FIELD OF THE INVENTION This invention relates to ignition resistant polymer compositions comprising a thermoplastic polymer, a phosphorous compound and an inorganic additive. This invention relates particularly to halogen-free ignition resistant thermoplastic polymer compositions having a good balance of physical properties and rated V-2, V-1, V-0 and/or 5V in the Underwriters Laboratories Standard 94 (UL 94) flammability test.

BACKGROUND OF THE INVENTION Polymer mixtures which comprise an aromatic polycarbonate, a styrene-containing copolymer and/or graft polymer, for example, ABS, and a flame-retardant are known, for example, from United States Patent (USP) 4,692, 488,5, 204,394, and 5,061, 745. According to this prior art an organic phosphate ester, for example, triphenyl phosphate, tricresyl phosphate, diphenylcresyl phosphate, and/or oligomeric phosphates, can be used as a flame- retardant for such mixtures. Tetrafluoroethylene polymers are often used in combination with such phosphate esters to provide flame retardant mixtures and moldings which can achieve a flammability rating of UL V-0 in the UL 94 vertical (UL 94 V) burning test typically at a thickness of 1.6 mm, together with good impact strength. In other prior art other additives may assist anti-dripping or flame retardancy such as aramid fibers (USP 5,272, 193).

However, thermoplastic molding compounds of the type described in the prior art have the disadvantage that if a UL 94 V-0 flammability rating is required in thinner sections or thinner molded articles, and it is generally more difficult to achieve flame retardancy in thinner sections, then it is not clear that such compositions could achieve such performance and still retain other useful properties.

Increasing the level of the phosphate flame retardant additive may not be successful in achieving the desired flame retardant rating at lower than typical thicknesses and may in any case significantly reduce other useful properties such as impact strength and/or heat distortion temperature. USP 6,448, 316 discloses that some inorganic fillers, such as talc, improve flammability properties at lower thicknesses while others, such as calcium carbonate, do not.

SUMMARY OF THE INVENTION It has surprisingly now been found that it is possible to impart ignition resistance to a thermoplastic polymer, in particular, a carbonate polymer, a styrene-based polymer, or blends thereof, by means of a moderate amount of a phosphorous compound and an effective amount of the particular stated inorganic additive. Said ignition resistant polymer composition having a good balance of physical properties is rated V-2, V-1, V-0 and/or 5V in the UL 94 flammability test.

The present invention relates to molding compounds and articles formed or molded from the polymer mixtures or compounds according to the invention.

In one aspect, the present invention is a process for preparing the abovementioned ignition resistant polymer composition by admixing a thermoplastic polymer, in particular a carbonate polymer, a styrene-based polymer or blends thereof, a moderate amount of a phosphorous compound and an effective amount of a particular stated inorganic additive, in particular calcium carbonate.

In a further aspect, the present invention involves a method of molding or extruding the abovementioned ignition resistant polymer comprising a thermoplastic polymer, in particular a carbonate polymer, a styrene-based polymer or blends thereof, blended with a moderate amount of a phosphorous compound and an effective amount of a particular stated inorganic additive, in particular calcium carbonate.

In yet a further aspect, the invention involves molded or extruded articles of the abovementined ignition resistant polymer composition comprising a thermoplastic polymer, in particular a carbonate polymer, a styrene-based polymer or blends thereof, blended with a moderate amount of a phosphorous compound and an effective amount of a particular stated inorganic additive, in particular calcium carbonate.

The ignition resistant polymer compositions of the present invention are especially useful in the preparation of molded objects notably parts required to meet UL 94 V-2 rating

or better. These compositions are particularly suited for use in thinwall instrument housings such as for power tools, appliances, consumer electronic equipment such as TVs, VCRs, web appliances, electronic books, etc. , or information technology equipment such as telephones, computers, monitors, fax machines, battery chargers, scanners, copiers, printers, hand held computers, etc.

DETAILED DESCRIPTION OF THE INVENTION Component (a) in the ignition resistant polymer composition of the present invention is a thermoplastic polymer. The thermoplastic polymer can be a homopolymer or a copolymer. Preferably, the thermoplastic polymer can be a polyolefin (PO) such as polyethylene (PE), and polypropylene (PP) made by conventional Ziegler-Natta or metallocene catalysts; a styrene-based polymer, such as polystyrene (PS), impact modified polystyrene, for example, high-impact polystyrene (HIPS), or polystyrene copolymers, for example, styrene and acrylonitrile copolymer (SAN), styrene graft polymers, for example, acrylonitrile, styrene, and butadiene terpolymer (ABS); a polyphenylene oxide (PPO), a polyester such as polybutylene terephthalate (PBT), polyethylene terephthalate (PET); a polycarbonate (PC); a polyamide polymer, for example, nylon; a thermoplastic polyurethane (TPU, for example, PELLATHANE or ISOPLASTTM made by The Dow Chemical Company); or blends thereof.

