Gel pen

A gel pen uses ink in which pigment is suspended in a water-based gel. Because the ink is thick and opaque, it shows up more clearly on dark or slick surfaces than the typical inks used in ballpoint or felt tip pens. Gel pens can be used for many types of writing and illustration.

The Gel pen consists of an ink-containing tube made of polypropylene, which opens into a metal tip and is usually taken in a shaft. To prevent the ink from drying out, the ink column is closed at the back by a silicone plug. Cap-sealed pens have a seal for the nib in it, while pusher-type nipples include a coil spring in its nib that, when not in use, seals the bullet against the nib of the nib.

The general design of a gel pen is similar to that of a regular [ink based pen], with a barrel containing the writing mechanism and a cap, and a reservoir filled with ink. The barrels can be created in many different sizes and designs; some have finger grips of rubber or plastic. The size of the nib or pen tip ranges from 0.18 millimetres (0.0071 in) to 1.5 millimetres (0.059 in).

Compared to other inks, gel ink has higher viscosity, which supports a higher proportion of pigments in the medium. The pigments are typically copper phthalocyanine and iron oxides, and the gel is made up of water and biopolymers, such as xanthan gum and tragacanth gum, as well as some types of polyacrylate thickeners. The pigments are opaque, and gel pens are available in several bright and pastel colours, as well as opalescent, metallic, and glittery colours which show up clearly on dark paper. Many gel inks are water resistant, and are not washed away by water once the ink has dried. Fraud resistant gel ink is unaffected by solvents such as acetone, and resists cheque washing.

Gel pens are suitable for different writing styles and can also be used in graphics and illustration. Because of the density and opacity of this type of ink, it is more visible on dark or smooth surfaces than the ink usually used in a ballpoint pen or marker.

The most evident advantage of gel ink is its high viscosity, which allows the use of a greater portion of pigment in the medium. The most commonly used pigments are based on copper phthalocyanine and iron oxide, while gels are usually based on water and biopolymers, such as xanthan gum and thickeners such as polyacrylates.

The tip of the gel pens most commonly found on the market varies from 0.18 mm to 1.5 mm. The ink of a gel pen is consumed more quickly than that of a ballpoint pen, either because it is used more, with the same size of the tip, and because of its viscosity characteristics.

Function and use:
The peculiarity of the gel is its viscosity of about 200 Pa • s, which decreases dramatically when applying a shear stress. The rotational movement of the writing ball generates at the interface with the ink column so high shear stresses that the ink is locally liquefied and can be tendered out similar to a rollerball pen. The occurring ink flow is five to ten times that of a ballpoint pen, whereby the writing ball is very well lubricated. This effect produces a very light, smooth typing feel, but it is also responsible for the short writing length of the gel roller. Side effects are the build-up of ink residue at the gap between ball and socket, which can be abruptly given change in writing direction and cause blotch, and the appearance of double lines as the ball accumulates the discharged ink left and right of their path. Gels have the advantage of producing smears even on light and dark paper substrates. Because the ink is thickened (usually by a polysaccharide such as xanthan), even large pigments can be held in the ink without settling, allowing for glitter ink or pigment ink for writing on dark paper.

Writing tips:
Gel tips are constructed analogous to ball tips in the ballpoint pen. The frame is usually made of stainless steel and the writing ball made of hard metal or ceramic. The ball diameter is usually between 0.3 and 1.2 mm, with East Asian products are available up to 0.2 mm.

Ballpoint pens use a paste ink based on a dye solute in an alcohol solvent. Compared to ballpoint pens, gel pens:

Create a bolder, more opaque line
Smudge more, due to ink being wetter
Have occasional skips, due to the ball being less evenly coated with ink
Use more ink, leading to more frequent refills or replacements
Are more likely to leak ink when the stopper fluid drains out
May be able to write on smooth, non-absorbent materials
Fountain pens and liquid-ink rollerball pens use a dye solute in a water-based solvent. Compared to these pens, gel pens:

Are less prone to bleed through to the other side of a piece of paper
Create finer, more controlled lines
Can create white or brightly coloured opaque lines on dark surfaces
May be able to write on smooth materials
Paint markers use an oil-based paint/ink that is very opaque and overlays all other colours beneath it. Compared to paint markers, gel pens:

Are smaller, with finer tips
Have no odour and do not require shaking to mix pigment with solvent
India ink (based on carbon black pigment) is perhaps the ink closest to gel ink in opacity, although it is usually made with an alcohol and shellac-based binder:

Another trait of gel ink is that it resists an analytical method commonly used to assess the potential age of ink for forensic purposes. The United States Secret Service has maintained the International Ink Library for many decades. Because manufacturers change their ink formulas slightly from year to year, thin-layer chromatography (TLC) can be used on ink from traditional pens to trace the manufacturer and date of manufacture of most inks. The pigments in gel ink do not dissolve, and therefore cannot be analyzed with TLC.

Countries of origin:
The country with the largest production is Japan, where this type of pen was developed in the 1980s (major manufacturers are Pilot, Uniball and Pentel). In recent years, China has established itself as a major producer of cheap gel rollers.