[
    {
        "id": 1,
        "chunk": "# Synthesis and characterization of UV curable urethane acrylate oligomers containing ammonium salts for anti-fog coatings  \n\nJ.W. Hong a, H.K. Cheon a, S.H. Kim a, K.H. Hwang a,  H.K. Kim b,∗  \n\na Department of Biochemical and Polymer Engineering, Chosun University, Gwangju 501-759, South Korea b Institute of Photonics &Surface Treatment, Q-Sys Co.Ltd., Gwangju, 61007, South Korea",
        "category": " Abstract"
    },
    {
        "id": 2,
        "chunk": "# a r t i c l e i n f o",
        "category": " Abstract"
    },
    {
        "id": 3,
        "chunk": "# a b s t r a c t  \n\nArticle history:   \nReceived 12 August 2016   \nReceived in revised form 2 March 2017   \nAccepted 6 March 2017   \nAvailable online 15 May 2017  \n\nKeywords:   \nUV-curing   \nAnti-fog   \nPhoto-DSC   \nSalts   \nCoating properties  \n\nUV-curable urethane acrylate oligomer (UV-UAO) containing ammonium salts,  suitable for  anti-fog (AF) coatings was synthesized. The expected UV-UAO structure was confirmed by FT-IR and $^1\\mathrm{H}$ NMR. This UVUAO was then formulated with reactive monomers and photoinitiator to form coating formulas. In order to compare the UV-curing behavior of  UV-UAO  with  conventional oligomers, the photopolymerization of UV-UAO and  SK  cytech EBECRYL-series urethane acrylates (EB  8210  and  EB  9260)  was  investigated by photo-differential scanning calorimetry (Photo-DSC). The  anti-fog properties of UV-cured AF coating were investigated by  contact  angle  test  and  anti-fog test.  Coating properties such as  pencil  hardness, pendulum hardness, gloss,  and  adhesion  of the UV-cured films  containing UV-UAO were investigated. The results showed that  the concentration of UV-UAO in  the  coating  formulation had  a great influence on the anti-fog properties of  UV-cured AF  coating. Especia  lly,  UV-cured AF  coating  containing UV-UAO 65 wt.%  showed excellent anti-fog properties without  sacrificing other  desirable properties such as  pencil hardness and  adhesion.  \n\n$\\mathfrak{C}$ 2017  Elsevier B.V.  All  rights reserved.",
        "category": " Abstract"
    },
    {
        "id": 4,
        "chunk": "# 1. Introduction  \n\nIn the past several years, there has been increasing interest in anti-fog coatings. In general, fog occurs when the difference between air temperature and dew point is generally less than $2.5^{\\circ}\\mathsf{C}.$ This fog begins to form when water vapor condenses onto a surface to form discrete and dispersed light–diffusing water droplets, thereby restricting light transmission and optical efficiency [1]. This undesirable fogging phenomenon occurs frequently on optical materials that are in use in everyday life such as bathroom mirrors, eyeglasses, safety glasses, swimming goggles, windshields, camera lenses, and skis as well as on analytical and medical instruments. In order to overcome this predicament, a method of applying an anti-fog treatment on the surface has been suggested.  \n\nThe basic concept of anti-fog is to create a hydrophilic surface that prevents the condensation of water in the form of small droplets so that light can transmit directly free of interference from scattering by the water droplets. In the early stages of anti-fog coating development, non-reactive anti-fog agents were conventionally introduced into a polymer matrix without chemical bonding. However, they do not produce stable long-term anti-fog properties because the anti-fog agents can be easily wiped off or partially lost during cleaning.  \n\nAccordingly, various materials and processes have been suggested for durable anti-fog coatings. For example, Maechler et al. have reported on a multilayer transparent anti-fog coating on a polycarbonate (PC) [2]. Nuraje at al. have reported on mechanically durable, long-lasting antifog coatings based on polysaccharides [3]. Cebeci et al. prepared stable superhydrophilic nanoporous thin films fabricated from layer-by-layer assembled silica nanoparticles and a polycation [4]. Chang et al. have developed a special hydrophilic/hydrophobic bilayer structure [5]. Yuan et al. have reported on UV curable hydrophilic acrylate polymers containing a sulfonic acid group for anti-fog coatings [6]. However, many of these fabrication processes involve complicated multi-steps and are often time consuming, which poses a hindrance for practical application. Accordingly, our research interest is to develop UV curable anti-fog coatings that can be obtained without the need for cumbersome and complicated synthesis and fabrication processes. This UV curable coating also offers other advantages such as higher productivity, energy savings, and lower capital investment for curing facilities.  \n\nIn this study, UV curable urethane acrylate oligomer containing ammonium salts for anti-fog coating was developed, and its antifog effectiveness and the surface properties of the coating network were investigated.  \n\n![](images/bc340d1c610cb8ebdd2b6663b2294eefa82257af5a993522eb0145dcd8ebf7b6.jpg)  \nScheme 1. Preparation of Ammonium Salt Monomer.",
        "category": " Introduction"
    },
    {
        "id": 5,
        "chunk": "# 2. Experimental",
        "category": " Materials and methods"
    },
    {
        "id": 6,
        "chunk": "# 2.1. Materials  \n\nThe monomers, including ethanolamine, and 2-butanone were purchased from Aldrich Chemicals and purified by vacuum distillation. SY-40M (glycidyl ether of C12 and C14 alcohol) was purchased from Sakamoto Yakuhin Kogyo Co., Ltd. (Japan), and was used without purification. Dimethyl sulfate was purchased from Aldrich Chemicals and purified by vacuum distillation prior to use. Isophorone diisocyanate (IPDI) was purchased from Evonik. Dibutyltin dilaurate (DBTDL) was purchased from Air Products. TLC Silica gel $60\\mathsf{F}_{254}$ (Merck) was used for TLC analysis. Pentaerythritol triacrylate (PETA) and dipentaerythritol hexaacrylate (DPHA) were all supplied by Miwon Specialty Chemical Co., Ltd. (Korea).",
        "category": " Materials and methods"
    },
    {
        "id": 7,
        "chunk": "# 2.2. Synthesis of ammonium salt (AS) monomer  \n\nEthanolamine $\\cdot10.16\\mathrm{g},0.166\\mathrm{mol}$ ) was added to a $250\\mathrm{mL}$ threeneck flask equipped with water bath, thermometer, refluxing condenser, dropping funnel, and magnetic stirring bar, and heated to $60^{\\circ}C$ with stirring. $86.55{\\mathrm{g}}$ of alkyl glycidyl ether (Sy 40M) was slowly added and the mixture was maintained for $^{2\\mathrm{h}}$ at $70^{\\circ}\\mathsf C$ . Dimethyl sulfate $\\cdot20.99,0.166\\mathrm{mol}$ ) and methyl ethyl ketone (MEK, $29.8{\\mathrm{g}}{\\mathrm{,}}$ were added dropwise to the stirred mixture over $3\\ensuremath{\\mathrm{h}}$ , while maintaining the temperature at $60^{\\circ}\\mathsf C.$ The salt group of the final product was identified by the titration of the remaining amine group with $0.1\\mathsf{N}$ HCl solution. $80\\%$ of the total amine group was converted into quaternary ammonium group. The reaction product was identified with $^1\\mathrm{H}$ NMR $(\\mathsf{C D C l}_{3}$ , ${300}\\mathrm{MHz}\\mathrm{\\cdot}$ ): 4.17 ppm $(\\mathrm{N^{+}{-}C H_{2}C\\underline{{{H}}}(-0H){-}C H_{2}})$ , $4.01\\mathrm{ppm}$ $(\\mathsf{N}^{+}{-}\\mathsf{C H}_{2}\\mathsf{C}\\underline{{H}}20\\mathsf{H})$ , 3.52 ppm $(\\mathrm{CH}_{2}\\mathrm{CH}(-0\\mathrm{H}){-}\\mathrm{C}\\underline{{{H2}}}{-}0),$ 3.43 ppm $(\\mathsf{N}{+}{-}\\mathsf{C}\\underline{{H}}_{2}\\mathsf{C}\\mathsf{H}_{2}{0}\\mathsf{H})$ , 3.39 ppm $\\left(\\mathsf{N}^{+}{-}\\mathsf{C}\\underline{{H}}_{2}\\mathsf{C}\\mathsf{H}(\\mathsf{O}\\mathsf{H})\\mathsf{C}\\mathsf{H}_{2}\\right)$ , 3.29 ppm ( $\\left(\\mathsf{N}^{+}{-}\\mathsf{C}\\underline{{{H_{3}}}}^{\\cdot}$ ), 1.22 ppm ${\\mathrm{O}}({\\mathrm{CH}}_{2}){\\mathrm{C}}\\underline{{{H}}}_{3};$ (Scheme 1).",
