TDI-TMP curing agent prepared from toluene diisocyanate (TDI) and trimethylolpropane (TMP) is a kind of polyurethane curing agent with large production volume and wide use in my country, and is widely used in coatings, adhesives and other products. However, at present most domestic curing agent enterprises produce TDI-TMP curing agents with a solid content of 75%, there are generally certain quality defects, such as high free TDI monomer content (mass fraction above 3.0%), It does not meet the national environmental protection requirements; or although it can reduce free TDI, it causes adverse effects such as high viscosity, poor compatibility, dull luster, and short storage period, and cannot reach the quality level of imported similar 75% solid content curing agents; Some enterprises are even unable to synthesize 75% high solid content curing agent because of unqualified technology, and can only synthesize lower solid content curing agent below 65% [2].
In this study, the TDI-TMP adduct system was used as the main body, and a small amount of mixed polyols were introduced to optimize the adduct. Then, by adding a suitable catalyst, the residual free TDI monomer was subjected to a trimerization reaction to synthesize a A new type of high-performance polyurethane environmental protection curing agent with low free TDI monomer content, high compatibility and high solid content, and a comparison test with imported similar curing agents for paint spray boards.
1 Experimental part
1. 1 Main raw materials and instruments
Toluene diisocyanate (TDI-80), BASF (Shanghai) company; Trimethylolpropane (TMP), Mitsubishi Corporation of Japan; Ethyl acetate, Jiangmen Qianxin Chemical Development Co., Ltd.; Mixed glycol (diethylene glycol/propylene glycol/ Neopentyl glycol mass ratio is about 1: 1: 1), Shenzhen Hui Chengzhong Industrial Co., Ltd.; 2,6-di-tert-butyl-4-methylphenol (antioxidant BHT), German LANXESS company; Dibutyltin dilaurate (DBT-DL), Guangzhou Wanggang Trading Co., Ltd.; lithium acetate, Guangzhou Shangbang Trading Co., Ltd.; tributylphosphine, Shanghai Rongli Chemical Technology Co., Ltd.; 2,4,6-tri( Dimethylaminomethyl) phenol (DMP-30), Guangzhou Green Trading Co., Ltd.; amine catalyst G-100, self-made; phosphoric acid, Guangzhou Yiyu Chemical Co., Ltd.; PU bright paint, matte paint, Guangzhou Panyu DISS PAINT CHEMICALS CO.,LTD. All of the above are industrial grade.
7820A Gas Chromatograph, Agilent Company, USA; DV-C Digital Display Viscometer, Brookfield Company, USA; QHQ-A Pencil Scratch Hardness Tester, Tianjin Zhonghuan Test Instrument Factory; WGG60-E4 Gloss Meter, Quanzhou Branch Shijia Photoelectric Instrument Co., Ltd.; QFZ Paint Film Adhesion Tester, QTX Paint Film Flexibility Tester, QCJ-120A/B Paint Film Impactor, Dongguan Tangxia Seiko Instrument Factory.
1. 2 Synthesis process
Put the set amount of TDI, ethyl acetate and antioxidant BHT into the reaction bottle, start stirring, put in the set amount of TMP and mixed polyglycol in batches, and react at 60-80 °C for 3-6 h. Then lower the temperature to 50-70 °C, put in a certain amount of catalyst G-100, and maintain a constant temperature of 60 °C for 1 h, start to track and test the NCO value and free TDI content of the reactants, and measure it every 30 min. (12. 1 ± 0. 5)%, after the mass fraction of free TDI ≤ 1. 0%, quickly add the polymerization inhibitor phosphoric acid, stir evenly, then raise the temperature to 80-90 ℃, and keep it for 30-40 min. Finally, reduce the temperature of the product to below 50°C, and filter out the material to obtain the desired curing agent product. Its technical indicators are shown in Table 1.
1. 3 Paint mixing performance test
Both the imported and the 75% solid content curing agent synthesized in this experiment were diluted with butyl acetate to form a 40% solid content curing agent. Mix PU varnish (matt paint)/dilute curing agent/PU diluent in a mass ratio of 1.0: 0.8: 0.7 (1.0: 0.5: 0.8) and perform PU respectively. Comparison experiment of spray board with gloss paint and matt paint.
