Triglycidyl isocyanurate (TGIC) is used as a curing agent in polyester powder coatings. It has excellent weather resistance, heat resistance, high temperature electrical properties and adhesion, and is resistant to acids, alkalis and other chemicals. It has high product stability and excellent cross-linking and curing properties. It is one of the important curing agents for base materials containing carboxyl functional groups. It is especially suitable as a curing agent for carboxylic acid polyester powder coatings. There are three chiral carbon atoms in the TGIC molecular structure, two of which correspond to racemates. The four symmetry points of its symmetric structure exist in the configuration of chiral carbon atoms, which are called RRR, SSS, RRS and SSR respectively. Therefore, the synthesized and commercially available TGIC are mixtures of these two corresponding racemates. Polyester powder paste with TGIC as curing agent. The coating formed through high-temperature curing has the characteristics of energy saving, resource saving, high labor productivity, no pollution and easy automation, and has become a rapidly developing new coating product. With the development of industries such as outdoor furniture, home appliances and equipment, the application of powder coatings has attracted more and more attention. Nowadays, weather-resistant powder coatings have huge markets and business opportunities. The main markets include: aluminum profiles, air conditioners, highway construction, automobile industry, outdoor furniture and lamps, etc.
This article reviews the synthesis methods, applications, and substitutes of triglycidyl isocyanurate, and provides information for the research and utilization of triglycidyl isocyanurate, and the selection and application of substitutes. Definitely a reference.
Research on Triglycidyl Isocyanurate and Its Substitutes 1 Synthesis Progress of TGIC
TGIC is a high-performance, versatile matrix resin. The synthesis methods of TGIC mainly include one-step method, two-step method and epoxidation method.
1.1 One-step method
The one-step method was first developed by the research team headed by Dr. M Budnowski of Henkel’s central laboratory. The main disadvantages of this method are that the ratio of reaction raw materials is too large, the output of a single tank is small, and the yield is low. The reaction process is shown in Figure 1.
1.2 Two-step method
The industrial synthesis of TGIC mainly adopts a two-step method. The first step is to use solid phase isocyanuric acid and liquid phase epichlorohydrin under the action of a catalyst to generate the intermediate 1,3,5-tris(1 `-Chloro-2`hydroxy-propyl)isocyanurate. Isocyanuric acid is a symmetrical six-membered compound. The carbon and nitrogen atoms on the ring are alternately arranged. There are two tautomers of cyanuric acid and isocyanuric acid. In the first step of the reaction, cyanuric acid The acid is converted into isocyanuric acid to participate in the reaction. The second step of the cyclization reaction is the reaction of 1,3,5-tris(1′-chloro-2`hydroxy-propyl)isocyanurate with NaOH to remove 1,3,5-tris(1′-chloro- The three HCIs in the 2`hydroxy-propyl)isocyanurate molecule generate TGIC. The synthetic route is shown in Figure 2.
1.3 Epoxidation method
The epoxidation method uses tripropyl isocyanurate as raw material to synthesize TGIC. The synthesis route is shown in Figure 3. Due to the expensive raw materials and lack of economic competitiveness, it is difficult to achieve industrial production scale and is rarely used now.
1.4 Other synthesis methods
In 1996, scientists such as Hideto Minami used a new method to obtain nano-sized cross-linked polyester particles with a hollow structure, which was named the SaPSeP method. In addition, relevant literature also reports on the preparation of triglycidyl isocyanurate using cyanuric acid chloride and glycidol as raw materials or the transesterification reaction between cyanuric acid toluene sulfonate barium carbonate and glycidyl ester to obtain isocyanuric acid. Triglycidyl ester However, all things considered, only the two-step synthesis route has important industrial value.
Research on Triglycidyl Isocyanurate and Its Substitutes 2 Application of TGIC Powder Coatings
TGIC is a crystalline heterocyclic epoxy compound, its structural formula is shown in Figure 4.
