EP1036668B1 - Printing plate, cylinder and method for wet offset printing - Google Patents

Abstract

The printing plate (12) is formed of upper (15) and lower (14) layers of hydrophilic material on a carrier (13). The upper layer top (image carrying) layer is wetted through ducts (5) from inside the plate cylinder (2). The rate at which the wetting agent can flow through the plate is reduced abruptly at the boundary between lower and upper layers. The lower layer can be formed of a mat of stainless steel metal fibres and the upper by plasma spraying

Description

The invention relates to a dampening medium-permeable printing form and a Druckfonnzylinder with a damp-medium-permeable printing plate for a wet offset printing. It further relates to a process for the preparation of a moisture-impermeable printing plate for a wet offset printing. In particular, the invention is used in newspaper offset printing, preferably newspaper offset printing.

In newspaper offset, as a result of the advancing development of computer technology, the precursor area has changed greatly. Operations that were previously performed manually have been replaced by so-called computer-to-technologies. The current state of development has been achieved in the newspaper section with Computer-To-Plate. The advancement is towards Computer-To-Press, i. in the direction of direct imaging in the machine.

A directly imageable printing plate cylinder is known from US-PS 5,293,817. The printing form cylinder has a porous outer shell. The dampening takes place through the interior of the cylinder through the porous outer shell. 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 is between 3 and 100 microns. The pores of the cylinder jacket communicate with each other. Imaging takes place via a thermal transfer or inkjet process by means of an image information transmission device. Alternatively, the use of a heated electrode in pin form is mentioned to apply oleophilic material to the cylinder jacket.

From GB 149 002 a method for duplicating originals made with water-repellent paint on a water-permeable fabric has become known. In this case, a printing form cylinder of a rotary machine is covered with a moisture-sensitive artwork and preferably moistened from the inside, so from the printing forme cylinder ago. For the transfer of liquid, a felt or similar material is provided between the artwork and the apertured printing form cylinder. The printing original produced with wasserabstossender color has from the felt interlayer on the inside of the printing supplied fountain solution and absorbs transferred from outside supplied ink.

The invention has set itself the task of creating a printing plate for a wet offset printing, which allows easy and precise dampening and imaging of their color-transmitting surface.

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

The invention relates to a dampening-permeable printing plate and a method for producing such a printing plate. It is a printing form for wet offset printing, in particular for a wet offset rotary printing press. The printing form has an imageable or imaged surface for transferring printing ink. The surface is referred to in the illustrated as well as in the unimaged state because of its function of the transfer of color hereinafter as a color-transmitting surface.

At least on its ink-transferring surface, the non-imprinted printing form is moisturizing-friendly, preferably hydrophilic. The printing form can, as known printing plates also, for example, be a printing plate or preferably a printing forme shell, which is mounted on a support cylinder, for example by means of a known clamping device. Such inherently stable, imageable or imaged printing forms are as such also an object of the invention. The carrier cylinder forms in this case together with the attached printing form the printing form cylinder. In principle, the printing form can also be a cylinder sleeve. Disadvantage of such a printing forme sleeve, however, would be that the support cylinder could only be rotatably mounted on one side in order to change the printing forme sleeve in a simple manner. Likewise, printing form cylinders are the subject of the invention, which have an imageable or already imaged printing form on a cylindrical surface,
the printing form can not be removed; At least the printing plate can not be removed without destruction in this training.

The printing form is permeable to a dampening solution in a radial direction. In the case of a printing plate, which is mounted on a support cylinder, the directional indication is based on 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 plate. When Carrier cylinder is understood in the context of the invention, that cylinder body of the printing forme cylinder on which the printing plate is mounted, either as a separate printing plate or, as already stated, as an integral part. In both embodiments, the fountain solution, in particular fountain solution, is brought from the back of the printing plate to the ink-transferring surface of the printing plate. Since, due to the radial permeability of the printing plate on the ink-transferring surface passage channels for the fountain solution, the dampening of the printing plate, ie the ink-transferring surface, and thus the ink acceptance or rejection can be effected by a targeted closing of passage channels at the ink-transferring surface. In the area of closed through channels, no dampening solution can reach the ink-transferring surface, so that in the region enclosing the through-channel color is assumed.

Although the ink-transferring surface can in principle be produced by perforation of an initially closed surface, the printing plate preferably has, as a printing layer, an outer material layer which is porous.

The printing form is constructed in layers according to the invention and has an outer printing layer with the imageable or imaged surface and an underlying lower layer. The flowability of the printing form at an interface from the lower layer to the printing layer preferably decreases abruptly by a multiple. Accordingly, the flow resistance increases. Advantageously, these two layers may be made of different materials and thereby also optimally adapted to different functions according to the invention.

Under flowability in the context of the invention, the volume of the dampening solution used is understood, which flows through a layer with an executed thickness based on acting on this layer differential pressure per time and area, wherein the surface of the outer surface of the layer is taken. The flow-through capability is referred to below as the material parameter in the unimaged state of the ink-transferring surface.

Under an abrupt decrease in the context of the invention is not only a sudden, for the practical interests regarded as unsteady change in flowability understood, but also a steady change. In the latter case, the flow-through properties during the transition from the lower layer to the printed layer have a steep gradient. A transition zone from the underlayer to the printing layer in which the inventive change in throughflow takes place is in any case thinner than the print layer. In accordance with the invention, the aim is to achieve as steep a decrease as possible in the flow through from the lower layer into the printing layer.

According to a method of manufacturing such a cylinder, the underlayer is first formed, preferably by a nonwoven fabric of stainless metal fibers. Such a nonwoven advantageously has a high tensile and compressive strength compared to materials of the same porosity. Sintered and rolled to a defined thickness nonwoven webs of stainless metal fibers are particularly suitable. Suitable nonwovens are known from the filter technology.

The print layer is obtained by coating the underlayer, preferably by means of plasma spraying. It is preferably formed as a ceramic layer.

The lower layer has in both the radial direction as well as in the axial and in the circumferential direction by a multiple greater flow through than the immediately adjacent printing layer. Preferably, its flowability is at least one hundred times, more preferably at least a thousand times greater than that of the print layer. The lower layer is sealed at its free edges preferably against dampening agent passage. Preferably, the entire printing forme is sealed at its free edges.

As a result of the layered construction of the printing form according to the invention, the flow resistance or the flowability of the printing form as a whole is determined in a practical approximation exclusively by the printing layer. The printing layer preferably has a uniform material structure and can not last therefore the required printing fineness be made optimally adapted. Their structure or their structure is such that it is traversed by capillary pores, which are very fine and have a high surface density at the ink-transferring surface. At least one such capillary pore opens on the surface per image pixel. At the same time, the porosity of the printing layer is kept low. Preferably, it is less than 20%. It is an open porosity.

