Ultraviolet light curing systems

Until recently, only long wave ultraviolet light curing systems (320 - 400 nm) were used. The first of these was a pit and fissure sealant which was reported in 1970 (1). This was followed by a composite restorative in 1973 (2). Shortly thereafter, this material was slightly modified for use as an orthodontic bracket adhesive. 

The foregoing results illustrate the complexily of these sterns and emphasize the importance of studying the ultraviolet light-cured ink system in addition to its individual components. 

The main chemical difference between the ultraviolet and the visible light curing systems is the photoinitiator which is employed. The ultraviolet systems use aliphatic ethers of benzoin, with the methyl ether being the typical, although not the exclusive, choice. 

Composite resins can be cured using a variety of methods. Intraoral curing can be done by chemical means, where amine—peroxide initiators are blended in the material to start the free-radical reaction. Visible light in the blue (470—490 nm) spectmm is used to intraoraHy cure systems containing amine—quin one initiators (247). Ultraviolet systems were used in some early materials but are no longer available (248). Laboratory curing of indirect restorations can be done by the above methods as well as the additional appHcation of heat and pressure (249,250). 

At present, systems cured by ultraviolet light or electron beams [12-14] are used primarily in wood coatings, which contain very little or no pigment they are employed to a lesser extent in paper coating and other applications. In contrast to the printing field, the comparatively thick layers in which paint systems... 

The main sources of energy for curing epoxy adhesives by radiation are electron beam (EB) and ultraviolet light (uv). Both provide instantaneous curing of resins that polymerize from a liquid to a solid when irradiated. The uv systems account for approximately 85 percent of the market for radiant cured adhesives, EB systems account for about 10 percent, and the remainder are chiefly adhesives that can cure by exposure to both visible and infrared light. 

In 1983, radiation curable 100 % solvent-free silicone acrylates were introduced into the market [4], This system provide the opportunity to be cured by either ultraviolet light (UV) or electron beam (EB). Similar in concept to peroxide initiation, silicone acrylate systems employ photoinitiators to generate free radicals and initiate cure, which is based on the polymerization of the acrylic C=C double bond via a radical chain reaction. 

One of the newer developments in adhesives is the growing use of ultraviolet light or electron beam radiation to cure adhesives. Adhesives designed for UV- or E-beam curing are usually pressure sensitive or hot-melt systems based on acrylates, functional rubbers, or epoxidized rubbers, and use special UV or EB lamps to provide the cure. These systems can provide greatiy improved heat resistance compared to hot melts, and avoid the soivent emission problems of some of the solvent-based systems with which they compete. 

Films were drawn down on cleaned 5"x20 aluminum panels using a 10 mil drawing bar and cured under ultraviolet light in air using a commercial 300 watt/inch medium pressure mercury lamp and conveyor system (Fusion Systems) at 105 fpm and evaluated as described previously (2). 

Ultraviolet curing UV curing adhesives use ultraviolet light to initiate curing. This allows a permanent bond to develop without any need for heating. UV curable adhesives use various chemical systems, which include acrylics and acrylates, epoxies, polyurethanes (PUR), polyesters, silicones, vinyl and vinyl esters Aaylics are the most common components of UV curable adhesives. 

Nearly 42% of the demand for all adhesives comes from the packaging sector. Radiation-curable adhesives are used primarily for packaging, with paper and paperboard the dominant materials used in the packaging. Radiation-curable adhesives can be used on glass, metal and some plastic materials. Other applications for radiation-curable adhesives are in healthcare, electronics, communications, pressure-sensitive tape and consumer applications. Ultraviolet (UV)-curable adhesives are best suited to small-scale applications, while electron beam (EB)-curable adhesives are more appropriate in high-volume applications (an EB system has a higher installation cost). One additional characteristic of EB-curable adhesives is that they can cure the area between two substrates. UV light-cured adhesives can also be applied on heat-sensitive substrates and are not affected by ambient temperature or humidity. 

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