GRUNDIG SUPER COLOR A4205 SERIE S1618 CHASSIS CUC120 CRT TUBE HITACHI 470NAB22-TC01.

 CRT TUBE HITACHI  470NAB22-TC01. Self-converging deflection yoke:

 A deflection yoke for use with a picture tube of a television receiver. A vertical deflection coil of the deflection coil has a larger winding angle on an electron gun side thereof than on a screen side thereof. A magnetic material piece is disposed inside the vertical deflection coil so that a vertical deflection magnetic field is formed into a strong barrel magnetic field on the electron gun side. As a result, a raster scanned on a faceplate of the picture tube is free from misconvergence and pincushion distortion. A core of the deflection yoke has sawtooth-shaped end surfaces, or auxiliary rings having sawtooth-shaped end surfaces are disposed on the end surfaces of the core. As a result, a wire of the vertical deflection coil is prevented from slipping on the end surfaces of the core although the wire of the vertical deflection coil is wound at a large winding angle on the electron gun side.

 1. A deflection yoke for a television receiver comprising:
a horn-shaped core having a larger opening and a smaller opening;
a horizontal deflection coil disposed inside said core;
a vertical deflection coil wound on said core so as to produce a pincushion shape magnetic field at said larger opening and a barrel shape magnetic field at said smaller opening with a winding angle of said vertical deflection coil at said smaller opening of said core being larger than a winding angle at said larger opening; and
a magnetic material piece disposed inside said vertical deflection coil at a position, on said vertical deflection coil, close to said smaller opening.


2. A deflection yoke according to claim 1, wherein said magnetic material piece is bonded to said vertical deflection coil.

3. A deflection yoke according to claim 1, wherein said magnetic material piece is attached to a separator.

4. A deflection yoke according to claim 1, wherein said magnetic material piece is an iron plate.

5. A deflection yoke according to one of claims 1, 2, 3 or 4 wherein said magnetic material piece is disposed at a position separated from said larger opening by 1/2-3/4 of a distance between said larger opening and said smaller opening.

6. A deflection yoke according to one of claims 1, 2, 3 or 4, wherein the width of said magnetic material piece is equal to 1/5-1/2 of the distance from said larger opening to said smaller opening of said core and the length of said magnetic material piece is chosen such that an angle looking into said magnetic material piece from the center of said deflection yoke is equal to 30°-70°.

7. A deflection yoke according to claim 1, wherein auxiliary rings, each having end surfaces formed into sawtooth shape, are attached to end surfaces of said core at said larger opening and said smaller opening to prevent a wire of said coil from slipping, said vertical deflection coil being wound on the sawtooth portions of said auxiliary rings.

8. A deflection yoke according to claim 1, wherein end surfaces of said larger opening and said smaller opening of said core are notched in sawtooth shape to prevent a wire of said coil from slipping, said vertical deflection coil being wound on the sawtooth portions of said end surfaces.

9. A deflection yoke according to claims 2 or 3, wherein said magnetic material piece is rectangularly shaped.

10. A deflection yoke according to claims 7 or 8, wherein said sawtooth shape includes small areas about which said wire of said coil is wound, each of said small areas defining a plane which is normal to said wire of said coil, whereby the tensile force acting on said wire is normal to said plane so as to prevent slipping of said wire.

Description:

FIELD OF THE INVENTION
The present invention relates to a deflection yoke for a color television receiver, and more particularly to a deflection yoke capable of reducing a pincushion distortion of a raster scanned on a faceplate of a picture tube.
In a conventional television receiver, a raster scanned on the faceplate of the picture tube includes much distortion and nonconvergence. In a self-converging deflection yoke for a color picture tube having inline electron guns, convergence is compensated by forming a magnetic field generated by a horizontal deflection coil into a pincushion field and forming a magnetic field generated by a vertical deflection coil into a barrel field, as is well known in the art. Accordingly, as for the pincushion deflection distortion (hereinafter referred to simply as pincushion distortion) at the left and right edge of a screen of a color television receiver, in addition to an inherent pincushion distortion due to a radius of curvature of the picture tube, a further pincushion distortion is added by the fact that the vertical deflection magnetic field is formed into an intensified barrel field in order to compensate for the convergence, resulting in the movement of electron beam normal to magnetic line of force created by the vertical deflection coil. A pincushion distortion compensation circuit is, therefore, usually provided to compensate for such pincushion distortion at the left and right edge of the screen. In order to simultaneously compensate for the convergence and the pincushion distortion by a deflection coil only, without using the pincushion distortion compensation circuit, it is necessary to form that portion of the vertical deflection magnetic field which faces the screen into a pincushion shape to compensate for the pincushion distortion, and at the same time to form that portion of the vertical deflection magnetic field which faces the electron guns into a barrel shape which is intensified enough to balance out the pincushion magnetic field on the screen side, to compensate for the convergence.
FIG. 1 shows a perspective view of a deflection yoke. A major section of the deflection yoke 1 includes a saddle-shaped horizontal deflection coil 2, a toroidal vertical deflection coil 3, a core 4 and a separator 5.
FIGS. 2A and 2B show the vertical deflection coil 3 which forms a pincushion magnetic field on the screen side and an intensified barrel magnetic field on the electron gun side. FIG. 2A is a perspective view and FIG. 2B is a front view. A feature of the vertical deflection coil 3 resides in that a winding angle φ₂ of a coil 6, wound on the core 4, at a larger opening 4a located on the screen side is smaller than a winding angle φ₁ at a smaller opening 4b located on the electron gun side. A drawback of this vertical deflection coil 3 resides in that a wire 7 is apt to slip on the surface of the core 4 and hence it is difficult to attain proper winding angles φ₁ and φ₂ because the wire 7 of the coil 6 wound at positions having larger winding angles φ₁ and φ₂ is wound obliquely to the core 4.
In the vertical deflection coil used for a picture tube having a large pincushion distortion such as a wide deflection angle picture tube, e.g. 90° deflection picture tube, the winding angle φ₁ of more than 150° and the winding angle φ₂ of approximately 80° are required. Therefore, the wire 7 wound at the position of the winding angle φ₁ is especially apt to slip. It is, therefore, necessary to form the magnetic field on the electron gun side into an intensified barrel field without increasing the winding angle φ₁ at the opening 4b located on the electron gun side to over 150°.

SUMMARY OF THE INVENTION
It is an object of the present invention to provide a deflection yoke having means for producing an intensified barrel magnetic field without materially increasing a winding angle at a smaller opening.
It is another object of the present invention to provide a deflection yoke in which a wire wound at a large winding angle position does not slip on a surface of a core.
The deflection yoke in accordance with the present invention comprises a vertical deflection coil having a smaller winding angle at a larger opening than a winding angle at a smaller opening, and a magnetic material piece disposed inside the vertical deflection coil. The deflection yoke of the present invention further includes a core having its end surfaces deformed or auxiliary ring for locking the wire. The deformed end surfaces of the core or the auxiliary ring are notched in sawtooth shape to prevent the wire of the vertical deflection coil from slipping.
When the magnetic material piece is disposed inside the vertical deflection coil, the shape of the vertical deflection magnetic field changes. Since the lines of magnetic force around the magnetic material piece pass in the body of the magnetic material piece or attracted thereto, the barrel magnetic field is further enhanced. Where the barrel magnetic field is enhanced, the pincushion magnetic field may be formed on the screen side. Accordingly, the pincushion distortion can be relieved.
If the end of the end surface of the core is normal to the wire of the vertical deflection coil, a force acting on the wire is normal to the end of the end surface and the slip of the wire on the end surface is prevented. The core of the deflection yoke of the present invention has its end surfaces notched in the sawtooth shape and the ends of the notched end surfaces are arranged to be normal to the wire of the vertical deflection coil, or the auxiliary ring having sawtooth-notched end surfaces is disposed over the end surfaces of the core. Consequently, the wire wound at the large winding angle position is prevented from slipping on the surface of the core.

BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a prior art deflection yoke.
FIG. 2A is a perspective view of a vertical deflection coil of the prior art.
FIG. 2B is a front view of the vertical deflection coil shown in FIG. 2A.
FIG. 3 is a front view of a deflection yoke of the present invention.
FIG. 4 is a sectional view of the deflection yoke of the present invention.
FIG. 5 shows a distribution graph of lines of magnetic force of a barrel magnetic field.
FIG. 6 shows a graph illustrating shapes of a pincushion magnetic field and a barrel magnetic field.
FIG. 7 is a side elevational view of a vertical deflection coil having an auxiliary ring of sawtooth shape.
FIG. 8 is a side elevational view of a vertical deflection coil wound on a core having its end surfaces deformed into sawtooth shape.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The preferred embodiments of the present invention will now be explained. Referring to FIG. 3, a deflection yoke 20 of the present invention includes a magnetic material piece 8 of iron or permaloy plate of rectangular or pedestal shape disposed inside a coil 6 of a vertical deflection coil 3. The magnetic material piece 8 is attached by bond or the like at a position closer to a smaller opening 4b in an inside of the coil 6, being separated from a larger opening 4a by 1/2-3/4 of a full distance between both openings. The width l₁ of the magnetic material piece 8 is approximately 1/5-1/2 of the distance from the larger opening 4a of the vertical deflection coil to the smaller opening 4b. The length of the magnetic material piece 8 is chosen such that an angle φ₃ looking into the magnetic material piece 8 from a center 0 is approximately 30°-70° C. By this magnetic material piece 8, the magnetic field on the side of the smaller opening 4b is formed into an intensified barrel field. In FIG. 3, a separator 5 is not shown. FIG. 4 shows a side sectional view of the deflection yoke 20 of the present invention, which clearly shows that the magnetic material piece 8 is attached to the vertical deflection coil 3 on the side of the smaller opening 4b. The magnetic material piece 8 may be attached to a horn-shaped portion 5b of the separator 5 instead of the vertical deflection coil 3, at a position close to a smaller opening 5a of the separator 5. In this case, a similarly intensified barrel field to that produced when it is attached to the vertical deflection coil 3 can be formed.

FIG. 5 shows a distribution graph of the lines of magnetic flux in the barrel magnetic field formed by the magnetic material piece 8, as looked from the larger opening side. The lines of magnetic force shown by dotted lines show lines of magnetic flux in the absence of the magnetic material piece 8 and the solid lines of magnetic flux show lines of magnetic flux in the presence of the magnetic material piece 8. Since the dotted lines of magnetic flux are altered to the solid lines of magnetic flux, the barrel magnetic field is enhanced.
FIG. 6 shows shapes of the pincushion magnetic field and the barrel magnetic field, in which an abscissa represents a center axis z of the deflection yoke 20 shown in FIG. 4. A strength B of the vertical magnetic field in the deflection yoke is generally expressed by: B=B_o +B₂ y²
where B_o is a strength of the magnetic field at any point on the z-axis and represents a strength of magnetic field in x-axis direction normal to the plane of drawing. A strength of magnetic field at a position displaced in y-axis direction from that point on the z-axis which assumes the magnetic field strength B_o is given by the magnetic field strength B. B₂ is a constant. An ordinate in FIG. 6 represents B₂ /B_o. If B₂ /B_o >0, the pincushion magnetic field is formed, if B₂ /B_o =0, a uniform magnetic field is formed, and if B₂ /B_o >0, the barrel magnetic field is formed. In FIG. 6, a solid line 16 shows a shape of the magnetic field in the presence of the magnetic material piece 8, and a broken line shows a shape of the magnetic field in the absence of the magnetic material piece 8. The z-axis of FIG. 6 corresponds to the z-axis shown in FIG. 4. It is seen from FIG. 6 that when the magnetic material piece 8 is attached, the barrel magnetic field is enhanced on the smaller opening side. As a result, the winding angle φ₁ may be in the order of 150° and need not be more than 150°.

Referring to FIG. 7, in the deflection yoke 20 of the present invention, there are provided auxiliary rings 11a and 11b on end surfaces 4c and 4d of the core 4 to prevent the wire 7 of the vertical deflection coil 3 from slipping on the end surfaces 4c and 4d of the core 4. When the wire 7 intersects a center line 18 with an angle θ₃, end surfaces of the auxiliary rings 11a and 11b are divided into small areas 12 and 13 in sawtooth shape with the small areas 12 and 13 intersecting a plane normal to the center line at angles of θ₄ and θ₅, respectively. When the angles θ₄ and θ₅ are equal to the angle θ₃, tensile force acting on the wire 7 is normal to the small areas 12 and 13 and hence the wire 7 does not slip.
In FIG. 8, the wire 7 of the vertical deflection coil 3 is wound on a core 24 having its end surfaces 4c and 4d deformed into sawtooth shape. The end surfaces 4c and 4d of the core 24 have small areas 14 and 15 formed in sawtooth shape, like in the case of the auxiliary rings 11a and 11b shown in FIG. 7. The wire 7 wound on the end surfaces 4c and 4d is prevented from slipping by the small areas 14 and 15 by the same reason described above in connection with the auxiliary rings of FIG. 7.
In the deflection yoke, the overall magnetic field spreading from the smaller opening on the electron gun side to the larger opening on the screen side influences the convergence, but the pincushion distortion is largely influenced by the magnetic field on the larger opening side. This is because the distance between the electron beam and the deflection coil when the electron beam is deflected is shorter on the larger opening side than on the electron gun side, and the electron beam on the larger opening side of the deflection coil travels through curved ends of the lines of magnetic flux so that the magnetic field on the larger opening side largely influences the pincushion distortion. It is seen from the above that the magnetic field distribution necessary to simultaneously compensate for both the nonconvergence and the pincushion distortion at the left and right edge of the screen only by the deflection yoke, is the vertical deflection magnetic field which forms the pincushion magnetic field on the larger opening side and the barrel magnetic field on the smaller opening side. Thus, the deflection yoke of the present invention can simultaneously compensate for both the misconvergence and the pincushion distortion at the left and right edges of the screen.
As described hereinabove, in accordance with the deflection yoke of the present invention, in order to form different shapes of magnetic field on the larger opening side and the smaller opening side, that is, in order to form the pincushion magnetic field on the larger opening side and form the barrel magnetic field on the smaller opening side, the winding angle of the vertical deflection coil at the larger opening is changed from that at the smaller opening, that is, the winding angle of the vertical deflection coil at the smaller opening is made larger than that at the larger opening. Furthermore, the magnetic material piece is disposed inside the vertical deflection coil to enhance the barrel magnetic field. As a result, the deflection yoke of the present invention can compensate for both the misconvergence and the pincushion distortion at the left and right edges of the screen.
Furthermore, the deflection yoke of the present invention includes a core having its end surfaces formed in sawtooth shape or auxiliary rings having sawtooth-shaped end surfaces. Accordingly, the wire of the vertical deflection coil is prevented from slipping on the end surfaces of the core although the wire of the vertical deflection coil is wound at the smaller opening with a large winding angle.

CRT TUBE HITACHI  470NAB22-TC01.Electrode of color picture tube electron gun and method for manufacture thereof:

Other References:
30AX Self-Aligning 110.degree. In Line Color TV Display, IEEE Spring Conference, Jun. 1978, presented by Philips.


A first grid electrode for an in-line type color picture tube electron gun and a method for fabrication thereof are disclosed. This electrode is formed of a single metal plate, and has a first recess having a predetermined width and depth formed in one surface of the metal plate and extending in the same direction as a direction in which a plurality of cathodes of the electron gun are arranged, and a second recess having a predetermined width and depth formed in the other surface of the metal plate and extending in the direction perpendicular to the extending direction of the first recess.

