Patent Application
20050178281
The method and device concerns generating a print image on a carrier material, wherein on the surface of the print carrier ink-attracting and ink-repelling regions are generated corresponding to the structure of the print image to be generated. The ink-repelling regions are provided with a layer from an ink-repelling medium. Ink that adheres to the ink-attracting regions and is not accepted by the ink-repelling regions is applied on the surface of the print carrier. The ink distributed on the surface is printed on the carrier material.
In the prior art, offset printing methods operating without water are known whose non-printing regions are fat-repelling and therefore accept no printing ink. In contrast, the printed regions are fat-attracting and accept the fat-containing printing ink. Ink-attracting and ink-repelling regions are distributed on the printing plate corresponding to the structure of the print image to be printed. The printing plate can be used for a plurality of transfer printing events. A new plate with ink-attracting and ink-repelling regions must be generated for each print image.
From U.S. Pat. No. 5,379,698, a method (called the Direct Imaging Method) is known in which a printer's copy is created via selective burning-off of the silicon cover layer on a multilayer, silicon-coated film in the printing device. The silicon-free locations are the ink-attracting regions that accept printing ink during the printing event. It requires a new film for each new print image.
In the standard offset method operating with water, hydrophobic and hydrophilic regions are generated on the surface of the print carrier corresponding to the structure of the print image to be printed. Before the application of the ink, a thin moisture film that wets the hydrophilic region of the print carrier is first applied onto the print carrier using application rollers or spray devices. The ink roller subsequently transfers ink onto the surface of the print carrier that, however, exclusively wets the regions not covered with the moisture film. The ink is finally transferred onto the carrier material after the inking.
In the known offset printing method, multilayer, process-less thermoprinting plates can be used as print carriers (compare, for example, WO00/16988). On the surface of the print carrier, a hydrophobic layer is removed via partial burn-off and a hydrophilic layer is uncovered, corresponding to the structures of the print image to be printed. The hydrophilic layer can be wetted with an ink-repelling fountain solution. The hydrophobic regions are ink-accepting and can accept printing ink during the print event. A new printing plate must be used to create a new print image.
Furthermore, a method is known from U.S. Pat. No. 6,016,750 in which an ink-attracting substance is separated from a film by means of a thermotransfer method, transferred to the hydrophilic surface of the print carrier and solidified in a fixing process. In the printing process, the hydrophilic regions remaining free are wetted with ink-repelling fountain solution. The ink is subsequently applied on the surface of the print carrier, the ink, however, bonding only on the regions provided with the ink-attracting substance. The inked print image is then transferred onto the carrier material. A new film with the ink-attracting substance is necessary for the creation of a new print image.
In the standard offset method or surface printing method, the wetting of the printing plate with the ink-repelling fountain solution is achieved via a specific roughening and structuring of the plate surface. The surface increase and porosity thereby created generates microcapillaries and leads to an increase of the effective surface energy and thus to a good wetting or spreading of the fountain solution. As further measures, in offset printing wetting-aiding substances are added to the fountain solution. These decrease the surface tension of the fountain solution, which in turn leads to an improved wetting of the surface of the print carrier. The literature Teschner H.: Offsettechnik, 5th edition, Fellbach, Fachschriften-Verlag 1983, pg. 193-202 and pg. 350 is referenced in this context.
From U.S. Pat. No. 5,067,404, a printing method is known in which a fountain solution is applied to the surface of the print format. The fountain solution is vaporized via selective application of radiant energy in image regions. The water-free regions later form the ink-bearing regions that are directed to a developing unit and are inked by means of an ink vapor. Energy-intensive partial vaporization processes are necessary to generate the structured fountain solution film.
Furthermore, the patent documents WO 97/36746 and WO 98/32608 are referenced. In the method specified in WO 97/36746, the fountain solution is generated via vaporization of a discrete water volume that condenses on the surface of the print carrier. According to WO 98/32608 and the U.S. Pat. No. 6,295,928 derived therefrom, a continuous ice film is applied and structured. In both cases, local high thermal energy must be applied for structuring. The aforementioned documents U.S. Pat. No. 5,067,404, WO 98/32608 (U.S. Pat. No. 6,295,928) and WO 97/36746 by the same applicant are herewith included by reference in the disclosure scope of the present patent application.
