Magnetoelastomer preparation method

Abstract

The invention provides a preparation method of a magnetoelastomer, which comprises the following steps: mixing Fe3O4 magnetic powder with liquid photosensitive resin, applying an external magnetic field to induce to form a Fe3O4 magnetic powder-resin pre-structured system, doping NdFeB magnetic powder-resin into the Fe3O4 magnetic powder-resin pre-structured system to realize high dispersibility and anti-sedimentation stability of the magnetic powder, and preparing the magnetoelastomer by using a photocuring printer. And the magnetoelastic body is printed, so that the force-magnetism conversion efficiency of the magnetoelastic body is remarkably improved.

Description

Technical Field

[0001] This invention relates to the technical field of composite materials, and more specifically, to a method for preparing a magnetic elastomer. Background Technology

[0002] The rapid development of wearable health monitoring, human-computer interaction, and intelligent robots is placing higher demands on magnetic tactile sensors. Flexible magnetic tactile sensors consist of a magnetoelastic body and a magnetic sensor, with the magnetoelastic body being the core component for force-to-magnetic conversion. The "force-to-magnetic conversion efficiency" determines the sensor's performance; the more uniformly the magnetic powder is dispersed in the flexible matrix, the stronger the magnetic properties, the more significant the change in magnetic signal caused by external force, and the better the sensitivity and linearity. Therefore, preparing a magnetoelastic body with "uniformly dispersed magnetic powder, stable magnetic properties, and matched mechanical properties" is a key bottleneck for industrialization.

[0003] Additive manufacturing (3D printing) allows for layered, free-form molding, bypassing the limitations of molds on complex structures and serving as the primary pathway for customizing magnetoelastics. Photopolymerization 3D printing, with its high precision (submicron level) and wide resin compatibility, is preferentially used for molding magnetic photosensitive resins. This resin, composed of "liquid photosensitive resin + micro / nano magnetic powder," must simultaneously meet the following requirements: Molding adaptability: viscosity 500-5000 cP, curing speed matched to exposure parameters, low shrinkage after curing, and good interlayer bonding; Magnetic functional stability: uniform dispersion of magnetic powder without long-term sedimentation, ensuring uniform magnetic properties of the molded part. Commonly used magnetic powders in existing technologies include: Fe3O4 nanoparticles (20-100 nm): good dispersion, low light absorption, and low cost, but soft magnets with weak magnetic properties; NdFeB micron particles (1-5 μm): hard magnets with high magnetic properties, but small specific surface area, large particle size, poor dispersion, and rapid sedimentation.

[0004] Therefore, there is an urgent need for a magnetoelastic that combines simple preparation process, high dispersibility, and stability. Summary of the Invention

[0005] In view of the above problems, the object of the present invention is to provide a method for preparing a magnetoelastic and a flexible tactile sensor to solve at least one problem existing in the prior art.

[0006] In a first aspect, the present invention provides a method for preparing a magnetic elastomer, comprising: ball milling soft magnetic powder and liquid photosensitive resin at a preset mass ratio, followed by vacuum defoaming using a homogenizer to obtain a soft magnetic powder-resin premix; magnetizing the soft magnetic powder-resin premix to obtain a soft magnetic-resin premix having a network structure; ball milling hard magnetic powder, followed by mixing it with liquid photosensitive resin at a preset mass ratio using a homogenizer to obtain a hard magnetic powder-resin premix; mixing the soft magnetic powder-resin premix and the hard magnetic powder-resin premix at a preset mass ratio, followed by homogenization using a homogenizer to obtain a magnetic powder-resin composite material; and printing the magnetic powder-resin composite material using a photopolymerization printer to obtain a magnetic elastomer.

[0007] In addition, an optional technical solution is that, during the magnetization process of the soft magnetic powder-resin premix liquid, the magnetic field is a uniform magnetic field provided by a Helmholtz coil, with a magnetic field uniformity error of <±2%; the magnetic field strength is 0.11T-0.29T, the magnetization time is 1-3 seconds, and the magnetic field direction is perpendicular to the bottom surface of the container.

[0008] In addition, optional technical solutions include a mass ratio of hard magnetic powder to liquid photosensitive resin of (1:1) to (1:5); and / or a mass ratio of soft magnetic powder to liquid photosensitive resin of (1:1) to (1:5); and / or a quantitative ratio of the soft magnetic-resin premix to the hard magnetic powder-resin premix of (1:1) to (1:4).

[0009] In addition, an optional technical solution is to pre-treat the soft magnetic powder before ball milling the soft magnetic powder and liquid photosensitive resin according to a preset mass ratio: vacuum drying the soft magnetic powder at 80-100℃ for 1.5-3 hours; and then screening the vacuum-dried soft magnetic powder using a sieve.

[0010] In addition, the optional technical solution is that the soft magnetic powder is one of Fe3O4, Fe2O3, Ni-Zn ferrite and permalloy powder; and / or the hard magnetic powder is one of NdFeB magnetic powder, SmCo samarium cobalt magnetic powder and AlNiCo aluminum nickel cobalt magnetic powder.

[0011] In addition, an optional technical solution is to ball mill the hard magnetic powder, including: ball milling the hard magnetic powder, oleic acid, and n-heptane at a mass ratio of (100:1:1) to (100:2:2); wherein the diameter of the grinding beads is 5 mm and the ball-to-particle ratio is 20:1; and / or ball milling the soft magnetic powder and liquid photosensitive resin at a preset mass ratio, wherein the diameter of the grinding beads is 5 mm and the ball-to-particle ratio is (5:1) to (20:1). In specific implementation, the ball milling process, in addition to surfactant-assisted methods (oleic acid, oleylamine, etc.), can also be based on inert gas or vacuum ball milling; or wet ball milling.

