FLAME-RETARDED TRANSPARENT POLYCARBONATE COMPOSITIONS

Abstract

The invention provides a transparent polycarbonate composition comprising a polycarbonate resin and a mixture of flame retardants comprising (A) tris(2,4,6-tribromophenoxy)-s-triazine and (B) an aromatic sulphone sulphonate in the form of an alkali metal salt. The composition achieves a UL-94 flammability test rating of V-0 at a polycarbonate thickness equal to or less than 1.6 mm. Processes for preparing the composition are also disclosed.

Claims

1. A polycarbonate composition comprising a polycarbonate resin and a mixture of flame retardants comprising (A) tris (2,4,6-tribromophenoxy)-s-triazine; and (B) an aromatic sulphone sulphonate in the form of an alkali metal salt, characterized in that the weight ratio between said tris(2,4,6-tribromophenoxy)-s-triazine and said aromatic sulphone sulphonate salt is not less than 5:1 and the concentration of said mixture of flame retardants is not less than 5% by weight based on the total weight of the composition, said composition being further characterized in that it is transparent and in that it achieves a UL-94 flammability test rating of V-0 at a thickness equal to or less than 1.6 mm.

2. A composition according to claim 1, wherein the aromatic sulphone sulphonate is potassium salt of diphenyl sulphone sulphonate (KSS).

3. A composition according to claim 2, comprising not less than 70% by weight polycarbonate, from 5 to 20% by weight of tris(2 ,4,6-tribromophenoxy)-s-triazine and from 0.1 to 1.2% by weight KSS.

4. A composition according to claim 3, comprising from 5 to 15% tris(2,4,6-tribromophenoxy)-s-triazine and from 0.1 to 0.6% by weight potassium salt of diphenyl sulphone sulphonate (KSS).

5. A composition according to claim 4, comprising from 5 to 10% tris(2,4,6-tribromophenoxy)-s-triazine.

6. A composition according to claim 1, which achieves a UL-94 rating of V-0 at a thickness of 0.8 mm.

7. A composition according claim 1, exhibiting light transmission of not less than 97% as determined by ASTM D1746-97.

8. A composition according to claim 1, wherein the polycarbonate resin has melt flow rate in the range from 2 to 10 [grams/10 minutes].

9. A process for preparing a polycarbonate composition as defined in claim 1, comprising processing a polycarbonate resin and a mixture of tris(2,4,6-tribromophenoxy)-s-triazine and an aromatic sulphone sulphonate metal salt, wherein said mixture is proportioned in the range from 5:1 to 30:1 in favor of tris(2,4,6-tribromophenoxy)-s-triazine.

10. A process according to claim 9, wherein the mixture of tris (2,4,6-tribromophenoxy)-s-triazine and the aromatic sulphone sulphonate metal salt is provided in a concentrate (masterbatch) form.

11. A process according to claim 9, wherein the aromatic sulphone sulphonate is potassium salt of diphenyl sulphone sulphonate (KSS).

12. A process according to claim 11, comprising: (i) providing masterbatch pellets comprising a) from 15 to 75% by weight of a polycarbonate carrier, and b) from 30 to 80% by weight of a mixture composed of tris (2,4,6-tribromophenoxy)-s-triazine and KSS, wherein the mixture is proportioned in a range from 10:1 to 25:1 in favor of tris (2,4,6-tribromophenoxy)-s-triazine, and (ii) processing said masterbatch pellets with the polycarbonate resin.

13. A process according to claim 11, comprising: (i) providing masterbatch pellets comprising a) from 18 to 40% by weight of a polycarbonate carrier; and b) from 60 to 80% by weight a mixture composed of tris (2,4,6-tribromophenoxy)-s-triazine and KSS, wherein the mixture is proportioned in the a range from 10:1 to 25:1, and (ii) processing said masterbatch pellets with the polycarbonate resin.

14. Concentrate pellets comprising: a) from 15 to 75% by weight of a polycarbonate carrier, and b) from 30 to 80% by weight of a mixture composed of tris (2,4,6-tribromophenoxy)-s-triazine and potassium salt of diphenyl sulphone sulphonate (KSS), wherein the mixture is proportioned in the a range from 10:1 to 25:1 in favor of tris(2,4,6-tribromophenoxy)-s-triazine.

