“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.

Adhesives Adhesives, Light Curable Adhesive, Light Curing Process, light-curable adhesives, substrate preparation, surface preparation, uv light-curable adhesives

“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.

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“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.

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“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.

Adhesives Adhesives, bond COC, bond polyolefin, Light Curable Adhesive, light-curable adhesives

“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.

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“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.

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“What bonding agent would you recommend for bonding soft PVC tubing to a polycarbonate connector? This is a sterile disposable tubing set.”

For this type of application I would recommend a light-curable adhesive. Dymax 1161-M could be a good candidate due to its ability to bond dissimilar substrates like PVC and polycarbonate together. This adhesive is solvent free, resistant to EtO, Gamma or Beta sterilization, and passes ISO 10993 biocompatibility testing. Via UV and visible light, the adhesive cures on demand within seconds using Dymax UV light-curing equipment.

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“How can I reverse adhesive crystallization? Will the adhesive be compromised in any way?”

Only a very small number of adhesives are susceptible to crystallization and the likelihood of this phenomenon actually occurring is slight. If you do experience crystallization, heat will reverse the process and restore the adhesive to its liquid state with no loss in performance. There is no effect on strength, viscosity, or any other adhesives property. Tests performed at Dymax indicate that heating the original container of crystallized adhesive (in an oven or in a warm-water bath) to 100°F (adhesive temperature) will return the adhesive to its uncrystallized, liquid state. The adhesive will reach 100°F in approximately 2 to 3 hours depending on container size. For consistent dispensing, the adhesive should be allowed to return to room temperature. We would also recommend that you purge any dispensing reservoirs, lines, valves, and needles before any prolonged periods of production shutdown (i.e., weekends, shutdowns, etc.). This will help prevent adhesive crystallization.

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“Can you suggest a medium-viscosity adhesive that is well suited for metal-to-metal bonding?”

“We are currently using Dymax 1184-M, M-B, and V for most applications. However, we’ve found out that they are not well suited for bonding metal to metal, partly because the cured hardness is too high and partly because the UV light cannot penetrate through metal seams.”

For metal-to-metal joints I would suggest looking at traditional epoxies rather than light-curable acrylates.

Epotec and Master Bond Inc. offer epoxies in medical-grade versions. There is an old article that describes the impact of Sterrad low-temperature hydrogen-peroxide-gas plasma on several adhesives. The article, along with the results, can be viewed at: http://www.mddionline.com/article/compatibility-medical-devices-and-materials-low-temperature-hydrogen-peroxide-gas-plasma.

According to the results in the article, some two-part epoxies from Epotec have a moderate compatibility with Sterrad.

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“We currently employ a solvent process using Cyclohexanone to bond a PVC tubing with an ABS molded hub. We are going to be switching from ABS to a Pebax (thermoplastic elastomer). We believe there are issues with the Cyclohexanone creating the bond with the Pebax that we desire, and I’m looking for some info regarding our process - is it appropriate to continue to solvent bond (maybe with a different solvent) or to switch to a new process (UV adhesive for example)?”

Solvent bonding typically works with amorphous thermoplastics such as PVC, ABS, PC, PMMA, and PS. Pebax belongs to the family of thermoplastic elastomers and has a good resistance to solvents in general. Depending on the grade and softness, it may swell in certain solvents but will not behave like amorphous thermoplastics do. If you replace the ABS with Pebax, you need to switch to a new bonding process. UV light-curable adhesives are a good option. I would recommend trying Dymax medical grade adhesives 204-CTH-F and 209-CTH. They both adhere well to PVC and Pebax and several other commonly used plastics.

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