Chemical reaction mechanism of pre-curing process of two-component adhesive based on deformation behavior for automobile hood

TL;DR

This study investigates the chemical mechanisms and deformation behavior of two-component acrylic and epoxy adhesives during pre-curing and high-temperature baking in automobile hoods, revealing key factors affecting deformation and strength.

Contribution

It provides a detailed analysis of the pre-curing mechanisms and deformation patterns for acrylic and epoxy adhesives, highlighting the influence of chemical reactions on mechanical properties.

Findings

Pre curing time affects hood deformation after baking.

Acrylic adhesives rapidly reach sufficient shear strength within 1 hour.

Epoxy adhesives require longer pre curing times for comparable strength.

Abstract

Shearing test is carried out on the joint which bonded under different pre curing processes with two component adhesives of acrylic and epoxy resin respectively. The pre curing strength is obtained, which used to analyze the relationship between the pre curing strength and time. The hoods with different pre curing strength are baking with high temperature. The deformation of different areas of the hood is measured with gauges, and the deformation characteristics of the hood after baking are acquired with comparative analysis. Combining the components of two component adhesives and DSC test, the pre curing mechanism of different adhesive systems are studied. Therefore, the key factors and regular pattern of the deformation for the hood are obtained. The results indicate that, finally deformation of the hood after high temperature baking varies with the pre curing time. The key of the pre curing time of acrylic adhesives lies in the chain initiation stage of the free radical polymerization reaction. Due to the influence of the chemical properties of methyl acrylate and its initiator, the pre curing reaction induced by free radical polymerization is very fast. The shear strength of this joint can reach to 3.67 MPa with a pre curing time of 1 h, which quickly achieving the pre cure strength required for deformation control. For epoxy adhesives, the rate determining step in pre curing process is the esterification reaction. Due to the influence of the structure of carboxylic acid, the esterification process is relatively long. Shear strength of this joint can only reach 0.87 MPa after pre curing for 4 h without external heating.