Smoke retardant vinyl chloride and vinylidene chloride polymer compositions
BACKGROUND OF THE INVENTION 
     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. 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. 
     SUMMARY OF THE INVENTION 
     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 NiSO 4 , nickel acetylacetonate, nickel formate and nickel oxalate, and (B) V 2  O 5 . 
    
    
     DETAILED DESCRIPTION 
     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 NiSO 4 , nickel acetylacetonate, nickel formate and nickel oxalate, and (B) V 2  O 5 . A more preferred smoke retardant synergistic mixture is (A) NiSO 4  and (B) V 2  O 5 . 
     The additive nickel compounds and V 2  O 5  used in this invention may be polycrystalline or amorphous fine powders, preferably with an average particle size from about 0.01 to about 800 microns, more preferably from about 0.1 to about 200 microns, and even 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 may be used in total amounts from about 0.01 to about 20 parts by weight, more preferably from about 1 to about 10 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 may affect adversely other important physical properties, such as tensile strength and the like. The amount of each additive may constitute from about 1  to about 99% by weight, more preferably from about 10  to about 90% by weight, of the additive compound mixture. Supporting media such as SiO 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/vanadium compound mixtures are synergistic, and it is difficult or impossible to predict synergism. Mixtures found to be nonsynergistic using the Goodrich Smoke-Char Test described hereinafter include Ni(BO 2 ) 2  and Ca 2  V 2  O 7 , NiI 2  and V 2  O 5 , NiMoO 4 .H 2  O and V 2  O 5 , NiO and Ca 2  V 2  O 7 , NiO and Na 3  VO 4 .16H 2  O, NiO and vanadium metal, NiO and VB 2 , and NiO and V 2  O 3 . Other nonsynergistic combinations include Ni 2  O 3  and V 2  O 4 , Ni 2  O 3  and V 2  O 5 , Ni 2  Si and VB 2 , Ni 2  Si and VN, NiSnO 3  and VN, NiSO 4  and NH 4  VO 3 , NiSO 4  and VOSO 4 .2H 2  O, nickel acetylacetonate and vanadium oxyacetylacetonate, and nickel citrate and LaVO 4 . Moreover, vanadium metal used alone was found to increase smoke formation in polyvinyl chloride compositions. Thus it was suprising and unexpected to find smoke reduction using the specific nickel compound/V 2  O 5  mixtures of this invention. 
     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 olefinically unsaturated monomer, more preferably at least one other vinylidene monomer (i.e., a monomer containing at least one terminal CH 2  =C&lt; group per molecule) copolymerized therewith, even more preferably up to about 20% by weight of such monomer. Suitable monomers include 1-olefins containing 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 containing 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, α-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 α-cyanomethyl acrylate, the α-, β- and γ- cyanopropyl acrylates and the like; olefinically unsaturated carboxylic acids and esters thereof, including α, β-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, methylmethacrylate, ethyl methacrylate, butyl methacrylate, glycidyl methacrylate and the like, and including esters of maleic and fumaric acid and the like; amides of the α,β-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-bisacrylamide, allyl pentaerythritol, and the like; and bis(β-haloalkyl) alkenyl phosphonates such as bis(β-chloroethyl) vinyl phosphonate and the like. 
     More preferred monomers include 1-olefins containing 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 α,β-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 α,β-olefinically unsaturated carboxylic acids such as acrylamide 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 polymers. The polymer and compounds may be mixed thoroughly in granular or powder form in apparatus such as a Henschel mixer or 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 polyme composition and level of additive compounds but will generally be in the range of about 300° to 400°F and 2 to 10 minutes. 
     Smoke retardancy may be measured using a NBS Smoke Chamber according to procedures described by Gross et al, &#34;Method for Measuring Smoke from Burning Materials&#34;, Symposium on Fire Test Methods - Restraint &amp; Smoke 1966, ASTM STP 422, pp. 166-204. Maximum smoke density (D 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 m ) is defined in units of min..sup. -1 . Percent smoke reduction is calculated using this equation: ##EQU1## The term &#34;D m  /g&#34; means maximum smoke density per gram of sample. D 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 2  -cooled grinder to assure uniform dispersion of the smoke retardant additives in the resin. Small (about 0.3g) samples of the polymer blend are pressed into pellets about one-quarter 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, Ohio) 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 more fully. 
     EXAMPLE 1-7 
     The following recipe was used:MATERIAL               PARTS______________________________________Polyvinyl chloride*    100Additive (A)**         VariableAdditive (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 NiSO 4 , nickel acetylacetonate, nickel formate, and nickel oxalate. The control sample contained no additive. ***V 2  O 5 . The control sample contained no additive. 
     Each experimental sample was prepared by blending resin and additives in a liquid N 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. 
     
                                           TABLE I                                 
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     Additive (A)    Additive (B)                                         
                             Smoke Formation                              
                                        Smoke                             
Example                                                                   
      (phr)          (phr)   Per Gram of Sample                           
                                        Reduction(%)                      
__________________________________________________________________________
Control                                                                   
      None           None    67.4       --                                
1    NiSO.sub.4 (10) --      13.8       80                                
       --            V.sub.2 O.sub.5 (10)                                 
                             23.7       65                                
     NiSO.sub.4 (5)  V.sub.2 O.sub.5 (5)                                  
                              6.3       91                                
2    Nickel Acetylacetonate (10)                                          
                     --      23.4       65                                
       --            V.sub.2 O.sub.5 (10)                                 
                             23.7       65                                
     Nickel Acetylacetonate (5)                                           
                     V.sub.2 O.sub.5  (5)                                 
                             14.4       79                                
3    Nickel Formate (10)                                                  
                     --      32.2       52                                
       --            V.sub.2 O.sub.5 (10)                                 
                             23.7       65                                
     Nickel Formate (5)                                                   
                     V.sub.2 O.sub.5  (5)                                 
                             14.8       78                                
4    Nickel Oxalate (10)                                                  
                     --      32.0       53                                
       --            V.sub.2 O.sub.5 (10)                                 
                             23.7       65                                
     Nickel Oxalate (5)                                                   
                     V.sub.2 O.sub.5  (5)                                 
                             12.1       82                                
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     These results demonstrate that the defined additive mixtures substantially reduce smoke evolution during forced burning 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. 
     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 may depend upon other factors as well, such as comonomer type and level, compounding ingredient type and level, polymer particle size and the like.