EP1415316B1 - Plate for a plasma panel with reinforced porous barriers - Google Patents

Abstract

A plate comprising a substrate (10) covered with at least one network of electrodes (11), said network being covered with a network of barriers (17) made of a mineral material with a porosity of more than 25 %, comprising a porous-based underlayer (18) which is placed inbetween the network of electrodes (11) and the network of barriers (17), and which is made of a mineral material with a porosity of more than 25 %. Reinforced porous barriers are obtained. Advantageously, the plate does not comprise a specific dielectric layer; the number of manufacturing steps is limited and the plate can be produced entirely at low temperature.

Description

The invention relates to an image display plasma panel slab comprising a substrate coated with at least one electrode array itself coated with a network of high porosity barriers; the document EP1017083 - THOMSON discloses such slabs.

The barriers are conventionally intended to delimit cells to form discharge zones in the plasma panel.

• la possibilité de les réaliser à plus basse température que les barrières classiques denses, dont la porosité ne dépasse pas 2% ;
• la facilité de pompage du panneau à plasma ; après assemblage de deux dalles de manière à ménager entre elles des zones de décharges délimitées par les barrières, il est nécessaire de pomper et d'évacuer le gaz emprisonné entre les dalles, puis d'injecter dans l'espace pompé du gaz de décharge ; lorsque les barrières sont denses, l'étape de pompage dure de nombreuses heures, sinon dizaines d'heures, ce qui est très pénalisant du point de vue économique ; en utilisant des barrières fortement poreuses, à porosité ouverte, on raccourcit considérablement le temps de pompage.

Advantages of porous barriers include:

• the possibility of producing them at a lower temperature than dense conventional barriers, whose porosity does not exceed 2%;
• the ease of pumping the plasma panel; after assembling two slabs so as to create between them zones of discharges delimited by the barriers, it is necessary to pump and evacuate the gas trapped between the slabs, then inject into the pumped space of the discharge gas; when the barriers are dense, the pumping step lasts many hours, if not tens of hours, which is very penalizing from the economic point of view; by using highly porous barriers with open porosity, the pumping time is considerably shortened.

Slabs of this type generally serve as a back panel of plasma panel; for the manufacture of the plasma panel, on the tops of the barriers of a slab of this type, it is generally applied a transparent front slab also provided with at least one electrode array oriented orthogonally with respect to the electrodes of the rear slab; at the intersections of the electrodes of the rear slab and the electrodes of the front slab, the zones delimited by the walls of the barriers, by the rear slab and by the front slab form zones of light discharges, produced by applying matched potential differences between the electrodes crossing these zones.

• pendant des périodes dites d'adressage, créer des charges électriques sur la couche diélectrique de la dalle avant dans les zones de décharges à activer et,
• pendant des périodes dites de maintien, à activer des séries de décharges lumineuses de maintien uniquement dans ces zones chargées en appliquant des séries d'impulsion de tension entre chaque paire d'électrodes sous la couche diélectrique.

For the manufacture of alternating plasma memory panels and coplanar electrodes, the front panel is provided with an array of coplanar electrode pairs covered with a dielectric layer; usually, the electrodes of the back slab are also covered with a dielectric layer; the plasma panel then comprises an electrodes power supply system adapted to:

• during so-called addressing periods, create electric charges on the dielectric layer of the front slab in the zones of discharges to be activated and,
• during so-called holding periods, activating series of light discharges for holding only in these charged areas by applying series of voltage pulses between each pair of electrodes under the dielectric layer.

The electrodes of the slab provided with the barrier network, opposite to the array of electrode pairs, then generally serve to activate the discharge zones, that is to say to the addressing of the cells.

To avoid electrical breakdowns and protect the slabs against the action and corrosion of the discharges, the dielectric layers applied to each slab are made of dense material generally based on lead-containing mineral glass for baking in the range 500-600 ° vs.

Thus, the method of manufacturing a slab of the type previously mentioned comprises, after the formation of the electrode array and before the deposition of the green layer of barrier material, the deposition of a green layer of homogeneous thickness based on a powder of a dielectric mineral material and an organic binder generally followed by a firing step under conditions adapted to remove the organic binder and to densify this dielectric material.

The dielectric layer thus densified also serves to protect the electrodes during the projection of abrasive material for the formation of the barriers.

But this additional step concerning the application and the baking of a dielectric layer is economically disadvantageous.

In addition, porous barriers are not without drawbacks; because of their structure, they are more fragile or less resistant than dense classical barriers; this effect is accentuated for barriers of small width, especially less than or equal to 70 microns.

The document JP11219659 discloses a slab for an image display plasma panel comprising a barrier network whose porosity is between 3 and 30% by volume, arranged on a porous base sub-layer whose porosity is less than or equal to 2% by volume.

The document EP1290711 (corresponding to WO01 / 99149 ), published after this document, describes the formation of barriers on a slab, by etching in a glass layer having a porosity of between 10% and 60% by volume; the etching is not necessarily carried out over the entire thickness of this layer, a full underlayer of indeterminate thickness can remain under the barriers.

The invention aims to provide a slab of the aforementioned type of simpler structure and reinforced porous barriers, which can be achieved by a more economical process.

To this end, the subject of the invention is an image display plasma panel slab comprising a substrate coated with at least one electrode array itself coated with a network of barriers of mineral material whose porosity is greater than 25%, intended to delimit cells to form discharge zones in said panel, also comprising a porous base sub-layer which is interposed between said electrode array and said network of barriers, which is made of mineral material whose porosity is greater than 25%. According to the invention, the thickness of the base sub-layer is between 10 μm and 40 μm in all points of the slab, at least in all points of the active surface of the slab which corresponds to the whole discharge areas; the bottom of the cells of the slab is then formed by the surface of the base sub-layer, which has no hole revealing areas of electrodes or areas of the substrate of the slab.

Each barrier conventionally comprises a base, slopes, and a summit; the base underlayer completely covers the electrodes in the active surface area of the slab; the active surface area of the slab that corresponds to the cells of the panel.

• que la sous-couche de base permettait d'améliorer sensiblement la stabilité des barrières poreuses et leur adhérence au substrat,
• l'obtention de telles sous-couches était particulièrement économique, parce qu'il est plus facile d'obtenir des sous-couches poreuses à basse température que des sous-couches non poreuses.

We observed :

• that the base underlayer significantly improved the stability of the porous barriers and their adhesion to the substrate,
• obtaining such sublayers was particularly economical because it is easier to obtain low temperature porous sub-layers than non-porous sub-layers.

The adhesion of the barriers to the substrate is more critical when the substrate has a low roughness and the barriers have a high porosity; thanks to the underlayment according to the invention, the barriers cover the entire surface of the substrate via the underlayer, which improves the stability of the barriers and their adhesion to the substrate.

Compared with dense barriers with a high proportion of glass, porous barriers pose more problems with mechanical stability and adhesion to the substrate; these substrates being generally made of glass, it is understood that a porous material adheres more difficultly to the glass than the glassy material of the dense barriers; the addition of a base underlayer according to the invention, which extends before and after firing over the entire effective surface of the slab, makes it possible to improve the mechanical stability of the barriers and the adhesion of these barriers to the substrate, especially when these barriers are narrow and porous; the base underlayer according to the invention therefore also has a function of anchoring the barriers on the slab, whether before or after firing; this anchoring advantage is particularly appreciated in the case where the formation of the barriers - in the raw state, that is to say uncooked - comprises a step of "sand-blasting" (see below) which requires the application preliminary of a protective mask having the reasons of the network of barriers, and which is followed by a step of eliminating this protective mask, because during this step, there is a particular risk of weakening or destabilizing these barriers .

