What are the reasons for non stick paper and moisture regain of gypsum board

                    What are the reasons for non stick paper and moisture regain of gypsum board

1、 The bonding between the face protection paper and the gypsum core is poor, resulting in the problem of bare board core or local non sticking paper. These problems are related to the production process of face paper, raw material quality and drying. First of all, the gray value of the air injection degree of the paper is too high, and the water absorption is too high or too low, which is easy to cause the rapid loss of water and lead to poor knot; Secondly, the grade of gypsum in raw materials is too low, there are many impurities, or the content of harmful impurities such as K and Na is too high, which affects the bonding between paper and gypsum core. Third, the setting time of building gypsum is too slow, and it fails to set completely or has false setting before entering the drying area, resulting in the incomplete hydration of building gypsum, which makes the dried board out of paper. Fourth, the molding and drying speed cannot be adjusted in time with the fluctuation of the face paper or slurry, resulting in the disharmony between the air permeability, water absorption and drying speed of the face paper, and the disharmony between the setting time of the gypsum slurry and the molding speed, resulting in the non bonding between the paper and the gypsum core or the over burning of the plate. Fifth, too thin slurry, uneven foam, dry or excessive or too concentrated in the board will cause the poor bonding of paper and core. 2、 Uneven phenomena such as ripple and groove on the plate surface. This kind of problem is related to the index and process control of paper. First, the paper factor. The banner quantity, uneven moisture and uneven air permeability of the face protection paper make the paper different in tightness, thickness and water absorption. In places with large moisture, the wet expansion is small, and in places with small moisture, the wet expansion is large, and the shrinkage is serious in the dry area, while in places with less surrounding moisture, the dry shrinkage is small, which leads to inconsistent expansion and contraction of the paper, resulting in ripples or grooves. Second, the problem of process equipment. If the flatness of the forming platform is not enough or the adjustment is not in place, it can also cause uneven plate surface. The problems caused by this reason are concentrated and easy to find, but the improvement of plate surface flatness must be realized through the improvement of process equipment. Third, the fluctuation of material properties and slurry is also one of the important reasons for uneven board surface. Due to the fluctuation of raw materials and additional materials, as well as the fluctuation caused by the pulverizing process, it is inevitable that the setting time, weight rise and other indicators of powder and slurry will change to some extent. However, if the fluctuation is too frequent or large, it will make the process of subsequent processes difficult to adjust and control in time, and can also lead to adverse phenomena such as plate surface grooves. 3、 Paper rubbing on the plate surface. Paper rubbing on the surface of the plate not only affects the appearance quality of the plate, but also has an adverse impact on the internal quality indexes such as the strength of the plate to a certain extent, which can not be ignored. The main influencing factor of paper rubbing on the surface of plate is face paper. The bonding force between the layers of the protective paper is poor and the water content of the paper is too high. In the process of forming and absorbing water, the bonding force between the layers of the paper will be further reduced. In the process of relative movement between the plate and the equipment and between the plates, the paper rubbing phenomenon will occur due to mutual friction. In serious cases, the paper balls produced by the paper rubbing will scratch the surface of the plate and cause serious quality problems such as easy fracture. Therefore, in the production process of paper faced gypsum board, we should try to choose face protection paper with stable indexes such as moisture and water absorption. 4、 Low strength, easy to break and crack. The broken plate is mainly characterized by transverse fracture. The bad operation during lifting the plate is eliminated. The main influencing factor of the broken plate should consider the longitudinal strength of the protective paper. The strength of face protection paper has an important relationship with its quantitative and other indicators. At present, with the development and competition of gypsum board and face protection paper industry, the quantitative of face protection paper is reduced from 230g / ㎡ ~ 250G / ㎡ to 180g / ㎡ ~ 210g / ㎡. The reduction of quantitative will inevitably lead to the reduction of strength and the change of other indicators. Gypsum is the main raw material of gypsum board. Its grade and physical properties are another important factor affecting the strength of gypsum board. For natural gypsum, the grade is generally required to be no less than 75%, and the 2H flexural strength of building gypsum is no less than 1.8MPa, which is the most basic requirement to ensure the strength of paper gypsum board In addition, the impurities and acid-base properties of gypsum will also have an adverse impact on the strength of gypsum. In the production of paper gypsum board, glass fiber is often used as reinforcement to improve the strength of the board Therefore, if the reinforcing fiber is not added enough in production, the strength of the plate will be reduced and the plate is easy to break At the same time, if the material of reinforcing fiber fails to meet the requirements, its reinforcing effect will be greatly reduced If glass fiber is used as reinforcing material, alkali free fiber is generally used, which has certain flexibility and high strength. If alkali containing or even high alkali fiber is used, due to the brittle material and low strength of alkali containing fiber, it will not play its due reinforcing role, resulting in the brittle fracture of the plate. It is also a cause that can not be ignored that the plate is easy to break due to the scratch on the plate surface In the production process, if there are hard particles such as rust and sand left on the plate surface, it is very easy to scratch the surface of the protective paper of the plate during the relative movement of the plate, so that the plate is easy to break along the scratch Such problems generally do not occur in large quantities. Careful observation is easy to find and remove. Plate cracking mainly occurs along the longitudinal direction of the plate In addition to the low transverse strength and gypsum strength of the protective paper, another important reason is the edge warping of the plate, which makes the plate crack at the stress concentration when the plate is pressed during storage and transportation There are many reasons for edge warping of plates If the expansion rate of face paper is large or the shrinkage rate of upper and lower paper is inconsistent; Too thin slurry or unstable material property will lead to unstable process control and poor operability, which will lead to plate edge warping. Therefore, in order to improve the strength of the board and reduce the problems such as fracture and crack, we should try our best to choose the protective paper and high-grade gypsum with strength, air injection and water content suitable for the production requirements; Strictly control the indexes of powder processing and molding process. 5、 The surface of the plate is bubbling and bubbling. Blistering and bulging on the surface of gypsum board are mainly caused by too thin slurry in production, improper use of foaming agent, poor gassing performance of face protection paper and other reasons. Sometimes the diameter of bubbles is less than 1cm, but almost all over the board. This is mainly because gypsum slurry is too thin or foaming agent has poor foam stability and large bubbles, so that a large number of bubbles are concentrated on the surface to form large bubbles, especially for a period of time. Some bubbles are larger and sometimes more regular, such as a straight line along the edge; In some cases, the number of bubbles is small, and it is difficult to determine its regularity, which is related to the low and uneven air injection of face paper and the low adhesion between layers. The air permeability of the paper is low, so that the water in it is not easy to evaporate, and the interlayer adhesion of the face protection paper is low. There is poor local bonding or paper delamination in the process of production or storage, which leads to the bulging of the plate surface, which is seriously manifested as non sticking in a large area. 6、 The plate is easy to deform. With the development and competition of gypsum board industry and related industries, the unit quality of face paper and gypsum board has been reduced to a certain extent. First of all, the quantitative reduction of the face protection paper and the large shrinkage of the paper make the tightness of the face protection paper insufficient, resulting in the insufficient stiffness of the paper gypsum board, and the machine is easy to deform after moisture absorption; Secondly, if the air permeability of the face paper is low, the air permeability is slow and the drying is slow, the deflection of the dried plate will be large after moisture absorption; In addition, in the forming process, if the slurry consistency is adjusted depending on the water consumption, the water consumption will be large, and a large gap will be generated in the plate after drying and evaporation. The plate is too light or soft, and the deformation deflection will increase. 7、 The production process is interrupted.