PHILIPS 16C929 /00S PHILETTA ROYAL 929 CHASSIS KT3 CRT TUBE PHILIPS A42-556X

The CRT TUBE PHILIPS A42-556X is a particular mask type.

Strengthening means for a CRT in-line electrode component:
 The invention relates to improved strengthening means for a substantially planar one-piece electrode component utilized in an in-line multi-beam CRT electron gun assembly. Advantageous ruggedizing properties are achieved by discretely formed longitudinal channels oriented along the sides of the component with defined ledge portions extending outward therefrom; beneficially dimensioned supporting projections are formed as integral extensions thereof. A plurality of cooperating mini-channels are included as transversals in the component to provide a markedly improved structure.
1. Improved strengthening means for a substantially planar one-piece electrode component in a plural electrode in-line multi-beam cathode ray tube electron gun assembly integrated by a plurality of longitudinal insulative support members, said electrode component evidencing alpha and beta surfaces and having opposed side and end regions with defining L--L' and W--W' axes thereacross; said component having a center and two side-related spatially positioned apertures therethrough located in an in-line relationship substantially coinciding with said L--L' axis, the center aperture being located at the intersection of said L and W axes, with said side-related apertures oriented equidistantly therefrom along said L--L' axis on either side of said W--W' axis; said strengthening means comprising: at least one longitudinal channel located in each of the side regions of said component in parallel relationship with said L--L' axis, each of said channels being indented inward from said beta surface of said component for the full length of said region to form a longitudinal rib projecting from said alpha surface, each of said channels being an open-ended trough formation having width and depth dimensions formed by three adjoining longitudinal surfaces defining an outer wall portion, an inner wall portion and a bottom portion therebetween, each of said channels displaced inwardly from either side of said component to form ledges in the beta surface between the channels and the side edges of the component, the ledge edges being substantially parallel with said L--L' axis and extending along the full length of said side region; each of the channel-related ledges having an outstanding dimension at least substantially equal to the thickness of the component material and supporting projections extending from either side of said component; the supporting projections being integral planar extensions of said ledge formations.
2. An improved electrode component of the in-line CRT electron gun assembly according to claim 1 wherein each of said channels evidences two longitudinal and parallel strengthening bends therein, said bends being separated to define the bottom width dimension of said channel.
3. An improved electrode component of the in-line CRT electron gun assembly according to claim 1 wherein each channel evidences a substantially uniform depth dimension that is at least substantially equal to the thickness of said component material.
4. An improved electrode component of the in-line CRT electron gun assembly according to claim 1 wherein each channel has a substantially uniform width dimension that is at least substantially equal to the thickness of said component material.
5. An improved electrode component of the in-line CRT electron gun assembly according to claim 1 wherein each of said channel-related ledges extends in a substantially right-angle relationship with the outer wall of said channel.
6. An improved electrode component of the in-line CRT electron gun assembly according to claim 1 wherein at least two mini-channels are formed as elongated lateral indentations in the beta surface of said electrode component, said mini-indentations transversing the area between said side longitudinal channels and being located substantially midway between said apertures in parallel relationship with said W--W' axis.
7. An improved electrode component of the in-line CRT electron gun assembly according to claim 6 wherein each mini-indentation forms an elongated protrusion from the alpha surface of said electrode component, the height of said protrusion being less than the thickness of said component material.
8. An improved electrode component of the in-line CRT electron gun assembly according to claim 6 wherein each of said apertures is oriented in an individual spaced-apart dish-like depression formed in said alpha surface to project as a separate protuberance from said beta surface, and wherein said mini-channel indentations are located in the spacings between said aperture protuberances.
