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    Home > Coatings News > Paints and Coatings Market > Study on the application of low temperature curing powder coating to the bottom of the bicycle

    Study on the application of low temperature curing powder coating to the bottom of the bicycle

    • Last Update: 2020-11-22
    • Source: Internet
    • Author: User
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    Syngenta:
    based on the general trend of "paint-to-powder" environmental protection policy, this paper studies the low temperature curing powder coating suitable for bicycle bottom application. Through the study of the main body epoxy resin of the film-forming system, the study of curing agent, the optimization of the amount of curing promoter and the study of additives and other formula optimization process, the final result in a fully cured bicycle bottom at 130 degrees C/20min conditions with low-temperature curing powder coating, the coating has excellent adhesion and corrosion resistance, but also has a high-level high-gloss appearance, is an environmentally friendly and energy-saving green paint.
    keywords:
    powder coatings, bicycles, low temperature curing
    1 Introduction
    bicycles are one of the main products of the light industry market, bicycle coatings in the entire paint market contributed to the market share can not be ignored . At present, the world's annual bicycle production of about 120 million vehicles, annual trade volume of about 75 million vehicles, China's bicycle exports accounted for more than 60% of the world, domestic consumption ranked first in the world. According to China Bicycle Association statistics, at present, China has all kinds of large-scale bicycle and parts enterprises more than 1000, more than 1000 electric bicycle enterprises. Bicycle-related enterprises are mainly distributed in Tianjin, Jiangsu, Zhejiang, Shanghai, Guangdong three coastal areas, because these coastal cities are relatively sound industries, upstream and downstream industries are more concentrated, bicycle industry concentration is relatively high, the associated driving effect is obvious. At present, the bicycle industry coating to solvent-based, mainly amino alcohol acid paint, polyester ammonia paint and acrylic amino paint, bicycle coating with many colors, varieties, colors, low value-added and so on, and with market demand, bicycle coating quality requirements are getting higher and higher, not only requires bright and plump tourism, with good mechanical properties, but also requires water resistance, wear and outdoor durability, with excellent protection. Solvent-based coating after decades of development, has fully adapted to the requirements of bicycle coating, but solvent-based coating construction is not less than 600g/L VOC content, it is difficult to cope with more and more stringent environmental requirements, so bicycle coating if you want to survive, in technology must be done to reduce environmental protection. With the emergence of shared bicycles, bicycles returned to the city, China returned to the status of a bicycle power.
    Traditional bicycle paint has a greater impact on environmental pollution and the health of construction workers, with the national attention to environmental protection in recent years and the imposition of environmental taxes on paint paint and other policy effects, paint coating switch to use environmentally friendly powder paint coating has become the trend. It is of great energy saving and environmental protection to develop a low temperature curing powder coating suitable for bicycles, replace traditional paint and reduce the curing temperature of general powder coating.
    2 Test part
    2.1 formula raw materials
    raw materials and basic ingredients as shown in Table 1 below: Table
    1 shared single-car bottom coating powder coating basic formula
    2.2 test equipment
    test equipment: mixer, extruder, shredder, electrostectoral spray gun, oven, salt spray test box, glosser, thickness meter.
    2.3 Test Method
    Weighing raw materials according to formula parts, said that the raw materials taken were initially mixed evenly by the mixer, and then the melting mixture with the twin screw extruder was evenly extruded, the pressure sheet was cooled, the high-speed shredder was crushed after crushing, and the standard sieve was over 180 mesh To obtain a powder coating with uniform particle size, the powder coating is sprayed with electrostatization and substrate, cured and molded at 130 degrees C/20min, then removed and naturally cooled to room temperature, after which the coating is tested for various properties.
    Table 2 Main performance indicators of powder coating for bicycle substrates
    3 Experimental results and discussion
    Traditional bicycle coating process for the process: spray primer - spray paint (or multi-layer) - spray essential oil (transparent paint).
    disadvantages:
    easy to appear primer spray thin, affecting the follow-up process, the need to spray paint or multi-layer paint to cover, the cost increases.
    bicycle new coating process:
    spray base powder - spray paint (or not spray) - spray essential oil (transparent paint) to solve the problem of primer spray thin, the base powder cover rate is good, can not spray paint, save costs, improve efficiency.
    This project research products are mainly shared single-car bottom coating powder coating, base powder spraying to achieve low temperature curing, only 130 degrees C/20min can be cured molding, can be exactly matched with color paint, transparent paint, without adjusting the site furnace setup or new furnace, improve customer productivity.
    3.1 Epoxy resin selection
    With the development of the market, the quality requirements of bicycle coating film is also higher and higher, not only requires bright and plump sightseeing, with good mechanical properties, but also requires water, wear and outdoor durability, with excellent light preservation, color preservation. It is difficult for a single coating to fully meet this requirement, and under current technical conditions, the coating of bicycles is still dominated by composite coatings. The base coating needs to have excellent adhesion, corrosion resistance, and high gloss and high level. Taking into account the above requirements, we choose pure epoxy system as the main body of the film to carry out the research and development work of powder coating on the bottom of the bicycle.


