Color aberration is a common defect in injection molding, and it is not uncommon for injection molding machines to be scrapped in batches due to the color difference of accessories.
There are many factors influencing color difference, involving raw material resin, masterbatch (or toner), mixing of masterbatch and raw materials, injection molding process, injection molding machine, mold, etc., because it involves a wide range of factors, so color difference control technology is also one of the recognized technologies in injection molding.

In the actual production process, the color difference is generally controlled from six aspects:

1. Eliminate the influence of injection molding machines and molds

Choose an injection molding machine that is comparable to the capacity of the injection molded product. For the color difference caused by the mold pouring system, exhaust groove, etc., it can be solved by the maintenance mold of the corresponding part of the mold. It is necessary to solve the problems of injection molding machines and molds before we can organize production to reduce the complexity of the problem.

2. Eliminate the influence of raw material resin and masterbatch

Controlling raw materials is the key to completely solving the color difference. Especially in the production of light-colored products, we cannot ignore the obvious influence of the different thermal stability of the raw material resin on the color fluctuation of the product.

For the masterbatch, we should conduct a sampling test before mass production, not only with the last proofreading, but also in this comparison, if the color difference is not large, it can be considered qualified, as the batch of masterbatch has a slight color difference, the masterbatch can be remixed and then used, in order to reduce the color difference caused by the uneven mixing of the masterbatch itself. At the same time, we also need to focus on testing the thermal stability of raw material resins and masterbatches, and it is recommended to replace them if the thermal stability is not good.

3. Eliminate the influence of uneven mixing of masterbatch and masterbatch

Poor mixing of plastic masterbatches with the same color masterbatch will also make the color of the product changeable. After the masterbatch and masterbatch are mechanically mixed evenly, when the masterbatch is sent to the hopper through the lower suction, due to the electrostatic action, the masterbatch is separated from the masterbatch, and it is easy to adsorb on the hopper wall, which will inevitably cause the change of the amount of masterbatch in the injection cycle, resulting in color difference.

This situation can be solved by the method of manual stirring after the raw materials are sucked into the hopper. For the production of colored products by adding toner, the most effective way is not to use a suction machine, but to use a hot air dryer, and use artificial feeding to prevent the color difference caused by the separation of toner and masterbatch.

4. Reduce the influence of barrel temperature on color difference

In production, it is often encountered that the temperature of the barrel changes drastically due to the damage and failure of a heating ring or the uncontrolled long-term burning of the heating control part, resulting in color difference. The color difference caused by this kind of reason is easy to judge, and the color difference caused by the damage and failure of the heating ring will be accompanied by uneven plasticization, and the uncontrolled long-term burning of the heating control part is often accompanied by gas spots, serious discoloration and even coking of the product. Therefore, it is necessary to check the heating part frequently in production, and replace and repair it in time when the heating part is damaged or out of control, so as to reduce the probability of such color difference.

5. Reduce the impact of injection molding process adjustment

When the injection molding process parameters need to be adjusted due to non-color difference, the injection temperature, back pressure, injection cycle and masterbatch amount should not be changed as much as possible, and the impact of the change of process parameters on the color should be observed at the same time.

As much as possible, avoid the use of injection molding processes that cause strong shear effects, such as high injection speed and high back pressure, to prevent color difference caused by local overheating or thermal decomposition. Strictly control the temperature of each heating section of the barrel, especially the nozzle and the heating part immediately adjacent to the nozzle.

6. Master the influence of barrel temperature and masterbatch on product color change

Before making color difference adjustment, it is also necessary to know the trend of product color change with temperature and masterbatch. With the change of the temperature or quantity of masterbatch of different color masterbatches, the color change law of the product is different. The law of change can be determined through the color testing process.

Unless the color variation of this masterbatch is known, it is not possible to adjust the color difference very quickly, especially when the color is produced with a new masterbatch.