Common solutions to silicone rubber mixes:
The factors and solutions that affect the resilience and vulcanization speed of silicone rubber mixes can be carried out from the following aspects.
The ethylene content in the silicone rubber mix is not enough, or the ethylene content of the raw rubber itself is unevenly distributed, the positive sulfur point cannot be reached during vulcanization, the vulcanization speed becomes longer, the vulcanization is not sufficient, and the elasticity of the rubber mix becomes worse. By increasing the overall ethylene content in the rubber, adding an appropriate amount of hydrogenated silicone oil to the formula, reducing the amount of filler used, and increasing the rubber content, the situation of poor resilience and slow vulcanization speed can be solved; using raw rubber with different types of ethylene content and using a small amount of high ethylene raw rubber can control the drawing deformation of the slurry. It is necessary to find the best balance in the formula to avoid the slurry from becoming brittle and achieve the purpose of improving the elasticity of the slurry.
The silicone rubber mix itself is acidic, which is also an important factor in the poor elasticity of the rubber and the slow vulcanization speed. Since white carbon black itself is acidic, the added structure control agent is mostly acidic, making the mixed rubber acidic. The acidic mixed rubber has a delayed effect on vulcanization and its high temperature resistance is also reduced. Adding appropriate weak alkaline substances can improve the acid content of the slurry. Generally, the pH value of the slurry in the neutral or weak alkaline range is conducive to the improvement of elasticity and vulcanization speed.
If the amount of silicone rubber compound or structure control agent added is too much, the rebound elasticity of the mixed rubber is poor and the vulcanization speed is slow; if too much internal plasticizer or structure control agent is added, the mixed rubber will have a delayed effect on vulcanization, resulting in the deterioration of the rebound elasticity of the mixed rubber and the slow vulcanization speed. Select raw rubber with narrow molecular weight distribution and certain volatile components to improve demoulding of mixed rubber and reduce the amount of plasticizer; Use alkoxysilane to treat the surface of white carbon black, use it with hydroxy silicone oil, and use a two-step method to give white carbon black molecules and raw rubber molecules a certain bonding reaction time, which can technically maintain health, reduce the use of structure control agents, and increase the resilience and elasticity of mixed rubber.
Reason:
Since silicone rubber mixes have high water permeability, especially rubber mixes made with precipitated white carbon black, as the relative humidity in the air increases, the moisture content in the mix also increases linearly. When there is too much water, the silicone rubber mix changes from transparent to opaque, especially in winter when the ambient temperature is low, so the water loss time of the mixed rubber surface will slow down, or it will not fall off at all, and the surface of the extruded product will easily become bubbles. General precipitated white carbon black is not suitable as a silicone rubber filler for extrusion molding because of its high water content.
Solution:
Use alkoxysilane to treat the surface of white carbon black, so that the hydrophilic surface becomes hydrophobic, which can reduce the water absorption rate; high temperature treatment can also be used to reduce the water absorption rate of the slurry and improve the bubbles of the extruded slurry. At present, the extruded rubber is in production. In the existing formula system, the extruded rubber is further subjected to vacuum heat treatment, and the effective mixing time and mixing temperature, that is, the mixing time and temperature in the high temperature section, are strictly controlled to improve the bubble problem of the extruded rubber. At the same time, drawing standard vulcanization curves for various types of rubber materials is also a means to stabilize the production quality of mixed rubber.
