Magnesium hydroxide-modified silica-coated paraffin-colored phase change microcapsules and their application in epoxy polyester powder coatings

Abstract

This invention relates to the field of phase change microcapsules, and discloses a magnesium hydroxide-modified silica-coated paraffin wax colored phase change microcapsule and its application in epoxy polyester powder coatings. The magnesium hydroxide-modified silica-coated paraffin wax colored phase change microcapsule of this invention comprises paraffin wax as a core material, a silica shell coating the surface of the paraffin wax, magnesium hydroxide nanosheets grown in situ on the surface of the silica shell through electrostatic attraction and in-situ precipitation, and an organic dye grafted onto the magnesium hydroxide nanosheets and the silica shell surface by γ-aminopropyltriethoxysilane. This microcapsule not only possesses temperature-regulating and flame-retardant functions, but also exhibits rich colors with excellent color-fixing ability. When the microcapsules prepared by the method of this invention are added as fillers to epoxy polyester powder coatings, they show good compatibility.

Description

Technical Field

[0001] This invention relates to the field of phase change microcapsules, and more particularly to a method for preparing magnesium hydroxide-modified silica-coated paraffin-colored phase change microcapsules and their application in epoxy polyester powder coatings. Background Technology

[0002] Phase change materials (PCMs), as latent heat storage materials, can maintain their temperature within a certain range by absorbing or releasing latent heat, and are considered a recyclable clean energy material with high energy conversion efficiency. Microencapsulated PCMs are designed to address the leakage problem of PCMs. They are composite PCMs with a core-shell structure, formed by coating solid-liquid PCM particles with a stable polymer or inorganic material film using microencapsulation technology. Studies have shown that mixing PCM microcapsules with coatings can significantly improve the temperature regulation performance of the coatings. For example, Lv et al. [Lv X, Guo P, Liu H, Cui L, Cui X. Preparation of paraffin-based phase-change microcapsules and application ingeopolymer coating[J]. Journal of Coatings Technology and Research, 2018, 15: 867-874.] prepared a PCM microcapsule / polymer coating with good external wall insulation performance using microencapsulation and in-situ polymerization technologies, which can be used for building energy conservation and emission reduction.

[0003] Epoxy polyester powder coatings, as a type of solid powder environmentally friendly coating, are widely used in household appliances, automobiles, and construction due to their advantages such as no volatile organic compounds and energy saving. Therefore, if temperature-regulating microcapsules are mixed with epoxy polyester powder coatings and sprayed onto various substrates, temperature-regulating functions can be added to the coating's original protective and decorative properties. However, the shells of traditional microcapsules are mainly composed of polymers such as urea-formaldehyde resin and polymethyl methacrylate, which, like epoxy polyester powder coatings, are flammable.

[0004] Magnesium hydroxide, as an inorganic flame retardant, has advantages such as being non-toxic and having high thermal stability. When heated, it decomposes to generate water vapor, which dilutes flammable gases. The resulting oxides promote the formation of a carbonized layer, thus achieving a flame-retardant effect. Given the flame-retardant characteristics of magnesium hydroxide and the phase change temperature-regulating function of paraffin, Song et al. [Song G, Ma S, Tang G, et al. Preparation and characterization of flame retardant form-stable phase change materials composed by EPDM, paraffin and nano magnesium hydroxide[J]. Energy, 2010, 35(5): 2179-2183.] attempted to disperse paraffin, magnesium hydroxide, and red phosphorus in EPDM rubber to obtain a phase change temperature-regulating composite material with flame-retardant properties. However, paraffin and magnesium hydroxide have a density difference, which leads to stratification when paraffin undergoes a solid-liquid phase change. More importantly, magnesium hydroxide and rubber have poor compatibility and exhibit agglomeration. These problems affect the flame-retardant and temperature-regulating functions of the composite material.

[0005] Pigments, as an important component of epoxy polyester powder coatings, impart color to the coating and produce good decorative effects. However, existing processes mainly involve directly mixing pigments and powder coatings, which are prone to peeling and fading after long-term environmental erosion, making it difficult to achieve the purpose of color fixation. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a magnesium hydroxide-modified silica-coated paraffin-based color phase change microcapsule and its application in epoxy polyester powder coatings. The magnesium hydroxide-modified silica-coated paraffin-based color phase change microcapsule of this invention uses paraffin as the core material, with a silica shell coating its surface. Magnesium hydroxide nanosheets are grown in situ on the surface of the silica shell, and organic dyes are further chemically grafted onto the surfaces of the silica shell and magnesium hydroxide nanosheets. This microcapsule not only possesses temperature-regulating and flame-retardant functions but also exhibits rich colors with excellent color-fixing ability. When the microcapsules prepared by this invention are added as fillers to epoxy polyester powder coatings, they demonstrate good compatibility.

