EP1268211B1 - Method of printing and corresponding print machine - Google Patents

Abstract

A printing process for the transfer of printing substance ( 8 ) from an ink carrier ( 2 ) onto an imprinting material, in which the printing substance ( 8 ) undergoes a change in volume and/or position by means of an induced procedure of an energy-releasing apparatus, and thereby a transfer of a printing point onto the imprinting material takes place. The invention further includes a printing machine suitable for practicing the process.

Description

The present invention relates to a printing method for transferring printing substance from a color carrier to a printing material according to the preamble of claim 1, and to a printing machine according to the preamble of claim 13.

Under a printing process is primarily a method for arbitrarily frequent duplication of text and / or image templates by means of a printing form, which is repainted after each reprint understood. In general, a distinction is made here between four fundamentally different printing methods. Thus, on the one hand, the high-pressure method is known, in which the printing elements of the printing form are raised, while the non-printing parts are recessed. These include, for example, the book printing and the so-called flexo or anil impression. Furthermore, planographic printing processes are known in which the printing elements and the non-printing parts of the printing form lie substantially in one plane. These include the offset printing but also more known in the art field methods such. B. the lithography. In the case of offset printing, the inked drawing on the printing plate is not printed directly on the printing substrate, but is first transferred to a blanket cylinder or blanket and then the substrate is first printed on it. If in the following of printing material is mentioned, but both the actual substrate, i. the material to be printed, as well as any transfer means, e.g. a rubber cylinder, to be understood. A third method is the so-called gravure printing process, in which the printing elements of the printing form are recessed. These include a number of manual techniques, such as: B. the copper engraving and the etching. An industrially applied gravure printing process is the gravure printing. Finally, a through-printing method, which is sometimes also referred to as a screen printing method, is known in which the ink is transferred to the printing material at the printing sites through sieve-like openings of the printing form.

These printing methods are all characterized by the fact that they require a more or less elaborate printing form, so that these printing process only at very high volumes, usually well over 1000 pieces, work economically. Thus, for example, in the case of high-pressure molding production, firstly a raster film of the original to be printed has to be produced, which is copied onto the material of the printing form by means of a photosensitive layer. Since the non-printing parts of a high-pressure mold must be recessed relative to the printed parts, the metallic printing plates are subsequently etched or plastic printing plates are washed out. However, these printing forms can only be used for printing a particular original. If another template to be printed, so a new high-pressure mold must be made.

For printing small runs printers are already used, which are generally connected to an electronic data processing system. These generally use digitally controllable printing systems that are capable of printing individual pressure dots as needed. Such printing systems use different methods with different printing substances on different substrates. Some examples of digitally controllable printing systems are: laser printers, thermal printers and inkjet printers. Digital printing processes are characterized by the fact that they do not require printing forms.

For example, from GB 2 007 162 an electro-thermal ink printing method is known in which in a suitable ink jet the water-based ink is briefly heated to boiling by electrical impulses, so that a gas bubble develops in a flash and an ink drop is shot out of the nozzle , This method is well known by the term "bubble jet". However, these thermal ink printing methods have the disadvantage that on the one hand they consume a great deal of energy for the printing of a single printing dot and on the other hand are only suitable for printing inks which are water-based. Moreover, each individual pressure point must be controlled separately with the nozzle. On the other hand, piezoelectric ink printing processes suffer from the disadvantage that the nozzles required thereby clog easily, so that only very special and expensive paints can be used for this purpose.

Furthermore, it is known from DE 195 44 099 that with the aid of a laser beam or an electrothermal heating solid printing substances can be melted and thereby transferred. A transparent cylinder is homogeneously provided with small wells on the surface. These cups are then filled with molten liquid paint and doctored by conventional methods. Subsequently, the color to be printed is selectively melted from the inside through the cylinder by laser beam bombardment or by electrothermal methods and thus emptied, thereby setting a pressure point. Also in this method, the selection of the printing substance is severely limited, since it is necessary for the printing process that the printing substance shows a phase transition from the solid to the liquid phase as quickly and energy-saving. Moreover, in this printing process, filling the cups with fusible paint is problematic.

From DE 197 46 174 it is known that a laser beam by very short pulses in a printing substance, which is located in wells of a pressure roller, a process induced so that the printing substance undergoes a change in volume and / or position. As a result, the printing substance grows over the surface of the printing form and the transmission of a pressure point on an approximate printing material is possible. In this method, however, is a disadvantage that the filling of the wells is very difficult due to the small well diameter. EP 0 947 324 A1 describes a printer in which ink is applied in a substantially continuous film on a color carrier. On the side facing away from the film of the ink carrier for printing a laser beam is directed, which penetrates the ink carrier to an absorption layer on the ink-facing side of the ink carrier. The laser beam triggers an acoustic pulse on this absorption layer which causes a transfer of an ink droplet from the ink carrier to the printing material.

When using a translucent ink carrier, in which the laser beam is focused from the inside through the ink carrier on the absorption layer, however, has shown in some cases that either the energy transferred to the printing substance is not sufficient to dissolve a drop of paint from the printing substance, or there is a risk that the absorption layer will be detached from the ink carrier by the amount of energy transferred,

Erfindungsgmäß these problems are solved by a printing method according to claim 1 and a printing machine according to claim 13. Because the printing substance forms a homogeneous film, it is achieved that due to the adhesion or the capillary force between the printing substance, ink carrier and optionally the printing form a simple filling Any cells or openings is achieved. This is apparently u. a. The fact that no air bubbles form when the printing substance is fed to the ink carrier.

As a color carrier, for example, a cylindrical body is used, which preferably rotates about its own axis. At this color carrier is advantageously the substrate, z. As paper, plastic film, metal foil, but also rigid materials such as glass or metal, moved past with a transport speed which corresponds approximately to the peripheral speed of the cylindrical body. However, it is understood that the peripheral speed of the cylindrical body can also be greater than the feed speed of the printing material.

