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  • How to control the color difference of injection molded products?

How to control the color difference of injection molded products?

The color difference is a common defect in injection molding, and it is not uncommon to see batch scrapping of injection molding machines due to the color difference of matching parts. Many factors are affecting the color difference, including the raw material resin. Color masterbatch (or color powder). The mixing of masterbatch and raw material. Injection molding process. Injection molding machine. Because of the wide range of factors involved, color difference control technology is also one of the more difficult technologies to master 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

To choose the injection molding machine with the same capacity as the injection product, if the injection molding machine has problems such as a material dead corner, it is better to replace the equipment. For mold pouring system. If the color difference is caused by the exhaust slot, etc., it can be solved by repairing the mold of the corresponding part. The problems of injection molding machines and mold must be solved first before organizing production to reduce the complexity of the problem.

2. Eliminate raw material resin. The influence of color masterbatch

Control of raw materials is the key to solving the color difference completely. Therefore, especially when producing light-colored products, we cannot ignore the obvious influence of different thermal stability of the raw material resin on the color fluctuation of the products.

Because most injection molding manufacturers do not produce plastic masterbatch or masterbatch themselves so that the focus of attention can be placed on production management and raw material inspection. That is, to strengthen the inspection of raw materials into the warehouse; production of the same product as far as possible using the same manufacturer. The same brand of masterbatch. Masterbatch production.

For color masterbatch, we need to carry out a sample color test before mass production, both with the last calibration and comparison in this time, if the color difference is not big, it can be considered qualified, such as the same batch of masterbatch has a slight color difference, the masterbatch can be mixed again and then used, to reduce the color difference caused by uneven mixing of the masterbatch itself. At the same time, we also need to focus on testing the raw material resin. If the heat stability of the masterbatch is not good, we suggest the manufacturer replace it.


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

Plastic masterbatch and color masterbatch are not well mixed will also make the product color change unpredictably. After mixing masterbatch and masterbatch mechanically, when feeding into the hopper through the lower section, the masterbatch will be separated from the masterbatch due to the electrostatic effect and easily adsorbed on the hopper wall, which will inevitably cause the change of masterbatch amount in the injection cycle and thus produce the color difference.

For this situation, we can adapt the method of manual stirring after the raw material is sucked into the hopper to solve the problem. For adding the color powder to produce colored products, there is the most effective way is not to use the suction machine, but the use of a hot air dryer, with a manual feeding method to prevent the color powder and masterbatch separation caused by color difference.

4. Reduce the influence of barrel temperature on color difference

In the production, we often encounter that the barrel temperature changes drastically due to a damaged heating ring or uncontrolled heating control part of the long burn, thus producing color difference. The color difference from these causes is easy to determine, generally, the damage to the heating ring failure to produce color difference will be accompanied by uneven plasticization phenomenon, while the heating control part of the uncontrolled long burn often accompanied by-product gas spots. Serious discoloration and even coking phenomenon. Therefore, it is necessary to check the heating part frequently during production and replace the heating part when it is damaged or out of control to reduce the chance of such color difference.

5. Reduce the impact of the adjustment of the injection molding process

When adjusting the parameters of the injection molding process for non-color difference reasons, do not change the injection temperature as much as possible. Backpressure. When adjusting the process parameters, do not change the injection temperature, back pressure, injection cycle, and color masterbatch addition as much as possible, and at the same time, observe the effect of the change of the process parameters on the color, and adjust the color difference in time.

As far as possible, avoid using high injection speed. Avoid using high injection speed, high backpressure, and other injection processes that cause the strong shearing effect 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 section close to the nozzle. 6.

6. master the barrel temperature. Effect of color masterbatch amount on product color change

Before adjusting the color difference, it is necessary to know the trend of product color change with temperature. The trend of color masterbatch volume change. Different color masterbatch with the change of production temperature or the amount of masterbatch, its product color change pattern is different. The color change pattern can be determined through the color test process.

Unless the color change law of this masterbatch is already known, it is impossible to adjust the color difference quickly, especially when using new color masterbatch production for color mixing.
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