Glossary of Terms: Polyester Film Production & Use

There are many specialized terms and acronyms related to PET film production. We hope the following list is useful to you. If you don't find the term you are looking for, please contact us.


A | B | C | D | E | F | G | H | I | L | M | N | O | P | R | S | T | U | V | W | Y
 

A

ANCHORED COATING
A coating applied to a base sheet (usually bonded) so it very strongly resists separation.
ANNEALING
Technique of keeping a material for a period of time at a temperature short of melting, to relieve internal stresses; the application of heat to a formed or oriented plastic article to relieve stress resulting from the forming or orientation process.
ANTI-BLOCK
The name for a treatment applied to plastic film surfaces to keep them from sticking together or “blocking” when they are tightly rolled up on a mandrel.
ANTIOXIDANT
A substance that prevents or reduces oxidation of the material by air or oxygen.
ASEPTIC
Free from septic matter or disease-producing bacteria. In food processing and packaging, this is an adjective that describes the system used to package food in a sterile fashion.

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B

BAG, CRIMP-BOTTOM
A flat bag with a crimp-seal bottom (no fold-over), usually heat-sealed using serrated dies. Not a particularly strong type of bag (see: Flat Bag).
BAG, DUPLEX
A bag constructed of two plies of material, generally spot-sealed to each other, especially at the mouth.
BAG, FLAT
Simplest form. A web of material folded into a flat tube with side or center seam, then cut off and sealed at one end. Has only two dimensions: length and flat width. Flat bags may have a crimped seal or a fold-over seal, in which a short section is turned back and sealed in place by heat, adhesives or a combination of both.
BAG, GUSSETED
Bag having bellows-like folds on each side that expand outward when bag is filled.
BAND
In cellophane, a dark-colored circumferential ring in a slit roll, caused by a slightly heavier moisture content, or very slight variations in base-sheet thickness.
BANDS, BAGGY
A defect in a roll of film; a slack lane or a baggy section which shows up when film is unwound and pulled taut.
BEAD
A thickened section at the edge of a roll of film. In cellophane slit rolls usually caused by moisture absorption into the cellulose base sheet.
BETA-RAY GAUGE
Consists of two facing elements, one emitting and one detecting beta radiation. The device accurately measures density or thickness when mounted above and below the web.
BIAXIAL ORIENTATION
A process for orienting a plastic film in both the transverse and the machine directions.
BLEEDING
Diffusion, especially of inks, into areas adjacent to those that were intended to be printed.
BLISTER PACK
Package formed from semi-rigid thermoplastic material so that the sheet forms a transparent dome over the package item.
BLOCK, BLOCKING
Undesired adhesion of two or more plies of material in roll or sheet form. May be caused in cellophane by exposure to excessive heat, pressure or humidity; in printed film, occasionally caused by improper or insufficient drying of inks, resulting in printed areas sticking together.
BLUSH, BLUSHING
Hazy or foggy appearance occasionally noted in coated films.
BON
Biaxially Oriented Nylon.
BREATHING
Passage of gases into or out of a package. Certain films are designed to permit it.