In order to increase the variety of usable printing substances, the energy is first transferred from the energy-emitting device into a mediating material and subsequently from the mediating material to the printing substance. The mediating material is preferably a light-absorbing material, which is advantageously arranged in the form of a layer on the ink carrier. The energy transfer from the switching material to the printing substance can be done for example by transfer of heat energy. D. h. That is first heated by the energy-emitting device at the relevant desired location, the switching material, which in turn emits heat energy to the printing substance. However, it is also possible that the energy transfer takes place by a momentum transfer. Ie. Here, a position and / or volume change of the material is induced within the mediating material, so that a pulse is transmitted to the printing substance by the movement or expansion of the mediating material. Preferably, in this indirect printing method, the energy absorbing layer is optimally adapted to the absorption of the energy beam, so that the energy to be used for the transmission of a pressure point can be further lowered.

It should be emphasized at this point that for the inventive method is not necessarily a printing forme in the classical sense necessary. Although it is possible to provide the cylindrical ink carrier with depressions forming a printing plate, the so-called wells, which are applied substantially on the outer surface of the ink carrier, but having a connection with each other, so that the printing substance, which is located in adjacent recesses who has a connection. However, it is also possible to completely dispense with special form elements. Thus, it is possible, for example, to carry out the cylindrical ink carrier without indentations. By delivering a focused laser beam to a selected location, a change in volume and / or position of the printing substance is locally induced, so that a color droplet locally peel off from the substantially homogeneous ink layer. In this case, the replacement does not have to be done solely because of the induced energy, but it is sufficient if the printing material is sufficiently close to the printing substance approached, completely, if the induced energy position change of the printing substance, so that by the local collection of the printing substance This touches the substrate and it comes thereby to the detachment.

The "printing form" is formed due to the inertia of the remaining printing substance quasi of the surrounding printing substance.

The thickness of the pressure point can be adjusted here preferably via the variation of the laser energy and / or via the variation of the pulse length.

Alternatively or in combination, it is possible for the diameter of the pressure point to be set via the variation of the laser energy and / or via the variation of the pulse length.

The resolution of the printing process can therefore be set almost arbitrarily. In addition, the positioning of the pressure point can be freely selected. In contrast, in the known method according to DE 197 46 174, only defined positions, namely the positions of the wells, are available. Even if, with a good resolution, the number of wells on the color carrier can well be more than 100 million, the dot pattern and the size of the points are predetermined by such a color carrier. In the event that is completely dispensed with such shaping elements, preferably a distance between ink carrier and printing material or printing substance on the ink carrier and printing substrate is maintained, which is preferably at least 10 microns, more preferably about 50 microns. In contrast to the known methods, the printing material here does not touch the "printing form" or the ink carrier. This has the advantage that expensive squeegee devices are not needed.

Advantageously, the pulse length of the laser pulse used is less than 1 μs, preferably less than 500 ns, more preferably between 100 to 200 ns. Due to the very short pulse length (with sufficient total energy), the laser energy is very well localized and thus achieves a clean printing of pressure points, without the capillary forces of a continuous film-forming printing substance have a negative impact. Advantageously, even laser pulses with a pulse duration of a few femtoseconds have already been used.

In the described printing method, a laser beam is focused on the color carrier or in the printing substance. If the laser light is absorbed, heat is generated in the printing substance, which causes the solvent to evaporate almost abruptly and some of the printing substance is thrown off the ink carrier. In order for the process to function optimally, care must be taken that the energy from the laser beam into the printing substance is fast and efficient is transmitted precisely. This energy transfer can be achieved either by using printing inks that are not absorbing for the laser beam, z. As pigmented paints, done because the laser light is absorbed directly on the pigment surface of the printing substance, or it must be provided an absorption layer, which initially absorbs the laser light and then transfers the energy to the printing substance.

The Lichstraht is not directed at the printing machine according to claim 13 through the ink carrier, but directed by the printing substance-prone side of the ink carrier on the absorption layer. In this case, the light beam is initially directed through the (non-absorbing) printing substance and then impinges on the absorption layer. It has surprisingly been found that in such an arrangement, the risk of detachment of the absorption layer of the ink carrier is significantly reduced.

Furthermore, it has surprisingly been found that the direction of movement of the energy-absorbing ink droplet only very weakly depends on the angle at which the light beam impinges on the surface of the printing substance. It is therefore not absolutely necessary, as in the above-described embodiment, the case that the color carrier opposite a translucent transfer means is arranged, through which the light beam is passed, so that it impinges approximately perpendicular to the surface of the printing substance.

Rather, as shown in connection with the embodiments shown in the figures, the laser beam may be inclined, i. with the normal on the printing substance surface an angle greater than 0 ° and preferably less than 75 °, more preferably less than 60 °. In order to ensure optimum transfer of the printing dot to the printing substrate or the transfer means, the distance between the focal point of the light beam and the location of the printing dot to be set on the printing substrate or transfer medium is less than 2 mm, preferably less than 1 mm, particularly preferably less than 0, 5 mm selected.

The claim 13 relates to a printing machine for printing a printing substrate with a color carrier and an energy-emitting device which is arranged and designed so that energy can be selectively transferred to certain areas of the color carrier, wherein the color carrier is provided for printing substance substantially a homogeneous or to make continuous film. It is the Ink carrier advantageously designed as a cylindrical body, which is preferably designed as a hollow cylinder with a substantially smooth surface.

Alternatively, however, it may be advantageous for some applications if the ink carrier is a flat plate. In principle, both the design as a cylinder and a flat plate are possible, wherein in the case of the hollow cylinder, the refilling of the printing substance is easily possible, while in the case of the flat plate, the supply of the printing material is easily feasible.

The ink carrier has, in an expedient embodiment, a thickness between 1 mm and 20 mm, preferably between 2 mm and 10 mm and particularly preferably about 5 mm.

The color carrier designed as a cylinder can have a maximum deviation from the ideal cylindrical shape below 200 μm, preferably below 100 μm, in particular below 80 μm.

