I) Influence of surface characteristics:
1. Cleanliness: The metal surface is adsorbed with a layer of low cohesive strength and low surface energy pollution layer and oxide film, which will reduce the bonding strength. Generally, when the metal surface is clean, the contact is small or even zero. After the material treatment, the contact changes with time, and it is easy to be polluted by the ambient atmosphere in the air, the contact angle increases, and the contact angle tends to be stable after about 5H. Contact angle and bonding strength before and after surface treatment
2. Roughness: The surface of the sticky material is polished with gauze or sandblasted, and proper surface roughening can improve the bonding strength. The roughening process removes the pre-existing surface layer. A new surface layer (purification) is formed, and the sandblasted surface has a larger actual bonding area than the polished surface. Too rough surface will reduce the bonding strength, because too rough surface cannot well invade the adhesive, and the air in the recess is easy to residual surface.
3, Surface chemical structure
The chemical composition and structure of the surface have an important influence on the bonding performance, durability and thermal aging performance of the adhesive material, and the influence of the surface structure on the bonding performance is often by changing the cohesive strength, thickness,
porosity, activity and surface energy.
2) Surface treatment method
1. Solvent lye and ultrasonic degreasing method:
Solvent degreasing method: the commonly used scrubbing method is to use oil-free cotton (absorbent cotton) with solvents such as acetone, gasoline, toluene, etc. to directly scrub the surface of the sticky material.
Alkali degreasing method: use hot lye to treat oil surface, such as 30-55% sodium phosphate (Na4P2O7), 10-50% NaOH, 10-6% Na2CO3 or 30-85% alkaline silicate. Although NaOH is a strong alkali, because its wetting performance is not very good, and not easy to rinse clean, its effect is not as good as alkaline silicate; alkaline silicate by SiO2 and Na2O mixture. When the ratio is 1:2, the cleaning effect is the best; when the ratio is 1:1, it is suitable for the cleaning of aluminum.
Ultrasonic degreasing method: general parts in the power of 20 watts/cm2 ultrasonic treatment for 20-60 seconds to get enough clean surface.
2. Mechanical processing: grinding and sandblasting
Sandpaper sanding is easy to operate, but the uniformity is poor, and it is difficult to obtain the same repetition effect. Sand blasting method can quickly and easily remove the dirt on the surface, and produce different roughness of the surface. 3. Chemical corrosion method:
After the above treatment, the sticky material shall be placed in acid or alkali solution for chemical corrosion treatment. This allows further removal of residual contaminants on the surface and the formation of an activated or passivated oxide layer on the surface with good cohesive strength (strict control of water purity).
4. Coating primer method:
On the treated surface, first apply a thin layer of primer to improve the bonding performance.
5. Plasma method
The bonding strength of PE, polypropylene, polytetrafluoroethylene and other difficult-to-stick materials treated by plasma method is greatly improved, because the contact angle is reduced after surface treatment, and the ultimate surface tension is increased, thus improving the adhesion and adhesion of the adhesive to it.
