SELECTIVE SINTERING OF POLYMER-BASED COMPOSITE MATERIALS

Abstract

Powder mixture for the use as building material for manufacturing a three-dimensional object by solidifying the building material layer by layer at the positions corresponding to the cross-section of the three-dimensional object in the respective layer, in particular by exposure to radiation, wherein the powder mixture comprises a first powder and a second powder, wherein the first powder comprises powder particles of a first thermoplastic polymer material and a reinforcement material, wherein the reinforcement material is at least partially embedded in the powder particles of the first powder and/or adhered to the surface of the powder particles of the first powder, wherein the second powder comprises powder particles of a second thermoplastic polymer material which is the same as or different from the first thermoplastic polymer material, wherein the powder particles of the second powder do not comprise the reinforcement material or comprise it only in an amount of at most 50% by weight relative to the amount of the reinforcement material in or on the powder particles of the first powder.

Claims

1. Powder mixture for the use as building material for manufacturing a three-dimensional object by solidifying building material layer by layer at the positions corresponding to a cross-section of the three-dimensional object in the respective layer by exposure to radiation, wherein the powder mixture comprises: a first powder and a second powder, wherein the first powder comprises powder particles of a first thermoplastic polymer material and a reinforcement material, wherein the reinforcement material is at least partially embedded in the powder particles of the first powder and/or adhered to the surface of the powder particles of the first powder, wherein the second powder comprises powder particles of a second thermoplastic polymer material which is the same as or different from the first thermoplastic polymer material, wherein the powder particles of the second powder do not comprise the reinforcement material or comprise it only in an amount of at most 50% by weight relative to the amount of the reinforcement material in or on the powder particles of the first powder, and wherein the powder mixture has a bulk density of 0.35 to 0.70 g/cm.sup.3.

2. Powder mixture according to claim 1, wherein the powder mixture is characterized by a lowest possible building temperature in a predefined process for manufacturing a three-dimensional object by solidifying a pulverulent building material layer by layer at the positions corresponding to the cross-section of the three-dimensional object in the respective layer by exposure to radiation, which is lower than the lowest possible building temperature of the first powder alone.

3. Powder mixture according to claim 1, wherein the powder mixture is characterised by a process window which is equal to or larger than the process window of the first powder alone, wherein the process window is defined as the difference between the highest possible building temperature and the lowest possible building temperature in a predefined process for manufacturing a three-dimensional object by solidifying a pulverulent building material layer by layer at the positions corresponding to the cross-section of the three-dimensional object in the respective layer by exposure to radiation.

4. Powder mixture according to claim 1, wherein the thermoplastic polymer material of the first powder and/or the thermoplastic polymer material of the second powder is a polymer material selected from the group consisting of homopolymers, copolymers and polyblends, wherein the thermoplastic polymer material of the first powder and/or the thermoplastic polymer material of the second powder comprises a polymer selected from the group consisting of polyetherimides, polycarbonates, polyarylene sulfides, polyarylether sulfones, polyphenylene oxides, polyether sulfones, acrylonitrile-butadiene-styrene copolymers, acrylonitrile-styrene-acrylate copolymers (ASA), polyvinyl chloride, polyacrylates, polyesters, polyamides, polyaryletherketones, polyethers, polyurethanes, polyimides, polyamideimides, polysiloxanes, polyolefins and copolymers which have at least two different repeating units of the aforementioned polymers, as well as polymer blends thereof, more preferably a polymer of the class of polyaryletherketones, polyphenylene sulfides, polycarbonates, polyetherimides, polypropylene, polyethylene and polyamides and copolymers and polymer blends thereof.

5. Powder mixture according to claim 1, wherein the reinforcement material is substantially completely embedded in the grain of the powder particles of the first powder.

