CN113388721B

CN113388721B - Magnetic field shielding sheet and preparation method and application thereof

Info

Publication number: CN113388721B
Application number: CN202110657511.0A
Authority: CN
Inventors: 张华�; 王湘粤; 曾志超; 李准; 马春博; 李豪滨
Original assignee: Shenzhen Yuneng Technology Co ltd
Current assignee: Shenzhen Yuneng Technology Co ltd
Priority date: 2021-06-12
Filing date: 2021-06-12
Publication date: 2022-10-25
Anticipated expiration: 2041-06-12
Also published as: CN113388721A

Abstract

The invention belongs to the technical field of wireless charging, and discloses a magnetic field shielding sheet, and a preparation method and application thereof. The preparation method comprises the following preparation steps: (1) Carrying out heat treatment on the nanocrystalline strip in an inert atmosphere; (2) Carrying out magnetic crushing treatment on the nanocrystalline strip subjected to the heat treatment in the step (1); (3) And (3) carrying out atmosphere oxidation treatment on the nano-crystalline strip subjected to the magnetic crushing treatment in the step (2), wherein the atmosphere oxidation treatment adopts hot and humid air atmosphere curing treatment at the temperature of 40-120 ℃ and the humidity of 80% -95%, so as to obtain the magnetic field shielding sheet. The method adopts an atmosphere oxidation process of hot and humid air atmosphere curing treatment at 40-120 ℃ and 80-95% of humidity, can preferentially generate an oxidation insulation layer in gaps of the crushed nanocrystalline strips, and obviously improves the uniformity and stability of the magnetic field shielding sheet after the oxidation treatment while improving the resistance and reducing the eddy current loss.

Description

Magnetic field shielding sheet and preparation method and application thereof

Technical Field

The invention belongs to the technical field of wireless charging, and particularly relates to a magnetic field shielding sheet and a preparation method and application thereof.

Background

The wireless charging technology, also called non-contact induction charging, is charging by using the electromagnetic wave induction principle or the magnetic resonance method. The wireless charging is realized by arranging coils on two sides of the power receiving device and the power supply device and utilizing the generated electromagnetic induction or frequency resonance. At present, the charging technology of more and more portable electronic devices gradually advances to tailless (non-contact charging), and the wireless charging technology develops rapidly, and charging in an electromagnetic induction mode is the most common. The electromagnetic induction principle is similar to that of a transformer, a coil is arranged at each of a transmitting end and a receiving end, the coil at the transmitting end is connected with a wired power supply to generate an electromagnetic signal, and the coil at the receiving end induces the electromagnetic signal at the transmitting end to generate current to charge a battery.

The wireless charging module mainly comprises a magnetic field shielding sheet, a charging coil and the like. The magnetic shielding sheet is mainly made of amorphous and nanocrystalline strips, ferrite, polymer sheets containing magnetic powder and other magnetic bodies. In which ferrite or a polymer sheet including magnetic powder is difficult to be made thin as a shielding material due to low magnetic permeability and low saturation induction. The amorphous and nanocrystalline materials are excellent ultrathin soft magnetic materials, can be prepared to the order of magnitude below 30 mu m, have the natural advantages of high intrinsic permeability and high saturation magnetic induction, are most suitable for ultrathin shielding materials, and are difficult to compare favorably with other materials. However, when a high-frequency ac magnetic field is applied to an amorphous ribbon, problems occur such as a decrease in application function due to the influence of eddy current loss on the ribbon surface, a decrease in efficiency and heat generation when wireless charging is performed. In order to meet the use requirement of the shielding function, a post-treatment process is needed to reduce the eddy current loss, the area of the magnetic conductive material is reduced, the eddy current loss can be reduced, namely the amorphous nanocrystalline magnetic conductive sheet integral sheet is subjected to small unit segmentation, the magnetic flux under the single small unit is small, the area is small, the eddy current is small, and meanwhile, the large circulation eddy current in the area of the whole magnetic conductive sheet is cut off, so that the loss after coupling is reduced, and the heat emission is reduced.

