Flexible OLED display is based on polymer flexible substrate. At present, curved surface flexible OLED display technology is developing towards folding and curling. In this development process, OLED displays need not only the flexibility of display units, but also the flexibility of conductive electrodes and other functional layers including touch units. The core material to realize flexibility is PI film.
In the future, when the display screen can be folded or crimped, other hard material layers on the screen will be continuously replaced by polyimide (PI) or transparent PI film.
PI has six main characteristics
High temperature resistance: more than 400 high temperature, long-term use temperature range-200 ~ 300, no obvious melting point.
High insulation performance: 103hz, dielectric constant is 4.0, dielectric loss is only 0.004 ~ 0.007, belonging to f ~ H class insulating material.
Excellent mechanical properties: the tensile strength of unfilled plastics is above 100 MPa.
Self extinguishing: polyimide is a self extinguishing polymer with low smoke rate.
Nontoxic: polyimide is nontoxic and can withstand thousands of experiments.
Stability: some polyamides are insoluble in organic solvents, stable in dilute acid, general varieties are not very resistant to hydrolysis.
In terms of flexible display, compared with several common basic materials, PI material has obvious advantages. The shape variation of pet is very large, but plastic deformation will occur under long-term bending.
CPI has a large shape variable and the best performance. It is an optically transparent film of flexible electrode, touch substrate, display substrate or cover plate. It can adapt to high temperature bending processing and more than 100000 times resistance. It needs high transparency and low coefficient of thermal expansion. At present, transparent polyimide PI film is one of the few organic film materials that can meet the high performance requirements. Therefore, the flexible material used to lay out the folding screen of smart phones is often CPI. In the process of transition from rigid OLED to flexible OLED, some materials can no longer meet the demand of flexibility due to the limitation of physical and chemical properties. The inherent brittleness of glass, ITO and other materials makes it difficult to meet a wide range of emerging applications, and can be converted to higher performance PI.
The main changes are as follows: (1) the glass substrate will be converted to PI substrate; (2) the touch ITO + pet substrate will be converted to nano silver wire + PI substrate. (3) Glass or metal cover converted to PI cover. In addition to the Yellow PI available on the substrate, CPI is required for touch and cover plate, which requires high optical properties.
PI is a high-tech barrier industry. At present, the demand for PI film in the domestic market is growing rapidly, with great potential. However, most of the products of PI film manufacturers in China are used for electrical insulation, and advanced electronic grade PI relies on imports, which is in short supply. PI synthesis is very difficult, and downstream product processing is more difficult.
In 2019, 5g construction upsurge will be set off all over the world, which will drive major manufacturers around the world to launch foldable mobile phones one after another. 5g and foldable mobile phones will bring more stringent performance requirements and huge market increment to PI film industry.
The folding screen mobile phone mainly adopts OLED technology. In the production process of OLED, the electrode or TFT materials need to be sputtered on the flexible substrate. The substrate is generally high temperature resistant polymer, and the most commonly used is high temperature resistant polyimide (PI) film. The folding mobile phone needs materials to meet the requirements of tens of thousands of times of bending, while the traditional glass is not competent, in which transparent Pi is the folding mobile phone cover plate For the ideal solution, PI membrane will usher in more application scenarios. Compared with the existing 4G, the transmission rate of 5g communication is increased by 10-100 times. Under this high-speed transmission, the demand for high-frequency and high-speed antenna modules is greatly increased, and the antenna module using modified PI (heterogeneous PI) also has a huge demand.
GGII believes that the PI membrane industry will have the following trends:
1) The entry threshold of PI membrane industry will continue to improve. In the future, more and more enterprises will use chemical method to produce high-end PI membrane. At present, chemical method is the most mature way to produce high-end polyimide . However, the threshold of chemical method is high, which is mainly reflected in: 1. Large equipment investment in the early stage, according to GGII research, a complete chemical method production equipment needs 600-800 million, the domestic chemical method production equipment is lack, and most production lines are purchased from Japanese manufacturers; 2. The commissioning time of production line and process is long, and the construction cycle of new material chemical method production line in the reference era (the company started production line construction from 2013 to 2017) It takes 3-5 years from chemical production line construction to mass production, and the construction period of 3-5 years greatly improves the industry thre shold; 3. The technical threshold is high, because PI membrane is widely used in the field of national defense, foreign enterprises have a high degree of confidentiality for PI membrane production process, and PI membrane needs to have rich production experience and the ability to continuously improve the production line and process.
2) The speed of industry reshuffle has accelerated. In 2019, many PI membrane production lines will be built and put into operation. Most of the production lines will use thermal amine method to produce PI membrane. However, there is a big gap between thermal amine method PI membrane and chemical method PI membrane in terms of high temperature resistance and corona resistance. Thermal amine method PI membrane is mainly facing the traditional application market. In the case of weak demand for traditional PI membrane, the industry reshuffle will be accelerated, and the financial strength and product competitiveness will be insufficient Weak enterprises will be eliminated.
In general, the Institute of membrane materials of high industry research believes that at this stage, the domestic PI membrane industry is constrained by production experience, equipment and technology, and needs more time to develop.http://www.china-polyimide.com