Film properties tests and details

Film and Package Tests Printable Version (.PDF)
Specular Gloss - ASTM-D-1223
Gloss is measured on a glossmeter. This instrument has an
incandescent light source and a photosensitive receptor
which responds to visible light.
Light shines onto the sample at a specified angle. Some of
this light is reflected into the photosensitive receptor. The
fraction of the original light which is reflected is the gloss of
the sample.
Gloss is an important merchandising factor and this test
makes it possible to specify and control this surface
characteristic so that the desired effect will be assured.
Haze - ASTM-D-1003
The haze of transparent packaging materials is measured on
a special hazemeter which has an incandescent light source
and geometrically arranged photocells that measure the
transmitted and scattered light.
The sample is placed between the light source and the
photocells. The amount of light transmitted by the sample,
the light scattered by the sample and the instrument and
the total incident light are measured. From these values the
percentage of transmitted light which is scattered can be
calculated. The hazemeter measures these variables and
interrelates them so that the percentage of scattered light
can be read on the meter.
this test is important to products or in uses where true color
and high visibility are required.
Transmittance - ASTM-D-1003
The percent of light transmission on translucent materials is
measured on the same instrument as haze. Using its
incandescent light source and geometrically arranged
photocells which ratio the amount of light transmitted
through the sample versus the amount transmitted with no
sample present. Transmittance, Opacity and Optical Density
are related mathematically as:
Opacity = 1 / Transmittance
Optical Density = Common Logarithm (Opacity)

Tappi Opacity - T-425
Tappi Opacity is a reflectance type of Opacity measurement.
It is a contrast ratio obtained by testing the samples
reflectance when backed by a black material versus the
reflectance when the film is backed by a white material. The
incandescent light source and photocell detector are on the
same side of the sample while the background is placed
behind the sample.
Tappi Opacity = Light reflected when sample backed by
black background / Light reflected when sample backed by
white background
Water-Vapor Transmission - ASTM-F372
The water vapor transmission rate (WVTR) through flexible
barrier films is measured using an infrared diffusometer.
The diffusometer establishes a condition of 90% relative
humidity at 100°F on one side of a film by means of a
heated saturated salt solution and a condition of 0% relative
humidity at 100°F on the other side using a stream of warm
dry air. When the source of dry air is turned off, moisture
vapor permeating the film from the moist side accumulates
on the dry side. The rate at which this moisture build up
takes place is sensed by an infrared detector and recorded
as WVTR.
This test is extremely important since it gives a "baseline"
value for comparing films in terms of moisture barrier.
However, it should be pointed out that WVTR is normally
measured on flat sheets and does not include end use
package variables such as heat seals, folds, and creases.
Tear-ASTM-D-1922
A tear tester has a stationary clamp and a movable clamp
on a pendulum, means for holding this pendulum in a raised
position, then quickly releasing it, and a scale that registers
the arc through which the released pendulum swings.
Samples of paper or film are clamped into the tester and
nicked to start the tear; then the pendulum clamp is
released. This tears the sample and the scale registers the
arc. As the arc is proportional to the tear strength of the
sample, calibration of the arc gives the tear strength.
Tear strength is reported in grams. It is the force necessary
to continue tearing a sample after a nick has been made.
This test is very important for all films as well as for paper.
High tear values may be needed for machine operations or
for package strength. However, low tear values are
necessary and useful for easy opening of some package
types.

Tensile and Elongation - ASTM-D-882
The testing machine of clamps to hold the sample, some
means of gradually increasing the load on the specimen
until it breaks and indicators which show the load and the
amount of elongation.
To perform the test, measured, gauged specimens are
clamped into the testing machine and stretched until they
break.
Tensile strength is usually reported in pounds per inch of
width necessary to pull the paper apart. For films, the usual
units are pounds per square inch of original cross-sectional
area. Tensile strength is quite literally the amount of force
necessary to pull a material apart. The elongation is the
amount a material will stretch before breaking.
Tensile strength is a most important value for materials
used in applications such as heavy-duty bags. A large value
for elongation is an index of toughness, since it indicates a
material will absorb a large amount of energy before
breaking.
Gas Transmission
Test specimens are clamped in the 100 cm2
diffusion cell.
Both sides of the cell are initially purged with an oxygen-
free carrier gas to remove residual oxygen from the system
and de-sorb oxygen from the sample.
When a stable zero reading has been established, oxygen is
introduced into the upper half of the diffusion chamber. The
carrier gas continues to flow through the lower half and into
the coulometric oxygen detector.
After a short interval, the first molecules of oxygen diffusing
through the barrier are conveyed by the carrier gas to the
detector. As displayed by the graphic recorder, the detector
current rises, finally leveling off at a value representative of
the equilibrium transmission rate of oxygen through the
barrier. It should be noted that this equilibrium transmission
rate is independent of the flow rate of the carrier gas.
Impact Strength - ASTM-D-3420
The pendulum impact tester can be used to measure impact
strength of papers, boards and films. An impacting head on
the end of a pendulum is swung through an arc into and
through sample. Tester has a means of measuring
difference between potential energy of pendulum at
maximum height in free swing and potential energy of the
pendulum after rupture of sample. This difference in energy
is defined as impact strength and is reported in units of
kilogram-centimeters. It is useful in predicting resistance of
a material to breakage from dropping or other quick blows.

A test similar in scope, method and significance is the dart
drop test (ASTM-D-1709). Weighted dart is dropped from
standard height onto taut sample. Significance and purpose
are the same as in the pendulum test. Dart unit is weight of
dart in grams that breaks sample 50% of the time.
These tests give an index of material's dynamic strength
and approximate what will occur when package is dropped.
*****************************************************************************************
*
Sealing Film Printable Version (.PDF)
Sealing Theory SEAL = HEAT + TIME + PRESSURE
The sum total of these three variables should remain constant in order to
effect consistent seals. For example, if dwell time is reduced, then heat or
pressure may be needed to be increased to compensate.
Heat & Time The effort to regulate heat is not as straightforward as simply setting the
temperature on a controller to the suggested sealing temperature of a
packaging material. Machine speeds effect the temperature of the crimper or
sealing jaw face, since heat is constantly being drawn off the face by the
packaging material. The heat must also be sufficient to penetrate from the
face of the crimper or jaw through the film or lamination to the sealant layer,
and not so high that it damages the film or lamination.
The more time available for contact between the crimpers and the packaging
materials (referred to as dwell time), the more heat can penetrate through to
the sealant layer. As production speeds are increased, sealant layer quality
and/or quantity may need to be enhanced.
Crimpers and sealing jaws can be manufactured from special materials that
are especially good at transferring heat. Easy Seal Crimpers utilize a special,
durable bronze alloy sealing face, and sealing jaws can also be manufactured
with copper bodies and durable Hastelloy sealing faces.
Col Seal films remove both heat and time as variables, since all that is
required to make a seal is pressure.

Pressure The variability of pressure can be made
constant through refinements in crimper
or sealing jaw setup and design.
Inadequate or uneven sealing pressure
can cause end seal leaks, especially at the
intersection of two and four layers of film
in areas such as the fin seal, wrinkles or
gussets. Sometimes additional heat or
dwell time can help sealant to flow into and plug leaks in these areas, but
these solutions may not be practical. Attempts to improve seals by
increasing sealing pressure can cause the crimpers/jaws to split or cut the
package.
Setup On all machines the serrations need to be aligned properly. On horizontal
wrappers the crimper clearance and spring pressure need to be set properly,
and backlash (independent movement of the upper and lower shafts) needs
to be controlled. It can take a great deal of skill and finesse to create enough
pressure to seal without having excess pressure split or cut the packaging
material. If no amount of adjusting allows you to achieve adequate results,
then a change in the design of the crimpers or sealing jaws is necessary.
Design
Design changes can entail an upgrade to Easy Seal Crimpers and/or a change
in the serration pattern. Either way, our goal is to provide even sealing
pressure across varying layers of film in the end seal area.
Serration Patterns It is rare to see crimpers and jaws on horizontal wrappers or vertical baggers
with smooth faces; they almost all have some type of serration pattern. As
the packaging material is stretched over the serration pattern extra sealing
pressure is exerted. The serrations also cause a "shearing" action, where
sealant layers from each side are forcibly mixed together, thus creating a
stronger bond.
The correct geometry and precision of the serration profile are critical for
achieving even pressure. In order to recommend the best serration design
we need to know about the variables specific to your situation, such as film
thickness and stiffness, if there are wrinkles or gussets, machine speeds and
conditions, etc. The best way to start this process is to provide us with
sample packages for evaluation.
The direction of the serrations is also
important. Horizontal patterns are usually best at sealing off leaks, however
in some cases diagonal or vertical serrations are the best choice. One study

found that a switch from vertical to horizontal serrations increased shelf life
by over 40%.
Easy Seal
On horizontal wrappers Quick Change Inserts allow for precise, accurate
setups that can be consistently repeated, so the variability of crimper setup is
significantly reduced. In addition, the flexible faces accommodate extra film
layers and provide even sealing pressure across the sealing face.
Easy Seal Crimpers, couples with the proper serration profile, are the best
tools for creating the even pressure necessary for dramatically improved
seals.
*****************************************************************************************
*
Gauge Printable Version (.PDF)
Definition
Relevance and non-relevance to performance
What affects film thickness
Test principles
Related Terminology
Definition
Gauge, or thickness, is a basic descriptive film property. Values are expressed as mils in the US
standard and microns in the metric (or SI) system.
The word gauge has two other meanings in the film industry that should be mentioned, but are not the
subject of this discussion.
1. "Gauge" is used as a unit of measure equal to a hundredth of a mil. For example, "70 gauge" refers
to 70 hundredths of a mil, or .70 mil thickness.
2. "Gauge" can also refer to the general profile of a roll of film. For example, "that roll has bad
gauge" means that the film is not flat across the width of the roll. This poor gauge profile
manifests itself as hard and soft areas and permanent stretch lanes, which can cause processing
problems.
back to top
Gauge, in and of itself, is not a functional parameter, but it has a direct relationship with many important
functional properties. As thickness increases, yield goes down and $/MSI goes up. Most other properties
improve, like strength and WVTR. The most notable exception is haze, which will tend to increase with
increasing thickness.
Film gauge is usually not a critical property, and most ExxonMobil products do not have specified tolerance
limits for this property. Instead, yield is the related property that is measured, controlled, and
guaranteed. It is not appropriate to calculate yield from a thickness measurement. Micrometers
lack the necessary accuracy and precision, and they only measure thickness at a small point. A
representative yield value must be measured over a large film area, as described in the test principles
section of the discussion about yield.

