abstract |
Processes for producing a polyurethane foam described herein include mixing a physical blowing agent with one or more of an isocyanate-reacting mixture and an isocyanate at a sorption pressure p sorp for a time t sorp , reacting the isocyanate-reacting mixture and the isocyanate at a pressure p 1 for a time t 1 , reducing the pressure to a pressure p 2 , maintaining the pressure at the pressure p 2 for a time t 2 , and reducing the pressure to atmospheric pressure p atm . In various embodiments, p atm <p 2 <p sat <p sorp and p sat <p 1 , where p sat is a saturation pressure for the physical blowing agent. |