Composite powder for laser selective sintering and method for preparing the same

Abstract

The present application relates to a kind of composite powder for laser selective sintering and its preparation method, belong to magnetic material technical field.The present application is used for the composite powder of laser selective sintering, comprising: thermoplastic resin powder, magnetic powder and binder;The average particle size of the thermoplastic resin powder is greater than the average particle size of the magnetic powder;The magnetic powder is coated in at least part of the surface of the thermoplastic resin powder.The three-dimensional magneto-rheological elastomer product made of laser selective sintering using the composite powder has high density, and under the action of external magnetic field, it shows significant magneto-rheological effect.

Description

Technical Field

[0001] This invention relates to the field of magnetic materials technology, and in particular to a composite powder for selective laser sintering and its preparation method. Background Technology

[0002] Magnetorheological elastomers (MLEs) are composite materials composed of a flexible polymer matrix and magnetic particles. Their mechanical properties, such as modulus and damping, can undergo rapid, reversible, and significant changes under the influence of an external magnetic field, making them widely used in vibration reduction, noise reduction, sensing, and actuators. MLEs are typically prepared using traditional molding, casting, or extrusion processes, but these methods suffer from technical limitations, such as difficulty in fabricating complex three-dimensional structures and the inability to achieve functional gradient distributions.

[0003] Existing technologies employ 3D printing to address the aforementioned issues by replacing traditional fabrication methods. This involves directly forming magnetorheological elastomers with complex geometries and gradient functions through a layer-by-layer accumulation process. However, fused deposition modeling (FDM) presents challenges for low-modulus, highly flexible elastomer substrates, including difficulties in filament feeding, which compromises the stability and precision of the printing process. Furthermore, the weak interlayer bonding in the printed structure affects overall mechanical properties, and precise control over the distribution and orientation of magnetic particles during printing is challenging.

[0004] Selective laser sintering (SLS) offers advantages such as no need for support, the ability to fabricate complex geometries, high material utilization, and good mechanical properties of the finished products. It is particularly well-suited for preparing magnetorheological elastomers from low-modulus, highly flexible elastomer matrices. However, in practical applications, it has been found that mixing low-density flexible polymer matrix powder with high-density magnetic particle powder can easily lead to uneven powder distribution during SLS, resulting in sintering failure, poor part density, and unsatisfactory performance. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a composite powder for laser selective sintering and its preparation method.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a composite powder for laser selective sintering, comprising: Thermoplastic resin powders, magnetic powders, and binders; The average particle size of the thermoplastic resin powder is greater than the average particle size of the magnetic powder. The magnetic powder is coated on at least a portion of the surface of the thermoplastic resin powder.

[0007] This invention combines small-particle-size magnetic powder with large-particle-size thermoplastic resin powder, and uses a binder to uniformly coat the magnetic powder onto the surface of the thermoplastic resin powder to form a composite powder with a coating structure. When this composite powder is used in laser selective sintering, it can solve the segregation problem caused by the density difference between magnetic powder particles and thermoplastic particles, thereby effectively improving the uniformity of powder spreading and molding shrinkage, and thus improving the density and mechanical properties of magnetorheological elastomer materials.

[0008] As a preferred embodiment of the composite powder for selective laser sintering according to the present invention, the average particle size of the thermoplastic resin powder is ≥45μm, and / or the average particle size of the magnetic powder is ≤20μm.

[0009] As a preferred embodiment of the composite powder for selective laser sintering according to the present invention, the average particle size of the thermoplastic resin powder is 45 μm to 105 μm, and / or the average particle size of the magnetic powder is 5 μm to 20 μm.

[0010] In some embodiments, the average particle size of the thermoplastic resin powder may be, but is not limited to, a range of any or both of 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, 100 μm, and 105 μm.

[0011] In some embodiments, the average particle size of the magnetic powder may be, but is not limited to, any or both of the following: 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm.

