EP0272468B1 - Print checking bars - Google Patents

Description

The invention relates to a print control strip for checking and controlling the printing process with individual color fields of different color and structure which are arranged in a row and which are divided according to the color zones of the ink fountain of a printing press.

Print control strips are a well-known means of assessing and controlling the print quality and the preliminary stage of printing in modern printing machines. For this purpose, they have different numbers and arrangements for each individual color to be printed, fields which are to be assessed visually, so-called signal fields and measuring fields. In addition, multicolored fields are usually specified for certain controls. A print control strip usually contains the following fields:

Full tones

- monochrome:

for measuring control of the ink layer thickness,

- two-tone:

for measuring control of the ink acceptance,

- tricolor:

for measuring control of the color acceptance and for visual assessment of the color balance.

Grid of dots

- monochrome:

for measuring control of the dot gain,

- tricolor:

for visual assessment of color balance.

Line grid

- monochrome:

for visual or metrological assessment of sliding and duplicating.

In addition, fields with microlines and microdots can be provided for specific purposes.

Densitometers have been used almost without exception as measuring devices for measuring the individual fields of the pressure control strip, and other color measuring devices have only been used in special cases.

Print control strips of this type, which are used for the control and / or regulation of the coloring, are matched in their division to the ink zone distances of the printing press in question. In each color zone there are single-color full-tone measuring fields for zonal control according to the measured variable "density full-tone DV". The control and / or measuring fields for assessing the other quality criteria are less common on the print control strips.

The "full tone control" is particularly advantageous because only the saturation as a measure of the color layer thickness is included in the measured value DV as a variable. The assignment of the measured value within the printing process is therefore clear. A disadvantage of the pure solid tone control has proven that, despite the matching solid ink density, the print and the print template do not have to match visually, both in the measuring field and in the image. There are a number of reasons for this, e.g. different pigments or dyes, different substrates and the like.

Practical tests have shown that in many cases - but not always - better results can be achieved when using monochrome dot matrix fields for color control, although the variable "density raster DR" also includes variables, that are independent of the coloring itself. Worth mentioning here are the pressure between the plate and blanket cylinders, the printing substrate, the blanket, the dampening solution and the dampening solution guide, the pressure plate, and pushing and duplicating.

Variables derived from solid density DV and screen density DR can also be used for color control. With the help of the Murray-Davies equation, the grid tone value can be determined as a controlled variable from DV and DR:

${\text{F = (1-10}}^{\text{-DR}}{\text{): (1-10}}^{\text{-DV}}\text{).}$

Measuring strips are used in both the regulation according to DR and the regulation according to the halftone tone value F, in which single-color dot matrix fields for all printing inks are present in each color zone. In contrast to the DV control, where the solid tone fields dominate in the measuring strip, the grid fields predominate here. All other fields are less common.

In the so-called "two-zone measurement", in which there are full-tone measurement fields for each color on the measuring strip in every second color zone, the zonal color compensation that takes place due to the lateral rubbing is used. In general, the lateral rub is equal to the width of a color zone plus a small overflow. Practice has confirmed that the coloring can be precisely controlled manually on the basis of a "two-zone measurement".

EP-A 0 255 924 relates to a method and a device for influencing the color appearance of a color area in a printing original and discloses in FIGS. 14 and 15 a print control strip in which a screen composed of the colored basic partial colors in each zone Control field is measurable and in every second or third zone a screen or solid color field is also black is measurable. This document therefore only reveals individual control fields. Since this document has not been previously published, it is of no importance for the question of inventive step.

The further known (DE-A 36 04 222 shows a set of individual color strips to achieve a uniform printing result, which makes it possible to now also print combination measurement fields which result from the overprinting of single color measurement fields. The measurement values obtained from these combination measurement fields are mainly used to control the inking units Here, the individual color fields are lined up with different colors and structures and are sized according to the color zones of the respective ink fountain of the printing press.

The object of the invention is to provide a pressure control strip which allows the optional use of both the full tone control / regulation and the screen tone control / regulation. In addition, the color control / regulation is to be made possible in an optimal manner according to sizes derived from solid full tone and density grid of single and / or multicolored grid fields.

According to the invention, the object is solved by the features of claims 1 to 3. The print control strip has, according to claim 1, zonal alternating single-color solid color fields for each printing color and single-color grid fields for each printing color. The main advantage of a print control strip constructed in this way is that the printer has the choice of using one or the other control strategy depending on the subject. He can e.g. also carry out the setup and adjustment according to standard solid ink densities and regulate the production to constant adjustment sheet screen densities or screen tone values. Conversely, it also makes sense if, for example, a "replacement proof" such as "Cromalin" or "Matchprint" is available as a print template. It is better here to adopt the screen densities or tone values from the control strip of the print template as target values and to adjust them to them and to switch to full-tone density control during production. Solid ink transfer of "replacement proof" would lead to a completely wrong color impression.

Another advantage offered by the two-zone structure of the print control strip for full tone and screen control: Compared to the single-zone structure, only half as many measured values have to be recorded and processed.

The printer is therefore not forced to buy, store and manage multiple types of print control strips, resulting in lower costs. Neither does he have to decide before the printing plate copy which control method should be used in printing.

Changes in the screen density or screen dot size cause much stronger color shifts in the image than changes in the solid density. Due to the same frequency of solid and grid fields A large number of halftone values are determined from immediately adjacent fields, which leads to safer monitoring and control than if DV or DR can only be determined sporadically.

