KAOLIN FOR THE MECHANICAL REINFORCEMENT OF POLYMERIC LASER SINTER POWER

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 polyimide (P) and in the range from 10% to 50% by weight of at least one aluminosilicate. The at least one aluminosilicate has a D50 in the range from 2.5 to 4.5 μm. The present invention further relates to shaped bodies obtainable by the process of the invention.

Claims

1.-14. (canceled)

15. A process for producing a shaped body by selective laser sintering of a sinter powder (SP), wherein the sinter powder (SP) comprises at least one polyamide (P) and in the range from 5% to 50% by weight of at least one aluminosilicate, based on the total weight of the sinter powder (SP), said at least one aluminosilicate having a D50 in the range from 2.5 to 4.5 μm, wherein the D50 values are determined by laser diffraction and, wherein the at least one aluminosilicate is kaolin.

16. The process according to claim 15, wherein the at least one polyamide (P) is selected from the group consisting of PA 4, PA 6, PA 7, PA 8, PA 9, PA 11, PA 12, PA 46, PA 66, PA 69, PA 610, PA 612, PA 613, PA 1212, PA 1313, PA 6T, PA MXD6, PA 6I, PA 6-3-T, PA 6/6T, PA 6/66, PA 66/6, PA 6/12, PA 66/6/610, PA 6I/6T, PA PACM 12, PA 6I/6T/PACM, PA 12/MACMI, PA 12/MACMT, PA PDA-T and copolyamides composed of two or more of the abovementioned polyamides.

17. The process according to claim 15, wherein the at least one polyamide (P) is selected from the group consisting of PA 12, PA 6, PA 66, PA 6/66, PA 66/6 and PA 610.

18. The process according to claim 15, wherein the at least one aluminosilicate has a D10 in the range from 0.5 to 1.5 μm, a D50 in the range from 2.5 to 4.5 μm and a D90 in the range from 8 to 15 μm.

19. The process according to claim 15, wherein the at least one aluminosilicate is a calcined sheet silicate.

20. The process according to claim 15, wherein the at least one aluminosilicate is amino-functionalized.

21. The process according to claim 15, wherein the sinter powder (SP) additionally comprises in the range from 0.1% to 10% by weight of at least one additive (A), based on the total weight of the sinter powder (SP).

22. The process according to claim 21, wherein the at least one additive (A) is selected from the group consisting of antinucleating agents, stabilizers, end group functionalizers and dyes.

23. The process according to claim 15, wherein the at least one polyamide (P) comprises the at least one aluminosilicate, where the polyamide (P) forms the continuous phase and the at least one aluminosilicate forms the disperse phase, and where the at least one aluminosilicate has a D50 in the range from 2.5 to 4.5 μm.

24. A process for producing a sinter powder (SP) comprising the following steps: i) mixing at least one polyamide (P) with at least one aluminosilicate and optionally at least one additive (A), where the at least one aluminosilicate has a D50 in the range from 2.5 to 4.5 μm, to obtain a mixture comprising at least one polyamide (P), at least one aluminosilicate and optionally at least one further additive (A), where the at least one aluminosilicate has a D50 in the range from 2.5 to 4.5 μm, ii) grinding the mixture obtained in step i) to obtain the sinter powder (SP).

25. The process according to claim 24, wherein step ii) comprises the following steps: iia) grinding the mixture obtained in step i) to obtain a polyamide powder, iib) mixing the polyamide powder obtained in step iia) with a free flow aid to obtain the sinter powder (SP).

26. A sinter powder (SP) obtainable by the process according to claim 15.

27. A sinter powder (SP), wherein the sinter powder (SP) comprises at least one polyamide (P) and in the range from 10% to 50% by weight of at least one aluminosilicate, based on the total weight of the sinter powder (SP), where the at least one aluminosilicate has a D50 in the range from 2.5 to 4.5 μm, where the at least one polyamide (P) comprises the at least one aluminosilicate and where the at least one polyamide (P) forms the continuous phase and the at least one aluminosilicate forms the disperse phase.

