DE60100691T2 - Inkjet printing process for the production of a lithographic printing plate - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a direct-to-plate process to produce a heat sensitive high quality lithographic printing plate using an inkjet printhead.

GENERAL STATE OF THE 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 one hydrophilic background imagewise oily or made bold colors attractive.

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-sensitized hydrophilic colloids and a variety of synthetic ones Contain photopolymers. 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 developed to contain the diazonium salt contained in the unexposed areas or remove 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.

heat-sensitive Imaging elements with an imaging layer with hydrophobic thermoplastic polymeric, in a water soluble or alkali-soluble or water-swellable or alkali-swellable resin dispersed particles and a compound that can convert light into heat are e.g. B. described in 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 832 739, EP-A 839 648, EP-A 839 647 and EP-A 849 091. Most make are as light in warmth converting compound soot and mentioned an IR absorbing dye.

For the production of a Imaging elements developable on the press are preferred Compounds used to absorb infrared light. Both soot and infrared light absorbent dyes or pigments are suitable.

The order to produce casting compositions used in lithographic printing plates mostly according to coating techniques such as dip coating, cascade coating and curtain coating. When coating on the press very often spray techniques are used. The term "spritz" indicates a process in which an aqueous solution or Dispersion of a resin (casting solution) by means of one atomizing the casting solution Spraying device sprayed on and is adsorbed and applied to a substrate. spraying techniques for coating a substrate clamped in a printing press are z. For example, described in US-A 4,626,484, EP-A 818 711, US-A 5 713 287 etc.

In DE 3 911 934 discloses a printing plate with printing and non-printing areas, the printing areas consisting of an ink-attracting material applied as a thin layer to a hydrophilic material.

In DE 4,339,493 discloses a method in which a radiation sensitive imaging material is jetted directly onto a printing plate by means of an ink jet printer. The sprayed-on material is hardened by radiation and is then able to absorb and transfer printing ink.

In US 5 871 879 a layer, preferably a radiation-sensitive or heat-sensitive layer, is applied to a glass substrate with defined physical properties.

• a) ein Medium mit einem Träger und einer hydrophilen Oberfläche und
• b) ein flüssiges Material mit einem reaktionsfähigen Übergangsmetallkomplex einer fluorierten organischen Säure, der eine Reaktion mit der hydrophoben Oberfläche einzugehen und dabei eine Farbe freisetzende Schicht zu erzeugen vermag.

WO 99 059 826 discloses a set consisting of a medium and a liquid material, comprising:

• a) a medium with a support and a hydrophilic surface and
• b) a liquid material with a reactive transition metal complex of a fluorinated organic acid, which is able to react with the hydrophobic surface and thereby produce a color-releasing layer.

In 94 011 191 there is an ink jet device described for the production of printing plates, in which by movement of the table several pages on large format lithographic Printing plates can be printed.

The experts are different Spray techniques known. With compressed air spraying, compressed air is used as the spraying technique used. With airless spraying (liquid pressure spraying) the pouring solution under atomized under high pressure. With electrostatic spraying, the casting solution is replaced by electrostatic Force atomized. Electrostatic spraying is advantageous for increasing the adhesion of the resin in the casting solution, wherein a grounded workpiece as an anode to be coated and a casting solution sprayer as Be used cathode and by applying a high negative voltage an electrostatic field is created between the anode and cathode, through which the resin particles are negatively charged and in an efficient manner on the workpiece to be coated be adsorbed.

When using airless spraying techniques for the application of lithographic casting solutions it is pretty difficult to get an end product with high cosmetic quality (mainly one level coating without streaking). To get high quality lithographic materials (both on the press as thermal printing plates that cannot be developed on the press) which high resolution, high sensitivity and good playback capabilities are required The strictest requirements regarding the cosmetic quality of the printing plate apply. This cosmetic quality can as the presence of strokes, a general flatness and the presence of a marbling pattern can be defined.

