EP1627407A2

EP1627407A2 - Plasma panel comprising cement partition barriers

Info

Publication number: EP1627407A2
Application number: EP04734527A
Authority: EP
Inventors: Armand Bettinelli; Jean-Philippe Browaeys
Original assignee: Thomson Plasma SAS
Current assignee: Thomson Plasma SAS
Priority date: 2003-05-27
Filing date: 2004-05-24
Publication date: 2006-02-22
Anticipated expiration: 2024-05-24
Also published as: DE602004005328D1; CN1795524A; US7710033B2; CN100474488C; DE602004005328T2; KR101026462B1; KR20060007438A; JP2007523442A; WO2004107381A3; WO2004107381A2; JP4633726B2; FR2855644A1; EP1627407B1; US20070024203A1

Abstract

The invention relates to a plasma panel comprising cement partition barriers. The inventive panel comprises two slabs defining a sealed space therebetween. The aforementioned sealed space is filled with discharge gas and partitioned into discharge cells (6R, 6G, 6B) which are defined between the slabs by means of barriers (3), said barriers being made from a material comprising a hydraulic binder-based inorganic binder and a mineral filler. Since a hydraulic binder is used in place of an inorganic vitreous binder, the panels can be produced at a lower temperature.

Description

PLASMA PANEL WITH PARTITION BARRIERS

ARE IN CEMENT. The invention relates to a plasma panel comprising two slabs forming between them a sealed space which is filled with discharge gas and which is partitioned into discharge cells delimited between these slabs by barriers forming a network.

Such a panel is generally used for viewing images. The cells are generally divided into rows and columns. The barriers generally extend at least between the columns, sometimes also between the rows.

The height of the barriers generally corresponds to the distance between the slabs, so that the barriers also serve as spacers.

The sides of the barriers as well as one of the slabs are generally covered with phosphors capable of emitting visible light under the excitation of plasma discharges; by adapting the composition of the discharge gas, visible light can also be obtained directly, without phosphors.

The manufacture of the barriers generally requires costly and penalizing heat treatments. Document WO00 / 36625 describes a manufacturing process in which the barriers are molded in a polymer reverse pattern produced by photolithography; on page 8, lines 7 to 22, to make the barriers, the use of a molding paste comprising ceramic powders, glass frits, Portland cement or other metal oxide powders is described; the only example given at the end of the document describes precisely the use of a paste containing 40% by weight of cement (page 10, line 32) and paraffin oil as carrier fluid; after molding, the paraffin oil migrates into the photopolymerized material of the mold, which makes it possible to increase the densification of the mineral powder in the mold channels; a final heat treatment at 600 ° C. makes it possible to remove the polymer from the mold and the paraffin oil, and to obtain solidification, here by sintering, of the cement powder. As can be seen in this document, no water is added at any stage of the cement barrier manufacturing process, which, for those skilled in the art

barrier materials, clearly means that the consolidation of the barriers is obtained by sintering the cement powder or its decomposition products, not by a hydration action on the cement of the paste, especially at 600 ° C, the hydration products of the cement would be degraded if not broken down to the point of preventing a consolidation effect.

An objective of the invention is to limit the number of heat treatments necessary to obtain sufficient consolidation of the barriers, and / or to lower the temperature, or even to avoid these heat treatments. To this end, the subject of the invention is a plasma panel comprising two slabs forming between them a sealed space which is filled with discharge gas and which is partitioned into discharge cells delimited between these slabs by barriers made of mineral material comprising a mineral binder and a mineral filler characterized in that said mineral binder is a hydraulic binder.

