Production Process and Product Specifications Requirements of Nano Calcium Carbonate for Sealant

Nano calcium carbonate with small particle size and good reinforcement effect is one of the main functional fillers used in sealants, widely used in varieties such as silicone glue, MS glue, polyurethane glue, etc.

There are three main issues with the application of nano calcium carbonate fillers in sealants:

One is the blending effect of fillers and colloids;

The second is the influence of fillers on thixotropic properties;

The third is the strengthening effect on the sealant.

The factors that affect the blending performance of specialized nano calcium carbonate in sealant mainly include particle size, crystal form, oil absorption value, specific surface area, pH value, sieve residue, and moisture. Among them, the factors that affect the alternating thixotropy are mainly particle shape, oil absorption value, surface modification, and pH value, while the factors that affect the strengthening effect are mainly particle size and dispersibility.

Production Process of Nano Calcium Carbonate

(1) Limestone and anthracite are calcined in a vertical kiln in a certain proportion to form lime (CaO) and kiln gas, then hot water is added to digest the lime to produce lime milk, which is sieved to remove impurities and obtain refined Ca (OH) 2 slurry; At the same time, the kiln gas is purified into clean kiln gas after multi-stage dust removal.

(2) Adjust the concentration and temperature of Ca (OH) 2 slurry, control the reaction temperature, concentration, gas-liquid ratio, crystal shape control agent and other process conditions in the carbonization tower to prepare nano CaCO3 slurry. The calcium carbonate slurry is aged to make the particles regular, undergo secondary carbonization, and reduce the pH value.

(3) Add calcium carbonate slurry to the activation tank, heat to above 60 ℃, add dissolved dispersant and surface treatment agent, and perform activation treatment. Keep warm and stir for 30-60 minutes.

(4) The surface treated nano calcium slurry is filtered, dried, crushed, and packaged to obtain nano calcium carbonate.

Specification Requirements for Nano Calcium Carbonate Products Used in Sealants

(1) The crystal form of crystalline nano calcium carbonate should be compatible with the production formula, processing technology, and equipment conditions of silicone sealant. Generally speaking, cubic, rhombohedral, and chain like crystal forms of cubic parts have a wide range of adaptability.

(2) The appropriate particle size is 60-100nm. If the particle size is too large, the thixotropy of the adhesive is poor, it is easy to flow and hang, and it will also affect the mechanical properties of the product. If the particle size is too small, it is difficult to disperse, and the kneading time is long, poor dispersion can easily cause the surface of the adhesive to become rough.

(3) As a sealant filler, the lower the moisture content of nano calcium carbonate, the better, generally requiring less than 0.5%. Excessive moisture content, long vacuum mixing time during processing, high power consumption, and impact on the quality of subsequent adhesive processes; Moisture may also cause certain components in the formula to hydrolyze and produce inorganic particles, thereby affecting the blending of fillers in the gel or the production of particles.

(4) The lower the pH value is, the better the pH value is. The alkalization of calcium carbonate is a common phenomenon in the production of light calcium. The existing alkali will generate water with the acidic components in the rubber compound. The water will easily hydrolyze the siloxane to produce inorganic particles, which will form densely distributed small particles in the rubber compound, and lead to the decline of colloidal stability and the appearance of gel, thus affecting the surface performance of the product.

(5) The effectiveness of surface treatment with nano calcium carbonate modification will affect the blending effect of its particles on colloids and the thixotropy of colloids. A good modification effect will make nano calcium carbonate have good affinity in polymers, and also make the sealing adhesive using nano calcium carbonate as a filler have thixotropic properties.

(6) Oil absorption value is a very important indicator of specialized calcium carbonate for sealants, which is a factor affecting the wettability of calcium carbonate in the adhesive. After compounding, it can be found that when the oil absorption value of calcium carbonate is high, the thixotropy and various mechanical properties of the adhesive are relatively ideal, but the viscosity of the adhesive is high and difficult to adjust.

(7) The optimal specific surface area for nano calcium carbonate in adhesives and sealants is 20-25 m2/g, which can achieve the most ideal slump resistance and compressibility. When the specific surface area is too large, the compressibility of the sealant appears poor, and the tensile strength increases with the increase of specific surface area, but the dispersibility decreases. Therefore, when nano calcium carbonate is applied in adhesives and sealants, a relatively moderate specific surface area should be pursued.

(8) The sieve residue should be less than 0.15% (45 μ m sieve). The main reason for the formation of surface particles in products is that the residual material is too high.