Why Does Epoxy Resin Turn Yellow?
Photo by Lisa Fotios
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July 21, 2024
How to Fix a Tacky Epoxy Surface After Curing
You mixed the epoxy carefully, waited the full cure time, and the surface is still sticky. A tacky epoxy surface is a common processing fault, not a ruined part. Understanding why it happens tells you whether to recoat, sand, or scrap, and how to keep it from recurring. Why epoxy cures tacky Off-ratio mixing: epoxy cures by a stoichiometric reaction between resin and hardener. Even a small error, especially too much hardener, leaves unreacted material that never hardens. Volumetric and weight ratios are not interchangeable; use the one the data sheet specifies. Under-mixing: resin and hardener that are not blended thoroughly, including the material clinging to the sides and bottom of the cup, leave streaks and pockets of uncured epoxy. Low temperature: most epoxies need a substrate and ambient temperature above roughly 18 to 21°C to cure fully. Below that, the reaction slows or stalls, leaving a soft or tacky film. High humidity and amine blush: some amine-cured epoxies react with atmospheric moisture and carbon dioxide to form a greasy carbamate layer on the surface, which feels tacky or waxy even when the bulk is hard. Insufficient cure time: thin films and cool conditions can extend cure well beyond the data sheet's nominal figure. First, identify the cause Press a gloved finger into the surface. If it dents and stays soft throughout, the mix was likely off-ratio or under-mixed and the whole layer is compromised. If only a thin surface film is greasy over a hard mass beneath, you are probably looking at amine blush, which is repairable without removing material. Fixing amine blush Blush is water-soluble. Wash the surface with warm water and a non-abrasive pad, dry it fully, then wipe with isopropyl alcohol. The tackiness should disappear, exposing hard epoxy underneath. Once clean and dry, the surface can be top-coated or finished normally. Fixing an under-cured layer If the epoxy is soft through its thickness, it will not harden further on its own. Two options: Recoat: scrape or wipe off as much uncured material as possible with isopropyl alcohol and a lint-free cloth, then apply a fresh, correctly measured and mixed coat over the sound surface and cure it in a warm space Remove and restart: for structural parts or thick pours, remove the bad layer entirely rather than trapping soft epoxy under a new coat Fixing a thin tacky film over sound epoxy Sand lightly with 120 to 220 grit until the stickiness is gone, staying well within the cured layer. Wipe off the dust with a damp cloth, let it dry, and apply a thin clear top-coat if a finished surface is needed. Email Us with your epoxy system and conditions if a tacky surface keeps recurring. Preventing it next time Measure with calibrated mixing cups or a graduated dispenser, not by eye, and follow the specified ratio by weight or by volume as stated Mix for the full recommended time and scrape the container sides and bottom, then transfer to a second cup and mix…
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July 19, 2024
Electronics Adhesives / Encapsulants / Eye Protection / Flood Lamps / UV Adhesives / UV Curing Equipments / UV LED Equipments / UV LED Spot Equipments
UV Cure Potting Compounds: A Guide to Precision Assembly
Potting protects delicate electronics by encasing them in a solid resin, but conventional epoxy potting can tie up a part for hours while it cures. UV cure potting compounds gel in seconds under ultraviolet light, letting a line pot, inspect, and pack in one continuous flow instead of parking trays of work in an oven. How UV Potting Differs A UV cure potting compound is a single-component resin that stays liquid until it absorbs enough ultraviolet energy, then crosslinks rapidly. Compared with two-part epoxy potting, it removes the mixing step, the pot-life clock, and the long thermal cure. Many formulations are also water-clear after cure, so components stay visible for inspection and rework decisions. What Potting Provides Mechanical protection: A rigid or semi-rigid shell resists vibration, shock, and handling damage. Environmental sealing: The cured mass blocks moisture, dust, and airborne contaminants. Electrical insulation: Good dielectric strength prevents tracking and short circuits between closely spaced conductors. Strain relief: Encapsulation supports wire terminations and component leads against fatigue. The Shadow-Cure Limitation UV energy only reaches what the light can see. In a potted assembly, resin under a component or deep in a cavity sits in shadow and will not cure by UV alone. Formulations address this with a secondary cure mechanism, usually heat or ambient