Uneven color is often resulted due to different phenomena with different causes. If the color near the feed inlet is uneven, it is generally caused by the uneven distribution of the colorant or the characteristics of the colorant that do not meet the application requirements of the custom plastic extrusion parts.
If the entire plastic part is discolored or uneven, it is often related to the plastic extrusion process conditions. When the temperature of the barrel is too high, the high-temperature melting will easily decompose in the barrel and cause the plastic part to change color. If the temperature at the nozzle is too high, the melt will coke and accumulate at the nozzle, which will also cause the uneven color on the surface of the plastic part.
In addition, many other factors can cause the surface color of the plastic part such as extremely high injection pressure, backpressure, screw speed; long time of injection and holding time or even dead corners in the barrel, too much lubricant
What is the solution to such problems?
In order to prevent the molten material from staying in the high-temperature barrel for too long to cause overheating and decomposition, the injection volume should not exceed two-thirds of the injection capacity of the injection molding machine.
When there is coked molten material accumulated in the barrel or nozzle, the barrel should be thoroughly cleaned, the nozzle should be removed and cleaned, and the nozzle tip should be checked for alignment with the sprue sleeve, and the nozzle temperature should be appropriately reduced.
For the adjustment of process parameters such as screw speed, back pressure, injection pressure, injection and pressure holding time, accurate adjustments can be made according to the actual situation and according to the principle of itemized adjustment.
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