1. An electrode of a color picture tube electron gun, having an aperture for passing an electron beam, said electrode comprising a first recess having a predetermined width and depth formed in a first surface of a single metal plate and having a predetermined length extending in a first predetermined direction substantially symmetrically with respect to an axis of said electron beam pass aperture, a second recess having a predetermined width and depth formed in said same single metal plate in a second surface opposite to said first surface and having a predetermined length extending in a second direction substantially perpendicular to said first predetermined direction substantially symmetrically with respect to the axis of said beam pass aperture, and a predetermined gap between the bottoms of said first recess and said second recess, said gap extending in the parallel direction with said surfaces of the metal plate only within an area defined by said electron beam pass aperture.

2. A method for producing an electrode of a color picture tube electron gun according to claim 1, comprising the steps of interposing said metal plate between a first die of the same shape as said first recess and a second die of the same shape as said second recess arranged with an axis thereof on the axis of said first die, coining said first surface and said second surface with a predetermined gap between said first die and said second die by pressing said first die on said first surface and said second die on said second surface simultaneously, and forming a through hole of a predetermined shape at a portion where said first recess and said second recess are overlaid one on the other as viewed in the direction perpendicular to the surface of said metal plate.

3. An electrode according to claim 1, wherein at least one of said first recess and said second recess has a side wall which is tapered.

4. An electrode of a color picture tube electron gun, having a plurality of electron beam pass apertures in alignment, said electrode comprising a plurality of first recesses each having a predetermined width and depth and formed in a first surface of a single metal plate, each of said first recesses having a predetermined length extending in a predetermined direction substantially symmetrically with respect to an axis of a corresponding one of said electron beam pass apertures, a plurality of second recesses each having a predetermined width and depth and formed in a second surface opposite to said first surface of said single metal plate, each of said second recesses having a predetermined length extending in a direction substantially perpendicular to said predetermined direction substantially symmetrically with respect to an axis of a corresponding one of said beam apertures, and a plurality of predetermined gaps between bottoms of said first recesses and said second recesses, respectively, each of said gaps extending in the parallel direction with said surfaces of the metal plate only within an area defined by a corresponding one of said electron beam pass apertures.

5. An electrode according to claim 4, wherein at least one of said first recess and said second recess has a side wall which is tapered.

6. In an electron gun of a color picture tube, having a plurality of cathodes aligned in a predetermined direction substantially parallel to a phosphor screen of said color picture tube for emitting electrons and a plurality of electrodes arranged in a direction substantially perpendicular to the phosphor screen, the electrode arranged nearest to said cathodes and having a plurality of electron beam pass apertures aligned in said predetermined direction and in correspondence with said cathodes, said electrode comprising a plurality of first recesses each having a predetermined width and depth and formed in a first surface of a single metal plate facing said cathodes, each of said first recesses having a length extending in a predetermined direction substantially symmetrically with respect to an axis of a corresponding one of said electron beam pass apertures, a plurality of second recesses each having a predetermined width and depth and formed in a second surface opposite to said first surface of said single metal plate, each of said first recesses having a length extending in a direction substantially perpendicular to said predetermined extending direction of the length of the first recess substantially symmetrically with respect to an axis of a corresponding one of said electron beam pass apertures, and a plurality of predetermined gaps between bottoms of said first recesses and said second recesses, respectively, each of said gaps extending in the parallel direction with said surfaces of the metal plate only within an area defined by a corresponding one of said electron beam pass apertures.

7. An electrode according to claim 6, wherein at least one of said first recess and said second recess has a side wall which is tapered.

8. An electrode according to claim 1, 3, 4, 5, 6 or 7, wherein the width of said first recess is greater than the width of said second recess.

Description:

The present invention relates to an electrode of an electron gun of a color television picture tube, or more in particular to a non-rotationally symmetrical first grid electrode having a cross slit and to a method for manufacture thereof.

The prior art and the present invention, and advantages of the latter will be described with reference to the accompanying drawings, in which:

FIG. 1 is a sectional view of a color television picture tube;

FIG. 2 is a sectional view of an electron gun arranged within the neck portion of the color television picture tube;

FIGS. 3A and 3B show an example of the first grid electrode, in which FIG. 3A is a plan view thereof and FIG. 3B is a sectional view taken in line IIIB--IIIB in FIG. 3A;

FIGS. 4A and 4B are plan views of constituent members of the electrode shown in FIGS. 3A and 3B;

FIGS. 5A and 5B are diagrams showing another example of the first grid electrode for explaining embodiments of the present invention, in which FIG. 5A is a plan view thereof and FIG. 5B is a sectional view taken in line VB--VB in FIG. 5A;

FIGS. 6A and 6B are diagrams showing a first embodiment of the first grid electrode according to the present invention, in which FIG. 6A is a plan view thereof, and FIG. 6B a sectional view taken in line VIB--VIB in FIG. 6A;

FIGS. 7A and 7B show a second embodiment of the first grid electrode according to the present invention, in which FIG. 7A is a plan view thereof and FIG. 7B is a sectional view taken in line VIIB--VIIB in FIG. 7A;

FIGS. 8A and 8B are diagrams showing a third embodiment of the first grid electrode according to the present invention, in which FIG. 8A is a plan view thereof and FIG. 8B is a sectional view taken in line VIIIB--VIIIB in FIG. 8A;

FIGS. 9A to 9F are diagrams for explaining a method for producing the electrode shown in FIGS. 8A and 8B, in which FIGS. 9A, 9C and 9E are plan views thereof in respective processes of fabrication, and FIGS. 9B, 9D and 9F are sectional views taken in lines IXB--IXB, IXD--IXD and IXF--IXF in FIGS. 9A, 9C and 9E respectively;

FIGS. 10A and 10B are perspective views of dies used for forming the cross slits in the fabrication of the electrode of FIGS. 8A and 8B;

FIG. 11 is a perspective view of a die used for forming an electron beam pass hole in the fabrication of the electrode shown in FIGS. 8A and 8B; and

FIGS. 12A and 12B are diagrams showing an example of the first grid electrode for an integrated electron gun according to the present invention, in which FIG. 12A is a plan view thereof, and FIG. 12B is a sectional view taken in line XIIB--XIIB in FIG. 12A.

Referring to FIG. 1, a color picture tube 1 comprises a phosphor screen 2 including a plurality of phosphor elements corresponding to the three primary colors and an electron gun 3 arranged within the neck portion of the tube. The electron gun 3 emits three electron beams corresponding to the three primary colors, which electron beams pass through a plurality of apertures in a color selective electrode 4 and impinge on the phosphor screen 2. The electron beams emitted from the electron gun 3 are deflected by a deflection magnetic field formed by a deflection coil 5 and scan the surface of the phosphor screen 2. As a result of the electron beams impinging on the phosphor screen 2, a picture image is reproduced.

In FIG. 2, the electron gun 3 includes cathodes 6, 6', 6", a first grid electrode 9, second grid electrodes 10 and 11, third electrodes 12 and 13, and fourth electrode 14. These electrodes are held by bead glasses 8 and arranged along a line which is substantially perpendicular to the phosphor screen 2. An integrated electron gun in which three electron guns for emitting three electron beams corresponding to the three primary colors are integrally formed is shown in the drawing. This integrated electron gun may be replaced with equal effect by three separate electron guns for emitting electron beams separately. In operation, the first grid electrode 9 is normally maintained at zero potential, and the second grid electrodes 10 and 11 are maintained at the potential of 600 to 700 volts and supplied with an accelerating voltage. The third grid electrodes 12 and 13 and the fourth grid electrode 14 constitute a main electronic lens. The electron gun shown in the drawing is what is called an in-line electron gun, in which the cathodes 6, 6' and 6" are aligned substantially in parallel to the phosphor screen 2, and the first grid electrode 9 has respective beam pass apertures arranged in the same direction as the direction of alignment of the cathodes in positions corresponding thereto. In the description below, the direction of alignment of the cathodes will be referred to as the lateral direction and the direction perpendicular thereto as the vertical direction.

