The vulcanization of liquid silicone refers to the process of forming a cross-linked structure between liquid silicone molecules through chemical reactions, thereby transforming it into a solid elastomer with a three-dimensional network structure. This process is the key to the transformation of liquid silicone from a fluid state to a solid state, and has an important impact on the physical and chemical properties of the material.
1. The basic principle of vulcanization
Cross-linking reaction
During the vulcanization process, the raw rubber in the liquid silicone (such as vinyl-terminated polydimethylsiloxane) and the cross-linking agent (such as hydrogen-containing silicone oil) undergo a silylation reaction under the action of a catalyst (such as a platinum complex) to form a cross-linked structure.
Reaction formula:
Si-H+CH2=CH−Si→Si-CH2−CH2−Si
Cross-linking density: The higher the degree of cross-linking, the stronger the hardness, strength and chemical resistance of the material.
Catalysts and inhibitors
Catalysts: such as platinum catalysts, accelerate the vulcanization reaction.
Inhibitors: such as acetylene compounds, slow down the vulcanization rate and ensure the stability of the material during storage and transportation.
2. Factors affecting vulcanization
Temperature
Increasing the temperature will accelerate the vulcanization speed, but it may cause uneven cross-linking structure and affect the material properties.
Usually, the vulcanization temperature of liquid silicone is between 120°C and 180°C.
Time
Too short vulcanization time will lead to incomplete cross-linking and insufficient material performance; too long time may cause over-vulcanization, causing the material to become brittle.
Pressure
Applying pressure during the vulcanization process can reduce bubbles and improve the density and mechanical properties of the material.
Raw material ratio
The ratio of raw rubber, cross-linking agent and catalyst needs to be precisely controlled to ensure the completeness of the vulcanization reaction and the stability of material properties.
3. Vulcanization method
Hot vulcanization
After the liquid silicone is injected into the mold, it is heated and cured by an oven or heating plate.
Advantages: mature process, suitable for most liquid silicone.
Disadvantages: high energy consumption and long production cycle.
Room temperature vulcanization
Liquid silicone is cured by chemical reaction at room temperature under the action of a catalyst.
Advantages: no heating equipment is required, suitable for heat-sensitive applications.
Disadvantages: Slow vulcanization speed, may produce by-products.
Platinum catalyzed vulcanization
Using platinum as a catalyst, the vulcanization process has no by-products and the product has high transparency.
Application: medical, optical and electronic fields.
Other methods
Double 2-pentane vulcanization: low cost, but may produce by-products.
UV or electron beam curing: suitable for liquid silicone with special formula, fast curing speed.
Microwave vulcanization: use microwave energy to heat and improve production efficiency.
4. The effect of vulcanization on the performance of liquid silicone
Physical properties
Hardness: The higher the degree of vulcanization, the greater the hardness.
Elasticity: Moderate vulcanization can improve elasticity, and over-vulcanization will cause the material to become brittle.
Wear resistance: The cross-linked structure enhances the wear resistance of the material.
Chemical properties
Chemical resistance: The vulcanized silicone is more resistant to acids, alkalis and solvents.
Thermal stability: The cross-linked structure improves the high temperature resistance of the material.
Processing performance
The vulcanization process needs to be precisely controlled to ensure that the material has good fluidity and filling properties during molding.
5. Application fields
Medical field
Used in the manufacture of catheters, prostheses and syringe seals, the sulfur-modified silicone has good biocompatibility and elasticity.
Electronic field
Used in the encapsulation and potting of electronic components, the sulfur-modified silicone provides excellent insulation and protection properties.
Automotive field
Used in the manufacture of seals and shock absorbers, the sulfur-modified silicone has high temperature resistance and aging resistance.
Consumer goods field
Used in the manufacture of pacifiers, kitchen utensils and smart wearable devices, the sulfur-modified silicone provides soft touch and safety.
6. Precautions
Raw material selection
Ensure that all raw materials are from reliable suppliers and meet relevant standards and requirements.
Mixing process
The vacuum degree and stirring speed should be strictly controlled during the mixing process to avoid the introduction of bubbles and impurities.
Post-processing
The sulfur-modified products need to be post-processed, such as trimming, cleaning and inspection, to ensure the final quality and appearance.
The sulfurization of liquid silicone is a key step in determining its performance and application. By precisely controlling the sulfurization conditions, high-performance silicone products that meet the needs of different fields can be produced.