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The curing speed and aging issues of EVA hot melt adhesive. Hot melt adhesive is a 100% solid adhesive without moisture or solvents. It is solid at room temperature and turns into a fluid and viscous liquid adhesive when heated to a certain extent. The agent, after melting, appears as a light brown semi-transparent substance or natural white.
The main component of EVA adhesive, namely the base resin, is copolymerized with ethylene and vinyl acetate under high pressure, and then mixed with tackifiers, viscosity regulators and antioxidants to make hot melt adhesive.
The general curing time required for use is 1 “Zhi” 10 Seconds. The curing speed required by an automatic sealing production line is generally within 4 seconds.
The factors that affect the curing speed of EVA hot melt adhesive are as follows:
1. The type of EVA adhesive has little impact on the curing speed, but the trend is that EVA with a lower melt index and lower VA content will cure faster.
2. Choosing a hot melt adhesive with a high softening point and increasing the amount of hot melt adhesive used can help improve the curing speed of the adhesive, while the use of hot melt adhesive can affect the curing speed.
The higher the melting point of wax is, the faster it will cure. Therefore, the more wax is used, the faster it will cure. However, the adverse effect of wax on bonding strength is particularly significant, so relying solely on wax to regulate the curing speed is greatly limited.
EVA hot melt adhesive must be heated and melted first. When the amount of adhesive applied is relatively slow, the problem of hot melt adhesive aging is likely to occur. If the amount of hot melt adhesive in the glue tank is relatively slow, it may even take many days to add new hot melt adhesive to the glue tank. In this case, the hot melt adhesive in the glue tank will be repeatedly heated, causing high-temperature oxidation of the hot melt adhesive and making it easy to form vinyl. Acetate, a rubber-like substance, either precipitates at the bottom or is dispersed in the form of small fragments in the hot melt adhesive liquid.
This phenomenon often creates the illusion that the temperature is insufficient, thus increasing the operating temperature and thereby accelerating the deterioration of the curing speed of EVA hot melt adhesive. In this case, if glue is used for bonding, the bonding strength will not meet the requirements.
To avoid this situation, it is necessary to strictly control the heating temperature of the glue tank and regularly compare and correct the actual temperature of the glue solution with the temperature displayed on the temperature controller. It is recommended that equipment such as glue tanks be cleaned at least once a month. Especially when there is skinning, the skinning hot melt glue must be thoroughly removed.
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