| Ethylene Copolymers are leading materials for formulating
hot-melts (pressure sensitive and non pressure sensitive) in applications
such as packaging, bookbinding, woodbinding and many other industrial
applications.
This success is due to the high technical versatilty
of Ethylene copolymer based formulations which can fullfil highly demanding
technical requirements covering both long open time and fast setting time,
resistance to very low temperatures (-40°C) or very high temperatures
( +80°C) with very high thermal and UV stability for water-white formulations.
Key parameters for choosing the right base polymer for
your formulations are:
- Choice of
Copolymer
- Content of
Copolymer
- Melt Flow
Index (MFI)
Copolymer selection will depend on final properties to
be achieved.
EVA products are the right choice for general
purpose hot-melts for packaging and bookbinding applications or to reach
high temperature resistance in transportation or assembly. High VA content
EVA would also be an interesting polymer for formulating Hot Melt Pressure
Sensitive (HMPSA) in applications such as bottle labelling or sanitary.
Ethylene / acrylic ester copolymers polymers
have a lower glass transition temperature than EVA (Tg) and provide a
better adhesion to difficult substrates as well as better performances
at very low temperatures. These polymers will help formulators to achieve
very high performances in deep-freeze applications or when a high level
of adhesion is required ( varnished carboard, plastic to paper bonding...).
Ethylene / acrylic ester copolymers based hot-melts also provide a very high resistance to degradation
and low odor when formulated with the right tackifiers and preservatives.
For the most challenging bonding (UV varnished substrates or demanding
ageing test) the "Ethylene - Acrylic esters - Maleic Anhydride"
or "Etylene - Vinyl Acetate - Maleic Anhydride" terpolymers will
be the ultimate choice for achieving very high performances.
The Copolymer content is a key parameter to adjust Adhesion
/ Cohesion balance in the hot-melt formulation as well as the performances
at low or high temperature. This copolymer content also impacts strongly
on polymer cristalinity with a high impact on the mechanical performances
of the formulated hot-melt.
Figure 1 : Crystallinity (%) = f(Comonomer % weight)
This parameter influences the polymer's viscosity. The
longer the polymer chain is, the higher the viscosity, and hence the lower
the melt flow index. A lower MFI will result in greater mechanical strength,
higher ring and ball softening point, and higher performances at high
temperature (SAFT or PAFT tests), but will also increase hot-melt viscosity
and strongly influence open time and setting time.
|
