DE69812871T2 - Heat-sensitive recording element and method for producing planographic printing plates therewith - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a heat sensitive Material for the production of a lithographic printing plate: the The present invention further relates to a method for the production a printing plate using this heat sensitive material.

GENERAL PRIOR ART

Lithographic printing is the process in which the printing of specially manufactured surfaces of which certain areas attract lithographic paint and other areas after wetting with water will repel the paint. The ink-attracting areas form the printing image areas, the ink repellent Areas the background areas.

In the field of photolithography a photographic material in the photo-exposed areas (negative working) or in the non-exposed areas (positive working). on image-wise attracting oily or bold colors on a hydrophilic background made.

More common in manufacturing lithographic printing plates, also as surface lithographic plates or planographic printing plates, becomes a support that has an affinity for water has or such affinity obtained through chemical processing with a thin layer coated with a radiation sensitive composition. As layers with a radiation-sensitive composition are photosensitive polymer layers, the diazo compounds, dichromate-sensitive hydrophilic colloids and a variety of synthetic photopolymers contain. In particular, diazo-sensitized layer dressings widely used.

While the imagewise exposure the exposed areas of the photosensitive layer insoluble and the unexposed areas remain soluble. The printing plate will subsequently with a suitable liquid designed to contain that contained in the unexposed areas Remove diazonium salt or diazo resin.

On the other hand, there are also procedures in which for the production of printing plates imaging elements are used that are rather sensitive to heat are sensitive to radiation. With the as described above Production of a printing plate used radiation sensitive Imaging elements have the particular disadvantage that they face Protected from light Need to become. Furthermore, they have a problematic sensitivity regarding shelf life and lower resolution. There is a clear trend in the market towards heat-sensitive Printing plate precursors from.

For example, Research describes Disclosure No. 33303, January 1992, a heat sensitive imaging member, that on a support a cross-linked hydrophilic layer with thermoplastic polymers Particles and an infrared absorbing pigment such as e.g. B. contains soot. at imagewise exposure with The thermoplastic polymers coagulate using an infrared laser Particles imagewise, whereby the surface of the imaging element in these areas without further development is made to attract colors. The disadvantage of this method is considered the high susceptibility to damage the printing plate obtained, because the non-printing areas can be exercise light pressure on these areas. Besides, can the lithographic performance of such a printing plate under critical Conditions will be weak and therefore such a printing plate a limited have lithographic printing leeway.

EP-A 514 145 describes a heat-sensitive Imaging element reveals a layer with particles of the core / shell type with a water-insoluble thermally softenable core component and one in an aqueous alkaline Medium soluble or swellable casing component contains. By direct imagewise exposure of the imaging element with red or infrared laser light selected Partially coalesce particles and create an image after which the non-coalesced particles selectively by means of an aqueous alkaline Developer. Afterwards the imaging element subjected to a baking stage. However, one thus preserved Printing plate has a low print run.

EP-A 599 510 discloses a heat-sensitive imaging element with a substrate which (i) is coated with a layer which (1) a disperse phase with a water-insoluble thermally softenable component A and (2) one from an in an aqueous , preferably aqueous-alkaline medium soluble or swellable component B existing binder or dispersant, at least one of components A and B containing a reactive group or a precursor thereof, whereby the layer at high temperature and / or upon exposure to actinic radiation made insoluble and (ii) which contains a substance which is very radiation absorbing and transfers the energy thus obtained as heat to the disperse phase, thereby triggering at least partial coalescence of the layer becomes. After imagewise exposure of the imaging member and development of the imagewise exposed plate, the plate is heated and / or actinic radiation to render it insoluble. The print run of a printing plate thus obtained is low.

EP-A 625 728 discloses an imaging element with a layer opposite UV and IR radiation is sensitive and both positive working can also be negative working. This layer contains a resol resin, a novolak resin, a latent Bronsted acid and an infrared radiation absorbing substance. The print results one by irradiating and developing this imaging element obtained lithographic printing plate are weak.

