Polymer composition

Abstract

A composition comprising a mixture of: (i) an aromatic polycarbonate; (ii) a graft copolymer including polyacrylonitrile; and, (iii) a non-crosslinked acrylic polymer having a weight average molecular weight (Mw) of less than or equal to 65,000 Daltons (Da).

Claims

1. A composition formed from a first mixture of components comprising: (i) a first amount of an aromatic polycarbonate; (ii) a second amount of a graft copolymer including polyacrylonitrile; and, (iii) 3 to 25 wt % of a non-crosslinked acrylic polymer obtained by polymerising monomers consisting of 60 to 100% by weight methyl methacrylate monomer and 0 to 40% by weight of one or more alkyl (alk)acrylate comonomers, and having a weight average molecular weight (Mw) of between greater than or equal to 30,000 Daltons (Da) and less than 50,000 Daltons (Da).

2. A composition as claimed in claim 1 wherein the non-crosslinked acrylic polymer has a weight average molecular weight (Mw) of 30,000 Da to 45,000 Da.

3. A composition as claimed in claim 1, wherein the non-crosslinked acrylic polymer comprises an acrylic copolymer obtained by polymerising 60 to 99.9% by weight of methyl methacrylate monomer and 0.1 to 40% by weight of one or more alkyl (alk)acrylate comonomers.

4. A composition as claimed in claim 3 wherein the acrylic copolymer is obtained by polymerising 80 to 99% by weight of methyl methacrylate monomer and 20 to 1% by weight of one or more alkyl (alk)acrylate comonomers.

5. A composition as claimed in claim 3, wherein the alkyl (alk)acrylate comonomer of the acrylic copolymer comprises an alkyl acrylate comonomer.

6. A composition as claimed in claim 5 wherein the one or more alkyl acrylate comonomers of the acrylic copolymer comprises one or more C.sub.1 to C.sub.8 alkyl acrylate comonomers.

7. A composition as claimed in claim 6 wherein the one or more C.sub.1 to C.sub.8 alkyl acrylate comonomers are selected from the group consisting of methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate and mixtures thereof.

8. A composition as claimed in claim 3, wherein the acrylic copolymer is obtained by polymerizing 90 to 99% by weight of methylmethacrylate monomer and 10 to 1% by weight of one or more alkyl (alk)acrylate comonomers.

9. A composition as claimed in claim 5, wherein the acrylic copolymer includes only one alkyl acrylate comonomer.

10. A composition as claimed in claim 1, wherein the non-crosslinked acrylic polymer is present in an amount of less than or equal to 20% by weight, based on the total weight of the composition.

11. A composition as claimed in claim 1, wherein the graft copolymer including polyacrylonitrile comprises an acrylic-styrene-acrylonitrile (ASA) polymer, acrylonitrile-EPDM-styrene (AES) polymer, olefin-styrene-acrylonitrile (OSA) polymer or acrylonitrile-butadiene-styrene (ABS) polymer.

12. A composition as claimed in claim 11 wherein the graft copolymer including polyacrylonitrile comprises an ASA polymer, an AES polymer or an ABS polymer.

13. A composition as claimed in claim 1, wherein the graft copolymer including polyacrylonitrile is present in an amount of greater than or equal to 0.5% by weight, based on the total weight of the composition.

14. A composition as claimed in claim 1, wherein the graft copolymer including polyacrylonitrile is present in an amount of less than or equal to 60% by weight, based on the total weight of the composition.

15. A composition as claimed in claim 1, wherein the aromatic polycarbonate is derived from a bis-phenol.

16. A composition as claimed in claim 1, wherein the aromatic polycarbonate is present in an amount of greater than or equal to 30% by weight, based on the total weight of the composition.

17. A composition as claimed in claim 1, wherein the aromatic polycarbonate is present in an amount of less than or equal to 90% by weight, based on the total weight of the composition.

18. A composition as claimed in claim 1, wherein the ratio by weight of the aromatic polycarbonate to the weight of the graft copolymer including polyacrylonitrile is 90:1 to 0.5:1.

19. A composition as claimed in claim 1, further including an impact modifier.

20. A composition as claimed in claim 19 wherein the impact modifier comprises an acrylic based impact modifier or a methacrylate-butadiene-styrene (MBS) based impact modifier.

