阅读说明：本技术 制造平版印刷印版的方法 (Method for making lithographic printing plate ) 是由 P.亨德里克斯 K.希姆斯舒特 S.韦布吕格 于 2018-11-30 设计创作，主要内容包括：公开了一种制造阴图制版平版印刷印版的方法,其包括对按图像暴露、显影并干燥的印版前体进行UV LED辐射。(A method of making a negative-working lithographic printing plate is disclosed which comprises subjecting an image-wise exposed, developed and dried printing plate precursor to UV L ED radiation.)

1. A method of making a negative-working lithographic printing plate comprising the steps of:

a) imagewise exposing a lithographic printing plate precursor comprising a hydrophilic support and a coating provided thereon, said coating comprising a crosslinkable and/or photopolymerizable composition;

b) developing the printing plate precursor;

c) drying and/or heating the printing plate precursor; and

d) the obtained lithographic printing plate was subjected to UV L ED radiation.

2. The method of claim 1, wherein the coating comprises a free radical polymerization initiator, a free radical polymerizable compound, and a binder polymer.

3. The method of claim 1, wherein the coating comprises a diazo compound.

4. A method according to claims 1 to 3, wherein said UV L ED radiation is irradiated with at least one radiation having a wavelength of 10^-6UV L ED to a power of 15 watts.

5. The method according to any one of the preceding claims, wherein the UV L ED emits light having a wavelength between 315 nm and 450 nm.

6. The method according to any of the preceding claims, wherein the printing plate is subjected to UV L ED radiation for a time between 0.1 seconds and 5 minutes.

7. The method of any preceding claim, wherein the precursor is image-wise exposed with light having a wavelength range between 200 nm and 450 nm.

8. The method according to any preceding claim, wherein the printing plate is not subjected to a pre-heating step between the image-wise exposing step and the developing step.

9. The method of any preceding claim, wherein the precursor is developed with a gum solution.

10. The method according to claim 9, wherein the precursor is developed in a gumming station comprising a first gumming unit and at least a second gumming unit, wherein the precursor is continuously developed with a gum solution in the first gumming unit and the second gumming unit, thereby removing unexposed areas of the photopolymerizable layer from the carrier and gumming the printing plate in a single step.

11. The method of claim 10, wherein said first gluing unit and said second gluing unit together have a stepped flow system configuration, whereby said glue solution used in said second gluing unit overflows to said first gluing unit, said first gluing unit and said second gluing unit together having a stepped flow system configuration.

12. The method according to claims 1 to 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 fountain solution and/or ink to the precursor.

13. An apparatus for treating a lithographic printing plate comprising a developing/gumming section and a drying section, characterized in that said drying section comprises at least one UV L ED radiation bar.

14. The apparatus of claim 13, wherein said development/gumming section comprises a first gumming unit and at least a second gumming unit interconnected by a stepped flow that allows liquid to overflow from said second gumming unit to said first gumming unit.

15. An apparatus for post-treating a treated printing plate comprises a heating element and at least one UV L ED radiation bar.

Technical Field

The present invention relates to a novel method of making a lithographic printing plate.

Background

Lithographic printing typically involves the use of a so-called printing master, such as a printing plate mounted on a cylinder of a rotary press. The master carries a lithographic image on its surface and a print is obtained by applying ink to the image and subsequently transferring the ink from the master to a substrate, usually paper. In conventional lithographic printing, ink and fountain solution (also called fountain solution) are supplied to a lithographic image consisting of oleophilic (or hydrophobic, i.e. ink-accepting and water-repelling) areas and hydrophilic (or oleophobic, i.e. water-accepting and ink-repelling) areas. In so-called driographic printing, the lithographic image consists of ink-accepting and ink-repelling (ink-repelling) areas, and during driographic printing, only ink is supplied to the master.

Lithographic masters are typically obtained by image-wise exposure and treatment of a radiation-sensitive layer on a lithographic support. Imaging and processing make a so-called lithographic printing plate precursor a printing plate or master. The radiation-sensitive coating is image-wise exposed to heat or light, triggering a (physico-) chemical process, such as ablation, polymerization, insolubilization by polymer cross-linking or by particle agglomeration of thermoplastic polymer latex, solubilization by breaking intermolecular interactions or by increasing the permeability of the development barrier layer, usually by digitally modulating an exposure device, such as a laser. Although some printing plate precursors are capable of producing lithographic images immediately after exposure, the most popular lithographic printing plate precursors require wet processing because of the difference in solubility between exposed and unexposed areas of the coating or the difference in dissolution rate in the developer. In a positive-working lithographic printing plate precursor, the exposed areas of the coating are dissolved in a developer, while the unexposed areas remain resistant to the developer. In a negative-working lithographic printing plate precursor, the unexposed areas of the coating are dissolved in a developer solution, while the exposed areas remain resistant to the developer solution. Most lithographic printing plate precursors comprise a hydrophobic coating on a hydrophilic support such that the areas that remain resistant to the developer define the ink-accepting areas (and hence the printing areas) of the printing plate, whereas the hydrophilic support is exposed in the non-printing areas by dissolution of the coating in the developer.

Photopolymer printing plates rely on a working mechanism in which a coating, typically comprising a free radical polymerizable compound, hardens upon exposure. "hardening" means that the coating becomes insoluble or non-dispersible in a developing solution and can be achieved by polymerization and/or crosslinking of the photosensitive coating upon exposure to light. Photopolymer printing plate precursors can be sensitive to blue, green or red light (i.e. wavelength range between 450nm and 750 nm), to violet light (i.e. wavelength range between 350 nm and 450 nm) or to infrared light (i.e. wavelength range between 750 nm and 1500 nm). Optionally, a heating step is performed after the exposing step to enhance or accelerate the polymerization and/or crosslinking reaction.

