The invention relates to a method for drying printed material, for example printed paper sheets, paper or material webs or plastic films, labels, etc.
In particular, during multicolor printing, it is difficult to dry the printing material quickly and effectively before it is either printed with the next color or finished through the use of an application of varnish or turned in the printing press for the purpose of printing the reverse side. That is because, due to the relatively short time in which the printing material dwells between the printing units, it is not simple to arrange for the necessary radiated power to act on the printing material without damaging the printed image, for example by overheating.
It has already been proposed to reduce the dryer power in such a way that only the parts of the printing material that are actually covered with ink are irradiated. For example, in European Patent EP 0 355 473 B1, corresponding to U.S. Pat. Nos. 4,991,506 and 5,115,741, a description is given of using an array of UV waveguides for drying so-called UV ink, in which the intensity of the UV radiation emerging from the individual fibers is controlled by a sensor which detects the ink coverage of the image being swept over.
German Published, Non-Prosecuted Patent Application DE 102 34 076 A1, corresponding to U.S. Pat. No. 6,857,368, explains that printing inks provided with IR absorbers can be dried with the aid of a two-dimensional array of IR laser diodes and, in the process, the image content can be taken into account, without it being explained in detail how that is to be done.
It is known from European Patent EP 0 993 378 B1, corresponding to U.S. Pat. No. 6,562,413, in the case of inkjet printing, to dry printed dots by sweeping over the surface of the printing material with laser radiation with the aid of a mirror wheel scanner, with the intention being for the radiation to reach only the points of the printing material that are covered with ink. In that case, too, there is no more specific explanation as to how that is to be done in detail.
Furthermore, German Published, Non-Prosecuted Patent Application DE 10 2004 015 700 A1 discloses using one-dimensional or multi-dimensional arrays of UV laser diodes in order to dry sheets printed with UV ink. There, however, it is not drying as a function of the image content which is desired but the most uniform possible illumination of the printing material with UV radiation.
It is accordingly an object of the invention to provide a method for drying printed material, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known methods of this general type and with which printing materials can be dried quickly and effectively.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for drying printed material. The method comprises driving a one-dimensional or two-dimensional array of radiation sources individually or in groups for drying the printed material. High-resolution image data, describing a printing image or a content of printing forms for individual color separations, is transformed into image data of lower resolution. Position data describing a position of the printed image in a transport direction is obtained from a device for transporting the printing material. Control data for modulation of an intensity of the radiation sources or groups of radiation sources of the array is generated from the image data of lower resolution and position data. Printing material is swept over in a transport direction with time-modulated radiation points each including a plurality of image points of a higher-resolution printed image.
The printing substrate, that is to say the material, for example a paper sheet or a material web, is dried with the aid of a one-dimensional or two-dimensional array of radiation sources. In this case, image data of low resolution already generated in the prepress stage, such as is used for example for presetting the ink key openings in offset presses, is also used to dry the printing material as a function of the image content. Accordingly, no sensors are required in order to first detect the ink coverage in the printed image. Furthermore, the expenditure on open-loop and closed-loop control which is needed in order to control the light sources or groups of light sources in the dryer in accordance with the ink content is within an acceptable order of magnitude, since image data with a reduced resolution is used and it is not necessary for each printed dot or each pixel of the rastered bit map to be addressed individually. The same applies to the optical outlay which is necessary to focus the radiation sources onto the surface of the printing material.
The image data of low resolution does not necessarily have to correspond to the grid spacing of the radiation sources of the array. This is because, expediently, the “coarse” image data picked up in the prepress stage is first converted into data with a further reduced resolution in a second step, with the resolution then being reduced further corresponding to the grid spacing of the radiation sources. The advantage of this two-stage method resides in the fact that data supplied from the prepress stage can be used in a standard way for quite different setting or operating procedures in the printing press, that is to say many times. The radiation sources of the array can, for instance, be the end face of waveguides or semiconductor radiators such as light-emitting or laser diodes. The wavelength of the radiation needed for the drying process is chosen as a function of the type of ink being used: for example UV radiation for reactively curing inks, visible light which is matched to the absorption by the pigments of the printed ink for offset inks, or infrared radiation in the case of inks with which IR absorbers are admixed.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for drying printed material, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
Referring now to the figures of the drawings in detail and first, particularly, to
The size and position of the regions to be exposed is different for the four printing plates, as is illustrated in the example according to
The prepress stage likewise includes a workstation 5 shown in
The CIP3/CIP4 specification recommends the use of the data from these rough images for presetting ink key openings, of which each of four printing units 7a to 7d of a printing press 7 or an inking unit 16a to 16d contained therein (see
According to one exemplary embodiment of the present invention, the data of the coarsely resolved preview images is also used for the purpose of drying the sheets printed in the printing press 7 or, in the case of a web-fed printing press, the printed web as a function of the image, that is to say substantially to apply radiation to the points at which printing ink is actually also located.
