Introduction: Adhesives/Sealants — the “close relative” industry of the coatings sector
Adhesives (Adhesive/bonding—transmitting structural stress) and sealants (Sealant/sealing—filling joints—blocking the penetration of water/air/dust) are the “close relatives” of the coatings industry, also based on polymer chemistry (epoxy/PU/acrylic/silicone)—but with different formulation design goals
—Coatings pursue ”thin (0.5mm)—high strength (>10MPa)—bonding” Sealants pursue ”thick (>3mm)—high elasticity (movement >25%)—sealing”. Adhesives/sealants and coatings are indispensable ”companions” in automotive manufacturing (structural bonding—replacing welding) + construction (curtain wall sealing—structural silicone) + electronics (chip encapsulation—epoxy underfill)
—and the extension of coatings factories’ product lines into adhesives/sealants is a ”natural expansion” to increase customer stickiness and profits.
I. Comparison of the Three Major Systems
| Product | Base Material | Strength (MPa) | Elongation (%) | Paintable | Core Applications |
|---|---|---|---|---|---|
| Epoxy Structural Adhesive | Two-component epoxy + amine | Shear >20 (strongest) | 1-5 (brittle) | Yes (after curing / sanding) | Automotive hem flange adhesive / aerospace structures |
| PU Sealant | One-component moisture-cure PU | 1-3 (elastic) | >400 (high elasticity) / movement >25% | No (surface — non-tacky — coating does not adhere) | Building joints / automotive windshield |
| MS Polymer | Silane-modified polyether | 1-3 | >300 / movement >25% | Yes (MS surface — coating adhesion “perfect combination of elasticity + paintability”) | Building joints (paintable) / automotive elastic bonding |
FAQ
Q1: Why can MS polymer (silane-modified polyether) achieve both “elasticity + paintable”, while PU and silicone cannot?
The surface of PU sealant——(1) PU has extremely low surface energy (<25mN/m)
——coatings cannot wet it, resulting in “non-stick”
; (2) Plasticizers in PU migrate to the surface——forming an “oil film” that prevents coating adhesion
. Silicone sealant (PDMS/siloxane)——(1) extremely low surface energy (<20mN/m) “sticks to nothing”
——coatings on it——shrink into water beads, paintability = zero
. MS polymer——polyether main chain (polar——coatings wet and adhere) + silane end groups (Si-OCH₃——moisture curing——reacts with moisture in air——cures——elasticity) MS simultaneously possesses the elasticity of PU and the weather resistance of silicone——and its surface is paintable——this is the “chemical innovation” of MS polymer.
Q2: What is the mechanism by which epoxy structural adhesive achieves >20% weight reduction by “replacing spot welding” in automotive manufacturing?
Automotive body — traditional manufacturingspot welding (resistance welding — thousands of weld spots — steel plate + steel plate — each weld spot — weight increase >0.1g)
. Epoxy structural adhesive — (1) replaces part of spot weldingadhesive bonding + spot welding (hybrid joining — adhesive transfers shear force — weld spots maintain positioning — number of weld spots can be reduced >30-50%)
— weight reduction; (2) theuniform stress distribution of adhesive bonding (continuous adhesive layer — stress dispersed over the entire bonded surface)
— stress concentration at weld spots (weld spot edges — fatigue cracks — vehicle NVH issues) — adhesive bondingNVH improvement + fatigue life extended >2 times
.
Related Reading
Summary
The three major adhesive/sealant systems—epoxy structural adhesives (>20 MPa / automotive structures), PU sealants (>400% elongation / building curtain walls), and MS polymers (the “perfect combination” of elasticity and paintability)—each hold unique value in automotive and construction applications. Kexin New Materials provides customers with a full range of adhesive/sealant products and application technical support.