WARPAGE-OPTIMIZED POLYMER POWDER

Abstract

Plastic powder for use as building material for additively manufacturing a three-dimensional object by selectively solidifying the building material 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 plastic powder comprises a mixture of polymer-based particles and particles of a particulate additive and wherein the particulate additive is selected such that the crystallization point of the mixture of the polymer-based particles and the particulate additive is substantially not increased compared to the crystallization point of a mixture of the polymer-based particles without the particulate additive.

Claims

1. A plastic powder for use as a building material for additively manufacturing a three-dimensional object by selectively solidifying the building material at the positions corresponding to the cross-section of the three-dimensional object in the respective layer, wherein the plastic powder comprises a mixture of polymer-based particles and particles of a particulate additive, and wherein the particulate additive is selected such that the crystallisation point of the mixture of the polymer-based particles and the particulate additive is substantially not increased compared to the crystallisation point of a mixture of the polymer-based particles without the particulate additive.

2. The plastic powder of claim 1, wherein the particulate additive comprises a particulate carbon material.

3. The plastic powder according to claim 1, wherein the particulate additive has an average primary particle diameter in the nm range.

4. The plastic powder according to claim 1, wherein the particulate additive comprises a gas black which has an average primary particle diameter in the range of 15-70 nm.

5. The plastic powder according to claim 1, wherein the particulate additive comprises a particulate NIR absorber.

6. The plastic powder according to claim 1, which is in the form of a dry mixture of the polymer particles with the particulate additive.

7. The plastic powder according to claim 1, wherein the weight percentage of the particulate additive to the total weight of polymer particles and particulate additive is from 0.01% to 5%.

8. The plastic powder according to claim 1, wherein the polymer-based particles comprise as polymer material at least one polymer selected from at least one polyaryletherketone (PAEK), polyarylethersulfone (PAES), polyamide, polyester, polyether, polylactide, polyolefin, polystyrene, polyphenylene sulfide, polyvinylidene fluoride, polyphenylene oxide, polyimide, polyetherimide, polycarbonate, and/or at least one copolymer which includes at least one of the preceding polymers or their monomer units and/or at least one polymer blend comprising at least one of the mentioned polymers or copolymers.

9. A method of preparing a plastic powder according to claim 1 which is suitable for use in a method for the additive manufacturing of a three-dimensional object by selective solidification of a pulverulent building material at the positions corresponding to the cross-section of the three-dimensional object in the respective layer, wherein the preparation comprises at least the following steps: (i) providing the polymer-based particles, (ii) providing the particles of particulate additive, and till) dry mixing at least the polymer-based particles and the particles of particulate additive, wherein the particulate additive is selected such that the crystallisation point of the mixture of the polymer-based particles and the particulate additive is substantially not increased compared to the crystallisation point of a mixture of the polymer-based particles without the particulate additive.

10. A three-dimensional object which has been manufactured by selective solidification of a pulverulent building material based on polymer-based particles and a particulate additive at the positions corresponding to the cross-section of the three-dimensional object in the respective layer, wherein the three-dimensional object has one or both of the following features: (a) microscopically observable crystalline regions in the form of spherulites with a spherulite size of at least 20 μm, (b) a distortion Δ(h.sub.centre−h.sub.left)+Δ(h.sub.centre−h.sub.right) of at most 0.50 mm.

11. The three-dimensional object according to claim 10, having a distortion Δ(h.sub.centre−h.sub.left)+Δ(h.sub.centre−h.sub.right) of ≤0.25 mm.

12. The three-dimensional object according to claim 10, made from a plastic powder for use as a building material for additive manufacture, wherein the plastic powder comprises a mixture of polymer-based particles and particles of a particulate additive, and wherein the particulate additive is selected such that the crystallisation point of the mixture of the polymer-based particles and the particulate additive is substantially not increased compared to the crystallisation point of a mixture of the polymer-based particles without the particulate additive.

13. A system for manufacturing three-dimensional objects by selectively solidifying a pulverulent building material at the positions corresponding to the cross-section of the three-dimensional object in the respective layer by exposure to a radiation, wherein the system comprises at least one radiation source, a process chamber which is formed as an open container with a container wall, a support arranged in the process chamber, wherein the process chamber and the support are movable relative to one another in a vertical direction, a storage container, and a recoater which is movable in a horizontal direction, wherein the storage container is at least partially filled with a plastic powder according to claim 1 as a building material.

