US3725106A

US3725106A - Method and apparatus of making color cathode ray tube

Info

Publication number: US3725106A
Application number: US00085337A
Authority: US
Inventors: K Hosokoshi
Original assignee: Matsushita Electronics Corp
Current assignee: Panasonic Holdings Corp
Priority date: 1970-10-30
Filing date: 1970-10-30
Publication date: 1973-04-03
Anticipated expiration: 1990-04-03

Abstract

In order to avoid undesirable loss of color disparity in the performance of a cathode ray tube of the multi-beam, multi-color, shadow mask type, it is preferable to limit the diameter of each color dot on the phosphor screen. In the process of fixing phosphor dots on a phosphor screen inside a face plate of the cathode ray tube during the fabrication thereof, a specially shaped light-emitting source is employed, in order to limit the diameter of each phosphor dot to no larger than that of each aperture in the shadow mask through which ultraviolet rays strike the screen to fix said dot. The light-emitting source has a small light-emitting point on the top of the transparent light conduit, which conduit is provided eccentrically on a shaft so that it rotates around in a small circle in a plane parallel with the face plate.

Description

United States Patent 1 9] Hosokoshi 51 Apr. 3,1973

[54] METHOD AND APPARATUS OF MAKING COLOR CATHODE RAY TUBE [75] inventor: Kakulchiro llosokoshi, Neyagawa,

[21] App1.No.: 85,337

[30} Foreign Application Priority Data Oct. 30, 1969 Japan ..44/87363 [56] References Cited UNITED STATES PATENTS 3,527,652 9/1970 Sadao Ozaki et al 1 17/335 CM 3,109,116 10/1963 Epstein et a1 ..313/92 B X 3,499,372 3/1970 Staunton ..313l92 B X 3,581,136 5/1971 Staunton ..313/92 B X FOREIGN PATENTS OR APPLICATIONS 1,168,826 10/1969 Great Britain .....313/92 Primary Examiner-Alfred L. Leavitt Assistant Examiner-Kenneth P. Glynn Attorney-Craig, Antonelli & Hill [57] ABSTRACT In order to avoid undesirable loss of color disparity in the performance of a cathode ray tube of the multibeam, mul'ti-color, shadow mask type, it is preferable to limit the diameter of each color dot on the phosphor screen. in the process of fixing phosphor dots on a phosphor screen inside a face plate of the cathode ray tube during the fabrication thereof, a specially shaped light-emitting source is employed, in order to limit the diameter of each phosphor dot to no larger than that of each aperture in the shadow mask through which ultraviolet rays strike the screen to fix said dot. The light-emitting source has a small lightemitting point on the top of the transparent light conduit, which'conduit is provided eccentrically on a shaft so that it rotates around in a small circle in a plane parallel with the face plate.

2 Claims, 4 Drawing Figures METHOD AND APPARATUS OF MAKING COLOR CATHODE RAY TUBE This invention relates to an improvement in a method and apparatus for forming phosphor dots on the screen of a color cathode ray tube for use in a color television set.

BACKGROUND OF THE INVENTION Hitherto, in a color cathode ray tube of the multibeam, multi-color, shadow mask type, phosphor dots have been fixed in a particular array on the face of the tube by means of the photo-chemical fixing method, wherein an emulsion containing phosphor and photofixing agent is irradiated by ultraviolet ray beams transmitted through apertures in the shadow mask, as explained in US. Pat. No. 2,885,935 to D. W. Epstein et al. According to this conventional method, the phosphor dot is inevitably formed with a diameter larger than that of the aperture in the shadow mask through which ultraviolet rays strike the screen to fix said dot. Accordingly, the phosphor dots are of sufficient size to be tangent to each other. On account of this close proximity of the phosphor dots, even a slight drifting of the path of the electron beam may cause undesirable striking of adjacent color dots, resulting in lack of color disparity or inaccurate color expression.

In order to solve this problem, it is preferable to limit the diameter of each color dot so that the color dots are arranged with suitable spaces therebetween. However, such limiting of the diameter of these very small dots is very difficult, especially with presently known methods of fabrication.

