A method for preparing uniformly spherical nylon powder for selective laser printing

Abstract

This invention discloses a method for preparing uniformly spherical nylon powder for selective laser printing. The method uses caprolactam, dodecyl lactam, styrene, sodium hydride, azobisisobutyronitrile, acetic anhydride, and toluene as raw materials, and ethanol as an excipient. The process involves three steps: preparation of a nylon pre-emulsion, water-cooled powdering, and washing and drying. The powder prepared by this invention exhibits uniform particle size distribution, good sphericity, and the ability to be stably harvested and continuously produced industrially.

Description

Technical Field

[0001] This invention relates to a method for manufacturing materials for selective laser printing, and more particularly to a method for preparing uniformly spherical nylon powder for selective laser printing. Background Technology

[0002] In recent years, 3D printing technology, especially selective laser sintering (SLS), has developed rapidly. Nylon (PA) materials, due to their regular molecular chains, offer advantages such as fast sintering speed, high sintering rate, and good mechanical properties of SLS-manufactured parts when applied to SLS. However, domestic research on nylon materials used in SLS, especially long-chain nylons, for 3D printing is relatively limited.

[0003] Currently, commercially available nylon powder generally suffers from the following problems: First, it has poor uniformity, with the main particle size ranging from 10μm to 200μm, resulting in poor particle size uniformity; second, it has a low degree of sphericity, with many powders appearing gourd-shaped or oval under a high-magnification optical microscope, and some even being unformed, failing to meet the uniformity and dimensional accuracy of the overall molding performance of high-precision products and thus unable to meet the needs of some high-precision products.

[0004] Therefore, there is a need for a method to prepare uniformly spherical nylon powder for selective laser printing that has a uniform particle size distribution, good sphericity, and can be stably harvested and continuously industrialized. Summary of the Invention

[0005] The present invention aims to provide a method for preparing uniformly spherical nylon powder for selective laser printing, which has a uniform particle size distribution, good sphericity, and can be stably harvested and continuously industrialized.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a method for preparing uniformly spherical nylon powder for selective laser printing, comprising the following stages:

[0007] S1: Raw Material Preparation

[0008] ① Raw material preparation: Prepare sufficient caprolactam, dodecyl lactam, styrene, sodium hydride, azobisisobutyronitrile, acetic anhydride, and toluene;

[0009] ② Preparation of auxiliary materials: Prepare sufficient ethanol;

[0010] S2: Preparation of Nylon Original Emulsion

[0011] ① Add the styrene solution prepared in step ① of stage S1 to a reaction vessel equipped with a magnetic stirrer and a reflux device, and then add sufficient toluene prepared in step ① of stage S1 as a reaction solvent. React at 78℃-85℃ for 21-23 hours. When the reaction time is 0h, 8h and 16h, add 1%-2% of azobisisobutyronitrile prepared in step ① of stage S1 according to the mass of styrene, until the reaction is completed, and obtain reaction solution A.

[0012] ②After the reaction in step ① is completed, remove the solid phase in the reaction solution A, and then add sufficient amount of the ethanol solution prepared in step ② of stage S1 to the liquid phase for reaction. During the reaction, flocculent precipitate is generated. Add ethanol solution until no more precipitate is generated.

[0013] ③ Filter out the flocculent solid, dry it in an oven and set aside for later use to obtain solid A;

[0014] ④ Add the acetic anhydride and caprolactam prepared in step ① of stage S1 at a mass ratio of (1.07-1.09):1, and react at 78℃-85℃ for 21-23 hours to obtain reaction solution B;

[0015] ⑤ The reaction solution B obtained in step ④ is treated by vacuum distillation, heated to 60℃-65℃, and the byproduct acetic acid is removed by distillation until the acetic acid is completely removed, to obtain reaction solution C;

[0016] ⑥ Heat the reaction solution C obtained in step ⑤ to 130℃-135℃ and collect the distillation product, which is an activator;

[0017] ⑦ The caprolactam prepared in step S1 ① and the solid A obtained in step S2 ③ are mixed in a mass ratio of 95:(5-8) and placed in a reaction vessel to obtain the reaction system.

