Written by Drew Richards
Marketing & Customer Experience Manager
UV curable adhesives offer 100% solid material, near-instant curing times, and immediate use or packaging directly from the assembly line. While significant, these features can only be fully appreciated compared to alternative curing methods.
For example, compare the 100% solid material with low-viscosity solvent-based coatings. Only 5% might remain after the solvent has completely evaporated. Up to 95% of the chemical solvent is off-gassed into the air.
As a result, the Environmental Protection Agency has prioritized reducing the use of solvent-based materials. U.S. manufacturing has also shifted away from these adhesives to decrease the volatile organic compounds created when the solvent evaporates.
With up to 95% material loss, 100% solid materials such as UV curable products typically offer more savings than solvent-based products. Consider a company purchasing 1,000 gallons of low-viscosity solvent-based materials. With a material that’s 5% solid, they’ll receive 50 gallons of solid material.
- 1,000 gallons * 0.05 solid material = 50 gallons yield of residual material to coat or adhere
If the solvent-based adhesive costs $80 per gallon, the invoice will be $80,000.00. When evaluated after evaporation, the cost is higher.
- $80,000 / 50 gallons = $1,600 per solid gallon
If the 100% solid material costs 10 times as much ($800 per gallon), the solid material gets the same 50 gallons of material coverage.
- $800 * 50 gallons = $40,000
- $80,000 cost for solvent materials – $40,000 cost for solid materials = $40,000 in savings
- The user saves 50% or $40,000
The savings continue. The user who switches saves logistically by transporting 50 instead of 1,000 gallons. The cost of filters for solvent-based material in the dispensing system and the labor are removed.
Most applications also require time to let the solvent evaporate. This necessitates a batch process and often includes a large amount of floor space for the drying racks. Sometimes heat is used to reduce the drying time, so switching also saves oven costs, related energy costs, and maintenance. The emission removal process and equipment (and any associated EPA penalties) are removed.
The UV advantage
To activate UV cure products, photo-initiators in the adhesive formula must be triggered by a UV light of the correct wavelength. For consistent results, the intensity of the light must be uniform and penetrate the adhesive materials to ensure sub-surface curing. There’s a science to distributing UV lights to ensure optimal conditions.
LED lights create spherical radiance zones, which must overlap and ensure consistent coverage. Getting too close or intense with the UV light leads to bubbling or burning in the adhesive material, requiring a goldilocks approach to each application. If more distance is needed, the UVs can be modified with a lens to focus the light into a concentrated beam. This extends the practical curing distance and improves efficiency.
For ammunition sealants, the sealant is exposed in a small area around the cartridge case mouth and primer, so focusing the light with a lens is useful. Six to seven seconds of UV exposure is required, set up in an array along the conveyor route at about 1.5 inches from the exposed sealant. The length of the array depends on the speed of the conveyor — the faster it is, the longer the array should be to ensure the correct exposure time.
Photo-initiators can also be used in multi-cure formulas to address specific manufacturing challenges. For example, in some electric motor manufacturing operations, an adhesive can bond magnets to the motor housing. The specifications call for enough material to create some squeeze-out.
Using a multi-cure formula, the adhesive under the magnet can be activated and cured using a pre-applied chemical activator or anaerobic curing process. The squeeze-out material can be rendered inert by hitting it with UV light. The near-instant speed of the UV cure process makes it ideal for this process, solving the problem with minimal time delay.
The high speed of UV curing allows for UV tacking, which is when the material is briefly exposed to UV light to alter the physical properties without full curing. UV tacking is employed for sealant dispensed as a bead around the outer diameter of a circular oil shaft seal.
For instance, one manufacturer had problems when a robotic arm moved parts from the dispensing station to the curing station. The force of the movement caused deformation and migration of the bead. The dispensing station had to be cleared to make room for the next part, so completely curing the bead in the same station did not work.
By UV tacking, the cure material (UV FOG, in this case) was fixed in place with only a second or two of UV exposure. The tacking raised the bead viscosity so it would not deform or migrate when transferred to the next station.
Tacking represents the unique ability of UV materials to cure to a set amount. The degree to which the material is cured can be directly controlled and manipulated through the control of UV light exposure. This allows materials to be cured to tacky or partially solid states.
Until the material is exposed to UV light, there’s an indefinite working life, allowing an operator to make fine adjustments.
Although the UV curing process typically costs more to implement with a conveyor and UV light arrays, this is partially offset by a simpler dispensing system. Most UV cure materials are one-part materials with the role of the second part (the activator) played by UV light. This means the dispensing system follows a single track with one reservoir, meter, and valve. There’s no need for ratio controls or static mixers and little chance of the material curing in the system.
These benefits make UV curing an excellent choice for countless industries. The transition from solvent-based adhesives to UV and other curing methods makes this industry likely to grow as manufacturing technologies upscale.