In modern polymer materials such as epoxy resin, silicone rubber, plastics and coatings, fillers occupy a large share . As one of the commonly used fillers in epoxy resin potting materials, silica powder has a significant effect on improving certain physical properties of epoxy resin. For example, adding active silica powder to epoxy resin potting materials can greatly improve the performance of epoxy resin. Improve the impact resistance of potting materials and reduce the viscosity of epoxy resin potting materials.
In order to better integrate epoxy resin and silica powder, the surface of the silica powder must be modified. The purpose of modification is to change the polarity of the surface of silica powder to non-polar through coupling agents and toughening agents, making it hydrophobic and organic solvent-friendly, with good wettability, thereby strengthening the relationship between silica powder and epoxy resin. The bonding force between interfaces.
The effects of active silica powder and inactive silica powder of different particle sizes on the epoxy resin potting process and the properties of the epoxy resin cured product were studied.
1. The relationship between the activity and physical properties of silica powder
Compared with the epoxy resin cured product adding inactive silica powder, the curing shrinkage, linear expansion coefficient and water absorption of the epoxy resin cured product adding reactive silica powder The rate is lower than that of the epoxy resin cured product with inactive silica powder added. The reason is that: during the activation process of the active silica powder, the composite silane coupling agent in the activator is adsorbed on the surface of the silica powder particles, forming an extremely thin and strong layer. membrane. The hydrolyzable groups of this film react with the surface of the silica powder to form covalent bonds, such as hydrolysis and condensation.
At the same time, the active treatment agent spreads on the surface of the silica powder to form a continuous film, thereby changing the original properties of the silica powder surface, making it hydrophobic and organic solvent-friendly It has good wettability, so the water absorption of epoxy cured products using reactive silica powder as filler is significantly lower than that of epoxy cured products using ordinary silica powder as filler. The impact on physical properties is less obvious, and the impact on volume resistivity and breakdown voltage is slightly reflected.
2. The relationship between the activity of silica powder and the impact strength of the cured product
The impact strength of cured epoxy resin modified by active silica powder is much greater than that of cured epoxy resin modified by inactive silica powder. Impact strength. This is because during the activation process of silica powder, the surface of the silica powder adsorbs the coupling agent and toughening agent in the activator, forming a continuous phase flexible molecular coating layer. When epoxy resin is mixed with reactive silica powder, there is a flexible molecular layer between the contact interface between the epoxy resin and the monomer reactive silica powder. In the mixture of reactive silica powder and epoxy resin, a densely connected three-dimensional flexible network structure is formed between the reactive silica powder and epoxy resin. When the internal stress generated by the epoxy resin mixture during the curing process is transferred to the surface of the active silica powder, it is induced through the flexible network structure, causing a large number of micro-cracks and shear bands to absorb energy, ultimately increasing the impact strength of the cured product.
3. Effect of the activity of silica powder on the viscosity of potting materials
As the temperature increases, the viscosity of epoxy resin potting materials with active silica powder and inactive silica powder decreases significantly. The viscosity of the active silica powder potting material added in the same amount is much smaller than the viscosity of the inactive silica powder potting material. This is because the activated silica powder forms a thin film on the surface under the action of the coupling agent, and this film is hydrophobic. After the activated silica powder and epoxy resin are mixed, a chemical bond is generated between the hydrophobic film on the surface of the silica powder and the epoxy resin. The binding force is intermolecular force. At this time, there is no air film between the silica powder and the epoxy resin. , so the affinity is good. Thereby reducing the viscosity of the epoxy resin potting compound.
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