JP2001253038A - Method for lithographic printing using recyclable substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for lithographic printing using a cleaning liquid which does not give an influence on hardwares of a printer and a cleaning unit by effectively removing an ink acceptive region of a printing master and recycling the substrate in a next printing cycle. SOLUTION: A direct-to-plate method of the lithographic printing capable of recycling a lithographic substrate of the printing master comprises the steps of (a) coating a hydrophilic substrate with a coating solution containing hydrophobic thermoplastic polymer particles and hydrophilic binder to manufacture a negative action image forming material, (b) exposing the image forming material as an image to manufacture the printing master having the ink acceptive region, (c) applying an ink and a dampening liquid to the printing master, and (d) supplying an alcohol and preferably an alkanolamine to remove the ink acceptive region from the master. In this case, the steps are preferably conducted on-press.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to a cleaning method for recycling lithographic substrates of a printing master.

[0002]

BACKGROUND OF THE INVENTION In conventional lithographic printing, ink and an aqueous fountain solution are applied to the surface of a printing master containing ink-receptive (lipophilic) and water-receptive (hydrophilic) areas. The inked image pattern is then transferred from the surface of the master to a blanket cylinder having a compressible surface.
The image is printed on paper from a blanket cylinder. 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 secured to the plate cylinder of the printing press by a mechanical clamping mechanism, which defines a positional registration between the plate and the surface of the cylinder. Press-After the end of operation, the mechanical clamping system can be released, the printing plate carrying the printed image can be removed and discarded, another printing plate positioned and clamped in place. A new printing job can then begin.

[0003] Print masters are generally known as the so-called computer-to-film method.
-Film method), in which 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 exposure of an imaging material, called a plate precursor, and after processing of the plate, a printing plate is obtained which can be used as a master. Usually, these steps are performed in dedicated exposure and processing equipment, and the printing plate is then transported to the printing press and mounted on the printing cylinder by the press operator using a clamping mechanism built into the cylinder itself. The mounting of the printing cylinder is generally a manual operation, but robotic means have been developed for positioning and fixing the printing plate.

In recent years, so-called direct printing plates (comp)
Uter-to-plate methods have gained much interest. Direct-to-plate
This method, also called the -plate method, bypasses the production of the film because the digital data is transferred directly to the plate precursor using a so-called plate-setter. On-press imaging is a direct-to-plate process that exposes an image on a plate while the plate is mounted on a plate cylinder of a printing press (direct-t-press).
o-press)). A major advantage of the latter method compared to off-press-to-make is the improved registration between the printing stations of a multi-color press.

[0005] Two types of such on-press imaging methods are known. According to the first type, the printing plate precursor is mounted on a printing press, exposed image-wise, optionally developed, and then used as a printing master, and finally removed from the printing press and discarded, thus each New plate material is needed for images. An example of this technology is Hei
delberg Druckmaschinen AG
Well-known Hei manufactured by (Germany)
delberg Model GTO-DI.
S 5,339,737. A disadvantage of this method is that it requires the use of a new plate for each press-run, thus increasing the cost of the printing process.

[0006] In the case of the second type of on-press imaging system, the same lithographic substrate is used in multiple press runs (hereinafter referred to as printing cycles). In each printing cycle, a heat-sensitive or photosensitive layer is coated on a lithographic substrate to create a printing plate precursor, and after image-wise exposure and optional development, a printing master is obtained.
After the press-run, the ink-receptive areas of the print master are removed from the lithographic substrate in a cleaning step, the substrate is recycled and the next cycle of coating, exposure and printing without the need to load a new plate on the cylinder. You can use it in Examples of such on-press coating and on-press imaging systems are described, for example, in US Pat.
5,188,033; US 5,713,287; EP
-A 786 337 and EP-A 802 457. The latter patent application discloses a printing member, means for applying a uniform coating, means for exposing the uniform coating scan-wise according to an image pattern, and developing the uniform coating to form an image on the printing member. Wherein the image comprises ink-repellent areas on an ink-repellent background or ink-repellent areas on an ink-receptive background. According to a preferred embodiment, the coating comprises hydrophobic thermoplastic polymer particles in a hydrophilic binder.