[0012] As a preferred embodiment of the composite powder for selective laser sintering according to the present invention, the mass percentage of the thermoplastic resin powder is 20% to 50% based on the total mass of the thermoplastic resin powder and the magnetic powder.

[0013] In some embodiments, based on the total mass of the thermoplastic resin powder and the magnetic powder, the mass percentage of the thermoplastic resin powder may be, but is not limited to, any one or any two of the following: 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50%.

[0014] By controlling the mass ratio of thermoplastic resin powder in thermoplastic resin powder and magnetic powder within the above range, it is possible not only to better improve the molding and processing performance and mechanical properties of magnetorheological elastomer materials, but also to better take into account their magnetic response performance.

[0015] In a preferred embodiment of the composite powder for selective laser sintering according to the present invention, the binder has a percentage content of 0.1% to 1% relative to the total mass of the thermoplastic resin powder and the magnetic powder.

[0016] In some embodiments, the percentage of the binder relative to the total mass of the thermoplastic resin powder and the magnetic powder may be, but is not limited to, a range of any one or both of 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, and 1%.

[0017] The main function of the binder is to effectively bond thermoplastic resin powder and magnetic powder into stable composite particles. By controlling the percentage of the binder relative to the total mass of thermoplastic resin powder and magnetic powder within the above-mentioned range, it is possible not only to better improve the strength, flowability and uniformity of the composite particles, but also to reduce the influence of residual binder on the magnetic and mechanical properties of magnetorheological elastomer materials.

[0018] As a preferred embodiment of the composite powder for selective laser sintering according to the present invention, the composite powder further includes a dispersing agent, which includes at least one of stearic acid, zinc stearate, and nano-silica.

[0019] Dispersants can reduce the interfacial energy between thermoplastic resin powder and magnetic powder. Adding dispersants not only makes it easier to form composite powder with a coating structure, but also further improves the particle size uniformity of the formed composite powder, thereby improving the powder spreading effect during selective laser sintering.

[0020] In some embodiments, the average particle size of the nano-silica is preferably 20 nm to 50 nm, for example, but not limited to any or both of 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, and 50 nm.

[0021] In a preferred embodiment of the composite powder for selective laser sintering according to the present invention, the dispersing agent has a percentage content of 0.01% to 0.1% relative to the total mass of the thermoplastic resin powder and the magnetic powder.

[0022] In some embodiments, the percentage of the dispersing agent relative to the total mass of the thermoplastic resin powder and the magnetic powder may be, but is not limited to, any one or any two of the following values: 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, and 0.1%.

[0023] By controlling the percentage content of dispersing agent relative to the total mass of thermoplastic resin powder and magnetic powder within the above range, the interfacial energy between thermoplastic resin powder and magnetic powder can be better reduced, and the formation of impurity phases can be avoided, so that the magnetorheological elastomer material has both good mechanical properties and excellent magnetic properties.

[0024] As a preferred embodiment of the composite powder for selective laser sintering according to the present invention, the thermoplastic resin powder includes at least one of thermoplastic polyurethane powder and styrene-based thermoplastic elastomer powder. And / or, the magnetic powder includes at least one of carbonyl iron powder, iron-cobalt alloy powder, iron-nickel alloy powder, and iron oxide powder; And / or, the adhesive includes at least one of polyvinyl alcohol, polyethylene glycol, and polyvinylpyrrolidone. The molecular weight of the adhesive can be conventionally selected based on the actual situation.

[0025] In some embodiments, the thermoplastic polyurethane powder includes, but is not limited to, at least one of polyester-type thermoplastic polyurethane, polyether-type thermoplastic polyurethane, polycaprolactone-type thermoplastic polyurethane, and copolymers thereof.

[0026] In some embodiments, the styrene-based thermoplastic elastomer powder includes, but is not limited to, at least one of styrene-ethylene / butene-styrene block copolymer (SEBS), styrene-ethylene / propylene-styrene block copolymer (SEPS), and their hydrogenated modified products.

