Understanding the process and application of BOPET films

BOPET is a polyester film made from stretched polyethylene terephthalate (PET). It is used widely for its brilliant features like-

•     High tensile strength
•     chemical and dimensional stability
•     transparency
•     reflectivity
•     gas and aroma barrier properties
•     electrical insulation.

Flat biaxial orientation
Flat biaxial orientation is the most prevalent film orientation process. Most of the biaxially oriented polypropylene (BOPP) and polyester (BOPET) films used in packaging by the bopet film manufacturers are produced using the technique detailed below. Very large units, capable of producing finished film over 300 inches wide, are being installed around the world, bringing down processing costs per pound and creating plentiful supplies for the growing global flexible packaging market.

The Process:

•     A unit commonly called a tenter frame line performs flat biaxial orientation. The term “tenter frame” refers to the CD orientation section. The process starts with plasticizing extruder feeding a first module that operates similarly to a cast film line.
•     With flat biaxial orientation, there are multiple chill and surface finishing rolls to handle the much thicker sheet that is formed. Orientation (or “stretching”) thins the polymer web proportionally to the orientation or stretch ratios.
•     Once the extruded sheet has been quenched and its temperature stabilized, MD stretching is accomplished by pulling the sheet using rolls rotating with progressively increasing surface speeds; stretching takes place in small gaps between successive rollers. The small gaps minimize the potential for “neck in,” which is a reduction of the width of the web during the drawing or thinning processes.
•     Following MD stretching, endless chains with clips grasp the edges of the moving web and carry it into a multistage hot-air oven. The first oven stage is used to equilibrate the web at the desired temperature; this is followed by CD stretching. Further temperature conditioning in the final oven sections provides annealing or stress relaxation for dimensional stability and cools the film prior to winding.

Applications-
BOPP and BOPET produced by plastic film manufacturers are workhorse flexible packaging films, principally in laminations, where they can be used in as-oriented form, but often are vacuum-metallized, where the films themselves do not offer sufficient barrier protection. BOPP is widely used in salty, dry snack packaging, as it offers better moisture vapor barrier than BOPET. BOPP also has the lowest density of the commonly oriented packaging films

Author’s bio-
This article states about the process used by the bopet film manufacturers for manufacturing plastic films and it also states about the various applications of these films.

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