Paper offset process stacking troubleshooting
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In the offset printing process, due to the sizing pore structure, smoothness, absorbency, viscoelasticity, etc. of the paper, the filler, the rubber compound and the colorant particles are rough in the papermaking process, and the appearance quality of the paper is dust, spots, fiber clusters, sand grains, etc. Poor quality, often resulting in heap failures. There are many reasons for the stacking. This article mainly talks about: paper hair removal, paper powder removal, pile paper wool on blanket, paper ash. The reasons for the paper stack are different and the solution is different.
1 paper hair removal stack
The failure of the paper pile in the offset printing process is mainly caused by the paper hair removal caused by the loose fiber structure on the paper surface. This phenomenon is mainly caused by the poor printing quality of the paper, and the failure is manifested by the paper surface of the imprinted ink being confusing. Whitening phenomenon, paper hair falling causes the surface of the printing plate and blanket to be covered with paper wool. In severe cases, it is necessary to wipe the printing plate and the rubber once for every 1000 sheets printed, which causes printing quality problems and delays the production schedule and delivery time.
Hair removal on the front and back of the paper is a technical problem in the papermaking raw materials and papermaking process. Offset printing is an indirect printing using an intermediate elastomer blanket cylinder. The printing plate transfers the image to the blanket cylinder. The blanket cylinder is transferred to the printing paper by the impression cylinder. The paper is printed during the offset printing process. It will be transferred from the surface of the blanket to the printing plate. As the number of printing increases, the paper hair remaining on the surface of the printing plate will accumulate more and more, causing the failure of the paper pile and the paper hair will stick to it. The printing plate is printed on the surface, thus affecting the quality of the printed product.
The fiber paper and paper ash on the paper have both water absorption and oil absorption. When the paper is absorbed on the printing plate, as the plate cylinder is transferred, it first hits the water roller and wets, while 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 it is attached to the printing plate and then inked by the ink roller. At this time, the wetted paper wool is oil-repellent, and although the ink is not absorbed by the four inking rollers, the whitening phenomenon occurs when the transfer to the blanket is performed.
Solution:
(1) Master the ink and water balance during offset printing, reduce the moisture of the layout and reduce the pressure of the water roller on the printing plate without the dirty version. The purpose is to minimize the wetting of the paper on the surface of the printing plate, thereby reducing the oil resistance of the paper and increasing the ink force, and try not to stick it to the plate.
(2) Increasing the fluidity and viscosity of the ink, adding a small amount of varnish, printing the product with less ink, and correspondingly increasing the pressure of the ink roller on the surface of the printing plate, the purpose of which is to pass the paper on the printing plate. When the inking roller is inked, the paper hair is pulled out and transferred to the ink roller, which is mainly accumulated on the ink roller.
In addition, adjust the printing suitability of the ink, add the varnish and auxiliary materials repeatedly and evenly. It is also possible to appropriately increase the amount of ink in the ink fountain to solve the problem.
2 paper powder off stack
The piled surface caused by the powder removal on the surface of the paper presents a honeycomb-like star. It is caused by the loss of countless fillers, rubber, pigments and auxiliary materials, which seriously affects the quality of printed products. It needs to be scrubbed once after printing about 1,000 pieces. The reason for the formation is similar to that of the paper pile, but the solution is different. The proportion of paper wool and powder is different, the paper wool area is large and light, and the powder is extremely fine and heavy.
Solution:
Increase the fluidity of the ink, add a thinner varnish in the ink, increase the viscosity and ink volume of the ink, increase the ink storage on the ink roller, and deepen the ink color of the ink. In addition, the pad can be added under the printing plate. The thickness of the paper increases the printing pressure.
3 pile of paper wool and paper ash on the blanket
Mainly due to the manufacturing process of the paper, the paper may be loosened and fluffed during the printing process, and accumulated on the blanket, which affects the ink dot of the imprinted ink, the correct transmission of the text, and the paper ash and paper powder on the paper. It will pass through the rubber and plate cylinder and pass through the ink roller to the inside of the ink fountain slot, thus affecting the transmission of the ink path. When the paper is seriously damaged, the paper is printed in the final ink fountain, which is paper ash, paper wool and paper powder. At this time, the amount of ink is opened to the maximum, and the ink color of the imprint is also light and revealing. When 1 000 sheets of paper are printed on the blanket, it is necessary to scrub the blanket.
Solution
(1) Wash the blanket with diligence.
(2) Before printing the paper, apply a white oil and water to make up for the lack of powder removal. White oil is a white translucent emulsion. It can dilute the ink color, reduce the viscosity of the ink, and evenly match the color. It is composed of magnesium carbonate, stearic acid, water, dry vegetable oil, etc. It is mainly used for setting white oil to reduce the phenomenon of powder removal and pulling of paper.
(3) Add a small amount of debonding agent to the ink. Do not add the smooth paper with good smoothness. Do not overdo it. The dosage should not exceed 3%.
(4) Add 0.05mm thick liner paper to the blanket cylinder, or adjust the center distance to increase the printing pressure.