“How should a substrate be prepared or treated prior to applying a light-curable material?”
Cleaning substrates prior to the application of a light-curable material is almost always a best practice. Removing contaminants allows for the best wetting of the application area and increases adhesion to substrates. When deciding on a cleaning process, it is important to consider both the contaminant and the substrate(s). Particulates can be removed with high-pressure air or brushing, while chemical contaminants require aqueous (water) or solvent-based cleaners. The aqueous or solvent-based cleaner should be selected such that it removes the contaminant without harming the substrate.
“Will exposing areas of a PCB board that are not covered by an adhesive or conformal coating to UV curing energy damage the board in anyway?”
Any frequency of energy that gets impinged onto a substrate has two options: it can get reflected, in which case it is harmless, or it can get absorbed, in which case it will turn into heat. Some light-curing equipment, like the Dymax BlueWave® spot lamps, have an intensity adjustment feature which allows for the ability to reduce unneeded energy. Adjusting the intensity reduces any excess energy that may turn into heat and damage temperature-sensitive substrates.
Adhesives, Curing Equipment, Electronic
“We have recently taken on some medical tubing device-assembly work from another company but the information supplied seems to be missing some crucial points. We are having bond-strength issues when fixing a flexible PVC tube into the female port of an ABS connector.
The instruction we had was to use 100% cyclohexanone, but my feeling and internet research seems to show some form of cyclo/THF and pellet combination would perform better. Would you agree or is there a ready-made alternative available?”
In general, adding pellets (PVC) to the solvent mixture can help avoiding stress cracks and allows more flexibility in the gap design due to its gap-filling properties. So far, we have not come across a readily available mixture.
If you consider moving away from using solvent, I would suggest looking at light-curable adhesives. Dymax offers a variety of products suitable for bonding PVC to ABS. Medical grade adhesive Dymax 1161-M for instance provides strong bonds to a variety of substrates and cures within seconds upon exposure to UV and/or visible light.
“What colors are Dymax adhesives available in? Can I add color to a Dymax adhesive?”
While a majority of Dymax light-curable materials are translucent or clear, we do also offer several colored materials, including blue, red, white, and even black formulations. Many of our SpeedMask® masking resins are colored, making it easy to see where the resin has been applied and ensuring full coverage of the masked area.
Dymax can add color to an existing formulation but it should be noted that colorants may negatively affect cure speed and depth of cure. If you are interested in a tinted adhesive, a full evaluation should be conducted to verify that there is no detrimental effect on the bond line. Oil-based dyes can be added to many adhesives without a significant impact, but pigments may limit the depth of cure if the pigment concentration is too high. Please contact our Application Engineering team if you are interested in more information on the subject.
“Common Dispensing Mistakes Made When Using Light-Curable Adhesives”
There are several mistakes that can be made when implementing dispensing systems for light-curable materials. Understanding these common pitfalls and taking the suggested precautions will help reduce problems when dispensing.
- Incompatible Materials – Dispensing system materials of construction should be compatible with your light-curable adhesive. Metal parts and fittings should only be 300-series stainless steel. Other metals can cause the adhesive to polymerize. Plastic materials that are compatible with Dymax light-curable adhesives include polyethylene, polypropylene, teflon, nylon, and acetals. Other plastics may be attacked by the resin.
- Transparent Fluid Lines – Black or opaque plastic fluid lines should be used to ensure that the adhesive is not exposed to ambient light, which may cause the adhesive to polymerize.
- Air Bubbles – Air bubbles may become trapped in fluid lines when an empty adhesive container is removed for replacement in a dispensing system. To avoid this problem, purge the fluid line after refilling or replacing the empty container. Maintaining only the line length necessary to transport the fluid from the reservoir to dispense point will facilitate the purging process.
- Pour-In Pressure Pot versus Drop-in Pressure Pot – For lower viscosity fluids (<500 cP) that naturally release air bubbles, either pour-in or drop-in pressure pots can be used. For fluids that do not release air bubbles naturally, drop-in pressure pots are recommended. Dymax recommends the use of a 10 gallon drop-in pressure pot for adhesives with viscosities up to 25,000 cP. For resins with viscosity >25,000, or where pressure exceeding 30 psi (0.2 MPa) is required for dispensing, ram-style pail pumps are recommended.
- Excessive Air Pressure – The application of excessive air pressure >30 psi (0.2 MPa) to pressure pots may cause air to dissolve into the adhesive. When this pressure is alleviated (either when the pressure pot is opened or the fluid is dispensed) this dissolved air may come out of the solution in the form of air bubbles that become trapped in the adhesive. To maintain appropriate pressure and prevent the formation of air bubbles in the adhesive, use larger ID fittings and tubing, minimize tubing length, fully open the dispense valve, and use a shorter and larger ID dispensing needle. If none of this is effective and pressure of 30 psi (0.2 MPa) or greater is still needed, a “ram-style pail pump” is recommended. This involves force being applied directly to the adhesive in the pail via a follower plate allowing for very high pressures without air. Ram-style pail pumps are recommended for resins with a viscosity of 25,000 cP or greater.
