Application For United States Letters Patent For Smoke Suppressed Flame Retardant Thermoplastic Resin Compositions

CROSS-REFERENCE

This application is a continuation-in-part of co-pending application Serial No. 289,973, filed December 22, 1988.

BACKGROUND OF THE INVENTION

Field of the Invention. This invention relates to flame retardant thermoplastic resin compositions that exhibit a reduc tendency to generate smoke under burning conditions. More particularly, this invention relates to thermoplastic compositions such as polyvinyl chloride ("PVC"), polystyrene an polyolefins, comprising bicyclic phosphate compound(s); and fla retardant agent(s). The compositions produced in accordance wi this invention exhibit a reduced tendency to smoke under burnin conditions.

Description of the Prior Art. It is known in the art that the flam ability of thermoplastics, such as polystyrene, polyolefins, and polyvinyl halides, can be reduced by incorporation of a flame retardant agent. Typical flame retardant agents include reactive or additive halogenated organ compounds, inorganic fillers, and special formulations based on phosphorous and ammonium salts.

Although efficient in suppressing the rate of combustion i a resin system, most flame retardants tend to affect adversely one or more key properties of the resin. For example, many fla retardant additives are ineffective at producing low smoke ("smoke suppressed") formulations.

Recent public awareness about risk and hazard assessment during fire situations, and technical limitations of conventi flame retardant additives warrant a need for improved flame retardant thermoplastic compositions. In particular, a need exists for a thermoplastic composition that passes flammabili standards with low smoke and combustion by-product formation, does not detract from overall polymer performance.

Many prior art references describe the use of a variety smoke additives in polystyrene and polyolefins. Modern Plast Encyclopedia, Vol. 63, No. 10A, McGraw-Hill, Inc., pp. 179-18 (1986). However, the selection of a suitable smoke suppressa for thermoplastic resins is not predictable. Selection is particularly difficult when flame retardants are employed, exacerbated by the complex interaction between the polymer an the flame retardant agent.

Hechenbleikner, et al. describe in U.S. Patent No. 3,293, the production of bicyclic phosphites, phosphonates, thiophosphates, and selenophosphates. These compositions are said to be stabilizers for vinyl halide resins. They are all to be useful as heat stabilizers for vinyl chloride resin, an antioxidants for fats and oils. The Hechenbleikner patent do not specify the use of bicyclic phosphates to achieve low smo thermoplastic resin compositions, nor does it disclose that cyclic phosphates of the present invention could be used with flame retardant agents to produce smoke suppressed flame retardant thermoplastic compositions.

British Patent No. 999,793 describes a process for produci organic phosphates by subjecting organic phosphites to reaction with peracetic acid. This patent shows a method for producing the most preferred bicyclic phosphate of the present invention, 2,6,7-trioxa-l-phosphobicyclo[2.2.2]-octane-4- methanol-1-oxide and teaches the use of acetal ring-containing phosphates as plasticizers or functional fluids. The British patent, however does not disclose the present invention. It does not mention bicyclic phosphates as being useful for flame retardant thermoplastic resins, nor that the most preferred bicyclic phosphate of the present invention can be used with flame retardant additives to yield improved smoke suppressed thermoplastic compositions.

Hills, et al. describe in U.S. Patent No. 3,873,496 a fla retardant polyester composition which contains 5 to 25 percent a hydroxymethyl bicyclic phosphate compound as a flame retarda additive. Hills did not observe the ability for bicyclic phos¬ phates to act as smoke suppressors for thermoplastic resin compositions which employ halogenated compounds as the primary flame retardant additive.

Halpern, et al. describe in U.S. Patent No. 4,341,694 a composition comprising 2,6,7-trioxa-l-phosphobicyclo[2.2.2]- octane-4-methanol-l-oxide and a nitrogen-containing co-additive which are intumescent and are adaptable to flame retard polyolefins, polyvinylaromatic resins, polycarbonates, PVC and blends thereof. Halpern did not observe any smoke suppression the present invention.

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Parr, et al. describe in U.S. Patent No. 4,801,625 a f resistant composition having (1) an organic polymeric subst in intimate contact with (2) a bicyclic phosphorous compoun (3) a gas producing compound. Parr is silent on the use of bicyclic compounds to attain smoke suppressed flame retarda thermoplastic compositions.

Accordingly, a primary object of this invention is to provide smoke suppressed flame retardant thermoplastic compositions.

A related object is to provide flame retardant thermopl polyvinyl chloride compositions with a reduced tendency to ε under burning conditions.

A further object is to provide polyvinyl chloride resin compositions incorporating bicyclic phosphate compound and flame retardants.

