Smoke Retardant Vinyl Chloride and Vinylidene Chloride Polymer Compositions

Vinyl chloride and vinylidene chloride polymers are known to be self-extinguishing and relatively more flame retardant than other polymers such as polyethylene, polypropylene and the like. However, a substantial amount of smoke may be produced upon exposure of vinyl chloride and vinylidene chloride polymers to a flame. Conventional flame retardants such as antimony oxide do not aid in smoke reduction.

The following art is related to the present invention. Salts and oxides of nickel or zinc are effective in amounts up to several percent as condensing agents for polyvinyl halides (U.S. Pat. No. 2,157,997). Zinc oxide can be used together with other materials to flameproof polyvinyl chloride (U.S. Pat. No. 2,610,920). Zinc oxide and zinc halides are known flame retardants in vinyl halide resins (U.S. Pat. No. 3,705,128). Anticorrosive vinyl chloride resins are obtained by compounding the resins with ZnO, ZnCO.sub.3 or certain other metallic compounds (Japan 73-37,742). The stabilizing effect of ZnSO.sub.4, zinc oxide and other compounds on unplasticized polyvinyl chloride was evaluated in 6 Kunstoffe-Plastics 165-168(1959) (53 Chem.Abs.23049f). The fact that an additive is a flame retardant does not necessarily mean that it will have good smoke retardant properties, as is well known to those skilled in the art. New smoke retardant vinyl chloride and vinylidene chloride polymer compositions are desired.

Smoke retardant vinyl chloride and vinylidene chloride polymer compositions are obtained by including therein a synergistic mixture of (A) at least one nickel compound selected from the group consisting of NiCO.sub.3 and nickel citrate and (B) at least one zinc compound selected from the group consisting of ZnO and ZnTiO.sub.3.

The present invention encompasses vinyl chloride and vinylidene chloride polymer compositions containing therein synergistic mixtures of (A) at least one nickel compound selected from the group consisting of NiCO.sub.3 and nickel citrate and (B) at least one zinc compound selected from the group consisting of ZnO and ZnTiO.sub.3.

Vinyl chloride and vinylidene chloride polymers used in this invention include homopolymers, copolymers and blends of homopolymers and/or copolymers. The vinyl chloride and vinylidene chloride polymers may contain from 0 up to about 50% by weight of at least one other vinylidene monomer (i.e., a monomer containing at least one terminal CH.sub.2 = C< group per molecule) copolymerized therewith, more preferably up to about 20% by weight of such monomer. These monomers include 1-olefins having from 2 to 12 carbon atoms, more preferably from 2 to 8 carbon atoms, such as ethylene, propylene, 1-butene, isobutylene, 1-hexene, 4-methyl-1-pentene and the like; dienes having from 4 to 10 carbon atoms including conjugated dienes as butadiene, isoprene, piperylene and the like; ethylidene norbornene and dicyclopentadiene; vinyl esters and allyl esters such as vinyl acetate, vinyl chloroacetate, vinyl propionate, vinyl laurate, allyl acetate and the like; vinyl aromatics such as styrene, .alpha.-methyl styrene, chlorostyrene, vinyl toluene, vinyl naphthalene and the like; vinyl and allyl ethers and ketones such as vinyl methyl ether, allyl methyl ether, vinyl isobutyl ether, vinyl n-butyl ether, vinyl chloroethyl ether, methyl vinyl ketone and the like; vinyl nitriles such as acrylonitrile, methacrylonitrile and the like; cyanoalkyl acrylates such as .alpha.-cyanomethyl acrylate, the .alpha.-, .beta.-, and .gamma.-cyanopropyl acrylates and the like; olefinically unsaturated carboxylic acids and esters thereof, including .alpha.,.beta.-olefinically unsaturated acids and esters thereof such as methyl acrylate, ethyl acrylate, chloropropyl acrylate, butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate, cyclohexyl acrylate, phenyl acrylate, glycidyl acrylate, methoxyethyl acrylate, ethoxyethyl acrylate, hexylthioethyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, glycidyl methacrylate and the like, and including esters of maleic and fumaric acid and the like; amides of the .alpha.,.beta.-olefinically unsaturated carboxylic acids such as acrylamide and the like; divinyls, diacrylates and other polyfunctional monomers such as divinyl benzene, divinyl ether, diethylene glycol diacrylate, ethylene glycol dimethacrylate, methylene-bis-acrylamide, allyl pentaerythritol, and the like; bis(.beta.-haloalkyl) alkenyl phosphonates such as bis(.beta.-chloroethyl) vinyl phosphonate and the like; and the like.

