Preparation and properties of weatherable reflective thermal insulation coating

HAN Li-dan*, CHEN Bing-yao, CHEN Ming-yi, CHEN Liang, LUO Zhi-bin

First-author’s address: Guangdong Sanvo Chemical Industry Technology Co., Ltd., Zhongshan 528429, China

Abstract: The effects of reflective thermal insulation material and functional fillers on thermal insulation property of acrylate coating were discussed and the optimal formulation of white paint was obtained as follows: Solarproof 15%, ceramic microspheres 16%, barium sulfate 4%, mica powder 8%, and kaolin clay 10% (all are with respect to the total weight of paint).Three kinds of colored coatings, including black, green and gray, prepared through adding different colorants, have not only good thermal insulation property, but also excellent weathering resistance, meeting the requirements of JG/T 235–2014 Architectural Reflective Thermal Insulation Coating and GB/T 9755–2014 Synthetic Resin Emulsion Coatings for Exterior Wall.

Due to the increasingly serious energy crisis and environmental problems, energy saving and emission reduction are imminent. The south of the Yangtze River in China relies on air-conditioning for cooling in summer and consumes a lot of power. The use of architectural reflective insulation coatings can actively reflect the energy of sunlight while decorating and protecting, reducing the temperature on the surface and interior of buildings, thereby reducing The heat accumulation on the wall will ultimately reduce the use of air conditioning and save energy.
At present, domestic research on reflective insulation materials is relatively mature. With the increase of national environmental awareness, coatings have changed from the original solvent-based to water-based. However, it is well known that water-based coatings have poor stain resistance and weather resistance. In addition, with the improvement of living standards, people’s needs for paint colors are diversified. Therefore, how to improve the weather resistance, stain resistance and color diversity of water-based thermal insulation coatings is an urgent problem to be solved. China has a vast territory and a large climate difference. Weather resistance is a major indicator of the performance of coatings, which can make it suitable for a wide range of climates such as cold, hot summer and cold winter, and mild weather. Weather resistance is related to many factors, such as pigments, colorants, and base paint formulations.
In this paper, a series of weather-resistant reflective insulation coatings are prepared. The combination of emulsion, color paste, and functional filler is used to achieve the purpose of heat insulation by reflecting visible light and near-infrared light. The added filler and colorant improve the weatherability of the paint film while reflecting and insulating. The effects of reflective insulation fillers, functional fillers and colorants on the coating properties were investigated.

1 Experiment
1.1 Main Materials
Propylene glycol, bactericide, dispersant COATEX PE908, Hai Enke Chemical; defoamer SF-208, thickener THIXOL 53L, Gaudis, France; pH adjuster APM-95, Dow Chemical; hydroxyethyl cellulose, sub- Shilan; Shuredun SP-105C, Kedeli Chemical; near-infrared reflective titanium dioxide IR-1000, Shandong Dongjia; hollow glass beads, 3M Company; pure acrylic copolymer emulsion, Dow Chemical; color paste iron red , Iron yellow, phthalocyanine blue, Mihara black, Clariant; water, homemade.
1.2 Instrument
small multi-functional grinding and dispersing machine, Laizhou Yinjiang Machinery Co., Ltd .; SDC-168 STM-IV (B) Stormer viscometer, Shanghai Pushun Electromechanical Technology Co., Ltd .; QSP type ISO scraper fineness meter, Shanghai Modern Environmental Engineering Technology Co., Ltd .; V-570 spectrometer, Japan Jasco; TMC-FS3 hemispheric emissivity test device and instrument, Dongguan Green Light New Energy Technology Co., Ltd.
Self-made thermal insulation temperature difference test device: use calcium silicate board as blank test board, fix the coating film mold on the blank test board, pour the paint into the mold, stir, and mix the surface with a steel scraper to mix it evenly for a while After demolding, under the proper conditions, the surface of the coating film is smooth and flat, without air bubbles or cracks. Then use the method shown in Figure 1 to test the temperature on the back of the sample, where the bulb is a 135 W iodine tungsten lamp with a distance of 30 cm.

