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What is UV?
1. UV Light - basics
2. Ultra Violet (UV) Curing
3. Germicidal Properties
UV Light - basics
Electromagnetic (EM) radiation is generally emitted from the sun, as well as man-made sources. The overall EM spectrum comprises of (going from long to short wavelengths) radio waves, microwaves, infra-red (heat), visible (light), Ultra-violet (UV), X-rays and Gamma rays. Ultra-violet radiation is the part of the electro magnetic radiation spectrum below visible light. That is, wavelengths from 180nm to 400nm.
UV has been classified by scientists according to the effect it has on living organisms as UVA, UVB, UVC and UVV.
UVA has long wavelength and starts at 315 nm and includes 400nm which is also where visible light (blue) starts. UVA is able to penetrate our skin or any substrate (such as coatings, paper etc) and is often used for "depth of cure" in industrial processes. Our skin has developed mechanisms to cope with UVA and is therefore not too harmful so long as the dose is no higher than you would get from the sun. However, it is worth bearing in mind that UVA Ages the skin.
UVB is defined as 280 - 315 nm. Having a higher energy than UVA, UVB does not penetrate so deep but can cure quicker. Our skin is not well protected from UVB as only small amounts penetrate the ozone layer. UVB Burns.
UVC is defined as below 240nm - 280 nm. This UV has very high energy, which it loses as soon as it hits a surface. Thus in industry UVC is used for surface cure. Life on earth has no protection from UVC and so it is highly dangerous, however our atmosphere filters this out for us (except for ozone ‘holes’ which is why global warming is of great concern). Therefore UVC is used for germicidal applications too as it will actually kill viruses and bacteria, as well as moulds and fungi.
UVV is defined as 390 - 445nm and is used to cure inks and coatings that contain titanium dioxide (TiO2). TiO2, the typical pigment for white is successfully cured at 400 - 430nm.
Ultra Violet (UV) Curing
Light-based curing can be defined as the process in which ultra-violet (UV) or infrared (IR) light is used to initiate a curing process in adhesive materials.
Typical UV curing materials, inks, coatings and adhesives, contain photo initiators that, when exposed to UV light create polymer chains that change the material from a liquid to a solid.
The thermal cure materials commonly used in industry are typically cured in convection ovens.
Some of the advantages light-based curing provides are as follows:
- Greater material control
- Increased throughputs and yields
- Ease of integration into automated processes
- Manufacturing scaleability
- UV materials are environmentally friendly
Germicidal Properties
Germicidal ultraviolet rays operate at wavelength of 253,7 nanometers (known as UVC). Such an emission has maximum germicidal strength against viruses, bacteria and fungi.
The action is exclusively physical, not chemical, thereby leaving no pollution residues at the end of treatment. In addition, as the UVC light affects the nucleic acids of the microbes DNA, there is no gradual build-up of resistance against UVC light, as can occur with antiseptics and antibiotics.
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