| In recent years, with the rapid development of flat panel display technologies, the traditional CRT (cathode ray tube) display products were gradually been replaced by flat panel displays, and the TFT-LCD (thin film transistor liquid crystal display) has became the mainstream display of flat panel display products on the market, and TFT-LCD substrate glasses are fundamental materials in TFT-LCD, and have been one of the key materials to restrict the development of TFT-LCD, each TFT-LCD panel uses two pieces of glass, respectively as the TFT (thin film transistor) array backplane and the CF (color filter) substrate.The chemical composition, performance requirements, and the forming process and condition are highly demanding in TFT-LCD substrate glasses, and the forming process and market of TFT-LCD substrate glasses have been mastered and controlled by four companies, they are Corning Incorporated, Asahi Glass Company, Nippon Electric Glass Company Limited and AvanStrate Incorporated. And the physical properties and chemical durability of substrate glasses are all determined by the chemical composition of substrate glasses, and TFT-LCD substrate glasses are alkali-free boro-aluminosilicate glasses. The basic requirements for TFT-LCD substrate glasses include a much lower CTE (coefficient of thermal expansion) (α50/300=30×10-7/℃～38×10-7/℃), good thermal resistance (the strain point temperature exceed 650℃) and mechanical stability, precise geometry control, a surface that is basically perfectly smooth, and no inclusions large enough to block a pixel in the final display. In addition, the glasses used as substrate materials must be essentially alkali-free so that they do not interact chemically or electronically with thin film transistors.In this paper, alkali-free boro-aluminosilicate glasses were taking as the research object, and made by traditional melting-annealing method, and CTE, strain point, glass transformation temperature, annealing point and dilatometric softening point of the glass were test by dilatometer, and high temperature viscosity was investigated by the rotation viscometer, and then fitting the temperature-viscosity curve with characteristic viscosity reference points by VFT (Vogel-Fulcher-Tammann) equation.Effects of raw materials of silica sands in glass melting, and effects of properties of doping of rare earth oxides of Y2O3 content in glasses, and effects of technical properties of n(SrO)/n(CaO) in glasses have been studied in this paper, and the research rusults are showed as follow:(1) The particle size of silica sands less than 75μm and uniform was suit to as the raw material of chemical composition of SiO2 in alkali-free boro-aluminosilicate glass melting, and no silica-rich phase layer in the melting process, which is meeting the melting requirement of TFT-LCD substrate glass.(2) CTE, density and viscosity reference points of glasses were increased with adding of rare earth oxides Y2O3 and also improved the glass network, and the optimal content of Y2O3 doped in alkali-free boro-aluminosilicate glass is 0.80 wt. %, and continue to increase the doping content will not improve the properties of glasses.(3) Keep the weight percent of alkaline earth oxides at 10.34 wt. % in alkali-free boro-aluminosilicate glasses, and adjusting the ratio of O/Si between 2.44 and 2.45, we can make the CTE of glasses toα50/300=32×10-7/℃.(4) The chemical composition of glasses are showed as follow (wt. %): SiO2 63.20%, Al2O3 17.30%, B2O3 8.00%, (SrO+CaO) 10.34%, Y2O3 0.80%, SnO2 0.16%, keep the weight percent of alkaline earth oxides at a constant, and with the replace of CaO by SrO, as the increase of n(SrO)/n(CaO), high temperature viscosity, working temperature, melting temperature, glass forming region and density of glasses have been increased, and the density of glasses between 2.41 g/cm3 and 2.46 g/cm3, which meet the development of light-thin of substrate glasses; and the CTE was decreased but between 29×10-7/℃and 38×10-7/℃, and characteristic viscosity reference points such as the strain point, glass transformation temperature, annealing point, dilatometric softening point and Vickers hardness first increased and then decreased and then got a balance value and got a maximum value when n(RO)/n(Al2O3)=0.96, and the strain point temperature exceed 710℃, Vicker hardness exceed 640 kgf/mm2, which met the requirements of thermal expansion and thermal resistance of TFT-LCD substrate glasses, and also got an excellent chemical durability.In this paper, chemical composition and technical properties of alkali-free boro-aluminosilicate glasses were studied, and provided the basis data to develop the independent intellectual proprietary about environmentally friendly alkali-free boro-aluminosilicate glasses for TFT-LCD.
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