The printing form has the further advantage that by means of a single, thin, uniform layer, the printing layer, a particularly well-defined pressure drop through this layer is adjustable. With regard to the dampening solution guide, the underlying lower layer has the task of distributing the dampening solution evenly underneath the printing layer over the surface. In it, the dampening agent level which co-determines the overpressure at the back of the outer printing layer is formed. As a result of the construction according to the invention, a kind of fountain solution lake forms on the rear side of the outer pressure layer. The fountain solution presses so particularly evenly against the print layer, so that set a total of defined pressure conditions and thus a precise dampening solution is possible. Furthermore, in acceleration and deceleration phases of the printing forme cylinder, for example during the raising or lowering of the machine, there is virtually no-delay adaptation of the dampening medium pressure to the respectively required dampening agent feed rates to the surface.

Preferably, the passage channels of the pressure layer, which are preferably the aforementioned Kapillarporen, an average diameter of 0.1 to 5 microns, in particular measured at the mouth points on the ink-transferring surface. The porous printing layer preferably has a center roughness Ra in the range from 0.2 to 5 μm and preferably an average roughness depth Rz in the range from 0.2 to 10 μm at the ink-transferring surface.

The lower layer is penetrated by passage channels, for example connected pores, which have a diameter of 10 .mu.m to 2 mm, preferably 10-50 .mu.m. The diameter is understood to mean the diameter of a circle which has the average cross-sectional area of the passage channels of the respective layer. Will she be through a fleece is formed to characterize the laminar diameter, determined analogously to ASTM F 902, the appropriate size. The laminar diameter is then between 10 and 100 microns.

The thickness of the printing layer in the radial direction is preferably between 50 and 500 .mu.m , and the thickness of the lower layer is preferably between 500 .mu.m and 3 mm.

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

Since in a first alternative method of imaging the dampening solution is preferably evaporated by infrared radiation and it comes in the near infrared when using dampening water as dampening only low absorption of preferably used infrared laser radiation in dampening solution film, heating and evaporation of a fountain solution is indirectly on the heating the printing layer instead. In order to achieve a strong local heating of the print layer, a material with a heat capacity which is less than the heat capacity of the dampening solution is preferably selected as the material for the print layer. Particularly preferably, the heat capacity of the print layer is less than 1 J / g. Furthermore, the pressure layer is formed so that the thermal conductivity of this layer is significantly lower than the thermal conductivity of the dampening solution. Preferably, the thermal conductivity is 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 at least three-layered with a printing plate support which passes dampening solution, the lower layer applied thereto and the printing layer applied to the lower layer. The printing plate support is preferably made of metallic material. It can be designed as a warped flat plate or as a preformed shell, in particular as a rigid cylindrical half shell. Such a multi-layered construction can also have a printing plate permanently attached to the carrier cylinder.

A perforated printing plate support has holes with a diameter preferably in the range of 0.5 to 5 mm or in-surface recesses, which have a distance from one another preferably in the range of 5 to 50 mm in the entire area of the printing form. However, the hole density can be significantly reduced by increasing the area per hole and / or forming a channel structure on the outer surface of the printing plate support.

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

The amount of fountain solution leaving the ink-transferring surface per unit of time is regulated by adjusting the dampening medium pressure, advantageously by adjusting the amount of dampening solution in the printing form cylinder. By increasing the amount of dampening solution at the back of the printing form, the dampening medium pressure is increased due to the centrifugal forces. Further, the fountain solution supply rate to the plate cylinder is increased and decreased in proportion to the printing speed.

The amount of dampening solution leaving the ink-transferring surface per unit of time, ie the flow rate of the printing forme, depends only on the flowability of the outer printing layer in an approximation that is completely sufficient for practice. The pressure difference across the outer pressure layer grows at a constant rotational speed approximately linearly with the fountain solution level, which adjusts to the back of the printing layer. The flowability of the print layer can be adjusted solely by the thickness of the print layer, since the print layer has a substantially constant porosity and capillary pore density everywhere. In this sense homogeneous is also the lower class. Due to the division according to the invention of the function of the uniform distribution of the dampening solution and the adjustment of the flowability of the printing forme, a particularly accurate metering of the amount of dampening agent emerging on the ink-transferring surface can be carried out. The thickness of the dampening solution film on the surface can be precisely, in particular very small, adjusted. At constant cylinder speed, just as much dampening solution is applied to the back of the printing form guided, as to exit at the ink-transferring surface. The equilibrium level of the dampening solution level in the lower layer at the back of the printing layer then adjusts itself as a function of the rotational speed of the printing forme cylinder. The setting at a speed change is also due to the construction of the printing plate according to the invention almost without delay.

The overpressure on the back of the print layer should not exceed 100 mbar. The dampening solution level at the back of the print layer should not exceed the thickness of the underlayer, at least in the equilibrium of inflow and outflow. Accordingly, the thickness of the lower layer and the flowability of the print layer are preferably matched to one another.

In an imaging of the printing form, a printed image is formed by the formation of ink-absorbing and ink-repellent points on the unimaged surface of the printing form. The ink-accepting points of the ink-transferring surface are formed by targeted closure of the opening on the ink-transferring surface passage channels.

The production of the printed image, ie, the imaging is carried out in a first alternative method by the still non-imaged ink-transferring surface is wetted with a dampening agent, those points of the moistened surface, which are to be formed ink accepting, specifically, ie imagewise, dried and then material, the Adopts printing ink and dampening preferably repellent, is applied to the ink-transferring surface with the still dry areas. The material, like ink, is rejected by the dampening solution, ie it is not transferred to the moist areas. Since a Feuchmittelzufuhr preferably takes place evenly and continuously during imaging, the material is preferably applied as quickly as possible after the imagewise drying of the ink-transferring surface, so that the dried areas are not wetted with dampening solution before applying the ink-absorbing material again.

A dampening solution film that wets the ink-transferring surface should be at most 1 μm thick, averaged over the area of an image pixel, to minimize the evaporation energy. Preferably, the thickness is adjusted to a value between 0.2 to 0.5 microns.

Without departing from the invention, the method can be modified so that initially a flowable material is uniformly applied to the ink-transferring surface for imaging, assumes the ink and preferably wipes dampening solution, this material then hardened specifically at the places to be formed ink accepting or hardening brought and at the ink-repellent trainees, where it is still flowable, is removed by dampening.

The two alternative methods have the advantage that first the ink-transferring surface is uniformly wetted or covered, for which once dampening solution and once ink-accepting and dampening agent-repellent material is used, and then the uniformly wetted or covered surface of the printing plate by drying the dampening solution or curing, especially drying, the ink-absorbing / moisture-repellent material is specifically provided with the printed image in which the dried areas or the sites with the hardened material form the ink-accepting sites. An application device with which an ink-absorbing and dampening agent-repellent material is applied directly in accordance with the image is not necessary for carrying out the process according to the invention. By only a uniform material application is made to produce the print image in both process alternatives, the cost of the application device for imaging significantly reduced.

