In some plastic injection molding products, there are many factors affecting color difference, including raw resin, masterbatch, mixing of masterbatch and raw material, injection molding process, injection molding machine, etc. Here in this article, we share some tips on controlling the color difference of injection molding products from below 6 aspects.
1. Machines and moulds
Choose the injection molding machine with the same capacity as the main product. If the injection molding machine has problems such as material terrible angle, it is better to replace the equipment. For the mold pouring system, exhaust slot and other causes of color difference, can be solved through the corresponding part of the mold maintenance mold. The problem of injection molding machine and mold must be solved before production can be organized to reduce the complexity of the problem.
2. Eliminate the influence of raw resin and color masterbatch
Control the raw materials is the key to solve color difference of plastic injection products. Therefore, especially in the production of light colored products, the obvious influence of the thermal stability of the raw resin on the color fluctuation of the products can not be ignored. In view of the fact that most injection molding 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 warehousing. In production, the same product should be produced by the same manufacturer, same brand masterbatch and color masterbatch. For the color masterbatch, we should carry out spot check and color test before mass production, which should be compared with the last proofreading and this time. If the color difference is not big, it can be considered as qualified. As if the batch masterbatch has slight color difference, the masterbatch can be re mixed before use, so as to reduce the color difference caused by uneven mixing of the masterbatch itself. At the same time, we also need to focus on the inspection of the thermal stability of raw resin and color masterbatch.
3. Eliminate the influence of uneven mixing of masterbatch and Masterbatch
Bad plastic masterbatch with color masterbatch mixing will also make the product color changeable. When the raw materials and masterbatch are mechanically mixed and fed into the hopper through the lower suction, due to the electrostatic effect, the raw material is separated from the masterbatch and easily adsorbed on the hopper wall, which is bound to cause the change of the masterbatch amount in the injection molding cycle, resulting in color difference.
This situation can be solved by manual mixing after the raw material is sucked into the hopper. For the production of colored products by adding toner, the most effective way is to use hot air dryer instead of suction machine to prevent color difference caused by separation of toner and masterbatch.
4. Reduce the influence of barrel temperature on color difference
In production, it is often encountered that the temperature of the barrel changes dramatically due to the damage of a heating ring or the heating control part is out of control for a long time, resulting in color difference. It is easy to judge the color difference caused by this kind of reasons. The color difference caused by the damage and failure of the heating ring will be accompanied by the uneven plasticization phenomenon, while the uncontrolled long-term burning of the heating control part is often accompanied by product gas spots, serious discoloration and even coking. Therefore, it is necessary to check the heating part frequently in production, and timely replace and repair the heating part if it is damaged or out of control, so as to reduce the probability of such color difference.
5. Reduce the impact when adjusting the injection molding process
When it is necessary to adjust the injection molding process parameters for non color difference reasons, the injection temperature, back pressure, injection cycle and the amount of Color Masterbatch should not be changed as much as possible. At the same time, the influence of process parameters on color should be observed. If 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 strong shear effect of injection molding process, to prevent local overheating or thermal decomposition and other factors caused by color difference. Strictly control the temperature of each heating section of the barrel.
6. Master the influence of barrel temperature and color masterbatch on product color change
Before adjusting the color difference, it is necessary to know the change trend of product color with temperature and color masterbatch. With the change of production temperature or color masterbatch quantity, the color change rule of different color masterbatch is different. The change law can be determined by the color test process. It is impossible to adjust the chromatic aberration quickly unless we have known the variation law of the color masterbatch.