Lithographic printing plate precursors

Abstract

A lithographic printing plate precursor is disclosed, comprising a support and a coating, the coating comprising (i) a photopolymerizable layer comprising a polymerizable compound and a photoinitiator, and a top layer provided above the photopolymerizable layer; characterized in that the top layer comprises a halogenated polymer and a nitrite and / or nitrate.

Description

Technical Field

[0001] The present invention relates to novel lithographic printing plate precursors. Background Art

[0002] Lithographic printing generally involves the use of a so-called printing master, such as a printing plate mounted on the cylinder of a rotary printing press. The master carries a lithographic image on its surface, and the printed product is obtained by applying ink to the image and then transferring the ink from the master to a receiving material, which is usually paper. In conventional lithographic printing, ink and an aqueous fountain solution (also called a dampening liquid) are supplied to the lithographic image, which consists of oleophilic (or hydrophobic, i.e., ink-receiving and water-repelling) areas and hydrophilic (or oleophobic, i.e., water-receiving and ink-repelling) areas. In so-called waterless offset printing, the lithographic image consists of ink-receiving and ink-resistant (ink-repelling) areas, and during waterless offset printing, only ink is supplied to the master.

[0003] Lithographic printing masters are typically obtained by image-wise exposure and processing of a radiation-sensitive layer on a lithographic printing plate support. Imaging and processing transform the so-called lithographic printing plate precursor into a printing plate or master. The radiation-sensitive coating is typically image-wise exposed to heat or light using a digitally modulated exposure device (such as a laser), which triggers physical and / or chemical processes such as ablation, polymerization, insolubilization by crosslinking of polymers or by agglomeration of particles of a thermoplastic polymer latex, solubilization by disrupting intermolecular interactions, or by increasing the permeability of a developer barrier. Although some plate precursors are capable of producing a lithographic image immediately after exposure, the most popular lithographic plate precursors require wet processing because exposure creates a solubility difference or dissolution rate difference in the developer between the exposed and non-exposed areas of the coating. In positive-working lithographic printing plate precursors, the exposed areas of the coating dissolve in the developer, while the non-exposed areas remain resistant to the developer. In negative-working lithographic printing plate precursors, the non-exposed 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, so that areas remaining resistant to the developer define the ink receptive, and hence printing, areas of the printing plate, while the hydrophilic support is revealed at the non-printing areas by dissolution of the coating in the developer.

[0004] Photopolymer printing plates rely on a working mechanism whereby a coating, typically comprising a free-radically polymerizable compound, hardens upon exposure. "Hardening" means that the coating becomes insoluble or non-dispersible in a developer solution and can be achieved by polymerization and / or crosslinking of the photosensitive coating upon exposure to light and / or heat. Photopolymer plate precursors can be sensitized to blue, green, or red light (i.e., wavelengths in the range of 450-750 nm), to violet light (i.e., wavelengths in the range of 350-450 nm), or to infrared light (i.e., wavelengths in the range of 750-1500 nm). Optionally, the exposure step is followed by a heating step to enhance or accelerate the polymerization and / or crosslinking reaction.

[0005] Typically, a topcoat or protective overcoat over the imageable layer is required to act as an oxygen barrier to provide the desired sensitivity to the printing plate. The topcoat typically comprises a water-soluble or water-swellable polymer, such as polyvinyl alcohol and / or its copolymers. In addition to acting as an oxygen barrier, the topcoat should preferably be easily removable during processing and sufficiently transparent to actinic radiation (e.g., 300-450 nm, 450-750 nm, or 750-1500 nm).

[0006] To enable evaluation of the image quality of a lithographic printing plate before it is mounted on a printing press, such as image resolution and detail rendering (usually measured using a densitometer), lithographic printing plate precursors typically contain a colorant, such as a dye or pigment, in a coating. After processing, such a colorant provides contrast between the image area containing the colorant and the hydrophilic support from which the coating has been removed, allowing the end user to assess the image quality and / or determine whether the precursor has been exposed to light. Furthermore, in addition to enabling evaluation of image quality, a high contrast between the image and the hydrophilic support is desirable to achieve good image registration (alignment) of different printing plates in multicolor printing, thereby ensuring image sharpness (resolution) and correct rendering of the colors present in the image.

[0007] However, for photopolymer lithographic printing plates that are processed on-press and therefore not developed before being mounted on the press, it is not possible to pre-inspect and identify the printing plates that include colorants. The art has offered a solution by including components in the coating that, upon exposure, form a so-called "print-out image" (i.e., an image that is visible prior to processing). However, in these materials, the photoinitiating system is typically a reactive component that induces the formation of a print-out image upon exposure and, therefore, can reduce lithographic variations.

[0008] The formation of printed images of violet-sensitive photopolymer systems has been disclosed, for example, in 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.

[0009] For thermosensitive photopolymer lithographic printing plates, the formation of printed images is also known. Such printing plates are usually exposed in an image-wise manner by means of an IR laser and, in addition to IR dyes as light-heat conversion compounds, usually contain dyes that absorb in the visible wavelength range and change color when heated. This color change can be obtained, for example, with thermally decomposable dyes that bleach when heated, such as disclosed in EP 897 134, EP 925 916, WO 96 / 35143, EP 1 300 241. Alternatively, this heat-induced color change can be the result of a shift in the absorption maximum of a dye that absorbs in the visible wavelength range, as disclosed in EP 1 502 736 and EP 419 095. Problems associated with these prior art materials, in which the printed image is

[0010] Contrast-providing colorants derived from so-called leuco dyes, which switch color when subjected to changes in pH, temperature, light (e.g., UV radiation), etc., are already widely used in the art. Leuco dye technology involves switching between two chemical forms, one of which is colorless. If the color switch is caused by, for example, pH or temperature, the transition is reversible. Irreversible switching is usually based on redox reactions.

[0011] The classic workflow for photopolymer printing plates consists of an initial exposure step of the photopolymer printing plate precursor in a UV or IR platesetter, followed by an optional preheating step, a washing step of the protective overcoat, an alkaline development step, and a rinsing and gluing step. However, there is a significant move towards simplifying the workflow, where the preheating and / or washing steps are eliminated, and where the processing and gluing steps are performed in a single step, or where processing is performed with a neutral gum and then gluing in a second step. Alternatively, on-press processing has become very popular, where the printing plate is mounted on the press and the coating is developed by interaction with fountain solution and / or ink supplied to the plate during the press run. During the first run of the press, the non-image area is removed from the support, thereby defining the non-printing area of ​​the printing plate.

[0012] Regardless of the processing method used, specially designed printing plates with lithographic coatings that are sufficiently soluble or dispersible in the developer and / or on the printing press are required to achieve good cleanout (complete removal of the coating from non-printed areas of the image). However, a major problem encountered in the prior art is the appearance of so-called "oxidation" or "scum" spots on the hydrophilic surface of the roughened and anodized aluminum support. These spots, also known in the art as "artifacts," typically degrade the lithographic performance of the printing plate. This has been observed in the art, particularly when halide ions (e.g., as counterions to certain components of the composition) are present in the photosensitive layer of the printing plate precursor. Furthermore, this phenomenon becomes more pronounced in the presence of moisture, such as during storage at high humidity, where the halide ions can act as acids and corrode the aluminum support. The formation of such oxidation spots is even more pronounced when using non-silicate developers and / or oxidizing inks and / or when halide ion levels are high in the dampening / rinsing water or in the coating.

[0013] EP 1 518 670, JP 2009 / 255506 and JP 2009 / 262523 disclose a negative-working printing plate precursor comprising a photosensitive layer which is not dyed in the non-image areas and in which the concentration of the halide ions is controlled within a specified range by selecting compounds such as a polymerization initiator which has no halide counter ions in its structure, an infrared absorber and a colorant. Summary of the Invention

[0014] It is an object of the present invention to provide a negative-working printing plate precursor comprising a roughened and anodized aluminum support which is less susceptible to forming defects and / or oxidation spots during storage and / or under humid conditions.

[0015] This object is achieved by the printing plate precursor as defined in claim 1 and the preferred embodiments as defined in the dependent claims. A particular feature of the printing plate material of the invention is that it contains a coating comprising at least two layers, wherein the top layer comprises at least one nitrite or nitrate (further also referred to as nitrite / nitrate) and a halogenated binder.

