ITOフィルムの代替技術: 印刷方式メタルメッシュ躍進の可能性?

ITOフィルムの代替技術: 印刷方式メタルメッシュ躍進の可能性?

ITOフィルムの代替技術: 印刷方式メタルメッシュ躍進の可能性?
透明導電性フィルム(TCF)業界では近年大きな変革が起きています。既存のソリューションにとって代わる様々な技術が開発されている一方で、既存のサプライヤーは低迷する市場でのシェアを確保しようと低価格化を進めています。
 
IDTechExの調査レポート 「透明導電性フィルム (TCF) 2017年-2027年: フォーキャスト, 市場, 技術」 Transparent Conductive Films (TCF) 2017-2027: Forecasts, Markets, Technologiesでは、TCF市場の詳細な技術評価、市場及びビジネス動向を提供します。IDTechExは長年にわたりこの分野を詳しく調査し、技術、参入企業の浮き沈みを目撃し、近年の統合状況等を正しく予測してきました。
印刷方式TCFの超えられない限界
既存のソリューションの代表的な代替技術としてメタルメッシュがあります。メタルメッシュは機能性も高く特に大面積に使用するときに効果を発揮しバリューチェーンもシンプルです。ただしメタルメッシュTCFの製造方法といっても様々なものがありそれぞれに違いがあります。
 
当初は安価な印刷装置を用いて短時間で追加製造できると期待された印刷方式が注目を集めました。しかしその開発はすぐに技術的限界にぶつかりました。それメタルメッシュのライン幅を15~20um以下に狭めるのが簡単にはいかないことです。それでは高精度の透明性を適用したとしても肉眼でメッシュが見えてしまうのです。
 
この問題によって印刷方式は劣勢になり写真パターンをベースにする方式など他のメタルメッシュ処理が脚光を浴びるようになりました。しかし、ダイレクト法やハイブリッド法など様々な形で使用できる印刷方式が再びTCF業界で注目されるようになっておりこれまでと状況が変わる可能性があります。ここでは最近我々が世界各地で直接目撃した最新の技術進化の概要をご紹介します。更に詳しい内容はIDTechExの調査レポート 「透明導電性フィルム (TCF) 2017年-2027年: フォーキャスト, 市場, 技術」 Transparent Conductive Films (TCF) 2017-2027: Forecasts, Markets, Technologiesをご覧ください。このレポートはウエブサイト上で直接購入することができます ご注文はこちらから。また、請求書の発行も可能です。お問い合わせはIDTechEx日本法人 アイディーテックエックス株式会社 m.murakoshi@idtechex.com まで。お見積書も発行いたします。
Progress on the use of printing in TCF production
The first commercial use of printing was as a hybrid process by the likes of Shenzhen O-Film. In this hybrid approach, a UV resin is first patterned using imprinting, the trenches are then filled using a printing process such as dispensing, and the excess ink is then cleared off. This creates embedded topographically-smooth metal mesh solutions with sub-5um linewidths. This approach was commercialized although we understood that O-Film had some customer issues in 2015. This approach continues to be developed by O-Film and others. An example demonstrating the process is shown below.
 
 
(Left): An example of the hybrid process for manufacturing metal mesh. Source: Fujikura Kasei. (Right) examples of O-Film metal mesh TCFs. I took these photos at Mobile World Congress 2014.
Direct sheet-to-sheet screen printing was also developed as a means of making metal mesh. This approach was limited by the traditional shortcomings: here the linewidths were around 24um. This approach is however now being applied to large-area touch tables and touch surfaces for use in, for example, outdoor areas where line visibility is not a concern. The picture below shows an example from Gunze. This product is currently in use in Japan in, for example, gaming panels installed in Akihabara, Tokyo.
 
Large-area touch tables with screen printed metal mesh with 24um linewidths. Source: Gunze. I took this picture at C-Touch Taiwan 2016
Others are developing gravure offset techniques for printing ultrafine metal mesh structures using silver nanoparticles. One example has been demonstrated by Komura-Tech which has achieved 5um linewidths. This result, shown below, is still in the prototyping stage and the web sizes are limited. As before, the challenge will be in scaling up the process without comprising yield or resolution.
 
