EP1476313B1 - Printing device and method, in which a humidity promoter is applied prior to the ink-repellent or ink-receptive layer - Google Patents

Abstract

In a method and device to generate a print image on a carrier material, a surface of a print carrier is coated with a layer which is one of ink-repelling and ink-attracting. In the structuring process, ink-attracting regions and ink-repelling regions are generated. Ink that adheres to the ink-attracting regions and that is not absorbed by the ink-repelling regions is applied on the surface. The applied ink is transferred onto the carrier material. Before a new structure process on the same surface of the print carrier, the surface is cleaned and recoated with said layer. Before the application of said layer, a wetting-aiding substance is applied with a molecular layer thickness. A surfactant with hydrophilic molecule sections is used as the wetting-aiding substance.

Description

The invention relates to a method according to the claims for producing a printed image on a carrier material, wherein on the surface of the print carrier ink-attracting and ink-repellent regions are generated according to the structure of the printed image to be printed, wherein the ink-repellent regions are provided with a layer of an ink-repellent medium in that ink is applied to the surface of the print substrate, which adheres to the ink-attracting areas and which is not accepted by the ink-repellent areas, and in which the color distributed on the surface is printed on the substrate.

In the prior art, waterless offset printing methods are known whose non-printing areas are fat-repellent and therefore do not accept printing ink. The printed areas, on the other hand, are fat-absorbing and pick up the greasy ink. According to the structure of the print image to be printed, ink-attracting and ink-repellent areas are distributed on the printing plate. The printing plate can be used for a variety of transfer printing operations. For each print image, a new plate must be created with ink-attracting and ink-repellent areas.

From the US-A-5,379,698 For example, a method is known which is called a direct imaging method in which a printing original is created in the printing device on a multilayer, silicone-coated film by selective burning away of the silicone top layer. The silicone-free areas are the ink-attracting areas that accept printing ink during the printing process. Every new print requires a new foil.

In the case of the standard offset process using water, hydrophobic and hydrophilic areas are produced on the surface of the print carrier in accordance with the structure of the print image to be printed. Before application of the paint, a thin film of moisture is first applied to the print substrate using applicator rollers or spraying devices, which wets the hydrophilic area of the print substrate. Subsequently, the inking roller transfers ink to the surface of the print substrate, which wets only those areas not covered by the moisture film. After dyeing, the color is finally transferred to the carrier material.

In the known offset printing process can be used as a print carrier multi-layer processless thermal printing plates, see. eg WO00 / 16988 , According to the structures of the print image to be printed on the surface of the print carrier, a hydrophobic layer is removed by partial burning away and exposing a hydrophilic layer. The hydrophilic layer can be wetted with an ink-repellent fountain solution. The hydrophobic areas are ink accepting and can absorb ink during the printing process. To create a new print image, a new printing plate must be used.

Furthermore, a method of the US-A-6,016,750 in which an ink-attracting substance is deposited from a film by means of a thermal transfer process, transferred to the hydrophilic surface of the print substrate and solidified in a fixing process. In the printing process, the remaining hydrophilic areas are wetted with ink-repellent dampening solution. Subsequently, the ink is applied to the surface of the print carrier, which, however, adheres only to the provided with the ink-attracting substance areas. The inked print image is then transferred to the substrate. For the creation of a new print image, a new film with the color attracting substance is necessary.

In the standard offset process or planographic printing process, the wetting of the printing plate with the ink-repelling dampening solution is achieved by targeted roughening and structuring of the plate surface. The resulting increase in surface area and porosity produces microcapillaries and leads to an increase in the effective surface energy and thus to a good wetting or spreading of the dampening solution. As further measures, wetting-promoting substances are added to the wetting agent during offset printing. These reduce the surface tension of the fountain solution, which also leads to improved wetting of the surface of the print carrier. In this connection, reference is made to the literature Teschner, H .: Offsettechnik, 5th edition, Fellbach, Fachschriften-Verlag 1983, pp. 193 - 202 and p. 350.

From the US Patent No. 5,067,404 a printing method is known in which a fountain solution is applied to the surface of the printing format. The dampening solution is vaporized by selective application of radiant energy in image areas. The anhydrous areas later form the ink-bearing areas, which are led past a development unit and colored by means of a paint vapor. To produce the structured dampening solution, energy-intensive partial evaporation processes are required.