moisture, that finishes the shadowed resin after the UV pass fixes the exposed surface. Confirm which mechanism a compound uses before designing the process around it. Selecting a UV Potting Compound Viscosity: Low viscosity flows around fine-pitch components and self-levels; higher viscosity stays put on a vertical or open edge. Match it to the dispense equipment and the cavity geometry. Clarity: Choose a clear grade where post-pot inspection matters; pigmented grades hide the assembly but improve UV blocking above the potted layer. Cure depth and secondary cure: Verify the compound can through-cure your deepest section, with a heat or moisture stage for shadowed resin. Thermal expansion: A large coefficient of thermal expansion mismatch between the cured resin and the substrate drives stress on temperature cycling; a lower-modulus grade absorbs it. Service temperature: Confirm the cured resin holds properties across the assembly's operating range. Shrinkage and Stress on Components All acrylate chemistry shrinks as it crosslinks, typically a few percent by volume. In a potted assembly that shrinkage pulls on the components and the cavity walls. On fine wire bonds, unsupported crystals, or pressure-sensitive sensors, the load can shift calibration or cause intermittent failures that only appear after temperature cycling. Lower-shrinkage grades, a lower-modulus cured resin, or a staged cure that lets the resin relax all reduce the effect. Where a component is truly stress-sensitive, a soft silicone gel barrier under a rigid pot is the conservative design. Getting the Dose Into the Depth A thin coating cures with a modest dose; a 5 mm pot needs far more, because the resin near the surface absorbs UV and shades the resin below it. Pigmented or filled grades make this worse. Practical steps: use a grade rated for your…
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July 18, 2024
UV Curing Conveyor Systems for High-Volume Production
High-volume lines cannot afford a curing step that stops the flow. A UV curing conveyor moves parts continuously under one or more lamp heads at a regulated speed, so the cure keeps pace with dispensing and assembly instead of becoming the bottleneck. Configuring the Conveyor A conveyor system is defined by a handful of adjustable parameters: Belt width and length: Width accommodates the widest part or fixture; length sets how many lamp heads fit and how much dwell time is available. Lamp head count: One head for a single-pass cure, two or more for staged curing or to double the dose at speed. Adjustable lamp height: Raising or lowering the head, commonly over a range of about 40–125 mm, trims irradiance at the part surface and clears tall fixtures. Variable belt speed: A regulated drive spanning roughly 0.5–6 m/min sets the exposure time under each head. Choosing the Lamp Head The conveyor is a transport; the lamp head does the curing. Mercury arc heads emit a broadband spectrum, cure deep and pigmented sections well, and need exhaust for ozone. UV LED heads emit a narrow band at 365, 385, or 405 nm, run cool, switch instantly, and last far longer between replacements. A platform that accepts both, such as Incure's CDM UV conveyor, lets a line change lamp technology without replacing the whole system. Bench comparisons of F-Series arc lamps and L-Series LED lamps help size the head before it goes on the belt. Dose at Line Speed The UV dose a coating absorbs equals lamp irradiance in mW/cm² multiplied by the exposure time, and exposure time is the illuminated window length divided by belt speed. To hold dose constant when speeding the line up, either add a lamp head, lengthen the window, or raise irradiance by lowering the head. Verify the result with a band-matched radiometer riding through on the belt. Single Pass or Multiple Heads A single lamp head over a short window forces a slow belt to give the adhesive enough exposure. Adding a second head, or lengthening the illuminated zone, lets the belt run faster for the same total dose. The arithmetic is direct: two identical heads over a combined 300 mm window at 6 m/min deliver the same dose as one head over 150 mm at 3 m/min, at double the line rate. Staging can also help chemistry, with a lower-intensity first head to gel the surface and a full-intensity second head to complete the cure. Lamp Height and Irradiance Raising or lowering the head changes irradiance at the part surface. Lowering it boosts dose without slowing the belt, but reduces clearance for tall fixtures and can push a heat-sensitive part past its limit under an arc head. Set the height to the lowest position that still clears the tallest part with margin, then trim belt speed to fine-tune dose. Part Presentation Consistent results need consistent part orientation and spacing on the belt. Parts that tumble, overlap, or shadow each other receive uneven dose. Use…