[0007] The specific technical solution of this invention is as follows:

[0008] In a first aspect, the present invention provides a magnesium hydroxide-modified silica-coated paraffin color phase change microcapsule, comprising paraffin as a core material, a silica shell coating the surface of the paraffin, magnesium hydroxide nanosheets grown in situ on the surface of the silica shell by electrostatic attraction and in-situ precipitation, and an organic dye grafted onto the surface of the magnesium hydroxide nanosheets and the silica shell by γ-aminopropyltriethoxysilane (KH-550).

[0009] The magnesium hydroxide-modified silica-coated paraffin-coated colored phase change microcapsules of this invention possess temperature-regulating and flame-retardant functions. Specifically, the microcapsules use paraffin as the core material, with a silica shell coating the paraffin to prevent leakage. Simultaneously, magnesium hydroxide nanosheets are grown in situ on the microcapsule surface using electrostatic attraction and in-situ precipitation methods, synergistically enhancing the flame-retardant effect of magnesium hydroxide. Furthermore, the magnesium hydroxide nanosheets and silica shell surface are modified with γ-aminopropyltriethoxysilane. This increases the compatibility of the microcapsules with epoxy polyester powder coatings and allows for the chemical grafting of organic dye molecules onto the microcapsule surface, transforming them into colored microcapsules with excellent color-fixing capabilities. Applying these magnesium hydroxide-modified silica-coated paraffin-coated colored phase change microcapsules with temperature-regulating and flame-retardant functions to epoxy polyester powder coatings not only imparts flame retardancy and heat insulation properties to the coatings but also enriches their color palette.

[0010] Secondly, the present invention provides a method for preparing magnesium hydroxide-modified silica-coated paraffin-based colored phase change microcapsules, comprising the following steps:

[0011] (1) Paraffin wax and tetraethyl orthosilicate (TEOS) were mixed and heated to obtain dispersion A; hexadecyltrimethylammonium bromide (CTAB) and formamide were mixed and stirred to obtain dispersion B; the obtained dispersion B was poured into dispersion A and stirred to form a non-aqueous O / W emulsion, and then hydrochloric acid solution was added dropwise and stirred to react. After aging, centrifugation, washing and drying, silica-coated paraffin phase change microcapsules were obtained.

[0012] (2) The silica-coated paraffin phase change microcapsules were dispersed in water, magnesium chloride solution was added, and ammonia was added under heating and stirring conditions. After centrifugation, washing and drying, magnesium hydroxide-modified silica-coated paraffin phase change microcapsules were obtained.

[0013] (3) Magnesium hydroxide-modified silica-coated paraffin phase change microcapsules were dispersed in water and ethanol to obtain dispersion C; γ-aminopropyltriethoxysilane (KH-550) was dispersed in ethanol, and the resulting mixture was added dropwise to the dispersion and heated to react to obtain dispersion D.

[0014] (4) Add ammonia and organic dye to dispersion D, heat and stir, centrifuge, wash and dry to obtain magnesium hydroxide modified silica coated paraffin color phase change microcapsules.

[0015] The preparation principle of the magnesium hydroxide-modified silica-coated paraffin-based colored phase change microcapsules of this invention is as follows: paraffin is used as the oil phase, tetraethyl orthosilicate as the aqueous phase, and hexadecyltrimethylammonium bromide is used as the emulsifier and formamide as the reaction solvent. The mixture is stirred and mixed under heating conditions to emulsify and form a stable non-aqueous O / W emulsion. The hydrophilic end of hexadecyltrimethylammonium bromide is connected to tetraethyl orthosilicate, and the hydrophobic end is inserted into the paraffin droplets, forming a micelle system. Hydrochloric acid is slowly added dropwise to the emulsion, causing tetraethyl orthosilicate to hydrolyze and condense on the surface of the paraffin droplets to form silica. Mg 2+ Magnesium hydroxide nanosheets are formed in situ on the surface of silica-coated paraffin phase change microcapsules through electrostatic attraction and aggregation on the silica surface under alkaline conditions. γ-aminopropyltriethoxysilanes hydrolyze to form silanol bonds, which then undergo hydrolytic condensation polymerization with the hydroxyl groups on the silica shell and magnesium hydroxide nanosheets. Simultaneously, γ-aminopropyltriethoxysilanes also undergo self-condensation polymerization, coating the microcapsule surface. The modified shell surface contains amino groups, which undergo nucleophilic substitution with the active groups of organic dye molecules, attracting and anchoring the active dye molecules, and chemically grafting them onto the phase change microcapsule surface. This results in magnesium hydroxide-modified silica-coated paraffin-coated colored phase change microcapsules with flame-retardant and temperature-regulating functions.

[0016] Preferably, in step (1), the ratio of the amount of paraffin, tetraethyl orthosilicate, hexadecyltrimethylammonium bromide, formamide and hydrochloric acid solution is 2-8g: 2-8g: 0.5-1g: 50-100g: 50-100ml.

