DE602004010592T2 - Heat-sensitive precursor for a planographic printing plate - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION

The The present invention relates to a heat-sensitive lithographic Printing plate precursor, which is an infrared absorbing compound and in a separate, attached to the imaging layer Layer further contains a colorant.

GENERAL PRIOR ART

at lithographic printing using a so-called Druckmaster like a printing plate mounted on a drum of the printing press. The master surface enters lithographic image and a print is obtained by first printing ink applied to the image and then the color of the master a receiving material, usually paper, is transmitted. In conventional Lithographic wet printing both ink and fountain solution water-based on the lithographic image, made of oleophilic (or hydrophobic, i.e., ink-receptive, water-repellent) And hydrophilic (or oleophobic, i.e. hydrophilic, ink-repelling) Areas constructed, appropriate. In so-called driographic The lithographic image consists of ink-receptive and ink-repellent prints (ie color repellent) Areas and will be during of driographic printing, just apply printing ink to the master.

print Master are usually after the so-called computer-to-film process (CtF method, data-driven film production) where different Pre-press such as font selection, scanning, production of color separations, Scraping, trapping, layout and imposition done digitally and each color separation on a film exposure a graphic film is exposed. After development, the Film as a mask for the exposure of an image-forming material, as a printing plate precursor designated, used and after the development of the plate becomes obtained a printing plate, which is used as a master. Since about In 1995, the so-called computer-to-plate process (CtP process, direct digital printing plate imaging) to a significant extent in importance won. In this process, also referred to as direct-to-plate method, is waived on the production of a film and that because the digital document about a so-called platesetter transferred directly to a printing plate precursor becomes.

by virtue of their daylight resistance especially find thermal plates that are sensitive to heat or Infrared light is widely used in computer-to-plate processes. Such thermal materials can although directly with heat be applied, for example by means of a thermal head included but preferably a compound that converts absorbed light into heat, making them for Exposure with a laser, in particular infrared laser diodes suitable are. The generated in the imagewise exposure Heat dissolves you (physical) chemical process such as ablation, polymerization, Insolubilization by crosslinking of a polymer, decomposition or Coagulation of thermoplastic polymer latex particles from and after any development becomes a lithographic image receive.

In EP-A 1 106 347 For example, there is disclosed a development-free, heat-sensitive lithographic printing plate precursor which contains on an support an image-forming layer and a cover layer. The imaging layer contains hydrophobic thermoplastic polymer particles dispersed in a hydrophilic polymeric binder. The topcoat is water-soluble and contains a water-soluble cyanine dye capable of absorbing infrared light and converting it to heat.

In EP-A 816,070 discloses a thermosensitive element containing an image-forming layer on a hydrophilic support. This layer contains hydrophobic thermoplastic particles and a compound capable of converting light to heat, the compound being contained either in the image-forming layer or in a layer adjacent thereto. The image-forming layer is further provided with a cover layer having a thickness of between 0.1 and 3 μm.

In US Pat. No. 6,245,477 there is disclosed a negative-working heat-sensitive composition containing a water-soluble binder and particles dissolved therein. Each particle is composed of two components, ie a pigment and a thermoplastic resin. The heat-sensitive composition may be applied as a dry layer to a substrate, whereby the solubility of the dry coating in aqueous developer is lowered when heated.

In EP 770 494 discloses a method in which an image-forming material is imagewise exposed becomes. The image-forming material contains an image-recording layer containing a hydrophilic binder, a compound capable of converting light to heat, and particles of a hydrophobic thermoplastic polymer. Upon exposure, the polymer particles coalesce (coalesce) and the exposed areas are converted to a hydrophobic phase that forms the print areas of the master printer. The print cycle can be started immediately after the end of the exposure without any additional treatment, because the film is developed by the interaction between fountain solution and printing ink applied to the printing cylinder during the printing cycle. During the first turns of the printing press, the unexposed areas are removed from the carrier and form the non-printing areas of the plate.

Problematic in known from the prior art thermal plate materials, on the thermally induced coagulation of particles of a based thermoplastic polymer, but is that after development images obtained on such plates have a poor contrast exhibit. For this reason, it is difficult for the end user to to identify the plates (for example, to distinguish which plate to use which set of plates belongs). Furthermore, the evaluation of the quality of the on the Plate, which makes it difficult to decide which plate is to be corrected and which plates even again to be illustrated. Therefore needed one for one such plates a test pressure step, in which it can be evaluated which plates are ready for printing.

In EP 1 342 568 discloses a process for producing a lithographic printing plate in which an image-forming material having an image-recording layer containing a hydrophilic binder, a compound capable of converting light to heat, and particles of a hydrophobic thermoplastic polymer is image-wise exposed, whereby the polymer particles flow together. coalesce). Thereafter, the imagewise exposed material is developed by applying to the image-recording layer a gum solution which removes the unexposed areas of the coating from the support. The colorants contained in the image-recording layer ensure that a visible image is obtained after development.

BRIEF PRESENTATION OF THE PRESENT INVENTION

The inventors of the document known from the prior art EP-A 1 342 568 have found that the addition of these colorants in the imaging layer impairs the coalescence of the polymer particles in the exposed areas and causes a reduction in sensitivity. Another problem with these colorants is staining, ie, ink acceptance in the non-image areas during the printing process. This problem is due to the adsorption of colorants remaining on the hydrophilic surface of the unexposed areas of the substrate after development, as a result of which the hydrophilicity decreases and / or the hydrophobicity increases.

task The present invention is to provide a heat-sensitive Image forming element with improved image contrast and reduced Spotting after development. This task is solved by the precursor defined in claim 1 with the specific identifier, that the precursor in an image recording layer and / or a Contrast layer contains an infrared absorbing compound and the Contrast layer, d. H. a separate layer on the imaging layer, further includes a colorant.

Further specific embodiments The present invention is defined in the subclaims.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

Accordingly, it is an object of the present invention to provide a heat-sensitive lithographic printing plate precursor comprising in sequence: (i) a lithographic base having a hydrophilic surface, (ii) an imaging layer containing hydrophobic thermoplastic polymer particles, and (iii) a contrast layer; wherein the precursor in the imaging layer and / or the contrast layer contains an infrared absorbing compound, the contrast layer further contains a colorant capable of giving a visible image upon exposure and development of the precursor, and the image recording layer contains substantially no colorant. By " substantially none " it is understood that in the preparation of the image-recording layer, no colorant is added in the coating solution or dispersion without, however, precluding the image-recording layer from containing traces of colorant, e.g. Due to partial mixing between the image recording layer and the contrast layer or because of partial overdiffusion of the color by means of the contrast layer in the image recording layer. For this reason, one or more intermediate layers may be interposed between the contrast layer and the image recording layer. However, it is also possible to apply the contrast layer as a neighboring layer in direct contact with the image recording layer.

The Colorant may be a dye or a pigment. The dye or the pigment can be used as a colorant when the the dye or pigment containing layer to the human Eye should appear colored.

In a preferred embodiment In the present invention, the colorant is a pigment. It come various types of pigments, such as organic pigments, inorganic pigments, carbon black, metal powder pigments and fluorescent Pigments. However, organic pigments are preferred.

When specific examples of organic pigments are quinacridone pigments, quinacridonequinone pigments, Dioxazine pigments, phthalocyanine pigments, anthrapyrimidine pigments, Anthanthrone pigments, indanthrone pigments, flavanthrone pigments, perylene pigments, Diketopyrrolopyrrolpigmente, Perinonpigmente, Chinophthalonpigmente, Anthrachinonpigmente, Thioindigo pigments, benzimidazolone pigments, isoindolinone pigments, To name azomethine pigments and azo pigments.

