JPH0917350A - Fluorescent screen of cathode-ray tube having high resolution - Google Patents

Abstract

PURPOSE: To obtain a clear image in which a void is reduced and there is no irregular distribution in light emitting brightness by precipitating and accumulat ing phosphor particles suspended in a polyvinyl alcohol aqueous solution. CONSTITUTION: Phosphor particles are suspended in a polyvinyl alcohol aqueous solution having the concentration of 0.02 to 0.5wt.% and pH of 6.0 to 7.5, and a suspension is obtained. This suspension is injected into a cathode-ray tube vessel, and is rotated at high speed, and after the phosphor particles are accumulated on a face plate, a supernatant is removed and the resulting accumulative is dried.

Description

Detailed Description of the Invention

The present invention relates to a fluorescent film for a cathode ray tube.

[Prior Art] A fluorescent film whose resolution of a cathode ray tube is mainly determined by an electron beam diameter is made of a powder fluorescent substance which emits light of a single color. An established method of making a monochromatic phosphor film in a cathode ray tube using a powder phosphor is to first disperse the powder phosphor in an aqueous solution of potassium silicate to make a suspension of the phosphor. Separately from this phosphor suspension, a solution containing an electrolyte such as barium acetate or barium nitrate is placed in the glass container of the cathode ray tube. The suspension of the phosphor is showered and uniformly poured into the electrolyte solution in the cathode ray tube. When the phosphor suspension and the electrolyte solution are mixed, the potassium silicate and the electrolyte in the suspension cause an electrochemical reaction, the potassium silicate is decomposed, and the silicon oxide gel is released into the solution. The liberated silicon oxide gel is physically adsorbed on the surface of each phosphor particle. The phosphor particles having the silicon oxide gel attached to the surface settle in the solution toward the glass substrate. The fluorescent film is formed by the natural deposition of the sedimented particles. The silicon oxide adsorbed on the surface of each phosphor particle acts as an adhesive between the phosphor particle and the glass substrate, and firmly adheres the phosphor particle to the glass substrate surface. The function of the silicon oxide gel is generally overlooked, but it does not only attach the phosphor particles to the substrate. The silicon oxide gel adsorbed on the surface of each particle also binds to the silicon oxide gel on the surface of another phosphor particle that has settled in the solution. As a result, the phosphor particles that have settled in the solution are aggregated in various sizes. Since the agglomerated particles are equivalent to the large particles having a large weight, the agglomerated particles settle down considerably faster than the sedimentation rate of the primary particles and are deposited on the substrate. The fast sedimentation of the phosphor particles is an advantage in terms of the production efficiency of the phosphor film, but is a disadvantage in the property of the phosphor film. As a result of depositing aggregated particles of various sizes on the substrate, many large voids are formed in the fluorescent film due to coarse filling of the aggregated particles. The presence of large voids not only reduces the disconnection of the image on the fluorescent film, but also thickens the fluorescent film that provides optimum brightness.

In many cases, the phosphor particles that emit light from the fluorescent film upon irradiation with an electron beam are particles arranged in the first layer when viewed from the electron beam irradiation side, and are interposed between the light emitting particles and the substrate. The particles act as a scattering medium for the emitted light. Bright phosphor screens are thus obtained with phosphor films with as few scattering media as possible. The light emitted from the phosphor particles arranged on the surface of the fluorescent film is reduced by the light scattering in the fluorescent film and then emerges from the substrate side. Since the light refractive index of the phosphor particles is large, the light scattering in the phosphor film is mainly reflected by the surface of the phosphor particles, not by the light absorption by the phosphor particles interposed between the phosphor film and the substrate. If the fluorescent film has a large void, the void serves as a channel for reflected light, so that the spread of light scattering increases in proportion to the size of the void. As a result, the image displayed on the fluorescent film with many voids is blurred. A fluorescent film with a good image cut can be obtained only by a fluorescent film with few voids.

