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Glossary of Flexible Material Terms

The language of packaging film and flexible material is expansive. You might know that biaxial orientation means the molecular orientation of plastic film runs in both machine and cross machine (transverse) directions by stretching. Did you know that a tie layer is material that bonds two incompatible layers in a coextrusion?

Here are lots of packaging terms and definitions for film materials.

Please contact Pro Pac or call 888-318-0083 for your shrink, stretch, and laminate films.

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Aclar: Trade name for a polychlorotrifluoroethylene (PCTFE) polymer. The polymer has outstanding moisture and excellent oxygen barrier properties, as well as being clear, rigid, and relatively easy to thermoform. Its main packaging application is for pharmaceutical blister packages.

Acrylonitrile: A monomer with the structure (CH = CHCN). Its copolymers have good gas barrier and chemical resistance properties. 

Air Gap: The distance from the die lips of a polymer-melt extruder and the chill roll.

Anilox Roll: Engraved ink metering roll used in flexo presses to provide a controlled film of ink to the printing plates which print onto the substrate.

Aluminum Foil: A thin gauge (.285-1.0 mil) aluminum foil laminated to plastic films to provide oxygen, aroma and water vapor barrier properties.

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.

Antioxident: 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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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.

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, Gusset: The fold in the side or bottom of the pouch, allowing it to expand when contents are inserted.

Baggy, Bagginess: (a) In processing flexible packaging materials, slack areas in the web that should be flat. Usually caused by bands of unequal thickness (gauge bands) in the rollstock. (b) A roll in which the tension is not even across the width of the roll. A slack floppy area in the web is caused by the material being stretched and permanently elongated in the tighter areas. Rolls of film or laminate where one side of the material coming off the roll is loose or baggy while the opposite edge is tight is said to have a baggy edge.

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.

Barex: A trade name for acrylonitrile plastic.

Barrier: In packaging, this term is most commonly used to describe the ability of a material to stop or retard the passage of atmospheric gases, water vapor, and volatile flavor and aroma ingredients. A barrier material is one that is designed to prevent, to a specified degree, the penetrations of water, oils, water vapor, or certain gases, as desired. Barrier materials may serve to exclude or retain such elements without or within a package.

Base Film: The original form in which a film exists before coating or laminating.

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: Orientation of plastic films in both machine and cross machine (transverse) directions by stretching. Biaxial stretched films are generally well balanced in both directions and much stronger in terms of tear strength.

Bleed: Image or color that extends beyond the trim edge of the finished printed piece.

Blister Packaging: A package type where the item is secured between a pre-formed dome or "bubble" and a paperboard/flexible surface.

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.

Breathing: Passage of gases into or out of a package. Certain films are designed to permit it.

Burst Strength: A measure of the ability of a sheet to resist rupture when pressure is applied to one of its sides by a specified instrument under specified conditions.

Butt Register: Where two or more colors meet with no significant overlap or space between.

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Cast Film: Plastic film produced from synthetic resins (such as polyethylene) by the cast process. In this process, the molten resin is extruded through a slot die onto an internally cooled chill roll.

Cast Nylon (CAN): Film used mostly for thermoformable packaging applications.

Cellophane: Transparent film made from regenerated cellulose, a fibrous material occurring in plants.

Cellophane Tape Test: 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.

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.

Chemical Resistance: Ability of a material to retain utility and appearance following contact with chemical agents. Chemical resistance implies that there is no significant chemical activity between the contacting materials.

Chemical Compatibility testing: Any procedure that exposes a material to chemicals or mixtures of chemicals to determine whether such exposure has a negative effect on the material being evaluated.

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.

Coefficient of Friction (COF): A measurement of “slipperiness” of plastic films and laminates. Measurements are usually done film surface to film surface. Measurements can be done to other surfaces as well, but not recommended, because COF values can be distorted by variations in surface finishes and contamination on test surface.

Co-Extrusion (COEX): Simultaneous extrusion of two or more different thermoplastic resins into a sandwich-like film with clearly distinguishable individual layers.

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.

Color Management: The process of translating specific color information from the computer screen image, through prepress, plate-making, printing presses and finally to a substrate in such a manner that color accuracy is maintained at acceptable levels throughout.

Color Value: The lightness or darkness of a color. A color may be classified as equivalent to some member of a series of shades ranging from black to white. The other two fundamental characterizers of color are hue and saturation.

Co-Monomer: A monomer that is mixed with one or more other monomers for a polymerization reaction, to make a copolymer.