In particular, in the event that substrate and ink carrier or printing plate are spaced apart from each other during the printing process, preferably a defined distance is maintained very accurately. Therefore, it is provided in an expedient embodiment that the cylindrical color carrier has an outer storage. By this external storage, the distance between the substrate and ink carrier can be set exactly. A generally existing ovality of the cylindrical color carrier is absorbed by the outer storage. The outer storage may for example consist of at least one, preferably two, more preferably 3 rollers or rollers on which the cylindrical ink carrier rests. Preferably, the outer storage is carried out so precisely that the distance between the ink carrier and substrate during rotation of the ink carrier by less than 50 microns, preferably less than 20 microns and more preferably varies by less than 10 microns. In addition, of course, a production of the cylindrical outer surface of the ink carrier (printing drum) with the lowest possible tolerances of advantage, especially for smoothness and compliance with a constant distance. However, it would probably be possible to dispense with the external support only if, for transparent hollow cylinders having an outer diameter of the order of magnitude of 300 mm, the tolerance deviations of the lateral surface can be kept below the above-mentioned variation values, preferably below 10 μm In order to increase the variety of usable printing substances, an absorption layer is arranged on the ink carrier, which preferably has a thickness of less than 10 .mu.m, preferably less than 5 .mu.m, more preferably less than 1 .mu.m or even better less than 0.5 .mu.m is.

In particular, in the applications in which a higher ink layer thickness is desired on the substrate, it has been shown that the surface of the printing substance receiving portion of the ink carrier is possible not completely smooth (in the sense of optically glossy) is executed, but somewhat dull or roughened , This can be done for example by the use of frosted glass. Particularly good results have been achieved with surfaces having an arithmetic mean roughness of at least 0.1 .mu.m, preferably between 0.5 .mu.m and 5 .mu.m, more preferably between about 1 .mu.m and 2 .mu.m. Also, such color carrier surfaces are still considered to be "substantially smooth" in the sense of the present invention, in contrast to surfaces specifically provided with macroscopic depressions (cups or grooves) or elevations. In these embodiments with matt surfaces, it is also possible to 'print' a plurality of color layers in succession. Characterized in that the surface of the ink carrier is not completely smooth, the ink carrier is able to absorb an increased amount of printing substance. The 'printing' of a point then has the consequence that at the same place enough printing substance remains on the ink carrier to print more pressure points.

The printing form may be in the form of a net, so that so-called meshes are provided instead of cells or grooves. The net shape has the advantage that the connection of the individual meshes with each other automatically results without corresponding connection channels must be provided. In other words, here too, the printing substance forms a substantially continuous film along the ink carrier.

The formation of the print carrier in such a manner that the printing substance forms a continuous, coherent layer, wherein the transfer of energy required for detaching a drop of pressure takes place so short that the drop peels off in a well-defined shape and size, allows the use of a wide variety of printing substances.

The energy-emitting device preferably consists of at least one laser source. Under certain circumstances, arrangements of laser diodes can also be used as laser sources, but at present "classic" lasers are still preferred, with a power of the order of 50-100 W or even more. An expedient embodiment also provides a focusing device that focuses the laser beam to a predetermined point on the color carrier. This focusing device may be, for example, an f-theta optic. Of course, however, all other appropriately focusing devices can be used.

The arrangement of a deflection device can be of great advantage, with the aid of which the laser beams emitted by the energy-emitting device are diverted to the printing substance.

The deflection device can be, for example, a deflection mirror, wherein preferably the solder on the reflective surface and the solder on the substrate level at the time of Bedrukkens an angle of about 45 °.

This arrangement has the advantage that the laser beam can be aligned substantially parallel to the axis of rotation of the ink carrier and thus the energy-emitting device can be arranged next to the ink carrier.

In a preferred embodiment, a separate from the energy-emitting device addressing is additionally provided, which is controlled to image the laser beam to the corresponding point on the print carrier. This addressing device may, for example, have a polygon mirror which can be rotated about its axis. This has the advantage that the energy-emitting device for addressing the individual pressure points does not have to be moved.

A polygon mirror with, for example, eight evenly (at 45 °) angled facets in principle allows the deflection of a laser beam between a minimum and a maximum angle, which includes a range of 90 °. However, for the use of the f-theta optic, the laser beam used must be considerably expanded and the polygon mirror, of course, has a finite size, and the laser energy can only be fully utilized if the expanded beam completely impinges on the currently active facet of the polygon mirror. The laser beam, which is basically available in continuous operation (even if it may be a pulsed laser with ultrashort pulses and correspondingly short pulse intervals), can not or at least not be used with its full power as long as the expanded beam extends to the corner region between two impinges on neighboring facets. In the expansions used in practice and a reasonably manageable size of the polygon mirror, this ultimately results in that only a deflection range of the laser beam at the polygon mirror of about 45 ° can be used (in the case of a polygon mirror with eight facets), so that within this 45th ° range must lie or be scanned a full line of printing. During the further rotation of the polygon mirror, during which the laser beam sweeps over a corner region between two adjacent facets, the laser beam can not be used, ie there is a brief printing pause.

In a particular embodiment of the present invention, it is therefore provided that the laser beam is split in a type of "time division multiplexing" or directed over two different paths, wherein the one beam part is directed so that it is then from a correspondingly selected and preferably 20 ° to 80 ° offset direction fully impinges on the relevant polygon facet, while the other branch of the beam would impinge on a corner region at the transition between two facets. The switching between the two beam branches, which preferably impinge on the polygonal mirror at an angle offset by 45 ° relative to one another, can be effected, for example, by a mirrored shutter disk which alternately has through openings and mirror surfaces and which is suitable with the rotation of the polygon mirror Synchronized so that the beam is either passed through or deflected by a mirror of the shutter disk so that it runs over a different path than the beam which passes through the corresponding gaps of the shutter disk and impinges on a first path on the shutter mirror.

Alternatively, instead of the shutter disk, the use of a polarized laser beam in conjunction with an electro-optical modulator would be possible. The electro-optical modulator rotates the polarization direction of the laser light, which is then subsequently reflected by a polarization filter either by 90 ° or, if the polarization direction of the laser is suitable, is completely passed through the filter. In this way, an alternate guidance or redirection of the beam along two different paths can be realized, which in turn is synchronized by appropriate electronic control of the electro-optical modulator with the rotation of the polygon mirror, so that at any time one of the two beams fully on a facet surface of the polygon mirror, while the beam on the other path otherwise on would hit a transition area between two polygon facets. In this way, one can increase the duty cycle of the laser beam, which is otherwise only about 0.5 due to the practical limitations, to the maximum value of 1.

It is understood that instead of a single laser and a laser array can be used.