A uniform order within the meaning of the invention is understood to mean any material order for imaging that does not itself already take place in accordance with the image. The application of material preferably takes place uniformly over the entire surface of the printing form or at least in surface strips.

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

A particular advantage of the method in both alternatives is that, for the application of the ink-accepting and preferably dampening-repellent material in the course of the illustration, an ink application device, for example an inking roller, which is present anyway for the current production can be used. The use of such an inking device, in particular an inking roller, also corresponds to a particularly preferred embodiment of the invention. However, it could also be a separate applicator roll or other suitable applicator, such as a spraying, be provided only for imaging or for imaging and for the subsequent application of paint. After all, even in such a training, the material order would not be controlled by the image.

According to the image, in each case only the drying of the dampening solution and / or the curing of the ink-accepting / preferably dampening-repellent material. An image transmission device which is preferably used for this purpose is formed with semiconductor lasers, in particular infrared lasers, preferably laser diodes, particularly preferably an array or a plurality of arrays of infrared laser diodes.

An imagewise, immaterial treatment of a previously uniformly applied to the ink-transferring surface of the printing form material or fountain solution also allows a more precise imaging than is possible by a direct imagewise material application.

The printing form is particularly preferably used in combination with the above-described imaging. However, it is not limited to this, but it can also be used profitably in combination with conventional methods and apparatuses for the imaging of internally-wetted printing plates.

In a further aspect, the invention relates to a device for imaging a printing form in a rotary printing press for wet offset printing. The machine is preferably a web press for the newspaper offset. The apparatus comprises a printing form cylinder with the printing forme, a dampening device for wetting a ink-transferring surface of the printing forme with moistening agent and an application and image transfer device, with the on the ink-transferring surface by applying an ink-accepting and dampening-repellent material a printed image with ink-accepting points and moisturizing receiving points is produced.

The application and image transfer device preferably has a coating means for the uniform application of a flowable material which assumes printing ink and preferably repels dampening solution, and an image transfer device, preferably an exposure device. The printed image is produced by a combination of material application by means of the application means and irradiation of those points of the ink-transferring surface by means of the image transfer device, which are designed to accept ink. The application means is preferably an application agent which transfers the printing ink to the printing form cylinder during ongoing production.

In a large rotary printing press with a plurality of printing forme cylinders, preferably each of these printing forme cylinders is assigned such an order and image transfer device. With increasing machine size, i. Number of Druckfonnzylinder grow with the direct imaging according to the invention, the cost advantages especially if the print productions change often and downtime should be minimized.

A preferred possibility of closure is effected by heat-induced, preferably laser-induced, image-dependent cloning. The wet offset pressure is known to be due to the repulsion of ink by fountain solution at the moistened areas of the printing plate. If not enough dampening solution, it leads to the assumption of color also at the non-image areas. This process is commonly referred to as toning.

In this first method alternative of the imaging, the ink-transferring surface of the printing form is moistened from the inside and then image-dependently dried by means of the image transfer device. In this case, the image areas are dried and immediately dyed. When dyeing, ink is transferred to the dried areas while the wet areas remain colorless. In the dried areas, the paint clogs the passageways, so that in these areas no fountain solution penetrates more to the ink-transferring surface.

In the second method alternative, the printing form is heated depending on the image by means of the image transfer device after dyeing. The paint dries in the heated areas and thus also in the passageways or at the mouths of the through channels. The dried in the passage channels color can not be displaced with subsequent dampening solution, while the flowable color is displaced by the dampening solution. Until the freewheeling of the printing forme the dampening medium pressure can be slightly increased compared to the dampening medium pressure in the production.

The illustration of the printing form, i. the ink dried in the passageways can be removed by a conventional printing form washing device and / or by the internal humidification with a higher than the dampening medium pressure.

As an alternative to the above-mentioned sealing by means of paint, in a sub-variant of the second process alternative, a monomer or mixture of monomers can also be applied to the ink-transferring surface of the printing form, in particular sprayed on. By means of the image transfer device, a polymerization is triggered. The plastic formed closes the passageways, for example by formation of polystyrene from styrene under heat. The closed pores can be made free again by reheating by the polymer decomposes again and is removed by feeding dampening solution. The dampening solution is preferably supplied from the inside when the image is deleted. However, external washing is also possible, in particular supportive.

In an exposure method for imaging the printing form, the printing form and an image transfer device perform a relative movement predetermined in terms of direction and speed, in which the surface of the printing form to be imaged is exposed pixel by pixel in accordance with the image. As with conventional printing forms, the pixels of the print image to be formed are arranged in columns and vertical lines on the ink-transferring surface of the printing form. A pixel column thus runs in the column direction and a pixel row in a vertical row direction. The above-mentioned relative movement takes place either in the column direction or in the row direction. If the printing form is the printing form of a printing form cylinder in a rotary printing press, the column direction is the printing direction and the line direction is the cylinder longitudinal direction. When imaging in the machine, the direction of relative movement to which the latitude and longitude indications of the light emitting surfaces are related is the printing direction. However, it is also conceivable to image a printing form outside a machine in which imaging can also be carried out in the line direction as the relevant direction of the relative movement.

The strip-shaped laser spot can advantageously also be used to set the area coverage and thus also the tone 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 extent can be generated in the direction of the relative movement. In particular, pixels can be generated which have very small areas, which are then not square but strip-shaped. As is known, the number of gray levels that can be displayed results from the grid width and the pixel area. In this case, the grid cell width is equal to the reciprocal of the grid width. The area of the grid cell is calculated by squaring. Dividing the result by the pixel area gives you the maximum number of tonal values that can be displayed. For example, a raster cell has an area of 250 * 250 μm ² for a 40 grid. 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 graduation of the tone levels makes it possible to compensate for nonlinearities occurring in printing, such as tonal gains and decreases, better than is possible with laser spots which do not have the very short extent in the direction of the relative movement. If the printing form is arranged on a printing form cylinder, an angle transmitter for the printing form cylinder or an associated blanket cylinder has a correspondingly higher resolution for this compensation, or intermediate increments with an electronic unit are formed by interpolation.

The image transmission device preferably comprises an array or a plurality of arrays of pulsed or current-pumped semiconductor lasers, in particular pulsed infrared lasers, particularly preferably laser diodes. By means of the semiconductor laser narrow, strip-shaped, preferably rectangular laser spots are generated on the surface to be imaged, each having a measured in the direction of the relative movement laser spot width on the surface to be imaged, which is several times smaller than a measured in the same direction width of an image pixel to imaged surface and also several times smaller than a laser spot width measured transversely to the laser spot width. A pulse duration per laser spot is then several times longer than a period of time in which during the relative movement between the printing plate and the laser array a distance is covered, which corresponds to the laser spot width.

