Open-Cell Vinyl Foams

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-... 

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 newer open-cell foams, based on polyimides (qv), polybenzimidazoles, polypyrones, polyureas, polyphenylquinoxalines, and phenolic resins (qv), produce less smoke, are more fire resistant and can be used at higher temperatures. These materials are more expensive and used only for special applications including aircraft and marine vessels. Rigid poly (vinyl chloride) (PVC) foams are available in small quantities mainly for use in composite panels and piping applications (see Flame retardants Hrat-rrststantpot.ymf.rs). 

Soft, very flexible vinyl foams used for garment insulation, upholstery and similar applications are made by this CBA process. The more rigid foams used as underlays for rugs and flooring can also be made by this method, but require different plastics and lower plasticizer contents. Open-cell chemically blown vinyl foams generally have densities in the range of 5 to 30 lb/ft3. 

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. 

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 1565-81 A Standard Specification for Flexible Cellular Materials Vinyl—Chloride Polymers and Copolymers (Open-Cell Foam), 9 pp (DOD Adopted) (FSC 9320) (MR) (Comm D-11)... 

ASTM D 1565, Flexible cellular materials Vinyl chloride polymers and copolymers (open cell foam). 1981. 

The elastomer process is very similar to the Dennis process involving a number of steps in which a gas, formerly carbon dioxide and now fluorocarbon, is mixed with a plastisol under pressure. When released to atmospheric pressure, the gas expands the vinyl compounds into a low density, open-cell foam that is then fused with heat. 

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. 

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