EP1036655A1 - Imaging a printing plate for wet offset printing - Google Patents

Abstract

The surface of the multi-layer plate is first wetted. Those points at which ink images are to be formed are dried to produce the required image. A material which absorbs printing ink at those points is then spread uniformly over the surface and hardened at those points. A wetting agent is then used to remove the material at those points where the ink is to be rejected

Description

The invention relates to a method and a device for imaging a Printing form for wet offset printing. In particular, the invention in Newspaper offset printing, preferably newspaper offset roll printing, used.

In newspaper offset, the Computer technology in the prepress area has changed significantly. Operations that so far carried out manually are replaced by so-called computer-to-technologies been. The current stage of development is in the newspaper sector with computer-to-plate been achieved. The further development goes in the direction of computer-to-press. i.e. towards direct imaging in the machine.

A directly imageable printing form cylinder is known from US Pat. No. 5,293,817. The Printing form cylinder has a porous outer jacket. The dampening is done by the inside of the cylinder through the porous outer jacket. The porosity of the Cylinder jacket is between 20 and 45%. The diameter of the pores of the Cylinder jacket decreases towards the outside of the cylinder jacket and lies between 3 and 100 µm. The pores of the cylinder jacket communicate with each other. The illustration takes place via a thermal transfer or an inkjet method by means of an image information transmission device. As an alternative, the use of a heated electrode mentioned in pin form to apply oleophilic material to the cylinder jacket.

The invention has set itself the task of imaging a printing form in a wet offset printing machine in a simple, inexpensive and precise way.

This object is solved by the subject matter of the independent claims.

The invention relates to a method for imaging a printing form for a Wet offset printing, which is on an unimaged surface of the printing form Print image created by forming ink-accepting and ink-repellent areas becomes. The surface is illustrated and also unillustrated because of its Function of the transfer of color in the following as a color transfer surface designated.

According to the invention, the print image is generated, i.e. the illustration by the still unimaged ink transfer surface is wetted with a dampening solution, those areas of the moistened surface that are to be ink-accepting, targeted, i.e. according to the image, dried and then material, the printing ink accepts and preferably rejects dampening solution on the ink-transferring surface is applied to the dry areas. The material, like printing ink, rejected by the dampening solution, i.e. it is not transferred to the damp areas. Since a dampening agent supply is preferably even and continuous even during the Imaging takes place, the material is preferably as soon as possible after the applied according to the image drying of the ink-transferring surface so that the Do not use dried areas again before applying the ink-accepting material Fountain solution are wetted.

A dampening film that wets the ink-transfer surface should be averaged over the area of an image pixel, at most 1 µm thick, by the evaporation energy to keep low. The thickness is preferably between 0.2 and 0.5 μm set.

Without departing from the invention, the method can be modified such that Imaging first a flowable material evenly on the ink-transferring Surface is applied, the ink accepts and dampening solution preferably rejects this material in a targeted manner at the points to be trained to accept the color hardened or hardened and in the paint-repellent areas where it is still flowable, is removed using dampening solution.

The two process alternatives mentioned have the advantage that initially the ink-transferring surface is evenly wetted or covered, for what once Fountain water and once ink accepting and dampening repellent material used and then the evenly wetted or covered surface of the printing form by drying the dampening solution or hardening, especially drying, the ink-accepting / dampening agent-repellent material specifically with the printed image in which the dried spots or the spots with the hardened material form ink-accepting areas. An application device with which an ink-accepting and dampening agent-repellent material is applied directly according to the picture It is not necessary to carry out the method according to the invention. By creating of the print image in both process alternatives only an even application of material is carried out, the costs for the order facility for imaging significantly reduced.

Any application of material is considered a uniform application in the sense of the invention understood for the purpose of illustration, which is not itself already done according to the picture. Preferably done the application of material over the entire surface of the printing form or at least in Surface stripes evenly.

The ink-accepting / dampening agent-repellent material is preferably printing ink, particularly preferred printing ink of the current production in which the illustrated printing form then used.

A particular advantage of the method according to the invention in both alternatives is that to apply the ink-accepting and preferably dampening agent-repellent material in the course of the imaging, a paint application device that is available anyway for ongoing production, for example, an ink roller can be used. The usage such an ink application device, in particular an ink roller, also corresponds a particularly preferred embodiment of the invention. However, it could also a separate application roller or other suitable application device, for example a spraying device, only for illustration or for illustration and for the subsequent paint application may be provided. After all, should also be in such training the material order is not controlled according to the image.

In any case, only the drying of the dampening solution and / or the hardening is in accordance with the picture of the ink accepting / preferably dampening agent repellent material. One for this Image transmission device used with semiconductor lasers, in particular Lasers, preferably laser diodes, particularly preferably through one or more arrays Arrays of infrared laser diodes.

The immaterial treatment according to the invention according to the image of a previously uniform the ink-transferring surface of the printing material or Dampening solution also allows more precise image formation than that of an immediate one pictorial material application is possible.

The invention further relates to a device for imaging a printing form in a Rotary printing machine for wet offset printing. The machine is preferably a web press for newspaper offset. The device comprises a printing form cylinder with the printing form, a dampening device for wetting a color transfer surface of the printing form with dampening solution and a Application and image transfer device, with the on the color transfer surface by applying an ink-accepting and dampening-repellent material a printed image with ink-accepting areas and dampening solution-accepting areas is produced.

According to the invention, the application and image transmission device has an application means for even application of a flowable material that accepts printing ink and Preferably rejects dampening solution, and an irradiation device, preferably Exposure device on. The print image is created by a combination of material application by means of the application means and irradiation of those places of the ink-transferring Surface created by means of the irradiation device to form the ink-accepting are. The application means is preferably an application means that is in transfers the printing ink to the printing form cylinder during ongoing production.

In a large rotary printing press with a plurality of printing form cylinders preferably each of these printing form cylinders such an order and image transmission device assigned. With increasing machine size, i.e. Number of printing form cylinders, the cost advantages grow with the direct imaging according to the invention especially when the print production changes frequently and downtimes are minimized should be.

The invention further relates to a dampening medium-permeable printing form and a method for the production of such a printing form. It is a printing form for a wet offset rotary press. The printing form has an imageable or Imaged surface for transfer of printing ink.

The unimaged printing form is at least on a ink-transferring surface dampening agent friendly or accepting, preferably hydrophilic. The printing form can, like also known printing forms, for example a printing plate or preferably one Printing form shell, which is attached to a carrier cylinder, for example by means of a known clamping device. Such intrinsically stable, imageable or illustrated Printing forms as such are also the subject of the invention. The carrier cylinder in this case forms the printing form cylinder together with the attached printing form. In principle, the printing form can also be a cylinder sleeve. Disadvantage of such a Printing form sleeve, however, would be that the carrier cylinder only rotatably supported on one side could be to be able to change the printing form sleeve in a simple manner. As well are printing form cylinders the subject of the invention that an imageable or already have illustrated printing form on a cylinder surface, the printing form cannot be removed; at least the printing form cannot in this training be removed non-destructively.

The printing form is permeable to a dampening solution in a radial direction. In the event of The direction is indicated on a pressure plate that is attached to a carrier cylinder related to the assembled state. The printing form cylinder including printing form has a device by means of which the dampening solution can be guided to the printing form. As In the sense of the invention, the carrier cylinder becomes the cylinder body of the printing form cylinder understood, on which the printing form is attached, either as an independent Pressure plate or, as already stated above, as an integral part. In both Embodiments of the dampening solution, in particular fountain solution, from the back the printing form brought to the ink-transferring surface of the printing form. Because due the radial permeability of the printing form on the ink transfer surface for the dampening solution, the dampening of the printing form, i.e. the color transfer surface, and thus the color acceptance or rejection by a targeted closing of passage channels on the ink-transferring surface become. In the area of closed through channels no dampening solution can reach the ink-transfer surface, so that in the one enclosing the through-channel Color area is accepted.