Suitable carbonate polymers employed in the present invention are well known in the literature and can be prepared by known techniques, for example several suitable methods are disclosed in USP 3,028, 365,4, 529,791, 4,677, 162, and 6,380, 303 which are hereby incorporated by reference in their entirety. The carbonate polymers that can be used in the present invention are well known and can be prepared from one or more multihydric compounds by reacting the multihydric compounds, such as an aromatic diol, with a carbonate precursor, such as phosgene, a haloformate or a carbonate ester such as diphenyl or dimethyl carbonate. Preferably the polycarbonate is prepared from one or more aromatic diols such as bisphenol A, tetrabromo bisphenol A, tetramethyl bisphenol A, 1, 1-bis (4-hydroxyphenyl)-1-phenylethane, 3,3-bis (para-hydroxyphenyl) phthalide, or bis hydroxyphenylfluorene. The carbonate polymers can be prepared from these raw materials by any of several known processes such as the known interfacial, solution or melt processes.

The carbonate polymers of the present invention may be linear, branched or mixtures

thereof. The carbonate polymers may be derived from (1) two or more different aromatic diols or (2) an aromatic diol and a glycol or a hydroxy-or acid-terminated polyester or a dibasic acid in the event a polycarbonate copolymer or heteropolymer rather than a homopolymer is desired. Also suitable for the practice of this invention are blends of one or more of the above polycarbonates. Also included in the term carbonate polymers are the poly (ester/carbonates).

Preferably, the carbonate polymer of the present invention is an aromatic carbonate polymer. A preferable branched carbonate polymer is a branched aromatic carbonate polymer. Branched aromatic carbonate polymers suitable for use in the present invention can be prepared by techniques known in the literature such as the known interfacial, solution or melt processes. Suitable types and amounts of chain terminators (typically monophenolic compounds) and/or branching agents (typically phenols having three or more hydroxy or condensation reactive groups) can be employed to obtain the desired molecular weight and branching degrees in the branched component. Suitable branching agents are generally one or more of the following: phloroglucin; phloroglucid; 2,6-dimethyl-2, 4,6- tri (4-hydroxyphenyl) heptene-3; 4,6-dimethyl-2, 4,6-tri (4-hydroxyphenyl) heptene-2; 4,6- dimethyl-2,4, 6-tri (4-hydroxyphenyl) pentene-2 ; 4,6-dimethyl-2, 4,6-tri (4- hydroxyphenyl) pentane; 1, 3,5-tri (4-hydroxyphenyl) benzene; 1, 3,5-tri (2- hydroxyphenyl) benzol; 1,1, 1-tri (4-hydroxyphenyl) ethane; 2,6-bis (2-hydroxy-5- methylbenzyl) -4-methylphenol; tetra (4-hydroxy-phenyl) methane; trisphenol; bis (2,4- dihydroxyphenyl) ketone; 1, 4-bis (4,4-dihydroxytriphenylmethyl) benzene; a, a', a"-tri (4- hydroxyphenyl)-1, 3,5-tri-isopropylbenzene ; 3,3-bis (4-hydroxyaryl) oxyindole;, isatinbisphenol; 5-chloroisatin; 5,7-dichloroisatin ; 5-bromoisatin; trimellitic acid; pyromellitic acid; benzophenonetetracarboxylic acid; and including for the appropriate compounds, the acid chlorides or other condensation reactive derivatives thereof such as trimellitic trichloride, trimesoylchloride and trimellitic anhydride chloride. Specifically preferred branching agents include phloroglucin; phloroglucid; 1, 1, 1-tri (4- hydroxyphenyl) ethane ; trimellitic acid; trimellitic trichloride; pyromellitic acid; benzophenonetetracarboxylic acid and acid chlorides thereof; 2,6-bis (2-hydroxy-5- methylbenzyl) -4-methylphenol and 1, 3,5-tri (4-hydroxyphenyl) benzene.

The branched aromatic carbonate polymer according to the present invention can be prepared (a) directly from a polymerization process (b) by the blending of two or more separately prepared carbonate polymer components, (c) by the addition of one or more

previously prepared carbonate polymer into the reaction process that is preparing or has prepared the other carbonate polymer, (d) by the appropriate operation of a sequence or series of reactors to prepare one or more linear or branched carbonate polymer in the presence of the previously prepared other carbonate polymer prior to the recovery of the carbonate polymer from the reaction mixture or (e) the appropriate operation of parallel reactors to prepare one or more linear and branched carbonate polymers followed by combining the unrecovered reaction products prior to the recovery of the carbonate polymer blend from the reaction mixture.