The absorption layer is preferably made of crystalline material, wherein the size of the individual crystals should be as small as possible. As absorption layer is advantageously nanocrystalline material, eg. As carbon or so-called "gas black" have been used, wherein the size of the individual crystals was approximately between 10 and 1000 nm. The size of the individual crystals is advantageously chosen smaller than the wavelength of the laser light used.

The absorption layer is preferably attached to the print carrier with polysilicate.

The absorption layer must on the one hand be active enough to absorb the light and at the same time be able to give as much as possible of this energy as directly as possible to the printing substance. On the other hand, the absorption layer must be such that it is not detached from the light beam by the color carrier.

Characterized in that the light beam is passed through the printing substance through the absorption layer, the transmitted from the laser beam to the absorption layer momentum transfer presses the absorption layer on the ink carrier and does not dissolve the absorption layer of the ink carrier.

It has surprisingly been found that the light beam does not necessarily have to impinge perpendicularly on the absorption layer or the ink carrier. The volume and / or position change induced by the light beam usually proceeds essentially in the direction of the normal on the surface of the color carrier.

• Figur 1 a) und 1 b)
  als Vergleichsbeispiel eine schematische Schnittansicht eines Ausschnittes durch den Farbträger einschließlich Druckform,
• Figur 2a) bis 2 d)
  schematische Darstellungen eines Druckverfahrens als Vergleichsbeispiele,
• Figur 3a) und 3 b)
  Schnittansichten für zwei alternative Ausführungsformen,
• Figur 4a) und 4 b)
  verschiedene Ausführungsformen eines Druckwerkes als Vergleichsbeispiele
• Figur 5a) und 5 b)
  Schnittansichten alternativer Vergleichsbeispiele
• Figur 6 eine schematische Darstellung einer Umlenkoptik als ein Vergleichsbeispiel,
• Figur 7 schematisch eine Strahlführung entlang zweier Pfade zur Erhöhung des Duty-Cycle und
• Figur 8 eine Prinzipdarstellung einer weiteren alternativen Druckanordnung,
• Figur 9 eine schematische Darstellung einer Druckanordnung, die auf dem in Figur 8 dargestellten Prinzip beruht und
• Figur 10 eine Prinzipdarstellung einer weiteren alternativen Druckanordnung und
• Figur 11 a) und 11b)
  eine schematische Darstellung einer Druckanordnung, die auf dem in Figur 10 dargestellten Prinzip beruht.

Further advantages, features and applications of the present invention will become apparent from the following description of preferred embodiments and the accompanying figures. Show it:

• FIG. 1 a) and 1 b)
  as a comparative example, a schematic sectional view of a section through the ink carrier including printing forme,
• FIGS. 2a) to 2d)
  schematic representations of a printing process as comparative examples,
• FIGS. 3a) and 3b)
  Sectional views for two alternative embodiments,
• FIGS. 4a) and 4b)
  Various embodiments of a printing unit as Comparative Examples
• FIGS. 5a) and 5b)
  Sectional views of alternative comparative examples
• FIG. 6 shows a schematic representation of a deflection optics as a comparative example,
• Figure 7 schematically shows a beam guide along two paths to increase the duty cycle and
• 8 shows a schematic representation of a further alternative pressure arrangement, FIG.
• Figure 9 is a schematic representation of a printing arrangement based on the principle shown in Figure 8 and
• Figure 10 is a schematic representation of another alternative pressure arrangement and
• FIGS. 11 a) and 11 b)
  a schematic representation of a printing arrangement based on the principle shown in Figure 10.

FIGS. 1 a) and b) and FIGS. 2 a) d) show various comparative examples, not claimed, of a color carrier with and without a printing form. In Figures 1 a) and b) of the ink carrier 2 is covered by a printing plate 1, which has on the side facing the ink carrier so-called pre-chambers 5, which are filled with an absorbent material 10. The antechambers 5 are separated from the wells 6, which are filled with pressure substance 8, by an elastic membrane 4. The cups 6 are here separated by so-called webs 3 on the side facing the substrate not shown. In addition, the individual wells are through corresponding connection channels (not shown) connected together so that the printing substance can form a substantial homogeneous film, which extends across several wells hinauserstreckt. The section shown in Figure 1 b) differs from the section 1 a) characterized in that the printing plate 1 no separate from the wells 6 have prechambers 5, but in this case the absorbent material 10 is anchored in the printing plate 1 at the bottom of the wells 6, so that the energy beam 7 is first converted into heat by an absorption material 10. The absorption material need not necessarily be arranged in separate chambers, but may for example be formed as a continuous layer.

Within the cylindrically shaped ink carrier 2 shown in the comparative example, there is an energy-emitting device, here in the form of a laser arrangement, which is capable of responding by means of at least one jet of each well 6. In this case, the laser light is controllable so that over the width of the ink carrier 2 in the region of the printing gap, d. H. in the region in which the printing material is approximated to the ink carrier or the printing form, the printing substance 8 located on the surface of the printing form 1 is selectively controllable.

FIGS. 2 a) to d) show further comparative examples. In these examples, the printing substance 8 is applied to the ink carrier. In Figure 2 a) is the energy-inducing process, d. H. the printing process, shown. The wells 6 are filled with printing substance 8, wherein here absorption material 10 was introduced as a dispersion in the printing substance 8. It should be emphasized at this point that the absorbent material 10 is not necessarily required if appropriately suitable printing substances are used. Only in the event that the printing substance is unable to absorb the introduced energy is the use of an absorbent, e.g. B. as a continuous layer or by adding the absorbent material into the printing substance, necessary.

The energy beam 7 is focused into the well 6 in FIG. 2 a). The absorption bodies 10 located in the printing substance 8 receive the energy of the energy beam 7 and convert it into heat, so that the solvent present in the printing substance 8 evaporates. By this sudden evaporation of the solvent, the printing substance 8 is thrown out of the well 6.

In the comparative examples with a membrane shown in FIGS. 1 a) and b), the transfer of energy does not necessarily take place by heat transfer. Rather, it is also possible that the absorbent heated by the laser beam expands and the printing substance transmits a pulse via the membrane 5, which ensures that the printing substance 8 rises above the outer contour of the ink carrier or the printing plate.