There are two circumstances when it is important to measure thickness in the laboratory.
1. When measuring certain film properties (tensiles, WVTR and OTR), the gauge of the sample is
always measured and noted.
2. Unlike solid films, cavitated OPPalyte films can have various thicknesses even when yield is
constant. So, the optical gauge of these films is measured in the Quality Control (QC) laboratory,
and the process is adjusted if the value is outside an acceptable range.
back to top
What affects film thickness
For solid, uncoated films, average film thickness is a direct function of film yield and resin density. It is
controlled automatically on the orienter by a feedback control loop that measures average film yield,
compares it to a target, and adjusts extruder screw speed to compensate for any difference.
To back up the on-line controls, yield is regularly measured by the QC laboratory. The average film
thickness for plain and coex OPP films can be calculated from yield with the following equations:
Gauge (mil) =
30,579 mil
Gauge (µ) =
1,104 µ · m2
/kg
Yield (in2
/lb) Yield (m2
/kg)
The average film thickness of cavitated white opaque films (OPPalyte) is a function of yield and the degree
of cavitation. (The more cavitation, the thicker the film.) With these films, yield is controlled with extruder
screw speed, and cavitation is controlled by optically measuring gauge in the laboratory and adjusting the
appropriate process parameters, as necessary.
For coated films, primer and top coats are applied to one or both sides of a base film with a separate
coating line. Coating weights are precisely controlled, and the added thickness is easily estimated. Coated
film yields are regularly measured by the QC laboratory.
back to top
Test principles
ExxonMobil has two procedures for measuring or calculating thickness, each using different commercially
available instruments.
1. #440 (Micrometer-measured gauge)
This procedure describes the appropriate use of a mechanical micrometer to determine the gauge
of a film sample being tested for tensiles or barrier. (These tests require that gauge is tested and
noted.) It is important that the specimen be free of creases, visible defects, and dirt. The
micrometer head and anvil must be clean. Mechanical micrometers should not be used on cavitated
white opaque films because they can easily crush the core which will lead to a faulty, thinner gauge
measurement. (See alternate procedure below. )
2. #598 (Optical gauge)
Shawnee developed a procedure for the optical measurement of gauge. Since Shawnee and
Macedon produce cavitated white opaque films, and traditional micrometers can be inaccurate with
these films, these plants use this non-contact optical procedure that utilizes laser technology.
It is important to select a measurement instrument that is designed for accuracy in the desired thickness
range. For more information from the instrument suppliers, contact Mahr Federal Inc., Providence, RI,
www.fedgage.com about mechanical micrometers or Beta LaserMike, Dayton, OH,
www.betalasermike.com about non-contacting measurement devices.

back to top
Related terminology
Mil Mil is a thousandth of an inch. A 0.70 mil film is 0.0007 inches thick.
Micron Micron (µ) is 10-6
meters and 25.4 mils. A 1 mil film is approximately 25µ thick.
*****************************************************************************************
*
Yield and Unit Weight Printable Version (.PDF)
Definition
What affects film yield and how well it is controlled
Test principles
Related Terminology
Definition
Yield is the measure of a film's coverage per unit weight. Values are expressed as in2
/1b in US standard
and m2
/kg in metric (or SI) units.
Unit weight is the reciprocal of yield and is presented in units of lb/ream or g/m2
. The film industry tends
to use yield values, while the paper industry favors unit weight. Our discussion here will focus on yield,
but the principles also hold true for unit weight.
back to top
Films are generally sold by the pound or kilogram; yet film area is what determines how many packages
can be wrapped or how many labels can be produced. Therefore, yield is a critical property for determining
the correct quantity of film to purchase, and it impacts the economics of the application.
OPP is a high-yield material, which makes it very economical compared to the alternatives. As show in
Table 2, pound-for-pound at equal gauges, OPP offers 53% more coverage than OPET and 28% more
coverage than oriented nylon.
Film Type Density Yield of 1 mil Film Unit Weight of 1 mil Film
g/cc in2
/lb m2
/kg lb/ream g/m2
OPP .906 30,600 43.5 14.1 23.0
LLDPE (linear low density polyethylene) .92 30,100 42.7 14.4 23.4
HDPE (high density polyethylene) .95 29,200 41.5 14.8 24.1
Hicor OHD (oriented high density polyethylene) .96 28,900 41.0 15.0 24.4
Biax Nylon 1.16 23,900 33.9 18.1 29.5
OPET (oriented polyester) 1.39 19,900 28.3 21.7 35.3
Cellophane 1.45 19,100 27.1 22.6 36.9
Table 2: Yield values of common films

back to top
What affects film yield and how well it is controlled
For a solid, uncoated film, yield is determined by resin density and average film gauge. Resin density is
altered negligibly by process conditions; so yield is controlled to the degree that thickness is controlled.
ExxonMobil has sophisticated on-line gauge measurement and control systems that keep machine and
transverse direction thickness profiles tight to target. Because yield is such a critical property, it is also
checked routinely in the lab. For all film types, film is rejected if it is outside the specification tolerance
limits of ±5% of target. But most ExxonMobil film yield measurements are well within 3% of advertised
yield.
Cavitated white films (OPPalyte) and coated films have additional factors that effect yield. The cavitated
core of OPPalyte films reduces film density to as low as 60% of solid OPP (as low as .53 g/cc). Therefore,
per unit thickness, OPPalyte films offer even higher yields than solid OPP films. Yield is the controlled
property, so if cavitation density varies slightly with process conditions, thickness (not yield) will be
impacted.
NOTE: For more information about thickness, review the section on gauge.
ExxonMobil coatings are applied as thin layers onto OPP base films. These coatings are denser than the
base films. Therefore, gauge for gauge, yields are slightly lower for coated films.
back to top
Test principles
To measure yield, a precise area of film is cut and then weighed on an analytical balance. The area is
divided by the weight, expressed as in2/lbor m2/kg,and reported to three significant digits. The
recommended minimum specimen size is 300 in2
(1940 cm2
) and should be obtained by folding a single
layer of film multiple times in the machine and transverse directions.
Example: Film is folded two times in the machine direction and two times in the transverse direction.
Therefore, 16 layers of film will be cut at once. The folded film is precision cut with a 5 inch (.127 m)
diameter round die, and the measured weight is 3.496 grams. Based on this example, the following
equations demonstrate the yield and unit weight calculations in US standard and metric units.
Yield
(in2
/lb) =
Total specimen
area
=
π(2.5)2
in2
× 16 ×
453.59 g/lb
=
40,761
in2
/lbWeight of
specimen
3.496 g
It is reported as 40,800 in2
/lb.
Yield
(m2
/kg) =
Total specimen
area
=
π(.0635)2
m2
× 16 ×
1000 g/kg
=
57.976
m2
/kgWeight of
specimen
3.496 g
It is reported as 58 m2
/kg.
Unit weight
(lb/ream) =
1
=
1 lb
×
432,000
in2
= 10.598 ~
10.6
lb/ream
Yield
40,761
in2 ream

Unit weight
(g/m2
) =
1
=
1 kg
×
1,000
g
= 17.249 ~
10.3
g/m2
Yield
57.976
m2 kg
CAUTION:
Although yield is related to thickness, it is inaccurate to use a micrometer to assess yield.
Micrometers lack the necessary accuracy and precision, and they only measure thickness at
a small point, whereas the previously described method directlymeasures average yield
over a large area. Also, thickness cannot be converted to yield without knowing the exact
density of the film.
back to top
Related terminology
Basis weight Basis weight is a common paper industry term for unit weight, or weight per unit
area. Units are lb/ream. "Ten pounds of poly" means 10 lb/ream, which equals
43,200 in2
/lb (because a ream equals 432,000 in2
) or .70 mils of LDPE (at a specific
gravity of .92).
MSI MSI stands for thousand square inches. Yield can be converted from in2
/lb to MSI/lb
by dividing by 1000. Film pricing is commonly quoted in $/lb or $/MSI, and yield can
be used to convert from one set of units to the other.
Ream Ream is a paper industry term equivalent to a coverage area of 3000 ft2
or 432,000
in2
.
*****************************************************************************************
*
Tensiles Printable Version (.PDF)
Definition
Relevance to performance
What affects a film's tensile properties
Test principles
Related Terminology
Definition
Tensile testers, such as an Instron, measure a film's resistance to being pulled apart at a constant rate of
speed. ExxonMobil uses this test to report three significant properties.
1. Ultimate tensile strength is the maximum force of resistance divided by the film's initial cross-
sectional area. Values are expressed in Ibf/in2
(psi) in US standard units and N/mm2 in metric (SI)
units.

