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    Home > Coatings News > Paints and Coatings Market > Effects of different curing systems on the performance of epoxy powder coatings

    Effects of different curing systems on the performance of epoxy powder coatings

    • Last Update: 2021-01-29
    • Source: Internet
    • Author: User
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    Han Junhua, Lu Jian, Xu Xiaowei, Bai Yafei, Wang Bing
    Guilin University of Technology School of Materials Science and Engineering, Nonferrous Metals and Materials Processing New Technology Ministry of Education Key Laboratory
    Read
    through non-equidioid temperature differential scanning volume thermal analysis (DSC), thermal reanalysing (TGA) and physical mechanical performance testing studied biscyanamine, methamphetamine, line phenyls as solidified agents;
    2-methyl methamphetumazole is the curing behavior of the epoxy resin system as a curing promoter, thermal stability and powder coating properties, and the theoretical curing temperature of different curing systems is found by extraterrorization.
    Introduction
    Epoxy Powder Coatings are recognized as high-productivity, excellent film coating performance, eco-friendly, economical 4E coating products.
    powder coating curing conditions are mostly in 170 to 200 degrees C, individual up to 200 degrees C, time 20 to 30 min, there is a higher baking temperature, longer time disadvantages

    . At present, the most commonly used curing agents are amines, phenols and methamphetamines.
    are mainly used in methylamine curing agents, which are cured in conditions of 200 degrees C /30 min. Phenol curing agents are mainly used in line phenolic resins, but phenolic resins and epoxy resins have poor reaction activity, generally need to be cured at more than 200 degrees C.
    low curing temperature, but because of its high activity, resulting in reduced storage stability of the product. Therefore, how to effectively reduce the curing temperature of powder coatings and reduce curing time has been a concern of the powder coating industry.
    this paper uses double cyanide, DDS, PF as curing agent, and 2-methyl mide as curing promoter for cross-experiment, and obtains a low temperature curing system with better comprehensive performance.
    01
    Experimental Part
    1.1 Main Raw Materials
    CYD - 014 (E - 12): Industrial Products, Epoxy Division of Balling Petrochemical Branch; Double cyanide: chemical pure, Shanghai Bangcheng Chemical Co., Ltd.; DDS: Industrial Products, Shanghai Xinyi Test Chemical Co., Ltd.; Line phenolic resin (PF): Industrial products, Shandong Jinan Sanquan Chemical Co., Ltd. 2 - Methyl methamphetium: analysis pure, Tianjin Comio Chemical Reagent Development Center; GLP503, Resting Incense: Industrial Products, Ningbo South China Sea Chemical Co., Ltd.; Titanium white powder: Industrial products, Ishihara, Japan.
    1.2 main instruments and equipment
    high-speed shredder DG - 120B, Ryan City, Zhejiang Province, Chunhai Pharmaceutical Equipment Factory; Micro twin screw extruder SJSZ - 10, Wuhan Ruiming Plastic Machinery Co., Ltd.; Vacuum drying box DZF - 6020, Shanghai Jinghong Experimental Equipment Co., Ltd. Mirror gloss meter KGZ -1B, lacquer film impactor QCJ, are Tianjin Veda test machine factory; Integrated thermal analyzer STA - 449, spread scan volume heat meter DSC -204, are the German Company Netzsch.
    1.3 Basic formulations for the preparation and testing
    powder coatings are found in Table 1. Weighing after the use of high-speed shredder for pre-smashing, and then with a miniature twin screw extruder for melt extrusion, to be cooled by the product, with high-speed shredder 2 times crushed, graded through the sieve.
    powder coatings with different curing systems. Using electrostation spray, the coating film of different curing systems is baked under certain curing conditions, and then the performance test of powder and coating film is carried out separately.
    Table 1 Basic Formula
    02
    Results and Discussion
    2.1 DSC Tests for Different Curing Systems
    The powders of different curing systems are tested using non-isothermal differential scanning amount heat (DSC) to analyze the main parameters of the DSC curve. Thermal analysis conditions: N2 atmosphere, different heating rates 5,10,15,20,25 degrees C /min, temperature 30 to 280 degrees C.
    the starting temperature of the curing reaction, T0, peak temperature TP, termination temperature Te. The non-iso-temperature DSC curve of different curing systems is shown in Figure 1.
    As can be seen from Figure 1: The position of the heating peak of the curing reaction is closely related to the heating rate, and with the increase of the heating rate, the starting temperature and peak temperature of the system curing reaction are increased, and the curing time is shortened, i.e. the thermal effect of the unit time increases, and the heating peak of the curing reaction moves in the direction of the high temperature accordingly.
    to the heating rate φ T0, Tp, Te, respectively, using extraterrorization to φ s 0, to determine the curing temperature of different curing systems, the corresponding temperature is the theoretical gel temperature (T0), theoretical curing temperature (Tp) and theoretical termination temperature (Te)
    the theoretical temperature of different curing systems can be determined by Figure 2.
    2 theoretical extraterrorization temperature of different curing systems
    it can be seen that different curing systems have a great influence on the curing temperature of epoxy powder coatings. Among them, the curing temperature of the double cyanide system is high at 182 degrees C, the loss of energy is large, and does not meet the standards required by merchants.
    DDS /2-methyl methamphetium curing temperature is 131 degrees C, but the softening point of the coating is 110 degrees C, the temperature difference between the two is not large, is not conducive to the curing process of the film level, thereby affecting the appearance of the coating film and the performance of the force.
    the curing temperature of the remaining curing system is about 140 to 150 degrees C, which not only increases the leveling time, but also reduces the curing temperature.
    2.2 Effect of different curing systems on the thermal stability of curing products
