| Polycarbonate (PC) sun plates have become one of the main materials for building energy-saving. However, their heat insulation performance mainly depends on the conduction and convection heat of the air interbedded them. This could not meet the increasing requirement for energy-saving. Improving the air layer numbers could resolve this problem but also makes the processing become more difficult and the efficiency decreased. Factually, among all the heat flux of sun light,60%is infrared radiation. Thus compared with lowering the conduction and convection coefficient, reducing the infrared transmission becomes more important in obstructing solar heat permeation.Antimony doped tin oxide(ATO) nanoparticle is a typical material with well selectivity to the solar spectrum, e.g., high transmittance in the visible light range while a high shield in the infrared region. Presently, ATO is mainly applied as a heat insulating and transparent coat on glass substrate by using waterborne polyurethane (WPU) as matrix resin. No report has been found regarding ATO application on the PC sun plate surface. This may be caused by the low adhesion strength between the WPU coat and PC surface. If this problem was resolved, high practical values and wide market prospects would be created.Thinking of practical application, ATO particles were first dispersed in a large scale by wet ball-milling method. The influence of ball-milling parameters on ATO nano suspension dispersibility and stability was studied systematically. The results indicated that when the pH value of the ATO suspension (30wt%) before ball-milling was adjusted to～10, the milling pot was made by stainless steel, the diameter of zirconia ball was0.2mm, the rotational speed was480r/min, the ball-milling was7.5h, and the ball-milled suspension was further treated by centrifuge at4000r/min for40min, well dispersed ATO nano suspension with average diameter～80nm and solid content～30%was obtained.Afterwards, the nano suspension was mixed with commercial WPU at different mass/volume ratio and coated onto glass surface to measure the properties of the dried coat (～40μm thickness). TEM confirmed that the ATO nanoparticles were well dispersed in the PU resin. Characterization by UV-Vis-NIR showed that when the ATO content approached9.1wt%, the transmissivity of the coat in visible light range was up to75%, while83%infrared radiation and80%UV were obstructed. Moreover, introduction of a small quantity of KH560(y-Glycidoxypropyltrimethoxysilane) in ATO/WPU system significantly enhanced the water resistance property of the dried coat. To enhance the adhesion strength of WPU coat on PC sun plate, the later was first modified with NaOH aqueous solution towards introducing hydroxyl and carboxyl groups, which can react with epoxy group and Si-OH group of KH560easily. Then the ATO/WPU/KH560(ATO content～9.1wt%) was coated on the modified PC surface. As a result, the adhesion strength of the ATO/PU coat was improved from class5to class1while the transparence and heat-insulating property of were still excellent. When the thickness of coat was30μm, the transmissivity of the sun plate in visible light range was up to80%, while65.6%infrared radiation and94%UV were obstructed. The temperature in foamed PS box covered with the ATO/PU-PC plate was much lower (～7℃) than that in the box covered with general PC plate when both irradiated under a250W infrared lamp. This demonstrated that the heat insulating effect of the ATO/PU-PC plate was remarkable.In the end, the heat insulating meahanism of ATO nanoparticles was analyzed by comparing the heat insulating effects of the ATO/PU-PC plate with that of PC plate prepared by melt mixing ATO nanoparticles in PC resin. The results showed that coating technique was much better than the mixing technique. This further confirmed that the shielding of ATO to heat flux of solar light mainly came from their absorbtion to infrared irradiaation but not reflection. When the two ATO/PU-PC plates were piled up, not better heat insulating effect was obtained. However, when introducing some wind over the ATO/PU-PC plate, heat insulating effect was improved. These phenomena demonstrated that the best heat insulating effect can be obtained when ATO was introducing on the PC surface and wind can strengthen such heat insulating effect. |
PDF Full Text Request