Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41N—PRINTING PLATES OR FOILS; MATERIALS FOR SURFACES USED IN PRINTING MACHINES FOR PRINTING, INKING, DAMPING, OR THE LIKE; PREPARING SUCH SURFACES FOR USE AND CONSERVING THEM
  • B41N3/00—Preparing for use and conserving printing surfaces
  • B41N3/006—Cleaning, washing, rinsing or reclaiming of printing formes other than intaglio formes
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41C—PROCESSES FOR THE MANUFACTURE OR REPRODUCTION OF PRINTING SURFACES
  • B41C1/00—Forme preparation
  • B41C1/10—Forme preparation for lithographic printing; Master sheets for transferring a lithographic image to the forme
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
  • B41J29/00—Details of, or accessories for, typewriters or selective printing mechanisms not otherwise provided for
  • B41J29/17—Cleaning arrangements

Definitions

• the invention relates to a method and a device for generating a print image on a substrate, in which ink-attracting and ink-repellent areas are produced on the surface of the print substrate in accordance with the structure of the print image to be printed, the 0 ink-repellent areas having a layer of an ink-repellent Medium are provided, on the surface of the printing medium, ink is applied, which adheres to the ink-attracting areas and which is not accepted by the ink-repelling areas, and in which the color distributed on the surface is printed on the substrate.
• Color is first applied to the print carrier using application rollers or spray devices, which wets the hydrophilic area of the print carrier.
• the ink roller then transfers ink to the surface of the print carrier, which, however, only wets the areas not covered by the moisture film. After coloring, the color is finally transferred to the substrate.
• multilayer processless thermal printing plates can be used as the printing medium, cf. e.g. WO00 / 16,988th
• a hydrophobic layer on the surface of the print carrier is removed by partial burning away and a hydrophilic layer is exposed.
• the hydrophilic layer can be wetted with an ink-repellent dampening solution.
• the hydrophobic areas are ink-accepting and can absorb ink during the printing process.
• a new printing plate must be used to create a new print image.
• a method is known from US-A- ⁇ , 016,750, in which a dye-accepting substance is deposited from a film by means of a thermal transfer process, transferred to the hydrophilic surface of the print carrier and solidified in a fixing process.
• the remaining hydrophilic areas are wetted with ink-repellent dampening solution.
• the ink is then applied to the surface of the print carrier, which, however, only adheres to the areas provided with the ink-attracting substance.
• the colored print image is then transferred to the carrier material. For creating a new print is a new film with the color. attracting substance necessary.
• Dampening solution achieved by targeted roughening and structuring of the plate surface.
• the resulting increase in surface area and porosity creates microcapillaries and leads to an increase in the effective surface energy and thus to a good wetting or spreading of the dampening solution.
• wetting-promoting substances are added to the dampening solution in offset printing. These reduce the surface tension of the dampening solution, which also leads to an improved wetting of the surface of the printing medium.
• a printing method is known in which a fountain solution is applied to the surface of the printing format.
• the dampening solution is evaporated by selective application of radiation energy in image areas.
• the water-free areas later form the ink-bearing areas, which are guided past a development unit and are colored by means of a color steam. Energy-intensive partial evaporation processes are required to generate the structured dampening solution film.
• the surface of a print carrier is coated with an ink-repellent or ink-attracting layer.
• ink-attracting areas and ink-repellent areas are correspondingly
• a wetting-promoting substance with a molecular layer thickness is applied to the surface of the printing medium before the dampening solution layer is applied and structured. Accordingly, the function loading wetting and coating separated from each other, so that the dampening solution does not have to be loaded with wetting agents.
• the method according to the invention allows the use of a very smooth surface of the print carrier, as a result of which the subsequent process steps are simplified, in particular the cleaning before a new structuring in digital printing. The wear on the printing surface is also reduced.
• a printing device is specified by means of which the method can be implemented.
• Advantageous exemplary embodiments are specified in the dependent claims relating to the method and to the printing device.
• ink-repellent or ink-absorbing layer often occurs in the further description. This layer is adapted to the color to be applied.
