Glossary of  Terms for PET Film, Polyester Film Production & Use

There are many specialized terms and acronyms related to PET film production.

Please feel free to let us know if you have any questions.

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.

BIAXIAL ORIENTATION
A process for orienting a plastic film in both the transverse and the machine directions.

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.

CLARITY
Freedom from haze; transparency.

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.

CORONA TREATMENT
Subjecting a polymer film to an electrical discharge to alter its surface characteristics.

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.

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.

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.

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.

ID
Inside Diameter.

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

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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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.

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.

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.

PACKAGING, FLEXIBLE
Packaging involving the use of such flexible material as foils, films, paper, etc. to form the container.

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.

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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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

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.

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.

THERMOWELD
To weld together two or more surfaces of a thermoplastic film material by means of heat.

TRANSPARENT
Transmitting rays of light so that objects can be clearly seen through the material.

VAPOR TRANSMISSION
The passage of vapor (usually water vapor) through a material.

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.

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.

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