How to control the color difference of injection molded products​

In the actual production process, we generally control color difference from the following six aspects.

1 Eliminate the influence of injection molding machine and mold factors

It is necessary to choose an injection molding machine with a capacity equivalent to that of the injection molded product. If the injection molding machine has problems such as material dead ends, it is best to replace the equipment. Color differences caused by the mold pouring system, exhaust grooves, etc. can be solved by repairing the corresponding parts of the mold. Problems with the injection molding machine and mold must be solved first before production can be organized to reduce the complexity of the problem.

2 Eliminate the influence of raw resin and color masterbatch

Controlling raw materials is the key to completely solving color differences. Therefore, especially when producing light-colored products, the obvious impact of different thermal stability of raw resins on the color fluctuation of the products cannot be ignored.

Since most injection molding manufacturers do not produce plastic masterbatch or color masterbatch themselves, the focus can be on production management and raw material inspection. That is to strengthen the inspection of raw materials entering the warehouse; in production, the same product should be produced from the same manufacturer, the same brand of masterbatch, and color masterbatch as much as possible; for color masterbatch, we must conduct random inspections and color tests before mass production, which must be verified with the last time and In this comparison, if the color difference is not big, it can be considered qualified. If there is a slight color difference in the batch of color masterbatch, the color masterbatch can be remixed before use to reduce the color difference caused by uneven mixing of the color masterbatch itself. At the same time, we also need to focus on testing the thermal stability of the raw resin and color masterbatch. For those with poor thermal stability, we recommend that the manufacturer replace them.

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

Poor mixing of plastic masterbatch with the same color will also cause the color of the product to change erratically. After the masterbatch and color masterbatch are mechanically mixed evenly, when they are sent into the hopper through the lower suction, the color masterbatch is separated from the masterbatch due to static electricity and is easily adsorbed on the hopper wall. This will inevitably cause a change in the amount of color masterbatch during the injection molding cycle, resulting in Color difference.

This situation can be solved by inhaling the raw materials into the hopper and then manually stirring them. For adding toner to produce colored products, the most effective way is not to use a suction machine, but to use a hot air dryer and use manual feeding to prevent color difference caused by separation of toner and masterbatch.

4 Reduce the impact of barrel temperature on color difference

In production, it is often encountered that a certain heating ring is damaged or fails, or the heating control part is out of control and burns for a long time, causing the temperature of the barrel to change drastically, resulting in color difference. The color difference caused by such reasons is easy to determine. Generally, the color difference caused by damage and failure of the heating ring will be accompanied by uneven plasticization. Uncontrolled and prolonged burning of the heating control part is often accompanied by gas spots, severe discoloration and even scorching of the product. Therefore, it is necessary to check the heating part frequently during production. If the heating part is found to be damaged or out of control, replace it and repair it in time to reduce the chance 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 reasons other than color difference, try not to change the injection temperature, back pressure, injection cycle and color masterbatch addition amount. At the same time, you need to observe the impact of changes in process parameters on the color. If color difference is found, make timely adjustments.

Try to avoid using injection molding processes that cause strong shear such as high injection speeds and high back pressures to prevent color differences caused by factors such as local overheating or thermal decomposition. Strictly control the temperature of each heating section of the barrel, especially the nozzle and the heating part close to the nozzle.

6. Understand the influence of barrel temperature and masterbatch amount on product color changes

Before adjusting the color difference, you must also know the trend of product color changes with temperature and masterbatch amount. Different masterbatch products will have different color changes as the production temperature or the amount of masterbatch changes. Its changing pattern can be determined through the color test process. Unless the color change pattern of this masterbatch is known, it is impossible to quickly adjust the color difference, especially when using new masterbatch production.