According to the invention, the mineral binder is in the hydrated state and aggregates the mineral filler. To obtain this hydrated state, as illustrated below, it is therefore necessary to use water in the steps for manufacturing the plasma panel. It is the hydraulic binder in the hydrated state which is responsible for the consolidation of the barriers, which aggregates the grains of the mineral filler, unlike the barriers described in document WO00 / 36625 where the skilled person understands that the effect consolidation is obtained by sintering grains of cement powder (or ceramic powder) and where, given the high processing temperatures, the cement is no longer in the hydrated state. The term “hydraulic binder” is understood to mean a material which, when it is formed in a block from a powder, can be hardened by a hydration reaction: thus, by mixing a mineral filler powder suitable for a hydraulic binder powder, by forming this powder mixture, for example by molding, the form obtained can be hardened after the hydration reaction. In practice, water is added to the powder mixture before pouring the liquid assembly into a mold; the addition of water constitutes what is generally called a mixing operation.

The panel cells are generally divided into rows and columns.

The barriers generally extend at least between the columns, sometimes also between the rows, in which case the barriers form a two-dimensional network. The height of the barriers generally corresponds to the distance between the slabs.

Such a plasma panel generally comprises at least two arrays of electrodes arranged so that each cell is crossed by an electrode of each array. Generally, each slab supports at least one network of electrodes, so that the electrodes of a network carried by one slab cross the electrodes of a network carried by the other slab.

Generally, at least one of the networks is covered by a dielectric layer, so as to provide a memory effect which facilitates the control of the panel.

Other plasma panels do not include electrodes to initiate discharges; microwave radiation is then used to trigger the discharges; a single network of electrodes can nevertheless be used in this case for addressing the discharges. Preferably, the hydraulic binder is a cement, for example based on aluminates or aluminosilicates.

Preferably, the proportion by weight of mineral filler in the mineral material of the barriers is greater than or equal to 50%.

Preferably, the mineral filler comprises more than 50% by mass of silica and / or alumina.

According to a variant, the porosity of the barriers is greater than or equal to approximately 15%, preferably greater than 25%. Thus, during the manufacture of the panel, the pumping operation is facilitated.

The invention will be better understood on reading the description which follows, given by way of nonlimiting example, and with reference to the appended figures in which:

FIG. 1 illustrates, in top view, three adjacent cells of a plasma panel according to an embodiment of the invention,

- Figure 2 illustrates a section of the panel of Figure 1, before assembly of the two tiles.

We will now describe a first family of methods for manufacturing a plasma panel according to the invention, here provided with cells arranged in rectilinear rows and columns, in particular specifying the manufacture of the slab carrying the network of also rectilinear barriers, here the back panel. In this first family of processes, organic resins are conventionally used as a temporary binder for forming barriers, which requires a heat treatment to remove these binders. Referring to Figure 2, we start from a slab 1 made of soda-lime glass 254 mm x 162 mm x 3mm provided with a network of electrodes A formed by silver conductors, itself coated with a dielectric layer 2 classic cooked at 540 ° C.

We will now describe the manufacture of a network of barriers 3 on this slab so as to obtain:

- barriers made of mineral material based on hardened hydraulic binder, here Portland cement;

- a series of parallel, continuous barriers, 60 to 70 μm thick, to separate the columns, distributed in a pitch of 360 μm; - and a series of parallel barriers, 220 to 230 μm thick, to separate the lines, distributed in a step of 1080 μm.

Each of the cells thus delimited by these barriers has a rectangular shape with a dimension of 850 μm x 290 μm approximately.

A paste is prepared intended to form, after application and drying on the slab, a raw barrier layer comprising 4% by weight of organic binder, 96% by weight of mineral barrier material, here based on cement:

- Portland type cement is used having a fairly fine particle size, for example an average grain diameter of the order of 1 μm; this cement is

lightly loaded with sub-micron silica powder, called "silica smoke"; this cement is considered to be a quick setting cement;

- a solution of 8 g of ethyl cellulose-based resin in 92 g of terpineol-based solvent is prepared; - 200 g of powder of mineral barrier material, here cement, are dispersed in 104 g of resin solution; homogenized by passing through a three-cylinder type mixer-attritor, so as to reduce the size of the powder aggregates below 7 μm; Terpineol is added if necessary to adjust the viscosity to around 50 Pa.s. The barrier paste is then applied to the slab, here by screen printing of six superimposed layers; each screen printing pass is followed by drying at 110 ° C .; a slab with a raw barrier layer, 150 μm thick, is then obtained.

