Display element

Abstract: A display element structure comprises a condensing lens 36 provided with filter characteristics by being colored so that a separate filter is made unnecessary. This application also contains methods of producing the display element. Said condensing lens may be formed of glass colored with a mixture of cadmium sulfide, cadmium selenide, iron, chromium and neodymium oxides. Said lens may also be formed of plastic colored by anthraquinone and phthalorganine pigments.

Description: BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The present invention relates to a display element which forms a light source, for example, for a single cell of an outdoor large-scale display unit, and particularly to a color display element provided with a condensing lens. DESCRIPTION OF THE RELATED ART When a large-screen display unit is formed by arranging monochromatic display tubes each utilizing the light emitted from a fluorescent substance and serving as one pixel in the form of a matrix, it is difficult to improve the resolution because of the occurrence of spaces in the connection portions between the respective display tubes, and an increase in the resolution creates an increase in the production cost. For example, the composite display tube for a light source disclosed in Japanese Patent Laid-Open No. 62-10849 has been thus proposed. Figs. 1 to 3 are respectively a front view of the basic structure of such a composite display tube for a light source, a sectional view taken along the line II-II in Fig. 1 and a perspective view of a principal portion thereof. In the drawings, fluorescent screens 5R, 5G, 5B each serve as a single pixel and are arranged in a matrix of 3 x 3 in terms of pixel number. A case 1 comprises a front panel 2 made of a transparent member such as glass, a back panel 3 and a cylindrical side panel 4, the interior being in a vacuum state. Red (R) florescent screens 5R, green (G) fluorescent screens 5G and blue(B) fluorescent screen are arranged in the form of a matrix comprising 3 lines and 3 columns, as shown in Fig. 1, on the back side of the front panel 2. Accelerating electrodes 6 are respectively disposed in the peripheries of the fluorescent screens 5R, 5G and 5B in correspondence with the fluorescent screens. Back electrodes 10 for selecting a line are disposed on the inner side of the back panel 3 in a form with stripes corresponding to the line directions of the fluorescent screens 5R, 5G, 5B. Cathodes 7 are provided above the back electrodes 10 in correspondence with the respective fluorescent screen 5R, 5G, 5B. For example, an indirectly heated cathode in which an oxide is coated on an Ni sleeve, or a directly heated cathode in which an oxide is coated on tungsten is used as each of these cathodes. These cathodes 7 are also supported on the back panel 3 by supporting members 15a, 15b. Control grids 8 for controlling the columns are disposed between the fluorescent screens 5R, 5G, 5B and the cathodes 7 in a form with stripes corresponding to the column directions. Each of the control grids 8 is provided with holes 9 through which electron beams pass. The electron beams 11 are respectively emitted from the cathodes 7 and applied to the fluorescent screens 5R, 5G, 5B. A high voltage is supplied to each of anodes 6 from a terminal 16. A given voltage is supplied to each of the control grids 8 and the back electrodes 10 from terminal pins 12. In addition, a filter and a condensing lens are provided on the surface of the front panel 2, as shown in Figs. 4 and 5, so as to prevent any decrease in the contrast owing to the effect of external light (for example, the sunlight or the like) on the fluorescent screens. In Figs. 4 and 5, on the front panel 2 are provided a filter 13 comprising color filters 13R, 13G, 13B and a condensing lens 14 disposed on the color filters 13R, 13G, 13B, the condensing lens 14 provided with the filter 13 being bonded to the front panel 2 by an adhesive 18a. Fig. 5 shows the case 1 which is mounted on a substrate 17 and which has an interior provided with the cathodes 7, the control grids 8 and the back electrodes 10, which are not shown in the drawing, in the same way as in Fig. 2. A description will now be given of the operation of the conventional display element. When a negative potential relative to the cathodes 7 is applied to each of the back electrodes 10, since the periphery of each of the cathodes 7 is at a negative potential, the electrons emitted from each of the cathodes 7 do not flow to the control grids 8 and the accelerating anodes 6, thereby bringing the display element into a cut-off state. When a potential of 0 V or a positive potential of several V relative to the cathodes 7 is then applied to the back electrodes 10, the electron beam 11 is emitted from each of the cathodes 7 and flows toward the control grids 8. If the potential of the control grids 8 is negative relative to the cathodes 7, the electron beams 11 respectively cannot pass through the holes 9 and thus cannot reach the accelerating electrodes 6. If the potential of the control grids 8 is positive relative to the cathodes 7, the electron beams respectively pass through the holes 9 and are accelerated by the accelerating electrodes 6 and then applied to the fluorescent screens 5R, 5G, 5B which thus emit light. It is therefore possible to selectively emit light from the fluorescent screens 5R, 5G, 5B, which are disposed at the positions