Patent CN 104011814A discloses a magnetic field shielding sheet for wireless charger. By the fragmentation processing of the amorphous ribbon, the loss caused by Eddy Current (Eddy Current) is greatly reduced, thereby shielding the influence of the magnetic field generated to the body and the battery of the portable terminal device and the like, and increasing the quality factor (Q) of the second coil, thereby ensuring excellent power transmission efficiency. After the amorphous ribbon is subjected to the chipping process, the gaps between the thin pieces of the amorphous ribbon are filled with an adhesive by a pressure bonding lamination process to prevent moisture penetration, and the thin pieces are insulated (isolation) from each other by covering all surfaces of the thin pieces with an adhesive (dielectric) to reduce eddy current, thereby preventing a reduction in shielding performance. As a result, the entire surface of the chip can be coated with an adhesive (dielectric substance) to prevent the amorphous ribbon from being oxidized by moisture penetration, thereby causing a change in appearance and deterioration in characteristics. However, according to the structure of this patent, the adhesive layer needs to be filled in the gap after the nano-crystal is crushed and insulated, and therefore, the thickness of the adhesive layer needs to be thick. The thickness of the bonding layer needs to exceed 50% of the thickness of the nanocrystalline, and from the design perspective, the thickness of the functional material of the nanocrystalline magnetic sheet is expected to be increased, and the thickness of the non-functional material such as the bonding layer is expected to be reduced. Obviously, this thickness of the patent is not enough to satisfy the application requirement of miniaturization of the present electronic equipment. Also according to the description of the patent, the gaps of the nanocrystals need to be filled with an adhesive layer and insulated. To achieve this, the gaps of the nanocrystals can be large to facilitate the adhesion layer to fill and achieve insulation. However, a larger gap means that the permeability of the nanocrystal will be significantly reduced. In fact, the decrease in magnetic permeability caused by the large gap causes a decrease in the saturation resistance of the magnetic sheet, and thus a high-power wireless charging cannot be realized.

Patent CN 209527065U discloses an electromagnetic shielding sheet, through filling some to some cracked gaps, in order to realize right the attenuate of glue film thickness, pack the less cracked gap of width through thinner glue film promptly, in order to realize adjacent isolation between the cracked sheet, thereby effectively reduced under the condition of guaranteeing the electromagnetic shielding performance the space thickness of electromagnetic shielding sheet, and then reduced the electromagnetic shielding sheet occupies small-size electronic equipment such as cell-phone, panel computer, intelligent wrist-watch, is favorable to electronic equipment's miniaturization. And utilize the glue film right the magnetism strip material layer seals to improve the leakproofness on magnetism strip material layer avoids magnetism strip material layer is because of air or moisture oxidation, thereby leads to magnetism strip material layer shielding performance descends or the impaired scheduling problem of outward appearance. However, the patent needs to realize that partial filling has high requirements on process operation, the preparation difficulty is high, the uniformity is poor, and the stability of the structural performance of the obtained product is not easy to guarantee. For example, the dielectric constant of the magnetic material between the material layers is different at a certain frequency, the performance is unstable, and the difference value of magnetic conductivity is too large.

Patent CN 109712800A discloses a magnetic sheet based on amorphous or nanocrystalline ribbon, comprising a magnetic layer, a bonding layer and an oxide layer. The magnetic layer has a scaly structure, and the scaly structure can increase contact resistance and reduce eddy current loss; the oxide layer has high resistivity, can replace conventional air or a bonding layer to play an insulating role, can control the gap of the scale-shaped structure by controlling the thickness of the oxide layer, and finally realizes the accurate control of the magnetic permeability of the magnetic sheet. The patent adopts water or weak acid solution spray oxidation treatment or hot water spray treatment to oxidize Fe simple substance in scaly amorphous or nanocrystalline strip, and a layer containing Fe is formed on the surface of the scaly structure and in the gap ₂ O ₃ 、Fe ₃ O ₄ Or an oxide film of FeO. However, the solution spray oxidation treatment or hot water spray treatment often preferentially generates an oxide layer on the surface of the scale-like structure, and the sprayed or sprayed aqueous solution is difficult to uniformly penetrate into gaps of the scale-like structure, so that the improvement on the uniformity and stability of the magnetic field shielding sheet after the oxidation treatment is limited.

