A UV-cure adhesive fixes instantly wherever light reaches it and does nothing wherever it doesn’t — which is exactly why a dual-cure silicone that finishes shadowed areas by moisture exposure solves a real problem on any assembly with a housing, an overlap, or a connector blocking the light path. Incure’s Pyra-Sil™ UV silicone line covers that dual-cure need across four grades, plus one grade that breaks from the UV-cure pattern entirely.
901 and 904 Are a Viscosity-Matched Pair for General-Purpose Bonding
Pyra-Sil™ 901 and 904 are both one-part, UV/moisture dual-cure, high-temperature silicones formulated for bonding a wide range of substrates as form-in-place gaskets, conformal coatings, and sealants — UV light fixes exposed surfaces fast, while ordinary moisture in the air fully cures whatever the light couldn’t reach within 72 hours. The two share the same -45°C to 260°C service range and dual-cure chemistry, differing mainly in viscosity and hardness: 901 runs thicker at 6,500–8,500 cP and cures to Shore A30–A40, while 904 is noticeably thinner at 2,000–3,000 cP and softer at Shore A20–A30. That gives a line running general-purpose bonding and sealing work a genuine choice between a heavier-bodied grade that holds its shape on a gap or seam and a thinner one that flows more readily into finer features, without giving up dual-cure convenience either way. Both are compatible with manual dispensing and automated or spray equipment, so the viscosity choice is driven by the joint geometry itself rather than by what equipment the line already runs.
905 and 909 Add High-Altitude Arcing Protection on PCBA, at a Softer Hardness Scale
Pyra-Sil™ 905 and 909 are also a matched dual-cure pair, but they’re built specifically as a conformal coating for PCB assemblies, protecting against moisture, ozone, and — notably — high-altitude arcing, a failure mode specific to circuit boards operating at reduced atmospheric pressure where dielectric breakdown happens more readily than at sea level. Both cure on the O-scale rather than the A-scale used by 901 and 904 — 905 and 909 both land at O65–O95, a softer, more gel-like hardness measurement suited to a thin conformal coating rather than a structural gasket material. The two differ mainly in viscosity: 905 is the thinnest grade in the entire line at 350–750 cP, suited to spray or dip coating over populated boards, while 909 runs thicker at 2,500–3,500 cP for more controlled bead or brush application. Both fix under UV light in seconds and fully cure shadowed areas by moisture within 72 hours, the same dual-cure logic as 901 and 904 but tuned specifically for board-level electronics protection. The arcing-protection framing is worth taking seriously as a real selection factor rather than boilerplate marketing language — a board that never leaves sea level doesn’t need it, but one destined for aerospace, high-altitude telecom, or any enclosure that depressurizes in service does, and the general-purpose 901/904 pair doesn’t make the same claim.
Email Us with your substrate, service temperature, and whether the assembly has shadowed areas UV light can’t reach, and Incure’s engineers can confirm which Pyra-Sil™ UV silicone grade actually fits.
913 Breaks From the UV-Cure Pattern Entirely
Pyra-Sil™ 913 is the outlier in this line: a solvent-free, one-component, moisture-cure-only silicone with no UV-cure path at all. It cures purely through ambient moisture exposure, releasing alcohol rather than the corrosive byproducts a standard moisture-cure silicone can generate, which reduces the corrosion risk on sensitive metal substrates nearby. It’s also isocyanate-free and compliant with RoHS and REACH, an eco-compliance profile the UV-curing grades above don’t specifically claim. Mechanically, 913 sits apart from the rest of the line too — by far the thickest at 50,000–100,000 cP, the hardest at Shore A50–A60, and rated to a notably narrower -45°C to 100°C service range against the other four grades’ -45°C to 260°C. That lower temperature ceiling is worth checking closely before substituting 913 into an application that assumed the line’s usual high-temperature range applies across every grade. In exchange, 913 explicitly bonds to a broad, named substrate list — polycarbonate, metal, glass, ceramics, and nylon — where the UV-curing grades describe substrate compatibility more generally.
Where the Line Fits
General bonding, gasketing, and sealing work with occasional shadowed geometry favors 901 or 904 depending on whether the joint needs a heavier gap-filling bead or a thinner, more flowable application. PCB assembly protection — especially boards operating at altitude, where arcing risk is a genuine design concern — favors 905 or 909’s O-scale conformal coating chemistry over the general-purpose pair. Applications that can’t tolerate any UV-cure byproduct concerns, need broad named-substrate compatibility, or stay within a moderate temperature range benefit from 913’s pure moisture-cure, eco-compliant formulation instead. Facilities running Incure’s Ultra-Illumina™ UV conformal coating line for fast UV-only PCB coating can add this dual-cure silicone line specifically where housing geometry leaves shadowed areas a UV-only chemistry can’t reach.
Contact Our Team to confirm the Pyra-Sil™ UV silicone grade for your substrate and cure requirement.
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