Nylon powder for 3D printing and preparation method thereof

Abstract

The invention relates to the technical field of 3D printing materials, in particular to nylon powder for 3D printing and a preparation method thereof.The nylon powder which is easy to color and has color stability and is used for 3D printing is prepared from modified nylon, a nucleating agent, an antioxidant, a dispersing agent and an auxiliary through a selective laser sintering technology; the low viscosity and high diffusivity of supercritical carbon dioxide are utilized, an active monomer 1, an active monomer 2 and isobornyl methacrylate are subjected to a free radical polymerization reaction, a polymer coating obtained through the reaction permeates into the nylon subsurface, the nylon powder is colored, and meanwhile the overall thermal stability and mechanical performance are improved; wherein a colored azo group in the active monomer 1 can enhance an intermolecular force through pi-pi accumulation energy, so that the thermal stability of the nylon powder is improved, the active monomer 2 has relatively good compatibility with nylon molecules, and the active monomer 2 and the antioxidant synergistically exert an antioxidant effect, so that the nylon powder has a wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of 3D printing materials technology, and in particular to a nylon powder for 3D printing and its preparation method. Background Technology

[0002] 3D printing technology is a rapidly developing rapid prototyping technology in recent years. It is a technology that uses digital model files as a basis and employs bondable materials such as powdered metal or plastic to construct objects by printing layer by layer.

[0003] Because 3D printing technology enables the rapid printing of single or small-batch products, it plays a significant role in product innovation. Based on different forming methods, 3D printing technology can be divided into three types: stereolithography (SLA), fused deposition modeling (FDM), and selective laser sintering (SLS). SLA primarily prints photosensitive resin materials, FDM mainly uses low-melting-point polymer filaments, while SLS printing technology primarily uses polymers, ceramics, metals, and their composite powders—powders that can melt and be bound together when heated. It can be said that materials are paramount to the development of 3D printing technology and also the bottleneck limiting its progress. Therefore, developing a special material suitable for 3D printing has great application prospects and practical significance.

[0004] Nylon powder, as a thermoplastic powder with excellent processing performance, is gaining an increasingly larger market share in the 3D printing market. This is based on the wide processing window and good mechanical properties of nylon materials. With the deepening of research on nylon powder, different powder preparation and printing processes are being continuously explored. Currently, there are two main powder preparation methods: solvent precipitation and cryogenic grinding. The former produces powders with good particle size morphology and flowability, but additives can generally only be added through physical mixing. Cryogenic grinding, on the other hand, is inferior to solvent precipitation in terms of powder morphology and flowability, but additives can be added in the early stages via a screw extruder, resulting in a more uniform addition compared to physical mixing.

[0005] Nylon has a milky white or slightly yellowish appearance, so it must be colored after printing using spray painting or reduction dyeing. This means the color only adheres to the surface and is easily scratched. Furthermore, multiple layers of paint can lead to dimensional inaccuracies, and the coloring process increases cost and complexity.

[0006] In the prior art, patent document CN109130187B discloses a method for preparing colored nylon powder materials for selective laser sintering, including the following steps: adding water-soluble dyes of red, yellow, and blue primary colors to water, heating and stirring until fully dissolved to obtain red, yellow, and blue primary color dye solutions; adding nylon powder for selective laser sintering to the red, yellow, and blue primary color dye solutions, heating and stirring, filtering and drying to obtain red, yellow, and blue primary color nylon powder materials for selective laser sintering; this invention provides a solution for simultaneous 3D printing of multiple colors, but the compatibility between water-soluble dyes and nylon is poor, and they are not bonded by chemical covalent bonds, so the dyes are easy to fall off the nylon surface, and the color stability at high temperatures needs further improvement.

[0007] Therefore, based on the relevant technologies mentioned above, there is an urgent need to develop a nylon powder for 3D printing and its preparation method. Summary of the Invention

[0008] In view of this, the purpose of this invention is to provide a nylon powder for 3D printing and its preparation method, so as to solve the problems of poor coloring and color stability of nylon powder for 3D printing in the prior art.

