EP0601259A1 - Method and device to determine the required quantity of printing ink for one image in offset printing - Google Patents

Abstract

To determine the required quantity of printing ink for any given printing order, the overall surface area to be printed of the raster film, on which the printing plate for the relevant printing ink is based, is determined and multiplied by the mass per unit area of the printing ink required to achieve a desired impression and by the desired run, taking into account correction factors for various system-related ink losses and safety factors. The method permits a very precise and early forecast of the required quantity of ink and, in this way, helps to avoid undesirable waste of printing ink. <IMAGE>

Description

The invention relates to a method and a corresponding device for determining the amount of printing ink required for a print job in offset printing.

When processing a print job, the question arises of the color consumption, firstly when calculating the offer and secondly when it comes to the technical preparation for the purchase of color. Despite experience, it is difficult for the printer to estimate how many kilograms of ink are required. In practice, more and more ink is purchased for safety than is really needed, because if the printing machine had to be shut down prematurely just because there was not enough color, this would result in unreasonably high costs.

In the case of the standardized scale colors, an inaccurate estimate is not particularly serious in that too much color purchased can be used again for a later order. However, the problem is more serious with spot colors, since these can often only be used for the given order, and an excess of the quantity purchased is first inventoried and later becomes waste. Considerable amounts of waste paint can accumulate over a year.

Color is toxic and must be disposed of as special waste. Color factories are not interested in taking back old colors, as these can rarely be processed again or mixed again. In addition, paint factories often already have enough of their own waste that they cannot handle in a satisfactory manner. For this reason, not only printers, but also paint manufacturers would be interested in estimating the required amount of ink more precisely beforehand and thus reducing waste.

The invention is now intended to remedy this problem and to create a method and a corresponding device with which the ink consumption can be predetermined at a time which is suitable in practice.

The method according to the invention is characterized by the features of independent claim 1. Further developments and preferred embodiments result from the dependent claims. The device according to the invention is described in independent claim 10.

Fig. 1

eine schematische Darstellung eines Ausführungsbeispiels der erfindungsgemässen Vorrichtung im Vertikalschnitt und

Fig. 2

das Ausführungsbeispiel der Fig.1 in teilweise geschnittener Draufsicht.

The invention is explained in more detail below with reference to the drawing. Show it:

Fig. 1

a schematic representation of an embodiment of the inventive device in vertical section and

Fig. 2

the embodiment of Figure 1 in a partially sectioned plan view.

• Anzahl Druckbogen (Druckauflage).
• Fläche des Bogens, die mit Farbe bedeckt ist.
• Farbmenge, die benötigt wird, um eine gegebene Fläche mit der gewünschten Farbkraft (Farbeindruck) zu bedrucken.
• Farbverlust durch Einrichten und Reinigen der Druckmaschine.

Ink consumption in offset printing depends on a number of factors:

• Number of printed sheets (print run).
• Area of the arch that is covered with paint.
• The amount of ink that is required to print a given area with the desired color strength (color impression).
• Loss of ink due to setting up and cleaning the press.

The print run is usually known. A somewhat larger number is usually expected to take waste into account.

The area of the printed sheet covered with color is not so easy to determine. Until now, visual estimates had to suffice, as there has so far been no practical measuring instrument with which the area to be printed could have been measured.

There are so-called plate readers or plate scanners that can determine the area coverage of the printed image on the printing plate. However, these devices are designed and designed to determine the ink consumption per ink zone on the printing press and thus make it possible to adjust the color profile in advance over the printing width on the printing press. It would certainly be conceivable to use such a conventional plate scanner for a purpose other than that in such a way that the total printed area of a printing form could be determined. However, such a measurement would not be very useful for determining the color consumption, since it takes place too late. In practice, when the printing plates are made, the ink must already be in the printing house.

By contrast, the method according to the invention makes it possible to obtain the required Determine the amount of printing ink much earlier, namely after the production of the original films on the basis of which the printing plates are made. This means that, according to the invention, each individual image for a printing form is measured for each printing ink according to its area coverage at the time of the original film production. Suitable devices for this are explained further below.