[0018] ⑧ Place the reaction system obtained in step ⑦ under nitrogen protection, then heat it to 100℃-105℃ and continuously stir and melt it for 2.5-3 hours to form a homogeneous liquid; then distill the homogeneous liquid under reduced pressure for 20 minutes to remove the trace amounts of water contained in it, and obtain the liquid to be treated.

[0019] ⑨ Add 0.42wt%-0.45wt% of sodium hydride prepared in step S1 ① to the solution to be treated obtained in step ⑧, then evacuate and heat to 142℃-148℃ for 15min-18min to obtain the first reaction solution C.

[0020] ⑩ The reaction solution C obtained in step ⑨ is heated again to 172℃-178℃ under vacuum. Then, 0.95wt%-1wt% of the activator obtained in step S2 ⑥ is added to it according to the mass of reaction solution C. The mixture is stirred evenly and allowed to react for 25min-28min. Then, it is stirred evenly again to obtain the desired nylon emulsion.

[0021] S3: Powdering

[0022] ① Prepare a water-cooled powder making equipment, which includes a water-cooled container base with an arc-shaped bottom and a constricted top for holding deionized water, a heating device adapted to the arc shape of the bottom of the water-cooled container base, an internal stirring device to make the deionized water flow according to the liquid flow trajectory, and a spray nozzle 1 set in the arc-shaped area of ​​the shoulder of the water-cooled container base, with the spray direction forming an angle of 105°-110° with the liquid flow source direction;

[0023] ② Heat the deionized water in the water-cooled powder making equipment to 65℃-70℃, stir the water flow, and make the water flow velocity at the spray nozzle 1 outlet 1 be 1.3m / s-1.5m / s;

[0024] ③ Spray the nylon emulsion obtained in step S2 (10) from spray nozzle 1 into the water stream obtained in step ② using nitrogen as a carrier. The spray pressure is 2.7 bar to 2.9 bar and the inlet temperature is 180°C to 185°C. After all spraying is completed, filter out the solid, wash and dry it to obtain the desired uniformly spherical nylon powder.

[0025] Compared with the prior art, the present invention has the following advantages due to the adoption of the above technical solutions:

[0026] (1) The nylon powder manufactured according to the method of this embodiment has a particle size distribution of 20-120μm (lower than the conventionally manufactured raw powder of 10μm-150μm). After sieving, a more precise and controllable particle size can be obtained with less loss. The single particle spheroidization rate is above 70%, and there is basically no adhesion between single particles. It is significantly improved compared with commercially available nylon raw powder for selective laser printing.

[0027] (2) This invention improves the size accuracy and spheroidization and adhesion problems of powder particles from the perspective of the underlying method, and develops a new type of spheroidized powder for selective laser printing technology. Compared with the conventional cooling crushing method or solution spray drying method, the powder preparation method of this invention has better mechanical strength, denser particles, higher spheroidization rate and better flowability. The sintered parts made from this invention have significantly improved comprehensive mechanical properties. Specifically, in the printing standard tensile test, the tensile strength of this invention is 47MPa-52MPa (superior to 40MPa-45MPa of conventional powder) and the elongation is 32%-35% (superior to 20%-28% of conventional powder).

[0028] (3) In the comparative analysis of the macroscopic morphology of the present invention and commercially available powder, it was found that the powder prepared by the present invention has a smoother feel, better flowability, and higher sphericity. Moreover, after being placed in the same environment for a long time, it ages and turns yellow later than commercially available powder. In the performance analysis of selective laser printing process conditions, the powder of the present invention has better sphericity, better dispersion between powders, and higher density.

[0029] Therefore, the present invention has the characteristics of uniform particle size distribution, good spheroidization, stable harvesting and continuous industrial production. Attached Figure Description

[0030] Figure 1 This is a particle size distribution diagram of nylon powder prepared according to the method of the present invention;

[0031] Figure 2 This is a particle size distribution diagram of commercially available nylon powder.

