Wu Bing 1, Hai Jing 2, Pi Yihui 1, Cheng Jiang 1, Yang Zhuoru 1
(1.School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou 510640, Guangdong, China; 2. South China Institute of Environmental Science, Guangzhou 510655, China)
Abstract: Nano-tin oxide (ATO) and other particles are an n-type semiconductor material. The film made of it has a very high infrared shielding effect and a good visible light transmittance. The application of nano-ATO in coatings can produce transparent glass thermal insulation coatings with extremely high application value. This article introduced the thermal insulation mechanism of nano-insulation coatings, and reviewed the research status of transparent thermal insulation coatings and the preparation methods of nano-thermal insulation composite coatings.
Keywords: thermal insulation coating; tin oxide antimony; nano-particles; glass; energy-saving CLC: TQ637 Document code: A
Article ID: 1004–227X(2011)12–0067–06
1. Preface At present, the exploration of energy conservation and new energy has become an important issue in the world. Building energy consumption accounts for 30% to 40% of the total human energy consumption. Most of them are energy consumption caused by heating and air conditioning, and heat lost through doors and windows accounts for the entire building heating and air conditioning energy consumption. 50%. Therefore, improving the thermal insulation performance of doors and windows is an effective way to reduce building energy consumption [1]. In order to save energy, people have invented energy-saving methods such as heat-reflecting glass, insulating glass, and heat-reflecting glass film. These are all aimed at blocking the excess heat radiation in sunlight and achieving cooling. However, some of these products have poor thermal insulation, some have low visible light transmittance, and some are too expensive, making them difficult to apply and promote. Due to the nature of nanomaterials that are not possessed by macroscopic objects, nanomaterials have become a hot topic for the development of novel coatings with unexpected effects. It has been found that n-type semiconductor materials with wide energy gaps, such as indium tin oxide (ITO), antimony tin oxide (ATO), aluminum doped zinc oxide (AZO), have similar optical properties, ie, high in the infrared region. The reflectance, high transmittance in the visible light region, and high absorptivity in the ultraviolet region are ideal transparent heat insulating materials. Applying this nanoparticle to a coating can produce a functional coating that has both transparency and infrared cut off. This article introduced the heat insulation mechanism, research progress, existing problems and solutions of glass thermal insulation coatings.
2. The thermal insulation mechanism of nano-tin oxide tin oxide and the spectral energy distribution of solar thermal radiation coating on the surface of the earth are: 200-380 nm in the ultraviolet region, 5% of the total energy; 380-780 nm in the visible region, accounting for the total 45% of the energy; near infrared region 780 ~ 2500nm, 50% of the total energy. Therefore, the energy of the solar spectrum is mainly concentrated in the visible and near-infrared regions. The nano-semiconductor heat insulation effect is related to its own physical structure on the one hand and particle size of its powder particles on the other hand. Normally, only nano-sized semiconductors can play a role in transparent heat insulation [2]. Tin oxide, antimony, and other particles are high-density, free-electron gas-type materials whose free carriers can excite plasma vibrations similar to those of gas plasmas. Therefore, doping semiconductors can increase their current-carrying capacity. The concentration of the sub-particles allows the doped semiconductor to have strong absorption of ultraviolet rays in the solar spectrum, transparency to visible light, and reflection of infrared rays [3]. The doping of semiconductors generally has two methods: one is doping of high-valence metals, and donor impurities are formed in an alternate manner, such as pentavalent Sb-doped semiconductor SnO2, Sn-doped semiconductor In2O3, etc.; and the other doping is non-metal. Element F substitutes for O to produce an electron donor to increase semiconductor carrier concentration, such as F-doped semiconductor SnO2. At present, widely used semiconductors in transparent heat insulation functional fillers include zinc oxide, indium oxide, tin oxide, cadmium oxide and their doping systems [4].
Huang Baoyuan et al. [5] found that the thermal insulation of sunlight by ATO nano-coatings is mainly due to its absorption of near-infrared light (average absorption rate of 86%, only 4.5% reflection). He Qiuxing et al. [6] studied that the heat insulation of nanoparticles is based on the absorption of infrared light. Other scholars [7-9] have studied the effect of nanoscale semiconductor particle size, doping and other factors on spectral selectivity, and achieved certain results, but have not yet formed a unified conclusion.
Nano-insulation coating is mainly used for energy-saving form, it can also be used in many fields, such as: (1) applied to windshields and building glass of automobiles, trains, and airplanes, and played a very good role in heat insulation and cooling , And no reflection of light pollution; (2) coated on glass, made of nano-transparent heat insulating glass, including single-layer glass, hollow glass and laminated glass; (3) coated on a transparent resin such as polycarbonate made of nanometer Transparent insulation board, its application is very wide, such as can be made on the top of the bus station transparent insulation board, etc.; (4) coated in polyester film, made of transparent heat insulation film, used in construction and automotive window glass [10].
3. Research status of transparent thermal insulation coatings The key to the preparation of transparent thermal insulation coatings is the selection of nano-semiconductor materials that are selective for the solar spectrum. Currently, these materials are mainly nano-silicon tin oxide (ATO) and indium tin oxide (ITO). . Among them, ATO has become a market acceptable product due to its relatively low cost.
3.1 Methods for Synthesizing Insulating Nanoparticle Powders At present, there are many researches on insulating nanoparticle powders at home and abroad. The synthesis methods of these nanosemiconductor powders mainly include coprecipitation method, hydrothermal method, sol-gel method, Solid phase method.
3.1.1 Co-precipitation method The co-precipitation method is to mix substances of different chemical composition in the solution state, add appropriate precipitant to the mixed solution to precipitate the metal cation coexisting in the solution, and then wash, dry or forge the precipitate. Burn to obtain the corresponding nano-powder. J. P. Coleman et al [11] used SnCl4 · 5H2O solution, and then mixed with the corresponding amount of SbCl5 and strong **, followed by NaOH solution, so that the end point of pH 2, after filtration and washing the filter cake vacuum dried at 60 °C , and calcined at 600 °C for 3 h, followed by rapid cooling in air to obtain ATO ultrafine powder. Kim et al. [12] used SnC14·5H2O and SbCl3 as raw materials, methanol as the medium, and ** as precipitant to obtain nano-ATO micro-powders without hard agglomeration and low-soft agglomeration, and discussed the use of methanol in low-agglomeration nano-ATO particles. Formation and important role of precursor particles in anti-agglomeration. This study shows that the lower surface tension of methanol than water is a key factor in eliminating the hydrogen bonding and capillary action between the precursor particles, which prevents the formation of hard agglomerations due to bridging during drying and sintering. The process replaces water with methanol as the reaction medium, eliminating the adverse effects of water as a medium, such as hydrogen bonds, but the disadvantage is that methanol is flammable, explosive, and expensive than water. However, by optimizing the process, fully recovering the solvent and improving the safety of production, the process should have a good industrialization prospect. Overall, the co-precipitation method is a convenient method for preparing nano-ATO particles. It has the advantages of simple preparation process, easy preparation of preparation conditions, short synthesis cycle, low cost, and is easy for industrial production. However, the powder prepared by this method is easy to agglomerate, and the particle size distribution range is wide.
