Film casting

FIGURE 9.16 (a) Sectional view of chUl-roll casting, (b) Sectional view of water bath casting. 

Consider the origin of the Cartesian coordinate system, Jtyz, at the intersection of the line of symmetry and the die lips (Fig. 9.17). The original width of the polymer film (in the X direction and at the die lips) is Wq and the extension length is L. The width of the film decreases along the z direction, because the film is being drawn in that direction by the chill-roll. Its width at the roll is wl. Similar drawing takes place in 

FIGURE 9.17 (a) Geometry of the front view of the film-casting process. The polymer film between 

The die swell effect is neglected here as was done in the fiber-spinning analysis. In film casting no significant cooling is obtained between the face of the die and the chill-roll (see Section 5.2), whereas in the melt spinning of fibers cooling was very important. If the z component of the film velocity at the die lips is v o and at the freeze line is v, then the draw ratio, T)r, is defined as (see Eq. 9.27) 

Typical values of the draw ratio range from 2 to 20. 

290 °C. Symbols represent experimental measurements, while full lines are simulation predictions using a Giesekus model with crystallization [108]. 

In contrast to the fiber-spinning process, the film-casting process has received less attention in the literature. Dobroth and Erwin [109] examined the causes of thick edges or the edge bead effect (also called the hone effect) and attributed it to the change from planar extension in the center of the film to uniaxial extension at the edges. 

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Cast babbitts Cast film Cast film process Casting... 

Fig. 8. Schematic of methods for MLC manufacturing (a) belt casting (b) carrier film casting using a doctor blade.

Extmsion technology is used to produce spunbond, meltblown, and porous-film nonwovens. Fabrics produced by these systems are referred to individually as spunbonded, meltblown, and textured- or apertured-film nonwovens, or genericaHy as polymer-laid nonwovens. These fabrics are produced with machinery associated with such polymer extmsion methods as melt-spinning, film casting, and extmsion coating. In polymer-laid systems, fiber stmctures are simultaneously formed and manipulated. 

In the filtration of small amounts of fine particles from liquid by means of bulky filter media (such as absorbent cotton or felt) it has been found that the preceding equations based upon the resistance of a cake of solids do not hold, since no cake is formed. For these cases, in which filtration takes place on the surface or within the interstices of a medium, analogous equations have been developed [Hermans and Bredee, J. Soc. Chem. Ind., 55T, 1 (1936)]. These are usefully summarized, for both constant-pressure and constant-rate conditions, by Grace [Am. In.st. Chem. Eng. J., 2, 323 (1956)]. These equations often apply to the clarification of such materials as sugar solutions, viscose and other spinning solutions, and film-casting dopes. 

Solution processes are used mainly for coating, film casting and fibre spinning, i.e. in processes where the distance the solvent has to diffuse out of the solution once coated, cast or spun is short. Regulation of this diffusion process is important if products of even quality are to be obtained. 

An important application for polypropylene is film tape. This is made by slitting unoriented film (cast or blown) into tapes 2 or 3.5 mm wide and stretching under heat about seven-fold. With cast film the orientation is more completely monoaxial and there is a tendency for the film to split along its length (fibrillate). Tubular film does not self-split so easily and also has a somewhat softer feel. Such tapes may be woven into sacks and these have... 

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. 

To produce resins for paints and for electrical insulation, film cast from solution copolymers based on bis-phenol A and bis-phenol Z (l,l-bis-(4-hydroxyphenyl)cyclohexane) have been used. 

Quite often, NBR adhesives are used to bond various kinds of gasketing (cork, fibre, foam, rubber, metal) to rigid superstructures, such as aircraft. Films cast from solution are often used to fabricate honeycomb structures for aircraft. 

As an indication of the changes in deformation modes that can be produced in ionomers by increase of ion content, consider poly(styrene-co-sodium methacrylate). In ionomers of low ion content, the only observed deformation mode in strained thin films cast from tetra hydrofuran (THF), a nonpolar solvent, is localized crazing. But for ion contents near to or above the critical value of about 6 mol%, both crazing and shear deformation bands have been observed. This is demonstrated in the transmission electron microscope (TEM) scan of Fig. 3 for an ionomer of 8.2 mol% ion content. Somewhat similar deformation patterns have also been observed in a Na-SPS ionomer having an ion content of 7.5 mol%. Clearly, in both of these ionomers, the presence of a... 