For the purpose of reducing the porosity in the fluorescent film, a method of applying a centrifugal force to the particles settling in the suspension has been developed. Voids are reduced using this method. However, since the aggregated particles formed during the sedimentation do not change, the thickness of the obtained fluorescent film becomes irregular as shown in FIG. Since the change in the thickness of the fluorescent film corresponds to the change in the number of layers of the phosphor particles, the intensity of the light extracted from the fluorescent film is observed as an irregular change in luminance depending on the location in the fluorescent film. That is, the brightness of the thick portion of the fluorescent film becomes dark. The image on the fluorescent film becomes unsightly due to the irregular distribution of the brightness of the fluorescent film, which causes defects in the fluorescent film, which must be avoided.

[Problem to be Solved by the Invention] A problem to be solved is a fluorescent film for a cathode ray tube produced by a sedimentation method, which produces a clear image with extremely few voids and no irregular distribution of emission brightness. The present invention provides a fluorescent film for a cathode ray tube.

[Means for Solving the Problems]

When the fluorescent film produced by the sedimentation method is carefully observed, the cause of the formation of voids and the irregular thickness of the fluorescent film is that the particles settled in the above-mentioned solution are aggregated. I understand that. Therefore, it can be seen that the solution to the problem can be solved by allowing the particles that have settled in the solution to settle without agglomerating and depositing them on the substrate. Examination of each process of sedimentation reveals that the phosphor particles are dispersed in the potassium silicate solution as primary particles which are close to ideal. Aggregation of the phosphor particles occurs when potassium silicate is mixed with an electrolyte solution having an electrochemical reaction. So, without using the electrolyte solution,
If the phosphor particles are allowed to settle, only the primary particles should be deposited on the substrate, and a fluorescent film without aggregation should be obtained. In fact, when the electrolyte solution is not used, the sedimentation rate of the particles becomes extremely slow, but a fluorescent film having a flat thickness is obtained. However, the fluorescent film has weak adhesion of the fluorescent particles to the glass substrate surface, and in the subsequent metal back process, the fluorescent particles easily fall off the substrate or the structure of the fluorescent film is destroyed and damaged. To do. As a result, even if the fluorescent film can be applied, the fluorescent film is not practical. In order to obtain a practical fluorescent film, the phosphor particles must firmly adhere to the glass substrate.

In order to firmly adhere the phosphor particles settled and deposited on the substrate to the substrate glass, an adhesive may be attached to the surface of each phosphor particle deposited and deposited. Such adhesives include organic compounds. In order to attach the adhesive to the surface of each particle in a thin film having a uniform thickness, the phosphor particles are suspended in a solution of an organic compound in which the phosphor particles are well dispersed, and then the phosphor particles are dried. Is uniformly attached to the surface of the phosphor particles as a thin film. In a solution containing an adhesive, phosphor particles must be dispersed as primary particles. Moreover, it is desired that the substance serving as an adhesive does not remain in the cathode ray tube when the production of the cathode ray tube is completed. Therefore, the selection criteria for the organic compound solution are as follows. (1) In the solution of the organic compound, the phosphor particles are dispersed by the primary particles, (2) when the phosphor film is dried, the phosphor particles are firmly adhered to the glass substrate surface,
(3) The organic compound used is completely decomposed by heating in the manufacturing process of the cathode ray tube, and the decomposed product does not remain in the manufactured cathode ray tube. Polyorganic vinyl alcohol (hereinafter P
Abbreviated as VA) and nitrification cotton which is soluble in a solvent of an ester such as acetic acid ester or a solvent of a ketone such as acetone. For mass production of the fluorescent film, it is more advantageous to use water than to use an organic solvent, and thus PVA is advantageous. The following description is an example of forming a fluorescent film using PVA, but the present invention is not limited to the following description and includes the use of nitrified cotton.

