Modified thermal insulation coating as well as preparation method and application thereof

Abstract

The invention discloses a modified thermal insulation coating and a preparation method and application thereof, and belongs to the field of building energy-saving materials. One modified compound is a thermo-sensitive polyelectrolyte layer-by-layer self-assembled alumina microsphere formed by alternately depositing polyethyleneimine and polyacrylic acid through electrostatic interaction, and the polyelectrolyte layer can dynamically swell or shrink along with the temperature to adjust the heat conductivity coefficient; and the other is magnesium silicate nanofiber coated with silicon dioxide and then grafted with fluorosilane, the hydrophobicity is improved by utilizing the low surface energy of the fluorosilane, and meanwhile, the binding force with a polymer interface is enhanced. The coating further comprises fumed silica, a dispersing agent, a defoaming agent and other auxiliaries. The preparation method comprises the following steps: sequentially adding the components into a high-speed dispersion machine, mixing, adjusting the viscosity, filtering and packaging. The coating has the advantages of intelligent temperature-sensitive adjustment, low heat conductivity, strong adhesion and weather resistance; the material is suitable for long-acting heat preservation in the fields of buildings, industrial equipment and cold chains.

Description

Technical Field

[0001] The invention relates to the technical field of building energy-saving materials, and in particular to a modified thermal insulation coating and a preparation method and application thereof. Background Art

[0002] As global energy demand continues to grow, the need for energy conservation in buildings and industrial equipment is becoming increasingly urgent. As a key carrier for reducing energy consumption, the performance optimization of thermal insulation materials has become a research hotspot. Traditional thermal insulation coatings mostly rely on single fillers (such as expanded perlite and aluminum silicate fiber). Although they have basic thermal insulation functions, they have significant defects: the filler surface is highly inert and has weak bonding with the polymer matrix, which can easily cause the coating to crack and fall off; the thermal conductivity coefficient is relatively high, making it difficult to meet the long-term energy-saving needs in severe cold or high temperature environments; the weather resistance is insufficient, and ultraviolet rays and humid and hot environments can easily cause filler agglomeration or matrix aging, shortening the service life of the coating. These problems limit the application of traditional thermal insulation coatings in complex environments, and there is an urgent need to develop new thermal insulation materials with better comprehensive performance.

[0003] In recent years, nano-aerogels and hollow glass microspheres have become the focus of research on modified fillers due to their low thermal conductivity. Although nano-aerogels have extremely low thermal conductivity, they have a large specific surface area and the surface hydroxyl groups easily absorb water, which leads to a decrease in the water resistance of the coating; the hollow glass microspheres have a smooth surface, poor compatibility with polymers, and uneven dispersion easily leads to coating defects. In addition, the modification of a single filler can only optimize the single performance of thermal conductivity or interface bonding, and it is difficult to achieve the synergistic improvement of "low thermal conductivity, strong adhesion, and weather resistance". For example, although physical blending modification is simple to operate, the filler and the matrix are only physically entangled and bonded, and the interface thermal resistance is high; although chemical modification can enhance the bonding strength, it is often difficult to apply on a large scale due to harsh reaction conditions or insufficient stability of the modifier.

[0004] Smart responsive materials and heterogeneous composite fillers provide a new direction for solving the above problems. Thermosensitive polyelectrolytes can adjust their own structure through environmental stimuli (such as temperature and pH) and dynamically change thermal conductivity; fluorosilane-grafted ceramic-based fibers can improve hydrophobicity through low surface energy characteristics, while enhancing interfacial bonding with polymers. However, in the prior art, the electrostatic deposition layer of the thermosensitive filler is easily detached due to changes in environmental pH, and the stability of intelligent regulation is insufficient; the interfacial bonding between the grafted layer of the ceramic-based fiber and the polymer still relies on physical adsorption, and the bonding strength is limited. In addition, the synergistic effect of the dual fillers has not been fully explored. How to balance the temperature sensitivity of the filler and the interfacial bonding force has become a key technical bottleneck restricting the development of intelligent thermal insulation coatings. The present invention provides a new idea for the development of high-performance thermal insulation coatings by designing a dual-modified filler system, taking into account dynamic thermal conductivity regulation and strong interfacial anchoring. Summary of the Invention

[0005] The purpose of the present invention is to provide a modified thermal insulation coating, its preparation method and application, which solve the technical problems of existing thermal insulation coatings, such as easy shedding of the coating, high thermal conductivity, and poor weather resistance due to the inertness of the filler surface and weak binding force with the polymer.

