Views: 0 Author: Site Editor Publish Time: 2021-10-04 Origin: Site
Recently, the price of various products has been increased. As another kind of strengthening filler of silicone glue, calcium carbonate has also started the price increase mode after the holiday. Since October 10, the price increase has been about 400 yuan/ton, and the price increase is also due to the rise of coal and other raw materials, as well as the reasons for power rationing.
As a new inorganic reinforcing filler, calcium carbonate powder occupies an important proportion in the formula of silicone sealant, and the dosage can be as high as more than 60%. It is one of the largest raw materials of silicone sealant. At present, the calcium carbonate powder used in silicone sealant is mostly modified nano-calcium carbonate. The nano-calcium carbonate not only has the quantum size effect, surface effect and macroscopic quantum effect that the general inorganic filler does not have, but also has hydrophobic and oil-philic properties, which can be well dispersed in the composite material.
However, the modified nano calcium carbonate also has the disadvantages of complex production process, certain pollution to the environment and high cost, so the heavy calcium carbonate with simple preparation method, no pollution and low price is favored to partially replace the nano calcium carbonate. But as a result of heavy calcium carbonate particle size distribution is wide, compatibility with composite material is a bit poor, after filling silicone sealant system easily when under stress caused by stress concentration and crack propagation in materials and cause material damage, so the industry can only use of modified calcium carbonate modified nanometer calcium carbonate as a reinforcing filler, In order to reduce the cost effect of silicone sealant.
The reason is that the maximum volume fraction of a multidisperse system will be larger because small particles can fill the space between large particles. Therefore, at any content, increasing particle size distribution can reduce the viscosity of the system. This can be explained by the lubrication effect of small particles in the movement of large particles, which makes the particles move more easily. It can also be seen from the data of oil absorption value that under the condition of a certain solid content, controlling the particle size distribution can effectively control the processing viscosity and extrusion rate of the system. Compared with the pure nano calcium carbonate with the same specific surface area, the compound of nano calcium carbonate and 1500 heavy calcium carbonate has better gloss and basically has no effect on the dispersion. This is because the oil absorption value of the compound filler is lower than that of the single filling system to a certain extent because of the interlaced filling structure, and it appears more oily and better gloss in the same processing formula.
Compared with the pure nano-calcium carbonate with the same specific surface area, nano-calcium carbonate and 1500 mesh heavy calcium carbonate have lower viscosity and higher extrusion rate, in which the viscosity of the base glue decreases by about 40%, the extrusion rate increases by about 30%, and the viscosity of the finished glue decreases by about 27%, and the extrusion rate increases by up to 28%.
Compared with 1500 mesh heavy calcium carbonate with the same specific surface area, the surface drying time of the composite calcium carbonate is slightly prolonged, the elastic recovery rate is slightly reduced, and the hardness of the composite calcium carbonate is similar to that of single calcium carbonate.
Compared with 1500 mesh heavy calcium carbonate, the mechanical reinforcing effect of nano-calcium carbonate is similar to that of single nano-calcium carbonate, and the elongation at break is slightly reduced, but the tensile strength and elongation retention rate are improved and the debonding area is also improved after soaking.
The reinforcing effect of silicone sealant is closely related to the dispersity of filler system. Only when good dispersity is obtained, can the reinforcing effect of nanoparticles be fully reflected. After the combination of nano calcium carbonate and heavy calcium carbonate, the heavy calcium carbonate plays a role as a dispersion medium in the system, which improves the dispersion of nano calcium carbonate particles to a great extent, so it has an excellent performance in mechanical properties. However, the composite packing system is inferior to the single packing system in terms of elongation, mainly because the heavy calcium carbonate with coarse particle size tends to cause stress concentration and crack propagation in the process of tensile stress, resulting in material damage. The improvement of immersion performance is because the compound system has lower oil absorption value, better dispersion, lower surface energy after filling silicone resin, and water vapor molecules are not easy to penetrate into the silicone system for degradation.