• – blaufarbige Pigmente, wie C. I. Pigment Blue 1, C. I. Pigment Blue 2, C. I. Pigment Blue 3, C. I. Pigment Blue 15:3, C. I. Pigment Blue 15:4, C. I. Pigment Blue 15:34, C. I. Pigment Blue 16, C. I. Pigment Blue 22, C. I. Pigment Blue 60 und dergleichen, sowie C. I. Vat Blue 4, C. I. Vat Blue 60 und dergleichen,
• – rotfarbige Pigmente, wie C. I. Pigment Red 5, C. I. Pigment Red 7, C. I. Pigment Red 12, C. I. Pigment Red 48 (Ca), C. I. Pigment Red 48 (Mn), C. I. Pigment Red 57 (Ca), C. I. Pigment Red 57:1, C. I. Pigment Red 112, C. I. Pigment Red 122, C. I. Pigment Red 123, C. I. Pigment Red 168, C. I. Pigment Red 184, C. I. Pigment Red 202 und C. I. Pigment Red 209,
• – gelbfarbige Pigmente, wie C. I. Pigment Yellow 1, C. I. Pigment Yellow 2, C. I. Pigment Yellow 3, C. I. Pigment Yellow 12, C. I. Pigment Yellow 13, C. I. Pigment Yellow 14C, C. I. Pigment Yellow 16, C. I. Pigment Yellow 17, C. I. Pigment Yellow 73, C. I. Pigment Yellow 74, C. I. Pigment Yellow 75, C. I. Pigment Yellow 83, C. I. Pigment Yellow 93, C. I. Pigment Yellow 95, C. I. Pigment Yellow 97, C. I. Pigment Yellow 98, C. I. Pigment Yellow 109, C. I. Pigment Yellow 110, C. I. Pigment Yellow 114, C. I. Pigment Yellow 128, C. I. Pigment Yellow 129, C. I. Pigment Yellow 138, C. I. Pigment Yellow 150, C. I. Pigment Yellow 151, C. I. Pigment Yellow 154, C. I. Pigment Yellow 155, C. I. Pigment Yellow 180 und C. I. Pigment Yellow 185,
• – orangefarbige Pigmente, wie C. I. Pigment Orange 36, C. I. Pigment Orange 43 sowie ein Gemisch aus diesen Pigmenten,
• – grünfarbige Pigmente, wie C. I. Pigment Green 7, C. I. Pigment Green 36 sowie ein Gemisch aus diesen Pigmenten,
• – schwarzfarbige Pigmente, wie die von der Mitsubishi Chemical Corporation hergestellten Schwarzpigmente, zum Beispiel Nr. 2300, Nr. 900, MCF 88, Nr. 33, Nr. 40, Nr. 45, Nr. 52, MA 7, MA 8, MA 100 und Nr. 2200 B, die von der Columbian Carbon Co., Ltd., hergestellten Schwarzpigmente, zum Beispiel Raven 5750, Raven 5250, Raven 5000, Raven 3500, Raven 1255 und Raven 700, die von der Cabot Corporation hergestellten Schwarzpigmente, zum Beispiel Regal 400 R, Regal 330 R, Regal 660 R, Mogul L, Monarch 700, Monarch 800, Monarch 880, Monarch 900, Monarch 1000, Monarch 1100, Monarch 1300 und Monarch 1400, und die von Degussa hergestellten Schwarzpigmente, zum Beispiel Color Black FW 1, Color Black FW 2, Color Black FW 2 V, Color Black FW 18, Color Black FW 200, Color Black S 150, Color Black S 160, Color Black S 170, Printex 35, Printex U, Printex V, Printex 140 U, Special Black 6, Special Black 5, Special Black 4A und Special Black 4.

Specific examples of colorant-usable pigments are listed below (CI stands for Color Index / blue-colored pigment is a pigment which appears blue to the human eye, and the other colored pigments are to be considered in an analogous manner):

• Blue-colored pigments such as CI Pigment Blue 1, CI Pigment Blue 2, CI Pigment Blue 3, CI Pigment Blue 15: 3, CI Pigment Blue 15: 4, CI Pigment Blue 15:34, CI Pigment Blue 16, CI Pigment Blue 22 , CI Pigment Blue 60 and the like, as well as CI Vat Blue 4, CI Vat Blue 60 and the like,
• Red-colored pigments such as CI Pigment Red 5, CI Pigment Red 7, CI Pigment Red 12, CI Pigment Red 48 (Ca), CI Pigment Red 48 (Mn), CI Pigment Red 57 (Ca), CI Pigment Red 57: 1 , CI Pigment Red 112, CI Pigment Red 122, CI Pigment Red 112, CI Pigment Red 168, CI Pigment Red 184, CI Pigment Red 202 and CI Pigment Red 209,
• Yellow pigmented pigments such as CI Pigment Yellow 1, CI Pigment Yellow 2, CI Pigment Yellow 3, CI Pigment Yellow 12, CI Pigment Yellow 13, CI Pigment Yellow 14C, CI Pigment Yellow 16, CI Pigment Yellow 17, CI Pigment Yellow 73, CI Pigment Yellow, CI Pigment Yellow, CI Pigment Yellow, CI Pigment Yellow, CI Pigment Yellow, CI Pigment Yellow, CI Pigment Yellow, CI Pigment Yellow, CI Pigment Yellow, CI Pigment Yellow, CI Pigment Yellow, CI Pigment Yellow, CI Pigment Yellow CI Pigment Yellow 128, CI Pigment Yellow 129, CI Pigment Yellow 138, CI Pigment Yellow 150, CI Pigment Yellow 150, CI Pigment Yellow 151, CI Pigment Yellow 154, CI Pigment Yellow 155, CI Pigment Yellow 180 and CI Pigment Yellow 185,
• Orange pigments, such as CI Pigment Orange 36, CI Pigment Orange 43 and a mixture of these pigments,
• Green-colored pigments, such as CI Pigment Green 7, CI Pigment Green 36 and a mixture of these pigments,
• Black-colored pigments such as the black pigments produced by Mitsubishi Chemical Corporation, for example, No. 2300, No. 900, MCF 88, No. 33, No. 40, No. 45, No. 52, MA 7, MA 8, MA No. 100 and No. 2200 B, black pigments prepared by Columbian Carbon Co., Ltd., for example, Raven 5750, Raven 5250, Raven 5000, Raven 3500, Raven 1255, and Raven 700, the black pigments produced by Cabot Corporation For example, Regal 400 R, Regal 330 R, Regal 660 R, Mogul L, Monarch 700, Monarch 800, Monarch 880, Monarch 900, Monarch 1000, Monarch 1100, Monarch 1300 and Monarch 1400, and the black pigments produced by Degussa, for example Color Black FW 1, Color Black FW 2, Color Black FW 2 V, Color Black FW 18, Color Black FW 200, Color Black S 150, Color Black S 160, Color Black S 170, Printex 35, Printex U, Printex V, Printex 140 U, Special Black 6, Special Black 5, Special Black 4A and Special Black 4.

other Pigment types, such as brown pigments, violet pigments, fluorescent Pigments and metal powder pigments also come as colorants in question. As a colorant in the contrast layer can be a single Pigment or a mixture of two or more pigments used become.

Prefers for use in the present invention are blue-colored Pigments, such as cyan pigments, most preferably blue-colored Phthalocyanine pigments or phthalocyanine-containing pigments.

The pigments can be used with or without surface treatment of the pigment particles. According to another preferred embodiment of the present invention, the pigments are subjected to a surface treatment.

Possible methods for surface treatment are methods in which a surface coating of resin is applied, methods in which a surfactant is applied, and methods in which a reactive material (for example, a silane coupler, an epoxy compound, polyisocyanate or the like) adheres the pigment surface is applied. Suitable examples of surface-treated pigments are those in WO 02/04210 described modified pigments. As colorants for use in the present invention, those described in particular WO 02/04210 described modified blue pigments preferred.

The pigments of the invention have a particle size that preferably less than 10 μm, more preferably below 5 microns and most preferably less than 3 microns. As a method for dispersing the Pigments come any of the known dispersion methods in question, for the production of ink, toner or the like can be used. As dispersion devices are an ultrasonic disperser, a sand mill, an agitating ball mill, a bead mill, a super mill, a ball mill, a rotary mixer, a dispenser, a high-speed dispersing machine, a colloid mill, a Dynatron device, a three-roll mill and a pressure kneader to call. More about these mills can be found in "Latest Pigment Applied Technology "(CMC Publications, published in 1986).

