Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2001-09-27
2002-10-08
Yao, Sam Chuan (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S330000, C156S331400, C156S335000, C264S109000, C427S393000, C427S385500, C427S391000, C427S382000
Reexamination Certificate
active
06461469
ABSTRACT:
This application is the National Phase of International Application PCT/IB00/01071 filed Aug. 1, 2000 which designated the U.S. and that International Application was published under PCT Article 21(2) in English.
BACKGROUND OF THE INVENTION
This invention relates to a method for the manufacture of a finished product from a lignocellulosic material.
Many methods for the manufacture of finished products from various types of lignocellulosic materials are known. For example, PCT/GB 97/00440 to Windsor Technologies Limited teaches a method of preparing a sheet of a lignocellulosic material for the manufacture of a finished product. The sheet is first impregnated with an impregnating composition containing a dicarboxylic anhydride or a tricarboxylic anhydride dissolved in a suitable non-aqueous solvent and an isocyanate thermosetting resin dissolved in a suitable non-aqueous solvent. Thereafter, any excess of the impregnating composition is removed and then the non-aqueous solvent or solvents are removed. Subsequently, the product may be subjected to suitable conditions of temperature and pressure to polymerise and/or cross-link the resin or resins in the sheet of lignocellulosic material to form the finished product.
As another example, PCT/GB 98/01715 teaches a method of manufacturing a finished product from a length of a lignocellulosic material by impregnating the lignocellulosic material with an impregnating composition comprising a solution of a mineral oil, a thermosetting resin, and a non-aqueous solvent. Thereafter, the non-aqueous solvent is removed and the product is subjected to an elevated temperature to polymerise the thermosetting resin to form the finished product.
As a further example, PCT/GB 98/01713 teaches a method of manufacturing a finished product from a lignocellulosic material by impregnating the lignocellulosic material with an impregnating composition comprising a mineral oil and a liquid thermosetting resin, in the form of a dispersion of the liquid resin in the mineral oil and compressing the 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.
While the three methods described above are very effective for the manufacture of finished products from lignocellulosic materials, each method does potentially have disadvantages. For example, the presence of an anhydride, while conferring highly desirable properties on the finished product, can be an irritant on the subsequent machining of the finished product, due to the acidic nature of the dust. Further, while the presence of a mineral oil in a finished product is highly effective in minimising the effects of water ingress, it has the disadvantage of having a tendency to exude from the finished product and to mitigate against its subsequent coating or glueing.
There is thus always the need for improved methods of manufacture of products from lignocellulosic materials.
SUMMARY OF THE INVENTION
According to the invention there is provided a method of manufacturing a finished product from a lignocellulosic material selected from the group consisting of a length of a lignocellulosic material: lignocellulosic particles or fibres; and soft boards; including the steps of:
(1) impregnating the lignocellulosic material with an impregnating composition comprising:
(i) a thermosetting resin dissolved in a suitable non-aqueous solvent;
(ii) a styrene polymer dissolved in a suitable non-aqueous solvent;
(iii) optionally a dicarboxylic anhydride or a tricarboxylic anhydride dissolved in a suitable non-aqueous solvent;
(iv) optionally a mineral oil or a vegetable oil dissolved in a suitable non-aqueous solvent;
(v) optionally a catalyst for the thermosetting resin; and
(vi) optionally a polymethyl hydrogen siloxane hydrophobic agent;
(2) removing from the impregnated lignocellulosic material any excess of the impregnating composition; and
(3) removing the non-aqueous solvent or solvents.
The method preferably includes the step of:
(4) subjecting the product of step (3) to suitable conditions of temperature and optionally pressure to polymerise the thermosetting resin to form the finished product.
The length of a lignocellulosic material may be for example a length of solid wood, wood veneer and plywood; a length of a preformed composite board such as chip board, medium density fibre board, high density fibre board, orientated strand board, flake board, and boards made from paper mill sludge, common mixed paper waste and sawdust; and lengths of virgin and recycled paper and cardboard.
Alternatively, the lignocellulosic material may be:
A. lignocellulosic particles or fibres, for examples 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; and
B. soft boards, by which there is meant a board which has not necessarily been impregnated or bound with 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.
In general, lignocellulosic material refers to any plant material emanating from the photosynthetic phenomenon.
The thermosetting resin is preferably selected from the group consisting of an isocyanate thermosetting resin, an unsaturated polyester resin, an epoxy resin, and a phenol formaldehyde resole resin.
DESCRIPTION OF EMBODIMENTS
The crux of the invention is a method of manufacturing a finished product from a lignocellulosic material.
The first step is to impregnate the lignocellulosic material with an impregnating composition.
The impregnation may be carried out in a suitable vacuum/pressure/vacuum impregnation apparatus or a pressure cylinder. Alternatively, the impregnation may be carried out by irrigating or preferably spraying a moving web of the lignocellulosic material or by immersing the lignocellulosic material in the impregnating composition to cause the penetration of the impregnating composition throughout the lignocellulosic material. Alternatively, particles of a lignocellulosic material may have applied to them the impregnating composition in a suitable mixer.
The first component of the impregnating composition is a thermosetting resin for the binding of the lignocellulosic material, preferably selected from the group consisting of an isocyanate thermosetting resin, an unsaturated polyester resin, an epoxy resin, and a phenol formaldehyde resole resin, dissolved in a suitable non-aqueous solvent, particularly an aromatic or chlorinated hydrocarbon solvent, or liquid carbon dioxide, or a combination thereof.
The preferred thermosetting resin is an isocyanate thermosetting resin.
Isocyanates are compounds containing the group—N═C═O and are characterised by the general formula:
R(NCO)
x
wherein x is variable and denotes the number of NCO groups, and R denotes a suitable group.
Examples of organic isocyanates include aromatic isocyanates such as m- and p-phenylenediisocyanate, toluene-2,4- and 2,6diisocyanates, diphenylmethane-4,4 diisocyanate, diphenylmethane-2,4-diisocyanate, and similar isocyanates.
Specific examples of suitable isocyanates are those having an (NCO) content percentage preferably exceeding 20%, more preferably exceeding 25%. These isocyanates promote latency or reduced reactivity because of the high number of NCO groups, and provide the maximum capacity for hydroxyl bonding. Examples are Desmadur VKS or Desmadur VK by Bayer, which are solvent free mixtures of aromatic polyisocyanates such as diphenyl methane-4,4 diisocyanate and polymeric matter. These and similar are among those referred to as MDIs in the industry. A further description used is a diisocyanate-diphenylmethane, further examples being Suprasec DNR-5005, which is a polymeric MDI, or Suprasec 2020 which is a monomeric MDI with available NCO percentages of 30.7% and 29% and which are polymeric MDI with standard functionality and monomeric MDI respectively. The
Windsor Technologies Limited
Yao Sam Chuan
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