Sinter powder containing a multivalent alcohol for producing moulded bodies

Abstract

The present invention relates to a method of producing a shaped body, wherein, in step i), a layer of a sinter powder (SP) comprising at least one polyhydric alcohol inter alia is provided and, in step ii), the layer provided in step i) is exposed. The present invention further relates to a method of producing a sinter powder (SP) and to a sinter powder (SP) obtainable by this method. The present invention also relates to use of the sinter powder (SP) in a sintering method, and shaped bodies obtainable by the method of the invention.

Claims

1. A method of producing a shaped body, comprising the steps of: i) providing a layer of a sinter powder (SP) comprising the following components (A) at least one semicrystalline polyamide, (B) at least one amorphous polyamide, (C) at least one polyhydric alcohol, (D) optionally at least one additive, (E) optionally at least one reinforcer and (F) optionally at least one mineral flame retardant, ii) exposing the layer of the sinter powder (SP) provided in step i).

2. The method according to claim 1, wherein component (C) has a number-average molecular weight (M.sub.n) of less than 2000 g/mol.

3. The method according to claim 1, wherein component (C) is selected from the group consisting of glycerol, trimethylolpropane, 2,3-di-(2-hydroxyethyl)cyclohexan-1-ol, hexane-1,2,6-triol, 1,1,1-tris(hydroxymethyl)ethane, 3-(2-hydroxyethoxy)propane-1,2-diol, 3-(2-hydroxypropoxy)propane-1,2-diol, 2-(2-hydroxyethoxy)hexane-1,2-diol, 6-(2-hydroxypropoxy)hexane-1,2-diol, 1,1,1-tris-[(2-hydroxyethoxy)methyl]ethane, 1,1,1-tris-[(2-hydroxypropoxy)methyl]propane, 1,1,1-tris-(4-hydroxyphenyl)ethane, 1,1,1-tris-(hydroxyphenyl)propane, 1,1,3-tris-(dihydroxy-3-methylphenyl)propane, 1,1,4-tris(dihydroxyphenyl)butane, 1,1,5-tris(hydroxyphenyl)-3-methylpentane, ditrimethylopropane, trimethylolpropane ethoxylates, trimethylolpropane propoxylates, pentaerythritol, dipentaerythritol, tripentaerythritol, cyclodextrins, D-mannose, glucose, galactose, sucrose, fructose, xylose, arabinose, D-mannitol, D-sorbitol, D-arabitol, L-arabitol, xylitol, iditol, talitol, allitol, altritol, gulitol, erythritol, threitol and D-gulono-?-lactone.

4. The method according to claim 1, wherein component (A) 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 6,10, PA 6,12, PA 6,13, PA 6/6,36, PA 6T/6, PA 12,12, PA 13,13, PA 6T, PA MXD6, PA 6/66, PA 6/12 and copolyamides of these.

5. The method according to claim 1, wherein component (B) is selected from the group consisting of PA 6I/6T, PA 6I and PA 6/3T.

6. The method according to claim 1, wherein component (B) comprises at least 3% by weight of PA 6I/6T, based on the total weight of component (B).

7. The method according to claim 1, wherein the sinter powder (SP) comprises in the range from 35% to 96.95% by weight of component (A), in the range from 3% to 45% by weight of component (B), in the range from 0.05% to 20% by weight of component (C), in the range from 0% to 10% by weight of component (D), in the range from 0% to 44.95% by weight of component (E) and in the range from 0% to 60% by weight of component (F), based in each case on the total weight of the sinter powder (SP).

8. The method according to claim 1, wherein component (D) is selected from the group consisting of antinucleating agents, stabilizers, conductive additives, end group functionalizers, dyes and color pigments.

9. The method according to claim 1, wherein component (E) is selected from the group consisting of carbon nanotubes, carbon fibers, boron fibers, glass fibers, glass beads, silica fibers, ceramic fibers, basalt fibers, aluminosilicates, aramid fibers and polyester fibers.

