Orientation roller drawing

The amorphous PEN resin pellets are first dried at 180 °C and then extruded at 290-300 °C through a die, formed into a sheet, which is then followed by a two-step orientation (forward draw and sideway draw process) just above the glass transition temperature (Tg) (>120°C). After the orientation process, the PEN film is conveyed between rollers at 210-220 °C to induce crystallization. At the end of the orientation and crystallization process, the film is cut and rolled into widths and lengths to suit individual customers [14-16], Two of the process used to produce such films are shown in Figure 10.3. 

Die drawing allows bars, tubing, and large-size sheets to be obtained. The polymer is drawn through a heated die with a conically shaped entrance. Sheets of oriented polymer can be produced by roller drawing while highly oriented films and rods can be obtained by co-extmsion. 

PE films are usually produced by the blown film extmsion method. The alternative method is sheet extrusion followed by passing through chilled rollers. Blown film is more economic biaxial orientation is introduced by the draw-off and blow ratios. Bubble stability is critical to the blown film process. Bubble stabihty is provided by the melt strength and rheological characteristics of the PE. Long... 

Cast-film extrusion LLDPE, HDPE Eilm is extmded through a slit-die then passed through chilled rollers to crystallize and smooth the surface orientation by cold drawing... 

Orientation is a continuous operation and occurs in the direction of the film motion or the machine direction (MD). Usually, a cast sheet is transported on heated rollers (Fig. 9) to permit the sheet to reach a uniform temperature at which the polymer molecules are sufficiently mobile. Having reached this temperature, the sheet is abruptly accelerated between two rollers of different speeds. This point is defined as the draw point. In some instances, additional heat may be required to boost the temperature, or nip rolls are needed to regulate tension and to prevent film slippage (Fig. 9). Uniaxial film can be obtained by orienting perpendicular (transverse) to the MD using tenter frames or melt inflation, where the melt removal rate is equal to the melt velocity at the die. However, these two methods are seldom employed. The properties required by the user determine the orientation required to develop the desired physical properties. 

Biaxially oriented PET and PEN films are exclusively produced by a stenter process where commonly the amorphous cast film is drawn in the machine direction (MD) by passing it over heated rollers and then fed into a stenter frame to achieve a draw in the transverse direction (TD) (see Films, Manufacture Films, Orientation). A schematic of the process is shown in Figure 1. 

Drawing System Orientation of the fiber - Five rollers - Adjustable take up rate, e.g., 12 m/min... 

Highly oriented films can be produced by drawing a sheet of polyethylene between a pair of freely rotating heated rollers [78,79], Orientation oceurs by two proeesses isothermal thickness reduction in the nip between the rollers (75-120°C) and nonisothermal post-roller solid-state drawing. As in many other orientation processes, the tensile strength and modulus of the product increase linearly with the draw ratio. Fibers with tensile moduli of 43 GPa and tensile strengths of 0.67 GPa have been obtained by this method. 

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