Development status and trend of building thermal insulation coatings

In China, the energy consumption of buildings (the energy consumption of buildings throughout the production and use process), together with the energy consumption for the maintenance of structural materials, account for about 30% of the total energy consumption in the country. Along with the advancement of urbanization in China, the proportion of building energy consumption in total energy consumption will continue to increase. Building energy conservation (refers to improving energy efficiency in buildings without reducing the use of buildings, Reducing building energy consumption will be a top priority for improving the efficiency of social energy use. Insulation coatings in building energy-saving materials are increasingly favored by people because of their advantages in economy, ease of use, environmental protection and energy-saving effects, and their development prospects are bright.

Building insulation coating and its classification

Paints that are applied to the surface of buildings to provide thermal insulation are called building insulation coatings. Building insulation coatings are classified into three types: barrier type heat insulation coatings, reflective heat insulation coatings and radiation type thermal insulation coatings according to different insulation mechanisms and heat insulation methods. These three types of coatings have different insulation mechanisms, and the applications and effects are also different.

Barrier type thermal insulation coating

Barrier-type heat-insulating coatings are coatings that achieve thermal insulation through significant resistance to heat transfer. Heat transfer is achieved through three ways: convection, radiation and molecular vibration heat conduction. The thermal conductivity of the material is the determining factor of its thermal insulation performance. The smaller the thermal conductivity of the material, the better the thermal insulation performance. This type of coating is generally used as a lightweight aggregate with a material having a small apparent density, a loose internal structure, a high porosity, and a low moisture content. By bonding together, it can be directly applied to the surface of the equipment or wall to achieve thermal insulation.

The barrier type heat insulation coating material is easy to obtain, the production equipment is simple, the input is small, the output is large, and the construction is convenient. The disadvantages are that the heat transfer effect of reducing convection and radiation is poor, the heat insulating layer is thick, the water absorption rate is high, the vibration resistance is not resistant, and the service life is short. Such heat-insulating coatings can only slow down the heat transfer rate, and can not reduce the heat transfer. After a long period of sunlight, the indoor temperature will rise. Similarly, when the indoor temperature is higher than the outdoor temperature, it will also pass the heat transfer. The heat is transferred out, so this type of thermal insulation coating is only suitable for cold winters, where the temperature is low for a long time and the summer heat is short.

Reflective thermal insulation coating

Reflective thermal insulation coatings are made by selecting suitable resin, metal or metal oxide pigments and production processes to produce high reflectivity coatings that reflect solar heat for thermal insulation purposes. By reflecting part of the light and heat, heat is prevented from being conducted through the film to the room, causing the room temperature to rise.

The reflective heat-insulating coating has good adhesion to various substrates and has strong weather resistance. The solvent used generally has no irritating odor, which greatly reduces the impact of construction on the environment, and the heat insulation effect is obvious compared with the barrier type heat-insulating coating. However, its thermal insulation performance has a great relationship with the flatness of the surface of the coating film. The smoother the surface of the coating film, the better the heat insulation effect. At the same time, the heat insulation effect has a certain relationship with the thickness of the coating film, and within a certain thickness range, The coating film reflectance increases as the thickness of the coating film increases. Such thermal insulation coatings have obvious heat insulation effects and poor thermal insulation effects, and are best for areas with short cold weather in winter and long hot summer weather.

Radiant insulation coating

The radiant heat-insulating coating emits sunlight and heat absorbed by the building into the air at a certain wavelength in the form of radiation, thereby achieving a good heat-insulating and cooling effect. Radiant thermal insulation coatings are different from barrier-type thermal insulation coatings and reflective thermal insulation coatings because the latter two can only slow down but not block heat transfer. When the heat slowly passes through the heat insulating layer and the reflective layer, the temperature of the internal space slowly rises, and at this time, even if the external temperature of the coating is lowered, the heat energy can only be trapped therein. Radiant heat-insulating coatings can radiate the absorbed heat in the form of heat emission, which causes the indoor and outdoor to cool at the same rate, so it is also suitable for areas with hot summer weather.

Radiation-type heat-insulating coatings Due to the complexity of the selection of raw materials and the sintering process, further research is needed to achieve a stable emissivity. Because of the high cost of such coatings, there are fewer applications on buildings.