The application of compressed air spraying techniques for the application of lithographic casting solutions yields a better one cosmetic quality of the final product. Lithographic prints made using this technique Printing plates are described in EP-A 1 084 380 and EP-A 1 084 862, both of which were filed on September 15, 1999. Of course, this is based Technology but on a strong atomization of the casting solution what to a low coverage efficiency on the lithographic substrate leads and because up to 50% of the atomized Pouring solution in the environment is lost. Another disadvantage is the high risk contamination of components of the printing press such as the inking rollers, Imaging units, cleaning units, etc.

It still exists Need for a technique to apply layers to a press clamped substrate, obtaining a layer without marbling and banding allows and does not cause contamination of the printing press.

BRIEF PRESENTATION THE PRESENT INVENTION

Object of the present invention is a direct-to-plate process to provide a high quality printing plate, where no casting solution is wasted and contamination of components of the printing press is prevented. Another object of the present invention is to provide a direct-to-plate method with a to provide recyclable lithographic substrate.

The above tasks are solved by a method as defined in claim 1.

To produce the high quality according to the invention Printing plate can be made from a radiation sensitive solution of an ink jet print head has a continuous layer on it lithographic substrate are applied, droplets of Pouring solution directly are sprayed onto the lithographic substrate. There is none here Waste of the casting solution in the environment instead. Furthermore, the risk of pollution other elements of the printing press such as the inking rollers or fix the imaging unit.

Other objects and preferred embodiments of the present invention will become apparent from the description below seen.

SUMMARY THE FIGURES

1 shows schematically a possible arrangement of an inkjet printhead in the vicinity of the part of the printing press carrying a lithographic substrate.

2 shows schematically a further possible arrangement of an ink jet print head in the vicinity of the part of the printing press carrying a lithographic substrate.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

To maintain a high quality Printing plate according to the Directto-Plate process is made from a radiation-sensitive solution a continuous layer using an inkjet print head applied to a lithographic substrate.

Any desired ink jet print heads known to those skilled in the art are suitable for the method according to the invention. Inkjet printing is basically done using two techniques: letterpress printing and drop-on-demand inkjet printing. In the method according to the invention, printheads for the high pressure ver prefer to drive. One of the advantages of such printheads is the extremely high speed (speeds up to 300 m / min are known to the experts). Typically, devices for producing a continuous stream of droplets include a nozzle or matrix of nozzles through which liquid is forced under pressure in a cylindrical stream. Such a cylindrical flow is not stable and will dissolve into a series of droplets. If the current is subjected to an oscillation whose frequency is close to the frequency of the fastest increasing natural disturbance within the current, the current can be broken up by this oscillation. In this method, the stream forms a series of droplets, the volume of which is equal to a cylindrical cross section of the stream, which corresponds to the length of the forced oscillation wavelength. Typical high pressure inkjet printers are e.g. B. described in EP-A 1 013 458, EP-A 1 013 438, EP-A 1 013 425 etc. As suitable high-pressure ink jet print heads are those used in VersaMark ink jet printers (sold by Scitex Digital Printing).

Drop-on-demand ink jet printer are also suitable. Drop-on-demand producers can electrostatically controlled type, in which at negative pressure in the nozzle a (by the surface tension retained) Drop formed and by applying a high voltage between the drop meniscus and a control electrode is released. Drop-on-demand producers can also be of the pressure pulse type, with a transducer, for example a piezoelectric crystal that is used in targeted Is excited to develop a compressive force on a liquid body and so a drop of this liquid through a nozzle to hurl at a separation area. Piezoelectric are preferred Drop-on-demand printheads such as those in US Pat. No. 5,855,713, WO-A 99 19147, WO-A 99 1284 and WO-A 95 18 717. Typical usable drop-on-demand piezoelectric ink jet printheads are z. B. XAARJET 500 with a printing width of 70 mm and 500 nozzles, XAARJET 64 with a print width of 8.6 mm and XAARJET 128 with a print width of 17.4 mm. Xaarjet is a trademark of XAAR pcl, UK.