In the conventional method of photo-chemical fixing of phosphor dots, a light source having a hemispherical light-emitting surface is employed to emit photochemical rays, such as ultraviolet rays, onto a screen coated with a phosphor slurry. Details of such process are described referring to FIG. land FIG. 2, wherein a phosphor-containing emulsion 9 applied on the inside face of the face plate 8 of a color cathode ray tube is struck by photo-chemical rays, such as ultraviolet rays 4', which are generated by an ultraviolet lamp 2 in a light box 1. The ultraviolet rays are then transmitted through the transparent lightconduit 3 in the light box 1 and are emitted from the hemispherical emitting face 4, so as to pass through the correcting lens 5 where they are suitably refracted. Finally, the rays pass through apertures 7 in the shadow mask 6, located at a specified distance inside the face plate 8, and strike the emulsion 9 in a pattern of dots. Details concerning the distribution of the ultraviolet rays on the emulsion 9, due to their passage through one of said apertures from said light-emitting surface, are shown in FIG. 2, wherein dimensions of parts and their arrangements as shown are exaggerated for the sake of easy understanding, and the correction lens 5 is omitted since it has no substan tial influence over the distribution of received rays.

As can be understood from FIG. 2, the emulsion 9 is struck by the ultraviolet rays 4' coming through each aperture 7, and the energy of the received rays is distributed in the form of a circular truncated cone, which cone is composed of a central part 10 and a surrounding outskirt part 10', the latter having an outer diameter larger than that of the aperture 7. The parts of the emulsion 9 thus exposed to the ultraviolet rays 4 are hardened by known photo-chemical reaction, and such hardnessdepends on the energy of the received rays. Accordingly, the central part of the exposed area acquires the greatest hardness 'and the hardness gradually diminishes towards the outskirt part of the dot until it becomes zero at the outmost boundary.

The exposed emulsion is then developed by being washed with a hot spray or a shower of washing liquid so as to retain dots at the exposed areas. In order to reduce the diameter of each dot, attempts have been made to remove the portion at the outskirt of each exposed area, where the hardness is comparably low, by applying a rather strong hot shower or spray thereto. However, since the portion at the outskirt of the exposed area has no critical zone where the hardness of the exposed emulsion changes abruptly, only the outermost part of the portion at the outskirt can be removed through the developing process, and in addition, the dots sometimes acquire a non-circular shape during such a process. Thus, it has hitherto been difficult to obtain phosphor dots with a diameter smaller than that of the apertures on the screen.

SUMMARY OF THE PRESENT INVENTION shaped light emitting source is employed in order to limit the diameter of each phosphor dot to a size no larger than that of each aperture in the mask through which ultraviolet rays strike the screen to fix the phosphor dot. i

BRIEF DESCRIPTION OF THE DRAWING Further objects and advantages of the present invention will be best understood from the following detailed description when read in conjunction with the accompanying drawings, in which:

FIG. 1 is an elevation, in section, of a photographic lighthouse having an optical system for use in making color cathode ray tubes, and a shadow mask and a screen plate of a color cathode ray tube set up thereon;

FIG. 2 is a partially schematic sectional view of the aforementioned prior art optical arrangement including a face plate, phosphor-containing emulsion, shadow mask, hemispherical faced light source top, together with a curve showing the distribution of the rays received by the emulsion; t

FIG. 3 is a detail view, partly in section, of a lightemitting source according to the present invention.

FIG. 4 is a partially schematic view of the embodiment of the present invention, in section, including a face plate, a phosphor-containing emulsion, a shadow mask and a specially designed light source, together with a curve showing the distribution of the rays received by the emulsion.

In FIGS. 2 and 4, the dimensions of the parts and arrangement thereof are not shown in exact proportions, but are exaggerated for the sake of easy understanding, and the correction lens is omitted since it has no substantial influence over the distribution of received rays.

DETAILED DESCRIPTION OF THE INVENTION In FIG. 3, the light conduit 11 in the light box 1 according to the present invention is made of a heat-resistive, transparent material of comparatively high refractive index, for example, quartz glass, and is shaped so as to have a small light-emitting point 12 on the top thereof and a light-intake face 17 at the bottom. The light conduit is eccentrically held on a rotating shaft 16 which is orientated so as to be substantially parallel with the axis of the face plate 8. Slightly below the top 12, a mask 11' is secured so as to block the ultraviolet rays of the lamp 2 from directly going out of the light box 1. A motor 15 is provided for driving the shaft 16 so as to rotate the light-emitting point 12 in a small circle in a plane parallel with the face plate 8. Similarly to what is shown in FIG. 1, a face plate 8 and a shadow mask 6 are mounted on a light house 1 which contains a correction lens and a light box 1. Phosphor-containing emulsion 9 applied on the inside face of the face plate8 is struck by photo chemical rays, such as ultraviolet rays 12", which are generated by the lamp 2 in the light box 1, and then are conducted through the light-conduit 11, so as to be emitted from the light-emitting point 12 rotating in the small circle. Next, the rays are suitably refracted by the correcting lens 5, and finally pass through aperture 7 in the shadow mask 6 located adjacent the face plate 8.

