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technical guide

fep uv transmission data


Current GMP practices in food and pharmaceutical processing plants demand that production areas are glass free, or that any glass, if broken, cannot find its way into the products. This poses problems in the use of EFKs (electronic fly killers) and sterilising plants which use ultraviolet emitting lamps.

This is because the UV radiation is notoriously harmful to polymers that would be able to protect the lamps. Any polymers used would not only have to be resistant to the UV, but also transparent to it over the whole life of the lamp.

Various polymers have been tried over the years, and many found to be totally useless, as they mostly age with the dose of UV radiation so that they become discoloured, and worse, become brittle. The most successful have been found to be the fluoropolymers containing high amounts of the -CF2- and -CF3 in the molecule chain, and the very best appear to be the completely fluorinated polymers.

Manufacturers' data on the UV transmission is variable or non-existent, and it has been found impossible to compare one material with another from their data. Tests commissioned by Adtech using a UV spectrophotometer to measure the transmission of flat polymer films showed up an unforeseen problem.

It was found that at UV frequencies the light was scattered by the polymer films, which were clear to visible light. The parallel beam of light used in the spectrophotometer was scattered passing through the film and gave a value significantly less than the total transmittance. The answer to this was to test the films or sleeves in situ and measure the loss in output of the UV lamp with the various coatings.

UVA Testing

The following test method was developed. A standard cylindrical UV lamp was mounted in a holder, and a calibrated UV radiometer mounted with its sensing head 25mm from the surface of the lamp.

As the output of UV lamps varies significantly over time, it was important to use one lamp for all tests, and not turn off the lamp in between testing.

Therefore, coatings were removed (cut) from lamps and reapplied to the standard lamp by making a join on the lamp opposite to the sensor head. The various coatings could be quickly applied and removed this way, yet the lamp could remain on and the sensor and lamp did not move from their relative positions.

Readings were taken as 1-minute total dose of UV, made alternatively on the various samples. This was then repeated 6 times including the lamp uncovered as control.

Technical Details

  • Lamp: Sylvania F15 T8 BL 15-watt 25mm diameter

  • Sensor: EIT UVIRAD UV integrating radiometer Model UR365CH1

  • Spectral Response: 320-390 nm (UV-A)


Sample Details

  • Sample 2 & 7: Adtech FEP 0.25mm

  • Sample 3: Adtech FEP 0.5mm

  • Sample 4 & 8: Competitive coating 1 0.22mm

  • Sample 5: Adtech development product XP 05 0.3mm

  • Sample 6: Adtech development product XM 04 0.2mm

UVA Test Results

in millijoules/cm²/min

Batch 1
Test 1 Test 2 Test 3 Test 4 Test 5 Test 6 Total % UV-A loss
No coating 258 257 249 255 255 249 1523 0
Sample 2 245 243 243 243 246 237 1457 4.33
Sample 3 221 243 226 229 232 227 1378 9.52
Sample 4 207 211 205 213 207 207 1250 17.92
Sample 5 225 224 220 218 220 218 1325 13
Sample 6 249 244 244 242 240 239 1458 4.26


Batch 2
Test 1 Test 2 Test 3 Test 4 Test 5 Test 6 Total % UV-A loss
No coating 252 253 255 252 253 253 1518 0
Sample 7 245 244 245 247 245 242 1468 3.30
Sample 8 211 210 214 218 211 214 1278 15.81

UVA Testing Conclusions

The test method is very consistent, easy to do, and gives the actual practical losses shown by lamp coatings as in use.

There is a very big difference between the coatings tested. A loss of 15% or more is unacceptable in EFKs, as the efficiency of the machine attracting and destroying flying insects is proportional to the UV-A output.

The test apparatus used here is portable and can be demonstrated by request.

© Adtech Polymer Engineering Ltd. 1999


UVC Research

Customers often ask for data regarding the long-term use of FEP with UVC lamps. Adtech did not have the data readily available and as such, gladly offered FEP heat shrink samples to be used for a research conducted by Light Sources on the long-term change in transmission of fluoroplastic heat shrink exposed to intense UVC radiations.

The research found that fluoropolymer heat shrink minimally degrades after 8000 hours. The UVC transmittance degradation amounted to approximately 3-7% on amalgam lamps and 0-3% on standard and high output lamps. The research also found that the UVC transmittance degradation levelled off to an approximately linear rate after 2000 hours.


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