WO2012041244A1 - Flexible anisotropic bonded ndfeb magnet with stress field orientation and fabrication method of same - Google Patents

Abstract

Provided is a flexible anisotropic bonded NdFeB magnet with stress field orientation and fabrication method of same. The magnetic powder used by the bonded magnet is a shape anisotropy flat NdFeB magnetic powder with the the axis that is prone to magnetization coincidental to the direction of the thickness of the powder, obtained by first breaking then flattening a MQIII magnet. The surface of the magnetic powder has an organic or inorganic coating in order to improve the corrosion resistance and the flame resistance of the flexible bonded NdFeB magnet. The coated magnetic powder is placed into a resin or rubber binder with other additives, mixed evenly, oriented and formed under the stress field, thus directionally aligning the magnetic powder within the binding system, producing an anisotropic flexible magnetic plate; after cross-linking and surface treatment, a flexible anisotropic bonded NdFeB magnet with stress field orientation is obtained.

Description

 Stress field oriented anisotropic flexible bonded NdFeB magnet and preparation method thereof

 Technical field

The invention belongs to the field of preparation of bonded NdFeB magnetic materials, in particular to an anisotropic flexible bonded NdFeB magnet with stress field orientation and a manufacturing method thereof.

Background technique

In the large family of permanent magnet materials, the Nd ₂ Fe ₁₄ B-based NdFeB permanent magnets, which were introduced in the 1980s, have the most excellent magnetic properties. They are mainly classified into sintered NdFeB and bonded NdFeB. Two major categories. Since the 1990s, with the strong demand of computer-based information industry, isotropic rigid bonded NdFeB magnets represented by quenching NdFeB have been widely used.

In the past, the isotropic bonded NdFeB magnet processing method mostly uses hard plastic, resin, etc. as a binder and NdFeB magnetic powder after mixing and granulation, molding, injection or extrusion molding, and the obtained magnets are all Rigid, brittle, inflexible, and the use of molding, injection molding process to produce different specifications of the product requires different molds, higher development costs, longer cycle. At the same time, although the rigid magnet has high magnetic properties and a certain degree of shape freedom, it is fragile, has the disadvantages of inconvenient transportation and assembly, and is made into an ultra-thin thickness (less than 0.6 mm) and a large-length (greater than 500 mm) magnet. very difficult.

To this end, people have designed and developed flexible bonded NdFeB magnets, which are different from rigid bonded NdFeB magnets. They are made of rubber as a binder and are produced by rubber processing. They do not require a large amount of mold development costs and production. High efficiency, free bending and no cracking, product size can be arbitrarily changed, thickness can be less than 0.6mm, easy for customers to assemble and use, has been widely used in home appliances, sensors, office automation and other fields, the demand is very large. This technique is disclosed in the applicant's patent ZL 200410052150.3. However, this patent uses isotropic quenched NdFeB magnetic powder. The maximum magnetic energy product of the flexible magnet is 18 kJ/m3-68 kJ/m ³ , which is lower than the rigid molded bond. The highest performance of the magnet is 88kJ/m ³ .

As the application field continuously proposes ultra-thin, ultra-light, stable, high-power requirements for components, such as concert halls, plazas, and homes, high-fidelity planar speakers that require larger areas, thinner thickness, and farther sounds; Laptop computers need thinner and more powerful fan motors to meet the heat dissipation requirements of high-speed processing chips; washing machines, fans and other home appliances also need smoother and more torque direct-drive motors; mobile phones, MP3, MP4 and other multimedia devices An ultra-thin, ultra-light flexible sensor is required. In order to meet the above requirements, magnetic materials are required to have higher performance, so anisotropic NdFeB materials have entered the field of researchers. At present, there are mainly two kinds of anisotropic NdFeB magnetic powders, one is anisotropic NdFeB magnetic powder prepared by HDDR process; the other is anisotropic NdFeB magnetic powder prepared by hot piercing process. When HDDR NdFeB magnetic powder is used as raw material to prepare flexible bonded magnet, HDDR magnetic powder only has magnetocrystalline anisotropy, and its Hcj is much higher than ferrite. Therefore, it is necessary to design a strong orientation magnetic field during molding. Complex, the size of the magnet cannot be made large, and the application range is limited.

