PREPARATION OF FIRE RETARDANT FLEXIBLE POLYURETHANE FOAMS HAVING REDUCED DISCOLORATION AND SCORCH

Abstract: Fire retardant flexible polyurethane foams are prepared with reduced scorch and discoloration by the addition of a stabilizing amount of from about 1 to about 12 parts by weight of a cyclic alkylene carbonate to the formulation, based on the weight of the polyether polyol employed, without affecting the fire retardancy of the foam product.

Description: BACKGROUND OF THE INVENTION Generally, flexible polyurethane foams are detrimentally affected by a discoloration and scorch during the production thereof. Various antioxidant compositions and methods for the use thereof in inhibiting color and/or scorch tendencies in polyurethane foams are known in the art. U.S. Patent Nos. 3,567,664, 4,007,230, 4,265,783 and 4,444,676 describe various antioxidants and the stabiliza­ tion of polyurethane foams. When fire retardant compounds are employed in the formulations to prepare flexible poly­ urethane foams with reduced flammability, discoloration and scorch of the foam are known to increase. As described for example in U.S. Patent No. 4,143,129, a further increase in antioxidants is required to overcome this phenomenon in an attempt to stabilize and reduce the discoloration and scorch to acceptable levels. There is no teaching in the prior art of the effect obtained to stabilize and reduce discoloration and scorch in fire retardant flexible poly­ urethane foams with the cyclic alkylene carbonate of the instant invention. SUMMARY OF THE INVENTION This invention relates to the novel method for the stabilization and reduction of discoloration and scorch in fire retardent flexible polyurethane foams. Specific­ ally the invention relates to a method for stabilizing and reducing the discoloration and scorch in fire retarded flexible polyurethane foams by the addition, to the formulation used in preparation of the foam, of from about 1 to about 12 parts by weight of a cyclic alkylene carbonate based on the weight of a polyether polyol employed in the formulation. It is an object of this invention to provide a novel method for the preparation of a fire retarded flexible polyurethane foam having reduced discoloration and scorch without adversely affecting the flammability charac­ teristics of the foam. These and other objects and advantages of this invention will become apparent from the description of the invention which follows and from the claims. DETAILED DESCRIPTION OF THE INVENTION According to the present invention, fire retar­ dant flexible polyurethane foams are stabilized to provide a reduction in discoloration and scorch by incorporating in the formulation to produce the foam, from about 1 to about 12 parts by weight of a cyclic alkylene carbonate based on 100 parts by weight of polyether polyol employed in the formulation, said carbonate having the formula wherein R is independently hydrogen, an alkyl group having from 1 to 8 carbon atoms an alkenyl group having from 1 to 8 carbon atoms or a phenyl group. Preparation of the fire retardant polyurethane foams which includes the stabilizing cyclic alkylene carbonate of the present invention may be accomplished by any of the standard prior art procedures. Typical poly­ urethane foam preparation is disclosed for example in U.S. Patent No. 3.567,664. Preparation includes the prepolymer, quasi-prepolymer or one shot methods. Generally the poly­ oxyalkylene polyether polyols are reacted with an organic polyisocyanate in the presence of a catalyst, a surfactant and a blowing agent as well as the stabilizing and various other additions such as fillers, dyes, etc., if desired. In order to obtain the optimum benefit of the stabilizing cyclic alkylene carbonate, it is preferably admixed with the polyoxyalkylene polyether polyol prior to employing the polyol with the isocyanate in the preparation of the urethane foams. However, the cyclic carbonate may be added alone or with other reactants such as the isocyanate when preparing the polyurethane foam. The proportion of the cyclic carbonate stabilizer when using the latter technique, would be based upon the proportion of polyalkylene poly­ ether polyol employed. The cyclic alkylene carbonates which may be employed as stabilizers to reduce discoloration and scorch in fire retarded flexible polyurethane foams in amounts of from about 1 to about 12 preferably 2 to 6 weight percent based on 100 parts of the polyoxyalkylene polyether polyol include for example ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, styrene carbonate, vinyl ethylene carbonate, phenyl ethylene carbo­ nate, mixtures thereof and the like. Liquid alkylene carbonates are preferred, however, solid or semisolid carbonates may be used if essentially liquified via the polyether polyol, isocyanate or other liquid carbonates. As an example, ethylene carbonate which is a solid at room temperature may be employed in admixture with propylene carbonate in which it is soluble. Mixture may range, for example, from about 5 to 80 weight percent ethylene carbonate to between 95 and 20 weight percent propylene carbonate. The flame or fire retardant