Typically, an upper layer 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 upper layer typically comprises a water-soluble or water-swellable polymer, such as polyvinyl alcohol. In addition to acting as an oxygen barrier, the upper layer should preferably be easy to remove during processing and sufficiently transparent to actinic radiation, for example from 300 nm to 450nm or from 450nm to 750 nm or from 750 nm to 1500 nm.

The traditional workflow of photopolymer printing plates includes: first an exposure step of the photopolymer printing plate precursor in a violet or infrared light plate recorder, a washing step of the protective overcoat, an alkaline development step, and a rinsing and gumming step. In the last years there has been a clear progress in the direction of a simplified work flow, in which the washing, developing, rinsing and/or gumming steps are carried out in one single step, or in which the treatment is carried out with neutral gum and then gumming in a second step. Alternatively, on-board processes have become very popular, in which the printing plate is mounted on a printing press and the coating is developed by interaction with the ink fountain and ink supplied to the printing plate during the printing run. During a first run of the printing press, the non-image areas are removed from the carrier and thereby define the non-printing areas of the printing plate.

Optionally, the exposing step is followed by a heating step to enhance or accelerate the polymerization and/or crosslinking reaction and/or to improve the adhesion of the image portion to the substrate. It is believed that the heating step selectively crosslinks those areas of the coating that are selectively imaged during the exposing step, such that they are preferentially insoluble in the developer. As a result, the robustness in terms of plate pressing, i.e., the press life, is significantly improved.

The entire heating step after imaging and before development is commonly referred to in the art as the "pre-heat step". To eliminate this energy and time consuming pre-heating step, photopolymer printing plates without pre-heating have been disclosed in the art. Such non-preheated photopolymer printing plates typically contain a relatively soft (i.e., low Tg) photosensitive layer in combination with an adhesion promoter to achieve both a high degree of polymerization and simultaneously good adhesion to the substrate. However, even though such non-preheated photopolymer printing plates are currently used and commercialized especially in IR imageable (thermo) photopolymer printing plates, they still lack the robustness of the photopolymer printing plates that need to be preheated. A typical heating step includes heating at a temperature of about 80 ℃ to 150 ℃ for a residence time of about 5 seconds to 1 minute. In fact, preheating the oven requires a long settling time and therefore a non-stop operation is preferred, resulting in high energy consumption.

The press life of photopolymer printing plates can also be improved by heating the image formed on the support after the development and/or gumming step (also called "baking" or "post-baking"). Typically, the post-baking step is performed by heating the plate in a large heating oven at a temperature of about 235 ℃ to 290 ℃ for a relatively long time of about 2 minutes to 5 minutes, even up to 10 minutes. This process can significantly extend the life of the printing plates on the press.

However, such a time consuming baking process is disadvantageous, since it significantly slows down the throughput of the printing plate precursor during its production, and such a baking step is disadvantageous from both an ecological and economic point of view, in view of high energy consumption. Another disadvantage is that such large ovens take up a lot of space. In addition, the heat generated during such baking steps is often excessive and/or unevenly distributed, resulting in a wavy plate that is difficult to accurately mount on a printer. Furthermore, in order to prevent background contamination during the post-baking step, protective glues are often applied to the printing plates, i.e. baking glues, which need to be removed after baking and replaced by a plate finisher. These actions are time consuming and laborious, making the production process of printing plates inefficient.

GB 2205419 discloses heat treating a treated printing plate by infrared radiation, thereby improving the solvent resistance of the plate. The method allows heating combined with development to be performed in a single automated processor, thereby eliminating the need for a separate roaster.

US 2009/0317601 discloses a method for improving the durability of printing plates comprising a post-development treatment with infrared radiation having a wavelength of about 780 to 1400 nm.

DE 2648438 and DE 2201936 disclose a method for fixing the printing areas of a metal offset printing plate by infrared radiation heating after image-wise exposure and processing.

WO 2015/055409 discloses a method of making a lithographic printing plate comprising a colorant in its coating, comprising the step of subjecting the plate to heat or radiation after the drying step, thereby inducing a color change in the printed area.

US 4,326,018 discloses post-curing diazo-based printing plates by air baking at elevated temperature for 5 to 30 minutes or by exposure to UV or mercury vapor lamps of 50 to 200 watts for a period of 10 seconds to 2 minutes.

EP 1506854 discloses a method for manufacturing a lithographic printing plate comprising a baking step performed in a dwell time of less than 1 minute and wherein the chemical resistance of the coating to printing liquids and printing chemicals is improved. The baking step is carried out by exposing the printing plate to a source of infrared radiation, preferably in a dynamic configuration.

US 2003/0118944 discloses a method of improving the durability of negative-working photosensitive lithographic printing plates comprising the step of further exposing to electromagnetic radiation comprising a wavelength of not more than about 300 nanometers after the imaging and developing steps. This exposure step further promotes the addition polymerization and/or crosslinking reaction of the photosensitive coating.

There remains a great need in the art for a process for making photopolymer printing plates which preferably does not involve a pre-heat step and provides improved press life, thereby eliminating or at least reducing the cost (energy consumption) and/or intensive labor associated with the post-baking processes of the prior art.

Disclosure of Invention

It is an object of the present invention to provide an improved process for the preparation of high quality negative-working violet-sensitive lithographic printing plates based on photopolymerization and/or crosslinking, preferably without preheating, having an excellent press life.

The method is particularly characterized in that after image exposure, development and drying and/or heating, the violet-sensitive printing plate precursor is post-treated with UV radiation, more particularly with one or more light emitting diodes (L ED) emitting UV-a radiation (herein also referred to as "UV L ED radiation").