Although the color transfer surface is basically perforated first closed surface can be produced, the printing form preferably has as Print layer on an outer layer of material that is porous.

The printing form is built up in layers according to the invention and has an outer Print layer with the imageable or illustrated surface and one adjacent underlying lower layer. The throughflow capacity preferably increases Printing form abruptly at an interface from the lower layer into the printing layer Multiple off. The flow resistance increases accordingly. Advantageously these two layers can consist of different materials and also thereby be optimally adapted to different functions according to the invention.

For the purposes of the invention, flow-through means the volume of the used Understanding dampening solution, which is covered by a layer with an executed thickness flows to a differential pressure acting over this layer per time and area, the outer surface of the layer being taken as the surface. The flowability is used as a material characteristic in the following on the unimaged condition of the color-transferring surface.

An abrupt decrease in the sense of the invention is not only a sudden, for the practical concerns as a change in the flowability that can be regarded as inconsistent understood, but also a constant change. In the latter case, the flowability shows a steep gradient at the transition from the lower layer to the printing layer on. A transition zone from the lower layer that can never be completely avoided in practice into the pressure layer in which the change in flowability according to the invention takes place is in any case thinner than the print layer. According to the invention, it becomes a The steepest possible decrease in flowability from the lower layer into the pressure layer sought.

According to a method of manufacturing such a cylinder, the underlayer is first formed, preferably by a fleece of rust-free metal fibers. Such a fleece advantageously has a high tensile strength compared to materials of the same porosity Compressive strength. Sintered and rolled to a defined thickness made of non-rusting Metal fibers are particularly suitable. Suitable nonwovens are from filter technology known.

The printing layer is made by coating the underlayer, preferably by means of Plasma spraying received. It is preferably formed as a ceramic layer.

The lower layer points in the radial direction as well as in the axial and in the circumferential direction a flow rate several times greater than that of the immediately adjacent one Print layer on. Their flowability is preferably around that at least Hundred times, particularly preferably at least a thousand times larger than that Print layer. The lower layer is preferably at its free edges against damp penetration sealed. The entire printing form is preferably free Sealed edges.

The flow resistance becomes due to the layered structure of the printing form according to the invention or the flowability of the printing form as a whole in a practical approximation determined solely by the print layer. The printing layer preferably has a uniform material structure and, last but not least, the required fineness of pressure can be optimally adapted. Their structure or structure is such that it is traversed by capillary pores that are very fine and on the color-transmitting Have a high surface density. Per image pixel ends on the surface at least one such capillary pore. At the same time, the porosity of the print layer kept low. It is preferably below 20%. It is an open one Porosity.

The printing form has the further advantage that by means of a single thin one uniform layer, the printing layer, through a particularly well-defined pressure drop this layer is adjustable. The underlying sub-layer has in relation to the dampening solution management the task, the dampening solution evenly below the print layer spread over the area. It forms the overpressure on the back the dampening solution level that also determines the outer pressure layer. By the invention Training forms a kind on the back of the outer print layer Fountain solution lake. The dampening solution presses particularly evenly against the pressure_ layer, so that a total of defined pressure ratios arise and thus a precise dampening solution guidance is possible. It also takes place in acceleration and deceleration phases of the printing form cylinder, for example when starting up or shutting down the Machine, practically a distortion-free adaptation of the dampening solution pressure to the respective required dampening solution supply rates to the surface instead.

The printing form is particularly preferred in combination with the invention Imaging method and / or used in a device according to the invention. However, it is not limited to this, but also in combination with conventional ones Methods and devices for imaging internally moistened printing forms usable for profit.

The passage channels of the pressure layer, which preferably have the The aforementioned capillary pores are, in particular, an average diameter of 0.1 to 5 µm measured at the mouths on the ink-transferring surface. The porous printing layer preferably has a on the ink-transferring surface Average roughness Ra in the range of 0.2 to 5 µm and preferably an average Roughing depth Rz in the range from 0.2 to 10 µm.

The lower layer is traversed by through channels, for example connected pores, which have a diameter of 10 microns to 2 mm, preferably 10-50 microns. As Diameter is understood to mean the diameter of a circle, which is the average cross-sectional area the passage channels of the respective layer. Will it be through a fleece is used to characterize the laminar diameter, determined analogously to ASTM F 902, the right size. The laminar diameter should then be between 10 and 100 µm.

The thickness of the printing layer in the radial direction is preferably between 50 and 500 µm, and the thickness of the underlayer is preferably between 500 µm and 3 mm.

The printing layer preferably has a high absorption coefficient for infrared radiation on. The absorption coefficient should be at least 0.9.

Since in the first alternative process the dampening solution is preferably by infrared radiation is evaporated and it is in the near infrared when using fountain solution as a dampening solution only for a low absorption of preferably used infrared Laser radiation comes in the dampening solution film, it heats up and evaporates a dampening solution takes place indirectly by heating the printing layer. To be a strong one Achieving local heating of the print layer is used as the material for the print layer preferably selected a material with a heat capacity that is less than that Heat capacity of the dampening solution. The heat capacity of the is particularly preferred Print layer less than 1 J / g. Furthermore, the printing layer is formed so that the Thermal conductivity of this layer is significantly lower than the thermal conductivity of the dampening solution is. The thermal conductivity is preferably less than 0.2 W / (m * K).

Preferred materials for the print layer are dark, ceramic materials, e.g. B. an Al ₂ O ₃ -TiO ₂ mixture.

An independent printing form is preferably constructed with at least three layers a printing form carrier that conducts dampening solution, the underlayer applied thereon and the printing layer applied on the underlayer. The printing form carrier is preferably made of metallic material. It can be used as a vaulted level Plate or as a preformed shell, in particular as a rigid cylindrical half shell, be trained. Such a multilayer structure can also be used on the carrier cylinder have firmly attached printing form.

A perforated printing form carrier has holes with a diameter, preferably in Range of 0.5 to 5 mm or recesses of the same area on the whole Range of the printing form from one another, preferably in the range from 5 to 50 mm have. However, the hole density can be significantly reduced by the areas enlarged per hole and / or one on the outer surface of the printing form support Channel structure is formed.

The underlayer is applied to the printing form support, in particular as a whole attached to it, preferably glued using a temperature-resistant adhesive or bonded.

The dry spots on the ink-transferring surface preferably result a dampening medium-permeable printing form by targeted closure of the on the ink-transferring Through-flow channels opening on the surface.

The amount of dampening solution exiting the ink-transferring surface per unit of time is regulated by setting the dampening solution pressure, advantageously by the Setting the amount of dampening solution in the printing form cylinder. By increasing the amount of dampening solution due to the centrifugal forces, the Dampening solution pressure increased. Furthermore, the dampening solution supply rate becomes the printing form cylinder increased and decreased in proportion to the printing speed.

The amount of dampening solution exiting the ink-transferring surface per unit of time, i.e. the flow rate of the printing form depends on one which is completely sufficient for practice Approximation only from the flow through the outer pressure layer. The Pressure difference across the outer pressure layer increases at a constant rotation speed approximately linear with the dampening solution level, which is on the back of the printing layer sets. The flow through the pressure layer can be determined solely by the thickness of the Adjust the print layer, since the print layer is essentially constant everywhere Porosity and capillary pore density. In this sense, the lower layer is also homogeneous. By dividing the function of the uniform distribution according to the invention of the dampening solution and the setting of the flow through the printing form can a particularly precise dosage of those emerging on the ink-transferring surface Amount of dampening solution can be made. The thickness of the dampening solution film on the The surface can be set precisely, especially very small. At constant Cylinder speed is exactly as much dampening solution on the back of the printing form out how to exit the ink-transferring surface. The equilibrium height of the dampening solution level in the lower layer on the back of the printing layer arises then on its own depending on the speed of the printing form cylinder. The Setting when changing the speed is also done because of the invention Construction of the printing form almost without delay.