10. The method according to claim 1, wherein the component (F) is based on magnesium and/or aluminum.

11. A method of producing a sinter powder (SP) according to claim 1, comprising the steps of a) providing the following components (A) at least one semicrystalline polyamide, (B) at least one amorphous polyamide, (C) at least one polyhydric alcohol, (D) optionally at least one additive, (E) optionally at least one reinforcer and (F) optionally at least one mineral flame retardant, b) grinding the mixture obtained in step a) to obtain the sinter powder (SP).

12. A sinter powder (SP) obtainable by the process according to claim 11.

13. The use of a sinter powder (SP) comprising the following components (A) at least one semicrystalline polyamide, (B) at least one amorphous polyamide, (C) at least one polyhydric alcohol, (D) optionally at least one additive, (E) optionally at least one reinforcer and (F) optionally at least one mineral flame retardant, in a sintering process.

14. A shaped body obtainable by a process according to claim 1.

15. A sinter powder comprising the following components (A) at least one semicrystalline polyamide, (B) at least one amorphous polyamide, (C) at least one polyhydric alcohol, (D) optionally at least one additive, (E) optionally at least one reinforcer and (F) optionally at least one mineral flame retardant.

16. The sinter powder (SP) according to claim 15, wherein the sinter powder has a median particle size (D50) in the range from 40 to 80 ?m.

Description

EXAMPLES

(1) The following components are used: Semicrystalline polyamide (component (A)): (P1) nylon-6 (Ultramid? B27E, BASF SE) Amorphous polyamide (component (B)): (AP1) nylon-6I/6T (Grivory G16, EMS), with a molar ratio of 6I:6T of 1.9:1 Polyhydric alcohol (component (C)): (C1) dipentaerythritol (Charmor DP15, Perstorp) Additive (component (D)): (A1) phenolic antioxidant (Irganox 1098 (N,N-hexane-1,6-diylbis(3-(3,5-di-tert-butyl-4-hydroxyphenylpropionamide))), BASF SE)

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

(3) TABLE-US-00001 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

(4) TABLE-US-00002 TABLE 2 Zero shear rate viscosity AEG CEG T.sub.G ?.sub.0 at 240? C. Type [mmol/kg] [mmol/kg] [? C.] [Pas] AP1 PA 6I6T 37 86 125 770

(5) 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) is dissolved in 30 mL of a phenol/methanol mixture (volume ratio of phenol:methanol 75:25) and then subjected to visual titration with 0.2 N hydrochloric acid in water.

(6) 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) is dissolved in 30 mL of benzyl alcohol and then subjected to visual titration at 120? C. with 0.05 N potassium hydroxide solution in water.

(7) 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.

(8) 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 first heating run (H1).

(9) 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 at half the step height of the second heating run (H2).

(10) The zero shear rate viscosity no 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 with an angular frequency range from 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.

(11) Production of Sinter Powders in a Twin-Screw Extruder

(12) For production of sinter powders, the components specified in table 3 were compounded in the ratio specified in table 3 in a twin-screw extruder (ZE25) at a speed of 230 rpm (revolutions per minute) at 270? C. with a throughput of 20 kg/h, pelletized and then processed with a liquid nitrogen-cooled pinned disk mill to give powders. Subsequently, the powders were sifted (the particle size was adjusted) and dried (particle size distribution 20 to 120 ?m).

(13) TABLE-US-00003 TABLE 3 (PI) [% by Example wt.] (AP1) (A1) (C1) V1 78.6 21 0.4 B2 77.6 21 0.4 1

(14) For the powders, the melting temperature (T.sub.M) was determined as described above.

(15) The crystallization temperature (T.sub.C) was determined by means of differential scanning calorimetry (DSC). 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 crystallization peak.

(16) 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.

(17) 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).

(18) To determine the thermooxidative stability of the sinter powders, the complex shear 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 (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.

(19) The results can be seen in table 4.

