Zeng Fanhui, Zhou Sheng, Liu Hanmao Zhuzhou Times New Material Technology Co., Ltd., Zhuzhou, Hunan 412007, China
Abstract : A fluorocarbon coating with excellent weatherability was prepared with tetrafluoro-fluorocarbon resin as the base material. The effects of different resins, curing agents and titanium dioxide on the weatherability of fluorocarbon coatings were studied. The surface conditions of the paint films after outdoor exposure were characterized by SEM. The results showed that when using tetrafluorocarbon fluorocarbon resin, trimer type isocyanate curing agent, coated rutile titanium dioxide, the accelerated aging resistance of fluorocarbon topcoat can reach 4 000 h, and the surface of the paint film after outdoor exposure for 30 months is basically the same. No change, the gloss retention rate is above 90%.
Key words: fluorocarbon coating; weathering resistance; artificial accelerated aging; railway tamping car 0. Introduction The polymer containing fluorocarbon bond (F-C) in the main chain or side chain is fluorocarbon resin. The fluorocarbon resin coating has excellent weathering resistance, and has been verified in foreign countries. The weathering resistance has reached 20 years [1], mainly due to the fact that the carbon-fluorine bond energy in the molecule is the highest among the known bond energy of 485 kJ/mol. And F-C key is very stable. The fluorocarbon resin can transmit more than 95% of the medium and long wavelengths in the ultraviolet (220-400 nm) range of sunlight. Only ultraviolet light with a wavelength of not more than 220 nm can destroy the F-C bond, but these shortwave ultraviolet rays account for the sunlight. The proportion is small and it is easily absorbed by the atmospheric ozone layer.
Railway tamping vehicles are a kind of large-scale railway maintenance engineering machinery. They play a role in the construction and maintenance of railway lines and reinforce the role of railway track beds, which play a decisive role in the quality of railway lines. At present, China's plateau railways include the Kunming Plateau Railway and the Qinghai-Tibet Plateau Railway, which is the highest in the world. The coating used for tamping vehicles operating in the plateau area must be resistant to strong ultraviolet radiation (30% stronger than plain areas), resistance to temperature changes (-30 to 60°C), and abrasion resistance. However, traditional coatings for railway vehicles generally cannot meet the requirements for use in harsh environments on the plateau. Therefore, research on high-performance coatings for high-grade vehicles has attracted increasing attention.
There are many factors that affect the weatherability of fluorocarbon films, including internal factors such as the types and types of fluorocarbon resins, pigments, and curing agents; and the effects of sunlight, changes in temperature, atmospheric composition, humidity, and other external factors can all affect the paint. The membrane is destructive. In this paper, through the study of these influencing factors, a fluorocarbon coating suitable for high weathering performance of cruising vehicles on the plateau railway was obtained.
1. Test section 1.1 Preparation and technics of fluorocarbon coating According to formula weight, fluorocarbon resin, pigment filler, auxiliaries and mixed solvents are weighed, uniformly dispersed by a high-speed disperser, and then ground to a fineness ≤ 15 μm in a sand mill. Adjust the viscosity of 40 ~ 60 s (ISO-6 # cup), filter out. The prepared paint component and curing agent component were formulated into a fluorocarbon paint in a ratio of 4:1 (mass ratio).
1.2 performance test according to national standard GB/T 14522. Fluorescent UV/condensation cycle test method was used. The light source was a UV-B (313 nm) lamp. The test conditions were: UV light: 60° C., 4 h; Condensation: 50° C., 4 h. The results were evaluated according to GB/T 1766. Test other properties according to the TB/T 1527-2004 standard.
2. Results and Discussion 2.1 Effect of Different Resins on Resistance to Artificial Aging Performance The railway construction vehicles in the plateau area are exposed to the atmospheric environment of the plateau, and the ultraviolet irradiance is strong, and the paints used for them need to have strong ultraviolet radiation resistance. The test results of the color difference (△E) and 60° gloss retention of several different types of resins in the accelerated UV aging test are shown in Figs. 1 and 2 .
