Talking about the imprints on the printed matter - printing bars

The imprint on the printed matter that is parallel to the axis of the roller is too dark or too light. It is called a printed bar, commonly known as "bar". There are two kinds of expressions of the printing bar. The deeper ones are called black bar, also known as ink bar, and are the bars that are consistent with the inks printed. The imprinted light is called a white bar, also called a water bar. It is easy to form a colorless bar.

No matter what kind of printing bar, it is caused by the improper contact between the blanket cylinder, the water roller, the ink roller and the plate surface. Print bars can appear in text, lines, flat screens, images, and full-size prints, but the bars that appear when printing flat screens with 60% outlets are most noticeable. Therefore, 60% flat screen printing is often used as a means of detecting bars.

According to the rules of bars, printing bars can be divided into two categories: gear bars and non-gear bars.

1. Gear bar

The gaps of the gear bars are regular, and their gaps are the same as those of the drum drive gears. The main cause of the gear bar is due to the wear of the drum drive gear, improper pressure of the bearer, wear of the bearing bush, etc., resulting in excessive gear clearance, bad meshing between each other, chatter during the operation of the machine, resulting in the printing plate cylinder, eraser, The roller and the impression roller 3 cause friction due to inconsistent surface line velocities. Thus, the surface of the printing plate generates a bar equal to the gear tooth pitch under the effect of this momentary friction, and is then transferred to a print to form a print. Bars.

I used a J2108 offset press to print ink sticks, and the ink sticks were fixed. When the machine was shut down and inspected, no gear was found to be damaged. Under the condition that the ink roller was ineffective, the new blanket was replaced with a new blanket, and the new liner was invalid. The machine was pressed to move and found the corresponding part of the ink bar. When the plate comes into contact with the blanket, the impression cylinder rubs against the rubber. Change the position of the blanket cylinder so that the cylinder dents do not touch the blanket cylinder. Then start printing and the ink stick disappears.

On another occasion, the position of the ink stick appeared in the printing was fixed. When inspecting the equipment, it was found that there was a ball on the root of the gear of the rubber roller drive gear. After removing the ball, it was found that the tooth surface was slightly damaged. The problem is solved by adjusting the damaged tooth surface to the empty position of the drum.

2. Non-gear type bars

The main difference between the non-gear type bars and the gear type bars is that the spacing of non-gear type bars is irregular, and the positions of consecutive bars are not fixed. The main reasons for non-gear printing bars are as follows:

(1) Improper pressure adjustment between the platen roller (water roller) and the plate and chain roller (serial water roller) (the effect of the two ink rollers after the four inking rollers is the most noticeable), causing the ink roller ( The water roller) does not have the same linear velocity as the surface of the printing plate, producing a rubbing bar.

(2) The pressure on the two sides of the printing roller or the reversing plate roller is not uniform with the printing plate. After passing through the roller, when it hits the edge of the printing plate mouth, it jumps to form a printing bar.

(3) The crystallization or wear of the ink roller surface causes printing bars.

(4) The print roller is caused by the bearing damage of the ink roller (water roller).

Non-gear bars are most familiar to printer operators. In the production practice, the author encountered a very special "melancholia." Once, when using the J2108 offset press to print books, it was found that there was an intermittent ink bar at about 7 cm from the mouth of the printed product, and that the handwriting on the printed sheet also had a ghosting phenomenon, but the ghosting was different from the common ghosting image and the graphic text. There is lateral displacement of the imprinting, and not all the layout has ghosting, but there is a ghost phenomenon in a certain part of the layout. After observing the analysis of the phenomenon of ink bars and ghosts, the possibility of gear bars was ruled out. Therefore, the pressure of the ink roller and the printing plate was checked, and the third ink roller was found to be lighter and the ink roller was touched by hand. It shakes because of bearing damage. Remove the 4 ink roller from the plate, clean it and clean it with "German Magic" rubber roller to restore the cleaning paste. Replace it with a new bearing. Adjust the pressure on the printing plate and the ink roller and start printing again. The bar has disappeared and the ghosting phenomenon has disappeared.

In addition to the several printing bars described above, slackening of the blanket can also result in printed bars on the printed product.

Source: Printing Technology, Zhejiang Yayuan Agricultural Testing Station, Jinhua, Zhejiang (Shoukun)