A radiometer is an important tool in the light-curing process. Below are a few of the benefits of using a radiometer to monitor your light-curing process.

Benefit 1: Maintain a Reliable Light-Curing Process

UV-curing bulbs, lightguides, and reflectors can deteriorate over time, causing less UV energy to reach the cure surface and result in incomplete cures. As the UV energy decreases, adjustments in the process must be made to maintain product quality. It can be difficult to determine when the UV energy is decreasing. UV wavelengths of light are too short to seen visually with just one’s eyes, requiring the use of a radiometer to monitor intensity. Radiometers measure the intensity and/or energy associated with light of specified wavelengths. A radiometer can measure whether a light-curing system is providing intensity above the minimum or “bulb change” intensity. A radiometer is to a light-curing process what a thermometer is to an oven-curing process.

Benefit 2: Provide a Safer Work Environment

A radiometer can also be used to determine if any stray UV light is reaching operators or bystanders. This can help insure a safer, more worker-friendly light-curing process. Dymax’s ACCU-CAL™ radiometers can measure the intensity of stray or reflected energy to as little as
1 mW/cm². It is recommended that workers do not exceed 1 mW/cm² of UVA exposure.

Benefit 3: Measure Transmission Rates Through Substrates

A radiometer can be used to measure the transmission rates of various wavelengths through substrates that sometimes absorb various frequencies of energy. To assure an effective curing process it is critical to measure the light intensity reaching the cure site below any intervening substrate.

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“Will exposing areas of a PCB board that are not covered by an adhesive or conformal coating to UV curing energy damage the board in anyway?”

Any frequency of energy that gets impinged onto a substrate has two options: it can get reflected, in which case it is harmless, or it can get absorbed, in which case it will turn into heat. Some light-curing equipment, like the Dymax BlueWave^® spot lamps, have an intensity adjustment feature which allows for the ability to reduce unneeded energy. Adjusting the intensity reduces any excess energy that may turn into heat and damage temperature-sensitive substrates.

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“What is ozone and how much ozone do Dymax flood lamps emit during operation?”

Ozone can be described as a gaseous form of oxygen which may be formed when air interacts with certain frequencies of ultraviolet light. It has a characteristic pungent odor which some people can detect in concentrations as low as several parts per hundred million.

Short-wave ultraviolet light (below 200 nanometers) can interact with air to create ozone. Low-pressure mercury and metal-halide discharge lamps emit energy in this region and therefore their operation does create ozone. With increased mercury pressure in the lamps, the shorter wavelength emissions are self-absorbed in the discharge and not emitted. All light sources produced by Dymax are supplied with lamps which operate in the higher pressure regions, which do not allow the shorter wavelengths to be emitted and do not emit ozone during operation. For more information about this subject, please contact a Dymax Application Engineer.

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“Dymax curing equipment can be outfitted with several different types of bulbs. How do I choose the right bulb for my application?”

Metal halide bulbs (lamps) come standard in Dymax UV light-curing systems to match the cure chemistry of most high-performance UV-curable acrylate and cationic epoxy adhesives and coatings. Other bulbs offered include Mercury bulbs and visible indium bulbs. For curing UV inks and some (usually very thin layer) UV coatings, Mercury bulbs provide better surface cures faster. For applications where visible light is predominantly required for curing bonds between UV-blocking plastics, visible indium or “V” bulbs are best. The best approach to selecting a bulb is to speak with a Dymax Application Engineer. With a little information about your application, an Application Engineer will be able to select the most efficient bulb for your application.

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“I’m looking for a UV-fixating adhesive to bond a steel cannula onto a polypropylene hub. The hub will be plasma or corona treated prior to gluing to increase the bonding performance and the hub will have annular rings as well. However, since the material is opaque I assume the adhesive has to have a secondary curing mechanism too? In addition to the above, the fixation time for bonding needs to be <10 seconds. Can you please advise which of your adhesives might be suitable?"

On occasion full cure via UV/Visible light can be achieved with opaque PP hubs.

Depending on the color and thickness of the polypropylene, some light from the side can transmit through the plastic and polymerize the UV/VIS adhesive. The largest area of the adhesive is usually cured from the top. However, due to limitations in depth of cure of most UV/VIS adhesives, I would recommend keeping the length/depth of the bond joint to a minimum and mold the annular rings near the top of the hub. Suitable UV/Visible light-curable products are DYMAX 1180-M-SV04 and 1-20777, which are medium viscosity and won’t flow deep inside the hub. Low-viscosity products such as DYMAX 1161-M or 1162-M can be used if the design of the bond joint prevents these materials from flowing too deep inside the hub.

In order to achieve short curing times I would recommend high-intensity UV lamps such as Fusion F300, which is a focused beam lamp or DYMAX BlueWave^® 200, which is a spot-lamp that can be equipped with multi-wand lightguides.

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“About ten years ago I worked for a start-up electronics manufacturer. In the lab we had a machine that dispensed UV-curable epoxy and had a UV spot lamp attached to the dispenser. It was all controlled by a foot switch for both adhesive dispensing and light control. We used it for numerous tasks such as bonding modification wires to the board as well as bonding components to the board. Does DYMAX offer anything like this or do you know of anyone who does?”

This unit was called the DYMAX PC-3D, with a dispensing system on one side, and a UV-curing system on the other. While there might be a few available units floating around eBay, these units are not manufactured anymore. At this point, they are stand-alone units. DYMAX can offer the individual lamps and air/pressure dispensing systems separately, but we do not have a combination unit like the PC-3D available anymore. I am not aware of anyone on the market making a unit like this currently. Sorry!

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"I am trying to determine the proper cure time for the Loctite 3106 using a Dymax PC-5 Light Welder. Can you help?"

To determine the proper cure time of any light-curable adhesive when exposed to light from any light source, there are a couple of different approaches that can help. The greatest tool is a radiometer, which will tell you how much intensity you have at the bond line. The PC-5 is an older model flood lamp, with an intensity of 50-150 mW/cm² over a 5" x 5" area. The different approaches depend on how you are using the adhesive. If you are using the adhesive between two substrates in a bond-line thickness of 0.002-0.006 inches, then measuring the fixture time should be sufficient. Per the Loctite TDS, fixture time at this intensity should be <5 seconds. If you are potting a deeper section, then depth of cure is important, and you can reach a depth of 2 mm in approx 12 seconds. The Loctite TDS plots the depth of cure at an intensity of 50 mW/cm². If the adhesive bond line has some squeeze out, or has a surface exposed to air, then a tack-free surface cure may be important. Tack-free time is the point when the adhesive is sufficiently cured that you will not get smearing or residue transfer onto a gloved finger.

With any of the three described situations, measuring this yourself is the best way to figure out the proper cure time, whether looking at fixture time, depth of cure, or tack free time. Set the bond line up at the lowest intensity you can use – say 50 mW/cm². Do this by increasing the distance away from the lamp until the radiometer measures 50 mW/cm². (You will want to manufacture your parts at a higher intensity to start, and within a window of intensity and time. This will control your process.) After setting a constant intensity, cure the adhesive for different times. You will see the tensile strength, burst pressure, tack-free time, depth of cure, durometer, or other datapoint climb to a max value and then plateau. Once you have identified the start of the plateau, add a safety margin, and you have the foundation for your process. You can also set the time constant, vary the intensity, and record the same datapoints. You want to define your process by knowing the minimum and maximum intensity and time needed to cure the adhesive.

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"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