There are often scenes like this in martial arts novels. A piece of yellowed paper is roasted on the fire, and the words are immediately displayed. If you look closely, it is a peerless martial arts secret book.
The disappearance and appearance of characters is not mysterious in the eyes of Cixi Chenyong Stationery Co., Ltd., because their pens can do it.
This is a pen called "Thermal Erasable". The development of this pen is not to write any secrets.
At first, because pencils consume a lot of wood and are not environmentally friendly, I wanted to find an alternative pen. To replace a pencil, it needs to be "erasable", that is, to be able to erase written words.

The "domestic trade erasable pen" looks the same as the neutral water pen used in daily life. It is also a tube of black, black, blue and blue ink, but an eraser part is added to the cap of the pen to erase the writing.
However, unlike the eraser of a traditional pencil that directly erases handwriting, the eraser of the "domestic trade erasable pen" is just a piece of plastic, and its erasability is actually to hide the words.
For example, when a person enters a sensor door, the sensor of the door will receive an instruction to open it, but the size of a small ant is too small to drive the sensor, that is to say, the size is a physical indicator of induction. So similar to the principle of the sensor door, the ink of the "domestic trade erasable pen" is equivalent to installing a "sensor". The difference is that its command is temperature. When the temperature is high, the written words will automatically disappear. And put it in a low-temperature environment, those words will appear again.
Based on this principle, it is not difficult to understand that the reason why a piece of plastic can become an eraser is because the plastic rubs against the paper during the erasing process, generating temperature, which makes the characters disappear.
In 2014, "Chenyong Stationery" introduced this kind of induction ink from Japan at a high price for the first time, intending to make it into a pen. The first batch of pens only had a "lifespan" of one day when they were assembled, and they couldn't write on the next day. He could only test the pens one by one, and finally found that the problem was in the nib. "The particles of this kind of ink are thicker than ordinary ink, and ordinary nibs will be blocked when they are written."

I searched for a matching nib, and I have done dozens of matching experiments before I found the right one. It is said that the machine for making this kind of nib is imported from Switzerland, and one set costs four million yuan.
After finally successfully producing the "domestic trade erasable pen", the first order was issued with great interest. Unexpectedly, after receiving the goods, the other party found that the pen could not write a single one.
"We use ordinary packaging to load and ship the car, but the temperature of the car on the road in summer is as high as 50 degrees. When the temperature is high, the ink will not develop directly, and there will be no traces on the paper." But at that time, there was no experience at all, until the goods were delivered. Go back and check again. "In fact, as long as the customer put it in the refrigerator to freeze it, it would be back to normal."
This lesson, he paid more than 1 million "tuition fees", which also made him start to think about the method of transporting this special pen. "Later, as long as we shipped to high-temperature areas, we used foam boxes to insulate the heat. We also improved the ink and raised the original 'invisible' zero point of 50 degrees to about 60 degrees, so that we can basically carry it through most parts of the country. It ’s hot in summer.”
Last year, the “invisible pen” began to be promoted on a large scale, and more than 60 million pens were sold a year.

The most interesting is the promotion plan, buy a box of pens with a hair dryer, called "study set". Many people are attracted by this cross-border combination, wondering what the hair dryer is for?
After a demonstration, he wrote words all over a piece of paper, then blew it with a hair dryer, all the words disappeared, and the paper could be written again. "It takes a lot of paper for students to practice calligraphy. With our pen, the paper can be reused." However, he joked that if you want to write an important signature, remember not to use this kind of pen!