In a preferred embodiment, the imaging in the machine takes place directly on the printing form cylinder. In this case, the relative movement between the printing form and the laser array is effected by a vertical movement by rotation of the printing form cylinder and a horizontal movement perpendicular thereto by displacement of the laser diode array. During the rotation of the printing forme cylinder, the image information is transferred in columns to the printing form. By horizontally shifting the laser array, successive adjacent columns are imaged until the entire image is recorded. The laser spots generated by means of the laser on the ink-transferring surface of the printing form then have a width measured in the vertical direction and a length measured in the horizontal direction. During imaging, the horizontal movement of the laser array is preferably continuous in the case of a rotating printing form cylinder. In this way, optimally short imaging times can be obtained. The resolution of the image transmission device is dependent on the distance by which the laser array is displaced during one cylinder revolution. This distance is preferably between 84 and 28 microns. This corresponds to a preferred resolution of 300 to 900 dpi. The laser spot length is preferably 30 to 90 μm, 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 takes place by axial displacement of the at least one array along the printing forme cylinder rotating in the imaging. The total laser array can be formed by exchangeable modules with, for example, 64 diodes per print zone.

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

An advantage of the image transmission device according to the invention is that a mechanically exact adjustment is not required. Preferably, a software adjustment is made.

The image transmission device preferably comprises one or more arrays of, for example, 256 semiconductor lasers in 4 arrays each having 64 lasers for one print zone.

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

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

The lasers emit preferably in the infrared or visible range, in particular in the wavelength range of 700-1400 nm.

An optical imaging device, preferably with at least one lens per light-emitting surface, is provided for the light-emitting surfaces. Preferably, lenses of the imaging device are arranged in the form of one or more arrays, advantageously as one or more lens arrays of plastic, which can be inexpensively mass-produced and easily assembled. The lasers are mounted in or on a housing in such an orientation with each other that their light emitting surfaces have parallel longitudinal directions. Finally, the image transmission device comprises a control electronics, with which the lasers are controlled so that a laser pulse duration is several times longer than a period of time in which during the relative movement a distance is covered, which corresponds to the width of the light-emitting surface.

A fiber output does not require the image transfer device. This also makes the device inexpensive and increases its efficiency. A laser carrier of the image transfer device is preferably water-cooled.

A control electronics for the image transmission device preferably comprises sufficient storage capacity for two bitmaps, namely a bitmap for a current image and the at least second bitmap for a subsequent image. Furthermore, the drive electronics includes power electronics for each of the lasers. The control electronics are coupled to a position transmitter of the plate cylinder, from which they determine the angular position of the plate cylinder and the position of the array, preferably of each array module, receives to synchronize the laser pulses with the movement of the plate cylinder. For data transfer, the control electronics are coupled to a server PC.

While the current image is being printed, the new image can be loaded into the memory of the control electronics. The new image is thus already available during production for the next production within the control electronics. After imaging the printing form, but at the latest after completion of the current production, the memory of the old image is freed up and can take over the data for the next but one production. The memory of the new image becomes the memory of the current image for the next production, and the memory of the previously current image becomes the memory of the new image. The control electronics is preferably an integral part of the image transmission device directly at the location of the laser array; it is preferably moved.

At the machine level, one or more server computers receive the separated and rasterized image data in the form of bitmaps. Each server is assigned one or more printing units of 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 operation of the control electronics and the division of tasks between server and control electronics can be used universally with advantage and are not bound to the printing form or to the imaging described Although the image transfer device is preferably used with such a printing form and / or for such an imaging.

Preferred embodiments are explained below with reference to drawings.

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.

Show it:

Fig. 1

a cylinder and roller assembly with a plate cylinder according to a first embodiment,

Fig. 2

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

Fig. 3

the printing form cylinder according to Fig. 2,

Fig. 4

the printing form of the printing forme 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 Fig. 5 to 7.

In Fig. 1, a printing substrate B is passed between two blanket cylinders 1 and printed on both sides in the pressure gap formed between the two blanket cylinders 1. The two blanket cylinders 1 are each associated with a printing form cylinder 2 in the manner shown for the left blanket cylinder 1. Likewise, a paint roller 3 is shown for the left blanket cylinder 1. The arrangement of cylinders and rollers is mirror-symmetrical on both sides of the web B. Preferably, the arrangement shown in Fig. 1 is repeated for each of the many blanket cylinders of the printing press.

The exemplary embodiment is a newspaper offset web-fed rotary printing press with rubber-rubber production, for example a WIFAG OF 370. Likewise, however, the machine may also be a machine for a rubber-steel production, for example with one or two central ones Steel cylinders and pressure column forming blanket cylinders per printing unit, for example a WIFAG OF 470 or OF 790.

The ink is transferred from the inking roller 3 to the printing form cylinder 2 and from the printing form cylinder 2 to the blanket cylinder 1, which prints the web B with the image obtained from the printing form cylinder 2 in the printing gap.

The printing form cylinder 2 has a hollow cylindrical support cylinder 10 with a central, axial cavity 4, which is in fluid communication with a dampening solution supply device. The fluid connection is formed by a rotary connection on one or both shaft journals of the plate cylinder 2. The fountain solution is passed through this shaft journal into the cavity 4. The dampening solution is filtered in advance to avoid disturbing deposits within a printing plate 12. The carrier cylinder 10 has through-channels 5 in the radial direction. The passageways 5 are designed as straight, exactly radial bores 5. In the exemplary 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 each other, measured between the centers of the holes.

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

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

In the cavity 4 of the plate cylinder 2 fountain solution is injected. Due to the centrifugal force, the damping solution is guided through the bores 5 of the carrier cylinder 10 and acting as a distributor, perforated printing plate carrier 13 to the back of the lower layer 14. Through the lower layer 14 and the printing layer 15, the fountain solution reaches the ink-transferring surface and causes no ink to be accepted at the wetted areas.

The dampening solution used is water which is provided with the additives customary in offset printing.

The printing form cylinder 2 is associated with an image transfer device 20. The image transmission device 20 comprises infrared laser diodes which are directed onto the surface of the printing form cylinder 2. The image transfer device is arranged so that the printing form cylinder 2 sweeps over the image transfer device 20 during its rotation as short as possible before reaching the point of contact with the inking roller 3.

Further, the printing form cylinder 2 is associated with a washing device 30, which is arranged in the embodiment in the direction of rotation behind the blanket cylinder 1 and in front of the image transfer device 20. By means of the washing device 30, paint 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 plates 12, which are formed independently and with a support cylinder 10 of the plate cylinder 2 by means of a conventional clamping device 6 are releasably attached.

