KR20010051401A - Color cathode-ray tube and manufacture for contrast improvement - Google Patents

Abstract

PURPOSE: A color CRT having improved contrast and a method of manufacturing the same is provided to improve contrast of the image formed on screen by reducing refractive index of faceplate in CRT. CONSTITUTION: A color CRT includes nearly flat faceplate(2) and periphery skirt(3). The faceplate(2) is connected to the funnel-shaped rear portion(4) of the CRT by glass-frit seal. An end portion of the CRT surrounds an electron gun(6) and beams emitted from the electron gun pass through a color selection mask(8) to radiate the screen of phosphors. A metal supporting elements(19,10,11,12) hold the mask with an exact distance from the screen inside of the CRT. Array of phosphors are disposed on the faceplate(2) to form a screen on the surface of the faceplate. Phosphors are laminated on the coating layer(22) formed of photo absorption materials.

Description

Color cathode ray tube with improved contrast and its manufacturing method {COLOR CATHODE-RAY TUBE AND MANUFACTURE FOR CONTRAST IMPROVEMENT}

The present invention relates to a method for producing a screen for color cathode ray tubes and a cathode ray tube incorporating such a screen. The present invention is particularly intended to improve the contrast of an image formed on a screen by reducing the reflectance of the cathode ray tube face plate.

In order to make possible and comfortable the visibility of the image formed on the cathode ray tube screen, it is necessary to increase the contrast of the screen under all illumination conditions that may occur in the home environment.

In order to improve the contrast of the image formed on the screen of the cathode ray tube, one commonly employed solution is to use a light impermeable carbon particle band matrix between the lines of luminescent materials that make up the screen. This structure has been improved by introducing screen faceplates made of glass with a small transmission coefficient. Moreover, this type of faceplate has a dark appearance when the cathode ray tube is turned off, which corresponds to the taste of the viewer. However, the use of glass with a small transmission coefficient actually involves many problems.

For example, the transmission coefficient should be adapted to the type of electron gun used and the dimensions of the cathode ray tube.

Moreover, current trends are directed towards cathode ray tubes with flatter face plates. That is, in order to mechanically withstand the vacuum present in the cathode ray tube, the thickness of the face plate is increased, especially at the corners. Therefore, there is a large thickness difference between the center portion and the corner portion of the face plate. As a result, in this type of cathode ray tube, it is impossible to use a glass having a transmittance too low because the light yield difference of the screen between the center and the edge becomes so obvious to the viewer.

In order to increase the contrast of the image, other techniques are used. For example, as disclosed in US Pat. No. 4,135,112, the use of a layer of filtering material between the inside of the screen and the luminescent material is complex and costly to implement. As disclosed in US Pat. No. 4,987,338, coating the outside of the screen with a layer of filter material is also costly and only applicable when the cathode ray tube is finished, furthermore the coating may be attacked by chemicals or Sensitive to abrasion

Therefore, there is a need to provide a solution that is simple to implement, not expensive, and that can reduce the reflectance of the cathode ray tube face plate to a predetermined value.

1 shows a cathode ray tube according to the invention, shown partially disassembled.

2 is a cross-sectional view of a video screen according to the prior art, made on the inner surface of a glass faceplate of a cathode ray tube.

3 is a cross-sectional view of an image screen according to the present invention.

Figure 4 is a view from above of the inner surface of the glass face plate of the cathode ray tube according to the present invention.

5 is a cross-sectional view showing the same inner surface in the present invention.

<Explanation of symbols for main parts of drawing>

22: coating

25: red phosphorus

26: blue phosphorus

27: green phosphorus

In the cathode ray tube according to the present invention, a glass face plate is included on an inner surface on which an array of phosphors is arranged to form a screen, and a coating of a light absorbing material is formed on the inner surface of the face plate. It is disposed between phosphorus to reduce the transmission coefficient of light passing through the face plate.

The invention and its advantages will be more clearly understood from the following detailed description with reference to the accompanying drawings.

As shown in Fig. 1, the cathode ray tube 1 according to the present invention includes a face plate 2 and a peripheral skirt 3 which are substantially flat. The face plate is connected to the funnel-shaped rear part 4 of the cathode ray tube by a glass-frit seal. The end 5 of the cathode ray tube surrounds the electron gun 6, and the beam from the electron gun passes through the color selection mask 8 to irradiate the screen of the phosphorous phosphor 13. Metal support members 19, 10, 11 and 12 support the mask at an exact distance from the screen inside the cathode ray tube.

