Vinyl closed cell foams

Foams made from vinyl resins are of two types, open-cell and closed-cell. The open-cell foams are soft and flexible, whUe the closed-cell foams are predominantly rigid. Both types are made from plastisols, which are suspensions of finely divided resins in a plasticizer. The polymer does not dissolve appreciably in the plasticizer until elevated temperatures are used. 

ASTM D 1667-76 (1986) Standard Specification for Flexible Cellular Materials—Vinyl Chloride Polymers and Copolymers (Closed-Cell Foam), 6 pp (DOD Adopted) (FSC 9320) (YD) (Comm D-11)... 

Nitrosan ). This blowing agent is unique in that its low decomposition temperature permits the expansion of vinyl plastisol prior to gelation (93°C). Subsequent fusion at 177°C produces open-cell vinyl foam. Closed-cell foam can be produced by heating to fusion in a closed mold, releasing the pressure and subsequently heating in an oven at 100°C. 

The Dynamit-Nobel extmsion process (252) utilizes a volatile plasticizer such as acetone which is injected into the decompression section of a two-stage screw and is uniformly dispersed in the vinyl resin containing a stabilizer. The resulting PVC foam has low density and closed cells. 

BXL Plastics ERP Division is to introduce new grades of antistatic and conductive closed-cell crosslinked PE and ethylene copolymer foam at the Internepcon Exhibition to meet a growing demand from the electronics industry, for ways of minimising the effect of static electricity on circuits embodying static-sensitive devices, particularly using metal oxide/silicone technology. Very brief details are noted of Evazote C conductive closedcell, crosslinked ethylene-vinyl acetate copolymer foam. 

The moisture resistance, low cost, and low-density closed-cell structure of many cellular polymers resulted in their acceptance for buoyancy in boats, floating docks, and buoys. Because each cell is a separate flotation unit, these materials cannot be destroyed by a single puncture. Foamed-in-place polyurethane between thin skins of high tensile strength is used in pleasure craft [98]. Other cellular polymers that have been used where buoyancy is needed are produced from polystyrene, polyethylene, poly(vinyl chloride), and certain types of rubber. Foams made from styrene-acrylonitrile copolymers are resistant to petroleum products [99,100]. 

According to Thomas elastic polymers often produce open-cell foamed plastics, whereas rigid polymers generally form closed-cell materials. However, there are many exceptions to this rule, owing to the variety of blowing techniques. Closed-cell structures are more likely to be produced from polyurethanes, epoxy resins, silicones, poly(vinyl chloride), polystyrene, etc., whereas open-cell materials mainly result from phenolic and carbamide foamed plastics. 

AMS 3635C-84 Plastic Sheet and Strip, Modified Vinyl, Foamed, Closed Cell, 7 pp (DOD Adopted) (FSC 9330) (AS)... 

The Kleber-Colombes rigid PVC foam (265,266) is produced by compression molding vinyl plastisol to react and gel the compound, followed by steam expansion. The process involves mixing, molding, and expansion. The formulation consists of PVC, isocyanate, vinyl monomers such as styrene, anhydrides such as maleic anhydride, polymerization initiators, FC-11, and nucleators. The ingredients are mixed in a Werner-Pfleiderer or a Baker Perkins type of mixer, and the resulting plastisol is molded under pressure. The initial temperature of the molds is 100-110°C, which increases to 180-200°C because of exothermic polymerization of the vinyl monomers and anhydride. The mold is cooled and the partially expanded PVC is removed and then further expanded by steam. After the water treatment, the foam is thermoset with a closed-celled structure and a relatively low thermal conductivity. 

Molded Vinyl Foam With other materials such as urethanes and elastomers, most foam products are molded. They are either allowed to expand under low pressure to fill the mold, yielding an open cell stmcture, often with a skin (as in, e.g., crutch pads) or molded and thermoset under pressure and subsequently expanded in an oven, yielding a closed cell structure (as with foam rubber shoe soles or mattress components). The products of oven expansion, referred to as buns, can be skived and die cut to gaskets or seals. The latter process is also carried out with vinyl. Molds are filled with plastisol, fused and cooled under pressure, and then expanded in an oven at 100-120 °C, softening the polymer and enabling the trapped gas to expand. For highly defined shapes, this step can be carried out in a second mold. 

The open-cell vinyl foams produced by mechanical frothing, is used to produce sheets, such as flooring underlay, wall coverings, and other applications requiring relatively close thickness tolerances. Plastisol is mixed with a given amount of air in a high-shear, temperature-... 

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