SUMMARY OF THE INVENTION The foregoing and other objects, advantages and features of the present invention may be achievable with smoke suppressed thermoplastic polyvinyl halide, polyolefin or polystyrene resin compositions incorporating an effective amount of an additive mixture comprising a flame retardant agent and a bicyclic phosphate compound of the following Formula (I):

where X is OH, OR' , or OC(0)R' ; R is H or a saturated or unsaturated straight-chain or branched-chain C ₁ ~C ₁₇ alkyl; and R' is a saturated or unsaturated straight-chain or branched-chain C.-C- _J - alkyl. Compositions in accordance with this invention exhibit a reduced tendency to smoke under burning conditions. DESCRIPTION OF THE PREFERRED EMBODIMENTS This invention relates to smoke suppressed flame retardant thermoplastic polyvinyl halide, polyolefin and polystyrene compositions. In particular, the invention relates to thermoplastic polyvinyl chloride, polyolefin and polystyrene resin compositions which are flame retardant and which exhibit a reduced tendency to smoke when burning. Compositions in accordance with this invention incorporate an additive mixture comprising one or more bicyclic phosphate compounds and one or more flame retardant agents.

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Preferred bicyclic phosphates in accordance with this invention are compounds of Formula (I) where X is OH or OC(0)R' . The most preferred bicyclic compounds are 2,6,7-trioxa- phosphobicyclo[2.2.2]-octane-4-methanol-l-oxide (Compound BCP, that is, Formula [I] when R is H and X is OH), and 2,6,7-trioxa-l-phosphobicyclo[2.2.2]-octane-4-methanol, acetate, 1-oxide (Compound BCP-A, that is, when R is H and X is OC(0)CH ₃ ).

The flame retardant agent employed in accordance with the present invention may be any common flame retardant agent which can be used to reduce the flammability of thermoplastic resins, such as halogenated compounds containing bromine and/or chlorine, or inorganic materials, such as metal hydrates, metal borates, antimony-containing compounds, or phosphorous-containing compounds.

Preferred halogen-containing compounds are di-(2-ethylhexyl)tetrabromophthalate, hexabromocyclododecane, tetrabromobisphenol A, tetrabromobisphenol A bis-(dibromopropylether), dibromo(dibromoethyl)cyclohexane, tetrabromocyclooctane, bis-(dibromonorbornane dicarboximido)ethane, bis-(tetrabromophthalimido)ethane, Diels-Alder adduct of chlorinated cyclopentadiene and an unsaturated cycloaliphatic compound, bis-(tribromophenoxyethyl) -tetrabromobisphenol A ether, pentabromodiphenyl ether, octabromodiphenyl ether, decabromodiphenyl ether, bis-(tribromophenoxy)ethane, bis-(pentabromophenoxy)ethane, chloropentabromocyclohexane, (tribromophenoxy)- (dibromononylphenoxy)ethane, pentabromoethylbenzene,

_ pentabromododecylbenzene, carbonate oligo ers of tetrabromobisphenol A, poly(bromostyrene), and brominated polystyrene, poly(bromophenylene) etner, and mixtures thereof. Particularly preferred is di-(2-ethylhexyl)tetrabromophthalate

Substantially any suitable metal hydrates and oxides may employed as flame retardant agents, including hydrates and oxi of aluminum, iron, zinc, magnesium, tin, molybdenum and antimo Alumina trihydrate, magnesium hydroxide, and antimony trioxide are the preferred compounds in this class.

Suitable metal boron-containing flame retardant compounds include zinc, barium, calcium, magnesium, cadmium and mercury. Zinc borate is the preferred compound in this class.

Substantially any suitable phosphorus-containing compound may be used as a flame retardant agent, including ammonium polyphosphate, arylphosphates, alkarylphosphates and alkylphosphates. Particularly preferred are phenyl isopropylphenyl phosphate and isodecyldiphenyl phosphate commercially available from FMC Corporation under the trademar Kronitex 100 and Santicizer 148.

The foregoing flame retardant compounds are added to ther plastic resins at effective levels such that the resultant res composition may be rendered flame retardant.

Thermoplastic resins which may be treated in accordance the invention include thermoplastics such as polyvinyl halid polystyrene, and homopolymers and copolymers of polypropylen polyethylene, and polybutylene. Polyvinyl chloride is most preferred in accordance with this invention.