To a preferred embodiment The present invention is used in the manufacture of the order In the contrast layer, coating solution used a pigment dispersion used. The pigment dispersion preferably contains one or more Dispersant. The dispersant stabilizes the dispersed Pigment particles and prevents coalescence of the particles. For this Purpose of suitable dispersants are preferably surfactants and / or Polymers which are soluble in the dispersion liquid.

The for the Pigment dispersion used inventive dispersion liquid is preferably an aqueous one Liquid. Such aqueous liquids are for example water and mixtures of water and water-miscible organic solvents, like alcohols, eg. Methanol, ethanol, 2-propanol, butanol, isoamyl alcohol, Octanol, cetyl alcohol, etc., glycols, e.g. As ethylene glycol, glycerol, N-methylpyrrolidone and methoxypropanol, and ketones, e.g. B. 2-propanone and 2-butanone, etc.

suitable Surfactants for use as dispersants in aqueous liquids are preferably anionic or nonionic surfactants or a combination from anionic and non-ionic Surfactants. The anionic surfactant preferably contains a sulfonate, Carboxylate or phosphate group. The nonionic surfactant contains preferably ethylene oxide groups and / or propylene oxide groups.

• GAFAC^TM RM710, ein Alkylphenoxypolyethoxydihydrogenphosphat von GENERAL ANILINS,
• ANTAROX^TM B290, ein Kondensationsprodukt von Rizinusöl mit einer etwa 40 Einheiten langen Polyethylenoxidkette von GENERAL ANILINS,
• ANTAROX^TM C0880, Nonylphenoxypolyethoxyethanol mit etwa 30 Polyethoxyeinheiten von GENERAL ANILINS,
• ULTRAVON^TM W, ein Natriumsalz eines Alkarylsulfonats von CIBA-GEIGY,
• MERSOLAT^TM H, ein Natriumsalz eines Alkylsulfonats von BAYER,
• MARLON^TM A-396, ein Natriumsalz eines Dodecylbenzolsulfonats von HÜLS,
• AEROSOL^TM OT, ein Natriumsalz des Bis-(2'-ethylhexyl)-esters von Sulfobernsteinsäure von AMERICAN CYANAMID,
• HOSTAPON^TM T, ein Natrium-β-(methyloleylamin)-ethylsulfonat von HOECHST,
• HOSTAPAL^TM BV, ein Natrium-2,4,6-tributylphenoxypolyethoxysulfonat von HOECHST,
• NEFAL^TM BX, ein Natriumsalz von 4,7-Dibutyl-2-sulfonaphthalin von BASF,
• AKYPO^TM OP-80, ein Natriumsalz von Octylphenoxypolyethoxyessigsäure von CHEMY,
• TERGITOL^TM 4, ein Natriumsalz von 1-Isobutyl-4-ethyloctylsulfat von UNION CARBIDE,
• ERKANTOL^TM BX, ein Natriumsalz von 4,7-Bis-(isobutyl)-2-Naphthalinsulfonsäure von BAYER und
• ALKANOL^TM XC, ein Natriumsalz von Tris-(isopropyl)-naphthalinsulfonsäure von DU PONT.

Examples of nonionic and anionic surfactants suitable as dispersing agents are:

• GAFAC ^™ RM710, an alkylphenoxy polyethoxydihydrogen phosphate from GENERAL ANILINS,
• ANTAROX ^™ B290, a condensation product of castor oil with an approximately 40 unit polyethylene oxide chain from GENERAL ANILINS,
• ANTAROX ^™ C0880, nonylphenoxypolyethoxyethanol with about 30 polyethoxy units from GENERAL ANILINS,
• ULTRAVON ^™ W, a sodium salt of an alkaryl sulfonate from CIBA-GEIGY,
• MERSOLAT ^™ H, a sodium salt of an alkyl sulfonate from BAYER,
• MARLON ^™ A-396, a sodium salt of a dodecylbenzenesulfonate from HÜLS,
• AEROSOL ^™ OT, a sodium salt of the bis (2'-ethylhexyl) ester of sulfosuccinic acid from AMERICAN CYANAMID,
• HOSTAPON ^™ T, a sodium β- (methyloleylamine) -ethyl sulfonate from HOECHST,
• HOSTAPAL ^™ BV, a sodium 2,4,6-tributylphenoxypolyethoxysulfonate from HOECHST,
• NEFAL ^™ BX, a sodium salt of 4,7-dibutyl-2-sulfonaphthalene from BASF,
• AKYPO ^™ OP-80, a sodium salt of octylphenoxypolyethoxyacetic acid from CHEMY,
• TERGITOL ^™ 4, a sodium salt of 1-isobutyl-4-ethyloctyl sulfate from UNION CARBIDE,
• ERKANTOL ^™ BX, a sodium salt of 4,7-bis (isobutyl) -2-naphthalenesulfonic acid from BAYER and
• ALKANOL ^™ XC, a sodium salt of tris (isopropyl) naphthalenesulfonic acid from DU PONT.

Typical examples of suitable as dispersants in aqueous liquids polymers are polymers with ionic or ionizable groups or polyethylene oxide-containing polymers. Examples of ionic or ionizable groups are acid groups or their salts, such as carboxylic acid, sulfonic acid, phosphoric acid or phosphonic acid. The acid groups in the polymer can be treated with an organic amine (eg Ammo nia, triethylamine, tributylamine, dimethylethanolamine, diisopropanolamine, morpholine, diethanolamine or triethanolamine) or an alkali metal (eg lithium, sodium or potassium). The polymer may be composed of an anionic group-containing monomer or two or more different types of anionic and / or nonionic group-containing monomers. Typical examples of anionic group-containing monomers are (meth) acrylic acid, crotonic acid, propyl (meth) acrylic acid, isopropyl (meth) acrylic acid, itaconic acid, fumaric acid, sulfoethyl (meth) acrylate, butyl (meth) acrylamide sulfonic acid and phosphoethyl (meth) acrylate, polystyrenesulfonic acid and their salts, such as sodium, potassium or ammonium salts. In general, the weight average molecular weight of the polymer is preferably between about 1,000 and 3,000,000.

In the preparation of dispersions of so-called self-dispersing pigments can be dispensed with the use of a dispersant. Typical examples of self-dispersing pigments are pigments whose surface has been rendered compatible with the dispersion liquid by a surface treatment. Typical examples of self-dispersing pigments in an aqueous medium are pigments containing ionic or ionizable groups or polyethylene oxide chains bonded to the particle surface. Examples of ionic or ionizable groups are acid groups or their salts, such as carboxylic acid, sulfonic acid, phosphoric acid or phosphonic acid and alkali metal salts of these acids. Suitable and preferred for use in the present invention examples of self-dispersing pigments are described in WO 02/04210 , Particularly preferred in the present invention are the in WO 02/04210 described blue-colored self-dispersing pigments, most preferably the in WO 02/04210 described phthalocyanine-containing blue-colored self-dispersing pigments.

Around Adsorption of the colorant on the hydrophilic surface of the To prevent plate in the non-exposed areas are the Pigment particles preferably not positively charged, d. H. is the number of the positive groups on the surface of the particles smaller than the number of negative groups. Preferably, the number of positive groups as possible kept small. For This purpose is used in the preparation of the pigment dispersion or the preparation of the coating solution of the contrast layer is preferred no cationic surfactants or polymers with cationic groups used.

In general, the amount of pigment in the contrast layer can be between about 0.005 g / m ² and 2 g / m ² , preferably between about 0.007 g / m ² and 0.5 g / m ² , particularly preferably between about 0.01 g / m ² and 0.2 g / m ² , very particularly preferably between about 0.01 g / m ² and 0.1 g / m ² .

