Stock material or miscellaneous articles – Composite – Of quartz or glass
Reexamination Certificate
2002-07-15
2003-11-25
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Composite
Of quartz or glass
C428S432000, C428S912200, C501S069000, C501S005000
Reexamination Certificate
active
06652973
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field to Which the Invention Pertains
The present invention relates to glass-ceramics, and to a substrate of a reflecting mirror (hereinafter referred to as “reflecting mirror substrate”), the substrate being formed from the glass-ceramic.
2. Background Art
Glass-ceramics, exhibiting excellent heat resistance, are useful materials for forming various apparatus parts used at high temperatures. An example of an apparatus part used at high temperatures includes a reflecting mirror. Together with a light source lamp mounted thereon, the reflecting mirror constitutes an illumination apparatus. Since the temperature of the reflecting mirror rises by heat generated from the light source lamp, the reflecting mirror is required to have high heat resistance. Therefore, the substrate of the reflecting mirror must also exhibit high heat resistance. Conventional reflecting mirror substrates are generally formed from PYREX (registered trademark) glass exhibiting excellent heat resistance.
In recent years, light source lamps of high luminance have been employed in illumination apparatuses and cineprojectors. In accordance with this trend, a reflecting mirror which constitutes an illumination apparatus employing a light source lamp of high luminance is required to have enhanced heat resistance.
In order to meet such requirements, Japanese Patent Publication (kokoku) No. 7-92527 discloses a reflecting mirror substrate formed from glass-ceramic containing, as primary components, a &bgr;-spodumene solid solution and a &bgr;-eucryptite solid solution. Since the glass-ceramic, which is known as a low-expansion glass-ceramic, exhibits excellent heat resistance, a reflecting mirror of high heat resistance can be formed from the glass-ceramic.
U.S. Pat. No. 5,786,286 discloses a reflecting mirror substrate formed from another type of glass-ceramic. Unlike the aforementioned reflecting mirror substrate, the substrate disclosed in this patent is not used at high temperatures. The substrate is formed from a glass-ceramic containing hexacelsian as a primary crystal phase and having a degree of crystallinity of about 50%, and has a thermal expansion coefficient &agr; (×10
−7
/°C. as high as 78 to 88.
In the course of forming the aforementioned substrates, the glass raw materials of the glass-ceramic must be melted at a temperature as high as 1,500° C. or more, since the glass raw materials have high melting points. The substrates are formed by forming methods, such as press forming, roll forming, casting, or blow forming. In such forming methods, since the glass raw materials are melted at 1,500° C. or higher prior to formation of a substrate, the surface of the forming die employed is oxidized, and the surface is roughened at an early stage, resulting in a shortened service life for the forming die.
Particularly, when the surface of a forming die is roughened, the resultant substrate fails to have the desired surface roughness. When the surface of the forming die is roughened, in order to impart the predetermined surface roughness to a substrate to be formed, the forming die must be exchanged for a new forming die at an early stage, resulting in a great increase in the costs required to prepare a large number of forming dies to be exchanged and the costs required for exchanging the forming dies.
In previously filed Japanese Patent Application No. 2000-299507, the present applicant proposed a reflecting mirror exhibiting excellent heat resistance, in which the substrate of the mirror is formed from glass-ceramic containing primary components differing from those of glass-ceramic containing a &bgr;-spodumene solid solution and a &bgr;-eucryptite solid solution, and exhibiting heat resistance similar to that of the glass-ceramic.
The reflecting mirror includes a glass-ceramic substrate and a thin reflection film deposited on the substrate. The substrate is formed from a glass-ceramic having celsian as a primary crystal phase and containing SiO
2
, Al
2
O
3
, and BaO as primary components and TiO
2
as a crystal nucleus component, and has a thermal expansion coefficient &agr; (×10
−7
/°C. of 30 to 45. The reflecting mirror does not involve the aforementioned problems attributed to the formation of reflecting mirror substrates, and exhibits excellent heat resistance.
SUMMARY OF THE INVENTION
The present inventors have conducted further studies on glass-ceramics having celsian as a primary crystal phase and containing SiO
2
, Al
2
O
3
, BaO, and TiO
2
as primary components, the glass-ceramic constituting the aforementioned reflecting mirror substrate, and have found that Li
2
O serving as a specific modification component greatly contributes to crystal formation in the glass-ceramic, and that a glass-ceramic containing no hexacelsian crystals or very small amounts of hexacelsian crystals; i.e., glass-ceramic whose crystal phase is substantially formed of celsian alone, can be obtained by varying the Li
2
O content of the glass-ceramic.
The present invention has been accomplished on the basis of this finding. An object of the present invention is to provide a very useful glass-ceramic material for forming apparatus parts exhibiting excellent heat resistance, mechanical strength, and optical properties; and a substrate which is formed from the glass-ceramic material and constitutes a high quality reflecting mirror.
The present invention relates to a glass-ceramic, and a first glass-ceramic according to the present invention has a celsian primary crystal phase comprising SiO
2
, Al
2 O
3
, BaO, and TiO
2
as primary components and Li
2
O as a modification component, and is characterized in that the amount of Li
2
O falls within a range of 0.05 to 1.0 wt. %.
A second glass-ceramic according to the present invention has a celsian primary crystal phase comprising SiO
2
, Al
2
O
3
, BaO, and TiO
2
as primary components and Li
2
O and K
2
O as modification components, and is characterized in that the amount of Li
2
O falls within a range of 0.05 to 1.0 wt. %, and the amount of K
2
O is 1.5 wt. % or less.
Each of the glass-ceramics of the present invention may further comprise one or more modification components selected from the group consisting of Na
2
O, P
2
O
5
, B
2
O
3
, Sb
2
O
3
, ZnO, and Bi
2
O
3
.
The present invention also relates to a reflecting mirror substrate. The reflecting mirror substrate of the present invention is a substrate on which a thin reflection film is deposited to thereby form a reflecting mirror, the substrate being formed from the first or second glass-ceramics of the present invention.
In the reflecting mirror substrate of the present invention, preferably, the glass-ceramic constituting the substrate has a thermal expansion coefficient &agr; (×10
−7
/°C.) in a range of 30 to 45, and the glass-ceramic has a crystal grain size in a range of 0.1 to 1 &mgr;m.
The reflecting mirror substrate of the present invention has a flexural strength in a range of 125 to 155 Mpa at room temperature, in a range of 145 to 175 Mpa at 300° C., and in a range of 180 to 220 Mpa at 600° C., and an elastic modulus in a range of 80 to 85 Gpa at room temperature, in a range of 70 to 75 Gpa at 300° C., and in a range of 35 to 40 Gpa at 600° C.
In the reflecting mirror substrate of the present invention, preferably, the shortest wavelength of light which passes through the glass-ceramic constituting the substrate is at least 800 nm when the glass-ceramic has a thickness of 0.1 mm, and the wavelength of light which passes, at a transmittance of 50%, through the glass-ceramic constituting the substrate is at least 850 nm when the glass-ceramic has a thickness of 0.1 mm.
In the reflecting mirror substrate of the present invention exhibiting the aforementioned properties, which has a thickness of 3 to 6 mm, the shortest wavelength of light which passes through the glass-ceramic constituting the substrate is at least 850 nm, and preferably, the shortest wavelength of light which passes through the glass-ceramic constituting the substrate is
Ohtoh Kazuki
Ota Takashi
Watanabe Atushi
Burr & Brown
Jones Deborah
NGK Insulators Ltd.
Sperty Arden
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