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) the provision of providing a powdered polymer material (M) comprising at least one polymer (P1) having a melting temperature (Tm) greater than 270 C., as measured by differential scanning calorimetry (DSC) according to ASTM D3418, and at least one polymer (P2) having a glass transition temperature (Tg) between 130 C. and 240 C., and no melting peak, as measured by differential scanning calorimetry (DSC) according to ASTM D3418, b) the deposition of successive layers of the powdered polymer material; and c) the selective sintering of each layer prior to the deposition of the subsequent layer, wherein the powdered polymer material (M) is heated before step c) to a temperature Tp ( C.): Tp<Tg+25, wherein Tg ( C.) is the glass transition temperature of the P2 polymer.

Claims

1. An additive manufacturing method for making a three-dimensional (3D) object, comprising: a) providing a powdered polymer material (M) comprising: from 55 to 95 wt. % of at least one polymer (P1) having a melting temperature (Tm) greater than 270 C., as measured by differential scanning calorimetry (DSC) according to ASTM D3418, and from 5 to 45 wt. % of at least one polymer (P2) having a glass transition temperature (Tg) between 130 C. and 240 C., and no melting peak, as measured by differential scanning calorimetry (DSC) according to ASTM D3418, based on the total weight of the powdered polymer material (M); b) depositing successive layers of the powdered polymer material (M); and c) selectively sintering each layer prior to deposition of the subsequent layer, wherein the powdered polymer material (M) is heated before step c) to a temperature Tp ( C.):
Tp<Tg+25 wherein Tg ( C.) is the glass transition temperature of the P2 polymer.

2. The method of claim 1, wherein the powdered polymer material (M) has a d.sub.0.5-value ranging between 25 and 90 m, as measured by laser scattering in isopropanol.

3. The method of claim 1, wherein P1 is selected from the group consisting of a poly(aryl ether ketone) (PAEK), a polyphenylene sulphide (PPS), a polyphtalamide (PPA), a semi-aromatic polyester and an aromatic polyesters (PE).

4. The method of claim 1, wherein P2 is selected from the group consisting of a poly(aryl ether sulfone) (PAES), a poly(ether imide) (PEI), a polycarbonate (PC), a poly(phenyl ether) (PPE), an amorphous polyamide with a glass transition temperature above 130 C. and an amorphous aromatic polyester.

5. The method of claim 1, wherein P1 is a PPS comprising at least 50 mol. % of recurring units (R.sub.PPS) of formula (U) (mol. % being based on the total number of moles of recurring units in the PPS polymer): ##STR00033## where R is independently selected from the group consisting of halogen, C.sub.1-C.sub.12 alkyl groups, C.sub.7-C.sub.24 alkylaryl groups, C.sub.7-C.sub.24 aralkyl groups, C.sub.6-C.sub.24 arylene groups, C.sub.1-C.sub.12 alkoxy groups, and C.sub.6-C.sub.18 aryloxy groups, and i is independently zero or an integer from 1 to 4.

6. The method of claim 1, wherein P2 is a poly(aryl ether sulfone) (PAES) selected from the group consisting of poly (PPSU), polysulfone (PSU) and poly(ether sulfone) (PES).

7. The method of claim 1, wherein the powdered polymer material (M) is heated before step c) to a temperature Tp ( C.):
Tp<Tg+20 wherein Tg ( C.) is the glass transition temperature of the P2 polymer, as measured by differential scanning calorimetry (DSC) according to ASTM D3418.

8. The method of claim 1, wherein the powdered polymer material (M) comprises: from 56 to 80 wt. % of at least one polymer (P1) having a melting temperature (Tm) greater than 270 C., as measured by differential scanning calorimetry (DSC) according to ASTM D3418, and from 20 to 44 wt. % of at least one polymer (P2) having a glass transition temperature (Tg) between 130 C. and 240 C., and no melting peak, as measured by differential scanning calorimetry (DSC) according to ASTM D3418, based on the total weight of the powdered polymer material (M).

9. The method of claim 1, wherein the powdered polymer material (M) further comprises 0.01 to 10 wt. % of a flow agent.

10. The method of claim 1, wherein the P2 polymer has a Tg ranging from 160 and 250 C., as measured by differential scanning calorimetry (DSC) according to ASTM D3418.

11. The method of claim 1, wherein the powdered polymer material (M) is obtained by grinding a blend of at least P1 and P2, the blend being optionally cooled down to a temperature a temperature below 25 C. before and/or during grinding.

12. The method of claim 1, wherein step c) comprises selective sintering by means of an electromagnetic radiation of the powder.

