Stock material or miscellaneous articles – Composite – Of carbohydrate
Reexamination Certificate
1998-04-27
2001-05-15
Hess, Bruce H. (Department: 1774)
Stock material or miscellaneous articles
Composite
Of carbohydrate
C428S704000, C428S907000
Reexamination Certificate
active
06231994
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates in general to protecting wood from wood destroying organisms, and, in particular, to substantially encapsulating a wooden workpiece in a waterproof thermoplastic sheath together with an effective amount of a water miscible infection controlling composition and, preferably, sufficient moisture to permit the composition to migrate throughout the workpiece.
2. Description of the Prior Art
It is well known that water soluble borates such as, for example, disodium octaborate tetrahydrate will control wood destroying organisms such as insects and fungi in wood and wood products. U.S. Borax, Inc., for example, sells a disodium octaborate tetrahydrate containing product under the “Tim-bor” mark which is intended to be used for this purpose. Such borates and other water soluble infection controlling compositions had generally been limited in their usefulness because, if treated wood were exposed to rain or substantial amounts of other ambient moisture, these water soluble compositions tended to leach out of the wood, leaving it exposed to infection. Treated wood, for example, could not be left exposed to the elements in use, storage or shipment. Thus, wood could not be treated at a central location, transported to and stored in the open at a construction site.
Attempts to seal treated wood to prevent leaching of water soluble compositions generally required careful preparation of the wood surface including thorough drying of the surface after treatment and before the application of sealing agents such as paint or stain. Such stain or paint sealing agents typically depended for their adhesion upon wetting the surface of the boron treated workpieces. Any localized failures in wetting based adhesion systems resulted in rapid overall failure of the system. Typically, the previous infection controlling reagents formed a crystalline deposit on the surfaces of the treated wooden object. Those deposits interfered with the adhesion of prior sealing agents to the surface. Typically, the treating processes did not maintain the wooden piece moist for a long enough period (typically weeks) to permit the reagent to penetrate all the way through the wood. This left most of the reagent on or near the surface with the inner parts of the wood untreated. The drying process which was previously required before the prior sealing agents could be applied produced checking and splitting which left pathways through the treated areas for the infection (termites and the like) to reach the untreated interior. Also, since the prior proposed sealants wet the surface when applied they tended to mix with and bind the reagent which was at the surface, thus rendering it largely ineffective. Since most of the active reagent was at or near the surface, this largely defeated the purpose of the treatment.
It is well known that the presence of moisture in treated woods promotes the migration of the water soluble treating agents into or throughout the wood. See, for example, Knudson et al. U.S. Pat. No. 4,879,083, and Dicker U.S. Pat. No. 4,620,990. The previous perceived need to dry the surface of treated wood prior to sealing it was counterproductive because it tended to remove the moisture which was needed to promote the migration of the treating agents into or throughout the wood, both initially and over the life of the product. Also green wood, that is, wood which had a moisture content of about 20 percent or more, tended to be difficult to seal as previously proposed unless first dried. When dried to the degree previously believed necessary prior to sealing it, the wood was subject to warpage, splitting, and the like. Also the drying process was generally costly.
The results from prior efforts to seal treated wood were generally partially or ineffectively treated wooden workpieces. Such partial or ineffectual treatment left the wood at least partially exposed to infection by wood destroying organisms. Partially sealed and reinforced wooden workpieces such as those proposed by Boyles U.S. Pat. No. 5,326,410 were generally at risk of becoming ineffective due to excessive leaching of the borate and of being weakened by reason of the borate containing bores formed in them.
Previous proposals to use glycols and glycol soluble borates with previously dried lumber were generally unsatisfactory, inter alia, because of economic and environmental factors. See, for example, Palmere et al. U.S. Pat. No. 5,104,664.
Wooden workpieces had previously been sealed in water impervious plastic sheaths to protect them from the elements. See, for example, Totten U.S. Pat. No. 4,181,764. In general the presence of significant amounts of moisture within the sealed sheath had been considered to be undesirable because of the risk of fungus attacking the encapsulated wood.
These and other difficulties of the prior art have been overcome according to the present invention.
BRIEF SUMMARY OF THE INVENTION
A preferred embodiment of the process of treating wooden workpieces according to the present invention comprises selecting a wooden workpiece which has a shaped surface, applying an admixture containing an effective amount of a water soluble infection controlling composition to the shaped surface, and substantially encapsulating the resultant treated surface by forming a generally molten mass of thermoplastic into a closely conforming non-wetting sheath over the treated surface. Sufficient moisture is preferably provided to enable an effective amount of the infection controlling composition to migrate substantially throughout the wooden workpiece within approximately 3 weeks.
The closely conforming sheath is conveniently formed, for example, by extruding molten thermoplastic around the wooden workpiece as the workpiece is passed through a die. In general the sheath has a thickness of at least approximately 0.005, and, preferably 0.015 inches or more. The sheath, although closely conformed to the surface of the workpiece, is not adhered to the surface of the workpiece through a wetted bond such as that formed between paint and a wooden surface. In general, the closeness of the sheath to the wood is such that there is less than about 0.001 inches of clearance between coating and the surface of the wood. Preferably, there is no clearance between the two. The nature of the thermoplastic is such that at the thickness used it is substantially impervious to liquid and vapor phase water. Polyethylene, for example, is an effective thermoplastic at thickness of, for example, at least about 0.005, and preferably 0.015 to 0.020 inches. In general, the thickness of the sheath is chosen to provide protection under the anticipated service conditions. Where there is a risk of some wear of the coating it is generally made thicker and/or of more durable plastic. Where the workpiece is expected to be used, for example, as a structural member in the wall of a building which will be closed up, the minimum thickness is generally adequate. Fence railings which are anticipated to be exposed to some wear generally require a thicker coating, up to, for example, 0.050 to 0.080 inches or more. The cost of the plastic generally limits the economically practical maximum acceptable thickness for most applications to less than approximately 0.2 inches.
Plastics which are particularly suitable for use as water impervious barriers according to the present invention are generally thermoplastic resinous polymers which are capable of being melt formed in situ to substantially encapsulate a wooden workpiece, and are substantially impervious to moisture, including, for example, thermoplastic homopolymers, copolymers, terpolymers and the like. Such thermoplastic resins include, for example, vinyl resins , poyvinyl chloride, polyethylene, polypropylene, polyolefins, acrylonitrilebutadiene, and the like. Such barriers are substantially impervious to both liquid and vapor phase water. Some very small amount of water migrates through these materials. However, over the expected life of the product (at least 10 years
Hess Bruce H.
Jagger Bruce A.
Shewareged B.
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