Formulation Components of Anaerobic Adhesives and Their Functions

Anaerobic adhesives are a balanced system in which initiators and inhibitors coexist; currently, there are three main types in the industry. The first type is a general-purpose anaerobic adhesive, typically formulated with monomers, initiators, accelerators, inhibitors, thickeners, dyes, and other components; the second type is a pre-coated anaerobic adhesive, with formulations divided into Component A and Component B. Component A consists primarily of methyl acrylate diesters, acrylic emulsions, accelerators, and inhibitors, while Component B consists of microcapsules containing dibenzoyl peroxide initiator encapsulated in urea-formaldehyde resin. The third type is an impregnation adhesive, whose formulation consists of methacrylic diesters, initiators, accelerators, and polymerization inhibitors.

Monomers

Commonly used monomers include polyethylene glycol dimethacrylate with various molecular weights, ethyl methacrylate or hydroxypropyl methacrylate, epoxy resin methacrylate, polyol methacrylate, and polyurethane acrylate. Since these monomers contain two or more double bonds capable of participating in polymerization reactions, they can serve as the main components of anaerobic adhesives. To improve the performance of anaerobic adhesives, prepolymers that enhance bonding strength and thickeners that adjust viscosity may also be added.

Poly(ethylene glycol) dimethacrylate CAS 25852-47-5

2-Hydroxypropyl Methacrylate CAS 27813-02-1

Common Monomers Used in Anaerobic Adhesives

2-Hydroxyethyl methacrylate CAS 868-77-9

2-Hydroxypropyl Methacrylate CAS 27813-02-1

Triethylene Glycol Dimethacrylate 109-16-0

Isobornyl Methacrylate CAS 7534-94-3

1,4-Butanedioldimethacrylate (BDDMA) CAS 2082-81-7

Bisphenol A Ethoxylate Dimethacrylate CAS 41637-38-1

Initiators

The curing reaction of anaerobic adhesives is a radical polymerization reaction; most use hydroperoxyisopropylbenzene as an initiator, with an initiator concentration of approximately 1% to 5%.

Peroxide Initiators Commonly Used in Anaerobic Adhesives

Accelerators

In the curing reaction of anaerobic adhesives, an appropriate amount of saccharin, tertiary amines, or similar substances is added as a reducing agent to promote the decomposition of peroxides; the amount of accelerator used ranges from 0.5% to 3%.

Accelerators Commonly Used in Anaerobic Adhesives

N,N-Dimethylaniline CAS 121-69-7

N,N-Dimethyl-p-toluidine(DMPT) CAS 99-97-8

Plasticizers

Not all anaerobic adhesives require high strength. To adjust the strength of the cured adhesive and facilitate disassembly and maintenance later on, a certain proportion of plasticizer is typically added to modulate the strength of the cured adhesive. Additionally, for anaerobic adhesives used for sealing, adding plasticizers can enhance the flexibility of the cured adhesive layer and improve the sealing performance. When using plasticizers, priority should be given to compatibility with the base materials (such as monomers), adhering to the principle of “like dissolves like” to prevent separation during storage and migration of plasticizers after curing.

Common Plasticizers for Anaerobic Adhesives

Polyethylene Glycol CAS 25322-68-3

Triethylene Glycol Monomethyl Ether CAS 112-35-6

Polyethylene glycol monooleate CAS 9004-96-0

Polyethylene glycol monolaurate CAS 9004-81-3

Diisononyl phthalate CAS 28553-12-0

Polymerization Inhibitors

To improve the storage stability of anaerobic adhesives, it is necessary to add certain polymerization inhibitors, such as hydroquinone and menadione.

Effects of Certain Polymerization Inhibitors on the Curing Time and Stability of Anaerobic Adhesives