Flame Retardant Flexible Urethane Foams

When polyvinyl chloride, antimony trioxide, and zinc oxide are added to a low density flexible and semiflexible polyetherurethane flame retardant foam formulation including the usual tertiary amines, water, and metal containing catalyst and the formulation is run on production equipment as commercially used to form buns (loaves or slabs) having, for example, a cross-section of about 30 .times. 76 inches and a length of about 40 feet or more, the foam discolors (dark pink or purple) in the center section of the bun as to be virtually unsalable as is commercially.

The only external heat applied to the bun as it moves down the conveyor is that received when it passes through an oven at a speed of about 5 to 12 feet/min. and at a temperature of about 180.degree. F. for the purpose of reducing or eliminating surface tack so that the outside paper can readily be removed without tearing large chunks from the foam.

At the end of the conveyer the buns are removed and stored for about 24 hours without any external heat being applied to permit the foam to finally cure or stabilize by itself. Then the foam is slit into mattress size units or into other sizes for further manufacturing operations. Even at this time the temperature of the center of the bun is well above room temperature.

The exothermic heat of reaction of the foam forming ingredients during foaming reaches temperatures of from about 270.degree. to 350.degree. F. These temperatures are determined by a pyrometer probe at the end of the conveyor line and can be higher than shown considering that the mass of the pyrometer is greater than that of the surrounding foam.

Accordingly, it is a primary object of this invention to avoid the difficulties alluded to above, and to provide flexible and semiflexible polyetherurethane flame retardant low density foams containing halogen containing polymers, antimony trioxide, and zinc oxide and which exhibit resistance to or freedom from discoloration after foaming and to provide a method for making the same.

These and other objects and advantages of the present invention will become more apparent to those skilled in the art from the following detailed description and example.

According to the present invention it has now been discovered that the addition of a small amount of a zinc salt selected from the group consisting of ##STR3## --halogen, --hydrogen, or a --nitro group, R' being a C.sub.1 to C.sub.10 alkyl, cycloalkyl, aralkyl, alkaryl or aryl group, preferably said zinc salt having the formula ##STR4## to a commercial bun or slab flexible and semiflexible polyetherurethane foam formulation, prior to the blowing thereof into a foam, and also containing finely divided zinc oxide, antimony trioxide, a chloride-containing solid polymer and optionally a chlorinated paraffin wherein the chlorinated paraffin is used to replace part of the chlorine-containing polymer and wherein the amount of the zinc oxide is reduced in proportion to the reduction in the chlorine-containing polymer, will provide foams in which the discoloration is reduced or substantially reduced.

The zinc salt is selected from the group consisting of ##STR5## --halogen, --hydrogen, or --nitro group, R' being a C.sub.1 to C.sub.10 alkyl, cycloalkyl, aralkyl, alkaryl or aryl group, preferably said zinc salt has the formula: Thus, R can be hydrogen, methyl, ethyl, propyl, isopropyl, butyl, amyl, decyl, cyclohexyl, cyclobutyl, phenyl, cycloheptyl, tolyl, benzyl, xylyl, mesityl, cumyl, phenylethyl, phenylpropyl, phenyl butyl, methoxy, phenoxy, propoxy, ethoxy, butoxy, phenylpropoxy, methyl phenoxy, chlorine, bromine, fluorine, iodine, and/or nitro (--NO.sub.2). See U.S. Pat. Nos. 2,102,547; 2,129,621; 2,170,670; 2,798,106; 2,754,303; and 3,043,847.

Preferably, the zinc salt used in the practice of the present invention is the zinc salt of 2-mercaptobenzothiazole and is available commercially as "ZETAX" (R. T. Vanderbilt Co., Inc.,) "Pennac ZT" (Pennwalt Corp.), and "ZMBT" (American Cyanamide Co.)

The zinc salt is used in finely divided form such as a powder and should be essentially free of impurities which would adversely affect the foam or foaming operation. The amount of the zinc salt to use will vary from about 0.05 to 5.00, preferably from about 0.2 to 1.0, parts by weight per 100 parts by weight of the total polyol used in the foam formulation.

