From the hot sale of the Samsung Galaxy Edge series flagship to a variety of curved screen bracelets and televisions, undoubtedly, the screen technology has been widely valued and sought after by consumers and industry in recent years. In the future, with the continuous development and improvement of fixed curvature curved screen technology, flexible touch screens that can achieve arbitrary bending will become an important development direction.
On the 25th, at the 13th International Touch Screen and Display Technology Development Forum, Huang Hanfeng, deputy general manager of touch development from Shenzhen Oufeiguang Technology, stood in the perspective of the industry chain, focusing on flexible display, flexible touch, flexible cover and flexible fit. The four key elements provide a detailed introduction to the flexible touch screen.
Flexible display
For LCD liquid crystal display, the liquid crystal is usually responsible for controlling the display gradation, and the three primary color filters control the display color, which requires that they must be one-to-one corresponding to display normal. If the LCD panel is used to make a curved screen, the inner perimeter and the outer perimeter will be unequal. The original one-to-one correspondence between the liquid crystal and the filter will be misaligned, resulting in color distortion and light leakage. Dark screen ghosting and snowflake and other issues. Therefore, for curved screens, OLED display technology represented by AMOLED is almost the best choice.
Huang Hanfeng said that at present, Samsung is the undisputed AMOLED overlord in terms of patent, production capacity, yield and technology accumulation. The sixth-generation AMOLED panel, which began mass production at the end of 2014, can now achieve 50,000 pieces per month. Yield, and yield can reach 60%. Next is LG, but LG has been the main target in the direction of large-screen curved TV. At present, with the trend of small-screen AMOLED becoming more and more obvious, LG is also accelerating the layout of small and medium-sized flexible screens, although its output is currently not as good as Samsung, but the yield is good. It can also reach more than 60%. The newly released Xiaomi Note 2 is the LG's flexible AMOLED screen. In addition, Japan's JDI and Sharp (has been acquired by Hon Hai), as well as Taiwan's AUO, domestic BOE, Rouyu and other screen manufacturers are also accelerating the layout of their own AMOLED technology, AMOLED has replaced the LCD has become the trend.
Flexible touch
In terms of touch, ITO (tin indium oxide) transparent conductive film has become the most important touch screen for non-curved LCD and OLED display screens due to many reasons such as good light transmittance, low thickness, excellent hardness and conductivity, and mature manufacturing process. Layer material. However, since ITO itself is a brittle material, it is not suitable for a flexible touch layer with large curvature or even bending at will, and the cost and cost are high. Currently, it accounts for about 30% of the upstream material of the entire touch screen industry. The cost of %, and the use of "indium", a rare metal with limited reserves, has been replaced by the surface and the era of flexibility.
Huang Hanfeng said that the most important substitutes for ITO materials are: graphene, carbon nanotubes, nano silver and metal grid. Among them, graphene and carbon nanotubes are very good substitutes for ITO from the characteristics of the material itself. However, graphene is still in the research and development stage, and there is still a long way to go from mass production. The industrialized mass production technology of carbon nanotubes has not been perfected, and the film products made by them are not as conductive as ITO. Therefore, from the perspective of technology and marketization, metal grid and nano-silver technology will be the protagonists in recent years. Among them, metal grid technology has been applied in some PC display markets.
The metal mesh technology mentioned here is a conductive metal mesh formed by pressing a metal conductive material such as silver or copper or an oxide on a film substrate such as PET. The main advantage is that the raw material cost is low and the wrapability is good, but due to the moire interference ripple caused by the yield, the output and the high line width and high pixel, it is more suitable for the application with low resolution and relatively long distance. On desktop products, laptops and TVs.
Nano-silver technology refers to the application of nano-silver ink materials on PET or glass substrates, and then uses laser lithography to describe a silver-line conductive network with nanometer level. Its main advantages are high yield, small line width, good electrical conductivity and resistance to winding. The disadvantage is high cost. Compared with the metal grid, the nano-silver material has a small radius of curvature and a small rate of change in resistance when bent, plus the line width, so it is more suitable for high resolution in mobile phones, smart watches and bracelets. Used in close range scenes.
"Integrated comparison, I think that nano silver is more advantageous than metal grid." Huang Hanfeng said.
Flexible cover
In order to be free to bend, in addition to solving the flexible display and flexible touch, the final and most critical part is the flexible cover and fit. However, due to its hard and brittle nature, the glass cover is not the best choice in the flexible field.
Huang Hanfeng said that PET and PI (polyimide) materials with high surface hardness and high light transmittance are better choices than glass, but there are still many problems to be solved in PET and PI. On the one hand, they are not resistant to high temperatures and have poor light transmission: PET and PI have problems of partial melting and trait change at less high ambient temperatures, and they do not have good light transmission compared to glass.
Secondly, it is difficult to achieve a balance between hardness and winding. Huang Hanfeng said that if a certain hardness requirement is required, the hardened layer should be applied. However, after the hardened layer is applied, the hardened layer will be cracked and the hardness will be lowered after repeated winding. Therefore, how to achieve a balance between the two is currently the biggest bottleneck.
Compared with the flexible cover that needs further development, the development prospect of the 3D glass cover required for the current curved screen mobile phone is very good.
According to statistics, 2018 will be the year of explosion of 3D glass cover. It is expected that by 32020, the penetration rate of 3D glass cover will exceed 50%, and with the maturity of 3D glass cover processing, the unit price Declining, the penetration rate will be further improved, and the market size in the future is expected to reach more than 19 billion yuan.
Huang Hanfeng said that the current 1R (single arc bending) and 2R cover manufacturing processes have been basically mature, basically through the hot bending technology to achieve a bending effect, the difference is mainly in the coating of the hardened layer. However, the yield is a problem to be solved, basically only 30%, and there is not much room for improvement in the short term. If you want to do 4R in the future, the yield will be lower. Therefore, the yield is one of the problems that need to be solved in the manufacture of the cover.
Flexible fit
After the cover is selected, it is fitted, that is, the cover and the underlying touch and display layers are integrated to form a complete module. At present, there are two types of roller type and vacuum bonding: among them, the roller has high efficiency and needs to be rolled. The efficiency of the vacuum type is relatively low, but it is not necessary to roll the object to be attached, and it is not easy to cause damage to the object to be attached.
Huang Hanfeng said that if the curvature is large, only vacuum fit can be chosen. However, for the 4R fit that may occur in the future, due to its special 4-sided bending characteristics, it is difficult to avoid wrinkles and bubbles in a large arc even with a vacuum method. At present, the industry has adopted a customized method of squeezing airbags or plastic parts to alleviate this problem, but it has not been completely solved. Therefore, there is still room for improvement in the industry of multi-curved and high-curvature bonding processes.
Huang Hanfeng said frankly: "From the perspective of the supply chain, the flexible screen that is arbitrarily wounded needs to be mass-produced. It will take several years, and the upstream and downstream supply chains are needed to jointly solve related technical problems."
For the future development, Huang Hanfeng believes that the integration of various modules will be the general trend. He said: "In the Incell technology of LCD liquid crystal display, the ITO touch film and the liquid crystal layer are merged together. This is a good integration. Now the fingerprint module is independent and can be integrated with the touch in the future. I think there will be a process of integration and progress between functional modules in the future.
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