METHOD FOR PRODUCING AN ADDITIVELY MANUFACTURED AND TREATED OBJECT

Abstract

The invention relates to a method for producing a treated object, comprising the steps: a) producing an object by means of additive manufacturing, the object being produced by the repeated arrangement, layer by layer, of at least one first material on a substrate spatially selectively in accordance with a cross-section of the object, the method comprising the additional method step: b) at least partially bringing the object, which is still on the substrate or has already been detached from the substrate and which has been produced by additive manufacturing, into contact with a liquid heated to ≥T or a powder bed of a second material heated to ≥T for a time ≥1 minute in order to obtain the treated object, T standing for a temperature of ≥25° C. The invention further relates to an object produced by a method of this type.

Claims

1. A method of producing a treated article, comprising: a) creating an article by additive manufacturing, wherein the article is created by arranging at least one first material on a substrate repeatedly in layers and in a spatially selective manner corresponding to a cross section of the article; and b) at least partly contacting the article created by additive manufacturing with a second material heated to ≥T for a period of ≥1 min in order to obtain the treated article, wherein the second material is a heated liquid or a heated powder bed, and wherein T is a temperature of ≥25° C.

2. The method as claimed in claim 1, further comprising one or more of the following: A) detaching the article created by additive manufacturing from the substrate before method step b); B) at least partly removing unreacted first material from the additively manufactured article before method step b); C) post-curing the article created by additive manufacturing in method step a) by means of actinic radiation; D) cooling the heated liquid or the heated powder bed to a temperature in a region of <200° C. before removal of the treated article after method step b); E) at least partly mechanically removing the second material from the article during or after method step b); or F) washing off the second material after method step b) with a solvent for a period of ≤30 min after removal of the article from the liquid or the powder, where the solvent is not a solvent or co-reactant for the first material at a temperature in a region of T ≤200° C.

3. The method as claimed in claim 1, wherein the additive manufacturing method is selected from the group consisting of high-speed sintering, selective laser melting, selective laser sintering, selective heat sintering, binder jetting, electron beam melting, fused deposition modeling, fused filament fabrication, build-up welding, friction stir welding, wax deposition modeling, contour crafting, metal powder application methods, cold gas spraying, stereolithography, 3D screen printing methods, light-scattered electrophoretic deposition, printing of highly metal powder-filled thermoplastics by a fused deposition modeling method, nanoscale metal powder by an inkjet method, direct light processing, ink-jetting, and continuous light interface processing.

4. The method as claimed in claim 1, wherein, during the contacting of the article with the liquid or the powder bed in method step b), the liquid or the powder bed is put at least intermittently under a pressure within a range from ≥1 bar to ≤1000 bar.

5. The method as claimed in claim 1, wherein, during the contacting of the article with the liquid or the powder bed in method step b), the liquid or the powder bed is put at least intermittently under a pressure within a range from ≥0.01 bar to ≤1 bar.

6. The method as claimed in claim 1, wherein, during the contacting of the article with the liquid or the powder bed in method step b), the second material in the form of the powder bed or of the liquid is flooded at least intermittently with an inert gas.

7. The method as claimed in claim 1, wherein the second material is water-soluble.

8. The method as claimed in claim 1, wherein the second material is soluble in an acid, a base, or an organic solvent.

9. The method as claimed in claim 1, wherein the second material is a powder bed consisting of comprising silicon dioxide, polytetrafluoroethylene, aluminum oxide, metals, a metal salts, a sugars, an organic salts, polyethylene wax, polyester, polyacrylic acid, polyethylene oxide, polyoxymethylene, polycarbonate, or mixtures thereof.

10. The method as claimed in claim 1, wherein the temperature T is on average ≤95% of a breakdown temperature of the first material.

