"I am trying to understand the UV-curing process. How can I determine when an adhesive is fully cured? What are the critical parameters that I need to control in order to gain good consistency for the curing? Also, I was trying to cure some adhesive on a piece of stainless steel coupon. One small drop of adhesive was placed onto the coupon and formed a kind of round shaped droplet. I am wondering if the curing is more efficient on the surface of the droplet or on the inside of the droplet. Thanks a lot for your help!"

Very good question! Light-curable adhesives (whether it is by UV light, visible light, or a combination of UV and visible light) cure from the surface closest to the lamp, and then cure to depth. If you have a droplet, the surface will cure first, and then the rest of the dome will follow. The last area to cure would be against the substrate, so this leads us to the question:

How do you know when the adhesive is fully cured?

• Adhesion to the substrate is one way to evaluate the full cure
• A simple test is to try and use a tool to get underneath the droplet. If there is liquid at the interface, then it is not fully cured. You would need to increase either the intensity of the lamp, or increase the amount of time of exposure.
• Most applications have a minimum energy needed to achieve good cure. The energy, or Joules/cm^2, is a multiplication of the intensity (Watts/cm^2) x dose (seconds). You want to build a process around the total amount of Joules needed to reach full cure, so you can vary either the intensity or time needed to cure, and as long as you reach the minimum energy for a given lamp, then you should have a robust process.

The best way to determine if you have a robust process would be to:

• Run adhesion strength tests (bond laps or components together to see when full or maximum strength is achieved) or physical characterization (i.e. durometer, elongation, tensile, or modulus) at different conditions. When full strength is reached, additional energy (intensity or time) does not lead to an increase in properties.
• Compare the results in your process to the manufacturers data sheet. The manufacturers data sheet may indicate that the material will ultimately reach a specific durometer (i.e. A-40, D-60, D-90). Under most conditions, if you were plotting durometer/hardness for example, the hardness will build (incomplete cure) and then plateau (complete cure).
• Build in enough time to add a safety margin

It is important to have a radiometer as this device will tell you the intensity in Watts/cm^2 or mW/cm^2, which will be critical in the application.

The ability to cure on the surface can be affected by a phenomenon called oxygen inhibition. Some older adhesive technologies may be affected by oxygen during the cure process, which leaves a slightly tacky residue on the surface. The best way to overcome this issue is to start with a higher intensity, which would allow you to cure for a shorter time. New materials are being designed to overcome this issue, but lamp selection and bulb spectrum are important when developing a new process.

DYMAX has a new technology to help you define the parameters of a robust process, and ensure that during production the material is fully cured. See-Cure Technology is a patent-pending adhesive technology available in many DYMAX products that allows the adhesive to appear bright blue in the uncured state. Upon reaching full cure under a light source, the blue color will disappear, leaving a colorless clear adhesive in the bond line. It will only go clear when it has reached enough energy to be fully cured. This adhesive color-changing technology was designed to incorporate a safety margin before the color change happens, so is a great way to not only build a process, but have a quality inspection system within the adhesive to tell you if you have reached full cure.

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“Should we install ventilation for our ultraviolet (UV) light-curing process?”

Well it depends… We’ve addressed this question from an overall chemical-usage perspective since our answer looks at the “bigger picture”, not just the UV light-curing process.

When determining the ventilation requirements for a specific chemical or process, you must consider the following:

1. The size of the room. (In a larger room, you may be able to incorporate normal room ventilation to dilute chemical fumes or vapors below permissible exposure limits)
2. The volume of chemical being used. (Larger volumes of chemicals may pose greater health and safety concerns)
3. The physical and health hazards of the specific chemical. (More hazardous chemicals such as corrosives, solvents or flammable liquids may require venting. Always consult the material safety data sheet for information and special instructions)
4. The chemical state, vapor pressure, and vapor density (i.e. gas, liquid or solid) will help determine whether ventilation is needed, will work, and where to install it if it is needed.
5. Monitoring chemical levels in the workplace. (If levels are below permissible exposure limits, there may be no need to vent or exhaust) Additionally, if a ventilation system is put into place you must re-evaluate exposure levels to chemical fumes or vapors within the work area. This will determine if additional protection is required.
6. Atomization of the airborne chemical. (It is always recommended to vent or exhaust a chemical if you are spraying it)
7. How often the chemical is being used? (When combined with other factors, this could help drive a company’s decision whether to vent or not)
8. Cost. (this is always an important factor)

In the case of a UV light-curing process the answer also depends on the amount of heat generated by the UV light-curing system and the impact it has on the performance of the HVAC system in the area.

Ultimately, the decision to install a ventilation system is up to the user of the chemical after a thorough hazard/risk analysis (including workplace monitoring) is completed.