It was surprisingly found that said post-treatment step carried out on a printing plate having still a high temperature due to the drying and/or heating step results in an excellent press life, or in other words, that the heat applied in e.g. the drying step enhances the effect of said post-treatment with UV L ED radiation.

According to the present invention, there is also provided an apparatus designed for carrying out said post-treatment, more particularly, another aspect of the invention consists in providing a treatment apparatus designed for carrying out the inventive UV L ED radiation, a preferred embodiment of such an apparatus of the invention is described in more detail below (see FIG. 1).

Other features, elements, steps, characteristics and advantages of the present invention will be apparent from the following detailed description of preferred embodiments of the invention. Particular embodiments of the invention are also defined in the dependent claims.

Drawings

FIG. 1 is a schematic view of a preferred embodiment of the treatment apparatus of the present invention, shown filled with a gum solution.

The figures in the drawings refer to the following features of the preferred apparatus according to the invention:

1 developing/gumming section

2 drying section

3 first gluing unit

4 second gluing unit

5 third gluing unit

6, roller pair: 6A, 6B, 6C, 6D and 6E (sized portions); 6F (drying part)

7 cleaning rollers 7A and 7C

8 spray bars 8A, 8B, 8C, 8D, and 8E

9 brushes 9A and 9B

10A first glue storage tank 10A, a second glue storage tank 10B and a third glue storage tank 10C

11 first developing/glue solution

12 second developing/glue solution

13 third developing/glue solution

1414A second step flow overflow and 14B first step flow overflow

15 discharge pipe

16 glue supply

17 drying device

18 UV L ED rod

19 direction of treatment

20 size application nozzles.

Detailed Description

According to the present invention there is provided a method of making a negative-working violet-sensitive lithographic printing plate comprising the steps of image-wise exposing a printing plate precursor, then developing the image-wise exposed precursor such that the unexposed areas are dissolved in a developing solution, drying and/or heating the exposed precursor, and finally post-treating the obtained plate with UV L ED radiation.

Lithographic printing plate precursors can be prepared by applying a coating as described below on a support and drying the precursor.

Printing plate precursor

The lithographic printing plate precursor used in the present invention comprises a support having a hydrophilic surface or being provided with a hydrophilic layer, and a coating comprising a photopolymerizable and/or crosslinkable layer. The precursor is negative-working, i.e. after exposure and development, the unexposed areas of the coating are removed from the carrier and define hydrophilic (non-printing) areas, while the exposed coating is not removed from the carrier and defines oleophilic (printing) areas. The hydrophilic area is defined by a carrier having a hydrophilic surface or being provided with a hydrophilic layer. The hydrophobic areas are defined by the coating, which hardens upon exposure, optionally followed by a heating step. Regions with hydrophilicity refer to regions with higher affinity for aqueous solutions than for oleophilic inks; the region having hydrophobicity refers to a region having higher affinity for an oleophilic ink than for an aqueous solution.

"hardening" means that the coating becomes insoluble or non-dispersible in the developing solution and can be achieved by polymerization and/or crosslinking of the photosensitive coating.

The coating has at least one layer comprising a photopolymerizable and/or crosslinkable composition. The layer mainly containing a photopolymerizable composition is also referred to as "photopolymerizable layer", and the layer mainly containing a crosslinkable composition is also referred to as "crosslinkable layer". The coating may comprise an intermediate layer between the support and the photopolymerizable and/or crosslinkable layer.

Photopolymerizable layer

The photopolymerizable layer comprises a polymerizable compound, an optional binder, a polymerization initiator capable of hardening the polymerizable compound in the exposed areas, and an optional sensitizer capable of absorbing light used in the image-wise exposing step. The coating thickness of the photopolymerizable layer preferably ranges from 0.2 g/m²To 5.0 g/m²More preferably 0.4 g/m²To 3.0 g/m²Most preferably 0.6 g/m²To 2.2 g/m²。

Polymerizable compound and initiator

The polymerizable compound is preferably a monomer or oligomer comprising at least one epoxy or vinyl ether functional group, and the polymerization initiator is a bronsted acid generator capable of generating a free acid upon exposure, optionally in the presence of a photosensitizer, hereinafter also referred to as "cationic photoinitiator" or "cationic initiator".

Suitable polyfunctional epoxy monomers include, for example, 3, 4-epoxycyclohexylmethyl-3, 4-epoxycyclohexanecarboxylate, bis- (3, 4-epoxycyclohexylmethyl) adipate, difunctional bisphenol A-epichlorohydrin epoxy resins and polyfunctional epichlorohydrin-tetraphenylolethane epoxy resins.

Suitable cationic photoinitiators include, for example, triarylsulfonium hexafluoroantimonate, diaryliodonium hexafluoroantimonate, and haloalkyl substituted s-triazines. It is noted that most cationic initiators are also free radical initiators, since in addition to generating bronsted acids, they also generate free radicals during photo or thermal decomposition.

According to a more preferred embodiment of the present invention, the further polymerizable compound is a polymerizable monomer or oligomer comprising at least one terminal alkenyl group, hereinafter also referred to as "free-radical polymerizable monomer", and the polymerization initiator is a compound capable of generating free radicals upon exposure, optionally in the presence of a photosensitizer, hereinafter referred to as "free-radical initiator". Polymerization involves linking together free-radically polymerizable monomers.