[0027] Secondly, the present invention provides a method for preparing composite powder for selective laser sintering, comprising the following steps: mixing thermoplastic resin powder and magnetic powder uniformly to obtain a mixed powder, spraying a binder solution onto the mixed powder, granulating, and drying to obtain composite powder for selective laser sintering.

[0028] Specifically, the following steps are included: S1. The thermoplastic resin powder and magnetic powder (and dispersing agent) are mechanically stirred and mixed to obtain a mixed powder; S2. Mix the binder and solvent evenly to obtain a binder solution, then spray it evenly onto the mixed powder obtained in S1, and then transfer it to a drum granulator for granulation. After drying, sieve to obtain the composite powder.

[0029] In some embodiments, the mechanical stirring speed in step S1 is 60 r / min to 200 r / min, and the mixing time is 10 min to 120 min.

[0030] In some embodiments, the solvent in step S2 includes, but is not limited to, water, ethanol, or acetone.

[0031] In some embodiments, the rotational speed of the drum granulator in step S2 is 20 r / min to 80 r / min, and the mixing time is 30 min to 90 min.

[0032] In some embodiments, the drying in step S2 is preferably vacuum drying, with a drying temperature of 80°C to 150°C and a drying time of 2 hours to 6 hours.

[0033] In some implementations, the sieving in step S2 can be performed using a sieve, and the mesh size of the sieve can be selected according to actual needs.

[0034] For example, the granulated powder can be sieved first using a 325-mesh sieve to obtain powder with a particle size ≥45μm, and then the granulated powder with a particle size ≥105μm can be sieved using a 150-mesh sieve to finally obtain a composite powder with a particle size of 45μm to 105μm.

[0035] In a preferred embodiment of the method for preparing composite powder for selective laser sintering according to the present invention, the binder solution is composed of a binder and a solvent, wherein the solvent has a percentage content of 1% to 5% relative to the total mass of the thermoplastic resin powder and the magnetic powder.

[0036] In some embodiments, the percentage of the solvent relative to the total mass of the thermoplastic resin powder and the magnetic powder may be, but is not limited to, any one or any two of 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Due to density differences, conventional powder mixing processes usually result in segregation between magnetic powder particles and thermoplastic particles. Through innovative granulation processes, the uniformity of powder spreading and the uniformity of molding shrinkage are effectively improved.

[0038] (2) The SLS process achieves complete fusion of powder particles through laser melting, and the resulting part is an isotropic dense entity with strong interlayer bonding force. Its overall mechanical properties are superior to the layered structure printed by the FDM process.

[0039] (3) SLS technology itself can manufacture extremely complex geometries and internal structures (such as lattices and porous structures) without support, which makes it possible to prepare magnetorheological elastomer devices with customized mechanical and magnetic response characteristics, which is difficult to achieve by extrusion process.

[0040] (4) The process of this invention is simple, the forming efficiency is high, and the finished product has good precision and consistency, making it suitable for mass production.

[0041] (5) Gradient changes in magnetic particle concentration and distribution can be achieved in a single part, thereby creating a magnetorheological elastomer with gradient function. Attached Figure Description

[0042] Figure 1 SEM images of the composite powder used for laser selective sintering in Example 1, as well as carbonyl iron powder and thermoplastic polyurethane powder. Figure 2 The image shows a physical diagram of a magnetorheological elastomer lattice structure formed by selective laser sintering of the composite powder used in Example 1. Detailed Implementation

[0043] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0044] Unless otherwise specified, all other materials and reagents used in the examples are commercially available.

[0045] <Raw Materials and Reagents> Nano-silica, average particle size 20nm, manufacturer Evonik, brand name AEROSIL R972; Polyvinyl alcohol, manufactured by Wanwei, brand name PVA 1788; Polyethylene glycol, manufacturer: Dow, grade: PEG-4000; Zinc stearate, manufactured by Shandong Haona, grade HN-ZnSt-10.

