Stock material or miscellaneous articles – Composite – Of carbohydrate
Reexamination Certificate
2000-04-14
2003-05-27
Cain, Edward J. (Department: 1714)
Stock material or miscellaneous articles
Composite
Of carbohydrate
C524S013000, C524S014000, C524S016000
Reexamination Certificate
active
06569540
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable.
BACKGROUND OF THE INVENTION
This invention relates to dimensionally stabilized wood composite products such as agglomerated structural board, oriented strandboard, medium density fiberboard, particleboard, and structural members such as posts, poles, beams or corrugated plates and moldings. The invention also relates to methods of manufacturing these wood composite products from wood particles. “Wood particles” is defined broadly in this specification to include wood strands, chips, flakes, refined chips or flakes, fibers, webs of splintered wood formed by twisting or crushing billets of wood, or other forms of wood particles. The invention further relates to a wood preservative that also improves the dimensional stability of the treated wood when the wood is exposed to a moist or humid environment.
Various types of structural members, such as utility poles, guard rails, fence and sign posts, building beams, construction pilings, railroad ties, and the like, are commonly made from solid wood. Solid wood is subject to increasing production costs, the limited supply of trees of suitable species and size, and more economically efficient uses of solid wood for other purposes. There is a growing need for a substitute wood composite material from which the above and other types of structural members can be made. In addition, there is a need for substitutes for plywood, as in residential sheathing.
The use of wood residues and surplus wood of low commercial value for making wood composite is quite desirable because of the vast supply and the lower, more stable cost of this source of wood. To be capable of being used for the same applications, the resulting structural members should have properties, particularly strength properties, which meet or exceed those of solid wood.
Wood composite products are well known. Wood composites are in widespread use in furniture and other consumer products. Some examples of specific wood composite products are particleboard, medium density fiberboard (MDF), and oriented strandboard (OSB).
Particleboard is formed by binding small wood flakes with an adhesive, then rolling or molding a billet or sheet of the treated flakes to form a board, beam, or other product form. Randomly oriented particleboard has different mechanical properties from ordinary sawn timber wood. Wood exhibits directional mechanical properties, owing to the natural alignment of long wood fibers along the direction of the tree trunk. Its tensile strength and elastic modulus, for example, are much greater in directions parallel to the grain direction than in the cross-grain direction. In contrast, the random alignment of wood flakes in particleboard and some other wood composite products results in substantially isotropic mechanical properties. But these isotropic properties are comparable to the relatively poor mechanical properties possessed by wood in directions perpendicular to the grain. In general, particleboard has exhibited a poor ability to sustain bending loads, as compared with natural timber, and thus has largely been unsatisfactory as a structural beam.
Medium density fiberboard is made similarly to particleboard, except that the flakes commonly are smaller, and are refined to release fibers before forming sheets.
More recently, wood composite products have been developed in which wood flakes or strands are oriented in a single direction, to provide a structure more like natural wood. One example is oriented strandboard. Such products possess relatively improved strength in directions parallel to the direction of alignment.
Also, more complex wood composite products have been developed, having several consolidated strata in which the particles are aligned in different directions. For example, a three-stratum beam or sheet or other composite article can be made in which the outer or facing layers have their orientation parallel to the longest dimension of the composite, as in conventional wood. The interior layer has its fiber orientation perpendicular to the longest dimension of the composite. Three-stratum boards are also known in which large flakes make up the center layer and smaller flakes make up the outer layers.
One problem with wood composite products is that they are dimensionally unstable after they are made. Even a stratified board with layers oriented in different directions will grow or shrink substantially in response to environmental moisture and weather conditions. This property has limited the value of wood composite members of substantial size for use in construction products.
The problem of dimensional instability can be addressed by increasing the adhesive content of the product, but at a substantially greater cost, as the adhesive composition is expensive.
Another way to improve the dimensional moisture stability of the resulting board product is to apply a suitable wax in emulsion or molten form to the wood particle mix at the binder blender station or elsewhere in the fabrication process. This approach reduces the problem, but the dimensional stability of the wood composite may still be deficient.
Other problems that must be addressed by wood composite products in some environments include preservation against one or more of termites, ants (for example, carpenter ants) and other wood-destroying insects or fungi, soft rot, and mold fungi. Examples of wood-destroying fungi and soft rot and mold fungi are:
Gloeophyllum trabeum, Trametes versicolor, Paxillus panuoides, Condrostereum purpurescens, Heterobasidium annosum, Bispora effusa, Stachybotrys atra, Chaetomium globosum, Trichoderma viride, Aspergillus niger,
Hormiscium spec., and Stemphylium spec. Wood products are preserved using amounts of wood preservative compounds known or believed to be effective against one or more of these organisms.
Yet another problem in the art has been how to effectively incorporate a water-borne wood preservative in a wood composite product, so the preservative compounds reach the interior of the product, without also incorporating a significant amount of additional water in the product. Any excess incorporated water must be dried out, using additional energy, time, equipment, factory space, and thus money. Another problem in the art is how to incorporate a water-borne preservative system into wood composite products without causing a negative impact on panel structural properties.
U.S. Pat. No. 4,241,133, issued to Lund, et al., discloses a wood composite containing about 5 to 12 weight % of a binder and, optionally, additives, such as wax, for waterproofing and preservatives for protection against decay fungi and insects. According to Lund, dried, classified particles are introduced into a conventional blender where predetermined amounts of a binder, and optionally a wax, a preservative and other additives are applied to the particles as they are tumbled or agitated in the blender.
Lund discloses that when the structural member is to be used for long-term exterior applications, a preservative for protecting the wood against attacks by decay fungi and insects can be added to the wood particles during or before the binder blending step. According to Lund, any preservative which is compatible with the adhesive system can be used, such as pentachlorophenol, creosote, chromated copper arsenate, ammoniacal copper arsenate and the like. Lund reports that effective amounts of such preservatives, up to about 5% by weight, can be added to the wood particles without producing an appreciable reduction in the structural strength of the resulting structural member. Lund states that the loss in strength is about the same as solid wood treated with the same preservatives.
Lund indicates that the binder, wax and other additives can be added separately or in any sequence or in combined form. U.S. Pat. No. 4,404,252, issued to Hetzler et al., discloses that powdered phenol formaldehyde resin and molten slack wax can be applied simultaneously to the
Archer Kevin J.
Fowlie David A.
Preston Alan F.
Cain Edward J.
Chemical Specialties, Inc.
McAndrews Held & Malloy Ltd.
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