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

What are the reasons for the non adhesion and moisture regain of paper gypsum board
Shijiazhuang Jingjin Machinery Equipment Installation Co., Ltd. - Zhou Yanhui 13833456715
1、 Poor adhesion between the face protection paper and the gypsum core, resulting in exposed board core or partial non sticking of the paper. This type of problem is related to production processes such as face protection paper, raw material quality, and drying.
Firstly, if the Grille value of the paper's aeration is too high, the water absorption is too high or too low, it can easily cause rapid loss of moisture and lead to poor bonding; Secondly, the grade of gypsum in the 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. Thirdly, the setting time of building gypsum is too slow, and it fails to fully solidify or has false setting phenomenon before entering the drying area, resulting in incomplete hydration of building gypsum and causing the dried board to peel off. Fourthly, the forming and drying speed cannot be adjusted in a timely manner with the fluctuations of the protective paper or slurry, resulting in a mismatch between the breathability, water absorption, and drying speed of the protective paper, as well as a mismatch between the setting time of the gypsum slurry and the forming speed, resulting in non bonding between the paper and the gypsum core or excessive burning of the board. Fifth, too thin slurry, uneven foam, and too many or too concentrated macropores in the dried board will also cause poor adhesion of paper and core.
2、 Uneven phenomena such as surface ripples and grooves. The occurrence of such problems is related to issues such as paper specifications and process control.
Firstly, the factor of paper. The banner weight, moisture content, and breathability of face protection paper are uneven, resulting in varying degrees of elasticity, thickness, and water absorption. In areas with high moisture content, the moisture expansion is small, while in areas with low moisture content, the moisture expansion is large, causing severe shrinkage in dry areas. In areas with low moisture content, the dry shrinkage is small, resulting in inconsistent expansion and contraction of the paper, leading to ripples or grooves.
Secondly, issues with process equipment. Insufficient flatness or inadequate adjustment of the forming platform can also cause unevenness of the board surface. The problems caused by this reason are more concentrated and easy to detect, but improvement of the board surface flatness must be achieved through the improvement of process equipment.
Thirdly, fluctuations in material properties and slurry are also important reasons for uneven board surfaces. Due to fluctuations in raw materials and additional materials, as well as fluctuations caused by the milling process, it is inevitable that certain changes occur in the setting time, weight rise, and other indicators of the powder and slurry. However, if the fluctuations are too frequent or significant, it will make it difficult to adjust and control the subsequent process in a timely manner, and can also cause adverse phenomena such as board grooves.
3、 The phenomenon of paper rubbing on the surface of the board.
Paper rubbing on the surface of the board not only affects the appearance quality of the board, but also has a negative impact on the internal quality indicators such as strength to a certain extent, which cannot be ignored. The main influencing factor of paper rubbing on the surface of the board is the protective paper.
The interlayer adhesion of face protection paper is poor, and the moisture content of the paper is too high. During the forming and water absorption process, the interlayer adhesion of the paper will further decrease. During the relative movement between the board and the equipment, there will be friction and paper rubbing phenomenon between the boards. In severe cases, the paper balls produced by paper rubbing can scratch the surface of the board, leading to serious quality problems such as easy fracture. Therefore, in the production process of paper-based gypsum board, it is advisable to choose face protection paper with stable indicators such as moisture content and water absorption.
4、 Low strength, easy to break and crack plates.