Preferably, the branched aromatic carbonate polymer is a combination of two or more branched carbonate polymer components of different molecular weights and different melt flow rates that are blended to obtain the desired degree of branching, intermediate molecular weight and melt flow rate branched aromatic carbonate polymer. Most preferably, the carbonate polymer of this invention comprises a branched aromatic carbonate polymer that is a combination of one or more branched carbonate polymer components having different molecular weights and different melt flow rates with one or more linear carbonate polymer components having different molecular weights and different melt flow rates to obtain the desired degree of branching, intermediate molecular weight and melt flow rate branched aromatic carbonate polymer. This type of system of blending carbonate polymer components of different molecular weights and different melt flow rates is practiced commercially to provide a broader range of polycarbonate resins of differing melt flow rate while reducing the overall number of different products the production facility must supply.

The styrene-based polymers and copolymers which can be used in the present invention are well known, for example see USP 4,666, 987,4, 572,819, 4,585, 825 and 6,380, 303. Preferably, the monomer is of the formula: wherein R is hydrogen or methyl, Ar is an aromatic ring structure having from 1 to 3 aromatic rings with or without alkyl, halo, or haloalkyl substitution, wherein any alkyl group contains 1 to 6 carbon atoms and haloalkyl refers to a halo substituted alkyl group.

Preferably, Ar is phenyl or alkylphenyl, wherein alkylphenyl refers to an alkyl substituted phenyl group, with phenyl being most preferred. Typical vinyl aromatic monomers which

can be used include: styrene; alpha-methylstyrene; vinylalkylbenzenes such as all isomers of vinyl toluene, especially para vinyl toluene, and all isomers of vinyl xylene; all isomers of ethyl styrene; propyl styrene; butyl styrene; vinyl biphenyl, vinyl naphthalene, vinyl anthracene, and mixtures thereof. The vinyl aromatic monomers may also be combined with other copolymerizable monomers. Examples of such monomers include, but are not limited to acrylic monomers such as acrylonitrile, methacrylonitrile, methacrylic acid, the lower alkyl esters of methacrylic acid such as methyl methacrylate, acrylic acid, the lower alkyl esters of acrylic acid such as methyl acrylate, maleimide, N-phenylmaleimide and maleic anhydride. In addition, the polymerization of the vinyl aromatic monomer may be conducted in the presence of predissolved elastomer to prepare impact modified, or grafted rubber containing products, examples of which are described in USP 3,123, 655,3, 346,520, 3,639, 522, and 4,409, 369.

Polymerization processes and process conditions for the polymerization of styrene- base polymers are well known in the art. Although any polymerization process can be used, typical processes are continuous bulk or solution polymerizations as described in USP 2,727, 884 and 3,639, 372.

Preferred styrene-based polymers are styrene homopolymers, alkylstyrene homopolymers such as alpha-methylstyrene, styrene copolymers and styrene graft polymers.

Preferred copolymers are styrene and acrylonitrile copolymers; styrene and methacrylic ester copolymers; styrene, acrylonitrile and maleic anhydride (SAMA) terpolymers ; styrene and maleic anhydride (SAM) copolymers and similar polymers including N-phenyl substituted and differently substituted and similar maleimides, and mixtures thereof. Highly preferred copolymers contain from 70 to 80 percent styrene monomer and 30 to 20 percent acrylonitrile monomer.

Preferred styrene graft polymers include impact modified polystyrene polymers, for example high impact polystyrene; acrylonitrile, butadiene and styrene emulsion and/or mass type polymers (ABS); methyl methacrylate, butadiene, acrylonitrile and styrene (MABS) polymers and methyl methacrylate, butadiene and styrene (MBS) polymers. The rubbery polymer backbone in styrene graft polymers normally constitutes from 5 to 80 weight percent, preferably from 5 to 50 weight percent, of the total weight of the graft polymer.

Suitable rubbers include the well known homopolymers and copolymers of conjugated dienes, particularly 1,3-dienes such as 1,3-butadiene, as well as other rubbery polymers

such as polyisoprene, nitrile rubber, styrene-diene copolymers such as styrene and butadiene (SB) rubber, olefin polymers, particularly copolymers of ethylene and propylene (EP) rubber and ethylene, propylene and a nonconjugated diene (EPDM) rubber, or acrylate rubbers, particularly homopolymers and copolymers of alkyl acrylates having from 4 to 6 carbons in the alkyl group. In addition, mixtures of the foregoing rubbery polymers may be employed if desired. Preferred rubbers are homopolymers of 1,3-butadiene and copolymers thereof with up to 30 percent by weight styrene. Such copolymers may be random or block copolymers and in addition may be hydrogenated to remove residual unsaturation.

