Plastic and nonmetallic article shaping or treating: processes – Forming articles by uniting randomly associated particles
Reexamination Certificate
1999-12-10
2002-06-11
Vargot, Mathieu D. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Forming articles by uniting randomly associated particles
C156S062200, C264S122000, C264S134000
Reexamination Certificate
active
06403000
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method for the preparing lignocellulosic particles, soft boards and board precursors in sheet form, for the manufacture of a finished product.
It is well known to manufacture composite board products from wood derived feed stocks. Examples are medium density fibre board (MDF), high density fibre board, orientated strand board, chip board and the like. Such boards are most frequently bound by condensation resins such as the urea, melamine or resole phenol formaldehydes. A new trend is to use agricultural fibre as a feed stock, because excellent fibre is produced, the resource is rapidly regenerative, it removes the pressure on the timber resource and logistical constraints are alleviated. In this case the isocyanates are the desired binder because the nature of the surface and composition of agricultural fibres, the particle shape and specific surface area give rise to more critical binder requirements.
In the case of all lignocellulosic composite board products, plywoods, paper products and solid timber, particularly the softwoods and the marginal hardwoods, water is by far the greatest contributor to degradation.
There is therefore a requirement for the treatment of lignocellulosic products to make them highly water resistant.
This requirement may be achieved by the pre-treatment of lignocellulosic materials in particulate form as feed stock for board production, or veneers for plywood production, or by the post treatment of composite boards themselves, such as chip board or MDF, pulp and paper products and solid timber. DE 4 223 604A discloses the impregnation of cellulosic materials with a solution of one or more water-insoluble polymers, copolymers, oligomers, prepolymers or monomers (inter alia isocyanate thermosetting resins) dissolved in organic solvents (inter alia petrol).
Subsidiary improvements such as improved mechanical properties, behaviour in fire, absence of formaldehyde and resistance to microbial or insect attack may also be provided for.
There is always the need for improved methods of manufacture of products from lignocellulosic materials.
SUMMARY OF THE INVENTION
According to a first aspect of the invention there is provided a method of manufacturing a finished product from a lignocellulosic material, selected from the group consisting of lignocellulosic particles or fibres, soft boards, and board precursors in sheet form, which method includes the steps of:
(a) impregnating the lignocellulosic material with an impregnating composition comprising:
(i) a mineral oil; and
(ii) a liquid thermosetting resin and, if necessary, a catalyst therefor; in the form of a dispersion of the liquid resin in the mineral oil; and
(b) compressing the impregnated lignocellulosic material with heating to allow the mineral oil to infuse the lignocellulosic material and to polymerise the thermosetting resin to form the finished product.
When the lignocellulosic material is lignocellulosic particles or fibres, the method of the invention preferably includes a further step, step (c):
(c) before step (a) or preferably before step (b) applying to the lignocellulosic material a thermosetting resin in finely divided dry powder form and, if necessary, a catalyst therefor, so that the thermosetting resin in finely divided dry powder form adheres to the surfaces of the lignocellulosic material.
The lignocellulosic material may be:
A Lignocellulosic particles or fibres, for example particles, chips, flakes, strands or fibres of wood or agrifibres, e.g those sourced from annual or bi-annual agricultural crop residues, and paper pulps and the like;
B Soft boards, by which there is meant a board which has not necessarily been impregnated or bound with a binder such as a thermosetting resin or the like. Examples are low density boards, i.e boards having a density between 180 and 400 kg/m
3
inclusive, formed typically by a wet process;
C Board precursors in sheet form, by which there is meant a coherent mat of a lignocellulosic material which has not been resinated with a binder such as a thermosetting resin. An example is a mat of medium density fibre, for the production of a medium density fibre board, preferably after initial pre-pressing of the medium density fibre, but prior to the final high pressure pressing of the medium fibre to form the medium density fibre board.
It is to be noted that the impregnating composition does not contain a solvent, which gives the method certain advantages, including the fact that there is no need to remove a solvent before step (b) can be carried out.
The thermosetting resin used in step (a) must be a liquid thermosetting resin so that it can infuse the lignocellulosic material and so that a dispersion of the resin in the mineral oil is formed.
The thermosetting resin used in step (a) is preferably an isocyanate thermosetting resin or a precursor thereof, more preferably a resin derived from diphenylmethane-4,4′-diisocyanate (MDI).
The thermosetting resin in finely divided dry powder form used in step (c) is preferably a novolac resin, based upon phenol and formaldehyde.
The liquid thermosetting resin used in step (a) is preferably used in an amount of from 1% to 20% inclusive by mass of the mass of the dry lignocellulosic material, preferably from 2% to 10% inclusive by mass of the mass of the dry lignocellulosic material.
The mineral oil is preferably used in an amount of from 5% to 30% inclusive by mass of the mass of the dry lignocellulosic material, more preferably in an amount of from 10% to 20% by mass of the mass of the dry lignocellulosic material.
The thermosetting resin in finely divided dry powder form used in step (c) may be used in an amount of from 0% to 20% inclusive by mass of the mass of the dry lignocellulosic material, preferably in an amount of from 3% to 10% inclusive by mass of the mass of the dry lignocellulosic material.
Preferably, prior to step (a), the lignocellulosic material is dried to a desired moisture percentage, preferably a moisture percentage of between 5% and 20% by mass inclusive.
In step (a) the lignocellulosic material may be impregnated with the impregnating composition in any suitable manner, for example by spraying or coating the impregnating composition onto the lignocellulosic material, by mixing the impregnating composition with the lignocellulosic material in particle or fibre form in conventional mixing equipment, or, when the lignocellulosic material is a soft board or a board precursor in sheet form, applying the impregnating composition to the board or board precursor, on one or both sides, by any coating, spraying or immersion technique.
In step (b), the impregnated lilgnocellulosic material may be compressed and heated in a suitable press or mould at temperatures between 120° C. and 250° C. inclusive preferably up to 220° C. and pressures of from 2 to 70 kg/cm
2
inclusive preferably from 10 to 60 kg/cm
2
inclusive for a time from 5 seconds to 20 seconds inclusive per mm of thickness, to allow the mineral oil to infuse the lignocellulosic material and to polymerise the thermosetting resin or resins present.
The impregnating composition may also include various optional components such as:
(iv) a preservative such as a bactericide, fungicide or insecticide, or the like preferably in an amount of from 0.25% to 10% inclusive by mass of the impregnating composition of the preservative;
(v) a wax soluble in the impregnating composition at elevated temperature or a wax in dry particle form;
(vi) other additives selected from fire retardants, ultraviolet light absorbers, and anti-oxidants, and the like
According to a second aspect of the invention there is provided a method of preparing an impregnated lignocellulosic material from a lignocellulosic material selected from the group consisting of lignocellulosic particles or fibres, soft boards, and board precursors in sheet form, for the manufacture of a finished product, which method includes the step of:
(a) impregnating the lignocellulosic material with an impregnating composition comprising:
Pillsbury & Winthrop LLP
Vargot Mathieu D.
Windsor Technologies Limited
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