MXPA05012701A - Plasma panel comprising cement partition barriers - Google Patents

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 THAT COMPRISES CEMENT DIVIDING BARRIERS DESCRIPTION OF THE INVENTION The invention relates to a plasma screen panel comprising two plates that leave between them a sealed space that is filled with a discharge gas and that is divided into discharge cells joined between these plates by barrier ribs forming an arrangement. Such a screen panel generally serves to present images. The cells are generally distributed in rows and columns. The barrier ribs generally extend at least between the columns and sometimes also between the rows. The height of the barrier ribs generally corresponds to the distance between the plates, so that the ribs also serve as spacers. The lateral walls of the ribs and one of the plates are usually covered with phosphors capable of emitting the visible under the excitation of the plasma discharges. By adapting the discharge gas composition, it is also possible to obtain visible light directly, without phosphors. The manufacture of the barrier ribs generally requires expensive treatments and a high heat consumption. WO 00/36625 describes a manufacturing process in which ribs are molded in a reverse polymer pattern produced by photolithography. To produce the ribs, said document describes, on page 8, lines 7 through 22, the use of a molding paste comprising ceramic powders, glass frits, Portland cement or other metal oxide powders. The only example provided at the end of the document specifically describes the use of a paste containing cement, 40% by weight (page 10, line 32) and paraffin oil as a carrier fluid. After molding, the paraffin oil moves into the light-cured material of the mold and thus increases the density of the mineral powder in the mold channels. A final heat treatment at 600 ° C removes the polymer and paraffin oil from the mold and causes the cement powder to solidify here by sintering. As can be seen in said document, no water is added at any stage of the process to manufacture the cement ribs. For a person skilled in the art of barrier rib materials, this clearly means that the ribs are consolidated by sintering the cement powder or its decomposition products and by hydrating the cement of the paste, at least as far as possible. At 600 ° C, the cement hydration products would degrade if they did not decompose to the point of avoiding a consolidation effect. An object of the invention is to limit the number of thermal treatments necessary to obtain sufficient consolidation of the barrier ribs to lower the temperature of these thermal treatments or even not to use them. For this purpose, the objective of the invention is a plasma screen panel comprising two plates that leave between them a sealed space that is filled with a discharge gas and that is divided to discharge cells joined between these plates by barrier ribs made of a mineral material comprising a mineral binder and a mineral filler, characterized in that the mineral binder is a hydraulic binder. According to the invention, the mineral binder is in the hydrated state and adds the mineral filler. To obtain this hydrated state, as will be illustrated in the following, it is therefore necessary to use water in the manufacturing steps to produce the plasma screen panel. The hydraulic binder in the hydrated state which is responsible for the consolidation of the barrier ribs, binder which adds the particles of the mineral filler, unlike the ribs described in WO 00/36625 in which a person skilled in the art will have understood that the consolidation effect is obtained by sintering the cement dust particles (or ceramic powder) and in which, due to the high treatment temperatures, the cement is no longer in a hydrated state. It is understood that the term "hydraulic binder" means a material which, when formed in block from a powder, can be hardened by a hydration reaction. In this way, by combining a suitable mineral filler powder with a hydraulic binder powder, forming this powder combination, for example by molding, the resulting form can be hardened after the hydration reaction. In practice, water is added to the powder combination before all the liquid is poured into the mold. The addition of water constitutes what is generally called a mixing operation. Cells in the display panel are usually divided into rows and columns. The barrier ribs generally extend at least between the columns, and also sometimes between the rows, in which case the ribs form a two-dimensional array. The height of the ribs generally corresponds to the distance between the plates. The lateral walls of the ribs and one of the plates are usually covered with phosphors capable of emitting visible light under the excitation of the plasma discharges. By adapting the composition of the discharge gas, it is also possible to obtain visible light directly, without phosphors. Said plasma screen panel generally comprises at least two arrays of electrodes positioned so that each cell is crossed by an electrode of each array. In general, each stage supports at least one arrangement of electrodes, so that the electrodes of an array carried by a stage pass through the electrodes of one array carried by the other stage. Generally, at least one of the arrays is covered by a dielectric layer in a manner that provides a memory effect that makes it easier to activate the display panel. Other plasma screen panels do not include electrodes to initiate discharges. Instead, microwave radiation is used to initiate the discharge.