US Pat. No. 5,340,699 is almost identical to EP-A 625 728, but with the difference that it is a Process for obtaining a negative working, towards infrared laser light sensitive imaging element disclosed. The IR sensitive Contains layer a resol resin, a novolak resin, a latent Bronsted acid and an infrared radiation absorbent substance. The printing results of one by radiation and development of this lithographic imaging element obtained Pressure plate are weak.

U.S. Patent 4,708,925 discloses a positive working imaging element with a radiation sensitive Composition that is an alkali-soluble Novolak resin and an onium salt and optionally an IR sensitizer contains. After imagewise exposure this imaging element. with UV light - visible light - or alternatively IR radiation and a subsequent one Development stage with an aqueous alkaline liquid a positive working printing plate is obtained. The print results one by irradiating and developing this imaging element obtained lithographic printing plate are weak.

EP-A 0 800 928 describes a heat-sensitive Imaging element disclosed that on a hydrophilic surface lithographic base an image-forming layer with hydrophobic thermoplastic, in a water-insoluble, alkali-soluble or alkali-swellable resin-dispersed polymer particles and a Contains connection the light in warmth capable of converting and in the imaging layer or one adjacent layer is included, the alkali-swellable or alkali-soluble Resin contains phenolic hydroxyl groups and / or carboxyl groups. at Exposure with short pixel times of the heat sensitive imaging element however, ablation occurs on the exposed areas, resulting in a insufficient color attraction.

Analog imaging elements that on a hydrophilic surface of a lithographic base imaging layer with hydrophobic thermoplastic polymers, in a water or alkali soluble or water or alkali swellable resin dispersed particles and contain a compound that can convert light into heat and in the imaging layer or a layer adjacent to it is described in z. B. EP-A 770 494, EP-A 770 495, EP-A 770 496, EP-A 770 497, EP-A 773 112, EP-A 773 113, EP-A 774 364, EP-A 800 928, EP-A 0 832 739, EP-A 0 839 648, EP-A 0 839 647 and EP-A 0 849 091. EP-A 0 832 739, EP-A 0 839 648, EP-A 0 839 647 and EP-A 0 849 091 represent the current state of the art in accordance with Article 54 (3) (4) EPC. Most of these patent applications include as thermoplastic polymer particles poly (meth) acrylate latices used and no specific hydrophilic resin is mentioned. As Connection that light into heat convert soot, mostly become soot or an IR-absorbing Dye mentioned.

To make one described above Imaging element that can be developed on the press preferably infrared-absorbing dyes are used. Is soot yes polluting the press when removing the unexposed areas. On the other hand, the fact is that at Use of infrared light absorbing dyes during the Development on the press did not completely remove the unexposed Areas is achieved, which leads to foam formation.

Furthermore, there is an improvement the color attraction and sensitivity of the imaging elements welcome .

TASKS OF PRESENT INVENTION

Object of the present invention is a heat sensitive Imaging element with higher Provide sensitivity that can be developed on the press is.

Another task of the present Invention is a heat sensitive Imaging element for the practical production of a lithographic To provide printing plate with excellent color attraction.

Yet another object of the present Invention is a heat sensitive Imaging element for the practical production of a lithographic To provide printing plate with good developability.

Yet another object of the present invention is to provide a heat-sensitive imaging member for practically making a lithographic printing plate without foaming len.

Yet another object of the present Invention is to provide a method in which using the imaging element in a practical way a negative working lithographic printing plate, the prints with excellent printing properties results, can be produced.

Other tasks of the present Invention are apparent from the description below.

SHORT PRESENTATION OF THE PRESENT INVENTION

The tasks according to the invention are solved through a heat sensitive Imaging element with a lithographic base a hydrophilic surface an imaging layer with thermoplastic particles Homopolymer or a copolymer of styrene and a carboxyl-containing contains hydrophilic polymer, characterized in that the Imaging element further an anionic IR absorbing Cyanine dye in or on an imaging layer bordering layer contains.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

We have found that under Use of an imaging element described above after method according to the invention High quality lithographic printing plates are available with which prints with excellent Color attraction can be made. We have in particular found that the Printing plates are high quality and manufactured in a practical way become what economic and ecological Brings advantages.