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C

CELLOPHANE
Transparent film made from regenerated cellulose, a fibrous material occurring in plants.
CELLULOSE, REGENERATED
Cellulose that has been chemically treated, then regenerated as a transparent film.
CEMENT
In the adhesive sense, a substance bonding two materials by chemical or solvent action.
CHEEK-PLATES
Discs used at each end of paper or rolls of film to prevent “telescoping” of material.
CLARITY
Freedom from haze; transparency.
CLING
Adhesion of packaging films to machine surfaces: “drag.” Often caused by tackiness or static electricity charges in plastic films.
COATING, FILM
A coating applied to provide protective, decorative, pressure-sensitive, waterproof or heat-sealable qualities to the base sheet.
COATING, HEAT-SEAL
A coating, applied to a base sheet, which may be activated by heat to permit the fusion or seal of one section of the film to another.
COEXTRUSION
Simultaneous extrusion of more than one polymer layer into a film.
COF
Coefficient of Friction.
COHESION
The tendency of a mass to hold together by primary or secondary valence forces (intermolecular attraction).
COLOR-OFF
In cellophane, slit roll edge may display variation in color or shade; off-color film is not usually defective, will almost always perform on machines.
CONTOUR PACKAGE
Package formed of semi-rigid material, usually by shaping a heated sheet by pressure or vacuum so that it follows the contours of the packaged item very closely.
CONVERTER, PACKAGING
Equipment which processes raw packaging stock such as cellophane, foil, etc. into a more advanced state, generally by forming, printing, gluing, laminating, etc.
CORE SIZE
Inside diameter of the core.
CORONA TREATMENT
Subjecting a polymer film to an electrical discharge to alter its surface characteristics.
CRATERING
Thin or bare spots in a film that appear as pockmarks.
CRAZING
Network of fine lines in or on a coating or transparent surface: “spider web” or “dried mud” pattern.
CRIMP SEAL
Seal produced in cellophane or other material by means of elements having corrugated surfaces; lends mechanical rigidity to seal areas as well as ensuring maximum area contact of film surfaces.
CROCKING
Smudging or rubbing-off of ink after printing.
CURL
In packaging films, distortion frequently caused by the absorption, or loss, of moisture at an uneven rate from one side of a sheet; curl may also be caused by uneven physical stresses, as in the case of laminations or coated materials.
CUT-OFF LENGTH
Length of sheet fed by automatic wrapping machine during operation.
CYCLE TEST
Test program in which items are exposed alternately to two or more test conditions.

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D

DEAD-FOLD
Fold in packaging material which will remain in place without sealing, as in the case of folds made in soft lead foil or aluminum foil.
DIMENSIONAL STABILITY
The absence of dimensional change of a material when subjected to changes in temperature, humidity, heat or aging.
DOCTOR-BLADE
Scrapers that regulate the thickness of adhesives, or inks, on a feed roller.
DOWNGAUGE
Use a thinner film than had been previously used.
DRAW-DOWN
Thinning in gauge or narrowing in width, especially of extruded materials, as a result of windup rate exceeding speed of extrusion, stretching.
DYNE
A measurement unit of force (centimeter-gram-second) traditionally used to quantify the energy on the surface of a film as an indicator of its ability to accept inks or coatings.

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E

ELECTRONIC SEALING
Sealing of surfaces in contact with one another by high frequency current, e.g., sealing vinyl sheet. Heat is generated within the film by high-frequency agitation of the sheet’s molecular structure.
EMULSION
A non-separating dispersion or suspension of a solid in a liquid.
EXTRUSION LAMINATION
A process for joining two webs by feeding them through a machine that extrudes a thin layer of plastic between them to act as an adhesive.

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F

FILM, CALENDERED
A film manufactured by forcing base material through rolls of a calendering machine, making it smooth and glossy.
FILM, CAST
(1) Film made by pouring or metering material onto a highly polished moving drum or endless belt, or (2) film produced by extruding into a solution, as in the case of cellophane.
FILM DENSITY
The ratio of the weight of a body to the weight of an equal volume of water at some specified temperature (same as SPECIFIC GRAVITY).
FILM, EXTRUDED
Film produced by the extrusion method.
FILM, NON-FOGGING
Film that does not become cloudy from condensation of moisture caused by temperature drops or humidity changes.
FILM, ORIENTED
Film in which the molecular structure is aligned mechanically in one or more directions, thus giving the film more strength while introducing shrinkage characteristics.
FIN SEAL
Seal that results when edges of two superimposed sheets are bonded, resulting in a pouch having fin-like protuberances.
FISH-EYES
Particles of undissolved extraneous material in a film or coating.
FLAT SEAL
A method of heat sealing thermoplastic films with a flat bar surface.
FLEX CRACK
Cracking in a film produced by repeated flexing.
FLEX STRENGTH
The ability of a sheet or film to withstand breakage by folding. Measured by a test to determine the number of folds required to cause failure.
FRACTIONAL PACKAGING
Interior packaging of individually wrapped units so that unused portions will be protected after outside package has been opened. Usually used for biscuits, crackers and ready-to-eat cereals.
FUSE
Weld of thermoplastic materials by heating to point just above that at which they soften.