Compatibility: The ability of a container or material to resist chemical degradation or physical change caused by the product, or where a container or material does not chemically degrade or physically change the contained product.

Conformability: The ability of a material to be bent or shaped around a form without being damaged or marred in any way.

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: 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: A treatment to alter the surface of plastics and other materials to make them more receptive to printing inks.

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.

Cross-Linking: A film conversion technique in which polymer chains are bound into a web or network to increase the web's heat stability and strength.

Curl: The tendency of a paper sheet to curl as humidity conditions change due to the hygroexpansive nature of paper. A paper sheet that is identical in construction on each side will expand and contract as humidity changes with little tendency to curl. However if the sheet is printed, varnished, or laminated to a plastic film or a foil, then the two sides will have different expansion and contraction rates and the paper will curl as the humidity changes from the conditions when the printing, varnishing or laminating were done. The greater the humidity difference, the greater the curl.

Curtain Coating: A method of applying wax or other coating to a material where the material is passed through a free-falling curtain or film of the fluid coating.

Cut Edge: The uncovered edge of a laminated product. For example a high-barrier paper/foil laminate made into a hermetically-sealed carton using lap seals would have an exposed cut edge of paperboard through which oxygen could still permeate into the product. Such edges are often skived and folded back on themselves to seal the cut edge.

Cut Off: ln web-fed processing, the cut or print length corresponding to the circumference of the plate cylinder.

Cycle Test: Test program in which items are exposed alternately to two or more test conditions.

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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.

Deck: A term used mostly in flexographic printing to describe a single print station with plate, impression cylinders, and inking rolls.

Degradation: A change or break-down in a material's chemical structure.

Delamination: Separation or splitting of laminate layers caused by lack of or inadequate adhesion, or by mechanical disruption such as peeling or shearing forces.

Dimensional Stability: The absence of dimensional change of a material when subjected to changes in temperature, humidity, heat or aging.

Directionality: The tendency for certain materials to have properties imparted by the flow direction through a machine.

Doctor Blade: Scrapers that regulate the thickness of adhesives, or inks, on a feed roller.

Dot Gain: A physical and/or optical measurement and theoretical calculation of the apparent increase in dot area from one medium to another. Normally expressed as the difference between a midtone (nominal 50%) dot area on a film negative and the printed dot area; for example, a 50% film dot area which prints as a 78% dot has 28% dot gain. Dot gain (and loss) are normal and must be controlled throughout the press and printing process.

Down Gauge: Use a thinner film than had been previously used.

Draw: ln flexible packaging laminates, the distance that a web travels between supporting rolls.

Drawdown: A swatch of color or coating made by spreading a small amount of ink or varnish across a sheet of material. Made for visual comparison to a standard color swatch or chip.

Drop Test: A package durability test. Filled containers are dropped from controlled heights. A special device insures uniformity of drops.

Drum Test: Rough-handling test for filled container, inside a revolving hexagonal drum.

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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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.

Elmendorf Tear Test: A method of testing film for resistance to tearing. The weight required to tear one of several layers of notched film is measured.

Emulsion: A non-separating dispersion or suspension of a solid in a liquid.

Ethylene Acrylic Acid (EAA): EAA is a copolymer of ethylene and acrylic acid. lts ionic nature allows for excellent adhesive bonding to metal foil and other polar surfaces. EAA's adhesive and toughness qualities are taken advantage of in high performance multi-layer laminates.

Ethylene-Ethyl Acrylate (EEA): The copolymerization of ethylene with ethyl acrylate produces an ethylene acid copolymer. The polymers are produced with varying percentages of acrylate content, most typically between 15 and 30%. EEA is compatible with all olefin polymers and often is blended with these to modify properties. EEA is used in hot-melt formulations. lt also can be used alone or as a component of heat-sealable coatings where it offers improved toughness at low temperatures, excellent adhesion to nonpolar substrates, and a broad service temperature range. EEA is used as a tie layer between mating laminate films.

Ethylene-Methyl Acrylate (EMAC): The copolymerization of ethylene with methyl acrylate produces an ethylene copolymer, one of the most thermally stable of the olefin copolymers. The polymers are produced with varying percentages of methyl acrylate content, most typically between 1 8 and 24o/o of the structure. Alone or in blends, it has found applications in film, extrusion coating, sheet, laminating, and co-extrusion.