[0012] Alternatively, an optional technical solution is to ball-mill the soft magnetic powder and liquid photosensitive resin according to a preset mass ratio, and then perform vacuum defoaming treatment using a homogenizer. In this process, the ball milling speed is 100-300 r / min, and the ball milling time is 1-3 hours; the homogenizer speed is 600-2000 r / min, and the homogenization time is 10-20 min.

[0013] In addition, an optional technical solution is that, after printing the magnetic powder-resin composite material using a photopolymerization printer, it further includes ultrasonic cleaning with isopropanol for 5 minutes, and at 30 mW / cm 2 Curing under ultraviolet light for 30 minutes.

[0014] Alternatively, the photosensitive resin may be an acrylic liquid photosensitive resin with a viscosity of 1500-2000 cP at 25°C and a curing wavelength of 405 nm.

[0015] In a second aspect, the present invention provides a flexible tactile sensor, comprising a magnetoelastic material prepared using the magnetoelastic material preparation method described above.

[0016] This invention discloses a method for preparing a magnetic elastomer and a flexible tactile sensor. To overcome the problems of "uneven magnetic powder dispersion, poor stability, low adaptability to photocuring, and mismatch between mechanical and magnetic properties," the magnetic elastomer preparation method of this invention proposes a dual magnetic powder system of "pre-structured network-induced dispersion": first, a three-dimensional network structure is constructed using pre-magnetized soft magnetic materials, consisting of NdFeB, SmCo, and SrFe. 12 O 19 Hard magnetic particles provide a dispersion framework, inhibiting agglomeration and sedimentation; the optimized mechanical blending process ensures that the dual magnetic powders are evenly distributed in the resin and well bonded to the matrix; ultimately, a magnetoelastic with uniform dispersion, stable storage, high flexibility, and high force-magnetic conversion efficiency is obtained, which is suitable for core sensing / driving units of flexible tactile sensors, micro magnetic actuators, flexible end effectors for robots, or wearable health monitoring devices.

[0017] To achieve the foregoing and related objectives, one or more aspects of the invention include the features that will be described in detail below. The following description and accompanying drawings illustrate certain exemplary aspects of the invention. However, these aspects indicate only a few of the various ways in which the principles of the invention can be used. Furthermore, the invention is intended to encompass all such aspects and their equivalents. Attached Figure Description

[0018] Other objects and results of the invention will become more apparent and readily understood with reference to the following description taken in conjunction with the accompanying drawings. In the drawings: Figure 1 Electron micrograph of Fe3O4-resin premixed liquid with network structure provided in Example 1 of the present invention; Figure 2 Electron micrograph of the cross-sectional morphology of the magnetoelastic body of Embodiment 1 provided by the present invention; Figure 3 EDS diagram of the magnetoelastic body provided in Embodiment 1 of the present invention; Figure 4 Electron micrograph of the unmagnetized Fe3O4-resin premix solution of Comparative Example 1 provided by the present invention; Figure 5 The results of magnetic photosensitive resin sedimentation tests provided in the embodiments and comparative examples of the present invention are shown in the figure. Figure 6 A comparison diagram of the force-magnetic coupling coefficients of the magnetoelastic bodies provided in the embodiments and comparative examples of the present invention.

[0019] In all the accompanying drawings, the same reference numerals indicate similar or corresponding features or functions. Detailed Implementation

[0020] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described in detail below. It should be noted that the following embodiments are only used to illustrate the implementation methods and typical parameters of the present invention, and are not intended to limit the parameter range described in the present invention. Reasonable variations derived therefrom are still within the protection scope of the claims of the present invention.

[0021] It should be noted that the endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0022] Unless otherwise defined, all terms, symbols, and other scientific terms used herein are intended to have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In some instances, terms having a conventional meaning are defined herein for clarification or ease of reference, and such definitions should not be construed as indicating a significant difference from conventional understanding in the art. The technical methods described or referenced herein are generally well understood by those skilled in the art and employed by conventional methods. Unless otherwise stated, the use of commercially available kits, reagents, and instruments shall be performed according to the manufacturer's instructions and parameters.

[0023] References to "one embodiment" or "some embodiments" as described in this specification mean that one or more embodiments of this application include a specific feature, structure, or characteristic described in connection with that embodiment. Therefore, the phrases "in one embodiment," "in some embodiments," "in other embodiments," "in still other embodiments," etc., appearing in different parts of this specification do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized. The terms "comprising," "including," "having," and variations thereof mean "including but not limited to," unless otherwise specifically emphasized.

[0024] The method for preparing the magnetoelastic of this invention includes: 1. Premixing soft magnetic nanoparticles with resin and constructing a three-dimensional network: Through "mechanical dispersion + uniform magnetic field magnetization," soft magnetic nanoparticles form a stable three-dimensional network in the resin, providing a "skeleton" for subsequent dispersion of hard magnetic particles such as NdFeB. 2. Surface modification and dispersion of NdFeB magnetic powder: This step ensures uniform dispersion of NdFeB micron-sized particles through "surface modification to reduce agglomeration tendency + mechanical dispersion to integrate into the soft magnetic network." 3. Mixing of the dual magnetic powder system and photocuring 3D printing to prepare the magnetoelastic: This step achieves precise curing of the dual magnetic powder system by optimizing printing parameters.