The anisotropic NdFeB magnetic powder prepared by the hot piercing process is obtained by coarse-breaking the isotropic NdFeB MQIII magnet, and then modified by a sand mill or a stirring mill, and has magnetocrystalline anisotropy. And an anisotropic sheet-like magnetic powder, and the easy magnetization axis coincides with the direction of the thickness of the magnetic powder. In the calendering process, when the sheet-like NdFeB magnetic powder passes between the two press rolls of the calender, the sheet-like magnetic powder rotates in the rubber base, and the flat surface of the sheet is regularly arranged perpendicular to the direction of the external force, and the roller is regularly arranged. The orientation of the easy magnetization axis is formed in the pressure direction, thereby realizing the orientation. This orientation does not require any external magnetic field, and is completely realized by the mechanical force between the twin rolls of the calender. The process is simple and can be made into ultra-thin, super long and super. Wide sheets, strips, and articles of various shapes, which are not achievable with magnetic field orientation.

The MQIII anisotropic NdFeB magnet is thickened by a full-density isotropic MQІІ magnet hot pier. When the MQ neodymium magnet is deformed by hot pressing at 700-750 °C, the Nd-rich phase of the Nd ₂ Fe ₁₄ B grain boundary has melted, and the Nd ₂ Fe ₁₄ B crystal grain is immersed in the Nd-rich liquid phase and subjected to a compressive stress. The Nd ₂ Fe ₁₄ B grain has anisotropy of strain energy, and the grain strain energy of the grain axis whose axis of easy magnetization is parallel with the pressure is low, and the grain strain energy of the magnetization axis and the pressure at a certain angle is high. The grain with high strain energy is unstable, and it will dissolve in the Nd-rich boundary layer liquid, so that the solid phase saturation of the Nd-rich liquid phase increases relative to 2:14:1, forming a concentration gradient and diffusing through the liquid phase. The Nd ₂ Fe ₁₄ B grain with low strain energy grows, and the preferred direction of growth is a 2:14:1 base plane, and finally those grains whose axis of easy magnetization is parallel to the pressure direction grow into pieces along the base plane. The physical model of the anisotropic neodymium iron boron magnet MQIII texture is shown in Fig. 1.

 when When MQIII is broken into coarse magnetic powder, most of them are broken along the grain boundary, so the easy magnetization axis of the obtained irregular flake powder is perpendicular to the plane of the flake powder.

The above irregular magnetic powder is added to a sand mill or a stirring mill, and when the flattening is optimized under the protection of the liquid medium, the slurry is pumped from the bottom of the cylinder to the upper part of the cylinder, and is subjected to the falling process. The friction, impact, etc. of the grinding ball are continuously pumped to the upper part of the cylinder by the pump, and the cycle is repeated several times. In the cylinder, the steel ball and the slurry are multi-dimensional cyclic motion and rotation motion. The steel ball and the material are exchanged in the cylinder up and down, inside and outside, because the tangential force of the sand mill or the stirring mill is large, the normal force is weak, plus The Nd-rich phase of the Nd ₂ Fe ₁₄ B grain boundary in the magnetic powder is brittle, so this method can achieve perfect flattening requirements. The force analysis of the logistics in different grinding modes is shown in the following table.

 Table 1. Force analysis of materials in various mills

Mill type	Normal force (impact force, impact force)	Tangential force (shear force, friction)	Grinding ball diameter	Power input mode
Roller ball mill	Big	small	Big	scroll
Vibration mill	Big	small	Larger	vibration
Stirring mill	small	Big	Smaller	Stirring and rolling
sanding machine	Very small	Very large	Very small	Stirring

Summary of the invention

The object of the present invention is to provide a stress field oriented anisotropic flexible bonded NdFeB magnet and a manufacturing method thereof, so as to meet the high-end application requirements of high-performance micro-motors, ultra-thin sensors, electroacoustic equipment and the like.

The magnetic powder used in the magnet of the present invention is a shape anisotropic NdFeB flat magnetic powder which is crushed by an MQIII magnet and then subjected to a special flattening treatment to obtain an easy magnetization axis and a magnetic powder thickness direction. The flattening treatment is to put the magnetic powder with the particle size of -80 mesh obtained by crushing the MQIII magnet into a sand mill or a stirring mill, and treat it under the protection of a liquid medium to obtain a flat having an average particle diameter D50 to an average thickness ratio of more than 10. Magnetic powder, the easy magnetization axis of the magnetic powder coincides with the thickness direction of the magnetic powder.

