Cooling closed-cell foam

Under pressure in a closed mould during gelation. After cooling and demoulding, the expanded parts are re-heated (post-expansion) to obtain closed-cell foams such as life jackets. 

Closed-cell foams result when the decomposition and gelation are carried out in a closed mold almost filled with plastisol. After the heating cycle, the material is cooled in the mold under pressure until it is dimensionally stable. The mold is then opened, and the free article is again subjected to heat (below the previous molding temperature) for final expansion. Protective padding, life jackets, buoys, and floats are some items made by this process. 

In one of the few studies of plastic foam behavior at cryogenic temperatures Hingst discovered that upon cooling of closed-cell PUR foam in the 30-70 K range, an abrupt change in the linear temperature dependence of heat conduction occurs (Fig. 15). This phenomenon is closely related to the problem which we are... 

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. 

Foaming by discharging the melt into the atmosphere, on the other hand, produced closed cells with a mean cell diameter of ca. 500 LLm. The foam cells were polyhedral in shape and quite uniform in size, which is comparable to a commercial foam with a mean cell size of ca. 1.0 mm. But, the DDC foams contained slightly collapsed cellular structures. Seemingly, this foaming process created a more rapid and uniform cooling of the melt, causing a rapid build-up of viscosity, which substantially stabilized bubbles. 

Answer by Author Although I have not had any experience with Freon-blown foams, 1 would suggest that the condensation effects would be similar to that found with other closed-cell materials. In order to minimize or eliminate these effects, it is necessary to provide a perfect gas seal around the insulation and thereby preclude the possibility of air contacting the cold tank surfaces during the cool-down time. 

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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