POLYCARBONATE COMPOSITIONS HAVING IMPROVED COLOR STABILITY AND MELT FLOW

Abstract: Pigmented polycarbonate compositions having improved color stability and melt flow stability are obtained by admixing a high molecular weight aromatic polycarbonate resin containing a pigment with a methyl hydrogen silicone fluid. Alternatively, the pigment can be coated with the methyl hydrogen silicone fluid and the thusly coated pigment can then be admixed with the aromatic polycarbonate resin.

Description: Description Polycarbonate compositions Having Improved Color Stability and Melt Flow This invention relates to polycarbonate compositions having improved color stability and melt flow, said composi¬ tions comprising an admixture of an aromatic polycarbonate, pigment and a methyl hydrogen silicone fluid. 5 BACKGROUND OF THE INVENTION In the past, much effort has been expended in preparing ther¬ mally stable polycarbonate compositions which would be color stable at elevated temperatures and particularly at the high molding temperatures generally employed to prepare molded polycarbonate 0 articles. Many different additives have been found that are quite suitable for rendering polycarbonates heat and color stable. Most recently, various phosphite and phosphonite compounds have been found particularly useful, including those containing epoxies and oxetanes, such as are disclosed in U.S. Patents 3,305,520; 5 3,729,440; 3,953,388; 3,794,629. DESCRIPTION OF THE INVENTION It has now been discovered that when a pigmented aromatic polycarbonate is admixed with a methyl hydrogen silicone fluid, the resulting polycarbonate composition has improved thermal 0 stability, as exemplified by its resistance to yellowing when subjected to high molding temperatures, as well as improved melt flow stability. More pronounced thermal stability and melt flow are realized when the pigment is coated with the methyl hydrogen silicone fluid prior tobeing mixed withthe aromatic polycarbonate. Ξ.' Pigments are typically included in polycarbonate compositions in amounts up to about 5.0 parts per .hundred (pph) of the aromatic polycarbonate, preferably about 0.1-2.0 pph. Polycarbonate composi¬ tions containing a white pigment such as titanium dioxide (Tiθ 2 ) are most subject torevealing thermal degradation and are generally O PI . used as the standard to determine the degree of thermal stability. The methyl hydrogen silicone fluids (MHSF) that can be employed in the practice of this invention are those which are commercially available such as those obtainable from Rhodia, Inc. under their trademark Rhodorsil hydrofugeant 68 fluid. When used as an additive, MHSF can be employed in amounts of about 0.01-1.0 pph, preferably 0.02-0.20 pph, of said aromatic polycarbonate. When used to pre-coat the pigment prior to adding the coated pigment to the aromatic polycarbonate, MHSF is employed in. amounts sufficient to provide about the same level of MHSF in the polycar¬ bonate composition. Typically, the amount of MHSF employed to coat a pigment is about 0.05-10.0 pph, preferably 1.0-5.0 pph, of the pigment. The aromatic polycarbonates that can be employed in the practice of this invention are homopolymers and copolymers and mixtures thereof that are prepared by reacting a dihydric phenol with a carbonate precursor. The dihydric phenols that can be employed are bisphenols such as bis(4-hydroxyphenyl)methane, 2,2-bis( -hydroxyphenyl)propane (bisphenol-A) , 2,2-bis(4-hydroxy-3-methylphenyl)propane, 4,4- bis (4-hydroxyphenyl)heptane, 2,2-bis(4-hydroxy-3,5-dichlorophenyl) propane, 2,2-bis(4-hydroxy-3,5-dibromophenyl)propane, etc.; dihydric phenol ethers such as bis ( -hydroxyphenyl)ether, bis (3,5- dichloro-4-hydroxyphenyl)ether, etc.; dihydroxydiphenylε such as p,p'-dihydroxydiphenyl, 