In an in-line color picture tube, the deflection magnetic field for deflecting the electron beams emitted from the electron gun is subjected to pincushion distortion and barrel distortion in order to attain self convergence. As a result, each electron beam is distorted as it passes through the deflection magnetic field, so that at the peripheral parts, especially, at the corners of the phosphor screen 2, the electron beam impinging on the phosphor screen is accompanied by a halo in the vertical direction due to its overfocus in that direction, thus reducing the resolution of the reproduced image. If the focus voltage is adjusted in an attempt to improve the focus characteristic (or the resolution of the reproduced image under the influence of the halo) at the peripheral parts of the phosphor screen, the focus characteristic at the central part of the fluorescent screen becomes deteriorated, thereby reducing the focus characteristic on the phosphor screen as a whole.

With the intention of attaining a uniform focus characteristic over the whole phosphor screen, an electrode having a cross slit as shown in FIGS. 3A and 3B is used as the first grid electrode 9 of the electron gun. The diagrams of FIGS. 3A and 3B show the first grid electrode of one of a plurality of separate electron guns, which may alternatively be considered to be a part, corresponding to each electron beam, of the first grid electrode of an integrated electron gun. In an example of forming this first grid electrode 9, as shown in FIGS. 4A and 4B, two plates 17 and 18 having rectangular slits 15 and 16 are arranged in such a manner that the slits 15 and 16 cross each other at a right angle and these plates 17 and 18 are welded to each other at welding points marked with x in FIG. 3A, thus forming a beam passage aperture 18 at the central portion of the assemblage. In incorporating this first grid electrode, the plate 17 having the lateral slit 15 is arranged on the cathode side and the plate 18 having the vertical slit 16 on the second grid electrode side. In this first grid electrode, the thickness distribution of the plates 17 and 18 in the direction at which the electron beam passes is appropriately determined in accordance with the design of the color picture tube involved, in order to improve the focus characteristic.

The function of the cross slit of the first grid electrode 9 will be discussed below. Since the lateral slit 15 of the first grid electrode is arranged on the cathode side, the cross sectional view of the electron beam emitted from the cathode takes a lateral oval form due to the function of the lateral slit 15, and this lateral oval beam tends to be corrected by the function of the vertical slit 16. And due to an electric field distribution formed in dependence on the shape of the wall of the beam passage aperture 19 defined by the lateral slit 15 and the vertical slit 16, a lateral cross-over point of the electron beam that has passed the first grid electrode is formed at a position nearer to the cathode than a vertical cross-over point. In other words, the vertical cross-over point is formed at a position nearer to the phosphor screen than the lateral cross-over point. A general cross-over point for the whole of the electron beam (hereinafter referred to as the true cross-over point) is formed at a position between the lateral cross-over point and the vertical cross-over point. At this true cross-over point, the electron beam has a substantially circular section due to the space charge effect.

The distance over which the electron to beam travels toward the central part of the phosphor screen 2 is different from that toward the peripheral parts of the phosphor screen, and the latter is longer than the former. For this reason, a higher focus voltage is required for the peripheral parts than for the central part. Assuming that by use of the focus voltage for the central part, an image at the true cross-over point is obtained at the central part of the phosphor screen 2 to form a substantially circular beam spot, an image at a position displaced several hundred μm toward the phosphor screen 2 from the true cross-over point is obtained at the peripheral parts. In the case where an image at the true cross-over point is obtained on the phosphor screen, the electron beam when passing through the deflection coil 5 has a shape of a laterally oval section. Since the deflection magnetic field having a pincushion distortion and a barrel distortion acts to overfocus the electron beam in the vertical direction at the peripheral parts of the phosphor screen 2, resulting in producing a halo, an electron beam having the laterally oval sectional shape with a vertical axis shorter than that of an electron beam having a circular cross section generates a halo less than an electron beam having a circular cross section. In this case, the beam spot of the electron impinging on the phosphor screen 2 may be considered to have a greater lateral length than the longitudinal length. Such a greater lateral length, however, is prevented by the self-convergence function and the lateral length may substantially be the same as that of a beam spot attained by an electron beam with a circular cross section passing through the deflection coil 5. The shape of the beam spots at the central part and the peripheral parts of the fluorescent screen can be determined by appropriately determining the thicknesses of the plates 17 and 18, namely, the depths of the lateral slit 15 and the longitudinal slit 16 along the direction of the travel of the electron beam.

The above-mentioned function of the cross slit will be understood from the disclosure of "30AX SELF-ALIGNING 110° INLINE COLOR TV DISPLAY" presented by PHILIPS in No. 19 IEEE SPRING CONFERENCE (June, 1978). The functions and effect of a non-rotationally symmetrical aperture equivalent to the above-mentioned cross slit are disclosed, for example, in the British patent specification No. 1,421,865.

The first grid electrode 9 having such a cross slit, if made of the two plates 17 and 18 welded to each other, has disadvantages such that a high manufacturing cost is inevitable and the cut-off characteristic and the focus characteristic are deteriorated by a deformation due to welding and an assembly error. Especially, in the case of an integrated electron gun, it is difficult to weld the two plates 17 and 18 closely to each other, often resulting in a gap being formed between the two plates. This causes a condition similar to a change in the thickness of the slit plates, thus greatly deteriorating the cut-off and focus characteristics.

In order to eliminate the disadvantages caused by the welding of the two plates 17 and 18, the present invention have conducted various researches and experiments on the shape of the first grid electrode comprising a single plate and the production thereof. It is theoretically possible but practically difficult and not suitable for mass-production to fabricate an electrode of the shape shown in FIGS. 3A and 3B by integrally press-forming a single plate as shown in FIGS. 5A and 5B. Specifically, in coining the form shown in FIGS. 5A and 5B by pressing, the upper surface of a lower die jig having a shape of the lateral slit 15' collides with the lower surface of an upper die jig having a shape of the vertical slit 16' at the slit bottom 20, and the resulting shock breaks the jigs. Further, it is actually impossible to cause the lower and upper surfaces of the upper and lower die jigs to completely coincide with each other at the slit bottom 20.

The present invention has been developed in view of the above-mentioned background and an object thereof is to provide a construction of an electrode, having a cross slit, of a color picture tube electron gun which can be mass-produced, and to provide a method for producing such an electrode.

According to one aspect of the present invention, there is provided an electrode of a color picture tube electron gun, having an aperture for passing an electron beam, the electrode comprising a first recess having a predetermined width and depth formed in a first surface of a single metal plate and extending in a predetermined direction substantially symmetrically with respect to the axis of the electron beam pass aperture, and a second recess having a predetermined width and depth formed in a second surface opposite to the first surface and extending in a direction substantially perpendicular to the predetermined direction substantially symmetrically with respect to the axis of the beam pass aperture.

According to another aspect of the invention, there is provided an electrode of a color picture tube electron gun, having a plurality of electron beam pass apertures in alignment, the electrode comprising a plurality of first recesses each having a predetermined width and depth and formed in a first surface of a single metal plate, the first recesses extending in a predetermined direction substantially symmetrically with respect to the axis of the corresponding one of the electron beam pass apertures, and a plurality of second recesses each having a predetermined width and depth and formed in a second surface opposite to the first surface of the metal plate, the second recesses extending in a direction substantially perpendicular to the predetermined direction substantially symmetrically with respect to the axis of the corresponding one of the beam pass apertures.