Ethylene-Vinyl Acetate (EVA): A polar copolymer of ethylene and vinyl acetate, retaining some of the properties of polyethylene but with increased flexibility, elongation, and impact resistance. EVA is frequently specified as the extrusion coating on polypropylene, aluminum foil and poly(ethylene terephthalate), to provide good heat-seals at high converting rates, or as the adhesion layer in some laminates.

Ethylene-Vinyl Alcohol (EVOH): Can be regarded as a copolymer of polyethylene in which varying amounts of the -OH functional group have been incorporated. A typical packaging EVOH is about 20 to 35% ethylene. EVOH is one of the best polymeric oxygen barriers available to packagers. However, its susceptibility to water requires that for most applications it be laminated or co-extruded into a protective sandwich with materials that will keep the EVOH layer away from water.

Extrusion Coating: A process where a film of molten polymeric material is extruded onto the surface of a substrate material and cooled to form a continuous coating.

Extrusion Lamination: A laminating process in which individual layers of multi-layer packaging materials are laminated to each other by extruding a thin layer of molten synthetic resin (such as polyethylene) between the layers.

Eye Mark Register: A printed rectangular mark most often found along the edge of rollstock that can be identified by an electric eye. The mark identifies a point on the web where an individual package is to be cut.

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Film: Generally used to describe a thin plastic material usually not more than 75 micrometres (0.003 inch) thick.

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.

Film, Extruded: Film produced by the extrusion method.

Film, Extrusion: The process of forming a thermoplastic film, container, or profile by forcing the polymer melt through a shaped orifice.

Film, Non-Fogging: Film that does not become cloudy from condensation of moisture caused by temperature drops or humidity changes.

Film, Orientation: The process of mechanically stretching plastic film or parts in order to produce a straightening and alignment of the molecules in the stretch direction. If done in one direction, the material is said to be uniaxial or monoaxially oriented. If done in two directions, the film is biaxially oriented.

Fin Seal: Seal that results when edges of two superimposed sheets are bonded, resulting in a pouch having fin-like protuberances.

Finishing: Any final operation done to packaging before shipping.

Fish Eyes: Particles of undissolved extraneous material in a film or coating.

Fitment: A device attached to the container finish to provide a performance function. For example, a pour-out fitment is plastic component for a glass, plastic or metal package, designed to improve the dispensing action of liquid products.

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.

Flexible Packaging: A package or container made of flexible or easily yielding materials that, when filled and closed, can be readily changed in shape. A term normally applied to bags, pouches, or wraps made of materials ranging in thickness from 13 to 75 micrometres (0.0b0á to 0.003 inch) such as paper, plastic film, foil, or combinations of these.

Flexographic Printing: A method of printing using flexible rubber or photopolymer printing plates in which the image to be printed stands out in relief. Fluid ink metered by an engraved roll is applied to the raised portions of the printing plate and then transferred to the substrate.

Folding Endurance Test: A test to evaluate the endurance of films to folding, frequently done on a Schopper machine.

Form-Fill-Seal (FFS): A packaging machine that forms, fills, closes and seals a package in one continuous or intermittent-motion operation. Flexible packaging stock fed from a roll is folded to the desired package shape and stabilized by heat sealing. The product is placed into the formed package, and the remaining opening is sealed. Machines can be configured so that the stock travels horizontally through the machine (horizontal form-fill-seal, HFFS) or vertically through the machine (vertical form-fill seal, VFFS).

Four-Color Process: Printing with cyan, yellow, magenta, and black ink (CMYK) using halftone screens to create a full color reproduction.

Four-Side-Seal Pouch: A pouch with seals along all four edges. Four-side-seal pouches can be made from a single stock or the front and back can be different stocks. These pouches are most commonly made on multilane pouch-forming machines where 16 or more pouches can be placed across the width of the web.

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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Gas Chromatography: An instrumental method of accurately determining the composition of volatile solvents and oils, and their residual presence in materials such as laminates or plastics.

Gas Transmission Rate (GTR): The quantity of a given gas passing through a unit area of the parallel surfaces of a film, sheet, or laminate in a given time under the test conditions. Test conditions may vary and must always be stated.

Gauge: Thickness. In North America, film thickness, measured in mils, is usually given in gauges. A 100 gauge shrink film is one mil, or 1/1000 of an inch, thick. In Europe, the film thickness metric is the micron. A quick equivalency equation is: 1 mil = 25.4 microns.

Gauge Band: A thickness irregularity found in rolls of film. A thicker area in the machine direction at some location across the width of a flat film will produce a raised ring in a finished roll. Gauge bands can cause winding problems and when unwound, the material tends not to be perfectly flat.

