DISPLAY DEVICE

Abstract: Light-emitting cells (RC, GC, BC) of a display device are individually provided with inner walls at least partially covered by white reflectors consisting of glass material (WG) contain­ ing transparent particles having different refractive index in an amount of 5 to 80% by weight, so that extremely high luminous efficiency, similar as that of an optical integrating sphere, can be realized. On the other hand, openings for emitting colored light are applied with color filters (RF, GF, BF) concerned, meanwhile the front surface other than those openings of the display device is covered with light-absorbing black material (BM), so that the reflectance for incident ambient light can be extremely reduced. According to the multiplexed effect of the above struc­ ture, remarkably high contrast of display can be readily real­ ized.

Description: The present invention relates to a display device, such as a gas discharge display device In various kinds of conventional gas discharge display devices, cell sheets are usually employed for providing discharge cells therein as exemplified by Fig. 1(a). In Fig. 1(a), a cell sheet CS sandwiched between a front glass plate FG and a rear glass plate RG is provided with plural spaces which are arranged in matrix for individually forming discharge cells, inner walls thereof being coated with fluorescent layers Ph, display anodes DA and cathode C being arranged in front and rear thereof respectively. These fluorescent layers are excited by ultraviolet rays emitted from gas discharges generated in those discharge cells, so as to radiate required visible light . As for the cell sheet consisting in the above structure of the gas discharge display device, mechanically workable ceramics exemplified by Macor (registered trade mark and/or trade name) have been employed and perforated by etching and the like. Otherwise, black banks B formed by firing multilayer-printed black glass paste as shown in Fig. 1(b) are employed for providing the discharge cells. Among these conventional formations of discharge cells, the former is too expensive to work cell sheets and difficult to form a large scaled display device, as well as to provide miniatualized discharge cells. On the other hand, in a gas discharge display device formed by the latter, the efficiency of reflection of the light emitted from the fluorescent layer Ph toward the front view side upon the light-absorbing black glass paste is too low and hence the luminous efficiency in the front view direction is worsened. The removal of black pigments from the black glass paste has been once tried, so as to improve the above efficiency of reflection thereon. However, effective improvement of efficiency could not be so obtained. Meanwhile, in order to increase the contrast of display in various kinds of display devices including cathode ray tube display devices,gas discharge display devices and low velocity electron beam fluorescent display devices, it is usual to increase the brightness of display as well as to lower the reflectance of displaying surface. Conventional measures for lowering the reflectance of displaying surface of the display device are as follows. (i) An absorption type neutral density (ND) filter is employed. (ii) A glass material consisting in the displaying surface is added with rare earth elements, for instance, Nd₂O₃ . (iii) A fluorescent material consisting in the display element is added with a suitable pigment. (iv) The portions other than the fluorescent layer of the display element are coated with black materials. (v) Granular pigments are deposited on the front surface of the fluorescent layer, so as to form a filter. In addition, in the display device as disclosed in Japanese Patent Application Laid-open Publication No. 59-36,280, which was filed by the present applicant, as shown in Figs. 2(a), (b), the contrast of display is increased substantially 4 to 6 times together with the brightness lowered only about by 20% on account of the application of optical filters formed of substantially transparent inorganic materials, through which color lights emitted from plural kinds of colored display elements combined with each other into a colored picture display device are transferred respectively, upon those colored display elements. However, even though the above remarkable increase of the contrast of display has been attained, the quality of displayed color picture cannot be satisfied under the high ambient illumination with respect to the contrast thereof. In this connection, Fig. 2(a) is a plan view showing a part of the above disclosed gas discharge display device, meanwhile Fig. 2(b) is a cross-sectional view-thereof along the line X₁-X₂. An object of the present invention is to provide a display device in which the luminous efficiency in the front view direction is remarkably improved, so as to facilitate the provision of a large scaled display device as well as to facilitate the formation of minuscule display elements, by regarding each of those display elements as a kind of optical integrating sphere. For attaining this object of the invention, at least a part of inner wall of each light-emitting display element is coated with reflective white material. According