Encapsulated Flame Retardant System

The invention will be more particularly illustrated by the following examples. The percentages are by weight unless otherwise specified.

The following examples demonstrate the production of the flame retardant microcapsules of the present invention.

Thirty-two grams of a 3:1 molar adduct of toluene diisocyanate and trimethylolpropane are dissolved in 64 grams of a low viscosity chlorinated aliphatic hydrocarbon (commerically available as Exchlor 4 from the Diamond Shamrock Chemical Co. and containing 45 percent chlorine) and then admixed thoroughly with 800 grams of tris(2,3-dibromopropyl)phosphate (commercially available as Fyrol HB-32 from Stauffer Chemical CO.). The resulting oily solution is emulsified in 3434 grams of a 7 percent by weight of a high molecular weight, 87 percent hydrolyzed, poly(vinyl alcohol) solution (commercially available as Elvanol 50--42 G from E. L. duPont de Nemours Co.) containing 240 grams on a dry basis, in a large Waring-type blender until the emulsion droplets have an average particle size of 3 microns. The emulsion is then cured for 2 hours at 60.degree. C. to harden the capsule walls. The cooled product is diluted at a ratio of 1:3 with water and allowed to stand for 3 days.

The supernatant liquid is poured from the sediment, and the sediment is redispersed in 3 liters of fresh water and permitted to settle once it began. The sediment is then spray-dried at 52 percent by weight solids at a temperature of 65.degree.-93.degree. C. to give a dry, free-flowing powder containing 85 percent by weight volatile oils. The dry powder comprises microcapsules having an average particle diameter of 3 microns and containing the flame retardant bis(2,3-dibromopropyl)phosphate.

Sixteen grams of the microcapsules as produced in Example 1 are combined with 300 grams of a latex flat paint. The mixture is stirred at high shear to provide a flame retardant, water-based paint. When applied to a substrate, the paint provides an opaque, flame-resistant coating.

Eighty-seven parts by weight of a white semigloss latex paint are admixed with 13 parts by weight of a dispersion of microcapsules produced in the manner described in Example 1, (the dispersion containing 79 percent solids). Prior to being incorporated into the paint, the microcapsules are freed of excess poly(vinyl alcohol) by repeated washing with water and centrifugation. A flame retardant paint is thereby provided.

The procedure of Example 3 is repeated with the exception that 82 parts by weight of a white semigloss paint are admixed with 13 parts by weight of the capsule dispersion of Example 3 and five parts by weight of antimony oxide in order to provide a flame retardant paint.

Forty-eight grams of an adduct of toluene diisocyanate and trimethylolpropane are dissolved in 64 grams of the low viscosity, chlorinated aliphatic hydrocarbon of Example 1, and the resulting solution is admixed with 800 grams of tris (2,3-dichloropropyl)phosphate. The resulting solution is emulsified in 2350 grams of an 8 percent by weight polyvinyl alcohol (commercially available as Elvanol 52-42 G) employing a homomixer in order to obtain microcapsules having an average particle diameter less than 2 microns. The resulting emulsion is diluted with 300 grams of water and cured for 2 hours at a temperature of 60.degree.-65.degree. C. The product is then diluted on a 1:1 basis with water, and the capsule solids are separated by centrifugation. The sediment is diluted to one gallon and spray-dried at 11.6 percent solids while at a temperature of 65.degree.-135.degree. C. to give a dry, free-flowing powder.

Microcapsules having an average particle diameter below one micron are provided by dissolving 4 grams of the adduct of toluene diisocyanate and trimethylolpropane employed in the previous examples in 45 grams of a chlorinated aliphatic hydrocarbon. The resulting solution is emulsified in 150 milliliters of a 7 percent by weight, high molecular weight, 87 percent hydrolyzed polyvinyl alcohol solution containing 0.25 grams of the surfactant, sodium lauryl sulfate (30 percent by weight).

The resulting emulsion has a uniform particle diameter of one micron and less. The emulsion is cured for 3 hours at 60.degree.-70.degree. C.

