Polystyrene powder for selective laser sintering and preparation method thereof

Abstract

The present invention relates to the technical field of polymer powder materials for additive manufacturing, and more particularly to a method for preparing epoxy resin-reinforced polystyrene composite powder for selective laser sintering. To address the common problem of low sintered component strength associated with polystyrene powder for selective laser sintering, the present invention directly produces epoxy resin-reinforced polystyrene composite powder for selective laser sintering by mixing styrene, epoxy resin, a flow aid, and the like, followed by a polymerization reaction. The powder particles are spherical or ellipsoidal, exhibit good powder fluidity, and the preparation method is simple, with low energy consumption and equipment investment. The reaction product is easily separated from the solid and liquid phases, resulting in significantly stronger components than those of polystyrene.

Description

Technical Field

[0001] The present invention is applied to the technical field of materials for additive manufacturing, and in particular relates to a polystyrene powder material for selective laser sintering and a preparation method thereof. Background Art

[0002] Additive manufacturing, which combines traditional manufacturing techniques with new materials manufacturing technology, represents a major technological revolution in the manufacturing sector and has been widely applied in new product design, medical devices, aerospace, and other fields. Selective Laser Sintering (SLS), one of the most widely used additive manufacturing technologies, uses software to construct a 3D model of a part. Using solid powder as the raw material, the actual object is created layer by layer, offering significant advantages for the integrated formation of complex structural components.

[0003] Currently, common polymer materials used for selective laser sintering include polystyrene, nylon, polyethersulfone resin, carbon fiber, polyamide, polyaryletherketone, etc. Among them, polystyrene (PS) has the advantages of low price, low molding shrinkage, low preheating temperature during the molding process, and low equipment requirements. It is the most widely used. However, the main problem with polystyrene is the low strength of the sintered products. To address this issue, Shi Yusheng et al. (Copolymer-based powder material for selective laser sintering and preparation method thereof, 200810048011.1) and Xu Bin et al. (SAN resin powder material based on selective laser sintering and preparation method thereof, 201911286791.8) proposed a method for preparing copolymer (SAN) powder of styrene and acrylonitrile to improve the strength of sintered parts while retaining the advantages of low preheating temperature and high molding precision of PS; Yang Laixia et al. used a method of mixing glass fiber powder and polymer powders such as ABS and PET with polystyrene powder to improve the strength of sintered parts (A method for preparing glass fiber and polystyrene composite powder materials for SLS, CN 107418079 A; Experimental study on coupling of SLS process parameters of PS / PET / GF ternary composite materials, China Plastics, Vol. 33, No. 2, pp. 62-68, PS / ABS Experimental Study on Process Parameters of Selective Laser Sintering of Composite Powders, Engineering Plastics Applications, Vol. 45, No. 5, pp. 57-62); Zheng Haizhong et al. prepared composite particles with nano-alumina as the core and polystyrene as the shell by emulsion polymerization and mixed them with polystyrene powder, effectively improving the impact strength of the sintered parts (Characterization of Core-Shell Nano-Al2O3 / PS and Study on Toughening Selective Laser Sintering of Polystyrene, Materials Engineering, 2007, 3; Effect of core-shell composite particles on the sintering behavior and properties of nano-Al2O3 / polystyrene composite prepared by SLS, Materials Letters, 2006, 60: 1219-1223). Other researchers have used wax or resin (epoxy resin) post-treatment methods to improve the mechanical properties and surface finish of the PS prototypes obtained by SLS. (A selective laser sintering PS post-processing process, CN2020102338200; A vacuum resin impregnation device for 3D printing polystyrene parts, CN2016110664455). The polystyrene powder, styrene copolymer powder, and polymer-modified polystyrene powder described in the above reports are all obtained by cryogenic grinding, which involves freezing the raw materials to a low temperature and then crushing them into a powder of the desired particle size. This method consumes a lot of energy and has high manufacturing costs.Another method for obtaining laser sintering powder is solvent precipitation, which involves dissolving a polymer in a suitable solvent and precipitating the polymer as a powder by varying the temperature or adding a second component. This method easily produces particles of good shape and size, but it requires a large amount of organic solvent and is relatively complex to prepare. Summary of the Invention

[0004] Aiming at the problems of low strength of existing polystyrene powder parts for SLS and the existing technology for preparing polystyrene powder for SLS, the present invention provides a method for preparing reinforced polystyrene powder for SLS.

