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GLOSSARY OF TERMS

Air Evacuation - A hole or series of holes placed in the film to allow the excess air in the bag to escape during the shrink process.

Antifog Film - A film containing a wetting agent which reduces the surface tension on the film to allow water to wet the surface rather than form water droplets, which causes a cloudy appearance.

Ballooning - The lifting action of the film away from the product caused by the pressurizing of the excess air in the bag during the shrink process.

Bead Seal - The resultant weld caused by the simultaneous sealing and cutting of two or more pieces of film.

Biaxial Orientation - A film that has been stretched under certain temperature conditions equally in both the machine and transverse directions.

Blocking - A condition where layers of film cannot be separated.

Blown Film - Film produced by extruding resin into a tube, which is expanded by air pressure.

Bubble - The inflated tube of film in the blown film extrusion process.

Burnthrough - A weakening of the film where the heat of the tunnel exceeded the heat resistance of film. Typically, it will appear as a hole or a very cloudy area.

Centerfolded Film - Film folded in half in the machine direction and then wound into roll form.

Centerfolder - A device used to produce center folded film from flat film.

Clarity - The transparency of the film, which is a function of surface gloss and internal haze.

Coefficient of Friction - A comparative value indicating the ability of the film surface to move against itself or another surface. The higher the coefficient of friction, the more difficult to slip or move.

Coextrusion - Two or more different materials simultaneously extruded into a composite film.

Copolymer - A resin polymerized from two or more monomers.

Core - A paper tube used as a base for forming a roll of film.

Crows Feet - The residual wrinkles that can be left in a poorly shrunk sample. They are normally associated with the excess film in the comers of the pouch.

Dancer Bar- A mechanical device used to control the tension of the film between the film unwind and the film sealing area.

Density - Weight per unit volume. Films with a low density offer more coverage per weight of film.

Dog Ears - The excessive film in the corners of the pouch formed by placing a three-dimensional item in a flat pouch. Excessive "dog ears" normally indicate poor shrink technique.

Electronic Hole Burner - A device that uses an electrical spark to burn a round hole in the film for air evacuation during the shrink process.

Electrostatic Seal - An electrostatic discharge is applied to the overlap of two edges of the film. This keeps the edges aligned until film seals together in the shrink tunnel .

Elmendorf Tear Resistance - A measure of the resistance to tear after the film has been cut.

Elongation - The percentage a film will deform or stretch prior to breaking.

Extrusion - A technique for producing film by melting a resin and forcing it through a die.

Fish Eyes - The circular or oval patterns that remain on a package that has been poorly shrunk. They are normally associated with the absence of adequate heat or air velocity.

Fogging - A buildup of water droplets on the surface of a film.

Forming Head (Plow) - A mechanical device used to shape flat wound film into the desired bag shape needed for a particular package.

Gas Transmission Rate (GTR) - A measure of the rate a gas will permeate through a film.

Gauge - The average thickness of a film.

Gloss - A measure of the reflected light from the film surface.

Haze - A measure of the cloudiness of the film.

Hole Burner - A device that uses a hot wire formed in a circular shape to burn a round hole in the film for air evacuation during the shrink process.

Hole Punch - A device to punch a round hole in the film for air evacuation during the shrink process.

Impact Resistance - The resistance to impact of a film.

Impulse Seal - A seal produced by an intermittent electric pulse, which heats a round, wire or ribbon to cut and seal film.

Initial Tear Resistance - A measure of the force needed to begin a tear in a film.

Inverting Head - A mechanical device used to separate and invert centerfolded film as the film is transferred into the sealing area of the wrapper.

Irradiation - A process that uses high-energy electrons to cross-link a film.

Lap Seal - A seal produced by overlapping film and then binding it together either thermally or electrostatically.

L-Sealer - The most common means of sealing film for heat-shrinkable applications.
An L shape sealer produces two seals simultaneously on folded film.

Low Temperature Flexibility - The lowest temperature at which a film can withstand a flexing test without cracking.

Machine Direction (MD) - The direction the film was manufactured and also comes off the roll .

Modulus - A measure of film stiffness.

Moisture Vapor Transmission Rate (MVTR) - The rate moisture vapor will pass through the film.

Monomer - A simple compound, which can react at high temperature and pressure to form a polymer.

Orientation - The stretching technique used to obtain molecular alignment in a film during manufacturing, which increases tensile strength and stiffness and decreases tear strength.

Oxygen Transmission Rate - A measure of the permeability of a packaging film to oxygen.

Plasticizer - A substance blended into plastics such as PVC to improve flexibility and softness.

Polyethylene - A resin made from ethylene gas, which produces tough transparent film.

Polymer - A high molecular weight, long chain compound formed from one or more simple molecules.

Polypropylene - A resin made from propylene gas, which produces lightweight, highly transparent, stiff film.

Polyvinyl Chloride (PVC) - A resin produced from vinyl chloride. Generally compounded with plasticizers and other additives to improve flexibility.

Sealing Wire - A nichrome wire, which is heated by its resistance to electrical current. It is used for sealing and cutting shrink film.

Shrink Film - A plastic film, which has been produced under special orientation conditions that will allow the film to shrink when heat is applied.

Shrink Force - The force exerted on the product by the film during the shrink process.

Shrinkage / Percent Shrink - The decrease in dimension of a film when it is subjected to heat.

Single Wound Film - Flat film wound on a core.

Slip - How easily one surface moves across another.

Slip Agents - Lubricants added to films to improve slip and reduce friction.

Static - An electric charge generated by film moving across itself (unwinding from the roll ) or any other surface.

Tear Strength - The ability of the film to resist tearing. Highly oriented films generally have reduced tear resistance.

Tensile Strength - The force exerted on the film from external sources.

Tension - A force exerted on the film from external sources.

Transverse Direction - The direction at right angles to the film movement during its manufacture, usually the same as the width of the film.

Trim - The edges of film, which are cut from a package formed on an L-sealer or side sealer when the seal is made.
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Uniaxially Oriented Film (Preferential Shrink Film) - A film that will shrink in only one direction.

Yield - Coverage of a film per unit weight (usually sq in/lb) rolls.

 

 

 

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