Furthermore, the patent documents WO 97/36746 and WO 98/32608 directed. In the in the WO 97/36746 described method, the dampening agent is generated by evaporation of a discrete volume of water, which condenses on the surface of the print carrier. According to the WO 98/32608 and the resulting US-A-6,295,928 a continuous ice film is applied and patterned. In both cases, locally high thermal energy must be used for structuring.

From the DE-A-10132204 (not prepublished) the same applicant, a CTP method (C omputer- T o P RESS process), wherein patterning processes can be performed repeatedly on the same surface of the print carrier. The surface of a print substrate is coated with an ink-repellent or ink-receptive layer. In a structuring process, ink-attracting regions and ink-repelling regions are produced according to the structure of the printed image to be printed. The ink-attracting areas are then colored with paint. Before a new patterning process, the surface of the print substrate is cleaned and coated again with an ink-repellent or ink-receptive layer. The layer used is a fountain solution layer or an ice layer.

It is an object of the invention to provide a printing method that has a simplified structure for digital printing with variable print image and ensures high print quality.

This object is achieved for a method by the features of claim 1.

According to the invention, a wetting-promoting substance in molecular layer thickness is applied to the surface of the print carrier before the application and structuring of the fountain solution layer. Accordingly, the function wetting and coating separated, whereby 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, whereby the subsequent process steps are simplified, in particular the cleaning before re-structuring in digital printing. In addition, the wear of the pressure surface is reduced.

It should be noted that in the further description often the term color repellent or ink-receptive layer occurs. This layer is adapted to the applied color. For example, in the case of a water-containing fountain solution layer and an oil-containing paint, the fountain solution layer is color-repellent. However, if the paint contains water, this fountain solution layer is color-attracting. In practice, mainly oily inks are used, so that a water-containing fountain solution layer is ink repellent.

Figur 1

eine Prinzipdarstellung einer Druckeinrichtung, bei der eine Tensidschicht aufgebracht wird,

Figur 2

schematisch einen Querschnitt durch den Druckträger vor und nach der Strukturierung durch einen Laserstrahl,

Figur 3

ein Ausführungsbeispiel, bei dem eine hydrophilisierte Schicht strukturiert wird,

Figur 4

ein Ausführungsbeispiel, bei dem eine aufgetragene hydrophile Schicht strukturiert wird,

Figur 5

einen schematischen Querschnitt durch den Druckträger vor und nach der Strukturierung der hydrophilen Schicht,

Figur 6

ein Ausführungsbeispiel, bei dem die Hydrophilisierung durch eine Koronaentladung erfolgt,

Figur 7

einen Querschnitt durch eine isolierte Elektrode,

Figur 8

eine Anordnung bei einem KunststoffDruckträger,

Figur 9

ein Beispiel für eine indirekte Koronaentladung, und

Figur 10

eine Druckeinrichtung mit einer Regelung der Feuchtmittel-Schichtstärke.

Embodiments of the invention are explained below with reference to the drawing. It shows:

FIG. 1

a schematic representation of a printing device in which a surfactant layer is applied,

FIG. 2

schematically a cross section through the print carrier before and after structuring by a laser beam,

FIG. 3

an embodiment in which a hydrophilized layer is structured,

FIG. 4

an embodiment in which a coated hydrophilic layer is structured,

FIG. 5

a schematic cross section through the print carrier before and after structuring of the hydrophilic layer,

FIG. 6

an embodiment in which the hydrophilization is carried out by a corona discharge,

FIG. 7

a cross section through an insulated electrode,

FIG. 8

an arrangement with a plastic print carrier,

FIG. 9

an example of an indirect corona discharge, and

FIG. 10

a printing device with a control of dampening solution layer thickness.

