Patent Publication Number: US-3875107-A

Title: Flame-resistant thermoplastic molding compositions and moldings made therefrom

Description:
Umted Stat 1111 3,875,107 Nouvertn et al. Apr. 1, 1975 1 FLAME-RESISTANT THERMOPLASTIC 3.112.292 11/1963 Bottenbruch et al. 260/47 MOLDING COMPOSITIONS AND 3,817,907 6/1974 Muller et al. 260/37 PC MQLDINQSMADE 2 THEREFROM [75] Inventors: Werner Nouvertn, Krefeld,  
  Germanyi Peter QF Lyons, The Chemistry and Uses of Fire Retardents; coraopohs, 4 Gunter Pellswcker; Wiley-lnterscience 1970; pp. 420421, 439. Hugo Vernaleken, both of Krefeld, I Germany &#39;Hattori et al.; The Effects of Fiber Glass Reinforcement on the Flammability Properties of Thermoplas- [73] Asslgnee&#39; Bayer Akhengesenschafl tics; Plastic Design and Processing; August 1967; pp  
 OTHER PUBLICATIONS Leverkusen, Germany 2.840 [22] Filed: Apr. 29, 1974 [21] Appl. No.: 465,023 Primary Examiner-Lewis T.. Jacobs Related us. Application Data Attorney, Agent, or Firm-Lawrence S. Pope [62] Division of Ser. No. 293,195, Sept. 28, 1972, Pat.  
 [ ABSTRACT [30] Foreign Application Priority Data Sept. 29 1971 Germany 2148598 H flame&#39;reslstamFhermoplast&#39;c m dmg tlons based on aromatic polycarbonates and including [52] US CL... 260/37 PC, 106/15 260/47 XA (1) small amounts of chlorine or bromine or alkali 51 1111. c1 C08g 51/10 metalsalts Salts F mixtures [58] Field of 260/37 106/15 bromine and the salts and (2) small amounts of glass fibers. The molding compositions have good process- [56] References Cited ability and high impact strength.  
 UNITED STATES PATENTS 6 Claims, No Drawings 3,062.78l l [/1962 Bottenbruch et al. 260/47 FLAME-RESISTANT THERMOPLASTIC MOLDING COMPOSITIONS AND MOLDINGS MADE THEREFROM This is a division of application Ser. No. 293,195, filed Sept. 28, 1972 now US. Pat. No. 3,845,007.  
 BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to flame-resistant thermoplastic molding compositions and to articles made therefrom.  
 2. Description of the Prior Art Various methods for reducing the flammability of aromatic carbonates from bis-hydroxy compounds are known.  
  It has not proved successful to add flameproofing additives which are known for other plastics, such as, for example, antimony trioxide, to high molecular thermoplastic carbonates of dihydric phenols, because the amount of such additives must be so great that the valuable properties of the polycarbonates are considerably impaired or the additives are incompatible with the polycarbonates or are unstable at the high processing temperatures of polycarbonates.  
  Additions of, for example, alkali or ammonium perfluoroalkane-sulphonates, preferably those with perfluorinated alkyl radicals with about 4-8 carbon atoms, which show good compatibility with the polycarbonates and are sufficiently heat-stable (according to German Offenlegungsschrift 1,930,257) have proved more successful. Small additions of these sulphonates, in amounts of about 0.01 to about 1 percent by weight, suffice to render the polycarbonates more flame-resistant.  
  However, it has been found that the flame-resistant properties of polycarbonates containing the added alkali or ammonium perfluoroalkane-sulphonates which have been mentioned in general do not yet suffice for practical requirements, and the grading, required for many instances of practical use, into a class of high non-flammability according to test methods, such as, for example, the burning test according to Underwriters Laboratories, item 94, is not achieved.  
  It is particularly the dripping behavior of a chemical material on exposure to flames which is important in as much as in cases of fire thermoplastic compositions which burn with difficulty but drip while burning, ignite substances which burn easily and can thus become the cause of greater damage. However, it has not yet been possible to improve the dripping behavior of nonreinforced polycarbonates by the additions of sulfonates which have been described.  
  A similar situation applies when using additions of nickel compounds (in accordance with German Offenlegungsschrift 1,918,216).  
