Pay attention to these 5 points—plastic coloring and pelletizing production can reduce waste by 50%.

Release time:

2023-02-24

One common issue that tends to arise during plastic pelletizing is color variation

One common issue that tends to arise during plastic pelletizing is color variation, even when production is carried out according to the original formulation. Many people find this puzzling: the same formulation has always been acceptable in the past, yet suddenly, upon starting up this time, it fails to meet specifications—sometimes with a significant difference. Or else, during the production process, the machine may start drifting off course, inevitably leading to downtime for troubleshooting, formula adjustments, and then restarting the machine. If you’re unlucky, you could easily spend an entire night—or even several days—just dealing with this problem, ending up with nothing to show for your efforts.

So, today I’d like to share with you several reasons why color differences can occur during the granulation process. If there are any errors, please feel free to point them out.

It’s a real-life experience the author has had: color masterbatches were directly used for pelletizing without being thoroughly tested for color matching. At the time, in order to reduce environmental pollution and shorten machine-cleaning times, the company decided to replace color powders with color masterbatches for nylon modification and pelletizing. The high-concentration color masterbatches that were substituted had been tested by the R&D department overseas, and the test results were deemed satisfactory. Consequently, during production, the formulation was initially based on the original color-powder proportions, with the ratios adjusted according to the color-powder content of the masterbatch. However, the outcome was disastrous—after dozens of start-up and shutdown tests, several tons of substandard products were produced, still significantly different from the standard samples. In the end, the company had no choice but to abandon the project. (Many people might ask: Why didn’t they just stop and conduct testing and adjustment on the pilot line? The author doesn’t wish to disclose too much about the specific reasons, but the incident did happen.) Therefore, when replacing color powders with high-concentration color masterbatches for pelletizing, if you’re not 100% confident, it’s strongly recommended that you first carry out thorough testing on the pilot line. Only after passing the pilot-line tests should you proceed to full-scale production on the main production line. Sometimes, even if a masterbatch passes the pilot-line tests, it may still fail on the production line, requiring further adjustments. Thus, careful color testing is a highly effective method for reducing production costs and minimizing waste.

There is a problem with the compatibility between color masterbatches and resins, which arises from improper selection of the carrier material in the color masterbatch or from manufacturers arbitrarily changing the resin grade. Different grades of resin may vary in density and melt flow index, leading to differences in resin performance and varying degrees of compatibility with the color masterbatch, thus causing color changes. Generally speaking, as long as the differences in density and melt flow index are not significant, the resulting color variations will also be relatively minor. The color can be adjusted by fine-tuning the dosage of the color masterbatch.

During use, inaccurate measurements are common—especially among small and medium-sized enterprises, where there’s a widespread practice of arbitrarily adjusting the amounts of color masterbatches and pigments. In the weighing process, proportions, weights, and product types are often confused, leading to discrepancies between the color of the produced masterbatch and the standard specifications. These are all relatively simple errors that can be easily overcome with careful attention. The higher the precision, the better the accuracy will certainly be, which, to some extent, can also help reduce the production of substandard products.

The heat resistance of color pigments can be compromised if the machine temperature is inappropriate—especially if it’s too high—or if the color masterbatch stays in the machine for an excessively long time, causing the pigment to burn and resulting in color variations. In general, inorganic pigments have relatively good heat resistance and can usually meet the requirements of plastic processing, whereas organic pigments tend to have poorer heat resistance. Typically, the higher the temperature, the shorter the duration of heat resistance. Therefore, when the machine temperature is too high and the color masterbatch or color pigment remains in the machine for an extended period, the pigment can get burned, leading to color differences.

The impact of the production process

1. In the drying stage, raw materials such as ABS, PA, and PC must be dried to remove moisture before color matching. However, excessively long drying times or excessively high drying temperatures can cause the base color of the raw materials to turn yellow or discolor, leading to color variations.

2. During the mixing process, if the mixing tank is not thoroughly cleaned, it may contain residues of other colors, leading to color variations. Insufficient mixing time can also result in color variations due to the inclusion of other colors. Additionally, insufficient mixing time or using an excessive amount of material can cause uneven mixing, thereby producing color differences.

3. Feeding Stage: When switching materials for production, be sure to thoroughly clean the料筒 and dry it completely before resuming production.

Pay attention to these 5 points—plastic coloring and pelletizing production can reduce waste by 50%.

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