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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 and solvents. At room temperature, it is a solid and when heated to a certain degree, it becomes a fluid and viscous liquid adhesive. After melting, it appears as a light brown translucent body 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 thickening agents, viscosity modifiers, and antioxidants to make hot melt adhesive.
The required curing time for general use is; 1 To 10 In seconds. The curing speed required for an automatic sealing assembly line is generally within 4 seconds.
There are several factors that affect the curing speed of EVA hot melt adhesive, including:
1. The type of EVA adhesive has little effect on the curing speed, but the trend is that EVA with lower melt index and VA content will cure faster.
2. Choosing hot melt adhesive with high softening point and increasing the amount of hot melt adhesive can help improve the curing speed of the glue, while the use of hot melt adhesive will affect the curing speed.
The higher the melting point of wax, the faster the solidification speed, so the more wax is used, the faster the solidification speed. However, the adverse effect of wax on adhesive strength is particularly significant, so relying solely on wax to regulate curing speed is greatly limited.
EVA hot melt adhesive must be heated and melted first, as it is prone to aging when the amount of adhesive is applied slowly. 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 the hot melt adhesive to oxidize at high temperatures and easily form vinyl groups. Acetate, a rubber like substance, either precipitates at the bottom or disperses in small fragments in the liquid of hot melt adhesive.
This phenomenon often creates the illusion of insufficient temperature, thus increasing the usage temperature and exacerbating 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 calibrate the actual temperature of the glue solution with the temperature displayed on the temperature controller. It is recommended to clean equipment such as glue troughs at least once a month, especially if there is a phenomenon of skinning, it is necessary to remove the skinning that has already occurredhot melt adhesiveClean it thoroughly.
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