Preparation method of micron-sized polymer conductive microspheres

Abstract

The invention relates to the technical field of polymer conductive microspheres, in particular to a preparation method of micron-sized polymer conductive microspheres, which comprises the following steps: (1) adding a polyol monomer into a flask, removing water at 120-160 DEG C, cooling to 70-90 DEG C, adding an isocyanate monomer into the flask, uniformly mixing, reacting for 4-8 hours, filtering, washing, and drying to obtain a polyurethane prepolymer; a polyurethane prepolymer is obtained; (2) dispersing the polyurethane prepolymer prepared in the step (1) in a solvent, adding a dispersing agent, adding a thiol monomer at room temperature, uniformly stirring, and reacting for 4-8 hours to obtain a dispersed solution; dropwise adding the chain extender dispersion liquid into the dispersion solution, continuously reacting for 4-8 hours to obtain a polyurea solution, and carrying out suction filtration, washing and drying to obtain polyurea microspheres; and (3) carrying out pretreatment, chemical nickel plating, suction filtration, washing and drying on the prepared polyurea microspheres to obtain the nickel-plated polyurea microspheres. The prepared conductive polyurea nickel-plated microspheres are spherical, high in strength, continuous and uniform in plating layer, good in storage stability and excellent in conductivity.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer conductive microspheres, and particularly to a preparation method of micron-sized polymer conductive microspheres. Background Technique

[0002] Electronic products are widely used, such as in folding screens, circuit tape fixing, outer layer fixing, etc. There is a need for a conductive adhesive with excellent electrical conductivity, adhesive stability, high temperature resistance, and electromagnetic shielding ability. Traditional conductive adhesives are usually composed of a matrix resin and conductive fillers. Their preparation process is simple, the operation method is convenient, and they have good electrical conductivity and certain ductility. Conductive fillers such as metal materials like copper powder and nickel powder can be used to prepare conductive adhesives with excellent electrical conductivity due to their excellent electrical conductivity and good corrosion resistance; however, their cost is relatively high, which limits the large-scale use of metal fillers. At the same time, traditional conductive adhesives are affected by the matrix during use, resulting in a deteriorated bonding effect. Moreover, in the preparation of conductive adhesives, a relatively large amount of conductive fillers is used, and the preparation cost is high. Therefore, it is necessary to prepare a conductive polymer filler with ideal electrical conductivity and low cost to replace the conductive adhesive prepared from pure metal conductive fillers, thereby further expanding the application scope of conductive adhesives.

[0003] To solve the above problems, the present invention provides a preparation method of micron-sized polymer conductive microspheres. Summary of the Invention

[0004] The purpose of the present invention is to provide a preparation method of micron-sized polymer conductive microspheres to solve the problems raised in the above background technique.

[0005] To achieve the above purpose, it is realized through the following technical solutions:

[0006] The first aspect of the present invention provides a preparation method of micron-sized polymer conductive microspheres, which is characterized by including the following steps:

[0007] (1) Add a polyol monomer to a flask. After removing water at 120 - 160 °C and then cooling to the range of 70 - 90 °C, add an isocyanate monomer to the flask, mix well, and react for 4 - 8 hours to obtain a polyurethane prepolymer;

[0008] (2) Disperse the polyurethane prepolymer prepared in step (1) in a solvent, add a dispersant, add a thiol monomer at room temperature, stir evenly, and react for 4 - 8 hours to obtain a dispersion solution; gradually add a chain extender dispersion dropwise to the dispersion solution, continue to react for 4 - 8 hours, and then obtain a polyurea solution. Obtain polyurea microspheres through suction filtration, washing, and drying;

[0009] (3) Subject the prepared polyurea microspheres to pretreatment, electroless nickel plating, suction filtration, washing, and drying to obtain polyurea nickel-plated microspheres.

