Cast film process

Cast babbitts Cast film Cast film process Casting... 

Melt Extrusion. By far the most important method for producing film and sheeting materials reties on one or another of the various melt extmsion techniques (5). The main variations of melt extmsion are the slot (or flat) die-cast film process, the blown films process, and the flat die sheeting-stack process. These may be combined with one or more steps such as coextmsion wherein multilayer film or sheet is formed, biaxial orientation, and in-line coating (6). 

One of the requirements of this process is that the melt maintain good contact with the chill roU, ie, air must not pass between the film and the roU. Otherwise, air insulates the plastic and causes it to cool at a rate different from the rest of the plastic and this spoils the appearance of an otherwise satisfactory product. The melt should not emit volatiles, which condense on the chill roU, reduce heat transfer, and mar the film s appearance. The cast film process allows the use of a higher melt temperature than is characteristic of the blown film process. The higher temperature imparts better optical properties. 

Lower-density E-plastomers have found alternate use in cast film processes to make elastic film laminates with good breathability which contain laminates of liquid impermeable extensible polymeric films with extensible-thermoplastic-polymer-fiber nonwovens and nonwoven webs of polyethylene-elastomer fibers as the intermediate layers. The development relates to a breathable film including an E-plastomer and filler that contributes to pore formation after fabrication and distension of the film. The method and extent of distension is designed to produce a breathable film by stretching the film to form micropores by separation of the film of the E-plastomer from the particulate solids. This film is useful for manufacture of absorbent personal-care articles, such as disposable diapers and sanitary napkins and medical garments. In detail, these constructions comprise a liquid impermeable extensible film comprising polyolefins. The outer layer contains extensible-thermoplastic-polymer-fiber nonwovens, and an elastic intermediate layer contains nonwoven webs of fiber E-plastomers. The intermediate layer is bonded to the film layer and the outer... 

Running an LLDPE Resin on a Cast Film Process with Unmixed Gels in the Extrudate... 

Table 11.7 Screw Channel Dimensions for a 114.3 mm Diameter, 32 L/D Barrier Screw for Running an LLDPE Resin on a Cast Film Process with an Improved Screw Design...

The process for making a cast film involves drawing a molten web of resin from a die onto a roll for controlled cooling. The cast film process is used to make a film with gloss and sparkle. The melt temperature in the cast film process is higher than in the blown film process. The higher the melt temperature the better are the optical properties of the film. 

Nylons are melt-processable using conventional extrusion. Film can be produced by either the cast film process or the blown film process. During film production, different degrees of crystallinity are obtained depending on the temperature and rate of quenching. When the cooling rate is increased, a less crystalline nylon is... 

The cast film process involves extruding a molten polymer through a slit die and drawing it around two or more highly polished... 

Production of flexible packaging begins with extrusion of plastic resin to yield sheet or film. For film, two main processes are used. In the cast-film process, the resin is extruded through a slit-shaped die onto a water-cooled chrome roUer, where it is solidified. After the edges are trimmed off, the film is wound onto a roll. The film may be oriented by stretching it in the machine direction (uniaxi-ally oriented) or in both the machine and cross directions (biaxially oriented) to improve mechanical and barrier properties. This process is also used to produce plastic sheet for thermoforming or other applications. 

Casting Process. The flat-die, chill-roll, cast-film process is more suitable for high volume production on dedicated lines because of higher output rates obtained by wide dies and more efficient cooling on chill rolls. Cast films usually have better clarity than blown films because of rapid quenching, but imiaxial orientation can cause the film to split in the machine direction for some structures. 

Progress in manufacturing techniques has been made. Although melt-extruded films were the norm, the industry is moving to a solution-cast film process to reduce costs and improve manufacturing throughput efficiency. In this process, the ionic form of the polymer is solubilized in alcoholic solution, such as propanol, and then fabricated into a film of desired thickness. The conversion of the non-ionic polymer to an ionic phase, ready for use in a fuel cell, is carried out prior to the solubilization step. 

Keller, R. Guidelines for Comparing the Blown and Cast Film Processes. SPE ANTEC, pp. 39-43, May 1989. 

Principles of extrusion Description of single screw extruder Smooth bore and grooved-feed extruders Blown film process Cast film process Extrusion coating Profile extrusion Materials for extrusion Auxiliary equipment Die design... 

RM/CastFilm Rotational molding or cast film process... 

The cast film process was developed in the late 1940s primarily by scientists at ICI, DuPont and Union Carbide. An early description of the cast film process was published in British Patents 474,426 (ICI) and 561,373 (DuPont).The cast film concept filed on June 26, 1948, and published as U.S. Patent 2,586,820, issued on February 26,1952, to WE Hemperly ef a/, and assigned to Union Carbide is shown in Figure 6.18. 

Figure 6.18 Early example of the cast film process.

The drawing illustrates the important features necessary for the cast film process which include (a) the melting of the polyethylene onto a heated roll, (b) a stretching zone where the molten polyethylene film thickness is reduced to a thinner gauge by moving the take-up roll at a faster rate than the take-off roll, and (c) the cooling tank where the polyethylene material solidifies to a thin film. 

An early description of the cast film process was published in Modem Plastics in 1952 [26] which was very similar to the cast-film scheme shown in Figure 6.19 which represents the process used today. The cast film process involves the extrusion of polyethylene through a die to form a thin molten layer of material that is drawn down to a thinner gauge based on the difference between the rate the molten polymer exits the extruder and the rate that the molten polymer is cooled onto a chill roll. The film cools very rapidly on the chill roll and film orientation is only in the machine direction. Optical properties are usually better with cast film as compared to blown film and line rates may be higher with the cast film process. A cast film line may also involve coextrusion of several layers of different types of thermoplastics to fabricate specialty films with improved properties. A... 

Chill RolL In the chill roll cast film process, a plasties web is extruded from a slit die (Fig. 8.6) against the surfaee of a water-cooled chill roll. The die is arranged to extrude vertically or obliquely downwards so that the film web is delivered approximately tangentially to the roll surface. The die is similar in principle to a sheet die but will usually not inelude a restrictor bar. Film thickness is partially regulated by the gap between the die lips but also by the rotational speed of the chill roll which is arranged so as to drawdown and thin the melt web. Consequently, the die gap... 

As in other plastic processes, the cast film process depends on many interactive variables, so that any defect may have one of several causes. A remedy for one defect may introduce another, so proeess problem solving is not straightforward. With these provisos, the troubleshooting chart (Table 8.1) provides a useful guide for problem solving. 

---