[0016] According to the present invention, it has surprisingly been found that by including a nitrite / nitrate in the top layer, the presence of defects and / or oxidation spots on the surface of the aluminum support can be minimized and even prevented. As a result, the presence of defects on the paper prints is significantly reduced compared to printing plates comprising a halogenated binder in the top layer without nitrite / nitrate. This reduction effect is particularly observed for printing plate precursors comprising a halogenated binder in the top layer, preferably comprising at least one monomer unit derived from a vinylidene monomer.

[0017] Other features, elements, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention. Specific embodiments of the present invention are also defined in the dependent claims. DETAILED DESCRIPTION

[0018] Lithographic printing plate precursors

[0019] The lithographic printing plate precursor according to the invention is negative-working, i.e. after exposure and development, the non-exposed 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 provided with a hydrophilic layer. The hydrophobic areas are defined by a coating that hardens upon exposure (optionally followed by a heating step). Areas having hydrophilic properties are understood to mean areas that have a higher affinity for aqueous solutions than for (oleophilic) inks; areas having hydrophobic properties are understood to mean areas that have a higher affinity for (oleophilic) inks than for aqueous solutions.

[0020] "Hardening" means that the coating becomes insoluble or non-dispersible in the developer 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 preferably heated at a temperature of about 80° C. to 150° C. and preferably during a dwell time of about 5 seconds to 1 minute.

[0021] 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 further comprise other layers, such as an intermediate layer between the support and the photopolymerizable layer and / or between the top layer and the photopolymerizable layer, an adhesion-improving layer, a hydrophilic layer, and / or other layers.

[0022] The printing plate of the present invention is characterized in that it can be exposed at low energy densities, i.e. below 190 mJ / m 2 ; preferably 70-190 mJ / m 2 More preferably, between 75 and 150 mJ / m 2 Between and most preferably between 80-120 mJ / m 2 between.

[0023] Top floor

[0024] The coating includes a topcoat or protective outer coating that can act as an oxygen barrier. Low molecular weight substances present in the air may degrade or even inhibit image formation, and therefore a topcoat is applied to the coating. The topcoat should preferably be easily removable during development, adhere well to the photopolymerizable layer or optional other layers of the coating, and should preferably not inhibit light transmission during exposure. The topcoat is provided on top of the photopolymerizable layer.

[0025] The top layer includes at least one nitrite / nitrate. Any nitrite / nitrate is suitable; sodium or potassium nitrite / nitrate is preferred. The nitrite / nitrate is preferably present in the top layer in an amount between 15 and 60 mg / m², more preferably between 20 and 50 mg / m², and most preferably between 25 and 45 mg / m².

[0026] The top layer comprises a halogenated polymer, also referred to as a "halogenated binder." The halogenated polymer is preferably a hydrophobic polymer, also referred to as a "hydrophobic binder." A hydrophobic polymer is a polymer that is preferably insoluble or non-swellable in water (i.e., at approximately neutral pH). The halogenated binder is preferably uncrosslinked or only slightly crosslinked. The halogenated polymer is preferably in particulate form. The halogenated polymer is preferably used in the top layer in the form of a dispersion; i.e., an emulsion or suspension. A dispersion of the particles in an aqueous medium is preferred.

[0027] Compared to printing plates of the prior art, the halogenated binder in the top layer exhibits superior resistance to damage in the imaged area caused by plate handling. Furthermore, the cleaning behavior of the printing plate during the start-up of a print run can be improved. Further details on halogenated binders can be found in EP 3 587 113.

[0028] The average particle size is preferably comprised between 10 nm and 1000 nm, more preferably between 25 nm and 250 nm, even more preferably between 30 nm and 200 nm and most preferably between 50 nm and 175 nm. In this article, particle size is defined as particle diameter, measured by photon correlation spectroscopy (Photon Correlation Spectrometry), also known as quasi-elastic or dynamic light scattering (Quasi-Elastic or Dynamic Light-Scattering). This technology is a convenient method for measuring particle size, and the particle size value measured is closely matched with the particle size measured by transmission electron microscopy (TEM), as disclosed in Stanley D. Duke et al., Calibration of Spherical Particles by Light Scattering, in Technical Note-002B, May 15, 2000, (revised on 1 / 3 / 2000 by the paper published in Particulate Science and Technology 7, p. 223-228 (1989)).

[0029] The amount of halogenated binder in the top layer is preferably between 30% and 96% by weight, more preferably between 40% and 90% by weight and most preferably between 50% and 85% by weight.

[0030] The halogenated binder preferably comprises at least one monomer unit derived from a vinyl and / or vinylidene monomer; preferably a vinylidene monomer. The halogenated binder may be a homopolymer or a copolymer. Copolymers are highly preferred. Copolymers are preferably random copolymers, gradient copolymers or multi-block copolymers. Multi-block copolymers are preferably block copolymers, graft copolymers or star polymers in which polymer chains are bonded to a core. Suitable examples of vinyl monomers include vinyl halides, such as vinyl chloride, vinyl bromide or vinyl iodide. Suitable examples of vinylidene monomers include vinylidene halides, such as vinylidene fluoride, vinylidene chloride, vinylidene bromide or vinylidene iodide.

[0031] In a highly preferred embodiment, the halogenated binder includes at least one monomeric unit derived from a vinylidene monomer. Suitable vinylidene monomers include vinylidene halides, such as vinylidene fluoride, vinylidene chloride, vinylidene bromide and / or vinylidene iodide. Most preferably, the halogenated binder includes at least one monomeric unit derived from vinylidene fluoride and / or vinylidene chloride, most preferably derived from vinylidene chloride, also referred to herein as PVDC binder. The halogenated binder preferably includes between 60 wt % and 95 wt %, more preferably between 65 wt % and 90 wt % and most preferably between 70 wt % and 85 wt % of monomeric units derived from vinylidene monomers.

[0032] The inventors believe that, for example, free chlorides present in PVDC interact with the substrate and cause numerous defects and / or oxidized spots; therefore, halide attack may be initiated by components in the coating (e.g., top layer), including free chlorides. It has surprisingly been found that by including the nitrite / nitrate salts according to the present invention in a top layer containing a halogenated binder comprising at least one monomer unit derived from a vinylidene monomer, the appearance of defects and / or oxidized spots in the aluminum surface is greatly reduced.

[0033] Halogenated binding agent can be synthesized by the conventional known method based on polyaddition reaction.The number average molecular weight (Mn) that is used for polymkeric substance of the present invention is preferably 5.000 g / mol-1.000.000 g / mol, more preferably 10.000 g / mol-500.000 g / mol and most preferably in the scope of 20.000 g / mol-150.000 g / mol.The weight average molecular weight (Mw) that is used for polymkeric substance of the present invention is preferably 10.000 g / mol-400.000 g / mol, more preferably 70.000 g / mol-350.000 g / mol and most preferably in the scope of 100.000 g / mol-250.000 g / mol.Number average molecular weight (Mn) and weight average molecular weight (Mw) use the mixture of THF and 5 % by weight acetic acid as eluent and polystyrene as calibration standard to pass through size exclusion chromatography.

[0034] The halogenated binder used in the present invention is preferably a copolymer, such as a gradient copolymer, which shows a gradual change in monomer composition from mainly one monomer to mainly another monomer; or a random copolymer, whose composition changes discontinuously. The halogenated binder may contain other monomer units in addition to the vinyl and / or vinylidene monomer units defined above. The halogenated binder preferably includes between 5% by weight and 40% by weight, more preferably between 10% by weight and 30% by weight and most preferably between 15% by weight and 25% by weight of these other monomer units. All amounts of monomer units are expressed in % by weight herein and refer to the sum of all monomer units of the copolymer. Other monomer units are defined as follows.

