Method of preparing closed cell phenol-aldehyde foam and the closed cell foam thus prepared

A method of preparing cured closed cell phenol-aldehyde foam consisting essentially of the steps of preparing a stable uncured closed cell froth of liquid phenol-aldehyde resole resin by frothing an admixture consisting essentially of

• (1) A frothable liquid phenol-aldehyde resole resin which consists essentially of the said aldehyde interpolymerized with the said phenol in a mole ratio of 2.0:10 to 3.0:1.0 under aqueous liquid phase conditions in the presence of an alkaline catalyst, the said liquid phenol-aldehyde resole resin initially having a pH above 3 as produced and also having a water content of less than 5% by weight and a viscosity of about 20,000-100,000 centipoises at a water content of 1% by weight and a temperature of 75.degree. F., the said liquid phenol-aldehyde resole resin being further characterized by a low exothermic heat of reaction whereby when 50 grams thereof having a pH of about 5 and a temperature of 80.degree. F. are placed in an open metal container of a size which results in a depth of the liquid resole resin of 3/8 inch and about 2 grams of an acid catalyst composition are vigorously admixed therein with a spatula for 30 seconds, the acid catalyst composition being present in an amount to provide a pH value below 3 and containing one gram of toluene xylene sulfonic acid and one gram of glycerin, then the internal temperature of the admixture while a liquid increases to a value not in excess of about 150.degree. F., the initially liquid admixture forms a solid within about 15 minutes, and the internal temperature of the said solid upon standing does not increase to a value in excess of about 180.degree. F. before decreasing to a lower value;
• (2) a volatile non-aqueous blowing agent for the said liquid phenol-aldehyde resole resin having a boiling point at atmospheric pressure of less than 212.degree. F.;
• and
• (3) a surfactant which is a stabilizing agent for frothed liquid phenol-aldehyde resole resin;
• the said uncured froth containing at least 90% of closed cells which have cell walls formed of the liquid phenol-aldehyde resole resin and the said closed cells being expanded by the volatile blowing agent in gaseous phase,
• shaping the said uncured froth into a desired configuration to provide an uncured preform thereof which likewise contains at least 90% of closed cells having cell walls formed of the liquid phenol-aldehyde resole resin,
• thereafter curing the liquid phenol-aldehyde resole resin in the cell walls of the said uncured preform to the solid state at a pH below 3 in the presence of a catalytically effective amount of an acid catalyst which promotes the curing of the liquid phenol-aldehyde resole resin to produce cured solid phenol-aldehyde foam containing at least 90% of closed cells, and
• maintaining the temperature throughout the interior of the said uncured preform during the curing thereof above the boiling point of the volatile blowing agent but less than 212.degree. F. and at a temperature sufficiently low to prevent further expansion of the said uncured preform in an amount to rupture the said cell walls of the closed cells and form an open cell structure, the liquid phenol-aldehyde resole resin in the said uncured preform having a sufficiently low exothermic heat of reaction in the presence of the said acid catalyst whereby the temperature throughout the interior of the said uncured preform may be maintained below 212.degree. F., and
• the said acid catalyst being present in the said uncured preform in an amount effective to provide a pH below 3 and promote the curing of the liquid phenol-aldehyde resole resin to the solid state and also present in a limited amount whereby the temperature throughout the interior of the said uncured preform may be maintained below 212.degree. F.

A method of preparing cured closed cell phenol-aldehyde foam consisting essentially of the steps of preparing an admixture consisting essentially of (1) a frothable liquid phenol-aldehyde resole resin which consists essentially of the said aldehyde interpolymerized with the said phenol in a mole ratio of 2.0:1.0 to 3.0:1.0 under aqueous liquid phase conditions in the presence of an alkaline catalyst, the said liquid phenol-aldehyde resole resin having initially a pH above 3 as produced and also having a low exothermic heat of reaction upon curing to the solid state at a pH below 3 in the presence of an acid catalyst whereby when 50 grams thereof having a pH of about 5 and temperature of 80.degree. F. are placed in an open metal container of a size which results in a depth of the liquid resole resin of 3/8 inch and about 2 grams of an acid catalyst composition are vigorously admixed therein with a spatula for 30 seconds, the acid catalyst composition containing one gram of toluene xylene sulfonic acid and one gram of glycerin and being present in an amount to provide a pH value below 3, then the internal temperature of the admixture while a liquid increases to a value not in excess of about 150.degree. F., the initially liquid admixture forms a solid within about 15 minutes, and the internal temperature of the said solid upon standing does not increase to a value in excess of about 180.degree. F. before decreasing to a lower value, (2) a volatile blowing agent for the said liquid phenol-aldehyde resole resin, (3) a surfactant which is a stabilizing agent for frothed liquid phenol-aldehyde resole resin, and (4) a catalytically effective amount of an acid catalyst which promotes the curing of the said liquid phenol-aldehyde resin, frothing the admixture to produce a stable uncured froth of the liquid phenol-aldehyde resole resin, the said uncured froth as produced being at a temperature below 212.degree. F. and below the effective minimum curing temperature therefor and having an exothermic heat of reaction which is sufficiently low to prevent the froth from reaching the said minimum curing temperature in the absence of heat supplied by an outside source, the said uncured froth containing closed cells which have cell walls formed of the liquid phenol-aldehyde resole resin and the said closed cells being expanded by the volatile blowing agent in gaseous phase, shaping the said uncured froth into a desired configuration to provide an uncured preform, heating the said uncured preform to an effective curing temperature above the boiling point of the volatile blowing agent but less than 212.degree. F., curing the liquid phenol-aldehyde resole resin in the cell walls of the said uncured preform to the solid state at a pH below 3, the said uncured preform being heated with heat supplied from an outside source and to a temperature sufficiently low to prevent further expansion of the said uncured preform in an amount to rupture the said cell walls and form an open cell structure, and maintaining the temperature throughout the interior of the said uncured preform during the curing thereof above the boiling point of the volatile blowing agent but less than 212.degree. F. and at a temperature sufficiently low to prevent further expansion of the said uncured preform in an amount to rupture the said cell walls of the closed cells and form an open cell structure to thereby produce cured closed cell phenol-aldehyde foam, the liquid phenol-aldehyde resole resin in the said uncured preform during the curing thereof to the solid state having a sufficiently low exothermic heat of reaction in the presence of the said acid catalyst whereby the temperature throughout the interior of the said uncured preform may be maintained below 212.degree. F.