Before this is explained in more detail, we refer to the basic sketch illustrated in
The varnishing unit 7e is followed by a drying tower 7f. In this drying tower, the sheet which is transported through is dried in the region of the cylinder 37f by hot air and infrared radiation if, for example, aqueous emulsified varnish is applied to the printed sheets in the varnishing unit 7e.
The dryer 7f is followed by a delivery 10 of the printing press. In the latter, gripper bars 18 circulate through the use of a chain guide 11. These gripper bars 18 pick up the varnished sheets and guide them through under the withdrawable or plug-in dryer units 110a to 110b, where the sheets are once more dried with infrared radiation and/or hot air and, in the process, the applied varnish is solidified. The sheets, which are dried in this way, are subsequently deposited on a sheet stack 12 in the delivery 10.
In the exemplary embodiment described, the printing press 7 is intended to print with so-called UV inks, i.e. inks which do not dry by oxidation under the action of heat or infrared radiation and by absorption into the paper, as is usual in offset printing, but are cured by the irradiation with ultraviolet light. Such inks and offset presses which are specifically equipped for printing with UV inks are known per se. In order to dry the inks, a so-called intermediate deck dryer 17a to 17d, which provides the necessary UV radiation, is disposed in the sheet transport path over the impression cylinders 13a to 13d in each case. There is also such an intermediate deck dryer 17e above the impression cylinder 13e of the varnishing unit 7e. By using this intermediate deck dryer 17e, for example UV spot varnish can be dried, specifically in the same way as in the intermediate deck dryers 17a to 17d, as a function of the printed image, that is to say in this case as a function of the varnish image.
For the case in which water-based varnish is printed in the varnishing unit 7e and, for example is also applied over the whole area of the printed image, the drying tower 7f disposed after the varnishing unit 7e can also be activated. The drying tower 7f contains a hot-air dryer 27a, with which water vapor is driven out of the water-based varnish.
The additional dryer units 110a and 110b can be provided in the region of the chain guide of the delivery 10 for the purpose of further drying of the printed and varnished sheets, as is known per se and generally usual. These can, for example, be infrared dryers or UV dryers, depending on the type of inks and varnishes being printed, in order to dry them still further before the deposition on the delivery stack 12. These dryers 110a and 110b are typically constructed as withdrawable or plug-in units, so that different dryer types can be inserted as required at this point.
The intermediate deck dryers 17a to 17e of this exemplary embodiment of the invention are constructed as described by using
UV diodes in this spectral range are currently offered with outputs in a range between several microwatts and several watts and, for example, can be procured through the Roithner Lasertechnik company in Vienna, Austria. UV diodes have typical housing dimensions of 3 or 5 millimeters in diameter, if they are individual diodes, and can be procured with different beam divergences 120. By using such diodes, it is possible to build up linear arrays from individually addressable UV light sources which, without specific front-end optics, with a working distance of several centimeters, generate spots of light of d=about 3 to 10 millimeters in diameter on a printed sheet 121, so that the sheet 121 running through under such an array can be irradiated with coverage from side to side.
Electronics 123 for driving the light-emitting diodes 119a to 119n are accommodated in the housing 118, as is a control computer 122 assigned to each intermediate deck dryer and illustrated schematically as a block diagram in
It is also possible for a plurality of rows of LEDs 219a to 219n to be disposed in an intermediate deck dryer 218. If a plurality of rows of LEDs, for example 50 rows, are disposed one after another in the transport direction of the printed sheet in such a way that corresponding LEDs lie on a line, the same image points of the printed image can be irradiated repeatedly one after another, in order to increase the output of the dryer. Furthermore, the intensity of the illumination on the sheet to be dried can be evened out through suitably selected coverage of the cones of radiation.