14. The system according to claim 13, wherein the radiation source is adapted to emit electromagnetic radiation specifically in a wavelength or wavelength range located in the NIR.

15. The system according to claim 13, wherein the radiation source emits electromagnetic radiation in the range from 500 nm to 1500 nm.

16. The system according to claim 13, wherein the radiation source emits electromagnetic radiation at the wavelengths selected from the group consisting of (980±10) nm, (940±10) nm, (810±10) nm and (640±10) nm.

17. A method for manufacturing a three-dimensional object by selectively solidifying a pulverulent building material at the positions corresponding to the cross-section of the three-dimensional object in the respective layer by exposure to radiation, the method comprising at least the following steps: providing a plastic powder for use as the building material, which plastic powder comprises a mixture of polymer-based particles and particles of a particulate additive, and selectively solidifying the building material by exposure to electromagnetic radiation emitted by a radiation source, wherein the crystallisation point of the mixture of the polymer-based particles and the particulate additive is substantially not increased compared to the crystallisation point of the polymer-based particles alone.

18. The method according to claim 17, wherein the radiation source is adapted to emit electromagnetic radiation specifically in a wavelength or wavelength range located in the NIR.

19. The method according to claim 17, wherein the radiation source emits electromagnetic radiation in the range from 500 nm to 1500 nm.

20. The method according to claim 17, wherein the radiation source emits electromagnetic radiation at the wavelengths selected from the group consisting of (980±10) nm, (940±10) nm, (810±10) nm and (640±10) nm.

Description

[0080] FIG. 1 shows by way of example a conventional laser sintering device for the layer-by-layer manufacture of a three-dimensional object.

[0081] FIG. 2 shows a magnified image of a cooled melt of PA 12. Large spherulites are visible.

[0082] FIG. 3 shows a magnified image of a cooled melt of a mixture of PA 12 and industrial carbon black using the example of Monarch® 570. Many small spherulites are visible.

[0083] FIG. 4 shows DSC iso-curves and conversions of mixtures of polymer particles and different types of carbon black.

[0084] FIG. 5 shows values for t.sub.peak [min] and t.sub.1/2 [min] and α [%] conversion determined from the DSC iso-curves and conversions of FIG. 4.

[0085] FIG. 6 shows a magnified image of a cooled melt of PA 12. Large spherulites are visible.

[0086] FIG. 7 shows a magnified image of a cooled melt of a mixture of PA 12 and industrial carbon black using Monarch® 570 as an example. Many small spherulites are visible.

[0087] FIG. 8 shows an enlarged image of a cooled melt of a mixture of PA 12 and gas black using the example of Spezialschwarz 4. The size of the spherulites is comparable to that of the melt in FIGS. 2 and 7.

[0088] The following examples are for illustrative purposes and are not to be understood as restrictive. They define further preferred embodiments of the invention.

EXAMPLES

Embodiment 1

[0089] Mixtures of polymer-based particles and different types of particulate additives were prepared. Various types of particulate carbon material were tested as particulate additives, wherein corresponding tests can equally be carried out with other particulate additives. The polymer-based particles were identical in all blends and, as a representative example, were made of PA 2201. They exhibited high sphericity and had a d50 value of 50-62 μm. PA 2201 was used as an example for polymer-based particles based on PA12.

[0090] Various commercial products containing industrial carbon black or graphite were used as types of particulate carbon material. The following types were used: [0091] Gas black: Spezialschwarz 4, Spezialschwarz 5, Spezialschwarz 6. [0092] Lamp black: Flammrufβ 101, Monarch 570, Mogul L, Printex 200, Printex G, Printex XE-2B; Ensaco 150 P, Arosperse 15 [0093] Graphite: Timrex SFG 6 Graphite

[0094] The different manufacturing methods result in significantly different particle size distributions (PSD). Lamp black has a wide PSD and gas black a narrow PSD. Gas blacks usually have oxidised surfaces.

[0095] The mixtures were homogeneously mixed by means of a container mixer of the company Mixaco CM150-D with standard blade design: 1 bottom scraper and 1 dispersion blade (blade with a diameter of 400 mm) with a two-stage mixing with 2 min at 516 rpm and 4 min at 1000 rpm and then subjected to a DSC measurement. The DSC measurement was carried out according to the ISO 11357 standard using a Mettler Toledo DSC 823.

[0096] The crystallisation temperature was then determined. The results are shown in Table 1 below.