3.1.2 Hydrothermal method The hydrothermal method is a special closed reaction vessel in which an aqueous solution is used as a reaction medium. By heating the reactor, a high-temperature, high-pressure reaction environment is created, so that substances that are generally insoluble or insoluble dissolve and are heavy. A method of making a powder that crystallizes. Bai et al. [13] used SnC12·5H2O and SbCl2 as starting materials to synthesize a monodispersed ATO suspension in one step at a temperature of 100 to 350°C using a programmed temperature program.
The results showed that the particle size of the ATO particles was 10 to 15 nm and the particle size distribution was narrow. The temperature-programmed process improves the doping level of Sb, and monodisperse doped oxide particles at lower temperatures are achieved.
Feng Bo et al [14] prepared nanometer ATO powders by hydrothermal method and found that the doping concentration was 11%, the hydrothermal reaction temperature was 180°C, the reaction pressure was 1 MPa, the heat treatment temperature was 700°C, and the heat treatment time was 2 hours. Under the conditions, the prepared nano-ATO powders have the best performance and the grain size is about 20nm. Zhang Jianrong et al.[15] used stannous oxalate and bismuth potassium tartrate as raw materials to synthesize nanostructured and monodisperse ATO in one step at 260°C using a high-temperature hydrothermal method, which eliminated the disadvantages of severe agglomeration of powders that are difficult to overcome by other methods. .
3.1.3 Sol-gel method The basic principle of the sol-gel method is to directly form a metal olate or inorganic salt by hydrolysis to form a sol or decondense to form a sol, then gel the solute polymer, and then dry the gel. Roasting to remove organic components, the basic reaction of the reaction of hydrolysis and polymerization. The method can prepare single- or multi-component mixtures with high purity, uniform particle size distribution and high chemical activity (up to molecular-level mixing) at a low temperature, and can prepare products that cannot be or can not be prepared by traditional methods, and is particularly suitable for preparing non-products. Crystalline material.
The sol-gel method is an effective method for synthesizing ultrafine particles, but some properties of the colloids prevent the formation of ultrafine particles. Especially in the dehydration, often due to the presence of surface tension, the pore structure collapses, the particles agglomerate, and the particle size becomes large. Gong Sheng et al [16] used inorganic salts SnCl4·5H2O and SbCl3 as raw materials and ethanol as solvent to prepare porous, well-doped, tetragonal structures using sol-gel method combined with supercritical fluid drying (SCFD) technology. The nano-ATO particles have a particle size of 15 to 30 nm and have good dispersibility. Xu Lijin et al [17] prepared ATO powders by sol-gel method, and studied the effects of heat treatment time, calcination temperature, and cerium ion concentration on the powders.
3.1.4 Solid phase method The solid phase method is to fully mix the powder raw materials in a certain proportion, ball mill, sieving and calcining to obtain new phase powder materials. Bernardi et al. [18] used the solid phase method to directly mix the analytically pure SnO2 and Sb2O3 sold in the market, ultrafine grinding, and then heat treatment at a temperature of 800-1200 DEG C to obtain a gray ATO powder. It was found that the prepared nanopowders have low reactivity and must be calcined above 1000°C to obtain single-phase ATO nanoparticles. The solid-phase doping method is simple and convenient, but it consumes large amounts of energy. At the same time, the high temperature often causes serious volatilization and segregation of the components, and the product has a large grain size and irregular morphology.
In addition to the above method, D. W. Jung et al. [19] used SnCl4 and SbCl5 as raw materials at room temperature and atmospheric pressure to prepare nano ATO powders by DC arc plasma spraying. By controlling the doping amount of Sb in the ATO particles and according to the optimum process conditions, ATO particles having an average particle diameter of 19 nm were prepared.
3.2 Preparation of Nanoparticle Slurry The dispersion and stabilization of nano-ATO in the coating system is the key to the development of transparent and heat-insulating nano-coatings. The research in this area is mainly focused on the preparation of nano-sized slurry. East China University of Science and Technology studied the preparation of ATO slurry, discussed the mechanism of slurry stability and the use of dispersants, but the stability of the prepared ATO slurry is not good, the storage period is generally only 2 to 3 months, Mainly used in fabric anti-static and other aspects [20-21].
Li Yanfeng et al [22] chose different coupling agents to modify the surface of nano-ATO powders, and selected the KH570 coupling agent with better modification effect, and obtained the effect of the amount, reaction time and reaction temperature on surface modification. Impact.
Cai Zhaojun et al. [23] studied the influence of pH, type of dispersant, and added amount on the dispersion stability of ATO aqueous slurries, and finally prepared nano ATO slurries with good dispersivity and stability. Nanoparticles have large surface tension and are prone to agglomeration. Therefore, in dispersing the nanoparticle slurry, a high-speed grinding and dispersing method is generally used to disperse aggregated microparticles. In addition, the dispersed nanoparticles must also have good dispersion stability. For this reason, it is necessary to select a dispersant that is compatible with the system, and the dispersant is bonded to the surface of the microparticles so that repulsive forces are generated between the microparticles, and then the microparticles are stabilized by electrostatic repulsion or steric hindrance. In addition, the surface modification of the particles in advance, the surface of the particles coated with a low molecular weight surfactant or polymer stabilizer, or using other dispersion methods (such as ultrasonic dispersion, etc.), is also worth studying.
