1、 Curing properties of silicone building sealant






Single component sealant sealed packaging in the container is stable, from the container hit out in the air will be solidified. This is a chemical reaction process. After the sealant contacts with the air, the base glue, cross-linking agent and catalyst in the sealant will react with the water in the air and gradually become an elastic solid, which is the curing of the sealant. After the sealant is made, the surface of the sealant is the first to contact the water, so the first to cure is the surface. After the surface is cured, the water will seep in from the cured surface, and the inner layer will be cured again. In this way, the sealant will be cured gradually from the surface to the inside, and the longer the time is, the thicker it will be cured. The thicker the sealant is applied, the longer it will take to fully cure, usually 3-6mm thick in 24 hours.






Two component sealant is carried out by chemical reaction between components a and B. A. It is stable to store component B separately and sealed. Once component A and component B are mixed, they will start to react. Therefore, component A and component B should be used immediately after mixing. The two-component curing reaction does not need the participation of water in the air, so its curing is carried out by the internal and the surface at the same time, and the complete curing time has nothing to do with the thickness of the adhesive, so the reaction has nothing to do with whether it contacts the air. As long as the components a and B are mixed together, they will be cured even in the closed state.






2、 Several concepts in the curing performance of sealant:






Surface drying: the sealant is paste like when it is punched out. When touching its surface with fingers or other materials, the sealant will adhere to the fingers or materials. After the sealant is put out, the surface contact moisture begins to solidify the skin. When the skin is formed, and then the fingers or materials are used to contact the surface, there will be no more adhesive on the fingers or materials. This is called surface drying.






Surface drying time: when the sealant is printed out from the container, the time required for it to dry is the surface drying time.






Debonding: after the sealant surface is dry, touch the surface with fingers. Although there is no adhesive on the fingers, there is still a certain adhesion between the rubber surface and fingers. This phenomenon is called "debonding". This is that the curing reaction on the surface of the adhesive has not been fully performed. With the extension of time, it will further solidify until a layer of skin with certain elasticity and strength is formed on the surface. It feels dry when touching with fingers, and there is no sense of adhesion. We call it anti adhesion.






Debonding time: when the sealant is printed out of the container, the time required for debonding is debonding time.






3、 Factors affecting the curing performance of sealant






Environmental factors have a significant impact on the curing performance of sealant. First of all, it is the effect of temperature. The higher the temperature is, the faster the curing reaction speed is. The phenomenon is that the surface drying and anti sticking are relatively fast. If the temperature is very low, such as below 5 ℃, the sealant curing will be very slow. If the temperature is too high, such as 40 ℃, the sealant will be too dry and inconvenient to use. Humidity also has a significant impact on the curing performance of sealant, because the curing reaction of sealant requires water in the air, so too dry weather such as relative humidity lower than 40 ℃ is adverse to the curing of sealant. But it is not that the higher the humidity is, the better it is, because the volatile small molecules should be released when the sealant is cured. If the air humidity is too high, the small molecules are not easy to volatilize, which is not conducive to the sealant curing. Experiments have proved that when the relative humidity is higher than 80 ℃, the debonding and deep curing of sealant will be affected. Sometimes after 2-3 days, the surface of sealant is still sticky. The standard conditions for sealant performance specified in national standards are temperature (23 ± 2) ℃, relative humidity (50 ± 5) ℃.