Compositions: ceramic – Ceramic compositions – Glass compositions – compositions containing glass other than...
Reexamination Certificate
2001-12-21
2003-12-16
Sample, David (Department: 1755)
Compositions: ceramic
Ceramic compositions
Glass compositions, compositions containing glass other than...
C501S067000, C501S069000, C501S070000, C501S072000
Reexamination Certificate
active
06664203
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an alkali free glass preferable for various kinds of flat display panels such as a TFT (Thin Film Transistor) liquid crystal display panel, various kinds of flat display panel using the same, and a method for producing the alkali free glass. Moreover, it ultimately relates to an alkali free glass not containing an arsenic or an antimony oxide, which is ordinarily used as a refining agent, various kinds of flat display panel using the same, and a method for producing the alkali free glass.
BACKGROUND OF THE INVENTION
At the time of melting a glass material, in general, a so-called refining agent having an effect of growing bubbles by a gas generation by the decomposition thereof and promoting removal of the bubbles contained in the molten glass, is added in the initial stage of a step for melting the batch. Moreover, the components also have an effect of absorbing the gas in residual minute bubbles and promoting elimination thereof.
As such a refining agent, in the case of an alkali free glass, in general, an arsenious oxide (As
2
O
3
) and an antimony trioxide (Sb
2
O
3
) are used. The As
2
O
3
provides a refining function owing to the effect that the As
2
O
3
added to the batch derives the oxygen from the vicinity in a temperature raising process so as to be an As
2
O
5
, and releases the oxygen at the time of returning to the As
2
O
3
at a higher temperature. Therefore, in the case of using an arsenious oxide as a refining agent, in order to promote the change from the As
2
O
3
to the As
2
O
5
at an initial stage of the material melting reaction, a nitrate is also added in the glass batch as an oxidizing agent. The same is applied to the case of the Sb
2
O
3
.
Recently, in various fields, use of hazardous substances tends to be reduced. Also in the field of the glass refining agent, movement of replacing the poisonous and highly hazardous As
2
O
3
with the less hazardous Sb
2
O
3
is being spread. Moreover, this movement is remarkable in the field of alkali free glass mainly used as an optical glass or a TFT liquid crystal display glass substrate, wherein the As
2
O
3
has been used ordinarily as the refining agent.
Moreover, in the field of the alkali free glass among the fields wherein the replacement of the As
2
O
3
with the Sb
2
O
3
is promoted, according to the performance of the TFT liquid crystal or change of the production step thereof, a composition with a higher thermal resistance is used. That leads to rise of the glass melting temperature. Accordingly, in the case the Sb
2
O
3
is used as the refining agent for refining a glass requiring a high melting temperature, the Sb
2
O
3
is required to be added in a larger amount. Furthermore, in order to strengthen the refining effect of the Sb
2
O
3
, it may be used in combination with other components.
For example, in the alkali free glass and the production method therefor disclosed in JP-A-10-114538 (the term “JP-A” as used here in means an “unexamined published Japanese Patent”), 0.05 to 3% of an Sb
2
O
3
and 0.05 to 2% of an SnO
2
based on % by weight are added as the refining agent.
In the alkali free glass and the production method therefor disclosed in JP-A-10-231139, 0.05 to 3% of an Sb
2
O
3
and 0.01 to 2% of a chloride in terms of Cl
2
are added as the refining agent.
Moreover, although it is not as serious as the case of the As
2
O
3
, the Sb
2
O
3
also is hazardous, and an alkali free glass using neither the As
2
O
3
nor Sb
2
O
3
and a production method therefor have been proposed.
For example, in the alkali free glass disclosed in JP-A-9-110460, 0.5% by weight or less of a fluoride in terms of F is added at the time of preparing the glass batch.
In the alkali free glass and the production method therefor disclosed in JP-A-10-25132, 0.005to 1.0% by weight of a sulfate in terms of SO
3
and 0.01 to 2.0% by weight of a chloride in terms of Cl
2
are added as the refining agent.