21. A composition as claimed in claim 19, wherein the impact modifier is in the form of core-shell polymeric particles.

22. A composition as claimed in claim 19, wherein the impact modifier is present in an amount greater than or equal to 1% by weight, based on the total weight of the composition.

23. A composition as claimed in claim 19, wherein the impact modifier is present in an amount of less than or equal to 20% by weight, based on the total weight of the composition.

24. A composition as claimed in claim 1, wherein the Melt Flow Index of the composition at 260 C. applying a 5 kg/cm.sup.3 load as determined in accordance with ISO 1133:1997 is at least 5% greater than a comparable composition containing an equivalent level of aromatic polycarbonate and not including the non-crosslinked acrylic polymer.

25. A composition as claimed in claim 1, for use in melt-processing applications.

26. A composition as claimed in claim 1, further including a reinforcement fibre.

27. A process for manufacturing a composition as defined in claim 1 comprising mixing the aromatic polycarbonate, the graft copolymer including polyacrylonitrile, and the non-crosslinked acrylic polymer.

28. A process as claimed in claim 27 wherein the mixing comprises melt blending the aromatic polycarbonate, the graft copolymer including polyacrylonitrile, and the non-crosslinked acrylic polymer.

29. A process as claimed in claim 27, further including the step of adding an impact modifier.

30. An article comprising a composition as defined in claim 1.

31. A method of manufacturing an article comprising adding a composition as defined in claim 1 in molten form to a mold, allowing the molten composition to solidify in the mold to form the article and removing the article from the mold.

32. A method of forming an article comprising injection molding a composition as defined in claim 1.

33. A method of forming the composition of claim 1, comprising mixing the non-crosslinked acrylic polymer with a component mixture comprising the aromatic polycarbonate and the graft copolymer including polyacrylonitrile and optionally including an impact modifier and/or a reinforcement fibre, whereby the melt flow rate of the component mixture is increased compared to the component mixture not containing the non-crosslinked acrylic polymer.

34. A method of forming an article by injection molding, comprising mixing a non-crosslinked acrylic polymer having a weight average molecular weight (Mw) of between greater than or equal to 30,000 Daltons (Da) and less than 50,000 Daltons (Da) with a component mixture comprising an aromatic polycarbonate and a graft copolymer including polyacrylonitrile and optionally including an impact modifier and/or a reinforcement fibre, and forming an article from a resultant mixture by an injection molding procedure, whereby the process cycle time for forming the article is decreased compared to the component mixture not containing the non-crosslinked acrylic polymer, wherein the non-crosslinked acrylic polymer is in the amount of 3 to 25 wt % and obtained by polymerising monomers consisting of 60 to 100% by weight methyl methacrylate monomer and 0 to 40% by weight of one or more alkyl (alk)acrylate comonomers.

35. A composition as claimed in claim 8, wherein the acrylic copolymer consists essentially of methyl methacrylate monomer and one or more alkyl acrylate comonomers.

36. A composition as claimed in claim 19, wherein the impact modifier comprises a MBS based impact modifier.

37. A composition as claimed in claim 4, wherein the alkyl (alk)acrylate comonomer of the acrylic copolymer comprises an alkyl acrylate comonomer.

38. A composition as claimed in claim 8, wherein the alkyl (alk)acrylate comonomer of the acrylic copolymer comprises an alkyl acrylate comonomer.

39. A composition as claimed in claim 20, wherein the impact modifier is in the form of core-shell polymeric particles.

40. A composition as claimed in claim 36, wherein the impact modifier is in the form of core-shell polymeric particles.

41. A process as claimed in claim 28, further including the step of adding an impact modifier.

42. A composition as claimed in claim 1, wherein the aromatic polycarbonate is derived from 2,2-bis-(4-hydroxyphenyl)-propane (bisphenol A).

Description

(1) FIG. 1 is a plot of the impact resistance of a composition versus the melt flow rate of a composition.

(2) FIG. 2 is a plot of the minimum cooling time of various compositions in an injection moulding application versus the melt flow rate of a composition.

