Coating processes – With post-treatment of coating or coating material – Heating or drying
Reexamination Certificate
2001-09-11
2003-05-06
Cameron, Erma (Department: 1762)
Coating processes
With post-treatment of coating or coating material
Heating or drying
C427S397000, C427S408000, C427S412200, C428S541000, C428S543000
Reexamination Certificate
active
06558748
ABSTRACT:
BACKGROUND OF THE INVENTION
Wood has been used as a structural material dating back into prehistoric times. Even today, despite of the development of several new species of composite materials, because of its excellent strength and stiffness, pleasing aesthetics, good insulation properties and easy workability wood remains one of the most widely-used structural materials.
Traditionally, less than half of harvested timber wood was converted to natural solid wood lumber for constructing buildings, homes and smaller items such as tools and furniture, the remainder being discarded as scrap. However, in recent years the cost of high-grade timber wood has increased dramatically as the supply of this wood has shrank due to the gradual depletion of old-growth and virgin forests. Accordingly, because of both the high cost of high-grade timber wood as well as a heightened emphasis to conserve natural resources, wood-based alternatives to natural solid wood lumber have been developed that make more efficient use of harvested wood and reduce the amount of wood discarded as scrap.
Plywood, particle board and oriented strand board (“OSB”) are some examples of wood-based composite alternatives to natural solid wood lumber that have replaced natural solid wood lumber in many structural applications in the last seventy-five years. These wood-based composites not only use the available supply of timber wood more efficiently, but they can also be formed from lower grade wood species, and even from wood wastes.
While the strength and insulation properties of these wood-based composites are comparable or superior to natural solid wood lumber, some users have complained that in certain high-moisture environments, such as exterior siding, the edges of the composite material experience swelling and cracking as water penetrates into the edges of the material and causes it to expand. To prevent this edge swelling, some wood composite manufactures have affixed metallic or polymeric moldings to the edges of the wood. This molding reduces the moisture penetration that causes edge swelling while also protecting against wear and abrasion of the edges. However, applying moldings to the wood composites considerably increases the cost and complexity of manufacturing wood composite materials.
A simpler approach that avoids the aforementioned problems is to apply a polymer elastomer film coating to the edges of the composite material. For example, U.S. Pat. No. 5,534,295 discloses applying a first polyisocyanate layer and a second layer composed of at least one of an amine and a polyol to form a polyurea elastomer coating on the edges of the wood composite material.
While this polymer elastomer coating provides a measure of protection against moisture penetration, it also has several disadvantages. First, applying the polyurea elastomer coating during manufacture of wood composites is difficult because the reaction rate between polyisocyanates and amines or polyols is difficult to control. If the reaction proceeds too slowly, then the elastomer remains uncured and has a strongly adhesive quality, so that adjoining wood composite boards that accidentally come into contact with each other may be inadvertently joined together. On the other hand, if the reaction proceeds too quickly, then the elastomer coating will not sufficiently adhere to the board and provide little protection against edge swelling.
Moreover, when applied to a wood composite the elastomer coating forms a hard, brittle film and does not appreciably penetrate into the interior of the wood composite material. Thus, this hard film layer formed on the wood composite edge by the elastomer coating forms a durable, wear-resistant surface, but does not provide a significant amount of protection against water absorption. Additionally, build-up of the film coating on profiled edges of wood composite materials may make fitting adjoining profiled edges together difficult. Yet another important disadvantage is that the amine and polyol chemicals used to form these elastomer coatings are expensive and significantly increase the overall cost of the wood composite product.
Given the foregoing, there is a continuing need to develop polymer coatings that can be applied to the edges of a wood composite material to reduce or eliminate edge swelling. Such coatings should preferably be inexpensive, have excellent water-resistant properties, and be of a consistency and viscosity so that they penetrate into the wood composite material. Additionally, it is preferred that when applied to a profiled edge surface, these coatings do not form a material build-up that will prevent interlocking profiled edges from fitting together.
BRIEF SUMMARY OF THE INVENTION
The present invention relates to a process for forming a polyurea coating on a wood composite substrate comprising the steps of applying an isocyanate mixture to an edge of the wood substrate to form a pretreated edge, and applying a polymer latex to the pretreated edge.
The present invention also relates to a process for preparing a polyurea coating for a wood substrate comprising preparing an isocyanate, and reacting, in-situ, on the wood substrate the isocyanate with a polymer selected from the group consisting of acrylics, and polyvinyl acetates to form the polyurea coating.
The present invention also includes a wood composite having a polyurea coating formed by applying an isocyanate mixture to an edge of the wood composite to form a pretreated edge, and applying a polymer latex to the pretreated edge to form the polyurea coating.
DETAILED DESCRIPTION OF THE INVENTION
The following describes preferred embodiments of the present invention, which provides a process for depositing a polymer coating layer on a wood composite material to reduce the amount of water absorbed by the composite material and thereby reduce edge swelling. This polymer coating layer is formed from relatively inexpensive materials, provides excellent protection against edge swelling, and is suitable for applying to the profiled edges of wood composite materials.
By “mixture” it is meant any combination of two or more substance, in the form of, for example without intending to be limiting, a heterogeneous mixture, a suspension, a solution, a sol, a gel, a dispersion, or an emulsion.
As used herein, “wood” is intended to mean a cellular structure, having cell walls composed of cellulose and hemicellulose fibers bonded together by lignin polymer.
By “wood composite material” it is meant a composite material that comprises wood and one or more other additives, such as adhesives or waxes. Non-limiting examples of wood composite materials include oriented strand board (“OSB”), waferboard, chipboard, fiberboard, and plywood. As used herein, “flakes”, “strands”, and “wafers” are considered equivalent to one another and are used interchangeably.
All parts, percentages and ratios used herein are expressed by weight unless otherwise specified. All documents cited herein are incorporated by reference. Concentrations of the polymer resins, waxes, fire retardants and other additives used to form the wood composite materials are calculated based on the oven-dried weight of the wood flakes or strands.
For the purpose of explaining to a person skilled in the art of wood composites how to make and use the present invention and to set forth the best mode contemplated by the inventor for carrying out the present invention, the invention will be described with particularity to a specific type of wood composite material, viz., oriented strand board. However, the present invention is equally applicable to other types of wood composite material, such as oriented strand board (“OSB”), waferboard, chipboard, fiberboard, and plywood. A non-exclusive description of wood composite materials to which the presently disclosed edge sealant compositions may be applied may be found in the Supplement Volume to the Kirk-Rothmer Encyclopedia of Chemical Technology, pp 765-810, 6
th
Edition.
OSB panels are derived from a starting material that is naturally occurring hard or soft wo
Ou Nian-hua
Palardy Robert
Cameron Erma
Goodrich D. Mitchell
J. M. Huber Corporation
Nieves Carlos
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