The carrier cylinder 10 substantially corresponds to the carrier cylinder 10 of the first embodiment. However, the central axial feed channel or cavity 4 is provided with a much smaller diameter. Accordingly, the radially branching channels 5 are longer than those of the first embodiment. The radial distribution channels 5 open into axial distribution channels, which are excluded on the outer circumferential surface of the support cylinder 10 in order to equalize the distribution of dampening solution as early as possible.

The arrangement of the plate cylinder 2 of FIG. 2 in a printing machine corresponds to that of the first embodiment, so that with respect to the illustration and all further details and features of the invention, reference is always made to both embodiments.

One of the two printing plates 12 of the second embodiment is shown individually in FIG. The printing form 12 is formed in the manner already described for the first embodiment by a perforated printing plate support 13, a porous lower layer 14 applied thereto and a porous, pressure-layer 15 layered thereon. The printing plate support 13 is formed by a single semicylindrical steel plate with uniform perforation.

The porous lower layer 14 is formed by a steel fiber fleece whose fibers are woven into so-called random fibers. After bonding, the nonwoven was sintered in a vacuum together with a wire mesh and rolled to a defined thickness, namely the layer thickness in the printing form 12. Due to the very high porosity of the steel fiber fleece of preferably more than 60%, an extremely large sum of pore cross sections results compared to the material fraction. In comparison to the particle size spectrum of powders, the diameter range of the fibers is very uniform, so that the pore size distribution is very narrow. In this way, the desired properties of the high flowability and the low pressure drop through the lower layer 14 result. Furthermore, the nonwoven fabric is pore-stable due to the sintering process.

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

Preferred material details and characteristic values for printing plates according to the invention, in particular for the printing plates 12 of the exemplary embodiments, are summarized in the following tables. Although a three-layered structure is preferred, a construction with more than three layers and also a two-layered structure are also the subject of the invention. Particularly preferred characteristic values or characteristic value ranges are indicated in each case in the second columns. The respective layer does not have to correspond to all information at the same time, although this is preferred. <u> TABLE 1: Print Layer 15 </ u> material hydrophilic eg TiO ₂ -Al ₂ O ₃ mixtures as used in the plasma coating thickness 50-500 μm 100-200 μm Kapillarporendurchmesser 0.1 - 5 μm 0.1-3 μm open porosity 3 - 30% <20% March 0.2-10 μm 1 - 5 μm Ra 0.2 - 5 μm through flow 2 - 20 l / (hm ² mbar) material Nonwoven fabric made of stainless metal fibers, sintered with wire mesh and then rolled thickness 0.5 - 3 mm 0.5 - 2 mm Laminardurchmesser 10-100 μm 10 - 60 μm porosity 50 - 80% > 60% through flow 1,000 - 40,000 l / (hm ² mbar) material stainless steel, one-piece or layered steel sheets thickness 1 - 5 mm Hole diameter 0.5 - 5 mm hole spacing 2 - 50 mm 5 - 50 mm through flow ≥ 200 l / (hm ² mbar) 200 - 20,000 1 / (hm ² mbar)

The dampening fluid permeability of the printing plate 12, based on the unimaged state, has a value which is in the range of 2-20 l / (hm ² mbar). she corresponds in an adequate approximation for the practice and the value of the flowability of the print layer 15th

Due to the high, isotropic permeability of the lower layer 14, the homogeneous distribution of the dampening solution in the lower layer 14 and thus at the back of the printing layer 15 is achieved.

The values given above and also in the tables for flow properties are based on dampening solution as dampening solution. However, they apply to other suitable dampening solutions with the same or similar flow characteristics as well. Furthermore, the values given for the throughflow properties are based on the unimprinted state of the printing form.

In order to achieve a flow, the fountain solution must be supplied with a pressure which overcomes the flow resistance of the individual layers, in particular the capillary pressure of the fine-pored pressure layer 15. This pressure is caused by the centrifugal forces acting on the dampening solution during the rotation of the plate cylinder 2. The pressure difference grows approximately linearly with the water level at the back of the printing form, i. set in good practical approximation at the back of the print layer 15.

Since the differential pressure occurs mainly at the pressure layer 15, because the flow resistance is greatest here, there is a tensile load of the lower layer 14. For reasons of strength, this load should be low. From known relationships between centrifugal force, cylinder radius, cylinder circumference, rotational speed and surface speed can be seen that the tensile load of the lower layer at constant surface velocity decreases with increasing radius. Therefore, the invention is particularly advantageous when using large radius cylinders, as is the case, for example, in double-wide newspaper presses. The weight of the printing layer 15 should also not be neglected. Compared to the existing in the lower layer 14 Feuchtmittelsee, for example, 1 mm deep, but the mass of the print layer 15 is because of their smaller thickness, of for example, 100 microns, small. From the same considerations, it will be appreciated that the use of a thick printing layer would be less advantageous. In such a case, either very porous material or a material with large pores would have to be used, which would adversely affect the strength of the print layer and also the print quality. Or it would have a high pressure on the back of a thick print layer are generated, which at constant cylinder speed cylinder with very small radii and concomitant high centrifugal forces or requires a fountain solution under pressure, but this would cause sealing problems in the introduction of dampening solution in the rotating cylinder ,

At a level of 0.1 mm results at a rotational speed of 36,000 revolutions / h and a cylinder radius of 200 mm by the centrifugal forces a dampening medium pressure of about 0.55 mbar at the back of the printing layer 15. The maximum differential pressure across the printing plate 12 should not exceed 100 mbar , Since, at a reduced machine speed, correspondingly less dampening solution must and should be present at the ink-transferring surface, the pressure may decrease as the cylinder speed is reduced, in particular linearly, with the speed. The fountain solution level at the back of the print layer 15 must not exceed the thickness of the underlying layers. It should be at most as high as the thickness of the lower layer 14 in the exemplary three-layer printing form 12. At a fountain 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 degraded by the printing layer 15, should be above the Pressure difference, which is required for a sufficient flow through the print layer 15. The printing layer 15 should accordingly have a material structure which, at least at the maximum differential pressure resulting from the thickness of the underlayer 14, is sufficient to adequately supply the ink-transferring surface with dampening solution so that printing is possible even at low rotational speed.