compounds which may be employed in the preparation of the scorch and discolora­ tion stabilized flexible polyurethane foams according to the invention are generally the halogenated alkyl phosphate esters and the poly (haloethyl-alkyoxy) phosphoric acid esters. Representative fire retardants include for example dibromoneopentyl alcohol, tricresylphosphate, triethyl­ phosphate, tris (2-chloroethyl) phosphate, tris (chloropropyl) phosphate, tris (dichloropropyl) phosphate, tris (dibromo­ propyl) phosphate and the like, or mixtures thereof, tetrakis (2-chloroethyl) ethylene diphosphate (Sold commercially under the trademark "Thermolin 101" by Olin Chemical), tetrakis [2-chloroethyl] bis-2 (2-chloromethyl) propylene diphosphate and oligomers thereof (Sold commercially under the trademark "Fyrol EFF" by Stauffer Chemical Company). In general between about 2 and about 25 preferably 5 to 15 weight percent of the flame retardant is employed based on 100 parts of the polyether polyol. The polyether polyols used in this invention include those polyols used to prepare flexible foams. The "flexible" polyether polyols have a hydroxyl number of from about 25 to 75 and a functionality of 2 to 3. The polyols may be diols or triols derived from alkylene oxides and may be, for example, made with alkylene oxide mixtures such as propylene oxide/ ethylene oxide mixtures. Molecular weight will generally range from about 1000 to 6500. Preferably the higher molecular weight polyols are employed. A typical polyether polyol used to prepare a flexible polyurethane foam is sold commercially for example, as "Olin 3256" (Olin Chemical Company) and is a 3000 molecular triol containing a high percentage of secondary hydroxyl groups. The organic di- or polyisocyanates employed as reactants in the present invention include aliphatic, alicylic and aromatic polyisocyanates characterized by containing two or more isocyanate (NCO) groups per molecule. Such polyisocyanates include the diisocyanates and higher functionally isocyanates, particularly the aromatic isocyanates. Mixtures of polyisocyanates may be used which for example are the crude mixtures of di- and higher func­ tional polyisocyanates produced by phosgenation of aniline­ formaldehyde condensates or as prepared by the thermal decomposition of the corresponding carbamates dissolved in a suitable solvent as described in U.S. Patent Nos. 3,962,302 and 3,919,279, both known as crude MDI. The isocyanates may contain impurities or additives such as carbodiimides, isocyanurate groups, urea, hydrolyzable chlorides and biurets. Illustative of such di- or poly­ isocyanates which may be employed are, for example, toluene-2,4- and 2,6-diisocyanate or mixtures thereof, diphenylmethane diisocyanate 4,4' and 2,4' isomers or mixtures thereof, napthalene-1,5-diisocyanate, 3,3'-dimethyl diphenylmethane-4,4'-diisocyanate, triphenylmethane triisocyanate, hexamethylene diisocyanate, 3,3'-ditolylene-4,4'-diisocyanate, butylene-1,4-diisocyante, octylene-1,8-diisocyanate, 4-chloro-1,3-phenylene diisocya­ nate, 1,4-, 1,3- and 1,2-cyclohexylene diisocyanates and in general the polyisocyanates disclosed in U.S. Patent No. 3,577,358. The preferred polyisocyanates are mixtures of toluene -2,4- and 2,6-diisocyanates and the diphenylmethane diisocyanate 2,4' and 4,4' isomers including the 2,2' isomer. The tertiary amine catalysts which may be employed in amounts of from about 0.1 to about 5.0 prefer­ ably 0.2 to 3.0 parts by weight based on the 100 parts of the polyether polyol mixture include, for example, N-methyl morpholine, dimethylaminocyclohexane, triethylenediamine, bis (2-dimethylaminoethyl) ether sold commercially as "NIAX A-1" by Union Carbide Company, dimethylethanolamine, trimethylaminopropylethanolamine, trimethylhydroxyethyl ethylenediamine and 1,8diazabicyclo[5.4.0] undec-7-ene and the like. Metal salts such as stannous octoate, lead octoate, dibutyltin dilaurate as well as mixtures of the tertiary amines and organic salts may be employed as catalysts. The metal salts may be employed in amounts of from about 0.01 to about 2.5 parts by weight based on the polyether polyol. The preferred blowing agent for use in the instant invention is CO₂ which is generated by the addition of water in amounts of from about 1 to about 9 preferably 2 to 6 parts by weight based on the weight of the polyol and which reacts with the isocyanate. Instead of water alone, fluorocarbons having a boiling point below about 60°C mixed with water as well as methylene chloride mixed with water may also be employed. Typical mixtures of organic blowing agents and water may be from 30 to 40 parts water and up to 40 parts organic blowing agent. The fluorocarbons which may be used include, for example, difluorodichlorome­ thane, difluorochloromethane, trichlorofluoromethane, difluoroethane, difluoropropane, difluorochloroethane, trifluorotrichloroethane, and the like. The silicone surfactant which acts to compatibi­ lize and stabilize the foam reaction mixture is added to the formulation in amounts of from about 1 to about 3 parts by weight per 100 parts of polyether polyol. These surfactants are organo-polysiloxanes