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.

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.

Good Manufacturing Practice (GMP): Good manufacturing practice implies that the entire manufacturing procedure has been designed in such a way as to produce a quality product that presents a minimum risk to the consumer. GMP will vary from industry to industry depending on the nature of the product being packaged. Many GMPs have been formalized and are required by law for critical industries such as food and pharmaceutical packaging. Typically these GMPs describe the kind of equipment to be used, its validation, manufacturing procedures, inspection types and frequencies, record keeping, container types and approvals, and registration of company and product.

Gravure Printing: Gravure is abbreviated from the term rotogravure. During gravure printing an image is etched on the surface of a metal cylinder and chrome plated for hardness. The ink fills the cells and is transferred onto the printing substrate.

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Heat-Seal Coating: An adhesive coating applied to a packaging material that is capable of being activated by heat and pressure to form a bond.

Heat-Seal Layer: A heat sealable innermost layer in plastic packaging films and laminates. Can be either adhesive laminated or extrusion coated onto a non-sealable film (or foil).

Heat-Seal Strength: Strength of heat-seal measured after the seal is cooled, (not to be confused with “hot tack”, see next item).

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: Airtight or impervious to gases or fluids under normal conditions of handling and storage.

HFFS: Abbreviation for horizontal form-fill-seal.

High Barrier: Describes a material or package that has very low gas permeability characteristics; that is, it offers a great deal of resistance to the passage of a gas through its volume.

High Density Polyethylene (HDPE): Polyethylene with a density of 0.95 to 0.965. Has much higher stiffness, higher temperature resistance and much better water vapor barrier properties than LDPE, but it is considerably hazier.

Hot Stamping Machine: Marking machine that applies a code mark or date on a package or a wrapper with a heated stamp.

Hot Tack: Strength of heat seal measured before the seal is cooled, which is very important for high-speed packaging operations.

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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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.

Impulse Sealer: Also known as a heat sealer. These units use an electrical current passed through a Ni-Chrome wire heating element to seal bags & tubing. Can be used on many plastic materials to create strong permanent welds.

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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Label, Heat Seal: A label coated on one side with a heat-seal coating; usually a thermoplastic resin.

Laminate: (a) A product made by bonding together two or more layers of material. (b) To unite layers of material to produce a multilayer material.

Laminated Film: An adhered combination of two or more films or sheets made to improve overall characteristics. Also multilayer film.

Lap Seal: A seal made with two layers of film overlapping one another. Because lap seals require less material than fin seals, packagers are converting to lap seals in the name of sustainability, lean operations and economics.

Laser Scoring: Use of high-energy narrow light beam to partially cut through a material in a straight line or shaped patterns. This process is used to provide an easy-opening feature to various types of flexible packaging materials.

Lidding, Lidstock: Material or stock used to form a lid. For example, material that can be heat-sealed over the open ends of pharmaceutical tablet blister cards.

Light Resistance: The ability of material to withstand exposure to light (usually sunlight or the ultraviolet part of the light spectrum) without change of color or loss of physical and/or chemical properties.

Linear Low Density Polyethylene (LLDPE): Tougher than LDPE and has better heat-seal strength, but has higher haze.

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.

Low Density Polyethylene (LDPE): Polyethylene with a density of 0.92 to 0.934. Used mainly for heat-seal ability and bulk in packaging.

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Machinability: The ability of a film to run on packaging equipment.

Machine Direction (MD): The direction that film moves through the packaging equipment.

Make Ready: In printing, preparation of press for a run; especially, making all printing surfaces uniform in height.

Manufacturing tolerance: Permissible variations from rated or marked capacities or dimensions established by standards or specifications for those.

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.

Medium Density Polyethylene (MDPE): Polyethylene with a density of 0.934 to 0.95. Has higher stiffness, higher melting point and better water vapor barrier properties.

Metallize: Applying a thin coating of metal to a nonmetallic surface by chemical deposition or by exposing the surface to vaporized metal in a vacuum chamber.

Metalized Oriented Polypropylene (MET-OPP): Film that has all the good properties of OPP film, plus much improved oxygen and water vapor barrier properties, though not as good as MET-PET. Not transparent.

Metalized Polyethylene Terephthalate (MET-PET): Metalized PET film. It has all the good properties of PET film, plus much improved oxygen and water vapor barrier properties. Not transparent.

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.

