KH-560 vs KH-570

Overview

KH-560 and KH-570 are both methoxy-functional silane coupling agents — they share the same trimethoxysilylpropyl anchoring group on the silicon end and are both widely used in glass fiber composite manufacturing. At first glance they can appear interchangeable to buyers who are not deeply familiar with silane chemistry. They are not. KH-560 carries an epoxide (glycidoxy) functional group; KH-570 carries a methacrylate functional group. These two groups react with completely different polymer chemistries, and substituting one for the other in a composite formulation will produce an inadequately bonded interface and significantly degraded mechanical properties.

Understanding the difference is commercially important: incorrect silane specification in a glass fiber sizing or composite formulation specification can mean the difference between a composite that meets performance requirements and one that fails wet retention testing. The situation arises because both silanes are used for glass fiber composites, both are methoxy-type, and both are available in similar drum packaging from similar sources — making the mix-up easier than it might appear.

Key Differences

When to Choose KH-560

Choose KH-560 whenever the composite, coating, or adhesive matrix uses an epoxy-type cure system or an acid/anhydride cure system:

Glass fiber composites in epoxy-anhydride systems: Electrical laminates (PCB prepregs), filament wound pressure vessels for hydraulic service, and composites cured with methylhexahydrophthalic anhydride (MHHPA) or similar anhydride curatives use KH-560-sized fiber. The glycidoxy ring reacts with the anhydride during cure, integrating the silane into the matrix network.

Optical fiber coatings: KH-560 is the standard silane in optical fiber coating formulations (both primary and secondary UV-cure coatings), where it bonds to the glass fiber surface and provides adhesion for the acrylate or urethane-acrylate coating. Note: in this application, the glycidoxy ring can react with UV-generated cationic species or with the amine groups in urethane-acrylate crosslinkers — KH-570 would not provide the appropriate reaction mechanism for conventional optical fiber coating chemistry.

Semiconductor encapsulant (EMC): KH-560 treated fused silica in epoxy molding compound reacts with the phenol-novolac hardener during molding at 170–180 °C. KH-570 would not participate in the novolac cure mechanism.

UV-cure epoxy hybrid coatings: Cationic UV-cure systems based on epoxy monomers use KH-560 as the silane coupling agent. The glycidoxy group is compatible with the acid-generated ring-opening mechanism of cationic UV cure.

Acid-cured systems and sol-gel applications: Acid-catalyzed sol-gel hybrid coatings used in scratch-resistant and anti-reflective coatings on glass and polycarbonate use KH-560 as the silane monomer component.

When to Choose KH-570

Choose KH-570 whenever the composite, coating, or adhesive matrix uses free-radical polymerization chemistry — which means unsaturated polyester, vinyl ester, and most acrylic systems:

GRP/FRP composites (unsaturated polyester matrix): This is the dominant application by volume. GRP pipe, tanks, boat hulls, car body panels, and sheet molding compound (SMC) all use unsaturated polyester or vinyl ester resins cured with peroxide initiators and styrene co-monomer (or styrene-free equivalents). KH-570's methacrylate group co-polymerizes with styrene under radical initiation, chemically bonding the glass fiber to the matrix. Using KH-560 here provides almost zero chemical coupling because the glycidoxy ring does not react with the radical cure system.

Acrylic adhesives and dental composites: UV-cure and redox-cure acrylic adhesives use KH-570 as the silane coupling agent for glass, silica, and ceramic filler adhesion. Dental composite restorative materials rely on KH-570-treated silica filler to bond the filler to the bis-GMA matrix.

Waterborne acrylic coatings: KH-570 at 0.3–0.8 wt% co-polymerizes with acrylic latex particles and bonds to glass or metal substrates via silanol groups — the dual mechanism requires the methacrylate group for latex incorporation. KH-560 does not co-polymerize with acrylic latex by radical mechanism.

Consequences of Substituting the Wrong Grade

Using KH-560 in a UP resin composite: The glycidoxy group does not co-polymerize with styrene or vinyl ester monomers. The silane may still provide some physical adhesion through the silanol-glass surface reaction, but no chemical coupling between silane and matrix occurs. The composite will show nearly the same wet strength retention as untreated fiber — typically 35–50% retention versus 80–90% with correct KH-570 sizing. This would fail most FRP composite wet property specifications.

Using KH-570 in an epoxy-amine or epoxy-anhydride composite: The methacrylate double bond does not react with amine or anhydride curatives at typical epoxy cure temperatures (80–180 °C). Again, silanol surface bonding still provides some adhesion, but the organic end provides no matrix coupling. Wet retention would be substantially reduced versus correct KH-550 or KH-560 sizing.

Sourcing and Pricing Notes

KH-560 and KH-570 are available in similar quantities and at similar price levels from Chinese suppliers — both are commodity-volume grades. CAS 2530-85-0 (KH-560) and CAS 2530-84-9 (KH-570) are the definitive identifiers. Always verify the CAS number on the Certificate of Analysis when receiving a new drum — the two CAS numbers differ by only one digit in the last three digits, and packaging labeling errors, while uncommon, do occur.

Storage: KH-570 contains a polymerization inhibitor (MEHQ) and should be stored below 25 °C, away from UV light and heat. KH-560 does not require inhibitor but should also be stored below 25 °C away from moisture. Both have a 12-month shelf life in sealed drums.