In Figure 2 b) substantially the same process is shown as in Figure 2 a). Here, however, the absorbent material 10 is not introduced into the printing substance 8, but arranged as a solid layer on the bottom of the pot in the printing form 1. It is clear that the absorbent does not necessarily have to be separated from the printing substance 8 by a membrane 5. The energy beam 7 is here converted into heat by the layered absorption material 10, which in turn causes the solvent in the pressure substance 8 to boil. By this sudden evaporation of the solvent, the printing substance 8 is thrown out of the well 6.

FIG. 2 c) shows a comparative example without a separate printing form. Here is only the printing substance 8 as a homogeneous film on the ink carrier 2. Again, a laser pulse 7 leads to a movement of the printing substance 8 on the outer contour of the ink carrier addition. In other words, the printing of dots can also be carried out completely without printing form 1, which leads to a kind of portioning of the printing substance 8. The control of the pressure point quantity and its expansion then takes place by the control of the pulse energy and the pulse length.

FIG. 2 d) shows a comparative example with specially shaped wells 6. It can be clearly seen that the wells consist essentially of a channel which widens on both sides. Characterized in that, as shown in the middle figure of Figure 2 d), the laser beam is focused in the extended region of the channel, which faces the ink carrier 2, the relatively weak gas bubble formation in the printing substance 8 is enhanced and due to the nozzle-like shape aligned in the direction of the substrate. Through this nozzle-like shape of the channel or the cells, the energy required for printing can be reduced.

In Figure 3 a) an embodiment is shown with printing form, in which the connection of the individual wells can be seen. Namely, the printing plate 1 has on the side facing the ink carrier 2 a roughened side 16, so that between ink carrier 2 and printing plate 1, a gap 13 forms a homogeneous distribution of the ink 8 of the wells 9 by occurring capillary forces between the printing plate 1, color carrier and printing substance 8 guaranteed. In addition, air pockets are prevented and a homogeneous and defined filling of the wells with printing substance is possible.

In the embodiment shown in FIG. 3 b), a printing plate 1 is likewise arranged on the ink carrier 2. However, the printing form 1 is here designed as a net 18 and therefore has so-called mesh 15 instead of the wells. The network also allows a homogeneous distribution of the printing substance 8 through the forming gap 13.

In the figure 4 a), the cylindrical ink carrier 2 is shown as a whole, wherein the printing form 1, the cylindrical printing cylinder or the ink carrier 2 encloses seamlessly. The laser arrangement 7 is located in the interior of the printing cylinder 2.

Alternatively, the printing form 1 can also circulate the cylindrical printing cylinder or the color carrier 2 as a band, as shown in FIG. 4 b). Again, the laser assembly 7 is located inside the printing cylinder. 2

As shown in the embodiment in Figure 4 c), the ink carrier 2 need not necessarily be formed as a rotating cylinder. Here, however, the printing plate 1 runs as a tape past a firmly anchored printhead 16. Inside the print head 16, a laser assembly 17 is arranged, which can be constructed on the basis of the limited space on semiconductor technology.

In the comparative example of FIG. 5 a), the ink carrier 2 is cylindrically shaped. With the ink carrier 2 no printing plate 1 is connected, but on the ink carrier 2, the printing substance 8 is applied as a homogeneous film. Provided here, however, a printing plate 1, which is arranged separately from the ink carrier 2 and which here has the shape of a diaphragm. By rotation of the ink carrier 2, the supply of the printing substance is secured by means of a standardized color system. In this example, it should be noted that the distance of the diaphragm-like printing form 1 from the ink carrier 2 corresponds approximately to the layer thickness of the printing substance film. By this measure, it is ensured that never too much printing substance 8 is supplied to the actual printing process and thus a swelling of the printing substance 8 is avoided.

In Figure 5 b) of the ink carrier 2 is formed as a flat disc, so that the printing substance 8 is located as a homogeneous film on the underside of the flat ink carrier 2. The printing form 1 is here also separated from the ink carrier 2 and also has a diaphragm shape. The supply of the printing substance is secured here by periodically reciprocating the flat printing medium 2.

Finally, Figure 6 shows a bypass optics, which is advantageously used together with a printing press. It is understood that this bypass optics can be used for all printing processes in which a laser beam is to be mapped specifically to a specific point of a color carrier.

Shown in Figure 6, the ink carrier 2, which is designed as a cylinder. Within the cylinder is a deflecting mirror 21, which encloses here with the central axis of the cylinder 2 at an angle of 45 °. The laser beam 7 is first directed to a first deflection mirror 24, which does not necessarily have to be present, on the addressing unit 23, which is designed here as a polygonal mirror. The addressing unit 23 is controllable, so that the deflection of the laser beam 7 can be determined with the aid of the polygonal mirror 23. After the laser beam 7 has been deflected by the addressing device 23, it passes through a focusing device, which is designed here as an f-theta arrangement and which carries the reference numeral 22. Then he meets the deflecting mirror 21 and is focused on the surface of the ink carrier 2. By way of example, two alternative beam paths 7 'are shown, which could result if the addressing device 23 has been set accordingly. By driving the polygon mirror 23 can be so without the actual laser must be moved, each point a line which runs on the surface of the ink carrier 2 parallel to the axis of rotation of the ink carrier 2, are driven. More specifically, during the rotation of the polygon mirror, the focal point of the laser traverses each point of that line, and it can be turned on or off at each point (or pixels corresponding to the possible resolution).

FIG. 7 shows a laser source 32 which generates a laser beam which is split into two different laser beams 7 and 7 '. However, this splitting does not take place with a conventional beam splitter, which would produce continuous beams 7 or 7 'of half power, but from a mirrored disc containing alternately gaps for passing a laser beam 7 and mirrored surfaces for deflecting the laser beam 7'. having. The gaps and mirrored surfaces preferably each occupy equal length angular sectors and alternate each other. In the preferred embodiment, which also uses an eight-faceted polygon mirror 23, the interrupter disk 28 also has eight ports and eight mirrored surfaces uniformly distributed about the circumference of the interrupter disk 28. The drive 29 for the interrupter disc 28 is synchronized via a synchronizer 33 in a suitable manner with the rotation of the polygon mirror 23, wherein the exact type of synchronization will be described below.

