As an inorganic superfine filler, Nano Calcium Carbonate is often used in the formula of silicone sealant through physical filling to reduce the production cost. However, inorganic ultrafine particles have hydrophilicity, so it is necessary to improve their compatibility with silicone sealant and their dispersion and stability in colloid through surface treatment, so as to improve the bonding and mechanical properties of silicone sealant products.

Silane coupling agent is a common surface treatment agent, which is widely used in the surface coating modification of talc powder, aluminum hydroxide, magnesium hydroxide and other inorganic powders.

However, because the number of hydroxyl groups on the surface of calcium carbonate is small, which is usually weakly alkaline, the binding of silane coupling agent on the surface of calcium carbonate is poor, so that the application performance improvement effect is weak.

1. Pretreatment of silane coupling agents modified by Nano Calcium Carbonate

Place the nano calcium carbonate suspension in the reactor, and add 3.0% stearic acid (calculated on the dry basis of calcium carbonate) at 70 ℃ for surface modification for 30 minutes; Then, continue to add 0.5% phosphate (calculated on the dry basis of calcium carbonate) for modification for 30min, and press filter and dry the semi-finished products after modification; When the moisture is dried to 0.8%, the sample is crushed and sieved.

2. Modification of silane coupling agent

The pretreated nano calcium carbonate is dry modified with different aminosilane coupling agents(γ- Aminopropyl triethoxysilane KH-550), and then crushed and sieved to obtain active nano calcium carbonate.

After modification with different aminosilane coupling agents, the specific surface area of the sample decreases slightly, but the particle size does not change significantly, and the particle dispersion is good, which may also be related to the secondary crushing and depolymerization of the sample.

Because the surface of ordinary Nano Calcium Carbonate is weakly alkaline and the content of surface hydroxyl is low, it is difficult to form a good chemical coating modification of silane coupling agent on the surface of calcium carbonate by using conventional treatment process.

The addition of phosphate ester in the pretreatment process of Nano Calcium Carbonate can effectively reduce the pH value of the product and provide a suitable reaction environment. On the other hand, the phosphate group can also be used as the living site for the reaction with silane coupling agent, and its moisture can be strictly controlled in a reasonable range during the drying process. In this way, the silane coupling agent can be effectively coated on the surface of Nano Calcium Carbonate through the chemical action of hydrolysis polycondensation.