to the present invention, there is provided a display device provided with a plurality of picture elements arranged in a plane each element being a cell having inner surfaces characterized by comprising, in each of said picture elements, a light-reflecting white layer of glassy material comprising at least 20% by weight of glass powder, 5% to 80% by weight of at least one kind of transparent powder material having a refractive index other than that of said glass powder whereby in case the transparent powder material is titanium oxide the range is 2% to 80% by weight, and optionally an amount of at most 0.1% by weight of black pigment, said light reflecting white layer being formed on an inner surface of said picture elements by firing after applying said glass material. The white inner reflector provided in the display element contributes to effectively transfer the color light emitted inside the display element toward the front view side, so as to increase the luminous efficiency of the display element. Another object of the present invention is to further increase the contrast of display in the above improved display element, which can be regarded as a kind of optical integrating sphere, by reducing the reflection of incident ambient light thereon. The display device according to a preferred embodiment is further featured in that the almost all of the front surface of the display device concerned is covered with absorbing material layers for incident ambient light except for the vicinities of openings of each display elements, the above mentioned white inner reflectors being arranged at least back to back with these absorbing material layers individually. For a better understanding of the invention, reference is made to the accompanying drawings, in which: Figs. 1(a) and 1(b) are cross-sectional views showing conventional gas-discharge display devices respectively as described above; Figs. 2(a) and 2(b) are a plan view and a cross-sectional view showing the other conventional gas-discharge display device respectively as described above; Figs. 3(a) and 3(b) are a plan view and a cross-sectional view showing an embodiment of a gas-discharge display device according to the present invention; Figs. 4 to 8 are cross-sectional views showing various embodiments of the gas-discharge display device according to the present invention Figs. 9(a) and 9(b) are plan views showing various embodiments of a fixed picture display device according to the present invention Figs. 10(a) and 10(b) are a plan view and a cross-sectional view showing an embodiment of another kind of a gas discharge display device according to the present invention and Figs. 11 to 14 are cross-sectional views showing various embodiments of the other kind of the gas discharge display device according to the present invention Throughout different views of the drawings, FG is a front glass plate, RG is a rear glass plate, DA is a display anode, DAB is a display anode bus, C is a cathode, CB is a cathode bus, Ph is a fluorescent layer, BM is a black lattice, CS is a cell sheet, WB is a white bank, WG is a white glass layer, RC is a red light discharge cell, GC is a green light discharge cell, BC is a blue light discharge cell, RF is a red light filter, GF is a green light filter, BF is a blue light filter, and F is a colored light filter. Various preferred embodiments of the display device according to the present invention will be described in detail hereinafter. Figs. 3(a) and 3(b) show a typical embodiment of a gas-discharge display panel according to the present invention, Fig. 3(a) being a plan view thereof, Fig. 3(b) being a cross-sectional view thereof along the line X₁-X₂. In this embodiment of the gas-discharge display device according to the present invention, a cathode bus CB is printed on a rear glass plate RG and fired, a white glass layer WG consisting of the following materials being printed thereon except for the vicinity of the cathode C and fired, a fluorescent layer Ph being coated further thereon. On the other hand, a display anode bus DAB is printed on a front glass plate RG and fired, a white bank WB similarly consisting of the following materials being printed thereon and fired. As for the materials for forming the white glass layer WG and the white bank WB, more than 20% by weight of transparent glass powder having the refractive index n₀ and containing no black pigment and 5 to 80% by weight of at least one kind of transparent powdered material having another refractive index n₁ which is different from the above refractive index n₀ are employed. According to the above structure of the gas-discharge display device, the ultraviolet ray generated by the gas discharge is converted into the visible light through the fluorescent layer Ph, this visible light being reflected by the white glass layer WG situated behind the fluorescent layer Ph toward the front view side therethrough and then non-directionally dispersed because of the diffusive light. The light components passing through the front glass plate FG are used for effective display, meanwhile the light components striking the wall of the white bank WB is further dispersed. However, in the situation where the bank were black similarly as in the