How much do you know about the film in the flexible screen?

Flexible screen, generally refers to flexible OLED. Compared with the traditional screen, the flexible screen has obvious advantages. It is not only lighter and thinner, but also consumes less power than the original device, which helps to improve the endurance of the device. At the same time, based on its bendable and flexible characteristics, its durability is also much higher than that of the traditional screen and reduces the probability of accidental damage to the device.

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as early as 1974, Xerox Palo Alto Research Center's Gyricon electronic paper, so that the concept of flexible display was born. This kind of material that can be bent like paper and can directly display images has been very attractive since it was proposed, but due to technical costs and other issues, it has not been able to get out of the laboratory for a long time. In the era of functional machines, NEC, Kyocera, Sony and other manufacturers have introduced electronic products similar to folding screens. This folding screen mobile phone is more like a variant of a flip phone. It uses an ultra-narrow frame + hinge design to simply superimpose two hard screens together. In fact, this is not a real flexible folding screen.

By 2012, the flexible screen had made a breakthrough. The screen manufacturer Plastic Logic to produce a flexible display screen completely made of plastic materials, and in 2013, it demonstrated the flexible screen mobile phone MorePhone jointly created by Intel.

In 2013, mobile phone manufacturers Sony, Samsung almost at the same time to invest in flexible screen related technology research and development. After five years, the folding screen mobile phone finally has a breakthrough entity display in front of the public. After several twists and turns, in October 2018, Ruoyu released the world's first folding screen mobile phone Ruopai. It is expected that in 2019, more mobile phone manufacturers will join the research and development and promotion of flexible screen mobile phones. So flexible display for our film practitioners, what kinds of films and materials are involved.

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polyimide film (PI film)

although the flexible screen can be bent, if it is bent frequently, it will have the same fatigue problem as metal paper. If the flexible screen is bent for many times and used for a long time, it may be damaged by creases in the middle of the screen after being subjected to multiple compression and tensile stresses. In addition, circuit boards and components may be damaged or other accidents when folded after being subjected to a large number of bending and non-bending. The existing glass panel can not meet its high frequency requirements, mobile phone manufacturers mainly use polyimide film (transparent PI film) to replace the existing glass cover, CPI itself has good foldability, but PI material can not meet the hardness requirements, need to add a coating on the surface of the PI film to enhance the hardness.

The number of global patent applications for transparent polyimide film only accounts for about 9% of the global patent applications for polyimide film, and the number of patent applications for transparent polyimide film in China only accounts for about 2.6 of the patent applications for polyimide film in China. In general, the patent technology reserve in the field of transparent polyimide film is low. Globally, manufacturers with CPI membrane technology capabilities include Kolon,SKC and Sumitomo Chemical, and domestic enterprises participating in the research and development of transparent polyimide film are also emerging.

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polyester film (BOPET film)

polyester film (BOPET film) is the base film or base film of various functional films in many flexible display screens. Among them, the most commonly used ITO film (indium tin oxide semiconductor transparent conductive film) is prepared by coating the conductive material indium tin oxide on the surface of the film with BOPET film as the base material. However, the brittleness of ITO is not suitable for the application of flexible screens. The industry proposes to use nano-silver wire AgNWs with heptathlon to replace ITO as the touch core conductive material, but nano-silver wire is difficult to do narrow border, etching marks obvious these problems need to be further improved. The core conductive material to replace ITO is mainly nano-silver conductive film, but the substrate of nano-silver conductive film is also mainly BOPET film.

In the OLED bending process, in order to prevent breakage and bending of the screen, it is generally necessary to stick a protective film at the bottom of the panel. The protective film has good rigidity, and its base material is also a BOPET film.

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cycloolefin polymer film (COP film)

by the Japanese company development and production of an early application in the medical resin, because of its high transparency, low birefringence, low water absorption, high rigidity, high heat resistance, good water vapor tightness and other characteristics, in some special high transparency and anti-ultraviolet conductive film demand field, the use of COP film instead of BOPET as a substrate.

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liquid Crystal Polymer Film (LCP Film)

LCP plastic raw materials full name Liquid CrystalPolymer, Chinese name liquid crystal polymer, it is a new type of polymer materials, in the molten state generally show liquid crystal. LCP film has good high strength, high rigidity, high temperature resistance, electrical insulation and other properties, and has better water resistance than PI film, so it is a better film type than PI film. At present, it is widely used in the flat cable of flexible screen, the antenna of flexible mobile phone, the vibration film of speaker, etc.

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PE protective film

in addition to the protective film to prevent the panel from being bent and damaged, in the process of production and transportation of the flexible screen, a large amount of polyethylene needs to be consumed at one time as a self-adhesive protective film of the substrate to protect the electronic screen from being scratched by foreign matters or stained by intermediate links. Common self-adhesive materials include EVA, ultra low density polyethylene, polyolefin plastomer resins. The characteristics of self-adhesive protective film: simple processing flow; long-term use of adhesive phenomenon; low material cost; fewer product varieties, used in high-end electronic equipment.

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polydimethylsiloxane film (PDMS film)

PDMS film is a kind of polymer elastic polymer film, which is prepared by special process with polydimethylsiloxane as raw material. Due to the characteristics of polydimethylsiloxane material, the PDMS film is endowed with certain specific properties. Elasticity, low Young's modulus, excellent gas permeability, chemical stability, thermal stability, low temperature flexibility (-60~200 ℃ to maintain excellent performance), full transparency, biocompatibility. At present, PDMS film in the scar patch, electronic flexible devices, microfluidic chips, gas separation technology, intelligent wearable products and other high-end products have different degrees of application.