Neoprene Calendering

Polychloroprene (Neoprene), 19 828-866 from butadiene, 4 384t calendering and extrusion of, 19 851 commercial conversion of, 19 846-851 compared with EPDM and natural rubber, 19 846t... 

Many different synthetic elastomers are also compounded and calendered to form sheet lining materials. Examples are neoprene, Hypalon, butyl and chlor-butyl rubber. 

Selfelastomeric materials may be compounded and calendered with a chemical curing agent which will, over a period of time, slowly cure the sheet at ambient temperatures. This type of curing is primarily noted in natural rubber and neoprene sprayed and troweled coatings, and has not, in recent years, been, to the writer s knowledge, employed for total cure of sheet linings. 

While calendering the Neoprene stock it must be prewarmed uniformly before being fed into the calender rolls. Stock temperature will change as the quantity of the stock at the nip varies. This causes fluctuation in viscosity of the stock and in roll pressure leading to rough sheet with differing thickness. Roll temperature in calendering must be accurately... 

While sheeting in a calender, the stock must be soft so that they penetrate the interstices of the layers easily, and tacky so that ready adhesion between plies is ensured. Inevitably, such stocks can give rise to handling problems and call for compromise compounding . Natural rubber and Neoprene rubbers compounded with resins such as coumarone indene or petroleum resin produce good sheeting stocks. 

Extrusion. Polychloroprene has been employed in a wide variety of extrusion (qv) processes. Intricate cross-sections such as highway compression seals, bulb weather-stripping, and hose represent a few examples. As with calendering, extrusion is very sensitive to nerve. The DuPont Dow neoprene sol/gel blend types are best suited for extrusion applications. Use of low levels of highly structmed furnace carbon blacks, stearic acid, petroleum, paraffin wax, triethanolamine benzoic acid, and calciiun stearate are particularly effective extrusion aids. The screw of the extruder should have a constant diameter root with increasing pitch. Heat history of the compound should be minimized, with only a brief warm-up before extrusion begins. The barrel and screw should be lun cool, 50°C, and the die hot, 95°C (96,119). 

Thiokol FA parts that require good tack for building may need a slight increase in the level of MBTS to 0.5 or 0.6 phr if the compound is calendered, but this would probably be too high for extrusion. The addition of 5 phr of a coumarone indene resin such as Cumar P25 will also improve tack. Blends of Thiokol FA with neoprene are usually tacky enough for most applications. 

Chem. Descrip. Epoxidized unsat. soy bean oils CAS 8013-07-8 EINECS/ELINCS 232-391-0 Uses Sec. plasticizer, costabilizer for flexible PVC, plastlsols, calendered and extruded prods., wetting of pigments, chlorinated paraffins, alkyd resins, neoprene, ethyl/cellulose, PVC/PVA emulsions Properties Gardner 3 max. cl. liq. dens. 0.99 g/ml vise. 3-7 poise acid no. 1.0 max. ref. index 1.473 7.0% min. cone. 

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