“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.

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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.

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“I am looking for an adhesive that can be used to bond tubes made of flurorocarbons (PVDF and FEP) to a titanium connector. This connection needs to withstand repeated autoclave sterilization at 134° celsius. Do you have any recommendations?”

Fluoropolymers such as PVDF, FEP, and PTFE (Teflon) are very difficult to adhere to. The only way to overcome this is by using a chemical etch solution. Two possible suppliers are www.actontech.com or www.fluorocarbon.co.uk. Both web sites also offer a variety of information regarding this topic.

The etching process removes a layer of fluorine atoms from the surface and allows oxygen and hydrogen from the atmosphere to attach, which enables adhesives to bond to it. The next challenge is the required resistance to repeated autoclave cycles. We recommend trying a two-part or heat-curable epoxy from Masterbond or Epoxy Technology.

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“Micro air bubbles are finding their way into my dispensing process. Do you have any tips on how to minimize or eliminate air bubbles? “

If you are ordering adhesive in syringes or cartridges, try storing the syringes or cartridges in an upright position. The cap should be pointed towards the ceiling. Storing syringes and cartridges in this manner allows the air to travel closest to the point of exit.

When you are ready to dispense the adhesive, make sure that the syringe remains in the upright position while you remove the syringe’s cap and attach it to the valve or the syringe needle. Purge the system (while upright) of any air bubbles that may have been produced by screwing or unscrewing the cap or valve. A threaded system has a tendency to introduce micro air bubbles. Purge at a high pressure to ensure that all of the air bubbles are forced out of the syringe or the valve. If you use low pressure, the bubbles may be caught on imperfections and left behind, only to come out during your production at some later time.

If you have a long length of tubing between the cartridge and the needle tip, you may need to purge for several minutes to get the air bubbles out of the tube. The best method to reduce the chance of air bubbles is to shorten the distance between the cartridge and the valve. An optimum system will have no tubing at all. Once you have purged the system, you can reduce the pressure to a normal working level.

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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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“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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“Can oxygen inhibition be removed from cured parts without damage to the fully-cured substrate area? We are looking to change our process to include a nitrogen blanket, but have many components that cannot be completed due to the tackiness on the outer surface.

We tried CRC Brakleen which effected the cured surface area as well as the tacky coating.”

First of all, I would like to refer to an older reply made regarding the inhibition of cure: http://mpmn.canon-experts.com/2009/03/

CRC Brakleen is a very strong cleaning agent that contains tetrachloroethylene and dichloromethane or ketone (depending on the packaging used). As you already noticed, these are chemicals that easily remove the tacky layer, but also dissolve the cured adhesive. If oxygen inhibition cannot be avoided, the tacky layer should be removed with an isopropyl alcohol (IPA) wipe. IPA is less aggressive and is commonly used for this purpose. We would always recommend a wipe rather than a soak.

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“We need to bond a silicone insulator between two gold-plated electrodes. All materials need to be medically approved for non-implatable use. Can you recommend options to explore?”

I would recommend a silicone adhesive to bond the silicone insulator to the gold-plated electrodes. Two possible candidates are: Dow Corning Medical Adhesive Type A (acetoxy cure system), or NuSil Med1-4213 (2-part platinum cure system). Both materials are insulators themselves.

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“We use two-part epoxies and UV-curable cements to seal Viton- or PVC-bending rubber onto the distal end of flexible endoscopes. Our current epoxy works well when it is sterilized using Steris or glutaraldehyde solutions. With the introduction of Sterrad H2O2 plasma processes, the epoxy fails after 20 to 30 cycles. What do you recommend that will hold up to more than 100 cycles?”

When ASP introduced Sterrad low-temperature hydrogen peroxide gas plasma, they tested many UV-curable adhesives and epoxies from different suppliers. The results showed that many adhesives were compatible and did not exhibit any material damage after 200 cycles. But some products were not compatible with this sterilization method. The article with the results can be viewed here: http://www.mddionline.com/article/compatibility-medical-devices-and-materials-low-temperature-hydrogen-peroxide-gas-plasma.

Since this article is more than 10 years old, some products may not be available anymore, but it is a helpful guide to identifying the most suitable product.

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“In our application we are looking for a light-curable silicone adhesive that cures within seconds, is not acidic, and does not outgas too much. Do you have suggestions? “

There are a few light-curable silicones on the market that are non-acidic. The tensile strength, and cohesion strength of most UV silicones on the market, is very low and although they may stick well to substrates, a bonded joint can usually be taken apart easily. The larger the surface area, the more suitable these products are for bonding or lamination applications.

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