Slit coating is a widely used forming method in high-precision hot melt coating process. With the characteristics of high coating accuracy, uniform thickness and strong adaptability, it is widely used in the production and processing of various polymer materials such as adhesive tapes, films and sealing materials. Compared with traditional coating methods, slit coating has higher requirements on equipment precision, process parameters and production environment, and it is prone to slight defects in the production process, which directly affects the appearance and performance of finished products. The problem of unstable yield in most coating production mainly stems from inaccurate process debugging and inadequate control of equipment parameters. The common defects, causes and standardized solutions in slit coating production are systematically sorted out below, which is convenient for the production end to quickly check the problems and stabilize the production process.

1. Non-uniform thickness of adhesive layer is the most common problem in slit coating, which is mainly manifested in the large fluctuation of the thickness of the entire roll of adhesive layer, the inconsistency between the left and right thickness, the thin middle or the thick sides. This problem is mainly caused by three factors. First, the gap adjustment of die slot is uneven, and the local gap deviation will directly lead to the difference of glue output at each position; Second, the pressure of the glue supply system is unstable, the rotating speed of the metering pump fluctuates, and the pipeline pressure is unbalanced, which will cause the instantaneous glue output to be large and small; Thirdly, the tension control of the substrate is not constant, and the conveying speed fluctuates, which does not match the glue-discharging rhythm, and finally forms obvious thickness deviation. To solve this kind of problem, it is necessary to calibrate the slit gap of the die regularly to ensure the uniformity of the whole gap, match the corresponding operating parameters of the metering pump according to the actual viscosity of the rubber compound, and stabilize the rubber supply pressure and the rubber outlet speed. At the same time, the tension system of the whole machine is calibrated regularly to ensure that the substrate is transported at a constant speed and smoothly throughout the process, and the problem of uneven thickness is completely avoided from the aspects of equipment and technology. Second, in the production process of stripes and scratches on the coating surface, longitudinal fine stripes and irregular scratches appear on the surface of the adhesive layer, which will directly destroy the coating smoothness and affect the appearance and use performance of the finished product. This kind of defects mainly come from rubber impurities, die pollution and abnormal rubber fluidity. High viscosity hot melt adhesive is easy to produce carbon deposit and fine particles when it runs at high temperature for a long time. If it is not filtered thoroughly, it will be extruded with the adhesive and form scratches on the adhesive surface. The residual glue and dust impurities on the lip of the die will continue to scrape the glue layer to form fixed stripes; Low processing temperature and insufficient fluidity of rubber compound will also cause unsmooth rubber production and produce fine lines. In daily production, it is necessary to thoroughly clean up the residual glue stains on the lip of the die before starting, and replace the filter components regularly to effectively intercept the particle impurities of the rubber compound. Strictly control the melting and coating temperature according to the process standards, ensure the uniform and stable fluidity of the rubber compound, and eliminate the defects such as stripes and scratches from the source. Jiayuan mechanical equipment is equipped with multi-stage filtration structure and precise constant temperature control system, which can effectively purify rubber, stabilize fluid state and greatly reduce the probability of stripe scratches on rubber surface.

   3. Glue breakage, partial glue shortage, glue breakage and glue shortage are serious coating defects, which will directly lead to the scrapping of finished products, mostly in the stage of high-speed mass production, rubber replacement or formula debugging. The main causes include insufficient melting of rubber compound, intermittent rubber supply and incomplete exhaust of die. Hard particles exist when the rubber compound is not completely melted, which will block the slit outlet and cause intermittent rubber breakage; Unstable air intake and pressure in the rubber supply pipeline will lead to the interruption of rubber discharge; After the equipment is stopped and restarted, air is trapped inside the die, which will also cause local glue shortage and coating leakage. The solution is to fully melt and mix the rubber before production, to ensure that the rubber is homogeneous and free from caking, and to complete the full exhaust operation of the die before starting. Regularly check the tightness of the rubber supply pipeline to prevent air intake and pressure relief, and at the same time match the reasonable rubber supply flow according to the production line speed to ensure continuous and stable rubber discharge throughout the process. Rui 'an Jiayuan Machinery has optimized the structure of the whole machine's hose supply and exhaust design, and cooperated with the constant-speed and constant-pressure conveying system, which can effectively avoid the problems of rubber breakage and lack in the high-speed production and refueling stage.

4. Pinholes in adhesive layer, bubble pinholes and bubbles will greatly reduce the sealing, waterproof and protective performance of coated products, which are the key defects that affect the service life of products. The problems mainly come from the air content in the rubber compound and the high humidity in the production environment. Hot melt adhesive is easy to get involved in the air during the process of stirring and conveying, and it is directly coated without defoaming in advance, and bubbles and pinholes will be formed after the adhesive layer is cooled and shaped; When the humidity of the production environment is too high, water vapor will be mixed with high-temperature rubber compound, and dense pinholes will also be formed when it is heated and volatilized in the later stage. In production control, it is necessary to add a defoaming process in the glue melting process to fully exhaust the air trapped inside the glue. At the same time, the production environment of the workshop is stabilized, the temperature and humidity are controlled to maintain the dry standard, and water vapor is prevented from mixing into the rubber compound. With the uniform cooling process, the bubble residue is reduced and the compactness of the rubber layer is improved. Five, edge overflow, irregular edge overflow and uneven edge are common appearance defects, which not only affect the regularity of finished products, but also increase the later trimming process and reduce production efficiency. This problem is mainly caused by the mismatch between the glue output of the die and the width of the substrate, the excessive coating pressure and the lax sealing at both ends of the slit. Excess rubber overflows from both sides of the base material and forms irregular thick rubber edges and hard rubber edges after cooling. In actual production, the effective glue delivery range of the die can be accurately matched according to the width of the substrate, the coating pressure and glue supply amount can be reasonably fine-tuned, and the sealing structures at both ends of the die can be regularly overhauled to prevent glue leakage and overflow at the edges, so as to ensure that the edges of the coated finished products are flat, regular and uniform. By optimizing the sealing structure at the end of the die and controlling the glue discharge rate in different zones, Jiayuan Machinery in Ruian City effectively solved the problems of glue overflow and uneven glue edge at the edge of slit coating, and reduced the later trimming loss.