[0017] This invention discovered that if the hydrolysis rate of TEOS is too fast, agglomeration will occur before the silica is fully coated. Extensive testing has shown that using formamide solution as the reaction solvent can reduce the hydrolysis rate of TEOS in water. Furthermore, in the preparation of silica-coated paraffin phase change microcapsules, this invention also explored the optimal mass ratio of paraffin to TEOS. The resulting microcapsules have suitable thickness and better coating efficiency, meeting the requirements for subsequent modification and dyeing. Preferably, in step (1), the concentration of the hydrochloric acid solution is 0.8–1.2 mol / L.

[0018] Preferably, in step (1), the paraffin is a single-melting-point paraffin or a mixed paraffin composed of multiple single-melting-point paraffins, with a melting point of 28-50°C.

[0019] Step (1) specifically includes: heating paraffin and tetraethyl orthosilicate to 50-65°C and stirring at 800-1200 rpm for 40-50 min to obtain dispersion A; stirring hexadecyltrimethylammonium bromide and formamide at 500-700 rpm for 40-50 min to obtain dispersion B; adding the obtained dispersion B to dispersion A at 50-65°C and reacting at 500-800 rpm for 3-5 h to obtain a stable non-aqueous O / W emulsion; adding hydrochloric acid solution and continuing stirring for 3-5 h; aging temperature of 40-50°C and aging time of 12-18 h; centrifugation speed of 4500-8000 rpm and centrifugation time of 5-10 min; washing method of washing with deionized water 2-4 times and washing with ethanol 2-4 times; drying at 50-65°C for 24-48 h.

[0020] Preferably, in step (2), the ratio of the amount of silica-coated paraffin phase change microcapsules, water, magnesium chloride solution and ammonia is 2.5-10g: 100-150g: 20-80ml: 20-100ml.

[0021] Preferably, in step (2), the concentration of the magnesium chloride solution is 0.08–0.12 mol / L; and the concentration of the ammonia solution is 0.18–0.22 mol / L.

[0022] Preferably, step (2) specifically includes: ultrasonicating the silica-coated paraffin phase change microcapsules and water at 40-45°C for 40-50 min, raising the temperature to 50-65°C, adding magnesium chloride solution at 500-800 rpm and stirring for 3-5 h; then adding ammonia water and stirring for 1-1.5 h; centrifuging at 4500-8000 rpm for 5-10 min; washing with deionized water 2-4 times and ethanol 2-4 times; and drying at 50-65°C for 10-12 h.

[0023] Preferably, in step (3), the ratio of the amount of magnesium hydroxide-modified silica-coated paraffin phase change microcapsules, water, ethanol and γ-aminopropyltriethoxysilane is 2.5g~10g∶5~10g∶20~250g∶2~10g.

[0024] Preferably, step (3) specifically includes: encapsulating paraffin phase change microcapsules with magnesium hydroxide-modified silica and ethanol and deionized water at 40-45°C for 40-50 min; heating the obtained dispersion C to 50-65°C, adding a mixture containing γ-aminopropyltriethoxysilane at 500-800 rpm, and heating and stirring the reaction for 2-3 h to obtain dispersion D.

[0025] Preferably, in step (4), the organic dye is CI Reactive Blue 4 (X-BR).

[0026] Preferably, in step (4), the ratio of ammonia water to organic dye is 10-20 ml: 0.5 g-1.2 g.

[0027] Preferably, in step (4), the concentration of the ammonia water is 0.18 to 0.22 mol / L.

[0028] As a preferred embodiment, step (4) specifically includes: adding ammonia and organic dye to dispersion D, heating and stirring for 2-5 hours; centrifuging at a speed of 4500-8000 rpm for 5-10 minutes; washing with deionized water 2-4 times and ethanol 2-4 times; and drying at 50-65°C for 10-12 hours.

[0029] Thirdly, the present invention provides an application of the above-mentioned magnesium hydroxide-modified silica-coated paraffin color phase change microcapsules in epoxy polyester powder coatings.

[0030] Preferably, the epoxy polyester powder coating comprises the following raw materials in parts by weight: 20-50 parts epoxy resin, 20-50 parts polyester resin, 0.1-0.5 parts 2-methylimidazole, and 10-30 parts magnesium hydroxide-modified silica-coated paraffin color phase change microcapsules.

[0031] Preferably, the preparation method of the epoxy polyester powder coating includes: uniformly mixing magnesium hydroxide-modified silica-coated paraffin colored phase change microcapsules with epoxy resin, polyester resin, and 2-methylimidazole, melting and mixing at 90-110°C, cooling to room temperature, and then pulverizing.

[0032] Compared with the prior art, the beneficial effects of the present invention are:

[0033] (1) The magnesium hydroxide-modified silica-coated paraffin-based colored phase change microcapsules of the present invention use paraffin as the core material, with a silica shell coating its surface. Magnesium hydroxide nanosheets are grown in situ on the surface of the silica shell, and organic dyes are further chemically grafted onto the surfaces of the silica shell and magnesium hydroxide nanosheets. These microcapsules not only have temperature-regulating and flame-retardant functions, but also possess rich colors with excellent color-fixing ability.