Preferably, for the last two passes, a denser screen fabric is used, for example at 90 threads / cm, and a less viscous paste, for example of the order of 20 Pa.s, to obtain surface sub-layers of smoothing on the surface of the barrier layer.

According to a variant, the slab is coated with this paste with a roller (“roller-coater” in English) and the applied layer is dried in a continuous-running tunnel furnace provided with blowing and air extraction means; a single pass then makes it possible to apply the raw layer of thickness 150 μm.

We will now describe the formation by abrasion of the network of barriers in the thickness of the green layer that we have just obtained.

A protective mask is first applied to this layer having openings or patterns at the location of the cells to be dug by abrasion in the thickness of the raw layer; for this purpose:

- a photosensitive dry film with a thickness of about 40 μm is laminated on the green layer, at a suitable temperature and pressure;

- this film is exposed at the locations of the barriers, under a UV light beam and for a suitable duration;

- This film is then developed using a 0.2% solution of sodium carbonate at approximately 30 ° C, so as to remove the portions of film outside the locations of the barriers;

- it dries quickly to avoid setting of the cement.

A protective mask is thus obtained on the raw layer.

For the formation of the barriers in the thickness of the barriers, an abrasive material is sprayed onto the mask using a nozzle with a linear slot of length 200 mm; as abrasive material, a metallic powder sold by the company FUJI, referenced S9 grade 1000, is used; during the so-called “sandblasting” projection operation, the sandblasting nozzle is kept approximately 10 cm from the slab, moves along the barriers to be formed at the speed of 50 mm / min. approximately, and the green slab being sanded moves in a direction perpendicular to that of the barriers at a speed of 70 mm / min. ; the blasting pressure is of the order of 0.04 MPa; the flow rate of metallic powder is approximately 2500 g / min.

On the top of the raw barriers thus formed, the mask is then removed by spraying with an aqueous solution at 35 ° C containing 1% soda (NaOH); after rinsing with water and drying under an air knife at 50 "C, a slab is obtained provided with a network of green barriers with a height of the order of 150 μm, width approximately 100 μm at the base and 70 μm These barriers comprise approximately 4% by weight of organic resin.

We will now describe the application of layers of phosphors 4R, 4G, 4B by direct screen printing of a paste of phosphors in the cells formed between the raw barriers. We then proceed as follows:

- preparation of phosphor pastes of different colors, by dispersing 60 g of phosphor powder in 140 g of an ethyl cellulose solution dissolved at 3% of the terpineol. - use of a screen printing screen comprising a metallic fabric with 120 threads per cm sealed by a photosensitive emulsion with the exception of strips of width 90 μm located in the areas where the dough must be transferred, that is to say arranged according to a step of 1080 μm (3 x 360 μm) corresponding to the distance between two consecutive columns of cells of the same color;

- direct screen printing of one of the phosphors pastes through this screen, that is to say with transfer of the paste localized in the zones where the metallic fabric is not sealed;

- drying 120 ° C.

These operations are repeated for each primary color using the same screen which is offset, in the direction of the lines, by a column pitch (360 μm) for the second color, and by another pitch for the third color. 5 A paste of sealing joint is then deposited on the periphery of the rear slab thus obtained; this sealing joint is here based on a fusible glass mashed in a cellulose solution giving a viscosity of the order of 100 Pa.s.

A rear slab is then obtained, which has a network of barriers.

10 floods whose slopes, among other surfaces, are coated with a raw layer of phosphors.

A heat treatment is then carried out to remove the organic binder from the barriers and the phosphor layers: first temperature rise to 10 ° C / min. up to 350 ° C then first stage of 20 minutes at

15,350 ° C, second temperature rise to 10 ^α C / min. up to 480 ° C, then second stage of 20 min at 480 ° C, and finally temperature drop to 10 ° C / min.