In FIG. 1 is a schematic representation of a printing device shown, which is constructed similar to that in the US Patent No. 5,067,404 the same applicant is described. A print carrier 10, in the present case an endless belt, is guided through a pretreatment device 12 which comprises a scoop roller 14 and an applicator roller 16 contains. The scoop roller 14 immersed in a liquid contained in a container 13, which contains a wetting-promoting substance. On the surface of the print carrier 10 is applied over the applicator roll 16, this substance containing surfactant in a molecular layer thickness. The layer thickness is typically less than 0.1 μm. The surface of the print carrier 10 is then guided in the direction of arrow P1 to a dampening unit 18, which applies a ink-repelling or ink-attracting dampening solution, for example water, from a dampening solution reservoir 24 to the surface of the print substrate 10 via a scoop roller 20 and an applicator roller 22. In principle, dampening solutions other than water can also be used. The order of the fountain solution layer can also be done by other methods, for example by steaming or spraying. The pressure-active surface of the print carrier 10 is completely provided with this fountain solution layer. The fountain solution layer typically has a layer thickness of less than 1 μm.

The generally ink-repellent fountain solution layer is then patterned by an imaging device 26. In the present case, laser radiation 28 is used for this purpose. In this patterning process, ink-attracting regions and ink-repelling regions are formed according to the structure of the printed image to be printed. Subsequently, the structured dampening solution layer reaches an inking unit 30, which transfers ink from a storage container 38 onto the surface of the print carrier 10 with the aid of the rollers 32, 34, 36. The oil-containing color deposits on areas without water-containing dampening solution. It should be noted that the ink can also be transferred to the surface of the print carrier 10 by spraying, knife coating or condensing.

Upon further transport of the print carrier 10, a transfer to a carrier material 40, generally a paper web. For transfer printing, the carrier material 40 is passed between two rollers 42, 44. During the transfer printing process, a blanket cylinder (not shown) and further intermediate cylinders can be connected between the roller 42 and the print carrier 10, which effects a color split, as is known per se from the field of offset printing methods.

During further transport of the print carrier 10, the surface of the print carrier 10 is cleaned in a cleaning station 46. In this case, the color residues and also the residues of the surfactant layer are removed. The cleaning station 46 includes a brush 48 and a wiper lip 50, which are brought into contact with the surface of the print carrier 10. Furthermore, the cleaning can be assisted by using ultrasound, high pressure liquid and / or steam. The cleaning can also be done using cleaning fluids and / or solvents.

Subsequently, a new application of the wetting-promoting substance, e.g. a surfactant, and a fountain solution and re-structuring done. In this way, with each revolution of the print carrier 10, a new print image can be printed. However, it is also possible to print the same image multiple times. The cleaning device 46, the device 12 and the device 26 are then switched inactive. The still present in color residues print image is then colored again by the inking unit 30 and reprinted. In this mode, therefore, a plurality of identical printed images can be printed.

FIG. 2 schematically shows a cross section through the print carrier 10 before and after structuring using the laser beam 28. According to the invention, the wetting is promoted by the application of a wetting-promoting substance on the print carrier surface 10. this happens within the printing cycle before the order of the Farbabsto-. fading fountain solution. Due to its physical and chemical properties, the wetting-promoting substance can be applied to the surface as an extremely thin layer of a few molecule layers, preferably smaller than 0.1 .mu.m. This layer is sufficient to favor on its free surface, the wetting with the ink-repellent fountain solution, so that this can also be applied as a very thin layer 54, preferably less than 1 micron. The continuing printing process is not affected by the small amount of wetting-promoting substance, in this case a surfactant layer 52. It can be easily removed by the cleaning process integrated in the printing cycle.

Advantages arise above all in the area of digital planographic printing or offset printing, ie a planographic printing method or offset printing method with changing printing information from printing cycle to printing cycle. By the wetting-promoting layer 52 can be dispensed with the otherwise roughened, porous printing plate surface. Instead, a smooth surface of the print carrier 10 is possible to clean with significantly less effort. A fast and stable cleaning process is indispensable for such a digital lithographic printing process or offset printing process and a decisive factor for its effectiveness. Accordingly, the surface of the print carrier 10 has a roughness which is smaller than the roughness used in the standard offset printing process. Typically, the mean roughness R _{z is} less than 10 microns, preferably less than 5 microns. Expressed as the average roughness value R _a , the roughness value lies in the range of less than 2 μm, preferably less than 1 μm.

A change in the molecular or atomic structure of the material of the print carrier as well as a permanent and wetting-promoting firmly anchored to the surface of the print carrier Layer is not necessary. The additionally applied wetting-promoting substance proposed here, for example the surfactant layer 52, develops its wetting-promoting action even at very low levels. Accordingly, its influence on the characteristics of the print substrate 10 is negligible in many respects. Another advantage arises from the now possible renouncement of the wetting-promoting additives usually present in offset printing in dampening solutions.

