Foamed cold-cure

PIPA polyols, in spite of some disadvantages (tendency to foam shrinkage, and scorching), are used successfully for continuous slabstock flexible PU foams and high resilience foams (cold cure moulding process). 

Cold-curing foams use polyethers of somewhat higher molecular weight (-4500-6000) and which have a higher proportion of primary hydroxyls than are used for hot moulding. In addition the isocyanates used have a functionality greater than 2, this being achieved by the use of modified isocyanates. 

Cold curing permits the formation of dual density foam products. We either sequentially inject different formulations or we mold the first foam then mold the second around or on top of it. When making dual density foams, it is important that the first component develop a continuous skin prior to the injection of the second reactive mixture. 

Cold cure" or high resilience PU foams tended to liquify before igniting were developed and gave good results in standard tests such as BS 4735(25) (similar to the discontinued ASTM D1692) but could still burn when used with flammable fabrics in furniture (Table IV). However they have been used most successfully in the UK in combination with flame retarded cotton interliners and fabrics of low flammability e.g. wool, nylon, FR cotton etc. and formed the basis of public area furniture used in the UK since the early 1970 s (Table V). 

Soviet scientists have developed a cold-cure EDS material87). Note that the epoxy binders used are in fact generally hot-cure oligomers (from the point of view of the functional groups used and the completion of cure). It turned out that the forced elastic limit and the compression elastic modulus of the matrix are the same for both hot and cold cures. The good mechanical properties of a cold cured syntactic foam seem to be due to strong intermolecular bonds. 

The mechanical characteristics of the epoxy and polyester cold-cured syntactic molded foams do not differ much from the hot-cured materials (Table 12)1),... 

Table 12. Properties of Cold-Cured Syntactic Foams...

In the author s opinion the most promising route is the rapid transition from the technology of producing materials to that of producing finished products which do not require secondary treatment. It should be noted that this teclmique has been successfully used for a long time to prepare models from foams on the basis of reactive oligomers cold-curing compositions enable to produce articles of the most intricate confipiration directly at the site of utilization ... 

In recent years, HR foams have been prepared by using almost the same molding conditions as cold-molded foams, i.e., low mold temperature using the MDI-TDI blend formulation. However, in the development stage of HR foam, only TDI-based formulations were used, which required hot-mold conditions. For these reasons HR foams are not exactly equal to cold-cure foams. However, in recent years, HR foams have been produced by blends of MDI and TDI. The resulting foam systems can be molded at the same molding conditions as those for cold-molded foam systems. 

C02 blown foam - A polyurethane foam in which all of the gas from expanding or blowing is carbon dioxide (CO2) generated by the chemical reaction between water and isocyanates also called water-blown foam (3). cold-cure foam - See Cold molding. 

The polyether triols are the most important class of polyether polyols and they are used in flexible PU foam fabrication. The majority of polyether triols used in flexible foams are copolymers of PO-EO. Random copolymers are used in continuous slabstock flexible foams and block copolymers (PO-EO), with terminal poly[EO] block, are used in moulded foams (hot moulding and cold cure moulding processes). 

PHD polyols are successfully used for high resilience flexible PU foams (made by the cold cure process), for continuous slabstock flexible PU foams and for elastomers obtained especially by reaction injection moulding (RIM) technology. 

Advances in urethane processing involve changes in starting chemicals as well as improvements in processes. The chemicals have led to the use of low-cost polyether polyols, high-resilience (HR) "cold cure" foams, safer to handle than prepolymers, catalysts, and chain extenders. A major process improvement was the use of flat-top bun technology for low-density urethane foams. This technology... 

A good deal of flexible urethane foam is now being made by the cold-cure technique. This involves more reactive polyols and isocyanates in special foaming formulations which would cure in a reasonable time to their maximum physical properties without the need for additional heat over and above that supplied by the exothermic reaction of the foaming process. 

Cold-cure foaming is used in the production of what is known as high-resilient foams having high sag factor (i.e., ratio of the load needed to compress foam by 65% to the load needed to compress foam by 25%), which is most important to cushioning characteristics. True cold-cure foams will produce a sag factor of 3-3.2, compared to 2-2.6 for hot-cured foams. 

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