The color layer thickness, i.e. The amount of the relevant printing ink per unit area (basis weight) required to achieve a certain color impression on a given substrate (type of paper) is not easy to assess. Today it is not yet possible to measure the ink layer thickness directly on a printed sheet. It is generally known that ink layer thicknesses of approximately one thousandth of a millimeter (1 micron) are used in offset printing for the European scale (various publications, e.g. by FOGRA and UGRA). In practice, however, the ink application on the printing press is not controlled in such a way that a specific ink layer thickness results, but rather that the ink has a predetermined optical color strength. Optical measuring devices are used in almost all printers in the graphics industry. These are densitometers and more recently also spectrophotometers. In order to achieve a given optical color strength, the ink layer thickness must be adjusted depending on the pigment concentration and pigment efficiency of the printing ink. There are natural limits, too thin or too thick ink layer thicknesses can no longer be processed for printing reasons. Unfortunately, it is not enough to know what percentage of pigments in the color are needed to achieve a certain color strength for a given color layer thickness. Depending on whether the pigments are finely or coarsely ground, and depending on how they are wetted by the varnish, they have a different pigment efficiency (coloring power). Because pigments are one of the most expensive components of an ink, a printing ink manufacturer may pigment less to make the ink cheaper. The result of this is that the printer has to apply a thicker color film (and therefore requires more color) in order to obtain the same optical effect.

As I said, it is not possible to measure the ink layer thickness directly on a print. But it is possible to apply a known paint layer thickness. This is a standardized procedure, such as is used in test printing devices such as those from IGT or Prüfbau. For example, a piece of overlay paper is weighed very precisely before and after printing. From the weight difference and the size of the printed area, the ink consumption can be calculated in weight units per area (e.g. grams per m2). In practice, there is only one way to determine the required ink layer thickness: the ink has to be experimentally printed on the paper in different thicknesses, and then the ink layer thickness can be determined or the color consumption at which the correct optical effect is achieved.

Usually, printers are hardly able to carry out such tests themselves, since they rarely have test printing devices. However, such a test is routine work for paint factories. The color factory can therefore indicate to the printer (within certain tolerances) how many m2 of full area with a kilogram of color can be printed on a given paper for a given color strength. In other words, the basis weight of the printing ink required for the desired color strength can be requested from the ink factory.

In the simplest embodiment of the method according to the invention, the size of the total printed area of the halftone film is determined and multiplied by the weight per unit area of the printing ink and the number of sheets to be printed (edition) including subsidy (practically a few percent). The result is the expected ink requirement for the printing ink in question for the print job.

In practice, the actual ink consumption is slightly higher than the value theoretically resulting from the total printed area, the weight per unit area and the number of copies. This is due to the inevitable loss of color that occurs when setting up the press. The resulting additional consumption depends on the operating conditions of the printing press and must be determined experimentally.

Darin bedeuten:

M =

gesuchte Menge Druckfarbe in Gewichtseinheiten (kg),

N =

Anzahl Druckbögen (Auflage) inklusive Zuschuss,

F =

Grösse der insgesamt bedruckten Fläche pro Druckbogen (m2),

D =

Farbmenge, die benötigt wird, um eine Flächeneinheit in der gewünschten Farbstärke zu bedrucken (Flächengewicht, kg/m2),

S =

Sicherheitsfaktor, um Ungenauigkeiten in der Bewertung von F und D zu kompensieren (z.B. etwa 1.2),

E =

Farbverlust, der durch das Einrichten der Druckmaschine entsteht (kg)

Die Bestimmung der Grösse der insgesamt bedruckten Fläche erfolgt gemäss einer bevorzugten Ausführungsform des erfindungsgemässen Verfahrens durch Messung der relativen Flächenbedeckung (0 = Fläche zu 0% bedeckt, 1 = Fläche zu 100% bedeckt) einer Vielzahl von einzelnen Bildelementen des Rasterfilms und durch eine Berechnung der gesamten, durch die ausgemessenen Bildelemente abgedeckten Fläche des Filmes. Für die Bestimmung der Grösse der insgesamt bedruckten Fläche ist z.B. die nachstehend beschriebene und in den Figuren 1 und 2 schematisch dargestellte erfindungsgemässe Vorrichtung geeignet.According to a preferred embodiment of the method according to the invention, the color requirement can be determined according to the following relationship:

$\text{M = N * F * D * S + E}$

Where:

M =

wanted amount of printing ink in weight units (kg),

N =

Number of printed sheets (edition) including subsidy,

F =

Size of the total printed area per printed sheet (m2),

D =

Amount of ink required to print a unit area in the desired color strength (basis weight, kg / m2),

S =

Safety factor to compensate for inaccuracies in the evaluation of F and D (e.g. about 1.2),

E =

Loss of ink caused by setting up the press (kg)

According to a preferred embodiment of the method according to the invention, the size of the total printed area is determined by measuring the relative area coverage (0 = area covered to 0%, 1 = area covered to 100%) of a large number of individual image elements of the raster film and by calculating the total area of the film covered by the measured image elements. The device according to the invention described below and shown schematically in FIGS. 1 and 2 is suitable for determining the size of the total printed area.

The film 1 is transported in the measuring device by a mechanism driven by an electric motor via rollers 2 to 5 line by line in the direction of arrow a, analogous to the paper feed in a printer. The line of the film to be measured is illuminated by an illumination unit 6, which is provided with a window 7 on the film side. The homogeneity of the lighting is only decisive within the measuring spot. A corresponding part of the incident light is absorbed by a partially covered film. The non-absorbed light portion passes through a window 8 into a measuring head 9. The measuring head 9 has light-sensitive electronics 10 inside, consisting of one or more photo receivers, which convert the light portion captured into an electrical signal S. The measuring head can be moved in columns in the direction of arrows b and c by a mechanism driven by an electric motor (Fig. 2). Due to the line-by-line film feed and the column-by-line feed of the measuring head, the entire image is thus divided into a large number of individual image elements. The size of an individual picture element (line width * column width) corresponds to the size of the light-sensitive electronics 10 in the measuring head 9. To determine the relative area coverage, the measurement signals S corresponding to the individual picture elements are compared by a computing unit 11 with previously measured calibration values. The size of the total printed area can be displayed directly on a display unit 12. The spectral sensitivity of the measuring device should be in the range of approx. 400nm to 500nm. There must be no sensitivity above 550nm, so that red originals (e.g. adhesive strips or ulano foils) can also be measured as black.

• 1. Durch Ausmessen aller Bildelemente einer Zeile eines Klarfilmes mit den Material-Eigenschaften des zu messenden Produktionsfilmes werden die Hellpunkt-Eichwerte für alle Bildelemente der Zeile direkt eingemessen.
• 2. Die Messung eines einzigen Bildelementes mit und ohne Klarfilm ist für die Bestimmung des Absorptionsverhaltens des Filmmaterials ausreichend. Die Hellpunkt-Eichwerte für alle weiteren Bildelemente der kompletten Messzeile können von der Recheneinheit 11 durch Verrechnung des Absorptionsverhaltens des Filmmaterials mit den aus einer Messung der Zeile ohne Film gewonnenen Messwerten bestimmt werden.
• 3. Auf eine Eichung mittels Film kann grundsätzlich verzichtet werden, wenn das Absorptionsverhalten des verwendeten klaren Produktionsfilmmaterials vom Anwender aus einer Tabelle ausgewählt werden kann. Die Hellpunkt-Eichwerte S₁₀₀ könnnen von der Recheneinheit 11 durch Ausmessen einer Zeile ohne Film und Verrechnung mit den bekannten Absorptionswerten des ausgewählten Filmmaterials ermittelt werden.

For an expedient linear light measurement, the measurement characteristic of the electronics for a single picture element is a straight line which is defined by two calibration points. The first point is determined by measuring a picture element without any light (dark point calibration S₀). Various methods can be used to determine the second calibration point (bright point calibration S₁₀₀):

• 1. By measuring all picture elements of a line of a clear film with the material properties of the production film to be measured, the bright point calibration values for all picture elements of the line are directly measured.
• 2. The measurement of a single picture element with and without clear film is sufficient for determining the absorption behavior of the film material. The light point calibration values for all further picture elements of the complete measurement line can be determined by the computing unit 11 by offsetting the absorption behavior of the film material with the measurement values obtained from a measurement of the line without film.
• 3. In principle, calibration using film can be dispensed with if the absorption behavior of the clear production film material used can be selected by the user from a table. The bright point calibration values S 1 can be determined by the computing unit 11 by measuring a line without film and offsetting it with the known absorption values of the selected film material.