[0005] To achieve the above-mentioned purpose, the embodiment of the present invention adopts the following technical solutions:

[0006] A method for preparing SLS polystyrene powder comprises the following steps:

[0007] Step a, adding epoxy resin, flow aid, and initiator to monomer styrene, stirring evenly to obtain a monomer mixture;

[0008] Step b, adding a nonionic emulsifier to the monomer mixture obtained in step a, and stirring evenly;

[0009] Step c, adding an alkaline aqueous solution of fatty acid salts to the mixture obtained in step b, and stirring until a stable oil-in-water emulsion is formed;

[0010] Step d, heating to react,

[0011] Step e: After the reaction is completed, the temperature is lowered and an acid solution is added, stirred, and the solid obtained by solid-liquid separation is the modified polystyrene powder.

[0012] Compared with the prior art, the method for preparing polystyrene nanoparticle composite powder for SLS provided by the present invention has the advantages of simple process, low energy consumption, easy product separation, good powder fluidity and high strength of sintered products.

[0013] In the present invention, since the epoxy resin, flow aid, and other components are mixed with monomers and then polymerized to directly obtain the modified powder containing the epoxy resin, the process is simple, equipment investment is small, energy consumption is saved, and microscopic differences between individual powder particles are small. The epoxy resin can impart higher mechanical strength to the finished product.

[0014] To achieve the above-mentioned purpose, the embodiment of the present invention adopts the following technical solutions:

[0015] Preferably, the monomer phase mixture in step a is composed of the following components in parts by weight: 20-30 parts of styrene, 0.3-0.7 parts of initiator, 2-6 parts of epoxy resin, and 0.1-0.3 parts of flow aid.

[0016] Preferably, the epoxy resin in step a is epoxy E-44; the bisphenol A skeleton of epoxy E-44 can give the material high strength and heat resistance, the hydroxyl group can increase the adhesion between powder particles, and the methylene chain can provide softness.

[0017] Preferably, the flow aid is one or more of polyethylene wax, paraffin wax, and carnauba wax.

[0018] Preferably, the initiator is azobisisobutyronitrile.

[0019] Preferably, the stirring speed in step a is 300-500 rpm.

[0020] Preferably, the nonionic emulsifier in step b is composed of sorbitan fatty acid ester and alkylphenol polyoxyethylene ether, with the weight ratio being 0.7-1.2 parts of sorbitan fatty acid ester and 0.65-1.0 parts of alkylphenol polyoxyethylene ether, and the amount of the nonionic emulsifier added being 6-8% of the weight ratio of the monomer styrene.

[0021] Preferably, the specific operation of adding the nonionic emulsifier in step b is: after uniformly mixing the emulsifier in the formula, add it at a stirring speed of 400-600 rpm and stir for 20-30 minutes.

[0022] Preferably, the fatty acid salt in step c is potassium stearate, and its weight portion is 1.1-1.5 parts. Potassium stearate can improve the emulsification effect and simultaneously increase the speed and separation rate of the solid powder product from the liquid phase, thereby improving the product yield. The alkaline aqueous solution is composed of 0.1-0.3 parts of sodium hydroxide and 150-200 parts of water.

[0023] Preferably, the temperature of the alkaline solution of fatty acid salt added in step c is 65-70°C.