2. Tensile modulus is a stress-strain ratio calculated from any point on the initial straight line
portion of the load-extension curve. It is measured just as the material begins to experience
tension. This value is an indicator of the film's stiffness and resistance to elongation in use. The
units are Ibf/in2
(psi) and N/mm2
.
3. Elongation is the percent change in length of the material under stress from start to break.
Elongation "at yield" is measured from start to yield point. The units are %.
back to top
Tensile properties are an important and common way to compare physical properties of diverse materials,
from steel to plastic. In the narrower realm of flexible films, these tests provide measurement of attributes
we can see and feel: strength, stiffness, and resistance to stretching. Some materials are stronger than
others, and some, like polypropylene, can dramatically improve their strength through orientation as
shown in Table 3.
Tensile Property
Cellophane Oriented PET Blown LDPE OPP
Ultimate strength (kpsi) 7-18 20-40 1.5-4 15-40
Elongation (%) 10-50 60-165 100-700 35-475
Table 3: Typical tensile values for common films*
*Although there is a wide range of property values for each material (because of the many choices
available in resin formula, processing, and direction of testing), Table 3 shows the characteristic
performance range for each type of film. The effect of orientation is reflected in the property differences
between cast PP (unoriented polypropylene) and OPP (biaxially oriented polypropylene).
Within the arena of OPP films, tensiles are generally not critical and rarely require discussion and
specification between supplier and customer. This is so because oriented polypropylenes provide a
dependable range of tensile values. Other properties are usually more important to successful
performance. There are two notable exceptions worthy of explanation.
1. Orientation method: blown or tentered
The orientation method causes characteristic differences in tensile properties. Blown films are
"balanced," having similar strength and elongation in the machine and transverse film directions.
Tentered films (as are all ExxonMobil films) have higher strength and lower elongation in the
transverse direction than in the machine direction. Most OPP manufacturers produce tenter-
oriented films, which work well in many diverse applications.
2. Modulus and web tension
Modulus, because it is a measure of strength characteristics in the film's elastic region, provides
valuable insight into stiffness and how extensible the film is under normal use tensions. When
comparing two films of identical thickness, the one with a higher modulus will be stiffer and stretch
less under the same tension force.
NOTE:
High temperature modulus testing and empirical trials on converting equipment have yielded an
industry rule of thumb: OPP web tensions should be controlled to .50lbf per inch of film width,
or less, for good registration and no permanent deformation (elongation, neck-in, gauge
bands). From a filmmaker's perspective, the lowest controllable web tension is best. Thinner
films and higher converting temperatures make this more critical.
back to top

What affects a film's tensile properties
Resin selection and orientation method are the primary variables that influence tensile values. Therefore,
tensile properties are almost entirely defined by product design itself. Small variations in tensiles will
inevitably result due to normal process variation, but the performance effect is insignificant.
back to top
Test principles
Each end of a film specimen, of specific width and measured thickness, is held by a clamp or grip. One
grip is stationary, while the other is pulled away from the first at a pre-selected velocity. The machine
continuously measures the changing distance between the grips and the force exerted on them as they
pull the film apart. The test is completed when the sample breaks.
Today, most machines run automatically after the operator selects settings, loads the specimen, and
initiates the test. Most are also equipped with microprocessors that perform the calculations and
automatically display all the resulting values. But, the test concepts are best understood by studying load-
extension curves like the ones shown in Graph 1. These are actual machine direction (MD) and transverse
direction (TD) load-extension curves for a typical, tenter-oriented, 75 gauge OPP. In Graph 1, load is
plotted as a function of extension, and the tensile tester software calculates the following properties that
are noted in Table 4.
Graph 1: Typical OPP load-extension curves
Results
Sample
Description
Thickness (mil) Ultimate
Strength (kspi)
Modulus (kpsi) Elongation (%)
1 MD pull .75 18.9 343 174
2 TC pull .75 39.3 687 45
Table 4: Tensile values from Graph 1
Table 4 values are software-generated results based on the following equations.
Ultimate Tensile Strength (psi) =
Max Load (lbf)
=
Max Load (lbf)
Initial cross-sectional area 1 in x .00075 in
Modulus (psi) = At any point on the elastic region tangent line (Stress ÷ Strain) =
Load (lbf) ÷ Extension (in) = Load (lbf) ÷ Extension (in)

Initial cross-sectional area Initial grip separation .00075 in2
2 in
Elongation (%) =
Extension at failure x 100
=
Extension at failure x 100
Initial grip separation 2 in
Test conditions like pull speed, initial grip separation, full-scale load, and sample width will affect the
results. ASTM test procedure D 882 describes a protocol for making choices about these settings. For
simplicity and accuracy in comparing values, ExxonMobil uses highly automated tensile testers and has
standardized to a particular set-up. These conditions are summarized in Table 5.
Test Condition Machine Direction (MD) Transverse Direction (TD)
Ultimate
Strength
Modulus Elongation
Ultimate
Strength
Modulus Elongation
Crosshead speed (in/min),
i.e. pull velocity
20 .5 20 20 .5 20
Grip separation (in) 2 2 2 2 2 2
Sample width (in) 1 1 1 1 1 1
Table 5: ExxonMobile standard conditions for tensile testing
ExxonMobil has two test procedures for tensile testing: one for use with Instron equipment (#506) and
one for use with Sintech machines (#510). With both tests, the specimen is subjected to identical
evaluation conditions.
NOTE:
The tensile properties for all coated and metallized films are measured on base sheet prior to
coating or metallization.
Tensile properties can change with small changes in temperature; so it is important to conduct tests in a
controlled environment. Standard laboratory temperature is 72°F (22°C) ± 2°F (1°C).
back to top
Related terminology
Young's modulus
Modulus of elasticity
Tangent modulus
Modulus of elasticity Tangent modulus These are all terms synonymous
with tensile modulus, a material property defined as the stress-strain ratio
of the initial portion of a load-extension curve. A higher modulus value
suggests that this material will be stiffer and have more resistance to
elongation in use (when comparing films of the same thickness). Standard
units are Ibf/in2
(psi) and N/mm2
.
Secant modulus Secant modulus is an alternate approximation of modulus and better
predictor of performance, when there is no straight line portion on the
load-elongation curve. It is the stress-strain ratio at the point on the curve
that corresponds to a specific designated extension. For example, a 1%
secant modulus would be the material's stress/strain, in psi or N/mm2
, at
the point of extension that is 1% of initial sample length. This can be a
useful value, because with no early straight line portion of the curve, the
traditional tangent calculation will render a result that predicts the
material to be stiffer and less extensible than it really is.

Strain Strain is the ratio of the change in length of the sample (also called
extension) to the original length of the sample. Strain is a unitless value
and is converted to % elongation by multiplying by 100.
Stress Stress is load (Ibf or N) divided by the original cross-sectional area (in2
or
mm2
) of the specimen. By definition, this value is normalized for gauge.
Yield point Yield point is the point during the test cycle when the specimen continues
to elongate, but there is no increase in load. OPP films typically do not
have a clear yield point.
*****************************************************************************************
*
Dimensional Stability Printable Version (.PDF)
Definition
What affects dimensional stability
Test principles
Definition
Dimensional stability is the change in length of an unrestrained film sample subjected to a specific
elevated temperature. ExxonMobil typically measures this property at 275°F (135°C). Machine direction
(MD) and transverse direction (TD) values are evaluated and reported separately. Units are reported as %
change from the original dimension.
back to top
In general, materials expand when subjected to elevated temperatures. Oriented films, on the other hand,
are likely to shrink because the polymer has "memory" and tries to return to its unoriented dimensions.
Dimensional stability values for different films (measured at the same temperature) provide a relative
comparison of how much film distortion will occur in heated processes, like oven drying or package
sealing. Acceptable temperatures for processing a film vary and are dependent on the film properties, the
type of process (contact with heated air or heated metal), the dwell time, and whether the film is
restrained or not.
OPP films are typically designed for minimal shrinkage. Most ExxonMobil OPP films can be used in very
high-speed, low-dwell heat seal applications with actual crimp jaw temperatures of up to approximately
355°F (180°C) without causing unsightly seal distortion. However, longer dwell exposures (> ½ second)
require that temperatures do not exceed about 300°F (149°C) to prevent severe shrinkage. OPP is
commonly used at temperatures between 220°F and 300°F (104.5°C to 149°C), where it can have a slight
dimensional change. Test values at 275°F (135°C) for tenter-oriented OPP are typically -2% to -8% in
both the machine and transverse directions.
Some films are designed to shrink in a predictable way, like the new, developmental ExxonMobil film Bicor
TYTE. TYTE provides a crisp, tight overwrap for products like CD jewel cases, video tapes, and food or
pharmaceutical boxes. Its dimensional stability values are -9% in the MD and -14% in the TD.

back to top
What affects dimensional stability
Dimensional stability is mostly determined by the OPP film's residence time and temperature in the
annealing section of the orientation process. The annealing section involves the last zones of the
transverse direction orienter and is where the oriented film continues to be held at the edges with tenter
clips while surrounded by temperature-controlled oven air. This relieves residual stresses and creates
"heat set" OPP. Without proper annealing, OPP is prone to greater shrinkage in heated environments.
back to top
Test principles
ASTM D 1204 and ExxonMobil procedure #438 follow the same principles, but differ in some specific
protocols. Both tests involve placing a film sample of known original dimensions into a temperature-
controlled convection oven for a certain period of time and measuring the length of the sample after
conditioning. Results are reported as % change. Negative numbers indicate shrinkage, while positive
numbers indicate expansion. Pertinent details of the two procedures are summarized in Table 6.
Test
Procedure
Test Conditions
Specimen
Size
Oven
Temperature
Time
in Oven
Pre/Post
Conditioning
Precision Reporting
ExxonMobil
#438
1" x 7" cut
in MD, and
one in TD
Convection
oven
controlled to
target,
typically
275°F
(135°C)
7 min None
Nearest .
02 inches
% change
ASTM D
1204
10" x 10"
Convection
oven
controlled to
target ± 1°C
As
appropriate
depending
on film
testing
Yes, as
standard
laboratory
temperature
and humidity
Nearest .
01 inches
% change
Table 6: Comparison of dimensional stability test conditions between ExxonMobil and ASTM
procedures
*****************************************************************************************
*
Haze Printable Version (.PDF)
Definition
What determines the haze level of a clear film
Test principles
Related Terminology
Definition

