Resin for a sizing composition, a process for its preparation and the sizing composition obtained

Claim 1

A composition of matter consisting essentially of a phenol formaldehyde and urea condensate for use in a sizing composition for mineral fibers wherein the phenol and formaldehyde are condensed by (a), heating together a preliminary mixture of phenol and formaldehyde at a temperature of about 45° C., the molar ratio F/P of formaldehyde to phenol being between 3 and 6 (b), raising the temperature up to between Ca 60° C. and 75° C. and thereby reacting phenol and formaldehyde after addition of a basic catalyst in an amount of 12 to 20 moles of hydroxyl equivalent for 100 moles of initial phenol, and maintaining this temperature until the phenol conversion rate is above 98% (c) cooling the reaction medium and introducing urea into the reaction medium, the molar ratio U/P of urea to initial phenol being between (F/P-2.55/2.6) and (F/P-2.55/0.7), said condensate being a liquid and having a free phenol content below 0.5%, a free formaldehyde content below 3% expressed by weight based on the total weight of liquid, a water tolerance measured at 20° C. of at least equal to 1000%, a storage stability of at least 15 days and a dry extract content of at least equal to 40%.