LU-8031 - High Irradiance UV Testers - Q-Lab

TECHNICAL BULLETIN LU-8031
High Irradiance
UV/Condensation Testers
Allow Faster Accelerated
Weathering Test Results
Introduction & Background
Weatherability is a necessary quality for coatings
used outdoors. Because outdoor exposures
are so time consuming, accelerated
laboratory testing is used extensively by
industry. One of the more popular laboratory
weathering testers is the ASTM G53 UV/Condensation
device, also known as the QUV. 1
In the QUV, test specimens are repetitively
exposed to alternating cycles of UV light and
condensing moisture at controlled temperatures.
Previously, exposure conditions could be
varied only by the selection of the fluorescent
UV lamp, the timing of the UV and condensation
exposures and the temperatures of the exposures.
This paper examines an enhancement
to the QUV weathering tester for precise control
of light output and higher irradiance. Data is
presented on the accelerating effect of higher
irradiance on several common polymers.
Irradiance Control System
The irradiance control system, marketed under
the name “Solar Eye,” consists of a programmable
controller that continuously monitors the
UV intensity via four sensors mounted in the
test sample plane. A four channel feedback loop
system maintains the programmed irradiance
level by adjusting power to UV lamps. The irradiance
level can be adjusted to varying intensities
for different applications. Figure 1 shows
a simplified schematic of how the irradiance
control system works.
Each sensor monitors the intensity of two
lamps. Each sensor is individually calibrated
Figure 1
1
Sample
Plane
Ballast 1
Controller
Ballast
Lamps
(all same age)
Detector
Sample
Plane
by the operator on a regular basis. The calibration
is traceable to the National Institute of
Standards and Technology (NIST) for ISO 9000
compliance.
Data presented previously 2 has shown that the
Solar Eye control system largely eliminates
variations in UV intensity and therefore greatly
reduces variations in test results.
Ballast 4
Ballast 3
3
4
1. ASTM G53, Standard Practice for Operating Light and Water Exposure Apparatus (Fluorescent UV-Condensation Type) for Exposure of
Nonmetalic Materials, Annual Book of ASTM Standards, Vol. 04.07, American Society for Testing and Materials, Philadelphia, 1992.
2. Fedor, G. R., Brennan, P. J., “Irradiance Control In Fluorescent UV Exposure Testers,” Accelerated and Outdoor Durability Testing of Organic
Materials, ASTM STP 1202, Warren D. Ketola, and Douglas Grossman, Eds., American Society for Testing and Materials, Philadelphia, 1993.

High Irradiance for Faster Results
The programmable, automatic irradiance control
system allows the operator to choose a higher than
standard level of irradiance for UV exposure tests.
For many materials, this results in faster degradation
and therefore shorter test times.
It is widely recognized the UVA-340 lamp is a more
realistic simulation of sunlight than the UVB-313
lamp. 3,4 Since its introduction, most of the plastics
industry has switched to the UVA-340 because it
gives more realistic results. However, in spite of its
limitations, a large number of coatings researchers
continue to use the UV-B lamps because they give
faster results. With the programmable controller,
the UVA-340 can now be operated at higher irradiance
levels to speed up test results. Figure 2
shows UVA-340 lamps at various irradiance levels,
compared to sunlight.
The recommended maximum increase over typical
G53 irradiance is 75%. Even though lamps are
capable of higher intensity levels at full power, it is
not recommended that tests be run at levels higher
than 1.75x normal. There must be some excess
power available to maintain the desired set point
and account for such things as lamp aging and other
factors which reduce the maximum irradiance
potential. It should be noted that lamps operated at
higher than normal irradiance will have a proportionally
shorter useful life span.
Exposure Results for Various
Polymers
The programmable, automatic irradiance control
system allows the operator to choose a higher than
standard level of irradiance for UV exposure tests.
For many materials, this results in faster degradation
and therefore shorter test times.
It is widely recognized the UVA-340 lamp is a more
realistic simulation of sunlight than the UVB-313
lamp. 3,4 Since its introduction, most of the plastics
industry has switched to the UVA-340 because it
gives more realistic results. However, in spite of its
limitations, a large number of coatings researchers
continue to use the UV-B lamps because they give
faster results. With the programmable controller,
the UVA-340 can now be operated at higher irradiance
levels to speed up test results. Figure 2
shows UVA-340 lamps at various irradiance levels,
compared to sunlight.
The recommended maximum increase over typical
G53 irradiance is 75%. Even though lamps are
capable of higher intensity levels at full power, it is
not recommended that tests be run at levels higher
than 1.75x normal. There must be some excess
power available to maintain the desired set point
and account for such things as lamp aging and other
factors which reduce the maximum irradiance
potential. It should be noted that lamps operated at
higher than normal irradiance will have a proportionally
shorter useful life span.
Figure 2 Figure 3
UVA-340 at Different Intensities
Acrylic Yellowing
Irradiance W/m /nm
1.5
1
0.5
Intensified
1.75x
UVA-340
Typical Irradiance
Reduced to .35
Noon Summer
Sunlight
Gloss
100
80
60
40
20
0.83
Material: Epoxy Coating (gray)
Test Conditions:
QUV/se
Lamp: UVA-340
Irradiance: 1.35 & 0.83 W/m2/nm @ 340nm
Cycle: UV Only
Temperature: B.P. 50C
0
270 290 310 330 350 370 390
Wavelength (nm)
1.3
0
0 500 1000 1500 2000 2500
Hours QUV/se Exposure

