Field of invention:
The present invention is in the field of plasma display panel filters and more precisely in the field of in built Infra Red & Near Infra Red (hereinafter referred to as IR & NIR) filter fabricated in situ in plasma display panel(hereinafter referred to as PDP) and a plasma display panel (PDP) produced by using such a filter.
Background art of the invention:
In recent years, attention has been drawn to PDP as a large size thin flat plate color display device. PDP has a structure wherein many cells (fine discharge spaces) are formed as partitioned by barrier such as wide horizontal and vertical view-angle and being thin and light in weight, and ribs between a pair of glass substrates, phosphors are provided on the surface of the respective cells, and a discharge gas is filled in such cells. Discharge takes place between electrodes in the cells to excite the discharge gas to let the phosphors in the ground state emit lights by ultraviolet rays thereby generated, to form pixels. Such PDP is a self emitting type flat display and has excellent characteristics further; it can be made to have a large size. Thus, it is one of the most prospective display devices. This type of conventional AC PDP is described in US Patent no. 5661500 by Shinoda et al.
Plasma display panels employed in television and other applications use discharging gas plasma which generates VUV, IR and electromagnetic emission. The VUV emission excites the phosphor which gives visible light.
Conventionally to improve the output performance a combination of filters are used comprising of EMI filter, orange notch filter, anti reflective filter, IR filter. IR filters have been employed commercially using different techniques. As per US patent application no 2004/0239251,the IR emmission has been selectively absorbed by using organic agent dispersed in poly vinyl butyral or ethylene vinyl acelate. As per US patent application no 2006/0051586 the NIR emmission is blocked by an NIR absorbing organic dye diammonium salt, quinine, metal complex, Phthalocyanine,napthalocyanine,cyanine dye and mixture thereof,which are embedded in an organic base. The filters are placed outside the plasma display panels.
In the case of glass filters, the filter is heavy, 3 to 4 mm thick and is placed at a minimum of 2mm from the front display glass. This causes increase in the set weight, allows multiple layer refraction resulting in visual aberration, decrease the brightness. Therefore, a good filter must be thin, have minimum gap from the Front glass plate.

IR filter in PDP must have stable absorption performance in near IR region, unaffected by fluctuation of temperature and humidity, lower cost of fabrication by increasing the yield through eliminating one layer of multiple layer filters. The US patent No's 6522463, 6117370 and US patent application no 2006/ 0051586 claim that the transmittance through the normally employed IR filter which contains di ammonium azo dye as the filter suffers degradation due to high temperature operating condition. Therefore, the life of the filter is very less and does not support the standard life cycle of 60,000hrs of PDPs.
In the film filter the thickness is low; the fixing is done over the glass directly, thereby improving performance of normal glass filters. Sectional view illustrating a structure of a discharge cell of a conventional plasma display panel with external film filter is shown in Fig 2. However, the process of laminate making is very costly, laminated film comes out of the glass due to bloating; sometimes the adhesion becomes poor because of the obvious oxidation of the organic adhesive.
Therefore, it is important to use an NIR emission filter for PDP which is thermally stable, easy to fabricate, of lower weight and is chemically stable for the life of the PDP.
Object of the invention:
It has been observed that in PDP discharging gas plasma generates VUV, IR and electromagnetic emissions. IR emission generally interferes in proper functioning of remote control for PDP Set. Earlier IR absorbent film coated glass filters were used but such glass filters were heavy, costly and had air gap between the front glass plate and filter. These glass filters were replaced by film filters which are laminated on front glass plate. These film filters are light but processes of laminating such film filter have several shortcomings like bloating, peel off and method of making a laminate is costly. Different types of IR filters have been proposed over long period of time having film coating placed on upper surface of front glass plate. In order to overcome all these problems a film capable of absorbing / reflecting IR emission inside the panel is provided.
The principal object of the present invention is to provide a film coating comprising a NIR absorbing agent. This NIR absorbing film which acts as a transparent dielectric coating is highly durable in high temperature condition and does not suffer any deterioration during display device operating life time since it does not contain any degradable organic material.
