KH-560

What is KH-560?

KH-560, known chemically as 3-Glycidoxypropyltrimethoxysilane, is an epoxy-functional silane coupling agent with CAS number 2530-85-0 and molecular formula C₉H₂₀O₅Si. It carries a glycidoxy (epoxide) group at the organic end and three methoxy groups on the silicon end. This combination makes KH-560 the standard coupling agent wherever an epoxide ring is needed to react with amine, anhydride, or acid curatives during polymer cure — which covers a broad swath of high-performance thermoset applications including optical fiber coatings, semiconductor encapsulation, and acid-anhydride-cured glass fiber composites.

KH-560 is the direct Chinese equivalent of Dow Corning Z-6040, Momentive Silquest A-187, and Shin-Etsu KBM-403. All share CAS 2530-85-0 and identical chemistry. Buyers switching from a Western brand to KH-560 require no reformulation, only a purity certificate confirming ≥98.0% GC purity and water content ≤0.1 wt%.

The methoxy hydrolysis groups on KH-560 hydrolyze moderately fast in the presence of moisture, forming silanols that condense with glass and silica surface hydroxyls to create Si–O–Si bonds. The glycidoxy organic end then participates in the polymer cure reaction, integrating the silane into the crosslinked network. The resulting covalent bridge between the inorganic surface and organic matrix is highly resistant to hydrolysis — a critical requirement in optical and electronic applications where delamination under humidity cycling would be catastrophic.

Key Properties and Performance

KH-560's relatively high boiling point (approximately 290 °C at 1 atm) compared with amino silanes reflects the bulkier glycidoxy group, but more practically it means lower volatility during processing. This makes KH-560 well-suited for high-temperature cure cycles used in electronics encapsulation, where oven temperatures of 120–175 °C are standard.

The methoxy hydrolysis groups provide fast hydrolysis compared with the ethoxy groups in KH-550. In aqueous sizing baths and waterborne coating formulations, this faster hydrolysis ensures rapid Si–OH formation for surface bonding. However, it also means the prepared aqueous solution has a shorter pot life — typically prepare only the volume needed for the same working day.

KH-560 is a colorless to very pale yellow liquid. Color is an important specification for optical applications: electronics-grade KH-560 is typically specified at APHA (Hazen) color ≤20, versus the ≤100 acceptable for general industrial use. The refractive index (approximately 1.428 at 25 °C) is relevant for optical fiber and waveguide coating applications where the coupling agent's optical contribution must be controlled.

Shelf life for sealed, properly stored KH-560 is 12 months. The main degradation pathway is hydrolysis of the methoxy groups by moisture ingress, which reduces surface coupling efficiency. Secondary degradation involves ring-opening of the glycidoxy group by trace acids or bases. Store in dry, cool conditions; inspect for color change or viscosity increase before use on critical applications.

Applications in Industry

Glass Fiber Composites

In glass fiber sizing for epoxy composite systems, KH-560 is specified when the matrix resin uses anhydride or Lewis acid curatives rather than amines. Epoxy-anhydride cured systems, common in electrical laminates (PCB prepregs), transformer windings, and filament-wound pressure vessels, require a silane that is compatible with the anhydride cure chemistry. KH-560's glycidoxy group ring-opens with anhydride to form an ester linkage, integrating the silane into the crosslinked matrix. Application is from dilute aqueous solution (0.3–0.8 wt%, pH adjusted to 4–5 with acetic acid) during glass fiber drawing.

For epoxy-amine cured composites, KH-550 (amino silane) is the standard choice because it participates directly in the amine-epoxy cure. KH-560 can also be used in epoxy-amine systems, but the mechanism differs — the glycidoxy ring opens with the amine curative, which may slightly alter the crosslink density profile compared with KH-550.

Semiconductor and Electronics Encapsulation

KH-560 is one of the two primary silane coupling agents in semiconductor epoxy molding compound (EMC), the thermoset used to encapsulate integrated circuits. EMC formulations contain 70–90 wt% fused silica filler; KH-560 treats the silica surface to bond it to the epoxy matrix, improving compound flowability, adhesion to leadframes, and thermal shock reliability. The glycidoxy group reacts with the phenol-novolac or cresol-novolac hardener during EMC cure at 170–180 °C.

