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Why do dyed aluminum anodic oxide films sometimes change color?

Release time:

2020-04-13 10:31

Discoloration of dyed aluminum anodized products due to sunlight and the like. Experiments show that there are differences in the degree of fading due to different dyes.

Main causes of 1.

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

1, due to heat caused by fading.

2, due to ultraviolet light caused by fading.
3. Slow fading due to oxidation and moisture in the air.

The dye shows various colors due to its molecular structure and can be recognized by the human eye. However, due to the above three main reasons, the molecular structure is destroyed, resulting in discoloration and fading, and the synergistic effect of these three factors should also be considered.

After being exposed to sunlight, the temperature rises. In places with high humidity, the oxygen containing moisture will also promote the decomposition of the molecular structure, resulting in a stronger aging factor of the dye molecules.

Attention points and measures for 2. fading.
1, due to heat and fade.

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

Considering the adhesion of screen printing ink, the method of high temperature baking is better, but in addition to the cracking of the anodic oxide film of the product due to heat, the dye itself will also cause obvious fading and aging due to heat. Since the type of screen printing ink is now very rich, even in the two-component curing, thermal curing, it is also desirable to choose as much as possible the corresponding temperature of the dye.

In the general aluminum oxide film, according to the different anodic oxidation conditions, the probability of cracking more than 100 degrees is large, so it is necessary to control the temperature of the curing furnace including the drying after the aluminum anodic oxidation treatment. In addition to the furnace temperature setting control, but also need to pay attention to the hot air outlet.

Taking the setting temperature of the curing furnace as an example, even if it is set to 80 degrees, it is difficult to manage the temperature distribution of the air. Since the temperature in the vicinity of the blowing hot air may reach the set temperature or more, the position of the product in the curing furnace becomes more important.

2. Fading due to ultraviolet rays, and slow fading due to oxidation.

As a result of exposure to ultraviolet light, the mechanism of the dye molecules is gradually destroyed. For example, in the case where there are 100 dye molecules and 300 fuel molecules in the pores of the aluminum oxide film of the same surface area, and the molecular structure is gradually destroyed under the same conditions, it is considered that there is a high possibility that 300 fuel molecules maintain the original color.

In order to adsorb more fuel, the aluminum anodic oxide film as an adsorption dye needs to be thickened. In order to absorb into the depth of the micropores of the anodic oxide film as much as possible, it is also very important to fully stir the dye solution.

In the sealing treatment, there are nickel acetate sealing, water vapor sealing, fluoride, low temperature sealing and other methods. Considering only the quality of the anodic oxide film, the water-sealed pores contain fluoride, and the pores are sealed at low temperature. More excellent performance. Sealing performance has a great relationship with the fading of dyes, and the degree of fading in low-temperature sealing treatment is very small, and the original color is still maintained. Moreover, in the anodizing of dyed aluminum, whether it is water vapor sealing or low-temperature sealing, the consistency of dyeing is very difficult, and dye overflow will occur, which is prone to uneven dyeing depth. According to these phenomena, the nickel acetate series high temperature sealing agent becomes the mainstream of the dyed aluminum anodic oxide film sealing.

High temperature nickel sealing management requires long processing time. Generally> 90 degrees, the ratio of sealing time to oxide film thickness is generally 1-3min/um, but the anodic oxide film below 1um should be sealed for at least 10 minutes. The raw material of low-temperature sealing agent is fluoride, which may be canceled due to environmental problems and may be difficult to use in the future.


Aluminum anode