6. Powder mixture according to claim 1, wherein the reinforcement material is selected from the group consisting of: (a) the reinforcement material comprises or consists of fibres, wherein the fibres are selected from the group consisting of carbon fibres, organic fibres, inorganic fibres, and combinations thereof; (b) the reinforcement material comprises or consists of nanotubes; (c) the reinforcement material comprises or consists of graphite nanoplatelets and/or fullerenes; (d) the reinforcement material comprises or consists of platelet-shaped reinforcement materials; (e) the reinforcement material comprises or consists of spherical fillers or irregularly shaped low aspect ratio fillers, selected from inorganic and mineral fillers, ceramic particles, aluminium oxide, zirconium oxide, silicon dioxide, zirconium (IV) oxide, titanium (IV) oxide, aluminium titanate, barium titanate, silicon carbide (SiC) and boron carbide (B4C), metals, dye pigments, carbon black, organic fillers; (f) the reinforcement material comprises or consists of flame retardants.

7. Powder mixture according to claim 1, wherein the mean particle size d.sub.50 of the powder particles of the first and/or the second powder is at least 20 μm.

8. Powder mixture according to claim 1, wherein the amount of the second powder is at least 1% by volume in each case based on the total volume of the powder mixture.

9. Powder mixture according to claim 1, having at least one of the properties (i) to (iv): (i) the bulk density is 0.4 to 0.65 g/cm.sup.3; (ii) the BET surface is <10 m.sup.2/g; (iii) the MVR value of the second powder is 0.1 to 10 times the value of the first powder; (iv) the melting point and/or the extrapolated initial temperature (T.sub.ei,m) of the second powder lower or higher by at most 30° C.

10. Method of preparing a powder mixture for the use as building material for manufacturing a three-dimensional object by solidifying the building material layer by layer at the positions corresponding to the cross-section of the three-dimensional object in the respective layer, wherein the first powder and the second powder are as defined as in claim 1 and are mixed together in a desired mixing ratio by dry mixing.

11. Method of preparing a polymer powder for the use as building material for manufacturing a three-dimensional object by solidifying the building material layer by layer at the positions corresponding to the cross-section of the three-dimensional object in the respective layer, wherein the preparation of the polymer powder includes the steps of melting a polymer material and compounding/incorporating at least one reinforcement material into the melt, then either still during this step of compounding/incorporating or after compounding/incorporating, spinning the melt containing the reinforcement material, and then granulating or cutting the fibres containing the reinforcement material.

12. Method according to claim 11, wherein the polymer material comprises a polymer selected from the group consisting of polyetherimides, polycarbonates, polyarylene sulfides, polyarylether sulfones, polyphenylene oxides, polyether sulfones, acrylonitrile-butadiene-styrene copolymers, acrylonitrile-styrene-acrylate copolymers (ASA), polyvinyl chloride, polyacrylates, polyesters, polyamides, polyaryletherketones, polyethers, polyurethanes, polyimides, polyamideimides, polysiloxanes, polyolefins and copolymers which have at least two different repeating units of the aforementioned polymers, as well as polymer blends thereof.

13. Polymer powder comprising reinforcement material, obtainable by the method according to claim 11.

14. Method of manufacturing a three-dimensional object comprising: providing, as building material, the powder mixture according to claim 1 or the polymer powder comprising reinforcement material according to claim 13; and solidifying the building material layer by layer at positions corresponding to the cross-section of the three-dimensional object in the respective layer.

15. Three-dimensional object that has been manufactured by solidifying a pulverulent building material layer by layer at the positions corresponding to the cross-section of the three-dimensional object in the respective layer, wherein the three-dimensional object comprises a reinforcement material that is heterogeneously distributed in at least an inner part or in the entire inner part of the three-dimensional object, and/or wherein the microstructure of the reinforcement material results from using the polymer powder comprising the reinforcement material according to claim 13.

