Stock material or miscellaneous articles – Composite – Of quartz or glass
Reexamination Certificate
2001-03-02
2002-10-08
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Composite
Of quartz or glass
C428S426000, C501S070000, C065S099100, C065S114000
Reexamination Certificate
active
06461736
ABSTRACT:
TECHNICAL FIELD
The present invention relates to soda-lime-based glass with a light color tone and a high light transmittance and to a method of manufacturing the same. Furthermore, the present invention relates to a glass sheet with a conductive film in which a transparent conductive film is formed on a surface of a glass sheet and to a method of manufacturing the same. In addition, the present invention relates to glass articles manufactured using the glass sheet with a conductive film, such as photoelectric conversion devices such as solar cells, multiple-glazing units, refrigerators, information displays, copiers, and the like.
BACKGROUND ART
Recently, lightly colored glass, particularly, hardly colored glass, so-called crystal clear glass tends to be preferred as building exterior glass. In addition, in the field of solar-electric power generation that receives attention again as a measure to reduce the carbon dioxide release amount and a countermeasure for fossil fuel exhaustion, there have been demands for a solar cell panel cover glass contributing to the improvement in power generation efficiency.
In order to meet such demands, conventionally, lightly colored high light transmittance glass has been used which is obtained by using high purity raw materials so that an iron content is reduced considerably as compared to that in conventional soda-lime-based glass.
A glass sheet with a conductive film in which a transparent conductive film is formed on a surface of a glass sheet is used in some applications. For instance, demands for such a glass sheet as low-emissivity glass (Low-E glass) have increased in a field of building window glass. In this field, in order to shield electromagnetic waves, a glass sheet with a conductive film may be used in some cases. The glass sheet with a conductive film also is used as a solar cell substrate. Furthermore, such a glass sheet also is provided as a base component of information displays such as liquid crystal displays (LCD), plasma display panels (PDP), or the like. The glass sheet with a conductive film also is used as a door plate of a display refrigerator for shops or a copier document plate.
Generally, in such applications, the glass sheet with a conductive film is required to have a high light transmittance. For example, in a solar cell, such a glass sheet is required to have a high transmittance in a wavelength region in which a photoelectric conversion device has high conversion efficiency. Similarly in various kinds of window glass, it is necessary to compensate for the decrease in visible light transmittance caused by the formation of a transparent conductive film.
A glass sheet with a conductive film can satisfy the aforementioned demands when using glass in which an iron content is reduced considerably as compared to that in conventional soda-lime-based glass.
The following description is directed to conventionally known high transmittance glass.
The glass disclosed in JP 4(1992)-228450 A contains, on a weight percent basis, less than 0.02% total iron oxide based on Fe
2
O
3
as a coloring component and has a composition in which a ratio of FeO to the total iron oxide is set to be at least 0.4. In this glass, a visible light transmittance of at least 87% (measured with the illuminant C) can be obtained when the glass has a thickness of 5.66 mm. This glass sheet has been developed exclusively for furniture and provides a pure and bright azure color tone.
Aragonite as calcium carbonate mineral or hydrated aluminum is used as a raw material of the glass disclosed in the above-mentioned publication. Such a special material is used so that iron is prevented from being mixed as impurities. In addition, the above-mentioned glass also is characterized by being manufactured using a batch composition with a small SO
3
content and being manufactured by a method including separate melting and refining stages as a melting operation.
A glass composition disclosed in JP 4(1992)-228451 A also contains a small amount of total iron oxide as described above and further contains trace amounts of Se and CoO. In this glass, a dominant wavelength of transmitted light is in a range of 570 to 590 nm, and this glass provides an appearance harmonizing with a wooden style. This glass also was developed exclusively for furniture.
Similarly in the glass disclosed in JP 4(1992)-228451 A, limestone or dolomite that contains a relatively large amount of iron oxide as an impurity cannot be used so that the amount of total iron oxide is suppressed to be less than 0.02% based on Fe
2
O
3
, on a weight percent basis, as in the glass disclosed in JP 4(1992)-228450 A. Therefore, a special material such as the calcium carbonate mineral described above is necessary, resulting in expensive glass.
In the glass disclosed in JP 4(1992)-228450 A, it is required to set the ratio of FeO to the total iron oxide to be at least 0.4 to obtain a desired pure and bright azure color. In order to obtain such a specific appearance, it is necessary to employ a special manufacturing method including separate melting and refining stages as a melting operation and to suppress the SO
3
content, resulting in further expensive glass.
On the other hand, a method also has been proposed in which oxidizing agents such as cerium oxide is added, so that a content of FeO that is a principal component causing the decrease in transmittance in the above-mentioned wavelength region is decreased.
For instance, in the glass disclosed in JP 5(1993)-221683 A, 0.1 to 0.5 wt % CeO
2
is contained as an oxidizing agent in conventional soda-lime-based glass containing 0.06 to 0.12 wt % impurity iron based on Fe
2
O
3
. In this glass, since a Fe
2+
/Fe
3+
ratio is lowered considerably, a higher transmittance can be obtained in a wavelength region around 600 nm or longer. In this glass, the Fe
2+
/Fe
3+
ratio is lowered to 3 to 10% from the ratio (38%) in the conventional soda-lime-based glass.
In this glass, since the Fe
2+
/Fe
3+
ratio is lowered considerably, the absorption of light with wavelengths around 400 nm caused by Fe
2
O
3
is increased. The increase in the Fe
2
O
3
content causes the glass color tone to be yellowish. Such an appearance is not suitable, for example, for building window glass. In addition, the increase in the Fe
2
O
3
content also lowers the light transmittance in a wavelength region around 500 nm or shorter. Such a transmission characteristic may be a hindrance when the glass is used as a substrate of an amorphous silicon solar cell having a high energy conversion efficiency in the wavelength region around 500 to 600 nm. Moreover, a relatively large amount of oxidizing agent is required for oxidizing a high concentration of iron. Therefore, the above-mentioned glass cannot always be manufactured at low cost.
None of the above-mentioned publications describes the formation of a transparent conductive film on a surface of a glass sheet.
With respect to the glass disclosed in JP 8(1996)-40742, consideration is given to the formation of a metal oxide coating film on a glass sheet. This glass was developed to be used for building windows and was developed for the purpose of shifting an absorptance in a near infrared region with the transmittance in the visible light region being maintained so that the absorption of solar radiation by glass windows is improved. According to the composition table specifically disclosed in the above-mentioned publication, this purpose is achieved through the reduction of a total amount of alkaline-earth metal oxide to be not more than about 10 wt % while an amount of Fe
2
O
3
is comparable to that in conventional soda-lime-based glass. In this glass, the content of the alkaline-earth metal oxide is reduced and therefore, the wavelength region of light absorbed by FeO is shifted to the longer wavelength side.
However, the glass disclosed in JP 8(1996)-40742 is not suitable for use where a light color tone and a high transmittance are required, although the wavelength region of light absorbed by FeO is shifted to
Hirata Masahiro
Hyodo Masato
Koyama Akihiro
Kuroda Isamu
Nagashima Yukihito
Blackwell-Rudasill Gwendolyn A.
Jones Deborah
Merchant & Gould P.C.
Nippon Sheet Glass Co. Ltd.
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