[0024] Preferably, the operation method of adding the alkaline aqueous solution of fatty acid salt in step c is: before adding, the monomer mixture is heated to 55-60°C, the stirring speed is 800-1100 rpm, and the stirring time is 30-40 minutes. During this process, the reaction system changes from a single oil phase to an oil-in-water system. The addition of potassium stearate improves the emulsification effect and increases the stability of the dispersed droplets. ， During the subsequent polymerization process, the carboxylic acid metal salt potassium stearate can partially participate in the curing reaction of the epoxy resin. Furthermore, under the alkaline environment of the reaction system, the -OH groups contained in the nonionic emulsifier added in step b can partially react with the epoxy groups in the epoxy resin. By adjusting the ratio and dosage of the nonionic emulsifier and fatty acid salt, as well as the stirring speed, the diameter of the dispersed oil phase droplets can be controlled from a few microns to tens of microns.

[0025] Preferably, the reaction in step d is carried out at 65-70° C. for 1-2 hours; the temperature is raised to 80-85° C. for 5-7 hours; the temperature is then further raised to 85-90° C. for 30-50 minutes; and the reaction is carried out at a stirring speed of 400-600 rpm.

[0026] Preferably, after the reaction in step e is completed, the temperature is lowered to 20-35°C and an acid solution is added. The acid solution is a 5-10% by mass hydrochloric acid solution in an amount of 10-15 parts. The addition of the acid solution can quickly break the emulsion, making the powder particles obtained by polymerization easier to subsequently separate and wash. This overcomes the shortcomings of polystyrene particles, which are difficult to separate and have a low separation rate due to their density being similar to that of water, and improves the separation speed and separation rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a scanning electron microscope photograph of the polystyrene composite powder obtained in an embodiment of the present invention. DETAILED DESCRIPTION

[0028] In order to make the technical means, creative features and achieved purposes and advantages of the present invention easy to understand, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0029] Example 1

[0030] The present invention provides a method for preparing polystyrene powder for selective laser sintering, comprising the following steps:

[0031] a. Mix 30 g of epoxy resin E-44, 2 g of polyethylene wax (BAKER HUGHES Polywax 400), and 220 g of styrene, then add 5 g of azobisisobutyronitrile and stir at 400 rpm for 20 min to obtain a monomer mixture;

[0032] b. Mix 8 g of sorbitan fatty acid ester and 7.2 g of alkylphenol polyoxyethylene ether and add them to the above mixture. At the same time, heat the mixture to 60°C at a heating rate of 0.25°C / min and stir at 400 rpm.

[0033] c. Increase the speed to 1000 rpm and add an aqueous solution of 1800 g distilled water, 12 g potassium stearate, and 2 g sodium hydroxide at 70°C;

[0034] d. After stirring for 30 min, reduce the stirring speed to 500 rpm, heat to 65 ° C and react for 2 hours, then heat to 78 ° C and react for 6 hours, and continue to heat to 87 ° C and react for 40 min;

[0035] e. Cool to 30°C and stop stirring; add 100 mL of 10% hydrochloric acid solution, stir to break the emulsion, separate, wash, and dry to obtain polystyrene composite powder.

[0036] Example 2

[0037] The present invention provides a method for preparing polystyrene powder for selective laser sintering, comprising the following steps:

[0038] a. Mix 60 g of epoxy resin, 2 g of polyethylene wax (BAKER HUGHES Polywax 400), 1 g of carnauba wax, and 300 g of styrene, then add 7 g of azobisisobutyronitrile and stir at 500 rpm for 25 min to obtain a monomer mixture;

[0039] b. Mix 12 g of sorbitan fatty acid ester and 10 g of alkylphenol polyoxyethylene ether and add them to the above mixture. At the same time, heat the mixture to 58°C at a heating rate of 0.3°C / min and stir at 600 rpm.

[0040] c. Increase the speed to 1100 rpm and add an aqueous solution of 2000 g distilled water, 12.8 g potassium stearate, and 3 g sodium hydroxide at 65°C;

[0041] d. After stirring for 40 min, reduce the stirring speed to 500 rpm, heat to 65 °C and react for 2 h, then heat to 75 °C and react for 7 h, and continue to heat to 90 °C and react for 30 min;

[0042] e. Cool to 25°C and stop stirring; add 150 mL of 8% hydrochloric acid solution, stir to break the emulsion, separate, wash, and dry to obtain modified polystyrene microbead powder.