However, a simple array of electrodes can be used in this case to direct the discharges. Preferably, the hydraulic binder is a cement, for example, one based on aluminates or aluminosilicates. Preferably, the weight portion of mineral binder in the mineral material of the barrier ribs is equal to or greater than 50%. Preferably, the mineral filler comprises more than 50% by weight of silica or alumina. According to one embodiment, the porosity of the barrier ribs is equal to or greater than about %, preferably greater than 25%. In this way, during the manufacture of the screen panel, the pumped operation is facilitated. The invention will be better understood upon reading the following description, which is provided by means of the non-limiting example and with reference to the accompanying figures, which: Figure 1 illustrates, in a view from the top, three adjacent cells of a plasma screen panel, according to one embodiment of the invention; and Figure 2 illustrates a cross-section of the screen panel of Figure 1, before the two platens are assembled.

Now a first family of processes for the manufacture of a plasma screen panel according to the invention will be described, which is provided in this case with cells distributed in rows and straight columns, specifying in particular the manufacture of the stage presenting the arrangement of the barrier ribs, which are also straight, in this case of the backplate. In the first family of processes, it is conventional to use organic resins as temporary binders to form the ribs. This requires heat treatment to separate these binders. With reference to figure 2, this shows a stage 1 made of glass of sodium hydroxide-quick lime with dimensions of 254 mm x 162 mm x 3 mm and which is provided with an array of electrodes A formed by silver conductors, the The arrangement itself is coated with a conventional dielectric layer 2 baked at 540 ° C. The manufacture of an array of barrier ribs 3 in this plate will now be described, so as to obtain: ribs made of a mineral material based on a hardened hydraulic binder, in this case Portland cement; a series of continuous parallel ribs 60 with up to 70 μm thickness in order to separate the columns, these are separated by a separation of 360 μm; and a series of parallel ribs with a thickness of 220 to 230 μm to separate the rows, which are separated by a separation of 1080 μm. Each of the cells joined in this way by these ribs has a rectangular shape with dimensions of approximately 850 μm x 290 μm. A paste is prepared, this is designed to form, after it has been applied to the stage and dried, a green rib layer comprising 4% by weight organic binder and 96% by weight mineral rib material. Here, based on cement: Portland cement having a very fine particle size is used, for example one having a mean particle diameter of the order of 1 μm. This cement is laid lightly with submicrometric silica powder called "fumed silica" - this cement is considered as a fast-setting cement; - a solution comprising 8 g of ethyl cellulose-based resin in 92 g of terpineol-based solvent is prepared; and - 200 g of powder of the mineral rib material, in this case cement, are dispersed in 104 g of resin solution. This dispersion is homogenized by passing it through a mixer / mill of the three-roller type, so that it reduces the size of the powder aggregates to less than 7 μm. If necessary, terpineol is added to adjust the viscosity to approximately 50 Pa. s. Afterwards, the rib paste is applied to the plate, in this case by stamping with six superimposed layers, each stencil stamping pass is followed by a drying operation at 110 ° C. In this way a plate is obtained which is provided with a green rib layer of 150 μm in thickness. Preferably, in the case of at least two passes, a denser screen printing fabric is used, for example having 90 strands / cm, together with a less viscous paste, for example one with a viscosity of about 20 Pa. s, in order to obtain smoother layers below the surface on the surface of the rib layer. According to one embodiment, the platen is coated with this paste using a roller coater and the applied layer is dried in a tunnel oven through which the platen runs continuously, the oven is provided with blowing air and a means of extraction.