[0009] To achieve the above objectives, the present invention provides a nylon powder for 3D printing and a method for preparing the same.

[0010] A nylon powder for 3D printing comprises the following parts by weight of raw materials:

[0011] Modified nylon 127-142 parts; nucleating agent 0.7-1.9 parts; antioxidant 0.4-1.4 parts; dispersant 0.2-0.5 parts; additives 0.2-0.5 parts;

[0012] The modified nylon was prepared from nylon, active monomer 1, active monomer 2 and isobornyl methacrylate;

[0013] The nylon is at least one of nylon 1010, nylon 1212, nylon 12 and nylon 11, and has a melting point of 140-190°C;

[0014] The active monomer 1 was prepared from 4-phenylazophenol, triethylamine and methacryloyl chloride;

[0015] The active monomer 2 was prepared from N-(2-hydroxyethyl)acrylamide, 3,5-dicyclohexyl-4-hydroxyphenylpropionic acid and N,N'-dicyclohexylcarbodiimide.

[0016] Preferably, the modified nylon is prepared by the following method:

[0017] Step A1. Add dichloromethane to 4-phenylazophenol and place it in an ice-water bath at 0-3°C. After mixing evenly, add triethylamine and continue stirring for 10-15 minutes. Then, add methacryloyl chloride dropwise and stir at 450-550 rpm for 4-5 hours. Then, quench with saturated sodium carbonate solution. Extract the aqueous layer with dichloromethane and wash and dry the organic layer with brine. Dissolve the obtained powder in petroleum ether and purify it with silica gel column chromatography to obtain active monomer 1.

[0018] Step A2. In a water bath at 0-5℃, 3,5-dicyclohexyl-4-hydroxyphenylpropionic acid and N-(2-hydroxyethyl)acrylamide are dissolved in dichloromethane, then transferred to a reactor and stirred for 20-30 minutes under nitrogen protection to obtain mixture A.

[0019] Step A3. Add dichloromethane to N,N'-dicyclohexylcarbodiimide, stir until dissolved, then drop it into mixture A, add 4-dimethylaminopyridine, stir and heat to react. After the reaction is complete, purify with eluent, then distill under reduced pressure and dry under vacuum to obtain active monomer 2.

[0020] Step A4. Degas nylon, isobornyl methacrylate, active monomer 1, active monomer 2, and azobisisobutyronitrile in an autoclave for 15 minutes. Introduce carbon dioxide and control the pressure at 0.27-0.41 MPa. Then, quickly turn off the key and increase the pressure to V1 and the temperature to T1. After stabilization, increase the pressure to V2 and the temperature to T2. After stabilization again, continue to increase the pressure to V3 and stir at 450-550 rpm for 22-24 hours. After completion, allow the autoclave to cool to room temperature and exhaust the carbon dioxide to obtain modified nylon.

[0021] Preferably, the ratio of 4-phenylazophenol, dichloromethane, triethylamine and methacryloyl chloride used in step A1 is 5-6.5g:200-260mL:5.78-7.51g:3.71-4.83g.

[0022] Preferably, the ratio of 3,5-dicyclohexyl-4-hydroxyphenylpropionic acid, N-(2-hydroxyethyl)acrylamide and dichloromethane in step A2 is 2.09-2.33g:0.86-0.96g:20-23mL.

[0023] Preferably, the ratio of dichloromethane, N,N'-dicyclohexylcarbodiimide, mixture A and 4-dimethylaminopyridine in step A3 is 10-20 mL: 2.3-4.6 g: 23-45 mL: 0.09-0.18 g;

[0024] The rinsing agent is obtained by mixing ethyl acetate and cyclohexane in a mass ratio of 1-2:1;

[0025] The heating reaction is carried out at a temperature of 18-23°C for 23-24 hours.

[0026] Preferably, the mass ratio of nylon, isobornyl methacrylate, active monomer 1, active monomer 2 and azobisisobutyronitrile in step A4 is 8.4-12.6:0.42-0.63:0.021-0.032:0.021-0.032:0.021-0.032.

