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How to Control the Chromatic Aberration of Injection Molded Products?
Ways to control the chromatic aberration
Chromatic aberration is a common defect in 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 chromatic aberration, including raw material resin, color masterbatch (or toner), mixing of color masterbatch and raw materials, injection molding process, injection molding machine, mold, etc.
Because of the wide range of involvement, chromatic aberration control technology is also recognized as one of the more 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 injection product. If the injection molding machine has problems like material dead ends, it is best to replace the equipment. The chromatic aberration caused by the mold pouring system, exhaust groove, etc. can be solved by repairing the corresponding part of the mold. We should solve the problems of injection molding machine and mold first. After that, organize the production 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 chromatic aberration. Therefore, especially when producing light-colored products, the obvious influence of the different thermal stability of the raw material resin on the color fluctuation of the product cannot be ignored.
Actually, most injection molding manufacturers do not produce plastic masterbatch or color masterbatch themselves. So, the attention can be placed on production management and raw material inspection. That is to strengthen the inspection of raw materials storage.
Let’s see how should we do to inspect the raw materials.
- Same masterbatch manufacturer and brand
In the production, use the same manufacturer and the same brand of masterbatch and color masterbatch to produce the same product.
- Conduct inspections before mass production
For the color masterbatch, we need to conduct random inspections before mass production. The color should not only be proofread last time, but also be compared in this time.If the color is not much different, it can be considered qualified. If there is a slight color difference in the same batch of masterbatch, we should remix the masterbatch before using it. So that it can reduce the color difference caused by uneven mixing of the masterbatch itself.
- Test the thermal stability
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 masterbatch
Poor mixing of plastic masterbatch and color masterbatch will also make the product color change impermanent. After the plastic masterbatch and the color masterbatch are mechanically mixed and 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 changes in the amount of color masterbatch in the injection cycle to change, resulting in chromatic aberration.
Solutions:
In this case, we can stir it manually, after the raw material sucking into the hopper. For the production of colored products, the most effective way is to use a hot air dryer instead of a suction machine. So that it can prevent the color difference caused by separation of the toner from the master batch.
4. Reduce the influence of barrel temperature on chromatic aberration
A certain heating ring is damaged or failed or the heating control part is out of control and burns. Then, it causes the temperature of the barrel to change drastically, resulting in chromatic aberration. Such a phenomenon are very common in the production.
How to judge the cause of chromatic aberration？
The chromatic aberration caused by this kind of reason is easy to judge. Generally, the chromatic aberration caused by the failure of the heating ring will be accompanied by uneven plasticization. While the out-of-control heating of the heating control part is often accompanied by product air spots, severe discoloration and even coking.
Solutions：
Therefore, it is necessary to check the heating part frequently during production. And replace and repair it in time when the heating part is found to be damaged or out of control, so as to reduce this kind of color difference.
5. Reduce the impact of injection molding process adjustment
When the injection molding process parameters need to be adjusted for non-chromatic aberration reasons, do not change the injection temperature, back pressure, injection cycle and the amount of masterbatch added as much as possible.
Besides, we need to observe the effect of process parameter changes on the color and luster.
If color aberration is found, it should be adjusted in time. Try to avoid the use of injection molding processes that cause strong shearing effects such as high injection speed and high back pressure. It is 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 amount on the color change of the product
Before adjusting the color difference, it is necessary to know the trend of product color changing with temperature and color masterbatch amount. Different color masterbatch changes with the production temperature or the amount of color masterbatch. The color change rule of the product is different. The color test process can be used to determine its changing law. Unless the color change law of this color masterbatch is known, it is impossible to adjust the color difference well soon, especially when using a new color masterbatch.
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