Two bottles of UV glue can look identical, cure under the same lamp, and behave completely differently in a product: one shatters at the first drop test, the other stretches, holds, and outlasts the housing. The difference was printed on the spec sheet the whole time. Here is how to read one.
Q: What is UV glue, and what do the numbers on its data sheet mean?
A: UV glue is a single-component, solvent-free acrylate or epoxy adhesive that stays liquid until 365–405 nm light triggers its photoinitiator, then cures in seconds. Its data sheet carries five numbers that predict how it will behave: viscosity (how it flows and where it can be applied), elongation (how far the cured bond stretches before breaking), Shore hardness (rigid vs. rubbery), tensile strength (load capacity, with a caveat below), and service temperature range. Wavelength and cure-equipment compatibility complete the picture.
Viscosity: Where the Adhesive Can Go
Viscosity in centipoise (cP) tells you the application method before anything else. Incure’s Uni-Weld™ plastic-bonder line spans 100 cP to 84,000 cP, and that range maps directly onto process: grades at 100–700 cP (3271, 1462, 1453) wick into an already-mated joint by capillary action; mid-range grades such as 1444 (1,900–3,800 cP) and 1417 (5,700–11,400 cP) dispense as a bead before assembly and fill small gaps; the 42,000–84,000 cP grade holds its shape for potting and structural bonding. Reading viscosity first eliminates half the catalog: a wicking grade on a gap-filling joint sits in the gap unfilled, and a paste on a capillary joint never reaches the bond line. The full ladder is in Incure’s Uni-Weld™ plastic bonder guide.
Elongation and Hardness: Rigid or Compliant
Elongation (%) and Shore hardness are read together, and they decide whether the bond survives movement. Uni-Weld™ 1072 cures to 13% elongation at Shore D76–D86 — rigid, dimensionally stable, right for a precision optical mount, wrong for a joint that flexes. Uni-Weld™ 1483 reaches roughly 3,800% elongation at Shore D50–D60 — a bond that absorbs vibration and thermal expansion instead of resisting it. Between them, 1417 (346%) and 1444 (355%) carry structural load while still damping movement on solder joints and wire tacks. The rule: match elongation to how much the joint will move, not to how strong it sounds. High elongation on a rigid alignment joint creeps; low elongation on a flexing joint cracks.
Email Us with the substrates, the joint geometry, and what the assembly experiences in service, and Incure’s engineers can translate those into the viscosity, elongation, and hardness window that fits.
Tensile Strength: Read the Footnote
Tensile figures on UV glue sheets are often marked with a fracture indicator — Incure’s Uni-Weld™ plastic-bonder grades list up to 10,800 PSI with that mark, meaning the polycarbonate test coupon broke before the bond did. That number describes the substrate’s ceiling, not the adhesive’s. On a tougher substrate the limiting factor may be different. For glass-to-metal work, Incure’s Uni-Weld™ UV glass and metal bonder line publishes metal-to-glass tensile directly — 3253 at 11,000 psi with 35% elongation, 1931 at 9,800 psi with 4% — and reading those two side by side shows the trade-off in one line: the stronger-sounding rigid grade transmits all of the load; the 35% grade absorbs some of it.
Service Temperature: The Number Most Often Skipped
Most UV-curable acrylates are rated around −55°C to 80°C; a minority reach 150°C. Incure’s highest-viscosity plastic-bonder grade carries the −55°C to 150°C rating, while most wicking grades stop at 80°C. A bond that passes every bench test and then sits behind a hot component or in an engine bay will fail on temperature alone. Read the range before the tensile figure, not after.
Wavelength and Cure Path: The Sheet Assumes a Lamp
A cure time on a data sheet is measured at a stated irradiance and wavelength. Uni-Weld™ grades cure in the 365–405 nm range and are qualified on Incure’s L-Series™ UV LED flood lamps and spot lamps; the same adhesive under a weaker or mismatched source cures slower or not through. If the sheet’s cure time doesn’t reproduce on your line, the lamp — not the glue — is usually the variable.
Depth of Cure and Shadow: What the Sheet Won’t Say
A spec sheet rarely states how deep a grade cures in one exposure, and it never knows your part’s geometry. UV glue cures only where light reaches: an opaque housing, a metal flange, or a black-pigmented plastic casts a shadow in which a pure UV-cure grade stays liquid indefinitely. Check whether the joint has full optical access to the bond line through at least one transparent member; if it doesn’t, the specification question changes from “which grade” to “which cure path,” and a dual-cure or a different chemistry is the answer.
A Five-Line Reading Order
- Viscosity → application method and gap.
- Elongation + hardness → rigid alignment or compliant joint.
- Service temperature → does it survive where it lives.
- Tensile → with the fracture footnote understood.
- Wavelength/irradiance → does your lamp match the sheet’s cure conditions.
Read in that order, a UV glue spec sheet answers the buying question before a sample is ever ordered.
Contact Our Team to match a Uni-Weld™ grade to your substrates, joint, and cure equipment.
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