Preparation method of annular flexible magnet

Abstract

The invention discloses a preparation method of an annular flexible magnet, which comprises the following steps: mixing, banburying and crushing raw materials to prepare an injection molding magnetic particle material, then primarily molding the injection molding magnetic particle material into an injection molding magnetic ring through an injection molding process, and then carrying out compression molding on the injection molding magnetic ring by adopting a mold pressing process to form a mold pressing magnetic ring. And finally, subsequent surface treatment, magnetizing and other procedures are carried out to complete preparation of the flexible magnetic ring, so that the flexible magnetic ring is prepared by adopting the injection and mold pressing processes in sequence, the advantages of the injection and mold pressing molding processes are achieved at the same time, and the prepared flexible magnetic ring is large in density, high in magnetic performance, uniform in performance, good in consistency and free of fracture risk; the material utilization rate is high, the production efficiency is high, the binding force in the magnet is high, and the strength is high.

Description

Technical Field

[0001] The invention belongs to the technical field of magnet processing, and in particular relates to a method for preparing an annular flexible magnet. Background Art

[0002] Flexible magnets are made by mixing binders with magnetic powder and additives through injection molding, extrusion molding, calendering molding, compression molding and other processes. They can be processed into products with complex shapes such as sheets, strips, and rings. They are easy to process, low cost, soft and do not damage objects. They are the most important magnets for adsorption and are widely used in toys, handicrafts, advertising products, electronic consumer products and other fields.

[0003] At present, the preparation of flexible magnetic rings mainly involves mixing rare earth magnetic powder, binder and processing aid, and forming them through a calendering process; then, after ultraviolet irradiation or vulcanization reaction, they are cut into ring magnets of corresponding sizes through a die cutter. This method is difficult to produce products with high density and high magnetic properties, and the material utilization rate is low.

[0004] Secondly, the magnetic strips can be prepared by extrusion molding, and then pressed into flexible magnetic rings by hot pressing, etc. The preparation process of this method is cumbersome, and the performance and density of the magnets at the closed part of the magnetic strips are different, which may cause the risk of breakage.

[0005] Injection molding is to mix magnetic powder and binder into particles, heat and melt them through an injection machine, and use a specific mold to inject the melted raw materials into magnetic rings. This preparation process has the advantages of being able to prepare complex shapes, good consistency, and strong corrosion resistance. However, the product prepared by this process has a low density and relatively low magnetic properties.

[0006] Compression molding is to mix magnetic powder with a binder and press it into shape through a mold. The advantages of this preparation process are high magnetic properties, strong corrosion resistance, good consistency of magnetic ring performance, flexible and diverse magnetization, and high production efficiency. However, this preparation process will be affected by the particle size of the magnetic powder. Too coarse particle size is not conducive to the preparation of thin magnets, and too fine powder is easy to oxidize, affecting the magnetic properties of the product. Summary of the invention

[0007] The purpose of the present invention is to provide a method for preparing an annular flexible magnet, which successively adopts injection molding and compression molding processes to prepare the flexible magnetic ring, so as to solve the problems of the existing preparation process, such as cumbersome preparation procedures, low density of the prepared magnetic ring, low magnetic properties, low material utilization rate, and differences in performance and density of the magnet at the closed part of the magnetic strip.

[0008] To achieve the above object, the present invention provides a method for preparing a ring-shaped flexible magnet, comprising the following steps: S1. Evenly mix the magnetic powder, binder and processing aid in a good ratio, and make the injection molding magnetic granules by mixing and crushing; S2, heating and melting the injection-molded magnetic particle material obtained in step S1 by an injection molding machine, and then injection-molding the injection-molded magnetic ring in an injection mold; S3, pressing the injection-molded magnetic ring formed in step S2 through a molding machine to obtain a more compact molded magnetic ring; S4, performing surface treatment on the molded magnetic ring obtained in step S3, and finally magnetizing it using a magnetizing fixture to obtain a final flexible magnetic ring.

[0009] Furthermore, in step S1, the weight percentage of the magnetic powder is 84-95 wt.%, the weight percentage of the binder is 3-10 wt.%, and the weight percentage of the processing aid is 2-6 wt.%.

[0010] Furthermore, in step S1, the magnetic powder is one or more of ferrite powder, neodymium iron boron powder, and samarium iron nitrogen powder.

[0011] Furthermore, in step S1, the binder is one or more of rubber, polyethylene, polyamide elastomer and polyester elastomer.

[0012] Further, in step S4, if rubber is used as the adhesive in step S1, the molded magnetic ring is vulcanized before the surface treatment of the molded magnetic ring, and the vulcanization temperature is 100-180°C and the vulcanization time is 5-60 min.

