1 Concept 1.1 What is color-changing fiber?
The so-called color-changing fiber is a fiber with a special composition or structure that can automatically change its color after being stimulated by external conditions such as light, heat, moisture, or radiation. At present, the main varieties of color changing fibers are photochromic and temperature-induced discoloration. The former refers to the fact that certain substances can produce discoloration under the irradiation of light of a certain wavelength, but under the irradiation of light of another wavelength (or the effect of heat), reversible changes will return to the original color; the latter refers to By adhering the special microcapsules on the surface of the fabric, the microcapsules can use the function of color change with temperature changes, so that the fibers produce a corresponding color change, and this change is also reversible.
Varieties of color-changing fibers are mainly concentrated on photochromism. In fact, as early as 1989, W. MARCKWALD discovered for the first time that certain solid or liquid compounds have photochromic properties, and substances with photochromic properties are usually organic substances having isomers such as naphthopyran, spiropyridazine, and norbornene derivatives. Due to the effect of light, these chemical substances undergo a change in the bonding mode or electronic state corresponding to the two compounds, and reversible changes in color, color, and discoloration may occur in two different states of the absorption spectrum.
The earliest application example was during the Vietnam War, the United States' CYANAMIDE company developed a fabric that can absorb light and change its color to meet the US military's requirements for combat clothing. China's Donghua University uses light yellow-green trimethyl spirooxazine as a photosensitizer, and it also has good properties when it is blended with polypropylene chips and then made into high-speed melt spinning. After irradiation with ultraviolet rays, the fiber can quickly change from colorless to blue, and after the light stops, it can quickly become colorless, and has good washing performance and certain light durability. The corresponding product is the photosensitive photochromic fabric of Japan Kanebo Company, and the T-shirt made from this fabric was supplied to the market as early as 1989. Several universities such as CLEMSON University and GEOR-GIA Institute of Technology in the United States have recently begun to study the change of the surface coating material of the photosensitive fiber, so that the color of the fiber can be automatically controlled. In the civilian field, photochromic fiber is mainly used in entertainment clothing, safety clothing and decorations, and anti-counterfeiting labels.
The general color changing material is a material having photochromic properties such as light, heat, and electricity. In particular, the wings of the glitter-colored fiber butterfly and the feathers of the peacock are more beautiful under the reflection of light. This is because the participation of light can make the color effect better. Based on this principle, for example, a professor in Japan invented flash color-changing fibers. Fabrics made from this fiber have a variety of colors that are fascinating. This fabric can be used to make clothing and interior decoration and so on.
1.2 Types of color-changing fibers The types of color-changing fibers can be roughly classified into photochromic fiber materials, thermochromic fiber materials, electrochromic fiber materials, and other color-changing materials.
1.2.1 Photochromic fiber materials Photochromic materials are classified into organic and inorganic types. Organic spiropyran derivatives, azobenzene derivatives. The advantages of this type of color-changing material are: light coloration and achromatism, but poor thermal stability and oxidation resistance, low fatigue resistance, and large environmental impact. Inorganic species are doped with single crystal SrTiO3, photochromism, it overcomes the organic photochromic materials, thermal stability and poor anti-oxidation, low fatigue resistance, and is not affected by the environment. However, inorganic photochromic materials have slower color development and decolorization and larger particle sizes. Photochromic fibers are fibers made by blending a photochromic material and a high polymer by solution spinning, blend spinning, or composite spinning techniques.
The photochromic fiber is a fiber whose color will change under the irradiation of sunlight or ultraviolet light, etc. When the light disappears, it will revert back to the original color reversibly. Since 1899, when certain solid and liquid compounds were found to have photosensitizing properties, the study of various photosensitive materials has attracted great interest. Japan first developed photochromic composite fibers, and based on this as a basis for a variety of light-sensitive fiber products, such as embroidery velvet, knitting yarn, woven yarn, etc., used to decorate leather, sports shoes, sweaters, etc., have been widely loved by people. .
There are many examples of photochromic fiber materials. For example, acrylic fabrics are dyed and finished with cationic dyes with discolored molecules, and they change color under different light sources. Therefore, they are called color-change knitted fabrics. Leveling agents and acid agents have a certain influence on the color change effect. The experimental results show that using 1227 leveling agent and glacial acetic acid, the fabric has the best discoloration effect. Acrylic acrylic knitted fabrics must be opened and finished before drying. The drying temperature should be 98°C～100°C. The fibers and fabrics prepared by this method have different shades at different wavelengths of light and all belong to the photochromic fiber fabrics. There is also a Japanese company will absorb 350nm ~ 400nm wavelength ultraviolet light from colorless to light blue or dark blue spirofuran photosensitive substances wrapped in microcapsules, used in printing process made of photochromic fabric. Microencapsulation can increase the antioxidant capacity of photosensitizers and thus extend the service life. The photochromic T-shirts produced using this technology have been available in the market in 1989. In recent years, similar products have been sold in China.
1.2.2 Thermochromic fibres Thermochromic fibres are fibres whose colour changes with temperature. The method for obtaining the thermochromic fiber is not only the thermochromic agent filled inside the fiber, but also the vinyl chloride polymer solution containing the thermochromic microcapsule is applied on the surface of the fiber, and the solution is gelled after being heat-treated. Reversible thermochromic efficacy.
For example, in 1988, Toray developed a temperature-sensitive fabric, Sway, in which thermal dyes were sealed in capsules 3 to 4 m in diameter and then coated on the fabric surface. The microcapsules of this glass substrate contain three main components: a thermochromic dye; a coloring agent capable of expressing another color in combination with a pigment; a combined pigment and coloration at a certain temperature An alcohol decolorizer that separates and dissolves pigments or color developers. By adjusting the composition ratio of the three components, the microcapsules whose color changes with temperature can be obtained, and this change is reversible. It has 4 basic colors, but it can be combined into 64 different colors

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