Magnetic microcapsule, preparation method thereof and magnetophoresis display handwriting board

Abstract

The invention relates to the technical field of magnetic microcapsules, in particular to a magnetic microcapsule, a preparation method thereof and a magnetophoresis display handwriting board. The preparation method provided by the invention comprises the following steps: mixing non-magnetic nanoparticles, magnetic nanoparticles, a solvent, a dispersing agent and a thixotropic agent, and uniformly dispersing to obtain a core material; heating and dissolving gelatin, a polyanionic compound and an emulsifier in water, and uniformly mixing to obtain a water phase; adding the core material into the water phase, emulsifying, and adding an acid solution to adjust the pH value to 3.9-4.3; cooling to 5-10 DEG C, adding a carbodiimide or polycarbodiimide aqueous dispersion, adding an aldehyde curing agent, heating to 25-30 DEG C, and discharging after the reaction is finished; and settling and washing to obtain the magnetic microcapsule. The magnetic microcapsule provided by the invention is provided with the elastic deformable shell, and a flat honeycomb structure is formed in a subsequent coating process, so that magnetophoresis color development is facilitated, and the contrast of writing is improved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of magnetic microcapsules, in particular to a magnetic microcapsule, a preparation method thereof and a magnetic display handwriting board. BACKGROUND

[0002] The magnetic microcapsule refers to a microcapsulated material formed by wrapping a fluid containing magnetic particles with a high polymer material, and one of the main applications is magnetic display. At present, the preparation methods of the microcapsules mainly include physical methods and chemical methods. The commonly used physical method is mainly a solvent evaporation method; the chemical method is divided into interfacial polymerization, in-situ polymerization and complex coacervation, etc. Among them, the microcapsule with a melamine resin shell prepared by the in-situ polymerization method has the best strength, but the melamine shell material has high rigidity and cannot produce elastic deformation, so that the single microcapsule is too small for display after film formation, and is not suitable for magnetic display microcapsules; the microcapsule prepared by the interfacial polymerization method will cause residual monomers in the microcapsule, which is not conducive to long-term storage and use of the microcapsule; the microcapsule prepared by the complex coacervation method has low overall strength and is prone to breakage.

[0003] Patent CN102600776B discloses a preparation method of a magnetic microcapsule, in which a volatile organic solvent, such as a high molecular compound polyacrylate and polystyrene, is dissolved in a magnetic fluid, and then the solvent is volatilized after emulsification to form a magnetic microcapsule. The method has simple process and low production cost, but volatile toxic solvents are used in the preparation process, and the shell material wrapped by the physical method has nanoscale micropores, which affects the subsequent application.

[0004] CN118571590B discloses a magnetic microcapsule, a preparation method thereof and a magnetic film, in which a compound cationic and anionic polymer is used as a wall material, and at least two magnetic particles with different magnetic strengths are used as core materials; the long-term high temperature and high humidity aging resistance is still poor.

[0005] Based on the above analysis, it is necessary to provide a magnetic microcapsule with good high temperature and high humidity aging resistance and long service life. SUMMARY

[0006] The embodiment of the application provides a preparation method of a magnetic microcapsule with a double-functional crosslinked high-density and high-elasticity shell material, so as to solve the problems that in the related art, only amino functional groups participate in chemical crosslinking in the microcapsule shell material coated by using a traditional complex coacervation method, the crosslinking degree is low, the shell material has poor density and poor high temperature and high humidity aging resistance, and the subsequent service life cannot be guaranteed.

[0007] In a first aspect, the application provides a preparation method of a magnetic microcapsule with a double-functional crosslinked high-density and high-elasticity shell material, including the following steps:

[0008] S1, the non-magnetic nanoparticles, magnetic nanoparticles, solvent, dispersant, thixotropic agent are mixed, uniformly dispersed, to obtain the core material;

[0009] S2, the gelatin, polyanion compound and emulsifier are heated and dissolved in water, mixed uniformly, to obtain the water phase;

[0010] S3, the core material is added to the water phase, emulsified, an acid solution is added to adjust the pH value to 3.9-4.3; the temperature is reduced to 5-10°C, a carbodiimide or a polycarbodiimide aqueous dispersion is added, then an aldehyde curing agent is added, the temperature is increased to 25-30°C, after the reaction is completed, the material is discharged; after settling and washing, the magnetic microcapsules are obtained.

