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How to control the color difference of injection products?
Browse: Release date:2018-05-23
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 with the raw material mixture, injection molding process, injection molding machine, mold, 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 six 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 organize 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 masterbatch and masterbatch as much as possible. For the masterbatch, we must conduct sampling test before the mass production, which is 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, color masterbatch, for poor thermal stability, we recommend manufacturers to exchange.
 
    3. Eliminate the influence of uneven mixing of masterbatch and masterbatch
 
    The poor mixing of plastic masterbatch with the masterbatch will also make the product color changeable. 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 result in a change in the masterbatch volume 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 inaccurate blanking, and even cause the feeder to stop rotating. 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, thereby generating a color difference. The color difference caused by this kind of reason is very easy to judge, generally the heating coil damages and fails to produce the color difference, at the same time, it will be accompanied by the phenomenon of uneven plasticization, and the uncontrolled long-time burning of the heating control part is often accompanied by the product air spot, serious discoloration or even coking phenomenon. Therefore, the heating part must be inspected frequently during production, and it is found that when the heating part is damaged or out of control, it is replaced and repaired in time to reduce the occurrence of such chromatic aberration.
 
    5. Reduce the impact of injection molding process adjustments
 
    Non-chromatism reasons need to adjust the injection molding process parameters, as far as possible not to change the injection temperature, back pressure, injection cycle and the amount of masterbatch to add, but also need to observe the impact of changes in process parameters on the color, such as color differences should be promptly adjusted. 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. Strictly control the temperature of each heating section of the barrel, especially the nozzle and the heating part close to the nozzle.