11. The method as claimed in claim 1, wherein the temperature T is within a range from ≥40° C. to ≤2000° C.

12. The method as claimed in claim 1, wherein the temperature T is greater than a temperature 50° C. below a Vicat softening temperature of the first material, and the temperature T is less than a temperature 150° C. above the Vicat softening temperature of the first material, where the Vicat softening temperature can be ascertained according to DIN EN ISO 306:2014-03.

13. The method as claimed in claim 1, wherein the contacting of the article obtained with the powder bed in method step b) is conducted for a period within a range from ≥1 minute to ≤174 hours.

14. The method as claimed in claim 1, wherein the temperature T of the powder bed or of the liquid is altered in the course of method step b).

15. A treated article obtained by the method as claimed in claim 1.

16. The article as claimed in claim 15, wherein the treated article in a tensile test in accordance with DIN EN ISO 527-2:2012 has a tensile strength greater than a tensile strength of an untreated article before step b).

17. The article as claimed in claim 15, wherein a density of the treated article is greater than a density of an untreated article before step b).

18. The method as claimed in claim 1, wherein the second material is a liquid comprising a silicone oil, a paraffin oil, a fluorinated hydrocarbon, a polyethylene wax, saltwater, a metal melt, an ionic liquid, or a mixture thereof.

19. The method as claimed in claim 14, wherein the temperature curve comprises a temperature from −190° C. to +2000° C., and wherein the contacting of the article obtained with the powder bed in method step b) is performed for a period of ≥1 minute to ≤72 hours.

Description

EXAMPLES

[0149] Detailed hereinafter are various experiments in which an article created by an FDM or SLS method or DLP method as additive manufacturing method in method step a) and treated by method step b) is examined for its properties before and after method step b).

Test Methods:

[0150] Shore A: In accordance with DIN ISO 7619-1:2012-02, the test specimen thickness required was attained by multiple stacking of the test specimens obtained.

[0151] Tensile test: In accordance with DIN EN ISO 527-2:2012, the test specimens were not stored under standard climatic conditions for 24 hours before the measurement.

[0152] IR (ATR): Evaluation of the ratio of the maximum height of the isocyanate band in the wavenumber range from 2170 to 2380 to the maximum height of the CH stretch vibration in the wavenumber range from 2600 to 3200.

Equipment:

[0153] FDM printer: For the experiments, a Massportal Pharaoh XD 20 FDM/FFF 3D printer was used. This features a very substantially closed build space and a Bowden extruder.

[0154] SLS printer: For the experiments, a Farsoon FS251P 3D printer was used.

[0155] DLP printer: For the experiments, an Autodesk Ember 3D printer was used.

Starting Materials:

[0156] Silicone oil (silicone oil bath): Silotherm200 Infrasolv from LABC Labortechnik Zillger KG, colorless

[0157] Silicone oil (heat carrier oil) was sourced via specialist laboratory suppliers and used as sourced.

[0158] NaCl: edible salt with grain size from 0.1 to 0.9 mm.

[0159] Sand (filter sand): quartz sand with grain size from 0.4 to 0.8 mm.

Resin A:

[0160] 25 g of the reaction product of the 1,6-HDI trimer with hydroxyethyl acrylate and the following idealized structure:

##STR00001## [0161] 50 g of the polyurethane acrylate Ebecryl 4101 (sourced from Allnex SA) [0162] 25 g of butyl acrylate (sourced from Sigma Aldrich) [0163] 3 g of the photoinitiator Omnirad 1173 (sourced from IGM Resins) [0164] (alternatively when the Autodesk Ember 3D printer was used, 1.5 g of the photoinitiator Omnirad BL 750 from IGM Resins and 0.13 g of 2,5-bis(5-tert-butylbenzoxazol-2-yl)thiophene were used as free-radical scavenger in place of Omnirad 1137). [0165] 0.5 g of a catalyst complex consisting of: 55.6% by weight of Desmodur® N 3600 (Covestro Deutschland AG) and 44.4% by weight of Jeffcat® Z 110 (sourced from Huntsman Co). These resin A starting materials were combined in a Thinky ARE250 planetary mixer and mixed at a speed of 2000 revolutions per minute at room temperature for about 2 minutes.

