Polyetherimide Powder

Question:

We manufacture a 25 micron thermoplastic polyetherimide powder. This is a fully polymerized amorphous resin with a Tg of 230C. We use a palletized version for injection molding applications that provides flame resistance, high strength, high heat and solvent resistance. We think that it will be useful in powder coating applications, but we know almost nothing about the details of what makes a good powder coating resin. We know that this polyetherimide powder will not be easy to melt without high heat. Do you have any suggestions on how we can determine if our hope for powder coating applications are realistic or absurd? R.G.

Answer:

Let me start by saying that I am not a chemist or a formulator of powder coatings. I hold a BS degree in Mechanical Engineering, which means that I am better at the process than coating development. However, I did make some calls to a couple of retired powder coating chemists to discuss your question. They said that thermoset powder coatings normally cure at < 200C, which means that your Tg of 230C (Tg means glass transition temperature is when coatings turn from a solid to a liquid) is pretty high. This means that your resin will not melt to form a smooth coating at a reasonable cure temperature as most powder coatings do. They also said that thermoset powders are melt-mixed in extruders at 120C, again a problem with your material. This means that if it cannot be melt mixed into a homogeneous compound in the extruder, it will have to be dry-blended in afterwards. It will be best used as an additive rather than a resin for powder coatings. You should probably discuss your material in terms of an additive to the powder coating formulators instead of a resin. As an additive, your material can have some heat resistance properties that can be beneficial to a formulator developing a powder coating that requires such a property. Go to PF Online (www.pfonline.com) or the PCI website (www.powdercoating.org) for a list of formulators to call. Good luck.