Synthesis Of Water Dispersible HDI-TDI Mixed Polymer Curing Agent And Its Application

With the improvement of people’s awareness of environmental protection and the increasingly strict requirements of national policies,the development of environment-friendly coatings is an inevitable trend.Among them,waterborne two-component polyurethane has attracted a lot of attention because of its excellent properties which is widely used in many fields such as coatings,adhesives and so on.As the key component of water-based curing agent,its research in China is relatively insufficient.At present,the preparation of water-dispersible polyisocyanate curing agents is generally based on hydrophilic modification of aliphatic polyisocyanates,such as HDI trimers.It has the advantages of excellent weather resistance and heat resistance,high solid content and low viscosity,good storage stability and good flexibility,but it has low reaction activity,low film hardness,slow drying speed and high price.In contrast,aromatic polyisocyanates have high reaction activity,high film hardness,fast drying speed and low price.In view of the shortcomings of HDI trimer,a water dispersible TDI-HDI mixed polymer curing agent can be developed.Combined with their advantages,it can reduce the cost of raw materials and improve the film performance.Firstly,HDI-TDI hybrid multipolymer curing agents with low free monomers were synthesized.In terms of raw materials,compared with the traditional synthesis which using TDI and HDI monomers as raw materials,this paper innovatively uses TDI monomers and HDI trimers as raw materials of the reaction,so we can avoid the step of removing the low reactive HDI monomer.HDI monomers need to be removed by thin film evaporation,so we can greatly simplify the process and save production costs.Then the catalytic effect of self-made Mannich base TDBA,triethylenediamine,tetramethyl ammonium hydroxide,and tributyl phosphate on the copolymerization of HDI trimer and TDI monomer were compared,and it is found that the self-made Mannich base TDBA shows the excellent catalytic effect.Then the catalytic law of the catalyst was studied,and the specific process was finally determined.The amount of TDI added is 5 wt%,the amount of TDBA is 0.2 wt%,and the reaction temperature is 65℃,and finally a product with a free monomer content as low as0.34 % is obtained.In the research process of the hydrophilic modification of the self-made low free monomer HDI-TDI mixed polymer,the feeding process,the amount of hydrophilic modifier,neutralizer,reaction temperature,etc.were explored,and the process was finally determined.Firstly,the HDI-TDI mixed polymer and CAPS should be pre-mixed before the reaction,and the DMCHA was added slowly at a rate of 0.01 g/s.The amount of CAPS was 3 wt%,the amount of DMCHA was 1.1 times of the molar amount of CAPS,and the reaction temperature was 110℃.The self-made water-dispersible HDI-TDI mixed polymer curing agent was compared with the commercially available water-dispersible polyisocyanate curing agent in physicochemical index,storage stability,water dispersion performance and comprehensive coating performance.To sum up,the comprehensive performance of the self-made water-dispersible HDI-TDI mixed polymer curing agent is close to that of the commercially available products,the paint film has higher hardness and faster drying speed,but the storage stability is insufficient.