Blow Molding Fluoropolymers

The best way for the reader to learn is to study actual examples of parts made by the blow molding of fluoropolymers. A majority of such parts have a multilayer construction to combine the properties of other plastics in a composite structure. The most common technique for producing multilayer sheet/film is coextrusion. The chemical resistance of fluoropolymers makes them attractive materials for inner layers of containers that come in contact with aggressive chemicals that can swell or degrade thermoplastics. 

Resin Type Oven Temperature, °C Transfer Pressure, MPa Cooling Pressure, MPa 

The three layers consisted of a fluoropol5mier inner layer, a polyolefin outer layer, and an intermediate tie layer that bonded them. The tie layer consisted of a polymer containing a blend of polyethylene-vinyl acetate and a block copolymer of styrene-ethylene-butadiene-styrene (SEES) or styrene-buta-diene-styrene (SBS) at a weight ratio in the range of 10 90 to 90 10. 

A container with a volume of about 2 liters was produced by coextrusion blow-molding according to the following procedure in aBekum BM-401 blowmolding machine (produced by Bekum America Corp., Williamston, Michigan). The fluoropolymer 

The materials were extmded and the molten parison was captured in a shuttle mold. The parison was blown with dry filtered air at 0.27-0.55 MPa at a mold temperature of 15°C-38°C. After molding, the container was allowed to cool in ambient air for 20 to 60 seconds. It was removed from the mold and had an average weight of 186 g. Thickness of the layers was 0.12-0.30 mm for the inner layer, 0.37-1 mm for outer layer, and 0.12-0.25 mm for the tie layer. 

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With the exception of two fluoropolymers, PVF and PTFE, the rest of the resins described in this entry can be processed by standard melt-processing techniques, such as injection, transfer and blow molding, extrusion, and rotational molding. Process equipment for fluoropolymers must be made from corrosion resistant alloys because of the corrosive compound that may be produced when fluoropolymers are heated above their melting points. Higher melt viscosity of these resins may require more powder and higher pressure rating equipment. 

Halar . [Ausimont] Ethylene chlorotri-fluoroeAylene copolymer, melt pro-cessable fluoropolymer for extrusion, itg. mtdding, blow molding, rotomold-ing, fluidized bed or electrostatic coating processes. 

The rest of this chapter discusses compression molding, transfer molding, blow molding, and vacuum bagging of fluoropolymers. 

Aside from PTFE and PCTFE, copolymers of TFE and a few other fluorocarbon polyuners are processed by melt-processing methods. Commercial fluoropolymers that have found application in chemical processing industries include PFA, FEP, ETFE, ECTFE, and PVDF. These plastics are fabricated into parts by common techniques such as injection molding, transfer molding, blow molding, compression molding, rotational molding, and extrusion (Table... 

Uses Fluoropolymer for extrusion, inj. moldrig, blow molding, rotomoldng this grade has low melt vise., suitable for inj. molding and extrusion (wire... 

Uses Fluoropolymer for extrusion, inj. molding, blow molding, rotomolding ... 

Uses Melt-processable fluoropolymer for extrusion (wire coating, tubing, film), inj. molding, blow molding, compr. molding, rotomolding, electrostatic coating, industrial... 

The many variations of the blow molding process are discussed later in this chapter, with an emphasis on those most important for processing fluoropolymers. Two features—the extruder and parison head—are common to many blow molding processes and will be discussed separately. 

The continuous extrusion blow molding process is the most widely used for working with fluoropolymers. In this process, the parison is extruded continuously from the parison head, between the open mold halves (Fig. 10.35). When the required length of parison has been produced, the mold is closed, trapping the parison which is severed by a hot knife. Land or pinch-off areas on the mold compress and seal the upper and lower ends of the parison to make an elastic air-tight object. Compressed air is introduced through the blow pin into the interior of the sealed parison which expands to take up the shape of the mold cavities. The cooled mold chills the blown object which can then be ejected when the mold opens. 

Another examplet 1 related to a coolant conduit consisting of multiple polymer layers that render the composite structure resistant to hydrolysis and pressure with high burst strength. Motor vehicle engines are an application for a tubular form of this conduit (Fig. 10.49). In a two-layer construction, the inner layer was comprised of a fluoropolymer such as ETFE, FEP, or PVDF that has been functionalized for compatibility with the polyamide outer layer. Such a tube was formed by blow molding. 

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