[0010] Preferably, the polyol monomer in step (1) is one or more of polyethylene glycol, polycarbonate diol, 1,4-butanediol, 1,6-hexanediol, polyether diol, and polytetrahydrofuran diol; the isocyanate monomer in step (1) is one or more of diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI), toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), dicyclohexylmethane-4,4'-diisocyanate (HMDI), and polymethylene polyphenyl isocyanate (PAPI); the solvent in step (1) is one or more of acetonitrile, absolute ethanol, 2-butanone, tetrahydrofuran, and N-methylpyrrolidone.

[0011] More preferably, 10 g of acetonitrile is added as a solvent during the reaction in step (1) to reduce the viscosity of the system.

[0012] Preferably, the dispersant in step (2) is one or more of sodium dodecyl sulfate, polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), polyethylene glycol (PEG), and polyethylene wax; the thiol monomer in step (2) is one or more of 1,3-propanedithiol, 1,4-butanedithiol, 1,6-hexanedithiol, ethanedithiol, and trimethylolpropane (3-mercaptopropionate); the chain extender in step (2) is one or more of 1,4-butanediol (BDO), diethylenetriamine (DETA), ethylenediamine (DA), sorbitol, and poly(propylene glycol) bis(2-aminopropyl ether) (PEA230).

[0013] Preferably, the pretreatment in step (3) includes roughening, sensitization, and activation, and activated polyurea microspheres are obtained after the pretreatment.

[0014] The roughening is as follows: hydrogen peroxide and polyurea microspheres are added to 100 ml of a hydrochloric acid solution with a concentration of 5 - 10 g / L at a ratio of 10 - 20 ml:20 g. At room temperature, after magnetic stirring for 0.5 - 1 h, the roughened polyurea microspheres are obtained by suction filtration, washing, and drying.

[0015] The sensitization is as follows: the roughened polyurea microspheres are added to a SnCl2 solution with a concentration of 10 - 20 g / L at a ratio of 20 g:40 - 50 ml, and then continuously stirred in a water bath at 50 - 60 °C for 0.5 - 1 h. Finally, the sensitized polyurea microspheres are obtained by suction filtration, washing, and drying.

[0016] The activation is as follows: The sensitized polyurea microspheres are added to deionized water at a ratio of 20 g: 5 - 30 ml, and hydrochloric acid solution and palladium chloride are added at a ratio of 20 g of sensitized polyurea microspheres: 2 - 10 ml of hydrochloric acid solution with a concentration of 5 - 10 g / L: 0.05 - 0.1 g of palladium chloride. After magnetic stirring for 0.5 - 1 h, filtration, washing, and drying are carried out to obtain the activated polyurea microspheres.

[0017] Preferably, in step (3), electroless nickel plating is as follows: 20 g of the activated polyurea microspheres are slowly added to 50 - 150 ml of a nickel plating solution at 40 - 50 °C. After stirring at a constant temperature for 0.5 - 1 h, the reaction ends, and filtration, washing, and drying are carried out to obtain polyurea nickel-plated microsphere powder; the nickel plating solution includes deionized water, nickel salt, reducing agent, and complexing agent. By mass ratio, activated polyurea microspheres: deionized water: nickel salt: reducing agent: complexing agent = 20: (50 - 150): (15 - 50): (1 - 5): (1 - 5).

[0018] Further preferably, when preparing the nickel plating solution in step (3), a pH regulator is used to maintain the pH value of the solution between 7.8 and 9.2, and a buffer is added to the nickel plating solution at a ratio of 20 g of polyurea microspheres: (3 - 10) g of buffer to ensure the stability of the pH value of the solution.

[0019] Preferably, the nickel salt is one or more of nickel sulfate (NiS04·7H20), nickel chloride (NiCl2·6H20), nickel acetate [Ni(CH3COO)2], nickel sulfamate [Ni(NH2S03)2], and nickel hypophosphite [Ni(H2P02)2]; the reducing agent is one or more of sodium hypophosphite, sodium borohydride, hydrazine, formaldehyde, and alkylamine borane; the complexing agent is one or more of tartaric acid, lactic acid, glycolic acid (hydroxyacetic acid), malic acid, glycine, and citric acid; the buffer is one or more of sodium acetate, borax, ammonia water, sodium succinate, and sodium hydroxide.