Description:
TECHNICAL FIELD
This invention relates to a substantially planar one-piece electrode component in a multi-beam in-line cathode ray tube electron gun assembly, and more particularly to improved strengthening means incorporated into the structure of a substantially planar electrode member.
BACKGROUND OF THE INVENTION
Cathode ray tubes (CRT's) commonly used in color television and related display applications conventionally utilize unitized electron gun assemblies which direct a plurality of controlled electron beams to the display screen of the tube. In certain gun assembly constructions, the first and second grid electrode components, such being norm
ally control and screen grid electrodes, are often formed as substantially planar members oriented in substantially parallel planes in spaced apart superposed relationship. In multi-beam guns each of these first and/or second planar electrodes contains several spatially related apertures to accommodate the respective electron beams generated within the assembly. It is very important that these several apertures be accurately and consistently spaced relative to the related apertures in the adjacent electrode components, and, in the case of the first electrode component, with the respective cathode surfaces from which the specific electron beams emanate. These and associated electrodes are conventionally affixed to at least two longitudinal insulative support members of the integrated gun assembly by supporting projections extending from the respective electrode components.
Fabrication of the gun assembly involves embedment of the supporting projections of the related electrode components into the temporarily heat-softened longitudinal insulative support members. In this operation, which is commonly referred to as "beading", the softened support members on opposed sides of the assembly are pressured inward toward the several electrode components thereby forcing the supporting projections thereof into the support members. The opposing compressive pressures tend to exert a distorting force upon the electrode components, this being especially critical to the planar components wherein a bowing or arcuate bending effect sometimes results. Such bowing, however slight, changes the aperture locations relative to those in the adjacent electrode components, thereby producing deleterious inter-electrode spacing relationships within the gun structure. These uncontrollable changes in the related aperture spacings are particularly troublesome in in-line gun constructions wherein the first and the second grid electrodes usually have related apertures of small diameter and close spacings.
Two serious manufacturing control problems are caused by the bowing or warping of the first (G1) and/or second (G2) electrode components. The first of these is variation of cutoff and associated cutoff ratio. Cutoff is defined as the positive cathode (K) voltage at which the electrons cease to flow through the G1 aperture. Cutoff ratio is the ratio of the highest cutoff voltage to the lowest cutoff voltage of the three guns in a given tube. Cathode cutoff ratio is now commonly specified at 1.25, a condition which requires precise G1, G2, and K-G1 spacing control. This has proven to be one of the more difficult manufacturing control problems.
The second control problem relating to bowed G1 and G2 electrodes is variation of focus quality. This is largely determined by gun design, but for the gun construction to be successful, three factors are essential: (a) high quality parts must be used, (b) parts alignment must be accurately maintained, and (c) K-G1 and G1-G2 spacings must be precisely controlled at or near design center for optimum focus performance. This factor is directly related to bow-free electrodes. The most difficult production control parameter is the endeavor to achieve consistent K-G1 spacings for the three associated beams.
There are disclosures in the prior art to ruggedize in-line planar type electrodes by incorporating strengthening ribs such as those taught by Floyd K. Collins in U.S. Pat. Nos. 4,049,990 and 4,049,991.
A second grid electrode having channels therein is also shown in the gun structure disclosed by Allen P. Blacker and James W. Schwartz in U.S. Pat. No. 4,058,753.
While teachings of incorporating strengthening ribs fulfilled the existing needs at the time of disclosure, the state of the CRT art has advanced to stages of greater constructional sophistication wherein gun assemblies are made smaller and more compact, and tube operating requirements more stringent and exacting. In view thereof, improved strengthening of planar type electrodes, to prevent bowing during tube fabrication, is essential to achieving the desired tube performance characteristics required in the present state of the art.
