POLYAMIDE BLENDS CONTAINING A REINFORCING AGENT FOR LASER SINTERED POWDER

Abstract

The present invention relates to a process for producing a shaped body by selective laser sintering of a sinter powder (SP). The sinter powder (SP) comprises at least one semicrystalline polyamide, at least one nylon-6I/6T and at least one reinforcing agent. The present invention further relates to a shaped body obtainable by the process of the invention and to the use of nylon-6I/6T in a sinter powder (SP) comprising at least one semicrystalline polyamide, at least one nylon-6I/6T and at least one reinforcing agent for broadening the sintering window (W.sub.SP) of the sinter powder (SP).

Claims

1.-13. (canceled)

14. A process for producing a shaped body by selective laser sintering of a sinter powder (SP), wherein the sinter powder (SP) comprises the following components: (A) at least one semicrystalline polyamide comprising at least one unit selected from the group consisting of NH(CH.sub.2).sub.mNH units where m is 4, 5, 6, 7 or 8, CO(CH.sub.2).sub.nNH units where n is 3, 4, 5, 6 or 7, and CO(CH.sub.2).sub.oCO units where o is 2, 3, 4, 5 or 6, (B) at least one nylon-6I/6T, (C) at least one reinforcing agent, wherein component (C) is a fibrous reinforcing agent in which the ratio of length of the fibrous reinforcing agent to diameter of the fibrous reinforcing agent is in the range from 2:1 to 40:1.

15. The process according to claim 14, wherein the sinter powder (SP) comprises in the range from 30% to 70% by weight of component (A), in the range from 5% to 25% by weight of component (B) and in the range from 15% to 50% by weight of component (C), based in each case on the sum total of the percentages by weight of components (A), (B) and (C).

16. The process according to claim 14, wherein the sinter powder (SP) has a D10 in the range from 10 to 30 m, a D50 in the range from 25 to 70 m and a D90 in the range from 50 to 150 m.

17. The process according to claim 14, wherein the sinter powder (SP) has a sintering window (W.sub.SP), where the sintering window (W.sub.SP) is the difference between the onset temperature of melting (T.sub.M.sup.onset) and the onset temperature of crystallization (T.sub.C.sup.onset) and where the sintering window (W.sub.SP) is in the range from 15 to 40 K.

18. The process according to claim 14, wherein the sinter powder (SP) has a melting temperature (T.sub.M) in the range from 180 to 270 C.

19. The process according to claim 14, wherein the sinter powder (SP) has a crystallization temperature (T.sub.C) in the range from 120 to 190 C.

20. The process according to claim 14, wherein the sinter powder (SP) is produced by grinding components (A), (B) and (C) at a temperature in the range from 210 to 195 C.

21. The process according to claim 14, wherein component (A) is selected from the group consisting of PA 6, PA 6.6, PA 6.10, PA 6.12, PA 6.36, PA 6/6.6, PA 6/6I6T, PA 6/6I and PA 6/6T.

22. The process according to claim 14, wherein component (C) is a fibrous reinforcing agent in which the ratio of length of the fibrous reinforcing agent to diameter of the fibrous reinforcing agent is in the range from 3:1 to 30:1.

23. The process according to claim 14, wherein component (C) is selected from the group consisting of carbon nanotubes, carbon fibers, boron fibers, glass fibers, silica fibers, ceramic fibers, basalt fibers, aramid fibers, polyester fibers and polyethylene fibers.

24. The process according to claim 14, wherein the sinter powder (SP) additionally comprises at least one additive selected from the group consisting of antinucleating agents, stabilizers, end group functionalizers and dyes.

