Glossary of Film terms


BUR - Blow-up-ratio - As the heated polymer exits the die, it expands to it's cooled state. It is effectively blown up to it's full size, where the film cools and the size is locked in. A BUR of 2.5 to 3 is desireable. It is calculated as the bubble diameter divided by the die diameter.

C&A FILM - Construction and Agriculture Film - finished product that has multiple uses as vapour barriers, drop sheets, etc.  (See the C&A Products page for further applications)

CGSB - Canadian General Standards Board - The governing body which regulates standards for Vapour Barrier manufacturing.

DDR - Draw-down ratio - As the heated polymer exits the die, it exits at a specific thickness, as defined by the die gap. It is then drawn down to a thinner gauge, based on the speed of the take-off equipment. This is known as draw down.

EVA - Ethyl Vinyl Acetate copolymer derived from the random copolymerization of vinyl acetate and ethylene.

HDPE - High Density Polyethylene

LDPE - Low Density Polyethylene - Typically includes a range of density from 0.915 - 0.925. 

LLDPE - Linear Low Density Polyethylene - A straighter chain molecule than LDPE.  This material is packed tighter on a molecular level because of it's straight chains, and thus often exhibits improvements in strength over LDPE.

MD - Machine Direction - During extrusion, this is the direction of travel of the film.

PTO - Perforated Tear-Off - refers to a very standard type of bag forming. A solid tube is run with a sealing/perforating machine placed in-line. The machine creates a seal across the width of the film web, and perforation holes immediately next to it. It is then possible to tear off individual bags, much like you find in the fruits and veggies aisles at your local supermarket. This can readily be applied to bags as large as pallet covers.

SOE - Slit-on-Edge - refers to an in-line process whereby a knife is placed into the edge of the film, opening one side up. Used in conjunction with a PTO, it has the ability to create envelope style, or twin-seal bags.

TD - Transverse Direction - During extrusion, this refers to the cross-direction of the film, 90 degrees from the direction of the travel.



BLOWN FILM EXTRUSION - This is one of two processes by which film is made, and this is the process that Layfield uses.  By heating plastic pellets and pushing them through an extruder, they form a molten polymer.  As they exit the extruder, they are pushed through a shaping orifice, (die), and the plastic becomes one solid form.  The round die forms into a tube, which is then shaped further by adding air into the middle, creating a bubble, hence, blown film.  The air is trapped in the bubble as the film is cooled while it travels several stories to the top of a tower.  It then passes through nip rolls, pinching off the film and trapping the air in a solid column.

GAUGE - This is the common term for the thickness of the film, typically measured in either Mils or Microns.

LAYFLAT - This is the distance across the TD of the film.

MICRON - An alternative unit of measure for film thickness. As mil is the more common measure, a Micron is 25.4 times larger than a Mil.

MIL - Unit of Measure for film thickness. One mil is equal to 1/1000th of an inch.

SLIP - Coefficient of Friction - This is the resistance to movement of one film surface to another, or to another surface entirely.

TREAT - Treating is a process wherein film is electrically, chemically, or otherwise altered to allow good ink adhesion.  Layfield uses the corona treat method, making use of a corona discharge which electrically alters the surface tension of the film.  Treat is measured in dynes per centimeter.  Typical treat levels for printed film is 38 - 40 dynes.