JP2002219303A - Planographic printing method using reusable substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for applying a simple solution for discarding a cleaning liquid capable of removing an ink acceptive region from a planographic printing master and a process of removing the ink acceptive region of the planographic printing master using a microemulsion obtained by the method. SOLUTION: A treatment method for the microemulsion capable of recirculating water from the used microemulsion and capable of being used for removing the ink acceptive region of the planographic printing master is disclosed. The method includes a process for heating the microemulsion to 50 deg.C or higher to obtain an aqueous phase and an organic phase and separating the aqueous phase from the organic phase.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating a microemulsion used as a cleaning liquid in a method for recycling a lithographic substrate for a printing plate.

[0002]

BACKGROUND OF THE INVENTION In conventional lithographic printing, ink and fountain solution are supplied to the surface of a printing master having ink-receptive (oleophilic) areas and water-receptive (hydrophilic) areas.
The inked image pattern is then transferred from the surface of the master to a blanket cylinder having a pressurizable surface. From the blanket cylinder, the image is pressed onto the paper. The master is typically a printing plate that carries the image on a dimensionally stable substrate such as an aluminum sheet. The imaged aluminum plate is fixed to the plate cylinder of the printing press by a mechanical locking mechanism that determines the positional registration between the plate and the surface of the cylinder. After the end of the operation of the printing machine, the mechanical fixing system can be removed, the printing plate carrying the printed image can be removed and discarded, and another printing plate can be placed,
Can be fixed in place. A new printing operation can then begin.

[0003] Print masters are generally referred to as so-called computer-to-film met- als.
hod), where each color selection is transferred to a graphic arts film using an image-setter. After processing, the film can be used as a mask for exposing the imaging material, referred to as a plate precursor, and a printing plate is obtained that can be used as a master after plate processing. These steps are generally performed in dedicated exposure and processing equipment, and the printing plate is then sent to the printing press, using a securing mechanism built into the cylinder itself by the operator of the printing press. Connected to the printing cylinder. The connection of the printing cylinders is generally a manual operation, but robotic means for positioning and fixing the printing plates have also been developed.

[0004] In recent years, the so-called computer-to-plate method has been of great interest. This method, also referred to as the direct-to-plate method, avoids the creation of a film because the digital data is transferred directly to the plate precursor by a so-called plate-setter. On-press image formation is performed using a direct-to-plate method (direct-to-press).
ess), wherein the image is exposed on the plate while the plate is placed on the plate cylinder of a printing press. The main advantage of the latter method over off-press plate making is the improved registration between the printing stations of a multicolor printing machine.

[0005] Two types of such on-press imaging methods are known. According to a first type, a printing plate precursor is placed on a printing press, exposed image-wise, optionally developed, then used as a printing master, and finally removed from the printing press and discarded Therefore, a new plate material is required for each image. One example of this technology is
Heidelb described in detail in US 5,339,737
Heid manufactured by erg DruckmaschinenAG (Germany)
elberg Model GTO-DI. A disadvantage of this method is the need to use a new plate for each printing press operation, which increases the cost of the printing process.

An on-press image forming system (on-press ima)
In a second type of ging system, the same lithographic substrate is used in the operation of multiple printing machines (hereinafter referred to as the printing cycle). At each printing cycle, the heat-sensitive or light-sensitive layer is coated on a lithographic substrate to produce a printing plate precursor, and a print master is obtained after image-wise exposure and optional development. After operation of the printing press, the substrate is recycled, as the ink-receptive areas of the print master are removed from the lithographic substrate in a cleaning step, and a new plate is placed on the cylinder in the next cycle of coating, exposure and printing. Can be used without the need for installation. Collars for such on-press coating and on-press imaging systems are described, for example, in US Pat.
8,033, US 5,713,287, EP-A 786
337 and EP-A 802 457. The latter patent application discloses a printed part, a means for applying a uniform coating, a means for exposing the uniform coating according to an image pattern according to scan, and developing the uniform coating to form an image. An apparatus is described which comprises means for leaving on a printed part, the image comprising an ink-repellent area on an ink-repellent background or an ink-repellent area on an ink-receptive background. According to a preferred embodiment, the coating comprises hydrophobic thermoplastic polymer particles in a hydrophilic binder.

[0007] All three cleaning liquids for lithographic printing plates are disclosed in EP-A-002 filed on January 18, 2000.
00176, EP-A-200 0177 and EP-
A-00200178 and DE-A-42 166
36.

