Talc-filled polycarbonate compositions

Abstract

The invention relates to the use of PMMI copolymers for reducing the decrease in molecular weight of the polymer induced by addition of talc in compositions based on aromatic polycarbonate. At the same time, the mechanical, optical and rheological properties of the thermoplastic composition, in spite of the addition of the PMMI copolymer, remain good and are in some cases even improved.

Claims

1. A composition comprising A) at least 60% by weight of aromatic polycarbonate, B) 5% to 35% by weight talc, C) 2% to 8% by weight of PMMI copolymer, wherein the PMMI copolymer has 4% to 55% by weight of methyl methacrylate units, at least 36% to 95% by weight of methylmethacrylimide units, a total of 0.5% to 12%% by weight of methylmethacrylic acid units and methylmethacrylic anhydride units, based in each case on the total weight of the PMMI copolymer, and an acid number, determined according to DIN 53240-1:2013-06, of 15 to 50 mg KOH/g, and D) optionally further additives.

2. A composition comprising A) at least 60% by weight of aromatic polycarbonate, B) 5% to 30% by weight talc, C) 2% to 8% by weight of PMMI copolymer, wherein the PMMI copolymer has 4% to 55% by weight of methyl methacrylate units, at least 36% to 95% by weight of methylmethacrylimide units, a total of 0.5% to 12%% by weight of methylmethacrylic acid units and methylmethacrylic anhydride units, based in each case on the total weight of the PMMI copolymer, and an acid number, determined according to DIN 53240-1:2013-06, of 15 to 50 mg KOH/g, and D) optionally further additives.

3. The composition according to claim 2, consisting of A) at least 68% by weight of aromatic polycarbonate, B) 15% to 25% by weight of talc, C) 2% to 6% by weight of PMMI copolymer and D) optionally one or more further additives selected from the group consisting of flame retardants, anti-dripping agents, impact modifiers, fillers other than component B, antistats, colourants, pigments, carbon black, lubricants and/or demoulding agents, thermal stabilizers, blending partners, compatibilizers, UV absorbers and/or IR absorbers.

4. The composition according to claim 2, wherein the composition contains 15% to 25% by weight of talc.

5. The composition according to claim 2, wherein the acid number of the PMMI copolymer, determined to DIN 53240-1:2013-06, is 20 to 45 mg KOH/g.

6. The composition according to claim 2, wherein the proportion of talc is 15% to 25% by weight, based on the overall composition, and the ratio of PMMI copolymer to talc is 0.15 to 0.6.

7. The composition according to claim 2, wherein the proportion of PMMI copolymer in the finished composition is 2% to 6% by weight.

8. A moulding comprising the composition according to claim 2.

9. The moulding according to claim 8, wherein the moulding is a heat sink for electronic components, a housing or part of a housing from the electrics and electronics sector.

10. The composition according to claim 3, wherein the proportion of talc is 15% to 25% by weight, based on the overall composition, and the ratio of PMMI copolymer to talc is 0.2 to 0.5.

Description

EXAMPLES

(1) Polymers:

(2) PC: A commercially available polycarbonate based on bisphenol A, having an MVR of 19 cm.sup.3/10 min (300° C./1.2 kg, ISO 1133-1:2011) and a softening temperature (VST/B 120; ISO 306:2013) of 145° C. (Makrolon® 2408 from Covestro Deutschland AG). M.sub.w, determined as described below, about 23 900 g/mol.

(3) Stabilizers:

(4) PMMI1: Poly(N-methylmethacrylimide) copolymer from Evonik (Pleximid® 8803) having a softening temperature (VST/B 50; ISO 306:2013) of 130° C. Acid number: 22.5 mg KOH/g, determined to DIN 53240-1 (June 2013). Proportion of MMI (methylmethacrylimide): 36.8% by weight, proportion of MMA (methyl methacrylate): 51.7% by weight, proportion of MMS (methylmethacrylic acid)+MMAH (methylmethacrylic anhydride): 11.5% by weight, based in each case on the total weight of the PMMI and determined by means of quantitative .sup.1H NMR spectroscopy.

