In offset printing production, poor ink balance control can produce a series of printing failures. Among them, the amount of water in the printing plate has caused the following hazards. First, the water, ink preset before starting The advanced printing machine is equipped with a printing plate reading and reading device (such as Heidelberg CPC3, Komori PSS plate scanning device, etc.), can provide water, ink preset data, and can automatically complete the settings. However, colleagues who have used similar devices must know that this preset is inaccurate and often requires real-time adjustments to achieve the desired ink-water balance. For machines without a printing plate reading and reading device, the preliminary water and ink presetting is mainly based on experience. Second, printing ink balance control
(1) The printed ink is dull and dull, the saturation is decreased, and the color is light.
(2) The ink is over-emulsified, resulting in a flower pattern.
(3) The drying speed of the blot slows down, resulting in smudging on the back of the print.
(4) Due to the blocking effect of water, the ink cannot be properly transferred and transferred, resulting in poor ink supply.
(5) The printed sheet is soft, the paper is not evenly distributed, there are water stains on both sides of the drum, and the machine will rust locally if left for a long time.
Too little water in the plate will have the following hazards.
(1) The printed ink becomes darker, the dots increase, and it is easy to paste the plate.
(2) The blank part of the printing plate and printed sheet is dirty.
According to the data, normal printing, when the printing plate graphic part of the ink layer thickness of 2 ~ 3μm, the blank part of the water film thickness of 0.5 ~ 1μm, the ink volume solution contained in the fountain fluid is 15% to 26% (It is better to be 21% and the maximum is not more than 30%). The ink balance can be basically achieved. However, in actual printing, the operator does not have enough time to use the instrument to perform the measurement, and the factors that affect the ink-water balance are more complex or constantly changing. Therefore, in actual work, the operator mainly judges the ink-water balance based on experience. control. Here are some work experiences for your reference.
Before the pre-adjustment, the installation of the water roller and the ink roller, the pressure adjustment and the test work must be performed first to avoid the occurrence of water and ink failures.
The preset method is as follows.
1. Analysis and setting
(1) Observe the distribution of the whole set of printing plates, decide the water and ink volume of each printing unit, and perform preliminary setting operations. The principle is: the layout of the text area is large, the amount of water is much, and vice versa is less; ink layer thickness is more water consumption, and vice versa is less.
(2) According to the nature of the ink used, the ink with a large emulsification value has a large amount of water, and vice versa.
(3) When the printing speed is fast, the ambient humidity is low, and the temperature is high, the amount of water is more, and vice versa.
(4) The paper has high smoothness and low water consumption, and vice versa.
(5) The water content of the sand in the new printing plate is large and the amount of water used is large; the old printing plate consumes less water. PS version uses less water; flat intaglio uses more water.
2. Put water and put ink
(1) First adjust the gap between the ink fountain and the ink fountain roller so that the ink flow of the entire ink fountain roller is even. During the operation, the ink fountain roller can be rotated by one-way rotation of the handle to observe the distribution of the output ink layer on the ink fountain roller.
(2) According to the layout of the printing plate, the gap between ink fountain and ink fountain roller should be adjusted accordingly. There are many graphics and texts with high density or large fields, and the gaps are correspondingly larger. The graphic and textual density is small or high-profile, and the gap is correspondingly smaller.
(3) Based on experience, estimate the number of teeth of the ink fountain roller in advance and adjust it well.
(4) Turn on the power, turn on the water and ink switch, and force the water and ink.
(5) Fully and quickly deliver ink to the ink roller.
(6) Increase the water volume of the roller fully and quickly. When adding water to the water supply roller, add it to the water roller. During operation, hold the sponge with your finger, and then apply the dampening solution in the bucket groove and evenly add it to the string of water rollers. Correct posture and safety. On the operating side of the machine, the left hand holds the safety part and the right hand adds water; when the drive side of the machine, the right hand holds the safety part and adds water with the left hand.
(7) During the operation of the machine, listen to the sound of the separation of the ink layer on the ink roller. The sound of separation is large, indicating that the ink volume is large, the separation sound is small, and the ink volume is small or moderate. When checking the water content of the water roller, it can be used to gently stroke the surface of the water roller with the finger after the machine stops. When the finger feels similar to the humidity of the wringer and damp cloth, it basically meets the requirements.
