| 摘要 |
Closed-cell phenolic foam having a uniform cell structure in which the cell walls are substantially free of both ruptures and perforations is disclosed. The phenolic foam has initial k values of less than 0.15 with substantially no increase of k value over time and good density and compressive strengths. The phenolic foam is prepared by foaming and curing a foamable phenolic resole composition containing an aqueous phenol formaldehyde resole, surfactant, fluorocarbon blowing agent, and optionally other additives with an acid foaming and curing catalyst in a substantially closed mold which exerts a restraining pressure on the foaming composition in excess of ambient atmosphericpressure of greater than about 3 pounds per square inch. The aqueous phenol formaldehyde resole is essentially a phenol formaldehyde condensation polymer having a molar ratio of formaldehyde to phenol of from about 1.7:1 to 2.3:1, preferably from 1.75:1 to 2.25:1 and most preferably about 2:1. The resole has a weight average molecular weight greater than 800 and preferably from 950-1500. The resole also has a number average molecular weight greater than about 350 and preferably from about 400 to about 600 and a dispersivity greater than about 1.7, preferably from 1.8 to 2.6. The acid foaming and curing catalyst is an anhydrous aryl sulfonic acid having a pKa less than about 2.0 and which changes the compatibility of the phenolic resole with water. The preferred anhydrous aryl sulfonic acid is a combination of toluene sulfonic acid and xylene sulfonic acid. |