Patent CN 112735801A discloses a preparation method of a modified nanocrystalline strip, which comprises the steps of performing acid etching on a micro-crushed nanocrystalline strip to enable dilute hydrochloric acid to enter micro-cracks, etching bridges between micro-crushing units and sharp corners of the crushing units, subsequently performing alkali washing, water washing and alcohol washing to remove acid, salt (sodium chloride generated by acid-base reaction) and deionized water which are remained on the surface of the nanocrystalline strip in a removing layer, and finally performing micro-oxidation treatment to enable the surface and the edge of a micro-crushing unit in the nanocrystalline strip to form an extremely thin oxide film, so that the insulativity of the nanocrystalline strip is improved, and the eddy current loss of the nanocrystalline strip is further reduced. However, the micro-oxidation treatment described in the patent is performed in an oxygen atmosphere with an oxygen concentration of not less than 85vol%, and before the micro-oxidation treatment, acid etching is used to be more likely to occur at micro-fragmented cracks and sharp corners, so that the insulativity among the micro-fragmented units is improved, the shapes of the micro-fragmented units are repaired, an oxide layer is preferentially generated on the surface of a strip material in the subsequent micro-oxidation treatment, the surface is excessively oxidized, the oxidation in the cracks and gaps is insufficient, and the improvement on the uniformity and stability of the magnetic field shielding sheet after the oxidation treatment is limited.

In addition, although the breaking and insulation treatment of the nanocrystalline ribbon can effectively reduce the eddy current effect, the nanocrystalline ribbon is limited by its material, so that the frequency characteristic is not particularly excellent, especially the loss characteristic at high frequency. The existing nanocrystalline strip cannot realize a high-power wireless charging function such as 30W and above under the limited overall thickness. How to reduce the magnetic loss under the high-power condition through process control to improve the wireless charging efficiency under the high-power condition is also a technical problem to be urgently solved by the technical personnel in the field.

Disclosure of Invention

Aiming at the defects and shortcomings of the prior art, the invention mainly aims to provide a preparation method of a magnetic field shielding sheet. The preparation method adopts the atmosphere oxidation process of the atmosphere curing treatment of the hot and humid air at the temperature of 40-120 ℃ and the humidity of 80-95%, can preferentially generate the oxidation insulation layer in the gaps of the crushed nanocrystalline strips, and obviously improves the uniformity and the stability of the magnetic field shielding sheet after the oxidation treatment while improving the resistance and reducing the eddy current loss.

Another object of the present invention is to provide a magnetic field shielding sheet prepared by the above method.

It is still another object of the present invention to provide a use of the above magnetic field shielding sheet in a wireless charging device.

The purpose of the invention is realized by the following technical scheme:

a preparation method of a magnetic field shielding sheet comprises the following preparation steps:

(1) Carrying out heat treatment on the nanocrystalline strip in an inert atmosphere;

(2) Performing magnetic crushing treatment on the nanocrystalline strip subjected to the heat treatment in the step (1);

(3) And (3) carrying out atmosphere oxidation treatment on the nano-crystalline strip subjected to the magnetic crushing treatment in the step (2), wherein the atmosphere oxidation treatment adopts hot and humid air atmosphere curing treatment at the temperature of 40-120 ℃ and the humidity of 80% -95%, so as to obtain the magnetic field shielding sheet.

Further, the component composition of the nanocrystalline strip is Fe _{(100-x-y-z-α-β-γ)} M _x Cu _y M’ _z Si _α B _β X _γ Wherein M is Co and/or Ni element, M' is at least one element of Nb, V, mo, ta, W, zr, hf, ti, cr, mn, al, sc, Y, zn and Sn, and X is at least one element of C, ge, P, ga, sb, in and S; x is more than or equal to 0 and less than or equal to 40, y is more than or equal to 0.1 and less than or equal to 1.5, z is more than or equal to 0 and less than or equal to 5, alpha is more than or equal to 1 and less than or equal to 18, beta is more than or equal to 5 and less than or equal to 15, and gamma is more than or equal to 0 and less than or equal to 5.

Still more preferably, the nanocrystalline strip has a saturation induction B _s Not less than 1.25T, and the component composition is Fe _{(100-x-y-z-α-β-γ)} M _x Cu _y M’ _z Si _α B _β X _γ Wherein M is Co and/or Ni element, M' is at least one element of Nb, V, mo, ta, W, zr, hf, ti, cr, mn, al, sc, Y, zn and Sn, and X is at least one element of C, ge, P, ga, sb, in and S; x is more than or equal to 0 and less than or equal to 40, y is more than or equal to 0.5 and less than or equal to 1.5, z is more than or equal to 1 and less than or equal to 5, alpha is more than or equal to 1 and less than or equal to 18, beta is more than or equal to 5 and less than or equal to 15, gamma is more than or equal to 0 and less than or equal to 3, and x + y + z + alpha + beta + gamma is less than or equal to 26.

