Compositions: ceramic – Ceramic compositions – Glass compositions – compositions containing glass other than...
Reexamination Certificate
2000-09-11
2003-07-08
Sample, David (Department: 1755)
Compositions: ceramic
Ceramic compositions
Glass compositions, compositions containing glass other than...
C501S018000, C501S020000, C501S026000, C501S032000, C501S079000
Reexamination Certificate
active
06589894
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to dielectric material useful in plasma display panels (PDPs) and, in particular, to a composition used for forming barrier ribs 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 plurality of barrier ribs (which will simply be referred to as “ribs” hereinafter) are formed in the gap to define and maintain the gap between the front and rear glass plates. The ribs are also serve for partitioning the gap into a plurality of discharge spaces for emitting R (red), G (green) and B (blue) lights.
Each of the ribs is formed by firing a mixture of glass powder and ceramics powder as fillers. In order to avoid deformation of the rear glass plates during the firing of the mixture, the mixture is desired to be able to be fired at about 600° C. or less. To this end, glass having a softening point of 630° C. or less is usually used for the glass powder. The glass contains PbO and/or alkali metal oxide for lowering the softening point of the glass.
However, the glass containing PbO has problems in that PbO badly affects to the health of workers handling the glass powder as well as in the environmental pollution by waste of the glass.
On the other hand, the use of alkali metal oxide is desirably avoided in the glass for ribs in PDP because alkali metal badly affects to electrical properties of electric and electronic components.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a glass for use in composition useful for forming the ribs in PDP which is free of PbO but has a low softening point of 630° C. or less.
It is an object of this invention to provide a glass for use in composition useful for forming the ribs in PDP which is free of alkali metal oxide but has a low softening point of 630° C. or less.
It is a further object of this invention to provide a composition for use in formation of ribs in PDP which comprises the PbO free and alkali metal oxide free glass powder and filler powder.
According to this invention, a glass for use in a material for forming ribs in a plasma display panel is obtained, which consists essentially of, by molecular percent, 5-40% BaO, 20-55% ZnO, 15-50% B
2
O
3
, 0-25% SiO
2
.
The glass preferably has a softening point of 630° C. or less.
The glass is free of PbO and free of alkali metal oxide.
According to another aspect of this invention, a composition for use in formation of barrier ribs in a plasma display panel is obtained. The composition comprises powder material which consists essentially, by weight percent, 50-95% glass powder and 5-50% ceramic filler powder. The glass consists essentially of, by molecular percent, 5-40% BaO, 20-55% ZnO, 15-50% B
2
O
3
, 0-25% SiO
2
, the glass being PbO free and alkali metal oxide free and having a softening point of 630° C. or less.
According to an embodiment of this invention, the composition further comprises binder, plasticizer, and solvent to form a paste. The paste comprises, by weight, the powder material of 30-90%, the binder of 0.1-20%, the plasticizer of 0-10%, and the solvent of 10-30%.
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, 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 embodiment, the composition further comprises binder and plasticizer to form a green sheet. The green sheet comprises, by weight, the powder material of 60-80%, the binder of 5-30%, and the plasticizer of 0-10%.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In order to use in a material for forming ribs in a plasma display panel, this invention uses BaO—ZnO—B
2
O
3
glass. The amount of ingredients in the glass is restricted in amounts so as to realize a softening point of 630° C. or less. Further, ZnO in the glass is increased in an amount comparing to the usual ZnO amount in BaO—ZnO—B
2
O
3
glass so as to obtain a thermal expansion coefficient compatible with that of the front and rear glass plates of PDP.
In the glass, BaO is contained for lowering the softening point of the glass. The content of BaO is 5-40%, preferably 10-30%, by molecular percent. If the content is less than 5%, the softening point is not sufficiently lowered. The content more than 40% results in an elevated thermal expansion coefficient which is not compatible with the front and the rear glass plates of PDP.
ZnO is an element contained to lower the softening point and adjusting the thermal expansion coefficient of the glass. The content of ZnO is selected 20-55% by molecular percent, preferably 30-50%. When it is selected less than 20%, the intended function of ZnO is not effected. When it is more than 55%, the resultant glass has crystals therein and makes it difficult to produce a dense body of the rib by firing.
B
2
O
3
is a glass forming element for widening a vitrification range. The content should be contained 15-50% by molecular percent, preferably 20-50%. B
2
O
3
contents less than 15% makes vitrification difficult. When the content is more than 50%, the resultant glass has a softening point higher than 630° C., and cannot therefore produce a sense body of the rib by firing at a temperature of 600° C. or lower.
SiO
2
is also a glass forming element and should be selected, in content, 0-25% by molecular percent, preferably 2-15%. Use of SiO
2
more than 25% also results in a softening point higher than 6300° C., and cannot therefore produce a sense body of the rib by firing at a temperature of 600° C. or lower.
It is possible for certain objects to add other ingredients in the glass, for example, Al
2
O
3
, ZrO
2
, TiO
2
, alkali-earth metal oxide such as MgO, CaO, and SrO, for improving water and chemical resistance, and P
2
O
5
for stabilizing the glass. The amount of the addition should be restricted up to 20%, preferably up to 15% in molecular percent.
The composition according to the present invention can include ceramics powder in addition to the glass powder to form a powdery admixture, so as to improve the mechanical strength of the fired layer. The ceramics powder comprises alumina, zircon, zirconia, titania, cordierite, mullite, silica, willemite, tin oxide, and zinc oxide. It is preferable that the maximum particle size Dmax of the ceramics powder is 15 &mgr;m or less.
In contents, the glass powder and the ceramics powder are 50-95% and 5-50% by weight, preferably 60-90% and 10-40% respectively. If the ceramic powder content is more than 50%, it is difficult to form the rib of a dense body by firing. Use of ceramics powder less than 5% results in lower strength of the rib fired.
In actual use, the composition according to this invention can be provided as a form of a paste or a green sheet.
In order to prepare the dielectric composition as a paste, the glass powder or the powdery admixture described above is mixed with binder, plasticizer and solvent. The glass powder alone and the powdery mixture will collectively be referred to as “powder material”, hereinafter.
The paste comprises, by weight, the powder material of 30-90% preferably 50-80%, the binder of 0.1-20% preferably 0.5-10%, the plasticizer of 0-10% preferably 0-9%, and the solvent of 10-30% preferably 15-25%.
In use of the paste for forming ribs between the front and rear glass plates of a PDP, the paste is coated on the rear glass plate by the screen printing or the b
Hadano Kazuo
Mito Takayuki
Oshita Hiroyuki
Ouji Masahiko
Collard & Roe P.C.
Nippon Electric Glass Co. Ltd.
Sample David
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