JP2005181963A - Heat-sensitive lithographic printing plate precursor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a positive-working heat-sensitive lithographic printing plate precursor having an improved sensitivity and at the same time a high underexposure latitude and a high developer resistance. <P>SOLUTION: The positive-working lithographic printing plate precursor comprises, on a support having a hydrophilic surface or which is provided with a hydrophilic layer, an oleophilic coating comprising an infrared absorbing agent, an alkali-soluble polymeric binder and a polysiloxane which comprises at least one carboxylic acid group or a salt thereof. The printing plate precursor has the improved sensitivity and at the same time the high underexposure latitude and the high developer resistance. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a thermosensitive positive-acting lithographic printing plate precursor.

  A lithographic printing machine uses a so-called printing master such as a printing plate mounted on the cylinder of the printing machine. The master carries a lithographic image on its surface, and a print is obtained by applying ink to the image and then transferring the ink from the master onto a receiving material, typically paper. In the case of the usual so-called “wet” lithographic printing, the ink as well as the aqueous fountain solution (also called dampening liquid) are oleophilic (or hydrophobic, ie ink-receptive, water- Supplied to a lithographic image consisting of areas which are repellent) as well as hydrophilic (or oleophobic, ie water-receptive, ink-repellent) areas. In the case of so-called driographic printing, a lithographic image consists of ink-receptive and ink-abhesive (ink-repellent) areas, during which only ink is the master. Supplied.

  Print masters are generally obtained by the so-called computer-to-film method, in which various pre-printing methods such as typeface selection, scanning, color separation, screening, trapping, layout and assembly are used. The pressing step is done digitally and each color selection is transferred to graphic art film using an image-setter. After processing, the film can be used as a mask for the exposure of the imaging material called the plate precursor, and after processing of the plate, a printing plate is obtained that can be used as a master.

  Typical printing plate precursors for computer-to-film processes include hydrophilic supports and photosensitive polymers including UV-sensitive diazo compounds, dichromate-sensitized hydrophilic colloids and a variety of synthetic photopolymers. Image-recording layer. In particular, diazo-sensitized systems are widely used. Typically, when exposed image-wise by a film mask in a UV contact frame, the exposed image areas become insoluble in aqueous alkaline developer and the unexposed areas remain soluble. The plate is then processed with a developer to remove the diazonium salt or diazo resin in the unexposed areas. The exposed area thus defines the image area (printing area) of the print master, and such a printing plate precursor is therefore called "negative-active". Also known are plates with a positive-active material in which the exposed areas define non-printing areas, for example novolak / naphthoquinone-diazide coatings which dissolve in the developer only in the exposed areas.

  In addition to the photosensitive materials described above, thermosensitive printing plate precursors have also become very popular. Such thermal materials offer the advantage of daylight-stability and are particularly used in so-called computer-to-plate processes in which the plate precursor is exposed directly, i.e. without using a film mask. The material is exposed to heat or infrared light, and the generated heat is (physico-) chemical processes such as ablation, polymerization, insolubilization by polymer cross-linking, heat-induced solubilization, degradation or particle aggregation of thermoplastic polymer latex. Start analysis.

  Patent Document 1 discloses a heat mode for preparing a lithographic printing plate comprising a lithographic base having a hydrophilic surface, an intermediate layer containing a polymer soluble in an alkaline aqueous solution, and an IR-ray sensitive uppermost layer. An imaging element is disclosed, wherein the top layer is exposed to IR-rays to reduce or increase the likelihood that an aqueous alkaline solution will penetrate and / or be solubilized thereby.

Patent Documents 2 and 3, IR-line sensitivity comprising a polymer which is impermeable with respect to an alkaline developing solution containing a soluble and is and SiO ₂ in a lithographic base as well as an alkaline aqueous solution as a silicate having a hydrophilic surface A heat mode imaging element comprising a top layer is disclosed.

  The last two heat-mode imaging elements have a very small difference between the solubility in the exposed and non-exposed areas, and the non-exposed areas also dissolve during processing of the element, making the plate a lithographic printing plate It has the disadvantage that it cannot be used.

  Patent Document 4 discloses an IR that is sensitive to IR light but not sensitive to UV light, and includes a support and a lipophilic polymer that is soluble in an aqueous alkaline developer and a dissolution inhibitor that reduces the solubility of the polymer in the developer. Describes a positive-acting heat-sensitive printing plate precursor comprising a sensitive coating.