    The curing products of different curing systems can be seen in Figure 3 from the thermal weight curve of 50 to 700 degrees C, and the stability of curing products can be analyzed by using the thermal weight loss curve. It can be seen that the main parameters of the thermal weight loss curve of different curing systems are such as Table 3.Table
    3 The main parameters of the thermal weight loss curve of different curing systems
    The starting decomposition temperature of the curing products of the four curing systems used by Table 3 is not much different from the temperature of the fastest heat weight loss, indicating that the thermal stability of the four curing systems has little effect on the curing products of epoxy.
    2.3 Effect of different curing systems on the physical properties of the coating
    2.3.1 non-swinging content
    called (2.0 ± 0.1) g powder, placed in a weighed aluminum foil dish. Place the foil dish in an oven with a constant temperature of (105 ± 2) to bake 1 h, remove the foil dish after the time has been reached, and cool to room temperature weighing, accurate to 0. 1 g。
    the content of non-volatiles is calculated as follows:
    NV - non-volatile content of the following calculations; C - The quality of the heated rear dish and the store, g; A - Disc weight, g; B - Powder weight, g.
    powder coating non-volatile content refers to the powder baked at a specified temperature conditions for a certain period of time, due to the volatile weight loss ratio, NV value is best to reach more than 99.6%. From Table 4, it can be seen that the NV value of the system of double cyanide and double cyanide/2-methylamine curing system is more suitable.
    Table 4 Non-volatile content of different curing systems
    2.3.2 gloss and impact
    will do a good job of powder coating film according to GB / T 9754-2007, the use of gloss meter, the use of gloss reflection principle, relative to the mirror gloss standard board, at a 60 degree angle to test the sample gloss.
    according to GB /T 1732-1993, the maximum height (cm) of the paint film with a fixed-quality hammer dropped on the test plate without causing damage to the paint film indicates the impact resistance of the paint film.
    Different curing systems have different effects on film gloss, adding several curing agents with different activities in the powder coating manufacturing process, using the differences in their chemical reaction activity, the curing speed is different, resulting in uneven contraction to produce a different effect of glazing (see Table 5).Table
    5 The effect of different curing systems on film gloss and impact
    Table 5 shows that the DDS/2-methyl methazole system has the worst gloss, mainly because its curing temperature is not much different from the softening point temperature, resulting in shorter leveling time, which in turn affects the appearance and performance of the coating film.
    the impact resistance of the coating coating is determined by the glass temperature, cross-link density and cross-link curing degree of the film.
    from Table 5, we can see that the impact of the double cyanide/2-methyl methamphetamine system is the best, indicating that the curing reaction between the resin and curing agent is the most complete, and the film resistance is also the best.
    2.4 Effects of different curing systems on the electrical properties of coating film
    Surface resistance is the ratio of DC voltage applied to the insulated paint film to surface conduction current between electrodes, and is an important data that is indicative of the electrical properties of dielectrics or insulation materials.
    test surface resistance using the industry standard HG/T 3331 "Insulated paint film volume resistance and surface resistance coefficient determination method" (see Table 6).
    Table 6 Effect of different curing systems on coating surface resistance
    It can be seen that the DDS and PF curing systems are two orders of magnitude less than the surface resistance of the dicyanide system, indicating that the insulation of the dicyanide system is better.
    and the comparison between the double cyanide/2-methylamine curing system can be known, the data difference between the two is not large, the comprehensive physical and physical properties of the above-mentioned determination of the double cyanide/2-methylamine system as the optimal curing system.
    2.5 E -12 / Dicyanide / 2-Methyl methamphetamine coating film performance test
    Comprehensive curing temperature and physical and physical properties can be concluded that the dicyanide/ 2-methyl methamphetamine system is the optimal curing system. The E-12 /double cyanide/2-methyl methamphetamine system is molded at 160 degrees C /15 min for performance testing.
    E - 12 / double cyanide / 2 - methamphetamine system achieved the performance of: 60 degrees gloss≥83; The non-volatile mass score is 99. 75%; Adhesion ≤1; The impact strength ≥ 50 cm; Acid-resistant alkaline ≥24 h; Surface Resistance 1. 33 × 1012Ω; The resulting data meet the performance targets proposed by the merchants.
    the fluidity and curing temperature of the powder did not change much within 2 months, which had no significant effect on the physical and physical properties of the coating film, indicating a storage period of 2 months.
    03
    Conclusion
    1) The theoretical gelization temperature (T0) of E-12 / double cyanide is 163. 17 degrees C, the theoretical curing temperature (Tp) is 182.41 degrees C, and the theoretical termination temperature (Te) is 207.16;
    3 temperatures of the ocyanide/2-methyl methamphetamine/epoxy system were 120.38 degrees C, 142.49 degrees C and 164.85 degrees C respectively;
    3 temperatures of the DDS/2-methyl methamphetoxycin/epoxy system were 111. 22 degrees C, 131. 26 degrees C and 151.35 degrees C, respectively; The 3 temperatures of the PF/2-methyl methazole/epoxy system are 121. 96 ℃、150. 6 degrees C and 176. 95 ℃;
    2) The application of thermal weight analysis (TGA) can be seen that the starting decomposition temperature of the four curing systems is not much different from the fastest temperature of thermal weight loss, indicating that their thermal stability is basically the same;
    3) The combined performance of the double cyanide/2-methyl methamphetamine system is the best.
    its curing process is 160 degrees C /15 min; 60 degrees gloss≥83; The non-volatile mass score is 99. 75%; Adhesion ≤1; The impact strength ≥ 50 cm; Acid-resistant alkaline ≥24 h; Surface Resistance 1. 33 × 1012Ω; The storage period is 2 months.
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