DISCLOSURE OF THE INVENTION
It is therefore an object of the invention to provide a substantially planar CRT in-line electrode component having improved ruggedizing structural means incorporated therein to counteract the distorting forces encountered during the electron gun assembly fabrication procedure.
Another object of the invention is to provide
an improved in-line ruggedized electrode component that is formed in a manner to optimize the maintenance of initial shaping when incorporated in a plural beam gun assembly thereby providing the desired subsequent inter-electrode spacings within the gun structure.
These and other objects and advantages are achieved in one aspect of the invention wherein improved strengthening means are provided for a substantially planar one-piece electrode component in a plural electrode in-line multiple beam CRT gun assembly integrated by a plurality of longitudinal insulative support members. The substantially planar component evidences alpha and beta surfaces wherein there are opposed side and end regions having L--L' and W--W' axes thereacross. The component contains a center and two side-related spatially positioned apertures located in an in-line relationship substantially coinciding with the L--L' axis. The center aperture is positioned at the intersection of the L and W axes, while the side-related apertures are located equidistantly therefrom along the L--L' axis on either side of the W--W' axis.
The invention relates to electrode component strengthening means in the form of at least one longitudinal channel located in each of the side regions thereof in parallel relationship with the L--L' axis. Each of these channels is indented inward from the beta surface to extend the full length of the respective side region to form a longitudinal rib projecting from the alpha surface. Extending outward from each channel, for the full length thereof, in the plane of the side region, is a defined ledge having a leading edge substantially parallel with the L--L' axis. Additionally, at least a pair of spatially-related supporting projections are extended outward equally from either side of the component as integral planar extensions of the respective ledge formations. The facing edges of each pair of projections are beneficially spaced from the W--W' axis by dimensions in the order of substantially half the separation distance between apertures.
Each of the ruggedizing longitudinal channels is further defined as an open-ended trough formation having width and depth dimensions formed by three adjoining longitudinal surfaces comprising an outer wall, an inner wall and a substantially planar bottom therebetween. As such, each channel evidences two separated longitudinal and parallel strengthening bends therein, the distance therebetween defining the bottom width dimension of the channel.
Each channel evidences a substantially uniform width dimension being in the order of at least twice the thickness of the component material. In like manner, a substantially uniform depth dimension is also evidenced, such being at least substantially equal to the thickness of the component material. Each of the channel-related ledges, which extends in a substantially right-angle relationship with the outer wall of each channel, has an outstanding dimension that is also at least substantially equal to the thickness of the component material.
The electrode component preferably also evidences at least two mini-channels formed as elongated lateral indentations in a surface thereof, preferably the beta surface, being located substantially midway between the center and side-related apertures in parallel relationship with the W--W' axis thereby transersing the area between the longitudinal side channels. Each of these mini-indentations forms an elongated protrusion from the opposite surface of the component, the height of this protrusion being less than the thickness of the component material.
The electrode component may be further defined as being fabricated in a manner wherein each of the apertures is oriented in an individual spaced-apart dish-like depression formed in the alpha surface in a manner to project as a separate protuberance from the beta surface. In keeping therewith, the aforedescribed mini-channel indentations are located in the spacings between the aperture protuberances.
The aforedescribed strengthening features incorporated in the structural configuration of a substantially planar electrode component effects the beneficial desired ruggedization thereof in a manner not heretofore achieved.