16. Method for enhancing the refreshment rate, or for improving the warpage, and/or for improving the mechanical properties of a three-dimensional object, the method comprising providing, as building material, the powder mixture according to claim 1, solidifying the building material layer by layer at the positions corresponding to the cross-section of the three-dimensional object in the respective layer, wherein at least one of the following modifications (i) to (viii) are obtained in the three-dimensional object: (i) compared to an object manufactured using only the second powder as the building material, the modulus of elasticity is higher; (ii) compared to an object which has been manufactured only from the first powder as building material, the modulus of elasticity is lower by at most 25%; (iii) compared to an object manufactured only from the first powder as building material, the refreshment factor is higher; (iv) compared to an object manufactured only from the first powder as building material, the preferential direction of the reinforcement material is lower and/or the isotropy in the xyz-direction is higher; (v) compared to an object manufactured using only the first powder as building material, the porosity is lower; (vi) compared to an object manufactured only from the second powder as building material, the ultimate tensile strength (UTS) is higher; (vii) compared to an object manufactured only from the first powder as building material, the ultimate tensile strength (UTS) is lower by at most 15%; (viii) compared to an object manufactured only from the first powder as building material, the elongation at break is higher.

17. Powder mixture according to claim 4, wherein the thermoplastic polymer material of the first powder and/or the thermoplastic polymer material of the second powder comprises a polyetherketoneketone (PEKK), a polyamide 11 (PA 11), a polyamide 12 (PA 12) or a polyamide 6 (PA 6).

18. Method of preparing a powder mixture according to claim 10, wherein the first powder and/or the second powder is/are produced according to any of the methods (i) to (vii): (i) by grinding; (ii) by melt spraying; (iii) by precipitation from solvents; (iv) by melt compounding and melt dispersion; (v) by melt compounding and by fibre spinning and fibre cutting, wherein after spinning the fibres are stretched to increase the crystalline amount; (vi) by coating the polymer onto the filler, or the filler onto the polymer by a mechanical or thermomechanical treatment; or (vii) by coating the polymer onto the filler, or the filler onto the polymer by spray coating with solvent or spray drying.

19. Method according to claim 11 wherein, further comprising subjecting the fibres to a rounding treatment.

20. Method according to claim 11, wherein the polymer material is polyaryletherketone (PAEK).

21. Method according to claim 11, wherein the polymer is selected from the group consisting of polyetheretherketone (PEEK), polyetherketoneketone (PEKK), polyetherketone (PEK), polyetheretherketoneketone (PEEKK), polyetherketoneetherketoneketone (PEKEKK), polyetheretheretherketone (PEEEK), polyetheretherketone-polyetherdiphenyletherketone (PEEK-PEDEK) and copolymers including at least one of the aforementioned polymers.

Description

EXAMPLES

[0261] In the following examples, contents are given in percent by volume unless otherwise stated.

Example 1

[0262] First Powder (PEKK-CF 1—Powder with Reinforcement Material)

[0263] Composite powder of 23 wt % carbon fibre filled PEKK copolymer with repeating units 60% terephthaloyl group and 40% isophtaloyl group (HT23; Advanced Laser Materials, Temple, Tex., USA). The mean fibre diameter is 7 μm. The fibres are essentially completely coated by the polymer matrix. The powder is characterised by a melt volume-flow rate (MVR) of 46.8 cm.sup.3/10 min and T.sub.ei,m at 268.0° C. The bulk density is 0.54 g/cm.sup.3, the particle size distribution is characterised by (D.sub.10/D.sub.50/D.sub.90): 45.9 μm/84.2 μm/113.1 μm.

Second Powder (K6003-2, -3, -4—Powder without Reinforcement Material)

[0264] Coarse powder of PEKK copolymer with repeating units 60% terephthaloyl group and 40% isophtaloyl group (Kepstan 6003PF, Arkema, France) is comminuted by grinding on an impact mill at room temperature and classified to the appropriate particle size using an air-floating classifier. The powder is then treated by thermomechanical treatment at 165° C. for 15 minutes in a commercial high-speed mixer. In a circulating air oven with nitrogen atmosphere (type Nabertherm N250/A) the powder is tempered at 250° C. (K6003-2), 262° C. (K6003-3) or 270° C. (K6003-4) for 3 hours. For this purpose, in each oven batch, 7 kg of the powder are layered in aluminium trays with a maximum height of 4 cm and annealed for 4 hours. The heating time to the annealing temperature is 2 hours. The powder is sieved with a tumbler sieve machine (Perflux 501, sieve disc mesh size: 150 μm, Siebtechnik GmbH, Mühlheim, Germany) to break up or remove agglomerates.

