Color difference is a common defect in injection molding, and it is not uncommon to see batch scrapping of injection molding machine due to color difference of matching parts. There are many factors affecting color difference, including raw material resin, color masterbatch, mixing of color masterbatch and raw material, injection molding process, injection molding machine, mold, etc. Because of the wide range of factors involved, color difference control technology is also one of the more difficult technologies to master in injection molding. 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 the injection molding machine with the same capacity as the main product, if the injection molding machine has problems such as material dead corner, it is better to replace the equipment. For the mold pouring system, exhaust slot, etc. causing color difference, can be solved by the corresponding part of the mold maintenance mold. The injection molding machine and mold problems must be solved first before organizing production to cut the complexity of the problem.
2. Eliminate the influence of raw material resin and color masterbatch
Control of raw materials is the key to completely solve the color difference. Therefore, especially when producing light-colored products, we cannot ignore the obvious influence of different thermal stability of raw material resin on the color fluctuation of products. In view of the fact that most injection molding manufacturers do not produce plastic masterbatch or masterbatch themselves, so that the focus of attention can be placed on production management and raw material inspection. In other words, we should strengthen the inspection of raw materials in the warehouse; use the same manufacturer and the same brand of masterbatch and masterbatch in the production as far as possible; for the masterbatch, we should carry out sample color test before mass production, not only to check with the last time, but also to compare in this time, if the color difference is not big, it can be regarded as qualified, if there is a slight color difference with the same batch of masterbatch, the masterbatch can be re-mixed and used again to reduce the color difference caused by the uneven mixing of the masterbatch itself. The color difference caused by the uneven mixing of the masterbatch itself. At the same time, we also need to focus on testing the thermal stability of the raw material resin and masterbatch, and we suggest the manufacturer to replace those with poor thermal stability.
3. Eliminate the influence of uneven mixing of masterbatch and masterbatch
Bad mixing of plastic masterbatch and color masterbatch will also make the product color change. After mixing the masterbatch and masterbatch mechanically, when feeding into the hopper through the lower suction material, the masterbatch will be separated from the masterbatch due to the electrostatic effect and easily adsorbed on the hopper wall, which will inevitably cause the change of masterbatch amount in the injection cycle and thus produce color difference. This will inevitably cause the amount of masterbatch to change during the injection cycle, thus resulting in color difference. This situation can be solved by taking the raw material into the hopper and then mixing it manually. Nowadays, many companies use feeder to add color masterbatch, which saves a lot of manpower and provides great help for color difference control, but many companies often have unsatisfactory results due to improper use. The amount of masterbatch added to the feeder at a fixed speed depends on the plasticizing time, which itself fluctuates and sometimes even fluctuates greatly, so to ensure a constant amount of feeding, the feeding time of the feeder needs to be fixed and the set time is less than the minimum plasticizing time. In the use of feeder need to pay attention to, because the feeder outlet is small, after using a period of time, may be due to the feeder screw in the accumulation of raw material powder particles caused by inaccurate feeding, or even cause the feeder to stop, so you need to regularly clean up.
4. Reduce the impact of barrel temperature on the color difference
Production often encountered due to a heating ring damage failure or heating control parts out of control long burn caused by barrel temperature changes dramatically, resulting in color differences. This kind of reason produces the color difference is easy to determine, the general heating ring damage failure produces color difference at the same time will be accompanied by uneven plasticization phenomenon, and heating control part of the uncontrolled long burning often accompanied by product gas spot, serious discoloration and even coking phenomenon. Therefore, it is necessary to check the heating part frequently during production, and replace the heating part when it is found to be damaged or out of control, in order to reduce the chance of such color difference.
5. Reduce the impact of the adjustment of the injection molding process
When adjusting the injection process parameters for non-color difference reasons, do not change the injection temperature, back pressure, injection cycle and the amount of color masterbatch added as much as possible, and at the same time, observe the impact of the change of process parameters on the color, and adjust the color difference in time if found. As far as possible, avoid using high injection speed, high back pressure and other injection molding processes that cause strong shearing effect to prevent 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 section close to the nozzle.
6. Master the influence of barrel temperature and color masterbatch amount on the color change of the product
Before adjusting the color difference, we must also know the trend of product color change with temperature and masterbatch quantity. Different color masterbatch with the change of production temperature or the amount of masterbatch, its product color change pattern is different. The color change pattern can be determined through the color test process. Unless the color change law of this masterbatch is already known, it is impossible to adjust the color difference quickly, especially when using new color masterbatch production for color mixing.