The overpressure on the back of the print layer should not exceed 100 mbar. The dampening solution level on the back of the print layer should at least be in equilibrium of inflow and outflow do not exceed the thickness of the lower layer. Corresponding the thickness of the underlayer and the permeability of the printing layer are preferred coordinated.

A preferred way of closing is by heat-induced, preferably laser-induced, image-dependent toning. As is known, wet offset printing is based on the repulsion of paint by dampening solution on the moistened areas of the Printing form. If there is not enough dampening solution, color will be accepted also at the non-image areas. This process is commonly referred to as toning.

In this first alternative method, the ink-transferring surface of the printing form moistened from the inside and then by means of the image transmission device, preferably using infrared laser, dried depending on the image. Here are the image points dried and immediately colored. When coloring, color is applied to the transfer dried areas, while the moist areas remain color-free. In the Dried areas, the paint clogs the passageways, leaving those areas no more dampening solution penetrates to the ink-transferring surface.

In the second method alternative, the printing form is made by means of the image transfer device warmed depending on the image after coloring. The paint dries in the warmed Areas and thus also in the through channels or at the mouths of the through channels on. The color dried in the through-channels can then Dampening solution supply can no longer be displaced while the flowable ink passes through the dampening solution is displaced. The dampening solution pressure can occur until the printing form runs free compared to the dampening solution pressure in production.

The illustration of the printing form, i.e. the color dried in the passage channels, can be removed by a conventional printing plate washer and / or due to the internal humidification with a higher dampening solution pressure than the production.

As an alternative to the above-mentioned closing by means of paint, a sub-variant can be used the second process alternative also a monomer or mixture of monomers the ink-transferring surface of the printing form are applied, in particular be sprayed on. A polymerization is carried out by means of the image transmission device triggered. The plastic formed thereby closes the passage channels, e.g. by Formation of polystyrene from styrene when exposed to heat. The closed pores can be freed by rewarming the polymer again disintegrates and is removed by adding dampening solution. The dampening solution is at the deletion of the image preferably fed from the inside. Washing from the outside is however also possible, especially supportive.

The printing form and lead in an exposure process for imaging the printing form the image transmission device has a predefined direction and speed Relative movement in which the surface of the printing form to be imaged pixel by pixel is exposed image-wise. As with conventional printing forms, the pixels of the print image to be generated in columns and vertical lines on the color transfer Surface of the printing form arranged. A pixel column therefore runs in Column direction and a pixel row in a row direction perpendicular to it. The above relative movement takes place either in the column direction or in the row direction instead of. Is the printing form the printing form of a printing form cylinder in a rotary printing press so the column direction is the printing direction and the Row direction is the longitudinal direction of the cylinder. If there is an image in the machine, it is Direction of the relative movement to which the latitude and longitude information of the light-emitting Areas are related, the printing direction. However, an illustration is also conceivable a printing form outside of a machine, in which an illustration is also in Row direction can be made as the relevant direction of the relative movement can.

The strip-shaped laser spot can advantageously also be used to set the area coverage and thus also the tonal value levels particularly finely without changing the geometry of an optical imaging device for focusing the laser light on the color-transmitting surface. By changing, in particular shortening, the duty cycle of the semiconductor laser, pixels of any extension in the direction of the relative movement can be generated. In particular, pixels can be generated which have very small areas, but which then are not square, but rather strip-shaped. As is known, the number of shades of gray that can be displayed results from the raster width and pixel area. The rule here is that the grid cell width is equal to the reciprocal of the grid width. The area of the grid cell is calculated from this by squaring. If the result is divided by the pixel area, the number of maximum tonal values that can be displayed is obtained. For example, a grid cell with a 40 grid has an area of 250 * 250 µm ² . With a pixel width of 62 µm, a maximum of 16 gray levels can be displayed in the case of square pixels. If rectangular pixels of 62 µm * 31 µm are generated, there are already 32 gray levels. The imaging time is the same in both cases. The finer gradation of the tone levels makes it possible to better compensate for nonlinearities occurring in the print, such as tone value increases and decreases, than is possible with laser spots which do not have the very short extension according to the invention in the direction of the relative movement. If the printing form is arranged on a printing form cylinder, then for this compensation an angle sensor for the printing form cylinder or an associated blanket cylinder has a correspondingly higher resolution, or intermediate increments are formed with electronics by interpolation.

The image transmission device preferably comprises an array or several arrays of pulsed or current-pumped semiconductor lasers, in particular pulsed infrared lasers, particularly preferably laser diodes. Using the semiconductor laser, narrow, Strip-shaped, preferably rectangular laser spots on the surface to be imaged generated, each on the surface to be imaged in the direction of the relative movement have measured laser spot width that is several times smaller than one in the same direction measured width of an image pixel of the surface to be imaged and is also several times smaller than a laser spot length measured across the laser spot width. A pulse duration per laser spot is then several times longer than a time period in which Relative movement between the printing form and the laser array covered a distance that corresponds to the laser spot width.

In a preferred embodiment, the imaging takes place directly on the machine Printing form cylinder. In this case, the relative movement between the printing form and the laser array by vertical movement by rotating the printing form cylinder and a horizontal movement perpendicular thereto by shifting the laser diode array causes. With the rotation of the printing form cylinder, the image information transferred column by column to the printing form. By moving the laser array horizontally adjacent columns are imaged one after the other until the entire image is recorded is. Using the laser on the ink-transferring surface of the printing form generated laser spots then have a width measured in the vertical direction and a length measured in the horizontal direction. The horizontal movement takes place during the imaging of the laser array with the printing forme cylinder rotating, preferably continuously. In this way, optimally short imaging times can be obtained.

The resolution of the image transmission device depends on the distance by which the laser array is shifted during one cylinder revolution. This distance is preferably between 84 and 28 microns. This corresponds to a preferred resolution from 300 to 900 dpi. The laser spot length is preferably 30 to 90 microns, and The laser spot width is preferably 1 to 10 μm. The laser pulse duration is between 1 and 50 µs, depending on the resolution of the device, the power of the laser and the imaging speed. The imaging is done by axially shifting the at least one array along the printing form cylinder rotating during the imaging. The total laser array can be replaced by exchangeable modules with, for example, 64 diodes per Pressure zone are formed.

The ratio of the laser spot length to the laser spot width is preferably at least 10: 1 and particularly preferably at least 20: 1.

An advantage of the image transmission device according to the invention is that a mechanical exact adjustment is not required. It will preferably be a software adjustment performed.

The image transmission device preferably comprises an array or several arrays For example, 256 semiconductor lasers in 4 arrays, each with 64 lasers for a printing zone.

Semiconductor lasers are used to produce a narrow, strip-shaped laser spot narrow, strip-shaped, preferably rectangular, light-emitting surfaces used as infrared laser diodes in particular. The emitted laser light is transferred to the ink-transferring surface via an optical imaging device focused. Because of the preferred elongated strip shape of the laser spot enabled the use of simple optics in conjunction with the corresponding narrow strip shape of the light emitting surfaces and the long pulse duration per The laser power can be kept low. The energy consumption is despite the longer pulse duration is also lower than when the laser spot is formed directly in or approximately in the form of the image pixel on the color transfer surface print image to be generated.