Since the inkjet printheads in the inventive method need to create a flat layer from a casting solution deleted the need for visual control the nozzles, d. H. Both the structure and driver of the printhead can be used Compared to imagewise inkjet printing to a noticeable degree be simplified.

The nozzles in the nozzle matrix the ink jet printer for use in the present invention can be one Diameter between 50 and 1,000 μm, preferably between 100 and 500 μm exhibit. The division of the nozzles the nozzle matrix can also fluctuate between the same values. The nozzle matrix preferably contains two rows, the nozzles one row exactly in the gap between two nozzles of the other row are. This ensures that a flat layer can be applied even when using Nozzles with a printing width of 500 μm or more with a pitch of 500 μm or more.

The distance (d) between the inkjet printhead and the lithographic substrate depends on the distance between the Nozzles (division) and the diameter of the nozzles. The distance can be quite small (on the order of 100 to 5,000 μm) are kept, which includes the advantage that the device for coating of a substrate clamped in a printing press can be made very compact can. Since the distance (d) is quite small and the lithographic Substrate-bearing roller very often within the distance range falling axial stroke, means are preferably added to the Keep distance (d) constant. The inkjet printhead can do this be provided with spacers, which with flexible means such Springs, spiral springs, rubber bands etc. are attached to the printhead. Main advantage of a constant Distance (d) is a greater homogeneity of the applied layer and the absence of banding.

The printhead for use in the present invention can be designed to reciprocate across the width of the lithographic substrate. In 1 such a construction is shown schematically. On a roller ( 100 ) there is a lithographic substrate. This lithographic substrate can be a plate drum of a rotary printing press or else a plate or sleeve attached to a plate drum of a rotary printing press. On a frame ( 101 ) with poles ( 102 ) and support elements ( 103 ), a shuttle element equipped with an ink jet print head is arranged so that it can be moved forwards and backwards in the direction of arrow A (which corresponds to the element driving the shuttle element). The support elements ( 103 ) of the frame also serve as a spacer in this case, the distance (d) between the frame and the roller ( 100 ) keep constant. For this, the support elements ( 103 ) brought into contact with the outer edges of the roller and by means of flexible elements - in 1 Springs ( 105 ) - withheld at this point. In this way, although the usable width of the lithographic substrate at the edges is slightly reduced, the advantages of a constant spacing (d) outweigh this possible (small) problem.

The ink jet print head according to the invention is not necessarily to be attached to a pendulum element. An offset arrangement of different print heads on the frame is also possible, the sum of the print widths of all individual print heads equaling the usable width of the lithographic substrate is. In this case, the inkjet printheads are fixed and do not have to be moved back and forth across the width of the lithographic substrate. In 2 such an arrangement is shown: all digits are the same as in 1 , only the pendulum element ( 104 ) is offset by three on the frame ( 102 ) arranged inkjet printheads ( 106a . 106b and 106c ) has been replaced. Methods and means for the offset arrangement of inkjet printheads are described in e.g. B. US-A 4 922 271, US-A 940 998 and US-A 5 428 375. A combination of a pendulum element with printheads arranged offset on the pendulum element is also a possible embodiment of an arrangement for carrying out the method according to the invention.

The radiation sensitive used in the invention solution contains preferably hydrophobic thermoplastic polymers, in a hydrophilic Binder dispersed particles with an average particle size between 40 nm and 2,000 nm, particularly preferably between 40 nm and 200 nm. Furthermore, the polymeric particles are preferably characterized by a coagulation temperature above 50 ° C and particularly preferably above 70 ° C. The coagulation temperature the polymeric particles are not subject to a specific upper one Limit, however, it should be sufficient are below the decomposition temperature of the polymeric particles. The coagulation temperature is preferably at least 10 ° C under the temperature, during the decomposition of the polymer particles entry.