This example demonstrates the incorporation of microcapsules into regenerated cellulose fibers.

Ten grams of filter paper are treated with caustic, then with carbon disulfide, and finally dissolved in dilute caustic in order to form an aqueous solution of sodium cellulose xanthate. After suitable aging or ripening of the viscose solution, 1.5 grams of microcapsules made in the manner of Example 6, but containing tris(2,3-dibromopropyl) phosphate and spray-dried, are dispersed in the sodium cellulose xanthate solution. The resulting mixture is filtered and then passed through a spinneret and extruded into a spinning solution containing 8-10 percent sulfuric acid, about 15 percent sodium sulfate, one percent zinc sulfate and about 6 percent glucose. The resulting solution from the spinneret is coagulated in the bath as a filament of regenerative cellulose containing the flame retardant microcapsules. The rayon fibers are then collected and upon testing have greatly reduced flammability, while their other physical characteristics remain similar to untreated rayon.

The following example demonstrates production of a urethane foam containing the microcapsules of the present invention.

Rigid, Freon-blown urethane foam is prepared by admixing 11. 7 grams of a polyol resin component, i.e., a polypropylene glycol, and 18.3 grams of polyisocyanate. This results in a rapid initiation of an exothermic reaction and production of a rigid foam.

A second batch is prepared with the same proportions, but additionally, 3 grams of the spray-dried capsules of Example 7 containing 85 percent active flame retardant are thoroughly dispersed in the resin component before admixing the resin and the isocyanate.

The resulting foam shows no impairment of physical properties due to the presence of the microcapsules. On the other hand, the untreated foam burns vigorously when ignited, while the foam containing the flame retardant microcapsules is self-extinguishing.

In a manner similar to Example 8, a rigid, carbon dioxide blown urethane foam is prepared by reacting 10.6 grams of a polyester base resin with 9.4 grams of a polyisocyanate in order to provide an exothermic reaction with rapid formation of a rigid foam. The procedure is repeated with the exception that one gram of spray-dried microcapsules of Example 5 are thoroughly dispersed in the resin component before combining the resin and the isocyanate. The resulting foam is self-extinguishing, while the microcapsule-less foam burns vigorously.

Three grams of an adduct of toluene diisocyanate and trimethylolpropane are dissolved in 50 grams of tricresyl phosphate. The resulting solution is emulsified in 156 grams of an 8 percent high molecular weight, 87 percent hydrolyzed poly(vinyl alcohol) under conditions of agitation to provide microcapsules having an average diameter of 5 microns or below. The emulsion is diluted with 78 grams of water and cured for 2 hours at 60.degree.-65.degree. C. in order to yield flame retardant microcapsules.

One gram of p,p'-diphenylmethane diisocyanate is dissolved in 10 grams of 1,2,4-trichlorobenzene and then mixed with 50 grams of tris(2,3-dibromopropyl)phosphate in order to provide a clear solution. The solution is then added slowly to 235 grams of an 8.5 percent by weight solution of a high molecular weight, 87 percent hydrolyzed, poly(vinyl alcohol) in a Waring blender in order to provide an emulsion with particles having an average diameter of less than 5 microns.

The emulsion is cured by stirring and heating for a period of 2 hours at 60.degree. C., after which it is cooled and treated with 5 grams of a 60 percent by weight solution of a water-soluble melamine-formaldehyde resin (commercially available as Virset 656-4 from the Virginia Chemical Co.).

Forty-three grams of a 7 percent by weight solution of methylcelluloe (15 centipoise viscosity) are mixed with 10 milliliters of acetylene tetrabromide (29.6 grams solids) and emulsified in a Waring blender. Next, three 10-milliliter portions of water are added to reduce the viscosity. The final particle size of the emulsion droplets is about 4.5 microns. Next, 2 grams of a 63 percent by weight solid solution of a urea-formaldehyde resin (commercially available as RPC 916 from Monsanto Chemical Co.) are added, and the mixture is stirred to provide a flame retardant capsule slurry.

This invention has been described in considerable detail with particular reference to preferred embodiments, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described in the appended claims.