[0265] The powders are characterised as shown in Table 1 below.

TABLE-US-00002 TABLE 1 Powder characteristics of K6003. MVR: melt volume-flow rate; T.sub.ei, m: extrapolated initial temperature; PSD: particle size distribution. oven MVR bulk PSD temperature [cm.sup.3/ T.sub.ei, m density (D.sub.10/D.sub.50/D.sub.90) Designation [° C.] 10 min] [° C.] [g/cm.sup.3] [μm] K6003-2 250° C. 75.9 256.3 0.38 34.0/66.5/123.1 K6003-3 262° C. 76.3 267.1 0.38 35.5/64.9/109.8 K6003-4 270° C. 76.3 272.6 0.38 33.8/62.5/100.6

Composite Blend Powder (Powder Mixtures)

[0266] In a commercial concrete mixer, the first and second powders are dry-mixed for 20 minutes according to the contents given in Table 2 below.

TABLE-US-00003 TABLE 2 Powder characteristics of the powder mixtures of Example 1. second percentage first powder of the MVR bulk PSD powder (not second M % [cm.sup.3/ T.sub.ei, m density (D.sub.10/D.sub.50/D.sub.90) (reinforced) reinforced) powder CF 10 min] [° C.] [g/cm.sup.3] [μm] PEKK-CF 1 K6003-2 10 21.4 49.6 255.8 0.54 44.3/83.2/114.4 PEKK-CF 1 K6003-2 20 19.9 50.9 255.3 0.51 42.5/81.5/114.5 PEKK-CF 1 K6003-2 30 18.3 53.4 256.3 0.50 41.3/78.7/114.3 PEKK-CF 1 K6003-3 10 21.4 50.8 265.1 0.54 43.5/82.4/113.5 PEKK-CF 1 K6003-3 20 19.8 51.2 265.7 0.52 42.3/80.6/112.2 PEKK-CF 1 K6003-3 30 18.3 54.5 265.6 0.51 41.5/79.6/113.9 PEKK-CF 1 K6003-4 20 19.8 51.6 269.1 0.53 42.8/80.9/113.3 PEKK-CF 1 K6003-4 30 18.3 54.1 270.2 0.51 40.6/79.3/111.8

Results

[0267] The exchangeable frame temperature and the building platform temperature was 265° C. for all examples. The mechanical data and relevant temperatures are summarised in Table 3 below.

TABLE-US-00004 TABLE 3 Mechanical data and relevant temperatures for Example 1. second percentage modulus first powder of the tensile of elongation powder (not second NCT UBT strength elasticity at break T.sub.PC (reinforced) reinforced) powder [° C.] [° C.] [MPa] [GPa] [%] [° C.] PEKK-CF 1 — 0 281 295 92.7 6.9 1.5 285 — K6003-2 100 269 277 68.3 4.4 1.6 277 — K6003-3 100 276 285 — — — — — K6003-4 100 281 289 — — — — PEKK-CF 1 K6003-2 10 265 287 91.5 6.6 1.5 285 PEKK-CF 1 K6003-2 20 265 286 87.6 6.5 1.5 285 PEKK-CF 1 K6003-2 30 265 285 89.3 6.1 1.6 285 PEKK-CF 1 K6003-3 10 273 294 90.5 6.5 1.5 285 PEKK-CF 1 K6003-3 20 270 291 88.6 6.1 1.5 285 PEKK-CF 1 K6003-3 30 270 291 91.6 6.1 1.6 285 PEKK-CF 1 K6003-4 20 276 290 90.0 6.1 1.5 285 PEKK-CF 1 K6003-4 30 276 294 86.3 6.5 1.5 285 NCT: Non-Curl Temperature; UBT: highest possible building temperature; T.sub.PC: Process Chamber Temperature. “—“ means “not determined”.

