GB694734A - Improvements in or relating to the preservative impregnation of wood - Google Patents

Abstract

Wood impregnated with oil-borne preservative compounds such as toxic salts is subjected in a closed space to solvent vapours whereby the wood is heated and excess toxic salts extracted from the wood by solvent condensing on the wood. The wood is then subjected to a vacuum to remove condensate and excess impregnant oil. The vapours may be those of the oil used in the impregnant or a different solvent of the same or lower or higher boiling point. In the last instance the vacuum treatment may be omitted. Preferably the treatment with vapour and vacuum is repeated until there is a uniform concentration of preservative throughout the wood and the wood is substantially free from impregnant oil. The heating temperature is kept below 400 DEG F to avoid damage to the wood, solvents with boiling points not higher than 320 DEG F and not lower than 240 DEG F, unless non-inflammable, being preferred. Examples of solvents are V M and P naphtha, Stoddard solvent, toluene, xylene, trichlorethylene and perchlorethylene. Examples of preservative compounds are copper zinc and mercury organic compounds, chlorinated and nitrated organic aromatic compounds and miscellaneous compounds such as beta-naphthol, orthophenylphenol, rosin amine and rosin amine acetate. Examples of the treatment of pine impregnated with copper naphthenate and using a variety of vapours are given, together with figures for copper, oil and moisture concentrations in various parts of the wood after treatment. The treatment is stated to prevent bleeding and surface accumulation of preservative and to remove natural wood resins and gums, making the surface receptive to paint. It is stated that the process is applicable to wood fibre compositions such as wallboard as well as wood in the natural state. Specifications 655,064, 687,113, [both in Group VIII], 6844/02, 19737/04 and 24451/04, [all in Class 140], are referred to.