Six Major Problems and Solutions in the Application of Color Masterbatches

1. Eliminating the Impact of Injection Molding Machines and Molds

   Select an injection molding machine with a capacity matching the primary injection-molded products. If the machine has issues such as material dead corners, it is advisable to replace the equipment. For color differences caused by the mold’s gating system, exhaust slots, etc., the problem can be resolved by repairing the corresponding mold components. It is essential to first address all issues related to the injection molding machine and mold before commencing production, so as to reduce the complexity of subsequent problems.

2. Eliminating the Impact of Raw Material Resins and Color Masterbatches

   Controlling raw materials is the key to thoroughly resolving color differences. Therefore, especially when producing light-colored products, the significant impact of varying thermal stability of raw material resins on product color fluctuations cannot be overlooked. Given that most injection molding manufacturers do not produce plastic masterbatches or color masterbatches themselves, the focus can be placed on production management and raw material inspection. Specifically, enhance the inspection of raw materials upon warehousing; for the same product during production, use masterbatches and color masterbatches from the same manufacturer and of the same grade as much as possible. For color masterbatches, conduct random sampling and color testing before mass production—comparing not only with the samples from the previous batch but also among the samples of the current batch. If the color difference is minimal, the batch can be deemed qualified. If there is a slight color difference within the same batch of color masterbatches, remix the color masterbatches before use to reduce color variations caused by uneven mixing of the masterbatches themselves. Meanwhile, it is also crucial to inspect the thermal stability of raw material resins and color masterbatches. For those with poor thermal stability, we recommend that the manufacturer replace them.

3. Eliminating the Impact of Uneven Mixing Between Color Masterbatches and Base Plastic

Poor mixing between base plastic and color masterbatches can also lead to inconsistent product color. After mechanically mixing the base plastic and color masterbatches thoroughly, when the mixture is fed into the hopper via vacuum suction, static electricity can cause the color masterbatches to separate from the base plastic and adhere easily to the hopper walls. This inevitably results in variations in the amount of color masterbatches during each injection cycle, thereby causing color differences. This issue can be resolved by manually stirring the raw materials again after they have been suctioned into the hopper. Currently, many companies use feeders to add color masterbatches, which saves a great deal of labor and provides significant assistance in color difference control. However, improper usage in many companies often leads to unsatisfactory results. At a fixed rotation speed, the amount of color masterbatch added by the feeder depends on the plasticizing time, which itself is subject to fluctuations—sometimes even substantial ones. Therefore, to ensure a constant feeding rate, the feeding time of the feeder must be fixed and set to be shorter than the minimum plasticizing time. When using a feeder, note that its small outlet may become clogged with raw material powder and pellets accumulated in the feeder screw over time, leading to inaccurate feeding or even feeder shutdown. Thus, regular cleaning is required.

4.Reducing the Impact of Barrel Temperature on Color Differences

  During production, color differences often occur due to drastic barrel temperature changes caused by damaged or malfunctioning heating bands, or uncontrolled continuous overheating of the temperature control system. Color differences stemming from such causes are easy to identify. Generally, a damaged or malfunctioning heating band will cause color differences accompanied by uneven plasticization. Meanwhile, uncontrolled continuous overheating of the temperature control system is often accompanied by product defects such as gas marks, severe discoloration, or even charring. Therefore, it is necessary to frequently inspect the heating components during production and promptly replace or repair any damaged or malfunctioning parts to minimize the occurrence of such color differences.

5.Reducing the Impact of Injection Molding Process Adjustments

  When adjusting injection molding process parameters for non-color-related reasons, avoid changing the injection temperature, back pressure, injection cycle, and color masterbatch dosage as much as possible. During the adjustment process, also observe the impact of parameter changes on product color and make timely adjustments if color differences are detected. Avoid using injection molding processes that induce strong shear forces, such as high injection speed and high back pressure, as far as possible to prevent color differences caused by local overheating or thermal decomposition. Strictly control the temperature of each heating zone of the barrel, particularly the nozzle and the heating section immediately adjacent to it.

6. Understanding the Impact of Barrel Temperature and Color Masterbatch Dosage on Product Color Changes

   Before adjusting for color differences, it is essential to understand how product color changes with variations in temperature and color masterbatch dosage. Different color masterbatches exhibit distinct color change patterns in response to temperature fluctuations or dosage adjustments during production. These patterns can be determined through color testing trials. Without prior knowledge of a color masterbatch’s color change characteristics, it is impossible to quickly correct color differences—especially when mixing colors with a new type of color masterbatch for the first time.