In the present invention, as the colorant in the contrast layer of the present invention, a dye may also be used. Suitable colorants for use in the contrast layer are all known dyes, such as commercial dyes and the dyes described in, for example, "Dye Handbook" (edited by the Organic Synthetic Chemistry Association, published in 1970) which color the human eye Typical examples thereof are azo dyes, metal complex salt azo dyes, pyrazolone azo dyes, anthraquinone dyes, phthalocyanine dyes, carbionium dyes, quinoneimine dyes, methine dyes, etc. Preferred dyes include salt-forming organic dyes which can be selected from oil-soluble dyes and basic dyes are (CI stands for Color Index) Oil Yellow 101, Oil Yellow 103, Oil Pink 312, Oil Green BG, Oil Blue GOS, Oil Blue 603, Oil Black BY, Oil Black BS, Oil Black T-505, Victoria blue, crystal violet (CI42 555), methyl violet (CI42535), ethyl violet, rhodamine B (CI415170B), malachite green (CI42000) and methylene blue (CI52015). Furthermore, also come in GB 2,192,729 dyes described as colorants into consideration.

Around Adsorption of the colorant on the hydrophilic surface of the To prevent plate in the non-exposed areas, the Dye does not favor a net positive charge. As colorants are Dyes having an anionic group (or acid group) are preferred.

In general, the amount of dye in the contrast layer can be between about 0.005 g / m ² and 2 g / m ² , preferably between about 0.007 g / m ² and 0.5 g / m ² , particularly preferably between about 0.01 g / m ² and 0.2 g / m ² , very particularly preferably between about 0.01 g / m ² and 0.1 g / m ² .

As already mentioned, staining can be minimized by using anionic or nonionic surfactants and / or anionic groups (or acid groups) or nonionic surfactants as dispersants in the preparation of the pigment dispersion or as binders in the preparation of the coating solution of the contrast layer Hydrophilic group-bearing hydrophilic polymers are used. Thus, a partial mutual mixing of the contrast layer with the image recording layer on is reduced to a minimum, it is advantageous to lower the pH of the coating solution of the contrast layer. Preferably, the pH of the coating solution of the contrast layer is less than 4, more preferably less than 3, most preferably less than 2.5.

Of the Contrast of the image obtained after development depends on the amount and the extinction coefficient of the exposed one Areas of the plate remaining colorant. The contrast the image obtained after development is defined as the difference between the optical density in the exposed area and the optical Density in the unexposed area. The following optical Dens are in the supervision with the help of one with different filters (eg a cyan filter, a magenta filter, a yellow filter) equipped optical densitometer. The measurement of optical densities is done with a filter whose color is the color corresponds to the colorant. So z. B. for measuring the optical Density of a blue-colored Image layer uses a cyan filter.

To the Obtained a sufficient for the purpose of the present invention Contrasts is this difference in optical density preferably at least 0.3, more preferably at least 0.4, and most preferably at least 0.5. The contrast value is not subject to any specific upper limit usually does not exceed 3.0 or even 2.0 out.

To the Get one for Furthermore, the human eye of good visual contrast can also the color type of the colorant be important. Preferred colors for the colorant are cyan or blue colors, d. H. Under blue color of course a color that appears blue to the human eye.

A limited Spotting is characterized by a small difference between the optical density in the unexposed areas and the optical Density of the hydrophilic surface of the lithographic base. This difference is preferably below 0.25, more preferably below 0.20, most preferably below 0.15. To simulate the shelf life of the material is the printing plate precursor 7 days at 35 ° C and 80% relative humidity aged. The measurement of the optical density in the non-image areas after this aging is a more critical Test for the evaluation of staining, as if you only have the material 7 days at room temperature would age.

task The present invention further provides that the contrast layer preferably also a hydrophilic polymeric binder or a Contains surfactant.

typical examples for hydrophilic polymers suitable for use in the contrast layer are gum arabic, alginic acid, Pullulan, cellulose derivatives, such as carboxymethylcellulose, carboxyethylcellulose or Methylcellulose, (cyclo) dextrin, poly (vinyl alcohol), polystyrenesulfonic acid and their salts, such as sodium, potassium or ammonium salt, poly (vinylpyrrolidone), Polysaccharide, homo- and copolymers of acrylic acid, methacrylic acid or Acrylamide, a copolymer of vinyl methyl ether and maleic anhydride, a copolymer of vinyl acetate and maleic anhydride or a copolymer of styrene and maleic anhydride. Very particularly preferred polymers are homo- or copolymers of monomers with carboxylic acid groups, sulfonic acid or phosphonic acid groups or their salts, z. As (meth) acrylic acid, vinyl acetate, styrene sulfonic acid, vinyl sulfonic acid, vinyl phosphonic acid or Acrylamidepropanesulfonic.

In a further preferred embodiment, the contrast layer contains an ionic surfactant or nonionic surfactant, more preferably an anionic surfactant. Typical examples of anionic surfactants suitable for use in the contrast layer include alifates, abietates, hydroxyalkanesulfonates, alkanesulfonates, dialkylsulfosuccinates, straight chain alkylbenzenesulfonates, branched chain alkylbenzenesulfonates, alkylnaphthalenesulfonates, alkylphenoxypolyoxyethylenepropylsulfonates, salts of polyoxyethylene alkylsulfophenyl ethers, sodium N-methyl-N-oleyl taurates, monoamide disodium N alkyl sulfosuccinates, petrol sulfonates, sulfated castor oil, sulfated tallow oil, aliphatic alkyl ester sulfuric acid esters, alkyl alcohol acid ester salts, aliphatic monoglyceride sulfuric ester salts, sulfuric acid ester salts of polyoxyethylene alkylphenyl ethers, salts of sulfuric acid esters of polyoxyethylene styryl phenyl ethers, salts of alkyl phosphoric acid esters, salts of phosphoric acid esters of polyoxyethylene alkyl ethers, salts of phosphoric acid esters of polyoxy ethylene alkylphenyl ethers, partially saponified compounds of styrene-maleic anhydride copolymers, partially saponified compounds of olefin-maleic anhydride copolymers and naphthalenesulfonate formalin condensates. Of these anionic surfactants, dialkylsulfosuccinates, salts of alkylsulfuric acid esters and alkylnaphthalenesulfonates are particularly preferred. Other examples of suitable anionic surfactants include sodium dodecylphenoxybenzene disulfonate, the sodium salt of alkylated naphthalenesulfonate, disodium methylenedithaphthalene disulfonate, sodium dodecylbenzenesulfonate, sulfonated alkyldiphenyloxide, Am mono- or potassium perfluoroalkylsulfonate and sodium dioctylsulfosuccinate. Suitable examples of the nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene polystyrylphenyl ethers, polyoxyethylene polyoxypropylene alkyl ethers, polyoxyethylene-polyoxypropylene block polymers, partial esters of aliphatic glyceric acids, aliphatic sorbitan acid partial esters, aliphatic pentaerythritol acid partial esters, aliphatic propylene glycol monoesters, aliphatic saccharic acid partial esters, alicyclic polyoxyethylene sorbitan acid partial esters, Partial esters of aliphatic polyoxyethylene sorbic acids, aliphatic polyethylene glycol esters, partial esters of aliphatic polyglycerol acids, polyoxyethylenated castor oils, partial esters of aliphatic polyoxyethylene glycerol acids, aliphatic diethanolamides, N, N-bis-2-hydroxyalkylamines, polyoxyethylene alkylamines, aliphatic triethanolamine esters and trialkylamine oxides. Of these nonionic surfactants, polyoxyethylene alkylphenyl ethers and poloxyethylene polyoxypropylene block polymers are particularly preferred. Furthermore, anionic and nonionic fluorine and silicone surfactants are suitable.

It can two or more of the above surfactants are combined. So can to Example, a combination of two or more different anionic Surfactants or a combination of an anionic surfactant and a nonionic surfactant are preferred. It can also be mixtures of Surfactants and hydrophilic polymers can be used.