According to an advantageous embodiment of the device, it should be possible to measure both positive and negative films and to be able to display the corresponding size of the total printed area on the display 12. Switching between positive and negative films takes place via input option 13.

ermittelt. Bei der Messung eines negativen Filmes berechnet sich die relative Flächenbedeckung RFN eines einzelnen Bildelementes nach der folgenden Formel:

${\text{RFN = (S}}_{\text{p}}\text{- S₀)/(S₁₀₀ - S₀)}$

Bei positiven wie negativen Filmen ist die relative Flächenbedeckung des gesamten Filmes gleich dem Durchschnitt der relativen Flächenbedeckungen der einzelnen Bildelemente.When measuring a positive production film, the relative area coverage RFP of a picture element for which the light quantity S _{p was} measured is calculated according to the following formula

${\text{RFP = 1 - (p}}_{\text{p}}\text{- S₀) / (S₁₀₀ - S₀)}$

determined. When measuring a negative film, the relative area coverage RFN of a single picture element is calculated according to the following formula:

${\text{RFN = (S}}_{\text{p}}\text{- S₀) / (S₁₀₀ - S₀)}$

With positive and negative films, the relative area coverage of the entire film is equal to the average of the relative area coverage of the individual picture elements.

The two formulas above for calculating the area coverage only apply to picture elements that are completely covered by the film. In practice, films are also required are measured, which are narrower than the width of a complete measuring line. Border elements that are only partially covered by the film and picture elements that lie outside the film material must not be taken into account when calculating the total area coverage. The built-in computing unit 11 is able to recognize those picture elements that lie outside the film material. For their determination, the formula S₁₀₀ <(S _p * 0.97) (incident light is absorbed to less than 3%) can be used, for example. Film edge elements, which must also not be taken into account for the calculation of the total area coverage, are those picture elements that one-sidedly adjoin the picture elements lying outside the film material.

The size of the total printed area in m2 is simply calculated by multiplying the relative area coverage of the entire film by the size of the actually measured area in m2. The size of the area actually measured by the measuring device can be determined by the built-in computing unit 11. For this purpose, the number of picture elements used for the measurement is multiplied by the known size of a single picture element.

Assembled films with adhesive strips and possibly different layers of clear film are not suitable for measuring, since the light point calibration cannot be exact.

According to a preferred embodiment of the device according to the invention, the measuring device for the area coverage of the film is connected to a computer 14 which has inputs 15 for the sizes or parameters N, D, E and S defined above and controls a display 16 on which the calculated amount of color M is output. The display 12 in the measuring device can of course be omitted in this case. It is understood that the inputs 15 of the computer 14 are arbitrary, e.g. can be realized by adjusting elements or a keyboard. Furthermore, at least some of the parameters can also be stored in the computer, so that they do not have to be re-entered every time.

A commercial scanner can of course also be used to determine the area coverage of the raster film. Suitable scanners are flatbed scanners, drum scanners, scanners based on the fax principle with Selfoc lenses, and scanners based on the plotter or printer principle with line-by-line film feed and column-wise moving measuring head.

Furthermore, the area coverage can also be captured pixel by pixel with a type of television camera will. The light table does not have to meet any special requirements regarding the homogeneity of the light distribution, since the individual picture elements can be treated separately by calculation. The same applies analogously to pixel-by-pixel measurement by means of a large number of photodiodes, each of which defines a pixel and covers the entire surface of the film or at least a section thereof.

The size of the total printed area is determined according to an embodiment of the method according to the invention that is particularly easy to implement in terms of apparatus by measuring the (percentage) area coverage of the raster film and by measuring (if not known, since e.g. standard size) the total area of the film. For the determination of the percentage area coverage, e.g. the device described briefly below.

