Page 68 - Plastics News March 2025
P. 68
PRODUCT NEWS
out slip additives produce high COF levels, but (PET, EVOH, Polyamide, adhesives) and very
most applications require a low COF on the inner sticky resins such as plastomers should be con-
sealing layer and a high COF on the outer side. sidered, as should the variation over time and
Manufacturers use slip additives to achieve this ambient temperature.
balance.
Amide migration steps in extruded plastic film.
Courtesy of The effect of film winding tension
and melt temperature on COF and others prop- This graph compares the COF vs time of LDPE
erties of PE blown film.
and LLDPE with 500 and 1000 ppm of eru-
More Options for Sticky Resins camide. The effect of polyolefin formulation and
processing variables on slip agent performance.
For more demanding packaging applications, Courtesy of The effect of polyolefin formulation
higher molecular weight amides are available, and processing variables on slip agent perfor-
which have a more controlled migration speed. mance.
For this reason, they are more stable to variables
such as temperature, time, roll tension, and the Antiblock Additives
presence of polar substrates in the structure.
Plastic films usually have smooth surfaces, which
Additionally, there are non-migratory slip addi- means they tend to stick together when they
tives, which allow obtaining an instantaneous come into contact, making it difficult to separate
and permanent low COF. These are especially them. This phenomenon is called blocking, mak-
useful for very thin films or applications that re- ing it difficult to open the package or bag during
quire distinct slip levels between the internal and the filling process or even for the end consumer.
external surfaces. As in migrating additives, the Blocking is the adhesion of two adjacent lay-
films do not require conditioning time to reach ers of film. This problem is more noticeable in
equilibrium.
polyethylene and polypropylene films (blown or
Some key aspects for slip additive performance cast) and is caused by Van der Waals forces be-
are the level of COF needed on the external and tween the polymer’s amorphous regions.
internal surface, total film thickness, distribu- An effective method for combating these is-
tion of layers in the coextrusion, and packaging sues is to add an anti-block additive. The most
structure. Also, the presence of polar substrates
common ones use minerals of fine particle size.
68 PLASTICS NEWS March 2025