Accordingly, the image transmission device comprises pulsed or current-pumped Semiconductor laser, in particular infrared laser, particularly preferably infrared laser diodes light-emitting, strip-shaped surfaces, one in the direction of relative movement have measured width that is several times smaller than one in the same direction measured width of an image pixel on the surface to be imaged and also several times is smaller than a length of the light emitting surface.

The lasers preferably emit in the infrared or visible range, especially in the Wavelength range from 700-1400 nm.

An optical imaging device is preferred for the light-emitting surfaces provided with at least one lens per light-emitting surface. Are preferred Lenses of the imaging device arranged in the form of one or more arrays, advantageously as one or more lens arrays made of plastic, which are inexpensive in Mass production and easy to assemble. The lasers are in or attached to a housing in an orientation such that their light-emitting Have surfaces parallel longitudinal directions. Finally, the Image transmission device control electronics with which the laser is controlled be that a laser pulse duration is several times longer than a time period in which Relative movement is covered a distance that is the width of the light-emitting Area corresponds.

The image transmission device does not require a fiber output. This also does that Device inexpensive and increases its efficiency. A laser carrier of the picture Carrier is preferably water-cooled.

Control electronics for the image transmission device preferably comprise sufficient storage capacity for two bitmaps, namely one bitmap for a current image and the at least second bitmap for a subsequent image. The control electronics also include power electronics for each of the lasers. The control electronics is on a position sensor of the printing form cylinder coupled, from which they the angular position of the printing form cylinder and the position of the array, preferably from each array module, receives the laser pulses with the movement of the printing form cylinder too synchronize. The control electronics are on a server PC for data transfer coupled.

While the current image is being printed, the new image can be stored in the control electronics memory Loading. The new picture is thus already in progress Production available for the next production within the control electronics. After imaging the printing form, but at the latest after the end of the current one Production, the memory of the old image is cleared and can be used for the data take over the next but one production. The memory of the new image is saved for the next one Production to save the current picture and save the previous current picture to the memory for the new image. The control electronics are preferably more integrated Part of the image transmission device directly at the location of the laser array; she will preferably moved.

At the machine level, one or more server computers receive the separated ones and rasterized image data in the form of bitmaps. Each server is one or more Printing units assigned to the machine. Data transmission to the control electronics takes place via a fast local network.

The image transmission device, in particular its arrangement in the printing press, the formation of one or more laser arrays, the assignment and functioning of the Control electronics and also the division of tasks between the server and control electronics can advantageously be used universally and are not in line with the claims specified procedure of the imaging or the device used for this bound, although the image transmission device prefers in this illustration and particularly preferred in combination with this illustration and that described above Printing form is used.

Fig. 1

eine Zylinder- und Walzenanordnung mit einem Druckformzylinder nach einem ersten Ausführungsbeispiel,

Fig. 2

eine Zylinder- und Walzenanordnung mit einem Druckformzylinder nach einem zweiten Ausführungsbeispiel,

Fig. 3

den Druckformzylinder nach Fig. 2,

Fig. 4

die Druckform des Druckformzylinders nach Fig. 3,

Fig. 5

eine Belichtungseinrichtung einer Bildübertragungseinrichtung in einem ersten Schnitt,

Fig. 6

die Belichtungseinrichtung in einem zweiten Schnitt,

Fig. 7

eine Belichtungseinrichtung einer weiteren Bildübertragungseinrichtung und

Fig. 8

eine Software-Justierung der Bildübertragungseinrichtungen der Fig. 5 bis 7.

Preferred exemplary embodiments are explained below with reference to drawings. Show it:

Fig. 1

a cylinder and roller arrangement with a printing form cylinder according to a first embodiment,

Fig. 2

a cylinder and roller arrangement with a printing form cylinder according to a second embodiment,

Fig. 3

2,

Fig. 4

3 the printing form of the printing form cylinder according to FIG. 3,

Fig. 5

an exposure device of an image transmission device in a first section,

Fig. 6

the exposure device in a second section,

Fig. 7

an exposure device of a further image transmission device and

Fig. 8

a software adjustment of the image transmission devices of FIGS. 5 to 7.

1 shows a printing material web B between two blanket cylinders 1 passed and in the formed between the two blanket cylinders 1 Printing gap printed on both sides. The two blanket cylinders 1 each have a printing form cylinder 2 in the manner shown for the left blanket cylinder 1 assigned. An inking roller 3 for the left blanket cylinder 1 is also shown. The arrangement of cylinders and rollers is mirror-symmetrical on both sides of web B. The arrangement shown in FIG. 1 is preferably repeated for each of the many Blanket cylinder of the printing machine.

In the exemplary embodiment, it is a newspaper offset web-fed rotary printing press with rubber-rubber production, for example a WIFAG OF 370. Likewise However, the machine can also be a machine for rubber-steel production act, for example with one or two central steel cylinders and thus blanket cylinders forming printing gaps per printing unit, for example one WIFAG OF 470 or OF 790.

The ink is transferred from the inking roller 3 to the printing form cylinder 2 and from the Transfer form cylinder 2 to the blanket cylinder 1, which in the printing nip Lane B is printed with the image obtained from printing form cylinder 2.

The printing form cylinder 2 has a hollow cylindrical carrier cylinder 10 with a central, axial cavity 4, which is in fluid communication with a dampening solution supply device stands. The fluid connection is made by a rotary connection on one or two shaft journals of the plate cylinder 2 are formed. The dampening solution is supplied through this shaft journal into the cavity 4. The dampening solution is previously filtered to avoid annoying deposits within a printing form 12. The Carrier cylinder 10 has through channels 5 in the radial direction. The through channels 5 are designed as straight, exactly radial bores 5. In the embodiment each of the bores 5 has a diameter of 6 mm. The holes 5 open on an outer jacket of the carrier cylinder 10 at a distance of 20 mm from one another, measured between the centers of the holes.

The outer jacket of the carrier cylinder 10 is of shell-like, surrounded perforated steel sheets. The steel sheets form a perforated one Printing form support 13 of the printing form 12 permanently connected to the support cylinder 10. In the exemplary embodiment there are four perforated steel sheets for such a printing form carrier 13 stacked. The lower layer 14 could also directly on the carrier cylinder be attached.

To form the printing form 12, an underlayer 14 is on the printing form support 13 bonded, which in turn serves as a support for a printing layer 15. The print layer 15 forms the ink-transferring surface of the printing form cylinder on its free outer surface 2. The printing layer 15 and the underlayer 14 are porous.

Dampening solution is injected into the cavity 4 of the printing form cylinder 2. Because of centrifugal force is the dampening solution through the holes 5 of the support cylinder 10 and the perforated printing plate carrier 13 acting as a distributor to the rear of the Underlayer 14 performed. This passes through the lower layer 14 and the printing layer 15 Dampening solution on the ink-transferring surface and causes that on the wetted Make no ink is accepted.

Water is used as the dampening solution, with the additives commonly used in offset printing is provided.

An image transmission device 20 is assigned to the printing form cylinder 2. The Image transmission device 20 comprises infrared laser diodes which are applied to the surface of the Printing form cylinder 2 are directed. The image transmission device is arranged that the printing form cylinder 2 rotates shortly before reaching the Contact point with the ink roller 3 sweeps the image transfer device 20.

Furthermore, the printing form cylinder 2 is assigned a washing device 30, which in the Embodiment seen in the direction of rotation behind the blanket cylinder 1 and is arranged in front of the image transmission device 20. By means of the washing device 30 ink can be washed off the surface of the printing form cylinder 2.