Suitable free radically polymerizable monomers include, for example, multifunctional (meth) acrylate monomers (e.g., (meth) acrylates of ethylene glycol, trimethylolpropane, pentaerythritol, ethoxylated ethylene glycol and ethoxylated trimethylolpropane, multifunctional urethanized (meth) acrylates and epoxidized (meth) acrylates) and oligomeric amine diacrylates. In addition to the (meth) acrylate group, the (meth) acrylic monomer may also have other double bonds or epoxy groups. The (meth) acrylate monomers may also contain acidic functionality (e.g., carboxylic acids) or basic functionality (e.g., amines).

Suitable free-radically polymerizable monomers are disclosed in EP 2916171 [0042] and [0050], and are incorporated herein by reference.

The coating contains a free radical initiator capable of generating free radicals upon direct exposure and/or in the presence of a photosensitizer. Suitable free-radical initiators are described on page 15, line 17 to page 16, line 11 of WO2005/111727 and in EP 1091247 and may include, for example, hexaaryl-bisimidazole compounds (HABI; dimer of triarylimidazole), aromatic ketones, aromatic onium salts, organic peroxides, thio compounds, ketoxime ester compounds, borate compounds, azinium compounds, metallocene compounds, active ester compounds and other compounds having carbon-halogen bonds.

The photopolymerizable layer may also comprise a co-initiator. Typically, a co-initiator is used in combination with a free radical initiator. Suitable co-initiators for use in photopolymer coatings are disclosed in US 6,410,205, US5,049,479, EP 1079276, EP 1369232, EP 1369231, EP 1341040, US2003/0124460, EP 1241002, EP 1288720 and references including cited references: chemistry & Technology UV & EB formation for coatings, inks & paints-volume 3-photomonitorizers for Free radiation and catalysis by K.K. Dietliker-P.K.T.Oldring eds-1991-ISBN 0947798161. As described in EP 107792, specific co-initiators may be present in the photopolymerizable layer to further increase the sensitivity. Preferred coinitiators are disclosed in EP 2916171 [0051] and are incorporated herein by reference.

Photosensitive agent

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 on page 24, line 20 to page 39. Other preferred sensitizers are blue, green or red absorbing sensitizers having an absorption spectrum between 450nm and 750 nm. Useful sensitizers may be selected from the group of sensitizers disclosed in US 6,410,205, US5,049,479, EP 1079276, EP 1369232, EP 1369231, EP 1341040, US2003/0124460, EP 1241002 and EP 1288720.

Binder

The photopolymerizable layer preferably comprises a binder. The binder may be selected from a wide range of organic polymers. Combinations of different binders may also be used. Useful binders are described on page 17, line 21 to page 19, line 30 of WO2005/111727, paragraph [0013] of EP 1043627 and page 16, line 26 to page 18, line 11 of WO 2005/029187.

Other ingredients

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, for example as described in US 7,108,956. Further details of suitable spacer particles described in EP 2916171 [0053] to [0056] are incorporated herein by reference.

The photopolymerizable layer may also comprise an inhibitor. Specific inhibitors for use in photopolymer coatings are disclosed in US 6,410,205, EP 1288720 and EP 1749240.

The photopolymerizable layer may also comprise an adhesion promoting compound. The adhesion promoting compound is a compound capable of interacting with the carrier, preferably a compound having an addition-polymerizable ethylenically unsaturated bond and a functional group capable of interacting with the carrier. "interaction" is understood to be any type of physical and/or chemical reaction or process whereby a bond is formed between a functional group and a support, which bond may be a covalent, ionic, complex, coordinative or hydrogen bond, and which may be formed by an adsorption process, a chemical reaction, an acid-base reaction, a complex formation reaction or a reaction of chelating groups or ligands.

The adhesion promoting compound may be selected from at least one low molecular weight compound or polymeric compound described in EPA 851299 page 3 line 22 to page 4 line 1, EP-A1500498 page 7 [0023] to page 20 [0052], EP-A1495866 page 5 [0030] to page 11 [0049], EP-A1091251 page 3 [0014] to page 20 [0018] and EP-A1520694 page 6 [0023] to page 19 [0060 ]. Preferred compounds are those which comprise a phosphate or phosphonate group as functional group which can be adsorbed on the aluminum support and those which comprise an addition-polymerizable ethylenically double bond-reactive group, in particular those described on page 3, line 22 to page 4, line 1 and on page 7, paragraph [0023] to page 20, paragraph [0052] of EP-A851299. Also preferred are those compounds which comprise a trialkoxysilane (tri-alkyl-oxy silane) group, hereinafter also referred to as "trialkoxysilane (trialkoxy silane)" group, wherein the alkyl group is preferably a methyl group or an ethyl group, or wherein the trialkoxysilane group is at least partially hydrolyzed to a silanol group as a functional group capable of being adsorbed on a support, in particular a silane coupling agent having an addition-polymerizable ethylenically double bond-reactive group, as described in EP-a 1557262, page 49, paragraph [0279] and EP-a 1495866, pages 5, paragraph [0030] to page 11, paragraph [0049 ]. The adhesion promoting compounds described in EP 2916171 [0058] are also incorporated herein by reference.

The adhesion promoting compound may be present in the photopolymerizable layer in an amount of from 1 to 50 wt%, preferably from 3 to 30 wt%, more preferably from 5 to 20 wt% of the non-volatile components of the composition.

The adhesion promoting compound may be present in the optional intermediate layer in an amount of at least 25% by weight, preferably at least 50% by weight, more preferably at least 75% by weight of the non-volatile components of the composition. Alternatively, the intermediate layer may be composed of an adhesion promoting compound.

Various surfactants may be added to the photopolymerizable layer to allow or enhance the developability of the precursor; especially with a gum solution. Both polymeric and small molecule surfactants (e.g., nonionic surfactants) are preferred. More details are described in EP 2916171 [0059], and are incorporated herein by reference.

