Phenol-formaldehyde adhesive for composite panels, e.g. plywood - obtd. by stagewise addn. of formaldehyde and alkali

摘要

Mfr. of aq. solns. of phenol-formaldehyde resins in a basic medium, comprises reacting phenol and formaldehyde, in a molar ratio of 1:0.3-1:0.9, by firstly condensing in a molten form. Resin obtd. is then condensed, if necessary after addn. of water, with corresp. quantities of alkali and supplementary formaldehyde at a pH 7 to the desired viscosity. Alkaline soln. is added in =2 stages, without exceeding 0.4 mole alkali per mole of phenol in the first stage, or in a continuous manner. Formaldehyde is introduced as paraformaldehyde. The phenol-formaldehyde mixt., if necessary under reduced press., is heated, and the reaction proceeds spontaneously. After the heat of reaction has abated the still liq. resin is dissolved in alkali and the mixt. heated, if necessary under reflux, until a clear soln. is obtd. Resins are used as glues for agglomerated panels, e.g., laminated plywood, their reactivity and stability to storage being little affected by the alkali content of the resin soln. They contain, per mole of phenol, 1.5-2.8 moles of formaldehyde and 0.6-1.6 moles alkali. For a viscosity of 150-600 mPas they have a dry residue of 35-48% by wt.