Carbonate Polymer Containing an Ignition Depressant Composition

This invention relates to carbonate polymer compositions containing additives which act as flame retardants.

Carbonate polymers derived from reactions of dihydroxyorganic compounds, particularly the dihydric phenols, and carbonic acid derivatives such as phosgene, have found extensive commercial application because of their excellent physical properties. These thermoplastic polymers are suitable for the manufacture of molded parts wherein impact strength, rigidity, toughness, heat resistance and excellent electrical properties are required.

Unfortunately, however, these polymers exhibit a brief but definite burning time when contacted with an open flame. More importantly, as is often the case, the carbonate polymers contain stabilizers and other additives which are often more combustible than the unmodified carbonate polymer. As a result, the modified carbonate polymers frequently exhibit substantially poorer resistance to combustion than does the unmodified carbonate polymer.

In attempts to increase the combustion resistance of carbonate polymers including the modified forms thereof, it has been a common practice to employ monomeric phosphites, phosphoric acid esters, thiophosphoric acid esters containing halogenated alkyl radicals and halogenated organic compounds into the carbonate polymer. However, in order to obtain any noticeable improvement in combustion resistance, these additives have been employed in such large quantities that they often adversely affect many of the desirable physical and mechanical properties of the carbonate polymer.

In view of the deficiencies of conventional fire retardant carbonate polymer compositions, it would be highly desirable to provide a carbonate polymer composition having improved resistance to burning when exposed to an ignition source.

The present invention is a carbonate polymer composition comprising a carbonate polymer having dispersed therein, in an amount sufficient to provide improved flame retardancy to said carbonate polymer composition, a fire retardant additive comprising (1) a member of the group consisting of a metal salt of an aromatic sulfonamide, a metal salt of an inorganic acid, and a metal salt of a perhalometalate complex, and (2) a halogenated organic compound. In another aspect of this invention, the carbonate polymer composition comprises a carbonate polymer having dispersed therein in an amount sufficient to provide improved flame retardancy to said carbonate polymer composition, a fire retardant additive comprising (1) a member of the group consisting of a metal salt of an aromatic sulfonamide or a metal salt of an inorganic acid, and a metal salt of a perhalometalate complex, (2) a halogenated organic compound, and (3) a melamine. Hereinafter, such compositions will be referred to as fire retardant carbonate polymer compositions. The fire retardant carbonate polymer compositions of the present invention exhibit surprisingly high resistance to combustion. In addition, said compositions exhibit physical properties comparable to a carbonate polymer containing no fire retardant additive.

The fire retardant carbonate polymer compositions of the present invention are suitably employed in most applications in which polycarbonates have been previously utilized. Applications of particular interest for the utilization of the said carbonate polymer compositions of this invention are as follows: automobile parts, e.g., air filters, fan housings, exterior components, housings for electrical motors, appliances, business and office equipment, and photographic equipment, lighting and aircraft applications.

The carbonate polymers employed in the present invention are advantageously aromatic carbonate polymers such as the trityl diol carbonates described in U.S. Pat. Nos. 3,036,036; 3,036,037; 3,036,038 and 3,036,039; polycarbonates of bis(ar-hydroxyphenyl)-alkylidenes (often called bisphenol-A type diols) including their aromatically and aliphatically substituted derivatives such as disclosed in U.S. Pat. Nos. 2,999,835, 3,038,365 and 3,334,154; and carbonate polymers derived from other aromatic diols such as described in U.S. Pat. No. 3,169,121.

It is understood, of course, that the polycarbonate may be derived from (1) two or more different dihydric phenols or (2) a dihydric phenol and a glycol or a hydroxy- or acid-terminated polyester or a dibasic acid in the event a carbonate copolymer or interpolymer rather than a homopolymer is desired. Also suitable for the practice of this invention are blends of any one of the above carbonate polymers. Also included in the term "carbonate polymer" are the ester/carbonate copolymers of the types described in U.S. Pat. Nos. 3,169,121; 4,287,787; 4,156,069; 4,260,731 and 4,105,633. Of the aforementioned carbonate polymers, the polycarbonates of bisphenol-A and derivatives, including copolycarbonates of bisphenol-A, are preferred. Methods for preparing carbonate polymers for use in the practice of this invention are well known, for example, several suitable methods are disclosed in the aforementioned patents which are hereby incorporated by reference in their entirety.

The salt form of aromatic sulfonamides which are employed herein are advantageously represented by the formula:

wherein Ar is an aromatic group, M is a suitable cation such as a metal cation and n is a number corresponding to the valence of M. M is preferably an alkali metal. Alternatively, M is a divalent cation, preferably alkali earth or multivalent cation obtained from copper, aluminum, antimony, and the like. Representative preferred sulfonamide salts includes the alkali metal salts of saccharin, N-(p-tolylsulfonyl)-p-toluenesulfonamide, N-(N'-benzylaminocarbonyl)sulfanilamide, N-(phenylcarboxyl)-sulfanilamide, N-(2-pyrimidinyl)-sulfanilamide, N-(2-thiazolyl)sulfanilamide and other salts of the sulfonamides disclosed in U.S. Pat. No. 4,254,015, which is incorporated herein by reference. Combinations of the above-identified salts can also be employed.