Analogous to the data transmission, one could also speak of a time-division division of the laser beam into the beams 7, 7 ', which, however, has nothing to do with the high-frequency switching on and off of the laser beam for addressing the individual pressure points of a scanning line, that of the comparatively low-frequency beam interruption and deflection is superimposed.

After beam splitting takes place in the units 30 and 31, a beam expansion, which is required later in the not shown in Figure 7, but shown in Figure 6 f-theta optics 22.

The one partial beam 7 passes through a gap of the interrupter disc 28 and the beam widening 31 passes, strikes a mirror 27 and is reflected from there at a fixed angle (corresponding to the position of the mirror 27) on the polygon mirror 23, which is perpendicular to his paper axis extending, central axis rotates. The beam 7 'is first deflected upwards by the mirrored segments of the interrupter disk 28, passes through the beam widening 30, then strikes a mirror 25 and from there onto a mirror 26, which in turn directs the beam onto the polygon mirror 23. Note that the mirrors are shown here only schematically and in any case the mirror 26 is aligned so that the beam is incident on the polygon mirror 23 falls. However, the impact points of the steel 7 or 7 'are selected on the polygon mirror so that they are about, measured in the circumferential direction of the polygon mirror, offset by half the length of a facet face against each other.

Assume that the polygon mirror 23 rotates counterclockwise, the laser beams 7, 7 'are always reproduced into individual packets, which corresponds to the alternate interruption of the two beams, but realistically, the individual "packets" are much longer and with correspondingly larger gaps would have to be displayed. The interrupted beam representation in Figure 7 therefore corresponds more to the individual pressure point pulses which are directed in a scanning line on the print carrier.

FIG. 7 shows a state in which the laser beam 7 still passes through a gap in the interrupter disk 28 and impinges on one of the facet surfaces via the mirror 27. The length of the gap or interruption in the interrupter disk 28 is dimensioned so that the relevant facet of the polygon mirror almost completely passes through the region on which the beam 7 impinges. That is, the beam 7 strikes the relevant facet of the polygon mirror for the first time when the preceding corner between adjacent facets has just passed that area. As the polygon mirror continues to rotate, the relative orientation of the polygon facet to the laser beam 7 changes, causing the laser beam 7 reflected by the polygon mirror to sweep over an angular range that is approximately from a horizontal to a 45 ° angle in the instantaneous view of Figure 7 this 45 ° angle is almost reached.

Shortly before the laser beam 7 hits the next corner at the transition to the next facet, the beam 7 is interrupted by the interrupter disc 28, so that now the beam 7 'is directed to the relevant facet, and thus immediately behind the corner to the preceding facet impinges on the same facet, which was previously painted by the beam 7. Here, the same process as in the case of the beam 7, i. the beam 7 'is pivoted, starting from a deflection about 45 ° down to a horizontal to about a horizontal, while the polygon mirror rotates further counterclockwise. Thereafter, the next corner to the transition of the next facet has happened the impact point of the beam 7 and at the same time the interrupter disc 28 again releases the beam 7, so that the beam 7 'disappears and the beam 7 now impinges on the next facet. As already mentioned, the illustration in FIG. 7 is purely schematic and the positions and angles depicted do not necessarily correspond exactly to those of a realistic construction of realized positions and angles.

The essential reason for this embodiment is that the beams 7, 7 'are relatively strongly expanded in relation to the effective length of the individual facets and are not usable, as long as they do not play with their full beam cross-section on one of the facets. The service life (duty cycle) of the laser is therefore only about 50% or 0.5. However, by dividing the laser beam into the two partial beams 7, 7 ', one can nevertheless achieve a duty cycle of 1 (duty cycle 1), ie during which one beam must be inactive because it passes the area of a corner at the transition between two facets , The other beam whose impact point is offset by at least the amount of the beam diameter or the beam width, and for example, about half a facet length, be active, so that one uses the substantially continuously available laser energy also continuously. It is understood that the interruption of the beam by means of the interrupter disc is independent of the other addressing interruption, with which the individual point of a printed image are driven.

Incidentally, instead of the interrupter disc, a polarizing filter can also be used when the laser is operating with polarized light, wherein an electro-optical modulator which is capable of rotating the plane of polarization by 90 ° is connected in front of a corresponding polarizing filter. Depending on whether the electro-optical modulator is active, then the polarization filter can pass through the laser radiation unhindered or reflected by appropriate arrangement by 90 °, so that you can get exactly the same division into the beams 7, 7 ', as described with reference to the interrupter disc ,

In the unclaimed comparative examples presented so far, the energy or the laser beam was focused through the (transparent) ink carrier into the absorption layer or into the printing substance. In contrast, FIG. 8 shows that this is not necessary. Rather, the laser beam from the other side, i. from the printing substance-afflicted side of the ink carrier, focused in the printing substance or the absorption layer.

In FIG. 8, the laser beam 7 is focused through the transparent glass cylinder, which here merely serves as transfer means, through the printing ink 8 onto the absorption layer 10 applied to the ink carrier 2 at the point 9. The absorption layer 10 absorbs at least part of the energy from the laser beam 7 and forwards it into the printing substance 8. This leads to a sudden local heating of the printing ink and an ink droplet 11 is explosively dissolved out of the ink layer 8. This ink drop 11 reaches the glass cylinder 12. In this way, a glass cylinder could be printed. In general, however, should be printed on non-transparent substrates 34, so that the placed on the glass cylinder 12 pressure point must be transferred to the substrate 34.

FIG. 9 schematically shows the structure of a printing press using the arrangement just described. A laser beam 7 is focused through the glass cylinder 12 onto the optionally provided with an absorption layer 10 ink carrier 2, which is formed here in roll form. If the ink carrier 2 equipped with a printing plate 1, so can Touch glass cylinder 12 and ink carrier 2. However, if the ink carrier does not have a specially designed printing form 1, but is merely wetted by the printing substance 8, then, as described above, glass cylinders 12 and ink carrier 2 should be spaced apart from one another.