(20) TABLE-US-00004 TABLE 4 Magnitude Ratio of of complex viscosity viscosity at after Sintering 0.5 rad/s, aging to Sintering window W 240? C. before T.sub.M T.sub.C window after aging Example [Pas] aging [? C.] [? C.] W [K] [K] V1 620 3.5 218.2 172.5 28.3 27.1 B2 415 1.3 217.2 180.6 21.1 21.6 *n.d.: not determined

(21) It is apparent that the sinter powder (SP) of the invention from example B2 comprising component (C), after aging, shows a distinctly smaller increase in viscosity and hence better recyclability than the sinter powder from comparative example V1.

(22) Furthermore, it is apparent that the sinter powder of the invention has a sufficiently broad sintering window for selective laser sintering, even after aging.

(23) In addition, for the sinter powders obtained, bulk density according to DIN EN ISO 60 and 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.

(24) The particle size distribution, reported as the D10, D50 and D90, was determined as described above with a Malvern Mastersizer.

(25) The avalanche angle was determined by means of a Revolution Powder Analyzer (RPA) with a speed of rotation of 0.6 rpm and 15 images per second. 128 avalanche events were averaged.

(26) The results can be seen in table 5.

(27) TABLE-US-00005 TABLE 5 Ava- Bulk Tamped lanche Ex- density density Hausner D10 D50 D90 angle amples [kg/m.sup.3] [kg/m.sup.3] factor [?m] [?m] [?m] [?] V1 460 570 1.24 38.76 65.24 107.31 52.7 B2 440 568 1.29 41.6 67.7 109.2 n.d.* n.d.*: not determined

(28) Laser Sintering Experiments

(29) The sinter powders (SP) were introduced with a layer thickness of 0.1 mm into the build space at the temperature specified in table 6. The sinter powders were subsequently exposed to a laser with the laser power output specified in table 6 and the scan spacing specified, with a speed of the laser over the sample during exposure of 15 m/sec. Scan spacing is also known as laser spacing or lane spacing. Selective laser sintering typically involves scanning in stripes. The scan spacing gives the distance between the centers of the stripes, i.e. between the two centers of the laser beam for two stripes. The laser sintering experiments were effected on Farsoon HT251.

(30) TABLE-US-00006 TABLE 6 Powder bed Powder bed Laser power Laser Point temperature temperature output speed spacing Example [? C.] [? C.] [W] [m/s] [mm] V1 201 190 25 5 0.2 B2 206 180 55 15 0.18

(31) 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 hours under reduced pressure. The results are shown in table 7. Charpy specimens were also produced, which were likewise tested in dry form (to ISO 179-2/1eA (F): 1997+Amd. 1: 2011 and ISO 179-2/1eU: 1997+Amd. 1: 2011).

(32) Tensile strength, tensile modulus of elasticity and elongation at break were determined according to ISO 527-2:2012.

(33) 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.

(34) The results can be seen in table 7.

(35) TABLE-US-00007 TABLE 7 Charpy Charpy Tensile Elon- impact impact modulus gation Ex- resistance, resistance, Tensile of at HDT HDT am- unnotched notched strength elasticity break A B ple [kJ/m.sup.2] [kJ/m.sup.2] [MPa] [MPa] [%] [? C.] [? C.] V1 7 2.4 57.3 3425 1.81 94 179 B2 n.d.* n.d.* 59.7 3686 1.79 n.d.* n.d.* n.d.*: not determined

(36) The sinter powders of the invention show good SLS processibility and low warpage.

(37) After heated storage under air at 160? C., tensile strength, tensile modulus of elasticity and elongation at break to ISO 527-2: 2012 were determined once again after 1000 hours.

(38) The results can be seen in table 8.

(39) TABLE-US-00008 TABLE 8 Tensile Tensile modulus of strength elasticity Elongation at Example [MPa] [MPa] break [%] V1 9.5 3690 0.25 B2 15.6 3880 0.4 n.d.*: not determined

(40) The inventive sinter specimen according to B2, after heated storage, shows distinctly higher tensile strength (factor 1.6) and elongation at break (likewise factor 1.6) than the sinter specimen from comparative example V1.