The bar marks are generally caused by the water delivery part, so it is called the water bar marks. The causes and solutions are:
1 The pressure of the water roller and the printing plate or string water roller is too heavy
Excessive pressure between the water roller and the printing plate or string water roller causes the water roller to jump when contacting the printing plate, and friction between the plates causes streaks.
Overcoming method: correct the pressure between the water roller and the printing plate or string water roller, reduce the water roller jump to avoid streaking.
2 Too much ink on the surface of the printing plate water roller
Due to the long-term use of the water roller, the ink deposits on the surface are not washed in time, or even dry to a solid, and gradually lose the hydrophilicity, which affects the water transfer performance. At the same time, it is easy to produce friction with the plate, light, the water roller jumps slightly, heavy , Damage the pattern foundation and trachoma, both will cause streaking.
How to overcome: When the accumulated ink is light, remove the cleaning water roller, and when it is heavy, update the water roller velvet.
3 Water roller bearing or shaft is seriously worn
The water roller has obvious axial movement. When running, the jump will contact with the printing plate to produce friction and cause streaks.
Overcoming methods: repair or replace bearings and worn parts.
4 Excessive moisture in the layout
The large amount of water supply causes excessive moisture on the plate surface, which causes water layer separation between the ink rollers and the graphic of the printing plate, which hinders the positive transfer of ink. 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 surface, the blanket and the ink roller, which increase the pressure and friction between each other and cause streaks.
Overcoming method; reduce water supply blanket and ink roller.
5 The fountain solution is too acidic to clean
The phosphate formed on the plate surface is dissolved, the inorganic salt layer cannot survive, and the fountain solution does not function. In addition, the acidity is too strong, corroding the plate surface trachoma, the dots are damaged, the ink emulsification is accelerated, and the plate surface loses the balance of water and ink, causing streaks.
Overcoming method: the medium light fountain solution is acidic, and the viscosity of the ink is appropriately increased. If necessary, the ink on the ink roller should be removed or the ink roller should be cleaned. If it is serious, a new printing plate can be considered.
6 Bearing wear
The characteristics of the streaks caused by the roller bearing wear are several wide streaks at the bite, and a few are equidistant streaks. Due to the long-term use of the roller, the natural wear causes the gap between the roller journal and the bearing to be too large. The fit is loose, after the bite is pressed, the yield value is large, and the tremor occurs during high-speed operation, causing "stripes". In addition, when the ellipse of the drum journal is severely worn, a similar situation occurs.
How to overcome: If it is confirmed that the bearing is seriously worn, a new bearing must be replaced.
7 Caused by gear vibration
The gears are embedded with paper wool, ink skin and other dirt. The machine is used for a long time and is not properly maintained. Some paper wool, dried ink skin and other dirt will be embedded between the gears, which will become small hard blocks after the gear is rolled, causing the drum gear to run. Vibration caused by streaking.
Overcoming method: strengthen the cleaning and maintenance of the machine, thoroughly remove the dirt, and ensure the smooth operation of the gear.
8 Ink roller pressure is too heavy
The pressure between the printing plate and the ink roller is too large, the plate pad paper is too thick or the pressure of the ink roller is not adjusted properly, so that the pressure between the printing plate and the ink roller is too large, causing the ink roller to jump and slip, producing streaks.
Method of Overcoming: Adjust the plate pad reasonably to make it suitable for the pressure of water, ink roller and rubber roller.
9 Caused by the ink system
(1) Improper adjustment of ink roller pressure, the part that causes "streaks" is generally close to the bite, and its position changes up and down.
(2) The unevenness of the outer circumference of the roller of the ink roller is not straight, causing the "streak" generally at the bite.
(3) The ink roller gear is worn or not accurate enough, causing "stripes" whose pitch is equal to the pitch of the ink gear.
Methods to overcome: (1) Adjust the pressure between the ink rollers; (2) Remove the ink rollers for grinding or replace the ink rollers with straight roller cores: (3) If the gears are seriously worn, you can replace them with new ones.
10 Caused by improper ink preparation
The ink is thin, it will not only produce greasy and paste, and the cohesion is small, affecting the transfer of ink. Ink rollers, printing plates and blankets gradually accumulate ink pigment particles, which increases surface friction and pressure and causes streaks.
Overcoming method: Add No. 0 ink to the ink cow to improve the viscosity and transfer performance of the ink.
11 Caused by printability
The surface roughness is poor, it is easy to peel off powder and fluff, and it is accumulated on the printing plate, ink roller and blanket, causing friction and pressure to increase and cause streaks.
How to overcome: When printing on paper with poor surface strength, wash the rubber cloth frequently, and add debonding agent or No. 6 ink to the ink to reduce the powder and hair loss.
In summary, only some of the factors that cause streaks, there are more and more complicated reasons that cannot be listed one by one. Therefore, once the streak is encountered in production, the location and characteristics of the streak must be analyzed to analyze the relevant factors to find out the cause of the streak.
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