[0011] In some embodiments, the non-magnetic nanoparticles are selected from any one of titanium dioxide, lithopone, zinc oxide, zinc white, zinc sulfide, etc., and the particle size of the non-magnetic nanoparticles is 0.1-0.5 μm. As light reflecting particles, the non-magnetic nanoparticles can provide good hiding power for hiding the color of the magnetic particles in the core material, and serve as the background color of the handwriting film when not written.

[0012] In some embodiments, the magnetic nanoparticles are selected from any one or a mixture of multiple of black iron oxide, porous iron oxide, iron oxide containing manganese dioxide, chromium dioxide, iron or nickel microparticles, etc. The particle size of the magnetic nanoparticles is 0.1-1 μm. As light absorbing particles, the magnetic nanoparticles can provide the blackness of the handwriting when the handwriting film is written.

[0013] In some embodiments, the solvent is a mixture of any one or multiple of 3# white oil, 5# white oil, 10# white oil, isomeric alkanes with different carbon chain lengths, silicone oil, etc. The solvent serves as the dispersion medium for the magnetic nanoparticles and the non-magnetic nanoparticles, and is the place where the magnetophoretic display is realized. The solvent used in the present application is stable in nature, colorless and odorless, and does not harm the production personnel, product users and the environment.

[0014] In some embodiments, the dispersant is a mixture of any one or multiple of polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene oleyl ether, polycarboxylic acid amine salt, sorbitan trioleate, sorbitan monolaurate, sorbitan monostearate, etc. The dispersant used in the present application is an oil-soluble dispersant with HLB≤5. The purpose of adding the dispersant is to ensure the uniform dispersion of the magnetic nanoparticles and the non-magnetic nanoparticles in the solvent, and to appropriately reduce the viscosity of the system to ensure the mobility of the nanoparticles in the solvent.

[0015] In some embodiments, the thixotropic agent is selected from a mixture of any one or more of silicate, alumina powder, silica powder, diatomite, kaolin, bentonite, ultra-fine calcium carbonate, ultra-fine active calcium carbonate, calcium hydrogen carbonate, barium sulfate, etc. The addition of the thixotropic agent can prevent the nanoparticles from settling in the core material system due to gravity, thereby maintaining the writing traces of the handwriting film. When the magnetic microcapsules are subjected to a magnetic field, the magnetic nanoparticles inside the magnetic microcapsules move along the magnetic field lines, generating a shearing force, and the viscosity of the core material decreases, and the movement of the magnetic nanoparticles is not limited.

[0016] In some preferred embodiments, the silicate is selected from a mixture of any one or more of sodium silicate, potassium silicate, aluminum silicate, calcium silicate, etc.

[0017] In some embodiments, the mass percentage of each raw material in the core material is: non-magnetic nanoparticles 25-35%, magnetic nanoparticles 1.5-3%, solvent 60-70%, dispersant 2-4%, and thixotropic agent 0.2-0.5%.

[0018] In some embodiments, the gelatin is selected from an alkali method gelatin with a strength of 120-240.

[0019] In some embodiments, the polyanionic compound is selected from any one of gum arabic, sodium carboxymethyl cellulose, sodium polyacrylate, sodium polystyrene maleate, or sodium polyethylene maleate.

[0020] In some embodiments, the total amount of gelatin and polyanionic compound added is 8%-12% of the mass of the core material, and the mass ratio of gelatin to polyanionic compound is 10:1-8:1.

[0021] In some embodiments, the gelatin and the polyanionic compound form a shell material, and the amount of carbodiimide or aqueous dispersion of polycarbodiimide added is 10%-30% of the mass of the shell material.

[0022] In some embodiments, the amount of aldehyde-based curing agent added is 20%-50% of the mass of the shell material.

[0023] In some embodiments, the emulsifier is selected from any one of sodium dodecyl benzene sulfonate, sodium dodecyl sulfate, sodium perfluoro-nonylene oxybenzene sulfonate, and diisooctyl succinate sodium sulfonate.

[0024] In some embodiments, the amount of emulsifier added is 0.2%-2.5% of the total mass of the gelatin and the polyanionic compound.