The main manifestation of plate breakage is lateral fracture, which eliminates the phenomenon of poor operation during plate lifting. The main influencing factor for plate breakage should consider the longitudinal strength of the protective paper. The strength of face protection paper is closely related to its quantitative indicators. Currently, with the development and competition of the gypsum board and face protection paper industry, the quantitative level of face protection paper has decreased from 230g/㎡ to 250g/㎡ to 180g/㎡ to 210g/㎡. The decrease in quantitative level inevitably leads to a decrease in strength and changes in other indicators. Gypsum, as the main raw material for paper gypsum board, its grade and physical properties are another important factor affecting the strength of paper gypsum board. For natural gypsum, it is generally required that its grade is not less than 75%, and the 2-hour flexural strength of building gypsum is not less than 1.8Mpa, which is the most basic requirement to ensure the strength of paper gypsum board. In addition, impurities and acid-base properties of gypsum can also have adverse effects on the strength of gypsum. In the production of paper gypsum board, glass fiber and other reinforcing materials are often used to improve the strength of the board. Therefore, if the reinforcing fiber is not added enough in production, it will reduce the strength of the board and cause it to break easily. At the same time, if the material of the reinforcing fiber does not meet the requirements, its reinforcing effect will be greatly reduced If glass fiber is used as reinforcement material, alkali free fibers are generally used, which have a certain degree of flexibility and high strength. If alkali containing or even high alkali fibers are used, due to the brittleness and low strength of the alkali containing fiber material, they cannot play the expected reinforcement effect, resulting in the board being prone to brittle fracture. Due to scratches on the surface of the board, it is also a cause that cannot be ignored that the board is easily broken. During the production process, if there are hard particles such as rust and sand left on the board, during the relative movement of the board, it is very easy to cause scratches on the surface of the protective paper of the board, making it easy to break along the scratches. This problem generally does not occur in large quantities, and it is easy to detect and remove when carefully observed. Cracking mainly occurs along the longitudinal direction of the board. In addition to the low lateral strength and gypsum strength of the protective paper, another important reason is the board edge warping, which causes cracks in the stress concentration area of the board during storage and transportation. There are many reasons for the board edge warping, such as the large expansion rate of the protective paper or the inconsistent shrinkage rate of the upper and lower paper; The slurry is too thin or the material properties are unstable, resulting in unstable process control and poor operability, which can lead to edge warping of the board. Therefore, in order to improve the strength of the board and reduce problems such as breakage and cracking, it is advisable to choose protective paper and high-grade gypsum with strength, aeration capacity, and water content suitable for production requirements as much as possible; Strictly control the various indicators of the powder processing and molding process.
5、 The problem of air bubbles and bubbles on the surface of the board.
The surface blistering and bulging of paper gypsum board are mainly caused by reasons such as too thin slurry or improper use of foaming agents in production, and poor gas injection performance of face protection paper. Sometimes the diameter of bubbles is less than 1cm, but it is almost all over the board surface. This is mainly because the gypsum slurry is too thin or the foam of the foaming agent has poor stability, and there are many large bubbles, so that a large number of bubbles concentrate on the surface to form large bubbles. Especially after the board is placed for a period of time and moisture absorption, the bubbles are more obvious. Some bubbles are larger and sometimes more regular, such as forming a straight line along the edges; There are also cases where the number of bubbles is relatively small and it is difficult to determine their regularity, which is related to the low and uneven aeration of the protective paper and the low interlayer adhesion. The low breathability of paper makes it difficult for the moisture to evaporate, and the interlayer bonding force of the protective paper is low. During production or storage, local poor bonding or delamination of the paper surface occur, resulting in bulging on the surface of the board, which is seriously manifested as a large area of non adhesion.
6、 Plate is prone to deformation.
With the development and competition of the paper gypsum board industry and related industries, the unit quality of face protection paper and gypsum board has decreased to a certain extent. Firstly, the quantitative reduction of the protective paper results in a higher shrinkage rate, which leads to insufficient tightness of the protective paper, resulting in insufficient stiffness of the gypsum board. After moisture absorption, the machine is prone to deformation; Secondly, if the breathability of the face protection paper is low, the breathability is slow, and the drying is slow, the deflection of the dried board after moisture absorption is large; In addition, during the forming process, if the consistency of the slurry is adjusted based on the water consumption, resulting in a larger water consumption, large voids will be generated in the board after drying and evaporation, and the board will become too light or soft, resulting in increased deformation and deflection.
7、 The phenomenon of paper interruption during the production process.