Causes and elimination methods of printing bar marks

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. Printing bar marks are particularly prominent in field printing and textured printing. There are two kinds of performance characteristics: First, the ink in the lateral stripe of the printing product is obviously darker than the ink in other parts; the second is the appearance of strips. The ink color of the bar is obviously lighter than that 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 factor.
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 the pressure of a few printing rollers is too large, 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. In addition, when the pressure between the ink roller and the iron roller is too large, the iron roller will produce a squeeze on the rubber roller and the glue roller will temporarily deform due to its elasticity, which will cause sliding friction to the printing plate and cause ink bars. Moreover, due to the different pressures of the collector roller and the serigraph roller and the printing plate, it is easier to cause the surface line speed of their surface to be out of synchronization to cause ink bars. Therefore, the pressure between the rubber roller and the chain iron roller should be adjusted properly to avoid the roller being squeezed, and the resistance and the friction force are increased and the ink bar easily occurs. There is also a situation where the roller core has a poor core and is not straight, and it is also prone to ink bars. This is because during the rolling process of the machine, the contact pressure between the rubber roller and the plate is inconsistent, and when the machine rolls, local friction increases to cause stripe marks. In this regard, high-precision ink rollers should be replaced for printing full-field and textured versions.
2. The roller gear is worn, the gear clearance is too large, or foreign matter accumulates between the gear teeth.
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 adjusted by re-adjusting the center distance between the rollers, and new gears should be replaced for those gears that are severely worn. Adhesion to foreign substances in the teeth should be cleaned before the effect of eliminating the ink bars can be achieved.
3. Roller bearing wear occurs.
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, the serious wear of the drum shaft head or bearing should be considered to take repair or replace the new bearing replacement to eliminate the traces of ink marks.
4. Plate cylinder or blanket cylinder liner 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 padding to the mouth part of the mouth, gradual padding should be adopted, and no padding should be added at once to avoid the appearance of ink marks.
5. The blanket is loose.
If the blanket has just been changed soon, the stretching during the printing process becomes loose, and it is not tightened in time, so that sliding friction easily occurs during rolling, and thus a stripe-like ink stick trace appears. Therefore, when the blanket has a loose condition, measures should be taken to tighten it in time to prevent the production of printing ink bars.
Second, the cause of the water mark and eliminate the method
1. The plate layout is too watery.
When the layout of the water supply is too large, there is a water film between the rollers or between the roller and the printing plate, hindering the normal transfer of ink, so that the printing process, the ink emulsification, so the ink fades, and the ink viscosity is reduced, Dispersion of structural organization, pigment particles accumulated on the ink roller, layout and blanket, 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. The dampening solution is not suitable for pH.
When the pH of the fountain solution is not properly controlled, the lack of acid will dissolve the inorganic salts formed on the layout, destroy the layout structure, reduce the hydrophilic properties, and make 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; adjust the concentration of the fountain solution, according to the actual situation of the printing, the pH of the fountain solution The appropriate adjustments can be made within the range of 3.8 to 4.6 to eliminate the need for deburr marks.
3. The pressure of the water roller and the water roller is too high.
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 roll and the string water roll should be properly adjusted to eliminate the detrimental mark caused by the water roll.
4. The pressure of the water roller and the plate is too high.
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 between the water roller and the printing plate should be properly adjusted to eliminate the detrimental marks caused by the pressure of the water roller on the printing plate.
5. The water roller shaft head and wheel bearing wear and looseness generate jumps. 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 fluff cover ink adhesion, aging hardening.
When the water roll cover fabric is used for a long time, the ink residue and the foreign matter adhere to cause aging and hardening, then, in the roll brushing process, on the one hand, water transfer unevenness and sluggishness are easily generated, and on the other hand, slipping is likely to occur. Print plate left water roller marks. In this regard, we should always pay attention to cleaning the water roller to reduce the chance of ink penetration. For the use of aging water jackets, new sleeves should be replaced in time to prevent the occurrence of water mark.
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 unfavorable conditions that exist together; there are wear and tear caused by parts and components of the equipment, and there are also improper methods of operation and discomfort. Only in the daily production focus on strengthening equipment maintenance and maintenance, scientific and rational use and adjustment of the machine in order to better prevent and avoid the occurrence of print 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. ("Chinese Printing")