Fig. 2 shows the printing form cylinder 2 in cross section with two printing forms 12, the formed independently and with a carrier cylinder 10 of the printing form cylinder 2 are releasably attached by means of a conventional clamping device 6.

The carrier cylinder 10 corresponds essentially to the carrier cylinder 10 of the first Embodiment. However, the central axial feed channel or cavity 4 is included equipped with a much smaller diameter. Accordingly, they are radial branching channels 5 longer than those of the first embodiment. The radial distribution channels 5 open into axial distribution channels on the outer surface of the carrier cylinder 10 are excluded to the distribution of the dampening solution to equalize as early as possible.

The arrangement of the printing form cylinder 2 of FIG. 2 corresponds to a printing press those of the first embodiment, so that in terms of imaging and all Further details and features of the invention always on both embodiments is referred.

One of the two printing forms 12 of the second exemplary embodiment is individual in FIG. 3 shown. The printing form 12 is described in the first exemplary embodiment Kind by a perforated printing form carrier 13, an applied thereon Porous underlayer 14 and a porous printing layer 15 layered over it. The printing form carrier 13 is made more uniform by a single semi-cylindrical steel plate Perforation formed.

The porous underlayer 14 is formed by a steel fiber fleece, the fibers of which are closed so-called tangled fibers are nonwoven. After the nonwoven, the nonwoven is bonded to a wire mesh sintered in vacuum and to a defined thickness, namely the Layer thickness in the printing form 12 has been rolled. Because of the very high porosity of the steel fiber fleece of preferably more than 60%, results in comparison to Material proportion an extremely large sum of pore cross sections. Compared to Particle size spectrum of powders, the diameter range of the fibers is very uniform, so that the pore size distribution is also very narrow. Surrender this way the desired properties of high flowability and low Pressure drop through the underlayer 14. Furthermore, the nonwoven is stable in pore shape due to the Sintering process.

The steel fiber fleece is attached to the printing form carrier using a temperature-resistant adhesive 13 bonded. The lower layer is by means of plasma injection molding, preferably in a vacuum 14 has been coated with the printing layer 14. In the embodiments the printing layer 14 is a ceramic layer.

Preferred material information and characteristic values for printing forms according to the invention, in particular for printing forms 12 of the exemplary embodiments, are summarized in the tables below. Although a three-layer structure is preferred, a structure with more than three layers and also only a two-layer structure are also the subject of the invention. Particularly preferred characteristic values or characteristic value ranges are given in the second columns. The respective layer does not have to correspond to all the information at the same time, although this is preferred. Print layer 15 material hydrophilic, for example TiO ₂ -Al ₂ O ₃ mixtures as used in plasma coating thickness 50 - 500 µm 100-200 µm Capillary pore diameter 0.1 - 5 µm 0.1 - 3 µm open porosity 3 - 30% <20% Margin 0.2-10 µm 1 - 5 µm Ra 0.2 - 5 µm Flow through 2 - 20 l / (hm ² mbar) Lower layer 14 material Fleece made of rustproof metal fibers, sintered with wire mesh and then rolled thickness 0.5 - 3 mm 0.5 - 2 mm Laminar diameter 10-100 µm 10 - 60 µm porosity 50 - 80% > 60% Flow through 1,000 - 40,000 l / (hm ² mbar) Printing form support 13 material stainless steel, one piece or layered steel sheets thickness 1 - 5 mm Hole diameter 0.5 - 5 mmm Hole spacing 2 - 50 mm 5 - 50 mm Flow through ≥ 200 l / (hm ² mbar) 200 - 20,000 l / (hm ² mbar)

The dampening medium flow rate of the printing form 12, based on the unimaged state, has a value which is in the range of 2-20 l / (hm ² mbar). In an approximation which is sufficient for practical use, it also corresponds to the value of the flow through the printing layer 15.

Due to the high, isotropic flowability of the lower layer 14, the homogeneous Distribution of the dampening solution in the lower layer 14 and thus on the back of the Print layer 15 reached.

The values and ranges for the values given above and also in the tables Flow rates are related to dampening water as a dampening solution. However, they apply to other suitable dampening solutions with the same or similar flow properties as well. Furthermore, the values for the flow rates are in the unillustrated state related to the printing form.

In order to achieve a flow, the dampening solution must be supplied with a pressure that overcomes the flow resistance of the individual layers, in particular the capillary pressure of the fine-pored printing layer 15. This pressure is created by the Centrifugal forces that act on the dampening solution during the rotation of the printing form cylinder 2. The pressure differential grows roughly linearly with the water level that is at the back the printing form, i.e. in a good practical approximation on the back of the print layer 15 sets.

Since the differential pressure mainly occurs at the pressure layer 15 because of the flow resistance is greatest here, there is a tensile load on the lower layer 14 For reasons of strength, this load should be low. From known contexts between centrifugal force, cylinder radius, cylinder circumference, rotation speed and Surface speed can be seen that the tensile load on the underlayer constant surface speed becomes smaller with increasing radius. Hence the Invention particularly advantageous when large radius cylinders are used as is the case, for example, in double-sided newspaper printing presses. The dead weight of the printing layer 15 should also not be neglected. Compared to the fountain solution lake present in the lower layer 14, which e.g. 1 mm is deep, however, the mass of the printing layer 15 is due to its smaller thickness, of for example 100 µm, small. From the same considerations, one can see that the Using a thick print layer would be less advantageous. It should be in such a way In one case, either a very porous material or a material with large pores is used be what is unfavorable on the strength of the print layer and also on the print quality would impact. Or there would have to be a high overpressure on the back of one thick print layer are generated, which at constant cylinder speed cylinder with very small radii and associated high centrifugal forces or one Fountain solution supply under pressure, which, however, sealing problems with the introduction of the Would cause dampening solution in the rotating cylinder.

At a level of 0.1 mm, this results in a rotation speed of 36,000 Revolutions / h and a cylinder radius of 200 mm due to the centrifugal forces a dampening solution pressure of about 0.55 mbar at the back of the print layer 15. The maximum Differential pressure across printing plate 12 should not exceed 100 mbar. Because with diminished Machine speed correspondingly less dampening solution on the ink-transferring Surface must and should be present, the pressure can decrease the cylinder speed, especially linear, decrease with the speed. The dampening solution level on the back of the printing layer 15 may be the thickness of the underlying layer Do not exceed layers. It should be in the exemplary three-layer Printing form 12 at most as high as the thickness of the underlayer 14. At a The dampening solution level of 3 mm results for the assumed cylinder radius of 200 mm at a rotational speed of 5,000 revolutions / h a differential pressure of about 0.45 mbar at the back of the printing layer 15. This overpressure, which is caused by the Pressure layer 15 is reduced, should be above the pressure difference for a sufficient flow through the pressure layer 15 is required. The print layer 15 Accordingly, it should have a material structure that is at least reflected in the the thickness of the underlayer 14 resulting maximum differential pressure to the sufficient Supply of the ink-transferring surface with dampening solution is sufficient, so that also with low rotation speed printing is possible.

Berechnungsgrundlage:

Zylinderradius 200 mm, Porosität Unterschicht 70%, Feuchtwasser

The table below summarizes calculation examples to illustrate the dependency of the dampening solution pressure on the cylinder speed and the dampening solution level on the back of the printing layer 15: Rotational speed [U / h] Dampening solution level [mm] Hydrostat. Pressure [mbar] 36,000 1 5.53 36,000 0.5 2.76 36,000 0.1 0.55 20,000 1 1.71 20,000 0.5 0.85 20,000 0.1 0.17 5,000 2nd 0.21 5,000 1 0.11 5,000 0.5 0.05

Basis of calculation:

Cylinder radius 200 mm, porosity lower layer 70%, fountain solution

As the speed of rotation decreases, the influence of gravity increases and must therefore be taken into account. The centrifugal force generated at a dampening solution level of 2 mm for the assumed cylinder radius of 200 mm at a rotation speed of 5,000 U / h a differential pressure of about 0.2 mbar at the back of the Printing layer 15. The centrifugal force still outweighs the gravitational force by about 30%.

