Deformation problems and solutions of the hottest

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Deformation problems and solutions of coated white paperboard Abstract: This paper introduces the deformation problems of flat paper in the production process of coated white paperboard, analyzes the causes of common lotus leaf deformation and warpage problems, and puts forward corresponding solutions

key words: coated white paperboard; Deformation; Ruffle edge; Warping

Shandong Sun Paper Co., Ltd. has three advanced multi cylinder paperboard machines, and the output of coated white paperboard is 300000 t/A. Among them, one paper machine is a round multi cylinder paper machine, with 6? 1500mm round cage, the pressing part is composed of one vacuum back pre pressing, two positive pressing and one light pressing. The coating is in the form of a metering bar precoating and an air knife. The finishing after coating is composed of a four roll hard calendering and a gloss drying cylinder

at the early stage of the production of coated white paperboard, the end face of the flat paper appeared wave deformation (commonly known as lotus leaf edge paper disease) and the warpage of the front side, which caused the paper not to enter the printing machine, caused losses to the printing factory and customers, and also affected the further opening of the product market. Among them, the lotus leaf edge paper disease is strongly reflected by customers in the south

in view of the deformation and warpage of the lotus leaf, sun paper set up a research team to track the whole production process and refer to relevant materials. Finally, the cause of paper disease was found out and the system was improved

1 Ruffle edge paper disease

1.1 cause analysis

due to the fact that the sun paper industry uses a circular shaper to copy coated white paperboard, the forming and pressing wool cloth are not washed thoroughly, the longitudinal and transverse quantitative difference of the finished paper, the moisture deviation is large, and the moisture control of the off machine is unreasonable, which leads to the moisture absorption or moisture release reaction in the process of cutting, transportation and use of the printing plant after the paper is off the machine, The fibrous tissue elongates or contracts at the same time. Due to the imbalance of fiber tissue, the quantitative and moisture content are not balanced, resulting in the inconsistent change proportion of each part of the paper, resulting in paper diseases such as lotus leaf edges. According to experience, if the moisture control under the machine is unreasonable, for example, when the moisture under the machine is low, the paper will be deformed due to long-term moisture absorption, among which the lotus leaf edge deformation problem is the most serious

1.2 solutions

sun paper has made corresponding rectification for the existing lotus leaf edge paper disease

1.2.1 reasonably control the moisture of the paper under the machine. First, determine the equilibrium moisture of various papers through experiments, simulate the ambient temperature and humidity of the printing plant, store various quantitative paper samples for a certain period of time, and then detect their equilibrium moisture; Then refer to the balanced moisture to formulate the next machine moisture. In the past, due to one-sided pursuit of stiffness index, the moisture control of the machine was low, resulting in moisture absorption and deformation in the subsequent process. Taking the 250 g/m2 product as an example, after increasing the moisture content of the under machine of the paper sheet from the original 6.5% to 7.5%, the deformation problem of the ruffle edge is significantly reduced

1.2.2 strictly control the vertical and horizontal quantitative difference and moisture difference. Paper is one of the few exhibitions in Zhejiang province that won this honor. The large vertical and horizontal quantitative difference and moisture difference is another key reason for the moisture absorption and deformation of paper. Through the installation of moisture quantitative microcomputer control system, which can also realize the stretching, tightening, bending, shearing and other types of experiments on different materials or products according to other standards, the original offline detection The manual adjustment mode reduces the whole quantitative difference and moisture difference of the finished paper

1.2.3 strengthen the washing of forming and pressing wool cloth. Incomplete washing of wool cloth will increase the quantitative difference and moisture difference in vertical and horizontal directions. Therefore, sun paper changed the original atmospheric water washing to high-pressure water washing, and increased the washing pressure of pressing wool cloth from 1.18 MPa to u 2.45 MPa, strengthening the washing with wool cloth

1.2.4 the tension drying method is adopted to appropriately increase the drying tension of the dryer and reduce the shrinkage deformation of the paper during the drying process

