Additive manufacturing method for making a three-dimensional object using selective laser sintering

Abstract

The present disclosure relates to an additive manufacturing (AM) method for making a three-dimensional (3D) object, comprising a) depositing successive layers of a powdered material (M), at least partially recycled, comprising at least one poly(ether ketone ketone) (PEKK), having a phosphorus content of more than 30 ppm, as measured by Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES), and b) selectively sintering each layer prior to deposition of the subsequent layer.

Claims

1. A method for manufacturing a three-dimensional (3D) object, comprising: a) depositing successive layers of a powdered material (M), at least partially recycled, comprising at least one a poly (ether ketone ketone) (PEKK), wherein the at least one PEKK has a phosphorus content of more than 30 ppm, which is obtained by a step of contacting a PEKK powder with a solution of alkali metal phosphate, this phosphorus content being measured by Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES), wherein the alkali metal phosphate is at least one of sodium dihydrogen phosphate (NaH.sub.2PO.sub.4), disodium hydrogen phosphate (Na.sub.2HPO.sub.4), potassium dihydrogen phosphate (KH.sub.2PO.sub.4), dipotassium hydrogen phosphate (K.sub.2HPO.sub.4) or mixtures thereof, and b) selectively sintering each of the successive layers prior to deposition of a subsequent successive layer, wherein the at least one PEKK is a polymer comprising at least 95 mol % of a first recurring unit (R.sup.M) and a second recurring unit (R.sup.P), respectively represented by formulae (M) and (P), the mol % being based on a total number of moles in the polymer: ##STR00005## wherein the at least one PEKK has a residual acidity 9 eq/g as measured by the Residual Acidity Test and a residual basicity 20 eq/g as measured by the Residual Basicity Test; and wherein the at least one PEKK is prepared by the synthesis method further comprising: i) polycondensing in a solvent, in the absence of a Lewis acid or in the presence of an amount of Lewis acid of less than 2 wt. %, based on the total weight of the monomers, the following monomers (POH), (M-OH), (PF) and/or (M-F): ##STR00006## wherein the molar ratio of moles of (POH) and (M-OH) to moles of (PF) and (M-F) is such that: $0.90\frac{n_{\left(P^{}-\mathrm{OH}\right)}+n_{\left(M^{}-\mathrm{OH}\right)}}{n_{\left(P^{}-F\right)}+n_{\left(M^{}-F\right)}}1.1,\mathrm{and}$ ii) extracting the solvent and salts, in order to obtain the PEKK powder.

2. The method of claim 1, wherein the at least one PEKK has a Td(1%) of at least 500 C., as measured by thermal gravimetric analysis according to ASTM D3850, heating from 30 C. to 800 C. under nitrogen using a heating rate of 10 C./min.

3. The method of claim 1, wherein the PEKK has a ratio of the second recurring unit over the first recurring unit (R.sup.P)/(R.sup.M) ranging from 50/50 to 70/30.

4. The method of claim 1, wherein the recycled powdered material (M) has a MFI90% wherein:
MFI=100(MFI.sub.r0MFI.sub.r1)/MFI.sub.r0 wherein: MFI is the Melt Flow Index as measured by ASTM D1238 at 340 C. with a 8.4 kg weight, MFI.sub.r0 is the MFI before a 744-hour exposure to a temperature of 260 C., MFI.sub.r1 is the MFI after a 744-hour exposure to a temperature of 260 C.

5. The method of claim 1, wherein the powdered material (M) has a d.sub.50-value from 30 to 80 m, as measured by laser scattering in isopropanol.

6. The method of claim 1, wherein the at least one PEKK is obtained by the synthesis method further comprising: iii) grinding the PEKK powder, and iv) exposing the ground PEKK powder to a temperature (Ta) ranging from a glass transition temperature (Tg) of the at least one PEKK to a melting temperature (Tm) of the at least one PEKK, both Tg and Tm being measured using differential scanning calorimetry (DSC) according to ASTM D3418.

7. The method of claim 1, wherein the powdered material (M) has a BET surface area ranging from 0.1 to 5 m.sup.2/g, as measured by ISO 9277, at a soak temperature of 25 C.