The image-forming layer or an adjacent layer contains an anionic IR-cyanine dye, that as light in warmth converting connection. It can be a mixture of anionic IR cyanine dyes are used, but use is preferred of a single anionic IR cyanine dye. Particularly usable anionic IR cyanine dyes are IR cyanine dyes with at least two Sulfonic acid groups. IR cyanine dyes with two indolenine dyes are particularly preferred. and at least two sulfonic acid groups. Compound I of the structure below is very particularly preferred. With compound II of the structure below are also very great good results can be achieved.

The amount of the anionic IR cyanine dye in the image-forming layer is preferably between 1% by weight and 40% by weight, particularly preferably between 2% by weight and 30% by weight and very particularly preferably between 5% and 20% by weight on the imaging layer.

According to one embodiment of the invention, the lithographic base with a hydrophilic surface can be an anodized aluminum support. The lithographic base with a hydrophilic surface is particularly preferably an electrochemically grained and anodized aluminum support. The aluminum support is very particularly preferably a support grained in nitric acid, as a result of which imaging elements with higher sensitivity are obtained. An anodized aluminum support according to the invention can be subjected to processing to improve the hydrophilic properties of the support surface. For example, the aluminum support can be processed by processing the support surface with a sodium silicate solution at elevated temperature, e.g. B. 95 ° C, silicated. As an alternative, phosphate processing can be carried out, the aluminum oxide surface being processed with a phosphate solution optionally also containing an inorganic fluoride. The aluminum oxide surface can also be rinsed with a citric acid or citrate solution. This treatment can be done at room temperature or at a slightly elevated temperature between 30 ° C and 50 ° C. Another interesting method is to rinse the aluminum oxide surface with a bicarbonate solution. Furthermore, the aluminum oxide surface can be processed with polyvinylphosphonic acid, polyvinylmethylphosphonic acid, phosphoric acid esters of polyvinyl alcohol, polyvinylsulfonic acid, polyvinylbenzenesulfonic acid, sulfuric acid esters of polyvinyl alcohol and acetals of polyvinyl alcohols, which are formed by reaction with a sulfonated aliphatic aldehyde be tested. Furthermore, it is obvious that one or more of these post-treatments can be carried out separately or in combination.

According to a further embodiment of the present invention the lithographic base with a hydrophilic surface flexible beam, such as B. a paper backing or a plastic film with a cross-linked hydrophilic Layer coated is. A particularly suitable cross-linked hydrophilic layer can from a hydrophilic, with a crosslinking agent such as formaldehyde, Glyoxal, polyisocyanate or a hydrolyzed tetraalkyl orthosilicate crosslinked binders can be obtained. The latter becomes a binder particularly preferred.

Come as a hydrophilic binder hydrophilic (co) polymers such as homopolymers and copolymers of vinyl alcohol, acrylamide, methylolacrylamide, methylolmethacrylamide, Acryhsäure, methacrylic acid, Hydroxyethyl acrylate, hydroxyethyl methacrylate or maleic anhydride-vinyl methyl ether copolymers in question. The hydrophilicity of the (co) polymer or (co) polymer mixture used is preferably higher or equal to the hydrophilicity of at least 60% by weight, preferably to at least 80% by weight hydrolyzed polyvinyl acetate.

The amount of crosslinking agent, in particular Tetraalkyl orthosilicate preferably at least 0.2 part by weight per part by weight of hydrophilic Binder is preferably between 0.5 and 5 parts by weight, especially preferably between 1.0 part by weight and 3 parts by weight per part by weight hydrophilic binder.