[0032] Figure 3 A digital micrograph at 100x magnification of nylon powder prepared according to the method of the present invention;

[0033] Figure 4 Micrographs of commercially available nylon powder at magnification;

[0034] Figure 5 A digital micrograph at 1000x magnification of nylon powder prepared according to the method of the present invention;

[0035] Figure 6 Digital micrograph of commercially available nylon powder at 500x magnification;

[0036] Figure 7 This is a structural diagram of the powder-making apparatus of the present invention;

[0037] In the diagram: 1. Spray nozzle; 2. Water-cooled container base; 3. Liquid flow; 4. Heating device. Detailed Implementation Example 1

[0038] A method for preparing uniformly spherical nylon powder for selective laser printing includes the following stages:

[0039] S1: Raw Material Preparation

[0040] ① Raw material preparation: Prepare sufficient caprolactam, dodecyl lactam, styrene, sodium hydride, azobisisobutyronitrile, acetic anhydride, and toluene;

[0041] ② Preparation of auxiliary materials: Prepare sufficient ethanol;

[0042] S2: Preparation of Nylon Original Emulsion

[0043] ① Add the styrene solution prepared in step ① of stage S1 to a reaction vessel equipped with a magnetic stirrer and a reflux device, and then add sufficient toluene prepared in step ① of stage S1 as a reaction solvent. React at 78℃-85℃ for 21-23 hours. When the reaction time is 0h, 8h and 16h, add 1%-2% of azobisisobutyronitrile prepared in step ① of stage S1 according to the mass of styrene, until the reaction is completed, and obtain reaction solution A.

[0044] ②After the reaction in step ① is completed, remove the solid phase in the reaction solution A, and then add sufficient amount of the ethanol solution prepared in step ② of stage S1 to the liquid phase for reaction. During the reaction, flocculent precipitate is generated. Add ethanol solution until no more precipitate is generated.

[0045] ③ Filter out the flocculent solid, dry it in an oven and set aside for later use to obtain solid A;

[0046] ④ The acetic anhydride and caprolactam prepared in step ① of stage S1 are added at a mass ratio of 1.082:1 and reacted at 80℃ for 22 hours to obtain reaction solution B;

[0047] ⑤ The reaction solution B obtained in step ④ is treated by vacuum distillation, heated to 60℃-65℃, and the byproduct acetic acid is removed by distillation until the acetic acid is completely removed, to obtain reaction solution C;

[0048] ⑥ Heat the reaction solution C obtained in step ⑤ to 130℃-135℃ and collect the distillation product, which is an activator;

[0049] ⑦ The caprolactam prepared in step S1 ① and the solid A obtained in step S2 ③ are mixed in a mass ratio of 95:6.2 and placed in a reaction vessel to obtain the reaction system.

[0050] ⑧ Place the reaction system obtained in step ⑦ under nitrogen protection, then heat it to 100℃-105℃ and continuously stir and melt it for 2.5-3 hours to form a homogeneous liquid; then distill the homogeneous liquid under reduced pressure for 20 minutes to remove the trace amounts of water contained in it, and obtain the liquid to be treated.

[0051] ⑨ Add 0.42wt%-0.45wt% of sodium hydride prepared in step S1 ① to the solution to be treated obtained in step ⑧, then evacuate and heat to 142℃-148℃ for 15min-18min to obtain the first reaction solution C.

[0052] ⑩ The reaction solution C obtained in step ⑨ is heated again to 172℃-178℃ under vacuum. Then, 0.95wt%-1wt% of the activator obtained in step S2 ⑥ is added to it according to the mass of reaction solution C. The mixture is stirred evenly and allowed to react for 25min-28min. Then, it is stirred evenly again to obtain the desired nylon emulsion.

