The fluffing and de-powdering of the paper is caused by the fact that the fibers on the surface are not strong enough and dense. In the printing process, when the paper and the rubber are peeled off, a certain pulling force is formed between them due to the mutual adhesion. If the fiber structure of the paper is strong and dense, then there will be no hair loss. On the contrary, it is easy to pull down the fibers on the surface of the paper and cause depilation and fluff.
In the printing process, the offset press is generally operated at a high speed of 6000 sheets / hour to 10000 sheets / hour, and the transfer of the pictures on the printing plate is completed in a very short instant. In this brief moment, there is an extremely complex mechanical force interaction between the ink on the printing plate and the paper. The speed of the offset press is very fast, and the influence of the inertial force is relatively increased accordingly. To make the ink transfer to the paper ideally, the paper must have a certain surface strength.
Paper fluffing can cause dirty plates, directly destroying the sharpness of the patterns on the printed sheets and reducing the printing quality.
Paper is made up of raw materials such as fiber, lignin, resin, filler, rubber and color. In addition to the low surface strength of the paper, the causes of de-powdering and fluffing of the paper are due to the improper selection of fillers and rubber compounds. Incomplete calendering is also the cause. In addition, it also occurs in the case of high-speed printing.
Paper fluffing and powdering failures are generally caused by poor paper product quality. In addition to recommending that paper manufacturers improve the quality of their products and require returns as soon as possible, operators of printing companies can also take corresponding remedial measures according to the specific conditions of the printed paper:
1) Due to the raw materials and manufacturing process, the paper may be powdered and fluffed during the printing process and accumulate on the surface of the blanket, thereby affecting the correct transmission of the dots. In serious cases, the blanket must be scrubbed every 1000 sheets or so. Otherwise, the blanket is covered with de-powder and lint, and the gloss of the printed product will obviously decrease. Under certain conditions, overprint a white ink and water on the surface of the paper. Generally, the rubber cloth should be scrubbed.
2) Properly adjust the viscosity of the ink used, add an appropriate amount of adhesive and diluent to the ink, reduce the viscosity of the ink, and thereby improve the effect of the ink's adhesion on the paper. Because the viscosity of the ink is too large, it is easy to make the paper fluff and powder.
3) Adjust the printing pressure so that the embossing force between the rubber cylinder and the embossing cylinder is properly reduced. Or choose the appropriate printing speed, it is better to reduce the speed appropriately. In this way, after stamping, the peeling force between the blanket and the paper can be reduced.
4) Rubber blankets have been used for a long time, producing vulcanization reaction, or exposed to light, heat, abrasion and aging, especially the hot summer weather. The old blankets are easy to be sticky and cause hair loss and powder removal. At this time, a layer of sulfur powder can be coated on the blanket. If it still doesn't work, you have to replace it with a new blanket.
5) For paper that is prone to linting and de-powdering, such as offset paper, letterpress paper, writing paper, etc., be sure to dry the paper before printing, and remove the paper dust, paper powder, paper dust and dust on the surface of the paper Remove paper, etc.
The difference between offset printing and other printing methods is that “water†is used for offset printing, and emulsification of ink and expansion and contraction of paper often occur in “waterâ€. De-powdering and fluffing of paper are also the same as “water†for offset printing. Direct relationship.
The paper used for offset printing generally needs to be filled. In order to increase the retention rate of the added filler in the paper, the surface strength and gloss of the paper should be increased. At the same time, the paper should have a certain degree of sizing, otherwise the paper Exposure to moisture will cause the soft cotton to become weak, resulting in undesirable phenomena such as filler shedding.
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