The flame retardant polyurethane foaming composition or formulation must contain per 100 parts by weight of the organic polyol, as flame retardant ingredients from about 0.1 to 10 parts, preferably from about 0.2 to 5 parts, of zinc oxide, from about 0.5 to 15 parts, preferably from about 1 to 10 parts, of antimony trioxide (Sb.sub.2 O.sub.3) and the chlorine-containing polymers as described below.

The chlorine-containing solid polymers employed herein include polymers, usually resinous in character, of vinyl chloride and vinylidene chloride and mixtures of these monomers as well as copolymers of a predominating molar amount of one or more of these monomers and a minor molar amount of vinyl acetate, acrylonitrile, methacrylonitrile, dimethyl or diethyl maleate or fumarate, methyl acrylate, methyl methacrylate, ethyl ethacrylate, vinyl stearate and the like and mixtures thereof. Still other halogen-containing resins can be used such as hydrolyzed or partially hydrolyzed copolymers of a major molar amount of vinyl chloride and a minor amount of vinyl acetate. Moreover, other resinous polymers can be used such as chlorinated rubber, chlorinated polyethylene, chlorinated polyvinyl chloride and the like. Mixtures of the chlorine-containing polymeric resins can be used.

These chlorine-containing polymeric resins should be finely divided (powders having average particle sizes of from about 0.00001 to 1 mm.) and have an intrinsic viscosity of from about 0.25 to 2.5, preferably from about 0.5 to 1.5. The chlorine-containing resinous polymers are generally used in an amount of from about 1 to 50 parts by weight per 100 parts by weight of the polyol, preferably from about 2 to 25 parts by weight. The larger particle size resins can be used in larger amounts within the given ranges. However, the finer or smaller particles size resins should be used in smaller amounts within the ranges shown to avoid the formation of viscous, difficult to pump or stir, fluids, gels or pastes. The chlorine-containing polymers can be made by bulk, solvent, emulsion or suspension polymerization process. A preferred polymer to use is polyvinyl chloride which has been prepared by emulsion polymerization. An added advantage in some cases in using these resins is an increase in the load bearing properties of the foam.

Optionally, part of the chlorine-containing polymeric resin used in the foam formulation can be replaced with a chlorinated paraffin or with mixtures of chlorinated paraffins. These materials are made by the chlorination of liquid paraffin fractions and/or paraffin waxes. The chlorinated paraffins have average molecular weights of from about 250 to 1400 and chlorine contents of from about 40 to 70% by weight. They can be liquids or solids; preferably the liquid (at room temperature, 20.degree. to 30.degree. C.) chlorinated paraffins are employed in the practice of the present invention. Also, it is preferred that the chlorinated paraffins be odor-free or substantially odor-free. Examples of chlorinated paraffins are the Cereclor (I.C.I. America, Inc.) chlorinated paraffins Nos. 42, S.45, S.52, and 70, and the Chlorowax (Diamond Shamrock Chemical Company) chlorinated paraffins Nos. 40, 50 and 70. Still other chlorinated paraffins can be used. The chlorinated paraffin is used in an amount by weight sufficient to replace from about 5 to 80% by weight of the chlorine-containing polymeric resin on essentially a percent by weight chlorine (Cl) basis. For example, based on 100 parts by weight of polyol in a given formulation, if 20 parts by weight of polyvinyl chloride (about 57% by weight of chlorine --]Cl) containing 11.40 parts of chlorine is reduced to 10 parts by weight of PVC in the formulation, a chlorinated paraffin containing 42% by weight of chlorine (Cl) should be added in an amount of about 13.7 parts by weight (to provide a total chlorine content of 11.45 parts by weight). Similar adjustments can be made with other chlorine-containing polymeric resins and other chlorinated paraffins.

The zinc oxide should be finely divided, for example, it should have an average particle size of from about 0.05 to 200 microns, preferably from about 0.15 to 50 microns. It should not contain any appreciable amount of impurities which would adversely affect the foaming reaction or the properties of the resulting foams. The zinc oxide may be American process zinc oxide, French process zinc oxide, or zinc oxides produced by other processes. Zinc oxide is a well known material and is shown by:

A. "Encyclopedia Of Chemical Technology," Kirk and Othmer, The Interscience Encyclopedia, Inc., New York, Vol. 15, 1956, pages 262-266;