• the dampening solution layer is ink-repellent.
• this dampening solution layer is ink-absorbing. In practice, predominantly oil-based inks are used, so that a water-containing dampening solution layer is ink-repellent.
• FIG. 1 shows a basic illustration of a printing device in which a surfactant layer is applied
• Figure 2 schematically shows a cross section through the print carrier before and after
• FIG. 3 shows an exemplary embodiment in which a hydrophilized layer is structured
• FIG. 4 shows an exemplary embodiment in which an applied hydrophilic layer is structured
• FIG. 5 shows a schematic cross section through the print carrier before and after the structuring of the hydrophilic layer
• FIG. 6 shows an embodiment in which the
• FIG. 7 shows a cross section through an insulated electrode
• FIG. 8 shows an arrangement with a plastic
• Figure 9 shows an example of an indirect corona discharge
• Figure 10 shows a printing device with a control of the dampening solution layer thickness.
• a printing medium 10 in the present case an endless belt, is guided through a pretreatment device 12, which has a scoop roller 14 and an application roller 16 contains.
• the scoop roller 14 is immersed in a liquid contained in a container 13 which contains a wetting-promoting substance.
• This substance which contains surfactant, is applied to the surface of the print carrier 10 via the application roller 16 in a molecular layer thickness.
• the layer thickness is typically less than 0.1 ⁇ m.
• the surface of the print carrier 10 is then guided in the direction of the arrow P1 to a dampening unit 18 which, via a scoop roller 20 and an application roller 22, applies an ink-repellent or ink-absorbing fountain solution, for example water, from a fountain solution reservoir 24 to the surface of the print carrier 10.
• dampening solutions other than water can also be used.
• the dampening solution layer can also be applied by other methods, for example by steaming or spraying.
• the pressure-active surface of the print carrier 10 is completely provided with this dampening solution layer.
• the dampening solution layer typically has a layer thickness of less than 1 ⁇ m.
• the generally ink-repellent dampening solution layer is then structured by an image forming device 26.
• laser radiation 28 is used for this.
• FAR banteilde areas and ink-repelling areas corresponding to the structure of the generated to 'print image.
• the structured dampening solution layer then arrives at an inking unit 30, which uses the rollers 32, 34, 36 to transfer ink from a storage container 38 onto the surface of the print carrier 10.
• the oil-based ink adheres to areas without water-based dampening solution. It is pointed out that the ink can also be transferred to the surface of the print carrier 10 by spraying, knife coating or condensing.
• a carrier material 40 generally a paper pierbahn.
• the carrier material 40 is between. see two rollers 42, 44 passed through.
• a blanket cylinder (not shown) and further intermediate cylinders can be connected between the roller 42 and the printing medium 10, which cause ink splitting, as is known per se from the field of offset printing processes.
• the cleaning station 46 contains a brush 48 and a wiper lip 50 which are brought into contact with the surface of the print carrier 10. Cleaning can also be supported by using ultrasound, high-pressure liquid and / or steam. Cleaning can also be carried out using cleaning fluids and / or solvents.
• a new application of the wetting-promoting substance e.g. a surfactant application, a dampening solution application and a new structuring take place.
• a new print image can be printed each time the print carrier 10 rotates.
• the cleaning device 46, the device 12 and the device 26 are then switched to inactive.
• the print image that is still present in color residues is then recolored and re-printed by the inking unit 30. In this operating mode, a large number of identical print images can be printed.
• FIG. 2 schematically shows a cross section through the print carrier 10 before and after structuring with the aid of the laser beam 28.
• the wetting is promoted by applying a wetting-promoting substance to the print carrier surface 10. This happens within the printing cycle before applying the ink-repellent dampening solution.
• the wetting-promoting substance may be due to their physical and chemical properties as an extremely thin 'layer of a few molecular küllagen, preferably less than 0, l ⁇ m, apply to the surface. This layer is sufficient to promote wetting of the ink-repellent dampening solution on its free surface, so that it can also be applied as a very thin layer 54, preferably less than 1 ⁇ m.