Example 1Preparation of a Non-Crosslinked Acrylic Polymer Comprising Methyl Methacrylate and Ethyl Acrylate (97:3)

(3) A 150 liter stainless steel autoclave equipped with a stirrer and a heating and cooling jacket is charged with 54 liters of deionised water, 30 kg of methyl methacrylate (97% by weight), 928 g of ethyl acrylate (3% by weight), 1259 g polymethacrylic acid (PMA-4.07% by weight based on the total amount of monomers), 260 g disodium hydrogen phosphate dehydrate (0.84% by weight based on the total amount of monomers), 62 g of 2,2-azobis(isobutyronitrile)-(AIBN) (0.2% by weight based on the total amount of monomers) and 343 g of dodecyl mercaptan (1.11% by weight based on the total amount of monomers) with agitation at room temperature. The autoclave is sealed and purged with nitrogen. The sealed autoclave is pressurised to 6 psi and then heated to 82 C. The reaction mixture is stirred while the reaction proceeds and maintained at 82 C. until the reaction exotherm begins to subside, after which the reaction mixture is heated at 95 C. for 20 minutes to reduce residual monomer levels and decompose any residual initiator. The reaction mixture is then cooled to room temperature, the contents removed from the autoclave and filtered. The filtered polymer is then washed with deionised water, spread onto trays and dried in an air oven at a temperature of 80 C. for 48 hours, to yield an acrylic copolymer comprising 97% by weight methyl methacrylate and 3% by weight ethyl acrylate having a weight average molecular weight (Mw) of 45,000 Da as determined by gel permeation chromatography.

Example 2Preparation of Non-Crosslinked Acrylic Polymer Comprising Methyl Methacrylate and Ethyl Acrylate (97:3)

(4) Example 1 was repeated except 247.5 g of dodecyl mercaptan (0.8% by weight based on the total amount of monomers) were employed. This produced an acrylic copolymer comprising 97% by weight methyl methacrylate and 3% by weight ethyl acrylate having a weight average molecular weight (Mw) of 50,000 Da as determined by gel permeation chromatography.

Example 3Preparation of Non-Crosslinked Acrylic Polymer Comprising Methyl Methacrylate and Ethyl Acrylate (97:3)

(5) Example 1 was repeated except 618.5 g of dodecyl mercaptan (2.0% by weight based on the total amount of monomers) were employed. This produced an acrylic copolymer comprising 97% by weight methyl methacrylate and 3% by weight ethyl acrylate having a weight average molecular weight (Mw) of 30,000 Da as determined by gel permeation chromatography.

Example 4Preparation of Non-Crosslinked Acrylic Polymer Comprising Methyl Methacrylate and Ethyl Acrylate (93.5:6.5)

(6) Example 1 was repeated except 28.918 kg of methyl methacrylate (93.5% by weight) and 2010 g of ethyl acrylate (6.5% by weight) were employed. This produced an acrylic copolymer comprising 93.5% by weight methyl methacrylate and 6.5% by weight ethyl acrylate having a weight average molecular weight of approximately 45,000 Da.

Example 5Preparation of a Non-Crosslinked Acrylic Polymer Comprising Methyl Methacrylate and Butyl Acrylate (97:3)

(7) Example 1 was repeated except 928 g of n-butyl acrylate (3% by weight) was employed instead of ethyl acrylate.

Example 6Preparation of a Non-Crosslinked Acrylic Polymer Comprising Methyl Methacrylate and Butyl Acrylate (93.5:6.5)

(8) Example 4 was repeated except 2010 g n-butyl acrylate (6.5% by weight) was employed instead of ethyl acrylate.

Example 7Preparation of a Composition Comprising an Aromatic Polycarbonate, ABS and an Acrylic Polymer

(9) A mixture of Lexan 103 an aromatic polycarbonate available from General Electric, now Sabic, (7.2 kg) pre-dried in an air circulating oven at 120 C. for 4 hours, Polylac PA 709 a high impact ABS (1.3 kg) available from Chi-Mei and the acrylic polymer of Example 1 (1.5 kg) pre-dried in an air circulating oven at 80 C. for 4 hours was added to a high density polyethylene bag and the contents tumbled by hand for 1 minute. The mixture was then starve fed into the feed hopper of a Werner Pfleider ZSK30 twin screw extruder equipped with two 30 mm co-rotating screws. The six temperature controllable zones of the extruder from the hopper to the die were set at 240 C., 255 C., 255 C., 255 C., 255 C. and 255 C., respectively. A vacuum (20 in Hg) was applied to the vent part between zones 5 and 6 of the extruder (zone 6 being nearest the die). Both of the co-rotating screws were run at 276 rpm and the throughput of the mixture was 11.8 kg/hour. The circular cross-section extrudate is delivered into a 5 meter long water both containing water at room temperature. The cooled extrudate is then passed over a series of guides to a strand pelletizing unit to produce the composition in the form of pellets having a length of 6 mm.