Yet another object of the present invention is to provide a novel glass composition for making glass powder which is suitable to work as a host to the NIR absorbing agent, used for making film coating which can act as transparent dielectric.

Yet another object of the present invention is to provide a process for the preparation of a glass composition to be used for manufacturing the film coating comprising a NIR absorbing agent which can act as a transparent dielectric.
Yet another object of the present invention is to provide a PDP using such a filter.
Detail description of the drawings:
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention.
Brief description of the drawing:
Fig 1 is a sectional view illustrating a structure of a discharge cell of a conventional plasma display panel with external filter
Fig 2 is a sectional view illustrating a structure of a discharge cell of a conventional plasma display panel with external film filter.
Fig 3 is a sectional view illustrating a structure of a discharge cell of a plasma display panel with inbuilt filter.
Fig 4. Illustrate the transmission of transparent di-electric paste with 0% additive.
Fig 5. Illustrate the transmission of transparent di-electric paste with 0.05% additive.
Fig 6. Illustrate the transmission of transparent di-electric paste with 0.15% additive.
Fig 7. It illustrates the transmission of transparent di-electric paste with 0.30% additive.
Fig 8. Illustrate the process flow chart of the preparation of transparent di-electric glass paste with additive added in the original transparent dielectric glass raw material directly.
Fig 9. Illustrate the process flow chart of the preparation of transparent di-electric glass paste with powdered additive added to the matrix Glass powder.

Detailed description of the Invention with reference to drawings & examples:
Before starting the detailed description of the present invention, it is necessary to discuss the conventional AC PDP for clear understanding of the present invention. Fig.1 is a sectional view of the conventional AC (Alternating Current) driven PDP possesses three-electrode structure on two glass plates forming front plate 1 and back plate 6. The front plate has formed therein a plurality of pairs of display electrodes known as sustain and scan electrodes. These electrodes are formed of ITO (Indium-Tin-Oxide) material 2. The ITO electrode sheet resistance is decreased with the introduction of metal bus lines of silver material 3 over the ITO electrodes. The display electrodes are covered with a transparent dielectric layer 4 to limit the discharge current. A thin layer of MgO (Magnesium oxide) 5 is formed over the transparent dielectric layer to emit secondary electrons and to protect the transparent dielectric layer from sputtering by ion bombardment. The back plate 6 is formed therein a plurality of address electrodes that are orthogonal to the display electrodes (not shown in the figure). A pair of sustain and scan electrodes along with an address electrode form a sub-pixel. A pixel comprises of Red, Green or Blue color phosphor 9 that make Red, Green or Blue sub-pixels respectively. A combination of Red, Green and Blue sub-pixels forms a pixel. The straight channel barrier ribs are formed on the back plate to create the discharge volume and also to separate different sub-pixels. The main co-planar discharge is created with the display electrodes pulsed AC. The VUV radiation 10 produced in the discharge phenomenon excites the phosphor to emit visible light 11 with some portion of the NIR. A filter 12 is employed to cut the NIR portion of the emitted light from the PDP.
Sectional view illustrating a structure of a discharge cell of a conventional plasma display panel with external film filter is shown in Fig 2.This figure is almost similar to fig .1 only film filter (13 ) is present on the front plate of PDP.
The transparent dielectric glass described in the present invention is prepared using the compositions in table 1(lead free transparent dielectric glass composition) & table 2(leaded transparent di-electric glass composition). These set of compositions are the base glass compositions for making the novel IR absorbing transparent dielectric film. The NIR absorbing agent can be added to the host matrix of the transparent dielectric in different processes.
The present invention will be described with reference to the fig.3. The front plate has formed therein a plurality of pairs of display electrodes known as sustain and scan electrodes. These electrodes are formed of ITO (Indium-Tin-Oxide) material 2. The ITO electrode sheet resistance is decreased with the introduction of metal bus lines of silver material 3 over
the ITO electrodes. This transparent di-electric layer 4 with additive mixed in it is applied on the top plate 1 of the PDF byiscreen printing, lamination method or any suitable method. This transparent di-electric layer 4 on the top plate with additive mixed in it acts as an inbuilt NIR absorbing film inside the PDF cell.
