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
Famous quotes containing the word composition:
“The composition of a tragedy requires testicles.”
—Voltaire [François Marie Arouet] (1694–1778)
“Boswell, when he speaks of his Life of Johnson, calls it my magnum opus, but it may more properly be called his opera, for it is truly a composition founded on a true story, in which there is a hero with a number of subordinate characters, and an alternate succession of recitative and airs of various tone and effect, all however in delightful animation.”
—James Boswell (1740–1795)
“I live in the angle of a leaden wall, into whose composition was poured a little alloy of bell-metal. Often, in the repose of my mid-day, there reaches my ears a confused tintinnabulum from without. It is the noise of my contemporaries.”
—Henry David Thoreau (1817–1862)