The barrier hardening treatment is then carried out, hardening which is obtained according to the invention by hydration reaction of the

20 cement which therefore requires the use of water at this stage of the process: after heat treatment, the slab obtained is passed through under a spray of water for 30 minutes, then the slab is dried with an air knife at room temperature , then with an air knife at 105 ° C. According to a variant of hardening treatment, the slab is immersed in water for 6 hours.

According to another variant of the hardening treatment, the slab is placed under steam pressure under suitable conditions of temperature and duration to obtain the hardening, that is to say the setting, of the cement.

A rear panel is obtained which has a network of hardened barriers 3 coated with layers of phosphors 4R, 4G, 4B.

Since the heat treatment of the process which has just been described only serves to remove the organic binders and not to harden the barriers as in the prior art, the duration of this treatment can be advantageously shortened, in particular by reducing the times landing, or even increasing speeds

temperature rise in certain temperature ranges; using vitreous mineral binders as in the prior art, the necessary landing times would have been of the order of 30 minutes, instead of 20 minutes here; shortening the heat treatment times, or even lowering the maximum temperatures during treatment, have a significant economic advantage.

According to an advantageous variant of the process, the operation of removing organic binders and the operation of hardening the barriers are combined: first temperature rise to 10 ° C./min. up to 350 ° C then first 30 minute plateau at 350 ° C, passage into humid air obtained by bubbling air through a water tank maintained at 80 ° C, second temperature rise to 10 ° C / min. up to 480 ° C, then second stage from 30miπ to 480 ° C, and finally lowering in temperature to 10 ° C / min up to 350 ° C, then passage into dry air until the slab is completely cooled. To obtain a plasma display panel according to the invention, a conventional front panel 5 is assembled on the rear panel according to the invention (see the two arrows designating the assembly in FIG. 2), the two panels are sealed by treatment thermal at 400 ° C., the air contained between the slabs is evacuated by pumping, the panel is filled with discharge gas under low pressure, and the pumping opening is sealed. The front panel 5 conventionally comprises two arrays of coplanar electrodes X, Y.

The plasma panel thus obtained, shown in plan view in FIG. 1, comprises two slabs forming between them a sealed space which is filled with discharge gas and which is partitioned into discharge cells 6R, 6G, 6B delimited by the barriers 3, which are, according to the invention, hardened mineral material, that is to say aggregated, by a hydraulic binder which is in the hydrated state.

The plasma panel thus obtained has good mechanical properties, in particular at the level of the barriers: no crushing of the barriers is observed.

According to an advantageous variant, instead of using a mineral material of barriers based on Portland cement, it is possible to use a mineral material further comprising a mineral filler, such as alumina or silica,

or any other material compatible with the manufacture and operation of a plasma panel. The hydration of the hydraulic binder therefore serves, according to the invention, to aggregate this mineral load.

According to a variant of the method which is particularly well suited for obtaining porous barriers, having an open porosity greater than 25%, as the barrier mineral material, a mixture of 50% of the cement described above and 50% of silica powder is used; as silica, we take for example a cristobalite type silica whose specific surface is less than 10 m ² / g and whose average particle size is less than 10 μm, typically

10 of the order of 5 μm; for example, the reference M4000 from the Sifraco Company is chosen. The barriers obtained also have good mechanical properties; thanks to the high porosity of the barriers, the pumping time required to evacuate the air contained between the slabs is greatly reduced.

Another way to obtain porous barriers with porosity greater than

25% would be to use foaming cement compositions well known to those skilled in the art of cements.

We will now describe a second family of methods for manufacturing a plasma panel according to the invention. In this second family of processes, there are no more organic resins in the raw layers of

20 barriers, which completely avoids heat treatment at high temperature, at least in the manufacture of the rear panel.

