Compositions – Electrically conductive or emissive compositions – Metal compound containing
Reexamination Certificate
2000-08-11
2003-10-21
Gupta, Yogendra N. (Department: 1751)
Compositions
Electrically conductive or emissive compositions
Metal compound containing
C252S500000, C252S506000, C252S512000, C252S519500, C252S519510, C252S519520, C252S520200
Reexamination Certificate
active
06635193
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a dielectric material useful in plasma display panels (PDPs) and, in particular, to a dielectric composition used for forming a light transparent dielectric layer on a front glass plate of a high strain point in PDPs.
A plasma display panel is known as a self-luminescent type flat display having excellent properties of such as a small weight, a thin type etc. and draws considerable attention because of its possibility of a large screen face.
Generally speaking, a PDP has a front glass plate on which a plurality of electrodes are disposed for generating plasma discharge by cooperation with electrodes deposited on a rear glass plate confronting the front glass plate with a gap therebetween. A light transparent dielectric layer is formed with a thickness of about 30-40 micrometers on the glass plate to cover the electrodes so as to maintain the plasma discharge generated.
Usually, the front glass plate is made of soda-lime glass or other high strain point glass and Ag is used for the electrodes, while the light transparent dielectric layer is formed from dielectric material comprising low fusion point glass powder, for example, high Pb-content glass powder.
When forming the light transparent dielectric layer, the dielectric material is fired or baked at the softening point of the low-fusion point glass powder so as to avoid the reaction with metal of the electrodes.
However, the conventional dielectric material has a problem that the glass powder and the Ag electrodes react with each other to make the dielectric layer color (change to yellow).
Further, it is important as known in the art that the dielectric material has various properties such as (1) thermal expansion coefficient compatible with glass plate, (2) firing temperature at 500-600° C., (3) excellent defoamability in firing to produce the dielectric layer of high light transmittance and high withstand voltage with a reduced amount of bubbles.
JP-A 11-21148 discloses a dielectric material using a glass powder of PbO—B
2
O
3
—SiO
2
—BaO glass which has the thermal expansion coefficient compatible with that of the high strain point glass plate. The PbO—B
2
O
3
—SiO
2
—BaO glass is rapid in viscosity change across the softening point and is, therefore, readily defoamed.
Although the dielectric material using PbO—B
2
O
3
—SiO
2
—BaO glass powder can provide a dielectric layer having a high light transmittance because of its excellent defoamability, it has a problem that the produced dielectric layer has residual large bubbles having diameters of 30 &mgr;m (micrometers) or more.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a dielectric material which is useful for providing a light transparent dielectric layer hardly reacting with Ag electrodes in PDPs thereby not to make color change.
It is another object of this invention to provide a dielectric material which is compatible with the high strain point glass plate in the thermal expansion coefficient, defoamable in firing about the softening point, and able to provide a light transparent dielectric layer without large bubbles left therein.
According to this invention, a dielectric composition for use in formation of a dielectric layer in a plasma display panel is obtained which comprises a powder material. The powder material comprises a powder of glass characterized by containing PbO of 50% or less and CuO as one of essential elements contained in the glass.
A content of CuO is preferably 0.01-20% by weight.
According to an embodiment of this invention, the glass consists essentially of, by weight, a total amount of 2-30% of BaO, CaO and Bi
2
O
3
, 0-35% ZnO, 10-40% B
2
O
3
, 1-15% SiO
2
, 25-50% PbO, and 0.01-20% CuO.
According to another embodiment, the glass consists essentially of, by weight, 15-45% BaO, 20-45% ZnO, 12-35% B
2
O
3
, 3-15% SiO
2
, 0-24.5% PbO and 0.01-20% CuO.
According to another embodiment of this invention, the glass consists essentially of, by weight, 25-45% ZnO, 15-35% Bi
2
O
3
, 10-30% B
2
O
3
, 0.5-8% SiO
2
, a total amount of 8-24% of CaO, SrO and BaO, and 0.01-20% CuO.