Preferably, the width of the barriers is less than or equal to 70 μm, especially at the slopes; indeed, such barriers are particularly fragile, whether in the cooked state or in the raw state before cooking, during the manufacture of the slab; the underlayer according to the invention is then all the more useful for reinforcing these barriers; in the case of slope gates, the width is measured at half height.

Preferably, the slab has no intermediate layer, especially dielectric, between the electrodes and said base sublayer.

The base underlayer which forms the bottom of the cells is sufficient to protect the electrodes against the action and erosion of plasma discharges, even if it is porous; indeed, this erosion is low because the proportion of discharges triggered from the electrodes of the slab according to the invention is low at view of the total number of discharges on a plasma panel in normal use comprising a slab according to the invention.

Indeed, when viewing images on such a panel, for example with the back of a slab according to the invention and on the front face of a slab comprising an array of pairs of coplanar electrodes coated with a layer. dielectric, most of the discharges take place between the paired electrodes of the front slab (coplanar discharges), far from the slab according to the invention; these discharges that arise between the pairs of coplanar electrodes are termed holding discharges; between the periods of maintenance, discharges can take place between the opposite electrodes of the two slabs, therefore in particular near the electrodes of the slab according to the invention; these discharges are in particular intended to activate the cells of the panel; they are commonly referred to as addressing discharges, and constitute only a minor proportion of the total number of discharges; the base underlayer which covers the electrodes of the slab according to the invention is sufficient, although porous, to protect them from the action and corrosion of the addressing discharges; the dielectric layer of the front face is then generally dense enough to avoid, on its own, the risk of breakdown and to ensure, if necessary, the conventional memory effect of the alternative panels.

According to one variant, the base sub-layer comprises a component adapted to reflect light; the titanium oxide is preferably used for this purpose.

Thanks to the reflective effect thus obtained, the radiation emitted towards the bottom of the cells is not lost and the luminous efficiency of the plasma panels comprising a slab according to the invention is increased.

The base underlayer according to the invention then has a triple function of protecting the electrodes during the manufacture of the panel (see below), anchoring the barriers, and improving the light output; the use of a single sub-layer for three functions is particularly advantageous economically, since it avoids inserting a specific dielectric layer and a specific reflection layer.

The barriers may also include a reflective component to improve light output.

Advantageously, in order to obtain porous barriers, the mineral material of the base sub-layer comprising a mineral filler and a mineral binder, the weight proportion of inorganic binder in the inorganic material of the barriers is less than 13%.

Preferably, the mineral material of the base sub-layer comprising a mineral filler and optionally a mineral binder, the weight proportion of inorganic binder in the mineral material of the base sub-layer is less than 13%; this is a preferred way to obtain a porous sub-layer; in the case, in particular, where the electrodes are silver and where the underlayer and / or the barriers have a reflection function for improving the light output, this low level of inorganic binder prevents the migration of silver in this underlayer and in the barriers, and prevents the coloring, including yellowing, of the mineral material which would degrade its reflective properties.

According to another variant, the material of the base sub-layer is identical to the material of the barriers, which simplifies the manufacture of the slab.

Without departing from the invention, the slab may comprise a plurality of base sub-layers, for example one in the same material as that of the barriers, and another comprising a component adapted to reflect light.

Preferably, the slab according to the invention comprises a layer of phosphors covering, at least partially, the slopes of the barriers and said sub-layer.

The nature of the phosphors of this layer differs generally according to the rows or columns of cells delimited by the barriers; the luminophores thus deposited on the walls of the cells have the function of transforming the ultraviolet radiation of the discharges into visible radiation in one of the three primary colors conventionally used to visualize images; in general, adjacent cells with different primary colors form an image element or pixel.

Preferably, these luminophores are deposited directly on the porous sub-layer and the porous barriers; it has been found that this porosity favored the adherence of phosphors; no intermediate layer of adhesion then is necessary.

Preferably, in all points of the surface joining the base of the barriers to the base sub-layer, the radius of curvature is greater than or equal to 10 μm; it has been found that such a radius of curvature is even more favorable to the stability of the barriers, but also to the regularity of the phosphor deposition.

• à former un masque de protection lorsqu'on forme les barrières par « sand-blasting » (cf. infra) ;
• et/ou à former un réseau noir, et/ou à former une couche de compensation d'irrégularités de hauteur des barrières.

Preferably, the barriers are themselves coated with an overlay; as described in the documents EP 722179 , EP 893813 , and US5909083 , this over-top layer of the barriers is intended, for example:

• to form a protective mask when forming the barriers by "sand-blasting" (see below);
• and / or to form a black network, and / or to form a barrier height irregularity compensation layer.

The subject of the invention is also an alternating-type and memory-effect image-viewing plasma panel comprising a first slab according to the invention and a second slab provided with coplanar electrodes for maintaining memory-effect discharges. , providing between them zones of discharges delimited by said barriers.

The invention also relates to a method of manufacturing a plasma panel slab according to claim 11.

The base sub-layer and the main layer are deposited on the starting slab, or substrate, provided with its electrode array, so as to have each an approximately uniform thickness on the active surface of the slab.

The abrasion speed of the underlayer is, according to the invention, lower than the abrasion speed of the main layer under comparable abrasion conditions, namely the use of the same abrasive material under the same operating conditions. than during the projection for the formation of the barriers.

Thus, after the step of forming the barriers by spraying abrasive material and obtaining, on the substrate, discharge cells delimited by these barriers, the bottom of these cells is then formed by the surface of the base sub-layer, which has no holes revealing areas of electrodes or substrate; the base sub-layer may have been partly penetrated by the abrasive material but must have withstood sufficient time for the slab electrodes to be completely covered by this base sub-layer; the main function of the underlayer therefore is, at this level, to protect the underlying electrodes during the formation of the green barriers by spraying an abrasive material; after cooking, the bottom of the cells is always formed by the surface of the fired base sublayer.

The base subbase mineral material comprises a mineral filler and optionally a mineral binder; the particle size of the powder of the mineral material of this underlayer, in particular of said mineral filler, if any, the nature of said inorganic binder and the proportions of this binder in this powder, the method of mixing the components of this powder, and the cooking conditions are adapted so that the apparent density of the base sub-layer obtained after cooking is also less than 75% of the theoretical density of the mineral filler of this underlayer.

For this purpose, preferably, the proportion of inorganic binder in the mineral material of the base sub-layer is less than 13%; this proportion can even be zero here.

By virtue of this underlayer thus having a porosity greater than 25%, and in the case where the formation of the electrode array has been carried out by deposition of a green layer comprising a conducting material and an organic binder, it is even more It is easy to carry out the firing of this layer of electrodes at the end of the process, at the same time as that of the base underlayer and the raw barriers, because the porosity of this base sub-layer and that of the barriers facilitate the removal of decomposition products from organic binders, including those from the electrode layer.

After the deposition of the base sub-layer and of the main layer and before the abrasion operation, a protective mask of polymer material with patterns corresponding to the network of the barriers to be formed is generally applied to this deposit; this mask is intended to protect against abrasion areas of the main layer corresponding to the tops of the barriers; therefore, after the abrasion operation but before cooking and, if necessary, before other operations such as the deposition of phosphors, this mask is removed, usually by projection of an aqueous alkaline solution (or "stripping ").