25. A shaped body obtainable by the process according to claim 14.

26. A process for broadening the sintering window (W.sub.SP) of a sinter powder (SP) compared to the sintering window (W.sub.A) of component (A), which comprises utilizing a nylon-6I/6T in the sinter powder (SP) comprising the following components: (A) at least one semicrystalline polyamide comprising at least one unit selected from the group consisting of NH(CH.sub.2).sub.mNH units where m is 4, 5, 6, 7 or 8, CO(CH.sub.2).sub.nNH units where n is 3, 4, 5, 6 or 7, and CO(CH.sub.2).sub.oCO units where o is 2, 3, 4, 5 or 6, (B) at least one nylon-6I/6T, (C) at least one reinforcing agent for broadening the sintering window (W.sub.SP) of the sinter powder (SP) compared to the sintering window (W.sub.AC) for a mixture of components (A) and (C), where the sintering window (W.sub.SP; W.sub.AC) in each case is the difference between the onset temperature of melting (T.sub.M.sup.onset) and the onset temperature of crystallization (T.sub.C.sup.onset).

Description

EXAMPLES

[0187] The following components are used: [0188] Semicrystalline polyamide (component (A)): [0189] (P1) nylon-6 (Ultramid B27, BASF SE) [0190] Amorphous polyamide (component (B)): [0191] (AP1) nylon-6I/6T (Grivory G16, EMS), with a molar ratio 6I:6T of 1.9:1 [0192] (AP2) nylon-6/3T (Trogamid T5000, Evonik) [0193] Reinforcing agent (component (C)): [0194] (RA1) Tenax E HT C604 carbon fibers, Toho Tenax (chopped fibers, 6 mm, size for polyamide) [0195] (RA2) Tenax A HT M100 carbon fibers, Toho Tenax (ground fibers, 60 m, unsized) [0196] (RA3) Tremin 939 300 AST wollastonite (Quarzwerke) (calcium silicate with aminosilane size) [0197] (RA4) glass fibers of diameter 6 m ECS-03T-488DE (NEG) (chopped fibers) [0198] (RA5) DS110 (3B) glass fibers, with aminosilane size, chopped fibers, 4 to 5 mm, diameter 10 m [0199] (RA6) glass fibers of diameter 6 m ECS03T-289DE (NEG) (chopped fibers) [0200] (RA7) glass beads, Potters Spheriglass 7025 CP03 (with aminosilane size for polyamide, mean bead diameter 10 m) [0201] Additive: [0202] (A1) Irganox 1098 (N,N-hexane-1,6-diylbis(3-(3,5-di-tert-butyl-4-hydroxyphenylpropionamide)), BASF SE) [0203] (A2) Spezialschwarz 4 (carbon black, CAS No. 1333-86-4, Evonik)

[0204] Table 1 states essential parameters of the semicrystalline polyamides used (component (A)), and table 2 states essential parameters of the amorphous polyamides used (component (B)).

TABLE-US-00003 TABLE 1 Zero shear rate viscosity AEG CEG T.sub.M T.sub.G .sub.0 at 240 C. Type [mmol/kg] [mmol/kg] [ C.] [ C.] [Pas] P1 PA 6 36 54 220.0 53 399

TABLE-US-00004 TABLE 2 Zero shear rate AEG CEG T.sub.G viscosity .sub.0 at Type [mmol/kg] [mmol/kg] [ C.] 240 C. [Pas] AP1 PA 6I/6T 37 86 125 770 AP2 PA 6/3T 45 59 150 72000 at 0.5 rad/s

[0205] AEG indicates the amino end group concentration. This is determined by means of titration. For determination of the amino end group concentration (AEG), 1 g of the component (semicrystalline polyamide or amorphous polyamide) was dissolved in 30 mL of a phenol/methanol mixture (volume ratio of phenol:methanol 75:25) and then subjected to potentiometric titration with 0.2 N hydrochloric acid in water.

[0206] The CEG indicates the carboxyl end group concentration. This is determined by means of titration. For determination of the carboxyl end group concentration (CEG), 1 g of the component (semicrystalline polyamide or amorphous polyamide) was dissolved in 30 mL of benzyl alcohol. This was followed by visual titration at 120 C. with 0.05 N potassium hydroxide solution in water.