To a preferred embodiment of the present invention the contrast layer further comprises a mineral acid, an organic acid or an inorganic salt. Examples of the mineral acids are u. a. Nitric acid, Sulfuric acid, phosphoric acid and metaphosphoric acid. As examples of the organic acids are carboxylic acids, sulfonic acids, phosphonic or their salts, for. As succinates, phosphates, phosphonates, sulfates and sulfonates. As typical examples of the organic Acid are citric acid, acetic acid, oxalic acid, malonic acid, p-toluenesulfonic acid, tartaric acid, malic acid, lactic acid, levulinic acid, phytic acid and organic phosphonic acid to call. As examples of the inorganic salt is magnesium nitrate, monobasic sodium phosphate, dibasic sodium phosphate, nickel sulfate, sodium hexametaphosphate and sodium tripolyphosphate. Other inorganic salts can be used as a corrosion inhibitor, for. As magnesium sulfate or Zinc nitrate. The mineral acid, the organic acid and the inorganic salt can be used separately or in combination.

Except the above, the contrast layer may further comprise a wetting agent such as ethylene glycol, propylene glycol, triethylene glycol, butylene glycol, Hexylene glycol, diethylene glycol, dipropylene glycol, glycerol, trimethylolpropane and diglycerol. The wetting agent can be used individually or in combination be used. In general, the above wetting agent is used preferably in an amount between 1 and 25 wt .-%, based on the coating solution for the Contrast layer.

Further can the contrast coating solution also contain a chelate compound. Calcium ions and others Impurities in the dilution water can affect the pressure and pollute the printed matter. This problem can be caused by Addition of a chelate compound to be handled in the dilution water. Preferred examples of such a chelate compound are u. a. organic phosphonic acids or Phosphonoalkanetricarboxylic acids. Typical examples are potassium or sodium salts of ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, triethylenetetraminehexaacetic acid, hydroxyethylethylenediaminetriacetic acid, nitrilotriacetic acid, 1-hydroxyethane-1,1-diphosphonic acid and Amintri (methylene). Except These sodium or potassium salts of these chelating agents are also organic amine salts usable. The chelating agent is preferably in an amount between 0.001 and 1.0% by weight, based on the coating solution for the contrast layer, added.

Further can the coating solution for the Contrast layer containing an antiseptic and a defoamer. When examples for such an antiseptic are phenol, phenol derivatives, formalin, Imidazole derivatives, sodium dehydroacetate, 4-isothiazolin-3-one derivatives, benzoisothiazolin-3-one, Benzotriazole derivatives, amidine guanidine derivatives, quaternary ammonium salts, Pyridine derivatives, quinoline derivatives, guanidine derivatives, diazine, To mention triazole derivatives, oxazole and oxazine derivatives. The antiseptic is preferably added in such an amount that it has a stable action on bacteria, mold, yeast or the like having. Although the amount depends on the type of bacteria, mold and yeast, it is preferably between 0.01 and 4% by weight, based on the coating solution for the Contrast layer. Furthermore, can preferably two or more antiseptics are combined so that an efficient aseptic effect on a difference of Mold and bacteria is achieved. Defoaming agents are silicone defoamers prefers. Of these defoaming agents can either be a defoamer of emulsion / dispersion type or solubilized (solubilized) Type can be used. An appropriate amount of such defoaming agent is between 0.001 and 1.0% by weight, based on the coating solution for the contrast layer.

Except the The above ingredients may optionally further include a color attractant in the coating solution for the Contrast layer to be incorporated. Examples of such Color attractants are u. a. Turpentine oil, xylene, toluene, heptane, solvent Naphtha (also solution benzene or heavy benzene), light oil, white spirit, hydrocarbons, like petroleum fraction having a boiling point between about 120 ° C and about 250 ° C, diester phthalate (eg dibutyl phthalate, diheptyl phthalate, di-n-octyl phthalate, di (2-ethylhexyl) phthalate, Dinonyl phthalate, didecyl phthalate, dilauryl phthalate and butyl benzyl phthalate), aliphatic dibasic esters (e.g., dioctyl adipate, butyl glycol adipate, Dioctyl azelate, dibutyl sebacate and di (2-ethylhexyl) sebacate dioctyl sebacate), epoxidized triglycerides (eg, epoxidized soybean oil), ester phosphates (eg tricresyl phosphate, trioctyl phosphate and trischloroethyl phosphate) and plasticizer having a solidification point of at most 15 ° C and a boiling point of at least 300 ° C at 1 atmospheric pressure, such as esters of benzoates (eg benzyl benzoate). Examples of others Solvent, with these solvents can be combined are u. a. Ketones (eg cyclohexanone), halogenated hydrocarbons (eg, ethylene dichloride), ethylene glycol ethers (eg, ethylene glycol monomethyl ether, Ethylene glycol monophenyl ether and ethylene glycol monobutyl ether), aliphatic acids (eg, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, undecynic acid, lauric acid, tridecylic acid, myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, arachic acid, behenic acid, lignoceric acid, cerotic acid, heptacosanoic acid, montanic acid, melissic acid, dotriacontanic acid and isovaleric) and unsaturated aliphatic acids (eg, acrylic acid, crotonic, isocrotonic, undecylenic acid, oleic acid, elaidic, cetoleic, erucic acid, Butecidinsäure, sorbic acid, linoleic acid, linolenic acid, arachidonic acid, Propiolic acid, stearolic acid, clupanodonic acid, taric acid and Licanic). Preferably, the solvent is an aliphatic acid, at a temperature of 50 ° C liquid is, and preferably between 5 and 25 carbon atoms, especially preferably has between 8 and 21 carbon atoms. The color attraction can be used individually or in combination. The amount of color attraction is preferably between 0.01 and 10 wt .-%, more preferably from 0.05 to 5% by weight The above color attractant Can be used as an oil-in-water emulsion used or solubilized by means of a solubilizing agent.

The viscosity of the coating solution for the contrast layer can be improved by adding a viscosity-increasing compound such as poly (ethylene oxide), e.g. B. has a molecular weight between 10 ⁵ and 10 ⁷ , to a value between z. B. 1.7 and 5 cP are set. Such compounds can be used in a ratio between 0.01 and 10 g / l.

The in the process according to the invention used lithographic printing plate precursor is negative working and results in development of hydrophobic exposed areas and hydrophilic unexposed areas constructed lithographic image. The hydrophilic areas become formed by the carrier, the a hydrophilic surface or provided with a hydrophilic layer. The support can a sheet-like material, such as a plate, or be a cylindrical Element, like a sleeve-shaped plate, which can be pushed around a printing drum of a printing press. Preference is given to a metal support, such as A carrier made of aluminum or stainless steel.

A particularly preferred lithographic support is an electrochemically roughened and anodized aluminum support. The anodized aluminum support may be subjected to processing to improve the hydrophilic properties of the support surface. For example, by processing the support surface with a sodium silicate solution at elevated temperature, e.g. B. 95 ° C, silicate. Alternatively, a phosphate processing may be performed wherein the alumina surface is processed with an optional further inorganic fluoride-containing phosphate solution. Further, the alumina surface may be rinsed with a citric acid or citrate solution. This treatment can be carried out at room temperature or at a slightly elevated temperature between about 30 ° C and 50 ° C. Another interesting method is to rinse the alumina surface with a bicarbonate solution. Further, the alumina surface may be processed with polyvinylphosphonic acid, polyvinylmethylphosphonic acid, phosphoric acid esters of polyvinyl alcohol, polyvinylsulfonic acid, polyvinylbenzenesulfonic acid, sulfuric acid esters of polyvinylalcohol and acetals of polyvinylalcohols formed by reaction with a sulfonated aliphatic aldehyde. Further, it is obvious that one or more of these post treatments may be performed separately or in combination. More detailed descriptions of these treatments can be found in GB-A 1 084 070 . DE-A 4 423 140 . DE-A 4 417 907 . EP-A 659 909 . EP-A 537 633 . DE-A 4 001 466 . EP-A 292 801 . EP-A 291 760 and U.S. Patent 4,458,005 ,

According to a further embodiment, the support may also be a flexible support, optionally coated with a hydrophilic layer, hereinafter referred to as a "primer layer." The flexible support is, for example, paper, a plastic film or an aluminum support art Sheet films are a film of polyethylene terephthalate, polyethylene naphthalate, cellulose acetate, polystyrene, polycarbonate, etc. The plastic film backing may be opaque or translucent.