corresponding to the intersections between the back electrodes 10 and the control grids 8 to which voltages are applied by selectively applying a given voltage to the back electrodes 10 for selecting a line in the arrangement of the fluorescent screen 5R, 5G, 5B and the control grids for selecting a column. Further, if a large number of such display elements each serving as one cell are arranged to form a large screen, it is possible to form a color display comprising the fluorescent screens 5R, 5G, 5B each serving as a pixel. The conventional display element configured as described above has a problem in that, when the filter 13 and the condensing lens 14 are bonded to the surface of the front panel 2 by using the adhesive 18a, the bonding work cannot be easily performed in such a manner that the positions of the color filters 13R, 13G, 13B and the condensing lens 14 respectively agree with the positions of the fluorescent screens 5R, 5G, 5B, and thus easily produces deviations in the positions. US-4 451 759 discloses a flat viewing screen having a matrix of selectively addressable picture elements, but this does not include filters or a condensing lens. US-2 734 142 discloses a viewing screen for use in a conventional television, in which a zero-power lens is coloured, to improve image contrast. SUMMARY OF THE INVENTION The present invention has been achieved with a view to resolving the above-desribed problem. In this regard, the invention provides a display element according to Claim 1. Preferred features of the invention are set out in Claims 2 to 11. Such a display element provides a structure which makes the filter unnecessary by imparting filter characteristics to the condensing lens by coloring it, thus solving the above-described problem. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a plan view of a conventional display element; Fig. 2 is a sectional view taken along the line II-II in Fig. 1; Fig. 3 is an exploded perspective view of a principal portion of the display element shown in Fig. 2; Fig. 4 is a perspective view which shows the positional relationship of a filter to the fluorescent screens of the front panel shown in Fig. 1; Fig. 5 is a sectional side view of a principal portion in a state wherein the case shown in Fig. 2 is provided with a filter and a condensing lens; Fig. 6 is a front view of a display element of an embodiment of the invention; and Fig. 7 is a side view of the display element shown in Fig. 6 with a sectional part taken along the line XI-XI in Fig. 6. DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention provides a high-quality display element which can be easily produced at a low cost and which is provided with filter characteristics by being colored so that the filter provided in a conventional display element is made unnecessary. A display element according to the invention comprises a colored condensing lens which is provided on the emission surface of one emission element (emission means), in which red, green and blue pixels are respectively formed, for the purpose of condensing the light from each of the pixels. The condensing lens may be uniformly colored so as to have uniform transmission properties for light transmitted therethrough or colored so as to selectively transmit red, green and blue light therethrough. Alternatively, the condensing lens may be colored so that the colors in places corresponding to the respective pixels are different from each other. The display element is provided with the colored condensing lens on the emission surface of one emission element so that an image with high luminance and high contrast can be displayed without using the filter provided in a conventional display element. It is therefore possible to realize a high-quality display element at a low cost which can be easily produced. If a lens which is uniformly colored so as to have uniform transmission properties for light transmitted therethrough is used as the colored condensing lens, the intensity of the light emitted from each of the pixels is reduced once when it is transmitted through the condensing lens, while the intensity of external light is reduced twice at the times of incidence and reflection, thereby increasing the contrast between the states of full emission and non-emission. If a lens which is uniformly colored so as to selectively transmit red, green and blue color therethrough is used as the condensing lens, the condensing lens sufficiently transmits the light from each pixel therethrough, while most of the external light is absorbed twice, thereby increasing the contrast between the states of full emission and non-emission. Further, if the condensing lens is colored so that the colors in the places corresponding to the respective pixels are different from each other for selectively transmitting the light emitted from the pixels therethrough, the contrast is increased. Display elements representing embodiments of the invention are described below with reference to drawings. Figs. 6 and 7 are respectively a front view of a display element defining an embodiment of the invention and a side view thereof with a sectional part taken along the line XI-XI in Fig. 6. In the display element shown in the drawings, red, green and blue pixels 27R, 27G, 27B are formed on the front panel 2 of one emission element la so that an intended color is displayed on each of the pixels 27R, 27G, 27B by controlling the light emitted from the