How to control the color difference of injection blow moldin

Chromatic aberration is a common defect in injection molding. It is not uncommon for injection molding machines to be discarded in batches due to the difference in color of matching parts. There are many factors affecting color difference, including raw material resin, color masterbatch (or toner), mixing of color masterbatch and raw material, injection molding process, injection molding machine, mold, etc. Because of the wide range of involved areas, the color difference control technology is also used in injection blow molding It is considered one of the more difficult techniques to master.

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 an injection molding machine with a capacity equal to that of injection blow molding products, if the injection molding machine has problems such as dead corners of materials, it is best to replace the equipment. For the mold casting system, exhaust grooves, etc., which can cause color difference, it can be solved by the maintenance mold of the corresponding part of the mold. The problems of injection molding machines and molds 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

(1) Controlling raw materials is the key to thoroughly solving color differences. Therefore, especially in the production of light-colored products, the obvious influence of the thermal stability of the raw material resin on the color fluctuation of the product cannot be ignored.

(2) Given that most plastic injection manufacturers do not produce plastic master batches or color master batches in this way, attention can be focused on production management and raw material inspection. That is to strengthen the inspection of raw materials in the warehouse; in production, the same product should be produced with the same manufacturer, the same brand of masterbatch and masterbatch as much as possible;

(3) As for the color masterbatch, we need to carry out random color test before mass production, which must be proofread with the last time 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 slight color difference. The color masterbatch can be re-mixed 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 resin and color masterbatch. For those with poor thermal stability, we recommend manufacturers to replace them.

3. Eliminate the effect of uneven mixing of color masterbatch and masterbatch

(1) Poor mixing of plastic masterbatch with color masterbatch will also make the product color volatile. After the masterbatch and the masterbatch are mixed uniformly, when they are fed into the hopper through the lower suction, the masterbatch is separated from the masterbatch due to the electrostatic effect and easily adsorbed on the hopper wall. This will inevitably cause the change of the amount of the masterbatch during the injection cycle, which will cause Chromatic aberration.

(2) In this case, the raw materials can be sucked into the hopper and then manually stirred. For adding colored toner to produce colored products, the most effective method is not to use a suction machine, but to use a hot air dryer, using artificial feeding to prevent the color difference caused by the separation of toner from the masterbatch.

4.Reduce the influence of barrel temperature on color difference

In production, it is often encountered that the barrel temperature is greatly changed due to the failure of a certain heating coil or the heating control part is out of control and long-term burning, resulting in color difference. The color difference caused by this kind of reason is easy to judge. Generally, the color difference caused by the damage and failure of the heating coil will be accompanied by the uneven plasticization phenomenon, and the uncontrollable long-heating of the heating control part is often accompanied by product air spots, severe discoloration and even coking. Therefore, the heating part needs to be frequently checked during production, and the heating part should be replaced and repaired in time if it is found to be damaged or out of control, so as to reduce the possibility of such color differences.

5, reduce the impact of injection molding process adjustment

(1) When it is necessary to adjust the injection process parameters for non-color difference reasons, try not to change the injection temperature, back pressure, injection cycle, and color masterbatch amount. At the same time, adjust the process parameters to observe the effect of color changes. If color changes are found, adjust them in time .

(2) Try to avoid using high injection speed, high back pressure, and other injection molding processes that cause strong shear effects to prevent color differences 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

Before adjusting the color difference, you must also know the trend of product color changes with temperature and color masterbatch. With the change of production temperature or the amount of color masterbatch, the color change rules of products are different. It can be determined through the color test process.