The latter is illustrated more clearly once more by using
Further evening out can be achieved if, as illustrated in
The length of each light bar which is needed to sweep over the auxiliary cell is given by the machine speed, that is to say the speed with which the printed sheet 121 moves past under the intermediate deck dryer 117 or under the UV LED array 119, and the turn-on time of the relevant LEDs. At full machine speed, the sheet moves at about 5 meters/second so that, given a turn-on time of 2 milliseconds, the result is a length of the light bars 129a and 129b of 10 millimeters. If use is made of LEDs which emit a light output of 500 mW, in each cell of the auxiliary grid, as the sheet passes, UV radiation with an energy of 2 diodes×two milliseconds×0.5 watt=2 milliwatt seconds is input, which corresponds to a dose rate of 2 mJ/cm2. This dose rate is already sufficient for the drying of UV inks. A higher radiation dose rate can be achieved by the configuration of a plurality of LED arrays one after another in the sheet transport direction.
What is important for the function of the present invention is the synchronization between the movement of the printed sheet through under the intermediate deck dryers 17a to 17d with the turn-on and turn-off times of the UV LEDs of the array 119 and also the correct assignment of the diodes to the printing image in the axial direction as referred to the cylinders of the printing press. This will be explained in detail below by using
As already mentioned at the beginning during the description of
In the control module 32, this data is prepared specifically for the machine and then transferred to the dryer controllers 122a to 122e in the intermediate deck dryers 17a to 17e. This includes, firstly, the determination of the starting time, that is to say the time at which the first sheet, for example, runs into the printing unit 7c and the drying in the associated intermediate deck dryer 17c begins. This value is calculated from an angular value φ which is supplied by an encoder 34 (see
As an alternative to the computational assignment of the start of the printing image through the machine constants, it is of course likewise possible instead to provide a sensor in each printing unit, through which the start of the printed image on the sheet conveyed through under the respective intermediate deck dryer or the edge of the sheet is detected.
The drying of the printed sheets additionally depends on the layer thickness of the ink with which they are printed. This can be determined, for example, with appropriate measuring instruments by using a sample print. Accordingly, the control module 32 in the machine control system 8 is connected to a photometer 33, through which an ink layer thickness ρ is measured. The corresponding values are used to preset the intensity of the LEDs 119a to 119n in the arrays 119 and/or 219. Furthermore, a possible manual correction is provided for setting the intensity of the LEDs. This can be any desired input tool, for example a potentiometer 39 or else an input, for example through a touchscreen, on a non-illustrated monitor belonging to the machine control system 8.
In addition, it can be expedient to check the LEDs 119a to 119n with regard to the radiation output emitted thereby. This can be done, for example, by an array of photo receivers, which continuously monitors the radiation output in the region of the LED array 119, or by a calibration operation provided regularly, for example before each print job.
Then, as in the simplified illustrated diagram, the signal waveforms calculated in the PPI 6 for the respective printing plates of the individual LEDs of the arrays 119 and/or 219 are transferred to the dryer controllers 122a to 122e of the intermediate deck dryers 17a to 17e, following appropriate modification by the module 32 of the machine control system 8. However, the variation of these signals over time depends on the machine speed v. The same is true of the intensity. This is because, when the machine is running slowly, the printed sheet is located for a longer time in the range of action of the radiation of the individual LEDs of the intermediate deck dryers, so that the intensity of the UV light-emitting diodes can be reduced or the LEDs can be operated in pulsed fashion with longer pause times between the pulses.
Within the drying cycle for a sheet, the turn-on and turn-off times for the individual LEDs are likewise controlled through the machine angle supplied by the encoder 34. To this end, the dryer controllers 122a to 122e are likewise connected to the encoder 34 and in this way are synchronized directly with the machine angle φ without the diversion through the control module 32 in the machine control system 8. This ensures that, even when starting up and running down the machine, the drying of the printed image is carried out with exact register, based on the circumferential register of the impression cylinders.
