How Ballpoint Pens Work

A pen is a tool used for writing or drawing with a colored fluid, such as ink. A ballpoint pen is a pen that uses a small rotating ball made of brass, steel or tungsten carbide to disperse ink as you write. It is very different than its pen predecessors -- the reed pen, quill pen, metal nib pen, and fountain pen (see A Brief History of Writing Instruments for details).

All of the pens that preceded the ballpoint used a watery, dark India ink that fed through the pen using capillary action. The problems with this technology are well-known. For example:

When you add to this list the fact that fountain pens tend to flood when you fly on an airplane with them, you can see that all pens up until World War II presented some significant problems for their users -- the world awaited a better solution.

Hungarian journalist Laszlo Biro was well aware of the problems with normal pens. Biro believed that the idea of a pen using a quick-drying ink instead of India ink came to him while visiting a newspaper. The newspaper's ink left the paper dry and smudge-free almost immediately. Biro vowed to use a similar ink in a new type of writing instrument. To avoid clogging his pen up with thick ink, he proposed a tiny metal ball that rotated at the end of a tube of this quick drying ink. The ball would have two functions:

In June 1943, Biro and his brother Georg, a chemist, took out a new patent with the European Patent Office and made the first commercial models, Biro pens. Later, the British government bought the rights to the patented pens so that the pens could be used by Royal Air Force crews. In addition to being sturdier than conventional fountain pens, ballpoint pens wrote at high altitudes with reduced pressure (conventional fountain pens flooded at high altitudes). Their successful performance for the Royal Air Force brought the Biro pen into the limelight, and during World War II the ballpoint pen was widely used by the military because of its toughness and ability to survive the battle environment.

In the United States, the first successful, commercially produced ballpoint pen to replace the then-common fountain pen was introduced by Milton Reynolds in 1945. It used a tiny ball that rolled heavy, gelatin-consistency ink onto the paper. The Reynolds Pen was a primitive writing instrument marketed as "The first pen to write underwater." Reynolds sold 10,000 of his pens when they were first introduced. These first publicly sold pens were very expensive ($10 each), primarily because of the new technology.

In 1945, the first inexpensive ballpoint pens were manufactured when Frenchman Marcel Bich developed the industrial process for making the pens that lowered the unit cost dramatically. In 1949, Bich introduced his pens in Europe. He called the pens "BIC," a shortened, easy-to-remember version of his name. Ten years later, BIC first sold its pens on the American market.

Consumers were reluctant to buy the BIC pens at first, as so many pens had been introduced in the U.S. market by other manufacturers. To counter this hesitancy, the BIC company created an exciting national television campaign to tell consumers that this ballpoint pen "Writes First Time, Every Time!," and sold it for only 29 cents. BIC also launched television ads that depicted its pens being fired from a rifle, strapped to an ice skate, and even mounted on a jackhammer. Within a year, competition forced prices down to less than 10 cents each. Today, the BIC company manufactures millions of ballpoint pens a day!

The key to a ballpoint pen is, of course, the ball. This ball acts as a buffer between the material you're writing on and the quick-drying ink inside the pen. The ball rotates freely and rolls out the ink as it is continuously fed from the ink reservoir (usually a narrow plastic tube filled with ink).

The ball is kept in place -- between the ink reservoir and the paper -- by a socket; and while it is in tight, it still has enough room to roll around as you write. As the pen moves across the paper, the ball turns and gravity forces the ink down the reservoir and onto the ball, where it is transferred onto the paper. It's this rolling mechanism that allows the ink to flow onto the top of the ball and roll onto the paper you're writing on, while at the same time sealing the ink from the air so it does not dry in the reservoir.

Because the tip of a normal ballpoint pen is so tiny, it is hard to visualize how the ball and socket actually work. One way to understand it clearly is to look at a bottle of roll-on antiperspirant, which uses the same technology at a much larger scale. The typical container of roll-on has the same goals a ballpoint pen does -- it wants to keep air out of the liquid antiperspirant while at the same time making it easy to apply. At this scale, it is easy to see how the mechanism works. Here's a shot of the ball end of a typical roll-on:

If you look inside the container, what you have is extremely simple -- the ball is exposed so it can pick up the liquid antiperspirant:

The following two photos show you how the ball fits into the socket:

A ballpoint pen works exactly the same way. The tiny ball is held in a socket, and the back of the ball is exposed so it can pick up ink from the reservoir.

