WCA November 2020

Run

1

2

3

4

5

6

UA-1

70

70

70

0

0

0

UA-2

0

0

0

70

70

70

Acrylates-2

24

22.5

21.2

24

22.5

21.2

N-vinyl monomer

6

5.6

5.3

6

5.6

5.3

Di-functional monomer

0

1.9

3.5

0

1.9

3.5

machine at tensile speed of 1mm/min with crosshead distance of 25mm. The modulus was defined by the secant modulus at 2.5% elongation. The tensile strength at break and tensile elongation were measured under the same condition except the tensile speed of 500mm/min was applied. 1.4 Analysis of dynamic mechanical response Dynamic mechanical response of the cured film was measured by using a visco-elastometer in the temperature range of -100°C to +100°C, with heating rate of 2°C/min and at a frequency of 3.5 Hz. Temperature dependence of storage modulus (E’) and loss tangent (tanδ) for the cured film was measured. ❍ ❍ Table 1 : UV curable resins with various amounts of di-functional monomer

2 Results and discussion The addition of the di-functional monomer enhanced the crosslink density, and Young’s modulus was controlled by the amounts of di-functional monomer. Table 1 lists the tested resins. The di-functional monomer to the resin was varied from 0 to 3.5 wt % to the formulations containing 70 wt % of UA-1 (Run1, 2 and 3) and UA-2 (Run4, 5 and 6). Figure 1 shows the relationship between Young’s modulus and tensile strength. The addition of di-functional monomer enhanced not only Young’s modulus but also tensile strength for both UA-1 and UA-2 formulations. As compared with Run1 and Run4 or Run2 and Run5 (the same formulation except for urethane acrylate oligomers), they had similar tensile strength in spite of their different Young’s modulus. This experiment yields that using UA-1 is more suitable to achieve high mechanical strength with low Young’s modulus than using UA-2. Dynamic mechanical analyses of the Run2 and Run5 films were carried out and the results are plotted in Figure 2 . Both tanδ curves of Run2 and Run5 showed bimodal shapes. This result implied the induction of the phase separation of lower Tg polyether diol and higher Tg acrylate polymer to Run2 and Run5 films. Run2 showed inflection points at -40°C and -4°C. Run5 showed inflection points at -54°C and 5°C. In light of the evidence, the phase separation status between Run2 and Run5 was different, and this different phase separation status might cause the different relationship between Young’s modulus and tensile strength. It is necessary to examine the nanoscale morphologies in order to elucidate the phenomenon. However, as far as we know, the morphologies of the films had not been examined. In general, UV curable urethane acrylates are known as they are composed of rigid polyurethane and acrylates sequences (hard segment) and flexible polyether segments (soft segment). Therefore, it might be possible to confirm the nanoscale morphology of the UV curable urethane acrylates films by measuring nanoscale modulus and adhesion maps. In this study, the AFM technology had been used to investigate the phase structure of the Run5 film.

❍ ❍ Figure 1 : Relationship between Young’s modulus and tensile strength

Tensile strength [MPa]

Young’s modulus [MPa]

❍ ❍ Figure 2 : Loss tangent (tanδ) of Run2 and Run5 films

tanδ

Temperature [°C]

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Wire & Cable ASIA – November/December 2020