The primer layer is preferably a crosslinked hydrophilic layer obtained from a hydrophilic binder crosslinked with a curing agent such as formaldehyde, glyoxal, polyisocyanate or hydrolyzed tetraalkylorthosilicate. The latter crosslinking agent is particularly preferred. The thickness of the hydrophilic primer layer may vary between 0.2 and 25 microns and is preferably between 1 and 10 microns. More details about preferred embodiments of the primer layer can be found, for example, in US Pat EP-A 1 025 992 ,

The image-recording layer contains particles of a hydrophobic thermoplastic polymer. Specific examples of suitable hydrophobic polymers are e.g. Polyethylene, poly (vinyl chloride), poly (methyl (meth) acrylate), poly (ethyl (meth) acrylate), poly (vinylidene chloride), poly (meth) acrylonitrile, poly (vinylcarbazole), polystyrene or copolymers thereof. Polystyrene and poly (meth) acrylonitrile or their derivatives are very particularly preferred embodiments. According to such preferred embodiments, the thermoplastic polymer contains at least 50% by weight of polystyrene, more preferably at least 60% by weight of polystyrene. To achieve adequate resistance to organic chemicals, such as the hydrocarbons used in plate cleaners, the thermoplastic polymer preferably contains at least 5% by weight, more preferably at least 30% by weight, of units of a nitrogenous monomer or units which are monomers having a solubility parameter of more than 20, such as (meth) acrylonitrile. Suitable examples of such units of a nitrogen-containing monomer are described in U.S. Patent Nos. 5,429,866 and 5,429,854 EP-A 1 219 416 ,

To a very preferred embodiment For example, the thermoplastic polymer is a copolymer of styrene and acrylonitrile units in a weight ratio between 1: 1 and 5: 1 (styrene: acrylonitrile), e.g. B. in a ratio of 2: 1.

The Weight average molecular weight of the particles of a thermoplastic Polymers can vary between 5,000 and 1,000,000 g / mole. The Number average of the particle diameter of the hydrophobic particles is preferably below 200 nm, more preferably between 10 and 100 nm. The amount of particles of a hydrophobic thermoplastic polymer in the image recording layer is preferably between 20 wt .-% and 65 wt.%, more preferably between 25 wt.% and 55 wt.% and most preferably between 30% and 45% by weight.

• – wird das hydrophobe thermoplastische Polymer in einem organischen was serunmischbaren Lösungsmittel gelöst,
• – wird die so erhaltene Lösung in Wasser oder einem wässrigen Medium dispergiert und
• – wird das organische Lösungsmittel abgedampft.

The particles of a hydrophobic thermoplastic polymer are contained as a dispersion in an aqueous coating liquid of the image recording layer and can be prepared according to the methods disclosed in U.S. Pat US 3 476 937 be prepared described methods. In a further process which is particularly suitable for the preparation of an aqueous dispersion of the particles of a thermoplastic polymer:

• The hydrophobic thermoplastic polymer is dissolved in an organic, water-immiscible solvent,
• - The solution thus obtained is dispersed in water or an aqueous medium and
• - The organic solvent is evaporated.

The Contains image recording layer preferably a hydrophilic binder, e.g. B. homopolymers and Copolymers of vinyl alcohol, acrylamide, methylolacrylamide, methylolmethacrylamide, Acrylic acid, methacrylic acid, Hydroxyethyl acrylate, hydroxyethyl methacrylate or maleic anhydride vinylmethyl ether copolymers. The hydrophilicity the (co) polymer or (co) polymer mixture used is preferred higher or higher equal to the hydrophilicity of at least 60% by weight, preferably to 80% by weight hydrolyzed polyvinyl acetate.

The thermosensitive Lithographic printing plate precursor also contains an infrared light absorbing compound. This compound is preferably a dye or a pigment having an absorption maximum in the infrared wavelength range and is able to convert infrared light into heat. Especially preferred become infrared light absorbing dyes. Especially usable and particularly preferred infrared absorbing dyes are infrared cyanine dyes, infrared merocyanine dyes, infrared methine dyes, Infrared naphthoquinone dyes or infrared squarylium dyes. Most notably preferred infrared cyanine dyes are the anionic infrared cyanine dyes, especially those with two sulfonic acid groups. Very particular preference is given to infrared cyanine dyes having two Indolenine and at least two sulfonic acid groups.

The infrared absorbing compound is in the image recording layer and / or the contrast layer included. The ratio of the infrared absorbing compound in the heat-sensitive coating is preferably between 0.25 and 20% by weight, more preferably between 0.5 and 10% by weight, based on the whole coating.

To the most preferred embodiment of the present invention the precursor a combination of an imaging layer, the infrared absorbing dye as infrared light contains absorbent compound, and a contrast layer containing a pigment as a colorant. Particularly preferred in the present invention is a combination from an anionic infrared cyanine dye-containing Image recording layer and a contrast layer which is a self-dispersing or surface-treated Contains pigment.

The Imaging layer may contain other ingredients, like additional Binders, development inhibitors or development accelerators.

The printing plate precursors used according to the invention are exposed to infrared light, for example by means of an infrared laser. Preferred is a near infrared light having a wavelength between about 700 and about 1500 nm emitting laser, e.g. A semiconductor laser diode, an Nd: YAG laser or a Nd: YLF laser. The laser power required depends on the sensitivity of the imaging layer, the pixel dwell time of the laser beam as determined by the beam width (a typical value at 1 / e ^{2 of} the maximum intensity is between 10 and 25 μm for modern platesetters), the scanning speed and the resolution of the Gelichters (ie the number of addressable pixels per unit length, often expressed in dots per inch or dpi / typical values are between 1,000 and 4,000 dpi). There are two types of common laser imagers, ie an inner drum plate setter (ITD platesetter) and an outer drum plate setter (XTD platesetter). ITD platesetters for thermal plates are usually characterized by very high scanning speeds up to 500 m / s and may require a laser power of several watts. XTD platesetter for thermal plates work at a lower scanning speed, z. Between 0.1 m / s and 10 m / s, and a typical laser power between about 200 mW and about 1 W.

Under Action of during The heat generated by the exposure step melts or coagulates the heat Particles of a hydrophobic thermoplastic polymer and form This results in a hydrophobic phase covering the printing areas of the printing plate will form. Coagulation may occur as a result of coalescence (coalescence), Softening or melting the particles of a thermoplastic polymer under the influence of heat. The coagulation temperature of the polymer particles is not subject to any specific upper limit, but should be enough below the decomposition temperature the particles of a hydrophobic thermoplastic polymer are. The coagulation temperature is preferably at least 10 ° C below the temperature, occurs in the decomposition of the polymer particles. The coagulation temperature is preferably more than 50 ° C, more preferably more than 100 ° C.

in the Development step becomes the unexposed areas of the image recording layer by removing a developer solution without doing so essentially a distance of the exposed areas is triggered d. H. without the treatment being so on the exposed areas affects the color attractiveness of the exposed areas becomes unacceptable. The developer solution may be water, an aqueous solution or an aqueous alkaline solution be. The development by order of a developer solution can with mechanical wiping, z. B. by means of a brush roller, be combined. The developer solution can either manually or in a development machine by z. B. wiping with a saturated swab, Dipping, coating, spin coating, spraying or pouring attached become.