Further, the thickness of the nanocrystalline strip is 10-30 μm.

Further, the magnetic crushing treatment in the step (2) adopts transverse or longitudinal roller shearing, rolling with a round roller or a flat plate with salient points, or other methods which can enable the nanocrystalline strips to have uniform fracture gaps.

Further, the size of the broken fine pieces after the magnetic crushing treatment in the step (2) is 0.1-3 mm; the width of the crack gap is 0.02-10 μm.

Further, in order to meet the requirements of the high-power wireless charging magnetic field shielding sheet and reduce high-frequency loss, the heat treatment in the step (1) is one-time heat treatment or two-time heat treatment;

the primary heat treatment procedure was as follows: heating to 0-50 ℃ below the crystallization starting temperature of the nanocrystalline strip at the speed of 1-5 ℃/min, preserving the heat for 10-60 min at the temperature T1, then heating to above the crystallization peak temperature at the speed of 0.5-3 ℃/min, preserving the heat for 30-240 min at the temperature T2, and then cooling to below 200 ℃ and discharging;

the two heat treatment procedure was as follows: heating to 0-50 ℃ below the crystallization starting temperature of the nanocrystalline strip at the speed of 1-5 ℃/min, preserving the heat for 10-60 min at the temperature T1, then heating to above the crystallization peak temperature at the speed of 0.5-3 ℃/min, preserving the heat for 30-240 min at the temperature T2, and then cooling to below 200 ℃; then heating to 0-50 ℃ below the crystallization initial temperature of the nanocrystalline strip at the speed of 1-5 ℃/min, preserving the heat for 10-60 min at the temperature T3, then heating to the temperature above the crystallization peak value at the speed of 0.5-3 ℃/min, preserving the heat for 20-240 min at the temperature T4, cooling to the temperature below 200 ℃, and discharging, wherein the temperature of T3 and T4 is 5-50 ℃ higher than that of T1 and T2 respectively.

Under the condition of the primary heat treatment or the secondary heat treatment, the material is firstly pretreated at a lower temperature (0-50 ℃ below the crystallization initial temperature), after a part of small-sized crystal grains are formed in the material, the temperature is raised to be higher than the crystallization peak temperature at a lower speed (0.5-3 ℃/min) for crystallization treatment, and further the secondary crystallization treatment is carried out. The wireless charging method can be applied to wireless charging scenes with larger current and larger power.

Further, the time of the curing treatment in the step (3) is 6 to 48 hours.

Further, the preparation method of the magnetic field shielding sheet further comprises the steps of coating protective films or double-sided adhesive tapes on two sides of the nanocrystalline strip after the atmosphere oxidation treatment, and pasting and compounding the multilayer nanocrystalline strip through the double-sided adhesive tapes.

A magnetic field shielding sheet is prepared by the method.

The application of the magnetic field shielding sheet in a wireless charging device.

The principle of the invention is as follows: after the nanocrystalline strip is subjected to magnetic crushing treatment, the nanocrystalline is fragmented, the roughness of the section of the magnetic flake in a fragmentation gap of the nanocrystalline strip is higher than the roughness of the upper and lower flat surfaces of the magnetic flake, the relative ratio surface area is larger, the nanocrystalline strip is easier to be oxidized preferentially to generate an oxide layer under the humid and hot air atmosphere at 40-120 ℃ and 80% -95% of humidity, the effect of improving the resistance among fragments is achieved, meanwhile, the controllability of the oxidation degree of the upper and lower flat surfaces of the nanocrystalline strip is strong, excessive oxidation can be prevented, and the uniformity and the stability of the magnetic field shielding sheet after oxidation treatment are obviously provided.

Compared with the prior art, the invention has the beneficial effects that:

(1) The invention adopts the hot and humid air atmosphere oxidation treatment under the conditions of 40-120 ℃ and 80% -95% of humidity, can preferentially generate an oxide layer on the section of the magnetic fine piece, achieves the effect of improving the resistance among the pieces, has strong controllability of the oxidation degree of the upper and lower flat surfaces of the piece, can prevent excessive oxidation, and obviously provides the uniformity and the stability of the magnetic field shielding piece after the oxidation treatment.