[0268] The specified data show that even a small addition of 10% by volume of unreinforced PEKK significantly increases the possible process window (difference between the lowest possible building temperature (non-curl temperature=NCT) and the highest possible building temperature (upper building temperature=UBT)). While the process window for PEKK-CF 1 is 14° C. and for unreinforced PEKK (K6003-2, -3, -4) it is 7-9° C., it increases to values between 14° C. and 21° C. for all mixtures. In particular, the lowest possible building temperature is significantly reduced compared to PEKK-CF 1, which allows the powder mixture to be processed at lower temperatures and thus slows down powder ageing. This results in a smaller change in viscosity and thus a better refreshment factor.

[0269] This increase of the process window and thus the process stability is accompanied by an almost constant tensile strength with respect to PEKK-CF 1 and a significant increase of the tensile strength compared to the unreinforced component.

[0270] The use of the different unreinforced powders shows that the increase in the process window is not exclusively due to the reduced (K6003-2) extrapolated initial temperature of the melting peak (T.sub.ei,m) compared to the reinforced powder, as the reduction in NCT can also be observed for unreinforced PEKK variants that have a T.sub.ei,m similar to (K6003-3) or higher than (K 6003-4) compared to the reinforced powder (PEKK-CF 1). If T.sub.ei,m of the second unreinforced PEKK powder is lower (K6003-2; 256.3° C.) or approximately the same (K6003-3; 267.1° C.) compared to that of the first reinforced powder PEKK-CF1 (268° C.), then the process window of the powder mixture (difference UBT-NCT) is the largest at 21° C., while it is higher at a higher T.sub.ei,m (K6003-4; 272.6° C.) is somewhat smaller at about 14° C., but still larger than that of the K6003-4 as the sole component being 8° C.

Example 2

First Powder (PEKK-CF 2)

[0271] Composite powder of 27 wt. % carbon fibre-filled PEKK copolymer (with repeating units 60% terephthaloyl group and 40% isophtaloyl group) prepared analogously to HT23 (ALM, Temple, Tex., USA). The powder is characterised by an MVR of 14.8 cm.sup.3/10 min and T.sub.ei,m at 268.2° C. The bulk density is 0.60 g/cm.sup.3, the particle size distribution is characterised by (D10/D50/D90): 429 μm/85.9 μm/124.5 μm.

Second Powder (K6003-2)

[0272] Analogous to Example 1

Composite Blend Powder (Powder Mixtures)

[0273] Preparation analogous to Example 1; the mixture conditions and the characterisation of the powder mixtures are specified in Table 4 below.

TABLE-US-00005 TABLE 4 Powder characteristics of the powder mixtures of Example 2. second percentage first powder of the MVR bulk PSD powder (not second M % [cm.sup.3/ T.sub.ei, m density (D.sub.10/D.sub.50/D.sub.90) (reinforced) reinforced) powder CF 10 min] [° C.] [g/cm.sup.3] [μm] PEKK-CF 2 K6003-2 10 25.3 17.0 254.6 0.57 42.5/85.7/125.8 PEKK-CF 2 K6003-2 20 23.6 21.5 254.7 0.56 42.8/84.4/127.9 PEKK-CF 2 K6003-2 24 22.9 21.1 255.5 0.53 41.8/85.2/126.4 PEKK-CF 2 K6003-2 30 21.9 21.5 255.5 0.52 41.4/84.7/130.9 PEKK-CF 2 K6003-2 40 20.2 24.8 255.7 0.50 40.2/81.6/126.6 PEKK-CF 2 K6003-2 50 18.5 29.7 255.7 0.48 40.3/80.1/125.9

Results

[0274] The exchangeable frame temperature and the building platform temperature was 265° C. for all examples. The mechanical data and relevant temperatures are summarised in Table 5 below.

TABLE-US-00006 TABLE 5 Mechanical data and relevant temperatures for Example 2. second percentage modulus first powder of the tensile of elongation powder (not second strength elasticity at break T.sub.PC (reinforced) reinforced) powder [MPa] [GPa] [%] [° C.] PEKK-CF 2 — 0 87.3 6.3 1.6 286 — K6003-2 100 68.3 4.4 1.6 277 PEKK-CF 2 K6003-2 10 81.6 5.8 1.6 286 PEKK-CF 2 K6003-2 20 83.7 5.8 1.6 286 PEKK-CF 2 K6003-2 24 84.9 5.9 1.6 286 PEKK-CF 2 K6003-2 30 84.6 5.7 1.7 286 PEKK-CF 2 K6003-2 40 79.5 5.8 1.5 286 PEKK-CF 2 K6003-2 50 79.0 5.3 1.6 286