We have seen that it was preferable that in all points of the surface joining the base of the barriers to the base sub-layer, the radius of curvature is greater than or equal to 10 microns; this radius of curvature is even higher than the difference between abrasive speed of the base sub-layer and that of the main barrier layer is low.

As for the conventional methods of manufacturing a barrier network on a slab, it will be chosen for the base underlayer and for the main layer an organic binder eliminating easily on baking; when applying this base sub-layer and the main layer by liquid in a solvent medium, a solvent-soluble binder will be selected which is easy to remove without danger; when a mask is applied before blasting and then it is removed by spraying with an aqueous alkaline solution, a water-resistant organic binder preferably chosen from the group consisting of cellulosic resins, acrylic resins, methacrylic resins, rosin resins, and cross-linked polyvinyl alcohol resins; preferably, the organic binder of the base underlayer is based on polyvinyl alcohol.

Preferably, especially when the organic binder of the base sub-layer is of the same family as that of the main layer, the proportion of organic binder in the base sub-layer is greater than the proportion of organic binder in the layer. main.

Preferably, the glass transition temperature of the organic binder of the base sub-layer is lower than that of the organic binder of the main layer, in particular less than or equal to 60 ° C.

Preferably, the method according to the invention does not include deposition of intermediate layer, especially dielectric, between the formation of the electrode array and the deposition of the base sub-layer; by avoiding to apply an intermediate dielectric layer, the method according to the invention is therefore much more economical than the methods of the prior art.

Preferably, the method according to the invention comprises only a single baking heat treatment after the formation of the at least one electrode array.

In the case where the formation of the electrode array passes through the deposition of a green layer comprising a conductive material, for example based on silver, aluminum, or copper, and an organic binder, the method according to the invention advantageously comprises only one final firing, without intermediate firing between the deposit of the green layer of electrodes and the deposition of the base sub-layer; thanks to the porosity of the underlayer, the decomposition products of the organic binder of the electrode network easily pass through this underlayer without damaging it; the almost non-vitreous nature of this sub-layer avoids, during cooking, the phenomena of parasitic diffusion of the material of the electrodes; advantageously, it is no longer necessary to bake the electrode array before the barriers are deposited.

Preferably, the method according to the invention does not include any step where the temperature of the slab exceeds 480 ° C.

The inorganic barrier material comprises a mineral barrier filler and a mineral binder; the particle size of the powder of this mineral material, in particular the mineral filler of the barriers, the nature of its inorganic binder and the proportions of this binder in this powder, the method of mixing the components of this powder, and the cooking conditions are adapted so that the apparent density of the barriers obtained after firing is less than 75% of the theoretical density of said mineral filler; Barriers having a porosity greater than 25% are thus obtained, which advantageously facilitates and shortens the pumping of the plasma panel.

In order to obtain barriers whose apparent density is, after firing, less than 75% of the theoretical density of the material of their inorganic filler, ie has a porosity greater than 25%, these barriers are preferably used for wherein the weight ratio of inorganic binder is less than 13%; as the inorganic binder, a glass or a low-melting sinter is generally used; in the case of these small proportions of inorganic binder, the inorganic binder advantageously comprises colloidal silica, silicates or hydrolysed silanes, which improve the strength of the porous barriers.

The method advantageously comprises the deposition of a raw layer based on phosphor and an organic binder, both on the green underlayer covering the electrode array and on the base and the slopes of the barriers; this step is, in itself, known from the prior art; thanks to the invention, the green phosphor layer wets the walls of the barriers and the bottom of the cells in the same way, since they consist of identical materials; a more uniform distribution and a better homogeneity of the phosphors are thus obtained; after firing, a better adhesion of the phosphors to the walls of the barriers and to the bottom of the cells is obtained without the use of an intermediate adhesion layer.

The invention will be better understood on reading the description which follows, given by way of non-limiting example and with reference to the figure 1 , which discloses a plasma panel having a slab with underlayer according to one embodiment of the invention and to the figure 2 which describes a slab with underlayer according to another embodiment of the invention; in the figures, in order to simplify, identical references are used for the elements which provide the same functions.

We start from a classic slab 10, usually soda-lime glass; other insulating materials can be used for the slab, as long as they resist firing temperatures.

• sérigraphie directe d'une pâte pour former un réseau d'électrodes crues, cette pâte étant à base d'une poudre de matériau conducteur et d'un liant organique ; puis, cuisson des électrodes crues adaptée pour éliminer le liant organique et, le cas échéant, pour obtenir un frittage de la poudre conductrice et une conductivité optimale des électrodes ;
• en utilisant un liant photosensible dans la pâte, application d'une couche uniforme de pâte, suivie d'une photolithographie et d'un développement pour obtenir le réseau d'électrodes crues ; puis cuisson dans les mêmes conditions que précédemment ;
• dépôt sous vide d'au moins une couche uniforme de matériau conducteur, en général un métal ou un alliage, dépôt d'une couche homogène organique photosensible, protectrice et résistante au décapage après photosensibilisation, photolithographie pour sensibiliser la couche et la rendre protectrice à l'endroit des électrodes, décapage des parties non sensibilisées pour gravure des zones de couche métallique sous-jacentes de manière à obtenir le réseau d'électrodes en matériau conducteur, et élimination de la couche photosensible résiduelle ; ce procédé ne comporte donc pas de cuisson.

A network of electrodes 11 is applied in a manner known per se on this slab, using, for example, one of the following conventional methods:

• direct screen printing of a paste to form a network of raw electrodes, this paste being based on a powder of conductive material and an organic binder; then, firing the green electrodes adapted to remove the organic binder and, where appropriate, to obtain sintering of the conductive powder and optimum conductivity of the electrodes;
• using a photosensitive binder in the paste, applying a uniform layer of paste, followed by photolithography and development to obtain the green electrode array; then cooking under the same conditions as before;
• vacuum deposition of at least one uniform layer of conductive material, generally a metal or an alloy, deposition of a homogeneous organic photosensitive layer, protective and pickling resistant after photosensitization, photolithography to sensitize the layer and make it protective location of the electrodes, etching the non-sensitized portions for etching the underlying metal-layer areas so as to obtain the electrode array of conductive material, and removing the residual photosensitive layer; this method therefore does not involve cooking.

The steps of formation of the barrier network are then initiated.

The barrier material powder generally comprises a mineral filler and a mineral binder based on glass; the temperature reached during the firing of the barriers is generally greater than or equal to the glass transition temperature of the glass, so as to activate the inorganic binder and to obtain sufficient consolidation after removal of the organic binder; to obtain a high porosity barrier material, especially greater than 25%, the weight content of this glass in the powder of the barrier material will preferably be greater than or equal to 2%, less than or equal to 10%; this content will be higher for narrower barriers.

The base undercoat material powder also comprises a mineral filler and, optionally, a mineral glass binder.

The inorganic filler of the barrier material is selected from stable mineral products in the range of firing temperature, high adsorbent; preferably, this charge is selected from the group comprising alumina, zirconia, yttrium oxide, titanium oxide and mixtures thereof; alumina in particular because it is an amphoteric powder with high adsorbent properties; zirconia or titanium oxide according to the desired dielectric constant; the mineral filler may also include products such as mullite, cordierite or zeolites; preferably, 80% of the elementary grains of the mineral filler have a size of between 0.3 μm and 10 μm; after cooking, the grain size is globally unchanged.

The mineral filler of the base sub-layer material may be the same as or different from that of the barrier material; according to a variant of the invention, this mineral filler comprises other components than the mineral filler for the main layer of barriers, such as for example a light reflecting material; to form a white background and reflective at the bottom of the discharge cells, it is thus possible to use titanium oxide as another component.

