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1. Problems in the level of paper machine equipment and early production Yueyang Paper Group's #3 paper machine was completed and put into operation in 1997, and the second mobile phone was imported from abroad. The paper machine has a width of 3800mm, a design speed of 800m/min, and a working speed of 540-620m/min. The sizing system has a pulse attenuator and the headbox is a floating chip type headbox. The forming section is a fourdrinier former and the press section is a four-roll, three-zone composite press. After the sheet has dried, it enters the metering size press. Immediately followed by 1 air-cushion steering and 1 infrared drying, dry after reentry. After drying, the sheet goes into a 2×2 calender and then goes into coiling. The soft roller calendered hot roller had a temperature of 160°C and a pressure of 350 kN/m. The coated pigments are dispersed and stored in DL1. The paint is prepared in a paint mixer at a certain ratio and order of addition. The mixed paint is stored in the storage tank, pumped to the coating terminal tank, the paint in the final tank is sent to the coating head through the positive displacement pump, and a small part of the coating is evenly measured on the sizing roll through the grooved metering rod. Most of the paint is screened back to the final tank, and the screened fibers and particles are discharged into the ditch. The diameter of the upper and lower sizing rollers is 1003mm. The sizing roller is a cast iron roller with a special coating material with a hardness of 15-25P&J. The line pressure between the sizing rolls is 30-60 kN/m, and the pressure between the metering rod and the sizing roll is 40-140 kPa. In the #3 machine test stage and trial production of coated paper, due to unstable operation of the paper machine, frequent failures, unsatisfactory base paper quality, defective coating formulations, and lack of experience for operators, the quality of the trial-produced LWC paper was not very high. ideal. The main problems are: the paper machine has low operating efficiency, low paper formation rate and low paper gloss.
2 Process Conditions and Product Quality By improving the quality of the base paper, improving the formulation of the coating, and improving the equipment operation rate, the operating efficiency of the paper machine has been gradually improved, and light-coated papers of 58, 60, 64, and 75 g/m2 have been successfully produced.
2.1 Production process conditions Slurry: Masson pine BKP ten poplar APMP Ten won bismuth BKP; retention system: PAM ten cationic starch dual retention system; sizing agent: AKD sizing agent, dosage 18kg/t paper; PCC or PCC talc; vehicle speed: 540m/min; coating weight: 14-19g/m2; soft roller calendering pressure: 300-340kN/m; soft roller calendering temperature: 160°C
2.2 Quality of LWC Paper Table 1 is the average of the main quality indicators of LWC paper produced by #3 machine in a certain production cycle. It can be seen from the above that the paper surface glossiness reaches more than 35%, and the printing glossiness is more than 70%. The value is 76.7%. The paper whiteness can be adjusted according to user requirements in 78%-88% ISO. Smoothness is greater than 500s, up to 800s, printing surface roughness is about 2pm, smooth and delicate paper surface, to meet the requirements of offset printing, multicolor printing, colorful, clear images, better leveling. The K&N ink absorption value is controlled reasonably. The printed surface strength of the paper is greater than 2m/s.
3 Experiences of using MSP to produce LWC paper 3.1 Coated base paper coating base paper is very important for producing high-quality LWC paper, especially for MSP production of LWC. The quality of the base paper not only refers to its physical strength, but more importantly its surface smoothness, longitudinal and transverse quantification, moisture uniformity and stability, absorbability and permeability of the base paper surface. Since MSP is a profiling coating, and the coating is applied simultaneously on both sides of a nip, the amount of coating is generally limited to 12 g/m2 per side, which means that more paint cannot be added to fill the uneven surface. The surface, so the smoothness of the base paper is very important for the uniformity of the coating and the coverage of the paint. After the process adjustment, the smoothness of the base paper increased from 6-7S to 10s. Through process improvement and enhanced management, the vertical and horizontal basis of raw paper, water fluctuations greatly reduced. Moisture and quantification of the base paper directly affect the absorption and migration of the coating on the surface of the base paper. This quantitative difference has a phenomenon of “magnification†after coating, that is, the locality with high quantification will absorb more paint, making the quantitation difference greater. During the process of decoration, due to uneven pressure and inconsistent tension, the formation of annular grooves and looseness may occur. Lateral quantification and moisture fluctuations also make the tension of the web inconsistent when entering the size press, and the web flutters or folds, resulting in uneven coating.