[0275] The data from table 5 show that up to a volume fraction of 30-40% of the unreinforced powder, the tensile strength as well as the modulus of elasticity drop by a comparable value of 2.7%-8.9% (tensile strength) and 6.3%-9.5% (modulus of elasticity), respectively, and are thus still clearly above the mechanical values of the unreinforced powder. The elongation at break of the very brittle material, on the other hand, does not change.

[0276] Example 2 involves a mixture with 24% by volume of unreinforced powder. This mixture corresponds to a powder with a carbon fibre content of 23 wt. % corresponding to the reinforced powder of Example 1. This comparison shows that an object with similar properties can be produced from the powder mixture according to the invention as from pure reinforced powder PEKK-CF 1. The general drop in mechanical properties compared to PEKK-CF 1 is due to the lower level of the starting material PEKK-CF 2.

Example 3

First Powder (PEKK-CF 3)

[0277] Composite powder of 23 wt. % carbon fibre-filled PEKK copolymer (with repeating units 60% terephthaloyl group and 40% isophtaloyl group) comprising fibres of a mean fibre diameter of 5 μm, prepared analogously to HT23 (ALM, Temple, Tex., USA). The powder is characterised by an MVR of 41.8 cm.sup.3/10 min and T.sub.ei,m at 267.8° C. The bulk density is 0.55 g/cm.sup.3, the particle size distribution is characterised by (D10/D50/D90): 42.2 μm/87.0 μm/125.0 μm.

Second Powder (K6003-1)

[0278] Analogous to Example 1, K6003-2. The powder was tempered at 250° C. for 4 hours, but it has a higher viscosity (MVR=50.1 cm.sup.3/10 min) and a T.sub.ei,m at 245.8° C.

Composite Blend Powder (Powder Mixtures)

[0279] Analogous to Example 1; the mixture conditions and the characterisation of the powder mixtures are specified in Table 6 below.

TABLE-US-00007 TABLE 6 Powder characteristics of the powder mixtures of Example 3. second percentage first powder of the MVR bulk PSD powder (not second M % [cm.sup.3/ T.sub.ei, m density (D.sub.10/D.sub.50/D.sub.90) (reinforced) reinforced) powder CF 10 min] [° C.] [g/cm.sup.3] [μm] PEKK-CF 3 K6003-1 10 21.5 41.5 245.1 0.54 40.3/85.0/120.6 PEKK-CF 3 K6003-1 20 20.0 43.4 244.2 0.52 38.6/82.1/120.6 PEKK-CF 3 K6003-1 30 18.5 45.5 245.3 0.50 34.6/77.6/120.2

Results

[0280] The results are shown in Table 7.

TABLE-US-00008 TABLE 7 Mechanical data and relevant temperatures for Example 3. second percentage modulus first powder of the tensile of elongation powder (not second NCT strength elasticity at break T.sub.PC (reinforced) reinforced) powder [° C.] [MPa] [GPa] [%] [° C.] PEKK-CF 3 — 0 290 75.3 7.5 — 290 — K6003-1 100 276 70-75 4.0 — 281 PEKK-CF 3 K6003-1 10 284 67.4 6.8 1.0 286 PEKK-CF 3 K6003-1 20 277 69.6 6.7 1.1 286 PEKK-CF 3 K6003-1 30 274 77.4 6.9 1.0 286

[0281] The results show that the process-stabilising effect of the powder mixture occurs independently of the fibre diameter of the carbon fibres used in the reinforced powder. Also in this example, the tensile strength drops only slightly compared to the pure first powder (reinforced), the NCT of the powder mixture, on the other hand, can even be reduced below the respective NCT of the two individual components at a content of the second powder (unreinforced) of 30 vol. %. Due to the therefore lower possible building temperature, a more process-stable building is possible. Furthermore, the recyclability of the powder is improved, as the ageing of the powder is slowed down at lower temperatures.