Preferred rubbers are linear, branched or mixtures thereof. Branched rubbers, as well as methods for their preparation, are known in the art. Representative branched rubbers and methods for their preparation are described in Great Britain Patent No.

1,130, 485, in Macromolecules, Vol. II, No. 5, pg. 8, by R. N. Young and C. J. Fetters and in USP 6, 380,303. A preferred branch rubber is a radial or star-branched polymer, commonly referred to as polymers having designed branching. Star-branched rubbers are conventionally prepared using a polyfunctional coupling agent or a polyfunctional initiator and have three or more polymer segments sometimes referred to as arms, preferably between three to eight arms, bonded to a single polyfunctional element or compound, represented by the formula (rubber polymer segment3kQ wherein preferably, k is an integer from 3 to 8, and Q is a moiety of a polyfunctional coupling agent. Organometallic anionic compounds are preferred polyfunctional initiators, particularly lithium compounds with Cl-6 alkyl, C6 aryl, or 7-20 alkylaryl groups. Tin-based and polyfunctional organic coupling agents are preferably employed; silicon-based polyfunctional coupling agents are most preferably employed. The arms of the star-branched rubber are preferably one or more 1,3- butadiene rubber, more preferably they are all the same type of 1, 3-butadiene rubber, i. e. , 1, 3-butadiene tapered block copolymer (s), 1, 3-butadiene block copolymer (s) or 1,3- butadiene homopolymer (s) or a combination thereof.

The styrene graft polymers such as ABS polymers may be prepared by a graft generating process such as by a bulk or solution polymerization and/or an emulsion polymerization of the copolymer in the presence of the rubbery polymer. In the emulsion polymerization to form graft copolymers of rubbery substrates it is previously known in the art to employ agglomeration technology to prepare large and small rubber particles containing the copolymer grafted thereto. In the process various amounts of an ungrafted

matrix of the copolymer are also formed. In the solution or bulk polymerization of a rubber-modified copolymer of a vinyl aromatic monomer, a matrix copolymer is formed.

The matrix further contains rubber particles having copolymer grafted thereto and occluded therein.

A particularly desirable product comprises a rubber modified copolymer blend comprising both the mass or solution polymerized rubber modified copolymer and additional quantities of an emulsion polymerized and preferably agglomerated rubber modified copolymer containing a bimodal particle-sized distribution.

The thermoplastic polymer component (a) is employed in the ignition resistant polymer compositions of the present invention in amounts of at least about 60 parts, preferably at least about 65 parts, more preferably at least about 70 parts, and most preferably at least about 75 parts by weight based on the weight of the ignition resistant polymer composition. In general the thermoplastic polymer is used in amounts less than or equal to about 99 parts, preferably less than or equal to about 95 parts, more preferably less than or equal to about 90 parts, even more preferably less than or equal to about 85 parts, and most preferably less than or equal to about 80 parts based the weight of the ignition resistant polymer composition.

Suitable phosphorous compounds employed in the present invention as component (b) are one or more phosphorous compounds which include organophosphates, organophosphonites, organophosphonates, organophosphites, organophosphinites, organophosphinates, or mixtures thereof. Suitable organophosphorous compounds are disclosed, for example, in USP Re. 36, 188 ; 5,672, 645; and 5,276, 077. A preferred organophosphorous compound is a monophosphorous compound represented by Formula I : wherein Rl, R2, and R3, each represent an aryl or an alkaryl group chosen independently of each other and mi, m2, and m3 each independently of each other are 0 or 1.

Most preferred monophosphorus compounds are monophosphates where mi, m2, and m3 are all 1 and Ri, R2, and R3 are independently methyl, phenyl, cresyl, xylyl, cumyl, naphthyl, clorophenyl, bromophenyl, pentachlorophenyl, or pentabromophenyl, for -8-

example, trimethyl phosphate, triphenyl phosphate, all isomers of tricresyl phosphate and mixtures thereof, especially tri (4-methylphenyl) phosphate, all isomers of trixylyl phosphate and mixtures thereof, especially tri (2,6-dimethylphenyl) phosphate, tricresyl phosphate, all isomers of tricumyl phosphate and mixtures thereof, trinaphthyl phosphate, all isomers of tri (chlorophenyl) phosphate and mixtures thereof, all isomers of tri (bromophenyl) phosphate and mixtures thereof, tri (pentachlorophenyl) phosphate, tri (pentabromophenyl) phosphate, or mixtures thereof.