3,3'-dichloro-4,4-dihydroxydiphenyl, etc.; dihydroxyaryl βulfones such as bis(4-hydroxyphenyl)εulfone, bis(3,5-dimethyl-4-hydroxyphenyl)εulfone, etc.; dihydroxy benzenes, resorcinol, hydroguinone, halo- and alkyl-substituted dihydroxy benzenes such as l,4-dihydroxy-2,5-dichlorobenzene, ^) l,4-dihydroxy-3-methylbenzene, etc.; and dihydroxy diphenyl sulfoxides such as bis(4-hydroxyphenyl)sulfoxide, bis(3,5-dibromo- 4-hydroxyphenyl)sulfoxide, etc. A variety of additional dihydric phenols are also available to provide carbonate polymers such as are disclosed in U.S. Patents 2,999,835, 3,028,365 and 3,153,008. Also suitable for preparing the aromatic carbonate polymers are copolymers prepared from the above dihydric phenols copolymerized with halogen-containing dihydric phenols such as 2,2-bis (3,5- dichloro-4-hydroxyphenyl)propane, 2,2-bis(3,5-dibromo-4-hydroxy- phenyl)propane, etc. It is also possible to employ two or more different dihydric phenols or a copolymer of a dihydric phenol with a glycol or with hydroxy or acid terminated polyester, or with a dibasic acid in the event a carbonate copolymer or inter- polymer rather than a homopolymer is desired for use in the prepar- ation of the aromatic polycarbonates of this invention as well as blends of any of the abov_r materials. The carbonate precursor can be either a carbonyl halide, a carbonate ester or a haloformate. The carbonyl halides which can be employed are carbonyl bromide, carbonyl chloride and mixtures thereof. Typical of the carbonate esters that can be employed are diphenyl carbonate, di-(halophenyl) carbonates such as di-(chlorophenyl) carbonate, di-(bromophenyl) carbonate, di- (trichlorophenyl) carbonate, di-(tribromophenyl) carbonate, etc., di-(alkylphenyl) carbonatessuch as di-(tolyl) carbonate, etc., di- (naphthyl) carbonate, di-(chloronaphthyl) carbonate, phenyl tolyl carbonate, chlorophenyl chloronaphthyl carbonate, etc., or mixtures thereof. The haloformates suitable for use herein include bishalo- formates of dihydric phenols (bischloroformates of hydroquinone, etc.) or glycolε (biεhaloformates of ethylene glycol, neopentyl OMPI _ glycol, polyethylene glycol, etc.). While other carbonate precur sors will occur to those skilled in the art, carbonyl chloride, also known as phosgene, is preferred. Also included are the polymeric derivatives of a dihydric 5 phenol, a dicarboxylic acid and carbonic acid. These are dis¬ closed in U.S. Patent 3,169,121 which is incorporated herein by reference. The.aromatic polycarbonates of this invention are prepared b employing a molecular weight regulator, an acid acceptor and a 10 catalyst. The molecular weight regulators which can be employed include monohydric phenols such as phenol, chroman-I, parater- tiarybutylphenol, parabro ophenol, primary and secondary amines, etc. Preferably, phenol is employed as the molecular weight regulator. 15 A suitable acid acceptor can be either an organic or an inorganic acid acceptor. A suitable organic acid acceptor is a tertiary a ine and includes such materials as pyridine, triethyl- amine, dimethylaniline, tributylamine, etc. The inorganic acid acceptor can be one which can be either a hydroxide, a carbonate, 20 a bicarbonate, or a phosphate of an alkali or alkaline earth metal The catalysts which can be employed can be any of the suitabl catalysts that aid the polymerization of bisphenol-A with phosgene Suitable catalysts include tertiary amines such as triethylamine, tripropylamine, n,n-dimethylaniline, quaternary ammonium compounds 25 such as tetraethylam onium bromide, cetyl triethylammoniu bromide tetra-n-heptylammonium iodide, tetra-n-propylammonium bromide, tetramethylammonium chloride, tetramethylammonium hydroxide, tetra n-butylammonium iodide, benzyltrimethylammonium chloride