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G

GAS PACKAGING
Packaging in a gas-tight container in which air has been replaced by a gas such as carbon dioxide or nitrogen.
GAS TRANSMISSION
The movement of gas, air, oxygen, etc., through a film material. The gas transmission property (permeability) of a film is measured in terms of the volume of gas (at standard temperature and pressure) transmitted through a given area of film of a given thickness, within a given time.
GASSING
(1) Development of gas in a sealed package. (2) Removing air from a filled package and replacing it with another gas such as carbon dioxide or nitrogen.
GAUGE
Thickness expressed in decimals of an inch or in millimeters.
GEL
A general term used to describe a defect consisting of insoluble polymer causing a visible discontinuity in a film.
GHOSTING
Reproduction, very faint, of printed design without actual ink transfer.
GLASSINE
Smooth, dense-structured super-calendered paper, translucent or opaque, made from heavily beaten fibrillated chemical wood pulp. Grease-resistant, tough, pliable.
GLASSINE, COATED
The coating types available include hot-melt-applied paraffin waxes and derivatives, as well as solvent-applied types made from cellulose nitrate, vinyl polymers and other synthetic or natural rubber polymers.
GLASSINE, LAMINATED
Glassine laminated to itself, or other paper, films and foils, to obtain added strength and made-to-order protective water-vapor properties.

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H

HDPE
Abbreviation for high density polyethylene.
HEAT SEALING
A method of bonding two or more surfaces by fusing thermoplastic or thermosetting coatings of films under controlled conditions of temperature, pressure and time (dwell).
HERMETIC SEAL
A seal that will exclude air and be leak-proof.
HOT-STAMPING MACHINE
Marking machine that applies a code mark or date on a package or a wrapper with a heated stamp.
HOT TACK
The property of an adhesive or seal layer to resist forces that would pull the seal apart while it is still hot.
HUMIDITY
Water vapor in air. Absolute humidity is the weight of water vapor contained in a unit of air. Relative humidity = percentage of actual humidity to the maximum humidity which air can retain without precipitation at a given temperature and pressure.
HYGROMETER
An instrument for measuring the moisture of relative humidity in the atmosphere.
HYGROSCOPIC
Having the property of absorbing moisture readily from the atmosphere.

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I

ID
Inside Diameter.
IMPACT STRENGTH
Resistance of a material or product to shock, such as from dropping and hard blows.
IMPREGNATION
Saturation of a material with another substance.
INK, GRAVURE
Pigment dissolved or dispersed in a vehicle made from resins and solvents; very fast drying.
INK, IMPRINTING
Ink specially designed to be used with a marking device.
INK, MOISTURE-SET
Ink formulated to be stable under normal humidity conditions, but to set up or harden when exposed to very high humidity.
INK, THERMOSETTING
Ink formulated to be stable and free from tack at ordinary temperature but to set up quickly at elevated temperatures.
IRREGULAR WINDING (Projecting film)
Peaks or ridges in a slit roll that extend out more than 1/32” from edge of main body of roll.
IRREGULAR WINDING (Lateral weave)
A defect whereby a difficulty shows up as failure of film to feed in straight line during use.

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L

LABEL, HEAT SEAL
A label coated on one side with a heat-seal coating; usually a thermoplastic resin.
LAMINATE
(noun) A structure made by bonding together two or more layers of material or materials. (verb) Action of combining finished films to produce the laminate.
LAMINATED FILM
Combination of two or more films or sheets made to improve overall characteristics.
LAP SEAL
Any seal made between two overlapping films. Used in contrast to a “fin seal”.
LDPE
Abbreviation for low density polyethylene.
LIP
That part of the tube of a flat or square bag, or pouch, extending beyond the face of the bag.
LITHOGRAPHY, OFFSET:
Printing process using etched metal plates. Ink adheres to etched area, is transferred to rubber printing blanket, from there to paper to be printed.
LLDPE
Abbreviation for linear low density polyethylene.