[0006] The present invention achieves the above purpose through the following technical solutions:

[0007] A modified thermal insulation coating, comprising the following raw materials in parts by weight:

[0008] Waterborne polyurethane-acrylic hybrid emulsion: 350 - 450 parts by weight;

[0009] Thermosensitive polyelectrolyte layer-by-layer self-assembled alumina microspheres: 180 - 250 parts by weight;

[0010] Fluorosilane grafted magnesium silicate nanofibers: 120 - 180 parts by weight;

[0011] Fumed silica: 60 - 100 parts by weight;

[0012] Polycarboxylate dispersant: 8 - 12 parts by weight;

[0013] Organosilicon defoamer: 3 - 6 parts by weight;

[0014] Hydroxyethyl cellulose: 3 - 5 parts by weight;

[0015] pH regulator: 1 - 3 parts by weight;

[0016] Among them, the preparation method of the thermosensitive polyelectrolyte layer-by-layer self-assembled alumina microspheres includes: A1. Add α-alumina microspheres to deionized water, and ultrasonically disperse until uniform; adjust the pH of the dispersion to 9.4 - 9.6, and dropwise add an aqueous solution of polyethyleneimine, and stir at room temperature to deposit polyethyleneimine on the surface of the alumina microspheres to form the first layer of polycationic layer; A2. Subsequently, adjust the pH to 4.4 - 4.6, and dropwise add an aqueous solution of polyacrylic acid, and stir at room temperature to deposit polyacrylic acid to form the first layer of polyanionic layer; repeat the polyethyleneimine-polyacrylic acid deposition step 3 - 4 times.

[0017] During the preparation process of the thermosensitive polyelectrolyte layer-by-layer self-assembled alumina microspheres of the present invention, after the α-alumina microspheres are ultrasonically dispersed, the pH is adjusted to 9.4 - 9.6, and the surface of the microspheres becomes negatively charged due to the dissociation of Al-OH groups to form ≡Al-O-; the primary amine (-NH2, pKa≈10.6) in polyethyleneimine (PEI) remains mostly protonated (-NH3 + ) because pH < pKa, and the secondary amine (-NH-, pKa≈9.8) is partially protonated (-NH2 +-) In the equilibrium state with the neutral (-NH-), the tertiary amine (-N<, pKa ≈ 8.0) is completely deprotonated to the neutral (-N<) because pH > pKa. At this time, PEI is adsorbed through electrostatic interaction (primary amine -NH3 + attracting) and hydrogen bond / coordination interaction (secondary / tertiary amine and surface hydroxyl groups of alumina), forming the first positively charged polycation layer. Subsequently, the pH is adjusted to 4.4 - 4.6, and ≡Al-O- on the surface of the microspheres combines with H - to form neutral ≡Al-OH, weakening the negative charge; the primary amine of PEI (pH << pKa ≈ 10.6) is completely protonated (-NH3 + )), the secondary amine (pH < pKa ≈ 9.8) is mostly protonated to -NH2 + + -, and the tertiary amine (pKa ≈ 8.0) is partially protonated to -NH + <, making PEI positively charged as a whole. The carboxyl group (-COOH, pKa ≈ 4.5) of polyacrylic acid (PAA) is partially dissociated to -COO - at pH = 4.4 - 4.6, and combines with -NH3 + / -NH2 + - of PEI through electrostatic interaction, supplemented by hydrogen bonds between the carboxyl group and the unprotonated amino groups (-NH- / -N<), forming a negatively charged polyanion layer. After repeating the above steps 3 - 4 times, a "PEI - PAA" multi - layer structure is formed on the surface, and the interlayer force is jointly dominated by the stable positive charge of the primary amine of PEI, the dynamic protonation degree of the secondary / tertiary amines, and the dissociation degree of the carboxyl group of PAA. This structure adjusts the interlayer distance by reversing the charge density and type of the polyelectrolyte when the pH changes; when the temperature changes, it realizes intelligent regulation of the thermal conductivity through the conformational transformation of the PAA chain segment (hydrophobic / hydrophilic balance) and the change of the interlayer hydration state.

[0018] According to a preferred embodiment of the present invention, the aqueous polyurethane - acrylic hybrid emulsion is purchased from Wanhua Chemical Group Co., Ltd., and the model is WANALON 5050.

[0019] According to a preferred embodiment of the present invention, the α - alumina microspheres are purchased from Shandong Guoci Functional Materials Co., Ltd., and the model is AT - 300.

[0020] According to a preferred embodiment of the present invention, the polyethyleneimine is purchased from Jiangsu Haian Petrochemical Co., Ltd., and the model is PEI - 25.

[0021] According to a preferred embodiment of the present invention, the polyacrylic acid is purchased from Beijing Dongfang Chemical Plant, and the model is PAA - 8.

[0022] ​According to a preferred embodiment of the present invention, the fumed silica is purchased from Shanghai Chlor-Alkali Chemical Co., Ltd., model N20.

[0023] According to a preferred embodiment of the present invention, the polycarboxylate dispersant is purchased from Wanhua Chemical Group Co., Ltd., and the model number is WANALON DP-50.

[0024] According to a preferred embodiment of the present invention, the organosilicon defoamer is purchased from Jiangsu Sixin Technology Application Research Institute, model number DF-891.

[0025] According to a preferred embodiment of the present invention, the hydroxyethyl cellulose is purchased from Dandong Fine Chemical Co., Ltd., model number HEC-250.

[0026] According to a preferred embodiment of the present invention, the pH regulator is purchased from Angel Yeast Co., Ltd., model number AMP-95.

[0027] According to a preferred embodiment of the present invention, the deionized water is purchased from Hangzhou Wahaha Group Co., Ltd., and the model is Wahaha DI Water.