8. The method of claim 1, wherein the powdered material (M) has a bulk density pp of at least 0.30.

9. The method of claim 1, wherein the powdered material (M) is heated before step b) to a temperature Tp ( C.):
Tp<Tm5, wherein Tm ( C.) is a melting temperature of the at least one PEKK, as measured on the 1.sup.st heat scan by differential scanning calorimetry (DSC) according to ASTM D3418.

10. The method of claim 1, wherein the powdered material (M) comprises a ratio of recycled powder/unrecycled powder ranging from 50/50 to 100/0.

Description

EXAMPLES

(1) The disclosure will be now described in more detail with reference to the following examples, whose purpose is merely illustrative and not intended to limit the scope of the disclosure.

Examples

Example 1. Heat Aging of Several PEKK Polymers

(2) Raw Materials

(3) Kepstan 6002 PEKK was obtained from Arkema.

(4) Diphenyl sulfone (polymer grade) was procured from Proviron (99.8% pure).

(5) Sodium carbonate, light soda ash, was procured from Solvay S.A., France and dried before use. Its particle size was such that its d.sub.90 was 130 m.

(6) Potassium carbonate with a d.sub.90<45 m was procured from Armand products and dried before use.

(7) Lithium chloride (anhydrous powder) was procured from Acros.

(8) NaH.sub.2PO.sub.4.Math.2H.sub.2O and Na.sub.2HPO.sub.4 were purchased from Sigma-Aldrich.

(9) Cab-O-Sil M-5 commercially available from Cabot

(10) Preparation of Monomers

(11) 1,4-bis(4-fluorobenzoyl)benzene (1,4-DFDK) and 1,3 bis(4-fluorobenzoyl)benzene (1,3-DFDK) were prepared by Friedel-Crafts acylation of fluorobenzene according to Example 1 of U.S. Pat. No. 5,300,693 to Gilb et al. (filed Nov. 25, 1992 and incorporated herein by reference in its entirety). Some of the 1,4-DFDK was purified as described in U.S. Pat. No. 5,300,693 by recrystallization in chlorobenzene, and some of the 1,4-DFDK was purified by recrystallization in DMSO/ethanol. The 1,4-DFDK purified by recrystallization in DMSO/ethanol was used as the 1,4-DFDK in the polymerization reactions to make PEKK described below, while 1,4-DFDK recrystallized in chlorobenzene was used as precursor for 1,4-bis(4-hydroxybenzoyl)benzene (1,4-BHBB).

(12) 1,4-BHBB and 1,3-bis(4-hydroxybenzoyl)benzene (1,3-BHBB) were produced by hydrolysis of the 1,4-DFDK, and 1,3-DFDK, respectively, following the procedure described in Example 1 of U.S. Pat. No. 5,250,738 to Hackenbruch et al. (filed Feb. 24, 1992 and incorporated herein by reference in its entirety). They were purified by recrystallization in DMF/ethanol.

(13) Synthesis of nPEKK #1No Lewis Acid

(14) In a 500 mL 4-neck reaction flask fitted with a stirrer, a N2 inlet tube, a Claisen adapter with a thermocouple plunging in the reaction medium, and a Dean-Stark trap with a condenser and a dry ice trap were introduced 112.50 g of diphenyl sulfone, 33.390 g of 1,3-BHBB, 6.372 g of 1,4-BHBB and 41.172 g of 1,4-DFDK. The flask content was evacuated under vacuum and then filled with high purity nitrogen (containing less than 10 ppm 02). The reaction mixture was then placed under a constant nitrogen purge (60 mL/min). The reaction mixture was heated slowly to 270 C. At 270 C., 13.725 g of Na2CO3 and 0.086 g of K2CO3 was added via a powder dispenser to the reaction mixture over 60 minutes. At the end of the addition, the reaction mixture was heated to 320 C. at 1 C./minute. After 2 minutes at 320 C., 1.207 g of 1,4-DFDK were added to the reaction mixture while keeping a nitrogen purge on the reactor. After 5 minutes, 0.529 g of lithium chloride were added to the reaction mixture. 10 minutes later, another 0.402 g of 1,4-DFDK were added to the reactor and the reaction mixture was kept at temperature for 15 minutes. Another charge of 25 g of diphenyl sulfone was added to the reaction mixture, which was kept under agitation for 15 minutes. The reactor content was then poured from the reactor into a stainless steel pan and cooled. The solid was broken up and ground in an attrition mill through a 2 mm screen. Diphenyl sulfone and salts were extracted from the mixture with acetone and water at pH between 1 and 12. 0.67 g of NaH2PO4.Math.2H2O and 0.62 g of Na2HPO4 were dissolved in 1200 mL DI water for the last wash. The powder was then removed from the reactor and dried at 120 C. under vacuum for 12 hours yielding 72 g of a yellow powder. The final PEKK polymer had a T/I ratio of 58/42.

