2026-07-14
Curing process for adhesives
(1) Hot-melt adhesives: Polymer melts solidify upon cooling after wetting the surfaces to be bonded.
(2) Solution adhesives: As the solvent evaporates and the solution concentration increases, the adhesive gradually cures and develops strength.
(3) Emulsion adhesives: As water within the emulsion gradually permeates into porous substrates and evaporates, the emulsion concentration rises; eventually, surface tension causes the polymer colloidal particles to coalesce. At higher ambient temperatures, the emulsion coalesces into a continuous adhesive film, whereas at temperatures below the Minimum Film-Forming Temperature (MFT), a discontinuous white film is formed. Emulsion adhesives primarily consist of polyvinyl acetate (and its copolymers) and acrylate copolymers.
(4) Thermosetting adhesives: Multifunctional monomers or prepolymers of thermosetting resins undergo polymerization; as molecular weight increases, molecular chain modification and cross-linking occur simultaneously, resulting in the formation of an insoluble, infusible gelled state—often referred to as primary curing. Extending the curing time and raising the curing temperature are not equivalent within a certain range; a reduction in curing temperature cannot easily be compensated for by extending the time, because a specific chemical interaction between the adhesive and the substrate surface is required, and this process necessitates a sufficiently high temperature.
Curing Pressure:
It facilitates the thorough wetting of the surface by the adhesive; aids in the removal of low-molecular-weight volatiles generated during the curing reaction; helps expel residual volatile solvents from the adhesive layer; and allows for control over the adhesive layer thickness (high-viscosity adhesives tend to form thicker layers, so adjusting the curing pressure regulates the thickness range).
A holding period after adhesive application—known as pre-curing—is often employed; pressure is applied once the adhesive viscosity has increased to ensure a uniform bond line thickness.
Curing Temperature:
If the curing temperature is too low, the cross-linking density of the adhesive layer will be insufficient, resulting in an incomplete curing reaction; conversely, if the temperature is too high, the adhesive may run off or become brittle, leading to reduced bond strength. Heating promotes molecular diffusion between the adhesive and the substrates, facilitating the formation of chemical bonds.
(1) Direct oven heating: Uses forced-air circulation to ensure uniform heat transfer.
(2) External heating: Rapidly transfers heat into the adhesive layer, significantly shortening the curing time. Ultrasonic heating: Suitable for viscoelastic adhesives and solvent-free adhesive systems; not applicable to rigid thermosetting adhesives.