Metal salts of inorganic acids and metal salts of perhalometalate complexes are most preferably alkali metal salts which include, for example, trisodium hexafluoroaluminate, disodium hexafluorotitanate, disodium hexafluorozirconate, sodium pyrophosphate, sodium tetrafluoroborate, sodium hexafluorophosphate, sodium bisulfate, and sodium phosphate. Also preferred are the potassium form of the salts listed above. Calcium sulfate and aluminum sulfate can be employed. Combinations of the above-identified salts can also be employed.

The halogenated organic compound can be virtually any halogenated organic compound commonly used as a fire retardant additive. The preferred compounds are the halo-substituted aromatic compounds (halo is fluoro, chloro, or bromo). Suitable compounds include, for example, decabromo diphenyloxide, tris-(tribromophenoxy)triazine, decabromo diphenyl carbonate, a tetrafluoroethylene polymer, and a copolymer of bisphenol A/tetrabromobisphenol A. Examples of other suitable monomeric and polymeric halogenated compounds are disclosed in U.S. Pat. No. 4,263,201, which is incorporated herein by reference.

The melamines of the present invention include cyanurotriamide and hexamethoxy methyl melamine as well as virtually any N-substituted melamine which is sufficiently pure and compatible with the carbonate polymer.

The fire retardant additives of this invention can comprise any amount of the aforementioned components in an effective combination which will provide improved fire retardancy to the carbonate polymer. Most preferred additive combinations comprise from about 10 to about 35, preferably about 15 to about 25, weight percent of a salt of an aromatic sulfonamide, salt of a perhalometalate complex, or salt of an inorganic acid, from about 10 to about 35, preferably about 15 to about 25, weight percent melamine, and from about 30 to about 80, preferably about 50 to about 70, weight percent halogenated organic compound, based on the total weight of the additive. Also preferred are those combinations comprising from about 15 to about 50, preferably about 20 to about 30, weight percent of a salt of an aromatic sulfonamide, salt of a perhalometalate complex, or salt of an inorganic acid, and from about 50 to about 85, preferably about 70 to about 80, weight percent halogenated organic compound, based on the total weight of the additive. It is also understood that the individual fire retardant additive components must be sufficiently heat stable and pure to survive processing temperatures common to carbonate polymers without causing severe molecular weight degradation of the carbonate polymer with which the component is blended.

The fire retardant carbonate polymer compositions of the present invention are suitably prepared by combining the carbonate polymer with an effective amount of fire retardant additive using any of a variety of blending procedures conventionally employed for incorporating additives into carbonate polymer resins. For example, dry particulates of the carbonate polymer and the fire retardant additive can be dry blended and the resulting dry blend extruded into the desired shape. By "effective amount" is meant that combination of the desired fire retardant additive components is sufficient to provide improved fire retardant character to the carbonate polymer with which it is blended.

While any amount of the fire retardant additive that imparts to the carbonate polymer an improved fire retardancy is suitable, preferred amounts of the fire retardant additive are in the range from about 0.001 to about 10, especially from about 0.005 to about 2, weight percent based on the weight of the carbonate polymer.

Fire retardant carbonate polymer compositions are considerably more difficult to ignite than unmodified carbonate polymer resins or carbonate polymer compositions containing only the individual fire retardant additive components. The fire retardant carbonate polymer compositions of this invention rapidly form a char at the surface of the sample once ignition is achieved. In addition, the compositions of this invention burn for a much shorter time than unmodified carbonate polymer resins or carbonate polymer compositions containing only the individual fire retardant additive components.

In addition to the aforementioned fire retardant additives, other additives can be included in the carbonate polymer composition of the present invention such as fillers (i.e., a tetrafluoroethylene polymer or glass fibers), pigments, dyes, antioxidants, stabilizers, ultraviolet light absorbers, mold release agents and other additives commonly employed in carbonate polymer compositions.

The following examples are given to further illustrate the invention and should not be construed as limiting its scope. In the following examples, all parts and percentages are by weight unless otherwise indicated.

Samples are prepared using a 3000-g portion of a bisphenol-A polycarbonate sold under the brand name Merlon M50F-1000 by Mobay Chemical Corporation, and a fire retardant additive comprising varying amounts of sodium N-(p-tolylsulfonyl)-p-toluenesulfonamide, decabromo diphenyloxide and hexamethoxy methyl melamine. The constituents are mixed using a Hobart brand mixer until thoroughly and evenly dispersed. The mixture is dried at 250.degree. F. for 4 hours, and extruded on a single screw, 11/4 inch, 20:1 L/D extruder operated at a barrel temperature of 525.degree. F. and a screw speed of 80 rpm. The extruded sample is redried at 250.degree. F. for 4 hours. The pellets are molded into test specimens using a Newbury brand Model H1-30RS injection molding machine under the following conditions: barrel temperature=575.degree. F., mold temperature=175.degree. F., injection polymer pressure sufficient to fill the cavity. The molded bars are tested for combustibility (oxygen index and fire resistance). Data is presented in Table I.

Samples are prepared and tested as in Example 1. The molded bars are tested for combustibility. Data is presented in Table II.

As evidenced by the data shown in Tables I and II, the fire retardant additives, when blended with the polycarbonate in amounts within the scope of this invention, provide substantial improvement in that the compositions exhibit a reduced tendency to burn.