Low-melting glass for covering substrate

Details Low-melting glass for covering substrate Low-melting glass for covering substrate

2001-01-09

2002-11-05

Jones, Deborah (Department: 1775)

Stock material or miscellaneous articles

Structurally defined web or sheet

Discontinuous or differential coating, impregnation or bond

C428S426000

Reexamination Certificate

active

06475605

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a transparent, electric insulating, low-melting glass for covering a substrate, particularly for covering a transparent electrode pattern or bus electrode pattern disposed on a plasma display panel (PDP) substrate. This glass serves as an electric insulating film of a PDP substrate.
Hitherto, lead-containing glass has been used as a low-melting glass for covering a substrate. Lead is an important component for making the glass have a low melting point. However, there is a recent trend to avoid the use of lead due to its adverse effect on human and environment. Furthermore, it is known to introduce an alkali metal(s) and/or bismuth component to a glass batch in order to produce a low-melting glass. However, the alkali metals tend to accumulate on the glass surface, thereby lowering electric insulation of the glass. Thus, there is a tendency to avoid such low-melting glass containing alkali metal in the field of electronics. For example, such low-melting glass may deteriorate a fluorescent material of a display panel (e.g., PDP) and may make the panel lifetime shorter. The above-mentioned bismuth component also may have an adverse effect on environment since bismuth is a heavy metal.
Japanese Patent Examined Publication JP-B-51-17027 discloses a glass for protecting a semiconductor device. This glass contains three major components of SiO
2
, B
2
O
3
and ZnO, but does not contain BaO.
Japanese Patent Laid-open Publication JP-A-59-131540 discloses a glass composition for making an insulating film. This glass composition contains 0.05-3.0 wt % of the total of Li
2
O, Na
2
O and K
2
O.
JP-A-61-242926 discloses a glass for bonding ferrite, containing SiO
2
, BaO, B
2
O
3
, Al
2
O
3
and ZnO.
JP-A-2-97435 discloses a glass sealant for a high temperature thermistor device.
Each of JP-A-7-291656 and JP-A-9-268026 discloses an insulating glass composition containing Bi
2
O
3
.
In general, it is necessary to have a sophisticated melting technique for producing phosphate-based glass, vanadium-oxide-based glass, and antimony-oxide-based glass. Furthermore, components of these glasses tend to evaporate during the melting step, thereby making these glasses unstable and colored.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a low-melting glass capable of easily providing a covering film that has a thermal expansion coefficient close to that of the substrate, a low softening point, superior dielectric characteristics, a superior transparency and a superior electric insulation.
According to the present invention, there is provided a transparent, electric insulating, low-melting glass for covering a substrate. This glass comprises chemical components of SiO
2
, B
2
O
3
, BaO and ZnO; a thermal expansion coefficient of from 65×10
−7
/° C. to 95×10
−7
/° C. within a range of 30-300° C.; a softening point of not higher than 600° C.; and a dielectric constant of not greater than 7.5 at a frequency of 1 MHz under room temperature.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A film of the low-melting glass according to the invention may directly cover the substrate (e.g., a display panel) or to cover an element disposed on the substrate. This element may be at least one of a conducting material and a semiconductor pattern, such as (a) a bus electrode pattern, for example, made of at least one of Cu and Ag, and (b) a transparent electrode pattern, for example, made of In
2
O
3
, SnO
2
and In
2
O
3
doped with Sn (ITO).
It is preferable that the glass comprises 0.1-10 wt % of said SiO
2
, 20-35 wt % of said B
2
O
3
, 25-55 wt % of said ZnO, and 15-50 wt % of a total of said BaO and RO representing at least one of MgO, CaO and SrO. Furthermore, it is preferable that the weight ratio of said BaO to the total of said BaO and said RO is 1:2 or greater.
According to one preferred embodiment of the present invention, there is provided a transparent, electric insulating, low-melting glass for covering a substrate. This glass comprises chemical components of SiO
2
, B
2
O
3
, BaO and ZnO; a thermal expansion coefficient of from 75×10
−7
/° C. to 85×10
−7
/° C. within a range of 30-300° C.; a softening point of not higher than 600° C.; and a dielectric constant of not greater than 7 at a frequency of 1 MHz under room temperature. This glass preferably comprises 2-10 wt % of said SiO
2
, 20-30 wt % of said B
2
O
3
, 34-43 wt % of said ZnO, and 30-37 wt % of said BaO. Furthermore, this glass is substantially free of PbO, Bi
2
O
3
and an alkali metal oxide. This glass may further comprise not greater than 15 wt % of a component substituted for said BaO. This component is at least one of MgO, CaO and SrO.
The substrate, which is to be covered by the low-melting glass, may be a transparent glass substrate, such as a soda-lime-silica glass or a similar glass (high strain point glass) or an alumino-lime-borosilicate glass. The substrate may have a thermal expansion coefficient of from about 65×10
−7
/° C. to about 95×10
−7
/° C. within a range of 30-300° C. The low-melting glass can have a thermal expansion coefficient close to that of the substrate. With this, it becomes possible to prevent exfoliation of the film from the substrate and/or warp of the substrate. The substrate may have a softening point of from about 720 to about 840° C. In contrast with this, the low-melting glass has a softening point of not higher than 600° C. Therefore, when the film is baked, it become possible to prevent softening, deformation and thermal contraction of the substrate.
In general, an insulating film (low-melting glass) formed on a display substrate is desired to have a lower dielectric constant. In particular, a low-melting glass of PDP is desired to have a lower dielectric constant (e.g., not greater than 9) in order to reduce the electric power consumption for driving PDP. According to the invention, the dielectric constant of the low-melting glass is not greater than 7.5, preferably not greater than 7, at a frequency of 1 MHz under normal temperature (room temperature). Thus, the low-melting glass can contribute considerably to electric power saving of PDP.
As stated above, the low-melting glass comprises chemical components of SiO
2
, B
2
O
3
, BaO and ZnO such that the glass can be adjusted to having the above-mentioned numerical ranges of thermal expansion coefficient, softening point and dielectric constant. It is preferable that said glass is substantially free of each of PbO and Bi
2
O
3
. With this, the adverse impact of the low-melting glass on human and environment can substantially reduced. It is also preferable that the glass is substantially free of alkali metal oxide. With this, the film of the low-melting glass becomes superior in electric insulation. Furthermore, it becomes possible to prevent damage caused by the alkali accumulation on the surface of the film.
As mentioned above, it is possible to directly cover a substrate with the film of the low-melting glass, for example, in order to prevent alkali migration from an alkali-containing glass substrate or to alter optical characteristics of the substrate. Furthermore, it is possible to form at least one of various functional films on the film of the low-melting glass. It is possible to prepare a frosted glass for reducing glare of the solar radiation and artificial illumination, by mixing a low-melting glass powder with a silica fine powder, an alumina fine powder and/or the like and by forming a film from the resulting mixture on a glass substrate.
The description of chemical components of the low-melting glass is as follows. SiO
2
is a glass forming component. It is possible to make a stable glass even with a small amount of SiO
2
, if it is coexistent with another glass forming component of B
2
O
3
. The SiO
2
content of the glass is preferably 0.1-10 wt %. If it is less than 0.1 wt %, the glass may become unstable. If it is greater than 10 wt %, the softening point of the glass may b

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