1.2.5 control the appropriate beating degree to avoid the high beating degree of the pulp and the great difference in the beating degree of the adjacent pulp layers of the paper, and strengthen the washing and sizing of the pulp

2 warpage of coated white paperboard

2.1 cause analysis

warpage of paperboard is also an important factor affecting product quality. In production, it is common that the front longitudinal travel of the experimental machine is limited (the travel of the experimental machine when installing standard fixtures) to warpage (MDTs, that is, machine derivationtop side warpage). The root cause of warpage is the uneven shrinkage of fibers during drying. It mainly includes two aspects: one is due to the uneven composition of paperboard "Z" structural fibers; The second is caused by the sequence of paper drying process. For the first point, bleached commercial wood pulp, deinked pulp of old newspapers, and mixed waste pulp are used for the surface, lining, core, and bottom pulp of coated white paper, which are also coated with different components. If the components of each layer are different and the beating degree is different, there will be inconsistent shrinkage during the drying process. For the second point, according to w.gallay's theory, the paper page always warps towards the inner side of the last dry side. The drying of the coated white paperboard base paper after coating focuses on the drying of the coating (i.e. the front side of the paperboard), so the paper page will warp towards the front (MDTP warping)

2.2 solutions

for the slight warpage of coated white paperboard, the printing factory can fold the paper back and then print to reduce the printing obstacles. But this is not the fundamental solution. In the production of paperboard, the following measures can be taken to solve it

2.2.1 strengthen the surface back sizing, that is, use the drying shrinkage of the surface back sizing layer to pull the warpage to the back, but the position of the back sizing is not easy to determine, and the effect is poor if it is installed in the position of the traditional surface sizing machine. It is best to install it at the second calender after coating to adjust warpage, but it will cause the paper to dry imperfectly when it is off the machine, resulting in poor stiffness and paper ruffles. According to the author's experience, the back sizing is most suitable to be installed in the middle of the coating process. But many paper mills do not have the conditions in this regard. Therefore, the general manufacturers install it in the form of a water scraper at the position of the base paper calender, which can basically play a role. In addition, increasing the back sizing concentration and increasing the proportion of PVA is conducive to adjusting the warpage of coated white board

2.2.2 adjust the temperature difference between the upper and lower drying cylinders, which is also an effective way adopted by many coated white board factories, that is, in the post drying stage, appropriately reduce the temperature of the upper drying cylinder to form a certain temperature difference with the lower drying cylinder, so that the paper can be properly warped downward before coating. Many manufacturers have considered this factor in advance at the design stage of the paper machine, and separately controlled the total steam pressure meter of the upper and lower drying cylinders. However, reducing the temperature of the single row dryer will seriously affect the drying capacity of the paper machine and cause a waste of resources

2.2.3 increase the tension of the dry blanket. Adopting tension drying in the drying section is conducive to reducing warpage, because increasing the tension of the dry blanket, reducing the traction, and then applying tension drying is conducive to reducing the shrinkage of the paper at the outlet of the dryer

2.2.4 adjust the beating degree of the pulp and the quantity of each layer of paper within the allowable range, appropriately reduce the beating degree of the surface pulp, improve the beating degree of the bottom pulp, and make the shrinkage of the bottom fiber larger than that of the surface layer, which is conducive to adjusting the warpage towards the front. Similarly, it can also reduce the quantity of surface slurry and appropriately increase the quantity of bottom slurry

2.2.5 increasing the thickness of the paperboard and increasing the thickness of the paperboard as much as possible is conducive to eliminating warpage, increasing the tightness of the paper, increasing the combination between fibers, and warpage is easy to occur in the thickness direction (z direction)

2.2.6 improving the dryness of the paper entering the drying section, improving the dryness of the paper entering the drying section and avoiding the rapid drying after coating are conducive to solving the problem of front warpage

3 conclusion

by taking the above improvement measures, sun paper has effectively solved the deformation problems such as ruffles and warps caused by coating white paperboard, improved the product quality of the company and increased economic benefits

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