I see smoke coming off the light-curable adhesive…what is it?
Before we can answer this question we have to first understand what it’s not.
By definition1, it’s not smoke or vapors or outgassing.
What you really are seeing coming off of the curing adhesive are fumes generated by the light-curing process. This phenomenon is the result of a very rapid polymerization or chemical reaction that occurs when the liquid adhesive is exposed to the correct wavelength of light. Both heat given off during the reaction (at the molecular level) and heat from the absorption of light energy can, in some instances, result in a small amount of adhesive fumes being emitted before the product has a chance to completely polymerize or cure.
Essentially, this phenomenon may emit trace amounts of some of the ingredients (or fractions of the ingredients) contained in the formulation. Please note that the volatilization may or may not be noticeable, but is almost always a very small amount.
Are the fumes hazardous? Always consult the MSDS to answer this question. However, if the liquid itself poses a risk to the user, then good manufacturing practices for the particular process may suggest incorporating an exhaust system in the bonding area to remove the fumes during the light-curing step.
Vapor: The gaseous state of a substance that is solid or liquid at temperatures and pressures encountered. NIOSH (National Institute for Occupational Safety and Health) Definition
Fume: A solid condensation particulate, usually of a vaporized metal. NIOSH Definition (This could also be generated from curing our adhesives)
Outgassing: The release of absorbed or occluded gases or water vapor, usually by heating in a vacuum. (Web definition)
Smoke: The vaporous system made up of small particles of carbonaceous matter in the air, resulting mainly from the burning of organic material. (Web definition)
Adhesives, Coatings, Medical, Safety, Structural
"Hello, currently I am working with 2 Cal Poly professors to make monitoring operating room packs easier. Our goal is to be able to attach micro RFID tags to surgical tools so that they can be scanned and bookmarked. What type of adhesive would work best to attach these tags to surgical tools? The adhesive needs to be biocompatible and be able to undergo sterilization."
Assuming most surgical tools are stainless steel, and need to survive repeated autoclave, I would recommend looking at 2-part epoxies as your base chemistry. Options are available from Loctite, 3M, and Epoxy Technology, to name a few, and some have biocompatibility certificates on file. If the surgical tools are disposable or plastic, and only need to withstand a single autoclave cycle, EtO, or Gamma sterilization, then a light-curable acrylated urethane like the DYMAX 1120-M-UR light-curable medical device adhesive would be my first choice. Acrylated urethane light-curable adhesives have excellent adhesion, are simple to apply as a 1-part material, and cure in less than a second.
"In my application I have a process where I apply UV adhesive between two pieces of plastic and I am seeing a short contraction period followed by a longer expansion period. Is it possible for UV adhesive to behave this way? How much does UV adhesive shrink during cure? Could this cause a pulling force between two plastic materials? If under an opposite force could the UV adhesive relax and expand somewhat?"
When light-curable adhesives cure, whether curing with UV light or visible light, crosslinks are forming between polymer chains. This pulls the chemical chains closer to each other very rapidly. We typically see a 1-2% linear shrinkage, which could translate into a 2-5% volumetric shrinkage. This may stress some plastics or optical components. There is a relaxation effect, usually over the next few hours or overnight, where the chains relax slightly as they rotate into an optimum alignment. In the spirit of valentine’s day – polymer chains like to spoon together and snuggle. If they are at odd angles to each other, they are still touching, but want to find that alignment where they are in the same direction and bending the same way. Chemical bonds can stretch and spin around their axes and allow for this relaxation. Also good to note, a product with a low modulus will stretch easier under stress, and a product with a very high modulus will not stretch much at all. A silicone (on one extreme) can have a modulus as low as 300 psi, whereas an epoxy can have a modulus as high as 2,000,000 psi. Many UV-curable adhesives are urethane acrylates and can vary in their modulus’ over a very wide range. The product data sheet should list this value.
Adhesives, Medical, Structural
"Are methanol, ethanol, acetone, or acetonitrile FDA approved?"