  Flame-resistant polycarbonates are hitherto preferentially manufactured in industry by incorporating halogen-containing divalent phenols, for example tetrachloroor tetrabromo-bisphenols into the polymeric molecule. The high halogen content which is required for grading in a category of high fire resistance, for example SE 1 according to Underwriters Laboratories, item 94, can, however, have adverse effects. (Compare US. Pat. No. 3,334,154). This is because the high halogen content causes a worsening of the processability of the polycarbonates in question, which manifests itself in diminished flow properties and reduced heat stability of these polycarbonates.  
  Glass fiber-reinforced aromatic polycarbonates of bis-hydroxy compounds, with a glass fiber content of 5 20 30 percent by weight, have proven to be of value in practical use, since the glass fiber reinforcement produces an improvement, relative to the non-reinforced polycarbonate, in a series of important properties such as, for example, the modulus of elasticity and the flexural strength.  
  preferably 30 percent by weight of glass fibers.  
  Admittedly, the addition of glass fibers, in the amounts mentioned, to aromatic polycarbonates causes an embrittlement of the thermoplastic molding composition and a substantial reduction in the impact 20 strength as compared to the non-reinforced material.  
 Hence glass fiber additions of 20 30 percent by weight, such as are used for reinforcing aromatic polycarbonates from bis-hydroxy compounds and for manufacturing dimensionally stiff thermoplastic molding compositions, are unsuitable for the manufacture of flameproof polycarbonates having a high impact strength. On the other hand, glass fiber contents of less than &#39;10 percent by weight when used as additives to aromatic polycarbonates do not produce any improvements in the fire resistance.  
 SUMMARY OF THE INVENTION It has now been found, in accordance with this invention, that the high flame-resistant categories desired of polycarbonate molding composition, such as the SE 1 and SE 0 classifications of Underwriters Laboratories, item 94, are achieved without appreciable effect on the processability or impact strength of the compositions by incorporating into the compositions 1) small amountsof chlorine or bromine or of alkali metal salts or nickel salts or of both the halogen and the salts and (2) small amounts of glass fibers.  
  The dramatic effect of the combination of glass fibers with halogen and or with salts is surprising because the amount of halogen or salts is, alone, generally not sufficient, in any case less sufficient to produce an SE 1 or SE 0 flame-resistant polycarbonate composition and the small-amount of glass fibers would not be expected to improve the flame-resistant properties of the polycarbonate compositions.  
 DETAILED DESCRIPTION The flame-resistant thermoplastic molding compositions and articles provided according to this invention comprise, with the percentages given being by weight based on the total weight of the molding compositions:  
 a. from about 93 to 98 percent of an aromatic polycarbonate;  
 b. an effective amount of i. up to about 3 percent of chlorine or bromine, or  
 &#39; ii. up to about 1 percent of alkali metal salts or nickel salts preferably those salts soluble in the aromatic polycarbonate, or  
  iii. mixtures of i and ii; and  
 the flame-resistant polycarbonate molding compositions in the form of halogen-containing aromatic polycarbonates based on tetrachloroor tetrabromobisphenol A-polycarbonates. The polycarbonates may be halogen-containing copolycarbonates alone or halogen-containing polycarbonate homopolymers or copolymers mixed with halogen-free polycarbonates,  
  The chlorine or bromine is incorporated into the polycarbonate molding composition in amounts up to 3 per cent by weight, and preferably 1.5 to 2.5 percent by weight, but if no flame-proofing additive is present, the chlorine or bromine should be at least 1 per cent by weight of the molding composition.  
  The alkali metal salts or nickel salts are incorporated into the polycarbonate molding compositions in amounts up to 1 percent by weight, and preferably 0.05 0.2 percent but if no halogen is present, the flameproofing additive should be at least 0.01 per cent by weight of the molding composition.  
  It should be noted that the amount of l) chlorine or bromine and (2) the alkali metal salt or nickel salt used when both (l) and (2) are present may be less than the amount required for each when one of them is not present in the composition. The amount of (l) and (2) needed in a mixture of (1) and (2) is that which will produce an SE 2 (explained below) polycarbonate material when no glass fiber is present in the composition.  
  The glass fibers are incorporated into the polycarbonate molding compositions in amounts of from about 2 to 6% by weight and, preferably, about 4% by weight. The glass fibers useful in the invention have average fiber lengths of 100 to 600 pm and, preferably, 200-400 um.  
  A particularly surprising fact is that even low viscosity polycarbonate, which flows easily and which tends to drip to an increased extent, can be employed for the manufacture of the thermoplastic molding composition according to the invention, with the additives according to the invention preventing both a reduction in the smoldering times and also the undesirable dripping.  
