Effect Of Pigments On Thermal Reflectivity Of External Wall Coatings

Heat reflective pigments are the core of heat reflective insulation coatings,which directly affect the heat reflective properties of exterior wall coatings.The study of heat reflective pigments is of great significance for improving the heat reflective performance of heat reflective insulation coatings and reducing building energy consumption.The main factors affecting the thermal reflectivity of coatings are raw materials(composition,particle size distribution),pigment treatment process,film state,film structure and so on.Among them,raw material composition,heat treatment temperature,paint film and pigment particle size distribution are the key factors affecting the thermal reflectivity of coatings.In this paper,the effects of raw material composition,heat treatment temperature,paint film and particle size distribution of titanium dioxide on the thermal reflectivity of coatings were studied.The red,yellow and blue pigments were used as raw materials to prepare color pigments and grey pigments,and the pigments were treated at high temperature to optimize the treatment process to improve the reflectivity of the paint.The effects of particle size distribution on thermal insulation and thermal reflectivity of coatings were studied.The suitable particle size of titanium dioxide in pigments was optimized to improve the thermal reflectivity of coatings.Firstly,the effects of pigments on the chroma and thermal reflectivity of polychromatic coatings were studied.Using red,yellow and blue pigments as raw materials,based on the principle of three basic tone,a multi-color pigments were prepared.The results show that when the mass fraction is 20%,the mass ratio of pigments needed for preparing orange film with better chroma is m(nickel titanate yellow):m(iron oxide red)=6:1,and the near infrared reflection ratio can reach 74.9%.The quality ratio of pigments needed to prepare green coatings with better chroma is m(nickel titanate yellow):m(phthalocyanine blue)=8:1,and the near infrared reflectance ratio can reach 67.7%.Medium gray paint film is prepared by using the mixture ratio of M(iron oxide red):m(titanium nickel yellow):m(phthalocyanine blue)=0.64:4.50:1.00.The brightness of the paint film is 54,ranging from 40 to 80,and the sunlight reflection ratio(TSR)can reach 41.8%.The blending ratio of m(iron oxide red):m(titanium chromium brown):m(phthalocyanine blue)=0.64:1.10:1.00 is better.The brightness of the paint film is 39,ranging from 0 to 40,and the solar reflectance(TSR)can reach 31.7%.Secondly,the effect of heat treatment temperature on the chroma and thermal reflection properties of coatings was studied.Four groups of pigments with the best chroma in the component test were used as raw materials.After heat treatment at 900?1100? for 4 hours,the samples were fully ground.The results show that the brightness and thermal reflectivity of pigments are affected by high temperature heat treatment.The brightness and thermal reflectivity of pigments are inversely correlated with heat treatment temperature.High temperature heat treatment can significantly reduce the a*value of the mixed pigments containing iron oxide red,and the degree of decline in the reflectivity of the pigments is proportional to the heat treatment temperature.Then,the effect of paint film on the chroma and thermal reflectivity of coatings was studied.Three groups of color pigments with the best chroma in the component test were used as raw materials to prepare coatings.Four kinds of film thickness were set with frame-type coater,which were 0.125 mm,0.15 mm,0.2 mm and 0.25 mm,respectively.The film was dried and the thickness of the film was measured by a spiral micrometer.The results show that when the film thickness is greater than 0.125 mm,the chroma and thermal reflectivity of the prepared pigments are almost unaffected.Finally,the effects of titanium dioxide particle size distribution on the chroma and thermal reflectivity of the coatings were studied.Three kinds of graded titanium dioxide were prepared by using 300,100 and 25 nm titanium dioxide powders based on Horsfield model and coMPact packing effect.T1(10%100nm,10%25nm TiO2),T2(10%300nm,5%1 OOnm,5%25nm TiO2),T3(20%300nm TiO2).The results show that with the optimization of the particle size distribution of titanium dioxide,the specific surface area of titanium dioxide increases,the reflective interface increases,the scattering effect of titanium dioxide on light increases,and the reflectivity of the coating increases.With the optimization of the particle size distribution of titanium dioxide,the thermal conductivity of the powder decreases and the thermal insulation and cooling effect of the coating becomes better.With the optimization of the particle size distribution of titanium dioxide,the adsorptive capacity of the coatings increases,and the scouring resistance of the coatings increases gradually.