B. "Zinc," Mathewson, Reinhold Publishing Corporation, New York, 1959, pages 346 to 385; and

C. "Compounding Ingredients For Rubber," Third Edition, 1961, Rubber World, New York, pages 65, 72, 77, 80, 81 and 88.

When part of the chlorine-containing polymeric resin is replaced with a given amount of the chlorinated paraffin, the amount of zinc oxide should be reduced by a proportionate amount essentially equivalent to the amount of polymer eliminated. For example, where 5% by weight of the chlorine-containing polymeric resin is replaced with the chlorinated paraffin, then the amount of zinc oxide normally employed should be reduced by about from 4 to 7%, usually 5%, by weight. Where the amount of the chlorine-containing polymeric resin is reduced by 50% by weight (and replaced with an essentially equivalent amount of the chlorinated paraffin on a chlorine basis), the amount of zinc oxide used should be reduced by about 50% by weight.

The antimony trioxide, also, should be finely divided, for example, it should have an average particle size of from about 0.05 to 200 microns, preferably from about 0.15 to 50 microns. It should not contain any deleterious materials which would adversely affect the foaming reaction or the properties of the resulting foam. The smaller particle sizes of antimony trioxide are most effective in the foam.

Polyols used in making the polyurethanes of the present invention are generally primary and secondary hydroxy-terminated polyoxyalkylene ethers havng from 2 to 4 hydroxyl groups and a molecular weight of from about 1,000 to 10,000. They are liquids or are capable or being liquefied or melted for handling in the polyurethane foaming apparatus or machine.

Examples of polyoxyalkylene polyols include linear and branched polyethers having a plurality of ether linkages and containing at least two hydroxyl groups and being substantially free from functional groups other than hydroxyl groups. Among the polyoxyalkylene polyols which are useful in the practice of this invention are the polypropylene glycols, the polypropylene-ethylene glycols, and the polybutylene ether glycols. Polymers and copolymers of alkylene oxides are also adaptable in the processof this invention as well as the block copolymers of ethylene oxide and propylene oxide and the like. Among the polymers and copolymers that deserve some special mention are the ethylene oxide, propylene oxide and butylene oxide adducts of ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, 2-ethylhexanediol1,3, glycerol, 1,2,6-hexanetriol, trimethylolpropane, trimethylolethane, pentaerythritol, triethanolamine, triisopropanolamine, ethylenediamine, and ethanolamine. Linear and branched copolymers of other alkylene oxides are also useful in making the foamed products of this invention as well as the polypropylene diols, triols and tetrols end-blocked with ethylene oxide to provide primary hydroxyl groups in the polymer and having molecular weights of from about 2000 to 5000.

Examples of useful types of polyetherpolyols are characterized by reference to the following general formulae: ##STR6## where in Formula A the total of subscripts, x, y, and z represent positive integers in the range of from 20 to 70 and the total of subscripts a and b of Formula B represent positive integers in the range of from 20 to 100.

Branched polyethers have the advantage of making possible cross linking without the interaction of urea or urethane groups with the isocyanate groups. This has the advantage of making a larger proportion of the isocyanate used available for the evolution of carbon dioxide and the reducing of the overall amount of isocyanate that is required in the preparation of the foamed polymer. Mixtures of polyether polyols can be used.

Likewise, there can be used as polyols grafts of ethylenically unsaturated monomers such as acrylonitrile, methacrylonitrile, vinyl acetate, methyl acrylate and the like on the polyols and having the functionality and molecular weight as shown above. Such graft polyols and methods for making the same are shown in U.S. Pat. Nos. to Stamberger, Nos. 3,304,273 and 3,383,351 and in U.S. Pat. No. to Von Bonin, No. 3,294,711 where the monomer or monomers are polymerized with a free-radical or other catalyst in admixture with the polyol.

