Color difference is a common defect in injection molding. It is not uncommon for the injection molding machine to be scrapped in batches due to the difference in color of the supporting parts. There are many factors affecting color difference, including the mixing of raw materials resin, chromophore(or chromophore), chromophore and raw materials, injection molding technology, injection molding machines, and molds. This is because of the extensive involvement. Therefore, color difference control technology is also recognized as one of the more difficult techniques in injection molding. In the actual production process, we generally control the color difference from the following six aspects.
1, eliminate the impact of injection molding machine and mold factors
To choose injection molding machine with the capacity of injection molding products, if there are problems such as the dead angle of the injection molding machine, it is best to replace the equipment. For mold pouring system, exhaust tank, etc., resulting in color difference, can be resolved through the corresponding parts of the mold maintenance die. The problem of injection molding machine and mould must be solved first before production can be organized to reduce the complexity of the problem.
2, eliminate the influence of raw materials resin, color mother
The control of raw materials is the key to the complete resolution of color difference. Therefore, especially when producing light-colored products, we can not ignore the obvious influence of different thermal stability of raw materials resin on the color fluctuation of the products.
Since most injection manufacturers do not produce plastic master or chromatin themselves, attention can be focused on production management and raw material testing. That is, strengthen the inspection of raw materials into storage; As far as possible, the same product is produced by the same manufacturer, the same brand base material, and the color mother.
With regard to chromatids, we must conduct a sampling test before mass production. We must not only check the color last time, but also compare it in this time. If the color is not different, we can consider it qualified, just as the batch of chromatids has a slight color difference. The chromatid can be remixed and then used to reduce the color difference caused by the mixing of the chromatid itself. At the same time, we also need to focus on the inspection of the thermal stability of the raw materials resin, chromatid, for the thermal stability is not good, we recommend that the manufacturers exchange.
3, eliminate the influence of color mother and parent mixture
The poor mixing of plastic master materials with the same color mother will also make the color of the product changeable. After mixing the mother material and the color mother machinery evenly, when the lower suction material is sent to the Hopper, the color mother is separated from the parent material due to electrostatic action and easily adsorbed on the material bucket wall. This will inevitably cause changes in the amount of color mother in the injection cycle. Color difference.
This situation can be solved by artificial stirring after the raw material is inhaled into the hopper. For the addition of toner to produce colored products, the most effective method is not to use a suction machine, but to use a hot air dryer to prevent the color difference caused by the separation of toner from the parent material.
4, reduce the influence of tube temperature on color difference
In production, it is often encountered that the temperature of the cartridge changes dramatically due to the failure of a heating ring or the uncontrolled heating control part, resulting in a color difference. The color difference caused by this type of reason is easily determined. The damage and failure of the general heating ring will be accompanied by the phenomenon of uneven plasticization, while the uncontrolled burning of the heating control part is often accompanied by product gas spots, serious discoloration, and even coking. phenomenon. Therefore, it is necessary to frequently check the heating part in production and find that the heating part is damaged or out of control to replace the maintenance in time to reduce the chance of such color difference.
5, reduce the impact of injection molding process adjustment
When the non-color difference needs to adjust the injection process parameters, do not change the injection temperature, back pressure, injection cycle, and the amount of color added. At the same time, it is also necessary to observe the effect of the change in the process parameters 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 strong shear 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 cartridge, especially the nozzle and the heating section close to the nozzle.
6, master the influence of tube temperature, color base quantity on product color change
It is also necessary to know the trend of the color of the product with temperature and color base before making color adjustment. With the change of the temperature or the amount of color matrix produced, the color variation of the product is different. It can be determined by the color test process.
Unless you already know the law of changes in this color, it is impossible to quickly adjust the color difference, especially when using the color palette produced by the new color mother.