According to the FIG. 2 For example, the dampening agent 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 by the inking unit 30 with color. Due to the very smooth surface of the print carrier 10, the cleaning is facilitated, the surfactant layer 52 is completely removed again. Furthermore, the wear of the surface of the print carrier 10 is reduced.

In the following figures, functionally identical elements are referred to the same. These figures are for information and make the in the Figures 1 and 2 described embodiments of the invention better understandable. The FIGS. 3, 4 and 5 show a further embodiment of the invention. In FIG. 3 takes place in contrast to the embodiment according to FIG. 1 before applying the ink-repellent or ink-receptive layer on the usable surface of the print carrier structuring of a hydrophilic layer having a molecular layer thickness. In the present example, a steam device 60 is used, which acts on the surface of the print carrier 10 with hot water vapor. The print carrier 10 is provided on its surface with a SiO 2 coating. After the steam treatment, the print carrier 10 is dried by a suction device 62. The hot water vapor generates a hydrophilic molecular structure on the outer surface, eg SiOH.

After the subsequent structuring by the structuring device 26 by means of laser radiation 28, hydrophilic regions and hydrophobic regions arise in accordance with the structure of the printed image to be printed. By the downstream dampening unit 18, the entire usable surface of the print carrier 10 is brought into contact with a dampening agent layer, wherein the fountain solution only attaches to the hydrophilic areas, so that ink-attracting areas and ink-repellent areas arise in accordance with the structuring. Subsequently, a paint is applied by the inking unit 30, wherein the oil-containing color attaches to areas without aqueous dampening solution. Subsequently, the transfer printing of the printed image onto the carrier material 40 takes place.

After the further transport of the print carrier 10, its surface is cleaned in a cleaning station 46. It will remove the paint residues as well as the remains of a possible wetting-promoting substance. Subsequently, a new structuring process can take place.

In the present example according to FIG. 3 the hydrophilic layer is patterned on the surface of the print carrier 10 according to the printed image. The hydrophilic layer is extremely thin and only a few nanometers, typically less than 4 nm. It can therefore be patterned with very little energy expenditure during a printing cycle, whereby the hydrophilic molecular layer disappears. This is followed by the fountain solution, which produces a moisture film only on the non-hydrophilic areas. Dyeing and transfer printing takes place according to the described known principles of planographic printing or offset printing. After cleaning, in which not only the color residues but also the hydrophilic layer can be removed, but not necessarily 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.

For example FIG. 3 the hydrophilic layer is formed by activating the surface of the print substrate and by suitably changing the outer molecular surface structure. For example, this can be made possible by the use of chemical activators, reactive gases and / or a suitable energy supply. In addition to the use of water vapor as in the example below FIG. 3 can also be formed by the action of hot water and by leaching, such as NaOH, a hydrophilic SiOH structure on the surface. The print carrier is to be provided for this purpose with a SiO2 coating. It is also possible for the print carrier to pass through an activator bath to produce hydrophilization of the surface. It is also possible to order an activator via a nozzle system. Another possibility is to produce the hydrophilic layer by flaming the surface of the print carrier 10. Here too, wetting-promoting surface structures in a molecular layer thickness are formed.

An advantageous arrangement is the combination of hydrophilization with cleaning. Thus, e.g. Both the cleansing and the hydrophilizing effect of a hot water jet or a hot steam jet can be used. The cleaning and the production of the hydrophilic layer are then carried out in a single process step.

In FIG. 4 another variant is shown. In this case, a wetting-promoting substance is applied to the surface of the print carrier to produce the hydrophilic layer. For example, in the embodiment of FIG. 1 described pretreatment device 12 can be used. With the help of the scoop roller 14 and the Application roller 16 may be applied from the container 13, a liquid which contains a wetting-promoting substance, for example a surfactant, applied in a molecular layer thickness. Again, the layer thickness is typically less than 0.1 microns. As a further wetting-promoting substance are also alcohols into consideration. The job can alternatively be done by doctoring, spraying and vapor deposition.