When desired, cross-linking materials having from 2 to 8 hydroxyl groups can be included in the foam formulation to increase cross link density and so forth. They have molecular weights of from about 60 to 600. Only small amounts of such materials are generally needed (about 0.3 to 10 mols per 100 mols of polyol). Examples of such crosslinking agents are glycol, diethylene glycol, propylene glycol, butane diol-1,4, dipropylene glycol, glycerol, trimethylolpropane, butane triols, hexanetriols, trimethylolphenol, various tetrols, such as erythritol and pentaerythritol, pentols, hexols, such as dipentaerythritol and sorbitol, as well as alkyl glucosides, carbohydrates, polyhydroxy fatty acid esters such as castor oil and polyoxy alkylated derivatives of poly-functional compounds having three or more reactive hydrogen atoms, such as, for example, the reaction product of trimethylolpropane, glycerol, 1,2,6-hexanetriol, sorbitol and other polyols with ethylene oxide, propylene oxide, or other alkylene epoxides or mixtures thereof, e.g., mixtures of ethylene and propylene oxides. Grafted crosslinkers can be prepared by the process of the aforementioned Stamberger and Von Bonin U.S. Patents. Mixtures of crosslinkers can be used. All of the polymer-forming ingredients should preferably be free of any amine function which is not sterically hindered or shielded.

Any organic di- or tri- isocyanate can be used in the practice of the present invention. Diisocyanates are preferred, particularly when there is any considerable amount of branching in the polyol or crosslinker to avoid the formation of rigid or semi-rigid foams. Examples of suitable organic polyisocyanates to use are ethylene diisocyanate, trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, propylene-1,2-diisocyanate, butylene-1,2-diisocyanate, butylene-1,3-diisocyanate, butylene-2,3-diisocyanate, alkylidene diisocyanates such as ethylidine diisocyanate and butylidine diisocyanate; cycloalkylene diisocyanates such as cyclopentylene-1,3-diisocyanate, cyclohexylene-1,2-diisocyanate, cyclohexylene-1,3-diisocyanate, and cyclohexylene-1,4-diisocyanate; cycloalkylidene diisocyanates such as cyclopentylidene diisocyanate and cyclohexylidene diisocyanate; aromatic diisocyanates such as m-phenylene diisocyanate, p-phenylene diisocyanate, polymethylene polyphenylisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, bitolylene diisocyanate, naphthalene-1,4-diisocyanate, and diphenylene-4,4'-diisocyanate; aliphatic-aromatic diisocyanates such as xylylene-1,4-diisocyanate, xylyene-1,3-diisocyanate, bis(4-isocyanatophenyl) methane, bis (3-methyl-4-isocyanatophenyl) methane, and 4,4'-diphenylpropane diisocyanate, durene diisocyanate, 4,4', 4"-tris (isocyanatophenyl) methane, 3,10-diisocyanatotricyclo[5.2. 1.0.sup.2, 6 ] decane, bis-(2-isocyanatoethyl) carbonate, and naphthalene triisocyanate and the like. Mixtures of polyisocyanates can be used.

The polyisocyanate is used in an amount sufficient to react with the active hydrogen atoms (as determined by the Zerewitinoff method, J.A.C.S., Vol. 49, p. 3181 (1972)) in the polyols, crosslinkers, water, chlorine-containing polymeric resins (such as partially hydrolyzed vinyl chloride-vinyl acetate copolymers) and any other active hydrogen-containing material in the polyurethane foam formulation to provide the desired degree of cross-linking, chain extension, urea groups, blowing and so forth to obtain the desired flexibility, strength and other physical properties.

Water is used as a blowing agent and is employed in amount of from about 1.0 to 6.5 parts by weight per 100 parts by weight of the polyol.

The water should be substantially or essentially pure, that is, it should be free of impurities such as ions, sols, etc. of mineral, vegetable or synthetic origin and the like which would adversely affect the foaming action or the properties of the resultant polyurethane foam. Deionized, distilled or otherwise purified water should be employed.

If lower density and softer foams are desired there additionally can be added to the polyurethane foam formulation separately or in admixture with one of the other components, i.e., polyol or polyisocyanate, etc., up to about 25 parts by weight of a flurocarbon blowing agent per 100 parts by weight of the polyol. Examples of such blowing agents are those fluorine substituted aliphatic hydrocarbons which have boiling points between about -40.degree. C. and +170.degree. C., and which vaporize or at below the temperature of the foaming mass. The blowing agents include, for example, trichloromonofluoromethane, dichlorodifluoromethane, dichloromonofluoromethane, bromotrifluoromethane, chlorodifluoromethane, 1,1-dichloro-1-fluoroethane, 1,1-difluoro1,2,2-trichloroethane, chloropentafluoroethane, 1-chloro-1-fluoroethane, 1-chloro-2-fluoroethane, 1,1,2-trichloro-1,2,2-trifluoroethane, 1,1,1-trichloro-2,2,2-trifluoroethane, 2-chloro-nona-fluoro-butane, hexafluorocyclobutene, and octafluorocyclobutane. Still other easily vaporizable fluorocarbons can be used. Mixtures of the fluorocarbons can be used. Still other blowing agents can be used in full or partial replacement of the fluorocarbons such as propane, butane, pentane, pentene, hexane and so forth, and mixtures thereof, particularly were precautions are taken to prevent explosions or where removal of the gasses is provided. See U.S. Pat. Nos. 3,072,582 and 3,391,093.