3.3 Preparation of Nano Thermal Insulation Coatings In the preparation and development of nano thermal insulation coatings, the United States and Japan started early in the research and development of transparent thermal insulation nano coatings, and are in the front rank of the world. Their research results are mostly published in the form of patents. In the first half of 2000, Nanophase Technologies of the United States prepared indium tin oxide nanoparticles with a particle size of 11 to 44 nm by a physical vapor-phase synthesis method, and a stable and dispersed nano-sized indium tin oxide powder slurry was prepared. The paste can be directly applied to the paint, but its price is higher, and the price per kg is up to 2,000 US dollars. American AirProducts also produces nano-ATO and ITO sols. WO 00/09446, published by World Intellectual Property Organization, describes a method for preparing a nano-sized indium tin oxide aqueous dispersion and a transparent conductive coating prepared using the slurry. Takeda et al [24] prepared a coating film capable of blocking solar heat radiation by incorporating ATO, ITO, or LaB6 in a resin matrix. The film has high transmittance in the visible light region and low light transmittance in the near infrared region. . Japan ** company developed a high-performance coating that can filter solar radiation without affecting daylighting. At present, the paint has been widely used in Japan to reduce energy consumption in building glass. After coating, ordinary glass can reduce 68% of infrared rays and 95% of ultraviolet rays without affecting the lighting conditions [25]. Chonan and Kuno [26] mixed ATO insulation paste with acrylic ultraviolet (UV) curable resin to produce thermal insulation coating, which was coated on PET film and baked at 80°C for 30s. Then, the heat-insulating coating is cured by ultraviolet irradiation, and the resulting coating has a solar radiation transmittance of less than 56.5%.
Nishihara et al [27] prepared nanometer ATO and ITO by co-precipitation method, and compounded with synthetic resin to obtain a transparent heat insulation coating with a light transmittance of more than 80% in the visible light region and very low transmittance in the near-infrared region. Kaneko et al. [28] used a composite coating formed of inorganic semiconductor nano-powders SnO2, ITO, ATO and polyacrylate, and had almost no absorption in the visible region, which has a good barrier effect to solar radiation.
In recent years, domestic companies and research institutes have also done many useful explorations in the preparation of nano-insulation coatings. Professor Zhao Shilin of Nanjing University of Technology conducted research on transparent thermal insulation coatings earlier, including the development of ATO and ITO thermal insulation coatings, and achieved certain research results[29-30]. Beijing Guobang uses inorganic alcohol-soluble transparent resin as a film forming material and mixes it with well-dispersed nano-scale conductive oxide (TCO) to obtain a transparent and heat-insulating coating with a visible light transmittance of 75%. The infrared blocking rate can reach 72%. The transparent heat-insulating paint for glass used by Runhe Technology is a blue water-based paint with a low viscosity (viscosity <100 Pa·s). The construction method is simple. It is coated by a shower coating method, and is placed at room temperature after coating. After about 15 minutes, dry [31-32]. In 2005, Jiangsu Chenguang Coatings Co., Ltd. [33-34] developed a glass-nano-transparent heat-insulation paint with a light transmittance of over 75% in the visible light region, an infrared shielding ratio of over 61%, and energy-saving retrofit at CCTV. The use of the 2000m2 window glass in the main building can save energy by 20% to 30%. Shanghai Huzheng Nano Technology Co., Ltd. [35] also has water-based and oil-based transparent thermal insulation coatings on the market.
According to reports, the visible light transmittance is 75% to 89%, the ultraviolet shielding rate is 95%, and the infrared blocking ratio is higher than 75%, and the temperature difference is 6 to 12°C. The transparent heat insulation coating produced by Shenzhen Donner Technology Co., Ltd. [36] has a visible light transmittance of 75%, an ultraviolet shielding ratio of 99%, and an infrared blocking rate of 75%. The company also developed a transparent insulating glass coating. Yao Chen et al. [10] developed a nano-transparent thermal insulation coating and compared it with a highly transparent and low-transparent LOW-E glass. It was found that the coating film has good solar spectral selectivity, and the transmittance in the visible light region is 78%, the infrared blocking rate is 61%. At present, more and more companies are engaged in the preparation of ATO and other nano-powders and their dispersions and nano-insulation coatings, which lays a good foundation for the development of thermal insulation coatings. However, there is still a long way to go before marketization. .
4. Preparation of Nano-Insulation Composite Coatings There are four main methods for the preparation of nano-insulating composites: in-situ polymerization, blending, sol-gel, and intercalation [3,37-38].
4.1 In-situ Polymerization This method first disperses the nanoparticles in the monomer solution and then polymerizes the monomers. The reaction conditions of this method are mild, and the particles are uniformly dispersed in the monomers, but their use has greater limitations. Because the method is only suitable for in-situ polymerization of monomer molecules in a solution containing metal, ruthenium or hydroxide colloidal particles to prepare nanocomposite coatings.
In addition, in-situ polymerization generally requires surface modification of the particles. Commonly used as surface modifiers are organic acids, coupling agents, surfactants, hyperdispersants, polymers, and the like. When choosing a surface modifier, observe the following principles: The surface modifier must have good bonding ability with the surface of the nanoparticles, must have good wetting behavior with the solvent and have good compatibility with the resin. Only comprehensive consideration of these three factors can obtain the best surface modifier suitable for nano-coating systems. Erdem et al [39] added TiO2 particles to a mixture of styrene and stabilizer OIOA370, ultrasonically dispersed to obtain droplets of microemulsions containing inorganic particles, followed by polymerization, and the inorganic particles could be partially coated. Hu Jinwei et al. [40] studied the preparation of polyurethane-titania water-dispersed composites (PU-TiO2) using polyurethane (PU), tetrabutyl titanate (TNB), triethylamine and ethanol as the main raw materials and in situ polymerization. The particle size distribution and distribution of the dispersion and the surface morphology of the PU-TiO2 composite film were observed and characterized. The results show that the PU-TiO2 water-dispersed composite has good stability and optical transparency.
4.2 Sol-gel method The sol-gel technique is a process in which a metal organic compound, a metal inorganic compound, or a mixture of the two are subjected to a hydrolytic polycondensation process, and then subjected to gelation or a corresponding post-treatment to obtain an oxide or other compound. Technology [41]. In general, alkoxy organosilanes and metal alkoxides are used as raw materials, under the action of a catalyst, they are hydrolytically condensed to form transparent colloidal dispersions, and additives such as pigments and fillers can be added, and can be applied at lower temperatures after coating. Cured film. The main reaction process can be divided into mixing, gelation, aging and drying.