Due to the very thin hydrophilic layer in molecular layer thickness, the partial removal of this hydrophilic layer can be done by local thermal energy supply. Due to the small layer thickness, the energy consumption can be low. In addition to the in the FIGS. 3 and 4 used laser radiation 28 and laser diodes, LEDs, LED combs or heating elements can be used.

Also in the example of the FIGS. 3 and 4 can be done per circulation of the print carrier 10, a re-structuring, whereby each circulation a new print image is printed. However, it is also possible, as in the example below FIG. 1 to print the same print image multiple times, wherein the existing print image is colored again by the inking unit 30 and reprinted. The devices for the restructuring are then switched inactive.

FIG. 5 shows a cross section through the print carrier 10 before and after patterning by the laser beam 28 for the example FIG. 4 , The surface of the print substrate 10 is very smooth, as is the case with the previous examples. The thin surfactant layer 52 is patterned by the laser beam 28, ie, hydrophilic regions 68 and hydrophobic regions 64 are produced. By the dampening unit 18, a thin water-containing wet film is applied only to the hydrophilic areas. The areas 64 are then through the inking unit 30 with a dyed color, which is repelled by the fountain solution 54 in the region of the hydrophilic areas 68.

The following embodiments according to the FIGS. 6 to 9 describe the hydrophilization of the surface of the print substrate 10 by applying free ions. These embodiments can also with the example FIG. 3 be combined.

In order to ensure good wetting with the generally ink-repellent dampening solution film, the surface energy of the print substrate 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 print carrier 10 and the fountain solution must have a value below 90 °. In practice, it is necessary that a contact angle of <25 ° must be achieved in order to produce the required liquid film with a thickness of about 1 micron. This places a high demand on the surface energy of the print carrier, which, especially when taking into account the extremely high surface tension value of water, namely 72 mN / M, as the basis of the ink-repellent fountain solution. Plastic print carrier or metallic print carrier can do this without further measures, such as roughening, application of surfactants, production of microcapillaries, etc., not afford. For example, the contact angle of water to polyimide or polycarbonate is about 75 °. Even metal surfaces, which in their purest form have very high surface energies and thus smallest contact angles, exhibit relatively hydrophobic behavior under normal environmental conditions. This is essentially due to the fact that the oxidation layer is effective on metal surfaces and always forms under normal conditions. Even the slightest impurities have a negative effect on the desired surface energy in this context. contact angle over 70 ° are often encountered in practice.

In the example after the FIG. 6 For the hydrophilization, a corona treatment of the surface of the print carrier 10 is carried out. A high voltage generator 70 generates an AC voltage in the range of 10 to 30 kV, preferably in the range of 15 to 20 kV, at a frequency of 10 to 40 kHz, preferably in the range of 15 to 25 kHz. An output terminal of the high voltage generator 70 is connected to an insulated electrode 72. The other output terminal is placed in the present case of a metallic print carrier 10 to a sliding contact 74 which is connected to the print carrier 10.

The relatively high voltage at the electrode 72 leads to the ionization of the air. The result is a corona discharge, wherein the surface of the print carrier 10 is bombarded with free ions. In the case of a plastic surface, in addition to a cleaning action in which typically organic impurities, such as grease, oil, wax, etc., are removed, the formation of free radicals on the surface, which in combination with oxygen form highly hydrophilic functional groups. These are mainly carbonyl groups (-C = O-), carboxyl groups (HOOC-), hydroperoxide groups (HOO-) and hydroxyl groups (HO-). For metallic printing media, the cleaning effect is in the foreground, whereby an increase in the surface energy and thus a reactivation of the hydrophilic properties of metals is achieved by degreasing the surface and removing the oxide layer. In this way, contact angles to water of up to less than 20 ° in plastic surfaces and metal surfaces can be achieved. The corona treatment previously alters the physical surface properties of the support, but not its mechanical properties. There are no visible changes detectable eg with a scanning electron microscope. By varying the height of the voltage or the frequency of the high voltage generator, the effect on the surface of the print carrier 10 can be influenced and tuned to the respective carrier material. The hydrophilization can be improved by supplying process gases, preferably oxygen or nitrogen.