28. A shaped body obtained by the process according to claim 15.

Description

EXAMPLES

[0148] The following components were used: [0149] Polyamide (P): [0150] (P1) Ultramid® B22 (nylon-6) from BASF SE [0151] (P2) Ultramid® B27 (nylon-6) from BASF SE [0152] (P3) Grivory G16 (nylon-6I/6T) from EMS-Grivory [0153] (P4) Ultramid® C33 (nylon 6/66) from BASF SE [0154] Aluminosilicate: [0155] (B1) Translink 445 kaolin from BASF SE d10=0.998 μm, d50=3.353 μm, d90=11.875 μm, determined by means of laser scattering with a Malvern Mastersizer [0156] Additive (A): [0157] (A1) nigrosin UB434 [0158] (A2) terephthalic acid [0159] (A3) Irganox 1098 (N,N′-hexane-1,6-diylbis(3-(3,5-di-tert-butyl-4-hydroxyphenylpropionamide))) from BASF SE [0160] (A4) Nylostab S-EED (1,3-benzenedicarboxamide, N,N′-bis(2,2,6,6-tetramethyl-4-piperidinyl) [0161] (A5) Special black 4 carbon black from Evonik
Production of the sinter powders (C1, I2, C3 and I4)

[0162] For production of the sinter powder, the components specified in table 1 were compounded in the ratio specified in table 1 in a twin-screw extruder (ZSK 40) at a speed of 200 rpm, a barrel temperature of 240° C. and a throughput of 50 kg/h with subsequent extrudate pelletization. The thus obtained pelletized material was subjected to cryogenic grinding to obtain the sinter powder.

[0163] After the grinding, the powder was dried to a water content of about 0.5% (Aquatrac 3E from Brabender Messtechnik, measurement temperature 160° C., amount of sample 3 to 5 g), and mixed with 0.4% by weight of free flow aid (Al.sub.2O.sub.3; Aeroxide® Alu C, from Evonik).

TABLE-US-00001 TABLE 1 Component C1 I2 C3 I4 P1 [% by wt.] 97.70 67.80 — — P2 [% by wt.] — — 78 68 P3 [% by wt.] — — 21 21 B1 [% by wt.] — 30   — 10 A1 [% by wt.] 1.9 1.9 — — A2 [% by wt.] 0.4 0.3 — — A3 [% by wt.] — — 0.5 0.5 A4 [% by wt.] — — 0.5 0.5

Production of Tensile Bars

[0164] The sinter powders C1 and I2 were used to produce tensile bars. The sinter powder was introduced with a layer thickness of 0.12 mm into the cavity at the temperature specified in table 2. The sinter powder was subsequently exposed to a laser with the laser power output specified in table 2 and the point spacing specified, with a speed of the laser over the sample during exposure of 5080 mm/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.

[0165] The tensile bars obtained were dried at 80° C. under reduced pressure for 14 days, and then tensile tests were conducted in accordance with ISO 527-2: 2012 at a measuring temperature of 23° C. and a relative air humidity of 50%. The testing speed for determining the modules of elasticity was 1 mm/min; for the determination of other parameters, a testing speed of 5 mm/min was selected. The results are likewise to be found in table 2.

TABLE-US-00002 TABLE 2 C1a C1b C1c C1d C1e I2a I2b I2c I2d I2e Sinter powder C1 C1 C1 C1 C1 I2 I2 I2 I2 I2 Laser power 22 26 22 26 30 22 26 22 26 30 output [W] Point spacing 0.3 0.3 0.25 0.25 0.25 0.3 0.3 0.25 0.25 0.25 [mm] Temperature 200 200 200 200 200 205 205 205 205 205 [° C.] Tensile stress 22.83 15.34 18.72 41.24 37.53 70.45 69.64 55.93 54.75 66.69 at yield [MPa] Elongation at 0.73 0.46 0.58 1.28 1.12 1.66 1.63 1.23 1.95 1.57 yield [%] Tensile stress 22.83 15.34 18.72 41.24 37.53 70.45 69.64 55.93 54.75 66.69 at break [MPa] Elongation at 0.73 0.46 0.58 1.28 1.12 1.66 1.63 1.23 1.95 1.57 break [%] Young's 3057 3253 3208 3370 3404 5210 5061 4983 5094 5081 modulus [MPa]

