A short time ago I received the following inquiry regarding our Heat-Sensitive Paper. One of the joys of being the president of Educational Innovations is having the opportunity to answer questions like this.
Q: What chemical coats your Heat-Sensitive Paper that makes it change color? My chemistry class wants to know the chemistry of what is happening on our heat-sensitive periodic tables. Can you please help us?
A: Some of the characteristics of our heat-sensitive periodic tables are easy to understand and some more challenging. The inks used provide color at lower temperatures and are colorless at higher temperatures. The change over temperature is called the “critical temperature.” Adding heat to the paper causes the paper to loose its color, an “endothermic” reaction. The reverse, going from colorless to colored, is an “exothermic” reaction and returns the heat.
To manufacture this paper, long rolls of white paper are unwound, coated on one side, dried, cut, and finally stacked into reams. This is done at a company that produces labels for cans. The paper is then printed with black ink to produce our periodic tables.
Educational Innovations, Inc. was one of the first companies to sell
thermochromic paper and drinking cups (see our Disappearing Dinosaurs Mug and our Global Warming Mug), over 15 years ago. We followed up on an article about this new discovery in the NY Times. At that time the “Touch-It” paper used two colors of heat sensitive inks: blue and red – both turning colorless when heated. From those two heat sensitive inks, five colors of paper could be manufactured: red paper which turned colorless; blue paper which turned colorless: orange paper which turned yellow; green paper which turned yellow; and purple paper which turned colorless. For the orange and green paper, the thermochromic inks were printed on yellow paper.
The complete chemistry of thermochromic, heat sensitive ink, involves micro-encapsulation techniques. Incidentally, you can increase the sensitivity of your periodic table by removing any absorbed moisture with a hair dryer or putting the paper through a copy machine.
I have found that kids of every age find this paper fascinating. Teachers use this paper to print newsletters home to parents, for special certificates or awards, and for printing diagrams or other papers the students should keep. They can even be laminated to use as bookmarks, hall passes, or as class syllabus.