[0207] The melting temperature (T.sub.M) of the semicrystalline polyamides and all glass transition temperatures (T.sub.G) were each determined by means of differential scanning calorimetry.

[0208] For determination of the melting temperature (T.sub.M), as described above, a first heating run (H1) at a heating rate of 20 K/min was measured. The melting temperature (T.sub.M) then corresponded to the temperature at the maximum of the melting peak of the heating run (H1).

[0209] For determination of the glass transition temperature (T.sub.G), after the first heating run (H1), a cooling run (C) and subsequently a second heating run (H2) were measured. The cooling run was measured at a cooling rate of 20 K/min; the first heating run (H1) and the second heating run (H2) were measured at a heating rate of 20 K/min. The glass transition temperature (T.sub.G) was then determined as described above at half the step height of the second heating run (H2).

[0210] The zero shear rate viscosity .sub.0 was determined with a DHR-1 rotary viscometer from TA Instruments and a plate-plate geometry with a diameter of 25 mm and a plate separation of 1 mm. Unequilibrated samples were dried at 80 C. under reduced pressure for 7 days and these were then analyzed with a time-dependent frequency sweep (sequence test) with an angular frequency range of 500 to 0.5 rad/s. The following further analysis parameters were used: deformation: 1.0%, analysis temperature: 240 C., analysis time: 20 min, preheating time after sample preparation: 1.5 min.

[0211] Blends Produced in a Miniextruder

[0212] For production of blends, the components specified in table 3 were compounded in the ratios specified in table 3 in a DSM 15 cm.sup.3 miniextruder (DSM-Micro15 microcompounder) at a speed of 80 rpm (revolutions per minute) at 260 C. for a mixing time of 3 min (minutes) and then extruded. The extrudates obtained were then ground in a mill and sieved to a particle size of <200 m.

[0213] The blends obtained were characterized. The results can be seen in table 4.

TABLE-US-00005 TABLE 3 (AP1) (RA1) (RA3) (RA4) (P1) [% by [% by [% by [% by (A1) Example [% by wt.] wt.] wt.] wt.] wt.] [% by wt.] C1 100 C2 90 10 C3 80 20 C4 79 21 I5 71.1 18.9 10 I6 63.2 16.8 20 C7 78.6 21 0.4 I8 58.6 21 20 0.4 C9 74.6 25 0.4 I10 53.6 21 25 0.4 C11 74.6 25 0.4 I12 53.6 21 25 0.4

TABLE-US-00006 TABLE 4 Magnitude of Ratio of complex viscosity viscosity at 0.5 after aging Sintering rad/s, 240 C. to before T.sub.M T.sub.C window W Example [Pas] aging [ C.] [ C.] [K] C1 220.2 182.5 21.5 C2 219.8 188.5 18.2 C3 219.5 186.9 18.7 C4 465 0.25 218.9 172.8 25.5 I5 217.9 175.6 25.6 I6 1120 0.55 217.3 174.1 26.5 C7 554 3.44 216.6 174.0 25.1 I8 1700 1.14 C9 219.2 188.9 18.5 I10 217.1 178.2 23.5 C11 218.9 188.8 16.8 I12 217.0 172.7 25.0

[0214] The melting temperature (T.sub.M) was determined as described above.

[0215] The crystallization temperature (T.sub.C) was determined by means of differential scanning calorimetry. For this purpose, first a heating run (H) at a heating rate of 20 K/min and then a cooling run (C) at a cooling rate of 20 K/min were measured. The crystallization temperature (T.sub.C) is the temperature at the extreme of the crystalization peak.