        "category": " Materials and methods"
    },
    {
        "id": 8,
        "chunk": "# 2.3. UV-curable urethane acrylate oligomer (UV-UAO) with ammonium salt  \n\nTo a solution of IPDI $\\left(34.5\\mathrm{g},0.16\\mathrm{mol}\\right)$ ), and PETA $(100\\mathrm{g})$ in MEK $\\mathrm{\\cdot100mL)}$ , DBTDL $(0.25{\\mathrm{g}})$ was added dropwise at $10^{\\circ}\\mathsf C$ with stirring. After complete addition, the mixture was stirred at $10^{\\circ}\\mathsf C$ for $\\boldsymbol{4\\mathrm{h}}$ . The reaction progress was analyzed by TLC using ethyl acetate: hexane $=1{:}2$ $(\\nu/\\nu)$ . And then, the AS monomer $(96.2{\\mathrm{g}})$ in MEK $(20\\mathrm{mL})$ was added to the above reaction product over 4 h, while maintaining the temperature at $20^{\\circ}\\mathsf C$ The reaction product was identified with $^1\\mathrm{H}$ NMR ( $\\mathrm{\\CDCl}_{3}$ , ${300}\\mathrm{MHz}^{\\cdot}$ and FT-IR: $^1\\mathrm{H}$ NMR $(\\mathsf{C D C l}_{3})$ ): 7.9 ppm $(-\\mathsf{N}H-)$ , $6.35{-}6.25\\mathrm{ppm}$ $\\scriptstyle(-{\\mathsf{C H}}={\\mathsf{C}}{\\underline{{H_{2}}}}$ ), $5.81{-}5.72\\mathrm{ppm}$ $\\scriptstyle(-{\\mathsf{C H}}={\\mathsf{C}}{\\underline{{{H_{2}}}}}$ ), $6.03\\substack{-5.92\\mathrm{ppm}}$ $(\\mathrm{-}\\mathsf{C}\\underline{{H}}\\mathrm{=}\\mathsf{C}\\mathsf{H}_{2}$ ); FT-IR spectrum: $-\\mathsf{N H}$ stretching $3300\\mathsf{c m}^{-1}$ ), ${\\mathsf{C}}{\\mathrm{-}}{\\mathsf{H}}$ deformation mode of the acryl groups $(811\\mathrm{cm}^{-1}$ ) (Scheme 2).",
        "category": " Materials and methods"
    },
    {
        "id": 9,
        "chunk": "# 2.4. Coating formulation and curing procedure  \n\nUV curable anti-fog (AF) compositions were prepared by mixing homogenously UV-UAO with reactive diluents (PETA:DPHA $_{.=8.5:1.5}$ by weight) and the photoinitiator (1- Hydrophenyl ketone, Irgacure 184 from Ciba Specialty Chemicals, maximum peak of absorption: $245{-}330\\mathrm{nm}$ ). Different amounts of UV-UAO $(55-70\\mathrm{wt}.\\%)$ were added into the above composition and the photoinitiator concentration was kept constant at $5\\mathrm{wt.\\%}$ all on the basis of final formulation. A $20\\mathrm{-}\\upmu\\mathrm{m}$ thick coating of the resin composition was applied on the polycarbonate (PC) using bar applicator and then cured with $80\\mathsf{W/c m}$ light a medium pressure mercury lamp of conventional UV equipment.",
        "category": " Materials and methods"
    },
    {
        "id": 10,
        "chunk": "# 2.5. Water contact angle and anti-fog tests  \n\nThe water contact angle of the UV-cured AF coating surface was determined by an SEO 300A from Surface & Electro-Optics Co., Ltd. This system is based on the sessile drop method. Temperature and relative humidity in the laboratory were within the range of  \n\n![](images/2545c52988ce1fea59b12cbf432ba0421c5eb983ffa72ddb047e3d3d8b7099f6.jpg)  \nScheme 2. Preparation of UV-UAO.  \n\n$21^{\\circ}\\mathsf{C}_{-}25^{\\circ}\\mathsf{C}$ and $30\\%$ , respectively. DI water was used as probing liquids.  \n\nAnti-fog properties were evaluated through two separate testing methods: First, a steam anti-fog test is done as follows. Hot water $(80^{\\circ}\\mathsf{C})$ was added into a cup to about half full. Then, the sample was placed on the cup with the coated surface facing down. Vapor condensed on the coating surface was observed and photographed [5]. Second, a cold anti-fog test is done as follows. The sample was put into a $-20^{\\circ}C$ refrigerator for 1 h and taken out in a $50\\%$ humidity environment.",
        "category": " Materials and methods"
    },
    {
        "id": 11,