[0020] Preferably, in step (1), the molar ratio of the isocyanate monomer to the polyol monomer is (2.5 - 1.2): 1; in step (2), the dosage of the dispersant accounts for 0.5 - 1.5% of the total mass of the polyol monomer and the isocyanate monomer, the molar ratio of the thiol monomer to the isocyanate in the polyurethane prepolymer is NCO: SH = 1: (0.1 - 1.5), and the dosage of the chain extender and the unreacted isocyanate in the dispersion solution are fed in a molar ratio of NH2: NCO = (2.5 - 1.2): 1.

[0021] The second aspect of the present invention provides a conductive microsphere, which is prepared by using the preparation method of the above-mentioned micron-sized polymer conductive microsphere. The diameter of the conductive microsphere is 5 - 50 μmm, and the coating thickness is 0.1 - 3 μm.

[0022] The third aspect of the present invention provides an application of conductive microspheres in the preparation of conductive adhesives.

[0023] The fourth aspect of the present invention provides a conductive adhesive, in which the above-mentioned conductive microspheres are added.

[0024] Beneficial effects:

[0025] 1. The present invention prepares polyurea microspheres by precipitation polymerization method, and through steps such as coarsening, sensitization, activation, electroless nickel plating, suction filtration, washing, and drying, deposits nickel salts on the surface of polymer microspheres to form a coating, thereby preparing polymer conductive microspheres with excellent conductive performance and low cost.

[0026] 2. The prepared polyurea microspheres have uniform particle size, controllable structure, high hardness, high strength, good toughness, and good wear resistance. They can be used as good carriers for electroless plating. Electroless nickel plating is carried out on the polyurea microspheres. Sulfur elements and nickel elements in the polyurea microspheres are prone to chemical bonding, and the nickel plating layer that plays a conductive role has better bonding with the polyurea microspheres.

[0027] 3. The prepared conductive polyurea nickel-plated microspheres are spherical, have high strength, continuous and uniform coatings, good storage stability, and excellent conductive performance.

[0028] 4. As a conductive filler, it has a low addition threshold, reduces the production and use costs, and further broadens the application scope of polymer nickel-plated microspheres. Description of the drawings

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on the structures shown in these drawings.

[0030] Figure 1 It is the synthesis process route of polyurea nickel-plated microspheres

[0031] Figure 2 It is the SEM morphology diagram of the polyurea microspheres prepared in Example 1

[0032] Figure 3 It is the SEM morphology diagram of the polyurea nickel-plated microspheres prepared in Example 1

[0033] Figure 4 It is the SEM morphology diagram of the polyurea nickel-plated microspheres prepared in Comparative Example 1 Specific embodiments

[0034] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0035] The raw materials used in the following examples and comparative examples are shown in the following table:

[0036]

[0037]

[0038] Example 1

[0039] (1) Preparation of polyurethane prepolymer

[0040] Weigh 30 g (0.06 mol) of polycarbonate diol (PCDL) and 0.9 g (0.02 mol) of 1,4-butanediol (BDO) into a flask, remove water at 140 - 145 °C for 8 - 10 min. After the temperature drops to 80 - 85 °C, add 25 g (0.2 mol) of diphenylmethane diisocyanate (MDI). React at a rotation speed of 200 r / min for 6 h to obtain a polyurethane prepolymer. During the reaction, add 10 g of acetonitrile as a solvent to reduce the viscosity of the system.