[0025] In some embodiments, the acid solution is selected from any one of hydrochloric acid, acetic acid, and citric acid.

[0026] In some embodiments, the aldehyde-based curing agent is selected from formaldehyde or glutaraldehyde.

[0027] In a second aspect, the application further provides the magnetic microcapsule prepared by the preparation method.

[0028] In a third aspect, the application provides a magnetophoretic display handwriting board comprising the magnetic microcapsule.

[0029] In step S3, the reaction system is first cooled to a low temperature of 5-10 DEG C, and then warmed to 25-30 DEG C. The phase separation can be better achieved by cooling, and the shell material is dehydrated and solidified. The reaction rate can be controlled by reacting for 1-2 hours at a low temperature, so that the reaction is more uniform. The warming reaction makes the solidification more complete.

[0030] The technical scheme provided by the application has the following beneficial effects:

[0031] 1. Compared with the traditional complex coacervation method, the carbodiimide is first added in the solidification process, and then the aldehyde curing agent is added. The network structure is formed on the amino group of the aldehyde curing agent crosslinked gelatin molecular chain segment, and the free carboxyl and polyanion on the gelatin molecular chain segment are activated to have complex coacervation with gelatin. The covalent bond is generated between the activated carboxyl and the amino group and the hydroxyl group on the gelatin chain segment, so that the internal crosslinking degree of the shell material is greatly increased, the strength and compactness of the microcapsule are improved, and the problem of leakage of the magnetic core material in the subsequent film coating process and use is avoided.

[0032] 2. Compared with the traditional in-situ polymerization prepared melamine resin shell microcapsule, the magnetic microcapsule provided by the application has an elastic deformable shell, which forms a flat honeycomb structure in the subsequent film coating process, is more conducive to magnetophoretic color development, and improves the contrast of written characters.

[0033] 3. Compared with the traditional interface polymerization method prepared polyurethane shell microcapsule, the magnetic microcapsule provided by the application has no monomer or prepolymer residue in the core material, and the service life of the magnetic microcapsule is increased.

[0034] 4. Compared with the traditional physical method prepared microcapsule, the magnetic microcapsule of the application does not have the problem of nanopore, and no volatile toxic solvent is used in the whole process.

[0035] 5. After the magnetic microcapsule provided by the application is made into a handwriting film, the handwriting film can still be normally written and erased after being baked at a high temperature of 50 DEG C for one month or at a high temperature of 90 DEG C for two weeks, and the magnetic microcapsule shows excellent long-term high-temperature aging performance. BRIEF DESCRIPTION OF DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the embodiments will be briefly introduced. Obviously, the drawings in the following description only constitute some embodiments of the present application, and for those skilled in the art, other drawings can be obtained without creative effort.

[0037] Figure 1 The optical microscope image of the magnetic microcapsule handwriting film of Example 1 of the present application.

[0038] Figure 2 The aging test result image of the magnetic microcapsule handwriting film of Example 1 of the present application.

[0039] Figure 3 The optical microscope image of the magnetic microcapsule handwriting film of Comparative Example 1 of the present application.

[0040] Figure 4 The aging test result image of the magnetic microcapsule handwriting film of Comparative Example 2 of the present application. DETAILED DESCRIPTION

[0041] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings of the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative effort belong to the scope of protection of the present application.

[0042] The embodiments of the present application provide a preparation method of a magnetic microcapsule with a high-elasticity shell material with double-functional crosslinking and high density, which can solve the problems in the prior art that only amino single functional group participates in chemical crosslinking in a microcapsule shell material coated by using a traditional complex coagulation method, the crosslinking degree is low, the shell material has poor density and poor high-temperature and high-humidity aging resistance, and the service life cannot be guaranteed.

[0043] The embodiments of the present application provide a preparation method of a magnetic microcapsule with a high-elasticity shell material with double-functional crosslinking and high density, which can solve the problems in the prior art that only amino single functional group participates in chemical crosslinking in a microcapsule shell material coated by using a traditional complex coagulation method, the crosslinking degree is low, the shell material has poor density and poor high-temperature and high-humidity aging resistance, and the service life cannot be guaranteed.