[0008] Known cleaning fluids typically contain solvents that are harmful to hoses, pumps and seals,
And / or requires a very thorough rinsing with water because these liquors are not compatible with the coating step in the next printing cycle.

[0009] In a known on-press coating method,
A suitable compromise has been found between the chemical reactivity of the cleaning liquid on the ink-receptive areas that must be removed on the one hand and the required inertness of the cleaning liquid on the fragile lithographic surface on the other hand. Because of this, the lithographic substrate cleaning solutions are often inadequate. Typical lithographic surfaces are extremely sensitive, both mechanically and chemically. The lithographic surface generally consists of a microporous structure in order to obtain a good difference between the spreading properties of the ink and the fountain solution. The anodized aluminum plate comprises a lithographic surface containing one or more metal oxides on which absorption phenomena can occur. These metal oxides are very sensitive to chemical conversion to a form that is no longer lithographically active.

[0010] The microporosity of the lithographic surface is also very sensitive to mechanical damage. The presence of solid particles in the cleaning liquid, often required for effective mechanical cleaning of the lithographic surface, necessarily interferes with the microstructure of the surface.
As the ink and the coated imaging layer penetrate into the microporous structure, it is necessary to perform vigorous cleaning to avoid ghost images during subsequent printing cycles due to incomplete removal of the previous image. is there.

A suitable cleaning liquid is a microemulsion of an organic compound in water. It is necessary to collect the cleaning liquid consumed in each cleaning step, and its disposal is a problem for the user.

[0012]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for providing a convenient solution for discarding a cleaning liquid capable of removing ink-receptive areas from a lithographic printing master. This object is achieved by the method of claim 1.

Another object of the present invention is to provide a method for removing ink-receptive areas of a lithographic printing master using a microemulsion as defined in claim 1. This object is achieved by the method of claim 2. The microemulsion defined in claim 1 completely removes the ink-receptive areas of the printing master. No ghost images are seen after several (> 10) printing cycles of coating, exposure, printing and cleaning. The rubber hose and seal are not affected by the cleaning liquid.
The water of the used microemulsion can be easily recycled because a simple heating step is sufficient to induce phase separation.

Further objects of the present invention will become clear from the description hereinafter.

[0015] Preferred embodiments of the method according to the invention are defined in the dependent claims.

[0016]

The present invention will be described with reference to the accompanying drawings, but the present invention is not limited thereto.

With respect to the term microemulsion as used herein, an emulsion is defined as having a particle size of less than 1 μm and preferably less than 200 nm.

According to the invention, it is provided that in a first stage a particular microemulsion is heated to a temperature above 50 ° C., thereby obtaining an aqueous phase and an organic phase, and separating the resulting phase in a second stage. A method for treating a microemulsion comprising the same is provided. Heating can be performed by a known method, for example, a heat resistor, microwave, or the like. The phases can be separated by known liquid separation techniques, such as membrane or diffusion separation methods, or by the methods described below with respect to FIG.

The microemulsion comprises a mixture of a cyclic organic compound containing at least one double bond, an alcohol, water and an emulsifier. Suitable examples of cyclic organic compounds containing at least one double bond include toluene, xylene, propylbenzene, 3-methyl-6-
Isopropyl-1,4-cyclo-hexadiene, 3- (1
-Methylpropylidene) -cyclohexene, 6-methyl-1- (1-methylethyl) -1,3-cyclohexadiene, 4-methyl-5- (1-methylethenyl) -cyclohexene, o-mentha-4,6- Diene, o-mentha-2
(8), 3-diene, o-mentha-1 (7), 4-diene, 6
-Methyl-1- (1-methylethenyl) -cyclohexene, 1-methyl-5- (1-methylethyl) -1,4-cyclohexadiene, isosylvestren
e), 4-ethyl-3-ethylidene-cyclohexene, 1
-Ethyl-6-ethylidene-cyclohexene, o-mentha-3,6-diene, o-mentha-2,5-diene, o-
Menta-1,4-diene, 3-methyl-4-isopropenyl-1-cyclohexene, 3-methyl-5-isopropenyl-1-cyclohexene, 2-methyl-3-propyl-1,3-cyclohexadiene, -Methyl-6-propylidene-cyclohexene, tetranaphthalene and preferably dipentene (formula II).

