This Old Mold 2 - Polishing

Tips for optimizing existing molds to run Eastman Tritan copolyester
Eastman Tritan™ copolyester provides excellent gloss and picks up mold finish very well. When using it in a mold designed for other plastics, however, there are factors you need to consider in order to achieve success.
Here are some guidelines for polishing Eastman Tritan copolyester:
  • Specify SPI mold finish standards.
  • Specify surfaces smooth enough to minimize ejection force.
  • Specify final polish in the direction of draw to minimize scuffing.
  • Add a light 320 dry grit blasting (SPI B3 finish) to drafted walls to reduce the possibility of a vacuum forming during ejection.
It’s important to keep in mind that surfaces polished smoother than required for ejection add to mold cost. In most cases, highly polished surfaces can hinder ejection if there is a vacuum drawn in low or no draft areas. Where no vacuum is drawn, polished surfaces generally eject better.
You may encounter the risk of surface defects when polishing Eastman Tritan copolyester. To prevent them, remember these tips:
  • Pay attention to the part design if a surface finish is expected on the final product. Abrupt changes in wall thickness, relatively thick sections, or heavy ribs can cause variations in surface gloss. Uniform mold temperatures are needed to ensure that the texture is even throughout the pattern.
  • To achieve a higher matte finish, double or triple the texture etching.
  • If weld lines are visible on the final product, one alternative is to move the gate positions so that the weld line is formed in a less visible place. If this is not possible, apply a rounded texture pattern to help hide the blemish.
  • If the material you are molding is expected to have poor scratch resistance, use a rounded texture pattern to hide potential marks.
Every combination of existing mold properties and molding requirements is different. Tritan experts can review your polishing and texturing methods and help you evaluate the results of optimizing your old mold.