A glass composition of the group SiO2-ZnO-B2O3-Bi2O3-BaO and PbO-ZnO-B2O3 and an additive in the form of oxide from the group of cobalt in periodic table is added to a definite proportion in the transparent dielectric to make it IR absorbing transparent dielectric film. In a manufacturing of such a dielectric layer, raw materials according to a characteristic requirement is mixed at a desired composition ratio and melted and then cooled by air quenching on a copper plate and thereby preparing a powder of fine grain size of 2-10µ in a rapid dry planetary grinder. The powder thus made was added to a predetermined vehicle composition to make a paste thereof. This paste was then applied on a PDF bus electrode coated front plate and sintered in liquid phase to have a pore free glass transparent dielectric structure.
In the first embodiment of the present invention, a transparent dielectric glass powder of SiO2-ZnO-B203-Bi203-BaO group or glass powder of PbO-ZnO-B203 is used. The Table 1 and Table 2 represent the glass compositions of SiO2-ZnO-B203-Bi203-BaO and PbO-ZnO-B203 respectively. A composition in Table 1 and Table 2 is given assuming that weight of the constituent oxides of the group mentioned above to be 100 weights percent.

TABLE 1
(Table Removed)

TABLE 2
(Table Removed)

The pure oxides powder Cobalt oxide,TABLE 1 silicon di oxide, Zinc
Oxide, Calcium oxide and aluminum oxide were taken as the raw materials
for preparation of the NIR absorbing agent. This precursor powder is made
to facilitate the reaction of the cobalt oxide with the transparent electric
glass powder in the later stage during the fabrication of the front plates of

the display panels. The required oxides were taken in a mixing
composition as detailed in Table 3.

(Table Removed)
The raw materials were mixed homogenously in a dry mixer and fired in a mullite saggar in oxidizing atmosphere at 1300C for 2 hrs. After sintering was complete the mass was powdered and washed with distilled water to remove the contaminants. This then was dried and de-agglomerated for further use.
According to the one aspect of the present invention a NIR absorbing agent up to a dose of 0.05% to 0.30% by wt which contains 10% to 40% cobalt oxide and rest silica and alumina is added to transparent dielectric glass material to make it NIR absorbing. The particle size of the NIR absorbing agent used is to be in the range of 2-10 micron preferably 2-5 microns.
The NIR absorbing agent was added in the present invention in different ways. In the first type the NIR absorbing agent in the form of an oxide was added to the glass raw materials in such a way that the glass forming raw materials form the 100% of the glass oxide composition and the NIR absorbing agent is in excess of it. The composition is detailed in Table 4.
The present invention also provides a process for preparing the glass composition comprising SiO2 (2-9)%, B2O3(14-30)%, ZnO (13-52)%, Bi2O3 (0-40)%, AI203 (0-6)%, CaO ( 0-2)%, BaO ( 9-16)%, Li02 (0-2)%, K2O (0-1)%, Na2O(0-4)% ) and NIR absorbing agent (0.05-0.3)% or SiO2 (1-28)%, B203 ( 2-38)%, ZnO (0-33)%, PbO (10-64)%, AI203 (0-8)%, BaO (0-2) and NIR absorbing agent (0.05-0.3)% which comprises the following steps: Mixing Oxide raw material batch composition, Melting and air quenching the batch to form glass, Grinding the glass to desired particle size of 2 to 10 µm, Making a glass paste by adding required vehicle achieving required dispersion, solid content and viscosity, applying the glass paste for forming a film which is NIR absorbing.
In another process for preparing the glass composition , the NIR absorbing agent was not added to glass forming raw materials, but it was added to the glass powder keeping the addition ratio same as above. The well mixed composition of the glass powder and the NIR absorbing agent as then subjected to a heat treatment at 500-600C to allow liquid phase sintering. The sintered mass is then powdered again to de-agglomerate. This powder was added to organic paste making vehicle to a predetermined ratio made into a paste.