[0028] According to a preferred embodiment of the present invention, in step A1, the particle size of the α-alumina microspheres is 5-15 μm; the ultrasonic dispersion time is 25-30 min, and the frequency is 30-40 kHz; the polyethyleneimine accounts for 7-9% of the α-alumina mass of the microspheres; the stirring time at room temperature is 1-2 h, and the rotation speed is 200-400 rpm.

[0029] According to a preferred embodiment of the present invention, in step A2, polyacrylic acid is added dropwise accounting for 5-7% of the mass of the microspheres; the stirring time at room temperature is 1-2 hours, and the rotation speed is 200-400 rpm.

[0030] According to a preferred embodiment of the present invention, the preparation method of the fluorosilane-grafted magnesium silicate nanofibers includes: B1, adding anhydrous ethanol to the magnesium silicate nanofibers and ultrasonically dispersing them until they are uniform; adding ethyl orthosilicate and ammonia water to the dispersion, heating the mixture to 60-62°C for reaction; after the reaction is completed, filtering, washing with anhydrous ethanol, and vacuum drying to obtain silica-coated magnesium silicate nanofibers; B2, adding toluene to the silica-coated magnesium silicate nanofibers, ultrasonically dispersing them, adding γ-fluoropropyltrimethoxysilane dropwise, heating the mixture to 80-82°C for reflux reaction; after the reaction is completed, cooling to room temperature, filtering and collecting solid particles, washing with toluene, and vacuum drying.

[0031] In the preparation of the fluorosilane-grafted magnesium silicate nanofibers of the present invention, the magnesium silicate nanofibers are dispersed in anhydrous ethanol and then ultrasonically dispersed to uniformly disperse them and reduce agglomeration; when tetraethyl orthosilicate and ammonia water are added, the ammonia water acts as a catalyst to promote the hydrolysis of tetraethyl orthosilicate to generate silanol (Si-OH), which undergoes a condensation reaction with hydroxyl groups (-OH) on the fiber surface to generate a silica (SiO2) coating layer, which not only improves the dispersibility of the fiber but also provides a stable substrate for subsequent fluorosilane grafting; the silica-coated fiber is then added toluene, and ultrasonic dispersion is used to further uniformly disperse the particles; after γ-fluoropropyltrimethoxysilane is dropwise added, it is hydrolyzed in toluene to generate fluorosilanol (FAS-OH), which undergoes a condensation reaction with the silanol (Si-OH) on the silica surface to form a Si-O-Si bond, thereby stably grafting the fluorosilane to the fiber surface, improving the hydrophobicity of the fiber and the bonding strength with the polymer interface.

[0032] According to a preferred embodiment of the present invention, the magnesium silicate nanofiber is purchased from Jiangsu Xianfeng Nanomaterial Technology Co., Ltd., and the model number is XF-Nano-MgSiO3.

[0033] According to a preferred embodiment of the present invention, the anhydrous ethanol is purchased from Jiangsu Sopo Group, and the type is 99.5% anhydrous ethanol.

[0034] According to a preferred embodiment of the present invention, the tetraethyl orthosilicate was purchased from Hubei Xingfa Chemical Group with the model number of XH-TES.

[0035] According to a preferred embodiment of the present invention, the ammonia water is purchased from Shandong Hualu Hengsheng Chemical Co., Ltd. and is concentrated ammonia water (25-28%).

[0036] According to a preferred embodiment of the present invention, the toluene is purchased from Sinopec Shanghai Petrochemical Co., Ltd. and is AR grade toluene.

[0037] According to a preferred embodiment of the present invention, the γ-fluoropropyltrimethoxysilane is purchased from Zhejiang Xin'an Chemical Group Co., Ltd. with the model number ZQ-FAS-17.

[0038] According to a preferred embodiment of the present invention, in step B1, the particle size of the magnesium silicate nanofibers is 0.5-2 μm; the ultrasonic dispersion time is 30-40 min, and the frequency is 40-60 kHz; the tetraethyl orthosilicate accounts for 11-13% of the mass of the nanofibers; the ammonia water accounts for 1-3% of the mass of the tetraethyl orthosilicate; the reaction time is 2-4 h, and the rotation speed is 150-200 rpm; the number of washings with anhydrous ethanol is 3-4 times; the vacuum drying temperature is 60-62° C., and the drying time is 8-10 h.

[0039] According to a preferred embodiment of the present invention, in step B2, the ultrasonic dispersion time is 20-40 min, the frequency is 25-30 kHz; γ-fluoropropyltrimethoxysilane accounts for 4-6% of the fiber mass; the reflux reaction time is 4-6 h, the rotation speed is 200-400 rpm; the number of toluene washings is 2-4 times; the vacuum drying temperature is 80-82°C, and the time is 12-24 h.

[0040] The present invention also provides a method for preparing the modified thermal insulation coating, comprising the following steps:

[0041] S1. First, add the water-based polyurethane-acrylic hybrid emulsion into a high-speed disperser, and then add the thermosensitive polyelectrolyte layer-by-layer self-assembled alumina microspheres, fluorosilane-grafted magnesium silicate nanofibers and fumed silica in sequence, and stir to mix them preliminarily;

[0042] S2, then add polycarboxylate dispersant, silicone defoamer, hydroxyethyl cellulose and pH adjuster, and stir;

[0043] S3. Finally, adjust the coating viscosity to 7000-10000 mPa·s with deionized water, filter and package.