[0007] In the known on-press coating method,
In many cases, the cleaning of the lithographic substrate fails, which on the one hand causes the chemical reactivity of the cleaning liquid to the ink-receptive areas to be removed and, on the other hand, the cleaning liquid required for brittle lithographic surfaces. This is because no suitable compromise between inertness can be found. Typical lithographic surfaces are very sensitive, both mechanically and chemically. The lithographic surface generally has a spreading property of ink and dampening solution.
It consists of a microporous structure in order to differentiate its operations. The anodized aluminum plate comprises a lithographic surface containing one or more metal oxides on which the absorption phenomenon can occur. These metal oxides
It is very susceptible to chemical conversion to a form that is no longer lithographically active.

[0008] The microporosity of the lithographic surface is also very susceptible to mechanical damage. The presence of solid particles in the cleaning liquid, which is often necessary for effective mechanical cleaning of the lithographic surface, necessarily results in a micro-structural disturbance of the surface.
Since the ink and the coated imaging layer penetrate into the micro-porous structure, it is necessary to perform heavy cleaning in subsequent printing cycles to avoid ghost images due to insufficient removal of previous images. It is.

Furthermore, known cleaning liquids typically contain solvents that are harmful to hoses, pumps and sealings, and / or these liquids are compatible with the coating step in the next printing cycle. No need to be very thoroughly rinsed with water.

[0010]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a lithographic printing method comprising a cleaning step which can effectively remove the ink-receptive areas of a printing master and reuse the substrate in the next printing cycle. It is to be. More particularly, there is a need for a cleaning step characterized by a low risk of degrading the lithographic surface of the substrate. It is also an object of the present invention to provide a printing method using a cleaning liquid which does not affect the hardware of the printing press or the cleaning device, especially a liquid which is inert to rubber and which does not require a long rinsing step after cleaning. Is the purpose.

The above object is achieved by the method of claim 1. The cleaning liquid as defined in claim 1 effectively removes the ink-receptive areas of the printing master as defined in claim 1. Several times of coating, exposure, printing and cleaning (>
10) After the print cycle, no ghost images are observed. Rubber hoses and seals are unaffected by the cleaning liquid, and a small amount of water is sufficient for the optional rinsing step.

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

[0013] Preferred embodiments of the method of the invention are defined in the dependent claims.

[0014]

DETAILED DESCRIPTION OF THE INVENTION The cleaning liquid used in the method of the present invention contains an alcohol. Suitable examples of alcohol are:
2-butoxyethanol, propanol, 2- (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-butoxyethanol and benzyl alcohol are highly preferred. The alcohol can be a liquid alcohol, which can be supplied to the printing master as an essentially pure liquid. More preferably, the cleaning liquid is an aqueous solution comprising alcohol in an amount of 1% to 20% by weight, more preferably 2% to 10% by weight, and most preferably 2% to 5% by weight.

In a preferred embodiment, the cleaning liquid also contains an alkanolamine at a concentration of at most 20% by weight.
Suitable examples of alkanolamines are: diethanolamine, diethylethanolamine, diisopropylamine, ethylamine, ethylene-diamine, isopropylamine, monoethanolamine, monoisopropylamine, morpholine, triethanolamine, triethylenetetramine, triisopropanolamine, aminoethoxy. Ethanol, aminoethylaminoethanol, monopropanolamine, methylaminoethanol, hydroxylamine, N-butyl-ethanolamine, N-ethyldiethanolamine, diglycolamine and dimethylglyoxime. Monoethanolamine is highly preferred.

The cleaning liquid preferably also comprises a surfactant in an amount of from 0.001% to 5% by weight.

The above cleaning fluid 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 imaging material thus obtained is negative-working, i.e., when exposed, hydrophobic areas are formed. These areas define the printing area of the master. The applied heat causes the coagulation of the hydrophobic polymer particles, thereby forming a hydrophobic phase, but it appears that the hydrophobic polymer particles remain unchanged in the non-heated regions. Coagulation can result from heat-induced softening or melting of the thermoplastic polymer particles.

The cleaning liquid of the present invention is capable of removing the ink remaining on the print area as well as the hydrophobic phase itself which causes the ink-acceptance of the print area. In a preferred embodiment, the method of the invention comprises two cleaning steps: first supplying alcohol to the master to remove the ink;
Subsequently, the hydrophobic region is removed using alkanolamine. In addition to alcohols and alkanolamines, other solvents such as amides, for example dimethylformamide or 2-N-methylpyrrolidone, can be fed to the master as a mixture with the alcohol or alkanolamine or in a separate cleaning step. it can.