According to still another aspect of the invention, there is provided, in an electron gun of a color picture tube, having a plurality of cathodes aligned in a predetermined direction substantially parallel to a phosphor screen of the color picture tube for emitting electrons and a plurality of electrodes arranged in a direction substantially perpendicular to the phosphor screen, the electrode arranged nearest to the cathodes and having a plurality of electron beam pass apertures aligned in the predetermined direction and in correspondence with the cathodes, the electrode comprising a plurality of first recesses each having a predetermined width and depth and formed in a first surface of a single metal plate facing the cathodes and extending in a predetermined direction substantially symmetrically with respect to an axis of the corresponding one of the electron beam pass apertures, and a plurality of second recesses each having a predetermined width and depth and formed in a second surface opposite to the first surface of the metal plate and extending in a direction substantially perpendicular to the predetermined direction and parallel to the phosphor screen substantially symmetrically with respect to an axis of the corresponding one of the electron beam pass apertures.

According to a further aspect of the invention, there is provided a method for producing the above-mentioned electrode, comprising the steps of interposing the metal plate between a first die of the same shape as the first recess and a second die of the same shape as the second recess arranged with an axis thereof on the axis of the first die, coining the first surface and the second surface with a predetermined gap between the first die and the second die by pressing the first die on the first surface and the second die on the second surface simultaneously, and forming a through hole of a predetermined shape at a portion where the first recess and the second recess are overlaid one on the other as viewed in the direction perpendicular to the surface of the metal plate.

An embodiment of the present inventon will be described below with reference to the accompanying drawings. A first embodiment of the first grid electrode 9 according to the present invention is shown in FIGS. 6A and 6B. This first grid electrode 9 has one surface formed with a substantially rectangular recess 21 of a predetermined width and depth extending in the lateral direction and the other surface formed with a substantially rectangular recess 22 of a predetermined width and depth extending in the vertical direction. The recesses 21 and 22 are formed by being coined with a predetermined gap 25 between the bottoms 23 and 24 thereof. A substantially square electron beam pass aperture 26, which has four sides each almost equal to or slightly smaller than the width of the lateral recess 21, is formed at a position where the recesses 21 and 22 are overlapped one on the other in a plan view of the electrode 9. The recesses 21 and 22 are respectively substantially symmetric with respect to the center axis of the electron beam pass aperture 26. For convenience sake, the shape obtained from the recesses 21 and 22 and the aperture 26 will also be referred to as a cross slit. In this embodiment, the recesses 21 and 22 have substantially the same width W. This electrode 9 is arranged in the electron gun 3 in such a manner that the surface thereof having the lateral recess 21 faces the cathode 6.

By constructing the electrode 9 in such a manner as to have a cross slit of the above-mentioned shape, it is possible to form the recesses 21 and 22 with the gap 25 therebetween, with the result that the upper die jig and the lower die jig are prevented from being broken by collision during the coining process, thus facilitating mass production of the electrode 9. After forming the recesses 21 and 22 by coining, the beam pass aperture 26 is formed by punching on a press thus producing the electrode 9.

A second embodiment of the first grid electrode 9 according to the present invention is shown in FIGS. 7A and 7B. Also in this embodiment, the lateral recess 21 and the vertical recess 22 are formed with a predetermined gap 25 therebetween. The embodiment under consideration is different from the embodiment of FIGS. 6A and 6B in that in this embodiment the vertical recess 22 (or the lateral recess 21) has a larger width W' than the lateral recess 21 (or the vertical recess 22) whose width is W. Each side of the electron beam pass aperture 26 is substantially equal to or slightly shorter than the width W. In this cross slit construction, when the electron beam pass aperture 26 is formed, the portion 26 to be punched off and a portion 27 which is left unpunched can be supported in the same plane on the upper surface of the lower die jig by inserting the lower die jig in the recess of the comparatively large width W', thereby improving the punching accuracy.

A third embodiment of the first grid electrode according to the present invention is shown in FIGS. 8A and 8B. In this embodiment, as in the embodiment of FIGS. 7A and 7B, the lateral recess 21 having the comparatively narrow width W and the vertical recess 22 having the comparatively large width W' are formed with the predetermined gap 25 therebetween. This embodiment is different from the embodiment of FIGS. 7A and 7B in that in this embodiment the side walls of the recesses 21 and 22 are tapered at a predetermined angle θ. By so doing, the outer peripheral edge of the top of the coining die is prevented from being broken or otherwise damaged, thus improving the service life of the die. Although this embodiment has been described by reference to tapering the recesses 21 and 22 of the embodiment shown in FIGS. 7A and 7B, the recesses 21 and 22 of the embodiment of FIGS. 6A and 6B may similarly be tapered. If desired from the viewpoint of the electrical characteristics, only a selected one of the recesses 21 and 22 may be provided with such a tapering.

The inventors have studied how the shape of the first grid electrode 9, namely, the width, depth and taper angle of the lateral recess 21 and the vertical recess 22 and the gap 25 between the recesses 21 and 22 affect the focus characteristic (or beam spot shape) or the cut-off voltage. As a result, it has been found that, by increasing the depth of the lateral recess 21 facing the cathode, the cross section of the electron beam becomes more laterally oval and, by increasing the depth of the vertical recess 22 on the second grid side, the cross section of the electron beam becomes more vertically oval, thereby accordingly changing the shape of the beam spot or the area of the halo on the phosphor screen 2. It has also been found that in this case the depth of the lateral recess 21 largely affects the area of the halo. Further, it has been discovered that the depth and width of the lateral recess 21 greatly affect the cut-off characteristic and therefore are limited by the desired cut-off characteristic of the picture tube involved, while the depth and width of the vertical recess 22 has a margin in design. If the width of the vertical recess 22 is reduced, for instance, the change in the effect on the characteristic can be regulated by reducing the depth appropriately. It has also been found that even when the gap 25 is formed between the lateral recess 21 and the vertical recess 22, the sectional shape of the electron beam at positions before and after the true cross-over point may be changed according to the depth of the vertical recess 22. Furthermore, the focus characteristic and cut-off characteristic are changed as a result of tapering the side wall of the recesses, but such a change can be suppressed by increasing the depth of the recesses in the case where the tapering increases the effective width of the recesses, or by reducing the depth of the recesses in the case where the tapering decreases the effective width of the recesses.

Thus, the shape of the cross slit is determined according to the degree of improvement in the cut-off characteristic and focus characteristic, required for each color picture tube involved. In other words, by properly designing the shape of the cross slit, the cut-off characteristic and the focus characteristic are improved to the required degree. An experiment has been effected, as an example, on the embodiment of FIGS. 8A and 8B, provided with the lateral recess 21 having the width of 0.7 mm and the length of 2 mm at the bottom thereof, the depth of 0.08 mm,, and the side wall tapering of 5/11; the vertical recess 22 having the width of 1 mm and the length of 2 mm at the bottom thereof, the depth of 0.11 mm, and the side wall tapering of 5/11; and the electron beam pass aperture 26 square in shape having the sides each 0.67 mm long. The results of the experiment showed the cut-off characteristic and focus characteristic satisfactory for the practical purposes.

An example of a method for fabricating the electrode 9 of FIGS. 8A and 8B will be described with reference to FIGS. 9A to 9F. As shown in FIGS. 9A and 9B, a metal plate member 28 having the thickness of about 0.33 mm is punched with a hole 29 of about 0.6 mm diameter. Next, as shown in FIGS. 9C and 9D, the lateral recess 21 and the vertical recess 22 are formed simultaneousl by a coining process with the gap 25, by means of the upper die jig 30 having a shape similar to the lateral recess 21 as shown in FIG. 10A and the lower die jig 31 having a shape similar to the vertical recess 22 as shown in FIG. 10B. In the process, a circular groove 33 is formed around the recesses 21 and 22 as shown in the drawings, which groove is not related to the present invention and therefore will not be described any further. While supporting the bottom 24 of the comparatively wide vertical recess 22 on the top flat surface 35 of the lower die jig 34 for punching the beam pass aperture shown in FIG. 11, the beam pass aperture 26 is punched as shown in FIGS. 9E and 9F by means of an upper die jig (not shown) having the same size as the beam pass aperture 26 through the lateral recess 21. At the last step, the metal plate member is punched to the desired outer dimension thereby to obtain the electrode 9. The change in the thickness of the metal plate member 28 which occurs during the coining is absorbed by the hole 29. The coining work is of course performed with the center axis of the lower die jig 30 and the upper die jig 31 aligned with each other.

