The effect of organo tin catalysts on the synthesis of polyester resins in powder coatings

Abstract:
Two polyester resins were synthesized from new glycol (NPG) and PTA monomers, as well as ethylene glycol (EG), glycol (DEG) and pTA monomers, and the catalytic properties of 5 organic tin catalysts in two groups of polyester resin synthesis were compared by analysis methods such as acid value, gel permeation chromatography (GPC). The results showed that the catalytic rate of PC9800 and PC4100 was fast, suitable for the preparation of polyester with high molecular weight, the reaction of PC779 catalysis was more intense, the binary alcohol loss was excessive, and the catalytic rate of PC380 was flat and slow, which was suitable for the preparation of polyester with low and medium molecular weight and narrow molecular weight distribution. The catalytic rate of PC918 is slow and the catalysis effect is not ideal, the catalytic rate of PC9800 is different in two polyester synthesis, and the catalytic rate of PC779, PC4100, PC380 and PC918 is less different in the two polyester synthesis.
powder coating is usually polyester resin as the main raw material, polyester performance has a great impact on the coating
China
. Polyester resin is composed of binary acid and binary alcohol heating, the performance of polyester mainly depends on the molecular weight of polyester resin and molecular weight distribution. Polyester resin synthesized with new glycol has the characteristics of good weather resistance and high film strength, and is mainly used as high-level paint, self-drying paint and so on. Polyester resins synthesized with ethylene glycol have good wear resistance and dimensional stability and are widely used in fiber and engineering plastics. Because of the new glycol molecule has a new pyro-based structure, in the polyester resin molecular chain plays a protective role, so that such resins as raw materials prepared powder coatings have excellent stability and mobility. Polyester synthesis can control the reaction rate by adding catalyst, thereby controlling the molecular weight and molecular weight distribution of polyester, in the reaction process, intense reaction heating will lead to the loss of polyols, incomplete reaction, by adjusting the ratio of binary alcohol and binary acid, the use of step-by-step heating process and the selection of a specific catalyst is also an important way to control the reaction process. There are a wide variety of catalysts for esterification reactions, such as tin, vanadium and titanium. Traditional polyester resin synthesis processes typically use organo tin compounds as esterification catalysts. Organo tin compounds by carbon and tin elements directly combined to form metal organic compounds, as a catalyst when the side reaction is less, does not affect the purity and quality of the product and other characteristics, catalytic effect is good, and organo tin catalyst has thermal stability and non-corrosive, reaction end without separation, no need for post-treatment, convenient production, but also greatly shorten the process cycle. Organotin catalysts are mainly organotin compounds such as monoclothyl tin and butyltin, of which monoclothyltin is one of the most widely used traditional high-efficiency organotin catalysts. In this paper, five organo tin catalysts are used to catalyticize the synthesis of two polyester resins, to study the catalytic properties of five catalysts and the impact on polyester resins, and to compare the catalytic rate of the same catalysts in two polyester synthesiss.
1 Experiments
1.1 Raw Materials
New Glycol, Industrial Grade, Wanhua Chemical Group Co., Ltd.;
PC9800, PC4100 and PC779 are white powders, and PC380 and PC918 are slightly yellow oily liquids. Pc4100 is a tin-butyl oxide, PC9800 and PC918 are tin chelates, PC779 and PC380 are a derivative of tin-butyl oxide. Because butyl tin is not environmentally friendly, PC4100, PC779 and PC380 containing butyl tin are restricted from export, while PC9800 and PC918 do not contain harmful ingredients such as butyl tin, is a new type of environmentally friendly catalyst.
