Preparation process of spherical wax micro-powder particles coated with nano silicon dioxide

Abstract

The invention relates to the technical field of nano materials, and particularly discloses a preparation process of nano silicon dioxide coated spherical wax micro powder particles. The preparation process comprises the following steps: weighing raw materials; the preparation method comprises the following steps: blending deionized water, absolute ethyl alcohol and ethidene diamine according to a ratio, adding an organic silicon source under normal temperature and stirring, and uniformly stirring to obtain silica sol; wetting the spherical wax micro-powder particles with hydrogen peroxide, adding vinyltriethylsilane and butyltin dilaurate, uniformly stirring, heating to a temperature below the melting point and above the glass transition temperature of the spherical wax micro-powder particles, and then cooling to normal temperature to obtain pretreated wax micro-powder particles; and adding the pretreated wax micro powder particles into silica sol under stirring, uniformly dispersing, grinding to obtain a thick slurry-shaped dispersion, carrying out solid-liquid separation, and drying to obtain the spherical wax micro powder particles coated with nano silicon dioxide. According to the method, the stability of the coating layer of the spherical wax micro powder particles coated with the nano silicon dioxide can be improved.

Description

Technical Field

[0001] The invention relates to the technical field of nanomaterials, in particular to a preparation process of spherical wax micropowder particles coated with nano-silicon dioxide. Background Art

[0002] Polyethylene wax, a low-molecular-weight polyethylene material, exhibits excellent lubricity, wear resistance, thermal stability, and chemical inertness, making it widely used in coatings, inks, plastics processing, and 3D printing consumables. However, conventional polyethylene wax powders suffer from irregular particle shape, wide particle size distribution, low surface polarity, and poor compatibility with polar substrates, limiting their application in high-end applications. To improve their performance, researchers have proposed imparting functional properties through surface modification or composite coating techniques.

[0003] Nanosilica, with its high specific surface area, strong adsorption properties, high temperature resistance, and surface modifiability, is often used to modify organic-inorganic composite materials. Related technologies have reported the composite of silica with polyethylene wax through methods such as physical mixing, melt blending, or emulsion polymerization.

[0004] However, physical mixing or melt blending easily leads to silica agglomeration, which makes it impossible to form a continuous and uniform coating layer. The polyethylene wax particles prepared by traditional pulverization methods are mostly in the form of flakes or blocks with poor fluidity, while the preparation process of spherical particles is complicated and it is difficult to achieve nano-coating simultaneously. If such nano-silica-coated spherical wax micropowder particles that do not form a continuous and uniform coating layer are used in coatings or inks, it will affect the stability of the wear resistance of the coating or ink; if used in phase change materials, the coated spherical wax micropowder particles will leak after heating and cooling, resulting in a decrease in phase change heat. Therefore, it is urgent to develop a method for preparing nano-silica-coated spherical wax micropowder particles that can be produced on a large scale to improve the coating stability of the nano-silica-coated spherical wax micropowder particles. Summary of the Invention

[0005] In order to improve the coating stability of nano-silica-coated spherical wax micropowder particles, the present application provides a preparation process of nano-silica-coated spherical wax micropowder particles.

[0006] The present application provides a preparation process for spherical wax micropowder particles coated with nano-silica, which adopts the following technical solution:

[0007] A process for preparing spherical wax micropowder particles coated with nano-silicon dioxide comprises the following steps:

[0008] S1. Weigh the following raw materials in parts by weight: 3-6 parts of deionized water, 2-4 parts of anhydrous ethanol, 0.1-0.3 parts of ethylenediamine, 0.7-1.0 parts of an organic silicon source, and 2-4 parts of spherical wax micropowder particles;

[0009] S2. Deionized water, anhydrous ethanol, and ethylenediamine are mixed according to a certain ratio, and an organic silicon source is added under stirring at room temperature, and the mixture is stirred evenly to obtain a silica sol;

[0010] S3. Wetting the spherical wax micropowder particles with hydrogen peroxide, adding vinyl triethyl silane and butyl tin dilaurate, stirring evenly, heating to a temperature below the melting point and above the glass transition temperature of the spherical wax micropowder particles, and then cooling to room temperature to obtain pretreated wax micropowder particles; the amount of vinyl triethyl silane is 0.2-0.4% by weight of the spherical wax micropowder particles, and the amount of butyl tin dilaurate is 0.05-0.15% by weight of the spherical wax micropowder particles;

[0011] S4. Add the pretreated wax micropowder particles to the silica sol under stirring, disperse them evenly, and grind them at a grinding temperature of ≤70°C and a grinding time of ≥2 hours to obtain a thick slurry dispersion, separate the solid and liquid, and dry them to obtain spherical wax micropowder particles coated with nano-silica.

