Ink supply device automatically presets possibilities and limitations (2)

There is a phenomenon in printing that the dot size on the substrate is larger than the size on the printing plate. This phenomenon is called dot gain, which can be clearly shown by the printing characteristic curve in Figure 3.

With known print characteristic curves, dot gain can be taken into account if the test equipment not only does integration measurements. However, it is not yet possible to distinguish between the half of the actual printed area, the half of the non-graphical composition, and the halftone composition. The system considers 50% flat screen as 50% area coverage, but contrary to the first assumption - 50/50 field/non-graphical text, the situation does not consider dot gain, resulting in errors.

Error Sources From Digital Database Values

There are many ways to generate preset data in modern times, but it is not entirely free of errors. When the plate scanner is not used, measurement and plate surface errors are no longer an element, but there are still errors. The image carrier is still required to use CtFilm. The exposure system in the film machine is also subject to errors that may occur due to aging. limit. Therefore, the difference between the database and the post-exposure color separation sheet, and the difference between the exposure color separation sheet and the printing plate prepared using this color separation sheet, are generated. Although the CtPlate system cancels the intermediate media step, it is still affected by the above errors in the platemaking process and the increase in the number of printed pages. The enlargement of dots on the printed sheet can only occur when the data distribution is sufficiently detailed and can distinguish the dot area and the solid area. Using CIP3 can in principle get the available and more accurate presets.

What should I inspect when using the calibrated ink supply?

The use of a calibrated ink supply must distinguish between the basic print colors (yellow, magenta, cyan, black) and special colors. For printing basic colors, it is not enough to define common standards such as FOGRA before. However, many printers have developed their own standards, and if necessary, they can match colors and deviate from commonly used standards.

In order to minimize the uncertainty, useful recommendations over the years are now strictly applied to the production process.

The nominal ink volume for a particular color ink is usually a color value (eg, Lab). Buyers are usually indicated by such requirements. Measurements from the sample can also produce correct results, but this requires the color management system to correctly compensate for any differences in the production of the sample.

Most of the special color calibration density values ​​do not yet know the nominal color density value is generally not known. Even measuring the density of the specimen may produce incorrect results due to physical effects (conditional matching).

Therefore, it seems that color measurement is better than density measurement.

The relationship between the calibration value and ink ink film thickness

There is a close relationship between the calibration ink quality and the relationship between the calibration value on the substrate and the ink film thickness. The quality of the substrate (paper) plays a decisive role. Even though the relationship between the density of the basic color and the thickness of the ink film is clearly understood on certain grades of paper, we should consider that the actual paper used in production is Deviation. Due to the change in the characteristics of the substrate, it is clear that the calibrated color value has a significant advantage over the density value. Since the density measurement channel matches the basic print color during measurement, the relationship between density and ink film thickness is clear on at least some papers. However, uncertainty is still greater when using color values.

How to minimize uncertainty

The only remedy is strict standardization or the use of a printability meter to measure the characteristic curve.

For special colors, if the printability meter is not used or the ink supplier does not provide relevant data, the only way is to make a rough evaluation. In this case, the pigments of the ink and the properties of the substrate play a decisive role.

Variables that affect ink metering

On the one hand, what is the relationship between the area coverage of the image and the thickness of the ink film on the substrate? On the other hand, what is the relationship between the area coverage of an image and the adjustment value of an ink metering element?

This is the performance tested by the press manufacturer. The press manufacturer must know what adjustments the metering component is set to, what area coverage, and the thickness of the ink film transferred to the blanket and substrate.

This is mainly determined by the actual adjustment of the ink metering element. Manroland also considered other variables:

First of all, the ink supply device influences the ink in the horizontal direction. The amount of ink entering the ink roller causes a portion of the ink of one ink spoon to be transmitted to the adjacent ink spoon due to the transverse ink stringing. This phenomenon can be calculated and compensated.

Second, when some ink keys are off, ink fountain ink flow. In the past, this phenomenon did not receive attention, but it had a great influence on the presupposition. It is very important that the relevant ink keys are precisely adjusted and turned off, otherwise this method does not work.

Consider other important variables

Including press adjustments. The adjustment of the ink roller and the water roller has a great influence on the ink. Periodically checking the ink supply device according to the manufacturer's specifications is very important for obtaining accurate ink preset results.

The feed of the fountain liquid also has a considerable influence on the transfer of the ink. The printing staff must have experience and technology to ensure that the fountain solution is sufficient and not excessive.

Finally, external influences also affect the results - especially the climate. This refers to the humidity in the pressroom and the temperature and humidity of each press. Every printer knows that using the same amount of ink supply, the print results of the "cold" printers on Monday morning are not the same as those printed on the last night of Friday night. To avoid this problem, the only way to do this is to air-condition the production area and install a temperature control system on the press to get stable production conditions.

Deviations that may be considered

For all the mentioned influencing factors, we can estimate the deviation that may occur in daily production in a completely normal printing factory. The percentage rate given in the table “Variables Affecting Auto Ink Supply Settings” is used as a guide. In a bad environment, or when you don't know the relationship, you must consider the preset result when the ink density exceeds the target value. The values ​​in the table are only a rough guideline for discussion, but they can provide references on where the major issues may be found.

summary

The precondition for achieving the best preset effect is the standardized parameter of the input value. Due to the long-standing criteria for printing basic colors, the computing system can use these known parameters to derive the appropriate amount of ink-key adjustment required for the required ink film thickness on the substrate.

However, for users, the basic requirement is printing standardization, and even more important is prepress standardization. This is because the computing system can only work with standard programs.

Equally important is a good color management system, regular maintenance, calibration and adjustment of all equipment, and stable production conditions.

If all of these factors are appropriate, the pre-set of the automatic ink-supplying device will greatly save work preparation time and materials - even though the special colour matching still requires more time and investment. At the same time, the use of CIP3 to obtain preset data can improve these potential savings and therefore minimize processing and measurement errors.