        "chunk": "# 2.6. Curing monitoring and coating properties  \n\nThe different photo calorimetry (Photo-DSC) experiments were conducted using a differential scanning calorimeter equipped with a photocalorimetric accessory (TA 5000/DSC 2920). The initiation light source was a 200 W high-pressure mercury lamp: the UV light intensity at the sample was $35\\mathrm{mW}/\\mathrm{cm}^{2}$ over a wavelength range of $200{-}440\\mathrm{nm}$ . The sample was placed in uncovered aluminum pans. TA Instruments software was employed to obtain the results from the photo-DSC experiments.  \n\nmeasured on Leneta test papers using a gloss meter from Sheen Co. (ASTM D 523). The recorded values were an average of five measurements. The adhesion of the coating was measured by using the cross-cut kit by Precision Gage & Tool Co. as described in ASTM D3359. A crosshatch pattern is made through the film to the substrate. Pressure-sensitive tape is applied over the crosshatch cut. Tape is removed by pulling it off rapidly back over itself at close to an angle of $180^{\\circ}$ . Adhesion is assessed on a 0–5 scale. Then the adhesion test was examined before the anti-fogging tests at $25^{\\circ}\\mathsf{C}$ and under relative humidity $30\\%$ .  \n\nThe surface hardness of the cured film was measured by using graphite pencils of increasing hardness as described in ASTM D 3363-74. Pendulum hardness (ASTM D4366-84) was measured as the time taken for the oscillations of a pendulum to reduce from $6^{\\circ}$ to $3^{\\circ}$ (König ref. 707KP from Sheen). The gloss of the coating was",
        "category": " Materials and methods"
    },
    {
        "id": 12,
        "chunk": "# 3. Results and discussion",
        "category": " Results and discussion"
    },
    {
        "id": 13,
        "chunk": "# 3.1. Curing behavior of UV-UAO  \n\nThe UV-curing behavior of the synthesized UV-UAO was compared with that of SK cytech EBECRYL-series urethane acrylate oligomers commonly used in UV-curable systems by Photo-DSC. The photo-DSC exotherms for the photopolymerization of EB 8210, EB 9260, and UA-UAO are illustrated in Fig. 1. The filled circles, open circles, and filled downward triangles are the measured heat flow of EB 8210, EB 9260, and UV-UAO, respectively. From the peak symmetry, induction time, and the time to peak maximum, one can obtain information such as the optimum ratio of monomer to oligomer, the photoinitiator efficiency, and the curing rate [7]. The amounts of heat released, induction time, peak to maximum, and the ultimate percentage conversions derived from Fig. 1 are collected in Table 1.  \n\n![](images/d1ec799a76c657b6871af27519ff3326f717f5c830819b179655c226e759a51b.jpg)  \nFig. 1. Photo-DSC exothermic curves for the photopolymerization of EB 8210, EB 9260, and UV-UAO.  \n\nTable 1 Data from photo-DSC studies on EB 8210, EB 9260, and UV-UAO (IT, induction time; PM, time to peak maximum).   \n\n\n<html><body><table><tr><td>Sample</td><td>Functionality</td><td>Mw (g/mol)</td><td>△H (J/g)</td><td>IT (s)</td><td>PM (s)</td><td>Conversion (%)</td></tr><tr><td>EB8210</td><td>4</td><td>600</td><td>310</td><td>1.00</td><td>1.98</td><td>83</td></tr><tr><td>EB 9260</td><td>3</td><td>1500</td><td>163</td><td>1.08</td><td>1.98</td><td>58</td></tr><tr><td>AF-UAO</td><td>3</td><td>830</td><td>154</td><td>1.10</td><td>2.58</td><td>53</td></tr></table></body></html>  \n\nTable 2 Curing Parameters of UV-cured AF coatings.   \n\n\n<html><body><table><tr><td>Sample</td><td>AF1</td><td>AF2</td><td>AF3</td><td>AF4</td></tr><tr><td>UV-UAO content (%)</td><td>55</td><td>60</td><td>65</td><td>70</td></tr><tr><td> H(J/g)</td><td>302</td><td>298</td><td>287</td><td>208</td></tr><tr><td>Induction Time (sec)</td><td>1.12</td><td>1.00</td><td>0.96</td><td>1.02</td></tr><tr><td>Time to Peak Maximum (sec)</td><td>2.76</td><td>1.98</td><td>1.92</td><td>2.34</td></tr><tr><td>Conversion (%)</td><td>75</td><td>74</td><td>70</td><td>59</td></tr></table></body></html>  \n\nAs expected, the results show (Table 1) that tetra functional EB 8210 with low molecular weight has the shortest induction time and