[0013] Furthermore, in step S1, the processing aid includes one or more of a plasticizer, a lubricant, a coupling agent, an anti-aging agent, and an antioxidant.

[0014] Further, in step S2, the heating temperature of the injection molding machine is 160-250°C.

[0015] Further, in step S3, the compression amount of the molding machine is 2-10%.

[0016] Further, in step S3, the compression amount of the molding machine is 3.5%.

[0017] Further, in step S1, the magnetic powder is neodymium iron boron powder, with a weight percentage of 94wt.%; the binder is thermoplastic polyurethane elastomer, with a weight percentage of 4wt.%; and the processing aids are coupling agent, plasticizer and lubricant, with a weight percentage of 2wt.%.

[0018] After adopting the above scheme, the beneficial effects of the present invention are: The present invention first mixes, kneads and crushes raw materials to prepare injection-molded magnetic granules, then preliminarily molds the injection-molded magnetic granules into injection-molded magnetic rings through an injection molding process, then uses a molding process to press-mold the injection-molded magnetic rings into molded magnetic rings, and finally performs subsequent surface treatment and magnetization processes to complete the preparation of the flexible magnetic ring.

[0019] The present invention firstly adopts injection molding, and a magnet of any shape can be molded by an injection mold. In the present invention, a complete annular magnet can be directly molded, and no subsequent trimming is required. The molding process can be directly performed, thereby improving material utilization. Moreover, the density of the finally molded magnetic ring is uniform, the consistency is good, there will be no problem of interface fracture, and defects such as powder loss and burrs can be reduced.

[0020] The present invention performs molding on the basis of injection molding. Injection molding has combined the magnetic powder and the auxiliary binder together. The magnetic powder has been wrapped and can be prevented from being oxidized when in contact with air. The use of magnetic powder with a finer particle size will not affect the magnetic properties of the product. In addition, injection molding has well combined the magnetic powder and the binder together. The magnetic powder can be further combined through molding to improve the density and magnetic properties.

[0021] Therefore, the present invention successively adopts injection molding and compression molding processes, and has the advantages of both injection and compression molding processes. The prepared product has high density, high magnetic properties, uniform performance, good consistency, no risk of breakage, and can also reduce defects such as powder loss and burrs. It solves the problem of low density and low magnetic properties of magnetic rings prepared by only injection molding process, and the defect of density difference and risk of breakage of magnetic rings prepared by extrusion molding and then hot pressing molding process. Moreover, there is no need to shear the magnetic rings, the material utilization rate is high, and the production efficiency is high, which solves the defects of low material utilization rate and low production efficiency of magnetic rings prepared by existing traditional calendering process. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a process flow chart of the present invention; Figure 2 It is a comparison diagram of the dimensions of the magnetic ring before and after molding of the present invention.

[0023] Description of labels: 1. Injection molded magnetic ring; 2. Molded magnetic ring. DETAILED DESCRIPTION

[0024] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0025] The present invention provides a method for preparing a ring-shaped flexible magnet. Figure 1 As shown, the following steps are included: S1. Evenly mix the magnetic powder, binder and processing aid in a good ratio, and make the injection molding magnetic particles through internal mixing and crushing.

[0026] Among them, the weight percentage of the magnetic powder is 84~95 wt.%, and the magnetic powder can be one or more of ferrite powder, neodymium iron boron powder, and samarium iron nitrogen powder; the weight percentage of the binder is 3~10 wt.%, and the binder can be one or more of rubber, polyethylene, polyamide elastomer and polyester elastomer; the weight percentage of the processing aid is 2~6wt.%, and the processing aid includes one or more of plasticizers, lubricants, coupling agents, anti-aging agents, and antioxidants.

[0027] S2, heating and melting the injection molding magnetic particles obtained in step S1 by an injection molding machine, the heating temperature is determined according to the raw materials of the prepared product, generally controlled at 160-250°C, and then injection molding into an injection molded magnetic ring 1 in an injection mold, the shape and size of the injection mold are determined according to the shape and size of the prepared product, the present invention is used to prepare a flexible magnetic ring, the injection mold is annular, and the shape and size of the obtained injection molded magnetic ring 1 are as follows Figure 2 In addition, in addition to the annular magnetic ring, magnets of other shapes can also be formed through this injection process.

[0028] S3, the injection molded magnetic ring 1 formed in step S2 is pressed by a molding machine to obtain a more compact molded magnetic ring 2, that is, the injection molded magnetic ring 1 is pressed by a molding process, and the size of the molded magnetic ring 2 after pressing is as follows: Figure 2 shown.