and quaternary phoεphonium compounds such as n-butyl-triphenyl phosphonium bromide and methyltriphenyl phosphonium bromide. Also included herein are branched polycarbonates wherein a polyfunctional aromatic compound is reacted with the dihydric phenol and carbonate precursor to provide a thermoplastic ran- do ly branched polycarbonate. These polyfunctional aromatic compounds contain at least three functional groups which are carboxyl, carboxylic anhydride, haloformyl or mixtures thereof. Examples of these polyfunctional aromatic compounds include trimellitic anhydride, trimellitic acid, trimellityl trichloride, 4-chloroformyl phthalic anhydride, pyromellitic acid, pyromellitic dianhydride, mellitic acid, melli¬ tic anhydride, trimesic acid, benzophenonetetracarboxylic acid, benzophenonetetracarboxylic anhydride, and the like. The preferred polyfunctional aromatic compounds are trimellitic anhydride or trimellitic acid, or their haloformyl derivatives. Also included herein are blends of a linear polycarbonate and a branched polycarbonate. Obviously, other materials can also be employed with the aromatic polycarbonates of this invention and include such materials as antistatic agents, mold release agents, ultraviolet light stabilizers, reinforcing fillers such as glass and ether inert fillers, foaming agents and the like. DESCRIPTION OF THE PREFERRED EMBODIMENT The following examples are set forth to more clearly illus- trate the invention. Unless otherwise specified, parts or percεnts are by weight. The following tests were used in the examples: Yellowness index was determined in accordance with ASTM Yellowness Index (YI) Test D-1925 on samples molded at 316 β C, 343°C. and 360°C. The Streak Test YI included a visual examination of samples for surface degradation typically manifested by increased darkening or marbling; i.e., "streaking", of the surface color. The test samples for this test were obtain by beginning with a mold temperature of 349°C for each fiv shot run and increasing the mold temperature 11°C for each successive shot beginning with each third shot of each fiv shot run, the third shot molded at 371°C being subject to YI test. 10 Melt flow (MF) was determined in accordance with ASTM D-1238, Condition 0. S-tensile impact results were determined in accordanc with ASTM D-1882. Gottfert stability was determined by placing a test 15 sample weighing about 15 grams in a rheometer, heating the sample to 149°C and maintaining this temperature for a per of 7 minutes following which the sample was pressed throug a capillary at a constant speed of 0.28 cm/sec. The pres¬ sure needed to maintain this rate of flow is related to 20 the melt viscosity (MV) of the test sample in the cylinder from which the melt stability (MS) is determined. Melt viscosity (MV) of the test sample is determined according to the following equation: MV = T/D = | 4V 25 *- * TR- wherein: T ■= shear stress (g/cm) D ■= shear rate (cm/sec) P >= pressure on the sample (g) R « capillary radius (cm) L ■ capillary length (cm) 30 V " rate of flow of sample (cc/εec) Tr * « 3.14 O . W - 7 - Melt stability (MS) is then determined by measuring the melt viscosity after 40 minutes residence time of the sample at 149°C and is calculated by using the following equation. MS = -^ **• 7 I**** ' n ' " -^ **• 40 min - X 100% MV § 7 in. The percent change in melt stability after the 40 minute residence time is shown as the % Δ. EXAMPLE 1 A polycarbonate composition of a homopolymer of 2,2-bis(4- hydroxyphenyl)propane (bisphenol-A) was prepared by reacting essentially equimolar amounts of bisphenol-A and phosgene in an organic medium with triethylamine, sodium hydroxide and phenol under standard conditions and was mixed with the stabilizers shown in Table I by tumbling the