Abstract: Urea-modified, highly reactive phenolic resins useful as center-layer bonding agents in the manufacture of particleboard are provided by condensing phenol and formaldehyde until shortly before gelation takes place such that, after addition of urea, relatively low-alkaline, urea-modified phenolic resins are obtained which my optionally be stored and to which, shortly before processing them into glues for center-layer particles, alkali is added in sufficient quantities to ensure rapid cross-linking of the phenolic resin.

Abstract: The inventive concept is to condense the phenol formaldehyde resins to a higher molecular weight than usual so far. Subsequent addition of urea thereto reduces viscosity to normal levels and increases solid content.The added urea does not take part in condensation reaction but partly reacts in the alkaline medium with formaldehyde to methylol urea (in a so called equilibrium reaction), which is formaldehyde donor for the phenol formaldehyde crosslinking reaction during the pressing of the particle board.The present invention relates to a process for producing modified phenolic resin bonding agents, characterized by preparing as known per se phenol-formaldehyde resins with a viscosity of more than 300 mPa.s (at 20.degree. C.