  PHILIPS 16C929 /00S PHILETTA ROYAL 929 CHASSIS KT3  CRT TUBE  PHILIPS  A42-556X.Reducing aperture-size of shadow mask in painting black matrix CRT screen:

 A method for making a black matrix type shadow mask color television tube. A shadow mask with standard size apertures is sprayed with a black brushing cellulose lacquer while at the same time drawing air, at high velocities, through the apertures to reduce the size of said apertures. A sufficient quantity of sprayed lacquer is utilized to obtain a 10% reduction in aperture size. The mask is then utilized to coat the tube's screen, i.e. its inside face, with a colloidal graphite paint to form the required adherent black matrix surface on said screen having a plurality of holes therein. The apertures of the shadow mask are then restored to their original size by rinsing the mask in acetone to remove the lacquer coating. The resultant original size apertures of the shadow mask are utilized to form the pattern of phosphor dots on the screen overlapping the holes in the black matrix.

1. A method of making a black matrix shadow mask color television picture tube having an apertured shadow mask and an adjacent faceplate screen comprising the steps of: stray-coating an opaque material on the apertured shadow mask to reduce the size of the apertures by a predetermined amount;
providing, in addition to said spray-coating operation, a separate forced air draft at a high velocity through said apertures;
forming a black matrix having a pattern of holes therein on the adjacent surface of said screen,
said holes being formed through said mask to be equal in size to the size of said reduced apertures;
enlarging the apertures in said mask to their original size; and
forming a pattern of phosphor dots in said holes of said, said dots being formed through said enlarged apertures of said mask so that the dots overlap and are larger than the holes.


2. The method of making a black matrix shadow mask color television picture tube, according to claim 1, wherein said coating deposited on said shadow mask is a cellulose laquer and said forced air draft provides air through the apertures of said mask during the period in which said lacquer is being deposited on said mask to control the reduced size of said apertures.

3. The method of making a black matrix shadow mask color television picture tube, according to claim 2, wherein forming said black matrix comprises the steps of: coating said screen with a photosensitive mixture containing polyvinylalcohol;
exposing said photosensitive mixture coated screen to ultraviolet light through the reduced apertures of said mask;

removing the regions of said photosensitive mixture not exposed to said ultraviolet light;
coating said screen with a colloidal graphite paint;
removing the portions of said photosensitive mixture exposed to said ultraviolet light and the regions of colloidal graphite overlying said ultraviolet exposed regions of said photosensitive mixture; and
baking on said remaining colloidal graphite paint.


4. The method of making a black matrix shadow mask color television picture tube, according to claim 2, wherein said shadow mask apertures are enlarged to their original size by the step of rinsing said mask in acetone to remove said lacquer coating.

5. The method of claim 2 wherein said apertures have chamfered edges on one side of said mask, said coating of lacquer being deposited onto the side of said mask opposite said chamfered edges.

Description:

BACKGROUND OF THE INVENTION
This invention relates to the manufacture of color television picture tubes incorporating shadow masks, and more particularly to such tubes utilizing the so-called "Black Matrix".
One serious drawback of the standard shadow mask tube is the appearance of its picture viewed in daylight conditions or high ambient lighting conditions. In the standard shadow mask tube there are two principal factors contributing to this deficiency. Firstly, in order to accommodate beam landing errors the diameters of the phosphor dots are made larger than those of the beams, and secondly the spaces surrounding these dots is covered by a highly reflective aluminum coating. These two factors together mean that approximately 10% of the screen area is never excited by any electron beam but will nevertheless diffusely reflect ambient light and hence impair the appearance of the picture. In order to reduce this effect to acceptable limits a dark-tint face plate is used. This reduces, by a certain factor, the brightness of the reflected ambient light; but it also reduces, though only by half that factor, the brightness of the picture. Thus although there is a net improvement in appearance, the general level of picture brightness is reduced. This effect can be compensated by driving the phosphor harder, but this reduces the life of the tube. Taking this fact into consideration a face plate with approximately 50% transmission is generally considered a reasonable compromise.
A novel approach to the problem is firstly to arrange to accommodate beam landing errors by making the electron beams larger than the visible portions of the dots, and secondly to fill the space between these portions with a non-reflecting coating.
With this arrangement, if only 50% of the screen area is excited by electron beams and the remainder is substantially non-reflecting, then an 80% transmission face plate could be used, thereby providing a 54% increase in brightness with a 30% better contrast ratio between the picture and the reflected ambient light.
The arrangement can be achieved in principle by producing an appropriate pattern of holes in a black coating on the inside of the tube facce. The holes are made undersize on the standard phosphor dots which are subsequently superimposed on these holes. The diameters of the electron beams are again standard size but beam landing errors are accommodated by virtue of the fact that the effective light emitting area of each phosphor dot is restricted to that portion lying in its associated hole.
A critical step in this process is the production of the pattern of undersize holes. Since a shadow mask is unique to a tube this pattern can only be achieved by a technique which involves the temporary reduction in size of the apertures of a shadow mask.
Two methods have previously been proposed. One of these involves making the shadow mask with undersize holes which are subsequently enlarged by etching after it has been used to make the pattern of undersize holes in the black coating. The other method involves using a shadow mask with standard size holes which is then plated with a different metal to reduce their size. After the pattern of undersized holes in the black coating has been made the holes of the shadow mask are opened out again to their original size using a selective etch which will remove the plated layer, but which will not attack the underlying material from which the shadow mask is constructed. Both these methods are complicated by the fact that the enlargement of the holes has to be performed after the shadow mask has been fitted to its supporting frame and formed. It will be realized that there is a risk of trapping the etching solution between the mask and its frame which may cause contamination within the completed tube. A further disadvantage of the plating method is that it is time consuming and expensive on materials. Yet another disadvantage of methods involving the use of etching solutions is that they are liable to remove the oxide layer created during the forming of the shadow mask. If this oxide layer has to be recreated by a further heat treatment there is a serious risk that the shadow mask will slightly change its shape and thus lose its compatibility with the deposited pattern of phosphor dots.