  U.S. Patent Nos. 5,057,049 and 5,037,697 describe thermosensitive printing plate precursors provided with a coating comprising a compound that improves the developer resistance of the coating. The compound is selected from the group of poly (alkylene oxides), siloxanes and esters or amides of polyhydric alcohols.

  Patent Document 7 and Patent Document 8 describe heat mode image formation for obtaining a lithographic printing plate comprising a base having a hydrophilic surface, a first layer containing a polymer soluble in an alkaline aqueous solution, and an infrared-sensitive top layer. Describes an element, wherein at least one of the layers comprises a surfactant, such as a polysiloxane.

  Prior art printing plate precursors containing compounds that improve the developer resistance of the coating, such as polysiloxanes, also have wide development latitude, i.e., the exposed areas are completely dissolved before the non-exposed areas begin to dissolve. In this sense, the differentiation between the development kinetics of exposed and non-exposed areas is improved. However, the minimum energy density of these printing plate precursors required to solubilize the exposed areas in the developer is high and thus more expensive exposure devices such as lasers with long exposure times and / or high laser power Must be used.

Accordingly, there is still a need for a printing plate precursor that has improved sensitivity and at the same time has high underexposure latitude and high developer resistance.
European Patent No. 0864420 EP 0908304 Specification European Patent No. 0908306 International Publication No. 97/39894 Pamphlet International Publication No. 99/21725 Pamphlet International Publication No. 99/21715 Pamphlet European Patent No. 0950517 European Patent No. 0950518

Summary of the invention

  An aspect of the present invention is to provide a positive-acting thermosensitive lithographic printing plate precursor with improved sensitivity while having high under-exposure latitude and high developer resistance.

  This object comprises an oleophilic coating comprising an infrared absorber, an alkali-soluble polymeric binder and a polysiloxane on a support having a hydrophilic surface or provided with a hydrophilic layer. This is realized by providing a printing plate precursor, wherein the polysiloxane comprises at least one carboxylic acid group or a salt thereof.

  Surprisingly, the heat-sensitive lithographic printing plate precursor of the present invention comprising a polysiloxane comprising at least one carboxylic acid group or salt thereof is a printing plate precursor comprising a prior art polysiloxane. Was found to have improved sensitivity without a significant decrease in developer resistance.

Particular aspects of the invention are defined in the dependent claims.
DETAILED DESCRIPTION OF THE INVENTION The positive working lithographic printing plate precursor of the present invention comprises a support having a hydrophilic surface or provided with a hydrophilic layer and an oleophilic coating provided thereon. The lipophilic coating includes an infrared absorber, an alkali-soluble polymeric binder, and a polysiloxane, wherein the polysiloxane includes at least one carboxylic acid group or salt thereof.

  In the following, polysiloxanes containing at least one carboxylic acid group or salt thereof are also referred to as “carboxylic acid modified polysiloxanes” or “CAM-polysiloxanes”. The CAM-polysiloxane contains a polysiloxane chain and at least one carboxylic acid group or salt thereof. The polysiloxane chain in the CAM-polysiloxane can be a linear, cyclic or complex cross-linked polymer or copolymer containing multiple siloxane repeat units. Siloxane repeat units can be represented by —Si (R, R ′) — O—, wherein R and R ′ are optionally substituted alkyl or aryl groups. Preferred siloxane repeat units are alkyl and / or aryl siloxanes; preferably diphenyl-siloxanes, dimethyl-siloxanes and phenylmethyl-siloxanes; most preferably dimethyl-siloxanes. The number of siloxane repeat units is at least 2, preferably at least 10, more preferably at least 20, and preferably less than 100, more preferably less than 60. Suitable CAM-polysiloxanes preferably contain about 15 to 25 siloxane units.

The alkyl group or aryl group of the siloxane repeat unit can be substituted with a substituent; preferred substituents are represented by polyalkylene-oxide groups. The polyalkylene-oxide group comprises a plurality of alkylene-oxide repeat units of the formula —C _n H _2n —O—, where n is preferably an integer in the range of 2-5. Preferred alkylene-oxide repeat units are typically ethylene oxide, propylene oxide or mixtures thereof. -C n _H 2n _- portion of the may include a straight or branched chain, may be substituted. The number of repeating units is preferably in the range of 2 to 10 units, more preferably 2 to 5 units and preferably less than 100, more preferably less than 60.

  The CAM-polysiloxane can also be a block copolymer comprising a polysiloxane chain as defined above, a polyalkylene oxide chain and at least one carboxylic acid group or salt thereof. The polyalkylene oxide chain comprises alkylene oxide repeat units as defined above for alkylene oxide groups.