Depending on the concentration of PVA, a solution of PVA can be made from a solution having a very high viscosity to a solution having a viscosity close to that of water. In order to use the PVA solution in the sedimentation method, it is advantageous in terms of production to make the viscosity of the PVA solution as thin as possible in order to shorten the sedimentation time of the phosphor particles.
According to the empirically obtained result, the concentration of PVA should not exceed 0.5% by weight. The lower limit of the PVA concentration is the concentration at which the surface of each deposited phosphor particle is completely covered with a thin film of PVA. The lower limit concentration at which the surface of each phosphor particle is covered with PVA can be determined as follows. The applied phosphor film is dried, and the phosphor particles in the phosphor film are observed with an optical microscope having a magnification of 300 times or more. PVA on the surface of phosphor particles
When the thin film is formed, light interference fringes are observed on the flat surface of each phosphor particle. If the concentration is equal to or higher than the concentration at which interference fringes are observed, the phosphor particles adhere firmly to the substrate. The lower limit concentration of PVA obtained empirically is 0.02% by weight. Therefore, P in the range of 0.02 to 0.5% by weight
VA solution can be used. PVA in such concentration range
Since the viscosity of the solution is higher than that of water, the settling time of the phosphor particles on the substrate glass becomes long. Since there is no difference in the obtained fluorescent film even when centrifugal force is applied for the purpose of shortening the sedimentation time of the phosphor particles, the centrifugal sedimentation method can be applied to the application of the fluorescent film. In that case, the upper limit concentration of PVA can be increased to 0.5% or more, but there is no advantage due to the increase of the PVA concentration, so a PVA concentration of 0.5% or less is recommended.

The PVA aqueous solution has a pH of 6.0 to 7.5.
When it is in the range, it acts as a good dispersant for many phosphor particles. When the pH value is lower or higher than the above range, the phosphor particles aggregate. When the pH value is adjusted to the above range, the phosphor particles are completely dispersed in the PVA solution without using a special surfactant for preparing the PVA-phosphor suspension. The above statement does not prohibit the use of surfactants. As shown in FIG. 2, there is no accumulation by aggregated particles in the fluorescent film formed by sedimentation of completely dispersed fluorescent material particles, so that there are no large voids. This fact can be confirmed by observing the cross section of the fluorescent film with the SEM. Although it is difficult to clearly show in the SEM photograph, the phosphor particles are arranged with a slight gap between the particles.
In the obtained fluorescent film, the fluorescent film is pressed with a press in order to further reduce the gaps between the particles. Then, a phosphor film in which the phosphor particles are well adhered is obtained, but the brightness of the phosphor film is significantly reduced. From the above results, in order to cause the fluorescent film to emit bright light, it is a necessary condition that the phosphor particles forming the fluorescent film do not adhere to each other and are arranged with a certain interval. The fluorescent film obtained by the centrifugal sedimentation method satisfies this condition. Experiments using a pressing machine have shown that in order to further improve the brightness of the phosphor film, it is preferable to remove the fine phosphor particles filling the spaces between the phosphor particles. In fact, the brightness of the phosphor film is improved by using the manufactured powder phosphor in which the fine particles of about 25% by weight distributed on the particle size side having a small particle size distribution are removed. Since the fine particles in the fluorescent film do not contribute much to light emission and act to scatter the emitted light, removing the fine particles also improves the resolution of the fluorescent film.

The brightness of the fluorescent film, which is optimized in resolution, is also optimized. The optimized fluorescent film is a fluorescent film in which the interposition of phosphor particles, which do not participate in light emission and only play a role of scattering light, between the light emitting particles and the glass substrate is minimized. A phosphor film so optimized is theoretically made of 1.5 layers of phosphor particles. However, it is extremely difficult to physically form a fluorescent film of 1.5 layers. Practically, it is sufficient if the grain arrangement of 2.5 layers or less in the SEM cross-sectional photograph. In order to apply such a thin phosphor film on a substrate with high accuracy and uniform thickness, the amount of PVA-phosphor suspension and the powder in the suspension are poured into a cathode ray tube container having a given substrate area. It can be realized by controlling the amount of phosphor. By controlling such simple items, a fluorescent film having a uniform film thickness can be obtained with good reproducibility. The fluorescent film according to the present invention is not only used as a fluorescent film of a cathode ray tube,
Needless to say, it can be used as a fluorescent film of any display device that emits an electron beam to display an image on the fluorescent film. The contents of the present invention will be described in more detail below with reference to an example in which a fluorescent film is formed on a 1.5-inch cathode ray tube.