[0027] Preferably, in step A4, V1 is 5.42-5.53 MPa and T1 is 47-52°C;

[0028] The V2 is 13.72-13.82 MPa and the T2 is 60-65°C;

[0029] The V3 is 20.65-20.73 MPa.

[0030] Preferably, the nucleating agent is either nano-sized talc powder or nano-sized calcium carbonate;

[0031] The antioxidant is tris(2,4-di-tert-butyl)phosphite.

[0032] Preferably, the additive is at least one selected from silicon dioxide, titanium dioxide, zinc dioxide, and metal soap;

[0033] The dispersant is polyvinylpyrrolidone.

[0034] A method for preparing nylon powder for 3D printing includes the following steps:

[0035] Step S1. Under a nitrogen atmosphere, add modified nylon, nucleating agent, dispersant, antioxidant, additives and ethanol into a high-pressure reactor, stir and heat to 140-150°C and keep at the temperature for 2-3 hours, then cool to 55-65°C and filter to obtain filter residue;

[0036] Step S2. After centrifugation, vacuum drying, and sieving of the filter residue, nylon powder for 3D printing is obtained;

[0037] The particle size of the nylon powder after sieving in step S2 is 42-48 μm.

[0038] The beneficial effects of this invention are:

[0039] This invention provides a nylon powder for 3D printing and its preparation method. The invention utilizes selective laser sintering technology, employing modified nylon, nucleating agents, antioxidants, dispersants, and additives to prepare a nylon powder for 3D printing that is easily colored and possesses color stability. Specifically, leveraging the low viscosity and high diffusivity of supercritical carbon dioxide, a free radical polymerization reaction is carried out in supercritical carbon dioxide to penetrate a polymer coating obtained by reacting reactive monomers 1 and 2 with isobornyl methacrylate onto the nylon subsurface. This process not only colors the nylon powder but also improves its overall thermal stability and mechanical properties. Reactive monomer 1 introduces colored azo groups. In nylon molecules, the π-π stacking of azo groups enhances intermolecular forces, thereby improving the thermal stability of nylon powder. Furthermore, the benzene rings within the molecule further enhance the chemical stability of the nylon powder. Active monomer 2, by introducing amide groups into the hindered phenolic antioxidant 3,5-dicyclohexyl-4-hydroxyphenylpropionic acid, can form hydrogen bonds with the amide groups in the nylon molecule to achieve a toughening effect. It also exhibits good compatibility with nylon molecules, which is beneficial for its antioxidant effect. Simultaneously, it forms a synergistic effect with the tris(2,4-di-tert-butyl)phosphite antioxidant, further enhancing the color stability of the nylon powder. Compared with existing technologies, this method has broad application prospects. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0041] The sources and properties of some of the raw materials used in this invention are as follows:

[0042] Nylon 12 was purchased from Huake 3D Technology Co., Ltd.; 4-phenylazophenol was purchased from Shanghai Maclean Biochemical Technology Co., Ltd.; methacryloyl chloride was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; 3,5-dicyclohexyl-4-hydroxyphenylpropionic acid was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; N-(2-hydroxyethyl)acrylamide was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; 4-dimethylaminopyridine was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; and azobisisobutyronitrile was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0043] Example 1: A method for preparing nylon powder for 3D printing, comprising the following steps:

[0044] S1. Add 200 mL of dichloromethane to 5 g of 4-phenylazophenol and place it in an ice-water bath at 0°C. After mixing evenly, add 5.78 g of triethylamine and continue stirring for 10 min. Then, add 3.71 g of methacryloyl chloride dropwise and stir at 450 rpm for 4 h. Then, quench with 80 mL of saturated sodium carbonate solution. Extract the aqueous layer with dichloromethane and wash and dry the organic layer with brine. Dissolve the obtained powder in petroleum ether and purify it with silica gel column chromatography to obtain active monomer 1.