Haze is the scattering of light by a film that results in a cloudy appearance or poorer clarity of objects
when viewed through the film. More technically, haze is the percentage of light transmitted through a film
that is deflected more than 2.5° (degrees) from the direction of the incoming beam. This property is used
to describe transparent and translucent films, not opaque films.
back to top
Film clarity is a highly desirable feature for most clear packaging and label applications. It tends to
symbolize quality and contributes to the positive visual display of the product. Compared to other flexible
plastic films, clear OPP has one of the lowest haze values, generally less than 3%.
back to top
What determines the haze level of a clear film
Haze is greatly influenced by material selections and product design. Resin characteristics, such as
crystallinity and molecular weight distribution, have a key impact. Copolymers are generally hazier than
homopolymers. Additives and coatings usually contribute to increased haze. All other things being equal,
thicker films will be hazier than thinner films. Additional variables, like process temperatures in the
different stages of film-making, can further affect haze, so they are tightly controlled.
back to top
Test principles
As represented in Figure 1, a unidirectional light beam is directed onto the film specimen. After it enters
an integrating sphere, a photo detector measures the total light transmitted by the film and the amount of
transmitted light that is scattered more than 2.5°. Haze is the percentage of total transmitted light that is
scattered by more than 2.5°.
Figure 1: Haze measurement
Commercial hazemeters are typically used for this testing, but ASTM D 1003 also allows the use of a
spectrophotometer, provided it meets the procedure requirements. ExxonMobii uses the SKY-Gardner XL-
211 Haze-gard and Haze-gard plus hazemeters consistent with ASTM guidelines. The hazemeter may also
be set up to measure and display light transmission.
back to top
Related terminology

Light transmission
Light transmission is the percentage of incident light that passes through a film,
which is represented by the following equation.
Light Transmission (%) =
T
t
x 100Ti
Translucent Translucent describes material that transmits light, but also diffuses it, so that
objects cannot be seen clearly.
*****************************************************************************************
*
Coefficient of Friction Printable Version (.PDF)
Definition
Relevance to application performance
How COF is modified in films
Test principles
Related terminology
Definition
Coefficient of friction (COF) is a unitless number that represents the resistance to sliding of two surfaces in
contact with each other. These values should be between 0 and 1. Higher values indicate more resistance
to sliding.
Static COF values are measured as two surfaces just begin to move against each other and kinetic values
are measured after constant motion is achieved. ExxonMobil reports kinetic COF values.
back to top
A laboratory film-to-film COF measurement is commonly used in the flexpack industry to quantify and
compare film frictional surface properties in a consistent and convenient way. There are no universally
good or bad COF values, but generally values over .50 are considered non-slip surfaces and values less
than .20 are considered high-slip films that can be prone to roll telescoping.
Optimal slip properties vary by application, but can be critical for good machinability and package
transport as represented in Table 7.
Situation Desired Effect Importance
Film passes over HFFS fin wheel
deck plates.
Low outside friction, film-to-metal Prevents drag and film jams.
On VFFS, film enters forming collar
as horizontal flat web and is
transformed into a vertical tube.
Low outside friction, film-to-metal Prevents film squealing, inconsistent
film feeding and inconsistent bag
lengths.
Filled packages are being stuffed
into corrugated shipping boxes.
Low outside friction, film-to-film Allows packs to slide against each
other and settle for easy carton
closing.

On friction belt drive VFFS, servo-
driven belts push and move film
against inside tube.
Moderate outside friction, low
inside friction
Belts must "grab" outside surface to
move film, while inside surface must
slide over stationary tube to prevent
jams.
Filled packages slide down a chute
to reach downstream packaging
operations.
Low outside friction, film-to-chute Keeps products moving.
Filled packages are carried on an
inclined conveyor belt.
Moderate or high outside friction,
film-to-conveyor
Keeps product from losing
placement or falling off conveyor.
Table 7: Examples of various applications requiring different fictional properties
You can see from the table above, that each different situation has very different stresses and
expectations. Sometimes the film is forced to change shape, or slide across a metal surface, or "grab"
against a drive belt. It's impossible for a laboratory measured film-to-film COF to predict performance in
all these applications. Instead, film-to-film COF measurements are used for process control to ensure the
consistent production of a film that has been proven during the product development process to work in
its target applications.
For example, a key to good performance on a VFFS machine is the film's outside frictional properties that
allow it to travel over the forming collar without squealing or inconsistent feeding. ExxonMobil produces
films with high-tech, non-migratory slip systems that have higher COFs than older fatty amide-type films,
but run flawlessly on these machines. Traditional thinking might claim that "the COF is too high" with
these films, but this is clearly not true. Then standard COF laboratory test is frequently not a good
comparison test for predicting performance.
CAUTION:
Do not draw conclusions about performance from small differences (differences of. 10 or
less) in the laboratory film-to-film COF values of different film products. Instead, two
different types of films should be compared by conducting trials in the desired application.
back to top
How COF is modified in films
An unmodified OPP film can have a COF of .70 or more. Most polymer films need to be specially
formulated to reduce COF and have slip properties that result in good machining, i.e., good performance
on packaging equipment.
The traditional technology to lower COF is to compound a fatty amide additive (generically called "slip")
into the resin prior to film production. Over time, the fatty amide will migrate to the film's surface
("bloom"), because it is not completely soluble in the polymer. Although still in common use, this film
technology has several problems.
1. With heat, fatty amides will migrate from the surface back into the body of the film causing COF to
increase.
2. There can be a wide variation of the COF value, and it will change with time.
3. These films are generally cloudier than films that don't contain fatty amides.
4. When laminated to a sealant web and wound into a roll, the fatty amide additive can transfer to the
sealing surface. This can cause a narrower sealing range and reduced seal strengths.

5. Fatty amide can deposit and accumulate on rollers and packaging machine surfaces.
6. The additive can interfere with print quality.
Most ExxonMobil films do not incorporate migratory fatty amide slip systems. Instead, the COF of these
uncoated films is optimized with proprietary resin and additive formulations, which provide consistent, low
friction performance. We refer to these as "non-migratory" slip systems. They eliminate the problems
associated with using fatty amides to achieve a lower COF.
NOTE:
The previous discussion refers to how COF is modified in uncoated coex and slip films.
Remember, ExxonMobil acrylic-coated surfaces have inherently low and stable COF and provide
excellent machine performance.
back to top
Test principles
COF is a simple ratio equal to the force required to slide one surface over another, divided by the force
perpendicular to the contacting surfaces.
COF =
Force to cause sliding of film surfaces (gf)
; a unitless coefficient
sled weight (gf)
ExxonMobil uses commercially available test equipment to measure film-to-film COF at conditions defined
by ASTM D 1894. Table 8 provides a summary comparison.
Test
Procedure
Test Conditions
Measurement
Apparatus
Contacting
Surfaces
Sled
Weight
(g)
Sled
Contact
Dimensions
(in)
Pull
Method
Pull
Speed
(in/min)
ExxonMobil
#430
TMI #32-06 Film to film 200 2.5 x 2.5 Moving
sled
6
ASTM D
1894
Not specified Not
specified
200 2.5 x 2.5 Moving
sled or
plane
6
Table 8: Comparison of COF test conditions between ExxonMobil and ASTM procedures
The TMI tester provides a digital display of static and kinetic COF. Static COF is a higher value and is
related to the force to get movement started. Kinetic COF is the number typically displayed in data sheets
and is an average value after Y2inch of travel.
COF values generated in different laboratories or on different testers show wide variation when measuring
the same film. For example, ASTM looked at the precision of COF data between laboratories and found
standard deviations (depending on film type) between .02 and .12. Therefore, it does not make sense to
assume that there is necessarily a real difference between, for example, a .28 measured by one company
and a .34 measured by another.
back to top
Related Terminology

Fatty amide Fatty amide is a very common migratory slip additive for plastic films.
Fatty amides are greasy organic compounds such as stearamide,
erucamide, behenamide and oleamide. They are compounded into resin
and bloom to the surface after the film is produced.
Kinetic COF Kinetic COF is the coefficient of friction value measured after surfaces are
in motion at a constant speed.
Machinability Machinability, also known as machine performance, is the ability of a film
to travel and track well through a packaging machine. Different machines
favor different film properties. Therefore, a film may demonstrate good
machinability on one piece of equipment and not on another.
Non-migratory slip
system Non-migratory slip system Non-migratory slip system refers to newer
technology that reduces the COF of films without the problems associated
with fatty amides. ExxonMobil has been a leader in this area by
engineering films with non-migratory additives and modified surfaces.
These films have stable COFs and excellent converting and packaging
machine performance.
Slip
Slip is the opposite of friction. "High slip" denotes low COF and low slip
denotes a high COF. A "slip film" is a non-sealable film that is specifically
formulated using additives or surface modification for reduced surface
friction. "Slip additive" usually refers to fatty amide.
Static COF
Static COF is the coefficient of friction value measured as two surfaces just
begin to move against each other.
*****************************************************************************************
*
Gloss Printable Version (.PDF)
Definition
What affects film gloss
Test principles
Definition
Gloss is a measurement of the relative luster or shininess of a film surface. ExxonMobil uses 45-degree
gloss, where the incident light beam strikes the film surface at a 45 degree angle from the perpendicular.
A sensor measures the amount of light reflected by the film at a mirror image angle. The gloss value is the
ratio of this reflected light to incident light and is reported in gloss units. Theoretically, the range of the
gloss scale is 0 to 100.

