How to Deal with Color Variation in Injection Molded Products

 

 

Color variation is a common defect in injection molding, severely impacting the product's appearance and potentially even causing losses. There are many factors contributing to color variation, including the choice of plastic raw materials, masterbatch mixing, injection molding process, mold design, and operator control. Therefore, color variation control is generally considered one of the most challenging techniques to master in injection molding. Huiwen Plastic Mold Manufacturer will now discuss how to deal with color variation in injection molded products.

 

1. Equipment

 

When selecting an injection molding machine, consider one with a capacity commensurate with the product being molded. If the machine has issues such as dead zones, the machine should be replaced. Color variation caused by issues such as the mold's gating system or venting slots can be addressed by repairing the corresponding mold sections. Resolving issues with the injection molding machine and mold before commencing production can reduce complexity.

 

2. Raw Material Masterbatch Selection

 

Controlling raw materials is key to addressing color variation. Therefore, especially when producing light-colored products, the significant impact of varying raw material resin thermal stability on product color fluctuations cannot be ignored.

 

Since most injection molding manufacturers don't manufacture plastic masterbatches or color masterbatches themselves, they can focus on production management and raw material inspection. This means strengthening incoming raw material inspections. During production, the same manufacturer and brand of masterbatch and color masterbatch should be used whenever possible.

 

For color masterbatches, we conduct spot checks and color tests before batch production, comparing them with the previous batch and the current batch. If the color difference is minimal, the batch is considered acceptable. If there is a slight color difference within the same batch, the masterbatch can be remixed and reused to minimize color variations caused by uneven mixing. We also need to verify the thermal stability of the raw resin and color masterbatch. If the thermal stability is poor, we recommend replacing the manufacturer.

 

3. Masterbatch Mixing Method

 

Poor mixing of plastic masterbatch and color masterbatch can also result in erratic product color. After the masterbatch and color masterbatch are mechanically mixed and fed into the hopper via suction, static electricity can separate the color masterbatch and cause it to adhere to the hopper walls. This can cause variations in the color masterbatch amount during the injection molding cycle, resulting in color variations.

 

This situation can be addressed by manually stirring the raw materials after they are drawn into the hopper. For the production of colored products with added color powder, a better approach is to avoid using a vacuum dryer and instead use a hot air dryer, manually adding the material to prevent color differences caused by separation of the color powder from the masterbatch.

 

4. Standardized Operations

 

To prevent errors caused by human error during the production process, key steps must be carefully controlled. New operators should not be allowed to operate the process, and experienced technicians should be consulted.

 

5. Understand the impact of barrel temperature and masterbatch quantity on product color changes.

 

Before adjusting color differences, it is important to understand how product color changes with temperature and masterbatch quantity. Different masterbatches exhibit different color variations with changes in production temperature or masterbatch quantity. This variation can be determined through color testing.

 

Unless the color variation patterns of the masterbatch are known, it will be difficult to quickly adjust color differences, especially when using a new masterbatch.

 

When adjusting injection molding process parameters for reasons other than color variation, minimize changes to the injection temperature, back pressure, injection cycle, and masterbatch dosage. While making adjustments, observe the impact of these process parameter changes on color. If color variation is detected, make adjustments promptly.

 

Avoid using injection molding processes that induce strong shear, such as high injection speeds and high back pressures, to prevent color variation caused by localized overheating or thermal decomposition. Strictly control the temperature of all heating sections of the barrel, especially the nozzle and the heating area immediately adjacent to the nozzle.