Others such as a major Korean companies had developed similar technology as early as 2012, but gave up because they judged that the cost benefit was not sufficient to dethrone ITO films. This is however a promising step in the right direction.
 
Note that flexographic printing with larger web sizes is also possible. This technique achieves 10um for the best case, but commercial printing is generally limited to 20um. The printed lines are also thin.
 
Gravure offset printed fine line metal mesh TCF. (left) microscope image of 5um line metal mesh. (right) plastic surfaces covered with printed Ag metal mesh with 5um linewidth. Source: Komura-Tech. I took the photos at the IDTechEx Show! USA 2016
Gravure offset fine line metal mesh demonstrated by Ishihara Chemical (materials supplier). I tool these photos at Nepcon Japan 2017.
Other novel processes are also being developed to bring printing into the metal mesh TCF business. For example, Toray is now targeting its photo-patterned screen-printable conductive paste at the TCF industry. This ink was initially introduced as a touch screen edge electrode material, enabling the industry to overcome the limitations of standard PTFs (pastes) to reach L/S of 20/20 or lower. This was a success achieving sales on the scale of several (e.g., 2) tonnes per month. Now Toray had demonstrated 3.5um metal mesh patterns using this technology as shown below. This technology is still in the prototyping phase and the cost is still high (we estimate around $40/sqm, far higher than competitors).
 
(Right) fine linewidth flexible metal mesh made using Toray's photo-patternable Ag conductive paste. (Left) image of medium-sized TCF where I could detect no visible lines. Source: Toray. I took these photos at Nepcon Japan 2017.
Tanaka Metal (recently acquired Metalor) has also developed a novel ink-based metal mesh TCF technology. The substrate is coated with a layer of amorphous fluoropolymer. This is then later patterned using UV irradiation. An image of an activated surface pattern that absorbs silver nanoparticles in then formed. The entire surface is then coated with silver nanoparticle using blade coating. The nanoparticles selectively chemisorb onto the patterned areas, giving rise to the metal mesh structure with ultra-fine linewidths. The Tanaka-estimated price is 200 yen per sqm (approx. $20/sqm). This is still an early stage development and the production process is currently sheet-to-sheet on a 500mm by 500mm substrate.
 
Tanaka Metal and AIST's silver nanoparticle ink-based approach to metal mesh TCFs. Source: Tanaka Metal. I took this photo based on brochures given to us by the developers.
The use of printing is also being developed to either laydown a catalyst which can then be later thickened using plating, or to deposit photoresists thus effectively replacing photolithography. The latter process is being developed by the likes of Screen Holding or LCY, whereas the former is by the likes of ITRI in Taiwan. The latter process is often envisioned as a stepping-stone towards full direct printing of the metal mesh lines.
 
Printing is used to deposit photoresist or to lay down plating catalysts. Source: (left) Screen Holdings and (right) ITRI/Kuraki. I took these photos at FineTech Japan 2016.
Yet others, such as Asahi Kasei, are developing printing technologies that can directly roll-to-roll deposit lines as narrow 100nm. This technology is currently under development and the prototyping drums have a 100mm diameter and 50mm width. This technology however may be overshooting the requirements of the TCFs, and might be better suited to other applications.
 
Ultra-fine roll-to-roll imprinting. Source: Asahi Kasei
Of course this has not been all progress on ink-based TCFs. There are many firms that have come with a bang and gone with an eerie silence. For example, ClearJet developed a novel approach to overlapping inkjet-printed conductive rings, and Cima Nanotech developed self-assembled Ag nanoparticles which created a random metal mesh structure. But for each one that leaves the scene another one appears to take its place. For example, we recently learned that XTPL, an early stage polish firm, has developed a printing technology for ultra-fine metal mesh printing.
 
This is a fast evolving space to watch. To learn more please refer to our report Transparent Conductive Films (TCF) 2017-2027: Forecasts, Markets, Technologies. This report outlines the latest on all technology options for TCFs, developed detailed application- and technology-segmented ten-year market forecasts, and provides interview-based company profiles.
 
Please do not hesitate to contact me on khasha@IDTechEx.com should you have any questions.
1 Raw indium prices have also falled from $750/ Kg to $225/Kg between 2014-2016, partially accounting for the fall in ITO film prices.