Color magnetic particle preparation method, color magnetic particle, magnetic microcapsule and magnetic film

Abstract

The invention discloses a colored magnetic particle preparation method, a colored magnetic particle, a magnetic microcapsule and a magnetic film, and relates to the technical field of magnetic particle preparation. According to the preparation method, ferric salt and an alkaline substance are adopted, a ferroferric oxide precursor precipitation solution is generated through a coprecipitation method, surface modification is conducted through oleic acid, the dispersity and stability of particles in an organic system are enhanced, a solvent is adopted for washing and drying, and the purity and chemical stability of the particles are further improved; subsequently, mixing the modified nano ferroferric oxide, a dye, a high polymer and a functional additive to obtain the colored magnetic particle. The method has the advantages that the preparation process is simple, and the prepared colored magnetic particles are excellent in dispersity, stability and functionality.

Description

Technical Field

[0001] The invention relates to the technical field of magnetic particle preparation, and in particular to a method for preparing colored magnetic particles, colored magnetic particles, magnetic microcapsules and magnetic films. Background Art

[0002] With the advancement of technology and the increasing demand of consumers for the performance of electronic products, traditional magnetic writing board technology has gradually failed to meet the market demand for writing clarity, resolution and colorful effects. Traditional magnetic writing boards generally use honeycomb structures or other large micro-chamber structures to accommodate magnetic particles and non-magnetic particles. Although this structural design has achieved simple writing functions to a certain extent, it has obvious limitations in writing accuracy and effect. Due to the large size of the honeycomb structure, the arrangement and distribution of magnetic particles in the chamber are relatively loose, resulting in blurred writing effects, especially in occasions where high details and fineness are required, the clarity and resolution of the handwriting are poor.

[0003] In order to overcome these problems, a new magnetic writing board technology has emerged in recent years, which uses microcapsule encapsulation technology to replace the traditional honeycomb structure. Microcapsule technology can effectively improve the problems of blurred handwriting and poor resolution in traditional magnetic writing boards by encapsulating magnetic particles and non-magnetic particles in tiny capsules. Compared with the honeycomb structure, the chamber size of the microcapsule is smaller, which enables each microcapsule to more accurately control the movement of magnetic particles, thereby significantly improving the handwriting resolution and clarity of the writing board.

[0004] At present, the core technology of most magnetic microcapsule writing boards on the market is still mainly focused on the use of black magnetic particles. These magnetic particles are usually black and cannot achieve color display. Although this structure can provide relatively clear writing effects, its single color limits its application needs in education, artistic creation and other fields. Especially in scenes that require richer visual experience and diversified expression, the limitations of black and white display are gradually exposed, becoming one of the bottlenecks restricting the development of magnetic writing board technology. Summary of the invention

[0005] In view of this, the embodiments of the present invention provide a method for preparing colored magnetic particles, colored magnetic particles, magnetic microcapsules and magnetic films, so as to solve the problem of single color of magnetic particles in the prior art.

[0006] In a first aspect, an embodiment of the present invention provides a method for preparing colored magnetic particles, the method comprising:

[0007] Dissolving iron salt in water and stirring evenly to obtain an iron salt mixed solution;

[0008] Under stirring conditions, adding alkaline substances dropwise into the iron salt mixed solution at a predetermined rate to obtain a ferroferric oxide precursor precipitation solution;

[0009] Add oleic acid to the ferroferric oxide precursor precipitation solution, stir until the reaction is completed, wash with the first solvent, and then dry to obtain modified nano ferroferric oxide;

[0010] The colored magnetic particles are obtained by mixing modified nano-ferroferric oxide, dye, polymer and functional additive.

[0011] Preferably, the high molecular weight substance is a polymer, the functional additive is a dispersant, and the color magnetic particles are obtained by mixing the modified nano-ferroferric oxide, dye, high molecular weight substance and functional additive, which comprises:

[0012] The modified nano-ferroferric oxide, polymer, second solvent and dye are mixed to form an oil phase solution, the oil phase solution is added into an aqueous solution containing a dispersant for stirring and dispersion, and the colored magnetic particles are obtained after the solvent is volatilized by heating.

[0013] Preferably, the polymer is a monomer, the functional additive is an initiator, and the color magnetic particles are obtained by mixing the modified nano-iron tetroxide, dye, polymer and functional additive, including:

[0014] The modified nano-ferroferric oxide, monomer, dye and initiator are stirred at a preset temperature until the reaction is completed to obtain the colored magnetic particles.

[0015] Preferably, in parts by mass, dissolving the iron salt in water and stirring evenly to obtain an iron salt mixed solution comprises: dissolving 16-20 parts of the iron salt in 300-500 parts of water and stirring evenly to obtain an iron salt mixed solution;

[0016] The step of adding the alkaline substance to the iron salt mixed solution at a predetermined rate under stirring conditions to obtain the ferroferric oxide precursor precipitation solution comprises: adding 100-140 parts of the alkaline substance to the iron salt mixed solution at a predetermined rate under stirring conditions, during which the reaction temperature is controlled to be maintained at 60-80 degrees Celsius and the pH value is maintained at 8.5-11.0, to obtain the ferroferric oxide precursor precipitation solution;

[0017] The step of adding oleic acid to the ferroferric oxide precursor precipitation solution, stirring until the reaction is completed, washing with a first solvent, and then drying to obtain modified nano ferroferric oxide comprises: adding 1-2 parts of oleic acid to the ferroferric oxide precursor precipitation solution, stirring at 60-80 degrees Celsius until the reaction is completed, washing with 250-400 parts of the first solvent for 2-4 times, and then drying to obtain modified nano ferroferric oxide;

[0018] The step of mixing the modified nano-ferroferric oxide, the polymer, the second solvent and the dye to form an oil phase solution comprises: mixing 1.5-3.0 parts of the modified nano-ferroferric oxide, 10-20 parts of the polymer, 40-60 parts of the second solvent and 3-5 parts of the dye to form an oil phase solution;

[0019] The step of adding the oil phase solution to an aqueous solution containing a dispersant for stirring and dispersing, and heating the solution to evaporate the solvent to obtain the colored magnetic particles comprises: adding 20-30 parts of the oil phase solution to 100-200 parts of an aqueous solution containing 0.1-1.0 parts of a dispersant for stirring and dispersing, and heating the solution to 70-90 degrees Celsius to evaporate the solvent to obtain the colored magnetic particles.

[0020] Preferably, in parts by mass, dissolving the iron salt in water and stirring evenly to obtain an iron salt mixed solution comprises: dissolving 16-20 parts of the iron salt in 300-500 parts of water and stirring evenly to obtain an iron salt mixed solution;

[0021] The step of adding the alkaline substance to the iron salt mixed solution at a predetermined rate under stirring conditions to obtain the ferroferric oxide precursor precipitation solution comprises: adding 100-140 parts of the alkaline substance to the iron salt mixed solution at a predetermined rate under stirring conditions, during which the reaction temperature is controlled to be maintained at 60-80 degrees Celsius and the pH value is maintained at 8.5-11.0, to obtain the ferroferric oxide precursor precipitation solution;

[0022] The step of adding oleic acid to the ferroferric oxide precursor precipitation solution, stirring until the reaction is completed, washing with a first solvent, and then drying to obtain modified nano ferroferric oxide comprises: adding 1-2 parts of oleic acid to the ferroferric oxide precursor precipitation solution, stirring at 60-80 degrees Celsius until the reaction is completed, washing with 250-400 parts of the first solvent for 2-4 times, and then drying to obtain modified nano ferroferric oxide;

[0023] The step of stirring the modified nano-ferroferric oxide, monomer, dye and initiator at a preset temperature until the reaction is completed to obtain the colored magnetic particles comprises: stirring 1.5-3.0 parts of the modified nano-ferroferric oxide, 10-30 parts of the monomer, 3-5 parts of the dye and 0.2-0.6 parts of the initiator at 65-75 degrees Celsius and a stirring speed of 600-800 rpm for 80-100 minutes until the reaction is completed to obtain the colored magnetic particles.