Catalysts for the polyetherpolyol-polyisocyanate reaction can be any catalyst heretofore used in the art particularly the metal-containing catalysts. Examples of such catalysts are (1) tertiary phosphines such as trialkylphosphines, dialkyl-benzylphosphines, and the like; (2) strong bases such as the alkali and alkaline earth metal hydroxides, alkoxides, and phenoxides; (3) acidic metal salts of strong acids such as stannic chloride, stannous chloride, antimony trichloride, bismuth nitrate, bismuth chloride, and the like; (4) alcoholates and phenolates of various metals such as Ti(OR).sub.4, Sn(OR).sub.4, Sn(OR).sub.2, Al(OR).sub.3, and the like, wherein R is alkyl or aryl, and the reaction products of alcoholates with carboxylic acids, beta-diketones and 2-(N,N-dialkylamino) alkanols, such as the well known chelates of titanium obtained by said or equivalent procedures; (5) salts of organic acids with metals such as alkali metals, alkaline earth metals, Al, Sn, Pb, Mn, Co, Bi, Sb, Ni, and Cu, including, for example, sodium acetate, potassium laurate, calcium hexanoate, stannous acetate, stannous octoate, stannous oleate, lead octoate, antimony trineodecanoate, antimony trioleate, bismuth trineodecanoate, metallic driers such as manganese, cobalt, and lead naphthenate and the like; (6) organometallic derivatives of tetravalent tin, trivalent and pentavalent As, Sb, and Bi, and metal carbonyls of iron and cobalt; and (7) the dialkyltin salts of carboxylic acids, e.g., dibutyltin diacetate, dibutyltin dilaurate, dibutyltin maleate, dilauryltin diacetate, dioctyltin diacetate, dibutyltin-bis (4-methylaminobenzoate), dibutyltin-bis(6-methylaminocaproate), and the like; as well as a trialkyltin hydroxide, dialkyltin oxide, dialkyltin dialkoxide, or a dialkyltin dichloride, such as trimethyltin hydroxide, tributyltin hydroxide, trioctyltin hydroxide, dibutyltin oxide, dioctyltin oxide, dilauryltin oxide, dibutyltin-bis(isopropoxide), dibutyltin-bis (2-methylaminopentylate), dibutyltin dichloride, dioctyltin dichloride, and the like and mixtures thereof. Preferred catalysts to use are the divalent tin salts of carboxylic acids having from 2 to 18 carbon atoms. These catalysts are used in an amount of from about 0.1 to 0.9 part by weight per 100 parts by weight of the polyetherpolyol. It is less preferable to use those catalysts, such as the metal salts, alcoholates, hydroxides, alkoxides and phosphines, especially in large amounts, where resins containing ester groups in a substantial amount are used since they tend to hydrolyze the ester linkages thereby causing scission of the backbone polymer chain and lowering of the physical and chemical properties of the resultant foams and so forth, especially under conditions of high temperature and humidity.

