Adhesive for wood products - contg. lignin sulphate deriv. and phenol- formaldehyde resin

摘要

Adhesive for prodn. of products from wood (e.g. plywood or chipboard) composed of (a) a lignin sulphate deriv. and (b) a phenol-formaldehyde resin, the predominant propn. by wt. of the lignin deriv. having a M.W. 5000. Pref. the wt. ratio of (a):(b) lies between 90:10 to 20:80, esp. between 70:30 to 20:80. (a) and (b) may be dissolved in water, the resulting soln. having a water content of 30-70 wt.%. Pref. the adhesive contains, a hardener, an effective amt. of an aldehyde chosen from formaldehyde, paraformaldehyde or furfural, and a diluent in the form of chalk, wood- or wheat-fluor. The adhesive may also contain paraffin. The adhesive is cheaper than prior art prods. contg. (b) alone. Since it is relatively alkaline it causes no corrosive or hydrolytic damage on veneers, in contrast to acidic adhesives. Suitable lignin derivs. are lignin sulphates obtd. from alkaline decompsn. processes, e.g. the Soda process, whose reaction medium contains NaOH, or thesulphate process, which contains NaOH, Na2S and NaSH, or the oxygen-alkali process. The M.W. distribution of the prod. should be such that 50 wt. % of the lignin sulphate has a M. W. 5000. In order to ob. this M. W. distribution, an ultra-filtration process can be used. Both resole and novalac types of phenol-HCHO resin can be used for the adhesive.