SUMMARY OF THE INVENTION
Therefore, the main object of the invention is to provide an improved method of making a black matrix shadow mask color television tube in which the size of the holes in said mask are reduced.
According to the present invention there is provided a method of making a black matrix shadow color televesion picture tube comprising the steps of depositing a coating on a shadow mask having apertures fromed therein to reduce the size of said apertures, forming a black matrix on the tubes inside foil having a pattern of holes therein on said mask, said holes being equal in size to the size of the reduced apertures, enlarging the apertures trough said mask to their original size and depositing a pattern of phosphor dots in said now enlarged apertures of said mask on said screen which overlap the holes in said black matrix.
It is a feature of the subject invention that the holes in the shadow mask may be reduced in size using a material, such as cellulose, dissolved in a common solvent, such as acetone. Acetone will not remove the oxide layer, and although it too can readily penetrate the crevices between mask and frame, it will not react with them and therefore is less likely to be a troublesome source of contamination.

 

PHILIPS 16C929 /00S PHILETTA ROYAL 929  CHASSIS KT3  CRT TUBE  PHILIPS  A42-556X.

Small phosphor area black matrix fabricating proces:

A process for fabricating matrix cathode ray tubes having phosphor receiving areas smaller than the areas exposed through an apertured mask includes the steps of coating the inner surface of a viewing panel with a first film of photo-sensitive resist material; exposing the first film through an apertured mask to provide insolubilized areas of a given size; depositing a second film of resist material onto said first film; removing the second film, soluble areas of the first film, and portions of the insolubilized areas of the first film to provide insolubilized areas of the first film of a size smaller than said given size; overcoating with an opaque film, removing the overcoated insolubilized areas of a size smaller than the given size; and depositing phosphors in place of the removed insolubilized areas of a size smaller than said given size. 

 1. In a cathode ray tube having a viewing panel with an inner surface, a multiple-apertured mask spaced from said inner surface, and a screen structure with a multitude of phosphor receiving areas smaller than said apertures of said mask interconnected by a webbing of opaque material affixed to said inner surface, a screen structure fabricating process comprising the steps of: coating said inner surface of said viewing panel with a photo-sensitive resist material to provide a first film capable of solubility alteration upon exposure to actinic radiation;
exposing said first film to actinic radiation directed through said apertured mask to provide insoluble film areas of a given size interconnected by a webbing of soluble film;
depositing a coating of resist material over said first film and drying to provide a second film adhered to said first film;
removing said second film, said soluble portions of the first film and portions of said insoluble areas of said first film to provide insoluble areas of said first film of a size smaller than said given size and interconnected by a bare inner surface of said viewing panel;
overcoating said bare inner surface of said viewing panel and said insoluble areas smaller than said given size of said first film with a third film of opaque material;
removing said insoluble areas smaller than said given size of said first film and said overcoating of said third film of opaque material thereon to leave an interconnecting web of opaque materials; and
depositing phosphor materials on said areas of a size smaller than said given size intermediate said web of opaque materials.