Another preferred organophosphorous compound is a multiphosphorous compound represented by Formula II : wherein Rl, R2, R3, and R4 each represent an aryl or an alkaryl group chosen independently of each other, X is an arylene group derived from a dihydric compound, mi, m2, ms, andm4 each independently of each other are 0 or 1 and n has an average value greater than 0 and r less than 0, when n is equal to or greater than 1 these multiphosphorous compounds are sometimes referred to as oligomeric phosphorous compounds.

Preferred multiphosphorous compounds are multiphosphates where mi, m2, m3, and m4 are 1, R1, R2, R3, and R4 are independently methyl, phenyl, cresyl, xylyl, cumyl, naphthyl, clorophenyl, bromophenyl, pentachlorophenyl, or pentabromophenyl, X is an arylene group derived from a dihydric compound, for example, resorcinol, hydroquinone, bisphenol A and chlorides and bromides thereof, and n has an average value greater than 0 and equal to or less than about 5, preferably n has an average value equal to or greater than about 1 and equal to or less than about 5, more preferably n is equal to or greater than about 1 and equal to or less then about 2.5, more preferably n is equal to or greater than about 1 and equal to or less then about 1.8 and most preferably n is equal to or greater than about 1 and equal 0 or less than about 1.2. For example, preferred oligomeric phosphates having an n value between 1 and 2 are m-phenylene-bis (diphenylphosphate), p-phenylene- bis (diphenylphosphate), m-phenylene-bis (dicresylphosphate), p-phenylene- bis (dicresylphosphate), m-phenylene-bis (dixylylphosphate), p-phenylene-

bis (dixylylphosphate), Bis phenol-A-bis (diphenylphosphate), Bis phenol A- bis (dicresylphosphate), Bis phenol A-bis (dixylylphosphate), or mixtures thereof.

A most preferred phosphorous compound is a mixture of one or more monophosphorous compounds of Formula I and one and/or more multiphosphorous compounds of Formula II.

The phosphorous compound component (b) is employed in an amount sufficient for the ignition resistant compositions of the present invention to meet UL 94 V-2, V-1, V-0 and/or 5V requirements, in an amount of at least about 0.1 part, preferably at least about 1 part, more preferably at least about 2.5 parts, even more preferably at least about 5 parts, and most preferably at least about 7.5 parts by weight based on the weight of the ignition resistant polymer composition. In general the phosphorous compound is used in amounts less than or equal to about 30 parts, preferably less than or equal to about 25 parts, more preferably less than or equal to about 20 parts, even more preferably less than or equal to about 15 parts, and most preferably less than or equal to about 10 parts by weight based on the weight of the ignition resistant polymer composition.

Component (c) of the present invention is a particular inorganic additive. The use of inorganic fillers or additives in molding compounds is well known and they are routinely used for providing reinforcements or stiffness and/or lowering cost. However, we have found that certain specific inorganic additives can be used advantageously to impart a surprising attainment of thin section flame retardancy, as measured by UL 94 V performance, at thicknesses equal to or below 3.2 mm, preferably equal to or below 2.0 mm and more preferably equal to or below 1.5 mm and at the same time can achieve reasonable impact strength, tensile strength, flexural modulus and heat distortion temperature suitable for use in the applications described. In this respect the particular inorganic additives are not selected for reinforcement but rather because of their apparent ability to impart enhanced flame retardancy and/or anti-dripping to the compositions. It appears that there may possibly be some synergism between such specific inorganic additives and the other components of the compositions particularly the other flame retardant or anti-drip additives present.

Particular inorganic additives which have been found useful to impart this combination of properties are calcium carbonate (CaC03), titanium dioxide (Ti02), kaolin, magnesium hydroxide, and mica, with calcium carbonate most preferred. Other commonly used fillers or reinforcements do not show this same ability to achieve such thin section UL

V-0 performance at similar thickness levels (flammability resistance as measured by the UL 94 V test is usually more difficult to achieve in thinner specimens) and also retain other good properties. Thus, for example, glass beads, aluminum oxide, wollastonite, and vermiculite, all of which are common fillers and often listed as examples of common fillers or reinforcements for plastic moldings do not show the same ability to achieve such thin section UL 94 V ratings such as below 3.2 mm and in particular at 2.0 mm or below or at 1.5 mm or below, and also achieve reasonable other properties such as impact strength and heat distortion temperature.

An effective amount of component (c), a particular inorganic additive which functions to impart enhanced ignition resistance in thinwall moldings, is equal to or less than about 20 parts, preferably equal to or less than about 15 parts, more preferably equal to or less than about 10 parts, even more preferably equal to or less than about 5 parts based on the weight of the ignition resistant polymer composition. An effective amount of a particular inorganic additive which functions to impart enhanced ignition resistance in thinwall moldings is equal to or greater than 0.1 part, preferably equal to or greater than about 0.2 part, equal to or greater than about 0.5 part, more preferably equal to or greater than about 0.7 part and most preferably equal to or greater than about 1 part by weight based on the weight of the ignition resistant polymer composition.

