| |
What is adhesion?
Adhesion refers to the bond between two adjacent materials and is related to the force required to affect their complete separation.
Type of failure
Cohesive failure (silicone breaks)
Adhesive ruptures leaving adhesive on both substrates involved in the bond
Adhesive failure (bond breaks):
Adhesive pulls cleanly away from the substrate
Why is surface preparation important.
Substrate preparation is critical to Preparation good adhesion
Poor substrate preparation can contribute to adhesion problems to remove contamination
▫ Process oils, mold release, dirt, grease, etc.
▫ Can be done by:
Appropriate solvent cleaning
- Acetone, IPA, ethyl acetate, toluene, etc.
- Wipe, immerse
Detergent cleaning
- Soap and water
- Wash and water rinse,dry thoroughly
For difficult to bond substrates / surfaces
Mechanical roughening
▫ Examples:
Substrates
- Sandpaper
- Sand blasting
- Metal wool
Chemical treatment
▫ Chemical treatment is the process of treating a clean surface by chemical means. The chemical nature of the substrate surface is altered to make it highly
receptive to adhesion
Examples:
- Etching with oxalic acid/ sulfuric acid/distilled water
- Etching with hydrofl uoric acid/distilled water
Use of primers
▫ One-component, no mixing
▫ Promote adhesion to diffi cult-to-bond substrates
▫ Apply in thin coats (0.5 mil)
▫ Dry at room temperature and ambient humidity conditions
- Allow the primer to air-dry for at least 30 minutes before applying silicone
- When drying, avoid touching the primer or allowing it to be exposed to dust or water
▫ Primers
- Flame treatment
▫ High temperature flame which oxidizes the surface of the substrate and provides new functional groups
▫ Used for many types of plastics
- Corona treatment
▫ High voltage, high frequency discharge in air; another oxidation method, in which new functional groups are produced on the surface
- Plasma treatment
▫ Neutral and charged species created by a discharge in the presence of a gas |
|
