“We are observing a cracking problem in the bonding of a PVC tube and component of PC-144R with a 50% Cyclohexanone + 50% Tetrahydrofuran solvent mixture. Please suggest an alternative solvent for bonding the above component. Also describe why the polycarbonate is showing cracks when used with aforementioned solvents.”
There are cases where the PC tends to crack upon contact to attacking chemicals like ketones (Cyclohexanone, MEK) , ethers, and esters (Tetrahydrofuran):
- Applied stress due to joint design: when both parts are pushed into each other putting them into tension. To resolve, we recommend changing the design.
- Residual stress due to the molding process: when the molded PC does not cool down consistently. An annealing step (time and temperature to be determined) will relieve residual stress.
I would recommend looking at the possibility of stress within the Polycarbonate and make changes to design and/or process accordingly.
You can also look into switching to a light-curable adhesive, which is typically less harsh to Polycarbonate. For bonding PVC to PC, Dymax has a variety of products if you are interested exploring this path further.
“We want to bond Polyurethane to PU, Polyurethane to latex, and PU to polycarbonate. A little flexibility would be helpful. Visibility of the bond would also be desirable. Do you have a product that meets these requirements?”
DYMAX offers 204-CTH-F light-curable adhesive, which is recommended for single-use medical devices made of Polyurethane, PVC, Polycarbonate, and many other plastics. This adhesive fluoresces blue under black light for quality purposes and is suitable for assembling rigid and flexible components due to its flexibility.
Since latex is very difficult to adhere to, 204-CTH-F may not provide the desired bond strength. Typically, a cyanoacrylate like DYMAX 222 Series is used for latex; however, it will not provide a flexible bond.
If you want to be able to see the adhesive while you dispense it and get confirmation of cure, I would suggest trying DYMAX 1201-M-SC or 211-CTH-SC. Both are light-curable adhesives equipped with DYMAX patented See-Cure color change technology. Adhesives formulated with See-Cure technology are visible when dispensed onto substrates due to their bright blue color while in the uncured stage. When fully cured, they become colorless to visually assure they have been cured.
“I need to attach this 1.58 mm polyethylene to another type of material such as wood-plastic-metal of various types. Any ideas?”
Polyethylene is a polyolefin and very difficult to achieve strong adhesion to. A common method to overcome this issue is to pre-treat the surface via corona discharge, gas plasma, flame treatment, or priming. These methods typically increase the surface energy of the substrate and the potential to adhere to it. Utilizing any of these pre-treatment methods will open up the choice of possible adhesive products. To bond surface-treated polyethylene to wood, plastic, or metal you can use a cyanoacrylate (RX-50 from Pacer, available through DYMAX), epoxy (Master Bond EP21), or polyurethane (Master Bond EP30D12).
The right adhesive choice for you is not only dependent on the dimension, design, and substrates you are trying to assemble, but also the environment the device/item is being subjected to. Is it being used indoors with no contact to moisture or outdoors with consistent contact to water? For a dry environment, a cyanoacrylate might be the right choice, whereas an epoxy might be better for a moist environment.
A recent question that came through:
“Do you have an adhesive recommendation for gluing polycarbonate to acrylic? We are currently using 3M Marine Adhesive/Sealant 5200.The adhesive holds initially but starts to “weaken” after some time. The adhesive seems to be sticking well to the acrylic (Plexiglas) but not to the polycarbonate. We tried sanding the polycarbonate surface before gluing, but the adhesive still did not hold. Any suggestions?”
Typically, bonding to polycarbonate and acrylic is a very feasible application for many adhesives. If you want to try a light-curable, acrylated-urethane adhesive, DYMAX 3099 or 3025 adhesive might be a good option.
The comment about the adhesive weakening after achieving good results the first time is concerning. I recommend that you speak to your polycarbonate supplier/molder to discuss why this might be happening. For instance, the raw resin supplier may be adding a mold release to improve molding with polycarbonate and allow the polycarbonate to release from the metal mold easier. If a monomeric mold release is used, it can sometimes migrate to the surface and push the adhesive away from the bond line, causing interference with adhesion over time. If they are using a polymeric mold release, it cannot migrate as easily and should not have a negative effect on adhesion. Or, maybe the polycarbonate molder is spraying a Teflon® mold release every 200th shot to help the part release from the mold.
I also suggest asking the polycarbonate supplier/molder about the levels of stabilizers being used. Most stabilizers in the plastic are at acceptable levels and do not interfere with bonding. On occasion, however, the supplier/molder adds additional stabilizers to give light or heat resistance and stability to the plastic. These stabilizers can also migrate to the surface over time and destroy a bond line. To be sure, you can submit samples of the polycarbonate before and after heat aging to an analytical laboratory to run a solvent extraction on the surface of the plastic, to see if there is a contaminant at the surface, and to identify the contaminant. I have even seen contaminants like finger oil at the surface of the plastic migrate along the bond line and eventually degrade the bond strength.
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?”
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.
A recent question came in about a recommended plastic-bonding adhesive:
“We’re looking for the best clear adhesive that will work with polyethylene terephthalate (PET) material. The adhesives we have tried in the past often react with PET and turn a translucent white color. Can you recommend an adhesive that will not have this reaction with PET and remain clear upon application?”
A large number of clear adhesives work with PET material. The material you select will depend on whether the part in question is a molded PET part or a thin film. It will also depend on whether you are looking for a medical, industrial, or packaging-grade adhesive. There is even an adhesive for use with PET material that changes color when it is cured, indicating that it has received enough ultraviolet light. Choosing the proper light source is also important and will depend on whether the application requires the curing of a 3-D part or whether it involves a web coating or lamination. All of these materials are designed to provide a crystal-clear bond line without stressing the PET material, which causes the translucent white effect you refer to.