[0046] Example 1 A method for preparing composite powder for laser selective sintering includes the following steps: S1. Add thermoplastic resin powder (polyether thermoplastic polyurethane powder (Covestro, Germany), average particle size 100μm), magnetic powder (carbonyl iron powder (Jiangxi Yuean New Materials), average particle size 5μm) and dispersant (nano silica) to a mixer for mechanical mixing (mixing speed 100r / min, time 60min) to obtain mixed powder; S2. Dissolve the binder (polyvinyl alcohol) in a solvent (water) to form a binder solution. Then, spray the binder solution evenly onto the mixed powder in step S1. Place the powder in a roller granulator and roll it at a low speed of 20 r / min for 30 min. Then, dry it at 80°C for 4 h to obtain a composite powder for laser selective sintering. The mass ratio of thermoplastic resin powder to magnetic powder is 40:60. The amount of dispersant added is 0.1% of the total mass of thermoplastic resin powder and magnetic powder; the amount of binder added is 0.1% of the total mass of thermoplastic resin powder and magnetic powder; and the amount of solvent added is 2% of the total mass of thermoplastic resin powder and magnetic powder.

[0047] SEM tests were performed on the above-mentioned thermoplastic resin powder, magnetic powder, and composite powder. The test results are as follows: Figure 1 As shown. Figure 1 In the image, (a) is magnetic powder, (b) is thermoplastic resin powder, and (c) and (d) are composite powders. According to... Figure 1 It can be seen that the magnetic powder is uniformly coated on the surface of the thermoplastic resin powder to form a composite powder with a coating structure.

[0048] Examples 2 to 3 Except for the difference in the average particle size of the magnetic powder in step S1 compared to Example 1, the rest is the same as in Example 1; the average particle size of the magnetic powder in Example 2 is 10 μm, and the average particle size of the magnetic powder in Example 3 is 20 μm.

[0049] Examples 4 to 5 Except for the difference in the average particle size of the thermoplastic resin powder in step S1 compared to Example 2, the rest is the same as in Example 2; the average particle size of the thermoplastic resin powder in Example 4 is 75 μm, and the average particle size of the thermoplastic resin powder in Example 5 is 45 μm.

[0050] Examples 6 to 7 Except for the difference in the mass ratio of thermoplastic resin powder to magnetic powder in step S1 compared to Example 2, the rest is the same as in Example 2; in Example 6, the mass ratio of thermoplastic resin powder to magnetic powder is 20:80, and in Example 7, the mass ratio of thermoplastic resin powder to magnetic powder is 50:50.

[0051] Example 8 Except for the types of thermoplastic resin powder and magnetic powder, the types and amounts of dispersing agents in step S1, and the types and amounts of binders and solvents in step S2, which are different from those in Example 2, the rest are the same as in Example 2. The thermoplastic resin powder is styrene-ethylene / butene-styrene block copolymer (Ningbo Changhong Polymer), the magnetic powder is iron(III) oxide (Qingdao Xinzhongji), the dispersing agent is zinc stearate, and its addition amount is 0.03% of the total mass of thermoplastic resin powder and magnetic powder; the binder is polyethylene glycol, and its addition amount is 0.1% of the total mass of thermoplastic resin powder and magnetic powder; the solvent addition amount is 5% of the total mass of thermoplastic resin powder and magnetic powder.

[0052] Comparative Example 1 Step S2 (which involves directly mixing thermoplastic resin powder, magnetic powder, and dispersant to obtain composite powder) is omitted; the rest is the same as in Example 1.

[0053] Comparative Example 2 Except for the difference between the average particle size of the thermoplastic resin powder and the average particle size of the magnetic powder in step S1 and Example 1, the rest is the same as in Example 1; wherein, the average particle size of the thermoplastic resin powder is 30 μm and the average particle size of the magnetic powder is 30 μm.

