| 摘要 |
PURPOSE: A color changeable film is provided on a food packing material to check whether or not the food is kept in optimal conditions. CONSTITUTION: A color changeable film(2) comprises synthetic resin as a main material. The synthetic resin is selected from the group consisting of polyethylene, polypropylene, nylon, and polyacetal resin. The color changeable film changes its color when a food is kept at higher temperature than reference temperature over a predetermined period, and maintains the changed color continuously. A thermochromic pigment is added to the synthetic resin so as to change the color of the film.
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