Color difference is a common defect in injection molding. Color difference requires the participation of many factors: raw materials, color resin, mixing of color masterbatch and raw materials, molding process, injection molding machine, etc. In the actual production process, we usually control the color difference from the following five aspects.
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 addition amount of Color Masterbatch shall not be changed as much as possible. At the same time, the influence of the change of process parameters on the color shall be observed. While observing and testing with the color difference instrument, if the color difference is found, it shall be adjusted in time. Avoid the use of injection molding process with strong shear effect caused by high injection speed and high back pressure as far as possible, and 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 close to the nozzle.

Professional spectrophotometer CS-420

Master the influence of barrel temperature and color masterbatch quantity on product color change
Before adjusting the color difference, we must also know the change trend of product color with temperature and color masterbatch. With the change of production temperature or the amount of Color Masterbatch, the change law of product color is different. The change law can be determined by the color difference tester. Unless we know the change law of the color of this color masterbatch, it is impossible to adjust the color difference quickly.
Barrel temperature to reduce the influence of color difference
In production, it is often encountered that the temperature of the barrel changes sharply 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 such reasons is easy to determine. Generally, the color difference caused by the damage and failure of the heating ring will be accompanied by uneven plasticization, while 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 it is found that the heating part is damaged or out of control, so as to reduce the probability of such color difference.

Eliminate factors affecting injection molding machines and molds
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 corner, it is best to replace the equipment. For the color difference caused by mold gating system and exhaust slot, it can be solved through the maintenance of corresponding molds. First, solve the problems of injection molding machine and mold before organizing production, so as to reduce the complexity of the problem.
Eliminate the influence of raw resin and Color Masterbatch
Controlling raw materials is the key to completely solve the color difference. Therefore, especially in the production of light color products, the obvious influence of different thermal stability of raw resin on the color fluctuation of products can not be ignored. Since most injection molding manufacturers do not produce plastic masterbatch or color masterbatch, we can focus on production management and raw material inspection. That is, strengthen the warehousing inspection of raw materials; In production, the same product shall be produced with masterbatch and color masterbatch of the same manufacturer and brand as far as possible; For the color masterbatch, we should use the color difference meter to conduct sampling inspection and color test before mass production, which should be compared with the last calibration and this time. If the color difference detected by the color difference meter is not large, it can be considered as qualified. As there is a slight color difference in the batch color masterbatch, the color masterbatch can be re mixed before use, so as to reduce the color difference caused by uneven mixing of the color masterbatch itself.