Generally speaking, the polymer will break or bond when it works in the environment above 170 ℃. When supplied to the manufacturer, high-quality hot melt glue must have good aging resistance and cracking thermal stability. Those with poor thermal stability will be carbonized rapidly during the high-temperature operation of the glue feeding system and attached to the melt tank wall, the die head or the glue feeding roller. These coking gums will affect the heat conduction of thermal medium or electric heating system, so it is necessary to continuously increase the working temperature to melt them, so as to accelerate their deterioration. Pressure sensitive adhesive with good thermal stability shall meet the following basic conditions.
When thermoplastic polymers work under high temperature and high shear force, various free radicals (R, RO, oh) with strong activity and cracking chain reaction will be produced due to chain breaking. An appropriate amount of antioxidants can be used to terminate the hot melt glue cleavage chain reaction.
Generally speaking, the hot melt glue system with good miscibility is clear and transparent, and can be stored in the rubber tank for a long time. It is not easy to separate the phases, resulting in carbonization; The system with poor miscibility is semi transparent and even completely opaque. When the rubber is used in high temperature rubber tank for a long time, the phase separation between components will occur gradually, and then the coking will be accelerated.
Oxygen is one of the main elements leading to the oxidation of hot melt glue. In order to prevent it from being oxidized due to contact with oxygen in the manufacturing process, it is necessary to fill the rubber tank with nitrogen to prevent oxygen or vacuum production.
The impurities in hot melt glue may be foreign matters carried in some raw materials or inadvertently carried during feeding, such as paper scraps, textiles, dust or metal, or may be carbonized glue peeled from the tank wall or polymer with too high molecular weight to melt. Without proper filtration procedures, impurities will be brought into the downstream melt rubber operating system, resulting in filter blockage or further deterioration of the rubber. If the melt rubber operating system does not have filtration equipment, impurities or cokes will be brought to the coating surface. In addition to contaminating the coating surface and scratches, impurities may also wear the die wheel and scraper, causing serious losses.
As a raw material, hot melt glue has been paid more and more attention in manufacturing. To ensure the thermal stability of pressure sensitive adhesive, the above basic conditions must be met.
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