With the continuous improvement of people’s material and cultural living standards, people’s requirements for the printing quality of newspapers and commercial prints are also increasing. The use of web offset presses will undoubtedly bring new opportunities and challenges for printers, and it is especially important to find and deal with printing failures in a timely manner.
Below, the author will briefly analyze the cause of the failure of the web offset press in the printing process and propose corresponding treatment methods. I hope to help readers.
First, bad ink (Wang version)
1. Inking part is not inked or slightly blurred Cause: Part of the printing plate is worn out; the dampening solution is too acidic to emulsify the ink; the pressure of the ink roller is too high and the ink roller is de-inked.
Treatment method: replace the printing plate; adjust the pH value of the fountain solution; spray the reducing agent on the ink roller or stop cleaning the ink roller, and adjust the pressure between the ink roller and the plate cylinder.
2. The inked part is completely inky or repeated light marks appear in the same part of each page. Cause: Blanket depression.
Remedy: Apply reductant or replace blanket on blanket.
Second, the entire surface of the printing plate stained with ink or ink stains occur when the reasons: the initial operation is stained with dry glue or dry plate when the machine is restarted; normal operation, a part of the water roller is not in contact with the plate, the brush roller Insufficient water pressure due to improper pressure on the fountain roller or abrasion of the brush roller.
Treatment method: Instantly increase the speed of the water supply motor to increase the amount of water so that the glue can be quickly removed. If it is not valid, it is necessary to check if the brush roller is worn. If the abrasion is severe, the brush roller needs to be replaced. If the wear is not serious, the pressure of the brush roller, plate roller and water roller must be adjusted.
3. At the beginning of printing, the non-inking part was stained with a lot of paper powder: When the printing was started, if the ink was reported to the front of the printing department, the water roller would contact the layout for a long time and the layout would be contaminated; if the ink was not adjusted beforehand, Printing is started when the ink roller is dry, which is particularly liable to cause this phenomenon.
Treatment method: stop immediately, wipe the layout. Then change the set time to start printing. Before starting up again, ink roller adjustment should be performed first. If only the amount of water is increased without shutting down the machine, not only can paper dust be quickly removed, but the water and ink ratios will be misaligned and the rejection rate will increase.
Fourth, bad words - words and outlets are damaged by ink Cause: excessive ink; high ink viscosity; ink roller pressure is too large; plate or blanket lining too thick; fountain solution pH is inappropriate; printing plate wear.
Processing method: reduce the speed of the ink supply motor or change the gap between the ink fountain and the ink fountain roller to reduce the ink volume; reduce the ink viscosity; re-adjust the pressure of the ink roller and the plate cylinder; reduce the thickness of the plate or blanket lining; change the pH of the fountain solution Value; replace the plate.
5. Particulate - Inked parts are thin and weak Cause: The speed of the water supply motor is too high; the ink is insufficient; the pressure of the plate cylinder and the blanket cylinder is insufficient; the blanket is cracked or stained; the printing plate is partially worn by the ink; the web paper powder excessive.
Treatment method: reduce the speed of the water supply motor; increase the gap between the ink fountain and the ink fountain roller to increase the ink volume; increase the thickness of the lining of the plate or blanket; wipe the blanket or replace the blanket; repair the plate or replace the plate; The web is subjected to paper dust elimination treatment.
6. Paper fluffing and ring-shaped white spots - White spots on the printing surface, black spots on the non-inked area. Causes: Contamination on blankets and ink rollers; Foreign matters in the ink; The surface of the blanket is sticky; The viscosity of the ink is too high. Causes the paper to fluff; too much paper on the web.
Treatment method: wipe the blanket and ink roller; replace the ink or add liquid to the ink to eliminate the foreign matter in the ink; replace the blanket; reduce the viscosity of the ink with a reducing agent; remove the paper powder from the web.