These solvents are generally not FDA approved. These particular solvents bond plastic together by melting the plastic, and then allowing the plastics to intermingle. As the solvent evaporates, the plastics harden to form a strong plastic weld between the plastics. The choice of which grade of solvent you buy is up to the medical device manufacturer (higher purity equals higher price). Since solvents evaporate and do not remain in the bond line, they are not normally tested for biocompatibility.
"I have an application bonding opaque parts with a Cyanoacrylate (Super Glue Type). There is much surface area and I have a very good bond. Will Gamma Sterilization effect my bond strength?"
Most cyanoacrylates will survive 1x, 2x, and sometimes even 3x gamma sterilization without a significant impact on bond strength. Repeated Gamma sterilization will start to add additional crosslinking, which will start to reduce elongation. As most cyanoacrylates are already brittle materials (depending on the grade), the adhesive may become even more brittle. Drop tests, impact testing, or tensile testing may be a good indicator of the final impact on your bond strength.
Adhesives, Cyanoacrylates, Medical
"I need an epoxy to join two BK7 glass parts together. Gap is around 0.2mm. Light will cross the interface. Reasonable index match to the glass required. Low stress/shrinkage so it doesn’t distort the parts please. Viscosity not too runny, as we want it to stay in place prior to cure."
Optical glass-bonding adhesives are available that have good adhesion to BK7 Glass, a close refractive-index match to the glass, low shrinkage (low modulus), and moderate viscosity to avoid running. Light-curable adhesives like OP-29, which is a one-part adhesive from DYMAX, are available exclusively through Fiber Optic Center. FOC also carries various 2 two-part epoxies or 1 one-part frozen epoxies which should meet your requirements. An alternative source would be to visit the Edmund Scientific website and review their adhesive selections. Epotek 353-ND and 353-T epoxy are also widely used in the glass-bonding/optical adhesives market.
"I have an application where we would like to cover the edge of a silicon die (that has been first tacked in place with epoxy that has been cured to a Valox/PBT base) with an uncured epoxy. Then add additional epoxy to a second bond location that ultimately bonds the Valox base to a Valox cover that has a slight press fit, covering the silicon die. After the press fit assembly, I would like to light or UV cure through the cover plate, causing both applications to cure. By both applications I am referring the bond line between the Valox cover plate & Valox base as well as the edge coating around the periphery of the silicon die, bonding it to the Valox base.
Are there any polymers that can transmit UV or light sufficiently to allow these types of cures? Is there a special light source required? Can the polymer be anything other then clear? Lastly, is there a medical-grade polymer that can achieve this?"
There are a couple of ways to handle this application.
There are a number of polymers that can be used for a cover plate that will let light through, whether UV or visible light. One way is to use a tinted plastic like polycarbonate or acrylic. Tinting the plastic with a dark blue dye will create the "illusion" of being opaque, but will let the proper wavelengths through the plastic to allow it to cure. Finding the right balance of dye will be critical. One way to judge the impact of the dye in the plastic, or the transmission through the plastic, is to measure the intensity of light coming through the plastic from the light source. You can calculate a % loss of transmission through the plastic in both the UV and visible regions. Most adhesives want to see a minimum of 200 mW/cm2, and some of the light sources on the market are emitting light of 20,000 mW/cm2. Even if the plastic blocks off 90% UV light, and 70% visible light, this might be enough to allow it to cure. If the plastic compounder uses a pigment to augment the tint, make sure the level of pigment is low, and they use a white pigment like Titanium Dioxide. A good field test – if you hold the plastic up to the light and can see a shadow as you wave your hand behind it – you might have enough light coming through to cure the adhesives. Stay away from yellow-orange-red colors. Whites, blues, and greens are better. There are a number of medical grade adhesives that can be used for this application, and various curing lamps. I might recommend contacting DYMAX Application Engineering to arrange for some free samples and to discuss our Trial Rental/Lease Equipment program. www.dymax.com.