Improvement of the evenness of the hottest newspri

2022-08-14
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Improvement of paper evenness

"evenness" is not only an important quality index of paper, but also the basis of paper physical strength and printability. However, the paper produced with domestic equipment just lags far behind foreign products in uniformity, which makes it at a disadvantage in market competition

there are different reasons for poor uniformity, but the macro conclusion of "backward domestic equipment" is probably accepted by everyone. However, this statement does not reveal the specific reasons for the poor uniformity. Starting with the research on the "behavior of each component fiber" in the pulp, the technicians of Tianjin Jinxing paper company finally revealed that the real reason for the poor uniformity was the excessive loss of "fine fiber components" (passing the 70 mesh sieve)

the normal paper structure is the result of the balanced existence and uniform interweaving of long and short fibers and fine fibers with different components. The long fiber components form the skeleton of the preparation work before the installation of the paper sheet 1. In the "hole" of the skeleton, the fine fibers "fill" and "glue" to "homogenize and strengthen" this loose skeleton structure. Without fine fibers, the homogenization and strengthening of paper pages will be impossible

the proportion of fine fiber slurry is about 20%, but its specific surface area is times that of long fiber. A large number of "hydroxyl groups" exposed by large specific surface area play a vital role in paper properties. When the slurry is dehydrated, the strong potential formed by the small fiber group increases the "electrostatic repulsion" of the fiber, effectively resists the "flocculation" of the fiber, and improves the evenness of the papermaking. When the wet paper is dried, the small fiber groups filled in the collateral cavities are "associated" with the long fibers in the form of "adhesive" to form a "hydrogen bond", which improves the tensile strength, tear strength and galling strength of the paper, and reduces the chance of printing wool off the paper. The filling of long fiber holes with fine fibers makes the appearance of the paper uniform and delicate, the gloss soft and uniform, and the printing clarity and opacity improved

paper needs fine fibers. The loss of fine fibers will make the system out of balance, and an unbalanced system is difficult to produce high-quality products. However, there are many links that lose fine fibers in the process (such as flotation, washing, concentration, dehydration, etc.). After the loss of fine fibers, the proportion of long fiber components in the slurry is too large, its winding effect is enhanced, the system potential shifts to "the isoelectric point and the upstream and downstream are interdependent", the electrostatic repulsion between fibers is reduced, the fiber flocculation becomes serious, and the uniformity is significantly reduced. The transparent observation paper has a "cloud flower" structure, and the joint between the cloud flowers becomes the weak point of strength and transparent printing. Under the microscope, the cavity of the long fiber network without the filling of fine fibers presents a concave shape, which not only makes the paper rough, increases the difference between two sides, and has poor tightness and smoothness, but also because of the lack of the adhesive effect of fine fibers, some long fibers are free from the paper surface, which makes the printing hair loss tendency more serious. Increasing the pressing and polishing pressure can solve these problems to a certain extent, but high pressure makes the paper produce "hard smoothing" (passive smoothing) and "bright spots", and at the same time, some fibers are crushed, which instead becomes a new source of hair loss. Pressing bright spots makes the paper lose its soft and uniform luster and delicate appearance, and the opportunity of through printing is greatly increased

improving the uniformity is the basis for comprehensively improving the paper quality, and restoring the proportion balance of fibers with different components in the length of the system is the only breakthrough. Then, the key to open the breakthrough is to efficiently improve the "screening" ability of the screening system. To this end, Jinxing paper has carried out experiments aimed at improving the screening capacity of traditional screening equipment (high concentration pressure screen, rotor screen) and achieved breakthrough results. In the test, the screening equipment divides the slurry into four parts: "good slurry", "light impurities" (hot melt adhesive, plastic sheet, thermosetting ink fragments and foam particles), "fiber impurities" (fiber bundles, long fibers and OCC fibers, etc.) and "heavy impurities". The screening of impurities not only significantly improves the "evenness" and cleanliness of the good slurry, but also improves the "retention" ability of the system. Therefore, sufficient machining allowance must be left from the cutting line of the sample blank to the edge of the sample to achieve the balance of the system. Paper defects such as paper holes and translucent spots disappear. The transformation of the desander has increased the screening efficiency of heavy impurities by nearly 20 percentage points. Therefore, the evenness of the paper made on the above basis has been greatly improved. The "soft smoothness" (active smoothness) of the paper is achieved by copying under low pressure. The paper surface is clean, uniform and delicate, with soft gloss and no bright spots of reading display value. Its quality is quite close to that of foreign products

the transformation of traditional equipment with less funds has become the characteristic of the implementation of this technology. At present, this achievement is gradually transferred to production. It is not only of great significance to paper, but also of reference value to the production of other kinds of paper. Therefore, the era of producing high-grade paper with domestic equipment is coming

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