-sulfone. 4) S0094 is an infrared absorbing dye, commercially available from FEW Chemicals, and has the following structure: 5) Ruco Coat EC4811 is a polyether polyurethane, commercially available from Rudolf Chemistry. 6) Tegoglide 410 is a surfactant and is commercially available from Evonik Tego Chemie GmbH; 7) Sipomer PAM 100 is a phosphonate methacrylate, commercially available from Rhodia; 8) Albritect CP 30 is a copolymer of vinylphosphonic acid and acrylic acid, and is commercially available from Rhodia as a 20% by weight aqueous dispersion.

[0122] Protective top layer An aqueous solution with the composition defined in Table 5 was applied to the top of the photosensitive layer and dried at 110°C for 2 minutes. A coating thickness of 2 g / m² was obtained. 2 The printing plate precursor PPP-05.

[0123] Table 5: Composition of the protective layer (g / m²) 1) Mowiol 4-88TM and Mowiol 8-88TM are partially hydrolyzed polyvinyl alcohol, while Mowiol 6-98TM is fully hydrolyzed polyvinyl alcohol, which can be commercially available from Kuraray. 2) IR-02 is an infrared absorbing dye with the following formula: 3) Acticide LA1206 is a biocidal agent and is commercially available from Thor; 4) Metolat FC 355 is ethoxylated ethylenediamine, which is commercially available from Munzing Chemie.

[0124] 5) Lutensol A8™ is a surfactant that is commercially available from BASF.

[0125] 2. Imaging Using a High Power Creo 40W TE38 heat treatment machine TM (200 lpi Agfa Balanced Screening (ABS)) imaging of the printing plate precursor PPP-05 at 2400 dpi, the thermal plate setter being commercially available from Kodak and equipped with an 830 nm IR laser diode at an energy density of 80 mJ / cm². 2 and 300 mJ / cm 2 Between. Obtain the printed version PP-05.

[0126] 3. Measurement of ∆E See Example 1 4. Results The total color difference ∆E was measured and the results are summarized in Table 6 below.

[0127] A total color difference ∆E greater than or equal to 2 is defined as a sharp printed image. A total color difference ∆E less than 2 is defined as an insufficient printed image.

[0128] Table 6: ∆E of printed plate PP-05 The comparison of samples clearly shows that when the total dry weight of the protective outer coating containing thermochromic dyes is too high, i.e. 2 g / m², the effect is more pronounced. 2 At this time, the formation of the printed image is inhibited: at a significantly increased dye concentration (157 mg / m³), the formation of the printed image is inhibited. 2 At 90 mJ / cm 2 Up to 150 mJ / cm 2 The printed image remains very weak under the exposed energy.

Claims

1. A lithographic printing plate precursor comprising a support and a coating, the coating comprising (i) a photopolymerizable layer comprising a polymerizable compound and optionally substituted trihaloalkylaryl sulfone photoinitiator, the photoinitiator being 4-hydroxyphenyltribromomethyl sulfone, and (ii) a top layer provided above the photopolymerizable layer; Its features are, The top layer comprises an infrared-absorbing compound capable of forming a printed image upon exposure to heat and / or IR radiation, wherein the infrared-absorbing compound is an infrared-absorbing dye that has predominant absorption in the infrared wavelength range of the electromagnetic spectrum before exposure to heat and / or IR radiation, and absorbs significantly more light in the visible wavelength range of the electromagnetic spectrum after exposure to heat and / or IR radiation, and wherein the infrared-absorbing dye is represented by formula I, II, or III: Formula I Formula II Formula III in Ar 1 Ar 2 and Ar 3 Independently representing an optionally substituted aromatic hydrocarbon group or an aromatic hydrocarbon group having an optionally substituted cyclic benzene ring. W 1 and W 2 Independently represent sulfur atoms, oxygen atoms, NR¨, where R¨ represents an optionally substituted alkyl group, NH or -CM. 10 M 11 Group, wherein M 10 and M 11 Independently, it is an optionally substituted aliphatic hydrocarbon group or an optionally substituted (hetero)aryl group, or wherein M is an optionally substituted aliphatic hydrocarbon group or a heteroaryl group. 10 and M 11 Together they contain the necessary atoms to form a ring structure, preferably a 5- or 6-membered ring; W 3 Represents a sulfur atom or -C(A) 3 )=C(A 4 )- group, W 4 Represents a sulfur atom or -C(A) 7 )=C(A 8 )- group, M 1 and M 2 Independently representing hydrogen, optionally substituted aliphatic hydrocarbon groups, or together containing the necessary atoms to form an optionally substituted cyclic structure, which may contain an optionally substituted cyclic benzene ring, preferably M. 1 and M 2 Together they contain the necessary atoms to form an optionally substituted cyclic structure, which may contain an optionally substituted cyclic benzene ring, preferably a 5- or 6-membered ring, more preferably a 5-membered ring, and most preferably a 5-membered ring having 5 carbon atoms. M 3 and M 4 Independently represents an optionally substituted aliphatic hydrocarbon group; M 5 M 6 M 7 and M 8 M 16 and M 17 Independently representing hydrogen, halogen, or optionally substituted aliphatic hydrocarbon groups, A 1 To A 8 Independently representing hydrogen, halogen atoms, optionally substituted aliphatic hydrocarbon groups, or optionally substituted (hetero)aryl groups, or wherein A 1 and A 2 A 3 and A 4 A 5 and A 6 Or A 7 and A 8 Each of them together contains the necessary atoms to form a ring structure, preferably a 5- or 6-membered ring; M 12 and M 13 and M 14 and M 15 Independently representing an optionally substituted aliphatic hydrocarbon group or an optionally substituted (hetero)aryl group, or wherein the M 14 M 15 A 5 Or A 7 The two components together contain the necessary atoms to form at least one ring structure, preferably a 5- or 6-membered ring; the M 12 M 13 A 2 Or A 4 The two together contain the necessary atoms to form at least one ring structure, preferably a 5- or 6-membered ring; M 9 It is transformed into a form that is more than M through exposure to IR radiation or thermally induced chemical reactions. 9 A group of stronger electron donors; and the transition provides an increase in the integrated light absorption of the dye between 350 nm and 700 nm; and optionally one or more counterions to obtain an electrically neutral compound; The top layer contains 0.25 g / m 2 and 1.0 g / m 2 The thickness between, and The combination of the photoinitiator in the photopolymerizable layer and the infrared-absorbing dye in the top layer having the aforementioned thickness, at energy densities of 80 and 120 mJ / m 2 Under imaging exposure conditions, it provides printed images characterized by a CIE1976 color distance ΔE of at least 2, while simultaneously providing improved image clarity on printed sheets.