1.4 Analysis and testing
Gloss is tested according to GB/T 9754-2007; pencil hardness is tested according to GB/T 6739-2006; impact strength is tested according to GB/T 1732-1993; flexibility is tested according to GB/T 1731-1993; adhesion Test according to GB/T 1720-1989 method; free TDI content is determined according to GB/T 18446-2009 standard; solid content is determined according to GB/T 1725-2007 method; NCO content is determined by di-n-butylamine method; viscosity is determined according to GB/T 9751. 1—2008 method test; Tolerance is measured by the ratio of tolerance after the curing agent and xylene are mixed and stirred evenly.
2 Results and discussion
2.1 Effect of catalyst
In the catalytic polymerization reaction, the catalyst needs to have the characteristics of high catalytic activity, strong selectivity, less side reactions, and mild reaction process. There are many kinds of catalysts commonly used in the trimerization reaction, such as amine compounds, organic phosphine compounds, alkali metal salts, organometallic compounds, etc. In this study, DBTDL, lithium acetate, tributylphosphine, DMP-30, self-made G-100 and other trimerization catalysts were used to perform comparative experiments in the same ratio under the condition of mixed diols replacing 20% TMP. The results are shown in Table 2 .
It can be seen from Table 2 that DBTDL can promote the reaction of NCO group and OH group, but it has no obvious effect on the trimerization reaction of TDI monomer; although lithium acetate, tributylphosphine and DMP-30 show considerable catalytic activity, their selection However, the self-made catalyst G-100 has excellent selectivity and can reduce the free TDI monomer mass fraction to below 1.0%, and the reaction efficiency is high, which is more satisfactory. trimerization catalyst.
2.2 Effect of reaction temperature
Considering time and efficiency, the reaction temperature should generally not be too low, otherwise the reaction will be slow; if the temperature is too high, the reaction will be difficult to control, side reactions will increase, and the relative molecular weight of the product will increase, which will easily lead to a rapid increase in product viscosity, and even solidification. Danger. In this experiment, under the condition that 20% TMP is replaced by mixed diol, self-made G-100 catalyst is used, and the same ratio (0.2% of the total formula) is used to conduct a comparative experiment of reaction temperature in the range of 40-80 ℃. The results are shown in Table 3.
It can be seen from Table 3 that the reaction is fast at 80 °C, and the end point can be reached in a short time, but the performance of the synthetic product is not good, showing low NCO content, high viscosity, and low tolerance; while at 40 °C, the reaction The time is too long and the production efficiency is low. Considering comprehensively, this experiment chooses to react at about 60 ℃, not only can obtain products with excellent comprehensive properties, but also the reaction is easy to control and the production efficiency is high.
2.3 Effect of the amount of mixed diols
The addition reaction of conventional TDI and TMP followed by trimerization can reduce the content of free TDI, but the performance of the synthesized product is not good, such as high viscosity, high content of free TDI, poor compatibility, and short storage period. . This experiment found that using part of the diol mixture to replace TMP in the TDI-TMP reaction system can effectively adjust the functionality of the reaction system to achieve the purpose of reducing product viscosity and improving compatibility. The impact of different substitution ratios is shown in Table 4.
It can be seen from Table 4 that if the ratio of replacing TMP with mixed diol is too low or too high, it will have a great impact on the performance of the product. However, if the mass fraction of the mixed diol in the polyol raw material is selected as 20%, the curing agent with low free TDI content, low viscosity and good compatibility can be obtained.
2.4 Comparison of paint matching performance
This experiment examines the performance of the curing agent by testing the performance of the paint film. The curing agent and the paint are used to match the spray board in a certain proportion. Under the same experimental conditions, the curing agent synthesized by this method is compared with the imported curing agent with the same solid content. The results are shown in Table 5.
As can be seen from Table 5, the curing agent synthesized by this method is compared with the imported curing agent, whether it is a gloss paint or a matte paint, the performance is not much different, but there is a slight difference in drying time and gloss. The same kind of imported curing agent has faster drying speed and lower gloss; other aspects such as hardness, impact strength and flexibility are basically the same. It can be seen that in the matte system, this curing agent can replace similar imported curing agents, and its performance is even superior.
3 Conclusion
(1) The self-made G-100 catalyst is selected, the reaction temperature is controlled at about 60 ℃, the mass fraction of free TDI in the curing agent can be reduced to below 1.0%, and the comprehensive performance is good.
(2) Replacing TMP with 20% mixed diol can reduce product viscosity and improve compatibility.
(3) The results of the comparison test of paint matching show that the performance of the synthesized curing agent is basically the same as that of imported similar curing agents, and can replace imported products for matte paint.