The coating of organic or inorganic materials by sol coating, chemical or physical deposition, reactive passivation of organic or inorganic surface coating, forming a coating on the surface of the flattened magnetic powder to improve the corrosion resistance of the flexible bonded NdFeB magnet Sex and flame retardant.

The surface-coated flat magnetic powder is added to a resin or rubber-based binder and other auxiliary agents, and after being uniformly mixed, orientation molding is performed under a stress field to realize alignment of the magnetic powder in the bonding system to form an anisotropy. The flexible magnetic sheet is cross-linked and surface-treated. The ratio of magnetic powder to resin or rubber-based binder and auxiliary agent is 75-95% of magnetic powder, 5-20% of binder, and 0-5% of other additives.

Different polymer materials have different filling properties for inorganic materials due to differences in cohesive energy, processing viscosity, density, etc. In the development of flexible rare earth magnets, how to select binders and binders It is a key task to carry out the modification in order to obtain the highest possible magnetic powder filling property under the premise of ensuring the degree of orientation. The rubber-based binder used in the present invention is selected from the group consisting of chlorinated polyethylene, nitrile rubber, ethylene propylene rubber, neoprene rubber, butadiene rubber, urethane rubber, styrene butadiene rubber, butyl rubber, polyisobutylene rubber, and poly Sulfur rubber, silicone rubber, hydrogenated nitrile rubber, polyisoprene rubber, thermoplastic polymers, and combinations thereof. In a preferred embodiment, one or more of nitrile rubber, chlorinated polyethylene, butyl rubber, and thermoplastic polymer are used.

The processing aid used in the present invention includes one or more of an antioxidant, a crosslinking agent, a coupling agent, a plasticizer, a lubricant, a solvent, and an antioxidant.

The invention provides a stress field oriented anisotropic flexible bonded NdFeB magnet by adding a flattened and surface coated anisotropic magnetic powder to a resin or rubber adhesive. The additive is uniformly mixed, and the mixing method adopts a mixing method, an opening method, and then the mixed compound is pressed or extruded to form a flexible magnet of a certain thickness.

Under normal circumstances, the strength of rubber products is low, which cannot be satisfied under many conditions of use. For this reason, the flexible NdFeB magnets must be cross-linked to the rubber in the case of strength requirements. A network crosslinked structure is formed to obtain higher strength. The crosslinking method may be one of the following: electron beam irradiation, infrared radiation, hot air heating, bubbling bed, microwave irradiation, radiation irradiation, flat plate heating, etc. In a more preferred embodiment, a flat plate or hot air heating method is used.

The invention relates to a method for manufacturing a stress field oriented anisotropic flexible bonded NdFeB magnet, and further comprising: the prepared magnet is subjected to surface protection treatment, and the treatment method comprises one of spraying, vapor deposition, and coating protective paint. Or several.

Compared with the existing isotropic flexible bonded NdFeB magnets, the stress field oriented anisotropic flexible bonded NdFeB magnets of the present invention have higher performance and can satisfy higher end applications. Compared with a flexible bonded NdFeB magnet prepared by anisotropic HDDR NdFeB magnetic powder, a flexible bonded NdFeB magnet prepared by flattening NdFeB having an anisotropy of shape, due to magnetic powder It has shape anisotropy and the easy magnetization axis coincides with the direction of the thickness of the magnetic powder. In the calendering process, when the sheet-like NdFeB magnetic powder passes between the two press rolls of the calender, the sheet-like magnetic powder rotates in the rubber base, and the flat surface of the sheet is regularly arranged perpendicular to the direction of the external force, and the roller is regularly arranged. The assembly of the easy magnetization axis in the pressure direction realizes the orientation, and the orientation does not require any external magnetic field, and is completely realized by the mechanical force between the twin rolls of the calender, so the process is simple, the preparation is large, and the production efficiency is high. The advantages, but also the good magnetic properties of the flexible magnet, the magnet can be wound on a shaft 10 times its thickness without cracking. The maximum performance of the magnet can reach 120kJ/m ³ , even exceeding the performance of the isotropic rigid molded magnet, further expanding the application field of the flexible magnet, meeting the global market demand, filling the gaps at home and abroad, and changing the rare earth permanent magnet industry in China. status quo.

detailed description

Example 1

1. Flattening process:

The magnetic powder obtained by crushing the MQIII magnet (particle size -80 mesh, grade 37-11) 2000g was added to an appropriate amount of pure alcohol to form a liquid slurry → flattened in a stirring mill for 3 hours (ball ratio 10:1, Φ2) And the balls of Φ4 each accounted for 50%) → baked in an oven at 60 ° C for 2 h → flattened flaky magnetic powder (the ratio of the average particle diameter D50 to the average thickness was 10).