The ball fits into the socket with just enough space to move freely.

The size of a ballpoint pen's line is determined by the width of the ballpoint. A "point five millimeter" (0.5 mm) pen has a ball that will produce a line that is 0.5-mm wide, and a "point seven millimeter" pen (0.7 mm) has a ball that will produce a 0.7-mm line. Ballpoints come as tiny as "point one millimeter" wide ("ultra fine").

Ink is a fluid or paste that comes in a variety of colors -- usually black or dark blue -- used for writing and printing. It is composed of a pigment or dye dissolved or dispersed in a liquid called the vehicle.

According to Encyclopedia Britannica, writing inks date from about 2500 BC and were used in hieroglyphics found in ancient Egypt and China. They consisted of lampblack ground with a solution of glue or gums. The resulting mixture was molded into sticks and allowed to dry. Before use, the sticks were mixed with water.

Various colored juices, extracts, and suspensions of substances from plants, animals, and minerals also have been used as inks, including alizarin, indigo, pokeberries, cochineal, and sepia. For many centuries, a mixture of a soluble iron salt with an extract of tannin was used as a writing ink and is the basis of modern blue-black inks.

Modern quick-drying inks usually contain three things:

The ink vehicle can be either plant-based (linseed, rosin, or wood oils), which dries by penetration and oxidation, or solvent-based (such as kerosene), which dries through evaporation. The vehicle is a faint bluish-black solution that is difficult to read.

To make the writing darker and more legible, coloring ingredients (dyes) are added. Coloring ingredients can be pigments, which are fine, solid particles manufactured from chemicals, generally insoluble in water and only slightly soluble in solvents; agents, made from chemicals but soluble both in water and in solvents; or lacquers, created by fixing a coloring agent on powdered aluminum.

Black, the standard ink color, is derived from an organic pigment, carbon. Colored pigments are inorganic compounds of chromium (yellow, green, and orange), molybdenum (orange), cadmium (red and yellow), and iron (blue).

The additives stabilize the mixture and give the ink additional desirable characteristics. Depending on the medium that the ink is being made for (pens, printing presses, printers) and the material to be printed, the proportions change.

In the case of ballpoint pen ink, the ink is very thick and quick-drying. It is thick so that it doesn't spill out of the reservoir, but thin enough that it responds to gravity. That is why a normal ballpoint pen cannot write upside-down -- it needs gravity to pull the ink onto the ball.

Two of the more interesting developments in the world of ballpoint pens include space pens and erasable pens.

Space Pens

Space Pens, or pressurized pens, are a technological novelty. Take, for example, the Fisher Space Pen. A space pen's ink reservoir is pressurized (~40 lb/sq. in.), and the ink is a special viscoelastic ink (like thick rubber cement). The ballpoint must rotate in order for the thick ink to liquefy, allowing it to write smoothly and dependably on most surfaces, even under water. Ordinary ballpoint pens rely on gravity to feed the ink and have an opening in the top of the ink cartridge to allow air to replace the ink as it is used. There is no hole in space pens, eliminating evaporated or wasted ink as well as leakage from the rear of the ink reservoir. In addition, a space pen can last up to 100 years, compared with the average two-year shelf life of a standard ballpoint pen.

Since the 1960s, when the "Space Race" began, space pens have been used by the U.S. astronauts on all manned space flights, including lunar trips, and were also used by many of the Russian cosmonauts on the Soyuz space flights and the MIR space station.

Erasable Pens

Erasable pens were tremendously popular when they were introduced in the early 1980s. They combine the readability of brightly colored or black ink with the eraser functionality of a pencil. While the pens are still manufactured under names like Gillette Eraser Mate, they aren't as commonly used as they were before. Patents US2966418 and US4097290, among others, describe these pens in detail.

What makes erasable ballpoint pens so different from traditional ballpoint pens is the "ink" -- instead of being made from oils and dyes, it is made of a liquid rubber cement. As you write, the ballpoint rolls on the paper and dispenses the rubber cement ink (the resulting mark is known as a trace). Modern erasable pens work by allowing a ballpoint pen to leave a definite and intense black or colored trace which looks like an ink trace, but is capable of being easily erased shortly after writing (usually up to 10 hours). After that time, the trace will harden and become non-erasable.

Erasable ink generally consists of 15 percent to 45 percent (by weight) natural rubber that is dissolved in a series of volatile organic solvents with varying boiling points.

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