[0166] Experiment 17: The free-radically curable resin A was drawn down onto a glass plate in 3 layers one on top of another with coating bars of different dimensions, hence simulating a 3D printing method in the manner of a DLP 3D printer. The glass plate had previously been treated with a 1% solution of soy lecithin in ethyl acetate and dried. The soy lecithin acted as a release agent to allow the cured films to be detached from the substrate again later. The dimensions were 400 μm, 300 μm and 200 μm. The respective layers applied were each cured in a Superfici UV curing unit with mercury and gallium radiation sources at a belt speed of 5 m/min. The lamp output and belt speed resulted in a radiation intensity of 1300 mJ/cm.sup.2 acting on the coated substrates. This resulted in a three-layer structure of around 900 μm in total. The cured films were carefully removed from the glass substrates in order to give test specimens for mechanical and IR spectroscopy characterization.

[0167] All infrared spectra were measured on a Bruker FT-IR spectrometer equipped with an ATR unit, unless stated otherwise.

[0168] For the relative measurement of the change in the free NCO groups on films, a Bruker FT-IR spectrometer (Tensor II) was used. The sample was contacted with the platinum ATR unit. The contact area of the sample was 2×2 mm. In the course of measurement, the IR radiation penetrated 3-4 μm into the sample according to wavenumber. An absorption spectrum was then obtained from the sample. In order to compensate for nonuniform contacting of the samples of different hardness, a baseline correction and a normalization in the wavenumber range of 2600-3200 (CH2, CH3) was performed on all spectra. The peak height of the “free” NCO group was determined in the wavenumber range of 2170-2380, and the ratio of the NCO signals to the highest peak was ascertained in the range of 2900-3200 (CH).

[0169] For the measurement of Shore A hardness to DIN ISO 7619-1:2012-02, individual layers of the film were combined to form a test specimen of height at least 6 mm and the hardness value was determined.

[0170] Experiment 18: The free-radically curable resin A was drawn down onto a glass plate as described in experiment 17, UV-cured and removed from the glass substrate. Subsequently, the self-supporting film was introduced vertically into a salt bed, such that it was completely surrounded by salt. Subsequently, it was stored under standard atmosphere in an oven at 185° C. for 1 hour. IR spectroscopy and hardness measurements were conducted on this post-cured film, as described in experiment 17.

[0171] Experiment 19*: The free-radically curable resin A was drawn down onto a glass plate as described in experiment 17, UV-cured and removed from the glass substrate. Subsequently, the self-supporting film was introduced into the oven vertically in a free-standing manner. Subsequently, it was stored under standard atmosphere in an oven at 185° C. for 1 hour. The film curved during the curing process to give a U, which was dimensionally stable after curing. IR spectroscopy and hardness measurements were conducted on this post-cured film, as described in experiment 17.

[0172] TPUs used in accordance with the invention were produced by two standard processing methods: the prepolymer method and the one-shot/static mixer method.

[0173] In the prepolymer method, the polyol or polyol mixture is preheated to 180 to 210° C., initially charged with a portion of the isocyanate, and converted at temperatures of 200 to 240° C. The speed of the twin-screw extruder used here is about 270 to 290 rpm. This preceding partial reaction affords a linear, slightly pre-extended prepolymer that reacts to completion with residual isocyanate and chain extender further down the extruder. This method is described by way of example in EP-A 747 409.

[0174] In the one-shot/static mixer method, all comonomers are homogenized by means of a static mixer or another suitable mixing device at high temperatures (above 250° C.) within a short time (below 20 s) and then reacted to completion and discharged by means of a twin-screw extruder at temperatures of 90 to 180° C. and a speed of 260-280 rpm. This method is described by way of example in application DE 19924089.

