Home' FLEXO Magazine : September 2015 Contents 60 FLEXO | SEPTEMBER 2015
thermal and laser welding. PETG roll sleeve performs poorly using
UVB adhesive technology currently on the market.
e red dots in Ta b l e 4 indicate the polymer can be seamed with the
given system or technology, but special application or procedure may
Lower density o ers a bene t for higher yields per unit of material.
OPP and polyole n o er the greatest yields, while PVC and PETG roll
sleeves have the lowest yields per unit within this group of materials.
Method of manufacture for these substrates is an additional consid-
eration, as average thickness and control can impact the actual yield.
Gauge variation can be high in blown and extrusion processes where
calendering can lead to variation within only a few microns. Most of
these substrates are either blown or extruded, but PVC roll sleeve is
Oriented lms are stressed at high strain rates, generally along a single
axis, such as the machine or transverse directions. is high strain
increases the tensile strength of the material in that axis by four to ve
times its unoriented condition. Substrates with higher tensile strength
are tougher and stronger than comparative lms and, as a result,
can be more di cult to cut. However, orientation along an axis also
weakens the material in that direction, due to alignment and order of
polymer chains, making cutting easier in the axis of orientation. is
can facilitate web trimming of roll fed shrink or TDO lms. Cross
direction cutting for either would require sharp blades and tight toler-
ances if die or compression cutting.
Elastic modulus is indicative of extensibility under load and will have
importance for web tensions applied during processing of substrates
on, for example, a printing press, where tight repeat lengths and
registration are required. Generally, higher modulus lms will stretch
less and exhibit greater sti ness. Although the di erences in elastic
modulus properties for the substrates observed in Ta b l e 5 are small,
PVC roll sleeve, PETG roll sleeve and polyole n have demonstrated
higher sti ness compared to the other substrates. Films with higher
natural dyne levels or surface energies can be processed with most
ink systems without surface alteration or treatment. Di erences can
be equated to intermolecular bonding and the electrostatic forces
between molecules, but can also result from additives employed to
aid substrate manufacture, i.e., lubricants and other modi ers. Based
on chemical structure and manufacturing, OPS and OPP have lower
For roll fed, shrink lms, there is a relationship to shrinkage and
shrink force. Typically, the higher the shrinkage, the higher the shrink
force. is can be demonstrated within a polymer group more so
than by comparison to other polymers, but generally higher shrink
materials also have higher shrink forces. It is important to note the 85
degree Celsius shrinkage is characteristic of the performance of these
substrates in a steam tunnel at high altitudes. e information in Ta b l e
5 displays the shrink limitations of OPP and OPS at 85 degrees Celsius
and 95 degrees Celsius.
Coe cient of friction (COF) is a measure of slip or how one surface
moves across another. e importance is in how a substrate moves
through and across print stations, conveyor belts, onto the container,
or released from a mandrel or loading a er processing. Films with
COF values greater than 0.5 are considered non slip. COF is usually
speci ed for a given process and adjusted by the printer with inks or
varnishes as needed.
Gloss indicates the level of brilliance and a higher gloss value is
considered desirable for aesthetics. All substrates listed have relatively
low haze, which is also preferred by converters and brand owners.
However, contact clarity o ered by materials with higher haze and
duller materials also nd application in shrink labeling.
COST VS VALUE
Cost versus value is another important comparison for material
substrates and is shown in Chart 2. Design value is de ned by the
shrinkage properties of the lm at 95 degrees Celsius. e higher
the material's shrinkage properties, the greater the designer's ability
for label design that will conform to more container shape variation.
Material cost shows a relative cost from low to high. PVC roll sleeve
has excellent design value relative to cost. OPS and PVC roll sleeves
have similar material costs, but a signi cant di erence in shrinkage
properties at 95 degrees Celsius. OPP rates low for both cost perfor-
mance and design value. PETG roll sleeve has a high relative cost, but
also delivers high shrink properties. Polyole n delivers relatively high
shrinkage for its design value. It is important to note that this cost
model is relevant for 95 degree Celsius steam tunnel shrinkage and
that other models can be used in a similar fashion for other tempera-
Additional consideration can be given to the type of material and the
type of label. Even some paper labels, which are considered to be a
lower material cost as compared to plastic labels, can have a higher
cost per container than the same container with a shrink label. For
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