This paste was applied to PDP front plate as described earlier. The process for the preparation of a glass composition capable of absorbing IR radiation, comprising SiO2 (2-9)%, B2O3(14-30)%, ZnO (13-52)%, Bi203 (0-40)%, AI203 (0-6)%, CaO ( 0-2)%, BaO ( 9-16)%, LiO2 (0-2)%, K20 (0-1)%, Na2O(0-4)% ) or SiO2 (1-28)%, B203 ( 2-38)%, ZnO (0-33)%, PbO (10-64)%, AI2O3 (0-8)%, BaO (0-2)% which comprises Mixing Oxide raw material batch composition; Melting and air quenching the said batch to form glass; Adding NIR absorbing agent (0.05-0.3) %to said batch; Heating the said glass and NIR absorbing agent at 500-600C for sintering in liquid phase, Grinding and mixing the said sintered glass with NIR absorbing agent to desired powder having particle size of 2 to 10µm; Making a glass paste by adding required vehicle achieving required dispersion, solid content and viscosity; applying the said glass paste for forming a film which is NIR absorbing.
In yet another process for preparing the NIR absorbing agent was first added to definite quantity of organic vehicle and made into a paste. The dielectric glass powder made earlier through characteristic composition ratio was also made into a paste separately by adding to an organic paste making vehicle. These two pastes were added to definite mixing ratio, mixed and properly dispersed in a three roller mill to prepare the final paste. This paste was then applied to the PDP front plate as described earlier. The process for the preparation of a glass composition capable of absorbing IR radiation comprising SiO2 (2-9)%, B2O3(14-30)%, ZnO (13-52)%, Bi2O3 (0-40)%, AI203 (0-6)%, CaO ( 0-2)%, BaO ( 9-16)%, LiO2 (0-2)%, K2O (0-1)%, Na2O(0-4)% ) or Si02 (1-28)%, B203 ( 2-38)%, ZnO (0-33)%, PbO (10-64)%, AI2O3 (0-8)%, BaO (0-2) % which comprises following steps Mixing Oxide raw material batch composition; Melting and air quenching the batch to form glass; Grinding the glass to desired powder having particle size of 2 to 10 µm; Making a glass paste by adding required vehicle achieving required dispersion, solid content and viscosity; Adding NIR absorbing agent (0.05-0.3) % with required vehicle achieving desired dispersion, viscosity and forming NIR absorbing agent paste; Mixing the said glass paste with said NIR absorbing agent paste with desired viscosity and dispersion value applying the said glass paste for forming a film which is NIR absorbing.
Example 1
In this example the dielectric glass powder is prepared by melting a composition of SiO2- 3%, B203-19%, ZnO-18%, Bi2O3-37%, AI203-4%, CaO-2%, BaO-16%, Na2O-1% and the IR absorbing agent prepared with a composition comprising AI203-40%,CoO-40%,ZnO-5%,CaO-5%,SiO2-5% was added in three different addition level so as to achieve cobalt oxide level at e.g. 0.05%,0.15% and 0.30% separately in three batches and melted and prepared glass. All the glasses are powdered to the desired level of 2-10µ. The glass powder was then added to sufficient quantity of organic vehicle (comprising of solvent like alpha -terpeneol, BCA, BC; binder like- ethyl cellulose, antifoaming agent, etc) to prepare a workable screen printable paste. These pastes were then applied on front plates of display panels and IR emission was checked there after. The process of preparation of the dielectric is summarized in Fig 4. The transmission results are shown in Fig.7. The transmission data can well be
compared to the fig 6 where the transparent dielectric was not modified with the IR absorbing agent.
