Tubular blown film

Poly(vinyl alcohol) is employed for a variety of purposes. Film cast from aqueous alcohol solution is an important release agent in the manufacture of reinforced plastics. Incompletely hydrolysed grades have been developed for water-soluble packages for bath salts, bleaches, insecticides and disinfectants. Techniques for making tubular blown film, similar to that used with polyethylene, have been developed for this purpose. Moulded and extruded products which combine oil resistance with toughness and flexibility are produced in the United States but have never become popular in Europe. 

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. 

The optical properties of tubular blown film depends greatly on the surface irregularities and the size of crystallites domain in film, which, in turn, are dependent on... 

Cakmak M. and Wang M.D., Structure development in the tubular blown film of PP/EPDM thermoplastic elastomer, Antec 89, 47th Annual Tech. Conference of SPE, New York, May 1, 1989, 1756. Hashimoto T., Todo A., Itoi H., and Kawai H. Domain boundary structure of styrene-isoprene block copolymer films cast from solution. 2. Quantitative estimation of the interfacial thickness of lamellar microphase systems. Macromolecules, 10, 377, 1977. 

The spiral die, commonly used to extrude tubular blown films, eliminates weld line effects and produces a thermally and geometrically homogeneous extrudate. The polymer melt in a spiral die flows through several feed ports into independent spiral channels wrapped around the circumference of the mandrel. This type of die is schematically depicted in Fig. 3.18. 

It is worth noting that, although in principle tube and tubular blown film dies are similar, in practice they are quite different in function, size, and complexity. Blown film dies are much longer, have a very small die lip opening, and are subject to more stringent product uniformity criteria because there is no sizing equipment downstream. Furthermore, blown film products are almost exclusively LDPE, and occasionally HDPE and PP. On the other hand, HDPE and rigid and plasticized PVC are the common polymers for pipes and tubes. 

Fig. 14.13 (a) Schematic representation of the tubular blown film forming operation, (b)... 

Vinex. [Air Prods.] Thennoplastic polyvinyl alcohol cqpOlymer lesin for extrusion, iiy. or blow molding, tubular blown film, bottles, fiber for industrial or personal care applies. 

Gusset g9-s9t [ME, piece of armor covering the joints in a suit of armor, fr. ME gousset] (ca. 1570) n. A tuck in the side of a bag, usually made in symmetrical pairs in both paper and plastic-film bags, that permit the bag to assume nearly rectangular-boxy form when opened. Gussets may be formed in the tubular blown film from which bags are made just before the film enters the pinch rolls. 

Bheda, J.H. and SpruieU, J.E. (1986) The effect of process and polymer variables on the light transmission properties of polypropylene tubular blown film. Polymer Engng Sci., 26, 736. 

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). 

Tubular-Blown Film Process. This process is more flexible with regard to the permissible polymer viscosity mismatch, control of film orientation balance in the transverse and machine directions through blow-up ratio, and easy randomization of film-thickness variations. Production rates are limited by flow rates per circumferential length of die (pressure drop) and cooling rates (heat transfer). 

Tubular-Blown Film Dies (Circular Dies). Tubular coextrusion dies were the earliest dies used to make multilayer plastic film. Successfiil design requires formation of uniform concentric layers in the annular die land formed by the mandrel and adjustable or nonadjustable outer die ring. Early designs included center-fed dies that had the mandrel supported by a spider (4). Feedports arranged a concentric melt stream that was pierced by the mandrel as it flowed to the die exit, forming anniJar layers. Limitations of this early design were discontinuity and nommiformity cansed by spider-induced weld lines in the layers. 

The design most commonly nsed today is the multimanifold spiral mandrel tubular-blown film die (Fig. la). This die consists of several concentric manifolds, one within the other. The manifolds are supported and secured through the base of the die. Each manifold consists of a flow channel that spirals around the mandrel. 

Another style of tubular-blown film die is the stackable plate die (Fig. lb). In this style of die, each layer is spread uniformly and formed into a tube in a single plate. Plates are then stacked on top of each other and the layers are added sequentially. This style of die is becoming popular for specific applications since the number of layers can be adjusted by simply changing the number of plates in the die. 

Tubular-blown- film dies are more tolerant of viscosity mismatch because the layers are arranged concentrically, ie, there are no ends. Since streamlines... 

Figure 10.39. Effect of nucleating agent on spherulite size in tubular blown films made out of polypropylene at different drawdown ratios. [Data from Bheda, J. H. Spruiell, J. E.,Pofym. Eng. Sci.,26,11,736 5, 1986.]...

Cao, B. and Campbell, G.A. (1990) Viscoplastic-elastic modeling of tubular blown film processing. AIChE J., 36, 420 30. 

Han C, Kwack T (1983) Rheology-processing-property relationships in tubular blown film extrusion. J Appl Polym Sci 28 3399-3418... 

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