  Because of the low glass fiber content, the high impact strength which is demanded in many cases of practical use and is valued in aromatic polycarbonates from bisphenol A is not worsened to any significant extent.  
  The small amounts of salts, flameproofing additives, and the small added amounts of halogen also do not cause any decrease in the impact strength which high impact strength is characteristic of polycarbonate.  
  The processability of the thermoplastic molding composition of polycarbonate is likewise not impaired to any significant extent by the small halogen content and glass fiber content according to the invention.  
  Polycarbonates that may be used in the composition of. the invention, include those derived from aromatic bis-hydroxy compounds, and in particular, for example, those manufactured from dihydric phenols, such as resorcinol, hydroquinone or dihydroxydiphenyl, from bis- (hyroxyphenyl)-alkanes, such as, for example, bis-(4- hydroxyphenyl)-propane-2,2, from trinuclear bisphenols such as (1,0:-bis-(4-hydroxyphenyl)-p-diisopropylbenzene, from halogenated bis-(hydroxyphenyl)-alkanes, such as, for example, 4,4-dihydroxy- 3 ,5,3 ,5 &#39;-tetrachloro-phenylpropane-2,2 or 4,4- dihydroxy-3 ,5 ,3 ,5 &#39;-tetrabromo-phenylpropane-2,2, bis-(hydroxyphenyl)-cycloalkanes, -sulphones, -sulphoxides, -ethers and -sulphides, optionally mixed with glycols, with derivatives of carbonic acid, for example its diesters or dihalides, optionally with the conjoint use of minor amounts of dicarboxylic acids or their derivatives which are suitable for the formation of an ester, and which possess an average molecular weight of about 10,000 to 100,000, preferably between about 20,000 and 50,000.  
  Suitable halogen-containing aromatic polycarbonates are, for example, copolycarbonates based on tetrachloroor tetrabromo-bisphenol-A and bisphenol-A or mixtures of halogen-free and halogen-containing polycarbonate or co-polycarbonate.  
  Possible glass fiber materials are all commercially available types of glass fibers, such as, for example, ground short glass fibers and rovings, but especially staple glass fiber, provided that they possess a fiber finish which is compatible with polycarbonate.  
  The additives to be used are the compounds which are known and suitable for the flameproofing of polycarbonate. Also useful are synergistically acting substances.  
  Examples of suitable compounds are alkali salts having an organic moiety, particularly those which are soluble in polycarbonate, and more particularly soluble alkali metal salts of organic carboxylic acids, preferably containing from 1 to 18 carbon atoms, and of perfluoroalkanesulfonic acid. Examples of these salts include potassium 2-ethyl-hexanate, sodium 2-ethylhexanate, lithium Z-ethyl-hexanate, potassium perfluorooctanate, sodium perfluorooctanate, lithium perfluorooctanate, potassium salts of 5-ethyl-dioxan-l,3- yl-(5)-carboxylic acid, rubidium 2-ethyl-hexanate, rubidium perfluorooctanate and potassium perfluoromethanesulfonate, potassium perfluorooctanesulfonate and potassium perfluorobutanesulfonate. Further examples of suitable salts are alkali salts of lauric acid, stearic acid, oleic acid, phthalic acid monobenzyl ester, adipic acid monobutyl ester, p-octylbenzoic acid, ptert.-butyl-benzoic acid, 3-(3,5-di-tert.-butyl-4- hydroxyphenyl)-propionic acid and diglycollic acid mono-decyl ester.  
  Additionally, soluble nickel salts, for example the soluble nickel salts of 2-ethyl-hexanoic acid, of lauric acid and of stearic acid may be used.  
  The glass fiber materials, like the flameproofing additives and halogen-containing polycarbonates described, can be added to the polycarbonates in various ways. They can be added to the reaction mixtures before, during or after the manufacture of the polycarbonates. They can furthermore be added to polycarbonate solutions or polycarbonate melts. Finally, they can be mixed with polycarbonate granules and these mixtures can be homogenized by subsequent melt extrusion.  
  In the same manufacturing process it is possible to add to the polycarbonate, in addition to the additives according to the invention, further additives such as, for example, the pigments and effect substances suitable for coloring the polycarbonate, and also moldrelease agents, stabilizers and anti-oxidants.  