[0020]

Embedded image

The alcohol is preferably an aliphatic alcohol ether. Suitable examples of such aliphatic alcohol ethers are methoxypropanol, propoxyethanol, 2-butoxyethanol, propanol,
-(Propyloxy) ethanol, phenoxyethanol, benzyl alcohol, butoxypropanol, ethoxypropanol, 1-isobutoxy-2-propanol, 1-isomethoxy-2-propanol, 1-propoxy-2-propanol, diacetone alcohol, tetrahydrofurfuryl alcohol , Catechol, trimethylolpropane, ethanediol, propanediol,
And butanediol. 2-butoxy alcohol is highly preferred. The alcohol and the cyclic compound are preferably present in amounts of 5 to 50% by weight each and most preferably in amounts of 10 to 30% by weight.

The emulsifier is preferably an anionic compound and / or preferably comprises an alkylene oxide chain. Suitable examples are AkypoOP80, AkypoRO
90 (both are commercially available from Chem-Y), Empicol
ESC70 (commercially available from Albright & Wilson),
Aerosol OT (commercially available from AM Cyanamid). The emulsifier is preferably present in an amount of 5 to 50% by weight and most preferably in an amount of 10 to 30% by weight. The above alcohols can also function as co-emulsifiers.

Furthermore, the microemulsion has the formula I:

[0024]

Embedded image

Wherein X is OH, O ^- or a polymer skeleton. The counter ion, depending on the pH, can be H or a metal, such as an alkali or alkaline earth metal or a transition metal, such as chromium.

Suitable examples of compounds according to formula (I) are polyvinylphosphonic acid, copolymers of vinylphosphonic acid with acrylic acid and vinyl acetate, acrylamidoisobutylenephosphonic acid. Preferably, the compound is a phosphate or phosphonate. The compound is preferably present in an amount of 1.5-6% by weight.

Microemulsions can be used in a method for removing ink-receptive areas of a lithographic printing master. The microemulsion can remove the ink remaining on the print area as well as the hydrophobic coating itself which provides the ink-accepting properties of the print area.

The microemulsion described above is used to remove ink-receptive areas from a printing master obtained by coating a hydrophilic substrate with a coating solution containing hydrophobic thermoplastic polymer particles and a hydrophilic binder. Very suitable. The image-forming layer thus obtained is negative-working, ie the hydrophobic areas are formed by exposure. These areas define the printing area of the master. It is believed that the applied heat induces the solidification of the hydrophobic polymer particles, thereby forming a hydrophobic phase, while in areas that are not heated, the hydrophobic polymer particles remain unchanged. Solidification can result from heat-induced softening or melting of the thermoplastic polymer particles.

The image forming layer preferably used in the present invention comprises:
Coatings comprising hydrophobic thermoplastic polymer particles having an average particle size of between 40 nm and 2000 nm, and more preferably between 40 nm and 200 nm, in order to improve sensitivity and yield and avoid fouling It contains. Further, the polymer particles preferably have a solidification temperature above 50 ° C and more preferably above 70 ° C. There is no specific upper limit for the solidification temperature of the polymer particles, but this temperature must be well below the decomposition temperature of the polymer particles. Preferably, the coagulation temperature is at least 10 ° C. below the temperature at which decomposition of the polymer particles occurs.

Preferred examples of thermoplastic hydrophobic polymer particles for use in the present invention have a Tg above 80 ° C. The weight average molecular weight of the polymer is 5,000 to 5,000,
000 g / mol. Preferably, the polymer particles are selected from the group consisting of polyvinyl chloride, polyvinylidene chloride, polyesters, polyurethanes, polyacrylonitrile, polyvinyl carbazole, and the like, and copolymers or mixtures thereof. Most preferred examples are polystyrene and polymethyl methacrylate or copolymers thereof.

The polymer particles exist as a dispersion in the coating solution and can be prepared by the method disclosed in US Pat. No. 3,476,937. Another method which is particularly suitable for producing an aqueous dispersion of thermoplastic polymer particles is:-dissolving the hydrophobic thermoplastic polymer in an organic solvent immiscible with water,-dissolving the solution thus obtained in water. Or dispersing in an aqueous medium and removing the organic solvent by evaporation.

The hydrophilic binder suitable for use in the present invention is preferably a water-soluble (co) polymer, such as a synthetic homo- or copolymer, such as polyvinyl alcohol, poly (meth) acrylic acid, poly (meth) acrylamide. Hydroxyethyl poly (meth) acrylate, polyvinyl methyl ether or natural binders such as gelatin, polysaccharides such as dextran, pullulan, cellulose, gum arabic, alginic acid, inulin or chemically modified inulin.

Further, the coating solution is anionic,
Surfactants which may be cationic, non-ionic or amphoteric may be included. Perfluorosurfactants are preferred. Nonionic perfluorosurfactants are particularly preferred. The surfactants can be used alone or, preferably, in combination.