2. The screen structure fabricating process of claim 1 wherein said first and second films are derived from a substantially identical photo-sensitive resist material.

3. The screen structure fabricating process of claim 1 wherein said photo-sensitive resist material is in the form of an aqueous solution of polyvinyl alcohol and an ammonium dichromate sensitizer.

4. The screen structure fabricating process of claim 1 wherein said photo-sensitive resist material is in the form of an aqueous solution including about 2% by weight of polyvinyl alcohol and about 0.25% by weight of an ammonium dichromate sensitizer.

5. The screen structure fabricating process of claim 1 wherein said third film of opaque material is derived from a colloidal suspension of electrically conductive graphite material.

6. The screen structure fabricating process of claim 1 wherein said step of removing said soluble areas smaller than said given size of said first film and said overcoating of said third film thereon includes the utilization of a chemically-digestive agent for said first film.

7. The screen structure fabricating process of claim 1 wherein said step of removing said insoluble areas smaller than said given size of said first film includes the utilization of an aqueous solution of hydrogen peroxide.

8. The screen structure fabricating process of claim 1 wherein said step of removing said second film and said soluble webbing and portions of said insoluble areas of first film provides insoluble first film areas of a size in the range of about 15-25% smaller than said given size.

9. The screen structure fabricating process of claim 8 wherein said provision of insoluble first film areas of a size in the range of about 15-25% smaller than said given size is effected within a period not greater than about 10 minutes after said step of depositing a coating of resist material over said first film and drying to provide a second film adhered thereto.

10. A process for fabricating a screen structure affixed to the inner surface of the viewing panel of a cathode ray tube having an apertured mask spaced from said inner surface, said screen structure fabricating process comprising the steps of: providing a first film of photo-sensitive resist material capable of solubility alteration upon exposure to actinic radiation on said inner surface of said viewing panel;
exposing said first film to actinic radiation directed through said apertured mask to provide insoluble areas of said first film of a given size interconnected by a webbing of soluble first film material;
coating said first film with a resist material and drying to provide a second film affixed to said first film;
removing said second film, said webbing of soluble first film material, and portions of said insoluble areas of said first film to provide insoluble areas of said first film of a size smaller than said given size and interconnected by a bare inner surface of said viewing panel;
overcoating said first film insoluble areas smaller than said given size and said interconnecting bare inner surface of said face place with a third film of opaque material;
applying a chemically-digestive agent to effect removal of said first film insoluble areas smaller than said given size and said overcoating of opaque material thereon; and
depositing phosphor materials into said areas of a size smaller than said given size wherefrom said first film and over-coating of said third film were removed.


11. The screen fabricating process of claim 10 including the step of wetting said exposed first film with water prior to coating said first film with a second film of resist material.

12. The screen fabricating process of claim 10 wherein said coating of said first film to provide a second film is effected with the photo-sensitive resist material of said first film.

13. The screen fabricating process of claim 1 wherein said photo-sensitive resist material in the form of an aqueous solution including about 2% by weight of polyvinyl alcohol and about 0.25% by weight of ammonium dichromate.

14. The screen fabricating process of claim 10 wherein said step of coating said first film with a resist material to provide a second film is effected within a period not greater than about 10 minutes after said step of providing a first film of photo-sensitive resist materials; and exposure to actinic radiation.

15. The screen fabricating process of claim 10 wherein said step of removing said second film, said webbing of soluble first film, and portions of said insoluble areas of said first film provides insoluble areas of said first film of a size in the range of about 15-25% smaller than said given size.

