Temperature detecting material, temperature detecting ink using same, temperature indicator, and product control system

A temperature detecting material comprising a first material containing a first temperature indicating material and a second material containing a second temperature indicating material,

• wherein
• the first temperature indicating material and the second temperature indicating material respectively contain a leuco dye, a color developing agent, and a decoloring agent, and respectively have hysteresis characteristics in their color density-temperature curves,
• wherein
• the first temperature indicating material has a color developing temperature Ta1 in a temperature increase process, which is lower than a decoloring temperature Td1 in the temperature increase process, and turns to a non-crystalline state and is kept in a decoloring state when cooled down lower than the color developing temperature Ta1 in the temperature increase process with a predetermined cooling speed or more after melting,
• wherein
• the second temperature indicating material has a color developing temperature Ta2, which is lower than a decoloring temperature Td2 in a temperature increase process,
• and wherein
• the color developing temperature Ta1 in the temperature increase process is lower than the decoloring temperature Td2 in the temperature increase process and the color developing temperature Ta2 is lower than the color developing temperature Ta1 in the temperature increase process, wherein
• the color developing temperature Ta2 of the second temperature indicating material is a color developing temperature in a temperature decrease process,
• and wherein
• the second temperature indicating material turns to a liquid state and is kept in a decoloring state when cooled down after melting to a temperature higher than the color developing temperature Ta2 and lower than the color developing temperature Ta1 in a temperature increase process of the first temperature indicating material.