[0034] (2) The microcapsules prepared by the method of the present invention are added to the epoxy polyester powder coating as fillers. The microcapsules have good compatibility with the epoxy polyester powder coating and can give the coating excellent temperature regulation, flame retardancy and rich colors. Attached Figure Description

[0035] Figure 1 This is a schematic diagram illustrating the synthesis of the magnesium hydroxide-modified silica-coated paraffin-colored phase change microcapsules of the present invention.

[0036] Figure 2Here is a SEM image of the silica-coated paraffin phase change microcapsules prepared in Example 1 of this invention;

[0037] Figure 3 Here is a SEM image of the magnesium hydroxide-modified silica-coated paraffin color phase change microcapsules prepared in Example 1 of this invention.

[0038] Figure 4 The images show the FT-IR spectra of the silica-coated paraffin phase change microcapsules, magnesium hydroxide-modified silica-coated paraffin phase change microcapsules, and magnesium hydroxide-modified silica-coated paraffin colored phase change microcapsules prepared in Example 1 of this invention.

[0039] Figure 5 The XRD curve of the magnesium hydroxide-modified silica-coated paraffin color phase change microcapsules prepared in Example 1 of this invention;

[0040] Figure 6 Time-temperature curves for pure paraffin and magnesium hydroxide-modified silica-coated paraffin color phase change microcapsules prepared in Example 1 of this invention. Detailed Implementation

[0041] The present invention will be further described below with reference to embodiments.

[0042] General Implementation Examples

[0043] A magnesium hydroxide-modified silica-coated paraffin color phase change microcapsule includes paraffin as the core material, a silica shell coating the surface of the paraffin, magnesium hydroxide nanosheets grown in situ on the surface of the silica shell by electrostatic attraction and in-situ precipitation, and an organic dye grafted onto the surface of the magnesium hydroxide nanosheets and the silica shell by γ-aminopropyltriethoxysilane.

[0044] A method for preparing magnesium hydroxide-modified silica-coated paraffin-based color phase change microcapsules includes the following steps (reaction process as follows): Figure 1 As shown):

[0045] (1) Paraffin wax and tetraethyl orthosilicate were heated to 50-65°C and stirred at 800-1200 rpm for 40-50 min to obtain dispersion A; hexadecyltrimethylammonium bromide and formamide were stirred at 500-700 rpm for 40-50 min to obtain dispersion B; dispersion B was added to dispersion A at 50-65°C and reacted at 500-800 rpm for 3-5 h to obtain a non-aqueous O / W emulsion; hydrochloric acid solution (0.8-1.2 mol / L) was added and stirring was continued for 3-5 h, followed by aging (40-50°C, 12-18 h), centrifugation (4500-8000 rpm, 5-10 min), washing (washing with deionized water 2-4 times and ethanol 2-4 times), and drying (50-65°C, 24-48 h) to obtain silica-coated paraffin phase change microcapsules.

[0046] Preferably, the paraffin wax is a single-melting-point paraffin wax or a mixed paraffin wax composed of multiple single-melting-point paraffin waxes, with a melting point of 28–50°C. The ratio of the paraffin wax, tetraethyl orthosilicate, hexadecyltrimethylammonium bromide, formamide, and hydrochloric acid solution is 2–8 g : 2–8 g : 0.5–1 g : 50–100 g : 50–100 ml.

[0047] (2) The silica-coated paraffin phase change microcapsules and water were sonicated at 40-45℃ for 40-50 min, heated to 50-65℃, and magnesium chloride solution (0.08-0.12 mol / L) was added at 500-800 rpm and stirred for 3-5 h; then ammonia water (0.18-0.22 mol / L) was added and stirred for 1-1.5 h; after centrifugation (4500-8000 rpm, 5-10 min), washing (washing with deionized water 2-4 times, washing with ethanol 2-4 times), and drying (50-65℃, 10-12 h), silica-coated paraffin phase change microcapsules were obtained.

[0048] Preferably, the ratio of the silica-coated paraffin phase change microcapsules, water, magnesium chloride solution, and ammonia is 2.5–10 g : 100–150 g : 20–80 ml : 20–100 ml.

[0049] (3) Magnesium hydroxide-modified silica-coated paraffin phase change microcapsules and ethanol and deionized water were ultrasonicated at 40-45℃ for 40-50 min; the resulting dispersion C was heated to 50-65℃, γ-aminopropyltriethoxysilane (KH-550) was dispersed in ethanol, and the resulting mixture was added to the dispersion at 500-800 rpm. The mixture was heated and stirred for 2-3 h to obtain dispersion D.

[0050] Preferably, the ratio of the magnesium hydroxide-modified silica-coated paraffin phase change microcapsules, water, ethanol, and γ-aminopropyltriethoxysilane is 2.5g~10g∶5~10g∶20~250g∶2~10g.

[0051] (4) Add ammonia (0.18-0.22 mol / L) and organic dye (CI reactive blue 4 (X-BR)) to dispersion D, heat and stir for 2-5 h; centrifuge (4500-8000 rpm, 5-10 min); wash (wash 2-4 times with deionized water and 2-4 times with ethanol); dry (50-65℃, 10-12 h) to obtain magnesium hydroxide modified silica-coated paraffin color phase change microcapsules.

