Pressure Sensitive Tapes Guide
Pressure Sensitive Adhesives (PSA)
Pressure Sensitive Adhesives (PSAs) are a unique category of adhesives which form an instantaneous bond under light pressure at room temperature. PSAs join similar or dissimilar materials without requiring activation by water, solvent, or heat. PSAs are permanently tacky and provide sufficient internal cohesive strength to hold and bond materials together without breaking apart. This ability to generate an instantaneous solvent free bond under light pressure allowed PSAs to gain world-wide acceptance in a variety of industries, markets, and applications. PSAs are used in tapes, labels, as assembly aids, and other products throughout the world. PSAs owe their success to being relative easy to use, convenient, increase productivity, and generally a cost effective bonding or decorating solution to alternative technologies.
PSA Performance
Pressure Sensitive Adhesives (PSAs) are viscoelastic in nature that is to say that PSAs behave like a fluid and/or a solid depending upon environmental and stress conditions they are under in a given application and situation. PSAs have a delicate balance between their viscous (ability to wet out and flow - bonding) and elastic (ability to resist flow, store energy - debonding) properties. The ability of Pressure Sensitive Adhesives to bond quickly and hold materials is influenced by a variety of factors such as
- Environmental conditions, e.g. time, temperature, humidity, etc
- Application condition, e.g. speed of application, light versus heavy pressure, cleanliness, etc.
- Chemical and structural composition of the adhesive itself.
Adhesive performance is characterized by tack (ability to bond instantly under light pressure), peel (ability to resist its removal from a surface), and shear (ability to resist internal cohesive failure when subjected to a shearing force).
PSA Classification
Pressure Sensitive Adhesives (PSAs) can be classified by their chemical composition, the type of construction they are used in, and/or the functional performance of the adhesive itself. Rubber, acrylic, and silicone-based adhesives are typical PSAs chemistries used by tape and label manufacturers. Rubber, acrylic, and silicone PSAs will perform differently due to their chemical nature. Rubber adhesives are generally known for their excellent tack and high initial adhesion, high affinity to low surface energy substrates such as polyethylene and polypropylene, poor to fair UV resistance, and tend to be yellow color. Acrylic adhesives generally offer excellent weatherability and good clarity, good solvent resistance, low initial adhesion that may build with time, good plasticizer resistance, and good convertability (not as gummy as rubber-based adhesives). Silicone adhesives offer higher temperature resistance (>400 F), low peels, and high shear.
PSAs are often referred to by their functional performance, i.e. removable, permanent, or repositionable. Permanent adhesives are difficult to remove without damaging or destroying either the tape/label or bonded surface. Removable adhesives separate cleanly from the bonded surface without leaving adhesive residue or damaging the surface or substrate. Repositionable adhesives are permanent in nature but allow a label or tape to be removed and reapplied over a short time span when initially applied to a surface.