After a period of use, the surface coating of metal roof will be weathered. Under the influence of many factors, chemical corrosion and electrochemical corrosion will occur, resulting in water leakage of metal roof. The conventional treatment method is to maintain the metal roof. The maintenance materials include asphalt waterproof roll, asphalt waterproof coating, TPO waterproof roll, common acrylic waterproof coating, metal roof acrylic high elastic waterproof coating, etc. Considering the factors of cost, safety and service life, the metal roof acrylic high elastic waterproof coating is the best choice.
In addition to good strength and toughness, the waterproof coating used for metal roof maintenance must also have good acid resistance. Therefore, the effect of filler type, Zinc Oxide content and emulsion content on the retention rate of acid treatment of acrylic high elastic water-proof coating (JWF) on metal roofing were discussed.
Experimental part
1. Main raw materials
Pure acrylic emulsion: EC1791, Dow Chemical; titanium dioxide: R706, komu; heavy calcium: 1250 mesh, omia; precipitated barium sulfate: 3000 mesh, Lee Teuk chemical; calcined kaolin: 1250 mesh, Hengyuan new material; silicon powder: 1250 mesh, Jiangxi energy saving; Zinc Oxide: Ya Chang zinc industry.
2. Preparation process
Add water and part of the additives into the container, stir evenly, add pigment and fillers, beat and stir until evenly; add the emulsion, stir until uniform and defoaming; adjust pH, add thickener to thicken to suitable viscosity.
3. The metal roof acrylic high elastic waterproof coating (jwf) prepared by performance test shall be tested in accordance with JG / T 375-2012 metal roof acrylic high elastic waterproof coating.
A kind of
The effect of filler types on the strength retention of acid treatment
In this experiment, precipitated barium sulfate was selected as the basic filler, and the effects of precipitated barium sulfate, precipitated barium sulfate / calcium bicarbonate (mass ratio 1:1), precipitated barium sulfate / silica powder (mass ratio 1:1) and precipitated barium sulfate / calcined kaolin (mass ratio 1:1) on the retention rate of acid treatment strength of jwf coating were studied. Among them, the mesh number of precipitated barium sulfate is 3000, and that of bicalcium, silica powder and calcined kaolin is 1250. In the four groups of experiments, the total mass of fillers is the same, and the type and content of other raw materials are the same. The results are shown in Table 1.
JC / T 375-2012 standard requires that the tensile strength without treatment shall be ≥ 1.5 MPa, and the retention rate of acid treatment strength shall be ≥ 80%. It can be seen from Figure 1 that the untreated tensile strength of jwf coating added with precipitated barium sulfate / calcined kaolin is the highest, and the untreated tensile strength of jwf coating added with precipitated barium sulfate, precipitated barium sulfate / calcium bicarbonate and precipitated barium sulfate / silica micropowder is almost the same, and the untreated tensile strength of the coating added with precipitated barium sulfate is slightly higher.
After acid treatment, the tensile strength of the film with precipitated barium sulfate / calcium bicarbonate decreased obviously, and the surface was bubbling. This is because the reaction of calcium bicarbonate and acid solution produced CO2, which destroyed the structure of jwf film, resulting in the decrease of the film strength. Barium sulfate and silica powder will not react with acid solution, calcined kaolin will have a little Al2O3 dissolved in acid, so jwf coating with these three filler combinations has a higher strength retention rate after acid treatment. However, the binding force between barium sulfate and silica powder and resin is slightly poor. In the process of acid treatment, part of the binding point between resin and filler will be destroyed, and its strength retention rate is lower than that of jwf coating with kaolin.
Therefore, the precipitated barium sulfate / calcined kaolin with a mass ratio of 1:1 was selected as the filler in this study.
A kind of
Effect of zinc oxide content on strength retention of acid treatment
The EC1791 side chain of pure acrylic emulsion has carboxylic acid group, which can crosslink reaction in the presence of Zinc Oxide, increase the crosslinking density of JWF film, increase the tensile strength of the material and maintain the strength after acid treatment. Zinc oxide is an amphoteric oxide, which can react with ammonia in jwf system to form zinc ammonia complex ion.
Choose precipitated barium sulfate / calcined kaolin as the filler, keep the other raw material types and content unchanged, study the influence of zinc oxide content on the retention rate of jwf coating acid treatment strength, the results are shown in Table 2.
It can be seen from Figure 2 that with the increase of zinc oxide content, the untreated tensile strength continues to increase, the acid treated tensile strength and acid treated tensile strength keep increasing first and then slowly decreasing, and the maximum is when the zinc oxide content is 2%.
A kind of
Effect of emulsion content on retention rate of acid treatment
Emulsion is the main film forming material in waterborne coatings. When the coating is applied to the substrate, the moisture in the coating evaporates, and the polymer emulsion particles gradually accumulate and accumulate. When the water is evaporated enough, the capillary channel is formed, resulting in capillary pressure, which makes the polymer emulsion particles further deform and agglomerate and form latex particles. When the distance between the polymer latex particles is reduced to a certain extent, van der Waals force makes the polymer latex particles together to form a compact coating. It can be seen that the performance and dosage of emulsion will have a direct impact on the performance of coatings.
The effect of different amount of emulsion on the retention rate of tensile strength and acid treatment strength of JWF film was studied. The results are shown in Table 3.
From Fig. 3, it is known that within a certain range, with the increase of emulsion content, the tensile strength, the tensile strength after acid treatment and the strength retention after acid treatment all increase rapidly. However, when the emulsion content exceeds 40%, the untreated tensile strength, acid treatment tensile strength and acid treatment strength remain basically unchanged.
With the increase of emulsion content, the strength retention rate increased after acid treatment, but the cost also increased. Comprehensive performance and cost factors, when the emulsion dosage is 40%, the price performance is the highest.
A kind of
conclusion
◆ the type of filler has a great influence on the retention rate of tensile strength after acid treatment. The jwf film prepared with precipitated barium sulfate / calcined kaolin as filler has the highest retention rate of tensile strength without treatment and tensile strength after acid treatment.
◆ with the increase of zinc oxide content, the tensile strength of acid treatment increased firstly and then decreased, and when the content was 2%, it was the largest.
In a certain range, the tensile strength retention rate of acid treatment is positively related to the amount of emulsion. However, when the amount of emulsion exceeds a certain amount, the non treatment tensile strength and acid treatment tensile strength retention rate tends to be stable. Comprehensive performance and cost factors, when the emulsion dosage is 40%, the price performance is the highest.
-END-
Author: Chang Zhi, Liu Xiaodong, Zhang Dongdong, Chen Yangfei