TABLE-US-00001 TABLE 1 Crystallisation temperatures of mixtures of polymer particles and different types of particulate carbon material. Differential Scanning Calorimetry (DSC), 20K/min 1st cooling crystallisation temperature Composition/ onset extrapolated peak details of components [° C.] [° C.] PA 2201 + 0.09 wt. % 150.71 145.27 Monarch ® 570 151.02 145.43 PA 2201 + 0.09 wt. % 148.24 144.18 Mogul L 148.31 144.02 PA 2201 + 0.09 wt. % 143.77 139.59 Spezialschwarz 4 144.03 139.85 PA 2201 + 0.09 wt. % 150.81 145.33 Printex 200 150.53 145.08 PA 2201 + 0.09 wt. % 150.40 145.20 Printex G 150.12 144.89 PA 2201 + 0.09 wt. % 150.39 144.80 FlammruB 101 150.34 144.77 PA 2201 + 0.09 wt. % 150.85 145.16 Ensaco 150 P 151.10 145.27 PA 2201 + 0.09 wt. % 150.67 145.21 Timrex SFG 6 Graphite 150.52 145.36 PA 2201 + 0.09 wt. % — 146.73 Printex XE-2B — 146.53 PA 2201 + 0.09 wt. % — 139.26 Arosperse 15 — 139.03

[0097] The results showed that the mixture containing gas black had the lowest crystallisation temperature of the test series. Since the mixtures differed only in the type of particulate carbon material, it follows that gas black resulted in the lowest increase in crystallisation temperature.

Embodiment 2

[0098] Mixtures of polymer particles and different types of carbon black were prepared. The polymer particles were identical to the particles used in embodiment 1. Various commercial products containing industrial carbon black were used as carbon black types. These differed in particular in their particle size distribution.

[0099] The mixtures were homogeneously mixed and subjected to a DSC measurement as described in Example 1. The crystallisation temperature was then determined. The results are shown in Table 2 below.

TABLE-US-00002 TABLE 2 Crystallisation temperatures of mixtures of polymer particles and different types of carbon black. Differential Scanning Calorimetry (DSC), 10K/min 1st cooling 2nd cooling crystallisation crystallisation temperature temperature extrapo- extrapo- Composition/ onset lated peak Onset lated peak details of components [° C.] [° C.] [° C.] [° C.] PA 2200 148.87 144.43 147.24 142.51 148.84 144.40 147.27 142.54 PA 2200 + 0.09 wt. % 154.54 150.56 153.04 149.27 Monarch ® 570 154.29 150.52 152.88 149.23 154.62 150.58 153.09 149.30 PA 2200 + 0.09 wt. % 148.90 145.30 147.38 143.64 Spezialschwarz 4 148.89 145.27 147.42 143.64 148.22 144.91 146.80 143.33 148.30 145.04 146.82 143.41 148.05 144.81 146.55 143.12 148.10 144.89 146.60 143.18 148.25 144.88 146.65 143.16 148.11 144.88 146.80 143.20 PA 2200 + 0.09 wt. % 147.67 143.46 — — Spezialschwarz 5 147.49 143.33 — — 147.62 143.50 — — PA 2200 + 0.09 wt. % 147.67 143.91 — — Spezialschwarz 6 148.01 144.21 — — 147.99 144.16 — —

[0100] The results show that the mixtures containing gas black had the lowest crystallisation temperature of the test series. This confirms for other gas black types that gas black leads to the lowest increase in crystallisation temperature.

Embodiment 3

[0101] Selected mixtures of the above embodiments were used as building material in a selective laser sintering method.

[0102] In an experiment not described in detail here, it was confirmed that the building material according to the invention can in principle be used on a conventional laser sintering machine equipped with a CO.sub.2 laser source, such as an EOS P 396 from EOS Electro Optical Systems, with the standard settings described by the manufacturer. In the present experiment, a light source comprising NIR laser diodes was used instead of a CO.sub.2 laser. For further details on the hardware and suitable settings, reference is made to European patent application EP14824420.5, published as EP 3 079 912.

[0103] Subsequently, the distortion of the obtained components is determined. To quantify the distortion, a cuboid of dimensions 250 mm×6 mm×21 mm was built in the rear part of the construction space. The measure of manufacturing distortion (distortion during the manufacturing process) is the difference in the height of the cuboid between the measuring points at the edges and a measuring point in the middle (x=125 mm) of the cuboid in relation to the actual height of the cuboid in the middle as a percentage, wherein the height of the cuboid in the middle is usually greater than at the edges.

