Film coextrusion

Lotryl . [Atochem N. Am.] Ethylene/ acrylic ester copolymers for films, coextrusion, gloves, sheets, coating, hot melts, compounding. 

Surlyn 1650. Blown film coextrusion good blend of toughness and low-temperature sealability. 

Film Processing Methods Extrusion, coextrusion, and Saran F- lacquer solution films. Multilayer Extrusion Saran resins are used in combination with a myriad of other polymers in flexible and rigid multilayer products. Multilayer cast and blown film coextrusion processes for Saran can be used with all polyethylenes, polypropylenes, and nylons. 

Uses For films, coextrusion, coating, hot-melt adhesives, compds. Properties Dens. 0.94 g/cm m.p. 80 C Lo-Vel 27 [PPG/Silica Prods.]... 

Uses Blown and cast film coextrusion food pkg. 

Vi nyl pyrrol idone/styrene copolymer film coextrusion, blown Nylon 6/69... 

A brief coverage of the topic of blown film coextrusion is provided in this chapter. Coextmsion is the process of feeding a single die with two or more different polymer melt streams. Within the die, the various flow streams are combined to form a single-ply film comprised of the individual layers (Fig. 5.1). Because of the high viscosity of polymer melts, the individual layers tend not to mix but to retain their positions within the combined flow stream. In some cases, over seven layers of polymer are extruded into a film. For each type of polymer layer in the final structure, a different extruder is connected to the die (Fig. 5.2). 

Extrusion—sheet and film Coextrusion Extrusion—blown film Extrusion—foam... 

Figure 9.38 shows a multi-manifold blown film coextrusion die enabling extrusion of three different polymers. 

Coextrusion is practiced on a wide scale in blown film. There are many five-layer blown film coextrusion dies used in the industry five-layer films are now considered a commodity [41], Even seven-layer dies are not unusual. Some coextrusion dies use as many as 8 to 10 layers. Most of these multi-layer dies are used in high-barrier packaging for food. Conventional blown film coextrusion dies have a concentric arrangement of spiral mandrel manifolds. In some cases conical spiral mandrel sections are used, while in other cases the spiral mandrel section is machined into a flat horizontal surface. The latter arrangement is referred to as a pancake coextrusion die, because the different sections of the die are stacked like pancakes. A schematic of a pancake coextrusion system is shown in Fig. 9.39. 

Although overlapping, in practice there are processes which are often run at rather moderate temperatures below 240°C, e.g. film extrusion, film coextrusion, blown film and the recently developed PP calendering. For these applications, most of the above-listed pigments are suitable due to their heat resistance. 

Coextruded films are produced by a tubular-blown film process and a flat-die, chill-roll casting process. Capital and operating costs for blown-film vs cast-film coextrusion lines are strongly dependent on product mix and utilization. Equipment suppliers provide comparative economic evaluations for specific products. Practical cast-film equipment has been discussed previously (3). Coextrusion dies are unique. Extruders used before the die and take-away equipment used afterwards are standard equipment for single-layer film manufacture of blown or cast film (see Extrusion). 

Flat Dies (Slit Dies). Flat dies, also called slit dies because the orifice is a wide rectangular opening, are used in chill-roll, cast-film coextrusion. These dies are used almost exclusively for multilayer coextrusion with sheet thickness >254 /um, as well as in coextrusion coating processes (2), where a multilayer web is extrusion-coated onto a substrate such as paperboard, aluminum foil, plastic foam, or textiles. 

Multilayer films are produced by both cast- and blown-film coextrusion. One of the key enabling technologies in the manufacture of these multilayer films has been preencapsulation of the VDC resin (205). Preencapsulation means that the VDC resin extrudate is completely encapsulated with a more thermally stable polymer, such as an ethylene-vinyl acetate copolymer, prior to entering the coextrusion die. Using this technique, the VDC resin is not directly exposed to the... 

The application of encapsulation technology to flat dies and cast film coextrusion is fairly easy to envision. As shown in Figure 14, the encapsulating material completely surrounds the VDC resin. When the edges are trimmed, a flat film with a continuous barrier layer is produced. 

Blown-film coextrusion presents the added difficulty of obtaining a continuous barrier layer. A die with a crosshead mandrel is preferred over a die with a spiral mandrel, because the spiral mandrel tends to lead to long residence time in the spirals. A standard crosshead mandrel, however, results in a weld line where the barrier layer is not continuous. As shown in Figure 15, this problem is solved by providing an overlap of the barrier layer at the weld line (206). Although the barrier layer is not continuous across the weld line, sufficient overlap will create a tortuous path for permeation, and the barrier properties will be maintained... 

Typical processing methods - extrusion (blown film, cast film, coextrusion), coating ... 

Just as in the production of film, coextrusion is now an essential technique in the production of high performance blow molded containers. The parison is coextruded with a number of different layers, each of which contributes an important property to the finished package. 

Figure 5b First normal stress difference in PC and PC-ABS layers near the developing interface. Obtained from PTT viscoelastic simulation of the Cap-PC-PCABS-1 film coextrusion.

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