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Polybags Direct is committed to providing packaging knowledge. The following list is a glossary of terms used in the packaging industry.

A

Anti-stat
Contains an anti-static additive that dissipates static electrical charges. Useful when the film is for packaging electrical components.

B

Bags on a roll
Continuous roll of seamless tubing perforated under bottom seal. Bags must be torn off to open.
Bottom seal bags
Individually cut bags from seamless tubing, sealed on the bottom. Flat or side gusseted bags with a strong seal – usually have a tail.
Butylated hydroxytoluene BHT
A fat-soluble organic compound that is primarily used as an antioxidant food additive as well as in cosmetics, pharmaceuticals, jet fuels, rubber, petroleum products and embalming fluid.
Butylated hydroxytoluene BHT
Material used for resealable lip and tape. This material offers an even higher grade of clarity and is resistant to tears and wrinkles.

C

Caliper: The thickness of sheet material expressed in "points" or mils (thousands of an inch).

Cast film: The fabrication of a film by continuously pumping the polymer through a straight slot die, then chilling this hot plastic immediately through contacts with a chilled roll. Film width is determined by how fast the chill roll pulls the film away from the die.

Center fold film: A film that has been folded in half,lengthwise.

Center folder: A mechanical device used to create center folded film.

Clarity: Transparency of the film based upon surface gloss and haze.

Closing machine: a device that seals or closes filled packages by crimping, folding or tucking. Adhesives, gummed tape and ultrasonic welding are often used, in addition to heat sealing.

Co-extrusion: Two or more polymers extruded and combined in a die, each forming a distinct layer in the final film.

Co-polymer: Result of two monomers being combined through polymerization.

Core: A paper tube on which film is wound.

Corrugated: A durable, lightweight material used for making cases. Corrugated packaging has an arched layer, called fluting, between smooth sheets, called liner. The corrugated cardboard most commonly used to make cases has one layer of fluting between two smooth sheets.

Cellophane: Clear film derived from wood pulp has a memory and will crinkle like paper, it is a thin, flexible, transparent film formed from cellulose fibres. Cellophane is widely used in food packaging due to its high moisture barrier properties and sealability and is biodegradable.

D

Die: A device used in extrusion processes to shape the extrudate.

Dwell time: The time usually expressed in seconds at a given temperature that is required for the application of heat to seal a heat sealing membrane.

E

Elasticity: The ability of paper or plastic to rebound back to its original state after being stretched.

Extensibility: The ability of paper or plastic to be stretched without breaking.

Extruder: A machine that makes stretch film. It consists of a large steel barrel surrounded by heaters, which melt the plastic resin pellets. Inside of the barrel is a large screw to force the liquid plastic under pressure through a die to be made into plastic sheeting by either the cast or blown processes.

Extrusion: A product formed by pushing material through a die.

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 polythene) between the layers.

End (bottom) weld: A bag with the seal at the base of the bag. The seal is separated from the end of the bag by a small skirt. Bag length is measured from top to bottom of the bag including the skirt.

Euro-pallet: A Euro-pallet measures 1200mm x 800mm. A Euro-pallet is smaller than a UK pallet.

Euroslot: A horizontal slot punched in the bag for hanging.

F

Flat bags: Two-dimensional bag (width x length) with bottom or side seals.

Flexibility: The property of a material, which will permit its being bent or twisted without breaking, the state of being non-rigid.

Four color process printing: Indicates the four-color plates or cylinders commonly used in color printing.

Flush: A term used in layflat tubing whereby the film is rolled right up to the edge of the core.

G

Gauge: A term used in referring to the thickness. The higher the gauge the thicker the material.

1 mil 1/1000 of an inch
1 mil 25.4 microns
1 micron One millionth of a meter
1 inch 25.4 mm
100 gauge 1 mil
80 gauge 8/10 mil

Gauge band: Thickness irregularity in films.

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

Gusseted bags: Flat style bag with both sides or bottom tucked in to form gussets. Designated with three dimensions; Side Gusset (width x depth x length) or Bottom Gusset (width x length + gusset).

Grip seal: A bag which is resealable and reclosable by two plastic components interlock at the top of the bag. The bag is reusable and flexible.

Gusset seals: A flat-style bag manufactured with both sides tucked in to form gussets.

GSM: Grams per square metre. Refers to the substance weight of paper, relating to an area of paper that remains constant. Standard printer paper is around 80gsm.

H

High density polythene HDPE: Film that has much higher stiffness, higher temperature resistance and much better water vapour barrier properties than LDPE film but is hazier.

Header bags: Side-weld bag with continuous seal along top, 2"-3" below fold. Bag is loaded and sealed from the bottom and typically has a hang hole.

Hole punch: A mechanical device used to produce an air evacuation hole.

Half moon hole punch: A punch hole that has not been completely cut through. Air is still able to escape through the bag.

Hot melt adhesive: Stick to almost anything: foams, corrugated cardboard, fabrics, plastics light-gauge metals. Hot melts are as strong as mechanical fasteners and sealing tapes. Hot melts are virtually invisible therefore improving overall aesthetic.

I

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. Impulse heat sealers be used on many plastic materials to create strong permanent welds.

Inch: A unit of length in the British Imperial systems.

J

K

Keyline: Also called a mechanical. This is the guide used in making plates or engraving cylinders and printing a piece - a diagram of copy and art for reproduction.