[0054] Performance Testing The composite powders from each embodiment and comparative example were loaded into an HRPS-IV laser selective sintering equipment for laser selective sintering (laser power 15W, scanning speed 4000mm / s, powder layer thickness 0.1mm, scanning interval 0.12mm) to obtain three-dimensional magnetorheological elastomer products (such as...). Figure 2 (As shown).

[0055] The three-dimensional magnetorheological elastomer product underwent the following performance tests, and the test results are shown in Table 1: 1) Density Test: According to GB / T 1033.1-2008 "Determination of density of non-foamed plastics - Part 1: Impregnation method, liquid pyrrhotide bottle method and titration method", the actual density ρ of the sample is determined by the impregnation method (Archimedes' displacement method). s Calculate using the following formula (1): ρ s =[m s / (m s -m s,l )]×ρ l (1) Where, ρ s The density of the sample is given in g / cm³. 3 ;m s The mass of the sample in air is expressed in g; m s,l The mass of the sample suspended in the immersion liquid is expressed in g; ρ l The density of the impregnating liquid at the test temperature, in g / cm³. 3 .

[0056] In actual batching, based on the known mass fraction of each component, the theoretical density ρ0 of the mixed powder sample is calculated using the following formula (2): ρ0=1 / (w1 / ρ1+w2 / ρ2) (2) Where w1 and w2 are the mass fractions of component 1 (thermoplastic resin) and component 2 (magnetic material), respectively (i.e., w1 + w2 = 1); ρ1 and ρ2 are the theoretical densities (g / cm³) of component 1 and component 2, respectively.3 ).

[0057] Based on the obtained actual density ρ s Given the theoretical density ρ0, the packing density D can be calculated using the following formula (3): D=ρ s / ρ0×100% (3) 2) Molding quality test: visual inspection, evaluation criteria are as follows: "Good": The edges are clear and there are no missing corners. The surface is smooth and there are no particles. The dimensions are accurate. The cross-section is dense and there are no pores. It has good flexibility. "Fair": Slightly damaged edges, slightly powdery surface, small dimensional deviation, a few micropores in the cross-section, and average flexibility; "Poor": The edges are severely collapsed or cracked, the surface is rough and unmelted, the size is severely deformed, the cross-section is loose, brittle or soft.

[0058] 3) Dimensional relative error: The length of the sample was measured using a high-precision caliper, and each sample was measured 5 times and the average value was taken; the dimensional relative error δ was calculated by the following formula: δ=(X0-X) / X0×100% (4) Where X0 is the design length of the specimen (nominal dimension in the CAD model), mm; X is the actual test length of the specimen, mm.

[0059] 4) Tensile strength test: According to GB / T 1040.1-2006 "Determination of tensile properties of plastics - Part 1: General", the tensile strength of the magnetorheological elastomer specimen was tested using a universal testing machine. The 1B dumbbell-shaped specimen fixed in the standard was selected, with a gauge length of 50 mm, a width of 10 mm for the parallel part in the middle, and a thickness of 4 mm. The tensile rate was 2 mm / min.

[0060] 5) Shear modulus change rate test: The test was conducted using a dynamic thermomechanical analyzer (DMA) according to ISO 1827:2016 "Determination of shear modulus of rubber or thermoplastic rubber - Fourfold shear method". A double shear specimen with dimensions of length × width × height = 20mm × 20mm × 4mm was used. The shear modulus of the specimen was tested under the same temperature range, and the shear modulus change rate MR was calculated by the following formula (5): MR=(G B -G0) / G0×100% (5) Where MR is the rate of change of shear modulus (relative magnetorheological effect), %; G B G0 is the shear modulus under magnetic field strength B, in MPa; G0 is the shear modulus under zero field, in MPa.

