How to produce a folding screen without creases?

We saw the first two pre research versions of Motorola Razr 5g at a presentation at Lenovo Research Institute. < / P > < p > one is a prototype version developed in 2017. It was originally designed to imitate the folding design of the first generation of Motorola Razr functional machine in 2004, because the purpose of the early stage was to verify the use of flexible screen in such folding design products. The first version of the product is wide and even a little awkward. The main thing is: we found that the flexible screen and the rear fuselage fit perfectly, so there will be creases in the middle of the screen when folding. < / P > < p > in 2018, an iterative version of the foldable prototype was launched, which mainly adjusted the first version of the screen, making the design of the whole fuselage narrower, and also had the feeling of inheriting the version of the functional machine in 2004. < p > < p > as early as April 2015, Lenovo Research Institute, which focuses on future technology research and development within Lenovo Group, has started the prospective research on flexible technology. It was after the product iteration that Lenovo Research Institute thought this product was feasible, so based on the two versions of technology, it cooperated with the product business department to officially launch the Motorola Razr 5g mobile phone we saw today. The most important part of Motorola Razr 5g is actually the axis between the upper and lower screens, which is called “star orbit”. The rotating shaft allows the screen to achieve a certain downward displacement in the process of bending, while reserving space in the bending part, so that the screen can be folded according to a certain curve. At the same time, it solves the dilemma that the screen will produce creases when the screen is completely folded, and can not restore the flatness when the corner is too large. < / P > < p > in our opinion, the inspiration of this shaft is closer to that of Lenovo’s Yoga product. However, a technician from Lenovo Research Institute, for example, said that the folding screen is like a piece of paper, so when it is folded into a flat state, it will leave a crease on the screen. < / P > < p > in order to solve the damage caused by folding screen completely, folding products on the market often adopt U-shaped scheme. However, for Razr, the U-shaped scheme often leaves a large gap in the middle of the folding screen, but the most classic Razr function machine is fully flat when it is closed, so this scheme can not meet the design requirements of Razr. < p > < p > < p > “drop shaped” bending design was proposed by Lenovo Research Institute. In this way, the upper and lower parts of the folded flexible screen can fit perfectly, but the bending part in the middle can be transferred in a more smooth way. < / P > < p > but then there are problems. Compared with the U-shaped shape, the water drop shape is actually a more complex bending shape – the top of the U-shaped shape is the place where the maximum force is exerted, and when it is far away from this vertex, the force will be reduced. However, the water drop shape has both inner bending part and two outer bending part, so the stress distribution is completely different from that of U shape. < / P > < p > in fact, the flexible screen in front of us is only a few hundred microns thick, but there are many invisible layers. It includes but is not limited to flexible cover plate, circular light piece, display touch and back film, and each layer has a more subdivided material composition, and their stress capacity for temperature and bending pressure is also different. Each layer is bonded by adhesive. This means that different from the U-shaped pressure structure, the superposition structure of the drop shaped flexible screen should be changed, and the stress structure of the drop shaped flexible screen should be changed by redesigning the superposition structure, such as adjusting the part of the stress difference to a relatively stable position. < / P > < p > after adjustment, the screen can be layered up to ten layers. At the same time, it can completely resist dynamic and static bending, flatness and recovery performance test, and even point pressure test, oil resistance and scratch test of the surface. < / P > < p > at Lenovo Research Institute, with the help of a high-definition camera, we saw the micro deformation of the Motorola Razr 5g flexible screen. < / P > < p > when a high-definition camera magnifies the micro world of screen bending, we can see that the screen layers are sliding. From a more microscopic material point of view, crease deformation is actually plastic deformation occurring inside the screen. In order to avoid this kind of situation, in the process of folding the “drop shaped” flexible screen, the adhesive should adhere to different layers and prevent them from separating in the folding process. In fact, different layers should form a certain “sliding displacement” to offset the stress structure display of the screen. < / P > < p > due to the external design of Motorola Razr 5g, its internal design space is much more compressed than the “large screen intelligent machine”. According to pinplay, its battery is divided into upper and lower parts, most of the parts are hidden in the chin, and even the circuit module of the flexible screen is completely attached to the back of the screen – the purpose is to save internal space. < / P > < p > this also means that for such a slightly “special” mobile phone, the radians on both sides of the top of the flexible screen need to be cut separately by laser, and the arc of the border also makes the circuit modules in the internal space need to be designed and customized separately. < / P > < p > combined with the “star orbit” folding structure and on-screen technology research, through dynamic and static tests in different environments, and repeated hundreds of thousands of tests on the testing machine developed by Lenovo, a Motorola Razr 5g was born. New product launch