Glasses, flat glasses in particular, are variously applied to window panes, window screens for vehicles, and mirrors and come in many different forms depending on its type and use.
Among various types of flat glasses, alkali-free glass substrates are widely used in flat panel display devices such as a liquid crystal display (LCD), a plasma display panel (PDP) and an organic electroluminescent (EL). This is because an alkali glass substrate containing an alkali metal oxide may deteriorate film characteristics due to the diffusion of alkali metal ions contained in the glass substrate into a film.
However, glass used in flat panel display substrates requires various characteristics.
For example, a glass for flat panel display substrates should be light weight. In particular, as display devices such as televisions and monitors are becoming larger and larger recently, glass substrates used therein are also enlarging in size. The enlarged size of the glass substrate may increase the bending of the glass substrate due to the weight thereof. Accordingly, in order to prevent such a problem, there is a need to manufacture a light weight glass substrate. Also, such a light weight glass substrate may be used in small portable devices including a mobile phone, a PDP and a notebook to increase portability.
In addition, a glass for flat panel display substrates should have proper melting properties (fusibility). If the melting property of the glass decreases, much time and energy is required for the glass to melt, and bubbles or foreign substances may generate in the glass to cause a fault. The bubbles or foreign substances present in the glass may hinder the penetration of light, deteriorating the quality of the glass, thereby making it difficult to use the glass for display devices.
Further, a glass for flat panel display substrates should have heat-resistance. For example, flat panel display devices such as a TFT-LCD may be subject to heat-treatment during the preparation thereof, at which a glass substrate may be exposed in rapid heating and cooling conditions. If the glass has insufficient heat-resistance, the glass may deform or bend, and may also even break due to tensile stress resulting from heat. In addition, in the case of a glass for a TFT-LCD, if its heat-resistance is low, a thermal expansion difference between the glass and the materials of TFT occurs and the pixel pitch of the TFT may distort to cause a display fault.