[0044] During the preparation of the coating of the present invention, each component is physically mixed by high-speed dispersion: the aqueous polyurethane-acrylic hybrid emulsion serves as the continuous phase, and the carboxyl groups (-COOH) on its molecular chain form weak bonds with the hydroxyl groups (-OH) and amino groups (-NH2) on the surface of the modified filler through hydrogen bonds or electrostatic interactions. At the same time, the dispersant (polycarboxylate) prevents filler agglomeration through electrostatic repulsion and steric hindrance, the defoamer (organic silicone) reduces the surface tension of the system and eliminates bubbles, and hydroxyethyl cellulose adjusts the viscosity to improve workability. Finally, large particle impurities are removed by filtration to ensure that the coating is fine and uniform, and maintains stable performance during storage and use after packaging. The synergistic effect of the dual modified fillers (dynamic thermal conductivity regulation of the temperature-sensitive layer and strong interfacial bonding of the fluorosilane grafting) and the synergistic effect of the additives together give the coating properties such as low thermal conductivity, high adhesion, and excellent weather resistance.

[0045] According to a preferred embodiment of the present invention, in step S1, the speed of the high-speed disperser is 300-400 rpm; the particle size of the fumed silica is 200-300 mesh, and the specific surface area is 200-250 m 2 / g; stirring time is 15-20min.

[0046] According to a preferred embodiment of the present invention, in step S2, the stirring speed is 800-1000 rpm, and the stirring time is 20-40 min.

[0047] According to a preferred embodiment of the present invention, in step S3, the filter screen size is 150-160 mesh.

[0048] The beneficial effects of the present invention are:

[0049] The modified thermal insulation coating described in the present invention has achieved significant breakthroughs in thermal insulation performance, interface bonding and environmental adaptability through the design of a double-modified filler system and a synergistic formula. Traditional thermal insulation coatings often face the problem of "insufficient thermal insulation at low temperatures and failure of thermal insulation at high temperatures" due to the surface inertness of the filler and the single thermal conductivity inhibition mechanism. The polyelectrolyte layer formed by electrostatic deposition of thermosensitive polyelectrolyte self-assembled alumina microspheres in the present invention can absorb water and swell in low temperature environments, increase the proportion of static air layers inside the coating, and enhance the thermal insulation effect; it dehydrates and shrinks in high temperature environments, reduces the heat conduction path, and dynamically adjusts the thermal conductivity coefficient, so that the coating maintains stable low thermal conductivity in a wide temperature range, effectively solving the technical bottleneck of poor environmental adaptability of traditional static thermal insulation coatings.

[0050] The synergistic effect of the dual-modified fillers further enhances the overall performance of the coating. Fluorosilane-grafted magnesium silicate nanofibers significantly reduce the coating's water absorption through the hydrophobic properties of the surface fluorosilane. Their high aspect ratio structure also forms a "physical barrier" within the coating, blocking the heat conduction path. The chemical bonding between the silane coupling agent and the polymer emulsion (such as ester and hydrogen bonds) increases the interfacial bonding strength between the filler and the matrix several times compared to traditional physically mixed fillers, effectively preventing cracking and shedding caused by thermal expansion and contraction. The coating's impact resistance and bonding strength are significantly improved, meeting the long-term use requirements of complex scenarios such as building exterior walls and industrial pipelines.

[0051] In addition, the overall formulation of the coating takes into account both construction-friendliness and environmental friendliness. As a film-forming substance, the waterborne polyurethane-acrylic hybrid emulsion not only provides good film-forming properties and flexibility, but also meets green building standards through its low VOC content. The addition of additives such as fumed silica adjusts the coating's thixotropy and anti-settling properties, allowing it to maintain uniformity under different construction methods, with a short surface drying time and high actual drying efficiency. At the same time, the polyelectrolyte layer of the temperature-sensitive microspheres and the hydrophobic layer of the fluorosilane synergistically resist UV aging, extending the coating's service life and significantly outperforming traditional commercially available thermal insulation coatings in terms of overall performance. DETAILED DESCRIPTION

[0052] The following specific implementation methods are only used to further illustrate the present application and should not be understood as limiting the scope of protection of the present application. Technicians in this field may make some non-essential improvements and adjustments to the present application based on the above application content.

[0053] 1. Implementation

[0054] Example 1

[0055] Preparation of thermosensitive polyelectrolyte layer-by-layer self-assembled alumina microspheres: 100 g of α-alumina microspheres with a particle size of 5-15 μm were added to deionized water and ultrasonically dispersed for 28 minutes (frequency 35 kHz) until uniform; the pH of the dispersion was adjusted to 9.5, 8 g of polyethyleneimine aqueous solution was added dropwise, and stirred at room temperature for 1.5 hours (speed 300 rpm) to allow polyethyleneimine to be deposited on the surface of the alumina microspheres to form a first polycation layer; then the pH was adjusted to 4.5, 6 g of polyacrylic acid aqueous solution was added dropwise, and stirred at room temperature for 1.5 hours (speed 300 rpm) to allow polyacrylic acid to be deposited to form a first polyanion layer; the above polyethyleneimine-polyacrylic acid deposition step was repeated 3 times to obtain thermosensitive polyelectrolyte layer-by-layer self-assembled alumina microspheres.

