Color Booster during the job change

Abstract

Method for controlling the amount of ink in a zonal inking unit of a printing press (1) with a control computer, wherein the ink supply is temporarily increased compared to the normal requirement during printing operation, characterized in that color differences between two successive printing jobs are calculated by means of the control computer and the color differences are compensated for by temporarily changing the ink supply between the two printing jobs.

Description

[0001] The present invention relates to a method for controlling the amount of ink in a zonal inking unit of a printing press with a control computer, wherein the supply of ink is temporarily increased compared to the normal requirement during printing operation.

[0002] Such a method for controlling the amount of ink in a printing press is known from German patent application DE 100 56 247 A1. It concerns a method for controlling the amount of ink in different inking zones in the inking unit of a printing press, in which the amount of ink is quickly adjusted in the different inking zones, whereby the adjacent inking zones also reach their stationary ink quantity as quickly as possible.This is achieved by setting time-dependent target ink quantity values ​​for each color zone in the printing press. Each target ink quantity corresponds to a specific ink flow rate supplied by an ink source to that color zone. If the target value for a zone remains constant, a constant ink quantity is maintained in that zone by supplying the ink flow rate corresponding to the target value from the ink source. If the target value for a given zone changes from a first to a second value, the ink quantity in that color zone is adjusted by setting a correction ink flow rate, which is set to the sum of the correction ink flow rate and the second target value for a transition period. This results in a briefly increased ink quantity being supplied to the inking unit when the target ink quantity values ​​are changed during printing press operation.This injection of an increased amount of ink is also known as a "color booster." However, this method is only suitable for accelerating changes in printing settings during a print job, in order to reduce the transition time and thus potentially also waste.

[0003] German patent application DE 41 28 537 A1 discloses a method for setting a continuous printing color profile in an offset printing press with a zonal inking unit. In this method, an inverse color profile is first set in the inking unit, and then this inverse color profile is adjusted to the actual desired color profile. In this context, "inverse color profile" means that a color profile is generated that is either over- or undersized compared to the desired continuous printing color profile. This method serves to quickly achieve the optimal continuous printing state and is used at the start of printing after an interruption of the printing process.

[0004] Patent application DE 197 39 283 A1 discloses a method for achieving the printing state in a rotary printing press, in which, during the inking unit setting, ink zone meters are briefly opened according to the subject to be printed, whereby they are overridden and wherein preferably those ink zones in which very little printing ink is required are overridden with a more pronounced deviation from the final ink zone setting than those ink zones in which a lot of printing ink is required.

[0005] Patent DE 197 27 387 C1 discloses a method for controlling ink supply in printing presses, in which layer thicknesses with predetermined values ​​are set in adjacent metering zones on an inkwell roller according to the ink requirements of the printing form, with no ink supply occurring in the metering zones outside the printing format. It is provided that, in order to generate an ink film on the lifter roller in the area outside the printing format, a non-zero ink layer thickness is set at least temporarily in at least one metering zone on the inkwell roller.

[0006] The object of the present invention is to provide a method for controlling the amount of ink in a zonal inking unit of a printing press with a control computer, which also allows the required amount of ink to be reached more quickly when changing between two print jobs.

[0007] Further methods for controlling color in a printing press are known from patents US 7,515,267 and US 7,884,926 B2.

[0008] This problem is solved according to the invention by claim 1; advantageous embodiments of the invention can be found in the dependent claims and the drawings. In the method according to the invention, the control computer is programmed to first calculate color differences between two successive print jobs based on the print images of the two print jobs and to compensate for these color differences by increasing the amount of ink supplied in two stages between the two print jobs. This means that additional ink required between the two print jobs is supplied more quickly and excess ink is removed more quickly.

[0009] In a first embodiment of the invention, the ink supply is increased at the beginning of the second print job if there is insufficient ink. In this case, more ink is supplied at the start of the second print job than is necessary to complete it. This brief increase in ink supply at the beginning of the second print job thus allows the desired target color of the second print job to be achieved more quickly.

[0010] In a further embodiment of the invention, the ink supply is increased towards the end of the first print job if there is too much ink. In this way, the increased ink consumption towards the end of the first print job, e.g., when the printing press is shut down, reduces excess ink on the remaining substrates, thus achieving a faster reduction of excess ink between the two print jobs.

[0011] The major advantage of the method according to the invention lies in the fact that it is not necessary to remove all the ink from the inking unit between the two print jobs and then rebuild it for the second print job. Furthermore, the invention provides that when very large quantities of ink are removed, the dampening solution supply is briefly switched off by the control computer at the start of the second print job and then switched back on after this period. This temporary shutdown of the dampening solution supply significantly accelerates the ink removal process.