- Narrow and Long Fluid Lines – Generally, the shorter and wider the fluid line, the better. A fluid line diameter of 3/8″ (10 mm) is desirable. The longer and narrower the line, the more air pressure is required to transfer the fluid to the dispense valve. This can result in a slow flow rate and the need for high pressure to move the material with the unfortunate result of air-bubble formation.
- High-Shear Pumps and Valves – The use of pumps that produce shear, such as gear pumps, is not recommended with light-curable materials. Shear occurs when the adhesive is caught between two tightly fitting, moving metal parts, which can cause the adhesive to polymerize and clog the system. Simple pressure pots with pneumatic and ram-style pail pump systems are recommended.
- Positive Displacement Valves – Positive displacement valves should be tested for compatibility with light-curable materials prior to their incorporation into a dispense system. Contact Dymax for further guidance in selecting an appropriate valve for dispensing a particular adhesive.
- Using Vacuum to Remove Air Bubbles – A vacuum should not be used to remove air bubbles from a light-curable material. The use of a vacuum may remove constituents from the adhesive, altering performance and/or reducing its shelf life.
- Excessive Vacuum Suck-Back on Syringe Dispensers – Caution should be taken to apply only the amount of suck-back or vacuum pressure needed to prevent adhesive drip following dispensing. Excessive vacuum pressure may pull the plunger out of the syringe barrel or suck air into the syringe, creating bubbles.
Adhesives, Dispensing Equipment
“We are looking for a medical-grade adhesive for bonding PEBAX (72D MED) tubing to latex nature rubber. We need shore hardness of a UV adhesive below 50D after cured. What is the best adhesive for this application? Also, which pre-surface treatment is suitable for PEBAX?
We also need a medical-grade adhesive for bonding PEBAX (72D MED) tubing to a colored ABS hub. Which fast setting adhesive is suitable for this?”
Latex nature rubber can typically be bonded with cyanoacrylates, also referred to as Super Glue. The Dymax medical grade 222 series cyanoacrylates might be a good place to start.
For bonding PEBAX I would suggest looking at Dymax 208-CTH-F, which is a medical grade, light-curable adhesive with shore D55. To combine PEBAX with latex or colored ABS, light-curable adhesives might not be suitable due to low adhesion to latex and problems with light curing through the colored ABS hub. Therefore, a cyanoacrylate is most likely the adhesive of choice.
Adhesives, Cyanoacrylates, Medical
“I’m looking for a UV-curable adhesive to bond polyolefin surfaces (cyclic olefin polymer), 100 cm2 max size. The surfaces could be pre-treated (primer, plasma). What adhesive/primer do you recommend?”
Bonding to COC is very difficult due to its low surface energy. Surface treatment has not shown big improvements. Since the demand of bonding COC is growing, adhesive suppliers are working on new adhesives that can handle such difficult surfaces.
You can contact Dymax with your specific inquiry to see if they have new products in their pipeline that fit your needs.
“Is there a UV-curable, medical-grade (safe to use in the body) biodegradable adhesive of any kind on the market right now? If not, would it be possible to formulate the adhesive?”
Dymax does not presently pursue implantable applications for our adhesives, and we are unaware of any adhesive on the market that would be biodegradable. Consequently, we cannot comment on the feasibility of such a product.
“I want to find an epoxy that can bond two pieces of polycarbonate materials and be sterilized using autoclave. We tried using epoxy 353ND from Epoxy Technology but it is very difficult to cure completely, and after the sterilization process, the epoxy failed.”
Similar to light-curable adhesives, polycarbonate is usually not suitable for repeated autoclaving cycles. If a strong bond between the two pieces of polycarbonate is achieved, 1-5 cycles may be possible without damaging the adhesive and the polycarbonate.
There are several light-curable adhesives for polycarbonate available that are also approved for medical applications. One example is Dymax 1161-M, which I recommend for further testing with your application.
“Guidelines for Protecting Light-Sensitive Adhesives from Curing in Dispensing Equipment in Manufacturing Environments”
Unfortunately, manufacturing facilities that use standard fluorescent lighting sometimes have a problem with the polymerization of UV/Visible light-curable adhesives in dispenser tips and lines. The chemistry of these products make them extra sensitive to light, so extra measures must be taken to insure that unwanted polymerization does not occur.
To prevent this problem, manufacturers should shield needle tips and lines from light exposure. Incorporating lines that are black, opaque, polyethylene plastic will completely block light from the adhesive and eliminate the chances of unwanted polymerization. Dymax provides light-blocking materials for syringe needle tips. If these measures are insufficient and a process can’t be shielded through use of light-blocking materials, the fluorescent lamps in the facility could be retrofitted for existing incandescent and fluorescent fixtures.
Adhesives, Coatings, Dispensing Equipment