From DE-A-10132204 (not published) by the same applicant, a CTP method (Computer-To-Press method) is specified whereby multiple structuring processes can be implemented on the same surface of the print carrier. The surface of a print carrier is coated with an ink-repelling or ink-attracting layer. In a structuring process, ink-attracting regions and ink-repelling regions are generated corresponding to the structure of the print image to be printed. The ink-attracting regions are then inked with ink. Before a new structuring process, the surface of the print carrier is cleaned and re-coated with an ink-repelling or ink-attracting layer. A fountain solution layer or an ice layer is used as a layer. This patent document DE-A-10 132 204 is herewith included by reference in the disclosure content of the present patent application.
It is an object to specify a printing method and a print device that has a simplified design for the digital printing with variable print image and ensures a high print quality.
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 an ink-repelling and ink-attracting. The layer is made from a fountain solution. In a structuring process, ink-attracting and ink-repelling regions are generated corresponding to a structure of the print image to be printed. Ink that adheres to the ink-attracting regions that is not absorbed by the ink-repelling regions is supplied on the surface. The applied ink is transferred onto the carrier material. Before a new structuring process on the same surface of the print carrier, the surface is cleaned and re-coated with said layer. Before the application of said fountain solution layer, a wetting-aiding substance is applied with a molecular layer thickness on the surface of the print carrier. A surfactant with hydrophilic molecule sections is employed as a wetting-aiding substance.
For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the preferred embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device, and/or method, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur now or in the future to one skilled in the art to which the invention relates.
According to the method and device, before the application and structuring of the fountain solution layer a wetting-aiding substance is applied on the surface of the print carrier in molecular layer thickness. The wetting and coating are accordingly separated from one another, whereby the fountain solution does not have to be loaded with a wetting agent. The method provides for the use of a very smooth surface of the print carrier, whereby the subsequent process steps are simplified, in particular the cleaning before a restructuring in digital printing. Moreover, the wear of the print surface is reduced.
It is to be noted that the term ink-repelling or ink-accepting layer occurs frequently in the further specification. This layer is adapted to the ink to be applied. For example, given a water-containing fountain solution layer and an oil-containing ink, the fountain solution layer is ink-repelling. However, if the ink is water-containing, this fountain solution layer is ink-attracting. In practice, oil-containing inks are predominantly used, such that a water-containing fountain solution layer is ink-repelling.
In
The generally ink-repelling fountain solution layer is subsequently structured via an image generation device 26. In the present case, a laser beam 28 is used for this. In this structuring process, ink-attracting regions and ink-repelling regions are generated corresponding to the structure of the print image to be printed. The structured fountain solution layer subsequently arrives at an inking system 30 which transfers ink from a reservoir 38 to the surface of the print carrier 10 with the aid of the rollers 32, 34, 36. The oil-containing ink attaches at regions without the water-containing fountain solution. It is to be noted that the ink can also be transferred onto the surface of the print carrier 10 via spraying, scraping or condensation.
Given further transport of the print carrier 10, a transfer printing onto a carrier material 40 (in general a paper web) occurs. For transfer printing, the carrier material 40 is directed through between two rollers 42, 44. In the transfer printing process, a rubber blanket cylinder (not shown) and further intermediate cylinders that effect an ink division as this is known from the field of offset printing methods can be inserted between the roller 42 and the print carrier 10.
Given further transport of the print carrier 10, the surface of the print carrier 10 is cleaned in a cleaning station 46. The ink residues as well as the residues of the surfactant layer are hereby removed. The cleaning station 46 comprises a brush 48 and a wiping lip 50 which are brought into contact with the surface of the print carrier 10. Furthermore, the cleaning can be supported via use of ultrasound, high pressure liquid and/or vapor. The cleaning can also occur using cleaning fluids and/or solvents.
A new application of the wetting-aiding substance, for example a surfactant application, and a fountain solution application as well as a restructuring can subsequently occur. In this manner, a new print image can be printed given every revolution of the print carrier 10. However, it is also possible to print the same print image multiple times. The cleaning device 46, the device 12 and the device 26 are then inactively interposed. The print image still present in ink residues is then re-inked and transfer-printed by the inking system 30. Given this operating type, a plurality of identical print images can thus be printed.
Advantages primarily result in the field of surface printing or offset printing, meaning a surface printing method or offset printing method with alternating print information from print cycle to print cycle. Via the wetting-aiding layer 52, the otherwise typical roughened, porous printing plate surface can be foregone. Instead of this, a smooth surface of the print carrier 10 is possible that is to be cleaned with clearly lesser effort. A faster and more stable cleaning event is indispensable for such a digital surface printing method or offset printing method and a decisive factor for its effectiveness. The surface of the print carrier 10 accordingly has a roughness that is smaller than the roughness used in the standard offset printing method. The average surface roughness Rz is typically smaller than 10 μm, and preferably smaller than 5 μm. Expressed as an average roughness value Ra, the roughness value is in a range smaller than 2 μm, and preferably smaller than 1 μm.