[0035] The halogenated binder may further comprise one or more other monomer units preferably derived from: an acrylate or methacrylate, for example an alkyl or aryl (meth)acrylate, such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, benzyl (meth)acrylate, 2-phenylethyl (meth)acrylate, hydroxyethyl (meth)acrylate, phenyl (meth)acrylate or N-(4-methylpyridyl) (meth)acrylate; (meth)acrylic acid; a (meth)acrylamide, for example (meth)acrylamide or an N-alkyl or N-aryl (meth)acrylamide, such as N-methyl (meth)acrylamide, N-ethyl (meth)acrylamide, N-phenyl (meth)acrylamide, N-benzyl (meth)acrylamide, N-hydroxymethyl (meth)acrylamide, N-(4-hydroxyphenyl) (meth)acrylamide; (meth)acrylamide, for example (meth)acrylamide or an N-alkyl or N-aryl (meth)acrylamide, such as N-methyl (meth)acrylamide, N-ethyl (meth)acrylamide, N-phenyl (meth)acrylamide, N-benzyl (meth)acrylamide, N-hydroxymethyl (meth)acrylamide, N-(4-hydroxyphenyl) (meth)acrylamide; ) acrylonitrile; styrene; substituted styrenes, such as 2-, 3- or 4-hydroxystyrene, 4-carboxystyrene esters; vinylpyridines, such as 2-vinylpyridine, 3-vinylpyridine, 4-vinylpyridine; substituted vinylpyridines, such as 4-methyl-2-vinylpyridine; vinyl acetate, optionally copolymerized vinyl acetate monomer units at least partially hydrolyzed to form alcohol groups, and / or at least partially reacted with aldehyde compounds such as formaldehyde or butyraldehyde to form acetal or butyral groups; vinyl alcohol; vinyl nitrile; vinyl acetal; vinyl butyral; vinyl ethers, such as methyl vinyl ether; vinyl amides; N-alkylvinylamides, such as N-methylvinylamide, caprolactam, vinylpyrrolidone; maleic anhydride, maleimides (e.g. maleimide) or N-alkyl or N-arylmaleimide (e.g. N-benzylmaleimide).

[0036] In a preferred embodiment, the binder further comprises monomer units selected from the group consisting of: (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate or phenyl (meth)acrylate, hydroxyethyl (meth)acrylate or benzyl (meth)acrylate; vinyl nitrile or vinyl pyrrolidone.

[0037] The halogenated binder most preferably comprises methyl acrylate units and / or butyl acrylate units.

[0038] Particularly preferred PVDC polymers are Ixan™ and Diofan™ available from Solvay, PVDC latex available from Asahi-Kasei, Daran™ available from Owensboro, Permax™ available from Lubrizol. Some of these copolymer grades are not water-based but can be dispersed in water to obtain water-based dispersions via various dispersion techniques well known in the art.

[0039] Other preferred binders for the top layer are disclosed in WO 2005 / 029190 (page 36, line 3 to page 39, line 25), US 2007 / 0020563 (paragraph

[0158] ), and EP 1 288 720 (paragraphs

[0148] and

[0149] ). The most preferred binder for the top layer is polyvinyl alcohol or a polyvinyl alcohol / polyvinyl acetate copolymer. The copolymer preferably has a degree of hydrolysis in the range of 74 mol % to 99 mol %, more preferably 80-89%. The weight-average molecular weight of the polyvinyl alcohol can be defined by measuring the viscosity of a 4% by weight aqueous solution at 20°C as defined in DIN 53 015, and the viscosity value (mPas) is preferably in the range of 2-28, more preferably 2-15, and most preferably 2-10. Modified polyvinyl alcohols or polyvinyl alcohol / polyvinyl acetate copolymers may also be used, for example polyvinyl alcohols or copolymers comprising carboxyl and / or sulfonic acid groups, preferably together with unmodified polyvinyl alcohols or polyvinyl alcohol / polyvinyl acetate copolymers.

[0040] The top layer may optionally include other ingredients, such as matting agents; surfactants, such as anionic surfactants (e.g. sodium alkyl sulfate or sodium alkyl sulfonate), amphoteric surfactants (e.g. alkylaminocarboxylates and alkylaminodicarboxylates), nonionic surfactants (e.g. polyoxyethylene alkylphenyl ethers, (co)polymers comprising siloxane and / or perfluoroalkyl units and / or oligo(alkylene oxide) units); fillers; (organic) waxes; alkoxylated alkylenediamines as disclosed, for example, in EP 1 085 380 (paragraphs

[0021] and

[0022] ); glycerol; inorganic particles; pigments or wetting agents, as disclosed in EP 2 916 171 and incorporated herein by reference.

[0041] The coating thickness of the top layer is preferably between 0.10 and 1.75 g / m 2 between 0.20 and 1.3 g / m 2between 0.25 and 1.0 g / m 2 In a more preferred embodiment of the present invention, the top layer has a thickness of 0.25-1.75 g / m 2 and comprising polyvinyl alcohol having a degree of hydrolysis in the range of 74 mol % to 99 mol % and a viscosity value in the range of 2 to 26 mPas as defined above.

[0042] Color Precursors

[0043] The coating preferably includes a color precursor that forms a colored compound upon exposure to UV light, infrared light, and / or heat, thereby forming the printed image. The contrast of the printed image can be defined as the difference between the optical density of the exposed areas and the optical density of the non-exposed areas and is preferably as high as possible. This enables the end user to immediately determine whether the precursor has been exposed, to distinguish between 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 areas, and the reflectance can be measured using a densitometer equipped with several filters (e.g., cyan, magenta, yellow). It has been observed that defects and / or oxidation spots on the surface of the aluminum support are much more noticeable when a color precursor is present in the top layer.

[0044] At least one color precursor may be in the photopolymerizable layer and / or in the top layer and / or in an optional further layer. The photopolymerizable layer, the top layer and optionally the further layer may comprise the same or different color precursors. Preferably, the color precursor is present in the top layer.

[0045] Many classes of color precursors can be used as color-forming compounds in the present invention, such as: spiropyran leuco dyes, such as; spirobenzopyrans (e.g., spiroindolinylbenzopyrans, spirobenzopyranochromenes, 2,2-dialkylchromenes), spironaphthooxazines, and spirothiopyrans; leucoquinone dyes; azines, such as oxazines, diazines, thiazines, and phenazines; phthalide and benzopyrrolone-type leuco dyes, such as triarylmethanephthalide (e.g., crystal violet lactone), diarylmethanephthalide, monoarylmethanephthalide, heterocyclic-substituted phthalide, alkenyl-substituted phthalide, bridged phthalide (e.g., spirofluorenephthalide and spirobenzoanthraphthalide), and bisphthalide; fluoran leuco dyes, such as fluorescein, rhodamine, and p-aminophenol; triarylmethanes, such as leuco crystal violet; ketazines; barbituric acid leuco dyes and thiobarbituric acid leuco dyes. Specific color precursors suitable for forming colored dyes upon exposure to heat and / or light are disclosed in WO2019 / 243037

[0035] to

[0060] .

[0046] Color precursor can be 0.01-0.1 g / m 2 The amount is preferably 0.02-0.08 g / m 2The amount is preferably 0.025-0.05 g / m 2 The amount exists in the top layer.

[0047] Highly preferred color precursors are IR-leuco dyes, also referred to herein as IR-thermochromic dyes or infrared-thermochromic dyes, which have a primary absorption in the infrared wavelength range of the electromagnetic spectrum (i.e., the wavelength range between about 750-1500 nm) and preferably do not have significant light absorption in the visible wavelength range of the electromagnetic spectrum (i.e., the wavelength range between 390-700 nm). Preferred IR-thermochromic dyes are disclosed in EP 1 736 312 and EP 1 910 082 and have a partial structure according to the following formula:

[0048]

[0049] Where * indicates the connection of a part of the structure to the rest of the structure, and where at least one R d A group is a group that is converted by a chemical reaction induced by exposure to IR radiation or heat to a group that is smaller than the R d A stronger electron donor group, or at least one of the R a A group is a group which is converted by a chemical reaction induced by exposure to IR-radiation or heat to a group which is smaller than the R a The electron accepting group is preferably defined as a group having a Hammett sigma para-value greater than or equal to 0.3, and the electron donor group is defined as a group having a Hammett sigma para-value less than or equal to 0.3. Details about sigma para-values ​​can be found in Chapman and Shorter, Correlation Analysis in Chemistry, Recent Advances, Plenum, New York, 1978, p. 439-540.

[0050] IR-thermochromic dyes preferably include at least one thermally cleavable group that is converted into a group that is a stronger electron donor through a chemical reaction induced by exposure to IR radiation or heat. As a result, the exposed IR-thermochromic dye absorbs significantly more light in the visible wavelength range of the electromagnetic spectrum, or in other words, the IR-thermochromic dye undergoes a blue shift, thereby forming a visible image, also called a printout image.

[0051] The concentration of the IR-thermochromic dye may be 0.1 wt% to 20.0 wt%, more preferably 0.5 wt% to 15.0 wt%, most preferably 1.0 wt% to 10.0 wt%, relative to the total dry weight of the coating.