Preferred examples of thermoplastic hydrophobic polymeric particles for use in the present Invention have a Tg of more than 80 ° C. The weight average of the Molecular weight of the polymers can be between 5,000 and 5,000,000 g / mole fluctuate. Preferred polymeric particles are polyvinyl chloride, Polyvinylidene chloride, polyester, polyurethane, polyacrylonitrile, Polyvinyl carbazole, etc., and copolymers or mixtures thereof. All polystyrene, polymethyl methacrylate or Copolymers of the same.

Suitable hydrophilic binders for use in the present invention are water soluble (co) polymers such as synthetic homo- or copolymers such as polyvinyl alcohol, a poly (meth) acrylic acid, a poly (meth) acrylamide, a polyhydroxyethyl (meth) acrylate Polyvinyl methyl ether or natural Binders such as gelatin, a polysaccharide such as e.g. B. dextran, pullulan, Cellulose, gum arabic, alginic acid, Inulin or chemically modified inulin.

The lithographic used in the present invention The substrate can be a flexible support such as paper or a plastic film, which is preferred is coated with a cross-linked hydrophilic layer. Particularly preferred becomes a metal support like an aluminum beam with a hydrophilic surface, z. B. an electrochemically and / or mechanically grained and anodized aluminum support. The lithographic substrate can be a sheet-like material such as a Plate, but the radiation-sensitive solution can also be direct applied to the plate drum of a rotary printing press be, the drum then serves as a substrate. The lithographic Substrate can also be in the form of a seamless sleeve-shaped printing plate, the z. B. can be obtained by a plate by means of a Laser is soldered together into a cylindrical shape. This sleeve-shaped plate can then be pushed onto the print drum instead of like one conventional Printing plate to be clamped in the printing press. More detailed information about sleeve-shaped pressure plates can be found in "Grafisch Nieuws ", 15, 1995, Pages 4 to 6.

In the imagewise exposure according to the invention it is preferably an imagewise scanning exposure under Use a laser or an LED. Preferred are in the infrared range or near infrared, d. H. in the wavelength range between 700 and 1500 nm, emitting laser. Nearby are very particularly preferred Infrared emitting laser diodes. Furthermore, the for the imagewise exposure laser also used on the one carrying the ink jet printhead Pendulum element are attached, making the application of the radiation sensitive solution and the imagewise exposure during the same passage of the pendulum element can be performed. in the The system described above uses the laser during the application of the radiation sensitive solution suffer less pollution than in a system where instead of Inkjet printhead a sprayer is used. In the latter case, the casting solution becomes strong atomized, what an elevated Risk of laser pollution.

The steps described above inventive method are preferably carried out on the press. After imagewise exposure printing is started by adding ink and fountain solution.

After printing, the ink-attracting areas are removed from the substrate by applying a cleaning liquid. Suitable cleaning liquids and methods for removing the ink-attracting areas are described in EP 1 118 470 . EP 1 118 471 and EP 1 118 472 all of which were submitted on January 18, 2000. After cleaning, the substrate can be recycled by repeating the above-described steps of the method according to the invention, e.g. B. by applying a continuous layer of a radiation-sensitive solution, imagewise exposure and application of printing ink and fountain solution.

EXAMPLES

Prepare the spray solution

A 2.61% by weight aqueous solution is passed through Relocation of a polystyrene latex, a heat absorbing compound (I) and Glascol E15 (a polyacrylic acid, trademark of N.V. Allied Colloids Belgium). After spraying and drying it contains so resulting layer 75% by weight of the polystyrene latex, 10% of the heat absorbing Compound (I) and 15% by weight Glascol E15.

Formel (I)

Formula (I)

manufacturing of the lithographic substrate

A 0.20 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 which contains 4 g / l hydrochloric acid, 4 g / l hydrochloric acid and 5 g / l aluminum ions, in order to obtain a surface topography with an arithmetic mean roughness Ra of 0.5 μm.