[0166] On the basis of the examples cited in table 2, it is clearly apparent that the use of at least one aluminosilicate in the sinter powder (SP) reinforces the shaped bodies obtained, since they have an increased modulus of elasticity and a greater tensile stress at break compared to the sinter powders that do not comprise any aluminosilicate. Moreover, they exhibit distinctly lower embrittlement, which is reflected in a greater elongation at break.

Thermooxidative Stability of the Sinter Powders

[0167] The thermooxidative stability of the sinter powders C3 and 14 was determined. To determine the thermooxidative stability of the sinter powders, the viscosity of freshly produced sinter powders and of sinter powders after oven aging at 0.5% oxygen and 195° C. for 16 hours was determined. The ratio of viscosity after storage to the viscosity before storage 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. In addition, the sintering window W was determined. The results are to be found in table 3.

TABLE-US-00003 TABLE 3 C3 I4 Viscosity ratio 3.1 1.3 Sintering window W [K] 24.9 26.7

[0168] The oven aging at 0.5% oxygen and 195° C. for 16 hours simulates typical cavity conditions during the selective laser sintering process. It is clearly apparent that the ratio of viscosities after storage to before storage, as a result of the addition of the at least one aluminosilicate to the sinter powder (SP), is only 1.3, whereas it is 3.1 in the case of a sinter powder without the at least one aluminosilicate. This shows that the increase in viscosity which results from the increase in molecular weight through thermooxidative damage to the sinter powder can be reduced significantly through the at least one aluminosilicate. Moreover, the use of the at least one aluminosilicate slightly increases the sintering window, which likewise has a positive effect on the sintering properties.

Production of the sinter powders (C5, I5, I6, I7, C8, 19 and I10)

[0169] 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., or 245° C. for formulations comprising (P4), with subsequent extrudate pelletization. The pelletize material thus obtained was subjected to cryogenic grinding to a particle size of 20 to 100 μm. After the grinding, the powder was dried to a water content of about 0.5% (Aquatrac 3E from Brabender Messtechnik, measurement temperature 160° C., amount of sample 3 to 5 g), and mixed with 0.4% by weight of free flow aid (Al.sub.2O.sub.3; Aeroxide® Alu C, from Evonik).

[0170] The sinter powders obtained were characterized as described above. In addition, the bulk density was determined according to DIN EN ISO 60 and the tamped density according to DIN EN ISO 787-11, as was the Hausner factor as the ratio of tamped density to bulk density. In addition, the particle size distribution, reported as the d10, d50 and d90, as described above, was determined with a Malvern Mastersizer.

[0171] The aluminosilicate content of the sinter powder (SP) was determined by gravimetric means after ashing.

[0172] The results are reported in tables 6a and 6b.

TABLE-US-00004 TABLE 5 (P2) (P3) (P4) (B1) (A3) (A5) Example [% by wt.] [% by wt.] [% by wt.] [% by wt.] [% by wt.] [% by wt.] C5 78.6 21 — — 0.4 — I5 68.2 21 — 10 0.5 0.3 I6 58.9 15.7 — 25 0.4 — I7 47.0 12.6 — 40 0.4 — C8 — 10 89.75 — 0.25 — I9 — 7.5 66.95 25 0.25 0.3 I10 — 6.0 53.45 40 0.25 0.3

TABLE-US-00005 TABLE 6a Magnitude of complex viscosity Ratio of Sintering at 0.5 rad/s, viscosity after Sintering window W 240° C. aging to before T.sub.M T.sub.C window after aging Example [Pas] aging [° C.] [° C.] W [K] [K] C5 659 2.0 217.0 170.8 26.9 27.1 I5 592 0.73 217.6 173.3 26.7 — I6 959 0.68 217.3 177.9 24.3 22.1 I7 1974 1.1 217.5 177.1 24.7 22.3 C8 No powder in SLS quality obtained: lumps formed after grinding I9 7184 1.1 193.1 150.7 26.0 — I10 12572 2.2 193.4 150.9 26.5 33.7 T.sub.M [° C.] melting peak temperature .Math. T.sub.C [° C.] crystallization peak temperature; each determined by means of DSC.

