Agc Inc.

Motoyuki Hirose

Takashi Enomoto

Kazutaka Ono

Hirofumi Tokunaga

The present invention relates to a float glass substrate including an alkali-free glass, the float glass substrate having a Cl content of from 0.10 to 0.50 mass %, containing substantially no SnO, and having a Pt content of, by mass, from 0.001 to 0.30 ppm. The float glass substrate may have a Rh content of, by mass, from 0.001 to 0.50 ppm.

Float glass substrate

An alkali-free glass has a strain point of 650° C. or more, an average coefficient of thermal expansion at 50 to 350° C. of from 30×10to 45×10/° C., and a temperature Tat which a glass viscosity reaches 10dPa·s of from 1,500 to 1,800° C. The alkali-free glass contains, as represented by mol % based on oxides, SiO: from 62 to 70%, AlO: from 9 to 16% BO: from 0 to 12%, MgO: from 3 to 10%, CaO: from 4 to 12%, SrO: from 0 to 6%, and FeO: from 0.001 to 0.04%, provided that MgO+CaO+SrO+BaO is from 12 to 25%. The alkali-free glass has a β-OH value of from 0.35 to 0.85/mm.

Alkali-free glass

An alkali-free glass substrate contains, as represented by mass % based on oxides: 54% to 68% of SiO; 10% to 25% of AlO; 0.1% to 5.5% of BO; and 8% to 26% of MgO+CaO+SrO+BaO. The alkali-free glass substrate has &#x3b2;-OH of 0.15 mmto 0.35 mm, and a Cl content of 0.15 to 0.3 mass %. A bubble growth index I of the alkali-free glass substrate given by the following formula is 320 or more: I=590.5&#xd7;[&#x3b2;-OH]+874.1&#xd7;[Cl]&#x2212;&#xd7;[BO]&#x2212;33.3. In the formula, [&#x3b2;-OH] is &#x3b2;-OH of the alkali-free glass substrate in mm, [Cl] is the Cl content of the alkali-free glass substrate in mass %, and [BO] is a BOcontent of the alkali-free glass substrate in mass %.

Alkali-free glass substrate

An alkali-free glass substrate contains, as represented by mass % based on oxides: 54% to 66% of SiO; 10% to 23% of AlO; 6% to 12% of BO; and 8% to 26% of MgO+CaO+SrO+BaO. The alkali-free glass substrate has &#x3b2;-OH of 0.15 mmto 0.5 mm, and a Cl content of 0.1 to 0.35 mass %. A bubble growth index I of the alkali-free glass substrate given by the following formula is 280 or more: I=590.5&#xd7;[&#x3b2;-OH]+874.1&#xd7;[Cl]&#x2212;5.7&#xd7;[BO]&#x2212;33.3. In the formula, [&#x3b2;-OH] is &#x3b2;-OH of the alkali-free glass substrate in mm, [Cl] is the Cl content of the alkali-free glass substrate in mass %, and [BO] is a BOcontent of the alkali-free glass substrate in mass %.

To provide an alkali-free glass, of which the compaction is low, the strain point is high, and the ultraviolet transmittance is high, and which is easy to melt. An alkali-free glass, which comprises, as represented by mol % based on oxides, wherein MgO+CaO+SrO+BaO is from 12 to 22, and 4.84[FeO]+5.65[NaO]+4.03[KO]+4.55[SnO] is at most 0.55, and of which the compaction is at most 80 ppm.

The present invention relates to an alkali-free glass substrate in which when the alkali-free glass substrate is melted, and while holding a temperature at 1400&#xb0; C., reduced in pressure from an atmospheric pressure to 33.33 kPa at a constant pressure reduction rate for 20 minutes and held at 33.33 kPa for 5 minutes, a diameter of a grown bubble is at least 3 times a diameter of an initial bubble. A bubble having a diameter of 0.1 to 0.3 mm contained in a molten glass at 1400&#xb0; C. before starting pressure reduction is defined as the initial bubble. A bubble after held at 33.33 kPa for 5 minutes corresponding to the initial bubble is defined as a grown bubble.

The present invention relates to an alkali-free glass and a method for producing the same. More specifically, the present invention relates to an alkali-free glass suitable as a glass for substrates of various displays such as liquid crystal display, and a method for producing the same. According to the present invention, an alkali-free glass suitable as a glass for display substrates, in which inclusion of bubbles is greatly reduced by virtue of containing a refining agent and suppressing the stirring reboil, is obtained.

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Tokyo, Japan

Motoyuki Hirose