In the printing process, sometimes one or several horizontal bars appear on the printed page, which is used in the industry as a print bar mark. There are two kinds of performance characteristics of the printed bar marks: First, the ink of the horizontal bars in the print layout is obviously darker than the ink of other parts; the second is the ink of the bar-shaped bars that is obviously lighter than the ink of other parts. The former belongs to the ink bar and the latter belongs to the water bar. The reasons they produce are various.
First, the reasons for the production of ink bars and eliminate methods
1, the roller caused by the roller bar. When the contact pressure between the rubber roller and the printing plate is too large, when the ink roller contacts with the printing plate during the operation of the machine, it is easy to generate shock and cause tremor, so that the increase of the frictional force causes a streaky streak. If several stencil-type ink fountain rollers are under too much pressure, the density of the bar marks will be greater. In this regard, by adjusting the contact pressure between the rubber roller and the printing plate to maintain uniform and moderate contact conditions, eliminating the excess resistance, the ink bar can be better eliminated.
2, roller gear wear, gear clearance is too large or foreign objects accumulate between gears. When the roller gear wears, gaps or adhesion of foreign matter in the teeth, during the operation of the machine, the roller gears can not be meshed with each other accurately, so that the line speed between the rollers is not consistent enough. In addition, the backlash is too large, the drum is also prone to tremor jitter, the formation of print marks, so that the printed layout of the track and the gear pitch similar to the ink marks. There is a foreign body obstacle in the backlash, and it is easy to cause the drum to tremble due to the "top gear" phenomenon, so that the horizontal layout of the print product forms a strip-like ink stick. In this regard, the distance between the rollers should be reduced by re-adjusting the center-to-center distance between the rollers; new gears should be replaced for those gears that are worn out badly; the adhesion of foreign materials to the teeth should be cleaned before the effect of eliminating ink bars can be achieved.
3, roller bearings have a greater wear and tear. When the roller shaft head lacks oil running or the machine wears naturally for a long time, the gap between the roller shaft head and the bearing is increased, and the cooperation is poor, and the ink mark is caused by the tremor when the pressure is combined. In this regard, it is advisable to make trapezoidal traps in the inner liner of the rubber in order to reduce the impact during the imprinting state and reduce the degree of ink bar marks. In addition, serious wear on the roller bearings should be considered to take repair or replace the new bearing replacement to eliminate the traces of ink marks.
4, plate cylinder or rubber roller lining is too large. If these two conditions exist, stripe ink marks will be caused due to the inconsistency of their surface line speeds, and at the same time, the rollers will suffer shock vibration when they are imprinted. Therefore, when the two rollers vibrate, they will easily cause friction and cause ink marks. In addition, there are cases where the ink stick is easily caused by the pad of the pad being too large due to insignificant imprinting of the mouthpiece (light pressure). In this regard, the thickness of the lining should be accurately adjusted, and the ink layer should be uniformly transferred with the minimum printing pressure so as to maintain the consistency of the line speed between the rollers as a precondition. When adding a piece of paper to the mouth part of the mouth, use a gradually heating pad method, and do not add a pad at once, so as not to produce traces of ink marks.
5, loose blankets, rolling friction is easy to produce, so there will be a strip of ink marks. Therefore, measures should be taken to tighten the tension in time to prevent the production of printing ink bars.
Second, the cause of the water mark and eliminate the method
1, the printing plate surface moisture is too large, so that there is a water film between the ink roller or between the ink roller and the printing plate, hindering the normal transfer of ink, so that the printing pressure increases to form friction and produce strips of light marks. In this regard, the emulsified ink should be removed and the proper amount of water supply adjusted by cleaning the water, the ink roller, the blanket, and the printing plate so as to eliminate the detrimental marks caused by the excessive water in the printing plate.
2, dampening solution pH discomfort. When the pH of the fountain solution is not properly controlled, the lack of acid dissolves the inorganic salts formed on the plate, destroys the layout structure, reduces the hydrophilic properties, and makes the layout ink lose its balance. The excessively acidic dampening solution tends to corrode the platen blisters, accelerating the ink emulsification, destroying the graphic basis, and also causing the water mark due to the imbalance of ink and water. In this regard, the elimination method is: the surface structure of the plate is damaged, should be replaced with a new version; on-board emulsified ink should be cleaned; high-speed fountain solution concentration, according to the actual situation of the printing, the pH of the fountain solution The purpose of eliminating the derailment marks can be achieved at a high speed in the range of 3.8 to 4.6.
3, the pressure of the water roller and the string water roller is too large. If the contact pressure between the water roll and the string water roll is too large, not only will the squeezing water on the roll surface be squeezed, the fountain solution will be unevenly distributed or the water will be transmitted, and the water roll will easily cause the diameter to be generated. Skip to slip, forming water marks. In this regard, the contact pressure between the water-water roller and the string-water roller should be properly adjusted to eliminate the detrimental marks caused by the water roller.
4, the pressure of the water roller and printing plate is too large. When the pressure between the water roller and the printing plate is too high, during the rotation of the printing machine, when the water roller passes through the blank section of the plate cylinder and is unengraved, it is easy to collide with the opening of the printing plate to make the printing product. Water marks are produced near the mouth. In this regard, the contact pressure of the water roller and the printing plate type should be appropriately adjusted to eliminate the detrimental effect of the water roller's excessive pressure on the printing plate.
5, water roller shaft head and wheel bearing wear, loosen and produce jump. When the water roller is used for a long time, or if the water roller head and the bearing are worn out due to poor lubrication, due to the runout or sliding defects in the layout during the rotation of the water roller, the surface will be scratched Water roller shadow traces. In this regard, it should be checked to see whether the water roller shaft head wear or bearing wear, take appropriate measures to repair, to eliminate gap loosening phenomenon, eliminate water roller bar. Usually also pay attention to the lubrication of the bearing to prevent the use of wear.
6, water piles ink adhesion, aging hardening. In this regard, we should always pay attention to cleaning water snails in peacetime to reduce the chance of ink penetration. For the use of aging water jackets, new sleeves should be replaced in a timely manner to prevent the occurrence of water marks.
In general, the reasons for the occurrence of print marks in the daily offset printing process are various and the situation is sometimes intricate. For one reason, there are also many kinds of non-spraying situations that exist together; there are wear and tear on parts and components of equipment, and there are also improper methods of operation and discomfort. Only in the daily production, we must pay attention to strengthening the maintenance and the maintenance of equipment, and scientifically and rationally use and adjust the machine in order to better prevent and avoid the occurrence of detrimental marks. If a print run has occurred during the production process, analysis and observation should be carried out carefully in order to accurately eliminate the breakage of the rung.
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