(15) Synthesis of nPEKK #2No Lewis Acid

(16) In a 500 mL 4-neck reaction flask fitted with a stirrer, a N2 inlet tube, a Claisen adapter with a thermocouple plunging in the reaction medium, and a Dean-Stark trap with a condenser and a dry ice trap were introduced 112.50 g of diphenyl sulfone, 31.800 g of 1,3-BHBB, 7.950 g of 1,4-BHBB and 40.810 g of 1,4-DFDK. The flask content was evacuated under vacuum and then filled with high purity nitrogen (containing less than 10 ppm O.sub.2). The reaction mixture was then placed under a constant nitrogen purge (60 mL/min).

(17) The reaction mixture was heated slowly to 220 C. At 220 C., 13.725 g of Na.sub.2CO3 and 0.121 g of K.sub.2CO.sub.3 was added via a powder dispenser to the reaction mixture over 60 minutes. At the end of the addition, the reaction mixture was heated to 320 C. at 1 C./minute. After 120 minutes at 320 C., 0.805 g of 1,4-DFDK were added to the reaction mixture while keeping a nitrogen purge on the reactor. After 5 minutes, 0.529 g of lithium chloride were added to the reaction mixture. 10 minutes later, another 0.402 g of 1,4-DFDK were added to the reactor and the reaction mixture was kept at temperature for 15 minutes.

(18) The reactor content was then poured from the reactor into a stainless steel pan and cooled. The solid was broken up and ground in an attrition mill through a 2 mm screen. Diphenyl sulfone and salts were extracted from the mixture with acetone and water at pH between 1 and 12. 1.34 g of NaH.sub.2PO.sub.4.Math.2H.sub.2O and 1.24 g of Na.sub.2HPO.sub.4 were dissolved in 1200 mL DI water for the last wash. The powder was then removed from the reactor and dried at 120 C. under vacuum for 12 hours yielding 72 g of a yellow powder. The final PEKK polymer had a T/I ratio of 60/40. The residual acidity and basicity and phosphorus content were determined on the final powder (table 1), as well as on CE1 material.

(19) Analysis Methods

(20) Determination of Melt Flow Index

(21) The melt flow index was determined according to ASTM D1238 at 340 C. with a 3.8 kg weight. The final MFI for a 8.4 kg weight, shown in Table 2, was obtained by multiplying the value obtained by 2.35.

(22) Determination of Elemental Impurities in Monomers and PEKK Polymers by ICP-OES

(23) A clean, dry platinum crucible was placed onto an analytical balance, and the balance was zeroed. One half to three grams of monomer/polymer sample was weighed into a boat and its weight was recorded to 0.0001 g. The crucible with sample was placed in a muffle furnace (Thermo Scientific Thermolyne F6000 Programmable Furnace). The furnace was gradually heated to 525 C. and held at that temperature for 10 hours to dry ash the sample. Following ashing, the furnace was cooled down to room temperature, and the crucible was taken out of the furnace and placed in a fume hood. The ash was dissolved in diluted hydrochloric acid. The solution was transferred to a 25 mL volumetric flask, using a polyethylene pipette. The crucible was rinsed twice with approximately 5 mL of ultrapure water (R<18 Mcm) and the washes were added to a volumetric flask to effect a quantitative transfer. Ultrapure water was added to total 25 mL in the flask. A stopper was put on the top of the flask and the contents were shaken well to mix.