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June 11, 2024
Incure S20 UV Arc Spot Lamp for High-Intensity Industrial Curing
Fast lines and thick, pigmented adhesives both demand high ultraviolet intensity at the bond. The Incure S20 is a mercury arc spot curing lamp that delivers more than 21 W/cm² at the light guide tip across a broad spectrum, giving industrial processes the energy to cure difficult chemistry in short cycle times. What the S20 Is The S20 is a compact arc spot lamp that focuses a broadband output, roughly 275–650 nm, into a light guide that carries the energy to the work. The wide spectrum reaches photoinitiators that narrow-band LED sources miss, and an adjustable intensity control lets an operator trim output from full power down to a level that suits heat-sensitive substrates. Why Broadband Intensity Helps Pigmented and filled adhesives: Colorants and fillers absorb and scatter UV. Broadband high intensity drives enough energy through to cure the full depth. Thick sections: A deep bond line needs energy delivered past the surface layer; peak intensity extends the effective cure depth. Shadowed geometry: Higher tip irradiance tolerates the loss from an oblique or partly obstructed light path. Short cycle times: More irradiance means less exposure time to reach the same dose. Dose and the Light Guide The energy the adhesive absorbs is tip irradiance in W/cm² multiplied by exposure seconds. Tip irradiance depends on guide diameter, length, working distance, and guide age. Because the S20 runs at high intensity, guide condition matters: a discolored or damaged guide can drop delivered energy well below the recipe target. Fix the working distance with a holder and verify tip irradiance with a band-matched radiometer on a schedule. Selecting and Operating the S20 Guide diameter: Larger cores carry more total energy; smaller cores concentrate it on tiny features. Intensity setting: Run only as hot as the substrate tolerates to limit heat and fuming. Ventilation: High-intensity arc output can warm the work zone; provide exhaust where needed. Bulb life: Replace the arc bulb at its rated hours; output and spectrum both shift near end of life. Operator protection: UV-blocking eyewear and a contained light path are mandatory. Cure Depth in Pigmented and Filled Adhesives Depth of cure falls as the adhesive's opacity rises. A clear adhesive may through-cure several millimeters in one exposure; the same chemistry loaded with pigment or filler may cure only a fraction of that. Broadband arc output helps because the longer wavelengths in the spectrum penetrate further than the short ones that cure the surface. Even so, verify depth on a representative sample: cure a test bond, section it, and check that the resin at the far interface has hardened, not just the surface skin. Managing the Exotherm High intensity into a thick bond can drive an exotherm that spikes the local temperature. On sensitive substrates or large masses this can distort the part or stress the joint. Where it shows up, step the exposure, a lower-intensity pre-gel followed by full-intensity cure, or reduce the intensity setting and lengthen the exposure to reach the same dose at a lower peak temperature.…
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June 11, 2024
High-Intensity UV Spot Lamps: Compact Power for Precise Curing
When a bond is small, buried, or surrounded by parts that must not see ultraviolet light, a spot lamp is the right tool. A high-intensity UV spot lamp concentrates energy through a light guide onto a point a few millimeters across, curing adhesives in seconds without flooding the whole assembly. Arc and LED Spot Lamps Two technologies dominate spot curing: Mercury arc spot lamps produce a broadband output from roughly 240–450 nm at very high intensity at the guide tip. The wide spectrum cures pigmented and shadowed bonds well. The trade-offs are a warm-up period, a bulb life on the order of 2,000 hours, and consumable reflectors and filters. UV LED spot lamps emit a narrow band at 365, 385, or 405 nm, switch on instantly, run cool, and last beyond 20,000 hours. They are the better fit where the chemistry matches an available band and heat must be kept low. Incure offers both: the S20 UV arc spot lamp for broadband high intensity and the L9000 UV LED spot lamp for narrow-band, low-heat curing. Dose at the Guide Tip The energy an adhesive absorbs equals irradiance at the guide tip in mW/cm² multiplied by exposure time. Tip irradiance depends on guide diameter, guide length, working distance, and guide condition. A short, large-core guide held close delivers the highest energy; a long, thin guide trades intensity for reach. Fix the tip-to-part