13. A three-dimensional (3D) object obtainable by laser sintering from a powdered polymer material (M) comprising: from 55 to 95 wt. % of at least one polymer (P1) having a melting temperature (Tm) greater than 270 C., as measured by differential scanning calorimetry (DSC) according to ASTM D3418, and from 5 to 45 wt. % of at least one polymer (P2) having a glass transition temperature (Tg) between 130 C. and 240 C., and no melting peak, as measured by differential scanning calorimetry (DSC) according to ASTM D3418, based on the total weight of the powdered polymer material (M).

14. The object of claim 12, wherein the powdered polymer material (M) comprises recycled material.

15. A method for manufacturing a three-dimensional (3D) object using selective laser sintering (SLS) with a powdered polymer material (M) comprising, based on the total weight of the powdered polymer material (M): from 55 to 95 wt. % of at least one polymer (P1) having a melting temperature (Tm) greater than 270 C., as measured by differential scanning calorimetry (DSC) according to ASTM D3418, and from 5 to 45 wt. % of at least one polymer (P2) having a glass transition temperature (Tg) between 130 C. and 240 C., and no melting peak, as measured by differential scanning calorimetry (DSC) according to ASTM D3418.

Description

EXAMPLES

[0306] 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.

[0307] Starting Materials

[0308] PPS: Ryton QA281 N having an MFI of 700 g/10 min (316 C./5 kg).

TABLE-US-00001 TABLE 1 PPS MFI (316 C./5 kg) 700 g/10 min Tm ( C.) 285 Tg ( C.) 100

[0309] PPSU: a poly(biphenyl ether sulfone) (PPSU) with a MFI of 17 g/10 min (365 C./5 kg), prepared according to the following process:

[0310] The synthesis of the PPSU was achieved by the reaction in a 1 L flask of 83.8 g of 4,4-biphenol (0.450 mol), 131.17 g of 4,4-dichlorodiphenyl sulfone (0.457 mol) dissolved in a mixture of 400 g of sulfolane with the addition of 66.5 g (0.481 mol) of dry K.sub.2CO.sub.3.

[0311] The reaction mixture was heated up to 210 C. and maintained at this temperature until the polymer had the expected Mw. An excess of methyl chloride was then added to the reaction.

[0312] The reaction mixture was diluted with 600 g of MCB. The poly(biphenyl ether sulfone) was recovered by filtration of the salts, coagulation, washing and drying.

TABLE-US-00002 TABLE 2 PPSU MFI (365 C./5 kg) 17 g/10 min Tg ( C.) 220

[0313] Test Methods

[0314] *Thermal Transitions (Tg, Tm)

[0315] The glass transition and melting temperatures of the polymers were measured using differential scanning calorimetry (DSC) according to ASTM D3418 employing a heating and cooling rate of 20 C./min. Three scans were used for each DSC test: a first heat up to 400 C., followed by a first cool down to 30 C., followed by a second heat up to 400 C. The Tg and the Tm were determined from the second heat up. DSC was performed on a TA Instruments DSC Q20 with nitrogen as carrier gas (99.998% purity, 50 mL/min).

[0316] *MFI

[0317] The melt flow indices of the polymers were measured according to ASTM D-1238, using a weight of 5 kg and a temperature of 316 C. or 365 C. The measurements were conducted on a Dynisco D4001 Melt Flow Indexer.

[0318] *PSD (d.sub.0.5)

[0319] The PSD (volume distribution) of the powdered polymer materials were determined by an average of 3 runs using laser scattering Microtrac S3500 analyzer in wet mode (128 channels, between 0.0215 and 1408 m). The solvent was isopropanol with a refractive index of 1.38 and the particles were assumed to have a refractive index of 1.59. The ultrasonic mode was enabled (25 W/60 seconds) and the flow was set at 55%.

[0320] Blend Compounding

[0321] The formulations were melt compounded using a 26 mm diameter Coperion ZSK-26 co-rotating partially intermeshing twin screw extruder having an L/D ratio of 48:1. The barrel sections 2 through 12 and the die were heated to set point temperatures as follows:

[0322] Barrels 2-12: decreasing from 350 C. to 300 C.

[0323] Die: 350 C.

[0324] The resin blends were fed at barrel section 1 using a gravimetric feeder at throughput rates in the range 30-40 lb/hr. The extruder was operated at screw speeds of around 200 RPM. Vacuum was applied at barrel zone 10 with a vacuum level of about 27 inches of mercury. A single-hole die was used for all the compounds to give a filament approximately 2.6 to 2.7 mm in diameter and the polymer filament exiting the die was cooled in water and fed to the pelletizer to generate pellets approximately 2.7 mm in length.