[0044] In step S1, 25-35% of non-magnetic nanoparticles, 1.5-3% of magnetic nanoparticles, 60-70% of a solvent, 2-4% of a dispersing agent and 0.2-0.5% of a thixotropic agent are mixed according to the mass percentage, and then the mixture is uniformly premixed by a dispersion machine, and then is put into a ball mill, a vertical sand mill, a horizontal sand mill or an ultrasonic dispersion machine, and after uniform dispersion, a core material is obtained.

[0045] Step S2, gelatin, polyanionic compound and emulsifier are mixed and heated to 45-50°C to dissolve in deionized water, mixed uniformly to obtain the water phase; the total amount of gelatin and polyanionic compound is 8%-12% of the mass of the core material;

[0046] Step S3, the core material is added to the water phase, emulsified at a speed of 200-500 rpm for 5-10 minutes, and the pH value is adjusted to 3.9-4.3 by adding acid solution dropwise; the temperature is reduced to 5-10°C, 10%-30% of the mass of the shell material is added to the water dispersion of carbodiimide or polycarbodiimide, and reacted for 1-2 h, then 20%-50% of the mass of the shell material is added to the aldehyde curing agent, the temperature is increased to 25-30°C, and the material is discharged after reacting for 4-6 h; after settling and washing, the magnetic microcapsule is obtained.

[0047] The magnetic microcapsule and the preparation method thereof provided in the present application will be described in detail below in combination with examples and comparative examples.

[0048] Example 1:

[0049] (1) 30 g of titanium dioxide with a particle size of 0.2 μm, 2 g of black iron oxide with a particle size of 0.5 μm, 65 g of 3# white oil, 2.5 g of polyethylene oxide lauryl ether (CAS number: 9002-92-0), and 0.5 g of silica powder are mixed, uniformly pre-mixed by a dispersion machine, and then put into an ultrasonic dispersion machine to obtain the core material after uniform dispersion;

[0050] (2) 8 g of alkali gelatin with a gel strength of 200, 0.8 g of gum arabic, and 0.2 g of sodium dodecylbenzenesulfonate are dissolved in 400 g of deionized water at 50°C to obtain the water phase after stirring and mixing uniformly;

[0051] (3) 80 g of the core material is added to the water phase, emulsified at a speed of 200 rpm for 10 minutes; the pH of the system is slowly adjusted to 4.0 by adding 1% hydrochloric acid dropwise; the temperature is reduced to 8°C, 1.5 g of water-soluble carbodiimide is added, and 2 g of formaldehyde is added after reacting for 2 h; the temperature is slowly increased to 30°C, and the material is discharged after reacting for 5 h; the material is settled and washed to obtain the magnetic microcapsule.

[0052] The magnetic microcapsule and the water-based polyurethane coating glue are weighed according to a mass ratio of 10:1, stirred and mixed uniformly, coated on a transparent PET film to form a film, the wet film is first dried at 45°C for 10 minutes, and then dried at 80°C for 10 minutes to obtain the magnetic microcapsule handwriting film.

[0053] The optical microscope image of the magnetic microcapsule handwriting film of Example 1 is shown in Figure 1 .

[0054] The magnetic microcapsule handwriting film of Example 1 is subjected to aging test under the conditions of a temperature of 90°C and a humidity of 90% for 72 h, and the results are shown inFigure 2 .

[0055] The magnetic microcapsule handwriting film of Example 1 was baked in a high temperature of 50℃ for one month, and the handwriting film could still be normally written and erased.

[0056] The magnetic microcapsule handwriting film of Example 1 was baked in a high temperature of 90℃ for two weeks, and the handwriting film could still be normally written and erased.

[0057] Comparative Example 1:

[0058] (1) 30 g of titanium dioxide with a particle size of 0.2 μm, 2 g of black iron oxide with a particle size of 0.5 μm, 65 g of 3# white oil, 2.5 g of polyethylene oxide lauryl ether, and 0.5 g of silica powder were mixed, uniformly pre-mixed by a dispersion machine, and then put into an ultrasonic dispersion machine. After uniform dispersion, the core material was obtained;

[0059] (2) Polystyrene sodium maleate was dissolved in 400 g of deionized water at 65℃, and stirred and dissolved as the water phase;

[0060] (3) 80 g of the core material was added to the water phase, and emulsified at a speed of 200 rpm for 10 minutes; 9 g of diluted melamine resin prepolymer was added, and reacted at 65℃ for 1 hour; the temperature was raised to 85℃, and reacted for 4 hours to discharge; the material liquid was washed by sedimentation to obtain the melamine resin coated magnetic microcapsule.