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M

MAKE-READY
In printing, preparation of press for a run; especially, making all printing surfaces uniform in height.
MASTER ROLL
The large roll of film wound during a film formation process, which is normally slit into smaller rolls for later processing or shipment.
MD
Abbreviation for machine direction.
METALLIZING
The process of applying an extremely thin metal coating to a non-metallic substrate.
MIL
One thousandth of an inch.
MODULUS
In packaging, used to denote the degree to which a film or sheet resists stretching before it reaches its elastic limit when an external force or stress is applied.
MSI
Abbreviation for a thousand square inches, a common unit for pricing laminated films.
MVTR
Abbreviation for moisture vapor transmission rate.

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N

NITROCELLULOSE
Any ester of nitric acid and cellulose.
NICKED EDGES
Edges of film split or torn.
NON-FLAMMABLE or NON-INFLAMMABLE
Will not support combustion.

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O

OD
Outside diameter.
OFFSET
Accidental transfer of printing inks or coating from surface of a sheet to back of another sheet.
OPACITY
Resistance of material to transmission of light.
OPP
Oriented Polypropylene.
OPTICAL DENSITY
A measure of opacity of a metallized film layer. It is the log of the ratio of the intensity of transmitted light to incident light.
OPTICAL DISTORTION
Change in appearance of object when viewed through a transparent material having certain defects, such as waviness of surface, etc.
OVERPRINT
The result of printing one layer over another, such as one layer of ink printed over another one to form color combinations.
OXIDATION
Reaction of any substance with oxygen.

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P

PACKAGING, FLEXIBLE
Packaging involving the use of such flexible material as foils, films, paper, etc. to form the container.
PACKAGING, FRACTIONAL
The breaking down of a unit package into two or more sub-units, with the objective of protection of the sub-units.
PAPER, SULFATE
Kraft paper, a chemical wood pulp paper (the strongest pulp paper made from wood).
PAPER, SULFITE
Any type of paper made from pulp produced by the sulfite chemical process. Used in packaging applications where appearance and printability are of primary importance.
PAPER, WAX or WAXED
All papers that have been impregnated, coated or otherwise treated with waxes or waxlike materials.
PAPERBOARD
A heavyweight thick sheet of paper, usually a thickness of 0.06” or over.
PARCHMENT, ARTIFICIAL
Certain greaseproof papers made by wholly physical means, but having no natural wet strength; resembles vegetable parchment.
PARCHMENT, VEGETABLE
A vegetable-base paper having no taste or odor, consisting only of pure cellulose. Highly greaseproof, and outstanding in wet strength.
PE
Abbreviation for polyethylene. Used when someone wants to avoid being specific, but is usually synonymous with low density polyethylene.
PEEL-SEAL
A package seal made using an adhesive that can readily be peeled open.
PEELING BOND
A type of bond that occurs when two adhered surfaces may be pulled apart without tearing the fibers.
PERMEABILITY
Ability to be permeated by gases or liquids; a measure of the freedom with which gases or liquids can diffuse through a material.
PET
Polyester film.
pH
Numerical representation of acidity or alkalinity. Neutral is pH 7, pH 1 is extremely acidic and pH 14 extremely alkaline.
P1 TEST PROCEDURES
A large body of standard test methods developed or recommended by Technical Committees of Packaging Institute to provide uniform and reliable tests.
PICK-UP ROLL
A spreading device where the revolving roll for picking up the adhesive runs in a reservoir of liquid adhesive.
PLASTICIZER
An agent or compound that is added to plastic materials to impart softness or flexibility.
PLASTICIZER MIGRATION
Movement of plasticizer to the surface of a plastic, or from one plastic to another, or from a plasticized substance into the atmosphere; causes embrittlement.
PLATE
(noun) Curved or cylindrical shape carrying printing impression, for use on a printing press.
POLYMER
A compound formed by the linking of simple and identical molecules having functional groups that permit their combination to proceed to higher molecular weights under suitable conditions.
POLYPROPYLENE
A synthetic thermoplastic material of high molecular weight resulting from polymerization of propylene gas under pressure and heat, plus catalysts.
POLYSTYRENE
A thermoplastic material derived from the polymerization of styrene monomers.
POROSITY
Of sufficiently loose texture to permit passage of liquid or gases through pores.
POUCH, PLICATED
A folded pouch having gussets.
PPR
Polypropylene.
PRESS POLISH
A finish for plastic sheet stock, produced by contact under heat and pressure with a very smooth metal, which gives the plastic very high sheen.
PRIMER, PRIMED
The act of putting a thin coating on a substrate so that it will be more receptive to printing inks or adhesives.
PRINTING COMPENSATOR
A mark printed at regular intervals on the film which actuates a photoelectric cell on the bag machine or wrapping machine to insure the perfect register of copy on a bag or package.
PRINTING, FLEXOGRAPHIC
Formerly called aniline printing. A method of rotary letterpress printing that employs flexible rubber plates and rapid-drying inks.
PRINTING, GRAVURE
A rotary printing process employing minute engraved “wells” in an etched metal cylinder. Deeply etched wells carry more ink than shallower ones, hence print darker values. A doctor blade wipes excess ink from the printing cylinder. Stock is web-fed from roll.
PSYCHROMETER
A hygrometer for measuring water vapor in the atmosphere.
PULLOUT, GOOD
No puckers or banded lanes showing when film is stretched.