Seventh, dirty version (dirty) - non-inked part stained with ink; ink viscosity is too high or too much ink to make non-ink part of the pro-inking cause: bad process plate; dirty water roller; ink roller Jumps or slips due to improper pressure; Blanking or damage of the blanket; Improper pH of the fountain solution or excessive water quality; Excessive humidity in the storage area of ​​the printing plate.
Treatment method: change the plate making process; wipe the water roller; reset the pressure of the ink roller; tension the blanket or repair the blanket through the tensioner; adjust the pH of the fountain solution or add softener and ion agent after inspection. Change the storage conditions of printing plates.
VIII. Ghosting - horizontal transverse stripes appear on the paper; the common reason is that the dots are damaged in the shadows. Cause: Thickness of the plate or blanket lining; excessive ink discharge; wear of the printing plate; wear pH of the fountain solution The ink on the layout is dry; the ink roller is set badly; the rubber covering of the rubber roller is uneven.
Processing method: reduce the thickness of the printing plate or blanket lining; reduce the speed of the ink supply motor or change the gap between the ink fountain and the ink fountain roller to reduce the amount of ink; repair the printing plate or replace the printing plate; adjust the pH value of the fountain solution; Supply the motor speed, increase the amount of water to prevent the ink on the plate from drying; Re-adjust the ink roller pressure; Check the parallelism of the ink roller rubber layer, replace the rubber roller if necessary.
Nine, ink roller ink failure - ink is not on the ink roller, ink uneven part of the reason: the ink roller pressure is not appropriate; the two ends of the rubber roller wear or depression to make contact without trace; ink roller cracking; string ink roller, heavy roller Plating wear; the dampening solution is too acidic to emulsify the ink; the ink composition is not correct.
Treatment method: If the ink cannot be evenly inked, do not use strong roller pressure to operate. The pressure of the seal line of the roller should be uniform as a whole, and the pressure should be as small as possible within a range that does not affect the print quality. If it is found that the rubber roller has worn or cracked phenomenon, it should be promptly replaced; the ink string roller and heavy roller coating should be promptly repaired if worn; adjust the pH of the dampening solution or replace the ink.
Ten, floating dirty - the printing surface as a whole irregular light-colored dirt and whitening reasons: blanket cleaning agent into the fountain solution; too much water; ink viscosity is too high; ink is insufficient.
Treatment method: Replace with a clean fountain solution; reduce the speed of the water supply motor to reduce the amount of water; reduce the viscosity of the ink with a reducing agent; increase the speed of the ink supply motor and increase the ink supply.
Eleven, take the paper loose - paper and paper folding machine between the reasons for paper slack: roll paper power is too low; rubber blanket lining too thick; blanket paper powder accumulation; folding machine pull paper roll pressure Low; The cutter roller (RTF roller) and the platen roller on the folding triangle are set incorrectly.
Processing method: by adjusting the spring or air pressure to increase the roll paper force; change the blanket lining thickness; scrub rub leather cloth; adjust the pull paper roll pressure and the pressure of the paper cutting roller and pressure roller until the correct paper.
12. Reasons for paper break: bad roll paper force or brake setting; excess amount of fountain solution; insufficient roll paper force; abnormality of the guide roller's parallelism.
Treatment method: Change the force of the web by adjusting the relevant elements, change the braking effect of the brake; reduce the amount of water; check the parallelism of the paper guide roller; replace the web.
XIII. Causes of paper creases: The blanket is dirty, damaged, slack, and the lining of the blanket cylinder is unsuitable; the amount of ink and dampening fluid is excessive; the tension of the web is too large; the parallelism of the paper guide roller is abnormal or the above There is ink and dirt; the folding machine is poorly adjusted; the web itself is defective.
Treatment methods: Scrub, tension blanket, change the thickness of its lining; reduce the amount of ink and water; reduce the roll paper force; wipe the paper guide roller, check the equality; re-adjust the folding machine; replace the web.
Although with the development of computers, many problems can be solved by computers, but the analysis and processing of printing failures also require operators to continuously accumulate experience.