[0025] Example 1 Experimental materials: Fe3O4, oleic acid, and n-heptane were purchased from Shanghai McLean Biochemical Technology Co., Ltd.; NdFeB magnetic powder was purchased from Guangzhou New Nord Transmission Components Co., Ltd. Other materials were commercially available.

[0026] S1. Ball milling dispersion: Add Fe3O4 magnetic powder and liquid photosensitive resin to the ball milling jar at a mass ratio of 1:4, and then add agate grinding beads (ball-to-material ratio of 10:1, i.e., mass of grinding beads: total mass of Fe3O4-resin = 10:1); install the ball milling jar into a planetary ball mill, set the rotation speed to 200 r / min, and the ball milling time to 2 hours.

[0027] It should be noted that the ball milling principle is as follows: through the "impact-grinding" action of the ball milling beads, the original Fe3O4 agglomerates (usually 500-1000nm) are broken down, and the particles are dispersed into monodisperse or small aggregates (<200nm). The parameter selection is based on the following: a ball-to-material ratio of (5:1) to (20:1) can ensure sufficient impact energy and avoid "insufficient dispersion due to too few balls and too much material". The rotation speed of 100-300 r / min can balance the dispersion efficiency and resin viscosity. Too high a rotation speed (>300 r / min) will cause the resin to heat up (temperature >40℃), triggering pre-curing. The time of 1-3 hours can ensure that the agglomerates are completely broken (the Fe3O4 particle size distribution PDI is <0.2 as detected by a laser particle size analyzer). The magnetite (Fe3O4) is nano-sized with a particle size of 50 nm and a purity ≥99.5%; the liquid photosensitive resin (acrylic type) has a viscosity of 1500-2000 cP (25℃) and a curing wavelength of 405 nm; the grinding beads are made of agate, with a diameter of 5 mm and a density of 2.6 g / cm³. 3 .

[0028] In the specific implementation process, before ball milling Fe3O4 magnetic powder and liquid photosensitive resin according to a preset mass ratio, the Fe3O4 magnetic powder is pretreated: the Fe3O4 magnetic powder is vacuum dried at 90°C for 2 hours; the vacuum-dried Fe3O4 magnetic powder is then screened.

[0029] S2. Homogenization and Defoaming: Transfer the ball-milled Fe3O4-resin system to the dispersion tank of a planetary homogenizer, set the rotation speed to 1000 r / min, the homogenization time to 20 minutes, and turn on the vacuum defoaming function.

[0030] It should be noted that the purpose of setting homogenization and defoaming is to further refine the Fe3O4 small aggregates, so that the viscosity of the resin system is uniform (fluctuation <5%); and to eliminate air bubbles introduced during ball milling.

[0031] S3. Uniform magnetic field magnetization: Pour the homogenized and defoamed Fe3O4-resin system into a transparent quartz container (the thickness of the quartz container is 5mm), place it in a magnetization device for magnetization, and obtain a Fe3O4-resin premixed liquid with a network structure; set the magnetic field strength to 0.2T, the magnetization time to 2 seconds, and the magnetic field direction to be perpendicular to the bottom surface of the container.

[0032] It should be noted that the uniform magnetic field is provided by a Helmholtz coil, with a magnetic field uniformity error of <±2%, ensuring uniform orientation of the Fe3O4 particles. The magnetic field strength is 0.11T-0.29T, the magnetization time is 1-3 seconds, and the magnetic field direction is perpendicular to the bottom of the container. That is, when the magnetic field strength is <0.1T, the Fe3O4 orientation is insufficient, and a continuous network cannot be formed; when it is >0.3T, the network is too dense, increasing the subsequent NdFeB dispersion resistance; a magnetization time of 1-3 seconds ensures stable particle orientation and avoids excessive time leading to resin flow (damaging the three-dimensional network structure).

[0033] Microscopic images of the Fe3O4-resin premix obtained in this embodiment are shown below. Figure 1 As shown. By observation Figure 1 It is evident that a three-dimensional mesh structure was generated in the Fe3O4-resin premix.

[0034] S4. Surface Modification and Dispersion of NdFeB Magnetic Powder: NdFeB magnetic powder (1500-2000 mesh), oleic acid (15 mL / 100 g NdFeB), and n-heptane (15 mL / 100 g NdFeB) were added to a ball mill jar at a mass ratio of 100:1:1, followed by the addition of agate grinding balls (ball-to-material ratio 20:1). The mixture was then mounted in a planetary ball mill, with a rotation speed of 300 r / min and a milling time of 4 hours. After washing and drying, NdFeB magnetic powder with an average particle size of 1.28 micrometers was obtained. The ball-milled NdFeB magnetic powder and liquid photosensitive resin were added to a planetary homogenizer at a mass ratio of 1:4, with a rotation speed of 800 r / min and a homogenization time of 15 minutes to obtain an NdFeB-resin premix.

[0035] It should be noted that in the specific implementation process, ball milling can be performed using surfactants (oleic acid, oleylamine, etc.), or it can be based on inert gas or vacuum ball milling; or wet ball milling. Neodymium iron boron (NdFeB) magnetic powder is micron-sized with a particle size of 5μm; modifiers include oleic acid (analytical grade, purity ≥98%) and n-heptane (analytical grade, purity ≥99%). This step ensures uniform dispersion of NdFeB micron-sized particles through "surface modification to reduce agglomeration tendency + mechanical dispersion" to integrate them into the Fe3O4 network.