(5) PMMI2: Poly(N-methylmethacrylimide) copolymer from Evonik (Pleximid® TT50) having a softening temperature (VST/B 50; ISO 306:2013) of 150° C. Acid number: 22.5 mg KOH/g, determined to DIN 53240-1 (June 2013). Proportion of MMI: 83.1% by weight, proportion of MMA: 13.6% by weight, proportion of MMS (methylmethacrylic acid)+MMAH: 3.3% by weight, based in each case on the total weight of the PMMI and determined by means of quantitative .sup.1H NMR spectroscopy.

(6) PMMI3: Poly(N-methylmethacrylimide) copolymer from Evonik (Pleximid® TT70) having a softening temperature (VST/B 50; ISO 306:2013) of 170° C. Acid number: 41.5 mg KOH/g, determined to DIN 53240-1 (June 2013). Proportion of MMI: 94.8% by weight, proportion of MMA: 4.6% by weight, proportion of MMS+MMAH: 0.6% by weight, based in each case on the total weight of the PMMI and determined by means of quantitative .sup.1H NMR spectroscopy.

(7) Stab1: An acid-modified ethylene wax from Mitsui Chemical America, Inc. (Hiwax™ 1105 A) having an average molecular weight (gel permeation chromatography in ortho-dichlorobenzene at 150° C. with polystyrene calibration) M.sub.w=6301 g/mol, M.sub.n=1159 g/mol and with an acid number of 52.6 mg KOH/g (test method JIS K0070). Maleic anhydride content: 4.4% by weight, based on the total weight of the terpolymer.

(8) Stab2: A maleic anhydride-modified polypropylene copolymer from Honeywell (AC907P) having an average molecular weight (gel permeation chromatography in ortho-dichlorobenzene at 150° C. with polystyrene calibration) M.sub.w=20 700 g/mol, M.sub.n=1460 g/mol and with an acid number of 78 mg KOH/g (ASTM D-1386)).

(9) Fillers:

(10) Talc: A compacted talc from IMI Fabi having a talc content of 99% by weight, an iron oxide content of 0.4% by weight, an aluminium oxide content of 0.4% by weight, ignition loss of 6.0% by weight, D.sub.50 (sedimentation analysis, Sedigraph5120) of 0.65 μm; BET surface area 13.5 m.sup.2/g, density (determined to DIN53193) of 2.8 g/cm.sup.3 (HTPultra5C).

(11) Production Parameters:

(12) The extruder used was a DSM Micro-Extruder MIDI 2000 having a capacity of 15 cm.sup.3. The melt temperature in the extruder was 290° C., the speed was 150 rpm, and the dwell time (DT) was 5 minutes or 10 minutes. A DSM injection moulding machine was used for the injection moulding. The melt temperature in the injection moulding was: 300° C., the mould temperature 80° C.

(13) Methods of Determination:

(14) M.sub.w: Gel permeation chromatography, calibrated against bisphenol A polycarbonate standards, using dichloromethane as eluent. Calibration with linear polycarbonates (formed from bisphenol A and phosgene) of known molar mass distribution from PSS Polymer Standards Service GmbH, Germany, calibration by method 2301-0257502-09D (from 2009 in German language) from Currenta GmbH & Co. OHG, Leverkusen. The eluent is dichloromethane. Column combination of crosslinked styrene-divinylbenzene resins. Diameter of analytical columns: 7.5 mm; length: 300 mm. Particle sizes of column material: 3 μm to 20 μm. Concentration of solutions: 0.2% by weight. Flow rate: 1.0 ml/min, temperature of solutions: 30° C. Injection volume; 100 μl. Detection by means of UV detector.

(15) Yellowness Index (Y.I.) was measured according to ASTM E313-10. Transmission values (Ty) were determined according to ASTM-E-308. Both Y.I. and Ty were evaluated as D65, 10° (illuminant: D65/observer:10°). The samples analysed had a geometry of 6.0 mm×3.5 mm×1.5 mm.

(16) The viscosity of the polymer melts was measured according to ISO 11443:2005 at a melt temperature of 300° C.