15. Concentrate pellets comprising: a) from 18 to 40% of a polycarbonate carrier; and b) from 60 to 80% by weight a mixture composed of tris (2,4,6-tribromophenoxy)-s-triazine and potassium salt of diphenyl sulphone sulphonate (KSS), wherein the mixture is proportioned in the a range from 10:1 to 25:1.

16. A method for reducing the flammability and retaining transparency of polycarbonate formulations containing from 0.1 to 1.2% by weight sulfonate salt, comprising adding 5 to 15% by weight, relative to the weight of the composition, of tris (2,4,6-tribromophenoxy)-s-triazine, to meet UL 94 V-0 test requirements at 0.8 mm.

17. (canceled)

18. An article formed from the composition of claim 1.

19. A process according to claim 12, wherein the masterbatch pellets further comprise at least one auxiliary additive.

20. A process according to claim 13, wherein the masterbatch pellets further comprise at least one auxiliary additive.

21. The concentrate pellets according to claim 14, wherein the concentrate pellets further comprise at least one auxiliary additive.

Description

EXAMPLES

[0037] Ingredients of the Compositions

[0038] The materials used for preparing the polycarbonate formulations are tabulated in Table 1 (FR is the abbreviation of flame retardant):

TABLE-US-00001 TABLE 1 Component (manufacturer) GENERAL DESCRIPTION FUNCTION PC Makrolon 3106 Polycarbonate (MFI = 6.5 g/10 min) Plastic (Bayer) matrix KSS-FR Potassium salt of a complex of FR (Arichem) diphenyl sulfone sulfonate and diphenyl sulfonedisulfonate FR-245 Tris(2,4,6-tribromophenoxy)triazine Brominated (ICL-IP) FR FR-1410 Decabromodiphenyl ethane Brominated (ICL-IP) FR FR-1025 poly (pentabromobenzyl acrylate) Brominated (ICL-IP) FR F-2400 Brominated epoxy resin Brominated (ICL-IP) molecular weight ~40,000-60,000 FR FR-803 P Brominated polystyrene Brominated (ICL-IP) FR Irganox B 225 Antioxidant/processing stabilizer Antioxidant (BASF) blend Ratio & heat Irganox 1010:Irgafos 168 = 1:1 stabilizer.

[0039] Flammability Test

[0040] The flammability test was carried out according to the Underwriters-Laboratories standard UL 94, applying the vertical burn on specimens of 1.6 mm, 0.8 mm or 0.4 mm thickness.

[0041] Optical Properties

[0042] The instrument used was Datacolor C600. Transparency was measured according to ASTM D1746 97 and haze according to ASTM D1003 standard test methods. Yellowness index: D1925-70.

Examples 1-2 (Comparative) and 3 (of the Invention)

Flame Retarded Transparent Polycarbonate Compositions (Compounding Accomplished Through Powder Addition)

[0043] In this set of examples, KSS and FR-245 were tested for their ability to reduce the flammability of polycarbonate test specimens with thickness of 1.6 mm and 0.8 mm. Additives were fed to the extruder in a powder form. KSS and FR-245 were used separately in the compositions illustrated in Examples 1 and 2, respectively, whereas in the composition of Example 3, they were used together. The compositions and their properties are described in Table 3 below.

[0044] To prepare the compositions, polycarbonate pellets (Makrolon 3106 pellets) and additives (additives are applied as powders) were fed into a twin-screw co-rotating extruder ZE25 with L/D=32 through its main feeding port. The operating parameters of the extruder were as follows:

[0045] Barrel temperature (from feed end to discharge end): 160 C., 180 C., 220 C., 250 C., 250 C., 260 C., 270 C., die 275 C.

[0046] Screw rotation speed: 350 rpm

[0047] Feeding rate: 12 kg/hour.

