Apparatus for coloring electric wire and method thereof

A method for coloring an electric wire consisting of the steps of:

• providing a coloring unit having a main body supporting a plurality of nozzles around the center of the electric wire and a plurality of nozzles along a longitudinal direction of the electric wire, each nozzle comprising a nozzle main body having disposed therein, a solenoid valve having a coil and a conductive main body that is moved when a voltage is applied to the coil, and a nozzle member having a tubular shape of uniform diameter, and for each nozzle:
• supplying a liquid coloring agent from a coloring agent supply source to the nozzle through a single supply conduit having a single passage, with said single supply conduit being free of any devices;
• injecting the liquid coloring agent through the nozzle member to an uppermost position of the electric wire along an axis of the nozzle member by using the coloring unit;
• making a droplet of the coloring agent to be adhered on the electric wire by using the coloring unit;
• opening or closing the solenoid valve disposed in the nozzle main body to inject or stop injection of the droplet of the coloring agent to the uppermost position of the electric wire, wherein a valve disposed on the conductive main body of the solenoid valve contacts a base end of the nozzle member of the nozzle, the other end of the nozzle member being an opening for injecting the coloring agent to the electric wire;
• and
• applying solely a spike voltage to the coil of the solenoid valve to open the valve, the spike voltage having a constant voltage with a pulse width of from 0.15 msec. to less than 0.5 msec., which corresponds to injection of a predetermined droplet mass, so as to form a single row of spaced dots on the uppermost position of the electric wire,
• wherein the distance between adjacent spaced individual dots is kept constant even when the moving speed of the electric wire through the coloring apparatus changes, and
• wherein the single row of the spaced dots is formed on the uppermost position of the electric wire with all of the nozzles.