Conventionally, colored cathode ray tubes include an array of phosphorous, which once emitted by an electron beam emitted by an electron gun emits light. The array includes red phosphorus, green phosphorus, and blue phosphorus, which represent the primary colors for producing a color image. The phosphorus is arranged in the form of continuous columns or in the form of dots of different colors arranged in a triangular structure. The technique of fixing the phosphor to the inner surface of the glass panel is in the form of photolithography, in which an array of three-color phosphorus is formed by exposing the photoresist layer to light passing through the aperture of the selection mask. Each array is developed and cured by firing to completely adhere to the glass substrate. In order to improve contrast and obtain good color separation, often a light impermeable material, such as a matrix of carbon particles, is pre-laminated onto a glass faceplate, and then an array of phosphorus is laminated to the opening of the matrix. 2 shows this structure in cross-sectional form. A matrix of carbon bands 21 is laminated on the inner surface of the face plate 2, followed by a column of red phosphorus 25, green phosphorus 26, and blue phosphorus 27. The entire assembly is then covered with an organic material film that serves as the substrate for the very thin metal coating 20. Such coatings, which are generally made of aluminum, have the function of reflecting light emitted by the luminescent material toward the viewer by the mirror effect to increase the brightness of the screen. In a subsequent manufacturing process step, the organic material film is removed by baking in a hot oven. The application of the prior art again poses a problem in new screens where the outer surface of the faceplate is substantially flat. In order to mechanically withstand the vacuum created in the cathode ray tube at the end of the manufacture, the flattening the faceplate should make the glass thicker. In order to avoid having to use an excessive amount of glass for reasons of cost or excessive weight while maintaining sufficient mechanical strength, the thickness of the faceplate can be varied with the thickness at the center portion less than the thickness at the edges. The use of glass with a low light transmission coefficient means that the passage of light through various areas of the screen becomes very uneven. This is because the damping effect is much smaller at the center than at thicker edges. As a result, the brightness of the screen becomes uneven and the edges and corners appear darker for the same energy provided by the phosphorus.

In the present invention, by laminating a coating of a light absorbing material before laminating phosphorus, glass having high transparency can be used as a base, and its appearance seen by the viewer can be modified. In this way, the light transmission coefficient of the face plate is deformed so that the coefficient becomes a desired value which is the light transmission coefficient of the face plate made of dark glass.

The use of such a coating is shown in FIGS. 3 to 5.

The coating 22 is laminated to the glass face plate 2 before the phosphor is deposited. This coating may be disposed on the matrix array 21 of the light impermeable carbon column or on the naked glass if the screen does not contain the matrix array 21. The solution used to form such a coating is an aqueous solution containing graphite in a suspension. It is preferable that the particles in the solution have a small diameter, which has several advantages as follows. In other words,

-The thickness of the layer can be finely controlled, so that the light transmittance of the face plate can be precisely controlled and the light transmittance can be adjusted to a desired value according to the thickness thereof.

The graphite particles fill the pores of the matrix array 21, the carbon particles having a larger diameter. As a result, the contrast of the screen is improved, and the graphite band appears blacker.

The interface created by the graphite coating 22 results in a smooth surface where the stack of phosphorus is better adhered directly to the carbon band of the matrix array 21. As a result, the weight of phosphorus used can be increased, increasing the image brightness on the screen without the fluorescent material falling off due to its weight.

For this reason, it is desirable to select a suspension that is in a distribution where the size of the graphite particles does not exceed 300 nm. The graphite used is selected, for example, from the CB family of products sold by Acheson Colloids. Preferred solutions to be used include conventional dispersants and surface active agents which are usually used in the manufacture of screens for cathode ray tubes.

Examples of solutions used to make the coating 22 are listed in the following table.

Concentration of substance Quantity of substance (× 10 kg) % Of substance in solution Graphite, 10% 500 0.5 Deionized water 8800 99.25 Dispersant, 1% 500 0.05 Surfactant, 10% 200 0.2

Various means may be used to laminate the solution to the inner surface of the faceplate. Spraying may be used, in which case the flow rate and number of passes through the inner surface determine the final thickness of the coating. This can be achieved by laminating at the center of the screen the amount of solution dispersed on the inner surface of the screen by centrifugal force, the initial amount of product and the centrifugal speed and time determine the thickness distribution of the coating deposited on the screen.

After lamination, the graphite suspension is dried, for example using a heating head that produces infrared radiation to form a coating 22.

In one advantageous embodiment, the thickness of the coating 22 is not uniform over the entire surface of the screen inner surface, but thicker at the center than at the edges and corners of the screen. As shown in FIGS. 4 and 5, the thickness of the coating 22 (as shown) when the thickness of the glass face plate 2 (shown with reference numerals 53 and 51) is greater at the corners than at the center of the screen. 50 and 52) are larger at the center than at the edge of the screen. In this way, the light transmittance of the face plate 2 becomes uniform, and the brightness of the screen during operation becomes uniform.

The ratio of the light energy transmitted through the faceplate to the square root of the reflectance coefficient of the faceplate (known as Brightness / Contrast Performance (BCP), usually measured at the center of the screen) is an index that must be kept large enough. . This represents a compromise between the fact that the faceplate must be sufficiently transparent to the light energy passing through the faceplate and that the screen's reflectance must be low enough to provide a contrasted image.