In FIG. 6 is like the example after FIG. 1 applied to the hydrophilized surface of the print carrier 10 in the dampening unit 18 a fountain solution; This is followed by structuring with the aid of laser radiation 28. The structured fountain solution layer is inked by the inking unit 30 and the ink is later transferred to the carrier material 40. In the cleaning station 46 paint residues are removed. Since the surface of the print carrier 10 is also very smooth as in the previous example, the cleaning process is easy to implement and with high efficiency. Following this, the cyclical printing process can start anew. Alternatively, a restructuring can also be omitted and the previous print image is dyed and reprinted again.

FIG. 7 shows the insulated electrode 72. A metallic core 76 is surrounded by a ceramic shell 78. In such a structure, electrical flashovers are prevented. This is especially advantageous if 10 metal is used as the print carrier. Alternatively, the insulation can also be produced by a plastic jacket.

FIG. 8 shows the structure of a print carrier 10 made of plastic. An electrode plate 80 is disposed on the side of the print carrier 10 opposite to the electrode 72. The electrode 72 may be made without isolation.

FIG. 9 shows a hydrophilization process with an indirect corona treatment. The output terminals of the High voltage generator 70 are connected to two electrodes 82, 84, which are arranged above the print carrier 10. The electrical discharges generated by the high voltage between the two electrodes 82, 84 generate ions which are conducted by an air stream or process gas stream to the surface of the print carrier 10 and here develop the wetting-promoting effect. To generate the flow, a blower 86 is used.

Alternatively, a low-pressure plasma treatment can be used, which increases the surface energy at the surface of the print carrier 10. Here, a high-voltage discharge is generated under vacuum conditions, for example in the range of 0.3 to 20 mbar, is ionized by the process gas and is added to the plasma state. This plasma comes into contact with the surface of the print substrate 10. The effect of the plasma is comparable to the effect of corona treatment.

Using the in the FIGS. 6 to 9 described Hydrophilisierungsprozesses a significant increase in the surface energy is achieved, which allows a very thin order of ink-repellent fountain solution. The layer thickness is typically in the range of 1 μm.

The described hydrophilization process offers various advantages. It is possible to dispense with the roughened porous printing plate surface as in the standard offest printing method. Instead, a very smooth surface is possible whose roughness range is very low, for example in a region of the average roughness value R _a <1 μm. This allows a quick and stable cleaning process for the surface. For the printing process described, neither a permanent change in the molecular or atomic structure of the material of the print carrier nor a permanent and firmly anchored to the print carrier wetting-promoting layer necessary. Due to the described hydrophilization process, the print carrier can be optimized without regard to the surface energy with regard to further requirements.

The described hydrophilization process also allows the waiver of the wetting-promoting additives used in offset printing for dampening solution. Another order of additional wetting-promoting substances is no longer required. This avoids a relatively complicated process management and reduces the overhead of consumables. Another advantage lies in the cleaning effect of the hydrophilization process. It supports the cleaning process necessary for the digital printing process and thus further reduces the required hardware expenditure.

FIG. 10 shows a further embodiment. In offset printing and in particular in the digital method, for example after the US Patent No. 5,067,404 and US-A-6,295,928 same applicant, the constant and well-defined thickness of the dampening solution layer on the surface of the print carrier plays a crucial role for the stability and efficiency of the printing process. According to the example FIG. 10 a printing device is described which allows and monitors a defined, controllable and controllable very thin application of dampening solution. The standardized offset printing process usually uses a dampening system consisting of a number of rotating rollers for the application of the dampening solution. Together with a roughened or porous well-water pressure plate results in a sufficiently stable for standard offset printing water film. The amount of dampening solution and the thickness of the fountain solution layer can be adjusted for example by the delivery of certain rollers to each other or the speed of the scoop roller. Here, the storage effect of the dampening unit and also the the pressure plate to a strongly retarding reaction to Einstellmaßnahmen. For the production of a sufficiently stable water film, however, the roughened, strongly water-storing printing plates are essential. From the prior art it is also known to produce a very thin film of water by cooling the printing plate and the consequent condensation of humidity on the printing plate. However, the thickness of the water film is highly dependent on the ambient conditions, such as humidity and temperature, and is to be kept constant over a long period of time.

According to the embodiment FIG. 10 a structure is used which is similar to that in the aforementioned DE-A-101 32 204 described structure which realizes a CTP (Computer-To-Press) method.