[0041] (2) Preparation of polyurea microspheres

[0042] Disperse the above-prepared polyurethane prepolymer in 270.19 g of acetonitrile solution, and add 0.559 g of polyvinylpyrrolidone (PVP) (1% of the mass of the reaction monomer) as a dispersant for the reaction system. At 25 °C, slowly dropwise add 13.29 g (0.1 mol) of trimethylolpropane (3-mercaptopropionate) (TMMP), set the rotation speed to 350 r / min and stir evenly. React for 6 h to obtain a dispersion solution; Disperse 1.548 g of the excessive chain extender diethylenetriamine (DETA) into 5 g of acetonitrile solution, and gradually add it dropwise to the dispersion solution. After continuing to react for 6 h, the reaction is completed to obtain a polyurea solution. Through suction filtration, ethanol washing, and drying, 62.25 g of polyurea microsphere powder is obtained, and the particle size of the polyurea microspheres is 10.1 ± 3.3 μm. The yield is about 88%.

[0043] (3) Preparation of nickel-plated polyurea microspheres

[0044] First, pretreat the polyurea microsphere powder by roughening, sensitizing, and activating, then perform electroless nickel plating, and then prepare nickel-plated polyurea microspheres through steps such as suction filtration, washing, and drying.

[0045] Measure 100 ml of hydrochloric acid solution with a concentration of 8 g / L, add 15 ml of hydrogen peroxide and 20 g of polyurea microsphere powder. At room temperature, after magnetic stirring for 45 min, the roughened polyurea microspheres are obtained through suction filtration, washing with water, and drying.

[0046] Add the roughened polyurea microspheres to 50 ml of SnCl2 solution with a concentration of 15 g / L to sensitize the microspheres so that a layer of stannous ions is adsorbed on the surface of the microspheres; then continuously stir in a water bath at 55 - 60 °C for 45 min, and finally obtain the sensitized polyurea microspheres after suction filtration, washing with water, and drying.

[0047] Add the sensitized polyurea microsphere powder to 20 ml of deionized water, add 5 ml of hydrochloric acid solution with a concentration of 8 g / L and 0.05 g of palladium chloride. After magnetic stirring for 45 min, perform suction filtration, washing with water, and drying to obtain the activated polyurea microspheres.

[0048] Weigh 20 g of nickel sulfate, 3 g of sodium hypophosphite, and 2 g of tartaric acid, add them to a beaker containing 100 g of deionized water, and stir evenly to obtain a nickel plating solution. During this period, use a pH regulator to maintain the pH value of the solution between 7.8 - 9.2, and add 5 g of sodium acetate as a buffer to ensure the stability of the pH value of the solution. Heat the nickel plating solution to 50 °C, slowly add the activated polyurea microsphere powder, use magnetic stirring for 45 min, end the reaction, perform suction filtration, washing, and drying to obtain the polyurea nickel-plated microsphere powder with a uniform coating. The measured particle size of the nickel-plated microspheres is 10.6 ± 4.9 μm.

[0049] Example 2

[0050] (1) Preparation of polyurethane prepolymer

[0051] Weigh 40 g (0.04 mol) of polyethylene glycol (PEG - 2000) and 3.37 g (0.075 mol) of 1,4 - butanediol (BDO) in a flask, remove water at 140 - 145 °C for 8 - 10 min, lower the temperature to 80 - 85 °C, add 25 g (0.287 mol) of toluene diisocyanate (TDI), and react at a rotation speed of 200 r / min for 6 h to obtain a polyurethane prepolymer. During the reaction, add 10 g of acetonitrile as a solvent to reduce the viscosity of the system.

[0052] (2) Preparation of polyurea microspheres

[0053] The polyurethane prepolymer prepared above was dispersed in 308.50 g of acetonitrile solution, and 0.684 g of polyvinylpyrrolidone (PVP) (1% of the mass of the reaction monomer) was added as a dispersant for the reaction system. At 25 °C, 8.63 g (0.115 mol) of 1,6 - hexanedithiol (DMH) was slowly added dropwise, and the rotation speed was set at 350 r / min and stirred evenly for 6 h to obtain a dispersion solution; 4.44 g of the excessive chain extender diethylenetriamine (DETA) was dispersed in 10 g of acetonitrile solution, and it was added dropwise to the dispersion solution. After reacting for another 6 h, the reaction was completed to obtain a polyurea solution. 70.5 g of polyurea microsphere powder was obtained by suction filtration, washing with ethanol, and drying, and the particle size of the polyurea microspheres was 12.3 ± 4.5 μm. The yield was about 86.6%.