The capillary action of the small pores in the pressure layer 15 advantageously results to compensate for the fluctuations in the dampening solution pressure. Therefore, too uniform wetting of the outside of the printing layer at low speeds 15 reached. The middle hydrostatic acting on the back of the printing layer 15 Pressure due to gravitation is 1 mbar per 10 mm dampening solution level * porosity the lower layer 14. At a cylinder speed of about 4,500 rpm or below, the gravitational pressure becomes greater than at the back of the printing layer 15 the pressure generated by the centrifugal forces. The dampening solution therefore flows down and causes an increase in the dampening solution level in the lower area of the lower layer 14. The dampening solution is pushed back into the printing form carrier 13. It increases with it not only the gravitational pressure, but also the centrifugal force in the lower area of the Printing form cylinder 2. Therefore, even at low speeds, dampening at least the lower cylinder area may be possible.

On the basis of the relationships explained above, the image transmission device 20 preferably facing the lower region of the printing form cylinder 2 arranged. This provides precise imaging of the printing form 12 down to the bottom Possible speed range of the cylinder. A lower limit for the cylinder speed in the case of imaging, the newspaper offset with two printing forms has 12 per printing form cylinder 2 approximately at 3,000 U / h.

If one considers the centrifugal forces that occur on the printing form 12, the greatest force acts on the holders of the printing form 12, with which the printing form 12 is fastened in the clamping device 6 of the printing form cylinder 2. Furthermore, a force acts on the bonded or bonded connection between the lower layer 14 and the printing form carrier 13. A lower force acts on the connecting surface between the printing layer 15 and the lower layer 14. With a printing form cylinder 2 with a radius of 200 mm, at a rotation speed of 36,000 U / h and a printing form 12 with a surface of 400 mm * 600 mm results per printing form 12: Dimensions Centrifugal force Printing form carrier 13: 5 mm thick half shell made of steel 9.6 kg 7.6 kN Lower layer 14: 2 mm fleece, 70% porosity 1.2 kg 947 N. Fountain solution lake in lower layer 14: 1 mm deep 170 g 134 N. Print layer 15: 100 µm thick, ceramic 50 g 40 N

In this calculation example there is a total force of approximately 8.7 kN which must be absorbed by the holders of the printing form 12. A force of 1.121 N acts on the glued or bonded connection between the printing form carrier 13 and the lower layer 14. This corresponds to a tensile load of 5 mN / mm ² . The fibers of the lower layer 14 are loaded with about 1 mN / mm ² at the connection to the printing layer 15. This corresponds to a pressure of 10 mbar. Higher pressures arise with increasing depth of the dampening solution lake or with faster rotation.

In a first alternative method of imaging, the image transmission device evaporates 20 the dampening solution on the surface. To illustrate a still "virgin" The dampening solution wetting the surfaces becomes the corresponding printing form of the image to be transferred to the blanket cylinder 1 by means of the image transfer device 20 evaporated. Before a point from which by means of the image transmission device 20 straight surface dampening solution was evaporated due to pressing Dampening solution is moistened again, the dried area passes the inking roller 3 and takes color. A pore that opens into the just dried surface area is closed by the color assumed in this area, so that no Dampening solution more reaches the now printing mouth area.

The image transmission device 20 can also do this instead of evaporating dampening solution be used, already applied with the inking roller 3 ink on the ink-transferring To dry the surface of the printing form cylinder 2 according to the image in order to the pores of the print layer 15 lying under the dried ink spots on this Way to lock. In this alternative method, the inking roller is used 3 Apply the color evenly to the still dry surface of the printing form cylinder 2. The dampening solution supply to the pressure cylinder 2 is preferably only started when the paint has been applied evenly. After the even The color is applied to the color that is still flowable at the image points of the color-transferring color Surface dried by means of the image transfer device 20. In the picture passages the pores are closed by dried paint. The picture passages of the color-transferring surfaces run in the course of the onset or progressing Moisture not free from the inside. As the dampening progresses, printing form 12 runs however free at the non-image areas.

In both process alternatives - induced toning and color drying - can the same arrangement shown in the figures can be used. In the second Alternative method of drying the printing ink can be an arrangement of the image transfer device behind the ink roller can also be advantageous.

The imaging can be done by washing off the color layer by means of the washing device 30 be deleted in both procedural alternatives.

With the same image transfer device 20, it is also possible to transfer one on the color transfer device To polymerize surface of the printing form cylinder 2 sprayed monomer and thereby close the pores on the ink-transferring surface. By reheating after the end of a print production by means of the same image transmission device 20 and removal of the polymer which has decomposed due to the heating the illustration can be deleted again. The monomer can already be applied to the ink-transferring surface of the printing form. Preferably however, there is an application device at the installation location of the printing form cylinder 2, in particular Spray device for spraying the monomer, arranged on site, with which in particular can also be repeatedly illustrated in this variant of the second method alternative can without having to remove the printing form 12 or the printing form cylinder 2.

5 shows an exposure device of the image transmission device 20 in one Cross-section. 6 shows the exposure device in a longitudinal section. Representative for the entire image transmission device, the exposure device is also included denotes the reference number 20.

The exposure device 20 is arranged in a line arrangement next to one another Infrared laser diodes formed in a housing 21 each with a fastener 22 are attached. Each of the laser diodes is replaced by a laser chip 23 formed with a light-emitting surface 24. The light-emitting surfaces 24 opposite the housing 21 is provided with an overlapping row of holes. In the overlapping holes of the row of holes are arranged optical lenses 25. Every laser chip 23 has an electrical connection 26 to control electronics.

5, one of the light emitting surface 24 becomes one of the Laser chips 23 emitted beam 27 from the opposite lens 25 the ink-transferring surface of the printing form 12 of the printing form cylinder 2 is bundled, so that it hits there as a narrow rectangular laser spot 28. The light-emitting surface 24 corresponds in shape to the laser spot 28 it produces. It preferably points also the same size. An enlargement or reduction to a certain extent In practice, however, size can also be advantageous.

To the left of the exposure device 20 is a single pixel of the one to be generated Print image shown greatly enlarged. Laser spot 28 is also shown in FIG Printed image pixels. The length Ls of the laser spot 28 measured in the longitudinal direction of the cylinder corresponds to the length of the individual printed image pixel measured in the same direction. The width Bs of the laser spot 28 measured in the printing direction is a multiple smaller than the width of the printed image pixel measured in the same direction. In the embodiment the printed image pixel is square with a length and width of 50 each µm. The laser spot length Ls is also 50 µm. The laser spot width Bs, however is 3 µm. The exposure time for the exposure of the printed image pixel is correspondingly long or pulse duration of the pulsed laser diodes 24. The duty cycle for the exposure a square pixel that has an edge length that is equal to the laser spot length Ls corresponds to the quotient of the laser spot length Ls and the surface speed the printing form 12.

64 laser diodes 23 are arranged in a line in the housing 21. Is per page width Such an array with 64 laser diodes is provided, which are evenly distributed over just under one Page width are arranged side by side. With a 1.8 m wide printing unit there are four such arrays are arranged side by side along a line.