[0029] After the molding machine is pressed, the size of the injection molded magnetic ring 1 will be compressed and reduced to form a molded magnetic ring 2. The proportional change of the magnetic ring before and after can be expressed by the compression amount of the molding machine. Assuming that the volume of the injection molded magnetic ring 1 is V1 and the volume of the molded magnetic ring 2 is V2, the compression amount of the molding machine = [(V1-V2) / V1]×100%. For example, Figure 2 In the figure, the inner diameter of the injection molded magnetic ring 1 is R1 = 19.4 ± 0.05 mm, the outer diameter is R2 = 24.2 ± 0.05 mm, and the thickness is L1 = 0.78 ± 0.04 mm. Then the volume of the injection molded magnetic ring 1 is V1 = (24.2 2 -19.4 2 )×0.78π=163.2π, the inner diameter of the molded magnetic ring 2 is R3=20±0.05mm, the outer diameter is R4=25±0.05mm, and the thickness is L2=0.7±0.04mm. Then the volume of the molded magnetic ring 2 is V2=(25 2 -120 2 )×0.7π=157.5π, so the compression amount = [(163.2π-157.5π) / 163.2π]×100%≈3.5%.

[0030] It should be noted that the compression amount should not be too large, otherwise the flexibility of the flexible magnetic ring cannot be maintained, nor should it be too small, otherwise the density of the flexible magnetic ring will be insufficient. After experiments, the compression amount of the molding machine needs to be controlled at 2%~10%, and 3.5% is the best, so that the final prepared flexible magnetic ring has high density and good flexibility.

[0031] S4, performing surface treatment on the molded magnetic ring obtained in step S3, and finally magnetizing it using a magnetizing fixture to obtain a final flexible magnetic ring. It should be noted that if the adhesive used in step S1 is rubber or other rubber-like adhesives, vulcanization treatment is required before surface treatment of the molded magnetic ring.

[0032] Optionally, the temperature of the vulcanization treatment is 100-180° C., and the vulcanization time is 5-60 min.

[0033] Optionally, the surface treatment can be performed by surface treatment processes such as UV, gluing, painting, and PET.

[0034] The present invention successively adopts injection and molding processes to prepare flexible magnetic rings, and has the advantages of both injection and molding processes, so that the prepared flexible magnetic rings have high density, high magnetic properties, uniform performance, good consistency, no risk of breakage, and can also reduce defects such as powder loss and burrs. There is no need to shear the magnetic rings, so the material utilization rate is high and the production efficiency is high.

[0035] The following is further described by specific examples: Embodiment 1: The raw materials are: the magnetic powder is neodymium iron boron powder, with a weight percentage of 89wt.%; the binder is nitrile rubber, with a weight percentage of 7wt.%; the processing aids are coupling agent, plasticizer and lubricant, with a weight percentage of 4wt.%; the preparation method of first injection and then molding of the present invention is adopted, and the specific steps are as described above, wherein the compression amount of the molding machine is 5%.

[0036] Embodiment 2: The raw materials are: the magnetic powder is neodymium iron boron powder, with a weight percentage of 94wt.%; the binder is thermoplastic polyurethane elastomer, with a weight percentage of 4wt.%; the processing aids are coupling agent, plasticizer and lubricant, with a weight percentage of 2wt.%; the preparation method is the same as Example 1.

[0037] Embodiment 3: The raw materials are: magnetic powder is 70wt.% neodymium iron boron powder and 20wt.% samarium iron nitrogen powder; the binder is 4wt.% polyethylene and 3wt.% polyester elastomer; processing aids are coupling agent, plasticizer and lubricant, with a weight percentage of 3wt.%; the preparation method is the same as Example 1.

[0038] Embodiment 4: The raw materials are: magnetic powder is 73wt.% of neodymium iron boron powder and 20wt.% of ferrite powder; the binder is 5wt.% of thermoplastic polyurethane elastomer; the processing aids are coupling agent, plasticizer and lubricant, with a weight percentage of 2wt.%; the preparation method is the same as Example 1.

[0039] Embodiment 5: The raw materials are: magnetic powder is 92wt.% neodymium iron boron powder; the binder is 3wt.% rubber and 3wt.% thermoplastic polyurethane elastomer; processing aids are coupling agent, plasticizer and lubricant, with a weight percentage of 2wt.%; the preparation method is the same as Example 1.

[0040] Embodiment 6: The raw material ratio and preparation method are the same as those in Example 2, except that the compression amount of the molding machine in this example is 2%.

[0041] Embodiment 7: The raw material ratio and preparation method are the same as those in Example 6, except that the compression amount of the molding machine in this example is 3.5%.

[0042] Embodiment 8: The raw material ratio and preparation method are the same as those in Example 6, except that the compression amount of the molding machine in this embodiment is 7.5%.

