Ink supply device automatically presets possibilities and limitations (two)
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There is a phenomenon in printing that the size of the dots on the substrate is larger than that on the printing plate. This phenomenon is called dot gain, which can be clearly indicated by the printing characteristic curve of FIG.
With the known print characteristic curve, if the test equipment not only performs integrated measurement, the dot gain can be considered. However, it is still impossible to distinguish whether the printed area to be tested is half of the field, half of the non-graphics, or by the network. The system considers the 50% flat net as 50% area coverage, but contrary to the first hypothesis - 50/50 field/non-graphic, the situation is not considered, resulting in errors.
Error source from numeric database values
There are many ways to generate preset data in modern times, but it is not completely error-free. When the plate scanner is not used, the measurement and plate surface error is no longer an element, but there are still errors, and the image carrier is still required to use CtFilm. The exposure system in the tablet is also subject to errors that may be caused by aging. limit. Therefore, a difference between the database and the post-exposure color separation sheet is generated, and a difference is produced between the exposure color separation sheet and the printing plate produced using the color separation sheet. Although the CtPlate system cancels the intermediate medium step, it is still affected by the above-mentioned errors in the plate making process and the increase in the printed net point. The dot gain on the sheet can only occur when the data distribution is sufficiently detailed and can distinguish between the dot area and the solid area. In principle, CIP3 can be used to correctly obtain available and more accurate presets.
What to check when using the calibrated ink supply?
The amount of ink supplied for calibration must be distinguished from the basic colors of printing (yellow, magenta, cyan, black) and special colors. For printing basic colors, it is too late to define common standards such as FOGRA. But many printers have developed their own standards, color matching if necessary, and deviations from common standards.
In order to eliminate uncertainty, the recommended standards that have been useful for many years are now strictly applied in the production process.
The nominal ink amount of a special color ink is usually a color value (for example, Lab). This is usually indicated by print buyers. Measured from the sample can also produce correct results, but this requires the color management system to properly compensate for any differences in the fabricated sample.
The calibration density values for most special colors are not known. The nominal density values for special colors are generally unknown. Even measuring the density of the sample may result in incorrect results due to physical effects (conditional color matching).
Therefore, it seems that the color measurement is better than the density measurement.
Relationship between calibration value and ink film thickness
The quality of the calibrated inking is closely related to the relationship between the substrate calibration and the thickness of the ink film. The quality of the substrate (paper) plays a decisive role. Even if the relationship between the density of the basic color printed on a certain grade of paper and the thickness of the ink film is well understood, we should consider that the paper actually used in production is Deviation. Due to changes in the characteristics of the substrate, it is determined that the calibrated color value has a significant advantage over the density value. Since the density measurement channel matches the printed base color during the measurement process, the relationship between density and film thickness at least on some papers is already clear. However, when using color values, the uncertainty is still large.
How to minimize uncertainty
The only remedy is to rigorously standardize or use a printability meter to measure the characteristic curve.
For special colors, the only way to do this is to make a rough evaluation if you don't use a printability meter or if the ink supplier does not provide the relevant data. In this case, the pigment of the ink and the nature of the substrate play a decisive role.
Variables affecting 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 the image and the adjustment value of the ink metering element?
This is the performance tested by the press manufacturer. The printer manufacturer must know what adjustment values are set for the metering component, what area coverage, and how much the ink film thickness is transferred to the blanket and the substrate.
This is mainly determined by the actual adjustment of the ink metering element. Manroland also considered other variables:
First, the ink supply device is affected by the cross-talking of the ink. The amount of ink entering the ink roller causes a portion of the ink of a certain ink spoon to pass to the adjacent ink spoon due to the cross-talking of the ink, which can be calculated and compensated.
Second, when some of the ink spoons are turned off, the ink fountain ink flows. In the past, this phenomenon has not been noticed, but it has a great influence on the preset. It is very important that the relevant ink key is precisely adjusted and turned off, otherwise this method does not work.
Consider other important variables
Includes adjustments to the press. The adjustment of the ink roller and the water roller has a great influence on the ink. Regularly checking the ink supply according to the manufacturer's specifications is important for obtaining accurate ink presets.
The feed of the water hopper also has a considerable influence on the transfer of the ink. The printer must have experience and technology to ensure that the fountain solution is adequate and not too much.
Finally, external influences also affect the outcome - especially the climate. This refers to the humidity in the pressroom and the temperature and humidity of each press. Every printer knows that with the same amount of ink, the printing results for the "cold" press on Monday morning are not the same as the results for the last Friday night. In order to avoid this problem, the only way is to air-condition the production area and install a temperature control system on the press to obtain stable production conditions.
Possible deviations
For all the mentioned influencing factors, we can estimate the deviations that may occur in daily production at a fully normal printing plant. The percentage ratios given in the table "Variables that affect the presets of the automatic ink supply device" are 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 by a percentage. The values in the table are just a rough guide for everyone to discuss, but they can provide a reference on where to find the main issues.
Summary
The prerequisite for achieving the best preset effect is the standardized parameter of the input value. Because of the long-standing standard for printing basic colors, the computing system can use these known parameters to derive the appropriate amount of adjustment for the desired amount of ink film on the substrate.
However, for users, the basic requirement is printing standardization, and even more important is prepress standardization. This is because computing systems can only work with standard procedures.
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 presets of the automatic ink supply will greatly save work time and materials - even though the matching of special colors requires more time and effort. At the same time, these possible savings can be improved by using CIP3 to obtain preset data, thus minimizing processing and measurement errors.