After rinsing with demineralized Water, the aluminum foil with an aqueous, containing 300 g / l 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 150 A / m ² for about 300 s in an aqueous solution containing 200 g / l of sulfuric acid to give an anodic, 3.00 Obtaining g / m ² Al ₂ O ₃ containing oxidation film, then washed with demineralized water, then first post-processed with a solution containing polyvinylphosphonic acid and then with a solution containing aluminum trichloride, then rinsed with demineralized water at 20 ° C. for 120 s and dried.

Comparative example 1

manufacturing of the heat sensitive Imaging element

The lithographic substrate produced as described above is clamped on a drum and at a line speed of 164 m / min. turned. The spray solution is applied by means of a VAU compressed air nozzle (trademark of Spraying Systems Belgium, Brussels) moving at a speed of 0.025 ms ^-1 in the transverse direction. The spray nozzle is attached at a distance of 60 mm to the lithographic substrate. The flow rate of the spray solution is 7 ml / min. set. During the spraying process, an air pressure of 6,327 kgm ^{-2 is} generated in the spray nozzle. The final coat weight is obtained by spraying in 6 passes through the spray nozzle as standard. The layer obtained is dried at a temperature of 70 ° C. during the spraying process and optionally afterwards for a further 30 s.

example 1

manufacturing of the heat sensitive Imaging element

A lithographic substrate prepared as described above is clamped on a drum and at a speed of 164 m / min. turned. The spray solution is by means of a Ge Speed of 0.33 ms ^-1 cross-directional high-pressure ink jet print head sprayed over the entire surface. A layer thickness comparable to that in Example 1 is obtained.

Checking the pollution behavior

Test 1

The ratio of the to the substrate applied layer to the amount of liquid used is calculated. The Strength the applied layer is with an optical densitometer measured. The amount of spray liquid used is measured after coating 10 plates.

Test 2

While the application of the spray solution the lithographic substrate will be paper strips on and next to the spray nozzle attached. After spraying of 10 plates, the color of the strips will be the color of unused Compared paper.

The results of these tests are listed in Table 1.

Table 1: Soiling behavior

The results listed in Table 1 show that at Apply the spray solution the lithographic substrate using an ink jet printhead no spray solution wasted and no pollution of the environment is caused.

Claims (10)

One identified by the steps below Direct-to-plate method for the production of a lithographic printing plate a) coating a lithographic substrate with a continuous layer from a radiation-sensitive solution using an inkjet printhead, b) imagewise exposure the layer, c) Application of printing ink and fountain solution the layer, d) removal of the ink-attracting areas from the Substrate by applying a cleaning liquid, e) Repetition steps (a) to (c) using the same substrate. A method according to claim 1, characterized in that the Inkjet printhead is a high pressure inkjet printhead. A method according to claim 1 or 2, characterized in that that the Inkjet printhead is a drop-on-demand printhead. A method according to claim 3, characterized in that the Drop-on-demand print head is a piezoelectric print head. Method according to one of the preceding claims, characterized characterized that the radiation sensitive solution hydrophobic thermoplastic polymer particles and radiation in warmth converting link contains. Method according to one of the preceding claims, characterized characterized that the A plate drum of a rotary printing press or a substrate mounted on a plate drum of a rotary printing press Plate or sleeve is. Method according to one of the preceding claims, characterized in that the substrate with a a flexible support coated with a cross-linked hydrophilic layer. Method according to one of the preceding claims, characterized in that step (a) by means of a device in which the ink jet print head is mounted on a shuttle element which can be moved over the lithographic substrate 104 attached, is carried out. Method according to one of claims 1 to 7, characterized in that that step (a) by means of a device in which a non-reciprocating Inkjet printhead is performed. A method according to claim 8, characterized in that on the pendulum element both the inkjet printhead and a light source for the imagewise exposure are attached to the layer.