Tubular process water quench

In addition, some Asian and Middle Eastern coimtries are using a water-quenched process for the conversion of PP tubular film, most of which needs good optical properties. The film tube has to be opened up by hand immediately after conversion, and this requires good antiblocking properties to prevent delays through sticking. 

Simultaneous Biaxial Orientation. There are two predominate systems available to do this, tubular and flat film. In the tubular process (see Fig. 9), also referred to as the double bubble process, a continuous tube is extruded and quenched. Typically, an interior cooled mandrel is hung from the die inside the tube. The surface of the mandrel may greatly influence the interior surface of the tube. Care must be taken not to impart scratch lines in the melt as it is pulled down over the mandrel. Air pressure in this primary tube is very critical. The melt needs to be held out over the mandrel but not too far away. A water bath on the external side of the tube helps quench the tube rapidly. A nip pulls the tube from the die and acts to isolate the casting bubble from the air pressime in the stretching bubble (27). 

The majority of plastics films made today are produced by the tubular process, although for certain applications the flat film casting process is used. The so-called water quench system in which film is extruded directly into water is now not in general use. 

The reaction section consists of the high pressure reactors filled with catalyst, and means to take away or dissipate the high heat of reaction (300-500 Btu/lb of olefin polymerized). In the tubular reactors, the catalyst is inside a multiplicity of tubes which are cooled by a steam-water condensate jacket. Thus, the heat of reaction is utilized to generate high pressure steam. In the chamber process, the catalyst is held in several beds in a drum-type reactor with feed or recycled product introduced as a quench between the individual beds. 

When the extrudate exits the die, it has to be quenched and possibly sized (drawn through a fixture) to maintain its final shape. Depending on the extrusion process, different methods are available to quench the final product. Cast film and sheet are quenched on rolls and in water baths, blown film is quenched by air in a blown film tower. Solid profiles, pipe, and tubing are quenched in calibration tanks filled with water and in some cases connected to a vacuum system. Polymer strands and monofilaments are quenched in air or water baths while wire coating is done horizontally in air or water. In small and large part blow molding, the melt is quenched in molds as the extruded tubular parison is inflated. 

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