(2) The magnetic field shielding sheet disclosed by the invention is not required to be filled into gaps formed after the nanocrystalline is crushed by adopting an adhesive layer to realize insulation, so that the thickness of non-functional materials such as the adhesive layer and the like can be reduced, and the application requirement of miniaturization of the conventional electronic equipment is met. And because the insulation is realized without adopting bonding layer filling, the controllable smaller gap of the nanocrystalline after magnetism crushing is realized, the reduction of the anti-saturation performance of the nanocrystalline material is improved, and the high-power wireless charging is better realized.

(3) The invention adopts one-time heat treatment or two-time heat treatment in a specific mode, firstly carries out lower-temperature pretreatment (0-50 ℃ below the crystallization starting temperature) on the material, and then heats the material to the crystallization peak temperature at a lower speed (0.5-3 ℃/min) after a part of smaller-size crystal grains are formed on the material to carry out crystallization treatment, thereby delaying the crystallization heat release process and avoiding the deterioration of the soft magnetic performance of the material due to the coarse crystal grains. And further through secondary crystallization treatment, as a part of crystal grains are grown on the amorphous matrix, the controllability of the secondary crystallization process is high, and the high-frequency loss of the material after heat treatment is remarkably controlled. The wireless charging method can be applied to wireless charging scenes with larger current and larger power.

Drawings

Fig. 1 and 2 are an appearance profile and a micro-profile of the magnetic crushed nano-crystalline strip before (a) and after (b) the atmosphere oxidation treatment in example 1.

Fig. 3 is a schematic structural diagram of the nano-crystalline strip after the magnetic crushing treatment in example 2.

FIG. 4 is a schematic structural diagram of a magnetic shielding sheet obtained by forming an oxide layer on a cross section of a magnetic thin sheet in example 2.

Fig. 5 is a schematic structural view of the magnetic field shielding sheet obtained by forming oxide layers on the cross section, the upper surface and the lower surface of the magnetic thin sheet in embodiment 2. In the figure, 1-nanocrystalline strip; 2-a fracture gap; 3-magnetic flakes; 4-an oxide layer; 5-an air gap; 6-double sided adhesive tape.

Fig. 6 is XRD patterns of the obtained nanocrystalline strip after the primary and secondary crystallization treatments in example 5.

Detailed Description

The present invention will be described in further detail with reference to examples, but the embodiments of the present invention are not limited thereto.

Example 1

The magnetic field shielding sheet of the present embodiment is prepared by the following method:

(1) Taking the Fe-Cu-Nb-Si-B nanocrystalline strip (the thickness is 20 mu m) to carry out heat treatment in a nitrogen atmosphere, wherein the heat treatment temperature is 560 ℃.

(2) And (3) carrying out magnetic crushing treatment on the nanocrystalline strip subjected to the heat treatment in the step (1) to enable the nanocrystalline strip to have uniform cracking gaps. The magnetic treatment is carried out by die pressing and crushing to obtain uniformly broken magnetic fine pieces. The size of the broken chip can be controlled to be 0.1-3 mm and the width of the broken gap is 0.02-10 mu m by adjusting the die and the pressure of die pressing and breaking. In this example, the size of the fragmentation chip was set to 0.5mm and the width of the fragmentation gap was set to 0.1. Mu.m.

(3) And (3) carrying out atmosphere oxidation treatment on the nanocrystalline strip subjected to the magnetic crushing treatment in the step (2), wherein the atmosphere oxidation process adopts high-temperature high-humidity air atmosphere curing treatment for 24 hours under the conditions of 85 ℃ and 85% humidity, so as to obtain the magnetic field shielding sheet for wireless charging in the embodiment.

In this embodiment, the appearance and morphology of the corresponding crushed and magnetically treated nanocrystalline strip before (a) and after (b) the atmosphere oxidation treatment is shown in fig. 1, and the microscopic morphology is shown in fig. 2. The resistivity test data (10 measurements from different positions and average calculation) of the nanocrystalline strip before and after the atmosphere oxidation treatment are shown in table 1 below.