[0043] Example 3

[0044] The present invention provides a method for preparing polystyrene powder for selective laser sintering, comprising the following steps:

[0045] a. Mix 20 g of epoxy resin, 1 g of polyethylene wax (BAKER HUGHES Polywax 400), 1 g of paraffin wax (No. 54), and 200 g of styrene, then add 4 g of azobisisobutyronitrile and stir at 300 rpm for 30 min to obtain a monomer mixture;

[0046] b. Mix 7 g of sorbitan fatty acid ester and 6.5 g of alkylphenol polyoxyethylene ether and add them to the above mixture. At the same time, heat the mixture to 60°C at a heating rate of 0.30°C / min and stir at 600 rpm.

[0047] c. Increase the speed to 900 rpm and add an aqueous solution of 1500 g distilled water, 14 g potassium stearate, and 1.2 g sodium hydroxide at 68°C;

[0048] d. After stirring for 30 min, reduce the stirring speed to 450 rpm, heat to 70 ° C and react for 1 hour, then heat to 80 ° C and react for 5 h, and continue to heat to 85 ° C and react for 50 min;

[0049] e. Cool to 25°C and stop stirring; add 120 mL of 5% hydrochloric acid solution, stir to break the emulsion, separate, wash, and dry to obtain modified polystyrene powder.

[0050] Example 4

[0051] The present invention provides a method for preparing polystyrene powder for selective laser sintering, comprising the following steps:

[0052] a. Mix 35 g of epoxy resin, 1 g of paraffin wax (No. 54), 1.5 g of polyethylene wax (BAKER HUGHES Polywax 400), and 250 g of styrene, then add 6 g of azobisisobutyronitrile and stir at 400 rpm for 25 min to obtain a monomer mixture;

[0053] b. Mix 8.4 g of sorbitan fatty acid ester and 8.2 g of alkylphenol polyoxyethylene ether and add them to the above mixture. At the same time, heat the mixture to 55°C at a heating rate of 0.25°C / min and stir at 500 rpm.

[0054] c. Increase the speed to 800 rpm and add an aqueous solution of 2000 g distilled water, 15 g potassium stearate, and 1.5 g sodium hydroxide at 65°C;

[0055] d. After stirring for 40 min, reduce the stirring speed to 450 rpm, heat to 70 ° C and react for 70 min, then heat to 80 ° C and react for 5 h, and continue to heat to 86 ° C and react for 50 min;

[0056] e. Cool to 28°C and stop stirring; add 130 mL of 8% hydrochloric acid solution, stir to break the emulsion, separate, wash, and dry to obtain modified polystyrene powder.

[0057] Example 5

[0058] The present invention provides a method for preparing polystyrene powder for selective laser sintering, comprising the following steps:

[0059] a. Mix 32 g of epoxy resin, 1 g of paraffin wax (No. 54), and 280 g of styrene, then add 3 g of azobisisobutyronitrile and stir at 300 rpm for 30 min to obtain a monomer mixture;

[0060] b. Mix 11 g of sorbitan fatty acid ester and 9.5 g of alkylphenol polyoxyethylene ether and add them to the above mixture. At the same time, heat the mixture to 58°C at a heating rate of 0.30°C / min and stir at 500 rpm.

[0061] c. Increase the speed to 1100 rpm and add an aqueous solution of 2000 g distilled water, 11 g potassium stearate, and 1 g sodium hydroxide at 65°C.

[0062] d. After stirring for 35 min, reduce the stirring speed to 450 rpm, heat to 70 ° C and react for 1 hour, then heat to 77 ° C and react for 6 h, and continue to heat to 85 ° C and react for 50 min;

[0063] e. Cool to 30°C and stop stirring; add 100 mL of 10% hydrochloric acid solution, stir to break the emulsion, separate, wash, and dry to obtain modified polystyrene powder.