[0036] S5. Mixing the dual magnetic powder system: Slowly pour the NdFeB-resin premix into the Fe3O4-resin premix (i.e., the "Fe3O4-resin three-dimensional network system") prepared in step S3 at a mass ratio of 1:1. Then, place it in a planetary homogenizer, set the rotation speed to 600 r / min, and the homogenization time to 5 minutes.

[0037] The mixed system parameters are as follows: viscosity is controlled at 2500 cP-3000 cP (25℃) to meet the feeding requirements of photopolymer printers; and the magnetic powder-resin are stably dispersed for 1-4 hours.

[0038] S6. Photopolymerization 3D Printing Preparation of Magnetolans: The dual magnetic powder-resin composite material, Fe3O4-NdFeB-resin (hereinafter referred to as "magnetic photosensitive resin") prepared in step S5, is poured into a photopolymerization 3D printer. The printing parameters are set as follows: layer thickness 25μm, exposure power 20 mW / cm². 2 Exposure time: 20 seconds / layer. After printing, the magnetic elastomer was removed from the printing platform and ultrasonically cleaned in isopropanol (100W power, 5 minutes) to remove uncured resin from the surface. It was then placed in a UV curing chamber for 30 minutes to ensure complete resin cross-linking. The magnetic elastomer of Example 1, a Fe3O4-NdFeB-resin (magnetized) printed magnetic elastomer, was obtained.

[0039] The photopolymer printer is one of a DLP photopolymer printer, a CLIP photopolymer printer, or a µCLIP photopolymer printer. The isopropanol has a purity of ≥99.5%, and the ultrasonic cleaning power is 100W to avoid over-cleaning and causing damage to the sample surface.

[0040] SEM (Scanning Electron Microscopy) images of the magnetoelastic material obtained in Example 1 were acquired under the following conditions: 15 kV, 300×, 9.6 mm working distance, HFVV secondary electron mode, 423 μm field of view, and 200 μm scale bar. The images are shown below. Figure 2 and Figure 3 As shown. Figure 2 Electron micrograph of the cross-sectional morphology of the magnetoelastic body of Embodiment 1 provided by the present invention; Figure 3 The EDS diagram of the magnetoelastic body of Embodiment 1 provided by the present invention; by observing Figure 2 and Figure 3 It is evident that the magnetic particles in the magnetoelastic are uniformly dispersed.

[0041] Example 2 Experimental materials: Ni-Zn ferrite, oleic acid, and n-heptane were purchased from Shanghai McLean Biochemical Technology Co., Ltd.; SmCo samarium cobalt magnetic powder was purchased from Guangzhou New Nord Transmission Components Co., Ltd. Other materials were commercially available.

[0042] S1. Ball milling dispersion: Add Ni-Zn ferrite magnetic powder and liquid photosensitive resin to the ball mill jar at a mass ratio of 1:5, and then add agate grinding beads (ball-to-material ratio 5:1, i.e., grinding bead mass: Ni-Zn ferrite - resin total mass = 5:1); install the ball mill jar into a planetary ball mill, set the rotation speed to 100 r / min, and the ball milling time to 1 hour.

[0043] It should be noted that the Ni-Zn ferrite magnetic powder is nanoscale with a particle size of 50nm and a purity ≥99.5%; the liquid photosensitive resin (acrylic type) has a viscosity of 1500 cP-2000 cP (25℃) and a curing wavelength of 405nm; the grinding beads are made of agate, with a diameter of 5mm and a density of 2.6 g / cm³. 3 .

[0044] In the specific implementation process, before ball milling Ni-Zn ferrite magnetic powder and liquid photosensitive resin according to a preset mass ratio, the Ni-Zn ferrite magnetic powder is pretreated: the Ni-Zn ferrite magnetic powder is vacuum dried at 80°C for 1.5 hours; the vacuum-dried Ni-Zn ferrite magnetic powder is then screened.

[0045] S2. Homogenization and Defoaming: Transfer the ball-milled Ni-Zn ferrite-resin system to a planetary homogenizing dispersion tank, set the rotation speed to 2000 r / min, the homogenization time to 10 minutes, and turn on the vacuum defoaming function.

[0046] S3. Uniform magnetic field magnetization: The homogenized and defoamed Ni-Zn ferrite-resin body is placed into a transparent quartz container (5mm thick) and then placed in a magnetization device for magnetization to obtain a Ni-Zn ferrite-resin premixed liquid with a network structure; the magnetic field strength is set to 0.11T, the magnetization time is 3 seconds, and the magnetic field direction is perpendicular to the bottom surface of the container.

[0047] Microscopic testing of the Ni-Zn ferrite-resin solution obtained in this embodiment showed that a three-dimensional mesh structure was generated in the Ni-Zn ferrite-resin premix.

[0048] S4. Surface Modification and Dispersion of SmCo Samarium Magnetic Powder: SmCo Samarium Magnetic Powder (1500-2000 mesh), oleic acid (15 mL / 100 g SmCo Samarium Magnetic Powder), and n-heptane (15 mL / 100 g SmCo Samarium Magnetic Powder) were added to a ball mill jar at a mass ratio of 50:1:1, followed by the addition of agate grinding balls (ball-to-powder ratio 20:1). The mixture was then mounted in a planetary ball mill, with a rotation speed of 300 r / min and a milling time of 4 hours. After washing and drying, SmCo Samarium Magnetic Powder was obtained. The ball-milled SmCo Samarium Magnetic Powder and liquid photosensitive resin were added to a planetary homogenizer at a mass ratio of 1:5, with a rotation speed of 800 r / min and a homogenization time of 15 minutes to obtain an SmCo Samarium Magnetic Powder-Resin Premix.