Figure 4
Acrylic Yellowing
delta b
10
9
8
7
6
5
4
3
Material: Acrylic Sheet (clear)
2
1.3
1
0.83
0
0 500 1000 1500 2000 2500
Hours QUV/se Exposure
Test Conditions:
QUV/se
Lamp: UVA-340
Irradiance: 1.35 & 0.83 W/m2/nm @ 340nm
Cycle: UV Only
Temperature: B.P. 50C
Figure 8
Acrylic Yellowing
delta b
0.0
-0.2
-0.4
-0.6
Material: Vinyl Film (green)
Test Conditions:
QUV/se
Lamp: UVA-340
Irradiance: 1.35 & 0.83 W/m2/nm @ 340nm
Cycle: UV Only
Temperature: B.P. 50C
1.3
-0.8
0 500 1000 1500 2000 2500
Hours QUV/se Exposure
0.83
Figure 5
Polystyrene Yellowing
Figure 9
Vinyl Yellowing
50
40
1.3
0.83
30
Material:
Polycarbonate Sheet (clear)
1.3
delta b
30
Material:
20
Polystyrene Reference Matl. (clear)
Test Conditions:
QUV/se
Lamp: UVA-340
10
Irradiance: 1.35 & 0.83 W/m2/nm @ 340nm
Cycle: UV Only
Temperature: B.P. 50C
0
0 500 1000 1500 2000 2500
Hours QUV/se Exposure
delta b
20
10
Test Conditions:
QUV/se
Lamp: UVA-340
Irradiance: 1.35 & 0.83 W/m2/nm @ 340nm
Cycle: UV Only
Temperature: B.P. 50C
0
0 500 1000 1500 2000 2500
Hours QUV/se Exposure
0.83
Figure 6
Vinyl Yellowing
Figure 10
Polycarbonate Yellowing
50
30
Material: P.V.C. Film (clear)
1.3
50
40
Material: CAB Sheet (clear)
1.3
delta b
20
10
Test Conditions:
QUV/se
Lamp: UVA-340
Irradiance: 1.35 & 0.83 W/m2/nm @ 340nm
Cycle: UV Only
Temperature: B.P. 50C
0
0 500 1000 1500 2000 2500
Hours QUV/se Exposure
0.83
delta b
30
20
Test Conditions:
QUV/se
Lamp: UVA-340
10
Irradiance: 1.35 & 0.83 W/m2/nm @ 340nm
Cycle: UV Only
Temperature: B.P. 50C
0
0 500 1000 1500 2000 2500
Hours QUV/se Exposure
0.83
Figure 7
Vinyl Gloss Loss
Gloss
100
90
80
70
60
50
40
30
20
10
Material: Acrylic Sheet (clear)
Test Conditions:
QUV/se
Lamp: UVA-340
Irradiance: 1.35 & 0.83 W/m2/nm @ 340nm
Cycle: UV Only
Temperature: B.P. 50C
0
0 500 1000 1500 2000 2500
Hours QUV/se Exposure
0.83
1.3
Figure 11
Polyester
Gloss
100
90
80
70
60
50
40
30
20
10
Material: Polyester Coating (tan)
Test Conditions:
QUV/se
Lamp: UVA-340
Irradiance: 1.35 & 0.83 W/m2/nm @ 340nm
Cycle: UV Only
Temperature: B.P. 50C
0
0 500 1000 1500 2000 2500
Hours QUV/se Exposure
0.83
1.3

