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 color difference of the components. There are many factors that affect the color difference, involving raw materials, resin, masterbatch, masterbatch and raw materials, injection molding, injection molding machines, molds, etc., because of the extensive coverage, color control technology is also recognized in injection molding is one of the more difficult to grasp technology. In the actual production process, we generally control the color difference from the following five aspects.
1. Eliminate the influence of injection molding machine and mold factors
To select an injection molding machine with an injection capacity of the main product, if the injection molding machine has problems such as material dead angle, it is best to replace the equipment. For the mold casting system, exhaust groove, etc. caused by color, can be solved by the corresponding part of the mold maintenance model. Must first solve the injection molding machine and mold problems can be organized production, in order to reduce the complexity of the problem.
2. Eliminate the influence of raw materials, resin and masterbatch
Controlling raw materials is the key to completely solving the color difference. Therefore, especially in the production of light-colored products, the thermal stability of the raw material resins must not be neglected to have a significant effect on the color fluctuation of the products. Since most injection molding manufacturers do not produce plastic masterbatches or masterbatches themselves, the focus of attention can be on production management and raw material inspection. That is to strengthen the inspection of raw materials into storage.
The same product in the production uses the same manufacturer, the same brand of masterbatch, and masterbatch production as much as possible; for masterbatch, we must conduct sampling test before mass production, not only the same as the previous proofreading, but also in this comparison, if the color The difference is not big, can be considered as qualified, as the color masterbatch has a slight color difference, the masterbatch can be re-mixed before use to reduce the masterbatch itself caused by uneven color mixing. At the same time, we also need to focus on testing the thermal stability of raw materials, resin and masterbatch. We recommend manufacturers to replace them for poor thermal stability.
3. Eliminate the influence of uneven mixing of masterbatch and masterbatch
The mixing of plastic master batches with color masters will also make the color of the product unpredictable. After the masterbatch and masterbatch machine are evenly mixed, when the material is fed into the hopper, the masterbatch is separated from the masterbatch due to the electrostatic effect and is easily adsorbed on the hopper wall. This will inevitably cause changes in the amount of masterbatch during the injection molding cycle. Chromatic aberration.
This situation can be solved by adopting a method of manually stirring the material into the hopper. Nowadays, many companies use feeders to add masterbatch, which saves a lot of manpower and provides great help for color difference control. However, many companies use them improperly, and the results are often unsatisfactory.
How much the feeder is added to the masterbatch at a fixed speed depends on the plasticizing time, and the plasticizing time itself is fluctuating, and sometimes the fluctuation is even large. Therefore, to ensure a constant feeding amount, the feeding time of the feeder needs to be fixed. , And the set time is less than the minimum plasticizing time. When using the feeder, it should be noted that due to the small outlet of the feeder, after a period of time, the raw material particles accumulated in the screw of the feeder may cause the inaccuracy of the material, and even cause the feeder to stop. Need to be cleaned regularly.
4. Reduce the influence of cylinder temperature on color difference
In production, it often happens that a certain heating coil is damaged or the heating control part is out of control and long burning causes the temperature of the barrel to change drastically, resulting in color aberration. The color difference caused by this kind of reason is very easy to determine. In general, the heating coil is damaged and the color difference is produced. At the same time, the plasticization and inhomogeneous phenomenon is accompanied. The uncontrolled burning of the heating control part is often accompanied by the product's air spot, serious discoloration, and even coking. Therefore, the heating part should be inspected frequently during production, and if the heating part is found damaged or out of control, it should be replaced and repaired in time to reduce the occurrence of such chromatic aberration.
5. Reduce the impact of injection molding process adjustments
When the non-chromatism reasons need to adjust the injection molding process parameters, do not change the injection temperature, back pressure, injection cycle and the amount of masterbatch 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. As far as possible, avoid the use of high injection speed, high back pressure and other injection molding processes that cause strong shear, to prevent the color difference caused by local overheating or thermal decomposition and other factors. The temperature of each heating section of the barrel is strictly controlled, particularly the nozzle and the heated portion of the nozzle.
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