UV-curing adhesives

A UV-curing adhesive requires investment in cure equipment but does offer the benefits of curing on demand and optical clarity. 

UV-curable adhesives, and, in general, radiation-curable adhesives, use UV light or other radiation sources to initiate curing. A permanent bond forms without application of heat by means of free-radical chemistry. The advantages of UV curing include lower application temperature (120—140° C), 

UV-curing adhesives are available in a number of chemical systems, most of which are polymer based. These systems include acrylics and acrylates, epoxies, polyurethanes, polyesters, silicones, and vinyl and vinyl esters. The most common UV-curable adhesive is the acrylics. Specially modified acrylic and epoxy adhesives can be cured rapidly by UV radiation. In the case of epoxy adhesives, the adhesives can be preirradiated after application to the substrate and before closing the bond fine. These adhesive systems are offered by most major suppliers. 

The cure time of different UV-curable adhesives varies, ranging from instantaneously to several hours. Typically, UV exposure starts the process, which begins with tackiness of the adhesive and requires a given length of time to set fully. Longer cure times are required at lower curing temperatures. 

There are a wide variety of UV-curing materials available for a broad range of applications. UV-curing resins are used to protect laminated flooring or to coat the peel and stick labels you use. We will look at two types of high-performance engineering adhesives that are typically used in product assembly. 

Firstly is an epoxy-based material adhesive. Although some people use the term epoxy as a generic reference to aU high-performance engineering adhesives, it has a specific meaning within flie adhesive world. It is also different from other adhesive types, particularly the acrylic-based adhesives. 

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Divakar, R., Butler, D., Papautsky, I., Room temperature low-cost UV-cured adhesive bonding for microfluidic biochips. Micro Total Analysis Systems, Proceedings 5th TTAS Symposium, Monterey, CA, Oct. 21-25, 2001. Kluwer Academic Publishers, Dordrecht, the Netherlands, 2001, 385-386. 

In PET films containing CaCOs, the adhesion of the film was less than that of unfilled film. This is due to the replacement of the adhesion promoting surface by filler which has no adhesive properties.In UV cured adhesives, quartz filler contributed to a faster development of adhesion due to its transparency to the UV radiation used for curing.In polymer blends filler was accumulated at the interphase between polymers. Adhesion depended on the interaction of filler with both polymers and on the particle size of filler. ... 

The UV-curing polyacrylates are particularly variable in terms of flexibility, viscosity adjustment (microdosing in the pg range), flow behavior (thixotropy), and adhesion. Flexibility is particularly important in hard-soft combinations such as plastic-metal and glass-plastic in order to compensate for expansion due to temperature variations. UV-curing adhesives are also used for cladding applications in composites. 

Apart from a suitable UV-curing adhesive, suitable UV-radiation sources are required, too, which are available in the form of flashlights or continuous lines. To achieve optimum curing, it is very important to adapt the UV-radiation precisely to the adhesive to be cured (Section 9.3.3). 

MagnacryL [Beacon] Acrylk (polyrad) adhesives and uv-curing adhesives coadngs. 

Norland Optical Adhesive. [Norland Prods.] uv-curing adhesive for assembling glass lenses. 

Ultrabond. (Hemon Mfg.] Uv-curing adhesives for electronics bonding, tacking, potth and encapsulation. 

Other properties of UV-cured adhesives of benefit to the electronics industry are one-part systems, 100% solids (no solvents), and can be stored at room temperature. 

Chem. Descrip. Ethyl 4-(dimethylamino) benzoate CAS 10287-53-3 EINECS/ELINCS 233-634-3 Uses Free radical initiator tor UV-cured adhesives, coalings (metal, paper, wood), electronics (solder masks), inks (flexo and gravure, litho, offset, screen) coinitiator Features Good sol. 

Chem. Descrip. Ben ldimethyl ketal with 100 ppm MEHQ CAS 2465042-8 EINECS/ELINCS 246-386-6 Uses Photoinitiator tor UV-cured adhesives (pressure sensitive, structural), coatings (metal, optical, paper, plastic, PVC floor, textile, wood), photopolymers, electronics (photoresists, conformal, encapsulants, solder maste), iniffi (flexo, gravure, litho, offset, screen)... 

Methyl isobutyl ketone peroxide crosslinking agent, urethane coatings 1-Aziridinepropanoic acid, 2-methyl-, 2-ethyl-2-[r3-(2-methyl-1 -aziridinyl)-1 -oxopropoxy] methyll-1,3-propanediyl ester crosslinking agent, urethanes t-Butyl peroxyisopropyl carbonate crosslinking agent, UV-cured adhesives... 

Basic acrylate chemistry. The basic acrylic monomers or oligomers contain unsaturated double bonds (vinyl groups), and consequently cure by addition polymerization involving a free-radical reaction. Free-radical-producing compounds such as peroxides, peracetic acids, and sulfones are added to acrylic resins to initiate polymerization. Free-radical polymerization of acrylics may also be induced by exposure to U V or visible light. These UV-curing adhesives, most of which are based on acrylic or modified acrylic... 

UV-curing adhesives are also finding an application in flat-panel electronics. Because the panel is glass and transparent to UV light, devices can be attached with a UV-curing adhesive on the topside and, after accurate positioning, exposed to UV light from the backside of the panel and cured in a few seconds. 

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