Therefore, a green layer of 150 μm thickness can be applied in a single pass. Now the formation of the rib arrangement, by means of abrasion, will be described in the thickness of the green layer that has just been obtained. First a protective mask is applied to this layer, the mask has perforations or features at the points where the cells must be recessed by abrasion in the thickness of the green layer. For this purpose: a dry photosensitive film with a thickness of about 40 μm is laminated at a suitable temperature and pressure on the green layer; - this film is irradiated in the places of the ribs with a beam of UV light for a suitable period; - later this film is revealed using a 0.2% sodium carbonate solution at about 30 ° C so that it removes the film portions from the rib sites; and - the assembly is dried quickly in a manner that prevents the cement from setting. In this way a protective mask is obtained on the green layer. To form the ribs in the thickness of the ribs, an abrasive material is applied to the mask using a nozzle with a linear slot of 200 mm in length. An abrasive material, metallic powder sold by Fuji, is used with the reference S9 grade 1000. During the jet application operation, the jet application nozzle is maintained at approximately 10 cm from the stage and moves at a speed of approximately 50 mm / min along the barrier ribs that form while the green plate during the jet application moves in a direction perpendicular to that of the ribs at a speed of 70 mm / min. The jet application pressure is approximately 0.04 MPa; and the flow rate of the metal powder is about 2500 g / min. The mask is then removed at the top of the newly formed green veins by spraying an aqueous solution of sodium hydroxide (NaOH) 1% at 35 ° C. After rinsing with water and drying with an air knife at 50 ° C, what is obtained is a platen which is provided with a green rib arrangement having a height of about 150μm, a width of about 100μm at the base and a width of about 70 μm at the top. These ribs comprise approximately 4% by weight of the organic resin. Now the application of the layers of the matches 4R, 4G, 4B will be described by stamping with direct stenciling of a phosphorus paste in the cells formed between the green ribs. The process is therefore as follows: - preparation of the phosphorous pastes for the various colors by dispersion of 60 g of phosphorus powder in 140 g of a 3% ethyl cellulose solution in terpineol; - use of a screen printing comprising a wire cloth having 120 threads per cm, it is sealed by a photosensitive emulsion except for 90 μm wide bands that are found in the areas where the paste must be transferred, ie separate regions with a period of 1080 μm (3 x 360 μm) corresponding to the distance between two consecutive columns of cells of the same color; - stamping by direct stenciling of one of the phosphor pastes through this screen, that is, with a paste transfer located in the regions where the wire mesh has not yet been sealed; and - dried at 120 ° C. These operations are repeated for each primary color using the same screen, but this is offset in the direction of the rows, by a separation column (360 μm) for the second color and for an additional period for the third color.