the shortest time to peak maximum as well as the highest value of $\\Delta{\\sf H}$ , indicating the fastest reaction system. Meanwhile, the synthesized UV-UAO and EB 9260 have a similar value for induction time, and UV-UAO has the longest time to peak maximum. In addition, the conversion of the UV-UAO is lower than that of EB 8210 and EB 9260, as shown by the lower value of $\\Delta{\\sf H}$ . This may be a result of the steric effect of quaternary ammonium salts. As shown, although the photopolymerization efficiency of the UV-UAO is lower than that of the commercially available EB 8210, it is similar to that of EB 9260 under the same experimental conditions. Therefore, it is obvious that the synthesized UV-UAO is suitable for practical use in UV coating formulations as the oligomer.  \n\nAt this point, it is necessary to investigate the effects of UV-UAO concentration on the curing behavior of the UV-curable coating formulations. The photo-DSC exotherms for photopolymerization containing variable concentrations of UV-UAO in the coating formulations are shown in Fig. 2; while the amount of the measured heat flow, the induction time, the time to peak maximum, and the ultimate percentage conversion are collected in Table 2.  \n\nHeat flow and percentage conversion decrease as the concentration of UV-UAO increases (Fig. 2 and Table 2); however, the AF3 containing $65\\%$ of UV-UAO has the shortest induction time and the shortest peak maximum, indicating that the initial curing rate is faster than that of the other AF samples. Although the mechanism for this improved initial curing rate is not clear yet, it can be tentatively explained as follows: The addition of UV-UAO into the UV coating formulation increases slightly the viscosity of the AF coating formulation. In general, it is known that increasing the viscosity of the coating decreases the oxygen diffusion into the coating and improves the surface cure [8]. Therefore, it could be expected that the improved curing rate may be attributed to oxygen inhibition. In addition, there is a sudden drop in curing properties as the UV-UAO concentration is increased above $65\\%$ . It is supposed that there are potential incompatibility problems with other components present in the coating formulation.  \n\n![](images/9c3134755512c2be3edb084d439f92c77bc957cf2c1ca3c23cb1e3b050db086e.jpg)  \nFig. 2. Photo-DSC exotherms for the photopolymerization of formulations AF1-AF4.  \n\n![](images/813f540bccb34bdfe088db7cfb97264baa1b04d3e3831248c30300b6d0cc96ce.jpg)  \nFig. 3. Steam anti-fog test of uncoated PC (left) and formula AF 3 coated PC (right).",
        "category": " Results and discussion"
    },
    {
        "id": 14,
        "chunk": "# 3.2. Antifogging properties  \n\nIn order to investigate the anti-fog properties of the prepared UV-cured anti-fog (AF) coatings containing variable concentrations of UV-UAO in the coating formulations, the water contact angle and AF tests of UV-cured AF coatings were examined under a variety of different fogging conditions and the results are summarized in Table 3. The neat PC surface is relatively hydrophobic with a high water contact angle of $74^{\\circ}$ , and the AF test shows a fog appearance (Figs. 3 and 4). After applying a UV-cured AF coating on PC, the water contact angle drops markedly from $58^{\\circ}$ to $5^{\\circ}$ as the content of UV-UAO in the formulation increases from $55\\%$ to $70\\%$ (Table 3). Especially, the AF 3 and AF4 with $65\\%$ and $70\\%$ of UV-UAO in the formulation exhibited lower static water contact angle values $\\mathrm{\\cdot}\\mathrm{AF}3=6^{\\circ}$ , ${\\mathsf{A F}}4=5^{\\circ}$ ) than the AF 1 and AF 2, suggesting that the addition of the UV-UAO into the coating formulation was effective for increasing the surface hydrophilicity of the hydrophobic PC substrate. The hydrophilic OH group and quaternary ammonium salts of UV-UAO were expected to provide excellent anti-fog capability to the coating film because both groups are able to imbibe water on the surface layer, and this hydrophilic surface decreases the water droplet contact angle and provides the anti-fog performance.  \n\nTable 3 Anti-fog test and coating properties of UV-cured AF coatings.   \n\n\n<html><body><table><tr><td colspan=\"2\">Sample</td><td>AF1</td><td>AF2</td><td>AF3</td><td>AF4</td></tr><tr><td rowspan=\"2\">Contact Angle（°）</td><td>Initial</td><td>58</td><td>50</td><td>6</td><td>5</td></tr><tr><td>After water soaking</td><td>56</td><td>49</td><td>5</td><td>Partly detached</td></tr><tr><td rowspan=\"2\">Antifog performance</td><td>Cold-fog test</td><td>fogging</td><td>Some -fogging</td><td>Anti-fog</td><td>Anti-fog</td></tr><tr><td>Steam-fog test</td><td>fogging</td><td>Some -fogging</td><td>Anti-fog</td><td>Anti-fog</td></tr><tr><td colspan=\"2\">Pendulum Hardness</td><td>208</td><td>213</td><td>228</td><td>203</td></tr><tr><td colspan=\"2\">Pencil Hardness</td><td>1H</td><td>1H </td><td>2H</td><td>1H</td></tr><tr><td colspan=\"2\">Gloss</td><td>133.5</td><td>134.8</td><td>135.2</td><td>135.5</td></tr><tr><td colspan=\"2\">Adhesion/cross-cuta</td><td>0</td><td>0</td><td>0</td><td>3</td></tr></table></body></html>\n\na 0: The edges of the cuts are completely smooth; none of the squats of the lattice are detached, 3: A cross-cut area significantly greater than $15\\%$ , but not significantly greater than $35\\%$ , is affected.  \n\n![](images/b981701bb4122e807df61732a8dc7d18140a22a5008c3d2669530d056cce0f37.jpg)  \nFig. 4. Cold anti-fog test of uncoated PC (left) and AF 3 coated PC (right) after removal from $-20^{\\circ}C$ freezer to humid environment.  \n\nIn practice, the durability of AF coatings is of major concern, in addition to the initial water wettability, particularly when the coating is to be used in high humidity conditions. In this regard, in order to test anti-fog durability, various AF coatings were soaked in water for an extended period of time. It was found that AF 4 with $70\\%$ UV-UAO content cannot withstand long-term water soaking with the AF layer of the AF 4 detaching partly from the PC substrate after being immersed in water for 1 day at $25^{\\circ}\\mathsf C$ whereas AF 3 with good water wettability and anti-fog performance retains its outstanding anti-fog durability (Table 3).  \n\nThe anti-fog performance of the AF 3 coatings is shown by the steam-fog test and the cold-fog test, and AF 1 and AF 2 do not exhibit acceptable anti-fog performance (Table 3). In the case of AF 4, excellent anti-fog ability was observed in the initial stages; however, it did not provide anti-fog durability. In contrast, AF 3 provided excellent antifogging capability under a variety of different fogging environments. In the steam fog test, the formula AF 3 coated PC (right part) was seen clearly and retained good transparency; however, the uncoated PC (left part) fogged immediately (Fig. 3). A more aggressive cold-fog test was performed by placing the AF 3 coated PC and the uncoated PC in a freezer at $-20^{\\circ}C$ for 1 h. Both samples were then removed into a humid environment. The uncoated PC (left part) was wholly fogged; however, the AF 3 coated PC (right part) remained fog free (Fig. 4).  \n\n![](images/869f57aed041489dcf3c3f49ec977b7acfeb234f9b9d92348909551387f1f40f.jpg)  \nFig. 5. FTIR-ATR spectra of UV-cured AF films at the film-air interfaces: (a) AF 1 (UV-UAO 55 wt.%); (b) AF 2 (UV-UAO 60 wt.%); (c) AF 3 (UV-UAO 65 wt.%).  \n\nHenceforth we will not discuss AF 4 because its anti-fog properties and conversion from Photo-DSC are outside the specification required in this paper.",
        "category": " Results and discussion"
    },
    {
        "id": 15,