(17) The Vicat softening temperature (VST/B/50) of the compositions was measured on test specimens according to ISO 306:2013.

(18) The tensile modulus and tensile strength of the compositions were measured on test specimens according to ISO 527-1:2012.

(19) The penetration force and penetration deformation of the compositions were measured on test specimens according to ISO 6603-2:2000.

(20) Results:

EXAMPLES

(21) TABLE-US-00001 TABLE 1 Talc-free polycarbonate and the effect of PMMI 1C 2C 3C 4C 5C 6C 7C DT % by % by % by % by % by % by % by [min] wt. wt. wt. wt. wt. wt. wt. PC 100 99.8 99.5 99 98 96 94 PMMI1 0.2 0.5 1 2 4 6 M.sub.w [g/mol] 5 23365 23408 23395 23409 23493 23554 23689 Y.I. 5 3.69 3.21 6.35 12.75 18.70 26.53 29.27 (D65, 10°) 10 4.01 3.49 7.57 14.41 19.25 30.29 32.57 Δ Y.I. 0.32 0.27 1.21 1.66 0.56 3.76 3.30

(22) In unfilled polycarbonate, there is essentially no degradation of the polymer chains. Therefore, no stabilizer is required. As apparent from Table 1, the addition of PMMI to filler-free polycarbonate does not have any adverse effect on the molar mass. The average molar masses are at a constant level within the scope of measurement accuracy. As can be seen in Table 1, the optical properties (Y.I.) and colour stability (ΔY.I. (5 min/10 min)) decrease with rising PMMI copolymer content. However, if these values are compared with the compositions in Table 4 that contain Stab 1 and Stab 2 (Examples 20C and 21C), yellowing with PMMI is significantly less marked. Moreover, both Stab1 and Stab2 lead to a significant reduction in transmission in unfilled polycarbonate.

(23) TABLE-US-00002 TABLE 2 Talc-containing polycarbonate compositions and the effect of PMMI 8C 9 10 11 12 13 14 DT % by % by % by % by % by % by % by [min] wt. wt. wt. wt. wt. wt. wt. PC 80 79.8 79.5 79 78 76 74 Talc 20 20 20 20 20 20 20 PMMI1 0.2 0.5 1 2 4 6 M.sub.w [g/mol] 5 15410 18328 19429 18596 20175 21731 21980 Y.I. 5 20.72 22.98 32.62 41.70 49.14 4.60 6.46 (D65, 10°) 10 36.71 35.91 38.87 46.32 39.50 11.58 10.13 Δ Y.I. 15.99 12.93 6.25 4.62 −9.64 6.98 3.67

(24) If talc-containing polycarbonate compositions are considered, distinct differences are apparent compared to talc-free polycarbonate compositions. The addition of talc leads, even after a dwell time of 5 minutes, to a considerable decrease in molecular weight (M.sub.w) of the polymer from about 23 900 g/mol to about 15 000 g/mol. With increasing PMMI content, however, polymer degradation can be distinctly reduced. With 2% by weight of added PMMI (based on the overall composition), the effect is already attractive. With about 4-6% by weight of added PMMI, an optimum has been attained (see also Examples 30-33 in Table 5). A decrease in molecular weight cannot be completely avoided by the addition of PMMI in economically attractive amounts, but can be brought to a level that means such a small decrease in molecular weight that it is negligible. It should additionally be taken into account that a dwell time of 5 minutes at elevated temperature constitutes more of an extreme case under real process conditions. This means that these present results can also show that good stabilization is achievable especially also for extruders with high dwell times, for instance co-kneaders. First of all, the addition of PMMI to talc-filled polycarbonate always leads to an increase in the Y.I. value and to a deterioration in optical properties. It is surprising that, however, unlike in unfilled systems, a considerable decline in Y.I. values can be observed here in the plateau region beginning from about 3% by weight, preferably from about 4% by weight (see Examples 13 and 14 in Table 2), and this leads to acceptable Y.I. values comparable with those for unfilled polycarbonate with the shorter residence time of 5 min.

