“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.

Adhesives 204-CTH-F, 209-CTH, Adhesives, bond Pebax, Cyclohexanone, light-curable adhesives, Pebax, Pebax to PVC, Plastic Bonding, solvent bonding

“What is the difference between newtonian viscosities and thixotropic viscosities? How would that impact my application?”

Newtonian products are materials which have the same viscosity even under different shear rates. Water, milk, and mineral oil are examples of common newtonian materials. Thixotropic materials on the other hand will flow when a shear force is put onto the material (like squeezing a tube of toothpaste), but when the force is removed, the material will not flow. A newtonian material might be used to pot an application or fill a cavity, while a thixotropic adhesive might be used to dispense a bead along a molded ridge.

Adhesives adhesive viscosity, newtonian, thixotropic, Viscosity

“What are some common sources of non-passive bulb failure?”

One cause of non-passive bulb failure is often overcooling or undercooling of the bulb. Overcooling can prevent the bulb from reaching an optimal operating temperature and under cooling can allow the bulb to exceed a safe operating temperature and result in failure. Contributing factors include (but are not limited to) clogged fan filters, restricted air flow, a worn fan, an environment that is excessively cold, hot, or humid, or excessive air flow through the unit. In addition to over or undercooling, rapid temperature changes can also cause stress on the bulb. This can occur if the unit is in a warm environment and a nearby air conditioning duct or opened window allows chilled air to enter the unit.

Another common mistake is using the bulb over 2,000 hours. While it may be tempting to reset the hour meter after it indicates a necessary bulb change without actually changing the bulb, DO NOT RESET. Even if the unit still has sufficient intensity, NEVER do this. Eventually, most bulbs will fail in a non-passive manner if operated beyond 2,000 hours.

Excessive cycling can also cause bulb failure. During the bulb’s warm-up phase, the different coefficients of thermal expansion between the quartz and metal components in the bulb cause stress in the quartz. The more frequently a bulb is cycled (more than 1 power-up cycle per 8 hours), the more fatigue and stress are imparted to the bulb. Best practice is to leave the unit on as long as possible to avoid excessive power on-off cycling.

Vibrations, contamination from finger oil, or not providing proper air clearance are also common problems that can result in non-passive bulb failure.

Uncategorized bulb failure, Curing Equipment, light-curing equipment, Uv flood lamp bulbs

“Will overexposure during curing have any effect on the adhesive?”

The effect of underexposure is obvious… incomplete cure. The effects of overexposure are more complex. Double and triple exposures (two to three times the dosage required to cure) typically have little effect on light-curable materials. However, significant overexposure to UV light with attendant heat may age DYMAX materials and some substrates (especially plastics). Severe aging may appear as cracking, physical distortion, changes in color, or chalking. Some physical properties such as an increase in hardness or decrease in elongation may also change. The degree of aging will depend upon several factors including intensity of the lamp, the wavelengths transmitted to the resin, temperature, exposure time, substrates, and specific formulations.

Aging from UV light is not the only concern associated with extra long exposures. Parts may get hot under UV lamps with extended exposures. Thermal aging can exhibit the same effects as UV aging. Some types of plastics may warp, scorch, or decompose from excessive heat absorption. A fan in the curing area may help keep parts cooler.

Significant overexposure of a resin to UV-curing light is unlikely to occur in a properly controlled curing process. End users should always test and validate their assembled device at the upper and lower limits of their process against the lifetime use of their device.

Adhesives Light Curing Adhesive, Light Curing Process, light-curable adhesives, overcuring adhesive, overexposing adhesives, uv light-curing adhesives

“One of the materials I’m using has exhibited syneresis. What is the best way to reverse the syneresis?”

A few thickened adhesives (VT and GEL grades) occasionally exhibit syneresis. Syneresis appears as a thin film or puddles of low-viscosity adhesive on top of the thicker adhesive. Sour cream and yogurt are familiar products that also exhibit syneresis. The composition of the low-viscosity syneresis liquid is chemically identical to the thickened material. It has the same chemical and bonding properties but the viscosity is much lower.

Time and colder temperatures can promote syneresis. We would recommend using a First In, First Out (FIFO) inventory control. FIFO inventory control can help control the amount of time a product is stored before use. We would also suggest that syneresis-prone materials are not refrigerated. In fact, mild heating can reverse the syneresis in some products.