Furthermore, an automatic offset printing press normally also has an automatic register control system, which acts on the axial position of the printing plate cylinders and accordingly is able to displace the printing image laterally, as well as a diagonal register adjustment. In order to rule out or to compensate for the influence of the register control system 36 on the drying as a function of the printed image, which is important in particular when the image-dependent drying is carried out at high resolution, signals Δx from a register control system 36 can likewise be transferred directly to the dryer controllers 122a to 122e. If then, for example, the register control system displaces the plate cylinder axially by 5 millimeters and the grid spacing of the LEDs is 2.5 millimeters, the stored signal waveforms in the dryer controllers 122a to 122e are displaced “by two LED positions”, that is to say re-assigned, for example by the seventh LED being driven with the signal waveform of the fifth LED and so on.
The preparation of the control data for the individual LEDs in the intermediate deck dryers 17a to 17e in the PPI 6 takes place as follows: normalized signal waveforms are generated over the length of the printing plate from the preview images for the individual color separations, resolved at 50 dpi, for each UV light-emitting diode, for example 119a to 119n. For this purpose, in a manner similar to that illustrated in
In the present case, the same resolution in both coordinate directions is assumed. Since the control signals for the LEDs are generated from the 50 dpi preview image, which corresponds to about 20 image pixels per centimeter, but the grid spacing of the LEDs is greater and, for example, is around 2.5 millimeters, a plurality of pixels, for example 50×50 image points of the preview image, are combined to form one cell and this cell is viewed as a unit.
It is then determined in the PPI 6 whether, for the color separation considered, color components are contained at all in the respective cell of the auxiliary grid or whether raster points are or have been set there at all by the exposer 3. If this is not the case, then the relevant LED(s) remain(s) dark for the corresponding time or machine angle interval. In the other case, when at least one raster point is located in the region of a cell of the auxiliary grid, the corresponding LED is turned on for the relevant time interval or machine angle interval. As opposed to the ink key presetting, however, in the dryer controller it is not a matter of the quantity and size of the raster points exposed on the plate but whether or not a raster point has been placed on the printing plate in the respective cell of the auxiliary grid during the exposure or whether or not a corresponding ink dot has been printed on the printed sheet. This is because, since each ink dot needs UV radiation in order to be dried, the intensity of the LEDs can only be reduced if not only the size of the raster points but also their layer thickness decreases. This is generally not the case. This becomes clear by using the simplified illustration according to
A reduction in the intensity with which the LEDs radiate or in the pulse duration in the case of pulse-operated LEDs is possible, however, if the raster points become so small that the ink layer thickness of the raster points in the print decreases and, in addition, the influence of scattered radiation on the curing of the UV ink increases. The corresponding functional relationship can likewise be taken into account in the PPI 6 by an intensity variation I(y) calculated for the individual LEDs by the PPI 6 as a function of location in the transport direction y of the sheet, together with the image lightness at the relevant point being provided with correction values which were determined previously and stored in a table, for example, and which describe the functional relationship mentioned.
As already explained above, the radiation sources of adjacent LEDs overlap. In this case, it is necessary to take into account the fact that not only is the intensity in the edge regions of the irradiated field firstly lower than at its center but, secondly, the duration of the irradiation on the moving sheet is also shorter because of the shorter secant in the edge region of the illuminated spot 171. It is therefore indicated to choose the auxiliary grid in such a way that the cells of the auxiliary grid are smaller than the spot of light produced by the respective LED, in any case with regard to the dimensions at right angles to the direction of movement.
In the above description, the invention was described by using LED diodes which emit UV light in order to dry sheets printed with UV inks. However, it is also possible and within the scope of the invention, when printing is carried out with offset inks, to use light sources or LEDs which radiate in the visible wavelength range and are matched to the absorption behavior of the pigments of the printed ink. Likewise, it is possible to use arrays of radiation sources which emit infrared radiation if, for example, the wavelength of the infrared radiation is matched to absorber substances which are mixed with the printing ink.