TABLE 1 resistivity Change of nanocrystalline strip before and after atmospheric Oxidation treatment

From the above results, it can be seen that the shape of the magnetic-fragmented nano-crystalline ribbon is changed to some extent by the special atmosphere oxidation treatment of the present invention. Good insulation effect is achieved without glue filling, and the resistivity of the magnetic shielding sheet is obviously improved. And the uniformity and the stability of the magnetic field shielding sheet after the oxidation treatment are better.

Example 2

(2) And (3) carrying out magnetic crushing treatment on the nanocrystalline strip subjected to the heat treatment in the step (1) to enable the nanocrystalline strip to have uniform cracking gaps. The magnetic crushing treatment adopts a mode of transverse (along the width direction of the strip) roller shear and longitudinal (along the length direction of the strip) roller shear. Magnetic fine pieces of 1mm in size were obtained with a slit width of 5 μm and uniform division.

(3) And (3) performing atmosphere oxidation treatment on the nanocrystalline strip subjected to the magnetic crushing treatment in the step (2), wherein the atmosphere oxidation process adopts high-temperature high-humidity air atmosphere curing treatment for 48 hours under the conditions of 45 ℃ and 95% humidity, and then fixing the nanocrystalline strip by covering double-sided adhesive tapes (2 micrometers) on two sides to obtain the magnetic field shielding sheet for wireless charging in the embodiment.

The structure of the nano-crystalline strip after the magnetic crushing treatment is schematically shown in fig. 3. Wherein the nanocrystalline strip 1 is divided into a plurality of magnetic flakes 3 by a fragmentation slit 2. Compared with the roughness of the upper flat surface and the lower flat surface of the magnetic flake, the roughness of the magnetic flake section in the fragmentation gap is higher, the relative ratio surface area is larger, the magnetic flake section is preferentially oxidized to generate an oxide layer 4 under the condition of moist and hot air at 45 ℃ and 95% humidity, and an air gap 5 exists between the oxide layers of the magnetic flake section in the fragmentation gap, so that the effect of improving the resistance among fragments is achieved. The structure of the magnetic shielding sheet is schematically shown in FIG. 4. By further increasing the atmospheric oxidation temperature to 85 ℃, oxide layers can be simultaneously formed on the upper and lower surfaces of the magnetic fine sheet, and the structural schematic diagram of the obtained magnetic field shielding sheet is shown in fig. 5.

Example 3

(1) Taking the component as Fe _bal. Cu ₁ Nb ₂ Si ₁₄ B _7.5 (at.%) nanocrystalline strip (20 μm thick) is heat treated in nitrogen atmosphere, the heat treatment process is heating to 560 ℃ at a rate of 10 ℃ per minute, holding for 120min, cooling to 200 ℃, and discharging. The saturation magnetic induction of the nanocrystalline strip after heat treatment is B _s ＝1.35T。

(2) And (3) carrying out magnetic crushing treatment on the nanocrystalline strip subjected to the heat treatment in the step (1) to enable the nanocrystalline strip to have uniform cracking gaps. The magnetic crushing treatment adopts a mode of die pressing and crushing, the size of a crushing chip is set to be 0.5mm, and the width of a crushing gap is set to be 0.1 mu m.

(3) And (3) carrying out atmosphere oxidation treatment on the nanocrystalline strip subjected to the magnetic crushing treatment in the step (2), wherein the atmosphere oxidation process adopts high-temperature and high-humidity air atmosphere curing treatment for 24 hours under the conditions of 75 ℃ and 90% humidity, then fixing the nanocrystalline strip by covering double-sided adhesive tape (2 microns) on two sides, and pasting and compounding the four layers of magnetic crushing and oxidized nanocrystalline strips by the double-sided adhesive tape to obtain the magnetic field shielding sheet for wireless charging in the embodiment.

Example 4

(1) Taking the component as Fe _bal. Cu ₁ Nb ₂ Si ₁₄ B _7.5 (at.%) nanocrystalline strip (thickness 20 μm; crystallization thereof)The initial temperature and the crystallization peak temperature are respectively 490 ℃ and 508 ℃, the heat treatment process is that the temperature is increased to 460 ℃ at the speed of 3 ℃ per minute, the temperature is preserved for 60min (pretreatment), then the temperature is increased to 560 ℃ at the speed of 2 ℃ per minute, then the temperature is preserved for 120min (crystallization treatment), and then the temperature is reduced to below 200 ℃ for discharging. The saturation magnetic induction of the nanocrystalline strip after heat treatment is B _s ＝1.35T。

The performance of the magnetic shielding sheets obtained in example 3 and example 4 above, including permeability, inductance, quality factor and saturation current characteristics, were compared, and the results are shown in table 2 below.