back to top
Shininess, brilliance, and sparkle are properties related to a film's gloss value. They can be valuable
appearance attributes for packages, labels, or graphic arts items.
Precise comparisons of gloss values can only be made when the measurements are performed on samples
of the same general type of material, using the same procedure and test angle. In particular, it is not valid
to compare the gloss values of transparent films and opaque films.
back to top
What affects film gloss
Gloss is primarily determined by material selection and surface smoothness, which are defined during
product and process development. Day-to-day process variations will have an insignificant effect on gloss.
Transparent films have two reflecting surfaces. Although rare, this can lead to gloss values that exceed
100.
back to top
Test principles
ExxonMobil uses commercially available glossmeters to measure 45-deg gloss consistent with ASTM
procedure D 2457. The simplified diagram in Figure 2 graphically summarizes the test.
Figure 2: Gloss measurement
************************************************************************************
WVTR Printable Version (.PDF)
Definition
Relevance to package performance
What affects the WVTR of OPP films
Test principles
Related Terminology
Definition
WVTR (water vapor transmission rate) is the steady state rate at which water vapor permeates through a
film at specified conditions of temperature and relative humidity. Values are expressed in g/100 in2
/24 hr
in US standard units and g/m2
/24 hr in metric (or SI) units. Test conditions vary, but ExxonMobil has

standardized to 100°F (37.8°C) and 90% RH, which is the most common set of conditions reported in
North America.
back to top
A critical function of flexible packaging is to keep dry products dry (potato chips, pretzels, fortune
cookies...) and moist products moist (cheese, muffins, chewing gum...). Without protective packaging,
products will quickly gain or lose moisture until they are at equilibrium with the environmental relative
humidity. At this point, crispy products are soggy, and chewy products are hard and dry.
WVTR is the standard measurement by which films are compared for their ability to resist moisture
transmission. Lower values indicate better moisture protection. Only values reported at the same
temperature and humidity can be compared, because transmission rates are affected by both of these
parameters.
One of the most valued properties of OPP is its exceptional moisture barrier. As shown in Table 9, gauge
for gauge, OPP provides the best WVTR of all common polymer packaging films. (For homogeneous films
like these, you can calculate the WVTR for a particular thickness by dividing the values in the table by the
desired gauge in mils.)
Film Type WVTR @ 100°F (38°C), 90% RH for 1 mil film
(g/100 in2
/24 hr) (g/m2
/24 hr)
Biax OPP 0.25 - 0.40 3.9 - 6.2
HDPE (high density polyethylene) 0.3 - 0.5 4.7 - 7.8
Cast PP 0.6 - 0.7 9.3 - 11
Biax PET (oriented polyester) 1.0 - 1.3 16-20
LDPE (low density polyethylene) 1.0 - 1.5 16 - 23
EVOH* (ethylene vinyl alcohol) 1.4 - 8.0 22 - 124
OPS (oriented polystyrene) 7 - 10 109 - 155
Biax Nylon 6 10 - 13 155 - 202
Table 9: Normalized WVTR values for common films
*Dependent on ethylene content of the particular grade.
CAUTION:
In order for film moisture barrier to contribute its full product protection value, package
seal integrity must be satisfactory. Poor quality seals can negate a film's good barrier by
allowing vapor transmission through channel leakers and imperfections.
Within the arena of OPP films, tensiles are generally not critical and rarely require discussion and
specification between supplier and customer. This is so because oriented polypropylenes provide a
dependable range of tensile values. Other properties are usually more important to successful
performance. There are two notable exceptions worthy of explanation.
1. Orientation method: blown or tentered
The orientation method causes characteristic differences in tensile properties. Blown films are
"balanced," having similar strength and elongation in the machine and transverse film directions.
Tentered films (as are all ExxonMobil films) have higher strength and lower elongation in the
transverse direction than in the machine direction. Most OPP manufacturers produce tenter-
oriented films, which work well in many diverse applications.

2. Modulus and web tension
Modulus, because it is a measure of strength characteristics in the film's elastic region, provides
valuable insight into stiffness and how extensible the film is under normal use tensions. When
comparing two films of identical thickness, the one with a higher modulus will be stiffer and stretch
less under the same tension force.
NOTE:
High temperature modulus testing and empirical trials on converting equipment have yielded an
industry rule of thumb: OPP web tensions should be controlled to .50lbf per inch of film width,
or less, for good registration and no permanent deformation (elongation, neck-in, gauge
bands). From a filmmaker's perspective, the lowest controllable web tension is best. Thinner
films and higher converting temperatures make this more critical.
back to top
What affects the WVTR of OPP films
The most obvious factor that impacts WVTR is thickness: if an OPP of the same product design is twice as
thick as another, its WVTR will be half the value. This is so because WVTR is an inherent, bulk film
property of OPP.
It is common to find variation in the reported WVTR values for same-gauge OPP films produced or
measured by different manufacturers. The primary factors causing these differences are:
1. Raw material: Homopolymer PP resin differences in average molecular chain length, range of
chain lengths, and degree of crystallinity can account for up to a 10% difference in WVTR.
Additives and copolymer resin layers can account for differences of up to 30%.
2. Process: Normal differences in process conditions between one orienter and another account for
about 5% variation in WVTR values. (WVTR is reduced through orientation, because the crystalline
regions of the polymer matrix are aligned. In other words, orientation efficiently "packs" polymer
chains, so that larger spaces are minimized. Process conditions affect this "packing," and therefore,
WVTR values.)
3. Measurement: The instrument manufacturer, MOCON®
,states a test precision of :t3% with their
PERMATRON-W®
product line. Therefore, trained operators using this type of instrumentation will
generate values from .34 to .36 when testing a 1 mil OPP with a nominal WVTR of .35 g/100 in2
/24
hr.
ExxonMobil performed WVTR testing on a wide range of coex (plain, uncoated) products and gauges
produced on different orientation lines. Graph 2 plots the average WVTR as a function of gauge and shows
the 95% confidence range that embodies variation from the factors described previously. (This only
involves ExxonMobil coex films. The confidence limits would be wider if other manufacturer's films were
included in the data, because there would be more material and process variation.)

Graph 2: Plain OPP WVTR as a function of thickness
The inherently good moisture barrier of OPP can be further enhanced by additives, coatings, or
metallization. ExxonMobil produces high barrier PVdC-coated and metallized films that dramatically
improve the WVTR of OPP and Hicor films. The values for four of these products, HBS-2, MET-HB, Hicor
OHD, and Hicor BIHD-M, are plotted in Graph 2.
back to top
Test principles
ExxonMobil uses MOCON Permatran W®
instruments for measuring WVTR. The instrument design and the
way we operate the instrument is consistent with ASTM F 1249. ExxonMobil standardizes its reporting to
test conditions of 100°F (38°C) and 90% RH. Conceptually, a test cell looks like Figure 3. Dry nitrogen gas
is swept through a chamber where the test film acts as the membrane separating this dry gas stream
from a "wet" nitrogen stream on the other side. The partial pressure difference creates a driving force for
the water vapor to permeate through the film to the low pressure side. The barrier of the film determines
how much water vapor can transfer, and this is continuously measured by an infrared detector in the
outgoing stream of the dry side.
Figure 3: Cross-section of a WVTR test cell
The test is complete when equilibrium, or steady state, is achieved, which is when the infra-red sensor
detects water molecules leaving the dry chamber at a constant rate. The amount of water vapor
permeating through the sample per unit time period is not changing. This rate is the sample WVTR and is
recorded in units of g-H2O/100 in2
/24 hr at 100°F (37.8°C), 90% RH.
This overview describes how ExxonMobil measures WVTR and was based on articles and product literature
provided by MOCON®
. There is much more to the science of mass transfer and to the instrumentation that

allows us to measure it. For more information, contact MOCON in Minneapolis, MN at (612) 493-6370, or
visit http://www.mocon.com.
back to top
Related terminology
Normalized WVTR Normalized WVTR is equal to the measured WVTR multiplied by the gauge
of the sample in mils. In other words, it is the approximated WVTR of the
material at 1 mil thick. We provided normalized WVTR values in the first
table of this write-up in order to compare the inherent moisture barrier
property of different classes of materials. This technique is only
appropriate with homogeneous films and is not appropriate for coated or
metallized films.
*****************************************************************************************
*
OTR Printable Version (.PDF)
Definition
What affects the OTR of films
Test principles
Related Terminology
Definition
OTR (oxygen transmission rate) is the steady state rate at which oxygen gas permeates through a film at
specified conditions of temperature and relative humidity. Value are expressed in cc/100 in2
/24 hr in US
standard units and cc/m2
/24 hr in metric (or SI) units. Standard test conditions are 73°F (23°C) and 0%
RH.
back to top
The air we breathe is about 21% oxygen and 79% nitrogen, with very small concentrations of other gases
like carbon dioxide and argon. Essential to human and animal life, oxygen gas is also a reactive compound
that is a key player in food spoilage. Most of the chemical and biological reactions that create rancid oils,
molds, and flavor changes require oxygen in order to occur. So, it is not surprising that food packaging
(and some non-food packaging for products where atmospheric oxygen causes harm) has progressed and
found ways to reduce oxygen exposure and extend the shelf life of oxygen-sensitive products.
There are two methods for reducing product exposure to oxygen via flexible packaging.
1. MAP (modified atmosphere packaging) is a process for replacing the air in the headspace of a
package with another gas before the final seal is made. This is also called gas flushing. The most
common replacement gases are nitrogen or nitrogen/carbon dioxide mixtures. The shelf lives of
potato chips, dried fruits, nuts, and shredded cheese are commonly extended by this packaging
method.