        "chunk": "# 3.3. Coating properties and degree of surface curing  \n\nSince pencil hardness and pendulum hardness are determined primarily by structural parameters such as cross-link density, it is appropriate to consider the cross-link density of the samples [9,10]. It is known that PC is relatively soft and tough with a pencil hardness $<2\\tt B$ . After being coated with AF coating formulation containing UV-UAO, its hardness was raised to 2H (AF 3 coating), which is sufficiently high for general purposes. Among the UV-cured AF coatings, AF 3 exhibited the highest pendulum and pencil hardness compared with the other AF coatings (Table 3), suggesting that the cross-link density of the AF 3 is higher than that of the other AF coatings.  \n\nIn order to confirm the above results, the unreacted acrylic double bonds at the film-air interface of the UV-cured AF coating films were measured by FTIR-ATR, and the results showed clearly (Fig. 5)  \n\nthat the intensity at $811\\mathrm{cm}^{-1}$ decreases with increasing amounts of UV-UAO. Since the infrared band at $811\\mathrm{cm}^{-1}$ is attributable to the $C{\\mathrm{-}}\\mathrm{H}$ deformation mode of the acryl groups, it can be concluded that the addition of UV-UAO into the formulation increases the degree of surface curing. These FTIR-ATR results are in very good agreement with the results of the pencil and pendulum hardness tests.  \n\nIn light of these results, it is evident that adding UV-UAO at $65\\%$ results in a cured film that achieves a good balance between anti-fog properties and hardness, two characteristics that are often difficult to achieve at the same time.  \n\nWe then turned to other coating properties such as gloss and adhesion. All of the UV-cured AF films containing UV-UAO (except that with $70\\mathrm{wt\\%}$ of UV-UAO) exhibited excellent adhesive properties for PC (Table 3). Since adhesion was related to the ion content, the higher ion content in the UV-cured AF films may increase the ion strength, which may improve the adhesion between the film and the PC substrate. In addition, increasing the UV-UAO concentration from 55 wt. $\\%$ to 70 wt. $\\%$ produced no detectable difference in gloss (Table 3).",
        "category": " Results and discussion"
    },
    {
        "id": 16,
        "chunk": "# 4. Conclusions  \n\nThis work demonstrates that UV-UAO is a useful oligomer that can provide excellent anti-fog properties for a UV-cured coating under a variety of environmental conditions. Surfaces coated with a coating formulation containing UV-UAO are capable of spreading and absorbing water, thereby preventing fog formation on the optical substrate. Specially, AF 3 containing UV-UAO 65 wt. $\\%$ in a coating formulation achieves a good balance between anti-fog properties and surface hardness. This UV curable anti-fog coating with UV-UAO also offers desirable product features such as simple wet chemical application methods and a fast curing process for maximum process yields.",
        "category": " Conclusions"
    },
    {
        "id": 17,
        "chunk": "# References  \n\n[1] J.A. Howarter, J.P. Youngblood, Macromol. Rapid Commun. 29 (2008) 455–466.   \n[2] L. Maechler, C. Sarra-Bournet, P. Chevallier, N. Gherardi, G. Laroche, Plasma Chem. Plasma Process. 31 (2011) 175–187.   \n[3] N. Nuraje, R. Asmatulu, R.E. Cohen, M.F. Rubner, Langmuir 27 (2011) 782–791.   \n[4] F.C. Cebeci, Z. Wu, L. Zhai, R.E. Cohen, M.F. Rubner, Langmuir 22 (2006) 2856–2862.   \n[5] C.C. Chang, F.H. Huang, H.H. Chang, T.M. Don, C.C. Chen, L.P. Cheng, Langmuir 28 (2012) 17193–17201.   \n[6] Y. Yuan, R. Liu, C. Wang, J. Luo, X. Liu, Prog. Org. Coat. (2014) 785–789.   \n[7] J.W. Hong, H.W. Lee, J. Korean Ind. Eng. Chem. 5 (1994) 860.   \n[8] R. Schwalm, UV Coating: Basics, Recent Development and New Applications, 2007, pp. 179–184.   \n[9] H.K. Kim, Y.B. Kim, J.D. Cho, J.W. Hong, Prog. Org. Coat. 48 (2003) 34–42.   \n[10] H.K. Kim, H.T. Ju, J.W. Hong, Eur. Polym. J. 39 (2003) 2235–2241.",
        "category": " References"
    }
]