Why do clothes that have been exposed to the sun for a long time fade？

Sunlight is a kind of magical existence, it can not only bring light and warmth to the world, but also play the role of sterilization and disinfection. To some extent, sun exposure is good for the body, but strong sunlight sometimes has a bad side. Exposing colored clothing to the sun for a long time can easily cause the color to fade. Why?

Under the irradiation of light, the dye absorbs light energy, the energy level increases, and the molecules are in an intensified state, and the color system of the dye molecules changes or is destroyed, which causes the dye to decompose and cause discoloration or fading. Commonly known as: sun exposure Degree becomes worse.

Factors leading to poor light fastness

1.1 The influence of dye/coating structure

The light fading principle of dyes is more complicated. But the most fundamental reason is that the electrons in the dye absorb photons after being irradiated by ultraviolet rays and are excited, and a series of photochemical reactions occur to destroy the structure, causing discoloration and fading. The light fastness of textiles mainly depends on the chemical structure of the dye, as well as its aggregation state, combination state and mixed color matching. Therefore, a reasonable choice of dyes is very important.

1.2 The effect of dyeing depth and floating color

Using the same dye to dye the same fiber, there is still a big difference in the light fastness of textile fabrics at different depths. In the case of darker color, the light fastness is much better than that of the same light-colored product. This is because the higher the concentration of dye on the fiber, the greater the degree of aggregation of dye molecules. The smaller the surface area of the dye contacting air, moisture and light, the lower the probability of the dye's photochemical reaction. Conversely, the lighter the color, the higher the dispersion of the dye on the fiber. There is a greater chance of being exposed to ultraviolet radiation, and it is more prone to photochemical reactions.

The combination of dyes on the fiber also has a relatively large impact on the light fastness. When the dye is fixed in the fiber in a stable form, the electrons are relatively stable and the probability of receiving ultraviolet radiation is low, and the photochemical reaction is not easy to occur after ultraviolet radiation. If it is attached to the surface of the fiber in the form of a floating color, the probability of the dye touching the ultraviolet light is greatly increased, and it is in an active state, and it is very prone to photochemical reaction.

1. The influence of fiber itself

The performance of the fiber itself also has a greater impact. In many cases, the poor light fastness of light-colored varieties is not only a problem of dyes, but more often because of the poor light aging properties of the fiber itself. In this case, it is futile to screen dyes anyway.