As can be seen from Figure 4, first of all, its structure has two or three reactive active groups, which can obtain a higher cross-linking density during curing. The rigid rings in the structure lead to a higher hardness of the cured coating film; secondly, Because after curing, there are single bonds in the molecular skeleton, so it has excellent weather resistance; thirdly, the nitrogen content in the molecule is high, and it is flame retardant and self-extinguishing. When TGIC cures polyester resin to form a powder coating, a highly active epoxy group can perform high-density cross-linking with the carboxyl groups in the resin, and the stability of the heterocyclic ring ensures excellent weather resistance of the powder coating using TGIC as the curing agent. sex.
2.1 TGIC is used as a powder coating curing agent
TGIC is the earliest curing agent used in weather-resistant powder coatings. 2001E. G. Belder et al. used a combination of differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and an improved version of DL-TMA technology to explore the different stages that occur during the curing process of powder coatings. The establishment of this program can determine the period when the powder coating melts and the sodium bicarbonate flows, and determines the gel point and gel transition., the results show that the stability of polyepoxy triglycidyl isocyanurate is comparable to TGIC, and is stronger than general cross-linking agents and glutaraldehyde. Research results show that TEPIC (polyepoxy triglycidyl isocyanurate) is an efficient aldehyde substitute and has great application prospects in the leather and textile industries.
3.2.2 UV-curing powder coating
Saeid Bastanil studied the curing of powder coatings by UV radiation, which have an interpenetrating polymer network structure, and investigated its advantages and disadvantages compared with thermoset powder coatings. In recent research, two different UV-curing systems have been applied, and their IPNs structures have been obtained. These improved radiation-cured powder coatings offer greatly improved physical properties and mechanical properties.
3.2.3 Flax oil substitute
A. Overeem et al. conducted research on linseed oil. The research results show that linseed oil with high oxygen content can replace TGIC as a cross-linking agent in powder coatings. According to work experience, seed oil is rich in linolenic acid and can be used to synthesize ethylene oxide. Unsaturated linseed oil can generate peracetic acid through epoxidation reaction to introduce epoxy groups. Linseed oil with high oxygen content can be used as a cross-linking agent in powder coatings. Compared to triglycidyl isocyanurate, which is widely used as a cross-linking agent. The biggest advantage of linseed oil as a cross-linking agent for powder coatings is that it is non-toxic and non-mutagenic. There are also two problems when using aliphatic ethylene oxide as a substitute for TGIC, the glass transition temperature of the powder coating is reduced and a deep yellowing of the powder coating can be observed. but. There is no doubt that aliphatic ethylene oxide is an ideal environmentally friendly cross-linking agent in powder coating systems.
3.2.4 Other alternatives
Dean C. Websterll reported that cyclic carbonates can be used as curing agents instead of TGIC in powder coatings. Research results by Massimiliano Barletta and others show that carbon fiber epoxy resin has good surface beautification and protective effects and can replace TGIC powder coatings used in the electronic spraying industry. Bart A.J. Noordover proposed that the introduction of biologically grown polyesters such as citric acid and glycerin into powder coatings can significantly enhance the mechanical and chemical properties of powder coatings.
3.2.5 Improvement directions of alternatives
In order to compare the relative stability of TGIC alternatives, S.Montserrat et al. studied the physical aging properties of some thermosetting powder coatings. The aging properties were measured by differential scanning calorimetry at room temperature and the kinetic parameters of the reaction enthalpy were determined by peak shift analysis. Their aging rates are very small compared to TGIC. Therefore, what needs improvement in the performance of the surrogate system is the stability of the surrogate.
Research on triglycidyl isocyanurate and its substitutes 4 Conclusion
With increasingly stringent environmental protection requirements, powder coatings have been vigorously developed due to their advantages of low pollution, high decoration, and good overall performance. Look at the entire world. The use of powder coatings is growing at a rate of more than 10% every year. Among them, TGIC powder coatings have developed extremely rapidly due to their excellent weather resistance and chemical resistance. The TGIC system has good weather resistance, but TGIC is toxic, which limits its further development. Consumers have expressed particular concern about the toxicity of TGIC, prompting manufacturers to adopt TGIC-free systems with performance comparable to toxic TGIC. The TGIC-free system is still in the early development stage and needs to improve the leveling and physical properties. In China, the use of TGIC still dominates, but since the introduction of its substitutes, many manufacturers have adopted substitutes in painting, and their usage has a gradually increasing trend.
