BOPP Films and its Manufacturing Process

BOPP film stands for- Biaxially Oriented Polypropylene films. It is a widely used thermoplastic polymer. It has become one of the most popular and highly demanded films across the globe due to its characteristics and uses.

MANUFACTURING BOPP FILMS
BOPP films are manufactured by the following processes:

a)    Sequential Orientation:
•    Stentor process
•    Double bubble process

b)  Simultaneous Orientation

Sequential orientation by Stentor is the most commercially employed process used by the bopp film manufacturers; therefore its process needs to be looked at in greater detail.

• •    Homopolymer polypropylene is processed with various functional additives like amides, ethoxylated amines, stearates etc. so that film's co-efficient of friction is reduced and static charge dissipation rate is increased. To provide different shades to the film it is also mixed with various fillers like talc and calcium carbonate and pigments like titanium dioxide.
• •    Polypropylene with the requisite additives, fillers and pigments are then melted and co-extruded as thick sheet and with the help of one or more satellite co-extruders, a random copolymer of polypropylene or other terpolymers are melt co-extruded on either one or both surfaces of the homopolymer sheet. The homopolymer core layer, which is generally between 70-90% of the total thickness, provides the mechanical strength, optical properties, reduction in density (in certain cases) and other relevant characteristics like anti-blocking.
• •    Bopet film manufacturers solidifies this sheet by passing it over a chill roll kept in a water bath and the cast sheet is then passed over several heated, chrome-plated rolls, which pre-heat it. Once the sufficient heat is achieved, it is passed over two or more pairs of rolls in which one set of rolls rotate at a speed faster than its preceding rolls.
• •    The mono-oriented film is then clipped by clippers, which carry them into a hot air circulated oven and the clippers are placed over a parallel chain track. The biaxially oriented film is then annealed to retain the oriented stresses and cooled to room temperature after sufficiently heating and transverse direction orientation to the tune of about 7-10 times. While the un-oriented gripped portions are trimmed, the final film is corona treated to enhance surface tension and wound in jumbo rolls.

BOPP films have wide range of applications
•    Grade F1 films are used for packing of food and their sealing
•    These are used for electrical applications, printing and lamination
•    Text book covering
•    Also used for extrusion coating, flower packing, reverse printing and lamination
•    These are also used as adhesive tapes and pressure sensitive tapes
•    White and opaque colored films are used for general purposes like printing pouching, cable over wrap, strip packaging for cough drops.
•    For general purpose and over wrapping heat sealable BOPP films are used.

Author’s bio-
This article describes about the manufacturing process used by bopp film manufacturers and also tells about the wide range of applications of bopp films.

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