Thermochromic Powders

Thermochromic powders are a type of pigment. They can change color at specific temperatures. This is due to electron transfer-induced molecular structure changes in the organic material. Thermochromic powders are also known as thermochromic pigment powders, thermosensitive pigments, temperature color-changing pigments, or thermoresponsive color-changing pigments. Thermochromic reversible microcapsules can change color repeatedly with temperature changes. The particles of this pigment are spherical, with an average diameter of 2-7 μm (1 μm = 1/1000 mm). Inside the pigment, there is a color-changing substance. This substance is protected from chemical erosion by a transparent shell. This shell is approximately 0.2-0.5 μm thick and is neither soluble nor meltable.

Thermochromic powders can change color repeatedly with temperature increase or decrease. The thermochromic color-changing effect occurs only within a certain temperature range. The thermochromic pigment involves color fading, color development, and color-changing effects. The thermochromic powder changes color depending on temperatures. Its basic temperature range is 10-70℃, and it works best when processed at 160-180℃. If the thermochromic powder doesn’t disperse well during the injection molding, a dispersing agent can be added. As the temperature increases or decreases, the microcapsule material can change color repeatedly. The commonly used temperatures are 15/18/22/28/31/33/45℃. The basic colors are bright red, vermilion, rose red, pink, orange-red, golden yellow, violet, navy blue, blue, green, black, and turquoise blue. The adjustable colors: All colors except for gold and silver can be adjusted. Only closely related colors can be adjusted for hue change.

Thermochromic pigments are prepared from an electron-transfer organic compound system. Electron-transfer organic compounds are a class of organic chromogenic systems with special chemical structures. They can change color at specific temperatures. This is due to electron transfer-induced molecular structure changes in the organic material. This color-changing material can not only produce bright colors but also change from a “colored” to a “colorless” state. Heavy metal complex and liquid crystal reversible thermochromic materials do not possess this characteristic.

Microencapsulated reversible thermochromic materials are called reversible thermochromic pigments (commonly known as thermochromic pigments, thermosensitive powders, or thermochromic powder). The particles of this pigment are spherical, with an average diameter of 2-7 μm (1 μm = 1/1000 mm). Inside the pigment, there is a color-changing substance. This substance is protected from chemical erosion by a transparent shell. This shell is approximately 0.2-0.5 μm thick and is neither soluble nor meltable. Therefore, it is very important to avoid damaging this outer shell during use.

The temperature ranges commonly used for thermochromic powders: 0-5°C, 8-12°C, 18-24°C, 26-31°C, 29-33°C, 38-43°C, 45-50°C, 50-54°C, 60-65°C, 65-70°C, and 70-78°C. The most common color-changing temperature is 31℃. This temperature is also known as touch-activated color-changing or hand-sensitive color-changing. Products containing thermochromic powder will undergo a color change at 4-6℃, with 31℃ as the center point. For example, for red thermochromic powder, the color change happens at 31℃. Above 31℃, it will appear red. Below 31℃, it will revert to its original color.

Usually, the final color-changing temperature is when the color change is complete. For example, a 31℃ thermochromic powder undergoes a color change between 27-34℃ (±3-4℃). This is referred to as a 31℃ color change. Some thermochromic powders are heat-erasable and irreversible. At low temperatures, it’s colored. At a certain point, the pigment changes to colorless or another color. The color-changing temperature range is 60-120°C.

Thermochromic powder is less stable than ordinary pigments; its properties such as light resistance, heat resistance, and aging resistance, are inferior. This is due to the inverse relationship between stability and change. Thermochromic powder is generally more expensive than ordinary pigments; hence, proper storage is essential. Then, in use and storage, we should also pay attention to:

Thermochromic pigments can fade and lose effectiveness in strong sunlight due to poor light resistance. To prevent loss of effectiveness, thermochromic pigments should be used indoors and protected from prolonged exposure to direct sunlight, intense sunlight, and ultraviolet light. This can help extend the service life of the color-changing pigments. What’s more, thermochromic pigments are not heat resistant and should not be mixed with strong acid or alkali compounds.

Thermochromic materials are harmless to the human body. These materials include thermochromic powders, thermochromic inks, thermochromic paints, etc. Microencapsulated reversible thermochromic materials are non-toxic, non-irritating to the skin, and generally do not contain toxic components.

Thermochromic materials produce different colors as the temperature changes. They are prepared from an electron-transfer organic compound system. Electron-transfer organic compounds are a type of organic chromogenic system that changes color due to electron transfer at a specific temperature. No toxic substances and harmless to the human body.

Thermochromic materials are produced by combining thermochromic pigments and plastics. Therefore, standardized product labels and instructions are very important. They can ensure these materials meet market needs, comply with the relevant national food safety standards, and follow the ROHS environmental certification requirements. Read the product manual carefully and follow the instructions when using thermochromic products.

1. Thermochromic materials are generally used in oil-based inks and coatings, water-based inks and coatings, plastic injection molding, extrusion, etc.
2. Thermochromic powders are a novel reversible coloring agent.Thermochromic powders can rapidly change color with temperature, creating a dynamic color-changing effect on the object.
3. At present, color-changing pigments have been increasingly applied in the printing industry.
4. Thermochromic powders can be used to prepare various inks, including screen printing inks. Screen printing color-changing inks are more widely used.

Different color-changing pigments can be mixed and matched since the reversible thermochromic powder is colorless in its hidden state. This results in a more diverse range of color-changing effects.

Thermochromic powders can be used to produce inks (such as screen printing, offset printing, intaglio printing, and flexographic printing) as well as coatings and other applications. Thermochromic powders can also be applied to various plastic materials such as PP, PVC, ABS, PU, EVA, PE, and silicone rubber for injection molding, compression molding, extrusion, injection molding, and extrusion molding. In addition, some new children’s products such as color-changing crystal clay, color-changing playdough, color-changing hand warmers, etc. have also been developed using thermochromic technology.