[0052] Preferably, the ratio of ammonia water to organic dye is 10-20 ml : 0.5 g-1.2 g.

[0053] An epoxy polyester powder coating comprises the following raw materials in parts by weight: 20-50 parts epoxy resin, 20-50 parts polyester resin, 0.1-0.5 parts 2-methylimidazole, and 10-30 parts magnesium hydroxide-modified silica-coated paraffin color phase change microcapsules.

[0054] The preparation method of the above-mentioned epoxy polyester powder coating includes: uniformly mixing magnesium hydroxide modified silica-coated paraffin colored phase change microcapsules with epoxy resin, polyester resin and 2-methylimidazole, melting and mixing at 90-110℃, cooling to room temperature and then pulverizing.

[0055] Example 1

[0056] (1) First, add 5g of paraffin (melting point 28-30℃) and 5g of TEOS to a three-necked flask, heat to 55℃ and mechanically stir at 1200rpm. At the same time, add 0.75g of CTAB and 100g of formamide to another beaker and magnetically stir at 700rpm for 40min. Keep the original temperature and stirring speed and add the obtained CTAB and formamide solution to the three-necked flask, react for 4h. Then, add 100ml of prepared hydrochloric acid solution (1mol / L) dropwise to the three-necked flask, continue stirring and react for 4h to obtain a white precipitate. Stop stirring and mature at 45℃ for 18h. Then, centrifuge at 8000rpm for 5min to obtain the precipitate product. Wash with deionized water and ethanol three times respectively, and dry at 65℃ for 48h to obtain silica-coated paraffin phase change microcapsules.

[0057] (2) The 2.5 g silica-coated paraffin phase change microcapsules obtained in step (1) and 100 g deionized water were sonicated at 45 °C for 45 min, transferred to a three-necked flask, heated to 65 °C, and 40 ml magnesium chloride solution (0.1 mol / L) was added dropwise at a stirring rate of 600 rpm. The reaction was stirred for 4 h. At the same temperature and stirring rate, 40 ml ammonia water (0.2 mol / L) was added, and the reaction was stirred for 1 h. Then, the product was centrifuged at 8000 rpm for 5 min to obtain the precipitate. The product was washed three times with deionized water and ethanol, respectively, and then dried at 65 °C for 48 h to obtain magnesium hydroxide-modified silica-coated paraffin phase change microcapsules.

[0058] (3) The 2.5g magnesium hydroxide-modified silica-coated paraffin phase change microcapsules obtained in step (2), 100g ethanol, and 10g deionized water were sonicated at 45℃ for 45min. At the same time, 5g KH-550 was placed in a beaker and 40g ethanol was added and mixed well. The dispersion of magnesium hydroxide-modified silica-coated paraffin phase change microcapsules, ethanol, and deionized water was transferred to a three-necked flask and heated to 65℃. KH-550 solution was added dropwise at a stirring rate of 600rpm, and the reaction was heated and stirred for 2h.

[0059] (4) While maintaining the temperature and stirring speed in step (3), add 15 ml of ammonia and 1 g of CI Reactive Blue 4 (X-BR), and heat and stir for 2 h. Then, centrifuge at 8000 rpm for 5 min to obtain the precipitate, wash with deionized water and ethanol three times each, and dry at 65 °C for 48 h to obtain magnesium hydroxide modified silica-coated paraffin color phase change microcapsules.

[0060] (5) Take 25g of magnesium hydroxide modified silica coated paraffin color phase change microcapsules obtained in step (4) and mix them evenly with 50g of epoxy resin, 50g of polyester resin and 0.5g of 2-methylimidazole. Melt and mix them at 100℃, cool them to room temperature and then crush them with a pulverizer to obtain epoxy polyester powder coating.

[0061] Example 2

[0062] (1) First, add 5g of paraffin (melting point 48-50℃) and 5g of TEOS to a three-necked flask, heat to 65℃ and mechanically stir at 1200rpm for 45min. At the same time, add 0.75g of CTAB and 100g of formamide to another beaker and magnetically stir at 600rpm for 45min. Keep the original temperature and stirring speed and add the obtained CTAB and formamide solution to the three-necked flask, react for 4h. Then, add 100g of prepared hydrochloric acid solution (1mol / L) dropwise to the three-necked flask, continue stirring and react for 4h to obtain a white precipitate. Stop stirring and mature at 45℃ for 18h. Then, centrifuge at 8000rpm for 5min to obtain the precipitate product. Wash with deionized water and ethanol three times respectively, and dry at 65℃ for 48h to obtain silica-coated paraffin phase change microcapsules.

