Today marks the last of our posts about common issues in your plastic production. This post belongs to a series aiming to describe the 20 most common issues you might encounter in your plastic production. If you want to start from the beginning, you can start here with our first post about short shot.
Color Streaks
What is color streaks？
The surface of the plastic part or the part where the flow direction changes will produce a local color deviation phenomenon, called color streaks (pictured below) :
There are many reasons for color streaks including uneven color powder diffusion during the injection molding process, incomplete cleaning of the feed barrel, mixture with other colors in the raw materials, the unstable proportion of recycling, and poor melt plasticization. The reasons for analysis and improvement are as follows:
Reasons and Solutions
| Reason analysis | Improving methods |
| Improper melt plasticization | Improve plasticizing condition and quality |
| Color powder clumps or poor diffusion | Grind or replace the color powder |
| Low material temperature or low back pressure | Increase material temperature, back pressure, and screw speed |
| Uncleaned cylinder (containing other residues) | Thoroughly clean the cartridge |
| The inner wall of screw rod and feed tube of injection was damaged | Repair or replace damaged screw/barrel or machine |
| Too little dispersant | Properly increase the dosage of the dispersant or replace the dispersant |
| The compatibility of plastics and color powder is poor | Replace the plastic or color powder |
| The recycled nozzle material has a mixed color | Check/replace raw material or water outlet material |
| Residual melt is retained on the head of the nozzle | Clean the residual melt on the outside of the nozzle |
Gloss differences
What is gloss differences ？
When the plastic part is formed, the finished surface loses its original luster of the material and forms an opalescent film, or is in a fuzzy state, which is called gloss differences, shown here:
The surface gloss differences between plastic parts is mostly due to the surface state of the mold. If the surface of the mold is not polished well or has mold scale, the surface of the finished product will not get a good gloss. Excessive use of release agents or oil release agents is also a cause of poor surface gloss. If the material is hygroscopic or contains volatile matter and foreign matter mixed in (polltion), this also is a cause that produces differences. Specific analysis and improvement methods are as follows:
Reasons and Solutions
| Reason analysis | Improving methods |
| Mold temperature is too low or material temperature is too low | Raise mold temperature or material temperature |
| The density of the melt is not enough or low back pressure |
Increase pressure keeping pressure/time or increase back pressure appropriately |
| Excessive mold release agent in the mold | Control the amount of mold release agent and wipe it clean |
| The surface of the mold is permeated with water or oil | Wipe clean water or oil and check for leakage or oil |
| The inner surface of the die is not smooth | Mold polishing or removing glue stains |
| The raw material is not sufficiently dry | Fully dry ingredients |
| Mold cavity with mold scale/glue stain | Remove mold scale/glue stain from the mold cavity |
| The molten material decomposes overheat or stays in the cylinder for too long | Reduce melt temperature or residue |
| Too small runner and gate (cold material) | Increase the size of runner and gate |
|
Injection speed is too slow or the mold temperature is uneven |
Improve injection speed or cooling system |
| The cylinder is not cleaned | Clean the cylinder thoroughly |
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More content on plastic production issues:
How to avoid Deformation in your plastic production
How to avoid silver mark and splay mark in your plastic production
How to avoid Short Shots in your plastic production
How to avoid fissure and burn mark in your plastic production
How to avoid dark spot visible ejector mark and scratch in your plastic production
How to avoid bulges and vacuum vesicles in your plastic production
How to avoid a weld line in your plastic production
How to avoid flashing and bubbles in your plastic production
How to avoid jetting and air lines in your plastic production
Come grab your free E book on Plastic Production issues and how to avoid them