In the FIG. 10 shown printing device allows to produce 10 different printed images on the same surface of the cylindrical print carrier. The printing device includes the inking unit 30, with a plurality of rollers, is transferred by the oily ink from the reservoir 38 to the surface of the print carrier 10. The inked surface of the print carrier 10 transfers the ink to a blanket cylinder 90. From there, the ink reaches the paper web 40, which is pressed by the impression cylinder 42 against the blanket cylinder 90.

The dampening unit 18 transfers dampening solution, eg water, from the dampening solution reservoir 24 onto the surface of the print carrier 10 via three rollers. Before application of the dampening solution layer, the surface of the print carrier 10 can be coated using wetting agents and / or surfactants or by corona and / or Plasma treatment are brought into a more hydrophilic state, as has already been described above. In the course of the dampening solution layer by energy supply by means of a Laser beam 28 selectively removed and there is the desired image structure. As mentioned, the inking by the inking unit 30 then takes place at the ink-attracting areas of the structuring. After patterning, the color may be solidified using a fuser 92.

Also in this example two modes are possible. In a first operating mode, a large number of printing processes take place before the surface is restructured. The print image located on the print carrier 10 is inked and reprinted once per print, ie there is a multiple inking of the printed image. In a second mode, a new print image is applied to the surface of the print carrier. Before that, the previous structured ink-repellent layer and the paint residues to be removed, for which the cleaning station 46 is provided. This cleaning station can be pivoted to the print carrier 10 according to the arrow P2 and swung away from it again. Further details of the structure of the printing device after FIG. 10 are in the mentioned DE-A-101 32 204 described.

As seen in the transport direction P1, after the dampening unit 18 there is arranged an energy source 94, which emits heat energy to the dampening solution film on the surface of the print carrier 10. This energy reduces the thickness of the fountain solution layer. As seen in the transport direction, the energy source is followed by a layer thickness measuring device 96. This layer thickness measuring device 96 determines the actual thickness of the dampening solution film and outputs an electrical signal corresponding to the thickness to a controller 98. The controller 98 compares the measured actual thickness with a predetermined target thickness. With a desired-actual value deviation, the energy source 94 is driven so that the thickness of the fountain solution layer is reduced to the desired target thickness.

The layer thickness measuring device 96 can operate without contact, for example, according to the triangulation method, the transmission method or the capacitive method. As energy source 94 is one or more IR lamps, radiant heaters, laser systems, laser diodes or heating elements into consideration.

The interaction of the energy source 94, the Schichtdikkenmeßgeräts 96 and the controller 98 may be such that only a monitoring function is performed. If the layer thickness exceeds or falls below a predetermined desired value, then a corresponding warning signal is emitted and then the energy supply for the energy source 94 is readjusted. However, the energy source 94, the Schichtdickenmeßgerät 96 and the controller 98 may also be combined to form a control loop in which the energy source 94 is driven so that at a control deviation between the actual value and target value of the layer thickness minimizes this deviation and preferably to zero is regulated.

The power source 94 may be driven by the controller using analog voltage regulation or digitally by pulse modulation, as indicated by the signal sequence 100.

According to the example FIG. 10 In a first process step over the usable width of the print carrier 10, a thick-constant dampening solution film is produced, which is reduced in its layer thickness defined in a subsequent second step. The result is a uniform fountain solution layer with a defined and very small thickness. The subsequent structuring can thus be carried out with minimal energy and with consistent results. Overall, the print quality is thus increased. The advantages of the printing device shown are that an immediate reaction to a change in the layer thickness of the dampening solution layer can be made that a known and defined thickness of the dampening solution layer can be adjusted and that extremely thin fountain solution layers can be produced. Furthermore, the required structuring energy can be minimized, in particular for digital printing methods.

Numerous other variations of the above-described embodiments are possible. For example, both an endless belt and a cylinder can be used as the print carrier. The transfer to the substrate can be done directly or with the interposition of a blanket cylinder or other intermediate cylinders for a color separation. The layer thickness control according to the example according to FIG. 10 can also be used for the other examples. Similarly, for the examples according to the FIGS. 1 to 9 a fixation of the applied color by means of a fixing device. Furthermore, the cleaning station 46, the dampening unit 18 and the image forming device can be switched inactive and active, for example by pivoting.