The scope of the present invention also includes the incorporation of other additives in the composition so far a produce a particular end result. Such additives include, wi limitation, blowing agents, heat stabilizers, light stabiliz plasticizers, pigments, preservatives, ultraviolet light sta lizers, fillers, antioxidants, antistatic agents and other materials well known to those skilled in the art, for example described in Modern Plastics Encyclopedia, Vol. j53_, No. 10A, McGraw-Hill, Inc. (1986).

The bicyclic phosphates of the present invention may be alone or as mixtures of any such compounds. When mixtures of bicyclic phosphates are employed, substantially any combinati of amounts and proportions of the individual compounds may be used. The use of Compound BCP and Compound BCP-A is especial preferred in accordance with this invention.

The bicyclic phosphate may be employed at substantially level because even very low levels are believed to assist in smoke suppression. Preferably it is present at a level of at least 2 percent and preferably about 3 percent up to about 20 percent by weight of the composition.

The flame retardant agents of the present invention may b used alone or as mixtures of any such compounds. When mixture of flame agents are employed, substantially any combinations o amounts and proportions of the individual compounds may be use The use of di-(2-ethylhexyl)- tetrabromophthalate, alumina trihydrate, magnesium hydroxide, zinc borate, antimony trioxid and alkylaryl phosphates are especially preferred in accordanc with this invention.

Desirably, flame retardants are employed at a level of ab 2 to 50 percent by weight of the composition, preferably about to 20 percent, depending on the specific flame retardant and thermoplastic resin employed. Operative and preferred ranges various flame retardants in accordance with this invention are given in the Table I.

TABLE I OPERATING RANGES

BrFr - di-(2-ethylhexyl)tetrabromophthalides brominated flame retardant AAP - alkylarylphosphate (Kronitex 100 - FMC Corp.) ATH - alumina trihydrate MgOH - magnesium hydroxide ZnBor - zinc borate SbOx - antimony oxide

Desirably, the bicyclic phosphate compound and flame retardant are provided as a mixture useful as an additive which may be added to polystyrene or polyolefin resin compositions. The additive mixture utilizes bicyclic phosphate and flame retardant in a weight ratio lying in the range of about 1:25 to 20:1, most preferably, about 3:20 to 20:3.

The additive mixture is incorporated into the polymer composition at an effective level such that the resulting resin composition is rendered flame retardant. In general, the additive mixture is provided in the flame retardant at a level of about 2 - 50 percent by weight of the resin composition, preferably about 3 - 30 percent by weight.

Practice of the present invention is illustrated by the following examples, which are given to illustrate the invention and should not be construed as limiting its scope.

EXAMPLES Preparation of Polyvinylchloride Resin Systems. A general purpose polyvinylchloride ("PVC") resin was used in the study. PVC resin, powdered additives and flame retardant were blended a mixing bowl and warmed to 90°C. Liquid plasticizer was added and the admixture was compounded on a two-roll mill at 160°C. The compounded PVC material was compression molded at 180°C. Table II shows examples of the use of Compound BCP in flexible PVC formulations. The general formulation used is as follows: Material % by weight

PVC Resin varied

Compound BCP varied (see Table)

Flame Retardant varied (see Table)

Dioctylphthalate Plasticizer varied (see below) Epoxidized Soya Plasticizer 5

Stabilizer 3

The amount of dioctyl phthalate ("DOP") plasticizer was adjuste to give compositions with comparable physical properties (i.e., approximately 90 Shore A hardness) and flammability (approximately 3001) performance.

Flammability Test Procedures. The following flammability tests were used throughout the study:

Test Method Description

ASTM D-2863 Limiting Measurement of the minimum oxygen Oxygen Index necessary to sustain burning of a vertically supported sample for three minutes. High values indicate improved resistance to burning.

NBS Smoke Chamber Smoke density determinations ASTM -662 under smoldering conditions. Low values indicate low smoke evolution.

A series of experimental and comparative studies were performed using the foregoing techniques. The data are given in Table II.

These data demonstrate the patentability of the subject invention as follows. The Control Example shows the effect of 5.0% BCP alone on the smoke performance of a 30 01 flexible PVC composition. Comparative Examples 2-6 show the effect of various flame retardants on smoke performance when Compound BCP is not present.

Example 1 illustrates the invention when the flame retardant is a bromine-containing flame retardant. Example 2 illustrates the invention when the flame retardant is phosphate-containing flame retardant (an alkarylphosphate) . Example 3-5 illustrate the invention when the flame retardant is an inorganic flame retardant.

In the case of each invention composition, compositions comprising a bicyclic phosphate (Compound BCP) and a flame retardant had lower smoke than the Control (i.e., a system without any additional flame retardant agent) or the corresponding Comparative Examples 2-6 (i.e., a system without bicyclic phosphate).