Extrusion-orientation process

Extrusion and biaxial orientation processes used by Solvay subsidiary Ondex in the manufacture of PVC sheets are described, and the properties and applications of these sheets are examined. 

It was discovered that a number of PVDF film properties, including electrical, could be altered by the extrusion and orientation conditions.The relationship between the extrusion and orientation process and the electrical properties of the film are important because of the application of PVDF films in miniaturized capacitors which are used in apparatus such as defibrillators. To compare the properties, extruded film, while in molten state, was brought in contact with chilled rollers at 80°C and cooled rapidly. The oriented film was stretched at 150°C in the longitudinal direction by a stretch ratio of 3.5, that is, its original length was increased by 3.5 times [Eq. (6.6)]. The dielectric constant and dissipation factor were measured as seen in Table 6.8. Orientation increased the dielectric constant and reduced the dielectric loss... 

BIAXIAL ORIENTATION PROCESSES FOR PP Tubular film extrusion... 

Keywords extrusion die, die design, biaxially-oriented PP (BOPP), heat sealing, manifold, coextrusion, extrusion parameter, process control, flow. 

Extrusion. The process of extrusion is closely related to pultrusion. In extrusion, the plastic material is pushed through a die under pressure rather than drawn through with continuous fiber-reinforcement materials. Random-oriented fiber-reinforcement materials can be used in the extrusion process if they are blended with the molten plastic before entering the die. Extrusion can be used only to produce structures that have a constant cross-sectional profile along their entire length, as determined by the die profile. Quite complex cross-sectional designs can be produced in this way, but they are essentially only two-dimensional. 

Virtually every polymer can be used in film form. Most thermoplastic polymer films are prepared by conventional extrusion techniques based on calendering, casting, and blown-film, or tenter-film systems. Other polymers, which cannot be easily melted, are formed into films by solvent casting. In the selection of a film for a particular application, the properties of the poljuneric materials must be considered in view of the application. Thermal properties, molecular characteristics, and crystallinity of the polymer affect processing and film properties. Additives influence extrusion and orientation processes and improve film properties. 

Molecular Weight and Molecular Weight Distribution. Molecular weight and molecular weight distribution affect extrusion and orientation processes and the physical properties of the film, eg, tensile strength, elongation, impact resistance, (qv) and optics (see Molecular Weight Determination). 

In another method, two or three melt streams from separate extruders can be combined and cast to form a multilayer structure. Alternatively, a melt stream and a quenched web or a quenched and uniaxially oriented web are combined on a chilled drum, providing the web with new surface functionality. This method is known as the extrusion coating process (14). 

The most common orientation process is used to produce fibres and is described in research disclosures from ICI, academic literature and manufacturer processing guidelines. Melt spun fibres of PEKEKK have exhibited moduli as high as 13 GPa [33]. There are also a number of academic references to oriented material which, as expected, shows enhanced mechanical performance. Techniques such as solid-state extrusion [34] and die drawing have been applied to PEEK and a modulus of 11 GPa has been obtained [35]. Orientation processes are similar to those used for polyethylene terephthalate but there are some key differences in terms of orientation-induced crystallisation [36, 37]. 

Ultrasonic sensors have also been applied in the study of physical foaming agents for foam extrusion [252]. For on-line monitoring of orientation processes birefringence, FTIR spectroscopy, fluorescence and ultrasonics are most suitable. 

The film can be further oriented uniaxiaUy via a secondary heated roll stacks, or oriented biaxially via a combination of machine direction and transverse direction stretching, which can be accomplished simultaneously or as a two-stage process. Greater detail of cast film extrusion and film orientation process, effects, and mechanics can be found in the referenced texts [18,19]. 

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