A sealant paste is then deposited around the perimeter of the backplate that is obtained in this way. This sealant is based here on a fusible glass made as a paste in a cellulose solution that provides a viscosity of the order of 100 Pa.s. What is obtained in this way is a backplate that is provided with an arrangement of green ribs, whose side walls, among other surfaces, are covered with a green layer of matches. Then a heat treatment is carried out in order to remove the organic binder for the ribs for the phosphorus layers, consisting of a first temperature increase at 10 ° C / min up to 350 ° C, and then it is maintained during 20 minutes at 350 ° C, a second temperature increase at 10 ° C / min up to 480 ° C, and then a second retention for 20 minutes at 480 ° C and finally a decrease in temperature at 10 ° C / min. Then, the hardening treatment of the rib, hardening which is obtained according to the invention is carried out by a cement hydration reaction which therefore requires the use of water in this stage of the process. After the heat treatment, the obtained stage is run under a sprinkling of water for 30 minutes. The stage is then dried with an air knife at room temperature and then with a knife at 105 ° C. to carry out the hardening treatment, the plate is immersed in water for 6 hours. According to another way of carrying out the treatment by hardening, the plate is placed in pressurized steam at a suitable temperature and for a suitable time in order that the cement hardens, that is, that it sets. What you get is a backplate that is provided with an array of hardened ribs 3 coated with match layers 4R, 4G and 4B. Since the heat treatment of the process just described serves only to separate the organic binders and not to harden the ribs, as in the prior art, the duration of this treatment can advantageously be shortened, in particular by reducing the time of retention or even by increasing the speeds of the temperature increase within certain temperature ranges. Using glass mineral binders, as in the prior art, retention times are needed to be about 30 minutes instead of 20 minutes in this case. The shortening of the heat treatment times or even a decrease in the maximum temperature during the treatment represents a significant economic advantage. According to an advantageous way of increasing the process, the operation of eliminating the organic binders and the hardening operation of the ribs combine, the first temperature increase at 10 ° C / min up to 350 ° C; then it is first maintained for 30 minutes at 350 ° C; it is passed in humid air, it is obtained by bubbling air in a water tank that is kept at 80 ° C, the second temperature is increased to 10 ° C / min up to 480 ° C; a second retention period for 30 minutes at 480 ° C and finally the temperature decreases at 10 ° C / min up to 350 ° C and then the passage in dry air until the stage has cooled completely. To obtain a plasma screen panel according to the invention, a conventional front stage 5 is attached to the back stage according to the invention (see the two arrows indicating the assembly in figure 2), the two stages are sealed by a treatment with heat at 400 ° C, the air contained between the platens is removed by pumping, the display panel is filled with low pressure discharge gas and the pumping bore is sealed. The front stage 5 conventionally comprises two arrays of coplanar electrodes X and Y. The plasma screen panel thus obtained, which is shown in a top view in FIG. 1, comprises platens that leave between they are a sealed space that is filled with a discharge gas and that is divided into discharge cells 6R, 6G and 6B joined by the barrier ribs 3 which, according to the invention, they are made of a hardened mineral material, that is, a material that is added by a hydraulic binder that is in the hydrated state. The plasma screen panel obtained in this way has good mechanical properties, especially in the ribs - no collapse of the ribs is observed. According to an advantageous method of implementation, instead of using a mineral material based on Portland cement, a mineral material may be used that also contains a mineral filler, such as alumina or silica or any other material compatible with the elaboration and operation of the plasma screen panel. The hydration of the hydraulic binder therefore serves, according to the invention, to add this mineral filler. According to a method of implementing the method which is particularly suitable for obtaining porous ribs, which have an open porosity greater than 25%, a mixture consisting of 50% cement described above and 50% silica powder is used as mineral material for the ribs. For example, silica of the cristobalite-type silica whose specific surface area is less than 10 m2 / g and whose average particle size is less than 10 μm, typically about 5 μm, is used as silica. For example, silica is selected with reference M4000 from Sifraco. The ribs obtained also have good mechanical properties. Thanks to the high degree of porosity of the ribs, the pumping time needed to extract the air contained between the plates is greatly shortened. Another way of obtaining porous ribs with a porosity greater than 25% will be the use of foaming cement compositions well known to those skilled in the art of cements. A second family of manufacturing processes for producing a plasma screen panel according to the invention will be described below. This second family of procedures no longer contains organic resins in the green rib layers. This completely eliminates the heat treatment at high temperature, at least with respect to the preparation of the backplate.

The procedure begins with a glass plate of sodium hydroxide-quicklime of 254 mm x 162 mm x 3 mm that is provided with an array of electrodes that are formed by silver conductors, in this case the array is not coated with a dielectric layer. Now we will describe the application of a slightly porous dielectric layer on this plate, together with the manufacture of a slightly porous array of ribs in order to obtain: - ribs made of a mineral material based on a hardened hydraulic binder, in this case the same Portland cement as previously described; - a series of continuous parallel ribs with a thickness of 100 μm at the base and 70 μm at the top, in order to separate the columns, which are separated by a separation of 360 μm; and a series of parallel ribs, with a thickness of 260 μm at the base and 230 μm at the top, in order to separate the rows, which are separated by a separation of 1080 μm. As indicated "previously, the panel cells are rectangular.

