Compositions – Fire retarding – For wood or cellulosic material other than textile
Reexamination Certificate
2000-07-13
2003-09-16
Medley, Margaret (Department: 1714)
Compositions
Fire retarding
For wood or cellulosic material other than textile
C252S601000, C252S37800R, C523S179000, C428S537100, C428S921000
Reexamination Certificate
active
06620349
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the field of treating wood products using fire-retardant, insecticidal, and fungicidal compositions and methods.
BACKGROUND OF THE ART
There are a number of properties in natural wood that make it the product of choice for building construction. Its strength, appearance, durability, accessibility and non-corrosive nature make it ideally suited for building supports, framework, decks and trims. However, wood is highly flammable and susceptible to living organisms. It is known that various compounds can be used to treat cellulosic products in order to impart a wood preservative, and flame resistant qualities thereto. The use of wood treated with such compounds came into common usage during World War II, when it was used for the construction of blimp hangars.
Due to the combustible nature of wood, building codes in virtually all U.S. municipalities restrict the use of untreated wood to certain applications. However, the preservative and/or fire-retardant treatment of wood has broadened the useful scope of both wood and wood substrates, because many of these municipalities will allow the use of treated wood as a non-combustible material in applications where untreated wood would not be permitted. Most municipalities in the United States rely on the specifications delineated within the Uniform Building Code (“UBC”) and Uniform Building Code Standards to certify treated wood as suitable for all types of construction. These municipalities also rely on outside certification agencies, such as Underwater Laboratories, Inc. (“UL”) to certify which preservative and/or fire-retardant treated materials meet the criteria for strength, durability, fire-retardance and other properties.
There exists in the art a uniform basis for recognition of quality control of fire-retardant treated lumber, as required by §207 of the UBC. In order to be used in structural applications, fire-retardant treated lumber must comply with UBC Chapter 8 Section 802 delineating the standards promulgated by the American Standard Testing Method (ASTM) E-84, which are equivalent to the standards of Underwriters Laboratories, Inc. (UL) Standard 723. The standards promulgated therein include UBC Standard 8-1 for Test Method for Surface-Burning Characteristics of Building Materials, UBC Standard 23-4 for hygroscopic properties, UBC Standard 23-5 for Design Values, UBC Chapter 8 Section 802 for flame spread, and the United States Military Specification No. MIL-L-19140E, Paragraph 4.6.5.2 (Amendment 1, dated Oct. 1, 1985) for corrosiveness. It is accepted that the certification standards promulgated by the International Conference of Building Officials (ICBO) provide the necessary procedures for testing treated wood products to determine whether the UBC standards are met. Fire-retardant treated lumber is qualified on the basis of testing in accordance with the applicable UBC standards, as conducted by an ICBO ES accredited laboratory. The quality control requirements include moisture content, solution concentration, chemical retention by gauge, fire tube tests, assay of borings, or other validated methods, as delineated in the Approved Quality Control Manual. These procedures are set forth in the ICBO Evaluation Service, Inc., Acceptance Criteria for Quality Control of Fire-Retardant Treated Lumber AC 66, Issued April 1997.
It is known that ammonium phosphates, aluminum sulfates, aluminum hydrates, or chlorinated paraffins can impart fire retardant qualities to treated wood. Most fire-retardant compounds make use of the same technical underpinning. These compounds comprise salt compositions which become acidic under elevated temperatures. These salts can form, for example, phosphoric and sulfuric acid and other, phosphate and sulfate derivatives under high temperatures. The acids and derivatives formed promote charring of the treated material during exposure to fire. The resulting char reduces flammability by insulating the material from the fire, thereby reducing flame spread and penetration. Many fire retardant compositions also include starches, such as molasses, in order to provide adequate charring. However, the use of such starches renders the treated materials susceptible to degradation by adventitious organisms such as insects and molds.
Plywood sheaths are often treated with fire-retardant compositions and used for roof decking. The temperature of roof decking at the interface between the overlying shingles and the roof deck can often exceed 170° F. Many prior art fire-retardant compositions begin to degrade at such temperatures, resulting in acid hydrolysis at temperatures well below those present during a fire. As a result, it has been found that many roof decks constructed from plywood sheaths treated with prior art fire-retardant compositions begin to loose structural integrity. This structural degradation occurs more rapidly in warmer climates. Furthermore, the presence of moisture has been found to accelerate the rate of thermal degradation of many treated products. Thus, in many cases, the treated plywood used as roof decking may require replacement in as little as two to seven years, because the degradation of wood products used for structural purposes results in the products being unsuitable for use.
Most known fire-retardant compositions require a drying step with high heat after application to wood materials. This high-heat step often leads to premature activation of the chemical processes designed to resist flame spread during fire, leading to acid hydrolysis of the cellulose fibers in the material treated, greatly weakening the treated product by compromising the structural integrity.
Many prior art fire-retardant compositions make use of active ingredients, such as ammonium sulfates and ammoniacal copper didecyldimethylammonium which have been found to be corrosive to metal, including common metal fasteners, such as staples or nails, which are used to secure the treated materials. Thus, for treatment of materials to be secured in place with metal fasteners, such as the majority of all materials, compositions making use of less corrosive active ingredients is critical. However, many of the replacement materials, such as ammonium phosphate are highly hygroscopic which results in high moisture pick-up by the treated product. Thus, there is a need for offsetting the hygroscopicity of the non-corrosive replacement salts.
The treatment of wood with most prior art wood fire-retardant compositions has generally required the use of incising the wood with small perforations in order to assure adequate penetration of the wood with the composition. However, in incising, the fibers of the wood are cut which leads to a reduction in the structural integrity of the treated wood.
Many prior art fire-retardant compositions discolor, as well as degrade, the material treated after prolonged exposure to the elements. For example, dark, reddish-brown charred spots soon begin to appear in wood products treated with prior art compositions. This discoloration prevents the use of the treated material where an exposed natural wood finish is aesthetically desirable.
Ammoniacal copper zinc arsenate (ACZA) and chromated copper arsenate (CCA) have been used for many years as wood preservatives. However, the prior art has demonstrated the problems presented when wood preservatives and fire retardants are combined. See White et al. “Flame Retardancy of Wood: Present Status Problems, and Future Fields.” in Lewan ed. Recent Advances in Flame Retardancy of Polymeric Materials: Proceedings of 3d Annual BCC Conference on Flame Retardance (Business Communications Co., Stamford, Conn. (1992)). These problems include leaching of the preservative and/or fire retardant, from the wood and the staining or discoloring of wood when leach-preventing materials are added. Id.
Inorganic boron containing compounds impart fungicidal, insecticidal, and fire retardant properties to wood products. Since inorganic boron compounds are readily soluble in water, exposure to atmospheric moisture
Medley Margaret
Wu Charles C. H.
Wu & Cheung, LLP
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