Dual curing adhesives

The disadvantages of UV adhesives are that one transparent substrate is normally required they suffer from oxygen inhibition and only a limited depth of cure can be achieved. The latter problem has been tackled by the development of dual-cure adhesives. In these systems, two independent curing mechanisms are incorporated into a single system. Thus the adhesive is cured first to a chemically stable form by UV irradiation and subsequently led to fiiU cure by a second means, for example, thermal cure. 

Radiation UV-acrylics, cationic epoxies, dual-curing adhesives Liquids UV-curing adhesives have shorter curing times than conventional adhesives and can therefore increase production speed and productivity... 

Dual curing adhesives offer more than one curing mechanism. They are designed for applications with shadow areas which are not accessible to the UV hght. Full cure in shadow areas will be achieved by anaerobic cure in the absence of oxygen with metal contact, or by adding heat. 

There are several limitations to the use of UV/EB-cured adhesives. EB equipment is expensive. UV equipment is less expensive, but the materials themselves are usually more costly because of the need for photoinitiators. To cure adhesives properly, one substrate must be transparent to UV radiation. However, the necessity of having a transparent substrate has been removed by the introduction of dual-curing adhesives. 

Typical film adhesives used for metal-metal bonding are AF 163-2 (3Ms), effectively a dual-cure adhesive curing at either 120 or 175°C, and FM-73 and FM-74 (Cytec-Fiberite) curing at 120°C and FM-300 (Cytec-Fiberite) curing at 175°C. 

Thanks to their versatility, dual-cure adhesives are suitable for a number of low to high performance applications. Experiments have shown that this two-step curing brings an additional benefit The fact that the cross-linking is not complete directly after irradiation allows one to irradiate the adhesive before the nip-station. Because these adhesives are based on the free-radical mechanism, the irradiation step must take place under an inert gas blanket... 

Goodman, D.L. and Byrne, C.A., Phase-separated dual-cure elastomeric adhesive formulations and methods of using the same. US Patent 5,997,682. 

Recently a solvent-free dual-cure laminating adhesive based on the combination of polyurethane chemistry and EB cure was developed that exhibits improved properties compared to laminates prepared by either method alone. ... 

Dual-cure resins for wood composites. These resins (heat and EB irradiation systems) are based on urethane-acrylate thermoplastic adhesive demonstrate efficacy to bond wood. Eow amounfs of EB radiation were needed to produce a wood bond that survived shipping and that improved the composite modulus. The system demonstrated promise and a new direction for wood adhesives. 

Increasing use of UV-curable acrylates is found in the assembly of medical, automotive, electrical, electronic and optical devices. Dual cure mechanism (UV and anaerobic) adhesives are often used for the assembly of ammunition and automotive air bag inflators. 

Saharil F et al (2013) Dry adhesive bonding of nanoporous inorganic membranes to microfluidic devices using the OSTE(+) dual-cure polymer. J Micromech Microeng 23 025021 Searson PC et al (1991) Porous sihcon membranes. Appl Phys Lett 59(7) 832 Sedlaclk R et al (1995) Photoconductivity study of self-supporting porous silicon. Thin Solid Films... 

Keywords Acrylates Crosslinking Dual cure Epoxides Glass laminates Interpenetrating polymer networks Isocyanates Photo initiated cationic polymerisation Photoinitiators Photopolymerisation Pressure sensitive adhesives Release coatings Structural adhesives Thiol/polyene UV radiation curing Vinyl ethers. 

When UV-curable resins are used as laminated adhesives to protect three-dimensional objects having complex shapes, it may happen that some remote areas wiU not be accessible to UV-radiation and therefore remain uncured. To address the issue of such shadowed areas, dual-cure systems combining UV-irradiation and thermal treatment have been developed [71]. They contain two types of reactive functions a UV-curable functional group (usually an acrylate double bond)... 

A state-of-the-art, dual cure (121 -177 ) modified epoxy 121 C service temperature film adhesive, particularly suitable for Nomex bonding. 

A dual cure (121 - 7T C) repair adhesive for high service temperature use. 

As a result of these reactions the materials eventually crosslink and become set] that is, they lose the ability to flow or to be dissolved. Cure most often is thermally activated hence the term thermoset, but network-forming materials whose cure is light- or radiation-activated are also considered to be thermosets (see Section 2.11, on differential photocalorimetry). Some thermosetting materials, such as certain adhesives, crosslink by a dual-cure mechanism, that is, by either heat or light activation. In contrast to the values for crosslinked elastomers or rubbers, the glass transition temperature of thermosets is generally above room temperature. 

The cross-linked nature of UV/EB-cured adhesives results in good chemical, heat, and abrasion resistance toughness dimensional stability and adhesion to many substrates. Unlike thermal curing, EB or UV curing requires pure raw material grades. The use of dual-curing systems allows opaque substrates to be cured. 

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