  The CAM-polysiloxane may also be a graft-copolymer comprising a polysiloxane chain as defined above, at least one macromonomer comprising a polyalkylene oxide group as defined above and at least one carboxylic acid group or salt thereof. it can.

One or more carboxylic acid groups or salts thereof are present in the CAM-polysiloxane; at least one of them can be located at the end of the polysiloxane chain and / or at the end of the polyalkylene oxide group or chain . Alternatively, they are bonded on the R or R ′ group of the repeating unit of the polysiloxane chain (—Si (R, R ′) — O—) or on the —C _n H _2n — moiety of the polyalkylene-oxide chain. Can be. The salt form of the carboxylic acid is preferably an alkali or ammonium salt such as a Li ⁺ , Na ⁺ or K ⁺ salt. A carboxylic acid group or a salt thereof, alkylene, arylene, _{heteroarylene, -O -, - O- (CH} 2) k -, - O-CO- (CH 2) k -, - (CH 2) k -O- _{CO- (CH 2) l -,} - (CH 2) k -CO- (CH 2) l -, - CO-O- (CH 2) k -, - (CH 2) k -COO- (CH 2) _{l -, - CO- (CH 2} ) k - or linked via a linking group L such as a combination thereof can have; where k and l are independently> indicates 1 of the integer. Preferred linking groups are represented by alkylene, —O— (CH ₂ ) _k —, — (CH ₂ ) _k —CO— (CH ₂ ) ₁ — or —CO— (CH ₂ ) _k —. The number of acid groups or salts thereof present in the CAM-polysiloxane is at least 1, preferably at least 2. The average molecular weight (M _w ) of the CAM-polysiloxane is preferably 500-10000 g / mol; more preferably 600-7000 g / mol, most preferably 700-5000 g / mol.

  Examples of CAM-polysiloxane are given below.

List of CAM-polysiloxanes SIL 1: SLM 441075/4 (01 M642) obtained from Wacker,
SIL 2: Rhodosolsil Huile 1669 obtained from Rhodia,
SIL 3: X22-3710 obtained from Shin Etsu
SIL 4: X22-162C obtained from Shin Etsu,
SIL 5: Tegomer C Si-2342 obtained from Goldschmidt
SIL 6: Tegomer C Si-2142 obtained from Goldschmidt,
SIL 7: DMS B12 obtained from ABCR.

  The lipophilic coating can comprise one or more separate layers, and the CAM-polysiloxane can comprise a layer containing a hydrophilic binder, optionally another layer or a separate top layer of the coating, ie the top of the coating. It can be present in the outer layer. In the latter embodiment, the CAM-polysiloxane can be applied in a second solution that is coated over the other layer or layers. Solvents that cannot dissolve the components present in the other layer or layers in the second coating solution so that a highly concentrated CAM-polysiloxane phase is obtained over the coating that forms the separated top layer. May be advantageous. This top layer can serve as a barrier layer that can protect the coating from the developer and reduce the rate of dissolution of the coating in the developer. Exposure to heat or infrared light can enhance the penetration potential of the barrier layer by the developer and increase the rate of dissolution of the coating in the developer.

The amount of CAM- polysiloxane in the heat-sensitive coating, 0.5~25mg / ^{m 2,} preferably and most preferably 0.5-15 / ^{m 2} can vary in 0.5 to 10 mg / ^{m 2.}

  The lipophilic coating can further contain other polymers comprising siloxane and / or perfluoroalkyl units. These polymers can act, for example, as spreading agents, can result in improved coating quality, and can further improve the developer resistance of alkali-soluble coatings. Upon exposure to heat and / or infrared light, the imaged portion is solubilized when developed, before the non-imaged portion begins to solubilize.

  Surprisingly, printing plate precursors of the present invention comprising CAM-polysiloxanes are known from prior art polysiloxanes such as Tego Glide 410, Tego Wet 265, Tego, all commercially available from Tego Chemie, Essen, Germany. It was found that developer resistance was not substantially reduced while showing improved sensitivity compared to printing plate precursors containing Protect 5001 or Silikophen P50 / X. “Not substantially reduced” means a reduction in developer resistance value as defined in the Examples section below, also referred to as “DR” below, of up to 7%, more preferably up to 5%, most preferably Means that it can be up to 3%. Sensitivity is also referred to below as "right exposed energy density" or "REED" and is also referred to below as "clearing point" or "CP". Determined by clearing point sensitivity. REED and CP are defined in the Examples section below. The increased sensitivity in the present invention is such that the underexposure tolerance as defined in the Examples section below, also referred to as “UEL” below, is at least 30%, preferably at least 40% and more preferably at least 50%. Meaning that the printing plate precursor is characterized by a low REED value and a low CP value.