[0045] S2. In a water bath at 0℃, 2.09g of 3,5-dicyclohexyl-4-hydroxyphenylpropionic acid and 0.86g of N-(2-hydroxyethyl)acrylamide were dissolved in 20mL of dichloromethane, and then transferred to a reactor. Under nitrogen protection, the mixture was stirred for 20min to obtain mixture A.

[0046] S3. Add 10 mL of dichloromethane to 2.3 g of N,N'-dicyclohexylcarbodiimide, stir until dissolved, then dropwise into 23 mL of mixture A, and add 0.09 g of 4-dimethylaminopyridine. Stir and heat at 18 °C for 23 h. After the reaction is complete, purify with a mixture of ethyl acetate and cyclohexane in a mass ratio of 1:1, then distill under reduced pressure and dry under vacuum to obtain active monomer 2.

[0047] S4. Degas 8.4g nylon, 0.42g isobornyl methacrylate, 0.021g active monomer 1, 0.021g active monomer 2 and 0.021g azobisisobutyronitrile in an autoclave for 15min. Introduce carbon dioxide and control the pressure at 0.27MPa. Then quickly turn off the key and increase the pressure to 5.42MPa and the temperature to 47°C. After stabilization, increase the pressure to 13.72MPa and the temperature to 60°C. After stabilization again, continue to increase the pressure to 20.65MPa and stir at 450rpm for 22h. After completion, allow the autoclave to cool to room temperature and exhaust the carbon dioxide to obtain modified nylon.

[0048] S5. Under a nitrogen atmosphere, 127g of modified nylon, 0.7g of nano-sized talc, 0.2g of polyvinylpyrrolidone, 0.4g of tris(2,4-di-tert-butyl)phosphite, 0.2g of silica and 180mL of ethanol were added to a high-pressure reactor, stirred and heated to 140°C for 2 hours, then cooled to 55°C and filtered to obtain filter residue.

[0049] S6. After centrifugation, vacuum drying, and sieving of the filter residue, nylon powder for 3D printing is obtained.

[0050] Example 2: A method for preparing nylon powder for 3D printing, comprising the following steps:

[0051] S1. Add 220 mL of dichloromethane to 5.5 g of 4-phenylazophenol and place it in an ice-water bath at 1°C. After mixing evenly, add 6.38 g of triethylamine and continue stirring for 13 min. Then, add 4.08 g of methacryloyl chloride dropwise and stir at 500 rpm for 4.5 h. Then, quench with 80 mL of saturated sodium carbonate solution. Extract the aqueous layer with dichloromethane and wash and dry the organic layer with brine. Dissolve the obtained powder in petroleum ether and purify it with silica gel column chromatography to obtain active monomer 1.

[0052] S2. In a water bath at 2℃, 2.18g of 3,5-dicyclohexyl-4-hydroxyphenylpropionic acid and 0.9g of N-(2-hydroxyethyl)acrylamide were dissolved in 21mL of dichloromethane, and then transferred to a reactor. Under nitrogen protection, the mixture was stirred for 24min to obtain mixture A.

[0053] S3. Add 14 mL of dichloromethane to 3 g of N,N'-dicyclohexylcarbodiimide and stir until dissolved. Then add the solution dropwise to 30 mL of mixture A, followed by 0.012 g of 4-dimethylaminopyridine. Stir and heat at 20 °C for 23.5 h. After the reaction is complete, purify the solution with a mixture of ethyl acetate and cyclohexane in a mass ratio of 1.5:1. Then, distill under reduced pressure and dry under vacuum to obtain active monomer 2.

[0054] S4. Degas 10.2g nylon, 0.48g isobornyl methacrylate, 0.025g active monomer 1, 0.025g active monomer 2 and 0.025g azobisisobutyronitrile in an autoclave for 15min. Introduce carbon dioxide and control the pressure at 0.32MPa. Then quickly turn off the key and increase the pressure to 5.46MPa and the temperature to 49°C. After stabilization, increase the pressure to 13.75MPa and the temperature to 63°C. After stabilization again, continue to increase the pressure to 20.68MPa and stir at 500rpm for 23h. After completion, allow the autoclave to cool to room temperature and exhaust the carbon dioxide to obtain modified nylon.