such as the polyalkylene oxide siloxane block copolymers which may contain hydrolyzable SiOC groups such as Union Carbide Corporation's "L-520", "L-560", "L-5750" or "L-6202". The following examples are provided to illustrate the invention in accordance with the principles of this invention, including examples of a comparative nature, but are not to be construed as limiting the invention in any way except as indicated by the appended claims. Discoloration and foam scorch were determined by preparing low density flexible foams with and without stabilizing cyclic carbonate which were then subjected to a scorch test. After mixing all the required foam ingre­ dients, the mixture was immediately poured into a 10" X 10" X 5" box and allowed to rise. After 5 minutes from the start of the isocyanate mixing, the polyurethane foam was placed into a preheated microwave oven for a specified time at 30% power setting. At the end of the microwave treat­ ment, the foam was allowed to cure for 24 hours at room temperature. The foam was then cut parallel to the foam rise and discoloration and scorch measurements taken by use of a Gardner XL-10 Tristimulus Colorimeter as described in "A Rapid Predictive Foam Test For Urethane Foam Scorch" by M. J. Reali and B. A. Jacobs in the Journal of Cellular Plastics Nov./Dec. 1979 (Volume 15, No. 6.). Greater discoloration values signify more discoloration and scorch. All numerical values in the examples are parts by weight unless otherwise noted. The results of Examples 1-4 show that addition of the propylene carbonate reduces the intensity of discolor­ ation and scorch and does not adversely affect the flammability results of the polyurethane foam. EXAMPLE 9 100 parts of a 35 hydroxyl number ethylene oxide capped triol is mixed with 3.2 parts water, 0.6 parts diethanolamine, 24 parts of a 43 hydroxyl number triol cell opener, 0.84 g. of silicon surfactant "L-5750", 9.6 parts of difluorodichloromethane blowing agent and 1.12 g. of a tertiary amine catalyst mixture consisting of triethylene­ diamine and bis(2-dimethylaminoethyl) ether in an 8 to 1 ratio. To this stirred mixture was added 57.6 parts of diphenylmethane diisocyanate (MDI) with 25% 2,4' isomer and 75% 4,4' isomer containing a 32% NCO value. Flexible polyur­ ethane foams prepared from this formulation showed decreased scorch and discoloration on the addition of 4 parts propylene carbonate.

Claims: 1. A method for the preparation of a scorch and discoloration stabilized fire retarded flexible poly­ urethane foam which comprises reacting an organic di- or polyisocyanate with a polyoxyalkylene polyether polyol having a hydroxyl number of about 25 to 75 and a function­ ality of 2 to 3 in the presence of a fire retardant compound, a polyalkylene oxide siloxane block copolymer surfactant, a tertiary amine or organic metal salt catalyst, a blowing agent selected from the group consisting of water which reacts with the di- or polyisocyanate to generate carbon dioxide and fluorocarbons having a boiling point below 60°C mixed with water and methylene chloride mixed with water and from about 1 to about 12 parts by weight, based on 100 parts by weight of the polyether polyol, of a cyclic alkylene carbonate of the formula wherein R is independently hydrogen, an alkyl group having from 1 to 8 carbon atoms, an alkenyl group having from 1 to 8 carbon atoms or a phenyl group. 2. A method according to claim 1 wherein the di- or polyisocyanate is selected from a mixture of toluene 2,4- and toluene 2,6-diisocyanates, and diphenylmethane diisoycanate. 3. A method according to claim 1 or claim 2 wherein the flame retardant compound is a halogenated alkyl phosphate ester. 4. A method according to claim 3 wherein the flame retardant is selected from tetrakis (2-chloroethyl) ethylene diphosphate, tetrakis (2-chloroethyl) bis-2(2 chloromethyl) propylene diphosphate and oligomers thereof. 5. A method according to any one of claims 1 to 4 wherein the tertiary amine catalyst is triethylenediamine. 6. A method according to any one of claims 1 to 4 wherein the organic metal salt is stannous octoate. 7. A method according to any one of claims 1 to 5 wherein the cyclic alkylene carbonate is selected from ethylene carbonate, propylene carbonate and mixtures thereof. 8. A method according to claim 7 wherein the cyclic alkylene carbonate is propylene carbonate. 9. A method for the preparation of a scorch and discoloration stabilised fire retardant flexible polyurethane foam which comprises reacting a mixture of 2,4'- and 2,6'toluene diisocyanate with a polyoxyalkylene polyether polyol having a hydroxyl number of about 25 to 75 and a functionality of 2 to 3 in the presence of a halo­ genated alkyl phosphate ester fire retardant compound, a polyalkylene oxide siloxane block copolymer surfactant, a triethylenediamine catalyst, stannous octoate catalyst, water and from about 2 to about 6 parts by weight propylene carbonate based on 100 parts by weight of the polyether polyol.

Inventors: GAUL, JAMES MICHAEL, STATTON, GARY LEWIS
Applicants: ARCO CHEMICAL TECHNOLOGY INC.
Application year: 1986
Main classification: C08K5
IPC codes: C08G18, C08K5