[0024] Preferably, the iron salt includes two or more of ferrous sulfate, ferric chloride and ferrous chloride; the alkaline substance includes one or two of ammonia water or alkali metal hydroxide.

[0025] Preferably, the first solvent is ethanol, the second solvent is any one or more of dichloromethane, acetone, ethyl acetate, butanone, n-pentane, and n-hexane; the polymer includes any one or more of polystyrene, polymethyl methacrylate, polypropylene, polyethylene, high-density polyethylene, polycarbonate, and polyethylene terephthalate; the dispersant includes any one or more of polyvinyl alcohol, gum arabic, sodium dodecyl sulfate, sodium carboxymethyl cellulose, and polyvinyl pyrrolidone.

[0026] In the second aspect, an embodiment of the present invention provides a colored magnetic particle, which includes modified nano ferrosoferric oxide, a dye, a polymer and a functional additive, wherein the polymer is a monomer or a polymer obtained by polymerization of the monomer, when the polymer is a monomer, the functional additive is a dispersant; when the polymer is a polymer, the functional additive is an initiator.

[0027] In the third aspect, an embodiment of the present invention provides a magnetic microcapsule, which includes a wall material and a core material, wherein the wall material is a mixture of anionic polymers and cationic polymers, and the core material is a mixture of colored magnetic particles, non-magnetic particles, oily solvents and suspension stabilizers as described in the second aspect; wherein the cationic polymer includes one or two of gelatin and ε-polylysine, and the anionic polymer includes one or more of sodium carboxymethyl cellulose, gum arabic and sodium alginate; and the non-magnetic particles are lipophilic nano-titanium dioxide.

[0028] In a fourth aspect, an embodiment of the present invention provides a magnetic film, comprising a PET substrate layer, a rubber-based self-adhesive layer located on the PET substrate layer, a water-based glue and magnetic microcapsule mixed layer located on the rubber-based self-adhesive layer, and an AG PET film layer on the water-based glue and magnetic microcapsule layer, wherein the magnetic microcapsules are the magnetic microcapsules described in the third aspect.

[0029] In summary, the beneficial effects of the present invention are as follows:

[0030] The embodiments of the present invention provide a method for preparing colored magnetic particles, colored magnetic particles, magnetic microcapsules and magnetic films. The preparation method uses iron salts and alkaline substances to generate a ferroferric oxide precursor precipitation solution by a co-precipitation method, and uses oleic acid to perform surface modification to enhance the dispersibility and stability of the particles in an organic system. A solvent is used for washing and drying to further improve the purity and chemical stability of the particles. Subsequently, the modified nano-ferroferric oxide, a dye, a polymer and a functional additive are mixed to obtain the colored magnetic particles. The method has a simple preparation process, and the prepared colored magnetic particles have excellent dispersibility, stability and functionality. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solution of the embodiment of the present invention, the drawings required for use in the embodiment of the present invention will be briefly introduced below. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work, and these are all within the protection scope of the present invention.

[0032] Figure 1 It is a schematic diagram of the process of preparing colored magnetic particles according to an embodiment of the present invention.

[0033] Figure 2 It is a schematic diagram of the colored magnetic particles prepared by the solvent volatilization method in Example 1 of the present invention.

[0034] Figure 3 It is a schematic diagram of the colored magnetic particles directly prepared by polymer monomers in Example 1 of the present invention.

[0035] Figure 4 It is a schematic diagram of colored magnetic particles prepared by solvent volatilization method in Example 2 of the present invention.

[0036] Figure 5 It is a schematic diagram of colored magnetic particles directly prepared by polymer monomers in Example 2 of the present invention.

[0037] Figure 6 It is a schematic diagram of colored magnetic particles prepared by solvent volatilization method in Example 3 of the present invention.

[0038] Figure 7 It is a schematic diagram of colored magnetic particles directly prepared by polymer monomers in Example 3 of the present invention.

[0039] Figure 8 It is a schematic diagram of the colored magnetic particles prepared by the solvent volatilization method in Comparative Example 1 of the present invention.

[0040] Fig. 9 It is a schematic diagram of the colored magnetic particles directly prepared by polymer monomers in Comparative Example 1 of the present invention.

[0041] Fig.10 Schematic diagram of a colored magnetic film according to an embodiment of the present invention.

[0042] Fig.11 Schematic diagram of a colored magnetic film according to an embodiment of the present invention. DETAILED DESCRIPTION

[0043] The features and exemplary embodiments of various aspects of the present invention will be described in detail below. In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and Examples. It should be understood that the specific embodiments described herein are only configured to explain the present invention and are not configured to limit the present invention. For those skilled in the art, the present invention can be implemented without the need for some of these specific details. The following description of the embodiments is only to provide a better understanding of the present invention by illustrating examples of the present invention.

[0044] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the statement "include..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0045] See also Figure 1 The first aspect of the present invention provides a method for preparing colored magnetic particles, the method comprising:

[0046] S1: dissolving iron salt in water and stirring evenly to obtain an iron salt mixed solution;

[0047] S2: adding alkaline substances to the iron salt mixed solution at a predetermined rate under stirring conditions to obtain a ferroferric oxide precursor precipitation solution;

[0048] S3: adding oleic acid to the ferroferric oxide precursor precipitation solution, stirring until the reaction is completed, washing with the first solvent, and then drying to obtain modified nano-ferroferric oxide;

[0049] S4: The modified nano-ferroferric oxide, dye, polymer and functional additive are mixed to obtain the colored magnetic particles.

[0050] In one embodiment, the high molecular weight substance is a polymer, the functional additive is a dispersant, and the color magnetic particles are obtained by mixing the modified nano-ferroferric oxide, dye, high molecular weight substance and functional additive, including:

[0051] The modified nano-ferroferric oxide, polymer, second solvent and dye are mixed to form an oil phase solution, the oil phase solution is added into an aqueous solution containing a dispersant for stirring and dispersion, and the colored magnetic particles are obtained after the solvent is volatilized by heating.

[0052] In one embodiment, the polymer is a monomer, the functional additive is an initiator, and the color magnetic particles are obtained by mixing the modified nano-ferroferric oxide, dye, polymer and functional additive, including:

[0053] The modified nano-ferroferric oxide, monomer, dye and initiator are stirred at a preset temperature until the reaction is completed to obtain the colored magnetic particles.