4.3 Blending The blending method is to physically disperse the nanoparticles directly into the film by physical means. The advantage of this method is that it is easy to control the size and morphology of the particles. The disadvantage is that it is difficult to solve the problem of agglomeration of nanoparticles, that is, it is difficult to ensure uniform dispersion of nanoparticles in the polymer matrix. Most nanomaterials have a high surface energy and can adsorb and react with foreign substances (such as water) to form a surface hydroxy layer [42]. The hydrophilic and oleophobic nature of the hydroxyl layer can easily lead to poor compatibility of the nanomaterial with the coating, thereby seriously affecting its dispersion and stability in the coating. Therefore, the surface modification of nano-materials, change its surface state, and improve the compatibility with the coating, is the key to the preparation of insulating nano-composite coatings.
Research progress on nano-insulation coatings for glass Chen Feixia et al. [43] found that transparent thermal insulation coating prepared with nano-ITO dispersed well in super-water dispersion has good spectral selectivity and visible light transmittance. Up to 80%, and most of the infrared light is effectively blocked. Gu Guangxin et al[44] prepared a vanadium dioxide powder with room-temperature phase transformation function by doping tungsten, and used a special grinding process to disperse the tungsten-doped vanadium dioxide powder and the powder of antimony tin oxide (ATO) into Asia. Nano or nano-sized slurries, and these slurries are added directly to the water-borne polyurethane coatings to obtain transparent heat-insulation coatings with certain intelligent functions. The paint has good adhesion to the glass and its near infrared transmittance is adjustable.
4.4 Intercalation Compounding Many inorganic materials (such as silicate clay) have a layered structure that can be embedded in organic matter. The monomer or polymer is inserted between the sheet layers by a suitable method, and then the sheet structure matrix unit having a thickness of 1 nm and a width of about 100 nm is peeled off to uniformly disperse in the polymer, thereby realizing the polymer and the inorganic layer material. Compounding on the nanoscale. This method is only applicable to layered inorganic materials such as montmorillonite. Intercalation polymerization can be further divided into in-situ intercalation, solution intercalation and melt intercalation. In the case of in-situ intercalation polymerization, for example, in-situ intercalation refers to the fact that the monomers are pre-intercalated into the inorganic structure of the layered structure and then polymerized to form a hybrid material, such as inserting the monomer or intercalating agent into the layer. The mica-like silicate in the structure (sheet thickness is about 1 nm, and the lamellar spacing is generally between 0.96 and 2.10 nm), after which the monomers are polymerized into macromolecules between silicate sheets. During this process, the lamellae were further expanded to dissociate so that the layered silicate fillers were dispersed in the polymer matrix to a nanometer size, thereby obtaining a nanoscale composite [45]. Yang Jintao et al.[46] used cation-surfactant octadecyltrimethylammonium bromide (STAB) copolymerized with styrene as intercalation agent to modify montmorillonite (VC18-MMT), and organic montmorillonite. Pre-dispersed in the emulsifier solution under the ultrasonic strong shearing action and emulsifier, and then introduced styrene monomer in situ emulsion polymerization to prepare a polyethylene/montmorillonite nanocomposite.
5. Application prospects and existing problems and countermeasures Compared with common coating films, nano transparent heat-insulation coating film not only has significantly improved mechanical mechanical properties, but also has excellent anti-aging and anti-corrosion properties, plus high transparency and thermal insulation properties. It is characterized by good quality and low price, so it has extremely high application value and broad market prospects. Nano thermal insulation coatings have become a hot topic at home and abroad in recent years, and have also achieved considerable results. However, domestic research on nano-insulation coatings started late and there is still some distance from industrialization. At present, there are still the following issues related to thermal insulation nano-coatings:
(1) Development of nano-ATO powders and dispersions. The agglomeration of nano-ATO itself and the dispersion in the media are the biggest difficulties for industrial applications. Although there are many literatures on the preparation and application of nano-ATO, there are few reports on the dispersion and surface modification of nano-ATO. The exploration of practical and feasible technologies that can solve the problem of ATO powder agglomeration is very important for solving the difficult application of nano ATO.
(2) The biggest problem with nano-coatings is the dispersion and stability of nano-particles. Coating is a very complicated multi-phase dispersion system consisting of four parts: film forming substance, solvent, pigment, filler, etc. The dispersion stability of nanoparticles in coatings is not only related to the dispersion method, but also related to the surface modification of nanoparticles. Therefore, according to different coating requirements, choose nanoparticles and resins, and select the appropriate dispersion method for the system.
(3) The coating has low viscosity. In China, the nano-insulation coating is generally produced by a blending method, ie, the nano-particle slurry and the resin are separately developed, and then the two are blended; and in order to maintain sufficient stability, the nano-paste is generally added very little, and the stabilizer needs to be added. Thickeners and other additives. Therefore, the obtained coating has a low viscosity and is not convenient for construction.
(4) The hardness and water resistance of the coating are poor.
At present, the domestic common nanoparticle slurry is dispersed in alcohols or water by nano-particles, the slurry is generally alkaline, and the resin with which the compound is mainly acrylic resin or amino resin and other acidic resin, therefore, Poor composition results in poor film hardness and poor water resistance. In areas with high rainfall, the use of paint is limited.
(5) Nanoparticle testing technology needs to be improved. In characterizing the particle size and distribution of nanopigments, gravitational settling, low-angle laser diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM), laser particle size analyzers, and atomic force microscopy (AFM) are currently used. Most of the instruments are very expensive. The traditional methods and methods for coating research cannot meet the testing requirements of nano-modified coatings. Therefore, new detection methods must be established. In addition, nano-modified coatings lack relevant standards, such as the performance of nanopigments in terms of purity, particle size, particle size distribution, storage stability, and testing standards. In order to solve the above problems, many domestic companies and scholars have also conducted related research. Shanghai Huzheng Nano Technology Co., Ltd. has been able to successfully formulate oily or aqueous slurries such as ATO and ITO, where the nanoparticle size is small and the slurry is stable. In addition, the ATO alcohol dispersion developed by the company can realize pH adjustment and can be made into an acidic ATO dispersion to realize the compounding of ATO dispersion and acidic resin. In order to solve the problem of poor water resistance of the coating, it is possible to use a monomer having a higher water resistance, or to add a water-resistant functional monomer (such as a silane coupling agent).
6. Conclusion Nano-insulation coating can not only take into account the heat insulation and light transmission, but also has excellent mechanical properties, anti-aging, corrosion resistance and other advantages. The development and application of nano transparent heat insulation coating can well solve the technical requirements of the transparent and heat insulation and energy saving for the lighting glass, and its own structural characteristics ensure the long service life of the coating, so the nano transparent heat insulation coating is common. The development and application of transparent carrier surfaces such as glass and plexiglass are not only environmentally friendly, but also economical and practical. In the current situation of increasing social energy crisis and environmental pressure, thermal insulation coatings will have a good application prospect.
