Amino silicone oil can be compounded with resins and can also act as a curing agent (crosslinking agent), especially in epoxy resin systems; it is also applicable to some silicone resin systems.
I. Core Principle (Why It Works as a Curing Agent)
Amino silicone oil contains primary amino groups (-NH₂) and secondary amino groups (-NHR) on its molecular chain. These active hydrogen atoms can undergo ring-opening addition reactions with epoxy groups (three-membered rings) in epoxy resins, forming a three-dimensional crosslinked network and curing the resin.
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Reaction schematic: -NH₂ + Epoxy group → -NH-CH₂-CH(OH)-
At the same time, the Si-O-Si backbone is introduced into the resin system, significantly improving heat resistance, weather resistance, low surface energy, toughness and hydrophobicity.
II. Applicable Resin Systems
1. Epoxy Resins (Most Common and Mature)
- Can be used alone as a curing agent (high amine value, multi-amino silicone oil).
- Can be compounded with traditional amines, acid anhydrides and dicyandiamide for synergistic curing.
- Typical applications: anti-corrosion coatings, electronic encapsulants, structural adhesives, high-temperature adhesive films, copper clad laminates.
2. Silicone Resins (Partially Applicable)
Reacts with silicone resins containing silanol groups (Si-OH) or alkoxy groups (Si-OR) to form Si-N crosslinks.
Mainly used in high-temperature resistant, weather-resistant coatings and insulating materials.
3. Other Resins (Mainly for Modification, Not Primary Curing Agent)
- Polyurethane: Reacts with NCO groups to improve toughness and reduce surface tension.
- Phenolic resins and polyimides: Amino groups participate in crosslinking/grafting to enhance toughness and heat resistance.
III. Key Selection and Ratio Guidelines
1. Selection of Amino Silicone Oil (Determines Curing Performance)
- Terminally amino silicone oil: High reactivity and crosslinking efficiency, suitable as the primary curing agent.
- Pendant amino silicone oil: Mild reaction and good compatibility, suitable for compound curing/modification.
- Amine value: 0.3–2.0 mmol/g; higher amine value means faster curing and higher crosslink density.
- Molecular weight / viscosity: Low viscosity for easy dispersion; high viscosity for better toughening effect.
2. Ratio Principle (Epoxy Systems)
Calculated at a 1:1 ratio of active hydrogen equivalent weight (AHEW) to epoxy equivalent weight (EEW).
Example: Epoxy E-51 (EEW ≈ 196) + amino silicone oil (AHEW ≈ 300)
Mass ratio ≈ 196:300 ≈ 1:1.53
Practical formulation: 5–30% amino silicone oil to balance curing and modification effects.
IV. Curing Process (Reference)
- Room temperature curing: Slow, requires post-curing for more than 7 days.
- Medium temperature curing: 80–120℃ for 1–4 hours, commonly used.
- High temperature curing: 150–200℃ for 30–60 minutes, optimal performance.
V. Advantages and Limitations
Advantages
- Imparts high toughness, low internal stress and high elongation (over 25%) to epoxy resins.
- Significantly improves high and low temperature resistance, weather resistance, salt spray resistance, damp heat resistance and flame retardancy.
- Low surface energy, good hydrophobicity, defoaming and leveling properties.
- Environmentally friendly, partially replacing restricted curing agents such as dicyandiamide.
Limitations
- When used alone for curing, crosslink density, hardness and mechanical strength are slightly lower than those of traditional polyamides and aromatic amines.
- Compatibility with non-polar resins is average, requiring pre-reaction, chain extension or coupling agents.
- Higher cost than conventional amine curing agents.
VI. Practical Formulation Recommendation (Epoxy System)
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Basic formulation (parts by weight)
- Epoxy resin (E-51): 100
- Amino silicone oil (amine value 0.8–1.2 mmol/g): 15–25
- Accelerator (DMP-30): 0.5–1.0
- Fillers / diluents: as needed
- Curing conditions: 100℃/2h + 150℃/1h
- Performance: Tg ≈ 80–120℃, good toughness and excellent weather resistance.
VII. Conclusion and Selection Suggestions
- Amino silicone oil can be used as a high-performance modified curing agent, especially suitable for epoxy systems.
- For high toughness, temperature resistance, weather resistance and low stress, prefer amino silicone oil curing or compounding.
- For ultra-high hardness and strength, it is recommended to use in combination with polyamides and aromatic amines.
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