TABLE 2 comparison of Properties of nanocrystalline magnetically permeable sheets of examples 3 and 4

Serial number	Saturation magnetic induction B _s	Mu 'of magnetic permeability'	Inductor L (mu H)	Quality factor	Saturation current
						Example 3	1.35T	1412	7.12	72	4.5A
Example 4	1.35T	1425	7.15	75	5.0A

The results of comparing the wireless charging efficiencies of the magnetic shielding sheets obtained in the above examples 3 and 4 at different charging powers are shown in the following table 3.

TABLE 3 comparison of wireless charging efficiency at different charging powers

It can be seen through table 2 and table 3 results, under the condition that composition and structure are the same, through carrying out the preliminary treatment of lower temperature with the material earlier, then heat up to crystallization peak value with lower rate and carry out crystallization processing on the temperature, compare ordinary direct rapid heating crystallization heat treatment mode, the saturation current of magnetic sheet has obtained the promotion of certain degree, the promotion that means the anti saturation characteristic of corresponding wireless charging module of increase of magnetic sheet saturation current, and the wireless charging efficiency under the high power condition descends more slowly, wireless charging efficiency is higher, can be applied to more heavy current, more powerful wireless charging scene.

Example 5

(1) Taking the component as Fe _bal. Cu _0.8 Nb _1.4 Si ₆ B ₁₀ (at.%) nanocrystalline ribbons (20 μm thick) were tested to have crystallization onset and peak temperatures of 445 and 462 ℃ respectively. Carrying out heat treatment on the nanocrystalline strip in a nitrogen atmosphere, wherein the heat treatment process comprises the following steps: heating to 430 ℃ (T1) at a speed of 3 ℃ per minute, keeping the temperature for 30min, heating to 505 ℃ (T2) at a speed of 2 ℃ per minute, keeping the temperature for 90min, cooling to 200 ℃ (finishing primary crystallization treatment), feeding the material into the furnace again, heating to 440 ℃ (T3) at a speed of 3 ℃ per minute, keeping the temperature for 30min, heating to 550 ℃ (T4) at a speed of 2 ℃ per minute, keeping the temperature for 30min, cooling to 200 ℃ (finishing secondary crystallization treatment), and discharging the annealed nanocrystalline strip with a saturation induction of B _s ＝1.55T。

(2) And (2) carrying out magnetic crushing treatment on the nanocrystalline strips subjected to the heat treatment in the step (1) to enable the nanocrystalline strips to have uniform cracking gaps. The magnetic crushing treatment adopts a mode of die pressing and crushing, the size of a crushing chip is set to be 0.5mm, and the width of a crushing gap is set to be 0.1 mu m.

The XRD patterns of the obtained nanocrystalline strip after the primary and secondary crystallization treatments in this example are shown in fig. 6, and the grain sizes and the volume fractions of the crystallized phases of the materials in the two states are shown in table 4. The result of XRD pattern analysis shows that a small amount of crystallization phase grows on the initial amorphous matrix after the primary crystallization treatment, the grain size is about 13.1nm, the crystallization process is more sufficient after the secondary crystallization treatment, the grain size slightly grows to 15.0nm, and the volume fraction of the crystallization phase reaches 76%. The data show that the method of two crystallization annealing treatments is effective, and the crystallization process is effectively controlled.

TABLE 4 crystallization State parameters of the nanocrystalline materials after the first and second crystallization

Sample (I)	Grain size (nm)	Volume fraction of crystallized phase (%)
			Primary crystallization	13.1	28
Second crystallization	15.0	76

The performance results of the magnetic shielding sheet obtained in this example are shown in table 5 below:

TABLE 5 results of performance of the field shield

Serial number	Saturation magnetic induction B _s	Magnetic permeability mu'	Inductor L (mu H)	Quality factor	Saturation current
						Example 5	1.55T	1398	7.10	73	6.0A

The wireless charging efficiency results of the magnetic shielding sheet obtained in this embodiment under different charging powers are shown in table 6 below:

TABLE 6 Wireless charging efficiency results at different charging powers

The results show that the invention further has high controllable degree in the crystallization process through secondary crystallization treatment, and the high-frequency loss of the material after heat treatment is obviously controlled. When the wireless charging power is increased from 15W to 27W, the wireless charging efficiency is only reduced by 0.12%, and when the wireless charging power is increased from 27W to 60W, the wireless charging efficiency is only reduced by 0.84% again. The high-frequency loss of the material after heat treatment by the invention is obviously controlled. The wireless charging method can be applied to wireless charging scenes with larger current and larger power.

