Glossary Packaging Films

​

BACK SEAM

The back seam is the longitudinal, or MD seal which is formed by sealing the sheet to make a tube. 

​

​

​

 

BACKFLUSH

Backflushing is the practice of filling the package with a neutral atmosphere to prevent oxidation.  Nitrogen is the usual choice.  It's simple.  Just put a small pipe of nitrogen at the top of the forming tube.  Nitrogen is heavier than oxygen so it naturally drops to the bottom.

BARRIER

Barrier to the ambient prevents the product from oxidizing, or spoiling. It is measured in terms of barrier to Oxygen ( OTR )  and Moisture Vapor Transmission Rate ( MVTR ).   Both are measured by ASTM test methods.  Barrier is achieved either through bulk thickness, Polyvinyl Alcohol ( EVOH ) core layer of a coextrusion or Polyvinyldichloride ( PVDC)  coating commercially known as Saranex.  When specifying an OTR limit, call out the maximum amount.  If the value is less, that is acceptable. 

​

The Achilles heel of EVOH is solubility.  If the other layers are too thin, water will migrate via a concentration gradient and break it down resulting in a nightmare product recall. 

​

BOPP

is the acronym for Biaxially Oriented Polypropynene or oriented in both the machine ( MD) and the transverse ( TD )  directions.   a/k/a "OPP " verbal shorthand for people who don't have time to say "BOPP "

 

CHANNEL LEAKER
When a foldover wrinkle on the end seal does not seal completely, the result is a " channel " which is a pathway for air and liquid.   To prevent a channel leaker, the film must be mulitlayer with differential seal initiation temperatures.

​

​

​

​

 

 

 

COEX PROP

Polypropylene film coextruded with a very thin layer ( usually only 2 or 3 microns ) of low denstiy polyethylene ( LDPE ) .  The polyethylene melts at a lower temperature than the propylene.  This enables sealing on bare metal "resistance " jaws.  Can be 1 or 2 side heat sealable.  Our BOPP is 2 side sealable coex prope.

​

CRIMP SEAL or END SEAL
The end, or transverse seals of a flow wrapper are made by what is referred to as crimpers.

​

​

​

​

FIN SEAL

The back seam of a form/fill/seal package, either flow wrap or vertical, so called because it protrudes from the pack like the fin of a fish.   Requires mulitiple layers.

 

​

​

​

​

​

 

 

FORMING CONE

Formed metal which transforms flat sheet film into a tube in the infeed of either a VFFS or Horizontal Flow Wrapper.  We are super fans of Formers by Ernie.  If Ernie does not already have a forming cone in stock, he will whip one up in record time.  

​

GLOSS

Amount of light reflected by a film.  Measured by ASTM ______.  Also referred to as Gardner Gloss.

​

HAZE

Measure of amount of light a substrate allows to pass through.  Synonymous with clarity.  The lower the number, the better the clarity.  Measured with ASTM ___________

​

LAP SEAL

End seal of a form/fill/seal package which is folded over.  Made with a

monolayer film; difficult to make pinhole free.  Common example is baby carrots.

 

​

​

​

LINESCREEN

A measure of fine process print.  The higher the number, the finer the print.

Flexographic and rotogravure printing deliver much finer print than screen printing.

​

​

​

​

MASTER ROLLS
Master rolls are our raw material.  Usually about 60 inches wide. 

​

PROCESS PRINT

Process print is print made with small dots to create certain effects such as half tones and vignettes.

​

STRUCTURE

Any multilayer package, whether achieved by coextrusion or lamination is said to be a "structure."

​

​

​