Composition
PSAs are usually based on an elastomer compounded with a suitable tackifier (e.g., a rosin ester). The elastomers can be based on:
- Acrylics, which can have sufficient tack on their own to not require a tackifier.
- Bio-based acrylate. Recently, a biological-based macromonomer was grafted onto a backbone of acrylate so that the resulting PSA uses 60% bio-based materials.
- Butyl rubber
- Ethylene-vinyl acetate (EVA) with high vinyl acetate content; can be formulated as a hot-melt PSA.
- Natural rubber
- Nitriles
- Silicone rubbers, requiring special tackifiers based on "MQ" silicate resins, composed of a monofunctional trimethyl silane ("M") reacted with quadrafunctional silicon tetrachloride ("Q").
- Styrene block copolymers (SBC), also called styrene copolymer adhesives and rubber-based adhesives, have good low-temperature flexibility, high elongation, and high heat resistance. Frequently used in hot melt adhesive applications, where the composition retains tack even when solidified; however non-pressure-sensitive formulations are also used. High heat resistance, good low-temperature flexibility. Lower strength than polyesters. They usually have A-B-A structure, with an elastic rubber segment between two rigid plastic endblocks. High-strength film formers as standalone, increase cohesion and viscosity as an additive. Water-resistant, soluble in some organic solvents; cross-linking improves solvent resistance. Resins associating with endblocks (cumarone-indene, α-methyl styrene, vinyl toluene, aromatic hydrocarbons, etc.) improve adhesion and alter viscosity. Resins associating to the midblocks (aliphatic olefins, rosin esters, polyterpenes, terpene phenolics) improve adhesion, processing and pressure-sensitive properties. Addition of plasticizers reduces cost, improves pressure-sensitive tack, decrease melt viscosity, decrease hardness, and improve low-temperature flexibility. The A-B-A structure promotes a phase separation of the polymer, binding together the endblocks, with the central elastic parts acting as cross-links; SBCs do not require additional cross-linking.
- Styrene-butadiene-styrene (SBS), used in high-strength PSA applications
- Styrene-ethylene/butylene-styrene (SEBS), used in low self-adhering non-woven applications
- Styrene-ethylene/propylene (SEP)
- Styrene-isoprene-styrene (SIS), used in low-viscosity high-tack PSA applications
- Vinyl ethers
Read more about this topic: Pressure-sensitive Adhesive
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