The Research On The Process Of Non-papermaking Mica Composite Plate And Its Mechanism Analysis

Mica widely used in electrical insulation materials industry because of its excellent electrical insulating properties. With the exhausting of large scale mica resource, mica flake is used to producing mica paper by hydraulic crushing in mica insulation industry, and achieve the comprehensive utilization of mica flake. Because low strength of the mica paper, the solvent type adhesive and reinforcing materials is needed when producing the multilayer mica composite insulation materials. Thereby making the process more complicated, and the emission of toxic and hazardous organic gases during the process, this will cause the environmental contamination and personnel health threats and other related issues. Meanwhile, due to the fine mica (<74μm) can not be used for papermaking, caused the waste of mica resources, therefore, the development of environmentally friendly insulation adhesive and improve the existing the mica plate production process is the sustainable development direction of the current mica electrical insulation materials industry.In order to solve such problems, the preparation of composite mica plate molding technology without papermaking and solvent-based insulation adhesive is introduced. Waterborne epoxy is used as insulation adhesive with the solvent of water; it is safe and non-toxic with good permeability and bond strength for the most materials. After curing crosslinkable, waterborne epoxy resin is fully meet the requirements of the mica insulation industry with a high mechanical strength, strong adhesion bonding capacity, a good chemical stability as well as excellent electrical insulating properties. Non papermaking technology is a new direct molding process. Mixing the mica slurry with the adhesive and preformed by settlement, then the mica composite plate material is directly obtained by hot press curing. The new process is more convenient, and the fine mica can be used to filling the gap between the coarse-grained mica. The densification of mica composite plate is enhanced and the utilization of mica resources is improved. Through extensive experimental research, a complete preparation process is obtained, and specific results are as follow:1. The raw material of mica composite plate is a kind of mixed mica. After comminuting, the quartz and other impurities in fine-grade mica (<74μm) is removed by hydraulic classification, and the ratio of diameter to thickness is improved by ultrasonic peeling. A reasonable gradation is accomplished, the coarse-grained mica(>74μm) as the skeleton and the fine-grade mica (<74μm) is for filling. In order to improve the adsorption of waterborne epoxy resin with mica slurry, silane coupling agent is introduced to modify the mica particle;2. According to the requirements of the mica insulation materials, the polyethylene glycol (PEG2000), phthalic anhydride (PA) and maleic anhydride (MA) are used to modify epoxy resin, the carboxyl groups is grafted and make epoxy resin hydrophilic. The polyethylene glycol (PEG2000) is used to improve the flexibility and hydrophilic of epoxy resin, phthalic anhydride (PA) containing a benzene ring in its structure, it is possible to improve the heat resistance and water resistance of the aqueous epoxy resin, maleic acid anhydride (MA) containing a reactive double bond, that can be improving the curing crosslinking density and enhancing the flexural strength of the mica composite plate. Considering the performance and water absorption of the aqueous epoxy insulating adhesive film-forming, highly methylated amino resin5747containing more cross-linking reactive groups is be chosen as the curing agent. In order to improve the performance of non papermaking mica composite plate, the mixing binder process is optimized.3. The closely structure composite mica blank is obtained after settling, filtering and drying. The program of hot forming process is introduced including heating up and the exhaust stage, the hot pressing and curing stage and holding pressure and cooling stage. The best hot curing process parameter is determined. The performance of the non-papermaking mica composite plate is improved by the completion of the process. The flexural strength of this product is increased from165.03N/mm2to245.79N/mm2, and also of the dielectric strength from21.96KV/mm to28.05KV/mm, all promoted32.9%and21.7%respectively, the water absorption decreased by0.72%to0.43%, a decrease of40.3%. The performance tests indicate that non papermaking mica composite plate is achieve the industry standard basically in appearance, layer structure, mechanical properties, electrical insulation performance, only the high temperature resistance somewhat less than the index. These results illustrate that the composite material have certain industrial applications prospects.4. The gradation enhancement mechanism, the interface mechanism and the waterborne epoxy curing mechanism is discussed. Explaining the reason of the strength improvement for the composite material, and providing a theoretical basis for the future.The completion of non papermaking mica composite plate solves the related issues in mica electrical insulation materials and increases the utilization of mica resource. The new process will play an active role to enhance the technical level of mica insulation materials and promote the development of mica electrical insulation industry.