[0052] The IR-thermochromic dye is preferably represented by formula I, II or III:

[0053]

[0054] in

[0055] Ar 1 、Ar 2 and Ar 3 independently represent an optionally substituted aromatic hydrocarbon group or an aromatic hydrocarbon group having an optionally substituted cyclic benzene ring,

[0056] W 1 and W 2 independently represents a sulfur atom, an oxygen atom, NR¨, wherein R¨ represents an optionally substituted alkyl group, NH or -CM 10 M 11 Group, where M 10 and M 11 are independently an optionally substituted aliphatic hydrocarbon group or an optionally substituted (hetero)aryl group, or wherein M 10 and M 11 Together contain the necessary atoms to form a cyclic structure, preferably a 5- or 6-membered ring;

[0057] W 3 represents a sulfur atom or -C(A 3 )=C(A 4 )-group,

[0058] W 4 represents a sulfur atom or -C(A 7 )=C(A 8 )-group,

[0059] M 1 and M 2 independently represents hydrogen, an optionally substituted aliphatic hydrocarbon group or together contain the necessary atoms to form an optionally substituted cyclic structure, preferably M 1 and M 2 together contain the necessary atoms to form an optionally substituted cyclic structure which may include: an optionally substituted cyclic benzene ring, preferably a 5- or 6-membered ring, more preferably a 5-membered ring, most preferably a 5-membered ring having a cyclic structure of 5 carbon atoms;

[0060] M 3 and M 4 independently represent an optionally substituted aliphatic hydrocarbon group;

[0061] M 5 、M 6 、M 7 and M 8 、M 16 and M 17 independently represent hydrogen, halogen or an optionally substituted aliphatic hydrocarbon group,

[0062] A 1 -A 8 independently represent hydrogen, a halogen atom, an optionally substituted aliphatic hydrocarbon group or an optionally substituted (hetero)aryl group, 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 which together contain the necessary atoms to form a cyclic structure, preferably a 5- or 6-membered ring;

[0063] M 12 and M 13 and M 14 and M 15 independently represents an optionally substituted aliphatic hydrocarbon group or an optionally substituted (hetero)aryl group, or wherein said M 14 、M 15 、A 5 or A 7 Two of the M together contain the necessary atoms to form at least one cyclic structure, preferably a 5- or 6-membered ring; the M 12 、M 13 、A 2 or A 4 Two of the together contain the necessary atoms to form at least one cyclic structure, preferably a 5- or 6-membered ring;

[0064] M 9 is a group which is converted by a chemical reaction induced by exposure to IR radiation or heat into a group which is smaller than the M 9 A stronger electron donor group; and the conversion provides an increase in the integrated light absorption of the dye between 350 nm and 750 nm;

[0065] and optionally one or more counterions to obtain a neutrally charged compound.

[0066] IR-thermochromic dyes can be neutral, anionic or cationic dyes, depending on the type of substituents and the number of each substituent. In a preferred embodiment, the IR-thermochromic dyes of formula I, II or III contain at least one anionic or acidic group such as -CO2H, -CONHS02R 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 are independently aryl or alkyl, preferably methyl, and wherein the salt is preferably an alkali metal salt or an ammonium salt, including a mono- or di- or tri- or tetra-alkylammonium salt. These anions or acidic groups may be present in Ar 1 、Ar 2 or Ar 3 The aromatic hydrocarbon group or cyclic benzene ring, or present in M 3 、M 4 or M 12 -M 15 On the aliphatic hydrocarbon group, or on the M 12 -M 15 Other substituents may be selected from halogen atoms, cyano groups, sulfone groups, carbonyl groups or carboxylate groups.

[0067] In another preferred embodiment, M 3 、M 4 or M 12 -M 15 At least one of is terminally substituted by at least one of these groups, more preferably by a -CO2H, -CONHSO2-Me, -SO2NHCO-Me, -SO2NHSO2-Me, -PO3H2 or -SO3H group or their corresponding salts, wherein Me represents a methyl group.

[0068] In a preferred embodiment, the IR-thermochromic dye represented by the above formula I, II or III comprises M represented by one of the following groups: 9 :

[0069] -(N=CR 17 )a –NR 5 -CO-R 4 ,

[0070] -(N=CR 17 )b -NR 5 -SO2-R 6 ,

[0071] -(N=CR 17 )c -NR 11 -SO-R 12 ,

[0072] -SO2-NR 15 R 16 and

[0073] -S-CH2-CR 7 (H) 1-d (R 8 ) d -NR 9 -COOR 18 ,

[0074] in

[0075] a, b, c, and d are independently 0 or 1;

[0076] 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;

[0077] R 4 Indicates -OR 10 、-NR 13 R 14 or -CF3;

[0078] where R 10 represents an optionally substituted (hetero)aryl group or an optionally branched aliphatic hydrocarbon group;

[0079] R 13 and R 14 independently represents 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;

[0080] R 6 represents an optionally substituted aliphatic hydrocarbon group or an optionally substituted (hetero)aryl group, -OR 10 、-NR 13 R 14 or -CF3;

[0081] R 5 represents hydrogen, an optionally substituted aliphatic hydrocarbon group, SO3 - Group, -COOR 18 group or an optionally substituted (hetero)aryl group, or wherein R5 With R 10 、R 13 and R 14 At least one of the together contain the necessary atoms to form a ring structure;

[0082] R 11 、R 15 and R 16 independently represents 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;

[0083] R 12 represents an optionally substituted aliphatic hydrocarbon group or an optionally substituted (hetero)aryl group;

[0084] R 7 and R 9 independently represent hydrogen or an optionally substituted aliphatic hydrocarbon group;

[0085] R 8 Indicates -COO- or -COOR 8’ , where R 8’ represents hydrogen, an alkali metal cation, an ammonium ion or a mono-, di-, tri- or tetra-alkylammonium ion;

[0086] R 18 represents an optionally substituted (hetero)aryl group or an α-branched aliphatic hydrocarbon group.

[0087] Suitable examples of IR-thermochromic dyes for use in the present invention are described in EP 1 910 082, pages 4-8, IRD-001 to IRD-101, and are incorporated herein by reference.

[0088] In a highly preferred embodiment, the IR-thermochromic dye is represented by formula I

[0089]

[0090] Among them, Ar 1 、Ar 2 、W 1 、W 2 and M 1 -M 9 As defined above.

[0091] Most preferably, the IR-thermochromic dye is represented by formula I, wherein

[0092] Ar 1 and Ar 2 independently represents an optionally substituted aryl group; optionally cyclized with an optionally substituted phenyl ring,

[0093] W 1 and W 2 represents -C(CH3)2;

[0094] M 1 and M 2 together contain the necessary atoms to form an optionally substituted 5-membered ring which may contain an optionally substituted cyclic benzene ring;

[0095] M 3 and M 4 independently represent an optionally substituted aliphatic hydrocarbon group,

[0096] M 5 、M 6 、M 7 and M 8 represents hydrogen;

[0097] M 9 express

[0098] -NR 5 -CO-R 4

[0099] -NR 5 -SO2-R 6

[0100] -NR 11 -SO-R 12

[0101] -SO2-NR 15 R 16

[0102] where R 4 、R 5 、R 6 、R 11 、R 12 、R 15 and R 16 As defined above;

[0103] and optionally one or more counterions to obtain an electrically neutral compound. Preferably, the IR dye comprises at least one anionic group or an 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 are independently aryl or alkyl. More preferably, M 3 or M4 At least one of the aliphatic hydrocarbon groups is terminally substituted with at least one of the anionic groups or acidic groups.

[0104] In a highly preferred embodiment, the IR-thermochromic dye is represented by Formula I, wherein

[0105] Ar 1 and Ar 2 independently represents optionally substituted aryl;

[0106] W 1 and W 2 represents -C(CH3)2;

[0107] M 1 and M 2 together contain the necessary atoms to form an optionally substituted 5-membered ring which may contain an optionally substituted cyclic benzene ring;

[0108] M 3 and M 4 independently represent an optionally substituted aliphatic hydrocarbon group,

[0109] M 5 、M 6 、M 7 and M 8 represents hydrogen;

[0110] M 9 express

[0111] -NR 5 -CO-R 4

[0112] -NR 5 -SO2-R 6

[0113] in

[0114] R 4 For-OR 10 , where R 10 is an optionally branched aliphatic hydrocarbon group;

[0115] R 5 represents hydrogen, an optionally substituted aliphatic hydrocarbon group or an optionally substituted (hetero)aryl group,

[0116] R 6 represents an optionally substituted aliphatic hydrocarbon group or an optionally substituted (hetero)aryl group; and

[0117] Optionally one or more counterions to obtain a neutral compound.