[0048] The strands produced were pelletized in a pelletizer 750/3 from Accrapak Systems Ltd. The resultant pellets were dried in a circulating air oven at 120 C. for 3 hours. The dried pellets were injection molded into test specimens using Allrounder 500-150 from Arburg under the conditions tabulated below:

TABLE-US-00002 TABLE 2 PARAMETER Set values T.sub.1 (Feeding zone) 270 C. T.sub.2 280 C. T.sub.3 290 C. T.sub.4 295 C. T.sub.5 (nozzle) 300 C. Mold temperature 90 C. Injection pressure 1500 bar Holding pressure 1000 bar Back pressure 80 bar Holding time 10 s Cooling time 15 s Mold closing force 500 kN Filling volume (portion) 35 ccm Injection speed 25 ccm/sec

[0049] Specimens of 1.6 mm and 0.8 mm thickness were prepared. The test specimens were conditioned for one week at 23 C., and were then subjected to the several tests to determine their properties. The compositions tested and the results are set out in Table 3.

TABLE-US-00003 TABLE 3 Example Example 1 Example 2 Example 3 (comparative) (comparative) (of the invention) Composition, wt % polycarbonate 99.4 89.4 91.9 KSS 0.4 0.4 FR-245 10.4 7.5 Irganox B-225 0.2 0.2 0.2 Bromine content 0 7 5 (calculated wt %) Properties Flammability UL 94V 1.6 mm V-2 V-2 V-0 UL 94V 0.8 mm V-2 V-2 V-0 Optical properties Transparency % 99.0 99.0 98.9 Haze 1.0 0.9 1.1

[0050] The results set out in Table 3 indicate the high efficacy of a combination consisting of FR-245 and KSS in reducing the flammability of low-thickness polycarbonate test specimens, achieving UL 94 V-0 rating while preserving the transparency of the polymer. It is worth noting that the transparency of the neat polycarbonate was 98.1%.

Example 4 and 6-9 (Comparative) and 5A-5B (of the Invention)

Preparation of Flame Retardant Concentrates

[0051] In this set of Examples, KSS-FR was compounded in a twin-screw extruder to form concentrate pellets with polycarbonate carrier. KSS-FR was used either as a sole flame retardant (Example 4) or together with a brominated flame retardant (Examples 5A, 5B and 6 to 9). To prepare the concentrate pellets, polycarbonate pellets (Makrolon 3106 pellets) and additives (premixed in a powder form) were fed into a twin-screw co-rotating extruder ZE25 with L/D=32 through its main feeding port. The operating parameters of the extruder were as follows:

[0052] Barrel temperature (from feed end to discharge end): 160 C., 180 C., 220 C., 250 C., 250 C., 260 C., 270 C., die 275 C.

[0053] Screw rotation speed: 350 rpm.

[0054] Feeding rate was 12 kg/hour.

[0055] The strands produced were solidified, and pelletized in pelletizer 750/3 (Accrapak Systems Ltd), to afford cylindrical pellets with average diameter of 1-5 mm and length of 2-6 mm. The compositions of the so-formed masterbatch pellets (MB) are presented in Table 4.

TABLE-US-00004 TABLE 4 Example 4 5A 5B 6 7 8 9 MB 4 MB 5A MB 5B MB 6 MB 7 MB 8 MB 9 PC 84.8 26.65 29.8 29.8 29.8 29.8 29.8 KSS 15.0 6.65 3.5 3.5 3.5 3.5 3.5 FR-245 66.5 66.5 FR-1410 66.5 F-2400 66.5 FR-1025 66.5 FR-803 P 66.5 Irganox 225 0.2 0.2 0.2 0.2 0.2 0.2 0.2

[0056] It should be noted that it was difficult to prepare the masterbatch of Example 4, containing 15 wt % KSS, due to the tendency of KSS to adhere to the internal surfaces of the hopper. Other masterbatch compositions (MB 5A, MB 5B and MB 6 to MB 9), with lower amounts of KSS, were extruded fairly easily.

[0057] In the next sets of Examples, the masterbatch pellets of Examples 4, 5A, 5B and 6 to 9 were incorporated into polycarbonate (the same polycarbonate grade used for the production of the masterbatch pellets). The masterbatch pellets were mixed with polycarbonate pellets and injection-molded into 1.6 mm thick test specimens (Example 10 to 16), 0.8 mm thick test specimens (Examples 17 to 22) and 0.4 mm thick test (Examples 23-24) specimens according to the conditions set out in Examples 1 to 3injection parameters are found in Table 2. The results of the tests (flammability and optical properties) are presented below.