[0056] Preparation of fluorosilane-grafted magnesium silicate nanofibers: 100 g of magnesium silicate nanofibers with a particle size of 0.5-2 μm were added to anhydrous ethanol and ultrasonically dispersed for 35 minutes (frequency 50 kHz) until uniform; 12% of the weight of ethyl orthosilicate and 2% of the weight of ethyl orthosilicate were added to the dispersion, and the temperature was raised to 61° C. for reaction for 3 hours (speed 180 rpm); after the reaction was completed, the fibers were filtered, washed three times with anhydrous ethanol, and vacuum-dried at 61° C. for 9 hours to obtain silica-coated magnesium silicate nanofibers; the fibers were added to toluene and ultrasonically dispersed for 30 minutes (frequency 28 kHz), 5% of the weight of the fibers were dropwise added with γ-fluoropropyltrimethoxysilane, the temperature was raised to 81° C. for reflux reaction for 5 hours (speed 300 rpm); after the reaction was completed, the fibers were cooled to room temperature, the solid particles were collected by filtration, washed three times with toluene, and vacuum-dried at 81° C. for 18 hours to obtain fluorosilane-grafted magnesium silicate nanofibers.

[0057] Preparation of modified thermal insulation coating: 400g of waterborne polyurethane-acrylic hybrid emulsion was added into a high-speed disperser (speed 350rpm), and 200g of thermosensitive polyelectrolyte layer-by-layer self-assembled alumina microspheres, 150g of fluorosilane-grafted magnesium silicate nanofibers, and fumed silica (200-300 mesh, specific surface area 200-250m 2 / g) 80g, stirred for 18min; added polycarboxylate dispersant 10g, silicone defoamer 5g, hydroxyethyl cellulose 4g, pH adjuster 2g, stirred at 900rpm (30min); adjusted the coating viscosity to 8500mPa·s with deionized water, filtered through 155 mesh, and packaged.

[0058] Example 2

[0059] The specific implementation method is the same as Example 1, except that, for the preparation of thermosensitive polyelectrolyte layer-by-layer self-assembled alumina microspheres: 100 g of α-alumina microspheres (particle size 5-15 μm) were ultrasonically dispersed for 25 min (frequency 30 kHz), the pH was adjusted to 9.4, and a polyethyleneimine aqueous solution (accounting for 7% of the mass of the microspheres) was added dropwise, and stirred at room temperature for 1 h (speed 200 rpm); the pH was adjusted to 4.4, and a polyacrylic acid aqueous solution (accounting for 5% of the mass of the microspheres) was added dropwise, and stirred at room temperature for 1 h (speed 200 rpm), and the deposition step was repeated 4 times.

[0060] Preparation of fluorosilane-grafted magnesium silicate nanofibers: 100 g of magnesium silicate nanofibers (particle size 0.5-2 μm) were ultrasonically dispersed for 30 minutes (frequency 40 kHz), and tetraethyl orthosilicate (accounting for 11% of the mass of the nanofiber) and ammonia water (accounting for 1% of the mass of the tetraethyl orthosilicate) were added, and the reaction was carried out at 60°C for 2 hours (speed 150 rpm); after filtration, the mixture was washed three times with anhydrous ethanol and vacuum-dried at 60°C for 8 hours; toluene was added and ultrasonically dispersed for 20 minutes (frequency 25 kHz), and γ-fluoropropyltrimethoxysilane (accounting for 4% of the fiber mass) was added dropwise, and the mixture was refluxed at 80°C for 4 hours (speed 200 rpm); after filtration, the mixture was washed twice with toluene and vacuum-dried at 80°C for 12 hours.

[0061] Preparation of modified thermal insulation coating: 350g of waterborne polyurethane-acrylic hybrid emulsion was added to a disperser (300rpm), and 180g of thermosensitive polyelectrolyte layer-by-layer self-assembled alumina microspheres, 120g of fluorosilane-grafted magnesium silicate nanofibers, and 60g of fumed silica (200-300 mesh) were added in sequence and stirred for 15min; 8g of polycarboxylate dispersant, 3g of silicone defoamer, 3g of hydroxyethyl cellulose, and 1g of pH adjuster were added and stirred at 800rpm (20min); the viscosity was adjusted to 7000mPa·s with deionized water, and the mixture was filtered through a 150-mesh filter and packaged.

