HAP and VOC regulatory requirements may dictate specified limits and carry financial penalties for amounts in excess of those limits. Other limits in HAP and VOC contents can arise as production increases, such as issues related to Title V operating permits for manufacturing sites. These can also limit HAPs and VOCs that can be processed at the site for continued production without obtaining a new operating permit.

Working Properties and Specifications: The next step in the resin selection process is to consider the working properties and specifications. Key working properties include gel time, viscosity, the ability to add various levels of fillers, the ability to make a thick part in a single step and mold/demold time. These affect how the resin works on the shop/production floor and productivity.

Selecting a resin that allows workers enough time to make the part with a small cushion to accommodate processing issues, but not too much extra time, will maximize productivity per shift. Being able to make a part in a single step rather than breaking it into several steps to control exotherm, cosmetics or other properties is another thing that factors into productivity. Some raw materials like peroxides and fillers have shipping limitations, so understanding what is available in the region is important.

Finished Properties: The final step in the resin selection process is determining which finished properties your application requires. Possible properties to consider include UV resistance, corrosion resistance, fatigue performance, fire resistance, surface cosmetics, stain resistance, stiffness, strength, toughness, blister resistance, thermo-shock and color/clarity. Some of these will be covered in the application/end use step, but there may be some property requirements outside of the basics ones. Let the resin supplier know you need a specific end property, such as a temperature capability that can be defined by the heat distortion or glass transition temperature or thermo-shock.

Overall, I recommend that you create your own set of requirements based on the above criteria and

pass along that important information to the resin representative. Even though you have requirements, make sure you keep an open mind. There may be a better product available. New resins and additives are being developed and current products are being expanded. An alternate resin may offer you some processing and/or performance advantages even though they may have some different working properties and specifications.

The guest columnist for this issue’s “Best Practices” column is David Herzog, director of research and development for Interplastic Corporation in Minneapolis. Email comments to dherzog@interplastic.com.