I - Preparation of the pastes: The following is prepared: - a paste of the rib sublayer designed to replace the dielectric layer of the previous embodiment; - a rib paste. Ia: rib paste: this is an aqueous paste produced from a combination of 50% cement and 50% silica "mixed" with 35% water: 100 g of Portland cement powder obtained by grinding, with selective classification so that it limits the size of the thickest particles to 11 μm (ioo < 11); - 100 g of silica powder with a mean particle size of 3 μm (d50 = 3 μm) in which the thickest particle size is limited to 10 μm (dioe <10); - dry mixing of the two powders, followed by the incorporation of 109 g of deionized water, homogenization using a disperser and vacuum degassing. A rib paste is obtained having a viscosity of 60 Pa.s. Ib: ribbed paste of the lower layer (sublayer): this is an aqueous paste consisting of a combination of 40% cement, 20% alumina and 40% titanium oxide "mixed" with 39% water: - 80 g of powder of fast-setting Portland cement obtained by grinding with selective grading in a manner that limits the coarser particle size to 11 μm (di0o <H); 40 g of alumina powder with a mean particle size of 3 μm (d50 = 3 μm) in which the coarser particle size is limited to 10 μm (dioo <10); 80 g of Ti02 powder with an average particle size of 1.5 μm (d50 = 1.5 μm) in which the coarser particle size is limited to 8 μm (d? 00 <10); and - dry mixing of the three powders, followed by the incorporation of 130 g of deionized water, homogenization using a disperser and vacuum degassing. A lower layer paste (sublayer) having a viscosity of 40 Pa.s. is obtained.

II - Application of the lower layer and formation of the ribs: la) a mold is produced with a distribution of grooves that has the geometry of the ribs, except that the depth of the grooves is increased by 20% over the height of these ribs . The mold consists of a separable upper portion consisting of a wedge whose thickness corresponds to the additional thickness of 20%. The mold is coated with a mold release agent and then placed on a vibrating container. The mold is then filled with freshly prepared rib paste and the excess is removed by scraping. The filled mold is then placed in an enclosure at 40 ° C in order to accelerate the setting reaction of the hydraulic binder, in this case cement. The setting of the cement corresponds to a cement hydration reaction; Ib) during setting, in parallel with step la) a sublayer with a thickness of 30 μm of sublayer paste is deposited by curtain coating on the stage and on the electrodes. The platen is then placed in an environment of 50 ° C in order to accelerate the setting reaction of cement in the sublayer; and 2) after allowing to set for one hour in the mold (step a), the upper wedge of the mold is removed so as to expose the upper surface of the mold that will form the basis of the future ribs, and this surface is sprayed very lightly with water. Then, the backplate of step Ib) is applied to this surface so that a still malleable sublayer is placed against the base of the future ribs. The entire assembly is then turned upside down so that gravity is applied to the mold and its ribs against the back face and then the entire assembly is placed in an environment at 40 ° C.

After 2 hours, the demolding operation can be carried out when removing the mold. This is then able to be cleaned with a high pressure mold jet. The platen covered with this sublayer and its ribs is stored for an additional 4 hours in a moisture-saturated atmosphere in order to complete the cement setting reaction and thus obtain a hydraulic binder in the hydrated state which adds the filling mineral of the ribs and consolidates them. Subsequently the stage is passed through a tunnel kiln regulated at 115 ° C in order to separate the waste water. In this way an arrangement or a distribution of hardened and consolidated ribs without sintering and without heat treatment is obtained, these are based on a sublayer that acts as a dielectric layer; the porosity of the sublayer and of the ribs obtained is approximately 15%, this is advantageous for pumping the screen panel. This porosity can be adjusted according to the water content of the paste.