High-speed coating machine (1200m/min) rarely considers the absorption of the base paper when coating, because the base paper stays in the nip for a short period of time, and generally does not perform paste sizing. When the vehicle speed is 540-640m/min, the absorption of the base paper has a certain influence on the quality of the coated paper and the running performance of the coater, and the influence on the base paper of different rations and different pulp ratios is different. When the basis weight is too high, the base paper absorbs too quickly, which can cause the paint and adhesive to transfer to the inside of the paper sheet, thereby affecting the coverage and gloss of the coating. At this time, the base paper is required to have a certain water resistance. When the basis weight of the base paper is relatively low and the coating amount is relatively large, the situation is opposite. Due to the limited absorption of the base paper, the coating is difficult to form an immobilized layer on the paper surface, which easily leads to the formation of "tears". Therefore, it is very important and very complicated to coordinate the relationship between the base paper quantification, coating amount, water absorption, and paint water retention.
3.2 Coating Formulations Due to the conditions of the paper machine equipment, such as the headbox, forming, pressing, coating and calendering, the primary issue is to improve the gloss of the coated paper and the running performance of the coating operation. . It is known that the increase in gloss can be achieved by increasing the amount of coating, but factors such as the coating method, coating equipment, and the amount of paper are limited in the amount of coating. Therefore, the gloss is improved by improving the formulation. Very important. The choice of coating pigments is very critical, LWC paper coating is relatively low, should be used to cover a good stripping soil, and some mixed with a certain percentage of high-gloss porcelain clay. The particle size of porcelain clay is very important, the particle size is too large, the surface area is small, and the covering is not good, so more than 5m particles are not allowed to exist; the particle size is too small and coating coverage becomes poor. At present, the supplier is recommending a narrow size distribution of porcelain clay, which is beneficial to the gloss, opacity and printing performance of the sheet. Therefore, it is necessary to fully consider the source of ore when choosing clay. Production methods, production process control. Particle size distribution, particle shape factor (d/p), etc. Through a large number of laboratory experiments in the current test and production practices to find suitable for LWC coating of higher gloss porcelain clay. The proportion of heavy calcium, plastic pigments or hollow spheres to the performance of the coating and the cost of the coating. Both coating and running performance have an important effect. Increasing the proportion of china clay can increase the gloss of the paper surface, but the cost increases, the paint viscosity increases, and the running performance decreases. Plastic pigments or hollow spheres can significantly increase gloss and cost can be significantly increased. The key issue is to find a balance between product quality, cost, and performance of the paper machine. The carboxylated styrene-butadiene latex and the starch are all adhesives, and the former is higher in terms of cost, but the starch has a certain influence on glossiness. The use of carboxylated styrene-butadiene latex should fully consider its mechanical stability and its sensitivity to calcium ions. Choosing a lubricant with good fluidity and good mechanical stability can change the leveling properties of the coating and the cleaning and performance of drying and finishing equipment. Experience shows that it is very important to select and optimize the order of all kinds of materials according to the characteristics and interactions of various materials.
3.3 Coating and Finishing In MSP, the coating is evenly measured on the sizing roller by a grooved metering rod. The solid content and leveling index of the coating directly affect the uniformity of the metering film. The solid content of the coating is increased. The lower, or the higher the flow index, the more uniform the measured film. However, if the solid content is too low, the drying cost will increase, the coating amount will not meet the process requirements, and paper diseases such as "tears", orange peels, and streaks will occur. In the high-speed coating machine is easy to produce fog splashing, coating solid content is too high or the leveling index is low, the glue film on the sizing roller will be very uneven, directly affect the uniformity of the coating, easy to produce ring groove, hiking cloth Jun, Song Jin poor and other issues. If the solid content is too high, the grooves on the metering rod will also be blocked, resulting in uneven coating distribution and reduced coating amount. The coating applied to MSP coating is a pseudo-plastic flow. In order to flow, the network structure is broken. As the shearing force increases, more molecules are arranged in a mesh shape, and the destruction of the internal structure accelerates the flow. It is called shear thinning. In general factory practice, the low shear viscosity is used to characterize the fluidity of the coating. The data shows that the coating viscosity suitable for the winding metering rod is 600-1600mPa.S (BfOOkfield, 100r/min), due to different speeds. The rotational speed of the coating material feeding pump is different. The pressure between the pressure measuring rod and the sizing roller in the sizing roller is different, and the viscosity of the material suitable for the specific machine is different.