(24) ICP-OES analysis was performed using an inductively-coupled plasma emission spectrometer Perkin-Elmer Optima 8300 dual view. The spectrometer was calibrated using a set of NIST traceable multi-element mixed standards with analyte concentrations between 0.0 and 10.0 mg/L. A linear calibration curve was obtained in a range of concentrations with a correlation coefficient better than 0.9999 for each of 48 analytes. The standards were run before and after every ten samples to ensure instrument stability. The results were reported as an average of three replicates. The concentration of elemental impurities in the sample was calculated with the following equation:
A=(B*C)/(D) wherein A=concentration of element in the sample in mg/kg (ppm) B=element in the solution analyzed by ICP-OES in mg/L C=volume of the solution analyzed by ICP-OES in mL D=sample weight in grams used in the procedure.
Determination of Residual Acidity (the Residual Acidity Test)

(25) 0.15-0.20 g of PEKK sample was weighted into a titration vessel and dissolved in 8 mL of m-cresol. After dissolving, the sample was diluted with 8 mL of chloroform, 50 L of 37 wt/vol % aqueous formaldehyde solution. The sample was then titrated potentiometrically with standard 0.1N KOH in methanol using a Metrohm autotitrator Titrando 809 with an 2 mL burette and Metrohm combined pH electrode (Solvotrode) with flexible ground-joint diaphragm, filled with 3M LiCl in ethanol. The titrator readings were plotted against the volume of titrant solution, and the end point was taken at the inflection in the titration curve. Blank solutions were run every time samples were run, and under the same conditions. The blank value was determined from the volume of titrant needed to achieve the same mV electrode potential as the sample titration endpoint potential.

(26) Variables:

(27) V_blankaverage volume of titrant to reach equivalence points from blanks, in mL V_samplevolume of titrant to reach equivalence points in from a sample, in mL Wsample mass in grams Ntitrant normality Residual acidity equation:

(28) $\frac{\left(V_{-}\mathrm{sample}-V_{-}\mathrm{blank}\right)N1000}{W}=\mathrm{Residual}\mathrm{acidity}\mathrm{in}\frac{eq}{g}$
Determination of Residual Basicity (the Residual Basicity Test)

(29) 0.10-0.15 g of PEKK sample was weighted into a titration vessel and dissolved in 24 mL of titration solvent (m-cresol). The sample was then titrated potentiometrically with standard 0.1N perchloric acid in glacial acetic acid using a Metrohm autotitrator Titrando 809 with 10 mL burette and a Metrohm combined pH electrode (Solvotrode) with flexible ground-joint diaphragm, filled with 3M LiCl in ethanol. The titrator readings were plotted against the volume of titrant solution, and the end point was taken at the inflection in the titration curve. Each sample (including a blank solution) was run in duplicate and the average of the two results was reported.

(30) Variables:

(31) V_blankaverage volume of titrant to reach equivalence points from blanks, in mL V_samplevolume of titrant to reach equivalence points from a sample, in mL Wsample mass in grams Ntitrant normality Residual basicity equation:

(32) $\frac{\left(V_{-}\mathrm{sample}-V_{-}\mathrm{blank}\right)N1000}{W}=\mathrm{Residual}\mathrm{acidity}\mathrm{in}\frac{eq}{g}$
Determination of Tensile Properties

(33) Type V tensile specimens were subjected to tensile testing according to ASTM method D638 at 0.05 inch/minute room temperature (i.e. 23 C.) on 3 specimens.

(34) Determination of the Glass Transition Temperature and Melting Temperature

(35) The glass transition temperature Tg (mid-point) and the melting temperature Tm were determined on the 2nd heat scan in differential scanning calorimeter (DSC) according to ASTM D3418-03, E1356-03, E793-06, E794-06. Details of the procedure as used in this invention are as follows: a TA Instruments DSC Q20 was used with nitrogen as carrier gas (99.998% purity, 50 mL/min). Temperature and heat flow calibrations were done using indium. Sample size was 5 to 7 mg. The weight was recorded 0.01 mg. The heat cycles were: 1st heat cycle: 30.00 C. to 400.00 C. at 20.00 C./min, isothermal at 400.00 C. for 1 min; 1st cool cycle: 400.00 C. to 30.00 C. at 20.00 C./min, isothermal for 1 min; 2nd heat cycle: 30.00 C. to 400.00 C. at 20.00 C./min, isothermal at 400.00 C. for 1 min.