2. Vacuum packaging is where the atmosphere is drawn out and eliminated, rather than being
replaced by another gas. This vacuum forces the flexible material to conform to the product shape.
Meats (fresh and processed) and cheeses are commonly packaged this way.
Once air has been replaced or eliminated from the package, there must be an adequate oxygen barrier
and seal integrity to keep a low oxygen concentration inside the pack. Otherwise, the driving force created
by the oxygen partial pressure differences (21% outside the bag and 0-2% inside the bag) will cause an
ingress of oxygen and destroy the benefit of removing it in the first place. OTR values are used to
compare the relative oxygen barrier capabilities of packaging films. An industry rule-of-thumb is that a
material is considered a "high oxygen barrier" if its OTR is less than 1 cc/100 in2
/24 hr (15.5 cc/m2
/24 hr).
Table 10 shows OTR values for common polymer packaging films. Note that the table is divided into two
sections. The first contains normalized (1 mil) values for common materials. The second section displays
the OTRs for coated or metallized films where the total film thickness is unimportant, because the barrier
is primarily coming from the additional layer.
Film Type OTR @ 73°F (23°C), 0% RH
(cc/100 in2
/24 hr) (cc/m2
/24 hr)
The following OTRs are bulk material properties displayed at 1 mil. You may divide by the gauge (in mil)
in order to approximate OTR at a different thickness.
EVOH* (ethylene vinyl alcohol) .005 - .12 .08 - 1.9
Biax Nylon-6 1.2 - 2.5 18.6 - 39
OPET (oriented polyester) 2 - 6 31 - 93
OPP 100 - 160 1550 - 2500
Cast PP 150 - 200 2300 - 3100
HDPE (high density polyethylene) 150 - 200 2300 - 3100
OPS (oriented polystyrene) 280 - 400 4350 - 6200
LDPE (low density polyethylene) 450 - 500 7000 - 8500
The following OTRs are enhanced by coating or metallizing. Therefore, these are not bulk film properties,
and total film thickness has little impact on the OTR value.
Metallized OPET .01 - .11 .16 - 1.7
PVOH-coated OPP (AOH) .02 .31
Metallized biax Nylon-6 .05 .78
PVdC-coated OPET .30 - .50 4.7 - 7.8
High Barrier PVdC-coated OPP .30 - .60 4.7 - 9.3
PVdC-coated biax Nylon-6 .35 - .50 4.7 - 7.8
Metallized OPP 1.2 - 10 19 - 160
Sealable PVdC-coated OPP 1.5 - 3.5 23 - 54
Table 10: OTR values for common films
*The range of possible values is especially wide for EVOH because the value is dependent on the ethylene
content of the particular grade. EVOH is typically a buried layer, either via coextrusion or lamination.
CAUTION:
In order for film oxygen barrier to contribute its full product protection value, package seal
integrity must be satisfactory. Poor quality seals can negate a film's good barrier by
allowing oxygen transmission through channel leakers and imperfections.

Related information: Many customers ask about the carbon dioxide (CO2) and nitrogen (N2) transmission
rates through film. ExxonMobil does not perform transmission testing with these gases, but a value range
can be estimated from OTR values by using the following relationships.
CO2 TR will be 3 to 5 times the OTR value at 73ºF (23ºC), 0% RH
N2 TR will be .2 to .4 times the OTR value at 73ºF (23ºC), 0% RH
For example, the OTR of 110 AXT is .40 cc/100 in2
/24 hr @ 73ºF (23ºC), 0% RH. Therefore, at the same
conditions, the CO2 TR is approximately 1.2 - 2.0 cc/100 in2
/24 hr and the N2 TR is approximately .08 to .
16 cc/100 in2
/24 hr.
back to top
What affects the OTR of films
Good oxygen barrier is achieved by combining functional layers to create a film with the required barrier,
as well as those other properties necessary to produce a serviceable package. For example, EVOH has
exceptional OTR properties, but needs moisture barrier and mechanical properties provided by layers that
are coextruded or laminated around it.
OTR is most affected by the following factors.
1. Thickness of barrier layer: Generally, the thicker the oxygen barrier-providing layer, the better
the barrier. But there are process and cost limitations that restrict the thicknesses that can be
realistically produced or successfully utilized.
2. Copolymer ratio, plasticizer content, and polymerization process: All PVdCs (or EVOHs or
PVOHs) are not created equal. Properties are compromised during polymer and product
development, so that total performance in target applications is optimized. There can be
substantial differences in OTR values depending on the selections made. For example, both ASB-X
and AXT are PVdC-coated and sealable, but their OTRs are 4.5 cc/100 in2
/24 hr and .40 cc/1 00
in2
/24 hr, respectively. ASB-X has the poorer OTR, but a broader seal range than AXT.
3. Base film surface compatibility: The physical and chemical characteristics of the base film
surface have a major effect on the OTR after metallization, and to a lesser degree, after coating.
This is evidenced by Met PET's exceptional barrier, as well as the difference in OTRs between
various metallized OPP products (refer to Table 10).
ExxonMobil only measures and controls OTR for those films that are modified through coating,
coextrusion, or metallization, and guarantee a maximum OTR value in the product specification. This
includes AXT, HBS-2, AOH, MET-HB, and MU842.
back to top
Test principles
ExxonMobil uses MOCON OX-TRAN@ instruments for measuring OTR. The instrument design and the way
we operate the instrument are consistent with the ASTM D 3985 standard. ExxonMobil standardizes its
reporting to test conditions of 73°F (23°C) and 0% RH.
Conceptually, a test cell looks like Figure 4. Dry nitrogen gas is swept through a chamber, where the test
film acts as the membrane separating this stream from an oxygen stream on the other side. The partial
pressure difference creates a driving force for oxygen molecules to diffuse through the film to the low

pressure side. The film barrier determines the rate of oxygen permeation, and this is continuously
measured by a MOCON®
patented coulometric sensor in the outgoing ,stream of the nitrogen side.
Figure 4: Cross-section of an OTR test cell
The test is complete when equilibrium, or steady state, is achieved; that is, it is complete when the sensor
detects a constant amount of oxygen in the nitrogen carrier stream. The rate of oxygen permeating
through the sample is not changing. This rate is the sample OTR and is recorded in units of cc/100 in2
/24
hr or cc/m2
/24 hr at 73°F (23°C), 0% RH.
This discussion is an overview of how ExxonMobil measures OTR and was based on articles and product
literature provided by MOCON®
. There is much more substance to the science and measurement of mass
transfer. For more information, contact MOCON®
in Minneapolis, MN at (612) 493-6370, or visit
www.mocon.com.
NOTE:
It is important to discuss the effects of relative humidity on OTR, even though the ASTM
standard procedure is at dry conditions. Relative humidity has a dramatic and negative effect
on the OTRs of some materials, most notably nylon, EVOH and PVOH. The effect is especially
pronounced at RHs over about 70%. AOH, with its PVOH coating, is the only ExxonMobil
oxygen-barrier film affected this way. AOH should only be used as an oxygen barrier in dry
applications. Consult your ExxonMobil representative.
back to top
Related terminology
PVdC PVdC stands for polyvinylidene chloride, but The Dow Chemical Company
points out in the 2nd edition of The Wiley Encyclopedia of Packaging
Technology that the use of this term is not precisely correct. PVdC
suggests a homopolymer resin; when in fact, all commercial resins are
VdC copolymers and should be referred to as such. Nevertheless, it is not
likely that our industry will change its ways, where "PVdC" has become a
generally accepted representation for the family of VdC copolymers.
Saran®
Saran®
is a trademark of The Dow Chemical Company for its family of
PVdC and VdC copolymer products.
Oxygen scavengers Oxygen scavengers are materials that chemically react with oxygen in a
package headspace. They can be used with MAP in order to attain very low
oxygen concentrations (ppm levels) that are not achievable with MAP
alone. Most oxygen scavengers used commercially are packets containing

iron powders that are placed inside a package and consume headspace
oxygen through oxidation reactions.
*****************************************************************************************
*
Opacity Printable Version (.PDF)
Definition
What affects the opacity of OPPalyte films
Test principles
Related Terminology
Definition
Opacity represents a substrate's light blocking ability. It is primarily used as a property of paper and
predicts the relative visibility on one side of the paper of the images that exist on the other side. Because
white opaque films are replacing paper in some applications, ExxonMobil measures opacity for some white
films.
There are two common types of opacity measurements, and ExxonMobil uses the one called "89%
reflectance backing," also called "contrast ratio." This value is equal to 100 times the ratio of the diffuse
reflectance of a film sample backed by a black body (<.5% reflectance) to the diffuse reflectance of the
same sample backed by a white body (89% reflectance). The units are percent, and a perfectly opaque
material will have an opacity value of 100%.
back to top
Originally developed for paper, this property predicts the appearance of two-side printed paper. Higher
opacity values allow better readability on one side, because the print showing through from the other side
is less noticeable.
Now, the same test used for paper is being applied to opaque polymer films that compete in paper
markets, most notably labels. Depending on the product design and film thickness, opacity values for
OPPalyte films range from 60% to 95%.
back to top
What affects the opacity of OPPalyte films
Opacity, like light transmission, is determined mostly by pigment and cavitation characteristics, which are
controlled by proprietary resin formulations and film-making process conditions. ExxonMobil technology
creates high opacity levels with a minimum use of inorganic fillers, such as calcium carbonate (CaCO3) and
titanium dioxide (TiO2).
back to top
Test principles
TAPPI procedure T 425 and ASTM procedure D 589 describe the same standard protocol for determining
the opacity of paper. ExxonMobil procedure #498 follows this protocol with only minor exceptions; the

most notable being that ExxonMobil does not precondition samples for 40 hours at standard laboratory
conditions prior to testing.
Although opacity has to do with light-blocking ability, the test actually measures two reflectance values.
The ratio of these values times 100 is equal to percent opacity. The equation, with descriptions of the
variables follows.
Opacity (89% reflectance backing) = CO.89 = 100 (R0 + RO.89)
CO.89 is the contrast ratio, which is another name for this type of opacity measurement.
R0 is the reflectance of the substrate when it is backed by a black body of 0.5% reflectance or less. Any
light that passes through a partially opaque sheet will reflect back negligibly.
R0.89 is the reflectance of the substrate when it is backed by a white body having a reflectance of 89%.
This value will be higher than R0 (or equal to it, if the sample is perfectly opaque) because any light that
passes through the substrate will largely be reflected, and a portion of that will transmit through the film a
second time (in the opposite direction).
Opacity measurements are made with commercially available opacity meters that meet criteria stated in
the standard procedures. The TAPPI Technical Services Department provides names of test equipment
suppliers. ExxonMobil uses a Technidyne BNL-3 Opacimeter.
back to top
Related terminology
Light transmission Light transmission is the percentage of incident light that passes through a
film. It is related to opacity, but cannot be calculated directly from it. In
general, the lower the light transmission, the higher the opacity.
Optical density Optical density is a measure of a material's light blocking ability and is
theoretically equal to log10 (100 ÷ % light transmission). ExxonMobil
uses optical density values with metallized films.
Oxygen scavengers TAPPI stands for the Technical Association of the Pulp and Paper Industry.
Among other things, it provides standard procedures for testing paper.
*****************************************************************************************
*
Light Transmission Printable Version (.PDF)
Definition
What affects light transmission
Test principles
Related Terminology