Preferably, the average grain size of the inorganic binder is less than or equal to that of the mineral filler.

To obtain, according to the invention, a high porosity base underlayer material, in particular greater than 25%, the weight content of binder optional mineral in the powder of the base underlayer material will preferably be less than 13%; the powder of the base underlayer material may contain no inorganic binder.

The inorganic filler and, where appropriate, the mineral binder are then mixed to obtain the barrier material powder or the base underlay material powder; as the proportions of two main mineral components of this powder are very different, their mixing mode is very important to best disperse the mineral binder around the grains of the mineral filler and allow it to ensure a significant consolidation of the barriers during baking step; a typical procedure for mixing about 1 liter of powder consists in placing this powder in a container of about 4 liters and shaking dry with a 150 mm diameter knife rotating at 7000 rpm for about 4 minutes.

Organic binders are preferably selected from the group consisting of cellulosic resins, acrylic resins, methacrylic resins, rosin resins, and cross-linked polyvinyl alcohol resins.

Preferably, the composition of the raw base sub-layer is adapted so that the abrasion rate of this base sub-layer is significantly lower than the abrasion speed of the main layer under the same projection conditions; the abrasion rate of a green layer or underlayer under predetermined abrasive material spraying conditions generally decreases as the proportion of organic binder increases in this layer, and / or when the intrinsic elasticity of this binder increases.

Those skilled in the art can, by performing routine tests, develop formulations of green layers having different abrasion rates under predetermined conditions of projection of abrasive material; projection conditions are not only the conditions of use of the abrasive material but also the nature, texture and structure of this material.

To adapt the composition of the raw base sub-layer for this purpose, it will be possible, for example, to use for the raw barrier main layer a organic binder much more sensitive to abrasion than that of the base sub-layer; As a binder particularly sensitive to abrasion, rosin (or "rosin" in English) is preferably used.

An advantageous solution consists in using for the underlayer an organic binder based on polyvinyl alcohol crosslinkable under UV.

In the context of the use of polyvinyl alcohol as organic binder of the undercoat, abrasion tests have shown that the abrasion rate decreases by 50% when the level of organic binder in the undercoat of base went from 5 to 10%.

To adapt to this effect the composition of the raw base sub-layer, it will preferably be used for this sub-layer an organic binder having a glass transition temperature lower than that of the binder of the main layer; advantageously, an organic binder having a glass transition temperature of less than or equal to 60 ° C can be used; for example, a very abrasion-resistant base underlayer was obtained by using as organic binder 4% by weight of an acrylic or methacrylic resin having a glass transition temperature of 57 ° C.

To adapt to this effect the composition of the raw base sub-layer using the same organic binder for the main layer and for the base sub-layer, for example, the base sub-layer with an organic binder content will be formulated. 2.5 to 8 times higher than in the main layer: for example, by taking as binder ethyl cellulose of grade N4 having a glass transition temperature of the order of 156 ° C, the proportion (weight of binder / weight of mineral powder) would be 2 to 4% in the main layer, against 10 to 15% in the base underlayer.

By using the same family of organic binder for the main layer and for the base underlayer, the abrasibility of the main barrier layer can be increased by using a binder of higher molecular weight; thus, a lower molecular weight grade will preferably be used in the base underlayer than in the main layer.

To increase the elasticity of the binder of the base underlayer in the projection conditions of the abrasive material and to give this undercoat a better resistance to abrasion, the binder will preferably be added to the binder. organic layer of this underlayer a plasticizer adapted to said binder, avoiding too high a content which could cause cracking of the green underlayer after application; with the ethyl cellulose of grade N4 mentioned above, 1 to 4% by weight of butyl benzyl phthalate can be used, always based on the weight of mineral powder.

In the context of the use of polyvinyl alcohol as an organic binder, abrasion tests have shown that the abrasion rate decreased by 25% by adding 5% plasticizer in this binder; the plasticizer content must remain limited, typically less than 25% so as not to compromise the cooked mechanical strength of this underlayment forming the base of the barriers.

Still for the same purpose, any other means may be used to lower the glass transition temperature of this binder in the base sub-layer, measured in the crosslinked state.

The powder of barrier material or underlay material is then mixed in a manner known per se with its organic binder.

The deposition of raw layers of barriers on the slab provided with its network of electrodes can then be carried out directly by liquid, or by transfer of a green film of this preformed layer ("green tape" in English), as described in the document EP 722179 (DUPONT ).

Here we will describe more precisely a liquid deposit; As a liquid deposition method, it is possible, for example, to use screen printing, slit coater, or curtain deposition.

• 1/ une composition liquide ou pâte d'application de la couche principale, en dispersant la poudre de matériau de barrière dans une solution d'un liant organique ;
• 2/ une composition liquide ou pâte d'application de la sous-couche de base, en dispersant la poudre de matériau de barrière dans une solution d'un liant organique ;

Before the deposit operations, we prepare:

• 1 / a liquid composition or paste for applying the main layer, by dispersing the powder of barrier material in a solution of an organic binder;
• 2 / a liquid composition or paste for applying the base underlayer, by dispersing the powder of barrier material in a solution of an organic binder;

• d'une manière connue en elle-même, on applique alors une sous-couche de la composition d'application de sous-couche de base, de manière à obtenir, après séchage, une épaisseur comprise entre 10 et 40 µm ;
• on sèche la sous-couche de base obtenue pour en évaporer le solvant,
• d'une manière connue en elle-même, on applique ensuite au moins une couche de la composition d'application de couche principale, de manière à obtenir, après séchage, une épaisseur de couche principale qui est fonction de la hauteur des barrières souhaitées ;
• on sèche la couche principale obtenue pour en évaporer le solvant.

To apply the whole of the raw barrier layer on the slab, on the electrodes side, the procedure is as follows:

• in a manner known per se, an underlayer of the base underlayer application composition is then applied, so as to obtain, after drying, a thickness of between 10 and 40 μm;
• the base underlayer obtained is dried in order to evaporate the solvent,
• in a manner known per se, at least one layer of the main coat application composition is subsequently applied, so as to obtain, after drying, a main layer thickness which is a function of the height of the desired barriers;
• the main layer obtained is dried in order to evaporate the solvent.

A slab is obtained with an electrode network covered with a base underlayer and a green barrier layer of uniform overall thickness.

The following steps concern the formation of barriers.

As an abrasive material, a solid powder or "sand" is generally used, for example glass beads, metal balls, or calcium carbonate powder; the operation is then referred to as "sandblasting" or "sand-blasting" in the English language; a liquid can also be used as an abrasive material.

It is therefore sought to form raw barriers in the raw main layer which is now provided slab; it is therefore a question of removing the green layer by abrasion only between the barriers and, on the contrary, to protect this layer from abrasion at the location of the barriers.

• appliquer, sur la couche crue de barrière, un masque de protection en matériau polymère doté de motifs correspondant au réseau des barrières à former,
• projeter le matériau abrasif de manière à enlever la couche crue entre les motifs du masque et à former les barrières crues au niveau de ces motifs,
• éliminer le masque.

For this purpose, a first conventional method consists of:

• applying, on the green barrier layer, a protective mask made of polymer material having patterns corresponding to the network of barriers to be formed,
• projecting the abrasive material so as to remove the green layer between the patterns of the mask and to form the green barriers at these patterns,
• eliminate the mask.

• dépôt pleine surface, exposition UV à travers un masque, développement, généralement à l'aide d'une solution de carbonate de sodium).

