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How to eliminate the color difference of masterbatch in injection molding production

by:Vowin Rapid Prototyping     2023-02-06
Color difference is a common defect in masterbatch injection molding. It is not uncommon for injection molding machines to be scrapped in batches due to color differences in matching parts. There are many factors affecting color difference, involving raw material resin, color masterbatch, mixing of color masterbatch and raw materials, injection molding process, injection molding machine, mold, etc. Because of the wide range of involvement, color difference control technology is also recognized as one of the most difficult technologies in injection molding. In the actual production process, we generally control the 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 the same capacity as the main injection molding product. If the injection molding machine has problems such as material dead ends, it is best to replace the equipment. For the color difference caused by the mold gating system, exhaust groove, etc., it can be solved by repairing the corresponding part of the mold. The problem of injection molding machine and mold must be solved first before the production can be organized to reduce the complexity of the problem.

2. Eliminate the influence of raw material resin and color masterbatch

Controlling raw materials is the key to completely solving chromatic aberration. Therefore, especially when producing light-colored products, the obvious influence of different thermal stability of raw material resins on product color fluctuations cannot be ignored. Since most injection molding manufacturers do not produce plastic masterbatches or color masterbatches, they can focus on production management and raw material inspection. That is to strengthen the inspection of raw materials entering the warehouse; the same product should be produced by the same manufacturer, the same grade of masterbatch and color masterbatch as much as possible in production; In this comparison, if the color difference is not large, it can be considered qualified, just like a batch of color masterbatch with slight color difference, the color masterbatch can be re-mixed 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 raw resins and color masterbatches. For those with poor thermal stability, we recommend manufacturers to replace them.

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

Poor mixing of plastic masterbatch and color masterbatch will also cause the color of the product to change. After the masterbatch and color masterbatch are mechanically mixed, when the material is fed into the hopper through the bottom suction, the color masterbatch is separated from the masterbatch due to static electricity, and it is easy to be adsorbed on the wall of the hopper. This will inevitably cause changes in the amount of color masterbatch during the injection molding cycle, resulting in chromatic aberration. This situation can be solved by manually stirring the raw materials after they are sucked into the hopper. Nowadays, many companies use feeders to add color masterbatches, which saves a lot of manpower and provides great help for color difference control, but many companies often fail to satisfy the results due to improper use. The amount of color masterbatch added to the feeder at a fixed speed depends on the plasticizing time, and the plasticizing time itself fluctuates, sometimes even relatively large, so to ensure a constant feeding amount, the feeding time of the feeder needs to be fixed , and the setting time is less than the minimum plasticizing time. Pay attention when using the feeder, because the outlet of the feeder is small, after a period of use, it may cause inaccurate feeding due to the raw material powder accumulated in the screw of the feeder, and even cause the feeder to stop, so Need to be cleaned regularly.

4. Reduce the influence of barrel temperature on color difference

In production, it is often encountered that the temperature of the barrel changes sharply due to the failure of a certain heating ring or the out-of-control long-term burning of the heating control part, resulting in color difference. The color difference caused by such reasons is easy to judge. Generally, 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, severe discoloration and even coking of the product. Therefore, it is necessary to check the heating part frequently during 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.

5. Reduce the impact of injection molding process adjustments

When the injection molding process parameters need to be adjusted due to non-color difference, try not to change the injection molding temperature, back pressure, injection molding cycle and color masterbatch addition amount. At the same time, it is necessary to observe the influence of the change of process parameters on the color. If the color difference is found, it should be adjusted in time. Hongrun Pigment: 3132 Big Red Powder, Fast Red BBN, Fast Red BBC, Golden Red C, Fast Red 2BP, Lithor Magenta 4BP, Lithor Red BK, Permanent Red F3RK, Permanent Red F5RK, Pigment Red 122, Pigment Red 254, Organic Medium Yellow, Organic Lemon Yellow, Fast Yellow G, Permanent Yellow 2G, Permanent Yellow HR, Pigment Yellow 81, Pigment Yellow 110, Pigment Yellow 139, Pigment Yellow 151, Pigment Yellow 180, Permanent Orange G, Pigment Orange 34, Pigment Orange 36, Pigment Orange 64, Phthalocyanine Blue BGS, Phthalocyanine Green G, Pigment Violet 19, Permanent Violet RL and other organic pigments. Try to avoid the use of high injection speed, high back pressure and other injection molding processes that cause strong shearing effects, so as 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 close to the nozzle.

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

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