(1.School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou 510640, Guangdong, China; 2. South China Institute of Environmental Science, Guangzhou 510655, China)
Abstract: Nano-tin oxide (ATO) and other particles are an n-type semiconductor material. The film made of it has a very high infrared shielding effect and a good visible light transmittance. The application of nano-ATO in coatings can produce transparent glass thermal insulation coatings with extremely high application value. This article introduced the thermal insulation mechanism of nano-insulation coatings, and reviewed the research status of transparent thermal insulation coatings and the preparation methods of nano-thermal insulation composite coatings.
Keywords: thermal insulation coating; tin oxide antimony; nano-particles; glass; energy-saving CLC: TQ637 Document code: A
Article ID: 1004–227X(2011)12–0067–06
1. Preface At present, the exploration of energy conservation and new energy has become an important issue in the world. Building energy consumption accounts for 30% to 40% of the total human energy consumption. Most of them are energy consumption caused by heating and air conditioning, and heat lost through doors and windows accounts for the entire building heating and air conditioning energy consumption. 50%. Therefore, improving the thermal insulation performance of doors and windows is an effective way to reduce building energy consumption [1]. In order to save energy, people have invented energy-saving methods such as heat-reflecting glass, insulating glass, and heat-reflecting glass film. These are all aimed at blocking the excess heat radiation in sunlight and achieving cooling. However, some of these products have poor thermal insulation, some have low visible light transmittance, and some are too expensive, making them difficult to apply and promote. Due to the nature of nanomaterials that are not possessed by macroscopic objects, nanomaterials have become a hot topic for the development of novel coatings with unexpected effects. It has been found that n-type semiconductor materials with wide energy gaps, such as indium tin oxide (ITO), antimony tin oxide (ATO), aluminum doped zinc oxide (AZO), have similar optical properties, ie, high in the infrared region. The reflectance, high transmittance in the visible light region, and high absorptivity in the ultraviolet region are ideal transparent heat insulating materials. Applying this nanoparticle to a coating can produce a functional coating that has both transparency and infrared cut off. This article introduced the heat insulation mechanism, research progress, existing problems and solutions of glass thermal insulation coatings.
2. The thermal insulation mechanism of nano-tin oxide tin oxide and the spectral energy distribution of solar thermal radiation coating on the surface of the earth are: 200-380 nm in the ultraviolet region, 5% of the total energy; 380-780 nm in the visible region, accounting for the total 45% of the energy; near infrared region 780 ~ 2500nm, 50% of the total energy. Therefore, the energy of the solar spectrum is mainly concentrated in the visible and near-infrared regions. The nano-semiconductor heat insulation effect is related to its own physical structure on the one hand and particle size of its powder particles on the other hand. Normally, only nano-sized semiconductors can play a role in transparent heat insulation [2]. Tin oxide, antimony, and other particles are high-density, free-electron gas-type materials whose free carriers can excite plasma vibrations similar to those of gas plasmas. Therefore, doping semiconductors can increase their current-carrying capacity. The concentration of the sub-particles allows the doped semiconductor to have strong absorption of ultraviolet rays in the solar spectrum, transparency to visible light, and reflection of infrared rays [3]. The doping of semiconductors generally has two methods: one is doping of high-valence metals, and donor impurities are formed in an alternate manner, such as pentavalent Sb-doped semiconductor SnO2, Sn-doped semiconductor In2O3, etc.; and the other doping is non-metal. Element F substitutes for O to produce an electron donor to increase semiconductor carrier concentration, such as F-doped semiconductor SnO2. At present, widely used semiconductors in transparent heat insulation functional fillers include zinc oxide, indium oxide, tin oxide, cadmium oxide and their doping systems [4].
Huang Baoyuan et al. [5] found that the thermal insulation of sunlight by ATO nano-coatings is mainly due to its absorption of near-infrared light (average absorption rate of 86%, only 4.5% reflection). He Qiuxing et al. [6] studied that the heat insulation of nanoparticles is based on the absorption of infrared light. Other scholars [7-9] have studied the effect of nanoscale semiconductor particle size, doping and other factors on spectral selectivity, and achieved certain results, but have not yet formed a unified conclusion.
Nano-insulation coating is mainly used for energy-saving form, it can also be used in many fields, such as: (1) applied to windshields and building glass of automobiles, trains, and airplanes, and played a very good role in heat insulation and cooling , And no reflection of light pollution; (2) coated on glass, made of nano-transparent heat insulating glass, including single-layer glass, hollow glass and laminated glass; (3) coated on a transparent resin such as polycarbonate made of nanometer Transparent insulation board, its application is very wide, such as can be made on the top of the bus station transparent insulation board, etc.; (4) coated in polyester film, made of transparent heat insulation film, used in construction and automotive window glass [10].
3. Research status of transparent thermal insulation coatings The key to the preparation of transparent thermal insulation coatings is the selection of nano-semiconductor materials that are selective for the solar spectrum. Currently, these materials are mainly nano-silicon tin oxide (ATO) and indium tin oxide (ITO). . Among them, ATO has become a market acceptable product due to its relatively low cost.
3.1 Methods for Synthesizing Insulating Nanoparticle Powders At present, there are many researches on insulating nanoparticle powders at home and abroad. The synthesis methods of these nanosemiconductor powders mainly include coprecipitation method, hydrothermal method, sol-gel method, Solid phase method.
3.1.1 Co-precipitation method The co-precipitation method is to mix substances of different chemical composition in the solution state, add appropriate precipitant to the mixed solution to precipitate the metal cation coexisting in the solution, and then wash, dry or forge the precipitate. Burn to obtain the corresponding nano-powder. J. P. Coleman et al [11] used SnCl4 · 5H2O solution, and then mixed with the corresponding amount of SbCl5 and strong **, followed by NaOH solution, so that the end point of pH 2, after filtration and washing the filter cake vacuum dried at 60 °C , and calcined at 600 °C for 3 h, followed by rapid cooling in air to obtain ATO ultrafine powder. Kim et al. [12] used SnC14·5H2O and SbCl3 as raw materials, methanol as the medium, and ** as precipitant to obtain nano-ATO micro-powders without hard agglomeration and low-soft agglomeration, and discussed the use of methanol in low-agglomeration nano-ATO particles. Formation and important role of precursor particles in anti-agglomeration. This study shows that the lower surface tension of methanol than water is a key factor in eliminating the hydrogen bonding and capillary action between the precursor particles, which prevents the formation of hard agglomerations due to bridging during drying and sintering. The process replaces water with methanol as the reaction medium, eliminating the adverse effects of water as a medium, such as hydrogen bonds, but the disadvantage is that methanol is flammable, explosive, and expensive than water. However, by optimizing the process, fully recovering the solvent and improving the safety of production, the process should have a good industrialization prospect. Overall, the co-precipitation method is a convenient method for preparing nano-ATO particles. It has the advantages of simple preparation process, easy preparation of preparation conditions, short synthesis cycle, low cost, and is easy for industrial production. However, the powder prepared by this method is easy to agglomerate, and the particle size distribution range is wide.