conventional gas-discharge display device as shown in Fig. 1(b), this further dispersed light is absorbed by the black bank B. On the contrary, in the situation where the white bank WB has the reflectance in the vicinity of 90% according to the present invention, almost all of the further dispersed light components are finally transferred toward the front view side. However, the above structure of the gas-discharge display device according to the present invention has such a demerit together with the above described merit as the overall reflectance of the display device for the incident ambient light is increased together with that of the individual display element for the emitted light. So that, it is preferable that the conventional black paste BM is printed on the front top of the white bank WB. Moreover, in the situation where the optical filters formed of inorganic materials for red, green and blue lights as described in Japanese Patent Application Specifications Nos. 59-125,016, 59-125,017 and 59-125,018 respectively are arranged in immediate front of red, green and blue discharge cells RC, GC and BC respectively, as shown in Fig. 4, since these optical filters have extremely large ratio of transmittance between respective allotted color light and the other color lights, the reflection of the incident ambient light upon the display device is effectively reduced and hence the operational effect of the present invention can be remarkably promoted. In the single color gas-discharge display, the above optical filter can be provided in front of the front glass plate FG, as well as the front glass plate FG proper can be provided with the necessary filtering performance. In these situations, any optical filter formed of organic materials can be employed. In this connection, the materials for forming these white banks or white layers are somewhat porous, so that, the insulation persistency of these white banks or white layers can be increased by additionally printing a conventional transparent glass paste on these filter materials, which have been dried or fired, and then firing it, and hence any metallic material can be printed thereon. Next, Fig. 5 shows an embodiment of the transmissive view type gas-discharge display device in which the light emitted from the fluorescent layer Ph is viewed through the fluorescent layer Ph concerned. In the conventional display device of this type, the light emitted from the fluorescent layer Ph toward the rear side are absorbed by various portions including the inner wall and the electrodes in the discharge cell, or, transmitted toward the rear side ineffectively. In contrast therewith, in the embodiment as shown in Fig. 5, the almost all inner surface of the display element consist of the white bank WB and the white glass layer WG other than the rear side electrode, namely, the cathode C, so that the almost all light emitted from the fluorescent layer Ph toward the rear side can be efficiently reflected toward in front view side, and, as a result, the luminous output and the luminous efficiency are remarkably increased. Next, Fig. 6 shows an embodiment of the discharge light direct view type gas-discharge display device filled, for instance, with neon gas. In this embodiment, the visible light components which were conventionally absorbed by the inner surface of the display element can be efficiently reflected toward the front view side just similarly as in the embodiment as shown in Fig. 5, because of the increased reflectance of the inner wall surface, so that the luminous efficiency can be increased by the same reason as mentioned above. In this situation, the aforesaid optical filters are required for selectively reducing the reflection of the incident ambient light. Fig. 7 shows another embodiment of the discharge light direct view type gas-discharge display device, in which the cathode C and the display anode DA are arranged on the front and the rear glass plates FG and RG respectively, just in opposite to the embodiment as shown in Fig. 6. In this embodiment materials F for the aforesaid optical filters are coated on the white bank WB and the white glass layer WG forming the inner wall of the display element. Accordingly, the light components emitted in the display element toward the rear side and the inner wall are passed through those layers of filter materials F and reflected on the white reflectors WB and WG, and thereafter transferred toward the front view side through the filter material layers F again. Meanwhile almost all of incident ambient light is absorbed by those filter material layers F. Fig. 8 shows an embodiment constructed substantially the same as that shown in Fig. 7, except that the transparent fluorescent layer Ph is arranged in immediate front of the display element. In this embodiment, the components of the visible light emitted from the fluorescent layer Ph excited by the ultraviolet ray towards the rear side and the inner wall are reflected toward the front view side just similarly as described above regarding that as shown in Fig. 7, meanwhile the incident ambient light is similarly absorbed, so that the reflection thereof is lowered. The fluorescent layers Ph in this embodiment can be formed by