Once syneresis has occurred, mixing is the most common method of returning the mixture to a homogeneous state. Mixing can be accomplished with a traditional paddle or spatula (being careful to minimize air entrapment) or mixing can be accomplished through the use of a static mixer.

Adhesives gel adhesives, light-curable adhesives, syneresis, syneresis in adhesives, UV Light Curing Adhesive, UV/Visible Light Curing Adhesive

“I am trying to adhere a Polyethylene (PE) foam material onto a Polyethylene (PE) rigid, smooth plastic material. I prep both surfaces with a primer (Loctite 7701) before dispensing the adhesive, which is Loctite’s 4011 cyanoacrylate medical-grade adhesive. The adhesive is anchoring or sticking really well to the PE foam, but not the rigid plastic. They are both PE materials and I am not sure why it would adhere to one and not the other.

Are there different primers that vary in performance?”

One reason why the adhesive might stick better to the foamed Polyethylene (PE) is its larger surface. Due to the holes and grooves, adhesives in general can hold on better and achieve a mechanical lock.

According to the suppliers web site, the primer you are using is recommended for PE. If it is not providing the desired results, you may want to look into another surface treatment method such as plasma or corona, which adds polar groups to the surface and usually results in higher bond strengths.

Adhesives, Cyanoacrylates adhesive for PE, bond polyethylene, Cyanoacrylates, PE, Plastic Bonding, polyethylene

“I would like to know the best adhesive to use in our cannula and metal-wire bonding processes. The details are as follows:

3. Nitinol wire to ABS/PC - need thicker adhesive for potting a wire into a slot in the plastic part. Wire is 0.010 to 0.021 inches in diameter, in a 0.025 inch slot.”

I would suggest you start trials with the DYMAX 1180-M family of adhesives. This series of products cures with UV and visible light, fluoresces for quality purposes, and is available in several viscosities. These adhesives are designed for bonding metal cannula or wires into plastic parts made of PC, ABS, or other plastics.

For application 1, I would recommend DYMAX 1180-M-UR, which has a nominal wicking-grade viscosity of 150 cP and fluoresces bright red.

For applications 2 and 3, DYMAX 1180-M-T-UR could be a good candidate with a nominal viscosity of 6,000 cP. This product also fluoresces red.

Adhesives, Medical cannula bonding, Light Curable Adhesive, light-curable adhesives, Medical-Grade Adhesive, needle bonding, Plastic Bonding, wire bonding

“What wavelengths are typically associated with depth of cure vs surface cure?”

Depth of cure is typically accomplished using long wave, UVA light (320-390 nm). Surface cure is typically done using short wave, UVB light (280-315 nm). For more information on curing with light, see DYMAX’s Comprehensive Guide to Light-Curing Technology.

Uncategorized curing with light, depth of cure, Light Curing Process, light wavelengths, light-curing adhesives, light-curing technology, surface cure, UV/Visible Light Curing Adhesive

“We use 1184-M-T, 1184-M-B, and 1184-M-VT epoxies for various uses. What is a good solvent that can take apart lenses glued together using 1184-M-T adhesive?”

If your lenses are made of glass you have several options, as glass is resistant to the solvent removal methods suggested below:

There are a few chemicals that will dissolve or swell 1184-M-T or any other light-curable acrylate, such as Dichloromethane, MEK, or Acetone. It may take some time for the solvent to migrate all the way in between the laminate, so the time depends on the size of your parts. A more gentile method is to soak the lenses in isopropyl alcohol (IPA) or even use warm IPA with the help of an ultra-sonic cleaner. I would also suggest this method if your lenses are made of plastic since the solvents mentioned first will also damage it.

Adhesives 1184-M Series, 1184-M-T, adhesive removal, bonding lenses, Light Curable Adhesive, light-curable adhesives, UV/Visible Light Curing Adhesive

“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.

Adhesives, Catheter Bonding, Medical 204-CTH-F, 208-CTH-F, bonding Pebex tubing, Catheter-Bonding, Medical-Grade Adhesive, Pebax, UV Light Curing Adhesive, UV/Visible Light Curing Adhesive