Thermal treatment and the nature of the casting solvent can also affect the deformation modes achieved in strained films of ionomers. For example, in films cast from polar dimethylformamide (DMF), the solvent interacts with ion-rich clusters and essentially destroys them, as is evident form absence of a second, higher temperature loss peak in such samples. As a result, even in a cast DMF sample of Na-SPS ionomer of high ion content (8.5 mol%), the only deformation mode observed in tensile straining is crazing. However, when these films are given an additional heat treatment (41 h at 210°C), shear... 

The diffusion of oxygen through polymer films has been examined by a number of workers. Guruviah measured the permeability to oxygen of films cast from five paints (Tabic 14.4) and compared the results with the... 

An examination has, therefore, been made of the effect of solutions of potassium chloride on the electrolytic resistance of films cast from a penta-erythritol alkyd, a phenolformaldehyde tung oil and an epoxypolyamide varnishPotassium chloride was chosen because its conductivity is well known and unpigmented films were first examined in order to eliminate the complexities of polymer/pigment interaction. 

The PIA-investigations were carried out under dynamic vacuum (p< 10 5 mbar) and at 77 K with films cast from toluene solution onto KBr substrates. For the dispersive method [29, 30] the globar, the KBr-prism premonochromator, and the grating monochromator of a Perkin Elmer 125 lR-spcctrometer were used in the spectral range of 0.25 to 1.24 eV. The pump beam was chopped mechanically... 

The microphase structure was clearly observed in transmission electron micrographs of the film of amphiphilic copolymers cast from aqueous solutions [29, 31]. An important finding was that no microphase structure was observed for the film cast from organic solutions. This difference indicates that a microphase structure is formed in aqueous solution, but not in organic solution. Different hydrophobic groups showed considerably different morphological features i.e. whether microphase separation leads to a secondary or higher structure depends on the type of hydrophobic units in the copolymers [31],... 

Clay films cast from a pure aqueous colloid appear to form a regular array of microplatelets, thin films of which show selective cation exchange, e.g. segregation of Ru(bipy)i from Na" and methylviologen dication and even partial separation of the enantiomers of Co bipy)3 Thicker films (approx. 3 pm) can be supported by the addition of polyvinyl alcohol additive also aids swelling of the... 

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. 

Buffington and Stevens measured the c.d. of 2-acetamido-2-deoxy-D-glucose as a film cast from HFIP. The spectrum is considerably more intense than that observed by Dickinson and coworkers for a solution in HFIP, but shows the same general features shifted somewhat towards the red. This vacuum-u.v. c.d. spectrum (see Fig. 18) has, at 218 nm, an intense, positive band due to the mr, an intense negative band due to the amide tttt at 200 nm, and a shoulder at 180 nm, but no other significant features down to 145 nm. 

The c.d. spectra of chitin, both in HFIP solution and as a film cast from HFIP, are shown in Fig. 21. Chitin gels have a c.d. spectrum similar to... 

A separate approach to the problem of VOC release during film formation is the use of polymer films cast from aqueous emulsions. Alkyd emulsions in particular have been proposed as new environmentally friendly paints and have therefore... 

Cyclic voltammetry was performed on precursor polymer thin films cast on platinum electrodes in order to assess the possibility of electrochemical redox elimination and consequently as an alternative means of monitoring the process. All electrochemical experiments were performed in a three-electrode, single-compartment cell using a double junction Ag/Ag+(AgN03) reference electrode in 0.1M... 

Figure 11,5 schematically outlines the process of film casting. The molten output from an extruder is pumped through a heated pipe to the top of a slot die, whose exit is pointed... 

We use extrusion coating to apply thin layers of polymer to the surface of non-polymeric substrates such as cardboard or aluminum foil. Extrusion coated materials are extensively used in food packaging. Products include the coated cardboard used to make milk cartons and the coated aluminum foil used to seal dairy product tubs. The process of extrusion coating has much in common with film casting. 

Rank the following polypropylene conversion processes in terms of their relative sensitivity to particulate contamination, film casting, injection molding or fiber spinning. 

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