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R

REGENERATED CELLULOSE
A cellulose hydrate. The term is used to designate films made from a cellulose base.
REVERSE PRINTED
The process in which a transparent film is printed backwards so that when it is flipped over, the printing appears right side up. When used in a package, reverse printed film will always have the printing ink on the inside where it is protected from scuffing and abrasion.
REWIND
To wind again; especially the winding of a roll of film after printing, slitting, etc.
RH
Relative humidity.
ROLL FORMATION
A general term denoting qualitatively how evenly, smoothly, and regularly film is wound on a roll.

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S

SERRATED
Saw-toothed. Describes the configuration used on heat-sealing equipment for obtaining a crimp seal.
SLIP
A measure of coefficient of friction (COF). High slip means low COF.
SLIT
To cut a roll of stock to narrower widths.
SLITTER
A machine to cut a roll of stock in the long direction.
SOLVENT SEALING
A method of adhering packaging materials which uses small amounts of volatile liquids to soften the coating of the material so it will bond. Examples: cellosolve ethyl lactate, etc.
SPECIFIC GRAVITY
The ratio of the weight of a body to the weight of an equal volume of water at some specified temperature (same as FILM DENSITY).
SPLICE:
To unite or join the ends of roll materials by mechanical or electrical means, or by an adhesive.
STATIC ELECTRICITY
Charges of electricity sometimes generated during handling or in machine operations; may cause undesired attraction of film to roller, flat surfaces, etc.
STERILE SEAL
A closure for bacteria-free medical supplies that must maintain sterility.
STERILIZABLE
The ability to withstand contact with steam (moist heat) at 30 lb. pressure for 30 minutes, or contact with dry heat (circulating hot air) at 200°C for 15 minutes.
STRIP-PACKAGING
Small articles packaged individually or in multiples in continuous strips, divided in segments or pockets that permit easy tearing off or cutting off.
SUBSTRATE
A film to which subsequent layers or coatings are added.
SURFACE PRINTING
Printing on the outside surface of a package as opposed to one of the inside surfaces (see “reverse printing”).
SURFACE WINDING
A method of winding film on rolls in which the winding force is provided by the driven roll in contact with the surface of the winding roll.
SURLYN
Dupont’s trademark for its line of ionomer resins. Films produced with this resin have excellent seal characteristics such as lower sealing temperatures and excellent hot tack.