Description:

BACKGROUND OF THE INVENTION
This invention relates to cathode ray tubes and more particularly to a process for fabricating a black matrix screen structure having phosphor receiving areas smaller than a given exposure area effected by directing actinic radiation through an apertured mask.
Generally, matrix screen structures for cathode ray tubes are of either the positive or negative tolerance type. In the positive tolerance type screen structure the matrix holes for phosphor deposition are larger than the electron beam spot size of an operating tube. In the negative tolerance type screen structure the matrix holes for phosphor deposition are smaller than the electron beam spot size of an operating tube. Moreover, the positive tolerance type screen structure, which is the least popular structure, is normally fabricated by merely overexposing through the apertured mask associated with present-day "shadow-mask" type structures.
However, the more popular negative tolerance type structure, wherein the matrix holes for phosphor deposition as smaller than the electron beam spot size, are fabricated in accordance with several techniques. In one known process, the structure is exposed through the associated apertured mask to provide matrix holes of a given size and suitable for receiving phosphors. Thereafter, the apertures of the mask are enlarged to provide a beam spot size larger than the matrix holes wherein the phosphors are deposited.
In another known process, a film of photo-sensitive resist is exposed through the apertured mask which has had the apertures partially filled with a liner. Thereafter, the liner is removed to provide enlarged apertures and a beam spot size larger than the matrix holes. In another similar technique, a temporary mask is affixed to the regular apertured mask in order to reduce the aperture size. The matrix holes are exposed and the temporary mask is removed to provide enlarged mask apertures whereby the beam spot size is larger than the matrix holes.
Other known methods for providing negative tolerance structures include an acid etch back process wherein a photo-sensitive resist film is exposed through the normal apertured mask and the exposed film reduced by an acid treatment. Thus, matrix holes of a size smaller than the beam spot size are achieved. Also, underexposure or a "print down" technique is utilized wherein a photo-sensitive resist film is underexposed through the apertured mask and a portion of the underexposed film is washed away to leave a film spot size smaller than the size of an electron beam passing through the same apertured mask and impinging the screen.
Although each of the above-mentioned techniques has been or still is employed for fabricating screens for cathode ray tubes, it has been found that each leaves something to be desired. For example, enlarging the apertures of the mask, filling the apertures with a liner, and utilizing a temporary mask have all been found to be extremely cumbersome, expensive and not particularly satisfactory techniques for fabricating negative tolerance type screen structures. Also, it has been found that acid treatment techniques are most difficult to use due to the problems of size control of the exposed film. Moreover, under-exposure techniques have a tendency to cause deposition of insolubilized film which is relatively thin or which has a tendency to loosen and leave the support to which it is affixed.
OBJECTS AND SUMMARY OF THE INVENTION
An object of the present invention is to provide an enhanced cathode ray tube screen structure fabricating process. Another object of the invention is to provide a cathode ray tube screen structure fabricating process which reduces the above-mentioned disadvantages of the prior art. Still another object of the invention is to provide a cathode ray tube screen structure fabricating process which is inexpensive of labor and materials. A further object of the invention is to provide an improved cathode ray tube screen structure fabricating process for providing a negative tolerance type structure having phosphor receiving areas of a size smaller than the area of an electron beam directed through an apertured mask.
These and other objects, advantages and capabilities are achieved in one aspect of the invention by a cathode ray tube screen structure fabricating process wherein the inner surface of a viewing panel is coated with a first film of photo-sensitive resist material, the first film is exposed to actinic radiation through an apertured mask to provide insoluble areas of film of a given size; a second film of resist material is deposited onto the first, dried, and the second film, soluble areas intermediate the insoluble areas of the first film, and portions of the insoluble areas of the first film are removed to provide insoluble areas of the first film of a size smaller than the given size; a third film of opaque material is overcoated on the insoluble areas of the first film of a size smaller than the given size and the bare surface of the viewing panel intermediate the insoluble areas; the insoluble areas and the overcoating of opaque material thereon are removed; and phosphors are deposited in the remaining areas smaller than the areas of a given size intermediate the coating of opaque materials.