depositing, sputtering, dipping, ion-implanting and the like and employed for multicolor display as well as single color display. The present invention can be applied to both of AC type and DC type of gas-discharge display device, particularly to various kinds of facial discharge type display device among the AC type display devices, moreover regardless of the difference between the positive column type and the negative glow type. The luminous efficiency can be also increased by coating the fluorescent material on the wall of the white bank WB. Furthermore, the present invention can be applied not only to the gas-discharge display device, but also the low velocity electron beam display device, in which the components of the light emitted from the fluorescent layer toward the rear side can be reflected toward the front view side by the aforesaid white reflection material deposited on the rear face of the electro-conductive film according to the present invention. In addition, the present invention can be naturally applied to the gas-discharge display device provided with the priming discharge, particularly in the situation of which where the priming discharge is shifted into the display discharge within the same discharge cell, it is efficient to apply the aforesaid white reflection material onto the inner wall of the display discharge section thereof. Moreover, in an embodiment of the reflective view type fixed picture display device provided with the piled combination of the respective inorganic optical filters R, G, B for red, green, blue lights as shown in Fig. 9(a) and the black masks for half tone display as shown in Fig. 9(b), the rear side of the black mask having the opening corresponding to the brightness to be displayed is covered with the white reflection material according to the present invention and then fired, so as to realize a long life display device. In the situation where the black mask is provided on the rear glass plate, black materials for forming the mask are preferably printed on the white reflection materials printed on the rear glass plate and fired. Next, the white reflection materials used for the display device according to the present invention will be described in detail hereinafter. Generally speaking, the light incident onto the interface between the transparent glass material having the refractive index n₀ and transparent particles residing therein with the different refractive index n₁ (n₁≠n₀) is totally reflected, refracted or scattered according to the respective laws in response to the refractive index absolute difference |n₀-n₁| and the density of those particles. As for the above glass material, any kind of glass material can be employed, so far as it can be glazed onto the glass substrate at the temperature below 700°C, preferably below 600°C. For example, the glass materials of PbO-SiO₂-B₂O₃ descent, PbO-SiO₂-B₂O₃-ZnO descent, PbO-B₂O₃-ZnO descent, Bi₂O₃-SiO₂-B₂O₃ descent and of these glass descents containing at least one of R₂O(R=Li,Na,K), BaO, CaO, MgO, TiO₂ , ZrO₂ , Aℓ₂O₃ , NaF and P₂O₅ are available. The filling material other than the above transparent glass material, including those particles having the refractive index n₁ is called as a filler, which is favorable to have the heat resistivity in the vicinity of 700°C and the thermal expansion coefficient similar to that of the glass material particularly in the situation where its large amount is filled therein. The refractive index n₀ of the glass material of PbO descent is about 1.7, so that it is required for increasing the reflectance thereof to fill the filler having the refractive index n₁ = l.5 to 1.9. The filler having the refractive index n₁ = n₀ may be filled therein by a little amount without expectable efficient result. The examples of the above filler can be enumerated together with the bracketed refractive index as follows. Sulfates including sodium sulfate, potassium sulfate, barium sulfate (1.63), zinc sulfate, calcium sulfate, magnesium sulfate and aluminum sulfate. Phosphates including calcium phosphate, magnesium phosphate, barium phosphate and zinc phosphate. Oxides including alumina (1.53), silica (1.55), zinc oxide, magnesium oxide, titanium oxide (2.5 to 2.9), zirconium oxide (2.4), calcium oxide, 1st tin oxide, 2nd tin oxide, barium oxide and antimony oxide. Sulfides including zinc sulfide. Silicates or minerals containing silica components including talc, cordierite, spodumene, kaoline, calcium silicate, zirconium silicate, zinc silicate, magnesium silicate and aluminum silicate. Fluorides, which are known to have comparatively low refractive index, including calcium fluoride, magnesium fluoride, barium fluoride and sodium fluoride. Nitrides including aluminum nitride and boron nitride. Glass having the glazing temperature higher than 700°c. Particularly, the reflectance of the glass material can be extremely increased by adding titanium oxide therein by 2 to 20%. Black materials optionally contained therein in an amount no more than 0.1% are exemplified by iron oxide, chromium oxide, copper oxide, manganese dioxide, nickel oxide and cobalt oxide. A practically sufficient reflectance can be realized according to the following empirical formuli in the situation where "ai" is the composition rate of the i-th filler. 