Solutions for Plastic Parts Color Unevenness

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The plastic parts color uneven is one of the injection molding defects. It is a critical aspect of manufacturing that significantly influences the overall quality of the final product. Consistent and even coloration not only enhances the aesthetic appeal of the product but also reflects precision and reliability in the manufacturing process. Any deviation from uniform color distribution can signal manufacturing defects, impacting not only the visual appeal but potentially the structural integrity of the plastic parts. In this blog, we will delve into the issue of plastic parts color unevenness, exploring its causes and practical solutions to maintain the highest standards of quality in injection molding processes.

What is Plastic Parts Color Unevenness?

Plastic parts color unevenness refers to the non-uniform distribution of color across the surface of molded plastic components. In an ideal manufacturing process, plastic parts should exhibit consistent and uniform coloration. However, unevenness can manifest as variations in hue, intensity, or shade, creating a visually inconsistent appearance.


This uneven color in plastic parts is a common defect in injection molding. Factors such as improper pigment dispersion, uneven cooling rates, or machine-related issues can lead to disparities in color across the molded parts. Plastic parts with color unevenness not only compromise the aesthetic appeal of the product but can also indicate potential flaws in the manufacturing process that may affect the overall quality and performance of the final product.


In the following sections, we will explore the specific causes of plastic parts’ color unevenness and practical solutions to address and prevent this issue in injection molding.

Causes of Plastic Parts Color Unevenness:

Inconsistent Pigment Dispersion:

Uneven distribution of color pigments within the plastic material can result from inadequate mixing during the preparation phase. This can lead to localized concentrations of pigments, causing color disparities in the final product.

Poor Colorant Diffusion:

The ability of colorants to evenly disperse throughout the plastic matrix is crucial. Issues with colorant diffusion can arise when the selected pigments or dyes do not integrate well with the base material, leading to uneven coloring.

Improper Molding Process Conditions:

Plastic parts color unevenness is also related to molding process conditions. If the barrel temperature is too high, the molten material in the barrel will easily overheat and decompose. That will make the plastic parts discolored. Excessive high screw speed, injection back pressure, and injection pressure will lead to the uneven color of plastic parts. Additionally, injection and holding time is too long, injection speed is too fast, poor plasticization, and too much lubricant will also lead to plastic parts color unevenness during injection molding.

Injection Mold Problems:

Issues with the injection mold, such as uneven venting, poor design, or surface imperfections, can affect the flow of plastic material during molding. This, in turn, may lead to variations in color across the molded parts.

Uneven Cooling:

Inadequate cooling rates can result in uneven coloration. Variations in cooling times for different sections of the mold can cause disparities in color intensity and appearance.

Injection Molding Machine-Related Problems:

Plastic parts color unevenness can arise from the injection molding machine. Such as excessive shot size, polluted barrel or nozzle, or nozzle tip not aligned with the sprue sleeve. Those factors all will cause plastic parts color unevenness.

Impurities in Raw Materials:

Contaminants or impurities in the raw materials, such as recycled plastics or additives, can introduce unexpected elements that affect color consistency. Quality control in material selection is crucial to prevent color unevenness.

How to Solve Plastic Parts Color Unevenness in Injection Molding?

Optimize Machine Settings:

Regularly optimize injection molding machine settings. This includes adjusting temperature profiles, injection speeds, and pressure conditions to ensure consistent and controlled processing of plastic materials.

Ensure Proper Colorant Diffusion

Choose high-quality colorants and pigments that diffuse uniformly within the plastic matrix. Thoroughly mix pigments during material preparation to prevent localized concentrations and achieve a homogeneous color distribution.

Maintain Equipment Regularly:

Conduct routine maintenance on injection molding equipment. Check and clean machine components, such as screws, barrels, and nozzles, to prevent issues that could disrupt the even flow of plastic material and compromise color uniformity.

Use High-Quality Raw Materials:

Source raw materials from reputable suppliers to minimize the risk of impurities or contaminants affecting color consistency. Opt for prime-grade resins and colorants to ensure a reliable and uniform base for the injection molding process.

Implement Effective Quality Control Measures:

Introduce robust quality control protocols throughout the manufacturing process. Regularly inspect and test raw materials, monitor colorant dispersion, and conduct in-process checks to identify and rectify potential issues before they impact the final product.

Address Injection Mold Problems:

Ensure that injection molds are designed and maintained to high standards. Address issues such as uneven venting, surface imperfections, or poor mold design promptly to prevent disruptions in the coloration process.

Control Cooling Rates:

Optimize cooling systems to achieve uniform cooling rates across the mold. This helps prevent variations in color intensity by ensuring consistent solidification of the plastic material throughout the molding process.


In the injection molding process, addressing the plastic parts color unevenness is important. Achieving uniform color distribution is not just about aesthetics, it is a testament to a precision-controlled manufacturing process. Analysis of the causes of injection molding defects, the manufacturer can not only rectify color unevenness but also improve the whole injection molding process and plastic parts quality. Cooperate with a reliable on-demand manufacturing company, they know the ways to avoid color unevenness and other plastic injection molding defects. If you would like to know more about the avoidance of defects or get a quote for your project, contact Zhongde now.

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