Surfactants or emulsifiers are generally necessary to provide the desired cell formation and growth. Polysiloxane-polyoxyalkylene block copolymers are preferred. Polysiloxane-polyoxyalkylene block copolymers are described in U.S. Pat. Nos. 2,834,748 and 2,917,480. The surfactant "non-hydrolyzable" polysiloxane-polyoxyalkylene block copolymers where the polysiloxane moiety is bonded to the polyoxyalkylene moiety through direct carbon-to-silicon bonds, rather than through carbon-to-oxygen-to-silicon bonds, can be used. Cyano containing polysiloxane-polyoxyalkylene copolymers also can be used as surfactants (U.S. Pat. No. 3,846,462); they, also, aid in reducing the amount of other flame retardants employed. These copolymers generally contain from 5 to 95 weight percent, and preferably from 5 to 50 weight percent, of polysiloxane polymer with the remainder being polyoxyalkylene polymer. The copolymers can be prepared, for example, by heating a mixture of (a) a polysiloxane polymer containing a silicon-bonded, halogen-substituted monovalent hydrocarbon group and (b) an alkali metal salt of a polyoxyalkylene polymer to a temperature sufficient to cause the polysiloxane polymer and the salt to react to form the block copolymer. Still other polysiloxane-polyoxyalkylene copolymers known to the art may be employed as well as silicones, turkey red oil and so forth. The surfactant is used in an amount of from about 0.3 to 2.5 parts by weight per 100 parts by weight of the polyether polyol.

It is advantageous to incorporate into the urethane compositions of the present invention at least one organic tertiary amine catalyst, preferably together with a metal-containing co-catalyst. The amount of organic amine catalyst may comprise, per 100 parts by weight of organic polyol, about 0.05 to 3.2 parts by weight. In the case of the polyether polyols where metal catalyst is used for the urethane-forming reaction, it is preferred to use only from about 0.05 to 1.1 part by weight of the amine. On the other hand, where the tertiary amine is taking care of both the foaming (H.sub.2 O+NCO) and network (-ROH+NCO) reactions, the tertiary amines should be used in somewhat larger amounts within the specified ranges. However, since some polyols may differ in residual acid content (from neutralization of KOH catalyst (used to form polyol) with acid) due to incomplete washing, filtering or ion-exchanging of the neutralized polyol and since antimony trioxide has some catalystic effect during the polyurethane foaming and forming reactions, the amount of tertiary amine may necessarily have to be reduced where large amounts of water are used as the primary blowing agent.

In the urethane compositions of the invention there may be used a wide variety of organic tertiary amine catalysts. Such organic amides, include, among others, triethylene diamine, triphenyl amine, triethylamine, N,N,N' ,N'-tetramethyl-1,3-butane diamine, N-methyl morpholine, N-ethyl morpholine, N-acetyl morpholine, N-octyl morpholine, N-coco morpholine, N-phenyl morpholine, N-hydroxyl ethyl morpholine, N-hydroxyl methyl morpholine, 4,4'-dithiodimorpholine, dimethyl piperazine, N,N,N',N'-tetramethyl propane diamine, trimethyl aminoethyl piperazine, N,N-dimethyl ethanolamine, dimethyl hexadecylamine, 1-(2-ethyl-1-hexenyl) piperazine, tri-n-octylamine, tri-methylamine, N,N-dimethyl benzyl amine, triethanolamine, 1,2,4-trimethylpiperazine, N-methyl dicyclohexylamine, and mixtures thereof. The sterically hindered organic tertiary amines, such as methyl dicyclohexylamine, especially those disclosed in U.S. Pat. No. 3,718,611, also, can be employed in the foam formulations if desired.

Other well known constituents can be added to the polyurethane foam recipe such as clay, talc, TiO.sub.2, silica and hydrated silica, CaCO.sub.3, metal chromates, barytes, phthalocyanine green or blue pigments, conventional stabilizers, carbon black, dyes, toners, extending oils, processing oils, epoxided soybean oil (Paraplex G-62), epoxides (Epon 828), tricresyl phosphate, plasticizers, antioxidants, fungicides, bacteriostats, reodorants and the like. These constituents can be added to various amounts to the foaming ingredients to achieve the desired properties in the resultant flexible, low density foams.

The flexible and semiflexible, cellular urethane polymeric foams of the present invention can be used as cushions, mattresses, pillows, packing, cushioning material for furniture, automobiles, rug underlay, interior automobile and other vehicle door panels, seats, arm rests, head rests, and so forth.

The preparation of the polyurethane foams of the present invention can be formed by a process known in the art as the "one-shot" process or by a two step process involving, first, the preparation of a "prepolymer", the well known "semiprepolymer" or "quasi-prepolymer" technique. There all or a portion of the polyol is reacted with all of the organic polyisocyanate, providing a reaction product which contains a high percentage free isocyanate groups and which is reacted with the remaining portion of the hydroxyl-terminated polyol or a crosslinker, together with water, catalysts, the zinc salt, the metal oxides, the chlorine-containing polymeric resin and chlorinated paraffin to form a rubbery, cellular, elastic product.