ingredients in a laboratory tumbler. This mixture was then fed to an extruder, which extruder was operated at about 500°F, and the extruded strands chopped into pellets. The pellets were then injected molded at 316°C and 360°C into test samples of about 7.6cm x 5_lcm x 0.3cm. thick. EXAMPLE 2 The aromatic polycarbonate of Example 1 was blended with commercially obtained phosphites, Ti0 2 and MHSF and test samples obtained, following extrusion and molding, all as described in Example 1. The commercially obtained phosphites employed were ,a phosphite-epoxide mixture (PE) , diphenyldecyl phosphite (DDP) and trinonylphenyl phosphite (TNPP) . YI results were obtained for samples molded at 316°C, 343°C and 360°C In addition, the melt flow (MF) and the Gottfεrt stability at 7 minutes and the differential percentage (%Δ) from 7-40 minutes were also obtained. The data is shown in Table I below. OMPl Table I Stabilized Polycarbonate Amount ___ Gottfert Stability Phosphite MHSF Tiθ 2 316°C 343°C 360°C Sample Phosphite (pph) (pph) (pph) MF 7 min. % Δ A TNPP 0.075 1.5 4.1 8.0 B 0.01 0.8 3.7 C 0.05 -2.7 ■2.4 *D 0.5 1.5 E 0.1 2.0 11.3 18.4 8.08 CO F 0.01 8.5 14.2 6.94 I G 0.05 5.2 6.7 5.82 11 0.1 4.7 5.8 5.66- I - 5.56 5.4 J PE 0.1. 2.0 7.96 31.0 K 0.05 5.98 12.0 L 0.1 5.89 10.0 M - 12.7 6.14 4150 34.0 N - 0.1 5.6 5.90 4950 17.0 * Included 0.3 pph of a silanol containing siloxy copolymers as described in Serial No. 867,534, filed 1-6-78. The results in Table I above reveal that as little as 0.01 pph MHSF lowers the YI and stabilizes the molded samples. In¬ creasing the MHSF concentration to 0.1 pph does not materially affect melt flow (MF) or Gottfert stability and shows only a small improvement in lowering YI (Compare sample H with sample G and sample L with sample K) . As little as 2.0 pph Tiθ 2 causes melt flow to drop about 2.5 units (Sample I vs. Sample J) whereas the addition of only 0.05 pph MHSF with Ti0 2 at the 2.0 pph level reduces the melt flow drop to about 0.42 units (Sample I vs. Sample K) . The data in Table I also indicates that the MHSF is a better color stabilizer than a phosphite (Sample N vs. Sample 0) , but a combination of both phosphite and MHSF improves both color and melt stability (Sample P) . EXAMPLE 3 The same procedure was followed as in Example 2 above using two different commercially obtained phosphites and two different commercially obtained methyl hydrogen silicone fluids (MHSF) . The phosphites employed were diphenyl decyl phosphite (DDP) and bis-2,4-di-t-butyl-pentaerithrytol diphosphite (PEDP) . The samples obtained all contained 2.0 pph Ti0 and were subjected to the same tests as in Example 2 and the results are set forth in Table II below. OMPI /.. IPO TABLE II STABILIZED WHITE POLYCARBONATES Amt. of YI Gottfert Phosphit .e MHSF 316°C 360°C Stabilitv Sample Phosohite (pph) (pph) 7 min. %Δ Q DDP 0.1 8.2 11.1 4390 11.7 R PEDP 0.06 - 10.5 13.6 4310 . 21.1 S - 0.1 6.1 7.6* 4910 16.1 T DDP 0.1 0.1 4.1* 6.0* 4990 7.1 u 0.1 3.0* 5.3* 4990 7.1 **v - 5.9 7.2 4870 8.3 w PEDP 0.06 0.1 5.1 6.6* 5060 7.8 * Samples splayed; i.e., streaked. ** Included 0.3 pph of a silancl containing siloxy copolymers as described in Serial No. 867,534,filed 1-6-78 The results in Table II above reveal that MHSF is a better stabilizer than either of the phosphites (DDP or PEDP) , but that MHSF in combination with either of the phosphites exhibits even more improved stability EXAMPLE 4 The procedure of Example 3 was followed to obtain the same compositions as in Example 3 except that the extruded pellets were molded into test bars measuring 12.7 cm x 1.3 cm x 0.3 cm thick. These test bars (samples q-w corresponding to Q-W of Example 3) were then subjected to the S-tensile impact test after being heat aged in an oven at 140°C. The results obtained are set forth in Table III below. «-§ O - 11 TABLE III OVEN AGED S-TENSILE IMPAC T S- -Tensile Impact After Aging at 140°C Sample Hours : 0 1000 2008 3000 4000 5000 q 293 164 164. 