emission element. A condensing lens 36 is provided in front of the front panel 2 of the emission element la, the condensing lens 36 and the front panel 2 being bonded together by a transparent adhesive layer 37. The condensing lens 36 is formed by uniformly coloring glass or plastics to an achromatic grey by a dye or pigment so as to have no selective transmission properties but exhibit transmittance which is wholly reduced over the entire region of the visible light. For example, cadmium sulfide, cadmium selenide, iron oxide and chromium oxide may be mixed in a case of glass, and an anthraquinone pigment and phthalocyanine pigment may be mixed in a case of plastics. The transparent adhesive layer 37 is formed by using a silicone, acrylic, epoxy or polyester transparent adhesive so as to sufficiently transmit the light emitted from each of the pixels 27R, 27G, 27B therethrough. The transparent adhesive layer 37 serves to bond the emission element la to the condensing lens 36 and seal between the emission element 1a and the condensing lens 36 so as to prevent a reduction in the amount of the light emitted from the emission element la owing to a stain produced on the emission surface thereof by dust, particularly rain water and dirt when the display element is used outdoors, which enters between the emission element la and the condensing lens 36. Further, the use of the transparent adhesive which becomes soft after solidification causes the deformation of the condensing lens 36 produced by thermal stress after bonding to be absorbed by the transparent adhesive layer 37 and thus enables the condensing lens 36 to be prevented from separating from the emission element la. The function of each embodiment based on the above-described configuration will be described below with reference to Fig. 7. The color light emitted from each of the red, greed and blue sections, i.e., the pixels 27R, 27G and 27B (in Fig. 7, the pixels 27R, 27G), which are arranged in the form of a matrix, is transmitted through the transparent adhesive layer 37 in which the intensity is reduced in accordance with the transmission properties possessed by the color condensing lens 36, and then emitted to the outside. The light, for example, the sunlight, incident on the surface is reduced in intensity in accordance with the transmission properties possessed by the condensing lens 36, transmitted through the transparent adhesive layer 37 and reaches the surface of each of the pixels 27R, 27G, 27B. The light is then reflected from the surface of each of the pixels 27R, 27G, 27B, transmitted through the transparent layer 37 and through the condensing lens 36, in which the intensity is again reduced in accordance with the transmission properties possessed by the condensing lens 36, so as to be condensed, and then emitted to the outside. In other words, in this display element, the intensity of the color light emitted from each of the red, green and blue pixels 27R, 27G, 27B is reduced by the colored condensing lens 36 only once, while the intensity of the light incident on the surface of each of the pixels 27R, 27G, 27B, which is reflected and emitted to the outside, is reduced twice, whereby the luminance of the black color in which no light is emitted from each of the pixels 27R, 27G, 27B is reduced. This causes an increase in the contrast between the states of full emission and non-emission in each of the pixels 27R, 27G, 27B. The light emitted from each of the pixels 27R, 27G, 27B is also condensed in the direction to the front of the display element and colored by the action of the colored condensing lens 36 so that the reduction in the intensity produced when the light is transmitted through the condensing lens 36 is made up for, whereby the luminance in the direction to the front of the display element can be increased. A description will now be given of a display element defining a second embodiment of the invention. In this embodiment, the coloured condensing lens 36 shown in Figs. 6 and 7 is uniformly colored so as to selectively transmit red, green and blue light therethrough and is made of glass or plastics colored with one kind of dye or pigment or a mixture of several kinds of dyes or pigments. For example, in a case of glass, the condensing lens can be formed by using a mixture of neodymium oxide and chromium oxide. In the second embodiment, the color light emitted from each of the red, green and blue pixels 27R, 27G, 27B is transmitted through the transparent adhesive layer 37 and through the condensing lens 36 and projected to the outside. On the other hand, the light, e.g., the sunlight, incident on the surface, which is reflected therefrom and emitted to the outside, is reduced in intensity in accordance with the transmission properties possessed by the condensing lens 36, is transmitted through the transparent adhesive layer 37 and then reaches the surface of each of the pixels 27R, 27G, 27B. The light is then reflected from the surface of each pixel, transmitted through the transparent adhesive layer 37 and again through the condensing lens 36 in which the intensity is again reduced in accordance with the transmission properties possessed by the condensing lens, so as to be condensed, and then emitted to the outside. That is, in the display element of this embodiment, although the colored condensing lens 36 sufficiently transmits the color light emitted from each of the red, greed and blue pixels 27R, 