Furthermore, the invention was described by using intermediate deck dryers which are assigned to each printing unit. However, it is likewise possible to provide a dryer following the four printing units, for example, in order to dry the ink printed on in its entirety. In this case, it is not necessary to process the data of the individual color separations individually. For instance, this can be the withdrawable or plug-in dryer units present in the delivery 10 which, in the case in which they are constructed as final UV dryers, are either provided with individually drivable UV sources in order to dry as a function of image content or else, if appropriate, over the entire area.
In a further exemplary embodiment, as an alternative to the method outlined, the procedure is as follows:
In a first step, the prepress interface PPI picks up the data of the already screened color image separation at the resolution of the rastered image of, for example, 2400 dpi from the RIP 2, if appropriate sequentially. The PPI then transforms this high-resolution image data directly into image data with the coarse resolution, which corresponds approximately to the grid spacing of the light-emitting diodes. In this case, the procedure is such that, for each cell of the corresponding coarse auxiliary grid it is determined whether there are raster points in the auxiliary cell and, if appropriate, how large these are in order that, by using the first exemplary embodiment described for the method, an adaptation of the intensity can be carried out. By using this information, the processor of the PPI then calculates the signal waveforms I(y) for the individual LEDs, stores them and transfers them to the machine control system 8, where the signal waveforms are transformed into those dependent on the machine angle φ. The method then proceeds in such a way as described above by using the other exemplary embodiment.
Number | Date | Country | Kind |
---|---|---|---|
10 2007 058 957 | Dec 2007 | DE | national |
This is a continuation application of application Ser. No. 12/329,923, filed Dec. 8, 2008; the application also claims the priority, under 35 U.S.C. §119, of German patent application No. DE 10 2007 058 957.5, filed Dec. 7, 2007; the prior applications are herewith incorporated by reference in their entirety.
Number | Name | Date | Kind |
---|---|---|---|
4989343 | Ericsson | Feb 1991 | A |
5115741 | Rodi | May 1992 | A |
5436710 | Uchiyama | Jul 1995 | A |
6435639 | Nakajima et al. | Aug 2002 | B1 |
6562413 | Morgavi | May 2003 | B1 |
6807906 | DeMoore et al. | Oct 2004 | B1 |
6857368 | Pitz | Feb 2005 | B2 |
7433627 | German et al. | Oct 2008 | B2 |
7672634 | Lofthus et al. | Mar 2010 | B2 |
7766473 | Hoshino | Aug 2010 | B2 |
7895968 | Miura | Mar 2011 | B2 |
7910899 | Platsch | Mar 2011 | B2 |
20040085423 | Bronstein et al. | May 2004 | A1 |
20040206260 | Pitz et al. | Oct 2004 | A1 |
20040218221 | Hirano et al. | Nov 2004 | A1 |
20050235851 | Beier et al. | Oct 2005 | A1 |
20060115306 | Lofthus et al. | Jun 2006 | A1 |
20070199457 | Cyman, Jr. et al. | Aug 2007 | A1 |
Number | Date | Country |
---|---|---|
3901165 | Aug 1990 | DE |
20201859 | Aug 2002 | DE |
10234076 | Apr 2003 | DE |
102004015700 | Nov 2005 | DE |
102004020454 | Nov 2005 | DE |
0349507 | Jan 1990 | EP |
0355473 | Feb 1990 | EP |
0978388 | Feb 2000 | EP |
0993378 | Apr 2000 | EP |
1739504 | Jan 2007 | EP |
1849603 | Oct 2007 | EP |
2764844 | Dec 1998 | FR |
2167748 | Jun 1990 | JP |
4119851 | Apr 1992 | JP |
11334114 | Dec 1999 | JP |
2004080065 | Mar 2004 | JP |
2004209880 | Jul 2004 | JP |
2005313639 | Nov 2005 | JP |
2006150971 | Jun 2006 | JP |
2006272294 | Oct 2006 | JP |
2007008162 | Jan 2007 | JP |
2007038429 | Feb 2007 | JP |
2007504979 | Mar 2007 | JP |
2007111984 | May 2007 | JP |
03028362 | Apr 2003 | WO |
2004056581 | Jul 2004 | WO |
Number | Date | Country | |
---|---|---|---|
20130021420 A1 | Jan 2013 | US |
Number | Date | Country | |
---|---|---|---|
Parent | 12329923 | Dec 2008 | US |
Child | 13630767 | US |