The imaging takes place at a speed of the printing form cylinder 2 of preferably about 10,000 rpm, with each of the arrays in its side area during the Cylinder rotation is shifted continuously in the longitudinal direction of the cylinder. A step by step Shifting one pixel column after every full revolution would also be possible, but more time consuming. The way around the laser array, in the case of several Laser arrays all of these arrays, horizontally shifted per cylinder revolution corresponds to the reciprocal of the image resolution. With an image resolution of, for example The laser array becomes 500 dpi per cylinder revolution by 51 µm across the printing direction postponed. The laser spot length Ls must not be less than the resolution-related one Feed of the laser array in order to be able to expose full areas. The maximal Resolution is by means of an angle encoder and the circumference of the printing form cylinder 2 given. The rotary encoder is an incremental encoder that arranged either on the printing cylinder 2 or the associated blanket cylinder 1 and measures the angular position of the cylinder. With a resolution of 40,000 Steps per cylinder revolution and a circumference of the printing form cylinder of 1.257 mm results in a resolution of 798 dpi. The one to be used for the illustration Laserspot 28 must have a length Ls of at least 32 µm for this resolution.

The laser power required to evaporate the dampening solution layer on the ink-transferring surface depends on the layer thickness, the surface speed of the printing form cylinder 2 and the geometry of the laser spot 28. At a dampening layer thickness of 1 µm and a surface speed of 3.5 m / s (radius 200 mm, rotation with 10,000 rev / h) and a laser spot 28 with a length Ls of 50 μm and a width Bs 3 μm, the laser spot 28 covers an area of 50 * 50 μm ² within approximately 14 μs, neglecting the displacement of the laser array in the longitudinal direction of the cylinder. On such an area there is a water mass of 2.5 * 10 ^-12 kg with fountain solution as dampening solution. In order to evaporate water, an energy of 2.3 * 10 ⁶ J / kg is required, ie 5.8 * 10 ^-6 J per pixel. If the evaporation should take place within 14 µs, a power of 0.41 W is necessary. The dampening solution is heated by heating the printing layer 15. The efficiency for the laser power depends on the absorption coefficient, the heat capacity and the thermal resistance of the printing layer 15. The proportion of the laser power which causes evaporation of dampening solution from the printing layer 15 should be as high as possible, preferably it should be at least 0.6 or greater. The laser power per diode is at least about 0.7 W. 1 W diodes are preferably used.

Since after drying on the ink-transferring surface the printing layer 15 has a high temperature at the dried areas, these areas cannot be moistened immediately because the dampening solution which flows in only at a low rate evaporates immediately upon contact with the heated area of the printing layer 15 . In order that the drying of the dried area before contact with the inking roller 3 is particularly reliably prevented, the inking roller 3 is arranged immediately after the exposure device 20. The dampening solution pressure on the back of the printing layer 15 should also be set such that the dampening solution layer is formed only slowly on the ink-transferring surface. In the example above, if the inking roller 3 is 200 mm behind the exposure device 20, as seen in the direction of rotation of the printing form cylinder 2, the time period from drying to pore closure is 0.06 s. The dampening solution supply on the back of the printing form 12 is set in such a way that no more than 0.5 g dampening solution per m ^{2 of} the ink-transferring surface and rotation are supplied. Since the dampening solution film splits on the inking roller 3 with every revolution and half of it is removed, a constant film layer thickness of 1 μm in front of the inking roller 3 and 0.5 μm behind the inking roller 3 is then established. With increasing imaging time, the dampening solution supply is reduced in accordance with the area coverage already achieved. Starting with water as a dampening solution and a dampening solution layer thickness of 1 μm which is to be evaporated, imaging of the printing form cylinder 2, ie of two printing formes 12, is possible in about one minute. The power requirement of the exposure device 20 is very low due to the very thin dampening solution layer in the process alternative in which dampening solution is previously evaporated to close the pores.

Per printing form cylinder 2, i.e. per exposure device 20, is a control electronics intended to generate constant current pulses, the duration of the exposure time for a pixel corresponds to for each of the 265 diodes. The current strength depends on the used Laser diode between 1 and 4 A. The control electronics also includes its own Bitmap memory with its own memory area assigned to each diode. Also includes the control electronics an addressing system for transferring the bits from the bitmap memory to the diodes. The address for the memory is made up of signals from one Angle of rotation of the printing form cylinder 2 or the blanket cylinder 1 and one Weggebers determined the horizontal displacement of the laser array in which the concerned Diode is arranged, measures or the motor for generating the horizontal movement pretends.

Finally, the control electronics include an interface to a control and buffer unit. In the control and buffer unit, the data from assigned printing form cylinders 2, preferably from such printing form cylinders 2, on the same side the train work, collected. Depending on the transmission and storage capacity, one Control and buffer unit several printing units, each with several printing form cylinders 2 be assigned.

As already described above, the imaging takes place by axial displacement of the Laser arrays along the rotating printing form cylinder 2. The speed of the Horizontal displacement is considerably less than the cylinder speed at the Illustration. If several of the laser arrays are next to each other in the longitudinal direction of the cylinder are arranged, all laser arrays are simultaneously, preferably by the same motor, axially shifted. Each time the pressure cylinder 2 rotates, a axial feed of the exposure device 20, which is slightly smaller than the width Bs of the laser spots 28. Axially adjacent pixels therefore slightly overlap. Thereby the adjacent columns of the printed image are illustrated one after the other without that blank areas remain between the columns. The width of the overlap of neighboring pixels depends on the sharpness of the image of the individual pixel. Blurring in the optical image and heat diffusion in the vicinity of the pixel lead to exposure blur caused by the overlay in the imaging is balanced.

The laser diodes 23 are roughly mechanically adjusted as a row of diodes in the housing 21 attached. Through the array of lenses 25, the light-emitting surfaces 24 of the Laser diodes 23 imaged on the printing form 12. Due to the mechanical rough adjustment of the laser diodes 23 ensures that the geometric deviation of the laser spots 28 a certain maximum deviation on the ink-transferring surface of the printing form 12 of target positions. A fine adjustment is made in the way a software adjustment.

FIG. 7 shows an exposure device that corresponds to the exposure device of FIG. 5 and 6 are completely identical except for the optical imaging device. The Optical imaging device of the exposure device of Figure 7 is for each of the light-emitting surfaces 24 are formed by two plane-convex lenses 25a and 25b. The curved surfaces of the lenses 25a and 25b face each other, so that the plane surfaces of the lenses 25a and 25b are those surfaces through which the laser light from the light emitting surfaces 24 enters and through which it towards the color-transmitting surface of the printing layer 15 out of the optical imaging device exit.

The focal lengths of the lenses 25 and 25a and 25b of the optical imaging devices Figures 5 to 7 are preferably the same for both directions. This is through the narrow strip shape of the light-emitting surfaces 24 allows. In the embodiment FIG. 7 shows the manufacturing costs through the use of the same lenses 25a and 25b kept low. In particular, plan-convex lenses are cheaper than Lenses that need to be ground on both sides. The lenses 25a and 25b can can advantageously be obtained by two plastic lens arrays, as in FIG. 7 shown are arranged to each other in lens holders 29a and 29b.

In FIG. 8, the software adjustment for a number of ones arranged side by side on a line is shown Laser diodes 23 of a laser array shown.

The lines entered in the upper part of FIG. 8 run in the longitudinal direction of the cylinder. Along the top line, the target positions P of the laser spots 28 are together with the actual positions S resulting from the mechanical rough adjustment of the same Laser spots 28 drawn.