A change in the molecular or atomic structure of the material of the print carrier as well as a wetting-aiding layer permanently and firmly anchored with the surface of the print carrier is not necessary. The additionally applied wetting-aiding substance (for example the surfactant layer 52) proposed here already deploys its wetting-aiding effect given the smallest quantities. Its influence on the properties of the print carrier 10 in all respects is accordingly negligible. A further advantage results from the now-possible abandonment of the typically present wetting-aiding additives in fountain solutions in offset printing.
According to
In the following Figures, functionally identical elements are designated identically.
After the subsequent structuring via the structuring device 26 by means of laser radiation 28, hydrophilic and hydrophobic regions are created corresponding to the structure of the print image to be printed. Via the downstream dampening system 18, the entire usable surface of the print carrier 10 is contacted with a fountain solution layer, whereby the fountain solution attaches only to the hydrophilic regions, such that ink-attracting regions and ink-repelling regions are created corresponding to the aforementioned structuring. An ink application via the inking system 30 subsequently occurs, whereby the oil-containing ink attaches to regions without water-containing fountain solution. The transfer printing of the print image onto the carrier material 40 subsequently occurs.
After the further transport of the print carrier 10, its surface is cleaned in a cleaning station 46. The ink residues and the residues of a possible wetting-aiding substance are removed. A new structuring process can subsequently occur.
In the present example according to
In the example according to
An advantageous arrangement is the combination of the hydrophilization with the cleaning. Thus, for example, both the cleaning and the hydrophilizing effect of a hot water jet or a hot water vapor jet can be used. The cleaning and the generation of the hydrophilic layer are then implemented in a single process step.
A further variation is shown in
Due to the very thin hydrophilic layer in molecular layer thickness, the partial removal of this hydrophilic layer can occur via local thermal energy supply. The energy expenditure can be low due to the low layer thickness. In addition to the laser radiation 28 used in
In the example according to
The subsequent exemplary embodiments according to
In order to ensure a good wetting with the generally ink-repelling fountain solution film, the surface energy of the print carrier 10 must be at least as high as the surface tension of the fountain solution film. This means that the value of the contact angle between the surface of the print carrier 10 and the fountain 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 generate the necessary liquid film with a thickness of approximately 1 μm. This places a high demand on the surface energy of the print carrier, primarily when one considers the extremely high surface tension value of water, namely 72 mN/M, as a basis of the ink-repelling fountain solution. Plastic print carriers or metallic print carriers can not achieve this without further techniques such as, for example, roughening, application of surfactants, generation of microcapillaries, etc. For example, the contact angle of water to polyimide or polycarbonate is approximately 75°. Even metal surfaces that, in their purest form, exhibit very high surface energies and thus the smallest contact angles show relatively hydrophobic behavior under normal environmental conditions. This is substantially connected with the oxidation layer acting on metal surfaces that always forms under normal conditions. Even the slightest impurities have a negative effect in this context for the desired surface energy. Contact angles of over 70° are herewith frequently to be encountered in practice.
In the example according to
The relatively high voltage at the electrode 72 leads to ionization of the air. A corona discharge is created, whereby the surface of the print carrier 10 is bombarded with free ions. Given a plastic surface, in addition to a cleaning effect in which organic impurities such as fat, oil, wax, etc. are typically removed, this leads to the creation of free radicals on the surface that form strongly hydrophilic functional groups in connection with oxygen. They are hereby primarily carbonyl groups (—C═O—), carboxyl groups (HOOC—), hydroperoxide groups (HOO—) and hydroxyl groups (HO—). Given metallic print carriers, the cleaning effect is in the foreground, whereby an increase of the surface energy, and thus a reactivation of the hydrophilic properties of metals, is achieved via degreasing of the surface and removal of the oxide layer. In this manner, contact angles to water of under 20° can be achieved with plastic surfaces and with metal surfaces. The corona treatment modifies the physical surface properties of the carrier beforehand, however not its mechanical properties. No visible changes are detectable, for example with a scanning electron microscope. Via variation of 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 attuned to the respective carrier material. The hydrophilization can be improved via supply of process gases, preferably oxygen or nitrogen.
In
Alternatively, a negative pressure plasma treatment can also be used that increases the surface energy on the surface of the print carrier 10. A high voltage discharge is hereby generated under vacuum conditions (for example in the range of 0.3 to 20 mbar), ionized by the process gas and excited into the plasma state. This plasma comes in contact with the surface of the print carrier 10. The effect of the plasma is comparable with the effect of the corona treatment.
