UV curing
UV curing is a speed curing process in which high intensity ultraviolet light is used to create a photochemical reaction that instantly cures inks, adhesives and coatings. UV Curing is adaptable to printing, coating, decorating, stereolithography and assembling of a variety of products and materials owing to some of its key attributes, it is: a low temperature process, a high speed process, and a solventless process—cure is by polymerization rather than by evaporation. [1] Originally introduced in the 1960s this technology has streamlined and increased automation in many industries in the manufacturing sector.[2]
Applications
UV curing is used whenever there is a need for curing and drying of inks, adhesives and coatings. UV cured adhesive has become a high speed replacement for two part adhesives, eliminating the need for solvent removal, ratio mixing and potential life concern. It is used in the screen printing process where the UV curing systems are used to cure screen printed products which range from T-shirts to 3d and cylindrical parts. It is used in fine instrument finishing (guitars, violins, ukuleles, etc.), pool cue manufacturing and other wood craft industries.
Other industries which take advantage of UV curing include medical, automotive, cosmetic, food, scientific, educational and art.
Advantages of UV curing
The primary advantages of curing finishes and inks with ultraviolet lie in the speed of which the final product can be readied to ship. In addition to speeding up production, this also can reduce flaws and errors, as the amount of time that dust, flies or any airborne object has to settle upon the object is reduced. This can increase the quality of the finished item, and allow for greater consistency.
The other obvious benefits are that manufacturers are able to devote less space to finishing items if they don't have to wait for them to dry. This creates inefficiencies that rippled through the entire manufacturing process.
Types of UV curing
Mercury vapor lamps are the industry standard for curing products with ultraviolet light. The bulbs work by high voltage passing through, vaporizing the mercury. An arc is created within the mercury which emits a spectral output in the UV region of the light spectrum. The light intensity occurs in the 240 nm-270 nm and 350-38-nm. This intense spectrum of light is what causes the rapid curing of the different applications being used. In the last few years an emerging type of UV curing technology called UV LED curing has entered the marketplace. This technology is growing rapidly in popularity and has many advantages over mercury based lamps although is not the right fit for every application [3]
Types of ultraviolet lamps
Mercury vapor lamp (H type)
The mercury lamp has an output in the short wave UV range between 220 and 320 nm (nanometers) and a spike of energy in the longwave range at 365 nm. The H lamp is a good choice for clear coatings and thin ink layers and produces hard surface cures and high gloss finishes.
Mercury vapor lamp with iron additive (D type)
The addition of iron to the lamp yields a strong output in the longwave range between 350 and 400 nm while the mercury component maintains good output in the short wavelength range. The D lamp is a good choice for curing heavily pigmented inks, adhesives, and thick laydowns of clear materials.
Mercury vapor lamp with gallium additive (V type)
The addition of gallium to the lamp yields a strong output in the longwave range between 400 and 450 nm. This makes the V lamp a good choice for curing white pigmented inks and base coats containing titanium dioxide which blocks the most shortwave UV.
Fluorescent lamps
Fluorescent lamps are used for UV curing in a number of applications. In particular, these are used where the excessive heat of mercury vapor is undesirable, or where finer grained control over the process is desired. Fluorescent lamps can be created that produce ultraviolet anywhere within the UVA/UVB spectrum. Additionally, lamps that have multiple peaks are possible, allowing a wider variety of photoinitiators to be used. While fluorescent lamps are less efficient at producing UV than mercury vapor, newer initiators require less total energy, offsetting this disadvantage. Fluorescent lamps in a wide variety of sizes and wattages are available.