Moisture Vapor Transmission Rate (MVTR): A depreciated term, usually measured at 100% relative humidity, expressed in grams/100 square inches/24 hours, (or grams/square meter/24 Hrs.) See WVTR.

MSI: Abbreviation for thousand square inches, a common unit for pricing laminated films.

Mullen Test: Widely used on film packaging materials to determine the relative bursting strength.

Mylar: Mylar is a registered trademark of the DuPont-Teijin Corporation. It is the industrial brand name for that corporation's polyester (PET) film. Polyester film is a staple of multilayer flexible packaging for a wide variety of applications.

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Neoprene: A synthetic chlorinated butadiene rubber used to make flexographic rollers resistant to alcohols, Cellosolve, water, aliphatic hydrocarbons, and esters.

Nicked Edges: Edges of film split or torn.

Nitrocellulose: Any ester of nitric acid and cellulose.

Non-Flammable / Non-Inflammable: Will not support combustion.

Nylon: Polyamide resins, with very high melting points, excellent clarity and stiffness. Two types are used for films - nylon-6 and nylon-66. The latter has much higher melt temperature, thus better temperature resistance, but the former is easier to process, and it is cheaper. Both have good oxygen and aroma barrier properties, but they are poor barriers to water vapor.

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OD: Outside diameter.

Off-Cut: Trim that is not utilized. In flexible packaging, a narrow roll of material left over when a material order does not call for the full roll width. Sometimes called a butt roll.

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.

Optics: The visual properties of a film, such as clarity, gloss, haze, opacity, etc.

Oriented Polypropylene (OPP): film. A stiff, high clarity film, but not heat sealable. Usually combined with other films, (such as LDPE) for heatsealability. Can be coated with PVDC (polyvinylidene chloride), or metalized for much improved barrier properties.

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.

Oxygen Transmission Rate (OTR): Varies considerably with humidity, therefore it needs to be specified. Standard conditions of testing are 0, 60 or 100% relative humidity. Units are cc/100 square inches/24 hours (or cc/square meter/24 Hrs). (cc = cubic centimeters)

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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.

Pass: One trip of a material through a production machine or manufacturing step.

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.

Pick-Up Roll: A spreading device where the revolving roll for picking up the adhesive runs in a reservoir of liquid adhesive.

Pillow Pouch: A bag or pouch in the form of a tube that is sealed at both ends. Pillow type pouches are most commonly produced on vertical-form-fill-seal (VFFS) machines and are characterized by seals across the top and bottom, and a longitudinal seal going down the center of one of the faces.

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: Curved or cylindrical shape carrying printing impression, for use on a printing press.

Plate Break: Non-print area where the two ends of flexo plate butt together after being wrapped around the plate cylinder on the printing press.

PMS Number: The Pantone Matching System is the universally accepted color definition system. Colors can be blended or individually specified to match a specified Pantone reference color exactly.

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.

Polyethylene (PE): Polyethylene film is by far the largest volume packaging film family, and is available in high density, low density, linear low density, and metallocene variations.

Polyethylene Terephthalate (PET): Tough, temperature resistant polymer film. Biaxial oriented PET film is used in laminates for packaging, where it provides strength, stiffness and temperature resistance. It is usually combined with other films for heat sealability and improved barrier properties.

Polyolefin: Family name for the polymers (plastics) derived by ethylene and propylene, such as polyethylene (PE) and polypropylene (PP)

Polypropylene (PP): Unoriented film is soft and clear but brittle at low temperatures. This property as well as stiffness, strength and clarity is improved by orientation.

Polystyrene: A thermoplastic material derived from the polymerization of styrene monomers.

Polyvinylidene chloride (PVDC): A very good oxygen and water vapor barrier, but not extricable. Therefore it is found primarily as a coating to improve barrier properties of other plastic films, such as OPP and PET, for packaging. PVDC coated and saran coated are the same.

Porosity: Of sufficiently loose texture to permit passage of liquid or gases through pores.

Pouch: A small bag usually constructed by sealing one or two flat sheets along the edges. There is no clear distinction between a pouch and a sachet other than the common understanding that a sachet is smaller.

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 Coat: A coating applied over a substrate for the purpose of improving an ink or adhesive bond.

Psychrometer: A hygrometer for measuring water vapor in the atmosphere.

Process Color: Color printing created by separating the copy into the primary colors to produce individual halftones of each color, that are recombined at the press to produce the complete range of colors of the original. Process printed photographic reproduction would normally be done with cyan, magenta, yellow and black (CMYK) inks.