(36) The melting temperature Tm was determined as the peak temperature of the melting endotherm on the 1st or 2nd heat scan. The heat scan (1.sup.st or 2.sup.nd) used is indicated in the results. In case the polymer has two melting temperatures, only the highest is presented.

(37) Determination of the Level of Crystallinity of Molded or Printed Specimens

(38) The degree of crystallinity of a molded or printed specimen is determined by measuring its enthalpy of fusion. The enthalpy of fusion is determined as the area under the melting endotherm minus the area under any melting exotherm on the 1st heat scan in the differential scanning calorimeter (DSC) according to ASTM D3418-03, E1356-03, E793-06, E794-06 and using heating and cooling rates of 20 C./min. It is taken as the area over a linear baseline drawn from above the Tg to a temperature above the end of the endotherm. The degree of crystallinity is calculated by considering that 100% crystallinity corresponds to 130 J/g.

(39) Characterization of the PEKK Polymers

(40) TABLE-US-00001 TABLE 1 residual acidity, basicity, P in PEKK materials Residual Residual acidity basicity [P] Tm 1.sup.st Material (eq/g) (eq/g) (ppm) heat ( C.) Kepstan 6002 10 12 <0.32 303 PEKK (comparative) nPEKK #1 4 12 310 286 (inventive) nPEKK #2 nd nd 606 294 (inventive)
Heat Aging of PEKK Powder

(41) Powder samples for heat aging (n-PEKK #1) were ground using a Restch Ultracentrifugal mill ZM200 grinder using a 1 mm screen, to ensure homogeneous particle size for the exposure testing.

(42) 75 g of Kepstan 6002 PEKK (comparative) and nPEKK #1 (inventive) were weighed up in aluminum loaf pans and the pans placed in an oven under air at 260 C., with fan for 744 hours. This aging test was aimed at evaluating the stability of the powder upon multiple recycling in an SLS process where the powder is kept at temperature close to its melting point under concentrations of oxygen around 0.5-2.0%. The Melt flow, thermal transitions and tensile properties were measured on the samples before and after aging. The results are detailed in tables 2 and 3.

(43) TABLE-US-00002 TABLE 2 heat aging MFI data MFI Material (g/10 min) MFI Kepstan 6002 PEKK Unaged 37.9 100% (comparative) Aged <1 (no flow) nPEKK #1 Unaged 42.3 70.7% (inventive) Aged 12.4
Creation of Tensile Specimens

(44) Tensile specimens for heat aging were created using a compression molding process. A 762 mm762 mm3.2 mm plaque was prepared from the polymer by compression molding of 25 g of polymer under the following conditions: preheat at 343 C., 343 C./15 minutes, 2000 kg-f 343 C./2 minutes, 2700 kg-f cool down to 30 C. over 40 minutes, 2000 kg-f

(45) The 762 mm762 mm3.2 mm compression molded plaques were machined into Type V ASTM tensile specimens.

(46) Results

(47) TABLE-US-00003 TABLE 3 heat aging data Tensile strength Elongation Tm 1.sup.st % at yield at break heat crystal- Material (psi) (%) ( C.) linity Kepstan 6002 Unaged 12,200 [57] 65 [40] 303 4 PEKK Aged 12,500 [64] 25 [19] 302 1 (comparative) nPEKK#1 Unaged 12,400 [81] 59 [39] 286 0 (inventive) Aged 12,300 [45] 50 [15] 287 0

(48) The results from Table 2 and 3 indicates that the inventive nPEKK #1 powder is much more stable in the powder form at 260 C. under air than the material of the comparative example 1. The MFI change for example is less than 71%, while Kepstan 6002 PEKK powder material was found to exhibit no flow at all after heat aging.

(49) The inventive nPEKK #1 powder retained 85% of the elongation at break after aging, as compared to 38% to Kepstan 6002 PEKK powder material.

Example 2. SLS Printing

(50) Powder samples for SLS printing were ground in a Retsch SR300 rotor mill. A well-mixed blend of nPEKK #2 (one portion) and crushed dry ice (two portions) was slowly fed to the feed port of the Retsch mill, fitted with a 0.5 mm opening Conidur screen mounted in the reverse flow position and standard 6-blade rotor with a speed of 10,000 rpm.