[0043] Embodiment 9: The raw material ratio and preparation method are the same as those in Example 6, except that the compression amount of the molding machine in this example is 10%.

[0044] The performance of the flexible magnetic ring samples prepared in the above embodiment is tested, and the performance testing method of the samples is as follows: 1. Density: drainage method.

[0045] 2. Tensile strength: Prepare samples and measure performance according to GB / T 528-2009.

[0046] 3. Flexibility: Wrap the magnetic strip around a cylinder with a diameter of 14 mm, keep it for 30 seconds, and then observe the surface of the sample to see if there are any cracks.

[0047] 4. Magnetic properties: The obtained flexible magnetic ring samples are subjected to demagnetization curve test.

[0048] The performance results obtained from the test are shown in the following table:

[0049] It can be seen from the above table that, compared with Examples 1-5, the density and magnetic properties of the flexible magnetic ring prepared by the raw material ratio of Example 2 are the best, and the raw material ratio of Example 2 is preferably used for preparation, so Examples 6-9 are prepared using the raw material ratio of Example 2. Comparing Examples 6-9 and Example 2, the greater the compression of the molding machine, the higher the density and magnetic properties (including remanence Br, intrinsic coercive force Hcj, and maximum magnetic energy product (BH)max), so that molding on the basis of injection molding can improve the density and magnetic properties; however, the higher the compression of the molding machine, the lower the tensile strength and flexibility. When the compression of the molding machine is 10%, the sample will have cracks after the flexibility test, so the compression of the molding machine needs to be controlled below 10%, and in order to ensure sufficient density and magnetic properties, the compression of the molding machine needs to be controlled above 2%, and the compression of the molding machine of 3.5% is the best for comprehensive flexibility.

[0050] The above description is only a preferred embodiment of the present invention and is not a limitation on the design of this case. Any equivalent changes made based on the design key of this case shall fall within the protection scope of this case.

Claims

1. A method for preparing an annular flexible magnet, characterized in that: The following steps are involved: S1. Evenly mix the magnetic powder, binder and processing aid in a good ratio, and make the injection molding magnetic granules by mixing and crushing; S2, heating and melting the injection-molded magnetic particle material obtained in step S1 by an injection molding machine, and then injection-molding the injection-molded magnetic ring in an injection mold; S3, pressing the injection-molded magnetic ring formed in step S2 through a molding machine to obtain a more compact molded magnetic ring; S4, performing surface treatment on the molded magnetic ring obtained in step S3, and finally magnetizing it using a magnetizing fixture to obtain a final flexible magnetic ring.

2. The method for preparing a ring-shaped flexible magnet according to claim 1, characterized in that: In step S1, the weight percentage of the magnetic powder is 84-95 wt.%, the weight percentage of the binder is 3-10 wt.%, and the weight percentage of the processing aid is 2-6 wt.%.

3. A method for preparing a ring-shaped flexible magnet according to claim 1 or 2, characterized in that: In step S1, the magnetic powder is one or more of ferrite powder, neodymium iron boron powder, and samarium iron nitrogen powder.

4. A method for preparing a ring-shaped flexible magnet according to claim 1 or 2, characterized in that: In step S1, the binder is one or more of rubber, polyethylene, polyamide elastomer and polyester elastomer.

5. The method for preparing a ring-shaped flexible magnet according to claim 4, characterized in that: In step S4, if rubber is used as the adhesive in step S1, the molded magnetic ring is vulcanized before the surface treatment of the molded magnetic ring. The vulcanization temperature is 100-180°C and the vulcanization time is 5-60 min.

6. A method for preparing a ring-shaped flexible magnet as claimed in claim 1 or 2, characterized in that: In step S1, the processing aid includes one or more of a plasticizer, a lubricant, a coupling agent, an anti-aging agent, and an antioxidant.

7. The method for preparing a ring-shaped flexible magnet according to claim 1, characterized in that: In step S2, the heating temperature of the injection molding machine is 160-250°C.

8. The method for preparing a ring-shaped flexible magnet according to claim 1, characterized in that: In step S3, the compression amount of the molding machine is 2-10%.

9. The method for preparing a ring-shaped flexible magnet according to claim 8, characterized in that: In step S3, the compression amount of the molding press is 3.5%.

10. The method for preparing a ring-shaped flexible magnet according to claim 8 or 9, characterized in that: In step S1, the magnetic powder is neodymium iron boron powder, with a weight percentage of 94wt.%; the binder is thermoplastic polyurethane elastomer, with a weight percentage of 4wt.%; and the processing aids are coupling agent, plasticizer and lubricant, with a weight percentage of 2wt.%.

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