1st example of white glass material A glass material consisting of PbO 63% by weight, SiO₂ 15% by weight, B₂O₃ 17% by weight and ZnO 5% by weight is melted at 1,000°C and then pulverized by a ball mill into particles having an average diameter 3 to 5 µm. A mixture powder of the above obtained glass powder 60% by weight together with rutile-type titanium oxide 12% by weight and alumina powder 28% by weight is stuck on a glass substrate and fired, so as to obtain the desired white glass material. However, in a situation where the printing thereof is required, the above mixture powder is mixed with an organic vehicle consisting of butyl carbitol 90% by weight, ethyl cellulose 8% by weight and polyvinyl acetatepolybutyral copolymer 2% by weight into the paste, which can be printed on a sodalime glass substrate through a 325 mesh screen. 2nd example of white glass material A mixture powder consisting of powdered glass material having the same composition as that of the above 1st example 80% by weight and rutile-type titanium oxide 20% by weight is employed similarly as the above 1st example being available for the thick sticking, meanwhile the 2nd example being available for the rear side sticking. In this connection, the photo-adhesion other than the printing can be employed for sticking these white glass materials. 3rd example of white glass material A glass material consisting of PbO 77% by weight, SiO₂ 2% by weight, B₂O₃ 10% by weight, ZnO 7% by weight, Na₂O 3% by weight and Aℓ₂O₃ 1% by weight is melted at 1,000°C and then pulverized by a ball mill into particles having an average diameter 3 to 5 µm. A mixture powder of the above obtained glass powder 30% by weight together with zinc sulfide 70% by weight is mixed with the same vehicle as that of the 1st example into the paste, which can be printed on a sodalime glass substrate through a 325 mesh stainless screen. 4th example of white glass material A glass material consisting of Bi₂O₃ 73% by weight, B₂O₃ 9% by weight, ZnO 8% by weight, SiO₂ 6% by weight, Aℓ₂O₃ 2% by weight and Na₂O 2% by weight is melted at 1,000°C and then pulverized by a ball mill into particles having an average diameter 3 to 5 µm. A mixture powder of the above obtained glass powder 82% by weight together with anatase-type titanium oxide 8% by weight and zinc oxide 10% by weight is mixed with the same vehicle as that of the 1st example into the paste, which can be printed on a sodalime glass substrate through a 325 mesh screen. Next, an embodiment of the display device provided for attaining the aforesaid subsidiary object of the present invention will be described in detail hereinafter by referring to the plan view thereof as shown in Fig. 10(a) and the cross-sectional view thereof as shown in Fig. 10(b). In this embodiment, almost all area of the inner surface of the front glass plate FG is stuck with black material layers BM, on which cathode buses CB accompanied with cathodes C are arranged. On these cathode buses CB except for the exposed cathodes C, white wall layers WW formed of the aforesaid white glass material is stuck, meanwhile the aforesaid white banks WB are stacked on either one of the front and the rear glass plates FG and RG, the anode buses AB accompanied with the anodes A being arranged on the inner surfaces of the rear glass plate RG, meanwhile almost all area of the inner surface of the rear glass plate RG is covered with the white wall layers WW except for the exposed anodes A, on which layers the fluorescent layers Ph are stuck. These fluorescent layers Ph are excited by the ultraviolet rays generated through the gas discharge, so as to emit the visible lights, a part of these lights being directly passed through the openings OP toward the front view side, meanwhile the other part of these lights being reflected by the inner surfaces of the white banks WB and the white wall layers WW and thereafter passed through the openings OP toward the front view side. In the situation where the reflectance of the white bank WB and the white wall layer WW is sufficiently high, the loss of the emitted visible light is very little, so that almost all of the emitted visible light can be transferred toward the front view side by the multiplexed reflection according to the same principle as that of the optical integrating sphere. On the other hand, the ambient light incident onto the black material layers BM on the front glass plate FG is absorbed thereby, meanwhile almost all of the ambient light passing through the opening OP is substantially reflected according to the above principle, so that, the reflectance for the ambient light is given by the ratio S OP /(S BM +S OP ) where S BM and S OP are the areas occupied by the black material layer BM and the opening OP respectively, and hence it can be reduced in order of 10% by reducing the area S OP occupied by the opening OP as narrow as possible with a remarkably efficient result in comparison with the conventional reflectance of about 60%. In this connection, the above ratio S OP /(S MB +S OP ) can be readily reduced into less than 4% together with the luminous output lowered only by 10%. In the embodiment of the gas-discharge display device as shown in