Example 2
This example provides a transparent dielectric powder which is prepared from a oxide composition comprising of SiO2- 2%, AI203-4%, B2O3- 22%, ZnO-10%, PbO -62%.The raw materials are melted at 1200C, air cooled and the prepared glass is powdered to desired particle size of 2-10µ. Three batch of this powder were mixed with three different quantity of IR absorbing additive comprising of cobalt alumina-silicate in such a ratio as detailed in Table 4 that the equivalent cobalt oxide content in the added material is equal to 0.05%, 0.15% and 0.3% respectively. These mixtures were mixed in a dry mixer separately for homogenous mixing. These three batches of mixed powder were fired at 625C for fifteen minutes in alumina crucible. The sintered batches were ground again to de- agglomerate and achieve the desired particle size of 2-10µ.These three batches were mixed to sufficient quantity of organic vehicle as described in case of example 1 and made workable paste. These pastes were applied on the front plates of display panels and IR emission was measured there after. The process of preparation of the dielectric is summarized in Fig 5. The transmission results are shown in Fig.8.
Table: 4
(Table Removed)
Example 3
In another example the dielectric powder is prepared with raw materials comprising SiO2- 18%, AI203-4%,B203-16%,Bao-10, ZnO-2%, PbO -50% . The raw materials were mixed and made into dielectric glass by heating it at 1225C. The molten glass was air quenched and was to 2-10µ particle size. The dielectric powder was converted into a workable paste as described in earlier examples. The IR absorbing material cobalt- alumino-silicate as described earlier in example 1 & 2. 70g of this stain powder was mixed with 30g of organic vehicles (as described in example 1) and was made into a workable paste. This paste was passed through three roller mill to ensure that the powder dispersion in the paste was optimum. This paste was added to the dielectric glass paste already made before in
such a ratio that the dielectric glass powder to the dry IR absorbing powder ratio remains at 100:0.15. This paste- mix was passed through high speed planetary mixer and subsequently through three roller mill to ensure that the dispersion value reaches min 7.5 in Hegmann gauge. This paste was then applied to the front plate of the displays and the IR emission was checked and reported in Fig.9
As an embodiment of the present invention a plasma display panel was made through the application of transparent dielectric explained in example 1, 2 and 3 and is shown in the sectional view illustrating a structure of a discharge cell of a plasma display panel with reduced IR emission in Fig 3. The inbuilt transparent di-electric glass with different additive is suitable to be used as IR filter as it absorbs the NIR of 90% at 850 nm and 95% at 950 nm.
Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternate embodiments of the invention, will become apparent to persons skilled in the art upon reference to the description of the invention. It is therefore contemplated that such modifications can be made without departing from the spirit or scope of the present invention as defined.

We Claim:
1) A glass composition capable of absorbing IR radiation comprising
Si02 (2-9)%, B203(14-30)%, ZnO (13-52)%, Bi203 (0-40)%, AI2O3 (0-
6)%, CaO ( 0-2)%, BaO ( 9-16)%, Li02 (0-2)%, K2O (0-1)%, Na20(0-
4)% ) and NIR absorbing agent (0.05-0.3)% where NIR absorbing
agent is added over and above the base glass composition .
2) A glass composition capable of absorbing IR radiation comprising
Si02 (1-28)%, B2O3 ( 2-38)%, ZnO (0-33)%, PbO (10-64)%, AI203 (0-
8)%, BaO (0-2) and NIR absorbing agent (0.05-0.3)% where NIR
absorbing agent is added over and above the base glass composition .
3) The glass composition as claimed in claim 1&2 , wherein said glass
composition absorbs the IR radiation ranging from 90-95% in the NIR
range of 800nm and above.
4) The NIR absorbing agent as claimed in claim1&2, wherein, said NIR
absorbing agent comprising Si02(0%-20% ), CoO(10-40%), ZnO(0-
20%), AI2O3( 40-75%), CaO(0-5%) .
5) The NIR absorbing agent as claimed in claim1&2, wherein, said NIR
absorbing agent having particle size with in the range of 2-10 micron
preferably 2-5 microns.