Figure 12
Urethane Gloss Loss
Gloss
delta b
100
90
80
70
60
50
40
30
20
10
Material: Urethane Coating (gray)
Test Conditions:
QUV/se
Lamp: UVA-340
Irradiance: 1.35 & 0.83 W/m2/nm @ 340nm
Cycle: UV Only
Temperature: B.P. 50C
1.3
0
0 500 1000 1500 2000 2500
Figure 13
Yellowing
50
40
30
Hours QUV/se Exposure
Material: ABS Sheet (white)
0.83
0.83
20
Test Conditions:
QUV/se
Lamp: UVA-340
10
Irradiance: 1.35 & 0.83 W/m2/nm @ 340nm
Cycle: UV Only
Temperature: B.P. 50C
0
0 500 1000 1500 2000 2500
Figure 14
Hours QUV/se Exposure
Polystyrene Yellowing
1.3
Figure 16
Polypropylene Yellowing
delta b
12
10
8
6
4
Test Conditions:
QUV/se
Lamp: UVA-340
2
Irradiance: 1.35 & 0.83 W/m2/nm @ 340nm
Cycle: UV Only
Temperature: B.P. 50C
0
0 500 1000 1500 2000 2500
Figure 17
Material: Polypropylene Sheet
1.3
Hours QUV/se Exposure
Automotive Paint Gloss Loss
Gloss
100
80
60
40
0.83
Test Conditions:
QUV/se
Lamp: UVA-340
20
Irradiance: 1.35 & 0.83 W/m2/nm @ 340nm
Cycle: UV Only
Temperature: B.P. 50C
0
0 500 1000 1500 2000 2500
Hours QUV/se Exposure
0.83
Material: Automotive Coating (blue/gray)
1.3
0
Material: Polyesthylene Sheet
Effect of Moisture
delta b
delta b
-1
-2
Test Conditions:
-3
QUV/se
Lamp: UVA-340
Irradiance: 1.35 & 0.83 W/m2/nm @ 340nm
Cycle: UV Only
Temperature: B.P. 50C
-4
0 500 1000 1500 2000 2500
Figure 15
Nylon Yellowing
5
4
3
Material: Nylon Sheet
Hours QUV/se Exposure
1.3
0.83
2
Test Conditions:
QUV/se
Lamp: UVA-340
1
Irradiance: 1.35 & 0.83 W/m2/nm @ 340nm
Cycle: UV Only
Temperature: B.P. 50C
0
0 500 1000 1500 2000 2500
Hours QUV/se Exposure
1.3
0.83
For materials which are sensitive to moisture, there
may be a further acceleration when moisture is
added to the UV cycle. Furthermore, some materials
may respond in a completely different fashion
in the presence of moisture. To test this, materials
were exposed under 4 different conditions:
• 100% UV Cycle (at 50 o C)
• UV + Moisture Cycle (4 hours UV at 50 o C,
alternating with 4 hours condensation at
50 o C)
• UV + Dark/dry Cycle (4 hours UV at 50 o C,
alternating with 4 hours dark at 50 o C)
• Moisture + Dark/dry Cycle (4 hours dark
and dry at 50 o C, alternating with 4 hours
condensation at 50 o C)
On the blue vinyl film, the UV+Moisture Cycle
degraded the material most rapidly. Although the
100% UV Cycle exposed the material to twice the
UV “dosage,” the results were not as severe.

Figure 18
Vinyl Gloss Loss
Gloss
100
100
90
80
70
60
50
40
Material: Vinyl Film (blue)
Test Conditions:
30
QUV/se
20 Lamp: UVA-340
Irradiance: 1.35 & 0.83 W/m2/nm @ 340nm
10 Cycle: UV Only
Temperature: B.P. 50C
0
0 500 1000 1500 2000 2500
Figure 19
Urethane Gloss Loss
Gloss
90
80
70
60
50
40
30
20
10
0
Figure 20
11
Hours QUV/se Exposure
Material: Urethane Coating (gray)
100% UV
UV + Moisture
Moisture + Dark/Dry
UV + Moisture
UV + Dark/Dry
100% UV
0 500 1000 1500 2000 2500 3000
Hours QUV/se Exposure
Polypropylene Gloss Loss
Moisture + Dark/Dry
UV + Dark/Dry
Material: Polypropylene Sheet (natural)
Test Conditions:
QUV/se
Lamp: UVA-340
Irradiance: 1.35 & 0.83
W/m2/nm @ 340nm
Cycle: UV Only
Temperature: B.P. 50C
Exposure Duration & Measurement
Intervals
As a general rule, exposures should be run until
the material has reached complete failure. This
is because the perceived difference in the rate of
degradation between any two exposures may vary,
depending on how the data is analyzed.
Figure 21 shows how running an exposure test
to a predetermined level of degradation (in this
case, yellowing) can cause confusion. If the exposure
had been terminated after a delta b of 8 was
reached, the higher irradiance exposure would
appear to be 48% faster. If the exposure had been
terminated at a delta b of 34, the higher irradiance
test would appear to be only 32% faster. Only running
the test to complete failure shows the true
relationship between the two exposures.
Figure 21
Comparison at Varying Levels of Yellowing
delta b
48
40
32
24
Material: ABS Sheet (white)
delta b = 34
3% faster
0.83
16
Test Conditions:
QUV/se
Lamp: UVA-340
8
Irradiance: 1.35 & 0.83 W/m2/nm @ 340nm
delta b = 8
Cycle: UV Only
4% faster
Temperature: B.P. 50C
0
0 500 1000 1500 2000 2500
Hours QUV/se Exposure
1.3
delta b
9
7
5
3
1
-1
100% UV
0 1000 2000 3000
Hours QUV/se Exposure
UV + Dark/Dry
Test Conditions:
QUV/se
Lamp: UVA-340
Irradiance: 1.35 & 0.83 W/m2/nm @ 340nm
Cycle: UV Only
Temperature: B.P. 50C
UV + Moisture
Moisture + Dark/Dry
Figure 22 shows the same data used in the previous
figure. However, here the exposures were
analysed after a predetermined number of hours. If
the two exposures are compared at 500 hours, the
difference appears to be 100%. If they are compared
at 1000 hours, the difference is 22%.
This moisture effect is even more dramatic on the
urethane. Again, although the UV+Moisture Cycle
exposed the material to only half the UV dosage
as the 100% UV Cycle, the rate of degradation is
much faster.
Sometimes the presence of moisture effects both
the rate and the type of degradation. This is illustrated
in Figure 20. In this case, the UV+Moisture
Cycle gave a very different result than the cycles
that omitted moisture.