[0063] (2) The 2.5 g silica-coated paraffin phase change microcapsules obtained in step (1) and 100 g deionized water were sonicated at 45 °C for 50 min, transferred to a three-necked flask, heated to 65 °C, and 50 ml magnesium chloride solution (0.1 mol / L) was added dropwise at a stirring rate of 600 rpm. The reaction was stirred for 3 h. At the same temperature and stirring rate, 50 ml ammonia water (0.2 mol / L) was added, and the reaction was stirred for 1.5 h. Then, the product was centrifuged at 8000 rpm for 5 min to obtain the precipitate. The product was washed three times with deionized water and ethanol, respectively, and then dried at 65 °C for 48 h to obtain magnesium hydroxide-modified silica-coated paraffin phase change microcapsules.

[0064] (3) The 2.5g magnesium hydroxide-modified silica-coated paraffin phase change microcapsules obtained in step (2), 100g ethanol, and 5g deionized water were sonicated at 45℃ for 45min. At the same time, 5g KH-550 was placed in a beaker and 40g ethanol was added and mixed well. The dispersion of magnesium hydroxide-modified silica-coated paraffin phase change microcapsules, ethanol, and deionized water was transferred to a three-necked flask and heated to 65℃. KH-550 solution was added dropwise at a stirring rate of 600rpm, and the reaction was heated and stirred for 3h.

[0065] (4) While maintaining the temperature and stirring speed in step (3), add 20 ml of ammonia and 1.2 g of CI Reactive Blue 4 (X-BR), and heat and stir for 2 h. Then, centrifuge at 8000 rpm for 5 min to obtain the precipitate, wash with deionized water and ethanol three times each, and dry at 65 °C for 48 h to obtain magnesium hydroxide modified silica-coated paraffin color phase change microcapsules.

[0066] (5) Take 20g of magnesium hydroxide modified silica coated paraffin color phase change microcapsules obtained in step (4) and mix them evenly with 50g of epoxy resin, 50g of polyester resin and 0.3g of 2-methylimidazole. Melt and mix them at 100℃, cool them to room temperature and then crush them with a pulverizer to obtain epoxy polyester powder coating.

[0067] Example 3

[0068] (1) First, add 5g of paraffin (melting point 48-50℃) and 7.5g of TEOS to a three-necked flask, heat to 65℃ and mechanically stir at 1200rpm for 45min. At the same time, add 1g of CTAB and 75g of formamide to another beaker and magnetically stir at 600rpm for 45min. Keep the original temperature and stirring speed and add the obtained CTAB and formamide solution to the three-necked flask, and react for 5h. Then, add 100g of prepared hydrochloric acid solution (1mol / L) dropwise to the three-necked flask and continue stirring for 5h to obtain a white precipitate. Stop stirring and mature at 45℃ for 18h. Then, centrifuge at 8000rpm for 5min to obtain the precipitate product. Wash with deionized water and ethanol three times respectively, and dry at 65℃ for 48h to obtain silica-coated paraffin phase change microcapsules.

[0069] (2) The 2.5 g silica-coated paraffin phase change microcapsules obtained in step (1) and 100 g deionized water were sonicated at 45 °C for 50 min, transferred to a three-necked flask, heated to 65 °C, and 80 ml magnesium chloride solution (0.1 mol / L) was added dropwise at a stirring rate of 600 rpm. The reaction was stirred for 5 h. At the same temperature and stirring rate, 80 ml ammonia water (0.2 mol / L) was added, and the reaction was stirred for 1.5 h. Then, the product was centrifuged at 8000 rpm for 5 min to obtain the precipitate. The product was washed three times with deionized water and ethanol, respectively, and then dried at 65 °C for 48 h to obtain magnesium hydroxide-modified silica-coated paraffin phase change microcapsules.

[0070] (3) The 2.5g magnesium hydroxide-modified silica-coated paraffin phase change microcapsules obtained in step (2), 150g ethanol, and 10g deionized water were sonicated at 45℃ for 45min. At the same time, 10g KH-550 was placed in a beaker and 80g ethanol was added and mixed well. The dispersion of magnesium hydroxide-modified silica-coated paraffin phase change microcapsules, ethanol, and deionized water was transferred to a three-necked flask and heated to 65℃. KH-550 solution was added dropwise at a stirring rate of 600rpm, and the reaction was heated and stirred for 4h.

[0071] (4) While maintaining the temperature and stirring speed in step (3), add 20 ml of ammonia and 1.2 g of CI Reactive Blue 4 (X-BR), and heat and stir for 3 h. Then, centrifuge at 8000 rpm for 5 min to obtain the precipitate, wash with deionized water and ethanol three times each, and dry at 65 °C for 48 h to obtain magnesium hydroxide modified silica-coated paraffin color phase change microcapsules.

[0072] (5) Take 15g of magnesium hydroxide modified silica coated paraffin color phase change microcapsules obtained in step (4) and mix them evenly with 50g of epoxy resin, 50g of polyester resin and 0.2g of 2-methylimidazole. Melt and mix them at 100℃, cool them to room temperature and then crush them with a pulverizer to obtain epoxy polyester powder coating.