In flip-chip underfill applications, KH-560 is incorporated into the underfill resin at 0.5–2.0 wt% to promote adhesion to the solder resist and substrate surface. The benefit is measured in terms of delamination resistance during JEDEC moisture sensitivity level (MSL) testing — packages treated with KH-560-containing underfill pass higher MSL ratings, indicating better moisture resistance.

Optical Fiber and Precision Optics

The combination of methoxy hydrolysis groups (fast surface bonding) and a glycidoxy ring that can react with amine, anhydride, or UV-cure photoinitiator-generated radicals makes KH-560 the preferred silane in optical fiber secondary coating formulations. The objective in optical fiber coating is to protect the glass fiber from moisture and mechanical damage while maintaining signal transmission quality. KH-560 in the primary coating formulation improves adhesion to the glass fiber surface and reduces moisture ingress at the glass-coating interface.

For precision optical bonding (lens assemblies, prism adhesives), KH-560 is used as a surface primer — a dilute ethanol solution (0.1–0.5 wt% KH-560) is applied to the glass surface, dried at 80–100 °C for 10 minutes, and then the optical adhesive is applied. This treatment can reduce the failure rate in thermal cycling tests by eliminating delamination at the glass-adhesive interface.

Handling, Dosage, and Storage

For aqueous pre-treatment: prepare a 0.5–2.0 wt% solution in deionized water adjusted to pH 4–5 with glacial acetic acid. The solution should appear clear; turbidity indicates premature condensation and the batch should be discarded. Apply by spray, dip, or wipe to a clean substrate, allow to dry at ambient temperature for 15–30 minutes or at 80–110 °C for 5 minutes before bonding or coating.

For direct addition to epoxy formulations: add 0.2–1.0 phr (parts per hundred resin) to the resin component. Mix thoroughly before adding the curative. The silane functions as an adhesion promoter and compatibilizer for any inorganic fillers present.

Flash point of KH-560 is approximately 135 °C, classifying it as a combustible liquid (not flammable at room temperature). Standard industrial PPE (nitrile gloves, eye protection, ventilation) is adequate. Avoid prolonged skin contact — wash immediately with soap and water if contact occurs.

Frequently Asked Questions

Can KH-560 be used in amine-cured epoxy systems? Yes. The glycidoxy ring opens with primary amines during cure. However, note that if using KH-560 as a coupling agent in an amine-cured epoxy composite, the glycidoxy group consumes some amine curative. This may require adjusting the amine-to-epoxy stoichiometry slightly. For most industrial applications the effect is small enough to ignore at typical silane loadings of 0.5–1.0 wt%.

What is the difference between KH-560 and A-187? None, chemically. Momentive Silquest A-187 and KH-560 both have CAS 2530-85-0. The trade names are different; the molecule is identical.

Why does my aqueous KH-560 solution turn cloudy? Cloudiness in an aqueous silane solution indicates silanol condensation — the hydrolyzed silane is polymerizing in solution rather than bonding to the substrate. This happens at pH above 6 or with hard water containing calcium/magnesium ions. Use deionized water and adjust pH to 4–5 with acetic acid. Prepare solutions fresh and use within 4–8 hours.

Is KH-560 suitable for UV-cure systems? Yes, for UV-cure epoxy (cationic photoinitiator) and acrylic-epoxy hybrid systems. The glycidoxy ring can open under cationic UV initiation. For purely acrylate-based UV systems, KH-570 (methacrylate silane) is the better choice as it co-polymerizes via free radical mechanism.

What minimum purity is required for electronics applications? Electronics-grade KH-560 typically requires GC purity ≥98.5%, water content ≤0.05 wt%, APHA color ≤20, and metals analysis (Na, K, Cl each below specified limits). Confirm with your encapsulant formulator for the precise specification used in their process.