TPO/BAPO PI that was shown in Figure 3.15. These two patents claim less than or equal to 2 % of the TPO/BAPO PI which just happens to be well under the 5% regulatory limit for this type of PIs in cosmetic products. The colorant option is also reviewed in these patents and was shown to meet SCCS testing requirements for the UV nail gel industry [15]. Another more recent patent application claims the compositional aspect of the UV-PUD in combination with the final use formulation. These formulations contain no solvents or co-solvents and can result in low viscosities of 500 to 3000 cPa.s at a application solids of 20 to 30% in water. These systems also respond to UV-A LED light sources by utilizing the TPO/BAPO PIs that were described earlier [16].
Figure 3.16 Typical UV Curable Polyurethane Dispersion Synthesis [12].
3.7.2 Bio-Based UV Cured Nail Gel Materials
Zareanshahraki and Mannari [17] have developed formulations from biobased raw materials that can be used for high solids and water-based technologies. They found that when using the SUNUV 48W UV-LED unit that operates in the 365 to 405 nm range they were able to output 0.691 J/cm2 of UV energy. As a baseline they use a UV-mercury system (Fusion) with an H-bulb that outputs 0.70 J/cm2 of UV energy. Results were compared to a known technology that had tack issue when cured under these same conditions.
As can be seen in Table 3.4 the bio-based high solids UV nail gel formulations performed well under the conditions of acetone double rubs, Koenig Hardness (Koenig pendulum damping test measures the number of oscillations that the pendulum exhibits according to ASTM D4366-16) and pencil hardness (ASTM D3363-05).
The bio-based UV-PUD formulations did not perform as well and need to be further studied [17].
3.8 Human Nail Mechanical and Surface Free Energy Properties
Now that we have reviewed technical aspects of the UV cure nail gel coatings technology, we must now look into what the human nail plate presents as a substrate to be coated.
Table 3.4 Properties of the bio-based high solids UV nail gels.
| Acetone double rubs | König hardness (Oscillations) | Pencil hardness | ||||
| Method of curing | UV-Mercury | UV-LED | UV-Mercury | UV-LED | UV-Mercury | UV-LED |
| Base coat | 170 | 180 | 126 | 110 | H | 2H |
| Polish | >200 | >200 | 120 | 114 | F | F |
| Top Coat | >200 | >200 | 136 | 120 | 3H | 5H |
Table 3.5 Properties of the bio-based UV-PUD formulations.
| Acetone double rubs | König hardness (Oscillations) | Pencil hardness | ||||
| Method of Curing | UV-Mercury | UV-LED | UV-Mercury | UV-LED | UV-Mercury | UV-LED |
| Polish | 15 | 12 | 86 | 90 | HB | HB |
| Polish including 10 wt.% TMPTA | 45 | 40 | 87 | 94 | F | F |
| Polish including 10 wt.% Bomar BR 952 | 15 | 20 | 76 | 76 | F | F |
| Non-pigmented formulation including 10 wt.% TMPTA | 40 | 38 | 85 | 90 | H | H |
1 a. Before one can coat the human nail plate, one must understand the conditions in which the human nail exists. Researchers determined the surface free energy of the nail plates in vivo. They found that the surface free energy of healthy human fingernail was 34 mJ/m2. Contact angle measurements were accomplished utilizing water, formamide, diiodomethane and glycerol. There are many ways to determine surface free energy of solids using contact angle measurements [18, 19] but here we have used the Lifshitz-van der Waals/acid-base (LW-AB) approach, also known as the van Oss, Chaudhury and Good approach. The in vivo method was performed on 8 females, 9 males who were 23 to 51 years old.
2 b. As can be seen in Table 3.6 the surface free energy values for in vivo subjects nail plates are determined using the water-formamide-diiodomethane (WFD) and water-glycerol-diiodomethane (WGD) liquids combinations. These values will be important to understand later in this chapter when we describe the application of UV cure nail gels based on acrylated oligomers and acrylated monomer systems as well as UV curable polyurethane dispersions [20].
