In the offset printing process, due to the paper's sizing pore structure, smoothness, absorption, viscoelasticity, etc., the paper is filled with filler, rubber, and pigment particles in the papermaking process. The appearance quality of the paper includes dust, spots, fiber clusters, sand particles, etc. The quality is poor and stack failures often occur. There are many reasons for stacking, this article mainly talks about: paper hair removal, paper stripping, piles of blankets, paper dust. The reasons for paper stacking are different and the solution is different.
1 Paper depilation
During the offset printing process, the occurrence of paper stacking failures was mainly caused by the paper unhairing caused by loose fiber structure on the surface of the paper. This phenomenon was mainly due to the poor printing quality of the paper. The failure was manifested as the imprinted ink surface was confusing like paper. With the phenomenon of graying, the surface of the printing plate and rubber blanket is covered with paper with the loss of paper wool. In case of severe printing, the printing plate and the eraser need to be scrubbed once for every 1,000 sheets printed, thereby causing print quality problems and delaying the production schedule and delivery time.
The dehairing on the front and back of the paper is a technical problem in the process of making paper and raw materials. Offset printing is indirect printing using an intermediate elastomer rubber blanket. The printing plate transfers the graphic image to the blanket cylinder. The blanket cylinder transfers a printing process to the printing paper under the effect of the impression cylinder. The paper is printed during the offset printing process. It will transfer from the surface of the blanket to the printing plate. As the number of printing increases, the pile of paper that stays on the surface of the printing plate will accumulate more and more, resulting in the failure of the stacking of the paper, which will stick to the Plates are printed on the surface of the blot, thus affecting the quality of the printed product.
The paper fiber paper and paper ash on paper have both water absorption and oil absorption. When the printing plate absorbs the paper, after the plate cylinder transfers, it first encounters the water roller and the water roller is wet. There is a certain pressure on the printing plate. After the paper wool is wetted and pressed by the water roller, most of the printings are closely attached to the printing plate graphic, and then ink is applied by the ink roller. At this time, the moistened paper has oil repellency. Although the ink is absorbed by the four ink rollers, the ink cannot be absorbed, and the ink is transferred to the blanket and appears white.
(1) Grasp the balance of water and ink during offset printing, reduce the moisture on the plate and reduce the pressure of the water roller on the plate layout under the premise of no dirty plate. The purpose is to minimize the wetting of the paper on the surface of the printing plate so as to reduce the oil resistance of the paper and increase the ink strength, and try not to cling to the surface of the plate.
(2) Increase the fluidity and viscosity of the ink, add a small amount of varnish, print the product with less ink, and increase the pressure of the ink roller on the plate surface. The purpose is to pass the paper on the plate. When the ink roller is inked, the paper is pulled out and transferred to the ink roller, mainly accumulating on the ink roller.
In addition, adjust the printability of the ink, add the ink and auxiliary materials to be mixed repeatedly. You can also increase the amount of ink in the ink fountain to solve the problem.
2 Paper de-stacking
The surface of the paper produced by the deinking of the paper surface presents a honeycomb-like starry sky, which is caused by the shedding of countless fillers, rubber materials, color materials, and auxiliary materials. This seriously affects the quality of the printed product, and printing of about 1,000 sheets requires scrubbing a printing plate once. The reason for this is similar to the formation of paper piles, but there are differences in the solutions. The proportions of paper and silty are different, and the paper area is light and heavy, and the powder is very fine and heavy.
Increase the fluidity of the ink, add more dilute ink in the ink, increase the viscosity of the ink and the amount of ink, increase the ink storage on the ink roller, make the ink deeper, and increase the pad below the plate. The thickness of the paper increases the printing pressure.
3 Blanket on pile of paper, paper gray
Mainly due to the paper in the manufacturing process reasons, in the printing process may appear in the paper off the powder off hair, and piled up on the blanket, affecting the blotted ink network, the correct transmission of images, paper on the paper gray, paper powder It passes through the rubber and plate cylinders and passes through the ink roller to the ink tank groove, affecting the transmission of the ink path. It encounters the paper with heavy powder. The ink is printed in the ink fountain, paper, and paper powder. At this time, the amount of ink reached the maximum, and the ink color of the ink was also pale and light. At the time when 1,000 sheets of white paper were printed on the blanket, it was necessary to scrub the blanket.
(1) Always wash the blanket.
(2) Before printing the paper, overprint a white oil and clear water, make up for the lack of paper off powder (white oil is a white translucent emulsion, use it to dilute the ink, can reduce the viscosity of the ink, color uniformity Consisting of magnesium carbonate, stearic acid, water, dry vegetable oil, etc. It is mainly used to coat white oil, reduce paper de-powdering and fluffing.)
(3) Add a small amount of retreating agent to the ink. Do not add smooth and smooth coated paper. Do not overdo it. The amount should not exceed 3%.
(4) Add 0.05mm thick liner paper to the blanket cylinder, or adjust the center distance to increase printing pressure.
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