Device for testing insulation performance of coating

1. 3 Preparation of coatings
Weigh 20.00% (mass fraction of total coating mass, the same hereinafter) into deionized water, put in 0.20% ~ 0.50% cellulose, 0.15% wetting agent, 0.70% at 300 ~ 600 r / min in turn Dispersant and appropriate amount of defoaming agent; increase the speed to 600 ~ 1 000 r / min, and then input 5.00% ~ 25.00% functional filler and 10.00% ~ 20.00% reflective insulation material, and continue to increase the speed to 1 200 ~ 1 500 r / min, high speed dispersion for 10 ~ 20 min. When the fineness is less than or equal to 40 μm, reduce the rotation speed to 100 ~ 400 r / min, and then add 0.15% pH regulator, 0.20% fungicide, 1.20% film-forming aid, 1.50% antifreeze glycol, 15.00% to 25.00%. Emulsion and 0.12% thickener, white reflective thermal insulation coating can be obtained after 5 to 10 minutes of dispersion. On this basis, an appropriate amount of color paste is added to obtain a color reflective heat-insulating coating.
1.4 Preparation of the coating The
base material is an aluminum alloy plate that meets the requirements of GB / T 3880.1–2012 “Aluminum and aluminum alloy plates and strips for general industrial use”. There is no anodized layer or colored layer on the surface. The paint was applied on the surface of an aluminum alloy plate with a dry film thickness of 0.15 mm, and cured for 168 h at about 23 ° C and a relative humidity of 50%.
1. 5 Characterization and performance test The
solar reflectance and hemispheric emissivity of the coating were determined according to WQ type in JG / T 235–2014 “Reflective Coatings for Buildings”. According to GB / T 9780-2013 “Test Method for Contamination Resistance of Coatings for Architectural Coatings”, contaminate the coating with fly ash, and then test the reflectance of the coating after pollution.
Measure the L * of the coating in accordance with GB / T 11186.2-1989 “Methods for measuring the color of coating films-Part 2: Color measurement”. Xenon lamp aging test according to GB / T 1865–1997 “Artificial Weathering and Artificial Radiation Exposure of Paints and Varnishes” for 250 h. Test the total solar reflectance (TSR) and near-infrared reflectance ( NTR). Weather resistance and light resistance refer to the color change and aging degree of the coating after long-term outdoor exposure and weathering. It is characterized by measuring the color difference (ΔE). The test lasts for 12 months and is in accordance with GB / T 1766-1995 “Color Rating methods for ageing of lacquer and varnish coatings “.

2 Results and discussions
2.1 The influence of reflective insulation materials on the thermal insulation effect of coatings
Near-infrared reflective titanium dioxide IR-1000, a new reflective insulation material, Shure Shield, and hollow glass microspheres were used. The effects of the layer solar reflectance, hemispheric emissivity and thermal insulation temperature difference are shown in Table 1.

Effects of the types of reflective insulation materials and their amounts on the thermal insulation properties of coatings

It can be known from Table 1 that with the increase of the content of reflective insulation materials, each index of the three coatings shows an upward trend. As the content increases, the solar reflectance of the coatings made by Shuredun and IR-1000 gradually reaches a balance. When the content of the two is small, it already has a good reflection and heat insulation effect, but when the content is low, The reflective materials are not arranged densely enough to completely cover the surface, so the reflective insulation effect can be further improved. The content continued to increase. On the surface of the coating film, the two kinds of particles, Shure shield and IR-1000, gradually became denser. The thermal insulation effect of the coating film became significantly better, and the sunlight reflectance was close to 90%. At the same content, compared with traditional hollow glass microbeads, the coating made of the new reflective insulation material Shuredun and IR-1000 has a better effect, especially the thermal insulation temperature difference (which can be considered as the solar reflection ratio and Characterization of actual thermal insulation performance after the two hemispheric emissivities are superimposed). Shure shield is a new type of polymer emission insulation material, which has excellent reflection ability for visible light and infrared light, and these two kinds of light occupy the main thermal energy of sunlight, so the thermal insulation effect of its coating is good. IR-1000 reduces the absorption of heat by the substrate by increasing the reflection intensity in the infrared region of the solar light spectrum, which can well reduce the temperature of the surface of the object. Although the thermal insulation effect of Scherer Shield is slightly better than IR-1000, but its cost is higher, so when the requirements for reflective thermal insulation performance are high and the coating area is not large, you can choose the Scherer Shield material.

Hemispheric emissivity refers to the ratio of the radiation emissivity of the thermal radiator in the direction of the hemisphere to the radiation emissivity of the total radiator at the same temperature. When the content of Shure Shield is 15%, the thermal insulation performance of the coating is very good, and the effect of increasing its content is not obvious. Considering economic factors, the content of Shure Shield is set to 15%.
In addition, when the content of Shuredun, near-infrared reflective titanium dioxide IR-1000 and hollow glass microspheres are taken at the same 15%, only the thermal insulation properties of the coatings made by the former two meet the solar reflection in JG / T 235–2014. The ratio ≥0.8, the hemispheric emissivity ≥0.8, and the thermal insulation temperature difference> 10 ° C are required. Therefore, in the actual production, you can consider adding Shure shield and IR-1000 at the same time to improve the reflective thermal insulation effect of the coating.
The reflectance spectra of the three coating films are shown in Figure 2. It can be seen that the reflectance of the coating using Shure shield and IR-1000 is significantly higher than that of the coating using hollow glass microspheres, and the heat insulation effect is more excellent. The results are consistent.

Sunlight reflection spectrum of coatings made of different insulation materials

2.2 Influence of filler on thermal insulation effect of coating film 2.2.1 Influence of
filler type and amount on reflection and thermal insulation effect of coating
Ceramic microspheres, barium sulfate, mica powder and kaolin are selected as fillers. The effect on the reflective insulation performance of the coating when used alone. The test conditions are: pigment volume concentration (PVC) is 45%, and the particle size of the filler is 600 mesh. The results are shown in Figure 3.