[0054] Specifically, first, the iron salt is dissolved in water and stirred to obtain a uniform iron salt mixed solution. Under stirring conditions, an alkaline substance is added at a predetermined rate to control the reaction rate to generate a ferroferric oxide precursor precipitation solution. At this time, the precursor of ferroferric oxide (such as iron hydroxide, etc.) begins to form, and due to its precipitation properties, it can lay the foundation for the subsequent synthesis of magnetic particles. Then, oleic acid is added to the ferroferric oxide precursor precipitation solution. Oleic acid, as a surfactant or dispersant, plays a role in surface modification during the synthesis process. Oleic acid can wrap the surface of ferroferric oxide particles, change its surface properties, prevent particles from aggregating, and promote the uniformity of the reaction and the stability of the magnetic particles. After stirring until the reaction is completed, the obtained product is washed with a first solvent to remove unreacted substances and impurities, and finally dried to obtain modified nano ferroferric oxide. After obtaining the modified nano ferroferric oxide, the next step is to mix it with a polymer, a second solvent and a dye to form an oil phase solution. The addition of dyestuff gives different colors or various colors to the ferroferric oxide particles, while polymer helps the stable combination of dyestuff and magnetic particles to avoid the dyestuff from falling off on the particle surface. This oil phase solution is then added to an aqueous solution with a dispersant, and stirred and dispersed so that the magnetic particles are evenly dispersed in the aqueous solution. By heating up the solvent to evaporate, what is finally obtained is colored magnetic particles, which have good dispersibility and stability. In another embodiment, after obtaining modified nano ferroferric oxide, it is also possible to stir and react modified nano ferroferric oxide, monomer, dyestuff and initiator at a preset temperature to generate the colored magnetic particles. This method utilizes the polymerization reaction of monomer and initiator, further enhances the stability and functionality of the colored magnetic particles, makes the dyeing effect more lasting, and simultaneously possesses stronger functionality, such as improving its performances such as heat resistance and chemical resistance.

[0055] In the embodiment of the present invention, the combination of dye and magnetic particles makes the obtained magnetic particles not only have magnetism, but also can display multiple colors, meeting the market demand for colorful display. Secondly, using oleic acid and polymer as surface modifiers can effectively improve the stability of magnetic particles and prevent particle aggregation, thereby improving the dispersion and uniformity of colored magnetic particles and ensuring the consistency of their effects in applications.

[0056] Preferably, in parts by mass, dissolving the iron salt in water and stirring evenly to obtain an iron salt mixed solution comprises: dissolving 16-20 parts of the iron salt in 300-500 parts of water and stirring evenly to obtain an iron salt mixed solution;

[0057] The step of adding the alkaline substance to the iron salt mixed solution at a predetermined rate under stirring conditions to obtain the ferroferric oxide precursor precipitation solution comprises: adding 100-140 parts of the alkaline substance to the iron salt mixed solution at a predetermined rate under stirring conditions, during which the reaction temperature is controlled to be maintained at 60-80 degrees Celsius and the pH value is maintained at 8.5-11.0, to obtain the ferroferric oxide precursor precipitation solution;

[0058] The step of adding oleic acid to the ferroferric oxide precursor precipitation solution, stirring until the reaction is completed, washing with a first solvent, and then drying to obtain modified nano-ferroferric oxide comprises: adding 1-2 parts of oleic acid to the ferroferric oxide precursor precipitation solution, stirring at 60-80 degrees Celsius for 60-120 minutes until the reaction is completed, washing with 250-400 parts of the first solvent for 2-4 times, and then drying to obtain modified nano-ferroferric oxide;

[0059] The step of mixing the modified nano-ferroferric oxide, the polymer, the second solvent and the dye to form an oil phase solution comprises: mixing 1.5-3.0 parts of the modified nano-ferroferric oxide, 10-20 parts of the polymer, 40-60 parts of the second solvent and 3-5 parts of the dye to form an oil phase solution;

[0060] The step of adding the oil phase solution to an aqueous solution containing a dispersant, stirring and dispersing the solution, and heating the solution to evaporate the solvent to obtain colored magnetic particles comprises: adding 20-30 parts of the oil phase solution to 100-200 parts of an aqueous solution containing 0.1-1.0 parts of a dispersant, stirring and dispersing the solution, and heating the solution to 70-90 degrees Celsius to evaporate the solvent to obtain colored magnetic particles;

[0061] Or the step of stirring the modified nano-ferroferric oxide, monomer, dye and initiator at a preset temperature until the reaction is completed to obtain the colored magnetic particles comprises: stirring 1.5-3.0 parts of the modified nano-ferroferric oxide, 10-30 parts of the monomer, 3-5 parts of the dye and 0.2-0.6 parts of the initiator at 65-75 degrees Celsius and a stirring speed of 600-800 rpm for 80-100 minutes until the reaction is completed to obtain the colored magnetic particles.

[0062] The above embodiment explains each preparation step in detail based on the mass value of the material. In the step of preparing nano-iron tetroxide, 16 to 20 parts of iron salt are first dissolved in 300 to 500 parts of water, and then stirred to obtain an iron salt mixed solution. During the dissolution of the iron salt, stirring helps to promote the complete dissolution of the iron salt and ensure the uniform distribution of iron ions. The dissolved iron salt will provide Fe 2+ and Fe 3+ ions, which are the basis for the generation of ferroferric oxide precursors. Next, 100 to 140 parts of alkaline substances are added to the iron salt solution at a predetermined rate under stirring conditions to control the rate and temperature of the reaction. In this step, the reaction temperature is controlled between 60°C and 80°C, and the pH value is controlled between 8.5 and 11. These conditions ensure that the precipitation reaction proceeds smoothly and a uniform ferroferric oxide precursor precipitate is obtained. Controlling the temperature and pH value within this range helps to optimize the particle size and distribution of the precipitate, thereby obtaining nano-scale ferroferric oxide particles. After the precursor precipitation is completed, 1 to 2 parts of oleic acid are added to the precipitation solution and stirred at a temperature of 60°C to 70°C for 60 to 120 minutes. The addition of oleic acid causes the surface of ferroferric oxide to undergo lipophilic modification, thereby improving its dispersibility in oily solvents. The stirring time and temperature are crucial to the completeness of the reaction. Too short a reaction time may result in incomplete surface modification, and too long a reaction time may produce unnecessary by-products. After the reaction is completed, 250 to 400 parts of the first solvent are used for washing, and the washing is performed 2 to 4 times to remove unreacted oleic acid and other impurities. Finally, the washed nano-iron tetroxide is dried. Through the washing step, not only can the excess oleic acid be removed, but also the purity and dispersibility of the particles can be improved, thereby laying a good foundation for the subsequent dyeing process.

[0063] In the process of preparing the oil phase solution, 1.5 to 3.0 parts of modified nano-ferroferric oxide, 10 to 20 parts of polymer, 40 to 50 parts of second solvent and 3 to 5 parts of dye are mixed to form the oil phase solution. The polymer helps to improve the binding force and stability of the final particles, and the second solvent helps the solubility and mixing effect of the dye. By mixing these ingredients in proportion to form a uniform oil phase solution, it can be ensured that the dye and polymer are evenly dispersed on the surface of the nano-ferroferric oxide.

[0064] Next, the oil phase solution is added to an aqueous solution with a dispersant for stirring and dispersion. The dispersant can help improve the dispersibility of the ferroferric oxide particles and avoid aggregation between particles. Preferably, the mass fraction of the dispersant in the aqueous solution is 0.1 to 1.0 parts, and the mass fraction of water is 100 to 200 parts. During the dispersion process, the solvent gradually evaporates under stirring, and the temperature needs to be increased to 70°C to 90°C to promote the volatilization of the solvent. The heating process of this step not only accelerates the volatilization of the solvent, but also helps the dye to evenly adhere to the surface of the ferroferric oxide particles, and finally obtains the dyed ferroferric oxide particles, i.e., the colored magnetic particles. The volatilization of the solvent ensures that the solid content of the final particles is more stable and has better dispersibility.

