Pignmet for Thermochromic Paint

The thermochomic paint is divided into reversible paint and irreversible thermochomic paint based on the thermochomic properties. Reversible thermochomic paint changes the color as the temperature rises and returns to their previous state as the temperature falls.

Reversible thermochomic paint has three categories due to their thermochomic temperature: cold discoloration, touch discoloration and thermal discoloration. Cold discoloration generally refers to discoloration below 20℃ (ambient temperature). It appears on the packages of cold drinks, such as beverages, ice cream, beer, etc. It is usually colorless and invisible at room temperature. When poured into a cold drink, the cup wall changes color, giving a refreshing feeling. Touch discoloration refers to the discoloration after contact with the human body. Its discoloration temperature is around 31℃. It is commonly used in accessories, temperature measuring products, children’s toys and other products. Thermal discoloration generally involves the temperatures higher than normal temperature, such as 40℃, 50℃, etc. It is commonly used on packages of hot drinks. For example, it is used on mugs, coffee cups, teacups, or electric appliances to warn the danger of high temperature.

Irreversible thermochomic paint changes the color as the temperature rises, and the color disappear as the temperature falls. However, it cannot restore original color. In general, such thermochomic paint can appear on disposable inspection products, such as electric motors, bearings, boilers and other devices, to indicate temperature and ensure production safety.

We can make thermochomic paint pigments by various methods and the common methods are as follows:

1.Chemical reaction

Mix two or more elements or compounds with different oxidation states and let them go an oxidation-reduction reaction at high temperature or by adding reaction-promoting substances to produce substances with different colors.

2.Solution co-precipitation

During the production process, mix one or more metal ions with one or more thermosensitive substances and let them precipitate in an aqueous solution to produce a thermochomic pigment.

If the thermochomic pigment paint is well preserved before use, its thermochomic effect remains unchanged after even five to ten years. Tests indicate that the number of color-changing cycles of thermochomic pigments is generally 2,000-4,000 times.