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From Fig. 1 and Fig. 2, it can be seen that the fluorocarbon resin has good resistance to artificial accelerated aging. The order of weather resistance performance is: tetrafluoro-type fluorocarbon resin> trifluoro-type fluorocarbon resin> acrylic resin. The main reason is that the C-F bond energy contained in the fluorocarbon resin is the highest among the currently known chemical bonds, and the bond energy is as high as 485 KJ/mol, and the interatomic bonding force is strong, and the photochemical reaction is not easy to be dissociated. Therefore, weather resistance is good. The extraordinary weathering resistance of fluorocarbon coatings is directly related to the fluorine content of the resin. The higher the fluorine content, the longer the durability of the paints prepared into coatings and the longer the chemical resistance [2]. The trifluorofluorocarbon resin is three. The copolymer of fluorovinyl chloride and vinyl monomer, fluorine content of fluorocarbon resin is only about 23%, and tetrafluorofluorocarbon resin is a copolymer of tetrafluoroethylene and vinyl monomer, chlorine-free molecules The fluorine content of up to about 27%, in addition to tetrafluorofluorocarbon resin does not contain chlorine, its molecular arrangement is more regular, the molecular chain is not easily broken by ultraviolet photolysis; and trifluorofluorocarbon resin due to chlorine, molecular arrangement Without regularity, the low molecular weight segments are easily destroyed by ultraviolet photolysis [3], so the weatherability performance is worse than that of the tetrafluorofluorocarbon resin. From Fig. 1 and Fig. 2, it can be seen that after the 4 000 h UV aging test, the color difference of the tetrafluorofluorocarbon coating is less than 5, and the gloss retention rate is above 80%.
2.2 The effect of different curing agents on the resistance to accelerated aging The different isocyanate curing agents have different structures and different reactive functional groups, and the performance of the film after cross-linking with hydroxyl-containing resins is also very different. Under the condition that tetrafluorocarbon fluorocarbon resin was selected as the base resin, the effects of different curing agents on the paint performance were examined. The results are shown in Table 1.
From Table 1, it can be seen that the properties of the HDI biuret (N75) and HDI trimer (N3390) isocyanate curing agents far outperform the ** diisocyanate curing agent TDI. This is mainly due to the fact that N75 and N3390 are aliphatic isocyanate curing agents, while TDI is an aromatic isocyanate. The isocyanate groups are directly attached to the benzene ring structure. Under the action of ultraviolet light and oxygen, the benzene ring is opened and the isocyanate group is opened. The group directly forms a p-benzoquinone structure with the benzene nucleus, and this structure contains a yellow chromophoric group, so the polyurethane coating using such a raw material as a curing agent is liable to yellowing [4], and the weatherability is extremely poor. On the other hand, since the isocyanate (-NCO) content of the TDI curing agent is much higher than that of N75 and N3390, together with the rigid benzene ring structure contained in the ** diisocyanate curing agent TDI, the cross-linked reaction film The hardness is high and the brittleness is large, so that the flexibility of the coating film is also poor. In addition, N3390 is an aliphatic HDI trimer compared with the curing agent N3390 and N75 because the trimer is a cyclic structure, chemical properties are more stable than aliphatic HDI biuret (N75), and the crosslink density is also It is higher than biuret, so it has better weatherability than HDI biuret (N75).
2.3 Effect of Different Titanium Dioxide on Weatherability The titanium dioxide (titanium dioxide) has been widely used in paints as a white pigment. Most of the colors in the paint are based on the titanium dioxide white paste. In this study, the effects of several different titanium dioxide powders on the weatherability of coatings were compared under the conditions of a tetrafluoro-fluorocarbon resin as the base material. The results are shown in Table 2.