Example 8Preparation of a Composition Comprising an Aromatic Polycarbonate, ABS and an Acrylic Polymer

(10) The procedure of Example 7 was repeated using Lexan 103 (5.5 kg), Polylac PA 709 (3.0 kg) and the acrylic copolymer of Example 4 (1.5 kg) to produce the composition in the form of pellets having a length of 6 mm.

Example 9Preparation of a Composition Comprising an Aromatic Polycarbonate, ABS and an Acrylic Polymer

(11) The procedure of Example 7 was repeated using Lexan 103 (7.0 kg), Polylac PA 709 (2.5 kg) and the acrylic polymer of Example 3 (0.5 kg) to produce the composition in the form of pellets having a length of 6 mm.

(12) General Procedure for Preparing a Composition comprising an Aromatic Polycarbonate, a Graft Copolymer including Polyacrylonitrile, an Acrylic Polymer and an Impact Modifier

(13) A mixture of an aromatic polycarbonate pre-dried in an air circulating oven at 120 C. for 4 hours, and a graft copolymer including polyacrylonitrile, the non-crosslinked acrylic polymer having a weight average molecular weight of less than or equal to 65,000 Da and an impact modifier all of which pre-dried in an air circulating oven at 80 C. for 4 hours are added to a high density polyethylene bag and the contents tumbled by hand for 1 minute. The mixture is then starve fed into the feed hopper of a Werner Pfleider ZSK30 twin screw extruder equipped with two 30 mm co-rotating screws. The six temperature controllable zones of the extruder from the hopper to the die were set at 240 C., 255 C., 255 C., 255 C., 255 C. and 255 C., respectively. A vacuum (20 in Hg) was applied to the vent part between zones 5 and 6 of the extruder (zone 6 being nearest the die). Both of the co-rotating screws were run at 276 rpm and the throughput of the mixture was 11.8 kg/hour. The circular cross-section extrudate is delivered into a 5 meter long water both containing water at room temperature. The cooled extrudate is then passed over a series of guides to a strand pelletizing unit to produce the composition in the form of pellets having a length of 6 mm.

Examples 10 to 16

(14) The compositions of Examples 10 to 16 as detailed in Table 1 are prepared in accordance with the general procedure as detailed above. Lexan 103 is an aromatic polycarbonate available from General Electric, now Sabic, Polylac PA 709 is a high impact ABS available from Chi Mei, KM355 is a MBS based core-shell impact modifier particle (Tg approximately 45 C. having a weight mean particle size of 200 nm) and is available from Rhm & Haas, Clearstrength E920 is a MBS based core-shell impact modifier particle (Tg approximately 80 C. having a weight mean particle size of 300 nm) and is available from Arkema.

Comparative Examples A to F

(15) The comparative compositions of Examples A to F to as detailed in Table 2 are prepared in accordance with the general procedure as detailed above but with the omission of the non-crosslinked acrylic polymer or both the non-crosslinked acrylic polymer and the impact modifier.

(16) The following is evident from the results displayed in Tables 1 and 2:

(17) (a) Increasing the amount of polycarbonate in a polycarbonate and ABS blend reduces the Melt Flow Rate of the blend (see MFI), increases the impact resistance of the blend (see Notched Izod) and increases the Vicat softening temperature of the blend (see Examples A to D of Table 2). (b) Increasing the amount of impact modifier in a polycarbonate/ABS/impact modifier blend reduces the Melt Flow Rate of the blend and increases the impact resistance (see Examples B, E and F of Table 2). (c) A decrease in the Melt Flow Rate (MFI) of a polycarbonate and ABS blend optionally including an impact modifier typically results in an increase in the impact resistance (Notched Izod @ 23 C.) of the blend (see Examples A to D of Table 2). (d) Adding the non-crosslinked acrylic polymer at the expense of ABS to a polycarbonate/ABS/impact modifier blend significantly increases the Melt Flow Rate of the blend. Compare Example F of Table 2 (MFI 8.6 g/10 min @ 260 C.) with Example 10 of Table 1 (MFI 14.5 g/10 min @ 260 C.) and Example E of Table 2 (MFI 10.7 g/10 min @ 260 C.) with Example 11 of Table 1 (MFI 25.6 g/10 min @ 260 C.). (e) The compositions of the present invention have comparable Vicat softening temperatures to polycarbonate and ABS blends which optionally include an impact modifier (compare Vicat B of Examples 10 to 16 of Table 1 with Examples A to F of Table 2). (f) Increasing the amount of non-crosslinked acrylic polymer and decreasing the amount of impact modifier in a composition of the present may provide an increase in the Melt Flow Rate without the loss of impact resistance of the composition (compare MFI @ 260 C. g/10 min and Notched Izod @ 23 C. kJ/m.sup.2 for Examples 13 and 14 and Examples 15 and 16).

(18) TABLE-US-00001 TABLE 1 % by weight Notched Notched Lexan 103 Polylac PA Flexural MFI@260 C. Izod 23 C. Izod 20 C. Vicat B Example (PC) 709 (ABS) Acrylic Polymer KM355 E920 Modulas GPa g/10 min kJ/m.sup.2 kJ/m.sup.2 C. 10 65 15 (Example 4) 10 10 2.3 14.5 90 129 11 65 15 (Example 4) 15 5 2.3 25.6 45 127 12 65 17.5 (Example 1) 10 7.5 2.09 11.4 82 20 129 13 65 17.5 (Example 1) 10 7.5 2.07 15 50 39 129 14 65 17.5 (Example 1) 5 2.15 17 55 41 129 12.5 15 80 2.5 (Example 1) 10 7.5 2.1 12.7 54 44 138 16 80 2.5 (Example 1) 5 2.18 14.6 64 20 138 12.5

(19) TABLE-US-00002 TABLE 2 Comparative Examples % by weight Notched Notched Lexan 103 Polylac PA Flexural MFI@260 C. Izod 23 C. Izod 20 C. Vicat B Example (PC) 709 (ABS) KM355 Modulus GPa g/10 min kJ/m.sup.2 kJ/m.sup.2 C. A 50 50 2.1 12.5 41 39 116 B 65 35 2.19 12.4 46 39 127 C 72.5 27.5 2.2 11.8 51 34 133 D 80 20 2.24 11.3 60 52 138 E 65 30 5 2.2 10.7 81 128 F 65 25 10 2.1 8.6 93 128 (g) The combination of a non-crosslinked acrylic polymer and an impact modifier in a polycarbonate/ABS blend typically allows an improvement of impact resistance and/or the Melt Flow Rate of the blend. In this respect, Example 11 of Table 1 has a Notched Izod @ 23 C. of 45 kJ/m.sup.2 which is comparable to a polycarbonate/ABS (65:35) blend - see Example B, yet the melt flow rate of Example 11 is 25.6 g/10 min @ 260 C. whereas that of Example B is 12.4 g/10 mins. Similarly, Example 10 of Table 1 has a Melt Flow Rate of 14.5 g/min @ 260 C. which is comparable to, albeit higher than, that of Example B (12.4 g/min @ 260 C.) yet Example 10 has a significantly higher impact resistance (Notched Izod 23 C. of 90 kJ/m.sup.2) than that of Example B (Notched Izod @ 23 C. of 46 kJ/m.sup.2). The improvement of impact resistance and/or Melt Flow Rate of a polycarbonate/ABS blend using the combination of a non-crosslinked acrylic polymer and an impact modifier is displayed graphically in FIG. 1.
General Injection Moulding Procedure

(20) The polymeric material is dried in an air circulating oven at 80 C. for 3 hours prior to moulding. The injection moulding apparatus consists of a Demag D40 machine equipped with a 28 mm diameter rotating screw which carries the molten polymeric material to a twin parallel bar mould. Each bar mould has the dimensions of 120104 mm and includes a 2 mm diameter circular gate (the entry point for the mould). The machine barrel is heated at 240 C., 250 C., 250 C. and 260 C. in the direction of the nozzle, which is heated at 260 C. The surface of the mould is heated at 80 C. The molten polymeric material is injected into the mould and pressure is applied to the mould so the molten polymeric material packs the entirety of the mould (holding phase). Once the gate freezes, the pressure is removed and the moulding allowed to cool in the mould until it is rigid enough to survive the ejection process (cooling phase). The moulding is then removed from the mould.

