POLYMER-BASED BUILD MATERIAL FOR SELECTIVE SINTERING

Abstract

Plastic powder for use as a building material for manufacturing a three-dimensional object by layer-by-layer melting and solidification by hardening of the building material at the positions corresponding to the cross-section of the three-dimensional object in the respective layer by exposure to radiation, preferably by exposure to NIR radiation, wherein the plastic powder comprises a dry blend of polymer-based particles and particles of a NIR absorber, wherein the NIR absorber comprises carbon black or is carbon black and wherein the weight percentage of carbon black in the total weight of polymer and carbon black particles is in the range of at least 0.02% and at most 0.45%, and/or wherein the carbon black has a mean primary particle diameter in the range of from 15 nm to 70 nm, preferably of at least 26 nm and/or at most 58 nm.

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 by exposure to NIR radiation, wherein the plastic powder comprises a dry mixture of polymer-based particles and particles of a NIR absorber, wherein the NIR absorber comprises carbon black, and wherein the weight percentage of the NIR absorber in the total weight of the plastic powder is in the range of 0.02% and 0.45%.

2. The plastic powder according to claim 1, wherein the weight percentage of the NIR absorber in the total weight of the plastic powder is at least 0.07% and/or at most 0.15%.

3. The plastic powder according to claim 1, wherein the plastic powder comprises a dry mixture of polymer-based particles and particles of a NIR-absorber and the NIR-absorber comprises carbon black, wherein the carbon black has an average primary particle diameter in the range of from 15 nm to 70 nm.

4. The plastic powder according to claim 1, wherein in the CIE L*a*b* colour model the lightness value (L* value) of the plastic powder, measured spectrophotometrically, is at most 75.00.

5. The plastic powder according to claim 1, wherein the plastic powder comprises reflection particles having a surface which at least partially reflects the NIR radiation.

6. The plastic powder according to claim 1, wherein the carbon black has at least one of the following properties: (i) it is amorphous industrial carbon black (definition according to EC number 215-609-9, CAS number 1333-86-4); (ii) the C content is more than 96% in quantitative elemental analysis.

7. The plastic powder according to claim 1, wherein in the powder analysis of the plastic powder by means of a rheometer at aeration 1.0 mm/s, the power consumption is at most 200 mJ.

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), polyarylether sulfone (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 said polymers or copolymers.

9. A method of preparation of a plastic powder according to claim 1, wherein the preparation comprises at least the following steps: (i) providing the polymer-based particles and the particles of the NIR absorber; and (ii) dry mixing at least the polymer-based particles and the particles of the NIR absorber, wherein the NIR absorber comprises carbon black, and wherein the weight percentage of the NIR absorber in the total weight of the plastic powder is in the range of 0.02% and 0.45%.

10. The method of preparation of a plastic powder according to claim 9, wherein the mixing of the polymer-based particles and the particles of the NIR absorber is carried out in one process step.

11. The method of preparation of a plastic powder according to claim 9, wherein the polymer-based particles are provided together with the reflective particles, which are dry-mixed with the particles of the NIR absorber.

12. The method of preparation of a plastic powder according to claim 9, wherein the plastic powder is provided without additional flow aids.

13. A three-dimensional object which has been manufactured 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, wherein a plastic powder according to claim 1 has been used as the building material.

14. 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, wherein a plastic powder according to claim 1 is used as the building material, and wherein the building material is selectively solidified by exposure to electromagnetic radiation emitted by a radiation source.

15. 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 radiation, wherein the system comprises at least one radiation source adapted to emit electromagnetic radiation specifically in a wavelength or wavelength range located in the NIR, a process chamber designed as an open container with a container wall, a support located in the process chamber, wherein the process chamber and the support are movable relative to one another in the vertical direction, a storage container and a recoater movable in the horizontal direction, wherein the storage container is at least partially filled with a plastic powder according to claim 1 as building material.