The same line is drawn again immediately below. Along this line is the error vector V is entered for each of the laser diodes 23. Each of the error vectors V results as a straight connecting line between the target position P and the measured one Actual position S for each of the laser diodes 23. The error vectors V each become one of the associated target position P outgoing correction vector C of the same length and opposite direction. Only the correction vector is shown in FIG C for the left laser diode 23 of the laser array in FIG. 8. The formation of the Correction vectors C for the other of the laser diodes 23 are made accordingly. As the third Line is entered per laser diode 23, the displacement X by which the laser array shifted in the longitudinal direction of the cylinder when imaging the printing form cylinder 2 becomes. This shift can be gradual after completing one Cylinder rotation take place or, which is preferred, continuously during the total imaging time of the printing form cylinder 2. The displacement X is slight longer than the distance between the actual positions measured in the longitudinal direction of the cylinder P from adjacent laser diodes 23.

Each of the laser diodes 23 is assigned an image area Ac which extends in the circumferential direction of the printing form cylinder 2 corresponding image strips. The lengthways of the printing form cylinder 2 measured length of this assigned image area Ac corresponds to the target distance between two adjacent laser diodes 23. Each of the A data memory in the control electronics is assigned to laser diodes 23. This Memory is larger than the image area Ac to be transferred. It includes the so-called Imaging area A, each in the longitudinal and circumferential direction of the printing form cylinder 2 is greater than the maximum error tolerance for the mechanical rough adjustment Image area Ac. If a laser diode 23 has an exact match of the actual position S. of the laser spot 28 generated by it, the image data of the memory for this Transfer laser diode 23 into the data memory for imaging. This is in Figure 8 for the fourth laser diode 23 from the left. The positioning of your image area Ac in the assigned exposure area A is compared to the outer left laser diode 23 shown in Figure 8. The error vector C of the outer left laser diode 23 points in Longitudinal cylinder direction a maximum permissible resulting from the rough adjustment Deviation on. Accordingly, their image area Ac is on in the longitudinal direction of the cylinder shifted the left edge of the assigned exposure area A. This shift takes place by means of appropriate software addressing of the data store, the latter Laser diode 23 is assigned. The image area Ac, in which lasering is carried out for each laser diode 23 individually in the respectively assigned exposure area A positioned.

The length measured in the cylinder longitudinal direction corresponds to each of the exposure areas A. the displacement X of the longitudinal displacement of the laser array. The cylinder circumferential direction measured width corresponds to the cylinder circumference plus the maximum permissible Deviation due to the mechanical rough adjustment. By using the image areas Ac the software adjustment around the respective correction vectors C by appropriate Shift of the address area within the respectively assigned exposure area A software-shifted, the exact positioning of each of the laser spots 28 on the ink-transfer surface through mechanical rough adjustment and software Obtain fine adjustment precisely.

Reference list

1

Blanket cylinder

2nd

Printing form cylinder

3rd

Ink roller

4th

axial cavity

5

radial channels, bores

6

Jig

7-9

----

10th

Carrier cylinder

11

----

12th

Printing form

13

Printing form carrier

14

Lower class

15

Print layer

16-19

---

20th

Image transmission device

21

casing

22

Fasteners

23

Laser chip

24th

light emitting surface

25th

lens

26

electrical connection

27

Bundle of rays

28

Laser spot

29

Lens holder

30th

Washing facility

B

train

P

Target position

S

Actual position

V

Error vector

C.

Correction vector

X

Displacement

A

Exposure range

Ac

Image area

Claims (20)

Method for imaging a printing form for wet offset printing, in which a printing image is generated on an ink-transferring surface of the printing form (12) by forming ink-accepting and ink-repellent areas,
characterized in that
for illustration a) the ink-transferring surface is wetted with a dampening solution, b) those areas of the moistened surface that are to be ink-accepting are specifically dried and c) a material that accepts printing ink is applied evenly to the ink-transferring surface with the areas that are still dry. Method for imaging a printing form for wet offset printing, in which a printing image is generated on an ink-transferring surface of the printing form (12) by forming ink-accepting and ink-repellent areas,
characterized in that
for illustration a) a flowable material which accepts printing ink is applied evenly to the ink-transferring surface, b) the material is hardened in a targeted manner at the places where the ink is to be trained; c) is removed at the ink-repellent areas using dampening solution. Method according to one of the preceding claims, characterized in that that the material that accepts ink and preferably repels dampening solution, Ink is. The printing form (12) has passage channels (16) for dampening solution through which through the dampening solution from a back of the printing form (12) to the ink-transferring Surface. Method according to the preceding claim, characterized in that a Dampening solution film on the ink transfer surface to a uniform thickness is set in the range from 0.2 to 1 µm. Method according to one of the preceding claims, characterized in that that the material that accepts ink and preferably repels dampening solution, closes the passage channels at the ink-accepting points. Method according to one of the preceding claims, characterized in that that the color-accepting areas to be trained when imaging with laser light be irradiated. Device for imaging a printing form of a rotary printing press for wet offset printing, the device comprising: a) a printing form cylinder (2) with the printing form (12), b) a dampening device (4, 5) for wetting an ink-transferring surface of the printing form (12) with dampening solution and c) an application and image transfer device with which a print image with ink-accepting and dampening agent-accepting locations is generated on the ink-transferring surface by applying a printing ink-accepting material, characterized in that d) the application and image transfer device comprises an application device (3) for a uniform application of the ink-accepting material via the ink transfer surface and an image transfer device (20) and e) the print image is generated by uniform application of the ink-accepting material by means of the application device (3) and targeted irradiation of those areas of the ink-transferring surface by means of the irradiation device (20) which are to be designed to accept the ink. Device according to the preceding claim, characterized in that the application device (3) is formed by an ink roller. Device according to the preceding claim, characterized in that the image transfer device (20) near an ink gap that the printing form cylinder (2) and the ink roller (3) form together, arranged in front of the ink gap is to moisten dampening solution, the ink-accepting places, to evaporate. Apparatus according to claim 9, characterized in that the image transmission device (20) near an ink gap that the printing form cylinder (2) and Form ink roller (3) with each other, is arranged behind the ink gap to print ink, the areas that are to be trained to take on ink are hardened. Device according to one of the preceding claims, characterized in that that the printing form (12) is permeable to moisture in a radial direction. Device according to the preceding claim, characterized in that the printing form (12) forms an outer printing layer (15) with passage channels Has capillary pores that open onto the ink-transferring surface and have an average diameter that is between 0.1 and 5 µm. Device according to one of the two preceding claims, characterized in that that the material of the printing layer (15) has an open porosity of at least 3 and less than 20%. Device according to one of claims 12 to 14, characterized in that Capillary pores forming passage channels on the ink-transferring surface of the Print layer (15) are closed and thereby the print image on the ink-transferring Surface is formed. Device according to one of the preceding claims, characterized in that that the printing form (12) has at least two adjoining one another Material layers with different flow resistances for the Has dampening solution, wherein the at least two layers of material an underlayer (14) and an outer printing layer (15), and that the printing layer (15) forms an ink-transferring surface of the printing form cylinder (2) and one several times higher flow resistance than the underlying layer (14). Device according to the preceding claim, characterized in that the lower layer (14) is formed by a fleece, in particular a metal fiber fleece is or comprises such a fleece. Device according to one of the preceding claims, characterized in that that the printing form (12) has a layer (14) made of moisture-permeable material has, which is applied to a perforated printing form carrier (13). Device according to one of the preceding claims, characterized in that that the printing form (12) has at least one porous material layer (14, 15), on a carrier cylinder (10) or on a carrier cylinder (10) (10) attachable plate or shell-shaped printing form carrier (13) applied is. Device according to one of the eight preceding claims, characterized in that that the directed towards the ink-transferring surface of the printing form (12) Irradiation device (20) with radiator elements (23), in particular Laser diodes is formed.

Images