[0061] The melamine resin coated magnetic microcapsule and the water-based polyurethane coating glue were weighed according to a mass ratio of 10:1, uniformly mixed by stirring, and coated on a transparent PET film to form a film. The wet film was first dried at 45℃ for 10 minutes, and then dried at 80℃ for 10 minutes to obtain the melamine resin magnetic microcapsule handwriting film.

[0062] The optical microscope image of the magnetic microcapsule handwriting film of Comparative Example 1 is shown in Figure 3 .

[0063] From Figure 1 and Figure 3 it can be seen that the magnetic microcapsule prepared in Example 1 formed a honeycomb flat structure during the coating process, greatly increasing the color development area of the magnetic microcapsule, and there was no continuous black mass; the melamine resin shell magnetic microcapsule prepared by the traditional in-situ polymerization method in Comparative Example 1 could not deform during the coating process due to its rigid shell material, and the point contact between the microcapsule and the PET film material was not a surface contact, and the color development area was very small; and under observation by an optical microscope, the contact points formed a continuous black mass, deepening the background color of the handwriting film and reducing the writing contrast; therefore, the melamine resin shell coated magnetic microcapsule is not suitable for high-contrast magnetophoretic display.

[0064] Comparative Example 2:

[0065] (1)Titanium dioxide 30 g with particle size of 0.2 μm, black iron oxide 2 g with particle size of 0.5 μm, 3# white oil 65 g, polyethylene oxide lauryl ether 2.5 g, silica powder 0.5 g were mixed, and then pre-mixed uniformly by a dispersion machine, and then put into an ultrasonic dispersion machine, and after uniform dispersion, a core material was obtained;

[0066] (2)8 g of alkali gelatin with gel strength of 200, 0.8 g of acacia and 0.2 g of sodium dodecyl benzene sulfonate were dissolved in 400 g of deionized water at 50°C, and then stirred and mixed uniformly as an aqueous phase;

[0067] (3)80 g of the core material was added to the aqueous phase, and emulsified at a speed of 200 rpm for 10 minutes; the pH of the system was slowly adjusted to 4.0 by dropwise adding 10% glacial acetic acid; the temperature was lowered to 8°C, and 2 g of formaldehyde was added; the temperature was slowly raised to 30°C, and after reaction for 5 h, the material was discharged; and after sedimentation and washing, the material was the magnetic microcapsule coated by the traditional complex coacervation method.

[0068] The magnetic microcapsule coated by the traditional complex coacervation method and the water-based polyurethane coating glue were weighed according to a mass ratio of 10:1, and then stirred and mixed uniformly, and then coated on a transparent PET film to form a film; the wet film was first dried at 45°C for 10 minutes, and then dried at 80°C for 10 minutes, and thus a magnetic microcapsule hand-writing film coated by the traditional complex coacervation method was obtained.

[0069] The magnetic microcapsule hand-writing film of Comparative Example 2 was subjected to aging test under the conditions of temperature of 90°C and humidity of 90% for 24 h, and the results are shown in Table 2. Figure 4 From Table 2, it can be seen that after the aging test, the magnetic microcapsule prepared in Example 1 did not show performance decline, and the magnetic microcapsule prepared in Comparative Example 2 had basically lost its performance. Figure 2 Figure 4 The applicant analyzed that this was because the magnetic microcapsule prepared in Example 1 was prepared by using double-functional crosslinking gelatin and polyanion complex coacervation, so that the carboxyl groups in the molecular structures of the gelatin and the polyanion also participated in the chemical crosslinking reaction, and a more compact and firm three-dimensional network structure was formed, which had stronger protection effect on the magnetic core material, greatly improved the high temperature and high humidity aging resistance, and improved the stability of the magnetic hand-writing film in later use; and the magnetic microcapsule prepared in Comparative Example 2 was prepared by the traditional complex coacervation method, and only the amino groups on the gelatin chain segment and the aldehyde crosslinking agent produced chemical crosslinking in the shell material, the crosslinking density was low, the shell material had low compactness, the high temperature and high humidity aging resistance was poor, and the subsequent use was affected.