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Regenerated Cellulose: A cellulose hydrate. The term is used to designate films made from a cellulose base.

Register: Exact alignment of one part or operation with another part or operation.

Release Coating: A coating applied to the non-sealing side of cold-sealable packaging films and laminates supplied in a roll form that will allow the packer to unwind these films or laminates on packaging machines.

Retort: The thermal processing or cooking packaged food or other products in a pressurized vessel for purposes of sterilizing the contents to maintain freshness for extended storage times. Retort pouches are manufactured with materials suitable for the higher temperatures of the retort process, generally around 121° C.

Reverse Printing: Printing wrong-reading on the underside of transparent film. In this case, the outermost layer is printed on the backside and laminated to the rest of the multi-layer structure. While not mandatory in all industries, it is the preferred method for the food industry as it guarantees there will be no ink contact with the food product. The majority of all products are reverse printed.

Rewind: To wind again; especially the winding of a roll of film after printing, slitting, etc.

Roll Formation: A general term denoting qualitatively how evenly, smoothly, and regularly film is wound on a roll.

Roll Stock: Any flexible packaging material that is in roll form.

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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. Ability of film to move easily over hard plastic, metal, or ceramic platforms or against another piece of film.

Slitting: The conversion of a given width of a film or sheet material into narrower widths. Web stock is unrolled past a series of knives set to the correct widths, and the slit web is rewound back into roll form.

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 Gravitiy: 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: Joining two pieces of web material to form a continuous web.

Spot Color: Solid colors not created by using screens. Usually a Pantone Matching System (PMS) color.

Stand-Up Pouch: A flexible pouch design where the bottom portion has been gusseted in such a way that that it provides a wide enough base to provide support so the pouch is able to be stood up for display or use.

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.

Stick Pack: A narrow flexible packaging pouch commonly used to package single-serve powder beverage mixes such as fruit drinks, instant coffee and tea and sugar and creamer products.

Sticky Back: Double-faced adhesive-coated material used for mounting elastomeric printing plates to the plate cylinder.

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 Print: The process whereby the ink is deposited directly onto the outermost surface of the packaging film or material. The process is most commonly used in short run printing. A UV (ultraviolet) coating may be added to provide a hard exterior finish that prevents the ink from flaking or chipping.

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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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 Resistance / Tear Strength: The ability of a film to resist the propagation of a tear.

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: The amount of pull a film can withstand without tearing apart or stretching.

Thermocouple: A bimetallic device to measure temperature electrically.

Thermoforming: A method of forming plastics where a plastic sheet is heated to a point where it is soft and formable.

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.

Threading: The placing of a web material through the various rolls and stations of any web-fed press such as a printer or laminator in preparation for production.

Three-Side-Seal Pouch: A pouch that is formed by folding the web material into a U-shape and then sealing the three open sides. The pouch may be made with a gusseted bottom. Three-side-seal pouches are typically made on horizontal form-fill-seal machines.

Tie Layer: A material that bonds two incompatible layers in a coextrusion.

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.

Transverse Direction (TD): The direction perpendicular to the machine direction.

Trapping: In printing, inks may be overlapped slightly by increasing the image size to ensure that no substrate shows through within the register variations of the printing press.

Tunneling: A laminating defect caused by incomplete bonding of the substrates.

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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.

Unit-Dose Package (UDP): A pharmaceutical package that holds individual items of use. A complete unit-dose package may hold a number of discrete items, but each unit of use must be released individually from the package, generally in a non-resealable manner.

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Vapor Barrier: A layer of material through which water vapor will pass only slowly, or not at all.

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.

Void: An emptiness or absence of a substance. For example, an area of coated film that is not coated.

Volatile: Passing from a liquid into a gaseous state.

Volatility: The rate of evaporation of a solvent.

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Water Vapor Transmission Rate (WVTR): A measure of the rate of water vapor transmission through a material. Usually measured at 100% relative humidity, expressed in grams/100 square inches/24 hours, (or grams/square meter/24 Hrs.) See MVTR.

Web: A continuous length of paper film, foil, or other flexible material as it is unwound from a roll and passed through a machine.

Worming: Channel-like delamination pattern in adhesive-laminated materials.

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

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Zipper Pouch: A flexible plastic pouch with a molded-in-place sealing device wherein a projecting rib or fin is inserted into a mating channel to effect a closure. A zipper seal can be repeatedly opened and closed.