16. The method according to claim 14, wherein the electromagnetic radiation is specifically emitted in the NIR range within a window of at most 50 nm, and/or wherein the radiation source emits electromagnetic radiation in the range from 500 nm to 1500 nm.

17. The method according to claim 14, wherein the radiation source comprises at least one laser diode.

18. The method according to claim 14, wherein the radiation source emits electromagnetic radiation at a wavelength selected from the group consisting of 980±7 nm, 940±7 nm, 810±7 nm and 640±7 nm.

19. The system according to claim 15, wherein the electromagnetic radiation is specifically emitted in the NIR range within a window of at most 50 nm and/or wherein the radiation source emits electromagnetic radiation in the range from 500 nm to 1500 nm.

20. The system according to claim 15, wherein the radiation source comprises at least one laser diode.

Description

[0082] FIG. 1 shows by way of example a conventional laser sintering device for the layer-by-layer manufacture of a three-dimensional object.

[0083] FIG. 2 shows a three-dimensional object according to the invention (right component) compared to a three-dimensional object according to a preferred embodiment of the invention (left component). The plastic powder from which the left-hand component was built contained titanium dioxide.

[0084] FIG. 3 shows a light microscopic magnification of the component surface of the components of FIG. 2. A: left component of FIG. 2; B: right component of FIG. 2.

[0085] The following methods are indeed suitable for determining certain properties of the objects according to the invention and were used in the experiments described below. They represent preferred methods for characterising certain properties of the articles according to the invention.

[0086] Tensile strength, Young's modulus, and elongation at break were determined in accordance with EN ISO 527, using test specimens of type 1BB. The conditioning state has relevant influences on the measurement results of the mechanical properties such as tensile strength, Young's modulus, and elongation at break. The mechanical properties of the test specimens were determined in dry condition, wherein the test took place a maximum of 3 hours after unpacking of the components. According to ISO 291, a temperature of (23±2) ° C. and a relative humidity of (50±10) % is used as preferred test climate for the determination of the mechanical properties. This test climate should be maintained when determining the mechanical properties. According to EN ISO 527-1, the test speeds should be agreed between the interested parties. A test speed of 50 mm/s was used.

[0087] The determination of the process reliability was based on the following criteria: [0088] Fluidisability of the powder according to the invention is necessary in the recoating unit so that sufficient powder can be applied to the entire build area. [0089] A uniformly dense coating of the area without zones with visibly lower bulk density, regardless of whether there is powder or a previously melted building material under the coated powder layer. [0090] Stable coating behaviour over the duration of an entire construction job over several hours. A build job refers to the building of a job, wherein a job is the assembly of positioned and parameterised three-dimensional objects in the software. [0091] A sufficiently large temperature window to tolerate inhomogeneity of the temperature distribution in the build area.

[0092] The following examples are for illustrative purposes and are not to be understood as restrictive. They define further preferred embodiments of the invention.

EXAMPLES

Example 1: Mechanical Properties in Dependence on the Concentration of Carbon Black

[0093] In this experiment, the mechanical properties of test specimens were investigated for which the building material, i.e. plastic powder, differed in the proportion by weight of carbon black in the total weight of the mixture of carbon black and polymer-based material. In this example, the carbon black was Monarch® 570 and the polymer-based material was PA 2201 from EOS GmbH.

[0094] For this purpose, homogeneous mixtures were first prepared by physically mixing polymer-based particles and carbon black particles in the mixing ratio given in Table 1 and then used as building material in a selective laser sintering process on two different test facilities.

[0095] 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 the company 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. Subsequently, the mechanical properties were determined according to the described procedures.

[0096] The mechanical properties were determined as described below. The test method and the component dimensions of the test specimens are specified in the EN ISO 527 standard for the tensile testing. The materials testing machine TC-FR005TN.A50, dossier no.: 605922 from the company Zwick with the software TestExpert II V3.6 is suitable for this purpose. In the standardised tensile test, test results such as Young's modulus [MPa] and tensile strength [MPa] were determined.