The coverage of the coated layer is preferably from 0.3 to 20 g / m ² , more preferably from 0.5 to 5 g / m ² .
m ² . The amount of hydrophobic thermoplastic polymer particles contained in the coated layer is preferably between 50 and 90%, and more preferably between 60 and 80% by weight of the total weight of the layer. is there.

[0035] The coating solution is preferably applied to the substrate by spraying or spraying, although other coating techniques may be used.

The substrate used in the present invention can be a plastic support or a ceramic, but is preferably a metal,
For example, aluminum. The metal has a hydrophilic surface,
And is preferably characterized by a roughness value of at least 0.2 μm, more preferably at least 0.3 μm, for example electrochemically and / or mechanically grained and anodized aluminum. The substrate may be a sheet-like material, for example a plate, but the coating solution may be applied directly to the plate cylinder of a rotary printing machine, which cylinder thereby functions as the substrate. The lithographic substrate may also be a seamless sleeve printing plate obtained, for example, by soldering the plate into a cylinder with a laser. Instead of installing a normal printing plate, the sleeve can then be slid around the plate cylinder. For more details on sleeves see "Grafisch Nieuws", 15, 1995, page 4 to 6
Is shown in

The exposure of the imaging layer obtained by coating the above-mentioned coating solution on a lithographic substrate can be carried out by direct thermal recording, for example using a thermal head or by irradiation with high intensity light. In the latter embodiment, the heat-sensitive material preferably comprises a compound capable of converting light to heat, preferably a compound having sufficient absorption in the wavelength range of the light source used for image-wise exposure. Particularly useful compounds are, for example, dyes, in particular EP-A 908 30
Dyes as well as pigments, especially infrared pigments,
For example, carbon black, metal carbides, borides, nitrides, carbonitrides, bronze structured oxides and oxides structurally related to the bronze family but lacking the A component, such as WO _2.9 . It is also possible to use conductive polymer dispersions, for example those based on polypyrrole, polyaniline or polythiophene. The lithographic performance obtained, and especially the printing durability, generally depends on the heat sensitivity of the imaging element. In this regard, it has been found that carbon black produces very good and favorable results.

The image-wise exposure in the method of the present invention is preferably an image-wise scanning exposure involving the use of a laser or LED. Infrared or near infrared, ie 700
Lasers operating in the wavelength range of -1500 nm are preferably used. Laser diodes emitting in the near infrared are most preferred.

The printing method of the present invention is further described below according to preferred embodiments. First, a grained and anodized aluminum plate is placed on the plate cylinder of a rotary printing machine. Next, the above coating solution is sprayed onto the hydrophilic lithographic surface of the plate to form a continuous imaging layer.
Preferred values of the spray parameters are described in EP-A No. 9920364 both filed on Sep. 15, 1999.
And EP-A No. 99203065. The imaging layer is then replaced, for example, in US Pat.
And imagewise exposed by means of a continuous device integrated in a printing machine as described in US-P-5 174 205, whereby the exposed areas are hydrophobic ink-receptive areas. But the unexposed areas remain hydrophilic. The hydrophobic area defines the printing area of the master. Subsequently, printing is started by applying ink and fountain solution to the print master. To completely dissolve and remove the unexposed areas of the coated layer, preferably only the fountain solution is applied several times on the printing machine (about 10
) And then ink is also supplied to the plate. After operation of the printing machine, the lithographic substrate is recycled by treatment with the microemulsion described above. Finally, the substrate can be rinsed with water or an aqueous solution and dried, and then a new printing cycle can be started by spraying the coating solution onto the recycled substrate.

The cleaning step can be performed in a cleaning unit similar to known blanket cleaning systems. According to this embodiment, the fabric is preferably moistened with the microemulsion and, during 1 to 50 rotations, more preferably during 2 to 10 rotations, 10 ^{4 to} 6
The printing plate is brought into contact with the printing plate at a contact pressure between × 10 ⁵ Pa and a rotation speed in the range of 2 to 50 m / min. Thereafter, the contact between the printing surface and the cleaning cloth is interrupted until a dry, clean part of the cloth is obtained.

Microemulsions can also be applied by spraying, coating or spraying a liquid onto a lithographic substrate or onto a cloth. Removal of the ink-receptive areas can also be accomplished using other absorbing media than cloth. Cleaning can also be performed by combining the treatment with the microemulsions of the invention with other mechanical cleaning means, such as by spraying a rotating brush or water or a volatile medium, such as air, solvent or dry ice pellets. Vacuum extraction can also be used during the cleaning process.

