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Why is it that in childhood memories, these beautiful fragrant erasers are often not easy to use, while those rubbed very clean are often ugly and smelly?

In fact, this problem has appeared since the birth of the eraser.

Eraser: when it comes to erasers, you have to talk about pencils first.

Before, the wooden pencil holder of the pencil was wrapped in real "lead". By the 16th century, lead in pencils was replaced by graphite, making the handwriting obvious and easy to erase, so it was naturally widely used. For engineers who need to draw drawings, it is simply a technological revolution.

But then comes the problem.

At first, people usually used bread to erase pencil marks. The principle behind it is not complicated: graphite is adsorbed on the surface of the paper to form handwriting, which can be erased as long as you find something stronger than paper. Although it is scribbled, it can handle it.

This erasure took a turn for the better in the 18th century. At that time, in Europe, there was an imported product from the American continent that aroused the interest of many people, that is, natural rubber.

In 1770, British chemist Priestley (and one of the earliest discoverers of oxygen) noticed that the substance seemed suitable for erasing pencil handwriting while experimenting with rubber. This is mainly because natural rubber has good elasticity and can better fit with the rough paper surface, so the erasing effect will naturally be improved.

So, according to this characteristic, Priestley named the rubber "rubber", which literally means "eraser". Up to now, "rubber" also has the meaning of "rubber" and "eraser", but it is also used to refer to "rubber condom" in daily life. Here is a piece of cold knowledge: the middle school English textbook published by our country in 1993 is the famous version of "Li Lei and Han Meimei". The eraser in the textbook is "eraser", and in the previous version it is "rubber".

However, the drawback of this "rubber eraser" is that natural rubber is too soft to use and the experience is not good enough.

In 1839, the turning point came again. An American named Charles Goodyear developed a rubber treatment process by heating sulfur and natural rubber to make the earliest vulcanized rubber. Vulcanization means that the molecules of rubber are connected by sulfur atoms, in which sulfur plays a fixed role. In this way, the rubber molecules can no longer move at will, and the shape of the finished product is determined.

In this way, the eraser in the modern sense was born.

Rubber paradox: good to use is not good to smell, good-looking and good-smelling is not good to use, but new problems follow. The advantage of this eraser made of vulcanized natural rubber is that it has a fixed shape and is more durable. The erasing effect is really good, but the taste is really bad. It is not surprising that the earliest raw material used in the vulcanization process is sulfur, a chemical element known as the "hell element", which smells really pungent. Even with modern vulcanizing agents, many of them still contain sulfur and inevitably have an unpleasant smell.

Eraser made of ▲ vulcanized natural rubber, its own color is goose yellow to brown yellow (putitonpaper.bigcartel.com)

In the 20th century, synthetic polymers have become the development trend of new materials. Among them, a kind of polymer called polyvinyl chloride (PVC), because of its low cost, quickly becomes one of the most commonly used and most widely used synthetic materials.

Polyvinyl chloride (PVC) is generally regarded as plastic. Sometimes, you will see a triangle sign on the packaging of some plastic products. if the number in the sign is "3", it means it is polyvinyl chloride, and sometimes people use "vinyl" for short.

However, this kind of plastic is very special, it is relatively brittle, it is not easy to shape, so you need to add plasticizer (also known as plasticizer), and then mix and heat before setting.

There is a lot of room to adjust the proportion of plasticizer added to PVC. If the addition is about 10%, then the final product can only be shaped, is still very brittle, and is usually used to make water pipes; however, if the addition is about 50%, the PVC becomes very soft and even elastic, just like rubber. Therefore, PVC in this state is also often called plastic, and it can also erase handwriting like natural rubber.

PVC eraser does have some advantages. For example, when a large amount of plasticizer is added, it becomes translucent. At this time, if some pigments are added, it can be made into a variety of interesting shapes, such as fruits or animals. On the other hand, a large amount of plasticizer is equivalent to a solvent, and the eraser can dissolve some flavors, thus becoming a scented eraser. It looks good, and it smells a little fragrant. Who doesn't like such an eraser?

Who doesn't like such an eraser? ? SKsiddhartthan / Wikimedia Commons

For manufacturers, the production of PVC rubber is a great test of the level of technology. Once the condition control is not ideal, it is easy to cause the quality of the rubber to be unstable.

Like the hardness of the rubber. If the content of plasticizer is not well controlled, the rubber may be too hard or too soft, which is not very practical, because the friction of the hard rubber is too small, the erasing effect is weak, and the wear resistance of the soft rubber is poor, and a lot of rubber shavings fall out as soon as you rub it.

Moreover, after long-term use or heating when placed, the plasticizer will separate, so that the material of the eraser will become harder and harder until it loses its ability to erase; on the other hand, if you put it with a plastic ruler, the oozing plasticizer will dissolve the plastic material of the ruler and then stick together, which may also be a childhood nightmare for many people.

The rubber head at the top of the pencil was originally used as an emergency about the eraser of childhood, and there is a special form of existence: the kind of rubber head installed on the top of the pencil.

Back in 1858, an American painter named Hyman L. Lipman came up with the idea of combining a pencil with an eraser and applied for a patent. The "eraser pencil with eraser" was popular with consumers, and the impoverished Lippman made a fortune and transferred the patent to the manufacturer at a high price of $100000 14 years later.

There is also an episode: because there are others on the market to imitate, so this two-in-one tool provoked a patent war. Lippman's patent was not upheld by the court, and the judge held that the invention was not innovative. Nevertheless, the patent war later became a classic case in the field of intellectual property.

Unfortunately, although this classic design remains to this day, from a practical point of view, the eraser on this kind of pencil is slightly chicken rib, which is also a very bad part of many people's childhood memories. However, I wonder if anyone has noticed that although this kind of eraser is not effective in wiping pencil handwriting, it can erase pen handwriting.

This is because pencil erasers are designed for emergencies, and manufacturers are not very attentive, often installing the cheapest "office erasers". The eraser contains some "light stone" minerals and is cheap to produce, but it scrapes a layer off the surface of the paper, erasing pen handwriting that permeates the paper fiber, but is too hard to be used to erase pencil handwriting.

The eraser on ▲ pencil (Unsplash)

Nowadays, although there are fewer and fewer applications, as consumers demand it more and more, the eraser has also made a lot of improvements.

For example, the most general-purpose PVC rubber, in which plasticizers often use phthalate esters, may cause precocious puberty and other effects on children's development. As a result, PVC Eraser began to transform to use more environmentally friendly and safer plasticizers. At the same time, natural rubber erasers, which have been left out because of their low appearance, have become popular again, which is, of course, related to the further weakening of the smell of vulcanizing agents.

In addition, the process of pencil with eraser has been greatly improved, and some manufacturers combine erasers with pencils that are more suitable for erasing handwriting, which are easy to use and are not easy to lose, and the erasing effect has also been improved.

Maybe when today's children grow up, they will have better childhood memories of erasers.

reference

[1] Historical Note. MRS Bulletin 19, 69 (1994). Https://doi.org/10.1557/S0883769400036824

[2] Grady, M.F., & Alexander, J. I. (1992). Patent law and rent dissipation. Va. L. Rev., 78,305-350. Https://doi.org/10.2307/1073310

This article comes from the official account of Wechat: fruit Shell (ID:Guokr42), author: sun Yafei, Editor: Maiyayang

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