Adding silicon micropowder filler to the polymer base can not only reduce the cost of the polymer material, but also improve the dimensional stability of the material, and impart special physical properties such as compression resistance, impact resistance, corrosion resistance, flame retardancy and insulation. Chemical properties.
How to improve the fluidity of silicon micropowder in high polymer, reduce its viscosity and increase the overall filling rate has been a hot research direction in the industry, and reducing the oil absorption value of silicon micropowder helps to improve its flow in high polymer. Sex.
The oil absorption value is also referred to as the resin adsorption amount, and represents an index of the filler absorption amount of the resin. In practical applications, most fillers use the oil absorption value to roughly predict the resin's demand for the resin. When the oil absorption value is different, the particle size, specific surface area, dispersibility, wetting degree and adsorption performance of the powder filler are different, which affects the compatibility of the powder and the polymer. Therefore, the oil absorption value directly affects the material quality, performance and use. .
Figure 1 Two main forms of powder absorption oil
The oil absorption value is related to the size and shape of the powder, the degree of dispersion and cohesion, the specific surface area and the surface properties of the particles. However, since silicon micropowder is mainly used as a filler in related industries, the particle size is highly demanded, so the method of reducing the specific surface area to reduce the oil absorption value by increasing the particle size has certain limitations. Therefore, as can be seen from Fig. 1, how to reduce the oil (resin) of the surface and voids of the silicon fine powder particles is the key to lowering the oil absorption value.
the first
Experimental material
The natural quartz ore is prepared by a ball mill, a vibration mill, a jet mill grading system, and an ultrafine silicon powder having an average particle diameter of 2.5-3.0 μm;
The average particle size is 20±0.5μm silicon micropowder finished product and the resulting bag dusting powder;
Three kinds of silicon micro-powders with an average particle diameter of 20±0.5μm (common silicon micropowder, silicon micropowder modified by aluminate modifier, silicon micropowder modified by silane coupling agent).
second
Effect of grinding equipment on the oil absorption value of silicon micropowder
Table 1 Particle size distribution and oil absorption value of silicon micropowder produced by different grinding and grading equipment
It can be seen from Table 1 that the average particle size of the silicon micropowder samples obtained by the ball mill , the vibration mill and the jet mill has little difference, so it can be considered that the oil absorption values ​​caused by the particle size do not change much. However, the results of the oil absorption test of the three are: airflow mill>ball mill>vibration mill, mainly the vibration milled silica micropowder sample has good distribution of coarse and fine powder in the whole system, and the fine particles are better filled between coarse particles and enlarged. The filling of the entire system reduces the amount of oil distributed in the voids of the particles, thereby reducing the overall oil absorption of the system.
Table 2 Tap density of silicon micropowder produced by different grinding and grading equipment
It can be seen from Table 2 that the vibrating milled silica powder sample has the highest tap density, and further verifying that the good particle size distribution can effectively reduce the void ratio between the powders and improve the powder filling property.
third
Effect of adding micropowder in the original powder system on the oil absorption value of silicon micropowder
Table 3 Particle size distribution of silicon micropowder finished products and bag dusting powder
Table 3 shows the particle size distribution of the 20±0.5μm silicon micropowder finished product and the dusting powder produced by the bag during the production process. Figure 2 shows the change of the oil absorption value caused by adding the bag dusting powder in different proportions of the silicon micropowder finished product (this is simulated production). During the process, the damper and the grading frequency control the whirlwind collection and the bag dust removal output ratio).
Fig. 2 Change of oil absorption value caused by adding bag dusting powder in silicon micropowder finished product
It can be seen from Fig. 2 that when the amount of the dust removing powder of the bag is controlled to be about 4%, the gap between the particles and the particles in the finished silicon powder can be effectively filled, thereby reducing the oil absorption value of the system. However, as the dust removal powder of the bag continues to increase, the oil absorption value of the system increases rapidly. This is because after the filling of the finished powder of the silicon micropowder is saturated, a new particle gap is formed between the new bag dust removing powder, and the particle size of the fine powder is small. The specific surface area is large, the surface energy is increased, and the surface also has a high oil absorption capacity, resulting in an increase in the system oil absorption value.
In actual production, the size of the silicon micronized particles can be controlled by adjusting the classification frequency and the size of the damper, thereby reducing the overall oil absorption value of the finished silicon micropowder.
fourth
Effect of modifier on oil absorption value of silicon micropowder
Figure 3 Dispersion of different silicon micropowders under an electron microscope
3 is a photograph of a silicon micropowder modified with an average particle diameter of 20±0.5 μm, a silicon micropowder modified by an aluminate modifier, and a silicon micropowder modified by a silane coupling agent under an electron microscope, and it can be seen from the figure that the silicon micropowder The dispersity is determined by the silane coupling agent modified silicon micropowder > aluminate modifier modified silicon micropowder > average particle size of 20 ± 0.5 μm silicon micropowder.
Table 4 Oil absorption values ​​of different modified silicon micropowder products
Table 4 shows the comparison of the oil absorption values ​​of the silicon micropowder modified by the silicon micropowder with the average particle size of 20±0.5μm, the alumina micropowder modified by the aluminate modifier, and the silane coupling agent: the average particle size is 20±0.5μm. Micropowder>Aluminum micropowder modified by aluminate modifier>Silicone powder modified by silane coupling agent.
The modifier can reduce the ability of the surface of the silicon micropowder to adsorb grease, reduce the interparticle voids generated by the agglomeration of the powder, thereby reducing the oil absorption value of the powder, and the modification effect of the silane coupling agent on the silicon micropowder is more obvious.
fifth
in conclusion
(1) The filling property of silicon micropowder produced by vibrating mill grading system is higher than that of jet mill and ball mill, so its oil absorption value is the lowest.
(2) Adding a certain proportion of fine powder in the finished silicon powder can effectively reduce the particle gap of the powder system, thereby reducing the oil absorption value of the product. In actual production, according to the production of powders of different particle sizes, the classification frequency and the size of the damper can be adjusted, and the amount of dust particles generated by the bag can be effectively changed, thereby improving the oil absorption value of the cyclone collection product.
(3) The modifier has obvious influence on the oil absorption value of the powder, and the silane coupling agent has the best effect on the modification of the silicon micropowder. In the actual production process, different silane coupling agents need to be selected according to different industry needs.
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