[0012] By adopting the above technical solution, in step S2, the organosilicon source is hydrolyzed in a deionized water / ethanol mixture. Ethylenediamine catalyzes the hydrolysis and regulates the pH, while also controlling the sol particle size and dispersibility. This produces a light blue silica sol. In step S3, hydrogen peroxide wets the spherical wax micropowder particles, introducing polar groups on the wax surface through oxidation, enhancing the bond with the silane. After hydrolysis, vinyltriethylsilane reacts with the hydroxyl groups on the wax surface to form chemical bonds. Butyltin dilaurate accelerates the hydrolysis and condensation of the silane, ensuring uniform grafting of the silane onto the wax surface in the subsequent step S4. Heating to a temperature below the melting point of the wax and above its glass transition temperature promotes the silane reaction while preventing melting and deformation of the wax particles, maintaining their spherical morphology. In step S4, the silica sol and the vinyl groups of the silane on the wax surface undergo hydrolysis and condensation to form a cross-linked network, thereby chemically grafting a silica coating onto the surface of the spherical wax micropowder particles. A temperature of ≤70°C prevents particle melting, and a grinding time of ≥2 hours ensures uniform coating and prevents the formation of oversized particles. Therefore, the present invention can produce bright, nano-silica-coated, loose, core-shell wax micropowder spherical particles with excellent coating stability, wear resistance, and phase change thermal stability, and can be used in coatings, inks, and phase change materials.

[0013] In a specific embodiment, when the nano-silica-coated spherical wax micropowder particles are applied to coatings or inks, the particle size of the spherical wax micropowder particles is 1-25 μm.

[0014] By adopting the above technical solution, high particle size requirements are met for wax micropowders used in coatings and inks. Spherical wax micropowder particles with a particle size of 1-25μm are selected as the raw material. Due to their small particle size, crosslinking between wax molecules or between wax and silane can occur, which further enhances wear resistance and temperature resistance, improves dispersibility and allows for higher operating temperatures, providing friction and stain resistance. Furthermore, because silica and wax transmit and reflect light at different angles, the coating's gloss is enhanced, and the color changes from different angles, creating a magical color effect. When used in water-based coatings, a concentrated slurry dispersion can be used directly, making it easier to achieve uniform dispersion. Furthermore, this product does not contain surfactants, so its application does not require consideration of surfactant effects.

[0015] In a specific embodiment, when the nano-silica-coated spherical wax micropowder particles are used in phase change materials, the particle size of the spherical wax micropowder particles is 30-300 μm.

[0016] By adopting the above technical solution, the surface of the silica-coated wax spherical microparticles of the present application not only has silica as a shell, but also cross-linking caused by silane hydrolysis, this cross-linking is the cross-linking of the wax itself, and this cross-linking will not melt when heated, so that the wax melt of the spherical wax powder particles melts, because the volume expansion causes the volume expansion of the core-shell material, and the shell will not be broken due to inconsistent coefficients, which can prevent the wax melt from flowing out. Silicon dioxide acts as a shell to increase thermal conductivity and has dielectric properties. When nano-silica-coated spherical wax powder particles are applied to phase change materials, silicon dioxide can improve the thermal conductivity of wax, and spherical wax powder particles with a particle size of 30-300 μm can obtain maximum volume density, so whether it is through 3D printing or casting, a more dense shape can be obtained, and its thermal conductivity is improved.

[0017] In summary, this application has the following beneficial effects:

[0018] 1. The present invention can produce loose wax micropowder spherical particles with bright surface, nano-silica coating, core-shell structure, good coating stability, wear resistance and phase change thermal stability, and can be used in the fields of coatings, inks and phase change materials.

[0019] 2. The nano-silica-coated spherical wax micropowder particles of the present application can be applied to coatings, inks or phase change materials. DETAILED DESCRIPTION

[0020] The present application is further described in detail below with reference to the following examples and comparative examples.

[0021] Example

[0022] Example 1

[0023] This embodiment provides a process for preparing spherical wax micropowder particles coated with nano-silicon dioxide, comprising the following steps:

[0024] S1. Weigh the following raw materials: 4 kg of deionized water, 3 kg of anhydrous ethanol, 0.2 kg of ethylenediamine, 0.9 kg of ethyl orthosilicate, and 3 kg of spherical polyethylene wax micropowder particles with a particle size of 1-25 μm.

