Winter vacation homework is put on the warm bed, and the handwriting mysteriously disappears? Don't worry, put it in the refrigerator and it will be saved!

Tragedy! Just because a child used an erasable pen, the homework he had worked hard on for two hours mysteriously disappeared on the warm bed at his grandmother's house...

Photo | Weibo @赵乐呵

As school is about to start soon after the New Year, we are very concerned about the completion of our students’ winter vacation homework.

Why did Huang Xiaokuai’s handwriting disappear?

Will lost homework ever come back?

So if I write an IOU with this kind of pen, does that mean I don’t have to pay it back?

…

The words are gone? Freeze them and you can still save them

If you have used this erasable pen, you will find that the "erasing part" attached to the pen tip is not an eraser. In fact, the way an erasable pen erases writing is completely different from the way an eraser erases a pencil. The eraser really "erases" the writing - during the friction, the pencil writing and the surface of the paper are taken away.

But the "eraser" of an erasable pen does not wipe the ink off the paper, it just uses friction to generate heat to make the ink colorless. The writing is still on the paper, but it is invisible.

The “erasing part” of an erasable pen is not an eraser | Photo by the author

According to the patent, the ink in the erasable pen will completely fade when it encounters a heat source above 60 degrees Celsius. Frictional heat can serve as a heat source, as can a hot bed or a teacup filled with boiling water. As long as it is hot enough, the writing will disappear.

Put a cup of hot water in it and the writing of the erasable pen will disappear. (The animated picture has been accelerated) | Photographed by the author

But don't worry, this is a reversible process and the disappeared handwriting can still be saved - just put the exercise book in the refrigerator and freeze it for a while.

How cold does it need to be? According to the patent of Pilot, the faded erasable pen writing can be restored to its original color as long as it encounters a cold source below -20 degrees Celsius. The product manual states that it should be -18 degrees Celsius. My own refrigerator is about -14 degrees Celsius, and after testing it, it can completely restore the writing to its original state.

The instructions on the back of the packaging of two erasable pens on the market both mention how to restore the disappeared ink. It is still necessary to read the instructions, students | Photo by the author

What is the principle of erasable pens?

The above information is enough to solve life troubles. Here is some extended reading for curious babies: What is the principle of erasable pens?

Unlike ordinary pigments, the color of erasable pen ink is actually the result of the cooperation of two chemical substances.

One is a "crypto-dye," which can switch between two chemical structures: colored and colorless. The other is called a "developer," which helps the crypto-dye molecule switch. (If you want to get a little more specific: crypto-dye is a substance that binds to protons to produce color, and the developer is responsible for providing the protons.)

However, just putting these two substances together is not enough. In order to ensure that the "switching reaction" occurs at the desired temperature, other ingredients need to be added to create a suitable reaction environment for the two molecules. To ensure the stability of the reaction environment, all of the above substances will be encapsulated in tiny microcapsules (the diameter of the capsule is about 2.5 microns). These microcapsules are the most critical component of erasable pen ink.

Clothes that change color when touched, using thermochromic microcapsule materials | insilico.co.kr

In addition, the thermochromic material used in erasable pen ink has another special feature - it has "color memory".

Specifically, when the ink is cooled from a high temperature to room temperature, the dye will remain colorless for a long time; and if it is heated from a low temperature to room temperature, the colored state can also be maintained for a long time at room temperature. It is precisely because of this characteristic that the writing of the erasable pen can remain stable at room temperature and will not disappear or appear suddenly.

The erasable pen is indeed a very convenient invention, but don’t use it to write very important documents, including IOUs!

References

[1]https://patents.google.com/patent/CN101965386A

Author: Window Knocking Rain

Editor: Dongfeng

An AI

Didn't do your winter vacation homework? Don't tell the teacher that you left your homework on the warm bed and it disappeared. The teacher has learned to put homework in the refrigerator!

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