According to the present invention, the alkali-soluble polymeric binder is preferably a phenolic resin such as novolak, resole, polyvinylphenol and a carboxy-substituted polymer. Typical examples of such polymers are described in German Offenlegungsschrift 4007428, German Offenlegungsschrift 4027301 and German Offenlegungsschrift 4445820. Further, the coating can include a polymer that improves the print run length and / or the chemical resistance of the plate. Examples thereof are sulfonamides (—SO ₂ —NR—) or imides (—CO—NR—CO, where R is hydrogen, optionally substituted alkyl or optionally substituted aryl. -) Polymers containing side groups, for example described in EP 894622, EP 901902, EP 933682 and WO 99/63407 Polymer.

  In a preferred embodiment of the present invention, the alkali-soluble polymeric binder is preferably a phenolic resin in which the phenyl group or hydroxy group of the phenolic monomer unit is chemically modified with an organic substituent. Phenolic resins that are chemically modified with organic substituents can exhibit improved chemical resistance to printing chemicals such as fountain solutions or printing press chemicals such as plate cleaners. Examples of such alkali-soluble phenolic resins that are chemically modified with organic substituents are described in EP 0 934 822, EP 1 724 432, US Pat. No. 5,641,608. , European Patent Application Publication No. 0982123, International Publication No. 99/01975 pamphlet, European Patent Application Publication No. 02102446 filed on October 15, 2002, filed on October 15, 2002 European Patent Application Publication No. 02102444, European Patent Application Publication No. 02102445 filed on October 15, 2002, European Patent Application Publication No. 02102443 filed on October 15, 2002, European Patent Application Publication No. 03102522 filed on August 13, 2003 It has been described in the book.

  The modified resin described in European Patent Application No. 02102446 filed on Oct. 15, 2002, in particular the phenyl-group of the phenolic monomer unit of the phenolic resin has the structure -N = N- Resins substituted with a group having Q are preferred, wherein the —N═N— group is covalently bonded to the carbon atom of the phenyl group and Q is an aromatic group, most preferably Q Is the following formula (I):

[Wherein n is 0, 1, 2 or 3;
Wherein each R ¹ is hydrogen, optionally substituted alkyl, alkenyl, alkynyl, cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl or heteroaralkyl group, —SO ₂ —NH—R ² , —NH—SO ₂ —R ⁴ , —CO—NR ² —R ³ , —NR ² —CO—R ⁴ , —O—CO—R ⁴ , —CO—O—R ² , —CO—R ² , —SO ₃ —R ² , —SO ₂ —R ² , —SO—R ⁴ , —P (═O) (— O—R ² ) (— O—R ³ ), —NR ² —R ³ , —O ^{-R 2, -S-R 2,} -CN, -NO 2, halogen,-N-phthalimidyl, selected from -M-N-phthalimidyl, or ^{-M-R 2,} wherein M 1 to 8 carbons A divalent linking group containing an atom,
Wherein R ² , R ³ , R ⁵ and R ⁶ are independently hydrogen or optionally substituted alkyl, alkenyl, alkynyl, cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl or hetero Selected from the aralkyl group,
Wherein R ⁴ is selected from an optionally substituted alkyl, alkenyl, alkynyl, cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl or heteroaralkyl group,
Alternatively, in the formula, at least two groups selected from each of R ^{1 to} R ⁴ together represent an atom necessary for forming a cyclic structure,
Or, in the formula, R ⁵ and R ⁶ together represent an atom necessary for forming a cyclic structure.]
It is.

  Another preferred alkali-soluble phenolic resin is a phenolic resin in which the phenyl group of the phenolic monomer unit or the hydroxy group of the phenolic monomer unit is substituted with a group having the structure of formula (I) as defined above. .

  The coating provided on the support is heat sensitive, thereby providing a plate precursor that can be handled for several hours in normal working lighting conditions (daylight, fluorescence). The coating preferably does not contain UV-sensitive compounds having an absorption maximum in the wavelength range from 200 nm to 400 nm, such as diazo compounds, photoacids, photoinitiators, quinonediazides or sensitizers.