We start with a 254 mm x 162 mm x 3 mm soda-lime glass slab with an array of electrodes formed by silver conductors, here not coated with a dielectric layer. 5 We will now describe the application, on this slab, of a slightly porous dielectric layer and the manufacture of a network of slightly porous barriers so as to obtain:

- barriers made of mineral material based on hardened hydraulic binder, here the same Portland cement as before; 0 - a series of parallel, continuous barriers, 100 μm thick at the base and 70 μm at the top, to separate the columns, distributed in a step of 360 μm;

- and a series of parallel barriers, 260 μm thick at the base and 230 μm at the top, to separate the lines, distributed in a step of 1080 μm.

As before, the cells of the panel are rectangular.

I - Preparation of the pasta: we prepare:

- A barrier undercoat paste, intended to replace the dielectric layer of the previous embodiment;

- a barrier paste. l-a: barrier paste: it is an aqueous paste produced from a mixture of 50% cement and 50% “mixed” silica with 35% water:

- 100g of Portland cement powder from grinding with selective sorting limiting the size of the largest particles to 11 μm (dιoo <11)

- 100g of a silica powder with an average particle size of 3 μm (d50 = 3 μm), where the size of the largest particles is limited to 10 μm (dtoo <10) - Dry mixing of the two powders, then incorporation of 109 g of deionized water. Homogenization using a disperser and degassing under vacuum. A barrier paste is obtained, the viscosity of which is 60 Pa.s. lb: barrier undercoat paste: it is an aqueous paste of a mixture of 40% cement, 20% alumina and 40% titanium oxide "spoiled" with 39% water:

- 80g of quick-setting Portland cement powder, resulting from grinding with selective sorting limiting the size of the largest particles to 11 μm (dιoo <11)

- 40g of alumina powder with an average particle size of 3 μm (d50 = 3 μm) where the size of the largest particles is limited to 10 μm (dιoo <10)

- 80g of Ti02 powder with an average particle size of 1.5 μm (d50 = 1.5 μm) where the size of the largest particles is limited to 8 μm (dιoo <0)

- Dry mixing of the three powders, then incorporation of 130g of deionized water. Homogenization using a disperser and degassing under vacuum.

An undercoat paste is obtained, the viscosity of which is 40 Pa.s. It - Application of the underlay and formation of the barriers:

1-a / We take a mold with a network of grooves having the geometry of the barriers, with the exception of the depth of the grooves increased by 20% relative to the height of these barriers. The mold consists of a removable upper part consisting of a click whose thickness corresponds to 20% of additional depth.

The mold is coated with a release agent, then placed on a vibrating pot; we then fill the mold with the freshly prepared barrier paste and scrape off the excess. The filled mold is then placed in an atmosphere at 40 ° C to accelerate the setting reaction of the hydraulic binder, here the cement. The setting of the cement corresponds to a hydration reaction of the cement.

1-b / During setting, in parallel with step 1a, a 30 μm thick undercoat of undercoat paste is deposited with the curtain on the slab and on the electrodes. The slab is then placed in a 50 ° C atmosphere to accelerate the setting reaction of the cement in the underlay.

2 / After 1 hour of setting in the mold (step 1-a), the upper foil of the mold is removed so as to uncover the upper surface of the mold which will constitute the base of future barriers, and a very light spray of water is performed on this surface. The rear slab from Step 1-b is then applied to this surface, so as to apply the still malleable underlay against the base of future barriers.

The assembly is then turned over so that gravity supports the mold and its barriers on the rear face; The whole is then placed in an atmosphere at 40 ° C. After 2 hours, it can be removed from the mold by removing the mold.

This can then be cleaned with a high pressure water jet. The slab coated with its undercoat and its baσières is stored for another 4 hours in an atmosphere saturated with humidity to perfect the setting reaction of the cement and thus obtain a hydraulic binder in the hydrated state which aggregates the mineral load of the barriers. and consolidates them. Then the slab is passed through a passage oven regulated at 115 ° C to remove the residual water.

