1. Technical Field
The present disclosure generally relates to a flexible substrate for a display panel and a manufacturing method thereof. More specifically, the present disclosure relates to a flexible substrate for a thin, transparent display panel that has low coefficients of thermal expansion and excellent flexibility, heat resistance, and surface roughness, which is formed by laminating a second film on a first film including a glass cloth.
2. Description of the Related Art
Display devices (e.g., liquid crystal display devices) that are commonly used at the present time often include transparent electrode substrates made of glass materials. However, glass substrates are typically thick and heavy, which limits their ability to achieve acceptable flatness and weight for liquid crystal display devices. Furthermore, glass substrates are vulnerable to impact and are particularly unsuitable for flexible displays because of their brittleness.
Accordingly, flexible substrates made of plastic optical film materials are now used as a substitute for glass substrates. Such flexible substrates exhibit good characteristics for advanced display devices, such as organic electroluminescent (EL) displays, electronic paper (e-paper), liquid crystal displays, and other displays.
Flexible substrates formed with the plastic optical film materials are thin and light as compared to glass substrates used in display panels. Moreover such flexible substrates have flexible properties and can be processed in various types. Hence, it is possible to realize lightness, flatness, surface display functions and other desirable features which are required for advanced display devices.
Thanks to the aforementioned advantages of the flexible substrates, significant research and development is being performed with respect to the flexible substrates' materials, structures and the like. Specifically, in an early stage of development, flexible substrates adopting transparent film materials that included plastic high molecules were used. Then, compositions using an epoxy resin, acid anhydride-series hardener and alcohol hardening catalyst were applied as materials for flexible substrates.
However, such originally produced flexible substrates exhibited large linear coefficients of expansion. In particular, when the flexible substrates formed with the above materials were used as active matrix display device substrates, various problems including bending during manufacturing and disconnection of aluminum wires occurred. In addition, the above materials have poor optical properties as compared to glass, such as CTE (Coefficient of Thermal Expansion), thermal characteristics and transparency or refractive index. Thus, such flexible substrates cannot be used in many situations.
Therefore, to use the plastic optical film materials as substrates for display panels, particularly, substrates for liquid crystal display devices, a need exists to develop plastic optical film materials having good heat resistance, high transmissivity, and low coefficients of thermal expansion and surface roughness.
Attempts to reduce coefficients of thermal expansion of the plastic optical film materials in accordance with such a need include a complex film structure configured by mixing an inorganic filler such as glass powder or a glass cloth with a resin. For instance, Japan Publicized Patent No. 2004-51960 discloses a resin sheet including an epoxy resin and glass fabric-type glass textile material, and Japan Publicized Patent No. 2004-233851 describes a transparent substrate made of a glass cloth and a resin. However, prior film structures and methods for manufacturing a transparent substrate by impregnating a glass cloth into a resin had various problems.
First, a process of manufacturing glass fiber in fabric type was particularly complex. In particular, if large films are manufactured using a hot process technique, film curling can occur. Such a process requires significant time and is complicated, which can result in increased production cost.
Second, when films into which a glass cloth is impregnated are manufactured using UV hardening resins, the completed films are not flat and are very rough, which can cause deterioration of picture quality of a display device due to contraction of the glass cloth and structural characteristics of the glass fiber.