  In addition to the layers discussed above and below, the oleophilic coating may further comprise, for example, a “priming” layer that improves the adhesion of the coating to the support, a topcoat layer that protects the coating against contamination or mechanical damage, and / or A light to heat conversion layer containing an infrared light absorbing compound can be included.

  The coating is positive-working and heat-induced solubilization is possible, i.e. the coating is resistant to developer in the non-exposed state, ink-receptive, heat or infrared light When exposed to water, it becomes soluble in the developer so that the hydrophilic surface of the support appears.

  In a preferred embodiment, the coating also contains one or more dissolution inhibitors, i.e., one or more materials that reduce the dissolution rate of the polymeric binder in the aqueous alkaline developer in the non-exposed areas of the coating. . Easy by coating on a support two samples: a reference sample containing only an alkali-soluble polymeric binder and another sample containing both a polymeric binder (in an amount equal to the reference) and an inhibitor In addition, the ability of the inhibitor to inhibit dissolution can be examined. A series of unexposed samples are immersed in an aqueous alkaline developer for a different time for each sample. After the dipping time, the sample is removed from the developer, immediately rinsed with water, dried, and then the dissolution of the coating in the developer is measured by comparing the weight of the sample before and after development. As soon as the coating is completely dissolved, no further weight loss is measured at longer immersion times, ie the curve showing weight loss as a function of immersion time reaches a plateau from the moment of complete dissolution of the layer. If the sample coating without the inhibitor completely dissolves in the developer before the sample containing the inhibitor is attacked by the developer to the extent that the ink-accepting capacity of the coating is affected, the material Has excellent suppression ability.

  The dissolution inhibitor (s) that can be added to the layer containing the alkali-soluble polymeric binder is developed by interaction between the polymeric binder and the inhibitor, e.g., due to hydrogen bonding between these compounds. Reduce the dissolution rate of the non-exposed coating in the liquid. The inhibitor's ability to inhibit dissolution is preferably reduced or destroyed by the heat generated during exposure, and in the exposed areas the coating dissolves easily in the developer. Such inhibitors are preferably at least one aromatic group and a hydrogen bonding site, such as a carbonyl group, a sulfonyl group or quaternized and can be part of a heterocyclic ring or of an organic compound An organic compound containing a nitrogen atom that can be part of an amino substituent. Suitable dissolution inhibitors of this type are disclosed for example in EP 825927 and 823327. Some of the compounds listed below can also act as dissolution inhibitors, for example, infrared dyes such as cyanine and contrast dyes such as quaternized triarylmethane dyes.

  Preferably, one or more development accelerators are also included in the coating, ie compounds that act as dissolution accelerators because they can increase the dissolution rate of non-exposed coatings in the developer. The simultaneous application of dissolution inhibitors and accelerators allows precise fine tuning of the dissolution behavior of the coating. Suitable dissolution promoters are cyclic acid anhydrides, phenols or organic acids. Examples of cyclic acid anhydrides include phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, tetrachlorophthalic anhydride as described in US Pat. No. 4,115,128. Maleic anhydride, chloromaleic anhydride, alpha-phenylmaleic anhydride, succinic anhydride and pyromellitic anhydride. Examples of phenols include bisphenol A, p-nitrophenol, p-ethoxyphenol, 2,4,4'-trihydroxybenzophenone, 2,3,4-trihydroxy-benzophenone, 4-hydroxybenzophenone, 4,4 ' , 4 "-trihydroxy-triphenylmethane and 4,4 ', 3", 4 "-tetrahydroxy-3,5,3', 5'-tetramethyltriphenyl-methane, etc. Examples of organic acids Examples include sulfonic acid, sulfinic acid, alkylsulfuric acid, phosphonic acid, phosphate and carboxylic acid as described in JP-B-60-88,942 and JP-A-2-96,755. Specific examples of organic acids include p-toluenesulfonic acid, dodecylbenzenesulfonic acid, p-toluenesulfinic acid, ethyl Acid, phenylphosphonic acid, phenylphosphinic acid, phenylphosphate, diphenylphosphate, benzoic acid, isophthalic acid, adipic acid, p-toluic acid, 3,4-dimethoxybenzoic acid, phthalic acid, terephthalic acid, 4-cyclohexene-1, 2-dicarboxylic acid, erucic acid, lauric acid, n-undecanoic acid and ascorbic acid are included The amount of cyclic acid anhydride, phenols or organic acid contained in the coating is preferably relative to the total coating. 0.05 to 20% by weight of a phenol-formaldehyde resin containing at least 70 mol% meta-cresol as repeating monomer units or at least 40 mol% monohydroxybenzene as repeating monomer units. Polymeric development acceleration Other examples of polymeric development accelerators are repeat units having at least one phenolic hydroxyl group and at least one alkali solubilizing group, such as resorcinol, pyrocatechol, hydroquinone. , Hydroxyhydroquinone, pyrogallol, phloroglucinol or a phenolic resin containing at least 5 mol% of dihydroxybenzoic acid.