TPU A 1.75 mm Filament

[0175] The TPU (thermoplastic polyurethane) was prepared by the prepolymer method from 1 mol of polyether polyol (DuPont) having a number-average molecular weight of 1000 g/mol, based on polytetramethylene ether glycol, and 5.99 mol of butane-1,4-diol; 6.99 mol of technical grade diphenylmethane 4,4′-diisocyanate (MDI) with >98% by weight of 4,4′-MDI; 0.25% by weight of Irganox® 1010 (pentaerythritol tetrakis (3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) from BASF SE) and 0.3% by weight of Loxamid 3324.

[0176] The filaments were extruded from the granular material by the standard method, cooled down in a water bath, dried in a hot air zone and taken up using a winder. Before use in the 3D printer, the filaments were dried at 40° C. for 48 h.

[0177] TPU powder blend composed of the raw materials TPU 1/TPU 2: The powder blend was produced from the powders of TPU 1 and TPU 2 by weighing out the respective components. The two materials were mixed in a commercial TM5 Thermomix at setting 10 for 2*5 s.

Raw Material TPU 1

[0178] TPU (thermoplastic polyurethane) 1 was prepared from 1 mol of polyester diol (Covestro) having a number-average molecular weight of about 900 g/mol, based on about 56.7% by weight of adipic acid and about 43.3% by weight of butane-1,4-diol, and about 1.41 mol of butane-1,4-diol, about 0.21 mol of hexane-1,6-diol, about 1.62 mol of technical grade diphenylmethane 4,4′-diisocyanate (MDI) with >98% by weight of 4,4′-MDI, 0.05% by weight of Irganox® 1010 (pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) from BASF SE), 1.1% by weight of Licowax® E (montanic esters from Clariant) and 250 ppm of tin dioctoate.

Raw Material TPU 2

[0179] TPU (thermoplastic polyurethane) 2 was prepared from 1 mol of polyester diol (Covestro) having a number-average molecular weight of about 900 g/mol, based on about 56.7% by weight of adipic acid and about 43.3% by weight of butane-1,4-diol, and about 2.38 mol of butane-1,4-diol, about 0.22 mol of hexane-1,6-diol, about 2.6 mol of technical grade diphenylmethane 4,4′-diisocyanate (MDI) with >98% by weight of 4,4′-MDI, 0.05% by weight of Irganox® 1010 (pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) from BASF SE), 1.1% by weight of Licowax® E (montanic esters from Clariant) and 250 ppm of tin dioctoate.

[0180] 0.2% by weight, based on TPU, of hydrophobized fumed silica was added as flow agent (Aerosil® R972 from Evonik) to the TPUs prepared under Raw material TPU 1 and Raw material TPU 2, and the mixture was processed mechanically under cryogenic conditions (cryogenic comminution) in a pinned-disk mill to give powder and then classified by means of a sieving machine. 90% by weight of the composition had a particle diameter of less than 140 μm (measured by means of laser diffraction (HELOS particle size analysis)).

[0181] 1.75 mm filament PC1 based on Makrolon® XT5010, MVR (300° C./1.2 kg) 34 cm.sup.3/10 min: The filaments were extruded from the granular material by the standard method, cooled with air and taken up using a winder.

[0182] In step 1, by the FDM printing method (for conditions see table 3), the TPU A filaments and PC1 S2 were used to produce tensile specimens in the form according to ISO 527-2 2012.

[0183] Also produced in step 1 by the SLS printing method (for conditions see table 3), from the powder mixtures of raw material TPU 1 and raw material TPU 2 S2, were tensile specimens according to ISO 527-2 2012.

[0184] Also produced in step 1 by the DLP printing method (for conditions see table 3) were S2 tensile specimens in the form according to ISO 527-2 2012.