[0097] The results are presented in the following Table 1.

TABLE-US-00001 TABLE 1 Determination of the mechanical properties: Tensile strength Young's modulus Elongation at break [MPa] [MPa] [%] Concentration (building direction (building direction (building direction carbon black ZYX building direction ZYX according to ZYX according to [wt. %] ISO ASTM 52921) ISO ASTM 52921) ISO ASTM 52921) 0.030 23.0 1100 2.3 0.050 38.3 1724 3.04 0.060 41.4 1743 3.23 0.075 46.7 1892 3.45 0.090 49.1 1659 4.21

[0098] In the test series, it has been shown that the use of a mixture of a dry blend with approximately 0.04 to 0.45 wt. % carbon black provides surprisingly better overall results compared to blends with other carbon black contents.

[0099] At lower concentrations the mechanical properties (tensile strength, Young's modulus, elongation at break) are lower, at higher concentrations the process becomes more unstable (smaller temperature window/smaller processing range).

Example 2: Improvement of Mechanical Properties Compared to Compounds Manufactured with a Multi-Stage Mixing Process

[0100] In this experiment, the mechanical properties of a three-dimensional object according to the invention were compared with a three-dimensional object for the manufacture of which a mixture of 75 wt. % “PA 2200” and 25 wt. % “PA 2202 black” was used, two commercially available building materials based on the polymer type PA 12, wherein PA 2202 black contains carbon black. The building material according to the invention contained 0.09 wt. % carbon black (in this case Monarch® 570) mixed with plastic particles (in this case polyamide type PA 12 with the trade name PA 2201 from EOS GmbH).

[0101] The test specimens were manufactured and tested according to Example 1. The results are shown in Tab. 2 below.

TABLE-US-00002 TABLE 2 Comparison of the mechanical properties of a three-dimensional object according to the invention and a three-dimensional object made of a multi-stage mixed building material. Tensile strength Young's modulus Elongation at break [MPa] [MPa] [%] (building direction (building direction (building direction XZY according to XZY according to XZY according to Test material ISO ASTM 52921) ISO ASTM 52921) ISO ASTM 52921) PA 2201 + 48.76 1731 15.02 Monarch ® 570 PA 2200 + 47.18 1604 12.72 PA 2202 black Tensile strength Young's modulus Elongation at break [MPa] [MPa] [%] (building direction (building direction (building direction ZYX according to ZYX according to ZYX according to Test material ISO ASTM 52921) ISO ASTM 52921) ISO ASTM 52921) PA 2201 + 46.38 1726 5.47 Monarch ® 570 PA 2200 + 39.31 1665 3.21 PA 2202 black

[0102] In the test series, it has been shown that the use of a blend of PA with Monarch® 570 is significantly more process reliable and leads to improved mechanical properties than the use of a blend of PA 2200 and PA 2202 black.

Example 3: Process Reliability as a Function of the Primary Particle Diameter of Carbon Black

[0103] Blends of polymer-based powder and different carbon black types were prepared. The proportion of the carbon black types in the total weight of the mixture was 0.09 percent by weight in each case. The polymer-based particles were identical in all mixtures and in this case were made of polyamide 12 with the trade name PA 2201 from EOS GmbH. Various commercial products containing industrial carbon black were used as carbon black types. These differed in the following properties, among others: primary particle size, BET surface area according to EN ISO 60, oil absorption number, pH value, manufacturing method, and ash content.

[0104] The mixtures were homogeneously mixed and used as building material in a laser sintering process. The process reliability was determined and the results presented in Tab. 4 below.