The mask can be made for example by direct screen printing, but this method has the disadvantage of offering a limited definition; this mask can also be achieved by photolithography of a photopolymerizable or photosensitive polymer layer, for example according to the following steps:

• full surface deposition, UV exposure through a mask, development, usually using a solution of sodium carbonate).

Advantageously, the polymeric material of the mask is based on polyvinyl alcohol (or "PVA") crosslinked; the advantage of this material is that it can be developed with hot water, which makes it possible to avoid the use of solution containing alkaline elements, that it is particularly resistant to abrasion and that it is can be easily removed by burning or pyrolysis after the abrasion operation; this method of elimination, compared to a conventional "stripping" operation, makes it possible to avoid weakening the barriers and to envisage even narrower barriers; using this method of elimination, it is again avoided the use of mask removal solution (so-called "stripping solution") containing sodium or potassium with all the risks inherent in the pollution of the slab, that d as much as a large developed surface difficult to rinse was generated during the sanding of the barriers; a very high resistance to abrasion was obtained with contents of (PVA + plasticizer) of 100%, with a plasticizer / resin ratio of 1 to 2.

Another method described in the document EP 722179 already mentioned is to apply on the main layer of barrier material, an overcoat not only loaded barrier material but containing a sufficiently large proportion of light-curing organic binder to be able to withstand the projection of abrasive material; thus, it is in the over-layer itself that the mask is made by photolithography; according to the document EP 722179 the advantage of this method is that it is not necessary to remove the mask directly after the abrasion operation since the photopolymerized binder is subsequently removed during the baking operation, its pyrolysis being facilitated by the porosity mineral charge; after cooking, the remaining part of this overlay forms the top of the barriers.

Advantageously, the organic photopolymerizable binder of the overcoat is based on crosslinked polyvinyl alcohol; the advantage of this material is that it is particularly resistant to abrasion; we got very strong resistances high abrasion with contents (PVA + plasticizer) typically from 20 to 50%, with a plasticizer / resin ratio typically from 1 to 2.

• dans la poudre minérale de cette sur-couche, on peut, comme décrit dans les documents EP 722179 et EP 893813 , introduire un pigment noir, comme de l'oxyde de cobalt et de fer, de manière à ce que le sommet des barrières forme, après cuisson, un réseau noir destiné à améliorer le contraste de visualisation des images du panneau à plasma ;
• comme décrit dans le document EP 893813 , la proportion de liant minéral dans cette sur-couche peut être beaucoup plus faible que dans la couche principale, voire même nulle, de manière à ce que le sommet des barrières puissent être légèrement écrasé lors de l'assemblage avec une autre dalle pour former un panneau à plasma, cet écrasement étant destiné à compenser les irrégularités de hauteur des barrières et à améliorer l'étanchéité de la jonction avec l'autre dalle tout le long des barrières.

Other variants applicable to the invention relate to the use of an over-layer intended to form the top of the barriers:

• in the mineral powder of this overcoat, it is possible, as described in the documents EP 722179 and EP 893813 introducing a black pigment, such as cobalt oxide and iron, so that the top of the barriers form, after firing, a black network for improving the display contrast of the images of the plasma panel;
• as described in the document EP 893813 , the proportion of inorganic binder in this overcoat can be much lower than in the main layer, or even zero, so that the top of the barriers can be slightly crushed during assembly with another slab to form a plasma panel, this crushing being intended to compensate for the irregularities in the height of the barriers and to improve the tightness of the junction with the other slab all along the barriers.

A slab is thus obtained with an array of electrodes and a network of raw barriers delimiting the future discharge zones or cells of the plasma panel, where the bottom of the cells and the electrodes crossing the bottom of the cells are covered with the base underlayer which has resisted the projection of abrasive material, and thus served, according to the invention, to protect the electrodes against the projection of abrasive material in the absence of dielectric layer.

• préparation d'une pâte liquide comprenant essentiellement le luminophore à appliquer, un liant organique, et au moins un solvant ou un liquide de suspension ne solubilisant pas le liant des barrières crues et de leur sous-couche crue,
• application de cette pâte sur la dalle au travers d'un écran de sérigraphie présentant des ouvertures au regard des zones à recouvrir de ce luminophore,
• évaporation du solvant.

The slab equipped with a network of raw barriers supported by a raw base sub-layer, is then ready for the operations of depositing the raw layer of luminophores on the slopes of the barriers and on the base sub-layer at the bottom of the cells; preferably, for a depositing operation, the conventional screen-printing technique is used in the following steps:

• preparation of a liquid paste essentially comprising the luminophore to be applied, an organic binder, and at least one solvent or a suspension liquid which does not solubilize the binder of the raw barriers and their raw underlayer,
• application of this paste to the slab through a screen printing screen having openings with respect to the areas to be covered with this phosphor,
• evaporation of the solvent.

By re-iterating these operations for each type of phosphor to be applied, a slab is obtained with an array of electrodes, a network of barriers, coated with phosphors.

For the deposition of phosphors, one could also use the photolithography technique which allows a better definition, associated with a full-surface deposition made for example by spraying to limit the mechanical stresses applied on the slopes of the barriers; nevertheless, this technique involves large discharges of material containing phosphors and expensive operations for recycling these discharges; other deposition techniques may be used, for example ink jet application, dispensing in English, or microdosing.

The firing of the assembly comprising the green underlayer, the green barriers and the green phosphor layers is then carried out under conditions adapted to remove the organic binder from the different green layers and, in the case of the barriers and their sub-layers. base layer, to obtain the consolidation of the mineral material; the organic compounds are generally removed below 380 ° C, and in a first step of the baking heat treatment, a gradual rise up to this temperature so as to eliminate these organic compounds without damaging the structure of the layers raw; in a second stage of the heat treatment, heating is carried out at least to a temperature close to the softening temperature of the inorganic binder incorporated in the barriers and, optionally, to their base underlayer.

The conditions of the second stage of the baking heat treatment are adapted so as to obtain sufficient consolidation of the barrier material while maintaining a high porosity for both the base sub-layer and the barriers; it has been found that cooking under these conditions causes almost no shrinkage.

It is found that, for the manufacture of the slab according to the invention, the number of heat treatments is considerably reduced, since it is even possible to manufacture the slab with only a single heat treatment after completion of the electrode array.

As the slab according to the invention does not comprise any specific dielectric layer interposed between the electrodes and the base sub-layer, it avoids the heat treatment relative to this dielectric layer.

By using conventional organic binders decomposable below 480 ° C and a mineral binder having a sufficiently low softening temperature to obtain the consolidation of the barriers below 480 ° C or at this temperature, it is even possible to completely achieve the slab without exceed 480 ° C, which allows, in the case of conventional slabs of soda-lime glass, to limit if not eliminate any risk of deformation of the slab during its manufacture; it is recalled that the deformations of the slab cause, in particular, problems of misalignment between the different elements of the back slab and, depending on the structures, those of the front slab and malfunction problems of the plasma panel.

The slab according to the invention is thus obtained, as represented in FIG. figure 1 or, alternatively, to the figure 2 ; this slab is provided with at least one electrode array 11 and a network of porous barriers 17 made of mineral material, delimiting cells for the discharge zones of the panel, where, at the bottom of the cells, the electrodes 11 are covered a porous base underlayer 18 based on a mineral material; on the figure 1 the slopes of the barriers and the bottom of the cells are covered with luminophores 41; on the figure 2 the luminophores are not represented.

The embodiment of the figure 2 differs from that of the figure 1 in that the barriers have sloped slopes which are not perpendicular to the slab plane, and in that, outside the zones where it supports the barriers, the base sub-layer has a rounded surface which results from its Partial and irregular abrasion during the barrier formation stage.

