Improving processability for in‐mold coating formulations: Part II: Two‐reinforcement formulations

• Published in: Polymer engineering and science Vol. 61; no. 10; pp. 2630 - 2638
• Main Authors: Cai, Kaiyu, Zhang, Dan, Straus, Elliott J., Villarreal, Maria G., Castro, Jose M.
• Format: Journal Article
• Language: English
• Published: Hoboken, USA John Wiley & Sons, Inc 01.10.2021; Society of Plastics Engineers, Inc; Blackwell Publishing Ltd
• Subjects: Analysis; Carbon; Carbon black; Carbon fibers; carbon nanofiber; Coating processes; Electrical conductivity; Electrical resistivity; Electrostatic coating; electrostatic painting; Graphene; grapheneblack; In-mold coating; Methods; Multi wall carbon nanotubes; multi‐wall carbon nanotube; Nanofibers; Nanoparticles; Nanotubes; Sheet molding compounds; Single wall carbon nanotubes; two‐reinforcement formulations; Viscosity; United States
• ISSN: 0032-3888; 1548-2634
• DOI: 10.1002/pen.25789

The in‐mold coating (IMC) process nowadays is well accepted by the sheet molding compound industry. The currently used IMC contains 2.8 wt% carbon black (CB) to provide enough electrical conductivity for maximum paint transfer efficiency (PTE) for electrostatic painting. Due to its relatively large viscosity, this formulation makes use of more than one injection gate for coating some large parts necessary. Our previous research investigated the possibility to replace the CB with higher conductivity carbon‐based nanoparticles, namely carbon nanofibers (CNFs), multi‐wall carbon nanotubes (MWCNTs), industrial graphene (grapheneblack [G]), and single‐wall carbon nanotubes (SWCNTs) and found that the IMC with 11.3 wt% G has the best processability among all IMC formulations. To improve this formulation, herein, we study the use of a second reinforcement in combination with G, i.e., CB, CNF, and MWCNT. Results from this study suggest that most G/CB‐reinforced IMC formulations have a better performance than the G‐reinforced IMC formulations, and IMC with 1 wt% CB and 6 wt% G is the best among all G/CB‐reinforced IMC formulations. To be specific, the new formulation allows parts to be painted to have a 300% increase in size when compared with the standard IMC. In this work, we evaluate the feasibility to use a second reinforcement to improve the industrial graphene‐reinforced in‐mold coating (IMC) formulation which has the best processability among all single‐reinforcement IMC formulations found in our previous research. A new formulation was found to allow parts to be painted to have a 300% increase in size when compared with the standard IMC (carbon black‐reinforced IMC).