[0062] Example 3

[0063] The specific implementation method is the same as Example 1, except that, for the preparation of thermosensitive polyelectrolyte layer-by-layer self-assembled alumina microspheres: 100 g of α-alumina microspheres (particle size 5-15 μm) were ultrasonically dispersed for 30 min (frequency 40 kHz), the pH was adjusted to 9.6, and a polyethyleneimine aqueous solution (accounting for 9% of the mass of the microspheres) was added dropwise, and stirred at room temperature for 2 h (speed 400 rpm); the pH was adjusted to 4.6, and a polyacrylic acid aqueous solution (accounting for 7% of the mass of the microspheres) was added dropwise, and stirred at room temperature for 2 h (speed 400 rpm), and the deposition step was repeated 3 times.

[0064] Preparation of fluorosilane-grafted magnesium silicate nanofibers: 100 g of magnesium silicate nanofibers (particle size 0.5-2 μm) were ultrasonically dispersed for 40 minutes (frequency 60 kHz), and tetraethyl orthosilicate (accounting for 13% of the mass of the nanofibers) and ammonia water (accounting for 3% of the mass of the tetraethyl orthosilicate) were added, and the reaction was carried out at 62°C for 4 hours (speed 200 rpm); after filtration, the mixture was washed four times with anhydrous ethanol and vacuum-dried at 62°C for 10 hours; toluene was added and ultrasonically dispersed for 40 minutes (frequency 30 kHz), and γ-fluoropropyltrimethoxysilane (accounting for 6% of the fiber mass) was added dropwise, and the mixture was refluxed at 82°C for 6 hours (speed 400 rpm); after filtration, the mixture was washed four times with toluene and vacuum-dried at 82°C for 24 hours.

[0065] Preparation of modified thermal insulation coating: 450g of waterborne polyurethane-acrylic hybrid emulsion was added to a disperser (400rpm), and 250g of thermosensitive polyelectrolyte layer-by-layer self-assembled alumina microspheres, 180g of fluorosilane-grafted magnesium silicate nanofibers, and 100g of fumed silica (200-300 mesh) were added in sequence and stirred for 20min; 12g of polycarboxylate dispersant, 6g of silicone defoamer, 5g of hydroxyethyl cellulose, and 3g of pH adjuster were added and stirred at 1000rpm (40min); the viscosity was adjusted to 10000mPa·s with deionized water, and the mixture was filtered through a 160-mesh filter and packaged.

[0066] Comparative Example 1

[0067] The specific implementation method is the same as that of Example 1, except that the modified thermal insulation coating raw materials include: 400g of waterborne polyurethane-acrylic hybrid emulsion, 200g of ordinary alumina microspheres (particle size 5-15μm, not layered self-assembled), 150g of fluorosilane-grafted magnesium silicate nanofibers, 80g of fumed silica, 10g of a polycarboxylate dispersant, 5g of an organosilicon defoamer, 4g of hydroxyethyl cellulose, and 2g of a pH adjuster. The preparation method is the same as that of Example 1 (omitting the microsphere preparation step).

[0068] Comparative Example 2

[0069] The specific embodiment is the same as that of Example 1, except that the modified thermal insulation coating raw materials include: 400g of waterborne polyurethane-acrylic hybrid emulsion, 200g of temperature-sensitive polyelectrolyte layer-by-layer self-assembled alumina microspheres, 150g of magnesium silicate nanofibers (ungrafted with fluorosilane), 80g of fumed silica, 10g of a polycarboxylate dispersant, 5g of an organosilicon defoamer, 4g of hydroxyethyl cellulose, and 2g of a pH adjuster. The fluorosilane grafting step is omitted in the preparation method, and magnesium silicate nanofibers are used directly.

[0070] Comparative Example 3

[0071] The specific implementation method is the same as Example 1, except that the raw materials of the modified thermal insulation coating are: 300g of water-based polyurethane-acrylic hybrid emulsion, 200g of temperature-sensitive polyelectrolyte layer-by-layer self-assembled alumina microspheres, 150g of fluorosilane-grafted magnesium silicate nanofibers, 80g of fumed silica, 10g of polycarboxylate dispersant, 5g of silicone defoamer, 4g of hydroxyethyl cellulose, and 2g of pH regulator.

[0072] 2. Performance Testing

[0073] The materials prepared in Examples 1-3 and Comparative Examples 1-3 were tested for performance according to the following method:

[0074] 1. Thermal conductivity test: According to GB / T 10294-2008 "Insulating materials - Determination of steady-state thermal resistance and related properties - Guarded hot plate method", the coating was applied to a 300mm×300mm×20mm aluminum plate (dry film thickness 100±10μm), and after curing for 7 days, a specimen was made. The steady-state thermal conductivity was measured using the guarded hot plate method in a constant temperature environment of 25℃ (test conditions: hot plate temperature 35℃, cold plate temperature 5℃, sample thickness 10mm).

[0075] 2. Weathering test: According to GB / T 1865-2009 "Paints and varnishes - Artificial weathering and artificial radiation exposure (filtered xenon arc radiation)", the sample is placed in a UV aging box with an irradiance of 0.89W / (m 2 ·nm) (340nm wavelength), blackboard temperature 65℃, condensation cycle 4h water spray / 4h drying, after 500h aging, test the thermal conductivity change rate ((thermal conductivity after aging - thermal conductivity before aging) / thermal conductivity before aging × 100%) and surface appearance (color change level according to GB / T 11186.2-1989, chalking level according to GB / T 11186.3-1989).