27G, 273 therethrough, it absorbs twice the external light incident upon the surface of each pixel, which is reflected therefrom and emitted to the outside. It is therefore possible to reduce the luminance of black in which no light is emitted from pixels 27R, 27G, 27B in each of the pixels and thus increase the contrast between the states of full emission and non-emission in each of the pixels 27R, 27G, 27B. The light emitted from each of the pixels 27R, 27G, 27B is also condensed in the direction to the front of the display element by the action of the colored condensing lens 36, and the reduction in the intensity produced when the light emitted from each pixel is transmitted through the condensing lens 36 is made up for, thereby increasing the luminance in the direction to the front of the display element. A description will now be given of a third embodiment of this invention. In this embodiment, the colored condensing lens 36 shown in Fig. 6 and 7 is colored with dyes which are different in the places corresponding to the respective pixels so as to selectively transmit the light emitted from each of the red, green and blue pixels 27R, 27G, 27B therethrough. The condensing lens 36 is formed of glass or plastics which is colored by dyes so that the cores in the places corresponding to the respective pixels are different from each other. For example, in a case of glass, the condensing lens can be formed by using a mixture of cadmium sulfide and cadmium selenide in the portions corresponding to the red pixels, iron oxide and chromium oxide in the portions corresponding to the green pixels, and iron oxide and cobalt oxide in the portions corresponding to the blue pixels. In a case of plastics, the condensing lens can be formed by using an anthraquinone pigment in the portions corresponding to the red pixels, a phthalocyanine pigment in the portions corresponding to the green pixels, and a phthalocyanine pigment in the portions corresponding to the blue pixels. The condensing lens 36 can be formed by separately producing the portions corresponding to the pixels and, particularly, in a case of plastics, it can be formed by molding as one unit at a time by using a three-color molding machine. In this embodiment, the color light emitted from each of the red, greed and blue pixels 27R, 27G, 27B is transmitted through the transparent adhesive layer 37 and sufficiently transmitted through the condensing lens 36 and then emitted to the outside. On the other hand, the light, e.g., the sunlight, incident on the surface of each of the pixels 27R, 27G, 27B from the outside is reduced in intensity in accordance with the transmission properties possessed by the condensing lens 36, transmitted through the transparent adhesive layer 37 and reaches the surface of each of the pixels 27R, 27G, 27B. The light is then reflected from the surface of each of the pixels 27R, 27G, 27B, transmitted through the transparent adhesive layer 37 and again through the condensing lens 36 in which the intensity is reduced in accordance with the transmission properties possessed by the condensing lens 36, so as to be condensed, and emitted to the outside. Namely, in the display element in this embodiment, the colored condensing lens 36 sufficiently transmits the color light emitted from each of the red, green and blue pixels therethrough, but absorbs twice the light incident on the surface of each pixel from the outside which is reflected therefrom and emitted to the outside. Thus, the luminance of black in which no light is emitted from the pixels is reduced, thereby increasing the contrast between the states of full-emission and non-emission in each of the pixels. The light emitted from each of the pixels is condensed by the action of the colored condensing lens 36 in the direction to the front of the display element so that the reduction in the intensity produced when the color light emitted from each pixel is transmitted through the condensing lens 36 is compensated for, whereby the luminance in the direction to the front of the display element is increased. Although each of the above-described embodiments of the invention employs as a single element an emission element in the form of a matrix having a pixel number of 4 x 4 therein , the pixel number on the emission element may be m x n (m and n each denote an integer). As described above, in the invention, since the colored condensing lens for condensing the light from each pixel is provided on the front panel of an emission element, in which the red, green and blue pixels are formed, it is possible to obtain a high-quality display element at a low cost which has a high level of luminance, which is capable of displaying an image with high contrast and which can be easily manufactured. The use as the colored condensing lens a lens which is uniformly colored so as to have uniform transmission properties for light transmitted therethrough causes an increase in the contrast between the states of full-emission and non-emission. In addition, the use as the condensing lens a lens which is uniformly colored so as to selectively transmit red, green and blue light therethrough causes an increase in the contrast. If the condensing lens is colored so that the colors in the places corresponding to the respective pixels are different for selectively transmitting the light emitted from the pixels therethrough, the contrast can be increased in the same way as described above.