(21) For each polymeric composition, the gate freeze time and the minimum cooling phase time was determined. The gate freeze time was determined as follows. The hold on pressure for an unmodified PC/ABS blend was adjusted to the minimum pressure that caused no sink marks to be observed on the mould surfaces. Starting at a low value of hold on time (i.e. application of hold on minimum pressure for a short period of time) the mouldings produced were weighed. The hold on time was then increased upwards by 1 second intervals until a plot of moulding weight versus hold on pressure plateaued. The time corresponding to the start of the plateau represents the gate freeze time. The minimum cooling phase time was determined by applying the hold on pressure for 1 second more than the gate freeze time and then starting at an overly long cooling period, the cooling period was reduced gradually for successive mouldings until the automatic ejector system was unable to fully eject the moulded article. The minimum total cooling time was then calculated as the gate freeze time plus the minimum cooling phase time.

(22) The following compositions as detailed in Table 3 were subjected to an injection moulding procedure as detailed above and the gate freeze time and minimum total cooling time measured.

(23) TABLE-US-00003 TABLE 3 MFI @ Gate Minimum Total Example 260 C. g/10 min Freeze Time (s) Cooling Time (s) Comparative A 12.5 20 51 Comparative B 12.4 19 40 Comparative C 11.8 20 38 Comparative D 11.3 18 30 12 11.4 23 30 13 15 20 39 14 17 20 30 15 12.7 19 22 16 14.6 17 26

(24) As can be seen from Table 3, typically increasing the Melt Flow Rate of a polycarbonate and ABS blend results in an increase in the minimum total cooling time for producing an article by an injection moulding procedure (compare Examples A to D). However, the inclusion of the non-crosslinked acrylic polymer in the composition typically permits an increase in the Melt Flow Rate of the polycarbonate and ABS blend and a reduction in the minimum total cooling time (compare MFI values and Minimum total cooling time of Examples 12 to 16 with Examples A to D). The cooling time versus MFI of compositions of the present invention (Examples 12 to 16) and standard polycarbonate/ABS blends (Examples A to D) is depicted in FIG. 2.

(25) Advantageously, the compositions of the present invention may be used to form more intricate shaped articles and articles having less residual stress due to the improved Melt Flow Rate. Additionally, due to a reduction in the minimum total cooling time compared with standard polycarbonate/ABS blends the composition of the present invention offer reductions in the process cycle time of an injection moulding procedure.

Examples 17 and 18Fibre Reinforced Materials

(26) The compositions of Examples 17 and 18 as detailed in Table 4 were prepared in accordance with the General procedure for preparing a composition comprising an aromatic polycarbonate, a graft copolymer including acrylonitrile, an acrylic polymer and an impact modifier as detailed herein except a glass reinforcement fibre (HP3786 short glass fibre from PPG) was compounded with the polymer mixture. Comparative compositions G and H were prepared in a similar manner.

(27) As is evident from the properties of the compositions detailed in Table 4, the compositions of the present invention including a reinforcement fibre exhibit enhanced Melt Flow Rates compared to comparable compositions not including a reinforcement fibre, whilst still maintaining satisfactory impact resistance and comparable Vicat B softening temperatures (compare Example 17 with Comparative G and Example 18 with Comparative H).

(28) TABLE-US-00004 TABLE 4 % by weight Notched Lexan 103 Polylac PA Glass MFI@260 C. Izod 23 C. Vicat B Example (PC) 709 (ABS) Acrylic Polymer KM355 Fibre g/10 min kJ/m.sup.2 C. 17 58.5 13.5 (Example 4) 13.5 4.5 10 21.8 7.0 127 Comparative 58.5 31.5 10 12.4 9.5 131 G 18 52 12 (Example 4) 12 4 20 18.5 5.4 130 Comparative 52 28 20 10.9 8.3 133 H