Definition
Light transmission is the percentage of incident light that passes through a film. ExxonMobil generally
evaluates this property for OPPalyte films.
back to top
This property is significant to the performance of opaque films like OPPalyte. Customers expect these
products to obstruct light transmission in a predictable way, which is important for the appearance of
printed graphics and protecting light-sensitive packaged products. OPPalyte film light transmission values
range from 15% to 50%, depending on the product design and film thickness.
NOTE:
Metallized films are very effective at blocking light transmission, but the preferred test for these
films is optical density.
back to top
What affects light transmission
In OPPalyte films, light transmission is determined mostly by pigment and cavitation characteristics, which
are controlled by proprietary resin formulations and film-making process conditions. Since light
transmission is usually a critical property for white opaque films, it is measured regularly. Product will be
rejected if values are outside the specified tolerance limits.
back to top
Test principles
A unidirectional perpendicular light beam is directed onto the film specimen, and a photo detector
measures the total light transmitted by the specimen after it enters an integrating sphere. Commercial
hazemeters are typically used for this testing, but ASTM D 1003 also allows for the use of a
spectrophotometer, provided that it meets the procedure requirements. ExxonMobil uses the BYK-Gardner
XL-211 haze-gard and haze-gard plus hazemeters consistent with ASTM guidelines.
The hazemeter when set up to measure light transmission will display the final result as a percentage to
the nearest tenth.
Light Transmission (%) =
Total light transmitted by specimen
x 100
Incident light
The same test equipment with a different setup is also used to measure and display haze.
back to top
Related terminology
Luminous transmission Luminous transmittance refers to the same thing as light transmission. It
is a more technical name used in the ASTM D 1003 test procedure title.

Haze Haze is the scattering of light by a specimen, which results in a cloudy
appearance or poorer clarity of objects when viewed through the film.
Translucent Translucent is an attribute used to describe material that transmits light,
but also diffuses it so that objects cannot be seen clearly.
Optical Density Printable Version (.PDF)
Definition
What affects the optical density of metallized films
Test principles
Related Terminology
Definition
Optical density, which ExxonMobil measures with a transmission densitometer, is a representation of a
material's light blocking ability. The optical density scale is unitless and logarithmic, and it enhances the
data resolution for materials that transmit only a small fraction of incident light. ExxonMobil uses optical
density measurements with metallized films only.
back to top
Transmission densitometers are traditionally used to evaluate the light transmission properties of
photographic film. The same test is now used to also represent the thickness of the aluminum layer of
vacuum-metallized films. Since layer thickness affects important performance-related properties like film
barrier, light transmission, and appearance, optical density provides critical data for process control of the
metallizing process.
Depending on the product design, ExxonMobil metallized films have optical density values ranging from
2.0 to 3.0, which is equivalent to light transmission values of 0.1% to 1.0%.
back to top
What affects the optical density of metallized films
Metallizing process parameters and base film characteristics control the aluminum layer thickness and
uniformity, and therefore, the optical density.
back to top
Test principles
ExxonMobil data are provided by commercial densitometers that meet standard conditions defined by
ANSI. A unidirectional, perpendicular light beam is directed onto the film sample. The light that is
transmitted through the film is collected, measured, and logarithmically amplified. The densitometer
calculates and displays the optical density value. ExxonMobil uses the Tobias TBX transmission
densitometer and Macbeth models TD903 and TD932.
The optical density values represent the following calculation and relationship to % light transmission.

Optical Density (unitless) = log10(
Incident light
) = log10(
100
)
Transmitted light Light transmission (%)
Optical density values are reported to two decimal places. Table 11 compares optical density values to
light transmission values in the range that exists for ExxonMobil metallized films.
Optical density 2.00 2.10 2.20 2.30 2.40 2.50 3.00
Light transmission (%) 1.0 0.8 0.6 0.5 0.4 0.3 0.1
Table 11: Light transmission values at various metallized film optical densities
back to top
Related terminology
ANSI ANSI stands for the American National Standards Institute.
Light transmission Light transmission is the percentage of incident light that passes through a
film sample. It can be calculated from optical density values.
Opacity Opacity is a common paper measurement that describes a substrate's
light-blocking ability. A perfectly opaque paper has an opacity value of
100%. Because white opaque films are replacing paper in some
applications, ExxonMobil measures TAPPI opacity for some OPPalyte films.
TAPPI TAPPI stand for the Technical Association of the Pulp and Paper Industry.
*****************************************************************************************
*
Crimp Seal Strength, MST & Range Printable Version (.PDF)
Definition
What determines a film's seal properties
Test principles
Related Terminology
Definition
Crimp seals, which are produced at controlled conditions of jaw design, temperature, pressure, and dwell,
are measured in terms of force required to open the seam. The following properties are calculated and
reported.
• Crimp seal strength is the maximum force to peel open a seal made at specified conditions. Units
are gf/in or gf/2.5 cm.

• Crimp minimum sealing temperature (Crimp MST) for a specified pressure and dwell, is the
temperature (°F or °C) required to achieve a certain minimum strength seal. ExxonMobil has
standardized with 200 g/in as the seal strength for minimum acceptable performance. Other values
may be more appropriate for particular applications.
• Seal range is the difference between the maximum and minimum temperatures that will produce
an adequate seal at a specified pressure and dwell. Units are of or °C.
back to top
The strength of a seal is important to package integrity, and many end-users specify a minimum
requirement.
Crimp MST and seal range are important, because they predict packaging machine efficiency and
productivity. A lower MST corresponds to a wider seal range and, therefore, a wider operating window.
This means that the packaging line will produce acceptably sealed packages even when the speed is
ramping up and down, or when there is variation in jaw temperature. On the other hand, a higher MST
and narrower seal range forces the packager to control these variables better, or else packages can be
rejected for weak, open seals, or distorted seals.
back to top
What determines a film's seal properties
A film's sealing surface is a coated or coextruded layer. The sealing properties can be impacted by several
factors:
• Formulation of sealant layer (resin and additive recipe)
• Thickness of sealant layer
• Total thickness of the film (With thicker films, it takes longer for heat to transfer from the sealing
jaws to the sealing surfaces than it does with thinner films. Therefore, both the effective sealing
temperature and the resulting seal strength are lower.)
• Bond strength of sealant layer to adjacent layer
• Contamination (An otherwise good-sealing surface may not seal well if additives from a laminating
web transfer onto it, or if dust/fines are trapped in the seal area.)
• Surface treatment, including backside treatment, can damage sealability
Seal properties are a key design criteria when developing a sealable film. In production, these properties
are regularly measured to make sure that the formulation or process has not shifted.
back to top
Test principles
In order to compare sealing properties among different films, ExxonMobil uses a set of standard conditions
for producing heat seals. They are summarized in Table 12.
Condition Description

Sealing
device
Wrap-Ade Crimp Sealer Model J or K, modified with new PID
temperature controllers
Jaw design Vertically serrated crimps
Temperature
Both jaws are heated and desired set point is controlled to ±
2ºF (1ºC)
Pressure 20 psi (1.4 bars)
Dwell ¾ sec
Table 12: ExxonMobil conditions for producing test crimp seals
After a test seal has been produced, its strength can be measured with a tensile tester or a Suter tester.
ExxonMobil typically uses the simpler Suter tester, which pulls the seal apart at 12 in/min and records
peak force.
ASTM and ExxonMobil test procedures have similarities and differences. Unlike ExxonMobil, the scope of
ASTM test procedure F 88 is only the measuring of the force to open the seal, not the making of the seal
at a set of standard conditions. ASTM specifies the use of a tensile tester, while ExxonMobil uses a Suter
tester. The 12 in/min pull rate of ExxonMobil is within the ASTM-defined a rate of 10 to 12 in/min.
It is often desirable to produce seals at a series of temperatures, measure the seal strengths, and develop
a seal curve that looks like in Graph 3.
Graph 3: Typical seal curve
Crimp Seal Strength is defined at a particular temperature, or as the average for a range of temperatures.
For the seal curve represented in Graph 3, the following properties can be derived.
Seal Strength at 260°F (SS260F) = 800 g/in
SS260 - 300F = 790 g/in
Minimum Sealing Temperature for a 200 g/in seal (MST200g) = 200°F (93°C)

