“I need a medical-grade adhesive to bond Ultem material to stainless steel (SS). This product will be a reusable medical product that will be autoclaved for 30 minutes @ 250° F”
To bond materials like Ultem and stainless steel, for a reusable device that will see autoclave conditions, the right choice in adhesives is important. As a general category, acrylates, urethanes, and cyanoacrylates will survive only limited autoclaving. Epoxies and silicones will have better success. Ultem is a difficult material, but with proper evaluation you might find a successful candidate. Silicone materials are available from companies like Dow Corning, Momentive, NuSil, and Wacker. Epoxy materials can be obtained from Epoxy Technology, Henkel/Loctite, and numerous others. Silicones will be softer and flex with the thermal stresses, while epoxies will be more rigid. It will ultimately depend on the part design and the number of autoclaving cycles the part will see.
“Our application requires a watertight seal between FEP tubing (0.8 mm OD, 0.2 mm ID) and a borosilicate glass capillary (0.17 mm OD, 0.10 mm ID) with an overlap of 1-3 mm. This is part of a one-time use, disposable cartridge. We are currently using a 5 minute epoxy because the zero shrinkage is advantageous. The cure time, however, is not. We have tried UV-cure epoxy in the past for this joint but found that the epoxy did not cure inside the FEP tubing. Any suggestions?”
UV light-curable epoxies typically cure with the UV spectrum from 300-390 nm and do not make use of visible light to cure. With the semi-hidden bond described in the application above, switching to a visible-light-curable, acrylated-urethane adhesive would be worth trying. A visible-light-curable adhesive will allow more of the available light to hit the adhesive and cure deep within the FEP tubing.
An important issue with this application is that the borosilicate glass capillary will act like a light fiber. It will take the light, carry it like a fiber-optic cable, not allow it to get to the adhesive (as it is bouncing the light internally within the glass), and move it past the bond area. The visible-light-curable adhesive should be exposed with high-intensity light. The adhesive should allow the light to penetrate into the gap.
One alternative to a visible-light-curable adhesive is a cyanoacrylate adhesive that could cure deep within the FEP tubing without light. Due to the deep overlap area in this application, only the top surface would be exposed to water and could provide enough protection to create a water-tight seal. Another alternative is a new product, DYMAX 9440 A/B, which is a light-curable silicone adhesive. This material is unique in that you can expose the adhesive to light during dispensing and assembly and still have enough time to assemble the part before the material starts to set up. DYMAX Applications Engineers can work with you one-on-one to discuss exact options and materials.
“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.”
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.