[0216] The magnitude of the complex shear viscosity was determined by means of a plate-plate rotary rheometer at an angular frequency of 0.5 rad/s and a temperature of 240 C. A DHR-1 rotary viscometer from TA Instruments was used, with a diameter of 25 mm and a plate separation of 1 mm. Unequilibrated samples were dried at 80 C. under reduced pressure for 7 days and these were then analyzed with a time-dependent frequency sweep (sequence test) with an angular frequency range of 500 to 0.5 rad/s. The following further analysis parameters were used: deformation: 1.0%, analysis time: 20 min, preheating time after sample preparation: 1.5 min.

[0217] The sintering window (W) was determined, as described above, as the difference between the onset temperature of melting (T.sub.M.sup.onset) and the onset temperature of crystallization (T.sub.C.sup.onset).

[0218] To determine the thermooxidative stability of the blends, the complex shear viscosity of freshly produced blends and of blends after oven aging at 0.5% oxygen and 195 C. for 16 hours was determined. The ratio of viscosity after storage (after aging) to the viscosity before storage (before aging) was determined. The viscosity is measured by means of rotary rheology at a measurement frequency of 0.5 rad/s at a temperature of 240 C.

[0219] Comparative examples C2, C3, C9 and C11 show clearly that a mixture of components (A) and (C) has a reduced sintering window (W.sub.AC) compared to the sintering window for pure component (A) (comparative example C1). This is a consequence of the nucleating effect of the components (C) used in these comparative examples.

[0220] By contrast, the inventive sinter powders (SP) from examples I5, I6, I10 and I12 have a broadened sintering window (W.sub.SP) both compared to the mixture of components (A) and (C) and compared to the pure component (A).

[0221] It can also be seen that the change in viscosity after aging in the inventive sinter powders (SP) is smaller than in the case of sinter powders that do not comprise a reinforcing agent (example 18 compared to comparative example C7). The recyclability of the inventive sinter powders (SP) is thus higher.

[0222] Blends Produced in a Twin-Screw Extruder

[0223] For production of sinter powders, the components specified in table 5 were compounded in the ratio specified in table 5 in a twin-screw extruder (MC26) at a speed of 300 rpm (revolutions per minute) and a throughput of 10 kg/h at a temperature of 270 C. with subsequent extrudate pelletization. The pelletized material thus obtained was ground to a particle size of 20 to 100 m.

[0224] The sinter powders obtained were characterized as described above. In addition, the bulk density according to DIN EN ISO 60 and the tamped density according to DIN EN ISO 787-11 were determined; as was the Hausner factor as the ratio of tamped density to bulk density.

[0225] The particle size distribution, reported as the d10, d50 and d90, was determined as described above with a Malvern Mastersizer.

[0226] The reinforcing agent content of the sinter powder (SP) was determined gravimetrically after ashing.

[0227] The results can be seen in tables 6a and 6b.

TABLE-US-00007 TABLE 5 (P1) (AP1) (AP2) (RA1) (RA2) (RA5) (RA6) (RA7) (A1) (A2) Example [% by wt.] [% by wt.] [% by wt.] [% by wt.] [% by wt.] [% by wt.] [% by wt.] [% by wt.] [% by wt.] [% by wt.] C13 78.6 21 0.4 I14 66.8 17.8 15 0.4 I15 58.9 15.7 25 0.4 I15a 58.6 15.7 25 0.4 0.3 C16 58.9 15.7 25 0.4 I17 46.7 12.6 40 0.4 0.3 I18 58.6 15.7 25 0.4 0.3 I19 46.7 12.6 40 0.4 0.3 C20 78.6 21 0.4 I21 66.8 17.8 15 0.4 C22 58.9 15.7 25 0.4