[0049] It should be noted that the SmCo samarium cobalt magnetic powder is micron-sized with a particle size of 5μm; the surface modifiers are oleic acid (analytical grade, purity ≥98%) and n-heptane (analytical grade, purity ≥99%). This step ensures the uniform dispersion of the SmCo samarium cobalt magnetic powder micron-sized particles through "surface modification to reduce agglomeration tendency + mechanical dispersion" to integrate into the Ni-Zn ferrite network.

[0050] S5. Mixing the dual magnetic powder system: Slowly pour the SmCo (Samarium Cobalt) magnetic powder-resin premix into the Ni-Zn ferrite-resin premix prepared in step S3 (i.e., the "Ni-Zn ferrite-resin three-dimensional network system") at a mass ratio of 1:4. Then, place the mixture in a planetary homogenizer, set the rotation speed to 2000 r / min, and homogenize for 8 minutes. The system parameters after mixing are: viscosity controlled at 2500-3000 cP (25℃), suitable for the feeding requirements of photopolymer printers; maintaining stable dispersion of magnetic powder and resin for 1-4 hours.

[0051] S6. Photopolymerization 3D Printing Preparation of Magnetoelastic Body: The dual magnetic powder-resin composite material prepared in step S5, Ni-Zn ferrite-SmCo samarium cobalt magnetic powder-resin (hereinafter referred to as "magnetic photosensitive resin"), is poured into a photopolymerization 3D printer. The printing parameters are set as follows: layer thickness 25μm, exposure power 20 mW / cm². 2 Exposure time: 20 seconds / layer. After printing, the magnetic elastomer was removed from the printing platform and ultrasonically cleaned in isopropanol (100W power, 5 minutes) to remove uncured resin from the surface. It was then placed in a UV curing chamber for 30 minutes to ensure complete resin cross-linking. This yielded the magnetic elastomer of Example 2, a Ni-Zn ferrite-SmCo samarium cobalt magnetic powder-resin (magnetized) printed magnetic elastomer.

[0052] The photopolymer printer is one of a DLP photopolymer printer, a CLIP photopolymer printer, or a µCLIP photopolymer printer. The isopropanol has a purity of ≥99.5%, and the ultrasonic cleaning power is 100W to avoid over-cleaning and causing damage to the sample surface.

[0053] Microscopic observation of the magnetic elastomer obtained in Example 2 showed that the magnetic particles in the magnetic elastomer were uniformly dispersed.

[0054] Example 3 Experimental materials: Permalloy powder, oleic acid, and n-heptane were purchased from Shanghai McLean Biochemical Technology Co., Ltd.; AlNiCo aluminum-nickel-cobalt magnetic powder was purchased from Guangzhou New Nord Transmission Components Co., Ltd. Other materials were commercially available.

[0055] S1. Ball milling dispersion: Add permalloy powder and liquid photosensitive resin to the ball milling jar at a mass ratio of 1:1, and then add agate grinding beads (ball-to-material ratio 20:1, i.e., grinding bead mass: total mass of permalloy and resin = 20:1); install the ball milling jar into a planetary ball mill, set the rotation speed to 300 r / min, and the ball milling time to 3 hours.

[0056] It should be noted that the permalloy powder is nano-sized with a particle size of 50 nm and a purity ≥99.5%; the liquid photosensitive resin (acrylic type) has a viscosity of 1500 cP-2000 cP (25℃) and a curing wavelength of 405 nm; the grinding beads are made of agate, with a diameter of 5 mm and a density of 2.6 g / cm³. 3 .

[0057] In the specific implementation process, before ball milling the permalloy powder and liquid photosensitive resin according to the preset mass ratio, the permalloy powder is pretreated: the permalloy powder is vacuum dried at 100°C for 3 hours; the vacuum-dried permalloy powder is then screened.

[0058] S2. Homogenization and Defoaming: Transfer the ball-milled permalloy-resin system to a planetary homogenizing dispersion tank, set the rotation speed to 600 r / min, the homogenization time to 15 minutes, and turn on the vacuum defoaming function.

[0059] S3. Uniform magnetic field magnetization: The homogenized defoamed permalloy-resin body is placed into a transparent quartz container (5mm thick) and then placed in a magnetization device for magnetization to obtain a permalloy-resin premixed liquid with a network structure; the magnetic field strength is set to 0.29T, the magnetization time is 1 second, and the magnetic field direction is perpendicular to the bottom surface of the container.

[0060] Microscopy and electron microscopy were performed on the permalloy-resin solution obtained in this embodiment. The results showed that a three-dimensional mesh structure was generated in the permalloy-resin premix.

[0061] S4. Surface Modification and Dispersion of AlNiCo Magnetic Powder: AlNiCo magnetic powder (1500-2000 mesh), oleic acid (15 mL / 100 g AlNiCo magnetic powder), and n-heptane (15 mL / 100 g AlNiCo magnetic powder) were added to a ball mill jar at a mass ratio of 100:1.5:1.5, followed by the addition of agate grinding balls (ball-to-powder ratio 20:1). The mixture was then mounted in a planetary ball mill, with a rotation speed of 300 r / min and a milling time of 4 hours. After washing and drying, AlNiCo magnetic powder was obtained. The milled AlNiCo magnetic powder and liquid photosensitive resin were added to a planetary homogenizer at a mass ratio of 1:1, with a rotation speed of 800 r / min and a homogenization time of 15 minutes to obtain an AlNiCo-resin premix.