6) A process for the preparation of a glass composition capable of absorbing IR
radiation, wherein said composition comprising SiO2 (2-9)%, B2O3(14-30)%, ZnO
(13-52)%, Bi2O3 (0-40)%, AI203 (0-6)%, CaO ( 0-2)%, BaO ( 9-16)%, Li02 (0-2)%,
K20 (0-1)%, Na2O(0-4)% ) and NIR absorbing agent (0.05-0.3)% or SiO2 (1-28)%,
B203 ( 2-38)%, ZnO (0-33)%, PbO (10-64)%, AI2O3 (0-8)%, BaO (0-2) and NIR
absorbing agent (0.05-0.3)% ; which comprises
Mixing Oxide raw material batch composition; Melting and air quenching the said batch to form glass; Grinding the said glass to desired particle size of 2 to 10 µm;
Making a glass paste by adding required vehicle achieving required dispersion, solid content and viscosity;
Applying the said glass paste for forming a film which is NIR absorbing.
7) A process for the preparation of a glass composition capable of absorbing IR
radiation, wherein said composition comprising SiO2 (2-9)%, B203(14-30)%, ZnO
(13-52)%, Bi203 (0-40)%, AI2O3 (0-6)%, CaO ( 0-2)%, BaO ( 9-16)%, Li02 (0-2)%,
K20 (0-1)%, Na2O(0-4)% ) or SiO2 (1-28)%, B2O3 ( 2-38)%, ZnO (0-33)%, PbO (10-
64)%, AI203 (0-8)%, BaO (0-2) which comprises
Mixing Oxide raw material batch composition;
Melting and air quenching the said batch to form glass; Adding NIR absorbing agent (0.05-0.3) % to said batch;
Heating the said glass and NIR absorbing agent at 500-600C for sintering in liquid phase,
Grinding and mixing the said sintered glass with NIR absorbing agent to desired powder having particle size of 2 to 10 urn;
Making a glass paste by adding required vehicle achieving required dispersion, solid content and viscosity;
Applying the said glass paste for forming a film which is NIR absorbing.
8) A process for the preparation of a glass composition capable of absorbing IR radiation, wherein said composition comprising SiO2 (2-9)%, B203(14-30)%, ZnO (13-52)%, Bi203 (0-40)%, AI203 (0-6)%, CaO ( 0-2)%, BaO ( 9-16)%, Li02 (0-2)%, K20 (0-1)%, Na20(0-4)% ) or Si02 (1-28)%, B2O3 ( 2-38)%, ZnO (0-33)%, PbO (10-64)%, AI2O3 (0-8)%, BaO (0-2) % which comprises Mixing Oxide raw material batch composition;
Melting and air quenching the said batch to form glass;
Grinding the said glass to desired powder having particle size of 2 to 10 urn;
Making a glass paste by adding required vehicle achieving required dispersion, solid content and viscosity;
Adding NIR absorbing agent (0.05-0.3) % with required vehicle achieving desired dispersion, viscosity and forming NIR absorbing agent paste;
Mixing the said glass paste with said NIR absorbing agent paste with desired viscosity and dispersion value
Applying the said glass paste for forming a film which is NIR absorbing.
9) A process as claimed in claim 8 , wherein, NIR absorbing agent paste
is added to the said glass paste in a ratio that so that the ratio of
glass powder in the glass paste to the inorganic material content of the
NIR absorbing agent paste lies within 100: 0.05 to 100 : 0.30.
10) A process as claimed in claims 6,7 & 8 , wherein, said NIR absorbing
agent comprises SiO2( 0-20%), CoO( 10-40%), ZnO(0-20%), AI203(40-
75%), CaO(0-5% ) .
11) A process as claimed in claims 6, 7 & 8, wherein, said NIR absorbing agent has particle size between the ranges of 2-10 micron preferably 2-5 microns.
12) The NIR absorbing film as claimed in above claims, wherein, said NIR
absorbing film is transparent dielectric and can be used as layer for
Flat Panel Displays.
13) A glass composition and a process for the preparation of glass for
manufacturing of NIR absorbing film substantially herein described with reference
to the accompanying examples and drawings.