Polyphenylene ether PPO resin is a thermoplastic resin, which belongs to the five general engineering plastics. It has excellent physical and mechanical properties, heat resistance and electrical insulation. Its low hygroscopicity, high strength, good dimensional stability, and creep resistance at high temperature are the best among all thermoplastic engineering plastics.
At present, blending modification is an important modification measure of polyphenylene ether. Blending modification has excellent comprehensive performance, and is widely used in many fields such as automobile industry, electrical and electronic, office machinery, precision instruments, and textile equipment.
Especially in the high-performance circuit board industry, polyphenylene ether has considerable application prospects.
As a blending component, it effectively improves the defects of ordinary circuit board substrates such as ring hydrogen and phenolic resin exposed to poor dielectric properties, poor heat resistance, high thermal expansion rate, and poor moisture resistance. In particular, low-molecular-weight resins can not only improve the wettability of the resin, realize impregnation at room temperature, and greatly improve the resin fluidity during molding, but also do not require pre-functionalization of raw materials. When modifying epoxy resins with smaller molecular weights, It can be dissolved relatively quickly in liquid epoxy resin at a certain temperature to obtain a system with appropriate viscosity, improve the impregnation of reinforcing materials, and improve the fluidity of adhesive sheets, so that it can achieve high content with good processing properties epoxy resin system. The cured system has better heat resistance, dielectric properties and fracture toughness.
Therefore, it is of great practical significance to prepare polyphenylene ether with high purity and low molecular weight.
Analysis of Existing Filtration and Washing Process of Polyphenylene Ether PPO Resin
After the polyphenylene ether is separated out, it needs to be filtered and washed before entering the dryer. Process requirements: 1. The total volatile matter in the filter cake is reduced to less than 60% of the total weight of the filter cake, and the good solvent (such as toluene) is reduced to 10% of the total weight of the filter cake. Below 10%, excessive good solvent content will cause polyphenylene ether to adhere to the inner wall of the dryer during the drying process, resulting in a decrease in drying efficiency and even damage to the dryer. 2. Minimize the breakage of particles during the filtration and washing process, especially the particles smaller than 100μm should be controlled within 15%, too much fine powder will increase the possibility of dust pollution and dust explosion in the downstream processing.
The post-treatment process of polyphenylene ether in the prior art is usually: solid-liquid separation (filtration)→dispersion and cleaning (usually dispersed by stirring)→secondary solid-liquid separation (refiltration)→drying and other steps. In most cases, at least: 2~3 times of solid-liquid separation (filtration), 1~2 times of dispersing cleaning, 1~2 times of drying, this process requires a lot of equipment and long processing time (dispersion time>10min), the efficiency is low, and the particle breakage rate is high. It is difficult to ensure that the particle breakage rate will not increase under the premise of reducing the concentration of good solvents (such as toluene) as much as possible.
In addition, in order to reduce the content of good solvent in the filter cake, it is often achieved by increasing the number of cleanings, increasing the amount of methanol, prolonging the cleaning time, and increasing the stirring intensity.
The ensuing problems are: the material processing time is long, the efficiency is low, and the broken rate increases, resulting in a high fine powder rate. Therefore, there is a contradiction between reducing the concentration of good solvent (toluene) and reducing the content of fine particles in polyphenylene ether in the prior art.
Technical Analysis of Two Conical Filters and One Filter in Pressure Filtration and Washing Process of Polyphenylene Ether PPO Resin
The current process is scattered, and many equipments are used. The production process of multiple equipments can be gathered into the conical two-in-one filter, and then the production is carried out step by step, that is, the solid-liquid separation is carried out in one equipment, and then Multiple times of dispersing and cleaning are carried out, and finally drying is carried out. During dispersing and cleaning, the problem of excessive pulverization of materials caused by enhanced mass transfer and stirring is avoided, and the continuity of production is maintained at the same time.
There is no secondary transfer of materials during the entire production process, which saves the time wasted due to material transfer. Generally, the material transfer does not take much time during normal production, but in actual production, there are always problems of material blockage in the pipeline, which prolongs the entire production cycle.