[0055] S5. Under a nitrogen atmosphere, 132g of modified nylon, 1.1g of nano-sized talc, 0.3g of polyvinylpyrrolidone, 0.8g of tris(2,4-di-tert-butyl)phosphite, 0.3g of silica and 180mL of ethanol were added to a high-pressure reactor, stirred and heated to 145°C and kept at that temperature for 2.5h. Then, the temperature was lowered to 58°C and filtered to obtain filter residue.

[0056] S6. After centrifugation, vacuum drying, and sieving of the filter residue, nylon powder for 3D printing is obtained.

[0057] Example 3: A method for preparing nylon powder for 3D printing, comprising the following steps:

[0058] S1. Add 240 mL of dichloromethane to 6 g of 4-phenylazophenol and place it in an ice-water bath at 2°C. After mixing evenly, add 6.91 g of triethylamine and continue stirring for 13 min. Then, add 4.52 g of methacryloyl chloride dropwise and stir at 500 rpm for 4.5 h. Then, quench with 80 mL of saturated sodium carbonate solution. Extract the aqueous layer with dichloromethane and wash and dry the organic layer with brine. Dissolve the obtained powder in petroleum ether and purify it with silica gel column chromatography to obtain active monomer 1.

[0059] S2. In a water bath at 3°C, 2.28 g of 3,5-dicyclohexyl-4-hydroxyphenylpropionic acid and 0.93 g of N-(2-hydroxyethyl)acrylamide were dissolved in 22 mL of dichloromethane, and then transferred to a reactor. Under nitrogen protection, the mixture was stirred for 27 min to obtain mixture A.

[0060] S3. Add 17 mL of dichloromethane to 3.9 g of N,N'-dicyclohexylcarbodiimide, stir until dissolved, then add dropwise to 37 mL of mixture A, followed by 0.15 g of 4-dimethylaminopyridine. Stir and heat at 20 °C for 23.5 h. After the reaction is complete, purify the product with a mixture of ethyl acetate and cyclohexane in a mass ratio of 1.5:1, then distill under reduced pressure and dry under vacuum to obtain active monomer 2.

[0061] S4. Degas 11.7g nylon, 0.56g isobornyl methacrylate, 0.029g active monomer 1, 0.029g active monomer 2 and 0.029g azobisisobutyronitrile in an autoclave for 15min. Introduce carbon dioxide and control the pressure at 0.36MPa. Then quickly turn off the key and increase the pressure to 5.49MPa and the temperature to 50°C. After stabilization, increase the pressure to 13.78MPa and the temperature to 63°C. After stabilization again, continue to increase the pressure to 20.7MPa and stir at 500rpm for 23h. After completion, allow the autoclave to cool to room temperature and exhaust the carbon dioxide to obtain modified nylon.

[0062] S5. Under a nitrogen atmosphere, 137g of modified nylon, 1.5g of nano-sized talc, 0.4g of polyvinylpyrrolidone, 1.1g of tris(2,4-di-tert-butyl)phosphite, 0.4g of silica and 180mL of ethanol were added to a high-pressure reactor, stirred and heated to 148°C and kept at that temperature for 2.5h. Then, the temperature was lowered to 63°C and filtered to obtain filter residue.

[0063] S6. After centrifugation, vacuum drying, and sieving of the filter residue, nylon powder for 3D printing is obtained.

[0064] Example 4: A method for preparing nylon powder for 3D printing, comprising the following steps:

[0065] S1. Add 260 mL of dichloromethane to 6.5 g of 4-phenylazophenol and place it in an ice-water bath at 3°C. After mixing evenly, add 7.51 g of triethylamine and continue stirring for 15 min. Then, add 4.83 g of methacryloyl chloride dropwise and stir at 550 rpm for 5 h. Then, quench with 80 mL of saturated sodium carbonate solution. Extract the aqueous layer with dichloromethane and wash and dry the organic layer with brine. Dissolve the obtained powder in petroleum ether and purify it with silica gel column chromatography to obtain active monomer 1.