In addition, it is reported that Zheng Qijun and others have comprehensively utilized the above three principles to produce a thin layer thermal insulation coating with high emissivity. The coating has excellent comprehensive performance, especially the reflectance is more than 85%, and the coating film after drying has good adhesion to the substrate, and the surface gloss is high. The coating is fast drying, convenient in construction, seamless in coating film, and both. Thermal and waterproof. It can be seen that the thermal insulation coatings using composite technology have been greatly improved in terms of coating performance and construction, and represent the development trend of such coatings in the future.

Development and research status of building thermal insulation coatings

In recent years, domestic and foreign architectural coatings have made great progress in terms of variety, scale application, quality level and research level. Architectural coatings are the largest output of foreign coatings. US architectural coatings account for more than 50% of coatings consumption; Japanese architectural coatings account for about 40% of coatings production; from 2008 to 2010, China's architectural coatings production has reached a growth rate of more than 20% for three consecutive years. In 2009, China's total coating output reached 7,554,400 tons, ranking first in the world for the first time. In 2011, the total output of national coatings exceeded 10 million tons for the first time. Among them, interior and exterior wall coatings accounted for about 36% of total coating production. On the floor coatings, waterproof coatings, etc., the production of architectural coatings accounted for about 46%. From the current development momentum, the architectural coatings consumer market will maintain a high growth rate in the next few years, and the prospects are broad, and building thermal insulation coatings will be the future development direction.

Foreign research status

In foreign countries, there are many research reports on thermal insulation coatings, and the research is also in-depth. There have been a lot of reports on literature and application. N.M. Nahar et al. studied the cooling technique of sunlight in arid regions and found that the temperature in the test chamber coated with the reflective coating was much lower than the temperature in the test chamber without the reflective coating. R.Neil uses a dibutyl maleate-vinyl acetate copolymer as a film-forming substance, and a water-based heat-insulating coating excellent in heat insulation is obtained by adding a CeramicSul32 pearlescent heat-insulating agent. MJWang studied the properties of composite powders. They coated a layer of dense potassium silicate on the surface of zirconia ceramic spheres and tested the scattering rate and reflectivity of the composite powder. Studies have shown that the scattering rate and reflectivity of light It is related to the thickness of the cladding layer and the size of the ceramic ball.

The prepared composite powder has a more excellent effect than a rutile-type titanium oxide pigment of the same size and a general-purpose ceramic ball. Researchers at American Solar Group Inc. announced that they have developed a thermal insulation coating that is 85% to 95% of the standard metal film used in the top floor of the building. The indoor temperature can be lowered by 5.5 to 14.5 °C. It means that it can save 8%~12% of air-conditioning costs, and in winter, it can prevent heat radiation from escaping from the house, which can save 1%~2% of heating costs. U.S. Patent No. 6,071,981 developed an infrared reflective coating which is based on a water-diluted acrylic resin, titanium white powder, chrome black, iron red, etc. as a pigment, talc powder, mica powder, etc. as a filler, coated on a white primer. A coating having a dry film thickness of 45 μm was formed, and the reflectance to infrared rays of 1200 to 2000 nm was more than 50%.

China's research status

China's building thermal insulation coatings were developed and applied in the late 1980s. At that time, they were mainly applied to some thermal insulation coatings with irregular shapes and high temperature pipes and equipment surfaces.

The silicate composite thermal insulation coating has the advantages of wide source and high temperature resistance, and it was the earliest developed. In the 1990s, people developed thermal insulation coatings for interior wall walls based on silicate composite thermal insulation coatings, and changed the base materials to inorganic materials based on the environmental conditions of the interior wall surfaces. In the case of an organic binder based on polyvinyl acetal rubber or synthetic resin emulsion, some coatings use organic materials instead of inorganic coarse light fillers.

In recent years, the external wall insulation has been paid attention to. There are many research reports on thermal insulation coatings. Liu Xianchun uses modified acrylic alkyd resin as the main film-forming material, and combines with pigments, solvents and additives to produce surface thermal insulation coatings. This coating has excellent physicochemical properties and extremely high brightness, and has a high reflectivity to solar heat, which can significantly reduce the temperature of the surface of the house.