TABLE-US-00008 TABLE 6a Magnitude of complex Ratio of viscosity at viscosity 0.5 rad/s, after aging Sintering 240 C. to before T.sub.M T.sub.C Sintering window W after Example [Pas] aging [ C.] [ C.] window W [K] aging [K] C13 659 2.0 217.0 170.8 26.9 27.1 I14 1068 0.83 217.2 175.6 24.1 26.0 I15 832 0.74 217.6 175.9 26.1 25.2 I15a 915 0.9 216.6 174.0 32.5 26.4 C16 3150 1.1 217.6 177.3 23.2 21.2 I17 1540 1.2 217.1 174.2 27.3 n.d. I18 819 0.9 217.6 174.9 27.0 25.2 I19 1190 1.0 216.9 172.0 26.2 26.6 C20 3310 1.5 217.4 175.9 23.2 21.1 I21 570 2.5 217.9 175.6 27.0 28.0 C22 733 1.3 217.3 176.5 24.6 24.3

TABLE-US-00009 TABLE 6b Reinforcing Tamped agent Mean fiber Length to Bulk density density Hausner d10 d50 d90 content length diameter Example [kg/m.sup.3] [kg/m.sup.3] factor [m] [m] [m] [% by wt] [m] ratio C13 0.51 0.64 1.25 35.0 65.0 111.7 0 n.d. n.d. I14 0.42 0.52 1.24 38.7 67.6 114.2 10.3 n.d. n.d. I15 0.42 0.51 1.226 32.2 61.3 118.1 18.9 91 9 I15a 0.50 0.63 1.26 34.6 64.0 115.5 18.0 102 10 C16 0.44 0.55 1.24 35.4 68.4 125.2 19.8 91 9 I17 0.49 0.62 1.26 32.0 65.9 138.4 35.8 119 12 I18 0.45 0.56 1.24 35.4 67.1 124.6 19.4 92 15 I19 0.46 0.60 1.31 34.7 69.5 144.1 33.9 119 20 C20 n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. I21 0.42 0.53 1.24 35.3 65.0 112.4 11.6 n.d. n.d. C22 0.50 0.63 1.26 36.4 63.6 106.1 23.7 10 1 (beads)

[0228] It is apparent that the sinter powders (SP) of the invention have a greater sintering window even after aging than sinter powders in which nylon-6,3T is present as component (B) rather than nylon-6I,6T. Therefore, the sinter powders of the invention also have a distinctly lesser tendency to warpage in the production of shaped bodies in the selective laser sintering method. As can be seen from table 7 below, as a result, a lower installation space temperature is also required with the sinter powders of the invention in the production of shaped bodies in the selective laser sintering method. This makes the process more cost-efficient.

[0229] Laser Sintering Experiments

[0230] The sinter powder was introduced with a layer thickness of 0.1 mm into the cavity at the temperature specified in table 7. The sinter powder was subsequently exposed to a laser with the laser power output specified in table 7 and the point spacing specified, with a speed of the laser over the sample during exposure of 5 m/s. The point spacing is also known as laser spacing or lane spacing. Selective laser sintering typically involves scanning in stripes. The point spacing gives the distance between the centers of the stripes, i.e. between the two centers of the laser beam for two stripes.

TABLE-US-00010 TABLE 7 Laser power Point Temperature output Laser speed spacing Example [ C.] [W] [m/s] [mm] C13 198 25 5 0.2 I14 197 25 5 0.2 I15 198 25 5 0.2 I15a 200 25 5 0.2 C16 206 25 15 0.2 I17 199 25 5 0.2 I18 198 25 5 0.2 I19 198 25 5 0.2 C20 206 25 15 0.2 I21 197 25 5 0.2 C22 198 25 5 0.2

[0231] Subsequently, the properties of the tensile bars (sinter bars) obtained were determined. The tensile bars (sinter bars) obtained were tested in the dry state after drying at 80 C. for 336 h under reduced pressure. The results are shown in table 9. In addition, Charpy bars were produced, which were likewise tested in dry form (according to ISO179-2/1eU: 1997+Amd.1:2011).

[0232] Tensile strength, tensile modulus of elasticity and elongation at break were determined according to ISO 527-1:2012.