The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such modifications are intended to be included in the scope of the present invention.

Claims

1. The preparation method of the magnetic field shielding sheet is characterized by comprising the following specific preparation steps of:

(2) Carrying out magnetic crushing treatment on the nanocrystalline strip subjected to the heat treatment in the step (1);

(3) Carrying out atmosphere oxidation treatment on the nanocrystalline strip subjected to the magnetic crushing treatment in the step (2), wherein the atmosphere oxidation treatment is carried out by carrying out hot and humid air atmosphere curing treatment under the conditions of 40-120 ℃ and 80-95% of humidity, so as to obtain the magnetic field shielding sheet;

the saturation magnetic induction intensity B of the nanocrystalline strip in the step (1) _s Not less than 1.25T, and the component composition is Fe _{(100-x-y-z-α-β-γ)} M _x Cu _y M’ _z Si _α B _β X _γ Wherein M is Co and/or Ni element, M' is at least one element of Nb, V, mo, ta, W, zr, hf, ti, cr, mn, al, sc, Y, zn and Sn, and X is at least one element of C, ge, P, ga, sb, in and S; x is more than or equal to 0 and less than or equal to 40, y is more than or equal to 0.5 and less than or equal to 1.5, z is more than or equal to 1 and less than or equal to 5, alpha is more than or equal to 1 and less than or equal to 18, beta is more than or equal to 5 and less than or equal to 15, gamma is more than or equal to 0 and less than or equal to 3, and x + y + z + alpha + beta + gamma is less than or equal to 26;

the heat treatment in the step (1) is twice heat treatment, and the twice heat treatment procedure is as follows: heating to 0-50 ℃ below the crystallization starting temperature of the nanocrystalline strip at the speed of 1-5 ℃/min, preserving heat at the temperature T1 for 10-60min, then heating to the temperature above the crystallization peak value at the speed of 0.5-3 ℃/min, preserving heat at the temperature T2 for 30-240min, and then cooling to below 200 ℃; then heating to 0-50 ℃ below the crystallization starting temperature of the nanocrystalline strip at the speed of 1-5 ℃/min, preserving the heat at the temperature T3 for 10-60min, then heating to the temperature above the crystallization peak value at the speed of 0.5-3 ℃/min, preserving the heat at the temperature T4 for 20-240min, cooling to the temperature below 200 ℃, and discharging, wherein the temperature of T3 and T4 is 5-50 ℃ higher than that of T1 and T2 respectively.

2. The method of claim 1 for preparing a magnetic field shield sheet, wherein: the thickness of the nanocrystalline strip is 10 to 30 micrometers.

3. The method of claim 1 for preparing a magnetic field shield sheet, wherein: in the step (2), transverse or longitudinal roller shearing, rolling by a round roller or a flat plate with salient points or other methods capable of enabling the nanocrystalline strips to generate uniform fracture gaps are adopted for the magnetic crushing treatment; the size of the broken chip after the broken magnetic treatment is 0.1 to 3mm; the width of the fracture gap is 0.02 to 10 mu m.

4. The method of claim 1, wherein the step of preparing the magnetic shielding sheet comprises: the curing time in the step (3) is 6 to 48h.

5. The method of claim 1, wherein the step of preparing the magnetic shielding sheet comprises: the preparation method of the magnetic field shielding sheet also comprises the steps of coating protective films or double-sided adhesive tapes on two sides of the nanocrystalline strip after atmosphere oxidation treatment, and pasting and compounding multiple layers of nanocrystalline strips through the double-sided adhesive tapes.

6. A magnetic field shield sheet characterized by: prepared by the method of any one of claims 1 to 5.

7. Use of a magnetic shield according to claim 6 in a wireless charging device.