[0054] (3) Preparation of nickel - plated polyurea microspheres

[0055] First, the polyurea microsphere powder was pretreated by roughening, sensitization, and activation, then electroless nickel plating was carried out, and finally nickel - plated polyurea microspheres were prepared through steps such as suction filtration, washing, and drying.

[0056] 100 ml of hydrochloric acid solution with a concentration of 8 g / L was measured, 15 ml of hydrogen peroxide and 20 g of polyurea microsphere powder were added. At room temperature, after magnetic stirring for 45 min, the roughened polyurea microspheres were obtained through suction filtration, washing with water, and drying.

[0057] The roughened polyurea microspheres were added to 50 ml of SnCl2 solution with a concentration of 15 g / L to sensitize the microspheres so that a layer of stannous ions was adsorbed on the surface of the microspheres. Then, it was continuously stirred in a water bath at 55 - 60 °C for 45 min, and finally, the sensitized polyurea microspheres were obtained through suction filtration, washing with water, and drying.

[0058] The sensitized polyurea microsphere powder was added to 20 ml of deionized water, 5 ml of hydrochloric acid solution with a concentration of 8 g / L and 0.05 g of palladium chloride were added. After magnetic stirring for 45 min, suction filtration, washing with water, and drying were carried out to obtain the activated polyurea microspheres.

[0059] 20 g of nickel sulfate, 3 g of sodium hypophosphite, and 2 g of tartaric acid were weighed and added to a beaker containing 100 g of deionized water, and stirred evenly to obtain a nickel - plating solution. During this period, the pH value of the solution was maintained between 7.8 - 9.2 through a pH regulator, and 5 g of sodium acetate was added as a buffer to ensure the stability of the pH value of the solution. The nickel - plating solution was heated to 50 °C, and the activated polyurea microsphere powder was slowly added. After magnetic stirring for 45 min, the reaction ended. Suction filtration, washing, and drying were carried out to obtain nickel - plated polyurea microsphere powder with a uniform coating. The particle size of the nickel - plated microspheres was measured to be 13.2 ± 3.9 μm.

[0060] Comparative Example 1

[0061] (1) Preparation of polyurethane prepolymer

[0062] Weigh 40 g (0.08 mol) of polyether polyol N210 and 2.30 g (0.03 mol) of 1,6 - hexanediol (HDO) into a flask, remove water at 140 - 145 °C for 8 - 10 min. When the temperature drops to 80 - 85 °C, add 25 g (0.30 mol) of hexamethylene diisocyanate (HDI). React at a rotation speed of 200 r / min for 6 h to obtain a polyurethane prepolymer. During the reaction, add 10 g of acetonitrile as a solvent to reduce the viscosity of the system.

[0063] (2) Preparation of polyurea microspheres

[0064] Disperse the above - prepared polyurethane prepolymer in 336.69 g of acetonitrile solution, and add 0.673 g of polyvinylpyrrolidone (PVP) (1% of the mass of the reaction monomer) as a dispersant for the reaction system. At 25 °C, then disperse 23.7 g (0.178 mol) of the excessive chain extender poly(propylene glycol) bis(2 - aminopropyl ether) (PEA230) into 20 g of acetonitrile solution, and add it dropwise to the dispersion solution. Set the rotation speed to 350 r / min and stir evenly. After continuing the reaction for 6 h, the reaction is completed to obtain a polyurea solution. Through suction filtration, ethanol washing, and drying, 77.53 g of polyurea microsphere powder is obtained, and the particle size of the polyurea microspheres is 5.3 ± 1.6 μm. The yield is about 85.2%.

