In the offset printing process, due to the sizing pore structure, smoothness, absorbency, viscoelasticity, etc. of the paper, the fillers, glues, and pigment particles are rough in the papermaking process. The appearance quality of the paper is dust, spots, fiber clusters, sand particles, etc The quality is poor, and stack failures often occur.
The main reasons for stacking are: paper hair removal, paper powder removal, paper pile pile on the blanket, and paper dust. The reasons for paper stacking are different, and the solutions are also different.
1. Paper hair removal pile
The fault of paper piles in the offset printing process is mainly caused by the depilation of the paper caused by the loose fiber structure on the surface of the paper. This phenomenon is mainly due to the poor printing quality of the paper. The fault surface is the imprinted ink surface and the paper is chaotic. The whitening phenomenon, the paper flakes off the surface of the printing plate and the blanket are covered with paper wool. In serious cases, the printing plate and the rubber need to be scrubbed every 1000 prints, which causes printing quality problems and delays the production schedule and delivery time.
The dehairing of the front and back sides of the paper is a technical problem in the papermaking raw materials and the papermaking process. Offset printing is indirect printing using an intermediate elastomer rubber cylinder. The printing plate transfers the graphics to the rubber cylinder. The rubber cylinder is transferred to the rubber cylinder under the action of the impression cylinder. A printing process on printed paper. In the offset printing process, paper wool will be transferred from the surface of the blanket to the printing plate. As the number of printing increases, the amount of paper wool remaining on the surface of the printing plate will also accumulate. This causes paper wool stacking failures, and these paper wool will stick to the printing surface of the printing plate, which will affect the printing quality.
The fiber paper wool and paper dust on the paper have both water absorption and oil absorption. After the paper wool is adsorbed on the printing plate text, as the printing plate cylinder transfers, it first encounters the water roller wet, and the water roller is There is a certain pressure on the printing plate. After the paper wool is wetted and pressurized by the water roller, most of the paper clings to the graphic of the printing plate, and then the ink roller injects the ink. At this time, the paper wool after wetting has oil resistance. Although the ink is not absorbed by the four inking rollers, it will appear white when transferred to the rubber stamp.
Solution:
(1) Master the balance of water and ink during offset printing. Under the premise of dirty cloth, reduce the moisture of the plate surface and reduce the pressure of the water roller on the plate surface. The purpose is to make the paper wool on the surface of the printing plate reduce wetting as much as possible, so as to reduce the oil resistance of the paper wool and increase the inking force, and try not to make it close to the plate surface.
(2) Increase the fluidity and viscosity of the ink, add a small amount of ink to adjust the ink, print the product with less ink, and increase the pressure of the inking roller on the surface of the printing plate, the purpose is to pass the paper wool on the printing plate When the inking roller is inking, the paper wool is pulled out and transferred to the inking roller, mainly accumulating on the inking roller.
In addition, adjust the printing adaptability of the ink, add the ink adjustment oil, and the auxiliary materials must be stirred repeatedly. The problem can also be solved by appropriately increasing the ink delivery volume of the ink fountain.
Second, the paper powder powder pile
The piled plates caused by de-powdering on the surface of the paper appear honeycomb gypsophila, caused by the shedding of countless fillers, glues, pigments, and auxiliary materials, which seriously affects the quality of printed products. It takes one scrubbing plate once to print about 1000 sheets The reason for this is similar to that of paper piles, but the solutions are different. The specific gravity of paper wool and powder is different. The large area of ​​paper wool is light and the powder is extremely fine and heavy.
Solution:
Increase the fluidity of the ink, add a relatively thinner ink to the ink, increase the viscosity of the ink and the amount of ink delivery, increase the amount of ink stored on the ink roller, and deepen the color of the blotting ink. In addition, you can add a pad under the printing plate The thickness of the paper increases the printing pressure.
3. Pile of paper wool on the blanket
Paper gray is mainly due to the manufacturing process of petroleum paper. During the printing process, the paper may be powdered and fluffed, and it will accumulate on the blanket, which affects the correct transmission of the dots and graphics of the printed ink. The paper dust and paper on the paper The powder will pass through the rubber and plate cylinder and pass through the ink roller to the ink fountain tank, which will affect the transmission of the ink path. When the paper is heavily powdered, the ink will be printed in the final ink fountain. At this time, the amount of paper powder is maximized, and the color of the printed ink is also light and bare. After printing 1,000 sheets of paper and sticking it to the blanket, the blanket needs to be scrubbed.
Solution:
(1) Wash the blanket frequently.
(2) Before printing on the paper, overprint a layer of white oil and water to make up for the lack of powder and hair loss (white oil is a white translucent emulsion, use it to dilute the ink color, can reduce the viscosity of the ink, uniform color matching It is composed of magnesium carbonate, stearic acid, water, dry vegetable oil, etc. It is mainly used as a white oil primer to reduce the de-powdering and drawing of paper.
(3) Add a small amount of debonding agent to the ink. Do not add or overdose coated paper with good smoothness. The dosage should not exceed 3%.
(4) Add 0.05mm thick liner paper to the rubber cylinder, or adjust the center distance to increase the printing pressure.
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