[0076] 3. Adhesion test: According to GB / T 9286-1998 "Cross-cut test for paints and varnishes", apply the sample to a tinplate (dry film thickness 50±5μm). After curing for 7 days, use a cross-cut tool (1mm spacing) to cross-cut the surface of the sample, covering 6×6 squares. Apply transparent tape and then tear it off. Observe the area of ​​shedding and grade it on 1-5 levels (Level 1: no shedding; Level 2: <5% shedding; Level 3: 5%-15% shedding; Level 4: 15%-35% shedding; Level 5: >35% shedding).

[0077] 4. Pencil hardness test: According to GB / T 6739-2006 "Paints and varnishes - Determination of film hardness by pencil method", use a Mitsubishi pencil (load 750g) to scratch the surface of the specimen (dry film thickness 50±5μm) at a 45° angle. Record the highest pencil hardness that does not scratch the surface (pencil hardness scale: 9H (hardest) - 9B (softest)).

[0078] 5. Application viscosity test: According to GB / T 9751-1988 "Determination of viscosity of coatings at high shear rates", use a rotational viscometer (model: NDJ-8S, rotor: 4#, speed 60rpm) to measure the initial viscosity of the coating (undiluted) and the application viscosity (mPa·s) after dilution with water by 10% at 25°C.

[0079] 6. Performance test results:

[0080] Table 1: Performance test results of various embodiments and comparative examples

[0081]

[0082]

[0083] As can be seen from Table 1, Examples 1-3 effectively solved the core problem of existing thermal insulation coatings caused by filler surface inertness and weak bonding with polymers through filler surface modification, which is specifically manifested as follows:

[0084] In terms of thermal conductivity, the thermal conductivity of Examples 1-3 (0.030-0.035 W / (m·K)) is significantly lower than that of Comparative Examples 1-3 (0.038-0.043 W / (m·K)). This is because the temperature-sensitive polyelectrolyte layer-by-layer self-assembled alumina microspheres are formed by alternating deposition of polyethyleneimine (PEI) and polyacrylic acid (PAA) to form a multilayer structure, which increases the polarity and reactivity of the filler surface, and forms stronger hydrogen bonds or electrostatic effects with the polar groups (such as carboxyl and hydroxyl) of the aqueous polyurethane-acrylic hybrid emulsion, thereby reducing the interfacial thermal resistance between the filler and the polymer; at the same time, the fluorosilane-grafted magnesium silicate nanofibers introduce hydrophobic groups through fluorosilane grafting, and the silane coupling agent reacts with the hydroxyl groups of the polymer matrix to form chemical bonds, further reducing the interfacial heat conduction efficiency, thereby significantly reducing the thermal conductivity.

[0085] Regarding the problem of coating shedding, the adhesion of Examples 1-3 is all level 1 (no shedding), which is much better than that of Comparative Examples 1-3 (levels 2-4). This is because the surface treatment of the modified filler enhances the interfacial bonding force with the polymer: the multilayer polyelectrolyte structure of the thermosensitive polyelectrolyte self-assembled alumina microspheres is tightly adsorbed with the polymer through electrostatic action, and the silane coupling agent of the fluorosilane grafted magnesium silicate nanofibers forms a covalent bond with the polymer. The two work together to form a stable interface layer between the filler and the polymer matrix, avoiding interfacial debonding caused by the inertness of the filler surface, thereby preventing the coating from shedding.

[0086] In terms of weather resistance, after aging for 500 hours, the thermal conductivity change rates of Examples 1-3 were all negative (-1.8% to -2.5%), and the discoloration and powdering levels were both level 1 (no discoloration, no powdering). However, the thermal conductivity change rates of Comparative Examples 1-3 were positive (Comparative Example 1 +1.2%, Comparative Example 3 +3.2%), and the discoloration and powdering levels were higher (Comparative Example 1 had a discoloration level of 2 and a powdering level of 1; Comparative Example 3 had a discoloration level of 3 and a powdering level of 2). This is because the surface treatment of the modified filler enhances the coating's resistance to environmental erosion: the multilayer structure of the thermosensitive polyelectrolyte self-assembled alumina microspheres can buffer the penetration of external moisture and oxygen, and the fluorosilane groups of the fluorosilane-grafted magnesium silicate nanofibers are hydrophobic and weather-resistant. The two synergistically inhibit damage to the interface from environmental factors such as ultraviolet rays and humidity, reducing aging degradation of the heat conduction path, thereby maintaining the long-term stability of the coating.

[0087] In summary, Examples 1-3 effectively improved the interfacial bonding between the filler and the polymer through filler surface modification (thermosensitive polyelectrolyte layer-by-layer self-assembly and fluorosilane grafting), solved the problems of easy peeling of the coating, high thermal conductivity and poor weather resistance caused by the surface inertness and weak bonding force of the filler in existing coatings, and achieved a synergistic improvement in thermal insulation performance, mechanical properties and weather resistance.

[0088] The above-described embodiments merely illustrate several implementations of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, and all such variations and improvements fall within the scope of protection of the present invention.