[0066] S2. In a water bath at 5°C, 2.33 g of 3,5-dicyclohexyl-4-hydroxyphenylpropionic acid and 0.96 g of N-(2-hydroxyethyl)acrylamide were dissolved in 23 mL of dichloromethane, and then transferred to a reactor. Under nitrogen protection, the mixture was stirred for 30 min to obtain mixture A.

[0067] S3. Add 20 mL of dichloromethane to 4.6 g of N,N'-dicyclohexylcarbodiimide, stir until dissolved, then dropwise into 45 mL of mixture A, and add 0.18 g of 4-dimethylaminopyridine. Stir and heat at 23 °C for 24 h. After the reaction is complete, purify with a mixture of ethyl acetate and cyclohexane in a mass ratio of 2:1, then distill under reduced pressure and dry under vacuum to obtain active monomer 2.

[0068] S4. Degas 12.6g nylon, 0.63g isobornyl methacrylate, 0.032g active monomer 1, 0.032g active monomer 2 and 0.032g azobisisobutyronitrile in an autoclave for 15min. Introduce carbon dioxide and control the pressure at 0.41MPa. Then quickly turn off the key and increase the pressure to 5.53MPa and the temperature to 52°C. After stabilization, increase the pressure to 13.82MPa and the temperature to 65°C. After stabilization again, continue to increase the pressure to 20.73MPa and stir at 550rpm for 24h. After completion, allow the autoclave to cool to room temperature and exhaust the carbon dioxide to obtain modified nylon.

[0069] S5. Under a nitrogen atmosphere, 142g of modified nylon, 1.9g of nano-sized talc, 0.5g of polyvinylpyrrolidone, 1.4g of tris(2,4-di-tert-butyl)phosphite, 0.5g of silica and 200mL of ethanol were added to a high-pressure reactor, stirred and heated to 150°C and kept at that temperature for 3 hours. Then, the temperature was lowered to 65°C and filtered to obtain the filter residue.

[0070] S6. After centrifugation, vacuum drying, and sieving of the filter residue, nylon powder for 3D printing is obtained.

[0071] Comparative Example 1:

[0072] Compared with Example 1, this comparative example did not add active monomer 1 during the preparation of modified nylon. All other steps and parameters were the same, and will not be repeated here. Nylon powder was finally obtained.

[0073] Comparative Example 2:

[0074] Compared with Example 1, this comparative example did not add active monomer 2 during the preparation of modified nylon. All other steps and parameters were the same, and will not be repeated here. Nylon powder was finally obtained.

[0075] Comparative Example 3:

[0076] This comparative example differs from Example 1 only in that "modified nylon" is replaced with "nylon 12". All other steps and parameters are the same, and will not be repeated here. The final product is nylon powder.

[0077] Comparative Example 4:

[0078] This comparative example differs from Example 1 only in that "3,5-dicyclohexyl-4-hydroxyphenylpropionic acid" is replaced with "2,6-dimethyl-4-hydroxyphenylpropionic acid". All other steps and parameters are the same, and will not be repeated here. Nylon powder is finally obtained.

[0079] Performance testing:

[0080] The nylon powders prepared in Examples 1-4 and Comparative Examples 1-4 were placed in a 3D printer (EOSNIT P396) with a powder thickness of 0.12 mm, a preheating temperature of 174 °C, a laser power of 70 W, and a scanning speed of 4 m / h. The tensile yield stress, elongation at break, notched impact strength of cantilever beam, and surface color of the samples were then tested.

[0081] An aging test was conducted on the sample, with the aging temperature set at 170℃ and the time gradient at 4h. After aging for 28h, the retention rate of elongation at break, the retention rate of notched impact strength of cantilever beam, and the surface color of the sample after aging were tested.