In a further embodiment of the present invention, the development of the imagewise exposed printing plate precursor can also be carried out by first mounting the precursor onto a printing cylinder of a printing press and then wetting the plate surface with fountain solution while the printing cylinder is rotating and / or inking it with printing ink. The end user preferably has enough latitude in plate handling (plate loading, mounting the plate on the press, etc.). For this reason, it may happen that he fails to avoid that the plate surface with ink (or with inked areas of the plate) comes into contact before the plate is wetted by the fountain solution. The ink-soiled areas during the on-press development step are difficult to develop (hereinafter referred to as "cleanout"). This object is achieved by adding a hydrophilic polymer or surfactant in the contrast layer. During on-press development, as known from prior art documents, it is more difficult to clean the plate when the ink is first applied to the plate surface. To the verrin like the number of prints you need to print before you can get a cleaned plate surface, it is recommended for the end user to wet the plate first with fountain solution and then color it with ink. The presence of the contrast layer, which further contains a hydrophilic polymer or surfactant, unexpectedly eliminates the need for the end user to first apply the dampening water to the plate surface to reduce the number of prints that need to be printed before obtaining a cleaned plate surface ,

In yet another embodiment the present invention, the printing plate precursor to a Clamped printing cylinder of a printing press and then exposed imagewise after which they may be developed on the printing press is made by dampening water and / or with rotating printing cylinder Ink on the plate surface is (are) attached.

EXAMPLES

COMPARATIVE EXAMPLE 1

Production of the lithographic support

A 0.30 mm thick aluminum foil is degreased by immersing the foil in an aqueous solution containing 40 g / l of sodium hydroxide for 8 seconds at 60 ° C. and rinsing with demineralized water for 2 seconds. The film is then electrochemically electrochemically reacted at a temperature of 33 ° C. and a current density of 90 A / dm ^{2 for} 15 seconds in an aqueous solution containing 12 g / l hydrochloric acid and 38 g / l aluminum sulfate (18 hydrate) roughened. After rinsing with demineralized water for 2 seconds, the film of the aluminum foil is removed by etching for 4 seconds at 70 ° C with an aqueous solution containing 155 g / l sulfuric acid, followed by rinsing with demineralized water at 25 ° C for 2 seconds. Subsequently, the film is anodized at a temperature of 45 ° C and a current density of 30 A / dm ^{2 for} 13 s in an aqueous solution containing 155 g / l sulfuric acid, then washed with demineralized water for 2 s, then for 10 s at Post-processed at 40 ° C. with a solution containing 4 g / l polyvinylphosphonic acid, rinsed with demineralized water at 20 ° C. for 2 s and finally dried.

The support thus obtained has a surface topography with an average roughness Ra of 0.22 μm and an anodic weight of 4.0 g / m ² Al ₂ O ₃ .

Production of printing plate precursor

• – 630 mg/m² Teilchen eines mit einem anionischen Netzmittel stabilisierten Copolymers aus Styrol und Acrylnitril (Gewichtsverhältnis 60/40) mit einer mittleren Teilchengröße von 65 nm,
• – 84 mg/m² des Infrarot-Farbstoffes Farbstoff-1,
• – 84 mg/m² der hochmolekularen Polyacrylsäure GLASCOL E15, die von ALLIED COLLOIDS vertrieben wird, und
• – 25 mg/m² des Kupferphthalocyaninpigments CABOJET 250, das von der CABOT CORPORATION vertrieben wird.

The lithographic aluminum support prepared as described above is coated with an aqueous coating solution at a wet thickness of 30 g / m ² . This aqueous coating solution is adjusted to a pH of 3.6 with ammonia and contains the following ingredients whose dry strengths are given in the image-recording layer composition in the following table:

• 630 mg / m ² particles of an anionic surfactant-stabilized copolymer of styrene and acrylonitrile (weight ratio 60/40) having an average particle size of 65 nm,
• 84 mg / m ^{2 of} the infrared dye Dye-1,
• - 84 mg / m ^{2 of} the high molecular weight polyacrylic acid GLASCOL E15 marketed by ALLIED COLLOIDS, and
• - 25 mg / m ^{2 of} the copper phthalocyanine pigment CABOJET 250 marketed by CABOT CORPORATION.

Alterung, Belichtung, Entwicklung und Messungen der optischen DichteThe infrared dye Dye-1 corresponds to the following formula:

Aging, exposure, development and optical density measurements

• – Bedingung 1: 7 Tage bei 35°C und 80% relativer Feuchtigkeit,
• – Bedingung 2: 7 Tage bei Zimmertemperatur und relativer Umgebungsfeuchtigkeit (Messwert: 50%).

The printing plate precursors thus obtained are aged under two different conditions:

• Condition 1: 7 days at 35 ° C and 80% relative humidity,
• Condition 2: 7 days at room temperature and ambient relative humidity (reading: 50%).

After aging, the plates are exposed using a CREO TRENDSETTER 3244 TH957 Platesetter available from CREO, Burnaby, Canada, with the following characteristics: power 40 watts, wavelength 830 nm, drum diameter 286 mm, number of rays 192, beam width 10.6 × 2 , 5 μm (slow scan × fast scan), operating at a power of 275 mJ / cm ² on the disk, a drum speed of 150 ppm and a resolution of 2,400 dpi.

Afterwards the exposure is developed in one of the AGFA-GEVAERT plates NV distributed HWP45 processor equipped with RC520, a stoving gum solution AGFA-GEVAERT NV, filled is.

To Development is the optical density of the illuminated areas and unexposed areas with a GRETAG D19C densitometer behind a cyan filter measured. These optical densities are behind in the supervision a cyan filter is measured, as a reference, the optical density an uncoated aluminum hydrophilic support is taken.

The results obtained are listed in Table 1.

INVENTIVE EXAMPLE 1

The preparation of the printing plate precursor of Inventive Example 1 is carried out analogously to Comparative Example 1, but with the difference that the 25 mg / m ^{2 of} the copper phthalocyanine CABOJET 250 in the image recording layer are omitted and the above-described image recording layer is coated with a separate contrast layer. The application of the contrast layer is carried out in a wet layer thickness of 20 g / m ² from an aqueous coating solution having a pH adjusted to 2.5 with HCl and contains as the only ingredient CABOJET 250, which gives a dry starch of 21 mg / m ² . After drying the coating, the aging, the exposure, the development and the measurement of the optical density are carried out analogously to Comparative Example 1.

The results obtained are listed in Table 1.

INVENTIVE EXAMPLE 2

The preparation of the printing plate precursor of Inventive Example 2 is carried out analogously to Example 1, but with the difference that instead of the 21 mg / m ^{2 of} the copper phthalocyanine CABOJET 250 21 mg / m ^{2 of} the copper phthalocyanine pigment HELIOGEN BLUE D7565 from BASF (Heliogen Blue D7565 is a copper and chlorine-free blue pigment) can be used. After drying the coating, the aging, the exposure, the development and the measurement of the optical density are carried out analogously to Comparative Example 1.

The results obtained are listed in Table 1.

INVENTIVE EXAMPLE 3

The printing plate precursor of Inventive Example 3 is prepared analogously to Example 1, except that the contrast layer solution is brought to a pH of 3.6 with HCl and the amount of the copper phthalocyanine pigment CABOJET 250 is from 21 mg / m ² to 42 mg / m ^{2 is} increased. After drying the coating, the aging, the exposure, the development and the measurement of the optical density are carried out analogously to Comparative Example 1.

The results obtained are listed in Table 1.

INVENTIVE EXAMPLE 4

The preparation of the printing plate precursor of Inventive Example 4 is carried out analogously to Erfin Example 3, but with the difference that the contrast layer solution is brought to a pH of 2.5 with HCl. After drying the coating, the aging, the exposure, the development and the measurement of the optical density are carried out analogously to Comparative Example 1.

The results obtained are listed in Table 1.

INVENTIVE EXAMPLE 5

The Preparation of printing plate precursor of the inventive example 5 is carried out analogously to Example 3 according to the invention, but with the difference being that the contrast layer solution is treated with HCl to a pH of 2 is brought. After drying the coating, the aging, the exposure, the development and the measurement of the optical density made analogously to Comparative Example 1.

The results obtained are listed in Table 1.

