In butyl adhesives, activated magnesium oxide plays a key role in the final formed pressure-sensitive adhesive performance through various mechanisms, with the specific functions as follows:
1. Acid neutralization and stability improvement
Neutralization of acidic substances: Butyl rubber may produce a small amount of acidic by-products (such as HCl) during processing or storage. These acidic substances will cause the colloid to be cross-linked or degraded in advance, affecting the stability and service life of the adhesive. As an alkaline substance, activated magnesium oxide can effectively neutralize these acidic components and maintain the pH stability of the system.
Inhibit side reactions: By neutralizing the acidic environment, magnesium oxide reduces unnecessary side reactions (such as main chain break or vulcanization delay), ensuring that the adhesive remains uniform during storage and extends shelf life.
2. Cross-linking promotion and vulcanization synergistic
Crosslinking density regulation: During the vulcanization (crosslinking), active magnesium oxide can be used as a vulcanization accelerator or synergist. It interacts with vulcanizing agents (such as sulfur and peroxides), accelerates cross-linking reactions, and increases cross-linking density. This enhances the cohesive strength, heat resistance and creep resistance of the colloid while maintaining moderate elasticity, which is crucial for the “visco-elastic balance” of pressure-sensitive adhesives.
Dynamic performance optimization: By adjusting the crosslinking network structure, magnesium oxide helps the pressure-sensitive adhesive achieve a balance between rapid adhesion (flow during pressurization) and anti-peel (rebound after pressure relief) when under stress.
3. Filling reinforcement and rheology performance adjustment
Mechanical performance enhancement: Magnesium oxide is a nano or micron-scale filler, dispersed in colloids to improve tensile strength, tear strength and wear resistance, and prevent the glue layer from rupturing during use.
Viscosity and coating properties control: Its particle characteristics affect the rheological behavior of the adhesive, adjust the viscosity to adapt to the coating process (such as scraping and roller coating), ensure that the adhesive layer is uniform and the thickness is controllable, thereby optimizing the adhesion performance of the final product. .
4. Aging resistance and durability improvement
Thermal stabilizer function: Magnesium oxide can absorb heat and slow down thermal degradation, improving the performance stability of the adhesive in high temperature environments.
Anti-UV and anti-oxidation: Some studies have shown that magnesium oxide can scatter UV rays or react with free radicals, delay photooxygen aging and extend the service life of pressure-sensitive adhesives.
5. Thixotropy and storage stability
Anti-settlement and anti-sag: The addition of active magnesium oxide may impart a certain thixotropy to the colloid, allowing it to maintain a high viscosity when left to stand (prevent filler settlement), while the viscosity is reduced under shear force (easy to construction), thereby improving Processability and storage stability.
6. Interface interaction optimization
Surface Energy Adjustment: Magnesium oxide may enhance initial adhesion by changing the surface energy of the colloid and affecting its wettability with the adhered material (such as plastics, metals).
“Active” Advantages of Active Magnesium Oxide
Compared with ordinary magnesium oxide, activated magnesium oxide can be dispersed more efficiently in the colloid and quickly participate in the reaction, thereby achieving a lower dosage. Significant effect to avoid excessive addition of colloid hardening or increased brittleness.
Active magnesium oxide plays a multifunctional additive in butyl pressure-sensitive adhesives. From chemical stability, cross-linking promotion to physical reinforcement, it optimizes the processability, durability and final adhesion properties of the adhesive in all aspects. The core of its function lies in the ability to achieve the “can be sticky, tear open, and stay for a long time” characteristics required by pressure-sensitive adhesives through precise acid and base regulation and structural modification.