Component (d) optionally employed in the present invention is an anti-drip agent selected from tetrafluoroethylene polymers or copolymers, vinylidene polymers or copolymers, other fluoropolymer, or red phosphorous or aramid fiber or powder or polyimide fiber or powder, though preferably a tetrafluoroethylene polymer present in an amount of about 0.1 to about 3 parts, preferably from about 0.1 to about 2.5 parts, more preferably from about 0.2 to about 1.0 parts and most preferably from about 0.3 to about 0.7 parts by weight based on the weight of the ignition resistant polymer composition.

Component (e) optionally employed in the present invention is an impact modifier.

Preferable impact modifiers are rubber materials having a Tg equal to or less than 0°C, preferably equal to or less than-10°C, more preferably equal to or less than-20°C, and most preferably equal to or less than-30°C. Suitable rubbers include polymers such as acrylate rubbers, particularly homopolymers and copolymers of alkyl acrylates having from 4 to 6 carbons in the alkyl group; or polyolefin elastomers, particularly copolymers of ethylene, propylene and optionally a nonconjugated diene. In addition, mixtures of the foregoing rubbery polymers may be employed if desired.

Preferably, the impact modifier is a grafted homopolymer or copolymer of butadiene that is grafted with a polymer of styrene and methyl methacrylate. Some of the preferred rubber-containing materials of this type are the known methyl methacrylate, butadiene, and styrene (MBS) core/shell grafted copolymers having a Tg equal to or less than 0°C and a rubber content greater than 40 percent, typically greater than 50 percent.

They are generally obtained by graft polymerizing styrene and methyl methacrylate and/or equivalent monomers in the presence of a conjugated diene polymer rubber core, preferably a butadiene homo-or co-polymer. The grafting monomers may be added to the reaction mixture simultaneously or in sequence, and, when added in sequence, layers, shells or wart- like appendages can be built up around the substrate latex, or core. The monomers can be added in various ratios to each other.

Other impact modifiers useful in the compositions of this invention are those based generally on a long-chain, hydrocarbon backbone, which may be prepared predominantly from various mono-or dialkenyl monomers and may be grafted with one or more styrenic monomers. Representative examples of a few olefinic elastomers which illustrate the variation in the known substances which would suffice for such purpose are as follows: butyl rubber; chlorinated polyethylene rubber; chlorosulfonated polyethylene rubber; an olefin polymer or copolymer such as ethylene/propylene copolymer, ethylene/styrene copolymer or ethylene/propylene/diene copolymer, which may be grafted with one or more styrenic monomers; neopren rubber; nitrile rubber; polybutadiene and polyisoprene.

If used, the impact modifier is preferably present in an amount of at least about 1 part, preferably at least about 2 parts, more preferably at least about 5 parts, even more preferably at least about 10 parts, and most preferably at least about 15 parts by weight based on the weight of the ignition resistant polymer composition. Generally, the impact modifier is present in an amount less than or equal to about 50 parts, preferably less than or equal to about 40 parts, more preferably less than or equal to about 30 parts, even more preferably less than or equal to about 25 parts, and most preferably less than or equal to about 20 parts by weight based on the weight of the ignition resistant polymer composition.

In addition, the ignition resistant polymer compositions may also optionally contain one or more additives that are commonly used in polymers of this type. Preferred additives of this type include, but are not limited to: antioxidants; plasticizers, such as mineral oil; antistats; flow enhancers; mold releases; fillers, such as clay, wollastonite, hollow glass beads, silica, carbon black, glass fiber, potassium titanate, single layers of a cation

exchanging layered silicate material or mixtures thereof; and ignition resistance additives such as, but not limited to a halogen-containing low-molecular weight compound and/or high molecular weight polymers, such as halogenated hydrocarbons, halogenated carbonate oligomers, halogenated diglycidyl ethers, perfloroalkane oligomers and polymers, metal compounds active as a synergist, such as antimony oxide, salts having flame-retarding properties such as metal salts of aromatic sulfur containing compounds or a mixture thereof, etc. Further, compounds which stabilize ignition resistant polymer compositions against degradation caused by, but not limited to heat, light, and oxygen, or a mixture thereof may be used.

If used, such additives may be present in an amount from at least 0.01 percent by weight, preferably at least about 0.1 part, more preferably at least about 1 part, even more preferably at least about 2 parts, and most preferably at least about 5 parts by weight based on the total weight of the ignition resistant polymer composition. Generally, the additive is present in an amount less than or equal to about 25 parts, preferably less than or equal to about 20 parts, more preferably less than or equal to about 15 parts, even more preferably less than or equal to about 12 parts, and most preferably less than or equal to about 10 parts by weight based on the weight of the ignition resistant polymer composition.