More preferred monomers include 1-olefins having from 2 to 12 carbon atoms, more preferably from 2 to 8 carbon atoms, such as ethylene, propylene, 1-butene, isobutylene, 1-hexene, 4-methyl-1-pentene and the like; vinyl esters and allyl esters such as vinyl acetate, vinyl chloroacetate, vinyl propionate, vinyl laurate, allyl acetate and the like; olefinically unsaturated carboxylic acids and esters thereof, including .alpha.,.beta.-olefinically unsaturated acids and esters thereof such as methyl acrylate, ethyl acrylate, chloropropyl acrylate, butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate, cyclohexyl acrylate, phenyl acrylate, glycidyl acrylate, methoxyethyl acrylate, ethoxyethyl acrylate, hexylthioacrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, glycidyl methacrylate and the like, and including esters of maleic and fumaric acid and the like; and amides of .alpha.,.beta. -olefinically unsaturated carboxylic acids such as acrylamide and the like.

Supporting media such as Al.sub.2 O.sub.3, SiO.sub.2 and other substantially inert inorganic supporting materials known in the art may be used for the smoke retardant additives and in many cases are preferred, since additive surface area is greatly increased for smoke reduction purposes.

Not all nickel compound/zinc compound mixtures are synergistic, and it is difficult or impossible to predict synergism. Mixtures found to be nonsynergistic include NiO and ZnO, NiO and ZnS, NiSO.sub.4 and ZnMoO.sub.4, NiWO.sub.4 and Zn.sub.2 P.sub.2 O.sub.7, and NiWO.sub.4 and Zn.sub.2 SiO.sub.4. Other nonsynergistic combinations include nickel citrate and ZnSO.sub.4, nickel formate and ZnS, NiMoO.sub.4 and zinc ammonium sulfate, NiMoO.sub.4 and zinc formate, and NiSO.sub.4 and zinc oxalate. Thus, it was surprising and unexpected to find synergistic smoke reduction using the specific nickel compound/zinc compound mixtures of this invention.

The additive compounds used in this invention are polycrystalline or amorphous fine powders, preferably with an average particle size less than about 200 microns, more preferably from about 0.5 to about 150 microns. Polymer compositions containing the additives may have colors similar to, although somewhat lighter than, the additives themselves. The additive compounds are used in total amounts from about 0.01 to about 20 parts by weight per 100 parts by weight of polymer. Use of more than about 20 parts by weight of additive per 100 parts by weight of polymer probably will affect adversely other important physical properties, such as tensile strength and the like.

The vinyl chloride and vinylidene chloride polymers may be prepared by any method known to the art such as by emulsion, suspension, bulk or solution polymerization. The additive compounds may be mixed with the polymer emulsion, suspension, solution or bulk mass before monomer recovery and/or drying. More preferably the compounds may be mixed with dry granular or powdered vinyl halide polymers. The polymer and compound may be mixed thoroughly in granular or powder form in apparatus such as a Henschel mixer and the like. Alternatively, this step may be eliminated and the mixing done while the polymer mass is fluxed, fused and masticated to homogeneity under fairly intensive shear in or on a mixer apparatus having its metal surface in contact with the material. The fusion temperature and time will vary according to the polymer composition and level of additive compound but will generally be in the range of about 300.degree. to 400.degree.F and 2 to 10 minutes.