No matter which particular technique is used, the zinc salt, the chlorine-containing polymeric resin, zinc oxide, antimony trioxide and/or chlorinated paraffin may not only be dispersed with the polyol alone, but alternatively with the organic polyisocyanate along. Still another method within the purview of the present invention involves dispersing these ingredients with a combination of the polyol and the organic polyisocyanate. In any case, it is advantageous to disperse these ingredients thoroughly into whatever particular initial composition is used.

The purple color developed in the polyetherurethane foam bun or slab during production may be caused by some interaction between the polyvinyl chloride and the amines present during the foam formation either present as catalysts (tertiary) per se or as amines (primary or secondary) momentarily present and produced from the isocyanate-water reaction which provides carbon dioxide for blowing. The color formation in the bun, also, is apparently enhanced by the exotherm produced during blowing and urethane/urea formation and by the retention for some period of time of elevated temperatures in the center of the bun due to the insulating nature of the mass of the bun itself. Moreover, while certain amines (primary, secondary and tertiary) have been disclosed as stabilizers or antioxidants for polyvinyl chloride, it is stated that zinc oxide can not ordinarily be used with vinyl chloride polymers. "Vinyl And Related Polymers," Schildknecht, John Wiley & Sons, Inc., New York, 1952, pages 422 and 423 and "Modern Plastics Encyclopedia," Vol. 46, No. 10 A, October, 1969, McGraw-Hill, Inc., New York, pages 1011 and 1061. Accordingly, the discoloration or degree of discoloration may be related to a number of factors including amount of the polyvinyl chloride, amount of amine, zinc oxide, exotherm temperature and so forth.

On the other hand, the present invention shows that by the use of a certain zinc salt in certain amounts the discoloration can be prevented or substantially reduced in production foam buns or slabs of flame retardant polyetherurethane foam containing polyvinyl chloride or other chlorine containing polymeric resin, antimony trioxide and zinc oxide. While the exact mechanism for preventing discoloration is unknown, it is postulated that upon the exothermic heat developed during reaction or by heat applied the zinc salt melts, decomposes or emits vapors within the bun and intermixes with the hot products of the urethane-urea-water reaction to prevent such products or even by-products from interacting with the ingredients of the foam during reaction to cause discoloration of the foam.

The following example will serve to illustrate the present invention with more particularity to those skilled in the art.

Flame retarded urethane foams were prepared using the following formulations:

The physical properties of the resulting polyurethane flexible foams were as follows:

The discoloration associated with these foams was as follows:

Run 1 -- center of bun turned pink and after heat aging for 90 minutes at 160.degree. C turned a dark purple.

Run 2 -- center of bun showed no discoloration and after heat aging for 90 minutes at 160.degree. C still showed no discoloration.

The foams of both runs passed the U.S. Government (FHA) flammability (pill) test No. DOC-FF-1-70.

notes:

1. Propylene oxide adduct of glycerol, secondary hydroxyl triol, 3000 m.w., approximate analysis: OH No. 56.3, Acid No. 0.038, H.sub.2 O 0.018%, Olin Corporation.

2. EH-250 from Ethyl Corp., high molecular weight, plastisol grade, emulsion polymerized. Similar to Geon 121 (The B. F. Goodrich Co.).

3. Finely divided, Red Star Grade from NL Industries.

4. French process, finely divided, Protox 169, New Jersey Zinc Company.

5. Zinc salt of 2-mercaptobenzothiazole, light cream colored powder, American Cyanamide Co.

6. Cyano containing polysiloxane-polyoxyalkylene copolymer, Union Carbide Corp.

7. Tertiary amine catalyst, Union Carbide Corp. (similar in effect to bisdimethylamino ethyl ether, 70% in dipropylene glycol).

8. 33% solution of triethylene diamine in dipropylene glycol, Air Products and Chemicals, Inc.

9. Methyl dicyclohexylamine, Abbott Laboratories, Chemical Marketing Division.

10. 50% solution of stannous octoate in dibutyl phthalate.

11. 80/20 mixture of 2,4-,2,6-isomers of tolylene diisocyanate.