gap with a holder so the dose repeats. Selecting a Spot Lamp Spectrum or wavelength: Broadband arc for pigmented or shadowed bonds; matched LED band for clear or thin-section work. Intensity: Enough tip irradiance to cure within the cycle time, with headroom for source aging. Guide count: Single guide for one point; multi-guide heads for several cure points on one part. Working distance and access: The guide must reach the bond without fouling adjacent parts. Consumables: For arc lamps, factor in bulb, reflector, and filter replacement intervals. Total Cost of an Arc Spot Lamp An arc spot lamp's running cost is more than the bulb. Over a year of single-shift use, plan for two or more bulb changes, periodic reflector replacement, and light-guide replacement as transmission falls. Each bulb change also needs a re-verification of tip irradiance and often a small recipe adjustment. An LED spot lamp removes the bulb and reflector consumables entirely and shifts the only wear item to the guide, which is common to both technologies. Where the chemistry allows an LED band, that difference compounds over the equipment life. Matching Guide Diameter to the Feature Guides commonly range from about 3 mm to 12 mm core diameter. A 3 mm guide concentrates energy onto a single small joint and fits into crowded assemblies; an 8 mm or larger guide covers a wider fillet or a cluster of close pins in one exposure but needs more standoff to avoid a hot center with a weak edge. Choose the smallest guide that covers the bond in one shot. Curing in Shadowed Geometry When part of the bond…
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June 11, 2024
Incure L9000 Compact UV LED Spot Curing Lamp for Precision Curing
Some cures need a small, intense pool of ultraviolet light aimed at one feature, not a flood field. The Incure L9000 is a compact UV LED spot curing lamp that drives up to four light guides, each able to run a different wavelength, so a single controller can serve several precise curing points at once. What the L9000 Is The L9000 delivers concentrated UV output through a fiber or liquid light guide that carries the light to the work. It supports 365, 385, and 405 nm LED sources, connects up to four guides, and lets each channel be triggered independently. LED emitters give it instant on operation, low radiant heat, and a service life beyond 20,000 hours, which removes the frequent bulb changes that arc spot lamps require. Why Spot Curing Beats Flooding for Small Features Targeted energy: The dose goes where the bond is, not across the whole assembly, so adjacent components are not exposed. Multiple points, one controller: Four guides can cure four joints on one part, or feed four stations, each on its own recipe. Wavelength per channel: A structural adhesive on one guide can run 365 nm while a clear coating on another runs 405 nm. Low heat: Narrow-band LED output avoids the infrared load that can fume solvent or distort thin plastic. Dose at the Guide Tip The energy the adhesive absorbs is irradiance at the guide tip in mW/cm² multiplied by exposure time. Irradiance depends on guide diameter, length, working distance, and guide condition. Fix the tip-to-part distance with a holder, and re-measure irradiance periodically, because light guides lose transmission as they age and yellow. Selecting an L9000 Configuration Wavelength: Identify the band each material's photoinitiator absorbs. Number of guides: One to four, based on how many cure points or stations the lamp must serve. Guide type and diameter: Larger cores carry more energy; smaller cores concentrate it on tiny features. Control: Independent channel triggering for sequenced or simultaneous curing. Fixturing: A rigid guide holder to keep working distance constant. Sequencing Four Channels Independent channel control opens two useful modes. In simultaneous mode, all four guides fire together to cure four identical joints on one part in a single station cycle. In sequential mode, the controller fires each channel in turn as a robot or indexer presents successive features, which suits a part with cure points that cannot all be reached at once. Mixing the two, two channels fixed on a part and two feeding a second station, lets one lamp serve more throughput than its guide count suggests. Guide Selection Trade-offs A larger-core guide carries more total energy and tolerates a slightly longer working distance, which helps on recessed features. A smaller-core guide concentrates energy on a sub-millimeter target and fits into tight spaces, at the cost of lower total power and less reach. Guide length matters too: every additional 500 mm of guide costs transmission, so specify the shortest guide that reaches the work. Heat at the Bond Even though LED spot…