[0065] (3) Preparation of nickel - plated polyurea microspheres

[0066] The preparation of nickel - plated polyurea microspheres is the same as that in Example 1. The measured particle size of the nickel - plated microspheres is 25.4 ± 1.8 μm.

[0067] Comparative Example 2

[0068] (1) Preparation of polyurethane prepolymer

[0069] Same as Example 1.

[0070] (2) Preparation of polyurea microspheres

[0071] Same as Example 1.

[0072] (3) Preparation of nickel - plated polyurea microspheres

[0073] Weigh 20 g of nickel sulfate, 3 g of sodium hypophosphite, and 2 g of tartaric acid, and add them to a beaker containing 100 g of deionized water. Stir evenly to obtain a nickel plating solution. During this period, use a pH regulator to maintain the pH value of the solution between 7.8 and 9.2, and add 5 g of sodium acetate as a buffer to ensure the stability of the pH value of the solution. Heat the nickel plating solution to 50 °C, slowly add 20 g of the polyurea microsphere powder prepared in step (2), stir magnetically for 45 min, then end the reaction, filter, wash, and dry to obtain polyurea nickel-plated microsphere powder. The measured particle size of the nickel-plated microspheres is 12.8 ± 5.6 μm.

[0074] Comparative Example 3

[0075] (1) Preparation of polyurethane prepolymer

[0076] Weigh 50 g (0.1 mol) of polycarbonate diol (PCDL) and 2.25 g (0.05 mol) of 1,4-butanediol (BDO) into a flask, remove water within the range of 140 - 145 °C for 8 - 10 min. When the temperature drops to the range of 80 - 85 °C, add 25 g (0.2 mol) of diphenylmethane diisocyanate (MDI). React at a rotation speed of 200 r / min for 6 h to obtain a polyurethane prepolymer. During the reaction, add 10 g of acetonitrile as a solvent to reduce the viscosity of the system.

[0077] (2) Preparation of polyurea microspheres

[0078] Disperse the above-prepared polyurethane prepolymer in 322.57 g of acetonitrile solution, and add 0.773 g of polyvinylpyrrolidone (PVP) (1% of the mass of the reaction monomer) as a dispersant for the reaction system. At 25 °C, disperse 3.87 g of the excessive chain extender diethylenetriamine (DETA) into 5 g of acetonitrile solution, and add it dropwise to the dispersion solution. Set the rotation speed to 350 r / min, continue to react for 6 h, and after the reaction is completed, obtain a polyurea solution. Through suction filtration, ethanol washing, and drying, 72.07 g of polyurea microsphere powder is obtained, and the particle size of the polyurea microspheres is 23.2 ± 1.2 μm. The yield is approximately 88.8%.

[0079] (3) Preparation of polyurea nickel-plated microspheres

[0080] Weigh 20g of nickel sulfate, 3g of sodium hypophosphite and 2g of tartaric acid, add to a beaker containing 100g of deionized water, and stir evenly to obtain a nickel plating solution. During this period, the pH value of the solution is maintained between 7.8 and 9.2 by a pH regulator, and 5g of sodium acetate is added as a buffer to ensure that the pH value of the solution tends to be stable. Heat the nickel plating solution to 50°C, slowly add 20g of the polyurea microsphere powder prepared in step (2), use magnetic stirring for 45 minutes, the reaction is terminated, and the polyurea nickel-plated microsphere powder is filtered, washed, and dried to obtain the polyurea nickel-plated microsphere powder. The particle size of the nickel-plated microspheres was measured to be 23.8±0.4μm.

[0081] The conductive microspheres obtained in Examples 1 to 2 and Comparative Examples 1 to 3 were tested for conductivity as follows:

[0082] Use FT-300 series conductor powder resistivity tester. Take an appropriate amount of nickel-plated microsphere powder, add it into a mold with an inner diameter of 16mm and a height of 15mm, set the test current to 200mA, use the pressure to 2MPa±0.02MPa, and measure the volume resistance of polyurea nickel-plated microsphere powder.