A conventional light table, available in every print shop or repro station, is used to illuminate the film. A housing is placed on this light table, which either has no floor on the lower side or has a translucent floor (opal plastic). The housing is black on the inside to prevent light reflections from the film surface from falsifying the measurement result (linearity). The top cover of the case has a small hole in the middle. The actual measuring device lies over this hole. The measuring device has a window at its bottom through which the light to be measured coming from the hole enters. The window is covered with a diffuser (e.g. opal glass or plastic) so that light is assessed uniformly from all directions. The inside of the measuring device has light-sensitive electronics, which linearly show the amount of light incident on a display, either digital or analog. The range of the display scale goes from 0 to 100 percent. The resolution of the ad should be 1%. A tenth of a percent display is too precise and only confuses. The spectral sensitivity to light should be in the range of approx. 400nm to 500nm, there must be no sensitivity above 550nm, so that red originals (e.g. adhesive strips or ulano foils) can also be measured as black.

For a suitably linear light measurement, the measurement characteristic of the electronics is a line that is defined by two calibration points. The first point that is easy to find is the one without any light (dark point calibration). Since, according to an advantageous embodiment of the device, it should be possible to measure both positive and negative films, it is desirable for the measuring instrument to display either positive or negative measured values. If there is no light, it means 100% coverage for positive films and 0% for negative films.

At the second calibration point, no light is covered, but all light comes through (bright point calibration). By adjusting the light sensitivity of the measuring instrument, 0% must be displayed for positive films in full light and 100% for negative films. It should be noted that the bright point calibration must be carried out with a clear film in the beam path, because when measuring the production film, the translucent areas are also covered with a clear film. The linearity of the measurement can be checked by measuring an even, calibrated, approx. 50% grid tone. The linearity is not only determined by the electronics, but also by optical factors such as. the color inside the housing and the reflection density of the film to be measured.

In practical use for measuring the percentage area coverage of a production film, it is exchanged for the clear film and the display on the device is read. For safety reasons, the bright point calibration should be checked from time to time.

The maximum size of the measuring field is determined by the size of the housing. Since normally single images or pages are to be measured and not entire printing forms, the measuring field can be relatively small, e.g. 30x40 cm. If a larger film still has to be measured, it must be possible to measure only a section of this film in order to then (seamlessly) add different sections together. In order to make it possible to measure even smaller films, it is desirable to have smaller, exchangeable orifice plates available.

In the case of negative films, it must be noted that the measuring area is smaller than the film to be measured, so that there is no false light at the edge of the film. In the case of positive films, the measuring area must also be smaller than the film so that there is no clear film-free zone at the edge of the measuring area.

The clear area (cm2) in the bright point calibration corresponds to 100% area. Therefore, the absolute area coverage (size of the entire printed area) is simply calculated by multiplying the percentage area coverage by the clear area.

The measurement arrangement described has the advantage that it is very simple and allows fast work. The housing can be improved by a door on the front wall so that the film to be measured can be replaced more easily. In addition, brief work instructions can be attached to the housing. As a rule of thumb, it can be said that the height of the housing must at least correspond to the diagonal of the measuring surface. The higher the housing, the less light is lost at the edges of the measuring surface due to the inclination incident light.

The quality of the light table limits the accuracy of the measuring arrangement. Temporal fluctuations in brightness, e.g. caused by fluctuations in the power grid can be greatly reduced by connecting a voltage stabilizer. It should also be noted that changes in the vicinity of the light table can also cause changes in the bright point. Whether the sun is covered by a cloud or not can have an impact on the calibration if the light table is next to a window. An object that is added or removed from the light table on the free glass surface also influences the light intensity in the measuring field. It may therefore be useful to cover the light table around the measuring housing in a suitable manner. If the illuminated area in the measuring field is illuminated unevenly, then various points on the measuring field are weighted unevenly. This can be checked, for example, by measuring a smaller piece of black film at various points on the measuring surface. If the measured values vary greatly, then a better place on the light table must be found, or a more uniform light table must be used. If this is not possible, a compensation mask could also be created to compensate for these irregularities.