Crosslinkable layer

The crosslinkable layer may comprise a diazo compound and preferably a binder.

The diazo compounds are preferably of the general structure A-N₂ ⁺X^-Characterized in that A is an aromatic or heterocyclic residue and X is the anion of an acid. Specific examples of photosensitive diazo coatings include higher molecular weightCompositions, for example obtained by condensation of certain aromatic diazonium salts with a reactive carbonyl compound such as formaldehyde in an acid condensation medium, are disclosed, for example, in US 2063631 and US 2667415. Suitable examples include the condensation products of diazonium salts of p-aminodiphenylamine (e.g. diphenylamino chloride-4-diazonium salt or diphenylamine bromide-4-diazonium salt or diphenylamine phosphate-4-diazonium salt) with formaldehyde in high concentrations of phosphoric acid. The term phosphoric acid also includes pyrophosphoric acid, metaphosphoric acid and polyphosphoric acid.

Another preferred class of diazo compounds is described in US 3849392. The compound is the polycondensation product of 3-methoxy-4-diazo-diphenylamine sulfate and 4,4' -bismethoxymethyl-diphenyl ether, precipitated as mesitylene sulfonate as taught in US 3849392. The most preferred diazonium salts are benzene diazo compounds, 2-methoxy-4- (phenylamino) -, 2,4, 6-trimethylbenzene sulfonate (1:1), polymers with 1,1' -oxybis [4- (methoxymethyl) benzene ]. The preparation of the diazonium salts is disclosed in DE 2024244A. Other diazonium salts disclosed in said document are also suitable for inclusion in the crosslinkable layer.

The diazonium salt is preferably present in the coating composition in an amount of from about 20% to 100% by weight of the solid composition components. More preferred ranges are from about 25% to 50%, and most preferably from about 30% to 45%.

A binder may be added to the diazo compound to improve the mechanical resistance of the crosslinkable layer and/or the handling properties of the printing plate.

Suitable binders are polyvinyl acetate, epoxy resins based on bisphenol-A-epichlorohydrin, p- (vinyl butyral-co-, vinyl acetate-co-vinyl alcohol), unplasticized urea resins with an acid number of about 2 (Resamin 106F), Recinen-modified alkyd resins, resins comprising polyvinyl acetate resins and styrene/maleic acid half-ester copolymers.

Suitable polyvinyl acetate resins have a weight average molecular weight in the range of about 40,000 to less than 800,000. A preferred maximum weight average molecular weight is about 700,000; more preferably 680,000. Most preferably the average molecular weight is in the range of about 80,000 to 200,000. Preferred binders are butyl half-esters of maleic anhydride/styrene copolymers (e.g. Scripset 540, commercially available from Monsanto) and styrene/maleic acid half-ester copolymers as disclosed in US 4511640A. A more preferred binder is a half-ester and half-acid obtained by reacting p- [ vinyl butyral-co-vinyl alcohol-co-vinyl acetate ] such as Mowital B30T or Mowital B60T (available from Kuraray Europe GmbH) with maleic anhydride, with OH of polyvinyl alcohol, as disclosed in preparative example 5 in US 5695905.

The binder is preferably present in the coating composition in an amount of about 8% to about 60% by weight of the solid composition components. More preferred ranges are from about 12% to 50%, and most preferably from about 18% to 45%.

The weight ratio of the binder to the diazo compound is not more than 20, preferably equal to or less than 10, more preferably 0.8 to 1.2.

The coverage of the crosslinkable layer is preferably 0.1 g/m²To 1.2 g/m²More preferably 0.5 g/m²To 0.8 g/m²。

The crosslinkable layer may also contain additives such as acid stabilizers including phosphoric acid, citric acid, tartaric acid, and p-toluenesulfonic acid. The acid stabilizer may be present in the coating composition in an amount of from about 1.5% to about 4.5% by weight of the solid composition components, more preferably from about 2.0% to 4.0%, and most preferably from about 2.5% to 3.5%.

The exposure indicator comprising p-phenylazo diphenylamine, Calcozine Fuchine dye, and crystal violet and methylene blue dye may be present in an amount of from about 0.05% to about 0.35% by weight of the solid composition components. More preferred ranges are from about 0.10% to 0.30%, and most preferably from about 0.15% to 0.25%.

Non-limiting examples of colorants that may be present in the coating include dyes such as Acetosol Fire Red3G L S, Sandolan Eosin E-G, Acetosol Green B L S, Genacryl Blue 3G, Sandolan cyanineN-6B, Sandoplast Blue R, Atlantic Alizarine Milling Blue FFR 200, Neozapon FieryRed B L, erythrosine, Methylene Blue IaD Extra, Victoria Pure Blue FGA, and pigments such as Geen GoldPigment and Sunfast Violet.

The colorant may be present in the coating composition in an amount of from about 0.25% to about 0.55%, more preferably from about 0.30% to 0.50%, and most preferably from about 0.35% to 0.45% by weight of the solid composition components.

Suitable solvents that may be used as a medium to combine the components of the coating include methyl cellosolve, glycol ethers, butyrolactones, alcohols (e.g., ethanol and n-propanol), and ketones (e.g., methyl ethyl ketone).