Moreover, in the alkali free glass and the production method therefor disclosed in JP-A-10-59741, 0.05 to 2.0% by weight of an SnO
2
is added as a refining agent.
In the alkali free glass disclosed in the U.S. Pat. No. 6,096,670, it is described that use of an SnO
2
and a CeO
2
in combination is effective as a refining agent in a production method using a float method and a dawn drawing method.
However, in the alkali free glass and the production method therefor disclosed in JP-A-10-114538, although the SnO
2
is added at the same time for reinforcing the refining effect of the Sb
2
O
3
, the refining effect comparable to that of the As
2
O
3
cannot be obtained by addition in a small amount, but phase separation of the glass or devitrification by precipitation of the SnO
2
itself are brought about in the case of addition in a large amount.
Moreover, in the alkali free glass and the production method therefor disclosed in JP-A-10-231139, although a chloride is added at the same time as a refining agent in order to reinforce the refining effect of the Sb
2
O
3
, the refining effect of a chloride is not so remarkable. Furthermore, since hazardous chlorine gas and hydrogen chloride gas are generated by the decomposition thereof, a countermeasure therefor is required.
In the alkali free glass and the production method therefor disclosed in JP-A-9-110460, although a fluoride is added as a refining agent, the effect thereof is not so remarkable. Moreover, since hazardous fluorine gas and hydrogen fluoride gas are generated by the decomposition thereof, a countermeasure therefor is required.
Furthermore, in the alkali free glass and the production method therefor disclosed in JP-A-10-25132, although a sulfate and a chloride are added as the refining agent, the refining effect there of is not sufficient. Moreover, also in this case, similar to the case of the alkali free glass and the production method therefor disclosed in JP-A-10-231139, since hazardous chlorine gas and hydrogen chloride gas are generated by the decomposition of the chloride, a countermeasure therefor is required.
Moreover, in the alkali free glass and the production method therefor disclosed in JP-A-10-59741, although an SnO
2
is added as the refining agent, similar to the case of the alkali free glass and the production method therefor disclosed in JP-A-10-114538, the refining effect comparable to that of the As
2
O
3
cannot be obtained by addition in a small amount, but phase separation of the glass or devitrification by precipitation of the SnO
2
itself are brought about in the case of addition in a large amount.
Furthermore, in the alkali free glass disclosed in the U.S. Pat. No. 6,096,670, although use of an SnO
2
and a CeO
2
in combination as the refining agent is disclosed. It is said that the cerium oxide exists in the form of a CeO
2
in the glass disclosed in the patent. However, even in an amount of about 0.5% of the upper limit, in the case the cerium exists in a tetravalent form, the glass is colored in yellow so that it is not preferable as a substrate for display, such as a TFT liquid crystal display. Moreover, a ZrO
2
is an essential component, and it is said to improve the chemical resistance and stabilize the SnO
2
and the CeO
2
. However, the ZrO
2
tends to be precipitated in the glass as the devitrification. In particular, in the case of the down drawing method wherein the molten glass is cooled down to a low temperature until forming, the devitrification can be brought about by the precipitation.
SUMMARY OF THE INVENTION
Accordingly, an object of the invention is to provide an alkali free glass capable of solving the problems of the As
2
O
3
substituent or As
2
O
3
, Sb
2
O
3
substituent refining agents for the alkali free glass, with a quality usable as a substrate for a flat panel display, and a production method therefor.
A first aspect of the invention is an alkali free glass comprising:
(A) a composition including:
50 to 70 wt % of SiO
2
;
7.5 to 20 wt % of Al
2
O
3
;
4 to 15 wt % of B
2
O
3
;
0 to 5 wt % ZnO; and
5 to 30 wt % in total of at least one of MgO, CaO, S
Nagashima Yukihito
Toshikiyo Yoshikazu
Nippon Sheet Glass Co. Ltd.
Sample David
Sughrue & Mion, PLLC
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