An example of the first grid electrode for an integrated electron gun of in-line type fabricated in this way is shown in FIGS. 12A and 12B.

Instead of a substantially square beam pass aperture 26 shown in the above-mentioned embodiments, a circular beam pass aperture may be formed. A circular beam pass aperture will affect the focus characteristic and the cut-off characteristic differently from the square beam pass aperture, and therefore this fact must be taken into consideration in determining the width and depth of the recesses 21 and 22. Also, in the above-mentioned embodiments, the recesses 21 and 22 are substantially rectangular in plan view, which may of course be replaced by any other shape which has an equal effect as the rectangular shape.

It will be understood from the foregoing description that, according to the present invention, the first grid electrode having the cross slit can be integrally formed of a single part, so that the number of parts is reduced and the need of the assembly work by welding is eliminated thereby to make its mass-production possible, thus reducing the production cost. Further, deterioration of the characteristics which might occur if two plates are overlaid one on the other, deformation by welding or reduction in accuracy can be obviated, thereby making it possible to produce an electrode which is superior in characteristics and uniform in quality.


 CRT TUBE HITACHI  470NAB22-TC01. Black matrix color picture tube:

 A black matrix color picture tube has a phosphor layer and black matrix layer formed on the inner surface of the faceplate. A layer of glass having a low softening point is provided between the phosphor layer and the inner surface of the faceplate and between the black matrix layer and the inner surface of the faceplate. The softening point of the glass is below the temperature at which the tube is subjected during a frit baking step employed in the fabrication of the tube. For example, a borophosphate glass is used as the layer of glass having a low softening point.

 1. A black matrix color picture tube having a phosphor layer and a black matrix layer on an inner surface of a faceplate, comprising said tube having a layer of glass between the inner surface of said faceplate and said phosphor layer and between the inner surface of said faceplate and said black matrix layer, wherein said glass of said layer is a borophosphate glass including 30-70 mol % of P₂ O₅ and 2-10 mol % of B₂ O₃, and further includes alkaline earth metal and alkaline metal oxide as remaining components.

2. A black matrix color picture tube having a phosphor layer and a black matrix layer on an inner surface of a faceplate, comprising said tube having a layer of glass between the inner surface of said faceplate and said phosphor layer and between the inner surface of said faceplate and said black matrix layer, wherein said glass of said layer is a borophosphate glass with a composition including 35-50 mol % of P₂ O₅, 3-7 mol % of B₂ O₃, 5-15 mol % of MgO, 5-15 mol % of CaO, 5-25 mol % of Li₂ O, 5-25 mol % of Na₂ O, 0-10 mol % of BaO, 0-10 mol % of K₂ O, and 0.01-1 mol % of CeO₂.

3. A frit baked black matrix color picture tube, comprising said tube having a faceplate with an inner surface, and a phosphor layer and a black matrix layer on the inner surface of the faceplate, said tube having a layer of glass between the inner surface of said faceplate and said black matrix layer, wherein the glass of said layer has a softening point lower than a predetermined frit baking temperature and wherein said glass comprises a borophosphate glass including 30-70 mol % of P₂ O₅ and 2-10 mol % of B₂ O₃, and further includes alkaline earth metal and alkaline metal oxide as remaining components.

4. A frit baked black matrix color picture tube, comprising said tube having a faceplate with an inner surface, and a phosphor layer and a black matrix layer on the inner surface of the faceplate, said tube having a layer of glass between the inner surface of said faceplate and said black matrix layer, wherein the glass of said layer has a softening point lower than a predetermined frit baking temperature and wherein said glass comprises borophosphate glass with a composition including 35-50 mol % of P₂ O₅, 3-7 mol % of B₂ O₃, 5-15 mol % of MgO, 5-15 mol % of CaO, 5-25 mol % of Li₂ O, 5-25 mol % of Na₂ O, 0-10 mol % of BaO, 0-10 mol % of K₂ O, and 0.01-1 mol % of CeO₂.

Description:

BACKGROUND OF THE INVENTION
This invention relates to a black matrix color picture tube and a method for its fabrication and particularly to a high-contrast black matrix color picture tube and a method for its fabrication.
The phosphor screen of a so-called black matrix color picture tube has on its faceplate the formation of a nonluminous, light-absorptive powder layer (black matrix) for partly covering the phosphor layer so that the phosphor layer appears through aperture sections (matrix holes).

Among the two major methods of forming such a phosphor screen, one is the wet process, which is typically as follows. On the inner surface of the faceplate, a photoresist is applied to form a film, and portions of the photoresist film where phosphor will be laid are hardened. After the development process, carbon suspension is applied to it to form a carbon application film and, thereafter, a removal agent is poured onto it to remove the hardened photoresist together with the overlaying carbon layer so that matrix holes are formed. Next, the photoresist slurry including phosphor is applied to form a film and the application film at positions where the phosphor will be laid is hardened. Following the development process, a phosphor layer is formed in the matrix holes. For making a phosphor layer of three colors, i.e., red, green and blue, the above process is repeated for each type of phosphor. Finally, the baking process is conducted to eliminate organic substances.
The second is the dry process which was developed by some of the inventors of the present invention (see JP-B-57-20651 which corresponds to JP-A-53-126861). This method typically includes the processes of forming an application film including aromatic diazonium salt, which exhibits adhesion or tackiness by being exposed to light, on the faceplate, and exposing it to the light radiation so that phosphor is deposited in the irradiated portions. For making a phosphor layer of three colors, the light irradiation and following processes are repeated three times. Next, the entire application film is exposed to light and carbon is deposited in portions other than the phosphor layer so that a black matrix is formed. Finally, a fixing process using a polymer aqueous solution, etc. is conducted so that these layers are made insoluble in water. In case of a striped phosphor pattern, it is also possible to form a black matrix layer before forming the phosphor layer.
In the formation of a phosphor screen by any of the above methods, there is created a gap partly between the phosphor layer and black matrix layer and the faceplate. When the light is incident from the outside (from the viewer's side), part of the light is reflected on the outer surface of the faceplate, and, because of the presence of the gap, part of the light is further reflected on the inner surface. The inner surface reflection, which depends on the refractivity of the faceplate, is over as much as 3-5% of the incident light. Therefore, suppression of the inner surface reflection is desired.
A method of reducing the inner surface reflection has been proposed, in which a material having virtually the same refractivity as the faceplate material, e.g., water glass, is filled in the gap between the faceplate and the black matrix layer. See, for example, JP-A-57-115749. This conventional technique, however, has a problem in that the water glass filled in the black matrix layer penetrates into the phosphor layer, causing a decrease in the light intensity of the phosphor.
Sticking of water glass to the phosphor surface by capillary action is unavoidable, and conceivably electron rays emitted by phosphor are retarded by the water glass, resulting in a decreasing intensity of the phosphor. Water glass does not much exist in the portion of the phosphor layer, but instead bubbles rest there and the inner surface reflection cannot be prevented completely in this portion. It is also undesirable to use water glass because of the mismatch of refractivity between water glass and the glass of the faceplate.