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June 11, 2024
High-Power UV LED Curing for Industrial Use
An industrial curing station runs thousands of cycles a day, integrates with a line controller, and cannot stop for lamp changes mid-shift. High-power UV LED curing equipment is suited to that duty because it switches instantly, holds a stable output over tens of thousands of hours, and exposes a defined field to a repeatable dose every cycle. What "Industrial Duty" Requires Continuous operation: The head must be rated for back-to-back cycles with active cooling, not intermittent bench use. Line integration: PLC or line-controller I/O lets the cure step handshake with upstream dispensing and downstream inspection. Stable, documented output: Cure becomes a process parameter that can be logged and audited, not an operator judgment. Predictable service intervals: Gradual, even output decline means lamp replacement is scheduled, not reactive. Dose Control on an Automated Line The energy a coating absorbs is its UV dose: irradiance in mW/cm² multiplied by exposure time. On an automated station the exposure time is fixed by cycle time, so the lamp must supply enough irradiance to reach the target dose within that window, with headroom for output decline over the lamp's life. Build the recipe from the material datasheet, verify it with a band-matched radiometer at the part plane, and confirm cure with hardness or pull testing. Specifying Industrial LED Curing Field size: Cover the full cured area or batch fixture in one exposure, within roughly 10–15 percent edge falloff. Wavelength: Match the photoinitiator, commonly 365, 385, or 405 nm. Irradiance headroom: Above the target dose divided by cycle-time exposure. Cooling: Rated for the station's duty cycle and ambient temperature. Control interface: Footswitch for manual cells, PLC handshake for automated lines. Integration form factor: Fixed mount over a conveyor or inside a chamber. Incure's L-Series UV LED flood lamps are built for fixed-station duty, the CDM UV conveyor carries LED heads over a moving belt, and B/C-Series cure chambers enclose the process for operator safety and dose consistency. Designing the Cure Station Into the Line A cure step that stalls the line is worse than a slow one. Size the station so its exposure time fits inside the line's takt time with margin, and give it a bypass or buffer so a lamp fault does not immediately stop upstream work. Where cycle time is tight, two lamp heads in series each delivering half the dose let the belt run twice as fast as a single head would allow. Fault Detection and Response An industrial cure station should detect and report at least three conditions: measured output below the dose threshold, over-temperature at the head, and a missing part-present signal during a commanded exposure. Tie the first to a line stop or a reject-diverter so under-cured parts never reach assembly. Log every fault with a timestamp so recurring problems, a marginal cooling fan or a lamp nearing end of life, show up as a pattern rather than a surprise. Maintenance Access Position the head so the emitting window can be wiped and the array inspected without removing guarding…
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June 11, 2024
UV LED Flood Lamps: Versatile Curing Solutions
A single production line often runs more than one light-curable material: a fast surface coating, a structural adhesive, a gasket resin. A UV LED flood lamp earns its place when it can cure that range reliably, which comes down to choosing the right wavelength and having enough irradiance headroom for the slowest chemistry. Wavelength Is the First Decision UV LED heads are built for a narrow band, typically centered at 365, 385, or 405 nm. The choice is driven by the photoinitiator in the material: 365 nm penetrates pigmented and filled chemistries well and is common for structural adhesives and thicker sections. 385 nm is a middle ground used across many general-purpose coatings and adhesives. 405 nm suits clear coatings and resins formulated for visible-light initiators and is gentler on light-sensitive substrates. Running a material under the wrong band gives slow cure, surface tack, or no cure at all. Where a line runs mixed chemistries, standardize the materials around one band or plan for interchangeable heads. Irradiance and Dose The UV dose a coating needs is irradiance in mW/cm² multiplied by exposure seconds. Higher irradiance shortens the exposure, but only helps if the uniform field covers the whole cured area. Size the lamp so the slowest material on the line still reaches its dose within the cycle time, then faster materials simply use a shorter exposure recipe. Selecting a Versatile Flood Lamp Field size and uniformity: Cover the largest bond or panel within about 10–15 