Cyanoacrylate adhesives

On steel, Henkel LOCTITE 401 fixtures in less than 5 s at 22°C and 50% RH at 0.1 N/mm² shear. Permabond 105 lists 10–15 s on steel using a 0.3 N/mm² handling threshold, with 24 h to full strength. Its handling table gives no fixed temperature or humidity. Match threshold, gap and environmental conditions before comparing. Verify the required cured properties separately from handling strength. LOCTITE 401 TDS, pp. 1–2 Permabond 105 TDS, p. 1

A moisture-initiated bond

Surface moisture initiates polymerization of a thin cyanoacrylate bondline. Permabond 105 is a one-part ethyl cyanoacrylate that requires neither mixing nor heat cure. Permabond, 105 Technical Datasheet, Revision 7, September 13, 2025, p. 1

“Cyanoacrylate” does not describe every acrylic adhesive. Permabond distinguishes this family from structural acrylics, anaerobic adhesives and UV-curing systems. Their initiating conditions and assembly processes differ. A cyanoacrylate is not selected as a threadlocker or a two-part structural adhesive merely because all may involve acrylic chemistry. This reference concerns conventional moisture-curing products; specialized formulations require their own instructions. Permabond, adhesive families and cyanoacrylate overview.

Bondline thickness, viscosity and substrate

Thin bondlines promote rapid cure. Increasing the gap slows the reaction, so a product's advertised fixture time cannot be assumed for a thick fillet. LOCTITE 401's data sheet also identifies substrate and relative humidity as cure variables; higher humidity accelerates its cure under the stated conditions. “Instant” is consequently a family description, not a guarantee of immediate load capacity. Henkel, LOCTITE 401 Technical Data Sheet, February 2012, p. 1.

Viscosity helps determine dispensing, wetting and resistance to flow. Permabond offers liquids, high-viscosity products and thixotropic gels, along with grades aimed at rubber, metal, low-bloom or water-resistant applications. A gel's ability to stay in place is different from demonstrated cure through a specified gap. Select the exact grade's gap capability and environmental performance rather than treating thicker adhesive as a universal repair material. Permabond, Cyanoacrylate adhesives, product variants.

Substrate identity includes its surface condition. A result for etched aluminum is not automatically a result for anodized aluminum, and a plastic trade name does not identify every filler, coating or mold-release residue. Henkel also warns that uncured cyanoacrylate remaining on stressed polycarbonate, acrylic or polysulfone can cause stress cracking. Compatibility therefore includes the assembly process, not just the final bond. Henkel, Cyanoacrylates, stress-cracking FAQ.

Primers and accelerators have different jobs

A low-energy-surface primer changes the bondability of a difficult substrate. LOCTITE SF 770's May 2021 TDS identifies polyethylene, polypropylene, PTFE and thermoplastic rubber among its intended difficult surfaces. It is a primer for compatible cyanoacrylates, not an adhesive by itself. Henkel does not recommend that primer system where high peel strength is required. LOCTITE SF 770 TDS, p. 1.

An accelerator changes curing speed. It does not establish that an otherwise unsuitable substrate or oversized gap has become a qualified joint. Henkel's LOCTITE 406 instructions distinguish primer, activator and adhesive placement: primer must dry, activator is not applied to the primed surface, and adhesive is not applied to the activated surface. Those are product-specific process instructions. Verify the selected combination instead of mixing auxiliary products freely. LOCTITE 406 TDS, February 2012, p. 2, “Directions for use”.

Fixture time is a defined test threshold

The following LOCTITE 401 values come from the currently supplied PDF whose technical header is February 2012. A recent download date is not a new formulation revision.

Henkel’s fixture threshold is 0.1 N/mm². Measure cured strength and chemical resistance separately. LOCTITE 401 TDS, pp. 1–2

Permabond 105 Revision 7 lists 0.1 mm maximum gap fill and 18–22 N/mm² steel shear under ISO 4587. The handling entry gives no fixed temperature or humidity. Its footnote says both affect timing, along with surface and gap. Permabond 105 TDS, p. 1

Qualify joint area, loading direction, peel, impact, temperature and aging before assigning a part allowable.

Dispensing, assembly and blooming

Prepare a joint that can be located accurately before the adhesive sets. LOCTITE 406's instructions call for clean, grease-free surfaces, adhesive on one bonding surface and fixed positioning until fixture. They also require full-strength development before service loads, typically 24–72 h depending on material, gap and ambient conditions. Excess liquid and repeated repositioning are not substitutes for controlled coverage and a repeatable bondline. LOCTITE 406 TDS, p. 2.

Blooming is the white or rainbow haze formed when airborne, unreacted cyanoacrylate reaches surrounding surfaces and reacts with surface moisture. Cyanotec recommends controlling exposed fillets, improving ventilation and considering a low-bloom formulation. Its discussion concerns appearance around the joint; a clean-looking surface by itself does not demonstrate adequate internal cure or strength. Cyanotec, Blooming in cyanoacrylate adhesives.

Temperature, fluids and storage

Distinguish a hot-strength test from strength measured after exposure and cooling. Permabond 105's hot-strength specimens receive a 24-hour room-temperature cure and 30 minutes at test temperature before loading. Its chemical-resistance specimens are immersed for 1,000 h at 22°C unless stated otherwise. The data sheet does not recommend contact with strong oxidizers or polar solvents, while distinguishing a solvent wash from prolonged exposure. These conditions do not establish every cyanoacrylate's service envelope. Permabond 105 TDS, pp. 1–2.

Storage instructions also depend on the product and whether it has been opened. Permabond recommends bringing unopened cyanoacrylates to ambient temperature before opening, limiting condensation inside the package. Follow the exact grade's storage temperature and label rather than using a universal refrigerated or frozen shelf life. Keep the opening and dispensing process from introducing moisture or contamination. Permabond, Application tips, storage recommendations.

Safety scope

Henkel's LOCTITE 401 US SDS, IDH 135429, Revision 002.2, issued October 23, 2025, identifies a combustible liquid, eye irritation, possible respiratory irritation and rapid skin bonding. Sections 7–8 address handling and exposure controls, including ventilation and eye protection. These statements apply to that product and US sheet; use the current SDS for the actual package and jurisdiction. A low-odor or low-bloom marketing description is not a hazard classification. No medical bonding use or first-aid procedure is established here. Henkel, LOCTITE 401 SDS, §§2, 7–8.