ABSTRACT
Pressure-sensitive tapes were first used about 150 yr ago. Pressure-sensitive labels came to the
market 90 yr later. About 10 yr after that pressure-sensitive protective films were manufactured.
Pressure-sensitive products (PSPs) such as pressure-sensitive adhesive (PSA) coated web have
been defined by the special nature of this adhesive although the definition of PSA is not completely
clear. The German technical term Haftkleber (i.e., adhesive which adheres) supposes that it is
possible to differentiate between adhesion and building up of an adhesive bond. In English the
term pressure-sensitive adhesives (i.e., adhesives that bond when pressure is applied) admits
pressure as an indispensable condition for their function. In reality, as known from loop tack
measurements and touch blow labeling, almost no pressure is required for label application but
high pressures are needed for protective films in coil coating. Autocollants, the French name
does not define the application conditions. It refers only to the bonding behavior. The common
characteristic of these products is ensured by their special viscoelastic behavior, manifested as
permanent cold flow, where the chemistry of the adhesive plays only a secondary role [1]. The
development of PSPs without a coated PSA layer (in the classical sense known from the converting
industry) makes the definition of this product group more difficult. Adhesive-free PSPs have been
developed some decades ago. In this case adhesive-free means that the self-adhesive component is
not coated on the product surface. It is included in the carrier, that is, the carrier per se is pressure
sensitive. In some cases, an adhesive-free composition is used and pressure sensitivity is provided
by physical treatment of the carrier surface or application conditions (temperature, pressure).
According to the definition given in Ref. [2], PSAs are adhesives “which in dry form are aggres-
sively and permanently tacky at room temperature . . . and adhere without the need of more than finger or hand pressure, require no activation by water, solvent, or heat.”
