Improvement of gas barrier properties by combination of polymer film and gas barrier Y. Tsumagari, H. Murakami, K. Iseki and S. Yokoyama Toyobo Co., LTD. RESEARCH CENTER, - Katata 2-chome, Otsu, Shiga, 520-0292 JAPAN Phone : +8-77-57-0062, Fax : +8-77-57-0065, E-mail : yumi_tsumagari@toyobo.jp Key Words: gas barrier film aluminum oxide defect gas permeation ABSTRACT High gas barrier films have been needed for electronic device applications, such as solar cell and organic light-emitting devices. From the analysis of the gas barrier films prepared by sputtering method, defects smaller than nm are the main factor for mechanism of water vapor permeation. The high gas barrier film with WVTR=5 0-3 g/m 2 /day is obtained by the combination of polymer film with low water vapor permeation constant. INTRODUCTION Gas barrier films have been widely used for food packaging, medical packaging, and electronic devices, such as solar cells and organic light emitting devices (OLED). In general, gas barrier films are composed of gas barrier and polymer film substrate. The gas barrier properties are around 0.~0 g/m 2 /day for food packaging application. On the other hand, higher gas barrier properties are needed for electric devices, especially for OLED application. Inorganic and organic stacked alternatively gas barrier s are the common solution for much higher application. However, in the industrial point of view, the cost of stacked films is very expensive, and furthermore, it is difficult to control the thickness of each. Objective of this study is improvement of the gas barrier property by combination of the polymer film substrate and the single gas barrier composed of transparent ceramic material. Especially, the authors tried to analyze the mechanism of gas permeation for water vapor permeation, and improve the gas barrier performance by combination of gas barrier film and polymer film. film (TOYOBO, Cosmo shine A400 00µm thickness) and the other polymer film (Film A) as substrates were set in the vacuum chamber with aluminum target. After evacuating below 3 0-4 Pa, oxygen or nitrogen for the reactive gas and argon for the discharge gas were introduced into the deposition chamber. The sputtering pressure was 0.6 Pa and the distance between target and substrate was 20 mm. The electric DC power, 3 W/cm 2 was inputted for the target. The substrate temperature was kept less than 50 C during the deposition. Aluminum, aluminum oxide and aluminum nitride with the thickness from 20 ~ 70 nm coated polymer films were prepared. The surface morphologies of the barrier films were evaluated by optical microscope, scanning electron microscope (SEM) and atomic force microscope (AFM). The cross-sectional morphology was evaluated by transmission electron microscope (TEM). The barrier properties were measured by equal pressure method and differential-pressure method. The equal pressure method is MOCON method at 40 C under 90% relative humidity condition. Water vapor transmission rate (WVTR) of the gas barrier films was measured by this equal pressure method. The differential pressure method was used for the gas permeation measurement for non-condensable gases like helium, neon, oxygen, and argon at room temperature. The equipment is shown in Fig. 2. Vacuum Chamber Al holder Substrate EXPERIMENTAL In this study, parallel plate magnetron sputtering machine was used as shown in Fig.. Polyester Ar O 2 Power Supply Fig. Sputtering equipment T.M.P R.P.
