In the printing process, sometimes one or several horizontal bar shadows appear on the printed product layout, which is commonly used in the industry as printing bar marks. There are two performance characteristics of printed streak marks: one is that the ink color of the horizontal stripe shadows appearing on the printed surface is significantly darker than the ink color of other parts; the second is that the appearance of stripe bar shadows is significantly lighter than the ink color of other parts. The former belongs to the ink bar, the latter belongs to the water bar. The reasons for their occurrence are varied.
1. The reason and elimination method of ink stick
1. Ink stick caused by rubber roller. When the contact pressure between the rubber roller and the printing plate is too large, then when the ink roller and the printing plate are in contact with the roller brush during the operation of the machine, it is easy to produce shock and cause tremor, so that the increased friction causes streaking. If the pressure of several inking rollers by the format is too large, the density of the streak 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. After removing excessive resistance, the ink bar can be better eliminated.
2. The roller gear is worn, the gear gap is too large, or there is foreign matter accumulation between the gears. When the roller gears are worn, or there is adhesion of foreign objects between the teeth, during the operation of the machine, the roller gears cannot be accurately meshed, so that the linear speed between the rollers is not consistent. In addition, if the tooth gap is too large, the cylinder is also prone to tremor and jitter, forming printed bar marks, so that there are ink bar marks on the printed board surface that are close to the gear pitch. There is a foreign object obstacle in the tooth gap, and it is easy to cause the roller to tremble due to the "top tooth" phenomenon, so that the horizontal layout of the printed product forms a strip-shaped ink bar. In this regard, the center distance between the rollers should be readjusted to reduce the gap between the teeth; the gears with severe wear should be replaced with new gears; the adhesion of foreign objects between the teeth should be cleaned to achieve the effect of eliminating ink sticks.
3. The roller bearing has large wear. When the roller shaft head runs short of oil or the machine wears naturally for a long time, the gap between the roller shaft head and the bearing is increased, the cooperation is poor, and the ink stick marks are caused by vibration when the pressure is combined. In this regard, it is advisable to make the grip of the rubber inner liner trapezoidal to reduce the impact during the imprinted state and reduce the degree of ink stick marks. In addition, if the roller bearing is seriously worn, it should be considered to repair or replace the new bearing to eliminate the traces of ink sticks.
4. The plate cylinder or rubber cylinder is too large. If these two conditions exist, the stripe ink stick marks will be caused by the inconsistent linear velocity on their surface. At the same time, due to the impact vibration of the cylinder during imprinting, the friction between the two cylinders during vibration will easily cause friction and cause ink marks. In addition, because the imprint on the bite part is not obvious (the pressure is light), if the pad is too much, it may also cause ink sticks. In this regard, the thickness of the liner should be accurately adjusted, and the minimum printing pressure should be used as far as possible to make the ink layer transfer evenly, so as to maintain the consistency of the surface linear speed between the rollers as a prerequisite. When adding paper strips to the bite area, the method of gradually heating the pad should be used. Do not pad more than one at a time to avoid ink stick marks.
5. The rubber cloth is loose, and it is easy to produce sliding friction when rolling, so there are traces of ink sticks. Therefore, measures should be taken in time for tightening to prevent printing ink sticks.
2. Causes and elimination of water streak marks
1. The excessive moisture on the printing plate surface causes a water film to exist between the ink roller or between the ink roller and the printing plate, which hinders the normal transmission of the ink, and increases the printing pressure to form friction and produce strips of light marks. In this regard, the emulsified ink should be removed and the appropriate water supply should be adjusted by cleaning water, ink rollers, blankets and printing plates to eliminate the streaks caused by excessive moisture on the plate surface.
2. The pH of the fountain solution is uncomfortable. When the pH value of fountain solution is improperly controlled, the lack of acidity will dissolve the inorganic salt formed on the plate surface, destroy the structure of the plate surface, reduce the hydrophilic performance, and make the ink on the plate surface unbalanced. The acidic fountain solution is easy to corrode the trachoma of the printing plate, accelerate the emulsification of the ink, destroy the foundation of the picture and text, and also cause water streaks due to the imbalance of the ink. In this regard, the method of elimination is: if the surface structure of the printing plate is damaged, a new version should be replaced; the emulsified ink on the machine should be cleaned; the concentration of the high-speed fountain solution, according to the actual printing situation, the pH value of the fountain solution The high speed can be achieved within the range of 3.8 to 4.6 to achieve the purpose of eliminating bar marks.
3. The pressure of the water roller and water roller is too large. If the contact pressure between the water roll and the water roll is too large, it will not only squeeze the dampening water on the surface of the roll, which will make the dampening liquid transfer uneven or hinder the water transmission, and it will also easily cause the diameter of the water roll Jump towards the slip, forming water bar marks. In this regard, the contact pressure between the water roller and the water roller should be lightened to eliminate the streak caused by the water roller.
4. The pressure between the water roller and the printing plate is too high. When the pressure between the water roller and the printing plate is too large, when the water roller passes through the empty section of the plate cylinder without plate wrapping during the rotation of the printing machine, it is easy to collide at the gripping portion of the printing plate starting, making the printed product Water streak marks near the mouth. In this regard, the contact pressure between the water roller and the printing plate should be adjusted lightly to eliminate the bar marks caused by the excessive pressure of the water roller on the printing plate.
5. Abrasion and looseness of the water roller shaft head and wheel bearing produce jumps. When the water roller has been used for a long time, or the shaft head and bearing of the water roller are worn due to poor lubrication, because the water roller rotates, there will be jumps or sliding defects in the layout, then the surface will cause strip Shaped water roller shadow traces. In this regard, it should be checked to see if the shaft head of the water roller is worn or the bearing is worn, and corresponding measures should be taken to repair it to eliminate loosening of the gap and eliminate the water roller bar marks. Usually also pay attention to the lubrication of bearings to prevent wear and tear.
6. The ink on the water-fleece sleeve adheres and ages and becomes hard. In this regard, you should always clean the water snails frequently to reduce the chance of ink penetration and adhesion. The use of aging water jackets should be replaced with new ones in time to prevent the chance of water streak marks.
In general, the causes of printing streaks in the daily offset printing process are various, and the situation is sometimes complicated. It is caused by one reason, and there are many kinds of non-spray conditions coexisting; some are caused by the wear of equipment parts, and some are due to improper operation methods and uncomfortable necessity. Only by paying attention to strengthening the maintenance and maintenance of equipment in daily production, and using and adjusting the machine scientifically and reasonably, can we better prevent and avoid the chance of bar marks. If printed streak marks have occurred during the production process, careful analysis and observation should be conducted to accurately eliminate the streak marks.
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