[0012] Furthermore, the control computer is designed to select the appropriate process based on a comparison of the print images from the first and second print jobs. The control computer compares the content of the print images from the two consecutive print jobs and determines whether and in which color zones more or less ink is needed. Depending on the determined ink requirement, the process for reducing excess ink or increasing ink supply is then applied to the relevant color zone. These adjustments can be made automatically, or the printer can first be shown corresponding suggestions on a screen and then accept the settings by confirming them. This significantly simplifies the printer's work, as it does not have to calculate and select the appropriate process itself.

[0013] In a particularly advantageous embodiment of the invention, the control computer, when switching between the first and second print jobs, takes into account the areas that will no longer print in the second print job when the substrate format is smaller than in the first. Sheet-fed printing presses can print in multiple formats. For example, a sheet-fed press with a 105 mm format can also print in 75 mm and 52 mm formats. If printing is performed first in a large format such as 105 mm and then on a 75 mm sheet, there are ink zones in the edge areas of the inking unit and the printing unit that no longer print, so that no ink is applied to these ink zones.This excess ink is compensated for by the control computer in such a way that, during moderate format reductions, the excess is balanced out at the last printing edges via lateral ink distribution and a correspondingly increased ink excess from the "Color Booster." In this way, ink is removed from the non-printing areas and supplied to the printing edges. In this case, the excess ink from the non-printing areas is used to temporarily increase the ink supply to the printing edges. Consequently, less ink needs to be introduced into the inking unit to increase the ink density.

[0014] The present invention is described and explained in more detail below with reference to several figures. These show: Fig. 1 Several adjustment processes of the inking unit during the change of the print job according to the prior art, and on the far right the method improved according to the invention, Fig. 2. the build-up of the ink layer in the inking unit across the inking unit rollers from the first rider roller to the inking roller and Fig. 3 the amount of paint depending on the area coverage.

[0015] In Fig. Figure 1 shows three printing processes, V1, V2, and V3, which can be performed during a print job change in a printing press 1. These three processes are known from the prior art. During a print job change, it is first checked whether a color profile reduction is necessary. If so, the printing plate is changed, and a so-called ink run-in 2 takes place. If no color profile reduction is necessary, the printing plate is also changed, and it is checked whether the inking unit needs to be washed. If washing the inking unit is necessary, a so-called ink run-in 1 is performed. If washing the inking unit is not necessary, printing can proceed directly. According to the invention, it is provided that settings on the printing press 1 resulting from the print job change are converted into corresponding color changes.Based on these color changes, the "Color Booster" is controlled with a briefly increased ink supply. This has the major advantage that the printer doesn't have to worry about the necessary color changes. With the first method, V1, it must be ensured that the color profile degradation occurs before the plate change. Printers often forget to trigger this function. This leads to printing until the end of the sheet stack, leaving no more sheets available for color profile degradation. Variant 2 has the major disadvantage that washing the inking unit is very time-consuming and also incurs costs, as ink is consumed and the washed-off ink must be disposed of. Method 3 has the significant disadvantage of generating a large amount of start-up waste when processing the second print job.

[0016] Fig. Figure 2 shows the basic structure of an ink layer in the inking unit, where it can be seen that the amount of ink consists of a base layer 2 proportional to the printed layer thickness and an area-coverage-dependent ink wedge 3. This ink wedge 3 is thickest near the ductor on the first anilox roller and reduces to the base layer 2 by the time it reaches the last ink-apply roller on the plate cylinder.

[0017] In Fig. Figure 3 shows the relationship between surface coverage (FD) and paint layer thickness. The corresponding amount of paint (FA) is assigned to this paint layer thickness. This means that for surface coverages from 0 to 100%, the amount of paint increases from 1 to approximately 1.25.

[0018] The amount of ink (FA) in the inking unit, as a function of the area coverage (FD) for a constant layer thickness, can be determined either using a simulation program (e.g., FASI) or through printing trials. Furthermore, the amount of ink (FA) in the inking unit is proportional to the printed layer thickness. Based on the area coverage (FD) of the old and new print jobs, the relative amount of ink in the inking unit for the new job is calculated. This relative amount of ink is then converted into a relative color value. Subsequently, at the start of a print run, this relative color value is adjusted using Color Booster and / or Ink Run-In 2 and / or Area Separations.

[0019] One example is: First print job: 80% area coverage FD of one color zone. Second print job: 40% area coverage FD of the same color zone.

[0020] From the table in Fig. The following values ​​can be read from 3: Color quantity 80% FD = 1.2; Color quantity 40% FD = 1.1

[0021] For the second print job, this results in an over-inking of 1.2 / 1.1 = 1.09 when switching between print jobs. Therefore, 9% of the ink must be removed from the ink zone when starting the second print job. This is done using the Color Booster, according to current technology.

[0022] Other variations are possible: Color can be added or, if necessary, removed before printing. Color zones that require more ink during the initial print job can receive this ink before the first print, e.g., via ink feed 2. This means that no color booster is required for these color zones during printing, and these color zones are nevertheless color-stable earlier.