INVENTIVE EXAMPLE 6

The Preparation of printing plate precursor of the inventive example 6 is carried out analogously to Inventive Example 3, but with the difference being that the contrast layer solution is treated with HCl to a pH of 1 is brought. After drying the coating, the aging, the exposure, the development and the measurement of the optical density made analogously to Comparative Example 1.

The results obtained are listed in Table 1.

INVENTIVE EXAMPLE 7

The preparation of the printing plate precursor of Example 7 according to the invention is carried out analogously to Example 5, but with the difference that a copolymer of acrylic acid and maleic acid (Aldrich 41,605-3) obtainable from ALDRICH is added to the contrast layer solution, which has a dry layer thickness of 63 mg after drying. m ² . After drying the coating, the aging, the exposure, the development and the measurement of the optical density are carried out analogously to Comparative Example 1.

The results obtained are listed in Table 1.

INVENTIVE EXAMPLE 8

The printing plate precursor of Example 8 according to the invention is prepared analogously to Example 7, but with the difference that a copolymer of acrylic acid and maleic acid (Aldrich 41,605-3) obtainable from ALDRICH is added to the contrast layer solution, which after drying has a dry layer thickness of 84 mg / m ² . After drying the coating, the aging, the exposure, the development and the measurement of the optical density are carried out analogously to Comparative Example 1.

The results obtained are listed in Table 1.

INVENTIVE EXAMPLE 9

The preparation of the printing plate precursor of Inventive Example 9 is carried out analogously to Example 5 according to the invention, but with the difference that the 84 mg / m ^{2 of} the infrared dye Dye-1 is not used in the image recording layer but in the same amount in the contrast layer. After drying the coating, the aging, the exposure, the development and the measurement of the optical density are carried out analogously to Comparative Example 1.

The results obtained are listed in Table 1.

COMPARATIVE EXAMPLE 2

• – 630 mg/m² Teilchen eines mit einem anionischen Netzmittel stabilisierten Copolymers aus Styrol und Acrylnitril (Gewichtsverhältnis 60/40) mit einer mittleren Teilchengröße von 65 nm und
• – 42 mg/m² des Kupferphthalocyaninpigments CABOJET 250, das von der CABOT CORPORATION vertrieben wird.

The lithographic aluminum support prepared as described in Comparative Example 1 is coated at a wet layer thickness of 30 g / m ² with an aqueous coating solution. This watery Coating solution is adjusted to a pH of 3.6 with ammonia and contains the following ingredients whose dry strengths are given in the imaging layer composition in the table below:

• 630 mg / m ² particles of an anionic surfactant stabilized copolymer of styrene and acrylonitrile (weight ratio 60/40) having an average particle size of 65 nm and
• - 42 mg / m ^{2 of} the copper phthalocyanine pigment CABOJET 250 marketed by CABOT CORPORATION.

• – 84 mg/m² der hochmolekularen Polyacrylsäure GLASCOL E15, die von ALLIED COLLOIDS vertrieben wird, und
• – 84 mg/m² des Infrarot-Farbstoffes Farbstoff-1.

After drying, this image-recording layer is coated from an aqueous coating solution in a wet layer thickness of 20 g / m ² with a separate layer. This aqueous coating solution has been pre-adjusted to a pH of 3.3 with HCl and contains the following ingredients whose dry strengths are given in the contrast layer composition in the table below:

• - 84 mg / m ^{2 of} the high molecular weight polyacrylic acid GLASCOL E15 marketed by ALLIED COLLOIDS, and
• - 84 mg / m ^{2 of} the infrared dye dye-1.

To Drying the coating, aging, exposure, Development and measurement of optical density analogous to Comparative Example 1 made.

The results obtained are listed in Table 1. Table 1: Example number pH of the contrast layer density Density in non-image areas after 7 days of aging at room temperature Density in non-image areas after 7 days of aging at 35 ° C and 80% RH See Example 1 - 0.68 0.063 0,610 invent. example 1 2.5 0.62 0,000 0,149 invent. Example 2 2.5 0.64 0,000 0,186 invent. Example 3 3.6 0.83 0,013 0,242 invent. Example 4 2.5 0.88 0,012 0.210 invent. Example 5 2 0.74 0,030 0,155 invent. Example 6 1 0.52 0,007 0.140 invent. Example 7 2 0.81 0,000 0,120 invent. Example 8 2 0.76 0,025 0.109 invent. Example 9 2 0.52 0,018 0,051 See Example 2 3.3 0.37 0.627 0.721

The Examples in Table 1 show that when using the colorant in a contrast layer, the optical density in the non-image areas after 7 days Aging at room temperature and after 7 days of aging at 35 ° C and 80% relative humidity is greatly reduced. In certain cases even not to distinguish the optical density from zero, what is on it indicates that no staining has occurred.

These Reducing staining can be achieved by lowering the pH the coating solution of Contrast layer even stronger become.

These Reducing staining can be further enhanced, by not including the infrared dye in the image-recording layer, but used in the contrast layer and the contrast layer Carboxylic acid groups containing polymer is added. In both cases there will be a reduction the adsorption of hydrophobic compounds on the hydrophilic surface of the carrier after development, thereby limiting the staining.

The comparative examples show that staining occurs when the colorant is used in the image-recording layer. Even if the infrared dye and the hydrophilic binder are not in the picture recording layer but are used in the contrast layer, staining occurs when the colorant is contained in the image recording layer.

Claims (11)

A heat-sensitive lithographic printing plate precursor comprising in sequence: (i) a lithographic base having a hydrophilic surface, (ii) an imaging layer containing hydrophobic thermoplastic polymer particles, and (iii) a contrast layer wherein the precursor is in the imaging layer and / or or the contrast layer contains an infrared-absorbing compound, characterized in that the contrast layer further contains a colorant capable of giving a visible image upon exposure and development of the precursor and the image-recording layer contains substantially no colorant. heat-sensitive Precursor according to claim 1, characterized in that the colorant a pigment is. heat-sensitive Precursor according to claim 2, characterized in that the pigment is a self-dispersing pigment or surface-treated pigment. heat-sensitive Precursor according to claim 3, characterized in that the pigment anionic or acid groups on the surface contains. heat-sensitive Precursor according to one of the preceding claims, characterized the contrast layer further comprises a hydrophilic polymer and / or contains a surfactant. heat-sensitive Precursor according to claim 5, characterized in that the hydrophilic Polymer contains anionic groups or nonionic groups. heat-sensitive Precursor according to claim 5, characterized in that the surfactant an anionic or nonionic Surfactant is. heat-sensitive Precursor according to claim 5, characterized in that the hydrophilic Polymer is a polymer or copolymer of polyvinyl alcohol, poly (meth) acrylic acid, polystyrenesulfonic acid, poly (meth) acrylamide, Polyhydroxyethyl (meth) acrylate, polyvinyl methyl ether, polyvinylpyrrolidone, Polysaccharide, gelatin, gum arabic, alginic acid or a salt thereof is. heat-sensitive Precursor according to one of the preceding claims, characterized that the particles of a hydrophobic thermoplastic polymer Copolymer of styrene and at least 5 mol% of a nitrogen-containing Monomers included. A marked by the following steps Process for making a lithographic printing plate precursor: - Provide a lithographic base with a hydrophilic surface, - coating the hydrophilic surface containing a particle of a hydrophobic thermoplastic polymer Image recording layer and - Coating of the image recording layer with a contrast layer, wherein the precursor is an infrared light absorbing compound in the image recording layer and / or contains the contrast layer, in which the contrast layer further contains a colorant capable of Exposure and development of the precursor to give a visible picture and wherein the image-recording layer is substantially no colorant contains. A marked by the following steps Method for producing a lithographic printing plate: - Provide a lithographic printing plate precursor according to any one of the preceding claims 1 to 9, - Exposure the precursor with infrared light, the particles of a thermoplastic Polymer in the exposed areas of the image recording layer flow together and - Development the precursor, wherein the image recording layer and the contrast layer be removed in the non-exposed areas of the carrier.