Page 49 - Market Analysis Report of Optical Communications Field in China & Global market 2018

2.2 Photo – Differential Scanning Calorimeter (DSC) Figure 6. Real-time FTIR-ATR set-up
DSC, differential scanning calorimeter, is a well-known laboratory
technique to measure the heat generated in a reaction (in this case
photopolymerization) and give us information such as percent
conversion and polymerization rate.
Photo-DSC is a traditional DSC equipped with a UV light source to
induce photopolymerization. To augment a conventional UV light
source that has been in place for many years, a UV-LED light source was
recently brought in-house.
2.2.1Equipment
At the heart of photo-DSC is a TA Instrument Q2000 DSC unit.
Providing the UV-LED light source is a ULM-2-395 LED head and
SA7050 AccuCure Intelligent Controller from Digital Light Lab. The data
were analyzed by Universal Analysis 2000 software, Version 4.5A. 2.3.1Equipment
Figure 4. Photo-DSC set-up Nicolet 8700 FTIR of Thermo Scientific is the spectrometer, ATR is from
ASI Applied Systems, and UV-LED light source were from ULM-2-395
LED head, supplied by Digital Light Lab.

2.3.2Experimental Description
A drop of coating was placed on top of a diamond ATR crystal, followed
by a draw down with a 3 mil draw down bar across the diamond to
create a 75 micrometer thick coating film. Then the adapter and UV-LED
lamp were set-up above the coating layer. Dry air purge was conducted,
and maintained throughout the test. Finally, a spectra collection was
started before turning on the UV- LED lamp at 2 seconds. 45 data points
were taken in 30 seconds.Data were analyzed by OMNIC 8.3 software, of
Thermo Scientific, as well.
2.2.2Experiment Description 3.Results and Discussion
A 1.5 mg sample was added to a Tzero pan using a capillary tube and 3.1Photo-DSC
the pan was put in the DSC unit. The sample was cured and monitored 3.1.1Peak Heat Flow
under the conditions listed in Table 3. Peak heat flow in Photo-DSC is a measurement of maximum reaction
Table 3. Photo-DSC test conditions (photopolymerization) rate. As shown in Figure 7, in terms of reaction
rate, coating C > coating B > coating A.
Figure 7. Photo-DSC Peak Heat Flow

2.3Real-time Fourier Transfer Infrared Spectroscopy – Attenuated
Total Reflectance (FTIR-ATR)
Fourier Transfer Infrared Spectroscopy (FTIR) is the most common
laboratory test to measure degree of cure, the percentage of carbon-
carbon double bond that have polymerized. Therefore, the degree of
cure (DOC) is also referred to as reacted acrylate unsaturation (RAU).

Real-time IR is more advanced. It is used to collect RAU data points in 3.1.2Total Heat Generated
a continuous fashion, while the radiation is ongoing, to allow following Total heat generated in Photo DSC is a good measurement of how much
cure for the whole process (vs traditional IR when RAU is taken after double bond of an acrylate group has reacted, which was obtained by
conversion has reached a plateau). integrating the area underneath the DSC curve for each coating sample.
Results are summarized in Table 4.
In this paper, coatings were analyzed by the ATR sampling technique, Table 4. Heat Generation in Photopolymerization
attenuated total reflectance. As illustrated in Figure 5, the ATR technique
allows for evaluating RAU in 0.5 to 2 micrometer thickness of sample,
making it a powerful tool to measure surface RAU (vs. conventional
transmittance IR for the whole thickness of the sample where IR beam
goes through).
Figure 5. ATR illustration [13]
It’s interesting to note that the total heat generated follows the same
relative reactivity as Peak Heat Flow, demonstrating excellent correlation
and consistency between the two measurements.
3.2Real time FTIR – ATR
Due to the dry air purge in the current experiment set-up, oxygen
inhibition is too great for the surface cure. What is measured instead
is thin film bottom % RAU, an estimation of the through cure. We are
49