Smoke retardancy may be measured using an NBS Smoke Chamber according to procedures described by Gross et al., "Method for Measuring Smoke from Burning Materials", Symposium on Fire Test Methods - Restraint and Smoke 1966, ASTM STP 422, pp. 166-204. Maximum smoke density (D.sub.m) is a dimensionless number and has the advantage of representing a smoke density independent of chamber volume, specimen size or photometer path length, provided a consistent dimensional system is used. Maximum rate of smoke generation (R.sub.m) is defined in units of min.sup..sup.-1. Percent smoke reduction is calculated using this equation: ##EQU1## The term "D.sub.m /g" means maximum smoke density per gram of sample. D.sub.m and other aspects of the physical optics of light transmission through smoke are discussed fully in the above ASTM publication.

Smoke retardance may be measured quickly using the Goodrich Smoke-Char Test. Test samples may be prepared by dry blending polymer resin and smoke retardant additives. The blend is ground in a liquid N.sub.2 -cooled grinder to assure uniform dispersion of the smoke retardant additives in the resin. Small (about 0.3 g) samples of the polymer blend are pressed into pellets about one-fourth inch in diameter for testing. Alternatively, test samples may be prepared by blending resin, smoke retardant additives and lubricant(s) or processing aid(s) in a blender such as an Osterizer blender. The blend is milled, pressed into sheets, and cut into small (about 0.3 gram) samples for testing. The test samples are placed on a screen and burned for 60 seconds with a propane gas flame rising vertically from beneath the sample. Sample geometry at a constant weight has been found not to be significant for the small samples used in this test. A Bernz-O-Matic pencil flame burner head is used with gas pressure maintained at 40 psig. The sample is immersed totally and continuously in the flame. Smoke from the burning sample rises in a vertical chimney and passes through the light beam of a Model 407 Precision Wideband Photometer (Grace Electronics, Inc., Cleveland, Oh.) coupled with a photometer integrator. Smoke generation is measured as integrated area per gram of sample.

The vinyl chloride and vinylidene chloride polymer compositions of this invention may contain the usual compounding ingredients known to the art such as fillers, stabilizers, opacifiers, lubricants, processing aids, impact modifying resins, plasticizers, antioxidants and the like.

The following examples illustrate the present invention are fully.

The following recipe was used: MATERIAL PARTS ______________________________________ Polyvinyl Chloride* 100.0 Additive (A)** Variable Additive (B)*** Variable ______________________________________ *Homopolymer having an inherent viscosity of about 0.92 - 0.99; ASTM classification GP-4-15443. **Nickel compound selected from the group consisting of NiCO.sub.3 and nickel citrate. The control sample contained no additive. ***Zinc compound selected from the group consisting of ZnO and ZnTiO.sub.3. The control sample contained no additive.

Each experimental sample was prepared by blending resins and additives in a liquid N.sub.2 -cooled grinder to assure uniform dispersion of the smoke retardant additives in the resin. Small (about 0.3 gram) samples of the polymer blend were pressed into pellets about one-fourth inch in diameter and tested using the Goodrich Smoke-Char Test described heretofore. Test results are given in Table I.

These results demonstrate that the defined additives substantially reduce smoke evolution during forced buring of rigid polyvinyl chloride in the Goodrich Smoke-Char Test. The results also demonstrate the smoke retardant effects of individual additives in the same test, except for ZnO. ZnO increases smoke production when used alone and exemplifies the unpredictability of the smoke retardation art.

The improved smoke retardant vinyl chloride and vinylidene chloride polymer compositions of this invention are useful wherever smoke resistance is desirable, such as in carpets, house siding, plastic components for airplane interiors, and the like. Of course, overall suitability for a particular use will depend upon other factors as well, such as comonomer type and level, compounding ingredient type and level, polymer particle size, etc.