Adjusting the viscosity and fluidity of silicone can be done from the aspects of diluent addition, process optimization, and formula adjustment. The following are specific methods and analysis:
1. Diluent addition
Silicone oil dilution
Using low-viscosity dimethyl silicone oil (50-100cst) or vinyl silicone oil as a diluent can reduce the overall viscosity of silicone.
Note: The amount of addition must be strictly controlled within 30%. Excessive addition will cause oil leakage or performance degradation after curing.
Volatile solvents
Solvents such as toluene can temporarily reduce viscosity, but the amount must be controlled (usually less than 5%) and protective equipment must be worn. After curing, the solvent volatilization must be ensured to be safe.
2. Process optimization
Mechanical stirring and temperature control
Use an electric drill or stirring equipment to reduce viscosity through mechanical shear force, and control the stirring temperature at 40-60℃ (avoid excessive cross-linking).
Example: For expired thickened silicone, stirring can restore its fluidity, but it must be cooled before use to prevent bubbles.
Vacuum dehydration and dispersion process
Use a heated vacuum device to remove water to avoid abnormal viscosity caused by moisture.
Control the shear speed (not too fast to prevent static electricity or powder damage) to ensure uniform dispersion.
3. Formula adjustment
Base polymer and crosslinker ratio
Reducing the amount of crosslinker can reduce viscosity, but the curing performance needs to be balanced. For example, the crosslinker accounts for 1-5 parts in addition-type silicone (based on 100 parts of PDMS).
Selection of fillers and reinforcing agents
Use reinforcing agents such as white carbon black with moderate specific surface area to avoid excessive processing difficulties or too small to affect performance.
Adjust the amount of filler (such as 50-100 parts of alumina thermal conductive filler) to balance viscosity and mechanical properties.
Catalyst and reaction conditions
Control the amount of catalyst (0.1-1 part) to adjust the curing speed to avoid abnormal viscosity due to too fast curing.
The curing temperature needs to be moderate (such as 20-30℃). Too high or too low will affect viscosity and fluidity.
4. Handling of special situations
Expired or thickened silicone
Use an electric stirring rod to stir until hot, and cool after restoring fluidity.
Avoid adding excessive silicone oil directly to prevent damage to the molecular chain structure.
Use after viscosity recovery
The stirred silicone needs to be left to cool and the bubbles eliminated before use to prevent bubbling during the curing process.