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Understand the technology of PC boards

by:UNQ     2021-04-28
The traditional phosgene interfacial polycondensation method is a two-step method, that is, a part of bisphenol A sodium salt aqueous solution and dichloromethane are slowly introduced into phosgene under agitation, so that oligomers are formed first, and then the catalyst is added and supplemented The remaining part of the bisphenol A sodium salt aqueous solution completes the polycondensation reaction. The whole process is divided into two steps: phosgenation and finishing. The disadvantage is that it takes a long time, bisphenol A is easy to oxidize and deteriorate under alkaline conditions, the space-time efficiency of the equipment is low, the saponification side reaction consumes more phosgene and alkali, the product has a wide molecular weight distribution and a large hydroxyl end group content. The continuity of the two-step method needs to be carried out in two steps, which is quite inconvenient. As an improvement to the two-step process, the one-step process is to suspend bisphenol A in water in a solid state, add the required solvent dichloromethane and additives, gradually add sodium hydroxide solution under stirring, and pass in phosgene. Its characteristic is that when the phosgenation reaction ends, the polycondensation reaction also ends, reducing the consumption of raw materials, and at the same time avoiding the oxidative decomposition of bisphenol A sodium salt in the alkaline medium, so that the product quality is improved. The one-step method described in many earlier patent documents, as mentioned above, all use gaseous phosgene, and the reaction time is still as long as half an hour to 12. The disadvantage is that the molecular weight distribution is very wide, the content of low molecular fraction is high, the molecular weight dispersion coefficient is very large, and the unit consumption of raw materials is still high. The Chenguang Research Institute of Chemical Industry of the former Ministry of Chemical Industry has systematically summarized previous experience, passed necessary theoretical analysis and confirmed, and created a new one-step synthesis process for polycarbonate based on a large number of experiments and practices. This method no longer uses gaseous phosgene, but dissolves phosgene in organic dichloromethane according to the required ratio to form an organic phase, and mixes bisphenol A, sodium hydroxide, molecular weight regulator, sodium bisulfite And an appropriate amount of catalyst is dissolved in water according to the required ratio to form an aqueous phase. The organic phase is placed at 0C or lower temperature for standby. Then the water phase and the organic phase are fed into the reactor according to an appropriate ratio to make them quickly mixed. Depending on the degree of dispersion and mixing of the two phases, the reaction is 1-10 min, and the desired result can be obtained. The advantages of the Chenguang one-step method are that the feeding method and reaction operation are simple, the reactor structure is simple, and it is suitable for continuous production and feedback automatic control. The reaction time is only 1~10min, and the space-time efficiency is as high as 1~5t/(m3•h). Because the main reaction time is very short, it not only helps to avoid the oxidation of bisphenol A sodium salt in the reactor, but also inhibits the side reaction of saponification. This is beneficial to reduce the hydroxyl end group content of the resin and improve the molecular weight distribution, and significantly reduce the unit consumption. The post-treatment process of the phosgenation interfacial polycondensation method is complicated and has always been a problem that plagues the entire production process. The main improvement of the post-treatment process is the development of a process route that combines evaporation and precipitation, and is equipped with a vented extruder. The methylene chloride glue solution dissolved with PC board and toluene vapor will be contacted in a countercurrent manner in the stripping tower to remove the dichloromethane which has a lower boiling point. Since the PC board is only slightly soluble in toluene, after the dichloromethane is removed, a slurry of polycarbonate and toluene will be obtained; a PC board-toluene mixture with a PC board content greater than 80% can be obtained by thin film evaporation; The air-type extruder removes residual toluene and extrudes it into pellets, which effectively simplifies the post-treatment process. Recently, new varieties of PC boards have emerged. Polyester carbonate was successfully developed by GE in the United States in 1979 and put into industrial production in 1982. Afterwards, United Chemical Company of the United States, Bayer of Germany, Dow Chemical of the United States and Mitsubishi Chemical of Japan have successively developed them. And produce. The glass transition temperature (eight) of ordinary bisphenol A PC board is 150C, while the pores of polyester carbonate can reach 160~212C, which combines the high heat resistance of polyarylate and the excellent impact strength of PC sheets. The trimethylcyclohexane bisphenol co-PC sheets is researched, developed and produced by Bayer. Trimethylcyclohexane bisphenol PC board itself not only has a Tg as high as 230 C, but also has good toughness, transparency and light stability. It can be blended with ordinary bisphenol A PC boards to produce a series of new PC board blends. The heat distortion temperature can be adjusted in the range of 160~205C. This blend has excellent transparency and impact strength, and has good molding fluidity and heat resistance.
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