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Adhesives are usually liquid or paste. These adhesives need to be cured before they can work. Therefore, the curing process of adhesive is also very important. If the curing is not good or you do not know what to pay attention to when curing, it will have a great impact on the bonding of the articles. Even if you use a good adhesive, it may affect the bonding effect.
Adhesive curing reaction is a process to obtain and improve adhesive strength and other properties through chemical reactions (polymerization and crosslinking). Curing is the key process to obtain good adhesion. The strength can be maximized only when fully cured. Curing is divided into initial curing, foundation curing and post curing.
1. preliminary curing
At a certain temperature, after a period of time to reach a certain strength, the surface has hardened and is not sticky, but the curing is not over.
2. foundation curing
After a period of time, most of the reaction groups participate in the reaction and reach a certain degree of cross-linking.
3. post curing
In order to improve the bonding performance or handle the basically cured adhesive due to the process needs, it is generally maintained at a certain temperature for a period of time to supplement the curing, further improve the curing degree, effectively eliminate the internal stress and improve the bonding strength.
In order to obtain a well cured adhesive layer, the curing process must be carried out under appropriate conditions.
The curing process of adhesive has a very important impact on the bonding quality. There are three basic process parameters in curing: temperature, pressure and time. These three parameters have great influence on the curing of adhesive.
1. curing temperature
Curing temperature is one of the important parameters of adhesive curing. If the curing temperature is too high, it is easy to cause loss of adhesive or embrittlement of adhesive layer, resulting in the decrease of bonding strength; The curing temperature is too low, the movement of matrix molecular chain is difficult, the crosslinking density of adhesive layer is too low, and the curing reaction cannot be completed. Therefore, during the curing process, the curing temperature must be strictly controlled, and each adhesive has a specific curing temperature.
2. Curing pressure
Curing pressure refers to the application of certain pressure during the curing process, which is conducive to the good connection between the adhesive layer and the adherend and ensure the quality. Due to different types of adhesives, the applied pressure is also different. Generally, it can be divided into the following three cases: the contact pressure is the pressure generated by the self weight of the adherend for curing, and no additional pressure is required, such as epoxy resin adhesive, a-cyanoacrylate adhesive, the second generation acrylate adhesive, unsaturated polyester adhesive and polyurethane adhesive.
Applicable to epoxy nitrile adhesive and 1.0 ~ 0.0mpa epoxy butyl adhesive. The pressure of 0.3 ~ 0.5MPa is applicable to film, powder, tubular and granular adhesives and hot melt adhesives. The purpose of increasing the pressure is to improve its wettability.
3. curing time
Curing time refers to the time required for curing in the bonding process under certain temperature and pressure conditions.
The curing time of different adhesives is also different, such as instant curing, a-cyanoacrylate adhesive, hot melt adhesive curing in a few hours, such as room temperature rapid curing epoxy adhesive, second-generation acrylate adhesive, curing in a few days, such as epoxy polyamide adhesive.
Curing time is also affected by curing temperature and pressure. Increasing the curing temperature can shorten the curing time. When the curing temperature is low, the curing time will be greatly prolonged. If it is lower than room temperature, sometimes it will not heal for several days.