  Using heat, the material can be exposed image-wise, for example directly by a thermal head or indirectly by infrared light, which is preferably converted to heat by an infrared absorbing compound, and infrared The light absorbing compound can be a dye or pigment having an absorption maximum in the infrared wavelength region. The concentration of sensitizing dye or pigment in the coating is typically 0.25 to 10.0% by weight, more preferably 0.5 to 7.5% by weight relative to the overall coating. Preferred IR-absorbing compounds are dyes such as cyanine or merocyanine dyes or pigments such as carbon black. Suitable compounds are the following infrared dyes:

  The coating can further contain an organic dye that absorbs visible light so that, when exposed imagewise and subsequently developed, a perceptible image is obtained. Such dyes are often referred to as contrast dyes or indicator dyes. Preferably, the dye has a blue color and an absorption maximum in the wavelength region of 600 nm to 750 nm. Although the dye absorbs visible light, it preferably does not sensitize the printing plate precursor, i.e. the coating does not become more soluble in the developer when exposed to visible light. A suitable example of such a contrast dye is a quaternized triarylmethane dye.

  Infrared light absorbing compounds and contrast dyes can be present in the layer comprising the alkali-soluble polymeric binder and / or in the top layer discussed above and / or optionally in other layers. According to a highly preferred embodiment, the infrared light absorbing compound is concentrated in or near the top layer, for example in an intermediate layer between the layer containing the polymeric binder and the top layer.

The printing plate precursor of the present invention can be exposed to infrared light using, for example, LEDs or lasers. Preferably, a laser emitting near infrared light having a wavelength in the range of about 750 to about 1500 nm, such as a semiconductor laser diode, Nd: YAG or Nd: YLF laser is used. The laser power required is the pixel residence time of the laser beam determined by the sensitivity of the image-recording layer, the spot diameter (typical values of modern plate-setters at 1 / e ² of maximum intensity: 10-25 μm), Depends on scan speed and exposure device resolution (ie number of addressable pixels per unit of linear distance, often expressed in dots per inch or dpi; typical values: 1000-4000 dpi) To do.

  Two types of laser-exposure devices are commonly used: internal (ITD) and external drum (XTD) plate-setters. ITD plate-setters for thermal plates are typically characterized by very high scanning speeds of up to 500 m / s and may require several watts of laser power. XTD plate-setters for thermal plates having a typical laser power of about 200 mW to about 1 W operate at lower scan speeds, for example 0.1-10 m / sec.

  A known plate-setter can be used as an off-press exposure apparatus, which provides the benefit of reduced press down-time. An XTD plate-setter arrangement can also be used for on-press exposure, providing a direct registration benefit in a multicolor press. Further technical details of the on-press exposure apparatus are described, for example, in US Pat. No. 5,174,205 and US Pat. No. 5,163,368.

  During the development stage, the non-image areas of the coating are removed by dipping in a normal aqueous alkaline developer, which can be combined with mechanical rubbing, for example with a rotating brush. The developer preferably has a pH higher than 10, more preferably higher than 12. The development stage can be followed by a rinsing stage, a gumming stage, a drying stage and / or a post-baking step.

  The printing plate thus obtained can be used for conventional so-called wet offset printing, in which ink and aqueous dampening liquid are supplied to the plate. Another suitable printing method uses so-called single-fluid ink without a dampening solution. Single-fluid inks include an ink phase, also called a hydrophobic or oleophilic phase, and a polar phase that replaces the aqueous fountain used in normal wet offset printing. Suitable examples of single-fluid inks are described in US Pat. No. 4,045,232; US Pat. No. 4,981,517 and US Pat. No. 6,140,392. In the most preferred embodiment, the single-fluid ink comprises an ink phase and a polyol phase, as described in WO 00/32705.

