As we all know, the Low Surface Materials like Plastic (Polypropylene, Polyethylene), Teflon, and other thermoplastic polyolefins are hard to bond to with conventional adhesives. This is because adhesives need materials with higher surface energy in order to sufficiently wet out the surface. Wetting out is required to form a strong bond and refers to the adhesive seeping into the surface.
When a material has low surface energy, the adhesive beads up rather than flow out. Unable to make intimate contact with the substrate, the adhesion level is reduced and bond failure is likely.
In general, there is 2 main way to increase the surface energy and make plastic bonding process easier as following:
1. Using Plasma Surface Treatment
Plasma is referred to as the fourth state of matter, contains positive ions, electronics, neutral gas atoms or molecules, UV light and also excited gas atoms and molecules. This solution brings many benefits to the fabrication such as: treat complex surface, environmentally friendly process, …
2. Using Primer or Adhesion Promoter
When using this method, the user should keep in mind the following necessary steps:
♦ Remove any contaminants and solvent
Contaminants can get onto a substrate from a variety of sources, including:
– Machining
– Handling
– Surroundings
– Cleaner residue
Even the slightest bit of contaminant on a surface can significantly impact an adhesive’s ability to adhere. Therefore, it is important to take caution in carefully removing any contaminants prior to adhesive application
♦ Roughen the Surface (optional)
Another step to increase surface energy is to roughen the surface of the substrate. Sanding is one easy way to do this, creating peaks and valleys on the substrate. These give the adhesive greater ability to grip the substrate, allowing for a better, stronger bond.
Chemical etching is another option, depending upon the specific substrate materials.
♦ Finally, using an appropriate primer or adhesive promoter
Users should carefully choose the fitting primer and adhesive promoter based upon the specific substrate and its level of surface energy. However, it is important to consult with your chosen adhesive manufacturer ahead of time to determine if one is needed.
For example:
3M Primer for 3M Adhesive and Tape: 3M Primer 94, 3M VHB Tape Universal Primer, 3M AC77
Momentive Primer for Silicone Adhesive: Momentive Primer SS4155
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