It can be seen that the base underlayer 18 according to the invention considerably improves the adhesion of the barriers to the substrate.

The slabs according to the invention can be used in all types of plasma panels with barriers delimiting cells or groups of cells.

With reference to the figure 1 , such an image-viewing plasma panel, of the reciprocal type and with a memory effect, comprises a first slab according to the invention, provided with barriers 17 supported by the underlayer 18 already described, and a second slab 30 equipped with coplanar electrodes 33, providing between them zones of discharges 40 delimited by the barriers 17; the electrodes 11 of the first slab, which serve for the addressing of the discharges, are fully covered by the underlayer 18 according to the invention, at least in the active part of the panel; the coplanar electrodes 33 of the second slab 30, which serve to maintain the discharges by memory effect, are covered with a dielectric layer 32 and a protective layer 31, based on MgO.

The following example illustrates more particularly the invention and relates to the manufacture of a back panel plasma panel.

Example 1

1. 1.- préparation d'une pâte de sous-couche de base adaptée pour obtenir une sous-couche de base crue et sèche contenant (10,6% + 3,3%) en poids de (liant + plastifiant organiques), et adaptée pour obtenir une sous-couche de base cuite présentant une porosité supérieure à 25% :
   • préparation d'une solution de liant organique par dissolution de 13g d'éthyl cellulose grade N4 dans 83g de terpinéol, puis addition de 4g de phtalate de butyle benzyle sous forme de produit référencé Santicizer 160 ;
   • pré mélange à sec d'une poudre de matériau minéral de barrière : dans un mixer grande vitesse, on mélange :
     • o charge minérale : 98g d'alumine : poudre bi modale avec grains élémentaires de 0,3 et 3 µm ; poudre ayant une densité pressée de 2.60g/cm3 ;
     • o liant minéral : 2 g de silicate de plomb contenant 15% en poids de silice : grains élémentaires essentiellement entre 0.5 et 2µm ; température de ramollissement : 380°C ;
   • dispersion de 100g de poudre de matériau minéral de barrière dans 95g de la solution de liant organique ci-dessus ;
   • passage de la dispersion au tri cylindre de manière à obtenir une dispersion de viscosité de l'ordre de 37000 mPa.s, et, dans cette dispersion, des agrégats de taille inférieure à 7 µm ;
2. 2.- préparation d'une pâte de couche principale de barrière adaptée pour obtenir une couche principale crue et sèche contenant 3 % en poids de liant organique et adaptée pour obtenir des barrières présentant une porosité supérieure à 25% :
   • préparation d'une solution de liant organique par dissolution de 8g de résine Ethyl cellulose grade N4 dans 92g de terpinéol ;
   • prémélange à sec d'une poudre de matériau minéral de barrière dans les mêmes conditions et avec les mêmes composants que précédemment ;
   • dispersion de 100g de poudre de matériau minéral de barrière dans 38,62 g de la solution de liant organique ci-dessus ;
   • passage de la dispersion au tricylindre de manière à obtenir une dispersion de viscosité de l'ordre de 80000 mPa.s, et, dans cette dispersion, des agrégats de taille inférieure à 7 µm ;
3. 3.- dépôt de la sous-couche de base
   Sur la face de la dalle dotée du réseau d'électrodes, on réalise une seule passe de sérigraphie de la pâte de sous-couche de base en utilisant une toile polyester à 48 fils par cm, puis on sèche la sous-couche obtenue à120°C pendant 12 minutes pour évaporer le solvant.
   On obtient une sous-couche de base crue d'épaisseur sèche de l'ordre de18µm.
4. 4.- dépôt de la couche principale de barrière
   Sur la sous-couche de base séchée, on réalise 4 passes de sérigraphie de la pâte de couche principale en utilisant une toile polyester à 48 fils par cm et 1 passe de sérigraphie de la même pâte en utilisant une toile polyester à 90 fils par mm, chaque passe étant suivie d'un séchage à 120°C pendant 12 minutes. On obtient une couche principale crue d'épaisseur sèche de l'ordre de 110µm.
5. 5.- application d'un masque de protection :
   • sur la couche principale de barrière crue, lamination d'un film sec photosensible d'épaisseur 40 µm dans les conditions suivantes : température 110°C, pression 4 10⁵ Pa ;
   • Insolation du film laminé à 100mJ/cm2 en utilisant un masque formé de lignes noires d'épaisseur 70µm ; cette épaisseur correspond à la largeur souhaitée des barrières ;
   • développement du film insolé avec à l'aide d'une solution aqueuse contenant 0.2% en poids de Na2CO3 dans les conditions suivantes : température 30°C, Pression 1.5 10⁵ Pa.
   
   La couche crue de barrière est alors couverte d'un masque de protection en matériau polymère doté de motifs correspondant au réseau des barrières à former.
6. 6.- Projection de matériau abrasif ou « sablage » :
   • matériau abrasif : particules métalliques : référencé S9, grade 1000, de la Société FUJI ;
   • conditions de mise en oeuvre du matériau abrasif : à l'aide d'une buse rectangulaire plate de longueur de l'ordre de 200mm ; distance entre la sortie de la buse et la dalle : 95mm ; débit du matériau abrasif : 1800 g/min ; direction de déplacement de la buse perpendiculaire à celle de la dalle :
     • variante 1 pour structure barrières droites : pression de sablage 0.035 MPa ; vitesse de balayage de la buse sur la dalle : 50mm/min - vitesse déplacement dalle 110 mm/min ;
     • variante 2 pour structure barrières en gaufre (« waffle » en langue anglaise) : pression de sablage 0.035 MPa ; vitesse de balayage de la buse sur la dalle 50mm/min ; vitesse déplacement dalle 105 mm/min ;
   
   Résultat obtenu : gravure régulière des barrières avec conservation d'une couche résiduelle de matière crue au fond de chaque cavité, dont l'épaisseur centrale est légèrement inférieure à celle de la sous-couche de base initialement déposée ; on ne constate aucun trou dans cette couche résiduelle et la surface des électrodes sous-jacentes n'apparaît nulle part dans la partie active de la dalle ; en comparaison avec les barrières obtenues par sablage avec un procédé classique (arrêt sur une couche diélectrique intermédiaire spécifique), on constate ici que la base des barrières est plus arrondi, ce qui favorise une répartition uniforme des luminophores dans les étapes ultérieures.
7. 7.- Élimination du masque par « stripage » :
   • application sur le masque d'une solution aqueuse à 1 % en poids de NaOH à une température de 35°C environ et sous une pression de 0.4 10⁵ Pa environ ;
   • rinçage à l'eau ;
   • séchage par couteau d'air à 50°C
8. 8.- Préparation des pâtes de luminophores
   Pour chacune des trois poudres de luminophores, rouge, verte et bleu :
   • utilisation d'une solution aqueuse de résine à base d'alcool polyvinylique (« PVA ») à 300 mPa.s de viscosité, rendue photosensible par l'addition de bichromate d'ammonium ;
   • dispersion de 60g de luminophore dans 100g de solution de PVA ; addition de 7g de NH4Cr2O7 + 11g d'additifs liquides, notamment de stabilisation, anti-moussage et brillanteurs.
9. 9.- Dépôt des couches crues de luminophores : pour chaque couleur :
   • sérigraphie pleine surface de la pâte de luminophores de cette couleur, à l'aide d'une toile à 71fils/cm, de manière à former un dépôt sec d'environ 15µm d'épaisseur, puis séchage de la couche crue de luminophores à 55°C pendant environ 15 minutes ;
   • insolation de la couche crue à 800 mJ/cm2, selon un motif fonction de la répartition souhaitée des luminophores ;
   • développement de la couche insolée par pulvérisation d'eau portée à une température de30°C environ, sous une pression de 2 10⁵ Pa, puis séchage à 65°C pendant environ 15 minutes ;
10. 10.- dépôt d'un joint de scellement sur le pourtour de la dalle
    Ce joint est destiné à réaliser un assemblage de la dalle avec une autre dalle pour former un écran à plasma et à ménager entre ces dalles des espaces étanches de décharge, destinés à être rempli de gaz de décharge.
11. 11.- Cuisson à 450°C, avec un palier durant environ 2h30.
    On élimine ainsi lors d'une même opération le liant organique du joint de scellement, de la sous-couche de base, de la couche principale de barrières et des couches de luminophores ; grâce au liant minéral contenu dans les pâtes de cette sous-couche et des barrières, on obtient la consolidation des barrières et de la sous-couche ; les barrières obtenues présentent une porosité supérieure à 25%, et sont soutenues et renforcées par la sous-couche continue selon l'invention, qui présente également une porosité supérieure à 25% ; on ne constate quasiment aucun retrait après cuisson.
12. 12.- Assemblage d'une dalle avant sur la dalle ainsi obtenue :
    • scellement des deux dalles assemblées à 400°C, suivi d'un pompage de l'espace situé entre les dalles, dans les conditions d'obtention d'un vide secondaire ;
    • remplissage du panneau à l'aide du gaz de décharge et scellement pour fermeture du panneau.