Example 4

First Powder (PEKK-CF 2)

[0282] Analogous to Example 2.

Second Powder (K6003-1)

[0283] Analogous to Example 3.

Composite Blend Powder (Powder Mixtures)

[0284] Analogous to Example 1. The mixture consists of 76% of the first powder component PEKK-CF 2 and 24% of the second, not reinforced powder component K6003-1. The bulk density is at 0.54 g/cm.sup.3, the particle size distribution is characterised by (D.sub.10/D.sub.50/D.sub.90): 39.7 μm/86.1 μm/127.2 μm.

Results

[0285] Both building jobs took place at a process chamber temperature of 286° C. and an exchangeable frame or building platform temperature of 260° C. 25 solid cuboids with the dimensions 20 mm×4 mm×13.56 mm are built distributed over the reduced building area of the EOS P800. The results are shown in FIG. 5. While 15 of the 25 cuboids built with the pure, reinforced powder PEKK-CF 2 (right) show sink marks, the cuboids built with the powder mixture according to the invention with 24 vol. % K6003-1 (left) show no sink marks. This example illustrates the slowed powder ageing of the powder mixture according to the invention. The tests indicate that better refreshing is possible.

Example 5

First Powder (HP11-30)

[0286] Composite powder of 30 wt. % carbon fibre-filled polyamide 11 (HP11-30; Advanced Laser Materials, Temple, Tex., USA). The mean fibre diameter is 7 μm. The fibres are essentially entirely coated by the polymer matrix.

Second Powder (PA11 D80)

[0287] Polyamide 11 powder (Rilsan d80, Arkema, France).

Composite Blend Powder (Powder Mixtures)

[0288] In a commercial concrete mixer, the first and second powder components are dry-mixed for 20 minutes according to the contents given in Table 8.

TABLE-US-00009 TABLE 8 Powder characteristics of the powder mixtures of Example 5. second percentage first powder of the MVR bulk PSD powder (not second M % [cm.sup.3/ T.sub.ei, m density (D.sub.10/D.sub.50/D.sub.90) (reinforced) reinforced) powder CF 10 min] [° C.] [g/cm.sup.3] [μm] HP11-30 — 0 30.0 80.9 166.9 0.41 40.4/80.4/118.8 — PA11 D80 100 0.0 52.6 177.5 0.48 58.5/104.3/156.3 HP11-30 PA11 D80 10 26.6 76.4 167.4 0.42 41.0/80.8/118.7 HP11-30 PA11 D80 20 23.2 63.7 170.5 0.42 41.6/84.9/134.3 HP11-30 PA11 D80 30 20.0 57.1 169.0 0.42 44.4/87.2/139.8 HP11-30 PA11 D80 50 13.8 42.2 177.8 0.43 48.0/90.0/143.3

Results

[0289] The process chamber temperature was 184° C. for all experiments, the temperature of the unloading chamber was 160° C. The results are summarised in Table 9.

TABLE-US-00010 TABLE 9 Mechanical data and relevant temperatures. second percentage modulus first powder of the tensile of elongation powder (not second NCT UBT strength elasticity at break (reinforced) reinforced) powder [° C.] [° C.] [MPa] [GPa] [%] HP11-30 — 0 182 185 56.3 2.7 9.6 — PA11 D80 100 179 188 52.1 1.5 41.0 HP11-30 PA11 D80 10 177 185 56.9 2.6 15.4 HP11-30 PA11 D80 20 176 185 56.4 2.5 16.8 HP11-30 PA11 D80 30 176 185 56.2 2.4 18.0 HP11-30 PA11 D80 50 176 185 54.6 2.1 34.2

[0290] In this example, a polyamide-11 was used as the base material that contains 30 wt. % carbon fibres in the reinforced variant. Comparable to Example 3, it can also be observed here that the NCT can be lowered below the respective NCT of the individual powders when adding unreinforced PA11 (PA11 D80), while maintaining approximately the same upper building temperature (UBT). This lowering of the NCT extends the process window by 5-6° C. and enables a more process-stable building process. Up to a content of 30% by volume of the unreinforced powder, the tensile strength of the manufactured test specimens remains approximately the same as that of the pure reinforced powder (HP11-30). The modulus of elasticity is only slightly reduced in this range by 3.7%-11.1% and still remains approx. 60% above the modulus of elasticity of the pure unreinforced powder (PA11 D80). With similar mechanical properties, the elongation at break in the range up to 30% by volume of the unreinforced powder is about 60%-88% above the elongation at break of the pure reinforced powder. Thus, the components exhibit significantly higher toughness than the pure reinforced powder (HP11-30).