  The surprising influence of the additive combination according to the invention on the fire resistance of aromatic polycarbonates based on bisphenol A, while retaining the impact strength characteristic of such polycarbonates, is illustrated by Tables 1 3. The undesired reduction in the impact strength caused by high amounts of glass fibers is recognizable. The flameresistant polycarbonates according to the invention can be processed in the form of powders or granules, in accordance with the known processing methods, such as, for example, by injection molding or extrusion, to give moldings of the most&#39;diverse kind.  
  Molding compositions from the flame-resistant thermoplastic polycarbonates according to the invention, which contain the additives according to the invention, are suitable for the manufacture of impact-resistant moldings of low flammability such as are employed, for example, in general instrument construction, precision engineering, the electrical industry and telecommunication, and also for the manufacture of semifinished goods, such as, for example, films, sheets, rods and profiles.  
 EXAMPLES Tables 1, 2 and 3 contain Examples 1 to 20. Examples marked with an asterisk do not relate to compositions of the invention and are included for comparison only.  
  In Tables 1 and 2 the results of flammability tests according to standards of Underwriters Laboratories, item 94 (UL 94), and IBM 6-0430-102, are listed.  
  In the UL 94 test individual specimens of the dimension 1/16 X k X 5 inches are vertically clamped and exposed twice for 10 seconds each time to a blue gas flame of 20 mm height, the top of the gas burner is positioned about 10 mm from the lower end of a test specimen. The specimens are positioned 12 inches above a horizontal layer of absorbent surgical cotton. For classifying the material in a fire class, 5 test pieces in the injection-fresh and in the tempered state (tempering is carried out at 70C for 7 days) are tested.  
 The following criteria are decisive for classification:  
 After burning times correspond to those of SE2 but 5 25 seconds 30 seconds material may not drip off burning.  
 Average after-burning time Maximal acceptable after-burning time: The material must not drip off burning s seconds seconds In the IBM 6-0430-102 test, test specimens measuring 120 X 10 X 4 mm are suspended vertically and exposed to a 2 cm high Bunsen burner flame (without an air supply). The distance of the top of the Bunsen burner is 1 cm from the bottom of the test specimen. The length of time is determined for which a test specimen can be exposed to the flame as described above without continuing to burn for longer than 30 seconds after removal of the flame, and without burning particles dripping off of the specimen and igniting a wad of cotton wool placed under the specimen. A material is classed as a Class A material if after a 60 second flame application time, the material will extinguish without producing flaming droplets. Class B materials are those that extinguish within 30 seconds after a 5 second or more flame application time but cannot withstand a 60 second flame application time without exceeding the foregoing. Thus, for example if a material extinguishes within 30 seconds for flame application times up to 45 seconds it is classified Class B/4 mm/45 see.  
  In the examples the polycarbonates described (granulate&#39;d) are dry mixed with the various amounts of flame&#34; proofing additive, e.g., in the form of the tetrachlorobisphenol A polycarbonate, or glass fibers by socalled tumbling. Thereafter, the granules are extruded at about 300 C., using a mixing screw, to give a ribbon that is then chopped to give granules. These granules are then converted into the required test sepcimens in an injection molding machine at about 300C. 7  
  The halogen-free polycarbonate of bisphenol A employed in Examples 1-20 is the reaction product of bisphenol A and phosgene having a relative viscosity of 1.28 measured on solutions of 0.5 g of polycarbonate in ml of methylene chloride at 25C. It is prepared by introducing under nitrogen atmosphere, 1825 parts by weight of phosgene into a mixture of 3420 parts by weight of bisphenol A, 70.0 parts by weight of p-tert. butylphenol, 2100 parts by weight of a 45 per cent by weight aqueous sodium hydroxide solution, 17,500 parts by weight of distilled water and 33,000 parts by weight of methylene chloride at 2425C. During the 10th and 90th minutes of the introduction period of phosgene further 1300 parts by weight of a 45 percent by weight aqueous sodium hydroxide solution are dropped in. After the introduction of the phosgene is finished 6 parts by weight of triethylamine are added and stirred further for an hour. Then the organic phase and the aqueous phase are separated. The organic phase is washed first with a 2 percent by weight aqueous phosphoric acid, second with a 2 percent by weight aqueous sodium hydroxide solution, third further two times with the 2 percent by weight phosphoric acid and finally with distilled water until the solution is neutral. Thereafter 7500 parts by weight of chlorobenzene is added to the methylene chloride solution and the main proportion of methylene is distilled off. After cooling the remaining mixture gells and the gel is chopped to small pieces which are dried at C. under vacuum during 48 hours.  