1.2 instrument
ZNHW intelligent thermostat, Shanghai Purdue Technology Co., Ltd.; WAY2S digital abe refractometer, Shanghai Precision Science Instrument Co., Ltd.; PLGPC50 type gel penetration chromatography, Beijing Priteko Instrument Co., Ltd.; SNBAI type high temperature viscosity meter, Shanghai Quasi Instrument Co., Ltd.; YT4507B softening point detector, Shanghai Yutong Instrument Factory.
of 1.3 polyester resins is
EG-PTA polyester resin is a polymerization system based on glycol (EG), glycol (DEG) and parabens (PTA), and NPG-PTA polyester resins are polymerization systems based on new glycol (NPG) and parabens (PTA). Synthesis of EG-PTA polyester resins: 18.93%, 15.37% and 65.75%, respectively, with a total mass of 1.6 kg of glycol, glycol and benzoic acid, the five organotin catalysts were 0.08% of the total quality. Pour the called glycol and glycol into a four-mouthed bottle of 2L, heat up to 85C and adjust the stirring speed to 150r/min. The organo tin catalyst and benzoic acid were added to the can, heated to 180 degrees C, and the stirring speed was adjusted to 200r/min. After returning 40min, the condensate is connected and heated up to 240 degrees C step by step, recording the reaction time, reaction temperature, condensation temperature and water outflow. The decrease in condensation temperature indicates that there is no water generation in the reaction process, which is regarded as the end point of the reaction, and the recline rate of esterified water is determined. The synthesis process of NPG-PTA polyester resins is the same as that of EG-PTA polyester resins, in which the total mass of 1.6kG of new glycol and benzoic acid was 1.6kG, respectively, according to the mass score of 40.19% and 59.81%, and the dosing of 5 organotin catalysts was 0.08% of the total quality.
1.4 Performance Test
Acid value of the polymerization system is tested by GB/T 2895-2008, polyester viscosity is tested by GB/T 2794-1995, and polyester softens by GB/T Tested from 4507 to 2014, the refractive index of esterified water was tested with an Abe refractometer, and the molecular weight of polyester was tested with a gel permeable chromatography, with tethydrofuran as the flow phase, with a flow rate of 1mL/min and a column temperature of 25 degrees C.
2 Results compared with the catalytic properties of
2.15 catalysts
acid values are a common indicator of the esterification reaction process, and the length of time it takes to reach specified acid values reflects the catalytic efficiency of a catalyst. Figure 1 compares the catalytic efficiency of five catalysts in the EG-PTA polymerization system. As can be seen from Figure 1, the catalytic efficiency of PC4100, PC9800 and PC779 is higher than that of PC380 and PC779, of which PC779 has the highest catalytic efficiency and PC918 has the lowest catalytic efficiency, while the environmentally friendly catalyst PC9800 is only slightly lower than the traditional high-efficiency catalyst PC4100. According to experimental experience, the acid value of polyester after the esterization fusion reaction is around 33 mg/g. Table 1 PC4100, PC9800 and PC779 need 6.4h to reach the specified acid value, PC380 needs 7.2h, PC918 needs 8.0h, combined with the five catalysts in the synthesis of the reaction degree and time relationship, PC4100, PC9800 and PC779 to make the reaction speed faster.
remnance rate, as a standard for the purity of liquid substances, is one of the commonly used physical constants, and the size of esterified water recrystination rate indicates the amount of polyol loss during the esterification reaction. From Table 1, it can be seen that the esterified water recrystination rate corresponding to the five catalysts is within a reasonable range, although the catalytic efficiency of PC779 is high, but from the recline rate, it can be seen that its catalytic reaction consumes more polyols than PC9800 and PC4100. Pc380 catalytic action is relatively peaceful, its recerle rate and catalytic efficiency of the PC9800 is similar, is the least polyol loss of the two catalysts. The pre-astrogenic reaction is mainly the process of lymers such as monomers and trimers, which slowly shrink into large molecules in the later stages of reaction. Ester reaction is a typical polymerization reaction, the catalytic efficiency of the pre-reaction can quickly reduce the acid value, thus shortening the reaction time, the late reaction system viscosity increases, not easy to dehydrate, catalytic efficiency will directly affect the molecular weight size and distribution of the final polyester resin. The catalytic efficiency of PC9800, PC4100 and PC779 is higher than that of the other two catalysts, and table 2 shows that the polyester molecular weight of these three catalysts is also greater than that of the other two, proving that high-efficiency catalysts can increase the molecular weight of polyester resins. PC380 catalytic action is weak, the reaction rate is relatively slow, polyester resin molecular weight is slightly lower, the reaction is more peaceful, polyol loss is less, you can get low and medium molecular weight and molecular weight distribution narrow polyester resin.