[0064] Comparative Example 1

[0065] a. Add 3 g of azobisisobutyronitrile to a mixture of 220 g of styrene, and stir for 20 min at a stirring speed of 400 rpm to obtain a monomer mixture;

[0066] b. Mix 5.6 g of sorbitan fatty acid ester and 5 g of alkylphenol polyoxyethylene ether and add them to the above mixture. At the same time, heat the mixture to 60°C at a heating rate of 0.25°C / min and stir at 400 rpm.

[0067] c. Increase the speed to 1000 rpm and add an aqueous solution of 1800 g distilled water, 8.4 g potassium stearate, and 2 g sodium hydroxide at 70°C;

[0068] d. After stirring for 30 min, reduce the stirring speed to 500 rpm, heat to 65°C and react for 2 h, then heat to 78°C and react for 6 h, and continue to heat to 87°C and react for 40 min;

[0069] e. Cool to 30°C and stop stirring; add 100 mL of 10% hydrochloric acid solution, stir to break the emulsion, separate, wash, and dry to obtain polystyrene powder.

[0070] Comparative Example 2

[0071] Sodium dodecylbenzenesulfonate was used instead of potassium stearate in Example 1. The rest of the preparation method was the same as that in Example 1. After the polymerization process was completed, the reaction system was in an emulsion state. When 500 g of a 10% by mass hydrochloric acid solution was added, no demulsification occurred.

[0072] Comparative Example 3

[0073] a. Mix 30 g of epoxy resin E-44, 2 g of polyethylene wax (BAKER HUGHES Polywax 400), and 200 g of styrene, then add 5 g of azobisisobutyronitrile and stir at 400 rpm for 20 min to obtain a monomer mixture;

[0074] b. Mix 16 g of sorbitan fatty acid ester and 14.4 g of alkylphenol polyoxyethylene ether and add them to the above mixture. At the same time, heat the mixture to 60 ° C at a heating rate of 0.25 ° C / min and stir at 400 rpm;

[0075] c. Increase the speed to 1000 rpm and add an aqueous solution consisting of 1800 g of distilled water and 2 g of sodium hydroxide at a temperature of 70°C;

[0076] d. After stirring for 30 minutes, reduce the stirring speed to 500 rpm and raise the temperature to 65°C. After reacting for 2 hours, 4-8 mm sticky particles were observed in the reaction system. Then raise the temperature to 78°C and react. After reacting for 40 minutes, the sticky particles were observed to aggregate into sticky lumps, and the reaction was stopped.

[0077] Test Example 1

[0078] The performance tests were performed on the styrene composite powders obtained in Examples 1 to 5 and the polystyrene powder obtained in Comparative Example 1.

[0079] (1) Determine the powder particle size (using a particle counter (RC-2100) produced by OMEC Technology Co., Ltd.). The results are shown in Table 1.

[0080] Table 1 Test results of powder particle size (statistical unit: particle)

[0081] sample Example 1 Example 2 Example 3 Example 4 Example 5 Comparative Example 1 Coefficient of dispersion / % 36.91 28.65 41.24 107.9 49.26 35.57 Standard deviation / μm 4.39 3.25 3.03 10.00 3.46 1.17 D2 / μm 20.24 17.80 14.64 36.92 15.45 7.01 D50 / μm 12.36 11.48 6.96 4.03 6.31 2.74 D98 / μm 2.48 3.59 2.69 2.06 2.33 2.24 Average particle size / μm 11.89 11.34 7.35 9.27 7.02 3.12 Volume average particle size / μm 16.04 13.79 13.96 32.75 11.95 5.68

[0082] (2) The modified polystyrene powder prepared in the embodiment of the present invention was tested by scanning electron microscope, as shown in the following photos: Figure 1 As shown, it can be seen that the powder particles are spherical or ellipsoidal, with a size ranging from a few microns to tens of microns.

[0083] (3) SLS molding performance test

[0084] The modified polystyrene powders obtained in Examples 1-5 were subjected to SLS molding using a continuous CO2 laser with a wavelength of 10.6 µm, an 18 W laser power, a scanning speed of 1500 mm / s, a powder layer thickness of 0.1 mm, a scanning interval of 0.1 mm, and a preheating temperature of 90°C. The results showed that the sintered samples of the powders obtained in Examples 1-5 exhibited good molding precision and showed no warping.