TABLE-US-00006 TABLE 6b Bulk Tamped Aluminosili- density density Hausner d10 d50 d90 cate content Example [kg/m.sup.3] [kg/m.sup.3] factor [μm] [μm] [μm] [% by wt.] C5 0.51 0.64 1.25 35.0 65.0 111.7 0 I5 — — — 15 43 83 10 I6 0.47 0.62 1.31 37.0 63.9 106.4 24.9 I7 0.54 0.69 1.28 36.9 63.0 104.7 38.0 C8 No powder in SLS quality obtained: lumps formed after grinding I9 0.53 0.67 1.26 38.3 67.3 114.4 25.6 I10 0.55 0.68 1.24 42.6 67.2 105.2 40.7

Production of Tensile Bars

[0173] The sinter powders C5, I5, I6, I7, C8, I9 and I10 were used to produce tensile bars.

[0174] The sinter powder was introduced with a layer thickness of 0.1 mm into the cavity at the cavity 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-00007 TABLE 7 Laser Point Temperature Laser power speed spacing Example [° C.] [W] [m/s] [mm] C5 198 25 5 0.2 I5 207 35 12.5 0.2 I6 200 25 5 0.2 I7 200 25 5 0.2 C8 No powder obtained, so no test specimens sintered I9 176 25 5 0.2 I10 182 25 5 0.2

[0175] Subsequently, the properties of the resultant tensile bars (sinter bars) were determined. The resultant tensile bars (sinter bars) 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 specimens were produced, which were likewise tested under dry conditions (according to ISO179-2/1eU: 1997+Amd.1:2011).

[0176] The tensile stress, tensile modulus of elasticity and elongation at break was determined according to ISO 527-1:2012.

[0177] The heat deflection temperature (HDT) was determined according to ISO 75-2:2013, using either Method A with an outer fiber stress of 1.8 N/mm.sup.2 or Method B with an outer fiber stress of 0.45 N/mm.sup.2.

[0178] The processibility of the sinter powder and the warpage of the sinter bars was assessed qualitatively using the scale given in table 8.

TABLE-US-00008 TABLE 8 Warpage of fractional bar Grade from SLS Processibility in SLS 1 Very low, flat components Very good 2 Low Good 3 Moderate Moderate 4 Marked Adequate 5 Severe Inadequate

TABLE-US-00009 TABLE 9 Charpy impact Charpy impact Tensile Warpage of resistance, resistance, Tensile modulus of Elongation flexural Processibility unnotched notched strength elasticity at break HDT A HDT B bar from in SLS Example [kJ/m.sup.2] [kJ/m.sup.2] [MPa] [MPa] [%] [° C.] [° C.] SLS [grade] [grade] C5 4.9 1.5 56.7 3660 1.7 94.4 150.4 3 2 I5 — — 70.4 4090 2.0 100.1 185.3 3 2 I6 8.7 1.8 80.0 5300 2.0 112.5 203.9 3 3 I7 10.3  3.2 88.0 7093 1.8 116.8 210.2 2 2 C8 No powder obtained, so no test specimens sintered I9 14.9  3.1 74.2 4200 3.9 93 182 2 2 I10 2.7 69.6 5040 2.0 110.3 176 1 2

[0179] 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 therefore has good usability in the selective laser sintering method.

[0180] In addition, significant advantages of the mechanical properties are apparent, for example elevated heat distortion resistance and also tensile strength and modulus of elasticity. Surprisingly, an elevated elongation at break and an elevated impact resistance (notched and unnotched) are even observed (I6 and I7).

[0181] I9 and I10 compared to C8 show that aluminosilicate leads to better grindability and improve mechanical properties of the sinter powder based on low-melting PA6 copolymers.