[0070] Example 2:

[0071] (1)Zinc oxide 28 g with particle size of 0.5 μm, chromium dioxide 2.5 g with particle size of 0.3 μm, 5# white oil 66 g, polyethylene oxide hexadecyl ether 3.2 g, and aluminum oxide fine powder 0.3 g were mixed, and then pre-mixed uniformly by a dispersion machine, and then put into an ultrasonic dispersion machine, and after uniform dispersion, a core material was obtained;​

[0072] (2) 8 g of alkali gelatin with a gel strength of 240, 0.8 g of sodium carboxymethyl cellulose, and 0.15 g of sodium dodecyl benzene sulfonate were dissolved in 400 g of deionized water at 45°C, and stirred and mixed uniformly as the water phase;

[0073] (3) 80 g of the core material was added to the water phase, and emulsified at a speed of 300 rpm for 8 minutes; the pH of the system was slowly adjusted to 4.2 by dropwise adding 1% citric acid; the temperature was lowered to 10°C, 2 g of water-soluble carbodiimide was added, and reacted for 2 h before adding 3 g of formaldehyde; the temperature was slowly raised to 25°C, and reacted for 6 h before discharging; the material liquid was washed by sedimentation to obtain the magnetic microcapsules.

[0074] The magnetic microcapsules and the water-based polyurethane coating glue were weighed according to a mass ratio of 8:1, stirred and mixed uniformly, coated on a transparent PET film to form a film, the wet film was first dried at 45°C for 10 minutes, and then dried at 80°C for 10 minutes to obtain the magnetic microcapsule handwriting film.

[0075] The magnetic microcapsule handwriting film of Example 2 was baked in a high temperature of 50°C for one month, and the handwriting film could still be normally written and erased.

[0076] The magnetic microcapsule handwriting film of Example 2 was baked in a high temperature of 90°C for two weeks, and the handwriting film could still be normally written and erased.

[0077] Example 3:

[0078] (1) 32 g of zinc barytes with a particle size of 0.1 μm, 2.5 g of iron microparticles with a particle size of 0.2 μm, 63 g of 3# white oil, 2 g of polyethylene oxide oil ether (CAS No. 68958-58-7), and 0.5 g of sodium silicate were mixed, uniformly premixed by a dispersion machine, and then put into an ultrasonic dispersion machine to obtain the core material after uniform dispersion;

[0079] (2) 8 g of alkali gelatin with a gel strength of 180, 0.8 g of polystyrene sodium maleate (CAS No. 65652-36-0), and 0.18 g of sodium diisooctyl sulfosuccinate were dissolved in 400 g of deionized water at 48°C, and stirred and mixed uniformly as the water phase;

[0080] (3) 80 g of the core material was added to the water phase, and emulsified at a speed of 500 rpm for 6 minutes; the pH of the system was slowly adjusted to 4.0 by dropwise adding 1% acetic acid; the temperature was lowered to 6°C, 2.2 g of poly-carbodiimide water dispersion (CAS No. 151-51-9) was added, and reacted for 2 h before adding 2.0 g of formaldehyde; the temperature was slowly raised to 28°C, and reacted for 5 h before discharging; the material liquid was washed by sedimentation to obtain the magnetic microcapsules.

[0081] The magnetic microcapsule and the water-based polyurethane coating glue are weighed according to the mass ratio of 6:1, mixed uniformly, coated on the transparent PET film to form a film, and the wet film is first dried at 45 DEG C for 10 minutes, and then dried at 80 DEG C for 10 minutes, to obtain the magnetic microcapsule handwriting film.

[0082] The magnetic microcapsule handwriting film of Example 3 is placed in a high temperature of 50 DEG C for baking for one month, and the handwriting film can still be normally written and erased.

[0083] The magnetic microcapsule handwriting film of Example 3 is placed in a high temperature of 90 DEG C for baking for two weeks, and the handwriting film can still be normally written and erased.