• the further printing process is not affected by the small amount of the wetting-requiring substance, in this case a surfactant layer 52. It can be easily removed by the cleaning process integrated in the print cycle.
• the wetting-promoting layer 52 makes it possible to dispense with the otherwise roughened, porous printing plate surface. Instead, a smooth surface of the print carrier 10 is possible, which can be cleaned with significantly less effort. A fast and stable cleaning process is essential for such a digital flat printing process or offset printing process and is a decisive factor for its effectiveness. Accordingly, the surface of the print carrier 10 has a roughness that is smaller than the roughness used in the standard offset printing method.
• the average roughness depth R z is typically less than 10 ⁇ m, preferably less than 5 ⁇ m. Expressed as the center roughness value R a , the roughness value is in the range less than 2 ⁇ m, preferably less than 1 ⁇ m.
• a change in the molecular or atomic structure of the material of the print carrier as well as a permanent and firmly anchored to the surface of the print carrier Requiring shift is not necessary.
• the additionally applied wetting-promoting substance proposed here for example the surfactant layer 52, develops its wetting-promoting effect even with the smallest amounts. Accordingly, their influence on the properties of the print carrier 10 is negligible in many ways. Another advantage results from the fact that it is now possible to dispense with the additives which are usually present in offset printing in dampening solutions.
• the dampening solution layer 54 and the surfactant layer 52 are removed by the laser beam 28 in accordance with the required image structure. These areas are then colored with ink by the inking unit 30. Because of the very smooth surface of the print carrier 10, cleaning is made easier, the surfactant layer 52 being completely removed again. Furthermore, the wear on the surface of the print carrier 10 is reduced.
• Figures 3, 4 and 5 show a further embodiment of the invention.
• the ink-repellent or ink-attracting agent is applied before the application
• Layer on the usable ' surface of the print carrier a structuring of a hydrophilic layer with a molecular layer thickness.
• a steam device 60 is used, which acts on the surface of the pressure carrier 10 with hot steam.
• Print carrier .10 has an Si02 coating on its surface. After the steam treatment, the pressure carrier 10 is dried by a suction device 62. The hot water vapor creates a hydrophilic molecular structure, eg SiOH, on the outer surface. After the subsequent structuring by the structuring device 26 by means of laser radiation 28, hydrophilic areas and hydrophobic areas are created in accordance with the structure of the printed image to be printed.
• the downstream dampening unit 18 Through the downstream dampening unit 18, the entire usable surface of the printing medium 10 is brought into contact with a dampening solution layer, the dampening solution accumulating only on the hydrophilic areas, so that ink-attracting areas and ink-repellent areas are formed in accordance with the structuring carried out.
• the inking unit 30 then applies the ink, the oil-containing ink accumulating in areas without water-containing dampening solution.
• the printed image is then reprinted onto the carrier material 40.
• the hydrophilic layer is structured on the surface of the print carrier 10 in accordance with the print image.
• the hydrophilic layer is extremely thin and is only a few nanometers, typically less than 4 hm. It can therefore be structured with very little energy expenditure during a printing cycle, the hydrophilic molecular layer disappearing.
• the dampening solution is then applied, which creates a moisture film only on the non-hydrophilic areas. Inking and transfer printing takes place according to the known principles of planographic printing or offset printing described.
• the hydrophilic layer can also be removed, but does not necessarily have to be removed, the printing cycle can begin again.
• the hydrophilic layer is regenerated or reapplied and then the hydrophilic layer is structured according to the new image data.
• the hydrophilic layer is generated by activating the surface of the print carrier and by a suitable change in the outer molecular surface structure. For example, this can be made possible by using chemical activators, reactive gases and / or a suitable energy supply.
• a hydrophilic SiOH structure can be formed on the surface.
• the print carrier must be provided with an Si02 coating. It is also possible for the print carrier to pass through an activator bath in order to produce a hydrophilization of the surface. It is also possible to apply an activator via a nozzle system. Another possibility is to generate the hydrophilic layer by flaming the surface of the print carrier 10. Here too, wetting-promoting surface structures are created in a molecular layer thickness.