The image-forming material used in the present invention preferably contains hydrophobic thermoplastic polymer particles having an average particle size of 40 nm to 2000 nm, and more preferably 40 nm to 200 nm, to improve sensitivity and throughput.
Avoid scum formation. Further, the polymer particles preferably have a coagulation temperature above 50 ° C, and more preferably above 70 ° C. Although there is no particular upper limit on the coagulation temperature of the polymer particles, it 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 the decomposition of the polymer particles takes place.

Preferred examples of thermoplastic hydrophobic polymer particles for use in the present invention have a Tg of greater than 80 ° C. The weight average molecular weight of the polymer is between 5,000 and 5,000.
It can be in the range of 0,000 g / mol. Preferably, the polymer particles are selected from the group consisting of polyvinyl chloride, polyvinylidene chloride, polyester, polyurethane, 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 are present as a dispersion in the coating solution and can be prepared by the method disclosed in US Pat. No. 3,476,937. Other methods particularly suitable for the preparation of aqueous dispersions of thermoplastic polymer particles are:-dissolving the hydrophobic thermoplastic polymer in an organic solvent immiscible with water,-dissolving the solution thus obtained in water or an aqueous medium. Dispersing; removing the organic solvent by evaporation.

Suitable hydrophilic binders for use in the present invention are preferably water-soluble (co) polymers such as polyvinyl alcohol, poly (meth) acrylic acid, poly (meth) acrylamide, polyhydroxyethyl (meth) Synthetic homo- or copolymers such as acrylates, polyvinyl methyl ether or natural binders such as gelatin, polysaccharides such as dextran, pullulan, cellulose, gum arabic, alginic acid, inulin or chemically modified inulin.

The coating solution preferably contains a surfactant, which can be anionic, cationic, nonionic or amphoteric. Perfluorinated surfactants are preferred. Particularly preferred are nonionic perfluorinated surfactants. The surfactants can be used alone or, preferably, in combination.

The coated layer preferably has a coverage of 0.3 to 20 g / m ² , more preferably 0.5 to 5 g.
/ M ² . The amount of hydrophobic thermoplastic polymer particles contained in the coated layer is preferably 2 to 40% by weight of the total weight of the layer, and more preferably 10 to 20% by weight.

The coating solution described above can be sprayed or sprayed onto the substrate, but other known coating methods are possible.

The substrate used in the present invention can be a plastic support or a ceramic, but is preferably a metal such as aluminum. The substrate 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 polished electrochemically and / or mechanically,
And anodized aluminum. The substrate can be a sheet-like material such as a plate, but alternatively, the coating solution can be applied directly to the plate cylinder of a rotary printing press, whereby the cylinder acts as the substrate. The lithographic substrate can also be a seamless sleeve printing plate, which is obtained, for example, by soldering the plate into a cylinder using a laser. The sleeve can then be slid around the plate cylinder, instead of loading a normal printing plate. For more information on sleeves, see “Grafis
ch Nieuws ", 15, 1995, page 4
6 are shown.

The exposure of the image-forming material obtained by coating the lithographic substrate with the above-mentioned coating solution can be performed, for example, by direct thermal recording using a thermal head.
Alternatively, it can be performed by irradiating strong light. In the latter embodiment, the thermosensitive 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, and especially E
Infrared dyes and pigments as disclosed in P.A. 908 307, and especially carbon blacks, metal carbides, borides, nitrides, carbonitrides, bronze-structured oxides and structurally related bronze groups An oxide having an A component but having no A component, for example, an infrared pigment such as WO _2.9 .
Conductive polymer dispersions, such as those based on polypyrrole or polyaniline, can also be used. The lithographic performance obtained, and in particular the printing durability, depends inter alia on the heat sensitivity of the imaging element. In this regard,
It has been found that carbon black gives very good and favorable results.

The image-wise exposure in the method of the invention is:
Preferably, a laser or L.P. E. FIG. D. Image-wise scanning exposure including the use of Preferably used are lasers operating in the infrared or near infrared, for example in the wavelength range from 700 to 1500 nm. Most preferred are laser diodes that emit in the near infrared.