[0118] Preferably the IR dye contains at least one anionic group 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 are independently aryl or alkyl. More preferably, M 3 or M 4 At least one of the aliphatic hydrocarbon groups is terminally substituted by at least one of the anionic groups or acidic groups. The salt is preferably an alkali metal salt or an ammonium salt, including a mono-, di-, tri- or tetra-alkylammonium salt.

[0119] Optional counterions for obtaining electrically neutral compounds may be selected, for example, from halogens, sulfonates, perfluorosulfonates, toluenesulfonates, tetrafluoroborate, hexafluorophosphate, arylborates, arylsulfonates; or cations such as alkali metal salts or ammonium salts, including mono- or di- or tri- or tetra-alkylammonium salts.

[0120] Particularly preferred IR-thermochromic dyes are represented by one of the following formulae IV-XI:

[0121]

[0122] in

[0123] X - represents a halogen, sulfonate, perfluorosulfonate, toluenesulfonate, tetrafluoroborate, hexafluorophosphate, arylborate or arylsulfonate; and

[0124] R 3 、R 3’ independently represents an optionally substituted alkyl group, preferably a methyl or ethyl group; or an ether group, preferably -CH2-CH2-O-CH3;

[0125]

[0126]

[0127]

[0128] in

[0129] M + = Li + 、Na + , K + NH4 + 、R'R''R'''NH+ , wherein R', R", R''' independently represent hydrogen, optionally substituted alkyl or aryl.

[0130]

[0131]

[0132]

[0133] definition

[0134] Aliphatic hydrocarbon groups preferably represent alkyl, cycloalkyl, alkenyl, cycloalkenyl or alkynyl groups; suitable groups thereof are described below. Aromatic hydrocarbon groups preferably represent hetero(aryl) groups; suitable hetero(aryl) groups (i.e. suitable aryl or heteroaryl groups) are described below.

[0135] The term "alkyl" herein means all possible variations for each number of carbon atoms in the alkyl group, i.e., methyl, ethyl; for 3 carbon atoms: n-propyl and isopropyl; for 4 carbon atoms: n-butyl, isobutyl and tert-butyl; for 5 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 isohexyl, 1,1-dimethyl-propyl, 2,2-dimethylpropyl and 2-methyl-butyl, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl and methylcyclohexyl. Preferably, the alkyl group is a C1-C6 alkyl group.

[0136] Suitable alkenyl groups are preferably C2-C6 alkenyl groups, such as ethenyl, n-propenyl, n-butenyl, n-pentenyl, n-hexenyl, isopropenyl, isobutenyl, isopentenyl, neopentenyl, 1-methylbutenyl, isohexenyl, cyclopentenyl, cyclohexenyl and methylcyclohexenyl.

[0137] Suitable alkynyl groups are preferably C2-C6 alkynyl groups; suitable aralkyl groups are preferably phenyl or naphthyl groups comprising one, two, three or more C1-C6 alkyl groups; suitable alkaryl groups are preferably C1-C6 alkyl groups comprising an aryl group, preferably a phenyl or naphthyl group.

[0138] The cyclic group or cyclic structure includes at least one ring structure and may be a monocyclic or polycyclic group, meaning one ring or multiple rings fused together.

[0139] The example of suitable aryl can be represented by for example optionally substituted phenyl, benzyl, tolyl or o-, m- or p-xylyl, optionally substituted naphthyl, anthracenyl, phenanthrenyl and / or its combination.Heteroaryl is preferably a monocyclic or polycyclic aromatic ring, which comprises carbon atoms and one or more heteroatoms in the ring structure, preferably 1-4 heteroatoms independently selected from nitrogen, oxygen, selenium and sulfur.Preferred examples thereof include optionally substituted furyl, pyridyl, pyrimidinyl, pyrazolyl, imidazolyl, oxazolyl, isoxazolyl, thienyl (thienyl), tetrazolyl, thiazolyl, (1,2,3) triazolyl, (1,2,4) triazolyl, thiadiazolyl, thienyl (thiofenyl) and / or its combination.

[0140] The cyclic group or cyclic structure includes at least one ring structure and may be a monocyclic or polycyclic group, meaning one ring or multiple rings fused together.

[0141] Halogen is selected from fluorine, chlorine, bromine or iodine.

[0142] The term "substituted", as in, for example, a substituted alkyl group, means that the alkyl group may be substituted with atoms other than the atoms normally present in such groups (i.e., carbon and hydrogen). For example, a substituted alkyl group may include a halogen atom or a thiol group. An unsubstituted alkyl group contains only carbon and hydrogen atoms.

[0143] Optional substituents on alkyl, cycloalkyl, alkenyl, cycloalkenyl, alkynyl, aralkyl, alkaryl, aryl and heteroaryl groups are preferably selected from hydroxy, -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), thioalkyl, thioaryl, thioheteroaryl, -SH, thioether (such as thioalkyl or thioaryl), ketone, aldehyde, sulfoxide, sulfone, sulfonate, sulfonamide, amino, vinyl, alkenyl, alkynyl, cycloalkyl, alkaryl, aralkyl, aryl, heteroaryl or heteroalicyclic group and / or combinations thereof.

[0144] Support

[0145] The lithographic printing plate used in the present invention comprises a support having a hydrophilic surface or provided with a hydrophilic layer. The support is preferably a roughened and anodized aluminum support well known in the art. Suitable supports are disclosed, for example, in EP 1843203 (paragraphs

[0066] -

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

[0146] The roughened and anodized aluminum support may be subjected to a so-called post-anodization treatment, for example, treatment with polyvinylphosphonic acid or its derivatives, treatment with polyacrylic acid or its derivatives, treatment with potassium fluorozirconate or phosphates, treatment with alkali metal silicates, or a combination thereof. Treatment of the edges of the support, as described, for example, in US 2017 / 320351, may help prevent the occurrence of printed edges. Alternatively, the support may be treated with adhesion-promoting compounds, such as those described in

[0010] of EP 1 788 434 and WO 2013 / 182328. However, for precursors optimized for use without a preheating step, it is preferred to use the roughened and anodized aluminum support without any post-anodization treatment.

[0147] Besides aluminium supports, it is also possible to use plastic supports, for example polyester supports, which are provided with one or more hydrophilic layers, as disclosed in, for example, EP 1 025 992 .

[0148] Photopolymer coating

[0149] Photopolymerizable compounds

[0150] The coating has at least one layer comprising a photopolymerizable composition, said layer also being referred to as a “photopolymerizable layer.” The coating may comprise an intermediate layer between the support and the photopolymerizable layer.

[0151] 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 0.2-5.0 g / m 2 More preferably, between 0.4-3.0 g / m 2 between 0.6 and 1.5 g / m 2 within the range between.

[0152] According to a preferred embodiment of the present invention, the polymerizable compound is a polymerizable monomer or oligomer comprising at least one terminal ethylenically unsaturated group, also referred to hereinafter as a "free radical polymerizable monomer". Polymerization comprises linking together free radical polymerizable monomers. Suitable free radical polymerizable monomers include, for example, mono- or polyfunctional (meth)acrylate monomers (such as (meth)acrylates of ethylene glycol, trimethylolpropane, pentaerythritol, ethylene glycol, ethoxylated trimethylolpropane, urethane (meth)acrylates) and oligomeric amine diacrylates. In addition to the (meth)acrylate group, the (meth)acrylate monomer may also have other ethylenically unsaturated groups or epoxy groups. The (meth)acrylate monomer may also contain acidic (such as carboxylic acid or phosphoric acid) or basic (such as amine) functional groups.

[0153] Suitable free-radically polymerizable monomers are disclosed in

[0042] and

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

[0154] initiator

[0155] According to the present invention, any free radical initiator that can generate free radicals directly or in the presence of a sensitizer when exposed is suitable initiator. Suitable examples of initiators include onium salts, compounds containing carbon halogen bonds such as [1,3,5] triazines with trihalomethyl groups, organic peroxides, aromatic ketones, sulfur-containing compounds, azo polymerization initiators, azides, ketoxime esters, hexaarylbisimidazoles, metallocene compounds, active ester compounds, borate esters (salts) and quinone diazides. Among them, considering storage stability, onium salts, especially iodonium salts and / or sulfonium salts are preferred.

