Application of Nano-Calcium Compound Heavy Calcium in the Preparation of Silicone Rubber

There are many kinds of fillers for silicone sealants, such as silicon dioxide, nano-calcium carbonate, wollastonite powder, heavy calcium carbonate, etc., of which the largest amount is nano-calcium carbonate. In the domestic sealant market, the addition ratio of nano-calcium carbonate in silicone rubber exceeds 60%, and the amount used is very considerable.

More than 70% of the so-called nano calcium carbonate is added with different proportions of heavy calcium carbonate, but it is actually micro-nano composite calcium. Some nano-calcium carbonate synthesis technology is backward, resulting in disordered crystal form (it is difficult to see regular cubes in crystals, mostly small spindles and chain-like mixtures), poor processing performance, and high oil absorption value. Adding heavy calcium carbonate is In order to improve its processing performance, reduce its oil absorption value.

At present, only a few manufacturers can synthesize regular cubic nano-calcium carbonate products, and other irregular nano-calcium carbonate products have poor thixotropy, low tensile strength, low elongation, and poor elastic recovery. , the only benefit is the low price.

These micro-nano composite calcium seem to be cheap, but there are many hidden dangers:
1) poor mechanical properties;
2) The original nano-calcium carbonate has poor crystal form, high surface porosity and high water content, which will lead to poor storage stability or even thickening of the alcohol-based glue;
3) Heavy calcium carbonate is originally a very stable product, and it is mixed with nano calcium carbonate through surface treatment and subsequent drying process, which increases its instability;
4) Nano calcium carbonate is mixed with heavy calcium carbonate, which increases the mixing cost, drying cost and transportation cost of heavy calcium carbonate. It seems to be cheap, but it is actually more expensive.

Compared with the seemingly cheap micro-nano composite calcium, silicone rubber manufacturers use pure nano-calcium carbonate and heavy calcium carbonate in their respective production lines, and the silicone rubber products produced are more stable in performance and lower in cost.

Select pure nano calcium carbonate products with different particle sizes (15nm, 30nm, 40nm, 50nm, 60nm, 70nm) and 1500 mesh inactive heavy calcium carbonate in different proportions to prepare silicone sealants. By comparing the viscosity of the base materials , consistency, extrusion rate and the density, viscosity, consistency, extrusion rate, surface drying time, tensile strength, maximum strength elongation, elastic recovery rate and other indicators of sealant products. The results show that:

(1) More heavy calcium carbonate can be compounded with pure nano-calcium carbonate with finer particle size, and the density and various properties of the obtained sealant meet the standard requirements, and the cost is lower.

(2) Whether it is the production process of directly adding micro-nano composite calcium, or the production process of adding pure nano-calcium carbonate to compound heavy calcium carbonate, it is especially critical to select high-quality (regular crystal morphology) nano-calcium carbonate as a reinforcing material. , which is the main factor determining the mechanical properties of the final silicone rubber product.

(3) Compared with the use of micro-nano composite calcium, the use of high-quality pure nano-calcium carbonate compounded with heavy calcium carbonate to produce silicone rubber not only reduces the production cost of silicone rubber, but also helps to improve its mechanical properties; In terms of management and quality control management, it is also conducive to maintaining long-term stability of product performance.