How a Ballpoint Pen Works

Roller Ball Basics

The basic shape of a ball point pen is that of a roller ball within a socket. The ball becomes coated with liquid (in this case, ink) as it rolls inside the bottle and carries it out, where it is rubbed onto the paper. The ball fits loosely enough in the socket to roll freely, but not loose enough to fall out or to allow liquid ink to leak or squirt.

Ink

The ink inside a ball point pen is different from inks that were used in former, fountain or dipped quill pens. While those inks would take some time to dry after being applied, ball point pen ink dries almost instantly upon contact with paper, being made of a highly viscous, volatile formula. The use of this thick ink also requires that the pen tip be protected from open air when not in use in order to prevent it from drying out or a sticky ball, either by capping the pen or retracting the tip in retractable pens.

Pressure

Early ballpoint pens distributed their ink from reservoirs entirely through gravity, but this was problematic, as the process of writing usually requires holding a pen at something of an angle. For this reason, modern ball point pen ink reservoirs are made with the ink inside them highly pressurized, causing it to flow easily from the pen when the ball in the tip rolls.