is available from Table 2: The higher the molecular weight of synthetic polyester, the higher the viscosity and softening point of polyester resin. If the melting of polyester resin is too large, its fluidity will become worse, after the powder is made, the coating skin phenomenon is serious, affecting aesthetics. If the molecular weight of polyester is too small, although the melting fluidity of polyester resin is improved, the surface level of the coating film after powder is better, but the flow hanging phenomenon is serious, and the curing time will be extended, resulting in the decline of the electrometic properties of the coating film, while its storage stability is also affected. Polyester resin's average molecular weight is generally in the range of 2000 to 5000, when the average molecular weight of polyester exceeds this range, its impact strength, adhesion and flexibility are not up to the technical index requirements.
2.2 PC9800 Comparing catalytic rates in two polyester synthesis
esterification reactions are a process of gradual polymerization, and in order to accurately and intuitively compare catalyst catalytic rates in EG-PTA and NPG-PTA polyester resin synthesis, the esterification rate is defined as the percentage of total esterified water generated at each point in time. As can be seen from Figure 2, the effect of PC9800 on the catalytic rate in two groups of polyester synthesis is significantly different, and the catalytic rate in the EG-PTA polymerization system is higher overall than that of NPG-PTA polymerization system, and high molecular weight polyester can be obtained; The catalytic rate in NPG-PTA polymerization system is slow and fast before, and higher molecular weight polyester can also be obtained, but the change of catalytic rate will lead to a wide distribution of polyester molecular weight, uneven molecular distribution in the molecular chain, and unstable performance of polyester.
2.3 PC4100 and PC779 have different catalytic rates in two polyester synthesiss
comparing Figures 2 and 3 shows that the difference in catalytic rates in PC4100 in two combinations is not as large as the PC9800. The catalytic rate of PC4100 in EG-PTA polymerization system is slightly higher than NPG-PTA, both combinations of catalytic properties are continuously efficient, however, the catalytic rate of PC4100 in EG-PTA polymerization system is obviously not as smooth as NPG-PTA polymerization system, which will eventually affect the molecular weight distribution of polyester, resulting in the stability of polyester is not as good as that of NPG-PTA polymerization system synthesis.
PC4100 and PC779 are both traditional high-efficiency catalysts, as can be seen from Figure 4: PC779 not only has a fast catalytic rate in two combinations, but also has a basically consistent catalytic effect, indicating that pc779 maintains the same catalytic properties in both EG-PTA and NPG-PTA polymerization systems.
2.4 PC380 and PC918 have different catalytic rates in two polyester synthesiss
comparing Figures 5 and 6 shows that the catalytic properties of PC380 and PC918 prior to reaction are approximately the same in both synthesises. The catalytic rate of the EG-PTA polymerization system is higher than that of NPG-PTA, and in the later stages of reaction, the catalytic rate of PC380 in the two combinations is similar, while the catalytic rate of PC918 in the NPG-PTA polymerization system is slightly higher than that of EG-PTA.
3 Conclusions
Pc9800 and PC4100 in polyester synthesis catalytic efficiency, greatly shorten the process cycle, suitable for the preparation of high molecular weight and narrow molecular weight distribution of polyester, PC9800 is an environmentally friendly catalyst, to some extent better performance than PC4100; The reaction is too intense, the loss of polyol is more, the catalytic efficiency of PC380 is general, the reaction is peaceful, suitable for the preparation of low and medium molecular weight and narrow molecular weight distribution of polyester products, pc918 catalytic efficiency is poor, the reaction time is too long, the catalytic effect is not ideal. Comparing the catalytic rate of the same catalyst between EG-PTA and NPG-PTA, the catalytic rate of PC779, PC918 and PC380 differed less between the two combinations;
Wen / Liu Gang 1, Wang Ting comfort 1, Di Chao 2
1. Nanjing University of Technology School of Materials Science and Engineering
2. Nanjing Dingchen Chemical Technology Co., Ltd