1 Main factors affecting color difference
1.1 Effect of Raw Resin
For the raw material resin itself will affect the color, many people in the injection molding production may be surprised, but the fact does exist, especially when the resin itself has a certain base color. Different types of plastic or the same model but different production batches, the product can sometimes appear color.
1.2 Influence of Color Masterbatch
There is no doubt that color masterbatch is the most important factor influencing the color difference. The color quality of plastic products directly depends on the color of the masterbatch. The thermal stability, dispersion, and hiding power of color masterbatch are not only the indicators for checking the quality of masterbatch, but also have a direct relationship with the color difference. Masterbatch is mainly produced by mixing colorants, dispersants, and plastic raw materials. Among them, colorants have the greatest influence on color, and slight changes in the proportion of colorants will directly affect the color of products.
1.3 Effect of Compatibility of Color Masterbatch and Raw Material Thumb
Color masterbatch is inhomogenously mixed with the raw material resin, which will cause the different amount of masterbatch to be added during the injection molding cycle, resulting in a color difference. The compatibility between the raw material resin and the color masterbatch will affect the color of the product by affecting the uniformity of the dispersion of the colorant, and if the compatibility between the two is not good, the color difference will also be caused.
1.4 Impact of Injection Molding Process
Changing the injection temperature can directly affect the material temperature and cause the product color to change. The injection speed can affect the material temperature by changing the shear rate of the stream, especially when high-speed injection, sometimes the product will change color or even local coking yellow.
1.5 Impact of Injection Molding Machines and Dies
The nozzle size of the injection molding machine can affect the color of the product by affecting the shear rate of the material. The material dead angle of the injection molding machine not only affects the color of the product, but also causes phenomena such as air spot and coking. If the mold runners and gates are too small, harmful strong shearing action will occur to discolor the plastics and cause local color aberrations, especially for those plastics with extremely high heat sensitivity; if the gates are too wide, the turbulence effects Poor, the temperature rise is not high, it is possible to bring non-uniform ribbons to the mold cavity, and similarly produce color differences. When the mold is poorly vented, the plastic is adiabatically compressed, and is strongly reflected by oxygen under high temperature and high pressure, which also causes local discoloration.
1.6 Influence of inventory time and other factors
After plastic products are molded, the internal polymer materials are still undergoing complex physical and chemical reactions. Although the process is slow, it will inevitably change the color of the products.
There are many factors that affect the color difference, such as impurities in raw materials (moisture, chips, etc.), additives, etc. These are not the main factors, but they also need appropriate attention.
The
2 Chromatic aberration control
2.1 Elimination of Injection Molding Machine and Mold Factors
To select an injection molding machine with an injection molding capacity, 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 slots and other issues caused by color, can be repaired by the corresponding part of the mold to solve. Must first solve the injection molding machine and mold problems before they can organize production to reduce the complexity of the problem.
2.2 Eliminating the Effect of Raw Resin and Masterbatch
Controlling raw materials is the key to completely solving the problem of color aberration. The obvious influence of the thermal stability of the raw material resin on the color fluctuation of the product cannot be ignored, especially when light-colored products are produced. Since most injection molding manufacturers do not produce plastic masterbatch or masterbatch themselves, attention can be focused on production management and raw material inspection, that is, to strengthen the inspection of raw materials for storage; the same product in the production uses the same manufacturer and the same brand as much as possible. Masterbatch, color masterbatch production; for masterbatch, before the batch production to conduct sampling test, both from the previous comparison. Also in this comparison, if the color is not the same, can be considered qualified, if there is a slight color difference in the same batch of masterbatch, the masterbatch can be reused after mixing to reduce the color difference caused by the uneven mixing of the masterbatch itself. . Need to focus on testing the thermal stability of raw materials, resin, masterbatch, for poor thermal stability, it is recommended that manufacturers replace.
2.3 Elimination of 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. When the masterbatch and masterbatch machinery are uniformly mixed and then sent to the hopper through the lower suction material, due to the electrostatic effect, the masterbatch is separated from the masterbatch and is easily adsorbed on the hopper wall, which will inevitably cause change in the masterbatch volume in the injection molding cycle, thus resulting in Chromatic aberration. This situation can be solved by taking the method of sucking human hoppers and then manually stirring them. Nowadays, many companies use feeders to add masterbatch, which saves a lot of manpower and provides a great help to the color difference control. When using the feeder, it should be noted that due to the small outlet of the feeder, after a period of time, the feeding material may become inaccurate due to the accumulation of raw material particles in the screw, and even the feeder is stopped. Clean up.
2.4 Reducing the Effect of Cartridge Temperature on Chromatic Aberration
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.
2.5 Reducing the Impact of Injection Molding 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 color differences 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.
2.6 Master the influence of cylinder temperature and color masterbatch on product color change
Before the color difference adjustment, it is also necessary to know the trend of product color change with temperature and color masterbatch. Different color masters change with the change of production temperature or color masterbatch, the color change rule of their products is different. The color change process can be determined by the color test process. Unless one already knows the rule of color change of the masterbatch, it is impossible to quickly adjust the color difference, especially when new color masterbatch is used to produce the color palette.
The
3 color difference adjustment
Due to the elimination of raw materials, injection molding machines, molds and other factors before production, such as the color difference found in production, in most cases only need to determine whether the masterbatch is mixed with the raw material resin, or the injection temperature problem is the mixing problem to solve the mixing problem. The temperature problem can be adjusted by changing the temperature or back pressure. This is extremely easy to do when you know the trend of color change.