Upper layer of

On top of the photopolymerizable layer, the coating may comprise an overlayer or a protective overcoat layer which acts as an oxygen barrier layer comprising a water-soluble or water-swellable binder. Printing plate precursors that do not contain an overlayer or protective overcoat are also referred to as overcoat-free printing plate precursors. It is well known in the art that low molecular weight species present in air may deteriorate or even inhibit image formation and therefore an upper layer is typically applied to the coating. The upper layer should be easily removed during development, sufficiently adhere to the photopolymerizable layer or optional other layers of the coating, and should preferably not inhibit light transmission during exposure. Preferred binders that can be used in the upper layer are polyvinyl alcohol and the polymers disclosed in WO 2005/029190, US 6,410,205 and EP 1288720, including the references cited in these patents and patent applications. The most preferred binder for the upper layer is polyvinyl alcohol. The polyvinyl alcohol preferably has a degree of hydrolysis in the range of from 74 to 99 mole%, more preferably from 88 to 98 mole%. The weight average molecular weight of the polyvinyl alcohol can be measured by the viscosity of a 4 wt.% aqueous solution at 20 ℃ as defined in DIN 53015, and the viscosity value preferably ranges from 2 to 26, more preferably from 2 to 15, most preferably from 2 to 10.

The overcoat may optionally comprise other ingredients, for example inorganic or organic acids, matting agents or wetting agents, as disclosed in EP 2916171, and incorporated herein by reference.

The coating thickness of the optional upper layer is preferably 0.25 g/m²To 1.75 g/m²More preferably 0.25 g/m²To 1.3g/m²Most preferably 0.25 g/m²To 1.0 g/m². In a more preferred embodiment of the invention, the optional upper layer has a thickness of 0.25 g/m²To 1.75 g/m²And comprises a degree of hydrolysis in the range of 7Polyvinyl alcohol of 4 to 99 mol% and having a viscosity number in the range of 2 to 26 as defined above.

Carrier

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 grained and anodized aluminum support as is well known in the art. Suitable vectors are disclosed, for example, in EP 1843203 (0066 th)]Paragraph to [0075 ]]Segment). The surface roughness obtained after the granulation step is generally expressed as the arithmetic mean centre line roughness Ra (ISO 4287/1 or DIN 4762) and can vary between 0.05 μm and 1.5 μm. The aluminum substrates of the present invention preferably have an Ra value of less than 0.45 μm, more preferably less than 0.40 μm, and most preferably less than 0.30 μm. The lower limit of the Ra value is preferably about 0.1. mu.m. More details on preferred Ra values for grained and anodized aluminium support surfaces are described in EP 1356926. Formation of Al by anodizing an aluminum support₂O₃Layer, and anode weight (g/m)²，Al₂O₃Formed on the surface of aluminum) in the range of 1 g/m²And 8 g/m²To change between. The weight of the anode is preferably more than or equal to 3g/m²More preferably ≥ 3.5 g/m²And most preferably not less than 4.0 g/m²。

The granulated and anodized aluminum support may be subjected to a so-called post-anodic treatment, for example, treatment with polyvinylphosphonic acid or a derivative thereof, treatment with polyacrylic acid, treatment with potassium fluorozirconate or potassium phosphate, treatment with an alkali metal silicate, or a combination thereof. Alternatively, the carrier may be treated with an adhesion-promoting compound, such as those described in EP 1788434 [0010] and WO 2013/182328. However, for precursors optimized for use without a pre-heating step, it is preferred to use grained and anodized aluminum supports without any post-anodic treatment.

In addition to 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, for example, in EP 1025992.

Exposing step

Preferably, the printing plate precursor is imagewise exposed off-line in a plate setter, i.e. an exposure device suitable for imagewise exposing the precursor with a laser (e.g. a laser diode) or by conventional exposure in contact with a mask. Preferably, imaging is performed using a UV radiation source or "violet" imaging or exposure radiation source at wavelengths of at least 150 nm and up to and including 475 nm, typically at wavelengths of 200 nm and up to and including 450nm, and more typically at wavelengths of 350 nm and up to and including 410 nm. The printing plate precursor is preferably image-wise exposed by a laser emitting UV light.

Preheating step

After the exposing step, the precursor may optionally be preheated in a preheating unit, preferably at a temperature of about 80 ℃ to 150 ℃, and preferably during a residence time of about 5 seconds to 1 minute. The preheating unit may comprise a heating element, preferably an IR lamp, a hot air system (heated air) or heated rollers. Such a preheating step may be used to enhance or accelerate the polymerization and/or crosslinking reaction of the photopolymerizable composition of the printing plate precursor.

In a highly preferred embodiment, the printing plate is not subjected to a preheating step between the image-wise exposing step and the developing step.

Developing step

After the exposure step or the preheating step (when present), the photopolymerizable printing plate precursor may be processed (developed). A pre-wash step may be performed prior to developing the imaged precursor, particularly for negative-working lithographic printing precursors having a protective oxygen barrier or topcoat. The pre-wash step may be performed in a separate apparatus, or by manually rinsing the imaged precursor with water, or the pre-wash step may be performed in a washing unit integrated in a processor for developing the imaged precursor. The washing liquid is preferably water, more preferably tap water. More details about the washing step are described in EP 1788434 [0026 ].

During the developing step, the unexposed areas of the image-recording layer are at least partially removed, while the exposed areas are not substantially removed. The treatment liquid, also called developing liquid, can be applied to the printing plate by hand or in an automated treatment apparatus, for example by rubbing with an impregnated pad, by dipping, immersion, coating, spin coating, spray coating, casting. The treatment with the treatment liquid may be combined with mechanical friction, such as by a rotating brush. Any water-soluble protective layer present is preferably also removed during the development step. The development is preferably carried out in an automated processing unit at a temperature of from 20 ℃ to 40 ℃.