Examples 10, 13-16 (Comparative) and 11-12 (of the Invention)

Flame Retarded Transparent Polycarbonate Compositions Prepared via Masterbatch Route (1.6 mm Thick Test Specimens)

[0058] Compositions and properties of the so-formed polycarbonate test specimens are presented in Table 5. The polycarbonate and the masterbatch were combined at 80:20 weight ratio.

TABLE-US-00005 TABLE 5 Example 11 12 10 MB 5A MB 5B 13 14 15 16 MB 4 (FR245:KSS) (FR245:KSS) MB 6 MB 7 MB 8 MB 9 (KSS) 10:1 19:1 (FR1410:KSS) (FR2400:KSS) (FR1025:KSS) (FR803:KSS) composition polycarbonate 80 80 80 80 80 80 80 MB 20 20 20 20 20 20 20 Properties Flammability, UL 94 1.6 mm thickness Maximum 3 3 6 3 6 7 3 flaming time, sec Total flaming 17 13 25 12 30 32 16 time, sec Maximal glow 10 0 0 0 0 0 0 time + second flaming Number of 5 1 2 2 5 1 0 specimen dripping Number of 5 0 0 0 2 0 0 specimen igniting cotton Rating V-2 V-0 V-0 V-0 V-2 V-0 V-0 Optical properties Appearance* opaque opaque opaque opaque Transparency, % 97.73 98.58 98.6 Haze 2.8 1.5 1.4 Yellow Index 18.49 7.72 5.72 * indicates transparent formulation by visual inspection.

[0059] The following conclusions can be drawn from the data tabulated in Table 5:

[0060] MB 4 should be rejected for the reason that the flammability of the polymer is not satisfactory.

[0061] MB 6, MB 7, MB 8 and MB 9 are unacceptable due to loss of transparency.

[0062] MB 7 is to be eliminated on account of both factors, that is, loss of transparency and unsatisfactory flammability behavior.

[0063] MB 5A and MB 5B clearly emerge as excellent FR additives.

[0064] Another trend shown by results tabulated in Table 5 is a slight drop in the optical properties of transparent polycarbonates upon increase of the concentration of KSS in the polymer (see Example 10 with content of 3% by weight KSS, in comparison with Examples 11 and 12, with 1% by weight KSS).

Examples 17, 21-23 (Comparative) and 18-20 (of the Invention)

Flame Retarded Transparent Polycarbonate Compositions Prepared via Masterbatch Route (0.8 mm Thick Test Specimens)

[0065] Compositions and properties of the 0.8 mm thick polycarbonate test specimens are presented in Table 6. For the sake of comparison, masterbatch pellets which were rejected in view of the results reported in Examples 10 to 16 were subjected to UL 94 V-0 0.8 mm test. The results are tabulated in Table 6.

TABLE-US-00006 TABLE 6 Example 18 19 20 17 MB 5A MB 5B MB 5B 21 22 23 MB 4 (FR245:KSS) (FR245:KSS) (FR245:KSS) MB 6 MB 8 MB 9 (KSS) 10:1 19:1 19:1 (FR1410:KSS) (FR1025:KSS) (FR803:KSS) Composition polycarbonate 80 80 85 80 80 80 80 MB 20 20 15 20 20 20 20 Properties Flammability, UL 94 0.8 mm thickness Maximum flaming 7 5 5 1 2 2 5 time, sec Total flaming 30 23 23 10 12 13 23 time, sec Maximal glow 0 0 0 0 0 0 0 time + second flaming Number of 5 3 5 0 5 4 0 specimen dripping Number of 4 0 0 0 0 2 0 specimen igniting cotton Rating V-2 V-0 V-0 V-0 V-0 V-2 V-0

[0066] It is seen that MB 5A and MB 5B can be compounded with polycarbonate to form transparent, UL 94 V-0 0.8 mm rated compositions. In particular, MB 5B achieves the these goals at a fairly low loading (15 wt %).

Examples 23 (Comparative) and 24 (of the Invention)

Flame Retarded Polycarbonate Compositions Prepared via Masterbatch Route (0.4 mm Thick Test Specimens)

[0067] MB 5B (based on FR245/KSS mixture with 19:1 weight ratio), which has emerged as the most efficient flame retardant in the tests reported above, was compounded with polycarbonate at 70:30 weight to form 0.4 mm thick polycarbonate test specimens. For the purpose of comparison, MB 4 was also tested. Compositions and properties of the 0.4 mm thick polycarbonate test specimens are presented in Table 7.