Claims

1. A modified thermal insulation coating, characterized in that: The composition comprises the following raw materials in parts by weight: Waterborne polyurethane-acrylic hybrid emulsion: 350-450 parts by weight; Thermosensitive polyelectrolyte layer-by-layer self-assembled alumina microspheres: 180-250 parts by weight; Fluorosilane-grafted magnesium silicate nanofibers: 120-180 parts by weight; Fumed silica: 60-100 parts by weight; Polycarboxylate dispersant: 8-12 parts by weight; Silicone defoamer: 3-6 parts by weight; Hydroxyethyl cellulose: 3-5 parts by weight; pH regulator: 1-3 parts by weight; The preparation method of the thermosensitive polyelectrolyte layer-by-layer self-assembled alumina microspheres includes: A1, adding α-alumina microspheres to deionized water and ultrasonically dispersing them until they are uniform; adjusting the pH of the dispersion to 9.4-9.6, adding a polyethyleneimine aqueous solution, stirring at room temperature, and allowing the polyethyleneimine to be deposited on the surface of the alumina microspheres to form a first polycation layer; A2, subsequently adjusting the pH to 4.4-4.6, adding a polyacrylic acid aqueous solution, stirring at room temperature, and allowing the polyacrylic acid to be deposited to form a first polyanion layer; and repeating the polyethyleneimine-polyacrylic acid deposition step 3-4 times.

2. The modified thermal insulation coating according to claim 1, characterized in that: In step A1, the particle size of the α-alumina microspheres is 5-15 μm; the ultrasonic dispersion time is 25-30 min, the frequency is 30-40 kHz; the polyethyleneimine accounts for 7-9% of the α-alumina mass of the microspheres; the stirring time at room temperature is 1-2 h, and the rotation speed is 200-400 rpm.

3. The modified thermal insulation coating according to claim 1, characterized in that: In step A2, polyacrylic acid is added dropwise at a concentration of 5-7% of the mass of the microspheres; the stirring time is 1-2 hours at room temperature and the rotation speed is 200-400 rpm.

4. The modified thermal insulation coating according to claim 1, characterized in that: The preparation method of the fluorosilane-grafted magnesium silicate nanofibers comprises the following steps: B1, adding anhydrous ethanol to the magnesium silicate nanofibers, and ultrasonically dispersing the magnesium silicate nanofibers until uniform; adding ethyl orthosilicate and ammonia water to the dispersion, and heating the dispersion to 60-62° C. for reaction; after the reaction, filtering, washing with anhydrous ethanol, and vacuum drying to obtain silica-coated magnesium silicate nanofibers; B2, adding toluene to the silica-coated magnesium silicate nanofibers, and ultrasonically dispersing the magnesium silicate nanofibers, and dropwise adding γ-fluoropropyltrimethoxysilane, and heating the dispersion to 80-82° C. for reflux reaction; after the reaction, cooling the dispersion to room temperature, filtering and collecting solid particles, washing with toluene, and vacuum drying.

5. The modified thermal insulation coating according to claim 4, characterized in that: In step B1, the particle size of the magnesium silicate nanofibers is 0.5-2 μm; the ultrasonic dispersion time is 30-40 minutes, the frequency is 40-60 kHz; the ethyl orthosilicate accounts for 11-13% of the mass of the nanofibers; the ammonia water accounts for 1-3% of the mass of the ethyl orthosilicate; the reaction time is 2-4 hours, and the rotation speed is 150-200 rpm; The number of washings with anhydrous ethanol is 3-4 times; the vacuum drying temperature is 60-62° C., and the drying time is 8-10 hours.

6. The modified thermal insulation coating according to claim 4, characterized in that: In step B2, the ultrasonic dispersion time is 20-40 minutes, the frequency is 25-30 kHz; the γ-fluoropropyltrimethoxysilane accounts for 4-6% of the fiber mass; the reflux reaction time is 4-6 hours, the rotation speed is 200-400 rpm; the number of toluene washings is 2-4 times; the vacuum drying temperature is 80-82°C, and the time is 12-24 hours.

7. A method for preparing the modified thermal insulation coating according to any one of claims 1 to 6, characterized in that the steps include: S1. First, add the aqueous polyurethane-acrylic hybrid emulsion into a high-speed disperser, and then add the thermosensitive polyelectrolyte layer-by-layer self-assembled alumina microspheres, fluorosilane-grafted magnesium silicate nanofibers and fumed silica in sequence, and stir to mix them preliminarily; S2, then add polycarboxylate dispersant, silicone defoamer, hydroxyethyl cellulose and pH regulator, and stir; S3. Finally, adjust the coating viscosity to 7000-10000 mPa·s with deionized water, filter and package.

8. The preparation method according to claim 7, characterized in that In step S1, the speed of the high-speed disperser is 300-400 rpm; the particle size of the fumed silica is 200-300 mesh, and the specific surface area is 200-250m 2 / g; stirring time is 15-20min.

9. The preparation method according to claim 7, characterized in that In step S2, the stirring speed is 800-1000 rpm, and the stirring time is 20-40 min.

10. The preparation method according to claim 7, characterized in that In step S3, the filter screen size is 150-160 mesh.

Images