[0084] Example 4:

[0085] (1) 25g of zinc sulfide with a particle size of 0.2μm, 3g of black iron oxide with a particle size of 0.6μm, 68g of 3# white oil, 3.6g of sorbitan monolaurate (CAS No.: 1338-39-2), and 0.4g of aluminum silicate are mixed uniformly by a dispersion machine, and then put into an ultrasonic dispersion machine to obtain a core material after uniform dispersion;

[0086] (2) 8g of alkali gelatin with a gel strength of 200, 0.8g of polyacrylic acid sodium (CAS No.: 9003-04-7), and 0.1g of sodium dodecyl sulfate are dissolved in 400g of deionized water at 45 DEG C to obtain an aqueous phase after uniform stirring;

[0087] (3) 80g of the core material is added to the aqueous phase and emulsified at a speed of 400rpm for 8 minutes; the pH of the system is slowly adjusted to 4.2 by adding hydrochloric acid with a mass concentration of 1%; the temperature is lowered to 8 DEG C, 2.5g of water-soluble carbodiimide is added, and the reaction is carried out for 1.5h; 3g of formaldehyde is added after the temperature is slowly raised to 30 DEG C, and the reaction is carried out for 5h; and the material liquid is obtained after sedimentation and washing, which is the magnetic microcapsule.

[0088] The magnetic microcapsule and the water-based polyurethane coating glue are weighed according to the mass ratio of 6:1, mixed uniformly, coated on the transparent PET film to form a film, and the wet film is first dried at 45 DEG C for 10 minutes, and then dried at 80 DEG C for 10 minutes, to obtain the magnetic microcapsule handwriting film.

[0089] The magnetic microcapsule handwriting film of Example 3 is placed in a high temperature of 50 DEG C for baking for one month, and the handwriting film can still be normally written and erased.

[0090] The magnetic microcapsule handwriting film of Example 3 is placed in a high temperature of 90 DEG C for baking for two weeks, and the handwriting film can still be normally written and erased.

[0091] Example 5:

[0092] (1) 27 g of titanium dioxide with a particle size of 0.5 μm, 2.5 g of manganese dioxide-containing iron oxide with a particle size of 1 μm, 66 g of 10# white oil, 4 g of sorbitan monostearate, and 0.5 g of kaolin were mixed uniformly by a dispersing machine, and then were put into an ultrasonic dispersing machine. After uniform dispersion, a core material was obtained;

[0093] (2) 8 g of alkali gelatin with a gel strength of 160, 0.8 g of sodium polyacrylate, and 0.08 g of sodium dodecylbenzenesulfonate were dissolved in 400 g of deionized water at 45°C, and were stirred and mixed uniformly as an aqueous phase;

[0094] (3) 80 g of the core material was added to the aqueous phase, and was emulsified at a rotation speed of 300 rpm for 10 minutes. The pH of the system was slowly adjusted to 4.0 by dropwise addition of 1% hydrochloric acid. The temperature was lowered to 5°C, 2.3 g of water-soluble carbodiimide was added, and reacted for 2 h. Then, 3.1 g of formaldehyde was added. The temperature was slowly raised to 25°C, and reacted for 6 h. After that, the material was discharged. The material was washed by sedimentation, and was a magnetic microcapsule.

[0095] The magnetic microcapsule and the water-based polyurethane coating glue were weighed according to a mass ratio of 5:1, were stirred and mixed uniformly, and were coated on a transparent PET film to form a film. The wet film was first dried at 45°C for 10 minutes, and then was dried at 80°C for 10 minutes. Thus, a magnetic microcapsule handwriting film was obtained.

[0096] The magnetic microcapsule handwriting film of Example 5 was baked in a high temperature of 50°C for one month. The handwriting film could still be normally written and erased.

[0097] The magnetic microcapsule handwriting film of Example 5 was baked in a high temperature of 90°C for two weeks. The handwriting film could still be normally written and erased.

[0098] In the description of the present specification, the description of the terms "one embodiment / way", "some embodiments / ways", "example", "specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment / way or example are included in at least one embodiment / way or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment / way or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments / ways or examples. In addition, the person skilled in the art can combine and combine the different embodiments / ways or examples described in the present specification and the features of the different embodiments / ways or examples without contradiction.