In the following, the printing cycle of the present invention will be further described according to a preferred embodiment. First, a polished and anodized aluminum plate is mounted on a plate cylinder of a rotary printing press. The coating solution is then sprayed onto the hydrophilic lithographic surface of the plate to form a continuous image forming layer. Preferred values for the spray parameters are both 199
EP-A no. 9920
3064 and EP-Ano. 99203065. The imaging layer is then image-wise exposed, whereby the exposed areas are converted to hydrophobic ink-receptive areas, while the non-exposed areas remain hydrophilic. The hydrophobic area defines the printing area of the master. Subsequently, printing is started by applying ink and dampening liquid to the printing master. In order to effectively dissolve and remove the non-exposed areas of the coated layer, preferably only a dampening solution is supplied to the plate during several revolutions of the printing press (about 10), and then also the ink. After the press-run, the lithographic substrate is recycled by treatment with the cleaning solution described above. Finally, the substrate can be rinsed and dried, and then a new printing cycle can be started by spraying the recycled substrate with the coating solution.

[0030] The cleaning step is performed by a known blanket cleaning system.
tem) can be implemented with a similar cleaning device. According to that embodiment, the cloth is moistened with a cleaning liquid and a contact pressure of 0.1-5 Pa is used at a rotation speed in the range of 2-50 m / min, between 1 and 50, more preferably between 2 and 10 rotations. To make contact with the printing plate. Later, the contact between the printing surface and the cleaning cloth is broken and the cloth is transported until a dry and clean part of the cloth is obtained.

The cleaning liquid can also be applied to the lithographic substrate or cloth by spraying, coating or spraying. Removal of the ink-receptive areas can also be accomplished using an absorbing medium other than a cloth. Cleansing is also possible by combining the treatment with the cleaning solution of the present invention with other means of mechanical scrubbing, such as a rotating brush or by spraying a volatile medium such as water or air, solvent or dry ice pellets. Can be performed. Vacuum extraction can also be used during the cleaning process.

The cleaning step is preferably followed by a rinsing step,
At that stage, water is sprayed onto the substrate. The plate can then be dried with a cloth, for example, using the same blanket cleaning system as described above. Preferably the rinsing step involves only a slight wetting of the lithographic surface, ie
Water of up to ml / m ² is supplied to the plate. Several rinsing steps,
Preferably, it can be repeated 2 to 5 times.

All steps of the process of the invention are preferably performed on-press. Alternatively, the lithographic substrate can be mounted on a drum in a dedicated coating apparatus (off-press coating) and subsequently mounted on a platesetter for image-wise exposure (off-press exposure). . The printing master thus obtained can then be mounted on the cylinder of a printing press and printing is started by supplying ink and dampening liquid. After the press-run, the plate can be cleaned on-press or in a dedicated cleaning device as described above, and the recycled substrate can then be used again in the next printing cycle.

[0034]

The following examples illustrate the invention without limiting it. All parts and percentages are by weight unless otherwise specified.

Example 1 Preparation of a lithographic substrate A 0.30 mm thick aluminum foil was degreased by submerging the foil in an aqueous solution containing 5 g / l sodium hydroxide at 50 ° C. and rinsing with deionized water. . Then 3
Using alternating current at a temperature of 5 ° C. and a current density of 1200 A / m ² , 4 g / l hydrochloric acid, 4 g / l boric acid and 5 g / l
The foil was electrochemically polished in an aqueous solution containing 1 aluminum ion to form a surface topology with an average centerline roughness Ra of 0.5 mμ.

After rinsing with deionized water, the aluminum foil was etched at 60 ° C. for 180 seconds using an aqueous solution containing 300 g / l sulfuric acid,
Rinse with deionized water for 0 seconds.

Subsequently, the foil was placed in an aqueous solution containing 200 g / l of sulfuric acid at a temperature of 45 ° C., a voltage of about 10 V and 150
Anodize at a current density of A / m ² for about 300 seconds to form an anodized film of 3.0 g / m ² Al ₂ O ₃ , then wash with deionized water and contain polyvinylphosphonic acid The solution is worked up with a solution and subsequently with a solution containing aluminum trichloride, and then treated with deionized water.
Rinse at 0 ° C. for 120 seconds and dry. Preparation of coating solution A 2.61% solution in water was prepared by mixing polystyrene latex, Dye I and hydrophilic binder.
After spraying and drying, the resulting layer contains 75% polystyrene latex, 10% Dye I and 15% Glasco
lE 15 ^TM was contained. Glascol E 15
Is N. V. Allied Colloids Berg
Polyacrylic acid commercially available from ium.

