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How To Control The Color Difference Of Injection Products?
Goodyear Mold Co.,Ltd | Updated: Dec 10, 2018

Chromatic aberration is a common defect in injection molding. It is not uncommon for the injection molding machine to be scrapped in batches due to the difference in color of the matching parts. There are many factors affecting chromatic aberration, involving raw material resin, color masterbatch (or toner), mixing of color masterbatch with raw materials, injection molding process, injection molding machine, mold, etc. Because of the wide range of exposure, color difference control technology is also recognized as difficult in injection molding. Master one of the techniques. 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


    To select an injection molding machine with the same capacity as the injection molding product, it is best to replace the equipment if there is a problem with the dead angle of the injection molding machine. For the mold casting system, the exhaust groove, etc., the color difference can be solved by the maintenance mold of the corresponding part of the mold. The injection molding machine and mold problems must be solved before the 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 chromatic aberrations. Therefore, especially in the production of light-colored articles, the significant influence of the difference in thermal stability of the raw material resin on the color fluctuation of the product 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 into the warehouse; the same product in production should be produced by the same manufacturer, the same brand masterbatch and color masterbatch;


    For color masterbatch, we must carry out sampling test color before mass production, both the same as the last proofreading, but also in this comparison, if the color difference is not big, can be considered qualified, as the batch color master has a slight color difference, can be The color masterbatch is remixed and then used to reduce the color difference caused by the uneven mixing of the color masterbatch itself. At the same time, we also need to focus on the thermal stability of the raw material resin and color masterbatch. For the poor thermal stability, we recommend that the manufacturer exchange.


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


    Poor mixing of the plastic masterbatch with the color masterbatch will also make the color of the product change. After the masterbatch and the color masterbatch are mechanically mixed, when the hopper is fed into the hopper through the lower suction, the color masterbatch is separated from the masterbatch due to the action of static electricity, and is easily adsorbed on the hopper wall, which is bound to cause a change in the amount of the masterbatch during the injection molding cycle, thereby generating Color difference.


    In this case, the raw material can be sucked into the hopper and then manually stirred. For the addition of toner to produce colored products, the most effective way is to not use the suction machine, but use a hot air dryer to manually prevent the color difference caused by the separation of the toner from the masterbatch.


    4. Reduce the influence of barrel temperature on chromatic aberration


    In production, it is often encountered that a certain heating coil is damaged or the heating control part is out of control, and the temperature of the barrel is drastically changed to cause chromatic aberration. The color difference caused by such reasons is easy to determine. Generally, the heating ring damages and the chromatic aberration is accompanied by uneven plasticization, and the heating control part is out of control and often burns with product spot, severe discoloration or even coking. Therefore, the heating part should be inspected frequently during production, and it is found that the heating part is damaged or out of control and replaced in time to reduce the occurrence of such chromatic aberration.


    5, reduce the impact of the injection molding process adjustment


    When the non-color difference reason needs to adjust the injection molding process parameters, the injection temperature, back pressure, injection cycle and color masterbatch addition amount should not be changed as much as possible. The adjustment also needs to observe the influence of the process parameter change on the color. If the color difference is found, it should be adjusted in time.


    Avoid using high injection speed, high back pressure and other injection molding processes that cause strong shearing to prevent chromatic aberration 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. Master the influence of barrel temperature and color masterbatch on product color change


    It is also necessary to know the trend of the color of the product as a function of temperature and color masterbatch before performing the color difference adjustment. Different color masterbatch varies with the temperature or color masterbatch of the product, and the color change law of the product is different. The color change process can be used to determine the law of change.


    Unless the color change of the color masterbatch is known, it is impossible to quickly adjust the color difference, especially when using the color tone produced by the new color masterbatch.