[0025] S2. Deionized water, anhydrous ethanol, and ethylenediamine are mixed according to the ratio, and ethyl orthosilicate is slowly added dropwise under the condition of keeping the mixture at room temperature and stirring. After the addition is completed, the mixture is stirred evenly to obtain a light blue silica sol.

[0026] S3. Evenly spray hydrogen peroxide onto the surface of the spherical polyethylene wax micropowder particles to wet them. Then, add vinyl triethyl silane and butyl tin dilaurate, stir evenly, heat to a temperature below the melting point and above the glass transition temperature of the spherical wax micropowder particles, and then cool to room temperature to obtain pretreated wax micropowder particles. The mass ratio of hydrogen peroxide to spherical polyethylene wax micropowder is 1:20, the amount of vinyl triethyl silane is 0.3% of the weight of the spherical wax micropowder particles, and the amount of butyl tin dilaurate is 0.1% of the weight of the spherical wax micropowder particles.

[0027] S4. While stirring, add the pretreated wax micropowder particles to the silica sol, stir until uniform, and then transfer to a stirred grinder for grinding at a grinding temperature of ≤70°C and a grinding time of ≥2 hours. In this embodiment, the grinding temperature is 70°C and the grinding time is 2 hours. After grinding, a thick slurry dispersion is obtained. The dispersion is then centrifuged to remove the liquid and the solid is dried to obtain nanosilica-coated spherical wax micropowder particles.

[0028] Example 2

[0029] The only difference between this embodiment and embodiment 1 is that, in step S1, the following raw materials are weighed: 3 kg of deionized water, 4 kg of anhydrous ethanol, 0.1 kg of ethylenediamine, 0.7 kg of ethyl orthosilicate, and 2 kg of spherical polyethylene wax micropowder particles.

[0030] Example 3

[0031] The only difference between this embodiment and embodiment 1 is that, in step S1, the following raw materials are weighed: 6 kg of deionized water, 2 kg of anhydrous ethanol, 0.3 kg of ethylenediamine, 1.0 kg of ethyl orthosilicate, and 4 kg of spherical polyethylene wax micropowder particles.

[0032] Example 4

[0033] The only difference between this embodiment and embodiment 1 is that in step S3, the amount of vinyltriethylsilane used is 0.2% of the weight of the spherical wax powder particles.

[0034] Example 5

[0035] The only difference between this embodiment and embodiment 1 is that in step S3, the amount of vinyltriethylsilane used is 0.4% of the weight of the spherical wax powder particles.

[0036] Example 6

[0037] The only difference between this embodiment and embodiment 1 is that in step S3, the amount of butyltin dilaurate used is 0.05% of the weight of the spherical wax micropowder particles.

[0038] Example 7

[0039] The only difference between this embodiment and embodiment 1 is that in step S3, the amount of butyltin dilaurate used is 0.15% of the weight of the spherical wax powder particles.

[0040] Example 8

[0041] The only difference between this embodiment and embodiment 1 is that, in step S4, the grinding temperature of this embodiment is 60° C. and the grinding time is 2.4 hours.

[0042] Example 9

[0043] The only difference between this embodiment and embodiment 1 is that, in step S4, the grinding temperature of this embodiment is 50° C. and the grinding time is 2.6 hours.

[0044] Example 10

[0045] The only difference between this embodiment and embodiment 1 is that, in step S4, the grinding temperature of this embodiment is 30° C. and the grinding time is 3.2 hours.

[0046] Example 11

[0047] The only difference between this embodiment and embodiment 1 is that the spherical polyethylene wax micropowder particles with a particle size of 1-25 μm are replaced by an equal amount of spherical wax micropowder particles with a particle size of 30-50 μm.

[0048] Example 12

[0049] The only difference between this embodiment and embodiment 1 is that the spherical polyethylene wax micropowder particles with a particle size of 1-25 μm are replaced by an equal amount of spherical wax micropowder particles with a particle size of 30-300 μm.

[0050] Example 13

[0051] The only difference between this embodiment and embodiment 1 is that the spherical polyethylene wax micropowder particles with a particle size of 1-25 μm are replaced by an equal amount of spherical wax micropowder particles with a particle size of 350-450 μm.

[0052] Comparative Example

[0053] Comparative Example 1

[0054] This comparative example differs from Example 1 only in that step S3 is as follows: vinyltriethylsilane and butyltin dilaurate are added to spherical polyethylene wax micropowder particles, stirred uniformly, heated to a temperature below the melting point and above the glass transition temperature of the spherical wax micropowder particles, and then cooled to room temperature to obtain pretreated wax micropowder particles. The amount of vinyltriethylsilane used is 0.3% by weight of the spherical wax micropowder particles, and the amount of butyltin dilaurate used is 0.1% by weight of the spherical wax micropowder particles.

