In the coating production of various hot melt adhesives, such as adhesive, protective film and non-woven fabric composite, coating and winding are the core links to determine the quality of finished products. Most production defects, product scrapping and low efficiency are concentrated in these two processes. Hot melt adhesive coating process requires extremely high adaptability of temperature, tension, speed and equipment precision, and slight deviation of parameters, slight loss of equipment and omission of operation details will cause batch quality problems.

In the long-term production practice, the failures of hot melt adhesive coater are mostly concentrated in fixed types, among which uneven coating thickness, striped bubbles on the surface, uneven winding, wrinkled finished products and uneven winding tightness are the five most common technological problems in the industry. Based on the mature production process experience, this paper dissembles the causes of each problem and standardized solutions and preventive schemes in detail to help the production line quickly troubleshoot and stabilize product quality. Ruian Jiayuan Machinery Co., Ltd. has been deeply involved in the research and development of hot melt adhesive coating equipment and process optimization for many years, and has accumulated mature equipment debugging and process adaptation schemes for various process pain points in mass production scenes, which can effectively adapt to the production needs of different substrates and different rubber compounds. First, the coating thickness is uneven, and the tolerance of the finished product exceeds the standard. The uniformity of coating thickness is the basic index of hot melt adhesive coating production. Excessive thickness deviation directly leads to the unstable bonding performance of the product and the subsequent composite bonding dislocation, which is also one of the main reasons for the scrap of the finished product. This problem is mainly manifested in the inconsistency of the left and right thickness of the substrate, the fluctuation of the thickness before and after, and the sudden change of the thickness in some areas. From the perspective of technology and equipment, the core causes can be divided into four categories. First, the temperature control is unstable. The viscosity of hot melt adhesive is extremely sensitive to temperature. The uneven temperature in the heating area of equipment, the deviation of temperature control instrument and the local aging damage of heating elements will lead to inconsistent melting degree and different fluidity of rubber compound, which will eventually lead to uneven sizing amount. The second is the gap deviation of coating head. After long-term operation, the gap between coating roller and die head appears slight wear or the gap between left and right is inconsistent, which directly changes the coating amount of colloid. 

The third is the accumulation of rubber impurities. The hot melt adhesive runs at high temperature for a long time to produce carbonized particles, and the impurities are attached to the outlet of the die, which prevents the colloid from flowing out evenly and forms a local thin rubber area. The fourth is the fluctuation of production line speed, the running speed of equipment is fast and slow, the coating time of rubber compound is inconsistent, and the thickness naturally deviates. To solve this problem, we should follow the principle of calibrating parameters first, then overhauling equipment, and finally standardizing operation. Before production, it is necessary to accurately calibrate the temperature control system, detect the temperature consistency of each heating zone, and replace the aging heating elements and failure sensors to ensure the constant temperature melting of the rubber compound. Regularly clean the coating die and runner, remove carbon deposits and impurities, and keep the colloid flowing smoothly. Fine-tune the left and right gap of the coating roller, record the gap parameters, and set the gap value according to the standard of the substrate. At the same time, it can stabilize the running speed of the equipment, avoid random speed regulation in production and ensure the constant coating speed. Second, stripes and bubbles appear on the coating surface, and appearance defects frequently appear on the surface of the coated finished product. These are high-frequency appearance defects in hot melt adhesive coating production, which not only affect the beauty of the product, but also destroy the integrity of the adhesive layer, resulting in a decline in bonding strength and poor weather resistance of the product, which cannot meet the quality inspection standards. The core inducement of stripe defects is mainly equipment blockage and uneven pressure. The die slot is partially blocked, and the surface of the coating roller is stuck with foreign objects, which will make the colloid flow out unsmoothly and form fixed longitudinal stripes; Uneven pressure on the roller and uneven wear on the roller surface will also cause uneven stress on colloid coating and form strip lines.