Another question that came in recently:

“I am investigating insert molding potential of PC/ABS or PC over PEEK tubing. With the significant melt temperature differential I am uncertain that I can achieve a secure bond. Can you suggest an adhesive that can be applied to the PEEK outer diameter prior to molding that will act as a bond layer?”

Answer:

I would recommend investigating a silane primer, sometimes called an adhesion promoter. These thin materials can be applied to the outer surface of the PEEK tubing, allowing it to dry (most contain some type of solvent), and then overmold as normal. The silane groups usually have two different reactive chemistries attached to them - one that will be attractive to the PEEK, and one that will be attractive to the PC. There are a number of different primers available from different companies. You might have to try a few different ones to determine which primer will work best for your combination. The primers can be applied with a brush, foam wipe, spray, or even a simple dip application (only coat the outside, not the inside). Apply the primer just short of the length of the overmold, and this will hide the primer under the PC.

Structural PEEK, Plastic Bonding, Plastics, Primer

Help needed:

“We are trying to glue a stack of coin cells to a .003 inch polyester substrate that has been printed with silver ink.  The bond must be electrically conductive. We’ve tried Loctite 401, 3M CA4, and 3M CA8.  Our problem is that the glue does not adhere consistently to the stainless steel can of the battery even when fixtured for 50 seconds. Roughing the surface of the battery has not helped.”

Recommendation:

A chemical primer on the surface of the stainless steel might help with the consistency. Cyanoacrylates generally cure with moisture in the air and on the surface. Controlling the environment goes a long way towards making a consistent process and getting consistent bond strength. Now we have to look at the level of moisture sitting on the surface of the stainless steel battery surface. Putting a primer onto the surface helps by putting a uniform concentration of -OH hydroxy groups on the surface. Be careful of how the operator is impacting your bonding process. Amazingly, an operator’s breath can apply a thin layer of moisture and help or hinder cure and adhesion. Plasma treatment systems can also be helpful in making a uniform bond line as it make a homogenous uniform surface each time. Cyanoacrylates are susceptible to these kinds of variations in the environment. If another alternative is required, two-part epoxies or one-part light curable acrylated urethanes or two-part acrylated urethanes (light and/or activator) are usually more consistent as they do not rely on environmental conditions for cure.

Structural Adhesives, CA's, Cyanoacrylates, Primer