[0055] Comparative Example 2

[0056] The only difference between this comparative example and Example 1 is that in step S3, the amount of vinyltriethylsilane used is 0.1% by weight of the spherical wax micropowder particles.

[0057] Comparative Example 3

[0058] The only difference between this comparative example and Example 1 is that in step S3, the amount of vinyltriethylsilane used is 0.5% of the weight of the spherical wax micropowder particles.

[0059] Comparative Example 4

[0060] This comparative example differs from Example 1 only in that step S3 is as follows: hydrogen peroxide is evenly sprayed onto the surface of the spherical polyethylene wax micropowder particles to wet them. The mixture is then heated to a temperature below the melting point and above the glass transition temperature of the spherical wax micropowder particles, and then cooled to room temperature to obtain pretreated wax micropowder particles. The mass ratio of hydrogen peroxide to spherical polyethylene wax micropowder is 1:20.

[0061] Comparative Example 5

[0062] The only difference between this comparative example and Example 1 is that in step S4, the grinding temperature of this comparative example is 75° C. and the grinding time is 1.5 hours.

[0063] Performance testing

[0064] For Examples 1-13 and Comparative Examples 1-5, the following performance tests were performed:

[0065] Abrasion Resistance Test: The concentrated dispersions prepared in each Example and Comparative Example were mixed with a water-based acrylic paint or ink at a mass ratio of 1:20. The mixture was dispersed at 1000 rpm for 30 minutes. The mixture was then evenly coated onto a tinplate (50 × 100 × 0.3 mm, meeting GB / T9271-2008 requirements) using a wire rod applicator (wet film thickness 50 μm, corresponding to a dry film thickness of approximately 20-25 μm). The mixture was cured at room temperature for 24 hours, with the dry film thickness of the cured coating controlled at 20 ± 2 μm. The mixture was then placed in a constant temperature and humidity chamber (23 ± 2°C, 50 ± 5% RH) for 48 hours to obtain a test specimen. The sample was then fixed on the friction tester platform (Taber linear abrader), and the position of the friction head (standard wool felt friction head, diameter 16 mm, pressure 500 g) was adjusted so that the friction head was in contact with the coating surface, the friction pressure was 500 g, the friction speed was 60 times / min, the single-stroke friction distance was 50 mm, and the friction head was replaced every 1000 frictions. After 2000 frictions, the color difference (ΔE*) between the friction area and the unrubbed area was measured using a colorimeter (compliant with ISO7724). The mass of the sample before and after friction was weighed (accuracy 0.1 mg) and the mass loss rate was calculated. The test was performed 100 times, and the average color difference and average mass loss rate of the 100 tests were recorded, as shown in Table 1. The larger the average color difference, the more obvious the discoloration, and the worse the wear resistance of the coating or ink. The larger the average mass loss rate after friction, the more the coating or ink coating fell off, and the worse the wear resistance of the coating or ink.

[0066] Coating stability test at high temperature: The nano-silica coated spherical wax micropowder particles were dehydrated in a vacuum drying oven at 40°C for 24 hours to remove adsorbed moisture and obtain a sample. Weigh 1.000±0.005g of sample and place it in a high-temperature crucible. Place the high-temperature crucible in a heating furnace and heat it at a rate of 5°C / min to 20°C above the melting point of the wax. Keep the temperature constant for 2h, and introduce nitrogen (flow rate 50mL / min) throughout the process. After cooling to room temperature, weigh the sample and calculate the mass loss rate. The experiment was repeated 20 times for the same batch of samples, and the average mass loss rate of the 20 experiments was recorded, as shown in Table 1. The smaller the average mass loss rate after high-temperature treatment, the better the coating stability of the nano-silica coated spherical wax micropowder particles, and the less leakage of the coated spherical wax micropowder particles.

[0067] Phase change thermal stability test: Nano-silica-coated spherical wax micropowder particles were dehydrated in a vacuum drying oven at 40°C for 24 hours to remove adsorbed moisture and obtain a sample. 10 mg of the sample was weighed and placed in a sealed aluminum crucible. A differential scanning calorimeter (DSC, TA Instruments Q2000) was used under the test conditions of a nitrogen flow rate of 50 mL / min, a temperature range of Tm-50°C to Tm+50°C, and a heating / cooling rate of 10°C / min. The test cycle was repeated for more than 20 times (heating and cooling constituted one cycle). In the first cycle, the phase change temperatures (Tm, Tc) and enthalpy values ​​(ΔH) of the melting peak (endothermic) and crystallization peak (exothermic) were recorded. The subsequent cycles of heating and cooling were repeated until the ΔH change rate for three consecutive cycles was ≤2% (determined to be constant heat of fusion). The decay rate of the phase change enthalpy (ΔH) was calculated. Phase change enthalpy decay rate = (|ΔH initial time - ΔH nth time|) ÷ ΔH initial time × 100%. The smaller the phase change enthalpy decay rate, the better the phase change thermal stability of the nano-silica-coated spherical wax powder particles.

