General knowledge of coatings: Study on environmental adaptability of functional fluorocarbon coatings

Core tip: fluorocarbon coating has good weather resistance and corrosion resistance, has been widely used in construction, transportation and other fields, and has become a synonym for high-performance coating With the development of China's construction industry, people put forward more functional requirements for fluorocarbon coatings For example, by adding thermal reflecting pigments and fillers, the solar light has a high reflectivity, which can slow down the heat conduction to the interior of the object and radiate the absorbed heat This kind of coating reduces the surface temperature of the building in the high temperature summer, and then affects the ambient temperature, making the energy consumption of air conditioning and other refrigeration equipment reduced In order to improve fluorocarbon coating Application scope and advantages of roller ceramic coating Recommended introduction: the surface of ceramic rubber plate used for roller ceramic coating is cast into durable rubber plate by hundreds of independent small ceramic pieces Each ceramic piece has raised characteristics Under general conveyor belt pressure, thousands of unique cast bumps can produce positive traction, prevent slipping and extend the service life of conveyor belt roller At the same time, the bottom layer adopts high-quality rubber, which has strong elasticity and can play a good impact resistance role The scope of application of roller ceramic coating is one three six 83857180 (the same as V) 1 Roller coating in extremely harsh working environment 2 The belt joint is not suitable for fixing with iron buckle; 3 It is suitable for leather Home of coatings news: fluorocarbon coating has good weather resistance and corrosion resistance, has been widely used in construction, transportation and other fields, and has become a synonym for high-performance coating With the development of China's construction industry, people put forward more functional requirements for fluorocarbon coatings For example, by adding thermal reflecting pigments and fillers, the solar light has a high reflectivity, which can slow down the heat conduction to the interior of the object and radiate the absorbed heat This kind of coating reduces the surface temperature of the building in the high temperature summer, and then affects the ambient temperature, making the energy consumption of air conditioning and other refrigeration equipment reduced In order to improve the surface of fluorocarbon coating, which is easy to form rain marks or not easy to clean, the surface of the coating is modified to increase its hydrophilicity, so as to obtain the self-cleaning function of the surface Through the modification of aluminum silver paste, its corrosion resistance and ultraviolet barrier are improved, so that the four coating system is changed into two coating system, greatly reducing the cost At present, the research of thermal reflective fluorocarbon coating in China mostly focuses on the properties of pigments and fillers, but neglects the influence of resin matrix In the course of coating service, the coating resin will be powdered, discolored and other aging After the coating is powdered, the functional filler will also break away from the coating system under the action of wind and rain, thus losing the function of thermal reflection At the same time, the stain resistance of the coating surface will also have a great impact on the thermal reflection ability The air pollution in China is serious If the coating does not have a certain self-cleaning ability, the surface crud will greatly reduce its thermal reflection performance after a short time of service At the same time, even if the coating surface is modified by self-cleaning, if there is no certain weather resistance, it will lose its effect because of the surface pulverization The current domestic standards for thermal reflective coatings are JC / t1040) 20075 thermal reflective and thermal insulating coatings for building external surfaces 6 and JG / T235) 20085 The former puts forward requirements for the thermal reflective performance of the coating after artificial aging, and the latter limits the attenuation of the thermal reflective capacity of the coating after the stain resistance test See Table 1 for details Table 1 the regulations o f domestic industry standards on aging resistance and stain resistance of thermal reflective coatings NOK = "F" O: CO necttype = "rect" gradientshapeok = "t" > it can be seen from table 1 that JC / t1040) 2007 has too low requirements on aging resistance of coatings, and only 500h for solvent based coatings; JG / T235) 2008 requires that all kinds of coatings meet the aging resistance requirements of corresponding resin based coatings, There is no requirement for thermal reflection attenuation At the same time, the stain resistance test method is GB / t9780) 2005 This method is mainly suitable for exterior wall coating, but not for metal coating 1.1 experimental instruments: Xenon lamp aging machine (q-pane, lq-sunxe-30s,); spectrophotometer (PerkinElmer lambda950,) 1.2 the results and the test results of the discussion test are shown in Figures 1 to 3 Fig 1 aging of sample a and changes of solar reflectance after contamination Fig 2 aging of sample B and changes of solar reflectance after contamination Fig 3 aging of sample C and changes of solar reflectance after contamination from the experimental results, it can be seen that the solar reflectance of coatings with poor weatherability decreases significantly with the increase of aging time, However, the solar reflectance of fluorocarbon coatings with excellent weatherability has little change after 2000 h aging test GB / t9780) 2005 has a weak characterization of the stain resistance of metallic paint, while the method of ASTM d3719 is more similar to the actual situation, which can well show the stain resistance of the coating in the natural environment After exposure according to ASTM d3719, the solar reflectance of the coating decreased significantly, especially after aging After 2000 h aging test, the solar reflectance of sample a has decreased to less than 0.6, which is the same as that of the common coating However, the solar reflectance of sample B and sample C with excellent weatherability and strong stain resistance is still about 0.8, which has obvious advantages At present, there are two main ways to modify self-cleaning fluorocarbon coatings: one is to add a layer of low fluorine acrylic coating on the surface of the coating, to improve the hydrophilicity of the coating surface, and at the same time to improve the interlayer adhesion and weather resistance of the coating by introducing fluorine element; the other is to introduce nano-TiO2 with photocatalysis on the surface of the coating, under ultraviolet irradiation, The hydrophilic and lipophilic substances on the surface of the film can be effectively removed and degraded In this study, the contact angle of a self-cleaning fluorocarbon coating sample before and after aging was characterized 2.1 experimental instrument xenon lamp aging machine; contact angle tester 2.2 see Figure 4 for the contact angle between the results and the samples before and after aging Fig 4 surface contact angle of different aging time from Fig 4, it can be seen that the hydrophilicity of the coating surface decreases gradually before and after aging through 1000h and 2000h xenon lamp aging The results show that the hydrophilic layer on the coating surface of the sample has been aged and decomposed, and the self-cleaning function has failed As a super weather resistant coating, the fluorocarbon coating, JG / t133) 2000, GB / t17748) 1999, GB / t23443) 2009, etc are all required to pass the aging test of 4000H, and aama2605 puts forward the requirements of exposure in Florida for 10A However, the weather resistance of the self-cleaning surface layer of the sample is low, which is far from the whole service life of the fluorocarbon coating, and it will not play a role of self-cleaning in the middle and later stages of the whole service process 3 PVDF fluorocarbon coating is used for aluminum plastic plate and aluminum single plate used as metal curtain wall Because of the bright luster of metallic flash paint, it is widely used If the paint uses large particles of metal pigment, the varnish must be added In addition, because PVDF has no absorption effect on UV, it is necessary to add isolation coating on the primer, usually PVDF (70%) fluorocarbon coating containing rutile titanium dioxide, or to effectively improve the weather resistance of the primer, a 3-coat or 4-coat system is adopted Because metal particles are easy to be oxidized, especially the ability to isolate ultraviolet light is very weak An enterprise claims to improve the corrosion resistance and UV barrier of aluminum silver paste by modifying it, so that the cost can be greatly reduced from 4 coating system to 2 coating system The coating has passed the requirements of GB / t17748) 1999 (the aging time is 2000h, and the aging time of the revised 2008 version is 4000H) after being used in the aluminum-plastic composite plate However, after being installed on the wall for 5a, the top coat has seriously peeled off, and the adhesion of the coating has been tested as grade 5 (grid method), as shown in Figure 5 The samples were characterized by DSC, SEM and FT-IR, and the reason of exfoliation was analyzed 3.1 DSC (taq100,), SEM, FT-IR (nexus670) 3.2 results and discussion the melting point of the top coat of the coating was tested by DSC See Fig 6 for the spectrum Fig 5 test results of sample adhesion (cross cut method) Fig 6 DSC spectrum of sample top coat according to Appendix A of GB / t23443) 2009, the PVDF content is more than 95%, indicating that polyacrylate in the top coat has been completely photolysis However, the PVDF coating system of non-metallic flash paint, due to the barrier effect of pigments and fillers on the UV, only the polyacrylate on the surface of the coating is subject to photolysis, while the coating under the surface is still protected by pigments and fillers and PVDF, and the UV can not penetrate to cause the photolysis of the inner layer of polyacrylate The polyacrylic acid ester in the sample finish has been completely cracked, indicating that ultraviolet light has penetrated the whole finish Fig 7 is a SEM photo of the back of the top coat and the surface of the primer Fig 7 SEM photos of the back (a) and the primer surface (b) of the sample finish can be seen from Fig 7 that due to the presence of PVDF, there is no obvious pulverization phenomenon of the finish, but due to the complete cracking of polyacrylic acid resin, many tiny pores appear on the back of the coating However, the primer has been severely powdered due to the UV radiation through the finish That is to say, due to the complete cracking of polyacrylate which provides adhesion in the top coat and the serious pulverization of the primer, the adhesion between the top coat and the primer is basically lost, which finally leads to the serious peeling off of the top coat Fig 8 is FT-IR spectrum of primer Fig 8 FT-IR spectrum of primer 1729cm-1 is the main characteristic peak of CO, 1161cm-1 is the characteristic peak of CH3) o) CO [6], the primer should be polyacrylate added with a small amount of PVDF, the main function of adding PVDF is to improve the adhesion with the top coat Due to the lack of isolation paint and effective improvement of the weather resistance of the primer, the primer is severely powdered Summary: the long-term energy-saving performance of thermal reflective coatings needs to be evaluated objectively by artificial aging first, and then by outdoor exposure The advantages of thermal reflective fluorocarbon coatings are obvious The method of GB / t9780) 2005 is far from the actual situation It is not suitable for metallic paint, so it is necessary to study a new simulation test method under standard conditions The weatherability of self-cleaning fluorocarbon coating needs to be verified by experiments If its aging resistance time is much shorter than the service time of fluorocarbon coating, it is not significant It is necessary to study the surface self-cleaning technology which has the same weather resistance as fluorocarbon coating At present, the most effective method is to apply a layer of insulating paint The aging mechanism of natural environment is different from that of artificial aging to some extent If the isolation paint is not applied, the metal flash paint is easy to be powdered in the service process, resulting in the peeling off of the top coat The experience and lessons from many environmental failure cases of functional fluorocarbon coatings illustrate the importance of environmental adaptability of such building materials Timely, systematic and full environmental test of building materials is the only way to 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