[0156] More specific suitable free radical initiators include, for example, derivatives of acetophenone (such as 2,2-dimethoxy-2-phenylacetophenone and 2-methyl-1-[4-((methylthio)phenyl-2-morpholinylprop-1-one); benzophenone; benzil; ketocoumarin (such as 3-benzoyl-7-methoxycoumarin and 7-methoxycoumarin); xanthanone; thioxanthone; benzoin or alkyl-substituted anthraquinone; onium salts (such as diaryliodonium hexafluoroantimonate, diaryliodonium trifluoromethanesulfonate, thioxanthone); sulfonates, (4-(2-hydroxytetradecyloxy)-phenyl)phenyliodonium hexafluoroantimonate, triarylsulfonium ammonium hexafluorophosphate, triarylsulfonium p-toluenesulfonate, (3-phenylprop-2-yl)triarylphosphine hexafluoroantimonate, and N-ethoxy(2-methyl)pyridinium hexafluorophosphate, as well as onium 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 salts, diphenyliodonium tetraphenylborate and triphenylsulfonium triphenyl (n-butyl) borate) and the borates described in U.S. Patent Nos. 6,232,038 and 6,218,076); haloalkyl-substituted s-triazines (such as 2,4-bis(trichloromethyl)-6-(p-methoxyphenyl)-s-triazine, 2,4-bis(trichloromethyl)-6-(4-methoxy-naphthalen-1-yl)-s-triazine, 2,4-bis(trichloromethyl)-6-piperonyl-s-triazine and 2,4-bis(trichloromethyl)-6-piperonyl-s-triazine methyl)-6-[(4-ethoxyvinyloxy)-phenyl-1-yl]-s-triazine and s-triazines as described in U.S. Pat. Nos. 5,955,238, 6,037,098, 6,010,824 and 5,629,354; and bis(etha.9-2,4-cyclopentadien-1-yl)bis[2,6-difluoro-3-(1H-pyrrol-1-yl)phenyl) titanium. Onium salts, borates and s-triazines are preferred free radical initiators. Diaryliodonium salts and triarylsulfonium salts are preferred onium salts. Triarylalkylborates are preferred borates. Trichloromethyl substituted s-triazine is the preferred s-triazine. These initiators can be used alone or in combination.

[0157] The optionally substituted trihaloalkylsulfones, wherein halo independently represents bromine, chlorine or iodine and sulfone, are particularly preferred initiators, which are compounds containing a sulfonyl functional group attached to two carbon atoms. Tribromomethylphenylsulfone is the most preferred initiator. More details about this initiator can be found in paragraphs

[0029] to

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

[0158] The amount of initiator is generally in the range of 0.1-30% by weight, preferably 0.5-15% by weight, most preferably 2-10% by weight, relative to the total weight of the non-volatile components of the photopolymerizable composition.

[0159] Very high sensitivity can be achieved by combining a fluorescent brightener as a sensitizer and a polymerization initiator.

[0160] The photopolymerizable layer may also include a coinitiator. Typically, a coinitiator is used in combination with a free radical initiator. Suitable coinitiators for photopolymer coatings are disclosed in US 6,410,205, US 5,049,479, EP 1 079 276, EP 1 369 232, 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 references: Chemistry & Technology UV & EB formulation for coatings, inks & paints - Volume 3 - Photoinitiators for Free Radical and Cationic Polymerisation, KK Dietliker - P.K.T. Oldring, ed. - 1991 - ISBN 0947798161. Specific coinitiators as described in EP 107 792 may be present in the photopolymerizable layer to further increase the sensitivity. Preferred coinitiators are disclosed in EP 2 916 171

[0051] and are incorporated herein by reference.

[0161] Very high sensitivity can be obtained by including a sensitizer such as an optical brightener in the coating. Suitable examples of optical brighteners as sensitizers are described in WO 2005 / 109103, page 24, lines 20 to 39. Useful sensitizers can 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 1 341 040, US 2003 / 0124460, EP 1 241 002 and EP 1 288 720.

[0162] Specific coinitiators as described in EP 107 792 may be present in the photopolymerizable layer to further increase the sensitivity. Preferred coinitiators are sulfur compounds, especially thiols, such as, for example, 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-n-decyl-3,5-dimercapto-1,2,4-triazole, 5-phenyl-2-mercapto-1,3,4-oxadiazole, 5-methylthio-1,3,4-thiadiazoline-2-thione, 5-hexylthio-1,3,4-thiadiazoline-2-thione, mercaptophenyltetrazolyl, pentaerythritol mercaptopropionate, 3-mercapto-pentaerythritol butyrate, pentaerythritol tetrakis(thioglycolate). Other preferred coinitiators are polythiols as disclosed in WO 2006 / 048443 and WO 2006 / 048445. These polythiols can be used in combination with the above-described thiols, such as 2-mercaptobenzothiazole.

[0163] The photopolymerizable layer may optionally include a violet or infrared light-absorbing dye as a sensitizer. Infrared light-absorbing dyes absorb light between 750 nm and 1300 nm, preferably between 780 nm and 1200 nm, and more preferably between 800 nm and 1100 nm. Particularly preferred sensitizers are the heptamethine cyanine dyes disclosed in paragraphs

[0030] to

[0032] of EP 1 359 008.

[0164] binder

[0165] The photopolymerizable layer preferably includes a binder. The binder can be selected from a wide range of organic polymers. Combinations of different binders can also be used. Useful binders are described, for example, in EP 1 043 627, paragraph

[0013] , WO 2005 / 111727, page 17, line 21 to page 19, line 30, and WO 2005 / 029187, page 16, line 26 to page 18, line 11.

[0166] A PVDC binder as described above may optionally be present in the photopolymerizable layer.

[0167] The photopolymerizable layer may include discrete particles, i.e., particulate polymers, including 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. Preferably, the discrete particles are particles suspended in the polymerizable composition. The presence of the discrete particles tends to promote developability of the unexposed areas.

[0168] The thermoreactive polymer fine particles include thermoreactive groups such as an ethylenically unsaturated group, a cationically polymerizable group, an isocyanate group, an epoxy group, a vinyloxy group, and a functional group having an active hydrogen atom, a carboxyl group, a hydroxyl group, an amino group, or an acid anhydride group.

[0169] Specific examples of polymeric binders according to this embodiment are described in US 6,899,994, US 2004 / 0260050, US 2005 / 0003285, US 2005 / 0170286, US 2005 / 0123853, and EP 2 916 171 at

[0029] ,

[0030] , and

[0031] . Other suitable binders, such as those described in EP 2 471 655, EP 2 492 748, and EP 2 660 068, include polyfunctional thiols having a core (central backbone) of 6 to 10 functional groups and polymer chains connected to the core via sulfide bonds. In addition to the polymeric binder of this embodiment, the imageable layer may optionally contain one or more co-binders. Typical co-binders are water-soluble or water-dispersible polymers, such as cellulose derivatives, polyvinyl alcohol, polyacrylic acid, poly(meth)acrylic acid, polyvinyl pyrrolidone, polylactic acid, polyvinylphosphonic acid, synthetic copolymers, such as copolymers of alkoxy polyethylene glycol (meth)acrylates. Specific examples of co-binders are described in US 2004 / 0260050, US 2005 / 0003285 and US 2005 / 0123853. Printing plate precursors, whose imageable layers comprise the binder according to this embodiment and optionally the co-binder, are described in more detail in US 2004 / 0260050, US 2005 / 0003285 and US 2005 / 0123853.

[0170] The average particle diameter of the polymer granules 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.

[0171] Other ingredients

[0172] The photopolymerizable layer may also contain particles that increase the resistance of the coating to manual or mechanical damage. The particles may be inorganic particles, organic particles or fillers, such as described in, for example, US 7,108,956. More details of suitable spacer particles are described in EP 2 916 171

[0053] -

[0056] , which are incorporated herein by reference.

[0173] The photopolymerizable layer may also comprise inhibitors. Specific inhibitors for photopolymer coatings are disclosed in US 6,410,205, EP 1 288 720 and EP 1 749 240.

[0174] The photopolymerizable layer may further comprise an adhesion-promoting compound. An adhesion-promoting compound is a compound capable of interacting with the support, preferably a compound having an addition-polymerizable ethylenically unsaturated bond and a functional group capable of interacting with the support. "Interaction" is understood to mean any type of physical and / or chemical reaction or process by which a bond is formed between the functional group and the support, the bond being a covalent bond, an ionic bond, a complex bond, a coordinate bond or a hydrogen bond, and which may be formed by an adsorption process, a chemical reaction, an acid-base reaction, a complex-forming reaction or a reaction of a chelating group or a ligand. The adhesion-promoting compounds described in EP 2 916 171

[0058] are incorporated herein by reference.