[0023] It is possible to automatically suggest or carry out the procedure.

[0024] The appropriate procedure can be automatically performed by the machine control based on a comparison of the image content of the first and second print jobs, or at least suggested a selection to the printer for confirmation.

[0025] The method according to the invention can also be combined with area reductions. If a large amount of ink needs to be removed during a job change in certain zones, such that the ColorBooster would have to override, for example, more than 100 sheets, the dampening solution supply can be switched off for a few revolutions when starting the second print job in order to significantly accelerate ink removal by means of so-called area reductions. After these area reductions, the dampening system is automatically switched back on by the control computer of printing press 1, and a modified ink feed or ColorBooster is performed. This modified ColorBooster then acts for all ink zones.

[0026] The following example is given: First print job in color zone 1, 80% coverage FD First print job in color zone 2, 8% coverage FD Second print job in the color zone 18% area coverage FD Second print job in color zone 2, 80% coverage FD

[0027] From the table in Fig. 3. is read off: Color quantity 80% FD = 1.2 Color quantity 8% FD = 1.02 When starting the second print job, approximately 18% of the ink must be removed for color zone 1 and approximately 18% of the ink must be added for color zone 2.

[0028] The amount of ink stored in the inking unit is approximately 20 mm, calculated here for simplicity across all zones. 3 / mm. The amount of ink stored is dependent on the area coverage in reality, see above. With each area subtraction, approximately 0.8 mm is removed, to simplify the calculation. 3 / mm of paint. So, for example, if you were to make 3 surface prints, you would have approximately 3 * 0.8 mm. 3 / mm / 20 mm 3 / mm = 12% color removed.

[0029] In this example, this means that for color zone 1, only a short color booster needs to be applied to extract 18% - 12% = 6% of the color. For color zone 2, 18% + 12% = 30% of the color needs to be added, which can be done either via a type of color feed 2, before or after the area deductions, or with a color booster. Adding color is always easier and better than removing color.

[0030] However, the method has its limitations. It becomes problematic with larger format changes, especially when switching from a larger sheet size. Area reductions are also critical with smaller substrate formats. The proposed method must take this into account. Therefore, there is an alternative approach that considers the non-printing areas during format reduction. For moderate format reductions, the effects can be compensated for by lateral rubbing and a suitably combined, increased color boost in the last printing edge color zones.

[0031] An example is also given for this: First print job in 105 format, all 32 color zones have 40% area coverage FD.

[0032] The second print job uses only color zones 3 to 30; that is, color zones 1 and 2, as well as 31 and 32, do not print. Color zones 3 to 30 have 80% ink coverage (FD), while the color zones outside these zones have 0% ink coverage.

[0033] From the table in Fig. 3 is read off: Color quantity 80% FD = 1.2; Color amount 40% FD = 1.1, color amount 0%FD = 1.0

[0034] This means that approximately 10% of the ink must be removed from the non-printing color zones, and approximately 10% must be added to the printing color zones. However, since no ink reduction occurs in the non-printing border color zones, color zones 3 and 4, as well as color zones 29 and 30, can use the ink from the non-printing border color zones. Therefore, no boost (+10% - 10% = 0%) is applied in these color zones 3 and 4, as well as 29 and 30. Reference symbol list 1 printing press 2 Base layer 3 color wedges depending on FD FD Area Coverage FA paint application quantity V1 first variant print job change V2 second variant print job change V3 third variant print job change V4 improved version print job change

Claims

[1] Method for controlling the amount of ink in a zonal inking unit of a printing press (1) with a control computer, wherein the amount of ink supplied is temporarily increased compared to the normal requirement during printing operation, characterized by , that the control computer calculates color differences between two consecutive print jobs and the color differences are adjusted by temporarily changing the amount of ink supplied between the two print jobs. [2] Method according to claim 1, characterized by , that the adjustment of the ink quantity feed is made at the beginning of the second print job if there is too little ink. [3] Method according to claim 1 or 2, characterized by , that the adjustment of the ink quantity feed is made towards the end of the first print job if there is too much ink. [4] Method according to claim 3, characterized by, that when removing very large quantities of ink at the start of the second print job, the dampening solution supply is switched off by the control computer for a short period of time and switched back on after the period of time has elapsed. [5] Method according to any one of the preceding claims, characterized by , that the control computer selects the appropriate procedure based on a comparison of the printed images of the first and second print jobs. [6] Method according to any one of the preceding claims, characterized by , that when switching between the first and second print jobs, the control computer takes into account the areas that will no longer print in the second print job if the substrate format is smaller than in the first print job. [7] Method according to claim 6, characterized by, that the excess ink during format reduction is compensated for by the lateral rubbing of the rubbing rollers in the inking unit of the printing press (1) and an excessive ink delivery to the last printing edge zones. [8] Method according to claim 7, characterized by that the non-printing color zones transfer their excess color to the printing edge zones.

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