“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.

Adhesives adhesive dispensing, Adhesives, air bubbles in adhesive, dispensing adhesive, trapped air in adhesive

“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.

Adhesives, Medical 1161-M, bond PC, bonding PVC, gamma sterilization, Light Curable Adhesive, light-curable adhesives, Medical-Grade, Medical-Grade Adhesive, Plastic Bonding, PVC Tubing, tubeset bonding

“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.

Adhesives adhesive crystallization, Adhesives, Light Curable Adhesive, Light Curing Adhesive, light-curable adhesives, UV Light Curing Adhesive

“We are looking for a good adhesive to pot Nitinol or Titanium wire into a hole in a Noryl device. The hole is 0.156″, while the wire is 0.125″. We are looking for an adhesive that can stand up to re-sterilization using various methods of sterilization including autoclave and EtO, and that will also fill the gaps well. Can you recommend an adhesive?”

If the number of sterilization cycles is limited to a few you may be able to utilize a light-curable adhesive for your application. Dymax 1128A-M is a medical-grade adhesive that cures with UV and visible light, and exhibits good adhesion to a variety of metals. Adhesion to the Noryl will have to be tested.

If more than 10 cycles of autoclave sterilization are required then the best choice of adhesive will be either a heat-curable or two-part epoxy. Masterbond and Epotec offers a variety of materials that are medical grade and suitable for repeatable sterilization.

Adhesives, Medical 1128A-M, medical grade adhesives, metal bonding, nitinol bonding, noryl bonding

“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.

Adhesives, Medical 1184-M Series, Light Curable Adhesive, light-curable adhesives, medical adhesives, medical device adhesives, Medical-Grade, Medical-Grade Adhesive, metal bonding, metal to metal bonding

“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