(8) The empty car runs for 1 to 2 minutes to make water and ink uniform.
1. Printing plate cleaning and maintenance
Before the test 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, the plate is coated with water or glue to form a water film or film on the plate. The non-graphic part of the plate is isolated from the air to prevent the plate from getting dirty. When the non-graphic part is dirty, the dirt can be removed with a glue solution, fountain solution or the like. When the text of the layout becomes lighter, it can be cleaned with gasoline, glue, and cleaning solution to improve the sensory power of the printing plate and make the graphics clear. These details of controlling the balance of ink and wash must not be too trivial and neglected.
2. How to identify the size of water and its control
(1) Sheet-fed printing press can preliminarily estimate the amount of water according to the reflection intensity of the layout
While watching the layout, the operator can stand on the side of the machine and observe the moisture on the surface of the printing plate by means of natural light or light. When the ink balance is correct, the layout has a slight brightness and feels like the reflection of the frosted glass. If the plate surface is dark black, there is no reflective feeling, indicating the surface of the plate is too small; if the layout is very bright, there is watery feeling, then the plate surface is too large. Reflective strength of the layout will be affected by factors such as the light above the printing press and the printing speed, and it will take more observation at ordinary times to form memory in the brain. When water is felt to be large, it is necessary to slowly reduce the amount of water, look for reflections on the layout for each reduction, and check if the prints are normal until the prints have a slight water-drying effect. Add water, and the water in the layout is the best. Ink wash reaches equilibrium.
When observing and analyzing, also pay attention to whether the printing plate is new or old. The new version of the sand is complete, the amount of water is more, the layout is not easy to reflect light, visual inspection should be dark gray, slightly shimmer. The surface of the old version was worn out and it was not able to hold water well. The water floated on the surface of the printing plate. The layout should have some reflective sensation.
Judging whether the amount of water is appropriate, you can also observe the proofs. If the sample ink is light and the ink is still light after the ink is added, the water is large; the proofs are soft, the jittering sound is not brittle, and the water is large; the proofs are filthy, and when the machine stops for a long time, the layout is still dry; the water is large; if the prints are not available Gloss, pattern, or the appearance of curled sheets, missing paper, etc., indicate that the layout may be too large.
The appearance of water droplets on the ink roller and in the ink tank is also a characteristic of the water.
(2) Judgment and control of slight water dryness in printing
When the water is slightly dry (low water content), slight ink is usually found at the non-image area of ​​the mouth, but it cannot be seen as dryness. If the water is very light, sometimes there will be no ink in the mouth. At this point, the most effective method of determining water-dryness is to use a magnifying glass to observe the printable area in the print area with large amounts of ink. When such scumming is severe, it is easy to see with the naked eye; when it is slight, you need to use a magnifying glass to see if the edge of the pattern is smooth and whether the dot is clear.
In the printing, it is necessary to observe samples and observe the ink and ink balance according to the observation conditions. Moreover, it is not necessary to be eager to achieve results. The amount of water, ink, and ink must be known, and there must be certain predictability for the adjustment effect so as to avoid repeated adjustments.
3. Effect of printing speed on the balance of water and ink
The printing speed is fast, the ink transfer rate is reduced, the ink color will be lighter, and at the same time, the layout temperature will increase, the moisture will evaporate quickly, and the demand for water will increase. This is particularly evident in high-speed rotary machines. A lot of operators found that the color of the control printing was lightened when they were speeding up. They thought that if the water was big, they increased the amount of ink, but they did not immediately follow the increase in the amount of water. So the water paste version would soon appear and the ink would darken. At this time, water was added quickly to reduce the amount of ink. After a certain number of inks were printed, water and ink appeared again. Such repeated adjustments, and always control is not good, resulting in the same batch of product color instability.
In summary, there are many factors that affect the balance between offset ink and ink, but as long as careful analysis and accumulation of rich experience, it is not difficult to control the balance of ink and wash.
Source: Printing Technology