Curing Equipment, Safety Curing Equipment, Safety, Ventilation

“We are running two DYMAX Fusion UV conveyors to package electronics, but have found when our barcode scanners are powered on channels 6 and 11 (in the 2400 to 2500 MHZ radio spectrum), they are absolutely unusable while the conveyors are turned on. We seem to have a severe conflict. Any suggestions on how to fix this problem?”

Fusion UV lamps generate microwave radiation to energize a UV-emitting bulb. This energy is generated by magnetrons which operate at a fundamental frequency of 2.45Ghz. Wireless communication equipment that operates at the same frequency will likely not be able to handle the interference.

Fusion equipment is classified as non-consumer industrial, scientific, and medical (ISM) equipment, as defined in Federal Communications Commission (FCC) rules and regulations, Volume 47, Part 18, and the International Telecommunications Union (ITU). Fusion also complies with EN 55011 (CISPR-11, Group 2, Class A).

The FCC and ITU give ISM equipment legal priority over all other RF devices in this band.

Wireless devices operating in the ISM band are required to be able to accept RF interference from ISM equipment. If your wireless system is having problems working in the same environment as Fusion equipment, then it is operating at the same frequency but is unable to accept the interference as FCC regulations require.

Some of our customers have had success by repositioning transmitters, antennas, and access points within the facility by using directional antennas and by frequency hopping. The only foolproof way to solve the problem is to change the frequency of the wireless system to a frequency outside of the ISM band, 900Mhz or 5.8Mhz.

If you have not done so already we recommend that you contact your wireless equipment provider to see if they can offer you a solution.

If they are unable or unwilling to help, you can try the following:

Per the  example below, you can try to ‘shield‘ the lamps to reduce the amount of RF emitted into the work environment. You can do this by placing metal mesh screen (1/4″ maximum opening) around the lamp units, by sealing the seams around the lamps and light shield with a metal tape (aluminum tape works well). You might also consider wrapping the cables in metal tape since they radiate some RF as well (you only need to go down a foot or so, its mainly around the connectors).

Image provided by Fusion Systems

You could also install a ground strap from the lamp housing to earth ground using 1″ tinned-copper braided strap.

Should you decide to pursue this approach you need to make certain that the equipment is accessible for servicing and none of the airflows are restricted or otherwise compromised, which could lead to overheating and premature failure of some components.

Curing Equipment Conveyors, Curing Equipment, Radio Interference

Ultraviolet (UV) light is a form of electromagnetic energy invisible to humans. UV light falls below visible light on the electromagnetic spectrum so it does not trigger the natural defenses of the eyes, such as pupil dilation experienced with bright visible light.  For this reason, it is important to use personal protective equipment and not to disable any safety controls designed into the UV light source.  Many people often mistake the bright light coming off these systems as harmful, but in reality what they are seeing is harmless visible light. 

While all UV light has the potential to harm an employee when used carelessly, the shortwave UV energy (UV-C) poses the greatest risk to those using these light sources.  Most UV sources sold in the light-curable adhesive market incorporate the safer UV-A energy.  It is important to review the specifications for your own UV source before using it. 

Ultraviolet light exposure is the primary cause of melanoma.  Most cases of melanoma, however, are preventable by protecting yourself from effects of UV exposure. 

In industrial settings UV exposure is often misunderstood, but it is in these settings where manufacturers have the greatest control over a worker’s health and safety.

Industrial UV light-curing systems are often designed with safety or engineering controls built into them.  These controls, such as shielding, safety interlocks, intuitive design, and light-absorbing plastics, allow operators to use them without ever exposing themselves to harmful ultraviolet light. Teaching employees how to protect themselves from UV exposure and training them to work safely around these UV systems will minimize any potential risk of harm. 

A device called a radiometer can be used to demonstrate the amount of UV light an employee is exposed to while operating a UV curing system.   Taking the radiometer’s sensor and holding it near a person’s exposed skin while the unit is on, and then comparing this to what a person is exposed to outside on a sunny day, will show the individual is experiencing greater exposure from the sun.  It is important to match the radiometer to the UV wavelength being measured.

When used properly and in conjunction with personal protective equipment and training, industrial UV light sources are safe and easy to use.

Safety Curing Equipment, Safety

DYMAX recently had a webinar informing people how to save 30% on their assembly bonding process. We talked about real-life ways to optimize assembly processes with cure-on-demand UV/Visible light-curable adhesives. This archived webinar is now available for viewing.

A lot of questions were asked during the webinar session. I decided to post a few below. Some of you may have the same questions in mind.

Adhesives, Curing Equipment Adhesives, Benefits UV Curing, Curing Equipment, Epoxies, Potting Materials, Removing Adhesive, Savings, See-Cure, Spot Lamps, Webinar