Anatase and rutile titanium dioxide belong to the same tetragonal system, but the crystal lattice is different, and the crystal structure is different. The anatase crystal has a large gap and the crystal is not very stable. Under the action of ultraviolet rays, the crystal is easily destroyed. The rutile type titanium White powder is the most stable crystalline form with dense structure and better anti-powdering ability than anatase type titanium dioxide [5]. It can be seen from Table 2 that the weather resistance of Formula 2 is much better than that of Formula 1. For rutile type titanium dioxide, the weather resistance is greatly improved after the weather-resistant Al2O3 and SiO2 surface coatings are more stable, which is particularly suitable for super weather-resistant fluorocarbon coatings. Therefore, Formula 3 has the best weather resistance. In addition, it was also found that after the rutile titanium dioxide coating treatment, its hiding ability slightly decreased, may be due to the coated surface, Al2O3 and SiO2 have a certain degree of transparency, reducing the hiding power of titanium dioxide, in addition Because the whiteness of anatase titanium dioxide is better than that of rutile titanium dioxide [5], its hiding power is also better than that of rutile titanium dioxide. After comprehensive comparison, this study finally determined the choice of coated rutile titanium dioxide.
2.4 Outdoor Exposure Aging Study Outdoor exposure test is the most realistic method to simulate the weathering performance of fluorocarbon paint film. The gloss retention rate of different resin paints after outdoor exposure for 30 months and under 5,000 times scanning electron microscope (SEM) The microscopic changes in the surface of the paint film are shown in Figure 3 and Figure 4.
From Figure 3, we can see that after 30 months of outdoor exposure, the retention rate of tetrafluoro-fluorocarbon resin coating is still about 90%, the retention rate of trifluoro-type fluorocarbon resin coating is about 82%, and acrylic The gloss of the resin coating has dropped below 60%. From the scanning electron microscope (5 000-fold) graph before and after the exposure of the tetrafluorofluorocarbon resin in Fig. 4, it can be seen that after 30 months of outdoor exposure, the surface of the tetrafluorofluorocarbon resin coating has only a slight change. The comparison shows that the tetrafluorofluorocarbon resin coating has good aging resistance, outdoor test results and artificial accelerated aging results are basically the same, artificial UV accelerated aging time and the paint film in the outdoor actual service life of the relationship has yet to be further research.
3. Conclusion Through the use of tetrafluorocarbon fluorocarbon resin, trimer isocyanate curing agent, coated rutile titanium dioxide, fluorocarbon topcoat can withstand artificial accelerated aging up to 4 000 h, outdoor exposure after 30 months paint film surface Basically no change, gloss retention rate of more than 90%, to meet the needs of the plateau railway construction vehicle coating.
Abstract : A fluorocarbon coating with excellent weatherability was prepared with tetrafluoro-fluorocarbon resin as the base material. The effects of different resins, curing agents and titanium dioxide on the weatherability of fluorocarbon coatings were studied. The surface conditions of the paint films after outdoor exposure were characterized by SEM. The results showed that when using tetrafluorocarbon fluorocarbon resin, trimer type isocyanate curing agent, coated rutile titanium dioxide, the accelerated aging resistance of fluorocarbon topcoat can reach 4 000 h, and the surface of the paint film after outdoor exposure for 30 months is basically the same. No change, the gloss retention rate is above 90%.
Key words: fluorocarbon coating; weathering resistance; artificial accelerated aging; railway tamping car 0. Introduction The polymer containing fluorocarbon bond (F-C) in the main chain or side chain is fluorocarbon resin. The fluorocarbon resin coating has excellent weathering resistance, and has been verified in foreign countries. The weathering resistance has reached 20 years [1], mainly due to the fact that the carbon-fluorine bond energy in the molecule is the highest among the known bond energy of 485 kJ/mol. And F-C key is very stable. The fluorocarbon resin can transmit more than 95% of the medium and long wavelengths in the ultraviolet (220-400 nm) range of sunlight. Only ultraviolet light with a wavelength of not more than 220 nm can destroy the F-C bond, but these shortwave ultraviolet rays account for the sunlight. The proportion is small and it is easily absorbed by the atmospheric ozone layer.
Railway tamping vehicles are a kind of large-scale railway maintenance engineering machinery. They play a role in the construction and maintenance of railway lines and reinforce the role of railway track beds, which play a decisive role in the quality of railway lines. At present, China's plateau railways include the Kunming Plateau Railway and the Qinghai-Tibet Plateau Railway, which is the highest in the world. The coating used for tamping vehicles operating in the plateau area must be resistant to strong ultraviolet radiation (30% stronger than plain areas), resistance to temperature changes (-30 to 60°C), and abrasion resistance. However, traditional coatings for railway vehicles generally cannot meet the requirements for use in harsh environments on the plateau. Therefore, research on high-performance coatings for high-grade vehicles has attracted increasing attention.