MST500g = 217°F (103°C)
Seal Range (SR) = Maximum - Minimum Sealing Temperature
SR200g = 300 - 200 = 100°F (56°C)
SR500g = 300 - 217 = 83°F (46°C)
The horizontal red line denotes a minimum acceptable seal strength of 200 g/in. It intersects the seal
curve at 200°F (93°C), so this is the MST200g. If you know that the minimum acceptable seal strength is
another value, the same curve may be used to determine the corresponding MST and seal range. For
example, 500 g/in seals occur at 217°F (103°C), so this is the MST500g.
Most OPPs will distort at temperatures above 300°F (149°C), if dwell time is in excess of ½ second or so.
Therefore, this value is used as the maximum sealing temperature. The difference between the maximum
and minimum sealing temperatures is equal to the seal range.
CAUTION:
Seal data cannot be compared when the seals are produced on different equipment or at
different conditions.
back to top
Related terminology
ASKCO sealer The ASKCO sealer is a laboratory heat sealer that ExxonMobil uses for
process control of coated films. It has nine separate temperature
controlled, one-side heated, low-pressure, flat-sealing stations. The
multiple stations allow a whole seal curve to be generated from one sealed
film strip.
Sentinel sealer The Sentinel sealer is a common laboratory heat sealer in the flexible
packaging industry. Like the ASKCO sealer, it is a one-side heated, flat
sealer. Unlike the ASKCO, there are no multiple stations, so it can only
make a seal at one temperature at a time. ExxonMobil does not use this
sealer. Data generated with the Sentinel sealer, by other companies, can
not be compared with ExxonMobil data.
Failure mode Failure mode refers to how the seal fails as it is being pulled apart. A
"peel" failure means that the films separated without tearing. A
"delamination" failure is a type of peel failure where the material
separates between two adjacent layers, rather than at the sealing
interface. (For example, a printed extrusion lamination can fail between
the ink and poly layers, because they formed a weak bond.) Finally, a
"tear" failure means that the film tears as the seal is being pulled apart.
This suggests that the seal and the bonding between layers are stronger
than the film.
Suter tester Suter tester is a device specifically designed to measure peak seal

strengths. It is simpler and speedier than using a tensile tester. Suter
testers are not commercially available.
*****************************************************************************************
*
Wetting Tension and Contact Angle Printable Version (.PDF)
Definitions
Relevance to converting performance
What affects the "treatment level" of OPP films
Test principles
Related Terminology
Definitions
All of the following terms are used in the polymer films industry to represent the relative receptivity of a
film surface to the addition of inks, coatings, adhesives and extruded polymers.
• Surface energy is a solid surface characteristic associated with the molecular forces of its
interaction with another material. Surface energy is the true film characteristic that we want to
measure, but it can't be measured directly. So, we deduce this property by measuring one of two
substitute properties: wetting tension or contact angle. Both of these measurements involve
observing the behavior of liquids placed on the film's surface.
• Surface tension is the force that exists between a liquid and the atmosphere it is in. For example,
in atmospheric air, a drop of water will bead up on some solid surfaces. It is the surface tension
existing between the water and the air that allows this to occur. The drop of water can spread, or
wet-out, on another solid surface if the new surface has molecular forces (surface energy) high
enough to overcome the water/air surface tension and draw the water flat onto it.
• Wetting tension is the maximum liquid surface tension that will spread, rather than bead up, on
the film surface. It is a measurable property that estimates a film's surface energy. ASTM D 2578 is
a procedure for determining wetting tension by applying different test solutions of increasing
surface tensions until one is found that just spreads (wets) the film surface. Units are dynes/cm.
• Treatment level refers to "how much" or "how well" the polymer film surface was treated in the
film-making process. It is most commonly quantified with a wetting tension value in units of
dynes/cm. Therefore, you will also hear it called "dyne level."
NOTE:
Treatment level, dyne level, surface energy, surface tension, and wetting tension are all terms
frequently used interchangeably. As you can see from the definitions, this is not precisely
correct. Wetting tension, which is the term ASTM uses, is the correct term to describe the value
determined by the test solutions procedure.
• Contact angle is a measurement of the behavior of pure water in contact with the film surface.
(Other liquids of known surface tension could be used, but water is most commonly used.) The
ASTM D 5946 procedure requires a precise volume droplet of pure water be placed on the film

surface. The surface energy of the film controls whether the droplet tends to stand up or flatten
out. This is quantified by measuring the contact angle of the droplet with the surface. A higher
energy ("higher treatment") film will cause the droplet to be flatter and closer to the surface, which
results in a smaller contact angle value (8). Units are degrees, or the result can be reported as
(unitless) cosine 8. ExxonMobil uses a dynamic contact angle (DCA) tester to evaluate the same
property. Our test is substantially different than the ASTM standard and may not produce
comparable results.
back to top
Relevance to converting performance
The surface energy of a film is critical to achieving good wet-out and adhesion of inks, coatings, and
adhesives. The film's surface energy must be higher than the surface tension of the solution being laid
down in order to get good wetting. The molecular forces that allow good wetting also contribute to
adhesion. Water-based systems have higher surface tensions than solvent-based systems and, therefore,
require a higher minimum level of film surface energy to perform well.
Film
Wetting Tension
(dynes/cm)
Polytetrafluoroethylene (PTFE, Teflon®
) 19
Polypropylene (PP) 29
Polyethylene (PE) 31
Polyester (PET) 43
Table 13: Wetting tensions (as an estimate of surface energy) of common untreated polymer
surfaces
In extrusion lamination or extrusion coating processes, a molten extrudate (not a liquid solution) is being
applied to the film surface. Wet-out is not an issue, but an adequate surface energy is required for good
bond strengths.
Some polymer films, most prominently, polyethylene and polypropylene, have inherently low surface
energies, and these surfaces need to be modified to be "converter-processable." The easiest and most
common modification is called "treatment" ExxonMobil uses two in-line treatment processes to increase
the energy, polarity, and processability of film surfaces.
1. Corona treatment involves exposing a moving film surface to a plasma discharge created in the
air gap between a grounded electrode and a high-voltage electrode. The plasma is purple glowing
ionized air that reacts chemically with the film surface. Oxidation reactions occur, which add polar
functional groups and increase surface energy.
2. Flame treatment exposes a moving film surface to a gas-fired flame at a high enough
temperature to create a plasma of free oxygen and nitrogen atoms, electrons, and ions. The
plasma reacts chemically with the film surface, which adds polar functional groups and increases
surface energy.
Depending on the product design, a treated OPP film will have a wetting tension between 35 and 55
dynes/cm. This whole range of values works well in most flexpack converting applications. Challenging
situations, like some water-based applications, may require films in the higher end of the range. For
example, the treated high-energy surfaces of LBW and CSR-2 with wetting tensions of 50 to 55 dynes/cm
provide exceptional wet-out and adhesion in challenging applications.
back to top

What affects the "treatment level" of OPP films
For many reasons, treatment level can be a controversial and complicated topic. Treatment level really
refers to the surface energy of a treated film, which can only be estimated by tests that quantify the
behavior of specific liquids on the surface. The following is a list of the primary factors affecting treatment
level.
1. Measurement: The method of using dyne solutions to measure wetting tension is notoriously
prone to a high variation of results. A few years ago, the Flexible Packaging Association (FPA)
performed a round-robin evaluation and found that wetting tension measurements of identical
materials, made in different laboratories, varied as much as 11 to 15 dynes/cm. Many factors
contribute to this high variation. Bottom-line, the wetting tension test is an unreliable predictor of
performance. Therefore, ExxonMobil has invested in contact angle testers, which provide more
reliable data.
2. Time: The effect of treatment can decay with time. Very old films may not convert well, but
ExxonMobil films are designed to have a good performance shelf-life of one year.
3. Treatment process: Many factors like voltage, residence time, and temperature affect the degree
of surface energy modification.
4. Polymer reactivity: Polymers vary in their reactivity to corona or flame treatment. With a more
reactive polymer, it is easier to achieve the chemical changes that increase surface energy.
Polypropylene is more challenging to treat than many other materials.
5. Additives: Most resins need one or more additives to produce films with maximized performance
in a particular application. Slip and anti-static additives, in particular, can either cause artificially
high or low wetting tension values, or interfere with wet-out and adhesion in the converting
process.
CAUTION:
Treatment pens or dyne pens are available from several manufacturers. They are magic
marker-type pens that contain liquid rated at a certain surface tension. The pen tip is
swiped onto a film surface, and if the liquid does not bead up, then surface is said to be
treated to a dyne/cm-Ievel equal to or greater than that pen rating. If it does bead up,
then the treatment level is said to be less than the pen rating. THESE RESULTS DO NOT
CORRELATE WELL WITH STANDARD TEST PROCEDURE VALUES. Pen solutions can be
contaminated with each film swipe. It is appropriate to use treatment pens to distinguish a
treated surface from an untreated surface, but not to assign a specific wetting tension
value.
back to top
Test principles
There are two tests used to estimate the surface energy of a film: wetting tension and contact angle. Each
has its advantages and disadvantages, which are described in Table 14. For over five years, ExxonMobil
has been expanding its use of the contact angle test as a process control measurement. Because of the
improved data quality, ExxonMobil will continue to do so.
ExxonMobil procedure #417 uses a Cahn Model DCA-312 or DCA-315 to measure dynamic contact angle
(DCA). Unlike the ASTM contact angle test that applies a single water droplet, our Cahn test immerses a
prepared film sample into a beaker of distilled water at a constant rate of speed, while a sensitive balance
records the wetting force. The Cahn DCA software contains well established theoretical calculations, which
convert this measurement into advancing and receding contact angle values. ExxonMobil has standardized
on recording the cosine of the receding contact angle value.

Test Attributes
Wetting Tension
(Dyne Solutions)
Contact Angle
Test results variation Poor Excellent
Cost of test equipment Low High
Speed and simplicity Very good Moderate
Table 14: Comparison of basic test attributes
A more common, but less reliable, test is wetting tension, as described in ASTM D 2578. This method uses
standard wetting tension solutions consisting of varying ratios of formamide in cellosolve to create
different surface tensions. A test solution is selected that is rated less than the anticipated film value.
Using a new cotton-tipped applicator, the solution is applied in a zigzag pattern over about one square
inch of film. If the applied solution holds together for more than two seconds, rather than breaking up into
droplets, then the test is repeated with the next higher surface tension solution. If the solution holds
together for less than two seconds, the test is repeated with a lower surface tension solution. This
scenario is reiterated until you can determine the solution that comes nearest to wetting the film surface
for exactly two seconds. This is the film's wetting tension. A new cotton applicator must be used each time
to prevent contamination of the solutions. A new section of film must be tested with each iteration.
back to top
Related terminology
Dyne test Dyne test is a commonly used name for the wetting tension test, because
it uses solutions that are rated at different dynes/cm.
Wet-out Wet-out is the spreading of a liquid on a film, rather that its beading up. It
is important that inks, coatings, and adhesives wet-out, or spread, on a
film's surface for proper appearance and adhesion.

Film properties tests and details

Recommandé

Recommandé

Contenu connexe

Tendances

Tendances (20)

En vedette

En vedette (15)

Similaire à Film properties tests and details

Similaire à Film properties tests and details (20)

Film properties tests and details