Fifteen common faults and solutions for offset printing are worth collecting!
1. Ink fountain deinking phenomenon: Ink cannot be transferred from the ink fountain to the ink roller, the ink supply is reduced or interrupted, and the color of the printed product becomes lighter.
Cause: The ink is poor in fluidity, the ink is too short (such as butter), the ink viscosity is small, the thixotropy is large, and a colloid is formed when it is not agitated.
Solution: Stir the ink in the ink fountain frequently, add the ink with high viscosity and good fluidity. Add high viscosity resin oil to improve the fluidity of the ink.
Second, the phenomenon of stacking rubber: the ink accumulates on the blanket and cannot be transferred to the paper.
Reasons: The viscosity of the ink is small, the water resistance is poor, the pigment and filler in the ink are too much, and the fineness is not enough. The peeling of paper powder mixed into the ink makes the ink shorter, and the amount of the anti-sticking agent and the detackifier is too large.
Solution: reduce the content of fountain solution as much as possible, add ink with high viscosity and good water resistance, reduce the amount of anti-sticking agent and degumming agent, and replace the paper.
3. Phenomenon of stacking rollers: The ink on the rollers cannot be transferred.
Reason: Poor water resistance of ink or too large amount of printing syrup causes ink emulsification, ink ink is too short, viscosity is low, and fluidity is poor.
Solution: reduce the amount of water or add isopropyl alcohol to improve wettability, increase volatility, and add ink with high viscosity and good fluidity.
4. Ink flying phenomenon: Ink droplets formed between the ink rollers are scattered around the machine.
Cause: The printing speed is too fast, the amount of ink is too large, and the ink layer on the ink roller is too thick. The ink is sticky, the filament head is long, and the ink roller is not properly installed or worn.
Solution: reduce the printing speed, switch to ink with high color density, reduce the amount of ink, reduce the viscosity of the ink with adhesive remover, adjust the pressure of the ink roller to make the thickness of the ink film uniform, adjust the ratchet to increase the axial movement of the ink roller To increase the amount of ink, replace the damaged ink roller.
5. Poor ink distribution: The ink color of the printed product is uneven, and the pattern is not clear.
Cause: The ink is too thick and too sticky, the ink dries on the printing plate and the ink roller, the plate cylinder liner and rubber cylinder liner are not suitable.
Solution: reduce the viscosity of the ink with ink-adjusting oil. If it dries too fast, add 525 anti-crust agent 1% ~ 3%; readjust the printing plate and blanket pad.
Sixth, pull the paper wool phenomenon: when printing, a small part of the paper wool fiber is pulled from the paper surface and accumulated on the graphic of the blanket.
Cause: The ink has high viscosity, the paper surface strength is low, the printing speed is too fast, and the pressure is too high.
Solution: reduce the printing speed, add the debonding agent to the ink to reduce the viscosity of the ink, and replace the paper with high surface strength.
7. Ring-shaped white spot phenomenon: ring-shaped white spots appear in the printed graphics.
Cause: The ink skin in the ink is mixed into the ink and attached to the printing plate blanket, and other foreign materials such as paper dust and dust are mixed into the ink.
Solution: When taking ink in the tank, do not take the ink belt into the ink, do a good job of cleaning the environment, and often clean the paper feed and paper scraps on the toilet paper device.
8. Poor overprinting phenomenon: In wet-to-wet overprinting, the ink printed later cannot be smoothly attached to the ink printed first.
Reason: The post-printed ink is too viscous than the pre-printed ink. The pre-printed ink has a slow fixation and a large amount of ink.
Solution: Change the printing color sequence. The ideal viscosity requirement should be reduced in order of overprint color; use fast-fixing ink printing, try to use overprinting printing to ensure the same amount of ink.
Nine, crystallization phenomenon: when wet to dry overprinting, the ink after printing can not be printed, even if it is barely printed, it can be easily wiped off Cause: the ink printed first dries too fast; the interval between front and back printing is too long; Too much dusting.
Solution: Reasonably control the interval time of overprinting; reduce the amount of powder sprayed in the first color; if crystallization has occurred, it can be remedyed by adding glaze once again.
Ten, powdering phenomenon: the ink is easy to wear off with a little pressure after drying.
Reasons: The initial drying of the ink surface did not completely dry; the wax content in the ink was insufficient; the amount of powder spray was too large; the viscosity of the ink was small and the water resistance was poor; the ink absorption of the paper was too strong.
Solution: Add dry oil to increase the drying speed of the ink; increase the abrasion resistance; reduce the amount of powder spraying; reduce the acidity of the potion to reduce the amount of water supply, and replace the less absorbent paper.
11. Slow drying phenomenon: The blot does not dry for 4 to 8 hours and is easily rubbed off.
Reasons: Insufficient desiccant in ink; excessive acidity of paper; excessive humidity of paper; emulsification of ink; excessive addition of wetting powder.
Solution: add a desiccant to increase the drying speed of the ink; replace the paper; pay attention to the paper not to be damp during storage, add an aqueous desiccant to the fountain solution or use a quick-drying wetting powder, adjust the PH value of the powder water, reduce wetting The amount of powder added.
Twelve, fast drying phenomenon: the viscosity of the ink increases during use, and the skin forms in the ink fountain.
Reason: Too much desiccant in the ink, the temperature in the printing workshop is too high or the humidity is too low.
Solution: Contact the printing factory, adjust the amount of desiccant; control the temperature and humidity of the workshop.
13. Floating dirt phenomenon: light color dirt is produced in non-graphic areas, because it is not dyed from the printing plate, it is easy to wipe off.
Reasons: The ink is weak and water resistance is poor. Due to the action of fountain solution, some of the ink emulsifies into the fountain solution to form an oil-in-water emulsion; the chemical substances in the paper and the soap or detergent in the wetting fluid cause the ink to emulsify .
Solution: Switch to thick emulsified ink; replace paper; adjust the composition and pH value of fountain solution.
14. Oil dirty phenomenon: There is a layer of floating dots in the non-graphic area of ​​the plate. In fact, the non-graphic area of ​​the printing plate becomes fat-sensitive, and the ink is attached to it.
Reasons: The ink is too weak, the viscosity is small, and the amount of ink is large; the ink is emulsified; the pressure of the dampening roller and blanket of the inking roller is too large, which damages the surface structure of the printing plate and oozes fat-sensitive substances from the paper.
Solution: replace the ink, adjust the ink supply, adjust the printing syrup, add isopropyl alcohol or alcohol, reduce the surface tension, adjust the ink roller pressure, and replace the paper.
15. The back side is dirty: when the printed matter just printed is stacked, the ink on the front side sticks to the back side of the printed matter on it.
Cause: Due to the slow drying of the ink, the amount of ink is too large, and the absorption of the paper is poor.
Solution: Change to fast-setting ink to reduce the amount of ink; add anti-sticking agent to the ink, spray powder on the surface, and replace the absorbent paper.
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