Apparatus and method for controlling coating solution level within substrate

An apparatus, to be used when an open end of a hollow substrate contacts a coating solution to define a solution free interior portion of the substrate, for controlling the level of the coating solution within the substrate interior, the apparatus comprising:

• a gas container capable of changing in volume and having an elastic property that spontaneously exerts increasingly greater pressure on the contained gas as the gas container increases in volume and that spontaneously exerts decreasingly lesser pressure on the contained gas as the gas container decreases in volume;
• and
• a channel connecting the gas container to the solution free interior portion of the substrate to allow gas flow in either direction between the gas container and the solution free interior portion.

A method, to be used when an open end of a hollow substrate contacts a coating solution to define a solution free interior portion of the substrate, for controlling the level of the coating solution relative to the substrate interior, the method comprising:

• establishing a channel to allow gas flow in either direction between a gas container capable of changing in volume and the solution free interior portion;
• and
• exerting a changeable, continuous pressure on the gas in the gas container that automatically exerts an increasingly greater pressure on the gas in the gas container as the gas container expands in volume and that automatically exerts a decreasingly lesser pressure on the gas in the gas container as the gas container decreases in volume.