Rollerball pen

Rollerball pens are pens which use ball point writing mechanisms with water-based liquid or gelled ink, as opposed to the oil-based viscous inks found in ballpoint pens. These less viscous inks, which tend to saturate more deeply and more widely into paper than other types of ink, give rollerball pens their distinctive writing qualities. The writing point is a tiny ball, usually 0.5 or 0.7 mm in diameter, that transfers the ink from the reservoir onto the paper as the pen moves.

1 Advantages
2 Disadvantages
3 Standards
4 Uses
5 See also
6 References
7 External links

Advantages

Roller Ball pens were introduced in early 1970's. There are two main types of rollerball pens, liquid ink pens and gel ink pens. The first type uses an ink and ink supply system similar to a fountain pen, and they are designed to combine the convenience of a ballpoint pen with the smooth "wet ink" effect of a fountain pen.

Gel inks usually contain pigments, while liquid inks are limited to dyestuffs, as pigments will sink down in liquid ink (sedimentation). The thickness and suspending power of gels allows the use of pigments in gelled ink, which yields a greater variety of brighter colors than is possible in liquid ink. Gels also allow for the use of heavier pigments with metallic or glitter effects, or opaque pastel pigments that can be seen on dark surfaces.

Liquid ink rollerball pens flow extremely consistently and skip less than gel ink pens do. The lower viscosity of liquid ink increases the likelihood of consistent inking of the ball, whereas the higher viscosity of gel ink produces "skipping", that is, occasional gaps in lines or letters.

In comparison to ballpoint pens,

Less pressure needs to be applied to the pen to have it write cleanly. This permits holding the pen with less stress on the hand, saving energy and improving comfort. This can also translate to quicker writing speeds. This is especially true of liquid ink pens.
The inks usually have a greater range of colors due to the wider choice of suitable water-soluble dyes and/or to the use of pigments.
They tend to write finer lines and more clearly than ballpoint pens do.

Disadvantages

There are a number of disadvantages inherent to rollerball pens:

Water-based rollerball ink is more likely to smudge than a ballpoint pen's oil-based ink because water-based ink dries more slowly than its counterpart. Also if one writes in a notebook, closing it before the ink dries can stain the opposite page. Gel ink dries much more rapidly than liquid-ink, making it much more, but not completely, resistant to smudging.
Rollerballs with liquid-ink much more frequently "bleed" through the paper. Liquid ink is more readily absorbed into the paper due to its lower viscosity. This viscosity also causes problems when leaving the tip on the paper (to pause for a thought for example). The bleed-through effect is greatly increased as the ink is continually absorbed into the paper, creating a blotch. This does not affect gel-ink rollerballs as much. This is one way through which the thickness of gel-ink gives it an advantage, in that it isn't as prone to being absorbed. Though the bleed-through effect of a gel-ink rollerball is greater than that of a ballpoint, it is usually not too significant.
Rollerball pens generally run out of ink more quickly than ballpoints because rollerballs use a greater amount of ink while writing. This is especially true of liquid-ink rollerballs, due to gel ink having a low absorption rate as a result of its thickness. Neither lasts as long as a ballpoint.
Uncapped rollerball pens are more likely to leak ink when, for example, placed into a shirt pocket, but this is easily avoided by recapping the pen.
A rollerball tip is more likely to clog and jam when writing over correction fluid that has not yet completely dried. This often renders the ink cartridge useless.
A liquid-ink Rollerball is likely to leak during flight on an airplane with a pressurized cabin, although variations that are leak-proof are created to be airplane safe.

Standards

The International Organization for Standardization has published standards for roller ball pens:

ISO 14145-1: 1998: Roller ball pens and refills – Part 1: General use^[1]
ISO 14145-2: 1998: Roller ball pens and refills – Part 2: Documentary use (DOC)^[2]

Most roller ball refills do not comply to the ISO 14145-2:1998 standard, meaning they are not approved for documentary use.

Uses

Former MI-6 agent Richard Tomlinson alleges that Pentel Rolling Writer rollerball pens were extensively used by SIS agents to produce secret writing (invisible messages) while on missions.^[3]