Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1997-07-15
2002-09-17
Gallagher, John J. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S281000, C156S316000, C427S214000, C427S325000, C427S399000, C428S326000, C428S420000
Reexamination Certificate
active
06451153
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method of preparing particles of a lignocellulosic material for the manufacture of a finished product and to a method of making a finished product from the particles of lignocellulosic material.
It is well known to manufacture particle board and other composites from chips, particles, fibres, veneers, flakes, strands or flours of natural fibrous plant materials such as wood. Such boards are most frequently made by using formaldehyde condensation resins such as urea, melamine or resole phenolics as binders. Polyureas and isocyanates are also used. It is desirable that free formaldehyde or other binder related toxic volatiles should be avoided, that swelling due to water wetting be minimised thereby increasing water resistance, that the binder system used should be water proof, that the surface integrity of the board should be such as to promote ease of finishing, that the strength and consistency of the composite lend itself to thin calliper board production, with strength properties comparable to plywood, and that the process should not be particle size critical as is the case with binder spray-on, followed by shear or “wet wipe” binder distribution. Further desirable properties are good machinability, good nail and screw holding and good edge finishing.
Natural fibrous plant materials or lignocellulosic materials are comprised of hemi celluloses, celluloses and lignin. A change in the moisture content of these materials results in swelling, because the cell wall polymers of the materials contain hydroxyl or other oxygen containing groups that attract water through hydrogen bonding. The hemi celluloses are the most hygroscopic, but lignin also contributes to the hygroscopicity of these materials. It is the moisture that swells the cell walls and causes the expansion of the material until the cell walls are saturated with water. This can obviously give rise to degradation as a result of attack by microorganisms, as well as bulking and dimensional instability. This phenomenon applies not only to lignocellulosic composites such as chipboard, particle board, plywood, strand board, medium density fibre board and hardboard, but also to sawn timber and pulp and paper products.
It is known to modify lignocellulosic materials chemically. The chemicals used are generally classified by the type of bond formed between them and the wood cell wall hydroxyl group. Various classes of chemical reactions have been used with wood and they are esters, acetals, and ethers produced inter alia by the use of anhydrides.
Examples of documents which teach the use of anhydrides include U.S. Pat. Nos. 4,832,987, 5,055,247 and 5,064,592.
Examples of (documents which teach the use of anhydrides to treat a cellulosic material to which there is then applied a polymer, are U.S. Pat. Nos. 5,120,776; 5,385,754 which teaches a process for modifying lignocellulosic material by a chemical treatment method, which method comprises treating the lignocellulosic material with phthalic anhydride and a thermosetting resin selected from phenol-formaldehyde resins, urea formaldehyde resins and urethane resins, and then curing the phthalylated resin impregnated product so formed; CA 119:227002; and CA 120:135905.
However, even if a lignocellulosic material is pretreated, conventional composite board production requires that where condensation resins such as ureas, phenols and melamines are used, the lignocellulosic material must be dried thoroughly before the application of the binder, because water is added back to the fibres during resination and it is essential that the hot pressing of the boards proceed without delay in a continuous production process, in order that neither the applied reactive binder resins, nor the lignocellulosic material itself, degrades as a result of extended storage.
There is a need for a composite board technology that allows for the chemical modification and resination of a lignocellulosic material, after which the material is in a dry and latent condition so that it may be stored, without degradation, and transported or made up, at a later time and place into its finished product form.
SUMMARY OF THE INVENTION
According to a first aspect of the invention there is provided a method of preparing particles of a lignocellulosic material for the manufacture of a finished product which method includes the steps of:
(a) chemically modifying the lignocellulosic material by impregnating the lignocellulosic material with an impregnating composition comprising a dicarboxylic anhydride or a tricarboxylic anhydride dissolved in a suitable non-aqueous solvent;
(b) applying to the particles an adhesion promoter to promote the adherence of a thermoplastic resin to the surfaces of the particles of lignocellulosic material;
(c) applying to the particles a thermoplastic resin in dry powder form, so that after the application of the adhesion promoter, the thermoplastic resin adheres to the surfaces of the particles of lignocellulosic material, the thermoplastic resin having been surface modified by irradiation or by fluorination; and
(d) after step (a) or step (c), removing the solvent.
Step (c) may precede step (a) or may follow step (a) or step (b).
In a first alternative, the adhesion promoter may be included in the impregnating composition of step (a).
In a second alternative, the adhesion promoter may be applied to the particles after step (a).
For either of these alternatives, the solvent is recovered after step (c).
In a third alternative, the solvent may be recovered after step (a) and thereafter the adhesion promoter may be applied to the particles of lignocellulosic material in a solvent for the adhesion promoter.
In a fourth alternative, the adhesion promoter may be applied to the particles of thermoplastic resin before step (c).
The dicarboxylic anhydride may be selected from the group consisting of maleic anhydride, phthalic anhydride, succinic anhydride and tetrahydrophthalic anhydride, and the tricarboxylic anhydride may be trimellitic anhydride. Suitable solvents include methyl acetate, ethyl acetate, methylethyl ketone, benzene, trichloroethylene and dichloromethane, preferably dichloromethane.
The impregnating composition preferably contains from 0,25% to 25% inclusive, more preferably from 0,25% to 15% inclusive of the anhydride by weight of the impregnating composition.
As the lignocellulosic material preferably takes up from 10% to 120% inclusive, more preferably from 30% to 110% inclusive of the impregnating composition by weight of the lignocellulosic material before removal of the solvent, after removal of the solvent the amount of the anhydride in the lignocellulosic material thus ranges from 0,025% to 30% inclusive by weight of the lignocellulosic material.
The adhesion promoter is preferably selected from the group consisting of convertible resins such as petroleum resins, hydrocarbon resins and coumarone indene resins; thermoplastic rubbers; styrene butadiene resins; styrene acrylate resins; chlorinated rubbers; phenolic resins; solvent soluble thermoplastic resins such as polystyrene or polyvinyl chloride; lignocellulosic derived gums or rosins; solvent swellable celluloses such as methylhydroxypropylcellulose; phenol formaldehyde novolac resins; urethane elastomers; resinous tackifiers; bitumen; coal tar; asphalt and pitch; if necessary dissolved in a suitable non-aqueous solvent such as those listed above for the anhydrides.
In the third alternative, the adhesion promoter may be one used in the water phase, such as those selected from the group comprising water soluble, dispersible or miscible polymers, which are stable to electrolytes with film forming temperatures between minus 15° C. and 40° C., including polyvinyl alcohol, polyurethanes, olefins, acrylate vinyl esters, polyvinyl halides, chloroprene copolymers, and dispersions of styrene butadiene rubber, butadiene vinyl acetate copolymers and polyacrylic acid esters, acrylics and the acrylic pressure sensitives.
The adhesion promoter is preferably applied to the particles
Gallagher John J.
Pillsbury & Winthrop LLP
Tower Technologies (Proprietary) Limited
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