[0082] Table 1. Summary of experimental data from Examples 1-4 and Comparative Examples 1-4

[0083] project Tensile yield stress (MPa) Elongation at break (%) <![CDATA[Izod impact strength (KJ / m 2 )]]> Surface color of sample before aging Example 1 49.4 42.6 5.9 yellow Example 2 47.2 39.3 5.4 yellow Example 3 48.5 40.3 5.5 yellow Example 4 45.7 38.6 5.2 yellow Comparative Example 1 42.2 34.1 4.8 White Comparative Example 2 35.6 28.4 4.2 yellow Comparative Example 3 28.5 21.2 3.6 White Comparative Example 4 43.6 35.7 5.0 yellow

[0084] Table 2 Summary of experimental data from Examples 1-4 and Comparative Examples 1-4

[0085] project Notched impact strength retention rate of cantilever beam after aging (%) Elongation at break retention rate after aging (%) Surface color of aged samples Example 1 80 76 yellow Example 2 82 80 yellow Example 3 73 70 yellow Example 4 75 72 yellow Comparative Example 1 70 65 White Comparative Example 2 59 56 light yellow Comparative Example 3 33 37 light yellow Comparative Example 4 68 67 yellow

[0086] Data Analysis:

[0087] As can be seen from Tables 1 and 2, the nylon powder prepared by this invention exhibits better color stability and mechanical properties. This is likely due to the use of the low viscosity and high diffusivity of supercritical carbon dioxide in this invention. Free radical polymerization is carried out in supercritical carbon dioxide to penetrate the polymer coating obtained by reacting reactive monomers 1 and 2 with isobornyl methacrylate onto the nylon surface. This not only colors the nylon powder but also improves its overall thermal stability and mechanical properties. Specifically, reactive monomer 1 successfully introduces colored azo groups into the nylon molecule through the acrylate groups contained in its molecule. This chemical bond makes the nylon molecule less prone to fading, and the azo groups... π-π stacking enhances intermolecular forces, thereby improving the thermal stability of nylon powder, while the benzene ring contained in the molecule further enhances the chemical stability of nylon powder. The core phenolic hydroxyl group of the 3,5-dicyclohexyl-4-hydroxyphenylpropionic acid molecule contains a large cyclohexyl group at the ortho position, which enhances antioxidant activity through steric hindrance and induction effects. By introducing amide groups, the active monomer 2 can form hydrogen bonds with the amide groups in the nylon molecule to achieve toughening effect. It also has good compatibility with nylon molecules, which is conducive to exerting antioxidant effects. At the same time, it also forms a synergistic effect with tris(2,4-di-tert-butyl)phosphite antioxidant, further enhancing the color stability of nylon powder.

[0088] This invention is intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A nylon powder for 3D printing, characterized in that, Includes the following quantities of raw materials: Modified nylon 127-142 parts; nucleating agent 0.7-1.9 parts; antioxidant 0.4-1.4 parts; dispersant 0.2-0.5 parts; additives 0.2-0.5 parts; The modified nylon was prepared from nylon, active monomer 1, active monomer 2 and isobornyl methacrylate; The nylon is at least one of nylon 1010, nylon 1212, nylon 12 and nylon 11, and has a melting point of 140-190°C; The active monomer 1 was prepared from 4-phenylazophenol, triethylamine and methacryloyl chloride; The active monomer 2 was prepared from N-(2-hydroxyethyl)acrylamide, 3,5-dicyclohexyl-4-hydroxyphenylpropionic acid and N,N'-dicyclohexylcarbodiimide.