    Divided by structure, epoxy resins can be divided into BPA epoxy resin, line phenolic epoxy resin, adjacent formaldehyde epoxy resin, Bisphenol F epoxy resin, Bisphenol S epoxy resin, hydrogenated biphenol A epoxy resin, silicone modified epoxy resin seven categories. According to the production process, epoxy resin can be divided into one-step method and two-step French epoxy resin. Epoxy resins commonly used in the preparation of powder coatings are mainly Bisphenol A epoxy resins and line phenolic epoxy resins.


    is often structurally determining performance for polymers. Bisphenol A (BPA) epoxy resin structure as shown in Figure 1, the ether bond on its main chain determines that it has a strong corrosion resistance, bisphenol A epoxy resin and end pyrethroid polyester cross-curing reaction is determined by its epoxy base.
    phenol ecyclic oxygen resin molecular structure contains both biphenol A phenolic components, and phenol phenol aldehyde components, the existence of a number of epoxy groups, with high cross-link density, high coating hardness, good wear resistance and so on, but the introduction of phenolic structure makes the coating yellowing performance worse, so when it is used in powder coatings need to consider the coating of yellowing factors.
    Figure 1 Bisphenol A epoxy resin structure map
    This experiment selected bisphenol A epoxy resin for research, for the one-step and two-step production process of bisphenol A epoxy resin, different epoxy-specific doses of bisphenol A epoxy resin with a specific curing agent, additive curing into a membrane coating, and the coating performance analysis and testing, the results are shown in Table 3 below.Table
    3 Performance comparison of several epoxy resins
    From the experimental results of the table above, it can be seen that the coating made from bisphenol A epoxy resin with a production process of two steps under the same conditions has better gloss and leveling effect, and its salt spray resistance is also better. Therefore, the next research test was carried out using 3 and 4 epoxy resins, which were distinguished by epoxy A and epoxy B codes respectively.
    3.2 Epoxy curing agent selection
    The curing reaction of epoxy resin mainly occurs on the epoxy base, due to the influence of epoxy ether bond and benzene ring large π bond, the electronic cloud distribution has a large offset to produce even moment, as shown in the following figure:
    pure epoxy system powder coating can achieve low temperature curing key is the choice of curing agent. The curing agent of epoxy resin can usually be divided into three categories: amines, acidic anhydrides (polyester resins containing endoplasmode) and phenolic resins. The amine curing agent is mainly double cyanide, the common double cyanide is not suitable for the study of this experiment because of its high melting point (207 to 209 degrees C), and the target curing condition of this experiment is 130 degrees C/20min. Aromatic hydrocarbon modified double cyanide can have a relatively low melting point, the reaction speed is fast, can be added curing promoter way to verify whether it can achieve 130 degrees C / 20min curing.
    most of the acidic acid curing agents will sublimation in the manufacturing process, there is a stimulating odor production, as well as poor storage stability, so this experiment does not choose such curing agents for experimental research.
    solidification reaction between phenolic resin and epoxy resin is mainly carried out by the addition reaction of phenolic hydroxyl and epoxy base, so no volatile substances are produced. The coating produced by phenolic resins together with epoxy resins has excellent corrosion resistance. In summary, under the guidance of the theory, this experiment uses aromatic hydrocarbons instead of accelerated binocyanide and phenolic resin to carry out experimental research. The results are as follows: Table
    4 Performance comparison of different epoxy curing agents
    the general dosage of curing promoter is 0.3% to 0.5% of epoxy resin, from the above table experimental results can be seen to choose accelerated double cyanide as a curing agent, even if the curing promoter added to 1.0%, 130 degrees C / 20min conditions coating can not be completely cured. When using phenolic curing agents, only 0.4% of the curing promoter is added as the trigger, and the coating can be fully cured at 130 degrees C/20min. From the results of the storage stability experiment, the formula of 4 is better than the formula of 3, both epoxy resin B is better than epoxy A, but there is still room for improvement.
