PHILIPS 14CT3205 PHILETTA COLOR CHASSIS KT3 CRT TUBE PHILIPS A37-554X.

PHILIPS 14CT3205 PHILETTA COLOR  CHASSIS KT3  CRT TUBE  PHILIPS  A37-554X.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 14CT3205 PHILETTA COLOR  CHASSIS KT3  CRT TUBE  PHILIPS  A37-554X.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.