Effects of the type and content of fillers on the thermal insulation effect of coatings

It can be seen from Figure 3 that kaolin does not affect the equilibrium temperature of the test panel. The amount of the other three fillers increases, and the reflective insulation effect of the coating gradually increases. At the same content, the effect of ceramic microspheres is better than the other three, and mica powder is better than barium sulfate. This may be caused by the difference in the properties of the filler itself, and the specific mechanism needs further study.
The temperature on the back of the coating test panel decreases with the increase of the content of ceramic microspheres, but the decline gradually slows down. When its content is 25%, the equilibrium temperature change becomes slower. This is because the content of ceramic microspheres increases, and its reflection effect increases. When it reaches a certain degree, it reaches saturation. At this time, the reflection effect is the best. Increasing the content will lead to poor dispersion. The addition amount of ceramic microspheres is preferably 10% to 15%.
2.2 Impact of filler particle size on the reflective insulation effect of the
coating One of the main factors affecting the reflective effect of the coating is the specific surface area of ​​the filler, which is closely related to the particle size of the filler. Keeping the PVC at 45%, the filler mass accounts for 10% of the total coating mass. The effect of the filler particle size on the equilibrium temperature was studied. The results are shown in Table 2. It can be seen that as the particle size of the filler decreases, the equilibrium temperature first decreases and then increases. When the particle size is 600 mesh, the equilibrium temperature is the lowest and the effect is the best. This shows that too large or too small particle size will affect the thermal insulation effect of the coating, mainly because: when the particle size is too small, agglomeration between particles is easy to occur, and the particles that play a role in reflection are relatively reduced; Due to its reduced specific surface area, the fewer particles per unit volume, the worse the reflection insulation effect. So the optimal particle size is 600 mesh.

Effect of filler particle size on equilibrium temperature

2. 2. 3 The influence of ceramic microspheres, mica powder, barium sulfate, kaolin on the reflective insulation performance of the coating when
used in combination Four-factor three-level orthogonal test L9 (34) was used to investigate the balance of various fillers when used in combination. The effect of temperature is shown in Table 3. It can be seen from Table 3 that the degree of influence is in order from ceramic microspheres, mica powder, barium sulfate and kaolin. The best formula of composite filler is A3B3C1D3, which is 16% ceramic microspheres, 8% mica powder, 4% barium sulfate, and 10% kaolin. After testing, the equilibrium temperature of the coating obtained by this formula is 45.2 ° C, and the thermal insulation effect is indeed better than that of all experimental groups in the orthogonal test.

Orthogonal test results of ceramic microspheres, mica powder, barium sulfate and kaolin

2.3 Effect of color paste on weathering resistance and heat insulation effect of
coatings 2.3.1 The formula of the basic paint for tinting
takes into account the above test results and economic factors, and 15% Shu is added to the basic formula (see 1.3) Thermal shield, 16% ceramic microspheres, 8% mica powder, 4% barium sulfate and 10% kaolin.
2. 3. 2 Color paste’s reflective heat insulation performance, weather resistance and light resistance
Although the white coating has better solar heat reflection performance, it cannot meet the requirements of color diversity. The visible light reflectance of color pigments limits its range of use. Infrared reflective pigments should be selected to increase the reflectivity of the coating in the infrared part [3]. Table 4 lists the specific tinting scheme and coating performance test results, and compares them with the requirements of JG / T 235–2014 listed in Table 5.

Insulation performance, weather resistance and light resistance of coatings made by different color pastes, JG / T 235–2014 standard on coating performance

It can be seen that all the test results meet the requirements of JG / T 235–2014, and the properties such as color difference, discoloration and chalking meet the requirements of GB / T 9755–2014 “Synthetic Resin Emulsion Exterior Wall Coatings”.

3 Conclusions The
effects of three types of reflective insulation materials on the solar reflectance, hemispheric emissivity, and thermal insulation temperature difference of the coating have been explored. The effects of Shuredun and IR-1000 are better than those of hollow glass microspheres. When the content is 15%, the performance of the obtained coatings meets the standard requirements.
The type and particle size of the functional filler can affect the heat reflection properties of the coating. Among them, ceramic microspheres have the largest impact. Kaolin has almost no effect on the equilibrium temperature. Mica powder and barium sulfate have a smaller effect. When the content of ceramic microspheres is 16%, the content of mica powder is 8%, the content of barium sulfate is 4%, and kaolin When the content is 10%, the thermal insulation performance of the coating is the best, which provides a basis for actual production.
The three primary color pastes were used to obtain black, green and gray coatings with different brightness. The corresponding total solar reflectance, the total solar reflectance change rate after pollution, the total solar reflectance change rate after artificial aging, and near infrared The reflectance meets the standard requirements.

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