Commonly used resins and their functions in SIS adhesive formulations, and how to select resins for cold-resistant and heat-resistant adhesives
Technical Specification of Resins in SIS Adhesive Formulations Key Resins and Functional Mechanisms in SIS Adhesive Systems
The principal resin components in SIS (Styrene-Isoprene-Styrene) adhesive formulations typically include hydrocarbon resins, terpene resins, and rosin derivatives. Their functional characteristics are elaborated as follows:
Hydrocarbon Resins Classification: Derived from petroleum cracking by-products, categorized into:
Aliphatic (C5 fraction)、Aromatic (C9 fraction)、Cycloaliphatic、Hydrogenated variants.
Functional modulation: Resin type and structural configuration (C5, C9, or C5/C9 copolymer) govern critical performance parameters including Softening point regulation、Hardness-softness balance、Toughness optimization. Thermal resistance adaptation This enables tailored solutions for diverse bonding requirements under varying temperature regimes and mechanical stress conditions.
1.1 C5 Aliphatic Hydrocarbon Resin
Tackification Performance:
1. Exhibits superior peel adhesion strength and rapid tack development
2. Functions as a high-efficiency tackifier in SIS systems
3 .Enhances initial adhesion and cohesive strength
Compatibility & Stability:
1. Demonstrates excellent polymer compatibility with SIS matrix
2. Facilitates homogeneous dispersion for structural integrity
3. Enhances aging resistance through UV stabilization
4. Improves chemical resistance (water/acid)
Rheological Modification:
1.Acts as plasticizer for low-temperature flexibility enhancement
2. Optimizes coating rheology through solvent miscibility
3. Improves substrate wetting characteristics
4. Environmental Profile:
5. Low VOC emission compliant with industrial sustainability standards
1.2 C9 Aromatic Hydrocarbon Resin
Tackification Characteristics:
1. Moderate tackifying efficiency compared to C5 variants
2. Requires synergistic formulation with other resins/additives
3. Primarily functions as adhesion promoter
4. Compatibility Considerations:
5. Requires chemical modification for SIS compatibility optimization
6. Demands precise process control (temperature/shear parameters)
7. Typically used in composite resin systems
Environmental Constraints:
1. Higher odor emission potential
2. Requires emission control measures in sensitive applications
2.1 Terpene Resin Classification: Modified natural resin with distinctive chemical architecture and performance characteristics.
Functional Properties:
Tackification and Rheology Modification: Enhances adhesive performance through viscosity regulation and cohesive strength optimization in SIS matrices. Demonstrates superior adhesion promotion and cohesive energy density improvement.
Matrix Compatibility: Exhibits excellent miscibility with SIS polymers, enabling homogeneous phase dispersion and stable network formation.
2.2 Rosin Resin Classification: Derived from natural rosin through industrial processing.
Liquid Rosin Resin: Lower molecular weight (Mn: 300-500 g/mol) with amorphous structure
Solid Rosin Resin: Higher molecular weight (Mn: 800-1200 g/mol) demonstrating increased structural regularity and reduced polydispersity (PDI <1.5)
Functional Properties: • Cure Acceleration & Tack Enhancement: Improves green strength development rate (t80 reduction ≥30%) while maintaining ultimate bond strength (ASTM D1002). • Durability Enhancement: Unique diterpene structure provides exceptional oxidation resistance (OIT >150 min per ASTM D3895), ensuring long-term performance stability under thermal and environmental stresses. • Rheological Control: Tunable viscosity (Brookfield RVF, 25°C: 500-5000 cP) and flow characteristics through processing parameter optimization. • Environmental Sustainability: Bio-based content exceeding 95% (ISO 16620), complying with REACH and FDA 21 CFR 175.105 regulations.
Supplementary Additives: • Hydrogenated Petroleum Resins: Improve optical clarity (haze reduction ≥15%) and elastic recovery (ASTM D412) • Plasticizers: Modulate Shore A hardness (adjustment range: ±10 points) and low-temperature flexibility • Stabilizers: Antioxidant packages (e.g., hindered phenols/phosphites) and UV absorbers (e.g., benzotriazoles) for weather ability enhancement
III. Resin Selection Methodology for Performance-Optimized SIS Adhesives Key formulation principle: Maintain optimal viscoelastic balance (tan δ @ application temperature ≈1) through strategic resin selection.
3.1 Cryogenic-Resistant Formulations (-40°C to -60°C service) a) Rosin System Modification:
Replace 20-40% solid rosin with liquid derivative (Tg reduction: 10-15°C)
Preferred specification: Acid number <20 mg KOH/g (ASTM D465)
b) Petroleum Resin Selection:
High aromaticity grades (C9 content >65%) with controlled crystallinity
c) Elastomer Matrix Engineering:
Incorporate SBS with high diblock content (>30%)
Partial substitution with SSBR (styrene ≤25%, vinyl ≤50%)
3.2 High-Temperature Resistant Formulations (90-120°C service) Critical parameters: Thermomechanical stability (SAFT >100°C) and oxidative resistance
a) Terpene Resins:
High softening point grades (Ring & Ball: 115-125°C)
Thermal stability: ≤2% weight loss @ 180°C (TGA)
b) Hydrogenated C5 Resins:
Hydrogenation degree >90% (iodine value <5 g I2/100g)
Enhanced thermal-oxidative stability: ΔG' <10% after 500h @ 85°C
c) Standard C5 Resins:
Cost-effective alternative requiring formulation compensation: Antioxidant loading increase (0.5-1.0 phr)
C5:C9 ratio optimization (70:30 recommended)
Compatibilizer addition (e.g., malleated SBS)