Polycarbonate containing a metal salt of a perhalometalate as an ignition depressant

#This invention relates to polycarbonates containing additives which inhibit combustion upon exposure of the polycarbonates to low temperature ignition sources.

#Polycarbonates 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 appear to be particularly 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 or comparable low temperature ignition source. More importantly, as is often the case, the polycarbonates contain stabilizers and other additives which are often more combustible than the unmodified polycarbonate. As a result, the modified polycarbonate frequently exhibits substantially poorer resistance to combustion than does the unmodified polycarbonate.

#To a 10,000-g sample of a homopolycarbonate of bisphenol-A, having a weight average molecular weight (M.sub.w) of 32,000 as determined by gel permeation chromatography and sold under the trade name Merlon M50F-1000 by Mobay Chemical, in the form of pellets (0.32 cm (dia).times.0.32 cm (length)) is added 0.5 g of the potassium salt of perfluorotitanate (K.sub.2 TiF.sub.6). These ingredients are dry blended and then dried at 250.degree. F. for 4 hours. The resultant blend is extruded and repelletized in a single screw extruder equipped with a static mixer and operating at 525.degree. F. The extruded pellets are redried at 250.degree. F. for up to 4 hours. These redried pellets are molded into test bars (12.7 cm.times.1.27 cm.times.0.32 cm) using a screw type injection molding unit wherein the molding temperature is 575.degree. F. The injection molded bars are tested for combustibility (oxygen index and fire retardance) and for optical properties (light transmission, haze and yellowness index). The results of these tests (Sample No. 1) are reported in Table I.

#For the purposes of comparison, three additional blends (Sample Nos. 2-4) are prepared using different amounts of K.sub.2 TiF.sub.6. These blends are also tested and the results are reported in Table I. Also recorded in Table I are the combustibility and optical properties of a control sample (Sample No. C) employing no fire retardant additive.

#TABLE I __________________________________________________________________________ Flame Retardance(3) Sample Perhalte Salt O.sub.2 Index(2) Flame Time, Light Trans- Haze(5) No. Amount(1), % % O.sub.2 sec. Rating mission(4), % % YI(6) __________________________________________________________________________ 1 0.005 31.8 6.8 V-2,V-2 87.9 6.6 4.8 2 0.020 36.0 3.8 V-0,V-2 87.1 7.5 6.3 3 0.050 36.1 3.7 V-0,V-0 85.8 19.3 7.1 4 0.200 33.3 5.4 V-1,V-1 81.3 64.6 10.2 C* -- 25.2 17.5 HB,HB 88.8 2.3 4.7 __________________________________________________________________________ *Not an example of the invention. (1)Amount weight percent based on polycarbonate (2)ASTM D2863-70 (3)Underwriters Laboratories Standard Test UL94 (4)ASTM D1003-61 (5)ASTM D1003-61 (6)ASTM D1925-70