Evaluation Method A suitable method for determining the energy density value for the actual exposure of the positive-acting thermal plate is described below. After exposing the halftone image at various energy density values on the plate and then processing according to the conditions used (time, temperature, developer), the actual dot area obtained on the plate is measured with a reflection densitometer. The target dot area set in the image setter software (RIP) is compared. A typical example of such a method is shown in FIG. 1, where the dot area obtained on a plate exposed using a 50% 200 lpi screen (approximately 80 lines per cm) is the exposure energy density. It is plotted against. Dot area values were obtained with a commercially available ^cc Dot ³ densitometer from Centurfax Ltd. FIG. 1 shows that at low energy density, the dot area on the plate is greater than the target value of 50%: due to underexposure, the coating immediately around the edge of the dot does not dissolve quickly enough in the developer. Seem. At energy density values that are too high, overexposure of the coating around the dot leads to dot edge dissolution, resulting in a dot area value lower than 50%. These effects are particularly significant when the laser spot has a pronounced Gaussian intensity distribution and a less steep intensity distribution. From the curve shown in FIG. 1, the energy density at which the resulting dot area matches the target value (50%) can be determined by interpolation: the value is herein referred to as “Proper Exposure Energy Density” (REED). Call it. In other words, the REED value is defined as the minimum energy density at which the dot area on the plate occupied by the screened image corresponding to 50% halftone in the image data matches the 50% target value. It will be apparent to the skilled person that lower REED values indicate higher plate sensitivity.

Another parameter that can be used for sensitivity quantification is the clearing point (CP), which is described here. Exposure of the positive-acting thermal plate at an energy density that is insufficient to raise the temperature of the coating to the imaging mechanism threshold has no significant effect on the dissolution kinetics of the exposed areas. Eventually, after processing according to the conditions used (time, temperature, developer), the coating usually remains on the support, i.e. the optical density of the coating is essentially equal to _Du , the optical density of the unexposed plate. At higher energy densities, the temperature in the coating reaches a threshold temperature and eventually exceeds it, resulting in a decrease in the concentration of coating remaining on the plate after processing. To thereby exposed and is reduced to 95% of the optical density of the processed version of the coating, i.e. the "clearing points" a minimum energy density required to produce an optical density of 0.05 * D _u herein Define.

CP exposes a solid wedge on the plate, that is, a series of completely 0% dots exposed on the plate at various energy density values (total for all imagesetter pixels). Exposure) can be measured. The method is described with reference to FIG. 2, where the energy density values from these series of individual values produce a step-wedge, but the energy density values are continuously varied to obtain a continuous wedge. It should be clear to skilled readers that they can also. Preferred continuous wedges vary at 10 mJ / cm ² or less per cm of wedge length. The minimum and maximum energy density for wedge exposure must be adjusted for the particular type of plate being examined. Step used for the present embodiment - wedges ranged 30~300mJ / cm ² with a spacing of 20 mJ / cm ^2. The wedge was made by software that controls the imagesetter, but similar results can be obtained by other means, for example by placing a wedge filter in the imagesetter's optical path, preferably in contact with the plate. CP plots the individual values of the optical density of the exposed and processed plate against the energy density, as shown in FIG. 2, and determines the energy density at which the optical density of the coating is reduced by 95% by interpolation. Determined by.

  In practice, it is observed that the CP value is less than REED. Herein, underexposure tolerance (UEL) is defined as the difference between the REED value expressed as a percentage of the REED and the CP value: UEL = (REED−CP) * 100 / REED. High UEL values are preferred because when UEL is high, i.e., when REED is large compared to CP, variations in process conditions, plate-to-batch sensitivity variations, etc. have no significant effect. If UEL is low, changes in CP and REED values can result in incomplete clean-out of exposed areas and toning (ink-acceptance in non-image areas).

Finally, a fourth parameter suitable for characterization of the plate precursor of the present invention is developer resistance (DR). DR is a measure for the resistance of non-exposed areas to developer and is defined as (D _o −D ₂ ) * 100 / D _{o where} D _o is the optical density of the plate coating that is not exposed and developed. Where D ₂ is the optical density of the unexposed plate coating after two passes through the treatment solution. Smaller values of DR indicate higher developer resistance.

Optical density values for CP and DR measurements were obtained with a GretagMacbeth D19C 47B / P densitometer, commercially available from Gretag-Macbeth AG. Such reflection densitometers are typically equipped with several filters (eg cyan, magenta, yellow): the optical density is measured using a filter corresponding to the color of the coating, eg a blue colored coating A cyan filter is preferably used for the measurement of the optical density. All optical density values were measured with reference to the uncoated substrate of the plate.
Production of Printing Plate Precursor A printing plate precursor is an electrochemically roughened and anodized aluminum sheet (oxide weight 3 g / wt) whose surface has been rendered hydrophilic by treatment with an aqueous solution of polyvinylphosphonic acid. m ² ) was prepared by coating the solution defined in Table 1 with a wet coating thickness of 26 μm and then drying. After drying the coating at 135 ° C., the resulting layer thickness was 1.07 g / m ² .