Figs. 10(a), 10(b), the position stuck with the fluorescent layer Ph is not restricted only to the inner surface of the white wall material layer WW stuck on the rear glass plate RG, but also the inner surface of the white wall material layer WW stuck on the front glass plate RG can be added thereto. In this connection, the fluorescent layers Ph concerned are available for reflecting the visible light as a kind of white reflector, together with the additionally increased luminous output of the fluorescent layers stuck on the front glass plate FG side, which can be directly stuck on the inner surface of the front glass plate FG also with a little increased thickness. The luminous efficiency can be further increased by additionally sticking the fluorescent layer Ph on the inner wall surface of the white bank WB. In the situation where the embodiment of the gas-discharge display device as shown in Figs. 10(a), 10(b) is provided for the colored display consisting of single colored light, for instance, red, green or blue light, or, of plural kinds of colored lights, the openings OP of the individual discharge cells are preferably applied with the optical filters provided for the respective colored lights, for example, those as disclosed in Japanese Patent Applicaion Laid-open Publication No. 59-32,680 and Japanese Patent Application Specifications Nos. 59-125,016, 59-125,017 and 59-125,018, which have been filed by the present applicants, namely, the optical filters RF, CF and BF made of inorganic materials provided for red, green and blue lights respectively. According to the multiplexed effect of the application of the optical filters, the reflectance of the incident ambient light toward the front view side is further reduced. Fig. 11 shows a cross-sectional view of an exemplified embodiment in which a discharge cell for emitting the red light only is shown, so that, in order to realize the tri-colored display, it is enough to arrange in order three kinds of similar discharge cells for emitting tri-colored lights respectively as shown in Figs. 2(a), 2(b). Next, Fig. 12 shows another embodiment of the discharge light direct view type gas-discharge display device of this kind. In this embodiment, the fluorescent layer is not required and hence the monochromatic display is effected. So that, the aforesaid optical filter is preferably applied not only on the opening OP, but also on almost all area of the front glass plate FG for the allotted single colored light regardless of the front side or the rear side thereof. In this connection, it is possible to give the front glass plate FG itself the performance of the optical filter of this kind. The above described embodiments of the display device according to the present invention can be similarly realized substantially as for all kinds of gas-discharge display devices. Particularly, as for the gas-discharge display device provided with the narrow area discharge electrodes, the efficient result can be obtained, since the inner absorption of emitted light is reduced. In this connection, the above effects of the present invention can be naturally attained regardless of the difference of the type of gas-discharge between the DC type and the AC type, as well as regardless of the sticking position of the fluorescent layer. Next, Fig. 13 shows an embodiment of the cathode ray tube display device applied with the present invention, in which the enlarged presentation is effected as for one element within the display panel thereof. In this one element separated from adjacent elements by white banks WB, a transparent cell glass CG is provided with a fluorescent layer Ph backed with an aluminum back AL on the rear surface thereof, meanwhile provided with a white wall material layer WW backed with a black material layer BM together with the central opening OP on the front surface thereof. In this embodiment, the light emitted from the fluorescent layer Ph excited by the scanning electron beam is passed through the opening OP toward the front view side just similarly as in the discharge cell of the gas-discharge display device, except that the inner space of the display element is filled with the transparent glass material. The reflectance inside the display element can be further increased by giving the filter performance at least to the opening portion OP of the cell glass CG. In addition, the present invention can be applied onto the display device utilizing the low velocity electron beam just similarly as described above, as well as naturally available for other kinds of display devices employing other kinds of light emitting elements including electroluminescent (EL) elements. Particularly, the structure of the display element as shown in Fig. 13 can be available for the other kinds of display devices. In this connection, in the situation where the light emitting element concerned is formed of a solid body such as an electrical bulb, the portion thereof corresponding to the portion CG as shown in Fig. 13 may be formed of a transparent material such as air, gas and plastics. By the way, it is efficient that the non-reflection coating or the non-glare treatment is additionally employed together with the above described structure as for the countermeasure