Biaxially Oriented Film

Biaxially oriented polypropylene (BOPP) film is film stretched in both machine and transverse directions, producing molecular chain orientation in two directions. BOPP film is produced by a tubular process, in which a tubular bubble is inflated, or a tenter frame process, in which a thick extruded sheet is heated to its softening point (not to the melting point) and is mechanically stretched by 300- 400%. Stretching in the tenter frame process is usually 4.5:1 in the machine direction and 8.0:1 in the transverse direction, although these ratios are fully adjustable. It is a widely used process, more common than the tubular process, and a glossy, transparent film is produced. Biaxial orientation results in increased toughness, increased stiffness, enhanced clarity, improved oil and grease resistance, and enhanced barrier properties to water vapor and oxygen. Impact resistance, low temperature impact resistance, and flexcrack resistance are substantially modified. BOPP films are used in food packaging and are replacing cellophane in applications such as snack and tobacco packaging due to favorable properties and low cost.

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