A New Optical Film with Antismudge Function and High Durability Jun Hee Lee  , Kyeong Jin Kim, Mi Kyung Park, Hyoung Jun Kim, Il Jeon, Sang-Ho Choi, Jin Ho Kim, Hyun Chul Choi, and Hyun Ho Shin Advanced Technology Development Department 2, LG Display, 1007 Deogeun-ri, Wollong-myeon, Pajusi, Gyeonggido 413-811, Korea Received September 24, 2008; accepted August 7, 2009; published online December 21, 2009 We describe a new surface treatment to obtain optical films for liquid crystal display (LCD) applications. The films consist of a phase- separated layer including a fluorine-containing (FC) compound and a widely used polymer resin for providing a hard coating after surface treatment of the optical film. The major features of the resulting configuration are high durability with a good hardness of above 4H and a surface that allows oily contaminants such as ink and fingerprints to be easily removed by gentle dry wiping, owing to the antismudge function of the FC compound with a low surface energy. # 2009 The Japan Society of Applied Physics DOI: 10.1143/JJAP.48.122401 1. Introduction Optical displays such as televisions, monitors, and notebook personal computers are widely used in everyday life. In particular, display devices including touch screens, which allow the input of information via the user’s hand or a stylus pen, have received much attention recently. Since touch screen displays are broadly used in many devices, the surface is frequently exposed to ﬁngerprints and may become blurred by users or auxiliary instruments touching the screen. Because it is necessary to maintain the display function by cleaning its surface, high hardness and anti- scratch surface treatments are required. As the upper most portion of a display screen is made of acrylic resin, which has a high surface energy of 40 – 60 mN/m, it is easily contaminated by dirt and very diﬃcult to clean owing to its strong interaction with contaminants. In addition, because of its medium hardness of 2 – 3 H, it can become damaged easily. 2. Experimental Procedure 2.1 Film concept The surface energy of an optical ﬁlm is very important for maintaining satisfactory antismudge characteristics. That is, if the surface energy of a certain material is high, its attraction increases, increasing the absorption characteristic towards diﬀerent materials, and if the surface energy is low, its attraction decreases, weakening the absorption character- istic towards diﬀerent materials. 1–4) These properties deter- mining the antismudge performance are applicable to our new optical ﬁlm with a strong antismudge function and high durability. Figure 1 shows a schematic diagram of antismudge optical ﬁlms with good hardness. One is a double-layer conventional ﬁlm [Fig. 1(a)] and the other is a new single- layer ﬁlm [Fig. 1(b)]. A conventional optical ﬁlm with an antismudge function is conﬁgured with two layers of coating solutions with diﬀerent surface energies; 5) however, this is complicated and expensive to manufacture. The new ﬁlm is conﬁgured with a single layer of coating solution by phase separation, which is a simple and inexpensive process. The new surface treatment is conﬁgured so that a single mixed layer is formed by mixing the polymer resin used in conventional ﬁlms to give a hard coating and a ﬂuorine- containing (FC) compound to provide the antismudge function. When these two materials, each having diﬀerent surface energies, are mixed, phase separation occurs at the interface of the two materials because they are thermody- namically unstable. Using this phenomenon, we obtain an FC compound with low surface energy and high antismudge performance located on the surface of the optical ﬁlm. The diﬀerence between the surface energy of the polymer resin used for the hard coating and the FC compound ranges from about 5 to 35 mN/m; the polymer used for the hard coating in normal optical ﬁlms has a surface energy in the range of 30 to 45 mN/m, and the FC compound has a surface energy in the range of 10 to 25 mN/m. 2.2 Film implementation Figure 2 shows the surface treatment used to obtain the new antismudge optical ﬁlm. In step 1, to fabricate the optical ﬁlm, a polymerization initiator is added to the monomers or oligomers to form the polymer resin used to achieve a hard coating. Next, the polymer resin and the FC compound are mixed to obtain a coating solution. Then the mixed coating solution is applied to the surface of a triacetyl cellulose (TAC) substrate. In the coating solution, the FC compound has a lower surface energy and becomes more stable when positioned higher than the monomers or oligomers in the surface layer. Accordingly, because the monomers or oligomers are polymerized by heat or UV light, the FC compound, having a smaller surface energy, moves towards the upper surface layer, causing phase separation (step 2). Applying additives at this stage helps form a strong network between the polymer resin and the FC compound in the ﬁnal optical ﬁlm, giving an optical ﬁlm of 4 H surface hardness. Finally, heat or UV light is applied to dry the coating solution and produce the optical ﬁlm (step 3). 3. Results and Discussion 3.1 Phase separation evaluation Figure 3 shows the atomic percent of ﬂuorine as a function of etching time, obtained using Angle Resolved X-ray Photoelectron Spectroscopy (ARXPS) equipment, for new optical ﬁlms with diﬀerent concentrations of the FC compound; samples 1– 4 are new optical ﬁlms with diﬀerent amounts of the FC compound and sample 5 is a conven- tional ﬁlm. The experiment was performed by irradiating X-rays onto the surface of the optical ﬁlm using a monochromatic X-ray gun. As a result, the proﬁle of  E-mail address: jh0529@lgdisplay.com Japanese Journal of Applied Physics 48 (2009) 122401 REGULAR PAPER 122401-1 # 2009 The Japan Society of Applied Physics