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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“How should a substrate be prepared or treated prior to applying a light-curable material?”

Cleaning substrates prior to the application of a light-curable material is almost always a best practice. Removing contaminants allows for the best wetting of the application area and increases adhesion to substrates. When deciding on a cleaning process, it is important to consider both the contaminant and the substrate(s). Particulates can be removed with high-pressure air or brushing, while chemical contaminants require aqueous (water) or solvent-based cleaners. The aqueous or solvent-based cleaner should be selected such that it removes the contaminant without harming the 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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“We have recently taken on some medical tubing device-assembly work from another company but the information supplied seems to be missing some crucial points. We are having bond-strength issues when fixing a flexible PVC tube into the female port of an ABS connector.

The instruction we had was to use 100% cyclohexanone, but my feeling and internet research seems to show some form of cyclo/THF and pellet combination would perform better. Would you agree or is there a ready-made alternative available?”

In general, adding pellets (PVC) to the solvent mixture can help avoiding stress cracks and allows more flexibility in the gap design due to its gap-filling properties. So far, we have not come across a readily available mixture.

If you consider moving away from using solvent, I would suggest looking at light-curable adhesives. Dymax offers a variety of products suitable for bonding PVC to ABS. Medical grade adhesive Dymax 1161-M for instance provides strong bonds to a variety of substrates and cures within seconds upon exposure to UV and/or visible light.

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“What colors are Dymax adhesives available in? Can I add color to a Dymax adhesive?”

While a majority of Dymax light-curable materials are translucent or clear, we do also offer several colored materials, including blue, red, white, and even black formulations. Many of our SpeedMask^® masking resins are colored, making it easy to see where the resin has been applied and ensuring full coverage of the masked area.

Dymax can add color to an existing formulation but it should be noted that colorants may negatively affect cure speed and depth of cure. If you are interested in a tinted adhesive, a full evaluation should be conducted to verify that there is no detrimental effect on the bond line. Oil-based dyes can be added to many adhesives without a significant impact, but pigments may limit the depth of cure if the pigment concentration is too high. Please contact our Application Engineering team if you are interested in more information on the subject.

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“Common Dispensing Mistakes Made When Using Light-Curable Adhesives”

There are several mistakes that can be made when implementing dispensing systems for light-curable materials. Understanding these common pitfalls and taking the suggested precautions will help reduce problems when dispensing.

• Incompatible Materials – Dispensing system materials of construction should be compatible with your light-curable adhesive. Metal parts and fittings should only be 300-series stainless steel. Other metals can cause the adhesive to polymerize. Plastic materials that are compatible with Dymax light-curable adhesives include polyethylene, polypropylene, teflon, nylon, and acetals. Other plastics may be attacked by the resin.
• Transparent Fluid Lines – Black or opaque plastic fluid lines should be used to ensure that the adhesive is not exposed to ambient light, which may cause the adhesive to polymerize.
• Air Bubbles – Air bubbles may become trapped in fluid lines when an empty adhesive container is removed for replacement in a dispensing system. To avoid this problem, purge the fluid line after refilling or replacing the empty container. Maintaining only the line length necessary to transport the fluid from the reservoir to dispense point will facilitate the purging process.
• Pour-In Pressure Pot versus Drop-in Pressure Pot – For lower viscosity fluids (<500 cP) that naturally release air bubbles, either pour-in or drop-in pressure pots can be used. For fluids that do not release air bubbles naturally, drop-in pressure pots are recommended. Dymax recommends the use of a 10 gallon drop-in pressure pot for adhesives with viscosities up to 25,000 cP. For resins with viscosity >25,000, or where pressure exceeding 30 psi (0.2 MPa) is required for dispensing, ram-style pail pumps are recommended.
• Excessive Air Pressure – The application of excessive air pressure >30 psi (0.2 MPa) to pressure pots may cause air to dissolve into the adhesive. When this pressure is alleviated (either when the pressure pot is opened or the fluid is dispensed) this dissolved air may come out of the solution in the form of air bubbles that become trapped in the adhesive. To maintain appropriate pressure and prevent the formation of air bubbles in the adhesive, use larger ID fittings and tubing, minimize tubing length, fully open the dispense valve, and use a shorter and larger ID dispensing needle. If none of this is effective and pressure of 30 psi (0.2 MPa) or greater is still needed, a “ram-style pail pump” is recommended. This involves force being applied directly to the adhesive in the pail via a follower plate allowing for very high pressures without air. Ram-style pail pumps are recommended for resins with a viscosity of 25,000 cP or greater.
• Narrow and Long Fluid Lines – Generally, the shorter and wider the fluid line, the better. A fluid line diameter of 3/8″ (10 mm) is desirable. The longer and narrower the line, the more air pressure is required to transfer the fluid to the dispense valve. This can result in a slow flow rate and the need for high pressure to move the material with the unfortunate result of air-bubble formation.
• High-Shear Pumps and Valves – The use of pumps that produce shear, such as gear pumps, is not recommended with light-curable materials. Shear occurs when the adhesive is caught between two tightly fitting, moving metal parts, which can cause the adhesive to polymerize and clog the system. Simple pressure pots with pneumatic and ram-style pail pump systems are recommended.
• Positive Displacement Valves – Positive displacement valves should be tested for compatibility with light-curable materials prior to their incorporation into a dispense system. Contact Dymax for further guidance in selecting an appropriate valve for dispensing a particular adhesive.
• Using Vacuum to Remove Air Bubbles – A vacuum should not be used to remove air bubbles from a light-curable material. The use of a vacuum may remove constituents from the adhesive, altering performance and/or reducing its shelf life.
• Excessive Vacuum Suck-Back on Syringe Dispensers – Caution should be taken to apply only the amount of suck-back or vacuum pressure needed to prevent adhesive drip following dispensing. Excessive vacuum pressure may pull the plunger out of the syringe barrel or suck air into the syringe, creating bubbles.