[0073] Performance testing and characterization

[0074] Table 1 shows the flame retardant performance parameters of pure epoxy polyester powder coatings and epoxy polyester powder coatings in Examples 1-3 with magnesium hydroxide-modified silica-coated paraffin color phase change microcapsules that have flame retardant and temperature-regulating functions. Wherein: t1 and t2 represent the average burning time of the sample after the first and second ignition in the vertical burning test, respectively; LOI% represents the limiting oxygen index of the material.

[0075] <![CDATA[t1+t2]]> LOI% Pure epoxy polyester powder coating - 21.1 Example 1 17.2 26.2 Example 2 21.3 25.1 Example 3 24.5 23.7

[0076] As shown in Table 1, pure epoxy polyester powder coatings did not exhibit self-extinguishing behavior in the vertical burning test. However, all examples using magnesium hydroxide-modified silica-coated paraffin-colored phase change microcapsules as fillers showed self-extinguishing properties, with Example 1 exhibiting the shortest burning time and the best self-extinguishing ability. Furthermore, compared to pure epoxy polyester powder coatings, the limiting oxygen index (LOI) was improved after adding microcapsules, with Example 1 showing the highest LIO. These results indicate that the addition of microcapsules significantly improves the flame-retardant properties of epoxy polyester powder coatings, and the flame-retardant performance increases with the increase in the proportion of microcapsules.

[0077] Figure 2 and Figure 3 SEM images of the silica-coated paraffin phase change microcapsules and the magnesium hydroxide-modified silica-coated paraffin color phase change microcapsules obtained in Example 1 are shown below. Figure 2 As can be seen, the silica-coated paraffin phase change microcapsules are regular spherical, smooth, and dense, with a particle size between 1 and 3 μm. Figure 3 It can be seen that magnesium hydroxide nanosheets are diffusely distributed on the surface of the microcapsules.

[0078] Figure 4The figures show the FT-IR spectra of the silica-coated paraffin phase change microcapsules, magnesium hydroxide-modified silica-coated paraffin phase change microcapsules, and magnesium hydroxide-modified silica-coated paraffin colored phase change microcapsules obtained in Example 1. As can be seen from the figures, the FT-IR spectrum of the silica-coated paraffin phase change microcapsules shows a high concentration of chromatic spectral density at 2850 cm⁻¹. -1 and 2917cm -1 The absorption peaks at 1393 cm⁻¹ correspond to the symmetric stretching vibration peak and the asymmetric stretching vibration peak of the CH bond in the chemical structure of paraffin, respectively. -1 The absorption peak at 1080 cm⁻¹ corresponds to the bending vibration peak of the CH bond. -1 and 464cm -1 The absorption peaks at 1637 cm⁻¹ correspond to the asymmetric stretching vibration peak of Si-O-Si and the bending vibration peak of Si-O-Si in the chemical structure of silica, respectively. The FT-IR spectrum of magnesium hydroxide-modified silica-coated paraffin phase change microcapsules shows all the absorption peaks present in the FT-IR spectra of paraffin and silica, except for the peak at 1637 cm⁻¹. -1 There is also a peak at 2358 cm⁻¹, which is the Mg-OH bending vibration peak in magnesium hydroxide crystals. Furthermore, in the FT-IR spectrum of magnesium hydroxide-modified silica-coated paraffin-based color phase change microcapsules, the peak at 2358 cm⁻¹ is also observed. -1 The absorption peak at that point is a characteristic absorption peak of the reactive dye cyano (-CN).

[0079] Figure 5 The XRD curves of the magnesium hydroxide-modified silica-coated paraffin color phase change microcapsules obtained in Example 1 are shown. The diffraction angles 2θ of 20.06°, 22.01°, 30.13°, 34.54°, 35.74°, and 39.22° observed in the XRD curves of the magnesium hydroxide-modified silica-coated paraffin color phase change microcapsules correspond to the (0012), (110), (0114), (0020), (2111), and (0120) crystal planes of paraffin (JCPDF 361591), respectively. The diffraction angles 2θ of 18.51°, 32.83°, 37.92°, and 58.61° correspond to the (001), (100), (011), and (003) crystal planes of magnesium hydroxide (JCPDS card 830114), respectively. No obvious diffraction peaks of silica were observed in the figure. This is mainly due to the overlap between the peaks of amorphous silica from the shell and the diffraction peaks of paraffin.

[0080] Figure 6The figures show the time-temperature relationship curves for the colored phase transition microcapsules of pure paraffin and magnesium hydroxide-modified silica-coated paraffin obtained in Example 1. As can be seen from the figures, the entire process can be divided into three stages. In the first stage, after the light exposure begins, the sample temperature rapidly rises to approximately 28°C, and the heating rate of the microcapsules is significantly higher than that of pure paraffin. This is because the melting point of paraffin is approximately 28–30°C. Before 28°C, paraffin does not undergo a solid-liquid phase transition and absorb heat; therefore, the sample heats up significantly after being exposed to light. The higher heating rate of the microcapsules compared to paraffin is due to their higher thermal conductivity. In the second stage, after the sample temperature reaches 28°C, the heating rates of both samples slow down significantly. This is because paraffin undergoes a solid-liquid phase transition and absorbs heat. Furthermore, the heating rate of the microcapsules remains near the melting point of paraffin for a shorter time than that of pure paraffin. This is because, for the same mass of sample, the mass of paraffin contained in the microcapsules is less than that in the pure paraffin sample. In the third stage, after the solid-liquid phase transition of paraffin ends, the temperatures of both samples begin to rise rapidly again until they reach the ambient temperature.