[0233] Heat deflection temperature (HDT) was determined according to ISO 75-2: 2013, using both Method A with an edge fiber stress of 1.8 N/mm.sup.2 and Method B with an edge fiber stress of 0.45 N/mm.sup.2.

[0234] The processibility of the sinter powder and the warpage of the sinter bars were assessed qualitatively according to the scale specified in table 8.

TABLE-US-00011 TABLE 8 Warpage of flexural Processibility Rating bar from SLS in SLS 1 very low, flat components very good 2 slight good 3 moderate moderate 4 marked adequate 5 severe inadequate

TABLE-US-00012 TABLE 9 Charpy impact Charpy impact Tensile resistance, resistance, Tensile modulus of Warpage of Processibility unnotched unnotched strength elasticity Elongation at HDT HDT flexural bar in SLS Example [kJ/m.sup.2] [kJ/m.sup.2] [MPa] [MPa] break [%] A [ C.] B [ C.] from SLS [rating] [rating] C13 4.94 1.5 56.7 3660 1.7 94.4 150.4 2 2 I14 79.3 4710 2.5 106.7 186.2 2 3 I15 9.5 2.8 79.2 5200 2.1 122 208.8 2 2 I15a 8.4 2.3 76.2 4770 2.0 113 215 2 2 C16 n.d. n.d. 83.1 4812 3.5 117 207 2 3 I17 16.7 2.9 94 7100 2.7 164 217 2 3 I18 8.3 2.7 84 5040 2.8 118 214 2 2 I19 14.9 3,1 93 6750 2.8 158 217 2 3 C20 n.d. n.d. 85.7 3656 5.7 n.d. n.d. 3 3 I21 7.1 2.6 83 4390 3.3 105 189 2 4 C22 6.5 2.2 78.4 4740 2.2 104 195 2 2

[0235] Table 10 shows the properties of the shaped bodies in the conditioned state. For conditioning, the shaped bodies, were stored after the above-described drying at 70 C. and 62% relative humidity for 336 hours. The water content was determined by weighing the samples after drying and after conditioning.

TABLE-US-00013 TABLE 10 Tensile Tensile modulus of Elongation at strength elasticity break Water content Example [mPa] [mPa] [%] [% by wt.] C13 49 1640 23 2.7 I15 48 2540 8.8 1.9 I15a n.d. n.d. n.d. n.d. C16 53.2 3086 12.6 n.d. I17 57 4170 6.1 n.d. I18 n.d. n.d. n.d. 1.96 I19 n.d. n.d. n.d. n.d. C20 n.d. n.d. n.d. n.d. I21 51 1950 12.9 n.d. I22 49 2190 9.4 1.7

[0236] It is apparent that the shaped bodies produced from the sinter powders of the invention have low warpage, and the sinter powder of the invention can therefore be used efficiently in the selective laser sintering process.

[0237] In addition, significant advantages are apparent in the mechanical properties, for example elevated heat resistance, and also tensile strength and modulus of elasticity. Surprisingly, an increased elongation at break is even observed (I15).

[0238] The use of fibrous reinforcing agents rather than, for example, glass beads (comparative example C22) gives better mechanical properties even with a small proportion of fibrous reinforcing agents. For instance, there is a distinct increase in the tensile modulus of elasticity, and likewise an improvement in Impact resistance and an increase in heat distortion resistance. These positive effects are also maintained in the conditioned state of the shaped bodies, such that they have good mechanical properties even after storage at elevated temperatures and humidity.

[0239] The use of nylon-6I/6T as component (B), compared to the use of nylon-6/3T, achieves a higher tensile modulus of elasticity and better heat distortion resistance. Moreover, the use of fibers in combination with nylon-6I/6T achieves a distinct improvement in the tensile modulus of elasticity and improves the tensile strength. By contrast, in the case of addition of fibers, when component (B) used is nylon-6/3T, a distinctly smaller Improvement in the tensile modulus of elasticity is achieved and the tensile strength is actually reduced.