against the exact reflection. At the last, Fig. 14 shows an embodiment of the display element in which the white bank WB provided for the separation from adjacent elements is shaped such as the corners thereof are made round, so as to reduce the light quantity lost at those corners. In this situation, it is required that the laminated layers of the round white bank WB are successively stacked on the inner surface of the front glass plate FG employed as for the substrate as shown in Fig. 14. In addition, when the rear end portion of the white bank WB is formed similarly as the front end portion thereof as described above, so as to shape the inner space of the display element as a sphere, the light quantity lost at the corner portions is further reduced, so as to realize the operation similar to that of the optical integrating sphere with the increased efficiency. On the other hand, the light emitting element employed for the display device according to the present invention can be provided not only with single opening, but also with plural openings, since the reflectance thereof can be sufficiently reduced, so far as the total area of these plural openings is not so large. By the way, in the display element provided with plural openings, the distance between displaying light dots is equivalently reduced, so that the dot interference conventionally caused in the displayed picture can be favorably reduced. In this connection, the position of these openings is not restricted to the central portion thereof, but also these plural openings can be arranged even in the corner portions of the display element. Next, the manufacturing materials and the manufacturing procedure of the aforesaid various embodiments provided for attaining the subsidiary object of the invention will be described hereinafter as for an example as shown in Fig. 10. Black glass paste used for forming the black light-absorbing material BM is printed on the inner surface of the front glass plate FG and fired. Thereafter, a material suitable for forming the cathode C and the cathode bus CB, for instance, Ni-paste is printed on the above black material layer BM and fired. Further thereafter, the white wall material WW and the white bank material WB are printed thereon and fired. As for these white glass materials WW and WB, the same materials as that used for the embodiment provided for attaining the principal object of the invention as shown in Figs. 3(a), 3(b) are favorably available. On the other hand, a material suitable for forming the anode A and the anode bus AB, for instance, Ni-paste printed on the inner surface of the rear glass plate RG and fired. Thereafter, the white wall material WW is printed on the above material and fired, the fluorescent layer Ph being printed further thereon and fired. The above described manufacturing process is principally effected by the printing. However, any other suitably selected manufacturing method, for instance, the adhesion methods including deposition and sputtering in combination with photoetching can be naturally employed under the application of respectively suitable materials. In this connection, the white wall material WW and the white bank material WB employed for the application onto the cathode ray tube display device are not restricted to the glass material, any other insulation materials and further electrically conductive materials, for instance, metals including Ag, Aℓ, which have sufficiently enough high reflectance for the white wall WW, being similarly available. As is apparent from the described above, according to the present invention, the luminous efficiency of the display device can be increased substantially by 50% in comparison with that of the conventional devices. Particularly, in the situation where the inner white reflector and the optical filter made of inorganic material are employed in common, the contrast of display can be remarkably increased on account of the sufficient suppression of the reflection of incident ambient light. Moreover, the light emitted from the fluorescent layer in the rear direction can be efficiently reflected by the inner white reflector toward the front view side, so that it is facilitated to emit the same light quantity through the less amount of fluorescent material. In addition, the present invention can be favorably applied onto the monochromatic display directly utilizing the colored light emitted, for instance, from the neon gas-discharge together with the optical filter for the colored light concerned. On the other hand, the remarkably high contrast of display can be realized also in the display device according to the present invention, since the low reflectance for the incident ambient light can be obtained by the light absorbing black material stuck on almost all front surface other than the opening areas for emitting the light. Moreover, this reflectance can be further reduced through the multiplexed effect obtained by the application of the color filter onto the opening for the colored light concerned, so that the contrast of display can be further increased. These evident effects of the present invention can be universally obtained as for various kinds of display devices similarly as described earlier.