The following table summarizes calculation examples for the depiction of the dependence of the damping agent pressure on the cylinder speed and the dampening agent level on the rear side of the printing layer 15: Rotationsgeschw. [U / h] Dampening solution level [mm] Hydrostatic. Pressure [mbar] 36,000 1 5:53 36,000 0.5 2.76 36,000 0.1 00:55 20,000 1 1.71 20,000 0.5 0.85 20,000 0.1 00:17 5,000 2 00:21 5,000 1 00:11 5,000 0.5 00:05

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

As the rotational speed 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 rotational speed of 5,000 U / h, a differential pressure of about 0.2 mbar at the back of the printing layer 15. Thus, the centrifugal force outweighs the gravitational force by about 30%. Due to the capillary action of the small pores in the pressure layer 15, it is advantageous to compensate for fluctuations in the dampening agent pressure. Therefore, uniform wetting of the outside of the printing layer 15 is achieved even at low speeds. The mean hydrostatic pressure due to gravity acting on the back of the printing layer 15 is 1 mbar per 10 mm fountain solution level * Porosity of the underlayer 14. At a cylinder speed of about 4500 rpm or less, the gravitational pressure at the back of the print layer 15 becomes greater than the pressure generated by the centrifugal forces. The dampening solution therefore flows downwards and causes an increase in the dampening agent level in the lower region of the lower layer 14. dampening solution is pushed back into the printing plate carrier 13 there. Thus, not only does the gravitational pressure increase, but also the centrifugal force in the lower region of the plate cylinder 2. Therefore, dampening of at least the lower cylinder region should be possible even at low speeds.

Due to the above-described relationships, the image transfer device 20 is preferably arranged facing the lower region of the printing form cylinder 2. As a result, a precise imaging of the printing plate 12 into the lower speed range of the cylinder is possible. A lower limit for the cylinder speed in the imaging is in the newspaper offset with two printing plates 12 per plate cylinder 2 at about 3,000 U / h.

If one considers the centrifugal forces which occur at 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. Further, a force acts on the bonded or bonded joint between the backsheet 14 and the printing plate support 13. A lesser force acts on the bonding surface between the print layer 15 and the backsheet 14. In a printing form cylinder 2 having a radius of 200 mm, at a rotational speed of 36,000 U / h and a printing plate 12 with a surface of 400 mm * 600 mm results per printing plate 12: Dimensions centrifugal Printing plate carrier 13: 5 mm thick half shell made of steel 9.6 kg 7.6 kN Sub-layer 14: 2 mm fleece, 70% porosity 1.2 kg 947 N Feuchtmittelsee in the lower layer 14: 170 g 134 N 1 mm deep Print layer 15: 100 μm thick, ceramic 50 g 40 N

In this calculation example results in a total force of about 8.7 kN which must be absorbed by the holders of the printing plate 12. On the glued or bonded connection between the printing plate support 13 and the lower layer 14 acts a force of 1.121 N. This corresponds to a tensile load of 5 mN / mm ² . The fibers of the lower layer 14 are loaded at the connection to the print layer 15 with about 1 mN / mm ² . This corresponds to a pressure of 10 mbar. Larger pressures occur with increasing depth of the dampening lake or with faster rotation.

In a first method alternative of the imaging, the image transfer device 20 evaporates the fountain solution on the surface. For imaging of a still "virgin" printing form, the wetting agent wetting the surfaces is evaporated by means of the image transfer device 20 in accordance with the image to be transferred to the blanket cylinder 1. Before a point from which surface moistening agent has just evaporated by means of the image transfer device 20 is rewetted due to dampening agent, the dried point passes the inking roller 3 and takes on color. A pore, which opens into the surface area which has just been dried, is closed by the ink assumed in this area, so that no dampening solution reaches the now printing mouth area.

Instead of evaporating dampening solution, the image transfer device 20 can also be used to selectively dry the ink already applied to the inking roller 3 on the ink-transferring surface of the printing forme cylinder 2 in order to close the pores of the printing layer 15 below the dried inking locations in this way , In this process alternative 3 color is evenly applied to the still-dry surface of the printing form cylinder 2 by means of the inking roller. The dampening solution supply to Druckfomrzylinder 2 is preferably taken only when the color has been applied evenly. After the uniform Application of the color, the still flowable color is dried at the image locations of the ink-transferring surface by means of the image transfer device 20. In the picture places here a pore closure by dried paint takes place. The image areas of the ink-transferring surface thus do not run free from the inside during the onset or progressing dampening. As moisture progresses, however, the printing plate 12 is released at the non-image areas.

In both process alternatives - the induced cloning and the color drying - the same arrangement shown in the figures can be used. In the second alternative alternative, the drying of the printing ink, an arrangement of the image transfer device downstream of the inking roller can also be advantageous.

By washing off the ink layer by means of the washing device 30, the imaging can be deleted in both process alternatives.

With the same image transfer device 20, it is also possible to polymerize a sprayed on the ink-transferring surface of the printing form cylinder 2 monomer and thereby to close the pores on the ink-transferring surface. By reheating after completion of print production by the same image transfer device 20 and discharging the polymer decomposed by the heating with the dampening solution, the image can be erased again. The monomer may already be applied to the ink-transferring surface of the printing form. Preferably, however, an application device, in particular spraying device for spraying the monomer, is arranged on site at the installation location of the printing forme cylinder 2, whereby in particular also in this variant the second process alternative can be repeatedly imaged without having to remove the printing forme 12 or the forme cylinder 2.

5 shows an exposure device of the image transfer device 20 in a cross section. Fig. 6 shows the exposure device in a longitudinal section. Representative of the entire image transmission device, the exposure device is also designated by the reference numeral 20.

The exposure device 20 is formed by linear arrayed juxtaposed infrared laser diodes, which are each secured in a housing 21 with a fastening means 22. Each of the laser diodes is formed by a laser chip 23 having a light emitting surface 24. Opposing the light emitting surfaces 24, the housing 21 is provided with an overlapping row of holes. In the overlapping holes of the row of holes, optical lenses 25 are arranged. Each laser chip 23 has an electrical connection 26 to a control electronics.

As can be seen in FIG. 5, a beam bundle 27 emitted from the light-emitting surface 24 of one of the laser chips 23 is focused by the opposing lens 25 onto the ink-transferring surface of the printing plate 12 of the printing plate cylinder 2 so that it impinges there as a narrow rectangular laser spot 28. The light-emitting surface 24 corresponds in shape to the laser spot 28 generated by it. Preferably, it also has the same size. However, enlargement or reduction to some extent may be beneficial in practice.

To the left of the exposure device 20, a single pixel of the print image to be generated is greatly enlarged. Also shown is the laser spot 28 in the print image pixel. The length Ls of the laser spot 28 measured in the cylinder longitudinal direction corresponds to the length of the individual print image pixel measured in the same direction. The width Bs of the laser spot 28 measured in the printing direction is several times smaller than the width of the print image pixel measured in the same direction. In the embodiment, the print image pixel is square with a length and width of 50 microns. The laser spot length Ls is also 50 μm. The laser spot width Bs, on the other hand, is 3 μm. The exposure time or pulse duration of the pulsed laser diodes 24 is correspondingly long for the exposure of the print image pixel. The duty cycle for the exposure of a square pixel having an edge length which corresponds to the laser spot length Ls results from the quotient of the laser spot length Ls and the surface speed of the printing form 12th

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

The imaging takes place at a speed of the plate cylinder 2 of preferably about 10,000 U / h, wherein each of the arrays is continuously displaced in its side region during cylinder rotation in the cylinder longitudinal direction. A stepwise shift by one pixel column after each full revolution would also be possible, but more time consuming. The path by which the laser array, in the case of several laser arrays all of these arrays, is moved horizontally per cylinder revolution, corresponds to the reciprocal of the image resolution. At an image resolution of, for example, 500 dpi, the laser array is displaced by 51 μm per cylinder revolution transversely to the printing direction. The laser spot length Ls must not be smaller than the resolution-related feed of the laser array in order to expose solid areas. The maximum resolution is given by a rotary encoder and the circumference of the plate cylinder 2. The rotary encoder is an incremental encoder, which is arranged either on Druckfomrzylinder 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 plate cylinder of 1.257 mm results in a resolution of 798 dpi. The laser spot 28 to be used for imaging must have a length Ls of at least 32 μm for this resolution.