[0065] Another method is to mix the modified nano-iron tetroxide, monomer, dye and initiator and stir them at a preset temperature until the reaction is completed. According to the mass value, the mass of the modified nano-iron tetroxide is 1.5 to 3.0 parts, the mass of the monomer is 10 to 30 parts, the dye is 3 to 5 parts, and the initiator is 0.2 to 0.6 parts. In this process, the monomer can be methyl methacrylate (MMA), styrene, etc., and the dye reacts with the monomer to form a complex. At a temperature of 65°C to 75°C, a stirring speed of 600 to 800rpm is used for 80 to 100 minutes. This reaction condition ensures that the monomer is more tightly combined with the ferroferric oxide particles, and the obtained colored magnetic particles have good structural stability and uniform dispersion. The role of the initiator is to start the polymerization reaction, so that a chemical reaction occurs between the monomer and the ferroferric oxide particles, thereby obtaining a stronger bond.

[0066] The embodiment of the present invention ensures that the prepared colored magnetic particles have excellent dispersibility, color stability and magnetism by precisely controlling the material mass fraction, temperature, pH value, stirring speed and other conditions in each step. By combining surface modification and dyeing technology, high-quality colored magnetic particles can be obtained, which are widely used in magnetic coatings, magnetic writing boards and other magnetic materials, and have broad market prospects.

[0067] Preferably, the iron salt includes two or more of ferrous sulfate, ferric chloride, and ferrous chloride; the use of ferrous sulfate, ferrous chloride, and ferric chloride can effectively provide the required iron ions, and form a ferric oxide precursor precipitate under different reaction conditions. Ferrous sulfate can dissolve at a lower reaction temperature and provide divalent iron ions (Fe 2+ ), which helps to generate ferroferric oxide nanoparticles with good magnetic properties; while ferric chloride can provide trivalent iron ions (Fe 3+ ), providing the necessary oxidation state for the synthesis of ferroferric oxide. Preferably, the composition and structure of ferroferric oxide can be precisely controlled by adjusting the ratio of the two iron salts, thereby optimizing the magnetic properties of the particles.

[0068] Preferably, the alkaline substance includes one or both of ammonia or alkali metal hydroxide. Ammonia or alkali metal hydroxide as alkaline substances help to adjust the pH value of the solution, ensure that the precipitation of iron ions in the reaction is uniform, and prevent the formation of by-products. Ammonia is relatively mild and is suitable for synthesis processes requiring lower pH conditions, while alkali metal hydroxides provide stronger alkalinity, which helps to rapidly precipitate ferroferric oxide at higher temperatures, ensuring that the reaction is efficient and the product purity is high. By rationally selecting and combining these materials, the morphology, size and magnetic properties of ferroferric oxide can be adjusted under different process conditions, thereby achieving excellent magnetic particle preparation effects.

[0069] Preferably, the first solvent is ethanol. After the surface of the ferroferric oxide particles is modified to be lipophilic, ethanol as a polar solvent can better dissolve oleic acid and other lipophilic substances, and remove unreacted impurities by washing, thereby ensuring the purity and surface uniformity of the modified nano-ferroferric oxide. In addition, ethanol has low volatility and good solubility, and can efficiently perform solvent exchange under appropriate temperature conditions and ensure the stability of the particles.

[0070] Preferably, the second solvent is any one of methylene chloride (DCM), acetone, ethyl acetate, butanone, n-pentane, and normal hexane. Methylene chloride (DCM), acetone, ethyl acetate, butanone, n-pentane and normal hexane all have good solubility and volatility, can effectively dissolve polymers, dyes and other oily substances. These solvents can provide necessary dissolving power when forming oil phase solution, so that polymers and dyes are evenly dispersed in the solution, avoid the aggregation of particles. In further dispersion process, the solvent with strong volatility can evaporate quickly in heating process, helps the removal of solvent, guarantees that the colored magnetic particles finally obtained have good dispersibility and stability.

[0071] Preferably, the polymer includes: any one or more of polystyrene, polymethyl methacrylate, polypropylene, polyethylene, high-density polyethylene, polycarbonate, and polyethylene terephthalate. The selection of these polymers helps to improve the performance and stability of the dyed magnetic particles. Specifically, polystyrene (PS) has good mechanical strength and processing properties, and can provide good particle support and stability during the dyeing process. Polymethyl methacrylate (PMMA) has excellent transparency and good UV resistance, which can improve the appearance and durability of the particles. Polypropylene (PP) and polyethylene (PE) have strong chemical resistance and excellent wear resistance, and are suitable for magnetic particles used in harsh environments, which enhances the durability of the particles. High-density polyethylene (HDPE) has a higher density and stronger tensile strength, which can provide better stability and uniformity for the particles. Polycarbonate (PC) has higher impact resistance and excellent thermal stability, so that the dyed magnetic particles are not easy to break or deform during use. Polyethylene terephthalate (PET) is a polymer with higher mechanical strength and heat resistance, which is suitable for application scenarios requiring stronger stability. Applying these polymers in the process of preparing dyed magnetic particles can provide excellent surface properties, enhance the stability of the particles, and ensure the high performance and long-term durability of the dyed magnetic particles during use.

[0072] Preferably, the dye comprises any one or more of oil-soluble red dye, oil-soluble blue dye, oil-soluble green dye, pearl powder, and modified pearl powder. The use of these dyes helps to achieve rich color effects and excellent appearance performance in dyed magnetic particles. Oil-soluble dyes, such as red, blue and green dyes, have strong solubility and color stability, which can ensure that the magnetic particles have bright and lasting colors. These oil-soluble dyes can be fully dissolved in the oil phase solution, provide a uniform dyeing effect, and avoid the common problems of uneven particles or non-persistent color during the dyeing process. In particular, the oil-soluble dye has a strong solubility in the oil phase solution, which helps to improve the binding of the dye to the surface of the magnetic particles and improve its light resistance and wear resistance. In addition, pearl powder and modified pearl powder can further enhance the appearance of the dyed magnetic particles, giving them a pearly luster and producing a unique visual effect. Pearl powder has excellent reflective properties and can show rich color changes by changing the light reflection on the surface of the particles. It is particularly suitable for applications that require high-end decorative effects. Modified pearlescent powder is a surface treatment on the basis of pearlescent powder, which makes it more stable and has stronger weather resistance during use, and can effectively improve the surface gloss of the particles and extend their service life. By selecting different types of dyes and pearlescent powders, the appearance of dyed magnetic particles can be customized in a diversified way to meet the needs of different applications for color and visual effects, and increase the competitiveness of products in the market.

[0073] Preferably, the dispersant includes any one or more of polyvinyl alcohol (PVA), gum arabic, sodium dodecyl sulfate (SDS), sodium carboxymethyl cellulose (CMC), and polyvinyl pyrrolidone (PVP). The use of these dispersants helps to improve the dispersibility and stability of magnetic particles in aqueous solution, avoid particle aggregation or precipitation, and thus ensure the uniformity and quality of particles during the preparation process. Polyvinyl alcohol (PVA), as a commonly used dispersant, has excellent hydrophilicity and adhesion properties, can effectively reduce the agglomeration of magnetic particles, enhance the compatibility of particles with aqueous solution, and thus keep the magnetic particles in a good dispersed state in water. As a high molecular polymer from natural sources, gum arabic has good dispersibility and low toxicity, and can form a stable colloidal solution in water. By providing a certain viscosity, it helps to prevent the magnetic particles from agglomerating or precipitating in water and maintain the uniformity of particle dispersion. Sodium dodecyl sulfate (SDS) is a common anionic surfactant with excellent detergency, dispersion and emulsification capabilities. It can form a stable micelle structure in water, adsorb on the surface of magnetic particles, reduce the mutual attraction between particles, and thus effectively prevent the aggregation of particles. SDS is particularly suitable for systems that require a strong dispersing effect, and has a significant promoting effect on improving the dispersibility and stability of particles. Sodium carboxymethyl cellulose (CMC) is a high molecular weight water-soluble material with good thickening, dispersing and stabilizing effects. CMC can form an electrostatic interaction with the particle surface through its carboxyl group, enhance the affinity of the particles and the solution, prevent the particles from agglomerating in the solution, and maintain the stability of the dispersed system. Polyvinylpyrrolidone (PVP) is a polymer with good water solubility that can effectively enhance the dispersibility of particles in the solution. PVP can effectively prevent the precipitation and aggregation of particles, maintain the uniform distribution of particles, and improve the stability of particles through the interaction between its polymer chain and the particle surface. PVP also has good solubility and low toxicity, and is suitable for dispersed systems that require high stability. By selecting these dispersants, the dispersion state of the particles can be adjusted according to actual needs, the uniformity of particle distribution during the preparation process can be improved, and the performance and quality of the final product can be improved.