A network of hardened and consolidated barriers without sintering is thus obtained without heat treatment, based on a sub-layer which acts as a

dielectric layer; the porosity of the underlay and of the barriers obtained is of the order of 15%, which is advantageous for pumping the panel; this porosity can be adjusted according to the water content of the dough. III -Application of phosphors: A suspension is prepared containing 70 g of phosphor powder dispersed in 130 g of a mixture of glycol ethers selected for their boiling temperature and their viscosity so as to obtain the temporary suspension of the phosphors without the use of resins. Colloidal suspensions of silica (or others) can however be used as thickener if necessary.

To apply these pastes to the sides of the barriers and the bottom of the cells between these barriers, an injection process (“dispensiπg” in English) is used for these pastes, using syringes whose outlet is oriented between the barriers: a multi-orifice head is used for this purpose (76 calibrated holes of 100 μm staggered, in steps of 1080 μm); the head is moved parallel to the columns, in several offset passes to cover the whole of the slab. Then dried at 120 ° C. This is done successively for the three phosphors, shifting by one column pitch (360 μm) as before. IV - Application of the sealing joint:

Using the same application method as for the phosphors, a paste of sealing joint is then deposited on the periphery of the rear panel thus obtained; this sealing joint is here based on a glass with very low melting point in a paste similar to that of the phosphors giving a viscosity of the order of 80 Pa.s. Then dried at 120 ° C. V- Brief final heat treatment at low temperature:

Despite the absence of resin, a rise in temperature with a level of 30mπ to 250 ° C is carried out to complete the evaporation of all the solvents.

To obtain a plasma display panel according to the invention, a conventional front panel is assembled on the rear panel according to the invention, the two panels are sealed by heat treatment suitable for obtaining at least partial fusion of the sealing glass, evacuates the air contained between the slabs

by pumping, the panel is filled with discharge gas under low pressure, and the pumping opening is sealed.

The plasma panel thus obtained has good mechanical properties, in particular at the level of the barriers: no crushing of the barriers is observed. The hydraulic binder of the barriers remained in the hydrated state despite the heat treatments.

The method according to the second family of embodiments of the invention therefore makes it possible to produce the plasma panel slabs which carry the barriers without ever exceeding 250 ° C., which is very advantageous economically and for maintaining the barriers in a hydrated state according to the invention.

According to an advantageous variant of the invention, a sealing joint based on sealing adhesive resistant to a temperature of 250 ° C., available on the market, is used, which makes it possible to seal the two slabs by heat treatment at only 250 °. VS ; in this case, thanks to the invention, none of the steps for manufacturing the panel does not exceed 250 ° C., which makes it easier to maintain the hydraulic binder of the hydrated state barriers, which advantageously limits any risk of degradation of the mechanical properties hydraulic barrier binder. Whatever the embodiment chosen for implementing the invention, other types of cement than Portland cement can be used without departing from the invention, in particular cements which, after setting, can withstand the temperatures of the treatments. thermal still necessary for the manufacture of the panel; other types of hydraulic binders than cement can be used without departing from the invention.

The present invention applies to any type of plasma panel whose cells are compartmentalized by barriers; these plasma panels can be of the coplanar type, of the matrix type, or else of radio frequency or microwave excitation.

Claims

1.- Plasma panel comprising two slabs forming between them a sealed space which is filled with discharge gas and which is partitioned into discharge cells (6R, 6G, 6B) delimited between these slabs by barriers (3) made of mineral material comprising a mineral binder and a mineral filler characterized in that said mineral binder is a hydraulic binder which is in a hydrated state and aggregates said mineral filler.

2.- Panel according to claim 1 characterized in that said hydraulic binder is a cement.

3.- Panel according to claim 2 characterized in that said cement is based on aluminates or aluminosilicates.

4.- Panel according to any one of the preceding claims characterized in that the weight proportion of mineral filler in said mineral material is greater than or equal to 50%.

5.- Panel according to any of the preceding claims characterized in that the mineral filler comprises more than 50% by mass of silica and / or alumina.

6.- Panel according to any one of the preceding claims characterized in that the porosity of said barriers is greater than or equal to about 15%.

7.- Panel according to claim 6 characterized in that the porosity of said barriers is greater than 25%.