Solution to Color Aberration in Injection Molding Plastic Products

There are many kinds of injection molding plastic products with wide application, but color aberration is a common defect in injection molding.

 

There are many factors affecting color aberration, including raw material resin, color masterbatch (or color pigment), mixing of color masterbatch with raw material, additive, injection molding process, injection molding machine, mould, etc. Because of its wide range, color aberration control has become one of the most difficult techniques in injection molding.

 

In the actual production process, the color aberration is generally controlled from the following six aspects.

 

1. Eliminate the influence of injection molding machine and mould

Select the injection molding machine equivalent to the injection molding product capacity. If the injection molding machine has problems such as material dead angle, it is best to replace the equipment.

If it is caused by mold gating system, exhaust groove, etc., it can be solved by the maintenance of the corresponding parts of the die.

The problem of injection molding machine and mould must be solved before production so as to reduce the complexity of the problem.

 

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

Control of raw materials is the key to thoroughly solve the color aberration. Therefore, the influence of the different thermal stability of raw materials on the color fluctuation should not be ignored, especially in the production of light colored products.

Since most injection manufacturers do not produce plastic masterbatch or color masterbatch, attention can be focused on production management and raw material inspection. That is, to strengthen the inspection of raw materials into storage; the same product is produced by the same manufacturer and the same grade masterbatch as far as possible.

For the color masterbatch, the color should be checked and tested before production. If the color is not different, it can be considered qualified.

If there is a slight color difference, the color masterbatch can be remixed and then used to reduce the color difference caused by uneven mixing of the color masterbatch.

At the same time, we also need to check the thermal stability of raw resin and color masterbatch.

 

3. Eliminating the effects of uneven mixing

Bad mixing of plastic resin with color masterbatch will also cause color aberration of products.

When the plastic resin and the color masterbatch are mixed evenly and fed into the hopper through the lower suction material, due to electrostatic action, the color masterbatch is separated from the resin and is easily adsorbed on the hopper wall, which will inevitably result in the quantity change of the color masterbatch in the injection molding cycle and thus cause color aberration.

This situation can be solved by manual stirring after the raw material is inhaled into the hopper.

The most effective way to produce colored products by adding pigment is to use hot air dryer and manual feeding to prevent color aberration caused by separation of pigment powder and masterbatch.

 

4. Reduce the influence of barrel temperature

In production, it is often encountered that the temperature of the cylinder changes dramatically due to the damage of a heating ring or the long burning of a part of heating control out of control, resulting in chromatic aberration.

It is easy to judge the color aberration caused by this kind of reason. The color aberration will be accompanied by uneven plasticization when the damage and failure of the heating ring, while the long burning out of control of the heating control part is often accompanied by the product gas spot, serious discoloration and even coking phenomenon.

Therefore, it is necessary to check the heating part frequently. Replace or repair im time once the heating part is damaged or out of control, so as to reduce the chance of such color aberration.

 

5. Reduce the influence of injection process adjustment

When adjusting the process parameters of injection molding, the injection temperature, back pressure, injection period and color masterbatch amount should not be changed as much as possible. At the same time, we also need to observe its influence on color, adjust in time if color aberration is found.

Avoid the injection molding process with high injection speed and high back pressure, and prevent color aberration caused by part overheating or thermal decomposition. Strictly control the temperature of each heating section of the cylinder, especially the nozzle and the heating part adjacent to the nozzle.

 

6. Control the influence of temperature and color master quantity

Before adjusting color aberration, we must know the trend of product color changing with temperature and color master quantity.

With the change of production temperature or color masterbatch quantity, the color variation law of different color masterbatch is different. The law can be determined by the process of color test.

It is not possible to adjust the color aberration quickly, especially when using new color masterbatch, unless the variation law of the color masterbatch is known.

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