Causes and elimination of printing bar marks

Causes and elimination of printing bar marks

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In the printing process, sometimes one or several horizontal bars appear on the printed page, which is used in industry as a printing bar mark. There are two performance characteristics of the printing bar mark: one is that the ink color of the horizontal bar-shaped bar shadow portion appearing on the printing plate surface is obviously deeper than the ink color of other parts; the second is that the bar-shaped bar shadow ink color is obviously lighter than other parts. The former belongs to the ink bar and the latter belongs to the water bar. The reasons they are produced are diverse.

First, the cause and elimination method of generating ink stick

1. The ink stick caused by the rubber roller factor. When the contact pressure between the rubber roller and the printing plate is too large, when the ink roller is in contact with the printing plate during the operation of the machine, the impact is easily generated and the tremor is caused, so that the frictional force increases the streaks. If the pressure of several inking rollers is too large, the density of the bar marks will be greater. In this regard, the contact pressure between the rubber roller and the printing plate should be adjusted to maintain uniform and moderate contact conditions, and the ink bar can be better eliminated after eliminating excessive resistance.

2. The roller gear is worn, the gear gap is too large, or foreign matter accumulates between the gears. When the drum gear wears, the gap or the foreign matter adheres between the teeth, during the operation of the machine, the drum gears cannot be precisely meshed, so that the linear speed between the rollers is not consistent. In addition, the backlash is too large, and the drum is also prone to chattering and shaking, forming a printed bar mark, causing a trace of the ink stick that is similar to the gear pitch. There is a foreign matter obstacle in the backlash, and it is easy to cause the drum to tremble due to the phenomenon of "top teeth", so that the horizontal layout of the printed product forms a strip of ink stick. In this regard, the center distance between the rollers should be re-adjusted to reduce the gap between the teeth; for gears with severe wear, the new gear should be replaced; if there is a foreign matter adhered between the teeth, it should be cleaned to achieve the effect of eliminating the ink stick.

3. The roller bearing has a large wear. When the roller shaft head is running out of oil or the machine wears natural wear for a long period of time, the gap between the roller shaft head and the bearing is increased, and the mismatching is caused, and the ink stick trace is caused by the chattering when the pressure is combined. In this regard, it is advisable to make the rubber inner liner into a trapezoidal shape to reduce the impact during the imprinting state and to reduce the degree of the ink stick. In addition, if the roller bearing is seriously worn, it should be considered to repair or replace the new bearing to eliminate the ink trace.

4. The plate cylinder or rubber roller liner is too large. If these two conditions exist, the strip-shaped ink stick marks will be caused by the inconsistent surface linear velocity, and the impact vibrating of the drum will also occur due to the embossing, so that the contact between the two rollers is likely to cause friction and cause the ink stick trace when the vibration occurs. In addition, sometimes the ink stick is easily caused by the fact that the imprinting of the bite portion is not obvious (the pressure is light) and the pad of the pad is too much. In this regard, the thickness of the lining should be accurately adjusted, and the minimum printing pressure should be used to make the ink layer uniformly transfer, so as to maintain the uniform line speed between the rollers as a prerequisite. When adding a paper strip to the bite area, the method should be carried out by gradually heating the mat. Do not pad more at once to avoid the occurrence of ink stick marks.

5. The blanket is loose, sliding friction is easy to produce when rolling, so there is a strip of ink traces. Therefore, measures should be taken in time to tighten to prevent the printing of ink sticks.

Second, the causes and elimination methods of water bar marks

1. The moisture of the printing plate is too large, so that there is a water film between the ink rollers or between the ink roller and the printing plate, which hinders the normal transmission of the ink, and causes the printing pressure to increase to form a friction and produce a strip-like pale bar shadow. In this regard, the emulsified ink should be removed and the appropriate water supply amount should be adjusted by washing water, ink roller, blanket and printing plate to eliminate the bar marks caused by excessive moisture in the layout.

2. The pH of the dampening solution is not suitable. When the pH value of the dampening solution is improperly controlled, the insufficient acidity dissolves the inorganic salt formed on the plate, destroys the plate structure, reduces the hydrophilic property, and makes the plate ink lose balance. The too acidic dampening solution is easy to corrode the printing plate blisters, accelerate the emulsification of the ink, destroy the image base, and cause the water bar marks due to the imbalance of the ink. In this regard, the elimination method is: if the surface structure of the printing plate is damaged, a new version should be replaced; the ink emulsified on the machine should be cleaned; the concentration of the high-speed fountain solution, according to the actual printing conditions, the pH value of the fountain solution The purpose of eliminating the bar marks can be achieved at a suitable high speed in the range of 3.8 to 4.6.

3. The pressure of the water roller and the water roller is too large. If the contact pressure between the water roller and the water roller is too large, not only the dampening water on the surface of the roller is squeezed, but the dampening solution is unevenly conveyed or the water is blocked, and the water roller is easily generated. Jump to the slip to form a water bar mark. In this regard, the contact pressure between the water roller and the water roller should be properly adjusted to eliminate the bar marks caused by the water roller.

4. The pressure of the water roller and the printing plate is too great. When the pressure between the water roller and the printing plate is too large, when the water roller passes through the empty portion of the plate cylinder without the plate wrapping during the rotation of the printing machine, it is easy to collide at the mouth of the printing plate to make the printing Water marks are generated near the mouth of the mouth. In this regard, the contact pressure between the water roller and the printing plate should be properly adjusted to eliminate the excessive pressure caused by the water roller on the printing plate to cause the bar mark.

5. The water roller shaft head and the wheel bearing are worn and loose to produce a jump. When the water roller is used for a long time, or the water roller shaft head and the bearing are worn due to poor lubrication, due to the jumping or sliding disadvantage in the printing surface during the rotation of the water roller, the strip will be caused by the surface slip. Shaped water roller bar shadow traces. In this regard, it should be checked that the water roller shaft head wear or bearing wear, take corresponding measures to repair, in order to eliminate the looseness of the gap, eliminate the water roller bar marks. Attention should also be paid to the lubrication of the bearings to prevent wear and tear.

6. Water velvet sets of ink adhesion, aging and hard. In this regard, you should pay attention to clean the water snails frequently, reducing the chance of ink penetration and adhesion. For the use of aging water jackets, new ones should be replaced in time to prevent the chance of water marks.

In general, the reasons for the printing of the bar marks in the daily offset printing process are various, and the situation is sometimes complicated. There is a reason for this, and there are also a variety of non-spraying conditions coexisting; caused by the wear and tear of equipment parts, there are also improper operation methods, and the discomfort. Only in the daily production to focus on strengthening the maintenance and maintenance of equipment, scientific and rational use and adjustment of the machine, can better prevent and avoid the opportunity of the occurrence of bar marks. If the printing bar marks have occurred during the production process, it should be carefully analyzed and observed to accurately eliminate the bar mark fault.