A cross-linked hydrophilic layer in one according to this embodiment used lithographic base preferably also contains substances, which improve the mechanical strength and porosity of the layer. To colloidal silica can be used for this purpose. The colloidal silica can be in the form of any commercially available water dispersion of colloidal silica for example with an average particle size up to 40 nm, e.g. B. 20 nm, to be used. Next to it inert particles with a larger grain size than that colloidal silica be added, e.g. B. silica, which, as in J. Colloid and Interface Sci., Volume 26, 1968, pages 62 to 69, by Stöber is made, or alumina particles or particles with an average diameter of at least 100 nm, wherein it particles of titanium dioxide or other heavy metal oxides is. By embedding these particles, the surface of the cross-linked hydrophilic layer with a uniform rough texture microscopic peaks and valleys, which as bearings for Serve water in background areas.

The strength of a cross-linked hydrophilic Layer in a lithographic used in this embodiment Underlay can be between 0.2 μm and 25 μm vary and is preferably between 1 μm and 10 μm.

Particular examples of usable according to the invention Suitable cross-linked hydrophilic layers are in EP-A 601 240, GB-P 1,419,512, FR-P 2,300,354, US-P 3,971,660; U.S. Patent 4,284,705 and EP-A 514 490.

As a flexible support for a lithographic base according to this embodiment is particularly preferred a plastic film, for. B. a subbed Polyethylene terephthalate film, a cellulose acetate film, a polystyrene film, a polycarbonate film, etc. The plastic film carrier can opaque or translucent his.

A polyester film carrier coated with an adhesion-improving layer is particularly preferred. For use according to the invention. Particularly suitable adhesion-improving layers contain a hydrophilic binder and colloidal silica, as described in EP-A 619 524, EP-A 620 502 and EP-A 619.525. The amount of silica in the adhesion-promoting layer. is preferably between 200 mg / m ² and 750 mg / m ² . Furthermore, the ratio of silica to hydrophilic binder is preferably above 1 and the specific surface area of the colloidal silica is preferably at least 300 m ² / g, particularly preferably at least 500 m ² / g.

The hydrophobic thermoplastic used according to the invention polymeric latices are copolymers or, preferably, homopolymers of styrene and preferably have a coagulation temperature above 50 ° C and especially preferably over 70 ° C. Coagulation can result from softening or melting of the thermoplastic polymeric latices enter under the influence of heat. The coagulation temperature The thermoplastic hydrophobic polymer latex is subject to no specific upper limit, but it should be sufficiently below the decomposition temperature of the polymeric latices. The coagulation temperature is preferably at least 10 ° C under the. Temperature at which the polymeric latices decompose entry. If the polymeric latices are at a temperature above that Exposed to coagulation temperature, they coagulate and form a hydrophobic agglomerate, which causes the hydrophobic latices on them Make insoluble in tap water or one. aqueous liquid become.

The weight average molecular weight of the hydrophobic thermoplastic polymer can be between 5,000 and 1,000,000 g / mol vary.

The particle size of the particles of the hydrophobic Thermoplastic polymer latex can be between 0.01 μm and 50 μm, especially preferably between 0.01 μm and 1 mm and very particularly preferably vary between 0.02 μm and 0.15 μm.

The hydrophobic thermoplastic polymer Latex is as a dispersion in the aqueous pouring liquid of the imaging Contain layer and can be described in US Pat. No. 3,476,937 Procedures are made. In another, for the creation an aqueous dispersion the thermoplastic polymer latex particularly suitable process

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

The amount in the imaging Layer of contained hydrophobic thermoplastic polymeric latex particles is preferably between 20% by weight and 95% by weight, particularly preferably between 40% by weight and 90% by weight and very particularly preferably between 50 wt% and 85 wt%.

It contains the imaging agent as a binder Layer also a carboxyl-containing hydrophilic polymer. On preferred carboxyl-containing polymer is a homo- or copolymer of poly (meth) acrylate.

The weight average molecular weight of the hydrophilic polymer can be between 2,000 and 1,000,000 g / mol vary, particularly preferably between 5,000 and 500,000 g / mol, very particularly preferably between 10,000 and. 100,000 g / mol.