3.1.2 Hydrothermal method The hydrothermal method is a special closed reaction vessel in which an aqueous solution is used as a reaction medium. By heating the reactor, a high-temperature, high-pressure reaction environment is created, so that substances that are generally insoluble or insoluble dissolve and are heavy. A method of making a powder that crystallizes. Bai et al. [13] used SnC12·5H2O and SbCl2 as starting materials to synthesize a monodispersed ATO suspension in one step at a temperature of 100 to 350°C using a programmed temperature program.
The results showed that the particle size of the ATO particles was 10 to 15 nm and the particle size distribution was narrow. The temperature-programmed process improves the doping level of Sb, and monodisperse doped oxide particles at lower temperatures are achieved.
Feng Bo et al [14] prepared nanometer ATO powders by hydrothermal method and found that the doping concentration was 11%, the hydrothermal reaction temperature was 180°C, the reaction pressure was 1 MPa, the heat treatment temperature was 700°C, and the heat treatment time was 2 hours. Under the conditions, the prepared nano-ATO powders have the best performance and the grain size is about 20nm. Zhang Jianrong et al.[15] used stannous oxalate and bismuth potassium tartrate as raw materials to synthesize nanostructured and monodisperse ATO in one step at 260°C using a high-temperature hydrothermal method, which eliminated the disadvantages of severe agglomeration of powders that are difficult to overcome by other methods. .
3.1.3 Sol-gel method The basic principle of the sol-gel method is to directly form a metal olate or inorganic salt by hydrolysis to form a sol or decondense to form a sol, then gel the solute polymer, and then dry the gel. Roasting to remove organic components, the basic reaction of the reaction of hydrolysis and polymerization. The method can prepare single- or multi-component mixtures with high purity, uniform particle size distribution and high chemical activity (up to molecular-level mixing) at a low temperature, and can prepare products that cannot be or can not be prepared by traditional methods, and is particularly suitable for preparing non-products. Crystalline material.
The sol-gel method is an effective method for synthesizing ultrafine particles, but some properties of the colloids prevent the formation of ultrafine particles. Especially in the dehydration, often due to the presence of surface tension, the pore structure collapses, the particles agglomerate, and the particle size becomes large. Gong Sheng et al [16] used inorganic salts SnCl4·5H2O and SbCl3 as raw materials and ethanol as solvent to prepare porous, well-doped, tetragonal structures using sol-gel method combined with supercritical fluid drying (SCFD) technology. The nano-ATO particles have a particle size of 15 to 30 nm and have good dispersibility. Xu Lijin et al [17] prepared ATO powders by sol-gel method, and studied the effects of heat treatment time, calcination temperature, and cerium ion concentration on the powders.
3.1.4 Solid phase method The solid phase method is to fully mix the powder raw materials in a certain proportion, ball mill, sieving and calcining to obtain new phase powder materials. Bernardi et al. [18] used the solid phase method to directly mix the analytically pure SnO2 and Sb2O3 sold in the market, ultrafine grinding, and then heat treatment at a temperature of 800-1200 DEG C to obtain a gray ATO powder. It was found that the prepared nanopowders have low reactivity and must be calcined above 1000°C to obtain single-phase ATO nanoparticles. The solid-phase doping method is simple and convenient, but it consumes large amounts of energy. At the same time, the high temperature often causes serious volatilization and segregation of the components, and the product has a large grain size and irregular morphology.
In addition to the above method, D. W. Jung et al. [19] used SnCl4 and SbCl5 as raw materials at room temperature and atmospheric pressure to prepare nano ATO powders by DC arc plasma spraying. By controlling the doping amount of Sb in the ATO particles and according to the optimum process conditions, ATO particles having an average particle diameter of 19 nm were prepared.
3.2 Preparation of Nanoparticle Slurry The dispersion and stabilization of nano-ATO in the coating system is the key to the development of transparent and heat-insulating nano-coatings. The research in this area is mainly focused on the preparation of nano-sized slurry. East China University of Science and Technology studied the preparation of ATO slurry, discussed the mechanism of slurry stability and the use of dispersants, but the stability of the prepared ATO slurry is not good, the storage period is generally only 2 to 3 months, Mainly used in fabric anti-static and other aspects [20-21].
Li Yanfeng et al [22] chose different coupling agents to modify the surface of nano-ATO powders, and selected the KH570 coupling agent with better modification effect, and obtained the effect of the amount, reaction time and reaction temperature on surface modification. Impact.
Cai Zhaojun et al. [23] studied the influence of pH, type of dispersant, and added amount on the dispersion stability of ATO aqueous slurries, and finally prepared nano ATO slurries with good dispersivity and stability. Nanoparticles have large surface tension and are prone to agglomeration. Therefore, in dispersing the nanoparticle slurry, a high-speed grinding and dispersing method is generally used to disperse aggregated microparticles. In addition, the dispersed nanoparticles must also have good dispersion stability. For this reason, it is necessary to select a dispersant that is compatible with the system, and the dispersant is bonded to the surface of the microparticles so that repulsive forces are generated between the microparticles, and then the microparticles are stabilized by electrostatic repulsion or steric hindrance. In addition, the surface modification of the particles in advance, the surface of the particles coated with a low molecular weight surfactant or polymer stabilizer, or using other dispersion methods (such as ultrasonic dispersion, etc.), is also worth studying.
