Shoyoukan Junior High School

Easy for everyone! Original Regenerated Chalk

誰でも簡単!オリジナル再生チョーク

Shoyoukan Junior High School

照曜館中学校

We started our research about chalk regeneration in 2002 until 2005 because we thought throwing shortened chalk away is wasteful. We received 3R Activity Promotion Award in 2011 from the mayor of Kitakyushu. Besides, we attended various events and we made regenerated chalk with more than 15,256 people.

By the way, do you know there are 2 kinds of chalk? One is plaster type chalk made by hydration bond of the sulfuric acid and the calcium. The other is the calcium carbonate chalk made by using adhesive bond.

Now, let me introduce the process of making regenerated chalk. First crash chalks and measure for 30g. If you measure 30g with 10g red and 20g White the you can make pink Chalk. If you measure 30g with 20g white and 10g yellow, then you can make cream colored chalk. Then grind and mix crashed chalks. After adding water equivalent to 60% of the mass of the chalk, and you have to knead chalk. Then you can shape anyway you want. You can make not only a shape of star, heart or other popular shape but also shape of cake, sushi and other original shaped chalk. After the shaping, dry it at a place with good ventilation for a day to two.

Currently we are researching about the relationships between water contents and drawability. We put 10% to 90% of water and measured drawability. We found out that it was most drawable when the water contents were between 50% and 70%. We also research about drying time and place. We dried chalk in both winter and summer and compared their dryness. In the winter we dried chalk at a window side, under a table and in a darkroom, a desiccator, a refrigerator and a freezer. In the summer we used an air-conditioned room instead of drying in refrigerator and freezer. We found out that the chalk can be dried at every place with high ventilation. However, in some cases, we ended up with very hard chalk which is not suitable for writing. Trying to find a factor to this phenomenon, we measured a particle size. When we made chalks with different particle size, we found out that the chalk made by the particle smaller than 0.25mm has tendency to create strong hydration bond making chalk very hard, and the chalk made with particle size greater than 0.5mm did not solidified due to gaps between particles. We concluded that the chalk made from the particle size between 0.25mm and 0.5mm has high drawability and erasability.

We would like to continue spreading knowledge about regenerated chalk to many people.

私たちは、短くなってしまったチョークを捨てるのはもったいない‼︎と考え、再生チョークについて2002年~2005年まで研究を続け、2011年に北九州市長より「3R活動推進表彰」をいただきました。その他にも様々なイベントに参加し、15,256人以上の人と再生チョークを作成してきました。

ところでみなさんはチョークが二種類あることをご存知ですか。一つ目は硫酸とカルシウムの水和結合で作られた石膏製、もう一つは接着剤を使った炭酸カルシウム製のチョークです。

それではここで再生チョークの作り方をご紹介します。まずチョークを砕き、30gはかります。この時に赤10gと白20gでピンクに、白20gと黄10gでクリーム色になります。次にすりこぎで潰し、チョークの質量に対し60%の水を入れてこねます。混ざったら好きな形を作り、1〜2日乾燥させたら完成です。星やハートなど人気の形だけでなく、寿司やケーキなど自分だけのチョークを作ることができます。

最後に研究内容についてです。まず私たちは含水量によるチョークの描きやすさの違いを調べました。チョークの粉に水を10%〜90%を入れて調べた結果、50%〜70%が最も描きやすくなることがわかりました。次に乾燥時間・場所について調べるため、冬と夏に分けて乾燥率を求めました。冬は窓辺・机の下・暗室・デシケーター・冷蔵庫・冷凍庫で、夏は冷蔵庫・冷凍庫の代わりにエアコンを加えて実験を行いました。その結果、風通しがよければどこでも乾かすことができることがわかりました。しかし、これらの研究結果を用いても固くて使えないチョークができることがありました。そこで粒径別にチョークを作ったところ、0.25㎜以下の粉では水和結合が強くなりすぎて固くなり、0.5㎜以上では粒と粒の間に隙間ができ固まらなくなりました。このことから0.25~0.5㎜の粒径でできたチョークが最も書きやすく消しやすいと分かりました。

これからも再生チョークを多くの人に広めたいです。