percent edge falloff. Power headroom: Choose irradiance above the slowest chemistry's requirement so an aging lamp still qualifies. Working distance: Fix it with a jig, since irradiance drops sharply as the head moves away. Recipe storage: A head that stores per-material exposure settings prevents changeover errors. Integration: Confirm the head mounts over a conveyor or in a chamber as volume grows. Incure's L-Series UV LED flood lamps are offered across wavelengths and field sizes, and the F-Series arc flood lamps remain an option where a broadband spectrum is genuinely needed. Standardizing a Mixed-Material Line The cleanest way to run several chemistries under one lamp is to standardize the materials around a single wavelength band during material selection, before the equipment is bought. Ask each adhesive and coating supplier for a grade whose photoinitiator absorbs at 385 nm, for example, and one lamp covers all of them. Where that is not possible, plan for interchangeable heads or a dual-band lamp, and document which recipe and head pairing goes with each part number so a changeover cannot apply the wrong combination. Reading a Photoinitiator Absorption Curve A datasheet often lists a recommended wavelength, but the absorption curve tells the fuller story. A material may cure acceptably across a range, with a peak where it cures in the shortest time and tails where it needs much more dose. Matching the lamp to the peak gives the shortest exposure and the widest process margin. Running at a tail wavelength wastes energy and leaves little room for output decline before…
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June 11, 2024
UV LED Flood Lamps for Large-Scale Curing Applications
Curing a large coated panel or several parts at once puts a hard requirement on the lamp: uniform ultraviolet energy across the entire field, not just a bright center. Large-format UV LED flood lamps are built to hold irradiance steady edge to edge so that every part in the field reaches the same cure state. The Uniformity Problem at Scale Irradiance from any lamp falls off toward the edges of its field and drops with distance from the emitter. Over a small field the falloff is minor. Over a large field it can leave the perimeter under-dosed while the center is fully cured or slightly over-cured. A large-format LED array manages this with denser edge emitters and a working-distance specification that keeps edge-to-center variation within roughly 10–15 percent. Why LED Suits Large Fields Even, stable output: Solid-state emitters do not develop the hot spots and spectral drift that aging arc lamps show across a wide reflector. Low heat load: A large arc lamp radiates significant infrared over its whole field; an LED array keeps large thin panels flat. Instant switching: Big arc lamps are often left idling because of warm-up time. LED heads switch off between cycles with no penalty. Predictable maintenance: Output declines gradually and evenly over tens of thousands of hours. Specifying a Large-Format Flood Lamp Field dimensions: The uniform window must cover the largest panel or the full batch fixture in one exposure. Irradiance at working distance: Request the measured map, not a single peak number. Wavelength: Match the photoinitiator band, commonly 365, 385, or 405 nm. Cooling and duty cycle: Large arrays need active cooling rated for continuous back-to-back curing. Mounting and integration: Confirm the head can be fixed over a conveyor or inside a chamber for higher volume. Incure's L-Series UV LED flood lamps cover large fields, and the CDM UV conveyor pairs those heads with a moving belt for continuous production. Single Large Head or Tiled Array Two approaches cover a large area. A single large head is simpler to fixture and control but concentrates cooling load and cost in one unit. A tiled array of smaller heads lets you match the lit area to the part, replace one module instead of the whole head on failure, and scale coverage later. The tiling seams must overlap enough that the boundary between modules is not under-dosed; aim for 15–20 percent overlap and verify irradiance directly on the seam lines. Thermal Management of the Part Even though LED heads add far less radiant heat than arc lamps, a large panel under a high-irradiance field for several seconds still warms. On thin films and low-glass-transition plastics, that warming can soften the substrate before the resin fully cures, causing distortion. Where this shows up, lower irradiance and lengthen exposure to reach the same dose at a lower peak temperature, or move air across the part during cure. Batch Fixture Curing A large field is also useful for curing many small parts at once on a single fixture. The…
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June 11, 2024