[0325] Powdered Polymer Material Preparation

[0326] The blended formulations were slowly fed in combination with crushed dry ice into the feed port of a Retsch SR300 rotor 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.

[0327] The materials were re-mixed 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.

TABLE-US-00003 TABLE 3 Blend PPS/PPSU 63/37 wt/wt d.sub.0.5-value (m) 43.1

[0328] Heat Treatment

[0329] The aim of the heat treatments was to simulate long-term printing conditions within the print bed of an SLS printer and evaluate recyclability of the materials. More precisely, the materials were subjected to different heat treatment temperatures for 16 hours in an air convection oven and then tested for their retained sintering (coalescence) capability, thereby simulating a printing cycle. Recyclability was tested by examining remaining particle coalescence ability. Additionally, the powders were evaluated for their aspect and their disaggregation following heat treatments, that-is-to-say their ability to be broken apart by traditional sieving.

[0330] Generally speaking, as an example, a color change from white to off-white was acceptable, while a color change from white or off-white to brown, dark brown or black was considered as failing the recyclability requirement. Also, a powder material which could not be broken apart by traditional sieving, after a 16-hour long heat treatment at a certain temperature, was also considered as failing the recyclability requirement.

[0331] Hot Stage Microscopy

[0332] The aim of the hot stage microscopy tests was to study particle coalescence under experimental conditions that simulate the sintering step of the method for making a 3D object of the present invention, in order to compare sintering behaviour as a function of the exposition of different materials to high-temperature conditions within an air convection oven for 16 hours.

[0333] Coalescence was evaluated on a Keyence VHX 600K optical microscope with a digital zoom of 200. A Linkam T96-PE hot-stage attachment was utilized in order to increase the temperature of the material in order to simulate the increased temperature of the material within an SLS printer upon printing.

[0334] The material was heated quickly (100 C./min) to 260 C. Following the rapid pre-heat, the material was subjected to a temperature increase at 20 C./min until reaching 400 C., at which point the temperature was held constant in order to observe coalescence. The temperature of 400 C. hereby simulates the energy source (for example laser) used to sinter selected regions of layer of unfused powder in a SLS equipment.

[0335] Coalescence was measured by observing two particles that were adjacent prior to heating. During the heating and isothermal phase at 400 C., the particles were observed to coalesce together, with a neck or bridge, formed between the two during intermediate steps.

[0336] Definitions and Results

[0337] Disaggregation

[0338] 0=Not Aggregated: Powder particles are not closely associated together and the powder is loosely flowing.

[0339] 1=Easy Disaggregation: Powder particles are closely associated together but can be easily broken back apart by traditional sieving.

[0340] 2=Difficult Disaggregation: Powder particles have slightly fused together and cannot be broken back apart by traditional sieving.

[0341] 3=No Disaggregation: Powder particles have fused together with no possible separation except by grinding.

[0342] Coalescence

[0343] Yes: Particles exhibit rapid coalescence between the temperatures of 285 C. and 295 C. during an increasing temperature ramp with rate of 20 C./min.

[0344] No: Particles do not exhibit any coalescence between the temperatures of 285 C. and 295 C. during an increasing temperature ramp with rate of 20 C./min.

TABLE-US-00004 TABLE 6 E1 E2 E3 E4c E5c Blend 1 (PPS/PPSU, Tg PPSU = 220 C.) Treatment none 200 230 245 270 temperature ( C.) Corresponding n/a Tg 20 Tg + 10 Tg + 25 Tg + 50 Tp ( C.) Powder aspect White Off-white Off-white Off-white Dark brown Disaggregation 0 1 1 2 3 Particule Yes Yes Yes Yes No coalescence

[0345] The color, the disaggregation and the coalescence ability of the powder of example E1 (no heat treatment) simulates the behaviour of the powder when used for the first time in a SLS printer.

[0346] The color, the disaggregation and the coalescence ability of the powder of example E2, which has been submitted to a 16-hour heat treatment at 200 C. (temperature lower than the glass transition of the amorphous polymer of powdered polymer material, i.e. PPSU) and E3, which has been submitted to a 16-hour heat treatment at 230 C. (temperature higher than the glass transition of the amorphous polymer of powdered polymer material, i.e. PPSU) are shown to be comparable to example E1.

[0347] The powder of example E4c however demonstrates difficult disaggregation ability. The powder of example E4C treated 16 hours at a temperature of 255 C. (temperature 25 C. higher than the glass transition of the PPSU polymer) cannot not be recycled.

[0348] The powder of example E5c demonstrates a non-acceptable change of color, no possible disaggregation and no coalescence, which make it not recyclable at all.