2. The nylon powder for 3D printing according to claim 1, characterized in that, The modified nylon is prepared as follows: Step A1. Add dichloromethane to 4-phenylazophenol and place it in an ice-water bath at 0-3°C. After mixing evenly, add triethylamine and continue stirring for 10-15 minutes. Then, add methacryloyl chloride dropwise and stir at 450-550 rpm for 4-5 hours. Then, quench with saturated sodium carbonate solution. Extract the aqueous layer with dichloromethane and wash and dry the organic layer with brine. Dissolve the obtained powder in petroleum ether and purify it with silica gel column chromatography to obtain active monomer 1. Step A2. In a water bath at 0-5℃, 3,5-dicyclohexyl-4-hydroxyphenylpropionic acid and N-(2-hydroxyethyl)acrylamide are dissolved in dichloromethane, then transferred to a reactor and stirred for 20-30 minutes under nitrogen protection to obtain mixture A. Step A3. Add dichloromethane to N,N'-dicyclohexylcarbodiimide, stir until dissolved, then drop it into mixture A, add 4-dimethylaminopyridine, stir and heat to react. After the reaction is complete, purify with eluent, then distill under reduced pressure and dry under vacuum to obtain active monomer 2. Step A4. Degas nylon, isobornyl methacrylate, active monomer 1, active monomer 2, and azobisisobutyronitrile in an autoclave for 15 minutes. Introduce carbon dioxide and control the pressure at 0.27-0.41 MPa. Then, quickly turn off the key and increase the pressure to V1 and the temperature to T1. After stabilization, increase the pressure to V2 and the temperature to T2. After stabilization again, continue to increase the pressure to V3 and stir at 450-550 rpm for 22-24 hours. After completion, allow the autoclave to cool to room temperature and exhaust the carbon dioxide to obtain modified nylon.

3. The nylon powder for 3D printing according to claim 2, characterized in that, The ratio of 4-phenylazophenol, dichloromethane, triethylamine and methacryloyl chloride used in step A1 is 5-6.5g: 200-260mL: 5.78-7.51g: 3.71-4.83g.

4. The nylon powder for 3D printing according to claim 2, characterized in that, The ratio of 3,5-dicyclohexyl-4-hydroxyphenylpropionic acid, N-(2-hydroxyethyl)acrylamide, and dichloromethane used in step A2 is 2.09-2.33 g: 0.86-0.96 g: 20-23 mL.

5. The nylon powder for 3D printing according to claim 2, characterized in that, In step A3, the ratio of dichloromethane, N,N'-dicyclohexylcarbodiimide, mixture A, and 4-dimethylaminopyridine is 10-20 mL: 2.3-4.6 g: 23-45 mL: 0.09-0.18 g. The rinsing agent is obtained by mixing ethyl acetate and cyclohexane in a mass ratio of 1-2:1; The heating reaction is carried out at a temperature of 18-23°C for 23-24 hours.

6. The nylon powder for 3D printing according to claim 2, characterized in that, The mass ratio of nylon, isobornyl methacrylate, active monomer 1, active monomer 2 and azobisisobutyronitrile in step A4 is 8.4-12.6:0.42-0.63:0.021-0.032:0.021-0.032:0.021-0.

032.

7. The nylon powder for 3D printing according to claim 2, characterized in that, In step A4, V1 is 5.42-5.53 MPa and T1 is 47-52°C. The V2 is 13.72-13.82 MPa and the T2 is 60-65°C; The V3 is 20.65-20.73 MPa.

8. The nylon powder for 3D printing according to claim 1, characterized in that, The nucleating agent is either nano-sized talc powder or nano-sized calcium carbonate; The antioxidant is tris(2,4-di-tert-butyl)phosphite.

9. The nylon powder for 3D printing according to claim 1, characterized in that, The additive is at least one of silicon dioxide, titanium dioxide, zinc dioxide, and metal soap; The dispersant is polyvinylpyrrolidone.

10. The method for preparing nylon powder for 3D printing according to any one of claims 1-9, characterized in that, Includes the following steps: Step S1. Under a nitrogen atmosphere, add modified nylon, nucleating agent, dispersant, antioxidant, additives and ethanol into a high-pressure reactor, stir and heat to 140-150°C and keep at the temperature for 2-3 hours, then cool to 55-65°C and filter to obtain filter residue; Step S2. After centrifugation, vacuum drying, and sieving of the filter residue, nylon powder for 3D printing is obtained; The particle size of the nylon powder after sieving in step S2 is 42-48 μm.