Patent ID: 7183330

Claim:
In a method for making a rigid polyurethane foam by reacting a polyisocyanate and a polyol in the presence of a urethane catalyst, a blowing agent, optionally water, and a silicone surfactant, the improvement which comprises employing a blowing agent comprising a C4 or C5 hydrocarbon, or mixtures thereof, with an average molecular weight of ≦72 g/mole and a boiling point in the range of 27.8 to 50° C., and 0.5 to 3.5 parts by weight per 100 parts polyol (pphp) of a silicone surfactant comprising a polyether-polysiloxane copolymer represented by the following formula: (CH 3 ) 3 —Si—O—(Si(CH 3 ) 2 —O) x —(Si(CH 3 )(R)O) y —Si(CH 3 ) 3 where R=(CH 2 ) 3 —O—(—CH 2 —CH 2 —O) a —(CH 2 —CH(CH 3 )—O) b —R″, and where R″ is H, (CH 2 ) z CH 3 , or C(O)CH 3 ; x+y+2 is 67–130; x/y is 5–14; z is 0–4; a+b is 10–18; the total surfactant molecular weight, based on the formula, is 7000–30,000 g/mole, the wt % siloxane in the surfactant is 32–70 wt %, the average molecular weight of the polyether portion is 450–1000 g/mole, and the mole % of ethylene oxide in the polyether portion is 70–100 mole %.