  The polycarbonate of bisphenol A and tetrachlorobisphenol A employed in Examples 1-9 has a relative viscosity of 1.27 and contains 6.5 percent chlorine. This product is prepared by treating a mixture of 2.992 parts by weight of bisphenol A, 686 parts by weight of tetrachlorobisphenol A (2.2-bis-(3,5- dichloro-4-hydroxyphenol)-propane), 50 parts by weight of p-tert. butylphenol, 2850 parts by weight of a 45 percent by weight aqueous sodium hydroxide solution, 17,500 parts by weight of distilled water and 33,000 parts by weight of methylene chloride with phosgene and by working-up the reaction product as described above for the halogen-free polycarbonate.  
  The polycarbonate of bisphenol A and tetrabromobisphenol A employed in Examples 10 16 has a relative viscosity of 1.293 and contains 6 percent bromine. This product is prepared by reacting 3246 parts by weight bisphenol A, 414.parts by weight of tetrabromobisphenol A, 54 parts by weight of p-tert.-butylphenol, 4300 parts by weight of 45 percent by weight of sodium hydroxide solution with the parts by weight of the remaining compounds set forth above for the tetrachlorobisphenol A-polycarbonate; the reaction product is worked up as described above for the halogenfree polycarbonate of bisphenol A.  
  The other copolycarbonates mentioned therein are prepared accordingly.  
 Table 1 Optimizing the fire resistance, while retaining the im act strength of polycarbonates based on bisphenol A, by adding chlorine in the form of tetrachloro isphenol-A-polycarbonate and/or glass fibers.  
  Burning test in accordance with Underwriters Laboratories Inc Impact strength-ll-) Chlorine Glass fiber Average Number of burning lBM accordin to content in 70 content in smoldering time samples which have Classification subj. CMl-l DIN 53 53 by weight by weight in seconds dripped 6-0430-102 cmkp/cm 1* 25 20 not self- Cl. B 4 mm/ did not break extinguishing l secs 2* 7 0 SE I Cl. A 4 mm/ 49 60 secs 3* 4 15 not self- Cl. B 4 mm/ did not break extinguishing 15 secs 4 4.5 l0 7 SE ll Cl. B 4 mm/ did not break 20 secs 5* 4.5 4 6 0 SE l Cl. A 4 mm/ did not break 60 secs 6* 4.5 6 3 0 SE 0 Cl. A 4 mm/ 93 60 secs 7* 2.25 20 12 not self- Cl. B 4 mm/ did not break extinguishing 20 secs 8 2.25 3 l l 0 SE 1 Cl. B 4 mm/ did not break secs 9 2.25 4.5 4 0 SE 0 Cl. A 4 mm/ did not break 60 secs 20 flame exposures were carried out in each case H-) l0 samples were tested in each case Table 2 Optimizing the fire resistance, while retaining the impact strength of polycarbonates based on bisphenol A, by addingtbromine in the form of tetrabromobisphenol-A-polycarbonate and/or glass fibers.  
  Burning test in accordance with Underwriters Laboratories lnc+) lmpact Strength++) Bromine Glass fiber Average Number of burning lBM according to content in 7! content in smoldering time samples which have Classification subj. CMH DlN 53 453 by weight by weight in seconds dripped 6-0430-102 cmkp/cm l0 25 20 not self- Cl. B 4 mm/ did not break extinguishing l0 secs 1 1* 20 7 0 SE l Cl. A 4 mm/ 49 60 secs l2 4 25 l5 not self- Cl. B 4 mm/ did not break extinguishing l5 sees 13* 6 8 5 SE ll Cl. B 4 mm/ did not break secs 14* 6 5 2 0 SE 0 Cl. A 4 mm/ did not break 60 secs l5* 3 8 9 SE ll Cl. B 4 mm/ did not break 40 secs l6 3 4 2 0 SE 0 Cl. A 4 mm/ did not break 60 secs 20 flame exposures were carried out in each case -H-) H] samples were tested in each case Table 3 Optimizing the fire resistance while retaining the impact strength of polycarbonates based on bisphenol A by adding flameproofing additives and/or glass fibers.  