In a highly preferred embodiment, the above processing steps 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 fountain solution and/or ink is fed onto the coating of precursor to remove the unexposed areas from the support. In a preferred embodiment, fountain solution is only provided to the printing plate during start-up of the press. After a certain number of revolutions of the plate cylinder, preferably less than 50 revolutions, and most preferably less than 5 revolutions, the ink supply is also switched on. In an alternative embodiment, the supply of fountain solution and ink may be started simultaneously, or only ink may be supplied during a number of revolutions before the supply of fountain solution is turned on.

The treatment step may also be carried out by combining the above embodiments, for example, by combining development with a treatment solution with on-press development by applying ink and/or an ink fountain.

Treatment liquid

The treatment liquid may be an alkaline developer or a solvent-based developer. Suitable alkaline developers have been described in US 2005/0162505. The alkaline developer is an aqueous solution having a pH of at least 11, more typically at least 12, preferably 12 to 14. The alkaline developer typically contains an alkaline agent, which may be an inorganic or organic alkaline agent, to achieve a high pH. The developer may comprise ionic, nonionic and amphoteric surfactants (up to 3% by weight of the total composition); biocides (antimicrobials and/or antifungals), antifoams or chelating agents (e.g. alkali gluconates) and thickeners (water-soluble or water-dispersible polyhydroxy compounds, e.g. glycerol or polyethylene glycols).

Preferably, the treatment liquid is a gum solution, whereby during the development step the non-exposed areas of the photopolymerizable layer are removed from the carrier and the printing plate is gummed in a single step. Development with a gum solution has the additional benefit that no additional gumming step is required to protect the carrier surface in the non-printed areas due to the residual gum in the non-exposed areas on the plate. As a result, the precursor is treated and gummed (also called development/gumming) in a single step, which involves a simpler development apparatus than one comprising a solution tank, a rinse section and a gumming section. The gluing section may comprise at least one gluing unit, or may comprise two, preferably three or more gluing units. These gumming units may have the configuration of a stepped flow system, i.e. the gum solution used in the second gumming unit overflows to the first gumming unit when a gum make-up solution is added in the second gumming unit or when the gum solution in the second gumming unit is used only once, i.e. only the starting gum solution is used to develop the precursor in said second gumming unit by means of a preferred spraying or jetting technique. The gluing section more preferably comprises three gluing units provided in a stepped flow configuration; i.e. the third glue solution overflows to the second glue solution and the second glue solution overflows to the first glue solution, whereby the third glue solution is regenerated with fresh glue and/or regeneration solution. More details about such gum development are described in EP 1788444.

The gum solution is typically an aqueous liquid comprising one or more surface protective compounds capable of protecting the lithographic image of the printing plate from contamination (e.g. contamination by oxidation, fingerprints, fats, oils or dust) or damage (e.g. damage by scratches during handling of the printing plate). Suitable examples of such surface protecting compounds are film forming hydrophilic polymers or surfactants. The layer remaining on the printing plate after treatment with the gum solution preferably comprises 0.005 g/m²To 20 g/m²More preferably 0.010 g/m²To 10 g/m²Most preferably 0.020 g/m²To 5 g/m²The surface protective compound of (1). Further details regarding surface-protecting compounds in gum solutions can be found on page 9, line 3 to page 11, line 3 of WO 2007/057348Found in line 6. Since the developed printing plate precursor is developed and gummed in one step, no post-treatment of the treated printing plate is required.

The gum solution preferably has a pH of from 3 to 11, more preferably from 4 to 10, even more preferably from 5 to 9, and most preferably from 6 to 8. Suitable gum solutions are described, for example, in EP 1342568 [0008] to [0022] and WO 2005/111727. The gum solution may also include inorganic salts, anionic surfactants, wetting agents, chelating compounds, preservative compounds, defoaming compounds, and/or ink-receiving agents and/or combinations thereof. Further details regarding these additional components are described in WO 2007/057348, page 11, line 22 to page 14, line 19.

The treatment of crosslinkable coatings is described in detail in unpublished patent applications EP16201734 [0038] to [0079], and incorporated herein by reference.

Drying step

After the treatment step, the printing plate is preferably 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 comprise at least one heating element selected from an IR lamp, a heated metal roll or a hot air system (heated air), preferably heated air.

During the drying step, volatile components and/or liquids (e.g., solvents and/or water) are at least largely removed from the coating. The plate is preferably dried at a temperature equal to or higher than 25 ℃. Preferably from 30 ℃ to 100 ℃, more preferably from 35 ℃ to 80 ℃, and most preferably from 40 ℃ to 60 ℃. When lower heating temperatures are used, longer heating times are generally used, and when higher heating temperatures are used, shorter heating times are used. The drying time is generally 3 seconds to 10 minutes, more preferably 3 seconds to 5 minutes, and most preferably 2 seconds to 2 minutes. The plate is preferably dried with heated air in the drying section of the processing apparatus or in a separate device, but most preferably in an apparatus as described below.

In the embodiment in which the printing plate is treated on the printing press (see above), the printing plate is preferably heated on the printing press by means of at least one heating element, such as an IR lamp or a hot air system, after the on-press treatment and before the UV L ED irradiation (on-press).

UV L ED irradiation step

According to the method of the present invention, after the drying step (or heating step in on-press process embodiments), the lithographic printing plate is subjected to a UV L ED irradiation step exposure of the printing plate to ultraviolet light emitted by diodes (UV L ED) preferably at least one UV L0 ED, more preferably at least two UV L ED, and most preferably more than three UV L ED, UV L ED are preferably aligned and then referred to as UV L ED bands or UV L ED bars preferably at least one UV L ED bar, more preferably at least two UV L ED bars, and most preferably at least three UV L ED bars are used.

