Brother MFC260C Service Manual page 67

[ Tip: Air bubble growth ]
Liquid ink contains trace amounts of air. The amount varies with the pressure on the ink because
increasing the pressure raises the ink's ability to absorb air from its surroundings and lowering the
pressure forces the ink to give up some of this air.
The ink pressure fluctuations caused by the piezoelectric ceramic actuators repeatedly expand and
contract any air bubbles, growing them larger gradually. This is because the amount of the air per
unit area passing through the boundary surface between the ink and the bubble is always constant
but the boundary surface area decreases or increases when the bubble contracts or expands,
respectively.
That is, when the pressure becomes high, the bubble contracts so that the amount of air moving from
the bubble to the ink decreases in proportion to the boundary surface area decreased. On the
contrary, when the pressure becomes low, the bubble expands so that the amount of air moving from
the ink to the bubble increases in proportion to the boundary surface area increased.
The design therefore compensates by allowing the purging/flushing of air bubbles during printing to
keep the amount of air dissolved in the ink to a minimum.
Ink pressure in the ink supply tubes
High Low
Bubble
Bubble
Ink
Ink
(GrowingBubble)
(GrowthBubble)
: Pressure
: Air flow
3-16
Confidential