Table 1
Materials Tester
Material Polymer Description Color Thickness
1 Vinyl film clear 0.006
2 Vinyl glossy film blue 0.003
3 Polystyrene ref. material plaque clear 0.110
4 Vinyl film green 0.004
5 Epoxy coil coating gray
6 Urethane coil coating gray
7 ? automotive paint blue
8 Polyester coil coating tan
9 Acrylic sheet clear 1/8"
10 Polycarbonate sheet clear 1/8"
11 Polyethylene sheet white 1/8"
12 ABS sheet white 1/8"
13 CAB sheet clear 1/8"
14 Polypropylene sheet natural 3/16"
15 Nylon sheet natural 3/16"
An even more dramatic example of this is shown
in Figure 23. After 1000 hours exposure, there is
no difference in the exposure results. However, at
1500 hours, there is an 18 to 1 difference. Because
the lower irradiance test was terminated before the
sample reached failure, there is no way to know
the actual relationship between the two exposures.
These examples also illustrate why degradation
should be measured at regular intervals during an
exposure, rather than at the end of a preset time.
Figure 22
Comparison at Various Exposure Times
delta b
48
40
32
24
Material: ABS Sheet (white)
@1000 hours
% more
yellowing
@00 hours
100% more
0.83
16 yellowing
Test Conditions:
QUV/se
Lamp: UVA-340
8
Irradiance: 1.35 & 0.83 W/m2/nm @ 340nm
Cycle: UV Only
Temperature: B.P. 50C
0
0 500 1000 1500 2000 2500
Hours QUV/se Exposure
1.3
Figure 23
Comparison at Varying Time Intervals
delta b
40
36
32
28
24
20
16
12
8
Material: P.V.C. Film (clear)
Test Conditions:
QUV/se
Lamp: UVA-340
Irradiance: 1.35 & 0.83 W/m2/nm @ 340nm
Cycle: UV Only
Temperature: B.P. 50C
@100 hours
18x more yellowing
than @ 1000 hours
4
0.83
0
0 500 1000 1500 2000 2500
Hours QUV/se Exposure
1.3

Summary & Conclusions
There is currently great interest in using high irradiance
exposures as a method of accelerating
laboratory weathering tests. One way to achieve
higher irradiance is with the programmable automatic
irradiance control system now available for
use in QUV/SE weathering testers. This system
was designed to maintain a precise UV intensity
level throughout an exposure test. With this system,
the operator can choose from a range of irradiance
levels, up to 75% over that of a standard
QUV device.
Acknowledgement
The authors would like to recognize Sandra Kalmbach
for her assistance in data collection and organization.
Accelerated laboratory weathering data from a variety
of materials indicates that, for some of these
materials, exposure to high light intensity levels in
a QUV/SE causes faster degradation. For these
materials, test times can be reduced by using
higher irradiance exposures.
However for other materials, moisture or temperature
may play a critical roll in degradation.
Moisture in the test cycle increased the rate of yellowing
or gloss loss for 5 of the 15 materials tested,
as compared to UV only exposures. Furthermore,
experience indicates that irradiance, moisture,
dark time, and temperature frequently have a synergistic
effect. Using high irradiance to reduce test
times is a promising technique for quality control
and product development. However it could have
a detrimental effect on correlations between laboratory
and outdoor results.

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