[0062] S5. Mixing the dual magnetic powder system: Slowly pour the AlNiCo (AlNiCo) magnetic powder-resin premix into the permalloy-resin premix prepared in step S3 (i.e., the "permalloy-resin three-dimensional network system") at a mass ratio of 1:3. Then, place the mixture in a planetary homogenizer, set the rotation speed to 1000 r / min, and homogenize for 10 minutes. The system parameters after mixing are: viscosity controlled at 2500-3000 cP (25℃), suitable for the feeding requirements of photopolymer printers; maintaining stable dispersion of magnetic powder and resin for 1-4 hours.

[0063] S6. Photopolymerization 3D Printing Preparation of Magnetolite: The dual magnetic powder-resin composite material prepared in step S5, permalloy-AlNiCo aluminum nickel cobalt magnetic powder-resin (hereinafter referred to as "magnetic photosensitive resin"), is poured into a photopolymerization 3D printer. The printing parameters are set as follows: layer thickness 25μm, exposure power 20 mW / cm². 2 Exposure time: 20 seconds / layer. After printing, the magnetic elastomer was removed from the printing platform and ultrasonically cleaned in isopropanol (100W power, 5 minutes) to remove uncured resin from the surface. It was then placed in a UV curing chamber for 30 minutes to ensure complete resin cross-linking. The magnetic elastomer of Example 3 was obtained: a permalloy-AlNiCo aluminum nickel cobalt magnetic powder-resin (magnetized) printed magnetic elastomer.

[0064] The photopolymer printer is one of a DLP photopolymer printer, a CLIP photopolymer printer, or a µCLIP photopolymer printer. The isopropanol has a purity of ≥99.5%, and the ultrasonic cleaning power is 100W to avoid over-cleaning and causing damage to the sample surface.

[0065] Microscopic observation of the magnetic elastomer obtained in Example 3 showed that the magnetic particles in the magnetic elastomer were uniformly dispersed.

[0066] Comparative Example 1 S1. Ball milling dispersion: Add Fe3O4 magnetic powder and liquid photosensitive resin to the ball mill jar at a mass ratio of 1:4, and then add agate grinding beads (ball-to-material ratio of 10:1); install the ball mill jar into a planetary ball mill, set the rotation speed to 200 r / min, and the ball milling time to 2 hours.

[0067] S2. Homogenization and Defoaming: Transfer the ball-milled Fe3O4-resin system to the dispersion tank of a planetary homogenizer, set the rotation speed to 1000 r / min, the homogenization time to 20 minutes, and turn on the vacuum defoaming function.

[0068] Electron microscopy was performed on the Fe3O4-resin premix obtained in this comparative example to obtain electron micrographs. Figure 4 As shown. By observation Figure 4It is evident that no three-dimensional mesh structure was generated in the unmagnetized Fe3O4-resin premix.

[0069] S3. NdFeB magnetic powder (1500-2000 mesh), oleic acid (15 mL / 100 g NdFeB), and n-heptane (15 mL / 100 g NdFeB) were added to a ball mill jar at a mass ratio of 100:1:1, followed by the addition of agate grinding balls (ball-to-material ratio 20:1). The mixture was then mounted in a planetary ball mill, with a rotation speed of 300 r / min and a milling time of 4 hours. After washing and drying, NdFeB magnetic powder with an average particle size of 1.28 micrometers was obtained. The ball-milled NdFeB magnetic powder and liquid photosensitive resin were added to a planetary homogenizer at a mass ratio of 1:4, with a rotation speed of 800 r / min and a homogenization time of 15 minutes to obtain an NdFeB-resin premix.

[0070] In the specific implementation process, the particle size of the ball-milled NdFeB magnetic powder is 1-2 micrometers.

[0071] S4. Mixing the dual magnetic powder system: At a mass ratio of 1:1, slowly pour the NdFeB-resin premix into the Fe3O4-resin premix (unmagnetized) prepared in step S2. Then, place it in a planetary homogenizer, set the rotation speed to 600 r / min, and the homogenization time to 5 minutes. This yields the dual magnetic powder-resin composite material Fe3O4-NdFeB-resin (unmagnetized), which is the magnetic photosensitive resin of Comparative Example 1.

[0072] S5. Preparation of the magnetoelastic body by photopolymerization 3D printing: The dual magnetic powder-resin composite material, Fe3O4-NdFeB-resin (unmagnetized), prepared in step S4, is poured into the photopolymerization 3D printer. The printing parameters are set as follows: layer thickness 25μm, exposure power 20 mW / cm². 2 Exposure time: 20 seconds / layer. After printing, the magnetic elastomer was removed from the printing platform and ultrasonically cleaned in isopropanol (100W power, 5 minutes) to remove uncured resin from the surface. It was then placed in a UV curing chamber for 30 minutes to ensure complete resin cross-linking. This yielded the magnetic elastomer of Comparative Example 1, a magnetic elastomer printed with Fe3O4-NdFeB-resin (unmagnetized).