• An advantageous arrangement is the combination of the hydrophilization with the cleaning.
• both the cleaning and the h 'ydrophil are used.
• the cleaning and the creation of the hydrophilic layer are then carried out in a single process step.
• a wetting-promoting substance is applied to the surface of the print carrier in order to produce the hydrophilic layer.
• the pretreatment device 12 described in the embodiment according to FIG. 1 can be used.
• a liquid containing a wetting-promoting substance for example a surfactant, can be applied in a molecular layer thickness.
• the layer thickness is typically less than 0.1 ⁇ m.
• Alcohols can also be considered as a further wetting-promoting substance.
• the application can also be carried out by knife coating, spraying on and vapor deposition.
• this hydrophilic layer can be partially removed by local thermal energy supply. Due to the small layer thickness, the energy consumption can be low.
• laser diodes, LEDs, LED combs or heating elements can also be used.
• a new structuring can take place per revolution of the print carrier 10, as a result of which a new print image is printed per revolution.
• the devices for the restructuring are then switched to inactive.
• FIG. 5 shows a cross section through the print carrier 10 before and after the structuring by the laser beam 28 for the example according to FIG. 4.
• the surface of the print carrier 10 is very smooth, as is also the case with the previous examples.
• the thin surfactant layer 52 is structured by the laser beam 28, ie hydrophilic areas 68 and hydrophobic areas 64 are generated.
• the dampening unit 18 applies a thin, water-containing moist film only to the hydrophilic areas.
• the areas 64 are then covered by the inking unit 30 with a ner inked ink, which is repelled by the dampening solution 54 in the area of the hydrophilic areas 68.
• the surface energy of the printing medium 10 must be at least as high as the surface tension of the dampening solution film. This means that the value of the contact angle between the surface of the pressure carrier 10 and the dampening solution must assume a value below 90 °. In practice it is necessary that a contact angle of ⁇ 25 ° has to be achieved in order to produce the required liquid film with a thickness of approx. 1 ⁇ m. This places high demands on the surface energy of the print carrier, which, especially when considering the extremely high surface tension value of water, namely 72 mN / M, as the basis of the ink-repellent fountain solution.
• Plastic print media or metallic print media cannot do this without further measures, such as roughening, application of surfactants, generation of micro capillaries, etc.
• the contact angle from water to polyimide or polycarbonate is approx. 75 °.
• metal surfaces, which in their purest form have very high surface energies and thus the smallest contact angles, show relatively hydrophobic behavior under normal ambient conditions. This is essentially due to the oxidation layer effective on metal surfaces, which always forms under normal conditions. Even the slightest contamination has a negative impact on the desired surface energy.
• Kunststoff- angles of over 70 ° can often be found in practice.
• a corona treatment of the surface of the print carrier 10 is carried out for hydrophilization.
• a high voltage generator 70 generates an alternating voltage in the range from 10 to 30 kV, preferably in the range from 15 to 20 kV, at a frequency from 10 to 40 kHz, preferably in the range from 15 to 25 kHz.
• An output terminal of the high voltage generator 70 is connected to an insulated electrode 72.
• the other output connection is placed on a sliding contact 74 which is connected to the pressure carrier 10.
• the relatively high voltage on the electrode 72 leads to the ionization of the air.
• a corona discharge arises, the surface of the print carrier 10 being bombarded with free ions.
• the cleaning effect is in the foreground, with degreasing of the surface and removal of the oxide layer increasing the surface energy and thus reactivating the hydrophilic properties of metals.
• contact angles to water of up to less than 20 ° can be achieved with plastic surfaces and with metal surfaces.
• Corona treatment changes the physical surface properties of the wearer beforehand, but not its mechanical properties. There are no visible changes, for example with a scanning electron microscope. weisbar.
• the hydrophilized capitalization can be improved by supplying process gases, preferably oxygen or nitrogen..
• a dampening solution is applied to the hydrophilized surface of the print carrier 10 in the dampening unit 18; Structuring is then carried out with the aid of laser radiation 28.
