“I would like to attach 72D Pebax extruded tubing into the ID of a Polycarbonate tube. What is the appropriate gap-per-side if I want to use DYMAX 204-CTH UV- curable adhesive?”

The optimum gap size for UV bonding applications (in general) is 0.002-0.006 inches, or 0.05-0.15 mm. In catheter bonding applications, where a Pebax tube is being bonded into a Polycarbonate Y-connector, we often see bond gaps around 0.1 mm per side. The DYMAX 204-CTH-F family is a very good choice of products to use for this type of application and substrate combination. Another product to consider is 208-CTH-F.

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"We have a segment of uncured adhesive inside a tube encapsulated with the adhesive DYMAX 204-CTH-F-VLV due to UV-opacity of the said tube’s segment. Does contact with uncured adhesive deteriorate properties of cured adhesive?"

Unfortunately, yes. Uncured adhesive will attack the bond line and the cured adhesive. The extent of deterioration is dependent on the area and volumes in contact with each other, and the duration of how long they are in contact. We would recommend sealing the tube, or removing the uncured adhesive if possible.

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"I have an application where the cuff is glued to the tube and I require a smooth, tapered transition between the cuff edge and the tube.
Writing will take place over this area; that is why I need the smooth, tapered glue connection."

It is very common to use an adhesive to make a nice, smooth, tapered transition between cuff edges and the tube, or marker bands, or transitions where there is a jump from one size tube to another. A low-viscosity adhesive in the 200-600 cP range, which cures rapidly to a smooth tack-free finish, is ideal. DYMAX light-curable materials like 1120-M-UR or 204-CTH-F are often used in these types of applications. Techniques include applying the adhesive in either a vertical or horizontal position, or even at a slight upward angle to achieve the taper. If it is a horizontal or tilted orientation, rotating the shaft during application and curing with a spot system for 1-8 seconds (typical), will allow the material to cure in the proper profile without risk of the adhesive slumping or running. Typically these transitions have a max height of 2-5 mils or less. Lower viscosities will have a sharper taper, and higher viscosities will have a shallower taper. Selecting the right needle dispense tip will help control adhesive quantity and position on the catheter shaft.

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"Our research lab is looking for a medical-grade adhesive to bond:
1.) Dacron cloth to silver plate and
2.) Glass and PMMA optical cylinder in a silver tube.
It needs to be moisture resistant and should last for a long time (20 years).
Please suggest a product."

Dacron is a commercial name for PET, or polyethylene terephthalate. Bonding cloth to a rigid substrate like a silver plate can be done in a few different ways. Bonding to cloth is mostly a mechanical lock that forms by encapsulating strands of the cloth and then locking them to the rigid substrate. The viscosity of the adhesive will play a role, as the thinner the viscosity, the more it will wick into the cloth. A very high viscosity will not wick very far into a cloth. A 2-part epoxy, such as found from Loctite or 3M, or a 2-part urethane, such as found from Lord Corporation, are just two products that you might want to explore. A silicone adhesive may also do the trick, and would suggest contacting representatives of Dow Corning, Momentive Performance Materials, NuSil Technology, or any of the other silicone manufacturers.

To bond glass and PMMA you may be able to use the same adhesive, but the application might require a lower-viscosity material, depending on the gap between the parts and method of assembly. The epoxy and silicone systems will be moisture resistant and have good usage life, but most manufacturers will not warrantee a 20-year usage lifetime. A 1-part, light-curable urethane acrylate, like 203A-CTH or 209-CTH from DYMAX, are options if you can get light to the adhesive.

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A question that came through:

“What is the best adhesive for bonding a polyethylene terephthalate (PET) balloon to a polyether block amide (Pebax) substrate? What is the recommended surface preparation? Are other catheter-shaft substrate materials more suitable than Pebax for bonding to a PET balloon?”

Answer:

You should select a medium-flexibility light-curing adhesive with the viscosity to achieve the level of wetting and gap filling appropriate to your design. For example, DYMAX’s 204-CTH-F and 208-CTH adhesives have viscosities ranging from 155 to 500 cP. Such adhesives bond well to both PET and Pebax. In addition, it is important to choose an adhesive that fluoresces under a black light, enabling operators to detect and fix voids or air bubbles before the assembly is cured. This feature results in a better-quality bond and greater yields during production.

You can perform a surface treatment using plasma together with oxygen gas. While a plasma treatment with air gas—which has a lower O₂ content than oxygen—is also effective, it is not as advantageous as using an oxygen plasma treatment. The oxygen deposits onto the surface of the material and increases the number of bond sites to which the adhesive can stick.

You ask whether other catheter-shaft substrate materials are more suitable than Pebax for bonding to a PET balloon. Pebax is commonly used for manufacturing catheter shafts because adhesives bond well to it. A polyether/nylon copolymer, the material can be mixed with higher proportions of nylon (polyamide) to create higher-durometer materials (72D), or it can be mixed with lower proportions of nylon to create lower-durometer materials (35D). The greater the amount of nylon in the Pebax, the farther apart are the bond sites and the more difficult it is to bond. For example, bonding PET to 35D Pebax is easier than bonding it to 72D Pebax. If you can incorporate a small layer of 35D Pebax at the bond location while retaining 72D Pebax underneath to achieve greater material stiffness, the bonding application will be improved. 

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