Polyethylene Plastic PE Films Glossary

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”.

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.

Resins which have no additives (slip or antiblock).

A degradable plastic in which the degradation results from the action of naturally occurring micro-organisms such as bacteria. There are three standards - EN 13432, ASTM D6400
and ASTM D6954-04

Can be used as a monomer in the formation of polymers, most commonly linear low density polyethylene, hence the name “butane LLD”.

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

                                            Centerfold "A" Wind                        Centerfold "B" Wind

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.

Measuring the COF of film against stainless steel is a more accurate predictor of PE film performance. It is also critical to measure the static COF and Kinetic COF.

For more in-depth information on coefficient of friction, visit:
http://www.tribology-abc.com/abc/friction.htm

One of the compounds that constitute a copolymer.

Determines resistance to puncturing of the film. Measured in grams.

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

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

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.

Originally developed to measure tear resistance of paper, this test measures the resistance to tearing.

The basic monomer building block of polyethylene, extracted from either natural gas or naptha. Note: neither of these feedstocks is suitable for deriving gasoline.

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.

      “J” Sheet “A” Wind                       “J” Sheet “B” Wind

       Layflat Tubing

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.

Polyethylene of a density ranging from .915 to .929 grams/cc.

Direction the film is being pulled through a machine.

Polyethylene having a density ranging from .929 to .940 grams/cc.

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.)

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.

One thousandths ( 1/ 1000 ) of an inch expressed as “001”. Metric equivalent is 25.4 microns.

Small molecule ( ethylene, propylene, styrene, etc. ) that may become chemically bonded to other monomers to form a polymer.

Comonomer in production of usually linear low density ( LLD ) polyethylene.

Oxygen transmission rate as measured by ASTM D 3985. Measure of the amount of oxygen which passes across the film.

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.

Measure of stiffness. Higher the number, the stiffer the film.

Single ply of film.

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.

Cross direction or sideways dimension 90° orientation to the machine direction.

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.

Specialized form of linear low-density polyethylene having density between .86 and .90 grams/cc.

Retards the degrading effect of sunlight on polyethylene.

Net weight per 1,000 lineal feet of film. We have Polyethylene Film Weights and Measures for calculating yields.