Although not required, the crosslinking agent is also incorporated into the imaging layer become. Preferred crosslinking agents are low molecular weight substances, which contain a methylol group, such as melamine-formaldehyde resins, Glycoluril-formaldehyde resins, Thiourea-formaldehyde resins, guanamine-formaldehyde resins and benzoguanamine-formaldehyde resins. Certain melamine-formaldehyde resins and glycoluril-formaldehyde resins are sold under the trade names CYMEL (Dyno Cyanamid Co., Ltd.) and NIKALAC (Sanwa Chemical Co., Ltd.).

An anionic IR cyanine dye according to the invention is very particularly preferred in the imaging layer embedded, but at least part of the anionic IR-cyanine dye can also be incorporated into an adjacent layer. Such For example, one layer can be the cross-linked hydrophilic layer of the lithographic base after the second explained above embodiment of lithographic documents.

According to a method according to the invention the imaging element is used to produce a printing plate figuratively with Exposed to infrared light and then with an aqueous solution a pH between 3.5 and 13, very particularly preferably between 4 and 8.

The imagewise exposure of the invention is preferred an imagewise scanning exposure using a laser or an LED diode laser. According to the invention very particularly preference is given to using one in the infrared range (IR) and / or near infrared, d. H. in the wavelength range between 700 and 1,500 nm, emitting laser. Particularly preferred for use in the present invention are near infrared emitters Laser diodes.

In a further embodiment according to the invention can the exposure of the imaging element with the already in the imaging element is clamped in the printing press. One runs a computer or another source of information LED or a laser then over a line of graphic and text information.

After developing an imagewise exposed Imaging element with an aqueous solution and drying can plate thus obtained used as a printing plate without further processing become.

According to a method according to the invention the imaging element is used to produce a printing plate exposed imagewise and subsequently mounted on a printing drum of a printing press. After a preferred embodiment the printing press is then started and rotating the printing drum with the imaging element clamped thereon, the Fountain water supply Dampening rollers and then the inking rollers are lowered onto the imaging member. As a rule, after a few revolutions of the printing drum first clear and usable prints obtained., According to a preferred method, the inking rollers and dampening rollers are lowered at the same time. After one alternative methods can the inking rollers are lowered first.

Fountain water usable according to the invention aqueous liquids usually with an acidic pH that is an alcohol like isopropanol contain. The usable according to the invention Fountain water is not subject to any particular restriction and it can commercial Fountain water can be used.

It may be advantageous to coat the imaging layer of an imagewise exposed imaging element with e.g. B. to wipe a water-soaked cotton ball or sponge before clamping the imaging element in the printing press or at least before starting the printing press. This removes certain non-image areas, but does not trigger the actual development of the imaging element. However, this procedure offers the advantage that the risk of a noticeable ver soiling from the dampening system of the printing press and the printing ink used is avoided.

EXAMPLE 1 (comparative Example)

Manufacture of the lithographic document

A 0.30 mm thick aluminum foil is degreased by immersing the foil in an aqueous solution containing 5 g / l sodium hydroxide at 50 ° C. and rinsed with demineralized water. The film is then electrochemically grained with alternating current at a temperature of 35 ° C. and a current density of 1200 A / m ² in an aqueous solution containing 4 g / l hydrochloric acid, 4 g / l hydrochloric acid and 5 g / l aluminum ions, to obtain a surface topography with an arithmetic mean roughness Ra of 0.5 mm.

After rinsing with demineralized Water is the 'aluminum foil with an aqueous, 300 g / l containing sulfuric acid solution 180 s at 60 ° C etched and subsequently 30 s at 25 ° C rinsed with demineralized water.

The film is then anodized at a temperature of 45 ° C, a voltage of about 10 V and a current density of about 150 A / m2 for 300 s in an aqueous solution containing 200 g / l of sulfuric acid to give an anodic, 3.00 g / m ² Al ₂ O ₃ containing oxidation film, then washed with demineralized water and post-processed with a polyvinylphosphonic acid solution, rinsed with demineralized water for 120 s at 20 ° C. and dried.

Manufacture of imaging elements

To produce an image-forming element according to the invention, the casting composition 1 below is prepared, poured onto the above-described lithographic base in an amount of 30 g / m ² (amount of wet layer) and dried at 35 ° C.