2. The printing plate precursor according to claim 1, wherein the coating is machine-developable with dampening solution and / or ink.

3. The printing plate precursor of claim 1, wherein the infrared absorbing compound comprises a thermally pyrolytic group that transforms into a stronger electron donor group upon exposure to heat and / or IR radiation.

4. The printing plate precursor according to claim 1, wherein M 1 and M 2 Together they contain the necessary atoms to form an optionally substituted 5- or 6-membered ring, which may contain an optionally substituted cyclic benzene ring.

5. The printing plate precursor according to claim 1 or 4, wherein the infrared absorbing dye is represented by formula I: Formula I in Ar 1 and Ar 2 W 1 and W 2 M 1 To M 9 As defined in claim 1, and Optionally, one or more counterions can be used to obtain an electrically neutral compound.

6. The printing plate precursor according to claim 1 or 4, wherein M 9 It represents one of the following groups: -(N=CR 17 )a-NR 5 -CO-R 4 、 -(N=CR 17 )b-NR 5 -SO2-R 6 、 -(N=CR 17 )c-NR 11 -SO-R 12 、 -SO2-NR 15 R 16 and -S-CH2-CR 7 (H) 1-d (R 8 ) d -NR 9 -COOR 18 , in a, b, c, and d are independently 0 or 1; R 17 Represents hydrogen, an optionally substituted aliphatic hydrocarbon group, or an optionally substituted (hetero)aryl group, or wherein R 17 and R 5 Or R 17 and R 11 Together they contain the necessary atoms to form a ring structure; R 4 Indicates -OR 10 -NR 13 R 14 Or -CF3; Where R 10 Indicates an optional substituted (hetero)aryl group or an optional branched aliphatic hydrocarbon group; R 13 and R 14 Independently representing hydrogen, an optionally substituted aliphatic hydrocarbon group, or an optionally substituted (hetero)aryl group, or wherein R 13 and R 14 Together they contain the necessary atoms to form a ring structure; R 6 Indicates an optionally substituted aliphatic hydrocarbon group or an optionally substituted (hetero)aryl group, -OR 10 -NR 13 R 14 Or -CF3; R 5 Indicates hydrogen, optionally substituted aliphatic hydrocarbon groups, SO3- groups, -COOR 18 A group or optionally substituted (hetero)aryl group, or wherein R 5 With R 10 R 13 and R 14 At least one of them together contains the necessary atoms to form a ring structure; R 11 R 15 and R 16 Independently representing hydrogen, an optionally substituted aliphatic hydrocarbon group, or an optionally substituted (hetero)aryl group, or wherein R 15 and R 16 Together they contain the necessary atoms to form a ring structure; R 12 Indicates an optionally substituted aliphatic hydrocarbon group or an optionally substituted (hetero)aryl group; R 7 and R 9 Independently representing hydrogen or optionally substituted aliphatic hydrocarbon groups, R 8 This indicates -COO- or -COOR 8’ , where R 8’ It represents hydrogen, alkali metal cations, ammonium ions, or mono-, di-, tri-, or tetra-alkylammonium ions; R 18 This indicates an optional substituted (hetero)aryl or α-branched aliphatic hydrocarbon group.

7. A method for manufacturing a printing plate precursor, the method comprising the following steps: - Coating a support with (i) a photopolymerizable layer comprising a polymerizable compound and an optionally substituted trihaloalkylaryl sulfone photoinitiator, wherein the photoinitiator is 4-hydroxyphenyltribromomethyl sulfone, and (ii) providing a top layer above the photopolymerizable layer comprising an infrared-absorbing dye as defined in any one of claims 1 to 6, and - Dry the precursor.

8. A method for manufacturing a printing plate, the method comprising the following steps: - The printing plate precursor as defined in any one of claims 1-6 is exposed to heat and / or IR radiation in an image manner, thereby forming a lithographic image consisting of image areas and non-image areas, and thereby inducing color changes in the image areas. - To develop the exposed precursor.

9. The method of claim 8, wherein the precursor is developed by mounting the precursor on a plate cylinder of a lithographic printing press and rotating the plate cylinder while feeding dampening solution and / or ink to the precursor.

10. The method according to claim 8 or 9, wherein the color change is characterized in that the CIE 1976 color distance ΔE between the image region and the non-image region is at least 2.

11. The method according to claim 8 or 9, wherein the energy density of the IR radiation is included in 80 mJ / m 2 -120mJ / m 2 between.

Images