By controlling the amount of auxiliary adhesive, water retention, and poor water retention, the adhesive easily migrates to the base paper, reduces the gloss of the paper, and also results in the formation of “tearsâ€. Therefore, the viscosity of the coating must be measured and controlled and should remain relatively stable. The amount of coating increases and the gloss of the sheet increases. However, as the coating amount increases, the breakage frequency of the coater increases. If the coating amount is too high, the distribution of the coating film will be uneven, the gloss of the final paper will not necessarily increase, and the difference in elasticity will increase, and the annular groove will increase. When the speed is fixed, the solid content of the coating and the base paper are constant, the means for adjusting the coating amount in the MSP device is limited, mainly adjusting the model of the measuring rod, and the pressure between the measuring rod and the sizing roller can be adjusted during the fine adjustment. In the actual production of #3 machine, the amount of coating is controlled reasonably, which not only satisfies the customer's requirements on the quality, especially glossiness and smoothness, but also ensures the better running efficiency of the paper machine.
The hardness of the sizing roll, the quality of the coating material, and the wettability are another important factors affecting the quality of the MSP coating. When using MSP for surface sizing, the sizing roll should have a low P&J value and a high hardness. When applying MSP to coating, the sizing roll should have a large P&J value and a low hardness. When the hardness is small, under certain pressure, a “boot†is formed between the two rollers, and the pressure change is relatively gentle, which is favorable for uniform transfer of the coating material to the paper surface and improvement of the transfer rate of the coating. The hardness of the sizing roller depends on the speed and operation method. Coating properties and other factors. It is found in actual production that when the coating film on the sizing roller is unevenly distributed, the quality of the normal operation and paper forming of the coating machine can hardly be guaranteed, and the sizing roller should be replaced in time. The gap between the windings on the metering rod is easy to be blocked, resulting in non-uniform metering film, frequent replacement of the metering rod, and short service life. Discussion is being made to change to a smooth rod. Soft roller calendering pressure and temperature have a significant impact on the sheet gloss and smoothness. After constant adjustment, the soft roller calendering operation is maintained to an optimal state, the temperature increased from 120 °C to 160 °C, the pressure can be Increase to 350kN/m. There is a balance between stress and tightness, and it should be properly balanced and applied.
4 Conclusion Because the application time of MSP in China is very short, and the related role of related process conditions and parameters is very complicated, the experience of engineering technicians and operators needs to be accumulated, therefore, it is necessary to effectively use this design.
Metering size press (MSP) is a roller coating machine that was successfully developed in the early 1980s. Different from the traditional double-roller coating, the size presses the coating liquid or paint through the metering element to the sizing roll to form a uniform film. When the paper passes through the two oppositely rotating squeezing roller nips, the glue The film was transferred to a paper web. Since the film is thin and uniform after a predetermined amount, the hydraulic pressure on the paper web is reduced in the nip, which reduces the breakage and improves the runnability of the paper machine. In the traditional size press, with the increase of the vehicle speed, the reflux of the turbulent pressure zone of the gum trough causes the liquid to splash, causing uneven feeding. By overcoming these drawbacks in MSP, the speed has been greatly improved. MSP can be applied to surface sizing, pigmented coating, and coating. The amount of coating can be varied from 0.5 to 12g/face to accommodate multiple paper grades. It is possible to coat one coat on both sides simultaneously, coat different coats on both sides simultaneously, and coat one surface at a time with high flexibility. This feature is very practical in special paper production. MSP still has a variety of different pulp ratios, regardless of whether the Han mechanical pulp can be applied. Because the MSP reduces the breakage of the size press, the strength of the base paper is not very high, the wall of the mechanical pulp in the base paper can be increased, and the cost of the material can be reduced. The #3 paper machine that Yueyang Paper Group put into production in 1997 installed the MSP device, which can be used for both surface sizing and coating. It has successfully produced double-glue paper, advanced color printing newsprint and high-quality light. Amount of coated paper.