What is the reason for poor gloss (dark color) of injection molded products?

The causes of poor gloss (dark color) in injection molded parts involve multiple factors. The following is a detailed summary of these factors:

1. Mold Factors

Inadequate mold finish:

Defects such as scratches, corrosion, micropores, rust, or poorly polished mold cavities can lead to poor surface gloss in injection molded parts.

Solution: Improve mold finish, remove rust and dirt, polish the mold cavity, and ensure the proper functioning of the mold venting system.

Improper mold temperature:

If the mold temperature is too low, the melt will solidify immediately upon contact with the mold cavity, reducing the reproducibility of the mold cavity surface and resulting in poor gloss.

If the mold temperature is too high, the melt may flow excessively or burn, also affecting the product's gloss.

Solution: Properly control the mold temperature, adjusting it according to the material properties and product structure to ensure uniform cooling of the melt within the mold cavity.

Mold design issues:

Problems such as too small a draft angle, sudden changes in section thickness, excessively thick ribs, and excessive shear in the gating system can all affect the surface quality of the molded part and lead to poor gloss. Solution: Optimize mold design to ensure a reasonable draft angle, uniform cross-section thickness, and appropriate rib thickness. Adjust the gating system to reduce shear.
II. Molding Process Factors
Improper Injection Speed:
Injection speeds that are too fast or too slow will affect the melt filling and cooling properties, thereby affecting the product's gloss.
Solution: Adjust the injection speed appropriately based on the material properties and product structure to ensure that the melt evenly fills the mold cavity.
Insufficient Injection Pressure:
Injection pressure that is too low will result in insufficient melt filling, resulting in shrinkage marks and affecting the product's gloss.
Solution: Increase the injection pressure to ensure that the melt fully fills the mold cavity.
Insufficient Holding and Cooling Times:
Insufficient holding and cooling times will result in incomplete solidification of the melt within the mold cavity, affecting the product's gloss.
Solution: Extend the holding and cooling times to ensure that the melt fully solidifies and cools within the mold cavity.
Inappropriate Barrel and Melt Temperatures:
Excessively low barrel and melt temperatures will reduce the melt's fluidity and fusion properties, affecting the product's gloss. Excessively high barrel and melt temperatures can cause the melt to burn or degrade, also affecting the product's gloss.
Solution: Properly control barrel and melt temperatures to ensure stable melt flow and fusion properties during the injection molding process.
III. Raw Material Factors
Poor Raw Material Quality:
Raw materials containing impurities, moisture, or other volatiles can affect the melt's flow and fusion properties, resulting in poor product gloss.
Solution: Select high-quality raw materials and conduct rigorous inspection and processing to ensure they are free of impurities, moisture, and other volatiles.
Uneven Raw Material Particle Size:
Uneven raw material particle size can lead to uneven melt flow during the injection molding process, affecting product gloss.
Solution: Screen and remove raw materials with significantly different particle sizes to ensure uniform raw material particle size.
Excessive Use of Recycled Materials:
Excessive use of recycled materials can affect the uniform plasticization and flow of the melt, resulting in poor product gloss.
Solution: Appropriately reduce the amount of recycled materials used, or select high-quality recycled materials for blending. IV. Other Factors
Improper Operation:
Inadequate operator skills or improper operation, such as improper settings of parameters like injection speed, pressure, and temperature, can also lead to poor product gloss.
Solution: Strengthen operator skills training to ensure they are proficient in injection molding machine operation and adjustment techniques.
Equipment Failure:
Failure or severe wear of the injection molding machine, such as excessive wear of components like the screw and barrel, can also affect the plasticization and flow properties of the melt, resulting in poor product gloss.
Solution: Regularly maintain and service the injection molding machine, promptly replace severely worn components, and ensure the equipment is in good working condition.
In summary, the causes of poor gloss (dark color) in injection molded products involve multiple factors, including the mold, molding process, raw materials, and other factors. To reduce or avoid the occurrence of poor gloss, it is necessary to address these issues and implement appropriate optimization and improvement measures.