[0061] Table 1 shows the performance of the three-dimensional magnetorheological elastomer products corresponding to each embodiment and comparative example. As can be seen from the data in Table 1, the density of the three-dimensional magnetorheological elastomer products corresponding to the composite powders used for selective laser sintering in Examples 1 to 8 is not less than 85.6%, the molding quality evaluation is "acceptable" or above, the dimensional relative error is ≤4.2%, the tensile strength is ≥8.9MPa, and the shear modulus change rate is ≥27.3%. This indicates that the three-dimensional magnetorheological elastomer products prepared by selective laser sintering using this composite powder have high density and exhibit significant magnetorheological effects under the action of an external magnetic field.

[0062] Meanwhile, as shown in Comparative Example 1, if thermoplastic resin powder and magnetic powder are directly mixed and laser selective sintering is performed, problems such as segregation, agglomeration, and uneven dispersion are likely to occur during the mixing process due to the significant differences in density and particle size between the two. This results in poor melt wetting and numerous internal defects during sintering. The final sample has low density, poor dimensional accuracy, and weak mechanical properties, and the uneven distribution of the magnetic phase leads to poor stability of the magnetorheological effect.

[0063] According to Comparative Example 2, it can also be found that when the particle size of thermoplastic resin powder and magnetic powder is similar, it is difficult to form a composite powder with a coating structure. This results in weak interfacial bonding and more interfacial defects between the magnetic powder and thermoplastic resin powder. During the selective laser sintering process, problems such as local agglomeration, high porosity, and low density are likely to occur, ultimately leading to poor mechanical properties and magnetorheological response stability of the sample.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A composite powder for selective laser sintering, characterized in that, include: Thermoplastic resin powders, magnetic powders, and binders; The average particle size of the thermoplastic resin powder is greater than the average particle size of the magnetic powder. The magnetic powder is coated on at least a portion of the surface of the thermoplastic resin powder.

2. The composite powder as described in claim 1, characterized in that, The average particle size of the thermoplastic resin powder is ≥45μm, and / or the average particle size of the magnetic powder is ≤20μm.

3. The composite powder as described in claim 2, characterized in that, The average particle size of the thermoplastic resin powder is 45 μm to 105 μm, and / or the average particle size of the magnetic powder is 5 μm to 20 μm.

4. The composite powder as described in claim 1, characterized in that, Based on the total mass of the thermoplastic resin powder and the magnetic powder, the mass percentage of the thermoplastic resin powder is 20% to 50%.

5. The composite powder as described in claim 1, characterized in that, The binder comprises 0.1% to 1% of the total mass of the thermoplastic resin powder and the magnetic powder.

6. The composite powder as described in claim 1, characterized in that, The composite powder also includes a dispersing agent, which includes at least one of stearic acid, zinc stearate, and nano-silica.

7. The composite powder as described in claim 6, characterized in that, The dispersing agent comprises 0.01% to 0.1% of the total mass of the thermoplastic resin powder and the magnetic powder.

8. The composite powder as described in claim 1, characterized in that, The thermoplastic resin powder includes at least one of thermoplastic polyurethane powder and styrene-based thermoplastic elastomer powder; And / or, the magnetic powder includes at least one of carbonyl iron powder, iron-cobalt alloy powder, iron-nickel alloy powder, and iron oxide powder; And / or, the adhesive includes at least one of polyvinyl alcohol, polyethylene glycol, and polyvinylpyrrolidone.

9. The method for preparing the composite powder for laser selective sintering according to any one of claims 1 to 8, characterized in that, Includes the following steps: Thermoplastic resin powder and magnetic powder are mixed evenly to obtain a mixed powder. Then, a binder solution is sprayed into the mixed powder, granulated, and dried to obtain a composite powder for laser selective sintering.

10. The preparation method according to claim 9, characterized in that, The adhesive solution consists of an adhesive and a solvent, wherein the solvent comprises 1% to 5% of the total mass of the thermoplastic resin powder and the magnetic powder.

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