(1) Solid-liquid separation process
Solid-liquid separation is performed on the slurry liquid to obtain a polyphenylene ether filter cake. The separation process adopts a pressure filtration method; in the pressure filtration of the solid-liquid separation process, boiling of low boiling point solvents can be avoided. The thickness of polyphenylene ether filter cake is controlled at 10~50mm, and the method of thin filter cake filtration is adopted to achieve high-efficiency filtration.
(2) Cleaning process
The filter cake obtained in the solid-liquid separation process is sprayed and cleaned with cleaning liquid, and the sprayed cleaning liquid is discharged at the same time; by controlling the amount of cleaning liquid, the temperature of the cleaning liquid and the cleaning pressure, a better washing effect can be further obtained.
The pre-drying process can adopt conventional drying methods, such as using gas purge drying or spin drying, to remove the solvent on the surface of the filter cake. The method of gas purging and drying, for example, using inert gas to purify and dry, and the temperature of the drying gas is set between 1 and 200°C
The conical two-in-one filter integrates the production process of polyphenylene ether PPO resin for filtration and washing, simplifies the pipeline, reduces the difficulty of refining and purifying high-molecular polymers, improves product purity, and is conducive to improving product quality stability: and makes the solvent, Catalysts and other recycling, as well as to achieve the effect of saving energy and protecting the environment.
Working principle of conical two-in-one filter
The cone or barrel of the conical two-in-one filter is equipped with a multi-layer orifice plate and a filter medium superimposed to form a filter device. The interior is equipped with a stirring shaft and a multi-angle variable-lead screw stirring device to filter the material. Stirring, lifting and scraping operations, automatically pushing out the filter cake when unloading, this machine can be used for vacuum filtration or pressure filtration. During the filtration process, the scraper in the machine continuously scrapes the filter cake on the filter screen, so that the material is filtered under the condition of a thin layer of filter cake, and the filtration rate is very high.
If the material needs to be washed, the slurry can be filtered and dried in the machine first, and then the washing liquid can be added, and the filter cake can be re-slurried by the scraper, agitator and extrusion screw in the machine, and then pressurized or The reslurry is filtered into a filter cake by vacuuming.
In this way, re-slurry filtration is repeated many times to wash the materials thoroughly, and finally all the filter cakes are discharged out of the machine.
(1) Pressure filtration or vacuum filtration
Feed the solid-liquid mixture produced by the upstream reaction kettle or crystallization equipment into the tank of two sets of one equipment, open the lower filtrate outlet, and pass compressed air or ammonia gas into the equipment to pressurize the reacted solid-liquid mixture Filter until the contents of the machine are pressed dry. Vacuum can also be drawn at the outlet of the filtrate to vacuum filter the material until the filtrate is drained.
When filtering, the hollow shaft and the hollow spiral belt can be rotated clockwise (viewed from the top) to lift the material, and the hollow spiral belt can limit the thickness of the filter cake layer when rotating, so that the material is in a thin fast cake Excessive speed under layer conditions to increase the filtration rate. For materials that are easy to filter, it is not necessary to stir the materials during filtration, and directly dry the materials.
(2) Can be washed and filtered multiple times
After some materials are filtered, they need to be washed several times. After the materials are dried in the machine, the washing liquid can be added to the top washing liquid inlet, and then the filter cake can be evenly repulped by stirring the hollow shaft and the hollow ribbon. , re-slurry and stir evenly and then dry the material. If washing once is not enough, it can be washed multiple times, and the above steps can be repeated many times. The operation is convenient and the labor intensity is extremely low.
Washing the materials with the above method is called the intermittent washing method. Since the materials are pressed dry each time and the washing liquid is added for washing, although the valves are opened and closed more times during operation, less washing liquid is used. , the machine can also carry out continuous washing on the material, that is, the washing liquid is continuously pressed in by a pump or other methods, and the pressure of the washing liquid is used to filter, the hollow shaft and the hollow ribbon are continuously stirred, and the filtrate is continuously discharged from the filtrate outlet. Until the washing requirements are met, the filter cake is finally pressed dry. This method of continuous washing generally requires more washing liquid than intermittent washing, but it is more convenient to operate.