2. Magnetic powder coating process:

200 g of the above magnetic powder, 4 g of nano-silica, and 12 g of silicone resin dissolved in toluene were added and uniformly mixed (temperature: 80 ° C) until the solvent was completely evaporated → heated in a vacuum oven at 260 ° C for 2 hours. The magnetic powder was subjected to a salt water immersion test (3% NaCl solution / 25 ° C * 72 h), and no rust was observed with a 5 times magnifying glass.

3. Magnet preparation process:

100g of the above magnet, 5.5g of nitrile rubber, 0.2g of silane coupling agent, 0.03g of crosslinking agent, 0.15g of strontium stearate, 0.2g of anti-aging agent, 0.25g of plasticizer, etc. To uniformity, the mixture was made into a magnetic sheet with a thickness of 2 mm on a calender, and heat-cured at 150 ° C for 20 min. The magnetic sheet was wound around a round rod of Φ 20 without cracks. The highest magnetic energy product of the obtained magnet was 100 kJ/m. ³ . The test tube has a flame retardant rating of V-2 of the UL94 standard.

Example 2

 1. Flattening process:

The magnetic powder (particle size -80 mesh, grade 37-11) 2000g obtained by crushing MQIII magnet was added to an appropriate amount of pure alcohol to form a liquid slurry → flattened in a stirring mill for 6 hours (ball ratio 7:1, Φ2) And the balls of Φ4 each accounted for 50%) → baked in an oven at 60 ° C for 2 h → flattened flaky magnetic powder (the ratio of the average particle diameter D50 to the average thickness was 11).

 2. Magnetic powder coating process:

200 g of the above magnetic powder, 4 g of nano-silica, and 12 g of silicone resin dissolved in toluene were added and uniformly mixed (temperature: 80 ° C) until the solvent was completely evaporated → heated in a vacuum oven at 260 ° C for 2 hours.

 3. Magnet preparation process:

100g of the above magnet, 5.5g of nitrile rubber, 0.2g of silane coupling agent, 0.03g of crosslinking agent, 0.15g of strontium stearate, 0.2g of anti-aging agent, 0.25g of plasticizer, etc. To uniformity, the mixture was made into a magnetic sheet with a thickness of 2 mm on a calender, and heat-cured at 150 ° C for 20 min. The magnetic sheet was wound around a round rod of Φ 20 without cracks. The highest magnetic energy product of the obtained magnet was 106 kJ/m. ³ . The magnet has a flame retardant rating of V-2 of the UL94 standard.

Example 3

 1. Flattening process:

The magnetic powder (particle size -80 mesh, grade 37-11) 2000g obtained by crushing MQIII magnet was added to an appropriate amount of pure alcohol to form a liquid slurry → flattened in a stirring mill for 6 hours (ball ratio 7:1, Φ2) And Φ4 balls each accounted for 50%) → baked in an oven at 60 ° C for 2 h → flattened flaky magnetic powder.

 2. Magnetic powder coating process:

200 g of the above magnetic powder, 3 g of nano-silica, and 9 g of silicone resin dissolved in toluene were added and uniformly mixed (temperature: 80 ° C) until the solvent was completely evaporated → heated in a vacuum oven at 260 ° C for 2 hours.

 3. Magnet preparation process:

100 g of the above magnet, 4.0 g of chlorinated polyethylene, 1.0 g of butyl silicone, 0.2 g of an alkyl coupling agent, 0.02 g of a crosslinking agent, 0.15 g of strontium stearate, 0.2 g of an antioxidant, 0.2 g of a plasticizer, etc. The components were kneaded and tempered to uniformity, and then the mixture was made into a magnetic sheet having a thickness of 2 mm on a calender, and heat-cured at 150 ° C for 20 min. The magnetic sheet was wound around a round rod of Φ 20 without cracks. The maximum magnetic energy product of the magnet is 110 kJ/m ³ .

