Biaxially stretched film

1 Overview

The abbreviation code for Biaxially Oriented Plastics Film is BOPF. In the production process of BOPF, by changing the process conditions, a film with basically the same physical and mechanical properties in the vertical and horizontal directions can be produced, which is usually called a Balance film (ie isotropic); it can also be produced The mechanical strength of one direction is higher than that of the anisotropic film in the other direction, which is usually called a strengthened (Tensilized) film or a semi-reinforced film. In general, the mechanical strength of the longitudinal direction is always greater than that of the transverse direction. The biaxial stretching of the film is to stretch the unstretched film or sheet in the longitudinal and transverse directions in the temperature range below the melting point and above the glass transition temperature, so that the molecular chain or specific crystal plane is parallel to the film surface orientation, followed by heat treatment under tension. Stretch film improves mechanical strength, such as increased tensile strength, impact strength, tensile elastic modulus, tear strength, fatigue bending and surface roughness, etc., and improves heat resistance, plug resistance, transparency , gloss, air permeability, moisture resistance, electrical insulation, thickness uniformity and dimensional stability, etc.

When the biaxially stretched film is heated, the molecular orientation relaxes and the film shrinks, so it is also called heat shrinkable film in the packaging industry.

At present, the varieties of BOPF that have been industrialized include BOPP, BOPET, BOPA, BOPS, BOPVC, BOCIPE (radiation cross-linked polyethylene), BOPVDC (polyvinylidene chloride copolymer), BOPVA (polyvinyl alcohol), etc. For the first 4 types.

There are two types of biaxially stretched film production methods, planar method and tubular film method

The process flow of the planar casting method is basically the same as that of the casting film, except that an expansion (that is, transverse stretching) process is added after the longitudinal stretching.

The planar bidirectional stretching method can be divided into three types: simultaneous biaxial stretching method (ie, one-time stretching method), vertical-horizontal stretching method (ie, secondary stretching method) and vertical-horizontal-longitudinal stretching method (ie, three times stretching method).