[0068] The test results are shown in Table 1.

[0069] Table 1

[0070]

[0071]

[0072] Combining Example 1 with Comparative Examples 1-5 and Table 1, it can be seen that compared to Example 1, the average color difference of Comparative Examples 1 and 4 is greater than 2, and the average mass loss rate after friction of Comparative Examples 1-2 and 4-5 is greater than 5%. The average mass loss rate after high-temperature treatment of Comparative Examples 1-5 is greater than 10%, and the phase change enthalpy decay rate of Comparative Examples 1-5 is greater than 5%. This shows that the preparation method of Example 1 helps improve the wear resistance, coating stability, and phase change thermal stability of nano-silica-coated spherical wax micropowder particles.

[0073] Combining Examples 1-13 with Table 1, it can be seen that the average color difference of Examples 1-12 is less than 2, the average mass loss rate after friction is no more than 5%, the average mass loss rate after high-temperature treatment is less than 10%, and the phase change enthalpy decay rate is less than 5%. This shows that the preparation methods of Examples 1-12 can all produce nano-silica-coated spherical wax micropowder particles with excellent wear resistance, coating layer stability, and phase change thermal stability.

[0074] However, compared to Example 1, the average color difference and average mass loss rate after friction in Examples 11-13 both gradually increased, with Example 13 exhibiting an average color difference greater than 2 and an average mass loss rate greater than 5%. Furthermore, the maximum particle size of the spherical wax micropowder particles used in Examples 1 and 11-13 gradually increased. This suggests that using spherical polyethylene wax micropowder particles with a particle size of 1-25 μm to produce nanosilica-coated spherical wax micropowder particles exhibits superior wear resistance, making them more suitable for use in coatings or inks.

[0075] Compared with Example 1, the average mass loss rate and phase change enthalpy decay rate of Examples 11-12 after high-temperature treatment gradually decrease, which shows that the nano-silica-coated spherical wax powder particles prepared by using spherical polyethylene wax powder particles with a particle size of 30-300 μm have better phase change thermal stability and are more suitable for phase change materials.

[0076] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A process for preparing spherical wax micropowder particles coated with nano-silicon dioxide, characterized in that: The steps include: S1. Weigh the following raw materials in parts by weight: 3-6 parts of deionized water, 2-4 parts of anhydrous ethanol, 0.1-0.3 parts of ethylenediamine, 0.7-1.0 parts of an organic silicon source, and 2-4 parts of spherical wax micropowder particles; S2. Deionized water, anhydrous ethanol, and ethylenediamine are mixed according to a certain ratio, and an organic silicon source is added under stirring at room temperature, and the mixture is stirred evenly to obtain a silica sol; S3. Wetting the spherical wax micropowder particles with hydrogen peroxide, adding vinyl triethyl silane and butyl tin dilaurate, stirring evenly, heating to a temperature below the melting point and above the glass transition temperature of the spherical wax micropowder particles, and then cooling to room temperature to obtain pretreated wax micropowder particles; the amount of vinyl triethyl silane is 0.2-0.4% by weight of the spherical wax micropowder particles, and the amount of butyl tin dilaurate is 0.05-0.15% by weight of the spherical wax micropowder particles; S4. Add the pretreated wax micropowder particles to the silica sol under stirring, disperse them evenly, and grind them at a grinding temperature of ≤70°C and a grinding time of ≥2 hours to obtain a thick slurry dispersion, separate the solid and liquid, and dry them to obtain spherical wax micropowder particles coated with nano-silica.

2. The process for preparing nano-silica-coated spherical wax micropowder particles according to claim 1, characterized in that: When the nano-silicon dioxide-coated spherical wax micropowder particles are applied to coatings or inks, the particle size of the spherical wax micropowder particles is 1-25 μm.

3. The process for preparing nano-silica-coated spherical wax micropowder particles according to claim 1, characterized in that: When the nano-silicon dioxide-coated spherical wax micropowder particles are used in phase change materials, the particle size of the spherical wax micropowder particles is 30-300 μm.

Images