1.3 Selection of raw materials
Selection of oligomer polyols
As mentioned above, most curing agents on the market are not water-based, and hydrophilic groups need to be introduced to improve their water solubility. Polyether compounds are widely used because of their good hydrophilicity, especially water-soluble alcohol ethers have linear structure and contain more ether bonds per unit mass, which makes their water solubility more prominent than ordinary polyether polyols.
However, in the water-soluble alcohol ether series, the molecular weight gradually increases from small to large. But the molecular weight is too large, the reaction activity is small, and the reaction conditions are harsh. Even after reacting with the trimer of polyisocyanate, its product is easier to crystallize than other products, which is inconvenient to use. According to the actual water-solubility requirements, the water-soluble alcohol ether with medium molecular weight [4-6] was selected.
1.3.2 Selection of Vinegars with Different Atmosphere
At present, the commonly used polyisocyanates in the market include aromatic isocyanates such as toluene diisocyanate (TDI) and 4,4-diphenylmethane diisocyanate (MDI), and aliphatic groups such as isophorone isocyanate (IPDI), hexamethylene diisocyanate (HDI), 1, 12 dodecane diisocyanate (c, ZDDI).
Considering that trimer curing agent has the characteristics of faster curing speed, weather resistance and light irradiation resistance than low molecular alcohol adduct, mixed trimer has better weather resistance and light irradiation resistance. Therefore, there are many such curing agents.
It is used in two-component polyurethane vinegar paint and less in adhesive. Moreover, the functionality of the curing agent is not less than 2, so the trimer and thick vein are selected.
The trimers and dimers commonly used in polyisocyanate are HDI trimer, TDI trimer, IPDI trimer and HDI dimer. For trimer, considering the price factor, TDI trimer is the cheapest, but the experiment shows that its reaction activity is too high, the experimental conditions are difficult to control, it is easy to gel, a lot of acetone needs to be added, and the water solubility of the product is poor, so TDI trimer is rarely chosen; Comparing HDI trimer and IPDI trimer, both belong to aliphatic polyisocyanate. However, because the former is a linear molecule and the latter is a six-membered ring, the steric hindrance increases, the reaction activity decreases and the water solubility of the product is poor, so HDI trimer is selected as the trimer [8].
Compared with HD I condensed second pulse, the performance of HDI trimer is better than HDI condensed second pulse [9l, that is, 1]. The viscosity of HDI trimer polyisocyanate vinegar is lower than HDI condensation second pulse, which is beneficial to the use of less solvents. Can be made into products with high solid content, reduces air pollution and is beneficial to environmental protection; (2) The isocyanate ring of 2)HD I trimer is very stable, not easy to deteriorate, and the viscosity changes little after long-term storage; (3) The light resistance of 3)HD I trimer is higher than that of condensed second pulse; (4) The life of 4)HD I trimer is longer than that of concentrated second pulse; (5) The product of 5)H D I trimer has higher hardness, and its toughness and adhesion are similar to those of the second contraction pulse.