Conventionally, a stepping motor stacked core or other motor component is electrodeposited, thereby assuring good anticorrosion and insulation.
For example, Japanese laid-open patent application No. 58-83559 proposes a method of insulating a stacked core of coil block for use in a stepping motor of a clock. In the method, by immersing the stacked core in aqueous epoxy solution containing amine, a cationic electrocoating of epoxy is formed on the stacked core, which is made a cathode for this purpose. Subsequently, the electrocoating is heat treated at temperatures ranging between 100.degree. C. and 300.degree. C. and is formed into an epoxy coating through condensation.
However, in the prior-art electrodeposited motor component, as shown in FIG. 7, when the thickness of the coating on the surface of the component is T, the thickness t of the coating on the edge of the component tends to be smaller than thickness T. The physical quantity defined as t/T is an edge covering ratio. A lowered edge covering ratio causes imperfect insulation. To raise the edge covering ratio, the curing temperature after the electrodeposition needs to be lowered, for example:
Conventionally, to lower the curing temperature, tin compound, for example, the compound of isobutyl tin oxide is generally added by about 0.05% by weight to the aqueous solution of electrodeposition paint, i.e., by about 0.2% by weight to the coating.
It was, however, reported that when the motor assembly of the stacked core, the magnet and the like with the insulation coating formed thereon in the aforementioned conventional manner was used in a hard disc drive unit, the content of memory in the hard disc collapsed. We reviewed this problem and concluded that the problem was caused by the content of the coating.