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Polyethylene Plastic PE Films Glossary

                                      For additional info on many of these subjects, visit our Youtube channel.

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ANTIBLOCK Additive used to give surface of film a rougher texture at a microscopic level. Without additives, film has tacky texture similar to cling wrap. Prevents film from sticking together, or "blocking".
ANTISTAT Plastic has a natural tendency to attract static electricity. Additives put in to dissipate static are referred to as antistats. There are many standardized tests, such as MIL B – 81705C to measure the effectiveness of antistatic agents.

CLICK HERE to learn more about our anti-stat film.
ASTM American Society for Testing and Materials
BAREFOOT POLYETHYLENE Resins which have no additives (slip or antiblock).

PE films made with barefoot resins are always very slow slip / high COF (Coefficient of Friction)
BIODEGRADABLE PLASTIC A degradable plastic in which the degradation results from the action of naturally occurring micro-organisms such as bacteria. There are a multitude of evolving standards.

Visit our biodegradable plastic film page to learn more.
BUTENE Can be used as a monomer in the formation of polymers, most commonly linear low density polyethylene, hence the name "butane LLDPE".

For more in-depth information on LLDPE visit our blog.
CAMBER As it applies to blown polyethylene film, camber is the tendency of any straight line to eventually curve. Also known as "dishing", any film which does not unroll perfectly straight will cause machinability issues in printing presses, bag machines, shrink tunnels and vertical form fill & seal VFFS machines.


CENTERFOLD Film which is folded on one side and open on the other.


centerfold "A" windcenterfold "B" wind
COF (COEFFICIENT
OF
FRICTION) /
ASTM D 1984
While COF is usually measured film-to-film which makes sense for applications such as beverage shrink wrap, the interface is usually between film and stainless steel in VFFS vertical form / fill / seal, HFFS horizontal form / fill / seal and bakery bread applications. Stainless steel has a high surface energy of around 75 dynes, so it is reasonable to expect different results vis-à-vis film-to-film.





What is high slip, medium slip and low slip?

The Flexible Packaging Association defines the ranges of slip (high, mediuim and low) and the kinetic coefficient of friction, when tested, film-to-film, in accordance with ASTM D 1984, as follows:

Surface                C.O.F.

1. Low Slip            Greater than 0.5

2. Medium Slip      0.2 to 0.5

3. High Slip           Less than 0.2
COMONOMER A monomer which is combined with a different monomer to make a polymer. A common example is EVA (ethylene vinyl acetate) / PEVA.
DART DROP TEST /
ASTM D 1709A
Determines resistance to puncturing of the film. Measured in grams.
DENSITY Measure of how closely molecules are packed together. Called out as the number of grams per cubic centimeter. General purpose low density PE films are around .925 gm/cc. Density affects characteristics of film.

Density ranges are as follows:

Low Density             Under .929

Medium Density      .930 to .940

High Density           Over .940
DIFFERENTIAL
SCANNING
CALORIMETRY (DSC)
MELTING POINT
Used to measure the melting point of plastics. Different test method that vicat softening point, so different values result.
DOUBLE
WOUND
SHEETING
Two plies of sheeting wound together.

double wound sheeting
DYNE LEVEL Measure of surface tension. Higher level of surface tension is achieved by passing an electrical charge across the film. The higher the value, the greater the amount of tension. Untreated film has a natural dyne level of about 33. For film to accept adhesive coatings and solvent-based ink for printing, it is necessary to treat film to 38 to 40 dynes. For water-based inks and laminations, a treat level of 45 dynes is required.



ELMENDORF
TEAR TEST /
ASTM D1922
Originally developed to measure tear resistance of paper, this test measures the resistance to tearing.
ETHYLENE C2H4 The basic monomer building block of polyethylene, extracted from either natural gas or naptha. Note: neither of these feedstocks is suitable for deriving gasoline.
EVA Short for ethylene-vinyl acetate. Also vinyl acetate copolymerized with polyethylene. It is a copolymer that enhances sealability and clarity. The higher the VA percentage, the lower the melting point and stiffness. High percentage EVA's are popular choice for total batch inclusion bags which must melt often at temperatures less than 200°F. Very low density metallocenes have rendered EVA obsolete for applications requiring fast tack and low seal initiation temperature.
FDA Approval The US Food and Drug Administration never actually approves a resin for prolonged and direct food contact. A resin can only be listed as compliant with CFR 212, section 177.1520, 175:30 (or 21 CFR 177.1630 sections h(1), (ii) ) for prolonged and/or direct contact for food packaging.

Visit our blog to learn more about what FDA compliance really means.
FRACTIONAL MELT Resin which has a melt index less than 1.0, as measured by ASTM D 1238 (see melt index below), hence the name "fractional" .
GAUGE Thickness of film. In English units, gauge is measured in mils or 1/1000 of an inch. The metric unit of measure is microns. The symbol for microns is μm. Click here to visit our Polyethylene Film Weights and Measures page to learn more about mils and microns.
GLOSS 45° /
ASTM D 2457
Measure of how much light is reflected by a film.
GUSSET Folds, or "pleats" put into film as it is collapsed. ½ of the total gusset width is on each side.
HAZE /
ASTM D 1003
Measure of clarity of film. Expressed in percent. For example, a resin which has a haze of 5.5 allows 94.5% of light to pass through the film.

