Extrusion films

The suitable extrusion conditions for PE are given in Table 6.3. The compression ratio ranges from 3 1 to 4 1. A length-to-diameter ratio of 20 can also be used for filled PE. The barrel can also 

PE type Temperature (°C) Pressure (MPa) Extrusion temperature (°C) Length/ diameter ratio 

In recent years LDPE has been increasingly replaced by all types of LLDPE, due to the latter s better mechanical properties compared to LDPE, and the resulting properties for reducing the film thickness. The problem of the poor processing properties of LLDPE has been resolved by the progressive improvement of film blowing machine technology. 

Metallocene-catalysed PE (mPE) grades are firmly established in almost all PE film applications. This class of raw materials plays an important role in the production of stretch films, heavy-duty bags, and laminating films. For heavy-duty film bags, processors have succeeded in reducing the minimum film thickness from 180 to 120 [xm by employing mPE in the last few years. Apart from the improvement in raw material, the trend towards three layer co-extrusion has certainly contributed to this application. 

Stretch film of all types of LLDPE can be produced very economically on cast film lines with throughput rates of up to 2 tonnes/hour. The state-of-the-art is five layer technology. 

Many plastic films are manufactured by extrusion processes, which can be subdivided into three major categories  

Most films used for packaging have a thickness in the range 15-50 urn. In building, agriculture and heavy-duty packaging, thicker films are used. Thicknesses of more than approx. 200 /an are seldom required. On the 

The molten film or web, when flowing freely, will have a thickness even larger than the slit width, owing to the so-called die-swell , the effect of the elastic recovery of the orientation in the die. Therefore a draw-down is always applied the material is removed from the die at a much higher 

Schematic representation of the tubular film extrusion process. 

The principal drawback of water-bath quenching is that very thin films cannot be made from crystalline polymers such as polyethylene or polypropylene. Above a certain draw-down ratio there are thickness variations in the longitudinal direction. This phenomena is called draw resonance and will be discussed in the next section. 

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Melt elasticity is of considerable importance in understanding much of the behaviour of polyethylene when processing by film extrusion techniques and when blow moulding. The complex relationships observed experimentally here have been summarised by the author elsewhere. ... 

Figure II.9. Equipment setting for TQ film extrusion. (After Gray reproduced with permission of The Plastics and Rubber Institute)...

P. C. Wu, Metallocene ethylene based resins in cast film extrusion and application, MetCon 94 Proceedings, USA, May 1994. 

According to the end use application, PEs are processed by various techniques, which include injection moulding, blow moulding, rotomoulding, and film extrusion. However, since the bulk of the processed material is used as film in the area of packaging, the discussion in this chapter focuses mainly on processing behavior and the ultimate properties of tubular blown film. 

Kalyan et al. [56] have also studied the effect of alpha-olefin comonomers on the rheological properties and processing of LLDPE. The characteristics of the resins are shown in Table 2. It is found that 1-octene-based LLDPE has the lowest shear viscosity as compared to 1-butene- and 1-hexene-based polymers (Fig. 9). Decrease in power consumption, pressure before the die, temperature in the die, and increase in output has also been found according to shear viscosities of the polymers during tubular film extrusion. 

Ljungberg, N., Andersson, T. and Wesslen, B. 2003. Film extrusion and film weldability of polyjlactic add) plasticized with triacetine and tributyl citrate. Journal of Applied Polymer Science 88 3239-3247. 

What process variables control the degree of orientation in a film manufactured via cast film extrusion and blown film extrusion ... 

Polypropylene film is found in a variety of applications. Films are thin plastic sheets with thicknesses less than 250 pm. Applications for these films include candy mappers, plastic label material, electrical capacitors (which requires very pure polymer), and fiber glass insulation backing. There are two general categories of polypropylene films unoriented and oriented. Films are manufactured through either a cast or a blown film extrusion process. Oriented films exhibit improved strength relative to unoriented films. This means that they can be... 

Extrusion Clothing fabrics Packaging films Extrusion coating films for food packaging Insulator films Photographic film base ... 

Processes such as film extrusion, fiber spinning, injection molding, and drawing tend to impart orientation to products made from semicrystalline polymers. Mechanical, dielectric, and optical properties, to mention only three, are often strongly influenced by orientation. X-ray diffraction offers a direct approach to studying crystallite orientation because the Intensity that is diffracted into a detector placed at an appropriate position is directly proportional to the number of crystal lattice planes that are in the correct orientation for diffraction. The principles of such measurements are well described in textbooks 0,2). 

Cross-file patent searches, 18 243-244 CrossFire Beilstein, 6 19 Cross-flow filtration, 11 383 15 827, 829 in porous pipes, 11 387-388 with rotating elements, 11 383-387 Cross flow model, 21 706 Cross-flow packed scrubber, 26 687-688 Crossflow plates, 6 762-763 Cross-flow screens, 22 282 Cross-flow velocity, 15 725 Crosshead mandrel, in VDC film extrusion, 25 732-733 Cross-lapping, 17 501 Cross-linkable epoxy thermoplastic system (CET), 10 436... 

Film adhesives, 25 582-583. See also Monolayer blown-film extrusion Multilayer blown-film extrusion Multilayer cast-film extrusion... 

Monolayer blown-film extrusion, VDC copolymers in, 25 725, 728-729 Monolayers, self-assembled, 77 57 Monolayer self-assembled systems, 16 800 Monolignols, 27 10—11, 13, 14 Monolithic drug delivery systems, 9 11 Monomagnesium phosphate, 78 839 Monomer addition, in PVC polymerization, 25 665-666... 

Multilayer blown-film extrusion, VDC copolymers in, 25 725, 729—733 Multilayer bottles, 20 52—53 Multilayer capacitors (MLCs),... 

Nylon film, extrusion of, 19 789-790 Nylon flocking, 19 755 Nylon food packaging, 18 43 Nylon hollow fibers, 16 21-22 Nylon-MXD6... 

Figure 5.12 displays a diagram of a blown film extrusion line. 

The basic principle is somewhat similar to cast film extrusion but the flow of the polymer is obtained by dissolving it in a solvent instead of heating it during mechanical shearing in an extruder. 

Butler, T.I., Eow-Density Polyethylene, Chapter 27 in Film Extrusion Manual, Process Materials, Properties, 2 ed., Butler, T.I. (Ed.) TAPPI Press, Atlanta, GA (2005)... 

Grob, C. and Wortberg, J., Optimizing Purging Time at Product Change in Blown Film Extrusion by Selective Modification of Process Parameters, SPE ANTEC Tech. Papers, 50, 261 (2004)... 

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