Coating Removing Of Polyester Enameled Wire By Alkali Solution And Its Application

In response to the situation that high quality copper resource is in short supply and the recovery utilization ratio of scrap copper is at low level, using scrap electromagnetic wire to produce oxygen free copper rod directly will be the major breakthrough in the copper resources recycling. Removing the polymer coating from the surface of enameled wire is the first step of electromagnetic wire recycling. The emphasis is on the research and development of paint removing process which is suitable for industrial mass production. Based on the analyzing the coating composition, comparing all kinds of paint removing methods, researching of polymer degradation principle, combination with the practical situation of the factory, the method using alkali solution to remove polyester coating from the surface of enameled wire was determined and the process condition of the method was explored. It could be found from the experiment that the polyester coating can be removed effectively by NaOH solution. Coating removing time decreased linearly with the increase of NaOH solution concentration and with the rising of temperature. Besides, the recycling performance of the paint remover was proved to be very good. The removing ability of NaOH solution didn’t change much after recycled five times. With the increase of cycling times, the cumulative copper loss ratio in solution was increased, the residual solution volume was decreased, and the amount of residual NaOH was decreased. NaOH solution should be supplied and purified in time. Using this method, polyester of paint film didn’t degrade excessively. Film recovery ratio was higher than 60%, copper recovery ratio was higher than 98%, copper loss ratio was lower than 0.02%, those data met the requirements of industrialization and cleansing process.Using alkali solution to remove polyester coating from the surface of enameled wire depends on alkaline hydrolysis of ester bond of the polyester in the coating film. It reduces the bonding force of paint film, so that the paint film can be removed from the copper base. Based on this, the degradation experiments of established polyester film, QZ130-1730 liquid paint and polybutyleneglycol adipate were explored. Using weight difference method to detect the degradation ratio and gel permeation chromatography to detect the degradation products and their molecular weight, polybutyleneglycol adipate was determined to be the research object. The results showed that the polyester degradation ratio was increased linearly with the extension of reaction time and also increased linearly with the increase of NaOH solution concentration. Besides, with the extension of reaction time and the increase of NaOH solution concentration, that of high molecular weight gradually reduce, and that of small molecular weight increases gradually which means the polyester degrade. The degradation of other polyester in the alkali solution follows similar rules by analogy.Based on the optimal process condition, the process flow diagram was designed. Considered the capacity requirements of production line for dealing with scrap electromagnetic wire 10000 tons/year and the actual situation of the factory, the equipment of the process flow diagram were designed and calculated. The preliminary requirements of equipment selection were decided, mainly including the capacity, size, power, materials and delivery quantity.The pilot scale test and engineering test were taken in Ningbo Jintian Copper Co. LTD. Environmental protection demonstrated production line of effectively separating and recycling copper and polymer coating was initially formed. Rocker type paint stripping furnace, stirring type paint stripping furnace and paint stripping furnace with circulative filtration unit were designed and developed in engineering test. Results showed that, the method of using alkali solution to remove the polyester coating from the surface of enameled wire under the optimal process condition was feasible to industrialize. Copper ion in NaOH solution was only 0.01%, at a very low level. Polymer didn’t degrade excessively. The phenomenon of alkali liquor aging didn’t appear. The results of preliminary estimates for raw materials and energy consumption showed that, while dealing with one ton enameled wire, the cost of NaOH was 20 Yuan, and the heating energy cost was expected to control at 100 Yuan.