[0074] Preferably, the monomer includes one or more of methyl methacrylate (MMA), styrene (St), acrylic acid (AA), acrylates (such as ethyl acrylate), acrylonitrile (AN) and epoxy acrylates (such as epoxy acrylate chloride). Methyl methacrylate (MMA) has good transparency and high mechanical strength. During the preparation process, after MMA is combined with magnetic ferroferric oxide particles, the hardness and wear resistance of the particles can be improved, ensuring the stability and durability of the particles in the application. In addition, MMA has a good affinity with dye molecules, which can effectively improve the coloring effect and color fastness of the particles. Styrene (St) has good thermal stability and good processing properties. After styrene is polymerized with ferroferric oxide particles, it can give the particles higher rigidity and stronger impact resistance. At the same time, styrene has a strong lipophilicity, which can improve the dispersibility of the particles, especially the better dispersion effect in the oil phase solution. Acrylic acid (AA) and acrylates (such as ethyl acrylate) have strong hydrophilicity and good dispersibility. Acrylic monomers can form a hydrophilic shell through polymerization, improve the dispersibility of particles, avoid particle aggregation, and ensure their stability in aqueous media. Acrylates can improve the interaction between particles and dyes through the chemical properties of the ester group, thereby improving the adhesion and coloring effect of the dye. Acrylonitrile (AN) is a monomer with good chemical corrosion resistance. During the polymerization process, acrylonitrile can provide strong chemical resistance and heat resistance, and enhance the stability of particles in extreme environments. After acrylonitrile is combined with ferroferric oxide particles, it can effectively improve the oxidation resistance and acid and alkali resistance of the particles and extend their service life. Epoxy acrylate (such as epoxy acrylate chloride) is a monomer with extremely high chemical reactivity, which can form stable chemical bonds with magnetic particles and other molecules during the polymerization process. Epoxy acrylate helps to improve the chemical stability and durability of particles, and also has strong adhesion, which can make the dye more firmly attached to the surface of the particles and improve the coloring effect of the particles.

[0075] Preferably, the initiator includes one or more of potassium persulfate (KPS), azobisisobutyronitrile (AIBN), benzoyl peroxide (BPO), ammonium persulfate (APS), tert-butyl peroxide (TBP) and hydrogen peroxide (H2O2). Among them, KPS and APS, as water-soluble initiators, can efficiently generate sulfate radicals in the aqueous phase system, ensure the uniform polymerization reaction, and improve the hydrophilicity and dispersibility of the particles; while AIBN and BPO, as oil-soluble initiators, show excellent initiation ability in non-aqueous phase or oily medium, and can significantly improve the hydrophobicity and mechanical properties of the particles. In particular, AIBN has a moderate decomposition temperature and high activity, and is suitable for use under a variety of polymerization conditions, while BPO has high thermal stability and good monomer compatibility, and can provide a stable source of free radicals under high temperature conditions, thereby improving the thermal stability and chemical corrosion resistance of the particles. In addition, TBP, as a high-temperature oil-soluble initiator, stably generates free radicals under high temperature conditions, which helps to improve the uniformity and high temperature resistance of the particles. Hydrogen peroxide (H2O2) reacts with a catalyst (such as Fe 2+ ) can form a highly active free radical system when used in combination, which can not only quickly initiate polymerization reactions, but also facilitate the control of particle size and distribution by adjusting their dosage. The use of these initiators can not only flexibly adapt to different reaction conditions, but also improve the chemical stability, mechanical strength and environmental adaptability of the particles, thereby giving the colored magnetic particles excellent physical and chemical properties to meet the needs of diverse applications.

[0076] In summary, the method for preparing colored magnetic particles of the embodiment of the present invention, in the process of preparing ferroferric oxide, uses iron salt and alkaline substances, and generates ferroferric oxide precursor precipitation solution by coprecipitation method to obtain uniform and high-purity ferroferric oxide particles. By introducing oleic acid for surface modification, not only the hydrophobicity of the particles is improved, but also the dispersibility and stability of the particles in the organic system are enhanced. The first solvent is used for washing and drying, which further improves the purity and chemical stability of the particles. Secondly, the method realizes the preparation of colored magnetic particles through two process routes. One is to mix the modified ferroferric oxide with a polymer, a solvent and a dye to form an oil phase solution, and then after stabilizing the system with a dispersant, the solvent is heated and volatilized to obtain dyed magnetic particles. This process effectively controls the particle size and distribution, while giving it excellent coloring and optical properties. Another process is to generate colored magnetic particles by monomer polymerization, and the modified ferroferric oxide is mixed with a monomer, a dye and an initiator to react, which can coat the particle surface with a polymer to improve the wear resistance, weather resistance and mechanical properties of the particles. In summary, this method has a simple preparation process, and the prepared colored magnetic particles have excellent performance in dispersibility, stability and functionality.

[0077] The second aspect of the present invention provides a colored magnetic particle, the colored magnetic particle comprises modified nano ferroferric oxide, a dye, a polymer system and a functional additive, wherein the polymer is a monomer or a polymer obtained by polymerization of the monomer, when the polymer is a monomer, the functional additive is a dispersant; when the polymer is a polymer, the functional additive is an initiator. The colored magnetic particle is prepared by the colored magnetic particle preparation method described in the first aspect, or prepared by other preparation methods. The colored magnetic particles prepared by the colored magnetic particle preparation method described in the first aspect have uniform particle size and good dispersibility, can remain stable in an aqueous or oily system, and are not easy to aggregate; secondly, the particle surface is coated with a polymer or adsorbed with a dye, so that it has a bright color and high gloss, while retaining the magnetic properties of ferroferric oxide; in addition, the introduction of surface modification and dyeing process makes the particle have excellent weather resistance and wear resistance, is not easily affected by environmental factors, ensures the stability of long-term use, and is suitable for preparing colored magnetic microcapsules.

[0078] The third aspect of the present invention provides a magnetic microcapsule, which includes a wall material and a core material, wherein the wall material is a mixture of anionic polymers and cationic polymers, and the core material is a mixture of colored magnetic particles, non-magnetic particles, oily solvents and suspension stabilizers as described in the second aspect; wherein the cationic polymer includes one or two of gelatin and ε-polylysine, and the anionic polymer includes one or more of sodium carboxymethyl cellulose, gum arabic and sodium alginate; and the non-magnetic particles are lipophilic nano-titanium dioxide.

[0079] The magnetic microcapsules are prepared by the following steps: adding colored magnetic particles and non-magnetic particles to an oily solvent at a preset mass ratio to obtain an oil phase mixture; adding a suspension stabilizer to the oil phase mixture and dispersing it at a preset dispersion speed to obtain a core material suspension; adding a cationic polymer and an anionic polymer to deionized water at a preset mass ratio to obtain an aqueous solution; adding the core material suspension to the aqueous solution, and dispersing the core material suspension by stirring to obtain a dispersion; adding an acid-base regulator to the dispersion to adjust the pH to a preset value, reacting for a first preset time, adding a curing agent, and continuing to react for a second preset time to obtain magnetic microcapsules.