UL 94 vertical (V) flammability test determines the upward-burning characteristics of a solid. Five test specimens, of a desired thickness measuring 0.5 inch (12.5 mm) by 5 inch (125 mm), suspended vertically over surgical cotton are ignited by a 0.75 inch (18.75 mm) Bunsen burner flame; two ignitions of 10 seconds each are applied to the samples. The rating criteria include the sum of after-flame times after each ignition, glow time after the second ignition, and whether the bar drips flaming particles that ignite the cotton. Table 1 lists the criteria for each V rating.

Table 1 Rating* V-2 V-1 V-0 Max individual burn time < 30 < 30 < 10 Burn time of 5 test specimens <250 <250 <50 Glow time after second ignition < 60 < 60 < 30 Ignites cotton Yes No No *Rating criteria are reported in seconds

The UL 94 5V flammability test utilizes a 5 inch (125 mm) Bunsen burner flame held at an angle of 20° to a test specimen, of a desired thickness measuring 0.5 inch (12.5 mm) by 5 inch (125 mm), suspended vertically over surgical cotton, for 5 seconds, then away from it for 5 seconds, alternating in this pattern for five applications of the flame.

After completion of the fifth ignition, the burning time must not exceed 60 seconds to achieve a 5V rating, nor can the cotton be ignited by flaming drips.

Preparation of the ignition resistant polymer compositions of this invention can be accomplished by any suitable mixing means known in the art, including dry blending the individual components and subsequently melt mixing, either directly in the extruder used to make the finished article or pre-mixing in a separate extruder (for example, a Banbury mixer). Dry blends of the compositions can also be directly injection molded without pre- melt mixing.

The ignition resistant polymer compositions of this invention are thermoplastic.

When softened or melted by the application of heat, the ignition resistant polymer compositions of this invention can be formed or molded using conventional techniques such as compression molding, injection molding, gas assisted injection molding, calendering, vacuum forming, thermoforming, extrusion and/or blow molding, alone or in combination.

The ignition resistant polymer compositions can also be formed, spun, or drawn into films, fibers, multi-layer laminates or extruded sheets, or can be compounded with one or more organic or inorganic substances, on any machine suitable for such purpose. Some of the fabricated articles include instrument housings such as for power tools, appliances, consumer electronic equipment such as TVs, VCRs, web appliances, electronic books, etc., or information technology equipment such as telephones, computers, monitors, fax machines, battery chargers, scanners, copiers, printers, hand held computers, etc.

EXAMPLES To illustrate the practice of this invention, examples of preferred embodiments are set forth below. However, these examples do not in any manner restrict the scope of this invention.

The compositions of Examples 1 to 3 and Comparative Example A are prepared by dry blending the PC and ABS polymer pellets and other additives, except the BAPP, in a tumble blender for 10 minutes. The dry blended mixture is fed to a 1.2 inch (30 millimeter (mm) ) Werner and Pfleider fully intermeshing corotating twin screw extruder. The BAPP is

preheated to 100°C and injected into the polymer melt during extrusion using a liquid feed system. The following conditions are used on the Werner and Pfleider extruder: all barrel temperature zones are set at 230°C ; RPMs are 300, torque is 70 to 80 percent, and the feed rate is 50 pounds per hour (lb/hr.) (22.7 kilograms/hr. (kg/hr. ) ). The extrudate is cooled in the form of strands and comminuted as pellets. The pellets are dried in an air draft oven for 3 hours at 90°C and then are used to prepare 0.125 inch (3. 2 mm) thick test specimens on a 90 ton Toyo SI 90 injection molding machine. The following conditions are used on the Toyo SI 90 injection molding machine: all barrel temperature zones are at 230°C giving a melt temperature of 235°C, injection pressure is 15,000 pounds per square inch (psi) 103 mega Pascal (MPa) ), holding pressure is 14,000 psi (96 MPa), back pressure is 600 psi (4 MPa), screw speed is 7.87 inches per second (in/sec. ) (200 millimeter per second (mm/sec.)), injection speed is 2.36 in/sec. (60 mm/sec.), cycle time is 20 sec. , cooling time is 15 sec. , and the mold temperature is 40 °C.