(51) The material was re-blended with crushed dry ice at 1 part resin and 2 parts dry ice to the Retsch SR300 with a 0.08 mm screen, also in the reverse flow position with a standard 6-blade rotor at 10,000 rpm.

(52) Once all the material had been ground through the 0.08 mm grinding screen, it was vacuum oven dried at 120 C. for about 16 hours.

(53) The powder was then mixed with 0.5 wt % of Cab-O-Sil M-5 and heat treated in a rotary drum dryer (Grieves oven) at 280-285 C. under nitrogen for 4-6 h.

(54) SLS Printing Process and Creation of Tensile Specimens

(55) Tensile specimens via SLS printing were created using an EOS P800 laser sintering printer. The powder was sintered into Type V ASTM tensile specimens using a laser power setting of 19 W, a processing temperature (Tp) of either 285 C. or 291 C., a print duration of less than 1.5 hours, and a cooling rate of less than 10 C./min.

(56) Results

(57) The results are detailed in tables 4 and 5.

(58) TABLE-US-00004 TABLE 4 SLS recycle printing at a 100% refresh rate (100% by weight recycled powder) and at 291 C. Processing Ultimate Elonga- Tm 1.sup.st temper- tensile tion at heat ature strength break Material ( C.) ( C.) (psi) (%) nPEKK #2 Fresh 309 291 12,200 [1070] 2.8 [0.48] (inventive) Recycle 1 307 291 10,800 [924] 2.6 [0.35] Recycle 2 308 291 11,400 [528] 2.9 [0.29]

(59) This data shows mechanical results from tensile bars printed via SLS (with a process of 100% recycling of the unsintered powder). Due to the nature of SLS, the powder is subjected to another type of heat aging process, similar to that of Table 2. The data indicates that the PEKK #2 powder is stable. The material retained 93% of tensile strength and demonstrated no loss in elongation at break.

(60) TABLE-US-00005 TABLE 5 SLS recycle printing at a 40% refresh rate (40% by weight fresh powder and 60% by weight recycled powder) and at 285 C. Elongation Processing Ultimate tensile at break Material temperature ( C.) strength (ksi) (%) nPEKK#2 Fresh 285 10,800 [1280] 2.7 [0.43] (inventive) Recycle 1 285 11,400 [307] 3.0 [0.15] Recycle 2 285 10,800 [1060] 2.6 [0.49] Recycle 3 285 11,100 [948] 2.8 [0.41]

(61) Similarly, this data also details the mechanical results from the SLS process, with the exception that the recycled powder is being refreshed with 40% by weight fresh powder for every iteration. In this case, the powder demonstrates an even higher stability, with no loss of mechanical properties.

Example 3. Heat Aging of a Blend of PEKK and Magnesium Phosphate (Comparative)

(62) Example 2 of CN 108606860 A was replicated to prepare a blend of PEKK with magnesium phosphate. Kepstan 6002 PEKK was used.

(63) The blend was characterized according to the methods described in example 1.

(64) TABLE-US-00006 TABLE 6 residual acidity, basicity, P and Td (1%) in PEKK blend Residual Residual Td (1%) acidity basicity [P] by TGA Material (eq/g) (eq/g) (ppm) ( C.) Kepstan 6002 PEKK + 5 0 6,838 303 magnesium phosphate (comparative)

(65) TABLE-US-00007 TABLE 7 tensile properties on compression molded samples Tensile Elongation Tensile Tensile strength at at break strength at modulus Material yield (psi) (%) break (psi) (ksi) Kepstan 6002 10,961 [976] 4 [2] 9,353 [1110] 462 [21] PEKK + magnesium phosphate (comparative)

(66) The blend was then exposed to the following heat treatment conditions defined: 260 C. for 744 h under air. The melt flow index was measured before and after heat treatment. The results are shown in table 8. The blend described in CN108606860 is not stable under the heat treatment conditions (100% change in MFI), indicating that the powder composites with magnesium phosphate do not exhibit the same stability as the PEKK of the present invention.

(67) TABLE-US-00008 TABLE 8 heat aging results MFI Material (g/10 min) MFI Kepstan 6002 PEKK + Unaged 22 100% magnesium phosphate Aged 0 (comparative)