(1) A 20 wt% solution of polymer MP-22, a modified novolak, in Dowanol PM (Dowanol PM is 1-methoxy-2-propanol from Dow Chemical Company). Polymer MP-22 is produced by the following method:
-Preparation of diazonium solution A mixture of 2.6 g AM-10 and 25 ml acetic acid and 37.5 ml water was cooled to 15C. Then 2.5 ml of concentrated HCl was added and the mixture was further cooled to 0 ° C. A solution of 1.1 g NaNO _{2 in} 3 ml water was then added dropwise, followed by continued stirring at 0 ° C. for a further 30 minutes. AM-10 is a compound having the following chemical structure:

-Preparation of phenolic polymer solution:
45.9 g ALNOVOL SPN452 (Alnovol SPN452 is a solution of 40 wt% novolak resin in Dowanol PM obtained from Clariant GmbH), 16.3 g NaOAc. A mixture of 3H ₂ O and 200 ml 1-methoxy-2-propanol was stirred and cooled to 10 ° C.
The diazonium solution prepared above was dropped into the phenolic polymer solution over 30 minutes, and then stirring was continued at 15 ° C. for 120 minutes. The resulting mixture was then added to 2 liters of ice-water over 30 minutes with continuous stirring. The polymer was precipitated from the aqueous medium and isolated by filtration. The desired product was finally obtained by washing with water followed by drying at 45 ° C.
(2) Cyanine dyes commercially available from FEW Chemicals. S0094 has the chemical structure IR-1 shown above.
(3) Surfactant commercially available from Tego Chemie Service GmbH. -1 wt% solution in 1-methoxy-2-propanol.
(4) 1 wt% CAM-polysiloxane solution in Dowanol.
Printing Plate Precursor Exposure and Development Using a CREO TRENDSETTER 3244 T (plate-setter available from CREO, Burnaby, Canada) operating at 2450 dpi, using 50% screen (200 lpi) and solid area (100%) The printing plate precursor was exposed at various energy densities ranging from 60 mJ / cm ^{2 to} 280 mJ / cm ² .

  After image formation, the plate was developed in the developer specified in Table 2 using an AUTOLITH T processor operated at 25 ° C. During development, the IR-exposed areas are removed.

(1): Commercially available from RODIA Developer resistance (DR), true exposure sensitivity (REED), clearing point sensitivity (CP) and underexposure tolerance (UEL) are determined and summarized in Table 3. .

  The results in Table 3 show that developer resistance while the printing plate precursor containing CAM-polysiloxane has improved sensitivity and slightly improved underexposure tolerance over the comparative examples (lower REED and CP). It clearly shows that sex DR is not significantly reduced (less than 3%).

A graph showing the relationship between dot area and exposure energy density on a plate of Example 1 of the present invention exposed using a 50% halftone screen at 200 lpi (about 80 lines per cm). 2 is a graph showing the relationship between the optical density of the coating of Example 1 of the present invention after treatment and the energy density of exposure.

Claims (5)

  Comprising a lipophilic coating comprising an infrared absorber, an alkali-soluble polymeric binder and a polysiloxane on a support having a hydrophilic surface or provided with a hydrophilic layer, the polysiloxane Comprises a positive-acting lithographic printing plate precursor, characterized in that it comprises at least one carboxylic acid group or salt thereof.   A positive-acting lithographic printing plate precursor according to claim 1 wherein the polysiloxane comprises at least two carboxylic acid groups or salts thereof. Positive according to claim 1, polysiloxane is present in an amount ranging from 0.5~25mg / ^{m 2} - working lithographic printing plate precursor.   On a support having a hydrophilic surface or provided with a hydrophilic layer, an infrared absorber, an alkali-soluble polymeric binder and a polysiloxane comprising at least one acid group or salt thereof. A process for producing a positive-acting lithographic printing plate precursor comprising applying a lipophilic coating comprising: a) exposing the heat-sensitive lithographic printing plate precursor according to any one of claims 1 to 3 to infrared light as imagewise;
b) A method for making a positive-working lithographic printing plate comprising the step of developing the image-exposed precursor with an aqueous alkaline developer, thereby dissolving the exposed areas.

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