| 摘要 |
Disclosed is an improved phenol formaldehyde (PF) resin that does not require fillers or extenders and is capable of bonding wafers or veneers having a moisture content of 10% or above. In the case of veneers exceptional results are obtained when the permeability of the veneer is increased by incising. The adhesive compositon is prepared by mixing together a caustic solution of a high molecular weight PF resin, a dispersion of PF resin which is characterised in that it can swell in aqueous caustic medium but not go into solution, and a chemical which is capable of reacting with resins in both the continuous and the disperse phase, such as alkylene carbonates or phenol resorcinol formaldehyde (PRF) resins. Optionally, a component may be used such as borax which is capable of complexing with resins in the continuous and the disperse phase. The disperse phase is made by converting a solution of a PF resin into a fine particle size particulate form by precipitation, spray drying or freeze drying and partially cross-linking the resin during or subsequent to the formation of the fine particle size dispersion. The PF resin is partially cross-linked by (a) heat, by (b) acid catalysis, or by (c) a reaction with cross-linking chemicals such as cyclic carbonates or epoxy compounds or by a combination of (a) (b) and (c). The disperse phase may be made from a PF resin or from a resin in which some of the phenol has been replaced by other phenolic chemicals such as resorcinol, catechol, or kraft lignin. The chemical capable of reacting with resins in the continuous and the disperse phase may be a cyclic carbonate or a phenol resorcinol resin. Also disclosed is a wood product produced from veneers having moisture contents at 10% or above and incised to improve their permeability to gases and liquids.
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