| In two-component polyurethane coatings,since TDI trimer curing agent has a strong isocyanate six-membered ring structure,it can effectively increase the drying speed and hardness of the paint film and improve the performance of the paint film after it is mixed with the resin component to paint.At present,the curing agent products produced or sold in China generally have a series of problems such as low tolerance,high free content,that is,insufficient comprehensive performance of the paint film.The implementation of the national standard means that most domestic manufacturers will adopt the method of importing foreign excellent products or mixing and repackaging,which will increase production costs.Therefore,the purpose of this article is to develop a bright TDI trimer curing agent with low free compatibility and good compatibility.Pilot experiments will be carried out on the basis of mature small-scale formulations.The specific work is as follows:Firstly,use single factor variable experiments to synthesize samples in a 1 L round-bottom flask,and screen out suitable catalysts TDBA and BDTP based on the physical and chemical indexes of curing agent samples.,and then explore the optimal reaction temperature and usage amount of these two catalysts.It was found that the activity of TDBA in the early stage of the reaction is stronger in the later stage and become weaker later,and the catalytic activity of BDTP is relatively stable throughout the reaction process.The best use conditions for the two were 0.18 wt%of TDBA reacted at 70?,and 0.40 wt%of BDTP reacted at 80?.By comparing the effects of different types of modified unit alcohols,it was determined that the addition of 4 wt%dodecanol is most beneficial to improve the compatibility of the trimer on the basis of ensuring low free content,and the tolerance of the obtained sample was 3.22 on the tolerance of the curing agent.According to the orthogonal experiments,the optimal amount of the compound of the catalyst was determined,and the small-scale test process was adjusted to reduce the amount of T-100 added..Finally,the trial product contain the following indexes:NCO content was 7.36%,the viscosity value was 255 cp,the solid content was 50.84%,the tolerance was 3.22,and the free TDI content was 0.41%.In order to estimate the possible problems in the scale-up of the pilot experiment,A 5 L round-bottomed flask was used to carry out a 5kg pre-preparation experiment based on a small test formula,and the method of cooling the pre-reaction of the ice-water mixture and reducing the catalyst by an appropriate amount was used to finally obtain a product close to the indexes of the pilot sample.The double-layer folding blade paddle mechanical stirrer and 150 L semi-closed batch reactor was selected as the reaction stirrer and reactor.A 100kg pilot test was carried out in a 150 L reactor.It was found that using 0.06 wt%TDBA and 0.12 wt%BDTP compound catalyst,while adding raw materials in batches,the reaction temperature can be well controlled.Pilot products with similar indexes.The comprehensive performance evaluation of the pilot-scale curing agent and other types of commercially available trimer curing agents showed that the indexes of the self-synthetic curing agent have reached the commercial standard,and the storage stability is slightly worse than that of Bayer L1451.The self-synthetic curing agent and Bayer L1451,Mitsui D262,Wanhua 6856F and Carpoly G03M was explored and compared on the overall performance of the paint film,and the effect of different amounts of TDI trimer on the performance of the paint film was studied.The added amount of self-synthetic curing agent is 24 wt%of the content of the curing agent component to obtain a paint film with the best overall performance,when mixing paint.The results show that the pilot-scale bright curing agent has reached the market standard in terms of the indexes and comprehensive performance,and further production planning and product optimization can be carried out. |
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