(25) TABLE-US-00003 TABLE 3 Talc-containing polycarbonate compositions and the effect of different types of PMMI 15C 16 17 18 DT % by % by % by % by [min] wt. wt. wt. wt. PC 80 79 79 79 Talc 20 20 20 20 PMMI1 1 PMMI2 1 PMMI3 1 M.sub.w [g/mol] 5 15410 18596 19730 19906 Y.I. 5 20.72 41.70 32.35 26.51 (D65, 10°) 10 36.71 46.32 39.31 39.53 Δ Y.I. 16.00 4.62 6.96 13.02

(26) The PMMI types used differ in their content of MMI, MMA, acid and anhydride.

(27) Surprisingly, what was found for talc-filled polycarbonate was not, as expected, that the PMMI having the lowest content of MMI (PMMI1) leads to the best compatibility—smallest decrease in molar mass, and also the least yellowing—but rather the PMMI having the highest MMI content and simultaneously lowest acid content (PMMI3). The measurements of the Y.I. values after a dwell time of 5 minutes show that yellowing is also reduced with rising MMI content (PMMI1<PMMI2<PMMI3). However, a comparison of the ΔY.I. values between dwell times of 5 and 10 minutes shows that the degree of yellowing increases more significantly with rising MMI content for shorter and longer dwell times compared to one another. Even though the starting Y.I. level of talc-filled polycarbonate without PMMI is the lowest, the difference between a dwell time of 5 minutes and 10 minutes is at its greatest (ΔY.I.=16). It can be concluded from this that the colour stability of PMMI copolymer+talc+PC systems depends on the MMI content and the duration of thermal stress on the material.

(28) TABLE-US-00004 TABLE 4 Comparison of different acids/maleic anhydride- functionalized copolymers as stabilizers 19C 20C 21C 22 23 24 DT % by % by % by % by % by % by [min] wt. wt. wt. wt. wt. wt. PC 99 99 99 79 79 79 Talc 20 20 20 PMMI1 1 1 Stab1 1 1 Stab2 1 1 M.sub.w [g/mol] 5 23409 23382 23104 18596 20816 22157 Y.I. 5 12.75 22.98 16.55 41.70 35.51 27.17 (D65, 10°) 10 14.41 29.53 25.70 46.32 54.72 46.49 Δ Y.I. 1.66 6.55 9.15 4.62 19.21 19.32 Ty (%) 80.87 48.25 61.77 — — —

(29) In combination with talc and 1% by weight in each case of additive, Stab2 shows the best stabilization, especially in the case of a prolonged dwell time, but the adverse effect on optical properties is manifested here. The compositions to which Stab1 and Stab2 have been added have a tendency to much more intense yellowing (greater Δ Y.I.). The compositions comprising the polyolefinic copolymers, even at 1% by weight in unfilled PC, also have a distinct reduction in transmission that has an adverse effect on colourability.

(30) TABLE-US-00005 TABLE 5 Comparison of different filler/additive ratios 25 26 27 28 29 30 31 DT % by % by % by % by % by % by % by [min] wt. wt. wt. wt. wt. wt. wt. PC 89 87.5 85 79.5 78 76 75 Talc 10 10 10 20 20 20 20 PMMI1 1 2.5 5 0.5 2 4 5 PMMI1/talc 0.1 0.25 0.5 0.025 0.1 0.2 0.25 M.sub.w [g/mol] 5 22465 22678 22915 19429 20175 21731 22270 32 33 34 35 36 DT % by % by % by % by % by [min] wt. wt. wt. wt. wt. PC 74 72 67 65 62.5 Talc 20 20 30 30 30 PMMI1 6 8 3 5 7.5 PMMI1/talc 0.3 0.4 0.1 0.16 0.25 M.sub.w [g/mol] 5 21980 22400 21136 20924 21038

(31) At filler contents of 10% or 20% by weight, the stabilizing effect of PMMI1 increases with rising PMMI copolymer content. This increase is particularly marked at 20% by weight. At 30% by weight of talc, however, stabilization in the range from 3% to 7.5% by weight of PMMI copolymer examined seems to remain at a constantly good level irrespective of the PMMI copolymer content. Conditions preferred in accordance with the invention therefore exist especially when the proportion of talc is 15% to 25% by weight and the ratio of PMMI copolymer to talc is 0.1 to 0.6, especially 0.2 to 0.5.

