Second, the causes of white streaks and their solutions
White streaks are generally caused by the water transfer section and are called watermarks. The causes and ways to overcome are:
1 Water roller and plate or string water pressure is too heavy
The pressure between the water roller and the printing plate or the water roller is too heavy, so that when the water roller comes into contact with the printing plate, a jump occurs, and friction between the plates causes scratches.
Ways to overcome: Correct the pressure between the water roller and the plate or the water roller, and reduce the water roller jump to avoid streaks.
2 plate water roller surface too much ink
Due to the long-term use of the water roller, it does not promptly wash the surface of the accumulated ink dirt, even dry solid, gradually lose the hydrophilicity and affect the water transfer performance, at the same time easy to produce friction with the layout, light, the water roller produces a slight beat, severe Damage to the texture base and trachoma, both of which can cause streaks.
To overcome the method: when the ink is light, remove the washing water roller, and when it is heavy, update the water roller velvet.
3, water roller bearing or shaft wear
The water roller generates a significant axial turbulence. During operation, the pulsation is brought into contact with the plate to cause scratches due to friction.
Ways to overcome: Repair or replace bearings and wear parts.
4. Moisture is too large
The large amount of water supply makes the layout excessively watery, which causes the water layer to separate between the ink roller and the ink plate, which hinders the positive ink transfer. Under the effect of pressure, the ink is emulsified seriously, and the viscosity is weakened. The pigment particles of the ink accumulate on the plate, the blanket and the ink roller, and increase the pressure and friction between each other and cause striae.
Overcome the method; reduce the amount of water supply blanket and ink roller.
5, fountain solution is too acidic to clean
Dissolving the phosphate formed on the plate, the inorganic salt layer cannot survive, and the fountain solution does not function. In addition, the acidity is too strong, corrodes the plateau trachoma, the network point is destroyed, accelerates the ink emulsification, the layout loses the water ink balance to cause the striae.
To overcome the method: In the light fountain solution acidity, appropriate to improve the viscosity of the ink, if necessary, should remove the ink on the ink roller or cleaning ink roller, serious, you can consider changing the printing plate.
In summary, it is only part of the factors that produce streak. There are more and more complicated reasons that cannot be enumerated. Therefore, once streak is encountered in the production, it is necessary to analyze the relevant factors and find out the cause of the streak.
(author / Yang Yong Shanghai Jie Long)
Excerpt "Printing Process Lithographic Offset Printing"