The ultraviolet light emitting diode (UV L ED) emits light in the UV-A spectrum, which refers to light having a wavelength of about 315 nm to 450nm, preferably, the UV L ED emits light of about 320 nm to 420 nm, and most preferably, 330 nm to 400 nm or 340 nm to 380 nm, preferably, 10 per L ED power is used^-6To 15 watts, more preferably 10 watts^-4To 10 watts, and most preferably 10 watts^-2Exposure time of UV L ED. UV L ED lamp to 5 watts is preferably 0.1 second to 5 minutes, more preferably 0.5 second to 1 minute, and most preferably 1 second to 30 seconds.

In a preferred embodiment, the time between the drying step and the UV L ED irradiation is less than 15 minutes, more preferably from 0.01 seconds to 10 minutes, more preferably from 0.1 seconds to 5 minutes, and most preferably from 0.5 seconds to 2 minutes.

Post-processing device

The present invention also provides an apparatus or device specifically designed for exposing treated printing plates to UV L ED radiation, as comprised by the method of the present invention, said post-treatment step is preferably carried out on printing plates still having a high temperature due to the drying step and/or the heating step, as explained above, thus UV L ED radiation can be accomplished by means of a separate (stand-alone) device comprising, in addition to one or more L ED bars, heating elements, such as (without limitation) IR lamps, heated metal rollers or a hot air system (heated air), or by means of a device comprising one or more L ED bars, said L ED bars being adapted to be comprised in a separate drying device and/or on the printing press, and/or in the drying part of the treatment device UV L ED radiation being preferably comprised in the drying part of the treatment device.

Preferred treatment apparatus

The distance between the heating element or elements in the drying section and the UV L ED used is preferably not more than 15 cm, more preferably not more than 10 cm, and most preferably not more than 5 cm.

Figure 1 shows a preferred treatment apparatus according to the invention, in which UV L ED sticks are included in the drying section of the treatment apparatus figure 1 represents a highly preferred embodiment of such a treatment apparatus, which comprises a development/gumming section (1), said development/gumming section (1) comprising three gumming units (3,4 and 5) interconnected by a stepped flow allowing the overflow of liquid from the third gumming unit to the second gumming unit (14B) and from the second gumming unit to the first gumming unit (14A).

Additional gumming units may be used, but preferred embodiments include two gumming units or three gumming units in the developing/gumming section, interconnected by a stepped flow that allows liquid to overflow from the second gumming unit to the first gumming unit.

Well-known features which are preferably present in the processing apparatus but which are not shown in fig. 1 are: a feeder for feeding the printing plates one by one to the developing/gumming section; (re) circulation and/or regeneration systems; including a supply of fresh gum solution or one or more make-up solutions; a waste liquor collection tank wherein exhausted gum solution is drained; a water tank for diluting the concentrated chemical; and other conventional components.

The gum solutions 1 and 2 are applied to the printing plate by spraying, jetting, dipping or coating techniques including spin coating, roll coating, slot coating or gravure coating. Preferably a spray or (valve) spray nozzle is used. All features of the nozzles as described in WO 2017/157571 [0093] to [0100] are applicable here, which nozzles may supply the gum solution depending on the plate area or even on the image data of the plate as described in EP 2775351.

Two spray bars are provided in the first gluing unit: one bar (8A) is able to spray glue both on the nip of the pair of rollers (6A) and on the brush (9A), and one bar (8B) sprays glue towards the nip of the pair of rollers (6B). In the second gluing unit, a rod (8C) is provided which is able to spray glue onto both the nip of the pair of rollers (6C) and the brush (9B), and a rod (8D) which sprays glue onto the nip of the pair of rollers (6D).

In the preferred embodiment of fig. 1, the pinch roller (6A) is provided with a cleaning roller (7A) to prevent glue contamination outside the development/gumming section. In the third gumming unit, a stripper roll 7C is combined with a sizing nozzle (20) to provide a final (gummed) layer on the surface of the printing plate.

The rod that sprays the glue to the nip of the roller pair preferably comprises at least one row of holes; the rods (8A and 8C) capable of spraying the glue onto both the roller and the brush (9A or 9B) preferably comprise at least two rows of holes. Preferably, the bar or bars used for spraying the first glue solution, more preferably the bars (8A) and (8B), are in the so-called nudge mode (jog-mode), i.e. glue is periodically supplied to prevent sticking of the pinch rollers and/or brushes even when no printing plate is present in the gumming unit. Preferably, the pinch rollers are engaged periodically; even when no plate passes. The second gluing unit also comprises spray bars (8C and 8D) able to keep the two pinch rollers (6C and 6D) in the second unit wet. These spray bars may also be in a nudge mode.

The third gum solution is preferably regenerated by means of an inlet (16) which supplies a regenerator liquid, which may be water, optionally diluted fresh gum and/or make-up solution, to the third gumming unit, for example to the storage tank (10C). Other well known elements of the regenerator system are not shown in fig. 1, such as supply tanks for holding fresh gum solution, water, or make-up solution; a pump and the necessary pipes to supply the regenerator liquid to the third gumming unit. Likewise, the first and/or second gum solutions can be regenerated by the same or similar regeneration system as used for the third gum solution. The first and/or second glue solution may also be regenerated by actively pumping the glue solution from the third gluing unit to the second gluing unit and/or from the second gluing unit to the first gluing unit.

After the final glue has been applied, the printing plate is preferably not rinsed, but immediately transported to a drying section (2) integrated into the apparatus drying can be achieved by heating elements (17) by emitting hot air, infrared and/or microwave radiation and other methods generally known in the art, including at least one UV L ED bar (18) in the drying section.

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 so-called single fluid inks without fountain 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 referred to as a hydrophobic or oleophilic phase, and a polyol phase as described in WO 00/32705.