The measurements given in Table 2 below indicate that the use of the coating layer 22 does not affect the BCP. This is because, although the luminous efficiency of the image screen decreases with the graphite concentration of the coating, as a result the transmission coefficient of light through the faceplate decreases, this reduction is compensated for by the increased contrast resulting from the decrease of the faceplate reflectivity. to be. Accordingly, the BCP only changes slightly depending on the concentration of graphite added to the solution to form the coating 22, as the graphite concentration is about 0.03% to 0.9% by weight.

Graphite concentration (% by weight) Permeability of faceplate (%) Luminous Efficiency of Cathode Ray Tubes (lumen / W) BCP Center Corner 0.00 42.7 38.3 28.3 265 0.30 24.1 33.7 21.8 263 0.70 12.8 16.8 17.2 266

After drying the coating 22, the phosphorus of each primary color is continuously deposited on top of the coating in a conventional manner. This method of preparation provides the particular advantage resulting from the lamination of green phosphorus, blue phosphorus and red phosphorus in turn. This is because these phosphorus do not have the same efficiency, and for the same energy given by the corresponding electron gun, the efficiency of green phosphorus is largest, next blue phosphorus is large, and finally red phosphorus is large. Accordingly, in order to obtain a near-realistic white color, an electron beam must be modified in terms of energy so that color images can be faithfully reproduced. The modification of the electron beam is based on the ratio between the current to the beam coming out of the electron gun to obtain a faithful image, and is made by an additional electronic circuit.

The present invention makes it possible to omit the above modifications made to the beam current values because, in the manufacturing process, green phosphorus is first deposited, developed, and subsequently blue phosphorus and red phosphorus are subsequently sequentially stacked. After each development, the coating 22 exposed in the development step is slightly thin. Thus, in the same screen area, the coating 22 is thicker under the green phosphorus than under the blue phosphorus and thicker under the blue phosphorus than under the red phosphorus. This difference in thickness makes it possible to obtain almost identical light yields for all forms of phosphorus at a given beam current. As a result, the ratio of the beam current to produce white becomes close to actual 1, thereby eliminating the need for a circuit to modify the intensity of the beam.

Moreover, the present invention provides several solutions and advantages to related problems.

The fact that more permeable glass faceplates can be used is advantageous in the home environment and in the regeneration of end-of-life cathode ray tubes because the glass used contains less heavy metals used to darken the glass.

From an industrial point of view, the present invention allows some types of cathode ray tubes to be made of the same glass, providing flexibility and reducing manufacturing costs. Previously, each type of faceplate had to have permeability, for example, to its size and to the technology used inside the cathode ray tube. From now on, the final transmittance is obtained by adjusting the thickness of the coating 22. As a result, the faceplate stock can be handled more easily.

Moreover, the present invention is not limited to using the graphite solution in the suspension for forming the coating 22, and graphite is conveniently selected preferentially since this raw material is usually employed in the manufacturing stage of the cathode ray tube. Any other material that has the property of absorbing light can be used as an alternative material.

According to the present invention, there is provided a solution which is simple to implement and inexpensive, and which can reduce the reflectance of the cathode ray tube face plate to a predetermined value, so that the same light yield can be obtained in almost all parts of the screen, and the final transmittance Can be obtained by adjusting the thickness of the coating 22.

Claims (10)

In a cathode ray tube 1 comprising a glass face plate 2 on which an array of phosphors 25, 26, 27 is arranged to form a screen 13 on a surface, Cathode ray tube (1), characterized in that the phosphor is deposited on a coating (22) of light absorbing material. 2. Cathode ray tube (1) according to claim 1, characterized in that the coating (22) of light absorbing material is disposed on a light impermeable matrix array (21). The cathode ray tube (1) according to claim 1 or 2, characterized in that the thickness (50, 52) of the coating (22) of the light absorbing material is larger at the center than at the edge of the screen (13). Cathode ray tube (1) according to claim 1 or 2, characterized in that the light absorbing coating (22) is made of graphite particles. 5. Cathode ray tube (1) according to claim 4, characterized in that the majority of graphite particles have a dimension of less than 0.3 [mu] m. As a manufacturing method of the screen 13 for cathode ray tubes 1, Cleaning the inner surface of the front face plate 12 of the cathode ray tube; Laminating a particle suspension of a light absorbing material to the inner surface; Drying the suspension to form a continuous coating 22 of light absorbing material, Laminating at least one layer (25, 26, 27) of luminescent material on said coating Method for producing a screen (13) for the cathode ray tube (1) comprising a. The method of manufacturing a screen (13) for a cathode ray tube (1) according to claim 6, wherein said light absorbing material is graphite. The method of claim 7, wherein the suspension of graphite particles comprises a dispersant and a surface active agent diluted in water, the amount of graphite is 0.03% to 0.9% by weight of the screen 13 for the cathode ray tube 1 production of Way. The method according to claim 7 or 8, wherein the majority of the graphite particles have a size of less than 0.3 µm. 9. The production of the screen 13 for a cathode ray tube 1 according to claim 7, wherein the suspension of graphite particles is applied to the inner surface of the front face plate 2 of the cathode ray tube 1 by a spray method. Way.