For the production of the imaging elements 2-3, the casting compositions 2-3 are prepared, poured in an amount of 30 g / m ² (amount of wet layer) onto the lithographic base described above and dried at 35 ° C.

Preparation of the casting composition 1

To 7.5 g of a 20% by weight dispersion of stabilized with a surfactant (1.5 wt .-%, based on the polymer) Polystyrene with a particle size of 60 nm in demineralized water are added 20 g of a 1 wt .-% solution of compound I.

Add to the solution thus obtained one afterwards 66.5 g demineralized water and 6 g of a 5% by weight solution of CARBOPOL WS801 (polyacrylic acid, available by Goodrich)

Preparation of the casting composition 2

To 7.5 g of a 20% by weight dispersion of stabilized with a surfactant (1.5 wt .-%, based on the polymer) Polystyrene with a particle size of 60 nm in demineralized water are added 20 g of a 1 wt .-% solution from compound F.

Add to the solution thus obtained one afterwards 66.5 g demineralized water and 6 g of a 5% by weight solution of MOWIOL 56 98 (polyvinyl alcohol available from Hoechst;

Preparation of the casting composition 3

To 7.5 g of a 20% by weight dispersion of stabilized with a surfactant (1.5 wt .-%, based on the polymer) Polystyrene with. a particle size of 60 nm in demineralized water are added 20 g of a 1 wt .-% solution from compound II.

Add to the solution thus obtained one afterwards 66.5 g demineralized water and 6 g of a 5% by weight solution of CARBOPOL WS801 (polyacrylic acid, available by Goodrich)

Preparation of the casting composition 4

To 7.5 g of a 20% by weight dispersion of stabilized with a surfactant (1.5 wt .-%, based on the polymer) Polystyrene with a particle size of 60 nm in demineralized water, 20 g of a 1% by weight solution are added solution from compound II.

Then 66.5 g of demineralized water and 6 g of a 5th % by weight solution of MOWIOL 56 98 (polyvinyl alcohol, available from Hoechst)

Production of a printing plate and Printing prints the template

Any of the imaging elements described above 1–4 will by scanning with a diode laser emitting at 830 nm (scanning speed 1 m / s, resolution 2540 dp and power on the plate surface 44 mW).

After exposure, one processes the plate on a Heidelberg GTO46 press, using as printing ink Van Son Rubberbase VS2329 and used as fountain solution Rotamatic become. When processing, the unexposed areas removed and a negative working lithographic printing plate is obtained.

Table 1 shows the results listed: a print without visible foaming in the unexposed Areas can only with the imaging elements of the invention be achieved.

Table 1

Distance: required number of sheets before the unexposed areas are removed.

EXAMPLE 2 (comparative Example)

Production of the lithographic base The lithographic base is produced analogously to Example 1.

manufacturing of the imaging elements

An imaging element 5 according to the invention is made by casting composition 5 set in an amount of 30 g / m? (Wet layer amount) to that described above the lithographic base is cast and dried at 35 ° C.

For the manufacture of imaging elements 6-7-8 become the casting compositions 6–7–8 made, in an amount of 30 g / m2 (wet layer amount) poured onto the lithographic base described above and at 35 ° C dried.

Preparation of the casting composition 5

To 7.5 g of a 20% by weight dispersion of stabilized with a surfactant (1.5 wt .-%, based on the polymer) Polystyrene with a particle size of 60 nm in demineralized water are added 20 g of a 1 wt .-% solution of compound I.

Add to the solution thus obtained one afterwards 66.5 g demineralized water and 5 g of a 5% by weight solution a copolymer of acrylamide and acrylic acid.

Preparation of the casting composition 6

To 7.5 g of a 20% by weight dispersion of stabilized with a surfactant (1.5 wt .-%, based on the polymer) Polystyrene with a particle size of 60 nm in demineralized water are added 20 g of a 1 wt .-% solution of compound I.

Add to the solution thus obtained one afterwards 66.5 g of demineralized water and 6 g of a 5% by weight solution of a Copolymers of acrylic acid, Ethanol and vinyl acetate.