[0175] Various surfactants may be added to the photopolymerizable layer to allow or enhance the developability of the precursor; in particular, development with a gum solution. Preferred are both polymeric and small molecule surfactants, such as nonionic surfactants. Further details are described in EP 2 916 171

[0059] and incorporated herein by reference.

[0176] Exposure Steps

[0177] The printing plate precursor is preferably exposed imagewise off-press in a platesetting machine, i.e. an exposure apparatus suitable for imagewise exposure of the precursor with a laser, such as a laser diode emitting at about 830 nm or an Nd YAG laser emitting at about 1060 nm, a violet laser emitting at about 400 nm or a gas laser such as an Ar laser, or with a digitally modulated UV exposure apparatus using, for example, a digital mirror apparatus, or conventional exposure by contact with a mask. In a preferred embodiment of the invention, the precursor is exposed imagewise by means of a laser emitting IR light or violet light, more preferably by means of a laser emitting IR light.

[0178] Preheating steps

[0179] After 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 during a dwell time of about 5 seconds to 1 minute. Such a preheating unit can comprise a heating element, preferably an IR lamp, a UV lamp, heated air or a heated roller. Such a preheating step can be used for printing plate precursors comprising a photopolymerizable composition to enhance or accelerate the polymerization and / or crosslinking reaction.

[0180] Development step

[0181] Following the exposure step or the preheating step, when present, the plate precursor may be processed (developed). Prior to developing the imaged precursor, a pre-rinsing step may be performed, particularly for negative-working lithographic printing precursors having a protective oxygen barrier or overcoat. This pre-rinsing step may be performed in a separate device or by manually rinsing the imaged precursor with water, or the pre-rinsing step may be performed in a washing unit integrated into the processing machine for developing the imaged precursor. The washing liquid is preferably water, more preferably tap water. Further details regarding the washing step are described in

[0026] of EP 1 788 434.

[0182] During the development step, the non-exposed areas of the image-recording layer are at least partially removed without substantially removing the exposed areas. The processing liquid, also known as the developer, can be applied to the printing plate by hand or by automated processing equipment, for example by rubbing with an impregnated pad, by dipping, immersing, coating, spin coating, spraying, or pouring onto it. Treatment with the processing liquid can be combined with mechanical rubbing (e.g., by a rotating brush). During the development step, any water-soluble protective layer present is preferably also removed. Development is preferably carried out in an automated processing unit at a temperature between 20°C and 40°C.

[0183] In a highly preferred embodiment, the processing steps described above are replaced by on-press processing, whereby the imaged precursor is mounted on a printing press and processed on-press by rotating the plate cylinder while simultaneously feeding fountain solution and / or ink to the precursor coating to remove unexposed areas from the support. In a preferred embodiment, the supply of fountain solution and ink is initiated simultaneously, or only ink may be supplied during a certain number of rotations before the fountain solution supply is initiated. In an alternative embodiment, only fountain solution is supplied to the printing plate during startup of the printing press, and the ink supply is also initiated after a certain number of rotations of the plate cylinder.

[0184] The processing steps can also be carried out by combining the above-described embodiments, for example combining development with a processing liquid with on-press development by applying ink and / or fountain solution.

[0185] Processing fluid

[0186] The processing fluid may be an alkaline developer or a solvent-based developer. Suitable alkaline developers are described in US 2005 / 0162505. Alkaline developers are aqueous solutions having a pH of at least 11, more typically at least 12, and preferably 12-14. Alkaline developers typically contain an alkaline agent to achieve a high pH, ​​which may be an inorganic or organic alkaline agent. The developer may include anionic, nonionic, and amphoteric surfactants (up to 3% by weight based on the total composition); biocides (antimicrobial and / or antifungal agents), defoamers or chelating agents (such as alkali gluconates), and thickeners (water-soluble or water-dispersible polyols, such as glycerol or polyethylene glycol).

[0187] Preferably, the processing liquid is a gum solution, whereby during the development step, the non-exposed areas of the photopolymerizable layer are removed from the support and the printing plate is gummed in a single step. Development with a gum solution has the additional benefit that, due to the residual gum in the non-exposed areas of the printing plate, an additional gumming step is not required to protect the support surface in the non-printing areas. As a result, the precursor is processed and gummed in a single step, which involves a less complex development apparatus than a development apparatus comprising a developer tank, a rinse section, and a gumming section. The gumming section may comprise at least one gumming unit or may comprise two or more gumming units. These gumming units may be configured as a cascade system, i.e., when a gum replenishing solution is added to a second gumming unit or when the gum solution in the second gumming unit is used only once (i.e., when the precursor is developed in the second gumming unit using only the starting gum solution, preferably by spraying or jetting), the gum solution used in the second gumming unit and present in the second tank overflows from the second tank into the first tank. Further details regarding such gum development are described in EP 1 788 444.

[0188] The gum solution is generally an aqueous liquid containing one or more surface protective compounds capable of protecting the lithographic image of the printing plate from contamination, such as oxidation, fingerprints, fat, oil or dust, or from damage, such as scratching during handling of the printing plate. Suitable examples of such surface protective compounds are film-forming hydrophilic polymers or surfactants. The layer remaining on the printing plate after treatment with the gum solution preferably contains 0.005-20 g / m 2 More preferably, between 0.010-10 g / m 2 between 0.020-5 g / m 2 Further details on the surface protective compounds in the gum solution can be found in WO 2007 / 057348, page 9, line 3 to page 11, line 6. Since the developed printing plate precursor is developed and gummed in one step, no post-treatment of the processed printing plate is required.

[0189] The glue solution preferably has a pH value between 3 and 11, more preferably between 4 and 10, even more preferably between 5 and 9, and most preferably between 6 and 8. Suitable glue solutions are described, for example, in EP 1 342 568

[0008] to

[0022] and WO 2005 / 111727. The glue solution may further comprise an inorganic salt, an anionic surfactant, a wetting agent, a chelating compound, an antimicrobial compound, a defoaming compound and / or an ink absorbent and / or a combination thereof. More details about these additional ingredients are described in WO 2007 / 057348, page 11, line 22 to page 14, line 19.

[0190] Drying and baking steps

[0191] After the processing step, the printing plate can be dried in a drying unit. In a preferred embodiment, the printing plate is dried by heating the printing plate in a drying unit, which may contain at least one heating element selected from IR-lamps, UV-lamps, heated metal rollers or heated air.

[0192] After drying, the printing plate can optionally be heated in a baking unit. More details about heating in a baking unit can be found in WO 2007 / 057348, page 44, line 26 to page 45, line 20.

[0193] According to the present invention, there is also provided a method for preparing a negative-working lithographic printing plate, comprising the steps of: exposing a printing plate precursor in an image-wise manner, and then developing the image-wise exposed precursor so that the non-exposed areas dissolve in a developer solution. Development is preferably carried out by treating the precursor with a gum solution, but more preferably, by mounting the precursor on a plate cylinder of a lithographic printing press and rotating the plate cylinder while feeding a fountain solution and / or ink to the precursor. 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 on a support and (ii) drying the precursor. Any coating method can be used to apply one or more coating solutions to the hydrophilic surface of the support. Multilayer coatings can be applied by continuously coating / drying each layer or by applying several coating solutions simultaneously. In the drying step, volatile solvents are removed from the coating until the coating is self-supporting and feels dry to the touch.

[0194] The printing plate thus obtained can be used for conventional so-called wet offset printing, in which ink and an aqueous fountain solution are supplied to the printing plate. Another suitable printing method uses a so-called single-fluid ink without a fountain solution. Suitable single-fluid inks are 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

[0195] 1. Preparation of Printing Plate Precursors

[0196] Preparation of aluminum support S-01

[0197] A 0.3 mm thick aluminum foil was degreased by spraying with an aqueous solution containing 26 g / l NaOH at 65°C for 2 seconds and rinsing with demineralized water for 1.5 seconds. The foil was then degreased at a temperature of 37°C and about 100 A / dm 2 At a current density of 15 g / lHCl, 15 g / l SO4 2- ions and 5 g / l Al 3+ The foil was electrochemically roughened in an aqueous solution containing 5.5 g / l NaOH for 10 seconds using alternating current. Afterwards, the foil was desmutted by etching with an aqueous solution containing 5.5 g / l NaOH at 36°C for 2 seconds and rinsing with demineralized water for 2 seconds. The foil was then desmutted at a temperature of 50°C and 17 A / dm 2 The foil was anodized in an aqueous solution containing 145 g / l of sulfuric acid during 15 seconds at a current density of 1.5 Å, then washed with demineralized water for 11 seconds and dried at 120° C. for 5 seconds.

