Offset ink balance discussion - control method

How to control ink balance

The theory of ink balance is not difficult to understand for general offset press operators, but it is not easy to follow the ink-water balance theory in practice. This is because the operator does not have enough time to use the instrument to perform the measurement. Different models have different operating methods. In addition, printing is performed under dynamic conditions, and there are too many factors that affect the balance of ink and water. Therefore, in actual printing, the operator mainly controls the ink and water balance based on experience. The key to ink and water balance is to control the size of the water, and the size of the water always changes with the amount of ink. This is what the ordinary saying goes.


Prepress Prepress

For advanced offset printing presses, there are printing plate reading and reading devices (such as Heidelberg CP2000, Komori PSS, etc.). Can provide ink preset data, and can automatically complete the set, in fact, this preset is also error, so, most offset ink ink balance preset experience-based, pre-tuning attention to the following points :

(1) Observe the distribution of the printing plate graphic and text. The area of ​​the layout picture is large and the amount of water consumption is large, and vice versa.
(2) Paper has high smoothness and low water consumption, and vice versa.
(3) In the printing of yellow, magenta, cyan, and black colors, the amount of water in the black plate should not be too large.
(4) The amount of water in gold and silver ink printing should not be too large.
(5) Printing speed, environmental humidity, and water consumption should not be large.

Specific adjustment method:
(1) First adjust the gap between the ink fountain and the ink fountain roller to make the ink output uniform. At the same time, according to the situation of the printing plate graphic, adjust the gap between the ink fountain and the ink fountain roller individually.
(2) The teeth of the ink fountain roller (or the ink fountain roller rotation) should be matched with the ink fountain gap and ink depth. When printing light colors, the ink fountain gap is small, and the ink fountain roller has more teeth to go. When the dark color is printed, the gap between the ink fountains is large, and the ink fountain roller has less teeth.
(3) Turn on the water and ink switch to force water and ink. Do not pay too much attention to water and ink when presetting, especially if the amount of water cannot be too large (you can feel the amount of water on the surface of the water roller by hand).
(4) Pre-adjusted water and ink are basically uniform.

[Expert Tips]
For the J2205 model, the water transfer roller of the two-color dampening device is opposite to the two-color printing plate cylinder when it passes water. Therefore, the two-color printing plate is often dirty, and should be particularly noticeable.

Second printing ink balance control

1, printing plate cleaning and maintenance

Before printing, the printing plate is washed with water to remove the protective film on the surface of the new printing plate. When the printing is stopped in the middle, it is necessary to dip water or glue to protect the non-graphic part, and the downtime is long. When the glue is applied, it must be flat. Otherwise, the non-graphic part of the plate will be destroyed.

[Case 5-1]

When a staff in a factory prints a copy, they forget to apply the glue to the new printing plate. The operator on the printing machine will try the printing after the printing plate is on the machine, only to find that the full version is dirty. At this time, use a cleaning solution to clean the printing plate. As a result, the dirtier the cleaner it is, the more reprinted. There is also a printing plant operator who used a printing plate to install the machine. Instead of cleaning the plate, the water roller is directly dropped. As a result, the layout is dirty. At this time, the operator adds water to the surface of the water roller with the sponge, resulting in a large amount of water. Increase.

[Expert Tips]

Both of these operations are illegal operations!

2, the size of the printing plate water

As mentioned earlier, the important aspect of ink-water balance is to control "water". Therefore, the identification and control of the amount of water is the first element of ink-water balance.

According to the degree of reflection of the layout to estimate the amount of water. Generally, when watching a printing plate in a printing process, the operator can stand on one side of the machine and observe the amount of water on the surface of the printing plate by means of natural light or light. When the ink is balanced, the layout has a slight brightness. If the plate surface is dark gray, there is no reflective feeling, indicating that the water on the surface of the printing plate is too small; if the reflection on the plate is bright and there is a feeling of watery, then the water volume of the printing plate is too large; the reflective strength of the plate will be affected by the machine. Side light, front light and printing speed and other factors. Different light and speed, the reflection of the layout is different, so this requires more observation at ordinary times, more experience, must form memory in the brain. Attention should be paid to the observation and analysis: The new plate has a complete sand spot, a large amount of water, and the layout is not easy to reflect. It is dark gray when viewed visually, and it is slightly shimmer. The surface of the old printing plate has been worn out and cannot hold water well. Water basically floats on the surface of the printing plate, so the surface of the printing plate looks bright.

Judging the amount of water can also be determined according to proofs: If the proofs are pale and the ink is still light after the ink is added, the water is large, if the prints are dull, the print version or the delivery is not uniform, the printed sheets are curled, etc., then the layout water may be is too big. In addition, on the ink roller, in the ink tank or imprinting, there is a drop of water in the dragging part of the blanket roller, which is also a characteristic of the water.

3、 Judgment and control of printing plates in printing

In the printing process, the operator often controls the amount of water to be relatively small, and if it is not noticed, it will be dirty. Generally, if the dirty version obviously occurs on the non-graphical portions on both sides of the printing plate, the amount of water is too small. At the mouth of the printing plate, the amount of water is slightly smaller; if it occurs in the dots of the printing plate, it indicates that the amount of water is small. When it is found that the amount of water is getting smaller, the treatment must be handled with care. It must be known and must not increase the amount of water in order to avoid quality accidents and to avoid repeated adjustments. If there is a dirty version, first use a sponge to drench some water onto the transfer roller or the water roller, and then take a few more teeth (the curvature of the water roller) or increase the speed of the roller.

4. Judgment and Treatment of Ink Balance

Due to changes in the speed of the printing press, pre-adjustment errors or mistakes in the printing halfway can cause ink imbalance. How to judge the imbalance of ink and water? According to practical experience, it can be summarized as "seeing and hearing three touches."

Look: Observe changes in the dots with the naked eye or a magnifying glass. See if the dot is clear and the edge of the pattern is smooth. When the ink is out of balance, most of the outlets are not very clear, and the patterns on the ground often produce hair and stings. Under the ink fountain roller shovel ink, or use the ink scoop to stir the ink of the ink fountain to observe the drawability of the ink in the ink fountain. When the ink ink loses balance, the ink head is short.

Listening: It is the sound of the ink roller when the machine is running. If the ink roller makes a "click" sound during operation, it indicates that ink is accumulated on the roller. (You can use the ink scoop to test the ink on the ink roller surface). Can not be applied very smoothly to the surface of the printing plate graphic, at this time can prove ink and water imbalance, in addition, any ink emulsification phenomenon of the offset press, the printing pressure is changed, that is, when the paper peeled off from the blanket when the abnormal sound .

Touch: It is the place where you touch the surface of the block or more than 70% of the dots. If you feel that these areas are sticky, you must pay attention. In addition, after stopping, touch the water and ink roller with your fingers to feel whether the water roller is “wet” or the roller is getting “fat”. In addition, you can also touch the plate and blanket by hand. The imprinting of the surface, when a stack plate or a blanket is produced, also indicates that the ink cannot be transferred well, and ink-ink imbalance may occur. When the ink and ink imbalance is serious, measures should be taken to clean the ink roller, replace the ink, and reopen the ink.

[Case 5-2]
One of the factory's art textbooks for printing elementary schools has a pattern of a red rooster. Because the captain failed to master the ink and ink balance, the red ink emulsification at the cockscage of the red rooster causes the back of the red ink to emulsify, and the 100,000 printed sheets are all scrapped.

[Expert Tips]
The back of the product caused by the severe emulsification of the ink is often irreparable.



Source: Ke Yin Network Author/Li Yongqiang