The surface preparation
Surface preparation is one of the most important steps to achieve high adhesive strength and improve the performance of the adhesive itself. For effective bonding, the adhesive must completely wet the surface of each substrate.
Most surfaces are covered with layers of contaminants, such as dust, oils, grease, and oxide. These contaminants adversely affect adhesion, and if they are not properly removed before applying the adhesive, bond failure can occur.
Surface pretreatments are aimed at removing all types of contaminants on the substrate surface, allowing the adhesive to settle on the actual surface instead of its apparent surface.Proper pretreatment can activate the surface energy of substrates and increase the active bond area to improve adhesion.
How to prepare surfaces before applying adhesive
A simple method to prepare surfaces is to degrease, abrade, and degrease. This method is suitable for most industrial applications; however, the type of pretreatment will depend on the type of substrate.
Degrease
Degrease the surface with isopropanol or acetone to remove any traces of oil, dust and any grease residue from the outer layer.
Abradere
Mechanical abrasion methods such as sandblasting or brushing will remove the layer of oxide and dirt from the surface.
Blasting can be used to remove surface deposits on metal surfaces.
Abrasion will increase the surface area allowing the adhesive to form a strong and durable bond.
Degrease
Additional degreasing and cleaning may be necessary to remove any residue released by the abrasion process.
The adhesive should be applied immediately after surface treatment to ensure that the surface is not recontaminated. All surfaces must be dry before the bonding process.
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The test for a clean surface – water break test
The test can be performed to check the cleanliness of the surface. It allows the user to check for hydrophobic contaminants and residues.The cleaned surface is placed upright and sprayed with drops of distilled water wetting the surface.
If the surface is clean, water will spread over the surface because of the high surface energy. This shows that the surface is free of contamination and the surface treatment was successful.