The solution to claim 2 offers the further advantage that the additional multicolored grid fields in the print control strip are optimally suitable for both densitometric and colorimetric measurement. The multicolored grid fields are integrated in the print control strips with the same frequency as the single-color solid and grid fields - i.e. also two-zone.

Claim 3 identifies an embodiment variant with single-color solid-color fields and multi-colored grid fields in a two-zone structure.

: DV in optimaler Weise zu regeln.Furthermore, the control strip can optionally be used for the control / regulation according to densitometric values or values from the color measurement / colorimetry. It therefore contains multi-colored grid fields in every second zone, especially for color measurement / colorimetry. It is therefore also possible, for. B. to colorimetry after multicolored grid fields and the production according to full or screen density, according to screen tone values or according to the relative print contrast K, which according to the formula $\text{K = (DV-DR)}$

: DV to regulate in an optimal way.

The subclaims characterize advantageous embodiments of the invention. It is assumed here that the measuring methods used in printing technology are the more precise the higher the area coverage at the measuring location. Solid tones, i.e. 100% covered areas, are measured most accurately. That is both in the Theory as well as proven in practice and understandable, because the higher the area coverage with color information, the larger the absolute measurement value and the smaller the relative measurement error, since the absolute measurement error is almost constant.

From this point of view, it makes sense for grid measurement to choose a tonal range near the three-quarter tone, since the proportion of covered area is relatively high here. In the case of densitometric screen measurement, which can only be carried out with sufficient accuracy due to the measurement method, only on single-color screen fields, the middle and three-quarter tone is therefore usually monitored. So far, multi-colored grids have only been checked visually. According to claims 2, 3 and 4, multi-colored dot matrix fields are provided which are optimally suited, in particular, for colorimetric measurement.

According to claim 6, a surface coverage composition of the individual colors involved is proposed according to the invention for the metrological control of multicolored grid fields, which, as a sum of all one, two and possibly three and four-color partial areas, result in approximately the same degree of area coverage as the single color grid fields used in the control strip.

An embodiment of the invention is shown schematically in the drawing for some color zones.

The print control strip 1 is provided with individual color fields 2 of different colors and structures which are lined up in a row. Border lines 3, which correspond to the pressure control strips 1, are attached for explanation divide the ink zones of the ink fountain of a printing press. The individual color zones are continuously identified by numbers 4. In the area of the boundary lines 3 between two color zones, the print control strip is alternately provided with single-color solid-color fields 5 for each printing color and with single-color grid fields 6 for each printing color. The monochrome grid fields 6 are advantageously designed as a dot grid. Both the solid tone fields 5 and the grid fields 6 are arranged alternately over the length of the print control strip 1. In addition, every second color zone between the grid fields 6 is provided with multicolored dot grid fields 7 in the region of the boundary lines 3. Here, the total covered area in each dot matrix 7 is almost identical to the covered areas of dot matrix 6 and preferably in the three-quarter tone range, it being immaterial whether a dot grid with 75% halftone tone value of one color or the dot grid 7 shown in the exemplary embodiment as a three-color grid, in which cyan has 40%, magenta 32% and yellow also 32%.

The necessary area coverage of the individual color separations as well as all partial areas resulting from the combined printing can be determined according to the "Neugebauer equation". Is z. If, for example, an average practical tonal value increase in printing of 15% at 40% screen tone value is taken into account, the following screen areas with identical coverage would result in printing.
Single color grids 75% screen value
Two-color grids 2 × 48% screen value
Three-color grids 3 × 35% screen value
The proportion of paper white is approx. 13% in all cases
Multi-color grid fields designed in this way also have the advantage that they do not overestimate color shifts due to changes in the ink acceptance behavior.

Since three-color grid fields are also used advantageously for visual assessment, it is advisable to match the area coverage of the individual colors to gray, which is particularly sensitive to color casts. For example, a print would normally result in a gray with about 13% paper white content for the following halftone values in the film:
Cyan: 40%
Magenta: 32%
Yellow: 32%

Claims (6)

1. Print control strip for controlling the inking in an inking unit of a printing machine, said print control strip comprising individual colour patches of different ink colours and structures which are arranged in a row and are divided according to ink zones, to be regulated, of an ink fountain, said print control strip (1) featuring single-colour solid patches (5) for all ink colours used, one colour patch of each ink colour, at intervals of two ink zones, and single-colour screen patches (6) for all ink colours at intervals of one ink zone and offset with respect thereto.
2. Print control strip for controlling the inking in an inking unit of a printing machine according to Claim 1,
   characterized in
   that multi-colour screen patches (7) are arranged at intervals of two ink zones.
3. Print control strip for controlling the inking in an inking unit of a printing machine, said print control strip comprising individual colour patches of different ink colours and structures which are arranged in a row and are divided according to ink zones, to be regulated, of an ink fountain, said print control strip (1) featuring single-colour solid patches (5) for all ink colours used, one colour patch of each ink colour, at intervals of two ink zones, and multi-colour screen patches (7) at intervals of one ink zone and offset with respect thereto.
4. Print control strip according to Claims 1 to 3,
   characterized in
   that the screen patches (6) are dot screen patches.
5. Print control strip according to Claims 1 to 3,
   characterized in
   that the solid patches (5) and the screen patches (6) are arranged in the area of the boundary lines (3) between two ink zones.
6. Print control strip according to any one of the preceding claims,
   characterized in
   that in each multi-colour screen patch (7) the area covered in total is almost equal to the area coverage of the single-colour screen patches (6) and lies preferably in the threequarter tone area.

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