According to the present invention, the photochemical rays, such as ultraviolet rays 12', are emitted from the rotating light-emitting point 12, as shown in FIG. 4, and the emulsion 9 is struck by the ultraviolet rays 12 coming through each aperture 7. Accordingly, when rays emitted from the rotating light-emitting point 12 continue to strike the emulsion 9 for a duration of several revolutions of said conduit, the accumulated energy of the received rays becomes equivalent to the energy emitted from a continuous ring-shaped light source, having a diameter which is the same as that of the path of the point 12. Therefore, as can be understood from FIG. 4, the energy of the received rays is distributed in a pattern resembling a two-storied circular truncated cone, which cone is composed of a higher central part 14 and a surrounding lower outskirt part 14'. It is a feature of the present process that there is a considerable difference between the light energy level of the central part 14 and that of the outskirt part 14', separated by a distinctive circular edge 14" inbetween. The higher central part 14 has a diameter considerably smaller than that of the lower outskirt part 14'. Moreover, the diameter of the central part 14 is made smaller when the diameter of the path of rotation of the light-emitting point 12 is made larger. The parts of the emulsion 9 thus exposed to the ultraviolet rays 12' are hardened by known photo-chemical reaction, and such hardness depends on the energy of the received rays. Accordingly, the central part of the exposed area acquires the greater hardness and the hardness of the outskirt part of the dot is distinctly less than that of the central area.

The exposed emulsion 9 is then developed by being washed with a hot spray or shower of washing liquid so as to retain dots at the exposed areas. During such development, the less-hardened outskirt part of the exposed dot on the emulsion 9 is selectively removed.

Since the exposed area has a discontinuity at the circular edge 14", the outskirt part is removed smoothly, and the central part having a higher hardness is retained in a satisfactorily clear circle matching the circular edge 14". Thus, phosphor dots having a diameter smaller than that of the apertures, as well as a smooth round periphery, separated by considerable space inbetween, are obtained.

Since the diameter of the phosphor dots can be made smaller than that of the aperture of the shadow mask, according to the present invention, it is possible to make the aperture larger than the conventional ones so as to make the picture on the screen face brighter without creating a crowding between adjacent phosphor dots and consequent undesirable loss of color disparity and unwanted mixing of the emitter colors.

While I have shown and described one embodiment in accordance with the present invention, it is understood that the same is not limited thereto but is susceptible of numerous changes and modifications as known to a, person skilled in the art, and I therefore do not wish to be limited to the details shown and described herein but intend to cover all such changes and modifications as are obvious to one of ordinary skill in the art.

What is claimed is:

1. Method for making a color screen for a shadowmask type cathode ray tube comprising:

coating one inside face of the cathode ray tube with a photochemically hardenable phosphor-containing emulsion,

irradiating said coating through an apertured mask with photochemical rays emitted from a lamp source, said apertured mask being spaced away from said inside face, rotating said lamp source during said irradiating in a circle substantially parallel with said coating, wherein the diameter of said circle of rotation is larger than that of the apertures in said apertured mask so as to create a ray energy distribution pattern resembling a two-storied circular truncated cone,

controlling said irradiating and said rotating so as to achieve greater hardness of the coating areas exposed to the energy represented by the portion above the truncation of said truncated-cone energy distribution pattern than of the coating areas exposed to the energy represented by the portion below the truncation of said truncated-cone energy distribution pattern, and

washing said irradiated coating to remove all the areas thereof except said areas exposed to the energy represented by the portion above said truncation,

whereby the phosphor dots of the color screen are of a smaller diameter than the diameter of the apertures of said apertured mask. 9

2. Method as defined in claim 1, wherein said photochemical rays are ultraviolet rays.

Claims

2. Method as defined in claim 1, wherein said photo-chemical rays are ultraviolet rays.