A significant increase of the surface energy, which enables a very thin application of the frequency range fountain solution, is achieved with the aid of the hydrophilization process specified in
Various advantages result via the specified hydrophilization method. The roughened, porous printing plate surface as in the standard offset printing method can be foregone. Instead of this, a very smooth surface is possible whose roughness range is very low, for example in a range of the average roughness value Ra<1 μm. A faster and more stable cleaning event is thereby possible for the surface. For the specified printing process, neither a permanent change in the molecular or atomic structure of the material of the print carrier nor a wetting-aiding layer permanently and firmly anchored with the print carrier is necessary. Via the specified hydrophilization process, the print carrier can be optimized with regard to further requirements without consideration of the surface energy.
The specified hydrophilization process also enables the omission of the wetting-aiding additives for fountain solution used in offset printing. A further application of additional wetting-aiding substances is no longer necessary. This prevents a relatively complicated process management and reduces the additional expenses on commodities. A further advantage is also in the cleaning effect of the hydrophilization method. It supports the cleaning process necessary for the digital printing method and thus further reduces the necessary hardware expenditure.
In the exemplary embodiment according to
The print device shown in
The dampening system 18 transfers fountain solution (for example water) via three rollers from the fountain solution reservoir 24 onto the surface of the print carrier 10. Before the application of the fountain solution layer, the surface of the print carrier 10 can be brought to a hydrophilic state (as this has already been specified further above) using wetting agents and/or surfactants or via a corona and/or plasma treatment. In the further course, the fountain solution layer is selectively removed via energy supply by means of a laser beam 28 and the desired image structure is created. As mentioned, the inking via the inking system 30 subsequently occur on the ink-attracting regions of the structuring. After the structuring, the ink can be solidified by means of a fixing device 92.
In this example, two operating modes are also possible. In a first operating mode, a plurality of printing events occurs before a restructuring of the surface. The print image located on the print carrier 10 is inked and transfer-printed once per printing, meaning a multiple inking of the print image occurs. In a second operating mode, a new print image is applied on the surface of the print carrier. For this, the previous structured ink-repelling layer as well as the ink residues are to be removed, for which the cleaning station 46 is provided. This cleaning station can be pivoted onto the print carrier 10 according to the arrow P2 and pivoted away again from said print carrier 10. Further details of the design of the print device according to
Viewed in the transport direction P1, an energy source 94 that emits heat energy onto the fountain solution film on the surface of the print carrier 10 is arranged after the dampening system 18. The thickness of the fountain solution layer is reduced with the aid of this energy. Viewed in the transport direction, a layer thickness measurement device 96 is encamped after the energy source. This layer thickness measurement device 96 determines the current thickness of the fountain solution film and emits an electrical signal corresponding to the thickness to a control 98. The control 98 compares the measured real thickness with a predetermined desired thickness. Given a desired-real value deviation, the energy source 94 is activated such that the thickness of the fountain solution layer is reduced to the desired thickness.
The layer thickness measurement device 96 can, for example, operate without contact according to the triangulation method, the transmission method or the capacitive method. One or more IR lamps, heat radiators, laser systems, laser diodes or heating elements are suitable as energy sources 94.
The cooperation of the energy source 94, the layer thickness measurement device 96 and the control 98 can be such that only a monitoring function is effected. When the layer thickness undershoots or overshoots a predetermined desired value, a corresponding warning signal is emitted and the energy supply for the energy source 94 is readjusted based thereon. The energy source 94, the layer thickness measurement device 96 and the control 98 can, however, also be incorporated into a control circuit in which the energy source 94 is activated such that, given a standard deviation between real value and desired value of the layer thickness, this standard deviation is minimized and preferably regulated to zero.
The energy source 94 can be activated by the control with the aid of an analog voltage regulation or digitally via a pulse modulation, as this is indicated by the signal series 100.
According to the example according to
Numerous further variations of the previously specified exemplary embodiments are possible. For example, both a continuous band and a cylinder can be used as a print carrier. The transfer printing onto the carrier material can occur directly or under interposition of a rubber blanket cylinder or further intermediate cylinders for an ink separation. The layer thickness regulation according to the example according to
While preferred embodiments have been illustrated and described in detail in the drawings and foregoing description, the same are to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiments have been shown and described and that all changes and modifications that come within the spirit of the invention both now or in the future are desired to be protected.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102 06 937.9 | Feb 2002 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP03/01496 | 2/14/2003 | WO |
