Why pen can ink flow out?

When you use a pen to write letters on paper, the ink immediately appears. You must have wondered: why when you write, ink in pens will always flow out; When you stop writing, the ink doesn’t flow anymore? Let’s experiment: Plug a small glass tube into a glass beaker containing water; the water quickly rises inside the tube,

Then we see the water surface in the tube is higher than the water in the glass cup. The phenomenon is called capillary phenomena. The fountain pen is designed to apply this capillary principle. It relies on a series of capillary grooves on the pen’s body and the small opening at the tip of the pen that transports the ink from the inside of the pen to the tip of the pen. When writing the words, the tip of the pen touches the paper, the ink immediately adheres to the paper, leaving the sharp strokes on it.
When I stopped writing, why did the ink in the fountain pen not flow? Let us do another small experiment to make this clear.
Grab a cardboard cover over the top of the glass filled with water, squeeze the cover tightly, and quickly flip the whole glass and cover upside down, then gently remove the cover. The cardboard board is then sucked into the top of the glass and caught the cup’s full amount of water. What is the strength that supports the cover so that the water in the glass does not flow out? That is the effect of atmospheric pressure. It is the atmospheric pressure that supports the cover and water in the cup. When not writing, the ink in the pen does not flow out because the atmospheric pressure outside the pen is larger than the internal pressure so that it can be kept.