Color paste, as the main auxiliary agent used in polyurethane foaming, is widely used in various polyurethane materials. Our factory, as a professional polyurethane color paste manufacturer in East China, produces color pastes with high color density, good fluidity, large additions without affecting foaming, bright colors, and strong weather resistance.......
Isocyanate
Like other polyurethane materials, isocyanate is the basic raw material for preparing polyurethane rigid foam. The isocyanate used is mainly TDI and crude MDI (sometimes called polyphenyl polymethylene polyisocyanate PAPI). Early production of rigid polyurethane foam mainly uses TDI, but there are two major problems in use. First, the mass percentage of NCO in TDI is too high (48.3%), the heat released during the reaction is too large, which is not conducive to the production control of hard foam. Second, the vapor pressure of TDI is large, which causes great damage to the production environment and operators during production. Therefore, in the production of rigid polyurethane foams, the use of TDI is gradually decreasing. Most of the modified products of TDI, that is, the end group generated by the reaction of TDI and polyol is a top polymer of an NCO group, reduces the content of one NCO to 25% ~ 35% (mass). At the same time, it increases the molecular weight of isocyanate, reduces its vapor pressure, and reduces the degree of harm to human health caused by the use of pure TDI. In addition, in the production of modern polyurethane hard foam, a large amount of crude TDI is used or blended with TDI and crude MDI to improve the production environment, foaming process and product performance. Crude TDI is produced during the TDI production process. In the distillation of pure TDI products, 10% to 15% of tar-like substance will be produced, which was discarded as waste liquid and waste residue in the past. After analysis, it was found that its main component is TDI polymer, and contains a certain amount of TDI active ingredients. On the basis of further comprehensive utilization research, it was found that the use of crude TDI added with a certain amount of pure TDI is a good raw material for the preparation of hard foam. Practice has proved that the rigidity of the polyurethane rigid foam prepared by using crude TDI or TDI prepolymer is even better than that of crude MDI-based rigid foam. Crude MDI is the product produced during the production of pure MDI. In the condensation reaction of aniline and formaldehyde, two molecules of aniline and one molecule of formaldehyde are condensed to obtain diphenylmethanediamine, which is then phosgenated to produce MDI. However, during the condensation reaction, due to reasons such as reaction condition control, the A certain amount of chain macromolecules will be condensed to produce polyphenyl polymethylene; the amine will generate a certain amount of polyphenyl polymethylene polyisocyanate in the MDI production with the phosgenation reaction. It can be seen that the product produced by MDI is a mixture before the MDI product is distilled, and its composition varies greatly with the changes of raw materials, reaction conditions, process control and other factors. In the production of MDI, after the pure 4, 4'-MDI and 2, 4'-MDI are extracted by distillation, the remaining material is basically a mixture of polyphenyl polymethylene polyisocyanates with a degree of polymerization greater than 1. Depending on the degree of polymerization, the viscosity and the content of one NCO are also different. When using them to prepare polyurethane rigid foams, different varieties of crude MDI should be selected according to processing conditions and product performance requirements. For example, when pouring rigid polyurethane foams with complex structural shapes, priority should be given to the viscosity and fluidity of the mixture. It is recommended to choose polymeric MDI with lower viscosity and lower functionality; when producing building insulation boards, choose moderate viscosity 1. Polymerized MDI varieties with higher functionality to shorten the curing time of the product and increase the compressive strength of the foam. Using polymeric MDI to prepare polyurethane rigid foam has the following advantages compared to TDI. First, due to the introduction of a polyphenyl ring structure in the polymer molecule, the thermal stability of the foam is improved, and the dimensional stability of the product is improved; second, due to the low vapor pressure and low volatility of the polymerized MDI product, it is used in Medium, the harmful gas has less volatilization, which is conducive to the improvement of the operator's health and industrial environmental protection and hygiene conditions. Third, the polymer MDI-based rigid foam products have a smooth surface, excellent mold release performance, and good resistance to oil and chemicals.
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