Compositions: coating or plastic – Coating or plastic compositions – Contains fireproofing or biocidal agent
Reexamination Certificate
1999-06-18
2001-05-15
Green, Anthony (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Contains fireproofing or biocidal agent
C252S401000, C252S403000, C252S404000, C514S383000, C514S456000, C514S646000, C514S667000, C514S731000
Reexamination Certificate
active
06231651
ABSTRACT:
BACKGROUND OF THE INVENTION
Hardwoods constitute over one-third of the U.S. timber resource. However, with the exception of cross-ties, hardwoods are rarely treated for exterior use applications, and demand for treated hardwood products has until recently been low. In view of the projected softwood timber shortage and relative abundance of hardwoods, expanded use of treated hardwoods for both composite and solid wood products is expected. The problem is that replacing softwoods with hardwoods is not straightforward since most wood preservatives, including second generation biocides, are considerably less effective when used to treat hardwoods. (Nicholas, D. D.,
Proc. of the Northern Hardwood Resource: Management and Potential Conference, Houghton, Mich
., Aug. 18-20 (1986); Preston, A. F., et al.,
Proc. Am. Wood Preservers' Assn
., 79, 207 (1983)). This disparity is attributable to the considerably higher toxic threshold values obtained when treated hardwoods are attacked by white- and soft-rot fungi as compared to softwoods treated with the same biocide and exposed to brown-rot fungi. (Nicholas, supra.) Accordingly, the object of the present invention is to provide wood preservative systems that are effective in protecting hardwoods and providing greater efficacy for softwoods.
An apparent solution to the problem of preserving hardwoods is to use substantially higher biocide levels, but this approach leads to higher costs and increased environmental risks. A more attractive solution would be to increase the efficacy of biocides for treating hardwoods.
In addition, more environmentally benign preservatives to treat softwoods are needed, since all major wood preservatives used today to protect softwoods have perceived environmental problems.
DESCRIPTION OF RELATED ART
Prior to the present invention, antioxidants have been used in wood treatments of various kinds to stabilize the mixture from chemical decomposition or as a color stabilizer. For example, U.S. Pat. No. 1,168,062 discloses the use of oxidation inhibitors as an additive in oil-in-water emulsions for use in wood preservatives which contain pentachlorophenol as the active ingredient. U.S. Pat. No. 3,889,020 provides di-tert-butyl cresol (also called butylated hydroxytoluene, or BHT) as a stabilizer for pentachlorophenol-based preservatives wherein the cresol is intended to improve the surface color of treated poles.
U.K. Patent Application GB 2,025,769A discloses the use of antioxidants, selected from such compound classes as sulfites, hydrosulfides, hydrazines and thiosemicarbazides. The purpose of the antioxidant there is to stabilize biocides from decomposition. U.S. Pat. No. 3,881,940 describes a composition containing an antioxidant stabilizer such as di-tert-butylcresol in a biocide comprising a heavy metal oxide and pentachlorophenol. The antioxidant served to prevent discoloration of wood and to prevent sludge formation during treating steps. U.S. Pat. No. 4,400,298 teaches the combination of dithiocarbamate and a borate with an antioxidant stabilizing agent, e.g., potassium metabisulfite, for the prevention of fungal decay in wood. U.S. Pat. No. 4,783,221 describes wood preservatives containing an isothiazolone and metal salts of carboxylic acids, to which various additives are added including antioxidants. U.S. Pat. No. 5,462,589 discloses a synergistic wood preservative composition comprising copper and organic derivatives, of which antioxidants are recited as possible additives.
Various biocides have also been used to preserve wood. U.S. Pat. No. 4,977,186 teaches a composition for preserving wood comprising iodopropargyl biocides with a pyrethroid-type insecticide. U.S. Pat. No.5,634,967 teaches a composition for preserving wood comprising a synergistically effective amount of a cuprammonium compound and a triazole biocide.