[0073] Comparative Example 2 NdFeB magnetic powder (1500-2000 mesh), oleic acid (15 mL / 100 g NdFeB), and n-heptane (15 mL / 100 g NdFeB) were added to a ball mill jar at a mass ratio of 100:1:1, followed by the addition of agate grinding beads (ball-to-particle ratio 20:1). The mixture was then mounted in a planetary ball mill, with a rotation speed of 300 r / min and a milling time of 4 hours. After washing and drying, NdFeB magnetic powder with an average particle size of 1.28 micrometers was obtained. The ball-milled NdFeB magnetic powder and liquid photosensitive resin were added to a planetary homogenizer at a mass ratio of 1:4, with a rotation speed of 800 r / min and a homogenization time of 15 minutes to obtain an NdFeB-resin mixture, which is the magnetic photosensitive resin of Comparative Example 2.

[0074] The single magnetic powder-resin composite material, namely the magnetic photosensitive resin and NdFeB-resin of Comparative Example 2, was poured into a photopolymerization 3D printer. The printing parameters were set as follows: layer thickness 25 μm, exposure power 20 mW / cm². 2 Exposure time: 20 seconds / layer. After printing, the magnetic elastomer was removed from the printing platform and ultrasonically cleaned in isopropanol (100W power, 5 minutes) to remove uncured resin from the surface. It was then placed in a UV curing chamber for 30 minutes to ensure complete resin cross-linking. This yielded the magnetic elastomer of Comparative Example 2, a magnetic elastomer printed with NdFeB resin.

[0075] The sedimentation tests of the magnetic photosensitive resins obtained in Example 1, Comparative Example 1, and Comparative Example 2 are as follows: Figure 5 As shown, by adding NdFeB magnetic powder-resin to the magnetized Fe3O4-resin, the time for NdFeB magnetic powder-resin to maintain stable dispersion was increased from 0.5 hours to 4 hours.

[0076] The magnetoelastic bodies printed with Fe3O4-NdFeB resin (magnetized), Fe3O4-NdFeB resin (unmagnetized), and NdFeB resin obtained in Example 1, Comparative Example 1, and Comparative Example 2 were subjected to force-magnetic coupling coefficient tests. The test results are as follows: Figure 6 As shown, the linear correlation coefficient R 2 If the linearity is greater than 0.98, it can be considered as qualified.

[0077] Through observation Figure 6 It can be seen that the slope of the change in magnetic induction intensity ΔB with respect to the pressure σ”, i.e. the force-magnetic coupling coefficient k = ΔB / Δσ, is expressed in μT·kPa. -1 The force-magnetic coupling coefficient k of the magnetoelastic body printed from Fe3O4-NdFeB resin (magnetized) obtained in Example 1 is 4.26 μT·kPa. -1The force-magnetic coupling coefficient k of the magnetoelastic body printed from Fe3O4-NdFeB resin (unmagnetized) obtained in Comparative Example 1 was 0.63 μT·kPa. -1 The force-magnetic coupling coefficient k of the NdFeB-resin-printed magnetoelastic obtained in Comparative Example 2 was 0.26 μT·kPa. -1 The method for preparing the magnetoelastic of this invention demonstrates that the hard magnetic particles in the magnetoelastic are well dispersed and magnetized in the resin. When an external force alters the demagnetizing field, a significant magnetic signal is generated, thus meeting the requirements of a high-sensitivity tactile sensor.

[0078] This invention is the first to use Fe3O4 pre-magnetized to construct a three-dimensional network, suppressing the agglomeration and sedimentation of NdFeB micron powder through "spatial confinement and magnetic adsorption," extending the resin system stabilization time from 0.4 h to 4 h. The dual magnetic powders work synergistically: Fe3O4 (soft magnetic) provides the framework and interface bonding, while NdFeB (hard magnetic) provides the main magnetic properties; the two work together to achieve a balance between "dispersion, magnetic properties, and mechanical properties." The process is simplified and integrated into a continuous "ball milling-homogenization-magnetization-printing" process, requiring no complex equipment and suitable for large-scale production. The resulting magnetic powder-resin composite is uniform and stable, possessing both magnetic properties and moldability, and can be widely used in 3D printing, magnetic sensors, and other applications.

[0079] Example 2 The magnetoelastic material 1 obtained in Example 1 is used to fabricate a flexible strain sensor. In one example, the magnetoelastic material 1 is subjected to electrode integration, in-situ encapsulation, or transfer bonding processes to obtain the flexible strain sensor.

[0080] Example 3 The magnetoelastic material obtained in Example 1 was used to fabricate a flexible tactile sensor. In one example, the upper layer is a 200 μm thick magnetoelastic film with a periodically arranged array of micro-magnetic domains embedded within it; the lower layer is a flexible coil on a PI substrate, with 5 turns of copper wire wound around it, with a linewidth of 100 μm; the outermost layer is fully encapsulated with a 500 μm thick EcoFlex material. External tactile loads cause deformation of the magnetoelastic film, which alters the orientation of the internal magnetic domains, resulting in a change in the magnetic flux passing through the lower coil, thereby inducing a voltage signal at the ends of the coil. Applications of the flexible tactile sensor include fingertip tactile sensing in robots and tactile feedback in medical prostheses.

[0081] Example 4 The magnetoelastic obtained in Example 1 was used to fabricate a micro-magnetic actuator. In one example, a cantilevered magnetoelastic with dimensions of 5 mm × 1 mm × 0.2 mm was obtained by photopolymerization 3D printing; one end was fixed to a non-magnetic substrate, while the other end was free; an external coil provided an alternating magnetic field of 1–50 Hz and <10 mT. Applications of the micro-magnetic actuator include micro-pumps, micro-valve, and flexible robot joints.