[0080] The colored magnetic microcapsules of the present invention not only have magnetic functions, but also significantly improve the color expression and visual effects, breaking through the monotonous color limitations of traditional magnetic microcapsules, so that the handwriting board can not only realize basic writing and display functions, but also show colorful visual effects and enhance user experience. Furthermore, by adjusting the type and proportion of dyes, the display color of the handwriting board can be flexibly customized to meet the needs of different scenarios such as education, creative design and commercial display.

[0081] The fourth aspect of the embodiment of the present invention provides a magnetic film, the magnetic film includes a PET substrate layer, a rubber-based self-adhesive layer located on the PET substrate layer, a water-based glue and magnetic microcapsule mixed layer located on the rubber-based self-adhesive layer, and an AG PET film layer on the water-based glue and magnetic microcapsule layer, wherein the magnetic microcapsules are magnetic microcapsules as described in the third aspect. The magnetic film prepared based on colorful magnetic microcapsules realizes the combination of magnetic response and colorful visual effects, can present dynamic color changes, and provide a more intuitive and rich display effect for the handwriting board, while giving a breakthrough in the color expression ability of traditional magnetic films. The magnetic film can be used in the fields of education, office, commerce and retail, etc., such as for displaying course content in teaching; for explaining, discussing and recording important information in training classes and meetings; students can use portable writing boards to take notes, practice writing and review at home; in restaurants, cafes and retail stores, it is used to display daily specials, menus and promotional information, etc.

[0082] The following is further described in conjunction with specific embodiments and comparative examples. The raw materials involved in the following specific embodiments and comparative examples, unless otherwise specified, can all be commercially available, the instruments used, unless otherwise specified, can all be commercially available, and the processes involved, unless otherwise specified, are all routinely selected by those skilled in the art.

[0083] Example 1

[0084] (1) Preparation of Nano-FeO4

[0085] Dissolve 6 g of ferrous sulfate and 10 g of ferric chloride in 300 g of water and stir evenly to obtain an iron salt mixed solution;

[0086] Under stirring conditions, 100 g of alkaline substance is added dropwise to the iron salt mixed solution at a predetermined rate, during which the reaction temperature is controlled to be maintained at 80 degrees Celsius and the pH value is maintained at 8.5 to obtain a ferroferric oxide precursor precipitation solution;

[0087] Add 2 g of oleic acid to the ferroferric oxide precursor precipitation solution, stir at 80 degrees Celsius at a stirring speed of 300 rpm for 60 minutes until the reaction is completed, wash twice with 300 g of the first solvent, and then dry to obtain modified nano-ferroferric oxide with an average particle size of 3 nm;

[0088] (2A) Preparation by solvent evaporation method

[0089] 1) Preparation of oil phase

[0090] 1.5 g of the modified nano-ferroferric oxide, 10 g of a polymer, 60 g of a second solvent and 5 g of a dye (red) were mixed, and stirred at a stirring speed of 700 rpm for 25 minutes at room temperature to form an oil phase solution;

[0091] 2) Preparation of colored magnetic particles by evaporation method

[0092] 20g of the oil phase solution was added to 200g of the aqueous solution containing 1g of the dispersant and stirred at 700rpm for 60 minutes at 35 degrees Celsius for dispersion, and then the temperature was raised to 70 degrees Celsius to evaporate the solvent to obtain colored magnetic particles, namely the colored magnetic particles.

[0093] like Figure 2 , which is a schematic diagram of colored magnetic particles prepared by solvent evaporation method in Example 1. Figure 2 The medium color magnetic particles are red, with stable color and high saturation, and no obvious color unevenness or variegated color. From the particle morphology, the particle size is uniform and the dispersion is good.

[0094] (2B) Direct preparation of polymer monomers

[0095] 2g of the modified nano-ferrosoferric oxide, 10g of the monomer, 5g of the dye (blue) and 0.2g of the initiator were stirred at 70 degrees Celsius at a stirring speed of 700 rpm for 90 minutes until the reaction was completed to obtain the colored magnetic particles, namely the colored magnetic particles.

[0096] like Figure 3 , which is a schematic diagram of colored magnetic particles directly prepared by polymer monomers in Example 1. Figure 3 The overall color tone of the medium color magnetic particles is blue, and the color purity and saturation are high. From the particle morphology, the particle size is uniform and there is no obvious agglomeration or adhesion between the particles, and the dispersion is good.

[0097] Example 2

[0098] (1) Preparation of Nano-FeO4

[0099] Dissolve 6 g of ferrous sulfate and 12 g of ferric chloride in 400 g of water and stir evenly to obtain an iron salt mixed solution;

[0100] Under stirring conditions, 120 g of alkaline substance is added dropwise to the iron salt mixed solution at a predetermined rate, during which the reaction temperature is controlled to be maintained at 70 degrees Celsius and the pH value is maintained at 9, to obtain a ferroferric oxide precursor precipitation solution;

[0101] Add 1 g of oleic acid to the ferroferric oxide precursor precipitation solution, stir at 70 degrees Celsius at a stirring speed of 300 rpm for 60 minutes until the reaction is completed, wash twice with 300 g of the first solvent, and then dry to obtain modified nano-ferroferric oxide with an average particle size of 3 nm;

[0102] (2A) Preparation by solvent evaporation method

[0103] 1) Preparation of oil phase

[0104] 3 g of the modified nano-ferroferric oxide, 15 g of a polymer, 40 g of a second solvent and 3 g of a dye (red) were mixed, and stirred at a stirring speed of 700 rpm for 25 minutes at room temperature to form an oil phase solution;

[0105] 2) Preparation of colored magnetic particles by evaporation method

[0106] 25g of the oil phase solution was added to 150g of an aqueous solution containing 0.5g of a dispersant, and the mixture was stirred and dispersed at 35 degrees Celsius at a stirring speed of 700 rpm for 60 minutes, and then the temperature was raised to 70 degrees Celsius to evaporate the solvent to obtain colored magnetic particles, namely the colored magnetic particles.

[0107] like Figure 4 , which is a schematic diagram of colored magnetic particles prepared by solvent evaporation method in Example 2. Figure 4 The medium color magnetic particles are red, deep and highly saturated, stable in color, excellent in color expression, and no obvious color unevenness or variegated color. From the particle morphology, the particle size is uniform and there is no obvious agglomeration or adhesion between the particles, and the dispersion is good.

[0108] (2B) Direct preparation of polymer monomers

[0109] 2g of the modified nano-ferrosoferric oxide, 20g of the monomer, 4g of the dye (blue) and 0.4g of the initiator were stirred at 70 degrees Celsius at a stirring speed of 700 rpm for 90 minutes until the reaction was completed to obtain the colored magnetic particles, namely the colored magnetic particles.

[0110] like Figure 5 , which is a schematic diagram of colored magnetic particles directly prepared by polymer monomers in Example 2. Figure 5 The medium color magnetic particles are blue, with uniform and stable color and high saturation, and excellent color expression. From the particle morphology, the particle size is uniform and the dispersion is good.