defects smaller than nm are the main factor for mechanism of water vapor permeation. Such defects in barrier, like boundary or pores, exist as reported in references [3, 4]. Gas supplying side Gas flux direction sample Al2O3 AlN Al WVTR(g/m2 day).0 Gas detecting side Detector Fig. 2 Gas permeation measurement equipment 0.8 0.6 0.4 0.2 RESULTS & DISCUSSIONS () Evaluation of the defects in the gas barrier Fig. 3 shows the thickness dependence of WVTR for the aluminum, aluminum oxide and aluminum nitride coated polyester films. The WVTR behavior for the thickness is almost the same for all gas barrier films. These WVTR values are almost the same as the ones reported []. First, the surface of the aluminum deposited polyester film was evaluated by an optical micro scope and SEM, to evaluate the pinhole size and area. Some pinholes are seen in Fig. 4 (a), and the size of one of them is about 00µm shown in Fig. 4 (b). The total area of the pinholes was observed -3 about 2.7 0 % to the total area of Fig. 4 (a). The value is too small than the one estimated from the WVTR value of the aluminum coated polyester film and the polyester film, assuming that there is no water permeation through the aluminum coated area [2]. From this result, some other smaller defects are expected to exist, which is unable to detect by optical microscope and SEM measurements. Next, the surface morphology of aluminum oxide coated polyester film was evaluated by AFM, and the cross-sectional morphology of it was evaluated by TEM. As shown in Fig. 5, no defects can be found from these images. These results might lead to the conclusion that there are no such small defects. However, the dynamic diameters of the gases are much smaller than the analyzable size of these analysis equipments. Gas permeation measurement is useful to study the gas permeation mechanism for such small defects less than nm, which are molecular diameter. Fig. 6 shows the results of the permeation constants of various gases for aluminum oxide coated polyester film. With a decrease of molecular diameter, the permeation constants increase. Therefore, permeation constant depends on molecular diameter. These results mean that the 0.0 0 20 40 60 80 Thickness(nm) Fig. 3 The thickness dependence of WVTR for the aluminum, aluminum oxide and aluminum nitride coated polyester films. (b) (a) ⑨ ⑧ ⑩ ⑪ ② ③ ⑫ ① ⑦ 0µm ⑥ 2mm Fig. 4 Surface morphologies of the aluminum deposited polyester film. (a) optical microscope, (b) SEM. (a) (b) Al2O3 50 nm Fig. 5 Morphologies of the aluminum oxide deposited polyester film. (a) the surface image by AFM, (b) the cross-sectional image by TEM. 2
Fig. 6 Permeation constants of various gases for the gas barrier film. (2) Improvement of WVTR performance In general, to improve gas barrier properties, the thickness of the gas barrier is increased. However, the WVTR performance is saturated with an increase of the thickness of the gas barrier, as shown in Fig. 7. In this study, low permeation polymer substrate was used to improve the gas barrier property. As shown in Fig. 8, the permeation constant of Film A is lower than the polyester film. However, the permeation constant of Film A with the gas barrier is much lower than that of the polyester film with the gas barrier. This mechanism is still under research. The characteristics of the gas barrier films are shown on Table. The gas barrier film composed of Film A has high gas barrier properties, WVTR= 5 0-3 g/m 2 /day. This value is much smaller than the one composed of polyester film. WVTR(g/m 2 day) Permeation 透過係数 constant (ml(stp)cm/cm2 sec cmhg sec cmhg) 0.20 0.5 0.0 0.05 0.00.0E-.0E-2.0E-3.0E-4.0E-5 0.2 0.25 0.3 0.35 0.4 Molecular diameter (nm) 0 40 80 20 60 200 Thickness(nm) He Ne O2 Ar Fig. 7 WVTR performance for the thickness of the gas barrier. Permeation constant (ml(stp)cm/cm2 透過係数 sec cmhg).0e-08.0e-09.0e-0.0e- Fig. 8 Permeation constants of water vapor for polyester film, low water vapor permeation Film A, and each film coated with aluminum oxide as barrier. Table. The characteristics of high gas barrier film Application Composition WVTR (g/m 2 day) Total Transmittance (%) Color b (%) CONCLUSION A400 PET ゼオノア FilmA A400 PET ゼオノア FilmA E-paper, PV Al 2 O 3 PET 0.2 90 + barrier + barrier OLED Al 2 O 3 Film A 0.005 The gas permeation mechanism was studied for the gas barrier film by variety of analysis and measurements. The gas barrier coated film has some pinholes. However, the total area of the pinholes is much smaller than the estimated one from the WVTR values. From the gas permeation measurements, the defects smaller than nm are the main factor for water vapor permeation mechanism. These results mean that water vapor penetrate the defect of the barrier, like pores or boundaries of it. The defect-less barrier will be a future task. However in this study, high barrier performance is achieved by combination of gas barrier and polymer film with low water vapor permeation constant. It also has high optical transmittance. That is why it is used as substrates for electric devices, such as E-paper, encapsulation for solar cell, and OLED. 9 3
REFERENCE [] J. Fahlteich, The quest for transparent barriers on flexible substrates, ICCG Proc. 55-60 (2007). [2] Prins W. and Herman J. J, J. Phys. Chem. 63(5), 76-79 (959). [3] S. Tukimoto, M. Moriyama, M, Murakami, Thin Solid Films. 460, 222-226 (2004). [4] A. P. Roberts, et al, J. Membrane. Sci. 208, 75-88 (2002). 4
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