The compositions of Examples 4 to 7 and Comparative Example B are prepared by dry blending the PC and ABS polymer pellets and other additives, except the BAPP, in a tumble blender for 10 minutes. The dry blended mixture was fed to a 1.6 inch (40 mm) Werner and Pfleider fully intermeshing corotating twin screw extruder. The BAPP is preheated to 100°C and injected into the polymer melt during extrusion using a liquid feed system. The following conditions were used on the Werner and Pfleider extruder : all barrel temperature zones are set at 230°C ; RPMs are 300, torque is 70 to 95 percent, and the feed rate is 350 lbs/hr. (159 kg/hr. ). The extrudate was cooled in the form of strands and comminuted as pellets. The pellets are dried in an air draft oven for 3 hours at 90°C and then are used to prepare 0.125 inch (3.2 mm) and 0.080 inch (2.0 mm) thick test specimens on a 90 ton Toyo SI 90 injection molding machine. The following conditions are used on the Toyo SI 90 injection molding machine: all barrel temperature zones are at 230°C giving a melt temperature of235°C, injection pressure is 15, 000 psi (103 MPa), holding pressure is 14,000 psi (96 MPa), back pressure is 600 psi (4 MPa), screw speed is 7.87 in/sec.

(200 mm/sec.), injection speed is 2.36 in/sec. (60 mm/sec.), cycle time is 20 sec. , cooling time is 15 sec. , and the mold temperature is 40°C.

The formulation content and properties of Examples 1 to 7 and Comparative Examples A and B are given in Table 2 below in parts by weight of the total composition.

In Table 2:

"PC"is a bisphenol-A polycarbonate homopolymer having a melt flow of 22 and commercially available as CALIBRE 300-22 polycarbonate resin from The Dow Chemical Company; "ABS-1"is a mass produced acrylonitrile butadiene styrene terpolymer with about 22 percent acrylonitrile and about 15 percent butadiene rubber commercially available as MAGNUM 562 ABS resin from The Dow Chemical Company; "ABS-2"is a mass polymerized acrylonitrile butadiene styrene terpolymer with about 20 percent acrylonitrile, about 15 percent polybutadiene rubber, and about 1.5 percent n-butyl acrylate commercially available as MAGNUM 3904 ABS resin from The Dow Chemical Company; "CaC03"is calcium carbonate available as SUPER-PFLEXM 200 from Specialty Minerals, Inc.; "Ti02"is titanium dioxide available as IONA RCL-4 from Millennium Chemicals; "BAPP"is bisphenol A bis (diphenyl phosphate) available as REOFOSTM BAPP from Great Lakes Chemical Company; "PTFE"is fibril forming polytetrafluoroethylene powder available as TEFLONTM 6C from DuPont Chemical Company; and "Stabilizer"is an antioxidant available as IRGANOXTM 1076 from Ciba Geigy.

The following tests were run on Examples 1 to 7 and Comparative Examples A and B and the results of these tests are shown in Table I : "UL 94"flammability test is performed on 0.125 inch (3.2 mm) or 0. 08 inch (2.0 mm) test specimens as identified hereinabove; "MFR"is determined according to ASTM D 1238 on a Tinius Olsen plastometer at 230 °C and an applied load of 3.8 kg.; and "Izod"impact resistance as measured by the Notched Izod test is determined according to ASTM D 256-90-B at 23 °C. Specimens are cut from rectangular 5 inch (125 mm) by 0.5 (12.6 mm) inch bars and measure 0. 125 inch (3.2 mm) in thickness and 0.64 inch (50.8 mm) in length. The specimens were notched with a TMI 22-05 notcher to give a 0.01 inch (0.254 mm) radius notch. A 48.5 pound (22 kilogram) pendulum is used, values are reported in Joules per meter (J/m).

Table 2 EXAMPLE 1 2 3 4 5 6 7 COMPARATIVE EXAMPLE A B COMPOSITION PC 50.9 47.9 41.9 53.9 63.6 63.2 63.6 63.2 63.9 ABS-1 33.9 31.9 27.9 35. 9 ABS-2 21. 2 21.1 21.2 21.1 21.4 CaCO3 5 10 20 0. 5 1 TiOz 0.5 1 BAPP 10 10 10 10 14 14 14 14 14 PTFE 0.5 0.5 0.5 0.5 0.5 Stabilizer 0.2 0.2 0.2 0.2 0.2 0. 2 0.2 0.2 0.2 PROPERTIES UL 94 Rating @ 3.2 mm V-2 V-2 V-2 NR Rating @ 2. 0 5V 5V 5V 5V NR Total bum time, sec 75.4 61.1 69.7 107 Longest bum time, sec 23.4 11. 1 13.1 33.7 7 10 7 9 12 Flaming drips Y Y Y Y N N N N Y MFR, g/10 min 13.8 21.6 22.2 18.4 12. 8 12.4 13.4 13.5 10.5 Izod, J/m 144 107 85 256 453 384 534 592 646 NR = not rated