Patent GB-1115942-A (GB)
Title: Wood products and their manufacture
IPC: C08L97/02
Filed: 1965-08-16
Abstract: A wood-containing product is formed by (a) depositing a mat of comminuted wood coated with thermosetting resin; (b) applying to the mat surface a layer of wood fibres mixed with an aqueous phenol-formaldehyde resole resin solution; (c) applying to the surface from (b) a coating of aqueous phenol-formaldehyde resole resin; and (d) heating and compressing to consolidate. In step (b) the wood fibres have bulk density up to 0.16 g./c.c. and have one dimension significantly greater than the other two dimensions; they may be formed by defibration of chips of e.g. Douglas Fir, Hemlock, Pine, Cedar, White Fir, Gum, Willow,Poplar, Cherry, Birch, Persimmon, Sycamore, Ash, Elm, Maple, Beech, Hackberry, Oak, or Hickory.  The aqueous resins used in steps (b) and (c) are alkali-catalysed phenol-formaldehyde resole with number-average MW up to 5000, e.g. 140-550, containing 1.0-3.0 mole combined formaldehyde per mole phenol.  The total moisture content just before hot-pressing is defined in terms of the MW of the resins by a formula and is desirably 15-65 wt. per cent based on dry fibre. The pH may be 4-8 or higher.  The fibre/resin mixture contains 5-50 wt. per cent resin solids, based on fibre. In step (c) 1-15 lb. resin solids per 1000 sq. ft. are employed. The resin in steps (b) and (c) may also contain oil, wax, soaps, surfactant, parting agent, vinyl or vinylidene polymer, pigments, metal flake, stone chips, clay, wollastonite, melamine - formaldehyde, urea-formaldehyde, or epoxy resins.  The thickness laid in step (b) should be 6-50 mils when consolidated. The comminuted wood of step (a) may be of any type, for example those named above, and may be in the form of hammermillground wood chips. The resin in step (a) may be a highly alkaline phenolic resin, phenolformaldehyde condensate, aminoplast, e.g. melamine- or urea-formaldehyde, epoxy resin, or proteinaceous adhesive, usually in aqueous solution or dispersion, preferably 5-20 wt. per cent resin solids being used, and the moisture content of the resin-wood mixture is preferably 4-15 wt. per cent, these percentages being based on dry wood.  Preferably, in step (a) a mat of 250-1000 lb./1000 sq. ft. is deposited. The step (b) mat may be formed on the substrate or preformed on a vacuum screen and transferred to the substrate; it may be rolled up and then unrolled on the substrate.  Step (c) may be performed by spraying, or by coating a caul with resin, drying, placing the coated caul on the fibre-resin layer previously formed on the mat from step (a), and hot-pressing the assembly. Step (d) may be performed at 240-320 DEG  F. at 175 p.s.i. for 6.5-7.5 minutes; the resulting structure may be e.g. 1/16 -\ba1/4 inch thick, and have s.g. of e.g. 0.45-0.85.  A paper sheet may be included in the overlay, or decorative thermoplastic films may be applied. The article may be used as a surface veneer in a plywood in which e.g. 4 plies are of Douglas fir veneers. Other surfaces to which the product may be applied are wood, metal, ceramics, tile, glass, cement, or plaster.ALSO:A coated wood-containing product is formed by (a) depositing a mat of comminuted wood coated with thermosetting resin; (b) applying to the mat surface a layer of wood fibres mixed with an aqueous phenol-formaldehyde resole resin solution; (c) applying to the surface from (b) a coating of aqueous phenol-formaldehyde resole resin; and (d) heating and compressing to consolidate.  The aqueous resins used in steps (b) and (c) are alkali-catalyzed phenol-formaldehyde resole with number-average MW up to 5000, e.g. 140-550, containing 1.0-3.0 mole combined formaldehyde per mole phenol.  The total moisture content just before hot-pressing is defined in terms of the MW of the resins by a formula and is desirably 15-65 wt % based on dry fibre.  The pH may be 4-8 or higher.  The fibre-resin mixture contains 5-50 wt % resin solids, based on fibre.  In step (c) 1-15 lb resin solids per 1000 sq. ft are employed.  The resin in steps (b) and (c) may also contain oil, wax, soaps, surfactant, parting agent, vinyl or vinylidene polymer, pigments, metal flake, stone chips, clay, wollastonite, melamine-formaldehyde, urea-formaldehyde, or epoxy resins.  Step (c) may be performed by spraying, or by coating a caul with resin, drying, placing the coated caul on the fibre-resin layer previously formed on the mat from step (a), and hot-pressing the assembly.  Step (d) may be performed at 240-320 DEG F at 175 psi for 6.5-7.5 minutes; the resulting structure may be e.g. 1/16 -\ba1/4 in. thick, and have s.g. of e.g. 0.45-0.85.