On a slab made of soda-lime glass measuring 254 mm x 162 mm, thickness 3 mm, equipped with an array of electrodes formed of aluminum conductors, which is not coated with a dielectric layer, we will deposit according to the invention a network of barriers defining discharge areas of dimensions 172 mm x 100 mm, distributed on the slab in a pitch of 360 microns.

1. 1.- Preparation of a basecoat base paste adapted to obtain a raw and dry base sub-layer containing (10.6% + 3.3%) by weight of (organic binder + plasticizer), and adapted to obtain a fired base sub-layer with a porosity greater than 25%:
   • preparation of an organic binder solution by dissolving 13 g of ethyl cellulose grade N4 in 83 g of terpineol, then adding 4 g of benzyl butyl phthalate in the form of Santicizer product 160;
   • dry premixing of a powder of barrier mineral material: in a high speed mixer, mixing:
     • o mineral filler: 98 g of alumina: bi-modal powder with elemental grains of 0.3 and 3 μm; powder having a pressed density of 2.60g / cm3;
     • o inorganic binder: 2 g of lead silicate containing 15% by weight of silica: elementary grains essentially between 0.5 and 2 μm; softening temperature: 380 ° C;
   • dispersion of 100g of barrier mineral material powder in 95g of the above organic binder solution;
   • passing the dispersion to the tri-roll so as to obtain a viscosity dispersion of the order of 37000 mPa.s, and in this dispersion aggregates of less than 7 μm in size;
2. 2.- preparation of a barrier main layer paste adapted to obtain a green raw layer and dry containing 3% by weight of organic binder and adapted to obtain barriers having a porosity greater than 25%:
   • preparation of an organic binder solution by dissolving 8 g of Ethyl cellulose grade N4 resin in 92 g of terpineol;
   • dry premixing of a powder of barrier mineral material under the same conditions and with the same components as before;
   • dispersing 100 g of barrier mineral material powder in 38.62 g of the above organic binder solution;
   • passing the dispersion to the three-cylinder so as to obtain a viscosity dispersion of the order of 80000 mPa.s, and, in this dispersion, aggregates smaller than 7 microns;
3. 3.- deposit of the base sub-layer
   On the face of the slab provided with the electrode array, a single pass of screen printing of the base underlayment paste is carried out using a polyester fabric with 48 threads per cm, then the underlayer obtained is dried at 120.degree. C for 12 minutes to evaporate the solvent.
   A raw base sub-layer with a dry thickness of the order of 18 μm is obtained.
4. 4.- deposit of the main barrier layer
   On the dried base underlayer, 4 screen passes of the main layer paste were made using a 48 thread count polyester web and 1 screen pass of the same paste using a 90 mesh polyester web per mm. each pass being followed by drying at 120 ° C for 12 minutes. A green main layer with a dry thickness of the order of 110 μm is obtained.
5. 5.- application of a protective mask:
   • on the main green barrier layer, lamination of a 40 μm thick photosensitive dry film under the following conditions: temperature 110 ° C, pressure 4 10 ⁵ Pa;
   • Insulation of the laminated film at 100 mJ / cm 2 using a mask formed of 70 μm thick black lines; this thickness corresponds to the desired width of the barriers;
   • development of the insoluble film with an aqueous solution containing 0.2% by weight of Na 2 CO 3 under the following conditions: temperature 30 ° C, pressure 1.5 10 ⁵ Pa.
   
   The green barrier layer is then covered with a protective mask made of polymer material having patterns corresponding to the network of barriers to be formed.
6. 6.- Projection of abrasive material or "sanding":
   • abrasive material: metal particles: referenced S9, grade 1000, from the FUJI Company;
   • working conditions of the abrasive material: using a flat rectangular nozzle of the order of 200 mm; distance between the outlet of the nozzle and the slab: 95mm; flow rate of the abrasive material: 1800 g / min; Direction of movement of the nozzle perpendicular to that of the slab:
     • variant 1 for straight barrier structure: sanding pressure 0.035 MPa; sweeping speed of the nozzle on the slab: 50mm / min - speed displacement slab 110 mm / min;
     • variant 2 for waffle barriers (English waffle): sandblasting pressure 0.035 MPa; sweeping speed of the nozzle on the slab 50mm / min; slab displacement speed 105 mm / min;
   
   Result obtained: regular etching of the barriers with preservation of a residual layer of raw material at the bottom of each cavity, whose central thickness is slightly less than that of the base subbase initially deposited; no holes are found in this residual layer and the surface of the underlying electrodes does not appear anywhere in the active part of the slab; in comparison with the barriers obtained by sanding with a conventional method (stopping on a specific intermediate dielectric layer), it is found here that the base of the barriers is more rounded, which promotes a uniform distribution of the phosphors in the subsequent steps.
7. 7.- Elimination of the mask by " stripping":
   • application to the mask of an aqueous solution at 1% by weight of NaOH at a temperature of approximately 35 ° C. and at a pressure of approximately 0.4 10 ⁵ Pa;
   • rinsing with water;
   • air knife drying at 50 ° C
8. 8.- Preparation of phosphor pastes
   For each of the three phosphor powders, red, green and blue:
   • use of an aqueous solution of polyvinyl alcohol ("PVA") resin at 300 mPa.s of viscosity, rendered photosensitive by the addition of ammonium dichromate;
   • dispersion of 60 g of phosphor in 100 g of PVA solution; addition of 7 g of NH4Cr2O7 + 11 g of liquid additives, in particular of stabilization, anti-foaming and brighteners.
9. 9.- Deposit of raw phosphor layers : for each color:
   • full-surface screen printing of the luminophore paste of this color, using a 71-wire / cm cloth, so as to form a dry deposit of approximately 15 μm thick, then drying the green luminophore layer at 55 ° C for about 15 minutes;
   • insolation of the green layer at 800 mJ / cm 2, in a pattern depending on the desired distribution of phosphors;
   • developing the insolated layer by spraying water heated to a temperature of about 30 ° C. under a pressure of 2 × 10 ⁵ Pa and then drying at 65 ° C. for about 15 minutes;
10. 10.- deposit of a seal around the edge of the slab
    This seal is intended to make an assembly of the slab with another slab to form a plasma screen and to arrange between these slabs of the sealed spaces for discharge, to be filled with discharge gas.
11. 11.- Cooking at 450 ° C, with a bearing for about 2h30.
    In this way, the organic binder of the sealing gasket, the base underlayer, the main barrier layer and the phosphor layers is eliminated during the same operation; thanks to the mineral binder contained in the pastes of this sub-layer and the barriers, the consolidation of the barriers and the underlayer is obtained; the barriers obtained have a porosity greater than 25%, and are supported and reinforced by the continuous underlayer according to the invention, which also has a porosity greater than 25%; there is virtually no withdrawal after cooking.
12. 12.- Assembly of a front slab on the slab thus obtained :
    • sealing the two slabs assembled at 400 ° C, followed by pumping the space between the slabs, under conditions of obtaining a secondary vacuum;
    • filling the panel with the discharge gas and sealing to close the panel.