[0053] S3: Powdering

[0054] ① Prepare a water-cooled powder making equipment, which includes a water-cooled container base 2 with an arc-shaped bottom and a constricted top for holding deionized water, a heating device 4 with the bottom of the water-cooled container base 2 adapted to its arc shape, a built-in stirring device to make the deionized water flow along the trajectory of the liquid flow 3, and a spray nozzle 1 set in the arc-shaped area of ​​the shoulder of the water-cooled container base 2 with the spray direction forming an angle of 105°-110° with the source direction of the liquid flow 3;

[0055] ② Heat the deionized water in the water-cooled powder making equipment to 65℃-70℃, stir the water flow, and make the water flow velocity at the spray nozzle 1 outlet 1 1.37m / s;

[0056] ③ Spray the nylon emulsion obtained in step S2 (10) from spray nozzle 1 into the water stream obtained in step ② using nitrogen as a carrier. The spray pressure is 2.85 bar and the inlet temperature is 180℃-185℃. After all spraying is completed, filter out the solid, wash and dry it to obtain the desired uniformly spherical nylon powder.

[0057] The nylon powder manufactured according to the method of this embodiment has the following particle size. Figure 1 As shown, the distribution ranges from 20 to 120 μm (narrower than the 10 μm-150 μm range of conventionally manufactured raw powders, see appendix). Figure 2 Furthermore, following a normal distribution, the proportion of powder within the usable range of 20μm-100μm is 98.2%-98.4%. Sieving yields more precise and controllable particle size with less loss compared to commercially available powders; single-particle spheroidization is as follows... Figure 3 , Figure 5 As shown, the sphericity rate is over 70%, and there is virtually no adhesion between individual particles, compared to Figure 4 , Figure 6 The commercially available selective laser printing nylon powder shown has been significantly improved, and the same applies below. Example 2

[0058] The overall structure is the same as in Example 1, except that:

[0059] S2: Preparation of Nylon Original Emulsion

[0060] ④ The acetic anhydride and caprolactam prepared in step ① of stage S1 are added at a mass ratio of 1.09:1 and reacted at 85℃ for 23 hours to obtain reaction solution B;

[0061] ⑦ The caprolactam prepared in step S1 ① and the solid A obtained in step S2 ③ are mixed in a mass ratio of 95:8 and placed in a reaction vessel to obtain the reaction system.

[0062] S3: Powdering

[0063] ② Heat the deionized water in the water-cooled powder making equipment to 65℃-70℃, stir the water flow, and make the water flow velocity at the spray nozzle 1 outlet 1 1.5m / s;

[0064] ③ Spray the nylon emulsion obtained in step S2 (10) from spray nozzle 1 into the water stream obtained in step ② using nitrogen as a carrier. The spray pressure is 2.9 bar and the inlet temperature is 180℃-185℃. After all spraying is completed, filter out the solid, wash and dry it to obtain the desired uniformly spherical nylon powder. Example 3

[0065] The overall structure is the same as in Example 1, except that:

[0066] S2: Preparation of Nylon Original Emulsion

[0067] ④ The acetic anhydride and caprolactam prepared in step ① of stage S1 are added at a mass ratio of 1.07:1 and reacted at 78℃ for 21 hours to obtain reaction solution B;

[0068] ⑦ The caprolactam prepared in step S1 ① and the solid A obtained in step S2 ③ are mixed in a mass ratio of 95:5 and placed in a reaction vessel to obtain a reaction system.

[0069] S3: Powdering

[0070] ② Heat the deionized water in the water-cooled powder making equipment to 65℃-70℃, stir the water flow, and make the water flow velocity at the spray nozzle 1 outlet 1 1.3m / s;

[0071] ③ Spray the nylon emulsion obtained in step S2 (10) from spray nozzle 1 into the water stream obtained in step ② using nitrogen as a carrier. The spray pressure is 2.7 bar and the inlet temperature is 180℃-185℃. After all spraying is completed, filter out the solid, wash and dry it to obtain the desired uniformly spherical nylon powder.

