Ball Point Pens
If you check out the history of these pens on Wikipedia for example, you will learn that a Hungarian named Biro emigrated to Argentina, filed for a patent in 1943 and started a factory. Many other people patented the ball tip, the ink tube, the ink etc. until the American Bic Pen became the gold standard for cheap, working, disposable pens. That’s enough history for this discussion.
The discussions in the literature go on endlessly about the design of the ink. Does it fail to coat the ball, is it so non-viscous that it runs right around the ball and makes a splotch, is it so viscous that gravity can’t pull it down to the ball, does it dry before it can be used and etc. Along the way, many formulations have been tried.
Interestingly enough, early designs did not have skinny plastic tubes full of ink, open at the top. Some were sealed at the top and some had pumps or extra sealed in pressure to push the ink down through the feed tube. The balls have changed in size and surface treatment. Today there are high class pens where the balls are made from very hard tungsten carbide with surfaces all full of channels for holding ink.
Tungsten carbide balls are interesting because they will probably last some kind of forever. They will not wear out from gliding over paper. Will they wear out the steel sockets that hold them in place? Possibly, but that is not the main failure mode. The reason most pens stop working, and are tossed into a garbage can today, is because the ink stops flowing so the pen stops writing.
Considering that the feed tubes are open to the air at the top and because the ink is required to have the property of drying quickly when applied to paper, it goes without saying that the top part of the ink begins to dry out as soon as the pen is filled with ink. Give it a few months and the ink at the top end of the feed tube will dry into a plug that prevents further air from passing. Thus when the ball sucks up some ink, and tries to pull down some more, this will create a vacuum above the still fluid ink and prevent further feeding.
If the dry ink doesn’t form a plug, but is permeable to air, then air can percolate down through the whole column of ink and cause it all to dry or set up hard, thus preventing it from flowing down to the ball point. This discussion parallels the problems with paint hardening when it sits unused in a can. What can be done?
The obvious solution is to exclude air and the oxygen it contains. It seems perfectly obvious that the top of the tube should be sealed, not open, and that inert nitrogen should be filling the space above the ink. However, this can cause a vacuum to form, preventing the ink from moving downward.
Another innovation was once tried as these pens developed. Instead of a gas, set a slideable plastic plug over the ink. This will exclude any air from the top surface of the ink. Then a wire can be used to push the plug – or piston – down to keep pressure on the ink column. A spring could maintain a gentle pressure. Not enough to force the ink to blot but just enough to keep the ball tip wet. A tight cap could not only fit over the end of the pen, but could snap right down on the ball tip itself to prevent drying out.
This might have a side effect that some ink might accumulate with time on the tip of the pen which would have to be wiped away on the first use after a long time of disuse. Is this considered to be unacceptable, and a defect, by users.? Probably. In our world of spoiled consumers, any attention to detail, any responsibility for maintenance, no matter how simple, is a negative marketing feature.
It is so much better to have a pen that is discarded after a short life, that uses up resources and that fills up a dump. In our wasteful, upside down world, the ubiquitous garbage can must be kept filled, and what better to fill it than a cheap (if exquisitely designed and formed) plastic utensil with a short shelf life. Our philosophy of consumption says that quick, continual discard of any and all products is normal and acceptable.
Not to me. I hope not to you.