| Blown Film |
The fabrication of a film by continuously pumping the polymer through a circular die and filling the tube with air. The volume of air contained within the tube stretches the tube out to the desired width and, in conjunction with the rate at which it is being pulled away from the die, the desired thickness is created. |
| Cast Film |
The fabrication of a film by continuously pumping the polymer through a straight slot die, then chilling this hot plastic immediately through contact with a chilled roll. Film width is determined by how fast the chill roll pulls the film away from the die. |
| Cling |
The characteristic of stretch film which makes it stick to itself or other clean, shiny objects. |
| Co-extrusion |
Fabrication of a multi-layer film by pumping the various materials through separate extruders and then merging the extruded material into a common die assembly. These die assemblies are constructed to maintain distinct material layers with fusion occurring at the boundaries due to the pressures and temperature of the extruded material. |
| Copolymer |
A plastic or polymeric whose chemical composition consists of more than one basic hydrocarbon. EVA is a copolymer. It is made by feeding more than one monomer to the reactor. |
| Die |
A device used in extrusion processes to shape the extruded material. |
| EVA |
Abbreviation for the copolymer Ethylene Vinyl Acetate. Small amounts of EVA are polymerized with ethylene to provide greater extensibility, greater low temperature strength, or to improve sealability. |
| Elastic Recovery |
The ability of a material to return to its original shape or size after having been deformed or subjected to strain. |
| Elmendorf Tear |
A testing method used to measure a material’s resistance to tearing forces. A sample is slit (initiated tear), then the force required to tear apart the sample is measured and given as the tear value. |
| Elongation at Break |
The strain or deformation required to break a sample. Expressed as a percentage by dividing the strain (distance) at which a sample breaks by the original sample length. |
| Extruder |
A device which uses thermal and mechanical means to convert a solid polymer into a molten polymer. This extrudate is then further process modified to a final product. |
| Film Yield |
The square inches of a film that weighs one pound if the film is 1 mil thick (.001”) Polyethylene yields 30,000 square inches/pound at 1 mil. |
| Gauge |
The thickness of a film. Sometimes expressed as 80 gauge or 100 gauge which equates to .8 or 1 mil respectively or .0008 or .001 inches. |
| Gauge Band |
Thickness irregularity. |
| Gel |
Small piece of undissolved resin causing imperfection in film. |
| Gloss |
The shine or sparkle of a surface. In LDPE film, it is described as the amount of light reflected from the surface. |
| Haze |
The lack of clarity or “see through” ability of a film, measured by determination of the percentages of light not transmitted through a film sample. |
| Homopolymer |
A plastic, resin or polymer whose entire chemical molecular structure is of a single basic hydrocarbon group. |
| Impact Strength |
The ability of an object or material to resist rapidly applied destructive forces. |
| LDPE |
Linear Low Density Polyethylene – any polyethylene homopolymer whose density is between .913 and .925 gms/cc. |
| MD |
Machine direction. |
| Modulus |
Modulus of elasticity which is a numerical value reflecting a material’s resistance to deformation. A film with a high “modulus” is hard to stretch or elongate. |
| Neck Down |
The “narrowing” tendency of a film when it is being stretched or pulled. |
| PVC |
Poly Vinyl Chloride. In film form, it is used as a meat or produce wrap, as stretch film, and a high clarity shrink wrap for consumer, retail packaging. |
| Polymer |
Means “many member”. A structure generated by the repetitious joining of many of the same elementary units. |
| Pre-stretch |
Stretch applied to film through a set of rollers in a prestretch pallet wrapper before application to the load. |
Puncture
Performance |
The relative comparison of a material’s resistance to failures caused by penetration |
| Reactor |
The equipment used to transform ethylene gas to polyethylene. |
| Roping |
A method of gathering stretch film on a pallet wrapper to increase strength in a certain area, used for wrapping loads inboard or outboard of pallet. |
| Spiral |
Twenty or thirty inch roll of film applied by a vertical carriage in a convoluted wrap. |
| Stress Retention |
The phenomenon of force retention as a function of time. This rate of decrease varies with different polymers. PVC has a very early decay versus a slower decay with LDPE. |
| Stretch |
The percentage change in film length due to a given pound pull. |
| Stretchability |
A combination of factors related to the ability of a material to be stretched or elongated. |
| TD |
Transverse direction. |
| Tack |
An adjective used to describe a film’s resistance to slide against itself or another surface or its resistance to separation from itself. |
| Tackifiers |
Chemical substances added to increase the “tack” of the parent or base material. |
| Tear Resistance |
The resistance of a film to be torn. This is measured by Elmenforf Tear testing, and is measured as the force required totear a sample in the MD or TD direction. |
| Tensile Yield |
The stress level, in PSI, beyond which permanent deformation occurs. |
| Tensile Ultimate |
The stress level, in PSI, beyond which the specimen will break. |
| Toughness |
An overall strength measurement which takes into account both the amount of pull and the amount of elongation a sample can withstand. |
| Wide Web |
Wrap with roll of film approximately the size of the load. |
| Wrap |
One revolution of pallet wrapper turntable. |
| Zippering |
Lack of resistance to tear propagation of an initiated TD cut or tear. Once the film has been torn or cut the resulting slit rapidly opens and completes a full web break. |
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