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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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“We are looking for a medical-grade adhesive for bonding PEBAX (72D MED) tubing to latex nature rubber. We need shore hardness of a UV adhesive below 50D after cured. What is the best adhesive for this application? Also, which pre-surface treatment is suitable for PEBAX?

We also need a medical-grade adhesive for bonding PEBAX (72D MED) tubing to a colored ABS hub. Which fast setting adhesive is suitable for this?”

Latex nature rubber can typically be bonded with cyanoacrylates, also referred to as Super Glue. The Dymax medical grade 222 series cyanoacrylates might be a good place to start.

For bonding PEBAX I would suggest looking at Dymax 208-CTH-F, which is a medical grade, light-curable adhesive with shore D55. To combine PEBAX with latex or colored ABS, light-curable adhesives might not be suitable due to low adhesion to latex and problems with light curing through the colored ABS hub. Therefore, a cyanoacrylate is most likely the adhesive of choice.

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“I’m looking for a UV-curable adhesive to bond polyolefin surfaces (cyclic olefin polymer), 100 cm² max size. The surfaces could be pre-treated (primer, plasma). What adhesive/primer do you recommend?”

Bonding to COC is very difficult due to its low surface energy. Surface treatment has not shown big improvements. Since the demand of bonding COC is growing, adhesive suppliers are working on new adhesives that can handle such difficult surfaces.

You can contact Dymax with your specific inquiry to see if they have new products in their pipeline that fit your needs.

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“Considerations for Selecting a Dome Coating”

With hundreds of dome coating options available on the market, selecting the right dome coating for your application can seem like a daunting task. When selecting the best coating for your application, it is important to consider five main criteria: viscosity, substrate flexibility, substrate adhesion, hardness, and environmental durability.

• Viscosity. How thick does the coating need to be? Decorative coatings are clear and usually thin. Dome coatings have curved domes, which optically magnify and enhance the appearance of a label. Higher-viscosity, thicker resins generally produce taller domes.
• Substrate Flexibility. Flexible substrates, like thin polyester labels, paper, or soft plastics, may require careful selection of coating and enhanced curing equipment. Flexible substrates may bow or warp when thick coatings cure. Soft coatings shrink less and are designed to reduce or eliminate warpage during cure. Rigid substrates don’t bend when stressed, so they can be coated with all of the products.
• Substrate Adhesion. Individual formulations may have excellent adhesion to some inks (or substrates) and little adhesion to others. The right coating should have good adhesion. Adhesion should be tested after product lifetime testing, as well as after cure. Inks and substrates from second source suppliers may improve or worsen adhesion. Some plastics require surface treatment to enhance adhesion.
• Hardness. Both soft and hard coatings can be scratch resistant. Hard coatings resist scratching because of their hardness. Soft coatings resist scratching because they momentarily dent and then spring back when the scratching object is withdrawn. Hard coatings are measured on the D-hardness scale. Soft coatings are measured on the hardness scale. On both scales, higher numbers imply harder coatings.
• Environmental Durability. Coatings should be lifetime tested on your product. Some properties, like UV weatherability, provide a relative guideline to distinguish endurance of clarity and durability among the available products offered.

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