According to an alternative embodiment, the area coverage can also be recorded by means of a light table and a CCD camera (charged coupled devices, charge coupled sensors). A large number of picture elements of a film are captured by a CCD camera mounted on a tripod above a light table and transmitted to a data processing system for further processing. Any section of the entire image captured by the camera can be selected for further processing on the associated monitor. To determine the area coverage, the individual picture elements of the desired image section are offset against calibration data obtained by a previous calibration measurement. Efficient calibration can be achieved, for example, by measuring a checkerboard patterned film, which enables the values for 100% and 0% area coverage to be determined simultaneously. In order to ensure a good match between calibration and measurement, any disturbing, temporally changing external light influences must be excluded by means of a suitable cover. In the prediction of the area coverage, inaccuracies are to be expected, which result from point broadening due to different gridings. To further improve the prediction accuracy, the user should be able to define the raster in lines / mm or a full tone input for partial image areas previously selected on the monitor.

If the films are measured with sufficient accuracy, e.g. In the variant with a light table and CCD camera is guaranteed, the results from the determination of the area coverage can be evaluated zonally and evaluated for presetting the ink guide elements of the printing press.

Of course, it is also possible to integrate the measurement of the area coverage as an additional function in a modern exposure device for raster films and to provide a corresponding data output. The measurement on the film has the advantage over the data output on the exposure device, however, that the area coverage of composite films can also be determined in a simple manner.

As already explained above, paper and color-dependent sizes must be included in the calculation of the required ink quantity. This can basically be done in two different ways.

According to a first variant, the desired color is e.g. selected from a standardized color fan and the amount of ink required to print a specific surface with the selected color and solid density is taken from the information provided by the paint manufacturer. The paper type is already taken into account in the information provided by the paint manufacturer. The ink consumption in kg / print order can be calculated in advance by entering the number of sheets per print job and size per sheet (print sheet).

A somewhat different procedure is also possible using a color formulation system, as is usually used in the production of printing inks. According to this second variant, e.g. the target value (color coordinates) of a color is measured using a spectrophotometer. A formulation system with weighing device, together with the spectrophotometer, enables interactive adjustment of the formulated color to the target value. The basis weight of the calibration stains used for the formulation is known to the formulation system from gravimetric measurements. The recipe can be used to determine the basis weight of the recipe color. By entering the number of printed sheets (number of copies) and the size of the total area per sheet, the ink consumption for the relevant print job can be calculated in advance from the measured area coverage.

Claims (10)

Method for determining the amount of printing ink required for a print job in offset printing, characterized in that a screen film is produced for the printing ink of interest, on the basis of which the printing plate for the printing ink in question is produced, that the size of the total printed area is determined on this raster film, that the basis weight of the printing ink of interest required to achieve a desired color impression on the respective substrate is determined, - And that the required amount of printing ink is determined from this size of the total printed area and the basis weight of the printing ink. A method according to claim 1, characterized in that the desired edition of the print job is also taken into account. A method according to claim 2, characterized in that the loss of printing ink caused by setting up and / or cleaning the printing press is also taken into account. Method according to one of the preceding claims, characterized in that the size of the total printed area is determined from the total area of the raster film and the area coverage. Method according to one of the preceding claims, characterized in that the required amount of printing ink according to the relationship

$\text{M = N * F * D * S + E}$

is determined in which mean: M: amount of printing ink in weight units (kg), N: number of prints (edition) including subsidy, F: size of the total printed area per printed sheet (m2), D: basis weight of the printing ink (kg / m2), S: safety factor in the range from 1.0 to approx. 1.3, to take into account inaccuracies in the determination of F and D, E: Color loss in weight units (kg) caused by setting up the press. Method according to one of the preceding claims, characterized in that the basis weight of the printing ink of interest required to achieve a desired color impression is determined on the basis of test prints with different layer thicknesses of the printing ink. Method according to one of the preceding claims, characterized in that the basis weight of the printing ink of interest required to achieve a desired color impression is determined from the recipe data of the printing ink. Method according to one of the preceding claims, characterized in that the size of the total printed area is determined by integrally determining the area coverage of the raster film. Method according to one of the preceding claims, characterized in that the size of the total printed area is determined by pixel-by-pixel determination of the area coverage of the raster film. Device for determining the amount of printing ink required for a print job in offset printing, characterized by a device for determining the absolute size of the total printed area of a film on which the production of a printing plate for the printing ink in question is based, and by computing means which cooperate with the device Calculate the required amount of the printing ink from the size of the total printed area, the weight per unit area of the printing ink required to achieve a desired color impression on the respective substrate, the number of printing sheets to be printed and, if applicable, various security factors.

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