[0291] Table 10 lists values for building and cooling warpage.

TABLE-US-00011 TABLE 10 Cooling and building warpage in Example 5. second percentage first powder of the building powder (not second warpage warpage (reinforced) reinforced) powder [curvature = κ] [%] HP11-30 — 0 2.96 8.8 — PA11 D80 100 HP11-30 PA11 D80 10 1.50 2.8 HP11-30 PA11 D80 20 1.22 1.7 HP11-30 PA11 D80 30 1.06 0.6 HP11-30 PA11 D80 50 0.18 0.5

[0292] This illustrates that pure HP11-30 exhibits significant warpage, which, however, decreases significantly with increasing content of PA11 D80 without significantly reducing tensile strength and modulus of elasticity. In particular, high building warpage leads to very unstable building processes, as exposed components can be pulled out by the recoating unit during powder application, similar to curl. It is striking how strongly the so-called cooling warpage (column 4, warpage [κ]) is reduced.

[0293] Laser-sintered components are often characterised by high crystallinity, which leads to comparatively brittle components with low elongation at break (compared to components from injection moulding). It can be seen that the elongation at break improves considerably compared to components made from the pure reinforced component even with a small admixture of unreinforced powder, but the resistance to fracture remains more or less the same. This means that the relationship between modulus of elasticity and elongation at break can be adjusted to suit the specific application.

[0294] In summary, Example 5 shows that the powder mixture according to the invention can be used to produce an object that may exhibit a higher elongation at break and thus a higher ductility with comparable tensile strength and only a slightly reduced modulus of elasticity. At the same time, the powder mixture exhibits a significantly reduced tendency to warp and, together with the reduced lower building temperature, a substantially higher process stability.

[0295] It follows from examples 1 to 5 that the powder mixture according to the invention can be used to manufacture objects whose mechanical properties drop only slightly compared to objects made of pure reinforced powder (pure composite), and in some cases even have a higher elongation at break, but the building process can be carried out at lower temperatures and with increased process stability.

[0296] Another advantage of composite blend powders is an improvement in the refreshment factor compared to pure composite powders: Fibre-reinforced composite powders in which the filler is present in the powder grain due to the manufacturing process (produced by e.g. melt compounding with grinding, melt spraying, precipitation from solvent) have the advantage that there is a significantly reduced preferential direction of the fibres in the recoating direction during the recoating process. This results in components with significantly more isotropic component properties (especially in the modulus of elasticity) in the xyz direction than is the case with dry blends of fibre and thermoplastic powder. The disadvantage of fibre-in-grain composites, however, is that the melt viscosity and surface tension of the powder grain is significantly higher, resulting in a qualitatively poorer and rougher melt film when melted by the irradiation unit. Dry mixing the composite powder with an unreinforced PEKK, which preferably has a lower melt viscosity than the PEKK-CF (higher MVR value), results in improved melt film formation. This, together with the possibility to build at lower temperatures, leads to an improvement of the refreshment factor of the composite blend compared to the pure composite and to an improved economic efficiency. This is shown by example 4 of a PEKK with 27% carbon fibre content. While components (density cubes) of the pure composite show PEKK sink marks, the components of the composite blend powder with 24% PEKK content show no sink marks.

[0297] Furthermore, the reduced crystallisation tendency of the composite blend powder may lead to a reduced warpage of the built objects. As a result, the composite blend can be used at a lower exchangeable frame temperature and/or process chamber temperature than the pure composite. This leads to a reduced ageing of the powder in the process and to an improved refreshment rate.