[0099] It has to be noted that, in the present application, terms like "first", "second", and the like in the description and in the claims are used to distinguish between similar elements and not necessarily to describe a sequential or chronological order. Furthermore, the terms "comprises", "comprising", or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can also include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by "comprises... a" does not, without more constraints, exclude the presence of additional identical elements in the process, method, article, or apparatus that comprises the element. The term "plurality" denotes two or more, for example two, three or four unless expressly specified otherwise.

[0100] The foregoing is considered as illustrative only of the principles of the application. Numerous modifications and changes will readily occur to those skilled in the art, and the generic principles defined herein can be applied to other embodiments without departing from the spirit or scope of the application. Accordingly, the scope of the application is indicated by the appended claims rather than by the foregoing description, and all changes that come within the meaning and range of equivalents are intended to be embraced therein.

Claims

1. A method for producing magnetic microcapsules, characterized by, The method comprises the following steps: S1, mixing non-magnetic nanoparticles, magnetic nanoparticles, solvent, dispersant and thixotropic agent, uniformly dispersing to obtain core material; S2, heating gelatin, polyanionic compound and emulsifier to dissolve in water, mixing uniformly to obtain water phase; S3, adding core material into water phase, emulsifying, adding acid solution to adjust pH value to 3.9-4.3; cooling to 5-10℃, adding carbodiimide or polycarbodiimide aqueous dispersion, then adding aldehyde curing agent, warming to 25-30℃, discharging after reaction; settling and washing to obtain magnetic microcapsule.

2. The method for preparing magnetic microcapsules according to claim 1, characterized by, The non-magnetic nanoparticles are selected from any one of titanium dioxide, lithopone, zinc oxide, zinc white and zinc sulfide, and the particle size of the non-magnetic nanoparticles is 0.1-0.5μm.

3. The method of producing magnetic microcapsules according to claim 1, characterized by, The magnetic nanoparticles are selected from any one or mixture of multiple of black iron oxide, porous iron oxide, iron oxide containing manganese dioxide, chromium dioxide, iron oxyhydroxide, iron or nickel microparticles, and the particle size of the magnetic nanoparticles is 0.1-1μm.

4. The method of producing magnetic microcapsules according to claim 1, characterized by, The solvent is any one or mixture of multiple of 3# white oil, 5# white oil, 10# white oil, isomeric alkanes with different carbon chain length and silicone oil; the dispersant is any one or mixture of multiple of polyethylene oxide lauryl ether, polyethylene oxide hexadecyl ether, polyethylene oxide stearyl ether, polyethylene oxide oleyl ether, polycarboxylic acid amine salt, sorbitan trioleate, sorbitan monolaurate and sorbitan monostearate.

5. The method of producing magnetic microcapsules according to claim 1, wherein The thixotropic agent is any one or mixture of multiple of silicate, alumina powder, silica powder, diatomite, kaolin, bentonite, ultra-fine calcium carbonate, ultra-fine active calcium carbonate, calcium bicarbonate and barium sulfate.

6. The method of producing magnetic microcapsules according to claim 1, wherein In step S2, the heating temperature is 45-50℃.

7. The method of producing magnetic microcapsules according to claim 1, wherein The mass percentage of each raw material in the core material is: non-magnetic nanoparticles 25-35%, magnetic nanoparticles 1.5-3%, solvent 60-70%, dispersant 2-4% and thixotropic agent 0.2-0.5%.

8. The method of producing magnetic microcapsules according to claim 1, wherein The polyanionic compound is selected from any one of gum arabic, sodium carboxymethylcellulose, sodium polyacrylate, sodium polystyrene maleate and sodium polyvinyl maleate; the emulsifier is selected from any one of sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, sodium perfluoroocteneoxybenzenesulfonate and sodium diisooctyl sulfosuccinate; the acid solution is selected from any one of hydrochloric acid, acetic acid and citric acid; and the aldehyde curing agent is selected from formaldehyde or glutaraldehyde.

9. A magnetic microcapsule, characterized by, The method is prepared by any one of claims 1-8.

10. A magnetic display handwriting tablet, characterized by The magnetic microcapsule is prepared by any one of claims 1-8 or the magnetic microcapsule of claim 9.

Images