After the cleaning step, the used microemulsion containing the dissolved ink and the hydrophobic coating is treated as described above. The resulting aqueous phase is
It can be used to produce a new microemulsion or to rinse the substrate before starting a new printing cycle of coating, printing and cleaning.

All steps of the process of the invention are preferably performed on-press. Alternatively, the lithographic substrate can be placed on a drum in a dedicated coating device (off-press coating) and subsequently placed on a plate setter for image-wise exposure (off-press exposure). next,
The printing master thus obtained can be placed on a plate cylinder and printing is started by supplying ink and fountain solution. After operation of the printing machine, the plate can be cleaned on-press or in a dedicated cleaning device, as described above, and the recycled substrate can then be reused in the next printing cycle. The used microemulsion can be collected and separated in a device that may be integrated into the printing machine or in a stand-alone device.

A preferred means for separating the resulting phases is described in Perry's Chemical Engineers Handbook, ed. McGr.
aw-Hill, 1999, Section 15 'Liquid-Liquid Extractio
n and Operations and Equipment '
And is shown diagrammatically in FIG.

A housing (4) containing an inlet (2) and an outlet (3). In this housing, the heating element (10)
Is configured to maintain a constant temperature of 50 ° C. The conductivity measurement cell (5) is used to keep the water level lower than the outlet (7) for organic-based compounds. This height is adjusted by a pump before the inlet (2) and by a valve system after the outlet (3) to ensure that part (1) is filled with water and part (6) is filled with organic components. You. This system can be used in a discontinuous manner, i.e. in batch mode, but in a continuous manner by introducing a plate (8) to avoid the inflow of microemulsion into the outlet (7). Can also be used.

Furthermore, according to the invention, a printing cylinder,
Means for placing a reusable substrate having a hydrophilic surface on the printing cylinder, means for coating the imaging layer on the hydrophilic surface, means for exposing the imaging layer image-wise, ink and A printing device is provided comprising means for applying a fountain solution to a printing cylinder. Furthermore, the printing device comprises means for supplying the microemulsion to the printing cylinder and means for processing the microemulsion as described above.

[0047]

The following examples illustrate the invention but do not limit it. All parts and percentages are by weight unless otherwise indicated. Example 1 Preparation of a lithographic base Aluminum foil 0.30 mm thick was degreased by immersion at 50 ° C. in an aqueous solution containing 5 g / l sodium hydroxide and rinsed with demineralized water.
The foil is then heated with an alternating current in an aqueous solution containing 4 g / l hydrochloric acid, 4 g / l hydroboric acid and 5 g / l aluminum ions at a temperature of 35 ° C. and a current density of 1200 A / m ² . , To form a surface morphology having an average centerline roughness Ra of 0.5 μm.

After rinsing with demineralized water, the aluminum foil was then etched with an aqueous solution containing 300 g / l of sulfuric acid at 60 ° C. for 180 seconds and with demineralized water at 25 ° C. for 30 seconds.

The foil is subsequently immersed in an aqueous solution containing 200 g / l of sulfuric acid, at a temperature of 45 ° C., a voltage of about 10 V and 1
Anodizing at a current density of 50 A / m ² for about 300 seconds to form an anodized film of 3.00 g / m ² Al ₂ O ₃ , then washing with demineralized water and a solution containing polyvinyl phosphonic acid It was subsequently worked up with a solution containing aluminum trichloride, rinsed with demineralized water at 20 ° C. for 120 seconds and dried. Preparation of Spray Solution A 2.61 wt% solution in water was prepared by mixing polystyrene latex, heat absorbing compound and hydrophilic binder. After spraying and drying, the resulting layer is 75% by weight of polystyrene latex, 10% by weight of a heat absorbing compound of formula (I) and 15% by weight of polyacrylic acid (commercially available from NV Allied Colloids Belgium).
Glascol E15).

[0050]

Embedded image

Preparation of Heat-Mode Imaging Element The spray solution was sprayed onto the lithographic base described above. Therefore,
The lithographic base was set on a drum rotating at a linear speed of 164 m / min. The imaging element was coated with a spray nozzle moving laterally at a speed of 1.5 m / min. The spray nozzle was located at a distance of 80 mm between the nozzle and the receptive substrate. The flow rate of the spray solution was set at 7 ml / min. During the spraying process, 90 psi air pressure was used on the spraying head. This layer was dried during the spraying process at a temperature of 70 ° C. and for a further 30 seconds.