[0072] The above description of the disclosed embodiments is merely intended to enable those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a uniform spheroidized nylon powder for selective laser printing, characterized by Comprise the following stages: S1: raw material preparation ① raw material preparation: prepare sufficient caprolactam, styrene, sodium hydride, azobisisobutyronitrile, acetic anhydride, toluene; ②Auxiliary material preparation: prepare sufficient ethanol; S2: preparation of nylon emulsion ①In the reaction kettle with magnetic stirring device, reflux device, add the styrene prepared in step ① of stage S1, then add sufficient toluene prepared in step ① of stage S1 as reaction solvent, react at 78-85℃ for 21-23h, among which the reaction time is 0h, 8h, 16h, respectively, 1%-2% of azobisisobutyronitrile prepared in step ① of stage S1 is added according to the mass of styrene, until the reaction is completed, and reaction solution A is obtained; ②After the reaction in step ① is completed, remove the solid phase in the reaction solution A, then add sufficient ethanol prepared in step ② of stage S1 dropwise to react, and there is flocculent precipitate produced in the reaction process, dropwise until no more precipitate is produced; ③Filter out the flocculent solid, dry it in the oven and wait for use, and obtain solid A; ④Put acetic anhydride and caprolactam prepared in step ① of stage S1 into the reaction kettle according to the mass ratio (1.07-1.09):1, and react at 78-85℃ for 21-23h, and obtain reaction solution B; ⑤Use vacuum distillation device to treat the reaction solution B obtained in step ④, heat to 60-65℃, and distill to remove byproduct acetic acid until the acetic acid is completely removed, and obtain reaction solution C; ⑥Heat the reaction solution C obtained in step ⑤ to 130-135℃, and collect the distillation product, which is an activator; ⑦Mix caprolactam prepared in step ① of stage S1 with solid A obtained in step ③ of stage S2 according to the mass ratio of 95: (5-8), and put it into the reaction kettle to obtain a reaction system; ⑧Put the reaction system obtained in step ⑦ into nitrogen protection completely, then heat to 100-105℃, continuously stir and melt for 2.5-3h to form a uniform liquid agent; then distill the trace amount of water contained in the uniform liquid agent under reduced pressure for 20min to obtain a treated liquid; ⑨Add 0.42wt%-0.45wt% of sodium hydride prepared in step ① of stage S1 to the treated liquid obtained in step ⑧ according to the total mass of the treated liquid, then vacuumize and heat to 142-148℃ for vacuum reaction for 15-18min to obtain a first reaction solution C; ⑩Reheat the first reaction solution C obtained in step ⑨ to 172-178℃ under vacuum, then add 0.95wt%-1wt% of the activator obtained in step ⑥ of stage S2 to the reaction solution C according to the mass of the reaction solution C, and stir uniformly, place for reaction for 25-28min, then stir uniformly again to obtain the required nylon emulsion; S3: powdering ①Prepare a water cooling powder preparation device, which comprises a water cooling container base (2) with a bottom arc and a top with a closed structure for containing deionized water, a heating device (4) arranged at the bottom of the water cooling container base (2) and adapted to the arc shape of the bottom, an internal stirring device for making the deionized water flow along the trajectory of the liquid flow (3), and a spray port (1) arranged at the shoulder arc area of the water cooling container base (2) and having a spray direction at an angle of 105°-110° with the source direction of the liquid flow (3); ②Heat the temperature of the deionized water in the water cooling powder preparation device to 65℃-70℃, and stir the water flow, so that the flow rate of the water flow at the outlet of the spray port (1) is 1.3m / s-1.5m / s; ③Spray the nylon primary emulsion obtained in step ⑩ of stage S2 into the water flow obtained in step ② using nitrogen as the carrier from the spray port (1), the spraying pressure is 2.7bar-2.9bar, and the inlet temperature is 180℃-185℃; after all the spraying is completed, filter out the solids, wash and dry to obtain the required uniform spheroidized nylon powder.

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