What's the mysterious liquid behind a gel pen? It turns out to be very useful!

Playing with gel pens in boring classes is probably a childhood memory shared by many people.

At the end of the gel pen refill, there is always a piece of colorless or yellow mysterious liquid.

Sticking a long mechanical pencil lead in and then stirring it seems to have infinite appeal to curious babies who don't want to listen to the class.

However, what exactly is this mysterious liquid?

Image source: Internet

01

Follow-up sealant: a stopper for ink

The official name of this mysterious liquid is "follower sealant", generally called "ink follower" in English.

It is actually a gel-like "plug" blocking the rear end of the ink.

The follow-up sealant can prevent the ink from flowing backwards and also has a certain anti-impact effect. It can prevent the gel pen from leaking ink whether it is placed upright, lying down or dropped on the ground.

At the same time, it prevents the water in the ink from evaporating.

It is very viscous, yet it can flow along with the ink as ink usage decreases – that’s what “follower” means.

This can avoid the formation of negative pressure in the sealed part, which would affect normal use.

The sealant moves forward with the ink

Image source: Internet

02

What is it made of?

There are many versions of the specific formula of the follow-up sealant, but they are generally a combination of the following things:

1. Base oil

Generally, it is a liquid that has a certain viscosity, is difficult to evaporate, and is not miscible with gel pen ink. For example, it can be silicone oil, polybutene, liquid paraffin, etc.

2. Thickener

It can make the base oil thicker and form a gel-like structure through intramolecular or intermolecular effects. For example, the thickener can be nano-silicon dioxide.

3. Other additives

Additives such as surfactants to adjust fluidity and mixing conditions.

A patented formula of follow-up sealant

Image source: Internet

Although it looks inconspicuous, the formula of the follow-up sealant is actually quite particular.

It needs to be very viscous and stable to prevent the ink from leaking, but on the other hand it must maintain a certain fluidity to follow the ink smoothly.

In order to achieve these two somewhat contradictory points at the same time, careful formulation and process adjustments are required.

03

Why is it not in the ballpoint pen?

Usually only gel pens have this follow-up sealant, but not in oil-based ballpoint pen refills. This is related to the difference in the properties of the two inks.

On the one hand, the viscosity of gel pen ink and ballpoint pen ink is very different, the former is much "thinner" than the latter.

The viscosity of gel pen ink is usually between 0.05 and 3 Pascal seconds, while the viscosity of oil-based ballpoint pen ink is as high as 3 to 20 Pascal seconds.

Low-viscosity gel pen inks must be supplemented with an additional "stopper" to prevent leakage, while ballpoint pen inks are already very viscous and difficult to spill.

Whether a follow-up sealant is needed depends on the nature of the ink

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On the other hand, ballpoint pen ink does not evaporate and dry as easily as water-containing neutral pen ink, so there is no need to add a "stopper" to prevent the ink from evaporating.

04

What happens if you accidentally eat it?

Although it's difficult to find definitive safety data, given that the base ingredients of follow-up sealants are some chemically stable oils, accidentally inhaling a little bit of it should not cause any problems.

Gel pen ink is generally not overtly toxic if ingested in small amounts.

Of course, it is better for children not to try it.

References:

[1]https://www.mrsilicone.co.in/2022/01/15/ink-follower-and-its-use-in-water-base-ballpoint-pen/

[2]https://patents.google.com/patent/US6530708

[3]https://www.nyelubricants.com/datasheet/SDS_US_English_INK+FOLLOWER+675A.pdf

[4] https://www.illinoispoisoncenter.org/my-child-ate/ink

[5]https://patents.google.com/patent/CN101280173B/zh

Source: Guokr

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