[0083] Table 1 shows the conductivity data of polyurea nickel-plated microspheres prepared in Examples 1 to 2 and Comparative Examples 1 to 3:

[0084] Table 1

[0085]

[0086] From Table 1 and Appendix Figure 2 ~~~4 We can know that:

[0087] In Example 1-2, the polyurea nickel-plated microsphere powder prepared by the technical solution of the present invention has a resistance lower than 10 mΩ, and the coating is uniform and continuous. Figure 2 This is the SEM morphology of the polyurea microspheres prepared in Example 1. Figure 3 This is the SEM morphology of the polyurea nickel-plated microspheres prepared in Example 1.

[0088] Comparative Example 1 does not add mercaptan monomer, and when the polyurea microspheres are combined with the nickel layer, there is no sulfur-nickel chemical bond and effect. Figure 4 This is a SEM morphology of the conductive microspheres prepared in Comparative Example 1. The nickel element in the system aggregates into particles, which leads to uneven coating on the surface of the polyurea microspheres, so the conductive performance is weak.

[0089] In Comparative Example 2, the polyurea microspheres were not pre-treated, and no active functional groups were formed on the surface of the polyurea microspheres. The nickel layer formed on the surface of the polyurea microspheres by chemical plating was discontinuous and uneven, and thus the conductive performance was poor.

[0090] In Comparative Example 3, no thiol monomer was added, and the prepared polyurea microspheres were spherical in shape with irregular morphology. Moreover, no pretreatment was carried out on the polyurea microspheres, and the prepared nickel-plated polyurea microspheres by electroless plating had wrinkled and uneven coatings, resulting in discontinuous conductive paths between the nickel-plated metal microspheres, thus leading to poor electrical conductivity.

[0091] The above are only alternative embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structural or equivalent process transformation made by using the content of the specification and drawings of the present invention under the inventive concept of the present invention, or directly or indirectly applied to other related technical fields, shall be equally included in the patent protection scope of the present invention.

Claims

1. A preparation method of micron-sized polymer conductive microspheres, characterized in that, It includes the following steps: (1) Add polyol monomers into a flask. After removing water at 120 - 160 °C, cool down the temperature to the range of 70 - 90 °C, then add isocyanate monomers into the flask, mix well, and react for 4 - 8 h to obtain a polyurethane prepolymer; (2) Disperse the polyurethane prepolymer prepared in step (1) in a solvent, add a dispersant, add thiol monomers at room temperature, stir evenly, and react for 4 - 8 h to obtain a dispersion solution; dropwise add an extender dispersion liquid into the dispersion solution, continue to react for 4 - 8 h, then obtain a polyurea solution, and obtain polyurea microspheres through suction filtration, washing, and drying; (3) Pretreat, electroless nickel plate the prepared polyurea microspheres, and obtain nickel-plated polyurea microspheres through suction filtration, washing, and drying.

2. The preparation method of a micron-sized polymer conductive microsphere according to claim 1, characterized in that, In step (1), the polyol monomers are one or more of polyethylene glycol, polycarbonate diol, 1,4-butanediol, 1,6-hexanediol, polyether diol, and polytetrahydrofuran diol; in step (1), the isocyanate monomers are one or more of diphenylmethane diisocyanate, hexamethylene diisocyanate, toluene diisocyanate, isophorone diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, and polymethylene polyphenyl isocyanate; in step (1), the solvents are one or more of acetonitrile, absolute ethanol, 2-butanone, tetrahydrofuran, and N-methylpyrrolidone.

3. The preparation method of a micron-sized polymer conductive microsphere according to claim 1, characterized in that, In step (2), the dispersants are one or more of sodium dodecyl sulfate, polyvinylpyrrolidone, polyvinyl alcohol, polyethylene glycol, and polyethylene wax; in step (2), the thiol monomers are one or more of 1,3-propanedithiol, 1,4-butanedithiol, 1,6-hexanedithiol, ethanedithiol, and trimethylolpropane (3-mercaptopropionate); in step (2), the extenders are one or more of 1,4-butanediol, diethylenetriamine, ethylenediamine, sorbitol, and poly(propylene glycol) bis(2-aminopropyl ether).