[0198] The support thus obtained is characterized by a surface roughness Ra of 0.35 μm-0.4 μm (measured with interferometer NT1100) and an oxide weight of 3.0 g / m 2 .

[0199] Preparation of reference printing plate PP-00, comparative printing plate PP-01 and inventive printing plates PP-02 to PP-06.

[0200] Photopolymerizable layer

[0201] The printing plate precursor was produced by coating the components as defined in Table 1 dissolved in a mixture of 35% by volume of MEK and 65% by volume of Dowanol PM (1-methoxy-2-propanol, commercially available from DOW CHEMICAL Company) onto the above-mentioned support S-01. The coating solution was applied to a wet coating thickness of 30 μm and then dried in a circulation oven at 120° C. for 1 minute.

[0202] Table 1: Composition of the photosensitive layer

[0203]

[0204] 1) FST 510 is the reaction product of 1 mole of 2,2,4-trimethylhexamethylene diisocyanate and 2 moles of hydroxyethyl methacrylate, commercially available from AZ Electronics as an 82 wt% solution in MEK;

[0205] 2) CN 104 is an epoxy acrylate oligomer commercially available from Arkema;

[0206] 3) Initiator-01 is bis(4-tert-butylphenyl)iodonium tetraphenylborate

[0207] 4) S2539 is an infrared absorbing dye commercially available from FEW Chemicals

[0208]

[0209] 5) Ruco coating EC4811 is a polyether polyurethane commercially available from Rudolf Chemistry

[0210] 6) Tegoglide 410 is a surfactant commercially available from Evonik Tego Chemie GmbH;

[0211] 7) Sipomer PAM 100 is a methacrylate phosphonate commercially available from Rhodia;

[0212] 8) Albritect CP 30 is a copolymer of vinylphosphonic acid and acrylic acid commercially available as a 20 wt% aqueous dispersion from Rhodia.

[0213] Protective outer coating

[0214] On top of the photosensitive layer, a dispersion in water (40 μm) having the composition as defined in Table 2 was applied and dried for 2 minutes at 110° C. Printing plate precursors PP-00 to PP-06 were obtained (Table 3).

[0215] Table 2: Composition of protective topcoats OC-01 to OC-06

[0216]

[0217] 1) Mowiol 4-88 is a partially hydrolyzed polyvinyl alcohol commercially available from Kuraray;

[0218] 2) Lutensol A8™ is a surfactant commercially available from BASF;

[0219] 3) IR-01 is a thermochromic infrared absorbing dye having the following formula:

[0220]

[0221] 4) PVDC-1 is Diofan A050, and PVDC-2 is Diofan A602. Both polyvinylidene chloride latexes are commercially available from Solvay.

[0222] 2. Imaging

[0223] The printing plate precursor was then heated using a High Power Creo 40W TE38 platesetter. TM (200 lpi Agfa Balanced Screening (ABS)) imaged at 2400 dpi on a thermal platesetter commercially available from Kodak equipped with an 830 nm IR laser diode at an energy density of 120 mJ / cm².

[0224] 3. Processing and printing

[0225] The imaged printing plate was then mounted on a Heidelberg GTO 52 printing press. Each print run was initiated using K+E Skinnex 800 SPEED IK black ink (trademark of BASF Druckfarben GmbH) and a 4 wt. % Prima FS303 SF (trademark of Agfa Graphics) and 8% isopropyl alcohol in water solution as a fountain solution. A compressible blanket was used and printing was performed on uncoated offset paper.

[0226] Before feeding the paper, the press makes 10 revolutions using only the dampening system and then 5 revolutions using only the inking roller.

[0227] 4. Results

[0228] The results of visual evaluation of print defects are given in Table 3.

[0229] Table 3: Results

[0230]

[0231] *Visual evaluation of printed materials:

[0232] 1: No defects;

[0233] 2: Some minor defects;

[0234] 3: Many defects spread over the entire surface.

[0235] The results in Table 3 show that the printing plates according to the invention prevent (PP-02, PP-03, PP-05 and PP-06) or highly reduce (PP-04) the occurrence of defects on the prints. The comparative printing plate PP-01 showed numerous defects on the prints.

Claims

1. A negative-working lithographic printing plate precursor comprising an aluminum support and a coating comprising a photopolymerizable layer and a top layer provided over the photopolymerizable layer; It is characterized by The top layer includes a halogenated binder and a nitrate selected from sodium nitrate or potassium nitrate to reduce the occurrence of defects and / or oxidation spots in the aluminum surface, and the halogenated binder is present in the top layer in an amount between 30 wt% and 96 wt%.

2. A printing plate precursor according to claim 1 , wherein the nitrate is present in an amount of 15 mg / m 2 relative to the total weight of the top layer. 2 -60mg / m 2 An amount between 5 and 100 Å is present in the top layer.

3. A printing plate precursor according to any one of the preceding claims wherein the nitrate is present in an amount of 20 mg / m2 relative to the total weight of the top layer. 2 -50 mg / m 2 An amount between 5 and 100 Å is present in the top layer.

4. A printing plate precursor according to any one of the preceding claims wherein the halogenated binder is a hydrophobic binder.

5. A printing plate precursor according to any preceding claim wherein the halogenated binder comprises monomer units derived from vinyl monomers and / or vinylidene monomers.

6. A printing plate precursor according to claim 5, wherein the halogenated binder comprises between 60% and 95% by weight of monomer units derived from vinylidene monomers.

7. A printing plate precursor according to claim 5 or 6, wherein the halogenated binder comprises between 5% and 40% by weight of monomer units derived from acrylate, methacrylate, styrene, acrylamide, methacrylamide or maleimide.

8. Printing form precursor according to any of the preceding claims, wherein the photopolymerizable layer and / or the top layer comprises a colour precursor.

9. A printing plate precursor according to claim 8, wherein the color precursor is an infrared thermochromic dye comprising a thermally cleavable group which is converted into a group that is a stronger electron donor upon exposure to heat and / or IR radiation and is capable of forming a printed image upon exposure to heat and / or IR radiation.

10. A printing plate precursor according to claim 9, wherein the infrared thermochromic dye is represented by formula I: in Ar 1 and Ar 2 W independently represent an optionally substituted aromatic hydrocarbon group or an aromatic hydrocarbon group having an optionally substituted cyclic benzene ring, 1 and W 2 independently represents a sulfur atom, an oxygen atom, NR¨, wherein R¨ represents an optionally substituted alkyl group, NH or -CM 10 M 11 Group, where M 10 and M 11 are independently an optionally substituted aliphatic hydrocarbon group or an optionally substituted (hetero)aryl group, or wherein M 10 and M 11 Together contain the necessary atoms to form a cyclic structure, preferably a 5- or 6-membered ring; M 1 and M 2 independently represents hydrogen, an optionally substituted aliphatic hydrocarbon group or together with the necessary atoms to form an optionally substituted cyclic structure which may include an optionally substituted cyclic benzene ring, preferably M 1 and M 2 together contain the necessary atoms to form an optionally substituted cyclic structure which may include: an optionally substituted cyclic benzene ring, preferably a 5- or 6-membered ring, more preferably a 5-membered ring, most preferably a 5-membered ring having a cyclic structure of 5 carbon atoms; M 3 and M 4 independently represent an optionally substituted aliphatic hydrocarbon group; M 5 、M 6 、M 7 and M 8 independently represent hydrogen, halogen or an optionally substituted aliphatic hydrocarbon group, M 9 is a group which is converted by a chemical reaction induced by exposure to IR radiation or heat into a 9 A stronger electron donor group; and said conversion provides an increase in the integrated light absorption of said dye between 350-700 nm; and optionally one or more counterions to obtain a neutrally charged compound.

11. A method for preparing a negative-working printing plate precursor comprising the steps of: - coating on a support (i) a photopolymerizable layer comprising a polymerizable compound and a photoinitiator, and (ii) a top layer as defined in any one of the preceding claims provided over said photopolymerizable layer, - Drying the precursor.

12. A method for preparing a negative-working printing plate, comprising the steps of: - exposing a printing plate precursor as defined in any one of the preceding claims to heat and / or light radiation in an image-wise manner, thereby forming a lithographic image consisting of image areas and non-image areas, - developing said exposed precursor.

13. The method according to claim 12, 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 fountain solution and / or ink to the precursor.

Images