(32) TABLE-US-00006 TABLE 6 Measurement of material properties on stabilized compounds.sup.[1] 37 38 39 40 41 42 % by % by % by % by % by % by wt. wt. wt. wt. wt. wt. PC 80 79 78 76 74 72 Talc 20 20 20 20 20 20 PMMI1 1 2 4 6 8 Stab1 Viscosity [Pa .Math. s].sup.[2] 58 176 213 216 209 209 Vicat temperature 140.1 141.6 143.3 143.5 144.2 145 [° C.] (Method B, 50 K/h) Tensile modulus 4520 4904 4932 4880 4946 5085 [MPa] Tensile strength 59.4 70.1 70.3 70.8 71.2 72.1 [MPa] Penetration, 385 3140 4225 4179 4098 3206 maximum force [N] Penetration, 4.3 8.7 11.7 11.2 10.8 9.1 deformation [mm] M.sub.w [g/mol].sup.[3] 17604 22614 23053 23420 23638 23816 43 44 45 % by % by % by wt. wt. wt. PC 79 78 76 Talc 20 20 20 PMMI1 Stab1 1 2 4 Viscosity [Pa .Math. s].sup.[2] 159 156 102 Vicat temperature 142.5 144.1 142.4 [° C.] (Method B, 50 K/h) Tensile modulus 4510 4248 4175 [MPa] Tensile strength 57.4 53.7 51.2 [MPa] Penetration, 4144 3885 1495 maximum force [N] Penetration, 14.1 13.9 10.6 deformation [mm] M.sub.w [g/mol].sup.[3] 23229 23876 24038 .sup.[1]The compositions were produced on a twin-screw extruder (ZE 25 AX 40D-UTX, speed 100 rpm, throughput 10 kg/h, melt temperature 300° C.) from Berstorff. The talc was added by means of a side extruder (at about half the length of the processing unit). .sup.[2]Melt viscosity was measured at 300° C. and a shear rate of 1000 s.sup.−1 in accordance with ISO 11443:2005. .sup.[3]The dwell time of the polycarbonate-talc mixture in the extruder was about 25 seconds (measured from addition of the talc via side extruder).

(33) The tensile modulus of the material increases with increasing PMMI1 content. There is likewise an increase in the tensile strength, and hence the interaction between filler and polymer matrix. It is likewise possible to increase heat distortion resistance, measured here using the Vicat softening temperature, with rising PMMI1 content. This is firstly because of the more efficient stabilization of the filler and thus reduced degradation of the polymer matrix. Secondly, the viscosity of the composition increases as a result of the higher viscosity of the additive itself. By comparison, there is a decrease both in the tensile modulus and in the tensile strength with increasing Stab1 content. Above 2% by weight, the plasticizing effect of the polyolefinic copolymer is manifested, particularly in the mechanical properties of the compounds. This is also reflected in the decreasing viscosity with rising wax content (Stab1). The rising wax content is manifested by increased delamination in injection moulding (Examples 43-45), which is not as marked in the case of use of PMMI1 (Examples 38-42). As shown in Table 6, the trend of stabilization by addition of PMMI can also be followed in a standard extruder. As a result of the significantly shorter dwell time of about 25 seconds, the absolute values are above the measurements from the previous test series. The optimum here too is above 1% by weight of PMMI1.

(34) If the results of the penetration test are compared, an optimum with regard to energy input and maximum deformation has been attained at 2% by weight to 6% by weight of PMMI1, based on the finished composition. Tensile modulus and Vicat temperature are high, molecular weight degradation is low, and the mixtures are homogeneous without any delamination at the surface.

(35) If the results from Tables 5 and 6 are compared, the polycarbonate with 20% by weight of talc is sufficiently stabilized (measured by the molecular weight) when 5-8% by weight of PMMI1 is added. Within this range, the material additionally has distinctly elevated heat distortion resistance and improved mechanical properties.