The fading of dyed aluminum anodized products due to sunlight and other factors. Experiments have shown that there are differences in the degree of fading caused by different dyes.

1、 Main reasons

In addition to fading caused by dyes, there are three other reasons.

1. Discoloration caused by heat.

2. Discoloration caused by ultraviolet radiation.

3. Slow fading caused by oxidation and moisture in the air.

Dyes exhibit various colors due to their molecular structure, which can be recognized by the naked eye. However, due to the three main reasons mentioned above, its molecular structure has been disrupted, resulting in discoloration and fading. At the same time, the synergistic effect of these three factors should also be considered.

After being exposed to sunlight, the temperature increases, and in places with high humidity, the oxygen containing water also promotes the decomposition of molecular structure, leading to a stronger aging factor of dye molecules.

2、 Precautions and measures for fading.

1. Fading due to heat.

In the heating process of dyeing aluminum anodized components, the dye fades due to heating, and attention must be paid, using screen printing as a classic example.

Considering the adhesion of screen printing ink, high-temperature baking method is relatively good. However, in addition to cracking of the anodic oxide film of the product due to heat, the dye itself will also undergo significant fading and aging due to heat. Due to the wide variety of screen printing inks available today, even in the case of dual component curing and thermal curing, it is desirable to choose dyes that correspond to lower temperatures as much as possible.

In general aluminum oxide films, according to different anodizing conditions, the probability of cracking exceeding 100 degrees is high. Therefore, it is necessary to control the temperature of the curing furnace, including the drying after aluminum anodizing treatment. In addition to setting and controlling the furnace temperature, it is also necessary to pay attention to the situation of the hot air outlet.

Taking the setting temperature of the curing furnace as an example, even if it is set at 80 degrees, it is difficult to manage the temperature distribution of the air. Due to the possibility of the temperature reaching above the set temperature near the blowing of hot air, the position of the product in the curing furnace has become even more important.

2. Discoloration caused by ultraviolet radiation and slow fading caused by oxidation.

Due to exposure to ultraviolet radiation, the structure of dye molecules is gradually destroyed. For example, in the case of 100 dye molecules and 300 dye molecules in micropores of aluminum oxide films with the same surface area, and under the same conditions, when the molecular structure is gradually destroyed, the likelihood of 300 dye molecules maintaining their original color becomes higher.

In order to adsorb more dyes, the aluminum anodized film used as an adsorbent for dyes needs to be thickened. It is also very important to thoroughly stir the dye solution in order to adsorb as much as possible into the micropores of the anodic oxide film.

In the sealing treatment, there are methods such as nickel acetate sealing, water vapor sealing, fluoride containing sealing, and low-temperature sealing. In anodizing of dyed aluminum, whether it is water vapor sealing or low-temperature sealing, it is very difficult to maintain the consistency of dyeing, and dye overflow will occur, which is prone to uneven dyeing depth. Based on these phenomena, the nickel acetate series high-temperature sealing agents have become the mainstream for sealing the pores of dyed aluminum anodized films.

High temperature nickel sealing management requires long-term processing. Generally>90 degrees, the ratio of sealing time to oxide film thickness is generally 1-3min/um. However, anodic oxide films below 10um also need to undergo sealing treatment for at least ten minutes. The raw material of low-temperature sealing agent is fluoride, which may be cancelled due to environmental issues and may be difficult to use in the future.