10

Druckträger

12

Vorbehandlungsvorrichtung

13

Behälter

14

Schöpfwalze

16

Auftragswalze

18

Feuchtwerk

20

Schöpfwalze

22

Auftragswalze

24

Feuchtmittelvorratsbehälter

26

Bilderzeugungsvorrichtung

28

Laserstrahl

30

Farbwerk

32, 34, 36

Walzen

38

Vorratsbehälter

40

Trägermaterial

42, 44

Walzen

46

Reinigungsstation

48

Bürste

50

Wischlippe

52

Tensidschicht

54

Feuchtmittelschicht

60

Dampfvorrichtung

62

Absaugvorrichtung

64

hydrophobe Bereiche

68

hydrophile Bereiche

70

Hochspannungsgenerator

72

Elektrode

74

Schleifkontakt

76

metallischer Kern

78

Keramikmantel

80

Elektrodenplatte

82, 84

Elektrode

86

Gebläse

90

Gummituchzylinder

92

Fixiereinrichtung

94

Energiequelle

96

Schichtdickenmeßgerät

98

Steuerung

100

Signalfolge

P1

Transportrichtung

P2

Richtungspfeil

LIST OF REFERENCE NUMBERS

10

print carrier

12

pretreatment device

13

container

14

scoop roller

16

applicator roll

18

dampening

20

scoop roller

22

applicator roll

24

Dampening solution reservoir

26

Imaging device

28

laser beam

30

inking

32, 34, 36

roll

38

reservoir

40

support material

42, 44

roll

46

cleaning station

48

brush

50

wiper lip

52

surfactant

54

Fountain solution layer

60

steam device

62

suction

64

hydrophobic areas

68

hydrophilic areas

70

High voltage generator

72

electrode

74

sliding contact

76

metallic core

78

ceramic shell

80

electrode plate

82, 84

electrode

86

fan

90

Blanket cylinder

92

fixing

94

energy

96

Coating Thickness

98

control

100

signal sequence

P1

transport direction

P2

arrow

Claims (10)

1. A method for generating a print image on a carrier material (40),
   in which the surface of a print carrier (40) is coated with an ink-repelling or an ink-attracting layer of a fountain solution (54),
   in a structuring process, ink-attracting regions and ink-repelling regions are generated on the surface coated with the liquid fountain solution (54) corresponding to the structure of the print image to be printed,
   ink that adheres to the ink-attracting regions and that is not absorbed by the ink-repelling regions is applied on the surface,
   the applied ink is transferred onto the carrier material (40) in the further course,
   before a new structuring process on the same surface of the print carrier (10), this surface is cleaned and re-coated with an ink-repelling or ink-attracting layer of fountain solution (54),
   before the application of the ink-repelling or ink-attracting layer of fountain solution (54) a wetting-aiding substance (52) is applied in molecular layer thickness on the surface of the print carrier (10),
   a surfactant with hydrophilic molecule sections is used as a wetting-aiding substance (52),
   and in which the layer thickness for the wetting-aiding substance (52) is smaller than 0.1 µm.
2. The method according to claim 1, in which a fountain solution (54) based on water is used as an ink-repelling layer.
3. The method according to one of the preceding claims, in which the layer thickness of the ink-repelling layer (54) is smaller than 1 µm.
4. The method according to one of the preceding claims, in which the average roughness R_z of the surface of the print carrier (10) is smaller than 10 µm, preferably smaller than 5 µm.
5. The method according to one of the preceding claims, in which the average roughness value R_a of the surface of the print carrier (10) is smaller than 2 µm, preferably smaller than 1 µm.
6. The method according to one of the preceding claims, in which digitally-controlled radiation is used for structuring.
7. The method according to claim 6, in which the radiation of a laser system, a laser, laser diodes, LEDs or a laser diode array is used.
8. The method according to one of the preceding claims, in which a plurality of printing events takes place before a restructuring of the surface, wherein the print carrier (10) is inked several times successively.
9. The method according to one of the preceding claims, in which the surface of the print carrier (10) is a continuous band or a generated cylinder surface.
10. The method according to one of the preceding claims, in which an ink separation takes place before the transfer of the ink onto the carrier material (40).

Images