SUMMARY OF THE INVENTION
An object of this invention is to provide a black matrix color picture tube and a method of fabricating the same, which reduces the reflection on the inner surface of the faceplate without sacrificing the intensity of the phosphor.
According to one aspect of the present invention, in a black matrix color picture tube having a phosphor layer and a black matrix layer on the inner surface of a faceplate, a layer of glass of a low softening point is formed between the inner surface of the faceplate and the black matrix layer, so that the black matrix layer optically contacts the faceplate.
According to another aspect of the present invention, in a black matrix color picture tube having a phosphor layer and a black matrix layer on the inner surface of the faceplate, a layer of glass of a low softening point is formed between the inner surface of the faceplate and the phosphor layer and between the inner surface of the faceplate and the black matrix layer, so that the black matrix layer and the phosphor layer optically contact the faceplate. In consequence, the reflectivity of the faceplate is lowered, and a high-contrast picture tube is realized.
In the fabricating method according to one embodiment of the invention, formation of a phosphor screen includes a step of forming a glass layer having a low softening point on the inner surface of faceplate, a step of forming a black matrix layer and phosphor layer on the glass layer, and a step of softening the glass layer by heating.
In the case of forming a glass layer of a low softening point only between the black matrix layer and the faceplate based on this invention, the following method is preferably followed. The method is characterized by the formation of a phosphor screen including a step of applying a film of photoresist on the inner surface of a faceplate a step of forming a desired film pattern by exposing the applied film to light using a shadow mask followed by development, a step of forming a glass layer of low softening point on the faceplate and the applied film pattern, a step of forming a black matrix layer on the glass layer, a step of removing the applied film pattern together with the glass layer and black matrix layer formed on it using a removal agent, a step of softening the glass layer by heating, and a step of forming a phosphor layer on the portion of the applied film where the pattern has been removed.
In any of the above methods, if phosphor layers of three different colors are to be formed, the step of phosphor layer formation is conducted three times for the three types of phosphor. The methods may be based either on the wet process or dry process.
In the former method, the wet process and dry process may be employed for forming the black matrix layer and phosphor layer respectively, or both layers may be formed by either the wet process or the dry process.
The low softening point glass is preferably one having a softening point in the range of 200°-450° C., or more preferably in the range of 200°-430° C. Namely, the softening temperature is chosen to be below the frit baking temperature which is slightly above 450° C. in the fabrication of color picture tubes. The low softening point glass needs to be nonaqueous or aqua-resistive.
An example of low softening point glass is borophosphate glass (see Glass Technology, Vol. 17, No. 2, pp. 66-71). A preferable composition of glass used for this invention includes 30-70 mol % of P₂ O₅, 2-10 mol % of B₂ O₃, with an alkaline earth metal and alkaline metal oxide as the remaining components, for example. Too much or too little of the P₂ O₅ results in a crystallization of the glass, and too much P₂ O₅ further deteriorates the phosphors. Inclusion of MgO and/or, CaO is favorable for preventing the blackening of the phosphor. However, too much MgO or CaO tends to raise the softening point, although resistivity against water is improved. In order to prevent the discoloring of glass attributable to the electron rays, it is preferable for the glass composition to include 0.01-1 mol % of CeO₂.
The following is an example of a composition of a low softening glass that is preferably used in practicing this invention.
P₂ O₅ --35-50 mol %, B₂ O₃ --3-7 mol %,
MgO--5-15 mol %, CaO--5-15 mol %,
Li₂ O--5-25 mol %, Na₂ O--5-25 mol %,
BaO--0-10 mol %, K₂ O--0-10 mol %,
CeO₂ --0.01-1 mol %
Glass of the above composition has a refractivity in the range of 1.50-1.55. To eliminate the inner surface reflection of the faceplate almost completely, it is especially desirable to use glass with a refractivity in the range of 1.52-1.54.
Use of glass including heavy metal such as Pb and Bi is unfavorable, since these heavy metals deteriorate the phosphors.
Low softening point glass in the form of a powder is more desirable, particularly glass powder with an average particle diameter ranging 0.5-20 μm is desirable.
The thickness of the glass layer is required to such an extent of flattening the roughness at the bottom of the phosphor layer and black matrix layer, and the presence of sole glass layer up to 0.1-60 μm is allowed.
The glass layer is softened by being heated, and it fills the space between the phosphor layer and black matrix layer. If the materials of the glass layer and faceplate have equal refractivity, the inner surface reflection of the face plate is eliminated. Practically, the condition is met unless the refractivities of both parts are greatly different. Generally, low softening point glass has similar refractivity to that of a faceplate material, except for special glass, and therefore the inner surface reflection of the faceplate can virtually be nullified. This point will further be described with reference to the, drawings
FIG. 2 shows a schematic partial cross-section of a faceplate used in a conventional color picture tube. Most of the light 1 is incident to the interior, although part of it is reflected on the surface of the faceplate 3. If there is a space between the faceplate 3 and phosphor layer 5 or black matrix layer 4, part of the incident light 1 is reflected on the inner surface of faceplate 3 to produce reflected light, indicated by light rays 2 and 2'. However, if the space is filled with low softening point glass 6 as shown in FIG. 1, which shows a partial schematic cross-section of a faceplate of the inventive color picture tube, reflection does not occur on the inner surface of the faceplate 3, and all of the incident light 1 is absorbed by the black matrix layer 4. Since the glass layer and phosphor layer have virtually equal refractivities, the surface of the phosphor layer 5 merely allows a little dispersion and does not reflect the light.
Since the glass layer does not melt at the above-mentioned processing temperature, it does not cover the phosphor layer, and the intensity of the phosphor does not fall.
Next, the formation of a black matrix film by employment of the dry process will be described. This work is done by a sequential process including a step of applying a light-sensitive material, which exhibits adhesion or tackiness by being exposed to light, on the surface of a substrate so as to form a thin layer, a step of exposing the thin layer in its portions of a figure pattern to light so that the exposed portions develop tackiness, and a step of sticking a nonluminous powder, thereby forming a pattern of nonluminous powder. The nonluminous powder pattern forming method is characterized by mixing the nonluminous powder with a low softening point glass powder and sticking the mixture to the exposed portions. The nonluminous powder pattern forming method further includes a subsequent step of developing the light-sensitive material to form a pattern of thin film, a step of forming a nonluminous powder layer on the light-sensitive thin film, and a step of removing the light-sensitive film together with the nonluminous powder layer on it, thereby forming the mixture of the nonluminous powder and low softening point glass powder on the pattern of the light-sensitive thin film.
In the dry process, the formation of the nonluminous powder pattern may be either before or after the formation of the phosphor pattern. However, in the case of a dot pattern of phosphor, the phosphor pattern is preferably formed first for the expedient of forming the exposure pattern. In the case of a striped pattern of phosphor, the patterns may be formed in an arbritrary order. In the wet process, the nonluminous powder pattern is formed first in general.

The mixing ratio of nonluminous powder and glass powder is preferably such that the nonluminous powder is 0.1-7 weight % of the mixture, and is more preferably 0.3-4 weight %. A lesser amount of nonluminous powder below 0.1 weight % spoils the effect of forming a black matrix and allows for the easy formation of pin holes. An excess amount of the powder above 7 weight % spoils the effect of the reduction of the inner surface reflection as shown in Table 1, which shows the results of measurements of reflection attained by varying the quantity of carbon black in the same condition as in FIG. 1, as will be explained later. The inner surface reflectivity represents the value of 5° regular reflection for a 550 nm wavelength.

TABLE 1

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Quantity of carbon Inner surface black (weight %) reflectivity (%)

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0.1 1 0.3 0 0.5 0 0.8 0 1.0 0 1.6 0 4.0 0 4.7 0 5.5 1 7.0 2 10.0 4 17.0 4

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BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partial schematic cross-sectional diagram showing the inventive color picture tube faceplate.
FIG. 2 is a partial schematic cross-sectional diagram showing the conventional color picture tube faceplate.