Example 4

 1. Flattening process:

The magnetic powder (particle size -80 mesh, grade 37-11) 2000g obtained by crushing MQIII magnet was added to an appropriate amount of pure alcohol to form a liquid slurry → flattened in a stirring mill for 6 hours (ball ratio 7:1, Φ2) And Φ4 balls each accounted for 50%) → baked in an oven at 60 ° C for 2 h → flattened flaky magnetic powder.

 2. Magnetic powder coating process:

200 g of the above magnetic powder was taken and added to a KH550 silane coupling agent (0.1 g) dissolved in acetone, and epoxy resin silicon (5 g) was uniformly mixed (temperature 80 ° C) until the solvent was completely evaporated → heated in a vacuum oven at 120 ° C * Cured for 2h.

 3. Magnet preparation process:

100 g of the above magnet, 4.0 g of chlorinated polyethylene, 1.0 g of butyl silicone, 0.2 g of an alkyl coupling agent, 0.02 g of a crosslinking agent, 0.15 g of strontium stearate, 0.2 g of an antioxidant, 0.2 g of a plasticizer, etc. The components were kneaded and tempered to uniformity, and then the mixture was formed into a magnetic sheet having a thickness of 1.0 mm on a calender. After heat-curing at 150 ° C for 15 minutes, a layer of paraxylene resin was vapor-deposited on the surface of the magnet. Body coating (parylene treatment). The magnet was subjected to a neutral salt spray test (5% NaCl solution / 35 ° C * 72 h) and observed with a 5x magnifying glass without rust. The magnetic sheet was wound around a round rod of Φ10 without cracks, and the highest magnetic energy product of the obtained magnet was found to be 105 kJ/m ³ .

Claims (9)

1. A stress field oriented anisotropic flexible bonded NdFeB magnet, comprising NdFeB magnetic powder having shape anisotropy, a resin or rubber type binder and other auxiliaries. The weight percentage of each component is: shape anisotropy NdFeB magnetic powder 75-95%, binder 5-20%, and other auxiliary agents 0-5%.
2. The stress field oriented anisotropic flexible bonded NdFeB magnet according to claim 1, wherein the NdFeB magnetic powder having shape anisotropy is a flat shape, and a ratio of an average particle diameter D50 to an average thickness is larger than 10.
3. The neodymium iron boron magnetic powder having shape anisotropy according to claim 2, wherein the easy magnetization axis coincides with the magnetic powder thickness direction.
4. The neodymium iron boron magnetic powder having shape anisotropy according to claim 2 is obtained by crushing with a MQIII magnet and then being flattened, and the apparatus for flattening treatment is selected from a sand mill or a stirring mill, and the grinding medium is Liquid protection medium.
5. The stress field oriented anisotropic flexible bonded NdFeB magnet according to claim 1, wherein the NdFeB magnetic powder having shape anisotropy is surface-treated to form a coating layer on the surface of the magnetic powder. The purpose of the magnet is anti-corrosion and flame retardant. The method of surface treatment is selected from the group consisting of organic-inorganic material sol coating, chemical or physical deposition, reactive passivation, and combinations thereof.
6. The stress field oriented anisotropic flexible bonded NdFeB magnet according to claim 1, wherein the rubber adhesive is selected from the group consisting of chlorinated polyethylene, nitrile rubber, ethylene propylene rubber, and chloroprene. One or more of rubber, butadiene rubber, urethane rubber, styrene butadiene rubber, butyl rubber, polyisobutylene rubber, polysulfide rubber, silicone rubber, hydrogenated nitrile rubber, polyisoprene rubber, and thermoplastic polymer.
7. The stress field oriented anisotropic flexible bonded NdFeB magnet according to claim 1, wherein the magnetic powder is oriented in a binder by orientation molding by calendering or extrusion.
8. The stress field oriented anisotropic flexible bonded NdFeB magnet according to claim 1, wherein the cross-linking method uses electron beam radiation, infrared radiation, hot air heating, bubbling bed, microwave radiation, and radiation radiation. Or plate heating.
9. The stress field oriented anisotropic flexible bonded NdFeB magnet according to claim 1, wherein the method for surface protection of the magnet is selected from one of spray coating, vapor deposition, and protective paint. Their combination.

Images