With the method according to the invention, a plasma panel slab with an abrasion barrier network is thus obtained, completely eliminating the additional steps of the methods according to the prior art. relating to the application and firing of a dielectric layer, intended inter alia to serve as a protective layer for the electrodes during the forming of the barriers by abrasion.

Moreover, the barriers, although porous and narrow, have good strength thanks to the underlayment according to the invention.

The ^2nd full following example to illustrate the invention:

Example 2

This example is intended to illustrate the advantage of using a polyvinyl alcohol as organic binder of the base underlayer, in the steps 1 of preparation of the base underlayment and 2 of preparation of the dough main layer of the process just described.

Example 2A:

Main layer with ethylcellulose binder with a resin content of 3% (terpineol solvent);

Base underbase with binder based on the same resin at a rate of 10.6% softened by 3.3% of a plasticizer (terpineol solvent);

In step 6 of projection of abrasive material or "sanding", there is a factor of 4 between the abrasion rate of the main layer and that of the underlayer.

Example 2B:

Main layer with ethylcellulose binder with a resin content of 3% (terpineol solvent), as in Example 1A;

Polyvinyl alcohol-based binder (15% PVA) binder without plasticizer addition, in which a diazo sensitizer allowed cross-linking under UV and water as a solvent;

The use of two different resins for the main layer and for the underlayer, and more particularly the non-solubility of the crosslinked polyvinyl alcohol in terpineol makes it possible to avoid partial redissolution of the underlayer at the time of application of the main layer; this results in a bottom of cavities between barriers advantageously flatter in Example 1 B than for Example 1A.

In step 6 of projection of abrasive material or "sandblasting", there is a factor 16 between the abrasion speed of the main layer and that of the underlayer.

It follows that the use of the crosslinked polyvinyl alcohol is particularly advantageous for the implementation of the method of the invention.

Claims (19)

1. Tile for a plasma image display panel comprising a substrate (10) coated with at least one array of electrodes (11) which is itself coated with an array of barrier ribs (17) made of a mineral material, the porosity of which is greater than 25%, these being intended to define cells in order to form discharge regions (40) in the said panel, comprising also a porous base underlayer (18) which is inserted between the said array of electrodes (11) and the said array of barrier ribs (17), which is made of a mineral material, the porosity of which is greater than 25%, characterized in that the thickness of the said base underlayer is between 10 µm and 40 µm at every point of said tile.
2. Tile according to Claim 1, characterized in that the width of the barrier ribs is less than or equal to 70 µm.
3. Tile according to any one of Claims 1 to 2, characterized in that it includes no interlayer, especially no dielectric interlayer, between the electrodes and the said base underlayer.
4. Tile according to any one of Claims 1 to 3, characterized in that the base underlayer includes a component suitable for reflecting light.
5. Tile according to any one of Claims 1 to 4, characterized in that, when the said mineral material of the base underlayer comprises a mineral filler and optionally a mineral binder, the proportion by weight of mineral binder in the mineral material of the base underlayer is less than 13%.
6. Tile according to any one of Claims 1 to 5, characterized in that the material of the base underlayer is identical to the material of the barrier ribs.
7. Tile according to any one of Claims 1 to 6, characterized in that it includes a layer of phosphors at least partly covering the sides of the barrier ribs and the said underlayer.
8. Tile according to any one of Claims 1 to 7, characterized in that, at every point on the surface joining the base of the barrier ribs to the base underlayer, the radius of curvature is greater than or equal to 10 µm.
9. Tile according to any one of Claims 1 to 8, characterized in that the said barrier ribs are themselves coated with an overlayer.
10. Plasma image display panel, of the AC type and with a memory effect, comprising a first tile according to any one of Claims 1 to 9 and a second tile (30) provided with coplanar electrodes (33) serving to sustain the discharges by the memory effect, providing between the tiles discharge regions (40) bounded by the said barrier ribs (17).
11. Process for manufacturing a plasma panel tile according to any one of Claims 1 to 9, characterized in that it comprises the following steps:

    - formation of at least one array of electrodes on a substrate;

    - deposition, on the said array of electrodes and on the substrate, of at least a green base underlayer and a superposed green main layer, both the green underlayer and the green main layer being based on a powder blend of a mineral material and an organic binder, from a paste of green base underlayer the preparation of which is adapted to obtain, after baking, a base underlayer having a porosity greater than 25%, and from a paste of green main layer the preparation of which is adapted to obtain, after baking, barriers having a porosity greater than 25%;

    - blasting with an abrasive material:

    ≅ so as to remove part of the said green main layer in order to form the said array of green barrier ribs, the said barrier ribs comprising a base, a top and sides, and

    ≅ so as to avoid the removal of the said green base underlayer so that there is not one hole over the entire coating;

    - baking under conditions suitable for removing the organic binder and for consolidating the mineral material of the barrier ribs and of the said base underlayer, and for obtaining a porosity greater than 25% of said mineral material,
    the composition and the thickness of the said green base underlayer being suitable for the rate of abrasion of this underlayer to be less than the rate of abrasion of the main layer under the conditions of the said blasting.
12. Process according to Claim 11, characterized in that, when the said mineral material of the base underlayer comprises a mineral filler and optionally a mineral binder, the proportion by weight of mineral binder in the mineral material of the base underlayer is less than 13%.
13. Process according to either of Claims 11 and 12, characterized in that the proportion of organic binder in the base underlayer is greater than the proportion of organic binder in the main layer.
14. Process according to either of Claims 11 and 12, characterized in that the glass transition temperature of the organic binder of the base underlayer is below that of the organic binder of the main layer.
15. Process according to any one of Claims 11 to 14, characterized in that the organic binder of the said base underlayer and that of the said main layer are chosen from the group comprising cellulosic resins, acrylic resins, methacrylic resins, rosin resins and resins based on crosslinked polyvinyl alcohol.
16. Process according to Claim 15, characterized in that the organic binder of the said base underlayer is based on polyvinyl alcohol.
17. Process according to any one of Claims 11 to 16, characterized in that it includes only a single baking heat treatment after at least one array of electrodes has been formed.
18. Process according to any one of Claims 11 to 17, characterized in that it includes no step during which the temperature of the tile exceeds 480°C.
19. Process according to any one of Claims 11 to 18, characterized in that the mineral filler of the base underlayer is identical to the mineral filler of the main barrier rib layer.

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