According to another embodiment, the glass consists essentially of, by weight, 26-60% B
2
O
3
, 15-50% ZnO, 0-30% SiO
2
, 0-10% Al
2
O
3
, 3-20% K
2
O, a total amount of 0-10% of Na
2
O and Li
2
O, a total amount of 0-15% of CaO and BaO, and 0.01-20% CuO.
The glass powder preferably has an average particle size D50 of 3.0 micrometers (&mgr;m) or less, and the maximum particle size Dmax of 20 micrometers (&mgr;m) or less.
According to another aspect of this invention, the dielectric composition is a paste which comprises, by weight, the powder material of 30-90%, binder of 0.1-20%, plasticizer of 0-10%, and solvent of 10-30%.
In an embodiment, the binder is at least one selected from a group of poly butyl methacrylate, polyvinyl butyral, poly methyl methacrylate, poly ethyl methacrylate, and ethyl cellulose. The plasticizer is at least one selected from a group of butyl benzyl phthalate, dioctyl phthalate, di-isooctyl phthalate, dicapryl phthalate, and dibutyl phthalate. The solvent is at least one selected from a group of terpineol, diethylene glycol monobutyl ether acetate, and 2,2,4-trymethyl-1,3-pentanediolmonoisobutylate.
According to another aspect of this invention, the dielectric composition is a green sheet which comprises, by weight, the powder material of 60-80%, the binder of 5-30%, and the plasticizer of 0-10%.
The glass powder can be mixed with ceramics powder selected from a group of alumina, zircon, zirconia, and titania (titanium oxide), to form an admixture. The admixture comprises the glass powder of 90-100 weight % and the ceramics powder of 0-10 weight %.
DESCRIPTION OF THE INVENTION
In order to prevent not only many fine bubbles but also large bubbles having a diameter of 30 &mgr;m or more from remaining in the dielectric layer formed by use of the dielectric composition, it is important to use glass having PbO content of 50 wt. % or less. Specifically, in case of PbO content more than 50 wt. %, glass composition containing SiO
2
of a relatively large amount is, on one side, excessively slow in viscosity change at the firing temperature to expel bubbles so that the dielectric layer has many fine bubbles, and glass composition containing SiO
2
of a relatively small amount is, on the other side, excessively rapid in viscosity change to promote growth of bubbles so that large bubbles remain in the dielectric layer formed.
The dielectric composition according to this invention includes, as a main component, powder of CuO containing glass. Inclusion of CuO in the glass as an essential ingredient makes the formed dielectric layer hardly change to yellow even when Ag is used for the electrode material. Therefore, the dielectric layer formed has a high light transmittance.
An example of glass of the glass powder consists essentially of, by weight, a total amount of 2-30% of BaO, CaO and Bi
2
O
3
, 0-35% ZnO, 10-40% B
2
O
3
, 1-15% SiO
2
, 25-50% PbO, and 0.01-20% CuO. The glass will be referred to as glass A and has properties that the viscosity change is rapid across the softening point so that bubbles are expelled at a relatively low temperature at a start of the firing operation, thus less fine bubbles remaining in the dielectric layer formed.
In the glass A, BaO, CaO and Bi
2
O
3
are contained for lowering the softening point of the glass and for adjusting viscosity at a high temperature to affect defoamability of the glass. The total content of BaO, CaO and Bi
2
O
3
is 2-30%, preferably 3-25%, by weight. If the total content is less than 2%, the intended function of these elements described above cannot be achieved. The total content more than 30% excessively lowers the softening point to promote foamability as well as elevates the thermal expansion coefficient of the resultant glass. Individual contents of BaO, CaO and Bi
2
O
3
are preferably 2-30%, 0-10%, and 0-10%, respectively.
ZnO is an element for lowering the softening point and adjusting the thermal expansion coefficient o
Fukushima Norikazu
Hadano Kazuo
Mito Takayuki
Oshita Hiroyuki
Ouji Masahiko
Collard & Roe P.C.
Gupta Yogendra N.
Hamlin D. G.
Nippon Electric Glass Co. Ltd.
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