Why do blemishes appear on the surface of the colored co-extruded profiles? And how should they be resolved?

Why do blemishes appear on the surface of the colored co-extruded profiles? And how should they be resolved?

The main possible causes for the appearance of pockmarks on the surface of co-extruded profiles are: 
① The quality and performance of co-extruded materials vary significantly. If the processing performance differences are too large and the temperature is too high, the low-molecular-weight components are prone to volatilization, forming bubbles that remain on the surface of the co-extruded layer, presenting as pinhole-like pockmarks. 
② In production, the vacuum degree of the exhaust hole of the main extruder is low. The moisture and low-volatile substances in the PVC material cannot be discharged in time and remain in the material. The density of the material is insufficient, and the surface is uneven. When it converges with the co-extruded material, it affects the surface flatness of the colored profile and may form surface pockmarks. 
③ The distance between the shaping mold and the die is too large or the vacuum degree of the shaping mold is too small. 
The main solutions are as follows: 
① Select co-extrusion materials with similar processing properties and reasonably control the forming temperature. 
② Appropriately increase the vacuum degree of the exhaust holes of the main extruder to fully remove moisture and low-volatile substances. 
③ Reducing the distance between the shaping die and the die mouth generally results in fewer pinholes when the distance is shorter, and more pinholes when the distance is longer. 
④Appropriately increase the vacuum degree of the shaping mold, so that the first shaping mold can directly adsorb the surface of the co-extruded layer of the profile coming out of the die onto the inner wall of the shaping mold, exerting a cooling effect and eliminating water vapor and entrained substances, which can effectively reduce the occurrence of pockmarks.
Top
Inquiry
Inquiry