Pressure-Sensitive Adhesives Chemicals

Acrylic PSAs (solvent-based acrylic copolymers or acrylic emulsions) dominate the label and tape markets due to excellent UV and aging resistance, clarity, and formulatability. Natural rubber-based PSAs provide unmatched initial tack (quick stick) and are used in masking tapes and general-purpose applications. Silicone PSAs are used for medical skin contact and high-temperature applications.

Tackifier resins increase tack (initial grab), peel strength, and adhesion of base polymers. Rosin esters (hydrogenated, disproportionated) and C5/C9 hydrocarbon resins are the main types. Low softening point tackifiers increase tack; higher softening point resins increase cohesive strength. Selection depends on polymer compatibility and the required tack-peel-shear balance.

Crosslinkers in PSAs increase cohesive strength (shear resistance) and reduce cold flow without significantly reducing tack and peel. In acrylic PSAs, aluminum acetylacetonate (Al-AcAc), isocyanates, or aziridines are added at 0.05–2% on binder. UV crosslinking using benzophenone-type initiators is used in UV-crosslinked PSA tapes. Over-crosslinking causes brittle film with poor tack — the balance is critical.

Standard PSA tests are: 180° peel (PSTC-101 or FINAT FTM 1), loop tack (FTM 9), and shear adhesion (FTM 8 or PSTC-107). Peel measures bond strength to substrate, tack measures initial grab, and shear measures cohesive strength. Each must be balanced for the application — labels need high tack and low shear, while industrial duct tape needs high shear with controlled peel.

Removable PSAs use lower-MW base polymers, selectively compatible tackifiers, and often microsphere geometry to limit substrate contact area. Acrylic microsphere PSAs (the Post-it Note technology) achieve true repositionability through partial wetting. Removable adhesion is typically 1–4 N/inch peel — enough to hold but allowing clean removal without residue, even after long storage.

Solventborne acrylic PSAs offer the highest performance — superior peel/shear balance, optical clarity, and aging — but VOC regulations are pushing replacement. Waterborne acrylic emulsion PSAs have closed most of the performance gap and dominate label adhesives now. Hot-melt PSAs (SBS/SIS/SEBS-based) offer 100% solids and fast processing for tape applications. Each chemistry has different processing requirements and equipment needs.