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UV CURING – A Guide

UV CURING – A Guide. Jon Anderson. Outline. Background to UV technology UV lamp technology types Temperature effect on UV curing UV curing troubleshooting case studies. Background to UV curing – medium pressure mercury lamps. Energy is applied to mercury causing it to vaporise

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UV CURING – A Guide

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  1. UV CURING – A Guide Jon Anderson

  2. Outline • Background to UV technology • UV lamp technology types • Temperature effect on UV curing • UV curing troubleshooting case studies

  3. Background to UV curing – medium pressure mercury lamps • Energy is applied to mercury causing it to vaporise • The vapour becomes a plasma and emits UV light • Visible wavelengths 200 to 400 nm are the most useful range for curing. • Curing is polymerization of monomers and oligomers - polymer cross linkingand a phase change from liquid to solid state Fusion UV

  4. Background to UV curing Dose (J/cm2): • Total energy delivered • Related to total energy emitted time spent underneath UV light i.e. conveyer speed Irradiance (W/cm2): • Intensity of light delivered • Related to lamp type and geometry of reflector

  5. Bulb types • Mercury used in bulbs to produce the UV energy • The metal can be doped with another metal (Iron or Gallium)to alter the UV output – used to cure different coating technologies such as thickfilm or pigmented systems • Different doping metals produce different spectral outputs Courtesy UVDoctors, Inc Standard H bulb Iron doped bulb

  6. UV Lamp technology

  7. Microwave – electrode-less UV light generated by microwaves irradiating the mercury • 300 to 600 watts/in power • 10 inch maximum length bulb • 10 sec start-up time • 3000 hour typical lifetime • Consistent doped lamp output

  8. Arc – with electrode • 200 to 750 watt/in power • Lengths up to 72 inches • 2 to 3 min start-up time • 1000 hour typical lifetime

  9. Curing UV product range • Cures with arc or microwave technology but….. • Sufficient dose and irradiance required • Bulb type important – UV range requires UVA, B and Cso ‘H’ bulb must be used Correct power but wrong bulb = uncured material

  10. Dose and Irradiance values These are the minimum values that will cure UV40 range and result in tack-free surface But….don’t take them as absolute. Always check the cure of the material!!! There may be other factors involved: • Temperature from excess IR can lower requirement for dose and irradiance • Reflectance – too much/too little can lead to surface defects

  11. Microwave Arc vs. Microwave? Lamp technologies deliver UV energy in different way Microwave delivers a higher peak irradiance than arc Irradiance Arc

  12. Temperature Effect on UV curing Experiment conducted to observe increased temperature effect on the UV curing of UV40-250: 1. After coating application test coupons were heated to a set temperature 2. Material was tested for tack-free surface after UV cure Microwave Arc

  13. Temperature Effect on UV curing Both lamp technologies will generate IR during operation. Increased IR can reduce the threshold required to provide a full cure i.e. tack-free surface Microwave threshold Arc threshold Lower arc threshold with increased IR

  14. Case Study 1: Tacky coating • Coating surface sticky after passing under UV light – surface should be tack-free • Due to insufficient UV C irradiance - check bulb type – should be mercury ‘H’ bulb - check lamp height. It may be out of focus = insufficient energy reaching surface - check reflector – may be dirty/oxidised so not reflecting effectively

  15. Lamp Focus UV Process Supply Inc.

  16. Lamp Focus Out of focus lamp does not deliver as high intensity UV energy to the coating In focus Irradiance Out of focus

  17. Case Study 2: Wrinkling • Coating surface is not smooth after UV curing

  18. Causes: • Excessive ventilation disturbing the coating surface • excessive temperatures – not enough cooling • Excessive reflection – too much UV light reflected is stressing the coating surface

  19. Case Study 3: Curing 3D device • Curing on flat devices (low standoff heights) is standard for most UV curing processes • What about sides of components or housings? – these can be difficult to cure fully

  20. Solution – additional reflector Standard ½ ellipse reflector for ‘flat’ surfaces – some energy is lost out the sides of the reflector Additional reflector to add depth to UV cure results in increased energy reflected UV Process Supply Inc.

  21. Summary • The lamp technology is irrelevant (UNLESS ITS LED!) • What matters is the wavelength, amount and intensity of UV energy reaching the coating Determined by: • Bulb type, lamp focus, reflectance, conveyer speed

  22. Useful links for further reading • www.fusionuv.com/uvlearning_center.aspx • www.uvcuring.com/ • www.pcimag.com/articles/96376-some-practical-advice-for-selecting-a-uv-curing-system

  23. Any questions?

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