[0111] Example 3

[0112] (1) Preparation of Nano-FeO4

[0113] Dissolve 6 g of ferrous sulfate and 14 g of ferric chloride in 500 g of water and stir evenly to obtain an iron salt mixed solution;

[0114] Under stirring conditions, 140 g of alkaline substance is added dropwise to the iron salt mixed solution at a predetermined rate, during which the reaction temperature is controlled to be maintained at 60 degrees Celsius and the pH value is maintained at 11, to obtain a ferroferric oxide precursor precipitation solution;

[0115] Add 1.5 g of oleic acid to the ferroferric oxide precursor precipitation solution, stir at 60 degrees Celsius at a stirring speed of 300 rpm for 60 minutes until the reaction is completed, wash twice with 300 g of the first solvent, and then dry to obtain modified nano-ferroferric oxide with an average particle size of 3 nm;

[0116] (2A) Preparation by solvent evaporation method

[0117] 1) Preparation of oil phase

[0118] 2 g of the modified nano-ferroferric oxide, 20 g of a polymer, 50 g of a second solvent and 4 g of a dye (red) were mixed, and stirred at a stirring speed of 700 rpm for 25 minutes at room temperature to form an oil phase solution;

[0119] 2) Preparation of colored magnetic particles by evaporation method

[0120] 30g of the oil phase solution was added to 100g of the aqueous solution containing 0.1g of the dispersant, and the mixture was stirred and dispersed at 700rpm for 60 minutes at 35 degrees Celsius, and then the temperature was raised to 70 degrees Celsius to evaporate the solvent to obtain colored magnetic particles, namely the colored magnetic particles.

[0121] like Figure 6 , which is a schematic diagram of colored magnetic particles prepared by solvent evaporation method in Example 3. Figure 6 The medium color magnetic particles are red in color, stable in color and high in saturation, with no obvious color unevenness or variegated color. From the particle morphology, the particle size is uniform, no obvious agglomeration or adhesion is observed between the particles, and the dispersion is good.

[0122] (2B) Direct preparation of polymer monomers

[0123] 2g of the modified nano-ferroferric oxide, 30g of the monomer, 3g of the dye (blue) and 0.6g of the initiator were stirred at 70 degrees Celsius at a stirring speed of 700 rpm for 90 minutes until the reaction was completed to obtain the colored magnetic particles, namely the colored magnetic particles.

[0124] like Figure 7 , which is a schematic diagram of colored magnetic particles directly prepared by polymer monomers in Example 3. Figure 7 The medium color magnetic particles are blue, stable in color, high in saturation, and the dye is evenly distributed inside the particles, without obvious color unevenness or variegated color. From the particle morphology, the particle size is uniform, there is no obvious agglomeration or adhesion between particles, and the dispersion is good.

[0125] Comparative Example 1

[0126] (1) Preparation of Nano-FeO4

[0127] Dissolve 6 g of ferrous sulfate and 10 g of ferric chloride in 300 g of water and stir evenly to obtain an iron salt mixed solution;

[0128] Under stirring conditions, 100 g of alkaline substance is added dropwise to the iron salt mixed solution at a predetermined rate, during which the reaction temperature is controlled to be maintained at 80 degrees Celsius and the pH value is maintained at 8.5 to obtain a ferroferric oxide precursor precipitation solution;

[0129] Add 0.5 g of oleic acid to the ferroferric oxide precursor precipitation solution, stir at 80 degrees Celsius at a stirring speed of 300 rpm for 60 minutes until the reaction is completed, wash twice with 300 g of the first solvent, and then dry to obtain modified nano-ferroferric oxide with an average particle size of 3 nm;

[0130] (2A) Preparation by solvent evaporation method

[0131] 1) Preparation of oil phase

[0132] 2 g of the modified nano-ferroferric oxide, 5 g of a polymer, 30 g of a second solvent and 2 g of a dye (red) were mixed, and stirred at a stirring speed of 700 rpm for 25 minutes at room temperature to form an oil phase solution;

[0133] 2) Preparation of colored magnetic particles by evaporation method

[0134] The 20 g oil phase solution was added to 200 g aqueous solution containing 0.05 g dispersant and stirred at 700 rpm for 60 minutes at 35 degrees Celsius for dispersion, and then the temperature was raised to 70 degrees Celsius to evaporate the solvent to obtain colored magnetic particles, namely the colored magnetic particles.

[0135] like Figure 8 As shown, it is a schematic diagram of the colored magnetic particles prepared by the solvent volatilization method in Comparative Example 1. The overall color tone of the colored magnetic particles is dark and not bright enough, the saturation is low, and the color quality is poor. There is some adhesion or accumulation between the particles, and the dispersibility is poor.

[0136] (2B) Direct preparation of polymer monomers

[0137] 2g of the modified nano-ferroferric oxide, 5g of the monomer, 3g of the dye (blue) and 0.1g of the initiator were stirred at 70 degrees Celsius at a stirring speed of 700 rpm for 90 minutes until the reaction was completed to obtain the colored magnetic particles, namely the colored magnetic particles.

[0138] like Fig. 9, which is a schematic diagram of colored magnetic particles directly prepared by polymer monomers in Comparative Example 1. The overall color tone of the colored magnetic particles is blue, and the color saturation is good. However, there is some adhesion or accumulation between the particles, and the dispersibility is poor.

[0139] Through the experiments of Example 1, Example 2 and Example 3, colored magnetic particles with uniform particle size, stable color and good dispersibility were obtained.

[0140] In Example 1, by controlling the reaction temperature (80°C), pH value (8.5) and adding an appropriate amount of oleic acid for surface modification, combined with the solvent volatilization method and the polymer monomer direct method, a color magnetic particle with balanced performance was obtained. In Example 2, by appropriately reducing the reaction temperature (70°C), increasing the amount of alkaline substances and optimizing the ratio of polymers and dyes, the color of the color magnetic particles is more uniform, the particle size distribution is more stable, and the dispersibility is further improved. In Example 3, the reaction conditions are further adjusted, the temperature is controlled to 60°C, the pH value is controlled to 11, and the monomer dosage and dispersant are optimized to ensure that the prepared color magnetic particles have excellent dispersibility. In comparison, in Comparative Example 1, although similar reaction conditions and methods are used, the obtained color magnetic particles have obvious deficiencies due to the lack of optimization in terms of the iron salt mixing ratio, oleic acid content, polymer and dispersant dosage. Specifically, the particle size distribution is uneven, and some particles aggregate, resulting in poor dispersibility. In addition, the color stability and uniformity of the color magnetic particles are also lower than those of the samples in Examples 1, 2, and 3. In summary, through the experimental comparison of Examples 1, 2, and 3, the present invention effectively improves the dispersibility, color uniformity, and stability of colored magnetic particles by optimizing the iron salt mixture ratio, the amount of alkaline substance, the temperature, the pH value, and the oleic acid modification conditions. In contrast, the preparation process of Comparative Example 1 failed to achieve the same level of performance.

[0141] After the preparation of colored magnetic particles is completed, the colored magnetic particles can be further used to prepare colored magnetic microcapsules and magnetic films. For the specific preparation method, please refer to the patent document with patent number 202411039100.5 and invention name "magnetic microcapsules and preparation methods thereof and magnetic films". The subsequent preparation of magnetic microcapsules and magnetic films is similar to it, so it will not be repeated here. The magnetic film made from the above-mentioned colored magnetic particles is as follows: Fig.10 and Fig.11 As shown. For the magnetic film made of black magnetic particles, Fig.10 and Fig.11 The colored magnetic film shown is more attractive in color and visual effect, which can greatly enhance the visual effect and increase the user experience.

[0142] It should be clear that the present invention is not limited to the specific configuration and processing described above and shown in the figures. For the sake of simplicity, a detailed description of the known method is omitted here. In the above embodiments, several specific steps are described and shown as examples. However, the method process of the present invention is not limited to the specific steps described and shown, and those skilled in the art can make various changes, modifications and additions, or change the order between the steps after understanding the spirit of the present invention.