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T

TAPE, CELLULOSE ACETATE
A translucent, pressure-sensitive adhesive tape of cellulose acetate laminated to strong tissue.
TD
Abbreviation for transverse direction — the direction perpendicular to the machine direction.
TEAR STRENGTH
The force required to propagate a tear already initiated by a cut on the edge.
TEAR STRIP
A narrow ribbon of film, usually incorporated in the wrapper or overwrap during the wrapping operation, to facilitate opening of the package.
TELESCOPING
Side-slipping of layers of a coiled material so that the edges no longer form a plane surface.
TENSILE STRENGTH
Resistance of a material to longitudinal tension.
TEST, CELLOPHANE TAPE
A simple test for determining the permanency of printing on plastic film. A length of pressure sensitive cellophane tape is pressed on a section of printing and then pulled off in one motion to see whether or not the ink lifts with it. The angle and speed of the pulls are important.
TEST, DROP
A package durability test. Filled containers are dropped from controlled heights. A special device insures uniformity of drops.
TEST, DRUM
Rough-handling test for filled container, inside a revolving hexagonal drum.
TEST, ELMENDORF TEAR
A method of testing film for resistance to tearing. The weight required to tear one of several layers of notched film is measured.
TEST, FOLDING ENDURANCE
A test to evaluate the endurance of films to folding, frequently done on a Schopper machine.
TEST, MULLEN
The Mullen is widely used on film packaging materials to determine the relative bursting strength.
THERMOCOUPLE
A bimetallic device to measure temperature electrically.
THERMOPLASTIC
Capable of being repeatedly softened by heat and hardened by cooling.
THERMOSTAT
An automatic device for regulating temperature; uses bimetallic strip to make and break contacts of electrical circuit.
THERMOSET
Plastic that is heat set.
THERMOWELD
To weld together two or more surfaces of a thermoplastic film material by means of heat.
TIE LAYER
The common term for a coextrudable adhesive.
TRACKING
A film that follows a desired path on a packaging machine without constant adjustment is said to “track” well.
TRANSLUCENT
Permitting passage of light, but diffusing it to such a degree that objects cannot be seen clearly; something short of transparent.
TRANSPARENT
Transmitting rays of light so that objects can be clearly seen through the material.

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U

UNDERFOLD
To fold wrapping material in such a manner that the end folds are turned under the bottom of the package, then sealed to the underside.

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V

VAPOR TRANSMISSION
The passage of vapor (usually water vapor) through a material.
VFFS
Abbreviation for vertical form-fill-seal.
VISCOSE
A viscous orange-colored liquid obtained by treating cellulose with caustic alkali solution, then with carbon disulfide.
VISCOSITY
That property of a liquid material that tends to resist flow.
VOLATILE
Passing from a liquid into a gaseous state.
VOLATILITY
The rate of evaporation of a solvent.

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W

WATER VAPOR PERMEABILITY
The ability of a material to permit transmission of water vapor.
WATER VAPOR TRANSMISSION RATE
Measure of permeability of a material, often stated in terms of grams of water passing through 100 square inches of material in 24 hours at 100°F and 90 percent relative humidity.
WAX, MICROCRYSTALLINE
A petroleum wax of high molecular weight, characterized by minute crystals and distinguished by its solid wax-like appearance at room temperature.
WEB
A term to denote a long film somewhere in the processing stage, frequently being drawn off a large roll. For example, a “printed web” would be a large roll of printed film.
WORMING
Channel-like delamination pattern in adhesive-laminated materials.
WRAP, BUNCH
Wrapping with packaging material gathered on the underside of package in somewhat irregular manner.
WVTR
Abbreviation for water vapor transmission rate.

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Y

YIELD
Area per unit of weight, usually expressed as square inches per pound.

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