The required laser power for evaporation of the fountain solution layer on the ink-transferring surface is dependent on the layer thickness, the surface speed of the printing forme cylinder 2 and the geometry of the laser spot 28. At a fountain solution thickness of 1 .mu.m and a surface speed of 3.5 m / s (radius 200 mm, rotation with 10,000 U / h) and a laser spot 28 with a length Ls of 50 .mu.m and a width Bs 3 .mu.m, neglecting the laser array 28 in neglecting the displacement of the laser array in the cylinder longitudinal direction within about 14 microseconds an area of 50 * 50 microns ² . On such a surface is with dampening water as dampening solution a water mass of 2.5 * 10 ^-12 kg. To evaporate water, an energy of 2.3 * 10 ⁶ J / kg is needed, ie 5.8 * 10 ^-6 J per pixel. If the evaporation takes place in a time of 14 μs, a power of 0.41 W is necessary. The warming the dampening solution takes place in that the printing layer 15 is heated. 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 laser power that 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. Preferably, 1 W diodes are used.

Since, after drying on the ink-transferring surface, the printing layer 15 has a high temperature at the dried areas, moistening of these locations can not take place immediately because the dampening solution flowing in at a low rate evaporates immediately upon contact with the heated location of the printing layer 15 , So that a dampening 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. Also, the dampening medium pressure should be adjusted at the back of the printing layer 15 so that the fountain solution layer is formed only slowly at the ink-transferring surface. If in the above example, the inking roller 3 seen in the direction of rotation of the printing form cylinder 2 200 mm behind the exposure device 20, the time from drying to pore closure is 0.06 s. The dampening solution supply at the back of the printing plate 12 is adjusted so that no more than 0.5 g of dampening solution per m ^{2 of} the ink-transferring surface and rotation are supplied. Since the dampening solution film splits at each revolution of the inking roller 3 and is discharged to half, then sets a constant film thickness of 1 .mu.m before the inking roller 3 and 0.5 .mu.m behind the inking roller 3 a. With increasing imaging time, the dampening solution supply is reduced according to the already achieved area coverage. Starting from water as a dampening solution and a dampening layer thickness of 1 .mu.m, which is to be evaporated, an imaging of the printing forme cylinder 2, ie of two printing plates 12, in about one minute is possible. The power requirement of the exposure device 20 is very low in the process alternative, in which dampening solution is vaporized beforehand to close the pores, because of the very thin dampening layer.

Per printing form cylinder 2, i. per exposure device 20, a drive electronics is provided for generating constant current pulses whose duration corresponds to the exposure time for one pixel for each of the 265 diodes. The current intensity is between 1 and 4 A, depending on the laser diode used. The control electronics also have their own bitmap memory with their own memory area allocated to each diode. Furthermore, the control electronics comprises an addressing system for transmitting the bits from the bitmap memory to the diodes. The address for the memory is determined from signals from a rotary encoder of the plate cylinder 2 or the blanket cylinder 1 and a displacement sensor, which measures the horizontal displacement of the laser array in which the diode in question is arranged or the motor for generating the horizontal movement.

Finally, the control electronics comprises an interface to a control and buffer unit. In the control and buffer unit, the data are collected from associated printing form cylinders 2, preferably from such printing form cylinders 2 operating on the same side of the web. Depending on the transmission and storage capacity, a plurality of printing units with a plurality of printing forme cylinders 2 can be assigned to one control and buffer unit.

The imaging takes place as already described above by axial displacement of the laser array along the rotating printing form cylinder 2. The speed of the horizontal displacement is considerably lower than the cylinder speed in the imaging. If several of the laser arrays are arranged next to one another in the cylinder longitudinal direction, all the laser arrays are displaced axially at the same time, preferably by the same motor. For each revolution of the printing cylinder 2, an axial feed of the exposure device 20 takes place, which is slightly smaller than the width Bs of the laser spots 28. Axially adjacent pixels are therefore superimposed slightly. As a result, the adjacent columns of the printed image are successively imaged without leaving any unimported areas between the columns. The width of the overlap of adjacent pixels depends on the sharpness of the image of the individual pixel. Blurring in the optical image and heat diffusion around the pixel lead to an exposure blur, which is compensated by the overlay in the imaging.

The laser diodes 23 are mechanically grobjusted fixed as a diode array in the housing 21. Through the array of lenses 25, the light-emitting surfaces 24 of the laser diodes 23 are imaged onto the printing plate 12. The mechanical coarse adjustment of the laser diodes 23 ensures that the geometric deviation of the laser spots 28 on the ink-transferring surface of the printing form 12 does not exceed a certain maximum deviation from nominal positions. A fine adjustment takes place by means of a software adjustment.

FIG. 7 shows an exposure device which is completely identical to the exposure device of FIGS. 5 and 6, with the exception of the optical imaging device. The optical imaging device of the exposure device of Figure 7 is formed for each of the light-emitting surfaces 24 by two plano-convex lenses 25a and 25b. The domed surfaces of the lenses 25a and 25b face each other so that the flat surfaces of the lenses 25a and 25b are the areas through which the laser light enters from the light emitting surfaces 24 and toward the ink transferring surface of the ink layer 15 out of the optical imaging device emerges.

The focal lengths of the lenses 25 and 25a and 25b of the optical imaging devices of FIGS. 5 to 7 are preferably the same for both directions. This is made possible by the narrow strip shape of the light-emitting surfaces 24. In the embodiment of Figure 7, the manufacturing costs are kept low by the use of the same lenses 25a and 25b. In particular, plano-convex lenses are less expensive than lenses that must be ground on both sides. The lenses 25a and 25b may advantageously be obtained by two plastic lens arrays arranged in lens holders 29a and 29b as shown in FIG.

FIG. 8 shows the software adjustment for a plurality of laser diodes 23 of a laser array arranged next to one another on a line.

The registered lines in the upper part of Figure 8 extend in the cylinder longitudinal direction. Along the uppermost line, the desired positions P of the laser spots 28 are drawn together with the actual positions S of the same laser spots 28 that result after the mechanical coarse adjustment.

