The reason why the passivation film layer did not show a rainbow color might be that the light emission process was not controlled properly or the pH value of the trivalent chromium colored zinc passivation solution was incorrect.
The outflow liquid and the outflow time were not controlled properly.
Since the trivalent chromium colored zinc passivation process is different from the hexavalent chromium colored zinc passivation process, the passivation solution of this process cannot play the role of chemical polishing during the film formation process. To obtain a passivation film layer with good brightness, it is necessary to rely entirely on the coating. Therefore, for those using the trivalent chromium colored zinc passivation process, the coating must be shiny. If the coating is not shiny, the passivated film layer will be a dull yellow color (without luster, affecting the normal delivery of the electroplating factory). Additionally, after the product is electroplated, before entering the trivalent chromium colored zinc passivation solution, it must undergo a light nitric acid brightening treatment.
If the outlighting process is not handled properly, it may result in an unsatisfactory appearance color of the passivation film. At this point, it is necessary to make reasonable adjustments to the outlighting solution and the outlighting time
Too high or too low pH value
When using the trivalent chromium chromate zinc passivation solution Zn-228, the pH value is a very important process condition. When the pH value is low, the bonding strength between the passivation film and the zinc coating is stronger, but the brightness of the passivation film layer is poor, and it looks opaque, as if there is a layer of mist covering it.
When the pH value increases, the appearance of the passivation film becomes yellow (not the rainbow color that the downstream customers desire). Based on this, the electroplating factory needs to control the pH value within the range of 2.0 - 2.5 under the guidance of Bigley. This will enable the desired film color to be obtained.
How to adjust the pH value? As we mentioned above, nitric acid, being a strong acid, not only has the function of chemical polishing but also can regulate the pH value. Therefore, adding a small amount of it can solve the problem.
About us
Guangdong Bigely Technology Co., Ltd. ,founded in 2003, is a high-tech enterprise integrating R & D，production, sales and service, specializing in the production of electroplating chemicals. As a fast growing electroplating chemicals supplier in China, Bigely has over 20 years' experience in electroplating additives production and own production base of 5000 square meters. We can produce 15,000 tons of electroplating additives every year, which can fully meet the needs of customers.
If you need our high-quality electroplating additives, please contact us. We can provide you samples for test, and also provide a series of services.