3.3 Preparation of Nano Thermal Insulation Coatings In the preparation and development of nano thermal insulation coatings, the United States and Japan started early in the research and development of transparent thermal insulation nano coatings, and are in the front rank of the world. Their research results are mostly published in the form of patents. In the first half of 2000, Nanophase Technologies of the United States prepared indium tin oxide nanoparticles with a particle size of 11 to 44 nm by a physical vapor-phase synthesis method, and a stable and dispersed nano-sized indium tin oxide powder slurry was prepared. The paste can be directly applied to the paint, but its price is higher, and the price per kg is up to 2,000 US dollars. American AirProducts also produces nano-ATO and ITO sols. WO 00/09446, published by World Intellectual Property Organization, describes a method for preparing a nano-sized indium tin oxide aqueous dispersion and a transparent conductive coating prepared using the slurry. Takeda et al [24] prepared a coating film capable of blocking solar heat radiation by incorporating ATO, ITO, or LaB6 in a resin matrix. The film has high transmittance in the visible light region and low light transmittance in the near infrared region. . Japan ** company developed a high-performance coating that can filter solar radiation without affecting daylighting. At present, the paint has been widely used in Japan to reduce energy consumption in building glass. After coating, ordinary glass can reduce 68% of infrared rays and 95% of ultraviolet rays without affecting the lighting conditions [25]. Chonan and Kuno [26] mixed ATO insulation paste with acrylic ultraviolet (UV) curable resin to produce thermal insulation coating, which was coated on PET film and baked at 80°C for 30s. Then, the heat-insulating coating is cured by ultraviolet irradiation, and the resulting coating has a solar radiation transmittance of less than 56.5%.
Nishihara et al [27] prepared nanometer ATO and ITO by co-precipitation method, and compounded with synthetic resin to obtain a transparent heat insulation coating with a light transmittance of more than 80% in the visible light region and very low transmittance in the near-infrared region. Kaneko et al. [28] used a composite coating formed of inorganic semiconductor nano-powders SnO2, ITO, ATO and polyacrylate, and had almost no absorption in the visible region, which has a good barrier effect to solar radiation.
In recent years, domestic companies and research institutes have also done many useful explorations in the preparation of nano-insulation coatings. Professor Zhao Shilin of Nanjing University of Technology conducted research on transparent thermal insulation coatings earlier, including the development of ATO and ITO thermal insulation coatings, and achieved certain research results[29-30]. Beijing Guobang uses inorganic alcohol-soluble transparent resin as a film forming material and mixes it with well-dispersed nano-scale conductive oxide (TCO) to obtain a transparent and heat-insulating coating with a visible light transmittance of 75%. The infrared blocking rate can reach 72%. The transparent heat-insulating paint for glass used by Runhe Technology is a blue water-based paint with a low viscosity (viscosity <100 Pa·s). The construction method is simple. It is coated by a shower coating method, and is placed at room temperature after coating. After about 15 minutes, dry [31-32]. In 2005, Jiangsu Chenguang Coatings Co., Ltd. [33-34] developed a glass-nano-transparent heat-insulation paint with a light transmittance of over 75% in the visible light region, an infrared shielding ratio of over 61%, and energy-saving retrofit at CCTV. The use of the 2000m2 window glass in the main building can save energy by 20% to 30%. Shanghai Huzheng Nano Technology Co., Ltd. [35] also has water-based and oil-based transparent thermal insulation coatings on the market.
According to reports, the visible light transmittance is 75% to 89%, the ultraviolet shielding rate is 95%, and the infrared blocking ratio is higher than 75%, and the temperature difference is 6 to 12°C. The transparent heat insulation coating produced by Shenzhen Donner Technology Co., Ltd. [36] has a visible light transmittance of 75%, an ultraviolet shielding ratio of 99%, and an infrared blocking rate of 75%. The company also developed a transparent insulating glass coating. Yao Chen et al. [10] developed a nano-transparent thermal insulation coating and compared it with a highly transparent and low-transparent LOW-E glass. It was found that the coating film has good solar spectral selectivity, and the transmittance in the visible light region is 78%, the infrared blocking rate is 61%. At present, more and more companies are engaged in the preparation of ATO and other nano-powders and their dispersions and nano-insulation coatings, which lays a good foundation for the development of thermal insulation coatings. However, there is still a long way to go before marketization. .
4. Preparation of Nano-Insulation Composite Coatings There are four main methods for the preparation of nano-insulating composites: in-situ polymerization, blending, sol-gel, and intercalation [3,37-38].
4.1 In-situ Polymerization This method first disperses the nanoparticles in the monomer solution and then polymerizes the monomers. The reaction conditions of this method are mild, and the particles are uniformly dispersed in the monomers, but their use has greater limitations. Because the method is only suitable for in-situ polymerization of monomer molecules in a solution containing metal, ruthenium or hydroxide colloidal particles to prepare nanocomposite coatings.
In addition, in-situ polymerization generally requires surface modification of the particles. Commonly used as surface modifiers are organic acids, coupling agents, surfactants, hyperdispersants, polymers, and the like. When choosing a surface modifier, observe the following principles: The surface modifier must have good bonding ability with the surface of the nanoparticles, must have good wetting behavior with the solvent and have good compatibility with the resin. Only comprehensive consideration of these three factors can obtain the best surface modifier suitable for nano-coating systems. Erdem et al [39] added TiO2 particles to a mixture of styrene and stabilizer OIOA370, ultrasonically dispersed to obtain droplets of microemulsions containing inorganic particles, followed by polymerization, and the inorganic particles could be partially coated. Hu Jinwei et al. [40] studied the preparation of polyurethane-titania water-dispersed composites (PU-TiO2) using polyurethane (PU), tetrabutyl titanate (TNB), triethylamine and ethanol as the main raw materials and in situ polymerization. The particle size distribution and distribution of the dispersion and the surface morphology of the PU-TiO2 composite film were observed and characterized. The results show that the PU-TiO2 water-dispersed composite has good stability and optical transparency.
4.2 Sol-gel method The sol-gel technique is a process in which a metal organic compound, a metal inorganic compound, or a mixture of the two are subjected to a hydrolytic polycondensation process, and then subjected to gelation or a corresponding post-treatment to obtain an oxide or other compound. Technology [41]. In general, alkoxy organosilanes and metal alkoxides are used as raw materials, under the action of a catalyst, they are hydrolytically condensed to form transparent colloidal dispersions, and additives such as pigments and fillers can be added, and can be applied at lower temperatures after coating. Cured film. The main reaction process can be divided into mixing, gelation, aging and drying.
4.3 Blending The blending method is to physically disperse the nanoparticles directly into the film by physical means. The advantage of this method is that it is easy to control the size and morphology of the particles. The disadvantage is that it is difficult to solve the problem of agglomeration of nanoparticles, that is, it is difficult to ensure uniform dispersion of nanoparticles in the polymer matrix. Most nanomaterials have a high surface energy and can adsorb and react with foreign substances (such as water) to form a surface hydroxy layer [42]. The hydrophilic and oleophobic nature of the hydroxyl layer can easily lead to poor compatibility of the nanomaterial with the coating, thereby seriously affecting its dispersion and stability in the coating. Therefore, the surface modification of nano-materials, change its surface state, and improve the compatibility with the coating, is the key to the preparation of insulating nano-composite coatings.