TABLE-US-00007 TABLE 7 Example 24 23 MB 5B MB 4 (FR245:KSS) (KSS) 19:1 Composition (wt %) polycarbonate 70 70 MB 30 30 Properties Flammability, UL 94 0.4 mm thickness Maximum flaming time, sec 10 3 Total flaming time, sec 40 13 Maximal glow time + second flaming 9 0 Number of specimen dripping 4 3 Number of specimen igniting cotton 3 0 Rating V-2 V-0

Examples 25 and 26 (Both Comparative)

Flame Retarded Polycarbonate Compositions

[0068] A mixture consisting of KSS-FR and FR-245 in 10:1 weight ratio (in favor of KSS-FR) was produced in a concentrate form with polycarbonate carrier. The intention was to prepare a concentrate with the following composition by feeding the flame retardants in a powder form to the extruder:

[0069] Polycarbonate carrier: 77.8% by weight

[0070] KSS-FR: 20% by weight

[0071] FR-245: 2% by weight

[0072] Irganox B225: 0.2% by weight.

[0073] However, powder addition of KSS-FR to the extruder met with difficulties due to the tendency of the material to cling to the internal walls of the hopper. The concentrate was therefore produced with the aid of previously prepared concentrates (MB 4 and MB 5Asee Table 4 above), which were appropriately proportioned to achieve the 10:1 weight ratio in favor of KSS-FR. The extrudate was solidified and pelletized according to the conditions described in Examples 4 to 9 to produce masterbatch pellets (hereinafter named MB 10).

[0074] Polycarbonate pellets and MB 10 pellets were processed to form 80:20 and 70:30 weight ratio compositions. 0.8 mm thick test specimens were produced by injection molding using the general procedure described above. The optical and flammability properties were measured. The compositions were found to be transparent, with % transmission of 97.88; haze of 2.5 and Yellowness index of 12.82. However, the results of the flammability tests were unsatisfactory, as shown by Table 8.

TABLE-US-00008 TABLE 8 Example 25 26 composition polycarbonate 80 70 MB 10 (KSS:FR-245 at 10:1 weight ratio) 20 30 Properties Flammability, UL 94 0.8 mm thickness Maximum flaming time, sec 8 12 Total flaming time, sec 34 24 Maximal glow time + second flaming 5 0 Number of specimen dripping 5 5 Number of specimen igniting cotton 2 2 Rating V-2 V-2

Examples 27 (Reference) and 28 (of the Invention)

Cone Calorimeter Analysis of Flame Retarded Polycarbonate Compositions

[0075] Behavior of plastic materials in fire can also be studied with the aid of a cone calorimeter, where a radiant heat is projected onto a sample before ignition and during burning of the sample, and several parameters are measured. Data was collected by the cone calorimeter (Stanton Redcroft, according to ISO 5660-1; injection molded plaques were tested, having dimensions of 100 mm75 mm3.2 mm) under a heat flux of 50 kW/m.sup.2. The parameters set out in Table 9 include time to ignition (TTI), average heat release rate, peak heat release rate (PHRR), total heat release, smoke (SEA), smoke parameter (calculated) and fire performance index (calculated).

TABLE-US-00009 TABLE 9 Example Example 27 (reference) Example 28 composition polycarbonate 100 91.9 KSS 0.4 FR-245 7.5 Irganox B-225 0.2 Bromine content (calculated wt %) 5 Flammability test based on cone calorimeter Time to ignition (s) 75 61 average heat release rate (kW/m.sup.2) 215 177 peak heat release rate (kW/m.sup.2) 623 347 total heat release rate (mJ/m.sup.2) 66.4 51.2 Smoke (m.sup.2/kg) 852 1219 Smoke parameter (pHRRRSEA .Math. 10.sup.3) 532 423 Fire performance index (TTI/PHRR) 0.12 0.17

[0076] The cone calorimeter study shows that a combination consisting of KSS and tris(2,4,6-tribromophenoxy)-s-triazine, used at 8% additive level, greatly improves the fire behavior of transparent polycarbonate formulations, seeing the reduced smoke parameter and the better (higher) fire performance index.