A method for preparing a polymer-based spherical powder for laser sintering

Abstract

This invention discloses a method for preparing polymer-based spherical powder for laser sintering, comprising the following steps: A self-heating plastic polymer is pretreated by drying and dehydration, and then cryogenically pulverized to obtain coarse powder; using an inert gas as a transport carrier, the coarse powder is fed into a plasma torch, where it is heated and melted to form molten droplets; the molten droplets enter a swirling cavity, where they form uniform droplets under the shearing and dispersing action of the swirling field, and spontaneously shrink and spherize under surface tension to form spherical droplets; using an inert gas as a carrier gas, the spherical droplets are cooled and solidified through a three-stage gradient cooling channel to obtain polymer-based spherical powder. Spherical powder with a particle size in the range of 1–125 μm and a sphericity of not less than 95% is obtained. This shoe-shaped powder exhibits high sphericity, excellent flowability and dispersibility, and can significantly optimize the uniformity of powder spreading and the density of packing during the powder bed melting process.

Description

Technical Field

[0001] This invention belongs to the field of powder preparation technology for laser sintering, and specifically relates to a method for preparing polymer-based spherical powder for laser sintering. Background Technology

[0002] Laser sintering (SLS) is a key forming process in additive manufacturing. With its advantages of moldless rapid manufacturing, high freedom of structural design, and excellent material utilization, it is widely used in high-end equipment fields such as aerospace, precision devices, electronic information, and biomedicine. The forming quality of SLS is highly sensitive to the morphology and properties of the powder raw materials. Polymer powders with high sphericity, excellent flowability, concentrated particle size distribution, and suitable sintering windows are core prerequisites for ensuring uniform powder spreading, sintering stability, and dimensional accuracy and density of the parts. Polymer-based powders have become the most widely used raw material system in SLS processes due to their wide processing window, large modification potential, and controllable cost.

[0003] Current mainstream technologies for preparing polymer-based spherical powders for SLS still have significant shortcomings: solvent precipitation, phase separation, and spray drying methods rely on large amounts of organic solvents, which can easily cause environmental pollution and solvent residues. Furthermore, these methods have lengthy process chains, poor versatility, and are difficult to adapt to various thermoplastic polymers. While traditional mechanical pulverization and cryogenic pulverization processes are simple and efficient, the resulting particles often have irregular morphologies, low sphericity, poor flowability, and are prone to agglomeration, failing to meet the requirements of high-precision SLS molding. At the same time, existing technologies generally struggle to simultaneously achieve environmental friendliness, uniform morphology, batch stability, and large-scale continuous production, thus hindering the industrial application of high-performance polymer spherical powders in additive manufacturing.

[0004] Therefore, developing a green, solvent-free, simple, and controllable polymer-based spherical powder preparation process that can suppress droplet aggregation and reduce internal stress of powder is of great engineering value and industrial significance for improving the performance of SLS molding materials and promoting the development of additive manufacturing technology. Summary of the Invention

[0005] To obtain a powder with high sphericity, excellent flowability, and stable performance, this invention proposes a method for preparing polymer-based spherical powders for laser sintering. To achieve the above objectives, the technical solution adopted by this invention is as follows: A method for preparing polymer-based spherical powder for laser sintering, the method comprising the following steps: Step 1: The self-heating plastic polymer is dried and dehydrated before being cryogenically pulverized to obtain coarse powder. Step 2: Using an inert gas as a transport carrier, the coarse powder is fed into the plasma torch, where it is heated and melted to form molten droplets. Step 3: The molten droplets enter the swirling cavity, where they form uniform droplets under the shearing and dispersing action of the swirling field, and spontaneously shrink and spherize under the drive of surface tension to form spherical droplets; Step 4: Using an inert gas as a carrier gas, the spherical droplets are cooled and solidified through a three-stage gradient cooling channel to obtain polymer-based spherical powder.

[0006] In a further improvement, the self-thermal plastic polymer mentioned in step 1 is one or more of polyamide, nylon, polylactic acid, thermoplastic polyurethane, polycarbonate, polyethylene, polypropylene, polyvinylidene fluoride, polyether ether ketone, and polystyrene.

[0007] Further improvements were made to the drying and dehydration pretreatment in step 1: the drying temperature was 60–80℃, and the drying time was 4–6 hours.

[0008] In a further improvement, the melting temperature of the coarse powder in step 2 is 200℃~350℃.