TABLE-US-00003 TABLE 3 Reliability of the laser sintering process when processing mixtures of polymer-based powder and different types of carbon black. Primary particle diameter [nm] (Data provided by the Mean primary supplier, not determined particle diameter Commercial name in accordance with the Process (values measured according of carbon black standard.) reliability to ASTM D3849) Monarch ® 570 21 very good (46 ± 12) nm +++ (44 ± 14) nm Mogul L 24 very good +++ Spezialschwarz 4 25 very good (42 ± 13) nm +++ (37 ± 10) nm Printex ® XE-2B 30 very good +++ Printex ® 200 47 good ++ Printex ® G 51 poor −− Flammruß 101 95 poor −− Arosperse 15 280 very poor −−−

[0105] Compared to other types of carbon black, which differ significantly from the particle size of approx. 15 to 50 nm, a significantly improved process stability can be seen, which was characterised in particular by better fluidisability of the plastic powder, constant coating behaviour, and better coating quality.

Example 4: Mechanical Properties Depending on the Type of Carbon Black Used

[0106] In this experiment, the mechanical properties of test specimens manufactured according to Example 1 were investigated. The mechanical properties were determined as described in Example 1. The results are shown in the following tables 4 and 5.

TABLE-US-00004 TABLE 4 Determination of the mechanical properties in the XZY direction of three-dimensional objects made from compounds of PA 2201 from EOS GmbH and different types of carbon black. Tensile strength Young's modulus Elongation at break [MPa] [MPa] [%] (building direction (building direction (building direction Commercial name XZY according to XZY according to XZY according to of carbon black ISO ASTM 52921) ISO ASTM 52921) ISO ASTM 52921) Monarch ® 570 48.76 1731 15.02 Mogul L 46.60 1614 17.19 Spezialschwarz 4 48.06 1652 12.68

TABLE-US-00005 TABLE 5 Determination of the mechanical properties in the ZYX direction of three-dimensional objects made from PA 2201 blends and various carbon black types. Tensile strength Young's modulus Elongation at break [MPa] [MPa] [%] (building direction (building direction (building direction Commercial name ZYX according to ZYX according to ZYX according to of carbon black ISO ASTM 52921) ISO ASTM 52921) ISO ASTM 52921) Monarch ® 570 46.38 1726 5.47 Mogul L 41.58 1722 4.24 Spezialschwarz 4 47.01 1847 5.18

[0107] In the test series, it was shown that in the compounds with the highest process reliability, the use of a mixture of PA 2201 with Monarch® 570 at the same concentration leads to an even better component quality (mechanical properties: tensile strength, Young's modulus, elongation at break) than the use of other carbon black types. Components made from compounds with Spezialschwarz 4 were also good in terms of mechanical properties (tensile strength, Young's modulus, elongation at break), but had inferior surfaces.

[0108] The determination of the primary particle diameters according to TEM examination in accordance with ASTM D3849 showed (46±12) nm and (44±14) nm for Monarch® 570 and (42±13) nm, (37±10) nm for Spezialschwarz 4.

Example 5: TiO.SUB.2.-Additivated Plastic Particles in a Dry Blend with Carbon Black

[0109] In this experiment, the optical properties of test specimens were compared, both of which were manufactured from plastic powder according to the invention (VESTOSINT® 1125 white). The plastic powders differed in that one contained titanium dioxide (VESTOSINT® 1125 white) while the other was free of titanium dioxide (PA 2201). The titanium dioxide content is believed to be around 1 wt. %.

[0110] The results are shown in FIGS. 2 and 3.

[0111] In FIGS. 2 and 3 it can be seen that when using the natural-coloured plastic PA 2201 (i.e. without titanium dioxide) in a mixture with carbon black, an inhomogeneous colour impression is obtained in the objects processed from it. The components appear “blotchy” (FIG. 2, component on the right; FIG. 3B). In experiments with VESTOSINT® 1125 white, in contrast, which contains the white pigment TiO.sub.2, it was possible to manufacture components with an even appearance, an extremely homogeneous shade and colour uniformity (FIG. 2, component on the left, FIG. 3A).