[0082] Example 5 The magnetoelastic material obtained in Example 1 was used to fabricate a flexible end effector for robots. In one example, a bionic finger was 3D printed using photopolymerization, with an internal hollow lattice whose pores were completely filled with the magnetoelastic material. A flexible drive coil was integrated into the base of the gripper or the back of the glove. Driven wirelessly by an external magnetic field, the finger can adaptively bend within a range of 0–90°; it outputs a grasping force >0.5 N under a 10 mT magnetic field, and can adapt to objects of different shapes. The flexible end effector for robots is applied to flexible robot end effectors and service robot grippers.

[0083] Example 6 The magnetoelastic material obtained in Example 1 was used to fabricate a wearable health monitoring device. In one example, a 150 μm thick magnetoelastic film was directly attached to the skin of the wrist, neck, or knee. A flexible Hall sensor or GMR sensor was integrated beneath the film and connected to a wireless Bluetooth module on a flexible PCB for real-time data transmission. The pulse wave measurement accuracy was ±1 bpm, the joint flexion angle resolution was ±1°, and the muscle vibration frequency response range was 0.1–50 Hz. This device can be applied to daily health monitoring, rehabilitation training feedback, and sports injury early warning systems.

[0084] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be embraced within the present invention. No reference numerals in the appended diagrams should be construed as limiting the scope of the claims. Furthermore, it is clear that the word "comprising" does not exclude other elements or steps, and the singular does not exclude the plural.

[0085] However, those skilled in the art should understand that various modifications can be made to the method for preparing the magnetic elastomer and the magnetic elastomer proposed in this invention without departing from the scope of this invention. Therefore, the scope of protection of this invention should be determined by the content of the appended claims.

Claims

1. A method for preparing a magnetoelastic body, characterized in that, include, After ball milling the soft magnetic powder and liquid photosensitive resin according to a preset mass ratio, the mixture is then subjected to vacuum defoaming treatment using a homogenizer to obtain a soft magnetic powder-resin premix. The soft magnetic powder-resin premix is ​​magnetized to obtain a soft magnetic powder-resin premix with a network structure; After ball milling, the hard magnetic powder is mixed with liquid photosensitive resin in a preset mass ratio using a homogenizer to obtain a hard magnetic powder-resin premix. The soft magnetic-resin premixed liquid and the hard magnetic powder-resin premixed liquid are mixed at a preset mass ratio and then processed using a homogenizer to obtain a magnetic powder-resin composite material. The magnetic powder-resin composite material is printed using a photopolymer printer to obtain a magnetic elastomer.

2. The method for preparing a magnetoelastic body according to claim 1, characterized in that, During the magnetization process of the soft magnetic powder-resin premix liquid The magnetic field is a uniform magnetic field provided by a Helmholtz coil, with a magnetic field uniformity error of <±2%; the magnetic field strength is 0.11T-0.29T, the magnetization time is 1-3 seconds, and the magnetic field direction is perpendicular to the bottom surface of the container.

3. The method for preparing a magnetoelastic body according to claim 1, characterized in that, The mass ratio of the hard magnetic powder to the liquid photosensitive resin is (1:1)–(1:5). And / or the mass ratio of the soft magnetic powder to the liquid photosensitive resin is (1:1) to (1:5); And / or the mass ratio of the soft magnetic-resin premix to the hard magnetic powder-resin premix is ​​(1:1) to (1:4).

4. The method for preparing a magnetoelastic body according to claim 1, characterized in that, Before ball milling the soft magnetic powder and liquid photosensitive resin at a preset mass ratio, the process further includes pretreatment of the soft magnetic powder: The soft magnetic powder is vacuum dried at 80-100℃ for 1.5-3 hours. The vacuum-dried soft magnetic powder is then screened using a sieve.

5. The method for preparing a magnetoelastic body according to claim 1, characterized in that, The soft magnetic powder is one of Fe3O4, Fe2O3, Ni-Zn ferrite and permalloy powder; And / or the hard magnetic powder is one of NdFeB magnetic powder, SmCo samarium cobalt magnetic powder and AlNiCo aluminum nickel cobalt magnetic powder.

6. The method for preparing a magnetoelastic body according to claim 1, characterized in that, The ball milling process of the hard magnetic powder includes: ball milling the hard magnetic powder, oleic acid and n-heptane in a mass ratio of (100:1:1) to (100:2:2); wherein the diameter of the grinding beads is 5 mm and the ball-to-powder ratio is 20:

1. And / or during the ball milling process of soft magnetic powder and liquid photosensitive resin according to a preset mass ratio, the diameter of the grinding beads is 5mm and the ball-to-material ratio is (5:1)-(20:1).

7. The method for preparing a magnetoelastic body according to claim 1, characterized in that, After ball milling the soft magnetic powder and liquid photosensitive resin according to a preset mass ratio, the process of vacuum defoaming using a homogenizer involves a ball milling speed of 100-300 r / min and a ball milling time of 1-3 hours; and a homogenizer speed of 600-2000 r / min and a homogenization time of 10-20 min.

8. The method for preparing a magnetoelastic body according to claim 1, characterized in that, After printing the magnetic powder-resin composite material using a photopolymerization printer, the process further includes ultrasonic cleaning with isopropanol for 5 minutes, and then... 2 Curing under ultraviolet light for 30 minutes.

9. The method for preparing a magnetoelastic body according to claim 1, characterized in that, The photosensitive resin is an acrylic liquid photosensitive resin with a viscosity of 1500-2000 cP at 25°C and a curing wavelength of 405nm.

10. A flexible tactile sensor, characterized in that, This includes magnetoelastics prepared using the magnetoelastic preparation method described in claim 1.

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