Example First, the treatment of the powder phosphor to be used is started. A commercially available white phosphor (Y ₂ O ₂ S: Tb: Eu) having an average particle diameter of 3.0 μm (microscopic method) is obtained. Since commercially available phosphor contains a large amount of fine particles, it is necessary to remove these fine particles.
Use a water sieve to remove fine particles efficiently. The water sieving method is as follows. 400 cc of deionized water containing 100 g of the obtained phosphor in a 500 cc container
Disperse in. When this suspension is left to stand, the particles settle down to the bottom of the container in order from the largest particles according to Stokes' law. From Stokes' law, the time required for particles of 1.5 μm to settle 10 cm from the surface of the suspension was calculated to be 3
8 minutes. 38 minutes after leaving the suspension, remove the liquid up to 10 cm from the surface of the suspension using a siphon. The removed liquid contains only particles of 1.5 μm or less. Since fine particles are still contained in the suspension remaining in the container and the settled phosphor, deionized water is added to the suspension again, and the above operation is repeated. When the number of repetitions of the operation is 5 times or more, the fluorescent substance in which the particles of 1.5 μm or less are substantially removed remains in the container. The target phosphor powder is obtained by drying the phosphor remaining in the container at 110 ° C.

Next, an aqueous solution having a PVA concentration of 0.10% by weight is prepared. When fresh deionized water is used, since the pH value is around 7.0, it is not necessary to adjust the pH value. When 1000 cc of the PVA solution described above was put in a container and 0.5 g of the powder phosphor was gradually added while gently stirring, PVA in which phosphor particles were well dispersed was added.
-A phosphor suspension is formed. 10 cc of this suspension is taken and poured into a 1.5-inch cathode ray tube container having a plane area of 8 cm ² . When the cathode ray tube container is rotated at a high speed of 2000 rpm for 10 minutes, phosphor particles are uniformly deposited on the face plate at a rate of 0.5 mg / cm ² .
When the cathode ray tube container is gradually tilted to remove the supernatant liquid, the fluorescent film remains on the face plate. Fluorescent film 110 ℃
When dried with, the phosphor particles firmly adhere to the face plate. When the cross section of the obtained fluorescent film is observed by SEM, the fluorescent film shown in FIG. 2 is obtained. Since the fluorescent film has a high adhesion strength, the fluorescent film is not damaged in any subsequent manufacturing process of the metal back.
The thin film of PVA attached to the surface of the phosphor particles as an adhesive is completely decomposed and removed into water and carbon dioxide gas by the heating applied in the subsequent manufacturing process of the cathode ray tube. Does not remain. When an electron gun is attached to this cathode ray tube container and a predetermined exhaust process is added,
A 1.5 inch cathode ray tube is obtained. Since the image on the fluorescent film of the cathode ray tube is cut off well, the cathode ray tube clearly shows an image with high resolution.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a phosphor film manufactured by a conventional method.

FIG. 2 is a sectional view of a fluorescent film according to the present invention.

[Explanation of symbols]

 1 is a glass substrate which becomes a festival plate 2 is phosphor particles

Claims (3)

[Claims] 1. A fluorescent film for a cathode ray tube, characterized in that the fluorescent film made of a powdered fluorescent substance disposed inside the cathode ray tube is composed of particles physically arranged in two layers or less. 2. Fluorescent light of a cathode ray tube according to claim 1, wherein the fluorescent film is made of a phosphor powder that does not contain fine particles that fill the particle gaps in the fluorescent film. film. 3. The fluorescent film defined in claim 1 and claim 2, characterized in that the fluorescent film is formed by sedimentation of phosphor particles suspended in an aqueous solution of poly (vinyl alcohol). Fluorescent film of cathode ray tube.