HEXENE Used as a monomer in the formation of polymers, usually LLDPE resin. Stronger film strength than butene. Visit our blog to learn more about the varieties of LLDPE.
HIGH DENSITY
POLYETHYLENE
( HDPE )
Polyethylene resin with a density over .940 gm/cc. Much stiffer than low density polyethylene. Common examples of HDPE are milk jugs, motor oil bottles and plastic grocery sacks.
IONOMER Copolymers of ethylene and acrylic acids that have been neutralized to some degree to form metal salts. The dramatic bond strength from the most commercial brand, Surlyn® from DuPont, results from an ion which shares orbits with adjacent molecules.
IQF
Individually
Quick-Frozen

Freezes bagged meat or vegetables rapidly by exposing it to blast of air at approximately -40° F.  To avoid cracking at sub-freezing temperatures, either a very low density metallocene or some EVA should be a component of the PE blend.

 

J SHEET Film which looks like the letter "J". Has a "short" and "long" side.
“J” Sheet “A” Wind“J” Sheet “B” Wind
LAY FLAT Flexible polyethylene tubing which has been pressed flat.


Layflat Tubing

layflat tubing     Layflat Tubing

LINEAR
LOW DENSITY
POLYETHYLENE
( LLDPE )
Polyethylene which has more crystallinity than LDPE. Can be produced with butene, hexene or octene comonomer for a wide variety of properties usually stronger than conventional LDPE.
LOW DENSITY
POLYETHYLENE
( LDPE )
Polyethylene having a density ranging from .915 to .929 grams/cc.
MACHINE DIRECTION
(MD)
Direction the film is being pulled through a machine much like the direction of woodgrain.
MEDIUM DENSITY
POLYETHYLENE
( MDPE )
Polyethylene having a density ranging from .929 to .940 grams/cc.
MELT INDEX (MI) a.k.a "melt flow index" or "melt flow rate".

Measure of viscosity (resistance to flow) of a resin by ASTM D 1238.

The amount of polymer which exits the die in ten minutes is measured in grams. In general terms, the lower melt index resin which has more viscosity will be stronger than a higher melt index and trade off clarity or haze. If the number of grams extruded is less than 1, the resin is referred to as a "fractional melt" (less than 1.0.)
METALLOCENE Latest generation of resin technology utilizing a metallocene catalyst which is basically tiny particles of positively charged metal ions sandwiched between two rings of carbon atoms that have five atoms apiece.

Metallocene is not a comonomer; it is a catalyst which imparts consistent molecules. Metallocenes are not necessarily stronger than LDPE or LLDPE.
MIL One thousandths ( 1/ 1000 ) of an inch expressed as "001". Metric equivalent is 25.4 microns.
MONOMER Small molecule ( ethylene, propylene, styrene, etc. ) that may become chemically bonded to other monomers to form a polymer.
OCTENE Comonomer in production of usually linear low density ( LLD ) polyethylene.
OTR Oxygen transmission rate as measured by ASTM D 3985. Measure of the amount of oxygen which passes across the film.
PROPOSITION 65 Proposition 65, otherwise known as the Safe Drinking Water and Toxic Enforcement Act of 1986 or Prop 65 was a voter initiative passed into law to address public concern over exposure to unsafe and toxic chemicals in the State of California.
SEAL INITIATION
TEMPERATURE
Measure of lowest temperature at which the required hot tack and seal strength levels are both achieved. Seal range is the temperature range over which hot tack and seal strength are greater than the acceptable minimum required levels. Maximum hot tack level indicates what maximum loading the sealing material can sustain during the packaging cycle.

SECANT MODULUS Measure of stiffness. Higher the number, the stiffer the film. ASTM D 882

SINGLE
WOUND

SHEETING

Single ply of film.


Single Wound Sheeting

Single Wound Sheeting

SLIP Slip is added to polyethylene resin to make it slipperier as the name implies. Slip agent, most commonly an erucamide or oleamide, exhibits a "blooming" phenomenon. Slip exudes to the surface of the polyethylene film to create a lubricated effect on the finish, or coefficient of friction (COF).

A common example of a very high slip film is a bread bag.

The same parts per million of slip produces a higher slip / lower COF film as gauge is increased. This is explained by what is known as the reservoir effect. The same parts per million exuding to the surface area of a thicker film has a larger reservoir of slip which all wants to get to the surface.

Two applications which should never have slip are medical applications involving gamma irradiation sterilization and tamper evident bags with a tape closure.
TRANSVERSE
DIRECTION


Cross direction or sideways dimension 90° orientation to the machine direction.
TREAT a.k.a. corona discharge treatment. Method
of raising the surface energy and to some
extent etching of films in order to accept
adhesives and inks. Most commonly achieved
by arcing of electricity across the film. "Corona"
refers to the original method of flame treating.
ULDPE /VLDPE Specialized form of linear low-density polyethylene having density between .86 and .90 grams/cc.
UVI
ULTRAVIOLET INHIBITOR
Retards the degrading effect of sunlight on polyethylene.
YIELD Net weight per 1,000 lineal feet of film. We have Polyethylene Film Weights and Measures for calculating yields.
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