18 A ' 56- ' 7 r 282 178 180 190 147 12 s 298 184 228 235 135 1S5 t 261 198 179 159 112 18 u 293 201 180 169 121 21 v 312 202 168 174 148 107 w 290 269 198 196 132 112 The results in Table III indicate that the samples containing only phosphite (q and r) did not age well, those containing phos¬ phite plus MHSF (t-w) aged somewhat better, but the sample con¬ taining only MHSF (sample s) aged the best. EXAMPLE 5 The procedure of Example 2 was followed to prepare additional samples containing 2.0 pph Ti0 2 to further compare the effects of employing MHSF and/or a phosphite in combination with Ti0 2 . The YI, melt flow (MF) and Gottfert stability results obtained are shown in Table IV below wherein the phosphite employed was diphenyl decyl phosphite (DDP) : TABLE IV STABILIZED WHITE PIGMENTED POLYCARBONATE YI Gottdfert DDP MHSF 316 β C. 360°C Stabi Llity Sample (pph) (pph) MF 7 min. % A X 0.05 10.53 4.4 5.3 3440 13.8 Y - 0.1 11.19 4.1 5.1 3280 13.3 z 0.05 0.05 10.49 3.3 4.0 3480 4.6 A' 0.05 0.1 10.67 '■ 3.1 3.5 3520 4.5 B * 0.1 0.05 11.03 3.0 3.7 3400 7.0 C 0.1 0.1 10.77 2.8 3.3 3440 3.5 D- -. 0.1 6.35 5.6 6.9 4670 11.0 E- 0.05 0.05 5.46 5.3 7.1 5140 8.5 F * 0.075 0.075 5.34 4.2 6.4 4990 4.8 G' 0.1 0.1 6.11 5.3 6.6 4790 6.6 H' 0.1 - 7.11 7.2 9.4 4190 13.0 *r 0.1 - 6.05 5.3 6.9 4870 11.0 ' 0.1 0.1 5.87 3.8 5.0 5100 9.3 ' 0.1 0.1 5.78 3.7 5.6 4990 7.9 L * 0.075 0.075 5.63 4.0 5.6 5020 4.7 M * n « 5.76 3.9 5.7 5020 5.5 N' - 0.1 5.60 5.0 7.2 4990 15.0 0' _ 0.1 5.69 4.7 6.2 5020 7.1 * Included 0.3 pph of a εilanol containing siloxy copolymers as described in Serial No. 867,534, filed 1-6-78. As the results in Table IV-above reveal, increasing the concen tration of either the phosphite (DDP) and/or MHSF from 0.05 pph to 0.1 pph only slightly improved color and melt stability, but ■ignificantly improved melt flow (MF) . However, when the phosphite and MHSF were each added at a concentration of 0.075 pph for a total concentration of 0.15 pph, color, melt stability and melt flow all showed marked improvement. - E OMP f WIP EXAMPLE 6 The procedure of Example 2 was followed except that the aro¬ matic polycarbonate was first mixed with 0.05 pph diphenyl decyl phosphite (DDP) and the Ti0 2 was first coated with MHSF before being blended with the polycarbonate. Coating the Ti0 2 was accom- pushed by charging a Patterson-Kelly twin shell blender with 5 Kg Ti0 2 , turning on the blender, metering 100 g MHSF into the blender over a period of about 2 minutes, and continuing rotation of the blender for an additional time to provide a 2 pph MHSF coating. A 10 pph MHSF coating on the Ti0 2 was similarly prepared/ all parts being based on the Ti0 . The additional blending time to provide these MHSF coating levels was about 5 minutes and 10 minutes, respectively. The coated Ti0 2 was then mixed with the polycarbonate to provide a Ti0 concentration of 2 p h. The YI and melt flow were determined for the samples obtained and this data is set forth in TABLE V below. TABLE V Polycarbonate Containing MHSF-Coated TiO, MHSF YI Coated Ti0 2 MHSF in 316*1 360°ς Sample (PPh) Resin (pph) MF pl - 7.85 8.0 11.0 Q * - 0.1 5.90 4.7 5.3* R- 2 0.04 5.91 4.9 5.6 S" 10 0.2 5.82 5.4 8.8 * Splayed slightly. ( . _.-,_. ! Ti0 was roughly equivalent in melt flow and YI to sample Q' containing 0.1 pph added MHSF. However, sample Q" molded at 680°F splayed whereas sample R 1 molded at 680°F did not. Sample S', containing 10 pph MHSF-σoated Ti0 2 and a higher level (0.2 pph) of added MHSF, shows no improvement over sample R' . EXAMPLE 7 The procedure of Example 6 was followed except that the Ti0 2 was coated with lower levels of MHSF and was incorporated in the polycarbonate resin in lower concentrations. In addition to obtaining the melt flow results of the samples at 6 and 12 minutes, the samples were also subjected to the YI Streak Test at 700°F. The results obtained are set forth in TABLE VI below. TABLE VI MHSF MF Streak Test Coated Ti0 2 MHSF in 37.