First, the reasons for anodic oxidation
1, oxidation dyeing principle
It is well known that the anodic oxide film is composed of a large number of hexagonal cells perpendicular to the metal surface. Each cell center has a membrane pore and has a strong adsorption force. When the oxidized aluminum product is immersed in the dye solution, Molecules through the diffusion into the membrane of the oxide film, while the formation of difficult to separate with the oxide film covalent bond and ionic bond. This bond is reversible, under certain conditions will occur desorption. Therefore, after dyeing, must be sealed, the dye fixed in the membrane hole, with the increase in the oxide film corrosion resistance, wear and other properties.
2, anodic oxidation process on the impact of dyeing
In the whole process of oxidative dyeing, it is common for the dyeing process to cause poor dyeing. The uniformity of the film thickness and the uniformity of the pores is the prerequisite and basis for obtaining the uniform and uniform color when dyeing. In order to obtain the uniform oxide film, it is necessary to ensure the sufficient amount of circulation and the amount of cooling to ensure good electrical conductivity.
Sulfuric acid concentration, controlled at 180-200g / l. Slightly higher concentration of sulfuric acid can promote the dissolution of the oxide film to accelerate, conducive to the expansion of the pores, easier to dye;
Aluminum ion concentration, controlled at 5-15 g / l. Aluminum ions less than 5g / l, the formation of the oxide film adsorption capacity decreased, affecting the color rate, aluminum ions greater than 15g / l, the uniformity of the oxide film is affected, prone to irregular film.
Oxidation temperature, controlled at about 20 ℃, the effect of oxidation bath temperature on the dyeing is very significant, too low temperature caused by the oxide film membrane density, significantly slow the dyeing speed; temperature is too high, oxide film pine, easy to powder , Is not conducive to the control of dyeing, oxidation tank temperature difference should be within 2 ℃ is appropriate.
Current density, controlled at 1-1.5A / dm2. The current density is too large, in the case of a certain thickness, it is necessary to shorten the aluminum products in the tank in the electrolysis time, so that the oxide film dissolved in the solution to reduce the film hole dense, longer dyeing time. At the same time, the film is easily pulverized.
Film thickness, dyeing requirements oxide film thickness is generally more than 10μm red solution. The film thickness is too low, dyeing is prone to uneven phenomenon, and in the dark color (such as black), because the film thickness is not enough, resulting in limited deposition of dyes, it can’t meet the required color depth
All in all, anodic oxidation is the basis of dyeing before dyeing. Anodic oxidation problems before dyeing, we are difficult to see or simply can’t see, once stained, we will clearly see such as the phenomenon of uneven color. At this time, the production workers tend to be the cause of the problem attributed to the abnormal dyeing, and ignore the oxidation process to find the reasons. I often make these mistakes when I just touch oxidation.
Second, the reasons for dyeing
1.1 Wash before washing
After anodic oxidation, the sulfuric acid solution remains in the membrane pores of the oxide film, so that the aluminum product must be thoroughly cleaned before dyeing. Avoid imposing impurity ions, especially phosphate ions, fluoride ions, etc., in the dyeing tank before the establishment of pure water cleaning, and to monitor the water quality is very necessary.
1.2 Preparation of dyeing tank
Among the dyes used in dyeing, most are organic dyes, organic dyes are easy to mold. In order to effectively prevent the mold mold, before the preparation of the tank, you can use bleach, phenol, a class of drugs will tank disinfection. When preparing the bath, adding the antifungal agent can effectively prolong the use time of the dyeing liquid. After the bath with a good number of hours to be stored in order to put into use, in order to ensure stable ph value, you can add acetic acid - sodium acetate slow
1.3 dyeing process control
(1) temperature During dyeing, the dyeing rate increases with increasing temperature, so the time required to dye a certain depth is shortened with increasing temperature. At the same time, the bath temperature rise, the synchronization seal will be accelerated, if the temperature is too high, synchronous sealing too fast, the dye molecules have not yet enough to adsorb in the membrane hole, the accumulation of dye will be due to oxide film membrane hole Closed and can not reach the required depth, and relatively low temperature dyeing, you can dye a deeper color, but the corresponding time to long, and therefore, for different color requirements, you can adjust the dyeing temperature, avoid dyeing time Too long or too short.
(2) Dye concentration
According to the law of adsorption, under certain working conditions, the adsorption amount of dye on the anodic oxide film increases with the increase of dye concentration. However, this rule applies only if the oxide film itself has an adsorption capacity. For different depth of color, the dye concentration should also be adjusted accordingly, in the initial preparation of the bath, as much as possible to prepare a lower concentration of the solution, with the production of the dye continue to consume, to continue to add the consumption of the part, To be a few times. If the concentration of dyes to determine, to consider the impact of impurity ions, the actual effective concentration and detection may have a greater difference, therefore, to the regular dyeing tank of the actual staining force for comparative testing. To ensure a stable dyeing power, after a period of production, you can partially replace the bath.
As with the electrolytic coloring, when the other conditions remain unchanged, the color gradually increases with time, the general situation, when the oxidation conditions to determine the concentration of dyeing solution, temperature and so on. We only have to adjust the dyeing time to obtain the customer request the color depth, if the dyeing time is too short has been required to obtain the desired color, which there are two disadvantages, one is too fast, to get uniform color is not easy; Is too fast color, the color of the obtained weather is not enough. Dyeing time is too long, or no matter how long the color can not get the required color depth, then we have to consider the oxide film is not too thin or too low dye concentration.
(4) PH value
Generally require ph value is 5 to 6, the stability of the ph value is very important for dyeing, especially for mixed dyes, different ph value, there may be different tones, in order to enhance the stability of ph value, in the preparation of the bath to join Buffer solution is a viable approach, at the same time to strengthen the washing before washing, to avoid taking acidic substances.
1.4 washed after washing
After dyeing, the aluminum product should be washed with water to remove the floating color attached to the surface of the aluminum product. At this time, attention should be paid to the water quality of the washing tank because the combination of the dye molecules and the oxide film is reversible. When there are more impurity ions in the water, Will promote the dye molecules and oxide film into the water, this time to show the fade, this fade is often uneven, and ultimately lead to the same material on the production of color.
Third, the reasons for the closure
Sealing treatment is an indispensable part of anodic oxidation. After oxidative dyeing, only the sealing treatment can only ensure the original color of the dyeing film. There are many kinds of sealing process, steam sealing, hot water sealing and medium temperature sealing Holes are a good choice, some dyes can also choose cold sealing process. After the hole may be due to fade and make the color slightly lighter than the front, but as long as a little attention can be.
Dyeing as a branch of anodic oxidation, because of its pleasing color, I believe will be vigorously applied, increasingly favored by the people.