III - Application of phosphors: A suspension is prepared containing 70 g of phosphorus powder dispersed in 130 g of a mixture of glycol ethers selected by their boiling point and their viscosity, so that they place the phosphors in temporary suspension without using resins. However, colloidal silica (or other) suspensions have been used as a thickener, if necessary. To apply these pastes to the side walls of the ribs and to the bottom of the cells between these ribs, a paste supply method is used, using syringes whose outlet holes are directed between the ribs - for this purpose an orifice head is used multiple (comprising 76 calibrated perforations 100 μm in diameter distributed alternately, and with a separation of 1080 μm). The head moves parallel to the columns, in several passes diverted in order to cover the entire plate, which then dries at 120 ° C. In this way, three phosphors are applied in succession, with a displacement of a column separation (360 μm), as previously indicated.

IV - Application of the sealant: Afterwards a sealant paste is deposited, using the same method of application as in the case of the matches, around the perimeter of the backplate that is obtained in this way. This sealant is based, in this case, on a glass having a very low melting point formed as a paste solution similar to that of phosphorus, which provides a viscosity of about 80 Pa.s. This is followed by a drying operation at 120 ° C.

V - Treatment with final heat at low temperature for a short period: Although there is no resin, the temperature is increased and kept at 250 ° C for 30 minutes in order to complete the evaporation of all solvents. To obtain a plasma screen panel according to the invention, a conventional front stage is assembled on the back stage according to the invention, the two stages are sealed by an appropriate heat treatment in order to at least partially fuse The sealing glass, the air contained between the platens is pumped to remove it, the panel is filled with low pressure discharge gas and the pumped hole is sealed. The plasma panel obtained in this way has good mechanical properties, especially in the ribs. No collapsing of the ribs is observed. The hydraulic binder of the ribs remains in a hydrated state despite heat treatment. The method according to the second family of implementation methods of the invention therefore makes it possible to produce plasma screen platens having ribs without ever exceeding 250 ° C, this is economically very advantageous, since the ribs are maintained in the hydrated state according to the invention. According to an advantageous alternative implementation of the invention, a sealant based on a commercially available sealant adhesive resistant to a temperature of 250 ° C can be used, which allows the two platens to be sealed by heat treatment at only 250 ° C. In this case, thanks to the invention, there are no steps in the manufacture of the panel that are at a temperature higher than 250 ° C. This makes it easier to maintain the hydraulic binder of the ribs in the hydrated state, and thus advantageously limits any risk of degradation of the mechanical properties of the hydraulic binder of the ribs. Whatever the method for implementing the invention, other types of cement than Portland cement can be used without departing from the invention, especially cement which, after setting, can withstand the temperatures of the heat treatments that are still necessary for manufacture the screen panel. Hydraulic binders of the types other than cement can be used without departing from the invention. The present invention is applicable to any type of plasma screen panel whose cells are divided into compartments by ribs. These plasma screen panels may be of the coplanar type, matrix type or radio frequency type or microwave excitation.

Claims (7)

1. A plasma screen panel comprising two plates or plates that leave between them a sealed space that is filled with a discharge gas and that are divided into discharge cells joined between these plates by barrier ribs made of a mineral material comprising a mineral binder and a mineral filler, characterized in that the mineral binder is a hydraulic binder which is in the hydrated state and adds the mineral filler.

2. Screen panel as described in claim 1, characterized in that the hydraulic binder is a cement.

3. Screen panel as described in claim 2, characterized in that the cement is based on aluminates or aluminosilicates.

4. Screen panel as described in any of the preceding claims, characterized in that the weight portion of mineral filler in the mineral material is equal to or greater than 50%.

Screen panel as described in any of the preceding claims, characterized in that the mineral filler comprises more than 50% by weight of silica or alumina.

6. Screen panel as described in any of the preceding claims, characterized in that the porosity of the barrier ribs is equal to greater than about 15%.

7. Screen panel as described in claim 6, characterized in that the porosity of the barrier ribs is greater than 25%.