Technical Terms

Additive

A compound or substance added to polymer to alter or improve its characteristics. Common additives include slip, antiblock, and color pigments.

Antiblock

Additive used in film production to prevent undesired adhesion between film layers during unwinding.

Antioxidant

Additive which prevents degradation and oxidation of material when exposed to ambient air during processing and storage of finished product.

Antistat

Additive which aids dissipation of static electricity.

Backside Treat

Film defect when areas of the untreated/lamination side of film test positive for corona treatment.

Barefoot

A resin or film containing no additives.

Barrier Resins

Polymers such as polyamide and EVOH which have very low permeability to gases.

Blend

The mixing of polymers with other polymers, copolymers, or additives to achieve desired physical properties.

Blocking

An undesirable adhesion between layers of film or sheeting which may develop during processing or storage.

Bloom

Migration of additives such as slip to the surface of the film over time.

Blown Film

Extrusion of a continuous thin walled tube of plastic through a round die and inflating it to form a bubble. The bubble is then collapsed flat between rollers and slit into layflat film which is wound onto rolls.

Blow Up Ratio (BUR)

Term used in blown film extrusion that is the ratio of the diameter of the bubble to the diameter of the die.

Calcium Carbonate

Mineral based additive used as filler, modifier, and sometimes antiblock agent.

Center Fold

A roll of film that has a fold on one side and slit on the other in the machine direction allowing the film to be unfolded to twice its roll width.

Coefficient of Friction (COF)

A unitless measurement used to quantify how slippery or tacky a film is. It is the ratio of the force required to slide an object over a frictionless surface to the force required to slide the same object over the actual surface being tested.

Coextrusion

Extrusion of film having multiple, distinct layers of materials using two or more extruders through a common die assembly. Co-extrusion allows resin combinations to be used to produce films having properties not obtainable through blending in a single layer extrusion.

Color Concentrate

A plastics compound which contains a high percentage of color pigment blended with a carrier resin.

Copolymer

A polymer resulting from the polymerization reaction between two chemically different monomers.

Core

Rigid cardboard tube onto which film is wound. Typical cores have either 3 inch or 6 inch inside diameters.

Corona Treat

The process by which the surface energy of plastic film is increased to allow adhesion of adhesives, inks, and coatings.

Dart Drop

Measurement of the puncture resistance/impact strength of film and its ability to withstand the shock of a falling "dart" without breaking. Expressed as gram weight of the heaviest dart which doesn't break the film when dropped from a specified height.

Density

Weight per unit volume of a substance, usually expressed in grams per cubic centimeter. Polyethylene resins often range between .890 - .965.

Die

A circular steel block made up of an inner and outer ring through which plastic is extruded and inflated into a large tube.

Die Gap

Distance between the metal surfaces which form the die opening.

Die Lines

Lines in the machine direction of film caused by buildup of oxidized materials on the die.

Differential Scanning Calorimetry (DSC)

Analytical method used to determine thermal histories of polymers such as melting temperatures and glass transition points.

Double Wound Sheeting (DWS)

Two layers of plastic film wound onto the same core.

Dyne

Unit of measure for surface tension (treat level).

Edge Wrinkles

Rough cut, or jagged edge followed by a wrinkle extending into the roll.

Elongation

Usually expressed as a percentage, it is the increase in length of a test specimen when a tensile load is placed on the sample. Such test data is often obtained by equipment such as an Instron during tensile testing.

Erucamide Slip

A fatty acid based additive commonly used in polyolefin resins to reduce coefficient of friction.

Ethylene Vinyl Acetate (EVA)

Random copolymerization of vinyl acetate and ethylene. Usually low density polyethylene is copolymerized with various levels of vinyl acetate to achieve a lower melt temperature resin.

Ethylene Vinyl Alcohol (EVOH)

Copolymer exhibiting outstanding barrier to many chemicals and gasses.

Extrusion

Compressing and melting a plastic material and forcing it continuously through a die.

Film

Plastic sheet material usually having a thickness of 10 mil or less.

Flame Retardant

Additive compounds used to make a polymer fire resistant.

Gauge

Thickness measurement of plastic film, often expressed in mils. One mil equals one thousandth of an inch (0.001" or 0.001in.).

Gauge Bands

Raised regions in the machine direction around the circumference of a roll, produced by winding areas of thicker film in the same place on a roll.  

Gel

Mass of unmelted polymer or degraded material causing a defect in plastic film.

Gloss

A measurement of a film's surface reflectivity of light shone from a given angle, commonly 45 degrees for blown film. Expressed as a percentage, the higher the number, the shinier the film.

Haze

A measurement of the clarity or transparency of film. It is expressed as the percentage of light that is not transmitted through a film sample. The lower the number, the higher the clarity.