[0085] Test Example 2

[0086] After SLS molding, the polystyrene composite powders obtained in Examples 1 to 5 and the polystyrene powder obtained in Comparative Example 1 were tested for tensile strength using a microcomputer-controlled universal testing machine (Shanghai Qisheng Instrument Co., Ltd., ETM104C) in accordance with GB / T 1040.1-2006 (specimen size: 75 mm × 5.45 mm × 4.25 mm). The impact strength was tested using an cantilever beam impact testing machine (Yangzhou Saisi Testing Equipment Co., Ltd., SMT-3002I) in accordance with GB / T 1843-2008 (specimen size: 80 mm × 10 mm × 4 mm, notch depth: 2 mm).

[0087] Table 2 Mechanical properties test data of sintered samples of polystyrene composite powders obtained in Examples 1 to 5 and polystyrene powder obtained in Comparative Example 1

[0088] sample Example 1 Example 2 Example 3 Example 4 Example 5 Comparative Example 1 Tensile strength (MPa) 45.12 42.68 37.10 43.97 40.45 27.27 Elongation at break (%) 23.21 8.59 22.93 22.77 21.53 3.67 <![CDATA[Impact strength (KJ / m 2 )]]> 6.97 5.75 6.06 6.92 6.52 4.01

Claims

1. A method for preparing polystyrene powder for selective laser sintering, characterized in that: The process steps include: Step a, adding epoxy resin, flow aid, and initiator to monomer styrene, stirring evenly to obtain a monomer phase mixture; the monomer phase mixture is composed of the following components in parts by weight: 2 to 6 parts epoxy resin, 20 to 30 parts styrene, 0.3 to 0.7 parts initiator, and 0.1 to 0.3 parts flow aid; the epoxy resin is epoxy resin E-44; the initiator is azobisisobutyronitrile; the flow aid is one or more of polyethylene wax, paraffin wax, and carnauba wax; Step b, the nonionic emulsifier is added to the monomer mixture obtained in step a, stirring uniformly; the nonionic emulsifier is composed of the following components in parts by weight: 0.7 to 1.2 parts of sorbitan fatty acid ester, 0.65 to 1.0 parts of alkylphenol polyoxyethylene ether, the amount of the nonionic emulsifier added is 6 to 8% of the number of parts of the styrene monomer; Step c, adding an alkaline aqueous solution of a fatty acid salt to the mixture obtained in step b, and stirring until a stable oil-in-water emulsion is formed; the fatty acid salt is potassium stearate; the alkaline aqueous solution of a fatty acid salt is composed of the following components in parts by weight: 150 to 200 parts of distilled water, 1.1 to 1.5 parts of a fatty acid salt, 0.1 to 0.3 parts of sodium hydroxide; Step d, heating to react; Step e: After the reaction is completed, the temperature is lowered to 40° C., an acid solution is added, stirred, and the solid obtained by solid-liquid separation is the polystyrene composite powder.

2. The method for preparing polystyrene powder according to claim 1, wherein The temperature of the alkaline aqueous solution is 65-70°C; the temperature of the reaction system is maintained at 55-60°C before the aqueous solution is added in step c, and the aqueous solution is added in the following manner: the stirring speed is 800-1100 rpm, and the stirring time is 30-40 min.

3. The method for preparing polystyrene powder according to claim 1, wherein The reaction in step d is carried out at 65-70° C. for 1-2 hours, at 75-80° C. for 5-7 hours, and then the temperature is continuously raised to 85-90° C. for 30-50 minutes. The reaction is carried out at a stirring speed of 400-600 rpm.

4. The method for preparing polystyrene powder according to claim 1, wherein After the reaction in step e is completed, the temperature is lowered to 20-35° C., and an acid solution is added. The acid solution is a hydrochloric acid solution with a mass fraction of 5-10%, and the addition amount is 10-15 parts.

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