How to Deal with Color Differences for Injection molding parts?

It is common to see the color difference in injection molding. Injection molding machines are scrapped due to color differences in matching parts, which is not uncommon. Color masterbatch, raw material resin, mixing of color masterbatch and raw materials, injection molding machines and molds and injection molding processes are the factors of color differences. Because of the wide range of involvement, the color difference control technology is also recognized as one of the difficult techniques in injection molding. Generally, the color difference can be controlled from the six aspects as follows in the actual production process:

Eliminating impacts of injection molding machines and molds
Select an injection molding machine with the same capacity as the injection product. It is best to replace the injection molding machine, If problems like material blind angles occur. The color difference caused by the gating system and discharge groove of the mold can be solved by the maintenance of the corresponding part of the mold. The problems of injection molding machines and molds must be solved first before production in order to make complexity of the problem reduced.

Eliminating impacts of raw material resin and color masterbatch
Controlling raw materials is critical to completely solving color differences, so when light-colored products are manufactured, obvious influences of the different thermal stability of the raw material resin on the color fluctuation of the product cannot be ignored.

In view of the fact that most injection molding factories don't manufacture color masterbatch. Raw material inspection and production management should be focused on. Inspection of raw materials in storage should be paid attention to. Choose the same factory and masterbatch with the same brand for one product in the production.

Before mass production, random inspections ought to be conducted for the color masterbatch. Compare the color masterbatch when they are checked, and also compare the color masterbatch now with the last inspection. If the color difference is not great, it can be considered qualified. If the color masterbatch in the same batch has a slight color difference, use the color masterbatch after they are mixed, reducing the color difference caused by uneven mixing of the color masterbatch itself. Meanwhile, the thermal stability of the raw material resin and color masterbatch should be tested. For those with poor thermal stability, it is recommended that the supplier should be replaced.

Eliminating impacts of uneven mixing of the color masterbatch and masterbatch
Uneven mixing of plastic masterbatch with color masterbatch will also change the color of the product. After the masterbatch and color masterbatch are mechanically mixed and sent to the hopper by the lower suction material, the color masterbatch is separated from the masterbatch due to static electricity and is easily adsorbed on the wall of the hopper. The amount of color masterbatch will inevitable change in the injection cycle, resulting in color difference.

In this case, after the raw materials being sucked to the hopper, manually stirring can be used to solve this problem. For the production of colored products by adding color materbatch, the most useful way is to use a hot air dryer instead of a suction machine to prevent the color difference caused by separation of the color masterbatch from the parent material.

Decreasing​ impacts of injection molding adjustment
When the injection molding process parameters need to be adjusted for non-color difference reasons, try not to change the injection temperature, injection cycle, back pressure, and the amount of masterbatch added as much as possible. At the same time, observe impacts of technological parameter changes on the color and luster. If color difference is found, technological parameters should be adjusted in time. Try to prevent using injection molding processes that cause strong shearing effects such as high injection speed and high back pressure to avoid color difference caused by partial overheating or thermal decomposition. The temperature of each heating section of the barrel, especially the nozzle and the heating part close to the nozzle should be strictly controlled.

Decreasing impacts of barrel temperature on color differences
It is often encountered that a certain heating ring is damaged or failed or the heating control part is out of control and the temperature of the barrel changes drastically in production, resulting in color difference. It's easy to determine color differences caused by this reason. Usually, the color difference caused by the failure of the heating ring will be accompanied by uneven plasticization. Severe discoloration, air spots and coking often occur when the heating control part is out of control and burnt for a long time. Thus, it is necessary to check the heating part frequently during production, and replace and repair it in time when the heating part is found to be damaged or out of control to reduce the chance of such color difference.

Grasping impacts of barrel temperature and color masterbatch volume on product color changes
Before adjusting color differences, you must also know that the color of the product changes with temperature and the amount of color masterbatch. Different color masterbatch has different color difference based on changes of the production temperature or the amount of color masterbatch. The color testing can be used to determine its changing rule. Unless the color change rule of this masterbatch is known, fast adjusting the color difference, especially with the use of new masterbatch in production is not possible.