[Resin Materials] Understand pressure-sensitive adhesives and choose the right one

[Resin Materials] Understand pressure-sensitive adhesives and choose the right one

① Elastomer-based pressure-sensitive adhesives
The elastomers used in these PSAs started with natural rubber and later expanded to various synthetic rubbers and thermoplastic elastomers. By the elastomer used, this type can be further divided into natural rubber PSA, synthetic rubber PSA, and thermoplastic elastomer PSA.
a. Natural rubber PSA
This is the earliest-developed rubber-based pressure-sensitive adhesive, and its output is still large today. It uses natural rubber elastomer as the main body, combined with tackifying resins, softeners, antioxidants, pigments/fillers, and crosslinking (vulcanizing) agents into a complex mixture. Natural rubber has both high cohesive strength and elasticity, and it also mixes well with many tackifying resins, giving high tack and good wetting of the adherend, so natural rubber is a fairly ideal main material for PSAs. Its main drawback is the unsaturated double bonds in the molecule, which make it poor at resisting aging from light and oxygen. But through measures such as crosslinking and using antioxidants, its weather resistance and heat resistance can be improved. With natural rubber PSA you can make almost every type of pressure-sensitive adhesive product.
b. Synthetic rubber and reclaimed rubber PSAs
PSAs made with synthetic rubbers such as styrene-butadiene rubber, polyisoprene rubber, polyisobutylene and butyl rubber, chloroprene rubber, and nitrile rubber as the main body, plus additives like tackifying resins, softeners, and antioxidants, each have their own characteristics. But none are as important as natural rubber PSA. Reclaimed rubber, especially PSA made from reclaimed natural rubber, also has decent performance and a relatively low price, so it gets attention too.
c. Thermoplastic elastomer PSAs
Thermoplastic elastomers represented by styrene-butadiene-styrene block copolymer (SBS) and styrene-isoprene-styrene block copolymer (SIS) are the main raw materials for hot-melt PSAs. Because hot-melt PSAs use no solvent, cause no environmental pollution, and have high production efficiency, in today's society where calls for energy saving and eliminating environmental pollution keep growing, this type of PSA is becoming more and more important.
② Resin-based pressure-sensitive adhesives
The resins used in these PSAs include polyacrylate, polyurethane, polyvinyl chloride, and polyvinyl ether. Among them, polyacrylate is the most used, and its output has already surpassed natural rubber PSA.
a. Acrylate PSA
Acrylate copolymers made by copolymerizing various acrylate monomers are the most important type of resin-based PSA. Compared with the rubber-based PSAs above, they have many advantages: they look colorless and transparent and have very good weather resistance; generally they don't need additives like tackifying resins, softeners, or antioxidants to get good pressure-sensitive bonding performance, so the formula is simple; and by copolymerization and crosslinking you can make PSAs that meet all kinds of different performance requirements. So in the past 20 years this type of PSA has developed very fast and has already replaced natural rubber PSA's dominant position.
b. Silicone and other resin-based PSAs
PSA made by mixing silicone resin and silicone rubber has excellent high-temperature resistance and aging resistance. It's a fairly important special PSA, mainly used to make various high-end pressure-sensitive adhesive products.