Electronic Thesis and Dissertation Repository


Master of Engineering Science


Chemical and Biochemical Engineering


Dr. Jesse Zhu

2nd Supervisor

Dr. Hui Zhang

Joint Supervisor


Enamelled wire is a conductive wire coated with a very thin layer of insulation, widely used in the field that requires tight coils of wire. The traditional enamelled wire is produced by liquid paint, which consists of resins, solvents, pigments, and additives. Organic solvent takes a relatively high content, normally of 75% to 90% by weight. Many efforts have been made to decrease the percentage of solvent in the insulation paint. On the other hand, increasing the solids content of given enamel results in the viscosity rises significantly, making it harder to flow. Therefore, powder coating technology as an alternative is developed in the production of enamelled wire, not only benefits the environment but also cuts cost of solvent.

Mechanical and chemical methods to prepare the fine powder of PVF type enamelled wire coating are reported in this thesis. For gradual solvent evaporation method, kinetics and thermodynamics of the fabrication of microspheres are adopted from reference to predict the operating parameters, such as the solidification time. Factors affecting average particle size and particle size distribution are investigated as well. Phase ratio of emulsion system (DP/CP), emulsion agitation speed, types and dosage of emulsifier, co-solvent and stabilizer are all taken into account. When the DP/CP was 1/15, the resins percentage in DP was 12wt%, the stirring speed was 6000 r/min, 1wt% SDS was used as emulsifier, 1wt% N-octanol and 0.5wt% PVA were employed as co-solvent and stabilizer, the powder of average particle size at around 12 micron can be obtained.

Initial PVF enamelled wire coating formulation, as adopted from references of liquid insulation paint, which consists of PVF-E resin, novolac epoxy resin and melamine resin, produced a non-continuous coating finish with many tiny holes formed during curing. This may be attributed to the thermal properties of PVF-E resin or the inappropriate ratio among the different components in the formulation. After that BPA epoxy and its hardener were introduced to the initial formulation to improve the surface quality of coating finish. Then, the paint formulation, powder spraying and curing conditions are optimized. The recommended formulation is with mole ratio of PVF-K, OCFER and melamine resin at 100:375:119, and with proper dosage of degassing and flow agent. The best spraying condition is gun voltage of 30 kV and air stream of 3.0 m/s. When the curing temperature ranged from 215 to 225℃, and the substrates were pre-treated, the number of defects on coating film was reduced.