Even if Styrene Block Copolymers (SBCs)
are the most common polymer base for formulating pressure sensitive hot-melts,
Ethylene Copolymers can also be a good choice, being able to match highly
demanding technical requirements in applications such as bottle labelling,
bookbinding or specialty labels.
In this type of adhesive, the flexibility provided by
a high content of Vynil Acetate or Acrylate (more than 30%) is enhanced
by adding a plasticizer, which ensures the "sticky" effect at
Ethylene copolymers based HMPSA can provide very high
adhesion on difficult substrates such as untreated polyolefins or various
plastics as well as high color stability in water white or white formulations.
For HMPSA formualtions, high coplymer content and high
MFI are preferred as they present a lower glass transtion temperature as well
as a lower cristallinity.
All these polymers can be formulated with a wide range
of tackifying resins
such as rosin derivatives or hydrocarbon resins. Water white hot-melts
can be formulated using hydrogenated tackifiers.
To adjust viscosity, reduce cost or enhance adhesion
properties, plasticizers or oils can be added. A broad range of plasticizers
or oils are used in combination with Ethylene copolymer based HMPSA including
Phtalates, benzoates, parrafinic oils , poly-isobutylene, etc.
A preservative system is always added to protect the
hot-melt from thermal degradation during manufacturing and application
as well as a UV/light stabilizer when needed.