[0185] In step 2, the tensile specimens obtained were subjected to thermal post-curing. Comparative experiments are identified by *; there is variation in the post-curing conditions, see table 4. Subsequent heat treatment was effected in an air circulation drying cabinet at the defined temperature, with horizontal positioning of the test specimens to be tested in the medium in a 250 ml aluminum dish, fully covered by the medium, and with heating of the drying cabinet from RT to the target temperature within 30 min. After attainment of the target temperature, the test specimen was heated at target temperature for the desired time. Thereafter, the aluminum dish was taken out of the drying cabinet while hot and cooled down to room temperature RT on a laboratory bench. After attainment of RT but no later than after 30 min, the samples were removed, dried and freed of the medium, for example by rinsing with water.

[0186] After the thermal post-curing, the tensile specimens obtained were analyzed further for mechanical and chemical composition; see table 5. Results of the comparative experiments are again identified by an *.

TABLE-US-00003 TABLE 3 Materials and methods conditions TPU blend TPU blend TPU 1/TPU 2 Material/SLS TPU 1/TPU 2 (50/50) (70/30) Build space temperature ° C. 80 80 Laser power [W] 48 48 Layer thickness [mm] 0.12 0.12 Number of exposures per layer 2 2 (fill scan count) Overlap of laser traces 0.15 0.15 (slicer fill scan spacing) [mm] Roller speed [mm/s] 180 180 Material/FDM TPU A PC1 Extruder temperature [° C.] 245 285 Build platform temperature [° C.] 60 100 Extrusion speed [mm/s] 40 40 Layer height [mm] 0.2 0.2 Nozzle size [mm] 0.4 0.4 Material/DLP Resin A Build space temperature [° C.] 23 Layer height [mm] 0.05 Exposure/layer [s] 1.7

[0187] In the FDM method, printing was effected without external layers (top solid layer/bottom solid layer). 2 outer tracks (perimeter) and an infill of 45° were used. All samples were printed in Z direction, i.e. vertically on the build platform.

[0188] The properties of the articles created after method step 1 are described in detail as comparative experiments in table 5 below.

TABLE-US-00004 TABLE 4 Post-sintering conditions Experiment Temperature Time Cooling time Medium (First material) [° C.] [min] to RT [min] (second material) TPU A  1* 23 — — —  2 180 60 30 Salt  3 190 60 30 Salt  4 200 60 30 Salt  5 210 60 30 Salt PC1  6* 23 — — —  7 190 60 30 Salt  8 180 60 30 Salt TPU blend TPU 1/TPU 2 (50/50)  9* 23 — — — 10 200 60 30 Silicone oil 11 200 60 30 Salt 12 200 60 30 Sand TPU blend TPU 1/TPU 2 (70/50)  13* 23 — — — 14 200 60 30 Silicone oil 15 200 60 30 Salt 16 200 60 30 Sand Resin A  17* 23 — — — 18 185 60 30 Salt Marked * means comparative experiment

TABLE-US-00005 TABLE 5 Properties after treatment Maximum Elongation at Shore A Tensile strength break ISO/CH band Experiment hardness [N/mm.sup.2] [%] ratio in IR TPU A  1* 2.8 1.4  2 8.8 8.6  3 8.6 12.7  4 9 9.1  5 11 6.2 PC1  6* 25 3  7 41 3.6  8 37 2.7 TPU blend TPU 1/TPU 2 (50/50)  9* 3.75 133.0 10 6.03 209.7 11 16.0 400.5 12 8.57 385.0 TPU blend TPU 1/TPU 2(70/30)  13* 3.48 118.0 14 5.56 168.9 15 17.2 386.6 16 11.2 441.2 Resin A 17* 70 1:1  18 90 1:10  19* 90 1:10 Marked * means comparative experiment

[0189] The comparison of the results for the method of the invention shows a distinct improvement in mechanical properties after thermal treatment according to the invention compared to non-heat-treated specimens. Moreover, heated storage in media having higher density than air achieved a distinct improvement in dimensional stability of the test specimens since these are less actively subjected to gravity. This is especially manifested when complex components having unsupported geometries as clearly apparent in the comparative example of experiment 19 are thermally post-cured. The unsupported geometries were deformed by gravity during the curing process and cure in this deformed shape.