U.S. Pat. No. 5,730,907 (U.S. '907) teaches the combination of an antioxidant with three organic biocides such as a quaternary ammonium compound, e.g., didecyldimethyl ammonium chloride (DDAC), an isothiazolone, or an isophthalonitrile gave an enhanced effect in protecting a hardwood against a white-rot fungus, Irpex lateus. The patent also provides a method for the use of such composition and compositions so treated.
For ecological and economic reasons, it is desirable to minimize the amount of biocide used to achieve a preservative effect. Accordingly, the addition of antioxidants in accord with the present invention should reduce the preservative retention levels required, and consequently, greatly improve the economics of both hardwood and softwood preservative systems, and thereby provide a more environmentally benign approach to the preservation of wood.
SUMMARY OF THE INVENTION
We have found the unexpected utility of adding antioxidants to selected commercial biocides to protect hardwoods and softwoods from fungal decomposition. Selected antioxidants significantly increase the activity and effectiveness of biocides to treat hardwoods and softwoods.
Accordingly, the present invention provides a wood preservative composition comprising (a) at least one biocide, i.e., an iodopropargyl compound or a triazole compound, and (b) at least one antioxidant. The composition is especially effective when the antioxidant is a hindered phenol derivative. In addition to being highly effective, the wood preservative composition is environmentally safe and inexpensive to apply.
None of the above biocides are taught by the U.S. '907 patent. The antioxidant and biocides combinations used in the present invention are effective against white-rot fungi, such as
Trametes versicolor
, to protect hardwoods, and brown-rot fungi, such as
Gloeophyllum trabeum
, to protect softwoods. Thus, the present invention greatly increases the utility of both hardwoods and softwoods in applications where the products are susceptible to biodeterioration. For example, to protect softwood lumber, which is used in residential construction and is susceptible to brown-rot fungi attacks.
The antioxidant alone, such as butylated hydroxy toluene (BHT), has no effectiveness against either of the above fungi. The combination of an antioxidant and the foregoing organic biocides give greater efficacy than either component alone with a variety of woods, such as the hardwoods sweetgum and aspen, and the softwood southern yellow pine. Thus, the combination of the antioxidants and biocides of the present invention is synergistic against fungi.
Of particular practical importance is the discovery that the low-cost antioxidant BHT, which is commonly used as a food additive, when combined with a biocide of the invention has an enhanced and synergistic biocidal effect with minimal environmental effects.
DETAILED DESCRIPTION
In one embodiment, the present invention provides a wood preservative composition comprising an effective amount of at least one biocide and an effective amount of at least one antioxidant; wherein the biocide is an iodopropargyl compound having the structure:
wherein R
1
is butyl, hexyl, cyclohexyl, or phenyl.
Preferably, R
1
is butyl (iodopropynylbutyl carbamate or IPBC).
In another embodiment, the present invention also provides a wood preservative composition comprising an effective amount of at least one biocide and an effective amount of at least one antioxidant; wherein the biocide is a triazole compound containing a triazole group having the structure:
Advantageously, the triazole compounds have the following formula:
wherein R
2
is a branched or straight chain C
1-5
alkyl group (e.g., tert-butyl) and R
3
is an unsubstituted phenyl group or a substituted phenyl group having one or more substituents, i.e., halogen (e.g., chlorine, fluorine or bromine), C
1-3
alkyl (e.g., methyl), C
1-3
alkoxy (e.g., methoxy), phenyl, or nitro group.
Particularly preferred is a triazole compound of Formula A wherein R
2
is tert-butyl and R
3
is 4-chlorophenyl (alpha-[2-(4-chlorophenyl) ethyl] -alpha(1, 1 -dimethylethyl)-1H-1,2,4-triazole-1 -ethanol, commonly known as Tebuconazole).
Alternat
Nicholas Darrel D.
Schultz Tor P.
Darby & Darby
Green Anthony
Mississippi State University
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