The structure of Dye I is as follows:

[0039]

Embedded image

Preparation of Image Forming Material The above aluminum substrate was mounted on a drum rotating at a linear speed of 164 m / min. Spraying Syst
air-assisted spray nozzle (air-assis) available from Ems Belgium (Brussels)
The above solution was coated on a substrate using ted spray nozzle, SUJ1 type. The spray nozzle was mounted at a distance of 80 mm from the substrate, and the flow rate of the spray solution was set at 7 ml / min. 6. During spraying, the nozzle was moved at a speed of 1.5 m / min and over the spray head.
An air pressure of 58 × 10 ⁵ Pa was used. The coated layer was dried by applying hot air (70 ° C.). 14. Printing stage with Creo 3244 ^™ external drum plate setter at 2400 dpi and 150 rpm.
The imaging material was exposed using a power setting of 5 watts.
The imaged plate is K + E on a GTO 46 printing press
800 Skinnex ink and Rot as fountain solution
Printed up to 5000 run-lengths using an organic. The print quality was excellent. Recycling of the lithographic substrate The plate was mounted on the drum of a cleaning device similar to a typical blanket cleaning system. The fabric was moistened with an aqueous cleaning solution containing 2.5% 2-butoxyethanol. Cleaning was performed by contacting the cloth with the printing plate at a pressure of 0.67 Pa for 5 rotations of the drum. Cloth is 20m against the plate
/ Min speed. Then 30 ml / m ² of water was sprayed on the printing plate as a rinsing liquid, followed by contacting the wet plate with a dry and clean part of the cloth (same setting as in the cleaning step, one revolution). The rinsing step was repeated four more times.

Example 2 2.5% 2-butoxyethanol and 3% cleaning solution
The same procedure as in Example 1 was repeated except that ethanolamine was contained.

Example 3 Two cleaning steps were performed, except that a first step was provided with a 2.5% aqueous solution of 2-butoxyethanol and a second step with a 3% aqueous solution of ethanolamine. The same procedure as in Example 1 was repeated. One rinsing step was sufficient. Results The above sequence of spraying, imaging, printing, cleaning, rinsing and drying was repeated ten times for each of the three cleaning liquids defined above. After each cycle, plate cleanliness,
The coating quality and print quality (stain, presence of ghost images) were evaluated visually. Each of the above cleaning solutions gave excellent results with respect to all of these criteria.

The above cleaning fluid is used in EPDM (ethylene, ethylene, etc.) which is often used in blanket cleaning systems.
(Terpolymers of propylene and non-conjugated dienes) were investigated for their chemical reactivity towards rubber. After soaking the rubber in the cleaning solution for 24 hours, the weight gain of the rubber (due to swelling) was measured. The cleaning liquid used in Examples 1, 2 and 3 resulted in a weight gain of up to 0.12%, which is considered acceptable.

Claims (10)

[Claims] 1. A negative-working imaging element is prepared by coating (a) a coating solution comprising hydrophobic thermoplastic polymer particles and a hydrophilic binder on a hydrophilic surface; (b) an image Making a printing master having ink-receptive areas by imagewise exposing the forming material; (c) applying an ink and a fountain solution to the printing master; (d) also comprising an alcohol and preferably also an alkanolamine. Removing the ink-receptive areas from the print master by providing a cleaning liquid consisting of
Lithographic direct-to-plate method using a reusable substrate with a hydrophilic surface. 2. The method according to claim 1, wherein the cleaning liquid is an aqueous solution comprising from 1% to 20% by weight of alcohol and up to 20% by weight of alkanolamine. 3. A method according to claim 1, comprising two cleaning steps, first supplying the alcohol to the printing master and then supplying the alkanolamine. 4. The method according to claim 1, further comprising the step of rinsing the substrate with water (e). 5. During step (e), add 50 ml / m ^{2 of} water.
5. The method according to claim 4, wherein the substrate is provided in the following amounts: 6. During step (d), the print master is clothed,
A method according to any of the preceding claims, wherein the rubbing is performed by mechanical means such as a rotating brush or by jetting water or a volatile medium. 7. The alcohol is benzyl alcohol or 2
-The method according to any of claims 1 to 6, which is butoxyethanol. 8. The method according to claim 1, wherein the alkanolamine is ethanolamine. 9. The method according to claim 1, wherein the substrate is a plate cylinder of a rotary printing press or a plate or sleeve mounted on a plate cylinder of a rotary printing press. 10. The method according to claim 1, wherein a coating solution or a cleaning solution is sprayed or sprayed on the substrate.