  Burning test in accordance with Underwriters Laboratories Inc.+)  
 Additive content impact strength-1+) (K perfluoro- Glass fiber Average Number of burning according to octanesulphonate) content in smoldering time samples which have Classification DlN 53 453 in by weight by weight in seconds dripped cmkp/cm l7 0.l 5 6 SE ll did not break 18 2O 7 0 SE l 49 i9 S 6 2 SE ll did not break 20 0.l 5 4 0 SE 0 did not break 20 flame exposures were carried out in each case -H-) l0 samples were tested in each case EXAMPLE 21 0.1 percent by weight of potassium perfluorobutanesulfonate and percent by weight of glass fibers of average length 400 um were incorporated into a copolycondensate of bisphenol A and tetrachlorobisphenol A containing 0.9 percent by weight of chlorine to give a molding composition. Appropriate test rods from the molding composition thus obtained conform to Class I of the fire test according to Underwriters Laboratories, subject 94, and are rated Class B/4 mm/45 secs. according to IBM Fire Test Subject CMI-I 6-0430-102. Test specimens corresponding to the standard specification do not break in the impact test according to DIN 53,453.  
 EXAMPLE 22 0.2 percent by weight of potassium isooctanate and 6 percent by weight of glass fibers of average length 110 um are mixed into the polycarbonate of bisphenol A to give a molding composition. Appropriate test specimens of the molding composition thus obtained conform to Class 1 of the fire test according to Underwriters Laboratories, subject 94, and are rated Class B/4 mm/4O secs. according to IBM Fire Test Subject CMH 6-0430-102. Some of the test specimens break in the impact test according to DIN 53,453 while the rest do not break.  
 EXAMPLE 23 0.5 percent&#39;by weight of nickel laurate and 4 per cent by weight of glass fibers of average length 400 ,um are mixed into the polycarbonate from bisphenol A to give a molding composition. Appropriate test specimens of the molding composition thus obtained conform to Class I of the fire test according to Underwriters Laboratories, and are rated Class B/4 mm/45 secs. according to IBM, Subject CMH 6-0430-102. Test specimens corresponding to the standard specification do not break in the impact test according to DIN 53,453.  
 EXAMPLE 24 EXAMPLE 25 0.1 percent by weight of sodium perfluorooctanate and 4 percent of glass fibers of average length 400 um are mixed into the polycarbonate from bisphenol A to give a molding composition. Appropriate test specimens of the molding composition thus obtained conform to Class 1 of the fire test according to Underwriters Laboratories, subject 94, and are rated Class B/4 mm/4O secs. according to IBM, Subject CMH 6-0430-102. Test specimens corresponding to the standard specification do not break in the impact test according to DIN 53,453.  
 EXAMPLE 26 0.05 percent by weight of potassium perfluorooctane-sulfonate and 5 percent by weight of glass fibers of average length 550 um are added to a polycarbonate from bisphenol A to give a molding composition. Appropriate test specimens of the molding composition thus obtained conform to Class 1 of the fire test according to Underwriters Laboratories, subject 94, and are rated Class B/4 mm/4O secs. according to IBM, Subject CMH 6-0430-102. Test specimens according to the standard specification do not break in the impact test according to DIN 53,453.  
  Thus from the examples it is seen that the molding compositions of the invention exhibit unexpected flame-retardant or flame-resistant properties but still retain a high impact strength and good processability.  
  It is to be understood that any of the components and conditions mentioned as suitable herein can be substituted for its counterpart in the foregoing examples and that although the invention has been described in considerable detail in the foregoing, such detail is solely for the purpose of illustration. Variations can be made in the invention by those skilled in the art without departing from the spirit and scope of the invention except as is set forth in the claims.  
 What is claimed is:  
  1. A high impact, flame resistant aromatic polycarbonate containing by weight:  
 a. 2-6 percent glass fibers having an average fiber length of to 600 um; and  
 b. an effective amount of i. up to 3 percent of chlorine or bromine chemi-&#39; cally bonded to an aromatic carbon atom of said aromatic polycarbonate, and ii. up to 1 percent of an alkali metal salt.  
  2. The aromatic polycarbonate of claim 1 wherein said alkali metal salt is soluble in said aromatic polycarbonate.  
  3; The aromatic polycarbonate of claim 1 wherein i is present in an amount of l to 3 percent, and ii is present in an amount of about 0.01 to 1 percent.  
  4. The aromatic polycarbonate of claim 1 wherein said chlorine or bromine is present in an amount of from 1.5 to 2.5 percent.  
  5 The aromatic polycarbonate of claim 3 wherein said alkali metal salt is present in an amount of from 0.05 to 0.2 percent.  
 6. Articles molded from the composition of claim 1.