Flame Treatment of Plastic Substrates for Adhesive Bonding

Obtaining an adequate bond strength when bonding plastic-to-plastic substrates or plastic to dissimilar substrates is often a challenge for resin system. In general plastic surfaces demonstrates poor ‘wettability’ or the ability of a liquid to form a continuous film.

These types of substrates or are called LSE or Low Surface Energy substrates and typically thermoplastic surfaces falls with in this category.

Teflon* or its generic name PTFE and other polyethylene derivatives such as HDPE, LDPE, UHMW and olefinic-based plastics demonstrate poor liquid wettability due to its low surface energy. To create a viably bondable surface condition to these types of plastics, it must be surface treated by creating a superficial oxidized surface to increase its dynamic surface tension. Various types of physical treatment can be used to increase the surface energy of plastics, mostly through oxidation of the superficial layer.

Flame treatment is the most widely used and cost effective pre-treatment for polyethylene (HDPE, LDPE, UHMW) and polyolefin based plastics prior to polymer bonding or printing. It consists of exposing the surface to be coated to a suitable oxidizing flame during a short period of time (0.2 to 3 sec.).
The resulting change of the surface by creating an oxidized surface greatly improves the liquids ability to wet-out the surface thus creating a strong adhesive bond between the surface and the coating.

A Flame Treating process consists of exposing the surface to a suitable oxidizing flame for a period in the range 0.2 to 3.0 seconds. This treatment brings about a change to the polymer surface that increases its surface energy allowing fluids to effectively wet-out the surface and permits a strong adhesive molecular and mechanical bond.

UHMW Sheets Flame Treated- Microscopic Surface Comparison

Commercially Available Propane Torch

Adjust the propane torch so that a low oxygen burning flame is achieved and pass over the area to be treated several times until a slight haze is noticed on the surface of the substrate.

Note the fluid behavior on the flame treated area demonstrating improved substrate wetting thus making adhesion possible for polymers such as adhesives and inks

Note the improved wettability of the flame treated side allowing the tension modified liquid to effectively wet-out the surface. By modifying the surface condition of the plastic, polymer bonding is now possible.