Heat Seal

The process of bonding two or more thermoplastic films using heat and pressure.

High-Density Polyethylene (HDPE)

Polyethylene resins/films ranging in density from approximately 0.940 to 0.965.

Homopolymer

The result of the polymerization of a single monomer, a homopolymer consists of a single type of repeating unit.

Hot Tack

Hot tack is a measure of the strength of a heat seal before the seal has cooled completely.

J Sheet

Similar to center fold, j-sheet is folded on one edge of the roll and slit in the machine direction on the other side allowing the film to be unfolded. The difference is that the fold is not directly in the center of the film, so the width of the film on either side of the fold is asymetrical when opened.

Layflat

Measurement of the transverse/cross direction of film, also known as film width.

Light Transmission

Measurement of the amount of light that color pigmented films allow to pass through them. Values range from 100% for clear film to 0% for opaque films.

Linear Low-Density Polyethylene

A process variation of low density polyethylene. It allows for higher draw down-gauging in extrusion and increased film strength.

Low-Density Polyethylene

A partially crystalline, lightweight thermoplastic with density ranging from 0.910 - 0.929 g/cm3 that is relatively soft, flexible, and will withstand moderate heat.

Machine Direction (MD)

Direction of the film corresponding to the way it exited the die.

Masterbatch

A concentrated blend of slip, additives, or color pigment in a base polymer carrier resin.

Melt Fracture

Extrudate or film having a surface that appears rough and wavy. Melt fracture may be evenly distributed throughout the film or concentrated in some areas only.

Melt Index

Grams of a thermoplastic resin which can be forced through a 0.0825 inch orifice by 2160 grams of force in 10 minutes at 190°C.

Melt Temperature

The temperature at which a resin changes from a solid to a liquid.

Mil

Gauge measurement commonly used in film manufacturing. One mil equals one thousandth of an inch (0.001" or 0.001in.).

Mono layer

Film comprised of a homogeneous mixture of one or more polymers blended together in a molten state and extruded through a die assembly to form a film or sheet.

Opacity

The amount of light that is blocked by a pigmented film.

Orange Peel

An uneven surface texture of a plastic article or its finished coating somewhat resembling the surface of an orange, see Melt Fracture.

Polyamide (PA)

Also known as nylon, a thermoplastic used for high strength, puncture resistance, heat resistance, and barrier to certain gasses.

Polyethylene (PE)

Resins of various densities produced by polymerizing ethylene gas. Examples are Low Density (LDPE), Linear Low Density (LLDPE) and High Density (HDPE).

Polypropylene (PP)

A tough, lightweight, rigid plastic made by the polymerization of high-purity propylene gas in the presence of an organometallic catalyst at relatively low pressures and temperatures.

Process Aid

Additives used in the production of plastics to improve extrusion performance and reduce surface defects of film

Polymerization

A chemical reaction in which the molecules of a simple substance (monomer) are linked together to form large molecules whose molecular weight is a multiple of that of the monomer.

Polyolefins

Class of polymers made by polymerizing relatively simple olefins, including ethylene, propylene, butene, isoprene, and pentene.

Resin

Term for the raw material from which film is made, usually in the form of pellets.

Sheeting

A term often used in the film industry as an abbreviation for single wound sheeting.  Actually, a web under 10 mils (.010 inch) thick is usually called a film, whereas a web 10 mils and over in thickness is usually called a sheet.

Shrinkage

A measurement of the percent of film shrinkage in the machine direction or transverse direction at a specified temperature and time.

Single Wound Sheeting (SWS)

A single layer of plastic film that is wound on a roll.

Slip Agent

Additive which lowers the coefficient of friction of film to make the sliding action easier on processing and filling equipment.

Talc

Additive composed of hydrous magnesium silicate, used frequently as a filler or antiblock agent.

Telescoping

Roll phenomenon characterized by layers of film sliding laterally in the transverse direction, causing the edge of the roll to have a conical shaped appearance resembling that of a telescope.

Tensile Strength

The maximum tensile stress sustained by the specimen before failure in a tension test.

Tin Canning

Roll defect appearing as raised ridges around the circumference of the roll resembling a tin can.

Titanium Dioxide

A white powder available in two crystalline forms, the anatase and rutile types.

Transverse Direction (TD)

Film direction which is at a right angle to the direction of extrusion, also called cross direction (CD).

Tubing

Blown film is extruded through a circular die which creates a tube of film. When the tube of film is collapsed and rolled onto a core, the finished product is called tubing.

Ultra Violet Inhibitor (UVI)

Additive used to prevent degradation of plastic materials from prolonged exposure to sunlight.

Wrinkle

An imperfection in plastic films that has the appearance of a crease, fold, or wave.

Yield

The area of film of a given thickness per unit of weight. Common units used are square inches of film per pound.

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