Preparation process of silicone masterbatch
The preparation of silicone masterbatch is a complex chemical process involving multiple links such as raw material mixing, reaction control, and post-processing. The following is a detailed introduction to its typical preparation process:
A. Raw material preparation
1.Base polymer
Silicone rubber prepolymer: such as hydroxyl-terminated polydimethylsiloxane (PDMS), is the core component of silicone rubber, providing flexibility and elasticity.
Vinyl silicone oil: used for cross-linking reaction to improve the strength after curing.
2.Filler
Fumed silica (white carbon black): enhance mechanical properties and improve colloid strength.
Calcium carbonate, aluminum oxide: reduce costs and adjust hardness.
3.Crosslinker
Peroxide (such as 2,5-dimethyl-2,5-di-tert-butyl peroxyhexane): trigger free radical cross-linking reaction.
Silane coupling agent (such as KH-560): promote the bonding of filler and matrix.
4.Catalyst
Platinum catalyst: highly efficient catalysis of addition reaction, commonly used in addition type silicone.
Organotin compounds: such as dibutyltin dilaurate, used for condensation type silicone.
5.Other additives
Flame retardants (such as aluminum hydroxide), pigments (such as red iron oxide), plasticizers (such as phthalates).
B. Preparation process
1.Raw material pretreatment
Drying: The filler needs to be dried at 100-120℃ for 2-4 hours to remove moisture and prevent it from affecting curing.
Sieving: Pass through a 200-mesh sieve to ensure uniform filler particle size.
2.Mixing and kneading
Steps:
Add silicone rubber prepolymer and vinyl silicone oil to the kneader and stir at low speed for 5-10 minutes.
Gradually add fillers and knead at high speed for 30-60 minutes until uniform.
Add crosslinking agent, catalyst and additives and continue stirring for 10-15 minutes.
Key points:
The temperature is controlled at 60-80℃ to avoid high temperature causing crosslinking of prepolymer.
Vacuum degassing: Degas at -0.09MPa for 15-30 minutes to eliminate bubbles.
3.Curing molding
Single-component moisture curing:
After coating, it is exposed to the air, moisture triggers a cross-linking reaction, and the curing time is 24-72 hours.
Two-component heating curing:
Component A (containing prepolymer, filler) and component B (containing cross-linking agent, catalyst) are mixed in proportion.
Inject into the mold, heat at 120-150℃ for 1-2 hours, and completely cure.
4.Post-processing
Finishing: remove excess colloid and polish the surface.
Testing: test hardness (Shore A/D), tensile strength, bonding strength and other properties.
C. Key technical parameters
Parameter Typical value Impact
Filler content 30-70% Hardness, strength, cost
Crosslinker dosage 0.5-5% Curing speed, crosslinking density
Catalyst dosage 0.1-1% Reaction rate, storage stability
Mixing temperature 60-80℃ Prevent premature crosslinking
Curing temperature 120-150℃ (two-component) Accelerate curing and improve performance
Curing time 1-72 hours Depends on the curing method and environmental conditions
D. Common problems and solutions
Bubble problem
Reason: uneven mixing, insufficient vacuum.
Solution: Extend the degassing time and add a defoaming agent (such as polydimethylsiloxane).
Poor storage stability
Reason: Catalyst activity is too high or crosslinker is excessive.
Solution: Adjust the type or dosage of catalyst and add an inhibitor (such as ethynyl cyclohexanol).
Insufficient bonding strength
Reason: Improper surface treatment of the substrate or incompatibility of the colloid with the substrate.
Solution: Add a primer (such as a silane coupling agent) and optimize the colloid formula.
E. Application Cases
1.Electronic potting glue
Formula: vinyl silicone oil (20%), fumed silica (40%), platinum catalyst (0.1%).
Process: vacuum degassing after two-component mixing, heating at 150℃ for 1 hour to cure.
Performance: volume resistivity>1×10¹⁴ Ω·cm, temperature resistance -60℃ to 200℃.
2.Medical grade adhesive
Formula: hydroxy silicone oil (30%), calcium carbonate (50%), organic tin catalyst (0.5%).
Process: single component moisture curing, fully cured in 72 hours.
Performance: biocompatibility meets ISO 10993 standards, non-toxic and non-irritating.
Summary
The preparation of silicone masterbatch requires strict control of raw material quality, mixing process and curing conditions to ensure the performance of the final product. By optimizing the ratio of fillers, crosslinkers and catalysts, high-performance glues that meet the needs of different industries can be developed. In the future, with the increasing requirements for environmental protection and intelligence, the preparation of silicone-based adhesives will pay more attention to green technology and functional design.