[0143] The above is only a specific implementation of the present invention. Those skilled in the art can clearly understand that for the convenience and simplicity of description, the specific working process of the system, module and unit described above can refer to the corresponding process in the aforementioned method embodiment, and will not be repeated here. It should be understood that the protection scope of the present invention is not limited to this. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be covered within the protection scope of the present invention.

Claims

1. A method for preparing colored magnetic particles, characterized in that: The method comprises: Dissolving iron salt in water and stirring evenly to obtain an iron salt mixed solution; Under stirring conditions, adding alkaline substances dropwise into the iron salt mixed solution at a predetermined rate to obtain a ferroferric oxide precursor precipitation solution; Add oleic acid to the ferroferric oxide precursor precipitation solution, stir until the reaction is completed, wash with the first solvent, and then dry to obtain modified nano ferroferric oxide; The colored magnetic particles are obtained by mixing modified nano-ferroferric oxide, dye, polymer and functional additive.

2. The method for preparing colored magnetic particles according to claim 1, characterized in that: The high molecular weight substance is a polymer, the functional additive is a dispersant, and the color magnetic particles are obtained by mixing the modified nano-ferroferric oxide, dye, high molecular weight substance and functional additive, and the method comprises: The modified nano-ferroferric oxide, polymer, second solvent and dye are mixed to form an oil phase solution, the oil phase solution is added into an aqueous solution containing a dispersant for stirring and dispersion, and the colored magnetic particles are obtained after the solvent is volatilized by heating.

3. The method for preparing colored magnetic particles according to claim 1, characterized in that: The polymer is a monomer, the functional additive is an initiator, and the colored magnetic particles are obtained by mixing the modified nano-ferroferric oxide, dye, polymer and functional additive, which comprises: The modified nano-ferroferric oxide, monomer, dye and initiator are stirred at a preset temperature until the reaction is completed to obtain the colored magnetic particles.

4. The method for preparing colored magnetic particles according to claim 2, characterized in that: In parts by mass, the step of dissolving the iron salt in water and stirring evenly to obtain an iron salt mixed solution comprises: dissolving 16-20 parts of the iron salt in 300-500 parts of water and stirring evenly to obtain an iron salt mixed solution; The step of adding the alkaline substance to the iron salt mixed solution at a predetermined rate under stirring conditions to obtain the ferroferric oxide precursor precipitation solution comprises: adding 100-140 parts of the alkaline substance to the iron salt mixed solution at a predetermined rate under stirring conditions, during which the reaction temperature is controlled to be maintained at 60-80 degrees Celsius and the pH value is maintained at 8.5-11.0, to obtain the ferroferric oxide precursor precipitation solution; The step of adding oleic acid to the ferroferric oxide precursor precipitation solution, stirring until the reaction is completed, washing with a first solvent, and then drying to obtain modified nano ferroferric oxide comprises: adding 1-2 parts of oleic acid to the ferroferric oxide precursor precipitation solution, stirring at 60-80 degrees Celsius until the reaction is completed, washing with 250-400 parts of the first solvent for 2-4 times, and then drying to obtain modified nano ferroferric oxide; The step of mixing the modified nano-ferroferric oxide, the polymer, the second solvent and the dye to form an oil phase solution comprises: mixing 1.5-3.0 parts of the modified nano-ferroferric oxide, 10-20 parts of the polymer, 40-60 parts of the second solvent and 3-5 parts of the dye to form an oil phase solution; The step of adding the oil phase solution to an aqueous solution containing a dispersant for stirring and dispersing, and heating the solution to evaporate the solvent to obtain the colored magnetic particles comprises: adding 20-30 parts of the oil phase solution to 100-200 parts of an aqueous solution containing 0.1-1.0 parts of a dispersant for stirring and dispersing, and heating the solution to 70-90 degrees Celsius to evaporate the solvent to obtain the colored magnetic particles.

5. The method for preparing colored magnetic particles according to claim 3, characterized in that: In parts by mass, the step of dissolving the iron salt in water and stirring evenly to obtain an iron salt mixed solution comprises: dissolving 16-20 parts of the iron salt in 300-500 parts of water and stirring evenly to obtain an iron salt mixed solution; The step of adding the alkaline substance to the iron salt mixed solution at a predetermined rate under stirring conditions to obtain the ferroferric oxide precursor precipitation solution comprises: adding 100-140 parts of the alkaline substance to the iron salt mixed solution at a predetermined rate under stirring conditions, during which the reaction temperature is controlled to be maintained at 60-80 degrees Celsius and the pH value is maintained at 8.5-11.0, to obtain the ferroferric oxide precursor precipitation solution; The step of adding oleic acid to the ferroferric oxide precursor precipitation solution, stirring until the reaction is completed, washing with a first solvent, and then drying to obtain modified nano ferroferric oxide comprises: adding 1-2 parts of oleic acid to the ferroferric oxide precursor precipitation solution, stirring at 60-80 degrees Celsius until the reaction is completed, washing with 250-400 parts of the first solvent for 2-4 times, and then drying to obtain modified nano ferroferric oxide; The step of stirring the modified nano-ferroferric oxide, monomer, dye and initiator at a preset temperature until the reaction is completed to obtain the colored magnetic particles comprises: stirring 1.5-3.0 parts of the modified nano-ferroferric oxide, 10-30 parts of the monomer, 3-5 parts of the dye and 0.2-0.6 parts of the initiator at 65-75 degrees Celsius and a stirring speed of 600-800 rpm for 80-100 minutes until the reaction is completed to obtain the colored magnetic particles.

6. The method for preparing colored magnetic particles according to any one of claims 1 to 5, characterized in that: The iron salt includes two or more of ferrous sulfate, ferric chloride and ferrous chloride; the alkaline substance includes one or two of ammonia water or alkali metal hydroxide.

7. The method for preparing colored magnetic particles according to any one of claims 1 to 5, characterized in that: The first solvent is ethanol, the second solvent is any one or more of dichloromethane, acetone, ethyl acetate, butanone, n-pentane, and n-hexane; the polymer includes any one or more of polystyrene, polymethyl methacrylate, polypropylene, polyethylene, high-density polyethylene, polycarbonate, and polyethylene terephthalate; the dispersant includes any one or more of polyvinyl alcohol, gum arabic, sodium dodecyl sulfate, sodium carboxymethyl cellulose, and polyvinyl pyrrolidone.

8. A colored magnetic particle, characterized in that: The colored magnetic particles include modified nano ferrosoferric oxide, dyes, polymers and functional additives, wherein the polymers are monomers or polymers obtained by polymerization of the monomers. When the polymers are monomers, the functional additives are dispersants; when the polymers are polymers, the functional additives are initiators.

9. A magnetic microcapsule, characterized in that: The magnetic microcapsule comprises a wall material and a core material, wherein the wall material is a mixture of anionic polymers and cationic polymers, and the core material comprises: a mixture of non-magnetic particles, an oily solvent and a suspension stabilizer, and the colored magnetic particles as described in claim 8; wherein the cationic polymer comprises one or two of gelatin and ε-polylysine, and the anionic polymer comprises one or more of sodium carboxymethyl cellulose, gum arabic, and sodium alginate; and the non-magnetic particles are lipophilic nano-titanium dioxide.

10. A magnetic film, characterized in that: The magnetic film includes a PET substrate layer, a rubber-based self-adhesive layer located on the PET substrate layer, a water-based glue and magnetic microcapsule mixed layer located on the rubber-based self-adhesive layer, and an AG PET film layer on the water-based glue and magnetic microcapsule layer, wherein the magnetic microcapsules are the magnetic microcapsules as described in claim 9.

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