The ink carrier 2 is integrated in an inking unit 20 which, in addition to the ink carrier 2, also has a dipping roller 19 and a printing substance bath 8. The fountain roller 19 dives with its outer contour in the printing substance 8 a. If the fountain roller 19 is rotated, this ensures that the surface of the fountain roller 19 is afflicted with printing substance. The fountain roller is at least so far approximated to the ink carrier 2, that a transfer of the printing substance 8 from the fountain roller 19 takes place on the print substrate 2.

By the inking unit 20 is thus ensured that at any time printing substance 8 is located on the surface of the ink carrier 2. If the laser beam now drifts onto the surface of the ink carrier 2, a change in volume and / or position of the printing substance 8 is induced locally, either directly or via an absorption layer 8, so that a drop of printing substance 8 is transferred from the ink carrier 2 to the glass cylinder 12 The glass cylinder is rotated in the arrangement shown in Figure 9 in a clockwise direction, so that the surface portion of the glass cylinder 12 was transferred to the pressure drops, at some point with the running between the support cylinder 35 and glass cylinder 12 printing material 34 comes into contact. Similar to the offset printing, therefore, the ink is first positioned on the glass cylinder 12 and positioned on the actual substrate 34 in a subsequent step.

Since in general the printing substance 8 is not completely transferred from the glass cylinder to the printing substrate 34, a cleaning roller 14 is advantageously used with which the glass cylinder 12 is cleaned.

As already stated, it is not absolutely necessary for the laser beam 7 to impinge perpendicularly on the ink carrier 2. In Figure 10, therefore, another arrangement is shown. Here, the laser beam 7 encloses an angle α with the normal on the color carrier surface. It has surprisingly been found that the angle β between the ink carrier surface and the direction of the dissolved from the printing ink ink dot is almost independent of the angle α. In FIG. 10, therefore, the printing substrate 34 approximates the ink carrier 2, the laser beam 7 being laterally concentrated between the printing substrate 34 and the ink carrier 2 on the focal point 9 in the absorption layer 10 or the printing substance 8 in order to print a printing dot. A drop 11 of the printing substance 8 undergoes a change in volume and / or position due to the evolution of heat in the printing substance 8, so that it leaves the printing substance film 8 almost perpendicular to the ink carrier surface.

In FIGS. 11 a) and 11 b), an example of a printing machine is shown which implements the laser arrangement just described. A ink fountain roller 2 is integrated in an inking unit, which in addition to the ink fountain roller 2, the transfer roller 36 and the storage bath with ink 8 comprises. With the help of the inking unit ensures that the ink fountain roller 2 is always wetted on its surface with printing substance 8. The laser beam 7 is directed directly onto the printing substance or the absorption layer on the ink fountain roller 2. In contrast to the previously described arrangements, the laser beam 7 is not initially guided through a transparent body, so that it impinges perpendicular to the surface of the printing substance on this or the underlying absorption layer.

As shown enlarged in FIG. 11a), the laser beam 7 impinges on the absorption layer of the ink carrier roller 2, which is inked continuously with an ink which is transparent to the laser beam. The focus of the laser beam 7 is projected at a certain angle on the surface of the ink roller. This angle is advantageously chosen so that the distance between the focus point and substrate is optimal. Subsequently, the laser beam is guided line by line in the manner described above the inking roller and transmitted by switching on and off the laser, the information or the pressure points. When the laser is on, the laser light is absorbed in the absorption layer, the solvent evaporates in the ink, and it is locally induced a change in volume and / or position of the printing substance, so that the resulting ink droplets sets the desired pressure point. The web support roller guides the substrate so that the distance between the substrate and the focal point is as small as possible, but the substrate neither interrupts the laser beam nor touches the ink roller.
Advantageously, the ink carrier roller 2 has a smaller diameter than the web support roller 35.

By the method according to the invention and the printing presses according to the invention, a digital printing method is provided which permits printing or printing of virtually all imaginable printing substances or substrates. Thus, for example, conductive coatings or corrosive substances can be applied to printed circuit boards. Another application is rapid prototyping. The ink rollers can be made of almost all materials, preferably metal or ceramic. Furthermore, they may be porous or have rough surfaces.

LIST OF REFERENCE NUMBERS

1

printing form

2

color carrier

3

Stege

4

elastic membrane

5

antechambers

6

wells

7, 7 '

laser beam

8th

printing substance

9

focus point

10

absorbent material

11

Printing substance drop

12

Glass cylinder 13 gap

14

cleaning roller

15

mesh

16

roughened side

17

laser assembly

18

network

19

dipping roller

20

inking

21

deflecting

22

f-theta arrangement (optics)

23

addressing

24

deflecting

25

mirror

26

mirror

27

mirror

28

Interrupter disc (shutter)

29

Drive the breaker disk

30

Device for beam expansion

31

Device for beam expansion

32

laser source

33

synchronizing

34

Substrate or substrate web

35

supporting cylinders

36

transfer roller

Claims (42)