Claims: A display device provided with a plurality of picture elements arranged in a plane each element being a cell having inner surfaces characterised by comprising, in each of said picture elements, a light-reflecting white layer (WG,WB) of glassy material comprising at least 20% by weight of glass powder 5% to 80% by weight of at least one kind of transparent powder material having a refractive index other than that of said glass powder whereby in case the transparent powder material is titanium oxide the range is 2% to 80% by weight, and optionally an amount of at most 0.1% by weight of black pigment, said light reflecting white layer (WG,WB) being formed on an inner surface of said picture elements by firing after applying said glass material. A display device as claimed in claim 1, wherein said display device is a gas-discharge display device. A display device as claimed in claim 1 or 2 wherein each of said picture elements comprises at least one optical filter (RF,GF,BF) made of inorganic material positioned for passing coloured light emitted in use by said picture element concerned. A display device as claimed in Claim 3, wherein each of said picture elements comprises a combination of said optical filter (RF,GF,BF) and a black mask (BM) provided with an opening positioned to define an area for emitting light for display. A display device as claimed in claim 2, wherein a fluorescent layer (Ph) is arranged on at least part of said light-reflecting white layer (WG). A display device as claimed in claim 1, wherein said light-reflecting white layer is at least partially constituted by a surface of a white bank (WB) formed of said glass material and arranged for mutual separation of said picture elements. A display device as claimed in claim 6, wherein a front end portion of said white bank (WB) is formed of black material (BM). A display device as claimed in any one of claims 1 to 7, wherein a layer of inorganic material (F) for passing a coloured light allotted to said picture element concerned is arranged on said light-reflecting white layer. A display device as claimed in any one of claims 1 to 8, wherein said glassy material (WG) is glazed onto a major surface of a supporting glass substrate (RG) at a temperature below 700°C. A display device as claimed in any one of claims 1 to 9, wherein said black pigment is contained in said glass powder in an amount of at most 0.1% by weight and belongs to a group consisting of at least iron oxide, chromium oxide, copper oxide, manganese dioxide, nickel oxide and cobalt oxide. A display device as claimed in any one of claims 1 to 10 wherein all filling material, including said transparent material for filling said glassy material has heat resistance to at least 700°C. A display device as claimed in any one of claims 1 to 11, wherein said glass material is formed by mixing said glass powder in an amount of 60% by weight, which consists of 63% PbO by weight, 15% SiO₂ by weight, 17% B₂O₃ by weight and 5% ZnO by weight, with rutile type titanium oxide in an amount 12% by weight and alumina powder in an amount of 28% by weight. A display device as claimed in any one of claims 1 to 11, wherein said glassy material is formed by mixing said glass powder in an amount of 80% by weight, which consists of 63% PbO by weight, 15% SiO₂ by weight, 17% B₂O₃ by weight and 5% ZnO by weight, with rutile type titanium oxide in an amount of 20% by weight. A display device as claimed in any one of claims 1 to 11, wherein said glassy material is formed by mixing said glass powder in an amount of 30% by weight, which consists of 77% PbO by weight, 2% SiO₂ by weight, 10% B₂O₃ by weight, 7% ZnO by weight, 3% Na₂O₃ by weight and 1% A ₂O₃ by weight, with zinc sulfide in an amount of 70% by weight. A display device as claimed in any one of claims 1 to 11 wherein said glass material is formed by mixing said glass powder in an amount of 80% by weight, which consists of 74% Bi₂O₃ by weight, 9% B₂O₃ by weight, 8% ZnO by weight, 6% SiO₂ by weight, 2% A ₂O₃ by weight and 2% NaO by weight, with anatase type titanium oxide in an amount of 8% by weight and zinc oxide in an amount of 10% by weight. A display device as claimed in any one of the preceding claims wherein the picture element is a light-emitting element and a light-absorbing material layer (BM) is arranged in front of each of said light-emitting elements except for the vicinity of an opening (OP) of said light-emitting element concerned and said light-reflecting white layer is arranged back to back with said light-absorbing layer. A display device as claimed in claim 16, wherein the inner side wall surfaces of said light-emitting elements are rounded.

Inventors: SAKAI, TETSUO C/O NIPPON HOSO KYOKAI TECHNICAL, WADA, MASATOSHI C/O OKUNO CHEMICAL IND. CO., LTD.
Applicants: NIPPON HOSO KYOKAI, OKUNO CHEMICAL INDUSTRIES CO., LTD.
Application year: 1985
Main classification: H01J17
IPC codes: H01J17