L

Lamination: Composite product consisting of two or more sheets or films joined together with glue or adhesive.

Low density polythene (LDPE): Resistant to punctures and tears, non-porous and stretchable. LDPE is relatively strong transparent film with good tensile strength. This resin has good clarity but week film strength. Primarily for food and utility bags.

Linear low density polythene (LLDPE): LLDPE film has higher tensile strength and higher impact and puncture resistance than the LDPE.

Lip: One side of the bag is longer than the other, allows bag to be opened more easily.

M

Medium density polythene MDPE: Film that has higher stiffness, higher melting point and better water vapor barrier properties.

Memory: The ability of a film to maintain its characteristics after shrinking.

Metric conversions:

1 kilogram (kg) 2.2046 pounds
1 meter 39.37 inches
1 pound 1.0936 yards
1 mill 1/1000 of an inch
1 micron 1/1000000 of a meter
1 inch 25.4 mm
100 gauge 1 mill
80 gauge 8/10 mill

Millimeter: A unit of length. One-thousandth of a meter or a one-tenth of a centimeter.

Mill: Thickness of material. The higher the mill, the stronger the material. 1 mill is 1-thousandth of an inch.

Micron: Thickness of material. 1 micron is 1-millionth of a meter.

N

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.

O

Opacity: Hiding power of pigmented (mostly white) plastic films. It is beneficial for packing materials sensitive to light (visible or ultraviolet).

Opaque: A coloured film where you can not see sunlight through the film.

P

Pallet: A rigid platform used as a base for transporting goods as a unit load. A standard UK pallet measures approximately 1000mm x 1200mm.

Pallet wrap: Pallet wrap stretchwrap that is used to bind a pallet together.

Perforations: The practice of creating a long series of holes so that plastic film can be torn more easily. Postage stamps are one common application of this.

Polythene: A simple thermoplastic polymer of ethylene. Highly puncture and tear resistant. Not affected by extreme temperatures. Does not possess barrier properties. Good clarity. Depending on its density, it may be low density (see LDPE). medium density (see MDPE). or high density (see HDPE).

Polymer: A material made through the process of polymerization.

Polyethylene: Polyethylene or polythene is the most common plastic. Polyethylene is of low strength, hardness and rigidity. Polyethylene has a high ductility and impact strength as well as low friction. It shows strong creep under persistent force. It feels waxy when touched. Most grades have excellent chemical resistance, meaning they are not attacked by strong acids or strong bases and are resistant to gentle oxidants and reducing agents. Depending on film thickness polyethylene can vary between almost clear (transparent), milky-opaque (translucent) or opaque. LDPE thereby owns the greatest, LLDPE slightly less and HDPE the least transparency.

Polymerization: A gas heated under pressure forms a solid.

Polypropylene: A thermoplastic polymer of propylene. Has much higher melting point, thus better temperature resistance than PE. Preserves freshness with vapor and moisture barriers. Non-porous and excellent clarity. Possesses ability to withstand high temperatures.

Poly Vinyl chloride PVC: A tough, stiff, very clear film. The oriented version is used mainly for shrink film applications.

Printed warning notice (PWN): A simple printed warning about the danger of suffocation with polythene bags.

Q

R

Reclosable bags: Seal-top reclosable bags can be made with or without a tamper-evident adhesive seal. Also includes zipper and slider zipper bags.

Recovery: Stretch film trying to return back to its original form after it has been stretched. This action constantly pulls the load together since the stretch film tightly form-fits the load. Stretch wrapping continues to tighten the load as it settles during shipment, due to the recovery property, keeping the load safe and secure during shipment.

Resin identification code: Resin identification codes (RIC) are codes defined by the European Commission. They identify the recyling status of a material.
#5 PP applies to polypropylene and indicates the material is recyclable.
#4 LDPE applies to low-density polyethylene and indicates the material is recyclable.

S

Seal strength: Measurement of force required to break or destroy a heat seal formed by any of the heat sealing sheets.

Sheeting: The cutting of a large master roll into sheets.

Shrink wrapping: A technique of packaging in which the strains in a plastic film are released by raising the temperature of the film, thus causing it to shrink over the package.

Side weld: Bags that are sealed on the side only. Has no bottom seal.

Singlewound film: A single layer of shrink film wrapped around a core.

Slitting: The cutting of a large master roll into smaller rolls used.

Static: An electrical charge built-up in plastic film.

Seal: Term used to describe the seal at the bottom of a can liner. The three types of seals are flat, gusseted and star.

Shielding bag: A bag used to shield the contents from electromagnetic radiation. A metallised bag is a form of shielding bag.

T

Tear resistance: The ability of a film to resist the propagation of a tear.

Tensile strength: The maximum load the film is capable of supporting. Determined by material thickness and width.

Tolerance: Allowable deviation from a nominal or specified dimension. Minimum/maximum range of measurement.

Top sheeting: A protective covering put on the top of a load to protect the top from dust, dirt, and other objects that might damage or dirty the load.

Transmission: Quantity of moisture and/or gas passing through the packaging film or foil over a specific period of time.

Trim: The amount of excess film severed during the sealing process.

Tint: Film where only a little masterbatch is added to give a tint of colour.

U

V

Vent hole: Air evacuation holes in a film made by pin perforators.

W

X

Y

Z

Zip top pouch: A reclosable or resealable pouch produced with a plastic track in which two plastic components interlock to provide a mechanism that allows for reclosability in a flexible package.

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