The Problem of Color Change and Dark Streaks on Injection Molded TPR/TPE Products 
Injection molded TPR/TPE products often exhibit color change or dark streaks on their surfaces due to overheating degradation or other causes. Here are some solutions to this problem:

  1. Poor thermal stability of materials
    * Solution: Choose materials with good thermal stability or add heat stabilizers to them.
  2. Presence of recycled materials in the raw material
    * Solution: Stop using recycled materials.
  3. Inconsistent R-value between the nozzle and die opening, causing accumulated material to enter the mold cavity with each injection
    * Solution: Ensure the R-value of the nozzle matches that of the die opening.
  4. Uneven plasticization of materials, causing unmelted particles to form within the product and create dark streaks.
    * Solution: Increase the backpressure to ensure even plasticization.
  5. Foreign objects in the raw material, such as dust from the mold, rusting of the hopper heater or flaking off of electroplating layers in the barrel or nozzle, or residual resin left over from previous uses in the barrel or nozzle
    * Solution: Clean the barrel, nozzle, or hopper.
  6. Defects in the barrel or screw (such as damage or nicks) that cause material to remain in the barrel for too long, leading to decomposition.
    * Solution: Repair or replace the defective parts.
  7. Poor exhaust of air in the mold, resulting in compressed air inside the mold during filling, increased temperature, scorching of the material, and burn marks along the weld lines.
    * Solutions: A. Add an additional exhaust groove or increase the size of the existing exhaust groove in the final filling area. B. Reduce clamping force. C. Redetermine the location of the gate.
  8. High melt temperature or excessively long molding cycle, causing overheating and degradation of the plastic.
    * Solutions: A. Lower the mold temperature. B. Shorten the molding cycle.

  9. Injection speed is too fast or injection pressure is too high, increasing frictional heat and causing degradation of the plastic.
    * Solutions: A. Decrease the last-stage injection speed. B. Decrease the injection pressure. C. Enlarge the size of the gate.