There are many factors that affect the weatherability of fluorocarbon films, including internal factors such as the types and types of fluorocarbon resins, pigments, and curing agents; and the effects of sunlight, changes in temperature, atmospheric composition, humidity, and other external factors can all affect the paint. The membrane is destructive. In this paper, through the study of these influencing factors, a fluorocarbon coating suitable for high weathering performance of cruising vehicles on the plateau railway was obtained.
1. Test section 1.1 Preparation and technics of fluorocarbon coating According to formula weight, fluorocarbon resin, pigment filler, auxiliaries and mixed solvents are weighed, uniformly dispersed by a high-speed disperser, and then ground to a fineness ≤ 15 μm in a sand mill. Adjust the viscosity of 40 ~ 60 s (ISO-6 # cup), filter out. The prepared paint component and curing agent component were formulated into a fluorocarbon paint in a ratio of 4:1 (mass ratio).
1.2 performance test according to national standard GB/T 14522. Fluorescent UV/condensation cycle test method was used. The light source was a UV-B (313 nm) lamp. The test conditions were: UV light: 60° C., 4 h; Condensation: 50° C., 4 h. The results were evaluated according to GB/T 1766. Test other properties according to the TB/T 1527-2004 standard.
2. Results and Discussion 2.1 Effect of Different Resins on Resistance to Artificial Aging Performance The railway construction vehicles in the plateau area are exposed to the atmospheric environment of the plateau, and the ultraviolet irradiance is strong, and the paints used for them need to have strong ultraviolet radiation resistance. The test results of the color difference (△E) and 60° gloss retention of several different types of resins in the accelerated UV aging test are shown in Figs. 1 and 2 .
From Fig. 1 and Fig. 2, it can be seen that the fluorocarbon resin has good resistance to artificial accelerated aging. The order of weather resistance performance is: tetrafluoro-type fluorocarbon resin> trifluoro-type fluorocarbon resin> acrylic resin. The main reason is that the C-F bond energy contained in the fluorocarbon resin is the highest among the currently known chemical bonds, and the bond energy is as high as 485 KJ/mol, and the interatomic bonding force is strong, and the photochemical reaction is not easy to be dissociated. Therefore, weather resistance is good. The extraordinary weathering resistance of fluorocarbon coatings is directly related to the fluorine content of the resin. The higher the fluorine content, the longer the durability of the paints prepared into coatings and the longer the chemical resistance [2]. The trifluorofluorocarbon resin is three. The copolymer of fluorovinyl chloride and vinyl monomer, fluorine content of fluorocarbon resin is only about 23%, and tetrafluorofluorocarbon resin is a copolymer of tetrafluoroethylene and vinyl monomer, chlorine-free molecules The fluorine content of up to about 27%, in addition to tetrafluorofluorocarbon resin does not contain chlorine, its molecular arrangement is more regular, the molecular chain is not easily broken by ultraviolet photolysis; and trifluorofluorocarbon resin due to chlorine, molecular arrangement Without regularity, the low molecular weight segments are easily destroyed by ultraviolet photolysis [3], so the weatherability performance is worse than that of the tetrafluorofluorocarbon resin. From Fig. 1 and Fig. 2, it can be seen that after the 4 000 h UV aging test, the color difference of the tetrafluorofluorocarbon coating is less than 5, and the gloss retention rate is above 80%.
2.2 The effect of different curing agents on the resistance to accelerated aging The different isocyanate curing agents have different structures and different reactive functional groups, and the performance of the film after cross-linking with hydroxyl-containing resins is also very different. Under the condition that tetrafluorocarbon fluorocarbon resin was selected as the base resin, the effects of different curing agents on the paint performance were examined. The results are shown in Table 1.
