Waterborne Bonding Agent Application

Applied film thickness is critical for use of these systems. If the film is too thin, then spotty bonding will result. Too much bonding agent applied will result in delamination and will cause flaking. Best film thicknesses have been determined by Bond [4] to be  

These levels of primer and adhesive cover were found to be resistant to salt cabinet attack after 72 hours, even if metals had only previously been grit blasted, without any chemical treatment of the metal surfaces. 

Correct viscosity of the applied bonding agent must be controlled by methods other than those used with solvent-based systems. Cup or rotary viscosity testers are not reliable methods of determining viscosity of emulsions. Hydrometer testing of specific gravity is a more reliable way of measuring viscosity and hence controlling deposited film thickness. 

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Although waterborne bonding agents can be air dried and successfully bonded the mechanical properties of film is greatly enhanced by heat application which causes the micelles to coalesce. 

Waterborne bonding systems do not have the same ability as organic solvents to wet out the metal surface or solubilise any greasy contamination during bonding agent application to the metal surface. Another factor is quick evaporation of the alternative carrier from the applied adhesive film. Use of water requires higher temperatures for its removal from a deposited film of adhesive. Incomplete removal will result in porous adhesive layers, or even in underbond corrosion at the metal surface. 

Figure 4.1 Effect of application thickness of bonding agent Chemosil 211 Chemosil 211 (primer solvent-based) 411 Chemosil 411 (topcoat solvent-based) XW7500 Chemosil XW7500 (topcoat waterborne) APIO Thixon APIO (primer waterborne) 5005 Thixon 5005 (topcoat waterborne) XW1190 Chemosil XW1190...

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