Color difference is a common defect in injection molding. There are many factors affecting color difference, including raw material resin, masterbatch, mixing of masterbatch with raw material, injection molding process, injection molding machine, etc. In the actual production process, we generally control color difference from the following five aspects.
- Eliminate the influence of injection molding machine and mold factors
Choose an injection molding machine with the same capacity as the main injection molding product. If the injection molding machine has problems such as material dead angles, it is best to replace the equipment. For color difference caused by mold pouring system, exhaust groove, etc., it can be solved by repairing the corresponding part of the mold. The problems of injection molding machine and mold must be solved first before production can be organized to reduce the complexity of the problem.
- Eliminate the influence of raw resin and masterbatch
Controlling raw materials is the key to completely solve the color difference. Therefore, especially when producing light-colored products, the obvious influence of different thermal stability of raw resin on the color fluctuation of products cannot be ignored. Given that most injection molding manufacturers do not produce plastic masterbatch or masterbatch themselves, the focus can be placed on production management and raw material inspection. injection molding
That is, strengthen the inspection of raw materials entering the warehouse; in production, the same product should be produced by the same manufacturer, the same brand of masterbatch and masterbatch as much as possible; for masterbatch, we should conduct random color inspections before mass production, both with the last proofreading 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 same batch of masterbatch, the masterbatch can be remixed and used to reduce the color difference caused by uneven mixing of the masterbatch itself. At the same time, we also need to focus on the thermal stability of raw resin and masterbatch. For those with poor thermal stability, we recommend that manufacturers replace them.
- Reduce the influence of barrel temperature on color difference
During production, it is often encountered that the barrel temperature changes drastically due to the failure of a heating coil or the uncontrolled long burning of the heating control part, resulting in color difference. The color difference caused by this kind of reason is easy to determine. Generally, the color difference caused by the failure of the heating coil is accompanied by uneven plasticization, and the uncontrolled long burning of the heating control part is often accompanied by product gas spots, severe discoloration and even coking. Therefore, the heating part needs to be checked frequently during production, and it should be replaced and repaired in time when the heating part is damaged or out of control to reduce the probability of such color difference.
- Reduce the influence of injection molding process adjustment
When the injection molding process parameters need to be adjusted for non-color difference reasons, the injection molding temperature, back pressure, injection molding cycle and the amount of masterbatch added should not be changed as much as possible. At the same time, the influence of the change of process parameters on the color should be observed. If color difference is found, it should be adjusted in time. Avoid using injection molding processes that cause strong shearing effects such as high injection speed and high back pressure as much as possible to prevent color difference 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.
- Understand the influence of barrel temperature and masterbatch quantity on product color change
Before adjusting the color difference, you must also know the trend of product color change with temperature and masterbatch quantity. Different masterbatch will have different color change rules with the change of production temperature or masterbatch quantity. The color change rule can be determined through the color test process. Unless the color change rule of this masterbatch color is known, it is impossible to adjust the color difference quickly.
