How to control the color difference of plastic mold products?

2019-12-23

Chromatic aberration is a common defect in injection molding. It is not uncommon for injection molding machines to be rejected in batches due to the different colors of matching parts. There are many factors affecting color difference. It touches material resin, color masterbatch (or toner), color masterbatch homogeneous material, injection molding process, injection molding machine, mold, etc. Because of the wide range of involved areas, the color difference control technology is also considered difficult in injection molding Master one of the techniques. In the actual production process, we generally control the color difference of plastic molds from the following six aspects.

1. Eliminate the influence of injection molding machine and mold elements:

To choose an injection molding machine with a capacity equivalent to that of the injection molded product, if the injection molding machine has problems such as material dead ends, it is better to replace the equipment. About the mold casting system, exhaust grooves, etc., the formation of color differences, can be handled by the corresponding part of the mold maintenance mold. The problems of injection molding machines and molds must be dealt with first to be able to organize production to reduce the complexity of the problem.

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

(1) Controlling raw materials is the key to thoroughly handling color differences. Therefore, especially when producing light-colored products, the significant influence of the thermal stability of the material resin on the color fluctuation of the product cannot be ignored;

(2) Since most injection molding manufacturers do not produce plastic masterbatch or color masterbatch themselves, in this way, attention can be focused 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 from the same manufacturer, the same brand of masterbatch and color masterbatch when possible;

(3) Regarding the color masterbatch, we need to carry out spot color test before batch production, which must be calibrated with the previous one and compared with this time. If the color difference is not large, it can be considered as qualified, just as the batch color masterbatch has. The slight color difference can be used after mixing the color master from scratch to reduce the color difference caused by the uneven mixing of the color master. Together, we also need to check the thermal stability of the material resin and color masterbatch. Regarding the poor thermal stability, we recommend manufacturers to exchange them.

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

Poor mixing of plastic masterbatch with color masterbatch will also make the product color changeable. After the masterbatch and the masterbatch are mixed evenly, the masterbatch is separated from the masterbatch due to the electrostatic effect when it is fed into the hopper through the lower suction. Chromatic aberration.

This kind of situation can be taken after the material is sucked into the hopper and then manually mixed. Regarding the addition of toner to produce colored products, the effective method is not to use a suction machine, but to use a hot air dryer, and artificially add to prevent the color difference caused by the separation of the toner from the masterbatch.

4. Reduce the effect of barrel temperature on color difference:

In production, it is often encountered that the temperature of the barrel is drastically changed due to the failure of a heating coil or the heating control part is out of control. The color difference caused by this kind of cause is easy to determine. Generally, the color difference caused by the failure of the heating coil will be accompanied by uneven plasticization, and the uncontrolled heating of the heating control part is often accompanied by product air spots, severe discoloration and even coking. Therefore, it is necessary to constantly check the heating part during production, and timely replace and repair it when it is found that the heating part is damaged or out of control, so as to reduce the occurrence of such color differences.

5, reduce the impact of injection molding process adjustment:

When it is necessary to adjust the injection molding process parameters for non-color difference reasons, the injection temperature, back pressure, injection cycle, and color masterbatch participation amount should not be changed as much as possible. The adjustment should also observe the impact of process parameter changes on color and luster.

Try to prevent the use of high injection speed, high back pressure, and other injection molding processes that cause strong shear, to prevent color differences due to partial overheating or thermal differentiation. 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:

Before adjusting the color difference, you must also know the trend of product color changes with temperature and color masterbatch. Different color masterbatches vary with the temperature or amount of masterbatch produced, and the product color change rules are different. You can go through the color test process to determine the rules.

Unless you know the rules for changing this masterbatch color, it is not possible to adjust the color difference quickly, especially when using new color masterbatch.

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