[0009] In a further improvement, in step 3, the swirling field is formed by introducing inert gas through 3 to 4 airflow nozzles arranged tangentially along the inner wall of the swirling cavity, with a gas pressure of 0.5 to 1 MPa.

[0010] Further improvements include a three-stage stepped cooling channel in step 4, with the temperature of the first stage controlled at 80–100°C, the second stage at 40–60°C, and the third stage at 25–35°C.

[0011] The beneficial effects of the present invention's method for preparing polymer-based spherical powders for laser sintering are as follows: A preparation strategy that synergistically couples dehydration pretreatment, pulverization, plasma melting, swirling shear dispersion, and three-stage gradient cooling of self-heating plastic polymers can effectively improve the sphericity and particle size distribution uniformity of polymer-based powders. The swirling flow field effectively inhibits droplet agglomeration, ensuring the powder's spherical morphology is complete and regular. The three-stage gradient cooling smoothly controls the cooling process, reducing internal stress caused by rapid cooling, minimizing cracking tendency, and significantly improving product structural stability. Precise control of the melting temperature range effectively prevents thermal degradation of raw materials during processing, maximizing the preservation of the material's intrinsic properties. This results in spherical powders with a particle size ranging from 1 to 125 μm and a sphericity of not less than 95%. This shoe powder exhibits high sphericity, excellent flowability and dispersibility, significantly optimizing powder bed uniformity and packing density during the powder bed melting process, thereby improving the dimensional accuracy, mechanical properties, and surface quality of molded parts, meeting the stringent requirements of additive manufacturing, electronic packaging, and functional coatings. Attached Figure Description

[0012] Figure 1Example 1 shows the SEM morphology of nylon 12 powder obtained by cryogenic pulverization. (This is from Example 1, which describes the preparation method of polymer-based spherical powders for laser sintering.) Figure 2 Example 1 shows the SEM morphology of nylon 12 spherical powder after plasma melting and spheroidization, swirling dispersion and three-stage gradient slow cooling. Detailed Implementation

[0013] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments: Specific embodiments of the method for preparing polymer-based spherical powders for laser sintering according to the present invention are as follows. Example 1: The thermoplastic polymer is nylon, specifically nylon 12 (PA12) granules.

[0014] Step 1: Weigh 5 kg of Nylon 12 (PA12) granules, perform drying and dehydration pretreatment, and then obtain coarse powder after cryogenic pulverization. The specific process is as follows: dry at 70℃ for 5 hours to remove residual moisture inside the granules; place the dried granules in a cryogenic pulverizer for cryogenic pulverization to obtain PA12 micron-sized coarse powder, and sieve using an 80-mesh standard sieve to collect the powder that passes through the sieve for later use.

[0015] Step 2: Using an inert gas as a transport carrier, coarse powder is fed into the plasma torch, where it is heated and melted to form molten droplets. Specifically, argon is used as the carrier gas to feed PA12 powder into the plasma torch at a flow rate of 0.1–0.15 m³ / h, where the powder is rapidly melted to form molten droplets within the 220°C melting range.

[0016] Step 3: The molten droplets enter the swirling cavity and form uniform droplets under the shearing and dispersion effect of the swirling field. Driven by surface tension, they spontaneously shrink and spherize to form spherical droplets. Specifically, the molten droplets enter the swirling cavity and are fully dispersed under the action of 0.7MPa swirling gas pressure, which inhibits droplet aggregation and forms spherical droplets under the drive of surface tension.

[0017] Step 4: Using an inert gas as a carrier gas, the spherical droplets are cooled and solidified through a three-stage gradient cooling channel to obtain polymer-based spherical powder. Specifically, the spherical droplets are carried by argon gas into the three-stage gradient cooling channel and gradually cooled and solidified at 85℃, 45℃, and 29℃. After cooling, the powder is filtered, dried, and graded through an 80-mesh standard sieve to obtain PA12 spherical powder.

[0018] The PA12 spherical powder obtained in this embodiment has a sphericity of ≥98%, an average particle size of 72.5μm, and a sintering window of 13.2℃. The powder has excellent flowability, uniformity of powder spreading, and molding stability, and can be directly applied to laser sintering (SLS) molding. Using this powder for SLS molding, PA12 molded parts with dimensional accuracy of ±0.1% and density of ≥98.5% can be produced.

[0019] Example 2: The self-thermoplastic polymer is thermoplastic polyurethane (TPU) granules.