Claims: A display element comprising: emission means (1a) having a front panel (2) which is divided into a plurality of pixel units (27) for generating red, green or blue light and side panels, and selectively generating red, green or blue light from each of said pixel units (27) of said front panel (2); a condensing lens (36) provided in front of said front panel (2) of said emission means for the purpose of condensing the light generated from each of said pixel units (27) of said front panel; and a soft and transparent adhesive layer (37) which causes said condensing lens (36) to be bonded to said front panel (2) of said emission means (1a) characterised in that the said condensing lens (36) is colored so as to improve the contrast by transmitting the colored light emitted from each of said pixel units (27) and reducing the effect of external light. A display element according to Claim 1, wherein said condensing lens (36) is uniformly colored so as to have uniform transmission properties for all types of light transmitted therethrough. A display element according to Claim 2, wherein said condensing lens (36) is uniformly colored achromatic grey. A display element according to Claim 3, wherein said condensing lens (36) is formed by glass colored with a mixture of at least one of cadmium sulfide, cadmium selenide, iron oxide and chromium oxide. A display element according to Claim 3, wherein said condensing lens (36) is formed of plastics colored with a mixture of at least one of anthraquinone pigments and phthalocyanine pigments. A display element according to Claim 1, wherein said condensing lens (36) is uniformly colored so as to selectively transmit only light which is red, green or blue. A display element according to Claim 6, wherein said condensing lens (36) is formed of glass or plastics colored with a mixture of at least one dye or at least one pigment. A display element according to Claim 7, wherein said condensing lens (36) is formed of glass colored with a mixture of neodymium oxide an chromium oxide. A display element according to Claim 1, wherein said condensing lens (36) is colored into different colors in places corresponding to said respective pixel units (27) so as to selectively transmit light of red, green or blue generated from each of said pixel units (27) of said front panel (2) of said emission means (1a). A display element according to Claim 9, wherein said condensing lens (36) is formed of glass in which the portions corresponding to said red pixel units (27) are colored with a mixture of cadmium oxide and cadmium selenide, the portions corresponding to said green pixel units (27G) are colored with a mixture of iron oxide and chromium oxide, and the portion corresponding to said blue pixel units (27B) are colored with a mixture of iron oxide and cobalt oxide. A display element according to Claim 9, wherein said condensing leans (36) is formed of plastics in which the portions corresponding to said red pixel units (27R) are colored with a mixture of anthraquinone pigments, the portions corresponding to said green pixel units (27G) are colored with a mixture of phthalocyanine pigments, and the portions corresponding to said blue pixel units (27B) are colored with a mixture of phthalocyanine pigments.

Inventors: FUTATSUISHI SHUNICHI, HARAGA KOHSUKE, NAKANO MASAAKI, SANOH MUNEHARU, TAKATANI SHIROH, TANI NAOKI, UESAKA KAZUO, UGAI YOSHIKAZU, FUTATSUISHI, SHUNICHI, HARAGA, KOHSUKE, NAKANO, MASAAKI, SANOH, MUNEHARU, TAKATANI, SHIROH, TANI, NAOKI, UESAKA, KAZUO, UGAI, YOSHIKAZU, Futatsuishi, Shunichi, c/o Nagasaki Seisakusho of, Haraga, Kohsuke, c/o Zairyo Kenkyusho of, Nakano, Masaaki, c/o Sangyo Shisutemu Kenkyusho of, Sanoh, Muneharu , c/o Zairyo Kenkyusho of, Takatani, Shiroh, c/o Zairyo Kenkyusho of, Tani, Naoki, c/o Nagasaki Seisakusho of, Uesaka, Kazuo, c/o Zairyo Kenkyusho of, Ugai, Yoshikazu, c/o Seisangujutsu Kenkyusho of
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1989
Main classification: G09F9
IPC codes: H01J31, H01J29