Radiometer Readings

Radiometer Readings:

With the help of my colleagues at Uvitron International (www.uvitron.com), I was able to obtain radiometer readings of my lab conveyor UV curing lamps manufactured by Systematic Automation (www.systauto.com). The radiometer used for this test was a UV Power Puck II by EIT. It is capable of reading four bandwidths at the same time. Here is a link to their TDS for this product: http://www.eit.com/instruments/PlusIIPuckIILiteratureWeb.pdf. The four band widths are UVA (320-390 nm), UVB (280-320 nm), UVC (250-260nm), and UVV (395-445 nm).

 

Gallium Doped Bulb 20 Feet/ Min   30 Feet/Min  
Fusion “V-Bulb” Dosage (mj/cm^2)

 

Peak Intensity (mW/cm^2) Dosage (mj/cm^2)

 

Peak Intensity (mW/cm^2)
UVA 585.9 583.2 390.2 578.9
UVB 805.4 794.6 537.1 789.2
UVC 172.0 171.3 114.2 169.2
UVV 1723.0 1541.3 1146.3 1531.4

 

Iron Doped Bulb 20 Feet/ Min   30 Feet/Min  
Fusion “D-Bulb” Dosage (mj/cm^2)

 

Peak Intensity (mW/cm^2) Dosage (mj/cm^2)

 

Peak Intensity (mW/cm^2)
UVA 1460.0 1401.7 957.5 1384.6
UVB 778.5 774.7 516.8 774.0
UVC 129.8 132.1 86.8 132.0
UVV 1072.6 1021.7 697.2 1000.0

 

Total lamps hours on my curing unit was only 66.73 and that was split between the two bulbs, about 80:20 V-bulb to D-bulb.

Peak intensity is the same regardless of conveyor speed. It is how bright the light is at the given band width. Dosage is the light intensity integrated over time. As you can see from the data above, dosage varies with time (conveyor speed).

This data is important from a process control standpoint because the intensity, and therefore dosage, decreases as the lamps age. This is particularly true of electroded bulbs that degrade until failure. However, the microwave powered lamps (electrodeless), made by Fusion (www.fusionuv.com)       among others, tend to supply a constant output until failure. This is one advantage that the microwave systems have because monitoring of the lamp’s output can be less of a burden to the process engineer responsible for the UV curing line or printing press.

Also, you can see that the output from the Gallium Doped bulb is different from the Iron Doped bulb at different wavelengths. This is an important fact for the UV ink or coating formulator who is evaluating the interaction of the components of the formulation with the output of the lamps.

As I discussed in my previous articles, Titanium Dioxide (the white pigment) is a strong UV light absorber which results in poor through-cure of thick films if the wrong combination of photoinitiators and lamp output are not taken into consideration. So, for highly pigmented inks or coatings, especially screen printed inks, the Gallium Doped bulb is very effective to cure the white inks because the wavelengths in the “UVV” range, mentioned in the chart above, can penetrate through the white ink better than the UVA and UVB.

Photoinitiator selection should always be a blend of initiators that take advantage of the different wavelengths that the lamp emits. This will maximize through-cure, utilizing the UVV wavelengths and surface cure, utilizing the UVA, UVB wavelengths.

Functional Inks, LLC UV inks for direct screen printing on plastic were designed to work with either bulb at 20 feet per minute. Please call Paul Giusto at the number above if you wish to discuss an application.

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