Dayton Ohio Plastic Injection Molding Company - Proto Plastics Proto Plastics Inc. (PPI) is a custom plastic injection molding company focusing on high-quality parts for a diverse range of industries and customer-centric solutions for more than 50 years. Proto Plastics Inc. (PPI) is a custom plastic injection molding company focusing on high-quality parts for a diverse range of industries and customer-centric solutions for more than 50 years.