The spray nozzle is a Brussels
It was an SUJI type air-assisted spray nozzle commercially available from Spraying Systems Belgium. Printing Step The above heat mode imaging element was subjected to 150 r at 2400 psi in a Creo 3244 ^™ external drum plate setter.
Imaged at a power setting of 15.5 watts at pm. GTO46 printing machine (Heidelberger Druckmas
(from chinen) using K + E800 Skinnex ink, fountain solution (Combifix XL (4%)-isopropyl alcohol in water (10%)) up to 5000 runs. Print quality was evaluated. Preparation of Microemulsion A: 10 g of dipentene (commercially available from Sigma-Aldrich) were mixed with 20 g of Aquipo OP80. While stirring, 14 g of butoxyethanol was added. In the next step, 50 g of water were added with stirring. Cleaning step: Preliminary Sprayer Division of Precision V, New York, on plate containing ink with 10 ml / m ² of Microemulsion A attached
The spraying was performed using a manual pressurized sprayer commercially available from alve corporation.

After a period of 30 seconds for the microemulsion to interact with the coating, the plate was cleaned using a standard high-pressure washer with an amount of water of 10 l / m ² .

Finally, the plate was dried with pressurized air at room temperature until the surface of the plate appeared to be visually dry.

The spent emulsion was collected and heated to 50 ° C. in the apparatus according to FIG. After 30 seconds, the organic compound was completely separated from the water. The water was collected and used to rinse the substrate after removing the ink receptive area with the microemulsion as described above. The substrate was then recoated with the spray solution as described above.

[Brief description of the drawings]

FIG. 1 is a schematic representation of an apparatus suitable for heating and separating the microemulsions described herein.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Peter Gaertz Belgium 2640 Malt Cell Septes Trat 27 Agfa-Gevert Na Mrose Fennoutjap F-term (reference) 2H096 AA06 EA04 EA23 LA12 LA25 LA30 2H114 AA04 AA14 AA22 AA24 BA01 BA10 DA25 DA79 EA01 EA08 EA10 GA27 GA29

Claims (13)

[Claims] 1. A method for treating a microemulsion comprising a mixture of a cyclic organic compound containing at least one double bond, an alcohol, water and an emulsifier,
(1) heating the microemulsion to a temperature above 50 ° C., thereby obtaining an aqueous phase and an organic phase, and (2)
Separating the aqueous phase from the organic phase. 2. A negative working image forming layer is prepared by coating (a) a solution comprising hydrophobic thermoplastic particles and a hydrophilic binder on a hydrophilic surface, and (b)
Producing a printing master with ink-receptive areas by exposing the imaging layer imagewise to heat or light,
(C) applying the ink and fountain solution to the print master,
(D) removing the ink-receptive areas from the print master by supplying the microemulsion as defined in claim 1 to the imaging layer, and (e) treating the microemulsion according to the method of claim 1. Direct-to-plate method of lithographic printing using a reusable substrate having a hydrophilic surface. 3. An additional step (f) using an aqueous phase to produce a new microemulsion or to rinse the substrate after step (d) or before step (a). 2. The direct-to-plate method described in 1. above. 4. The method according to claim 1, wherein the cyclic organic compound is dipentene. 5. The method according to claim 1, wherein the alcohol is an aliphatic alcohol ether. 6. The method according to claim 5, wherein the aliphatic alcohol ether is butoxyethanol. 7. The method according to claim 1, wherein the emulsifier is an anionic compound. 8. The method according to claim 1, wherein the emulsifier comprises an alkylene-oxide chain. 9. The microemulsion of formula I: 9. The method according to any of the preceding claims, further comprising a compound according to the formula, wherein X is OH, O ^- or a polymer skeleton. 10. The method according to claim 2, wherein the reusable substrate is a plate cylinder of a rotary printing machine or a plate or sleeve mounted on a plate cylinder of a rotary printing machine. 11. The method according to claim 2, wherein the solution and the microemulsion are sprayed or jetted on the substrate. 12. A printing device comprising means for processing a microemulsion according to the method of claim 1. 13. A printing cylinder,-means for placing a reusable substrate having a hydrophilic surface on the printing cylinder,-means for coating the image-forming layer on the hydrophilic surface,-the image-forming layer Means for exposing the microemulsion to the printing cylinder; means for applying the microemulsion to the printing cylinder; and processing the microemulsion according to the method of claim 1. 13. The printing device according to claim 12, comprising means for performing.