FIGS. 3 and 4 are diagrams of reflectivity used to explain the present invention.
FIG. 5 is a spectral diagram of 5° regular reflection on the nonluminous powder layer resulting from the inventive method and conventional method.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
EMBODIMENT 1
The following materials were metered, mixed in an agate mortar, heated gradually from room temperature in a crucible, and baked at 800° C. for one hour in air. Borophosphate glass was yielded with the composition (mol %) of: 45P₂ O₅.5B₂ O₃.11MgO. 11CaO.9Li₂ O.19Na₂ O. The softening point was 400° C. (Generally, the measurement of the softening point involves an error of around ±10° C.). The glass was powdered.
Phosphoric acid (85% H₃ PO₄)--51.88 g, Boron oxide (B₂ O₃)--1.83 g, Basic magnesium carbonate ((MgCO₃)₄.Mg(OH)₂.5H₂ O)--5.46 g, Calcium carbonate (CaCO₃)--5.69 g, Lithium carbonate (LiCO₃)--3.27 g, Sodium carbonate (Na₂ CO₃)--9.99 g.
On the inner surface of the faceplate, the aqueous solution including 1% polyvinyl alcohol, 2% diethylene glycol and 2% diglycerol was applied by rotatary application to a thickness of about 1 μm. The applied surface was dusted with the glass powder so that a glass powder layer was formed. The faceplate was heated gradually from room temperature to 450° C. for 30 minutes, and a borophosphate glass layer with a thickness of about 10 um was formed. Photoresist was applied to the faceplate to form a film, and the light was irradiated through a shadow mask to positions where phosphor dots of three types (R, G, B) would be formed. Through, the development process, hardened photoresist dots were formed. Colloidal black carbon suspension was applied to the inner surface of the faceplate, and it was dryed. By pouring a removal agent to remove the hardened photoresist dots together with carbon on them, matrix holes were formed.
Through the application, light exposure and development using the photoresist phosphor slurry for the three types of phosphors sequentially, as in the conventional method, phosphor layers were formed.
The above process was followed by aluminizing, frit baking, and mounting of electron guns to complete a color picture tube. The glass layer was softened in the process of frit baking.
For the comparison purposes, a conventional color picture tube, in which the borophosphate glass layer was absent and the rest of the tube was constructed according to the inventive method, was fabricated. FIG. 3 shows the result of measurement of 5° regular reflection on the red, green and blue phosphor layers of both picture tubes. Indicated by 31, 32 and 33 are reflectivities of the conventional blue, red and green phosphor screen, while 34, 35 and 36 indicate the counterparts of this invention. As will be appreciated from the figure, the inventive phosphor screen has almost no reflectivity on all phosphor layers in a wide range of wavelength. FIG. 4 shows the reflectivity on the black matrix layer. Also in this case, the inventive color picture tube has almost no reflectivity on the black matrix layer. The light release factor of phosphor was 108-112% greater than that of the conventional one.
EMBODIMENT 2
The following materials were used to obtain borophosphate glass of 40P₂ O₅.5B₂ O₃.12MgO.12CaO.10Li₂ O. 21Na₂ O. The process was identical to Embodiment 1. The glass has a softening point of 410° C. The measurement result was virtually identical to Embodiment 1.
Phosphoric acid (85% H₃ PO₄)--46.12 g,
Boron oxide (B₂ O₃)--1.83 g, Basic magnesium carbonate ((MgCO₃)₄.Mg(OH)₂.5H₂ O)--6.01 g,
Calsium carbonate (CaCO₃)--6.26 g,
Lithium carbonate (LiCO₃)--3.59 g,
Sodium carbonate (Na₂ CO₃)--10.99 g.
EMBODIMENT 3
The same process as Embodiment 1 was conducted, except that borophosphate glass was used. The measurement result was virtually identical to Embodiment 1.

TABLE 2

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Composition No. (mol %) 1 2 3 4 5 6 7 8 9 10 11 12

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P2 O5 35 40 45 50 45 45 45 45 45 45 50 55 B2 O3 5 5 5 5 5 5 5 5 5 5 3.6 5 MgO 13.5 12.5 12 9 9 12.5 9 11.2 7 5 -- 9 CaO 13.5 12.5 12 9 9 12.5 9 11.2 7 5 -- 9 BaO -- -- -- -- 9 4.7 -- -- -- -- -- -- Li2 O 10.5 15 9 7 10 10 7 8.8 20.8 20 20 7 Na2 O 22.5 14.7 16.7 20 12.7 10 10 18.8 15 19.75 10 15 K2 O -- -- -- -- -- -- 9.7 -- -- -- 16.4 -- CeO2 -- 0.3 0.3 -- 0.3 0.3 0.3 -- 0.2 0.25 -- -- Softening point 410 410 420 410 400 420 410 400 360 320 280 370 (°C.)

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EMBODIMENT 4
Light-sensitive polymer compound was applied by rotation on the inner surface of the faceplate. Using a super high pressure mercury lamp as a light source, positions where phosphor dots of red, green and blue would be put were exposed to the light through a shadow mask. After development in water, 3-color dots made of light-hardened resist were obtained. After the panel had been dried, an adhesive of the following composition was applied thinly and evenly.
Composition of adhesive:
Zinc chloride--3%; Polyvinyl alcohol--0.15%; Water--rest
Subsequently, powder of borophosphate glass was dusted to form a powder layer. After exposure to ammonia vapor, the plate was washed in water, and a fixed layer of borophosphate glass was formed. Colloidal liquid of black carbon was applied over the layer, and it was dried. After the light-hardened photoresist dots had been processed using a removal agent, the dots and borophosphate glass and carbon on it were removed using a hot water spray, and black matrix holes were obtained. Next, by completing the conventional application, exposure, development and dry processes for each of the 3-color phosphors sequentially, phosphor films were formed. Finally, aluminizing, frit baking and mounting of electron guns were conducted following the conventional method, and a black matrix color picture tube was completed.
EMBODIMENT 5
The glass produced in Embodiment 1 was powdered and mixed with black carbon in the following proportion, and the following mixture was obtained.
Glass of low softening point--25 g;
Carbon black--1 g
EMBODIMENT 6
A film of the following composition was applied as a light-sensitive material on a glass substrate.
Zinc chloride double salt of N,N-dimethylaniline-p-diazonium chloride--95 weight %; Polyvinyl alcohol--5 weight %
Using a super high pressure mercury lamp, the film was exposed to the ultraviolet rays through a mask, and the exposed portions developed stickiness.
The black powder produced in Embodiment 5 was dusted and developed in air blow. The black powder sticked in the stickiness portion, and a pattern of nonluminous powder layer was formed. Following the process in ammonia vapor and then washing in water, the powder layer was fixed, and it was baked at 430° C. for 30 minutes. A pattern of a nonluminous powder layer, with the inner surface reflectivity being lowered, was obtained.
It was tried to expose an application film of light-sensitive material to a pattern of ultraviolet rays in advance and, following the deposition of phosphor on the exposed portions, the entire surface was exposed, which was followed by dusting of the black powder produced in Embodiment 5, development, ammonia process, washing in water, and baking at 430° C. for 30 minutes, as in the same manner as Embodiment 5, and as a result the intensity of the phosphor was not spoiled at all and the inner surface reflectivity was lowered.
FIG. 5 shows the reduction of inner surface reflectivity. In the figure, indicated by (a) is the spectrum of 5° regular reflectivity on the nonluminous powder layer produced by the conventional method (wet process), and (b) is the result accomplished by the present invention. The measurement of reflectivity was conducted by making the light incident at 5° to normal on the surface. The reflectivity of the glass surface was subtracted from the measurement result. The same result as when the film produced by the inventive method in close contact with the substrate was reached, and the inner surface reflectivity was nullified at any wavelength.