• the structured dampening solution layer is inked by the inking unit 30 and the ink is later printed onto the carrier material 40. Color residues are removed in the cleaning station 46. Since the surface of the print carrier 10 is also very smooth, as in the previous examples, the cleaning process is simple and can be implemented with high effectiveness. The cyclical printing process can then start again. Alternatively, a restructuring can also be omitted and the previous print image is inked and reprinted.
• FIG. 7 shows the insulated electrode 72.
• a metallic core 76 is surrounded by a ceramic jacket 78. With such a structure, electrical flashovers are prevented. This is particularly advantageous' when 10 metal is used as a carrier. Alternatively, the insulation can also be created by a plastic jacket.
• Figure 8 shows the structure of a print carrier 10
• An electrode plate 80 is arranged on the side of the print carrier 10 which lies opposite the electrode 72.
• the electrode 72 can be designed without insulation.
• FIG. 9 shows a hydrophilization process with an indirect corona treatment.
• the output connections of the High-voltage generator 70 are connected to two electrodes 82, -84, which are arranged above the pressure carrier 10.
• the electrical discharges generated by the high voltage between the two electrodes 82, 84 generate ions which are directed to the surface of the pressure carrier 10 by an air stream or process gas stream and which develop the wetting-promoting effect here.
• a blower 86 is used to generate the flow.
• a low-pressure plasma treatment can also be used, which increases the surface energy on the surface of the print carrier 10.
• a high-voltage discharge is generated under vacuum conditions, for example in the range from 0.3 to 20 mbar, by which process gas is ionized and brought into the plasma state.
• This plasma comes into contact with the surface of the print carrier 10.
• the effect of the plasma can be compared with the effect of the corona treatment.
• the layer thickness is typically in the range of 1 ⁇ m.
• Drophilticians Kunststoffmaschine by the method described Hy there are various advantages. There is no need for the roughened porous printing plate surface as in the standard off-printing process. Instead, a very smooth surface is possible, the roughness range of which is very low, for example in a range of the average roughness value R a ⁇ 1 ⁇ m. This enables a quick and stable cleaning process for the surface.
• the described printing process there is neither a permanent change in the molecular or atomic structure of the material of the print carrier nor a permanent wetting promoting layer firmly anchored to the print carrier necessary.
• the described hydrophilization process enables the print carrier to be optimized with regard to other requirements without taking the surface energy into account.
• the described hydrophilization process also makes it possible to dispense with the additives required for wetting in offset printing. A further application of additional wetting-promoting substances is no longer necessary. This avoids a relatively complicated process control and reduces the additional expenditure on consumables. Another advantage is the cleaning effect of the hydrophilization process. It supports the cleaning process necessary for the digital printing process and thus further reduces the hardware expenditure required.
• Figure 10 shows another embodiment.
• the constant and precisely defined thickness of the dampening solution layer plays on the surface of the printing medium play a crucial role in the stability and efficiency of the printing process.
• a printing device is described which allows and monitors a defined, controllable and controllable very thin application of the dampening solution.
• the standardized offset printing process generally uses a dampening unit consisting of a number of rotating rollers to apply the dampening solution. Together with a roughened or porous printing plate with good water content, a water film is obtained which is sufficiently stable for standard offset printing.
• the amount of dampening solution and the thickness of the dampening solution layer can be adjusted, for example, by the delivery of certain rollers to one another or the speed of the scoop roller. This leads to the storage effect of the dampening system and also the pressure plate to a strongly delayed reaction to adjustment measures.
• the roughened, strongly water-storing pressure plates are absolutely necessary for the generation of a sufficiently stable water film. It is also known from the prior art to produce a very thin film of water by cooling the printing plate and the consequent condensation of the atmospheric moisture on the printing plate.
• the thickness of the water film is strongly dependent on the ambient conditions, such as air humidity and temperature, and can hardly be kept constant over a long period.
• a structure is used which is similar to the structure described in DE-A-101 32 204 mentioned at the outset and which implements a CTP method (computer-to-press method).