Immediately below, the same line is drawn again. Along this line, the error vector V is registered for each of the laser diodes 23. Each of the error vectors V results as a straight connecting line between the setpoint position P and the measured actual position S for each of the laser diodes 23. From the error vectors V is formed in each case one of the associated desired position P outgoing correction vector C of the same length and opposite direction. In FIG. 8, only the correction vector C for the left-hand laser diode 23 of the laser array shown in FIG. 8 is plotted. The formation of the correction vectors C for the other of the laser diodes 23 takes place accordingly. As a third polyline, the displacement path X per laser diode 23 is entered, by which the laser array in the imaging of the printing form cylinder 2 in the cylinder longitudinal direction is shifted in total. This shift can be carried out stepwise in each case after completion of a cylinder revolution or, as is preferred, continuously during the entire imaging time of the plate cylinder 2. The displacement X is slightly longer than the distance measured in the cylinder longitudinal direction between the actual positions P of adjacent laser diodes 23.

Each of the laser diodes 23 is associated with an image area Ac which corresponds to an image strip extending in the circumferential direction of the printing form cylinder 2. The length of this associated image area Ac measured in the longitudinal direction of the printing form cylinder 2 corresponds to the nominal distance between two adjacent laser diodes 23. Each of the laser diodes 23 is assigned a data memory in the control electronics. This memory is larger than the image area Ac to be transmitted. It comprises the so-called imaging area A, which is greater than the image area Ac in the longitudinal and circumferential direction of the printing form cylinder 2 by the maximum error tolerance for the mechanical coarse adjustment. 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 laser diode 23 is transferred to the data memory for the imaging. This is in FIG. 8 for the fourth laser diode 23 from the left of the case. The positioning of its image area Ac in the associated exposure area A is shown in FIG. 8 in comparison with the left-hand laser diode 23. The error vector C of the outer left laser diode 23 has, in the cylinder longitudinal direction, a maximum allowable deviation resulting from the coarse adjustment. Accordingly, its image area Ac is shifted in the cylinder longitudinal direction to the left edge of the assigned exposure area A. This shift takes place by appropriate software addressing of the data memory, which is assigned to this laser diode 23. As a result of this software adjustment, the image area Ac, in which the laser is being lasered, is positioned individually for each laser diode 23 in the respective associated exposure area A.

The length of each of the exposure areas A measured in the cylinder longitudinal direction corresponds to the displacement path X of the longitudinal displacement of the laser array. The width measured in the cylinder circumferential direction corresponds to the cylinder circumference plus the maximum permissible deviation due to the mechanical coarse adjustment. By the image areas Ac are software-shifted by the software adjustment to the respective correction vectors C by corresponding displacement of the address area within the respective associated exposure area A, the exact positioning of each of the laser spot 28 on the color-transmitting surface is obtained precisely by mechanical coarse adjustment and software fine adjustment.

LIST OF REFERENCE NUMBERS

1

Blanket cylinder

2

Plate cylinder

3

ink roller

4

axial cavity

5

radial channels, bores

6

jig

7 - 9

----

10

support cylinder

11

----

12

printing form

13

Printing plate carrier

14

underclass

15

print layer

16-19

---

20

Image transfer means

21

casing

22

fastener

23

laser chip

24

light-emitting surface

25

lens

26

electrical connection

27

ray beam

28

laser spot

29

lens holder

30

wash

B

train

P

target position

S

Actual position

V

error vector

C

correction vector

X

displacement

A

exposure range

Ac

image area

Claims (12)

1. A multiple-layer printing forme for a forme cylinder for wet offset printing, the printing forme (12) having an ink-transferring surface which is imaged or capable of being imaged, and through-ducts which open onto the ink-transferring surface for a dampening agent, characterized in that an underlayer (14) permeable to dampening agent and consisting of a first material is applied to a printing-forme carrier, and a porous printing layer (15) of a second, different material is applied to the underlayer by means of coating.
2. A printing forme according to Claim 1, characterized in that the printing forme (12) has an outer printing layer (15) with the ink-transferring surface and an underlayer (14) situated under it in a contiguous manner, and the permeability of the printing forme (12) abruptly decreases from the underlayer (14) into the printing layer (15), the permeability of the underlayer (14) being several times greater than the permeability of the printing layer (15).
3. A printing forme according to the preceding Claim, characterized in that the permeability of the underlayer (14) is greater than the permeability of the printing layer (15) by at least a hundred times, preferably by at least a thousand times.
4. A printing forme according to any one of the preceding Claims, characterized in that the printing forme has an outer printing layer (15) with the ink-transferring surface and an underlayer (14) situated under it in a contiguous manner, the printing layer (15) having an open porosity in which the through-ducts are formed by capillary pores, and the underlayer (14) has a material structure such that the dampening agent in the underlayer (14) is distributed uniformly on a rear side of the printing layer (15).
5. A printing forme according to the preceding Claim, characterized in that the porosity of the printing layer (15) amounts to from 3 to 30%, and the capillary pores of the printing layer (15) have an average diameter which amounts to between 0-1 to [sic] 5 µm.
6. A printing forme according to any one of the preceding Claims, characterized in that the printing forme (12) has an underlayer (14) which is formed by a fleece, in particular a metal-fibre fleece, or comprises such a fleece.
7. A printing forme according to any one of the preceding Claims, characterized in that the underlayer (14) has a porosity which amounts to between 50 and 80%, with through-ducts with a laminar diameter which, determined in a manner similar to ASTM F 902, amounts to between 10 and 100 µm.
8. A printing forme according to any one of the preceding Claims, characterized in that the printing forme (12) has a coated printing-forme carrier (13) which is fastened or capable of being fastened to the forme cylinder (2) and which is permeable by dampening agent.
9. A forme cylinder for a rotary printing press for wet offset printing, which has a printing forme (12) having an ink-transferring surface which is imaged or capable of being imaged, and through-ducts which open onto the ink-transferring surface for a dampening agent, and a device (4, 5) by means of which the dampening agent is capable of being supplied to the printing forme (12), characterized in that the printing forme (12) is constructed in accordance with any one of the preceding Claims.
10. A method of producing a printing forme for wet offset printing, the printing forme (12) having a porous printing layer (15) with an ink-transferring surface and through-ducts which open onto the ink-transferring surface for a dampening agent, characterized in that an underlayer (14) permeable to dampening agent and consisting of a first material is applied to a printing-forme carrier (13), and the porous printing layer (15) of a second, different material is applied to the underlayer (14) by means of plasma spraying.
11. A method according to the preceding Claim, characterized in that fleece material is used for the underlayer (14).
12. A method according to one of the two preceding Claims, characterized in that ceramic material is used for the printing layer (15).

Images