Preparation of the casting composition 7

To 7.5 g of a 20% by weight dispersion of stabilized with a surfactant (1.5 wt .-%, based on the polymer) Polystyrene with a particle size of .60 nm in demineralized water are added 20 g of a 1 wt .-% solution from connection r.

Add to the solution thus obtained one afterwards 66.5 g of demineralized water and 6 g of a 5% by weight solution of a Polyacrylamidhomopolymers.

Preparation of the casting composition 8th

To 7.5 a of a 20 wt .-% dispersion stabilized with a surfactant (1.5 wt .-%, based on the polymer). Polystyrene with a particle size of 60 nm in demineralized water are added 20 g of a 1 wt .-% solution of compound I.

Add to the solution thus obtained one afterwards 66.5 g demineralized water and 6 g of a 5% by weight solution of CARBOPOL WS801 (polyacrylic acid, available by Goodrich)

Production of a printing plate and Printing prints the template

Any of the imaging elements described above 5-8 will with a laser diode emitting at 830 nm (scanning speed 75 ppm at 2,540 dpi and total output on the plate surface 11 W) illustrated Creo 3244T thermal imagesetter.

After exposure, one processes the plate on a Heidelberg GT046 press, using as printing ink Van Son Rubberbase VS2329 and used as fountain solution Rotamatic become. When processing, the unexposed areas removed and a negative working lithographic printing plate is obtained.

Table 2 shows the results listed: a print without foaming in the unexposed areas can only in the imaging elements of the invention be achieved.

Table 2

Distance: required number of sheets before the unexposed areas are removed.

Claims (10)

A heat-sensitive imaging element which contains, on a lithographic base having a hydrophilic surface, an imaging layer with thermoplastic particles of a homopolymer or a copolymer of styrene and a carboxyl-containing hydrophilic polymer, characterized in that the imaging element further contains an anionic IR-absorbing cyanine dye in the imaging Layer or an adjacent layer contains. A heat sensitive Imaging element according to claim 1, characterized in that the carboxyl-containing hydrophilic polymer is a polymer of acrylic acid or methacrylic acid. A heat sensitive Imaging element according to claim 1 or 2, characterized in that the anionic IR absorbing cyanine dye is an IR absorbing cyanine dye with at least two sulfonic acid groups is. A heat-sensitive imaging element according to claim 3, characterized in that the anionic IR-absorbing cyanine dye is an IR-absorbing cyanine dye having two indolene groups and at least two sulfonic acid groups. A heat-sensitive imaging element according to claim 3, characterized in that the anionic IR-absorbing cyanine dye has the following structure

A heat sensitive Imaging element according to one of Claims 1 to 5, characterized in that that the Amount of anionic IR cyanine dye in the imaging Layer between 1 wt .-% and 40 wt .-%, based on the imaging Layer. A heat sensitive Imaging element according to one of Claims 1 to 6, characterized in that that the lithographic base with a hydrophilic substrate grained and pin anodized aluminum support is.  A heat sensitive An imaging element according to claim 7; characterized in that the anodized aluminum support with a polymer from the group consisting of polyvinylphosphonic acid, polyvinylmethylphosphonic acid, phosphoric acid esters of polyvinyl alcohol, polyvinyl sulfonic acid, polyvinyl benzene sulfonic acid, sulfuric acid esters of polyvinyl alcohol and acetals of polyvinyl alcohols by Reaction with a sulfonated aliphatic aldehyde are formed is processed. A procedure identified by the step below for the production of a lithographic printing plate (1) imagewise exposure with infrared light from a heat sensitive Imaging element according to one of Claims 1 to 7, (2) and the Development of an imagewise exposed imaging element thus obtained, by mounting it on a printing drum of a printing press and. with the printing drum of the imaging layer rotating. fountain and / or printing ink supplied become. A method of making a lithographic printing plate according to claim 9, characterized in that the heat-sensitive imaging element before the imagewise exposure is clamped in the printing press.