Fire retardant

Details Fire retardant Fire retardant

2001-11-08

2003-11-25

Green, Anthony J. (Department: 1755)

Compositions: coating or plastic

Coating or plastic compositions

Contains fireproofing or biocidal agent

C106S015050, C106S018140, C106S018150, C252S601000, C252S607000

Reexamination Certificate

active

06652633

ABSTRACT:

FIELD OF THE INVENTION
This invention is in the area of improved fire retardants that include guanylurea phosphate [(H
2
N—C(NH)—NH—C(O)—NH
2
).H
3
PO
4
] (GUP) and boric acid, to materials, including wood and composite wood products that include these fire retardants, and to methods of making and using same.
BACKGROUND OF THE INVENTION
Wood products, especially wood products used in the building construction industry, are commonly treated with chemical fire retardants that reduce the inherent ability of the wood to catch fire and combust. Many of these fire retardants contain acidic components which, when exposed to high heat, are activated and catalyze the dehydration of cellulose. This reaction converts the cellulose in the wood into water and char, and reduces the susceptibility of the wood to continuous combustion. Because these acid-based fire retardants decompose the wood in order to prevent combustion, it is important to prevent premature activation of the acid components. This is especially true for building products that are used to construct roofs, because of the extremely hot temperatures that these materials experience.
Many fire retardant chemical treatments for wood have been based on amine-phosphorus compounds.
For example, Goldstein et al., U.S. Pat. No. 2,917,408 disclose the preparation of fire retardant wood with a combination of dicyandiamide (H
2
N—C(NH)—NH—CN) and phosphoric acid (H
3
PO
4
). Goldstein et al., U.S. Pat. No. 3,159,503 disclose the preparation of fire retardant wood with a combination of dicyandiamide, phosphoric acid and very small amounts of formaldehyde. In addition, Juneja, U.S. Pat. No. 3,832,316 discloses a composition for imparting fire retardancy to wood comprising dicyandiamide, melamine, formaldehyde, and phosphoric acid and suggests that minor amounts of other materials may be substituted for some of the phosphoric acid, such as boric acid. Juneja, Canadian Pat. No. 917,334 discloses a composition for treating wood to impart fire retardancy, in which the composition comprises dicyandiamide, urea, formaldehyde and phosphoric acid. The document suggests that minor amounts of other materials may be substituted for some of the phosphoric acid, such as boric acid. Other similar patents include U.S. Pat. Nos. 2,935,471; 3,137,607; 3,874,990 and 4,010,296.
While most of the above described chemical compositions based on dicyandiamide, melamine, urea, formaldehyde and phosphoric acid are effective for imparting fire retardancy to wood, they suffer from one or more drawbacks. Compositions containing solids of more than about 15 percent urea render the wood hygroscopic. Further, compositions that contain formaldehyde tend to be resinous and require high drying temperatures of about 100° C. to 110° C. to completely cure the resin, thereby impairing the strength of the wood.
U.S. Pat. No. 4,373,010 to Oberley (the Oberley '010 patent) reported that the aforesaid disadvantages could be obviated, and that a superior fire retardant could be formed, by partially reacting water, phosphoric acid, dicyandiamide and boric acid. The Oberley '010 patent describes several liquid fire retardants that contain guanylurea phosphate (GUP) and boric acid, and several methods for preparing the GUP/boric acid retardants. The retardants preferably contain about 70 weight parts of GUP and about 30 weight parts of boric acid. Dicyandiamide and phosphoric acid are mixed at a 1:1 molar ratio to produce the GUP.
In a preferred method, Oberley '010 reacts dicyandiamide with phosphoric acid for 35 to 45 minutes in water to form guanylurea phosphate (GUP), in a solution that contains 50-70 percent solids. The reaction is only allowed to proceed to about 80-95 percent completion, in order to prevent the formation of insoluble precipitates. Boric acid is then mixed with the GUP solution, and the mixture cooled to ambient temperature and diluted to from 3 to 18 percent solids.
In one example, Oberley '010 formed a 15 percent aqueous treating solution from dicyandiamide, phosphoric acid and boric acid (DPB) in a ratio of 70 percent combined dicyandiamide and phosphoric acid to 30 percent boric acid. While agitating, the dicyandiamide was charged to a glass reaction flask, followed by the water and phosphoric acid. The mixture was then heated to 80° C. over a period of 20 minutes and maintained at that temperature for 3½ hours. The boric acid was then added and the solution cooled to room temperature over a period of 30 minutes. The resultant solution comprised principally guanylurea phosphate, unreacted dicyandiamide and phosphoric acid of about 10 percent of the original amount, and boric acid.
In another method disclosed in the Oberley '010 patent, dicyandiamide, phosphoric acid, and boric acid are initially heated together. The patent does not give any further details about this process, except to indicate that the method is prone to yield aqueous mixtures with insoluble precipitates, especially at high solids concentrations of from 50 to 80 percent.
At least one other method, that is not disclosed in the Oberley '010 patent, is used commercially to prepare a GUP/boric acid fire retardant. This method is used to produce solid GUP/boric acid fire retardants that are bagged and sold in large super sacks for pressure treatment of wood products. To use the solid material, pressure treaters pour the contents of the bag into a large vat of heated pressure treating solution, and allow the solids to dissolve before using the solution in their pressure treating operation.
These commercially available solid GUP/boric acid fire retardants are sold in large super sacks of chunks that are 0.5-1.5 inches in size. The solids contain boric acid and GUP, and result from a reaction that gives about 90% yield, and are typically sold. When a wood pressure treater receives a super sack of solid GUP/boric acid fire retardant, he dissolves the entire bag in water for use in his pressure treatment process.
The GUP/boric acid fire retardants disclosed and used in the prior art suffer from a number of disadvantages. First and foremost, the process for making the fire retardants wastes a considerable amount of raw materials. In the commercial process discussed above, about 10% of the dicyandiamide and phosphoric acid raw materials is wasted because the reaction only proceeds to about 90% of its theoretical yield. Oberley '010 intentionally wastes a considerable amount of raw materials by preventing more than 80-95% conversion of dicyandiamide and phosphoric acid into GUP. As a result, the pressure treater ends up with raw materials and intermediates from the GUP production process in his wood products.
The GUP/boric acid fire retardants of the prior art also contain unwanted by-products from the GUP production process. One of these by-products is seen when a solution of the fire retardant is subjected to potentiometric titration, because it produces an equivalence point at pKa 3.2. It is believed that this by-product is a salt of dicyandiamide and phosphoric acid. A purer product that did not contain such by-products and unreacted raw materials would be desirable from a quality point of view.
The solid GUP/boric acid fire retardants that are sold commercially also suffer from a number of distinct disadvantages. For example, they are presently sold in super sacks and are very difficult to manage by the wood treater, because they frequently harden during transport in the bag, and an entire bag of the material must be added to a pressure treating solution in order to assure adequate and proportional mixing between the GUP and boric acid. A homogenous blend of solids would reduce the packaging that is needed when a customer needs a smaller portion of material than present in a super sack, because a homogenous blend would allow customers to use only a portion of the retardant in the super sack packaging (as opposed to having to dissolve an entire super sack).
The liquid fire retardants disclosed in Oberley '010 similarly suffer from several di

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