The characteristics and discoloration principle of thermochromic powder

Thermochromic powders are prepared from electron transfer organic compound systems. The temperature-changing powder changes the molecular structure of the organic matter due to electron transfer at a specific temperature, thereby realizing color change. Thermochromic powder is not only bright in color, but also can achieve color change from “colored to colorless” state, which is not available in heavy metal double salt complex type and liquid crystal type reversible thermochromic substances.

Microencapsulated reversible thermochromic powder is called reversible thermochromic pigment (commonly known as: thermochromic pigment, thermosensitive powder or thermochromic powder). The particles of this pigment are spherical, with an average diameter of 2 to 7 microns (a micron is equal to one thousandth of a millimeter). The inside is a color-changing substance, and the outside is a transparent shell with a thickness of about 0.2~0.5 microns that neither dissolves nor melts. It is this that protects the color-changing substance from other chemical substances. Therefore, it is very important to avoid damage to this shell during use.

Thermal powder application

1. Thermochromic powder is a microencapsulated reversible thermochromic substance called reversible thermochromic pigment (commonly known as: thermochromic pigment, thermochromic powder or thermochromic powder).

2. This product can be used for injection molding and extrusion molding of transparent or translucent plastics such as polypropylene (PP), soft polyvinyl chloride (S-PVC), AS, ABS and silicone. It can also be mixed into unsaturated polyester, epoxy resin, plexiglass or nylon monomer for casting, molding and curing to form a suitable ink substrate.

3. When used for injection molding, extrusion molding or casting, molding, curing molding, the amount of color-changing pigment is 0.4~3.0% of the plastic amount, usually 0.6~2.0%. The color-changing pigment and plastic particles should be thoroughly mixed evenly (a small amount of white oil can be used when mixing). If it is a color matching between ordinary pigments and color-changing pigments, the amount of ordinary pigments (or dyes) is about 0.5-2.5% of the color-changing pigments.

4. Color masterbatch: In mass production, color-changing pigments can be added to polyethylene wax or polystyrene wax to make color masterbatch with a pigment content of 10%, and then mixed with plastic particles. This allows the color-changing pigment to be dispersed more uniformly. The preparation method of color masterbatch can refer to the technical information provided by our company.

5. Temperature: The processing temperature should be controlled below 200 °C, the highest should not exceed 230 °C, and the heating time of the material should be minimized. (High temperature and prolonged heating will damage the color changing properties of the pigment).

Thermal powder storage method

The reversible thermochromic pigment itself is an unstable system (it is difficult to change if it is stable), so its light resistance, heat resistance, aging resistance and other properties are far less than ordinary pigments, and should be paid attention to in use.

1. Lightfastness

Thermochromic pigments have poor light fastness and will fade quickly when exposed to strong sunlight, so they are only suitable for indoor use. Strong sunlight and ultraviolet light should be avoided, which is beneficial to prolong the service life of color-changing pigments.

2. Heat resistance

Thermochromic pigments can withstand high temperature of 230 °C in a short time (about 10 minutes), and can be used in injection molding and high temperature curing. However, the thermal stability of the color-changing pigments in the color-developing state and the decolorizing state is different, and the stability of the former is higher than that of the latter. In addition, when the temperature is higher than 80 °C, the organic matter that constitutes the discoloration system will also begin to degrade. Therefore, color-changing pigments should avoid working at temperatures higher than 75 °C for a long time.