4. The preparation method of a micron-sized polymer conductive microsphere according to claim 1, wherein, In step (3), the pretreatment includes roughening, sensitization, and activation; The roughening is as follows: Add hydrogen peroxide and polyurea microspheres in a ratio of 10 - 20 ml:20 g into 100 ml of a hydrochloric acid solution with a concentration of 5 - 10 g / L. At room temperature, stir magnetically for 0.5 - 1 h, then obtain roughened polyurea microspheres through suction filtration, washing, and drying; The sensitization is as follows: Add the roughened polyurea microspheres in a ratio of 20 g:40 - 50 ml into a SnCl2 solution with a concentration of 10 - 20 g / L, then continuously stir in a water bath at 50 - 60 °C for 0.5 - 1 h, and finally obtain sensitized polyurea microspheres through suction filtration, washing, and drying; The activation is as follows: Add the sensitized polyurea microspheres in a ratio of 20 g:5 - 30 ml into deionized water, add hydrochloric acid solution and palladium chloride in a ratio of 20 g of sensitized polyurea microspheres:2 - 10 ml of hydrochloric acid solution with a concentration of 5 - 10 g / L:0.05 - 0.1 g of palladium chloride, stir magnetically for 0.5 - 1 h, then suction filter, wash, and dry to obtain activated polyurea microspheres.

5. The preparation method of a micron-sized polymer conductive microsphere according to claim 1 or 4, characterized in that, In step (3), electroless nickel plating is carried out as follows: 20 g of activated polyurea microspheres are slowly added to 50 - 150 ml of nickel plating solution at 40 - 50 °C. After stirring at a constant temperature for 0.5 - 1 h, the reaction ends. Then, filtration, washing, and drying are carried out to obtain polyurea nickel-plated microsphere powder; The nickel plating solution includes deionized water, nickel salt, reducing agent, and complexing agent. By mass ratio, activated polyurea microspheres: deionized water: nickel salt: reducing agent: complexing agent = 20:(50 - 150):(15 - 50):(1 - 5):(1 - 5).

6. The preparation method of a micron-sized polymer conductive microsphere according to claim 5, characterized in that, The nickel salt is one or more of nickel sulfate, nickel chloride, nickel acetate, nickel sulfamate, and nickel hypophosphite; the reducing agent is one or more of sodium hypophosphite, sodium borohydride, hydrazine, formaldehyde, and alkylamine borane; the complexing agent is one or more of tartaric acid, lactic acid, glycolic acid, malic acid, glycine, and citric acid; the buffer is one or more of sodium acetate, borax, ammonia water, sodium succinate, and sodium hydroxide.

7. The preparation method of a micron-sized polymer conductive microsphere according to claim 1, characterized in that, In step (1), the molar ratio of the isocyanate monomer to the polyol monomer is (2.5 - 1.2):1; in step (2), the dosage of the dispersant accounts for 0.5 - 1.5% of the sum of the masses of the polyol monomer and the isocyanate monomer, the molar ratio of the thiol monomer to the isocyanate in the polyurethane prepolymer is NCO:SH = 1:(0.1 - 1.5), and the dosage of the chain extender and the unreacted isocyanate in the dispersion solution are fed in according to the molar ratio NH2:NCO = (2.5 - 1.2):

1.

8. A conductive microsphere is prepared by using the preparation method of a micron-sized polymer conductive microsphere according to any one of claims 1 - 7. The diameter of the conductive microsphere is 5 - 50 μm, and the coating thickness is 0.1 - 3 μm.

9. Use of a conductive microsphere according to claim 8 in the preparation of a conductive adhesive.

10. A conductive adhesive, characterized in that, The conductive microsphere according to claim 8 is added to the conductive adhesive.

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