°<_ Sample (PPh) Resin (p? ■h) 6 min. 12 min. T * - 7.17 20.0 u 1 - 0.05 5.76 - 13.5 V - 0.1 5.54 - 12.5 w 2.0 0.04 5.63 - 11.8 X" 0.5 0.01 6.67 6.99 13.9 Y' 1.0 0.02 6.10 6.94 11.9 Z' 1.0 0.02 6.07 6.19 12.6 A' ' - _ 8.32 10.56 15.7 The results in Table VI above indicate that sample Y' contain¬ ing 1.0 pph MHSF coated Ti0 2 performed about as well as sample W containing 2.0 pph MHSF coated Ti0 2 . Samples Y' and Z 1 with lower MHSF-coated Ti0 2 and lower concentrations of Ti0 2 in the resin significantly improve melt flow at both the 6 and 12 minute levels over sample A' ' containing no MHSF and no TiO j . High temperature color results shown by the streak Test are better for samples containing 1.0 pph and 2.0 pph coated Ti0 2 (samples Z' and W 1 ) than when 0.05 pph MHSF was added (sample U' ) . In general, the results in Table VI indicate that samples containing 1.0 pph MHSF-coated • - 15 - Ti0 2 provide significantly better melt flow and color stability than samples containing 0.5 pph MHSF-coated Ti0 2 . From the results set forth in the foregoing Examples and Table* it can be seen that the color stability and melt flow of polycar- bonate resins containing a white pigment such as Ti0 2 is greatly improved when the resins also contain MHSF. Further, where Ti0 2 is precoated with MHSF prior to being incorporated in polycarbonate resins, splay is virtually eliminated and melt flow and color stability are obtained with lower concentrations of MHSF than when MHSF is added separately to the polycarbonate resin.

Claims: Claims - 16 - 1. An aromatic polycarbonate composition having improved color stability and melt flow stability, said composition compris¬ ing an admixture of a high molecular weight aromatic polycarbonate resin; pigment in an amount of up to about 5.0 pph of said resin; and, from about 0.01-1.0 pph of a methyl hydrogen silicone fluid. 2. The composition of claim 1 wherein said pigment is titanium dioxide. 3. The composition of claim 1 wherein said methyl hydrogen silicone fluid is present in an amount of about 0.05-0.20 pph. 4. An aromatic polycarbonate composition having improved color stability and melt flow stability, said composition compris¬ ing a high molecular weight aromatic polycarbonate resin; and, pigment in an amount of up to about 5.0 pph of said resin, said pigment being coated with a methyl hydrogen silicone fluid in an amount of about 0.05-10.0 pph of said pigment. 5. The composition of claim 4 wherein said pigment is titanium dioxide. 6. The composition of claim 4 wherein the amount of coated pigment in said resin is about 0.1 - 2.0 pph of said resin. 7. The composition of claim 6 wherein the methyl hydrogen silicone fluid is coated on said pigment in an amount sufficient to provide about 0.002-0.1 pph of said fluid in said resin. 8. The composition of claim 7 wherein said amount of methyl hydrogen silicone fluid is about 0.01 - 0.05 pph. < • §. OM 9. A particulate pigment coated with a methyl hydrogen silicone fluid in an amount of about 0.05 - lO.O pph of said pigment. 10. The coated pigment of claim 9 wherein the amount of methyl hydrogen silicone fluid is about 1.0 - 5.0 pph. 11. The coated pigment of claim 9 wherein said pigment is particulate titanium dioxide.

Inventors: SCOTT S, WILLIAMS J
Applicants: GEN ELECTRIC, GENERAL ELECTRIC CO
Application year: 1979
Main classification: C08L69
IPC codes: C08K3, C08K5, C08L69, C08L83