[0081] Unless otherwise specified, the raw materials and equipment used in this invention are all commonly used in the field; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0082] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing magnesium hydroxide-modified silica-coated paraffin-colored phase change microcapsules, characterized in that... Includes the following steps: (1) Paraffin wax and tetraethyl orthosilicate were mixed and heated to obtain dispersion A; hexadecyltrimethylammonium bromide and formamide were mixed and stirred to obtain dispersion B; the obtained dispersion B was poured into dispersion A and stirred to obtain a non-aqueous O / W emulsion, and then hydrochloric acid solution was added dropwise and stirred to react. After aging, centrifugation, washing and drying, silica-coated paraffin wax phase change microcapsules were obtained. (2) Disperse 2.5~10g of silica-coated paraffin phase change microcapsules in 100~150g of water, add 20~80ml of 0.08~0.12mol / L magnesium chloride solution, add 20~100ml of ammonia water under heating and stirring conditions, centrifuge, wash and dry to obtain magnesium hydroxide modified silica-coated paraffin phase change microcapsules; (3) Magnesium hydroxide-modified silica-coated paraffin phase change microcapsules were dispersed in water and ethanol to obtain dispersion C; γ-aminopropyltriethoxysilane was dispersed in ethanol, and the resulting mixture was added dropwise to dispersion C and heated to react to obtain dispersion D. (4) Add ammonia and organic dye to dispersion D, heat and stir, centrifuge, wash and dry to obtain magnesium hydroxide modified silica coated paraffin color phase change microcapsules.

2. The preparation method according to claim 1, characterized in that: In step (1), The ratio of paraffin, tetraethyl orthosilicate, hexadecyltrimethylammonium bromide, formamide, and hydrochloric acid solution is 2~8g: 2~8g: 0.5~1g: 50~100g: 50~100ml; The concentration of the hydrochloric acid solution is 0.8~1.2 mol / L.

3. The preparation method according to claim 2, characterized in that: In step (1), the paraffin is a single melting point paraffin or a mixed paraffin composed of multiple single melting point paraffins, with a melting point of 28~50℃.

4. The preparation method according to claim 1, characterized in that: In step (2), the concentration of the ammonia water is 0.18~0.22 mol / L.

5. The preparation method according to claim 1, characterized in that: In step (3), the ratio of magnesium hydroxide-modified silica-coated paraffin phase change microcapsules, water, ethanol and γ-aminopropyltriethoxysilane is 2.5g~10g:5~10g:20~250g:2~10g.

6. The preparation method according to claim 1, characterized in that: In step (4), The organic dye is CI Reactive Blue 4; The ratio of ammonia water to organic dye is 10~20ml:0.5g~1.2g; The concentration of the ammonia water is 0.18~0.22 mol / L.

7. The magnesium hydroxide-modified silica-coated paraffin-colored phase change microcapsules obtained by the preparation method according to any one of claims 1-6, characterized in that: The product includes paraffin wax as the core material, a silica shell covering the surface of the paraffin wax, magnesium hydroxide nanosheets grown in situ on the surface of the silica shell by electrostatic attraction and in-situ precipitation, and organic dyes grafted onto the surface of the magnesium hydroxide nanosheets and the silica shell by γ-aminopropyltriethoxysilane. The particle size of the silica-coated paraffin phase change microcapsules is 1-3 μm; Magnesium hydroxide nanosheets were dispersed in water by silica-coated paraffin phase change microcapsules, and then magnesium chloride solution was added. 2+ It is formed by electrostatic adsorption and aggregation on the surface of silica, and in-situ growth under alkaline conditions.

8. The application of magnesium hydroxide-modified silica-coated paraffin color phase change microcapsules obtained by any one of claims 1-6 or the magnesium hydroxide-modified silica-coated paraffin color phase change microcapsules of claim 7 in epoxy polyester powder coatings.

9. The application as described in claim 8, characterized in that: The epoxy polyester powder coating comprises the following raw materials in parts by weight: 20-50 parts epoxy resin, 20-50 parts polyester resin, 0.1-0.5 parts 2-methylimidazole, and 10-30 parts magnesium hydroxide-modified silica-coated paraffin color phase change microcapsules.

10. The application as described in claim 9, characterized in that: The preparation method of the epoxy polyester powder coating includes: uniformly mixing magnesium hydroxide modified silica-coated paraffin colored phase change microcapsules with epoxy resin, polyester resin, and 2-methylimidazole, melting and mixing at 90~110℃, cooling to room temperature, and then pulverizing.

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