[0020] Step 1: The self-heating plastic polymer is dried and dehydrated before being cryogenically pulverized to obtain coarse powder; 3 kg of thermoplastic polyurethane (TPU) granules are weighed and dried at 60°C for 6 hours to remove residual moisture inside the granules; the dried granules are placed in a cryogenic pulverizer for cryogenic pulverization to obtain TPU micron-sized coarse powder, which is then sieved using an 80-mesh standard sieve, and the powder passing through the sieve is collected for later use.

[0021] Step 2: Using an inert gas as a transport carrier, the coarse powder is fed into the plasma torch, where it is heated and melted to form molten droplets. Specifically, using argon as the carrier gas, TPU powder is fed into the plasma torch at a flow rate of 0.3 m³ / h, and the powder is rapidly melted into liquid droplets within the 350°C melting range.

[0022] Step 3: Molten droplets enter the swirling cavity, where they form uniform droplets under the shearing and dispersion effects of the swirling field, and spontaneously shrink and spherize under the drive of surface tension to form spherical droplets. The specific process is as follows: the droplets enter the swirling cavity, where they are efficiently dispersed under the action of 1MPa swirling air pressure, which inhibits droplet aggregation, and shrink under the drive of surface tension to form spherical droplets.

[0023] In step 4: Using an inert gas as a carrier gas, the spherical droplets are cooled and solidified through a three-stage gradient cooling channel to obtain polymer-based spherical powder. Specifically, the spherical droplets are carried by argon gas into the three-stage gradient cooling channel and gradually cooled and solidified at 100℃, 60℃, and 35℃. The cooled powder is then filtered, dried, and sieved through an 80-mesh standard sieve to obtain TPU spherical powder.

[0024] The TPU spherical powder obtained in this embodiment has a sphericity of ≥96%, an average particle size of 88μm, and a sintering window of 19.2℃. The powder has excellent flowability, uniformity of powder spreading, and molding stability, and can be directly applied to laser sintering (SLS) molding. Using this powder for SLS molding, TPU molded parts with dimensional accuracy of ±0.15% and density of ≥99% can be produced.

[0025] In other embodiments, the self-thermoplastic polymer may be one or more of polyamide, polylactic acid, polycarbonate, polyethylene, polypropylene, polyvinylidene fluoride, polyether ether ketone, and polystyrene, instead of thermoplastic polyurethane (TPU) or nylon.

[0026] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0027] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and substitutions can be made without departing from the technical principles of the present invention, and these improvements and substitutions should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing polymer-based spherical powder for laser sintering, characterized in that, The preparation method includes the following steps: Step 1: The self-heating plastic polymer is dried and dehydrated before being cryogenically pulverized to obtain coarse powder. Step 2: Using an inert gas as a transport carrier, the coarse powder is fed into the plasma torch, where it is heated and melted to form molten droplets. Step 3: The molten droplets enter the swirling cavity, where they form uniform droplets under the shearing and dispersing action of the swirling field, and spontaneously shrink and spherize under the drive of surface tension to form spherical droplets; Step 4: Using an inert gas as a carrier gas, the spherical droplets are cooled and solidified through a three-stage gradient cooling channel to obtain polymer-based spherical powder.

2. The method for preparing polymer-based spherical powder for laser sintering according to claim 1, characterized in that, The self-heating plastic polymer mentioned in step 1 is one or more of polyamide, nylon, polylactic acid, thermoplastic polyurethane, polycarbonate, polyethylene, polypropylene, polyvinylidene fluoride, polyether ether ketone, and polystyrene.

3. The method for preparing polymer-based spherical powder for laser sintering according to claim 1, characterized in that, In step 1, the pretreatment for drying and dehydration is carried out at a temperature of 60–80°C for 4–6 hours.

4. The method for preparing polymer-based spherical powder for laser sintering according to claim 1, characterized in that, The coarse powder described in step 2 is heated to a melting temperature of 200℃~350℃.

5. The method for preparing polymer-based spherical powder for laser sintering according to claim 1, characterized in that, In step 3, the swirling field is formed by introducing inert gas through 3 to 4 airflow nozzles arranged tangentially along the inner wall of the swirling cavity, with a gas pressure of 0.5 to 1 MPa.

6. The method for preparing polymer-based spherical powder for laser sintering according to claim 1, characterized in that, In step 4, the temperature of the three-stage stepped cooling channel is controlled at 80-100℃ for the first stage, 40-60℃ for the second stage, and 25-35℃ for the third stage.

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