• the printing device shown in FIG. 10 makes it possible to generate different print images on the same surface of the cylindrical print carrier 10.
• the printing device contains the inking unit 30, with a plurality of rollers, through which the oil-containing ink is transferred from the reservoir 38 to the surface of the printing medium 10.
• the colored surface of the printing medium 10 transfers the ink to a blanket cylinder 90. From there, the ink reaches the paper web 40, which is pressed against the blanket cylinder 90 by the impression cylinder 42.
• the dampening unit 18 transfers dampening solution, for example water, from the dampening solution storage container 24 to the surface of the printing medium 10 via three rollers Plasma treatment can be brought into a more hydrophilic state, as has already been described above.
• the dampening solution layer is supplied by means of an energy supply Laser beam 28 selectively removed and the desired image structure is created.
• the inking 30 then takes place at the ink-attracting areas of the structure. After structuring 'is the color using a fixing solidified 92nd
• Two operating modes are also possible in this example.
• a first operating mode a large number of printing processes take place before the surface is structured again.
• the print image located on the print carrier 10 is inked and re-printed once per print, i.e. the printed image is colored several times.
• a second operating mode a new print image is applied to the surface of the print carrier.
• This cleaning station can be pivoted towards the pressure carrier 10 according to the arrow P2 and pivoted away from it again. Further details of the construction of the printing device according to FIG. 10 are described in the aforementioned DE-A-101 32 204.
• an energy source 94 is arranged after the dampening unit 18, which emits thermal energy to the dampening solution film on the surface of the printing medium 10. This energy reduces the thickness of the dampening solution layer.
• the energy source is followed by a layer thickness measuring device 96.
• This layer thickness measuring device 96 determines the current thickness of the dampening solution film and emits an electrical signal corresponding to the thickness to a control 98.
• the controller 98 compares the measured actual thickness with a predetermined target thickness. In the event of a deviation between the target and actual values, the energy source 94 is controlled in such a way that the thickness of the dampening solution layer is reduced to the desired target thickness.
• the layer thickness measuring device 96 can, for example, operate in a contactless manner using the triangulation method, the transmission method or the capacitive method.
• One or more IR lamps, radiant heaters, laser systems, laser diodes or heating elements can be considered as energy source 94.
• the interaction of the energy source 94, the layer thickness measuring device 96 and the control 98 can be such that only a monitoring function is carried out. If the layer thickness exceeds or falls below a predetermined target value, a corresponding warning signal is emitted and the energy supply for the energy source 94 is then reset.
• the energy source 94, the layer thickness measuring device 96 and the controller 98 can, however, also be combined to form a control loop in which the energy source 94 is controlled in such a way that, in the event of a control deviation between the actual value and the target value of the layer thickness, this control deviation is minimized and preferably to zero is regulated.
• the energy source 94 can be controlled by the control with the aid of an analog voltage regulation or digitally by a pulse modulation, as is indicated by the signal sequence 100.
• both an endless belt and a cylinder can be used as the print carrier.
• the transfer printing onto the carrier material can take place directly or with the interposition of a rubber blanket cylinder or further intermediate cylinders for color splitting.
• the layer thickness control according to the example according to FIG. 10 can also be used for the other examples.
• the applied color can be fixed using a fixing device.
• the cleaning station 46, the dampening unit 18 and the image generation device can be switched inactive and active, for example by pivoting.

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• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Printing Methods (AREA)
• Printing Plates And Materials Therefor (AREA)
• Duplication Or Marking (AREA)

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• 2002
  • 2002-02-19 DE DE10206937A patent/DE10206937A1/de not_active Withdrawn
• 2003
  • 2003-02-14 EP EP03708101A patent/EP1476313B1/fr not_active Expired - Lifetime
  • 2003-02-14 DE DE50310699T patent/DE50310699D1/de not_active Expired - Lifetime
  • 2003-02-14 WO PCT/EP2003/001496 patent/WO2003070481A1/fr not_active Application Discontinuation
  • 2003-02-14 AT AT03708101T patent/ATE412533T1/de not_active IP Right Cessation
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