[0104] As a measure of the cooling distortion (distortion after the construction process not resulting in missing material in contrast to the manufacturing distortion), the curvature of the underside of the component is given at x=125 mm (centre of the component), wherein the shape of the curved underside is mathematically approximated with a parabola.

[0105] The following applies: f(x)=ax.sup.2, with a=0 for a non-warped component.

[0106] The curvature of a graph is defined as κ(x)=((∂.sup.2f(x))/∂x.sup.2)/[(1+(∂f(x)/∂x){circumflex over ( )}2)]{circumflex over ( )}(3/2).

[0107] Thus, at the centre of the component corresponding to the vertex of the parabola, κ(0)=2a.

[0108] The results are shown in Table 3 below.

TABLE-US-00003 TABLE 3 Distortion measurements on three-dimensional objects made from mixtures of embodiments 1 and 2. Distortion measurement on formed three- Composition/ dimensional objects: details of components Δ(h.sub.centre − h.sub.left) + Δ(h.sub.centre − h.sub.right) in [mm] PA 2201 + 0.09 wt. % 0.17 Spezialschwarz 4 PA 2201 + 0.09 wt. % 0.53 Printex XE-2B PA 2201 + 0.09 wt. % 0.56 Monarch ® 570

[0109] The evaluation of the distortion tests showed a significantly lower construction distortion for gas black than for the other types of carbon black tested. This confirms the assumption that the crystallisation temperature of industrial carbon black correlates with the distortion, i.e. the lower the crystallisation temperature, the lower the distortion.

Embodiment Example 4

[0110] In this example, light microscopic images were taken of cooled melt of PA 12 (here PA 2201). These images are shown in FIGS. 2 and 3. FIG. 2 shows a cooled melt of PA 12 with large spherulites. FIG. 3 shows a cooled melt of a mixture of PA 12 and industrial carbon black using the example of Monarch® 570. This type of carbon black acts as a nucleating agent and leads to many small spherulites during crystallisation. Not shown is a cooled melt of a mixture of PA 12 and gas black using the example of Spezialschwarz 4. This type of black does not act as a nucleating agent and does not significantly change the size of the spherulites during crystallisation.

[0111] Further results of such experiments are shown in FIGS. 6 to 8.

Embodiment 5

[0112] In this example, mixtures of polymer particles and different types of carbon black were prepared. The polymer particles were identical to those used in Embodiment 4. The carbon black types differed by the manufacturing method and therefore in their particle size distribution (PSD). As a further comparison, a mixture containing no carbon black type was investigated.

[0113] DSC iso-curves and conversions of the blends were recorded and shown as examples in FIG. 4. From these, t.sub.peak [min] and t.sub.1/2 [min] and α [%] conversion were determined. t.sub.peak refers to the time of the highest crystallisation rate. t.sub.1/2 refers to the time until half of the total crystallisation has been achieved. These values are presented in Table 4 below and in FIG. 5.

[0114] The different crystallisation kinetics of gas black (here: Spezialschwarz 4) become visible via the DSC iso-curves and the crystallisation conversion curves determined therefrom.

TABLE-US-00004 TABLE 4 Composition/ Sample details of components T [° C.] t.sub.peak t.sub.1/2 T [° C.] t.sub.peak[min] t.sub.1/2 236 PA 2200 160 10.6 13.4 162 27.5 31.7 237 PA 2200 + 0.09 wt. % 3.0 4.4 8.3 11.2 Monarch ® 570 238 PA 2200 + 0.09 wt. % — — 30.0 33.1 Spezialschwarz 4 239 PA 2200 + 0.09 wt. % 13.9 16.2 32.8 36.9 Spezialschwarz 4 240 PA 2200 + 0.09 wt. % 13.6 16.3 39.3 39.9 Spezialschwarz 4 241 PA 2200 + 0.09 wt. % 13.9 16.3 39.2 41.4 Spezialschwarz 4 242 PA 2202 black — — 14.4 18.2 243 PA 2200 + 0.09 wt. % — — 7.3 10.2 Monarch ® 570 244 PA 2200 + 0.09 wt. % — — 7.5 10.0 Monarch ® 570 245 PA 2200 + 0.09 wt. % 3.1 4.4 7.5 11.0 Monarch ® 570 246 PA 2200 + 0.09 wt. % 3.1 4.7 7.1 9.9 Monarch ® 570 249 PA 2200 + 0.09 wt. % 5.7 8.5 14.6 17.8 Mogul L 250 PA 2200 + 0.09 wt. % 6.0 9.0 16.3 20.1 Mogul L