    At the same time, we analyzed the DSC curing behavior of the 3 and 4 formula powder coatings, and the results are as follows:
    From the results of the DSC analysis experiment, the Tg of the 4-formula is higher than the 3-formula, which explains why the 4-formula storage stability is better than the 3-formula. At the same time, the curing conversion rate of the 4-formula is significantly greater than that of the 3-formula at the same temperature. In summary, it is determined that epoxy resin B and phenol curing agent are selected as film-forming subjects coated with powder coating on the bottom of the bicycle.
    3. Effect of the dosage of curing promoter
    The role of curing promoter is to reduce the curing temperature and shorten the curing time, and the curing promoter of pure epoxy system is mainly mide and its salts. There are three common ones.
    the physical and chemical properties of Table 5 Mimi compounds
    the above three curing promoter's active temperature is relatively low, added to the epoxy formulation system will inevitably affect the storage stability of the product to varying degrees. We select a high melting point of 2.4-MDMA to test, in order to ensure that the product achieves low-temperature curing conditions to optimize its dosage, in order to reduce the curing promoter on the storage stability of the product.
    Table 6 Effect of Curing Promoter Dosage on Product Storage Performance
    Under the same conditions as experimental results, as the dosage of Curing Promoter increases, the storage stability of the product decreases and the product life decays. Under the condition of ensuring low temperature curing, the amount of curing promoter should be between 0.4% and 0.5%. Powder coating products should not be stored at a temperature of more than 25 degrees C after production, it is recommended that the product be used within 6 months.
    3.4 Effects of anti-group additives
    the average particle size of powder coatings is generally between 30 and 50 m, the smaller the average particle size of the powder, the wider the particle size distribution, the higher its surface energy, the stronger the activity, the easier it is to clump. In order to improve the product's anti-group performance, in the production process to add a certain amount of anti-grouping additives to reduce the surface activity of the powder, help to improve the storage stability of the product and the looseness of the powder, its use on the looseness of the powder and anti-group performance has a greater impact.
    Table 7 Effect of anti-grouping additives on powder storage
    From the above experimental results, the addition of anti-group additives can significantly improve the looseness of powder coating powder at 1.5

    to 2.0 inches, to a certain extent, improve the anti-group performance of powder.
    3.5 Product Performance Test Results
    Through the study of the main epoxy resin of the film-forming system, the selection of curing agents, the optimization dosage of curing promoters and the study of additives and other formula optimization process, the results were obtained in 130 degrees C/ 20min conditions completely cured bicycle bottom with low temperature curing powder coating performance test results as shown in Table 8 below, the main key performance to meet the testing standards. The main performance test results of
    Table 8 products
    Concluding:
    through the film-forming system main body epoxy resin research, curing agent selection, curing promoter optimization dosage and additive research and other formula optimization process, the final preparation of the bicycle bottom coating powder coating products at 130 degrees C / 20 minutes to achieve full cross-curing, its coating provides excellent adhesion and corrosion resistance. Can be used in perfect match with color paint, transparent paint, improve customer productivity. Compared with the traditional bicycle coating process, it has the advantages of energy saving and environmental protection.
    Liang Yongtian Koo Zhengjun Luo Miansheng Cheng Lei / Guangzhou Dynasky Materials Technology Co., Ltd
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