1. Printing process for the transfer of printing substance (8) from an ink carrier (2) onto an imprinting material or a transfer means, in which the printing substance (8) undergoes a change in volume and/or position by means of an induced procedure of an energy-releasing apparatus, and thereby a transfer of a printing point onto the imprinting material or the transfer means takes place, wherein the printing substance (8) is applied essentially forming a continuous film on the ink carrier (2), characterised in that energy from the energy-releasing apparatus is initially transferred into an exchange material and then from the exchange material onto the printing substance (8), wherein the energy-releasing apparatus releases energy in the form of light through the printing substance onto the exchange material and thereby induces a change in the volume and/or position of the printing substance (8).
2. Printing process according to claim 1, characterized in that there is used as an ink carrier (2) a cylindrical body which is preferably rotated about its own axis.
3. Printing process according to claim 2, characterized in that the imprinting material is moved past the ink carrier (2) at a transport speed which is matched to the circumferential speed of the cylindrical body.
4. Printing process according to one of claims 1 to 3, characterized in that there is used as an energy-releasing apparatus an apparatus emitting laser radiation (7), the laser beam (7) being directed towards and preferably focused on selected points to be imprinted on the ink carrier (2)
5. Printing process according to one of claims 1 to 4, characterized in that energy from the energy-releasing apparatus is transferred directly into the printing substance (8).
6. Printing process according to one of claims 1 to 5, characterized in that there is used as an exchange material a light-absorbing material which is preferably arranged in the form of a layer on the ink carrier (2)
7. Printing process according to one of claims 1 to 6, characterized in that the release of energy takes place by emission of a laser pulse.
8. Printing process according to claim 7, characterized in that the thickness of the printing point is set via the variation of the laser energy and/or via the variation of the pulse length.
9. Printing process according to claim 7 or 8, characterized in that the diameter of the printing point is set via the variation of the laser energy and/or via the variation of the pulse length.
10. Printing process according to one of claims 1 to 9, characterized in that there is maintained between the ink carrier (2) and the imprinting material a distance which is preferably at least 10 µm, particularly preferably roughly 50 µm.
11. Printing process according to one of claims 1 to 10, characterized in that a laser pulse with a pulse length of less than 1 µs, preferably of less than 500 ns, particularly preferably less than 200 ns is used for the energy transfer.
12. Printing process according to one of claims 1 to 10, characterized in that the laser beam is guided in short time intervals alternately over two different paths and from various directions and on points, staggered by at least the width of the beam up to roughly half a facet length, onto the polygonal mirror, the angle ranges of the part-beams deflected by the polygonal mirror joining one another.
13. Printing machine for the imprinting of an imprinting material with an ink carrier (2) and an energy-releasing apparatus, which is arranged such that energy can be transferred in a targeted manner onto specific areas of the ink carrier (2), wherein the ink carrier (2) is provided in order to receive printing substance (8) essentially forming a continuous film, characterized in that an absorption layer (10) is arranged on the ink carrier (2), and the energy-releasing apparatus is arranged such that the energy is directed onto the absorption layer from the side of the ink carrier to which printing substance adheres.
14. Printing machine according to claim 13, characterized in that the ink carrier (2) is a cylindrical body which is preferably developed as a hollow cylinder or is a flat plate.
15. Printing machine according to one of claims 13 to 14, characterized in that the ink carrier (2) consists of translucent material, preferably of glass.
16. Printing machine according to claim 15, characterized in that the ink carrier (2) has a thickness of between 1 mm and 20 mm, preferably between 2 mm and 10 mm, particularly preferably roughly 5 mm.
17. Printing machine according to one of claims 13 to 16, characterized in that the absorption layer (10) preferably has a thickness which is smaller than 10 µm, preferably smaller than 5 µm, particularly preferably smaller than 1 µm.
18. Printing machine according to one of claims 13 to 16, characterized in that the surface of the section of the ink carrier (2) receiving the printing substance (8) has an arithmetic central roughness of at least 0.1 µm, preferably between 0.5 µm and 5 µm, particularly preferably roughly between 1 µm and 2 µm.
19. Printing machine according to one of claims 13 to 17, characterized in that the surface of the ink carrier has an extensive tolerance deviation from an ideal plane or cylindrical surface of at most 20 µ, preferably at most 5 µm.
20. Printing machine according to one of claims 13 to 19, characterized in that the printing machine has a printing plate (1).
21. Printing machine according to claim 20, characterized in that the printing plate (1) has a plurality of cells and/or grooves which are provided to receive printing substance (8).
22. Printing machine according to claim 20 or 21, characterized in that the printing plate (1) has a roughly grid form.
23. Printing machine according to one of claims 20 to 22, characterized in that several recesses of the printing plate (1) which serve to receive printing substance (8) are connected to one another.
24. Printing machine according to one of claims 20 to 23, characterized in that the printing plate (1) is arranged secured to the ink carrier (2).
25. Printing machine according to claim 24, characterized in that the printing plate (1) and the ink carrier (2) are developed in one piece.
26. Printing machine according to claim 24, characterized in that the printing plate (1) can be secured in detachable manner to the ink carrier (2).
27. Printing machine according to one of claims 20 to 24 or 26, characterized in that the printing plate (1) is designed as a belt, preferably as a continuous belt.
28. Printing machine according to claim 20, characterized in that the printing plate (1) has the form of a diaphragm that is arranged separate from the ink carrier (2) and between the latter and the imprinting material.
29. Printing machine according to one of claims 13 to 19, characterized in that no printing plate (1) is provided.
30. Printing machine according to one of claims 13 to 29, characterized in that the energy-releasing apparatus consists of at least one laser source.
31. Printing machine according to claim 30, characterized in that a focusing apparatus (22) is provided which focuses the laser beam (7) on a predefined point on the ink carrier (2).
32. Printing machine according to claim 31, characterized in that the focusing apparatus is an f-theta lens system (22).
33. Printing machine according to one of claims 30 to 32, characterized in that a reflection apparatus (21) is provided.
34. Printing machine according to claim 33, characterized in that the reflection apparatus (21) is a reflecting mirror (21), the vertical on the reflecting surface and the vertical on the imprinting material plane preferably forming an angle of roughly 45° at the time of imprinting.
35. Printing machine according to one of claims 30 to 34, characterized in that an addressing apparatus is provided.
36. Printing machine according to claim 35, characterized in that the addressing apparatus has a polygonal mirror rotatable about its axis.
37. Printing machine according to claim 36, characterized in that a reflection apparatus is provided by which the laser beam is guided in short time intervals alternately over two different paths and directed by deflecting mirrors alternately from two different directions and in circumferential direction of the polygonal mirror onto points, staggered by at least the width of the beam and for example by roughly half a facet length, onto the polygonal mirror.
38. Printing machine according to claim 37, characterized in that the deflection apparatus is a shutter disk, synchronizable with the polygonal mirror, which alternately has metallized surfaces and passage openings.
39. Printing machine according to claim 37, characterized in that the laser is a polarized laser and the deflection apparatus consists of an electro-optical modulator in combination with one or more polarization filters.
40. Printing machine according to one of claims 13 to 39, characterized in that the ink carrier developed as a cylinder is housed on its outside, and preferably has in the angle range bearing elements in which the imprinting material also achieves the smallest distance from the surface of the ink carrier.
41. Printing machine according to one of claims 13 to 40, characterized in that a transfer means (12) is provided which preferably consists of light-permeable material.
42. Printing machine according to one of claims 13 to 41, characterized in that the energy-releasing apparatus is arranged such that it can emit a light beam at an angle α to the normal on the imprinting substance surface of more than 0° and preferably less than 75°.

Images