From Table 1, it can be seen that the properties of the HDI biuret (N75) and HDI trimer (N3390) isocyanate curing agents far outperform the ** diisocyanate curing agent TDI. This is mainly due to the fact that N75 and N3390 are aliphatic isocyanate curing agents, while TDI is an aromatic isocyanate. The isocyanate groups are directly attached to the benzene ring structure. Under the action of ultraviolet light and oxygen, the benzene ring is opened and the isocyanate group is opened. The group directly forms a p-benzoquinone structure with the benzene nucleus, and this structure contains a yellow chromophoric group, so the polyurethane coating using such a raw material as a curing agent is liable to yellowing [4], and the weatherability is extremely poor. On the other hand, since the isocyanate (-NCO) content of the TDI curing agent is much higher than that of N75 and N3390, together with the rigid benzene ring structure contained in the ** diisocyanate curing agent TDI, the cross-linked reaction film The hardness is high and the brittleness is large, so that the flexibility of the coating film is also poor. In addition, N3390 is an aliphatic HDI trimer compared with the curing agent N3390 and N75 because the trimer is a cyclic structure, chemical properties are more stable than aliphatic HDI biuret (N75), and the crosslink density is also It is higher than biuret, so it has better weatherability than HDI biuret (N75).
2.3 Effect of Different Titanium Dioxide on Weatherability The titanium dioxide (titanium dioxide) has been widely used in paints as a white pigment. Most of the colors in the paint are based on the titanium dioxide white paste. In this study, the effects of several different titanium dioxide powders on the weatherability of coatings were compared under the conditions of a tetrafluoro-fluorocarbon resin as the base material. The results are shown in Table 2.
Anatase and rutile titanium dioxide belong to the same tetragonal system, but the crystal lattice is different, and the crystal structure is different. The anatase crystal has a large gap and the crystal is not very stable. Under the action of ultraviolet rays, the crystal is easily destroyed. The rutile type titanium White powder is the most stable crystalline form with dense structure and better anti-powdering ability than anatase type titanium dioxide [5]. It can be seen from Table 2 that the weather resistance of Formula 2 is much better than that of Formula 1. For rutile type titanium dioxide, the weather resistance is greatly improved after the weather-resistant Al2O3 and SiO2 surface coatings are more stable, which is particularly suitable for super weather-resistant fluorocarbon coatings. Therefore, Formula 3 has the best weather resistance. In addition, it was also found that after the rutile titanium dioxide coating treatment, its hiding ability slightly decreased, may be due to the coated surface, Al2O3 and SiO2 have a certain degree of transparency, reducing the hiding power of titanium dioxide, in addition Because the whiteness of anatase titanium dioxide is better than that of rutile titanium dioxide [5], its hiding power is also better than that of rutile titanium dioxide. After comprehensive comparison, this study finally determined the choice of coated rutile titanium dioxide.
2.4 Outdoor Exposure Aging Study Outdoor exposure test is the most realistic method to simulate the weathering performance of fluorocarbon paint film. The gloss retention rate of different resin paints after outdoor exposure for 30 months and under 5,000 times scanning electron microscope (SEM) The microscopic changes in the surface of the paint film are shown in Figure 3 and Figure 4.
From Figure 3, we can see that after 30 months of outdoor exposure, the retention rate of tetrafluoro-fluorocarbon resin coating is still about 90%, the retention rate of trifluoro-type fluorocarbon resin coating is about 82%, and acrylic The gloss of the resin coating has dropped below 60%. From the scanning electron microscope (5 000-fold) graph before and after the exposure of the tetrafluorofluorocarbon resin in Fig. 4, it can be seen that after 30 months of outdoor exposure, the surface of the tetrafluorofluorocarbon resin coating has only a slight change. The comparison shows that the tetrafluorofluorocarbon resin coating has good aging resistance, outdoor test results and artificial accelerated aging results are basically the same, artificial UV accelerated aging time and the paint film in the outdoor actual service life of the relationship has yet to be further research.
3. Conclusion Through the use of tetrafluorocarbon fluorocarbon resin, trimer isocyanate curing agent, coated rutile titanium dioxide, fluorocarbon topcoat can withstand artificial accelerated aging up to 4 000 h, outdoor exposure after 30 months paint film surface Basically no change, gloss retention rate of more than 90%, to meet the needs of the plateau railway construction vehicle coating.
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