Research progress on nano-insulation coatings for glass Chen Feixia et al. [43] found that transparent thermal insulation coating prepared with nano-ITO dispersed well in super-water dispersion has good spectral selectivity and visible light transmittance. Up to 80%, and most of the infrared light is effectively blocked. Gu Guangxin et al[44] prepared a vanadium dioxide powder with room-temperature phase transformation function by doping tungsten, and used a special grinding process to disperse the tungsten-doped vanadium dioxide powder and the powder of antimony tin oxide (ATO) into Asia. Nano or nano-sized slurries, and these slurries are added directly to the water-borne polyurethane coatings to obtain transparent heat-insulation coatings with certain intelligent functions. The paint has good adhesion to the glass and its near infrared transmittance is adjustable.
4.4 Intercalation Compounding Many inorganic materials (such as silicate clay) have a layered structure that can be embedded in organic matter. The monomer or polymer is inserted between the sheet layers by a suitable method, and then the sheet structure matrix unit having a thickness of 1 nm and a width of about 100 nm is peeled off to uniformly disperse in the polymer, thereby realizing the polymer and the inorganic layer material. Compounding on the nanoscale. This method is only applicable to layered inorganic materials such as montmorillonite. Intercalation polymerization can be further divided into in-situ intercalation, solution intercalation and melt intercalation. In the case of in-situ intercalation polymerization, for example, in-situ intercalation refers to the fact that the monomers are pre-intercalated into the inorganic structure of the layered structure and then polymerized to form a hybrid material, such as inserting the monomer or intercalating agent into the layer. The mica-like silicate in the structure (sheet thickness is about 1 nm, and the lamellar spacing is generally between 0.96 and 2.10 nm), after which the monomers are polymerized into macromolecules between silicate sheets. During this process, the lamellae were further expanded to dissociate so that the layered silicate fillers were dispersed in the polymer matrix to a nanometer size, thereby obtaining a nanoscale composite [45]. Yang Jintao et al.[46] used cation-surfactant octadecyltrimethylammonium bromide (STAB) copolymerized with styrene as intercalation agent to modify montmorillonite (VC18-MMT), and organic montmorillonite. Pre-dispersed in the emulsifier solution under the ultrasonic strong shearing action and emulsifier, and then introduced styrene monomer in situ emulsion polymerization to prepare a polyethylene/montmorillonite nanocomposite.
5. Application prospects and existing problems and countermeasures Compared with common coating films, nano transparent heat-insulation coating film not only has significantly improved mechanical mechanical properties, but also has excellent anti-aging and anti-corrosion properties, plus high transparency and thermal insulation properties. It is characterized by good quality and low price, so it has extremely high application value and broad market prospects. Nano thermal insulation coatings have become a hot topic at home and abroad in recent years, and have also achieved considerable results. However, domestic research on nano-insulation coatings started late and there is still some distance from industrialization. At present, there are still the following issues related to thermal insulation nano-coatings:
(1) Development of nano-ATO powders and dispersions. The agglomeration of nano-ATO itself and the dispersion in the media are the biggest difficulties for industrial applications. Although there are many literatures on the preparation and application of nano-ATO, there are few reports on the dispersion and surface modification of nano-ATO. The exploration of practical and feasible technologies that can solve the problem of ATO powder agglomeration is very important for solving the difficult application of nano ATO.
(2) The biggest problem with nano-coatings is the dispersion and stability of nano-particles. Coating is a very complicated multi-phase dispersion system consisting of four parts: film forming substance, solvent, pigment, filler, etc. The dispersion stability of nanoparticles in coatings is not only related to the dispersion method, but also related to the surface modification of nanoparticles. Therefore, according to different coating requirements, choose nanoparticles and resins, and select the appropriate dispersion method for the system.
(3) The coating has low viscosity. In China, the nano-insulation coating is generally produced by a blending method, ie, the nano-particle slurry and the resin are separately developed, and then the two are blended; and in order to maintain sufficient stability, the nano-paste is generally added very little, and the stabilizer needs to be added. Thickeners and other additives. Therefore, the obtained coating has a low viscosity and is not convenient for construction.
(4) The hardness and water resistance of the coating are poor.
At present, the domestic common nanoparticle slurry is dispersed in alcohols or water by nano-particles, the slurry is generally alkaline, and the resin with which the compound is mainly acrylic resin or amino resin and other acidic resin, therefore, Poor composition results in poor film hardness and poor water resistance. In areas with high rainfall, the use of paint is limited.
(5) Nanoparticle testing technology needs to be improved. In characterizing the particle size and distribution of nanopigments, gravitational settling, low-angle laser diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM), laser particle size analyzers, and atomic force microscopy (AFM) are currently used. Most of the instruments are very expensive. The traditional methods and methods for coating research cannot meet the testing requirements of nano-modified coatings. Therefore, new detection methods must be established. In addition, nano-modified coatings lack relevant standards, such as the performance of nanopigments in terms of purity, particle size, particle size distribution, storage stability, and testing standards. In order to solve the above problems, many domestic companies and scholars have also conducted related research. Shanghai Huzheng Nano Technology Co., Ltd. has been able to successfully formulate oily or aqueous slurries such as ATO and ITO, where the nanoparticle size is small and the slurry is stable. In addition, the ATO alcohol dispersion developed by the company can realize pH adjustment and can be made into an acidic ATO dispersion to realize the compounding of ATO dispersion and acidic resin. In order to solve the problem of poor water resistance of the coating, it is possible to use a monomer having a higher water resistance, or to add a water-resistant functional monomer (such as a silane coupling agent).
6. Conclusion Nano-insulation coating can not only take into account the heat insulation and light transmission, but also has excellent mechanical properties, anti-aging, corrosion resistance and other advantages. The development and application of nano transparent heat insulation coating can well solve the technical requirements of the transparent and heat insulation and energy saving for the lighting glass, and its own structural characteristics ensure the long service life of the coating, so the nano transparent heat insulation coating is common. The development and application of transparent carrier surfaces such as glass and plexiglass are not only environmentally friendly, but also economical and practical. In the current situation of increasing social energy crisis and environmental pressure, thermal insulation coatings will have a good application prospect.
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